Fall 2002 Abstracts for Georgia Southern Faculty

Pranoti Asher - Geological Society of America Meeting, Denver, CO
Denise Battles - Geological Society of America Meeting, Denver, CO
Jonathan Geisler - Society of Vertebrate Paleontology Meeting, Norman, OK
Michael Kelley - Geological Society of America Meeting, Denver, CO
Dallas Rhodes - Geological Society of America Meeting, Denver, CO
Chuck Trupe - Geological Society of America Meeting, Denver, CO



PETROGRAPHIC AND GEOCHEMICAL ANALYSIS OF A DIABASE DIKE FROM NORTH HARPSWELL, MAINE: A PRELIMINARY REPORT
ASHER, Pranoti M., Department of Geology and Geography, Georgia Southern University, Statesboro, GA 30460-8149, pasher@gasou.edu

Feeder dikes and flood basalts across northeastern North America are believed to be closely related to the creation of new oceanic crust during the Jurassic opening of the Northern Atlantic Ocean. Such feeder dikes extend all the way from Southern New England to coastal Maine and even into Nova Scotia (McHone et al., 1995). In Connecticut, the Higganum diabase dike cuts many different lithologies as it traverses Southern New England and is believed to have fed the earliest lava flow in the Mesozoic Hartford basin. The Christmas Cove dike in Maine, an extension of the Higganum, is exposed along the southern coast of Maine (McHone et al., 1995, pers. comm., 2002).

The petrography and geochemistry of one such exposure of the Christmas Cove dike from North Harpswell, Maine is the subject of this study. At this location the nearly 60-ft-wide dike intrudes the Ordovician Cape Elizabeth schist which is part of the early Paleozoic sequence of metamorphic rocks from the Casco Bay Group. Neither of the dike contacts with the schist are exposed at this location. The dike, which dips approximately 40° to the south, exhibits the typical spheroidal weathering and rusty brown color observed in diabase. Near the contacts with the schist the diabase is fine-grained and porphyritic whereas the grain size increases towards the interior of the dike. Close to the contact with the schist, phenocrysts of augite, bronzite, and plagioclase make up approximately 25% of the rock. Glomeroporphyritic clusters of augite and plagioclase are also present.

Chemically, the "chilled margin" of the Christmas Cove dike at Harpswell is similar to that of the Higganum dike in Connecticut (Asher, 1995) and from Christmas Cove, the type locality for this dike (McHone, unpublished data). SiO2, Al2O3, CaO, and Na2O contents show no systematic variation with distance across the width of the exposure. However there is a slight increase in the abundance of MgO, Cr and Ni towards the interior of the dike exposure suggesting the presence of a greater percent of mafic minerals or a more primitive composition.

EXPLORING THE INTERDISCIPLINARY CONNECTIONS OF GEOLOGY AND ART: A COURSE MODULE ON EUROPEAN ICE AGE CAVE ART

BATTLES, Denise A., Department of Geology and Geography, Georgia Southern Univ, P.O. Box 8149, Statesboro, GA 30460, dbattles@gasou.edu and HUDAK, Jane Rhoades, Department of Art, Georgia Southern Univ, P.O. Box 8032, Statesboro, GA 30460

The teaching of geology in conjunction with art is an appealing approach to non-majors science instruction. An introductory-level course, "Art and Geology," has been developed as a means of allowing students to explore the unexpected connections between these two disciplines. The course is organized into distinct modules which provide an overview of fundamental geologic and art concepts. The format is non-traditional and highly interactive, integrating content learning with hands-on activities. Classes meet in two-hour-long blocks, a structure conducive to incorporating significant student activities.
The topic of European ice age cave art is well-suited for launching this course and constitutes the first thematic module, occurring over two class meetings. In preparation for the first one, students are assigned readings that provide background on ice ages, Cro-Magnon art, European cave art, and the origins of human creativity. They also explore the excellent official websites for Lascaux and Chauvet caves, which include image-rich virtual tours and information on age, setting, and significance of the decorated sites. The session begins with an overview of relevant geologic and art concepts and leads into a discussion of the reading and web materials. A discussion of the origin of caves is supported by the investigation of calcite's reaction in dilute acid. Mineral properties of hardness and streak are examined in the context of earth materials used in cave paintings. Absolute and relative dating techniques are considered, as are issues of preservation of ancient materials, the incomplete nature of the geologic record, and human evolution. A provocative case study is presented in order to illustrate the scientific method; in small groups, students consider the "problem" and develop hypotheses and possible tests.
The next session focuses on art. To prepare, students are given instructions on collecting and creating natural pigments and then develop their own from local earth materials, such as red clay. They bring these to class, along with natural "brushes" and rocks large enough to paint. With cave art images as their inspiration, students create, both individually and in groups, naturalistic and symbolic art on simulated cave surfaces, using multiple techniques consistent with those of actual cave paintings.


