LANDSLIDE TERRAIN ANALYSIS OF A SPATIALLY AND TEMPORALLY HUMAN INFLUENCED HILLSLOPE, CINCINNATI, OHIO

Session No. 195
Humans as a Geologic Agent: In Honor of George Kiersch
Colorado Convention Center: A111/109
8:00 AM-12:00 PM, Wednesday, October 30, 2002

AGNELLO, Tim J., 3869 Kilbourne Ave, Cincinnati, OH 45209-1814, agnello@fuse.net.

An engineering geology study of chronic landsliding on a 168-acre hillslope on the western side of Mill Creek Valley in Price Hill, Cincinnati, Ohio finds that most of the landsliding can be associated with past land use initiated over the last 195 years. The majority of the hillside has moved or is in quasi-equilibrium from human activity. Historic quarry operations, deforestation, clear cutting, grading for housing (both historic and ongoing), road construction, loading of the slope from dumping (landfill, construction debris, etc), and modification of the natural hydrology have set the stage for past and ongoing destabilization of the hillside.

Research of past land use patterns and examination of historic photographs, maps, newspaper accounts, directories, and books complemented mapping of human landforms, instability features, and surface water drainage. The majority of the study data was collected in the field however; historical documentation revealed landsliding and/or preexisting human made features that today would not be recognized in a traditional field investigation. Additionally, some of the landforms identified in the study area could be validated as landslide or human made features by examination of the historical data. Examination of the historic record and past human landforms that at present may be completely or partially indistinct gives a different perspective on the extent of hillside instability. A stake survey combined with inclinometers may be necessary to delineate the true extent of ground movement in areas absent of human made earthen landform, structure, or lacking historical data.

Session No. 160--Booth# 106
Paleontology/Paleobotany (Posters) I
Colorado Convention Center: Exhibit Hall
1:30 PM-5:30 PM, Tuesday, October 29, 2002

CENTIMETER-SCALE CHARACTERIZATION OF EVENT BEDS WITHIN THE ALEXANDRIA SUBMEMBER OF THE KOPE FORMATION (UPPER ORDOVICIAN, EDENIAN) IN THE CINCINNATI, OH, NORTHERN KENTUCKY REGION

KOHRS, Russell H., Department of Geology, Univ of Cincinnati, H.N. Fisk Laboratory of Sedimentology, 500 Geology Physics Building, Cincinnati, OH 45221, piperconan@hotmail.com.

Well preserved Konservat Lagerstätten can be found preserved by obrution deposits within the shales of the Cincinnatian Series. These deposits, formed as distal tempestites, can provide insight into the depositional processes which formed the meter-scale cycles present today. Obrution deposits provide a paleoecological snapshot of the composition of fossil communities prior to burial, due primarily to the rapid deposition of mud. This rapid mud deposition suggests that the shale portions of these cycles represent relatively short periods of time relative to the thinner, time-averaged, limestone cycle caps. Centimeter-scale characterization of the shale portion of the cycles within the Alexandria Submember of the Kope Formation was conducted at five sites following the inferred paleoslope toward the Sebree Trough to the northwest of the study area. Meter-scale cycles within this unit were correlated over 140 km while many of these single event beds were correlated over a distance of 10 to 40 kilometers. Two of these event Lagerstätten occur within cycle 29 of the Alexandria Submember (cycle nomenclature of Holland et al., 1997), where whole Cryptolithus bellulus and Flexicalymene meeki have been found in two obrution deposits over a distance of 20 km. Other faunal epiboles occur within cycle 28 where Isotelus maximus and Triarthrus eatoni have been found to occur over similar distances. Other beds within the meter-scale cycles, such as thin grainstones and calcisiltites can also be correlated over these same distances. Some show changes in proximality as they are traced downslope as thin grainstones grading into calcisiltites and eventually into distal mud. The fauna which can be found within these deposits of the Kope Formation are restricted to a select few taxa. The excellent preservation of the fauna within obrution deposits and their common occurrence indicate that the shales of the Kope Formation were deposited rapidly, in a series of individual tempestite deposits in deep water well below storm wave base. Other beds within these cycles such as thin grainstones and hummocky cross-stratified calcisiltites suggest deposition within storm wave base. These deposits contrast sharply with the highly time-averaged limestones which cap these cycles which were formed over a comparatively long period of time near the upper level of storm wave base.

Session No. 246--Booth# 148
Tackling Transpression and Transtension in Orogenesis: Tools of Structural Geology from Microfabric to Tectonic Reconstruction (Posters)
Colorado Convention Center: Exhibit Hall
1:30 PM-5:30 PM, Wednesday, October 30, 2002

STRUCTURAL STYLE OF THE KOHAT PLATEAU, PAKISTAN: TRANSPRESSION TECTONICS, MULTIPLE DETACHMENT FAULTING, AND GRAVITY SPREADING

DEJONG, Kees A., Geology, Univ. Cincinnati, Cincinnati, OH 45221, Kees.DeJong@uc.edu and BECK, Richard A., Geography, Univ of Cincinnati, Cincinnati, OH 45221

Fold-and-thrust belts form the geological backbone of Pakistan, and strike-slip faults are subordinate to the folds and thrust faults, with the possible exception of the Kohat Plateau where the main E-W structures have been recently explained as the result of transpression tectonics (Sercombe, Pivnik, et al, Bull.AAPG, 1998). Fault structures with a vertical offset of a few km were described as ‘flower’ structures. Seismology and faults with subhorizontal striae indeed indicate the presence of E-W strike-slip faults.

An overview of the structural style of the Kohat Plateau was derived from satellite imagery analysis, and near the village of Gandiali a 120 km2 area was mapped 1:25,000. Detachment occurred below the Jurassic in the Tolanj Anticlinorium, below the Ghazij shale (Paleocene) and in the Kuldana shale (Eocene). N-S shortening in the study area, mainly by tight upright folds, is 10-15 km min. whereas offset resulting from E-W strike-slip faults appears absent. The overturning of E-W oriented anticlines towards both N and S could be considered as the result of transpression tectonics (flower structure) but ‘collapse’ of a fold during its growth is an alternative explanation. The termination of minor folds at the Algad River in the Tolanj anticlinorium is also suggestive of ‘morphotectonics’.

The major structural features of the Kohat Plateau include a regional detachment fault below the Jurassic and local detachments in Eocene formations resulting in thrust sheets and folds. These detachment features indicate crustal compression, although the smallest klippen may have been emplaced gravitationally. The doubly-overturned folds and other small structural features probably resulted from gravity tectonics. Transpression tectonics is evident in the area of the N-S oriented Kalabagh fault.

Session No. 221--Booth# 55
Quaternary Geology/Geomorphology (Posters) III
Colorado Convention Center: Exhibit Hall
1:30 PM-5:30 PM, Wednesday, October 30, 2002

PALEOCLIMATE RECONSTRUCTION OF THE LAST TERMINATION, CAMPAIGN CO., OHIO

GLOVER, Katherine, Department of Geology, Univ of Cincinnati, 500 Geology/Physics Bldg, Cincinnati, OH 45221-0013, kcglover@hotmail.com and LOWELL, Thomas V., Geology, University of Cincinnati, 500 Geology/Physics Bldg, Cincinnati, OH 45221-0013

The climate transition at the end of the Last Glacial Maximum (LGM, 25,000 – 13,000 14C years BP) is not well understood for the North American Midwest, due to a scarcity of data for this time period. A number of relict basins in the interlobate complex of western Ohio contain geoarchives that span the late LGM transition, thus providing ideal sites for further examining climate change.

Site 0201 of the Mechanicsburg township holds the oldest archive, with a basal date of 16,197 ±97 14C years BP (Lab #AA45079). Within the sedimentary archive, a sharp transition from older, mottled clays to banded silt 4.5 m above the core base dates to 13,370 ±280 14C years BP (Lab #Beta – 158295). High resolution loss-on-ignition (LOI) analysis shows consistently low organic productivity before this later date, then a dramatic increase in organic productivity above this transition. Chlorophyll content analysis, which yields a measure of phytoplanktonic biomass within the basin through time, corresponds with the LOI data.

