Fluvial or aeolian? Unravelling the origin of the silty clayey sediment cover of terraces in the Hanzhong Basin (Qinling Mountains, central China)

This study is focused on a silty clayey sedimentary sequence on a terrace in the intramontane Hanzhong Basin, located in the Qinling Mountains (QLM), central China. Traditionally, the QLM are considered to have blocked dust transport from northwest to southeast China. However, in recent years, geo-archaeological studies have documented loess-palaeosol sequences at numerous locations in and surrounding the QLM. In the loess deposits overlying the terraces of the Hanjiang River in the Hanzhong-, Ankang- and Yunxian basins, abundant artefacts, flakes, stone tools (e.g., scrapers and choppers) and cores are commonly found. The loess deposits have been deposited with lower sedimentation rates, and they are finer grained and more intensely weathered compared to the loess deposits on the Central Loess Plateau (CLP). The loess deposits overly coarse sandy and gravely fluvial deposits (terraces). Silty fluvial deposits are situated in between them. Discrimination between these two types of deposits could prove difficult because both deposits are fine grained (silt and clay) and can have similar grain size distribution characteristics. This is, however, crucial for palaeo-environmental interpretations during hominin occupation, understanding fluvial morphodynamics, and for pedostratigraphic correlation with the typical loess-palaeosol sequences on the CLP. The aim of this research is to determine and characterize the transition of the fluvial to aeolian depositional environment in a fine grained sequence, based on field observations, organic matter and carbonate content, grain size and shape analyses, mineral content (mica's) and end-member modelling of the grain size dataset. In addition, terrestrial cosmogenic nuclides (TCN) burial dating is used to determine the age of the basal, coarse grained fluvial deposits. The determined age, 0.6 ± 0.14 Ma, allows for a chronological correlation of the deposits to the loess-palaeosol sequence on the CLP independent from the pedostratigraphic correlation. This age also gives insight in terrace abandonment and the fluvial morphodynamics of the Hanjiang River. The result indicates a clear distinction between sediments deposited in a fluvial environment and those formed in an aeolian depositional environment. However, the aeolian (loess) deposits show some atypical characteristics. For example, the end-member model results show a coarsening in the five palaeosol layers. This is in contrast with the fine grained nature of palaeosols on the CLP. The coarsening observed in the studied palaeosol layers is interpreted as the result of local surface runoff processes, eroding fine sediment and/or depositing relatively coarse material during interglacial periods. Because of the known depth of the fluvial-aeolian transition and the absolute age of the TCN burial dated terrace deposits, pedostratigraphic correlation of the palaeosol layers with the Central Loess Plateau is possible. The oldest palaeosol is correlated with S5 (0.625–0.503 Ma). The transition from a fluvial to aeolian environment takes place in L6, between 0.625 and 0.693 Ma. This is consistent with the TCN age of 0.6 ± 0.14 Ma. This age also marks the abandonment of the terrace caused by incision of the Hanjiang River, which is possibly related to an uplift phase of the QLM

Fluvial terrace formation and its impacts on early human settlement in the Hanzhong basin, Qinling Mountains, central China

The Qinling Mountains (QLM) form the climatic boundary between the temperate north and subtropical south of China. Many important Paleolithic archaeological sites located on fluvial terraces in this area have been reported in recent decades. Abundant artifacts have been excavated in silt layers overlying fluvial gravels and coarse sands. These silt layers have thus far been interpreted as aeolian deposits. However, in principle they could also represent (in part) fluvial (floodplain) deposits, especially near the base of fine-grained sequences. Reconstruction of fluvial terrace formation is crucial for the correct interpretation of the environment of hominin occupation. In this paper, two sediment sequences from two Paleolithic sites, located on different terrace levels of the Hanjiang River in the Hanzhong basin, are studied mainly using grain-size and grain-shape analyses. In addition, grain-size distributions have been unraveled by applying end-member modelling to distinguish different sedimentary environments. The results show that three different units can be discriminated in each section. The lower unit, consisting of gravelly sand mixed with fine silt, is interpreted as shallow-channel-fill sediment deposited during the start of the transition from a channel to a floodplain environment. The middle unit comprises a fine-grained, gradually fining-upward sequence, representative a floodplain environment. At its base, it reflects a high-energy floodplain situation; at its top, the sequence is interpreted as a low-energy floodplain environment with aeolian input (settling in static water). The third, uppermost unit consists of aeolian loess interbedded with paleosol(s) and sediments that are interpreted as the results of episodic surface runoff. The gradual transition between the 3 units and the gradual fining upward trend of the middle unit indicates that there is no considerable age gap (no hiatus) between the fluvial- and aeolian sedimentary environments. Stone artifacts have been found in all 3 units, with difference abundance, indicating that both the aeolian and floodplain depositional environments provided favorable living conditions. For the floodplain environment, the resources of water and raw materials (fluvial gravels) for tool making may have offered fundamental resources for hominin settlement

