Environment Reconstruction for a Part of the Glen Rose Limestone, Central Texas

Abstract

SUMMARY An approximately 50 ft. stratigraphic section of the Lower Cretaceous Glen Rose Limestone was sampled at 24 separate localities in central Texas from the standpoint of reconstructing the depositional environment. Among these samples 199 representative specimens were selected and subjected to point‐count analyses, X‐ray analyses, and insoluble residue determinations. Statistical analysis of the accumulated data with an IBM 7090 computer yielded the following facies: Corbula facies—characterized by a relative abundance of thick‐shelled ostracods, thin‐walled miliolid foraminifers, and the small pelecypod Corbula martinae; steinkern facies—characterized by large mollusc steinkerns, cellular mollusc shells and the foraminifer Orbitolina; mudstone facies—typified by less than 10% sand‐sized grains; and mixed particle facies—characterized by worn skeletal and nonskeletal carbonate grains. The mud‐stone facies subsequently was divided into two subfacies: (1) lime mudstones—characterized by delicate skeletal constituents and lime mud, and (2) marly mud‐stones—consisting of a mixture of lime mud and terrigenous clay‐sized material. Similarly the mixed particle facies was divided into four subfacies: skeletal calcarenites—characterized by sand‐sized skeletal debris; skeletal wackestones—consisting of sand‐sized skeletal particles floating in a mud matrix; nonskeletal calcarenites—characterized by nonskeletal carbonate grains; and nonskeletal wackestones—consisting of nonskeletal carbonate grains floating in a mud matrix. In addition limey sandstone, dolomite, and stromatolite facies were distinguished on the basis of relatively obvious textures and compositions. The attributes of these facies as evidenced by the 199 statistically analyzed specimens were then used to assign each of the additional samples (350) to a particular facies and to identify the distribution of these facies in the field. A reconstruction of the depositional environment was made for each facies, and the following depositional history was interpreted from the resulting facies pattern. The lowermost beds of the unit, consisting largely of stromatolites and nonskeletal calcarenites, are interpreted as representing deposition in very shallow, probably intertidal, waters, Following the deposition of these beds, the depth of water increased

Bioturbation-influenced fluid pathways within a carbonate platform system: The Lower Cretaceous (Aptian–Albian) Glen Rose Limestone

“…; Milioid sp. ; Adkins, 1928;Behrens, 1965; Clark and Morris, 2015). In some localities, LowerGRL beds grade laterally into discontinuous rudist facies dominated by Caprinid sp.…”

“…Stratigraphic control has traditionally been maintained using the distinct fossil beds such as the Corbula and Selenia marker beds (e.g., George, 1952;Whitney, 1952;Ward and Ward, 2007;Clark and Morris, 2015). Central Texas Platform GRL strata are characterized by cyclic successions of facies grading from fine-grained mudstones and wackestones to fine-to medium-grained packstones and grainstones (Behrens, 1965;Clark 2003Clark , 2005. Regional subsurface architecture forms clinoforms that span from the Llano Uplift to the Stuart City Reef (Cleaves, 1977;Braun, 2011).…”

“…In the study area, the GRL is subdivided into nine end-member lithofacies listed in deceasing order of relative abundance: (1) nodular and massive marly wackestone-packstone Table 1 and illustrated in Figures 3 and 4. The described lithofacies are specific to the study area and do not include the full extent of previously published depositional environments for the GRL (e.g., Lozo and Stricklin, 1956;Behrens, 1965;Perkins, 1974;Pittman, 1989;Mancini and Scott, 2006).…”

“…The Lower GRL was deposited in shallow subtidal-supratidal environments with some terrestrial input. Diversity of the fossil assemblage indicates normal ocean salinity (Behrens, 1965). The presence of dasycladaceae algae in thin section indicates < m of water depth during deposition (Riding, 2007).…”

Sedimentology

“…Pusey states further that a very shallow-marine environment is suggested by the micrite-rimmed skeletal grains, which are probably evidence of algal-fungal boring. Miliolid-rich carbonate muds and sands are characteristic of restricted shallow shelf deposits in the Lower Cretaceous (Edwards and Glen Rose formations) of Texas and northern Mexico (Behrens, 1965, Griffith et al, 1969.…”