stabilization of the coupled oxygen and phosphorus cycles by the evolution of bioturbation animal burrowing and sediment mixing bioturbation began during the run up to the ediacaran cambrian boundary1 2 3 initiating a transition4 5 between the stratified precambrian6 and more well mixed phanerozoic7 sedimentary records against the backdrop of a variable8 9 global oxygen reservoir probably smaller in size than present10 11 phosphorus is the long term12 limiting nutrient for oxygen production via burial of organic carbon13 and its retention relative to carbon within organic matter in marine sediments is enhanced by bioturbation14 15 16 17 18 here we explore the biogeochemical implications of a bioturbation induced organic phosphorus sink in a simple model we show that increased bioturbation robustly triggers a net decrease in the size of the global oxygen reservoir the magnitude of which is contingent upon the prescribed difference in carbon to phosphorus ratios between bioturbated and laminated sediments bioturbation also reduces steady state marine phosphate levels but this effect is offset by the decline in iron adsorbed phosphate burial that results from a decrease in oxygen concentrations the introduction of oxygen sensitive bioturbation to dynamical model runs is sufficient to trigger a negative feedback loop the intensity of bioturbation is limited by the oxygen decrease it initially causes the onset of this feedback is consistent with redox variations observed during the early cambrian rise of bioturbation leading us to suggest that bioturbation helped to regulate early oxygen and phosphorus cycles

a model for microbial phosphorus cycling in bioturbated marine sediments significance for phosphorus burial in the early paleozoic abstract a diagenetic model is used to simulate the diagenesis and burial of particulate organic carbon c org and phosphorus p in marine sediments underlying anoxic versus oxic bottom waters the latter are physically mixed by animals moving through the surface sediment bioturbation and ventilated by burrowing tube dwelling organisms bioirrigation the model is constrained using an empirical database including burial ratios of c org with respect to organic p c org p org and total reactive p c org p reac burial efficiencies of c org and p org and inorganic carbon to phosphorus regeneration ratios if p org is preferentially mineralized relative to c org during aerobic respiration as many previous studies suggest then the simulated p org pool is found to be completely depleted a modified model that incorporates the redox dependent microbial synthesis of polyphosphates and p org termed the microbial p pump allows preferential mineralization of the bulk p org pool relative to c org during both aerobic and anaerobic respiration and is consistent with the database results with this model show that p burial is strongly enhanced in sediments hosting fauna animals mix highly labile p org away from the aerobic sediment layers where mineralization rates are highest thereby mitigating diffusive po 4 3 fluxes to the bottom water they also expand the redox niche where microbial p uptake occurs the model was applied to a hypothetical shelf setting in the early paleozoic a time of the first radiation of benthic fauna results show that even shallow bioturbation at that time may have had a significant impact on p burial our model provides support for a recent study that proposed that faunal radiation in ocean sediments led to enhanced p burial and possibly a stabilization of atmospheric o 2 levels the results also help to explain c org p org ratios in the geological record and the persistence of p org in ancient marine sediments

trace fossils and substrates of the terminal proterozoic cambrian transition implications for the record of early bilaterians and sediment mixing the trace fossil record is important in determining the timing of the appearance of bilaterian animals a conservative estimate puts this time at 555 million years ago the preservational potential of traces made close to the sediment water interface is crucial to detecting early benthic activity our studies on earliest cambrian sediments suggest that shallow tiers were preserved to a greater extent than typical for most of the phanerozoic which can be attributed both directly and indirectly to the low levels of sediment mixing the low levels of sediment mixing meant that thin event beds were preserved the shallow depth of sediment mixing also meant that muddy sediments were firm close to the sediment water interface increasing the likelihood of recording shallow tier trace fossils in muddy sediments overall trace fossils can provide a sound record of the onset of bilaterian benthic activity

depositional history and sequence stratigraphy of the precambrian cambrian boundary stratotype section chapel island formation southeast newfoundland abstract facies relationshps in the vendian to lower cambrian chapel island formation of southeast newfoundland are used to establish a sequence stratigraphic framework for this important boundary stratotype section the formation consists of five members of sandstone mudstone and minor limestone deposited in a variety of shoreline to shelf environments peritidal sandstone and shale units in member 1 are overlain by sandstone and silstone deltaic and shelf deposits of member 2 these make up a transgressive system tract in which small scale changes in relative sea level are superimposed on autocyclic deltaic processes the thickness 400 m of nearshore and inner shelf sediments resulted from high sediment accumulation rates which for member 2 nearly kept pace with subsidence upper member 3 and member 4 consist of inner shelf mudstone and peritidal limestone that were deposited in a low energy oxygen stratified basin these deposits are arranged in three large scale shoaling cycles representing three foresteping parasequences of one highstand systems tract an extensive limestone bed at the tope of member 4 contains a sequence boundary associated with or shortly postdating development of this surface is a significant epeirogenic event that resulted in basin reorganization increased subsidence and progradation of a thick clastic sequence represented by member 5 the deposits of this upper member consist of an upward coarsening storm dominated shelf to shoreface succession of sandstone and silstone deposits of nearly identical character are also found in new brunswick and suggest that these sediments and the underlying sequence boundary could be significant for interregional correlation global correlation of the paleobathymetric curve developed for the chapel island formation is considered unfeasible given the long history of epeirogenic movements during the vendian and early cambrian in this region

