Abundant Trace Fossils Research Articles

Non-tetrapod trace fossils from the Middle Devonian tetrapod tracksite at Zachełmie Quarry, Holy Cross Mountains, Poland

The Middle Devonian (Eifelian) dolomites exposed in the Zachełmie Quarry (Holy Cross Mountains, southern Poland) contain the earliest fossil record of tetrapods. Low-diversity, but unique assemblages of trace fossils characterize the track-bearing interval within the Lower Complex of the Wojciechowice Formation. The reconstructed environment of the trace fossil-rich beds includes ephemeral lakes and/or shallow-water lagoons separated from an open marine area by sparsely vegetated islands and spits. The most abundant non-tetrapod trace fossils from these beds are large, horizontal-to-vertical burrows, and dish-, circular- to oval-shaped, shallow depressions. The burrows are abundant on the upper surfaces of thick dolomicritic beds, especially in some palaeosol levels, but they are also associated with tetrapod trackways. Large, semi-aquatic or terrestrial animals (e.g., arthropods or vertebrates) most likely produced these burrows. The circular- to oval-shaped depressions observed on a large surface and other smaller, isolated blocks from the same stratigraphical level are interpreted as fish feeding/nesting/resting traces. Piscichnus sanctacrucensis isp. nov. is proposed as a new ichnospecies of the oval-shaped fish trace fossil from the Middle Devonian of Poland. A single, medium-sized Undichnia specimen, a fish swimming trace, is associated with the Piscichnus traces. The described trace fossils provide new insight into the palaeoecology and taphonomy of the Middle Devonian tetrapod tracksite from Poland and clarify remaining controversies regarding the interpretation of some poorly preserved trace fossils from the Zachełmie Quarry.

The Tumblagooda Sandstone revisited: exceptionally abundant trace fossils and geological outcrop provide a window onto Palaeozoic littoral habitats before invertebrate terrestrialization

AbstractThe establishment of permanent animal communities on land was a defining event in the history of evolution, and one for which the ichnofauna and facies of the Tumblagooda Sandstone of Western Australia have been considered an archetypal case study. However, terrestrialization can only be understood from the rock record with conclusive sedimentological evidence for non-marine deposition, and original fieldwork on the formation shows that a marine influence was pervasive throughout all trace fossil-bearing strata. Four distinct facies associations are described, deposited in fluvial, tidal and estuarine settings. Here we explain the controversies surrounding the age and depositional environment of the Tumblagooda Sandstone, many of which have arisen due to the challenges in distinguishing marine from non-marine depositional settings in lower Palaeozoic successions. We clarify the terminological inconsistency that has hindered such determination, and demonstrate how palaeoenvironmental explanations can be expanded out from unambiguously indicative sedimentary structures. The Tumblagooda Sandstone provides a unique insight into an early Palaeozoic ichnofauna that was strongly partitioned by patchy resource distribution in a littoral setting. The influence of outcrop style and quality is accounted for to contextualize this ichnofauna, revealing six distinct low-disparity groups of trace fossil associations, each related to a different sub-environment within the high-ichnodisparity broad depositional setting. The formation is compared with contemporaneous ichnofaunas to examine its continued significance to understanding the terrestrialization process. Despite not recording permanent non-marine communities, the Tumblagooda Sandstone provides a detailed picture of the realm left behind by the first invertebrate pioneers of terrestrialization.

Novel track morphotypes from new tracksites indicate increased Middle Jurassic dinosaur diversity on the Isle of Skye, Scotland.

Dinosaur fossils from the Middle Jurassic are rare globally, but the Isle of Skye (Scotland, UK) preserves a varied dinosaur record of abundant trace fossils and rare body fossils from this time. Here we describe two new tracksites from Rubha nam Brathairean (Brothers’ Point) near where the first dinosaur footprint in Scotland was found in the 1980s. These sites were formed in subaerially exposed mudstones of the Lealt Shale Formation of the Great Estuarine Group and record a dynamic, subtropical, coastal margin. These tracksites preserve a wide variety of dinosaur track types, including a novel morphotype for Skye: Deltapodus which has a probable stegosaur trackmaker. Additionally, a wide variety of tridactyl tracks shows evidence of multiple theropods of different sizes and possibly hints at the presence of large-bodied ornithopods. Overall, the new tracksites show the dinosaur fauna of Skye is more diverse than previously recognized and give insight into the early evolution of major dinosaur groups whose Middle Jurassic body fossil records are currently sparse.

