FACULTY ABSTRACTS
- ASTRONOMY
- BIOLOGY
- CHEMISTRY
- Michael C. Miller, Joshua B. Resnick, Bradley T. Smith, and Charles M. Lovett, Jr.
- J. Hodge Markgraf, Professor of Chemistry, Raymond Chang, Professor of Chemistry,
- J. Hodge Markgraf, Professor of Chemistry, Poorab K. Sangani 97,
and Manuel Finkelstein, Part-Time Lecturer in Chemistry
- Katherine L. Queeney 92, Ethan P. Marin 93, Cory M. Campbell,
and Enrique Peacock-López, Associate Professor of Chemistry
- Enrique Peacock-López, Associate Professor of Chemistry, and Katherine L. Queeney 92
- Elizabeth Juang 95 and Enrique Peacock-López, Associate Professor of Chemistry
- Enrique Peacock-López, Associate Professor of Chemistry, Daniel B. Radov 96
and Carolyn S. Flesner 94
- Anne R. Skinner, Senior Lecturer, and Mark N. Rudolph 96
- P. H. Paul, J. A. Gray, J.L. Durant, Jr., and J.W. Thoman, Jr., Associate Professor of Chemistry
- COMPUTER SCIENCE
- GEOSCIENCES
- B. Gudveig Baarli, Research Associate
- Mark E. Brandriss, Visiting Assistant Professor, Dennis K. Bird, Stanford University, James R. ONeil, University of Michigan, Robert L. Cullers, Kansas State University
- Mark E. Brandriss, Visiting Assistant Professor, James R. ONeil, Mark B. Edlund, Stephanie R. Langusch and Eugene F. Stoermer, University of Michigan
- Rónadh Cox, Assistant Professor of GeosciencesDonald R. Lowe, Stanford University
- Rónadh Cox, Assistant Professor of GeosciencesR. A. Armstrong, Australian National UniversityL. D. Ashwal, I. L. Raoelison, Rand Afrikaans University
- David P. Dethier, Professor of Geosciences, Steven L. Reneau, Los Alamos National Laboratory
- Steven L. Reneau, Los Alamos National Laboratory, David P. Dethier, Professor of Geosciences
- Steven L. Reneau, Los Alamos National Laboratory, David P. Dethier, Professor of Geosciences
- David P. Dethier, Professor of Geosciences, William H. Crane 97, Mary Ann Hirshfeld 96, Joanna K. Holbert 97, and Willard S. Morgan 96, Williams College; Richard E. Sylwester, Northwest Geophysical Services
- Demian M. Saffer, University of California, Santa Cruz, David P. Dethier, Professor of Geosciences
- Markes E. Johnson, Professor of Geosciences
- Markes E. Johnson, Professor of Geosciences, Maximino E. Simian 95
- Markes E. Johnson, Professor of Geosciences
- Maximino E. Simian 95, Markes E. Johnson, Professor of Geosciences
- Markes E. Johnson, Professor of Geosciences Jorge Ledesma-Vazquez, Universidad Autonoma de Baja CaliforniaMark A. Mayall 93 John Minch, Mission Viejo, California
- Jorge Ledesma-Vazquez, Universidad Autonoma de Baja CaliforniaRichard W. Berry, San Diego State UniversityMarkes E. Johnson, Professor of GeosciencesSonia Gutierrez-Sanchez, Universidad Autonoma de Baja California
- Roger J. Cuffey, Pennsylvania State University, Markes E. Johnson, Professor of Geosciences
- Markes E. Johnson, Professor of Geosciences, Laura Libbey 95
- Laura K. Libbey 95, Markes E. Johnson, Professor of Geosciences
- Paul Karabinos, Professor of Geosciences
- Paul Karabinos, Professor of Geosciences, John Leftwich, Old Dominion UniversityRónadh Cox, Assistant Professor of Geosciences
- Paul Karabinos, Professor of Geosciences
- Jeffrey B. Noblett, Christine S. Siddoway, Colorado CollegeReinhard A. Wobus, Professor of Geosciences
- R. A. Wobus, Professor of Geosciences, et al.
- MATHEMATICS
- Colin C. Adams, Professor of Mathematics
- Colin C. Adams, Professor of Mathematics; Alan Reid
- Colin C. Adams, Professor of Mathematics
- Edward B. Burger, Assistant Professor of Mathematics
- Edward B. Burger, Assistant Professor of Mathematics
- Edward B. Burger, Assistant Professor of Mathematics; Christopher Kollett 95
- Edward B. Burger, Assistant Professor of Mathematics; Thomas Struppeck
- Edward B. Burger, Assistant Professor of Mathematics
- Edward B. Burger, Assistant Professor of MathematicsFrank Morgan, Dennis Meenan (54) Centennial Professor of Mathematics
- Thomas Garrity, Associate Professor of Mathematics; Robert Mizner
- Susan Loepp, Assistant Professor of Mathematics
- Frank Morgan, Dennis Meenan (54) Centennial Professor of Mathematics
- Frank Morgan, Dennis Meenan (54) Centennial Professor of Mathematics; Joel Hass
- Frank Morgan, Dennis Meenan (54) Centennial Professor of Mathematics; Gary Lawlor
- Frank Morgan, Dennis Meenan (54) Centennial Professor of Mathematics
- Frank Morgan, Dennis Meenan (54) Centennial Professor of Mathematics
- Frank Morgan, Dennis Meenan (54) Centennial Professor of MathematicsEdward B. Burger, Assistant Professor of Mathematics
- Frank Morgan, Dennis Meenan (54) Centennial Professor of Mathematics
- Frank Morgan, Dennis Meenan (54) Centennial Professor of Mathematics
- Frank Morgan, Dennis Meenan (54) Centennial Professor of Mathematics
- Cesar E. Silva, Associate Professor of Mathematics; A. del Junco
- PHYSICS
- S. R. Bolton, S. Bar-Ad, G. Sucha, D. S. Chemla, D. L. Sivco, and A. Y. Cho
- Charles H. Bennett, David P. DiVincenzo, John A. Smolin, and William K. Wootters, Professor of Physics
- Kevin Jones, Professor of Physics, et al.
- Kevin Jones, Professor of Physics, et al.
- Kevin Jones, Professor of Physics, et al.
- Kevin Jones, Professor of Physics, et al.
- Kevin Jones, Professor of Physics, et al.
- PSYCHOLOGY
- Phebe Cramer, Professor of Psychology
- Phebe Cramer, Professor of Psychology
- Paul R. Solomon, Bridget Kelly, Mahri Relin, Richard Deveaux, MaryEllen Groccia and William W. Pendlebury
- Elliot Friedman, Assistant Professor of Psychology; Teresa M. Reyes and Christopher L. Coe, University of Wisconsin
- Elliot Friedman, Professor of Psychology, Michael Irwin and David Overstreet
- Robert Kavanaugh, Professor of PsychologyBetty Zimmerberg and Steven Fein, Associate Professors of Psychology
- P. L. Harris, Robert Kavanaugh, Professor of Psychology, and L. Dowson
- Betty Zimmerberg, Associate Professor of Psychology
- Betty Zimmerberg and A. L. Morrow
- Betty Zimmerberg, Associate Professor of Psychology and Brenna McDonald 94
- Saul Kassin, Professor of Psychology
- Saul Kassin, Professor of Psychology and H. Sukel
- Saul Kassin, Professor of Psychology and M. Dunn
Pitfalls in the Science Standards
Bull. Am. Phys. Soc., 42, 1121, 1997.
The National Science Standards promulgated by the National Academy of
Sciences/National Research Council have much to recommend them, but can lead to
a diminishment of student interest in physics and astrophysics because of their
emphasis on relevance and on concrete thinking.
An Atlas of Ancient Planetary Nebulae and Their Interaction With the
Interstellar Medium
The Astrophysical Journal, 107, No. 1, Supplement Series, 1996.
We present an imaging atlas of the largest planetary nebulae (>8'), taken at
Ha, [N II], and [O III]. Using this data, we have developed a set of simple
criteria for determining whether a planetary nebula (PN) is indeed interacting
with the interstellar medium (ISM). On this basis, we conclude that most in
our sample reveal significant interactions with the ISM. We discuss also how a
large sample of ancient planetary nebulae can be used to derive a filling
factor for coronal gas in the ISM. Subject headings: atlases -- ISM:
structure -- planetary nebulae: general
A New Look at Carbon Abundances in Planetary Nebulae. II. BB 1, NGC 650, NGC
1535, NGC 2440, and NGC 7027
The Astrophysical Journal, 473, 304-309, 1996.
This paper is the second in a series that reports on the outcome of a study of
carbon abundances in a carefully chosen sample of planetary nebulae
representing a large range in progenitor mass and metallicity. We use the
Final Archive IUE database containing consistently reduced IUE spectra to
measure line strengths of [C III] [lambda]1909, along with numerous other UV
lines for the planetary nebulae BB 1, NGC 650, NGC 1535, NGC 2440, and NGC
7027. Combining these measurements with optical data from the literature, we
determine values for the abundance ratios He/H, O/H, C/O, N/O, and Ne/O for
these five objects using a five-level program, but we fine-tune the results
with corrections derived from detailed photoionization models constrained by
the same set of emission lines. All five objects show enhanced levels of C/O
and N/O but depleted O/H with respect to the Sun.
Subject headings: ISM: abundances -- planetary nebulae: general --
stars: evolution -- ultraviolet: ISM
Spectrophotometry of Planetary Nebulae. III. IIDS Observations of Compact Nebulae
Publications of the Astronomical Society of the Pacific, 108, 980-985, 1996.
We give spectral line intensities, electron temperatures, electron densities,
and chemical compositions for 25 compact planetary nebulae observed with the
IIDS at Kitt Peak. Several (Ha 3-75, He 2-15, K 3-89, M 1-16, M 2-52, and M
3-28) are found to be especially rich in helium and/or nitrogen (He/H>0.15;
N/O>1). The results minimally confirm the correlation between N/O and He/H,
but also confirm the intrinsic scatter in the relation, as N-rich nebulae can
be unenriched in He and vice versa.
CHARACTERIZATION OF SPHINGANINE KINASE ACTIVITY INCORN SHOOT MICROSOMES
Ar chives of Biochemistry and Biophysics, 337, 284-290 (1997)
The activity of sphinganine kinase, the enzyme catalyzing the first step in the
breakdown of the sphingoid long-chain base sphinganine by converting it to
sphinganine 1-phosphate, was characterized in microsomes isolated from corn
shoots. Activity was assayed by monitoring the conversion of
[3H]sphinganine to [3H]sphinganine 1-phosphate, which was
recovered in the aqueous phase following lipid extraction. Sphinganine kinase
was found to utilize D-erythro-sphinganine and ATP as substrates.
Maximum product formation required the presence of Mg2+. The
apparent Km for ATP was 0.81mM. GTP also served as a source of
phosphate, whereas CTP and UTP were not effective substrates in this assay.
Maximum product formation was observed at sphinganine concentrations of
approximately 100 uM. Results of competition experiments suggested that the
enzyme could also phosphorylate D-erythro-sphingosine but not
DL-threo-sphinganine or D-phytosphingosine. Enzyme activity was
greatest in the microsomal fraction obtained by differential centrifugation,
and was localized to the Golgi and endoplasmic reticulum using marker enzymes.
The specific activity of the enzyme under optimal conditions was 1.08
nmoles/min/mg protein, a value 25-fold higher than that reported for
preparations from brain tissue. Fumonisin, a mycotoxin that disrupts
sphingolipid metabolism, did not alter sphinganine kinase activity in vivo or
in vitro. The results of this study demonstrate, for the first time, the
presence of sphinganine kinase activity in plant tissue, and suggest that the
properties of the kinase from corn microsomes are distinct from those of the
mammalian and protistan enzymes in some respects.
