tectono sedimentary evolution of the bowland basin n england during the dinantian the bowland basin is a ne sw trending sedimentary basin lying between the askrigg bowland high to the n and nw and the central pennine high to the se the basin was initiated in late devonian tournaisian times sediment thickness and facies variations within the dinantian succession show marked asymmetry on both a basin wide and intra basin scale as a result of approximate nw se to n s extension across normal faults thickening of the sedimentary sequence from ne to sw over much of the basin resulted from fault controlled extension along the se margin of the basin with downthrow to the nw giving the basin a half graben character extension occurred in two distinct episodes marked by basin wide debris flow and sedimentary slide slump deposits during the late chadian early arundian the simple half graben became modified by a series of ne sw trending antithetic and nw se trending transfer faults associated with local unconformities and marked lateral thickness and facies variations this interval marks the transition from carbonate ramp to slope sedimentation and a temporary halt in carbonate supply to the basin the second episode of extension the late asbian early brigantian marks the break up of the northern basin margin ending major carbonate deposition within the basin reactivation of these structures at the end of the carboniferous created the ribblesdale fold belt as a result of nw se to n s compression transpression application of this research to areas surrounding the bowland basin has led to the recognition of additional shelf basins the orientation of which suggests control by normal and transfer fault systems discussion and

on diagenesis dolomitisation and mineralisation in the irish zn pb orefield marine calcite cementation and lithification of carboniferous carbonate sediments hosting zn pb mineralisation in the irish orefield occurred at or near the seafloor a relatively early fine grained grey replacive dolomite preferentially developed in micrite is widely developed in the waulsortian limestone formation the main host to mineralisation and is pervasive in the southeastern midlands in proximity to the leinster massif this dolomite formed after the first four main stages of calcite cementation but probably also developed within tens of metres of the seafloor as evidenced by incorporation of clasts of dolomite in intraformational sedimentary breccias later coarse grained white dolomite preferentially replaced coarser components of the waulsortian limestone and infilled residual vuggy porosity whilst some of this coarse dolomite may be related to the fine replacive dolomite event a common spatial association with fault zones coupled with primary fluid inclusion data suggest that a significant proportion of this phase precipitated during the onset of fault controlled subsidence and widespread hydrothermal circulation within the irish midlands area fluids up to 250 c and 10 15 wt nacl equivalent sourced from a lower palaeozoic basement equilibrated fluid reservoir infiltrated the carbonate sequence via faults and fractures the more localised development of dolomite cemented breccias white matrix breccias that are frequently associated spatially with mineralisation was a consequence of the increased focusing of these hydrothermal fluids ore formation was broadly synchronous with development of the white dolomite breccias but only happened where mixing occurred between the hydrothermal ore fluids and localised near surface reservoirs of low temperature h2s rich brine in the waulsortian this process led to the precipitation of a distinctive black dolomite that forms a broad halo to massive sulphides although ore stage sulphides postdate significant diagenesis of the host rocks and often display epigenetic textures the fact that much of the cementation occurred soon after carbonate deposition means that mineralisation does not have to have formed after significant burial in fact the occurrence of clasts of hydrothermal dolomite and sulphides in intraformational debris flow breccias is only consistent with mineralising processes occurring in the near seafloor environment relatively soon after host rock deposition the regional development of a distinctive pink dolomite associated with faults and fractures was a post ore event and is considered to mark a regional brine migration linked to the onset of the variscan orogeny the development of this new tectonic and flow regime may have been responsible for the cessation of economic mineralisation in ireland

