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Thalassinoides and the Enigma of Early Paleozoic Open-Framework Burrow Systems
Abstract
Specimens of a new ichnospecies of Thalassinoides from the lower Paleozoic Manitou and Peerless formations of Colorado, herein defined as Thalassinoides horizontalis, consist of bedding-parallel polygonal networks of smooth-walled, unlined, horizontally branching burrows. Burrows form both Y- and T-junctions but contain no swellings at junctions or elsewhere. Five styles of preservation related to the presence or absence of burrow-fill and patterns of mineral replacement and weathering. The extremely small burrow diameters, lack of some features such as scratchings and swellings, absence of vertical shafts, and the common regularity of branching separates this new ichnospecies from other Thalassinoides ichnospecies in either Paleozoic or post-Paleozoic strata. The open-framework burrow systems may record the activities of some of the oldest vagile suspension feeders to colonize infaunal habitats. -from Author
... Thalassinoides is a dwelling structure, and the burrows of T. horizontalis are assigned to small crustaceans or soft-bodied organisms in firmground sediments (Myrow 1995). ...
... Vertical and irregular branching in T. paradoxicus indicates a firm, semi-consolidated substrate (Myrow 1995). Small blunt protuberances indicate offshoots of the burrow ( Figure 4G). ...
The Narmada Basin in west‐central India forms the northern part of the Central Indian Tectonic Zone (CITZ). The Cretaceous Bagh Group rocks of the Western Lower Narmada Valley (WLNV) succession was studied for sedimentary facies analysis and ichnology. Textural and mineralogical characteristics along with primary and secondary sedimentary structures revealed 11 lithofacies, of which the calcareous sandstone, fine‐grained sandstone‐siltstone‐shale and sandy/silty allochemic limestone lithofacies are highly bioturbated. WLNV contains a well‐preserved, less diverse, and relatively abundant ichnofauna; a total of 24 ichnospecies belonging to 15 ichnogenera with pseudotrace fossils are identified and described. The trace fossils belong to the Skolithos , Cruziana and Glossifungites Ichnofacies. The Skolithos Ichnofacies suggest an upper shoreface environment with moderate‐to‐high energy conditions and shifting substrate; the Cruziana Ichnofacies suggest a lower shoreface environment with low‐to‐moderate sedimentation rates and energy conditions and the Glossifungites Ichnofacies suggest dewatering of sediments and a slow rate of sedimentation. Early ichnological studies in the different Tethys‐related Cretaceous basins of the Indian subcontinent (Eastern Lower Narmada Valley, Kachchh, Cauvery, Jaisalmer, Barmer and Saurashtra) primarily focused on identifying the trace fossils, describing the new species and interpreting them in relation to trace producers and depositional environment. However, many of the ichnogenera and ichnospecies established from these basins need special attention because they either have been described as invalid, revised or assigned an unclear taxonomic status. The Cretaceous trace fossils reported to date from these basins are compiled along with their paleoenvironmental interpretation. The study also discusses the present status of the ichnogenera and ichnospecies names of the trace fossils reported to date from these basins. These data can be further used to enhance our understanding of how paleoenvironmental conditions control the distribution of trace‐making communities across space and time.
... (Fig. 7A Rhizocorallium is an element of the Cruziana ichnofacies and the firmground Glossifungites ichnofacies (Buatois and Mángano, 2011) it is interpreted as a dwelling and feeding structure (domichnial and fodinichnial). Polychaetes are the most likely producers of marine Rhizocorallium (Knaust, 2013) and in firmgrounds as a component of the Glossifungites Ichnofacies (Myrow, 1995). ...
