Magnetic susceptibility and natural gamma radioactivity as indirect proxies for characterization of sandstones and limestones of the Sabinas basin

Abstract

An analysis of magnetic susceptibility and natural gamma radioactivity is presented as indirect proxies of the characteristics of sandstones and limestones of the Sabinas basin. These rocks are located in the sedimentary sequence ranging from the Upper Jurassic to the Cretaceous. The magnetic susceptibility indicates changes in the magnetic composition of these rocks and suggests changes in their weathering degree. Ranges of values of magnetic susceptibility in sandstones and limestones allow classifying them into different groups, suggesting variability regarding conditions of origin and evolution. High values of magnetic susceptibility in limestones can be linked to sedimentation in anoxic or reducing environment, as well as with its siliciclastic content. The natural gamma radioactivity expressed in the contents of Th and relationships U / K and Th / U also suggest the degree of weathering of these rocks, mainly in the sandstones. These relations also highlight others characteristics in the sandstones related the probable provenance of sediments, its distance, degree of weathering and transport dynamics. Using the values of U / K ratio in the sandstones, it is possible to suggest the probable quartz-feldspar relationships. These ratio values classified rocks as arkose or quartzarenite, indicating the maturity of the sandstones. According to the U / K ratio values, most of these rocks which show little maturity are called arkose. Using the values of the Th / U ratio, it is possible to suggest the textures of quartzarenites, classifying them as rocks with fabric that is clast-supported or matrix-supported.

In situ magnetic susceptibility and gamma radiation data in the Candela-Monclova intrusive belt, Northeast Mexico: case studies of the Cerro Colorado and Cerro Marcelinos plutons

“…Specifically, the limestones of transect 2 have higher MS than those of transect 1 (Figure 10), showing the greater intensity of the metasomatic process in the rocks of transect 2 and, therefore, greater enrichment in paramagnetic (e.g., epigenetic sulfides) and ferromagnetic minerals coming from the intrusion. Generally, it is observed that the host rocks close to the plutons have higher MS values than the same facies remote from the influence of these plutons (Batista-Rodríguez et al, 2017). This corroborates the observed effect of emplacement of the plutons on the magnetic composition of host rocks.…”

“…with a cubic habitus, are observed (Figure 5b), showing the epigenetic origin of this mineral. It is possible that this mineral has been incorporated into the sedimentary rock through hydrothermal processes during the emplacement of the pluton (Batista-Rodríguez et al, 2017).…”

Magnetic Susceptibility and Natural Gamma Radioactivity as Indirect Indicators of Impurities in Limestones of the Sabinas Basin: Possible Relationships with the Sedimentation Environment

“…have the highest contents of paramagnetic minerals or at least medium to low ferromagnetic mineral content [9]. Considering the typical composition of sedimentary rocks [14] and the results of petrographic analyzes in this research ( Figure 5 and Figure 6) and previous ones [25], these minerals could be mainly iron oxides and hydroxides (e.g. magnetite, ilmenite, hematite and goethite) and iron sulphides (e.g.…”

“…In this case, the high values of κ and the high concentrations of U probably linked to the iron sulfides and organic matter, respectively. Previous studies report both components in these rocks [25]. It is likely that these minerals were acquired during the accumulation of organic matter.…”

“…The descriptions of the outcrops and the analysis of the thin section indicate some of the above mentioned minerals in the rocks studied in this research ( Figure 5 and Figure 6). Other research in this region also reports these magnetic minerals on carbonate rocks [25]. These minerals were probably formed during the enrichment of organic matter that occurs in most of the limestones in the region [1] [5].…”