reactivation of ancient antarctic rift zones by intraplate seismicity buried deep beneath the antarctic polar ice sheet the geological structure and tectonic activity of east antarctica have long remained unknown the apparent lack of tectonic seismicity was thought to be anomalous relative to other continental interiors and has been attributed to a lack of intraplate stress due to the surrounding spreading ridges and low absolute plate velocity or to the weight of ice sheets increasing the normal stress here we report 27 intraplate tectonic earthquakes detected by the agap gamseis seismic array during 2009 in the interior of east antarctica which represents locally recorded seismicity in the region the earthquakes are primarily extensional and located at shallow to mid crustal depths beneath sedimentary basins aligned linearly adjacent to the gamburtsev subglacial mountains the basins may be part of an ancient continental rift system which provides a zone of pre existing tectonic weakness that focuses the seismicity these events when combined with events in published catalogues of antarctic seismicity indicate levels of seismicity in east antarctica of the same order of magnitude as that of other stable cratons such as the canadian shield

environmental interpretation and a sequence stratigraphic framework for the terminal proterozoic ediacara member within the rawnsley quartzite south australia abstract fossils of the ediacara biota are confined to preservational windows in the ediacara member of the rawnsley quartzite pound subgroup from the flinders ranges south australia the base of the ediacara member is a type 1 sequence boundary incised into the partly lithified chace quartzite member of the rawnsley quartzite the ediacara member and the upper half of the rawnsley quartzite comprise the rawnsley depositional sequence bounded above by the early cambrian uratanna depositional sequence the rawnsley sequence developed over an erosional surface cut into the chace quartzite member with some 250 m of relief southeasterly directed palaeovalleys are filled with a sequence of massive sandstone and laminated siltstone passing up into well bedded sandstone at lowstand local channels were filled by massive sand the highstand systems tract consists of several parasequence sets of laminated siltstone and channelized amalgamated massive sandstone overlain by interbedded siltstone and sandstone grading up into well bedded clean sandstone impressions of soft bodied ediacaran organisms are preserved above the valley fill facies on sandstone partings within upward shoaling delta front environments between storm and fairweather wavebase the ediacara member is in places conformably overlain by up to 500 m of sandstone of the same lithofacies as those underlying the member distinctive microbial mat bound sand laminae described as petee structures are characteristic of the rawnsley quartzite above and below the ediacara member during deposition of the ediacara member colonization of the deeper substrates by microbial mat communities enabled preservation of the ediacara biota the erosional surface at the base of the ediacara member is one of at least four incision events recorded in the terminal proterozoic and early cambrian succession of the adelaide geosyncline the similarity of incision filling lithofacies of the rawnsley and uratanna sequences has in condensed sections led to confusion between the depositional sequences characteristic trace and body fossil assemblages provide the only clear distinction between depositional cycles spanning the proterozoic cambrian boundary

re evaluation of the middle miocene eagle mountain formation and its significance as a piercing point for the interpretation of extreme extension across the death valley region california u s a abstract the death valley area of eastern california and southern nevada has been highly influential in the development of ideas about extreme crustal extension one of the tightest constraints on death valley extension is apparently provided by clasts in inferred alluvial fan deposits of the eagle mountain formation 15 11 ma and their source in the hunter mountain batholith now located 100 km from some of the deposits because alluvial fans are usually less than 10 20 km in radius the remaining separation has been interpreted as tectonic new research reported here suggests that the eagle mountain formation at its type location was deposited in a fluvial lacustrine setting and provides no constraint on either the magnitude or the direction of tectonic transport and or crustal extension confidence in palinspastic reconstruction thus depends on resolving ambiguities in the correlation of pre extensional markers or on the recognition of demonstrably proximal facies tectonically distributed across the region the succession at eagle mountain comprises 1 diffusely stratified monolithologic carbonate breccia and sandstone 140 m onlapping cambrian carbonate rocks at an unconformity with 110 140 m of relief fluvial or fluvially influenced 2 10 m of tabular bedded siltstone diamictite and sandstone lacustrine 3 cross stratified and channelized sandstone and polymict conglomerate bearing hunter mountain clasts with minor siltstone and carbonate 110 m mostly fluvial and 4 tabular bedded sandstone siltstone and minor carbonate 140 m mostly lacustrine eight prominent stratigraphic discontinuities mapped within the third interval are characterized by up to 15 m of local erosional relief and by abrupt upward coarsening from siltstone or carbonate to conglomerate or sandstone a fluvial interpretation for the same critical part of the succession is based upon the existence of the mapped surfaces the ubiquitous development of channels trough cross stratification and upward fining trends particularly between the mapped surfaces and the abundance of well rounded clasts in conglomerate paleocurrents are generally directed between southward and eastward although with considerable dispersion and they shift from approximately southward or southeastward in the mostly fluvial deposits to approximately eastward in the upper lacustrine interval an unusual feature of the eagle mountain formation at eagle mountain is the presence of five crosscutting conglomerate bodies interpreted as vertically infilled fissures of tectonic origin numerous normal reversed normal and oblique slip faults with up to 34 m of stratigraphic separation are thought to postdate sedimentation and tilting of the eagle mountain formation after 11 ma

