volcano sedimentary processes operating on a marginal continental arc the archean raquette lake formation slave province canada abstract the 200 m thick volcano sedimentary raquette lake formation located in the south central archean slave province represents a remnant arc segment floored by continental crust the formation overlies the gneissic sleepy dragon complex unconformably is laterally interstratified with subaqueous mafic basalts of the cameron river volcanic belt and is considered the proximal equivalent of the turbidite dominated burwash formation a continuum of events associated with volcanism and sedimentation and controlled by extensional tectonics is advocated a complex stratigraphy with three volcanic and three sedimentary lithofacies constitute the volcano sedimentary succession the volcanic lithofacies include 1 a mafic volcanic lithofacies composed of subaqueous pillow pillow breccia and subaerial massive to blocky flows 2 a felsic volcanic lithofacies representing felsic flows that were deposited in a subaerial environment and 3 a felsic volcanic sandstone lithofacies interpreted as shallow water wave and storm reworked pyroclastic debris derived from explosive eruptions the sedimentary lithofacies are represented by 1 a conglomerate sandstone lithofacies consistent with unconfined debris flow hyperconcentrated flood flow and talus scree deposits as well as minor high energy stream flow conglomerates that formed coalescing steep sloped coarse clastic fan deltas 2 a sandstone lithofacies interpreted as hyperconcentrated flood flow deposits that accumulated at the subaerial subaqueous interface and 3 a mudstone lithofacies consistent with suspension sedimentation in a small restricted lagoon type setting the raquette lake formation is interpreted as a fringing continental arc that displays both high energy clastic sedimentation and contemporaneous effusive and explosive mafic and felsic volcanism modern analogues that develop along active plate margins in which continental crust plays a significant role include japan and the baja california peninsula

relative sea level change along the slave craton coastline characteristics of archean continental rifting abstract the 2 8 ga siliciclastic dominated craton cover succession with subordinate mafic volcanic rocks at beniah lake in the slave craton has been informally referred to as the bell lake group the beniah lake succession up to 1 km thick is composed of 7 120 m thick coarsening upward cu sequences arranged with the following lithofacies architecture 1a argillite sandstone 1b mafic volcanic lithofacies 2 sandstone argillite 3a quartz arenite and 3b conglomerate lithofacies a pan slave unconformity indicating an autochthonous 2 8 to 4 013 ga basement cover relationship is present and locally well exposed the lithofacies and their arrangement are consistent with a tide influenced coastal setting whereby the change from argillite sandstone to quartz arenite lithofacies represents an initial estuary system defining transgression with a maximum flooding surface evolving into a fan delta defining progradation with a maximum regressive surface the mafic volcaniclastic lithofacies and associated pillowed flow units suggesting drowning of the siliciclastic succession coincide with a change from rift to drift tectonics as crustal attenuation facilitated magma ascent the slave wide unconformities and lithofacies contacts permit a sequence stratigraphic approach with the major slave basement quartz arenite unconformity suggestive of a 1st order sea level change coinciding with the proposed super continent break up or rifting the consistent stacking of cu sequences with capping subaqueous volcaniclastic volcanic units are considered the expression of 2nd order sea level cycles probably caused by changes of spreading rates at oceanic ridges the cu sequences and their thicknesses constitute 3rd order sea level changes and reflect the immediate response to crustal thinning time constraints for all these orders remain elusive but the hierarchy is consistent with sequence stratigraphic events the observed relative sea level change is attributed primarily to tectono eustasy where mantle dynamics caused rifting basin subsidence and mafic volcanism the latter occurred as the crust was sufficiently attenuated

episodic and short lived granitic pulses in a post collisional setting evidence from precise u pb zircon dating through a crustal cross section in corsica abstract in western corsica a large granitoid batholith was emplaced during carboniferous and permian times these rocks display an evolution through time from high mg k calc alkaline to calc alkaline then alkaline affinities moreover the magmatic processes can be observed at different crustal levels new and precise isotope dilution and thermo ionisation mass spectrometry id tims u pb dating suggests that granite magmatism in corsica did not simply reflect the continuous thermal evolution of a thickened crust a precise timing for the post collisional magmatism is documented with four distinct short lived episodes respectively at 345 338 305 and 280 ma separated by periods of inactivity these four magma pulses display variable nd isotopic signatures related to mantle crust interactions granite magma generation and emplacement is strongly connected to the thermal and tectonic activity of the lithosphere an increasing contribution of a depleted mantle to the magmatic processes is documented for the last igneous event this is interpreted to reflect the emplacement of depleted mantle materials in the lower crust which enhanced heat flow and triggered partial melting of previously underplated mafic rocks this increasing contribution of mantle materials marks the onset of a new geodynamic cycle characterised by an extensional tectonic regime preluding to the opening of the alpine orogenic tract

sedimentary geology of the palaeoarchaean buck ridge south africa and kittys gap western australia volcano sedimentary complexes abstract the two palaeoarchaean volcano sedimentary complexes of the buck ridge barberton greenstone belt south africa and kittys gap coppin gap greenstone belt east pilbara australia have a similar geological setting and age 3 45 ga the predominantly volcaniclastic sediments are concentrated at the top of these complexes and experienced thorough very early diagenetic silicification in many places the silicification process has led to excellent preservation of the primary sedimentary structures elsewhere it has resulted in their obliteration or replacement by diagenetic structures the buck ridge chert forms a regressive transgressive succession deposited around base level with lacustrine and littoral marine facies deposition of the kittys gap chert was also close to base level almost exclusively subaqueous with tidal influence and a regressive sequential trend in both volcano sedimentary complexes these low energy sediments are juxtaposed with high energy breccia pods and layers with often a high fe oxide content the breccias are interpreted as being the result of explosive hydrothermal activity sedimentation was strongly controlled by normal faulting

the alpine tethys rifted margins reconciling old and new ideas to understand the stratigraphic architecture of magma poor rifted margins this study focuses on the assessment of the stratigraphic architecture of the proximal and distal jurassic alpine tethys rifted margins the aim of the study was to reconcile the major observations performed in the alps through time with what is observed in present day magma poor rifted margins the proximal and distal rifted margins reflect two evolutionary phases of rifting involving different structures and isostatic evolutions leading to different stratigraphic records the proximal rifted margins formed from upper triassic to pliensbachian times and resulted in the formation of classical half graben basins rift evolution changed drastically during pliensbachian to toarcian times when extension started to localize in the future distal rifted margins low angle detachment faults become the new elementary structure controlling final crustal tapering and eventually mantle exhumation to the sea floor new structural elements controlling the stratigraphic architecture of the distal rifted margins include extensional allochthons and breakaway blocks both resulting from the delamination of a keystone block also referred to as hangingwall block during hyper extension processes to define the stratigraphic architecture of the proximal and distal rifted margins three stratigraphic marker horizons are used namely the top of the pre rift sequences the top of the proximal margin syn tectonic sequence and the base of post rift sequences based on the distribution of these stratigraphic marker horizons across the alpine units and a structural re evaluation of the rift structures a synthetic tectono stratigraphic evolution of the alpine tethys domain is proposed that reconciles old and new ideas about how rift systems may evolve in space and time

proterozoic sedimentation and volcanism in the singhbhum crustal province india and their implications abstract the proterozoic volcano sedimentary succession comprising successively younger dhanjori chaibasa dhalbhum dalma and chandil formations of the singhbhum crustal province india records sedimentation and volcanism in a rapidly changing tectonic scenario cooling of the vast volume of archaean singhbhum granite possibly induced an isostatic readjustment the associated tensional regime and deep seated fractures controlled the formation of the proterozoic singhbhum basin the dhanjori formation unconformably overlies the singhbhum granite and is entirely terrestrial dominantly fluvial at the base the conglomerate deposits coarse grained sandstone and shale represent the distal fringe of an alluvial fan complex the rest of the formation including the volcaniclastic rocks consists almost entirely of fining upward fluvial cycles the base of the dhanjori formation is a sequence boundary and the formation itself represents a lowstand systems tract the dhanjori volcano sedimentary succession displays evidence of having passed through passive as well as active phases of continental rifting with an increasingly important influence of volcanism on the sedimentation through time the chaibasa formation sharply overlies the dhanjori formation and a transgressive lag demarcates their contact the basal part of the chaibasa formation immediately overlying the transgressive lag deposit represents a transgressive systems tract while offshore shales that sharply overlie the shallow marine sandstones up section represent marine flooding surfaces the shallow marine subtidal sandstones bear an excellent record of sandwave migration and provide a rare opportunity to unlock the late palaeoproterozoic lunar orbital periodicities unlike the chaibasa the overlying dhalbhum formation is entirely terrestrial fluvial aeolian indicating that the chaibasa dhalbhum contact is a sequence boundary the dalmas overlying the dhalbhum formation represents concordant lava outpourings without any break in sedimentation these lavas are genetically related to mantle plume upwelling in an intracontinental rift setting the volcano sedimentary package lying north of the dalma volcanic belt chandil formation is of mesoproterozoic age the entire late palaeoproterozoic volcano sedimentary package displays post depositional compressional deformation and greenschist to amphibolite facies metamorphism dated at ca 1600 ma forming the so called north singhbhum fold belt the volcano sedimentary package lying south of the dalma volcanic belt was pushed further south towards the singhbhum granite batholith complex as a result of uplift related to the dalma plume the singhbhum granite batholith acted as a rigid body this gave rise to a compressional stress regime that induced shearing thrusting at ca 1600 ma along the singhbhum shear zone the dalma plume magmatism was possibly part of a 1600 ma global tectono thermal event

