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Three sandstone samples each from Stratigraphic Units III and IV were studied to determine their diagenetic history. The sandstone bodies probably had a common provenance and were essentially granitic debris when deposited. Because grains were deposited in different environments, they followed totally different diagenetic pathways. Sands in Unit III, which possibly were deposited as fan deltas in a marine setting, are interbedded with carbonate mud. The inferred sequence of diagenetic events that the sediment underwent includes the formation of thin K-feldspar overgrowths on detrital K-feldspar grains; replacement of much feldspar (chiefly Plagioclase) by micrite; dolomitization of much micrite; development of secondary porosity (~ 10%) by dissolution of feldspar and micrite; generation of pyrite, possibly by reaction of migrating H2S with hematite that was present as grain coatings (now gone) on detrital grains. Sands of Unit IV, which were deposited as alluvial deposits, first underwent diagenesis under the influence of meteoric water, later by formation water of uncertain origin. The inferred diagenetic sequence includes the development of clay skins on detrital sand grains during the infiltration of meteoric water; hydrolysis and oxidation of unstable detrital grains (chiefly Plagioclase and ferromagnesian minerals) to produce kaolinite, mixed-layer clays, and hematite that precipitated in the pores of the sand; trivial development of secondary pores by late-stage dissolution of K-feldspar along cleavage planes; and migration of H2S through the sandstone to locally reduce the hematite and bleach the rocks.

Diagenesis of Sandstone from Stratigraphic Units III and IV, Site 537