tonian cryogenian boundary sections of argyll scotland abstract the tonian cryogenian system boundary is to be defined at a gssp global boundary stratigraphic section and point beneath the first evidence of widespread glaciation a candidate lies within the dalradian supergroup of scotland and ireland which is least deformed and metamorphosed in argyll western scotland we present new stratigraphic profiles and interpretations from the isle of islay and the garvellach islands update the chemostratigraphy of the appin group tonian carbonates underlying the thick ca 1 km glacigenic port askaig formation paf and demonstrate an environmental transition at the contact the appin group forms a regionally extensive 4 km thick succession of limestones shales and sandstones deposited on a marine shelf on islay the upper part of the lithostratigraphy has been clarified by measuring and correlating two sections containing distinctive stratigraphic levels including molar tooth structure oolite stromatolitic dolomite and intraclastic microbial mounds significantly deeper erosion at the unconformity at the base of the overlying paf is demonstrated in the southern section carbonate facies show a gradual decline in 13 c vpdb from 5 to 2 upwards in ne garbh eileach garvellach islands a continuously exposed section of appin group carbonates 70 m thick here designated the garbh eileach formation gef lies conformably beneath the paf the gef and the gef paf boundary relationships are re described with new sedimentological logs petrological and stable isotope data interstratified limestone and dolomicrosparite with 13 c of 4 to 7 a feature named the garvellach anomaly replacing the term islay anomaly are overlain by dolomite in which the isotope signature becomes weakly positive up to 1 upwards shallow subtidal conditions become peritidal upwards with evidence of wave and storm activity gypsum pseudomorphs and subaerial exposure surfaces are common near the top of the gef the basal diamictite d1 of the paf is rich in carbonate clasts similar to slightly deeper water parts of the underlying succession d1 is typically several metres thick with interstratified sandstone and conglomerate but dies out laterally scattered siliciclastic coarse sandstone to pebble conglomerate with dropstones associated with soft sediment deformation is interbedded with carbonate below and above d1 dolomite beds with derived intraclasts and gypsum pseudomorphs are found above d1 or equivalent position where d1 is absent published and new sr isotope studies including successive leach data demonstrate primary tonian 87 sr 86 sr values of 0 7066 0 7069 on islay decreasing to 0 7064 0 7066 in the younger gef limestones on the garvellachs with 1700 2700 ppm sr other typically tonian characteristics of the carbonates are the sr rich nature of limestones molar tooth structure and dolomitized peritidal facies with evidence of aridity seabed surveys suggesting uniformly dipping strata and shallow borehole core material illustrate the potential for extending the tonian record offshore of the garvellachs a candidate tonian cryogenian gssp is proposed on garbh eileach within the smooth 13 c profile at the cross over to positive 13 c signatures 4 m below the first occurrence of ice rafted sediment and 9 m below the first diamictite although lacking radiometric constraints or stratigraphically significant biotas or biomarkers the scottish succession has a thick and relatively complete sedimentary record of glaciation coherent carbon and strontium chemostratigraphy lateral continuity of outcrops and 100 exposure at the proposed boundary interval

structural channelling of metamorphic fluids on islay scotland implications for paleoclimatic reconstruction analysis of the delta o 18 and delta c 13 values of carbonate rocks from islay scotland reveals structural channelling of metamorphic fluids through the axial region of a major en echelon anticlinal fold system metamorphic fluid flow produced axial planar veins with higher vein density in the axial region of the fold fluid rock ratios were more than 30 1 within this axial region at least four times greater than the regional mean ratio of 7 6 1 5 1 for carbonate rocks on islay this supports the interpretation that metamorphic fluids were channelled through the axial region of the islay anticline fluid rock ratios were calculated using a model for coupled delta o 18 and delta c 13 exchange with a metamorphic fluid the metamorphic fluid was calculated to have delta o 18 and delta c 13 values of 15 3 parts per thousand and 6 1 parts per thousand respectively and x co2 of 0 2 this is in isotopic and chemical equilibrium with chlorite and graphite bearing metamudstones that are structurally below the folded metacarbonate rocks on islay devolatilization of these metamudstones is therefore a likely source mechanism for this metamorphic fluid removal of the effects of metamorphic fluid flow on delta c 13 values recorded by metacarbonate rocks on islay allows us to re evaluate evidence used to reconstruct neoproterozoic climate this evidence includes a large negative delta c 13 excursion reported from the lossit limestone formation this unit underlies the port askaig formation which is dominated by diamictites that have been interpreted as glacial tillites this islay anomaly has been correlated with other such anomalies worldwide and together with overlying tillites has been cited as evidence of major worldwide glaciation events in this study we show that the magnitude of this negative delta c 13 anomaly can partly be explained by exchange with metamorphic fluids however we also show that extremely negative delta c 13 values in the bonahaven dolomite formation which overlies the port askaig formation and has been interpreted as a cap carbonate cannot be attributed to metamorphic fluid flow

