Diagenesis and Burial History of Lower Cretaceous Travis Peak Sandstone, East Texas
Shirley P. Dutton
Fine-grained quartzarenite and subarkose in the Lower Cretaceous Travis Peak Formation have been extensively modified during burial diagenesis. Permeability in much of this gas-bearing formation has been reduced to less than 0.1 md as a result of compaction, extensive precipitation of authigenic minerals, and minor pressure solution. Timing of the diagenetic events can be constrained by combining petrographic and geochemical data with subsidence and thermal history.
The Travis Peak Formation in east Texas is approximately 600 m thick. Depth to the top of the formation ranges from 1,800 to 2,900 m now, but maximum burial depth was probably 450 m deeper during the Eocene. Variable amounts of uplift of the formation also occurred during mid-Cretaceous movement of the Sabine uplift. The geothermal gradient is 38°C/km now, but it may have been as high as 44°C/km when the Travis Peak was deposited because of elevated heat flow caused by crustal stretching associated with rifting of the Gulf of Mexico.
Illite rims and dolomite were the first authigenic minerals to precipitate in Travis Peak sandstone. Dolomite probably formed soon after deposition at about 25°C from water with a ^dgr18O composition of 0 ^pmil (SMOW). Next, extensive quartz cement, averaging 17% of the rock volume in well-sorted sandstone, occluded much of the primary porosity. The ^dgr18O composition of quartz overgrowths indicates they precipitated from meteoric fluids at temperatures of 55° to 75°C, which equate to depths of 900 to 1,500 m. Dissolution of orthoclase and albitization of plagioclase followed quartz cementation and occurred prior to mid-Cretaceous movement of the Sabine uplift. Illite, chlorite, and ankerite precipitated after feldspar diagenesis. The ^dgr18O composition of pore fluids evolved during ankerite precipitation from -4 to +3 ^pmil (SMOW); +3^pmil is the present composition of Travis Peak water. Most diagenesis ended when oil migrated into the Travis Peak about 65 Ma. Later deasphalting of the oil by solution of gas filled much of the remaining porosity in some zones near the top of the formation with reservoir bitumen.
AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.