The palaeoenvironments of the Campanian‒lower Palaeocene composite succession in the Dakhla Oasis, Egypt, are interpreted based on the integration of sequence-stratigraphy, macrobenthic associations, and trace fossils. This succession comprises six rock units, corresponding to several transgression-regression cycles. These rock units include the Quseir Formation, the Duwi Formation, and the Mawhoob, Beris, Lower Kharga, and Upper Kharga members of the Dakhla Formation. Six unconformities delineate seven 3rd-order depositional sequences, including the lower‒middle Campanian DS-Q1, the upper Campanian DS-D1 and DS-D2, the lower Maastrichtian DS-Dk1, the upper Maastrichtian DS-Dk2 and DS-Dk3, and the lower Danian DS-Dk4. The invertebrate macrobenthic elements sporadically occurred throughout the studied succession, representing three bivalve associations: the late Campanian Nicaisolopha-Plicatula association, the late Maastrichtian Exogyra overwegi association, and an early Danian Venericardia association. At least 12 ichnotaxa have been identified, representing two ichnoassemblages: the late Campanian Thalassinoides-Psilonichnus and the latest Maastrichtian‒early Danian Rhizocorallium jenense-Tisoa siphonalis, both belonging to the Glossifungites Ichnofacies. Sequences characteristics indicate palaeoenvironments ranging from brackish, littoral, and near-shore to inner and outer neritic settings, reflecting the influence of syn-sedimentary tectonics combined with sea-level fluctuations, which resulted in varied depositional features. The distribution and the trophic structure of the body and trace fossil assemblages confirm the role of several environmental parameters, such as substrate characteristics, bathymetry, water energy, productivity level, sedimentation rates, and oxygen availability, in shaping the occurrence of different elements within these faunal assemblages.
... Crustaceans became important trace makers from the late Paleozoic (Briggs and Clarkson 1990;Carmona et al. 2004), and crab trace fossils have been reported already from the Permian (Buatois et al. 2005), Triassic (Hasiotis and Mitchell 1993), and Upper Jurassic (F€ ursich 1981). Possible crustacean burrows from the early Paleozoic have been also speculated upon (Myrow 1995;Ekdale and Bromley 2003). However, Krobicki and Zaton (2008) and Schweitzer and Feldmann (2007) state that, most likely, true crab (brachyurans) burrows did not appear until at least the Cretaceous. ...
Intertidal burrowing crabs produce distinctive biogenic sedimentary structures on tidal flats and salt marshes of the mesotidal Mira River estuary in southwestern Portugal. This study shows that the morphology and spatial distribution of crab burrows vary depending on the activity of the producer, its age, tidal cycles, tidal range, time of the day, and substrate consistency. The Atlantic shore crab Carcinus maenas was observed during the daylight hours roaming the tidal flats and marshes at neap low tide (1.29 m) as well as occupying burrows and cavities. A variety of traces and tracks are attributed to C. maenas, including cheliped scratch marks, tracks and trackways, burrows/cavities with associated root penetration structures (rhizoliths), and fecal pellets. Scratch marks are understudied in neo- and paleoichnology and are often interpreted as structures resulting from crab grazing and feeding activity (fodichnia/pascichnia), and occasionally from mating behavior. Digit traces and trackways predominantly concentrate around burrows and cavities on the upper tidal flat and resemble Coenobichnus currani, representing crab locomotion (repichnia). With morphology regarded as the most important criteria for ichnotaxonomy, wide burrow apertures and cavities found on the tidal flats are most similar to Psilonichnus upsilon, P. tubiformis, and Spongeliomorpha-type crustacean burrows, representing permanent- to semi-permanent crab domichnia. Finally, cylindrical, semi-consolidated pellets are interpreted as crab fecal pellets (coprolites) similar to Favreina. Carcinus maenas is a prolific bioturbator in intertidal and supratidal habitats; however, the preservation of its traces in the rock record is dependent on the preservation potential of the host sediments.
... The monospecific retrusive Teichichnus rectus (Seilacher, 1955) suite (BI 3) ( Figure 6.3) in the mudstone of the lower part of the CM indicates marine incursion and sedimentation likely under a stressed brackish-water condition following the initiation of transgression at the KNF-CF boundary. The overall trend in the trace-fossil assemblage within the biostromal carbonate beds of the CM is characterized by an assemblage of Thalassinoides suevicus (Rieth, 1932), T. horizontalis (Myrow, 1995), Cylindrichnus concentricus (Toots in Howard, 1966 Ekdale andHarding, 2015), and, Skolithos linearis (Haldeman, 1840), (Clifton and Thompson, 1978), ...
