mangrove forest evolution in a sediment rich estuarine system opportunists or agents of geomorphic change the majority of the world s mangrove forests occur on mostly mineral sediments of fluvial origin two perspectives exist on the biogeomorphic development of these forests i e that mangroves are opportunistic with forest development primarily driven by physical processes or alternatively that biophysical feedbacks strongly influence sedimentation and resulting geomorphology on the firth of thames coast new zealand we evaluate these two possible scenarios for sediment accumulation and forest development using high resolution sedimentary records and a detailed chronology of mangrove forest avicennia marina development since the 1950s cores were collected along a shore normal transect of known elevation relative to mean sea level msl activities for lead 210 pb 210 caesium 137 cs 137 and beryllium 7 be 7 and sediment properties were analysed with pb 210 sediment accumulation rates sars compensated for deep subsidence similar to 8 mm yr 1 used as a proxy for elevation gain at least four phases of forest development since the 1950s are recognized an old growth forest developed by the late 1970s with more recent seaward forest expansion thereafter excess 210pb profiles from the old growth forest exhibit relatively low sars near the top 7 12 mm yr 1 and bottom 10 22 mm yr 1 of cores separated by an interval of higher sars 33 100 mm yr 1 a general trend of increasing sar over time characterizes the recent forest biogeomorphic evolution of the system is more complex than simple mudflat accretion progradation and mangrove forest expansion surface elevation gain in the old growth forest displays an asymptotic trajectory with a secondary depocentre developing on the seaward mudflat from the mid 1970s two to ten fold increases in 210pb sars are unambiguously large and occurred years to decades before seedling recruitment demonstrating that mangroves do not measurably enhance sedimentation over annual to decadal timescales this suggests that mangrove forest development is largely dependent on physical processes with forests occupying mudflats once they reach a suitable elevation in the intertidal copyright c 2015 john wiley sons ltd

treptichnus pedum and the ediacaran cambrian boundary significance and caveats the ediacaran cambrian e c boundary is based on the first appearance of the ichnofossil treptichnus pedum investing an ichnotaxon with such biostratigraphic pre eminence has been the focus of criticism points of contention have revolved around four main issues 1 ichnotaxonomy 2 behavioural significance 3 facies controls and 4 stratigraphic occurrence first confusion results from the fact that treptichnus pedum was originally referred to as phycodes pedum and more recently some authors have placed it in trichophycus or manykodes however the overall geometry of these burrows indicates they belong in treptichnus second regardless of its precise mode of feeding the behaviour involved is iconic of the cambrian explosion third objections are based on the idea that trace fossils show a closer link to facies than body fossils notably in contrast to common assumptions t pedum is not only present in the low energy offshore of wave dominated marine settings but it occurs at considerably shallower water in intertidal and shallow subtidal zones of tide dominated systems as well as in mouth bars of deltaic systems and lower shoreface to offshore transition zones of wave dominated marine settings its broad environmental tolerance supports evolutionary innovations rather than facies controls as the main mechanism underlying the observed vertical pattern of distribution of t pedum in most e c successions comprising shallow marine deposits fourth although treptichnids have been documented below the e c boundary t pedum is not known from ediacaran rocks the delayed appearance of t pedum in e c successions should be analysed on a case by case basis

structural outline of a tertiary basement cored uplift inversion structure in western spitsbergen svalbard kinematics and controlling factors the tertiary fold and thrust belt of spitsbergen can be divided into a western basement involved fold thrust stack and a central eastern foreland fold and thrust belt in western nordenskiold land the first order structure is an ene verging basement cored fold and fault complex involving paleozoic to tertiary strata the northern part reveals an upright monocline geometry of east tilted sedimentary cover units with associated layer parallel to low angle thrusts and folds these structures consist of two populations oriented both parallel to nnw sse and oblique to wnw ese the general structural trend of the fold complex in the central and southern parts of west nordenskiold land the fold complex involves tilted basement cut by steep transverse faults and late normal faults the east limb of the fold complex displays repeated basement and paleozoic strata orustdalen formation in its core and mesozoic triassic strata influenced by map scale chevron folds and two decollement levels all located above an eastward rotated major detachment fault the kleivdalen thrust establishing fold fault relations includes a three stage structural history in the fold complex as follows 1 a phase of early nne ssw shortening associated with wnw ese folds and thrusts and 2 a dominant ene wsw basement involved shortening leading to the first order nnw sse striking fold complex followed by 3 approximately e w extension the resulting structures and structural variability along strike as well as across strike appear to have been controlled by basement and carboniferous basin structures underlying the permian cretaceous platform strata restored stratigraphic sections based on thrust repetition of basement and cover e g within a type section of the carboniferous orustdalen formation support such an interpretation a tentative inversion tectonic model reproduces the position s of local and major thrust ramps and associated folds as a result of inheritance from carboniferous basin structures

calcium isotopes as a record of the marine calcium cycle versus carbonate diagenesis during the late ediacaran abstract calcium isotope ratios in ancient carbonate rocks can provide insight into the global marine calcium cycle as well as local conditions during carbonate mineral precipitation and diagenesis we compare two extraction techniques for the separation of calcium from other ions before 44ca analysis using an automated ion chromatograph and using manual gravity columns the two techniques produce the same 44ca within error 2 we present 31 44ca analyses of carbonate rocks from the nama group namibia which record a negative shift in 44ca of 0 35 between 550 and 547 ma from 1 25 to 1 60 followed by persistently low 44ca 1 48 0 06 between 547 and 539 ma very low 44ca

evolution of the central tertiary basin of spitsbergen towards a synthesis of sediment and plate tectonic history abstract the central tertiary basin of spitsbergen developed east of a strike slip boundary between the eurasian and greenland plates in response to the initiation of rifting and later seafloor spreading in the norwegian greenland sea using a new plate model for the opening of the north atlantic we attempt to relate the sediment history of the central tertiary basin to its plate tectonic framework and suggest a basin development in four phases the central tertiary basin was formed in the early paleocene during a right lateral strike slip phase after the plate boundary between greenland and svalbard had jumped eastward to the hornsund fault zone phase 1 the onset of seafloor spreading between greenland and eurasia and a drastic counterclockwise change in spreading direction between greenland and north america after chron 25 late paleocene induced compression dominated transpression between greenland and svalbard until chron 24 lower eocene phase 2 the first sedimentary evidence for tectonic uplift along the strike slip zone is found in a wedge shaped delta fan in the northwestern part of the basin strike slip dominated transpression prevailed from chron 24 to chron 21 lower middle eocene contemporaneous with successive basin narrowing and an eastward migration of the depocenter phase 3 after chron 21 lower middle eocene the relative motion between greenland and svalbard first changed to strike slip terminating the transpressional phase and then to transtension after chron 13 lower oligocene phase 4

late cretaceous cenozoic intraplate contractional deformation at the norwegian continental shelf timing magnitude and regional implications abstract contractional structures large anticlines and synclines reverse faults and inverted centres of deposition of assumed late cretaceous cenozoic age are common in cretaceous tertiary basins of the northwestern european margin the similarities in style orientation and timing of these structures are striking the present detailed analysis of one anticline the ormen lange dome of the mid norwegian continental shelf indicates that the total contraction is moderate less than 2 3 and that the analysed anticline has been growing almost continuously since its initiation in eocene till present inversion in the barents sea started already in the late cretaceous this episode is suggested to be related to far field effects of active plate margin processes and transfer of stresses across the plate as a consequence of the sub hercynian and paleocene laramide event of the alpine orogeny the development of co axial structures was facilitated by stress focusing along pre existing high relief n s and ne sw trending fault complexes far field plate tectonic stresses originating mainly from the alpine orogeny seem to have been the most important cause of contractional deformation on the nw european shelf in addition ridge push from the north atlantic spreading may have contributed significantly particularly during the neogene

wave attenuation in coastal mangroves in the red river delta vietnam abstract wave attenuation was studied in a coastal mangrove system in the red river delta vietnam on the coast north of do son from sea towards land the study area consisted of a bare mudflat covered by a sandy layer with embryonic cheniers abruptly changing into a muddy tidal flat overgrown with mangroves three instrumented tripods a c placed in a cross shore profile were used to measure current velocity and water level at the open tidal flat at the beginning of the mangrove vegetation and in the mangrove vegetation respectively measurements were conducted in the wet season in july and august 2000 the elevation of the area was surveyed using a levelling instrument over the bare sandy surface of the mudflat the incoming waves are reduced in height and energy density due to bottom friction this reduction decreases with increasing water depth in the mangrove vegetation the bottom friction exerted by the clay particles is very low however the dense network of trunks branches and above ground roots of the mangrove vegetation causes a much higher drag force for the mangrove vegetation which mainly consists of kandelia candel the drag force can be approached by the function c d 0 6e 0 15 a with a being the projected cross sectional area of the under water obstacles at a certain water depth for the same muddy surface without mangroves the function would be c d 0 6

multiple s isotopic constraints on paleo redox and sulfate concentrations across the ediacaran cambrian transition in south china abstract changes in oceanic chemical conditions are frequently invoked as a primary driver of biodiversification and mass extinction events in earth history during the ediacaran cambrian transition two major biological events including the extinction of the ediacaran biota and the cambrian explosion occurred approximately coincident with perturbations of the carbon and sulfur cycle these dramatic biological changes and coeval geochemical events are commonly thought to be linked but their causal relationships remain controversial here we present multiple s isotopic compositions of pyrite 34spy and 33spy from the xiaotan section spanning the ediacaran cambrian transition interval in south china our isotopic results show that negative 33spy values together with positive 34spy values occurred across the ediacaran cambrian boundary the negative 33spy data suggest mixing of sulfide from deep waters during the upwelling of sulfidic waters into oxygenated shallow waters the coincidence between the negative 33spy and the approximate timing of the extinction of the ediacaran biota implies that paleo redox perturbations may have contributed to the disappearance of the ediacaran biota negative 33spy values coupled with positive 34spy values were also observed in the cambrian zhongyicun member when the phosphorites were deposited suggesting a strong linkage between the upwelling of nutrient rich sulfidic deep waters and the deposition of the phosphorites in oxygenated shelf areas in addition using box models and stoichiometry calculations we quantitatively estimated elevated burial rates of organic matter and pyrite based on the parallel positive 13ccarb 34spy and 33spy excursions observed at xiaotan within cambrian stage 2 our mass balance modelling results provide an independent constraint on sulfate concentrations which were 4 mm or lower in the early cambrian oceans the probable increase in oxygen levels resulting from the enhanced burial of pyrite and organic matter could have provided a more habitable environment for early animals and thus paved the way for the radiation of early cambrian animals

