Ref. 1844:
The Upper Permian in South Mexico includes the Olinala Formation in the state of Guerrero. This formation is the youngest Paleozoic sedimentary cover of the Mixteco Terrane. This formation contains the youngest Permian beds reported in Mexico (Woardian, Capitanian). The lower and middle part, containg fosilss of goniatits, of Woardian age, consists of silisiclastic rocks, while the upper part is a carbonate sequence of Late Guadalupean age. The carbonate sequence overlies the siliciclastic sequence by erosional contact. This carbonate sequence is a ramp deposit, the inner shallow ramp deposits are mainly composed of echinoderm debris grainstone-packstones, in which are found, crinoids, pelecypods, gastropods, as well as microfossils such as Parachaetes sp, seaweed (Tubhyfites sp; Tubhyfites obscurus Maslov 1956), boundstones type LLH(C), and organic bank crinoids boundstones and shoal bioclastic grainstones.  The middle ramp is characterized by interbeded finegrained limestones and sandstones. The limestones are bioclastic packstone-wackestones with echinoid fragments (crinoids mainly), bryozoa, pelecypod shells of, brachiopod spines, small Foraminifera (Abadehella ex gr.coniformis) and fusulinids (Codonofusiela extensa Skinner& Wilde, 1955; Rauserella errática, Dumbar 1944, Condofusiella extensa Skinner & Wilde 1955) of Woardian-Capitanian age. The sanstones are litarenites and sub litarenites.  The deep ramp deposits consist of carbonate mud mount of cyanobacterium (Tubiphytes, Aelisaccus), calcareous sponges, Prorichtofenids, and bryozoa, that trap the calcareous mudstone, forming typical stromatactitis. 