Ceramide Glucosylation in Bean Hypocotyl Microsomes: Evidence that Steryl
Glucoside Serves as Glucose Donor
Archives of Biochemistry and Biophysics, 340, 311-316 (1997)
The formation of glucosylceramide, the predominant sphingolipid in plant
tissues, was examined in microsomes from wax bean hypocotyls. Membranes were
incubated with UDP-[14C]glucose in an assay mixture. The lipid
extracts obtained from the assays were separated by thin-layer chromatography,
and the radioactivity incorporated into glusylceramide, steryl glocoside and
acylated steryl glucoside was determined. Although the formation of
glucosylceramide was detected and characterized, several lines of evidence
contradicted the assumption that UDP-glucose is the immediate glucose donor for
glucosylceramde formation in plants: PDMP
(Dl-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol), an
inhibitor of ceramide glucosyltransferase in animal tissues, did not inhibit
glucosylceramide formation in bean microsomes. Addition of UDP-glucose
pyrophosphatase during the assay to degrade UDP-(14C)glucose blocked
the further production of labeled steryl glucoside, but did not prevent the
continued formation of labeled glucosylceramide. Omitting
UDP-(14C)glucose and including steryl (14C)glucoside in
the assay resulted in the formation of labeled glucosylceramide. Collectively,
these results suggest that glucosylceramide formation in plants does not
utilize UDP-glucose as the immediate glucose donor, as has been demonstrated
for the reaction in animal tissues, and that steryl glucoside serves as glucose
donor for ceramide formation. This study, the first to examine glucosylceramde
formation in plants, provides evidence for a novel enzymatic reaction in
sphingolipid synthesis as well as a new, metabolic role for steryl glucoside in
plant tissues.
Influence of Feeding Guild on Insect Response to Host Plant Fertilization
Ecological Entomology, 21, 270-278 (1996)
1. The densities of insect herbivores in fertilized and unfertilized field
plots of goldenrods, Solidago altissima (Compositae) were monitored over a
period of 4 years.
2. A total of seventeen insect taxa occurred on the plots over the course of
the study, including sap feeders, leaf chewers, leaf miners, leaf gallers, and
stem gallers with multiple representatives in each of these feeding guilds.
3. Nine of the seventeen taxa significantly increased in density on fertilized
plots in at least one year of the study, two taxa showed marginally significant
increases on fertilized plots, two significantly decreased in density on
fertilized plots in at least one year, and the remaining taxa were unaffected
by the fertilizer treatment.
4. The effects of fertilization on the insects were not strongly related to
feeding guild; the group of insects that increased on fertilized plots was
functionally diverse, and for the most part members of the same guild did not
respond to the fertilizer treatment in consistent ways.
5. Differences between fertilized and unfertilized plots were greatest in the
fourth year. The insects that showed delayed responses to fertilizer treatment
may have been affected by changes in microclimate that developed slowly over
the course of the study, suggesting that long-term studies may be necessary to
detect effects of host plant stress on insect herbivores.
Purification and Characterization of the Vaccinia Virus Deoxyuridine
Triphosphatase Expressed in Escherichia coli
The Journal of Biological Chemistry, 271(38), 23506-23511 (1996)
The deoxyuridine triphosphatase gene of vaccinia virus, encoded by the open
reading frame F2L, was cloned into Escherichia coli and expressed under the
control of a bacteriophage T7 promoter. After induction of T7 RNA polymerase
by isopropyl [beta]-D-thiogalactopyranoside, a 16.5~kDa peptide accumulated to
high levels. This 16.5~kDa protein was purified to homogeneity and
characterized. Gel filtration of the purified protein revealed a trimeric
native structure. Biochemical analysis revealed the enzyme to be a
metalloenzyme; enzymatic activity is inhibited by EDTA. This inhibition was
reversed by the addition of Mg2+, Mn2+, or
Zn2+. While the enzyme activity was highly specific for dUTP with
an apparent Km of 0.94 uM, inhibition studies show
that 8-azido-ATP acted as a competitive inhibitor of dUTP with a
Ki of approximately 173 uM. Also, protection studies
demonstrated that nucleotide competitors inhibit photoincorporation of the
photoaffinity analogues [[gamma]~32P]5-azido-dUTP and
[[gamma]~32P]8-azido-ATP. This suggests that while catalytic
activity is limited to dUTP, other nucleotides can bind the active site.
The Bacillus subtilis dinR Gene Codes for the Analogue of Escherichia coli
LexA: Purification and Characterization of the DinR Protein
The Journal of Biological Chemistry, 71, 33502-33508 (1996)
The Bacillus subtilis dinR gene encodes a 23-kDa protein that
shares about 34% homology with the Escherichia coli LexA protein. We
have purified the dinR gene product to near homogeneity and we describe
its activities. The purified DinR protein binds specifically to the promoter
regions of three B. subtilis SOS genes: dinB, dinC, and
recA. Electrophoretic mobility of DinR-promoter complexes in each case
is identical to that of promoters bound by the B. subtilis SOS repressor
(Lovett, et al., (1993) J. Bacteriol. 175, 6842-6849). Analysis
of hydroxyl radical footprints of DinR bound to the dinC promoter
indicates that DinR interacts with one side of the DNA providing access to the
consensus operator site (5'-GAACN4GTTC-3') within two adjacent major
grooves. Consistent with its proposed role as a transcriptional repressor,
purified DinR displaces B. subtilis RNA polymerase from the recA
promoter and represses transcription of the recA gene in vitro.
We also show that purified DinR protein undergoes general base-catalyzed
autodigestion as well as RecA-mediated cleavage at the peptide bond between
Ala-91 and Gly-92. Corresponding to its cleavage by activated RecA following
DNA damage, the level of DinR is significantly reduced in RecA+
B. subtilis cells following exposure to mitomycin C. Thus, the DinR
protein is structurally and functionally analogous to the E. coli LexA
protein and, accordingly, we propose renaming the protein B. subtilis
LexA.
Protodediazoniation of Aryldiazonium Fluoroborates
by Dimethylformamide
John R. Cort `91, Joseph L. Durant, Jr., Manuel Finkelstein, Part-Time Lecturer
in Chemistry, Andrew W. Gross `78 Michael H. Lavyne `68, W. Michael Moore,
Raymond C. Petersen, and Sidney D. Ross
Tetrahedron, 53, (1997)
The protodediazoniation of aryldiazonium fluoroborates can be effected by warm
dimethylformamide (DMF). The conversion of 4-nitrobenzenediazonium
fluoroborate to nitrobenzene was studied in detail. Products derived from
trapping experiments were consistent with a homolytic process. Studies with
deuterated DMF established that H atom abstraction occurred from both sites in
DMF with a formyl:methyl preference of 3.5:1.0. This mechanism was consistent
with bond energies and kinetic isotope effects for the DMF cation radical
calculated at the 6-311G level.
Oxidation of Benzylamines to Amides
Synthetic Communications, 27, 1285-1290 (1997)
A convenient and novel method was developed for the conversion of tertiary
benzylamines to benzamides. Oxidation by potassium permanganate in
dichloromethane was effected by phase transfer catalysis with
benzyltriethylammonium chloride. Yields were good. Regioselectivities were
consistent with a carbocation intermediate derived from an initial cation
radical.
Chemical Oscillations in Enzyme Kinetics
The Chemical Educator, 1, 369-385 (1996).
The Higgins model is a two variable model in enzyme kinetics. In contrast to
other popular simple dynamical models like the Lotka-Volterra model, the
Higgins model shows steady states, damped oscillations and stable limit cycles.
For these three dynamical behaviors, stability analysis yields expressions of
the eigenvalues, which are easy to obtain either analytically or with the use
of Mathematica. With these expressions we can find the boundaries between the
three dynamical regions in parameter space and the bifurcation point. Also, we
have compared the Higgins model with the other two variable models and find
that the origin of the richer dynamical behavior of the Higgins model is due to
the enzymatic step in the mechanism.
Chaos in a Minimal Model of the Alternative Pathway of the
Complement System
Biophysical Chemistry, 63, 167-183 (1997)
In previous work, we introduced a minimal model of the alternative pathway of
the complement. And we limited our analysis to a reduced set of parameter
values since for some parameters, experimental supported estimates were not
found. On the other hand changes in value of some parameters may be a result
of a pathological condition. Therefore, here, we extend our analysis and
include a wider range of values of five of the physiologically relevant
parameters. For all the parameters considered, we observe chaotic
oscillations, we construct bifurcation diagrams using Poincarè sections
of local maxima.
Steady State Approximation in the Minimal Model of the Alternative
Pathway
of Complement
Biophysical Chemistry, 63, 525-533 (1997).
Complement is a response mechanism of the immune system. Two initiation
pathways have been characterized for complement. The classical pathway is
antibody mediated while the alternative pathway is not. Since the alternative
pathway is independent of antibodies, it is always active. For the alternative
pathway we have previously developed a minimal model. Using parameters within
physiological bounds, the model showed complex behavior also within
physiological bounds. Thus the model seems to be an appropriate representation
of the alternative pathway response.
By applying a steady state assumption to the Michaelis Menten step of the
minimal model, we reduce the number of variables from six to five. A
comparison between the dynamics of the minimal and contracted models reveals
that the two descriptions may not be compatible. Although both systems show
chaotic behavior it occurs in different regions of parameter space.
Mixed-mode oscillations in a self-replicating dimerization mechanism
Biophysical Chemistry, 63, 534-541 (1997).
Recently, self-replicating molecules have been synthesized in the laboratory by
Rebek. Given the importance of such molecules, we proposed a simple model of a
self-replicating dimer, which works as a template for its own formation. Here
we consider a three variable model. For the model, we obtain mixed-mode and
chaotic oscillations. Also, we find coexistence between two periodic
attractors as well as a periodic and a chaotic attractor.
The Use of the E' Signal in Flint for ESR Dating
Applied Radiation and Isotopes 47, 1399-1404 (1996)
The E' signal in silica has been used to date quartz in geological
applications. However the behaviour of this signal in flint is quite
different. Resetting the signal by heating is difficult, and the signal
intensity saturates both with respect to artificial dose and to microwave
power. Nonetheless, ages determined for flints from Northwestern Florida are
in reasonable agreement with C-14 ages, suggesting that the method should be
studied further.
Collisional Electronic Quenching Rates for NO A2[Sigma]+
(v'=0)
Chemical Physics Letters 259, 508-514 (1996)
We report rate coefficients for electronic quenching of NO
A2[Sigma]+ (v'=0) by CO, CO2, H2,
H2O, O2, NO, N2O, NO2, and Ar
measured at room temperature and at elevated temperatures behind reproducible
shocks. The magnitudes of the rates and the observed temperature dependencies
of NO A2[Sigma]+ quenching by these collision partners
are found to be in accord with a charge-transfer (harpoon) collision model for
the process.
Imperative Programming Languages
Handbook of Computer Science and Engineering, (1996), pp. 1983-2005.
In this chapter we address the fundamental principles underlying imperative
programming languages and examine the way the constructs of imperative
languages are represented in several languages. We devote special attention to
features of more modern imperative programming languages, among them support
for abstract data types and newer control constructs such as iterators and
exception handling. Examples in this chapter are given in a variety of
imperative programming languages, including FORTRAN, Pascal, C, C++, Modula-2,
and Ada 83.
Subtyping is not a good "Match" for object-oriented languages
ECOOP `97 Proceedings, LNCS 1241, Springer-Verlag, pp. 104-127.
We present the design and rationale of a new statically-typed object-oriented
language, LOOM. LOOM retains most of the features of the earlier language,
PolyTOIL. However the subtyping relation is dropped from LOOM in favor of the
matching relation. "Hash types," which are defined in terms of matching, are
introduced to provide some of the benefits of subtyping. These types can be
used to provide support for heterogeneous data structures in LOOM. LOOM is
considerably simpler than PolyTOIL yet is just as expressive. The type system
for the language is decidable and provably type safe. The addition of modules
to the language provides better control over information hiding and allows the
provision of access like that of C++'s friends.
Proximity drawings of outerplanar graphs
Springer Lecture Notes in Computer Science 1190 (1996), pp. 286-302
(proceedings of Graph Drawing 96)
A proximity drawing of a graph is one in which pairs of adjacent vertices are
drawn relatively close together according to some proximity measure. We
consider an infinite family of proximity drawings called
[beta]-drawings. These drawings include the well-known Gabriel drawings
([beta]=1), and relative neighborhood drawings ([beta]=2). We show that all
biconnected outerplanar graphs are [beta]-drawable for all [beta] such that 1
<= [beta] <= 2. As a consequence of this fact, we settle in the
affirmative a conjecture of Lubiw and Sleumer, that any biconnected outerplanar
graph admits a Gabriel drawing. We also describe biconnected outerplanar
graphs which admit no convex outerplanar drawing, and give upper bounds on the
maximum number of biconnected components sharing a given cut-vertex in a
[beta]-drawable connected outerplanar graph.