geochemical evidence for widespread euxinia in the later cambrian ocean it has been suggested that the cambrian ocean was oxygen deficient but physical evidence for widespread anoxia has been lacking gill et al present sulphur isotope data from cambrian rocks at six different locations around the world and find a positive sulphur isotope excursion in phase with a large excursion in the marine carbon isotope record which is thought to be indicative of a global carbon cycle perturbation at the time a prolonged period of anoxia during the cambrian may explain the previously enigmatic peculiarities seen in the fossil record it has been suggested that the cambrian ocean was oxygen deficient but physical evidence for widespread anoxia has been lacking now sulphur isotope data from cambrian rocks at six different locations around the world is presented with the finding of a positive sulphur isotope excursion in phase with a large excursion in the marine carbon isotope record which is thought to be indicative of a global carbon cycle perturbation at the time with the help of a box model these isotope shifts support the idea of large scale anoxic and sulphidic conditions in the later cambrian ocean widespread anoxia in the ocean is frequently invoked as a primary driver of mass extinction as well as a long term inhibitor of evolutionary radiation on early earth in recent biogeochemical studies it has been hypothesized that oxygen deficiency was widespread in subsurface water masses of later cambrian oceans1 2 possibly influencing evolutionary events during this time1 2 3 physical evidence of widespread anoxia in cambrian oceans has remained elusive and thus its potential relationship to the palaeontological record remains largely unexplored here we present sulphur isotope records from six globally distributed stratigraphic sections of later cambrian marine rocks about 499 million years old we find a positive sulphur isotope excursion in phase with the steptoean positive carbon isotope excursion spice a large and rapid excursion in the marine carbon isotope record which is thought to be indicative of a global carbon cycle perturbation4 5 numerical box modelling of the paired carbon sulphur isotope data indicates that these isotope shifts reflect transient increases in the burial of organic carbon and pyrite sulphur in sediments deposited under large scale anoxic and sulphidic euxinic conditions independently molybdenum abundances in a coeval black shale point convincingly to the transient spread of anoxia these results identify the spice interval as the best characterized ocean anoxic event in the pre mesozoic ocean and an extreme example of oxygen deficiency in the later cambrian ocean thus a redox structure similar to those in proterozoic oceans6 7 8 may have persisted or returned in the oceans of the early phanerozoic eon indeed the environmental challenges presented by widespread anoxia may have been a prevalent if not dominant influence on animal evolution in cambrian oceans

complex trace fossils from the terminal proterozoic of namibia we document for the first time the occurrence of the complex trace fossil treptichnus from the terminal proterozoic nama group namibia these traces differ in detail from the cambrian index fossil treptichnus pedum but document precursors with the same basic behavior the producer of the trace is not known in its complexity however this trace fossil provides strong evidence for advanced latest proterozoic bilaterians

textured organic surfaces associated with the ediacara biota in south australia abstract the ediacaran period takes its name from the fossils of the ediacara biota which represent the first appearance of large and diverse assemblages of organisms in the fossil record although the global record of these distinctive body fossils is now well known a previously unrecognized megascopic organic record of textured organic surfaces tos occurs in the ediacara biota however tos is also a feature over a wider range of paleoenvironmental settings where body fossils are unknown in ediacaran siliciclastic successions that have been studied in australia namibia and western north america paleoecological analysis of successive bedding planes of strata from the late ediacaran rawnsley quartzite in the flinders ranges of south australia reveals that tos represent the most common organic features in bedding surface assemblages of the ediacara biota the tos consist of preserved patterned assemblages of textured organic mats fibers and simple tubular body fossils complex ediacara body fossils while striking for their distinctive body plans and dominating some of the beds are relatively minor components of combined overall surface area many elements of tos have previously been miss diagnosed as trace fossils which are in practice limited to two or at most three morphotypes that indicate the presence of bilateria although tos represent a simpler grade of organismic construction than discrete and more complex ediacara body fossils they were preserved in a similar manner marked variability in all components of the biota between successive surfaces suggests that ediacara ecologies fluctuated at short intervals despite an apparently consistent sedimentary regime

mean mixed depth of sediments the wherefore and the why the activities and consequently the bioturbational effects of deposit feeding organisms are largely restricted to a narrow surficial zone of marine sediments with a worldwide environmentally invariant mean of 9 8 cm with a standard deviation of 4 5 cm currently available theories of infaunal behavior cannot predict quantitatively this observation a new simple model that accounts for the feedback between resource food abundance its reactivity and the intensity of bioturbation leads to a quantitative estimate of 9 7 cm this model constitutes a fundamental advance in our understanding bioturbation

