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Abstract: Evidence for Source Areas and Depositional Environments of Santa Rosa Sandstone (Late Triassic) of East-Central New Mexico

Dennis J. Lapoint, David K. Christensen

Paleocurrent studies conducted west of Santa Rosa, New Mexico, indicate two sources of sediment for both the upper and lower members of the fluvial Santa Rosa Sandstone of Late Triassic age. North of a line extending from T9N, R17E, to T9N, R21E, south-trending current directions indicate a source area in north-central New Mexico, as shown previously on Triassic paleotectonic maps. South of this line, current directions show north-flowing streams. There is little evidence for an east-west drainage pattern where these two systems meet. In general, the current directions show a broad, fan-shape distribution with local variations, possibly owing to dissolution of Permian evaporites during Triassic time.

Sediments associated with copper-lead deposits in the Permian Abo Formation in the Sacramento Mountains were derived from an area in the vicinity of the Sierra Blanca Mountains. Similar copper deposits, also with anomalous lead values, are present in that part of the Santa Rosa Sandstone which originated in a southern source area. In contrast, copper deposits in sediments derived from a northern source are low in lead. It is suggested that the Permian source area for the Abo Formation in the Sacramento Mountains was also active during Triassic time.

The Santa Rosa Sandstone represents braided streams on low-gradient alluvial fans. Evidence is the limited variations in stream direction, few overbank deposits, abrupt changes in flow regime that represent flood conditions, widespread lateral deposition of conglomerate, and laterally continuous sandstone units, especially in the upper member.

AAPG Search and Discovery Article #90969©1977 AAPG-SEPM Rocky Mountain Sections Meeting, Denver, Colorado