catastrophic mass failure of a neoproterozoic glacially influenced continental margin the great breccia port askaig formation scotland abstract the great breccia is a thick over 50 m diamictite that occurs close to the base of the neoproterozoic port askaig formation in scotland and contains matrix supported clasts up to 100 m across in a poorly sorted dolomitic matrix detailed logging and mapping of cliff and shoreline exposures through the great breccia on the garvellach islands show that it is not a simple megabreccia but consists of three sedimentary units including a megabreccia unit 1 diamictites interbedded with dolomitic conglomerate sandstone and mudstone unit 2 and a diamictite with metre sized dolomite clasts unit 3 the sedimentological characteristics of the great breccia indicate that it formed by a variety of subaqueous sediment gravity flow processes including matrix rich debris flows and turbidites clasts up to 100 m across contained within the megabreccia unit record catastrophic collapse and failure of local calcareous siliciclastic deposits other diamictite units were deposited by debris flows conglomerates were deposited from high concentration turbulent flows and sandstones and fine grained facies also exhibit characteristics typical of turbidites continued downslope remobilization of sediment in the basin following deposition of the great breccia is recorded by overlying deformed diamictites detrital dolomites and siltstones of the disrupted beds the great breccia and associated facies within the lowermost part of the port askaig formation are similar to those found in carbonate megabreccia successions that record catastrophic mass failure of carbonate platforms failure events in the port askaig formation most likely relate to localized faulting and subsidence of the dalradian basin although the port askaig formation is considered a neoproterozoic glacial succession there is little direct evidence for glacial influence on sedimentation in the great breccia making it difficult to fully assess paleoclimatic conditions

ikaite pseudomorphs in neoproterozoic dalradian slates record earth s coldest metamorphism calcite pseudomorphs have replaced euhedral ikaite caco 3 6h 2 o porphyroblasts in dalradian calcareous slates and metadolostones of western scotland with a volume decrease of at least 47 porphyroblast fabric relationships indicate that the initial growth of ikaite post dates a penetrative tectonic fabric developed during upright folding this is the first reported occurrence of metamorphic ikaite porphyroblasts and points towards growth within the slates during an ultra low temperature metamorphism with an exceptionally low geothermal gradient this event is associated with the penetration of long lived and extreme permafrost deep into subaerially exposed bedrock during neoproterozoic glaciation the presence of the well preserved pseudomorphs within the easdale slates of the argyll group implies that a neoproterozoic orogenic unconformity exists above the stratigraphic position of these rocks

glaciomarine model for upper precambrian diamictites of the port askaig formation scotland descriptive techniques lithofacies codes and vertical profile analysis emphasizing lithofacies contacts and geometry allow objective characterization and comparison of diamict ite sequences irrespective of geologic age upper precambrian diamictites 650 600 m y of the middle dalradian port askaig formation in scotland are traditionally interpreted as products of repeated ice sheet advances over an emergent shallow marine shelf and deposition by in situ basal melt out the dalradian sequences are however fundamentally different from modern and pleistocene diamicts deposited by either lodgment or basal melt out and fail to show evidence of tractional processes associated with basal ice movement scottish diamictite sequences are similar to assemblages of massive and stratified diamict lithofacies of late pleistocene age deposited subaqueously below floating ice and recently described from the lake ontario basin of north america a glaciomarine depositional model may have implications for the origin and paleogeographical setting of other upper precambrian diamictites of similar age and stratigraphic context in east greenland spitsbergen and scandinavia

dolomitic breccia veins as evidence for extension and fluid flow in the dalradian of argyll veins of red dolomite occur extensively in the dalradian rocks of argyll scotland and adjacent areas the veins represent brittle extensional deformation preferentially reactivating caledonian quartz veins the dolomite is associated with reddening of the adjacent dalradian country rock which it partially replaced dolomite was also precipitated in overlying old red sandstone and probably dates to late carboniferous early permian fluid inclusion studies show that the veining involved moderate temperature 75 to 115 c fluids stable isotope data suggest that these fluids were basinal brines traces of chalcopyrite paragenetically late in the veins may reflect the mineralization which occurs more widely in the dalradian rocks of argyll the red colour of the dolomite is due to abundant haematite crystallites that grew in the dolomite crystal fabric palaeomagnetic analysis yields a consistent late permian early triassic age for the haematite growth in the dolomite veins and the reddened dalradian country rocks this age represents the time of haematite precipitation from iron rich dolomite that may have been related to deep oxidizing weathering gold anomalies associated with reddened basement rock must be of this age or younger

some guidelines in reconstructing ancient sea conditions from wave ripplemarks abstract the collection of substantial field data on wave ripple mark spacing wavelength steepness grain size and symmetry index from the miocene burdigalian sandstones of western switzerland has allowed apparently close reconstruction of sea conditions results indicate however that ancient wave reconstructions must be restricted at present to data from relatively steep ripple marks vfi less than 7 5 i e vortex ripples data from the flatter ripple marks post vortex types formed at high oscillatory shear stresses do not provide reasonable estimates of wave conditions penecontemporaneous overwashing and or post depositional compaction ripple formation near the destruction condition rather than the threshold of sediment movement orbital diameters far exceeding ripple spacing and superimposed unidirectional currents are all factors which seriously affect wave reconstructions evaluation of ancient wave conditions provides insight into geologically important phenomena such as local water depth and basin size

