New luminescence ages for the Galería Complex archaeological site: resolving chronological uncertainties on the acheulean record of the Sierra de Atapuerca, northern Spain

Abstract

The archaeological karstic infill site of Galería Complex, located within the Atapuerca system (Spain), has produced a large faunal and archaeological record (Homo sp. aff. heidelbergensis fossils and Mode II lithic artefacts) belonging to the Middle Pleistocene. Extended-range luminescence dating techniques, namely post-infrared infrared stimulated luminescence (pIR-IR) dating of K-feldspars and thermally transferred optically stimulated luminescence (TT-OSL) dating of individual quartz grains, were applied to fossil-bearing sediments at Galería. The luminescence dating results are in good agreement with published chronologies derived using alternative radiometric dating methods (i.e., ESR and U-series dating of bracketing speleothems and combined ESR/U-series dating of herbivore teeth), as well as biochronology and palaeoenvironmental reconstructions inferred from proxy records (e.g., pollen data). For the majority of samples dated, however, the new luminescence ages are significantly (∼50%) younger than previously published polymineral thermoluminescence (TL) chronologies, suggesting that the latter may have overestimated the true burial age of the Galería deposits. The luminescence ages obtained indicate that the top of the basal sterile sands (GIb) at Galería have an age of up to ∼370 thousand years (ka), while the lowermost sub-unit containing Mode II Acheulean lithics (base of unit GIIa) was deposited during MIS 9 (mean age = 313±14 ka; n = 4). The overlying units GIIb-GIV, which contain the richest archaeopalaeontological remains, were deposited during late MIS 8 or early MIS 7 (∼240 ka). Galería Complex may be correlative with other Middle Pleistocene sites from Atapuerca, such as Gran Dolina level TD10 and unit TE19 from Sima del Elefante, but the lowermost archaeological horizons are ∼100 ka younger than the hominin-bearing clay breccias at the Sima de los Huesos site. Our results suggest that both pIR-IR and single-grain TT-OSL dating are suitable for resolving Middle Pleistocene chronologies for the Sierra de Atapuerca karstic infill sequences.

Figure 1. Geographical location of the Galería site within the abandoned railway trench at Atapuerca, Spain.

The plan view of the Galería karstic complex shows the three conduits (Zarpazos: TZ, Galería: TG, and Tres Simas norte: TN) that have contributed to the infilling of the cavity.

Figure 2. Stratigraphic sequence of the cave deposits at Galería Complex.

(a) Ages/sample positions of teeth previously dated by combined ESR/U-series and ages/sample positions of speleothem samples previously dated using U-series and/or ESR , , . (b) Location of the luminescence dating samples and ages obtained in this study. Legend: (1) Cretaceous limestone; (2) Speleothem; (3) Main stratigraphic uncomformity – allostratigraphic unit (e.g., GII); (4) Lithologic/archaeo-palaeontological level (e.g., TG7); (5) Palaeomagnetic reversal; (6) Zarpazos – tentative GIa/GIb boundary; (7) Soil; (8) Clayey silt/small gravel boundary; (9) Gravels/breccia boundary; (10) Limestone clasts and boulders; (11) Organomineral layer (includes bat guano); (12) U-series and/or ESR speleothem samples; (13) ESR/U-series teeth samples; (14) Luminescence samples (this study).

Figure 3. Photos showing the location of the luminescence dating samples and the types of deposits investigated at Galería.

(a) and (c) show the sampling positions in unit GIII; (b) shows the stratigraphic sequence sampled at Covacha Zarpazos (northern wall); (d) sampling of the upper guano in unit GIIa (level TN2A); (e) and (f) shows sampling of the lower part of unit GIIa (level TG7).

Figure 4. Selected examples of dose-response curves and signal decay curves.

(a-d) TT-OSL single-grain measurements and (e-f) pIR-IR₂₂₅ measurements of the Galería samples.

Figure 5. Examples of single-grain TT-OSL D_e distributions plotted as histograms (logarithmic x-axis) and radial plots.

Data is shown for selected Galería samples. See Figure S4 in File S1 for the D_e datasets of all other samples.

Figure 6. Radial plots showing pIR-IR₂₂₅ D_e distributions of representative Galería samples.

See Figure S5 in File S1 for the D_e datasets of all other samples.

Figure 7. Published ages obtained using different dating methods (including this study) for the various allostratigraphic units and lithologic/archaeo-palaeontological levels at Galería.

The data included here has been derived from combined ESR/U-series dating of teeth , TL and IRSL dating of sediment , ESR dating of calcite/speleothems , , U-series dating of calcite/speleothems , . The numerical age estimates are shown against the Marine Oxygen Isotope curve record . Two additional TL ages of 1340±170 ka (unit GIV) and 3000±1800 ka (unit GI) are not shown on this plot as they lie beyond the x-axis limits (see Table 2 for a full summary of the dataset in [14]).