Abstract: Abenaki Formation, Nova Scotia Shelf, Canada--Depositional and Diagenetic Model for Mesozoic Carbonate Platform

L. S. Eliuk

Seismic data and 11 wells permit preliminary modeling of the 3,000 to 4,000-ft (900 to 1,200 m) thick Abenaki Formation of Middle Jurassic to earliest Cretaceous age. The lowest member (Scatarie) which overlies the deepening upward Mohican Formation clastic rocks shows a cyclicity of oolitic, then oncolitic to muddy limestones, and culminates in the neritic middle shale member (Misaine). These regionally developed cycles are interpreted as transgressive pulses marking the opening of the Atlantic Ocean. The thick upper limestone member (Baccaro) was deposited at the paleocontinental shelf edge and adjacent to the early Sable Island delta. A neritic "moat" zone separates a nearshore sandy basement ridge zone from the shallow-water Baccaro platform. Oolitic bar, mud shoal an shelf-edge, stromatoporoid-coralgal reef, and possible channel depositional environments are distinguished. Interpreted eustatic sea-level changes affected both deposition and diagenesis. During lowered sea levels, paleohighs whether reefal, salt, or basement-cored, may have been subjected to freshwater diagenesis in a humid, subtropical climate (Tethyan realm). The only significant dolomitization appears to have occurred in freshwater-marine phreatic mixing zones beneath subaerially exposed reefs. Porosity is associated with the dolomite when present and the overlying freshwater and vadose environments. Most of the Abenaki has little porosity and shows mainly submarine and deep subsurface diagenesis. If not buried by the delta complex, the Baccaro finally was drowned, and deeper water, slightly phosphatized, shelf-edge sponge reefs capped it locally before being covered by the Verrill Canyon Formation shale.

AAPG Search and Discovery Article #90972©1976 AAPG-SEPM Annual Convention and Exhibition, New Orleans, LA