enigmatic chambered structures in cryogenian reefs the oldest sponge grade organisms abstract previously undescribed chambered structures are common and widespread in the cryogenian post sturtian glacial carbonates of the oodnaminta reef complex adelaide geosyncline south australia the rasthof berg aukas formation namibia and the gauss formation namibia these carbonate structures have millimetre to centimetre scale chambers separated by well defined and generally thin micritic walls chamber walls now consist of dolomite but were probably originally aragonitic the chambers may have a lobate polygonal or dendritic morphology and are often further divided into smaller chambers chambered structures occur as reefal growth frameworks as cavity fillings in neptunean dykes and growth cavities and as intercolumnar material within stromatolite frameworks in the oodnaminta reef complex these structures are only present in the sub photic deep water framework these structures probably represent the calcified remains of an organism or community of organisms that was globally distributed and widespread for a significant time period following the sturtian glaciation no precisely analogous structures have been previously described from modern or ancient settings but the complexity and degree of organization suggests a significant evolutionary advance over older proterozoic fossils the closest morphological analogues for the structures are a some types of reef dwelling sponges and b some complex microbialites from archaean and paleoproterozoic carbonates the structures lack spicules and ostia found in sponges ruling out a true poriferan origin however it is plausible that they are proto sponges sponge grade organisms or complex microbial precursors to sponge grade organisms whatever their affinity we suggest these structures record a significant evolutionary event on the path towards organic complexity

neoproterozoic cap dolostone deposition in stratified glacial meltwater plume abstract neoproterozoic cap carbonates host distinctive geochemical and sedimentological features that reflect prevailing conditions in the aftermath of snowball earth interpretation of these features has remained contentious with hypotheses hinging upon timescale and synchronicity of deposition and whether or not geochemical signatures of cap carbonates represent those of a well mixed ocean here we present new high resolution sr and mg isotope results from basal ediacaran cap dolostones in south australia and mongolia least altered sr and mg isotope compositions of carbonates are identified through a novel incremental leaching technique that monitors the purity of a carbonate sample and the effects of diagenesis these data can be explained by the formation of these cap dolostones involving two chemically distinct solutions a glacial meltwater plume enriched in radiogenic sr and a saline ocean residue with relatively lower 87sr 86sr ratios model simulations suggest that these water bodies remained dynamically stratified during part of cap dolostone deposition most likely lasting for 8 thousand years our results can potentially reconcile previous conflicts between timescales estimated from physical mixing models and paleomagnetic constraints geochemical data from cap carbonates used to interpret the nature of snowball earth and its aftermath should be recast in terms of a chemically distinct meltwater plume

87sr 86sr chemostratigraphy of neoproterozoic dalradian carbonates below the port askaig glaciogenic formation scotland abstract the neoproterozoic cambrian dalradian supergroup of scotland contains three glaciogenic sedimentary units the port askaig formation the stralinchy reelan formation and the loch na cille boulder bed in ascending order although the idea that relatively cold climates occurred during the latest proterozoic is widely accepted the cause of the onset of glaciation is still controversial we use new carbonate 87 sr 86 sr data to better constrain this environmental change some dalradian limestones have high strontium contents 1000 ppm low manganese contents and mn sr ratios 87 sr 86 sr values of paleoseawater in the neoproterozoic the 87 sr 86 sr values of limestones of the islay formation ca 0 7067 sampled on the island of islay are similar to the values of previous studies however the 87 sr 86 sr values of limestones just below the port askaig formation ca 0 7064 collected on the island of garbh eileach have the lowest values recorded in the dalradian supergroup comparing these 87 sr 86 sr values with coeval 87 sr 86 sr values of other regions in the world such low 87 sr 86 sr i87 sr 86 sr ratio from the tonian through the cryogenian and ediacaran to the earliest cambrian the results show that the 87 sr 86 sr ratio of seawater decreased just before the older cryogenian glaciation that it increased by two steps in the early and middle ediacaran and that there were at least two abrupt positive excursions in the middle ediacaran and at the precambrian cambrian boundary the decline of the 87 sr 86 sr ratio of seawater just before the older cryogenian sturtian glaciation suggests that enhancement of weathering related to break up of the rodinia supercontinent and continental flood basalt volcanism was a likely driver for generating global cooling for the snowball earth conditions godderis et al 2003 donnadieu et al 2004

strontium isotopic composition of modern and holocene mollusc shells as a palaeosalinity indicator for the baltic sea abstract the 87sr 86sr isotope ratio in subfossil carbonate mollusc shells from raised beach sediments is used as a palaeosalinity indicator for the baltic sea the main purpose is to demonstrate the applicability of the method in a formerly glaciated area using 87sr 86sr ratios found in modern shells mytilus edulis macoma baltica and radix balthica to elucidate the parameters and conditions to be used for palaeosalinity determinations based on subfossil shells proxy salinity data are calculated assuming that the sr concentration in baltic sea water is controlled by a two component conservative mixing between seawater and river water based on replicate determinations of the 87sr 86sr ratio in modern shells proxy salinity data can be quantified with a relative precision of better than 5 for salinities up to 10 comparison with measured present day salinities indicates that the accuracy is generally better than 5 for the proxy data with this precision and accuracy the present day salinity differences between the major baltic sub basins bothnian bay bothnian sea and baltic proper can be detected palaeosalinities were determined using subfossil shells m edulis and m baltica with calibrated 14c ages of 6770 3070 cal bp the shell deposits occur from 65 m a s l down to the present day sea level the palaeosalinities determined for the bothnian bay 4 8 10 3 and the bothnian sea 7 3 10 3 are in good agreement with earlier estimates of the maximum littorina sea stage palaeosalinity in these sub basins 8 10 at one locality two different shell species from the same shell deposit were dated m edulis and m baltica the shells differed in age by 460 70 14c years a possible indication that the ecological conditions at a locality may have been favourable to different faunas at different times