Climate conditions within the 0201 site thus remained relatively stable during the time period from 16,197 ±97 to 13,370 ±280 14C years BP. On a more regional scale, site 0201 is one of a cluster of basins with basal radiocarbon dates that range from 15,350 ±100 to 16,197 ±97 14C years BP. These dates suggest that the ice margin had receded north of the region as early as16,197 ±97 14C years BP in order to allow this suite of kettles to form in a periglacial environment.

Session No. 193
Chemostratigraphy: An Emphasis on Metal-Rich Black Shale Deposits
Colorado Convention Center: C201
8:00 AM-12:00 PM, Wednesday, October 30, 2002

ESTIMATING PALEO-BOTTOMWATER DEGREE-OF-ANOXIA (DOA) USING FAUNAL, ICHNOFABRIC, AND GEOCHEMICAL DATA: EXAMPLES FROM CORE SHALES OF UPPER PENNSYLVANIAN CYCLOTHEMS OF THE EASTERN MIDCONTINENT SHELF (KANSAS), U.S.A

ALGEO, Thomas J., Univ of Cincinnati, Cincinnati, OH 45221-0013, thomas.algeo@uc.edu, SCHWARK, Lorenz, Geologisches Institut, Universität zu Köln, Zülpicher Str. 49a, Köln, 50674, Germany, and MAYNARD, J. Barry, Department of Geology, Univ of Cincinnati, P.O. Box 210013, Cincinnati, OH 45221

Bottomwater oxygen levels, an important control on the preservation of sedimentary organic matter, can be estimated on the basis of faunal, ichnofabric, and geochemical data. Three core shales (Hushpuckney, Stark, and Muncie Creek) of Missourian Stage cyclothems from the Eastern Midcontinent Shelf provided an excellent case study. The inorganic and organic geochemistry of these 1- to 2-m-thick shales was characterized using XRF, Leco, Rock Eval, and GC-MS, and cm-scale sampling permitted detailed study of vertical compositional trends. The shales are divisible (from the base upward) into four zones: (1) a high-TE, laminated lower black shale, (2) a low-TE, weakly bioturbated upper black shale, (3) a moderately bioturbated, non-fossiliferous lower gray shale, and (4) a fully bioturbated, fossiliferous upper gray shale. Within the black shale, TOC falls only slightly from zone 1 to zone 2 but redox-sensitive TEs (U, Mo, V) fall abruptly, suggesting crossing of a critical O2 threshold. Bioturbation is limited to a few macroburrows (Planolites, Zoophycos) in zone 2 but includes complex, tiered ichnocoenoses in zone 3. Preliminary organic geochemical data suggest substantial variation in the type (marine algal vs. terrestrial plant) and quality of organic matter between zones as well. We infer a fairly steady increase in bottomwater O2 levels throughout core shale deposition. While the black shale is commonly described as "anoxic," reduced TE concentrations in zone 2 suggest merely dysoxic conditions (ca. 0.1-0.2 ml O2 l-1 H2O). Intensification of bioturbation in zone 3 reflects a further rise in O2 levels, to weakly dysoxic conditions (ca. 0.2-0.5 ml O2 l-1 H2O) that supported a bioturbating, probably worm-dominated, infauna.

Session No. 203
Seafood Through Time—The Ecologic Context of the History of Life I: In Honor of Richard K. Bambach
Colorado Convention Center: A102/104/106
8:00 AM-12:00 PM, Wednesday, October 30, 2002

SEAFOOD THROUGH LIME: SECULAR CHANGES IN FOOD AVAILABILITY IN CARBONATE ENVIRONMENTS DURING THE PALEOZOIC ERA

MILLER, Arnold I., Department of Geology, Univ of Cincinnati, 500 Geology Physics Building, University of Cincinnati, Cincinnati, OH 45221, Arnold.Miller@UC.EDU.

In his classic “Seafood Through Time” essay, Richard Bambach discussed the diversification of bivalve molluscs in the context of increasing food availability through the Paleozoic Era. He argued that, during the Early Paleozoic, bivalve diversification was impeded, compared to articulated brachiopods and other taxa that dominated most Paleozoic seafloors, because insufficient food was available to meet the energy requirements of a diverse and abundant bivalve biota. With the mid-Paleozoic diversification of land plants, Bambach hypothesized that food availability in marine settings increased significantly, thereby fueling an appreciable diversification of bivalves, beginning in the late Paleozoic.

Several years ago, I conducted an analysis of Paleozoic bivalves from the paleocontinent of Laurentia, in which I documented a siliciclastic/carbonate dichotomy among Ordovician faunas: bivalve diversity and abundance were significantly greater in Ordovician siliciclastic settings than in carbonates. However, during the Carboniferous and Permian, this dichotomy began to break down, and bivalves diversified appreciably in carbonates. Bambach suggested that this pattern might be explained by a particularly significant late Paleozoic rise in primary productivity in carbonate settings, where food limitations may have been especially acute prior to the advent of land plants.

Here, I consider anew two aspects of the aforementioned scenario, based on data and models that have become available since the earlier studies: 1) the global veracity of siliciclastic/carbonate distributional patterns among Paleozoic bivalves, which had been documented previously only for Laurentia; and 2) the possibility of assessing directly, with geochemical data, the evolution of food availability in Paleozoic carbonate environments. With respect to the latter, the increase in weathering associated with the rise of land plants may have increased dramatically the mobility of iron and other elements viewed as crucial fertilizer components that stimulate marine primary productivity, thereby increasing their abundances in marine environments, including carbonate settings, that were far removed from areas of direct siliciclastic input.

Session No. 74
Three Billion Years of Reef Evolution II: Onshore-Offshore Paleoenvironmental Reconstructions
Colorado Convention Center: A105/107
8:00 AM-12:00 PM, Monday, October 28, 2002

SUBTLE VARIATION IN PALEO-OXYGENATION AND ITS EFFECTS ON BIOTIC TURNOVER IN THE MIDDLE DEVONIAN APPALACHIAN BASIN OF NEW YORK

SESSA, Jocelyn A., MILLER, Arnold I., and BRETT, Carlton, Geology, Univ of Cincinnati, 500 Geology Physics Building, University of Cincinnati, Cincinnati, OH 45221, jocelynsessa@hotmail.com

The Middle Devonian succession of the Appalachian Basin of New York preserves a series of rapid biotic turnovers, influenced by depth and lithology. In this study, multivariate statistical analyses of faunal data collected from multiple horizons indicate an asynchronous, depth mediated replacement of various biofacies of the Windom Shale of the Hamilton Group by faunas of the overlying Tully Limestone. This complex pattern runs counter to previous views that the Hamilton and Tully units contain the same repetitive biofacies, and should thus be grouped as one ecological evolutionary subunit. Biotic elements typical of the most dysoxic and deepest shelf settings of Tully first appear earlier in the deepest regions of the latest Windom. In slightly shallower dysoxic settings of the latest Windom these faunas interfinger with biofacies common to more oxygenated settings seen slightly earlier in the Windom. Once onset of Tully Limestone deposition occurs in this facies, a fauna distinctive from that of the deepest Tully is found. Thus, the dysoxic biofacies of the deepest Tully settings is coeval with more typical Windom biofacies, but both are replaced in slightly shallower settings of the Tully by yet a third dysoxic biofacies.

A detailed analysis of these dysoxic biofacies was performed to better understand the paleoenvironmental constraints on this regional biotic transition. Although almost all samples of the latest Windom Shale and the lower Tully Limestone contain some percentage of silt, a correlation of other lithologic components with biofacies is observed. The most dysoxic fauna is nearly always found in siltstones or sandstones that contain at least one mineral from a suite of pyrite, phosphate, or chamosite. The moderately dysoxic biota occurs in rocks with a higher calcareous component. Finally, the more oxygenated Windom faunas are found in shalier units that are often bioturbated.

