Biogenic Sedimentary Structures Research Articles

Full-Body Impressions: A category of trace fossils unique to exceptionally preserved bedding planes and indicators of true substrates

Certain biogenic sedimentary structures can be considered to be reliable indicators of true substrates. Full-body impressions, or FBIs, are trace fossils that are shallow, highly-detailed impressions of the ventral axial anatomy of low body mass animals made while living . Their mode of preservation makes FBIs distinct from undertracks, body moulds, or passive tool marks. FBIs are made at the air- or water-substrate interface during sedimentary stasis. Associated trace fossils, like those that exhibit excavations with preserved waste mounds and very near-surface burrow roofs, located on the same bedding plane, can support the interpretation of true substrate preservation. Integration of the biogenic and sedimentological data from both Carboniferous and Pleistocene sites with well-preserved bedding-plane trace fossil assemblages has confirmed the conditions under which true substrates are preserved. These include periods (as brief as days to weeks) of sedimentary stasis, followed by gentle deposition without erosion, and without the need to invoke biofilms or biomats as consolidants. The potential for these taphonomic conditions exist in both alluvial and lacustrine environments, as well as intertidal-estuarine valleys, as described by other published examples of FBI preservation. Future FBI discoveries will prove useful in identifying true substrates across a range of time periods and environments.

Effects of X-ray computed tomography (CT) on the ichnologic interpretation of the Mira River estuary sediment core, SW Portugal

Computed tomography (CT) is a relatively new technique in ichnofossil analysis, which permits superior identification of individual trace fossils, their morphology, infill, tiering relationships, and preservation potential, thus providing better environmental interpretations. It also allows non-professional ichnologists to interpret trace fossils in 3D slices with ease, especially in relatively homogeneous and mud-rich sediments. Herein, CT imagery results have been compared with conventional core logging results based on two push core samples from a muddy tidal flat of the Mira River estuary, Portugal. CT images provide a significantly more accurate description of cores and their environmental interpretation due to enhanced visibility of physical and biogenic sedimentary structures. They also reveal complex tiering relationships between burrows with preferential preservation of deeper tiers. The appearance of stacked Scalichnus-like and other siphonichnidal burrows made by infaunal bivalves indicates discontinuous deposition on a tidal flat likely caused by seasonally related fluctuations in an estuarine environment.

Sediment reworking of intertidal sediments by the benthic foraminifera Haynesina germanica: the importance of motion behaviour and densities.

This study aimed to describe for the first time the vertical motion behaviour of the intertidal foraminifera Haynesina germanica and its contribution to bioturbation. Its infaunal behaviour leads to the creation of a one-end tube within the first centimetre of sediment. In addition, a vertical trail following behaviour was described for the first time in foraminifera, which may be linked to the sustainability of the biogenic sedimentary structures. As a consequence, H. germanica produces a vertical transport of both mud and fine sediment fractions similarly to the sediment reworking mode reported for gallery-diffusor benthic species. This finding allows us to refine the bioturbating mode of H. germanica, previously classified as surficial biodiffusor. Furthermore, sediment reworking intensity appeared to be dependent on the foraminiferal density. H. germanica would adapt its motion behaviour to deal with the intra-specific competition for food and space that may occur when density increases. Consequently, this behavioural modification would affect both the species and the individual contribution to sediment reworking processes. In fine, sediment reworking in H. germanica may further contribute to the bioirrigation of intertidal sediments, which has implications for oxygen availability in sediments and on aerobic microbial processes involved in carbon and nutrient cycling at the sediment-water interface.

Sedimentological and ecological significance of a biodeformational structure associated with an unusual feeding behavior in gulls (Larus sp.)

Shorebirds produce a range of biogenic sedimentary structures related to their feeding behaviors, the most common of which are probing behaviors that result in morphologically simple impressions or indentations on the surface of a sedimentary substrate. Here we describe an unusual biodeformational structure made by a feeding gull (Larus sp.) produced as the tracemaker kneaded the sediment by moving its feet back and forth in place. This process liquified the sediment making it easier to catch invertebrate prey — the most common of which is the varnish clam (Nuttallia obscurata) — that are advected to the top of the liquified sediment. The bird retreated slowly backward as the sediment was liquified, an effort that is interpreted to represent continued and ongoing feeding in the sediment of prey-rich substrates. The resulting structure comprises a series of nested, concavo-convex sediment mounds and a terminal bowl-shaped impression. The aim of this paper is to document the trace–tracemaker association and provide a means of comparison with similar structures. Most notably, the structure bears similarities to Piscichnus, which represents ray feeding traces produced by hydraulic jetting (fodichnia) or nesting behaviors (calichnia) in fish. Piscichnus, however, lacks the nested mounds that result from the tracemaker systematically moving backward as it searches for food.

