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Clay-Mineral Diagenesis in Rocks of Morrowan and Springeran Age, Anadarko Basin, Oklahoma--Relationship to Time-Temperature History

Richard M. Pollastro, James W. Schmoker

Whole-rock and clay mineralogies of shales and sandstones of Morrowan and Springeran age (Lower Pennsylvanian) were determined by x-ray powder diffraction from core samples from 14 wells constituting a profile across the Anadarko basin. Interstratified illite/smectite (I/S) clay is the most abundant clay mineral in the shales; I/S is less abundant than other clay minerals in sandstones, unless the sandstones are clay mottled or contain shale laminae. The sandstones and shales commonly contain randomly interstratified I/S at present depths down to about 10,000 ft (3,050 m). Below 11,000 ft (3,350 m), only ordered I/S is present.

Regional mean random vitrinite-reflectance profiles for the Anadarko basin, compiled from the literature, suggest erosional removal of at least 2,600 ft (800 m) of sediment. Assuming a geothermal gradient of 1.3°F/100 ft and a surface temperature of 65°F (18°C) at the time of maximum burial (about 60 Ma), the transition from randomly interstratified I/S to short-range ordered I/S for the Morrowan-Springeran interval corresponds to a maximum burial temperature of 230°-245°F (110°-115°C). This temperature range is in good agreement with clay-mineral temperature stability models for this I/S transition, which have been published for younger rocks.

Time-temperature reconstructions using Lopatin's method relate the clay-mineral diagenesis documented in this study to thermal history and stages of hydrocarbon generation in the Anadarko basin and provide insight into the importance of time relative to temperature in the burial diagenesis of clay minerals.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.