h2o transport and release in subduction zones experimental constraints on basaltic and andesitic systems phase relationships in natural andesitic and synthetic basaltic systems were experimentally investigated from 2 2 to 7 7 gpa and 550 c to 950 c in the presence of an aqueous fluid in order to determine the stability of hydrous phases in natural subducted crustal material and to constrain reactions resulting in the release of water from subduction zones to the mantle wedge water reservoirs in subducted oceanic crust at depths exceeding the amphibole stability field 70 80 km are lawsonite 11 wt h2o mg chloritoid 8 wt talc 5 wt and zoisite clinozoisite 2 wt in basaltic rocks and lawsonite zoisite clinozoisite phengite 4 wt and staurolite 2 wt in andesitic compositions the thermal stability of lawsonite at 6 0 gpa extends to 800 c and 870 c in basaltic and andesitic compositions respectively at pressures above amphibole out 2 3 2 5 gpa lawsonite reacts through continuous reactions with steep positive dp dt slopes to zoisite clinozoisite until 3 0 3 2 gpa and at higher pressures to more than 7 7 gpa to assemblages containing garnet clinopyroxene and garnet clinopyroxene kyanite in basaltic and andesitic compositions respectively on the contrary the breakdown of zoisite clinozoisite is mainly pressure sensitive phengite represents the hydrous phase with the largest stability field encountered in this study in andesite phengite is stable to more than 7 7 gpa and more than 920 c talc and staurolite contribute in minor amounts to the water balance in basaltic and andesitic rock compositions a model for water release from the subducted slab is developed combining thermal models for subduction zones with the experimentally determined phase relationships up to 1 wt and 2 wt h2o in basaltic and andesitic rocks respectively can be stored to depths beyond 200 km in cold subduction zones mainly by lawsonite and phengite dehydration rates are high until amphibole out and relatively low at greater depths the amphibole out reactions are found to release a significant amount of water in a depth interval of several kilometers however they do not represent a discrete pulse of fluid and do not completely dehydrate the descending slab fluid release at depths greater than 200 km through phengite and progressive lawsonite breakdown would hydrate the overlying mantle causing the generation of amphibole or phlogopite peridotite at higher geothermal gradients epidote zoisite contributes to fluid flux to the mantle wedge at 100 120 km depth the extensive stability field of phengite may greatly enhance the role of sediments and the small amount of potassium in mafic compositions for the fluid budget in subduction zones at increasing depth

depositional and halokinetic sequence stratigraphy of the neoproterozoic wonoka formation adjacent to patawarta allochthonous salt sheet central flinders ranges south australia parts of two third order neoproterozoic marinoan depositional sequences are documented in the wilpena group wonoka formation and bonney sandstone at patawarta diapir located in the central flinders ranges south australia these sequences represent an overall regressive succession transitioning upwards from outer to middle wave dominated shelf deposits to a tidally dominated barrier bar to coastal plain the lower middle upper limestone and green mudstone informal members of the wonoka formation comprise the highstand systems tract of the lower sequence the sequence boundary is at the top of the wonoka green mudstone member and is overlain by the lowstand systems tract of the upper sequence which includes the lower dolomite sandstone and upper dolomite beds of the patsy hill member of the bonney sandstone the upper sequence transgressive systems tract comprises thebonneysandstone theseunitscompriseonecompletetaperedcompositehalokineticsequence chs the lower halokinetic sequence boundary is associated with the maximum flooding surface of the lower depositional sequence and the upper halokinetic sequence boundary is interpreted as the transgressive surface of the overlying depositional sequence where an angular truncation of up to 908is documented the majority of our knowledge of salt tectonic processes is derived from the analysis of subsurface datasetsfromoffshorepetroleum bearingsaltbasins such as the gulf of mexico brazil west africa and

problematic fossils in the late neoproterozoic wonoka formation south australia abstract complex biogenic structures are described from the upper wonoka formation late neoproterozoic of the adelaide geosyncline south australia the structures are preserved within silty limestones and calcareous siltstones as dark bedding plane markings defining branching arrays of parallel elongate curved elements the fossils bear at least a superficial resemblance to the putative trace fossil palaeopascichnus normally preserved in siliciclastic sediments and reported from a number of late neoproterozoic sections worldwide the material from the wonoka formation is not a trace fossil and seems most likely to represent a surface encrusting alga the nature of palaeopascichnus needs to be carefully reassessed in the light of the possibility that the wonoka fossils represent a different preservational window into the same phenomenon the thin ca 2 m but widespread nature of the fossil horizon makes it a useful stratigraphic marker within the wonoka formation with the potential to aid in regional correlation within the adelaide geosyncline

