ABSTRACT: Basin Development, Petrology, and Paleogeography--Early Permian Carbonates, Northwestern Bolivia
K. L. Canter, P. E. Isaacson
Early Permian carbonate rocks of the Yaurichambi Formation in northwestern Bolivia demonstrate in-situ, low-paleolatitude development within a complexly interbedded sequence punctuated by siliciclastics apparently derived from a western source. The Yaurichambi Formation (Copacabana Group) occurs above a regional caliche surface that caps Upper Carboniferous quartzarenites. Lower beds of the formation are characterized by interbedded carbonate and quartz-rich lithologies. This interval is gradationally overlain by a shallowing-upward, carbonate-dominated sequence. Mud-rich wackestones and packstones grade upward to bioclastic packstones and grainstones. Common allochems in bioclastic-rich lithologies include echinoderms, brachiopods, fenestrate bryozoans, intraclasts, and ess common corals. Uppermost beds contain abundant siliciclastic interbeds. Where exposed, this carbonate sequence is terminated by the Tiquina Sandstone. Permian rocks were deposited in a northwest-southeast-oriented basin. Siliciclastic flooding from the western and southwestern margin of the basin dominated throughout the Carboniferous and occurred intermittently during the Permian, with apparent shallowing to the south.
A low-latitude paleogeographic setting for these rocks is indicated by the carbonate lithologies dominating the Lower Permian sequence. Sedimentary and diagenetic features diagnostic of semi-arid, warm-water deposition include penecontemporaneous dolomites, fenestral fabric, and calcretes. Furthermore, the faunas are similar to those found in equivalent strata of the Permian basin area of west Texas, indicating that deposition occurred at relatively low latitudes.
AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990