Sphenodiscus pleurisepta (Conrad, 1857) from the Maastrichtian La Tabla Formation in the Upper Magdalena Valley, Tolima, Colombia

摘要

The La Tabla Formation is an important petroleum reservoir in the Upper Magdalena Valley of Colombia. It was deposited in regressive and lowstand systems tracts and comprises a succession of lower shoreface to coastal plain deposits. A section in the Talora Creek, near the village of Piedras, Department of Tolima, exposes 90 m of a progradational to aggradational succession composed of very fine sandstones to medium-grained pebble conglomerates, with abundant planktic and benthic foraminifers as well as bivalves and ammonites. A few well-preserved phragmocones of the ammonite Sphenodiscus pleurisepta (Conrad, 1857), collected from a level 63 m above the base of the formation, are here described and the chronostratigraphic position of the species discussed. In the Western Interior Basin of North America, S. pleurisepta ranges from the upper lower Maastrichtian Baculites dinolobatus Zone through the upper Maastrichtian Jeletzkytes nebrascensis Zone. The present findings support previous datings of the La Tabla Formation as Maastrichtian on the basis of foraminifers.