influences of storm erosion and deposition on rhythmites of the upper wenchang formation upper ordovician around tonglu zhejiang province china abstract tonglu rhythmites upper ordovician in zhejiang province east central china display three orders of cyclicity in sandstone and mudstone layer thickness millimeter thick alternations of sandstone and mudstone laminae are ascribed to single tidal cycles centimeter thick alternations of sand dominated layers sdls and mud dominated layers mdls are interpreted to be related to alternation of storm and calm weather conditions with a periodicity longer than that forced by neap spring tidal cyclicity the sdls are interpreted as storm deposits on the basis of presence of scour structures abundant intraformational mud pebbles oscillation ripples and thinning upward trends in the sandstone laminae a third meter thick cycle of variations in sandstone lamina thickness is interpreted as a reflection of cross shore changes in coastal dynamics and water depth in the subtidal intertidal environment storm waves usually considered to be random destructive factors to normal cyclic deposits are here highlighted as effective agents of sediment transport and deposition of the sand dominated layers this study aims at improving our facies level understanding of the genesis and preservation of storm related tidal flat rhythmites on open coasts and highlights the fact that storm related facies can mimic the cyclicity that is commonly ascribed to neap spring tidal variation

quantifying the oldest tidal record the 3 2 ga moodies group barberton greenstone belt south africa the 3 2 ga moodies group in the barberton greenstone belt south africa contains the oldest preserved record of tides the tidal record is preserved in a tidal sand wave deposit in the lower moodies group as bundles of sandstone foresets separated by mudstone drapes detailed analysis of rhythmic foreset bundles permits quantification of the tidal record and reveals a hierarchy of diurnal fortnightly and monthly tidal periodicities thick thin pairs of foreset bundles reflect deposition from semidiurnal dominant and subordinate flood tidal currents respectively cyclic variations in foreset bundle thicknesses record longer period changes in strength of the dominant semidiurnal tidal currents consistent with neap spring neap tidal cyclicity alternating thicker and thinner neap spring neap cycles are comparable to anomalistic perigean apogean tidal signatures this quantitative record of tides in the middle archean moodies group represents by 2 2 b y the oldest such documentation tidal cyclicity recognized in the moodies sand wave deposit is comparable to that recorded in modern tidal settings and identified in the carboniferous rock record and is most compatible with a lunar orbital shape similar to that existing today

late archaean tidalites from western margin of chitradurga greenstone belt southern india abstract tidalites are preserved within a metavolcano sedimentary succession of the late archaean bababudan group dharwar supergroup along the western boundary of the nnw sse trending chitradurga greenstone belt west dharwar craton southern india these may represent the oldest record of tidal processes in peninsular india millimetre thick sand mud alternations bidirectional cross strata mudstone draped sandy foresets reactivation surfaces indicating time velocity asymmetry sigmoidal cross strata and mudstone draped flaser lenticular bedding are displayed by the sandstone mudstone heterolithic facies in the upper part of the bababudan succession together implying a tidal depositional system thick thin pairs of rhythmic foreset bundles correspond to neap spring tidal cycles within a semidiurnal tidal system development of the studied coastal sediments suggests formation of stable platform along the western margin of the late archaean chitradurga greenstone belt

origin and timing of the post variscan gabbro granite complex of porto western corsica the post variscan complex of porto consists of metaluminous to slightly peraluminous a type biotite granites mingled with gabbro dioritic rocks and late dykes with basaltic to trachyandesitic composition u pb zircon dating by la icp ms on two mafic intrusive samples constrains the time of the gabbro granite crystallisation at 281 3 ma and 283 2 ma hornblende 40ar 39ar ages from a late trachyandesite dyke date the dyking event at 280 2 ma which is within error the u pb zircon ages of the intrusives biotite granites show variable major and trace element compositions and similar initial end 0 3 to 0 9 whole rock chemistry variations and trace element compositions of plagioclase and allanite indicate that the granites are genetically linked essentially through fractional crystallisation of feldspars and minor allanite on the basis of whole rock chemistry e g initial end 4 9 to 1 7 and trace element clinopyroxene compositions we have ascertained that the mafic intrusives and basic dykes formed from isotopically depleted mantle source derived melts with similar trace element signature these basic melts experienced slightly different evolutionary histories controlled by fractional crystallisation and crustal contamination mainly by the acid magma that gave rise to the associated biotite granites but also by the enclosing older variscan granitoids u pb zircon data suggest that the porto complex was affected by hydrothermal fluid circulation at 259 9 ma

the bayesian probabilistic prediction of strong earthquakes in the hellenic arc abstract the bayesian probability theory in conjunction with the poisson process model is used to develop a bayesian discrete distribution to estimate or predict the inter arrival times tj for strong earthquakes in the hellenic arc the bayesian posterior probabilities may be computed from the relationship p t r m t r e t r 1 e t r j 1 m t j e t j 1 e t j where p t r m is the conditional probability of the event tr given that an earthquake of magnitude m has occurred the bayesian discrete analysis is performed first by using the poisson process to determine the prior probability distribution for tj and the likelihood function we can imagine the random earthquake experiment involved in the application of bayes theorem to earthquake prediction to be a two stage experiment the first stage was initiated a long time ago when the real time arrival dates of strong earthquakes were first recorded the second stage was initiated in 1935 when the earthquake magnitude scale was introduced by richter 1935 in southern california richter probably never thought that this measure of the earthquake magnitude then will be an experiment designed to give us information about the outcome of the earthquake inter arrival times the first stage the earthquake data analyzed in this study have been taken from the earthquake catalog for the hellenic arc prepared by ambraseys 1981 the discrete bayesian analysis suggests determining the most likely outcomes for the length of earthquake inter arrival times by using some maximum values of the final bayesian probabilities the following inferences concerning future strong earthquake occurrences in the hellenic arc area may be drawn 1 1 our western northwestern zone is a seismic region which approximately coincides with the region studied by wyss and baer therefore we agree with the geographic location of the expected earthquake forecasted by wyss and baer 1981 2 2 using probability theory bayes theorem poisson process we concluded that a period of strong earthquake activity is expected to occur in the same geographic location during the decade 1992 2002 this conclusion supports ambraseys conclusion however it should be noted that our conclusion indicates that the period of strong earthquake activity will occur anyway a decade later than predicted by wyss and baer

timing of deposition and deformation of the moodies group barberton greenstone belt south africa very high resolution of archaean surface processes abstract thin and largely discontinuous volcanic tuff beds in the alluvial fluvial and marginal marine siliciclastic strata of the middle archaean moodies group barberton greenstone belt bgb contain rare to abundant zircon dating of magmatic zircon grains from five tuff beds and one cross cutting dike yield ages which span the entire spectrum of bgb history from ca 3550 ma to 3215 ma and show variable degrees of post depositional alteration until ca 2500 ma the youngest pristine zircon grains in all tuff samples analyzed by ca id tims chemical abrasion ion dissolution thermal ion mass spectrometry yield upper intercept and concordia ages between 3227 6 0 3 and 3216 0 3 ma and those grains analyzed by la sf icp ms laser ablation sector field inductively coupled plasma mass spectrometry and shrimp sensitive high resolution ion microprobe yield ages between 3228 9 and 3214 9 ma most of these ages are either identical within error or significantly older than a ca id tims age of 3223 4 0 3 ma obtained from zircon grains of a tuff horizon of the schoongezicht formation at the top of the underlying fig tree group we interpret this age to mark the time of volcanic eruption whereas the significantly older and overlapping ages of the stratigraphically higher moodies tuff zircon grains point either to a high degree of magmatic inheritance and or a detrital contribution from surrounding sedimentary rocks during or after ash tuff deposition the minimum age for deposition of moodies group sediments and deformation is provided by a la icp ms zircon u pb age of 3219 9 ma obtained from an undeformed felsic dike which crosscuts folded moodies strata this age overlaps with a precise ca id tims u pb zircon age of 3216 0 0 3 ma obtained from a tuff horizon of the upper moodies group overall the new age data collectively imply that the up to 3 7 km thick sandstone dominated moodies group was deposited and deformed within

earth moon system planetary science and lessons learned the origin and evolution of the moon is now well understood many bizarre theories were proposed to account for our satellite before these were swept away by the data from the apollo missions we now understand with the benefit of hindsight that we are looking at a very ancient object whose surface has changed little for the past 3 5 b y nevertheless the moon remains a unique body in the solar system the moon formed as the result of a glancing collision with the earth of a mars sized impactor late in the accretional history of the earth when both bodies had differentiated into metallic cores and silicate mantles the impactor is derived from the neighborhood of the earth as shown by similarities in o and cr isotopes our satellite is mostly derived from the mantle of the impactor rather than from the mantle of the earth the moon melted perhaps entirely and a thick 50 km feldspathic crust dated at 4460 40 ma floated on the ocean of magma the closest analogue may be the crust of mercury the interior crystallized into cumulate zones of differing mineralogy from which the mare basalts were later derived by partial melting the impact history of the lunar surface has provided insights into planetary accretion the planetesimal hypothesis and the bombardment history in the inner solar system debate continues whether the concentration of impact produced basins constitutes a cataclysm or the tail end of accretion a notable example and a target for future missions is the 2500 km diameter south pole aitken basin that may provide insights into the nature of the deep lunar crust remaining significant problems include whether the moon has a small metallic core while the deep interior structure is not well understood new seismic and heat flow data are an urgent priority

