Several stratigraphic sections of the La Luna Formation in the MMVB have been studied in the La Sorda, La Azufrada, Agua Blanca and Agua Buena streams, the Tablazo sector and the Galembo Hill (e.g., Rangel, et al., 2000a, 2000b; Bernal, 2009; Ballesteros and Parra, 2012; Casadiego, 2014; Torres, et al., 2015), the last of them being the closest to the study area.
The investigated samples come from outcrops of the Galembo Member in the MMVB. Thin sections were prepared for petrographic analyses from offcuts of the rock samples with the plane of the section normal to the macroscopic lamination.
A generalized stratigraphic column of the Galembo Member of the La Luna Formation as part of the Cretaceous sequence outcropping at the MMVB is shown in Figure 2S, http://www.
According to Torres (2013), the deposition of organic carbon rich intervals of the La Luna Formation in the MMVB was governed by the development of paleobathymetric barriers, which enhanced the development of anoxia in the Cretaceous sea by causing poor circulation and limited ventilation, and also by high evaporation and low precipitation rates (high salinity bottom water) and high levels of marine algal productivity (high organic matter flux).
In this work, we illustrate several examples of the pore types that are present in the Galembo Member of the La Luna Formation sedimentary rocks at the MMVB. Porosity is associated to interparticle and intraparticle (framboidal pyrite and cleavage pores within clay minerals) pores, organopores, microchannels and microfractures.
Left, generalized stratigraphic column of the Cretaceous sequence at the MMVB (modified after Reyes, et al., 2000; Barrero, et al., 2007).