Cretaceous stratigraphy, paleontology, petrography. Depositional environments, and cycle stratigraphy at Cerro de Cristo Rey, Dona Ana County, New Mexico

Abstract

Cretaceous marine and nonmarine strata of late Albian–middle Cenomanian age are exposed around the Cerro de Cristo Rey uplift in southern Doña Ana County, New Mexico. These strata comprise a section approximately 350 m thick and are assigned to the (ascending order) Finlay, Del Norte, Smeltertown, Muleros, Mesilla Valley, Mojado (=“Anapra”), Del Rio, Buda, and Mancos (=“Boquillas”) Formations. Macrofossils and microfossils from these strata indicate that the Finlay, Del Norte, Smeltertown, Muleros, and Mesilla Valley Formations are of late Albian age, whereas the Del Rio, Buda, and Mancos Formations are of Cenomanian age. The base of the Cenomanian is most likely at a trangressive surface within the uppermost Mojado Formation. The late Albian (Manuaniceras powelli Zone) to early Cenomanian (Neophlycticeras hyatti Zone) sedimentary succession at Cerro de Cristo Rey consists of alternating fossiliferous limestone, shale with limestone and sandstone intercalations, and sandstone. Muddy limestone types are commonly wavy to nodular and represent deposits of an open-marine shelf environment below wave base. Intercalated coquina beds rich in mollusc shells are interpreted as storm layers. Shale was deposited in an open-shelf environment below or near wave base during periods of increased siliciclastic influx. Intercalated thin limestone and sandstone beds are inferred to be storm layers. The siliciclastic Mojado Formation is a regressive-transgressive succession formed in depositional environments ranging from lower shoreface to upper shoreface and even fluvial, again overlain by shallow-marine siliciclastics. Although the Washita Group section at Cerro de Cristo Rey is much thicker and displays some differences in facies, the succession shows similar transgressive and regressive trends compared to the Washita Group of north Texas. Thus, we recognize eight unconformity-bounded depositional cycles in the Cretaceous section at Cerro de Cristo Rey, the upper Finlay Formation (youngest cycle of the Fredericksburg Group), lower Mancos Formation (base of Greenhorn cycle), and six Washita Group cycles: WA1 = Del Norte Formation, WA2 = Smeltertown Formation, WA3 = Muleros Formation, WA4 = most of Mesilla Valley Formation, WA5 = uppermost Mesilla Valley Formation and most of Mojado Formation, and WA6 = uppermost Mojado and Del Rio and Buda Formations. The persistence of cycles from the tectonically passive, openmarine margin of the Gulf of Mexico into the tectonically active Chihuahua trough suggests that regional if not global eustasy, not local tectonism, drove late Early to early Late Cretaceous sedimentation at Cerro de Cristo Rey. Introduction Cerro de Cristo Rey is a prominent peak in Doña Ana County, New Mexico, just north of the U.S.–Mexican border and just west of the city of El Paso, Texas (Fig. 1). The mountain was long referred to as the Cerro de Muleros, but was renamed Cerro de Cristo Rey (“Sierra” de Cristo Rey of Hook 2008 and Cobban et al. 2008, also appears on the U.S. Geological Survey topographic map of the area) in recognition of the large statue of Christ on the cross at its crest. The mountain has an elevation of 1,425 m (4,675 ft) (Lovejoy 1976; Hook 2008). The core of Cerro de Cristo Rey is an andesite laccolith, the Muleros Andesite of Eocene age (Fig. 2). The laccolith is surrounded by “an annulus of...faulted Cretaceous marine strata, locally strongly deformed by gravity-glide structures triggered by andesite intrusion” (Lovejoy 1976, p. 24). The Cretaceous strata, a section approximately 350 m thick, include rocks of Early Cretaceous (late Albian) and Late Cretaceous (early–middle Cenomanian) age (Figs. 3–4). These rocks have been studied for more than a century, most notably by Böse (1910) and Strain (1976). Here, we present the first detailed lithostratigraphy and sedimentary petrography of the Cretaceous strata exposed around the New Mexican periphery of the Cerro de Cristo Rey uplift. We combine these data with paleontology and regional correlations to present the first detailed interpretation of the depositional environments and cycle stratigraphy of the Cretaceous section. FIGURE 1—Location of Cerro de Cristo Rey in southern Doña Ana County, New Mexico (after Lovejoy 1976). ∆ indicates Eocene igneous intrusions—Cerro de Cristo Rey, Cerro de la Mina, Campus Andesite, the Three Sisters, and Vado Hill.