The growth and subsequent dissolution of salts on or within sediment may alter sedimentary structures and textures to such an extent that it is difficult to identify the depositional origin of that sediment and, as a result, the sediment may be misinterpreted. To help to overcome such problems with investigating ancient successions, results are presented from a comprehensive study of the morphology and fabrics of three large areas of modern salt flats in SE Arabia: the Sabkhat Matti inland region and the At Taf coastal region, both in the Emirate of Abu Dhabi, and the Umm as Samim region in Oman. These salt flats are affected by tidal‐marine, alluvial and aeolian depositional processes and include both clastic‐ and carbonate‐dominated surficial sediments. The efflorescent and precipitated salt crusts in these areas can be grouped into two main types: thick crusts, with high relief (>10 cm) and a polygonal or blocky morphology; or thin crusts, with low relief (<10 cm) and a polygonal or blister‐like appearance. The thin crusts may assume the surface morphology of underlying features, such as ripples or biogenic mats. A variety of small‐scale textures were observed: pustular growths, hair‐like spikes and irregular wrinkles. Evolution of these crusts over time results in a variety of distinctive sedimentary fabrics produced by salt‐growth sediment deformation, salt‐solution sediment collapse, sediment aggradation and compound mixtures of these processes. Salt‐crust processes produce features that may be confused with aeolian adhesion structures. An example from the Lower Triassic Ormskirk Sandstone Formation of the Irish Sea Basin demonstrates how this knowledge of modern environments improves the interpretation of the rock record. A distinctive wavy‐laminated facies in this formation had previously been interpreted as the product of fluvial sheetfloods modified by soft‐sediment deformation and bioturbation. Close inspection of laminations seen in core reveals many of the same sedimentary fabrics seen in SE Arabia associated with salt crusts. This facies is the product of salt growth on aeolian sediment and is not of fluvial origin.
We propose that the so-called ''terminal fan'' facies model should be abandoned since it is flawed on several counts and it is leading to misunderstanding and poor communication. Rivers in drylands may experience excessive downstream discharge reduction such that they terminate subaerially rather than reach the sea or a lake. The facies model predicts that the distal reaches of such rivers form a network of bifurcating distributary channels producing a fan-shaped sediment body, with downstream thinning and fining of sedimentary units, ending in sand-filled ribbons encased in mud.Extensive review of modern rivers has failed to turn up convincing examples that fit the model. Rivers in drylands do not ubiquitously end in fans. Fan-shaped fluvial bodies are common wherever rivers are released from confinement and the discharge conditions promote frequent avulsion. Channels on such fans generally do not repeatedly bifurcate downstream. Where they are seen to do so, it can usually be shown they are lacustrine deltas inherited from wetter times. The term ''distributary'' is being used carelessly and is conveying incorrect understanding of sediment geometry and architecture. The proposed synonym of ''fluvial distributary systems'' is unsatisfactory as it perpetuates the same misunderstandings. Reliance on planform alone in analogue selection is highly risky.The fluvial fan is a composite sediment body resulting from frequent nodal avulsions in a setting without horizontal constraints. Channels on fans range in planform as much as any other river. The resultant sedimentary record differs little from that expected from non-fan fluvial systems except having a regionally radiating orientation when viewed over geological time scales. Contrary to the implications of the facies model, there is no distinctive ''terminal fan'' sedimentary succession.
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