priapulid worms pioneer horizontal burrowers at the precambrian cambrian boundary the major evolutionary events that characterize the precambrian cambrian transition are accompanied by profound ecological changes in the composition of benthic communities the nature of the substrate and the occupation of marine ecospace the increased animal activity on and within the substrate is attested to by numerous trace fossils such as the cosmopolitan treptichnus pedum whose fi rst appearance is used as the global stratotype section and point gssp to mark the base of the cambrian in spite of its major importance in biostratigraphy the maker of treptichnus trace fossils and more generally of treptichnids has long remained an enigma treptichnids were subhorizontal burrow systems produced in the subsurface and had a worldwide distribution throughout the cambrian here we show by using experimental ichnology that the treptichnid burrow systems were most probably produced by priapulid worms or by worms that used the same locomotory mechanisms as the recent priapulids e g priapulus their typical three dimensional morphology with repeated arcuate probing branches suggests that their function was related to the feeding strategy of the worm such as predation or scavenging upon small epibenthic or endobenthic invertebrates this interpretation is strongly supported by the preserved gut contents of cambrian priapulids from the burgess shale lagerstatte that contain effectively a variety of small epibenthic prey the antiquity of treptichnids would designate priapulids as one of the earliest infaunal colonizers of the substrate that possibly interacted with epibenthic communities thus playing a leading role 1 in the construction of the early marine food chain and 2 as important subhorizontal bioturbators in the early stages of the cambrian substrate revolution

ediacara type fossils in cambrian sediments fossil assemblages that preserve soft bodied organisms are essential for our understanding of the composition and diversity of past life the worldwide terminal proterozoic ediacara type fossils from 600 544 myr bp are unique in consisting of soft bodied animals which are typically preserved as impressions in coarse grained sediments1 2 3 4 these lagerstatten are also special because they pre date the major burst of skeletonization which occurred near the start of the cambrian period3 most ediacara type fossils are interpreted to be cnidarians but higher metazoans such as annelids and molluscs may also be represented1 2 3 4 however the unique style of preservation and difficulties in finding convincing morphological homologies with definite animals have led some specialists to prefer non metazoan interpretations such as vendobionta5 in addition the rarity of ediacara type fossils in younger sediments has led to suggestions of a terminal proterozoic mass extinction6 here we report typical ediarcara type frond shaped fossils that occur together with an assemblage of cambrian type trace fossils in unequivocally cambrian aged sediments of the uratanna formation south australia this occurrence bridges the apparent divide between the terminal proterozoic and cambrian fossil assemblages and also suggests that closure of a taphonomic window an interval of time with unique preservational conditions was as important as extinction in the disappearance of ediacara type organisms

swimming reptiles make their mark in the early triassic delayed ecologic recovery increased the preservation potential of vertebrate swim tracks fossil tetrapod swim tracks have been reported from deposits throughout the world ranging in age from the carboniferous mississippian to the neogene pleistocene a normalized analysis of these occurrences demonstrates that lower triassic strata contain an anomalously high number of occurrences lower triassic swim tracks also tend to be better preserved showing exceptionally detailed features such as scale striae and crescent shaped claw margins preservation of these features required a firm and semicohesive substrate in order to maintain track detail before and after burial swim track localities from the lower triassic moenkopi formation in utah usa are characterized by sedimentary and trace fossil features that demonstrate the widespread development and persistence of firmground substrates in a large delta plain complex within this delta complex low diversity invertebrate trace fossil assemblages consist of locally high densities of diminutive millimeter scale traces characteristic of stressed brackish water faunas we suggest that the depauperate infauna characteristic of such environments was repressed due to delayed biotic recovery following the end permian mass extinction resulting in extremely low intensities of bioturbation lack of biogenic mixing promoted semiconsolidation of dewatered mud substrates and the widespread production and persistence of firmgrounds capable of recording and maintaining swim tracks thus a combination of factors unique to the early triassic increased the preservation potential of detailed swim tracks 1 depositional environments that promoted the production of firmground substrates 2 delayed ecologic recovery resulting in the lack of well bioturbated sediment and 3 the swimming behavior of various early triassic tetrapods

exceptional fossil record distribution of soft tissue preservation through the phanerozoic preservation of soft bodied fossil biotas konservat lagerstaten that preserve traces of volatile nonmineralized tissues readily degraded by bacteria are not evenly spaced through geologic time when compared to outcrop area exceptional faunas appear to be over represented in the cambrian and jurassic these concentrations in time correspond to particular environments indicating that controls on the distribution of exceptional faunas may have operated on a global scale the reduction in the number of exceptional faunas after the cambrian may reflect the evolution and diversification of deep bio turbators specific conditions favoring stagnation and episodic burial were required to ensure preservation in younger rocks

post cambrian closure of the deep water slope basin taphonomic window exceptional faunas konservat lagerstatten that preserve traces of volatile nonmineralized tissues are statistically overabundant in the cambrian period almost all examples preserved in continental slope and shelf basin environments are of this age the hypothesis that an increase in the amount and complexity of bioturbation was an important agent in the elimination of this deep water slope basin taphonomic window is supported post cambrian ichnofaunal assemblages contain a higher proportion of pascichnia and agrichnia ethologies produced by a mobile infauna they also illustrate the lateral partitioning of organisms into different environmental niches both opportunistic and equilibrium infaunas occur in low oxygen environments in which the preservation of nonbiomineralized tissues was favored direct consumption of carcasses by bioturbating organisms was less important than changes to sediment properties as a result of bioturbation notably enhanced microbial degradation of reactive organic matter increased permeability and the disruption of geochemical gradients necessary for mineral authigenesis