organic buildups and reefs on the palaeozoic carbonate platform margin pechora urals russia abstract in the pechora urals palaeozoic organic structures are widespread and are represented by various types from small bioherms to large barrier reefs which can be observed throughout upper ordovician lower permian strata in the pre orogenic history of palaeozoic carbonate sedimentation and reef growth three stages are distinguished each stage is characterized by a distinct reef geometry growth rate and depositional setting 1 the reefs of the lower palaeozoic ashgillian lower emsian stage were restricted to the outer shelf margin and they were wave resistant stromatolite rich frameworks except for upper llandoverian knoll and patch reefs the total thickness of the lower palaeozoic reefs is 60 1200 m 2 the middle palaeozoic middle frasnian lower tournaisian organic buildups are quiet water carbonate bank type structures generally between 300 and 700 m thick they were formed on both the outer and the inner shelf margin however they are better developed and more characteristic of the latter setting stromatoporoid microbial and microbial associations form the main buildup facies separated by bedded interbuildup sediments the upper palaeozoic upper visean sakmarian organic structures are represented by both isolated wave resistant shelf margin reefs up to 200 m thick and quiet water carbonate banks up to 330 m thick these buildups were located in the outer and inner shelf margin framework builders were mainly branching and platy stromatoporoids associated with stromatolites in the reefs and calcified microbes and phylloid algae in the carbonate banks the distribution and geometry of the buildups was mainly determined by regional tectonic events caused by the passive to active margin transition of the northeastern european platform the size of the reefs depended on the magnitude and duration of sea level fluctuations

coastal erosion processes timing and magnitudes at the bluff toe abstract five lake erie bluffs one interlaminated clay and silt three clay rich diamicts and one shale were surveyed at about 2 week intervals and after wind storms for up to 5 years erosion of the bluff toes along this low energy coast occurred during northeast wind storms which produced surges of up to 1 m and surf zone waves of up to 1 2 m wave impact and or uprush caused quarrying which removed most of the toe material and abrasion there were from 1 to 23 erosion events sites with maximum magnitudes of erosion ranging from 12 to 55 cm event timing and magnitude were linked to erodibility maximum water level storm surge storm duration and beach width a threshold maximum water level and a threshold surge were necessary for erosion at these thresholds the beach was submerged and wave energy was directly expended on the toe erosion did not take place when there was shorefast ice or when debris slopes shielded the toe from waves the originally cohesive toe materials are easily eroded when they weather to an essentially noncohesive state wave erosion is the crucial erosion process removal of material from the toe prevents the development of a stable slope

ploughing boulders along shorelines with particular reference to the st lawrence estuary abstract ploughing boulders are defined as large stones moved by drift ice with a ploughing action into the substrate leaving a linear depression on the back and building a frontal push ridge they are commonly found on unconsolidated tidal flats and on rock shore platforms along cold region shorelines in the marine lacustrine and fluvial environments it is an erosional process of great significance particularly for consolidated substrates a total of 176 ploughing boulders were measured in eighteen localities along the st lawrence estuary the largest boulder weighed 176 tons and was moved 3 m while a 50 t boulder was moved 40 m on shore platforms cut in shales one boulder 49 t has scoured a depression 19 m long and up to 40 cm deep and built a frontal ridge 40 cm high along the st lawrence estuary about 95 of ploughing boulders were moved seaward by ice floes entrained by ebb currents

ice action on lakeshores near schefferville central quebec labrador canada ice push action causes considerable shore and vegetation damage on lakes located 10 40 km southeast of schefferville in central quebec labrador the damage occurs mainly on shores of large lakes

trace metals and organic carbon in sediments of the northeastern chukchi sea abstract concentrations of al fe and selected trace metals as ba be cd cr cu hg mn ni pb sb se sn v zn in surface sediments from the northeastern chukchi sea necs varied considerably as a function of sediment texture i e grain size however essentially all metals when normalized to al were present at natural background values total organic carbon content ranged from 0 06 1 56 with a marine origin for at least two thirds of the organic matter at each station based on 13c values and c n ratios recent sedimentation rates from 137cs and 210pb dating were 0 03 0 14 cm yr 1 corresponding vertical distributions for most metals in age dated sediment cores showed 100 yr records of uniform metal al ratios including pb and hg concentrations of as mn and cd were modified in surface sediments at a few stations by early chemical diagenesis surveys around two exploratory oil and gas drilling sites that were occupied in 1989 showed that ba concentrations were as high as 10 000 g g 1 within 200 m of one drilling site relative to background values of 700 g g 1 barium enrichment was from barite a drilling mud additive that was discharged to the seafloor above background concentrations of cu hg pb and zn also were found in sediments from 3 4 stations within 200 m of the two drilling sites at present sediments in the necs are essentially pristine with respect to trace metals of anthropogenic origin excluding small areas around drilling sites these data should be of value for detecting and tracking future chemical changes in the sediments of the necs particularly in light of planned oil and gas exploration and production as well as environmental changes that may be associated with climate change

