Micro-framework reconstruction from peloidal-dominated mud mounds (Viséan, SW Spain)

Abstract

Currently, the different roles of peloidal micrites are not well understood in matrix-supported bioconstructions such as mud mounds. Upper Viséan outcrops from Guadiato Valley, Cordoba Province, SW Spain provide well-preserved peloidal-dominated mud mounds. Microstructual analysis of these mud mounds has allowed us to establish 13 microfabrics. Although peloids are conspicuous constituents in the microfabrics, they have been differentiated into seven peloidal-dominated types, grouped into three categories: (a) homogeneous fine peloidal types (3 subtypes); (b) homogeneous coarse peloidal types (2 subtypes); and (c) heterogeneous coarse peloidal types (two subtypes). Fast cm-scale microfabric changes were mapped directly onto thin sections. This methodology allows the researcher to recognize the micro-framework of these mud mounds as a complex, multiepisodic organization of microframes and intermicroframes that are formed by primary and secondary automicrites (non-reworked and reworked automicrites, respectively), autochthonous internal sediment, and allomicrite and marine fibrous cements. The thin-section mapping was also used to estimate the automicrite-allomicrite relationship, which is crucial in separating the microbial and biodetrital mud mounds.