## 4 Results
### Structure
#### 4.2.2 Microstructure  
The thin sections studied under petrographic microscope can be divided into feldspathic arenites, sandy lutites, silicate sands, and silicate clays. * Feldspathic arenite (level 1, level 2, level 4, and level 5)  
These levels appear at the top of the outcrop, sometimes laminated and containing the remains of ostracods (Figure 4A,B). Their skeleton's clasts are mainly quartz, although feldspar can also be seen, with sizes ranging from 0.06 mm to 0.1 m and subangulous morphologies, frequently corroded at their edges due to the action of the carbonate cementation. Micaceous straws are occasionally identified. Pelloids or spheroidal masses of calcareous-micrite nature, similar in size to those of quartz grains, may also be considered as clasts, and react with calcareous limestone cementum. The whole skeleton is joined by a matrix of equal composition, but practically obliterated by a micrite or microspaprite mosaic of carbonate crystals, showing a lighter color than the micrite of the pelloids. Regarding the arrangement of the solid particles, the lamination observed is created by the vertical alternation in grain sizes (Figure 4A), a common feature in lake deposits frequently associated with seasonal precipitation of carbonates or with periodic influxes of sediment into lakes [35]. In this case, sometimes the lamination appears interrupted by carbonate nodules that partially or totally replace previous grains and the matrix with a dark micrite (Figure 4A). These nodules have varied sizes, from 0.1 to several millimeters, and present round to sub-round morphologies. They are associated with post sedimentary processes, where the larger ones are visible to the naked eye. Inside them, only strongly birefringent clay remains. Finally, some fossil content (ostracods) appears as straws oriented parallel or subparallel to bedding, resembling the micas. * Sandy carbonated lutite (level 3)  
This is a sandy carbonated lutite, with developed processes of carbonate crust. The largest clasts, between 0.2 and 1.5 mm, are quartz and feldspar having poorly rounded morphologies. The matrix is entirely clayey and is reorganized with the formation of birefringent domains, adopting highly variable geometries (grain-strated, parallel, porous-striations, and reticulated and cross-reticulated striations) (Figure 4C,D). The incipient crusting is shown by the replacement of clay material by a dark micrite mass, forming nodules. Figure 3: Discontinuities identified in the outcrop. * Clay (level 6 and level 8)  
Clays with sandy clasts and unevenly developed carbonate crusts (Figure 4E,F), with some micas in the shape of straws were occasionally observed. Carbonate cement corrodes the previous clasts, the ostracods--only present in the areas where the crust is smaller--and the micritic pelloids that appear. After the crusting process, a bioturbation was developed in the crust creating holes that were filled by sand-size particles (Figure 4G). Some microstructures or reorientation of the S-matrix type were observed. * Silicate sand (level 7)  
This is a silicate sand with no cohesion among its particles. The sizes of the clasts range between 0.4 and 1 mm, and present sub-rounded to slightly rounded morphologies; quartz and feldspar were mainly identified, although fragments of quartzite with occasional sizes up to 4 mm were found, in addition to occasional micas in the form of straws and some tourmallines. The skeleton is surrounded by a clayey-silty matrix with evidence of post-sedimentation processes, such as the reorganization of the clay component around the biggest grains, which caused a systematic birefringent surrounding boundary (Figure 4H). It is a grain-striated b-fabric [24], and it is usually related to post-sedimentation graphic activity [36]. The general view observed under scanning electron microscopy displays a massive and laminar texture due to the presence of an oriented clayey plasma (Figure 5A) caused by a well-dispersed material sedimentation.