Lower Cretaceous Carbonate Research Articles

Geology of Parras Basin and Adjacent Areas of Northeastern Mexico

The Parras basin, in southern Coahuila and western Nuevo Leon, Mexico, contains 4,500-6,000 meters of Upper Cretaceous and lower Tertiary terrigenous sedimentary rocks. Approximately 1,500-2,100 meters of Lower Cretaceous carbonate rocks and 2,000-3,000 meters of Triassic and (or) Jurassic evaporites, carbonates, and terrigenous rocks flank parts of the basin and underlie large areas within the basin. The Triassic and (or) Jurassic sedimentary rocks exhibit complex facies relations. Lower Cretaceous carbonate rocks are remarkably uniform in large areas of northeastern Mexico. Most of the Upper Cretaceous and lower Tertiary sediments were deposited in a boot-shaped, shallow, subsiding basin between the present-day Sierra Madre Oriental and Coahuila platform. The Upper Cretaceous-lower Tertiary Difunta Group displays intertonguing relations between two distinct lithic types: red, non-marine to brackish-water sandstone and shale alternate with gray to black, brackish-water to marine, calcareous sandstone and shale. Regionally the red strata pinch out or change facies toward the north and east in the basin where marine deposition was continuous from Late Cretaceous to early Tertiary time. Some redbeds change facies down depositional dip into gray marine strata. Red strata also have been discovered in the Upper Cretaceous Parras Shale, which normally is gray to black, calcareous shale, 1,200-1,500 meters thick. During Paleocene or Eocene time, the sediments of the Parras basin were deformed contemporaneously with the adjacent Sierra Madre Oriental structural belt. Deformational intensity in the Upper Jurassic and Lower Cretaceous carbonate rocks of the nearby Sierra Madre appears to be related to the distribution and thickness of the Minas Viejas (Triassic and [or] Jurassic) evaporites. The type and degree of deformation within the Parras basin are not uniform as indicated by three factors. (1) Overturned folds and imbricate thrusts, which probably do not extend below the Parras Shale, characterize the constricted western part of the basin; (2) broad, elongate, open folds in the southeastern part extend downward to folds in Lower Cretaceous strata; and (3) broad, open, domal folds in the n rtheast are related to Lower Cretaceous uplifts on the surface and at depth.

Stratigraphy and Structure of Parras Basin and Adjacent Areas of Northeastern Mexico: ABSTRACT

The Parras basin, in southern Coahuila and western Nuevo Leon, contains 15,000-20,000 feet of Upper Cretaceous and lower Tertiary terrigenous clastic sediments. From 5,000-7,000 feet of Lower Cretaceous carbonate rocks and 6,000-10,000 feet of Triassic and (or) Jurassic evaporites, carbonate, and terrigenous clastic rocks flank parts of the basin and underlie large areas within the basin. The Triassic and (or) Jurassic sedimentary rocks exhibit complex facies relations. Lower Cretaceous carbonate rocks are remarkably uniform over large areas of northeastern Mexico. Most of the Upper Cretaceous and lower Tertiary calcareous-arenaceous-argillaceous sediments were deposited in a boot-shaped, shallow, subsiding basin between the present-day Sierra Madre Oriental and the Coahu la Platform. The Upper Cretaceous-lower Tertiary Difunta Group displays intertonguing relations between two distinct lithic types; red, non-marine, arenaceous-argillaceous End_Page 639------------------------------ strata alternate with gray to black, brackish, calcareous-arenaceous-argillaceous strata. The red formations pinch out or change facies toward the north and east in the basin. Marine deposition was continuous from Late Cretaceous to early Tertiary in the eastern part of the basin. A few redbeds grade down depositional dip into gray, marine strata. Red strata have been discovered in the Upper Cretaceous Parras Shale, which normally is a gray to black, calcareous shale, 4,000-5,000 feet thick. During Paleocene or Eocene time, the sediments of the Parras basin were deformed contemporaneously with the adjacent Sierra Madre Oriental. Deformational intensity in the Lower Cretaceous carbonate rocks of the Sierra Madre appears related to the distribution and thickness of the Minas Viejas (Jurassic?) evaporites. The type and degree of deformation in the Upper Cretaceous Parras basin is not uniform as indicated by the following: (1) overturned folds and imbricate thrusts, which probably do not extend below the Parras Shale, characterize the constricted western part of the basin; (2) broad, elongate, open folds in the southeastern part extend downward to folds in Lower Cretaceous strata; and (3) broad, open, domal folds in the northeast are related to Lower Cretaceous uplifts on the surface and at depth. End_of_Article - Last_Page 640------------

