CENOZOIC TURRITELLIDAE (GASTROPODA) FROM SOUTHERN PERU

Journal of Paleontology, Mar 2007 by DeVries, Thomas J

ABSTRACT-

Cenozoic marine deposits of forearc basins in southern Peru contain a molluscan fauna that includes 15 species of turritelline gastropods. Twelve species were previously known; ten from northern Peru or Chile and two species solely from southern Peru. Three new fossil species are described: Turritella riverae, Turritella cruzadoi, and Turritella salasi. Six species of turritellines with crenulated primary spirals, a distinctive spiral ontogeny, and which are mostly endemic to Peru and Chile, are assigned to Incatella n. gen., including I. cingulata (Sowerby, 1825), I. cingulatiformis (Möricke, 1896), I. chilensis (Sowerby, 1846), I. leptogramma (Philippi, 1887), I. hupei Nielsen, new name (= Turritella affinis Hupé, 1854), and I. trilirata (Philippi, 1887). Most Paleogene taxa range from northern to southern Peru, while most Neogene taxa, including all species of Incatella, range from Peru to Chile. This biogeographic asymmetry is attributed to a series of biotic events (e.g., extinctions, immigrations) impelled by global oceanographic changes acting locally in a regime of coastal upwelling.

INTRODUCTION

THE MODERN Peruvian Faunal Province contains just one species of turritelline gastropod, Turritella cingulata Sowerby, 1825. The adjacent southern end of the Panamic Faunal Province, which includes northernmost Peru, has five Recent species (Alamo and Valdivieso, 1997; DeVries, 2003a) and was just as rich in Turritella taxa throughout the Cenozoic (see Olsson, 1928, 1930, 1931, 1932). Studies by Sowerby (1846), Philippi (1887), Tavera (1947, 1979), Herm (1969), and Nielsen (2003) have produced a list of about 10 Cenozoic species from Chile.

Fossils of Cenozoic Turritella Lamarck, 1799 from southern Peru are less well known than those from northern Peru or Chile. Only two paleontologists have contributed to the taxonomy of turritellines from the Pisco, Sacaco, and Camana basins (Fig. 1). Lisson (1925) described two new species from Caraveli, T. woodsi Lisson, 1925 and T. portaroi Lisson, 1925, to which he assigned an Eocene age. Rivera (1957) described two new Eocene turritellines from the Paracas area, T. paracasensis and T. lagunillasensis.

In this paper, I report several species of Cenozoic turritellines from southern Peru formerly known only from more than 1,000 km away in Chile or northern Peru. Three new species are described: Turritella riverae and Turritella cruzadoi, both from Upper Oligocene to Lower Miocene strata, and T. salasi, from Middle Miocene beds. Neotypes are designated for T. paracasensis and T. lagunillasensis. Turritella woodsi is recognized as the senior synonym for T. conquistadorana Hanna and Israelsky, 1925. lncatella n. gen. is created for a largely endemic group of turritellines present off Peru or Chile since the Late Oligocene.

GEOLOGY

The stratigraphy of the Pisco Basin has been described by Dunbar et al. (1990) and DeVries (1998) (Fig. 1). Within this forearc basin, the Middle to Upper Eocene Paracas Formation overlies crystalline bedrock. Unconformably overlying the Paracas sequence is the uppermost Eocene/Lower Oligocene Otuma Formation, which in turn is overlain by the uppermost Oligocene to Middle Miocene Chilcatay Formation and Middle Miocene to Pliocene Pisco Formation. Each Cenozoic formation is characterized by a transgressive sandstone member representing nearshore paleoenvironments and a finer-grained, tuffaceous, and diatomaceous silty sandstone member representing outershelf paleoenvironments. Every formation can be found locally in contact with crystalline basement rocks with associated deposits of bioclastic gravel characteristic of intertidal and rocky shoreface paleoenvironments.

To the south of the Pisco Basin are Miocene and Pliocene marine sandstones of nearshore to shoreface origin around Sacaco (Muizon and DeVries, 1985). A larger Cenozoic sedimentary basin surrounding the city of Camaná and a smaller area of outcrop south of Caravelí have been discussed by DeVries (1998, 200Ia), Vega and Marocco (2004), and Sempere et al. (2004).

METHODS AND MATERIALS

Most Peruvian fossils in this study were found by the author. Some were collected by J. Macharé (INGEMMET, Lima, Peru). Comparative material was provided by the Paleontological Research Institution (Ithaca, New York), the California Academy of Sciences (San Francisco), S. Nielsen (Freie Universitat Berlin, Germany), and W. J. Zinsmeister (Purdue University, West Lafayette, Indiana). Fossil turritellines from Chile were examined in 1993 at the Museo Nacional de Historia Natural and the Universidad de Chile, both in Santiago, Chile. The latter site housed the collections of J. Tavera, some of which are now stored at the Museo Nacional de Historia Natural. Radiometric and biochronostratigraphic ages are reported by Muizon and DeVries (1985), Dunbar et al. (1990), and DeVries (1998).

Abbreviations for repositories of fossil specimens and localities are as follows: CAS-California Academy of Sciences; F&C-Collections of D. Frassinetti and V. Covacevich, Museo Nacional de Historia Natural, Santiago, Chile; JM-José Macharé; MNHN-LG-Muséum National d'Histoire Naturelle, Laboratoire de Géologie, Paris; MUSM INV-Departamento de Paleontología de Vertebrados, Museo de Historia Natural, Universidad Nacional Mayor de San Marcos, Lima, Peru; OSU-Orton Museum, Ohio State University, Columbus, USA; PRI-Paleontological Research Institution; SGO.PI.-Departamento de Paleontología de Invertebrados, Museo Nacional de Historia Natural, Santiago, Chile; USNM-United States National Museum of Natural History, Washington, DC, USA; UWBM-Burke Museum of Natural History and Culture, University of Washington, Seattle, USA; and WJZ-W. J. Zinsmeister.