In the Rio Grande rift of southern New Mexico, the intrabasinal East Robledo fault in the Mesilla basin and the Jornada fault in the Jornada del Muerto basin experienced hundreds of meters to kilometers of offset during late Miocene to early Pliocene time and tens of meters of offset since middle Pleistocene. Late Pliocene and early Pleistocene activity on the faults is assessed by comparing sedimentological characteristics of the Camp Rice Formation, which is correlated by reversal magnetostratigraphy, on either side of the faults. The Jornada fault is interpreted to have been inactive from approximately 3.4 to 2.5 Ma, because Gauss-age fluvial strata at Rincon Arroyo, located on the hanging wall, have similar sediment accumulation rates, degree of development of calcic paleosols, and relative abundance of fluvial channel lithofacies as coeval footwall strata at Cedar Hill and Lucero Arroyo. In contrast, syndepositional movement on the Jornada fault along the northern flank of the Dona Ana Mountains from 2.5 to 0.7 Ma is suggested by a condensed Matuyama interval characterized by mature stage III and IV calcic paleosols at Lucero Arroyo. The northern segment of the East Robledo fault was active during Gauss time, based on an abundance of relatively thick (59 m), fluvial-channel deposits in the hanging-wall section at Northeast Robledo. The southern segment of the East Robledo fault, however, was probably not active during most of Gauss time, because of the presence on the footwall of a thick (50 m) section of fluvial strata of Gauss age at Picacho Mountain. Major movement on the East Robledo fault near the end of Gauss time terminated sedimentation at Picacho Mountain and in the Corralitos basin, abandoning the upper La Mesa geomorphic surface.

Abstract The Paleocene chicontepec Formation outcrops along the western margin of the Tampico embayment, also known as the Tam- pico-Misantla Basin, located in northeastern Mexico. The sequence records deposition in a deep-marine, foreland basin between the Golden Lane atoll and the Sierra Madre Oriental. In the northern part of this outcrop belt, slope deposition is recorded primarily by undeformed and deformed thin-bedded turbidites with occasional sand-rich lobes, channel-fills, and debrites. The sedimenttransport and slumping direction was to the east and southeast