high precision u pb monazite geochronology of the c 806 ma grampian shear zone and the implications for the evolution of the central highlands of scotland two pegmatites and mylonitic rocks from the grampian shear zone yield u pb monazite ages of 806 3 ma 808 9 11 ma and 804 12 13 respectively these confirm that shearing and pegmatite crystallization was essentially synchronous lower intercepts of c 440 ma indicate disturbance during ordovician reworking these new data question the concept of a single latest proterozoic early palaeozoic orogeny in the grampian terrane and the significance of the great glen fault

possible seismic origin of molar tooth structures in neoproterozoic carbonate ramp deposits north china the xinmincun formation forms the uppermost unit of a thick neoproterozoic section which accumulated near the east margin of the north china block and is overlain by two thin nearshore to continental formations below fossiliferous lower cambrian sediments although tectonically deformed sedimentary structures are preserved undeformed on cleavage parallel surfaces and an 80 m section has been reconstructed by correlation across minor folds and faults in the golden stone beach area 50 km ne of the city of dalian southern liaoning province the measured section shows 65 m of storm dominated deposits consisting of alternations of micrites and sharp based graded intraclastic grainstone beds tempestites some with rudaceous commonly erosional or guttered bases the top 15 m of section shows three alternations of similar subtidal lithofacies with partly to completely dolomitized peritidal deposits laminated sometimes fenestral and desiccated micrite beds and intraclastic rudite and grainstone beds tempestite beds become thinner and less abundant upwards towards a muddy upper shoreface zone this environment was characterized in part by the occurrence of micrite with thin or streaky lamination probable storm resuspended sediment interbedded tempestites numerous erosion surfaces and evidence of liquidization and sediment slumping into hollows molar tooth structures are widespread in micrite beds of the xinmincun formation and are present in lesser abundance in tempestites and liquefied channel fills originally the structures were sub vertical cracks 1 20 cm long tapering upwards and downwards subsequently they became filled with microspar cement and buckled rigidly during compaction of surrounding sediment during burial evidence of repeated episodes of cracking presence of brecciated cracks and localization of cracking within beds together with variable degree of development and variation of preferential alignment in plan indicates a mechanical origin crack generation may have been by seismic surface waves generated by movement along faults defining either the basin s margins or its internal structure or possibly by wave action during storms a seismic origin for molar tooth structure is consistent with other neoproterozoic occurrences their preferential occurrence in precambrian deposits arises from the relative rigidity of micritic sediment at this time related to lack of bioturbation incipient cementation and possibly microbial binding

a burial diagenesis origin for the ediacaran shuram wonoka carbon isotope anomaly marked negative 13c excursions in ediacaran age carbonate sediments have been identified in several sections globally but are not recognized in all sections of similar age the presence of 13ccarb values as low as 12 has been interpreted as recording fundamentally different processes in the global carbon cycle than those recognized today the 13ccarb anomalies are strongly correlated with 18ocarb values but are not represented in 13corg records while no primary depositional processes have been identified that can produce the correlated 18o 13c arrays simulations show that fluid rock interaction with high pco2 fluids is capable of producing such arrays at geologically reasonable pco2 and water rock ratios variations in the mg ca ratio and sulfate concentration of the altering fluid determine the extent of dolomite vs calcite and anhydrite in the resulting mineral assemblage incorporation of an initially aragonitic mineralogy demonstrates that high sr low mn sr and modest alteration of 87sr 86sr in ancient carbonates are all compatible with a burial diagenesis mechanism for generation of the 13c anomalies and do not necessarily imply preservation of primary values the profound ediacaran negative 13c anomalies can be adequately explained by well understood diagenetic processes conflated with the difficulty of correlating precambrian sections independently of chemostratigraphy they are not a record of primary seawater variations and need not have independent stratigraphic significance

short paper the depositional age of the dalradian supergroup u pb and sm nd isotopic studies of the tayvallich volcanics scotland zircons from a keratophyre associated with the tayvallich volcanics in the dalradian rocks of the sw scottish highlands have been dated by u pb methods yielding an age of 595 4 ma this age indicates that most or all of the dalradian is precambrian in age and that dalradian sedimentation may have lasted for about 200 million years the age also constrains the time interval between cessation of dalradian sedimentation and subsequent crustal thickening and regional metamorphism during the grampian orogeny sm nd isotopic data for the tayvallich volcanins and related metadolerite sills yield initial ond values of 2 to 4 which are thought to reffect the effects of melting of lithospheric mantle

