Trace Fossil Content Research Articles

Facies and trace fossils of the Upper Cretaceous Sillakudi Formation (Cauvery Basin, S. India) and their palaeoenvironmental significance

The Sillakudi Formation is a sandstone-dominated succession bounded by unconformities. It represents the oldest unit of the Ariyalur Group deposited during the Campanian under fully established passive margin depositional conditions. The present study is an attempt to interpret the depositional palaeoenvironment of Sillakudi Formation based on its trace fossil content, supported by sedimentological evidences. Detailed sedimentological and ichnological observations were undertaken in multiple traverses and spot locations across the Sillakudi Formation. The Sillakudi Formation is subdivided into four facies associations, each represented by a distinct ichnology and environment of deposition. Unit 1 comprises conglomerates grading upwards into pebbly sandstones almost devoid of trace fossils except a few Planolites isp. indicating a high-energy foreshore-to-shoreface environment. Unit 2 consists of glauconitic sandstones with Ophiomorpha nodosa, O. annulata, Thalassinoides isp. and Skolithos linearis, belonging to the Skolithos ichnofacies indicating deposition in shoreface to offshore transition environments. Unit 3 comprises pebbly to very coarse-grained massive sandstones, characterised by an almost monospecific Skolithos ichnofacies indicating rapid colonisation of beds in a delta-front associated debris flows and calcareous sandstones alternating with claystones containing a diverse Cruziana ichnofacies with an ichnoassemblage comprising of Trichichnus isp., Scolicia prisca var. laminites, S. ?prisca, S. vertebralis, Palaeophycus tubularis, Planolites beverleyensis, P. montanus, Taenidium isp., Thalassinoides suevicus, Ophiomorpha isp., Chondrites isp. and Phycodes isp., pointing towards deposition in calmer, possibly dysoxic outer shelf prodeltaic environments. Unit 4 has pebbly to gritty cross-bedded sandstones exhibiting the development of networks of Thalassinoides isp. and Ophiomorpha isp., indicating shallow sub-tidal to intertidal conditions of deposition. The overall succession is interpreted to show initial deepening followed by shallowing.

Tidal Modulated Shoreface Facies in Eocene Agbada Formation, Niger Delta Basin, Nigeria

Tidal influence shoreface are shoreface deposit generated by wave induced tidal action. The extent of the tidal impact from lower to upper shorefaces depend mostly on the tidal range thereby controlling the impact of different shoreline wave action on sediment distribution across shorefaces. The Tidally influenced shoreface sediment display wave generated structure, however the structure are strongly associated with tidal generated structures and trace fossil consistent with tidal depositional setting. Shoreface successions in Titun well display a wide range of variability, largely restricted to the lower and middle shoreface intervals. This variation was controlled by relative wave dominance and intermittent pulsating nature of associated tidal bed deposition. The successions were subdivided into three end members, although a complete gradation between them exists. High energy shoreface consist almost entirely of erosively based amalgamated tide and wave beds with minimal bioturbation. Intermediate energy shoreface consist of stacked laminated to burrowed intervals, recording repeated erosive storm bed emplacement, followed by opportunistic colonization, and commonly overprinted by resident fairweather burrowing. Weakly storm-affected low energy shorefaces typically show intense bioturbation with minimal preservation of high energy beds. Based on the association of the facies, facies vertical build-up patterns, sedimentary structures and trace fossil content, the T1 sands in Titun well are interpreted as a prograding tidally influence shoreface deposit. This interpretation is supported by presence of tide generated structures and marine trace fossil, due to the prevalence of several tidal imprint as suggested by several mud drapes and flasers, couplets of sands and shale’s in heterolithic sequences, and bidirectional current structures (herringbone cross stratification), a tidally influence shoreface geological model is suggested for deposit.