The Kutch basin is well-known for its thick sequences of sedimentary rocks ranging from the Mesozoic to the Cenozoic era. The Aquitanian Khari Nadi Formation (KNF) is bounded by unconformities separating it from the underlying Maniyara Fort Formation (Oligocene) and the overlying Burdigalian Chhasra Formation (CF). Earlier literature has established a 3rd-order sequence-stratigraphic cycle for the early Miocene succession of the Kutch Basin. However, the detailed evaluation of sequence-stratigraphic and paleoenvironmental implications of the Cenozoic trace fossils especially for the early Miocene was deficient in the literature and was much needed. The present study proposes an integrated process-ichnological and high-resolution sequence-stratigraphic investigation of the early Miocene stratal units of the Kutch Basin. A stratum-bound series of sand volcanoes belonging to the Khari Nadi Formation (KNF) is exposed along the banks of Khari River. They separate the shallow-marine deposits below and non-marine deposits above with their characteristic marine and paleosol trace-fossil suites, respectively. Although a seismogenic origin has been much debated for the SSDS, the ichnofabric analysis of the sand-volcano-bearing stratum unequivocally points toward such an origin under a shallow seafloor condition. The sedimentary regime changes from an open shallow-marine setting to a continental depositional environment concomitant with basinal uplift. The behavior of the burrowing crustaceans testifies to a syn-depositional development of a fault network associated with the fluidization, and sand volcanism. While the ichno-sedimentological evidence differs from the previous works, the paleoseismic activity, its ichnologic signature, and the depositional regime change refer to a higher-resolution (i.e., lower-order) sequence-stratigraphic change causing a short-duration regression within a longer-duration cycle of baselevel rise. Trace-fossil analysis, especially the evaluation of ichnofabric and ichnotaphonomic pathways, demonstrates the new approach in defining the sequential processes of seismite development, hence designated as “ichnoseismite”, i.e., a seismite, in which sequential processes during its development have been ichnologically delineated. The CF is subdivided into two members: the lower Claystone (CM) and the upper Siltstone (SM) members. Three CM outcrops (P1–P3) comprising buried paleosols, which formed under specific environmental setting involving imperfectly to poorly drained conditions, are exposed near Ramwada Temple, Kachchh. The biostromal carbonate beds, alternating with the paleosols, contain invertebrate bioclasts (bivalves, gastropods, echinoids, etc.), and are characterized by a firmground Thalassinoides suevicus ichnofabric. The carbonate bed is also found to be affected by secondary biogenic infestation, evidenced by the presence of a now-established bioerosional ichnotaxon, Teredolites solitarius. At P1, below the contact between underlying paleosol and overlying carbonate, T. suevicus transforms into firmground Gyrolithes isp. inside the paleosol forming a compound ichnotaxa. The paleosol interval P1–P2 consists of a Vondrichnus-Termitichnus-root trace ichnofabric defining the Termitichnus Ichnofacies. At P3, lenses of fully-bioturbated siltstones with a monospecific firmground Thalassinoides paradoxicus ichnofabric can be observed within an overall silty paleosol horizon, thereby, locally crosscutting the pedogenic features. The ichnofabric of P3 indicates a polyphase pedogenesis with three stages. The CM shows an apparent low-order T–R cyclicity within a 3rd-order TST that is supported by pedogenic intensity, ichnofabrics, and reciprocal sedimentation near the Miocene basin margin, though the cyclicity can be the result of both autogenic and/or lower-order allogenic changes. Along the Kankawati River section, both the KNF and CF are exposed. The CM succession commences at its unconformable contact with the underlying KNF demarcated by a monospecific firmground Thalassinoides suite (BI 4) (Figure 2). The subaerial unconformity developed at the top of KNF is directly modified during the subsequent transgression creating a co-planar surface. The lag concentration deposit at the base of CM indicates the onset of transgression and juxtaposition of the subsequent development of wave/tide ravinement surfaces on top of the paleosol bed of the older KNF. The monospecific Teichichnus rectus suite (BI 3) in the mudstone of the lower part of the CM indicates marine incursion and sedimentation likely under a stressed brackish-water condition. The overlying sand-dominated heterolithic lithofacies is characterized by a trace-fossil suite of Skolithos linearis, Diplocraterion parallelum, Macaronichnus segregaris, Planolites isp., Bergaueria hemispherica, Cylindrichnus concentricus, Rosselia rotatus, and Fugichnia representing the archetypal Skolithos Ichnofacies (BI 3). The ensuing 4th-order deepening of the basin is evidenced by the dominance of biostromal carbonates intercalated by mudstone facies. The presence of large-scale gutter casts filled with cross-stratified sands in the upper part of the CM, marking the Basal Surface of Forced Regression (BSFR), along with subsequent transgressive lag deposits and bioturbation, indicates multiple regressive and transgressive events. The sequence of erosional surfaces, transgressive lags, and biostromal intercalations reflects a dynamic depositional environment with frequent shifts between marine and subaerial conditions. The Siltstone Member represents the last and the HST part of the 3rd-order early Miocene sequence. The SM is manifested by the siliciclastic-dominated deposits with very limited biogenic input. The trace-fossil assemblage of the SM comprises – Skolithos linearis, Ophioimorpha nodosa, Arenicolites isp., Thalassinoides suevicus, Rhizocorralium jenense, Teichichnus rectus, Cylindrichnus concentricus, and Taenidium isp., forming the Skolithos ichnofacies. The SM is characterized by the repeated occurrence of silty shale, siltstone, and sandstone facies, forming at least 11 parasequence sets. The sedimentologic, bioclastic, and trace-fossil distributions in the CM suggest a tidally-influenced, subtidal to shallow-marine environment with moderate to low sediment supply. This setting experienced a 3rd-order transgressive trend with intermittent 4th-order regressive events impacting lithofacies and trace-fossil suites. The SM was deposited in a tide-dominated, upper shoreface, shallow-marine environment with high siliciclastic input.