Upper Pliocene bivalve shell concentrations from the Lower Chelif basin (NW Algeria): Systematics, sedimentologic and taphonomic framework

Sedimentologic and palaeontological investigation of the Upper Pliocene Slama Formation in the Lower Chelif Basin (NW Algeria) led us to collect important bivalve assemblages for taxonomic and taphonomic purposes. A rather comprehensive inventory list of Upper Pliocene bivalves from northwestern Algeria is now available and consists of 30 species, 17 of which are extinct ones. Four principal taphonomic attributes were analysed: bioerosion, encrustation, fragmentation, and abrasion. Physical and biogenic sedimentary structures are used for palaeoenvironmental interpretations. The taphonomic, sedimentologic and ichnological characteristics of most of the deposits suggests they originated from discontinuous processes of winnowing and bypassing of sediments, probably due to the action of storms in shallow waters, mainly in the shoreface depositional environment. The bivalve assemblage is dominated by disarticulated valves and displays significant taphonomic alteration in the shells. Sclerobionts traces in shells particulary affect the oyster shells. Bioerosion traces are predominately those of clionid sponges (Entobia isp.), polychaetes (Maeandropolydora isp. and Caulostrepsis isp.), bivalves (Gastrochaenolites isp.), and of predatory gastropods (Oichnus isp.). Among the sclerobionts, the identified encrusters were juvenile oyster recruits, barnacles, polychaetes (serpulid tubeworms), bryozoans (Microporella sp. and Acanthodesia sp.), and vermetid gastropods (Petaloconchus intortus).

The late Holocene Erin deflected and asymmetric wave-dominated delta – Puerto Grande Bay, Trinidad

The Erin modern marginal-marine depositional system sits along the Trinidad southwestern coastline. It is among the many unstudied and undocumented modern, dynamic coastal depositional systems around Trinidad. Our study defines the Erin system as being a deflected and asymmetric wave-dominated delta, and in so doing, elucidates the dynamics of the Erin system. This was done using a compendium of satellite images, temporal cross-shore elevation profiles, modern shallow sediment cores, and sediment samples.Geomorphologically, the Erin system comprises a vegetated delta plain and the unvegetated modern deposits. The delta plain has four amalgamated sand bars with intercalated lagoonal deposits. The unvegetated modern deposits is defined as the fifth bar of the system. These five bars were loosely correlated to the five 6th order eustatic cycles of the Holocene highstand. The modern, unvegetated deposit of the fifth bar is divided into an updrift segment and a downdrift segment relative to the inlet mouth. The updrift segment comprises a spit and beach depositional elements, while the downdrift segment comprises a barrier spit, back-barrier lagoon, rip-channels, and sometimes a bayhead delta at the Erin River mouth. The dynamic, annual evolution of the spit reflects a seasonally controlled, possibly cyclical evolution wherein the delta transitions from being asymmetric to deflected-asymmetric. This phenomenon is postulated to be brought on by seasonal changes in the wave regime, and not, as one might expect, seasonally controlled river discharge. That is, during the summer wave season, when net-deposition occurs, the system morphology is deflected as a consequence of increase sedimentation in the nearshore. During the winter wave season, when net-erosion is expected, the system morphology reflects that of a typical asymmetric delta, as a consequence of reduced sedimentation in the nearshore. This cyclical movement of sediment is also observed in cross-shore elevation profiles.Sedimentologically, six depositional elements were sampled using sediment cores: foreshore, updrift spit, channel bars, mouth bar, barrier spit (downdrift), and back-barrier lagoon. Physical sedimentary structures reflected wave energy dominance across the system with an increase in tidal signatures within the lagoon deposits and lower foreshores. Biogenic sedimentary structures were limited across much of the system, but the traces recorded were mostly isolated in the downdrift back-barrier lagoon deposits, and few in the upper barrier spit. Grainsize distributions showed an average grainsize of fine sand across the system with coarse-grained, poorly sorted, bio-clastic sands present as channel lag deposits. An increase in mud content was recorded in the downdrift segment of the delta. The geomorphological, sedimentological, and ichnological data described above provided sufficient evidence to define the Erin system as an asymmetric wave-dominated delta with seasonally controlled deflected morphology.

