Exploring the potential of buried paleosols and paleodunes sequences for unraveling Late-Pleistocene climate change in subtropical Coastal Chile

<p>We have started a program of detailed mapping and sampling buried paleosols and paleodunes sequences that occur along the semiarid coast of central Chile (32-34ºS). Previous work has postulated these stratigraphic records afford evidence for past climate change linked to the latitudinal oscillations/intensification of the southern westerly winds (SWW): Bt horizons resembling humid conditions associated with north shifted SWW, and paleodunes with arid conditions and south shifted SWW. Nonetheless, multiple factors can affect long-term (e.g., orbital to suborbital time-frames) eolian dune variability (stabilization-reactivation, expansion-contraction, pedogenesis-morphogenesis), including sea level, sediment supply, wind intensity, and tectonics. It is therefore a pending work to expand our research in these eolian archives and understand their causes and environmental implications. Here, we present preliminary research results from the Ritoque paleodune, Comuna de Quintero, Chile (32ºS). The study site is a 15 m deep gully incision that allowed us to built a very complete sediment stratigraphic sequence postdating the Miocene-Pliocene marine Horcón Formation. Previous luminescence geochronologic control in nearby paleodune deposits indicate eolian morphogenetic and pedogenetic activity during the last glacial period. We interpret the geomorphic context together with standard sediment field and laboratory data to discriminate between stratigraphic units and their origin. A total of 13 sediment units were mapped, which include mostly couplets of buried paleosols (Bt horizons) and underlying paleodunes. Other units resembling rather paleowetlands and possibly sea side sand beaches were also found. We discuss our results in light of available evidence to unravel the environmental meaning of this extraordinary well-preserved terrestrial record in the SE subtropical Pacific.</p>

Evolution of the Upper Yellow River as Revealed by Changes in Heavy-Mineral and Geochemical (REE) Signatures of Fluvial Terraces (Lanzhou, China)

Despite decades of study, the factors that controlled the formation and evolution of theupper reaches of the Yellow River, including uplift of the northeastern Tibetan Plateau, Pliocene-Pleistocene climate change, and autogenetic processes are still poorly constrained. The stratigraphicrecord of such paleogeographic evolution is recorded in the sequence of nine terraces formed duringprogressive incision of the Yellow River in the last 1.7 Ma. This article investigates in detail forsediment provenance in terraces of the Lanzhou area, based on heavy-mineral and geochemical(REE) signatures. Two main provenance changes are identified, pointing each to a majorpaleogeographic reorganization coupled with expansion of the upper Yellow River catchment andenhanced sediment fluxes. The first change took place between the deposition of terrace T9 (formedaround 1.7 Ma) and terrace T8 (formed around 1.5 Ma), when rapid fluvial incision point to tectoniccontrol and active uplift of northeastern Tibetan Plateau. The second change took place betweendeposition of terrace T4 (formed around 0.86 Ma) and terrace T3 (formed around 0.14 Ma), duringa period of low incision rates and notably enhanced sediment fluxes as a response to enhanced EastAsian Summer Monsoon and consequently increased precipitations, pointing instead chiefly toclimatic control.

A dynamic continental moisture gradient drove Amazonian bird diversification

The Amazon is the primary source of Neotropical diversity and a nexus for discussions on processes that drive biotic diversification. Biogeographers have focused on the roles of rivers and Pleistocene climate change in explaining high rates of speciation. We combine phylogeographic and niche-based paleodistributional projections for 23 upland terra firme forest bird lineages from across the Amazon to derive a new model of regional biological diversification. We found that climate-driven refugial dynamics interact with dynamic riverine barriers to produce a dominant pattern: Older lineages in the wetter western and northern parts of the Amazon gave rise to lineages in the drier southern and eastern parts. This climate/drainage basin evolution interaction links landscape dynamics with biotic diversification and explains the east-west diversity gradients across the Amazon.