Magnetic properties of the detrital deposit of the Granite Cave (Bujaruelo Valley, Central Pyrenees)

Abstract

This work presents the magnetic properties analyzed in the detrital deposit of the Granito Cave. The cave is located in the Bujaruelo Valley, Southpyrenean Zone). The cave has a sub-horizontal development in carbonatic rocks of Paleocene-Eocene age. Inside, there are different deposits of chemical origin as stalagmites (the oldest is dated as 153.6 +/- 1.2 ky, MIS6, Bartolomé et al., 2021), flows and flags and a detrital sequence of 60m along the whole cavity. The sediments are mainly composed by clays, silts and sands and are finely laminated. Three main facies are observed, backswamps, slackwater y channel, related to the processes of cut and fill in response to the snow melt or precipitations. Among the sedimentary structures are horizontal laminations, cross-bedding laminations, climbing ripples, and liquefaction structures, the last ones probably linked to the increase in the hydrostatic charge. The concentration of the ferromagnetic minerals varies rhythmically along the sedimentary sequence, diminishing towards the top. The main carrier seems to be magnetite (results of the thermomagnetic curves), but the values of the S-ratio indicate the presence of a high coercivity mineral too (goethite and/or hematite). The relationship of the magnetic properties with the geochemical information will help determine the paleoenvironmental implications of those magnetic parameters.