new high resolution age data from the ediacaran cambrian boundary indicate rapid ecologically driven onset of the cambrian explosion the replacement of the late precambrian ediacaran biota by morphologically disparate animals at the beginning of the phanerozoic was a key event in the history of life on earth the mechanisms and the time scales of which are not entirely understood a composite section in namibia providing biostratigraphic and chemostratigraphic data bracketed by radiometric dating constrains the ediacaran cambrian boundary to 538 6 538 8 ma more than 2 ma younger than previously assumed the u pb ca id tims zircon ages demonstrate an ultrashort time frame for the lad of the ediacaran biota to the fad of a complex burrowing phanerozoic biota represented by trace fossils to a 410 ka time window of 538 99 0 21 ma to 538 58 0 19 ma the extremely short duration of the faunal transition from ediacaran to cambrian biota within less than 410 ka supports models of ecological cascades that followed the evolutionary breakthrough of increased mobility at the beginning of the phanerozoic

using sims to decode noisy stratigraphic δ13c variations in ediacaran carbonates abstract carbonate carbon isotope 13ccarb chemostratigraphy is a valuable tool in precambrian stratigraphic correlation the effectiveness of this tool rests on the assumption that 13ccarb data record global seawater signals however in some cases 13ccarb data exhibit rapid and noisy stratigraphic variations that may have been influenced by authigenic or diagenetic carbonate minerals to assess the contribution of non primary minerals towards bulk carbonate carbon isotope values we acquired sims secondary ion mass spectrometry 13ccarb data electron microscopic data and cl cathodoluminescence microscopic data from two ediacaran successions the lower member ii of the doushantuo formation in south china and the mooifontein member of the zaris formation in southern namibia the doushantuo samples came from a stratigraphic interval with noisy meter scale 13ccarb variations of up to 10 whereas the mooifontein member is characterized by consistent 13ccarb values with limited meter scale variations of less than 4 our data show that the meter scale stratigraphic variations in 13ccarb are also mirrored in the sims data at m mm scales in both doushantuo and mooifontein samples in the doushantuo samples sims 13ccarb values of authigenic calcite vary by up to 10 over m mm scales and can be either higher or lower than those of the co existing dolomite matrix which also appears to be affected by authigenic carbonate on the basis of petrographic observation bulk sample 13ccarb values measured on powders microdrilled from the same sims specimens are within the range of sims 13ccarb values thus we infer that bulk sample 13ccarb values of doushantuo samples represent mixtures of different carbonate components the doushantuo and mooifontein sims 13ccarb data validate the traditional method of using chemostratigraphic consistency to evaluate authigenic diagenetic alteration but given that secondary phases may be 13c enriched relative to matrix carbonate caution is warranted when taking maximum values to approximate primary chemostratigraphic trends

the terminal ediacaran tubular fossil cloudina in the yangtze gorges area of south china abstract the advent of biomineralizing metazoans in the terminal ediacaran age ca 550 539 ma represents a remarkable biological innovation in the history of life as a poster child of this evolutionary episode cloudina is widely regarded as a weakly biomineralizing tubular fossil with a global distribution therefore cloudina can both inform the evolution of animal biomineralization and facilitate terminal ediacaran stratigraphic correlation however this key taxon has not been fully described from the yangtze gorges area of south china where classical terminal ediacaran strata have been investigated extensively by paleontologists stratigraphers and geochemists here we document an assemblage of three dimensionally silicified tubular fossils from siliceous dolostone of the terminal ediacaran baimatuo member of the dengying formation in the yangtze gorges area western hubei province south china the baimatuo assemblage consists of sinotubulites which has been previously known in the baimatuo member as well as cloudina including c ningqiangensis c hartmannae c cf carinata and c sp indet and other unnamed tubular forms this discovery adds to the diversity of early biomineralizing metazoans in the yangtze gorges area and facilitates the biostratigraphic correlation of the cloudina sinotubulites co occurrence assemblage in terminal ediacaran strata

discussion of first finds of problematic ediacaran fossil gaojiashania in siberia and its origin y cai h hua comment zhuravlev gamez vintaned ivantsov 2009 reported the problematic ediacaran fossil gaojiashania annulucosta in siberia and they considered that this is the first find of gaojiashania outside china since gaojiashania had previously only been reported from the gaojiashan member of the middle dengying formation in the ningqiang area southern shaanxi province south china however we believe that the so called siberian gaojiashania was mis identified and what was described as gaojiashania annulucosta by zhuravlev gamez vintaned ivantsov 2009 is more appropriately ascribed to shaanxilithes ningqiangensis another problematic ediacaran fossil that has also been known from the gaojiashan member in shaanxi province of south china chen chen lao 1975 xing et al 1984 as well as the stratigraphically equivalent taozichong formation in guizhou province hua chen zhang 2004 and the jiucheng member dengying formation in yunnan province of south china zhu zhang 2005 the zhoujieshan formation in qinghai province shen et al 2007 and the zhengmuguan formation in ningxia hui autonomous region of north china shen et al 2007

the margin between senja and spitsbergen fracture zones implications from plate tectonics abstract analysis of multichannel seismic data from the continental margin off svalbard between the senja and spitsbergen fracture zones suggests that the transition between continental and oceanic crust is located at or close to the hornsund fault zone in the late paleocene early eoeene 57 m y the region between svalbard and northeast greenland was subjected to regional shear movements associated with a transform system between the young lofoten greenland basin and the arctic ocean approximately 50 m y ago the spreading axis migrated to the northeast creating a deep basin north of the greenland senja fracture zone forming the passive margin between bear island and 76 5 n north of 76 5 n the regional transform was maintained at the time of the main reorganization of relative plate motion 36 m y the northern margin evolved a continental fragment was possibly cut off from the svalbard margin forming a small microcontinent the microcontinent appears as the submarine ridge which has been associated with the hovgaard fracture zone it is suggested that the sediments west of the hornsund fault zone are not older than eocene in the south and mid oligocene in the north the position of the spreading axis has greatly influenced the margin sedimentation

the application of δ13c and c n ratios as indicators of organic carbon sources and paleoenvironmental change of the mangrove ecosystem from ba lat estuary red river vietnam in this study two sediment cores 70 cm were collected from separate mangrove forests straddling the ba lat estuary red river of northern vietnam to examine the origins of sedimentary organic carbon soc and reconstruct the paleoenvironment in addition mangrove leaves and particulate organic matter were collected and measured for 13c to trace the origins of soc the cores were analyzed by high resolution sections for 13c toc c n ratios sediment grain size water content and porosity with values of 13c toc and c n ratios ranging from 28 19 to 22 5 2 14 30 94 mg g and 10 29 18 32 respectively the 13c and toc relationship indicated that there were some small residual effects of diagenetic processes on toc and 13c values in mangrove sediments however the shifts of 13c and c n ratios from the bottom to the surface sediment of the cores explained the change in organic matter sources with values of c n 12 and 13c 25 indicated terrestrial e g mangrove litter and marine phytoplankton sources respectively the covarying 13c c n ratios and sediment grain sizes during the past 100 years in sediment cores showed that the paleoenvironment may be reconstructed into three environments subtidal tidal flat and intertidal mangrove general trends in 13c and c n followed a gradual increase in the c n ratio and a concomitant decrease in 13c from the subtidal through to tidal flat and to the intertidal mangrove 13c and c n ratios are therefore effective in measuring the continuum of environmental change in mangrove ecosystem

a complex trace fossil from the spitskop member terminal ediacaran lower cambrian of southern namibia streptichnus narbonnei igen et isp nov a new trace fossil from the upper part of the spitskop member of the urusis formation southern namibia consists of clusters of unidirectionally curved radial elements in which individual elements typically are composed of imbricated sickle shaped segments somewhat comparable to those of treptichnus pedum such complex trace fossils generally are found only in cambrian or younger strata this opens to question the position of the ediacaran cambrian boundary in the nama group suggesting that it may locally be within the uppermost part of the urusis formation rather than at the base of the nomtsas formation

microbial metazoan reefs of the terminal proterozoic nama group c 550 543 ma namibia thrombolite and stromatolite reefs occur at several stratigraphic levels within the terminal proterozoic nama group c 550 543 ma of central and southern namibia the reefs form integral parts of several carbonate platforms within the nama group including the kuibis platform of the northern nama basin zaris subbasin and huns platform witputs subbasin of the southern nama basin the reefs are composed of both thrombolites and stromatolites that form laterally continuous biostromes isolated patch reefs and isolated pinnacle reefs ranging in scale from a metre to several kilometres in width in the majority of cases the reefs occur stratigraphically as an integral facies within the transgressive systems tracts of sequences making up the kuibis and huns platforms this suggests that a regime of increasing accommodation was required to form well developed reefs though reefs also occur sporadically in highstand systems tract settings within a given transgressive systems tract a regime of increasing accommodation through time favours the transition from sheet like biostromal geometries to more isolated patch and pinnacle biohermal geometries similarly increasing accommodation in space such as a transect down depositional dip shows a similar transition from more sheet like geometries in updip positions to more isolated geometries in downdip positions reefal facies consist of thrombolitic domes columns and mounds with well developed internal clotted textures in addition to stromatolitic domes columns and mounds with crudely to moderately well developed internal lamination stromatolites are better developed in conditions of relatively low accommodation and updip locations under conditions of higher current velocities and greater sediment influx thrombolites are better developed in conditions of relatively high accommodation and low sediment influx both types of microbialites are intimately associated with the first calcifying metazoan organisms which may have attached themselves to the sediment surface or otherwise lived within sheltered depressions within the rough topography created by ecologically complex mats the appearance of thrombolitic textures during terminal proterozoic time is consistent with colonization of cyanobacterial mats by higher algae and metazoans which would have been an important process in generating clotted textures fabrics in the nama thrombolites are well preserved and show evidence of thrombolitic mesoclots being overgrown by fibrous marine carbonate interpreted as former aragonite this was followed by emplacement of geopetal micrite fills and precipitation of dolomite as an isopachous rim cement followed by occlusion of remaining porosity by blocky calcite spar

