ABSTRACT: Pyritization in the Shublik Sandstones, Prudhoe Bay, Alaska

Mack Gipson, Jr., Leonard R. Gardner

Detailed thin-section petrographic analyses of sandstones of the Shublik Formation of Prudhoe Bay field, Alaska, reveal that pyrite is a common constituent of the rocks. Pyrite occurs in several modes, which can be combined into two broad categories: (1) grain replacements and (2) pore fillings. Pyrite grain replacement occurs predominantly in microporous chert and argillaceous lithic clasts, and to a lesser degree in dense (nonporous) chert, and shale clasts and microlaminae.

Early pyritization is selective, first attacking microporous chert and microporous argillaceous lithic clasts, followed by shale clasts and microlaminae. Late-stage pyritization is pervasive, including remaining framework grains, cements, and matrix; pore space is completely obliterated, resulting in local concretionary aggregates.

The main constraint to pyritization in the Shublik probably was the availability of sulfur, iron being a common constituent of the formation waters. Sulfur is believed to have been supplied by (1) organic matter incorporated in the initial organic-rich (fossiliferous) facies and (2) sulfate-bearing formation fluids.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990