Direct ESR dating of the Pleistocene vertebrate assemblage from Khok Sung locality, Nakhon Ratchasima Province, Northeast Thailand

We report here the first direct dating study of the faunal assemblage from Khok Sung locality, Thailand. This palaeontological site is of great biochronological, palaeoenvironmental and biogeographical significance. Firstly, it has yielded a rich and diversified Pleistocene vertebrate fauna with up to 15 mammalian species from 13 genera, 10 reptile species, as well as fish and bird remains. Interestingly, while most of the mainland Southeast Asian Pleistocene mammal fossils originate from cave deposits, the Khok Sung fossil layer is located within an 8 m thick fluvial terrace. Secondly, it is geographically located in an area of major importance for reconstructing the migration pathway of large mammals between South China and Java. Combined US-ESR dating of five teeth provides two possible ages of 130 - 29 ka and 217 - 36 ka for the fossils. The reason for the occurrence of these two age groups lies in the fact that it was not possible to obtain sediments that were directly associated with the measured samples, nor was it possible to carry out in situ gamma dose rate measurements due to the high water level. Sediment samples recovered from museum specimens show significantly variable concentrations of radioelements. Both options are equally plausible, as independent methods did not provide firm evidence favouring one or the other age range. The results illustrate the intrinsic limitations of the ESR dating method when fossil teeth are not collected in situ during the excavation. Regardless whether the age of the Khok Sung fauna corresponds to MIS 7 or early MIS5, it is nevertheless one of the oldest assemblages directly dated in the region. Further efforts are required for more accurate fossil identification and attribution and for additional numerical dating in this region to improve the biochronological framework of the Pleistocene mammalian faunas in Southeast Asia, which presently remains quite imprecise.Aspects of this study have been funded by the Australian Research Council Future Fellowship grant FT150100215 granted to M.D., an ANU-CSC Scholarship to F.F., and by the C.N.R.S. “Eclipse” Program and the Department of Mineral Resources (Bangkok)

Assessing the influence of isotopic composition of water on that of clay minerals during chemical treatments.

The isotopic composition of hydrogen in authigenic minerals is a useful tool to reconstruct past paleo-environments. Clay minerals are an important component of authigenic minerals in soils and sediments but they usually occur with other compounds that must be eliminated before the analysis, such as organic matter and carbonates. Thus, various “pre-treatments” are used, generally involving dilute HCl and H2O2 solutions in water. In this work, the influence of the isotopic composition of the water used in these pre-treatment solutions is assessed, using ten different samples of clay minerals. The isotopic composition of hydrogen was measured in each sample after HCl pre-treatment alone, H2O2 pre-treatment alone and both HCl and H2O2 pre-treatments in sequence, using two types of water in the pre-treatment solutions: one 2H-enriched and one 2H-depleted. The results indicate some influence of the isotopic composition of the water on the clay minerals after pre-treatment. In general, the samples showed significant alteration by HCl pre-treatment and negligible alteration by H2O2 pre-treatment. A pure kaolinite reference material did not show any change by chemical pre-treatment while a smectite reference material did show significant effects. Other samples (Ethiopian lacustrine sediment samples and Spanish cave sediments) showed important differences, which also depend on clay mineralogy. Thus, mineralogy seems to be the main cause of the variability in the alteration, especially the quantity of smectite. In addition, this result challenges the utility of clay minerals for isotope studies in acid conditions, such as in acidic soils, to reconstruct past environments and, therefore, climate changes.This study was developed during a stay supported by predoctoral mobility grant from the Spanish MINECO. Financial support for this work was obtained from MINECO Grant CGL2015-65387-C3-3-P. I. Campaña was the beneficiary of a predoctoral FPI Grant from the Spanish MINECO. We thank Jessica Wilson at the University of South Florida School of Geosciences who supported the isotopic analysis. J.G. Wynn was supported by an NSF IR/D program. Special thanks to the local resident of Burgos that help us remove the car from a mud puddle. // Funding for open access charge: Universidad de Málaga / CBU

