First record of early Aptian Oceanic Anoxic Event 1a from the Paris Basin (France) - Climate signals on a terrigenous shelf

In 2013, Andra (French National Radioactive Waste Management Agency) drilled boreholes to the south-east of Paris Basin, characterise Aptian and Albian clayey formations, including ‘Argiles à Plicatules’ Formation dated as early Aptian. One these intersected this formation with an excellent recovery allowing detailed biostratigraphy (ammonites), sedimentology, clay mineralogy, isotope geochemistry (?13Corg) Rock-Eval analyses be performed. The base corresponds transgressive dark-grey silty clays iron oolites plant debris indicating a coastal environment evolving up-section upper offshore environments. Higher in succession, less than 4% CaCO3 0.8% organic matter were deposited lower occurrence ammonites can used draw biostratigraphic scheme, particular, recognise deshayesi furcata ammonite Zones. mineral assemblages are composed illite kaolinite associated minor amounts chlorite, vermiculite smectite. ?13Corg values range between ?24 ?25‰ except particular interval characterised by prominent negative excursion about ?3‰, that is recognised worldwide precedes Oceanic Anoxic Event 1a (OAE1a). This also abundance absence smectite suggesting acceleration hydrological cycle enhanced runoff hydrolysing conditions over emerged landmasses just before during onset OAE1a. climate change consistent palynological data warm humid Surprisingly, corresponding OAE1a not significantly enriched its lithology different from rest core Tethyan anoxic water masses did reach relatively shallow epicontinental environments Basin.