along strike changes in fault array and rift basin geometry of the carboniferous billefjorden trough svalbard norway abstract the billefjorden fault zone bfz of svalbard norway is a long lived major tectonic lineament with significant influence on the structural style of the northwestern barents shelf the fault zone can be traced for around 2 300 km in an n s direction where it is made up of three major fault strands all dipping 50 70 to the east field and seismic data delineate gradual shifts in displacement between master faults northern odelfjellet balliolbreen and southern dronbreen faults and suggest that two c 20 km long 2 3 km wide relay zones exist along strike the western fault strand consistently has a pre carboniferous reverse character placing basement on top of devonian sedimentary units with a throw estimated at 10 km subsequent carboniferous extensional reactivation of segments of the bfz resulted in formation of the billefjorden trough with a rift basin showing a fairly consistent polarity for its length this suggests a profound control by the older devonian reverse faults on the extensional structural style the billefjorden trough extends for a minimum of 110 km along strike and is 20 30 km wide at the most a gentle north plunge of the basin axis in the south is mirrored by an opposite plunge in the north offering a depth thickness of around 2000 m in the central realm diminishing to 500 m in the south geometries of the trough suggest sedimentary response to fault growth with weak lithologies such as evaporites promoting fault monocline formation and associated lenticular basin geometries on the contrary wedged shaped fill geometries toward major faults is consistent with significant fault movement and growth sequences subsequent mild tertiary reactivation of fault segments of the bfz is suggested by local reverse faults and deep seated anticline syncline pairs

tertiary tectonism and basin inversion of the st jonsfjorden region svalbard abstract deformed basement and cover rocks of the st jonsfjorden area further define the character of spitsbergen s tertiary fold and thrust belt three major thrusts comprise a folded ca n060 e directed foreland propagating thust stack with likely additional subsurface thrust faults the folded vegardbreen robertsonfjellet thrust is the most significant fault in the complex and re emerges in the core of a disrupted synclinal structure in triassic strata shortening across the area indicated from line length restoration is of the order of 13 km differences in stratigraphy between and within thrust sheets indicate the thrust stack initiated along the edge of a westward deepening carbonbiferous basin with a fault step margin and represents basin inversion early structures related to basin formation had a major control on later thrust sheet evolution and the complexity of inversion structures reflects the initial complexity of the basin geometry such basin inversion could characterize the length of the fold and thrust belt the st jonsfjorden structures are primarily contractional and together with areas farther southeast in the fold thrust belt indicate shortening took place perpendicular to the fold belt across much of the length of the evolving margin

integrated ediacaran chronostratigraphy wernecke mountains northwestern canada abstract terminal neoproterozoic ediacaran ca 600 543 ma strata of the upper part of the windermere supergroup are well exposed in the mackenzie mountains and the wernecke mountains of northwestern canada windermere strata in the mackenzie mountains contain an exceptional ediacaran biostratigraphic and isotopic c and sr record while the sequence stratigraphic record is subtle throughout this predominantly deep water succession coeval strata in the wernecke mountains can be correlated with the succession in the mackenzie mountains on a formational level in contrast to the deep water setting of the mackenzies succession the werneckes succession preserves a predominantly shallow water succession amenable to detailed sequence stratigraphy integrated lithostratigraphy chemostratigraphy biostratigraphy and sedimentology partitions the wernecke mountains succession into five depositional sequences and constrains correlation with strata in the mackenzie mountains the siliciclastic and carbonate sediments deposited along the margin of the proto pacific ocean record accumulation in continental slope neritic and terrestrial paleoenvironments distinctive temporal chemostratigraphic and biostratigraphic attributes allow these strata to be correlated with other ediacaran successions worldwide integrating sequence stratigraphy with these attributes is a robust yet under utilized correlation tool and is a step toward erecting a more detailed working neoproterozoic chronostratigraphy

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

extinction of cloudina and namacalathus at the precambrian cambrian boundary in oman biostratigraphic carbon isotope and u pb zircon geochronological data from the ara group of oman indicate an abrupt last appearance of cloudina and namacalathus coincident with a large magnitude but short lived negative excursion in the carbon isotope composition of seawater that is globally coincident with the precambrian cambrian boundary u pb zircon age data from an intercalated ash bed directly define this negative excursion to be at 542 0 0 3 ma consistent with previous age constraints from siberia and namibia combined with the global biostratigraphic record these new data strengthen hypotheses invoking mass extinction within terminal proterozoic ecosystems at or near the precambrian cambrian boundary

tertiary or cretaceous age for spitsbergen s fold thrust belt on the barents shelf several publications propose that main phase fold thrust development on spitsbergen was late cretaceous and not tertiary as previously thought the question of timing is crucial to models for crustal response to transpressive plate motions involvement of tertiary strata in fold thrust structures the sedimentology of the tertiary basin strata and studies of paleo stress field evolution all indicate paleocene to eocene fold thrust development during opening of the norwegian greenland oceanic basin a regional angular unconformity of 1 between paleocene and early cretaceous strata is consistently disconformable to the eye and precludes any significant older deformation in the immediate area pre unconformity deformation was likely strike slip in character and concentrated in the west the proposal for late cretaceous fold thrust belt formation is inconsistent with the geology

structural evolution of a frontal ramp section of the west spitsbergen tertiary fold and thrust belt north of isfjorden spitsbergen the geometry and kinematic evolution of a frontal ramp section associated with the tertiary west spitsbergen orogenic belt has been investigated in a small area lappdalen north of isfjorden the previously recognized thrust front corresponds to a complex step or ramp in the position of the sole thrust in the area the sole thrust is localized to the evaporites of the permian gipshuken formation to the west of the footwall ramp whereas to the east it continues as a bedding parallel thrust in triassic shales sassendalen group the area to the west of the footwall ramp is characterized by large scale thrusts and folds involving the permian gipshuken and kapp starostin formations and the lower part of the triassic sassendalen group east of the footwall ramp both permian and triassic strata are sub horizontal and apparently undeformed three major thrust sheets are recognized based on the geometric relationship between folds and faults in the area both fault bend and fault propogation mechanisms of folding are inferred restoration of the kapp starostin formation to its pre deformational state indicates a minimum of 35 shortening structural observations within the sassendalen group in the study area and on dickson land suggest that some of this shortening is transmitted eastwards along one or more bedding parallel thrusts in the sassendalen group

currents and sediment transport in mangrove forests abstract a field study of the tidal currents cohesive sediment dynamics and transport of organic carbon in a highly vegetated mangrove swamp was carried out at middle creek cairns australia the interaction of tidal currents and the vegetation generated jets eddies and zones of stagnant waters which were numerically modelled a high value of the manning friction coefficient n 0 1 was derived by the dense vegetation about 80 of the suspended sediment brought in from coastal waters at spring flood tide was trapped in the mangroves corresponding to about 10 12 kg of sediment m 1creek length spring tide resulting in a rise of the substrate by about 0 1 cm year 1 the selective trapping of clay was caused by flocculation of the finer particles in the mangroves there was an indication of a slight inwelling of organic carbon creek water was readily differentiated from mangrove water by large differences in the molecular weight distribution of the dissolved organic carbon

mangroves and intertidal morphology in westernport bay victoria australia abstract westernport bay a marine system produced by holocene submergence of a sunkland was initially a mainly sandy embayment but erosion and dispersal of clay derived from bordering freshwater swamps and weathered basalt cliffs has resulted in the formation of extensive tidal mudflats the upper part of the intertidal zone consists of a salt marsh terrace fringed seaward by mangroves avicennia marina field measurements have shown sustained accretion under this mangrove fringe in contrast with alternations of erosion and accretion on the mudflats to seaward and the trapping of sediment by mangrove pneumatophore networks has been demonstrated by surveys and simulated experimentally it is deduced that the mangroves have here shaped the pattern of sedimentation in such a way as to build a depositional terrace at high spring tide level on which they have been succeeded by salt marsh communities where the mangrove fringe has died back or been cleared away this terrace has been degraded to an intertidal wave cut platform but where the mangroves have revived after such an episode the depositional terrace is being rebuilt it is concluded that mangroves have influenced the geomorphology of the shores of westernport bay

early cambrian palaeogeography and the probable iberia siberia connection abstract the end of the proterozoic beginning of the cambrian is marked by some of the most dramatic events in the history of earth the fall of the ediacaran biota followed by the cambrian explosion of skeletonised bilaterians a pronounced shift in oceanic and atmospheric chemistry and rapid climatic change from snowball earth to greenhouse conditions all happened within a rather geologically short period of time these events took place against a background of the rearrangement of the prevailing supercontinent some authors view this as a sequence of individual supercontinents such as mesoproterozoic midgardia neoproterozoic rodinia and early cambrian pannotia assembled in the mesoproterozoic this supercontinent appears to have existed through the neoproterozoic into the early cambrian with periodic changes in configuration the final rearrangement took place during the precambrian cambrian transition with the cadomian and related phases of the pan african orogeny the distribution of early cambrian molluscs and other small shelly fossils ssf across all continents indicates a close geographic proximity of all major cratonic basins that is consistent with the continued existence of the supercontinent at that time subsequently rodinia experienced breakup that led to the amalgamation of gondwana separation of laurentia baltica siberia and some small terranes and the emergence of oceanic basins between them spreading oceanic basins caused a gradual geographic isolation of the faunal assemblages that were united during the vendian early cambrian