the significance of tournaisian tectonism in the dublin basin implications for basin evolution and zinc lead mineralization in the irish midlands abstract recently acquired seismic reflection data combined with detailed subsurface stratigraphic analysis core analysis and gamma ray logs reveal a new view of lower carboniferous stratigraphy and tectonism in ireland seismic stratigraphic relationships and stratal thickness variations within tournaisian units indicates that the ballinalack high and associated faulting was produced by tectonism during the mid to late tournaisian moathill event 348 ma a second major tectonic event dominated by regional subsidence rather than faulting occurred during the lower visean tober colleen event 345 ma each of these tectonic events was associated with major subsidence in the basin producing strong transgressions within the stratigraphy we suggest that the late tournaisian moathill event was responsible for producing the structural setting of the ballinalack and other zn pb deposits in the irish midlands the suggested earlier timing of fault movement in the basin has implications for arguments about the origin of irish type zn pb deposits and the necessity or not for having active faulting during mineralization

a gravity and magnetic interpretation of the structure of the irish midlands and its relation to ore genesis regional gravity and magnetic data from the irish midlands have been studied in an attempt to map the structures within and beneath the lower carboniferous limestones the magnetic data suggest that the precambrian crystalline basement is at a depth of 3 4 km and is overlain by ordovician volcanics of varying magnetization a fourier analysis of the gravity field has been used to construct a residual gravity map which represents principally the gravity effect of shallow sources these sources are probably the topographic variations of dense ordovician volcanics beneath a less dense succession of ordovician to carboniferous sediments the residual gravity clearly shows the presence of a series of linear volcanic blocks and sedimentary troughs trending ne sw the major mineralized zones in the area all occur close to the margins of these troughs this investigation indicates that the initial position of the midland plain was controlled by caledonide factors some of which modified the later subsidence which we attribute to hercynian plate margin processes the genesis of the major ore bodies is probably associated with de watering of the shale filled troughs the subsequent concentration of metal bearing fluids along the trough margins and their deposition in relatively unloaded carbonate host rocks on the up standing blocks

fluid circulation and fault and fracture related diagenesis in mississippian syn rift carbonate rocks on the northeast margin of the metalliferous dublin basin ireland

dolomitization of the waulsortian limestone lower carboniferous in the irish midlands the waulsortian limestone lower carboniferous of the southern irish midlands is dolomitized pervasively over a much larger region than previous studies have documented this study indicates a complex multistage multiple fluid history for regional dolomitization partially and completely dolomitized sections of waulsortian limestones are characterized by finely crystalline 0 01 0 3 mm planar dolomite planar replacive dolomite is commonly followed by coarse 0 5 mm nonplanar replacive dolomite and pervasive void filling saddle dolomite cement is frequently associated with zn pb mineralization planar dolomite has average 18o and 13c values pdb of 4 8 and 3 9 respectively these are lower oxygen and slightly higher carbon isotope values than averages for marine limestones in the waulsortian 18o 2 2 13c 3 7 mean c and o isotope values of planar replacive dolomite are also distinct from those of nonplanar and saddle dolomite cement 7 0 and 3 3 7 4 and 2 4 respectively fluid inclusions indicate a complex history involving at least three chemically and thermally distinct fluids during dolomite cementation the petrography and geochemistry of planar dolomites are consistent with an early diagenetic origin possibly in equilibrium with modified carboniferous sea water where the waulsortian was exposed to hydrothermal fluids 70 280 c planar dolomite underwent a neomorphic recrystallization to a coarser crystalline planar and nonplanar dolomite characterized by lower 18o values void filling dolomite cement is isotopically similar to nonplanar replacive dolomite and reflects a similar origin from hydrothermal fluids this history of multiple stages of dolomitization is significantly more complex than earlier models proposed for the irish midlands and provides a framework upon which to test competing models of regional vs localized fluid flow