Three-dimensional stromatolites from Maastrichtian–Danian Yacoraite Formation, Argentina: modelling and assessing hydrodynamic controls on growth patterns

AbstractStromatolites are biogenic sedimentary structures formed by the interplay of biological (microbial composition) and environmental factors (local hydrodynamic conditions, clastic input and/or water chemistry). Well-preserved, three-dimensional (3D) fossil stromatolites are key to assessing the environmental factors controlling their growth and resulting morphology in space and time. Here, we report the detailed analysis of well-exposed, highly informative stromatolite build-ups from a single stratigraphic horizon within the Maastrichtian–Danian Yacoraite Formation (Argentina). This study focuses on the analysis of depositional processes driving intertidal to shallow subtidal stromatolites. Overall depositional architecture, external morphology and internal arrangement (mega, macro, meso and microstructures) of stromatolite build-ups were analysed and combined with 3D photogrammetric models, allowing us to decipher the links between stromatolite structure and tidal dynamics. Results suggest that external morphology and architecture of elongated and parallel clusters grew under the influence of run-off channels. The internal morphology exhibits columnar structures where the space between columns is interpreted as recharge or discharge channels. This work supports the theory that stromatolites can be used as a high-resolution tool in the assessment of water dynamics, and provides a new methodological approach and data for the dynamic reconstruction of intertidal stromatolite systems through the geological record.

Impact of diagenetic processes on the petrophysical properties and quality of the Miocene “Reefal limestone” reservoir in Al-Hamd field, Gulf of Suez, Egypt

Unconventional reservoirs have burst with a great force in the oil and gas worldwide production. Reefal limestone reservoir is one of them. The present study deals with the reefal carbonate Hammam Faraun Member in Al-Hamd oil field. This study focus on the interpretation of sedimentological and petrophysical data to show the effect of diagenetic processes on middle and lower Miocene reefal carbonate reservoirs in Al-Hamd oil field. Comprehensive petrophysical analysis for Hammam Faraun Member was performed using wireline logs and core data to determine the proper petrophysical parameters. Of the reservoir intervals. The analytical reservoir rock achieving the main reservoir parameters as shale content (Vsh), effective porosity (Oeff), water and hydrocarbon saturation (SW and Shr) as well as the net-pay thickness. The Formation Micro Imager (FMI) was also applied to detect the variation, types, and directions of the fracture systems that present in the lower and middle Miocene reefal limestone reservoir. Petrographic analysis was done, indicating the presence of a clear effect of diagenetic factors on the quality, productivity, and efficiency of the reefal limestone reservoirs behavior. The diagenetic factors include dolomitization, slicification, recrystallization, and solution process which affect greatly the petrophysical characteristics of the reefal carbonate Hammam Faraun reservoir in the study area. The core analyses were also used to detect the paleo environment, associated textural/ lithological and sedimentological characteristics to gain and understand the factors responsible for the productivity behavior of the reservoir in the Al-Hamd oil field. Rock facies have been divided as specific characteristics and were further described considering their color, texture, grain-size characteristics, and the depositional and biogenic sedimentary structures.

Origin of compound biogenic sedimentary structures in Eocene strata of Wadi El-Hitan universal heritage area, Fayum, Egypt: Mangrove roots or not?

