Abstract

The Lower Permian (Wolfcampian) Hueco Formation in the Dona Ana Mountains of south-central New Mexico contains a 30-m-thick, mixed siliciclastic-carbonate succession exposed for up to 1 km perpendicular to regional paleoslope. The succession was deposited in shallow-marine, wave- and tide-dominated estuarine, and fluvial environments, and is arranged into three fourth-order sequences. The lower two sequence boundaries incise marine fossiliferous packstone and offshore to lower-shoreface mudstone-siltstone and are overlain by fluvial sediment comprising the lowstand systems tract. Fluvial-channel sedimentation above the lower two sequence boundaries changed from vertical to lateral accretion in response to decreasing gradient in the incised valley.

The transgressive systems tract of the lower two sequences begins with a tidal ravinement surface, which is mantled locally by a pebble–cobble lag of rip-up clasts and fossils. The tidal ravinement surface cuts channels up to 4 m deep, locally removing transgressive-estuarine and some lowstand-fluvial sediment. Symmetrically rippled sandstone-siltstone deposited near the mouth of the estuary overlies the tidal ravinement surface and is overlain and locally truncated by a wave ravinement surface. In sequence 2, the highstand systems tract consists of a progradational package of heterolithic mudstone–siltstone–sandstone and bivalve packstone deposited in the central basin of the estuary; and sandstone with wood and bivalves, and carbonaceous mudstone and sandstone deposited in bayhead deltas and marshes. Sequence boundary 3 is characterized by a restricted-marine ostracode packstone sharply overlying a marsh mudstone with a vertic Calcisol and burrows of the Glossifungites Ichnofacies, and was produced on an interfluve. Sequence 3 is not present in the northern exposures, having been removed by erosion associated with sequence boundary 4. The temporal scale (105 yrs) of the fourth-order sequences implies a glacial-eustatic origin. Interbeds of shallow-marine fossiliferous packstone and mudstone–siltstone in the lower part of the succession resemble fifth-order sequences in the Midcontinent, but also may represent parasequences or autocycles.

You do not currently have access to this article.