The Devonian Gamoneda section of southern Bolivia: new biostratigraphical and palaeobiogeographical data

Abstract

Reconsideration of the Devonian marine lithological succession in the Gamoneda section of southernmost Bolivia evidences that the distinction of the Gamoneda Formation is not justified. Corresponding deposits have to be assigned to the Icla Formation of the central Subandean Zone. Indeed, in the Gamoneda area the local Devonian sequence only differs from that of the typical lcla and Presto areas in the better development of sandy levels. The occurrence of the Lower Devonian Scaphiocoelia boliviensis Zone in the lowermost beds of the section, just above the Santa Rosa Formation, is established for the first time. An eodevonariid chonetoidean brachiopod (Lomaella sp. cf. L. primoris) is recorded for the first time from Bolivia, and a new fissiculate blastoid is described: Brachyschisma? gamonedensis. The whole fauna allows to establish correlations both with the central Subandean Zone and with the Argentine Precordillera. Discovery of extra Malvinokaffric fauna) elements raises again the palaeobiogeographical relationships between these areas.