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The distribution of conventional subichnofacies in deep‐water fan systems (i.e. Ophiomorpha rudis–Paleodictyon–Nereites‐subichnofacies) depends on the presence of fully turbulent non‐cohesive flows such as low‐density turbidites and high‐density turbidites. However, changes in flow state between laminar and turbulent conditions can affect the distribution style of conventional subichnofacies. This study deals with the effects of environmental or ecological stressors as a result of hybrid sediment gravity flows (hybrid event beds) on distribution and composition of trace fossils in the deep‐marine depositional system of the Ordovician Ghelli Formation in the north‐eastern Alborz Range. The spatial distribution and sedimentological character of hybrid sediment gravity flows, in particular their abundance in the down‐dip parts of lobe‐related facies associations, are interpreted as products of longitudinal and lateral transformation from turbidity currents to debris flows promoted by incorporation of significant claystone and mudstone clasts into the flow by seafloor erosion and flow bulking. Seven trace‐fossil assemblages were recognized in the channel and lobe‐related facies associations. The observed spatial distribution of trace‐fossil assemblages in the interpreted frontal and lateral lobe fringes, somewhat contrasts with conventional subichnofacies distribution models. The development of cohesive flows and rapid emplacement of turbidite, banded and debrite beds could be accompanied by fluctuations in physico‐chemical conditions and, hence, the time available for colonization and the lifestyle of producers. This study suggests that, compared to the archetypal models of the subichnofacies in down‐dip parts of lobe‐related facies associations, ichnodiversity and density of bioturbation are drastically reduced, and trace fossils are limited to simple, shallow‐tier feeding strategies. Commonly, the presence of cohesive flows may have forced the producers in the Paleodictyon and Nereites‐subichnofacies to migrate into lateral lobe fringe with more participation of low‐density turbidites. This study shows that, in addition to sedimentological and architectural criteria, ichnological criteria can also be used to distinguish between frontal and lateral lobe‐fringe deposits in unconfined systems. [ABSTRACT FROM AUTHOR]

The Lower Ordovician Shirgesht Formation in central Iran is composed of siliciclastic and carbonate rocks deposited in diverse coastal and marine shelfal environments (tidal flat, lagoon, shoreface, offshore-shelf and carbonate ramp). Five facies associations contain diverse ichnofossil assemblages that show distinct proximal to distal trends formed in a wide range of physical-chemical conditions. The ethological groups of trace fossils in the Shirgesht Formation reflect a gradient of depositional stress conditions across a wave-influenced shoreline and shelf. Deposits of wave-influenced environments make up a significant component of the geological record of shallow marine settings, and the ability to determine paleoenvironments in detail in such successions is critical for reconstruction of depositional histories and sequence-stratigraphic interpretation. The Cruziana ichnofacies of the study shows highly diverse suites that record the establishment of a benthic community under stable conditions and a long-term colonization window. The Skolithos ichnofacies recognized is a low diversity opportunistic ichnocommunity suite that resulted from colonization after tempestite deposition in a stressed environment. The strata record an onshore to offshore replacement of the Cruziana ichnofacies (with abundant feeding traces of deposit-feeders) by the Skolithos ichnofacies (dominated by suspension-feeders and predators). A transitional zone between the two ichnofacies coincides with the offshore-transition/distal lower-surface deposits. The distribution of ichnofacies, the diversity and range of ethological characteristics reflected by the ichnogenera, and the wide range of wave-dominated coastal facies demonstrate the potential to use individual trace fossils and ichnofacies for significantly refined palaeoenvironmental analysis of wave-dominated coastal settings, particularly in Ordovician successions. [ABSTRACT FROM AUTHOR]