Animal–substrate interactions preserved in ancient lagoonal chalk

Trace-fossil assemblages reflect the response of the benthos to sets of paleoenvironmental conditions during and immediately after sedimentation. Trace fossils have been widely studied in pelagic shelf and deep-sea chalk deposits from around the globe but never documented from ancient lagoonal chalk successions. Here we report the first detailed ichnologic analysis of a lagoonal chalk unit, using as an example the Upper Cretaceous Buda Formation from the Texas Gulf Coast Basin. In this unit, variable interconnection with the open ocean, accompanied by marked fluctuations in physicochemical parameters inherent to lagoonal circulation (e.g., salinity, hydrodynamic energy, bottom-water oxygenation), highly influenced the resultant trace-fossil content of the chalk. These lagoonal chalk deposits contain twenty ichnotaxa, displaying a clear dominance of Thalassinoides isp. and Chondrites isp., which are present in most of the bioturbated strata. The dominance of Thalassinoides isp., both in softgrounds as an element of the Cruziana Ichnofacies and in firmgrounds as a component of the Glossifungites Ichnofacies, highlights similarities with trace-fossil assemblages from shallow-water shelf-sea chalks. In contrast to both (open) shallow-water shelf-sea chalks and deep-sea chalks, the Buda Formation chalk exhibits more diverse assemblages and sharp fluctuations in ichnodiversity and ichnodisparity during relatively short periods of time. The increased ichnodiversity and ichnodisparity in this lagoonal chalk (in comparison with its open ocean counterparts) may reflect a complex interplay of taphonomic (i.e., incomplete bioturbation allowing preservation of shallow-tier trace fossils and ecologic (i.e., increased spatial environmental heterogeneity in the carbonate lagoonal setting) factors.

Ichnofabric logs and the geochemistry of sapropels (Miocene, Maldives)

An ichnofabric log analysis was carried out on the organic-rich sediments (sapropels) alternating with organic poor oceanic carbonates in Late Oligocene and Early Miocene strata in the Maldives Archipelago with the objective of determining the utility of such logs in tracing paleoenvironmental changes recognized by well-established geochemical proxies. Ichnofabric logs proved to correlate well with natural gamma radiation logs (NGR), which in the study case are indicative of the amount of preserved organic matter in the sediment. However, the relationship between different geochemical proxies for paleo-oxygenation/organic-matter preservation in the sediment and the trace-fossil content was still to be determined. The trace-fossil assemblage of the sapropels consists of Thalassinoides, Planolites, Palaeophycus, Zoophycos, Chondrites, Phycosiphon, and Scolicia. This ichnoassemblage is characteristic of Zoophycos ichnofacies and in the study section was attributed to five ichnofabrics according to the intensity of bioturbation, main ichnotaxa and type of sediment. The ichnofabrics characterized by high bioturbation indices correspond to intervals with white sediment and low content in organic carbon, <0.1%. The ichnofabrics characterized by low bioturbation indices and low diversity of ichnotaxa are coincident with organic-rich intervals containing up to 30% organic carbon and trace element signatures distinctive of anoxic bottom waters (Al, Ba, Fe, K, Mo, S, and U). The presence of discrete burrows within the black beds is the result of high-frequency seafloor ventilation superimposed to the orbital scale controlling the occurrence of sapropelic intervals. The ichnofabric logs proved to be a valuable tool to reconstruct in detail the evolution of paleo-oxygenation of sapropels.

Ordovician trace fossils from southern Jordan with particular consideration to the Cruziana rugosa group: Taxonomy, stratigraphy and trans-regional correlation throughout the Middle East and northern Africa

