Progressive Cementation from Marine to Deep Subsurface Environments, Upper Smackover Formation: ABSTRACT

Abstract

Several generations of carbonate cement are present in high-energy oolitic grainstones of the upper Smackover in seven wells in Arkansas, Texas, Louisiana, and Mississippi. The complete pattern of cementation reflects progressive lithification during burial. However, no single sample displays all cement types. The earliest cement was precipitated in the marine environment shortly after deposition; it consists of fibrous rims of nonferroan calcite isopachously surrounding grains. Small blocky crystals of either ferroan or nonferroan calcite formed after the marine cement. These crystals, which occur on the fibrous rims or irregularly encrust grains, are thought to have precipitated in the shallow phreatic environment. Subsequent compaction of the sediments with burial as inversely related to the degree of development of these early cements. Postcompactional cements consist of dolomite and coarse ferroan or nonferroan calcite, both of which are interpreted to have formed in the deep subsurface. The dolomite not only occurs as a void-filling cement, but also partially replaces grains. In places, dolomite rhombs transect sutured grain boundaries, providing conclusive evidence of their late origin. The coarse calcite comprises the final generation of cement and is the most common cement type. This cement may be poikilotopic; it commonly replaces dolomite rhombs. Porosity reduction is mainly the result of compaction and pore occlusion by this late calcite cement. End_of_Article - Last_Page 445------------