Thus, a multifaceted turnover event is recognized between the Windom and Tully, in which three distinct faunas interacted with one another. Each fauna can be assigned separate, but related, depth and lithologic parameters. These results suggest that detailed dissections of turnover boundaries may reveal depth influenced changes and previously unrecognized paleoenvironmental gradients.

Session No. 164
Quaternary Geology/Geomorphology III
Colorado Convention Center: C207
1:30 PM-5:30 PM, Tuesday, October 29, 2002

BIG RIVER SYSTEMS AND PLATE TECTONICS

POTTER, P.E., Department of Geology, Univ of Cincinnati, Cincinnati, OH 45221-0013, k.hamblin@attbi.com and HAMBLIN, W.K., Department of Geology, Brigham Young Univ, Provo, UT 84602, k.hamblin@attbi.com

The geological characteristics and origins of big river systems - 22 in Eurasia, 15 in the Americas, 8 in Africa, and one in Australia - are the result of plate tectonics, climate, and changes in relative base level. It is these three, but mostly plate tectonics, that have determined the location, size, shape, and orientation of a large watershed, its longevity and much of its river pattern since 4.2 billion years ago. Big river systems are, in broad terms, relatable to the Wilson Cycle of intracontinental rifting--new passive margins--ocean-continental convergence--new direction of continental tilt and occasional inter continental collisions. Thus big river longevity, like global landscape evolution, has the same time scale as tectonic cycles. The break up of Gondwana was responsible for much of the world's present drainage. The closing of the Tethyan Ocean created most of the mountain chains and basins of southern Eurasia from Spain to Vietnam, a distance of some 13,000 km. In North and South America, ocean-to-continent convergence and accretion of microcontinents created the Cordilleran and Andean orogens and much of the drainage of the Americas. A second important result is the number of rivers that came into existence, essentially in their present form, in the Miocene; a few have ancestors traceable back to the Carboniferous and perhaps even earlier. The key to the long-term survival of a large river is location on a long-lived craton or passive margin, persistence of continental tilt, and ample rainfall all without interruption by desertification, continental glaciation, or volcanism. Conversely, orogenies both destroy and create big rivers.

Session No. 133
Special Session I in Honor of John C. Butler: Water Where the Grass Is Greener—Emerging Uses of Technology in Geoscience Education
Colorado Convention Center: A112
8:00 AM-12:00 PM, Tuesday, October 29, 2002

JOHN C. BUTLER – THE VIRTUAL GEOSCIENCE PROFESSOR

HUFF, Warren D., Department of Geology, Univ of Cincinnati, Cincinnati, OH 45221, warren.huff@uc.edu and LAMBERSON, Michelle N., #201 2389 Health Sciences Mall, WebCT, Inc, Vancouver, BC BC V6T 1Z4, Canada

John Butler passed away in October, 2001. But for those of us who are exploring the many ways in which technology can be harmonized with pedagogy to improve the quality of education his legacy continues to serve as an inspiration. A visit to his virtual home at http://www.uh.edu/~jbutler/anon/anonfield.html provides some examples of how John saw the future of teaching with technology. There is a superb compilation of good practices examples of courses using Internet resources, a special page devoted to geophysics resources; ANON, his link to Computers & Geosciences for which he was an associate editor; a valuable directory of geoscience departments and organizations worldwide; and, his most recent addition, a listserv which he entitled the VirtualCoffeeRoom. His good practices site is based on 5 years of continuous data collection and, in his words, “As of March 21, 2001 there are approximately 4,750 geoscience course resources stored in a FileMakerPro database. The resources have been arranged according to broad categories with each category subdivided into content-based subcategories. You may search by category, subcategory and/or by words. The entire database can be searched for key words. The purpose of this page is to focus on those resources which illustrate good practices and might be adopted by, or prove suggestive, to others. Clearly, there is an element of personal judgment in producing such lists and the author bears full responsibility for the contents.” There are over 300 listed opportunities for independent travel and study, 450 examples of supplementary teaching materials, 200 Internet-based homework and laboratory exercises, and 200 geoscience images. One of John’s key concerns was that the pedagogical use of the Internet started as a highly individualized process, so he took great pleasure in the fact that his archival efforts were aiding in the formation of faculty technology resource centers in colleges and universities across the continent. He was ahead of his time.

Session No. 61
Stratigraphy (Posters) I
Colorado Convention Center: Exhibit Hall
8:00 AM-12:00 PM, Monday, October 28, 2002

MULTIPLE ASH ACCUMULATION EVENTS PRESERVED IN INDIVIDUAL LOWER PALEOZOIC K-BENTONITES: STRATIGRAPHIC IMPLICATIONS

HUFF, Warren, Department of Geology, Univ of Cincinnati, Cincinnati, OH 45221-0013, warren.huff@uc.edu, KOLATA, Dennis R., Illinois State Geological Survey, 615 E. Peabody Drive, Champaign, IL 61820, and BERGSTRÖM, Stig M., Ohio State Univ - Columbus, 155 S Oval Mall, Columbus, OH 43210-1308

Explosively erupted volcanic ash preserved as bentonites and K-bentonites can serve as ideal regional stratigraphic markers as well as recorders of tectonomagmatic events. However, tephra deposits are often the result of multiple rather than single eruptive episodes. Moreover, individual explosive eruptions can generate secondary co-ignimbrite plumes which can add complexity to the internal stratigraphy of the tephra deposit. Co-ignimbrite ash clouds are entrained from hot, dense pyroclastic flows resulting from collapsed plinian columns, and may originate either close to or at some distance from the vent. They tend to be enriched in fine vitric ash and rise by convection to as much as 30 km. Sustained co-ignimbrite plumes can be responsible for the distribution of ash at distances in excess of 1000 km compared to plinian eruption columns, which tend to distribute clasts on the order of hundreds of km maximum from the vent. However, if the co-ignimbrite (or Phoenix) plume originates above or close to the vent theoretical plinian column models might be used to estimate minimum mass eruption rate and column height. The co-ignimbrite column will achieve the shape of a buoyant plume as it acts to conserve mass during upward acceleration. Estimates of the amount of pyroclastic material entrained in this process are on the order of 35 percent of the total erupted mass so the missing proximal facies may amount to as much as twice the volume of the preserved ash. Microprobe data on biotites from the Caradocian Deicke and Millbrig beds in North America suggest that the Deicke represents a compositionally homogeneous magma and a single eruptive event. However, the Millbrig shows considerable within-bed variability and most likely contains a co-ignimbrite phase. Millbrig biotite crystals range from only slightly different from Deicke to those characteristic of a more highly evolved parental magma. The magnesium number (Mg2/(Mg2+Fe2)) of the biotites, which serves as a differentiation index, suggests that the Millbrig variability is the product of a continuously evolving magmatic source.

Session No. 222
Stratigraphy
Colorado Convention Center: A112
1:30 PM-5:30 PM, Wednesday, October 30, 2002

THE DISTRIBUTION OF SEISMITES: A SEQUENCE STRATIGRAPHIC AND SEDIMENTOLOGICAL APPROACH

MCLAUGHLIN, Patrick I. and BRETT, Carlton E., Department of Geology, Univ of Cincinnati, H.N. Fisk Laboratory of Sedimentology, 500 Geology Physics Building, Cincinnati, OH 45221, pimclau@hotmail.com

Seismites are not ubiquitous throughout the rock record. They are restricted to times of active tectonism, as well as to specific portions of depositional cycles corresponding to deformation prone sedimentary architecture. Eight large-scale (3rd-order) depositional sequences from the Late Ordovician together with examples from the Early to Middle Silurian of the eastern United States are examined for presence of specific deformation features and stratigraphic position of those intervals. Within these strata seismites are developed in two specific depositional facies. First, rhythmite facies include rhythmically interbedded, thin, tabular calcisiltites and shale representing deep shelf deposition in early highstand systems tracts. Second, laminite facies begin with a basal shale overlain by laminated, fine-grained calcarenites interbedded with thin mud drapes, which preferentially form in the late highstand. Seismites display a range of sedimentary features including: convolute bedding and intraformational conglomerates (restricted to rhythmite facies), and saucer structures, mudstone diapirs, ellipsoids, foundered blocks (restricted laminite facies). These features give information about the environment and timing of deformation. Mobilization of mud caused deformation of the surrounding sediments. We suggest it is the thixotropic properties of the clays within these muds that allow them to become unstable, in going from a gel to sol state. In the gel state the muds were cohesive enough to record prod marks, flutes, and grooves, as is witnessed on the undersides of saucer structures. However, during episodes of seismic shaking muds flowed upward as diapirs, evacuating from the lower part of a deformed interval to be redeposited on top. Truncation of the upper surface of deformed intervals indicates that deformation occurred near the sediment-water interface and is occasionally marked by a bored and encrusted hardground. The regular distribution of deformation prone facies within a single depositional sequence seems to be regulated by eustatic fluctuations. Tectonics simply provides the triggering mechanism to disrupt deformation prone strata. The record of deformed intervals provides a meter of intensity and timing of pulses of tectonism during orogeny.

