A revised age-model for the Eocene deep-marine siliciclastic systems, Aínsa Basin, Spanish Pyrenees

Abstract

Using new palaeomagnetic and biostratigraphic data, we revise the age-model for the middle Eocene, deep-marine Aínsa Basin (Spanish Pyrenees), a tectonically active basin formed at a convergent-plate margin. This new age model provides a framework for evaluating the depositional history and sediment accumulation rates. New integrated magneto- and biostratigraphy data identify two normal and two reverse chrons of the geomagnetic polarity timescale (C21r, C21n, C20r, C20n) and place these Upper Hecho Group deposits in the middle Eocene (Lutetian). Nannofossil analysis identifies a biostratigraphic range from Subzone NP14b in the Gerbe System to Subzone NP15b at the top of the Aínsa System using key, age-diagnostic marker species such as Blackites inflatus, Blackites piriformis and Coccolithus gigas. We also present new nannofossil biostratigraphy from the Lower Hecho Group. This new Aínsa Basin chronostratigraphy enables inter-basinal correlations between the proximal fluvio-deltaic Tremp-Graus Basin and the more distal Jaca Basin, thereby providing a better understanding of the basin evolution.Supplementary materials: Field photographs of the sampled sections, magnetostratigraphic results, biostratigraphy results, alternative age model scenario and discussion on previous age model are available at https://doi.org/10.6084/m9.figshare.c.5083076

Magnetostratigraphy and stable isotope stratigraphy of the middle-Eocene succession of the Ainsa basin (Spain): new age constraints and implications for sediment delivery to the deep waters

“…Detrital zircon (U-Th)/He ages for the Arro sandy system support the hypothesis of shortfrequency tectonic or climatic pulse during the deposition of this system (Thomson et al, 2017). More recently, nannofossil Subzone NP14a was identified in the Arro SGF system that could be associated with both sea-level highstand or lowstand (Cantalejo et al, 2020). From Banaston to Guaso SGF systems, the relationship between sea-level, sediment supply, tectonic and climatic modulations causing siliciclastic deposition in deep marine environment remain poorly known and acknowledged.…”

“…The activation of La Fueba thrust system is coeval with major truncation in the Ainsa basin and induced deformation of the lower Hecho Group (Muñoz et al, 2013). In comparison, the upper Hecho Group (Gerbe, Banaston, Ainsa, Morillo and Guaso SGF systems) deposited during the Lutetian (Mochales et al, 2012a;Cantalejo et al, 2020) is less deformed despite the active tectonic evolution of the basin (Pickering and Corregidor, 2005). During the middle Eocene (early Lutetian), the Sobrarbe fold system was developed.…”

“…The Ainsa basin was developed from Lutetian to Priabonian times (Bentham and Burbank, 1996;Pickering and Corregidor, 2005;Payros et al, 2009;Mochales et al, 2012a;Cantalejo et al, 2020). Structurally, the basin is defined by its confinement between the lateral ramp of the Peña Montañesa-Montsec to the east, as well as the Gavarnie thrust and Boltaña anticline today to the west (Figs.…”

“…SGF systems were deposited during Ypresian and Lutetian (lower to middle Eocene) ages (Bentham and Burbank, 1996;Pickering and Corregidor, 2005;Payros et al, 2009;Cantalejo et al, 2020). The sand-shale packages of the Ainsa basin have been extensively described and studied (e.g., Mutti, 1983;Mutti et al, 1985;Remacha and Fernández, 2003;Pickering and Corregidor, 2005;Pickering and Bayliss, 2009;Pohl and McCann, 2014;Pickering, 2014, 2015;Clark et al, 2017;Cantalejo et al, 2020) but one of the main issues in deciphering the relative roles of external forces on stratigraphic records remains the availability of a robust chronostratigraphic framework that could be used to tune geochemical proxies in the basin. From Fosado to Banaston SGFs, noted that the stratigraphic cycles detected in the Ainsa basin have periodicities of approximately 1 Myr (Million year).…”

“…The main task of this study was thus to improve the chronostratigraphic constraints on the studied succession in order to tune newly acquired geochemical proxies. Several studies and age models based mainly on biostratigraphy (Jones et al, 2005;Pickering and Corregidor, 2005; and magnetostratigraphy (Holl and Anastasio, 1993;Bentham and Burbank, 1996;Mochales et al, 2012a;Cantalejo et al, 2020) exist in the Ainsa basin. To build on these existing datasets, three approaches were used conjointly: magnetostratigraphy, stable isotope stratigraphy and biostratigraphy.…”