ABSTRACT An ~10-m-thick sequence of Quaternary eolian sands from the island of Vis (Croatia) was investigated with the aim to unravel and understand their origin, characteristics, and age. The sand deposit is situated in a karstic depression in the eastern part of the island at an altitude of ~100 m above sea level (a.s.l.), and it is composed of a subhorizontally laminated unit at the bottom underlying a cross-bedded unit. The sand is very well sorted and fine grained and composed predominantly of carbonate lithic fragments, which most likely originated from the Dinaric karst region. The siliciclastic component of these sands reflects a more complex lithological source, including older sedimentary (e.g., flysch successions in the area, as well as older Quaternary deposits), magmatic, and metamorphic rocks probably originating from the Inner Dinarides, which were eroded and comminuted by glacial and periglacial activity during the last glacial period, and transported toward the Adriatic foreland by major rivers such as the Cetina and Neretva. Grain size and shape characteristics of the sands as well as their sedimentary structure indicate their eolian origin. Optically stimulated luminescence (OSL) dating was applied to determine the depositional age of the sediment. The obtained ages can be correlated to the Last Glacial Maximum (oxygen isotope stage [OIS] 2), implying that during the peak of that glaciation, the central Adriatic basin was dry land, a vast plain exposed to eolian deflation.

Abstract Eolian dune fields self-organize through a hierarchy of autogenic processes that culminate at the dune-field pattern level. Interactions that occur between flow and grains, flow and dunes, and dunes and dunes define the levels of this hierarchy. These autogenic processes occur within sets of boundary conditions, which impart a uniqueness to each emergent dune-field pattern. The interpretation of allogenic forcing on dune-field patterns and their stratigraphic record requires an understanding of how these external environmental variables are manifested at the dune-field pattern level. The fundamental process in eolian systems is a wind event with basic boundary conditions of sediment supply, sediment availability, and the transport capacity of the wind. It is hypothesized that the basic high-frequency boundary conditions are remade at each level of the hierarchy of autogenic processes or have a cumulative effect over many wind events. The influence of these boundary conditions “trickles up” to and is manifested at the dune-field pattern level. Tectonic, climatic and hydrologic boundary conditions are low frequency and operate over much longer timescales than a wind event. It is hypothesized that these “trickle down” to be remade as high-frequency boundary conditions, which then trickle up. Analysis of the White Sands Dune Field in New Mexico supports these hypotheses by the manifestation of the influence of boundary conditions in the dune-field pattern. The dune field originated by wind deflation of a lacustrine sediment supply, which was made available episodically by climatic forcing that controlled the hydrodynamics of the tectonic basin. Although the dune-field pattern arose through autogenic dune interactions, the morphologies of which are ubiquitous throughout the field, the influence of boundary conditions is evident in the dune morphologies and field-scale pattern heterogeneity.

The evolution of surface topography in an orogen provides information about the dynamics of the deep lithosphere. Within the high-elevation Altiplano-Puna Plateau of the central Andes, there are several local basins (~100 km wide) that sit >500 m lower than the surrounding plateau. These areas correspond to positive isostatic gravity anomalies, indicating high density in the lithosphere. There are also examples of former basins that are now at high elevation (e.g., the Miocene Arizaro Basin), suggesting that the basins are transient features that may be related to convective removal of lithosphere. Two-dimensional numerical models are used to investigate the topographic expression associated with removal of a high-density lithosphere root. A key result is that the presence of thick orogenic crust, as found in the Altiplano-Puna Plateau, can greatly affect the surface deflection above the detaching root. Three types of deflection are observed: (1) >500 m subsidence, followed by uplift, (2) little subsidence, and (3) uplift followed by collapse. The main control on the deflection is the viscous coupling between the root and surface, which decreases with increased root depth or weaker crust. If the crust is weak, the dense root induces crustal flow, resulting in thickened crust and either limited subsidence or uplift above the dripping lithosphere. Significant subsidence only occurs if the deep crust is relatively strong and the density anomaly is located within the crust. To produce surface deflection over a width of ~100 km, the near-surface rocks must be relatively weak.