... Considering the abundance of Thalassinoides in modern and ancient shoreface settings, the interpretation of sandstone facies of Rudig section as a shoreface seems plausible. Substrate consistency is an important factor controlling the distribution of Thalassinoides in marine environments (e.g., Myrow, 1995;Pemberton et al., 2004;Mikuláš, 2006). Thalassinoides is most common in softgrounds, although they can occur in firmgrounds (Pemberton et al., 2004;El-Sabbagh et al., 2017;Bendella et al., 2021). ...
This study focuses on sedimentation patterns and paleoecological conditions during the Upper Miocene in Southeast Iran, specifically analyzing the Rudig section. The sedimentation was predominantly terrigenous and occurred in marine conditions, forming multiple shallowing upwards sequences comprising silty marl, siltstone, and sandstone. The analysis of molluscan shells from this period indicates minimal bioerosion, with encrusters represented solely by Balanus sp. This low level of encrustation suggests rapid sedimentation and brief exposure times. Bioerosion was limited, with Caulostrepsis taeniola borings found only in the shells of vermetid Thylacodes sp. and predatory gastropod Conus sp. Predatory drillings, identified as Oichnus paraboloides were present in the shells of Turritella sp., Corbula sp., and Bursa sp., along with occasional shell aperture peeling repairs in Turritella sp. The presence of abundant large Thalassinoides burrows in the sandstone facies, along with moderate ichnodiversity supports the interpretation of the sandstone facies as shoreface. The rare occurrence of Ophiomorpha nodosa in siltstone facies, and the dominance of burrowing crustaceans in shallow water facies and suspension-feeding mollusks in deeper facies, provides further insight into the paleoenvironment. This study offers a detailed reconstruction of the sedimentary and ecological dynamics during the Upper Miocene in this region, enhancing our understanding of paleoenvironmental conditions and faunal interactions. Keywords: biofacies, sedimentary facies, bioerosion, encrustation, predation, Cenozoic.
... The thinner and relatively mud-poor units may represent the lowermost shoreface environment, well below the mean fairweather wave base (Ainsworth and Crowley 1994). The Ophiomorpha and Thalassinoides burrows indicate a neritic environment (Myrow 1995 ...
This study describes the sedimentary facies associations of the İhtiyarlı shoal-water fan delta complex in the Manavgat Basin, south Türkiye, to interpret the forces acting on base-level changes and the basinal processes controlling sedimentation. The fan delta complex sharply overlies the offshore transition deposits. It consists of three main fan delta wedges, each composed of several mound-shaped delta lobes of the shoal-water deltas stacked upon one another with a lateral offset. The first delta wedge deposited by forced regression consists of deltaic shoreface, delta-front beach, and fluvial distributary channel deposits, indicating that the fluvial sediment discharges exceeded the rate of frontline marine reworking. The overlying deltaic wedges deposited by normal regression consist only of deltaic shoreface and delta-front beach facies, which are attributed to less incised river channels no longer promoting sediment delivery, while seaward protrusion made the delta front more vulnerable to wave action. The normal regressive delta wedges are considered to be parasequences, implying episodic drowning of progradational wedges due to minor subsidence episodes or eustatic sea level rise. The thick and laterally extensive delta-front beach facies overlying the deltaic shoreface sediments formed in both forced and normal regressive wedges, indicating that the fan deltaic shoreline was subjected to wave-dominated marine processes during and after deposition. The biostratigraphic dating of the İhtiyarlı fan delta complex suggests an age of approximately 9.54–7.80 Ma, which can be assigned to the zonal interval from the middle part of Zone MMi 11 to the lower part of Zone MMi 12 of the Late Tortonian, based on planktonic foraminifera from the underlying mudstones and heterolithic deposits just beyond the shoal-water deltaic wedges toward the basin interior. The İhtiyarlı fan delta complex began to develop in response to the Middle–Late Tortonian relative sea level fall that partially exposed the Manavgat Basin, indicating a regional forced regression. Due to the forced regression corresponding to the transgressive part (9.2–7.62 Ma) of the third-order eustatic sea level cycle of post-Tor2, we interpret this event as related to the tectonic uplift of the Tauride Mountains.