Session No. 224--Booth# 81
Volcanology (Posters)
Colorado Convention Center: Exhibit Hall
1:30 PM-5:30 PM, Wednesday, October 30, 2002

ORIGIN OF ALKALIC ROCKS FROM HUALALAI VOLCANO, HAWAII

FAY, Lisa C., WISCHER, Stephanie, and KILINC, Attila, Department of Geology, Univ of Cincinnati, P.O. Box 210013, Cincinnati, OH 45221-0013, faylc@email.uc.edu

At least two different processes in the mantle can produce alkalic magmas. These are (1) low degrees of melting of peridotite source rocks in the mantle or (2) differentiation of tholeiitic magmas at high pressures. In order to test which of these processes are responsible for the alkalic rocks of the Hualalai Volcano in Hawaii, we analyzed ten samples with known ages ranging from less than 200 years to more than 12,950 years.

Recasting bulk compositions of these rocks into normative olivine, diopside, nepheline, albite, anorthite and TiAl2(Mg Si2)-1, Fe(Al)-1, Fe(Mg)-1, Mn(Mg)-1 and K(Na)-1 exchange components using the algorithm of Sack et al., (1987) and then projecting the bulk compositions of the Hualalai rocks onto the nepheline-olivine-diopside base from the plagioclase apex shows that all compositions fall between 8-30 Kb and 1 bar cotectics. All bulk compositions plot closer to high-pressure cotectics and away from the 1 bar cotectic suggesting that the rocks originated under high-pressure conditions.

To constrain the temperature of the magmas of these rocks, we have retrieved the temperature data from a normative "olivine/(albite+anorthite)"-temperature plot using Takahashi and Kushiro (1983) data. Using Sack et al., (1987) "nepheline/(nepheline+olivine+diopside)"-temperature plot, we derived an equation relating temperature to pressure for multiply saturated magmas. Finally, we use our calculated temperatures to solve for pressures.

When plotted on an experimentally determined solidus and liquidus P-T diagram for peridotite (Takahashi et al., 1993), our points show that the alkalic rocks from the Hualalai Volcano plot very close to the solidus suggesting that they represent low degrees of melting of upper mantle rocks.

Session No. 52
Economic Geology I: Magmatic PGE-Cr-Cu-Ni, VMS, Sed-hosted Pb-Zn-Cu, and Alaska Au Deposits
Colorado Convention Center: C201
8:00 AM-12:00 PM, Monday, October 28, 2002

A FLUID MIXING MODEL FOR KONKOLA NORTH, ZAMBIAN COPPERBELT

SUTTON, S.J., Earth Resources, Colorado State Univ, Earth Resources, Colorado State University, Fort Collins, CO 80523, sally.sutton@colostate.edu and MAYNARD, J.B., Geology, Univ of Cincinnati, PO Box 210013, Cincinnati, OH 45221

The origin of Cu mineralization in the Zambian Copperbelt has long been disputed, but is known to reflect underlying basement topography, with barren gaps overlying basement highs. The geological setting and distribution of mineralization suggest similarities between the Copperbelt and the Pb-Zn mineralized St. Francois Mountains, Missouri. Both are hosted in rift-related sediments, show marked basement paleotopography, which is overlain by clastics and then carbonates. Both also show K-metasomatism, more pronounced in the Copperbelt where bulk K2O approaches 15 wt. %, overprinting by hematite, and evidence of Ti mobility. That the St. Francois mineralization formed as a result of fluid mixing is widely accepted, and we propose Konkola North mineralization also resulted from paleotopography-driven fluid-mixing. Geochemical and mineralogical evidence suggest that a Cu-bearing lower fluid moved laterally through the footwall, but was forced upward into the hanging wall by basement topography. As the Cu-bearing fluid rose, it encountered an upper fluid travelling through higher strata. The lower fluid was oxidizing and enriched in Ba, as well as Cu, and possibly K and Cl. In contrast, the upper fluid was reducing and carried sulfide, and possibly Co, Mg, and minor Sr. Fluid mixing resulted in both Cu and Comineralization and spatially associated barite precipitation. Where the oxidizing lower fluid encountered sulfide, sulfate formed and, with the Ba, precipitated barite. These barite concentrations are immediately below, coincident with, or immediately above the Cu-mineralization and may demarcate the mixing interface. Where barite is coincident with mineralization, Cu is in malachite, not sulfide, which suggests the ore zone was locally oxidizing. Where the barite is above or below, much of the Cu is in sulfide, suggesting the fluid mixture in contact with the host shale was reducing. Massive K-metasomatism has also affected these rocks, and is spatially associated with Cu-mineralization. Where Ba-rich fluids failed to encounter sufficient sulfide/sulfate to exhaust the Ba via barite precipitation, Ba-rich K-feldspar cement is common. Because of the insolubility of barite, Ba was removed from the mineralizing fluid more efficiently than Cu and has correspondingly larger barren gaps.

Session No. 91
Wetlands Paleoecology Through Time
Colorado Convention Center: A101/103
1:30 PM-5:30 PM, Monday, October 28, 2002

THE HANCOCK COUNTY TETRAPOD FAUNA: IMPLICATIONS FOR THE ORIGIN OF TERRESTRIALITY

GARCIA, William J., Department of Geology, Univ of Cincinnati, 500 Geology/Physics Building, Cincinnati, OH 45221, garciaw@email.uc.edu.

Early tetrapods are first recorded from the Frasnian of eastern Greenland and their record extends from the Late Devonian into the Early Carboniferous. The early record of tetrapods in the Devonian and Carboniferous contains significant gaps; the most notable is a 30 million year period at the base of the Mississippian that is represented by only two localities. In addition to temporal biases in the early tetrapod fossil record both geographic and environmental biases exist. A majority of Early Mississippian localities are located in Great Britain and North America and represent deposition in pond or estuarine paleoenvironments. A new Early Carboniferous tetrapod locality in Hancock County, KY preserves a number of tetrapod fossils from a fully terrestrial environment. A rich tetrapod fauna has been collected from the Buffalo Wallow Formation (Mississippian, Chesterian). The locality preserves a gray to black shale interpreted as a fresh- to brackish-water oxbow lake deposit. In addition many fossils are derived from a 10 cm thick horizon within a tan to buff paleosol lateral to the shales. Three distinct vertebrate taxa have been reconized from the horizon: an anthracosaur, a temnospondyl, and a previously unknown form. The anthracosaur is represented by numerous embolomerous vertebrae, pectoral and pelvic material, as well as limb elements. Based upon the number and sizes of known limb elements at least two individuals are represented. Temnospondyl material includes pelvic material and ertebrae. The third taxon is represented by numerous dorsal vertebrae possessing morphologic features normally attributed to stratigraphically younger groups. Fusion of the centra to the neural arch and the orientation of the zygopophyses are characters associated with a higher degree of terrestriality than is previously assigned to Mississippian forms.

Session No. 226
Evolution of the Early Atmosphere, Hydrosphere, and Biosphere II: Constraints from Ore Deposits
Colorado Convention Center: Ballroom 4
1:30 PM-5:30 PM, Wednesday, October 30, 2002

SUPERHEAVY S ISOTOPES FROM GLACIAL-ASSOCIATED MN ORES OF THE NEOPROTEROZOIC OF SOUTH CHINA: OCEANIC ANOXIA OR SULFATE LIMITATION?

