WESTERN GONDWANAN FAUNAS, DIVERSITIES AND FACIES DURING THE CAMBRIAN

Western Gondwana includes numerous occurrences of Cambrian, often richly fossiliferous rocks. These occurrences are frequently limited by structural complications, and the strata show significant lateral facies changes. A striking differentiation of the Cambrian biota prevents simple correlations of coeval assemblages and rocks. The reason is a southward drift of western Gondwana as suggested by paleomagnetic data and lithologic indicators. An enhanced insight in the climatic and biogeographic constraints allows to reconstruct the distribution benthic communities. Early Cambrian trilobite faunas show a high degree of substrate control and endemicity although parallel changes in faunal compositions are a result of transgressional events. Characteristic for the lower part of the trilobite-bearing strata are fallotaspidine and neoredlichiine trilobites, which are replaced in the late Early Cambrian by holmiid, antatlasiine, and ellipsocephaline trilobites with protolenines characterizing the Lower-Middle Cambrian boundary interval. Middle Cambrian faunas, by contrast, are relatively uniform across western Gondwana and tuned to relatively monotonous siliciclastic deposition. Characteristic are moderately diverse assemblages with paradoxidine, ptychopariacean and agraulid trilobites. Latest Middle Cambrian and Late Cambrian associations generally show similarities with Asiatic trilobite faunas. However, the Late Cambrian was a period in which many areas in western Gondwana were not inundated so that faunas are sparse and require further studies to permit a reliable portrait.