PALEOGEOGRAPHY OF THE NORTHERN PORTION OF THE MIXTECA TERRAIN, SOUTHERN MEXICO, DURING THE MIDDLE JURASSIC

A preliminary paleogeographic reconstruction of the northern Mixteca terrain in southern Mexico is presented for the Middle Jurassic. The reconstruction is derived from combined analyses of spatial distribution of marine-continental Jurassic sedimentary units, identification of sediment source, and observations based on sedimentary indicators of environment and transport directions, as well as paleomagnetic and anisotropy of magnetic susceptibility (AMS) results. There is an overall agreement between the AMS magnetic fabric results and the sedimentary indicators of current directions and paleogeographic elements. The results suggest a coastline at the south-southwest portion of this terrain, a general transport of fluvial sediments to the south and southwest, and marine influxes from the south. A Pacific margin provenance is supported by the paleomagnetic results for the northern portion of the Mixteca terrain.