Ichnology and sedimentology of aeolian and shallow‐marine interactions in the Permian Unayzah Group of central Saudi Arabia: Towards a mechanism for infaunal colonization of coastal dune fields and erg margins

Abstract

This paper documents aeolian and shallow-marine interactions and describes their ichnofossil suites from the early Permian Tinat Member of the Nuayyim Formation of subsurface Saudi Arabia, thereby confirming marine sedimentation in an interval historically interpreted as being dominated by continental settings wherein aeolian processes prevailed. This paper attempts to characterize in situ animal-sediment interactions in coastal dune fields and erg margins in arid to semiarid settings; where the description of organism-sediment relationships, until now, has been focused on the landward portion including freshwater suites. Sedimentological and ichnological assessments in the Tinat Member allowed the identification of aeolian and marginal-marine, tidally influenced interactions in two facies associations that are conformably interbedded. Facies Association 1 includes sediment deposition in aeolian and continental, groundwater table-related environments such as: aeolian dunes (facies 1); dry and damp aeolian interdunes (facies 2 and 3); ephemeral and perennial stream deposits (facies 4 and 5); and palaeosols (facies 6). Facies Association 2 reflects sedimentation in shallow-marine, tidally influenced environments and includes punctuated occurrences of tidal flats and sheltered shallow bay deposits (facies 7 and 8) displaying a brackish-water trace fossil assemblage. This suite exhibits a diminutive, highly stressed mixture with structures reflecting an impoverished Skolithos Ichnofacies and Cruziana Ichnofacies associated with tidal flat deposits displaying synaeresis cracks, lenticular bedding, low-angle and wavy lamination, flaser bedding, reactivation surfaces, carbonaceous double mud drapes, current ripples and tubular tidalites. Aeolian sedimentation and trace fossil associations presented in this paper are significant because they provide evidence for shallow-marine, tidally influenced and aeolian processes in the Unayzah Group during deposition of the Tinat Member of the Nuayyim Formation. More importantly, documenting marine and aeolian interactions and their resulting ichnofossil suite can be used: (i) to build integrated sedimentological and ichnological facies models; 1797 and (ii) to characterize the resulting trace fossil association in this particular interactive setting that can be used to identify similar successions elsewhere in the rock record.