Sedimentary Petrology and History of the Haymond Formation (Pennsylvanian), Marathon Basin, Texas

This report treats the sedimentary petrology and history of the Haymond Formation, a monotonous sequence of interbedded sandstone and shale that has a maximum preserved thickness of 4,300 feet. The upper part of the formation includes massive coarse sandstone beds and a complex of pebbly mudstones and slumped beds that encase exotic and erratic rock fragments up to 130 feet long. The Haymond is part of a 12,000-foot sequence of flysch that was deposited during late Paleozoic time in the Marathon geosyncline, a part of the Ouachita geosyncline located in Trans-Pecos Texas. The formation is exposed on a structurally high part of the Ouachita structural belt, most of which is known only in the subsurface in Texas...within the topographic Marathon Basin, a sub-rectangular area that has dimensions of 50 miles in a NE-SW direction and 35 miles in a NW-SE direction. Deformed Paleozoic rocks trend NE-SW in the Basin and are exposed through a veneer of Quaternary alluvium; the Basin is rimmed by Permian rocks to the northwest (Glass Mountains) and by Cretaceous rocks in other directions. Paleozoic sedimentary rocks that have a composite thickness of approximately 15,000 feet were deposited in the geosyncline. The rocks were folded and thrust-faulted as the result of crustal shortening that culminated during late Pennsylvanian time and subsequently faulted and domed during Mesozoic and Tertiary time (P. B. King, 1937). Flysch of Mississippian and Pennsylvanian age comprises nearly 12,000 feet of the geosynclinal sequence. The Haymond is the youngest flysch unit; it is separated from the Tesnus, a siliciclastic flysch unit similar in many respects to the Haymond...by the Dimple Limestone, a calcarenite-shale flysch unit... Older Paleozoic rocks in the Basin are chert, novaculite, limestone, and shale, with lesser amounts of sandstone and conglomerate that have a total thickness of approximately 3,000 feet. The Haymond is of sedimentologic interest because of the problems of the mode of emplacement of the erratic and exotic rocks of the boulder beds and of the deposition of innumerable alternations of sandstone and shale; in addition, it is of interest as a partial record of the geologic history of the Marathon geosyncline.