Stratigraphy and Structure of the Parras and La Popa Basins, Northeastern Mexico E. F. McBRIDE Department of Geological Sciences, The University of Texas at Austin, Austin, Texas 78712 A. E. WEIDIE \ mm Department of Earth Sciences, University of New Orleans, New Orleans, Louisiana 70122 J. A. WULLhBhN R. C. LAUDON Shell Oil Company, I Shell Square, New Orleans, Louisiana 70160 ABSTRACT that trended north-northwest and extended thick of terrigenous sedimentary rocks and from northern Canada to at least southern minor carbonate lenses was deposited in the The Parras and La Popa basins of Mexico (Gill and Cobban, 1966). Uplift of Mexican depocenters. Detritus of sedimen- Coahuila and Nuevo Leon, Mexico, have a the continent west of the sea during Late tary, volcanic, and hypabyssal rocks eroded composite thickness of about 5.4 km of Cretaceous time resulted in paralic from a highland area to the southwest, paralic sedimentary rock (Parras Formation sedimentation of largely terrigenous de- west, and northwest of the depocenters was and Difunta Group) deposited during Late tritus. Much deposition was in deltas and transported several hundred miles by Cretaceous to Paleocene time. Detritus of flanking paralic environments; many sepa- streams and deposited in deltaic, sedimentary, volcanic, and hypabyssal rate deltaic bodies have been identified delta-flank, strand-plain, and marine-shelf rocks eroded from a highland to the west along the western margin of the seaway. environments. Progradation and rétrogra- and southwest of the Parras basin arid This report summarizes the stratigraphy dation of the deltas in response to basin northwest of the La Popa basin was depos- and structural geology of two Late Cre- subsidence and variable sediment influx re- ited in deltaic, delta-flank, strand-plain, arid taceous and early Paleocene depocenters, sulted in the complicated lithostratigraphic marine-shelf environments. Progradation the Parras and La Popa basins, located in sequence described here. These sediments and rétrogradation of deltas in each basin northeastern Mexico (Fig. 1). were subjected to various diagenetic proc- in response to basin subsidence and vari- A composite sequence about 5,500 m esses that extended to the time of deforma- able sediment influx resulted in a comp.i- cated intertonguing of rock units. Using wedge-shaped red-bed bodies and sand- stone marker-beds, the Difunta Group is divided into nine formations in the Parras basin and five formations in the La Popa basin. The correlation of stratigraphie units between the basins is uncertain, because only one formation (Muerto Formation) can be mapped across the basin margins, and diagnostic fossils are absent. Fence diagrams and isopach maps document the geometry of the major stratigraphie units. The clastic basin-fill was deformed dur- ing a post-Paleocene (Laramide) event that formed the main folds of the Sierra Madre Oriental. Both tight and broad folds, thrust faults of small displacement, and minor tear faults characterize the deformation within the study area. The relations of the stratigraphie units, the geometry of the units, and the internal anatomy of the units suggest that the Parras and La Popa basins acted as subsiding ele- ments on the craton and were filled by deltaic and shelf sediments. The basins were not sites of linear géosynclinal deposition as suggested by some workers, and characteri- zation of the basins as foredeeps is undesir- able because of the ambiguous meaning of the term. Key words: stratigraphy and his- torical geology, lithostratigraphy, struc- tural geology, deltaic fades. CD. VICTORIA INTRODUCTION Figure 1. Structural elements of northeastern Mexico and southern Texas and location of study area. Elements of During Cretaceous time, North America the Rio Grande Embayment are those underlined plus the Parras and La Popa basins. Solid line across Parras and La was the site of an elongate epeiric seaway Popa basins shows orientation of Figure 7. Geological Society of America Bulletin, v. 84, p. 1603-1622, 18 figs., October 1974 1603 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/85/10/1603/3418133/i0016-7606-85-10-1603.pdf by guest on 30 September 2021 1614 McBRIDF, AND OTHERS tion of the sequence during a post- Paleocene (Laramide) event which formed the main folds of the Sierra Madre Oriental. REGIONAL GEOLOGIC FRAMEWORK OF NORTHEASTERN MEXICO General Features Major geologic element!; of northeastern Mexico (Fig. 1) that can be distinguished on the bases of physiography, structure, and stratigraphy are (1) Rio Grande Embay- ment, (2) Coahuila Platform, and (3) Sierra Madre Oriental. The Parras and La Popa basins are located in the southern part of the Rio Grande Embayment. The characteristics and development of the above features are related to the geologic history and development of the Gulf coastal province to the northeast and central Mexico to the south. Northeastern Mexico cannot be regarded