Sedimentología e icnología de un delta fluvio-dominado, Formación Lajas (Jurásico Medio), cuenca Neuquina, Argentina

Sedimentologic and ichnologic analysis of the Middle Jurassic Lajas Formation in Bajada de Los Molles area allow recognizing upper offshore-lower shoreface deposits in transition to prodelta, delta front and interdistributary bay succesions. This system is classified as a river-dominated delta due to the presence of distributary channel deposits with huge amounts of particulate organic matter and low diversity and abundance of trace fossils. Hyperpycnites are common in the basal and upper part of the studied section, and form channel-levee and distributary-channel systems, integrated by massive sandstones and load deformation structures, or transitional and recurrent passages of tractive sedimentary structures with abundant particulate organic matter on the foresets. The greatest diversity and abundance of trace fossils are recognized in the upper offshore-lower shoreface deposits where Skolithos and Cruziana ichnofacies occur. Deltaic deposits show trace fossil associations with lower diversity and abundance than the fully marine ones, whereas the hyperpycnite deposits are either unbioturbated or show the lowest diversity and abundance of trace fossils, reflecting the most stressed conditions within the system.

Quo vadis, Tommotian?

AbstractThe concept of the Tommotian Regional Stage of the Siberian Platform has been closely linked to the idea of the ‘Cambrian Explosion’ of animals and protists when the entire Earth system shifted rapidly into Phanerozoic mode. We conducted a multidisciplinary study of an informal ‘synstratotype’ of the lower Tommotian boundary in the upper Mattaia Formation, Kessyusa Group in the Olenek Uplift, NE of the Siberian Platform. The Mattaia Formation characterizes an upper shoreface to inner-shelf depositional setting and provides important faunal ties and correlation with carbonate-dominated and aliminosiliciclastic open-shelf areas. A section of the upper Mattaia Formation at Boroulakh, Olenek River is suggested here as a model for the Global Boundary Stratotype Section and Point for the base of the Cambrian Stage 2. This level contains the lowermost occurrence of the cosmopolitan fossil helcionelloid molluscAldanella attleborensis. Section global markers near the base of the stage include a positive excursion of δ13C values reaching +5.4‰, a U–Pb zircon date of 529.7 ± 0.3 Ma, massive appearance of diverse small skeletal fossils (includingWatsonella crosbyi), a sudden increase in diversity and abundance of trace fossils, as well as a conspicuous increase in depth and intensity of bioturbation. Coincidently, it is this level that has always been regarded as the lower Tommotian boundary on the Olenek Uplift.

Ichnological analysis of the Cenomanian–Turonian boundary interval in a collapsing slope setting: A case from the Rio Fardes section, southern Spain

The Cenomanian–Turonian Boundary interval (CTB) at the Rio Fardes section (Betic Cordillera, southern Spain) is characterized by pelagic and hemipelagic deposition mixed with mass-flow conglomerates and sandstones. The Rio Fardes section lends itself to high-resolution ichnological analysis of the late Cenomanian Oceanic Anoxic Event (OAE-2) on a collapsing slope affected by gravity-flow sedimentation. The trace fossils include Alcyonidiopsis isp. A., Alcyonidiopsis isp. B., Chondrites intricatus, C. stellaris, C. targionii, Planolites isp., ?Pilichnus isp., Thalassinoides isp., and Trichichnus isp. This ichnoassemblage differs from most CTB sections given the presence of small Alcyonidiopsis isp., Chondrites stellaris, and ?Pilichnus isp., and the absence of Zoophycos. The particular depositional setting, affected by coarse clastic gravity flow sedimentation, may be responsible for these differences by affecting palaeoenvironmental conditions. The lower part of the Rio Fardes section shows a more or less continuous record of diverse and abundant trace fossils, generally produced under aerobic/low dysaerobic conditions. The middle part is characterized by a diminution in trace fossil diversity and abundance, related to moderately/highly? dysaerobic conditions disrupted by short intervals of anoxia. Both the lower and middle parts represent pre-Bonarelli event conditions. The upper part reflects the most significant change in ichnological characteristics. The absence of discernible trace fossils caused by decreasing oxygenation corresponds to the Bonarelli Level. In comparison with previously studied CTB sections, the lower number and thickness of anoxic layers in the Rio Fardes section point to generally better oxygenation on the sea-floor. A variable influence of factors limiting the macrobenthic trace maker community during the OAE-2 can be related to depositional or palaeogeographic contexts. Oxygenated water in the Rio Fardes section was delivered from shallower areas along with gravity-flow deposits. The usually bioturbated background pelagic or hemipelagic deposits above the coarse gravity-flow deposits suggest rapid re-establishment of the macrobenthic trace maker communities following each mass depositional event.