redox dependent distribution of early macro organisms evidence from the terminal ediacaran khatyspyt formation in arctic siberia abstract the ediacaran period witnessed the first appearance of macroscopic animal life in earth s history however the biogeochemical context for the stratigraphic occurrence of early metazoans is largely uncertain in part due to the dearth of integrated paleobiological and chemostratigraphic datasets in this study a comprehensive geochemical analysis was conducted on the fossiliferous khatyspyt formation in arctic siberia in order to gain insights into the ediacaran paleoenvironments this study was designed to specifically address the relationship between paleoredox conditions and ediacaran fossil occurrences in the khatyspyt formation our data reveal a dramatic shift in pyrite sulfur isotope compositions 34 s pyrite from ca 20 to ca 55 and this shift is intriguingly associated with the first occurrence of ediacara type macrofossils at the studied section suggesting a possible link between seawater redox conditions and distribution of early macroscopic organisms based on multiple lines of sedimentological and geochemical evidence we propose that the development of oceanic euxinia which may be widespread in the continental margins due to enhanced oxidative weathering in the terminal ediacaran period may have locally prohibited the colonization of ediacara type organisms and resulted in low 34 s pyrite values in the lower khatyspyt formation in the middle and upper khatyspyt formation progressive secular transition from euxinic to non euxinic and more habitable conditions may have allowed for the colonization of ediacara type and other macro organisms

the importance of planolites in the cambrian substrate revolution abstract early cambrian subtidal shelf substrates were characterized by low water content and steep chemical gradients conditions likely facilitated by the presence of microbial mats as reflected by an abundance of microbially mediated sedimentary structures in lower cambrian strata such substrate conditions would have been unfavourable for burrowing by benthic metazoans a combination of environmental restrictions and a lack of adaptations to vertical burrowing likely prevented most benthic metazoans from burrowing infaunally in early cambrian subtidal shelf substrates the eventual acquisition of burrowing adaptations by benthic metazoans later in the cambrian promoted an increase in the depth and intensity of bioturbation and initiated a transition toward well hydrated substrates in which extensive infaunal activity was possible siliciclastic units of the lower cambrian succession in the white inyo mountains eastern california contain abundant horizontal bioturbation on bedding planes as documented by bedding plane bioturbation indices but little vertical bioturbation as shown by ichnofabric indices and x radiography planolites a simple horizontal trace fossil represents the dominant type of bioturbation in these units planolites is found in a range of diameters indicating that more than one species of tracemaker likely produced this type of trace although these planolites do not have a vertical component their abundance on bedding planes indicates that the activities of planolites tracemakers had a significant impact on subtidal shelf substrates represented by lower cambrian units in the white inyo mountains early in the cambrian substrate revolution

trace fossil preservation and the early evolution of animals abstract the trace fossil record is an important element in discussions of the timing of appearance of bilaterian animals a conservative approach does not extend this record beyond about 560 555 ma crucial to the utility of trace fossils in detecting early benthic activity is the preservational potential of traces made close to the sediment water interface our studies on the earliest cambrian sediments suggest that shallow tiers were preserved to a greater extent than typical for most of the phanerozoic this can be attributed both directly and indirectly to the low levels of sediment mixing the low levels of sediment mixing meant that thin event beds were preserved the shallow depth of sediment mixing also meant that muddy sediments were firm close to the sediment water interface increasing the likelihood of recording shallow tier trace fossils in muddy sediments preservation of surficial trace fossils in this type of setting remains problematic but the above factors suggest that also these can be expected to have left a reasonable record overall the trace fossil record can be expected to provide a sound record of the onset of bilaterian benthic activity the lack of convincing trace fossils significantly before the cambrian supports models of late appearance of macroscopic benthic bilaterians

earth s oldest jellyfish strandings a unique taphonomic window or just another day at the beach discoidal macrofossils reported herein from the lower cambrian zabriskie quartzite great basin western united states record the oldest phanerozoic medusozoan body fossils as well as the oldest medusozoan stranding event on record moreover these fossils provide evidence of a significant shift in the taphonomic mode characteristic of preservation of nonmineralized taxa in coarse grained siliciclastic successions near the onset of the phanerozoic taphonomic and sedimentological evidence recorded by these and younger examples of stranded cambrian medusae is consistent in suggesting that several of the requirements for preservation of these fossils were holdovers from the ediacaran period including the presence of microbial mats and a lack of carcass disturbance by scavenging and or bioturbating taxa to shed further light upon the taphonomic factors necessary for the preservation of cambrian medusae we compared the biostratinomy and sedimentology of cambrian medusa strandings to those of ediacara biota assemblages from lithologically similar successions we find key secular disparities in the taphonomic histories of these two types of fossil assemblage inconsistencies between the preservational styles characteristic of fossil assemblages preserved in sandstone lithofacies on each side of the precambrian cambrian boundary are explained by a considerable change in the preferred depositional setting in which these macrofossil assemblages are preserved thus rather than documenting a single taphonomic continuum through the precambrian cambrian transition the zabriskie and younger medusozoan body fossil assemblages record the advent of an entirely new yet still very rarely exploited taphonomic window exclusive to the cambrian period

