Pleistocene loess records of the Khovaling Loess Plateau (KLP) in Tajikistan provide rich collections of lithic artifacts demonstrating past human presence in the region. To understand the timing of human activity and environmental conditions prevailing at that time U-Th dating and clumped/stable C/O isotope measurements have been applied to modern and Pleistocene soil carbonates (SCs) collected at several sites on the KLP and surroundings. U-Th ages were corrected by two methods: 1) assuming an initial [Th-230/Th-232] activity ratio of 0.85 +/- 0.25 based on gamma spectrometry of loess/paleosol samples, and 2) the isochron technique using leachates and fully dissolved subsamples. Diagenetic alteration and potential U/Th mobilization and related isotope fractionation due to alpha-recoil was also modelled and found to be minor in the studied soil carbonates. Compared to model ages as references, uncorrected 230 Th ages are only acceptable if measured [Th-230/Th-232] activity ratios of leachates are high (>30), while Th-230 ages derived using method 1 are mostly overcorrected. It appears that SCs can be reliably dated by the U-series disequilibrium method in this sedimentary setting, but isochron dating cannot be spared. Application of the isochron method is required to derive (230)Thmodel ages, which ensures that the non-zero initial (230) Th and possible U-Th gain/loss due to alpha-recoil can be simultaneously corrected and reliable U-Th ages obtained. U-Th ages of Pleistocene SCs clearly demonstrate postpedogenic ingrowth of multiple, non-contemporaneous populations of SCs within loess/paleosol units, and that SC formation happened in many cases under cold, presumably dry glacial climate conditions. Considering that U-Th ages of SCs provide minimum ages of the sediment in which they form, these ages can be useful in developing loess stratigraphic models and for correlation of paleosols with marine isotope stages. This implies that the age of a given paleosol and any lithic artifacts it may contain, indicating human activity, cannot be younger than the age of SCs formed in that paleosol. This is due to the nature of soil carbonates, which can be the product of both syn- and post-depositional processes. Clumped isotope thermometry of SCs collected from modern soils at three sites in Tajikistan provide evidence for SCs dominantly recording summer season soil temperatures, while the calculated soil water oxygen isotope signatures reflect annual signals and carbonate precipitation from source waters incorporating rainfall from prior to and during SC formation. In contrast, some Pleistocene SCs record soil temperatures and stable isotope compositions more appropriate to glacial conditions, confirming the findings of U-Th ages, and highlighting the primary role of aridity-driven soil moisture changes in SC precipitation in this setting. Considering the interpretative complexities of SC stable isotope compositions, involving issues such as SC formation depth within a soil/paleosol profile, seasonality of SC growth and violation of the law of superposition, SC stable isotope proxy records of past climates cannot be considered as a set of clearly sequential data through time. This implies that such SC-based stable isotope records must be accompanied by U-Th dating of carbonates to be meaningful.

Laboratory and field tests were performed on sandy soils from six Pleistocene-age sites in the South Carolina coastal region to investigate the age-related resistance to liquefaction. Stress-controlled cyclic triaxial tests were used to determine the cyclic strength of soils with geologic ages ranging from approximately 59,000 to 1,200,000 years. Three sites have evidence of liquefaction in the form of sand blows that are 467 to 4,185 years old as determined from C14 dating of embedded organic material. The other three sites show no indications of liquefaction. Cyclic stress ratios ranging from 0.095 to 0.225 were applied to undisturbed and reconstituted soil specimens that were consolidated to an effective stress equal to 100 kPa. Soil specimen liquefaction was defined to occur when the excess pore pressure was equal to the confining effective stress. Estimates of the at-rest earth pressure coefficient were determined using measurements from the flat plate dilatometer and the cone penetrometer and were applied to the laboratory cyclic stress ratio occurring at the 15th loading cycle to determine the laboratory-field equivalent cyclic resistance ratio. The age-dependent liquefaction resistance was determined using additional data from the inner coastal plain of South Carolina and assessing the cyclic resistance ratios and their associated KDR ratios relative to the base data and applying one of the more recently developed liquefaction triggering model. It was found that the development of the aging factor should be independent of the liquefaction triggering model. Subsequently, the aging factor is developed using an offset that is constrained at 20 years and a KDR=1.0, and was found to range from 1.00 at 20 years to 1.45 at 1.0 Ma for the original deposition ages of the soils and 1.00 at 20 years to 1.51 at 1.0 Ma for the data set consisting of the last disturbance and original deposition ages of the soils.

We use a landscape evolution model to infer the effect of Late Pleistocene climate change on the incision-aggradation behaviour of the Rhine-Meuse fluvial system. We model the routing of runoff and sediment in the catchment in order to predict grainsize trends and the incision and aggradation behaviour in the downstream reach, where we compare it to the sequence of events and grainsize characteristics inferred from borehole corings. This sequence starts with an important incision taking place around the MIS 3 to MIS 2 climatic transition. During the coldest part of MIS 2, a coarse-grained sedimentary unit is deposited that shows an upward increase in the sand/gravel ratio. The model experiments do not predict an incision at the MIS 3 to MIS 2 transition. Therefore, the incision should be attributed to other causes, most likely effects of glacio-isostatic uplift. However, a relative upward increase in sand content of the sediments is predicted by the model. This increase is the result of the difference in transport rates between sand and gravel. Starting from a homogeneous pre-existing (MIS 3) deposit, the gravel content in the active layer increases because the sand is removed quickly and transported further downstream, whereas the gravel travels slowly and piles up with gravel originating from immediately upstream, resulting in a net accumulation. At a later stage, sand originating from much further upstream progrades fan-like over the gravelly deposits. According to the record, during the early Late Glacial warming part of MIS 2 (Bolling-Allerod interstadial), neither incision nor aggradation has taken place. This is in accordance with modelling results which show that, despite the reduction of sediment input due to re-vegetation of hillslopes, sufficient sediment remains available for fluvial transport in the channel network itself. It takes several thousands of years before effects of sediment depletion in the catchment are noted downstream. That is why we argue that the inferred incision at the late Late Glacial (the start of the Younger Dryas) in our downstream study area might reflect depletion effects related to the preceding early Late Glacial conditions. In general, our modelling results show that terraces along one large fluvial system are diachronic features. in particular, terrace surfaces are older upstream compared to downstream. In addition, complex responses to climate change are likely to occur in a large fluvial system like the Rhine-Meuse, and correlation of morphological features in the fluvial record to specific short term palaeo-climatic events, for example Dansgaard-Oeschger events could be risky without consideration of catchment (size) characteristics and associated response times. (C) 2009 Elsevier B.V. All rights reserved.

This paper reviews the literature on cold-adapted micro-organisms which might exist in ice and permafrost. Properly identified, microbial markers in the cryolithozone could be used in palaeoenvironmental reconstructions, in distinguishing between epigenetic and syngenetic depositional sequences, and in the recognition of secondary thaw unconformities. Cryobiological problems include (1) whether the bacteria are dead, dormant or in the active state, and (2) what factors determine the preservation of cell structures. A possible consequence of permafrost thawing, based upon predicted global warming scenarios, is that there may be an increase in microbial activity and an increase in active layer thickness.