RUI: Taphonomic Character of Plant Fossil Assemblages at the Permian-Triassic Boundary, Karoo Basin, South Africa

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PROJECT SUMMARYPage AMany hypotheses have been proposed for the response of the land plants, insects, andvertebrates to the P/Tr boundary extinction event. Many of these hypotheses are based onpoorly unconstrained spatial and/or temporal data. Most lack any contextual constraintof the paleontological data used in the analysis used to support the interpretation.Hence, it is not possible to know if the ?trends? or ?changes? seen to occur from thepreboundary assemblages into the transitional and post-boundary assemblages are a truereflection of the ecosystem or are biased taphonomically.This proposal hypothesizes that an isotaphonomic data set of pre-boundary,trans-boundary, and post-boundary plant-fossil assemblages will allow for the emergence ofa credible characterization of the response within this part of the terrestrial ecosystemat this critical point in Earth history. Will the isotaphonomic plant-fossil recordparallel or be tangential to the well established response in the marine realm? Or, willthere be no change in biodiversity; might the replacement and/or turnover occur earlier orlater in time than directly at the P/Tr boundary?Research conducted, to date, in KwaZulu Natal Province, South Africa, in the northeasternpart of the Karoo Basin indicates that Late Permian megafloral assemblages are preservedin four different sedimentologic and taphonomic conditions. Each megafloral assemblagetype preserves a very different signature of the vegetation contributed to the fossilrecord. These are: (1) parautochthonous assemblages within abandoned fluvial channel fillsequences, similar to modern and other ancient oxbow lakes; (2) dispersed and isolated,allochthonous assemblages preserved on foreset beds and reactivation surfaces withinlarge, fine-grained fluvial regimes; (3) concentrated, mat-like allochthonous assemblageswithin bedload dunes of coarse siltstone channels; and (4) dispersed, sorted assemblagesin turbidites. Data presented in the text concerning two localities ? Bulwer andWagendrift Dam ? demonstrate that previous interpretations of the fossil assemblages inthese sites are incorrect. And if these data are used from the literature as the basisfor interpretation, the resulting suppositions are inappropriate.With an increasing continentalization of the sedimentary package in the Karoo into theTriassic, all but the last taphonomic assemblage type should be encountered in thetransitional and post-boundary sections. Seven cross boundary and post boundary sectionshave been identified in which plant fossils and/or vertebrates are preserved, and willserve as the basis for the 2004 field season. It is anticipated that identification ofisotaphonomic assemblages in this part of the stratigraphy will allow for directcomparison of biodiversity indices with those presently being determined by other membersof an international research team, involving U.S., Dutch, and South African scientists.The present proposal requests funds to support undergraduate student research designed toassist in the acquisition of an isotaphonomic data set in the Karoo Basin, South Africa.Through the next two years of field work and laboratory analysis, P/Tr and early to middleTriassic localities will be assessed to identify and characterize those depositionalsequences as found in the latest Permian.