First detailed palaeoichnological research is presented from all the Ordovician formations and members of the Southern Desert of Jordan. The exclusively siliciclastic succession is of fluvial, fluvial-deltaic and fully marine origin and develops continuously from Cambrian strata until late Hirnantian glacial deposits. The ichnofauna occurs on large outcrop surfaces and is quite rich and of high diversity. Based on numerous taxonomic identifications from the excellently preserved material of various stratigraphic levels a biostratigraphic determination of the sequence is concluded as late Early to early Late Ordovician. Twenty-four ichnotaxa, two morphotypes and fifteen ichnogenera within five ethological groups based on the categories of architectural designs were identified. (1) horizontal burrows and trails (arthropod traces): Cruziana rugosa, C. furcifera, C. goldfussi, C. rouaulti, C. almadenensis, C. isp., Diplichnites cf. D. gouldi, D. morphotype A, D. morphotype B, Monomorphichnus cf. lineatus, cf. Monomorphichnus, Rusophycus didymus, R. aff. petraeus, ?R. aff. almadenensis; (2) vertical burrows: Arenicolites isp., Monocraterion isp., Rosselia socialis, Skolithos linearis; (3) plug-shaped burrows: Bergaueria perata, B. sucta; (4) horizontal branched burrows: Treptichnus cf. T. pedum; (5) horizontal burrows and trails: Gyrochorte isp., Palaeophycus tubularis, Planolites beverleyensis, Psammichnites gigas, Zoophycos isp. Whereas the ichnofauna of the Early Ordovician upper Disi Formation (Fm.) is dominated by cruzianid (C. rugosa group) and diplichnid arthopod traces (“trilobite highways”), the late Middle to early Late Ordovician Dubaydib Fm. contains distinctly smaller, nearly monoichnospecific, but completely surface covering arthropod tracks (C. almadenensis). In places, an amazing monospecific mass occurrence (Skolithos piperock ichnofabric) points to very special palaeoecological conditions during the deposition of the lower Dubaydib Fm. Ichnoassociations of the lower part of the Mudawwara Fm. (middle Late Ordovician) indicate a primarily shallow environment (e.g., Zoophycos isp.). Based on the trace fossil content and lithofacial characteristics, a correlation with North African regions is possible. So, the upper part of the Disi Fm. and the lower part of the Umm Sahm Fm. From Jordan is correlated with the Early Ordovician strata from southeastern Libya by the occurrence of C. goldfussi and C. furcifera. Additional correlations are possible by the shared occurrence of C. rouaulti with western Egypt, Sudan and western Libya. Within the Middle East (Jordan, Saudi Arabia, United Arab Emirates, Iran and Turkey), similar trace fossil assemblages composed of the C. rugosa group and related traces as well as common lithofacies characteristics point to closer palaeogeographic vicinity on a connected shallow shelf region along the costal margin of the Gondwana palaeocontinent.

Ichnological and sedimentological features of the Hongguleleng Formation (Devonian–Carboniferous transition) from the western Junggar, NW China

Two sections of the Late Devonian to Early Carboniferous Hongguleleng Formation in the Sha'erbuerti and Xiemisitai mountains of western Junggar, NW China were logged in detail and studied with particular reference to their trace fossil content and sedimentary features. The Hongguleleng Formation is composed essentially of shallow marine deposits formed in a volcanic arc-related setting. It contains trace fossils including indeterminate ellipsoid structures, indeterminate shallow-pit structures, Chondrites intricatus, Chondrites targionii, Chondrites isp., Dolopichnus gulosus,?Multina isp., Nereites missouriensis, Nereites isp., Palaeophycus tubularis, ?Phycosiphon isp., ?Phymatoderma isp., Rhizocorallium commune, Rosselia cf. socialis, Teichichnus rectus, Teichichnus ispp., Thalassinoides isp., and Zoophycos ispp. These ichnofossils and related bioturbation structures constitute five distinct groups of ichnofabrics: Chondrites–?Phymatoderma, Rhizocorallium commune, anemone dwelling/burrowing, Teichichnus, and Zoophycos ichnofabrics, conforming to an upward trend from the Cruziana to Zoophycos ichnofacies. The volcanic arc setting provides a natural laboratory to investigate the colonisation styles of benthic faunas during the Devonian, especially for environments with widespread and relatively frequent depositional events disturbing background deposition. The distal event beds are especially suitable for the distinction of the relationship between background and post-event ichnofaunas. Simple and composite ichnofabrics have been distinguished. The simple ichnofabrics are typified by the indeterminate ellipsoid “ichnofabric” made by sea anemones, representing short colonisation event and in situ death and burial resulted from relatively high sedimentation rates even during the periods between volcanic explosions. The composite ichnofabrics are characterised by the Chondrites–?Phymatoderma, ?Multina–Zoophycos and multi-tier Zoophycos ichnofabrics, representing vertical migration of benthic faunas in pace with either distal event deposition or steadily accreted sea floor. The colonisation window in the arc-related setting is closely related to sedimentation rates and frequency of depositional events, determining the completeness of burrow system structure and maturity of benthic communities.