MAYNARD, J. Barry1, LIU, Tie-bing2, and ALTEN, John1, (1) Department of Geology, Univ of Cincinnati, P.O. Box 210013, Cincinnati, OH 45221, maynarjb@uc.edu, (2) Institute of Geology, Chinese Academy of Sciences, P. O. Box 634, Beijing, 100029, China

Black-shales and Mn carbonate ores interbedded with glacial deposits from the Neoproterozoic of southern China exhibit extremely heavy values of pyrite d34S that may reflect the peculiar environment of the Earth at that time. d34S averages +30 permil at Tanganshan and +44 permil at Xiangtan, with no distinction between the shale and carbonate lithologies, unlike younger deposits, which show much lighter d34S in the shales than in the Mn ores. Trace element patterns of both the shales and the Mn ores are entirely similar to those of Phanerozoic deposits. REE patterns of the Mn ores lack the positive Eu anomaly that characterizes Archean Fe-Mn accumulations, but have a moderate positive Ce anomaly on NASC normalized plots. The sum of the REE is higher than in other Mn deposits, but lower than in modern deep-sea crusts.

d34S values of sulfide S from many localities in this time period tend to be exceptionally variable and to often show much heavier values than can be found in marine strata from the Phanerozoic. Therefore the anomalous d34S values we observed reflect peculiar conditions in the world oceans at this time rather than purely local effects. A possible cause is post-glacial ventilation of a stagnant ocean that was formed during a "Snowball Earth" episode. Deglaciation would have produced a sea level rise and deep-water overturn of a previously anoxic ocean that would have brought Mn, Fe, and isotopically heavy sulfate S into shallow waters. Some evidence contrary to this scenario comes from the similarity in whole rock geochemistry of the host rocks and Mn ores to typical black shales and Mn carbonates from younger rocks. Moreover, the absence of a positive Eu anomaly in the REE patterns suggests that the oceans were oxidizing enough to precipitate abundant Fe oxides at mid-ocean ridges and the presence of a positive Ce anomaly in Mn-rich sediments suggests generally oxidizing oceanic conditions. Because all of the other chemical systems look normal, a better explanation of the heavy S is an ocean with highly variable, but generally low dissolved sulfate.

Session No. 162--Booth# 125
Petrology, Igneous and Experimental (Posters)
Colorado Convention Center: Exhibit Hall
1:30 PM-5:30 PM, Tuesday, October 29, 2002

HIGH PRESSURE ORIGIN OF ALKALIC ROCKS FROM HALEAKALA VOLCANO, HAWAII

CRAVEN, Keri M. and KILINC, Attila, Department of Geology, Univ of Cincinnati, P.O. Box 210013, Cincinnati, OH 45221-0013, kericraven@hotmail.com

Nine alkalic rock samples from Haleakala Volcano, East Maui, Hawaii, ranging in composition from basalt to hawaiite to mugearite have been analyzed to test the hypothesis that alkalic rocks represent low degrees of melting of mantle rocks at high pressures. Four of these samples are from the post-erosional stage highly-alkaline historical flow (1790?) and five are from the older alkalic-stage Hana Volcanic Series (HVS). Bulk chemical analyses were determined using X-ray Fluorescence. These analyses were recast into normative minerals using the algorithm of Sack et al. (1987). When plotted on Sack et al.’s (1987) olivine-nepheline-high calcium pyroxene diagram, Haleakala rocks plot close to the high-pressure cotectic. This indicates that they have a deep-seated origin but additional calculations were made to confirm this finding.

Pressure-temperature (P-T) conditions of the Haleakala alkaline rocks were determined using the data of Takahashi et al. (1983) and Sack et al. (1987). Calculated P-T conditions for two of our historic flow samples yield 1417°C/ 21.7 kilobar and 1415°C/ 21.5 kilobar. The P-T conditions of the HVS rocks range from 1240°C/ 7.6 kilobar to 1353°C/ 14.7 kilobar. These results, as compared to the experimentally determined high-pressure mantle peridotite solidi (Kushiro, 1983; Takahashi et al., 1993), indicate that all of the alkalic rocks used in this study formed from less than 10 percent melting of mantle material and the alkalic rocks of the historic flow originate at a greater depth than the HVS rocks.

Session No. 11
Paleontology/Paleobotany II: Paleoecology and Preservational Bias
Colorado Convention Center: A112
8:00 AM-12:00 PM, Sunday, October 27, 2002

THE EFFECTS OF FAUNAL PATCHINESS ON THE USE OF GRADIENT ANALYSIS FOR REGIONAL, HIGH-RESOLUTION CORRELATION IN THE TYPE CINCINNATIAN SERIES (UPPER ORDOVICIAN)

WEBBER, Andrew J., Dept of Geology, Univ of Cincinnati, 500 Geology Physics Bldg, Cincinnati, OH 45221, webberaw@email.uc.edu.

High-resolution faunal gradient analysis in the type Cincinnatian Series has been effective in regional correlation at vertical scales of a few meters by numerically comparing stratigraphic trends in fossil composition among localities. Correlating finer-scale trends has been hampered not only by a lack of lateral persistence of individual strata from outcrop to outcrop, but also by significant vertical variation in faunal composition at scales of less than a meter. The source of this finer-scale stratigraphic variation in biotic composition is unknown: it might reflect small-scale environmental differences among localities, or it might indicate random fluctuations in biotic composition. Here, fine-scale patchiness in the distribution of fossils is assessed as a potential cause of fine-scale stratigraphic variation in biotic composition, and the effects this spatial variability has on the use of fossil data for regional correlation are examined.

Previous studies in the Cincinnatian recognize spatial heterogeneity in the distribution of faunal assemblages. Sampling from a single point along a particular bed potentially will capture only a subset of the entire suite of fossils from that bed, such that stratigraphic patterns of biotic transitions in the same interval may differ from one sampling site to another at one locality. If spatial variation is greater than stratigraphic variation, then patchiness is likely to mask the true stratigraphic signal of biotic composition at a fine scale, and minimizing the effects of patchiness may be necessary for regional high-resolution correlation.

In the present study, the degree to which patchiness affects fine-scale trends in faunal composition is assessed by using gradient analysis to quantify faunal composition along multiple stratigraphically limited vertical transects at a single locality. Spatial variation is evaluated by comparing the numerical faunal composition values among transects. Results indicate that spatial variation in faunal composition is significant enough to affect stratigraphic trends, often with certain taxa absent from single transects across multiple successive beds. Despite this, similar fine-scale stratigraphic patterns can be detected in all transects, suggesting that patchiness does not completely obscure the biotic signal.

MICROSTRATIGRAPHY OF AN AMALAGAMATED STORM BED: SPATIO-TEMPORAL RESOLUTION IN THE FOSSIL RECORD

BARBOUR WOOD, Susan L., Department of Geological Sciences, Virginia Tech, 4044 Derring Hall, Blacksburg, VA 24061-0420, susanwood@vt.edu and MILLER, Arnold I., Department of Geology, Univ of Cincinnati, 500 Geology Physics, Cincinnati, OH 45221

Studies of modern storm processes indicate that post-mortem transport of benthic marine organisms is often negligible, suggesting that subfossil death assemblages may commonly preserve spatial community structure with good fidelity, albeit time-averaged. To test the implication that the same fidelity is to be expected in ancient assemblages, the Upper Ordovician strata of the type Cincinnatian provide highly fossiliferous, laterally extensive outcrops that are ideally suited for assessing fine-scale spatial and temporal patterns in a storm-dominated setting.

In this investigation, we analyzed spatial and microstratigraphic patterns of fossil distribution preserved in an amalgamated, multi-event Cincinnatian horizon that is traceable for a lateral distance of some 60 km. A previous study of this horizon, contained in the lower Fairview formation, suggested that biologically meaningful spatial variation was preserved down to the 10 m scale, despite extensive storm reworking of the unit. However, in the earlier study, no effort was made to assess variation among the microhorizons that comprise the bed. By contrast, we conducted a microstratigraphic dissection of samples collected at 1- and 10-m lateral scales along a 150-m transect at the primary, “anchor” locality. Collections were also made of the same horizon at four additional localities arrayed throughout the study area.

