LAVAS LA SIERRA IN CAMAGÜEY.FORMATION OR INFORMAL UNIT?

Abstract

The lithostratigraphic unit named “La Sierra Formation” was described by Tchounev et al. in 1981. In its composition there are no sedimentary or volcanic-sedimentary rocks. The original descriptions suggest that they are banded (fluidal) and brecciated acid lavas, later, others add that massive, fluid lavas predominate, sometimes banded and sometimes with micro-folds, subordinate brecciated lavas are presented. In some cases, secondary alterations such as oxidation and some recrystallization of the quartz occur. Regarding its stratigraphic relationships, the authors point out that they cut off the Camujiro and Piragua formations. It is discordantly covered by the Durán and Jimaguayú dam formations, while nothing is said about the underlying, evidently because there is no such. These are lavas from last residues from magmatic chambers that fed bodies of the intrusive complexes of region, now characterized by a predominantly acid composition, poor in volatile, fluid in nature, which favors the formation of extrusive domes and complexes of fluidal domes. All these characteristics make it possible to question the category of Formation, which it has traditionally had, and propose its redefinition as an informal unit, more in accordance with what is established in the Cuban Code of Stratigraphy, proposing the name of informal unit Lavas La Sierra.