Mid-Cenomanian Event Controls the Bioproductivity and Organic Preservation of Bituminous Limestones From North Jordan

Document Type

Article

Source of Publication

Geological Journal

Publication Date

1-14-2026

Abstract

The Mid-Cenomanian event has been recognised in a sedimentary outcrop exposed in north Jordan. A section belonging to the Cenomanian was logged in the Ajloun area to investigate calcareous nannofossil biostratigraphy, microfacies, the carbon and oxygen isotope composition and elemental compositions. The Ajloun section is assigned to the UC-2 biozone (early Cenomanian) based on the occurrence of the calcareous nannofossil marker species Gartnerago segmentatum and Cylindralithus sculptus. The first occurrence of Lithraphidites acutus in Sample 18 marks the base of the UC-3 biozone (middle Cenomanian). The Ajloun bituminous limestone comprises four microfacies, namely wackestone, packstone, pack-wackestone and mudstone. The X-ray fluorescence (XRF) results indicate that the pre-existing sediments underwent episodic erosion and weathering processes during the early-middle Cenomanian. Moreover, TiO2 exhibited the same trend as P2O3, SiO2 and Al2O3. The organic carbon isotope (δ13C) signatures reveal a trend towards the negative excursion that marked the onset of the anoxic event during the middle Cenomanian, indicating an increased abundance of light carbon within the Cenomanian seas. The following rapid positive shift of δ13C values in the middle part suggests that marine organic carbon accumulation rates were high as a result of the increasing ocean organic productivity. The relatively high TiO2, P2O5, SiO2 and Al2O3 contents confirm this observation since productivity increased significantly, followed by the extreme burial of organic carbon. The oxygen isotope (δ18O) data also trend towards negative values in samples deposited during the high productivity interval, reflecting an increase in temperatures associated with the enhancement of the hydrologic cycle in such a restricted and occasionally subaerially exposed setting, leading to a sea-level rise that could have been the main factor controlling the terrigenous input.

ISSN

0072-1050

Publisher

Wiley

Disciplines

Life Sciences

Keywords

bioproductivity, carbon and oxygen isotopes, mid-Cenomanian, nannofossils

Scopus ID

105027793967

Indexed in Scopus

yes

Open Access

yes

Open Access Type

Bronze: This publication is openly available on the publisher’s website but without an open license

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