The Middle-Late Ordovician Ghelli Formation in the Kopet Dagh region northeastern Alborz range of Iran is composed of siliciclastic rocks deposited in a variety of turbidite to marginal marine environments (deep marine clastic fan and related environments and prodelta, distal delta front, proximal delta front and distributary channels). The ichnology of the middle member of the Ghelli Formation is here reported. Combined sedimentological and ichnological analysis allows recognition of a tide-influenced deltaic succession in the middle member of the Ghelli Formation consisting of three main facies associations: lower distributary channels, delta front and prodelta facies. Twenty-two ichnogenera have been identified in this marginal marine succession: Arenicolites, Arthrophycus, Bergaueria, Chondrites, Conichnus, Cruziana, Cylindrichnus, Didymaulichnus, Diplichnites, Diplocraterion, Helminthopsis, Gyrochorte, Lockeia, Macaronichnus, Monomorphichnus, Palaeophycus, Planolites, Rosselia, Rusophcus, Skolithos, Teichichnus and ?Scolicia. Their distribution is clearly linked with lithofacies and depositional palaeoenvironments. The ichnological analysis reveals that the trace fossil suites developed in these environments indicate low diversity and low to moderate abundance of burrows, poor development of tiering and sporadic distribution. Low ichnodiversity and low bioturbation intensities with higher bioturbation clusters consist of facies-crossing ichnogenera, and the impoverishment of suspension-feeding trophic types indicates 'stressed', non-archetypal expression of the Cruziana ichnofacies. The periodic higher intensities of bioturbation due to variations in hydrodynamic regimes of tidal currents reflect the archetypal of the Cruziana ichnofacies (and rare Skolithos ichnofacies). [ABSTRACT FROM AUTHOR]

The trace fossil assemblages from the Upper Cretaceous Neyzar Formation are described for the first time from Kopet-Dagh, Iran, enhancing the record of this fossil group in the Cretaceous of the Middle East. Thirty-one ichnogenera have been identified in open marine successions: Agrichnium , Asteriacites , Asterosoma , Bergaueria , Chondrites , Cylindrichnus , Halopoa , Helminthopsis , Gordia , Gyrochorte , Laevicyclus , Lockeia , Megagrapton , Nereites , Neonereites , Ophioichnus , Ophiomorpha , Palaeophycus , Phycodes , Phycosiphon , Planolites , Protovirgularia , Rhizocorallium , Rosselia , Scolicia , Sinusichnus , Skolithos , Spongeliomorpha , Taenidium , Teichichnus , and Thalassinoides. The Neyzar Formation accumulated on a gently dipping shelf dominated by storm- and fair weather-wave processes and includes shelf, lower offshore, upper offshore, lower shoreface-proximal offshore, middle-upper shoreface and foreshore deposits. Identification and interpretation of ichnological signatures and the spatial arrangement of sedimentary structures in the successions are used to further refine sedimentary interpretations of parameters such as wave energy, substrate properties, the nature of the available food supply, variability in sedimentation rates and proximal–distal trends of the wave-dominated shoreface–offshore complex. The prevalent palaeoceanographic situation during the deposition of the studied successions was ideal for tropical storms, thus promoting tempestite deposition and the occurrence of a tropical and subtropical trace fossil suite. According to this study, increasing mobility and infaunality with more complex trace systems or sophisticated feeding strategies, climax population strategies and the high diversity, associated with rapid increase in the abundance and depth of infaunal structures, indicate a major reorganization of the shallow-marine benthic communities that occurred in response to the Mesozoic marine revolution. [ABSTRACT FROM AUTHOR]

