Marine Trace Fossils Research Articles

Sequestrichnia – an ethological category of marine trace fossils recording the collection and stowage of nutritional material within burrows

Sequestrichnia – an ethological category of marine trace fossils recording the collection and stowage of nutritional material within burrows

Diving neoichnology: underwater fieldwork focusing on organism and seafloor ecosystem interactions

Because almost all marine trace fossils were produced in underwater settings such as shoreface, offshore, continental shelf, slope, trench, and abyssal plain, investigating their modern analogues in these settings is important. In this discussion, I delve into a range of recent developments in the field of underwater neoichnology, concentrating on both my own contributions and those of fellow researchers. These advancements have been achieved through investigations conducted in various underwater settings, spanning from shallow coastal waters to the depths of the ocean floor. Our research methods have involved SCUBA diving as well as participation in submersible scientific expeditions.

Ichnological evidence of marine incursions in the lacustrine–palustrine Bembridge Limestone Formation (Eocene), Isle of Wight, southern England

Trace fossils are described from the Eocene Bembridge Limestone Formation from the Isle of Wight and used to constrain the paleoenvironmental interpretation. The lacustrine–palustrine succession contains three limestone beds, which are separated by clay and marl. The middle and upper limestone beds reveal complex burrow systems developed at their top. Based on their characteristics, these burrow systems are assigned to the ichnotaxon Balanoglossites triadicus Mägdefrau, which is associated with the shallow superficial grooves Sulcolithos variabilis Knaust. B. triadicus is a common marine trace fossil mainly known from shallow-marine carbonate successions throughout the Phanerozoic. It is accompanied by other marine ichnotaxa such as Arachnostega gastrochaenae Bertling, Gastrochaenolites isp. aff. G. ornatus Kelly and Bromley, Spongeliomorpha iberica Saporta and Thalassinoides suevicus (Rieth). This ichnological evidence confirms the occurrence of short-term marginal-marine incursions in a predominantly lacustrine to palustrine environment.

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.

Insect trace fossils as indicators of climatic conditions during the uppermost Pleistocene deposits in southern Brazilian Atlantic coast

AbstractThe Rio Grande do Sul Coastal Plain records sea-level oscillations driven by climatic changes during Quaternary glaciations, represented as four lagoon-barrier systems, the last one forming after the last glacial maximum and still active. Marine trace fossils are reported in the Pleistocene deposits, but terrestrial burrows also occur in the eolian deposits. The insect trace fossil assemblages from the uppermost Pleistocene deposits of the lagoon-barrier system III are used as relative proxies to infer the climate regimes that controlled sedimentation prior to the last glacial maximum. Two suites occur in the eolian deposits: the Vondrichnus suite, dominated by structures produced by termites, in the basal eolian beds; and the Celliforma suite, dominated by hymenopteran (bees and wasps) structures, in the upper eolian beds. The dominance of termite nests indicates humid conditions. The shift upward to the Celliforma suite signals a change in the humidity regime and the prevalence of drier conditions. The stratigraphic position of the ichnoassemblage, above the uppermost Pleistocene marine transgressive beds that formed during the last interglacial and below the record of the last glacial maximum in this coastal plain, suggests that the last glacial interval controlled this humid-dry fluctuation.

Storm-dominated shallow marine trace fossils of the Lower Devonian Teferguenite Formation (Saoura valley, Algeria)

The mixed siliciclastic-carbonate Teferguenite Formation (Pragian-Emsian) occurring in the Ougarta Range (SW Algeria) is subdivided into two members: the Lower Member consists of three thick limestone beds (namely bars) intercalated with clay and sandstone deposits; the Upper Member is composed of intercalated sandstone, silty limestone and clay. Sedimentological data and their associated ichnological content were used for the interpretation of depositional settings. Lithofacies analysis evidenced that the studied succession was deposited in a shallow marine (shoreface to upper offshore), storm-influenced setting. Ichnological data document moderate to high bioturbation intensity, while ichnodiversity consists of 29 ichnospecies, namely: Arenicolites isp., Arthraria antiquata, Arthrophycus isp., Bergaueria perata, Bolonia lata, Chondrites targionii, Cochlichnus anguineus, cf. Cruziana isp., Cruziana rusoformis, Diplichnites isp., Gordia marina, Helminthopsis abeli, Hormosiroidea isp., Lockeia siliquaria, Megagrapton irregulare, Monomorphichnus cf. multilineatus, Neonereites uniserialis, N. multiserialis, Nereites isp., Phycodes isp., Protovirgularia isp., Rusophycus isp., Thalassinoides isp., T. suevicus, Palaeophycus isp., P. striatus, P. tubularis, and Zoophycos ispp. (types A and B). These trace fossils are gathered in three trace-fossil assemblages: the Palaeophycus-Thalassinoides-Arenicolites ichnoassemblage (PTAI), Cruziana-Thalassinoides ichnoassemblage (CTI) and Neonereites-Zoophycos ichnoassemblage (NZI). The trace- fossil records within the Teferguenite Formation is represented by different behaviours, corresponding to the archetypal Cruziana ichnofacies occurring from the shoreface to upper offshore zones.

