Umhverfi og loftslag Nihewan-dalsins í norðausturhluta Kína á fyrri hluta pleistósen

The Nihewan Basin in northern China preserves abundant Early Pleistocene Palaeolithic sites and represents one of the earliest locations of hominins outside Africa. Sediments from three excavation trenches at the Dachangliang ridge in the northeastern part of the Nihewan Basin were investigated in the PhD study to reconstruct the environmental and climatic changes and assess their relationship with hominin activities during the Early Pleistocene. A multi-proxy approach was applied, integrating field-based observations with grain-size, magnetic susceptibility and ostracod assemblage (bivalved micro-crustacean) analyses, as well as parameterized grain-size end-member modeling, cyclostratigraphic analysis and stable isotope analysis of ostracod shells (δ¹⁸O and δ¹³C values). The studied sediments were mostly interpreted as fluvially reworked, originally aeolian deposits which accumulated through six depositional cycles, alternating between dominantly a wetland with periods of lake and alluvial plain settings. The grain-size distributions of the synthetic NH-T composite section were attributed to a mixture of four distinct end members (EMs 1-4). EMs 1-3 were used to infer the history of East Asian winter/summer monsoons (EAWM/EASM) in the region. Inferred EASM conditions dominated during periods from ca. 1.66-1.62 Ma, 1.52-1.25 Ma and after 0.82 Ma, whereas EAWM conditions prevailed from ca. 1.62-1.52 Ma and during the Mid-Pleistocene transition (MPT) 1.25-0.82 Ma. The unexpectedly high δ¹⁸O-δ¹³C covariance suggests that the basin was mostly hydrologically closed, and waters affected by evaporation. Hydrological state shifts between more standing and flowing waters were detected. Assessed together with the synthetic archaeological record, hominins apparently occupied the basin during periods of prevailing EASM climate and more standing waters. Collectively, these insights refine our current perspectives of the favorable and less favorable climatic conditions that shaped the Early Pleistocene hominin activities in the region. Thus, this study establishes a foundation for continued research on the palaeoenvironments of Early Pleistocene hominins in East Asia.