neoproterozoic to early cambrian small shelly fossil assemblages and a revised biostratigraphic correlation of the yangtze platform china abstract small shelly fossils ssfs occur widely on the yangtze platform and have great potential for biostratigraphic subdivision of pre trilobitic early cambrian strata based on the ssf record of the shallow water realm five biozones can be recognized for the meishucunian stage in ascending order the biozones are anabarites trisulcatus protohertzina anabarica assemblage zone paragloborilus subglobosus purella squamulosa assemblage zone watsonella crosbyi assemblage zone formerly heraultipegma yunnanensis zone poorly fossiliferous interzone sinosachites flabelliformis tannuolina zhangwentangi assemblage zone in addition one ssf biozone is recognized for the overlying qiongzhusian stage pelagiella subangulata taxon range zone the formerly used siphogonuchites triangularis paragloborilus subglobosus zone and heraultipegma yunnanensis zone are discussed and redefined approximately 80 species of ssfs were screened for their spatial and temporal distribution on the yangtze platform variations in lithofacies and biofacies can be recognized throughout the yangtze platform extending over an area of 2000 900 km in a deeper water shelf setting the first zone is represented by the protohertzina anabarica kaiyangites novilis assemblage zone while younger zones are not recognized in the southern region at the northern platform margin the qiongzhusian is represented by the ninella tarimensis cambroclavus fangxianensis assemblage zone and the rhombocorniculum cancellatum taxon range zone the southeastern shaanxi western hubei region followed a slightly different lithological and faunal development than the rest of yangtze platform indicating a stronger similarity with parts of east gondwana some taxa such as w crosbyi p subangulata r cancellatum microdictyon effusum a trisulcatus protohertzina unguliformis and p anabarica occur nearly worldwide and support an international correlation of early cambrian sequences between the yangtze platform and smaller west gondwanan blocks siberia newfoundland and australia the six investigated zones of the yangtze platform comprise an interval spanning the early nemakit daldynian to the late atdabanian early botoman stage on the siberian platform palaeobiogeographic analysis revealed a strong taxic similarity between the yangtze platform and the tarim platform a smaller number of species are shared with other west gondwanan platform fragments such as india and iran palaeobiogeographic results do not support the previously reported position of the south china block between australia and siberia during the early cambrian

cretaceous and tertiary inversion in the bjornoyrenna fault complex south western barents sea a system of half flower like structures folds reverse faults and footwall cut offs is observed adjacent to the bjornoyrenna fault complex in the south western barents sea although the bjornoyrenna fault complex itself is principally an extensional feature with its period of maximum extensional activity in the early cretaceous these structures suggest that the subsidence along the fault complex was interrupted in the hauterivian aptian by left lateral transtension and in the late cretaceous early tertiary by head on inversion both these episodes caused relatively intense deformation and seem to have regional significance consequently the events need to be seen in relation to the plate tectonic development of the south western barents sea

millennial scale vegetation dynamics in an estuary at the onset of the miocene climate optimum article i nfo pollen analyses have been proven to possess the possibility to decipher rapid vegetational and climate shifts in neogene sedimentary records herein a c 21 kyr long transgression regression cycle from the lower austrian locality stetten is analysed in detail to evaluate climatic benchmarks for the early phase of the middle miocene climate optimum and to estimate the pace of environmental change based on the coexistence approach a very clear signal of seasonality can be reconstructed a warm and wet summer season with c 204 236 mm precipitation during the wettest month was opposed by a rather dry winter season with precipitation of c 9 24 mm during the driest month the mean annual temperature ranged between 15 7 and 20 8 c with about 9 6 13 3 c during the cold season and 24 7 27 9 c during the warmest month in contrast today s climate of this area with an annual temperature of 9 8 c and 660 mm rainfall is characterized by the winter season mean temperature 1 4 c mean precipitation 39 mm and a summer mean temperature of 19 9 c mean precipitation 84 mm different modes of environmental shifts shaped the composition of the vegetation within few millennia marshes and salt marshes with abundant cyperaceae rapidly graded into taxodiaceae swamps this quick but gradual process was interrupted by swift marine ingressions which took place on a decadal to centennial scale the transgression is accompanied by blooms of dinoflagellates and of the green alga prasinophyta and an increase in abies and picea afterwards the retreat of the sea and the progradation of estuarine and wetland settings were a gradual progress again despite a clear sedimentological cyclicity which is related to the 21 kyr precessional forcing the climate data show little variation this missing pattern might be due to the buffering of the precessional related climate signal by the subtropical vegetation another explanation could be the method inherent broad range of climate parameter estimates that could cover small scale climatic changes

analysis of fault populations in western spitsbergen implications for deformation partitioning along transform margins mesoscale faults expressed in the paleogene central basin and cretaceous basement along the west spitsbergen orogenic belt are used to define the history of continental deformation associated with the development of the transform system that accompanied the opening of the eurasian basin and the norwegian greenland sea a fundamental change in the orientation of faults from dominantly north south in the basal part of the basin to northeast striking in the upper units broadly correlates with a major shift in plate motion during late paleocene early eocene time the two main populations of faults are interpreted as extension fractures that were variably reactivated as shear fractures and formed in response to north south compression followed by northeast southwest compression paleostress stratigraphy or the analysis of striated faults measured in successive stratigraphic units of the central basin corroborates this interpretation and allows a time sequence of paleostress tensors to be defined results show that a late cretaceous early paleocene north south compression consistent with plate motion was followed by three relatively short lived and regionally limited faulting events leading up to a change in plate motion during late paleocene time post chron 25 major transpressive tectonism followed producing northeast trending fractures that were reactivated as dextral and sinistral faults defining a prolate shape paleostress ellipsoid with a horizontal 1 this regionally reproducible tensor consistent with the prediction of dextral transpression along the paleotransform was probably initiated at approximately the paleocene eocene boundary finally a post early eocene deformation pervasively recorded in the study area by an oblate shape paleostress ellipsoid with horizontal 3 is tentatively correlated with the dextral transtension that characterized the post chron 13 opening of the norwegian greenland sea and eurasian basin this study offers documentation of deformation partitioning during the evolution of a transform margin the late cretaceousearliest paleocene compression associated with the prototransform did not involve substantial partitioning and a north south maximum principal stress pervaded the continental crust away from the transform in contrast the late paleocene eocene transpression reflects total partitioning of deformation along the evolved mature transform margin oblique plate motion was presumably partitioned into a strikeslip zone s offshore whereas the onshore central basin recorded only the orthogonal component of oblique convergence and divergence a pattern similar to modern orogenic belts developed in zones of oblique plate motion

eurekan transpressive deformation in the wandel hav mobile belt northeast greenland 1 besides the w e trending kap cannon thrust zone and harder fjord fault zone the 300 km long and nw se striking wandel hav mobile belt represents the third major fault zone in north greenland structural analyses in several areas of this belt suggest that compressive deformation is characterized by transpressive dextral strike slip kinematics this is demonstrated by a combination of folding around w e axes approximately north and south directed reverse faulting and dextral strike slip displacements along nw se trending fault lines the initial formation of the long linear faults is interpreted to be related to deformational events in late paleozoic triassic jurassic and late cretaceous times due to the lack of structural evidence we assume that deformations led to the generation of extension faults which probably were reactivated during dextral strike slip tectonism it is suggested that dextral transpressive deformation was coeval with n s compression at the harder fjord fault zone and cap cannon thrust zone and took place during eocene eurekan times dextral strike slip tectonism in the wandel hav mobile belt was the result of n s compression due to a general northward movement of the greenland plate as a zone of crustal weakness the belt can be interpreted as the onshore equivalent of the main transcurrent fault zone de geer fault which caused the intracontinental dextral slip of svalbard barents shelf relative to north greenland during early tertiary eurekan times and prior to their separation in this configuration it represents one part of the belt of eurekan deformation which extends from the canadian arctic islands over north greenland to the barents shelf where compressive deformation is recorded in the west spitsbergen fold and thrust belt

sedimentation in an estuarine mangrove system abstract sediment dynamics were studied in a mangrove system in the ba lat estuary of the red river vietnam the study area was situated on a riverbank which consisted of a bare mudflat containing a vegetation gradient from pioneering mangroves to 5 to 7 year old mangroves measurements were conducted in the dry season february march 2000 and in the wet season july august 2000 actual sedimentation rates were measured using sediment traps and the elevation of the area was surveyed in both periods two undisturbed sediment cores were taken in the densely vegetated area for 210pb dating analysis and showed long term sedimentation rates of 0 22 g cm 2 yr 1 and 0 36 g cm 2 yr 1 sedimentation rates recorded by the sediment traps in the vegetated area were 2 94 g cm 2 yr 1 in the dry season and 3 46 g cm 2 yr 1 in the wet season in both seasons the sedimentation rates on the bare mudflat were five to ten times higher than in the densely vegetated area however the elevation of the mudflat was slightly lower in the wet season than in the dry season this implies that erosion must have taken place between march and july this study demonstrates that the bare mud bank of an estuary is highly dynamic until mangroves cover it sediment delivery to the vegetated zones is low but the protective effect of vegetation against erosion by waves and currents is strong this results in small but steady actual sedimentation rates under mangroves and therefore sustained long term accretion the study further identifies the need for similar measurements to be made in different seasons covering the effects of periodic storm events

