Abstract
Abstract. The numerical age of the Jurassic–Cretaceous boundary has been controversial and difficult to determine. In this study, we present high-precision U–Pb geochronological data around the Jurassic–Cretaceous boundary in two distinct sections from different sedimentary basins: the Las Loicas, Neuquén Basin, Argentina, and the Mazatepec, Sierra Madre Oriental, Mexico. These two sections contain primary and secondary fossiliferous markers for the boundary as well as interbedded volcanic ash horizons, allowing researchers to obtain new radioisotopic dates in the late Tithonian and early Berriasian. We also present the first age determinations in the early Tithonian and tentatively propose a minimum duration for the stage as a cross-check for our ages in the early Berriasian. Given our radioisotopic ages in the early Tithonian to early Berriasian, we discuss implications for the numerical age of the boundary.
Highlights
The age of the Jurassic–Cretaceous (J–K) boundary remains one of the last standing Phanerozoic system boundaries with a numerical age not tied by adequate radioisotopic data
The nannoliths are represented by Conusphaera mexicana, Polycostella senaria, Hexalithus noeliae, Nannoconus globulus, and N. kamptneri minor
An increase in the diversity of nannofossils is identified with 11 species, among which the presence of N. steinmannii steinmannii stands out (Fig. 2b)
Summary
The age of the Jurassic–Cretaceous (J–K) boundary remains one of the last standing Phanerozoic system boundaries with a numerical age not tied by adequate radioisotopic data. The ill-defined age of the boundary has led to widely variable timescales for the Late Jurassic to Early Cretaceous (Channell et al, 1995; Gradstein et al, 1995; Lowrie and Ogg, 1985; Malinverno et al, 2012; Ogg, 2012; Ogg et al, 1991; Ogg and Lowrie, 1986; Pálfy, 2008; Pálfy et al, 2000) These various approaches attempted to ascribe an age to the J–K boundary; the different estimates for the age of the boundary lacked reproducibility, varying from 135 to 145 Ma, with a high degree of uncertainty and very little overlap. The age of the polarity changes in the northwestern Pacific was dated by key fossiliferous da-
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