nonuniform cratering of the moon and a revised crater chronology of the inner solar system abstract we model the cratering of the moon and terrestrial planets from the present knowledge of the orbital and size distribution of asteroids and comets in the inner solar system in order to refine the crater chronology method impact occurrences locations velocities and incidence angles are calculated semi analytically and scaling laws are used to convert impactor sizes into crater sizes our approach is generalizable to other moons or planets the lunar cratering rate varies with both latitude and longitude with respect to the global average it is about 25 lower at 65 n 90 e and larger by the same amount at the apex of motion 0 n 90 w for the present earth moon separation the measured size frequency distributions of lunar craters are reconciled with the observed population of near earth objects under the assumption that craters smaller than a few kilometers in diameter form in a porous megaregolith varying depths of this megaregolith between the mare and highlands is a plausible partial explanation for differences in previously reported measured size frequency distributions we give a revised analytical relationship between the number of craters and the age of a lunar surface for the inner planets expected size frequency crater distributions are calculated that account for differences in impact conditions and the age of a few key geologic units is given we estimate the orientale and caloris basins to be 3 73 ga old and the surface of venus to be 240 ma old the terrestrial cratering record is consistent with the revised chronology and a constant impact rate over the last 400 ma better knowledge of the orbital dynamics crater scaling laws and megaregolith properties are needed to confidently assess the net uncertainty of the model ages that result from the combination of numerous steps from the observation of asteroids to the formation of craters our model may be inaccurate for periods prior to 3 5 ga because of a different impactor population or for craters smaller than a few kilometers on mars and mercury due to the presence of subsurface ice and to the abundance of large secondaries respectively standard parameter values allow for the first time to naturally reproduce both the size distribution and absolute number of lunar craters up to 3 5 ga ago and give self consistent estimates of the planetary cratering rates relative to the moon

siliciclastic associated banded iron formation from the 3 2 ga moodies group barberton greenstone belt south africa most models proposed for banded iron formation bif deposition are based on observations of well preserved late archean and paleoproterozoic bif efforts to push the understanding gained from younger successions deeper in time have been hampered by the high metamorphic grades that characterize early archean bif this study focuses on a unique occurrence of well preserved and contextualized bif from the early archean 3 2 ga moodies group in the barberton greenstone belt south africa the moodies bif occurs thinly interbedded with fine grained and cross stratified sandstones indicating deposition during times of decreased clastic sediment supply in the moodies bif chert is present as concretions and is never observed in direct contact with the siliciclastic material but is always associated with iron minerals this observation suggests that the processes leading to the formation of both chert and iron minerals were coupled the dominant iron rich minerals within unweathered moodies bif are hematite and magnetite with less common occurrences of fe carbonate phases mainly ankerite petrographic textures reveal that hematite constitutes an early mineral phase while magnetite and ankerite display textures indicative of a late diagenetic or metamorphic origin carbonaceous particles are present in close association with the magnetite crystals these c bearing phases may be the preserved organic matter of microbes involved in the production of the ferric iron precursor phases though it is difficult to rule out an origin from abiotic processes involving thermal decomposition of siderite to magnetite and organic carbon compounds nonetheless the range of textures mineralogies and valence states supports the view that diagenetically stabilized bif mineralogies reflect the interaction of ferric iron phases with reducing fluids during diagenesis these patterns are commonly observed in younger archean and paleoproterozoic iron formations and imply a continuity of processes operating in the iron and silica cycles across both a range of paleoenvironments and long intervals of archean time

jurassic sedimentary record and tectonic evolution of the northwestern corner of africa abstract the history of the opening seaway from the westernmost tethys to the central atlantic is traced by the analysis of the sedimentary facies development in the external rif basin of northern morocco and the geological and seismic data from the moroccan atlantic continental margin in the rif basin after the early sinemurian sedimentary facies dated by ammonites foraminifers and brachiopods indicate a progression of rapid subsidence resulting from extensional tectonic tilted blocks escarpment fault breccias neptunian dykes etc from the n and ne to the s and sw from the toarcian to the bajocian deltas progress from the w and sw into the rides sud rifaines realm from the late bathonian to the oxfordian deep sea fans develop in the external rif during the same period deltaic sediments fill in the middle atlas basin of eastern morocco and progress into the external rif the top of the jurassic is characterised by carbonate deposits at the northwestern corner of africa the subsidence of the sedimentary basins by rifting is initiated in the late triassic however at the mazagan transect of the atlantic continental margin the tectonic pattern characteristic of a passive continental margin appears clearly only in the early jurassic at the foot of the mazagan escarpment the sedimentary record shows a foundering of the first bloc during early to middle lias a thermal uplift phase is indicated by emersion of the african margin shoulder in late liassic and thermal relaxation starts in the middle jurassic the morphology of this transect compared with the conjugate side of the american continent is most easily explained by the uniform sense simple shear model

provenance of oligocene synorogenic sediments of the ligurian alps nw italy inferences on belt age and cooling history mineral chemistry 40ar 39ar geochronology on white micas and apatite fission track thermochronology aftt are applied here to study the provenance of the synorogenic molare formation lowermost unit of the tertiary piedmont basin clastic sequence the molare formation was deposited during transgression onto the ligurian alps nappe stack in the early oligocene depositional facies show that clastic distribution remained transversal with local sources located just landward from the coastline phengite mineral chemistry together with 40ar 39ar data clearly shows two distinctive source areas each one mirroring the composition of the basement directly beneath the clastic sequence amphibole mineral chemistry allows second order provenance distinctions within each sector reflecting heterogeneous metamorphic evolution of the bedrock complexes integrated 40ar 39ar dating and aftt suggest that following a fast cooling exhumation episode of the ligurian alps during the oligocene very little net uplift has since occurred this is due to a period of general subsidence from the oligocene late miocene followed by comparable uplift from late miocene pliocene to the present in general our data provide an image of the ligurian alps during the oligocene which is very similar to the present day one

mesozoic alpine facies deposition as a result of past latitudinal plate motion the fragmentation of pangaea as a consequence of the opening of the atlantic ocean is documented in the alpine mediterranean region by the onset of widespread pelagic sedimentation1 shallow water sediments were replaced by mainly pelagic limestones in the early jurassic period radiolarian cherts in the middle late jurassic period and again pelagic limestones in the late jurassic cretaceous period1 during initial extension basin subsidence below the carbonate compensation depth ccd is thought to have triggered the transition from early jurassic limestones to middle late jurassic radiolarites1 it has been proposed that the transition from radiolarites to limestones in the late jurassic period was due to an increase in calcareous nannoplankton abundance when the ccd was depressed below the ocean floor1 but in modern oceans sediments below the ccd are not necessarily radiolaritic here we present palaeomagnetic samples from the jurassic cretaceous pelagic succession exposed in the lombardian basin italy on the basis of an analysis of our palaeolatitudinal data in a broader palaeogeographic context we propose an alternative explanation for the above facies tripartition we suggest that the lombardian basin drifted initially towards and subsequently away from a near equatorial upwelling zone of high biosiliceous productivity our tectonic model for the genesis of radiolarites adds an essential horizontal plate motion component to explanations involving only vertical variations of ccd relative to the ocean floor it may explain the deposition of radiolarites throughout the mediterranean and middle eastern region during the jurassic period

tidal rhythmites in a deep sea environment an example from mio pliocene misaki formation miura peninsula japan abstract the mio pliocene misaki formation miura peninsula japan is characterized by alternation of mafic scoriaceous pebbly sandstone pumiceous sandstone and siltstone and mudstone formed in a fore arc basin in an arc arc collisional zone the qualitative as well as quantitative evidences of tide during the misaki sedimentation in the jogashima area miura peninsula are presented here the lunar synodic period of 28 days lunar month extracted from the misaki tidal rhythmite agrees well with the published miocene tidal rhythmite data the couplet series of the misaki tidal rhythmite however is often interrupted by downslope resedimentation via turbidity currents intense penecontemporaneous deformation and bioturbation association of deep sea turbidites mass flow deposits and tidal rhythmite suggest misaki sedimentation in the miura peninsula took place in a submarine canyon setting

diachronous cooling on both sides of a major strike slip fault in the variscan maures massif south east france as deduced from a detailed 40ar 39ar study abstract a detailed 40ar 39ar geochronological study was performed in the maures massif se france to define the thermal history of this geochronologically poorly constrained segment of the variscan belt a total of 22 plateau ages were obtained on single grains and bulk samples of amphibole muscovite and biotite extracted from 21 metamorphic and magmatic rocks sampled on both sides of the grimaud fault migmatites micaschists gneisses pegmatites and granites displayed muscovite and biotite plateau ages ranging from 317 2 1 0 to 322 9 1 7 ma on the western side and from 300 2 0 6 to 306 0 2 4 ma to the east of the grimaud fault in the western block amphiboles from amphibolites yielded plateau ages of 328 1 2 8 and 329 9 2 1 ma whereas in the eastern block amphiboles from amphibolite and magmatic bodies yielded variable ages ranging from 307 9 1 2 to 317 4 2 4 ma these data clearly demonstrate distinct cooling histories between at least 330 and 300 ma on both sides of the grimaud fault which consequently appears as a major crustal fault during the late variscan orogeny as shown by the concordant for each type of mineral data obtained on biotite muscovite and amphibole from magmatic and metamorphic rocks the two crustal blocks cooled down independently each one homogeneously in the range of temperatures 550 300 c two distinct periods of fast cooling appear at 320 ma to the west and 305 300 ma to the east these data are consistent with those previously obtained on other regions of the european variscan belt

