--> ABSTRACT: New Perspectives on Depositional and Thermal History of Georges Bank, by Michael A. Smith and Pieter Van Gijzel; #91022 (1989)

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New Perspectives on Depositional and Thermal History of Georges Bank

Michael A. Smith, Pieter Van Gijzel

The stratigraphic framework and details of early sedimentary evolution of the Georges Bank rift basins and overlying passive margin continue to be controversial topics. Palynological assemblages in several of the 10 wells drilled to date have been affected by only minor reworking, and a biozonation has been established for the Mesozoic section of the U.S. North Atlantic margin. Combining the biostratigraphic data with well-log and lithologic correlations demonstrates the existence of a thick Upper Triassic-Lower Jurassic restricted marine synrift section that was thought to be younger in previous studies based largely on seismic interpretation. The Carnian-Norian shallow marine incursion may have been connected with oceans in the Tethyan region and Arctic Canada, and the Georges Bank deposits can be correlated with massive evaporites and carbonates in other basins on both margins of the North Atlantic.

Earlier studies also report conflicting data on the levels of thermal maturity and depth of the oil window in these wells. Indigenous vitrinite is lacking in much of the older carbonate section, making depth-reflectance profiles questionable at best. Amorphous kerogen from most Georges Bank wells was analyzed using a new maturity indicator, the transmittance color index (TCI). The TCI covers all zones of thermal maturity and provides data that closely correlate with mean vitrinite reflectance. TCI measurements for Georges Bank show that liquid hydrocarbons can still occur in at least the upper synrift sedimentary sequence and also provide detailed maturity profiles that contain local increases connected with the higher heat conductivity of anhydrite.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.