295 D22. From Processes to Stratigraphy

Wednesday, 25 October 2017
8:00 AM - 12:00 PM
Ballroom 6C

FACIES AND STRATIGRAPHY OF THE LATEST CRETACEOUS TO EARLIEST PALEOGENE PLATFORM CARBONATE SUCCESSION WITH CORAL PATCH REEFS: THE ISLAND OF BRAč, CROATIA

Paper number: 295-15
Program: Technical Sessions
Time: 11:30 AM – 11:45 AM

Authors

Abstract

A Maastrichtian–Paleocene section on the Island of Brač (Croatia) was examined to reconstruct environmental changes and describe coral patch reefs across the Cretaceous–Paleogene (K–Pg) transition. Benthic foraminifera (Dicyclina schlumbergeri, Murgeina apula, Rhapydionina liburnica, Fleuryana adriatica) confirm the latest Maastrichtian to the earliest Paleocene age for this section.

The Cretaceous strata consist of: (1) lower part made of wackestone and floatstone with rudist fragments, peloids, ostracods, discorbid and large benthic foraminifera, and fenestral laminites deposited in low energy restricted shallow subtidal and intertidal environments; (2) middle part containing a brecciated surface with speleothems and blackened lithoclasts, indicating subaerial exposure, and multiple coral patch reefs with preserved globular and domal growth fabric despite intense weathering and reddish color; (3) upper part composed of laminated fenestral micritic limestones with peloids, ostracods, discorbids, and rare thin-shelled rudist fragments overlain by grain-supported limestones with miliolids, peloids and intraclasts immediately below the K–Pg boundary level indicating higher energy shallow subtidal conditions.

These strata abruptly transition upward into burrowed micritic limestones of Paleocene age with discorbids, ostracods and planktonic foraminifera deposited in deeper and more open marine environments. Above this only 5 m thick horizon with pelagic influence, a sudden return to micritic limestones with discorbids, ostracods and charophytes indicates re-establishment of low-energy shallow subtidal conditions with nearshore brackish and freshwater influence. Top of the section has the largest and best developed coral patch reefs which were exposed and karstified during a relatively long hiatus between these older Paleocene and the overlying Paleocene/Eocene deposits.

This Brač succession indicates deposition on a very shallow inner platform with coexisting rudists and scleractinian corals during the late Maastrichtian. After a brief episode of relative deepening, slowed carbonate production and biotic crisis in the earliest Paleocene, the development of scleractinian reefs indicates a relatively rapid restoration of environmental conditions and coral recovery.

Geological Society of America Abstracts with Programs. Vol. 49, No. 6

doi: 10.1130/abs/2017AM-298384

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