Depositional environments and carbon isotope excursions of the Middle Oxfordian (Transversarium Zone) sediments in the Central Saharan Atlas, Southwestern margin of the Tethys

Abstract

This study examines the Middle Oxfordian sediments of the Theniet Et-Temar Formation in the Central Saharan Atlas (NW Algeria), which was located in the southwestern part of the Tethys Ocean during the Late Jurassic. Using microfacies analysis and δ13Ccarb isotopes, this research aims to elucidate the sedimentological and isotopic signatures of these sediments.Ten microfacies types were identified and grouped into four facies associations: nearshore (FA1), inner lagoon (FA2), shoal bar (FA3), and outer lagoon (FA4). Sequence stratigraphy, employing the T-R sequence concept, delineates the evolutionary stages of the studied succession into prograding deltaic front facies (LST1), retrogradational open marine facies (TST2), and deltaic plain facies within the highstand systems tract (HST2).Stable carbon isotopes from three sections namely, El Bayadh, Ghassoul, and Sidi Tifour of the Middle Oxfordian (Transversarium Zone) provide insights into carbon cycle perturbations and paleoenvironmental conditions. There are two δ13Ccarb excursions in the studied sections. A major positive excursion in the El Bayadh, Ghassoul and Sidi Tifour sections shows similar records in both southern (Saudi Arabia, Iraq) and northern Tethys regions (France, Poland, Scotland, Spain, Switzerland, and Uzbekistan). The negative δ13Ccarb shifts with values of −2.77‰ at the top of the Ghassoul section and −2.28‰ in the middle member of the Sidi Tifour section are coupled with more negative δ18Ocarb values suggesting alteration of isotopic values due to meteoric diagenesis.The variations in carbon isotopes suggest synchronous changes in the global marine dissolved inorganic carbon pool, potentially influenced by sea level fluctuations, climatic changes, and/or Jurassic dysoxic to anoxic events.