The OAE1a in Cuchía (Early Aptian, Spain): C and O geochemistry and global correlation

Abstract

ABSTRACT:García-Mondéjar, J., Fernándes-Mendiola, F. and Owen, H.G. 2015. The OAE1a in Cuchía (Early Aptian, Spain): C and O geochemistry and global correlation. Acta Geologica Polonica, 65 (4), 525-543. Warszawa.C-isotopes, TOC and O geochemical data from the lower Aptian Cuchía section in the western BasqueCantabrian basin (BCB) allow an accurate delimitation of the OAE1a-equivalent and its geochemical Menegatti´s segments, a detailed δ 13 C carb correlation with regional and interregional sections, and a high-resolution construction of TOC and bulk-rock δ 18O carb curves and their interpretation. The δ 13C carb values range from -2‰ and +4‰ (VPDB). They agree with previous data from the eastern BCB sections (Aralar) confirming the ammonite age of the OAE1a in the Basque-Cantabrian basin: Deshayesites forbesi, Deshayesites deshayesi, and Deshayesites deshayesi-Dufrenoyia furcata transition Zones. Interregional δ 13 C carb correlation with pelagic (Cismon, Italy, and Mid-Pacific Mountains, DSDP Site 463) and neritic (Roquefort-La Bédoule, France) core sections, reveals a common profile of a wide negative excursion characteristic of the OAE1a. It consists of a double trough separated by a flat relative maximum, with two negative spikes in the upper trough of neritic sections. TOC absolute values range from 0.12% to 1.37%. Segments of the TOC curve with persistent low values closely correspond with descending segments of the δ 13 C carb curve, and are attributed to lesser organic productivity in the BCB. Detailed bulk-rock δ 18O carb data (-5.71‰ to -1.05 ‰ PDB) and variation curve show two main positive O-isotope shifts and three minor positive inflections, within a general negative trend characteristic of the OAE1a. The two major positive shifts correspond to both shallowing upwards sequences and the lowermost can be related to a eustatic sea level fall. Independent interregional correlation of the O-isotope shifts with C-isotopes supports their interpretation as punctuating colder events within a general warming trend.

The Early Aptian (Cretaceous) stratigraphy of Mount Pagasarri (N Spain): Oceanic anoxic event‐1a

“…( M .) parva in the top of the Early Aptian, a view supported by Masse () and in the Mount Pagasarri area as well as in other recent reviews of the Basque‐Cantabrian Basin (Fernández‐Mendiola et al, ; García‐Mondéjar, Owen, Raisossadat, Millán, & Fernández‐Mendiola, ; García‐Mondéjar, Owen, et al, ; García‐Mondéjar, Fernández‐Mendiola, & Owen, ; Millán, Weissert, Fernández‐Mendiola, & García‐Mondéjar, ).…”

“…The OAE1a in the Mount Pagasarri succession spans the oglanlensis (top part) and forbesi and deshayesi (lower part) Zones and correlates positively with Aralar and Cuchía succession (García‐Mondéjar, Owen, et al, ; Millán et al, ). A similar age is reported in Cassis‐La Bédoule (García‐Mondéjar, Fernández‐Mendiola et al, ; García‐Mondéjar, Owen, et al, ; Lorenzen et al, ).…”

“…The growth of this Urgonian platform is coincident with the Kharaibian Persian Gulf carbonate platform (Granier & Busnardo, ), and with the Madotz carbonate platform of the oglanlensis Zone. The age of the demise is oglanlensis in Madotz‐Aralar Mountains and the Umbrera platform of the Cuchía section (García‐Mondéjar, Fernández‐Mendiola et al, ; García‐Mondéjar, Owen, et al, ; Figure ), whereas in Granier and Busnardo (), a forbesi age is recorded for the demise episode, pointing to a diachronous boundary for different locations within the Tethys. The low sea‐level stand marked in the Vercors by incised valleys tens of kilometres in length and up to 30 m in depth (e.g., Arnaud‐Vanneau & Arnaud, ) could be time equivalent.…”

“…Early Aptian stratigraphic correlation between the Aralar and Mount Pagasarri areas. Three main carbonate platform development phases are recognized: Phase 1 is D. oglanlensis and occurs in the Aralar area (Abrevadero limestone of the Madotz event, Millán et al, ) and also corresponds in the Cuchía area to the Umbrera Formation (García‐Mondéjar, Fernández‐Mendiola et al, ; García‐Mondéjar, Owen, et al, ). Phase 2, deshayesi‐furcata transition, is recognized in the Aralar area (Sarastarri Formation) and also in the Cuchía area (San Esteban Formation), and Phase 3, furcata , is present in the Bilbao area (Peñascal Formation).…”

Aptian carbonate platform development in the Southern Iberian Palaeomargin (Prebetic of Alicante, SE Spain)

“…et al, 2014), similar to those of the co-eval Llopis Formation. Meanwhile, though rudists are not mentioned from the coralbearing Umbrera Formation in the northern Spanish Basque-Cantabrian Basin, García-Mondéjar et al (2015a, 2015b describe these shallow-water calcarenites as being overlain by ammonite-rich marly facies of the Patrocinio Formation, the first metres of which record the C3 to C6 segments of Menegatti et al (1988). Thus, as with the Llopis Formation, the termination of the Umbrera Formation likewise predated the positive excursion phase of OAE1a.…”