740 ma vase shaped microfossils from yukon canada implications for neoproterozoic chronology and biostratigraphy biostratigraphy underpins the phanerozoic time scale but its application to pre ediacaran strata has remained limited because proterozoic taxa commonly have long or unknown stratigraphic ranges poorly understood taphonomic constraints and or inadequate geochronological context here we report the discovery of abundant vase shaped microfossils from the callison lake dolostone of the coal creek inlier yukon canada that highlight the potential for biostratigraphic correlation of neoproterozoic successions using species level assemblage zones of limited duration the fossiliferous horizon dated here by re os geochronology at 739 9 6 1 ma shares multiple species level taxa with a well characterized assemblage from the chuar group of the grand canyon arizona usa dated by u pb on zircon from an interbedded tuff at 742 6 ma the overlapping age and species assemblages from these two deposits suggest biostratigraphic utility at least within neoproterozoic basins of laurentia and perhaps globally the new re os age also confirms the timing of the islay 13ccarbonate anomaly in northwestern canada which predates the onset of the sturtian glaciation by 15 m y together these data provide global calibration of sedimentary paleontological and geochemical records on the eve of profound environmental and evolutionary change

descent into the cryogenian abstract the cryogenian period brackets an interval of profound glaciation commonly referred to by the evocative epithet snowball earth according to its recent redefinition the cryogenian began before the onset of low latitude glaciation ca 717 ma and ended during its final and catastrophic melting phase ca 635 5 ma pending future ratification of a global stratotype section and point or gssp the onset of the cryogenian period is estimated at about 720 ma however no consensus has yet been reached concerning the best section or criteria for its definition the articles in this special issue represent the state of the art in tonian cryogenian transition stratigraphy around the world and will contribute to the selection of the future gssp

application of geochemistry to the stratigraphic correlation of appin and argyll group carbonate rocks from the dalradian of northeast scotland 240 samples from appin and argyll group carbonate rock units of the dalradian of northeast scotland have been analysed for 10 major oxides and 14 to 19 trace elements in order to classify and correlate them using geochemistry the carbonate rocks are chiefly limestones with some dolostones rocks with 0 38 mgo cao 0 03 are classed as dolomitic limestones those with mgo cao 0 38 are classed as dolostones the data have approximately lognormal distributions at a high level of significance except for cao mgo and sr cao and sr have negatively skewed distributions median values for groups of sample analyses plotted on normalized multi element variation diagrams and a nonlinear mapping nlm algorithm have been used to classify groups of samples in the appin group multi element diagram patterns are distinctive for each unit allowing correlations to be made though distinctive compositions do occur locally in argyll group carbonate rocks correlation on a regional scale is not possible the plot of nlm coordinates for suites of samples is consistent with the results from the spider diagrams suites of appin group samples cluster closely whereas there is wide spread in samples from the argyll group in several areas most notably at sandend bay the data have allowed reinterpretation of the stratigraphy the data are consistent with other geological data in suggesting that crustal conditions were relatively stable during the deposition of the appin group but not during the deposition of the argyll group

iceberg drop dump and grounding structures from pleistocene glacio lacustrine sediments scotland abstract dropstone dump and grounding structures resulting from the melt out of debris contained in floating and grounded icebergs are described from a pleistocene ice marginal glacio lacustrine sequence in scotland dropstones display bending penetration rucking and complete rupture of stratum occurring beneath them and onlap above them with the degree of deformation varying as a function of the size shape and axial disposition of the clast and of the sediment type into which they fell dump structures are conical mounds of gravel or diamict formed by the break up and overturning of dirt laden icebergs and the consequent release of large quantities of debris to the lake floor grounding structures are caused by the grounding of icebergs the down warping of underlying lake floor se iment and the subsequent in situ melt out of contained debris to form isolated troughs of diamict

indicators of relative completeness of the glacial record of the port askaig formation garvellach islands scotland abstract the port askaig formation paf is a diamictite bearing succession in the dalradian supergroup of scotland that provides an excellent archive of a cryogenian glaciation in the garvellach islands and islay argyll the formation is 1100 m thick comprises 5 members and includes 47 diamictite beds interbedded with siltstones dolostones and sandstones here we document seven features of the paf that indicate its relative stratigraphic completeness there are gradual progressive changes up section in the lithologies of the diamictites their interbeds and clast lithologies the sharp basal surfaces of the diamictites each show the same repeated pattern of environmental change from non glacial to glacial many of the top surfaces of the diamictites show evidence of periglacial conditions the succession in the paf records a total of 76 climatically related stratigraphic episodes 28 glacial episodes 25 periglacial episodes and 23 non glacial episodes parts of member 1 diamictites 1 12 and diamictites 16 18 and member 2 diamictite 31 to the base of member 3 are most compete on the east coast of garbh eileach the paf in the garvellach islands occurs within a succession that is several kilometres thick as newly revealed by sea floor mapping compared with other cryogenian and phanerozoic glacial successions the paf is exceptional in its combination of formation thickness the number of climatically related stratigraphic episodes and the considerable thickness of its host supergroup furthermore these indicators of relative stratigraphic completeness provide evidence that the base of the paf on the east coast of garbh eileach is a succession without a major break in deposition supporting the account of the strata at and below the base of the paf in the companion article by fairchild et al 2018

