Depositional Facies and Sea-Level Variation of the Cryogenian Glacial System: An Example from the Outcropping Fiq Formation, Abu Mahara Group, Jabal Akhdar Area, Northern Oman

The Cryogenian Snowball Earth episode is represented in Oman by the Fiq Formation of the Abu Mahara Group. Although the Fiq Formation is an important hydrocarbon target in Oman, its spatial and temporal depositional facies distribution is still poorly understood. This study aims to build on previous outcrop studies and develop a depositional model based on detailed sedimentological logging of the well-exposed Fiq Formation in the Jabal Akhdar area of northern Oman. This study has revealed that the Fiq Formation is of glaciomarine (i.e., proximal and distal) and proglacial facies. Proximal glaciomarine facies consist of discontinuous, thin, clast-rich diamictite intervals. The clast-rich nature suggests rainout diamictites formed by the continuous source of debris below an ice sheet, extending some distance from the grounded ice margin. Distal glaciomarine facies make up most of the logged section and consist of thick massive mud-prone, clast-poor dilute diamictite intervals. They are of rainout ice-rafted based diamictites, sourced by iceberg-based debris flows, and deposited towards the distal area of the basin, distant from an active ice margin. Local glacier features (i.e., ice-rafted granitic dropstones) display clear evidence of active glaciation during the deposition of the Fiq Formation. The proglacial, gravity flow elements comprise gravity flow facies consisting of massive, locally graded sandstones with rippled tops, displaying pulse-like features, representing bottom-current-based turbidites, sourced from meltwater bottom-currents from sub-glacial tunnel-mouth outlets, and deposited on unstable slope setting. Proglacial, gravity flow facies are also represented by parallel and thinly laminated siltstones and deformed mudstones, massive pebbly sandstones and clast-supported conglomerates with moderate to well-sorted texture, and rippled fine-grained sandstones and siltstones. Altogether this suggests suspension fallout from turbid plumes, intensively reworked debris and dilute current-based ripples formed in a deep water setting. Thick intervals of structureless sandstone represent lithofacies deposited in a braided fluvial environment. The Fiq Formation represents cycles of sea-level rise and fall events formed during local and multiple glaciation and deglaciation events. The outcome of this study may serve as a reference to test Fiq’s potential development as a play and to define its regional variation in further studies.