Hinge-Line Growth Faults and the Expanded Frio Formation of the Coastal Bend Area of Texas
McCARTHY, JAMES A., Cavalla Energy Exploration Company, Houston, TX
Southern parts of the coastal bend area of Texas from southeastern Calhoun County to southern Aransas County are well south and east
of the fairway sand development of the Frio Formation. Downdip Frio Formation sands in these counties are usually dirty, shaly, thin-bedded sands, or there is no sand development whatsoever.
Located 10-12 mi inland from the coast, there are a series of large hinge-line growth faults, striking generally parallel to the coast, which control and rejuvenate sand deposition on the downthrown blocks of these regional down-to-the-coast faults, causing a significant increase and expansion in the amount of Frio Formation deposition due to movement on the fault contemporaneously with deposition. The source of the sands appears to be the result of density flow or turbidity currents, moving clastics originally deposited in a neritic, relatively shallow-water environments to a location normally associated with a deep-water environment.
On the downthrown block of these hinge-line growth faults in areas of local anticlinal development, the crest of the structures is devoid of sand. As the section is traversed in the subsurface northwest from the anticlinal crest into the trace of the hinge-line growth fault plane, there is a substantial increase in the amount and quality of the sands deposited, most of which contain commercial hydrocarbon deposits when associated with local structures. These sands vary in physical characteristics from shaly, thin-bedded sands to moderately permeable, well-developed sands varying in thickness from a few feet to several feet. Northwest and southwest Powderhorn fields in Calhoun County at the northeastern extremity of the area and the Nine Mile Point field at the southwestern extremity o the area in Aransas County are two examples of this type of downdip Frio deposition and structures associated with producing gas-condensate fields.
AAPG Search and Discovery Article #91006 © 1991 GCAGS and GC-SEPM Meeting, Houston, Texas, October 16-18, 1991 (2009)