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the Provenance and Basin History of the Quartzose Paso del Sapo Formation: Evidence for Intense Weathering During the Late Cretaceous, Chubut Province, Argentina

Jessica, Lopez

University of Wisconsin-Madison, Department of Geology and Geophysics

Madison, Wisconsin

[email protected]

The Cretaceous Paso del Sapo Formation of the Chubut Province, Argentina consists of fluvial and tidal deposits dominated by quartzose sediments. These sediments are separated from underlying andesitic volcanics by a distinct peneplain surface suggesting a period of intense weathering. Understanding the weathering processes that created this nonconformity and developed the quartzose sediments within a mafic context will provide an analog for petroleum explorers to identify possible high quality reservoirs where abundant mafic rocks are present.

The goals of this project are to determine provenance of the Paso del Sapo Formation, evaluate sediment maturity and associated weathering processes, and develop a model for generating reservoir quality quartz arenites. Stratigraphy, petrology, and the chemical index of alteration will be used to test provenance and degree of weathering.

A field study was conducted in February and March of 2006. Two complete stratigraphic columns and 5 smaller columns were constructed from various parts of the basin and seventy-five samples were collected. Sandstone samples were collected for point counting and zircon analysis to determine provenance. Mudstone samples will be analyzed using the chemical index of alteration to examine the degree of weathering. Samples were also collected from the underlying andesite as it approached the nonconformity with the Paso del Sapo Formation to examine if a weathering profile is recorded within the andesite. The results of these techniques will be compared and combined to understand sediment transport and weathering processes, and develop depositional environment models.

AAPG Search and Discovery Article #90060©2006 AAPG Foundation Grants-in-Aid