Abstract: Paleoenvironment of Moffat Mound, Edwards Formation, Central Texas
James L. Brown, Jr.
The Moffat Mound facies of the Edwards formation is a shallow marine-carbonate complex, which developed in response to the shallow-water conditions of the Fredericksburg seas along the northeastern flank of the Belton high. This sedimentary package abruptly interrupts the typical south-to-north (updip) thinning trend of the Edwards throughout most of north-central Texas.
Deposition of the Moffat Mound began with the establishment of isolated rudist communities on the Belton high, some of which developed into local patch reefs. These scattered patch reefs and rudist communities provided a major source of sediment for a newly developing, shelf-edge marine sandbody. This sandbody, throughout most of deposition of the Moffat Mound, separated the prograding tidal-flat facies of the Central Texas platform from the open-shelf carbonate mudstone-wackestones of the North Texas-Tyler basin. A widespread regression of Fredericksburg seas terminated Moffat Mound deposition. The regression resulted in the subaerial exposure and subsequent freshwater (meteoric) leaching of the uppermost limestone units.
Eight distinct but interrelated depositional environments controlled sedimentation within the Moffat Mound complex. These included a subtidal (lagoon) or restricted shelf; scattered patch reefs (bioherms); a prograding-beach sequence; a low-energy, open shallow-marine environment; a deeper open shelf; an oolitic-carbonate shoal; and a coexistent supratidal-intertidal environment.
AAPG Search and Discovery Article #90968©1977 AAPG-SEPM Annual Convention and Exhibition, Washington, DC