Death march of a segmented and trilobate bilaterian elucidates early animal evolution.

The origin of motility in bilaterian animals represents an evolutionary innovation that transformed the Earth system. This innovation probably occurred in the late Ediacaran period-as evidenced by an abundance of trace fossils (ichnofossils) dating to this time, which include trails, trackways and burrows1-3. However, with few exceptions4-8, the producers of most of the late Ediacaran ichnofossils are unknown, which has resulted in a disconnection between the body- and trace-fossil records. Here we describe the fossil of a bilaterian of the terminal Ediacaran period (dating to 551-539million years ago), which we name Yilingia spiciformis (gen. et sp. nov). This body fossil is preserved along with the trail that the animal produced during a death march. Yilingia is an elongate and segmented bilaterian with repetitive and trilobate body units, each of which consists of a central lobe and two posteriorly pointing lateral lobes, indicating body and segment polarity. Yilingia is possibly related to panarthropods or annelids, and sheds light on the origin of segmentation in bilaterians. As one of the few Ediacaran animals demonstrated to have produced long and continuous trails, Yilingia provides insights into the identity of the animals that were responsible for Ediacaran trace fossils.

Trace fossils evidence of a complex history of nutrient availability and oxygen conditions during Heinrich Event 1

Abstract The relationship between the behavior of tracemakers and paleoenvironmental conditions has been shown to be a useful tool in paleoceanographic studies. Here we present a detailed ichnological analysis of Heinrich Event 1 (H1), the youngest glacial North Atlantic large iceberg discharge, from Integrated Ocean Drilling Program Site U1308 in the central North Atlantic, located 2800 km from the mouth of the Hudson Strait. The ichnoassemblage consists of small trace fossils such as Phycosiphon, “Mycellia”/Trichichnus and Chondrites, and large ones including Planolites and Thalassinoides. The bioturbation index is generally low, from no bioturbation, to 30% of total bioturbated surface. Significant variations in composition, diversity and abundance of trace fossils are recorded, associated with the dual nature of H1 (comprising H1.1 and H1.2) and the period intervening between the two. Bottom- and pore-water oxygenation and benthic food availability are found to be the main limiting conditions for the tracemaker community, with some variations during the time span of H1, while factors such as sea water temperature had a minor impact.

The Phycosiphon record in the Ladrilleros-Juanchaco section (Miocene, Colombian Pacifi c): palaeoecological implications

Miocene rocks of the Ladrilleros-Juanchaco section, located on the NW margin of South America, contain a high diverse and abundant trace fossil assemblage. The relative abundance of Phycosiphon, together with its morphological variations, provides new insights into the environmental conditions. Detailed outcrop stratigraphic, ichnological, and geochemical analyses carried out in the section focused on the trace fossil assemblages (distribution, relative abundance), ichnofabric index, and, especially, in the general ichnological features of Phycosiphon . In addition, the detailed photographic documentation and the use of the digital image treatment technique facilitate the precise study of particular ichnological properties. Based on the stratigraphic analysis of the section, together with the abundance, size and distribution of the specimens of Phycosiphon , as well as the analysis of total organic carbon, the record of Phycosiphon is proved as related to the food content in the sediment, and then as a proxy in the study of ancient environments.