Shallow marine trace-fossils from the Middle Miocene of the Tebessa Basin (NE Algeria) and their paleoenvironmental implications

The northeastern part of Algeria is characterized by Meso–Cenozoic fossiliferous deposits. All the previous studies have been focused on invertebrate and vertebrate body fossils from this region. In the present paper we provide the first ichnological study from the region of Ouenza, Tebessa Wilaya (northeastern Algeria). An ichnoassemblage composed of eight ichnotaxa, namely cf. Archaeonassa isp., Arenicolites isp., Diplocraterion isp., Helminthopsis isp., Palaeophycus tubularis, Skolithoscf. linearis, cf. Taenidium isp., and Thalassinoides isp., reported from the lower Langhian (Middle Miocene) of Aïn Sidi Salah locality (Tebessa Basin) is discussed. These trace-fossils belong to the Skolithos and proximal Cruziana ichnofacies indicating deposition within a shallow marine (littoral). The large size of Thalassinoides suggests well-oxygenated setting, under moderate- to high-energy conditions, with occasional storm events. Keywords: trace-fossils, paleoenvironments, shallow marine, Middle Miocene, Tebessa.

PROBLEMS IN USING ICHNOFACIES FOR DEPOSITIONAL ENVIRONMENT INTERPRETATION CASE STUDY: THE CISAAR FORMATION, SUNGAI CISAAR, SUMEDANG DISTRICT, WEST JAVA, INDONESIA

Although numerous researchers have used trace fossils method to determine depositional environment, this method is still considered less robust. This is due to the finding of several similar trace fossils in two or more diverse environments, leading to irrelevancy in environmental interpretation. Therefore, we conducted this study in order to verify how powerful the trace fossil analysis is, by applying this method to interpret the depositional environment of the Cisaar Formation in the Cihanyir Tonggoh area, Sumedang Regency, West Java. We combined trace fossil study with foraminiferal assemblage analysis and vertical succession of related sedimentary units. For this study, 19 rock samples that have been collected from outcrop along 16 m traverse and 14 m measured stratigraphic sections were examined.The result of the study shows that shallow marine trace fossils which were developed at the edge of the shelf, were transported into the basin by gravitational mass flow and re-deposited as deep marine turbidites. Trace fossils were generally found in sandstones, while planktonic foraminifers were found in claystones-sandstones interbeds. This study concludes that to avoid inconsistency in the interpretation of the depositional environment, performing trace fossils method must be integrated with other methods, e.g. analysis of lithofacies and biofacies.

Tidally-influenced fluvial channel systems from the Miocene Malay Basin, Malaysia: Evidence from core facies and seismic geomorphological analyses

The interpretation of tidal influence in a depositional system or stratigraphic interval buried deep in the subsurface is mainly based on sedimentary structures, fossils and trace fossils preserved in conventional cores. Studies of modern tidal depositional settings have shown that certain geomorphological features can be used as reliable tidal indicators. In this study we present evidence of tidal influence associated with Miocene channels in the Malay Basin, based on an integrated analysis of sedimentary facies from cores, well logs and high-quality 3D seismic data. Six facies associations identified in cores were interpreted as inter-distributary bay/offshore, tidal flat, subaqueous delta platform/prodelta, tide-influenced channel/bar, mouth bar, and mangrove/overbank deposits. Evidence for tidal influence include rhythmites, thick heterolithic successions, mud drapes, abundant bidirectional current indicators and the presence of an impoverished marine trace fossil assemblage. Channels identified in 3D seismic show unique geomorphological features indicative of tidal influence in the depositional system, such as flaring channel mouths, cuspate meanders, high-sinuosity, as well as dendritic and parallel channel networks comprising several orders of dead-end and through-flowing tributary channels. Identification of tidal geomorphological features in 3D seismic may help in predicting channel fill lithology in the subsurface, and in better planning of hydrocarbon exploration and development in basins with paralic channel-bearing reservoirs.