controls on precambrian sea level change and sedimentary cyclicity abstract although uniformitarianism applies in a general sense to the controls on relative and global sea level change some influences thereon were more prominent in the precambrian short term base level change due to waves and tides may have been enhanced due to possibly more uniform circulation systems on wide low gradient precambrian shelves the lack of evidence for global glacial events in the precambrian record implies that intraplate stresses and cyclic changes to earth s geoid were more likely explanations for third order sea level change than glacio eustasy higher heat flow in the earlier precambrian may have led to more rapid tectonic plate formation transport and destruction along with an increased role for hot spots aseismic ridges and mantle plumes superplumes all of which may have influenced cyclic sedimentation within the ocean basins a weak cyclicity in the occurrence of plume events has an approximate duration comparable to that of first order supercontinental cycle sea level change second order cyclicity in the precambrian largely reflects the influences of thermal epeirogeny changes to mid ocean ridge volume as well as to ridge growth and decay rates and cratonic marginal downwarping concomitant with either sediment loading or extensional tectonism third order cycles of sea level change in the precambrian also reflected cyclic loading unloading within flexural foreland basin settings and filling deflation of magma chambers associated with island arc evolution the relatively limited number of studies of precambrian sequence stratigraphy allows some preliminary conclusions to be drawn on duration of the first three orders of cyclicity archaean greenstone basins appear to have had first and second order cycle durations analogous to phanerozoic equivalents supporting steady state tectonics throughout earth history in direct contrast however preserved basin fills from neoarchaean palaeoproterozoic cratonic terranes have first and second order cycles of considerably longer duration than phanerozoic examples supporting less evolved tectonism affecting cratonic plates it is possible that oceanic tectonic realms underwent more rapid and dynamic plate movements and arc generation whereas early continental cratonic plates offered more stable platforms and may have been subject to slower migration rates the wide range of controls on precambrian sea level change allied to their apparent variability in rates and periodicity through precambrian time supports the conclusion that each order of cyclicity is relative and must be defined within the stratigraphic context of each individual case study this underlines the importance of establishing a hierarchical order of cyclicity in sequence stratigraphic interpretations of precambrian basins based on the relative importance of sequences rather than their temporal duration

paleoenvironmental reconstruction of the ediacaran araras platform western brazil from the sedimentary and trace metals record ocean and atmosphere oxidation in the ediacaran period paved the way for the dawn of animals in an attempt to better document the record of seawater redox state at the onset of the ediacaran we performed a paleoenvironmental study of post marinoan 635 ma carbonate strata from the southeastern margin of the amazon craton western brazil five sections were sampled along the araras carbonate platform outcrop based facies analysis complemented by petrographic description of representative samples was performed on these sections seven facies associations fa were recognized four fa are encountered in the inner shelf from the basal glacio marine deposits of the puga formation to shallow and moderately deep platform facies which are systematically covered by deeper caco3 over saturated facies five fa occur on the outer shelf including storm wave influenced facies below storm wave base facies and slope intraformational breccia these facies associations indicate a transgressive systems tract over the carbonate platform trace metals u mo zn pb cd cu ni v and al concentrations pyrite abundance and total organic carbon toc contents in these sections are generally low they nonetheless present from base to top of the sections significant stratigraphic variations which can be traced along the platform with successive enrichments of i pb and zn ii u and iii both u and mo in the thin marl levels containing the highest amount of organic carbon and pyrite 0 4 and 1 9 respectively we interpret this succession to record the progressive evolution of sediment pore waters from oxic to more reducing conditions driven by an increase in sedimentary organic matter accumulation the lack of evidence for persistent sulphide mineralization and associated enrichments in mo suggests that sulfidic conditions were only achieved in sediment pore waters in the aftermath of the marinoan glaciation the water column must then have been essentially oxic on the araras platform with anoxia only sporadically reaching the sediment water column interface in the deepest parts of the platform

discussion on mantle plume uplift in the sedimentary record origin of kilometre deep canyons within late neoproterozoic successions south australia journal vol 157 2000 759 768 scientific editing by nick rogers nicholas christie blick writes kilometre deep buried canyons in the upper neoproterozoic successions of south australia are unusual by any standard and any viable explanation for their origin will probably involve an unusual set of circumstances williams gostin 2000 review published geological constraints and competing hypotheses and suggest a role for uplift and crustal deformation associated with the passage of a mantle plume on the basis of available evidence i continue to favour an alternative explanation that they are due to the short lived evaporative drawdown of sea level in a marine embayment that became temporarily isolated from the global ocean von der borch et al 1989 christie blick et al 1990 christie blick 1998 spatial and temporal distribution of erosion canyons more than 1 km deep in the wonoka formation of the adelaide fold belt and up to 700 m deep in the subsurface of the eastern officer basin are reasonably interpreted as coeval and of common origin with a length scale of order 1000 km comparable erosional features are found nowhere else in australia even in the kimberley region and western officer basin coats preiss 1980 walter et al 1994 1995 where flood basalts of possible plume origin are widespread bultitude 1976 jackson van de graaff 1981 bender 2000 independently noted the distribution of late neoproterozoic to early palaeozoic magmatism in western australia and analyzed the possible role of plume related uplift and erosional thinning of the crust in early palaeozoic subsidence of the canning basin however that basin is some 2000 km to the northwest of the adelaide fold belt where the canyons are best known a rather thornier problem is that in the adelaide fold belt prominent erosion surfaces are present at three other horizons above the level of marinoan glaciation and below cambrian strata