... Ichnospecies: Thalassinoides horizontalis Myrow, 1995 (Plate 3, Figure 5) ...
The Yellow Flagstone is the oldest member of the Goradongar Formation exposed in the Pachchham Island, Kachchh Basin. The members exposed in four sections are mapped for trace fossils, and 17 ichnofossils have been documented. The concept of ichnoguild (IG) is applied to reveal the infaunal tiering structure and the strategies organisms adapt to exploit the resources. Ten IG of similar characteristics and ecological functions have been identified. Five are shallow-tier IGs ( Asterosoma IG, Gyrochorte IG, Nereites IG, Planolites IG and Bolonia IG), three middle-tier IGs ( Rhizocorallium IG, Arenicolites-Diplocraterion IG and Zoophycos-Teichichnus IG) and two deep-tier IGs ( Skolithos Arenicolites IG and Thalassinoides-Ophiomorpha IG). The analysis of three ichnological tiers and their IGs, namely shallow, middle and deep-tiers across the stratigraphy of Yellow Flagstone Member suggests a transition from a lower shoreface environment to offshore transition environments. The transition is supported by an increase in deep-tier IG and the marginal increase in the ichnodiversity and density. Changes in the composition and abundance of IGs over time can indicate shifts in sedimentation patterns, sea level fluctuations and paleoenvironmental conditions within the basin. Thus, the findings suggest an environmental shift from shoreface to offshore transition indicative of a transgression during the deposition of upper Bajocian to lower Bathonian Yellow Flagstone Member in the Kachchh Basin. The study also examines the temporal and spatial changes in the IGs, contributing to a better understanding of ecological changes within the basin. The findings contribute to the broader knowledge of paleoecology and provide valuable data for sedimentological and stratigraphic interpretations in sedimentary basins.
... In the present samples, burrow of relatively large size (1-3 cm in diameter) of circular and elliptical cross sections and straight horizontal cylinders were assigned to Thalassinoides (Figs. 2-5). It is interpreted as a dwelling structure produced by callianassid shrimps among other potential tracemakers (e. g., Bromley and Frey, 1974;Myrow, 1995;Rodríguez-Tovar et al., 2017). ...
Palaeontological investigation of the Pliocene Tahria and Slama formations in the Lower Chelif Basin (NW Algeria) led us to collect significant gastropod assemblages for taxonomic and taphonomic purposes. There is presently a very complete inventory list of Pliocene gastropods from Algeria, with 16 species from the Zanclean Tahria Formation and 54 species from the Piacenzian Slama Formation, some of which are recorded for the first time from the Pliocene of the Mediterranean. The northwestern Algeria gastropods represent a shallow-water, fully marine fauna, sandy substrate, and show a typical Upper Pliocene Mediterranean assemblage.
The gastropod shells show significant taphonomic alteration; most specimens are abraded and decalcified to a variable degree. Fragmentation was mainly a result of mechanical and biological processes. Bioerosion traces are uncommon, but when they are present, they are predominantly those of predatory gastropods (Oichnus simplex and Oichnus paraboloides), polychaete activity (Maeandropolydora isp.), and acrothoracican barnacle borings (Rogerella isp.). Integration of taphonomical, palaeoecological, and sedimentological characteristics of the gastropod-bearing beds suggests sedimentological concentrations originated from discontinuous processes of winnowing and bypassing sediments, most likely due to storm action in the shoreface depositional environment.
