Lithofacies Analysis of the Sierra Ladrones Formation Near the Sevilleta National Wildlife Refuge Headquarters (southern Albuquerque Basin, New Mexico): Implications for Cliff Fault Movement During the Early Pleistocene

The north-striking, 19 km-long Cliff fault passes 1.5 km west of the Sevilleta National Wildlife Refuge headquarters. My study uses stratigraphic relationships to interpret tectonic activity of the Cliff fault during the early Pleistocene. Previous work had suggested the latest movements occurred during the late and middle Pleistocene (Machette, 1978), but early Pleistocene activity remained uncertain. It is necessary to use Santa Fe Group stratigraphy because potential early Pleistocene activity on the Cliff fault antedates preserved geomorphic surfaces or fault scarps. The Cliff fault is the easternmost of a trio of Quaternary normal faults in the southwestern Albuquerque Basin, the other two being the east-down Loma Pelada and Loma Blanca faults to the west. Because these faults have been mapped as extending southward into the northern Socorro Basin, interpreting their long-term displacement behavior is important in understanding how strain is transferred between the Albuquerque and Socorro Basins. Long-term (10 6 -10 7 yr) paleoseismic records of the fault trio can also be used to evaluate if fault activity has migrated towards the center of the basin. The Cliff fault offsets strata of the Sierra Ladrones Formation, a Pliocene-early Pleistocene deposit composed mainly of sand with lesser gravel and silt-clay. The studied sediment lies stratigraphically above a sample locality of a 3 Ma tooth fossil. My field research illustrates several lithofacies in the Sierra Ladrones formation, including two different types of channel fills, floodplain deposits, hyper-concentrated or debris flow deposits, and possible colluvium and slope wash deposits. The two different types of channel fills are: (1) sandstone-dominated and trough cross-stratified, with southerly paleoflow and abundant chert clasts,