stratigraphic evolution in the ligurian alps between variscan heritages and the alpine tethys opening a review abstract the ligurian alps are the southernmost segment of the alpine orogenic belt their formation is the result of a multistage process that comprises two orogenic cycles the variscan and the alpine one since the late paleozoic onwards superposed sedimentary successions deposited in this area as a response to the changing tectonic setting in the frame of the western mediterranean evolution the transition between the two orogenies was characterized by the formation of a net of sedimentary basins controlled by diffused extension which is not correlated to a clear geodynamic context yet as the fault network is severely affected by alpine reworking the multiple pre alpine tectonic stages experienced by the ligurian sector can be unravelled only by the analysis of the well exposed stratigraphic succession which offers very distinctive feature for each tectonic phase from the present day situation of a nappe pile orogen backward to the originary basinal setting the aim of this work is to reconstruct the paleogeographic evolution of the ligurian alps between permian and jurassic through a detailed stratigraphic analysis several sedimentary packages belonging to different tectonic units are analysed grouped into specific domains and correlated five major steps in the evolution of the ligurian alps have been pointed out they have been contextualized within the latest paleogeographic reconstructions of the alpine sector contributing to detail the role of the study area in the plate tectonic dynamics the sedimentary record is referred to successive geodynamic stages from the pangea break up and variscan belt dismantling through a triassic diffused extension to the alpine tethys rifting and finally to the spreading that generated the piedmont ligurian oceanic branch the stratigraphic reconstruction of the ligurian sector also indicates the lacking of an ocean interposed between the european continent and the alpine collisional wedge thus representing the southward termination of the valais basin on the whole the paleogeographic reconstructions provided in this work highlight that the ligurian alps were a domain in which for over a hundred million years orogenesis rifting and oceanisation strongly affected the integrity of the upper crust the heterogeneity of the crust that suffered multiple mantle uplifts partial melting and extensive faulting over a long period is testified by field evidences and several effusive events the last and most important rifting and the following alpine tethys oceanisation developed around a narrow elongated area of crustal weakness generated by multiple geodynamic events

tectono thermal evolution of a distal rifted margin constraints from the calizzano massif prepiedmont brianconnais domain ligurian alps the thermal evolution of distal domains along rifted margins is at present poorly constrained in this study we show that a thermal pulse most likely triggered by lithospheric thinning and asthenospheric rise is recorded at upper crustal levels and may also influence the diagenetic processes in the overlying sediments thus representing a critical aspect for the evaluation of hydrocarbon systems the thermal history of a distal sector of the alpine tethys rifted margin preserved in the ligurian alps case tuberto calizzano unit is investigated with thermochronological methods and petrologic observations the studied unit is composed of a polymetamorphic basement and a sedimentary cover providing a complete section through the prerift synrift and postrift system zircon fission track analyses on basement rocks samples suggest that temperatures exceeding 240 25 c were reached before 150 160 ma upper jurassic at few kilometer depth neoformation of green biotite stable at temperatures of 350 to 450 c was synkinematic with this event the tectonic setting of the studied unit suggests that the heating cooling cycle took place during the formation of the distal rifted margin and terminated during late jurassic 150 160 ma major crustal and lithospheric thinning likely promoted high geothermal gradients 60 90 c km and triggered the circulation of hot deep seated fluids along brittle faults causing the observed thermal anomaly our results suggest that rifting can generate thermal perturbations at relatively high temperatures between 240 and 450 c at less than 3 km depth in the distal domains during major crustal thinning preceding breakup and onset of seafloor spreading

organic walled microfossils in 3 2 billion year old shallow marine siliciclastic deposits the discovery of relatively large cell like structures in early archaean shale and siltstone deposits adds further evidence that diversified living organisms thrived on earth at a very early date claims for fossils of this age are often controversial as non biological processes can produce life like microstructures and chemical signatures resembling those of the remains of living organisms extensive efforts were therefore made to rule out a non biological origin for these microstructures they survive this examination and appear to be organic walled microfossils derived from large microorganisms that cohabited with previously reported microbial mats living in the sunlit shallows of earth s early oceans around 3 2 billion years ago claims that life existed on earth in the early archaean eon 3 2 billion years ago are often controversial as non biological processes can produce life like microstructures and chemical signatures that mimic those of the remains of living organisms now however the discovery of relatively large carbonaceous spheroidal microstructures interpreted as organic walled microfossils in early archaean deposits adds further evidence that life existed thrived and survived on earth at a very early date although the notion of an early origin and diversification of life on earth during the archaean eon has received increasing support in geochemical sedimentological and palaeontological evidence ambiguities and controversies persist regarding the biogenicity and syngeneity of the record older than late archaean1 2 3 non biological processes are known to produce morphologies similar to some microfossils4 5 and hydrothermal fluids have the potential to produce abiotic organic compounds with depleted carbon isotope values6 making it difficult to establish unambiguous traces of life here we report the discovery of a population of large up to about 300 m in diameter carbonaceous spheroidal microstructures in mesoarchaean shales and siltstones of the moodies group south africa the earth s oldest siliciclastic alluvial to tidal estuarine deposits7 these microstructures are interpreted as organic walled microfossils on the basis of petrographic and geochemical evidence for their endogenicity and syngeneity their carbonaceous composition cellular morphology and ultrastructure occurrence in populations taphonomic features of soft wall deformation and the geological context plausible for life as well as a lack of abiotic explanation falsifying a biological origin these are the oldest and largest archaean organic walled spheroidal microfossils reported so far our observations suggest that relatively large microorganisms cohabited with earlier reported benthic microbial mats8 in the photic zone of marginal marine siliciclastic environments 3 2 billion years ago

episodic exhumation of hp rocks inferred from structural data and p t paths from the southwestern massif central variscan belt france abstract in the southwestern massif central france hp rocks are found in lower allochthonous units i e hp units sandwiched between upper allochthonous units i e lp units and the parautochthonous unit both devoid of hp rocks hp rocks were formed at minimum conditions of 1 7 gpa 700 c in response to the northward subduction of gondwana beneath armorica during the silurian 430 390 ma their exhumation results from an 80 ma long sequence of tectonic processes effective at various scales and active specifically at each main stage of the evolution of the gondwana lithosphere hp rocks were first exhumed by upward southwestward extrusion during the early devonian 390 380 ma in relation to late stage of subduction in the northern area exhumation is achieved by rifting during the upper devonian 365 ma the most obvious event corresponds to the northwestward thrusting of lp units above hp units during early stages of continental collision 355 ma hp rocks were exhumed for a second time during orogen parallel transpression in response to late stage of continental collision 350 345 ma exhumation in internal zones is achieved by crustal scale normal faulting and erosion during the middle carboniferous 335 315 ma synorogenic extension while compression was still active in the southern external zones exhumation of the whole region is completed by regional uplift and erosional denudation during the upper carboniferous 310 290 ma postorogenic extension subduction and collision have played a key role for driving hp rocks to the surface but their efficiency and the resulting strain pattern depend on the angle of convergence upper devonian rifting and the subsequent early carboniferous crustal thickening prevents to consider exhumation of variscan hp rocks as a single and continuous process and open new questions on the related paleozoic lithosphere history

synrift sedimentation on the northern tethys margin an example from the ligurian alps upper triassic to lower cretaceous prepiedmont domain italy the prepiedmont domain succession of the ligurian alps is formed by a thick mesozoic sedimentary cover tectonically detached from its substratum the arnasco castelbianco unit preserves the most complete record of the ligurian prepiedmont although completely overturned and deformed due to alpine tectonics it is composed of carbonate and clastic rocks deposited during the upper triassic to lower cretaceous interval this paper is focused on the stratigraphy of the jurassic series and its relationships to the tethyan rifting each term of the sedimentary record is seen as a witness of the several phases through which the rifting took place an early rifting phase late hettangian to early sinemurian brought to the formation of a normal fault system affecting the carbonate platform and favoured the development of condensed sedimentation on pelagic highs the rapid transition from open platform carbonates to slope basin cherty limestones testifies the increased subsidence of the margin in the late sinemurian during which moderate fault activity is recorded intraformational breccia horizons until the early pliensbachian a tectonic pause brought to the sedimentation of a succession of pelagic carbonates occasionally interrupted by clastic flows during the late pliensbachian to toarcian the rifting phase followed evidenced by the large amount of clastics and generated by renewed fault activity clastics flowed down into the basin as fluxoturbidites first and then passed to breccias during the maximum tectonic pulse in the late toarcian to aalenian the thermal uplift of the brianconnais shoulder generated a basin fill of fine clastics the following thermal subsidence aalenian to tithonian favoured the restoration of quiet basinal conditions evidenced by the deposition of radiolarites

from rifting to passive margin the examples of the red sea central atlantic and alpine tethys abstract evolution of the red sea gulf of suez and the central atlantic rift systems shows that an initial transtensive rifting phase affecting a broad area around the future zone of crustal separation was followed by a pre oceanic rifting phase during which extensional strain was concentrated on the axial rift zone this caused lateral graben systems to become inactive and they evolved into rift rim basins the transtensive phase of diffuse crustal extension is recognized in many intra continental rifts if controlling stress systems relax these rifts abort and develop into palaeorifts if controlling stress systems persist transtensive rift systems can enter the pre oceanic rifting stage during which the rift zone narrows and becomes asymmetric as a consequence of simple shear deformation at shallow crustal levels and pure shear deformation at lower crustal and mantle lithospheric levels preceding crustal separation extensional denudation of the lithospheric mantle is possible progressive lithospheric attenuation entails updoming of the asthenosphere and thermal doming of the rift shoulders their uplift provides a major clastic source for the rift basins and the lateral rift rim basins their stratigraphic record provides a sensitive tool for dating the rift shoulder uplift asymmetric rifting leads to the formation of asymmetric continental margins corresponding in a simple shear model to an upper plate and a conjugate lower plate margin as seen in the central atlantic passive margins of the united states and morocco this rifting model can be successfully applied to the analysis of the alpine tethys palaeo margins such as rif and the western alps