The Tortonian transgression is expressed in the Lower Chelif Basin by the deposition of the Blue Marls Formation highlighted at the base by a deposition of sandstone and conglomerate, including ante-Neogene cobble-size clasts, in which the ichnological investigation shows moderately diversified invertebrate ichnofossils preserved mainly in the detrital-dominated deposits. The trace fossil record consists of 18 ichnospecies belonging to 13 ichnogenera, including Arenicolites carbonaria, Diplocraterion parallelum, Gastrochaenolites isp., Gyrolithes isp., Macanopsis isp., Macaronichnus cf. segregatis, Ophiomorpha nodosa, Palaeophycus tubularis, Phycodes circinnatum, Phycodes cf. curvipalmatum, Rhizocorallium isp., Rosselia socialis, Skolithos annulatus, Skolithos linearis, Skolithos verticalis, Thalassinoides horizontalis, Thalassinoides cf. suevicus, and Thalassinoides isp., produced mostly by deposit-, suspension-, and rarely detritus-feeder organisms. Among these traces, Gastrochaenolites isp. is the only specimen being recorded within the conglomerate deposits and represents, therefore, the evidence of the first colonization after the Tortonian marine ingression. The remaining trace fossils are exclusively reported from the sandstone deposits and are typical of shallow-marine settings composed of vertical and horizontal structures, largely dominated ethologically by domichnia, fodinichnia, and combined domichnia/fodinichnia behaviour groups. The lower interval of the sandstone deposits is dominated by mid- to deep-tier, vertical post-depositional dwelling (domichnia) forms (Arenicolites, Diplocraterion, Skolithos, Macanopsis, Ophiomorpha, and Gyrolithes) attributed to opportunistic suspension-feeding organisms, corresponding to the archetypal Skolithos ichnofacies that documents an upper-middle shoreface environment, whereas the upper interval is predominantly represented by shallowest- to shallow-tier horizontal deposit-feeders burrows [Macaronichnus, Ophiomorpha (horizontal components), Palaeophycus, Phycodes, Rhizocorallium, Rosselia (vertical components), and Thalassinoides] displaying intense degree of bioturbation, reflecting a perfect palaeoecological condition reigning in the water column and sea floor. Thus, the association commonly corresponds to the proximal trend of the Cruziana ichnofacies developed within the lower shoreface zone. Consequently, the ichnological investigation reveals that the detrital-dominated deposits show a slight deepening of the environment, shifting from a suspension feeder-dominated to a deposit feeder-dominated association, in which polychaete annelid and crustacean animals are the main benthonic epi- and infaunal trace makers of the recorded ichnofossils. The ichnotaxa Arenicolites carbonaria, Phycodes circinnatum, Phycodes cf. curvipalmatum, Rhizocorallium isp., Rosselia socialis, and Skolithos verticalis are reported herein for the first time from the Cenozoic of Algeria.
The cyclic nature of the Phanerozoic sedimentary rock distribution, carbon-sulphur coupling, and material transfer among sedimentary reservoirs appears to be controlled by tectonic factors. The distribution of preserved sedimentary mass in terms of rock mass remaining U. geologic age shows a minimum c . 300-350 Ma ago, which separates two subcycles of erosion and deposition of sedimentary rocks. The older subcycle was interrupted because of the major continental collisions of the Devonian and late Carboniferous. These collisions resulted in a reduction of outcrop areas of rocks of the older cycle relative to their masses, leading to a decline in the probability of destruction and an increase in half-life of these older sediments.
A strong correlation exists between the long-term cyclicity in the Phanerozoic global sea level curve and the distribution of carbon and sulphur among their major exogenic reservoirs. This correlation is related to two principal tectonic modes of the Phanerozoic: oscillatory and submergent.
It is postulated that the submergent mode of active plate convergence, obduction and subduction of sediments, large ridge volume, and high sea level gave rise to low erosion and sedimentation rates, less restricted environments of carbonate deposition, and relatively high atmospheric CO 2 levels (high temperatures ?), resulting from an increased rate of production of CO 2 from diagenetic and metamorphic reactions at subduction zones. As sea level rose carbon was transferred from the sedimentary reservoir of reduced organic carbon to that of oxidized inorganic carbon in limestones, whereas sulphur moved from the oxidized sulphate reservoir to the reduced sulphide reservoir. As sea level fell, reservoir transfers were opposite to those above culminating in the oscillatory mode of generally elevated continental interiors. These reservoir transfers are consistent with secular changes observed in the distribution of δ ¹³ C and δ ³⁴ S in Sedimentary materials during the Phanerozoic.
Petrographic examination of Phanerozoic oolite formations shows that öoids with preserved calcitic relict textures are characteristic of pre-Carboniferous carbonate rocks, whereas öoids with relict textures indicative of initial aragonite mineralogy are dominant in rocks of younger age. These changes in öoid mineralogy may be interpreted as reflecting changes in CO 2 levels of the ocean-atmosphere system consistent with the above tectonic considerations. Atmospheric CO 2 levels were higher prior to Carboniferous time, favouring formation of calcitic öoids and skeletal parts; after the Carboniferous, CO 2 levels fell and aragonite and Mg-calcites of greater than 8 mol % Mg increased in abundance as precipitates.
