The thick-splay depositional style of the Crevasse Canyon Formation, Cretaceous of west-central New Mexico
Steven J. Johansen
An understanding of the genesis and geometry of alluvial units is useful or necessary for the development of their water and mineral resources (Galloway, 1981). The resources of the Crevasse Canyon Formation, a unit of Late Cretaceous age in west-central New Mexico, have attracted interest, yet little is known of its internal stratigraphy or genesis. This is a description of some deposits in the Crevasse Canyon Formation that represent diverse depositional settings but record similar depositional processes. Because these processes produced thick cre- vasse-splay sandstone bodies, I refer to these processes and their prod- ucts as the thick-splay depositional style. This style is initimately associated with other fluvial and deltaic depositional styles, but here I only discuss the thick-splay style. Illustrated outcrops are in La Jara Canyon, Socorro County, and Third Canyon Mesa, Catron County (fig. 1).
Allen and Balk (1954) defined the Crevasse Canyon Formation in their study of the southwestern margin of the San Juan basin. There the unit conformably overlies the Gallup Sandstone of Sears (1925). The top of the Gallup in that area is a lithologically distinct unit known informally as the Torrivio sandstone. It is of probable fluvial origin, in contrast to the delta front and littoral origin of the major underlying Gallup sandstone bodies (Molenaar, 1974). No widespread lithologic units in the Rio Salado drainage are comparable to the Torrivio sand- stone. For this area, I have followed the usage of Molenaar (1974) and have picked the top of the Gallup, and hence the base of the Crevasse Canyon, as the upper surface of the littoral sandstone unit.
The Gallup and Crevas,se Canyon Formations comprise a wedge of coastal plain and littoral sediments which prograded northeastward into the western interior seaway beginning in latest Turonian time (Molenaar, 1974; Peterson and Kirk, 1977). McGookey (1972) suggested that the climate was probably humid and warm, similar to the present south- eastern coast of the United States. Lloyd (1982), who modeled world paleogeography for a mid-Cretaceous time interval 10 million years prior to the latest Turonian, concluded that southern North America was then subjected to a greater seasonality in wind patterns with possibly a monsoonal climatic regime.
Three facies are present in outcrops representing the thick-splay style. The mudstone facies, although volumetrically the most important, is poorly exposed. It serves as a matrix for the two sandstone facies. The splay sandstone facies is composed of laterally continuous, sheet-like bodies of sandstone. These commonly are stacked and pinch out laterally; they are the principle repositories for sand in the thick-splay style. The channel sandstone facies is composed of shoestring-shaped bodies, commonly within the stacked splay sandstone packet and sep- arated from underlying sediments by a prominent scoured base. They are a volumetrically small part of the total sediment packet.
- Johansen, Steven J., 1983, The thick-splay depositional style of the Crevasse Canyon Formation, Cretaceous of west-central New Mexico, in: Socorro region II, Chapin, C. E., New Mexico Geological Society, Guidebook, 34th Field Conference, pp. 173-178.