--> Abstract: Multistage Diagenesis of a Pleistocene Limestone from the Arabian Gulf, by H. S. Chafetz and P. F. Rush; #90987 (1993).
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CHAFETZ, HENRY S., Department of Geosciences, University of Houston, Houston, TX, and PATRICK F. RUSH, Reservoirs, Inc., Houston, TX

ABSTRACT: Multistage Diagenesis of a Pleistocene Limestone from the Arabian Gulf

An extensive suite of diagenetically altered late Pleistocene low-magnesian calcites occurs in the shallow subsurface of the Arabian Gulf, offshore of M Jubayl, Saudi Arabia. Thirty-one borings, oriented in a straight line perpendicular to the shoreline and approximately 300m apart, penetrated on the average 25 m of limestone. The low-magnesian calcites are underlain by dolomites and overlain by a thin veneer of Holocene aragonitic deposits.

In the diagenetic low-magnesian calcitic facies (dLMC), plots of the vertical distribution of 131 stable isotopic values display opposite trends in the nearshore versus offshore parts of the section. The (isotope){18}O values (PDB) range from 0.0 at the top of the dLMC to -4.0 Previous HitdownwardNext Hit in the nearshore part of the section, whereas they range from -3.0 at the top to -1.0 Previous HitdownwardNext Hit in the offshore part of the section. The (isotope){13}C values (PDB) range from 1.8 at the top to 2.5 Previous HitdownwardNext Hit in the nearshore part of the section, and from 3.0 at the top to 0.5 Previous HitdownwardTop in the offshore part of the section. Twenty-eight whole rock analyses of the overlying Holocene aragonitic material average 0.0 ((isotope){18}O) and 3.3 ((isotope){13}C). The values and their vertical trends in the dLMC indi ate meteoric water altered the (isotope){18}O of these marine sediments to -4.0. These sediments were then altered again by descending sabkha waters which resulted in high (isotope){18}O values near the surface. The low (isotope){13}C values in the lower part of the offshore section must be due to an unidentified source. Thus, these late Pleistocene deposits display complex multistage diagenesis.

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