This paper examines some of the taphonomic variables that may bias the arthropod fossil record. The short-term preservation potential of the modern carid shrimp, Pandalus danae, was studied in a variety of laboratory and field settings. Destruction by scavengers (crabs?) was the probably primary cause of carcass destruction in the field. Further breakdown was caused by bacterial decomposition and disturbance by burrowing infauna. Shrimp remains were placed in a series of glass jars in the laboratory. Decomposition destroyed nearly all soft tissues within a period of two weeks. The cuticle became extremely soft, resulting in loss of physical integrity of the remains. Differences between oxic and anoxic decomposition were minor. These results suggest that disturbance by scavengers or burrowing infauna is a major factor in the destruction of buried arthropod remains. The absence or inhibition of bioturbation may be a necessary condition for arthropod preservation. The preservation potential of arthropods, and of other soft-bodied forms, may have declined since the Paleozoic.-from Author
Distinctive biogenic sedimentary structures (trace fossils) in sedimentary rocks reflect the burrowing behavior of the animals that made them. Because the distribution of these animals is influenced by environmental factors such as water depth and substrate type, trace fossils have been used widely as paleoenvironmental guides. The massive, ungraded sandstones in the Point Loma Formation have sharp upper and lower contacts, thick lenses of mudstone clasts, and common load-deformation structures, suggesting deposition largely by grain-flow processes. Foraminifers and most of the trace fossils suggest deposition in a deep, probably bathyal environment. However, two abundant trace fossils, Qphiomorpha and Thalassinoides, are widely held to represent very shallow-water to intertidal paleoenvironments, and they usually occur in such facies. Two morphologic forms of a third trace fossil, Zoophycos, have been thought to reflect different environmental conditions, but they occur here in the same strata. These occurrences emphasize the point that paleoenvironmental interpretations should not be based on individual trace-fossil taxa, but that such traces should be considered only in conjunction with other available evidence.
Marine benthic animals have lived within the sediment since the late
Precambrian. An abundant early Paleozoic infauna is indicated by
bioturbated zones and diversity of deposit-feeder and suspension-feeder
trace-fossil genera. Burrow depths extended tens of centimetres below
the sediment-water interface. Trace-fossil evidence of an abundant early
Paleozoic infauna conflicts with evidence from the shelled fauna, which
lacks infauna. This requires reinterpretation of early Paleozoic
community structure and raises new questions about interactions between
early Paleozoic soft-bodied and skeletonized animals.
Crustacean burrows are common in Recent sediments associated with fringing reefs around Mahé, Seychelles. Burrow morphology is related to function. Unbranched burrows produced by the crabs Cardisoma, Sesarma, Ocypode spp., Uca and Macropthalma are primarily dwelling, whereas multiramous systems constructed by the shrimps Callianassa spp. serve in addition as a means of sediment exploitation.The distribution of morphotypes shows only general correspondence to recognised biofacies zones, and well-preserved burrows from Pleistocene limestones on Aldabra demonstrate that, while providing useful corroborative evidence, burrows are of limited value as primary zone indicators.
The infaunal habitat was colonized in the early Phanerozoic primarily by soft-bodied organisms. To understand the early biotic history of this environment, it is necessary to examine the overall record of bioturbation, or ichnofabric. We present here results documenting trends in ichnofabric from Ordovician strata of the Great Basin in California, Nevada, and Utah, collected by a method devised to semiquantitatively measure the extent of early Paleozoic utilization of infaunal ecospace. When combined with similar Cambrian data, a two-phase stepwise pattern of increasing bioturbation contemporaneous with the Cambrian and Ordovician radiations of skeletonized metazoans is apparent. These data represent evidence independent of the body fossil record of increasing ecospace utilization in the early Paleozoic.