Stratigraphic Implications from Studies of the Mesozoic of Central and Southern Mississippi: ABSTRACT

ABSTRACT Beds of Mesozoic age hold much promise of further oil and gas production in Central and Southern Mississippi without getting farther downdip and drilling deeper. Examination of cuttings and cores from many wells in this area, and correlation with electrical logs of these wells, point out some areas which may contain favorable facies for oil and gas accumulation. In Southwestern Mississippi, sediments from the Upper Tuscaloosa suggest a return to depositional environments prevalent in Lower Tuscaloosa time. The Lower Tuscaloosa is productive in this area from deltaic stream channel deposits. Some production is already established from the Upper Tuscaloosa. Recent deep tests have added to knowledge of the Lower Cretaceous carbonate section in Southern Mississippi and this information can be used in interpreting the environment of deposition of the section. No porosity trends have been established but a few zones with some porosity are present. In Central Mississippi, beds of Jurassic age can be reached at depths which are economically feasible to drill. The Cotton Valley is for the most part continental, but a few wells pierce beds which may be rich enough in organic material to be source beds. The Smackover Formation has possible objective zones in this area, but the belt of possible porosity is very narrow. Stratigraphic cross sections in these favorable areas show the possible extent of favorable zones and help to explain the depositional history of these areas. Lack of identifiable fossils makes paleontological determinations very difficult. Lithologic studies with consideration of the environment and paleogeography are the most useful tools of study in this area.

Upper Cretaceous and Tertiary Stratigraphy of Guatemala

Upper Cretaceous and Tertiary sediments cover more than half of Guatemala and were deposited in the Chapayal basin, an extension of the Gulf Coast embayment. The basin's foredeep lies between a southern borderland and the Yucatan foreland. Deposition in the Caribbean was connected during late Mesozoic and early Cenozoic time with the deposition in the Chapayal basin by the Sarstun portal. The first age-identifiable sediments are the Carboniferous and Permian. The earliest Gulf Coast embayment deposition in the Chapayal basin was probably that of the late Jurassic Todos Santos Formation, followed by the thick Lower Cretaceous carbonates and evaporites of the Coban Formation. Overlying the Coban, the Upper Cretaceous units--which have an aggregate thickness of approximately 1,750 meters--include Senonian limestones of the Campur Formation and younger clastics of the Verapaz group. The latter consists of the Chemal, Sepur, and Lacandon Formations deposited in early episodic Laramide stages, with the Chemal and Sepur in the foredeep region and the Lacandon on the foreland. The Chemal and Sepur are an argillaceous facies, but the Chemal was deposited only in the region of the present-day Cuchumatanes Mountains and is preserved under distinct environmental conditions in synclinal and downfaulted valleys at elevations exceeding 10,000 feet. The shelfal Lacandon Formation is detrital limestone. Five early Tertiary and six late Tertiary formations occur in the Chapayal basin and Amatique embayment, and cover more than one-third of Guatemala. Previously, only the Rio Dulce and Toledo have been mentioned formally in the literature. The Sepur, thought by Sapper (1937) to be Eocene, is now known to be Cretaceous at the type locality and in other areas. The early Tertiary formations are assigned to the lower Eocene Peten Group. They were deposited contemporaneously and are differentiated on lithology and basin position. The Reforma, Cambio, and Toledo are the shaly formations in the foredeep region. The Toledo occurs only in the Amatique embayment. Shales with conglomeratic lenses characterize the Cambio, and softer clay shales identify the Reforma. The shelfal formations are the anta Amelia and Buena Vista, defined separately by an extensive basal gypsum bed in the overlying Buena Vista. Carbonates and evaporites occur in both formations, but evaporites predominate in the Buena End_Page 425------------------------------ Vista. The thickness of the Peten Group is 1,500 meters. Mid-Tertiary non-deposition divided Tertiary sedimentation into early and late periods. Late Tertiary sedimentation is represented by Oligocene to Pliocene deposits in the Chapayal basin and by Miocene to Pliocene(?) deposits in the Amatique embayment. The Chapayal basin formations are the Desempeno conglomerate, the Lacantun, and the Caribe which have an aggregate thickness of 1,500 meters of terrestrial and deltaic claystones, sandstones, and conglomerates. The Amatique embayment is a graben continuation of the Bartlett trough. The Miocene Rio Dulce Limestone is its oldest late Tertiary formation. Following late Miocene uplift, clastics of the Pliocene(?) Herreria and Armas Formations were laid down. The Rio Dulce has a thickness in excess of 1,000 meters, the Herreria 240 meters, and the Armas 2,500 meters. The seas withdrew at the end of the Pliocene. Quaternary depo its mask older rocks in some areas.