--> Abstract: The Stratigraphy and Paleoceanography of Cretaceous Carbonate Buildups, Porcupine Basin, Offshore Ireland, by D. B. Macurda, Jr., D. Bradford, H. R. Nelson, Jr., and G. Jones; #90987 (1993).

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MACURDA, Jr., D. BRADFORD, The Energists, Houston, TX; H. ROICE NELSON, Jr. Walden 3D Inc., Houston, TX; and GARY JONES, Landmark/LGC, Houston, TX

ABSTRACT: The Stratigraphy and Paleoceanography of Cretaceous Carbonate Buildups, Porcupine Basin, Offshore Ireland

The Porcupine Basin is a thermal sag basin southwest of Ireland; it is approximately 300 km north-south and 130 km east-west. The initial fill in the Lower Cretaceous was clastic; carbonates replaced clastics from the Coniacian to Lower Tertiary (Danian).

A unique set of constructional mounded features are present in the Upper Cretaceous in seismic lines along the eastern basin margin. These mounds are asymmetric; they are elongate in an east-west direction (up to 12-13 km in length) and symmetrical in a north-south direction (up to 7 km in width). Downlaps are found at the base, the amplitude is lower in their interior, and slight velocity pullups are present beneath them. There are shingled reflections on the southern flanks of the mounds and steeper faces on the northward side of the some of the more westerly mounds.

The Upper Cretaceous mounds are interpreted as carbonate buildups. The elongate form (east-west) was controlled by tidal currents; the winds were strongest from the present day northwest, causing steeper northerly faces and carrying detritus to the south. The builders are unknown. The northernmost known Upper Cretaceous rudists are found in Spain and southern France, bryozoans form small buildups in Denmark and sponge buildups are known from eastern Canada.

The buildups have never been drilled; their hydrocarbon potential is unknown. Their size could trap large volumes of hydrocarbons if the proper combination of porosity and source was available.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.