Architecture of a transgressive systems tract: Tocito sandstone, New Mexico
A sequence boundary is identified at the erosional base of the seaward units of the Tocito Sandstone by (1) a hiatus spanning three Inoceramus faunal zones, (2) basal onlap in the sequence above the hiatus as mapped in a pattern of progressively farther landward extent of younger bentonites, and (3) abrupt shallowing of facies across the hiatus. Traced up the depositional dip, the sequence boundary continues beneath a coarse fluvial sandstone (Torrivio sandstone) as demonstrated by incision of this unit into an underlying strand plain, the Gallup Sandstone. Individual Tocito sand bodies climb successively higher in the stratigraphic section when traced updip. Underlying these inferred shelf sand ridges is a landward-thickening wedge of fluvial strata (Dilco Coal Member of the Crevasse Canyon Formation), the expected consequence of trapping of siliciclastics on the transgressive coastal plain. The retrogradational deposits (Borrego Pass sandstone) constitute parasequences within the overall transgressive systems tract of the Tocito depositional sequence. The Tocito sand bodies are underlain by a stair-stepping set of ravinement surfaces, cut during episodes of shoreface retreat. They are overlain by parasequence condensed sections which appear to merge seaward into a major regional condensed section within the calcareous lower part of the Mulatto shale member of the upper Mancos Shale.
- Research Organization:
- Louisiana State Univ., Baton Rouge (USA)
- OSTI ID:
- 5879217
- Report Number(s):
- CONF-880301-
- Journal Information:
- AAPG Bull.; (United States), Journal Name: AAPG Bull.; (United States) Vol. 72:2; ISSN AABUD
- Country of Publication:
- United States
- Language:
- English
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