diagenetic versus biotic accretionary mechanisms of bryozoan sponge buildups lower silurian anticosti island canada abstract lower silurian mud rich fenestrate bryozoan sponge buildups of anticosti island quebec canada display facies ranging from fenestrate bryozoan cementstone to crinoid and fenestrate bryozoan hash mudstone wackestone with distinctive polymud fabric sponge spicules and stromatactis these buildups consist of a massive core with thinner stratiform counterparts that show no significant compositional variation raising the question as to how such a deposit could have accreted these features are similar to those mentioned for many paleozoic carbonate mounds in particular the lower carboniferous waulsortian or waulsortian type mounds here the combination of petrographic fluorescence spectrometric and geochemical evidence carbon and oxygen stable isotopes rare earth elements yttrium shows that the accretionary mechanisms of the anticosti buildups were the results of marine cement precipitation near the sea floor for the fenestrate cementstone facies and of early calcification of sponge derived organic matter organogenic lithification within the sediment for the crinoid and fenestrate bryozoan hash mudstone wackestone facies thus the accretionary mechanisms of anticosti fenestrate bryozoan sponge buildups are essentially diagenetic and conventional mechanisms invoked for reef growth such as frame building or sediment trapping or binding based on the preserved fauna or flora do not constitute an appropriate explanation for such paleozoic mud rich buildups these conclusions may well shed light on the more general ongoing debate as to the origin and accretionary mechanisms of carbonate mudmounds

sedimentation rates and growth potential of tropical cool water and mud mound carbonate systems carbonate fixation in the ocean proceeds in three basic modes abiotically biotically induced with organic trigger and biotically controlled where organisms determine timing location and composition of the product the three modes combine in a variety of ways to produce carbonate sediment when viewed on the scale of formations and global facies belts three benthic carbonate production systems or factories emerge 1 the tropical shallow water system dominated by biotically controlled mainly photoautotrophic and abiotic precipitates 2 the cool water system dominated by biotically controlled mainly heterotrophic precipitates and 3 the mud mound system dominated by abiotic and biotically induced mainly microbial precipitates the sedimentation rates of all three factories decrease as the time span of observation increases this scaling trend is not just an artifact of ratio correlation it is almost certainly related to the episodic pulsating nature of sedimentation the growth potential of the three systems can be estimated by drawing the envelope of the maximum observed rates of aggradation the tropical system shows the highest rates 10

mid dinantian waulsortian buildups in the dublin basin ireland abstract the sedimentary history and biostratigraphic setting of waulsortian carbonate buildups of the feltrim limestone formation late courceyan to early chadian within the dublin basin are described there is no unique precursor or successor facies to this formation and the massive waulsortian banks are composed predominantly of peloidal skeletal wackestones and lime mudstones with packstones near the tops of banks these banks form tabular bodies of moderate relief and are interbedded with thin shales and argillaceous crinoidal limestones of inter bank facies in the southwest of the basin inter bank facies are rare and the bank facies have abundant stromatactis cavities and uniquely at roselawn a fauna of rugose corals all buildups in the dublin basin have phase c and or d component assemblages of lees and miller 1985 and are interpreted as accumulating in moderately shallow water depths near or within the photic zone isopachs for the feltrim limestone formation show a ne sw trending axial depocentre where the waulsortian facies is in excess of 400 m thickness deposition appears to have taken place on this double sided ramp in a manner similar to the model of lees 1982 for belgium and southern britain soft sediment deformation such as large scale slumping shale injections and water escape structures not previously recorded from these rocks is widespread the upper surface of the feltrim limestone formation is fissured and displays a prominent erosion surface termination of waulsortian facies deposition and influx of terrigenous sediment was caused by rapid uplift attributed to chadian tectonism however eustatic sea level fall cannot be ruled out as a partial cause of the demise of the waulsortian