Stable deep-sea macrobenthic trace maker associations in disturbed environments from the Eocene Lefkara Formation, Cyprus

Ichnological analysis of Eocene deep-pelagic whitish chalky calcilutites interstratified with high-energy calcarenite beds in the lower part of the Petra Tou Romiou section (southern Cyprus) was conducted to interpret the development and evolution of the trace maker associations during calcilutite deposition after high-energy episodes. The trace fossil assemblage from the chalky calcilutites consists of Chondrites isp. (Chondrites intricatus and Chondrites targionii), Planolites isp., Taenidium isp., Thalassinoides isp., and Zoophycos isp., typical of the Zoophycos ichnofacies. A composite chalky ichnofabric reveals a multi-tiered association of burrowing animals: the uppermost tier determines a mottled background, the upper tier shows the highest trace fossil abundance and diversity (Planolites, Taenidium and Thalassinoides), the middle tier features Zoophycos and large Chondrites, and the deepest tier consists mainly/exclusively of small Chondrites. This ichnofabric has an autocomposite character, associated with bioturbation by a single ichnocoenosis and gradual upward migration of the tiered macrobenthic community as the pelagic calcilutite sedimentation slowly progresses. There are no changes in the trace fossil assemblage between or within calcilutite intervals, regardless of the associated calcarenite beds. This supports a stable, mature, background calcilutite trace maker association, which recovers shortly after the deposition of high-energy calcarenites. In turn, there would have been a rapid re-establishment of paleoenvironmental conditions during pelagic calcilutite accumulation after episodic deposition of any calcarenitic material.

A diverse deep-sea trace fossil assemblage from the Adriatic Flysch Formation (middle Eocene – middle Miocene), Montenegro (central Mediterranean)

Our study of ichnofossils in the Adriatic Flysch suggests that mid-fan environments, with 30 ichnospecies and 13 architectural designs, provided most productive and best preservation conditions in the fine-grained turbidite system of the Dinarides-Albanides-Helenides deep foreland basin. The Adriatic Flysch Formation at its type section in Crnjak Cove (Montenegro) represents a 300-m-thick turbidite succession deposited from the middle Eocene to the middle Miocene. The flysch is exposed in an asymmetrical syncline in a 750-m-long outcrop. The conglomerates, sandstones, and mudstones are arranged in seven distinct turbidite facies, which represent three superimposed submarine fans. The inner-, mid-, and outer-fan facies of the submarine fans contain sixteen ichnogenera and thirty three ichnospecies, which exhibit thirteen architectural designs. The inner fan conglomerates and coarse-grained sandstones contain a low diversity (Ophiomorpha rudis, Ophiomorpha annulata, and Halopoa imbricata), a low disparity (two architectural designs), and a low-density post-depositional trace fossil assemblages of the Ophiomorpha rudis ichnosubfacies of the Nereites ichnofacies. The mid-fan greywackes contain very diverse pre-depositional trace fossils (Belorhaphe zickzack, ?Cosmorhaphe isp., Desmograpton dertonensis, Gordia isp., Helminthopsis isp., Helminthorhaphe flexuosa, ?Megagrapton isp., Paleodictyon arvense, Paleodictyon hexagonum, Paleodictyon itallicum, Paleodictyon latum, Paleodictyon majus, Paleodictyon maximum, Paleodictyon strozzii, Paleodictyon isp., Scolicia strozzii, Squamodictyon isp.) having six architectural designs and abundant post-depositional trace fossils (Halopoa imbricata, Ophiomorpha annulata, Ophiomorpha nodosa, Ophiomorpha rudis, Planolites beverleyensis, Planolites montanus, Palaeophycus alternatus, Palaeophycus striatus, Palaeophycus tubularis, Rhizocorallium commune, Scolicia prisca, Scolicia strozzii, Zoophycos isp.) exhibiting seven architectural designs, which constitute the Paleodictyon-Ophiomorpha rudis ichnosubfacies of the Nereites icnhnofacies in the Adriatic Flysch. The waning turbidity currents with slower rates of sediment deposition and deficiency of nutrients favored grapholyptid colonization of the outer fans. Relatively low abundance, and great diversity of graphoglyptids (Helminthorhaphe flexuosa, Desmograpton dertonensis, ?Megagrapton isp., Paleodictyon arvense, Paleodictyon hexagonum, Paleodictyon majus, Paleodictyon minimum, Paleodictyon strozzii, Paleodictyon isp., Squamodictyon isp.), but low disparity (three architectural designs), represents the Paleodictyon ichnosubfacies of the Nereites ichnofacies in the outer fan facies of the Adriatic Flysch. The diversity of pre-depositional ichnofossils in the Adriatic Flysch exceeds post-depositional forms, reflecting a dominance of K-selected over r-selected population strategies in a stable oligotrophic environment.

