About This Item
Share This Item
The Smackover Formation (Upper Jurassic) in northeast Texas is a transgressive-regressive carbonate sequence which has been extensively dolomitized. The extent of dolomitization is directly related to the presence of the overlying Buckner anhydrite which has provided the magnesium-rich brines necessary for dolomitization.
The Smackover Formation is subdivided informally into a lower and upper member based on distinctive lithologic characteristics. The lower member, which rests conformably on the fluvial-deltaic sandstones of the Upper Jurassic Norphlet Formation, contains a laminated, organic carbonate mudstone facies that grades into an overlying locally fossiliferous, pelletalmicritic facies. The vertical sequence of facies indicates a transgression of the sea. They are interpreted to represent an inter-tidal mudflat to shallow-marine, low-energy platform or protected lagoonal environment. The upper member of the Smackover Formation consists mainly of broken skeletal debris and pelletal allochems in a micritic matrix. The sediments are better winnowed and better sorted upward in the sequence. Interbe ded with and overlying the skeletal-pelletal facies is a clean well-sorted dolomitized oolitic-grainstone facies. This uppermost informal member marks the beginning of a progradational sequence which lasts throughout the remainder of Smackover deposition and continues through deposition of the evaporites and red beds of the overlying Buckner Formation.
Deposition of the Smackover Formation most closely resembles Holocene carbonate sedimentation in the southern Persian Gulf. Both areas are represented by a similar carbonate ramp depositional framework together with closely approximated salinity and climatic conditions.
Most of the Smackover production in northeast Texas occurs along the Mexia-Talco fault zone in the deeper gentle salt-related anticlines and salt-graben systems. Reservoir rocks are primarily leached and dolomitized oolitic grainstones and dolomite. Laminated organic carbonate mudstones which characterize the lower, transgressive phase of the Smackover Formation provide an excellent source rock for petroleum.
Exploration targets for the Smackover Formation are the areas where dolomitized oolitic and skeletal grainstones occur on top of structurally high areas such as over salt ridges or swells in the deeper portions of the basin. Along with this are those areas along the updip limit of the Smackover Formation in which the upper member has been leached and dolomitized and occurs in a stratigraphically favorable position.
End_of_Article - Last_Page 478------------