dalradian slides and basin development a radical interpretation of stratigraphy and structure in the sw and central highlands of scotland movements on syndepositional listric faults are responsible for many of the lateral variations in dalradian stratigraphy sedimentary facies and thickness variations show that the surface traces of these faults correspond in many cases to what have previously been interpreted as tectonic slides although normal faults thrusts and sedimentary contacts may also mark their position three main episodes of faulting are described in the islay to lochaber area appin group sedimentation was controlled by a fault now represented by the loch skerrols thrust fort william slide ossian steep belt in the islay jura area an anomalously thick islay subgroup succession accumulated in a half graben bounded by a listric normal fault to the nw and terminated by transfer faults at each end the deposition of a thick easdale subgroup section was controlled by movements on what is now the benderloch ballachulish slide this listric fault terminates southwards in the scarba fault and probably extends north into the ossian steep belt the thinness of the appin and lower argyll group succession between the ericht laidon and bridge of balgie faults is an original feature the stratigraphic gap represented by the boundary slide here is reinterpreted as a disconformity however further east the boundary slide may well be a listric fault movement on which accommodated the thick succession around schiehallion the development of the major structure was influenced by the geometry of the sedimentary basins the schiehallion tummel area is reinterpreted as lying on the lower limb of the ben lui fold this resolves the problem of the emplacement of the tay nappe which is likely to be a gravity structure derived from above the ossian steep belt

continental flood basalt weathering as a trigger for neoproterozoic snowball earth abstract atmospheric co2 levels and global climate are regulated on geological timescales by the silicate weathering feedback however this thermostat has failed multiple times in earth s history most spectacularly during the cryogenian c 720 635 ma snowball earth episodes the unique middle neoproterozoic paleogeography of a rifting low latitude supercontinent likely favored a globally cool climate due to the influence of the silicate weathering feedback and planetary albedo under these primed conditions the emplacement and weathering of extensive continental flood basalt provinces may have provided the final trigger for runaway global glaciation weathering of continental flood basalts may have also contributed to the characteristically high carbon isotope ratios 13 c of neoproterozoic seawater due to their elevated p contents in order to test these hypotheses we have compiled new and previously published neoproterozoic nd isotope data from mudstones in northern rodinia north america australia svalbard and south china and sr isotope data from carbonate rocks the nd isotope data are used to model the mafic detrital input into sedimentary basins in northern rodinia the results reveal a dominant contribution from continental flood basalt weathering during the ca 130 m y preceding the onset of cryogenian glaciation followed by a precipitous decline afterwards these data are mirrored by the sr isotope record which reflects the importance of chemical weathering of continental flood basalts on solute fluxes to the early middle neoproterozoic ocean including a pulse of unradiogenic sr input into the oceans just prior to the onset of cyrogenian glaciation hence our new data support the hypotheses that elevated rates of flood basalt weathering contributed to both the high average 13 c of seawater in the neoproterozoic and to the initiation of the first sturtian snowball earth

87sr 86sr chemostratigraphy of neoproterozoic dalradian limestones of scotland and ireland constraints on depositional ages and time scales new calcite 87 sr 86 sr data for 47 limestones from the metamorphosed and deformed neoproterozoic cambrian dalradian supergroup of scotland and ireland are used to identify secular trends in seawater 87 sr 86 sr through the dalradian succession and to constrain its depositional age dalradian limestones commonly have sr 1000 ppm indicating primary aragonite and marine diagenesis low mn mn sr 18 o and trace element data indicate that many 87 sr 86 sr ratios are unaltered since diagenesis despite greenschist to amphibolite facies metamorphism consistent with the documented behaviour of sr and o during metamorphic fluid rock interaction thus the 87 sr 86 sr data are interpreted largely to reflect 87 sr 86 sr of coeval seawater currently available data show that neoproterozoic seawater 87 sr 86 sr rose from c 0 7052 at 850 900 ma to c 0 7085 or higher in the latest neoproterozoic temporal changes at c 800 ma and c 600 ma bracket the range in 87 sr 86 sr values of calcite in grampian appin and lowest argyll group c 0 7064 0 7072 and middle and uppermost argyll group c 0 7082 0 7095 limestones consistent with a rise in seawater 87 sr 86 sr around 600 ma 87 sr 86 sr data are consistent with the sedimentary affinity of the islay subgroup with the underlying appin group and with a possible time interval between deposition of islay and easdale subgroup rocks they indicate that the dalradian as a whole is younger than c 800 ma

possible animal body fossils in pre marinoan limestones from south australia the neoproterozoic era was punctuated by the sturtian about 710 million years ago and marinoan about 635 million years ago intervals of glaciation in south australia the rocks left behind by the glaciations are separated by a succession of limestones and shales which were deposited at tropical latitudes here we describe millimetre to centimetre scale fossils from the trezona formation which pre dates the marinoan glaciation these weakly calcified fossils occur as anvil wishbone ring and perforated slab shapes and are contained within stromatolitic limestones the trezona formation fossils pre date the oldest known calcified fossils of this size by 90 million years and cannot be separated from the surrounding calcite matrix or imaged by traditional x ray based tomographic scanning methods instead we have traced cross sections of individual fossils by serially grinding and scanning each sample at a resolution of 50 8 m from these images we constructed three dimensional digital models of the fossils our reconstructions show a population of ellipsoidal organisms without symmetry and with a network of interior canals that lead to circular apertures on the fossil surface we suggest that several characteristics of these reef dwelling fossils are best explained if the fossils are identified as sponge grade metazoans the trezona formation of south australia pre dates the 635 million year old marinoan glaciation fossils found at this location are up to several millimetres in size and share morphological characteristics with sponge grade animals

