The sand sea that composes a large part of the Namib Desert in South West Africa covers approximately 34,000 km 2 and extends from the Great Escarpment on the east to the Atlantic Ocean on the west, south of the Kuiseb River. This sand sea, or erg, contains most of the principal dune types that have been recognized throughout the world, many of them of great height and separated by broad, flat interdunes. The dominant type and by far the most common form is the linear (seif, longitudinal) dune that extends as a series of long, nearly parallel ridges with north-south orientation across the length of the dune field. Studies of dune structure were made largely by trenching the various dune types to expose sections of cross-strata in selected parts. The trenches showed that those dunes attributed to unidirectional winds—barchan, barchanoid ridge, and transverse—with low-angle foresets on the windward sides and high angles on the lee sides, are mostly located along a narrow belt on the Atlantic Coast. The large interior dunes of linear type showed high-angle dips on both sides of the ridges and are believed to result from alternating two-directional winds. Because the genesis of these dunes has long been controversial, a review is given of the other principal hypotheses—deflation, helical roll, modification of simple dune forms, and outcrop-controlled lee-side accumulation—and evidence is presented for and against each. The most complex of dune types, in which arms radiate from a central point, is referred to as a star dune and is fairly numerous in various parts of the sand sea, especially near the vleis and along the northern dune margin. Such dunes are considered, both on the basis of data from trenching and from records of measured winds, to be the product of wind from three or more directions. Star dunes form along the ridges of linear dunes and also as isolated mounds on the desert floor, and they attain considerable heights. Minor dune types that are described and briefly discussed are those controlled by vegetation and referred to as coppice dunes. Also the small types known as dome dunes and blowouts, both of which were structurally analyzed, are discussed.

Abstract Eolian and adjacent deposits of Great Sand Dunes, Colorado form a small but sedimentologically complex deposit. Eolian sediments can be subdivided into three provinces trending downwind (northeast): I) low, (as much as 10 m high) alkali-cemented dunes forming discontinuous rings around broad, flat-bottomed, ephemeral lakes; II) undulating, vegetated dunes as high as 10 m, of barchan, parabolic shrub-coppice, and transverse type, with varying interdune types; III) high (as much as 200 m) transverse dunes with little or no vegetation and no true interdune deposits. Eolian deposits are in contact with, or intercalated with, fluvial, lacustrine, and alluvial-fan deposits and lap onto crystalline basement rocks of the Sangre de Cristo Range. Analysis of a 40-year span of aerial photographs and field observation of sand transport and cross-bedding dip directions indicate that the main dune mass (province III) is accreting vertically and that dune types are growing in complexity, in particular the star dunes. This change from lateral migration to vertical growth most probably reflects Holocene changes in wind regime. The Great Sand Dunes are an example of a localized, cool-climate, intermontane eolian deposit, characterized by extensive fluvial reworking. With its rapid variation in thicknesses, sedimentary structures, and associated sedimentary deposits, such a deposit would be difficult to interpret accurately in the ancient rock record. However, such a deposit could be of economic importance in petroleum and uranium exploration, and in aquifer evaluation.

Abstract The Holocene eolian barrier of the Younghusband peninsula, South Australia, is an accessible and well-studied modern analog for ancient eolian carbonate and mixed quartz-carbonate barriers, as well as the associated suites of sedimentary structures that might be expected in such settings. The barrier has formed from the shoreward drift of Lacepede Shelf biogenic carbonate fragments as well as the longshore drift of quartz sand from the Murray River. The Younghusband barrier carbonate content increases from roughly 12 percent at the mouth of the Murray River southeastward to nearly 75 percent at Lacepede Bay, near Kingston. The barrier consists mainly of eolian dune and sand-sheet deposits. Dune bedforms consist of parabolic, blowout, coppice, and various subtypes of transverse dunes including barchan, barchanoid ridge, and transverse ridge dunes. There is a low foredune along the shore, landward of which lies a narrow sabkha mat separates this foredune from the main barrier. Where vegetation has been destroyed or thinned, deflation forms large blowouts, parabolic dunes, and transverse dunes, whose advance is causing the barrier to shift northeastward into the Coorong Lagoon. The abundant carbonate material within the barrier includes transported bryozoans and coralline algae that originated on the cool-water Lacepede Shelf. These materials, along with broken shells of lagoonal and nearshore fauna such as gastropods and mollusks, have been incorporated into the cross stratification. This process has produced such coarse, shelly textures in the eolian barrier sediments, particularly the sand-sheet deposits, that it would be difficult to identify these sediments as eolian in the ancient record. This is not merely because of the presence of shell debris but also because of unusual sedimentary structures. Nevertheless, common eolian sedimentary features are present and identifiable, and provide a key to proper interpretation of this group of sediments in ancient rocks. The Holocene Younghusband barrier and the landward Pleistocene carbonate barriers are viable analogues for subsurface petroleum reservoirs. The Younghusband barrier, if buried and preserved, would be a very narrow but elongate sand lens about a kilometer wide at maximum, and up to 30 meters thick, with enormous reservoir volume because of its great length. It would consist mainly of clean eolian sands, composed dominantly of either quartz or carbonate depending upon position along the barrier. These sediments would be interbedded with nearshore and lagoonal facies (potential source rocks). Recognition of the eolian nature of such a barrier-originated petroleum reservoir would allow correct paleogeographic placement of the sediments, and would facilitate both development drilling and further exploration for new barriers or extensions of the current field. Further, the knowledge that the modern barriers exist in trends controlled by sea-level stands would suggest that petroleum reservoirs in such ancient systems might occur in multiple fields parallel to bathymetric contours of an ancient marine shelf. The current preservation of eolian parts of older barriers in the South Australia region onshore but below sea level (observed in shallow-drilling programs) and offshore as subsea “ranges” proves that such preservation of the eolian component of barriers is not only possible but should be expected in the ancient record.