STRATIGRAPHIC ARCHITECTURE OF THE ESPAÑOLA BASIN AND ABIQUIU EMBAYMENT, RIO GRANDE RIFT, NEW MEXICO: TECTONIC, CLIMATIC, AND VOLCANIC CONTROLS ON SEDIMENTATION

Extensive exposures in the Española Basin allow study of how depositional systems in a rift basin may be affected by external controls. The Española Basin is complexly faulted and includes a northwestern structural bench called the Abiquiu embayment (AE) and a west-tilted eastern half-graben, in whose western part lie three deep half-grabens adjoining a NNE-striking central fault system (CFS). Being an important contributory segment of the ancestral Rio Grande drainage, this basin contains evidence of five major depositional systems: 1) arkosic alluvial-slope sediments (AAS) on the hanging-wall ramp derived from the Sangre de Cristo Mts.; 2) volcanic-bearing alluvial fan deposits derived from the Jemez Mts.; 3) lithic to arkosic arenite associated with two southward flowing axial rivers on the basin floor; 4) south-flowing, volcanic-bearing alluvial-slope deposits in the AE; and 5) an eolian dune field in the northwest part of the basin.

Correlation of distinctive lithofacies and abundant dated tephra allow basin-wide correlations that document the dynamics of these depositional systems. Between 28-25 Ma, the AAS prograded west during subsidence and probable tilting of the eastern half-graben. In the NE part of the basin, eastward migration of the basin-floor fluvial system during 18-16 Ma may be a response to localized, fault-related subsidence there. Between 16 and 6 Ma, the AAS progressively prograded west towards the CFS. Inferred linkage of these faults by the late Miocene led to erosion of the AE. Eolian sedimentation dominated the northwestern basin between 13.4-12 Ma, paradoxically a time of marked coarsening in the basin fluvial systems. Shortly afterwards (11-12 Ma), two rivers merged to form the ancestral Rio Grande. Between 12-9 Ma, the basin floor narrowed and briefly migrated 2.6 km onto the CFS footwall ca. 11 Ma. Late Miocene development of the Jemez volcanic field produced alluvial fans on the western flank of the basin. In the late Miocene through Pliocene, sediment preservation was greatest in the three deep half-grabens adjoining the CFS. Comparison of facies distributions and faults indicate that deposition was influenced by faulting. Invoking only tectonic controls, however, do not fully explain these distributions, so upland drainage evolution and climatic influences were also important.