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Late highstand patterns of shifting and stepping coastal barriers and washover-fans (late Messinian, Sorbas Basin, SE Spain)


Roep, Th.B. and Dabrio, Cristino J. and Fortuin, A.R. and Polo Camacho, María Dolores (1998) Late highstand patterns of shifting and stepping coastal barriers and washover-fans (late Messinian, Sorbas Basin, SE Spain). Sedimentary Geology, 116 (1-2). pp. 27-56. ISSN 0037-0738

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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. They
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.

Item Type:Article
Uncontrolled Keywords:Messinian; Sea-level fluctuations; Beach barriers; Washover fan; sequence stratigraphy
Subjects:Sciences > Geology > Stratigraphic geology
ID Code:10643
Deposited On:12 May 2010 10:48
Last Modified:12 May 2010 10:48

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