tube construction and life mode of the late ediacaran tubular fossil gaojiashania cyclus from the gaojiashan lagerstatte abstract gaojiashania cyclus is a phylogenetically problematic tubular fossil that is only known from the late ediacaran gaojiashan lagerstatte in southern shaanxi province south china it is a cm sized tube that consists of a series of repeated units each unit consists of a rigid ring and an originally flexible bucket shaped tube wall each tube maintains a constant diameter the rigid ring elements typically range from 1 to 2 mm in length whereas the bucket components are more variable at 0 5 5 mm in length and are ornamented with transverse annuli tubes display curving extension and constriction at free angles indicating the original flexibility of the bucket components the construction of g cyclus tubes is unique in both fossil and modern tubular organisms and strikingly differs from that the structure of other known ediacaran and cambrian tubular fossils integrated morphological taphonomic and paleoecological data suggest that g cyclus may have exhibited a procumbent epibenthic life mode possibly using the ring structures as anchors to microbially bound muddy substrate the preserved tubes are interpreted as the original exterior of the organism as opposed to a life mode reconstruction as a tube dweller the currently available evidence suggests that g cyclus had non mineralized or weakly mineralized tubes and its phylogenetic affinity remains unresolved

sensitivity of the sediment trapping capacity of an estuarine mangrove forest intertidal mangrove forests exist in a dynamic coastal environment that is increasingly impacted by human interference leading to habitat fragmentation reduced habitat quality and changing hydrodynamic and geomorphological conditions biophysical feedback mechanisms are essential to maintain mangrove ecosystems under such changing conditions for example by facilitating sediment deposition during periods of tidal flooding to allow for long term coastal accretion however human interferences affect these biophysical interactions this study investigated the consequences of two widespread anthropogenic intervention scenarios on biophysical interactions in mangroves sediment starvation reduced sediment supply and coastal squeeze limited landward accommodation space field observations of hydrodynamics and sediment dynamics were conducted in mandai mangrove fringing the sheltered northern shore of singapore a process based numerical model delft3d of this field site was set up providing accurate approximations of the observed flow velocities and deposition rates this model was used for a scenario analysis of the initial response of the sediment trapping capacity in the mangrove system to instantaneous changes related to anthropogenic interventions this analysis showed increased deposition rates in major parts of the mangrove when sediment supplies increased up to three times more deposition after 1 tide or when the landward accommodation space of the mangrove was extended 17 deposition a comparison of the outcomes of these scenarios with the current state of the mangrove underlined a lack of short term sediment trapping capacity affecting the longer term adaptive capacity of the system thus at present mandai mangrove is potentially affected by reduced sediment supply and limited landward accommodation space importantly actions to reduce this anthropogenic influence could enhance mangroves sediment trapping capacity facilitating increased resilience to future projected changes such as sea level rise understanding this influence of anthropogenic interventions on mangrove resilience is essential if we are aiming to maintain coastal ecosystem stability especially along rapidly changing and urbanizing tropical shorelines

seaweeds through time morphological and ecological analysis of proterozoic and early paleozoic benthic macroalgae abstract benthic marine macroalgae or seaweeds are key ecological players in oceans today and have been since the proterozoic to date however morphological and evolutionary patterns for precambrian macroalgae have been documented only in rather broad terms to refine our understanding in this critical interval we updated a dataset of proterozoic to early paleozoic noncalcified macroalgal fossils preserved as macroscopic carbonaceous compressions the data were analyzed using non parametric multidimensional scaling nmds and functional form group ffg approaches in order to characterize morphological and ecological evolutionary patterns of these macroalgae at the broadest scale the results show progressive increases in thallus size morphospace range and aspects of ecological complexity such as canopy heights surface area volume ratios and functional form groups through time these trends however are not always monotonous in particular significant increases in proterozoic macroalgal morphological diversity and maximum size appear to have occurred in the neoproterozoic tonian and ediacaran periods respectively analysis of ediacaran macroalgal assemblages shows that macroalgae broadly follow the ediacara like fossil assemblages with a significant drop in most studied metrics in the terminal ediacaran stage 550 539 ma the latter event occurs during the kotlinian crisis experienced by ediacara type macro organisms highlighting the possibility that this extinction event during the ediacaran cambrian transition affected both macroalgae and ediacara type macro organisms our analysis also confirms an ordovician increase in the morphological and ecological diversity of macroalgae

trace fossil evidence for ediacaran bilaterian animals with complex behaviors abstract distinguishing ediacaran trace fossils from tubular body fossils can be a challenge and several ediacaran fossils previously interpreted as animal traces have been shown to be tubular body fossils nonetheless true ediacaran trace fossils are present but they are relatively few and morphologically simple dominated by horizontal trails and shallow burrows such simple morphologies have been taken as evidence for a modest behavioral complexity and limited geobiological impact of animal bioturbators before the cambrian explosion here we report three types of trace fossils horizontal tunnels surface tracks trails and vertical traces from the latest ediacaran dengying formation 551 541 ma in the yangtze gorges area of south china cross cutting tunnels and the presence of scratch marks indicate that these traces are unlikely tubular body fossils instead these three types of traces likely represent animal activities related to under mat feeding epibenthic locomotion and temporary dwelling respectively we show that these three types of traces were constructed by the same bilaterian animals that had moderately complex interactions with microbial mats to exploit nutrients and o 2 resources these animals heralded a new age in ecosystem engineering animal sediment interaction and biogeochemical cycling

chemostratigraphy of the cerro victoria formation lower cambrian uruguay evidence for progressive climate stabilization across the precambrian cambrian boundary abstract petrographic isotopic and geochemical data are reported for the cerro victoria formation of the arroyo del soldado group uruguay it is divided into four informal lithostratigraphic units a to d which are mainly composed of an alternation of stromatolitic oolitic and clastic dolostones the genesis of dolomite as a primary or penecontemporaneous precipitate is discussed considering excellent preservation of textural details whereas 87 sr 86 sr ratios in the least altered samples are too high 0 7106 0 7109 to represent seawater values 13 c determinations are interpreted as reflecting near seawater composition the curve obtained for the cerro victoria formation is characterized by negative values at its base 3 5 pdb passing into a slightly positive plateau up section peak values of 0 64 pdb are encountered in the upper unit c the upper cerro victoria formation is characterized by a return to moderately negative values the shape of the 13 c curve is consistent with the data reported for the nemakit daldyn stage of the lower cambrian we suggest that the precambrian cambrian boundary is located at the cerros san francisco cerro victoria transition or slightly lower in the succession thalassinoides bearing dolostones of the upper cerro victoria formation might reach the tommotian or atdabanian in the arroyo del soldado group 13 c excursions parallel sea level oscillations transgressive events being characterized by positive 13 c values falling amplitudes of coupled 13 c sea level fluctuations recorded in these carbonates are in accordance with the trend observed in ediacaran lower cambrian successions worldwide covariance of 13 c and sea level might be explained by bioproductivity fluctuations affecting the carbon cycle atmospheric co 2 concentrations climate ice volume and ultimately sea level while these oscillations were of large magnitude in the late neoproterozoic they progressively faded away in the cambrian giving place to a more stable environment the cause of the amplitude decrease in biogeochemical climatic and sea level perturbations might be the decreasing rates of nutrient input at mid ocean ridges as reflected by rising 87 sr 86 sr values between 800 and 500 ma punctuated by at least three events roughly coincident with rifting episodes of rodinia

wave attenuation in mangroves a quantitative approach to field observations coastal mangroves dwelling at the interface between land and sea provide an important contribution to reducing risk from coastal hazards by attenuating incident waves and by trapping and stabilizing sediments this paper focusses on relations between vegetation densities wave attenuation rates sediment characteristics and sedimentation rates in mangroves these processes were studied along two cross shore transects through mangroves fringing estuaries in the southern andaman region of thailand volumetric vegetation densities in these mangroves were ranging up to 32 depending on the water depth generalized total wave attenuation rates increased from 0 002 m 1 in the sparsely vegetated forest fringes with avicennia and sonneratia species up to 0 012 m 1 in the dense rhizophora vegetation in the back of the forests the total wave attenuation rates integrate effects of shoaling and energy losses due to various bio physical interactions within the mangrove ecosystem wave attenuation in the mangroves is presumably dominated by energy losses due to vegetation drag since wave attenuation due to bottom friction and viscous dissipation on the bare mudflats is significantly lower than those inside the mangrove vegetation additionally wave attenuation in the mangroves was found to facilitate enhanced net sediment deposition and a gradual fining of the bed material these findings corroborate the coastal defence function of mangroves by quantifying their contribution to wave attenuation and sediment trapping the explicit linking of these properties to vegetation composition and structure facilitates modelling studies investigating the mechanisms determining the coastal defence capacities of mangroves