Ichnology and sedimentology of the Triassic carbonates of North‐west Sardinia, Italy

AbstractThe classical Middle to Upper Triassic carbonate sections at Monte Santa Giusta and Punta del Lavatoio, North‐west Sardinia (Italy), referred to the Muschelkalk and Keuper lithofacies group, are revisited and their trace fossil content is investigated for the first time. A combined ichnological and sedimentological study reveals insights into the depositional environments, regional context, palaeogeography and sequence stratigraphy. The results indicate deposition on a homoclinal carbonate ramp with broad facies belts. All recognized trace fossils are also known from time‐equivalent deposits of Germany and thus indicate a close affinity between the North‐west Sardinian Triassic and the Germanic Basin. Only a few trace fossils are particularly abundant and these indicate opportunistic colonization by their producers, which is probably related to restricted endobenthic conditions due to reduced oxygen and/or increased salinity. The trace fossil association can be grouped into a softground suite belonging to the Cruziana ichnofacies, and a firmground suite of the Glossifungites ichnofacies. This discrimination enables an interpretation of the northern Monte Santa Giusta section as a carbonate ramp with extensive tidal flats and abundant carbonate accumulation in a relatively proximal position, whereas the southern Punta del Lavatoio section exhibits broad lagoonal environments with reduced sedimentation in a deeper and more Tethys‐influenced area. The Sardinian sections are ichnologically similar to the Anisian–Ladinian succession known from the Tatra Mountains, but differ from it by having a slightly higher ichnodiversity, which again can be attributed to a less restricted lagoonal environment. This study demonstrates the importance of integrating trace fossil analysis in sedimentological and palaeontological investigations of carbonate systems.

Ichnology and sedimentology of the “Argiles de Saïda” formation (Callovo-Oxfordian) of the Djebel Brame (Tiaret, Algeria)

Abstract The focus of this note is an ichnological study of the “Argiles de Saïda” formation (Callovo-Oxfordian) in the Djebel Brame, a region representing the eastern extremity of the Tlemcenian domain and marked by rhythmic clay-sandstone sedimentation. From a lithostratigraphic viewpoint, the formation is composed of two units with a distinct sequential organization and trace fossil content. These deposits are characterized by weak to moderate bioturbation, eleven ichnogenera were found: Bergaueria, Chondrites, Diplichnites, Megagrapton, Neonereites, Nereites, Ophiomorpha, Palaeophycus, Rhizocorallium, Taenidium and Thalassinoides. The basal unit is mainly characterized by fine sediments organized into small turbiditic sequences. Most of the beds are around one centimeter thick except for the conglomerate layer, channelized by the debris flow. This layer is heterometric and polygenic. The soles of the beds are generally marked by flute and groove casts, proof of their erosion by the currents. Most of these siliciclastic beds are organized around a repetitive model, with a massive base and flat, parallel and/or wavy laminae at the summit. Occasionally there are also beds of complex ripple marks, fluid escape structures and convoluted laminae. This sedimentation was deposited in an offshore environment, below the storm action influence threshold. Most of ichnogenera are associated with episodic silica-clastic deposits. The disappearance of Bergaueria and Diplichnites ichnogenera corresponds to the period when the basal conglomerate layer was established, and constituted stressful conditions for the organisms responsible for the two traces. Conversely, above this level, the appearance of Taenidium and Thalassinoides seems to correspond to a colonization by opportunistic endobenthic organisms. The weak hydrodynamism of the depositional environment, as well as the associated trace fossils content, point to the distal part of the Cruziana ichnofacies. The other, coarser, unit is an alternation of greenish clays, carbonate rocks and occasionally slumped sandstone. It is dominated by storm sequences. The more proximal summit shows shoreface deposits marked by phases of emersion. As well as episodes of storms and oolitic deposition, there are, at the top of this unit, deposits from a reefal environment (“Subreefal Layer”). These are indicative of shallow depths. Observable trace fossil content points to the most proximal part of the Cruziana ichnofacies. The trace fossil distribution and sedimentology both reveal hitherto undisclosed bathymetric fluctuations. A major fluctuation, most likely due to tectonic instability, was recorded before the second sequence was established. These results call for the biostratigraphic and structural study of the “Argiles de Saïda” formation in the Tlemcenian domain.