Analysis of the 72 bulk samples (5,150 specimens) indicated that a subtle gradient is present at the anchor locality. Statistical analyses, including randomization tests, demonstrated that greater heterogeneity was preserved among the samples than can be expected by chance. Moreover, in several instances, microhorizons within a given bulk sample of the entire interval maintained a consistent biotic composition that was distinguishable from that of adjacent samples.

Thus, non-random spatial variability appears to be preserved in these ancient fossil assemblages, despite the myriad of storms and other post-mortem processes that may affect faunal assemblages between death and final preservation. Furthermore, the discovery of a consistent stratigraphic signal through several microhorizons suggests that biological patchiness on the Ordovician sea floor sometimes survived the effects of several storms.

Session No. 74
Three Billion Years of Reef Evolution II: Onshore-Offshore Paleoenvironmental Reconstructions
Colorado Convention Center: A105/107
8:00 AM-12:00 PM, Monday, October 28, 2002

A MODERN, SOFT-BOTTOM, SHALLOW-WATER, TROPICAL CRINOID FAUNA, WITH A COMPARISON BETWEEN LIVING COMATULA ROTALARIA AND FOSSIL UINTACRINUS SOCIALIS (ECHINODERMATA: CRINOIDEA)

MESSING, Charles G., Oceanographic Center, Nova Southeastern Univ, 8000 N. Ocean Dr, Dania Beach, FL 33004, messingc@nova.edu, MEYER, David L., Dept of Geology, Univ of Cincinnati, Cincinnati, OH 45221, and ROUSE, Greg, South Australian Museum, Nth Terrace, Adelaide, SA 5000, Australia

Current understanding of modern, shallow-water, tropical crinoid ecology derives almost entirely from assemblages associated with coral reefs and adjacent hard bottoms. Only Amphimetra and Heterometra have been observed regularly on unconsolidated low-energy bottoms. A recent preliminary survey reveals that about a dozen species (all unstalked comatulids) occur on a gentle sandy slope (15-18 m depth) west of Watson’s Bay, Lizard I., Great Barrier Reef, Australia. Dominant macroorganisms are chlorophyte algae (e.g., Caulerpa spp., Halimeda spp., Udotea sp., Penicillus sp.), seagrasses (Halophila spp.) and small free-living scleractinian corals (see Fisk, 1983, Mar. Biol. 74:287-294). Several of the crinoids (e.g., Comatella nigra) also occur on reefs. Several others appear restricted to unconsolidated substrates but cling to sponges or algae (e.g., Amphimetra tessellata, Zygometra microdiscus and Z. elegans), or hide beneath rubble or sponges (Heterometra crenulata). A. tessellata arranges its arms in a radial fan or funnel, while Zygometra spp. form parabolic filtration fans similar to those of Pontiometra andersoni on reefs and stalked Isocrinidae in deep water. Comatula cf. purpurea was uniformly observed irregularly coiled but visible beneath sprawling branching sponges. Comatula rotalaria, which lacks anchoring cirri and bears ~20 arms up to 0.3 m long when mature, rests directly on the sediment with its central calyx elevated by flexing 5-7 of its long interior arms to form a shallow U or V; a few other long arms flex slightly but do not touch the bottom, while the shorter exterior arms orient more or less upward as a central tuft. C. rotalaria offers a potential model for substrate adaptations and arm postures in Late Cretaceous Uintacrinus socialis, which, though it bears fewer longer (>1 m) arms, also lacks cirri and exhibits similar brachial morphology. U. socialis may have oriented its arms vertically despite their great length. Its arm bases are 8 mm across; anterior arms of modern confamilial Alloeocomatella pectinifera, held vertically for feeding, are <2.5 mm across the base and reach 0.5 m long. A similar, elevated-calyx posture occurs in a few reef-dwelling species without cirri (e.g., Comanthus alternans, Comaster nobilis), but these are extremely bushy taxa with >100 much shorter arms.

Session No. 74
Three Billion Years of Reef Evolution II: Onshore-Offshore Paleoenvironmental Reconstructions
Colorado Convention Center: A105/107
8:00 AM-12:00 PM, Monday, October 28, 2002

PRESERVATION OF IN SITU REEF FRAMEWORK IN REGIONS OF LOW HURRICANE FREQUENCY: PLEISTOCENE OF CURAÇAO AND BONAIRE, SOUTHERN CARIBBEAN

MEYER, David L.1, GREENSTEIN, Benjamin J.2, and BRIES, Jill M.1, (1) Geology, Univ of Cincinnati, Cincinnati, OH 45221, david.meyer@uc.edu, (2) Geology, Cornell College, Mt Vernon, IA 512314

The Lower Terrace Limestone (Pleistocene, ca. 125 ka) of Curaçao and Bonaire is remarkable for its spectacular preservation of coral colonies in growth position. Over the modern recorded history of tropical storms these islands are among the lowest in severe storm frequency within the tropical Atlantic region. We propose that the existence of similar conditions of low storm frequency during the late Pleistocene highstand were conducive to preservation of reef framework in growth position. Line transects across terrace exposures of seaward-marginal reef facies from both windward and leeward sides of Curaçao revealed 93% of colonies in growth position. As a test of the hypothesis, elevated reefs formed during the same highstand were examined in the Bahamas where some of the highest modern frequency of hurricanes is recorded. Fossil reefs with similar facies on Great Inagua, Bahamas, revealed 79% of colonies in growth position. On San Salvador, Bahamas, the coeval Cockburn Town Reef exposes considerable broken, collapsed rubble of Acropora palmata and A. cervicornis as well as numerous head corals in growth position. In another region of high hurricane frequency, the Florida Keys, the well-known Key Largo Limestone has an apparently high proportion of head corals in growth position, possibly a consequence of a more protected setting behind the shelf-marginal reef tract. Comparison of Holocene reef fabrics in high vs. low frequency hurricane regions of the Caribbean from previous coring studies may also support the hypothesis but are limited by problems of recognition of in situ corals in cores. Further regional quantitative comparisons between exposed fossil reefs are needed to test the role of hurricane frequency in reef coral taphonomy.

Session No. 123--Booth# 96
Quaternary Geology/Geomorphology (Posters) II
Colorado Convention Center: Exhibit Hall
8:00 AM-12:00 PM, Tuesday, October 29, 2002

CHEMICAL AND MINERALOGICAL ANALYSIS OF A SANGAMON SOIL EXPOSURE, SOUTHWESTERN OHIO

APPLEGATE, Patrick, GLOVER, Katherine, KING, Lisa, NICKLEN, Brian, SIKORSKI, Janelle, TOPRAK, Funda Özlem, LOWELL, Thomas V., and HUFF, Warren D., Department of Geology, Univ of Cincinnati, Rm 500 Geology/Physics Bldg, Cincinnati, OH 45221-0013, shoggoth@fuse.net

The Sangamon soil, which developed between the Illinoian and Wisconsinian glaciations, has been described from many locations in the Midwestern United States. However, quantitative data on the Sangamon from Ohio and Indiana are lacking, except for some published grain size profiles. We analyzed samples from a paleosol exposed near Sharonville, in southwestern Ohio, which we identified as the Sangamon based on its stratigraphic position beneath late-Wisconsinian drift. In our outcrop, the Sangamon is developed on a fining-upward diamicton. The origin of this diamicton is uncertain, but it may be colluvium derived from Illinoian till or the local bedrock. X-ray fluorescence analysis of this diamicton shows that the relative proportions of certain immobile elements such as Nb and Zr decrease with depth through the soil profile, reflecting their relative enrichment due to the selective removal of mobile alkalies and alkaline earths. Enrichment of the clay component of the soil in the lower zone is indicated by a downward increase in Al, suggesting eluviation of the upper part of the unit. Scanning electron micrographs reveal the presence of highly altered primary minerals such as mica and feldspar in the soil zone. Powder X-ray diffraction analysis shows that the upper and lower parts of the unit have different clay mineralogies. The less than 2 micrometer fraction of bedrock shale and the lower, unweathered diamicton, the likely parent materials for the soil, is characterized by well crystallized mica and chlorite, whereas the soil zone consists of randomly interstratified illite/smectite and chlorite/smectite. This difference is consistent with a model of a leached soil resting on the parent diamicton.

