Primera datación radiométrica (U-Pb, LA-ICP-MS, en circones detríticos) de la Formación Punta Topocalma: observaciones sobre la sedimentación marina durante el Cretácico Tardío en Chile central.

Alfonso Encinas,Wolfgang Stinnesbeck,Victor A Valencia

doi:10.5027/andgeov41n2-a08

Alfonso Encinas, Wolfgang Stinnesbeck + Show 1 more

Open Access

https://doi.org/10.5027/andgeov41n2-a08

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Abstract

Upper Cretaceous marine rocks crop out along the Pacific coast of central and south-central Chile between 33° and 37°S. These strata constitute an important reference for the Upper Cretaceous of South America due to their diverse fossil fauna and flora. The type unit of these deposits is the Quiriquina Formation, near Concepcion. This unit is considered Maastrichtian in age based on ammonites. Upper Cretaceous marine strata from other localities of central and south-central Chile are largely unstudied and their biostratigraphic ages are not precisely known. We present the first radiometric dating (U-Pb on detrital zircons) for Upper Cretaceous marine strata of the Chilean forearc at Punta Topocalma that indicates a probable depositional age of 71.9+0.9 Ma (latest Campanian-earliest Maastrichtian). Provenance analysis indicates that the source of sediments of the Punta Topocalma Formation was plutonic and volcano-sedimentary rocks from the Coastal Cordillera and the Central Depression of central Chile. The Lo Valle Formation, a volcano-sedimentary unit in the Central Depression, recorded deposition of the Upper Cretaceous volcanic arc that was coeval with marine sedimentation in the Topocalma area.

Highlights

Campanian?-Maastrichtian (Upper Cretaceous) marine rocks crop out along the Pacific coast of central and south-central Chile between Algarrobo (33°S) and the Arauco Peninsula (37°S) (Stinnesbeck, 1986) (Fig. 1)
We present the first radiometric dating (U-Pb on detrital zircons) for Upper Cretaceous marine strata of the Chilean forearc at Punta Topocalma that indicates a probable depositional age of 71.9+0.9 Ma
Provenance analysis indicates that the source of sediments of the Punta Topocalma Formation was plutonic and volcano-sedimentary rocks from the Coastal Cordillera and the Central Depression of central Chile

Summary

Introduction

Campanian?-Maastrichtian (Upper Cretaceous) marine rocks crop out along the Pacific coast of central and south-central Chile between Algarrobo (33°S) and the Arauco Peninsula (37°S) (Stinnesbeck, 1986) (Fig. 1). The Quiriquina Formation is biostratigraphically constrained to the Maastrichtian in its type sections around the bay of Concepción (e.g., Las Tablas, Cocholgüe, Tomé; Stinnesbeck 1986, 1996; Salazar et al, 2010), but the precise ages of potentially correlative Late Cretaceous units to the north and south of Concepción (Arauco, Chanco, Algarrobo, and Punta Topocalma) are less well known and it remains unclear to date whether deposition in these localities was strictly coeval or may have initiated earlier, during the Campanian (e.g., Pérez and Reyes, 1980; Biró-Bagóczky, 1982; Tavera, 1988). We present the first radiometric age from Upper Cretaceous marine deposit of the Chilean forearc basin and discuss possible stratigraphic implications for the regional geology

The Punta Topocalma Formation

U-Pb Geochronology

Discussion

Conclusions