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Dynamic Systems modeling suggests that complex coastal dinoflagellate biosystems can be modeled using environmental parameters such as temperature, salinity, and bulk nutrient levels. The former Salisbury Embayment of northern Virginia and Maryland is modeled here, using STELLA I and FORTRAN models based on physical oceanography and temperature, salinity, and nutrient conditions of the modern Yellow Sea. In these models, dinoflagellate assemblages are predicted based on environmental conditions associated with depth. Cluster analyses of fossil dinoflagellate frequency data from Tertiary Pamunky Group (Aquia and Nanjemoy Formations) of the Salisbury Embayment produce 17 discrete groupings. Samples within the Salisbury fossil cluster groups are statistically similar (via ANOVA analysis), but not the same. Therefore they represent paleocommunity types rather than paleocommunities. Although individual sinofiagellate species recur in similar environmental settings, the paleocommunity types do not appear to repeat. In the past, such associations have been used as depth indicators. It is suggested here that they relate to estuarine, nearshore, and offshore coastal regions because of the temperature, salinity, and nutrient conditions of each. In the modern Yellow Sea, nearshore and offshore regions are separated by discrete lateral fronts in some areas, and by gradational regions of mixing in others. Both types of water mass boundaries are modeled in this study. Results suggest that evidences that discrete water mass boundaries might have occurred between some fossil dinoflagellate associations. Circulation patterns of the Salisbury Embayment may have been roughly similar to those of the modern Yellow Sea. Master of Science

Early Ordovician Knox Group carbonates consist of meter-scale dolomite cycles deposited on a passive margin. The meter-scale cycles were deposited under warm, semi-arid conditions, under low amplitude sea level fluctuations on a relatively ice-free earth. The overlying Knox unconformity (~10 m.y. duration), formed by global eustatic sea level fall and tectonic uplift of the subducting margin at the onset of Taconic orogenesis. Middle Ordovician carbonates were deposited on a ramp peripheral to a foredeep in Tennessee. The Middle Ordovician High Bridge Group consists of a 2nd-order supersequence with three 3rd-order sequences (each 30 to 100 m thick), which record a long term change from humid conditions in TST's into more arid conditions during HST's. Peritidal cycles formed under low-amplitude eustatic fluctuations. The late Middle to Late Ordovician carbonates and clastics comprise a 2nd-order supersequence deposited on a ramp peripheral to the Taconic foredeep. The supersequence is composed of four 3rd-order sequences (each 40 to 80 m thick), which contain 11 parasequence sets (2 to 20 m thick). The small sequences are composed of stacked, predominantly subtidal meter-scale cycles (parasequences). Meter-scale subtidal cycles contain facies that suggest they formed under moderate amplitude (20 to 40 m) sea level fluctuations, likely produced by glacio-eustasy. However, peritidal cycles in the HST's indicate they formed under low-amplitude sea level fluctuations, thus suggesting the amplitude of sea level fluctuations decreased during 3rd-order sea level falls. The facies in the supersequence indicate they formed under cool, humid conditions during the 2nd-order TST and became more arid during the 2nd-order HST. The unconformity at the top of the supersequence formed during eustatic sea level drawdown associated with extensive Latest Ordovician glaciation. Ph. D.

Four intervals of Middle Pennsylvanian marine strata in the Breathitt Formation of eastern Kentucky, the Elkins Fork, Kendrick, Magoffin, and Stoney Fork, were measured, sampled for fossils, and described. Each marine interval was shown to be the product of a single episode of transgression and regression that led to the establishment of a variety of marine habitats in the central Appalachian basin. These habitats included marginal marine, nearshore normal marine, nearshore stressed, offshore normal marine, and offshore dysaerobic environments. Fossil collections were made and species abundance distributions were obtained for each paleontological sample. Multivariate statistical analyses such as cluster analysis and principle components analysis were used to classify fossil assemblages sampled into a variety of paleocommunity types, each associated with a particular lithological facies. Paleocommunity types that were found to occur in more than one of the four marine intervals were resampled at selected localities, with replicate samples taken at each locality. These additional samples were used to test for the presence of the same statistically defmed paleocommunity at different localities within the same marine units and to test for the recurrence of statistically defmed paleocommunities between marine units. Results of the analyses suggest that recurrence of similar fossil assemblages (paleocommunity types) is common in the Breathitt marine units whenever there is recurrence of comparable marine facies. However, recurrence of the same statistically defined paleocommunity is rare, with significant variation in the abundances of member species appearing each time a particular paleocommunity type recurs. This suggests that the recurrence of distinct fossil assemblages over intervals of geologic time can be explained by the repeated reinvasion of suitable habitats by the individual members of a persistent species pool, without recourse to ecological mechanisms needed for preserving or perpetuating particular community structures. Ph. D.