Ichnological data are integrated with sedimentologic data and body fossil content to reconsider the origins of the biogenic sedimentary structures in upper middle Eocene strata of Wadi El-Hitan (UNESCO universal heritage area) in Egypt. Three types of rhizoliths (Type 1 to 3) are recognized, in addition to co-occurrence of six common marine ichnogenera (Ophiomorpha, Skolithos, Thalassinoides, Palaeophycus, Teichichnus and Taenidium). Fossil content comprises bivalves (Ostrea sp., Cardia sp., Cardium sp., Carditopsis sp. and Pinna sp.), gastropods (Turritella sp.), scaphopoda (tusk shells), arthropods (crabs and Balanus sp.) and the larger foraminifer Nummulites sp. as well as bony fossils of Basilosaurus isis, Dorudon atrox, crocodiles, sharks, rays and saw fish. Facies characteristics, fossil content, rhizoliths and invertebrate trace-fossil suites imply a bay-margin origin of the plant-and animal-associated biogenic sedimentary structures. Importantly, characteristics such as downward tapering and/or branching into smaller branches in addition to external and internal ornamentations are used to distinguish rhizoliths from burrows. Comparison between modern mangrove environments (i.e., substrates, fauna and flora) with the examined biogenic sedimentary structures can be used to support the marginal marine mangrove-swamp origin. Importantly, living mangrove roots are characteristically associated with marine bioturbation, which can be compared to the structures reported in the Eocene bioturbated bed. Large vertical Type-1 rhizoliths are interpreted as mangrove tree trunks. Type-2 rhizoliths correspond to prop/stilt roots similar to those of living Rhizophora sp. and locally to pneumatophore / anchor roots of living Avicennia sp. Type-3 rhizoliths are ascribed to sea-grasses roots and / or tertiary roots and root hairs. The examined compound biogenic sedimentary structures represent an excellent example for distinguishing previously misinterpreted plant roots (rhizoliths) from animal trace fossils (burrows) in marine setting as well as recognizing mangrove rhizoliths in the rock record.

BURROWS OF THE POLYCHAETE PERINEREIS AIBUHIUTENSIS ON A TIDAL FLAT OF THE YELLOW RIVER DELTA IN CHINA: IMPLICATIONS FOR THE ICHNOFOSSILS POLYKLADICHNUS AND ARCHAEONASSA

Abundant biogenic sedimentary structures produced by Perinereis aibuhitensis (formerly Nereis) occur in tidal flats of the Yellow River Delta in China. The burrows of Perinereis are visible as vertical tubes and irregular strings in slabbed cores. The cores were studied by X-ray radiography, computed tomography and VGStudio MAX to obtain three-dimensional images of the burrows and their inner structure. The burrows are vertical to steeply oblique, Y-shaped tubes with multiple branches. They are considered as analogues of the trace fossil Polykladichnus. Some gutter-like surface traces are similar to the trace fossil Archaeonassa. Perinereis burrows and trails occur mainly in the mixed flat, less frequently in the mud flat or sand flats. Potentially abundant occurrences of some analogous fossil burrows and trails (Polykladichnus, Archaeonassa) could mark position of the intertidal zone.

Stratigraphy and Sedimentology of Middle Jurassic Sequence of Chorar Island, Patan District, Kachchh Basin, Gujarat

ABSTRACT Chorar Island exposes ∼109 m thick middle Jurassic (Bathonian-Callovian) succession in the eastern most part of the Kachchh Basin, Patan District, Gujarat and is divided into two, Khadir and Gadhada formations. It mainly comprises of mixed siliciclastic-carbonate sediments and limestones; the shales dominate the lower part of the succession while the top of the succession is marked by ferruginous sandstone which also forms the vast, prominent peripheral zone of the Chorar dome. The field and laboratory analysis of the succession reveals nine lithofacies which includes ferruginous sandstone, cross bedded white sandstone, micritic sandstone, allochemic sandstone, sandy micrite, mudstone, sandy allochemic limestone, coralline limestone and shale. The mix siliciclastic-carbonate sediments and ferruginous facies are fossiliferous in nature and display sedimentary structures, like ripple marks, cross- and planar-lamination with biogenic sedimentary structures. Coralline limestone facies comprise of large size (>1m diameter) corals, which are diagenetically modified severely and have lost its original internal structures. The sediment characteristics and associated bioclasts indicates low to moderate wave and current energy in shoreface-offshore subsequently changing to wave dominated shoreface during the deposition of the middle Jurassic sediments of the Chorar Island.

