Environmental changes and platform demise during the early Aptian OAE 1a (Prebetic platform, western Tethys)
| Autor: | Castro, José Manuel, Quijano, María Luisa, Gea, Ginés A. de, Jiménez de Cisneros, C., Ruiz Ortiz, Pedro, Caballero, Emilia, Pancost, Richard |
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| Rok vydání: | 2019 |
| Zdroj: | Digital.CSIC. Repositorio Institucional del CSIC instname |
| Popis: | 34th IAS Meating of Sedimentology, helded in Rome (Italy), 10-13 September, 2019 It has been widely accepted that the Early Aptian demise of carbonate platforms in the Tethyan realm reflects the impact of environmental changes that eventually led to the deposition of organic organic-rich basinal sediments during Oceanic Anoxic Event (OAE) 1a. Here we present the study of an Early Aptian section from the Southern Iberian Paleomargin (SIP, western Tethys), where an Early Aptian carbonate platform is covered by hemipelagic organic-rich sediments recording the OAE 1a. The Almadich Fm. (Lower Aptian) is a characteristic feature of the distal parts of the Prebetic platform (deposited on the SIP) and crops-out extensively in the so-called Prebetic of Alicante (SE Spain). It is a hemipelagic unit intercalated between the shallow carbonate platform materials of the Llopis Formation (Lower Aptian) and the Seguilí Formation (Upper Aptian). We have carried out a multidisciplinary study of the Agres section in the Sierra de Mariola (Alicante), including stratigraphy, biostratigraphy, geochemistry (C and O stable isotopes, trace and major elements, biomarkers) and mineralogy, embracing the uppermost part of the Llopis Formation and the Almadich Formation. The biostratigraphic study included planktonic foraminifers and calcareous nannofossils, and integrated previous data on ammonites leading to a precise dating of the late Early Aptian to early Late Aptian interval. The OAE 1a has been identified from the integration of the C-isotope stratigraphy and biostratigraphy. Our data indicate enrichments and oscillations in the redox-sensitive trace elements concentrations within the OAE 1a interval. Calcite is the dominant mineral, although quartz is abundant in some levels, and clays are minor components, composed of muscovite and illite. Biomarkers are dominated by n-alkanes, derived from marine and continental plants, isoprenoids (pristane and phytane) of marine origin, hopanes, derived from bacteria, and steranes, originated from eukaryotic organisms; lycopane is also locally present, and could indicate anoxic conditions during sedimentation. The presence of 2-methylhopanoids is interpreted as a proxy for environmental stress. The data integration has allowed the recognition of the timing of events related to the establishment of hemipelagic conditions in the distal Prebetic during the Early Aptian: a first episode of environmental change that occurred during the deposition of the shallow carbonate platform (Llopis Formation) gave place to the deposition of the mixed siliciclastic-carbonate Agres Bed, under more open marine conditions with a higher nutrient content in the waters. Subsequently the platform was affected by a complex drowning event marked by the deposition of the hemipelagic sediments of the Almadich Formation. The onset of the OAE 1a (negative C-isotope excursion) was coeval to final stages of deposition and the demise of the carbonate platform, and the overlying hemipelagic deposits record the subsequent main phase of development of OAE 1a (positive C-isotope excursion). This study documents the interaction between regional and global factors controlling the sedimentation during the early Aptian OAE in the Prebetic. |
| Databáze: | OpenAIRE |
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