Magnetic properties of the cave sediments at Gran Dolina in Sierra de Atapuerca, Spain

Abstract

This study is being carried out at the Sierra de Atapuerca, near the city of Burgos (north of Spain), that represents one of the most important archaeological and paleontological sites of the Middle and Early Pleistocene in Europe. Magnetostratigraphic work in the Atapuerca site has provided a paleomagnetic age as revealed by the Matuyama-Brunhes boundary, the latest major geomagnetic reversal (0.78 Ma). Now, the goal of the current work is to analyse the environmental conditions to further understand the human presence in the occupational period. Our samples are taken at the cave entrance and cave interior sediments of Gran Dolina Cave, a cavity infilled by 25m of Pleistocene sediments from which was discovered almost 170 hominin bones that allowed the definition of a new species, Homo Antecessor. This work has two intimately related goals: i) univocally identifying the ultimate magnetic carriers and ii) further exploring the environmental coupling between of the magnetic properties and paleoclimatic framework. Preliminary results indicate that the samples contain two main magnetic minerals: magnetite and hematite. Its concentrations change within facies and also between cave entrance and cave interior sediments. It seems that the upper level of the cave entrance is characterized by a high concentration of magnetic minerals while the cave interior presents a variation of concentration, due to the different facies contained in that cave. Results summarized in the so called Day plot suggest that samples are in the PSD field (pseudo-single-domain) particle range. As far as grain-size, results show that cave entrance sediments are dominated by smaller magnetic grains, while in the cave interior includes also larger magnetic particles. Our study will help us better understanding the paleoenvironment at the time the first Europeans began to migrate into Europe.