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In order to understand the paleogeographic evolution of Viedma Lake (252 masl) sedimentary sequences with glaciolacustrine and lacustrine strata between 307 masl and 266 masl and bathymetric fluctuations between 27 ka. and 2.4 ka. were identified. The paleoenvironmental interpretation of the stratigraphic profiles was carried out based on the analysis of facies and their associations. The oldest age was recorded at 301 masl (27 ka) and the youngest corresponds to 266 masl (2.4 ka). The record of 27 ka was compared with another dated record of the Tar-San Martin Lakes basin showing that Viedma – Tar-San Martín Lakes were formed at similar ages. Taking into account that the deposits of Bahía Túnel are located at 266 masl and that the level of the lake would be above this height, it is proposed that this lake level would have restricted the movement of hunter-gatherer populations along the coast and to the west. From 2.4 ka on a new space started to be available for these populations broadening the wintering grounds (≤400 masl). The chronology of the archaeological record found in this new space fits the proposed paleogeographic evolution. This paper complements the research on the evolution of lacustrine systems in the Patagonian Mountain range and broadens the discussion of human mobility in the Viedma Lake basin during the Holocene. [ABSTRACT FROM AUTHOR]

The Salawusu River Valley cuts through the Mu Us Desert in north central China, and lies at the interface of the East Asian Summer and Winter Monsoonal regions. Exposed at numerous locations in the valley side are extensive late Quaternary deposits, consisting of interbedded aeolian sands, fluvio-lacustrine units and palaeosols. Due to the importance of the location in potentially elucidating both summer and winter monsoonal regimes, and the quality of the sedimentary record, the region has a rich history of study, and yet even within the Holocene sequence, many conflicting interpretations have arisen based on studies on different sections. This paper aims to synthesize and explore these differences by exploring the lateral continuity of the Holocene sequences along a ~ 45 km reach of the valley, and presenting new, detailed physical and geochemical analyses of three sections, focusing on the lacustrine Holocene Dagouwan Formation. The absence of the lacustrine unit at several locations confirms that rather than representing a single lake, the Dagouwan Formation instead represents a series of palaeolakes, probably at least partially hydrologically isolated from each other by aeolian sands. All begin with sand-dominated deposits during the early−/mid-Holocene, which is interpreted as the result of abundant sand-supply to the north and west, under the influence of an enhanced East Asian Winter Monsoon, and all switch to silt-dominated, more carbonate-rich deposits during the mid−/late-Holocene, which is attributed to an enhanced East Asian Summer Monsoon bringing loessic silts from the Chinese Loess Plateau to the east and south. The timing of this change, perhaps as late as 5.5 ka, supports the idea of a relatively enhancement late mid-Holocene of the summer monsoonal circulation in the region. However, despite the proximity of the sections and consistent analytical approaches, marked differences between the sections occur in all proxies studied. The timing and rate of the switch from sand- to silt-dominated lacustrine deposition varies between the sites by as much as 2000 years within just a few kilometres of each other, and at some sites the switch was gradual, whereas at others it was very rapid. Similar dramatic variations are also seen with organic carbon content, carbonate content, C:N ratio, and especially the δ13C isotopic ratio. These point to the lake basins behaving very differently, and emphasize that consideration must be given to the local geomorphology and palaeolimnological evolution of individual sections. • Differences in lacustrine Holocene monsoon records in northern China are explored. • The occurrence of the lakes is geomorphologically, not climatologically, controlled. • Different sections of similar units represent different lakes with varied histories. • Consistent changes in sediment suggest mid-Holocene decline of winter monsoon. • Study of individual sections or proxies cannot be used to infer regional climate. [ABSTRACT FROM AUTHOR]

In this paper, we examine the Early to Middle Holocene evolution of a prominent group of ground-water fed lakes in the southeastern hinterland of the Badain Jaran Desert (BJD) of northwest China. Specifically, we describe a sediment profile record from the Taoerlegetu (TR) palaeolake basin using multiple proxies of total organic carbon (TOC), total nitrogen (TN), C/N ratio, δ13C org , grain size and mineral composition based on a well-dated trench profile. As C/N values suggest that sedimentary organic matter mainly originated from aquatic plants, δ13Corg values can be used as a qualitative proxy for water level because aquatic plants in different biotopes (water depth) have different δ13C values. Our results show that from 10.9 to 9.1 cal kyr B.P., water level rose slowly, and aquatic macrophytes occupied the lake basin. From 9.1 to 5.5 cal kyr B.P., water level reached an even higher level and phytoplankton replaced macrophytes as the major contributor to organic matter. The humid episode of the lakes in the hinterland of the BJD in the early Holocene might be related to the increased groundwater supply from the northeast region of the Tibet Plateau. These findings are consistent with earlier studies of lacustrine and peat sediments found in periphery of the modern lake group, which indicate that their geographic extent may have been larger in the past. A relative drought period recorded in the studied succession from 8.5 to 8.0 cal kyr B.P. marks an interval of reduced ground-water transport from the Tibet Plateau. This interval probably corresponds to the "8.2 ka cold event" and provides evidence that this widespread climate episode influenced groundwater processes across inland Asia. • The δ13C org value could be used as a qualitative indicator for the change of water level. • Lakes in the hinterland of the Badain Jaran Desert shows different evolution progress with these in the edge. • The main water source of lakes in the hinterland of the BJD in the Early Holocene comes from the Tibet Plateau. [ABSTRACT FROM AUTHOR]