Sedimentological Changes Across the Ordovician-Silurian Boundary in Hadeland
and Their Implications for Regional Patterns of Deposition in the Oslo
Region: a Comment
Norsk Geologist Tidsskrift, 76, 252-255 (1996)
In Norsk Geologist Tidsskrift, 1995, Vol. 75, pp. 199-218 Braithwaite,
Owen & Heath describe a model for sedimentation during latest Ordovician
to early Silurian time, where an easterly source of sediments is interpreted to
be a general feature of the basin. They also indicate down-warping to the west
and south, generating a general east-southeast to west-southwest depth gradient
across the basin. This scenario may be plausible for Ordovician and earliest
Silurian (Rhuddanian) time, although there are contradictory evidences from the
Rhuddanian sections. For the ensuing Aeronian Stage, petrologic and
sedimentary evidence found in the central Oslo Region points to a source from
the west, while benthic faunal and sedimentary data corroborate a slope from
west to east.
Dehydration, Partial Melting and Assimilation of Metabasaltic Xenolithsin
Gabbros of the Kap Edvard Holm Complex, East Greenland
American Journal of Science, 296, 333-393 (1996)
Partially assimilated xenoliths of metabasaltic lava are locally abundant in
Eocene gabbros of the Kap Edvard Holm Complex in East Greenland. The xenoliths
range from centimeters to >100 m in length and consist mainly of hornfelsic
augite, orthopyroxene, plagioclase, olivine, magnetite, and ilmenite, with
two-pyroxene equilibration temperatures of ~1050oC. The hornfelses
have been strongly depleted in incompatible elements due to extraction of an
anatectic liquid. Melt fractions of roughly 30 to 50 percent are estimated
from trace element modeling. Devolatilization or dehydration-melting of
xenoliths released hydrous liquids into the gabbroic magma, locally causing
replacement of gabbroic cumulates by bodies of peridotite and coarse-grained to
pegmatitic gabbro.
The xenoliths contain hornfelsic minerals with d18O values as low as
-5.5 permil. The low-d18O values were inherited from the country
rock protoliths, which had previously been altered by low-d18O
hydrothermal fluids of meteoric origin. Oxygen isotope fractionations between
plagioclase and pyroxene are close to equilibrium values for magmatic
temperatures, indicating that the xenoliths recrystallized in isotopic
equilibrium during heating and subsequently underwent little or no oxygen
isotope exchange during subsolidus cooling and alteration of the pluton.
Many xenoliths contain igneous bodies that crystallized from trapped partial
melts. These include pegmatitic pods consisting of hornblende, andesine,
apatite and phlogopite, and plagioclase-rich leucosomes in which pockets of
hornblende-rich pegmatite are locally developed. The abundance of hydrous
minerals in these melt bodies suggests that melting was facilitated by the
presence of H2O in the hydrothermally altered metabasaltic
protoliths. Alteration and hydration of the country rock metabasalts thus
enhanced the potential for contamination of magmas with hydrous fluids and
partial melts.
Formation of Anorthosite and Leucotonalite During Magma Hybridization in the
Koperberg Suite of Namaqualand, South Africa
Mark E. Brandriss, Visiting Assistant Professor, R. Grant Cawthorn, University
of the Witwatersrand
South African Journal of Geology, 99, 135-151 (1996)
The Koperberg Suite comprises thousands of small dioritic, noritic,
anorthositic, and tonalitic intrusions that were emplaced into the granitic
crust of Namaqualand, South Africa, under granulite facies conditions during
the 1200 - 1000 Ma Namaqua Event. In this study, genetic relationships among
the different rock types have been elucidated through detailed study of the
Hoogkraal Intrusion, a small (~0.1 km2) but petrologically complex
Koperberg Suite body. The rocks of the intrusion can be divided into two
groups: 1) an early group of leucotonalites and anorthosites with high initial
87Sr/86Sr ratios (0.722 - 0.727); and 2) a later group of
diorites, leucodiorites, monzodiorites, and leuconorites with lower initial
87Sr/86Sr ratios (0.706 - 0.720, mainly <= 0.710).
The range of Sr isotope ratios reflects mixing of two genetically distinct
components: 1) a relatively felsic and radiogenic component, derived from
granitoid crust; and 2) a more mafic and less radiogenic component, probably
derived from the mantle. Hybridization between these components took place as
mantle-derived mafic magmas underwent differentiation and contamination during
their ascent through the granitoid crust. Cumulus anorthosites formed when
dioritic magmas became supersaturated with plagioclase as a result of reaction
with felsic country rocks. Tonalites formed when these cumulates entrained or
assimilated quartz-rich residua of country-rock melting. Evidence for such
processes is preserved in outcrops that expose the contacts between granitic
xenoliths and their host leucodiorite body. Along the contacts, the
leucodiorite has an anorthositic marginal zone and the xenoliths have
leucotonalitic selvages. Major bodies of anorthosite and leucotonalite formed
when these processes, operating at large scales, produced cumulus mushes that
coalesced and rose diapirically through the crust. The association of
anorthosite, tonalite, and diorite is a conspicuous feature of several other
Proterozoic intrusive suites in the Namaqualand Metamorphic Complex, suggesting
that similarly complex processes of hybridization were characteristic of mafic
to intermediate magmatism throughout the region during the Namaqua Event. It
is likely that crustal assimilation and magma hybridization were greatly
facilitated by the near-anatectic temperatures of regional metamorphism during
that time.
Temperature Dependence of Oxygen Isotope Fractionation Between Diatomaceous
Silica and Water
Geological Society of America Abstracts with Programs, 28 (7), 428 (1996)
The temperature dependence of oxygen isotope fractionation between diatomaceous
silica and water was determined by analyzing laboratory cultures of a single
species of freshwater diatom (Stephanodiscus niagarae) grown over a range of
temperatures in water of known isotopic composition. Prior to fluorination of
the opaline diatom frustules, organic matter was removed from the specimens by
digestion in concentrated nitric acid. The clean frustules were then
dehydrated in vacuum (1.5 hours at 120oC, followed by ten minutes at
1060oC) prior to loading into a conventional fluorination line.
Measured silica-water fractionations (1000lna) were 35.3, 34.4, and 33.4 at
3.6oC, 9.1oC, and 13.9oC, respectively
(experiments at 20oC are in progress). These initial results
correspond to a temperature coefficient of approximately 0.2 permil per
oC over this range of temperature. This is significantly lower than
the value of about 0.3 permil per oC proposed by Leclerc and
Labeyrie (1987) from analyses of diatoms from marine sediments. The
silica-water fractionations we measured were between 4 and 5 permil smaller
than published estimates of equilibrium quartz-water fractionations at these
temperatures. Part of this difference may be attributed to systematic isotopic
shifts produced by our analytical procedures, and some may reflect
disequilibrium isotopic fractionation during diatom growth (a vital effect).
If real, such systematic isotopic shifts could affect the magnitudes of
measured of oxygen isotope fractionations substantially, but the regularity of
the results and the reasonable temperature coefficient obtained for the oxygen
isotope fractionation between diatomaceous silica and water indicate that the
diatoms in our experiments recorded potentially useful thermometric information
during growth. Further experiments with biogenic silica may therefore have
applications to paleothermometric studies of freshwater and marine systems.
Quantification of the Effects of Secondary Matrix on the Analysis of Sandstone
Composition, and a Petrographic-Chemical Technique for Retrieving Original
Framework Grain Modes of Altered Sandstones
Journal of Sedimentary Research, 66, 548-558 (1996)
Most studies of sandstone provenance involve modal analysis of framework grains
using techniques that exclude the fine-grained breakdown products of labile
mineral grains and rock fragments, usually termed secondary matrix or
pseudomatrix. However, the data presented here demonstrate that, when the
proportion of pseudomatrix in a sandstone exceeds 10%, standard petrographic
analysis can lead to incorrect provenance interpretation. Petrographic schemes
for provenance analysis such as QFL and QFR should not therefore be applied to
sandstones containing more than 10% secondary matrix.
Pseudomatrix is commonly abundant in sandstones, and this is therefore a
problem for provenance analysis. The difficulty may be alleviated by the use
of whole-rock chemistry in addition to petrographic analysis. Combination of
chemical and point-count data permits the construction of normative
compositions that approximate original framework grain compositions.
Provenance analysis is also complicated in many cases by fundamental
compositional alteration during weathering and transport. Many sandstones,
particularly shallow marine deposits, have undergone vigorous reworking, which
may destroy unstable mineral grains and rock fragments. In such cases it may
not be possible to retrieve provenance information by either petrographic or
chemical means. Because of this, pseudomatrix-rich sandstones should be
routinely included in chemical-petrological provenance analysis.
Because of the many factors, both pre- and post-depositional, that operate to
increase the compositional maturity of sandstones, petrologic studies must
include a complete inventory of matrix proportions, grain size and sorting
parameters, and an assessment of depositional setting.
The Geology of the Itremo Group, Central Madagascar: Deformed Remnant of a
Proterozoic Continental Shelf Sequence
Proceedings of the UNESCO-IUGS-IGCP-368 International Field Workshop on the
Proterozoic Continental Crust of Southern India: Trivandrum, Gondwana Research
Group, 86-88 (1996)
The Itremo Group of central Madagascar is a quartzite-pelite-carbonate
continental shelf sequence of Proterozoic age. The stratigraphy of the
sequence has been interpreted differently by different workers in the past.
However, extensive work by Moine (1967, 1974), reconfirmed by our field
investigations, has established that the succession consists of a lower
quartzite sequence (minimum thickness 1000 m); a middle pelitic unit (minimum
500 m) and an upper carbonate sequence (minimum 1000 m). The carbonate
sequence is further subdivided into a lower stromatolitic unit consisting of
almost pure dolomite, and an upper sandy carbonate unit containing about 10-50%
siliciclastic detritus. Thicknesses are minima because (1) neither the base
nor the top of the sequence is seen and (2) deformation has disrupted regional
stratigraphic continuity.
SHRIMP data from detrital zircons provide constraints on the age of the
sedimentary sequence. The maximum depositional age is approximately 1.8 Ga,
which is the age of the youngest concordant zircons. Lead loss in the zircons
points to a minimum age around 700-800 Ma, which is supported by 770-800 Ma
U-Pb zircon crystallization ages (Ashwal et al., this volume) from crosscutting
granitoids.
Metamorphic grade in the Itremo Group ranges from sub-greenschist to
amphibolite, and the rocks have been deformed in a series of upright to
recumbent folds separated by ductile shear zones. The intrusive granitoids
are unmetamorphosed and essentially undeformed, but in some cases they contain
a weak subsolidus foliation that parallels the regional foliation in the
strongly deformed metasediments. We interpret this to represent late
syn-deformational intrusion of the granitoids, and therefore interpret the
770-800 Ma age of the granitoids as an estimate of the age of deformation of
the metasediments.
Clastic sediment compositions indicate a continental provenance. The large
thickness of clean quartz arenites is suggestive of continental derivation, but
the absence of any lithic fragments or feldspar hinders more specific
provenance analysis. The ratios of low-solubility trace elements in pelitic
sediments have been shown to relate to their source rocks and tectonic setting
(Taylor and McLennan, 1985; Bhatia and Crook, 1986; Condie and Wronkiewicz,
1990 a, b). Ratios of Th/Cr, Th/Sc and Zr/Cr for the Itremo Group pelites are
close to or higher than those of the North American Shale Composite (Gromet et
al., 1984), indicating a continental source terrane. Rare earth element data
also support a continental source: Eu/Eu* values range from 0.59 to 0.70 and
cluster around 0.65, which is the value for the average upper continental crust
(Taylor and McLennan, 1985). None of the sediments analyzed show any
compositional evidence for an active margin or island arc source component, and
we conclude that they represent either a passive margin or an epeiric sea.