deep valley incision in the terminal neoproterozoic ediacaran johnnie formation eastern california usa tectonically or glacially driven neoproterozoic sedimentary successions worldwide display evidence for multiple low latitude glacial events and continental rifting episodes related to the fragmentation of the supercontinent rodinia in death valley eastern california these events are represented by two intervals of glacial diamictite and two episodes of synsedimentary extensional faulting in the kingston peak formation deep incised valleys of uncertain origin in the upper johnnie formation approximately 1 km stratigraphically above the kingston peak formation may provide evidence either for a third glacial episode or for an additional tectonic event eleven measured sections indicate that one of these incised valleys is 120 m deep and approximately 2 5 km wide detailed mapping of the paleovalley has revealed the presence of numerous synsedimentary normal faults that offset underlying units but are capped by incised valley breccia abrupt incision occurs across buried normal fault scarps several large olistoliths up to 15 m in diameter are located near the fault scarps and the average clast size of the breccia decreases in general away from mapped normal faults incised valley clasts are derived exclusively from underlying neoproterozoic formations nearly entirely from the johnnie formation itself there is no evidence for direct glacial influence as no striated clasts or dropstones were observed the absence of glacial indicators coupled with the strong correlation between incision and synsedimentary normal faulting imply a primary tectonic control on valley formation the valley represents a significant tectonic reactivation of the neoproterozoic passive margin similar to early paleozoic extensional events in the northern cordillera of western north america 2005 elsevier b v all rights reserved

a syn depositional age for earth s deepest δ13c excursion required by isotope conglomerate tests terra nova 24 318 325 2012 abstract the most negative carbon isotope excursion in earth history is found in carbonate rocks of the ediacaran period 635 542 ma workers have interpreted the event as the oxidation of the ediacaran oceans rothman et al proc natl acad sci usa100 2003 8124 fike et al nature444 2006 744 mcfadden et al proc natl acad sci usa105 2008 3197 or as diagenetic alteration of the 13c of carbonates 13ccarb knauth and kennedy nature460 2009 728 derry earth planet sci lett 294 2010 152 here we present chemo stratigraphic data from the ediacaran aged wonoka formation fm of south australia that require a syn depositional age for the extraordinary range of 13ccarb values 12 to 4 observed in the formation in some locations the wonoka fm is 700 metres m of mixed shelf limestones and siliclastics that record the full 16 13ccarb excursion in other places the wonoka fm is host to deep 1 km palaeocanyons which are partly filled by tabular clast carbonate breccias that are sourced from eroded wonoka canyon shoulders by measuring the isotopic values of 485 carbonate clasts an isotope conglomerate test we show that canyon shoulder carbonates acquired their 13ccarb 18ocarb values before brecciation and redeposition in the palaeocanyons

sequence stratigraphy and sedimentology of the neoproterozoic kuibis and schwarzrand subgroups nama group southwestern namibia abstract the kuibis and schwarzrand subgroups of the nama group form a succession of shallow marine and minor fluvial sedimentary rocks that is exposed over much of central and southern namibia ediacaran type body fossils and the stratigraphic carbon isotope variability indicate a vendian age for much of these strata the precambrian cambrian boundary is in the uppermost part of the schwarzrand subgroup radiometric dating of abundant volcanic ash beds which span much of the vendian and extend into the cambrian part of the section could make the nama group the best calibrated reference section for vendian chronostratigraphy here we describe the sedimentology and sequence stratigraphy of exposures of the kuibis and schwarzrand subgroups in southwestern namibia we place tighter environmental constraints on the paleontology and geochemistry and we identify seven depositional sequences the boundaries of the depositional sequences correspond to the more important disconformities in the kuibis and schwarzrand subgroups their identification is crucial for defining rates of organism evolution and isotopic differentiation

