Relating eolian bounding-surface geometries to the bed forms that generated them: Etjo Formation, Cretaceous, Namibia. Subsequent erosion has resulted in the exposure of these bed forms and provides a rare opportunity to accurately reconstruct the three-dimensional geometry of an ancient eolian system and to relate bed-form morphology to bounding-surface geometries. The bounding surfaces of a bed form its upper and lower surfaces and represent intervals of non-deposition or erosion. Most beds that are produced are never preserved; they are eroded by subsequent events. The recognition and use of bounding surfaces continues to be a problem in the study of modern and ancient aeolian sediments. Further, aeolian deposition and preservation is more complex and episodic than can be accommodated by the restrictive requirements of the climbing bedform model.
In geology, the sedimentary structures known as cross-bedding are the (near-) horizontal units that are internally composed of inclined layers. Cross bedding forms during deposition on the inclined surfaces of bedforms such as ripples and dunes, and indicates that the depositional environment contained a flowing medium (typically water or wind). Trough cross-bedding, on the other hand, consists of cross-bedded units in which the bounding surfaces are curved, and hence limited in horizontal extent. In cross-section, 2D bedforms have identical forests and bounding surface strikes. 3D bedforms have sinuous crestlines and troughs (in plan or elevation) or variable across-crest profiles giving 3D cross-bedding. Bedform cross sets are nearly ubiquitous in sandy fluvial strata and provide a detailed record of bedforms as a function of flow and sediment transport conditions over short timescales.
Bounding surfaces and interdune deposits provide keys for detailed interpretations of aeolian bedforms, as well as overall sand sea conditions. Scallops deposited by alongslope-migrating, superimposed bedforms have cross-bed and bounding-surface dip patterns that lack bilateral symmetry and have cross-bed dips that are asymmetrically distributed relative to bounding-surface dips. Scallops deposited by alongslope-migrating, superimposed bedforms have cross-bed and bounding-surface dip patterns that lack bilateral symmetry and have cross-bed dips that are asymmetrically distributed relative to bounding-surface dips. A bedform is a depositional feature whose genesis is through the action of a forcing fluid (e. 2D bedforms have identical foresets and bounding surfaces strikes.