There is growing evidence that Madagascar preserves a record of at least two
phases of Pan-African deformation, probably reflecting multi-stage Gondwana
assembly (Cox et al., 1995). Similar ages of deformation, metamorphism and
intrusion are seen in supracrustal sequences in east Africa (e.g., Key et al.,
1989; Mosley, 1993; Shackleton, 1993). We infer that the older ages seen in
central Madagascar reflect incorporation of this part of the island into
Gondwana by at least 770-800 Ma, and that the Itremo Group probably represents
a depositional basin that was closed and deformed during the accretion process.
Evaluation of this hypothesis requires further field and laboratory work.
Trends in Mudrock Chemistry Through Time: Implications for the Evolution of
Continental Crust
Rónadh Cox, Assistant Professor of Geosciences
Geological Society of America Abstracts with Programs, 228, A-492
(1996)
At the global scale, it is known that there is a correlation between age and
average trace element composition of mudrocks, implying a systematic change in
average source rock composition with time. Evaluating this change is therefore
relevant to understanding the long-term growth and evolution of continental
crust.
Compilation of trace element data from the literature indicates that, on
average, Th/Sc and La/Sc values increased and Eu/Eu* values decreased
progressively through the Archean and post-Archean, with no sharp compositional
shifts at the Archean-Proterozoic boundary. The gradual changes in globally
averaged mudrock chemistry may reflect in part the buffering effects of
sediment recycling, which would tend to mask any rapid change in average
crustal composition. However, at the scale of individual continental blocks,
evolution of mudrock chemistry is more episodic. Therefore, the smoothness of
the global mudrock chemistry trends may represent the average of numerous
smaller systems evolving at different times and possibly at different rates.
The influence of tectonic setting on mudrock composition has also changed
through time. Archean mudrocks from quartzite-pelite stratigraphic sequences
(continental settings) have similar average trace-element compositions to those
from greenstone sequences (non-cratonic settings). However, as time
progressed, average Th/Sc and La/Sc values for continental mudrocks increased
at a significantly greater rate than did those for non-cratonic mudrocks. The
increasing differences between mudrocks from differing tectonic settings may be
explained by increasing proportions of evolved granitic continental crust
relative to juvenile crust exposed at the surface and by growth or amalgamation
of large continental masses with stable interiors effectively isolated from
their active edges.
Lacustrine Chronology Links Climate Change and Landslide Activity, White Rock
Canyon, New Mexico
Geology, 24, 539-542 (1996)
Well-dated lacustrine deposits in northern White Rock Canyon, New Mexico,
record damming of the Rio Grande by at least four separate failures of a slump
complex between about 17.5 and 12.4 14C ka, a period of rapid
climate change in the western United States. Failure of metastable slumps
probably resulted from removal of lateral support during downcutting and
lateral erosion by the Rio Grande and from the decrease in resisting forces due
to additional groundwater recharge. Our chronology suggests that the older
lakes in White Rock Canyon record pulses of glacial melt and pluvial runoff and
that the younger lakes reflect mainly pluvial activity. The lake that formed
between 17.5 and 15.0 ka probably records glacial melt and pluvial activity,
the youngest lake (~ 12.4 ka) pluvial influence, and the intermediate lakes
(13.7 to 13.1 ka) pluvial and minor meltwater activity. We have not found
extensive lacustrine deposits younger than about 12.4 ka, suggesting that
Holocene slumping was minor, or occurred at rates too low to dam the Rio Grande.
Late Pleistocene Landslide-Dammed Lakes Along the Rio Grande, White Rock
Canyon, New Mexico
Geological Society of America Bulletin, 108, 1492-1507 (1996)
Massive slump complexes composed of Pliocene basaltic rocks and underlying
Miocene and Pliocene sediments flank the Rio Grande along 16 km of northern
White Rock Canyon, New Mexico. The toe area of at least one slump complex was
active in the late Pleistocene, damming the Rio Grande at least four times
during the period from 18 to 12 14C ka and impounding lakes that
extended 10 to 20 km upriver. Stratigraphic relationships and radiocarbon age
constraints indicate that three separate lakes formed between 13.7 and 12.4
14C ka. The age and dimensions of the ca. 12.4 ka lake are best
constrained; it had an estimated maximum depth of ~30 m, a length of ~13 km, a
surface area of ~2.7 km2, and an initial volume of ~2.5 x
107 m3. The landslide dam responsible for this lake was
apparently stable, and the lake filled completely with laminated silt-rich
lacustrine sediment and overlying coarse sands and gravels that represent
bedload of the Rio Grande. A lake that formed at <=17.5 ka was
approximately 21 km long and apparently failed catastrophically, recorded by
probable outburst flood deposits that extend downriver from the landslide dam.
An older (>=43 14C ka) landslide-dammed lake is less well
constrained, but it had a maximum depth of at least 57 m, an estimated minimum
length of 25 km, and a surface area of 25 km2. Deposition of coarse
sands and gravels of the Rio Grande over lacustrine sediments indicates that
the landslide dam responsible for this older lake also was stable;
extrapolation of historic Rio Grande sediment yield data suggests that this
lake persisted for 100 to 1000 yr. The stability of the dam may have been due
to armoring of the outflow channel with basalt boulders.
The youngest landslide-dammed lakes formed during a period of significantly
wetter regional climate, strongly suggesting that climate changes were
responsible for reactivation of the slump complexes. We are not certain about
the exact triggering mechanisms for these landslides, but they probably
involved removal of lateral support due to erosion of the slope base by the Rio
Grande during periods of exceptionally high flood discharge or rapid incision;
increased pore pressures associated with higher water tables; higher seepage
forces at sites of ground-water discharge; or some combination of these
processes. Seismic shaking could also have contributed to triggering of some
of the landslides, particularly if aided by wet antecedent conditions.
Pliocene and Quaternary History of the Rio Grande, White Rock Canyon and
Vicinity, New Mexico
New Mexico Geological Society Guidebook 47, 317-324 (1996)
Surface and subsurface evidence shows that the elevation of the Rio Grande in
the vicinity of White Rock Canyon fluctuated greatly during the Pliocene and
the Quaternary, influenced by volcanism, tectonism, and climatic changes.
Initial establishment of the Rio Grande as a through-going drainage at ca.
4.5-5 Ma was followed by 250 m or more of incision into rift-filling sediments
of the Santa Fe Group. The elevation of the Rio Grande then rose 300 m by
about 2.4 Ma, coinciding with eruption of and repeated damming of the river by
basaltic lavas of the Cerros del Rio volcanic field. Simultaneous deposition
of thick Puye Formation fanglomerates to the north may have been aided by
blockage of the valley by the lavas and the resultant rise in local base level.
By early Pleistocene the Rio Grande had incised a narrow canyon up to 180 m
deep through the western Cerros del Rio field. Eruption of the Tshirege Member
of the Bandelier Tuff at 1.22 Ma completely buried the early Quaternary
paleocanyon and dammed the river, impounding a lake with a possible length of
75 km. The low spot on the dam was east of the paleocanyon, forcing the Rio
Grande to cut a new channel through 200 m of basaltic rocks to reach its former
grade. Relatively slow erosion through the basalt probably produced a
persistent knickpoint that controlled base level upriver. Extensive slumps
developed in northern White Rock Canyon after the river had incised into
mechanically weak sediments beneath basalts, probably beginning in
mid-Pleistocene time. Reactivation of slumps in wetter periods in the late
Pleistocene repeatedly dammed the river, producing lakes up to 60 m deep and 25
km long. By early Holocene the Rio Grande was within 5 m of its present grade,
and the river has remained near its modern level through the Holocene.
Morphology and Seismic Stratigraphy of Marine Banks, Northern Puget Lowland,
Washington
Geological Society of America Abstracts with Programs, 28 (7), A-435 (1996)
Single-channel seismic reflection records from >320 km of trackline in NW
Washington demonstrate that marine banks of the E. Strait of Juan de Fuca and
adjacent areas are composed mainly of stratified late Quaternary sediment.
Gently sloping banks rise 50 to 150 m above the surrounding sea floor to within
20 m of sea level and cover areas of 5 to 50 sq. km. We studied Alden,
Eastern, Hein and other large banks using seismic imaging techniques that
included bubble pulser (400 Hz) and higher frequency sources. Our geomorphic
and seismic evidence suggests that most banks developed as glaciomarine
moraines during calving retreat of Cordilleran ice from NW Washington between
13,800 and 13,100 radiocarbon yr B.P. Bedrock "anchors" areas of Salmon Bank
and the western edge of Lawson Reef and acoustically opaque sediment dominated
by hyperbolic reflectors (probably till) lies 30 to 180 m beneath the surface
of several banks. Planar and cross-stratified reflectors are dominant, locally
covered with or grading laterally into acoustically transparent pebbly muds.
Cross-stratified deposits perched on the margins of banks probably represent
spits and other tidal deposits formed and submerged during Holocene sea-level
rise. Cobble to boulder gravel covers surfaces of banks.
Marine evidence and nearby subaerial exposures suggest that the south and
west-dipping stratified sediments of most banks were deposited mainly as
submarine outwash where retreating lobes of Cordilleran ice grounded. Seismic
stratigraphy, morphology and distribution suggest banks formed at major
meltwater conduits that carried sediment hydraulically eroded from a few tens
of km up ice. Larger banks such as Alden and Hein each contain >1 cu. km of
sediment and must have taken tens of years to form near subglacial tunnel
complexes. Some banks, however, may be eroded remnants of older glacial and
fluvial deposits.
Mechanics and Stress Analysis of the Pine Cobble Landslide, Williamstown
Massachusetts
Northeastern Geology and Environmental Sciences, 118 (3), 237-242 (1996)
The Pine Cobble development in Williamstown, MA, is plagued by a well known,
but poorly understood slump failure. The slumping was initiated by a road cut
that oversteepened glacial sediments which cover the hillside. This
investigation estimates the location and geometry of the failure surface for
this slump, and quantitatively identifies the factors contributing to motion.
Cross sections of three transects across the major slump were constructed,
using data from drill logs and surface measurements. Under the assumption that
the slump moves as a cohesive block, the dip angle of the failure surface below
several measurement stations on each transect was determined using data from
surface motion. To estimate the failure plane's location, the assumption of a
circular arc rotational slump was adopted, and an axis of rotation was
constrained by the geometry of surface motion and the subsurface bedrock
profile.
From cross sections, shear stress at the failure plane was calculated using the
Fellinius method, by dividing each transect into several linear sliding blocks.
Combining this data with the geometry of the failure surface and estimates of
shear strength from drill blow counts, the relative importance of variables
that contribute to slope motion was evaluated with a spreadsheet program.
This investigation provides probable values for cohesion and internal friction,
and suggests that pore pressure plays a negligible role in causing instability.
Instead, the principal factors which cause slumping appear to be the removal of
substantial amounts of material from the toe of the slope, the presence of weak
zones in the soil mass with angles of internal friction of
22o-24o, and decreases in friction angle caused by water.
In addition, this study offers a quantitative explanation for the slump's
present boundaries.
Stable Cratonic Sequences and a Standard for Silurian Eustasy
Geological Society of America Special Paper, 306, 203-211 (1996)
The Silurian System is the most widely correlated of the Paleozoic systems in
terms of biostratigraphically well defined patterns of eustasy.
Standardization of all its series and many stages has promoted international
cooperation with respect to sea-level studies. Stable cratonic sequences,
typically fossil-rich carbonate cycles, have proven to be a major source of
comparative intercontinental data. A key sequence representative of the Lower
Silurian Llandovery Series occurs in the east-central Iowa Basin on the North
American craton (Laurentia). Up to four distinct and coeval highstands in sea
level may be correlated with five other paleocontinents or microcontinents,
including Avalonia (Wales and England), Baltica (Norway and Estonia), Bohemia
(central Europe), Cathyasia (South China), and Gondwana (Brazil and New South
Wales, Australia).
Another key sequence representative of the Wenlock and Ludlow series occurs in
Estonia on the Balto-Scandinavian craton. At least three highstands in sea
level may be widely correlated on the basis of this standard. The Upper
Silurian Pridoli Series remains undefined in terms of stages and its tendency
toward eustasy is poorly understood. The type locality for the Pridoli Series
in the Prague Basin (Barrandian) of Bohemia records two highstands in sea
level, one of which is strictly local in occurrence. The overall record of
Silurian eustasy has practical applications, including assessment of
tectonism, development of an ancillary time scale, reconstruction of cratonic
bathymetry, and study of associated extinctions and radiations.
