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New Observations of Facies A of the Eagle Ford (Boquillas) Formation in West Texas: Does It Represent a Shallow or Deep-Water Depositional Environment?

Wehner, Matthew; Gardner, Rand; Pope, Micheal C.

The Eagle Ford Formation (Boquillas Formation) in West Texas near Del Rio is a well-known unconventional reservoir in south Texas. Well-exposed outcrops of Eagle Ford Formation, north of Del Rio in Lozier and Antonio Canyons (Terrell County, Texas), offer a natural laboratory to study depositional environments in both cliff-face outcrops and on bedding plane surfaces. The basal portions of these outcrops, commonly referred to as Facies A of the Lower Eagle Ford Formation, contain sedimentary structures whose interpretations are contentious. One description and interpretation of these strata are low-angle cross-laminated beds, interpreted as wave and hummocky cross-bedding formed in relatively shallow waters within storm-wave base. A second one is that they are pinch-and-swell beds interpreted as deep-water bottom currents (contourites), which have been differentially compacted. A third hypothesis suggests these structures are antidunes formed in turbidity currents and sediment gravity flows in deep water environments. To reconcile these observations and interpretations we undertook a study which included detailed digital photography, 3-D reconstruction of sedimentary structures from slabbed blocks, paleocurrent data, and ichnofossils to constrain interpretation of paleodepth and depositional environment. Our results negate the hypothesis of differential compaction in Facies A and confirm the existence of hummocky cross- bedding and wave-ripples, the latter two favors a shallow-water interpretation.


AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013