Deep-time geometricians and hints on motor control evolution of marine invertebrates

Motor control is an important component of animal movement that relies on the nervous system to conduct coordinated locomotion. Marine trace fossils, recording a myriad of movement patterns of principally invertebrate bilaterians, provide unique geological evidences for the evolution of animal locomotor behaviour. Here we report highly geometrical circular trace fossils from the Upper Ordovician deep-water slope deposits of North China. They consist of a small-sized ring-like main burrow with around 8 or 12 regularly-spaced tangential branches, contributing to semi-octagonal or semi-dodecagonal patterns with an average turning angle between successive branches of about 45° and 30°, respectively. The individual specimens also display regular and locally highly symmetric combination patterns like a Venn diagram. The ordered geometric expression of tiny circular trace fossils here suggests a relatively high level of motor control from minute invertebrate animals. Bilaterian motor control evolution in the early Palaeozoic as evidenced by the marine trace fossil record could be a key ingredient of biological evolutions during the Cambrian and Ordovician radiations. The Ordovician Radiation as an ecological expansion in the marine realm was accompanied by distinct offshore migration of the shallow-shelf ichnofauna and compositional change in the deep-sea ichnofauna. The greatly ameliorated deep-sea food content and relatively homogenous deep-sea food distribution may have promoted more geometrical and patterned trace fossils with a high level of motor control in the deep-sea regime during the Late Ordovician. It is speculated that after the latest Ediacaran–early Cambrian that set up the bilaterian behavioural toolkit, the Ordovician and Cretaceous represent two periods with distinct behavioural and motor control evolution of the deep-sea ichnofauna, which were in pace with revolutions in pelagic organic matter circulation during the corresponding periods.

Ediacaran and Cambrian paleosols from central Australia

Ediacaran to Cambrian red sandstones of the Northern Territory, including Arumbera Sandstone, and Grant Bluff and Central Mount Stuart formations, have been reexamined and sampled in order to reconstruct paleoenvironments from sedimentary facies and paleosols. Sedimentary facies include green-gray calcareous sandstone (Member III of Arumbera Sandstone only), red siltstone with calcareous nodules (also only Member III), and also non-calcareous red-green siltstone, interbedded red siltstone and sandstone, and trough bedded sandstone. The green-gray facies has diverse and distinctive Cambrian marine trace fossils, not found in the red beds which have instead an assemblage of problematic body fossils including Arumberia, Noffkarkys, Hallidaya, Ernietta, Trepassia, and Dickinsonia. The red facies are interpreted as fluvial paleochannels (trough cross bedded), fluvial levees (interbedded siltstone and sandstone), poorly drained floodplain (red-green siltstone), and well drained floodplain or low terrace (calcareous nodular). The carbonate nodules have micritic, replacive fabrics and a significant positive correlation of δ13C and δ18O characteristic of pedogenic carbonate of Calcid soils. Other red beds have pseudomorphous sand crystals after gypsum, like those of Gypsid soils. Individual red beds show negative strain and mass transfer for cationic bases typical of soils, as well as gradational alteration down from fossiliferous tops characteristic of soils. Their varied degree of pedogenic differentiation is identified as Psamment, Aquent and Ochrept paleosols. Phosphorus depletion in the paleosols is evidence that organisms lived in the paleosols, and were not introduced by transient marine incursions. The problematic quilted fossils Arumberia, Noffkarkys and Hallidaya formed a distinctive inland terrestrial polsterland during the Ediacaran and early Cambrian.

