Revision of TD1 and TD2 stratigraphic sequence of Gran Dolina cave (Sierra de Atapuerca, Spain)

Gran Dolina is a cavity infilled by at least 25 m of Pleistocene sediments divided into 12 lithostratigraphic units and 19 sedimentary facies. These sedimentary facies have been divided into allochthonous facies, defined as sediment inputs from the outside, and autochthonous facies, defined as sediments generated within the karst; but this division has been challenged in recent works. In this study, TD1 and TD2 units of Gran Dolina have been detailed studied and the use of autochthonous facies has been assessed. For that purpose, we have studied the stratigraphic excavation profile, combining field observation with laboratory sedimentary analysis (sieving, laser diffraction, and XRD) to characterize the texture and structure of the sediments. Based on these studies, a total of 8 sedimentary facies have been identified. Consequently, TD1 unit has been separated into two sub-units and 13 layers, while the TD2 unit has been divided into three sub-units. The facies associations indicate a succession of phreatic and vadose phases that would define together epiphreatic conditions inside the cave, related to the transition between Arlanzón valley terraces T3 and T4. Interior facies (and entrance facies for allochthonous facies) is proposed to define Gran Dolina's sediments since the facies analyses indicate transport by underground flows.