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

shell structure and distribution of cloudina a potential index fossil for the terminal proterozoic cloudina bearing biosparites and biomicrites in the lower part of the nama group namibia contain a wide morphological diversity of shell fragments that can all be attributed to the two named species c hartmannae and c riemkeae the curved to sinuous tubular shells of cloudina were multi layered each shell layer was 8 to 50 micrometers thick and in the form of a slightly flaring tube with one end open and the other closed growth appears to have been periodic with successive shell layers forming within older layers each added layer was slightly elevated from the previous layer at the proximal end and was asymmetrically placed within the older layer so that only a portion of the new shell layer was fused to the previous layer this type of growth left a relatively large unminerialized area between the shell layers which was often partially or fully occluded by early marine cements the thin shell layers exhibit both plastic and brittle deformation and were likely formed of a rigid caco3 impregnated organic rich material often the shell layers are preferentially dolomitized suggesting an original mineralogy of high magnesian calcite both species in the nama group formed thickets or perhaps bioherms and this sedentary and gregarious habit suggests that cloudina was probably a filter feeding metazoan of at least a cnidarian grade of organization the unusual shell structure of cloudina gives rise to a characteristic suite of taphonomic and diagenetic features that can be used to identify cloudina bearing deposits within the nama group and in other terminal proterozoic deposits around the world species of cloudina occur in limestones from brazil spain china and oman in sequences consistent with a latest proterozoic age assignment in addition supposed lower cambrian pre trilobitic shelly fossils from northwest mexico and the white inyo mountains in california and nevada including sinotubulites nevadatubulus and wyattia are all either closely related to or con generic with cloudina hence it is probable that these outcrops are latest proterozoic in age and that cloudina or cloudina like organisms were widely distributed at that time it is possible moreover to suggest that metazoan biomineralization occurred on a global scale by the latest proterozoic at the same time that evidence for complex multicellularity and locomotion in animals appears in siliciclastic ediacaran rocks in the form of body and trace fossils

late holocene sedimentary and environmental development of the northern mekong river delta vietnam abstract a sedimentological and palynological study of three sediment cores from the northern mekong river delta shows the regional sedimentary and environmental development since the mid holocene sea level highstand a sub to intertidal flat deposit of mid holocene age is recorded in the northernmost core shoreline deposits in all three cores show descending ages from n to s documenting 1 the early stages of the late holocene regression and 2 the subsequent delta progradation the delta plain successions vary from floodplain deposits with swamp like elements to natural levee sediments the uppermost sediments in all cores show human disturbance to varying degrees the most intense alteration is recorded in the northernmost core where the palynological signal together with a charcoal peak indicates the profound change of the environment during the modern land reclamation the sediments from at least one of the three presented cores do not show a true delta facies succession but rather estuary like features as also observed in records from southern cambodia this absence is probably due to lack of accommodation space during the initial phase of rapid delta progradation which impeded the development of true delta successions as shown in cores from the southern mekong river delta

subsidence analysis of the cordilleran miogeocline implications for timing of late proterozoic rifting and amount of extension tectonic subsidence of the cordilleran miogeocline in the western united states during late proterozoic through early paleozoic time is best explained by rifting and subsequent thermal contraction of the lithosphere the tectonic component of subsidence can be calculated by removing the isostatic effects of sediment and water loading the resultant subsidence curves indicate that rifting began about 600 m y ago and that extension of the lithosphere during rifting was in excess of a factor of 1 3

oxygen carbon and strontium isotope records of ediacaran carbonates in central iberia spain carbon oxygen and strontium isotope ratios were determined in the uppermost neoproterozoic carbonate rocks at pastores sw salamanca central iberia the low 18o v smow values 15 19 indicate an alteration of the whole stratigraphic series however the alteration process does not seem to have affected most of the 13c and 87sr 86sr data these data reveal that only one particular level of the carbonate section shows simultaneous relative increases in mn sr and 87sr 86sr ratios decreases in the 18o and 13c values and covariations between 87sr 86sr and the other parameters despite this most of the carbonate section lacks these covariations and its 13c 4 6 to 0 5 and 87sr 86sr 0 70845 0 70853 ratios probably reflect the seawater isotopic features at the time of sedimentation the data for c and sr isotopes at the pastores carbonate section and the presence of cloudina in platform carbonates together with an overlying major sub cambrian unconformity following a relative sea level fall are features comparable to those frequently shown by proterozoic cambrian boundary series across the world thus our results consistently support the notion that the carbonates at pastores are equivalent to other carbonates deposited close to the ediacaran cambrian boundary

discussion on pre ocean opening compression of the northwestern atlantic margin evidence from eastern greenland journal vol 157 2000 707 710 scientific editing by nick rogers h d maher jr s bergh alvar braathen write manby lyberis 2000 argue for a cretaceous palaeocene age and a convergent setting for both the fold structures of the wandel sea basin and for the west spitsbergen fold thrust belt as an alternative to models of decoupling during palaeocene eocene transpressive motions between greenland and the barents shelf in this context we discuss evidence on the timing and kinematics of the west spitsbergen fold thrust belt and constraints on the timing of deformation in the wandel sea basin multiple lines of evidence constraining the timing of fold thrust formation in spitsbergen are discussed in maher et al 1995 and clearly indicate major fold thrust development in the palaeocene eocene space limitations prevent their description here the nature of additional late cretaceous deformation on spitsbergen is another question it is partly constrained by the unconformity at the base of the tertiary sequence which is well exposed in many places and is consistently disconformable to the eye this unconformity involves differential uplift to the north with a regional tilt of a degree or less has a character inconsistent with previous fold thrust development along the islands western margin and can be related to a second pulse within the high arctic large igneous province maher 2001 more recent work confirms a palaeocene eocene age for the spitsbergen contractional structures manby lyberis refer to blythe kleinspehn 1998 as indicating a late cretaceous age for spitsbergen fold thrust belt uplift in their summary figure blythe kleinspehn indicate uplift and erosion of source terranes initiating at 70 ma and continuing until c 43 ma six detailed thermal histories generated from track length modelling of samples taken from the tertiary foreland basin sediments provide particular insight as the authors note three samples with depositional ages of

preservational modes in the ediacaran gaojiashan lagerstatte pyritization aluminosilicification and carbonaceous compression abstract burgess shale type bst fossils often are preserved as two dimensional carbonaceous compressions sometimes aided by two mineralization processes pyritization and aluminosilicification defined by a thin and sometimes localized coating of authigenic pyrite or aluminosilicate minerals on the carbonaceous materials here we report similar mineralization modes within the late ediacaran gaojiashan lagerstatte of southern shaanxi province south china examination of two common gaojiashan fossils conotubus hemiannulatus and gaojiashania cyclus hereafter referred by generic names only indicates that pervasive pyritization is the primary taphonomic pathway in this deposit responsible for the preservation of 80 of the collected fossils pervasive pyritization of gaojiashan fossils results in their three dimensional preservation as opposed to two dimensional carbonaceous compression with thin pyrite coatings seen in some bst lagerstatte however microscale investigation using environmental scanning electron microscopy esem and energy dispersive x ray spectroscopy eds shows that some flattened specimens of conotubus and gaojiashania are preserved as carbonaceous compressions which are in some cases associated with aluminosilicate minerals rare compressed specimens of conotubus are replicated by greenish clay minerals which are interpreted as diagenetic products of aluminosilicate precursors our taphonomic analysis shows that pervasive authigenic pyritization tends to replicate more labile tissues than aluminosilicate aided carbonaceous compression but both pyritization and aluminosilicification processes can facilitate the replication and preservation of soft bodied organisms in siliciclastic sediments building upon this conclusion we propose that multiple taphonomic processes including kerogenization or polymerization of organic molecules pyritization and aluminosilicification can contribute to the mode of bst preservation viewed in this light various siliciclastic hosted lagerstatten that are facilitated by kerogenization pyritization and aluminosilicification can be plotted on a ternary diagram based on the relative importance of these taphonomic processes

morphology and paleoecology of the late ediacaran tubular fossil conotubus hemiannulatus from the gaojiashan lagerstatte of southern shaanxi province south china a b s t r a c t conotubus hemiannulatus zhang and lin 1986 is a phylogenetically problematic tubular fossil that is only known from the late ediacaran ca 551 541 ma gaojiashan lagerstatte in southern shaanxi province south china it is a cm sized conical tube that tapers adapically from an aperture to a rounded apex the tube consists of a series of nested cylindrical to funnel shaped tube walls cylinders hereafter this conotubular construction of nested cylinders is similar to that of the late ediacaran fossil cloudina integrated morphological taphonomic and paleoecological data suggest that c hemiannulatus occu pied an epibenthic life mode with the apex anchoring to muddy substrate and the aperture extending upwards into the water column it was probably a suspension feeding organism this soft bottom dweller employed specialized paleoecological strategies to rejuvenate and self right the tubes after being sub jected to sediment obrution indicating strong burial resistant capabilities the tube likely provided space for the living organism with successively larger cylinders added episodically to accommodate growth currently available evidence suggests that c hemiannulatus likely had non biomineralized tubes and although potentially closely related to cloudina its phylogenetic affinity remains unresolved 2011 elsevier b v all rights reserved

tectonic inversion in the wandel sea basin a new structural model of kilen eastern north greenland the seminunatak kilen in eastern north greenland with its complexly deformed carboniferous cretaceous strata is a key area to understand the tectonic history of the transform plate boundary between eastern north greenland and svalbard detailed 3 d geological mapping from oblique photogrammetry along with limited ground fieldwork and interpretation of previously published data forms the basis for a new structural model of kilen previous structural models interpreted rhombic shaped fault patterns as the evidence for strike slip tectonics these structures are here interpreted to be the result of a post coniacian ne sw extension with nw se trending normal faults followed by later n s compression of presumable paleocene eocene age folding the faults passively and suggesting the presence of a basal detachment furthermore two thrust sheets have been distinguished on kilen a lower kilen thrust sheet and an upper hondal elv thrust sheet separated by a subhorizontal fault the central detachment the style of deformation and the structures described are interpreted as the result of paleocene eocene n s directed compression resulting in basin inversion with strike slip faults only having minor status this indicates that the greenland margin as exposed on kilen and the conjugate svalbard margin in the west spitsbergen fold and thrust belt are more similar than previously anticipated

suspended sediment transport on a temperate microtidal mudflat the danish wadden sea abstract time series measurements of suspended sediment transport and bed level change on a microtidal mudflat of the danish wadden sea were carried out between february 1997 and september 2000 the data show that the mudflat is generally accreting except for periods with onshore winds when wave induced erosion takes place during periods of low water levels at the site in general a continuous net input of mud was recorded during periods of weak or offshore winds i e the import is not event controlled and this was interrupted by episodic loss of mud during a few tidal periods with onshore winds the net landward transport of suspended sediment during calm weather or periods of offshore wind is caused by settling and scour lag and tidal asymmetry a very large input of suspended material was observed in the period following a strong storm the landward directed net transport during the five tidal periods following the storm being equivalent to approximately 40 of the net annual accumulation in the area the typical depth of sediment reworking at the intertidal study site is 2 5 cm some seasonal variation can be deduced from the data set with a tendency for deposition during spring and summer and erosion in the winter period the seasonality was especially clear at the most landward station where accretion following periods of ice formation in the area is due to grounding of sediment transported by ice floes but otherwise deposition is mainly taking place in the warmer seasons net accretion over the three year measuring period along the transect varies between 0 6 and 1 9 cm a 1 deposition is largest at the most landward station and the accretion found on the basis of repeated bed level measurements compares well with 210 pb and 137 cs dating