Discrimination Between Coastal Ramps and Marine Terraces at Punta Chivato on
the Pliocene-Pleistocene Gulf of California
Journal of Geoscience Education, 44, 569-575 (1996)
The seven km2 promontory at Punta Chivato in Baja California Sur
(Mexico) is a natural laboratory in which to explore the geomorphologic
differences between marine terraces and coastal carbonate ramps and their
relative ages. During Early Pliocene time, the area was an igneous island that
slowly subsided into the Gulf of California from an elevation 100 m above sea
level. Erosional retreat of the andesitic coastline resulted in long coastal
ramps with an average slope of 6.5o dipping away from the island's
center in a radial pattern. An intertidal molluscan fauna thrived on a
substrate of andesite cobbles, but selective colonization by the coral
Solenastrea fairbanksi occurred only on the north side. Probably less
than 25 m of eustatic sea-level rise added to the drowning of the island, with
the rest due to tectonic subsidence at a low rate of 0.05 mm/year through the
mid-Pliocene. Subsequently uplifted and rejoined to the Baja California
peninsula sometime in the later Pleistocene, a marine terrace formed around the
promontory's perimeter during the last interglacial period (oxygen isotope
substage 5e). A coral reef dominated by Porites californica occupied
the promontory's southern terrace at that time.
Silurian Event Horizons Related to the Evolution and Ecology of Pentamerid
Brachiopods
Paleontological Events: Stratigraphic, Ecological, and Evolutionary
Implications, Columbia Univ. Press 162-180 (1997)
The big-shell communities dominated by pentamerid brachiopods formed some of
the most simple but spatially prolific Silurian associations. They attained a
broad intercontinental distribution and thrived equally well in carbonate,
mixed carbonate-clastic, and siliciclastic settings. Species diversity is
variable but often verges on monotypic. The Llandovery or Wenlock species
Borealis borealis, Virgiana decussata, Pentamerus oblongus, P. dorsoplanus,
and Pentameroides subrectus frequently occur in large numbers preserved in
growth position. Late Wenlock to Ludlow forms such as Kirkidium sp.
contributed to the fabric of bioherms but are also known from biostromes in
growth position. What constitutes a fossil community is difficult for
paleontologists to agree on, but genuine pentamerid populations are well
documented. Pentamerid ecology is summarized on the basis of North American,
northern European, Siberian, and Chinese material, with emphasis on a variety
of large to small-scale event horizons related to evolutionary novelty,
biogeography, fluctuations in sea level, local seafloor typography, and
generation of tempestites.
Development and Foundering of the Pliocene Santa Ines Archipelago in the Gulf
of California: Baja California Sur, Mexico
Geological Society of America Special Paper 318, 25-38 (1997)
Parts of an archipelago consisting of five Pliocene islands with high rocky
shorelines are preserved in the Punta Chivato region of Baja California Sur,
Mexico. The name for this old island group is taken from Islas Santa Ines
(three small islands that originally formed one of the Pliocene islands)
located 2 km southeast of the Punta Chivato promontory in the Gulf of
California. With an elevation more than 100 m above early Pliocene sea level,
the largest of the islands was 7 km2. It now forms the Punta
Chivato promontory. Island cores are composed of resistant Miocene volcanics
(mostly andesite) belonging to the Commondu Group. They are skirted by
carbonate ramps sloping at angles averaging 6.5[currency] from
present sea level up to elevations of approximately 80 m. Lithofacies
representing intertidal conglomerates and siltstone to offshore limestones and
siltstones are attributed to the lower Pliocene San Marcos and upper Pliocene
Marquer Formations. Significant index fossils include the echinoid
Clypeaster bowersi, the sand dollars Encope sverdrupi and E.
shepherdi, the pectens Aequipecten deserti and A.
sverdrupi, and the coral Solenastrea fairbanksi.
At their fullest development during the early Pliocene, the islands blocked and
refracted waves driven by strong seasonal winds from the north. Windward
biofacies found on the north and east sides of the Punta Chivato promontory
include a diverse fauna of intertidal molluscs. Colonies of the coral
Solenastrea fairbanksi also occur on the north side. Leeward biofacies
occurring only on the sheltered south side of the Punta Chivato promontory
include concentrations of oysters, the sand dollar Encope sverdrupi, the
small echinoid Agassizia scorbiculata, and extensive horizontal burrows
typical of "ghost shrimp." Fragments of fossil bone incorporated in basal
conglomerate indicate that whales navigated the archipelago. A computer model
is used to simulate Pliocene wave refraction around the main island at Punta
Chivato. The archipelago completely sank below the surface of the Gulf of
California by the start of late Pliocene time. Limestones rich in rhodoliths
and siltstones bearing abundant pectens transgressed the onshore facies and
buried the islands. Relative change in sea level was at lest 100 m, based on
the topography of the Pliocene-Miocene unconformity.
Upper Pliocene Stratigraphy and Depositional Systems: The Peninsula Concepcion
Basins in Baja California Sur, Mexico
Geological Society of America Special Paper 318, 57-72 (1997)
Geological mapping and stratigraphic differentiation of members belonging to
the Upper Pliocene Infierno Formation at the base of Peninsula Concepcion in
Baja California Sur, Mexico, are the subjects of this chapter. Because of the
regionally distinctive nature of chert deposits, names derived from local
features are proposed for four new members. The stratigraphic order and
lateral extent of these units indicate that at least two separate marine
transgressions cover an area approximately 35 km2. Three peninsulas
and four islands up to 2 km2 in size effectively subdivide the
embayment into four basins interconnected with the Pliocene Bahia Concepcion.
The islands and surrounding mainland are composed of andesite and basalt
belonging to the Miocene Comondu Group. Included in the basins are some or all
of the following units assigned to the upper Pliocene Infierno Formation
(oldest to youngest): (1) Calabaza Member (mainly alluvial fans), (2) El Mono
chert Member (includes fossil mangroves), (3) Bahia Concepcion Member (lower
and upper limestone units separated by an alluvial siltstone with a
well-developed rhizolith), and (4) Cayuquitos chert Member. Buttress
unconformities between the Miocene volcanics and Pliocene marine units
delineate rocky shorelines of a well-sheltered nature. The extensive limestone
beds of the Bahia Concepcion Member are flat lying over most of the region,
although they are cut by as many as four faults tending northwest by southeast.
Two paleo hot springs are associated with faults within the study region, and
another example is located nearby.
El Mono Chert: A Shallow-Water Chert From the Pliocene Infierno Formation,
Baja California Sur, Mexico
Geological Society of America Special Paper 318, 73-81 (1997)
A well-bedded, 14-m-thick chert unit assigned to the Infierno Formation is
located near the southeast corner of Bahia Concepcion at the base of the
Concepcion Peninsula in Baja California Sur, Mexico. Previously unknown, the
age of this chert is restricted by fossils that date conformably overlying
limestones as late Pliocene in age. The chert beds, as well as the rest of the
associated sequence, were deposited in an interconnected set of small basins
flooded from the direction of present-day Bahia Concepcion. A shallow-water
environment for the chert is indicated by the occurrence of fossil mangrove
roots preserved in life position along the margin of one basin and the abundant
presence of the ichnofossil Ophiomorpha in a laterally extensive
horizon within the chert body. Stratigraphic bracketing of the chert unit by
an underlying subaerial fan-deposit conglomerate and an overlying fossiliferous
limestone confirms a likely water depth between intertidal and 10 m. X-ray
diffraction and microscopic analyses of the chert suggest that a portion of the
silica was deposited originally as a particularly silica-rich tuff.
Basin-cutting faults acted as conduits, transporting silica-enriched hot water
that eventually transformed most of the volcanic glass and all the original
carbonates to opal-A and low cristobalite.
Bryozoan Nodules Built Around Andesite Clasts From the Upper Pliocene of Baja
California: Paleoecological Implications and Closure of the Panama Isthmus
Geological Society of America Special Paper 318, 111-117 (1997)
Fossil bryozoan nodules ("bryoliths," "ectoproctaliths," or "bryozoan
macroids") are found in upper Pliocene deposits estimated to have formed at 2.4
Ma in the Loreto Basin, located two-thirds of the way down the gulf coast of
Baja California (at 26o05'10"N, 111o21'05"W). The
nodules occur abundantly, along with numerous pectinid bivalves, in a shelly
sandy conglomerate interpreted as part of a marginal-marine fan delta now
exposed in Arroyo Arce. The nodules, mostly between 4 and 8 cm in diameter,
range up to 19 cm long by 12 cm wide by 9 cm high. Smooth surfaced and well
rounded in form, each consists of many thin sheetlike laminae encrusting an
andesite-cobble core. Except for the largest specimen recovered, growth was
concentric as a result of frequent overturning of the nodules by storm waves,
tidal currents, and perhaps bioturbators. Bryozoan crusts are composed of
laminae all belonging to the anascan cheilostome Conopeum commensale.
Nodules of this species today are concentrated in tidal inlets along
barrier-island coasts, such as the Delmarva Peninsula of Virginia (where it may
possibly be intergrown with an encrusting variety of Membranipora
arborescens). Conopeum commensale ranges farther south along the
coasts of Brazil and west Africa. Its modern Atlantic distribution, compared
to its occurrence in the upper Pliocene of Baja California, shows that this
species migrated to the Pacific Ocean before closure of the Panama Isthmus no
later than about 3.5 Ma. Invasion of the Pliocene Gulf of California by this
Atlantic species substantiates the influence of a northerly directed coastal
current in the east Pacific related to the flow-through of marine waters from
the Atlantic to the Pacific.
Global Review of Upper Pleistocene (Substage 5e) Rocky Shores: Tectonic
Segregation, Substrate Variation, and Biological Diversity
Journal of Coastal Research, 13, 297-307 (1997)
A bibliographic search using the computerized system, Georef, allowed effective
screening of the geological and paleontological literature for research
articles on abandoned rocky shores correlated with oxygen isotope substage 5e
(mid-point of the last interglacial epoch approximately 125,000 years before
present). Sixty articles covering 54 localities with a global distribution
were selected for synopses, including information on substrate lithology,
present elevation, and faunal character. The sites are sorted by tectonic
regime: 37% occur on active continental margins (modest uplift); 13% on
passive continental margins (little or no uplift); 35% on island arcs
(significant uplift); 15% on island chains or continental margins affected by
hot spots (minor uplift to modest subsidence). In terms of their geographical
latitude, the sites represent a range from temperate shores with dominantly
molluscan faunas to subtropical shores with mixed molluscan and colonial coral
faunas, to tropical shores with dominantly colonial coral faunas. During the
peak of the last interglacial epoch, the subtropical limits were extended
between 300km and 600km farther north and south than at present. Differences
in biological diversity are difficult to gauge based on the highly selective
species lists available in this data set. Nevertheless, enough information is
at hand to clearly demonstrate that encrusting, intertidal to very shallow
subtidal biotas are being retained in the geological record.
Upper Pleistocene Rocky Shores and Intertidal Biotas at Playa La Palmita (Baja
California Sur, Mexico)
Journal of Coastal Research, 13, 216-225 (1997)
Four examples of Upper Pleistocene, rocky shores and associated biotas are
preserved in ecological detail at Playa La Palmita in Bahia Santa Ines on the
Gulf of California (Baja California Sur, Mexico). A 2 m-high sea cliff eroded
from Miocene andesite reaches 6.25 m above present sea level and retains 15
species of encrusting organisms. Dominant space occupiers are the bivalves
Pseudochamma janus, Ostrea fischeri, O. palmula, Arca
pacifica, Cardita affinis, and Chama mexicana together with
coralline red algae. Carbonate sediments burying the sea cliff include
rhodoliths, 15 additional species of free-dwelling bivalves and 15 species of
gastropods, most of which are intertidal to shallow-subtidal in habit. At the
top of the sea cliff is a hydrothermal deposit of dolomite, which formed a
broad abrasion platform extensively bored by a bivalve species attributed to
Thracia curta.
