CORRELATION OF THE MIDDLE AND UPPER ORDOVICIAN ROCKS OF BALTOSCANDIA USING CONSTRAINED OPTIMIZATION (CONOP9)

The Middle and Upper Ordovician rocks of Baltoscandia have been divided into spatially distinct, composite litho- and biofacies units called confacies belts. A regional correlation of outcrops and boreholes in different confacies belts has always been problematic due to the pronounced biogeographical and lithofacies differentiation. Chronologically, the traditional Baltoscandian Stages were also defined by combined litho- and biofacies assemblages, primarily by benthic macrofossil faunas. The Stage boundaries, therefore, do not closely coincide with commonly used microfossil biozone boundaries (North Atlantic conodont zones, graptolite zones, or chitinozoan zones). We used the quantitative correlation method constrained optimization (CONOP9) to analyze the stratigraphic range information of 404 chitinozoan, conodont, ostracod, and graptolite species and construct a best fit correlation model among 14 boreholes and one outcrop in Baltoscandia (Poland, Latvia, Estonia, and Sweden). These sections span three confacies belts, the Scanian (slope, black shale), Central Baltoscandian (outer shelf, argillaceous limestones), and North Estonian (carbonate platform) belts. Generally, the Central Baltoscandian sections are more continuous and contain substantially more events (taxon FAD's and LAD's) than the North Estonian platform sections. This is especially true in the Upper Ordovician where the North Estonian strata contain numerous and large unconformities. In order to examine the synchronicity of the Baltoscandian Stage boundaries we coded each one as a unique event within every section and examined their placement in the CONOP composite. The Lasnamagi, Uhaku, Pirgu and Porkuni Stage bases were not well constrained with respect to the microfossil range data. Conversely, the Kukruse through Nabala stages (lower Upper Ordovician) have boundaries that better approximate synchronous surfaces. Conodonts had the lowest per taxon, per occurrence penalty assessment indicating that for the available data, conodont ranges were the most consistent across the study area. Penalty assessments for chitinozoans and ostracods were not significantly different.