Depositional environment of the San Miguel lignite deposit in Atascosa and McMullen Counties, Texas
An analysis of the environment of deposition of the San Miguel lignite deposit was carried out in order to understand newly discovered characteristics of the deposit. The environment of deposition of the overburden and underburden was evaluated through an interpretation of three continuous cores. Four coal cores and a highwall section were carefully described to determine the depositional environmental of the coal seams and partings. These studies were supplemented by the construction of seam and parting isopachs, and the analysis of the distribution of sulfur isotopes, sulfur, forms, and total sulfur within the coal. The sedimentary package is composed of a basal prograding barrier that beach, dune, and back-barrier sands. This unit correlates with a downdip sand that was also interpreted as a prograding barrier by other authors. The barrier is overlain by a series of slit and clay deposits of lagoonal, tidal flat, and tidal channel origin. These deposits are capped by restricted lagoon sediments composed of green, calcareous clays that occasionally contain shell layers. The restricted lagoon deposits formed when the barrier closed the lagoon off from the sea. Peat forming freshwater swamps eventually became established behind the barrier and on top of the restricted lagoon sediments. The parting isopachs reveal a reticulate morphology similar to the mangrove swamps located lateral to the modern Niger River Delta. The partings represent vegetated tidal flat deposits that formed during periodic invasions by the sea that killed the swamp and inundated the peat with sulfate rich water. The lignite interval is capped by open lagoon and tidal flat sediments.
- Research Organization:
- Texas A and M Univ., College Station (USA)
- OSTI ID:
- 7015880
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
011000* -- Coal
Lignite
& Peat-- Reserves
Geology
& Exploration
AQUATIC ECOSYSTEMS
COAL DEPOSITS
COAL SEAMS
DEPOSITION
DISTRIBUTION
DRILL CORES
ECOSYSTEMS
ELEMENTS
ENERGY SOURCES
FEDERAL REGION VI
FOSSIL FUELS
FUELS
GEOLOGIC DEPOSITS
GEOLOGIC HISTORY
MINERAL RESOURCES
NONMETALS
NORTH AMERICA
ORGANIC MATTER
ORIGIN
PEAT
RESOURCES
SEDIMENTATION
SULFUR
SWAMPS
TERRESTRIAL ECOSYSTEMS
TEXAS
USA
WETLANDS