An andesite shoal 2,600 m2 in area occurs at a slightly higher
elevation 7.75 m above present sea level and preserves zoned populations of
Glans affinis and Periglypta multicostata (bivalves), as well as
vermetid "worm-shell" colonies. A flat andesite island 12,500 m2 in
area occurs at a slightly higher elevation in area with an elevation of 11 m
is completely surrounded but not covered by carbonates. Nestled among boulders
in the lee of the paleo-island are bivalve populations of Chione
californiensis, P. multicostata, and Codakia distinguenda.
Based on previous studies employing U-series analyses at Playa Palmita and
nearby Mulege, these features can be correlated to oxygen isotope substage 5e,
that is, developed about 125,000 years ago as a facies of the Mulege Formation.
Evidence for Contemporaneous Movement on Multiple Thrusts From Footwall
Slivers Caught Between Hanging-Wall Imbricates
Geological Society of America Abstracts with Programs, 28 (7), A-508 (1996)
The debate between foreland vs. hinterland progression of thrusting has
polarized the kinematic interpretations of thrust belts and has been
intensified by the often unstated assumption that only one thrust in a system
is active at a time, in other words, that initiation of a new thrust
deactivates older thrusts. Allowing for the possibility that multiple thrusts
are contemporaneously active can help explain complex geometric features of
thrust belts such as footwall-derived slivers found between hanging-wall
imbricate sheets in the Taconian thrust belt of western New England and eastern
New York.
The Taconian thrust belt in the northern Appalachians developed as the
Laurentian margin collided with a magmatic arc in the Ordovician. Taconic
sequence rocks deposited on the continental slope and rise were thrust westward
over shelf sequence rocks. Duplexes comprised of Grenvillian basement and
overlying basal clastics developed near the shelf-slope transition but the
overlying Early Cambrian to Middle Ordovician carbonate rocks are missing from
the duplexes. West of the duplexes, ridges composed of Taconic sequence rocks
(phyllite and slate) alternate with valleys underlain by less resistant shelf
sequence rocks (marble). However, not all ridges of Taconic sequence rocks are
klippen structurally above the shelf sequence rocks as previously interpreted.
Some, if not most, of the ridges are interleaved with thrust-bounded carbonate
slivers. The largest slivers are greater than ten kilometers long and one
kilometer thick. Further west there are abundant smaller carbonate slivers
which have long been recognized and have been incorrectly used as evidence for
a hinterland progression of thrusting. The footwall slivers were accreted to
the hanging-wall when the imbricate stack of Taconic sequence rocks ramped over
the shelf sequence rocks. The current geometry can best be explained by
contemporaneous movement on the basal sole thrust and pre-existing imbricates
above the sole. The carbonate slivers were dismembered and carried up along
the imbricate faults.
Carbonate Fault Slivers Control the Orientation and Location of Valleys on the
Greylock Massif, Berkshire County, Massachusetts
Proceedings, Tenth Keck Research Symposium in Geology, 94-95 (1997)
Mount Greylock is the highest point in Massachusetts at 1063 m (3487 ft) and
together with several other separately named peaks it forms the Greylock
massif. The Greylock Schist structurally overlies Cambrian and Ordovician
marbles and quartzites of the Stockbridge Formation and Ordovician flysch (now
phyllite to schist) and marble of the Walloomsac Formation that were deposited
on the continental shelf of Laurentia. Westward thrusting during the
Ordovician Taconian orogeny carried the Greylock Schist over the Stockbridge
and Walloomsac Formations.
Ridges and valleys on and surrounding the Greylock massif trend consistently at
20o, parallel to regional strike. Marbles of the Stockbridge
Formation are much more susceptible to chemical weathering than the aluminum
rich rocks of the Greylock Schist. Rapid chemical weathering promotes
extensive erosion of the marble layers compared to the schist on the Greylock
massif. The long linear valleys commonly coincide with narrow bands of marble
not only near the base of the massif, but also at higher elevations. We
examined, in detail, the contacts between schist and marble near the valleys to
understand the kinematic development of the marble layers on the Greylock
massif.
NNE-SSW striking and east-dipping belts of marble coincide with the major
valleys flanking the Greylock massif as well as numerous minor valleys on the
massif, even at higher elevations (approximately 800 m). The fault-bounded
marble slivers formed when Taconic sequence rocks overrode the carbonate shelf
rocks and large portions of the foot-wall became accreted to the hanging-wall.
The present location of these slivers between thrust sheets of the Taconic
sequence rocks indicates that the imbricate faults were active during westward
transport along the basal sole thrust. The carbonate slivers were carried into
their present positions along the imbricate splays which separated Taconic
sequence rocks. The marked contrast in resistance to chemical weathering and
erosion between the schist and the thin marble layers present on the Greylock
massif explains the long, narrow, deeply incised valleys.
The NNE-SSW striking prominent joint set and crenulation cleavages are closely
parallel to the major ridges and valleys and exert an enormous influence on the
topographic development of the area. The WNW-ESE striking prominent joint
set is approximately parallel to many of the tributary streams. Many tributary
streams are influenced by both joint sets and follow a roughly rectilinear path
down the sides of ridges to the major valleys. This pattern is especially
pronounced in deeply incised valleys where surficial cover is thin or absent.
Does the Northern Termination of the Alleghanian Fold and Thrust Belt Record a
Reversal in Subduction Polarity?
GSA Abstracts with Programs, 29(1), 56 (1997)
The Alleghanian fold and thrust belt dominates the Central and Southern
Appalachians and its abrupt termination in southern New York is one of the
most dramatic features of the Appalachians. In contrast, Alleghanian
deformation and metamorphism are aerially restricted in the New England
Appalachians. Furthermore, instead of crustal shortening, much of the evidence
for Alleghanian deformation and metamorphism in New England indicates low-angle
extensional faulting, probably due to gravitational collapse. Late Paleozoic
intrusives and sedimentary basins in the northern Appalachians are also
consistent with extension. The striking contrasts in Alleghanian orogenesis
noted above can be explained by a reversal in subduction polarity leading up to
continental collision such that the Central and Southern Appalachians were part
of a lower plate below an east-dipping subduction zone whereas the Northern
Appalachians were part of an upper plate above a west dipping subduction zone.
A transfer zone at the latitude of Long Island Sound formed the boundary
between these regions.
Segments of Avalonian crust accreted to Laurentia during the Acadian Orogeny,
but originally east of the zone of Acadian deformation, were underthrust below
the zone of strong Acadian deformation in central New England during an early
phase of Alleghanian crustal shortening. Such segments of Avalonian crust are
exposed in the Massabesic gneiss complex and the Willimantic and Pelham domes.
Rocks with very different P-T-t histories described by Wintsch et al. (1992)
were juxtaposed by extensional faulting.
The transfer zone did not produce large horizontal displacements within
Laurentian crust, rather it accommodated the different tectonic position of the
crust north and south of Long Island Sound. The transfer zone also appears to
have been an important feature during Mesozoic rifting. It may link the
west-dipping eastern border fault of the Connecticut Valley basin with the
east-dipping western border fault of the Newark basin.
Precambrian Geology of Central Colorado
Proceedings, Tenth Keck Research Symposium in Geology, 244-248 (1997)
The Precambrian rocks of Colorado consist of greenschist to amphibolite facies
(minor granulite) metamorphic rocks (1792 to 1694 Ma) intruded by granitic
plutons at roughly 1700 Ma, 1400 Ma and 1080 Ma. Nd-Sm determinations show
that the source of these rocks separated from the mantle at approximately 1800
Ma, from a widespread, homogeneous, depleted-mantle reservoir similar to that
found beneath modern magmatic arcs (Nelson and DePaolo, 1985). The Colorado
rocks are part of a 1300-km-wide Proterozoic orogenic belt in the southwestern
U.S. Within roughly 200-m.y., a region twice the width of the Appalachian or
Cordilleran mountain belts formed from juvenile crust and was accreted to the
Archean Wyoming craton terrane by terrane. This amounts to assembly of more
than 50% of the present crust of North America between 2000 Ma and 1600 Ma.
The significance of the Keck project in Colorado lies in understanding the
history and mechanism of continental growth (Karlstrom and Bowring, 1988). The
Wet Mountains and Southern Front Range have not been studied enough to
determine how they are connected to nearby metasedimentary rocks of the Idaho
springs region or bimodal metavolcanic terranes of central Colorado. The
Colorado project was designed to describe the petrology and kinematic history
of rocks in the Wet Mountains and Southern Front Range, and then to relate that
data to on-going debate over the assemblage of crustal rocks in the Southwest.
Structural Geology of Mid-Proterozoic Gneisses and Granitic Rocks East of the
Ilse Fault, Wet Mountains Colorado
Geological Society of America Abstracts with Programs, 29 (2), 43-44 (1997)
Mid-Proterozoic amphibolite-grade biotite-hornblende gneisses are intruded by
several generations of granitoids in the Wet Mountains, east of the Ilse Fault.
NW- to WSW-striking foliations in isoclinally folded migmatitic gneisses
characterize the rocks between South Hardscrabble Creek and Locke Park.
Mineral lineations plunge generally downdip to the NE or NNE, with some
subhorizontal E-W lineations also measured. Axial surfaces of folds broadly
parallel foliation and hinge lines of folds coincide with lineations,
suggesting that folding and tectonic lineation developed during the same event.
Kinematic shear sense interpreted from mesoscopic textures associated with
lineation is top-to-SW. A later, down-to-NE extension crenulation developed
locally. Static mineral recrystallization textures overprinted the gneissic
fabrics throughout the study area.
Fabrics within a broad shear zone (Newlin Creek shear zone) in gneissic
granodiorite broadly parallel fabrics in host gneisses. The granodiorite
resembles the Boulder Creek pluton, found north of the study area. It contains
foliated xenoliths of biotite gneiss. The shear zone is truncated by fine- to
medium-grained granite with weak to moderate foliation. Granite bodies and
sills also cut gneissic foliation and segregation layering throughout the study
area. At intrusive margins, included blocks of granodiorite or
biotite-hornblende gneiss country rocks show wispy foliation, irregular passive
folds, and ghost-like textures indicative of high temperature assimilation.
Thermal metamorphism induced by the intrusive bodies may have been responsible
for the observed regional textural overprint.
Splitting Versus Unlinking
Journal of Knot Theory and its Ramifications, 5, 295-299, (1996)
We prove there exists a link consisting of two components, each of which is
individually unknotted, such that the link can be split with a single crossing
change, however any such crossing change must knot one of the components.
Unknotting Tunnels for Two-Bridge Knots and Links
Commentarii Mathematici Helvetici, 71, 617-627, (1996)
We give a complete classification of the unknotting tunnels in 2-bridge link
complements, proving that only the upper and lower tunnels are unknotting
tunnels. Moreover, we show that the only strongly parabolic tunnels in
2-cusped hyperbolic 3-manifolds are exactly the upper and lower tunnels in
2-bridge knot and link complements. From this, it follows that the upper and
lower tunnels in 2-bridge knot and link complements must be isotopic to
geodesics of length at most ln(4), where length is measured relative to maximal
cusps. Moreover, the four dual unknotting tunnels in a 2-bridge knot
complement, which together with the upper and lower tunnels form the set of all
known unknotting tunnels for these knots, must each be homotopic to a geodesic
of length at most 6ln(2).
Knotted Tilings
The Mathematics of Long Range Aperiodic Order, ed. by R. Moody, Kluwer
Academic Pub. 1-8, (1997)
This paper is a discussion of tilings of 3-space by knotted tiles. A proof of
the fact that for any topological shape in Euclidean 3-space with one boundary
component, there exists a tiling by tiles, all of which are congruent and all
of which have that topological shape is reviewed. The work of S. Oh is then
extended to show that for any topological shape in the 3-sphere with one
boundary component, there exists of tiling of the 3-sphere by eight congruent
tiles, all of that topological shape. Finally, it is shown that given a
topological shape in 3-space with one boundary component, there exists a tiling
of Euclidean 3-space by tiles that fall into two congruence classes, such that
all of the tiles have that same topological shape and such that the tiling is
aperiodic in the sense that it has no translational symmetry.
Small Solutions to Systems of Linear Congruences Over Number Fields
Rocky Mountain J. of Math, 26, 875-888, (1996)
Here we give new, sharp upper bounds for the size of solutions to systems of
linear congruences over number fields. Such theorems generalize and improve
results of Aubry, Thue, Brauer, Reynolds, and Cochrane. Fundamental to our
method is an analysis of ideals through the geometry of numbers of the adele
space.