Abstract: The paleoenvironmental significance of deep marine trace fossil assemblages in the upper Maastrichtian–Paleocene Amiran Formation has been done for the first time in Lurestan Province (NW Zagros) from the Zagros Fold–Thrust Belt. A semi-quantitative study of trace fossil abundance (bioturbation indices) in the Amiran Formation shows that trace fossil assemblages can be very powerful discriminators of deep-marine clastic fan and related environments. The Amiran Formation is a sand-rich, thick-bedded, and coarse-grained turbidite succession. Deep marine paleoenvironments from basin slope to basin floor settings are preserved. These strata contain a diverse and abundant pre- and post-depositional ichnofauna. Proximal and axial parts of the sandy systems show low-diversity and low-density trace fossil assemblages dominated by post-depositional trace fossils, but distal environments show a general increase in trace fossil diversity, abundance and number of pre-depositional trace fossils. The post-depositional association essentially consists of dwelling, feeding, and grazing traces. The pre-depositional assemblage is rich in graphoglyptids and grazing trails, and feeding structures also occur. The ichnodiversity, composition, ethology, and morphologic complexity of the pre-depositional association of the heterolithic successions of thin to thick-bedded turbidite sandstone and inter-turbidite mudstone are characteristic of three ichnosubfacies of the Nereites ichnofacies. These ichnosubfacies are identified in Amiran Formation deposits, the typical succession of ichnosubfacies can express a bathymetric trend from shallower to deeper parts and from higher-to-lower hydrodynamic conditions. They are: (1) the Ophiomorpha rudis ichnosubfacies (the proximal and axial parts with thick bedded channel and lobe related environments), (2) the Paleodictyon ichnosubfacies (channel-lobe transition in the distal lobe facies), and (3) the Nereites ichnosubfacies (distal part of off-axis lobe or fan fringe–basin floor transition and overbank settings). There is also mixed O. rudis to Paleodictyon ichnosubfacies (channel–margin, lobe–fringe in the proximal lobe facies). The dominance of Zoophycos and Chondrites in poor-oxygen basin floor facies may represent Zoophycos ichnofacies. The number of graphoglyptids increases from distal (basin floor) to proximal (fan fringe–basin floor transition, fan fringe, lobe complex fringe/lobe complex off-axis) settings. They are absent in the most proximal/axial lobe environments due to increased volume, frequency, erosive power of turbidity current events and sedimentation rate, grain size, decreased preservation potential of shallow tier, and pre-turbidite trace fossils. The ichnosubfacies method used here, as utilized by other authors, has the potential to improve paleoenvironmental analysis of other deep marine depositional settings, and in outcrop investigation of turbidite systems. [Copyright &y& Elsevier]

The Lower Carboniferous Mobarak Formation in the east of Central and Eastern Alborz Mountains, northern Iran, is deposited on a distally steepened carbonate ramp. Detailed facies analysis allowed to differentiate seven facies associations, includes deep marine basinal (FA1), toe-of-slope/outer ramp (FA2), ramp/slope (FA3), shallow open marine (FA4), bioclastic bars or shoal (FA5), lagoon (FA6) and intertidal flat (FA7). The trace-fossil suites of the studied successions are shown for the first time. Twenty eight ichnogenera were identified, i.e. Arenicolites, Asterosoma, Bergaueria, Chondrites, Cochlichnus, Diplocraterion, Halopoa, Helminthopsis, Helminthorhaphe ? , Helminthoidichnites, Gordia, Gyrochorte, Lockeia, Mammilichnis, Megagrapton, Nereites ? , Palaeophycus, Phycodes, Phycosiphon, Planolites, Protovirgularia, Rhizocorallium, Rosselia, Sinusichnus, Skolithos, Taenidium, Thalassinoides, and Zoophycos. The seven facies associations deposited in a wide range of physico-chemical conditions, show distinct proximal to distal trends. As a result of oxygen-depleted depositional conditions, only the tracemakers of Zoophycos survived in deep marine slopes, which were close to turbiditic sedimentation zones. The development of a benthic community under the stable condition and a long-term colonization window were documented by highly diverse suites of the Cruziana ichnofacies. Under a stressed environment (after tempestite deposition), the Skolithos ichnofacies displayed a low diversity of opportunistic ichnocommunity suite. The mixed Skolithos – Cruziana ichnofacies occur in the middle to distal lower inner ramp. The identification of the archetypal ichnofacies may document broad changes of environmental parameters such as variability in sedimentation rates, energy level, salinity, substrate properties/consistency, nature of nutrient supply and dissolved oxygen content. Relationships among different modes of ethology of tracemakers and sedimentary structures in the studied successions are used to clarify sedimentary conditions. • The Lower Carboniferous Mobarak Formation in the east Central and Eastern Alborz Mountains, is deposited on a distally steepened carbonate ramp. • Detailed facies analysis allowed to differentiate seven facies associations, including FA1 to FA7. • The trace-fossil suites of the studied successions are shown for the first time. • The ichnofacies in the Mobarak Formation including. [ABSTRACT FROM AUTHOR]