ABSTRACT

The end-product of ongoing geoinformatics initiatives in stratigraphy and paleontology will be an online electronic stratigraphic record. It faces three challenges: to compile sufficient data, to integrate multiple databases, and to maintain tools that can assemble all the local data records into a geologic time line. The third challenge amounts to sequencing the fossil record and we propose to address three of the obstacles it faces: (1) Fossil biotas of the same age may differ as a result of habitat and preservation effects; (2) Very large data sets must be sequenced in smaller pieces and the results stitched seamlessly together; (3) Increasing numbers of dated and fingerprinted ash beds need to used more effectively. We propose a case study of manageable geographic and temporal extent that, nevertheless, raises these same issues. The Ordovician and Silurian periods span almost 100 million years of early Paleozoic time and are traditionally subdivided by graptolites and conodonts - two fossil clades with different ecological and preservational traits that restrict their use to largely mutually exclusive domains. The Mohawkian (Late Ordovician) of eastern North America presents precisely the type of challenging geological environment in which to build and test the temporal sequencing and stitching approaches that we envision. Mohawkian strata are widely exposed in the region and yield a rich fossil record that includes diverse, but somewhat endemic, conodont faunas. The epicratonic succession is rimmed along the Appalachian margin by deeper water sediments of the Taconic foreland basin. These strata contain a suite of inter-continentally distributed graptolite faunas, but few described conodont assemblages. Numerous altered volcanic ash deposits (K-bentonites) link these facies through a set of transitional facies along the interior basin margin. Despite these advantages, the prevalence of short sections, structural complexity, and facies limitation of the faunas impedes precise and reliable correlation between the cratonic and basinal successions, consequently limiting our ability to compare their disparate faunas and tectonic histories.
Intellectual Merit: We propose to combine (1) geochemical fingerprinting (tephrochronology) and
U-Pb geochronology of K-bentonites from the Mohawkian and early Cincinnatian with (2) a restudy of late Mohawkian conodonts and graptolites from eleven regions across eastern North America and (3) computer assisted sequencing of the global Ordovician conodont and graptolite fossil record. This work will provide a detailed temporal and paleoecological framework within which to refine the application of biofacies information to the temporal sequencing of the fossil record via rigorous quantitative techniques. We will focus in steps 1 and 2 particularly on conodont and graptolite-bearing successions that contain Kbentonites, and especially on regions where conodonts and graptolites occur in close association. The results of our work in a time interval that remains troublesome in spite of a wide range of timestratigraphic information will bear upon fundamental questions in both local and global stratigraphy. In the course of this study we will test existing alternate correlation models for the mid Upper Ordovician of central and eastern North America. The results will provide an improved, age-calibrated basis for studies of faunal turnover and diversity change in the Ordovician and Silurian. Most importantly, the work will lead to the development of improved techniques for time scale construction and validation.
Broader Impact: The data and tools we develop will be shared immediately through the CHRONOS
project and will investigate technological solutions that are not being addressed by CHRONOS to
sequence events. The project meets the EARTHTIME goal of cross-training stratigraphers and
geochronologists in developing high precision time-scales. We will train two PhD students (one a
minority), and three undergraduates. We will integrate the efforts of four institutions, two with large
minority enrolment (UCR, UALR), in a new collaboration that will facilitate the interaction of all the
students and PIs at each institution. Undergraduates will participate as field and lab assistants for the PIs and for the graduate students, and will be given pieces of the project as senior research projects. Each student will present aspects of the research at a professional meeting. The project will also include a secondary school teacher who will work alongside PI Leslie during the summer as part of the Arkansas STRIVE program. The teacher will develop class projects based on their experiences. The project thus impacts future generations of students by enhancing a secondary education teacher's knowledge base and scientific curriculum.

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