Variations in sedimentology, mineralogy and geochemistry on a turbiditic continental margin during an early Eocene negative carbon isotope excursion

Expanded deep-marine sedimentary successions were deposited on the North Iberian continental margin in Eocene times. These deposits are well exposed along accessible coastal cliffs of the Biscay province, being of great interest for paleoenvironmental and paleoclimatic studies. This study dealt with the 110 m-thick lower Ypresian (early Eocene) succession from Solondota, which is mainly composed of hemipelagic limestones and marls interspersed with abundant turbidites.

Biomagnetostratigraphic and geochemical records allowed correlation of a prominent negative carbon isotope excursion (CIE) with the Ypresian hyperthermal event J, also known as C24n.2rH1. In order to disentangle the environmental evolution of the Solondota turbiditic area during the CIE, high-resolution sedimentological, geochemical (stable isotopes, major, minor and trace elements) and mineralogical (general and clay mineralogy) studies were carried out. The large size of the dataset hindered straightforward identification of relevant variables and interpretation of their relationships. However, a multivariate analysis provided invaluable information about significant trends and variations in the dataset, avoiding empirical or arbitrary selection of representative elements. A good correspondence was found between some elemental trends obtained from the analysis and the sedimentological and mineralogical records. Major and minor elements from the hemipelagic fraction across the Solondota CIE suggest a temporarily more humid continental climate, which caused increased terrigenous material input into the marine environment. While fine-grained terrigenous sediment boosted hemipelagic carbonate dilution, the coarser terrigenous sediment was transported by temporarily more frequent and voluminous turbidity currents. Thus, the results from the Solondota CIE show similarities with deep marine records from other early Eocene minor hyperthermal events. Taking everything into account, this study demonstrates the validity of deep-marine turbiditic successions for providing reliable sedimentological, mineralogical and geochemical records of paleoclimatic significance. Indeed, the expanded nature of turbiditic continental margin successions provides paleoenvironmental records at very high resolution, enriching, and perhaps improving, the commonly condensed and sometimes discontinuous record of hemipelagic-only successions.

 

Research funded by the Spanish Government project MCI PID2019-105670GB-I00 and the Basque Government project IT-930-16. NM-B received a pre-doctoral grant from the Basque Government and a post-doctoral Dokberri grant from the University of the Basque Country.