Marine organic-walled microplankton biostratigraphy of the Maastrichian Prairie Bluff Chalk is documented. A total of 69 dinoflagellate species were identified in the Prairie Bluff Chalk. Samples were studied from three sites in central and western Alabama (Tombigbee River, Millers Ferry, and Braggs). Also included were several samples of the overlying Clayton Formation, and the underlying Ripley Formation. The species and their stratigraphic ranges were compared with other coeval sections in the U. S. and Europe. Dinoflagellate Zones Va and Vb of Wilson (1974) are recognized in the Prairie Bluff Chalk. This suggests the age of the Prairie Bluff Chalk is restricted to late Maastrichtian. The Prairie Bluff Chalk correlates to the upper Providence Formation of Georgia (Firth 1984); the lower Providence being early Maastrichtian. The basal Clayton Formation may be latest Maastrichtian in age Master of Science

A newly discovered fern-like fossil plant is described from the Lower Upper Devonian of southern Ellesmere. This plant occurs as an element of an Archaeopteris dominated flora preserved in sediments of the Nordstrand Point Formation (mid-late Frasnian) at Bird Fiord. The plant demonstrates a pinnate vegetative system with three orders of branch and laminate pinnules, of a general sphenopteroid type. Primary pinnae usually diverge from the main axis in distichous pairs (Le., in a quadriseriate manner), but rarely depart singly (i.e., in a biseriate manner). Each primary pinna bears an aphlebia in the catadromic position. Laminate pinnules are broadly lobed with a proximally overtopped vein system. Anatomically, this plant is characterized by an elongate, mesarch, bipolar protostele that is ribbon to clepsydroid in shape. Proximal to each primary pinna node, an initially crescent-shaped, bipolar pinna trace diverges from the main axis stele. This trace appears to become four-ribbed before dividing to yield a pair of bipolar primary pinna traces. A pair of circular, centrarch aphlebia traces depart from the catadromic ribs of a primary pinna trace in its four-ribbed stage. Protoxylem is helically thickened, with metaxylem pitting ranging from scalariform to circular. Secondary xylem is unknown. Both the morphology and anatomy of this plant are non-gymnospermous and suggest affinity instead with zygopterid ferns. Within the Zygopteridales, this plant seems to align most closely with the Rhacopytaceae. The Frasnian dating of this plant suggests that laminated foliage had been achieved by some zygopterid ferns long before previously recognized. The presence of Sphenopteris-like pinnules in this Frasnian plant also shows that one should be careful in attributing such foliage to early gymnosperms. Master of Science

Several questions regarding the nature of extinction in the fossil record of marine invertebrates were investigated using statistical methods and familial diversity data. First, a series of analyses were performed to determine whether the magnitudes of mass extinctions were statistically distinguishable from the magnitudes of background extinctions. The expected proportions of familial extinction for each order in a stage (based on an estimate of the ordinal probability of familial extinction for each of 134 orders) were compared to the observed proportions of familial extinction in the stage using a simple X2 goodness-of-fit test. The results indicate that eight stages in the Phanerozoic had a statistically significant excess of extinction. A second set of X2 analyses was done using estimates of per taxon familial extinction rates for the orders, rather than familial extinction probabilities. The X2 tests resulted in four additional stages that contained a statistically significant surplus of familial extinction. To test the results further, a set of bootstrapping analyses was done for each of five different extinction metrics. Two stages, the Ashgillian and the Dzhulfian, had a statistically significant excess of extinction in both Xl analyses and in four out of five of the bootstrapping analyses. Two additional stages, the Guadelupian and the Maestrichtian, had a statistically significant magnitude of extinction in every analysis. Thus, the results provide strong support for the argument that mass extinctions comprise a distinct group of evolutionary phenomena. Familial extinction rates have declined from the early Phanerozoic to the Recent. Some have suggested that familial extinction rates have been constant through time within most major taxonomic groups and that the decline in familial extinction rates is the result of the successive elimination of groups with relatively high familial extinction rates (a process referred to as taxon sorting). A model of total familial extinction rates through time based on stationary probabilities of familial extinction within orders closely mimics the observed decline in total familial extinction rates supporting the taxon sorting hypothesis. Linear regressions of the familial extinction probabilities of orders versus the geologic time of both their first and their last occurrences suggest that the observed decline in extinction rates resulted from the early elimination of orders with characteristically high probabilities of extinction, and the later origination of orders with relatively low probabilities of extinction. In addition, a statistical analysis comparing the evolutionary volatility of extinct versus extant taxa suggests that extinct orders had greater volatility in their diversity histories which may have contributed to their early demise. The taxonomic selectivity of both background and mass extinctions was investigated using simple X2 analyses. The results suggest that familial extinction during mass extinctions was taxonomically more selective than extinction during background extinctions. In addition, the magnitude of familial extinction experienced by an order in a stage was compared to the familial extinction probability estimated for the order using the binomial theorem. Then, those orders that suffered an unusual excess of familial extinction during particular stratigraphic stages were separated from the remaining orders in the stage. The results suggest that sessile filter feeders (particularly those groups important in ancient reefs) and pelagic groups suffered the greatest during intervals of mass extinction. Finally, the potential relationship of familial diversity to both sea level and I7Sr/86Sr ratios was statistically examined using linear regression techniques. No statistically significant correlation was found between sea level and familial diversity. However, a significant correlation was discovered between diversity and I7Sr /86Sr ratios. Strontium ratios are believed to be an indirect measure of the aerial extent of exposed continental crust. Thus, the relationship between 17 Sr/86Sr ratios and diversity suggests that familial diversity has been a function of 1) the aerial extent of epeiric seas and 2) the amount of clastic material being supplied to these seas. The last factor could have affected familial diversity by restricting normally diverse, shallow carbonate environments. Master of Science