Paleoflooding reconstruction from Holocene levee deposits in the Lower Meuse valley, the Netherlands

This study investigates the Holocene levee deposits and paleoflooding history of the Lower Meuse in the Netherlands based on archeological investigations and sedimentary analyses (grain size, end-member modelling, magnetic susceptibility and thermogravimetric analyses). The levee on the left bank in the study area near Ooijen contains a continuous sedimentary record in the NW downstream part. The archeological evidence and sedimentary results, including a grain size based flood energy index (LFEI), indicate that the Lower Meuse experienced a quiescent flooding period and low sedimentation rates during the mid-late Mesolithic when the levee was low and human influence was minor. Deposition during the Mesolithic shows a fining-upward trend and a highly-developed soil containing abundant artefacts. During the Neolithic and Bronze Age, the flooding intensity was low but gradually increased to a moderate level probably because of deforestation and increased runoff. Limited Bronze Age findings may reflect decreased human activity because of the increased flooding. Starting from the Iron Age, the Meuse experienced a generally enhanced flooding regime, which is reflected by erosion and coarsened sedimentation in the Iron Age and Roman Period. The high peak discharges during the Iron Age may have re-opened a low-lying paleochannel near to the levee during the intensified floods. This general increasing trend is interrupted by the lower flooding phase in the early Middle Ages (Dark Ages). From the middle to the late Middle Ages, the floods intensified again. The coarsening deposition and higher sedimentation rates since the Iron Age resulted from increased floods and higher sediment supply by deforestation and soil erosion. The findings of this study agree with a recent paleoflood reconstruction for the Lower Meuse by using a floodplain archive, implying that levee sediment records have potential in paleohydrological studies if the completeness of the record and chronological information is guaranteed

Macroevolutionary and macroecological response of Iberian rodents to late Neogene climatic oscillations and events

Biozones are routinely used for chronological purposes, but their nature is seldomly questioned. Here, we attempt to find the evolutionary-ecological basis for Iberian rodent biozones for the interval 8.5-2 Ma based on currently available paleontological, stratigraphic and paleoclimatic information. Our comparison of biozone boundary age uncertainty intervals to records of marine SST, δ18O and δ13C, terrestrial hydrological proxies and astronomical parameters suggests an orbitally forced climatic origin for the majority of biozones. Zone boundary ages during the late Miocene are mostly associated with humidity changes during 1.2-Myr obliquity nodes and 405-kyr eccentricity minima. Tectonics and strong regional cooling may additionally explain faunal change during the Messinian (7-5 Ma). A partly reversed pattern characterizes most Pliocene zone boundaries, which are mostly associated with wetter conditions during obliquity nodes and 405-kyr eccentricity maxima. A third configuration culminates in the early Pleistocene and consists of the combination of strong obliquity amplitude maxima and 2.4-Myr eccentricity minima. It is suggested that larger-scale, European Neogene mammal (MN) units have an astronomical basis as well, with an important role of 2.4-Myr eccentricity cycle and the 1.2-Myr obliquity cycle, with the latter becoming especially important after the mid-Miocene cooling (∼14 Ma). Whereas rodent events on the Iberian Peninsula during the late Miocene are shaped by replacements within resident communities dominated by dry-adapted clades of true mice (Murinae) and hamsters (Cricetinae), transitions during the cooler Pliocene involve invasions of newly emerging Eurasian clades of 'microtoid hamsters' and voles (Arvicolinae) preferring wetter and cooler environments. A new model of stepwise clade displacement is proposed in which the combination of long-period Milankovitch cycles and gradual long-term climatic change allows for the periodic functioning of migration corridors, along which increasingly pervasive dispersal events by members of new clades cause the gradual extinction of old clades

