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Highlights: [•] Loess has accumulated in Wrangell-St. Elias National Park, Alaska over the past ∼10,000years. [•] Concentrations of Fe in the silt+clay fraction of the loess are higher than most other loess bodies. [•] The loess contains many minerals that can yield bioavailable Fe to primary producers in the ocean. [•] Satellite imagery shows that dust from this region is transported to the open North Pacific Ocean. [•] Contemporary glaciogenic dust at high latitudes may play an important role in the global dust budget. [Copyright &y& Elsevier]

Abstract: The alluvial fill in the Upper Mississippi River Valley (UMV) is a palimpsest of past landscapes, environments, and physical evidence of human life ways. The valley has undergone significant changes in fluvial style during the time humans have occupied its landscapes, including changes in channel pattern, location of depocenters, and sediment lithology. Remnants of late-glacial braidplains that predate human presence in the Upper Midwest occur as sandy terraces and terrace fills. A subsequent major change in alluvial architecture resulted from fundamental changes in seasonal water and sediment input that marked the end of glacial meltwater input into the valley about 12.4 ka (10,500 14C yr B.P.). A shift to net transport of sandy bedload and storage of fine-grained overbank sediment on the floodplain accompanied the change to an island-braided channel pattern at that time. The Holocene channel belt has been significantly narrower, and the zone of sediment storage is reduced relative to that of the late-glacial river. Major Holocene depocenters include alluvial fans and colluvial slopes, floodbasins, natural levees, and fluvial fans at the junction of large tributaries. Climate models, and paleobotanical, and isotopic studies indicate that shifts in large-scale patterns of atmospheric circulation and moisture transport into the mid-continent of North America induced hydrologic and vegetation changes that strongly influenced flood frequency and magnitude, the delivery of sediment from tributary basins, and the evolution of the UMV landscape. Understanding the alluvial architecture of the valley, and the temporal/spatial distribution of biotic environments and processes that have buried, mixed, altered, or destroyed archaeological deposits is essential to develop strategies for sampling the valley for evidence of past human activity and for properly interpreting the archaeological record. [Copyright &y& Elsevier]

Abstract: Constraining the ages and mass accumulation rates of late Quaternary loess deposits is often difficult because of the paucity of organic material typically available for 14C dating and the inherent limitations of luminescence techniques. Radiocarbon dating of small terrestrial gastropod shells may provide an alternative to these methods as fossil shells are common in loess and contain ∼12% carbon by weight. Terrestrial gastropod assemblages in loess have been used extensively to reconstruct past environmental conditions but have been largely ignored for dating purposes. Here, we present the results of a multi-faceted approach to understanding the potential for using small terrestrial gastropod shells to date loess deposits in North America. First, we compare highly resolved 14C ages of well-preserved wood and gastropod shells (Succineidae) recovered from a Holocene loess section in Alaska. Radiocarbon ages derived from the shells are nearly identical to wood and plant macrofossil ages throughout the section, which suggests that the shells behaved as closed systems with respect to carbon for at least the last 10 ka (thousands of calibrated 14C years before present). Second, we apply 14C dating of gastropod shells to late Pleistocene loess deposits in the Great Plains using stratigraphy and independent chronologies for comparison. The new shell ages require less interpretation than humic acid radiocarbon ages that are commonly used in loess studies, provide additional stratigraphic coverage to previous dating efforts, and are in correct stratigraphic order more often than their luminescence counterparts. Third, we show that Succineidae shells recovered from historic loess in the Matanuska River Valley, Alaska captured the 20th century 14C bomb spike, which suggests that the shells can be used to date late Holocene and historic-aged loess. Finally, results from Nebraska and western Iowa suggest that, similar to other materials, shell ages approaching ∼40 ka should be viewed with caution as they may reflect trace amounts of contamination. In sum, our results show that small terrestrial gastropod shells, especially from the Succineidae family, provide reliable ages for late Quaternary loess deposits in North America. [Copyright &y& Elsevier]

Abstract: Here we present palynological records from alluvial deposits in four outcrop sequences along the lower reaches of Arroyo Claromecó, Buenos Aires Province, Argentina (38° 50′ S latitude, 60° 05′ W longitude). These data indicate development of soils and grasslands with associated halophytic vegetation in the higher elevations of the floodplains between ca. 7200 and 6000 14C yr BP (ca. 8000 and 7000cal yr BP). At lower elevations halophytic saltmarsh vegetation was replaced by wetland communities (sedges) in response to a sea-level highstand at 6500 14C yr BP (ca.7400cal yr BP). Soils were buried by expanding wetlands at ca.6000 14C yr BP, a trend that persisted until ca. 3400 14C yr BP (ca. 3700cal yr BP). Over this interval we observe repeated fluctuations between grassland and halophytic vegetation in response to variations in water level and physical–chemical conditions resulting from desiccation or flooding events. These variations are caused by hydrologic variability in a subhumid–dry climatic mean state. Channel incision occurred between ca. 3400 and 2500 14C yr BP (ca.3700–3200cal yr BP), concurrent with sporadic and intermittent sediment deposition at higher elevations of the floodplain. The pollen record from the paleochannel infilling indicate grasses accompanied by halophytic taxa between ca. 2500 and 800 14C yr BP (3200 and 700cal yr BP) deposited in a shallow brackish-to-fresh water body. The palynological spectra from sediments deposited sporadically at higher elevations show halophytic vegetation and a trend toward wetland desiccation followed by development of psammophytic communities after ca. 1100 14C yr BP. The tops of the alluvial sequences are covered by sand dunes whose modern spectra are characterized by psammophytic vegetation along with exotic tree taxa. Our results and inferences are consistent with previous studies and provide more detailed insights into the impacts of Holocene sea-level and climatic variations, aspects that are relevant for the coastal Pampa grasslands under various scenarios in a warming world. [Copyright &y& Elsevier]