cementation hydrothermal alteration and zn pb mineralization of carbonate breccias in the irish midlands textural evidence from the cooleen zone near silvermines county tipperary a reply sir we are delighted to respond to the comments of reed and wallace on our paper on the origin of breccia hosted base metal mineralization in the irish ore field lee and wilkinson 2002 reed and wallace s thesis is that the mineralized breccias we have described within the mississippian waulsortian limestone formation at cooleen are not of sedimentary origin and therefore by extension that synsedimen tary breccias do not exist elsewhere in the ore field if correct one of a number of lines of evidence that have been used to infer a near sea floor origin for at least a component of sulfide mineralization in ireland that of reworked clasts of sulfide within sedimentary breccias would be invalidated contrary to the suggestion of reed and wallace the existence of sedimentary breccias spatially associated with mineralization in the waulsortian is universally accepted in the literature mine based investigations that include underground observations as well as drill core data and sedimentological studies have concluded that the stratiform wedge shaped breccia bodies commonly developed within the waulsortian limestone facies are sedimentary debris flows of courceyan age boyce et al 1983 taylor 1984 andrew 1986 clifford et al 1986 somerville et al 1992 submarine fault scarp sedimentary breccias are common in sediment hosted zn pb deposits e g goodfellow et al 1993 and display the same characteristics as the breccias at cooleen hitzman and beaty 1996 p 125 also recognized that synsedimentary breccias are present within the waulsortian at both silvermines and lisheen but went on to state that textural and field relationships clearly show that the principal episode of brecciation postdated regional burial dolomiti zation inferring a hydrothermal origin for the ore hosting breccias while we would not agree with this conclusion particularly in relation to the silvermines area we accept that the ore hosting breccias at lisheen galmoy and silvermines have been

chemical mass transfer during hydrothermal alteration of carbonates controls of seafloor subsidence sedimentation and zn pb mineralization in the irish carboniferous abstract petrographic and geochemical data were acquired to evaluate models for the formation of hydrothermal dolomite breccias that host zinc lead orebodies in the rathdowney trend of the irish orefield and assess element mobility during hydrothermal alteration of carbonates macroscopic and microscopic textures indicate that the breccias largely formed by a pseudobrecciation process involving dissolution and replacement of precursor waulsortian dolomite of diagenetic origin during subseafloor hydrothermal fluid flow geochemical analyses show that compared with the waulsortian dolomite precursor breccia clasts and matrix contain respectively higher concentrations of al ti and light rare earth elements which are linearly correlated indicative of mass loss during hydrothermal interaction bulk rock mass loss estimates average 33 indicating extensive dissolution of carbonate although petrographic evidence and limited clast rotation or translation rule out the development of significant open space this supports a mechanism of alteration whereby hydrothermal fluids migrating along grain boundaries microcracks and solution seams drove dissolution and replacement of the surrounding host rock with partial collapse of the transient microporosity produced progressive interaction led to the gradual isolation of domains clasts surrounded by replacement dolomite matrix massive sulfide mineralization formed subsequently by stratabound replacement of the dolomite pseudobreccia by hydrothermal fluids preferentially focused within the more permeable and possibly more reactive lithology this process involved further volume loss 30 of the replaced rock quantitative mass transfer analysis indicates that during hydrothermal interaction net loss of na p mn sr and sometimes cu and net gain in li k fe as well as the ore associated elements typically occurred marked fractionation of the ree is observed eu was added implicating elevated temperature acidic and reduced hydrothermal fluids ce was also added possibly derived from remobilization of pre sulfide oxide mineralization the lree were typically immobile or partially removed and the hree were preferentially mobilized and transported beyond the scale of sampling thus the hree together with na p mn sr and possibly cu may form a distal chemical anomaly at the base of the waulsortian limestone formation the net addition of li k and be in dolomite breccia matrix samples combined with their increase in concentration due to dolomite dissolution produced a broad anomaly of these elements extending for at least 1 5 km from the center of the lisheen deposit these various geochemical anomalies have potential utility in mineral exploration a total volume loss of up to 68 at lisheen is consistent with a marked thinning of the waulsortian biomicrite facies above massive sulfide the observed thickening of upper and supra waulsortian facies in the trough developed above this zone is interpreted to reflect infill of a seafloor depression up to 90 m deep developed in response to underlying hydrothermal dissolution this model implies mineralization initiated during the latter stages of waulsortian deposition in the late courceyan early chadian at a depth of approximately 150 m below the seafloor

timing of mineralization at the navan zn pb deposit a post arundian age for irish mineralization navan is the largest of the irish zn pb deposits and contains some of the most important evidence for the inferred early timing of mineralization in ireland clasts of ore above a middle carboniferous erosion surface we have examined diagenetic fabrics within the main ore pale beds and the overlying erosion surface boulder conglomerate in order to determine the timing of mineralization this diagenetic analysis and particularly the presence of premineralization dolomite in the boulder conglomerate has revealed that all of the mineralization postdates the erosion surface and therefore must be post arundian 345 ma in age furthermore the navan mineralization must be entirely epigenetic in origin i e similar to mississippi valley type deposits and is likely to be holkerian 343 ma in age or younger this conclusion disagrees with the previous model of at least partially syngenetic mineralization and has important implications for the age of other deposits in ireland and the nature of irish type deposits in general