Bioturbation is ubiquitous in Cenozoic outer-ramp settings. The Oligo-Miocene ramp carbonate sequences of SE Sicily and the Maltese Islands provide specific examples to illustrate the effects of sediment retexturing by burrowers and provide significant conclusions which must be taken into account by sedimentologists when interpreting palacoenvironments.Thalassinoidean burrow systems may penetrate several metres into the underlying beds with evidence of concentrated activity at selected levels. The general intra-bed process of this (?) crustacean-dominated bioturbation is well documented: however, the effects when several beds are involved can be dramatic: 1.(a) Buried, homogeneous wackestone beds can be depleted in lime mud by gallery excavation. The dumping of this mud at the sediment surface leads to lime mud enrichment of the contemporary accumulating layer and might be a major factor in the development of the tabular outer-ramp bedforms.2.(b) Vertical reworking of unlithified sediment between beds (both upwards and down) is capable of homogenising two distinctly dissimilar lithologies, producing a third which in no way reflects the surface processes of the depositional setting.3.(c) Bioturbation often continues during incipient, near-seafloor lithification. This produces random lateral variations in lithology within single beds. The degree of lateral dissimilarity is proportional to the intensity (longevity) of the bioturbation episode.Bio-retexturing destroys primary depositional fabrics and masks inorganic process-related structures. It can be as effective a remodelling agent as tidal energy. It can texturally remodel areas of high primary permeability into irregular, interconnected zones of low permeability. As the outer ramp provides a potential fluid migration route from basin to shallow water, clearly, bio-retexturing must exert a major influence on longer-term formation-wide diagenetic processes.
The feeding activities and excretory products of the marine decapod Callianassa major Say and the marine annelid Onuphis microcephala Hartman have been studied in shallow marine environments of the southern Atlantic and eastern Gulf of Mexico coasts of the United States. These filter-feeding organisms produce depositionally significant quantities of argillaceous fecal pellets that are transported and deposited as granular clay with hydraulically equivalent quartz sand grains. At average population densities observed in shallow marine environments, these organisms are calculated to be capable of removing and pelletizing approximately 12 metric tons of suspended materials per square kilometre per year and of depositing fecal pellet mud as thick as 4.5 mm yearly. Recent deposits of Onuphis pellets up to 30 cm thick and Callianassa pellets as thick as 60 cm have been observed. The complex, species-specific, sand-sized fecal pellets are composed of 80 to 90 percent clay-mineral particles and 5 to 10 percent undigested organic particles and small amounts of quartz sand and silt grains. The digestive systems of the organisms significantly alter the clay mineralogy of the sediments extracted from suspension, and Callianassa major produces fecal pellets of different clay-mineral compositions from fecal pellets produced by Onuphis microcephala. The digestive processes wholly or partly destroy chlorite. Mixed-layer clay minerals are partly destroyed, and kaolinite and illite are in part disordered. Fecal pellets, rich in organic matter, enter the coprophagic cycle where further clay-mineral alteration takes place. Decay of the organic matter creates microreducing conditions within the pellets, thus promoting the processes of glauconitization. Whereas flocculation is the important process in the deposition of argillaceous sediments in deltaic environments, biogenic pelletization may be the most important process in depositing argillaceous sediments in shallow marine interdeltaic environments.
More than 20 trace fossil species occur in marine facies of the Cretaceous Star Point and Blackhawk formations in the Book Cliffs and Wasatch Plateau provinces of Utah. Major genera include Ancorichnus, Arenicolites, Aulichnites, Chondrites, Conichnus, Cylindrichnus, Medousichnus Ophiomorpha, Palaeophycus, Planolites, Rosselia, Schaubcylindrichnus, Scolicia, Skolithos, Teichichnus, Teredolites, and Thalassinoides. Newly named taxa include Ancorichnus capronus, Medousichnus loculatus, and Rosselia chonoides. Most trace fossils occur in characteristic, albeit intergradational ichnofacies correlative with major lithofacies of regressive nearshore to offshore sequences. Characteristic ichnofacies and lithofacies in the Cretaceous of E-central Utah should provide potentially useful models for reconstruction of nearshore to offshore sequences elsewhere especially in the Western Interior Region of North America.-from Authors
Uppermost Devonian and Lower Mississippian strata in the southernmost Canadian Rocky Mountains and adjacent Montana record part of a widespread low-oxygen episode in middle Paleozoic epicontinental and shelf seas and provide information concerning the oceanographic setting of the western continental margin of Euramerica. During early-middle Famennian time, the region was the site of a westward-deepening carbonate ramp that was bordered to the west by a shale basin. Sedimentation patterns changed in middle-late Famennian time with the termination of carbonate ramp sedimentation and ultimate deposition of organic-rich sediments in an oxygen stressed, deep-water setting. Sedimentation of anaerobic to marginally aerobic, deep-water, lower Banff facies occurred into middle and late Tournaisian time prior to the westward progradation of carbonate ramp sediments of the middle and upper Banff. -from Author