Occurrence of the Lower Cambrian anemone-style trace fossils in the Zabuk Formation (Mardin–Derik, SE Turkey)

The Zabuk Formation of the Derik Group exposed over much of south-eastern Turkey presents a succession composed of shallow marine and fluvial siliciclastic sedimentary rocks. The Lower Cambrian assemblages containing abundant anemone-style trace fossils are known from most major palaeocontinents such as Laurentia, Baltica, and Gondwana. These have possible affinities with semi-infaunal dwelling anemones on siliciclastic mid-latitude shelves of West Gondwana in early Fortunian deposits. Among them is Bergaueria, characterized by plug-shaped burrows as exemplified by Bergaueria perata, that is, a characteristic trace fossil of the Cambrian globally.

Trace Fossils from the Late Pleistocene Marginal Marine Deposits of Jeju Island, Korea: Implications for the Psilonichnus and Skolithos Ichnofacies

Moderately diverse, but very abundant trace fossils are found from the Late Pleistocene deposits of Jeju Island, Korea. Vertical I-, Y- and U-shaped domichnia of annelids or decapods are, over 2500, extremely abundant, 3D network domichnia of callianassids are, over 200, very abundant, and small sinuous trails of nematode repichnia are, over 50, abundant in number. Horizontal trails attributable to polychaete or worm-like animals are, less than 50, common, but horizontal spreiten burrows, fish traces and crab trackways are, less than 10, rare in occurrence. Of these trace fossils, Taenidium barretti, Undichna britannica and Undichna unisulca represent the first record from the Pleistocene in Asia. Psilonichnus upsilon is the second record in Asia. Crab trackways probably produced by underwater punting gait of sideway walking crabs may represent the first record in the world. In addition, diverse and very abundant footprints of more than 500 hominids, more than 200 birds and more than 1000 mammals are closely associated with these invertebrate trace fossils. Trace fossil assemblage integrated with sedimentary facies is interpreted to have been formed in the marginal marine foreshore to backshore environment corresponding to the Psilonichnus and Skolithos ichnofacies.

Prograding muddy shelves in the Paleogene Wilcox deltas, south Texas Gulf Coast

Core facies analysis integrated with subsurface well-log correlations and seismic horizon mapping document two thick mudstone-dominated deltaic successions in the Wilcox Group along the south Texas Gulf Coast. Meters to tens of meter-thick upper slope to outer shelf mudstones form units that lie at the base of upward-coarsening successions which are interpreted as fluvial or storm/wave dominated shelf deltas. The muddy character of the deposits is observed in cores and inferred from well logs, whereas the larger depositional architecture is interpreted from well log correlations and seismic data.Physical sedimentary structures described from a lower Wilcox core reflect deposition on a mud dominated prodelta controlled by hyperpycnal processes. Normally and inversely graded beds are present indicating sustained flows that waxed and waned. Upward-coarsening facies successions contain current ripples, organic matter, and siderite cemented bands, low trace fossil abundance and low diversity, which suggest deposition in a fluvial prodelta to shelf environment. Centimeter-thick interbeds of normal and inversely graded mudstones, siltstones and very fine-grained sandstones with low intensities of bioturbation, reflect the high physical and chemical stresses of hyperpycnal environments. Heterolithic stratification with lenticular, wavy and flaser bedding indicates some tidal influence.On the other hand cores of the middle Wilcox reflect deposition on a muddy wave-storm dominated shelf. Bioturbation intensities tend to be high, with unstressed, fully marine ichnological suites. Pervasively bioturbated sandy mudstones and muddy sandstones with Cruziana ichnofacies, wavy parallel and low angle lamination, and structureless sandstones with Ophiomorpha record deposition in a wave-influenced prodelta to shelf environment. Hyperpycnal flows associated with river floods might have transported mud across the shelf to the outer shelf where prevailing wave and storm conditions facilitated suspension and transport of mud beyond the shelf edge.Previous studies have shown that Wilcox delta sandstones are largely trapped on the shelf by contemporaneous growth faults. However, this paper illustrates that at times the Wilcox shelf margin prograded through mud accretion.