the importance of relict burrow structures and burrow irrigation in controlling sedimentary solute distributions abstract some areas of the seafloor particularly the deep sea are characterized by large numbers of apparently uninhabited or relict burrow structures formed by macrobenthic organisms because of low sedimentation rates or lack of physical disturbance these structures are stable for long periods of time and could potentially influence solute diffusion patterns in surface sediments a two dimensional diffusionreaction model which allows for diffusive rather than advective transport within stagnant water filled burrows demonstrates that in the absence of advective irrigation relict burrow structures are unlikely in most cases to significantly alter average solute distributions from those predicted by one dimensional vertical models this conclusion assumes changes in diffusive transport properties alone and does not account for any effects of relict structures on reaction rates or physical ventilation of deposits by bottom currents significant changes 5 in solute distributions are generally produced only when the ratio of the halfdistance between burrows to relict burrow radii is 10 and sedimentary diffusion coefficients are 60 that in free solution because solute distributions in stagnant burrow waters are nearly that in surrounding sediment sediment water solute fluxes are also essentially unaffected by relict burrows except at extremely high abundances or fairly large differential diffusion rates between sediment and free solution in contrast even at low abundance biologically irrigated or physically ventilated burrows produce major changes in solute transport and build up patterns

burgess shale type biotas were not entirely burrowed away burgess shale type biotas occur globally in the cambrian record and offer unparalleled insight into the cambrian explosion the initial phanerozoic radiation of the metazoa deposits bearing except

trends in depth and extent of bioturbation in cambrian carbonate marine environments western united states cambrian carbonate strata of the great basin deposited below fairweather wave base but above mean storm wave base inner shelf and below mean storm wave base but above maximum storm wave base middle shelf were examined for extent and depth of bioturbation data indicate that initial extensive colonization of marine infaunal habitats occurred between tommotian and atdabanian time throughout the remaining 65 m y of cambrian time bioturbation increased although depth of bioturbation remained relatively constant at less than 6 cm during this time the amount of bioturbation in the inner shelf was greater than that in the middle shelf

widespread delayed mixing in early to middle cambrian marine shelfal settings abstract the radiation of burrowing metazoans in the early phanerozoic dramatically altered the properties of marine sediment an event commonly referred to as the cambrian substrate revolution or agronomic revolution the advent of infaunalization and especially biogenically mediated sediment mixing profoundly impacted the development of phanerozoic biogeochemical cycling including nutrient fluxes organic carbon burial seafloor oxygenation and sediment ecology however the timing of the development of mixed seafloor sediment has historically not been well constrained mixing has been assumed in the absence of data to occur at the precambrian cambrian boundary with the appearance of the index fossil and three dimensional burrow treptichnus pedum herein we present new ichnological stratigraphic and taphonomic data suggesting that although significant developments in infaunalization paleobiologically complex animal substrate interactions particularly burrow construction occurred during the early and middle cambrian mixing remained suppressed throughout this interval we demonstrate using a novel multi proxy approach that shelfal sediment in the earliest cambrian was essentially unmixed moreover our findings indicate that even as late as the middle cambrian 30 million years after the precambrian cambrian transition and well after the appearance of supposedly deposit feeding trilobites seafloor heterolithic shelfal sediment remained largely unmixed on a global scale these findings challenge the current assumption that mixing occurred with the first appearance of three dimensional burrows and hold important implications for the advent and development of modern style biogeochemical cycling

remarkable preservation of microbial mats in neoproterozoic siliciclastic settings implications for ediacaran taphonomic models abstract it is beyond doubt that the appearance of infaunal bioturbation and metazoan biomineralization across the ediacaran cambrian transition irreversibly affected the nature of marine sediment architecture and biogeochemistry here we review those changes in relation to their likely effect upon the processes of fossil preservation especially within siliciclastic sediments processes of soft tissue preservation in siliciclastic settings from the ediacaran period including microbes and microbial mats as well as ediacaran macrofossils are here reviewed within this context highlighted examples include the exceptional preservation of microbes found in association with wrinkle structures and ediacaran macrofossils in england and newfoundland replicated by silicate minerals and in the white sea region of russia replicated by iron sulphide these occurrences show that soft tissue preservation in siliciclastic settings went well beyond that typical for ediacaran macrofossils alone and also extended to similar modes of preservation in associated microbes using these new observations it can be argued that several existing explanations for ediacaran fossil preservation can be united within a biogeochemical model that involves evolution of the sediment mixed layer across this transition

biogeochemistry oxygen burrowed away multicellular animals probably evolved at the seafloor after a rise in oceanic oxygen levels biogeochemical model simulations suggest that as these animals started to rework the seafloor they triggered a negative feedback that reduced global oxygen