the problems and potential of using animal fossils and trace fossils in terminal proterozoic biostratigraphy abstract despite the discovery of soft bodied megascopic fossils of late neoproterozoic age at numerous localities world wide there has been slow acceptance of their potential for intercontinental correlation the stratigraphic thickness of sediments separating individual occurrences of such fossils from the base of the cambrian is very varied basic questions have also been posed as to the classification of the organisms represented and hence their likely time significance recent geochronological studies support notions of a narrow time distribution well studied neoproterozoic sequences in eurasia eastern and western north america and southern australia show strikingly similar patterns of increase in the numbers and diversity of trace fossils and soft bodied megascopic remains up section though strata immediately preceding the cambrian are relatively barren other than for a sparse palynoflora and compressions of primitive plants trace fossils from australian sections relating to an early part of the ediacaran apparently overlap a time of abundance of large process bearing acritarchs and big leiosphaerids this overlap of early animal traces and distinctive acritarchs may prove to be of significant biostratigraphic importance rare discoveries of forms resembling rangea gurich in the flinders ranges of south australia precede the classical ediacara assemblage and may provide a possible correlation with occurrences of this genus in namibia the distinctive remains and trace fossils at this level constituting the rangeid hiemalora assemblage zone resemble a biota from the podolia region of the ukraine and show a similarity to finds in parts of the windermere supergroup of the northwest territories canada similarly the offshore frondose assemblage of newfoundland is comparable with the biota of charnwood forest england the type ediacara assemblage of the flinders ranges characterizing the dickinsonia costata assemblage zone is a climax biota with diverse taxa and large individual species as well as some 20 ichnogenera it closely correlates with a late redkinian or early kotlinian assemblage in the upper part of the section on the zimny gory coast of the white sea northern russia the trace fossils of these levels show that significant diversification began before the cambrian

sedimentary geology and evolution of an outcropping shelf margin delta late proterozoic wonoka formation south australia discrete sand units or accumulations crop out within the late proterozoic wonoka formation northern flinders ranges south australia these sand wedges are unique in their size contacts facies and associations to other sands in the formation and are interpreted as shelf margin deltas the wedges can be divided into a main body and a series of discrete feeder channels the main body consists of basal slump masses a sandstone dominated succession and an overlying shale dominated facies lithofacies grossly define a deepening upward succession from a lower shoreface to outer shelf setting the formation and deposition of the feeder channels and sand wedges was controlled largely by relative sea level changes initial exposure of the shelf and subaerial erosion produced a regional erosional surface and incised valleys across the paleoshelf prior to deposition of the wedges slope instabilities and minor uplift occurred sediment was then transported across the shelf and deposited near or at the shelf break and reworked in a shallow marine environment deposition of the shelf margin deltas continued during relative sea level rise but ended with shelf drowning

the neoproterozoic of southwestern africa with emphasis on platform stratigraphy and paleontology abstract neoproterozoic sediments in southwestern africa occur in the pan african kaoko khomas gariep vanrhynsdorp and saldania belts they were deposited in response to rifting break up of a supercontinent formed at 1000 ma and subduction and collisions of the congo kalahari rio de la plata and malvinas plates these collisions led to the formation of a neoproterozoic cambrian supercontinent this paper deals with the geology of the platform successions of the kaoko khomas gariep and vanrhynsdorp belts deposition of the sediments occurring in these belts commenced 900 to 1000 ma ago and probably ended between 500 and 520 ma the sediments record wilson cycles that ended with the deposition of red beds palaeontological and carbon isotope studies on the damara sequence gariep complex nama group and vanrhynsdorp group make intra and inter basinal correlations possible prior to deposition of the nama group two or perhaps three glaciations took place over an extensive area in southwestern africa these being the kaigas chuos 725 700 ma numees 650 600 ma or 610 590 ma and possibly the varianto 745 725 ma glaciations the numees tillite is overlain by a stratigraphic unit containing pinkish dolomite during deposition of the nama group the minor vingerbreek 600 545 ma glaciation or cold water period occurred the major kaigas chuos and numees and minor vingerbreek glaciations correspond with low 13c isotope ratios and appear to have taken place at relatively low palaeolatitudes the riphean sediments were deposited predominantly during rifting and break up of a supercontinent during the late vendian to early cambrian deposition of the nama group in southern namibia and the penecontemporaneous vanrhynsdorp group in the republic of south africa took place in the nama foreland basin detrital micas indicate that deposition of the nama group took place between 635 and 530 ma the nama foreland basin which was connected to a major ocean to the south formed as a result of collisions between the congo kalahari and rio de la plata plates with the exception of the nama group little is known about the palaeontology of the neoproterozoic in southwestern africa the lower nama group is latest proterozoic in age it contains an ediacaran fauna a depauperate assemblage of organic walled microfossils and a relatively well diversified ichnofauna with brooksella diplocraterion and nereites which are atypical of vendian strata many trace fossils are exceptionally small the occurrence of the shelly fossil cloudina and probable calcified metaphytes in the lower nama group suggest that skeletalization in animals and metaphytes occurred almost simultaneously towards the end of the proterozoic the upper nama group is early cambrian in age as indicated by the occurrence of the trace fossil phycodes pedum the upper nama group dominated by red beds contains a low diversity ichnofauna with trace fossils of normal size bio and chemostratigraphy combined with sequence stratigraphy will probably establish how the prominent unconformities which occur in the neoproterozoic of southwestern africa are related to the periods of formation of the wonoka canyons in south australia

