Rockmagnetic study in cave sediments from Gran Dolina (Sierra de Atapuerca, Burgos, Spain)

Environmental magnetism is based on sedimentary rocks records of environmental changes in the form of magnetic parameters variations, such as composition, concentration and grain size. There is a wealth of literature showing environmental changes that result in measurable variations in magnetic mineral properties in soils, but much less so in cave sediment.

We study the Gran Dolina cave sediments, one of the most complete Quaternary stratigraphic sequences in Spain with a rich archaeo-paleontological record, part of the so-called archaeological site of Sierra de Atapuerca, declared by the UNESCO in 2000 as Outstanding Universal Value. Our initial measurements include thermomagnetic curves, hysteresis loops and coercivity analysis, which reveal the contribution of three magnetic minerals: magnetite, goethite and hematite. In order to determine their relative concentration, we also carried out a particular study based on the application of a saturation magnetization (SIRM) of 5T to the samples followed by alternating field demagnetization at 100 mT to remove the contribution of any ferrimagnetic minerals (e.g., magnetite). Next, thermal demagnetization at 130ºC to remove the goethite contribution.

Finally, we should illustrate two ratios to distinguish the contribution of the magnetite vs goethite-hematite and the contribution of the goethite vs hematite: the first one shows a clear contribution of the magnetite and individuates an interval where its presence decreases; the second one illustrates a more variability of the goethite in the profile.