Big bedding planes: Outcrop size and spatial heterogeneity influence trace fossil analyses

Roadcuts, core, cliffs and even mountainside exposures often limit the lateral extent to which we can assess bioturbation on bedding planes, simply because exposures of such surfaces are generally rare or small. Such constraints may hamper paleoenvironmental and paleoecological interpretations drawn from facies where most bioturbation is bed-parallel or patchily distributed. To explore how acute such constraints are, we conducted a pilot study of bioturbation in three exceptionally large (>5 m2), well-exposed, paleoenvironmentally similar bedding planes from the Cambrian of Wisconsin. The goal was to test the hypothesis that trace fossils and biogenic sediment disruption can be distributed heterogeneously at the scale of meters to decameters. Mapping the size variation and distribution of trace fossils across these bedding planes reveals variable patchiness. Individual bioturbated patches tend to be large (m-scale), but the density of biogenic sediment disruption within these patches is quite heterogeneous. In addition, bioturbated areas are separated by zones of undisturbed sediment that vary in size from <0.5 m2 to >3 m2. These observations suggest that ancient bedding planes, like modern substrate surfaces, can exhibit considerable lateral bioturbation heterogeneity at a range of spatial scales. Caution is thus urged when extrapolating the distribution and diversity of trace fossils and other biogenic sedimentary structures across broad sedimentary horizons based on small (≤1 m2) bedding plane exposures.

The applicability of modern tidal analogues to pre‐vegetation paralic depositional models

AbstractIn modern siliciclastic environments terrestrial and aquatic vegetation binds substrate, controls weathering and erosion rates, influences run‐off, sediment supply and subsequent depositional architecture. This study assesses the applicability of modern depositional models that are impacted by vascular vegetation, as analogues for ancient pre‐land plant systems. A review of pre‐Devonian published literature demonstrates a paucity of described tidal successions; this is possibly due to the application of modern analogues for interpreting the record when there is a lack of tidal indicators. This paucity suggests a need for revised models of tidal deposition that consider the different environmental conditions prior to land plant evolution. This study examines the Ordovician–Silurian Tumblagooda Sandstone, which is exposed in the gorge of the Murchison River and coastal cliffs near Kalbarri, Western Australia. The Tumblagooda Sandstone comprises stacked sand‐rich facies, with well‐preserved bedforms and trace fossils. Previous interpretations of the depositional setting have proposed from a mixed sheet‐braided fluvial and intertidal flats; to a continental setting dominated by fluvial and aeolian processes. An enigmatic element is the rarity of mud‐rich facies preserved in the succession. Outcrop logging, facies and petrographic analysis record dominantly shallow water conditions with episodes of emergence. Abundant ichnotaxa indicate that marine conditions and bi‐directional flow structures are evidence for an intertidal and subtidal depositional environment. A macrotidal estuary setting is proposed, with evidence for tidal channels and repeated fluvial incursions. Physical and biogenic sedimentary structures are indicative of tidal conditions. The lack of clay and silt resulted in the absence of flaser or lenticular‐bedding. Instead cyclic deposition of thin beds and foreset bioturbation replaced mud drape deposits. Higher energy conditions prevailed in the absence of the binding activity of plants in the terrestrial and marine realm. This is suggestive of different weathering processes and a reduction in the preservation of some sedimentary features.

Sedimentological and Ichnological Characterization of the Middle To Upper Devonian Horn River Group, British Columbia, Canada: Insights Into Mudstone Depositional Conditions and Processes Below Storm Wave Base