microstructures in metasedimentary rocks from the neoproterozoic bonahaven formation scotland microconcretions impact spherules or microfossils abstract microscopic spherules in relatively undeformed mudstones of the neoproterozoic bonahaven formation islay scotland are differentiated from their matrix by a sharp micron scale smoothly rounded boundary these elongate spherules were earlier interpreted as hollow bodies filled penecontemporaneously by glauconite and subsequently metamorphosed to phengite but their origin remains a matter of debate spherules observed in thin section are predominantly rounded 74 but can exhibit a flat edge or protrusion at one end in 11 of a sample population two or more spherules are conjoined x ray diffraction indicates that spherule bearing mudstones consist mainly of muscovite with variable amounts of kaolin group minerals and minor iron chlorites a range of physical origins for the spherules including microconcretions or metamorphic microstructures deposition from the sky as micrometeorites microtektites microkrystites or accretionary volcanic ash particles and detrital grains is considered but rejected on distributional morphological and mineralogical evidence biological origins are considered most likely especially protistan tests similar to the vase shaped microfossils found in somewhat older neoproterozoic rocks if correct this provides the first report of eukaryotic life in the dalradian succession that passes critical tests for biogenicity and new evidence for testate microfossils in post sturtian but pre marinoan aged rocks

marine cements reveal the structure of an anoxic ferruginous neoproterozoic ocean neoproterozoic oceans provided the setting for the rise of animals yet little is known of their chemical composition marine carbonates from the cryogenian oodnaminta reef complex south australia reveal the chemical structure of a neoproterozoic ocean pseudo depth profiles from shallow to deep water reef facies have been constructed from geochemical and sedimentological analysis of marine cements evidence suggests that under a peritidal oxic anoxic chemocline the water column was largely anoxic strongly ferruginous and had a chemistry profoundly different from that of modern seawater these geochemical data suggest early archaean like conditions for this late cryogenian ocean posing problems for metazoan evolution in extremely anoxic conditions supplementary material detailed methods and data tables are available at www geolsoc org uk sup18764

stable isotopes of oxygen and hydrogen in meteoric water during the cryogenian period we measured delta o 18 and delta h 2 values of muscovite and carbonate mineral separates from metamorphosed carbonate bearing mudstone layers in late tonian to early cryogenian strata including s

neoproterozoic environmental change recorded in the port askaig formation scotland climatic vs tectonic controls abstract the snowball earth hypothesis suggests that the neoproterozoic was characterized by several prolonged and severe global glaciations followed by very rapid climate change to hot house conditions the neoproterozoic port askaig formation of scotland consists of a thick succession of diamictite sandstone conglomerate and mudstone sedimentological and stratigraphic analysis of port askaig deposits exposed on the garvellach islands was carried out to establish the nature of neoproterozoic palaeoenvironmental change preserved in this thick succession particular emphasis was placed on identifying and distinguishing between climatic and tectonic controls on sedimentation port askaig formation diamictite units are attributed to deposition by sediment gravity flow processes or rainout of fine grained sediment and ice rafted debris in a glacially influenced marine setting associated facies record various depositional processes ranging from sediment gravity flows conglomerate massive sandstone and laminated mudstone to deposition under other unidirectional currents cross bedded and horizontally laminated sandstone the port askaig formation is also characterized by abundant soft sediment deformation features that occur at discrete intervals and are interpreted to record episodic seismic activity stratigraphic analysis of the port askaig formation on the garvellach islands reveals three phases of deposition phase i was dominated by sediment gravity flow processes and sedimentation was primarily tectonically controlled phase ii was a transitional phase characterized by continued tectonic instability an increased supply of sand to the basin and the preservation of current generated facies in the third and final phase of deposition the interbedded units of sandstone and diamictite are interpreted to reflect development of large sandy bedforms and ice margin fluctuations in a tectonically stable marine setting sedimentological and stratigraphic analysis of the port askaig formation demonstrates that tectonic activity had a significant influence on development of the lowermost parts of the succession climatic influences on sedimentation are difficult to identify during such phases of tectonic activity but are more easily discerned during episodes of tectonic quiescence e g phase iii of the port askaig formation the thick succession of diamictite interbedded with current deposited sandstone preserved within the port askaig formation is not consistent with deep freeze conditions proposed by the snowball earth hypothesis

