Paper No. 11
Presentation Time: 10:45 AM
A HIGH-RESOLUTION CARBON-ISOTOPE RECORD OF THE TURONIAN STAGE CORRELATED TO A SILICICLASTIC BASIN FILL: IMPLICATIONS FOR MID-CRETACEOUS SEA-LEVEL CHANGE
A basin-scale record of high-frequency transgressive-regressive fluctuations of Turonian age in the Bohemian Cretaceous Basin (Central Europe) has previously been interpreted as being influenced by short-term eustasy. In our study, nearshore siliciclastic strata in two separate sub-basins are correlated to a multi-stratigraphic dataset from a new research core (Bch-1) drilled in offshore marine sediments of the central basin. A high-resolution δ13Corg record from the Bch-1 core is presented along with major- and minor-element proxies, TOC, carbonate contents, terrestrial to marine palynomorph ratios, and detailed macro- and microfossil biostratigraphy. The 400 m thick Turonian through Lower Coniacian interval permits correlation to the highest-resolution C-isotope curves available: all carbon-isotope events demonstrated by δ13Ccarb studies in the British Chalk, NW Germany and other reference sections are recognised in the δ13Corg curve from Bch-1, thus offering a significantly improved resolution of temporal correlation of relative sea-level changes and other events. A number of short-term, basin-wide regressions in the Bohemian Cretaceous Basin show a recurrence interval of 100 kyr or less , implying probably a glacio-eustatic mechanism. This is an order of magnitude shorter than the timing of sea-level falls inferred from the New Jersey margin and the Apulian platform, previously interpreted as driven by glacioeustacy. The relatively small magnitude of the Bohemian Basin sea-level falls, typically 10-20m, and generally below 40 m, indicates that the 2.4 Myr period suggested by others to generate 3rd -order cycles, is too long to be the principal cycle generating unconformities in tectonically active basins, where the rate of eustatic fall must exceed the subsidence rate. Unconformities in low-accommodation settings such as passive margins must represent amalgamated records of multiple cycles of sea-level fluctuations of 100 kyr scale, recognizable only in high-resolution datasets from expanded basinal sections. This research was supported by the Czech Science Foundation (GACR) grant No. P210-10-1991.