The group was first described by Alexander Von Humboldt around 1810 as the " Villeta Tonschiefer", German name for Villeta's clay slate.[1] The group was subsequently published in 1892 by Hettner in his book Die Kordilleren von Bogotá and named after its type locality Villeta on the western flanks of the Eastern Ranges of the Colombian Andes.[2]
Description
Lithologies
The sequence comprises an alternation of sandstones, shales and limestones and the lithologies and lateral facies variations are described in detail in the various formations comprising the group. Mineralizations of zinc, cadmium and molybdenum have been found in the Villeta Group.[3]
Stratigraphy and depositional environment
The Villeta Group overlies the La Naveta Formation and is overlain by the Guadalupe Group. The age has been estimated to be Aptian-Coniacian and the unit is subdivided into the Conejo, La Frontera, Simijaca, Hiló, Pacho Formations, the Chiquinquirá Sandstone, and the Capotes, Socotá, El Peñón, and Trincheras Formations. The core extent of the group has been defined by Cáceres and Etayo in 1969, running from Apulo in the south to Muzo in the north.[2][4] The Villeta Group has been deposited in a marine environment and the organic rich shales and pelagic limestones and cherts of the Villeta Group and equivalent units comprise 60-70% of the Cretaceous record in the Eastern Ranges. They provide a good opportunity to study the interactions between tectonics eustatic sea level and sedimentation that regulate relative sea level in a basin.[5]
Villamil, Tomas (2012), Chronology Relative Sea Level History and a New Sequence Stratigraphic Model for Basinal Cretaceous Facies of Colombia, Society for Sedimentary Geology (SEPM), pp. 161–216