the anatomy of a deep water mud mound complex to the southwest of the dinantian platform in derbyshire uk an elongate waulsortian mud mound complex developed at dovedale on a ramp to the southwest of a developing carbonate platform in derbyshire during chadian early visean times the complex occupied an area of approximately 6 km2 and grew to a maximum relief of 80 m with longitudinal and transverse valleys developed near the southern margin five mound associated facies have been identified mound core mound flank fine mound flank coarse intermound fine and intermound coarse the mound core facies is a massive skeletal wackestone with comminuted sponge debris foraminifera ostracodes and crinoid debris set in a matrix of clotted micrite the mound flank sediments display moderately inclined bedding surfaces while the mound flank fine contains sponge debris the mound flank coarse is dominated by articulated crinoid columnals and includes algal encrusted micritized intraclasts and coarse peloids the well bedded intermound fine facies is bituminous and micritic while the intermound coarse facies is composed of skeletal peloidal intraclast grainstones which locally contain calcified algae although the fauna is diverse the density of colonization by metazoans was low and the supply of macrofossil debris modest the clotted micrite texture is interpreted as the product of micro organisms which precipitated and trapped fine grained sediment the mud mound complex is dominated by the bathymetric assemblages b and c proposed by lees hallet hibo which on their model of the belgian waulsortian indicate depths of between 220 and 280 m intercalation of assemblages b c and c d on the northern margin of the complex is interpreted as the result of local storm disturbance a deep water drift is postulated to explain the nw se alignment of the complex which probably fitted the export model of bosence rowlands quine beneath the sediment surface phreatic flow eroded unlithified sediments and developed interconnected cavities which were filled by cement and sediment relatively eariy mound instability triggered the opening of fissures which filled with crinoid debris peloids indurated lithoclasts and micrite

genesis of stromatactis cavities between submarine crusts in palaeozoic carbonate mud buildups it is concluded that the sedimentary structure stromatactis is a calcite cement fill of a swarm of labyrinthine cavities developed in marine carbonate muds of palaeozoic bioherms commonly with geopetal sediment field and petrographic evidence is examined from the ordovician of dalarna sweden the devonian of the canning basin australia and of belgium and the carboniferous of lancashire u k in all four occurrences the host microspar encloses masses of radiaxial fibrous calcite with sub horizontal floors following other workers radiaxial fibrous calcite is regarded as an altered marine cement a conclusion supported by the presence of overlying geopetal sediments with marine fossils widespread evidence of early submarine cementation in palaeozoic mud mounds isotopic analyses and the presence of microdolomites the stromatactis masses are separated from each other by laminae of host biomicrospar which show discontinuities resembling fractures which are healed with the early marine cement or filled with marine internal sediments the fractures are therefore of submarine origin the evidence points to episodic submarine lithification of the carbonate muds yielding successive crusts between which cavities were eroded and then filled the crusts were broken and rotated during bioturbation differential compaction or shearing during burial

the role of internal erosion and sedimentation in the formation of stromatactis mudstones and associated lithologies abstract a distinctive suite of lithologies occurs in the lower devonian rocky camp mound of eastern victoria lime mudstones contain abundant stromatactis cavities and wackestones contain shelter cavities beneath skeletal constituents together with unsheltered stromatactis cavities irregularly distributed muddy masses occur in grain supported lithologies together with abundant shelter cavities and perched internal sediment these lithologies are completely intergradational and clast content is the principal variant controlling the fabric developed it is proposed that the fabrics in this lithological suite resulted from a process of internal erosion and sedimentation internal reworking which occurred directly below the sediment water interface each stromatactis cavity was subject to erosion of carbonate mud from the roof and redeposition of this material on the floor either directly below the point of erosion or downstream from it in this way cavities migrated upwards leaving a trail of internal sediment beneath in wackestones the migrating cavities were trapped beneath skeletal constituents forming diagenetic shelter cavities the fabrics of grain supported lithologies can be similarly explained a precursor cavity system of organic or inorganic origin is required to initiate the process of internal erosion there is no evidence relating to the origin of this cavity system in the rocky camp mound