the tectono stratigraphic evolution of distal hyper extended magma poor conjugate rifted margins examples from the alpine tethys and newfoundland iberia abstract in order to capture the general tectono stratigraphic framework of a magma poor conjugate rifted margin two examples have been analysed and compared the seismically imaged and drilled iberia newfoundland rifted margins e g seismic sections screech1 ise1 and the fossil distal tethys rifted margins exposed in the alps the lower austroalpine and the ligurian brianconnais units exposed in se switzerland and nw italy respectively are here considered and described for the first time as conjugate margins they form like the iberia newfoundland rifted margins conjugate upper and lower plate margin both pairs of margins show a similar first order morpho tectonic arrangement using the top of pre rift succession tprs and the base of post rift successions bprs as stratigraphic marker levels and two syn tectonic sequences sts 1 2 three major rift domains can be identified which experienced different evolutions and preserved different stratigraphic architectures i the proximal margin soled by normal 30 5 km thick continental crust it is characterized by widespread fault bounded graben half graben basins filled by the sts 1 showing growth structures followed by a succession time equivalent unit to sts 2 that does not show any evidence for syn depositional tectonic activity ii the upper plate distal margin floored by thinned to ultra thinned continental crust it can be subdivided into a distal high and a distal low separated by a major fault system the high is characterized by the occurrence of a marked syn rift unconformity leading to the erosion and or non deposition of the whole syn tectonic sequence sts 1 sts 2 the low displays complete stratigraphic successions in which the sts 2 becomes very characteristic and exclusive of this part of the margin iii the lower plate distal margin floored by hyper extended crust exhumed crust and subcontinental mantle the pre tectonic sequence and the sts 1 are only present inside extensional allochthons that are excised from the upper plate and passively transported on top of major exhumation faults the sts 2 deposited during the formation of the most distal domain is mostly formed by clasts derived from the dismantling of the extensional allochthons and of the surrounding exhumed basement it is overlain by deep marine turbidites and hemi pelagic sediments the nature of basement serpentinized mantle and hydrated upper or lower continental crust will selectively condition the composition of the sts 2 in the distal lower plate margin the recognition of a complex rift stratigraphy in the two conjugate pairs of margins shows that simple stratigraphic models are unable to describe the complete evolution of rifted margins from their initial stage preserved in the proximal margins to the final evolution leading to upper and lower plate margins in the conjugate distal margins this paper describes for the first time the stratigraphic relationships at distal conjugate rifted margins which is a key to understand the rift evolution and architecture of these yet little investigated systems

breccias of the adnet formation indicators of a mid liassic tectonic event in the northern calcareous alps salzburg austria stratigraphy lithology and depositional structures of liassic red limestone breccias of the adnet formation including the adnet scheck were studied at several outcrops of the northern calcareous alps nca south east of salzburg a four fold lithostratigraphic division is proposed for the adnet formation of the osterhorn mountains the hemipelagic schmiedwirt sinemurian and kehlbach carixian members are separated from the pelagic saubach member toarcian by a layer of amalgamated breccias scheck member probably domerian to early toarcian several other breccia beds occur locally from the base of the kehlbach member up to the lower saubach member although the sediments overlying the scheck member breccias are of coeval age the ages of the underlying strata are very different this can be explained by submarine liassic erosion during a period of resedimentation from the middle carixian until the early toarcian at least 10 15 m of partly lithified sediments were eroded by gravity flows the entire kehlbach member and up to two thirds of the schmiedwirt member were removed at adnet the breccias originated from submarine debris flows repeated flows over a long period and the depositional setting exclude a triggering by sea level fluctuations most probably they arose from tectonically triggered slumps and slides of superficial sediments the scheck was initiated on the steep upper slope of the drowned triassic adnet reef and flowed to the north east the pliensbachian to early toarcian period of tectonic activity indicated by the breccias was the most important during the liassic in the osterhorn mountains and other parts of the nca from the large scale regional distribution of the breccias and in accord with published data a roughly northeast trending strike slip fault zone is proposed crossing the nca south of the osterhorn block with a peaking activity during the pliensbachian to early toarcian as the cause of the tectonic movements

carbon isotope anomalies and demise of carbonate platforms in the sinemurian early jurassic of the tethyan region evidence from the southern alps northern italy despite its global impact on ecosystems the triassic jurassic boundary event had only a modest effect on the carbonate depositional systems of the southern alps whereas a fundamental reorganization of the same palaeogeographic area took place during the sinemurian age this paper investigates whether or not the well documented demise of sinemurian carbonate platforms in the tethyan region was a response to a global event by examination of carbon isotope anomalies in successions of different facies that record this interval of time a chemostratigraphic transect from lake garda up to the eastern italian border is illustrated by four stratigraphic sections high resolution 20 cm over key intervals chemostratigraphic sampling allowed detection of a major negative 13 c anomaly of 1 5 preceded by a positive excursion both in shallow and deep water successions over the stratigraphical range of the ammonite genus arnioceras a comparison with sections from the uk suggests that the positive excursion belongs to the turneri zone and the succeeding negative excursion falls within the obtusum zone in the deep water belluno basin the negative anomaly occurs in a biogenic chert rich unit recording the onset of mesotrophic conditions in the basin in the platform carbonate successions this major negative carbon isotope excursion is developed within a calcarenitic unit corresponding to the lowest occurrence of the foraminifer paleomayncina termieri this evidence for deepening and transgression across the carbonate platform suggests pre conditioning for drowning hence rather than tectonic subsidence alone environmental factors may have aided the demise of tethyan carbonate platforms during the early jurassic sinemurian age

depositional processes of the zhushadong and mantou formations early to middle cambrian shandong province china roles of archipelago and mixed carbonate siliciclastic sedimentation on cycle genesis during initial flooding of the north china platform to understand the depositional processes and environmental changes during the initial flooding of the north china platform this study focuses on the lower to middle cambrian zhushadong and mantou formations in shandong province china the succession in the jinan and laiwu areas comprises mixed carbonate and siliciclastic deposits composed of limestone dolostone stromatolite thrombolite purple and grey mudstone and sandstone a detailed sedimentary facies analysis of seven well exposed sections suggests that five facies associations are the result of an intercalation of carbonate and siliciclastic depositional environments including local alluvial fans shallowing upward carbonate siliciclastic peritidal cycles oolite dominant shoals shoreface and lagoonal environments these facies associations successively show a transition from an initially inundated tide dominated carbonate platform to a wave dominated shallow marine environment in particular the peritidal sediments were deposited during a large number of depositional cycles these sediments consist of lime mudstone dolomite stromatolite and purple and grey mudstones these shallowing upward cycles generally resulted from carbonate production in response to an increase of accommodation during rising sea level the carbonate production was however interrupted by frequent siliciclastic input from the adjacent emergent archipelago the depositional cycles thus formed under the influence of both autogenetic changes including sediment supply from the archipelago and allogenic control of relative sea level rise in the carbonate factory a low relief archipelago with an active tidal regime allowed the development of tide dominated siliciclastic and carbonate environments on the vast platform siliciclastic input to these tidal environments terminated when most of the archipelago became submerged due to a rapid rise in sea level this study provides insights on how a vast cambrian carbonate platform maintained synchronous sedimentation under a tidal regime forming distinct cycles of mixed carbonates and siliciclastics as the system kept up with rising relative sea level during the early stage of basin development in the north china platform

morphological adaptations of 3 22 ga old tufted microbial mats to archean coastal habitats moodies group barberton greenstone belt south africa microbial life was well established and widespread by the paleoarchean however the degree of evolutionary advancement such as microbial motility intra and inter species interactions phototropism or oxygenic photosynthesis by that time remains highly debated the 3 22 ga moodies group in the barberton greenstone belt bgb south africa are earth s oldest well preserved siliciclastic tidal deposits they exhibit a unique assemblage of microbial mats providing an excellent opportunity to decipher the morphological adaptations of microbial communities to different paleoenvironmental settings the fossil mats are preserved as kerogenous laminations 0 5 1 mm thick that can be traced laterally for 15 km in a 1000 m thick succession of fine to coarse grained tidal sandstones and conglomerates we here present a detailed stratigraphic and depositional facies analysis documenting the association of the three principal mat morphotypes with specific environmental settings 1 planar type in coastal floodplain 2 wavy type in intertidal and 3 tufted type in upper inter to supratidal facies all mat types indicate a flourishing phototrophic biota moreover the tufted morphology suggests an intricate level of coordinated growth commonly known from cyanobacterial mats in modern environments