triassic continental rifting of pangaea direct evidence from the alpujarride carbonates betic cordillera se spain abstract evidence is presented for triassic rift related palaeo structures from the alpujarride complex carbonates of the betic cordillera se spain direct evidence of synsedimentary extensional tectonics is provided by macro to meso scale normal faults overstepped by younger strata most faults define domino like horst and graben structures the faults are associated with an expanded synrift sedimentary prism in which soft sediment deformation gravity flow deposits and unconformities are widely developed syntectonic mafic igneous intrusions also occur the age of this phase of extension is constrained as ladinian carnian c 237 216 ma from a palaeogeographical standpoint the thick triassic carbonates of the betic internal zone together with comparable successions in northern calabria southern apennines occupied a belt with elevated subsidence connecting the neo tethys to the east with the eastern north american intracontinental rift system to the west their carbonate facies intermediate between classical alpine and germanic type triassic facies recorded the main episodes of rifting affecting central pangaea

the early paleozoic development of bioturbation evolutionary and geobiological consequences abstract bioturbation the physical and chemical mixing of sediments by burrowing animals is a critical engineering process in modern seafloor environments and exerts an important control on not only benthic ecology and sediment properties but also ocean wide biogeochemical cycling well mixed sediments have long been assumed to appear at the precambrian cambrian boundary with the first occurrence of the index fossil and three dimensional burrow treptichnus pedum however field based analyses synthesizing ichnological stratigraphic sedimentological and taphonomic data collected from lower paleozoic successions worldwide indicate that sediment mixing in marine shelf environments remained limited until at least the late silurian 120 million years after the precambrian cambrian transition in spite of early advances in complex modes of infaunalization mixed layer development had a much more gradual trajectory and did not occur in step with the first appearance of three dimensional burrows the delayed appearance of modern style intensities of sediment reworking postdating both the cambrian explosion and the great ordovician biodiversification event may be due to the late stage radiation of mobile infaunal deposit feeders biological bulldozers the organisms which are in modern marine settings the most efficient bioturbators the protracted development of the sediment mixed layer holds important implications for contemporaneous biogeochemical cycling and oxygenation of the ocean atmosphere system the delayed development of intensive sediment mixing may have also mediated exceptional preservation of both fossilized soft tissues and shallow tier trace fossils and may therefore have contributed to the anomalous preponderance of konservat lagerstatten and exceptionally preserved shallow tier trace fossils and bioglyphs characteristic of the lower paleozoic stratigraphic record

protracted development of bioturbation through the early palaeozoic era mobile organisms first appeared in the fossil record prior to the precambrian cambrian transition sediment textures indicate that the degree of sediment mixing by animal activity remained low for 120 million years following the transition

paleoecology of benthic metazoans in the early cambrian maotianshan shale biota and the middle cambrian burgess shale biota evidence for the cambrian substrate revolution abstract as the depth and intensity of bioturbation increased through the proterozoic phanerozoic transition the substrates on which marine benthos lived changed from being relatively firm with a sharp sediment water interface to having a high water content and blurry sediment water interface microbial mats once dominant on normal marine proterozoic seafloors were relegated to stressed settings lacking intense metazoan activity this change in substrates has been termed the agronomic revolution seilacher a pfluger f 1994 from biomats to benthic agriculture a biohistoric revolution in krumbein w e ed biostabilization of sediments bibliotheks and informationsystem del carl von ossietzky universitat oldenburg 97 105 and the impact of the subsequent development of the mixed layer on benthic metazoans has been termed the cambrian substrate revolution bottjer d j hagadorn j w dornbos s q 2000 the cambrian substrate revolution gsa today 10 9 1 7 because the early cambrian was a transitional time in this substrate revolution it is hypothesized that benthic metazoans adapted to typical proterozoic style soft substrates co existed with benthic metazoans adapted to more typical phanerozoic style soft substrates paleoecological examination of the benthic metazoans of the early cambrian maotianshan shale chengjiang biota and middle cambrian burgess shale biota combined with examination of core samples from the rocks in which the maotianshan shale biota is preserved was performed in order to test this hypothesis results of the core analysis reveal that the rocks in which the maotianshan shale biota was preserved and therefore the substrate on which it lived contains almost no evidence for bioturbation of any kind while the immediately underlying rocks of similar lithology are dominated by intermediate levels of horizontal bioturbation and contain some evidence for the beginning of mixed layer development these results suggest that benthic metazoans of the maotianshan shale biota lived on a typical proterozoic style soft substrate and that environmental conditions associated with the exceptional preservation of the maotianshan shale biota may have also suppressed bioturbation levels results of the paleoecological analysis indicate that the maotianshan shale and burgess shale biotas contain mobile and sessile benthic metazoans adapted to typical proterozoic style soft substrates and others adapted to typical phanerozoic style soft substrates in addition the maotianshan shale biota is dominated by benthic suspension feeding genera adapted to typical proterozoic style soft substrates indicating that this biota lived during the early stages of the cambrian substrate revolution the burgess shale biota however contains more benthic suspension feeding genera adapted to typical phanerozoic style soft substrates than the maotianshan shale biota which suggests that the soft substrate on which they lived had more advanced levels of mixed layer development this research suggests that the adaptive radiation of benthic metazoans during the cambrian explosion was driven in part by the cambrian substrate revolution as benthic metazoans were forced to adapt to the development of the mixed layer in subtidal siliciclastic soft substrate environments during the cambrian