The Phycosiphon Ichnofacies and the Rosselia Ichnofacies: Two new ichnofacies for marine deltaic environments

ABSTRACTSeilacherian Ichnofacies have been established, to date, for characterizing relatively stable depositional settings. Environments characterized by temporally and spatially varying physico-chemical stresses, however, have languished and been described ichnologically in the context of their “departures” from the archetypal expressions of otherwise ambient environments. Correspondingly, discrimination between shoreface and marine deltaic deposits have been addressed mainly by identifying variations in the individual trace-fossil suites without an over-arching ichnological model. Based on trace-fossil suites reported from globally distributed strata throughout the Phanerozoic, the case can now be made for erecting two new temporally and geographically recurring Seilacherian Ichnofacies for marine deltaic successions—the Phycosiphon Ichnofacies for muddy prodelta environments and the Rosselia Ichnofacies for sandy delta-front settings.The Phycosiphon Ichnofacies is characterized by variable bioturbation intensities (BI 0–5), although many sandstone and mudstone beds may have very low bioturbation intensities (BI 0–1), pointing to their rapid, event-style deposition. Most biogenic structures record grazing or deposit-feeding behaviors, with subordinate horizontal dwellings that reflect deposit feeding and/or carnivory. Meiofaunal cryptic bioturbation is locally present in tempestites. Episodic deposition is accompanied by common escape structures and locally, sediment-swimming structures. The Phycosiphon Ichnofacies typically shows beds characterized by diverse, fully marine trace-fossil suites intercalated with discrete beds dominated by low-diversity, facies-crossing traces. Such bed-scale juxtaposition points to short-term but recurring alternations between stable marine conditions and physico-chemically stressed conditions.The Rosselia Ichnofacies is also characterized by variable (BI 0–5; though typically BI 0–3) bioturbation intensities and sporadically distributed burrows. Most ichnogenera record deposit-feeding behaviors, many associated with vertically and horizontally oriented permanent dwelling structures. Dwelling structures commonly display re-equilibration and escape structures are typically abundant, both characteristic of elevated sedimentation rates and sporadic deposition. Most spreitenated structures are markedly retrusive, also attesting to elevated rates of sedimentation. Cryptic bioturbation is only locally abundant, particularly associated with erosionally amalgamated tempestites lacking mudstone drapes. While many of the trace fossils constitute facies-crossing elements, fully marine (ambient) ichnogenera also occur in some suites. Associated mudstone interbeds display low BI values, sediment-swimming structures, and top-down bioturbation, consistent with their rapid deposition as fluid mud.The two ichnofacies may pass gradationally into one another vertically, associated with lobe progradation or autogenic lobe abandonment. Further, the two ichnofacies may pass along depositional strike into their non-deltaic counterparts—the Phycosiphon Ichnofacies grading into the Cruziana Ichnofacies in distal positions, and the Rosselia Ichnofacies passing into the Skolithos Ichnofacies in shallow-water locales.The erection of these new ichnofacies will enhance the reliable identification of deltaic successions, particularly in wave-dominated settings, and their differentiation from classical strandplain shoreface deposits. As well, the two ichnofacies better explain animal–substrate relations in the context of the detailed sedimentological characteristics of delta deposits, refining the overall facies characterization of shallow-marine environments.

The oldest record of a tyreophoran track in Gondwana: Geological implications of subaerial exposure in the lower part of the Lajas Formation at the Covunco section (Neuquén Basin), Patagonia, Argentina

