Sequence Development Influenced by Intermittent Cooling Events in Cretaceous Aptian Greenhouse, Adriatic Platform, Croatia

Husinec, Antun¹; Read, Fred²
¹Geology, St. Lawrence University, Canton, NY.
²Geosciences, Virginia Tech, Blacksburg, VA.

Aptian platform carbonates, southern Croatian Tethys, were studied to define the sequence stratigraphy constrained by C-isotope chemostratigraphy which allowed the platform succession to be tied to well documented and dated coeval pelagic sections in Europe. The Aptian supersequence consists of four 3rd order depositional sequences, some of which are separated by sequence boundary zones of breccia interlayered with peritidal facies. Sequence Ad1 (latest Barremian-Early Aptian) is dominated by shallow subtidal carbonate parasequences that commonly are amalgamated and a well-developed late highstand, sequence boundary zone. Sequence Ad2 (Early Aptian to earliest Late Aptian) 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. Sequence Ad3 probably is early Late Aptian, and likely is separated by a major hiatus from sequence Ad4 (latest Aptian) 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, although this might have been emphasized locally by tectonic warping of the platform.

The evidence for glacio-eustatic sea level falls recorded in the platform stratigraphy by emergence breccias, the eccentricity driven parasequences, the common restriction of peritidal facies to late highstands, all suggest some ice-forcing of sea level and that the Aptian greenhouse climate was punctuated by intermittent cooler periods and ice buildup at high latitudes.

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012