USING CLIQUES TO INCREASE THE INFORMATIVENESS OF
CLASSIFICATIONS: EXAMPLES FROM DINOSAURIA

GEISLER, Jonathan, Georgia Southern University, Statesboro, GA 30460

Authors of recent dinosaur classifications assert that their classification should be accepted because it is more stable, thus recognizing stability as one of the primary goals of systematics. Unfortunately, the most stable taxa (i.e. the least likely to be rendered redundant or inconsistent with new data) are also the least informative. For example, Sauropodomorpha has been defined as "Plateosaurus, Saltasaurus, their most recent common ancestor, and all its descendents." Although this taxon is probably stable to future fossil discoveries or analyses, its definition does not specify what other taxa are considered sauropodomorphs. The definition relies either on an assumed consensus or the discretion of the reader for a list of the members of the taxon. Although stability is important, I suggest that informativeness should have a greater role in the naming of taxa. Informative definitions for taxa have several benefits including: effective communication, informative classifications, and testable taxa. Cladistics would be the method for testing taxa, and monophyly would be the criterion used to choose among competing taxonomic names.

Both node and stem-based taxa can be made more informative by redefining them as cliques (i.e. listing multiple taxa that are included in the taxon, and those that are excluded). For example, Sauropodomorpha could be redefined as the clique excluding Theropoda but including Prosauropoda, Diplodocoidea, Camarasaurus, Brachiosauridae, Titanosauria, their most recent common ancestor, and all of its descendents. Supraspecific taxa can be used in clique definitions as long as their taxonomic content is enumerated, or an existing classification cited. Making taxon definitions more informative would decrease stability; however, this is not necessarily a negative. Naming a new taxon to replace an existing one would indicate the discovery of contradictory evidence while stable taxa would indicate continued corroboration.



THE MARIA DYNAMICAL ASSOCIATION AND 433 EROS: THE FIRST MINERALOGICAL TEST

KELLEY, Michael S., Geology and Geography, Georgia Southern Univ, Herty Building Room 1100, Statesboro, GA 30460-8149, mkelley@gasou.edu, GAFFEY, Michael J., Dept. of Space Studies, Univ. of North Dakota, Box 9008, Grand Forks, ND 58202-9008, and ABELL, Paul A., Dept. of Earth & Env. Sci, Rensselaer Polytechnic Inst, 110 8th St, Troy, NY 12180-3590

The 81-member Maria dynamical asteroid group is located adjacent to the outer boundary of the 3:1 mean motion resonance with Jupiter near 2.5 AU. This group could be an important contributor to the terrestrial meteorite flux and may be a source of ordinary chondrites.

Based on dynamical arguments, this group was identified previously as the most promising potential source of large near-Earth asteroids, including 433 Eros. Visible-region spectra for several Maria group asteroids compare favorably with spectra in the same wavelength region for Eros. While the visible spectra are grossly similar and suggest a potential connection between Eros and some members of the Maria group, they fall short of demonstrating a quantified compositional link. A mineralogical investigation of this family will shed light on the important issues of the source of ordinary chondrites and the rate of orbital diffusion adjacent to a major resonance.

As part of the Family Asteroid Compositional Evaluation Survey (FACES), we obtained near-IR spectra of 433 Eros on June 29, 2000 at the NASA Infrared Telescope Facility. Analyses of the spectra allowed us to derive the mineralogy (olivine-to-pyroxene abundance ratio and pyroxene chemistry) for Eros. On the same night in June 2000 we also collected near-infrared spectra for three members of the Maria dynamical group, including 652 Jubilatrix, 714 Ulula, and 1215 Boyer. Ulula is an S-class asteroid, but Jubilatrix and Boyer have not been classified taxonomically. The spectra of the three Maria group asteroids exhibit silicate absorption features typical of olivine-pyroxene mixtures. Analyses of the new near-IR spectra for these asteroids should provide detailed mineral abundances and chemistries. These data will allow us to apply the first rigorous geologic test to the Maria dynamical association and to test the proposed genetic connection to 433 Eros. Early results for Jubilatrix show it to be within or near the S(VII) subclass of asteroids. Meteorite analogs for this asteroid may include basaltic achondrites or mesosiderites. At least two possibilities exist at this stage: (1) Eros and Jubilatrix are not genetically related, or (2) Jubilatrix represents the basaltic component of the Eros parent body. The latter case would infer that Eros is a mantle fragment of a differentiated parent body.