Session No. 124--Booth# 129
Stratigraphy (Posters) II
Colorado Convention Center: Exhibit Hall
8:00 AM-12:00 PM, Tuesday, October 29, 2002

BASAL PENNSYLVANIAN CLASTIC SEDIMENTS ON FLANK OF NEMAHA UPLIFT, EASTERN NEBRASKA-KANSAS BORDER, USA

JOECKEL, R.M.1, NICKLEN, B.L.2, and CARLSON, M.P.1, (1) Conservation and Survey Division, Univ of Nebraska-Lincoln, 113 Nebraska Hall, Lincoln, NE 68588-0517, rjoeckel3@unl.edu, (2) Department of Geology, Univ of Cincinnati, P.O. Box 210013, Cincinnati, OH 45221-0013

Basal Pennsylvanian clastic strata (BPC) near the eastern Nebraska-Kansas border on the eastern flank of the Nemaha Uplift (NU) contain coarse, feldspathic sandstones and conglomerates derived from Proterozoic granitic basement in the NU. BPC are sedimentologically distinct from overlying limestone-rich cyclothems and older, shale-rich, Pennsylvanian clastic sediments in the adjacent Forest City Basin. Three well cores penetrating the BPC (KC81-1 at Nebraska Conservation and Survey Division; Kansas Geological Survey Emery Trust #1 and Heinen #1) capture multiple (perhaps 20-25 in one case), well-defined, fining-upward (FU) packages (0.2-5.0 m thick). These packages show upward transitions from coarse, poorly-sorted, clay-cemented, feldspathic sandstones into shales and/or mudstones with paleosols. The basal contacts of FU packages are usually sharply erosional, and the upper contacts are sometimes marked by filled desiccation cracks up to 40 cm deep. In several cases, the lowermost sandstone within a FU package contains mm-scale mud laminae, which effect a distinct laminite-like appearance. In KC81-1 and Heinen #1, BPC directly overlie slightly weathered igneous basement rock.

Several hundred meters of Ordovician-Mississippian sediments, as well as weathered basement rock, were stripped from the NU to yield BPC sediments, which were then trapped in small fault-block basins at the NU margin. Paleosols and desiccation cracks in FU packages indicate a strong subaerial overprint on sediments, and it is likely that BPC were deposited on alluvial fans or, possibly, fan deltas. Gradational contacts between the BPC and overlying Missourian strata indicate that the deposition of BPC closely preceded local cyclothem deposition as sea level rose over the NU during the Late Pennsylvanian. Because of their context relative to a major uplift with complex faulting, BPC may provide new information about the relative roles of tectonics and eustatic sea-level cycles in local sedimentation, as well as the comparative importance of autocyclic and allocyclic depositional mechanisms.

Session No. 160--Booth# 105
Paleontology/Paleobotany (Posters) I
Colorado Convention Center: Exhibit Hall
1:30 PM-5:30 PM, Tuesday, October 29, 2002

RATES OF DISARTICULATION IN CRABS AND URCHINS ON THE CONTINENTAL SHELF AND SLOPE: HOW SPINELESS AND CRABBY WOULD YOU BE AFTER EIGHT YEARS ON THE SEA FLOOR?

PARSONS-HUBBARD, Karla1, ALTIERI, Jim1, KRAUSE, Richard2, LINCOLN, Rebecca3, and SHEPARD, Rebekah4, (1) Geology Dept, Oberlin College, Oberlin, OH 44074, Karla.Hubbard@Oberlin.edu, (2) Geology Dept, Univ of Cincinnati, Cincinnati, OH 45221, (3) 2022 Massachusetts Ave, Cambridge, MA 02140, (4) Geology Dept, Univ of California, Davis, CA 95616

Decapod crustaceans and echinoids are two types of animal that are rarely found preserved intact. When they are preserved articulated, the deposit is considered an example of rapid burial, low oxygen, or other mode of exclusion of scavengers and microbes. To test these assumptions, frozen blue crabs (Callinectes sapidus) and echinoids (Heterocentrotus mammillatus and Echinometra lucunter) were deployed in mesh bags attached to weighted PVC poles and placed in a wide variety of depths and environments of deposition in both the Bahamas and Gulf of Mexico.

Urchin tests were found to be surprisingly durable. All specimens were rapidly denuded of spines. The corona, however, was recovered intact more often than not after 5 - 8 years on the sea floor. Urchins deployed at15m were recovered whole in 4 out of 9 specimens. At 33m, 75% of urchin tests (n=12) remained intact after seven years. At depths from 70m to 100m, 66% of tests were intact after 5+ years (n=31) despite some being deployed on hardgrounds. Sites below the photic zone had 67% whole tests 5+ years after deployment (n=42). Disturbance of the mesh bags was minimal, but did occur at some shallow Bahamas sites where test breakage was no higher than at undisturbed sites.

Crab claws (the dactyl and fixed finger of the chela) showed remarkable longevity on the sea floor. Crabs at all depths at all sites in both the Bahamas and Caribbean had some remains left after 7-8 years. Crabs deployed in the Bahamas for 7 years at 15m had only a few disarticulated chelae left. At 33m, claws remained in the bag, along with the mandibles and a few lateral spines from the carapace. From 73m – 267m, crab deployments typically retained many disarticulated parts after 7 years. Even pieces of the delicate carapace were recovered. In the Gulf of Mexico, articulated claws were recovered at two different sites after 8 years at 60m. Exceptional preservation was observed in a sulfurous brine pool (>200ppt salinity) in which crab remains were recovered “pickled,” the dominant affect of the brine being decalcification of hard parts. Deeper Gulf of Mexico sites yielded a predominance of disarticulated claws. Petroleum seep sites at 550m-570m resulted in the least amount of crab remains after 8 years, while sites with carbonate sand and hard ground bottoms at 60 to 90 m yielded many more disarticulated remains.

Session No. 122
Precambrian Geology (Posters)
Colorado Convention Center: Exhibit Hall
8:00 AM-12:00 PM, Tuesday, October 29, 2002

THE SUNSAS OROGEN IN WESTERN AMAZON CRATON, SOUTH AMERICA AND CORRELATION WITH THE GRENVILLE OROGEN OF LAURENTIA, BASED ON U-PB ISOTOPIC STUDY OF DETRITAL AND IGNEOUS ZIRCONS

SANTOS, João Orestes, Geology, Geol Survey of Brazil, Av. Borges Medeiros 3200 - 1905, Praia de Belas, Porto Alegre, 90110-150, Brazil, orestes1@uol.com.br, EASTON, Robert M., Ontario Geol Survey, 933 Ramsey Lake Rd Rm B7064, Sudbury, ON P3E 6B5, Canada, POTTER, Paul E., Univ of Cincinnati, Department of Geology, Cincinnati, OH 45221-0013, Pepotter@if.ufrgs.br, RIZZOTTO, Gilmar Antônio, Geol Survey of Brazil, Av. Lauro Sodré 1400, Porto Velho, 78904-300, Brazil, HARTMANN, Léo Afraneo, Univ of Rio Grande do Sul, Av Bento Gonçalves 9500, Agronomia, Porto Alegre, 91540-000, Brazil, and MCNAUGHTON, Neal J., Geology and Geophysics, Univ of Western Australia, Nedlands, Perth, 6907, Australia