Ichnostratigraphy of the Ediacaran-Cambrian boundary: new insights on lower Cambrian biozonations from the Soltanieh Formation of northern Iran

AbstractStrata in the Central Alborz Mountains, northern Iran, are interpreted to show continuous sedimentation from Ediacaran through Cambrian times. The Soltanieh Formation consists of five members: Lower Dolomite, Lower Shale, Middle Dolomite, Upper Shale and Upper Dolomite members. The clastic units (Lower and Upper Shale members) represent sedimentation in distal marine settings, ranging from the shelf to offshore, and contain abundant trace fossils of biostratigraphic utility. Four ichnozones have been recognized. Ichnozone 1, containingHelminthoidichnites tenuis,Helminthopsis tenuis, andCochlichnus anguineus, is early Fortunian based on small shelly fossils, and is interpreted as a distal expression of theTreptichnus pedumzone. Ichnozone 2, comprising the first occurrence ofT.pedum, is middle Fortunian, and is best regarded as the upper half of theTreptichnus pedumZone. Ichnozone 3 is late Fortunian–Cambrian Age 2, characterized by a sudden change in abundance and complexity of trace fossils. Main elements in this ichnozone includeCruziana problematica,Curvolithusisp., Phycodesisp.,Treptichnus pedum,Treptichnus pollardi, andTreptichnusisp. Ichnozone 4 is of Cambrian Age 2–Age 3 and marked by the first appearances ofPsammichnites gigas,Rusophycus avalonensis, andDidymaulichnus miettensis. Integration of trace fossils with small shelly fossils suggests that the Ediacaran–Cambrian boundary should be placed at the base of the Soltanieh Formation or within the Lower Dolomite Member. The delayed appearance ofT.pedumand the low ichnodiversity in the Lower Shale and lower interval of the Upper Shale reflect limited colonization of settings below storm wave base during the early Fortunian.

Fentou Biota: A Llandovery (Silurian) Shallow-Water Exceptionally Preserved Biota from Wuhan, Central China

An exceptionally preserved biota is described from the middle Telychian (Llandovery, Silurian) Fentou Formation of Wuhan, Central China, which preserves nontrilobite arthropods, cnidarians, echinoderms, sponges, fish, and algae as well as abundant shelly fossils and trace fossils in the Skolithos-Cruziana ichnofacies. This biota can be divided into two assemblages on the basis of the biological characteristics, fossil-bearing strata, and their sedimentary environments. Assemblage 1 comprises nonbiomineralized phyllocarids, Sphenothallus, conulariids, complete crinoids and stelleroids, and Burgess Shale–type sponges as well as some uncertain fossils in taxonomy and abundant marine shelly fossils. Assemblage 2 consists of numerous eurypterids, agnathans, chondrichthyes, and a few conulariids, algae, as well as shelly euryhaline fossils. Discoveries of the Fentou biota expand the temporospatial distribution and sedimentary environment of the exceptionally preserved Silurian biota and advances a deeper understanding of the biological assemblage and ecological system in the Llandovery. It also provides new data for studying the biological recovery and radiation under the background of the littoral sea (assemblage 1) and estuary-delta (assemblage 2) environments after the latest Ordovician mass extinction.

