Abstract
ABSTRACTThis paper is the first integrated account of the sedimentology, stratigraphy, and vertebrate paleontology for the marine strata of the Chilcatay Formation exposed at Ullujaya, Pisco basin (southern Peru). An allostratigraphic framework for the investigated strata was established using geological mapping (1:4000 scale) and conventional sedimentary facies analysis and resulted in recognition of two unconformity-bounded allomembers (designated Ct1 and Ct2 in ascending order). The chronostratigraphic framework is well constrained by integration of micropaleontological data and isotope geochronology and indicates deposition during the early Miocene. The marine vertebrate fossil assemblage is largely dominated by cetaceans (odontocetes), whereas isolated teeth and spines indicate a well-diversified elasmobranch assemblage. Our field surveys, conducted to evaluate the paleontological sensitivity of the investigated strata, indicate that vertebrate remains only came from a rather restricted stratigraphic interval of the Ct1 allomember and reveal the high potential for these sediments to yield abundant and scientifically significant fossil assemblages.
Highlights
The Chilcatay Formation, southern Peru, has received wide attention in the past few years due to numerous significant discoveries of fossil cetaceans (Bianucci, Urbina, & Lambert, 2015; Lambert et al, 2017; Lambert, Bianucci, & Urbina, 2014; Lambert, de Muizon, & Bianucci, 2015)
Stratigraphic architecture of a proximal portion of the Chilcatay Formation and fossil distribution within its strata have been constrained by the integration of geological field mapping, section measuring, facies analysis, and age estimates from both isotope geochronology and microfossil biostratigraphy
The data reported here provide a crucial background for future comparisons among Chilcatay localities and a first picture of the spatial and stratigraphic distribution of the fossil marine vertebrates and of the quantitative and qualitative composition of the whole vertebrate assemblage
Summary
The Chilcatay Formation, southern Peru, has received wide attention in the past few years due to numerous significant discoveries of fossil cetaceans (Bianucci, Urbina, & Lambert, 2015; Lambert et al, 2017; Lambert, Bianucci, & Urbina, 2014; Lambert, de Muizon, & Bianucci, 2015). Most studies of fossil vertebrates from the Chilcatay Formation have suffered from a lack of a detailed stratigraphic information and the accurate placement of these discoveries into a proper stratigraphic context remains a largely unresolved issue bearing upon uncertain intraformational correlations and poor age control. Stratigraphic architecture of a proximal portion of the Chilcatay Formation and fossil distribution within its strata have been constrained by the integration of geological field mapping, section measuring, facies analysis, and age estimates from both isotope geochronology and microfossil biostratigraphy. The data reported here provide a crucial background for future comparisons among Chilcatay localities and a first picture of the spatial and stratigraphic distribution of the fossil marine vertebrates and of the quantitative and qualitative composition of the whole vertebrate assemblage
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