Frank E. Kottlowski

Sedimentary Basins of South-Central and Southwestern New Mexico

Major sedimentary basins in this, the eastern part of the Basin-and-Range province, are the Orogrande and Pedregosa basins of Mississippian, Pennsylvanian, and Wolfcampian age, the San Mateo and Lucero basins of Pennsylvanian age, the Carrizozo and Quemado-Cuchillo evaporite basins of Leonardian age, the Early Cretaceous basin near the Hatchet Mountains, and the continental basins containing much volcanic debris of Late Cretaceous age in central Sierra County and near Steeple Rock. Numerous Cenozoic intermontane grabens occur in the region, including the southern part of a long north-south string of interconnected grabens now followed by the Rio Grande and called the Rio Grande structural depression. Sediments filling the Cenozoic basins are mainly of Miocene, Pliocene, a d Pleistocene ages. Pre-Devonian strata, the Cambrian-Ordovician Bliss Sandstone, the Ordovician El Paso Limestone and Montoya Dolomite, and the Silurian Fusselman Dolomite, thin northward and westward mostly because of periodic erosion but the thinning is partly depositional. The Devonian shaly beds are relatively uniform in thickness, although marking the first large-scale influx of clay and silt. As with all older Paleozoic sediments, they appear to have been deposited in shallow epicontinental seas. The Pedregosa basin was autogeosynclinal, receiving thick deposits of Middle Mississippian crinoidal limestones, Late Mississippian arenaceous calcarenites, Pennsylvanian limestones, and Wolfcampian interbeds of limestone, black shale, and redbeds. The Orogrande basin began as a poorly defined autogeosyncline in which siliceous Middle Mississippian limestones were deposited, then became zeugogeosynclinal during late Pennsylvanian time as detritus was swept westward from the Pedernal landmass, and during Wolfcampian time was filled by limestone and shale that grade northward into redbeds. The San Mateo and Lucero basins were small autogeosynclines that connected the Pennsylvanian seas northward with the San Juan and Paradox basins. Source beds and possible petroleum reservoir rocks occur in the Paleozoic and Mesozoic sequences. The reservoir beds include porous sandstone, bioclastic calcarenite, dolomite, reef masses, porous lenses beneath truncating unconformities or amid intertongued redbeds and marine limestones.

Pre-Tertiary Strata of Tres Hermanas Mountains, Luna County, New Mexico

Partial sections of the Paleozoic and Mesozoic sequence of southwestern New Mexico are exposed amid the Tertiary igneous rocks of the Tres Hermanas Mountains. Several hundred feet of the Silurian Fusselman Dolomite occur in a small fault block. Only the upper 360 feet of the Mississippian Escabrosa Limestone is exposed beneath 20-40 feet of the Paradise(?) Formation. The overlying Pennsylvanian is about 560 feet thick and consists of limestone, a few shale lenses, and a 60-foot-thick sandstone unit. The Wolfcampian Hueco Formation is at least 525 feet thick, is erosionally unconformable on the Pennsylvanian strata, and is composed of lower chert-limestone conglomerates and upper dark gray fossiliferous limestones. Lower Cretaceous rocks are more than 1,530 feet thick and onsist of four lithic units: (1) lower 375 feet of chert conglomerate, sandstone. pale red siltstone, and silty limestone; (2) 395 feet of massive limestone; (3) 425 feet of limestone conglomerate and reddish sandstone; and (4) upper 340 feet of sparsely fossiliferous limestone.

Remnant Mountains in Early Ordovician Seas of the El Paso Region, Texas and New Mexico

The Thunderbird mass of Precambrian rhyolite porphyry in the Franklin Mountains of westernmost Texas is a low remnant mountain that protruded above the floor of the Early Ordovician seas. This extrusive rhyolite, dated at 950 m.y., is surrounded and overlapped by limestone of the Early Ordovician El Paso Group. Sparite-cemented masses of rhyolite talus border the mountain, grading into dolomitized biointrasparrudite containing many large angular clasts of rhyolite. This rhyolite mountain and other Precambrian-rock islands in the region provided detritus to the Early Ordovician seas of southern New Mexico, west Texas, and northern Mexico. Preservation of such highlands for much of Early Ordovician time appears to be extraordinary. The El Paso limestone of the Franklin Mountains, however, reflects in entirety an environment ranging from supratidal to shallow-water marine, as evidenced by the occurrence of such features as polygonally cracked micrites, algal stromatolites, digitate algae, and archaeoscyphid mounds. Protection of the remnant mountains from high-energy waves can be attributed to the regional, virtually intertidal, mudflatlike environment; the occurrence of archaeoscyphid biohermal barriers; periods of submergence below wave base; or a combination of these factors. The sedimentary features imply that a vast region of remarkably uniform shallow-water to supratidal environmentals existed during Early Ordovician time.

Sedimentary Basins of Central and Southwestern New Mexico: ABSTRACT

Major sedimentary basins in this, the eastern part of the Basin and Range province, are the Orogrande and Pedregosa basins of Mississippian, Pennsylvanian, and Wolfcampian age, the San Mateo-Lucero and Estancia basins of Pennsylvanian age, the Carrizozo and Quemado-Cuchillo (Foster, 1957) evaporite basins of Leonardian age, the Early Cretaceous basin near the Hatchet Mountains, and the continental basins of vols canic piles of Late Cretaceous age near Elephant Butte and Steeple Rock. Numerous Cenozoic intermontane graben basins dot the region, with the southern part of a long north-south string of interconnected grabens now followed by the Rio Grande and called the Rio Grande structural depression. Sediments filling the Cenozoic basins are mainly of Late Miocene. Pliocene and Pleistocene in age. Pre-Mississippian Paleozoic rocks remain only south of about 33°45^prime N. Lat. The basal Paleozoic unit, the Cambrian-Ordovician Bliss Sandstone, thickens depositionally southward and southwestward. The Early Ordovician El Paso Limestone thins northward due to intra-Ordovician erosion whereas the Middle and Late Ordovician Montoya Dolomite is relatively uniform in thickness where overlain by Silurian rocks. The Silurian Fusselman Dolomite thins northward partly due to erosion during Late Silurian and Early Devonian time. The Devonian shaly strata are relatively uniform in thickness, although marking the first large scale influx of clay and silt; as with all older Paleozoic rocks they appear to have been deposited in shallow epicontinental seas. The Pedregosa basin was autogeosynclinal, receiving thick deposits of Middle Mississippian crinoidal limestones, Late Mississippian arenaceous calcarenites, Pennsylvanian limestones, and Wolfcampian interbeds of limestone, black shale, and redbeds. The Orogrande basin began as a poorly defined autogeosyncline in which siliceous Middle Mississippian limestones and Late Mississippian arenaceous calcarenites were deposited, then became zeugogeosynclinal during Late Pennsylvanian time as detritus was swept westward from the Pedernal landmass, and during Wolfcampian time was filled by limestones and shales that grade northward into redbeds. The Estancia basin was a small Pennsylvanian zeugogeosyncline, and the San Mateo-Lucero basins were autogeosynclines connecting the Pennsylvanian seas orthward toward the San Juan and Paradox basins. End_of_Article - Last_Page 1879------------