Depositional setting and trace fossil suites of the early Cambrian (series 2, stage 4) Khussak Formation, east-central salt range, north-west sub-Himalayas, Pakistan

This is the first integrated ichnologic-sedimentologic study of the Khussak Formation at the Salt Range, Pakistan. This integrated approach led to identifying thirteen lithofacies and six recurring facies associations. Facies association 1 (FA-1) is made up of massive to parallel laminated mudstone with rare interbeds of sandstone. FA-1 is moderately bioturbated with trace fossils belonging to the Cruziana ichnofacies (Cruziana, Planolites, Rusophycus). FA-1 is interpreted to record deposition in the upper intertidal mud flat setting. Facies association 2 (FA-2) consists of thinly interbedded sandstone (wavy and current rippled) and mudstone (massive to parallel-laminated). The heterolithic wavy bedding is the dominant bedding type. FA-2 is variably bioturbated (BI = 0–5). Trace fossils of moderate diversity of the Cruziana ichnofacies are present. FA-2 represents deposition in the middle intertidal mixed flat setting. Facies association 3 (FA-3) comprises gradational-based, laterally extensive, crudely bedded to massive, medium to lower fine-grained sandstone with thin (cm-scale) mudstone beds. FA-3 is intensely bioturbated (BI = 3–5). Robust and diverse trace fossils belonging to the Skolithos ichnofacies are present (Arenicolites, Cylindrichnus, Diplocraterion, Phycodes, Planolites, Siphonichnus, Skolithos, and Treptichnus). FA-3 records deposition in the lower intertidal sand flat setting. Facies association 4 (FA-4) consists of muddy to silty lower-upper fine-grained sandstone with rare mudstone drapes. FA-4 displays inclined heterolithic stratification (IHS). Tidal couplets (mud and mica drapes) and mud clasts are common. Bioturbation is absent to sparse (BI = 0–2) with low-diversity trace fossils of Skolithos ichnofacies (Cylindrichnus, Diplocraterion, Palaeophycus, Planolites, Skolithos, and rare fugichnia). FA-4 is interpreted to represent deposition in an intertidal creek point bar. Facies association 5 (FA-5) consists of well sorted sandstone (upper medium to fine-grained). The sandstone is erosionally based, and laterally extensive. Planar parallel lamination, trough cross-stratification, reactivation surfaces, and mud drapes are present only locally. The degree of biogenic reworking is low to moderate (BI = 0–4), and traces are sporadically distributed. Trace fossils present are of moderate diversity and abundance, including Arenicolites, Cylindrichnus, Diplocraterion, Monocraterion, Palaeophycus, Planolites, Siphonichnus, and Skolithos. FA-5