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Sedimentary Evidence of Uppermost Early Aptian Sea Level Fluctuations of Glacio-Eustatic Previous HitMagnitudeNext Hit in the Western Maestrat Basin (Iberian Chain, Spain)

Bover-Arnal, Telm1
 Salas, Ramon2
 Moreno-Bedmar, Josep A.2
 Clavera-Gispert, Roger1
 Bitzer, Klaus1
 García-Sellés, David3

1Abteilung Geologie, Fakultät für Biologie, Chemie und Geowissenschaften, Universität Bayreuth, Bayreuth, Germany.
Departament de Geoquímica, Petrologia i Prospecció Geològica, Facultat de Geologia, Universitat de Barcelona,
Barcelona, Spain.
Departament de Geodinàmica i Geofísica, Facultat de Geologia, Universitat de Barcelona,
Barcelona, Spain.

The occurrence of high-frequency, high-amplitude sea level fluctuations along the Cretaceous has been a subject of controversy in recent years. The main driving mechanism governing such sea level oscillations is glacio-eustasy. The uppermost lower Aptian carbonate succession that crops out in the central Galve sub-basin (western Maestrat Basin) provides ample evidence of rapid high-amplitude sea level change and may contribute to a better understanding of the processes that governed sea level fluctuations during this stage. A highstand carbonate platform with rudist bivalves and corals largely constitutes these sediments. The top of this carbonate shelf presents a subaerial unconformity with a palaeokarst development. Basinwards, a forced regressive wedge lies at the toe-of-slope of the highstand platform. The relative height between the top of the preserved highstand strata and the top of the regressive deposits is 64 m. This height could be indicative of the Previous HitmagnitudeTop of this sea level drop. Several high-amplitude sea level falls have been reported from other coeval Tethyan sedimentary successions, suggesting a probable global occurrence of this sea level drop. The ammonites collected in the Galve sub-basin indicate that this relative sea level fall and the subsequent sea level rise occurred within the Dufrenoyia furcata biozone, which is considered to span around 1 My. Total subsidence curves measured in the Galve sub-basin show that the uppermost Early Aptian was characterised by an interval of subsidence deceleration, indicating that regional tectonism did not control this sea level drop. Hence, another mechanism or various mechanisms that could trigger a sea level fall of tens-of-meters in less than 1 My should be considered. Glacio-eustasy is the only known mechanism that falls into this domain. Therefore, at least one significant cooling event could have occurred along the late Early Aptian in support of this hypothesis. In this respect, several authors have proposed a mid-Aptian cooling episode. Despite of that the oxygen isotopes are largely susceptible to diagenetic alteration, the O-isotope curve measured in marl and bulk-rock samples throughout the succession displays a progressively cooling trend with temporary reversals from before the onset of the oceanic anoxic event 1a (OAE1a) to the preserved highstand deposits containing the Dufrenoyia furcata biozone.

AAPG Search and Discover Article #90100©2009 AAPG International Conference and Exhibition 15-18 November 2009, Rio de Janeiro, Brazil