RT Journal Article
T1 Strontium-isotope stratigraphy as a constraint on the ageof condensed levels: examples from the Jurassic of the SubbeticZone (southern Spain).
A1 Nieto, Luis M.
A1 Ruiz-Ortiz, Pedro A.
A1 Rey, Javier
A1 Benito Moreno, María Isabel
AB Condensed levels are often characterized by reworked fossils that may lead to incorrect age assessments. Strontium-isotope stratigraphy is an important chronostratigraphic tool that can be used to verify the biostratigraphic information from condensed beds. This paper describes a study of the 87Sr/86Sr isotope ratios of 56 belemnite samples collected from 28 stratigraphic sections of the boundary between the Upper Member of the Gavila´n Formation and the Zegrı´ Formation (Pliensbachian, Subbetic Zone). The petrographic and geochemical data (d18O, d13C, concentrations of Fe, Mn and Mg, and the Sr/Mn ratio) suggest that the belemnites have preserved their original marine geochemical composition. After plotting the samples in diagrams of 87Sr/86Sr values against time according to their biostratigraphic age, four different groups (A, B, C and D) were obtained with respect to the reference curve. In groups A and B, the age deduced from the Sr-isotope ratio is in total or partial agreement, respectively, with the biostratigraphic age; therefore the 87Sr/86Sr ratio is a good method for the dating, correlation and assessment of biostratigraphic results. In groups C and D, the SIS age and the biostratigraphic age do not coincide. A graphic procedure is presented as a suitable methodology to constrain the age of the samples showing an SIS age that differs from the relative age deduced (by biostratigraphy or stratigraphic correlation) for the bed they were collected in. These situations are interpreted as being the result of reworking of the belemnites (group C) or ammonites (group D) that are included in condensed levels. These condensed levels formed during the maximum flooding event that led to the drowning of the Gavila´n carbonate platform. The methodology supplied in this paper represents a valuable tool in identifying reworking processes, improving correlation and constraining biochronostratigraphic results. The values of 87Sr/86Sr represent a new contribution to the data set of 87Sr/86Sr ratios for the Pliensbachian.
PB Blackwell Publishing Ltd
SN 0037-0746
YR 2008
FD 2008
LK https://hdl.handle.net/20.500.14352/52343
UL https://hdl.handle.net/20.500.14352/52343
LA eng
DS Docta Complutense
RD 17 abr 2025