SEA-LEVEL CHANGES AND GEOCHEMICAL ANOMALIES ACROSS THE CENOMANIAN-TURONIAN BOUNDARY - PECINOV QUARRY, BOHEMIA

Relationships between geochemical anomalies, sea-level change and othe r events were studied in the Cenomanian-Turonian boundary interval in the Pecinov quarry in southwestern part of the Bohemian Cretaceous Bas in (Czech Republic). A major 3rd-order sea-level rise at the base of t he late Cenomanian M. geslinianum Zone was followed by deposition of o rganic-enriched mudstones in a succession of parasequences, deposited in response to high-frequency (4th-order) sea-level fluctuations and r ecording a stepwise decrease in bottom oxygenation towards intensely d ysaerobic conditions. A complex delta(13)C excursion occurs in total o rganic matter of the late Cenomanian deposits. A sequence boundary of latest Cenomanian age in the Pecinov section is correlated to a global sea-level fall during the N. juddii Zone. A renewed sea-level rise oc curred during the early Turonian W. coioradoense Zone and reached maxi mum flooding during the M. nodosoides Zone. During the early Turonian, bottom waters were generally aerobic, and the positive delta(13)C exc ursion waned early in the W. coloradoense Zone. The magnitude of the d elta(13)C excursion: more than 4 parts per thousand, is approximately the same as in North America and Not-them Africa, confirming that it w as controlled by a global paleoceanographic mechanism. The absence of anoxia and a delta(13)C anomaly during the peak flooding of early Turo nian age suggests that widespread deposition of organic-enriched depos its, as well as the positive shift in delta(13)C generally did not dep end on the absolute elevation of sea level but, rather, on the area of newly flooded land during transgression. Abrupt, small-scale shifts i n delta(13)C towards higher values coincide with the flooding surfaces of parasequences and may reflect either regional changes in the propo rtion of marine and terrestrial organic matter or rapid global changes in isotopic composition of marine organic matter related to high-freq uency sea-level changes, Abundances of Ir, Sc, Cr, V and other element s previously reported as forming anomalous concentrations in the bound ary interval showed no enrichment in the Bohemian section. This is mos t probably due to the large distance of the depositional site from the presumed volcanic source of element-enriched, deep waters in the prot o-Caribbean region. Anomalous concentration of Mn at the base of the T uronian deposits was caused by diagenetic incorporation of Mn into sid erite. (C) 1997 Elsevier Science B.V.