Gravity Field Variations Associated with the Buried Geological Structures: San Marcos Fault (NE Mexico) Case Study

Abstract

Gravity data are sensitive to local vertical offsets across high-angle faults, where rocks with different densities are juxtaposed. Yet high densities in some Mesozoic sedimentary rocks just above the basement may smear out the subtle gravity signatures of basement faults. At this study the gravity data processing tends to avoid ill-described “black-box” techniques. The study area is situated in the Palomas site, Cuatrociénegas region, Coahuila, NE Mexico. The San Marcos Fault is at least 300 km long and has WNW-ESE trend from the central part of Nuevo León State through Coahuila, and finally to the eastern part of Chihuahua State. Gravimetric data shows that the lowest values of free air and Bouguer anomalies are in the southern part of the area, and the highest values are in the western and central part of the area. Between these parts exists a zone of high horizontal gravity gradient. Configuration of linear elements of gravity field (gradient zones) delimited the San Marcos Fault in the San Marcos valley below thickness of recent sedimentary cover. Two density models were carried out, which showed that the Cretaceous rocks are in discordant contact with the Paleo- zoic rocks that can be related to the San Marcos Fault. The density was determinate using to Nettleton’s method, which results highlight the presence of the San Marcos Fault. Density models showed that the Quaternary sediments are in direct contact with the San Marcos Fault

Sedimentary cover and structural trends affecting the groundwater flow in the Nubian Sandstone Aquifer System: Inferences from geophysical, field and geochemical data

“…The anomalies caused by the physical property differences can cause lineaments that reflect a disruption in the contour patterns at several places along the opposite sides of the lineaments. There have been numerous studies on the analysis of the lineaments in delineating basement and basin structures deduced from magnetic and gravity data (Berendsen et al, 1983;Johnsgard, 1983;Al Fasatwi and van Dijk, 1989;Fichler et al, 1999;Lyatsky et al, 2004;Hassan and Peirce, 2008;Aydogan, 2011;Davy et al, 2012;Feumoe and Ndougsa-Mbarga, 2012;Yutsis et al, 2012). Due to the fact that gravity anomalies can be caused by varying mass distributions at different depths, interpreting them is not a unique problem involving subsurface density structures (Blakely, 1996;Senosy et al, 2013).…”