Following the middle of the twentieth century, Earth scientists increasingly became aware of the significant role played by the incorporation of dust in the formation of soils. Dust plays an especially important role in the development of aridland soils, given the usually abundant supply of dust and generally limited magnitude of chemical weathering that characterizes aridland soils. The recognition that virtually all calcium in pedogenic carbonate is derived from calcium-bearing dust that primarily accumulates in a very common horizon of aridland soils, the calcic horizon, was critical in convincing scientists that soil formation in aridlands differs in fundamental respects from that in more humid settings. Research conducted by Leland Gile and his colleagues in the Desert Soil Geomorphology Project in southern New Mexico produced one of the most important bodies of published research in the 1960s to the early 1980s, that demonstrated both the significant impact of dust on aridland soils and their geomorphic significance. Subsequent research in the Cima volcanic field of the Mojave Desert, southwestern United States, showed that the nature of soil development associated with the formation and evolution of desert pavements is markedly different from that proscribed by the “canonical” A/B/C model of soil profile development described by V. Dokuchaev, the profile model most familiar to the majority of Earth scientists. The soils that develop beneath desert pavements form in parent materials increasingly composed of entrapped dust that is subsequently translocated below the pavement. Vesicular horizons, the key surface horizon of desert pavement soils, and subjacent, thickening clay and calcium carbonate–enriched B horizons form mainly through accretionary and inflationary profile (AIP) development, a type of cumulative soil development associated with rising desert pavements. The “upward growth” model of desert pavement formation profoundly contrasts with the “deflation” model. The behavior of the vesicular A horizon is important in maintaining a balance between rates of dust entrapment and translocation that enables continued AIP, while maintaining desert pavement at the surface. Soil chronosequence studies show that AIP and desert pavement formation are favored on other landforms (e.g., alluvial fans), providing that a weathering-resistant rock type is available to form a persistent pavement. Once desert pavements and soils have formed, most have likely survived exposure to “glacial” periods, despite effectively greater precipitation and locally significant changes in the nature of biotic communities that are characteristic of such periods. AIP is also an important mode of soil profile development in semiarid regions where desert pavements cannot form and vesicular horizons are weakly developed or absent. Increased plant density continues to favor the dust entrapment rates necessary to maintain AIP, as well as to provide a surface stabilizing function. Given the ecologically limiting role of water in aridlands, the nature of and time-dependent changes in soils forming by AIP strongly influence patterns of recruitment and composition of plants in aridland landscapes and their response to environmental change. The hillslopes of aridland hills and mountains are excellent dust traps, and in favorable circumstances, weathering and dust entrapment promotes the development of thick, vegetated and smooth soil-mantled hillslopes. Toposequence studies in selected areas of the southwestern United States indicate that the presence of dust-entrapping colluvium is probably necessary to maintain AIP on hillslopes over long periods of time. Vegetation also promotes entrapment of dust, but vegetation on hillslopes is highly sensitive to episodic drought and/or fires that temporarily eliminate or drastically reduce vegetation cover. Episodically increased erosion potential prevents sustained AIP, and accumulated dust in soils is quickly transported from the hillslopes. Certain types of bedrock in aridland hillslopes weather rapidly and favor the development of soil-mantled, transport-limited hillslopes, but the typically thin, weakly developed soils are prone to rapid erosion, especially when subject to a combination of extreme drought followed by large increases in rainfall. Glacial-to-interglacial changes in climate also cause substantial changes in biotic communities, rates and processes of weathering, and soil development that influence the behavior of aridland hillslopes. Models that employ the soil production function have been developed recently to enable calculation of rates of soil production on soil- and vegetation-mantled upland hillslopes. The results of a half century of soil geomorphological research in aridlands, relying largely on the “CLORPT”-based approach, complemented by studies of the behavior of biotic communities in aridlands, suggest that maintaining the necessary conditions fundamental in the application of soil production functions in studies of hillslopes (transport solely by diffusive processes maintaining steady-state soil thickness and a spatially and temporally constant diffusion coefficient) for thousands to tens of thousands of years is highly unlikely in aridlands. Changing the word soil , in the term soil production function to the term mobile regolith will reduce confusion concerning the actual meanings of these different terms and facilitate a greater degree of integration of very different approaches in the study of soil landscape evolution.

Abstract Aeolian processes, involving erosion, transportation, and deposition of sediment by the wind, occur in a variety of environments, including the coastal zone, cold and hot deserts, and agricultural fields. Common features of these environments are a sparse or nonexistent vegetation cover, a supply of fine sediment (clay, silt, and sand), and strong winds. Aeolian processes are responsible for the emission and/or mobilization of dust and the formation of areas of sand dunes. They largely depend on other geologic agents, such as rivers and waves, to supply sediment for transport. Areas of sand dunes occur in inland and coastal settings, where they often provide a distinctive environment that provides habitats for endemic and rare or threatened species. In both coastal and inland settings, dune migration and sand encroachment may impact neighboring ecosystems and resources, as well as infrastructure. Transport of fine sediment by wind may cause dust storms, events in which visibility is reduced to less than 1 km by blowing dust. Dust storms impact air quality in their immediate vicinity as well as in areas downwind. Deposition of dust may have a significant effect on the composition and nature of soils in arid regions and beyond. Far-traveled dust from distant sources may have a significant effect on soil chemistry and nutrient status (e.g., Farmer, 1993 ).

Lakes in one form or another have characterized the western Mojave Desert since at least Miocene time. The most recent of these, Lake Thompson, developed in the late Pleistocene, when it covered as much as 950 km 2 and rose to at least 710 m above sea level. During Holocene time, the lake desiccated, and is now represented by Rogers, Rosamond, and Buckhorn dry lakes, which may flood up to 200 km 2 during unusually wet phases. The spatial dimensions of the former lake are defined by modest geomorphic and lithostratigraphic units, mostly exposed lake beds and beach ridges interbedded with and later mantled by fluvial and eolian deposits. The lake's temporal devolution is revealed by four cores, and ages are constrained by accelerator mass spectrometry 14 C dating of organic sediment. These cores show a deep perennial lake from before 36 ka to at least 34 ka, a shallow but variable perennial lake from before 26 ka to 21 ka, followed by lowering and at least partial exposure of the lake floor to deflation and alluviation. A shallow perennial lake returned during the terminal Pleistocene, from around 16.2 ka to at least 12.6 ka, forming distinctive beach ridges beyond the margins of the present dry lakes, and it may have reappeared in the early Holocene. During subsequent Holocene desiccation, lake segmentation occurred as waves and currents generated lower sequences of beach ridges around contracting lakes. These ridges became mantled with eolian sand, but, as fluvial sediment inputs diminished with increasing aridity, these dunes were degraded, and their roots survive today as indurated yardangs.