Gastropods and ostracods are widely used in Quaternary paleoenvironmental reconstructions but the taphonomic studies that should precede them are not as common. In this paper we compare the taphonomic information obtained from assemblages recovered in Holocene fluvial sequences of the Salado River basin (Buenos Aires, Argentina) and analyze the changes or similarities between species, localities and stratigraphic units. Using taphonomic grades, gastropod shells were cataloged based on three attributes: fragmentation, discoloration and dissolution. For ostracods, discoloration and dissolution together with the population structure (adults-juveniles A/J, valves-carapace V/C and male-female ratios) were analyzed. For gastropods, Heleobia parchappii , Biomphalaria peregrina and Succinea meridionalis showed similar preservation patterns, and Miradiscops brasiliensis showed least evidence of alteration. In ostracods, these patterns varied among species. For V/C ratio, 7% of assemblages were formed only by valves, 82% were dominated by valves and 11% were dominated by carapaces. Fragmentation and population structure allowed autochthonous and allochthonous associations to be distinguished. Gastropod assemblages with low levels of fragmentation were recovered mainly from the uppermost levels of the stratigraphic profiles. For ostracods, the A/J ratio showed that 52% of the assemblages were dominated by adults with most ontogenetic stages represented and 29% retained their original population structure suggesting they would be autochthonous associations, whereas 19% of the assemblages were dominated by juvenile valves therefore assuming allochthonous associations. Our results indicate that taphonomic analysis is an effective tool that allows identifying autochthonous assemblages, which are the most reliable for robust paleoenvironmental reconstructions. • First taphonomic study combinating ostracods and gastropods in Argentina. • The most abundant species of gastropod showed similar preservation pattern. • In ostracods, the preservation states varied among the most abundant species. • Ostracod population structure allows recognizing autochthonuos or allochtonous assemblages. [ABSTRACT FROM AUTHOR]

The Holocene terrestrial malacofauna of the northern shore of the Mediterranean remains poorly known. Its importance however is twofold, first to better understand the recolonization of Europe by woodland snails from different kinds of glacial refugia, secondly to bring to light the development of Mediterranean ecosystems. This paper is based on molluscan analyses of three sedimentary sequences from a catchment basin near Aix-en-Provence, all of which being representative of the most common pedo-sedimentary and malacological postglacial successions in southeastern France. A special effort has been made to establish the chronology. The results first show the lasting of temperate steppes, lasting in places all the way into the Boreal period (∼9000 cal yr BP). Less open environments appeared soon after with assemblages including thermophilic species. The Boreal period shows unstable conditions in an open and heterogeneous woodland landscape. A malacofauna indicating true woodland developed during the Older Atlantic (∼8000 cal yr BP). Dominated by "semi-forest" snails, it still contained some xerophilic ones. These assemblages lost their true woodland character between ∼7000 and ∼6500 cal yr BP due to anthropogenic influence. An increase in human activity and merchandise flow within a more open landscape caused a progressive but deep turnover of land snail communities since the Early Neolithic. It must be admitted that, during the Holocene as a whole, Mediterranean ecosystems remained heterogeneous and frequently open. The human impact is such that it is difficult to discuss the role of climate since ∼7000 cal yr BP. • Temperate steppe environments lasted, in places, until ∼9000 cal yr BP. • True open woodland snail assemblages date from the Older Atlantic at ∼8000 cal yr BP. • First clear anthropogenic impacts occur between ∼7000 and ∼6500 cal yr BP. • Anthropization is the cause of a progressive but deep renewal of land snail communities from ∼7000 cal yr BP. • The weight of human impact masks the evidence for climate events since ∼7000 cal yr BP. [ABSTRACT FROM AUTHOR]