Chemostratigraphic signals and sea-level changes from the Jurassic and Early Cretaceous in the Sierra de Quipar: Betic Cordilleras, southern Spain
Title:
Chemostratigraphic signals and sea-level changes from the Jurassic and Early Cretaceous in the Sierra de Quipar: Betic Cordilleras, southern Spain
Author:
Rey, J. Delgado, A.
Appeared in:
GFF
Paging:
Volume 127 (2005) nr. 1 pages 25-32
Year:
2005-03-01
Contents:
Positive carbon-isotope excursions have been recorded within the Jurassic-Early Cretaceous sedimentary successions in the pelagic facies of the External Zones of the Betic Cordilleras. Despite significant impact of diagenesis, the observed changes in $13C can be correlated with deep-water sections from different Tethyan basins. There exists a correspondence between sea-level curves and the carbon-isotope profile, which suggests a relationship between the two phenomena. Early Toarcian, middle Oxfordian and Valanginian high $13C values related to global transgressions are documented. Additionally, the values of $18O may be influenced not only by global factors (isotopic composition and temperature of seawater) but also by local tectonics: in the pelagic swells, subsidence and uplifts lead to changes in depth, and thus, in the rate of sedimentation and in the diagenetic conditions. The evolution of $18O values is compared in pelagic troughs and pelagic swells during the late Tithonian-Valanginian. In deeper sites, $18O-depleted values could reflect diagenesis at higher burial temperatures. On the crest of tilted blocks higher $18O values are preserved. The isotopic evolution is compared with previous studies on facies and tectonics. This comparation reveal the importance of local or global factors in the genesis of the sedimentary breaks of the region. It is shown that the main sedimentary breaks of this paleomargin, in particular the intra-Carixian and the Dogger-Malm boundaries are controlled by regional tectonics.
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