A new rodent chronology for the late Neogene of Spain

The number of late Neogene Spanish micromammal-containing continental sections with a correlation to the Geomagnetic Time Scale is steadily growing. Nonetheless, well-calibrated sections with dense micromammal records are still rare, biostratigraphic correlations between basins are not straightforward, and ages of uncalibrated sites are poorly constrained. Here, we aim at improving the chronology of Iberian micromammal sections and sites for the interval 8.5–2 Ma by: (i) analyzing qualitative and quantitative similarities between rodent assemblages and turnover in the different basins, (ii) formulating a system of fifteen Iberian assemblage biozones, and (iii) constraining the ages of zone boundaries, assuming isochroneity across basins. Age uncertainty ranges for most known Iberian micromammal sites are obtained by combining regional biozone boundary ages with local magnetostratigraphic records, sedimentation rates and/or evolutionary rates. In addition, our results include new, integrated stratigraphic records from the Jumilla-La Celia and Teruel Basins, which are used to constrain the thus far poorly dated interval covering the latest Tortonian and earliest Messinian (8–7 Ma)

Macroevolutionary and macroecological response of Iberian rodents to late Neogene climatic oscillations and events

Biozones are routinely used for chronological purposes, but their nature is seldomly questioned. Here, we attempt to find the evolutionary-ecological basis for Iberian rodent biozones for the interval 8.5–2 Ma based on currently available paleontological, stratigraphic and paleoclimatic information. Our comparison of biozone boundary age uncertainty intervals to records of marine SST, δ18O and δ13C, terrestrial hydrological proxies and astronomical parameters suggests an orbitally forced climatic origin for the majority of biozones. Zone boundary ages during the late Miocene are mostly associated with humidity changes during 1.2-Myr obliquity nodes and 405-kyr eccentricity minima. Tectonics and strong regional cooling may additionally explain faunal change during the Messinian (7–5 Ma). A partly reversed pattern characterizes most Pliocene zone boundaries, which are mostly associated with wetter conditions during obliquity nodes and 405-kyr eccentricity maxima. A third configuration culminates in the early Pleistocene and consists of the combination of strong obliquity amplitude maxima and 2.4-Myr eccentricity minima. It is suggested that larger-scale, European Neogene mammal (MN) units have an astronomical basis as well, with an important role of 2.4-Myr eccentricity cycle and the 1.2-Myr obliquity cycle, with the latter becoming especially important after the mid-Miocene cooling (∼14 Ma). Whereas rodent events on the Iberian Peninsula during the late Miocene are shaped by replacements within resident communities dominated by dry-adapted clades of true mice (Murinae) and hamsters (Cricetinae), transitions during the cooler Pliocene involve invasions of newly emerging Eurasian clades of ‘microtoid hamsters’ and voles (Arvicolinae) preferring wetter and cooler environments. A new model of stepwise clade displacement is proposed in which the combination of long-period Milankovitch cycles and gradual long-term climatic change allows for the periodic functioning of migration corridors, along which increasingly pervasive dispersal events by members of new clades cause the gradual extinction of old clades

Aeolian dust supply from the Yellow River floodplain to the Pleistocene loess deposits of the Mangshan Plateau, central China : Evidence from zircon U-Pb age spectra