Uniformly Approximable Numbers and the Uniform Approximation Spectrum
J. of Number Theory, 61, 194-208, (1996)
We say a real number a is uniformly approximable if the upper bound in
Dirichlet's theorem, from diophantine approximation, of 1/(Q+1)q may be
sharpened to c(a)/(Q+1)2 for all sufficiently large Q. We begin by
showing that the set of uniformly approximable numbers is precisely the set of
badly approximable numbers. In addition, the optimal lower bound of
c(a), referred to as the uniform approximation constant, is explicitly
given. This allows us to introduce the notion of a uniform approximation
spectrum. We conclude with a determination of the smallest values of this new
spectrum and a comparison of this spectrum with other spectra.
On the Structure of Quadratic Irrationals Associated with Generalized Fibonacci
and Lucas Numbers
Fibonacci Quarterly, 34, 200-212, (1996)
Here we determine the explicit structure for irrational numbers of the form
(Fn(a)/Lm(a))[phi]a, where Fn and
Lm are generalized Fibonacci and Lucas numbers, respectively, and
[phi]a is the generalized golden ratio. This work extends
and generalizes previous results of Long and Jordan, and also resolves two open
questions regarding the structure of the periods for such a class of numbers.
Does [Sigma]1/n! Really Converge? Infinite Series and p-adic
Amer. Math. Monthly, 103, 565-577, (1996)
Here we begin with an entertaining introduction to p-adic analysis and
then consider infinite series which converge simultaneously at all spaces of Q.
This result answers a question posed by Koblitz. We also prove a transcendence
result.
On Liouville Decompositions in Local Fields
Proc. of the Amer. Math. Soc., 124, 3305-3310, (1996)
In 1962, Erdos proved that every real number may be decomposed into a sum of
Liouville numbers. Here we consider more general functions which decompose
elements from an arbitrary local field into Liouville numbers. Several
examples and applications are given. As an illustration, we prove that for any
real numbers a1, a2, ... , aN, not equal to 0
or 1, there exist uncountably many Liouville numbers L such that a, a, ...,
aare all Liouville numbers.
Fermat's Last Theorem, the Four Color Conjecture, and Bill Clinton for April
Fools' Day
Amer. Math. Monthly, 104, 246-255, (1997)
In the spirit of April Fools' Day, we celebrate important mistakes made in 19th
century mathematics and their important implications. Specifically, we give
"proofs" of Fermat's Last Theorem, the Four Color Conjecture, and the "fact"
that one of the authors is Bill Clinton.
The Equivalence Problem for Higher-Codimensional CR Structures
Pacific Journal of Mathematics, 177, 211-235, (1997)
The equivalence problem for CR structures can be viewed as a special case of
the equivalence problem for G-structure. This paper uses Cartan's methods (in
modernized form) to show that a CR manifold of codimension 3 or greater with
suitably generic Levi form admits a canonical affine connection, and
consequently that the automorphisms of the CR manifold constitute a Lie group.
The most difficult technical step is to construct a smooth moduli space for
generic vector-valued hermitian forms, which is tied to the CR manifold via the
Levi map. The techniques used to construct this space are drawn from the
classical invariant theory of complex projective hypersurfaces.
Constructing Local Generic Formal Fibers
Journal of Algebra, 187, 16-38, (1997)
Until recently, it was not known whether rings with local generic formal fiber
rings exist. In this paper, we answer this question by constructing rings
possessing local generic formal fiber rings. In fact, our construction shows
that all possible dimensions of generic formal fiber rings are realized.
Moreover, we show that for a complete local unique factorization domain,
T, and a chain of prime ideals p0 [propersubset]
p1 [propersubset] ... pn of T (satisfying minor
conditions), it is possible to construct a corresponding chain of unique
factorization domains An [propersubset] An-1
[propersubset] ... [propersubset] A0 all with completion T
such that the generic formal fiber ring of Ai is local with maximal
ideal pi.
Calculus Lite
AK Peters, Wellesley, second edition, (1997)
This lean text covers single-variable calculus in under 300 pages by (1)
getting right to the point, and stopping there, and (2) introducing some
standard preliminary topics, such as trigonometry and limits, by using them in
the calculus.
Geodesic Nets on the 2-sphere
Proc. AMS, 124, 3843-3850, (1996)
We prove the existence of certain nets of geodesics meeting in threes or more
in equilibrium on certain Riemannian 2-spheres.
Curvy Slicing Proves that Triple Junctions Locally Minimize Area
J. of Diff. Geom., 44, 514-528, (1996)
In soap films three minimal surfaces meet at 120-degree angles. We use a novel
curvy slicing argument to prove that small pieces minimize area for given
boundary. The argument applies in general dimension and codimension.
An Isoperimetric Inequality for the Thread Problem
Bull. Austral. Math Soc., 489-495, (1997)
Given a fixed curve C0 in Rn of length L0 and
a variable curve C of fixed length L <= L0, the thread problem
seeks a least-area surface bounded by C0 + C. We show that an
extreme case is a circular arc and its chord. We provide some counterexamples
and generalizations to higher dimensions.
Math Chat
The Christian Science Monitor, biweekly, starting June 14, 1996
Biweekly column with questions, answers, and prizes, based on the call-in show
on Willinet Cable TV Channel 15 from Williamstown, Massachusetts, available at
http://www.csmonitor.com/emonitor/our_place/science/
science.html.
Fermat's Last Theorem, the Four Color Conjecture, and Bill Clinton for April
Fools' Day
Amer. Math. Monthly, 104, 246-255, (1997)
In the spirit of April Fools' Day, we celebrate important mistakes made in 19th
century mathematics and their important implications. Specifically, we give
"proofs" of Fermat's Last Theorem, the Four Color Conjecture, and the "fact"
that one of the authors is Bill Clinton.
Review of The Parsimonious Universe (Hildebrandt/Tromba)
Amer. Math. Monthly, (April, 1997)
Coffee Bubbles. Why Is It? #149
Mutual Radio Network, (February 4, 1997)
Bubbles in your coffee congregate around the edges to minimize surface energy.
Radio program based on a telephone interview with me, produced by Justin
Warner.
Teaching Mathematics at Williams
Parents' Newsletter, (Spring, 1997)
Williams students come not only with talent but also with a great capacity for
growth, that soon makes them the mathematicians and teachers.
Prime Type III-Lambda Automorphisms: An Instance of Coding Techniques Applied
to Non-Singular Maps
Algorithms, Fractals and Dynamics, Plenum, New York, 101-115, (1995)
Rudolph and Silva introduced a notion of minimal self-joinings for non-singular
automorphisms and used it to construct an example T of each Krieger type which
commutes only with its powers and has only trivial invariant sigma-algebras.
Here we show that such examples can be obtained more directly using coding
ideas. In fact, coding techniques yield results which do not seem obtainable
via joinings, e.g., a complete classification of the factor algebras of T x T.
Such coding ideas are quite standard in the context of finite
measure-preserving maps but have not, as far as we know been applied to
non-singular maps. In the classical setting the d-bar-metric on sequences
plays a central role and here we use a weighted version of it. The example T
which we work with is a type III-lambda version of Chacon's map.
Effects of Confinement on Energy-Dependent Dephasing in Heterostructures
Physical Review B, (to be published-1997)
To study the effects of confinement by quantum well potential discontinuities
on excitonic dephasing, we performed a spectrally and temporally resolved study
of band edge Four Wave Mixing emission from a series of InGaAs quantum wells.
Our measurements reveal an array of dynamics as we move from the three
dimensional to the two dimensional limit. Spectral resolution allows us, for
the first time, to resolve a slowly dephasing excitonic contribution in bulk
InGaAs. In measurements on quantum well samples of intermediate width, we find
no change of the dephasing time as the quantum well width becomes smaller than
the bulk Bohr diameter. This indicates that the dominant dephasing mechanism
in this regime is scattering by alloy disorder and interface roughness. For
quantum well widths below 200 Angstroms we observe a substantial increase of
the dephasing time. Spectral resolution allows us to associate the slow
dephasing in this regime with localized excitons.
Mixed-State Entanglement and Quantum Error Correction
Physical Review A, 54, 3824 (1996)
Entanglement purification protocols (EPPs) and quantum error-correcting codes
(QECCs) provide two ways of protecting quantum states from interaction with the
environment. In an EPP, perfectly entangled pure states are extracted, with
some yield D, from a mixed state M shared by two parties; with a
QECC, an arbitrary quantum state |[xi]> can be transmitted at some rate Q
through a noisy channel X without degradation. We prove that an EPP
involving one-way classical communication and acting on mixed state
M(X) (obtained by sharing halves of Einstein-Podolsky-Rosen pairs
through a channel X) yields a QECC on X with rate
Q=D, and vice versa. We compare the amount of entanglement
E(M) required to prepare a mixed state M by local actions
with the amounts D1(M) when M is Bell diagonal.
While EPPs require classical communication, QECCs do not, and we prove Q
is not increased by adding one-way classical communication. However, both
D and Q can be increased by adding two-way classical
communication. We show that certain noisy quantum channels, for example a 50%
depolarizing channel, can be used for reliable transmission of quantum states
if two-way communication is available, but cannot be used if only one-way
communication is available. We exhibit a family of codes based on universal
hashing able to achieve an asymptotic Q (or D) of 1-S for
simple noise models, where S is the error entropy. We also obtain a
specific, simple 5-bit single-error-correcting quantum block code. We prove
that if a QECC results in high fidelity for the case of no error then the QECC
can be recast into a form where the encoder is the matrix inverse of the
decoder.
Direct Measurement of the Ground-State Dissociation Energy in Na2
Physical Review A, 54, (2), R1006 (1996)
We report a direct measurement of the
ground-state dissociation energy. Three spectroscopic measurements are
combined to directly yield the energy of the lowest ([upsilon] = 0) vibrational
level relative to the free-atom limit. The
([upsilon]' = 0->31) splitting is measured by double-resonance spectroscopy;
([upsilon]=31)->
([upsilon]' = 165) by laser-induced fluorescence; and free atoms ->
([upsilon]'
= 165) by photoassociation of ultracold atoms. The result is Do =
5942.6880(49) cm-1. The uncertainty is a factor of 6 improvement
over a previous (indirect) determination.
Measurement of the Atomic Na(3P) Lifetime and of Retardation in the Interaction
Between Atoms Bound in a Molecule
Europhysics Letters, 35, (2), 85 (1996).
From molecular spectroscopy of the Na2 purely long-range
0g- state we determine the Na(3P) lifetime and measure
the predicted but previously unobserved effect of retardation in the
interaction between two atoms. Our lifetime, [tau](P3/2) =
16.230(16) ns, helps to remove a longstanding discrepancy between experiment
and theory. Electron cloud overlap is unimportant in the
0g- state (R > 55ao) and the spectrum is
calculated, ab initio, from atomic properties. By measuring the binding
energies the 120 MHz correction due to retardation of the resonant-dipole
R-3 interaction is confirmed.
A Spectroscopic Determination of Scattering Lengths for Sodium Atom Collisions
Journal of Research of the National Institute of Standards and Technology, 101,
505 (1996).
We report a preliminary value for the zero magnetic field Na 2S(f =
1, m = -1) + Na 2S(f = 1, m = -1) scattering length,
a1.-1. This parameter describes the low-energy elastic two-body
processes in a dilute gas of composite bosons and determines, to a large
extent, the macroscopic wavefunction of a Bose condensate in a trap. Our
scattering length is obtained from photoassociative spectroscopy with samples
of uncondensed atoms. The temperature of the atoms is sufficiently low that
contributions from the three lowest partial waves dominate the spectrum. The
observed lineshapes for the purely long-range 0g+
molecular state enable us to establish key features of the ground state
scattering wavefunction. The fortuitous occurrence of a p-wave node near the
deepest point (Rc = 72 ao) of the
0g+ potential curve is instrumental in determining
a1.-1 = (52 +/- 5) ao and a2.2 = (85 +/- 3)
ao, where the latter is for a collision of two Na 2S(f =
2, m = 2) atoms.