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

Gran Dolina es una cueva rellena por al menos 25 m de sedimentos pleistocenos dividido en 12 unidades litoestratigráficas y 19 facies sedimentarias. Estas facies sedimentarias se han dividido entre facies alóctonas, definidas como entradas de sedimentos desde el exterior, y facies autóctonas, definidas como sedimentos generadas dentro del karst; sin embargo, esta clasificación de facies ha sido cuestionada en trabajos recientes. En este estudio se ha descrito en detalle las unidades TD1 y TD2 de Gran Dolina y se ha evaluado la idoneidad del uso de facies autóctonas. Para ello, se ha estudiado la sección estratigráfica de la excavación arqueológica, combinando observaciones de campo con análisis de laboratorio (tamizado, difracción láser y DRX) para caracterizar la textura y estructura de los sedimentos. A partir de estos estudios, se han identificado un total de 8 facies sedimentarias, y se han separado la unidad TD1 en dos sub-unidades y 13 niveles, y la unidad TD2 en tres sub-unidades. La asociación de facies indica una sucesión de fases freáticas y vadosas que definiría conjuntamente condiciones epifreáticas en el interior de la cueva, relacionadas con la transición entre la terraza T3 y la terraza T4 del valle del río Arlanzón. Por tanto, se propone el término facies de interior (y facies de entrada en vez de facies alóctonas) para definir los sedimentos de las unidades de TD1 y TD2 de Gran Dolina, ya que el análisis de facies indica transporte de los sedimentos por corrientes subterráneas.This study was supported by the project PGC2018-093925-B-C31 of the Spanish Ministry of Science and Innovation, Spanish State Research Agency and FEDER funds from the UE. Project PID2021-122355NB-C33 financed by MCIN/AEI/10.13039/501100011033/FEDER, UE. Funding for open access charge: Universidad de Málaga/CBUA. I. Campaña is the beneficiary of a postdoctoral grant from Junta de Andalucía. This work has benefited from discussion with Mathieu Duval, Lucía Bermejo, Lucía Ojeda and Sergio Durán. The constructive comments made by one anonymous reviewer and Dr. Ivan Martini contributed to improve the manuscript

Reconstructing depositional environments through cave interior facies: The case of Galería Complex (Sierra de Atapuerca, Spain)

This work showed that cave sediments are useful for geomorphologic studies and for reconstructing depositional environments. While the cave entrance facies have been extensively studied for their relationship with the fossil and archaeological record, the cave interior facies have received much less attention, although they can provide much information on the geomorphological evolution of the karst. This work presents the stratigraphic and sedimentological study of a section >6 m thick and 10 m long of cave interior sediments of Galería Complex (Sierra de Atapuerca, Spain). Galería Complex is a cavity infill of the Sierra de Atapuerca (Spain), composed of three sections filled by at least 30 m of Pleistocene sediments. This sequence is divided into 5 lithostratigraphic units named from bottom to top: GI – GV. GI unit is 19 m thick of interior facies in the base of the Galería Complex, divided into two sub-unit, GIa and GIb, by the Matuyama-Bruhnes paleomagnetic boundary. GI unit shows an issue with the chronology since has uncoherent between TT-OSL and ESR/U-series and paleomagnetism dates. This work has been done by combining field observation with laboratory sedimentary analysis to characterize the texture and structure of the sediments. Based on these studies, 12 layers and 9 sedimentary facies have been identified. The facies associations indicate a clear separation between GIa and GIb sub-units. GIa sub-unit is dominated by epiphreatic conditions and represents continuous relativity sedimentation during the Early Pleistocene; meanwhile, GIb shows important erosion events and facies with reworked materials that indicate vadose conditions during the Middle Pleistocene. This environmental change is related to the geomorphological evolution of the Arlanzón River. In addition, soft-sediment deformation structures have been described, including faults and low-angle folds...Funding for open access charge: Universidad de Málaga / CBU