SYNCHRONOUS GEOMORPHIC RESPONSE TO HOLOCENE CLIMATE CHANGE IN THE CARRIZO PLAIN, CALIFORNIA
RHODES, Dallas D., Department of Geology and Geography, Georgia Southern University, Statesboro, GA 30460, DRhodes@GaSoU.edu; ARROWSMITH, J Ramon, Department of Geology, Arizona State University, Tempe, AZ 85287; EIGENBRODE, Jennifer L., Department of Geosciences, Pennsylvania State University, University Park, PA 16802; LIU, Jing, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125; PRATT, Lisa M., Department of Geological Sciences, Indiana University, Bloomington, IN 47405

Paleoseismological and neotectonic studies of the San Andreas Fault in the Carrizo Plain, California provide an impetus to characterize landscape responses to Holocene climate change. Five independently dated and studied elements of the Carrizo Plain's geomorphic system display synchronous change following the end of Mid Holocene Thermal Maximum (~4,500 cal BP). Wallace Creek, small channels a few hundred meters southeast of Wallace Creek, and Phelan Creeks-about 1.6 km to the southeast (John D. Sims, unpublished data) have been extensively studied for paleoseismology by trench investigations and their history of channel abandonment and incision is well constrained with 14C dates. The fluvial systems drain to closed Soda Lake basin. Analysis of isotopic data from lake sediment cores provided a history of relative water depth. Mapping and thermal luminescence dating of the final geomorphic element--clay dunes developed along the edge of Soda Lake--further contribute to this record of landscape response to climate change.
By 3.3+/-0.2 ka (TL date), Soda Lake had become hypersaline and a 9.5-km long clay dune had grown along its eastern and southern limits. With the cooler and wetter climate that followed, the average lake level began to rise and reached a high stand (2.9-2.6 ka). During this same period, channel incision occurred at Wallace Creek (after 3.7 ka), the small channels nearby, and the Phelan Creeks (3.5-2.5 ka). With higher lake levels, the clay dune system was stabilized and underwent a period of erosion and soil formation. The average level of Soda Lake dropped precipitously at ~2.1 ka and then remained relatively low. This interval was characterized by stability in the fluvial systems. A short-lived slightly higher lake level occurred at the same time that incision occurs in the small channels (1.35 ka). The other drainages were stable. The average lake level remained low until the modern level was achieved at 0.8 ka. Incision occurred at Phelan Creeks about 0.5 ka. Most of the dune complex is now eroding. Fluvial, aeolian, and lacustrine processes of this closed system show synchronous response to climate change as recorded by channel incisions and dune stability during high lake level and channel stability and dune formation during low lake level.

AN EVALUATION OF THE POST-GRENVILLE TECTONIC HISTORY OF THE ROCKS OF WESTERN NORTH CAROLINA: IMPLICATIONS FOR UNDERSTANDING THE GRENVILLE OROGENY IN THE SOUTHERN APPALACHIANS

TRUPE, Charles H., Department of Geology & Geography, Georgia Southern University, Statesboro GA 30460, chtrupe@gsaix2.cc.gasou.edu; STEWART, Kevin G., Department of Geological Sciences, University of North Carolina, Chapel Hill, NC 27599-3315; ADAMS, Mark G., Department of Geology, Appalachian State University, Boone, NC 28608 and Unimin Corporation, Harris Mining Company Rd., Spruce Pine, NC 28777; FOUDY, John P., Department of Geological Sciences, University of North Carolina, Chapel Hill, NC 27599-3315

 

The western Blue Ridge province of the southern Appalachians contains a rich record of the Mesoproterozoic Grenville orogeny, but subsequent Paleozoic metamorphic events have variably overprinted Grenville rocks and Paleozoic thrusting has telescoped Grenville rock units. To decipher the Grenville record, one must be able to accurately strip away the effects of Paleozoic orogenesis. Our recent work in northwestern North Carolina and eastern Tennessee has resulted in a revised model for the structural setting and Paleozoic history of basement thrust sheets of the of the Blue Ridge. Grenville basement rocks in the Blue Ridge of reside in a stack of Alleghanian thrust sheets that lie above the Grandfather Mountain and Mountain City windows. Within these thrust sheets Neoproterozoic igneous rocks crosscut Grenville fabrics and assemblages, and were subsequently metamorphosed during the Paleozoic. Field relationships, metamorphic grade, and isotopic ages in the igneous rocks are thus very useful in clarifying the post-Grenville history of the thrust complex. The structurally highest unit in the stack is the composite Fries thrust sheet, which contains metasedimentary and metavolcanic rocks of the eastern Blue Ridge (Ashe Metamorphic Suite) juxtaposed against Grenville basement rocks (Pumpkin Patch Metamorphic Suite) along the Devonian Burnsville fault. The Burnsville fault is an amphibolite-facies dextral strike-slip shear zone and is the only identifiable Acadian structure in the thrust stack. Structurally lower thrust sheets are juxtaposed along greenschist-facies Alleghanian thrust faults. West of the Grandfather Mountain window, the Sams Gap-Pigeonroost thrust splays off the Fries fault. Only the Fries and Sams Gap-Pigeonroost sheets appear to have been affected by Ordovician Taconic metamorphism. Below the Fries and Sams Gap-Pigeonroost sheets, Grenville basement rocks in the Fork Ridge and Linville Falls-Stone Mountain thrust sheets display widespread greenschist-facies metamorphism and deformation associated with Alleghanian thrusting. The lowest basement sheet is the Little Pond Mountain thrust sheet, which experienced only Late Paleozoic chlorite-grade metamorphism due to burial beneath thrust sheets during Alleghanian assembly of the Blue Ridge thrust complex.