the great atlasian reef complex an early cambrian subtropical fringing belt that bordered west gondwana abstract the so called great atlasian reef complex developed during early cambrian time throughout the moroccan margin souss basin of west gondwana according to the syndepositional tectonic activity associated with its intracratonic ediacaran cambrian rift the great reef complex can be subdivided into four major archaeocyathan microbial reef episodes i the atdabanian episode is recorded by a sw ne trending 400 km long barrier reef that extended across the western anti atlas it was controlled by large scale reactivation of an inherited rifting branch which resulted in the nucleation and growth of linear reef complexes located along its margin the interplay of block tilting sharp modifications in accommodation space and relative sea level rise led to a composite retrogradational aggradational reef systems tract characterized by archaeocyathan microbial kalyptrate complexes tiout member and amouslek formation that protected stromatolite dominated back barrier environments lower member of the igoudine formation ii the western anti atlas recorded an early botoman reactivation of the same rifting branch that triggered a lateral migration of frame building centres of carbonate productivity as a result the involved grabens and half grabens recorded the development of fringing mound complexes lower issafen formation these occupied some linear intra platform deeper depressions capped by marls and shales whereas laterally equivalent shallower environments recorded the development of patch reefs and bioherms iii the western anti atlas subsequently recorded a late botoman interval of tectonic quiescence superimposed to a local interval of progradational pulses this favoured the nucleation of dispersed archaeocyathan microbial patch reefs and bioherms iv a distinct palaeogeographic area is recognized in the southern high atlas where the entire atdabanian botoman interval recorded small scale synsedimentary block tilting and high rates of volcaniclastic input as a result this sector was characterized by the record of microbial and archaeocyathan microbial patch reefs and bioherms preferentially developed on the uplifted parts of tilted blocks the end of reef development and carbonate productivity in the souss basin is related to the progradation of siliciclastic depositional systems toyonian regression considered to have caused the collapse of reef communities throughout west gondwana

ramp sedimentation in the dinantian limestones of the shannon trough co limerick ireland abstract during the late chadian and arundian lower carboniferous an extensive carbonate ramp limerick ramp developed over county limerick southwest ireland dipping northwestwards three distinct facies can be recognised corresponding to position on this ramp inner mid and outer ramp the inner ramp facies of oolitic and crinoidal grainstones herbertstown limestone formation in east limerick formed a major shoal behind which peritidal limestones were deposited the mid ramp facies of muddy bioclastic limestones and shales cooperhill facies in north limerick formed between fairweather and storm wave bases the outer ramp basinal facies of mudstones and thin graded resedimented limestones rathkeale beds in west limerick developed below storm wave base when fine terrigenous input was high later in the arundian there was progradation of the nearshore oolitic and crinoidal grainstones over the mid ramp facies by the holkerian the deep water basinal facies in west limerick was buried beneath mid ramp facies durnish limestone the initiation of the limerick ramp is closely related to the formation of the shannon trough in the late courceyan accelerated subsidence in the shannon area during deposition of waulsortian facies marked the onset of a sag phase following a quiescent period in early chadian subsidence was renewed in the late chadian and arundian when major facies changes occurred on the ramp comparison of the shannon trough with the dublin basin shows that in the latter tectonic events in the chadian and arundian particularly syn sedimentary faulting created a sharp division between platform and basinal sedimentation such tectonic influence is not recognised in the shannon trough here differential subsidence and eustatic sea level changes led to more permanent ramp existence modified only by westwards progradation