The Monmouth and Brightseat Formations contain a rich and diverse dinoflagellate assemblage. Thirty-five genera and sixty-six species, of which two genera and eight species are new, are described in this study. The stratigraphic distribution of the taxa is summarized in Figure 4. The content of the assemblage changes suddenly at the Cretaceous-Tertiary boundary with thirteen species making the~r first appearance at or just above the boundary. Nineteen species cross the boundary and thirty-five species are restricted to the Cretaceous. The rather sudden change in the nature of the dinoflagellate assemblage at the boundary is interpreted by the author to indicate a paraconformable relationship between the Cretaceous and Paleocene sediments. The term paraconformity is used since there is little field evidence (a few pebbles, some lignite, and evidence of boring) indicating any extensive period of erosion at the boundary. Master of Science

This study describes the biostratigrapaic distribution of Meramecian conodonts from three measured sections of the Greenbrier Limestone (Meramecian-Lower Chesterian), located in the Greendale and Hurricane Ridge Synclines of southwestern Virginia and southern West Virginia. The Little Valley Formation, Hillsdale Limestone and lower portions of the "Denmar-Gasper" and "Ste. Genevieve" Formations, consisting of rocks deposited in a variety of shallow carbonate-ramp environments, were investigated. Two new multielement conodont apparatuses were recognized: Kladognathus sp. A and Hindeognathus ("Apatognathus") laevipostica. Elements of Kladognathus sp. A are morphologically distinct from homologous elements of the K. levis-K. tenuis group. Evolutionary change from K. levis to K. tenuis is marked by slight Sa and Sb element changes, and the addition of an X element, DE Lambdagnathus fragilidens. Species of Kladognathus are promising Meramecian biostratigraphic markers. Also recognized in this study are species of: Cavusgqnathus, Gnathodus, Hindeodus, Idioprioniodus, Lochriea, Rhachistognathus, “Spathognathodus," Synprioniodina? and Taphrognathus. Meramecian formations in the study area can be correlated with the Mississippian stratotype (Illinois Basin) based on the following zones: Taphrognathus varians - "Apatognathus," "A." scalenus - Cavusgnathus aad Gnathodus bilineatus - Cavusgnathus charactus. Southward thickening of the "A." scalenus zone from the Hurricane Ridge Syncline (11 m) to the Greendale Syncline (180-200 m) reflects higher rates of sedimentation and subsidence in the depositional area of the latter. In addition, thinness of the zone in the Hurricane Ridge Syncline may be due to a hiatus between this zone and the younger G. bilineatus zone. This hiatus is not indicated by conodont faunas from the Greendale Syncline, which preserves a more complete Meramecian biostratigraphic record. Conodont and litahologic evidence for a coeval hiatus exists in other areas of eastern North America: the Illinois Basin stratotype, eastern Kentucky, Southern Ohio and eastern Tennessee. Master of Science

A detailed statistical study was performed on molluscan fossil assemblages collected from the Pliocene Morgarts Beach Member of the Yorktown Formation, located in Isle of Wight County, southeast Virginia. The principal objectives of this study were to examine potential sampling problems and biases inherent in paleontological research. This has been accomplished by statistically testing for the homogeneity, or lack thereof, in species assemblages obtained from samples collected from three localities within the Morgarts Beach Member. Multivariate analysis of variance, two-way analysis of variance, multiple comparison tests and cluster analysis were performed on data collected from a five horizon by five section sampling grid (18 feet [5.5 meters] high, 21 feet [6.4 meters] long) located at Morgarts Beach, Virginia. The results of this analysis demonstrate that the relative abundances of species present in the five horizons are significantly different, whereas the relative abundances of species present in the five sections are not significantly different. Results from cluster analysis show that species assemblages contained in samples collected from the Morgarts Beach Member located at Rushmere are substantially different from the Morgarts Beach type area assemblages, in terms of relative abundances of species. The reason for the lack of faunal similarity relates to the documented facies change between the two localities. The results demonstrate that there is no reliable method to obtain accurate census data (frequency abundance curves) from biostratigraphic or lithostratigraphic units deposited during anything but a restricted time interval. In addition, replicate sampling was found to be unnecessary when attempting to determine the relative abundances of species contained in closely spaced sections within the Morgarts Beach Member. Species accumulation curves were constructed from the data collected from the Morgarts Beach Member. Examination of these curves demonstrate that many rare species will not be found unless extensive collecting is undertaken. Master of Science