Two modern fluvial‐aeolian depositional systems (Great Sand Dunes National Monument, Colorado and the Mojave River Wash, California) are remarkably similar in spite of different climates, sizes, fluvial sediment textures, and relative directions of aeolian and fluvial transport. Dune growth and migration, and deflation of blowouts create 8–10 m of local relief in unflooded aeolian landscapes. There are six prominent fluvial‐aeolian interactions. (1) Fluvial flow extends into the aeolian system until it is dammed by aeolian landforms; (2) interdune areas (overbank‐interdunes) upstream of aeolian dams, and alongside channels are flooded; (3) water erodes dunes alongside channels and interdunes; (4) flood waters deposit sediment in interdune areas; (5) fluvially derived groundwater floods interdunes (interdune‐playas); (6) wind erodes fluvial sediment and redeposits it in the aeolian system. Unique and characteristic sediments are deposited in overbank‐interdunes and in interdune‐playas, reflecting alternate fluvial and aeolian processes and rapidly changing flow and salinity conditions. These fluvial‐aeolian interdune deposits are characterized by irregular, concave‐up bases and flat upper surfaces containing mudcracks or evaporite cement. Characteristic low‐relief surfaces form in aeolian systems as an effect of flooding. Fluvial deposits are resistant to aeolian deflation. Aeolian sand is preserved when flood sediments are deposited around the bases of the dunes. Thus repetitive fluvial and aeolian aggradation tends to be ‘stepwise’ as interdune floors are suddenly raised during floods. The effects of flooding should be easy to recognize in ancient aeolianites, even beyond the area covered with overbank muds.

An understanding of fluvial‐aeolian deposition derived from modern case‐examples in a previous study is applied to the Permian Cutler Formation and Cedar Mesa Sandstone on the Colorado Plateau. These formations supply an excellent three‐dimensional exposure of intertonguing fluvial and aeolian strata. Four distinct facies associations form the bulk of the Cutler Formation and Cedar Mesa Sandstone: (1) aeolian dune deposits; (2) wet interdune deposits; (3) fluvial channel deposits; and (4) overbank‐interdune deposits. In addition, two distinctive types of erosion surfaces are found within the Cutler Formation and Cedar Mesa Sandstone: pebble‐ to granule‐rich erosion surfaces (aeolian deflation surfaces) and flood surfaces. Fluvial and aeolian intertonguing result in extensive tabular sheets of aeolian sandstone separated by flood surfaces and overbank‐interdune deposits. Fluvial channels are associated with the deposits overlying flood surfaces and are incised into the underlying aeolian sandstones. Overbank‐interdune deposits and wet interdune deposits cover flood surfaces and intertongue with overlying aeolian sandstones. The primary characteristics of ancient fluvial‐aeolian deposition are overbank‐interdune deposits and pronounced extensive erosion surfaces (flood surfaces), which are parallel to underlying fluvial sandstones and thus trend parallel to the palaeoslope and palaeohydrological gradient.

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Abstract. Because geomorphology can readily be mapped, our ability to characterize unsaturated flow over large areas would be greatly enhanced if relationships between geomorphic settings and unsaturated flow could be identified. The purpose of this study was to evaluate relationships between geomorphic settings and spatial and temporal variability in unsaturated flow at a field site in the Chihuahuan Desert of Texas. This study differs from most previous studies in the variety of geomorphic settings studied, including drainage areas (Blanca Draw and Grayton Lake playa) and interdrainage areas (basin-fill deposits, eolian sheets, alluvial fans, and a fissure), density of data (-- Noninvasive techniques, such as electromagnetic (EM) induction and ground-penetrating radar, are becoming increasingly popular for evaluating unsaturated flow because they can be used to evaluate unsaturated flow rapidly over large areas and because they provide an evaluation of conditions between point measurements from boreholes. In an Australian study the correlation coefficient r between apparent electrical conductivity and recharge estimated according to unsaturated zone chloride data was 0. The geomorphic evolution of the landscape was described by Scanlon et al. [1999]. The study area has been subdivided into interdrainage and drainage areas. The interdrainage area consists of fine-grained basin-fill deposits and eolian sheets surrounded by a narrow rim of alluvial fans at the margin of the basin. An earth fissure is also found in the interdrainage area. The drainage area includes Bianca Draw and Grayton Lake.-The floor of Eagle Flat basin consists mostly of muds overlain by the Arispe Surface, which has well-developed soils. The basin-fill deposits are overbank deposits from the braided streams and from the toes of the alluvial fans. These deposits are stable, vegetated landforms that do not exhibit channels or erosional or depositionai features resulting from fluvial or alluvial activity. Three calcic soil horizons are found at depths of 0 to 1, 3, and 6 m, which suggest extremely stable conditions Boreholes were drilled with a hollow-stem auger without any drilling fluid, and samples were collected with a split spoon. Particle-size analyses were conducted on sediment samples from 37 boreholes using sieving and hydrometer analyses [Gee (Figure 1 and Table A1). Many samples were collected from the same boreholes as those that had been sampled for texture. To determine Samples were collected for tritium analysis from boreholes EF 79 and EF 117 in the interdrainage eolian sheet, EF 92 beneath the fissure, EF 96 10 rn from the fissure, and GL 2 in Grayton Lake. Water was extracted from core samples in the laboratory by toluene azeotropic distillation and purified using paraffin wax [Ingraham and Shadel, 1992]. The samples were enriched and analyzed using liquid scintillation methods at the University of Arizona Tritium Laboratory or using gas proportional counting at the University of Miami Tritium Laboratory. 4.Results and Discu...

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Descriptions of exposed salt structures help improve the ability to interpret the geometry and evolution of similar structures imaged in seismic reflection data from salt‐bearing sedimentary basins. This study uses detailed geologic mapping combined with well and seismic data from the southeastern end of the Gypsum Valley diapir (Paradox Basin, Colorado), to investigate the three‐dimensional geometry of the terminations of both the salt wall and its associated megaflap. The salt wall trends NW‐SE and is characterized by highly asymmetric stratal architecture on its northeastern and southwestern flanks, with thicker, deeper, gently dipping strata in the depositionally proximal (NE) minibasin and thinned older strata rotated to near‐vertical in a megaflap on the distal (SW) side. The megaflap terminates to the SE through a decrease in maximum dip and ultimately truncation by a pair of radial faults bounding a down‐dropped block with lower dips. East of these faults, the salt wall termination is a moderately plunging nose of salt overlain by gently southeast‐dipping strata, separated from the down‐dropped NE minibasin by a counterregional fault. From this analysis, and by comparison with analogue structures located elsewhere in the Paradox Basin and in the northern Gulf of Mexico, we propose a series of simple end‐member models in which salt walls and megaflaps may terminate abruptly or gradually. We suggest that controlling factors in determining these geometries include the original thickness and spatial distribution of the deep salt, the presence of nearby diapirs (which determines the fetch area for salt flow into the diapir), spatial patterns of depositional loading, and variations in the nature and location of salt breakout through the roof of the initial salt structure.