Linear dunes are the most abundant type of desert dune and the dominant land-form on the continent of Australia. This paper reports the results of GPR surveys across linear dunes in the deserts of central Australia including parts of the Simpson and Strzelecki deserts. The GPR data suffered from severely limited penetration and poor resolution due to signal attenuation associated with a high proportion of mud, which, probably due to progressive illuviation, increases with dune age. However, although such conditions prevail in much of central Australia, useful stratigraphic information can still be obtained there using GPR. Buried palaeosol horizons within dunes have been identified, and taken in conjunction with thermoluminescence (TL) ages from the dunes, it is possible to make some interpretations of linear dune evolution. TL ages show that some dunes are older in the south and young toward the north. It is possible to place some constraints on rates of vertical, lateral, and dune-front accretion within the linear dunes with ∼2–6 m, 0–50 m and 3000 m, respectively, over the last ca. 10 ka. The combination of GPR profiles and TL dating of linear dunes in the Simpson and Strzelecki deserts confirms Holocene modification of preexisting linear dunes with minor easterly accretion that has contributed to the asymmetry of vegetated linear dunes in central Australia. The results support the hypothesis that linear dunes in Australia are composite forms with a long and sometimes complex history.

Subaerial exposure surfaces in the Middle and Upper Mississippian Slade Formation of northeastern Kentucky are largely composed of cutanic concentrations of micritic calcite within the former Ccam horizons of caliche soils. The association of this material with soil horizons and structures, as well as with abundant root traces, strongly indicates a pedogenic origin. In fact, the contribution of plants and small soil organisms was far greater than has been previously recognized. The caliches occur as “interformational” profiles on disconformities separating lower Slade members and as “intraformational” profiles within three lower Slade units. Paleoexposure was related to position on a structurally active margin of the Appalachian Basin and to episodes of regional and local regression. The caliches resulted from soil and ground-water conditions in a semi-arid climate characterized by seasonal rain and drought and an overall net moisture deficit. Growth of roots, desiccation, and displacive crystallization broke up parent limestones, allowing access of vadose waters and creating framework (skeleton) grains that were easily transformed into a mobile plasma fraction by solution. Solution of carbonate grains and eluviation of carbonate-bearing solutions primarily occurred during the moist rainy season, whereas illuviation rapidly followed the onset of drought. The calcium carbonate was deposited largely as internal, laminar plasma concentrations called cutans, which have been incorrectly referred to as “crusts” in previous work on the Slade. Accumulation of these cutanic laminae formed indurated laminar calcrete deposits near the bases of the caliche profiles. These calcretes may be of physicochemical or rhizocretionary origin, depending on conditions of exposure. More diffuse, irregular calcretes apparently developed along avenues of porosity and were formed by plasma separation, the in situ micritization of other limestone textures. Although climate in the Meramecian and earliest Chesterian epochs was the major factor responsible for caliche formation, the length of exposure and the type of carbonate lithology controlled the nature and thickness of caliche profiles. “Intraformational” profiles are always thin and immature, representing short-lived exposure on porous lithologies like calcarenite. Conversely, “interformational” profiles are always mature or composite and represent longer periods of exposure on more impermeable lithologies such as calcilutite. Impermeable lithologies were important, because they prevented migration of soil waters and plasma below the soil profile. By late Early Chesterian time, the climate had become more humid, and the latest formed caliches were partially destroyed by solution, creating a leached, clayey residual soil on top of earlier caliche soils. On structurally elevated areas, where exposure was long and drainage was good, this period of humid pedogenesis resulted in composite terra rossa paleosols produced from the humid weathering of older caliche profiles.