Petrographic study of the limestones of the Rosablanca Formation Region of the Mesa de los Santos Region

Abstract

A sequence of the Rosablanca Formation in the Sogamoso River Canyon, W of the La Mesa de Los Santos, is done. The sequence about 318 m thick consist of massive limestones with alternating marls and shales and a sandstone level in his upper section. The limestones are most abundant et the base and summit of the sequence whereas the shales and marls become important in the middle part of the formation. The petrographic study of limestone beds permit to divide the sequence into several petrographic zones which sometimes agree with the lithological field divisions. The petrographic zones show that the depositional environment changes during the deposition of this sequence. There are evaporitic facies deposits at the base of the formation suggesting high salinity and quietness in the environment of deposition. The rest of the sequence was deposited in an open and shallow environment where low-energy (deposits of micrite, fossiliferous micrite and biomicrite) and high-energy (deposits of intraesparite, oosparite, intramicrite and oomicrite) alternate. There are three high-energy zones in the sequence of decreasing importance form the base to the summit. These high-energy zones are thinner than the low-energy ones and are related to the arrival of terrigenous material.