the cambrian substrate revolution and the early evolution of attachment in suspension feeding echinoderms abstract the cambrian characterized by the global appearance of diverse biomineralized metazoans in the fossil record for the first time represents a pivotal point in the history of life this period also documents a major change in the nature of the sea floor neoproterozoic type substrates stabilized by microbial mats were replaced by unconsolidated soft substrates with a well developed mixed layer the effect of this transition on the ecology and evolution of benthic metazoans is termed the cambrian substrate revolution csr and this is thought to have impacted greatly on early suspension feeding echinoderms in particular according to this paradigm most echinoderms rested directly on non bioturbated soft substrates as sediment attachers and stickers during the cambrian epoch 2 as the substrates became increasingly disturbed by burrowing forming a progressively thickening mixed layer echinoderms developed new strategies for attaching to firm and hard substrates to test this model we evaluated the mode of attachment of 83 cambrian suspension feeding echinoderm species attachment mode was inferred based on direct evidence in fossil specimens and interpretations of functional morphology these data were analyzed quantitatively to explore trends in attachment throughout the cambrian in contrast to previous studies the majority of cambrian clades eocrinoids helicoplacoids helicocystoids isorophid edrioasteroids and solutes are now interpreted as hard shelly substrate attachers only early edrioasteroids attached directly to firm substrates stabilized by microbially induced sedimentary structures contrary to the predictions of the csr paradigm our study demonstrates that cambrian echinoderms were morphologically pre adapted to the substrate changes that occurred during the cambrian allowing them to fully exploit the appearance of hardgrounds in the furongian we find no support for the claim that the csr explains the peak in echinoderm diversity during cambrian epochs 2 3 or that it caused the extinction of helicoplacoids

quantitative ichnology of modern pelagic deposits in the abyssal atlantic abstract quantitative sedimentologic aspects of bioturbation were investigated in a series of deep sea box cores which were collected over a broad latitudinal range 35 n to 30 s and bathymetric range 1 4 to 5 7 km in the central atlantic ocean all cores were thoroughly bioturbated and numerous generations of burrowing could be discerned in many instances preservation of individually distinct burrows ranged from poor to excellent and eight ichnogenera plus several unnamed biogenic structures were recognized the distribution of calcium carbonate organic carbon selected species of planktic foraminifera and sediment grain size were examined in several cores these measurements indicated that the surficial mixed layer which ranged from 3 to 10 cm thick was statistically more homogeneous than the underlying transition layer this relationship is seen most clearly with respect to lateral and vertical variations in the calcium carbonate content of the cores bioturbation of abyssal pelagic deposits appears to be a two phase process consisting of a homogenization of the upper few centimeters i e the mixed layer by shallow burrowing meiofauna and b heterogeneous mixing of the underlying strata i e the transition layer by relatively deep burrowers the heterogeneously mixed transition layer becomes the preserved trace fossil record under normal circumstances the homogenized mixed layer is not preserved

gyrolithes from the ediacaran cambrian boundary section in fortune head newfoundland canada exploring the onset of complex burrowing abstract the beginning of the cambrian explosion is characterized by the onset of infaunalization and the appearance of systematic patterns of burrowing the trace fossil gyrolithes is common in the ediacaran cambrian global stratotype section and point where it shows a higher diversity and burrow depth than previously reported from any cambrian spiral vertical burrows two ichnospecies are present g scintillus isp nov exhibits a small burrow radius to whorl radius ratio whereas g gyratus hofmann exhibits an exceptionally large ratio that formerly led to its identification as an aberrant ichnospecies of skolithos the helical morphology of these cambrian gyrolithes is interpreted as having served two purposes as an anchor in a relatively high energy environment and as an optimal shape for maximizing surface area for bacterial gardening these shallow marine gardening burrows share a similar feeding strategy as graphoglyptids suggesting that shallow early cambrian sediments may have been relatively poor in organics and thus further supporting the model for onshore offshore migration of gardening burrows

the application of ichnology to palaeoenvironmental and stratigraphic analysis it has been increasingly realized by sedimentologists in the petroleum industry and academia that integration of ichnological information into sedimentological models and vice versa is one of the main means by which we can improve our understanding of ancient depositional environments this volume aims to provide an analytical review of the ichnology of all major depositional environments and the use of ichnology in biostratigraphic and sequence stratigraphic analysis as well as highly refined palaeoenvironmental studies the remit of the book is achieved through a combination of review articles and novel research papers that outline methodologies and protocols for improving our understanding of ancient palaeoenvironments trace fossils from microscopic borings to dinosaur footprints are considered the comprehensive coverage of ancient depositional environments means that the book will be of use as a course text for undergraduates as well as an invaluable reference text for all students of ichnology whether they are ichnologists sedimentologists or petroleum geologists by trade

when the worm turned concordance of early cambrian ichnofabric and trace fossil record in siliciclastic rocks of south australia studies of sedimentary fabrics and trace fossils across the precambrian cambrian interval in south australia demonstrate that the appearance of treptichnus pedum which defines the base of the cambrian also marks the initial development of preservable infaunal activity there is a significant shift in the amount and nature of bioturbation at this time these results support the broad scale utility of t pedum as the indicator of the base of the cambrian