messinian subaerial erosion of the proto nile delta abstract the evaporitic drawdown and subsequent dessication of the mediterranean basins during the messinian salinity crisis has been confirmed by detailed seismic mapping of the ensuing erosion surface in the nile delta region the basal messinian unconformity determined by seismic analysis and borehole correlation extends from almost sea level in the southern delta area to depths of at least 5 km in the nile cone the onlap of the contemporaneously deposited fluvio deltaic clastics of the qawasim formation occurs at between 2 5 to 4 km below present gradual initial drawdown of the mediterranean sea with occasional sudden sporadic falls is implied by the presence of entrenched meanders and impaired rejuvenation terraces in the nile canyon formed as the proto nile river cut down into the pre existing tortonian delta complex the former tortonian delta slope became an extensive linear erosional front with over 3 km of vertical relief the uppermost levels of which were protected by tabular oligocene basalt flows preserved as mesas and buttes the lower slopes were the site of coalescing piedmont fans fed by upper slope wadi systems the piedmonts merged into the qawasim fluvio deltaic deposits of the proto nile fluvial flood plain the subcrop beneath the basal messinian unconformity reveals a remarkable diversity of rock type each with its own distinctive control on the geomorphology and geometry of the ensuing messinian erosional surface fracture patterns within the oligocene basalts produced a trellis drainage network which became later captured by a dendritic system developed on less resistant prodelta shales of the former tortonian delta slope close study of seismic profiles clearly demonstrates that the basal messinian erosional disconformity can be traced northwards to depths of at least 2 5 3 0 km before becoming affected by later pliocene faulting this validates a deep dessication model for the evolution of the messinian evaporites

hummocky cross stratification like structures in deep sea turbidites upper cretaceous basque basins western pyrenees france by mulder et al 2009 sedimentology 56 997 1015 discussion

stratigraphic expression of earth s deepest δ13c excursion in the wonoka formation of south australia the most negative carbon isotope excursion in earth history is found in carbonate rocks of the ediacaran period 635 541 ma known colloquially as the shuram excursion workers have long noted its broad concordance with the rise of abundant macro scale fossils in the rock record collectively known as the ediacaran biota thus the shuram excursion has been interpreted by many in the context of a dramatically changing redox state of the ediacaran oceans for example a result of methane cycling in a low o2 atmosphere the final destruction of a large pool of recalcitrant dissolved organic carbon doc and the step wise oxidation of the ediacaran oceans more recently diagenetic interpretations of the shuram excursion have challenged the various redox models with the very negative 13c values of ediacaran carbonates explained via sedimentary in growth of very 13c depleted authigenic carbonates meteoric alteration or late stage burial diagenesis a stratigraphic and sedimentological context is required to discriminate between these explanatory models and to determine whether the shuram excursion can be used to evaluate oxygenation in terminal neoproterozoic oceans here we present chemo stratigraphic data 13c 18o and trace element abundances from 15 measured sections of the ediacaran aged wonoka formation fm of south australia in some locations the wonoka fm is 700 meters m of mixed shelf limestones and siliciclastics that record a 17 permil 13c excursion 12 to 5 further north in the basin the wonoka fm is host to deep 1 km paleocanyons which are partly filled by tabular clast carbonate breccias canyon filling ceased during ongoing sedimentation on the shelf interior the canyon shoulder as evidenced by upper canyon shoulder units that overlie and cap certain canyon fill sequences the unprecedented size of the chemostratigraphic dataset presented here 2671 13c 18o measurements from the canyon shoulder 1393 13c 18o measurements from canyon clasts and 11 different trace elements measured on 247 wonoka fm carbonate samples when coupled with the unique canyon shoulder to canyon fill depositional system of the wonoka fm allows for new insights into ediacaran carbon isotope systematics the excursion is preserved in a remarkably consistent fashion across 12 000 km2 of basin area fabric altering diagenesis where present occurs at the sub meter vertical scale results in

shelf valley compound fill produced by fault subsidence and eustatic sea level changes eocene la meseta formation seymour island antarctica incised valley compound fills are currently modeled in terms of multiple cycles of relative sea level fall and rise in contrast the eocene la meseta formation from seymour island is a shelf valley geometrically compound fill the development of which was governed mainly by local subsidence along fault controlled valley margins and associated amplified tidal circulation the valley contains a 330 m thick festoonlike stack of transgressive regressive marine estuarine cycles affected by slumping and sliding growth faulting and warping near the margins aggradational stacking of the transgressive regressive cycles reflects transgressions initiated or enhanced by episodic subsidence of the valley floor whereas sequence boundaries record those base level falls having rates that exceeded the rate of valley floor subsidence compound fills particularly those of shelf valley systems developed along active basement structures should not necessarily be attributable to regional base level changes alone

