Abstract
ABSTRACT Based on mapping of laterally traceable stratigraphic discontinuities, we propose a high-resolution allostratigraphic scheme for one of the world’s foremost fossil marine vertebrate Lagerstätten: the lower Miocene strata of the Chilcatay Formation exposed along the Ica River near Zamaca, southern Peru. Measured sections combined with 1:10,000 scale mapping of a 24 km2 area provide an overview of the stratal architecture, as well as a general facies framework and interpretation of the various depositional settings. As a whole, the Chilcatay alloformation is bounded by the CE0.1 unconformity at the base and the PE0.0 unconformity at the top. An internal Chilcatay surface, termed CE0.2, splits the alloformation into two distinct allomembers (Ct1 and Ct2). The Ct1 allomember comprises three facies associations recording deposition in shoreface, offshore, and subaqueous delta settings. The Ct2 allomember comprises two facies associations, recording deposition in shoreface and offshore settings. Using these data, we place the rich marine vertebrate assemblage in a precise spatial and stratigraphic framework. The well-diversified vertebrate assemblage is dominated by cetaceans (mostly odontocetes) and sharks (mostly lamniforms and carcharhiniforms); rays, bony fish, and turtles are also present. Taxonomic novelties include the first records of baleen whales, platanistids, and eurhinodelphinids from the Chilcatay Formation.
Highlights
The infill of the East Pisco Basin is a globally renowned marine vertebrate Lagerstätte (e.g. Bianucci, Di Celma, Urbina, & Lambert, 2016c, 2018a; Collareta et al, 2015, 2017; Esperante, Brand, Chadwick, & Poma, 2015; Gariboldi et al, 2015; Gioncada et al, 2016, 2018a, 2018b; Lambert et al, 2015, 2017a, 2017b, 2018; Landini et al, 2017a, 2017b; Martinez-Caceres, Lambert, & de Muizon, 2017; Marx, Lambert, & de Muizon, 2017a; Marx et al, 2017b)
This new map focuses on the area of Zamaca (Main Map), which has yielded a rich assemblage of fossil marine vertebrates
To establish a robust stratigraphic framework for the Chilcatay strata exposed in the fossil-bearing locality of Zamaca, an area covering approximately 24 km2 was geologically mapped at 1:10.000 scale and a 59 m-thick composite section was logged at decimetre scale
Summary
The infill of the East Pisco Basin (southern Peru) is a globally renowned marine vertebrate Lagerstätte (e.g. Bianucci, Di Celma, Urbina, & Lambert, 2016c, 2018a; Collareta et al, 2015, 2017; Esperante, Brand, Chadwick, & Poma, 2015; Gariboldi et al, 2015; Gioncada et al, 2016, 2018a, 2018b; Lambert et al, 2015, 2017a, 2017b, 2018; Landini et al, 2017a, 2017b; Martinez-Caceres, Lambert, & de Muizon, 2017; Marx, Lambert, & de Muizon, 2017a; Marx et al, 2017b). Colbert, 1944; de Muizon, 1988; de Muizon & DeVries, 1985), integrated studies elucidating the spatial and stratigraphic distribution of the fossil assemblage have only recently been performed (Bianucci et al, 2016a, 2016b; Brand, Urbina, Chawick, DeVries, & Esperante, 2011; Di Celma et al, 2017). The aim of the latter is to create a firm basis for future geological and paleontological investigations, as well as to encourage the preservation and promotion of this extraordinary paleontological heritage. The primary objectives of this paper are: (i) to gain a better understanding of stratal geometry and depositional settings of each of the facies associations recognized within the study area; (ii) to place the local fossil assemblage within an accurate spatial and stratigraphic framework; and (iii) to provide a quantitative and qualitative evaluation of marine vertebrate distribution
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