lipid taphonomy in the proterozoic and the effect of microbial mats on biomarker preservation the pre ediacaran biomarker record has several characteristic features that distinguish it from its phanerozoic counterpart including high concentrations of unresolved complex mixture ucm low concentrations or absence of eukaryotic steranes and a conspicuous carbon isotopic enrichment of n alkyl lipids relative to bulk sedimentary carbon we propose that these derive from a common non actualistic taphonomy based on the pervasive presence of microbial mats prior to the cambrian substrate revolution such mats would have formed a significant mechanical and biochemical barrier to in falling plankton leaving a biomarker record dominated by benthic microbial lipids most of which would have originated from the lower heterotrophically reworked layers of the mat most proterozoic biomarker assemblages studied in this work derive from shallow water sediments where cyanobacteria dominated upper mats represent a focused source of corrosive molecular oxygen this mat seal effect was broken with the onset of bioturbation in the ediacaran and early cambrian at which point the primary source of fossil biomarkers switched from the benthos to the plankton

phosphogenesis associated with the shuram excursion petrographic and geochemical observations from the ediacaran doushantuo formation of south china abstract the ediacaran period witnessed one of the largest phosphogenic events in earth s history coincidently some phosphorite deposits in south china are associated with the largest known carbon isotope negative excursion i e shuram excursion suggesting an intimate coupling of the biogeochemical carbon and phosphorous cycles however the geomicrobiological linkage between these anomalies remain poorly understood in this study we investigated the phosphorite samples from the uppermost doushantuo formation in south china carbon isotope compositions of authigenic calcite cements and nodules in the phosphorites are as low as 34 vpdb petrographic and geochemical investigations indicate that the 13 c depleted carbonates likely formed as the result of microbial sulfate and iron reduction that released phosphorous from iron oxyhydroxide concentrating phosphorous in pore waters and thereby promoting phosphate mineralization the timing of this event appears to coincide with enhanced sulfate delivery to seawater through continental weathering the basin scale distribution of doushantuo phosphorites suggests a redox control on the availability of iron oxyhydroxide and the recycling of pore water phosphorous both inner and outer shelf regions were likely characterized by an oxic water column and were the main loci for phosphogenesis on the contrary intra shelf and slope regions which are lean in phosphorite were subjected to euxinic or ferruginous water column conditions the intimate coupling between ediacaran phosphogenesis and the shuram excursion suggests strong links among seawater redox conditions c s p fe cycling and fossil phosphatization increased microbial sulfate reduction driven by enhanced sulfate reservoir in the ediacaran ocean may have played an essential role on these biogeochemical events

composite ichnofabrics and tiering of burrows infaunal communities in marine environments typically are tiered that is different taxa live at different depths within the sediment tiered suites of biogenic structures yield complex biogenic sedimentary fabrics ichnofabrics with the traces of deep burrowing organisms overprinted on those of shallow burrowing organisms careful analysis of crosscutting relationships of burrows in such composite ichnofabrics allows reconstruction of the tiered nature of fossil endobenthic communities it is important to recognize that the best preserved and most prominently displayed trace fossils in most assemblages usually represent the deepest tier thus they were farther removed from the sea floor and therefore less indicative of actual sea floor conditions than the more poorly preserved traces of the shallower tiers on which the deeper traces are juxtaposed

stratigraphic completeness tiered trace fossils provide a measuring stick trace fossil associations commonly display a characteristic vertical zonation tiering within the substrate when burrows of a particular tier become truncated by turbidites tempestites or other results of catastrophic events they provide a simple but quantitative caliper for estimating stratigraphic incompleteness the minimum amount of penecontemporaneous sea floor erosion can be determined by types and sequences of trace fossils preserved below event deposits

high resolution geochemical evidence for oxic bottom waters in three cambrian burgess shale type deposits abstract the cambrian radiation of complex animals is a fundamental event in the history of life on earth much of our understanding of this event is made possible through the study of exceptionally preserved fossils in burgess shale type bst deposits based on bioturbation levels in bst deposits they are often interpreted as representing restricted oxygen settings this study tests the low oxygen interpretation through analysis of geochemical paleoredox proxies and bioturbation levels in three bst deposits the early cambrian maotianshan shale china the middle cambrian wheeler shale usa and the middle cambrian spence shale usa results from 96 samples show fine scale geochemical evidence for oxic bottom water conditions during the deposition of these three bst deposits trace element paleoredox indices pi give consistent oxic signals in all three shales in addition total organic carbon toc and total sulfur ts levels in the spence shale are extremely low the average c s ratio is 3 1 comparable to values for modern oxic marine water bioturbation levels in all three shales are low with rare development of minimal to moderate horizontal bioturbation while short term oxygen fluctuations or poikiloaerobic conditions could still have sporadically existed in these settings this study shows that these bst deposits were deposited in a dominantly oxic paleoredox setting evidence for low bioturbation levels coupled with paleoredox geochemistry indicative of oxic bottom waters suggests that pervasive exaerobic conditions with an oxic water column positioned above oxygen depleted sediment pore waters may have existed in many cambrian bst deposit paleoenvironments