CENOZOIC TURRITELLINES (MOLLUSCA: GASTROPODA) IN SOUTHERN PERU: FEW SPECIES DESPITE COLD COASTAL UPWELLING AND HIGH PRIMARY PRODUCTIVITY

Cenozoic molluscan faunas of the southern Peruvian Pisco basin collectively have fewer turritelline species (13) than found in northern South America, Central America or southern North America. Species richness was at a maximum (three) from the middle Eocene to latest Oligocene, then declined to one by the early late Miocene and thereafter. Five taxa comprise an early Miocene endemic lineage leading to the extant Turritella cingulata. Two other species were also endemic to the Peruvian Province. Six species had ranges encompassing part of the warm-water Panamic Province.

Strong coastal upwelling and high primary productivity have been present for the entire recorded Cenozoic history of the Pisco basin, as shown by the presence of phosphatic, dolomitic, and diatomaceous sediments with abundant clupeoid fish and marine mammal fossils. That productivity never translated into large numbers of turritelline taxa. In contrast, Cenozoic turritelline species richness has always been higher closer to the Equator in the Talara and Sechura basins of northern Peru, an area distinguished during much of the Cenozoic by upwelling sedimentary facies in the south and deltaic and submarine fan facies in the north.

In northern and southern Peru, times with higher marine productivity correlate imperfectly with times of higher turritelline diversity. In southern Peru, coastal upwelling and cooler sea-surface temperatures alone were not sufficient to promote higher levels of turritelline diversity. Higher inputs of organic matter from coastal terrestrial environments, however, indicated by abundant debris from vascular plants in nearshore marine deposits, do correspond well with turritelline diversity maxima, both temporally (middle to late Eocene) and geographically (northern Peru).