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Our work progressed in two principal areas during the past year. The results are listed below:

1) Bedding plane co-occurrence of graptolites and conodonts in Ordovician dark shale sequences:

Bedding plane co-occurrence of biostratigraphically useful conodonts and graptolites in Ordovician shale sequences enhances the overall correlation precision between platform and deep water successions.  Darriwilian shale successions in Tarim, western China, and Alabama and Idaho in North America contain the key conodont zonal indicator species Pygodus anitae, P. serra, and P. anserinus (as well as more long-ranging taxa) on bedding planes with Pterograptus elegans to Nemagraptus gracilis Zone graptolites.  Three of the Pygodus bedding plane associations appear to be partial conodont apparatuses. The occurrence of bedding plane conodonts with graptolites across the Sandbian-Katian boundary at Black Knob Ridge (Atoka County, Oklahoma, U.S.A.) was a key factor in the selection of Black Knob Ridge as the GSSP for the base of the Katian, the middle stage of the Upper Ordovician Series.  The Amorphognathus tvaerensis Zone - A. superbus Zone boundary is tentatively identified at 5.7 meters above the base of the Bigfork Chert in the lower Diplacanthograptus caudatus graptolite Zone.

New collections across the Sandbian-Katian succession at the Hartfell Score section near Moffat, Scotland also contain biostratigraphically important conodonts. Amorphognathus tvaerensis is present 1.6 meters below the FAD of D. caudatus and A. superbus is present 9.4 meters above it.  Thus, at Hartfell Score the A. tvaerensis Zone - A. superbus Zone boundary occurs within an interval of 11 meters in the D. caudatus graptolite Zone.  These bedding plane co-occurrences provide more precise ties between graptolite and conodont biozonations and support the potential for additional resolution with further collecting at these and other localities.  Not all Sandbian-Katian successions have yielded biostratigraphically important conodonts.  For example, the succession on Bornholm yields is dominated by long-ranging, coniform conodont taxa (e.g., Scabbardella altipes).  This suggests that graptolite-bearing dark shale successions may contain at least two distinct conodont biofacies.

2) High-resolution stratigraphic correlation and Biodiversity Dynamics in Middle and Late Ordovician Marine Fossils From Baltoscandia:

During the early Late Ordovician there was a significant decline in marine biodiversity that has been variously attributed to sea level, facies, and climatic changes. In the East Baltic area several workers have described such a marked diversity decline and faunal turnover in microfossils at the Keila -Oandu Stage boundary, an event called the Oandu Crisis. To get a better understanding of microfossil diversity dynamics in the Baltoscandian Middle and Upper Ordovician succession we used constrained optimization (CONOP9) to construct a composite range chart from the stratigraphic data of 505 chitinozoan, conodont, ostracod, and graptolite species from 20 boreholes and 8 outcrops. We employed the CONOP composite as a timescale in which to calculate biodiversity, extinction, and origination rates through the Middle and Late Ordovician.  Traditional biodiversity metrics, and more recent probabilistic methods based on capture-mark-recapture analysis, were used to estimate biodiversity and fossil recovery patterns. We divided the CONOP composite into 860 Kyr intervals spanning the Lasnamägi through Porkuni stages. Our data show that overall biodiversity increased steadily from the beginning of the Keila to the middle Rakvere stages, mainly due to an increase in ostracod diversity. Chitinozoan diversity reached a zenith in the late Keila, dropped through the Oandu Stage, and then gradually declined during the rest of the Ordovician. Chitinozoans exhibited constant origination but variable extinction rates and underwent a dramatic diversity decline associated with the d13C isotope excursion known as the GICE event. Conodonts had diversity peaks in the early Uhaku and early Kukruse stages, and then declined gradually through the Late Ordovician. Conodonts exhibited constant extinction and origination rates and their diversity decline is attributable to higher extinction than origination rates. Interestingly, the fossil preservation and recovery rate was highly variable and appears to exert a strong influence on the observed biodiversity pattern.