Ichnology of Carboniferous tide-influenced environments and tidal flat variability in the North American Midcontinent

Abstract Trace fossils are sensitive indicators of environmental fluctuations and, accordingly, ichnological studies have the potential to improve facies characterization of marginal-marine systems. Carboniferous intertidal deposits in eastern Kansas and western Missouri accumulated under contrasting palaeoenvironmental conditions, ranging from the open shoreline to fluvio-estuarine transitions. Comparative analysis of these exposures illustrates lateral variations in trace-fossil content and allows characterization of the intertidal ichnofaunas developed in three sub-environments: open marine, restricted bays and fluvio-estuarine transitions. Openmarine tidal flat ichnofaunas are characterized by (1) high ichnodiversity, (2) marine ichnotaxa produced by both euryhaline and stenohaline forms, (3) the presence of both infaunal and epifaunal traces, (4) the presence of simple and complex structures produced by presumed trophic generalists and specialists respectively, (5) dominance of horizontal trace fossils of the Cruziana ichnofacies, (6) presence of multispecific associations, (7) high density, and (8) wide size range. This ichnofauna is present in heterolithic deposits and reflects the activity of a biota that inhabited tidal flats dominated by normal-marine salinities and connected directly to the open sea. Restricted-bay ichnofaunas display (1) low ichnodiversity, (2) ichnotaxa commonly found in marine environments, but produced by euryhaline organisms, (3) dominance of infaunal traces rather than epifaunal trails, (4) simple structures produced by opportunistic trophic generalists, (5) a combination of vertical and horizontal trace fossils from the Skolithos and Cruziana ichnofacies, (6) the presence of monospecific associations, (7) variable density, and (8) small size. This assemblage occurs in heterolithic facies and records the activity of a brackish-water benthic fauna inhabiting intertidal areas of estuarine basins and embayments. Fluvio-estuarine ichnofaunas are characterized by (1) moderate to relatively high diversity, (2) forms typically present in continental environments, (3) the dominance of surface trails and absence of burrows, (4) temporary structures produced by a mobile deposit-feeding fauna, (5) a mixture of trace fossils belonging to the Scoyenia and Mermia ichnofacies, (6) moderate density of individual ichnotaxa, (7) absence of monospecific suites, and (8) small size. This assemblage occurs in tidal rhythmites and records the activity of a typical freshwater/terrestrial benthos inhabiting tidal flats that were developed in the most proximal zone of the inner estuary under freshwater conditions. Through integration of ichnological and sedimentological data, conventional sedimentological interpretations of marginal-marine depositional systems can be refined and enhanced.

Orbital forcing in a ‘Boreal’ Cretaceous epeiric sea: high-resolution analysis of core and logging data (Upper Albian of the Kirchrode I drill core — Lower Saxony basin, NW Germany)

A 245 m (0–245 m subsurface) core of Upper Albian marine sediments from North Germany (research well Kirchrode I) was studied to identify sequences and cycles of sedimentation and related forcing mechanisms on sedimentation in an epeiric sea of the (sub)-‘Boreal’ realm. The core consists of monotonous gray marls with an exceptionally high sedimentation rate of 8–12 cm ka −1. In total, it represents a period of approximately 2.5–4 Ma. A silty glauconite-rich condensed layer marks a change in the succession at 132 m and is paralleled by the first occurrence of E. turriseiffelii and G. bentonensis. The lower part of the core shows lenticular bedding, siderite nodules, average CaCO 3 content of ca. 40% and an abundance of inoceramids ( Inoceramus anglicus, Birostrina lissa, Actinoceramus sulcatus). The upper part is characterised by plane bedding, common siderite layers, an average CaCO 3 content of ca. 35% and an abundance of aucellinas ( Aucellina gryphaeoides). According to lithology and ichnofacies, the succession represents a transgressive–regressive cycle with distinct bimodality of lithology, fossil, and trace fossil content together with reworking and redeposition at the base and top. We studied well-log-data, sediment composition, sediment color, and carbonate content and applied various mathematical analysis techniques to these data (principal component analysis, spectral analysis (Fourier-transform), autocorrelation). Spectral analysis revealed well-pronounced periodic cyclicity in the upper part of the Upper Albian (12, 8, 4.5, 3.4, 1.7 m). The 12 m-eccentricity cycles are the most intense cycles reflecting periodic changes in the terrigenous clastic supply. Chaotic transitional intervals occur around the Middle–Upper Albian, Upper Albian and topmost Albian parts of the core. They are characterised by non-cyclic changes in litho- and biofacies. Mathematically, these changes correspond to singularity points. They are preceded by non-orbital high-frequency variations in carbonate content and in γ-ray.