Selective incidence of the toarcian oceanic anoxic event on macroinvertebrate marine communities: a case from the Lusitanian basin, Portugal

A macroinvertebrate assemblage has been studied from the Thin Nodular Limestones Member (TNL) of the Fonte Coberta section (Lusitanian Basin, Portugal), giving special attention to its trace fossils. The assemblage was studied to analyse the influence of the Toarcian Oceanic Anoxic Event (T-OAE) on the macroinvertebrate community. The TNL consists of thin alternations of marl/limestone and nodular limestone beds, showing clear differentiations from bottom to top. Integrative analysis of the macrofossil assemblage for the studied interval, conducted for the first time in the Lusitanian Basin, reveals three major features: (1) abundant trace fossils with dominance or near exclusiveness of Thalassinoides, and a local record of Spongeliomorpha; (2) scarcity, but not extinction, of ammonoids; and (3) the absence of previously abundant brachiopods. The findings reveal a selective incidence of the T-OAE on the macrobenthic community, with a major influence (extinction) of brachiopods, severe changes (diminution in abundance and diversity) on ammonoids and a minor effect on macrobenthic tracemakers. A complex relationship between different palaeoenvironmental conditions during the T-OAE can be interpreted, discarding anoxic conditions in the seafloor, although low oxygen conditions in the water column are a possibility. The increase in seawater temperature and availability of nutrients on the seafloor would have played an influential role.

Sedimentology and depositional environments of the Ordovician Umm Sahm Sandstone Formation in southern Jordan

The Ordovician Umm Sahm Sandstone Formation of Jordan comprises approximately 200-m-thick succession of fluvial quartzarenites with subordinate claystone and siltstone lithologies of shallow marine conditions. The Umm Sahm Formation is characterized by its dark brown color, frequent jointing, and steep scarps. The Umm Sahm Formation is bounded by the marine claystones of Hiswah Formation at the top and the fluvial sandstones of the Disi Formation at the bottom. The Umm Sahm Formation is composed of two main facies: fluvial facies and tidal facies. The fluvial facies constitutes about 93% of the total thickness. The lower few meters of the succession passes upward from the Disi Sandstone Formation into similar massive white sandstone facies exhibiting similar white color, fine- to coarse-grained sandstone, with round-shaped pebbles. Trough and planar cross-bedding show a northwest unidirectional palaeocurrent trend. Light brown colored quartzarenites similar to those of the Cambrian Umm Ishrin Sandstone Formation are most common in the upper part of the succession. The tidal facies occupies three intervals in the middle part of the succession. It is composed of laminated and thin-bedded sandstones, siltstones, and claystones. They are rippled and varicolored with abundant trace fossils (Cruziana, Harlania, ruzophycus). The presence of hummocky cross stratification indicates the earliest short-lived tempestite conditions during the Paleozoic erathem of Jordan. The first appearance of Graptolites in the Ordovician rocks of Jordan was recorded during this study in the tidal facies of the Umm Sahm Formation. The vertical arrangement of both fluvial and tidal facies indicates three successive short-lived transgressions and regressions. These marine incursions indicate the successive shoreline advances of the Tethys Ocean, which was located northward, and inundated the southern braid plain. The three short-lived transgressive events took place, and the Tethys marine margin was displaced southward, giving rise to deposition of tidal facies in an open coast tidal flat. Following the transgressive events, renewed progradation and strandline retreat took place, fed by large amounts of siliciclastics derived from the continent and transported by braided streams across the intertidal zone.

Deltaic coastline of the Siwalik (Neogene) foreland basin: evidences from the Gish River section, Darjeeling Himalaya

