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

Abstract

The late Messinian Sorbas Member, up to 75 m thick, consists in it;; lype area of a parasequence sel of three prograding coastal barriers (sequences I-III). associated with lagoon and washover sedimenlS. Around the town of Sorbas these strata can be studied exceptionally wel! 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 careí'ully correlated. This permits to reconstruct and discuss pattems of relative sea-Ievel movements between decímetres. up to 15 m within a parasequence. Excellent examples oí' non-tidal transgressive facies are characterized by lagoon and washover sedimenls instead oí' the usual combinatíon oí' wa,hover and tidal deposits (channel and ftood-tidal delta). Implications í'or the sandstone connectivity are given. The lower two sequences are deposited in ,J, relatively tectonically enhanced wedge-shaped accommodation space. They show both fining-up, deepening sequences, followed by prograding eoarsening-up shoaling sequences and can be compared lO the c1assical parasequences of lhe 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 coasta! sands. The architecture of sequence lIT Is more complex due to limited accommodation spaee characterístic for the late híghstand, so tha! this sett'.ng was very sensitive to sea-Ievel tluctuations. This resulted in an intricate pattem of juxtaposed and superposed lagoonal muds, washover üms and swash zones. So-called 'stranded' coast;:J barriers occur, which were lef! behind after seaward Jump of the coastline over more than 1.5 km during forced regression. The pattem oí' reconstructed sea-Ievel 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-Ievel rise. The intluence oí' 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 ¡he Sorbas Member the sea withdrew from the Sorbas Basin, probably as a result of the majar downdrop in lhe Mediterranean at the maximum i,olation during the Salinity Crisis. It 15 suggested that the semi-enclosed selting of the basin resulted only in Iímited. localized eros ion, in contrast to the deeper adjacent Vera Basin, which was more open to the Mediterranean.

Late Miocene Mediterranean desiccation: topography and significance of the ‘Salinity Crisis’ erosion surface on-land in southeast Spain: Comment

“…It is this Sorbas-Zorreras contact that we consider the most likely candidate to reflect the Messinian drawdown event in the Sorbas Basin. As pointed out by Roep et al (1998) visual effects of erosion at this level are only locally developed, probably because the Sorbas Basin has been protected from vigorous erosion during the major drawdown event, caused by its topographically almost enclosed position towards the end of the Messinian. Indications for local, vigorous erosion that could be related to a downdrop event at this level can be found in the adjoining Vera Basin (Fortuin et al, 1995).…”

“…All Sorbas Basin investigators agree that the Yesares gypsum is conformably overlain by the Sorbas Member, a unit developed either as chiefly muds in the basin centre, or as prograding coastal sequences, well developed around the town of Sorbas (Roep et al, 1998). Riding et al (1999) conclude that the Sorbas Member reflects a normal marine environment and therefore has been deposited following marine reflooding of the basin after the drawdown event when the sill separating the basin from the Mediterranean was eliminated.…”

“…Basin specialists have found no clear evidence for a major erosional hiatus that is indicative of a large downdrop event (Roep et al, 1998). If there is any, they suggest, it is represented by local scours occurring at the top of the Sorbas Member ( Fig.…”

Astrochronology for the Messinian Sorbas basin (SE Spain) and orbital (precessional) forcing for evaporite cyclicity

“…The latter scenario requires a correlation of the Yesares Member to the`Upper Evaporites'/Lago Mare units and the Zorreras Member to the Pliocene (Dronkert, 1985;Cunningham et al, 1994;Riding et al, 1998). In contrast, the Zorreras Member is correlated to the latest Messinian, based on the observation of caspibrackish ostracod fauna with a strontium signal equivalent to the Lago Mare ostracods (latest Messinian) of the other Mediterranean basins (Mu Èller and Hsu È, 1987;Gautier et al, 1994;Roep et al, 1998).…”

“…The markedly cyclic alternation of gypsum beds and sapropellike sediments in the evaporite unit (Dronkert, 1985) suggests that these gypsum cycles are astronomically controlled as well, and hence that they are potentially suitable for astronomical dating purposes. In addition, also the post-evaporitic deposits show a distinct sedimentary cyclicity (Ott d'Estevou, 1980;Roep et al, 1998).…”