Depositional Environments and Diagenesis of D Sandstone, Wild Horse Field, Weld County, Colorado: ABSTRACT

Wild Horse field is located on the gentle east flank of the Denver basin, northwest of Fort Morgan, Colorado. Production was established during 1981 from a 12-ft (3.7 m) thick porous sandstone in the lower part of the D sandstone of Cenomanian age. To date, 10 producing wells have been completed. Proven productive area is 1,800 ac and estimated reserves are 1.2 million bbl oil equivalent. D sandstone facies form complex reservoirs associated with regressive deltaic and marine sandstone deposited during a regional sea level drop 95 Ma. Traps are primarily stratigraphic in nature although fracturing has enhanced production. The D sandstones in the Wild Horse field area are interpreted to be the product of an episodic northwestward progradation of a lobate river-dominated delta system. On the basis of differences of the internal structure, textures, mineral composition, and trace-fossil content, the D sandstone is divided into five lithofacies: shoreface, prodelta platform, delta front, delta plain, and transgressive marker sandstone. The producing sandstones occur in overlapping bars proximal and lateral to principal channels in a bay-filled sequence. Calibration of well logs using cores allows detailed subsurface mapping of producing facies for more efficient development of the field. Original porosity has been reduced mainly by quartz overgrowth cementation. Porosity interconnection is present due to dissolution of framework grains and of the early diagenetic calcite cement. Pore-filling cements such as chlorite, kaolinite, and pyrite may produce formation damage if not treated during completion operations. End_of_Article - Last_Page 871------------

Differentiation of Delta-Front and Barrier Lithofacies of the Upper Cretaceous Pictured Cliffs Sandstone, Southwest San Juan Basin, New Mexico

The Upper Cretaceous Pictured Cliffs Sandstone represents a regressive littoral marine unit deposited during the final retreat of the Cretaceous epeiric sea in the southwestern San Juan Basin, New Mexico. Differences in rock type, internal and penecontemporaneous deformation structures, textural sequences, mineral composition, and trace fossil content permit recognition of laterally contemporaneous delta-front and barrier lithofacies in the Pictured Cliffs Sandstone. The delta-front lithofacies consists of distal bar, distributary mouth bar, and distributary channel deposits. The barrier lithofacies consists of shoreface, beach, washover channel, tidal inlet, tidal channel, and ebb-tidal delta deposits; these lithofacies are coarsening-upward sequences of shale, siltstone, and sandstone, locally scoured in the upper part by fining-upward channel deposits. The delta-front lithofacies contain abundant penecontemporaneous deformation structures in the form of ball-and-pillow, diapiric, and slump structures as well as convolute bedding and microfaults. In contrast, the laterally equivalent shoreface deposits of the barrier lithofacies lack these deformation structures. The channel deposits of the delta-front lithofacies contain large-scale convolute lamination and a few burrows, in contrast to the channel deposits of the barrier lithofacies, which contain common herring­bone crossbeds separated by reactivation surfaces, bidirectional but ebb dominated festoon crossbeds, and more abundant burrows. Quartz content of the barrier lithofacies varies from 43 to 74 percent, whereas in the delta­ front lithofacies it varies from 29 to 60 percent. The difference in quartz content between these lithofacies suggests some cleaning-up process in the deposition of the barrier lithofacies, particularly in the preserved beach deposit. The delta-front and barrier lithofacies were probably deposited along mesotidal shorelines. The recognition of laterally contemporaneous delta-front and barrier lithofacies of the Pictured Cliffs Sandstone allows delineation of potentially economic coal-producing deposits in the delta-plain lithofacies flanked by back­ barrier lithofacies in the overlying prograded Fruitland Formation.