--> The Trace Fossil Fauna of the Early to Middle Permian Tinat Member of the Nuayyim Formation in Subsurface Saudi Arabia: Towards a Mechanism for Colonization of Inland Arid to Semiarid Environments

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The Trace Fossil Fauna of the Early to Middle Permian Tinat Member of the Nuayyim Formation in Subsurface Saudi Arabia: Towards a Mechanism for Colonization of Inland Arid to Semiarid Environments

Abstract

Continuous refinement on the understanding of the Nuayyim Formation across central Saudi Arabia, based on core observations, reveals a complex facies mosaic with significant facies variations. Marine influence on sedimentation within this interval has been historically debated and remains a matter of some dissent. Two burrowed intervals can be identified within the predominantly eolian Tinat Member. The lower interval consists of fine- to medium-grained sandstone with abundant silica cementation, low angle, wavy- and crinkly-lamination. The trace fossil fauna is characterized by a suite that displays a diminutive, locally, monospecific assemblage dominated by infaunal dwelling and grazing structures of ichnogenera suggesting mostly deposit-feeding behaviours (i.e., Planolites and Palaeophycus). Sediment deposition took place in marginal- to shallow-marine settings and embayments mostly within fair weather wave base. Colonization by tracemakers of this interval is interpreted to be the consequence of sea level rise that flooded low lying topographic relief, coastal embayments and interdune playa lakes inland. This is the result of a water table influenced by sea level and seasonal fluctuations in coastal dune fields as seen in many modern settings across the Arabian Peninsula. Rising sea level conditions subjected previously ephemeral and isolated coastal and inland playa lakes to marine influence. As transgression progressed, standing water bodies could have found connection to already established marine embayments followed by bioturbating infauna. Modern analogues for seasonal variability of the groundwater levels can be seen in coastal desert areas such as Qatar and Saudi Arabia as well as the Namib Desert in the Arabian Peninsula and west Africa respectively. The upper interval does not differ significantly in terms of lithology and primary sedimentary structures but exhibits a contrasting ichnofossil fauna when compared to the aforementioned interval. A robust and abundant assemblage that displays a mixture of vertical, inclined and horizontal structures typifies this segment. Particular identification of specific ichnogenera for this interval is challenging and is an ongoing process at the time of submission of this abstract. Preliminary identifications suggest an assemblage that bears similarities with the archetypical Skolithos ichnofacies. Alternatively, the morphology of some structures suggest a suite that may display continental affinities.