AUTHOR=Melinte-Dobrinescu Mihaela , Ion Gabriel , Anton Eliza , Apotrosoaei Vlad , Briceag Andrei , Lazăr Constantin 

TITLE=First record of Oceanic Anoxic Event 2 in the Eastern Carpathians: implications for chemostratigraphic and biostratigraphic correlations

JOURNAL=Frontiers in Earth Science

VOLUME=11

YEAR=2023

URL=https://www.frontiersin.org/journals/earth-science/articles/10.3389/feart.2023.1155482

DOI=10.3389/feart.2023.1155482

ISSN=2296-6463

ABSTRACT=<p>This study aims to investigate a marlstone and claystone succession located at the southern end of the Eastern Carpathians, a region where oceanic anoxic event 2 (OAE2) has not been pointed out so far. Toward the upper half of this succession, a 17-cm-thick black shale was identified. The investigated depositional interval lies within the late Cenomanian–early Turonian, encompassing the UC3d up to UC7 nannofossil zones. The δ<sup>13</sup>C values fluctuated between 2.06‰ and 3.89‰, showing a positive isotope excursion that was assigned to OAE2. The δ<sup>13</sup>C isotope curve displays the following intervals: pre-excursion, first build-up, trough, second build-up, plateau, and post-excursion. Within the second build-up interval of OAE2, a substantial shift in CaCO<sub>3</sub> values, accompanied by high concentrations of total organic carbon and a significant decline in the abundance and diversity of calcareous nannofossil assemblages, was observed. The nannofossil turnover related to OAE2 climax revealed predominance of <italic>Watznaueria barnesiae</italic> and temporary disappearance from the record of surface-water higher fertility taxa, such as <italic>Biscutum constans</italic>, <italic>Zeugrhabdotus erectus</italic>, and <italic>Discorhabdus ignotus</italic>. Above OAE2, peaks of <italic>Eprolithus floralis</italic>, followed by increased abundance of <italic>Eiffellithus turriseiffelii</italic> and <italic>Nannoconus</italic> spp., were identified. In the lower part of the studied succession (i.e., the upper Cenomanian UC3d nannofossil subzone), during the pre-excursion characterized by low δ<sup>13</sup>C values and less negative δ<sup>18</sup>O values, a small group of nannofossils more related to mid- and high-paleolatitudes, such as <italic>Crucibiscutum salebrosum</italic>, <italic>Repagulum parvidentatum</italic>, and <italic>Seribiscutum primitivum</italic>, is present, always showing a low abundance.</p>