科研之友
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摘要
Relict beach ridges of aeolian origin and associated soils are often used for inferring relative sea level and climate with contrasting results. Most studies link the aeolian coastal deposits to regressive phases, some to high sea-level stands, and a few to intermediate relative sea-level positions. %26lt;br%26gt;We interpret the apparent contradictions as indicating the lack of an over-arching concept and the inconsistent usage of sea level-related terms. In this paper we present an integrated morpho-sedimentological concept for a microtidal, mid-latitudinal coast and review existing data from the Levant (East Mediterranean) coast to evaluate the concept and to eliminate nomenclatural confusion. %26lt;br%26gt;A coastal depositional environment in a semi-arid environment consists of shallow-marine, aeolian and alluvial facies which together form an aeolian beach-ridge complex as a package of strata which respond simultaneously to sea-level change. A transgressive complex forms through reworking or overstepping of the coastal foredune and a regressive complex forms by downstepping. Under transgression the aeolian beach ridge represents the highstand deposit and its adjacent shallow marine sediment is the transgressive deposit. Under regression the complex represents the falling stage and the associated downdip surface marks the lowstand. %26lt;br%26gt;On the Levant coast we find chronologically well-constrained, offlapping aeolian beach ridges as parts of six downstepping beach ridge complexes formed between similar to 200 ka and 10 ka. The complexes represent the falling stage systems tract (FSST) of a short-lived (5th-order) depositional sequence when the shoreline shifted from a position close to the modern coastline to the shelf or below the shelf edge. Three of these FSSTs and their up dip and down dip super bounding surface together form the 4th order (similar to 100 ka) sequence of the last interglacial/glacial cycle. %26lt;br%26gt;The absence of transgressive, highstand and lowstand systems tract is explained by the poor preservation potential due to the small sediment budget of the complex. The falling stage complex has a high preservation potential because sediment source area increases while the sand drift potential remains above the local threshold. On the Levant coast, sand delivery to the backshore continued during relative sea-level falls for distances of up to 10 km between dune and coastline which is unprecedented in most modem analogues. %26lt;br%26gt;The significance of the dune-soil succession for climate is limited because the dunes are governed by relative sea-level change; the vegetation response to changes in precipitation is non-linear and the dune dynamics are characterised by low resilience and hysteresis.
- 出版日期2013-6