the initiation of waulsortian buildups in western ireland the contact zone at the base of the waulsortian upper tournaisian carbonate mud bank complex in western ireland has been investigated at four localities spaced over a distance of 120 km at all localities a transition facies up to 3 m thick characterized by several types of grumous clotted and or peloidal carbonate muds immediately underlies the waulsortian facies these muds show a developmental sequence provisionally interpreted as a necessary precursor to the formation of waulsortian polymuds such pre bank precursors produced thin a few decimetres units of transition facies the same mud types also persisted as an aureole around growing banks mud mounds migration of the aureole during bank progradation produced thicker units of transition facies the distribution of skeletal grain types in the waulsortian banks the transition facies and the background argillaceous bioclastic limestones show two trends one regional and one local the regional trend is expressed by progressive north south attenuation and in some cases for example plurilocular foraminifera the disappearance of organism groups it parallels changes in waulsortian phases defined by skeletal grain type assemblages and is thought to indicate a southerly increase in water depth the local trend which occurs only in the two southern localities deeper water expresses differences between the skeletal grain content of the various lithofacies these differences result partly from increased sensitivity to substrate texture by organism groups suffering southward attenuation notably gastropods hyalosteliid sponges aoujgaliids earlandia and kirkbyacean ostracods and partly from selective colonization particularly of the transition facies by tabulate corals and stick ramose bryozoans however the developmental sequence of precursor carbonate muds is the same at all localities indicating that the mud making process probably microbial was independent of water depth

sedimentology and origin of deposits from a small ice dammed lake leirbreen norway this paper describes recent proglacial lacustrine sediments exposed by the drainage of a small probably never more than 0 03 km2 ice dammed lake basin at leirbreen central jotunheimen norway the dominant facies include ripple laminated massive and horizontally stratified sands massive and horizontally laminated silts and irregularly laminated fine sands and silts the major control on lake circulation and the nature and distribution of these facies was an underflow driven by a subglacial meltwater stream which formed the major lake input although much of the sedimentary sequence indicates a pulsatory input the proximal character of this small lake prevented the development of classic varved silts compressional deformation of shoreline sediments was due to winter lake ice push other deformational processes included the grounding of icebergs water escape and syn sedimentary downslope collapse observations from an adjacent small ice marginal lake at leirbreen provide support for several of the inferences drawn from the sediments of the former ice dammed lake

origin and composition of carbonate buildups and associated facies in the fort payne formation lower mississippian south central kentucky an integrated sedimentologic and paleoecologic analysis an integrated sedimentologic paleoecologic and taphonomic analysis is used to test competing hypotheses for the origin of the fort payne formation of south central kentucky characteristics of eight distinct facies both carbonate and siliciclastic support the hypothesis that the lower mississippian fort payne formation is a progradational shallowing upward basin filling sequence five facies are considered in detail including the autochthonous fossitiferous green shale facies two autochthonous carbonate facies wackestone buildups and crinoidal packstone buildups and two transported carbonate facies channelform packstone facies and sheetlike packstone facies the two types of carbonate buildups are independent features but both developed on mounds of green fossiliferous shale the fort payne wackestone buildups are interpreted to be waulsortian buildups the fort payne waulsortian and associated facies were deposited in the lower portion of the photic zone which is phase d the shallowest phase of the lees and others 1985 waulsortian model the source of carbonate mud in the buildups must have been autochthonous all autochthonous facies had distinct faunas dominated by crinoids and bryozoans the channelform and sheetlike packstone facies are interpreted to be proximal and distal portions respectively of carbonate apron deposits both are composed principally of crinoid packstones and represent deeper water portions of the fort payne basin filling sequence the siltstone facies records background sedimentation

the waulsortian type mound in the lower namurian of the lublin basin se poland abstract a unique waulsortian like mound is recognized in the lower namurian succession of the central part of the lublin basin se poland the carboniferous succession is characterized here by yoredale type cyclothems with carbonate units of relatively constant thickness an unexpected increase in thickness of the carbonate unit in the minkowice 4a well indicates the occurrence of an organic buildup at least 35 m thick sedimentological analysis reveals that its skeletal composition as well as its peloidal matrix abundant stromatactoid cavities and succession of cements indicate close analogies to similar facies in lower carboniferous waulsortian type mud mounds oxygen isotope data indicates that the formation and growth of the described mound were probably stimulated by hot water vents the occurrence of hot water vents in the open marine setting of the lublin basin is interpreted as a consequence of early namurian tectonic activity when a local tectonic compressional regime occurred in some parts of the basin the mound does not function as a hydrocarbon reservoir however its characteristics point to the presence of sedimentary traps which hitherto have not been recognized in this region