Abstract The Middle and Upper Devonian Horn River Group in northeastern British Columbia, Canada, consists predominantly of organic-rich mudstones that are typically described as black shales. This stratigraphic unit has seen substantial exploration and development for natural gas during the last decade. Although black shales such as the Horn River Group have historically been interpreted as deposited in anoxic deep-water basins, detailed sedimentological and ichnological analyses of eleven Horn River Group cores indicate that the depositional conditions varied significantly with respect to paleoenvironments, redox conditions, and physical processes, resulting in distinctive sedimentary facies. This study integrates data on lithology and physical and biogenic sedimentary structures from detailed core descriptions combined with total-organic-carbon content to better understand depositional processes and conditions. Ten mudstone lithofacies and three lithofacies associations are identified. Massive mudstones and pyrite-rich mudstones display very rare planar lamination and graded beds and scarce bioturbation (BI 0–1), and are interpreted to represent anoxic waters, below storm wave base (SWB), with conditions of relatively low to moderate energy. Heterolithic, laminated, and more bioturbated lithofacies are interpreted to represent oxygenated waters below SWB with relatively high-energy conditions. Overall bioturbation intensity varies between moderate to intense (BI 3–6). Where these lithofacies are not intensely bioturbated, oxygenated lithofacies show combinations of well-preserved physical sedimentary structures, including horizontal parallel lamination, soft-sediment deformation, double mud drapes, graded beds, and current ripples. A third lithofacies association represents conditions intermediate between anoxic and oxygenated lithofacies associations, mainly based on local changes in the ichnological characteristics. These lithofacies show either intense or sparse bioturbation (BI 4–6 or BI 0–1, respectively) depending on the core location, possibly indicating local changes in the depositional conditions and processes (e.g., variations in the oxygen content and/or sedimentation rate). They can also be found in thick anoxic and oxygenated deposits. These lithofacies display intervals of faint lamination, amalgamated current ripples, and normally graded bedding. The cores collectively display significant spatial and stratigraphic heterogeneity in lithology, sedimentary structures, and bioturbation that are related to relative water depth, oxygen content, sediment input, and deep-water currents. We interpreted bioturbation intensity to vary mainly as a function of oxygen content related to proximity to the basin margin and sea–level fluctuations, although secondary stress conditions (e.g., nutrient content and sedimentation rate) may also be important. Unbioturbated and massive fabrics represent anoxic to dysoxic conditions. Current-generated structures are present, mainly in the central and distal parts of the basin, and are interpreted to represent the presence of contour currents. In the proximal parts of the basin, laminated and heterolithic units are more common and more bioturbated than in the central and distal basin. This study thus can provide significant insights into other shale basins that show similar lateral and vertical variations. Integration of multidisciplinary studies, particularly sedimentology, ichnology, and total organic carbon aids in understanding and modeling the complexity of these systems.

Modeling core-scale permeability anisotropy in highly bioturbated “tight oil” reservoir rocks

A high-resolution simulation model of a heterogeneous low-permeability rock sample is used to investigate the effects of physical and biogenic sedimentary structures on scaling and anisotropy of absolute permeability at the core scale. Several simulation sub-samples with random locations and volumes were also selected for evaluation of the effects of scale and lithological composition on the calculated permeability. Vertical and horizontal permeability values (from whole core simulation) are in good agreement with routine core analysis (RCA) measurements from offsetting cores. Despite relatively good reservoir quality associated with geobodies of biogenic and relic bedding structures, results from the full diameter core simulation demonstrate that their limited volumetric abundance and restricted connectivity prevent these features from controlling fluid flow in these rocks. In fact, permeability seems to be dominated by the tighter encasing matrix, which exhibits average permeability values very close to those reported from RCA. Geometric averaging offers a better representation for the upscaling of horizontal permeability datasets; whereas, both geometric and harmonic averaging work similarly well for the vertical measurements. The methodology used in this work is particularly applicable to the detailed characterization of reservoir rocks with a high degree of heterogeneity caused by biological reworking and diagenesis.

Sedimentology and ichnology of the fluvial reach to inner estuary of the Ogeechee River estuary, Georgia, USA

