Publication: Late highstand patterns of shifting and stepping coastal barriers and
washover-fans (late Messinian, Sorbas Basin, SE Spain)
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Publication Date
1998-02
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Elsevier Science B.V.
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Abstract
The late Messinian Sorbas Member, up to 75 m thick, consists in its type area of a parasequence sel of three prograding coastal barriers (sequences I-III), associated With lagoon and washover sediments. Around the town of Sorbas these strata can be studied exceptionally well due 10 absence of burrowing by raised Messinian salinities and exposure along a network of up to 30 m deep canyons. Fifteen vertical sections were logged and careífully correlated. This permits to reconstruct and discuss pattems of relative sea-level movements between decímetres. up to 15 m within a parasequence. Excellent examples of non-tidal transgressive facies are characterized by lagoon and washover sedimenls instead of The usual combinatíon of washover and tidal deposits (channel and flood-tidal delta). Implications for the sandstone connectivity are given. The lower two sequences Are deposited in a relatively large tectonically enhanced wedge-shaped accommodation space. The show both fining-up, deepening sequences, followed by prograding coarsening-up shoaling sequences and can be compared to the c1assical parasequences of the Westem Interior Basin (USA). Progradation of sequence II was intemlpted by a major slide event (most likely triggered by an earthquake), which caused more than 400 m seaward slumping of a stretch of 1 km of coastal sands. The architecture of sequence III is more complex due to limited accommodation space characterístic for the late híghstand, so that this setting was very sensitive to sea-level fluctuations. This resulted in an intricate pattem of juxtaposed and superposed lagoonal muds, washover üms and swash zones. So-called "stranded" coastal barriers occur, which were lef behind after seaward Jump of the coastline over more than 1.5 km during forced regression. The pattem of reconstructed sea-level positions is weIl comparable to the sequential partem shown by the correlated equivalent, along the northem basin margin, which belong to the so-called Terminal Carbonate Complex. The problem of ranking the complex sequence III as one or more parasequences and it, consequences for cyclostratigraphy are shortly discussed. Two models of washover formation are given, respectively during more rapid and more slow sea-level rise. The intluence of synsedimentary folding on the location of barriers is discussed and also the source arca of extra and intraclasts supplied to barriers and washovers. After deposition of the Sorbas Member the sea withdrew from the Sorbas Basin, probably as a result of the majar downdrop in lhe Mediterranean at the maximum colation during the Salinity Crisis. It 15 suggested that the semi-enclosed selting of the basin resulted only in límited localized eros ion, in contrast to the deeper adjacent Vera Basin, which was more open to the Mediterranean.