This paper presents the sedimentological analysis of about 1.3 km succession of Neogene Siwalik Group exposed in the Gish River section, Darjeeling foothills. Contrary to the existing alluvial fan‐braided stream depositional model, the facies analysis shows that the succession accumulated in a shallow marine deltaic setting. Nine facies identified represent deposition from various processes related to unidirectional and oscillatory current, suspension settlement in quiet water and also to processes related to soil formation. Abundant trace fossils of marine affinity occur throughout the succession and include Cylindrichnus, Rosselia, Teichichnus, Rhizocorallium, Chondrites and Zoophycos. The studied succession has been subdivided into seven facies associations that can be interpreted in terms of the different sub‐environments of a river‐dominated delta. The lower ~550 m of the succession comprises sand–mud alternation of delta front, delta mouth and delta plain deposits (FA3, 4, 5 and 6), organized in stacked, 10–30 m coarsening‐upward units, and is inferred to represent progradation of the delta lobes. The overlying 300 m mud‐dominated interval is dominated by prodelta to open marine bay‐fill succession (FA1 and 2); the pebbly sandstones and conglomerates of the uppermost ~500 m represent a braidplain delta environment. A kilometre‐scale coarsening‐upward trend of the Siwalik deposits of this section is attributable to southward propagation of the thrust front related to the activity of the Main Boundary Thrust (MBT). The sedimentological analysis shows that a marine embayment existed in the Eastern Himalaya during the Siwalik time and the deltaic succession reported here provides the link between the upland transverse drainages recorded from Western Himalaya and the deep marine Bengal Fan succession. Copyright © 2017 John Wiley & Sons, Ltd.

Depositional environment of Himmatnagar Sandstone (Lower/Middle Cretaceous): a perspective

Himmatnagar Sandstone (lower to middle Cretaceous) is exposed in between Sabarmati River in the west to Vantada in the east around Himmatnagar Town in north Gujarat, India. The sequence is divisible in two members: The lower member is 65 m thick, mostly massive, horizontally stratified to hummocky stratified with abundant plant and trace fossils in assorted shales and sandstones. The upper member is ~ 12 m thick, cross–stratified and medium to coarse grained–gritty to cobbly in nature. Six lithofacies have been identified in the sequence, viz. 1. grey wacke (GW), 2. silty–shale (SS), 3. cross–stratified sandstone (CS), 4. horizontally stratified sandstone (HSS), and 5. planar cross–stratified sandstone (PCS) in the lower member; and 6. gritty–cobbly cross–stratified sandstone (GCCS) in the upper member.
 The lower member consists of plant fossils which are poor to moderately preserved and transported. The silty–shale lithofacies contains plant fossils (Pagiophyllum, Brachyphyllum, Gleichenia, Araucarites, circinate vernation of ferns, Williamsonia flower, twigs, petrified wood, conifer and its cone, etc.), body fossil (insect wing) and trace fossils (Skolithos, Monocraterion, Psilonichnus, Thalassinoides, Chondrites, Planolites, Palaeophycus, Calycraterion, Circulichnus, Ophiomorpha, Phoebichnus, etc.). In the cross–stratified sandstone lithofacies, body fossils (mainly fragmented bivalves, plant fossils (Weichselia reticulata, Matonidium indicum, Ptilophyllum, cycadean frond and fossil wood) and trace fossils (Monocraterion, Chondrites, Calycraterion, Thalassinoides, Psilonichnus and Skolithos) are recognized. On the other hand, in horizontally stratified sandstone lithofacies plant fossils (Sphenopteris, Pagiophyllum, Gleichenia, Elactocladus, Brachyphyllum, ferns, petrified wood, etc.) and trace fossils (Skolithos, Ophiomorpha, Psilonichnus, Monocraterion, Arenicolites, Diplocraterion, Thalassinoides, Teichichnus, Palaeophycus, Planolites, etc.) are present. While, large crustacean and vertebrate burrows, Skolithos, Thalassinoides, Ophiomorpha, etc are found in planar cross–stratified sandstone lithofacies. The trace fossils belong to Psilonichnus, Skolithos and Cruziana ichnofacies as per Seilacher (1967). The member also contains wedge shape geometry of beds similar to tidal partings as well as ridge and runnel structures, low–angle to hummocky cross–stratification, herringbone structure and parting lineation. Here, north to northeast palaeo–current direction is indicated by cross–stratification in the member. All these features lead to the depositional environment, which seems to be foreshore–tidal flat to middle shoreface for the lower member of the sequence.
 The upper member is composed of trough cross–stratified sandstones showing prominently southwest to south palaeo–current direction with angular to sub–rounded pebbles and cobbles of underlying rocks and fossil wood with lower erosional contact and channel structures at places. Based on above characteristics, depositional environment of upper member can be interpreted from estuarine to fluvial.