sedimentology of the paleoproterozoic kungarra formation turee creek group western australia a conformable record of the transition from early to modern earth abstract this paper presents the first detailed sedimentological analysis of the paleoproterozoic kungarra formation the lowermost of three formations comprising the turee creek group in western australia which was deposited across the rise in atmospheric oxygen the great oxidation event or goe and the transition from early to modern earth the data show that the kungarra formation has a gradational conformable lower contact with underlying banded iron formation of the hamersley group and predominantly comprises an upward shallowing succession from deepwater shales and siltstones through rippled fine grained sandstones and stromatolitic carbonates to tidal flat deposits that immediately underlie coastal fluvial deposits of the overlying koolbye formation at the base of the kungarra formation is a gradual transition from alternating units of magnetic green shale and thin units of banded iron formation that pass upsection to units of non magnetic shale and ferruginous chert and grey chert reflecting a gradual loss of iron from the world s oceans accompanying the rise of atmospheric oxygen a falling stage systems tract is recognised above this transition in the hardey syncline area capped by stromatolitic carbonates and a period of exposure marked by an erosional unconformity and carbonate beachrock two glacio eustatic cycles are recognised within the middle to upper parts of the kungarra formation each of which is marked by the rapid onset of falling systems tracts and characterised by falling systems tracts during and following diamictite deposition stratigraphic data are used to infer a depobasin filled by a sediment wedge prograding from southeast to northwest in contrast to previous models of a north northeastward deepening foreland basin the lack of seismites or internal unconformities within the formation precludes a foredeep setting rather deposition is interpreted as having occurred within an intracratonic basin with detritus sourced from erosion of uplifted bedrock to the southeast

gondwana derived microcontinents the constituents of the variscan and alpine collisional orogens abstract the european variscan and alpine mountain chains are collisional orogens and are built up of pre variscan building blocks which in most cases originated at the gondwana margin such pre variscan elements were part of a pre ordovician archipelago like continental ribbon in the former eastern prolongation of avalonia and their present day distribution resulted from juxtaposition through variscan and or alpine tectonic evolution the well known nomenclatures applied to these mountain chains are the mirror of variscan resp alpine organization it is the aim of this paper to present a terminology taking into account their pre variscan evolution at the gondwana margin they may contain relics of volcanic islands with pieces of cadomian crust relics of volcanic arc settings and accretionary wedges which were separated from gondwana by initial stages of rheic ocean opening after a short lived ordovician orogenic event and amalgamation of these elements at the gondwanan margin the still continuing gondwana directed subduction triggered the formation of ordovician al rich granitoids and the latest ordovician opening of palaeo tethys an example from the alps external massifs illustrates the gradual reworking of gondwana derived pre variscan elements during the variscan and alpine tertiary orogenic cycles

from rifting to drifting tectonic evolution of the south alpine upper crust from the triassic to the early cretaceous abstract the tectonic evolution of the south alpine rifted margin is discussed on the base of four palinspastic upper crustal profiles extension related to the movements between adria and europe began in the norian after variscan orogeny late carboniferous to middle permian orogenic collapse and continental scale wrenching from the late triassic to the early liassic stretching was mostly limited to the lombardian basin during this time extension was mainly controlled by four major listric faults symmetrically centred around the late carboniferous early permian collio grabens smaller faults which also started in the norian were progressively de activated during the late triassic after the middle liassic faulting in the lombardian basin gradually ceased and the site of extension shifted westwards i e towards the future site of crustal separation extension was then controlled by a set of west dipping normal faults oceanic crust was formed not later than 157 ma the overall extension along the profile which had a final length of 290 km was 52 km which corresponds to a stretching factor of 1 22 for the whole length of the preserved margin the strain rate is ca 1 10 16 s the sedimentation history suggests that the extension of the south alpine margin was a continuous process from the norian to the middle jurassic the changes in tectonic pattern are related to progressive hardening of the lithospheric segment undergoing slow extension

physico chemical tuning of palaeogeographic shifts bhuj formation kutch india abstract the long standing dilemma between two extremes in palaeogeographic interpretation is resolved for the basal 115 m of the eastern exposures of the lower cretaceous bhuj formation at the top of the hydrocarbon prospective mesozoics of kutch india an explicit record of a mega scale event of relative sea level rise is found sandwiched between two fluvial stratigraphic intervals that amalgamate only at the eastern extremity of the exposure of the formation a localized estuary in the middle had its axis roughly parallel to the pre and post inundation river channels although a tributary made a significant detour variation in the fine sandstone mudstone lithology documents decline in depositional energy in the mid estuary amenable to coal formation sediment within the estuary had been routed through both the ends palaeocurrent turning shore parallel only at the estuary mouth exception arises in case of some isolated lenses of very poorly sorted and coarse grained deposits depicting flash floods in the tributary burrow characteristics change delicately in response to the inferred changes in the depositional scenario along the estuary resting on a coarsening upward ramp the initially fining and then coarsening upward estuarine succession is prograding though not steadily it was wave dominated but tide left imprint behind the estuary mouth bar gaining in intensity because of valley constriction macroscale changes in relative sea level perhaps eliciting local tectonics are recorded in the transient hysteresis in the stratigraphic trend with or without palaeocurrent diversions the fluvial stratigraphic intervals encasing the marine interval have in terms of architectural elements many commonalities but also some significant disparities the latter indicates channel meandering in the pre inundation period and braiding after inundation unlike the marine sandstones bar channel sandstones of the riverine deposits are distinctly less sorted bimodal even polymodal in grain size distribution mineralogical composition identifies the sandstones as craton derived but their geochemical distinctions point to variation in parent rock composition under the maze of palaeogeographic overprints

tidal rhythmites in offshore shale a case study from the palaeoproterozoic chaibasa shale eastern india and implications abstract tidal rhythmites have been documented from modern continental shelves and distal offshore settings in significant contrast to their modern counterparts sedimentological studies of ancient tidal rhythmites formed in distal offshore settings and quantification of tidal rhythms encoded therein are however scarce this paper presents sedimentological analysis of vertically accreted tidal rhythmites from the palaeoproterozoic chaibasa shale facies in india and quantification of their tidal rhythms the facies characteristics of the chaibasa shale coupled with harmonic analysis of the laminae thicknesses of the sandstone inter layers corroborate a distal shelf palaeogeography for the generation of the vertically accreted tidal rhythmites the latter are the distal counterparts of laterally accreted tidal bundle deposits well preserved within the shallow marine chaibasa sandstones the number of lunar days in a synodic month 23 estimated from the chaibasa shale facies is however considerably lower than that estimated from the chaibasa sandstone facies 32 suggesting that the tidal record encoded from the chaibasa shale facies is incomplete

paleo to mesoarchean polymetamorphism in the barberton granite greenstone belt south africa constraints from u pb monazite and lu hf garnet geochronology on the tectonic processes that shaped the belt the barberton granite greenstone belt bggb of south africa is an exceptionally well preserved meso paleoarchean metamorphic supracrustal belt one of only a few in the world studies of metamorphism in the bggb have considerable potential to advance our understanding of tectonic processes in the archean crust two current hypotheses persist to explain the origin of amphibolite facies metamorphism in the southern bggb the first interprets these rocks to be the consequence of accretionary tectonics while the second proposes a dome and keel vertical tectonic process driven by sinking of greenstone layers and the doming of the underlying granitoid crust in this study metamorphic pressure temperature p t analysis has been combined with garnet lu hf and monazite u pb geochronology to directly date the amphibolite facies metamorphism within the stolzburg terrane of the bggb a garnet biotite chlorite bearing sample yields a lu hf garnet age of 3233 17 ma and a garnet staurolite kyanite bearing sample produces a u pb monazite age of 3191 9 ma whereas an andalusite kyanite bearing sample produces a u pb monazite age of 3436 18 ma phase diagrams and garnet compositional modeling produce a clockwise p t evolution with rocks reaching peak p t conditions of 8 5 kbar and 640 c for the ca 3200 ma event and minimum peak p t conditions of 4 5 kbar and 550 c for the ca 3435 ma event the duration of metamorphism for the ca 3200 ma event is estimated to be 50 20 m y based on differences in age between u pb and lu hf systems and durations needed to fit models of diffusionally modified garnet chemical zoning similarly shaped p t paths over the stolzburg terrane indicate that the metamorphism occurred in response to crustal thickening due to an accretionary tectonic process thus the stolzburg terrane constitutes an orogenic core exhumed along the komati fault

late mississippian prodeltaic rhythmites in the appalachian basin a hierarchical record of tidal and climatic periodicities abstract the pride shale is a 60 m thick succession of thinly interlaminated dark shales siltstones and fine grained sandstones within the bluestone formation upper mississippian of southern west virginia a hierarchy of submillimeter to meter scale cycles in this succession preserves a spectrum of tidal and climatic periodicities submillimeter thick fine grained sandstone shale or siltstone shale couplets are interpreted as the product of suspension settling associated with individual ebb tidal flows up to 17 couplets systematically thicken and thin within millimeter to centimeter scale bundles interpreted as neap spring tidal cycles successive neap spring cycles display a thick thin relationship interpreted to reflect unequal perigean and apogean tides the fine scale and abbreviat d character of these microlaminated rhythmites is suggestive of a distal subtidal setting wherein subordinate daily and neap and apogean ebb flows were generally of insufficient strength to transport sand and silt decimeter scale cycles in the pride shale are manifested by the progressive upward thickening and thinning of up to 18 millimeter to centimeter thick neap spring cycles this bundling is interpreted to reflect a climatic monsoonal signal which defines that part of the year when adequate fluvial tidal discharge forced suspended sediment into the basin lastly a multi year cyclicity is recognized in thick exposures where 17 22 annual beds display a crude upward thickening and thinning within meter scale bundles this bundling is interpreted to reflect the 18 6 year lunar odal cycle with the thick annual beds representing years during which the inclination of the lunar orbital plane favored increased tidal amplitudes decompacted thicknesses of cycles indicate that accumulation rates for the pride shale typically ranged between 3 and 20 cm per year but reached over 60 cm per year where sandy rhythmites developed as the marginal infill of large slump scars the stratigraphic relationships and sedimentation rates for the pride shale are consistent with paleontological evidence of rapid sedimentation in turbid waters seaward of multiple points of fluvial discharge the pride shale is interpreted as an extensive prodeltaic deposit which in places records hundreds of years of nearly continuous tidal sedimentation along the eastern margin of the appalachian basin