The outcrops of the Lajas Formation at the Covunco section expose a succession that contrasts with the classical localities for the unit, due to subaerial exposure confirmed by a vertebrate track documented in the basal section of the unit. The stacking pattern, facies distribution, subaerial exposure in the previously interpreted prodelta facies and the documented unconformity in the middle part of the unit are incompatible with the continuous deltaic evolution suggested previously for the studied locality. Regardless of the absence of a precise age for the succession, the regional literature of subsurface data, the paleontological remains and the intra-Callovian unconformity at the top of the unit, suggest a Bathonian (late?) up to Early Callovian age for the unit in the area. It is younger than the classical deltaic deposits extensively studied in outcrops or subsurface to the north-east and south of the Huincul High and confirms the diachronism between the south and north of the high and it sheds light on the late evolution of the unit. The younger age in Covunco section is compatible with the suggested age differences. The sedimentary record in the logged section was divided in three parts: a lower section containing marginal-marine deposits with tidal features like sigmoidal structures and muddy and coaly drapes, marine trace fossils (Asteriacites quinquefolius) and bioclastic deposits that are transitionally overlying the Los Molles Formation and end with fluvial deposits containing the vertebrate track. It is documentedat the top of an interval with3D dunes. The track is tridactyl and assigned to cf. Deltapodus. It constitutes the oldest record in Gondwana of a track attributed to tyreophorans. Isaberrysaura (Neoornitischia/Tyreophora) is the candidate producer, taking into account the stratigraphic and geographical proximity of the underlying Los Molles Formation that contains the skeletal remains. The track has some morphological features that suggest a possible swimming-wading behaviour as was previously proposed for stegosaurs. Overlying the fluvial interval, the middle section is composed of transgressive deposits containing abundant bioclastic conglomerates and channels with trunks. The upper section was deposited after a facies dislocation overlying a previously interpreted unconformity that suggests an abrupt change in the sedimentary record, containing pebbly sandstones intercalated with sandstone beds with Skolithos resembling “pipe rocks”. They are replaced upward by fine-grained sandstones with HCS, suggesting open marine conditions over the storm wave base level and a deepening upward trend. Then, the succession becomes sandier and highly bioturbated with abundant Rhizocorallium specimens and some lenticular channels with lateral accretion and abundant symmetrical wave ripple levels developed during a regressive phase.

The Early Ordovician Middle Shale Member (Am3) of the Amdeh Formation and further evidence of conodont faunas from the Sultanate of Oman

AbstractThe Middle Shale Member of the Amdeh Formation is interpreted to be of Early Ordovician age based on its trace fossils, stratigraphic context and a newly discovered fauna of conodonts. The member abruptly overlies the Lower Quartzite Member, which may be Early Cambrian, and passes gradationally-upward into the Upper Quartzite Member, which is probably Early–Middle Ordovician. The 542.5 m thick Middle Shale Member can be divided into two parts: a shaly lower part, and a sandy upper part that contains an influx of heavy minerals. Bioturbation by marine trace fossils is one of the most obvious characteristics of the member. The shales and sandstones are interpreted to be ofCruzianaandSkolithosichnofacies and represent shallow-marine shelf, shoreface, beach and coastal deposits. Sparse shelly fossils occur in the sandy upper part, principally bivalves, inarticulate brachiopods, ostracods and conodonts. The small assemblage of conodonts includes elements interpreted to be Tremadocian (Tetraprioniodus,Drepanoistodus,Drepanodus,Scolopodus, ?Tropodus,SemiacontiodusandTeridontus), and others which may be Floian or ancestral forms of Floian taxa (Balognathidae gen. et sp. indet. A & B and aff.Erraticodon). No acritarchs have been recovered, probably due to high temperatures experienced during burial to >6 km. It is likely that the Middle Shale Member is the seaward equivalent of the Mabrouk and Barakat formations, and an outcrop gamma-ray log supports such a correlation. The trace fossils, sedimentology, conodont fauna and the general lack of macrofossils are in keeping with the regional Tremadocian–Floian of the Arabian margin of Gondwana.

A New Ichnospecies of Gyrolithes from the Austin Chalk, Upper Cretaceous, Texas, USA

ABSTRACTGyrolithes, a helical marine trace fossil, occurs in beds of the Austin Chalk near Waco, McLennan County, Texas. The new ichnospecies Gyrolithes texanus is characterized by unique morphology and wall construction. This discovery expands the current geographic and environmental range of Gyrolithes, extending this ichnogenus into the chalk-dominated beds of the Cretaceous of Texas. Irregular bedding features from the Gyrolithes locality indicate this section of the Austin Chalk was deposited within a storm-dominated depositional regime, interspersed with periods of quiescence which allow for firm ground formation and colonization by the trace maker. Occurrences of Gyrolithes have been associated by previous publications with marginal marine settings but not associated with storm deposits; therefore, this discovery constitutes an expansion of associated environment for this ichnogenus.

Facies, Backwater Limits, and Paleohydraulic Analysis of Rivers in a Forced-regressive, Compound Incised Valley, Cretaceous Ferron Sandstone, Utah, U.s.a.

