Except for a few wells such as the Cost No. G-2 on Georges Bank, Mesozoic carbonates along the United States Atlantic seaboard are known only from seismic interpretation or from shallow or outcropping data collected by research vessels. Other sources of information are analogy from Florida-Gulf of Mexico wells, from European- West African Tethyan facies, or from wells on the Nova Scotia Shelf. Nova Scotia data that may be useful for comparison to offshore U.S.A. follows.

(1) Carbonate and deltaic sedimentation are synchronous during much of the Late Jurassic and earliest Cretaceous. (2) Smaller scale cycles and younger large scale vertical facies changes indicate repeated relative sea-level changes. (3) Shelf-edge profiles vary from rimmed/platform to prograding ramp near the Sable Island Delta where slope carbonate-shale deposits have been drilled. (4) Shelf-edge platform profiles also vary from reef-rimmed to channel to possible open sediment-bypass margins with ooid sands. Some faulted margins occur. (5) From Early to Late Jurassic, there is a reduction in evaporitic sediments, an increase in biotic diversity, and an increase in coals indicating an increasingly humid climate. (6) Depositional facies zones are easily distinguished and may be of shal ow or deeper water aspect at a particular location. In the upper Abenaki, the skeletal-rich shelf margin has invariably been preserved. (7) True reefs occur. (8) Along the upper Abenaki shelf edge, carbonate facies also vary to include reef complexes, mud mounds, islands, oolite shoals, skeletal and oncolitic sands. (9) Termination of Abenaki carbonate sedimentation is either diachronous burial by deltaic sands or widespread synchronous Valanginian drowning possibly immediately preceded by brief subaerial exposure. (10) Abenaki diagenesis is dominated by porosity reduction due to burial, but dolomitization and early intraformational leaching occur at the shelf edge. (11) Later subaerial (or submarine) erosion at the top of the Abenaki occurs in a few widely separated areas. (12) Hydrocar on shows are rare but do occur in the carbonates on some salt domes or in geopressured zones.

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