the end of the ediacaran two new exceptionally preserved body fossil assemblages from mount dunfee nevada usa evaluation of hypotheses that relate environmental to evolutionary change across the ediacaran cambrian transition has been hampered by a dearth of sections that preserve both the last appearance of ediacaran body fossils and the first appearance of treptichnus pedum within carbonate rich strata suitable for chemostratigraphic studies here we report two new exceptionally preserved latest ediacaran fossil assemblages from the deep spring formation at mount dunfee nevada usa further we report these occurrences in a high resolution carbon isotope chemostratigraphic framework permitting correlation on a regional and global scale the lower of the two horizons at the base of the deep spring formation hosts a body fossil assemblage that includes gaojiashania other vermiform body fossils and possible wutubus annularis interbedded with cloudina shell beds the upper of the two fossil horizons in the esmeralda member of the deep spring formation contains conotubus and occurs within the basal cambrian negative carbon isotope excursion establishing it as the youngest ediacaran fossil assemblage discovered to date this is the first report of gaojiashania conotubus and wutubus in laurentia extending the known stratigraphic ranges and biogeographic distributions of these taxa to a global scale these data refine the relative ages of defining characteristics of the ediacaran cambrian boundary and confirm that a large perturbation to the carbon cycle and surface ocean conditions coincided with the extinction of ediacaran organisms

sedimentation in paleogene foreland basin spitsbergen the upper part of the sedimentary succession in the tertiary central trough on spitsbergen comprising the hollendardalen gilsonryggen battfjellet and aspelintoppen formations has been studied with respect to basin formation and basin filling thickness data from the lower marine part of this succession indicate an asymmetric thickening to the west distribution of the several theories on how space was generated to accommodate the sequence tectonic subsidence driven by lithospheric loading from the flanking fold and thrust belt appears to be the most probable the position of the basin between the front of the west spitsbergen fold belt and the adjacent craton suggests a foreland basin setting most of the basin fill constitutes a major regressive sequence gilsonry gen battfjellet and aspelintoppen formations deposited by the eastward progradation of a deltaic system evidence of eastward displacement of the depocenter through time together with the incorporation of the orogenic flank of the basin fill into the deformation suggests cratonward migration of the fold and thrust belt foreland basin couplet the present tertiary central trough represents the uplifted remnants of the latest oligocene foreland basin

paleostress stratigraphy a new technique for analyzing tectonic control on sedimentary basin subsidence the authors propose a new technique paleostress stratigraphic analysis based on the orientation of minor structures particularly striated fault surfaces in the strata of sedimentary basins these structures are interpreted to be the response to local or regional stress field controlling subsidence of tectonically active basins a method is used that allows multiple stress tensors to be extracted from a fault population by extracting the stress tensor from the youngest part of a stratigraphic sequence and by imposing that same tensor on the underlying rocks one can in principle isolate the faults associated with the youngest tectonic event by reiterating this procedure on progressively older units until the fault data are exhausted a chronologic succession of paleostress tensors during basin subsidence emerges the authors paleostress stratigraphy to the relatively undeformed paleogene central basin of spitsbergen and its underlying cretaceous strata and define five major paleostress tensors coeval with the earliest stages of the opening of the norwegian greenland sea a late cretaceous dextral transpressive regime was probably responsible for the major pre tertiary unconformity and possibly initiated development of the central basin during subsequent sedimentation movement reversed yielding well constrained sinistral shearing during early danian time a composite compressional event followed that themore authors interpret as being coeval with the culmination of folding and thrusting west of the central basin the youngest strata studied record a final extensional event that they correlate with rifting of spitsbergen from greenland less

boron paleosalinity proxy for deeply buried paleozoic and ediacaran fossils abstract boron content is an indicator of paleosalinity for mesozoic and cenozoic clayey sediments but is compromised by clay diagenesis in deeply buried sediments of paleozoic and ediacaran age this study of north american russian and australian paleozoic and ediacaran fossils showed tight covariance of b ppm and k wt confirming common wisdom that boron is carried largely by illlite smectite clays ratios of b k 40 g g distinguish modern marine and freshwater sediments but this discrimination threshold declines to 21 g g for sequences with bituminous coal just below the anchimetamorphic zone and to 5 g g for sequences within the anchimetamorphic zone toward greenschist facies marine and non marine threshold b k values can be predicted from weaver and kubler indices of illite crystallinity as a measure of b depletion during deep burial and metamorphism deviations from that expectation b k weaver and b k kubler are positive in marine rocks and negative in non marine rocks trilobites stromatolites and other marine fossils were correctly identified as marine by this proxy and fossil land plants identified as non marine though in some cases by small margins because of declining b content with increased clay crystallinity cryogenian to devonian problematic quilted fossils dickinsonia arumberia rangea pteridinium ernietta aspidella rutgersella protonympha are indistinguishable from devonian to triassic plants using this proxy and significantly different from trilobites brachiopods ammonites and other securely marine fossils

palaeomagnetic rock magnetic and mineralogical investigations of the lower triassic vardebukta formation from the southern part of the west spitsbergen fold and thrust beltk dudzisz and otherspalaeomagnetism of triassic rocks spitsbergen

svartfjella eidembukta and daudmannsodden lineament tertiary orogen parallel motion in the crystalline hinterland of spitsbergen s fold thrust belt within metamorphic basement rocks of the hinterland of spitsbergen s tertiary fold thrust belt a 35 km long zone of notably deformed carboniferous strata and cretaceous intrusives forms a major orogen parallel lineament from svartfjella to eidembukta to daudmannsodden sedl orientations and geometries of map scale fault duplexes and associated fault plane striae populations of folds and associated cleavage and of tension gashes all indicate orogen parallel motion occurred along the sedl structural analyses indicates three phases 1 ene directed overthrusting 2 sinistral motion with a backthrust component and 3 dextral strike slip motion this history indicates a change from orogen perpendicular to orogen parallel movements orogen parallel movement was likely coeval with orogen perpendicular fold thrust transport to the ene in the foreland a model where dextral transpressive motion between greenland and svalbard was decoupled explains the hinterland foreland difference basement fabric aligned with carboniferous carbonates on the steep foreland face of an antiformal stack provided a through going weak surface a prerequisite for decoupling sinistral orogen parallel motion is explicable by short lived episode of sinistral plate motion or by local wedge extrusion during dextral transpression the evolution of decoupling patterns has significant implications for deducing plate motions from local kinematic and paleostress studies

thrust tectonics on broggerhalvoya and their relationship to the tertiary west spitsbergen fold and thrust belt the tertiary fold and thrust belt on broggerhalvoya is characterized by a ne vergent pile of nine thrust sheets the sole thrust of the pile is located in precambrian phyllites and climbs up section to the northeast four lower thrust sheets consisting predominantly of upper palaeozoic sediments are overlain by two thrust sheets in the central part of the stack which contain a kilometre scale syncline and anticline the fold is cut by juxtaposed thrusts giving rise to the formation of three structurally higher basement dominated thrust sheets a multiple stage kinematic model is proposed including 1 in sequence foreland propagating formation of the lower thrust sheets in response to n s subhorizontal bedding parallel movements 2 a change in tectonic transport to ene and out of sequence thrusting and formation of the kilometre scale fold structure followed by 3 truncation of the kilometre scale fold and stacking of the highest basement dominated thrust sheets by hind ward propagating out of sequence thrusting the strain of the thrust sheets is predominantly compressive with the exception of the structurally highest thrust sheets reflecting a temporal change to a more transpressive regime thrusting was followed by 4 n s extension and 5 w e extension comparison of the structural geometry and kinematic evolution of broggerhalvoya with the data reported for the fold belt further south allows us to assume a coeval evolution with the fold belt a latest paleocene early eocene age for the main phase of thrusting is suggested for the west spitsbergen fold and thrust belt the main phases therefore pre date the separation of svalbard and greenland due to right lateral movements along the hornsund fault zone the fold belt s temporal evolution followed by the formation of the forlandsundet graben can be linked with the plate kinematic framework in the span between latest paleocene and middle eocene times

the origin of the west spitsbergen fold belt from geological constraints and plate kinematics implications for the arctic abstract the west spitsbergen fold belt which extends for 300 km along the western margin of svalbard and is up to 80 km wide has much in common with foreland fold and thrust belts the near foreland segment of the fold belt exhibits ramp flat thrust trajectories whilst structurally higher nappes are typified by more listric thrusts higher nappes to the west contain imbricated carboniferous and basement rocks showing that the latter were actively involved in the fold belt deformation and a minimum of 80 km total shortening perpendicular to the western margin of svalbard is estimated the early stages of the eurekan deformation in north greenland can be linked to that of the west spitsbergen fold belt and the combined shortening across the two fold belts may exceed 80 km in ellesmere island eurekan structures are distributed in an arc like belt which records between 50 to 100 km of shortening since the late cretaceous kinematic reconstructions suggest that before the opening of the eurasian basin and norwegian greenland sea chron 25 svalbard was linked to north america in the late cretaceous palaeocene interval the motion across the greenland svalbard margin was mainly convergent giving rise to the west spitsbergen fold belt and the eurekan structures of north greenland the dextral separation of greenland and svalbard in post chron 24 time was accompanied by extension followed by pure extension in post chron 13 time