Abstract We analyze a compound, piedmont-linked, coastal-plain incised-valley system from the Turonian Ferron sandstone, Utah, to evaluate valley-fill facies models in the context of bayline and backwater effects, as well as presenting quantitative estimates of paleohydraulic parameters, such as slope and discharge. Three photomosaics and eight measured sections along variably oriented cliffs show three terraces formed by a single-thread meandering trunk river that was about 7 m deep, forming a compound valley with up to 28 m of erosional relief. Channel fills in some of the terrace deposits show double mudstone drapes, tidal reworking, and brackish-water to marine trace fossils, suggesting deposition in both the tidal backwater and bayline regions. Paleoslope estimates are on the order of 2.6 to 5.3 × 10–4, and corresponding backwater lengths are estimated to range from 3 to 25 km. Assuming microtidal conditions, the bayline limit was likely less than 7 km and the shoreline was likely positioned within 20 km of the study area. Each successive valley-fill terrace is punctuated by a transgressive then regressive episode of cut and fill thus forming stepped forced-regressive fluvially dominated, tidally affected valley fills. There is a lack of extensive transgressive marine or estuarine fill, consistent with an ever-wet tropical climate and a steep gradient that resulted in a high-sediment supply system, rather different from the transgressive, estuarine to marine simple valley-fill facies models that dominate much of the literature. Width-to-thickness ratios are 10:1, < 100:1, and about 1000:1 for channels, channel belts, and valleys respectively. These are consistent with ratios from modern systems, and the lower channel-belt widths are also consistent with deposition in the lower backwater, which favors aggradation versus lateral migration of channels.

Termite nests, rhizoliths and pedotypes of the Oligocene fluviomarine rock sequence in northern Egypt: Proxies for Tethyan tropical palaeoclimates

The present study gives an account of the development of several associations of the continental trace fossils within a particular type of palaeosols on the Oligocene fluviomarine rock sequence that is equivalent to the Jebel Qatrani Formation and their palaeoclimatic and palaeoenvironmental implications in the northern Western Desert of Egypt. This study made use of field observations, binocular and polarizing microscopy investigation of isotropism and anisotropism of the materials and the birefringence fabric of the finest materials. Also, the study carried out scanning electron microscopy investigation and X-ray diffraction analysis of termite nests, rhizoliths and palaeosols. The present contribution recognises four pedotypes represented by Oxisols, Aridisols, Entisols and Spodosols based on the macro- and micromorphologic attributes, mineralogy and by comparison with extant soils. The four pedotypes bear similar types of rhizoliths and termite nests, but with variable abundance and depths of emplacement. The pedogenic features associated with the studied continental trace fossils overprint the marine trace fossils and the sedimentary facies of the studied fluviomarine rock sequence. The features of the developed associations reveal that during the Oligocene, the northern Western Desert terrain of Egypt was closely similar to the Fayum Depression where the lowland coastal plain was characterised by wet soil and seasonal rainfall. The developed associations on the coastal plain represent in situ proxies for the palaeoclimatic setting under which they were formed. Their attributes indicate that tropical wet-dry conditions with the fluctuating moisture regime were prevalent during the deposition of the studied rock sequence.

Middle to late Cambrian shallow marine trace fossils from the Imfout Syncline (Western Meseta, Morocco): Palaeoecological and palaeoenvironmental significance in NW-Gondwana

The present research provides the first evidence of invertebrate activity assigned to the ichnogenus Selenichnites occurring together with moderately diverse ichnofossils from the middle to late Cambrian of the Moroccan Meseta. The invertebrate traces occur in sandstone strata of the El Hank Formation within the Imfout Syncline, in the northern part of the Rehamna Massif (Coastal Block, western Moroccan Meseta). Bedding surfaces from the top of the El Hank Formation near the Imfout Dam show diverse forms of current ripples and distincts crescentic ichnofossils in concave epirelief scattered on the surface. In this section, the traces provide evidence of the ethology of an organism inhabiting the relatively shallow waters of the area during this time. Selenichnites co-occurs with the ichnogenera Arenicolites, Diplocraterion, Lingulichnus, Monocraterion, Skolithos and unidentified burrows, and the ichnoassemblage is referred to the Skolithos ichnofacies.These traces can be referred to arthropods (e.g. polychaete worms and amphipod crustaceans), lingulid brachiopods, annelids and/or phoronids. The Imfout Selenichnites represents the first occurrence of this ichnogenus from the Cambrian of the Moroccan Meseta, and the second from the Cambrian deposits of Morocco. The potential tracemakers are still questionable, but were most likely xiphosurans, trilobites, euthycarcinoids or crustaceans. If so, the Imfout traces could be among the oldest pieces of evidence for the presence of horseshoe crabs during the Cambrian.The combination of sedimentological and ichnological data indicates that the El Hank Formation was deposited in a sublittoral soft ground environment next to a sandy shore. It was originally part of an early Palaeozoic shallow marine epicontinental platform in west-central Morocco. In addition to the equivalent Cambrian deposits from the Anti-Atlas, the El Hank Formation constituted a part of the northern Gondwana platform domain during the transgression coming from the Rheic Ocean onto the West African Craton margin.