The thick loess-palaeosol sequences in the Mangshan Loess Plateau (MLP; central China) along the south bank of the lower reach of the Yellow River provide high-resolution records of Quaternary climate change. In addition, substantial increases in grain-size and accumulation rate have been inferred in the upper part of the loess sequence, above palaeosol layer S2. This study investigates the sources of the long-term dust supply to the MLP and explores the mechanism behind the sudden increase in sediment delivery and coarsening of the loess deposits since S2 (similar to 240 ka) by using end member modelling of the loess grain-size dataset and single-grain zircon U-Pb dating. Our results indicate that the lower Yellow River floodplain, directly north of the MLP, served as a major dust supply for the plateau at least since the deposition of loess unit L9 and indirectly suggest that the integration of the Yellow River and the disappearance of the Sanmen palaeolake took place before L9 (similar to 900 ka). The sudden change in sedi-mentology of the Mangshan sequence above palaeosol unit S2 may result from an increased fluvial sediment flux being transported to the lower reaches of the Yellow River because of tectonic movements (initiated) in the Weihe Basin around 240 ka. Furthermore, sediment coarsening can be explained by the gradual southward migration of the lower Yellow River floodplain towards the MLP since the deposition of palaeosol S2. The migration is evidenced by the formation of an impressive scarp, and is likely caused by tectonic tilting of the floodplain area. (C) 2018 Elsevier Ltd. All rights reserved.Peer reviewe

Between local zones and MN units: A new inter-basinal rodent zonation for the late Neogene of Spain

Since the appearance of the first major magnetostratigraphic studies covering the late Neogene of Spain (e.g., Opdyke et al., 1997; Garcés et al., 1998) the number of Spanish continental sections with a correlation to the Geomagnetic Time Scale has steadily grown. Nonetheless, well-calibrated sections with a dense record are still rare, between-basin biostratigraphic correlation is not straightforward, and ages of uncalibrated sites are poorly constrained. Given the overall similarity of rodent assemblages between Iberian basins during the interval MN11–MN17 (9–2 Ma), the definition of a system of Iberian rodent zones for this interval is a logical and necessary step leading to improved correlations. Our revision thus entails the integration of local biozonations into a single Iberian biostratigraphic framework. The inferred series of zone boundary ages are used to improve the age estimates for most Iberian micromammal sites. The chronological backbone in our approach is formed by the available Iberian magnetochronologic records (Teruel, Cabriel, Júcar, Jumilla-La Celia, Fortuna and Guadix-Baza Basins). After analyzing similarities in taxonomic composition and turnover across basins with a defined biozonation (Teruel, Bajo Segura, Alcoy, Granada and Guadix-Baza Basins), 15 Iberian biozones were defined for the 9–2 Ma interval. Age uncertainty intervals for each boundary and for most Iberian micromammal sites were inferred using additional information on local sedimentation and/or evolutionary rates. Among our results are new ages for the latest Tortonian and earliest Messinian (MN12–MN13 transition, 8–7 Ma), a thus far poorly dated interval on the Iberian Peninsula. The new chronology for this interval is based on the integrated stratigraphic records of the Jumilla-La Celia and Teruel Basins. Sections in the Jumilla-La Celia basin (eastern Betic Cordillera; Van Balen et al., 2015) were sampled paleomagnetically, further constraining the ages of various MN12-correlative sites (Van Dam et al., 2014). Finally, regular bedding patterns in sections near Concud in the Teruel Basin (eastern Central Spain) were interpreted cyclostratigraphically and used as a tool in addition to magnetostratigraphy for dating several classical and newly sampled MN12-correlative mammal sites in the area

Glacial geology of Saalian relief around Midwolda, eastern Groningen, the Netherlands

Due to canal-digging activities in 2011 and 2014, two small and one large temporary exposure, all ranging from 4 to 5 m in depth, were studied with respect to the sedimentology and structural geology, in the glacial ridge of Midwolda, Groningen, the Netherlands. The lowermost unit consists of clay of Elsterian age and is composed of glaciolacustrine and turbiditic deposits (Peelo Formation). These show synsedimentary deformations due to loading, as well as post-sedimentary Saalian glaciotectonic deformations, consisting of folding, and faulting structures. The overlying Saalian till sequence consists of two main units. The lower unit, with clear features of a subglacial deformation zone (e.g. lateral heterogeneity), has a local origin and strongly resembles the underlying Elsterian clay. Glacial tectonic and morphological observations indicate a primary NE-SW ice-flow direction. The second till layer has a sandy texture and high crystalline gravel content, while glacial-tectonic indicators point to a NW-SE ice-flow direction. The deformation of the till layers has caused a repetition and mixing of till layers, due to the last ice movement. The NW-SE ice movement is supported by the morphology as well as data from erratic gravel counts. Correlation with geological cross-sections strongly suggests regional subsurface control on ice-sheet behaviour