implications of lunar orbital periodicity from the chaibasa tidal rhythmite india of late paleoproterozoic age harmonic analysis of the sandstone foreset laminae thickness series from the chaibasa tidal rhythmite india clearly shows that a normal semidiurnal tidal system with synodic month of 32 lunar days was in effect during the late paleoproterozoic 2100 1600 ma the minimum number of solar days in a lunar sidereal month was 31 published quantitative tidal rhythmite data of others in combination with data derived from the chaibasa tidal rhythmite indicate long term stability of the lunar orbit and progressive increase in the earth moon distance during the proterozoic

temporal distribution of diastems in deposits of an open coast tidal flat with high suspended sediment concentrations abstract based on field observations of the preservation potential and genesis of couplets and small sequences diastems occur within tidal flat deposits at scales of semi tidal daily monthly and yearly intervals thus tidal flat deposition is riddled with more diastems of different scales than previous assumptions units that are apparently complete when examined at longer time scales actually contain many diastems when examined at a shorter time scale diastems within tidal flat deposits are generated not only by high magnitude storm waves which occur during typhoon seasons but also by daily erosion produced by tides and weak waves during calm weather seasons the missing intervals in diastems generated by storm waves can be several days to several years preservation potential of storm generated small sequences is of the order of one third diastems generated by erosion by tides and weak waves can have spans from a semidiurnal cycle to several days they are easily overlooked because of the low magnitude destruction and lack of distinctive sedimentary features net erosion by tides and weak waves is unexpectedly increased by day to day processes alternations of sandy and muddy laminae are related to tidal rhythm but individual laminae can be separated by a significant diastem documentation of erosion by tides and weak waves under normal non typhoon conditions is the principal focus of this report

sedimentological consequences of arc arc collision an example from mio pliocene miura group japan abstract this paper presents brief sedimentological inventory of the misaki and the overlying hasse formation constituting the miura group based on observations made at jogashima island miura peninsula and infers the nature of the stratigraphic transition from tectonic viewpoint the lower part of the misaki formation is made of very coarse to coarse grained scoriaceous normally graded sandstones fine grained sandstones siltstones and mudstones and indicates a deep sea submarine canyon depositional setting there is no evidence of storm reworking shallow marine processes in the lower parts of the misaki formation at least in the jogashima island as suggested by stow et al 1998 however the upper part of the misaki succession formed in a shallow marine depositional setting the overlying hasse formation characterized by brownish coloured very coarse to coarse grained large scale trough cross stratified very poorly sorted sandstones very poorly sorted polymictic and matrix dominated mass flow conglomerates with siltstone fine grained sandstone clasts derived from the underlying misaki formation and occasional reverse grading in significant contrast to the underlying misaki formation the hasse formation lacks very fine grained sandstone siltstone mudstone facies unlike the tholeiitic basalt composition of the lapilli and pebbles of the misaki sandstone beds the scoriaceous lapilli and pumiceous beds of the hasse formation are of calc alkaline composition the hasse sedimentation probably took place in much shallower paleogeography compared to the underlying misaki formation most probably in an alluvial fan braided fluvial setting the misaki hasse stratigraphic contact is very sharp and erosional and represents a subaerial unconformity i e depositional sequence boundary our sedimentological data from the jogashima island clearly indicate progressive shallowing of the depositional setting during the terminal phase of the misaki sedimentation and much abrupt shallowing across the misaki hasse transition possibly as a consequence of ongoing collision between the izu bonin and honshu arcs

reassessment of archean crustal development in the barberton mountain land south africa based on u pb dating this paper presents u pb ages for 23 samples from the barberton mountain land an archean granite greenstone terrain in the kaapvaal craton of south africa a reexamination of the geology of this area in the light of previous u pb dating and the new ages indicates that much of its deformation can probably be accounted for by a single short lived compressional event within the time span 3230 3215 ma which was synchronous with deposition of the moodies group and the upper part of the fig tree group sediments this event may have been responsible for thrusting of much older sequences in the onverwacht group including slivers of 3 54 ga old gneiss circa 3 47 ga old komatiitic and tholeiitic sequences and circa 3 45 ga old felsic sequences key constraints on the timing of deformation are previously determined 3227 3225 ma ages for detrital zircons in thrusted units of the fig tree group a 3229 4 3 ma age for a deformed porphyry which is pre or synthrusting a previously determined 3227 3 ma age for an undeformed porphyry in an inferred thrust fault 3227 1 ma ages for both the kaap valley pluton and an ignimbrite in the stolzburg syncline both of which predate regional upright folding and a 3216 2 ma age for the dalmein pluton which appears to cut regional upright ne sw trending folds in the kromberg syncline part of the final phase of deformation associated with regional compression areally extensive granitoid sheets and syenogranitic plutons were subsequently emplaced into the barberton region at about 3105 ma the linear configuration of the syenogranitic plutons which are also aligned with the gabbroic usushwana complex as well as the geometry of the granitoid sheets suggests that the circa 3105 ma magmatism was caused by incipient rifting around a nw se trending crustal fracture this episode was probably coeval with a late regional transtensional phase of deformation recorded in the greenstone belt some of the above interpretations are in conflict with previous models for early development of the barberton greenstone belt a 3352 6 ma age from a metagabbro which is comagmatic with a proposed ultramafic sheeted dike complex is over 100 m y younger than the probable age of volcanic rocks which host the dikes this conflicts with the suggestion that much of the onverwacht group comprises an ophiolitic section obducted in an intraoceanic setting at circa 3 45 ga that partially melted to form trondhjemitic magmas which intruded along active thrust faults present data suggest that despite its antiquity and the diversity of ages and lithologies found within it the barberton greenstone belt can generally be understood in terms of actualistic tectonic processes at convergent margins

pelagic carbonate platforms in the geologic record their classification and sedimentary and paleotectonic evolution drastic differences in thickness and abrupt lateral facies changes in synrift and postrift pelagic sequences usually indicate structural control over deposition although the highs and the basins in pelagic carbonate systems have long been recognized in ancient rifted continental margins relatively little detailed information has been available on facies transitions between the two and on the geometries of pelagic sediment bodies outcrops in the umbria marche apennines central italy provide new constraints for jurassic paleogeographic reconstructions allowing for the development of models for these depositional systems pelagic carbonate platforms pcps are submarine highs that are drowned fragments of an ancestor regional peritidal carbonate platform pcps can be horsts or crests of rotated blocks the extensional regime and drowning history exert a major control over the pcp type and over the composition of sediment which fills inter pcp basins given the very low rates of pelagic sedimentation a few mm 1000 yr the effects of faulting on submarine topography are drastic block tilting is of great importance creating pelagic carbonate ramps that are the source area of most of the gravity flow deposits in half grabens excessively rapid tilts cause nondeposition in horst and graben settings on the other hand basins are sediment starved and there are comparatively only minor gravity flows ma s transport there is mostly in the form of collapse of platform margins the margins of pcps are erosional during most of pcp history becoming depositional when adjacent basins are filled stepped margins develop through fault induced reduction of the pcp area back stepping

3 2ga eolian deposits from the moodies group barberton greenstone belt south africa implications for the origin of first cycle quartz sandstones abstract the 3 2 ga moodies group in barberton greenstone belt south africa contains the oldest recognized evidence for eolian processes on earth these eolian facies indicate that significant wind regimes existed in the archean atmosphere eolian deposits are developed in the lower moodies group in the central part of the belt and consist of stacked inversely graded strata ranging in thickness from 2 to 10 mm individual strata consist of fine to medium grained quartz sandstone at the base that passes vertically into very coarse to coarse grained quartz sandstone strata make up cross bed sets up to 3 5 m thick sets of wind ripple strata are either tabular tangential or in the form of broad troughs this type of inversely graded stratification is the product of wind ripple migration the coarse grain size of the sediment combined with the low angle of inclination of the strata is best interpreted as the product of sand sheet or dune plinth preservation based on the geometry of eolian set boundaries dunes were probably simple barchan form the tens of meters thick eolian deposits are underlain by braided stream deposits composed of subfeldspathic pebbly sandstones the vertical change from braided stream subfeldspathic sandstones to eolian quartz arenites highlights the underappreciated capacity of eolian processes to generate first cycle quartz sandstones on landscapes pre dating the advent of land vegetation

salt tectonics in the sw alps italy france from rifting to the inversion of the european continental margin in a context of oblique convergence abstract the sw alps result from the inversion of the european continental margin during the oblique convergence between europe and adria since the cretaceous the orogenic deformation is controlled by two factors the inherited sedimentary and structural record and the geodynamic interaction between the two plates in this paper we present a stratigraphic and structural analysis of the external sw alps ventimiglia menton area in order to define the sedimentary and deformational geometries of the chain and to reconstruct the evolutionary history the field data highlight the preeminent role played by inherited salt structures which derive from the depositional history experienced by the european margin since the mesozoic onwards from late triassic to jurassic evaporites and carbonates deposited as a response to the thetyan rifting the following emplacement of the cretaceous flysch and of the eocene foreland basin succession was strongly influenced by the extensionally triggered salt diapirism and by the interactions with deformations connected to the pyrenees dynamics the resulting geologic discontinuities i e diapir induced highs and basins inherited normal and trasform faults strongly influenced the successive oligo miocene evolution of the belt in the study area observed changes in the thrusts and folds kinematics are considered as the results of rotation during their approaching to inherited highs furthermore the overturning of thrusts and folds in the front of the diapiric flanks are associated with the progressively salt squeezing into the anticlines cores promoted by ongoing alpine compression finally the kinematic data from the study area show radical differences in the tectonic transport direction with respect to the rest of the sw alps nw to w ward in the ventimiglia menton area s to sw ward in provence and ligurian alps this difference is interpreted to be caused by the relative motions of crustal blocks dominated by transpressive tectonics in the frame of the oligo miocene western mediterranean geodynamics