conveniently as a continuation of either adjacent area; however, it does show similarities as well as dissimilarities to both. The stratigraphic framework is basically similar throughout northeastern Mexico. Lower Cretaceous rocks (Fig. 2) are pre- dominantly carbonate; they grade upward into middle Cretaceous shale and carbon- ate. This transition marks the initiation of tectonic activity in the area. Upper Creta- ceous and lower Tertiary terrigenous rocks reflect increased intensity of tectonism throughout widespread regions in northern Mexico. Rio Grande Embayment The Rio Grande Embayment trends northwest, plunges to the southeast, and is generally transverse to the axis of the Gulf coast geosyncline. The embayment is defined in the United States by the San Marcos arch to the northeast, and the Bal- cones fault system which trends westward to the vicinity of Del Rio, Texas, on the Rio Grande. In Mexico, the inner limit of the embayment and the Gulf coastal province is less well defined. In northeastern Mexico, we recognize the following physiographic-structural- stratigraphic elements within the Rio Grande Embayment: (1) Burro-Salado arch; (2) Sabinas basin; (3) Coahuila Mar- ginal Folded Belt, which includes the La Gloria-La Gavia anticlinal folds; and (4) Parras-La Popa basins. Burro-Salado Arch. Murray (1961, p. The Burro-Salado arch trends southeast and disappears beneath the Ter- 131) defined the Serranías del Bur- northwest-southeast and plunges to the tiary sediments of the coastal plain. ro-Salado arch as ". a persistent axis southeast. It is flanked on the southwest by Sabinas Basin. The Sabinas basin was a of folding for more than 300 miles across the Sabinas basin and on the northeast by major negative area of the Rio Grande em- northeastern Mexico on the southwestern the Eagle Pass sync ine. The arch is man- bayment and is a slight topographic basin flank of the Rio Grande embayment." This ifested at the surface by the outcrop of today. It is bounded on the northeast by the arch basically coincides with the northern Lower Cretaceous strata amid the normal Burro-Salado arch and on the southwest by portion of the Tamaulipas peninsula (Sierra Upper Cretaceous arid Tertiary rocks of the the La Gloria-La Gavia fold trend (Weidie Tamaulipecas) of Humphrey (1956). surrounding areas. The arch plunges to the and Murray, 1967). The basin persisted as Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/85/10/1603/3418133/i0016-7606-85-10-1603.pdf by guest on 30 September 2021 STRATIGRAPHY AND STRUCTURE OF THE PARRAS AND LA POPA BASINS, MEXICO 1605 a distinct negative element for a long period southeastern extension of the trend. To the westward to the vicinity of Torreon. The of time and contains a virtually unnter- northwest, the prominent anticlinal folds of basin is bounded on the south by the frontal rupted sequence of Upper Jurassic to Upper Sierra de La Gavia and Sierra de La Gloria folds of the Sierra Madre Oriental, on the Cretaceous rocks. define the location of the fold trend. The north by the Coahuila platform, and on the The Upper Jurassic rocks are shallow- northwestern limit or extent of the trend is northeast by the La Gloria-La Gavia folds. water carbonate, clastic, and evaporite not clearly defined, and it appears to merge Only Upper Cretaceous and lower Tertiary strata. Carbonate rocks characterize the into the east-central portion of the strata (mainly Parras Shale and Difunta Lower Cretaceous, whereas Upper Cre- Coahuila platform (Coahuila peninsula of Group) crop out in the basin proper, but taceous rocks are carbonates grading up- Late Jurassic age). exposures of Upper Jurassic and Lower ward into clastics (Fig. 2). Upper Jurassic and (or) Lower Creta- Cretaceous rocks are common in the Sierra The rocks of the basin were defo::med ceous rocks are exposed at the surface in Madre Oriental to the south and occur in during the Laramide revolution into doubly the anticlinal uplifts which mark the fold the La Gloria-La Gavia folds to the north- plunging anticlinal folds, which presently trend. Upper Cretaceous sedimentary rocks east. expose Upper Jurassic and Lower Creta- flank the trend to the northeast and south- The Parras basin can be divided into ceous rocks in the cores. The folds show a west, in the Sabinas and Parras-La Popa western, central, and eastern parts on the predominant northwest-southeast trend basins, respectively. basis of different stratigraphic and struc- and are flanked by Upper Cretaceous rock. The folds possibly became significant tural features (Fig. 3). The western part ex- Coal beds occur in the Upper Cretaceous in paleogeographic elements during Late Cre- tends from the vicinity of General Cepeda part of the basin. This area has been termed taceous time. Upper Cretaceous carbonate to Torreon and is characterized by the the "Sabinas Coal Basin" (Roebeck and reefs or banks in the Difunta Group were relative homogeneity of the marine and others, 1956).