A SHRIMP U-Pb study of zircon and titanite from eight rocks indicates that the Sunsás Orogen was built in a broad time range (1450-1100 Ma) corresponding to a full orogenic cycle. The Sunsás Orogen contains three main orogenies: Santa Helena (mostly juvenile), Candeias (continental arc), and Nova Brasilândia (collisional), comparable in age to those present in the Grenvillian Orogen of North America. Eighty-nine detrital zircon grains from five samples were collected from late-Sunsás and post-Sunsás rocks and have age profiles with distinctive modes at 1560 Ma, 1450 Ma, 1320 Ma, and 1190 Ma. Ages about 1560 Ma are interpreted as derived from Serra da Providência granitoids, located to the east and northeast of the Sunsás Orogen inside the older Juruena Province (1.81-1.51 Ga), and may be comparable to circa 1540 Ma rocks present in the eastern Grenville Orogen in the Wakeham Group. Ages about 1450 Ma are typical of Santa Helena (SW Mato Grosso) and San Ignácio (Bolivia) Belts, and represent the first orogeny of the Sunsás Cycle, correlated to the Pinwarian of the Grenville Orogen and the Eastern Granite Rhyolite Province of Laurentia. The cluster of 1320 Ma ages represents the imprint of the second, Candeias Orogeny, comparable in age to the 1350-1310 Ma gneisses of the Mount Holly Complex of Vermont. The Candeias Granite has an age about 1337 ± 8 Ma and Candeias metamorphism is detected in metamorphic zircon rims (1324 and 1339 Ma) from both Serra Providência (GR333, 1510 Ma) and Jamari Complex (JL78, 1752 Ma). The third orogeny corresponds to zircon ages of 1190-1128 Ma (Nova Brasilândia Orogeny), which are equivalent in age to the Elzevirian Orogeny of the Grenvillian Orogen. The four youngest detrital zircons (1099-1060 Ma) are not related to any known orogeny in Southwest Amazon Craton. Possible correlatives include post-orogenic tin granites such as Santa Clara and Rio Pardo suites. Rocks comparable in age to the Ottawan Orogeny of Laurentia were not detected. Zircon populations from the post-Sunsás Palmeiral and Pacaás-Novos Formations suggest that they are Sunsás-derived foreland basins and are broadly correlative to the Dardanelos, Apiacás, Aguapeí II and Prainha Formations of the Amazon Craton. These units are comparable to the post-Grenvillian Middle Run basin in the eastern Midwest, USA and the Torridon basin, Scotland.

Session No. 10
Paleontology/Paleobotany I: Quantifying Morphology and Morphological Trends
Colorado Convention Center: A108/110
8:00 AM-12:00 PM, Sunday, October 27, 2002

DIFFERENCES IN SIZE OF EARLY PALEOZOIC BIVALVES AND BRACHIOPODS: THE INFLUENCE OF INTRINSIC AND EXTRINSIC FACTORS ON BODY SIZE EVOLUTION

KRAUSE, Richard A. Jr1, STEMPIEN, Jennifer1, KOWALEWSKI, Michal1, and MILLER, Arnold I.2, (1) Department of Geological Sciences, Virginia Polytechnic Institute and State Univ, 4044 Derring Hall, Blacksburg, VA 24061, ronk001@hotmail.com, (2) Department of Geology, Univ of Cincinnati, 500 Geology Physics, Cincinnati, OH 45220

Body size is commonly recognized as one of the most important biological characteristics of organisms. Trends in body size can offer key insights into evolutionary and long-term ecological processes, yet temporal patterns in size of organisms through the Phanerozoic remain largely unexplored. This preliminary study focuses on a comparative analysis of body size in Early Paleozoic brachiopods and bivalve mollusks.

Body size of mature specimens was estimated with linear shell dimensions measured using photographs in taxonomic monographs. The data compiled so far are focused primarily in the Ordovician period (>1000 specimens; ~150 genera of brachiopods and bivalves).

Results indicate that, in the Ordovician, the maximum linear dimension of an average bivalve (mean=1.8cm) was more than two times that of an average brachiopod (mean=0.8cm). This pattern is statistically significant (p<<0.05) and persists when data are analyzed separately for the Early, Middle, and Late Ordovician and when calcitic and phosphatic brachiopods are analyzed separately.

The results mirror present day patterns in body size for these groups. On average, present-day brachiopods, often confined to cryptic, high-latitude, and low-nutrient habitats, tend to be smaller than present-day bivalves. This parallel pattern is somewhat surprising given that, unlike today, Early Paleozoic brachiopods were not confined to low-nutrient settings and, in fact, were predominant compared to bivalves in terms of niche occupation, diversity, and overall abundance in many environments. Thus, for at least these two groups, extrinsic environmental factors such as nutrient supply may not be as important in dictating typical body size as intrinsic physiological characteristics, such as metabolic rates. This study also suggests that the average body size of a higher taxon need not be strongly correlated with factors that affect evolutionary and ecological success.

Session No. 11
Paleontology/Paleobotany II: Paleoecology and Preservational Bias
Colorado Convention Center: A112
8:00 AM-12:00 PM, Sunday, October 27, 2002

LONG-TERM DECAY RATES IN ORGANISM REMAINS FROM 15 – 600M DEPTH: PROGRESS REPORT FROM 8-YEAR EXPERIMENTS OF THE SHELF & SLOPE EXPERIMENTAL TAPHONOMY INITIATIVE

PARSONS-HUBBARD, Karla, Geology Dept, Oberlin College, Oberlin, OH 44074, Karla.Hubbard@Oberlin.edu, POWELL, Eric N., Haskin Shellfish Research Laboratory, Rutgers Univ, 6959 Miller Ave, Port Norris, NJ 08349, eric@hsrl.rutgers.edu, STAFF, George M., Geology Dept, Austin Community College, 11928 Stonehollow Drive, Austin, TX 78758, CALLENDER, W. Russell, Oceanic and Atmospheric Research, National Oceanic and Atmospheric Administration, 1315 East-West Highway, Silver Spring, MD 20910, WALKER, Sally E., Department of Geology, Univ of Georgia, Athens, GA 30602, BRETT, Carlton E., Department of Geology, Univ of Cincinnati, 500 Geology Physics, Cincinnati, OH 45220, and RAYMOND, Anne, Department of Geology and Geophysics, Texas A&M Univ, College Station, TX 77843-3115

The Shelf and Slope Experimental Taphonomy Initiative began a long-term study of taphonomic processes in 1993. Mesh bags containing crabs, urchins, mollusks and wood were placed at depths from 15 – 300 m off the Bahamas carbonate platform and in a variety of depositional environments on the shelf and slope of the Gulf of Mexico (70 – 600m). Upon recovery, each specimen was characterized as to degree of fragmentation, disarticulation, surface condition and infestation by bionts.

After 6 to 8 years, shells within the photic zone are weakened, fragmented or lost. Much of this loss is biologically mediated. Shells deployed below100m are generally unaltered after 8 years, with the exception of discoloration and very minor dissolution in both carbonate and siliciclastic settings. However, taphonomic alteration is proceeding more quickly at petroleum seeps. These sites offer heterogeneous bottom conditions with strongly sulfurous pore waters. Dissolution, breakage, and edge alteration are more common here, but are restricted to regions in the immediate vicinity of the seep.

Urchins and crabs were deployed frozen in 2-mm mesh pouches as part of each experimental array. After eight years all urchins had lost spines and the lantern had disarticulated, but a majority of urchins were recovered with the corona intact, even at 15m depth. Chelipeds of the crab Callinectes were nearly always recovered and, below the photic zone, carapace fragments were also common. The endurance of echinoderm and crab remains despite lack of burial (and thus exposure to microbial activity, if not scavengers) is remarkable. Wood quickly became consumed by Teredo and limnorid isopods, particularly below the photic zone. Shallow deployments (above 100m) show greater resistance to decay. Intermittent burial and overgrowth by encrusters likely slows the activity of the shipworms within the photic zone.

This long-term experimental taphonomy project continues to provide invaluable information on the fate of organism remains. Hard parts exposed at the sediment/water interface within the photic zone will likely not survive more than 10-15 years, depending on species. Deeper shelf/slope settings exhibit a slower rate of taphonomic loss, with the exception of wood that is slightly more durable in shallow shelf settings.