--> Abstract: Variations in Sedimentology and Mineralogy of Condense Sequences: An Example from Venezuela, by B. Aguado; #90987 (1993).

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AGUADO, BERNABE. INTEVEP S.A., Caracas 1070A, Venezuela

ABSTRACT: Variations in Sedimentology and Mineralogy of Condense Sequences: An Example from Venezuela

The widely used Sequence Stratigraphy concepts and methods require the precise identification of sequence boundaries and maximum flooding surfaces in order to determine the distribution of the environments of deposition and basin infilling mechanisms. Accordingly, in the last few years special attention has been paid to condensed sequences. The sedimentological and mineralogical analysis of three condensed sequences occurring in a 700 ft interval, in the Boqueron Field, Eastern Venezuelan Basin, resulted in a clear differentiation among them. The lower Condensed Sequence, of Cretaceous age, is composed of abundant collophane pellets partially recrystalized to apatite, and minor glauconite on a clay matrix, deposited as a platform shale. The middle interval, Eocene in age, consists on glauconie section up to 60 ft thick, resting erosively on a carbonate platform. It is composed of glauconite altered to chlorite and mixed layer glauconite/smectite, cemented by calcite, siderite and dolomite. It was deposited at the shelf-slope break. The upper Condensed Section is separated from the middle one by only 25 ft of shale and silt, which have contorted bedding and water-scape structures. This section consists of highly altered glauconie pellets on a mud matrix, composed of mixed layer illite/smectite and chlorite, and cemented by siderite and calcite. Sedimentary features suggests that this interval is allochtonous and was deposited as a slump down the slope. The differences encountered in these flooding surfaces indicate that care should be taken when analizing condensed s quences in order to get a better understanding of the distribution of the environments of deposition in a basin.

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