Palaxius caucaensis n. sp., a Crustacean Microcoprolite from the Basal Nogales Formation (Campanian to Maastrichtian) of Colombia

Abstract

From a sandstone layer of the basal Nogales Formation (Campanian to Maastrichtian) of Colombia (South America) the new crustacean microcoprolite Palaxius caucaensis is described. It represents the first finding of these microfossils in Cretaceous beds in South America. INTRODUCTION Until now crustacean microcoprolites from South America have been known only from Triassic and Jurassic sediments (Forster and Hillebrandt 1984, Senowbari-Daryan and Stanley 1986, Blau et al. 1993, Blau and Senff 1993). Whereever these coprolites occur, they are often the only fossil group preserved and therefore of great stratigraphical interest. The value of crustacean microcoprolites for biostratigraphy has been demonstrated by Molinari Paganelli et al. (1980, 1986). Additionally, crustacean microcoprolites are a good tool for paleobiogeography and the reconstruction of faunal migration paths (e.g., Blau et al. 1993). In this paper, we describe the first Cretaceous crustacean microcoprolite from South America. ORIGIN OF THE SAMPLE The investigated outcrop is situated SE of Monteloro (Departamento Valle del Cauca) at the western flank of the Central Cordillera of Colombia on sheet 261 Tulua. Close to the locality known as El Paraiso, about 200m of shallow marine conglomerates, sandstones and claystones crop out in a nameless eastern confluent of the Quebrada (creek) La Mina (text-fig. 1). The sample which yields the coprolites originates from a sandstone layer near the base of the profile. The Nogales Formation The Nogales Formation crops out in a narrow north-south directed strip along the western flank of the Central Cordillera of Colombia, southeast of the city of Tulua. It is limited to the west by a fault against rocks of the Amaime Formation and the batolith of Buga, while to the east the Nogales Formation disappears under the tertiary cover. It was described first by Nelson (1957) as a unit consisting of black cherts and grey sandstones. Pardo et al. (1993) subdivided the Nogales Formation into three units. The lower part contains (graded) sandstones and matrix-supported conglomerates which sometimes have an important content of carbonate. The conglomerates are composed of metamorphic, volcanic and sedimentary rock fragments and show diameters up to 10cm. The middle part of the Nogales Formation shows an alternation of sandstones and claystones with some intercalated chert layers. Slumping structures are frequent. The upper part is dominated by claystones and cross-bedded, fine-grained sandstones. Especially in the lower part, the Nogales Formation yields plant remains, internal molds of bivalves, gastropods and ammonites. F. Etayo-Serna (Bogota) kindly determined Trochoceramus sp. and Nostoceras sp., which indicate a Late Cretaceous (Campanian to Maastrichtian) age for the lower part of the Nogales Formation which also contains the finding horizon of the coprolite-bearing sandstone layer. In the upper part of the Nogales Formation van der Hammen (1960) found a sporal assemblage of Paleocene age. According to these data, the Nogales Formation is the youngest marine sedimentary unit at the western flank of the Colombian Central Cordillera. SYSTEMATIC PALEONTOLOGY Phylum ARTHROPODA Subclass MALACOSTRACA Superorder EUCARIDA Order DECAPODA Family THALASSINIDAE Genus Palaxius Bronnimann and Norton 1960 The genus Palaxius was defined by Bronnimann and Norton (1960) as having crescent shaped canals in cross-sections. Recently, Blau et al. (1994) have demonstrated that crescent-shaped canals also oc ur together with triangle-shaped canals in Parafavreina thor netensis Bronnimann et al. 1972a. Palaxi s caucaensis Blau, Moreno and Senff n. sp. Text-figures 2a-e, 3a-d Etymology: Named after the Valle del Cauca, where the coprolites were found. Holotype: The specimen illustrated in text-fig. 2c, thin section no. M-12, tored at the Institut fur Angewandte Geowissenschaften, Fachgebiet Palaontologie, Justus-Liebig-Universitat, Diezstrasse 15, D-35390 Giessen. Type locality: Nameless eastern confluent of the Quebrada La Mina (text-fig. 1). micropaleontology, vol. 41, no. 1, pp. 85-88, text-figures 1-5, 1995 85 This content downloaded from 157.55.39.159 on Fri, 09 Dec 2016 05:24:19 UTC All use subject to http://about.jstor.org/terms Joachim Blau et al.: Palaxius caucaensis n. sp., a crustacean microcoprolite from the basal Nogales Formation of Colombia