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AAPG Bulletin

Abstract


Volume: 67 (1983)

Issue: 6. (June)

First Page: 953

Last Page: 962

Title: Depositional and Diagenetic Relationships Between Gulf of Elat (Aqaba) and Mesozoic of United States East Coast Offshore

Author(s): Samuel A. Epstein (2), Gerald M. Friedman (3)

Abstract:

The tectonic setting and depositional environments along the ancient margin during the Mesozoic of the East Coast of the United States may have been similar to those in the present Gulf of Elat (Aqaba). The Gulf of Elat (Aqaba) is the northern continuation of the Red Sea rift zone, where carbonates are accumulating contemporaneously with clastics under arid conditions. Clastics are deposited primarily in alluvial-fan complexes which spill out onto a narrow shelf. Carbonate deposits, including reef complexes, occur along the shelf break. In comparison, along the United States East Coast margin, Triassic to Early Jurassic rifting coincided with carbonate and clastic deposition. The Middle Jurassic and Cretaceous strata reflect the transition from synrift to postrift stages f tectonic evolution. Seismic and well data of the Jurassic and Cretaceous sections show an increase in the carbonate content approaching the United States East Coast shelf break. A discontinuous belt of carbonate buildups is inferred along the United States East Coast shelf and slope. The Gulf of Elat (Aqaba) represents an analogous model for the Early Jurassic East Coast margin of the United States. Beginning in the Middle Jurassic, the East Coast shelf-edge carbonate sequences were being deposited on a passive margin. Carbonate growth may have outpaced subsidence and may be similar stratigraphically to the Gulf of Elat (Aqaba) where carbonate deposits are prograding seaward.

In the Gulf of Elat (Aqaba), calcium carbonate cementation has significantly reduced the porosity (28%) and permeability (0.01 md) of still-submerged carbonate reefs. However, Pleistocene carbonates on uplifted blocks in the adjacent onshore have undergone leaching and development of secondary porosity as a result of dissolution by meteoric fresh water. The uplifted carbonates contain high secondary porosity (60%) and permeability (10,000 md). Emergent carbonate strata exposed to percolating meteoric waters generally develop such high porosities. In the subsurface, former emergent surfaces are recognized as unconformities; among examples of Mesozoic carbonate reservoirs formed during subaerial exposure and marked by unconformities are the Casablanca (Upper Jurassic, Spain) and Golden ane (Cretaceous, Mexico) oil fields. Unconformities in the Mesozoic carbonate rocks of the United States East Coast suggest that potential carbonate reservoirs (one Jurassic and one Cretaceous) formed during periods of subaerial exposure. Hydrocarbons generated during the Early or Late Cretaceous may have moved into the reservoirs prior to deep burial, possibly inhibiting further subsurface diagenesis, including porosity and permeability changes, and preserving the reservoirs.

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