64 Carbonates in Time and Space: Sedimentology, Stratigraphy, and Diagenesis

Monday, 5 November 2012
8:00 AM - 12:00 PM
203A

APTIAN CARBONATE SEQUENCES OF A COOLER PHASE WITHIN CRETACEOUS GREENHOUSE, ADRIATIC PLATFORM, CROATIA

Paper number: 64-14
Program: Technical Sessions
Time: 11:15 AM – 11:30 AM

Authors

Abstract

Aptian platform carbonates, southern Croatian Tethys, record the sequence development, parasequence stacking, effects of oceanic anoxic events on platform stratigraphy, and global climate. The Aptian supersequence consists of four 3rdorder depositional sequences. Latest Barremian to Early Aptian Sequence Ad1 is 17-to-60-meters thick, rests on Barremian carbonates and is unconformable updip. It is dominated by shallow subtidal carbonate parasequences that commonly are amalgamated and a well-developed late highstand, sequence boundary zone. The Early to earliest Late Aptian Sequence Ad2 is 7-13-meters thick, and has a significant flooding event associated with OAE 1a, marked by deposition of relatively shallow water, but dysaerobic laminated carbonates. Sequences Ad2, Ad3 and Ad4 are dominated by peritidal carbonate parasequences updip, especially in the early TST and late HST, and subtidal parasequences elsewhere. The Latest Aptian Sequence Ad3 (3-to-8-meters thick) is separated by a major hiatus from Sequence Ad4 (latest Aptian; 8-to-20-meters thick) which spans OAE1b. Sequence Ad4 is dominated by shallow subtidal parasequences, with peritidal facies and breccias occurring in the late highstand, sequence boundary zone.

The well-developed breccias capping sequences, together with the well documented evidence of sea level changes of tens of meters, suggests that 3rd order sea levels likely were driven by glacio-eustasy associated with waxing and waning of moderate sized ice sheets. The strong eccentricity dominated cyclicity observed in coeval pelagic sections are manifested on the platform by 4th order parasequences (100 to 400 k.y. duration). The low subsidence rate (~1 cm/k.y.) of the platform allowed the full effects of sea level fall to be recorded as multiple breccia horizons. Based on the evidence for glacio-eustatic sea level falls recorded in the platform stratigraphy by emergence breccias, the eccentricity driven parasequences, and the common restriction of peritidal facies to late highstands, this study suggests some ice-forcing of sea level and that the Aptian greenhouse climate was punctuated by intermittent cooler periods and ice buildup at high latitudes.