Atomic Lifetimes from Molecular Spectroscopy
Optics and Photonics News, 23, Dec. 1996 (Optics in 1996 news item)
Although molecular properties are clearly related to the properties of the
constituent atoms, it has seldom been possible to make precision measurements
of these atomic properties by examining the molecules. Over the last year or
so, however, molecular spectroscopy has been shown to be a powerful technique
for determining atomic lifetimes and has provided the most precise alkali
lifetimes yet reported, at levels ranging from 0.3% to 0.03%.
Two-Color Photoassociation Spectroscopy of Ultracold Sodium
Journal of Physics B, 30, 289 (1997).
We demonstrate a number of two-color spectroscopy techniques where the first
step is the photoassociation of laser-cooled and trapped sodium atoms to form
bound states of Na2. High resolution (~0.001 cm-1)
spectra of Na2 are obtained. Spectra of the
0g- (3S + 3P3/2) "purely long range" state
demonstrates the use of two-color spectroscopy to open up an ionization channel
for detecting the occurrence of photoassociation. The utility of
photoassociation as a technique for producing cold molecular samples in a
well-defined covibrational state is demonstrated with spectra showing bound
-> bound and bound -> free (Condon internal diffraction) transitions
after the photoassociation. Starting from states in the
0g- and 1g (3S + 3P3/2) potentials,
these transitions include upward transitions to autoionizing potentials
dissociating near 3P = 3P and downward transitions back to the 3S + 3S ground
state potentials. Spectroscopic constants for 6 levels of a doubly-excited
1u state of Na2 are given.
Identity, Personality and Defense Mechanisms: An Observer-based Study
The relationships among identity, defense mechanisms, and self-esteem,
demonstrated in a previous study (Cramer, 1995), were investigated again using
different measures and a different subject population. Consistent with the
previous findings, there was a clear relationship between identity crisis and
the use of defense mechanisms; the use of defenses was found to be a linear
function of the degree of crisis associated with the identity status. In
addition, as in the earlier study, the Achieved and Foreclosed personalities
were both associated with positive self-regard, while the noncommitted
personalities (Moratorium and Diffusion) were related to low self-esteem.
Evidence for Change in Children's Use of Defense Mechanisms
Journal of Personality, 65, 233-247 (June 1997)
Using a cohort-longitudinal design, children's use of the defenses of denial,
projection, and identification was assessed at four points over a 2-year time
span, covering the age period from 6 years, 6 months to 9 years, 5 months. The
results showed a clear decrease in the use of denial from early to middle
childhood, a sharp increase in the use of projection, and an increase in the
use of identification. These findings, predicted by a theory of defense
mechanism development, are consistent with cross-sectional results reported
previously.
Toward a "7-Minute" Screening Battery Sensitive to Alzheimer's Disease
Annals of Neurology, 40(3), 502 (1996)
One challenge for primary care physicians is to differentiate between cognitive
changes associated with the normal aging process (NAP) and those indicative of
dementing disorders such as Alzheimber's disease (AD). To facilitate this
process, we have begun to develop a brief screening battery for use in primary
care practices. Our goals in developing this screening instrument were to
select a series of tests that (1) could be rapidly administered and as such be
appropriate for use in a primary care setting. (2) require no clinical judgment
and minimal training to use, (3) take advantage of recent developments in
cognitive neuropsychology, (4) survey multiple cognitive areas, and (5) are
capable of reliably distinguishing AD from NAP. The screening battery consists
of modifications of existing neuropsychological tests that have been shown to
be sensitive to AD. Memory is evaluated using a variation of the enhanced cued
recall test. Visuospatial abilities were evaluated using clock drawing.
Orientation was evaluated using the Benton scoring system that takes into
account magnitude of errors. Expressive language was evaluated using verbal
fluency (number of animals in 1 minute). AD patients consisted of 61 successive
admissions to the Memory Disorders Clinic. All patients met the NIH criteria
for probable Alzheimer's disease (PRAD). Control subjects, who were age and
education matched, were recruited from the community. All control subjects
reported being independent in activities of daily living (ADLs) and scored
below 4 on the Blessed Information Memory Concentration test. A subset of
these patients subsequently underwent extensive neuropsychological evaluation
and all performed in the normal range. Performance on individual tests
indicated sensitivity ranging from 80 to 93% and specificity ranging from 90 to
100%. Combining all four tests in a logistic regression correctly classified
58 of 61 AD patients (95% sensitivity) and 61 of 61 of control subjects (100%
selectivity). Study is supported by the NIH and Parke Davis.
Context-dependent Behavioral Effects of InterLeukin-1 in the Rhesus Monkey
(Macaca Mulatta))
Psychoneuroendocrinology, 21(5), 455-468 (1996)
The behavioral effects of recombinant human interleuklin-1x (IL-1) in
rhesus monkeys (Macaca Mulatta) were assessed in 3 experimental paradigms: (1)
a testing situation in which an initial quiescent period was followed by a
challenge designed to evoke agitation; (2) a novel environment with a social
partner; and (3) a working memory-dependent nonspatial cognitive task. In the
first two experiments we replicated our previous observations that a high Il-1
dose (25 ug) induces somonolence in a quiet setting within 1 h. A lower Il-1
dose (1 ng) did not have these sedative properties, but both Il-1 doses
significantly reduced the number of vocalizations made by the monkeys. In
contrast, when the monkeys were challenged through direct eye contact with a
human experimenter, the 25 ug Il-1 dose significantly increased agonistic
behavior. Finally, performance on a working memory-dependent task (delayed
non-matching-to-sample) was unaffected by doses of Il-1 ranging from 1 to 25
ug, possibly because the monkeys were tested after learning the task rather
than during the acquisition phase. These results demonstrate that high levels
of Il-1 in peripheral circulation can have potent behavioral effects in the
nonhuman primate, but that the nature of the influence will depend on the
context in which the animal is evaluated. Manifestation of cytokine-induced
`sickness behavior' appears to require a permissive environment. Copyright
1996 Elsevier Science Ltd.
Natural and Cellular Immune Responses in Flinders Sensitive and Resistant Line
Rats
Neuropsychopharmacology, 15, 314-322, 1996
Major depression is associated with impairments in natural and cellular immune
responses. This study characterized baseline natural and cellular immune
function in the Flinders Sensitive Line (FSL) genetic animal model of
depression and in Flinders Resistant Line (FRL) controls. Splenic natural
cytotoxicity per natural killer (NK) cell as significantly lower in the FSL
rats, suggesting that NK cells are less activated at rest in the FSL rats than
in the FRL controls. Neither lymphocyte proliferative responses nor
interleukin-2 production differed between the two strains. Resting baseline
concentrations of plasma adrenocorticotropic hormone and corticosterone were
similar between the FSL and FRL rats, indicating that hypothalamo-pituitary
adrenal axis activation did not mediate immunological differences. FSL rats
show abnormalities in natural immunity similar to those found in clinically
depressed human beings, indicating that this animal model may be useful in
understanding the neural and neuroendocrine mechanisms associated with immune
alterations in depression. Emotion: Interdisciplinary Perspectives.
Emotion: Interdisciplinary Perspectives
Mahwah, New Jersey: Lawrence Erlbaum Assoc. (1996)
The Depiction of Imaginary Transformations: Early Comprehension of a Symbolic
Function.
Cognitive Development, 12, 1-19 (1997)
Children were tested for their ability to imagine a pretend transformation and
select a representation of its outcome. In Experiment 1, children aged 2 years
and above were successful in choosing the correct representation of the
imagined transformation, whether represented by a picture or toy. Children
below 2 years were unsuccessful on both types of representation. In Experiment
2, children below 2 years, unlike children above 2 years, were unsuccessful in
selecting a representation of an actual as well as a pretend transformation.
Implications for children's understanding of pretense and iconic symbolism are
discussed.
Brown Adipose Tissue: A Model System to Investigate Fetal Alcohol Effects on
Thermoregulation
In E. Able Fetal Alcohol Syndrome: From Mechanisms to Prevention, Tarrytown:
Elsevier Science, 285-316 (1996)
The Role of Neurosteroids in Alcohol-related Behaviors: New studies from the
Laboratory and Clinic
Alcoholism: Clinical and Experimental Research, 20, 250-255, 1996.
Prenatal Alcohol-exposure Influences the Effects of Neuroactive Steroids on
Separation-induced Ultrasonic Vocalizations in Rat Pups.
Pharmacology, Biochemistry and Behavior, 55, 541-547, 1996
Fetal alcohol exposure has been reported to be associated with
hyper-responsiveness to stress. Using a maternal separation paradigm, this
study examined whether prenatal alcohol exposure affected sensitivity to
neurosteroid modulation of stress. We have shown that the neuroactive steroid
allopregnanolone reduces ultrasonic vocalizations (USVs) after brief maternal
separation in week-old rat pups. Prenatal alcohol exposure, however, resulted
in reduced sensitivity to this neurosteroid. In this study's first experiment,
the behavioral effects of pregnenolone sulfate, a neurosteroid with reportedly
opposite modulatory effects on the GABAA receptor, were
characterized. Pregnenolone sulfate had a triphasic effect on the production
of ultrasonic vocalizations and on open field activity. Blockade of conversion
of pregnenolone to allopregnanolone via the 5a-reductase inhibitor 4-MA also
blocked the low dose anxiolytic effect. The enzyme inhibitor alone had no
significant effects on USV production, nor did progesterone. These results
suggest that the neuroactive steroid pregnenolone may play an independent role
in the stress response after maternal separation as well as being a precursor
for the anxiolytic neurosteroid allopregnanolone. In the second experiment,
prenatal alcohol exposure was found to eliminate both the low dose anxiolytic
effect and the higher dose anxiogenic response. These results support previous
results demonstrating that prenatal alcohol exposure may cause an altered
sensitivity to the neuromodulatory effects of neurosteroids.
The Psychology of Confession Evidence
American Psychologist, 52, 221-233, (1997)
Basic questions were raised concerning police interrogations, the risk of false
confessions, and the impact that such evidence has on the jury. Based on
available research, it was concluded that the criminal justice system does not
now afford adequate protection to innocent people branded as suspects and that
there are serious dangers associated with confession evidence. The specific
problems are threefold: (1) the police routinely use deception, trickery, and
psychologically "coercive" methods of interrogation; (2) these methods may, at
times, cause people to confess to crimes they did not commit; (3) when coerced
self-incriminating statements are presented in the courtroom, juries do not
sufficiently discount the evidence in reaching a verdict. It is argued that the
topic of confession evidence has largely been overlooked by the scientific
community and that further research is needed to build a useful empirical
foundation.
Coerced Confessions and the Jury: An Experimental Test of the "Harmless
Error" Rule
Law and Human Behavior, 21, 27-46, (1997)
Prompted by the U.S. Supreme Court's landmark decision in Arizona v.
Fulminante (1991), two studies evaluated the proposition that an
erroneously admitted coerced confession can be considered "harmless error."
Mock jurors read transcripts of a murder trial containing a confession that was
(1) elicited in a high-or low-pressure interrogation, and (2) ruled admissible
or inadmissible by the judge (no-confession control groups were also included).
As prescribed by law, jurors saw the high-pressure confession as less
voluntary, correctly recalled the judge's ruling, and reported that it had less
influence on their decisions. On verdicts, however, the confession increased
the conviction rate -- even when it was seen as coerced, even when it was
stricken from the record, and even when jurors said it had no influence. These
results suggest that appellate courts should exercise caution in applying the
harmless error rule to the admission of coerced confessions.
Computer-animated Displays and the Jury: Facilitative and Prejudicial Effects
Law and Human Behavior, 21, 269-281, (1997)
Two experiments assessed the effects of computer-animated displays on mock
jurors. In both, participants watched a trial involving a dispute over whether
a man who fell to his death had accidentally slipped or jumped in a suicide.
They watched a pro-plaintiff or pro-defendant version in which the body landed
5'-10' or 20'-25' from the building. Within each condition, the distance
testimony was presented orally or with an animated display. When the tape
depicted the event in a neutral manner, judgments were more consistent with the
physical evidence. But when the plaintiff and defense used the tape to depict
their own partisan theories, participants increasingly made judgments that
contradicted the physical evidence. Results suggest that computer-animated
displays have greater impact than oral testimony. Whether that impact is to
facilitate or mislead a jury, however, depends on the nature of the display.