Basement Tectonics and Origin of the Sabine Uplift
Richard L. Adams
Carr Resources, Inc., 305 S. Broadway Ave., Tyler, Texas 75702
The same processes that formed the Gulf of Mexico Basin formed the Sabine Uplift. The Sabine Uplift is supported by a large rhombic area of basement fault blocks that originated as a mid-rift high during the Triassic rifting phase of the opening of the Gulf of Mexico. Sometimes referred to as a basement block, it covers an area that is 90 miles long (northwest-southeast) and 60 miles wide (southwest-northeast). Across the uplift the depth to magnetic basement is up to 10,000 ft shallower than in the middle of the East Texas Salt Basin. The northeast and southwest boundaries of this basement high are major transform fault systems that parallel the opening of the Gulf of Mexico. The northwest boundary is the East Texas Salt rift basin and the southeast side steps down into the South Louisiana Salt Basin. Within this mid-rift high, multiple smaller transform faults with horst and graben structures are evident by mapping the base of the Louann Salt from seismic data. Within the overall uplift area, these internal structures have influenced sedimentation on a smaller scale. Further uplift of this mid-rift high occurred during the middle to late Cretaceous and also during the Paleocene-Eocene.
While the mid-rift high has a thin Louann Salt cover, an estimated 5,000 to 7,000 feet of salt was deposited off this high in the East Texas Salt Basin. Salt isochrons infer both the external and internal shape of the mid-rift high. The Halbouty Ridge, located along the Smith-Rusk county line, and the San Augustine High are salt isochron thins that are evident on the mid-rift high.
The shape of the mid-rift high has also influenced later sedimentary depositional patterns. In the areas adjacent to it, i.e., southwest of the Trinity River and east of the Louisiana State Line, the Haynesville–Bossier–Cotton Valley System is aggradational due to very large available accommodation spaces. Conversely, in the area supradjacent to the mid-rift high, the Haynesville–Bossier–Cotton Valley System prograded across a flat marine shelf environment over an area nearly three times as large due to a loss of available accommodation space.
The Cotton Valley sands across this shallow marine mid-rift high are shoreface sands that were deposited along a shoreline that extended from southwest to northeast across the shelf. The sands of Overton Field, as well as the sands at Oak Hill, Willow Springs, and Carthage fields, are all examples of this deposition. Thin widespread limestone beds are present within the Cotton Valley across the Sabine Uplift. These limestones are interpreted as transgressive shell lags and back-bay oyster beds. The position of successive active shoreface systems prograded through time, with the oldest system to the northwest and the youngest migrated to the southeast.
Middle to late Cretaceous Laramide foreland tectonics applied lateral compression from the southwest and formed a foreland fold pair (the Sabine Uplift and the North Louisiana Salt Basin). Later, Paleocene-Eocene compression reactivated the uplift again. Pre-Jurassic transform fault lineations along northwest-southeast lines strongly influenced the shape and style of the resultant uplift. The current outline of the Sabine Uplift is defined by the edge of the Wilcox outcrop, resulting in a rectangular shape along a northwest-southeast axis.
Any exploration program for the Sabine Uplift area should include a serious consideration of Laramide compressional tectonics, subsalt structures, and both gravity and magnetic mapping early in the evaluation process.