Through the integration of sedimentological and ichnological observations, this paper explores the character of sediments deposited across the fluvio-tidal transition zone of the upper microtidal, mixed-energy, sand-dominated Ogeechee River estuary, Georgia, USA. A transect of tidally influenced to fluvial channel-bars and their facies variability is reported. Field and laboratory methods were employed, including observation of physical and biogenic sedimentary structures on the point-bar surfaces and in trenches, collection of grab samples, suction and box coring, grain size and total organic carbon analyses, optical microscopy, core logging, and daylight photography. The data presented in the paper can help in predicting facies changes across the fluvio-tidal transition of sand-dominated fluvio-tidal deposits in the rock record.The lower inner estuary is characterized by medium-fine and fine-medium sand with planar and trough cross-bedding, small-scale ripple lamination, tidal sedimentary structures (flaser and wavy bedding, herringbone cross-stratification), abundant organic debris, and mud rip-up clasts. Bioturbation of the intertidal point bars is low, but cryptobioturbation is locally observed. Upper inner estuary deposits comprise coarse-medium- and medium-coarse-grained sand, and are characterized by faint high-angle planar and trough cross-bedding. Organic debris, mud rip-up clasts, herringbone and current-ripple lamination are rarely observed. Bioturbation is absent to sparse. The fluvio-tidal transition is represented by very-coarse- to coarse-grained sand and granules. Physical sedimentary structures constitute massive, graded planar and trough cross-bedding with abundant plant detritus. Except for rare Siphonichnus- and Lockeia-like traces, bioturbation is absent. The fluvial setting is characterized by coarse-medium sand with unidirectional cross-bedding, current-ripple lamination, and rare organic-rich mud clasts. Bioturbation is absent. Inner estuary and fluvio-tidal transition zones are bounded by supratidal marsh deposits, and may develop a substrate-controlled Glossifungites ichnofacies, comprising Psilonichnus-like burrows. The fluvial reach is surrounded by forested floodplain with crayfish domes and chimneys, forming Camborygma-like traces.

Biogenic-sedimentary structures of the Ordovician-Khabour formation from the Northern Thrust Zone, Kurdistan, Iraq

The Ordivician-Khabour Formation from the Northern Thrust Zone of Iraqi-Kurdistan comprises between 500 and 800 m of alternating predominantly greenish-gray sandstones, siltstones, and shales. The succession has revealed an abundant ichnofossils characterized by 11 ichnogenus, namely: Helminthopsis, Gordia, Cruziana, Rusophycus, Monomorphichnus, Rhizocorallium, Thalassinoide, Planolite, Paleophycus, Deplocraterion, and Skolithose. Ethologically, the ichnofossils are distributed among domichnia and fodinichnia groups. This association of ichnofossils contains elements of the Skolithose and Cruziana ichnofacies. The presence of these ichnofacies indicates variations in energy of the sedimentary environment. High-energy condition with sandy-shifting substrate in foreshore zone is related to the Skolithos ichnofacies, while the Cruziana ichnofacies indicates unconsolidated-soft substrate developed under low-energy condition in the shoreface/offshore zone. These ichnogenera indicate shoreface-offshore zone of shallow-marine environment for the deposition of the rocks of the Khabour Formation.

Tubular Tidalites: A Biogenic Sedimentary Structure Indicative of Tidally Influenced Sedimentation

Abstract The most conclusive evidence of tidal sedimentation consists of deposits that exhibit evidence of rhythmic sedimentation attributable to tidal cyclicity. Until now such deposits have been limited to physical sedimentary structures. Tubular tidalites, defined herein, are combined biogenic–physical sedimentary structures that provide compelling evidence for tidal mediation in sedimentary successions. These structures consist of rhythmically bedded alternating layers of fine-grained and coarse-grained laminae deposited within open framework burrows such as Arenicolites, Ophiomorpha, Palaeophycus, Psilonichnus, and Thalassinoides. Importantly, the open framework burrows represent natural sediment traps that potentially preserve depositional cycles that might be missing due to high levels of bioturbation in settings such as intertidal flats and lagoons. The interpretation of the burrow infills as being tidally modulated is tested and supported in three ways: using exponential smoothing of thickness data on burrow-infilling laminae to identify rhythmic trends in laminae thicknesses, visually fitting sinusoidal curves to the raw thickness distributions, and using Fast Fourier Transform analysis. Considering the morphology of tubular tidalites presented, the parameters that promote the occurrence of tubular tidalites include an open aperture, bimodal sediment availability, tidal influence in sedimentation, and low overall sedimentation rates. Tubular tidalites have been identified from tidally influenced successions in Mesozoic, Cenozoic, and modern deposits and provide evidence of tidal influence in sedimentary successions where other indicators may be ambiguous.