Thalassinoides in the Middle Miocene succession at Siwa Oasis, northwestern Egypt

At Siwa Oasis, the carbonate-rich Middle Miocene Marmarica Formation includes several firmground discontinuity surfaces, characterized by extensive burrow systems. These surfaces are confined to the boundary between the Oasis and Siwa Escarpment members in addition to several intraformational marine firmground discontinuities at several horizons within these two members. The marine trace fossils from all these discontinuities are represented mainly by the ichnogenus Thalassinoides. In all occurrences, Thalassinoides are characterized by a sharp erosional lower contact and grades upward into fossiliferous argillaceous limestone facies. Three Thalassinoides ichnospecies have been reported, including: Th. horizontalis Myrow, 1995, Th. suevicus (Rieth, 1932) and Th. paradoxicus (Woodward, 1830). They are mostly recorded as hypichnial/endichnial forms at the sole of fossiliferous argillaceous limestone facies. Rare exichnial occurrences are also recorded. Thalassinoides ichnospecies displayed considerable variations in their stratigraphic distribution, in addition to remarkable variations in their complexity and dimension. These variations are mostly reflecting environmental conditions prevailed during the trace-maker life. Paleoenvironmental interpretation of these burrows confirmed a well-oxygenated shallow marine environment with extremely slow or nearly nil rate of sedimentation.

Sequence Stratigraphic Analysis of the Youngest Nonmarine Sequence In the Cretaceous Ferron Notom Delta, South Central Utah, U.S.A.

Abstract This study evaluates the nature and internal complexity of high-frequency fluvial aggradational cycles and linked paleosols that were previously not recognized in nonmarine sequences of the Turonian Ferron Notom Delta in Central Utah. Detailed facies analysis of the ∼ 33-meter-thick youngest nonmarine sequence (Sequence 1) reveals 11 depositional facies that build 33 fluvial aggradational cycles, 9 fluvial aggradation cycles sets, and 3 sequences, in what was previously classified as a single 100 ka, 4th- or 5th-order sequence. Fluvial aggradation cycles in the succession are either simple floodplain bedsets or single channel stories that are bounded by paleosols or erosional surfaces. They represent depositional events that likely do not span more than 2 ka. Depositional periods are followed by short hiati (10 to < 400 a) characterized by subaerial exposure, and soil development, possibly reflecting floodplain abandonment or short-term river avulsions. Fluvial aggradational cycle sets show systematic stacking of fluvial aggradational cycles, and are analogous to parasequence sets. They are represented by either compound floodplain bedsets or multi-story channel sandstones, bounded by relatively mature paleosols or erosionally top-truncated. They represent multiple small-scale depositional events that span not more than 14 ka followed by relatively long (100 a to < 1 ka) hiati, characterized by subaerial exposure and soil development, which suggest a relationship to longer-term floodplain abandonment, due to either longer-term avulsion or fluvial entrenchment during base-level falls. Fluvial aggradational cycle sets are often capped by coals and carbonaceous strata. Marine trace fossils and dinocysts above coal beds suggest marine transgression due to compactional subsidence or sea-level rise. The scale of cyclicity of the fluvial aggradation cycle sets (14 ka) is similar to underlying marine parasequences (10 to 15 ka) and suggests that nonmarine and marine cycles have a similar control. Fluvial sequences are aggregates of fluvial aggradational cycle sets that are bounded by unconformities or their correlative conformities that represent longer periods (1 to 5 ka) of subaerial exposure and pedogenic development. Cyclicity on the sequence scale in this succession is attributed to high-frequency Milankovitch-scale (∼ 20 ka, 40 ka) rises and falls in sea level.