Chronostratigraphic Framework of the Pre-Khuff Section in Bahrain, Evidence of Carboniferous in Awali Field

The understanding of Bahrain's subsurface geology has long been guided by interpretations suggesting the absence of Carboniferous deposits in the Pre-Khuff section. Traditionally, the stratigraphy was thought to consist of the Middle Devonian Jubah Formation underlying the Unayzah Formation, which in turn was believed to lie directly beneath the Late Permian Khuff carbonates. This model led to a simplified yet problematic lithostratigraphic framework. However, recent studies from Saudi Arabia and Eastern Arabia suggest that the Jubah Formation may extend beyond the Middle Devonian into the Early Carboniferous, contradicting earlier interpretations that dismissed Carboniferous units due to erosion or non-deposition. Furthermore, Basal Khuff Clastics have been widely documented in neighboring countries, yet Bahrain has historically maintained a classification that overlooks their presence. This study re-evaluates these assumptions through a multidisciplinary approach, integrating palynological analysis and stable isotope geochemistry to redefine the chronostratigraphic framework of Bahrain's Pre-Khuff section. This study analyzed 185 drill cuttings from four wells located in Awali Field: W1, X1, Y1, and Z1. These samples underwent palynological processing, allowing the identification of biostratigraphic markers that determine depositional age. The extraction and microscopic examination of palynomorphs, specifically spores and pollen, provided insight into chronological biozones, allowing correlation with previously published regional biostratigraphic frameworks. Stable carbon isotope analysis was conducted on organic matter extracted from these samples, specifically measuring the delta carbon thirteen organic values to detect global carbon cycle shifts and establish correlations between wells. These geochemical signatures were compared against documented global isotope trends, such as the Tournaisian Carbon Isotope Excursion, to improve stratigraphic age determination. The palynological results reveal the presence of three distinct stratigraphic intervals beneath the Khuff Formation. The uppermost interval, based on the identification of Late Permian pollen assemblages, is consistent with the Basal Khuff Clastics instead of the historically assumed Unayzah Formation. This finding marks an essential revision in Bahrain's geological classification. The second interval, distinguished by Early Carboniferous palynomorphs, suggests the presence of Upper Jubah or Berwath Formation, confirming that Carboniferous deposits, long presumed absent, may indeed exist within Bahrain's subsurface. The third and lowest interval, identified through Middle Devonian palynomorphs, corresponds to the traditional Jubah Formation, yet is separated from younger Carboniferous units by an intra-Jubah unconformity, a substantial break in deposition. Stable isotope trends reinforce these stratigraphic distinctions, particularly in detecting two significant unconformities. The Pre-Khuff or Hercynian Unconformity, observed at the boundary between Basal Khuff Clastics and Early Carboniferous deposits, indicates a substantial hiatus between Late Permian and Tournaisian sediments, consistent with regional erosional phases. Additionally, the intra-Jubah unconformity, marking the separation between Middle Devonian Jubah and Early Carboniferous deposits, highlights previously undetected stratigraphic complexity. These unconformities align with known tectonic and sedimentary events that influenced subsurface deposition across the Arabian Peninsula. This study challenges and redefines Bahrain's lithostratigraphic framework, offering compelling evidence that Carboniferous deposits are not entirely absent, as previously assumed. By demonstrating the presence of Early Carboniferous deposits and correctly identifying Basal Khuff Clastics rather than Unayzah Formation beneath the Khuff, this research significantly alters interpretations of Bahrain's geological history. These revised classifications provide new opportunities for hydrocarbon exploration, especially in refining reservoir models and re-evaluating hydrocarbon migration patterns. The results call for additional validation through core sampling and seismic interpretation, ensuring that this preliminary study serves as the foundation for future geological assessments and petroleum exploration strategies.