Sedimentologic, Stratigraphic and Diagenetic Analysis of Microbialite-Bearing Lacustrine Rift Sequence, Lower Cretaceous Yucca Formation, Indio Mountains, West Texas
Institute of Tectonic Studies, Department of Geological Sciences, University of Texas at El Paso, El Paso, TX79968, US
This study documents and interprets the depositional/diagenetic features and stratigraphic framework of the Lower Cretaceous syn-rift lacustrine microbialite facies of the upper member of the Yucca Formation deposited on the eastern margin of the Chihuahua trough and provides an analog for the South Atlantic pre-salt lacustrine reservoirs. The syn-rift succession was inverted during Laramide-age shortening and is exceptionally well-exposed within 3 thrust panels in the Indio Mountains of West Texas.
Three distinctive types of microbialite facies are recognized: (1) gray to greenish microbial carbonate concretions within reddish to light purple calcareous siltstone to mudstone matrix. Concretion interiors contain septarian-style fractures and spherulites. Fractures are filled by coarse-crystalline calcite and siliceous cements, but still could have moderate porosity; (2) stromatolitic bindstone with very low porosity. Calcite, dolomite and siliceous cements subsequently filled out the primary porosity of microbial framework, even though stylolites generate secondary porosity; (3) light green thrombolite (~1cm across) with low porosity within light purple siltstone to mudstone matrix. The three facies are organized into 3 to 5m thick lacustrine cycles progressing upward from concretions, to stromatolites, to thrombolites. Each cycle is bounded by fluvial siliciclastic facies. The lacustrine cycles are commonly erosionally terminated laterally by fluvial channels containing various clast types including microbialite facies. The field and petrographic analysis suggests that the microbial lithofacies are highly variable over short distances, possibly related to faults significantly and suggest microbial reservoir quality is mainly improved by dissolution and fracturing during burial diagenesis.
AAPG Search and Discovery Article #90183©2013 AAPG Foundation 2013 Grants-in-Aid Projects