AN ETHOLOGICAL INTERPRETATION OF ZOOPHYCOS BASED ON PERMIAN RECORDS FROM SOUTH CHINA AND SOUTHEASTERN AUSTRALIA

Research Article| May 01, 2015 AN ETHOLOGICAL INTERPRETATION OF ZOOPHYCOS BASED ON PERMIAN RECORDS FROM SOUTH CHINA AND SOUTHEASTERN AUSTRALIA LI-JUN ZHANG; LI-JUN ZHANG 1Key Laboratory of Biogenic Traces and Sedimentary Minerals of Henan Province, Henan Polytechnic University, 2001 Century Avenue, Jiaozuo, Henan, 454003, China e-mail: ljzhanghpu@gmail.com Search for other works by this author on: GSW Google Scholar G.R. SHI; G.R. SHI 2School of Life and Environmental Sciences, Deakin University, Melbourne Burwood Campus, 221 Burwood Highway, Burwood, Victoria 3125, Australia Search for other works by this author on: GSW Google Scholar YI-MING GONG YI-MING GONG 3State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, 388 Lumo Road, Wuhan, Hubei, 430074, China Search for other works by this author on: GSW Google Scholar PALAIOS (2015) 30 (5): 408–423. https://doi.org/10.2110/palo.2013.060 Article history received: 18 Jun 2013 accepted: 11 Feb 2015 first online: 14 Jul 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation LI-JUN ZHANG, G.R. SHI, YI-MING GONG; AN ETHOLOGICAL INTERPRETATION OF ZOOPHYCOS BASED ON PERMIAN RECORDS FROM SOUTH CHINA AND SOUTHEASTERN AUSTRALIA. PALAIOS 2015;; 30 (5): 408–423. doi: https://doi.org/10.2110/palo.2013.060 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyPALAIOS Search Advanced Search Abstract Abundant, well-preserved Zoophycos is common in the lower and middle Permian paleotropical neritic limestone of South China and in the middle Permian glaciomarine lithic wackestone of southeastern Australia. Zoophycos from both regions is composed of a marginal tube and a tongue-like spreiten complex, the latter itself consisting of primary lamellae in planar view and backfill structures (dark and light menisci) in cross-sectional view. The Zoophycos tracemaker is interpreted to have periodically collected and fed on the surrounding nutrient-enriched sediments within a shallow depth of the seafloor. The dark menisci may correspond to the burrowing phase, whereas the light menisci may be related to a multiple-behavior phase, including dwelling, feeding, farming, resting, and excreting. Symbiotic microorganisms (e.g., sulphate-reducing bacteria) may have been closely involved with the Zoophycos tracemaker in producing the complex structures of the spreiten, based on the abundant pyrite framboids that were found in the Zoophycos spreiten. We suggest that Zoophycos is not simply a biogenic sedimentary structure formed by the motion of the tracemaker; rather it represents a set of complex and elaborate biogenic structures formed by a succession of life behaviors of the tracemaker along with its symbiotic microorganisms. The complete formative process of Zoophycos is reconstructed and linked to its morphology, based on this interpretation. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Sedimentary features of Onagawa Bay, northeastern Japan after the 2011 off the Pacific coast of Tohoku Earthquake: sediment mixing by recolonized benthic animals decreases the preservation potential of tsunami deposits

The huge tsunami waves induced by the 2011 off the Pacific coast of Tohoku Earthquake severely affected shallow marine ecosystems along the Pacific coast of northeastern Japan. This study examined core samples using X-ray radiography, computed tomography scanning, and grain size analysis to identify temporal changes in the physical and biogenic sedimentary structures of seafloor deposits in Onagawa Bay, northeastern Japan, following the 2011 tsunami. Cores were sampled during research cruises in October 2012, December 2013, and April 2014. The seafloor sediments consisted of two lithological layers. The upper section (between the surface and a depth of 8 cm) was composed of muddy sediments deposited by normal depositional processes and/or the weakening tsunami currents. In contrast, the lower part of the cores (below a depth of 8 cm) consisted of tsunami-induced deposits, i.e., horizontally laminated sandy sediments generated by the strong currents associated with the 2011 tsunami. Sampling of these sediments in 2012 and 2013 showed burrows of up to 10 mm in diameter, but restricted to the upper mud layer. In contrast, in 2014, 20–40-mm-diameter mud-filled burrows were seen in both the upper mud and lower sand layers, indicating that recolonization of the seafloor sediment by large and deep-burrowing animals began within 3 years of the 2011 tsunami. The intense sediment mixing by large burrowing animals will homogenize the seafloor sediment and decrease the preservation potential of the tsunami deposits in this bay.