revised wonoka isotopic anomaly in south australia and late ediacaran mass extinction the global late ediacaran shuram wonoka carbon isotope anomaly has been regarded as the largest and longest known isotopic anomaly in the ocean assuming that all ediacaran carbonate is marine disregarding carbonate in south australia shown here to be palaeosol or palaeokarst the synchronous marine organic carbonate excursion is only 8 for 13 c organic and 6 for 13 c carbonate and lasted less than a million years this revised magnitude and duration is comparable with perturbations across the permian triassic boundary and correlative with a global late ediacaran acritarch mass extinction like permian triassic isotopic excursions the revised organic carbonate wonoka excursion may also have been a greenhouse palaeoclimatic warm spike which terminated valley incision and glacioeustatic drawdown during the mid ediacaran fauquier glaciation and preceded chill of the late ediacaran billy springs glaciation supplementary material measured sections and tables of mineral and grain size proportions major element and stable isotope analyses are available at www geolsoc org uk sup18756

sedimentology diagenesis and stratigraphic occurrence of giant ooids in the ediacaran rainstorm member johnnie formation death valley region california the rainstorm member of the late neoproterozoic johnnie formation contains several distinctive features of possibly regional to global significance the johnnie oolite an incised valley with a carbonate breccia fill and an enigmatic bed of giant ooids the rainstorm giant ooids although the johnnie oolite and the incised valley occur in most johnnie formation outcrops scattered throughout the death valley region the giant ooids have only been observed in one area restricted to the southern nopah range if these giant ooids were deposited as part of the rainstorm member they would represent the youngest known occurrence of neoproterozoic giant ooids and the only such unit deposited after the last precambrian glaciation the gaskiers however since the giant ooid bed is associated with the incised valley fill it could simply be a large block of oolite derived from the stratigraphically lower beck spring dolomite known to contain giant ooids this study uses mapping petrography and isotope geochemistry to compare giant ooids from the rainstorm member and the beck spring dolomite with the goal of determining the provenance of the rainstorm giant ooids all lines of evidence suggest that the rainstorm giant ooids form a unit distinctly different from those of the beck spring dolomite carbon isotope values from the ooid bed indicate that it was probably deposited after the shuram 13 c excursion making this the youngest known precambrian giant ooid unit the most plausible explanation for this bed is that it is a raft derived from a so far unobserved pre incision rainstorm member giant ooid bed which would also have been the source of many of the giant ooid clasts in the incision breccia

submarine origin for the neoproterozoic wonoka canyons south australia abstract an examination of the deeply incised ediacaran wonoka canyons in the adelaide geosyncline most recently interpreted as subaerial valleys demonstrates their submarine origin and confirms them as some of the best examples of ancient outcropping submarine canyons in the world the entire canyon fill succession is interpreted to be of deep water below wave base origin consisting of calcareous shale and siltstone together with a variety of mass flow deposits including turbidites grain flows and debris flows the canyon fill lacks definitive shallow water structures e g mud cracks fenestral fabrics or wave ripples at all stratigraphic levels canyon lining carbonate crusts that have previously been interpreted as non marine calcretes or tufas and used to suggest a non marine origin for the canyons are argued to be of deep water marine microbial origin extremely negative carbon isotope values from the canyon fill and canyon lining crusts have a primary marine origin previously interpreted deepening upward trends in the canyon fill used as evidence of a subaerial erosion episode followed by drowning are suggested to be fining upward trends caused by the transition from canyon cutting to canyon filling with the majority of the fill being of deep water slope origin the basal conglomeratic canyon fill sediments represent the last vestiges of the high energy deep water canyon erosion environment in which the incisions formed a deep water origin for the canyons is consistent with all previous stratigraphic observations of the wonoka canyons including the conspicuous lack of regional unconformities in the lower wonoka formation and their emanation from the deep water facies of the wonoka formation a submarine canyon origin also removes the need for extreme 1 km relative sea level fluctuation and associated problems i e an enclosed basin with messinian style evaporative drawdown or thermal uplift above a migrating mantle plume required by the subaerial valley hypotheses

