Articles
Publication Date: 2026
Palaeoworld (1871174X)35(1)
The Cenomanian/Turonian (C/T) boundary, marked by the global oceanic anoxic event 2 (OAE2), coincides with a significant tectonic event and widespread unconformity across much of the Zagros Basin (southwestern Iran), except within intrashelf basins. The northern Mish Anticline section, situated in one such intrashelf basin, preserves a continuous sedimentary record of OAE2 within the Albian–Turonian Sarvak Formation. This study examines the stratigraphy of the Sarvak Formation, with particular emphasis on δ13C and environmental variations during the OAE2, to evaluate the interplay between global events and regional tectonics in this region. Analysis of a 517 m thick section reveals a succession assigned to the late Albian–Turonian based on the Cretaceous planktonic foraminiferal biozones for tropical and subtropical regions. The δ13C profile shows a positive excursion across the C/T boundary, capturing the global carbon isotope record's three diagnostic peaks (A, B, and C). The late Albian and most of the Cenomanian intervals reflect deposition in a relatively uniform, deep, and quiet environment, characterized by abundant planktonic foraminifera and oligosteginids. In contrast, the C/T interval records significant environmental changes, driven by OAE2 and regional tectonic activity in the Arabian Plate. A planktonic foraminiferal turnover, including the extinction of rotaliporids and Laeviella bentonensis, as well as the “Heterohelix” shift, is observed at the onset of the carbon isotope excursion between peaks A and B. These events are associated with the expansion of organic-rich layers, which point to the development of an oxygen minimum zone in the late Cenomanian. The regional tectonic activity culminated in two uplift phases within the basin, leading to the appearance of shallow-water carbonate facies during the early Turonian and the development of an unconformity at the top of the Sarvak Formation in the middle Turonian. © 2025 Elsevier B.V.
Publication Date: 2025
Sedimentary Geology (00370738)486
Basement highs and adjacent basins are significant structural elements controlling regional facies architecture. Overprinted by fluctuating sea-levels, the correlation of facies units from the crest into the flank environments is often challenging. Here, a case example of an upper Turonian–lower Campanian palaeohigh on the northeastern margin of the Arabian Plate is presented. Two stratigraphic sections (Jarhum and Qazi, respectively) compare the depositional dichotomy between crest and flank. The palaeohigh Jahrum section documents a deepening upward succession that includes brackish carbonates at the base, followed by shallow–marine carbonates, and culminates in basinal deposits. The sedimentary record of Santonian deposits in the Qazi section (flank) comprises stratigraphically thick calciturbidites, calcidebrites, slump folding, clinoforms, and channel-fill deposits, which conformably overlie deep-water deposits. This case study provides insights into processes that are rarely documented in the Tethyan realm. Data shown here exemplify the interaction between regional uplift (related to tectonic inversion) and eustatic sea–level changes. The regional correlation of the facies architecture highlights important lateral variations in facies and stratigraphic thickness controlled by bathymetry and seafloor inclination related to the geometry of the palaeohigh. We suggest that the redeposited carbonates described here are characteristic of tectonically active intervals along slope settings. Furthermore, we demonstrate that sustained carbonate production on unrimmed, distally steepened ramps supports the deposition of calciclastics. The data presented are crucial for understanding redeposition processes in Cretaceous carbonate systems along the Arabian margin and beyond. © 2025 The Author(s)
Publication Date: 2024
Boletin de la Sociedad Geologica Mexicana (14053322)76(1)
The 1st order mass extinction at the Devonian/Carboniferous transition, known as the Hangenberg Crisis, is characterized by major transgressive/regressive cycles which led to widespread ocean anoxia during the Hangenberg Black Shale Event, as well as to a global major sea-level fall and the worldwide deposition of regressive Hangenberg Sandstone equivalents. The Devonian/Carboniferous transition at the Tuye-Darvar section in the eastern Alborz Range is studied in terms of conodont biostratigraphy, litho-, microfacies and sequence stratigraphy. In order to examine the biostratigraphical framework, forty conodont samples were systematically taken from the studied interval. Thirty-two conodont species belonging to ten genera led to the discrimination of twelve conodont zones, ranging from the Pseudopolygnathus granulosus Zone to the Scaliognathus anchoralis-Doliognathus latus Zone. Due to facies, the conodont record also exhibits some hiatuses. Field observations and sedimentological and microfacies studies led to the identification of thirteen facies types from sub-tidal environments to the fully marine environments, including seven microfacies types. The sediments deposited in a mixed carbonate-siliciclastic platform, revealed four third-order sequences. The Hangenberg Black Shale is not recorded in the Tuye-Darvar section as a result of depositional facies. In comparison with other studied Devonian/Carboniferous Boundary (DCB) sections of the central and northern Iran, the Tuye-Davar section suggests a tectonic position, which is most likely placed on a separate tectonic block. © (2024), (Boletin de la Sociedad Geologica Mexicana). All rights reserved.
The Upper Cretaceous Gurpi Formation represents a pelagic interval composed of shale and marly limestone rich in planktonic foraminifera. This study focuses on the analysis of planktonic foraminifera from the Gurpi Formation in the Zard-Shehneh Anticline section in southwestern Iran. The formation is of significant importance in parts of the Zagros foreland basin, as it acts as both a cap rock and a source rock. The presence of the Cretaceous/Paleogene (K/Pg) boundary at the upper boundary of this formation further emphasizes the significance of studying it. Therefore, the study of its biozonation and bioevents is crucial. Through the recovery of planktonic foraminifera from 125 samples in thin sections and washed residues, 30 genera, 88 species, and 10 biozones were identified for the Gurpi Formation, as well as 7 genera, 12 species, and one biozone for the base of the overlying Pabdeh Formation. In addition, high accuracy was achieved in the placement of bioevents, including: 1) the occurrence of Globotruncana linneiana at the base of the Gurpi Formation, indicating the Santonian age; 2) the highest occurrences of Dicarinella asymetrica and most species of marginotruncanids, marking the Santonian/Campanian boundary; 3) the earlier occurrence of Globotruncana aegyptiaca; 4) the occurrence of the Campanian/Maastrichtian boundary in the lower part of Gansserina gansseri Zone; 5) the occurrences of five abundance events including: V. eggeri in the upper half of the Dicarinella asymetrica Zone, benthic foraminifera in the middle to upper half of the Radotruncana calcarata Zone, G. linneiana, G. lapparenti, and G. esnehensis in the lower part of Globotruncana falsostuarti Zone, G. esnehensis in the upper part of Globotruncana falsostuarti Zone, and G. gansseri at the end of the Pseudoguembelina hariaensis Zone; and 6) the disappearance of most keeled planktonic foraminifera species during the late Maastrichtian, starting from the middle parts of the Abathomphalus mayaroensis Zone. In this study, the K/Pg boundary, which is considered the upper boundary of the Gurpi Formation, exhibits unconformity and condensation. The high-resolution biozonation and bioevents framework not only allows for accurate dating of the Gurpi Formation in the Zard-Shehneh section, but also enhances the ability to precisely correlate sedimentary sequences and paleoenvironmental intervals at regional or global scales in future studies. © 2024 Elsevier Ltd
