Abstract: Sandstone Diagenesis in Bromide Formation, South-Central Oklahoma

Mark W. Longman

Many factors combine to control diagenesis in sandstones. These include (1) composition, (2) depositional environment and associated rock types, (3) migration patterns and chemistry of interstitial fluids, (4) pressure and temperature, (5) time, and (6) local setting relative to faults and folds. Quartzarenites generally are cemented with quartz or calcite; arkoses by quartz, feldspar, kaolinite, or illite; volcanic arenites by chlorite and zeolite; and calclithites by calcite. Depositional environment affects diagenesis through composition of connate water, availability of fossil fragments (a source of calcite), associated shales (a source of magnesium for dolomite, silica for quartz, etc.), and associated evaporites. Fluid migration in the subsurface is a complex variab e that may promote cementation by bringing in ions from other areas or may inhibit cementation either by filling pores with an inert diagenetic fluid such as hydrocarbons or by bringing in undersaturated solutions. Pressure affects diagenesis mainly via pressure solution. The role of temperature still is poorly understood.

Sandstones in the Ordovician Bromide Formation of south-central Oklahoma were deposited in shallow-marine shoreface and tidal-flat environments in a sporadically transgressing sea. The sandstones are supermature quartz arenites with quartz, calcite, and dolomite cements. In these sandstones depositional environment acted in conjunction with composition as the primary control on diagenesis. Dolomite cement is most commonly associated with algal mats in tidal-flat sediments. Shoreface sandstones with common fossil fragments generally contain calcite cement. Thin unfossiliferous shoreface sandstones enclosed by shale tend to be cemented with quartz. Porosity is preserved locally in thick unfossiliferous shoreface sandstones where relatively early migration of hydrocarbons inhibited late- tage cementation by quartz.

AAPG Search and Discovery Article #90961©1978 AAPG Annual Convention and Exhibition, Oklahoma City, Oklahoma