sequence stratigraphy and the interpretation of neoproterozoic earth history abstract the application of sequence stratigraphy to neoproterozoic successions is important for improving the resolution of time correlation within individual sedimentary basins and potentially at a global scale the methodology is illustrated in this paper by reference to two contrasting examples from the flinders ranges adelaide geosyncline of south australia where the younger part of the neoproterozoic to earliest cambrian succession 770 ma to 540 ma has been divided into thirteen unconformity bounded depositional sequences one of the most prominent sequence boundaries at or near the base of the wonoka formation is characterized by a series of buried canyons as much as 1 km deep high resolution sequence stratigraphic studies at umberatana syncline continue to support the view that the canyons were cut subaerially and filled by fluvial and shallow water sediments in contrast to the wonoka canyons sequence boundaries interpreted at the base of the nuccaleena formation seacliff sandstone and near the top of the abc range quartzite are relatively subtle with only limited evidence for erosion and valley incision four sequence boundaries at the level of the sturtian and marinoan varanger glacial deposits and in the vicinity of the precambrian cambrian boundary are thought to correlate with surfaces in the amadeus basin of central australia other prominent sequence boundaries including the wonoka canyons and surfaces within the upper part of the wonoka formation and at the base of the ediacara member of the rawnsley quartzite correspond with a relatively condensed section in the amadeus basin and their lateral persistence beyond the adelaide geosyncline is therefore difficult to evaluate given the lack of precision in biostratigraphy and isotope geochemistry in neoproterozoic rocks and in a marked departure from phanerozoic practice we recommend placement of a terminal proterozoic gssp at a sequence boundary a prime candidate in australia is the sequence boundary at the base of the nuccaleena formation seacliff sandstone immediately above the marinoan glacial rocks in the adelaide geosyncline and its likely correlative at or near the base of the gaylad sandstone in the amadeus basin

mantle plume uplift in the sedimentary record origin of kilometre deep canyons within late neoproterozoic successions south australia in south australia canyons 200 250 km long are incised to depths of c 1 5 km in late neoproterozoic after c 590 ma marine deposits of the adelaide fold belt and canyons 90 km long and 700 m deep occur in correlative marine strata of the officer basin 1000 km to the nw in the adelaide fold belt the isotopic signature of limestone veneering canyon walls canyon sinuosity and sedimentary structures in canyon fill suggest that the canyons were cut subaerially and filled by shallow water marine deposits during coastal onlap eustacy cannot account for the kilometre scale change in sea level required for subaerial canyon erosion and chemostratigraphy and the lack of evaporites at that stratigraphic level in southern australia argue against a messinian style drawdown in each region uplift and crustal extension preceding or coeval with canyon incision are indicated by a regional unconformity turbidite or mass flow deposition and extensional faults these features and canyon incision may be explained by regional uplift above a rising mantle plume over a distance of 1000 km in southern australia flood basalt volcanism in the officer basin tentatively dated at 563 40 ma may have followed this uplift mantle plume uplift is expressed in the sedimentary record by emergent trends in facies regional thinning regional unconformities turbidites gravity slides normal faults and incised canyons and palaeovalleys

the record and stratigraphie implications of organic walled microfossils from the ediacaran terminal proterozoic of south australia two assemblages of organic walled microfossils have been recognized in drillcore samples from the late proterozoic rodda beds in the eastern officer basin south australia the fossils include tube like remains and large simple and sculptured acritarchs lithostratigraphic studies and seismic information in conjunction with previous albeit limited acritarch finds allow local correlation of the rodda beds with ediacaran or terminal proterozoic sequences in the northern adelaide fold belt site of the nominated ediacaran stratotype the new palynofloras are comparable with acritarch assemblages in the amadeus basin of central australia and suggest tentative correlations with sequences in china and the u s s r the presence of isotopically heavy marine carbonate in the lower fossiliferous horizons of the rodda beds pcpdb 3 to 6 0 is consistent with isotopic data from the equivalent interval in china in contrast the upper fossiliferous strata occur higher in the rodda beds where carbonate is significantly lighter 13 cpdb 1 to 3 o

the effect of rising atmospheric oxygen on carbon and sulfur isotope anomalies in the neoproterozoic johnnie formation death valley usa abstract carbonates within the rainstorm member in the terminal neoproterozoic johnnie formation of death valley california record a remarkable negative carbon isotope anomaly to a nadir of near 11 that accompanies a dramatic rise in trace sulfate abundance and fall of carbonate associated sulfate 34 s values the carbonates including the laterally extensive johnnie oolite were deposited during marine flooding atop a sequence boundary best observed in cratonward sections the 12 c rich alkalinity delivered to the seawater pool was likely associated with a dramatic rise in atmospheric o 2 which resulted in 1 the oxidation of exposed continental shelf sediments rich in fossil organic matter and sulfides and 2 the ventilation of the oceans similar carbon isotope anomalies are recorded in broadly equivalent successions that post date known marinoan glacial deposits and pre date the precambrian cambrian boundary in oman india china australia and namibia supporting the view that the oxygenation event was global thus the biogeochemical anomaly post dates the last widely recognized neoproterozoic ice age but is nonetheless associated with sea level drawdown that is likely to be eustatic in origin the radiation of a high diversity microbiota and the first appearance of large metazoan fossils ediacaran animals follow this carbon isotope anomaly suggesting that a critical threshold with respect to atmospheric o 2 had been crossed by this time a negative excursion of similar magnitude occurs in overlying strata at the precambrian cambrian boundary which likely reflects similar processes