depositional and tectonic setting of the archean moodies group barberton greenstone belt south africa the 3 22 3 10 ga old moodies group uppermost unit of the swaziland supergroup in the barberton greenstone belt bgb is the oldest exposed well preserved quartz rich sedimentary sequence on earth it is preserved in structurally separate blocks in a heavily deformed fold and thrust belt north of the inyoka fault moodies strata reach up to 3700 m in thickness detailed mapping correlation of measured sections and systematic analysis of paleocurrents show that the lower moodies group north of the inyoka fault forms a deepening and fining upward sequence from a basal alluvial conglomerate through braided fluvial tidal and deltaic sandstones to offshore sandy shelf deposits the basal conglomerate and overlying fluvial facies were derived from the north and include abundant detritus eroded from underlying fig tree group dacitic volcanic rocks shoreline parallel transport and extensive reworking dominate overlying deltaic tidal and marine facies the lithologies and arrangement of moodies group facies sandstone petrology the unconformable relationship between moodies strata and older deformed rocks presence of at least one syndepositional normal fault and presence of basaltic flow rocks and airfall fall tuffs interbedded with the terrestrial strata collectively suggest that the lower moodies group was deposited in one or more intramontane basins in an extensional setting thinner moodies sections south of the inyoka fault generally less than 1000 m thick may be correlative with the basal moodies group north of the inyoka fault and were probably deposited in separate basins a northerly derived southward thinning fan delta conglomerate in the upper part of the moodies group in the central bgb overlies lower strata with an angular unconformity this and associated upper moodies conglomerates mark the beginning of basin shortening by south to southeast directed thrust faulting along the northern margin of the bgb and suggest that the upper moodies group was deposited in a foreland basin timing orientation and style of shortening suggest that this deformation eventually incorporated most of the bgb into a major fold and thrust belt

transpressional tectonics and carboniferous magmatism in the limousin massif central france structural and 40ar 39ar investigations new structural microstructural and 40ar 39ar data from the nw massif central france provide additional constraints on the timing and tectonic setting of late variscan granite magmatism previous studies had emphasized the role of late orogenic extension in the emplacement of granite plutons in the limousin region in contrast the new data set is consistent with syntectonic emplacement of magma in a dextral simple shear active from 350 to 300 ma in a transpressional regime as an alternative hypothesis to late orogenic extension we propose that magmas migrated into tensional bridges between active p shears associated with a lithospheric shear zone comparable to a pop up structure the galician region in the western end of the ibero armorican tectonic arc exhibits major left lateral ductile shear zones which can be interpreted as conjugate structures to the limousin and armorican shear zones citation ge belin a m brunel p monie m faure and n arnaud 2007 transpressional tectonics and carboniferous magmatism in the limousin massif central france structural and 40ar 39ar investigations

u pb zircon ages for post variscan volcanism in the ligurian alps northern italy abstract ages of permian volcanic rocks from the ligurian brianconnais domain western italian alps have been determined by laser ablation inductively coupled plasma mass spectrometry u pb dating of zircon three major volcanic units yielded zircons that were dated calc alkaline rhyolites 285 6 2 6 ma andesites with inherited cores yielded ages c 476 ma and older and voluminous rhyodacites rhyolites 272 7 2 2 ma following an amagmatic sediment starved time gap of c 14 ma alkaline volcanic activity is recorded at the top of the sequence by k alkaline rhyolites dated at 258 5 2 8 ma the ligurian segment of the southern variscan belt records transtensional and then extensional tectonics associated with the volcanic activity the switch from calc alkaline to alkaline activity corresponds to the transition from a post orogenic to an anorogenic setting in the southern variscides it may represent progressive and increasing delamination of the continental lithosphere accompanied by partial melting of the lithospheric mantle supplementary material technical and data acquisition parameters u th pb isotope analyses and calculated ages of zircons from samples and standard and trace element compositions of selected zircons are available at http www geolsoc org uk sup18322

seismic quiescence in the western hellenic arc may foreshadow large earthquakes south of crete the seismicity rate was constant in space and time between 1950 and 1978 but in the western hellenic trench the rate was the same as that south of crete until 1962 whereupon it decreased by 80 we now suggest that the anomaly constitutes a warning of large earthquakes within the coming decade

chronology of early archaean granite greenstone evolution in the barberton mountain land south africa based on precise dating by single zircon evaporation abstract we report precise 207 pb 206 pb single zircon evaporation ages for low grade felsic metavolcanic rocks within the onverwacht and fig tree groups of the barberton greenstone belt bgb south africa and from granitoid plutons bordering the belt dacitic tuffs of the hooggenoeg formation in the upper part of the onverwacht group yield ages between 3445 3 and 3416 5 ma and contain older crustal components represented by a 3504 4 ma old zircon xenocryst fig tree dacitic tuffs and agglomerates have euhedral zircons between 3259 5 and 3225 3 ma in age which we interpret to reflect the time of crystallization a surprisingly complex xenocryst population in one sample documents ages from 3323 4 to 3522 4 ma we suspect that these xenocrysts were inherited during the passage of the felsic melts to the surface from various sources such as greenstones and granitoid rocks now exposed in the form of tonalite trondhjemite plutons along the southern and western margins of the bgb and units predating any of the exposed greenstone or intrusive rocks several of the granitoids along the southern margin of the belt have zircon populations with ages between 3490 and 3440 ma coeval with or slightly older than onverwacht felsic volcanism while the kaap valley pluton along the northwestern margin of the belt is coeval with fig tree dacitic volcanism these results emphasize the comagmatic relationships between greenstone felsic volcanic units and the surrounding plutonic suites some of the volcanic and plutonic units contain zircon xenocrysts older than any exposed rocks these indicate the existence of still older units possibly stratigraphically lower and older portions of the greenstone sequence itself older granitoid intrusive rocks or bodies of older unrelated crustal material our data show that the onverwacht and fig tree felsic units have distinctly different ages and therefore do not represent a single tectonically repeated unit as proposed by others unlike the late archaean abitibi greenstone belt in canada which formed over about 30 ma exposed rocks in the bgb formed over a period of at least 220 ma the complex zircon populations encountered in this study imply that conventional multigrain zircon dating may not accurately identify the time of felsic volcanic activity in ancient greenstones a surprising similarity in rock types tectonic evolution and ages of the bgb in the kaapvaal craton of southern africa and greenstones in the pilbara block of western australia suggests that these two terrains may have been part of a larger crustal unit in early archaean times

climatic and geochemical implications of archean pedogenic gypsum in the moodies group 3 2 ga barberton greenstone belt south africa abstract lithic sandstones of braided fluvial to supratidal facies in the paleoarchean moodies group 3 22 ga barberton greenstone belt south africa include several regionally traceable units with common to abundant in places rock forming nodular concretions of megaquartz pseudomorphs after gypsum barite and calcite concretionary accumulations are stratiform and commonly associated with aqueously reworked fine grained tuffaceous sediment of originally rhyodacitic composition and can grow to fist sized agglomerates in crusts tens of m in lateral extent weathering of tuffaceous material and feldspar delivered alkali cations such as ca ba and k while carbonates were likely supplied by silicate weathering of mafic to ultramafic volcanic rocks during exposure to a co2 rich atmosphere sulfate ions were partly delivered by oxidative pyrite dissolution which may have included microbial and abiotic disproportionation of volcanic s or so2 concretionary growth apparently took place under pedogenic to early diagenetic conditions within unconsolidated granular sediment in the vadose zone dominated by seasonal fluctuations of the groundwater level under evaporitic conditions the concretions likely represent the oldest terrestrial evaporites known to date and form part of the oldest known compound paleosols their formation and composition constrain the local occurrence of sulfate in the archean atmo and hydrosphere their interaction with the emerging biosphere archean weathering regime local climate and vadose zone hydrodynamics

quantifying the oldest tidal record the 3 2 ga moodies group barberton greenstone belt south africa comment and reply eriksson and simpson 2000 1 claimed that the moodies tidal data demonstrate the potential for constraining the lunar orbital periods and orbital shape during the archean their claim however will remain undersubstantiated until the following issues are clarified first figure 5a of

combined tide and wave influence on sedimentation of lower gondwana coal measures of central india barakar formation permian satpura basin the coal bearing barakar succession of the satpura basin is typical of the gondwanan coal basins of peninsular india in that it has previously been interpreted as continental in origin the succession comprises three main facies associations which are documented within this paper medium to fine grained muddy sandstone deposits of 5 75 m thickness are reinterpreted as tidally influenced delta deposits mudstone deposits of 3 20 m thickness with subordinate sandstones coals and carbonaceous shales are reinterpreted as delta top deposits and medium to coarse sandstones of 3 38 m thickness are interpreted as braided delta top channels the evidence for tidal influence arises from documentation of bidirectional cross strata tidal bundles tidal rhythmites and periodic variation in foreset thickness the recognition of tidal deposits indicates marine depositional conditions and significantly changes existing palaeogeographical models this in turn has important implications for our understanding of the depositional setting and distribution of the permian coals that occur across much of the southern supercontinent furthermore to the best of the authors9 knowledge coal bearing tidal delta deposits have not previously been described from continental interior basins