GONDWANAN CONODONT BIOSTRATIGRAPHY CONFIRMS CLIMATE CHANGE DURING THE LATE CARBONIFEROUS

Conodont biostratigraphy supports transgression of warm marine waters onto the northern Bolivian craton during the Late Carboniferous. Conodonts were recovered from the Lower Member of the Copacabana Formation in the northern Bolivian Madre de Dios subsurface. The Lower Member is comprised of a transgressive and shallow marine highstand interval that consists of wackestones and packstones in the lower intervals of the Mobil-Oxy Manuripi X-1 exploration well. Neognathodus symmetricus (Lane) occurs in the lowermost carbonate intervals and indicates an Early Bashkirian (Middle Morrowan) age. The uppermost carbonate intervals contain the Adetognathodus lautus (Gunnell), Idiognathodus suberectus (Dunn), and Diplognathodus coloradoensis (Murray and Chronic) assemblages suggests a Middle Moscovian (Early Desmoinesian) age. Typical late Paleozoic faunas containing brachiopods, pelmatozoans, bryozoan, and foraminifera are also present within these intervals. The shallow water conodont biostratigraphy, lithologies, and associated faunas support that deposition occurred within warm shallow nearshore marine waters. Based on these data, the initiation of the transgressive sequence into the intracratonic Madre de Dios Basin began during the Early Bashkirian and continued to a highstand in the Middle Moscovian. The conodont assemblage of North American affinities entered the basin from the north as eustatic sea levels fluctuated in response to an increase in global temperatures and as Gondwana drifted northward.