a deep root for the cambrian explosion implications of new bio and chemostratigraphy from the siberian platform much uncertainty remains as to the temporal relationship between the ediacaran and cambrian biotas yet this is critical to our understanding of the rise of metazoans here we present new high resolution carbon isotope chemostratigraphy and biostratigraphy for a terminal ediacaran to cambrian succession on the eastern siberian platform russia which shows the presence of a succession of diverse fossil assemblages before the start of the basal cambrian negative carbon isotope excursion bace soft bodied ediacaran biota beltanelliformis occur before the start of the late ediacaran positive carbon isotope plateau epip a mixed ediacaran and cambrian skeletal biota cloudina anabarites cambrotubulus appears within the epip and diverse cambrian type small shelly fossils including protohertzina and other protocondonts halkieriids chancelloriids hyoliths hyolithelminthes and the burrowing trace fossil diplocraterion appear at the beginning of the bace these integrated data show that taxa attributed to so called ediacaran and earliest cambrian skeletal biotas in fact overlap without notable biotic turnover and thus refute the presence of a large isotope excursion coincident with mass extinction of all ediacaran biota we propose a new biozone the cloudina namacalathus sinotubulites assemblage zone to precede the known small shelly fossil ssf zones these observations raise doubts as to whether there is any true separation between the ediacaran and cambrian skeletal biotas and suggest that there is a deep root for the cambrian explosion of metazoans

tidal scale flow routing and sedimentation in mangrove forests combining field data and numerical modelling tidal scale biophysical interactions establish particular flow routing and sedimentation patterns in coastal mangroves sluggish water flows through the mangrove vegetation and enhanced sediment deposition are essential to maintain these valuable ecosystems thereby enabling their contribution to coastal protection and stabilization spatially explicit field observations of tidal scale flow routing and sediment deposition were obtained in an elevated mangrove stand dissected by tidal creeks located in the trang river estuary at the thai andaman coast an accurate and efficient depth averaged process based numerical model of this field site was developed in delft3d to study the contributions of various biogeophysical mangrove settings to the observed tidal dynamics and to study the impacts of changes of these environmental conditions the creeks are found to form the major pathway for the tidal inflow during the lower tides while the sheltered interior of the forest is an effective sediment sink during the higher tides a numerical sensitivity analysis of the initial response or adaptive capacity of the studied mangrove system to instantaneous environmental changes reveals the stable state of the study site deposition rates are largely imposed by the topography and relative elevation while they are rather independent of the vegetation density deeper inundations of the mangroves favor sheet flows through the forest and spatially averaged deposition rates decrease particularly when this coincides with decreasing vegetation densities moreover the sediment trapping efficiency is found to reduce significantly with diminishing sediment inputs and with mangrove area losses these results clearly indicate the sensitivity of mangroves ecosystem engineering ability in terms of sedimentation to climate change and anthropogenic threats

some problems concerning the precambrian cambrian transition and the cambrian faunal radiation in siberia the so called khailakh and manykay stages of pre tommotian age are inferred to be partly coeval with the type tommotian and to be based on a misunderstanding about the control of facies on faunal distributions evolutionary patterns are being studied through this interval using a variety of approaches synoptic reviews are presented on diversity changes on changes in skeletal composition and on archaeocyathan morphology the latter group appear to have originated on the siberian platform just prior to the tommotian and migrated globally during the atdabanian and botomian to form secondary centres of diversification olenellid trilobites may have dispersed in a similar pattern but other groups such as volborthella and relatives appear to have had a separate siliciclastic centre of origin the decline in diversity of small shelly fossils after the tommotian and the coeval expansion in archaeocyathans and trilobites may be related to basinal changes connected with the break up of palaeopangea

northwest africa s ediacaran to early cambrian fossil record its oldest metazoans and age constraints for the basal taroudant group morocco abstract the anti atlas area in southern morocco preserves one of the most complete latest ediacaran to cambrian shallow marine carbonate records in the world and serves as a standard for global chemostratigraphic 13ccarb curves contrary to the excellent chemostratigraphic coverage neither metazoan fossils only stromatolites and calcified algae nor radiometric age constraints were hitherto available for the basal part of this carbonate record the tifnout member of the adoudou formation of the taroudant group we report an ediacara type fauna from shallow marine sandstones from the basal tabia member and microfossils from dolostones from both the tabia and the tifnout members of the adoudou formation the former are discoidal fossils and share many characteristics with the form genus aspidella and exhibit a peculiar style of preservation pointing towards an early diagenetic two stage carbonate followed by silica cementation history leading to good preservation of these supposedly once soft bodied organisms the dolostone hosted microfossils are preserved as sparite filled molds enclosed by a thin opaque envelope despite their small size they resemble late ediacaran calcifying metazoans such as namacalathus and tubular small shelly fossils together these fossils constitute the oldest known direct evidence for presumably metazoan life from northwest africa we also report new time constraints for the adoudou formation and fossils enclosed therein based on combined la icp ms and high precision ca id tims u pb zircon geochronology of detrital and volcanic zircons together with new chemostratigraphic 13ccarb and literature data these new age constraints suggest a late ediacaran age time span between ca 561 and 542 ma for the discoidal ediacara type fossils from the basal tabia member and a latest ediacaran to earliest cambrian time span between ca 544 and 540 ma and an early cambrian age time span between ca 528 and 523 ma for the two microfossil faunas from the tifnout member

a transpressional origin for the west spitsbergen fold and thrust belt insight from analog modeling 1 the west spitsbergen fold and thrust belt formed along the transform plate boundary between greenland and the western barents sea during paleocene eocene breakup in the northern north atlantic approximately 20 40 km margin perpendicular shortening accumulated in the belt has been attributed to transpression and strain partitioning in a restraining bend but also to head on collision we have applied scaled analog tectonic modeling to test the former hypothesis a pack of brittle quartz sand with a shallow thin layer of silicon putty was deformed by transpression at a 15 convergence angle by movement of a basal plate the kinematics was quantified by means of digital particle image velocimetry the result was a doubly vergent transpressional wedge consisting of a steeply tapered retrowedge and a strongly internally deformed steeply tapered prowedge separated by a central strike slip zone and an adjacent low taper thin skinned fold and thrust belt the doubly vergent wedge evolved through several kinematic phases three main stages were identified namely 1 initial distributed deformation 2 development of an oblique doubly vergent wedge with progressive evolution of local strain partitioning along the marginal shear zones and finally 3 a stage of full strain partitioning between a central strike slip zone and reverse displacement along marginal shear zones with folding and thrusting in a thin skinned belt on the proside the analog model convincingly reproduced the geometry and the kinematic evolution of the west spitsbergen fold and thrust belt supporting the hypothesis of its formation by strain partitioning in transpression with a small angle of convergence and significant lateral displacement

state of stress and tectonic evolution of the west spitsbergen fold belt abstract the west spitsbergen fold belt is the result of a e w to ene wsw oriented compression which affected the whole of spitsbergen a late cretaceous palaeocene age for the fold belt deformation is indicated by the involvement of only the basal tertiary conglomerates in the folding and thrusting in western spitsbergen this compressional event was followed by a strike slip stress pattern with nw se oriented extension and ne sw compression which generated micro structures within the tertiary rocks on the map scale normal faults produced by a ne sw oriented extension overprint the compressional structures the later strike slip and extensional stress patterns correspond to the svalbard greenland dextral motion along the de geer zone in latest palaeocene eocene time the latest tectonic event which affected the whole of svalbard was an e w oriented extension related to the spreading along the knipovich ridge in oligocene neogene time

ediacaran and cambrian paleosols from central australia abstract ediacaran to cambrian red sandstones of the northern territory including arumbera sandstone and grant bluff and central mount stuart formations have been reexamined and sampled in order to reconstruct paleoenvironments from sedimentary facies and paleosols sedimentary facies include green gray calcareous sandstone member iii of arumbera sandstone only red siltstone with calcareous nodules also only member iii and also non calcareous red green siltstone interbedded red siltstone and sandstone and trough bedded sandstone the green gray facies has diverse and distinctive cambrian marine trace fossils not found in the red beds which have instead an assemblage of problematic body fossils including arumberia noffkarkys hallidaya ernietta trepassia and dickinsonia the red facies are interpreted as fluvial paleochannels trough cross bedded fluvial levees interbedded siltstone and sandstone poorly drained floodplain red green siltstone and well drained floodplain or low terrace calcareous nodular the carbonate nodules have micritic replacive fabrics and a significant positive correlation of 13c and 18o characteristic of pedogenic carbonate of calcid soils other red beds have pseudomorphous sand crystals after gypsum like those of gypsid soils individual red beds show negative strain and mass transfer for cationic bases typical of soils as well as gradational alteration down from fossiliferous tops characteristic of soils their varied degree of pedogenic differentiation is identified as psamment aquent and ochrept paleosols phosphorus depletion in the paleosols is evidence that organisms lived in the paleosols and were not introduced by transient marine incursions the problematic quilted fossils arumberia noffkarkys and hallidaya formed a distinctive inland terrestrial polsterland during the ediacaran and early cambrian

precambrian cambrian transition death valley united states the death valley region contains one of the best exposed and often visited precambrian cambrian successions in the world but the chronostratigraphic framework necessary for understanding the critical biologic and geologic events recorded in these sections has been inadequate the recent discovery of treptichnus phycodes pedum within the uppermost parasequence of the lower member of the wood canyon formation allows correlation of the precambrian cambrian boundary to this region and provides a necessary global tie point for the death valley section new carbon isotope chemostratigraphic profiles bracket this biostratigraphic datum and record the classic negative carbon isotope excursion at the boundary for the first time biostratigraphic chemostratigraphic and lithostratigraphic information from pretrilobite strata in this region can be directly compared with similar data from other key sections that record the precursors of the cambrian explosion few precambrian cambrian boundary sections contain both the facies restricted boundary fossil t pedum and carbon isotope data as found in death valley thus the death valley succession provides a critical link toward our understanding of the correlation between siliciclastic dominated and carbonate dominated precambrian cambrian transition sections