a geologic perspective on the miocene evolution of the antarctic circumpolar current system abstract the dominant geologic feature of pelagic sediment accumulation patterns at intermediate water depths in the southern ocean is the sequential northward migration and replacement of a calcareous ooze sedimentary facies by a siliceous ooze facies following the late oligocene opening of the drake passage and the subsequent initiation of the antarctic circumpolar current closely spaced whole core measurements of bulk density are evaluated for four sites drilled in the southern ocean during ocean drilling program odp legs 113 sites 689 and 690 and 120 sites 747 and 751 these sites are all located on submarine rises in open ocean pelagic depositional environments south of the polar front a major oceanographie and sedimentologic boundary high resolution profiles of bulk density are used to correlate between adjacent drill holes on the maud rise where multiple overlapping sedimentary sequences were recovered using the advanced hydraulic piston core barrel apc stratigraphie age models have been applied to the bulk density data to provide a temporal framework for a discussion of the sedimentologic basis for paleoceanographic interpretations and also to constrain future acoustic research studies the early to middle miocene intervals at sites 689 and 690 are marked by distinct sequences of meter scale alternating carbonate and siliceous units separated by several proposed stratigraphie hiatuses at least six dissolution productivity events are identified in the middle to late miocene on the maud rise and others are noted at the odp sites on the kerguelen plateau the downhole profiles are used to identify the density signature and position of sediment facies changes and proposed stratigraphie hiatuses in sediment cores of late oligocene to late miocene age based on the reversals inflections and discontinuities in the downhole bulk density trends an analysis of the observed bulk density trends at these sites is combined with a review of other tectonic sedimentologic oceanographie and modeling studies to develop a hypothesis for explaining the observed sediment accumulation patterns at intermediate water depths of the southern ocean

neoproterozoic chemostratigraphy and correlation of the port askaig glaciation dalradian supergroup of scotland the 13 c of preglacial carbonates beneath the glaciogenic port askaig formation falls from 5 to negative values while least altered 87 sr 86 sr values are close to 0 7067 postglacial cap carbonates of the bonahaven formation begin with negative 13 c carb values jumping sharply to 11 7 near the top which we correlate with excursions above the elbobreen wilsonbreen glaciations of svalbard and putative sturtian not varanger glaciations elsewhere dated at c 720 ma much of the succeeding terminal neoproterozoic is missing in ne svalbard and east greenland raising doubts about their use for global sr and c isotope curves in the neoproterozoic

the dynamics of orographic wake formation in flows with upstream blocking the development of orographic wakes and vortices is revisited from the dynamical perspective of a three dimensional 3d vorticity vector potential formulation particular emphasis is given to the role of upstream blocking in the formation of the wake scaling arguments are first presented to explore the limiting form of the 3d vorticity inversion for the case of flow at small dynamical aspect ratio it is shown that in the limit of small the inversion is determined completely by the two horizontal vorticity components that is the part of the velocity induced by the vertical component of vorticity vanishes in the small limit this result leads to an approximate formulation of small fluid mechanics in which the three governing prognostic variables are the two horizontal vorticity components and the potential temperature the remainder of the study then revisits the problem of orographic wake formation from the perspective of this small vorticity dynamics framework previous studies have suggested that one of the potential routes to stratified wake formation is through the blocking of flow on the upstream side of the barrier this apparent link between blocking and wake formation is shown to be relatively straightforward in the small vorticity context in particular it is shown that blocking of the flow inevitably leads to a horizontal vorticity distribution that favors deceleration of the leeside flow at the ground this process of leeside flow deceleration as well as the subsequent time evolution of the wake is illustrated through a series of numerical initial value problems involving flows past 2d and 3d barriers it is proposed that the initiation of the wake flow in these stratified problems resembles the flow produced by a retracting piston in shallow water theory

subglacial and proglacial glacitectonic deformation in the neoproterozoic port askaig formation scotland abstract the recognition and interpretation of glacigenic sediments in the ancient rock record has important implications for understanding processes and patterns of climate change diamictite facies from the neoproterozoic port askaig formation scotland have been variously interpreted as evidence for grounded glacier ice mass movements on a glacially influenced submarine slope and subaqueous mass movements in a non glacial environment these contrasting interpretations imply widely differing degrees of ice cover and have contrasting implications for neoproterozoic snowball glaciations in this paper we focus on the great breccia and the disrupted beds two controversial units in the port askaig formation we present evidence that they were formed by the proglacial and subglacial deformation respectively of pre existing shallow marine facies during an advance of grounded ice quaternary examples provide remarkably exact analogues for the great breccia and disrupted beds illustrating the potential value of applying litho and tectono facies models to ancient sedimentary successions

submarine glacial landforms record late pleistocene ice sheet dynamics inner hebrides scotland we use 7000 km2 of high resolution swath bathymetry data to describe and map the submarine glacial geomorphology and reconstruct late pleistocene ice sheet flow configurations and retreat dynamics within the inner hebrides western scotland frequently dominated by outcrops of structurally complex bedrock the seabed also comprises numerous assemblages of well preserved glacigenic landforms typical of grounded ice sheet flow and punctuated ice margin retreat the occurrence and character of the glacially streamlined landforms is controlled in part by the shallow geology and topography however these factors alone cannot account for the location orientation and configuration of the observed landforms we attribute the distribution of these elongate streamlined landforms to the onset zone of the former hebrides ice stream his part of a major ice stream system that drained 5 10 of the last british irish ice sheet biis we suggest this geomorphic signature represents the transition from slow sheet flow to streaming flow as ice accelerated out from an environment characterized by numerous bedrock obstacles e g islands headlands towards the smooth sediment dominated shelf the majority of streamlined landforms associated with the his indicate ice sheet flow to the southwest with regional scale topography clearly playing a major role in governing the configuration of flow during maximal glacial conditions 29 23 ka we infer that the his merged with the north channel malin shelf ice stream to form a composite ice stream system that ultimately reached the continental shelf edge at the barra donegal trough mouth fan taken collectively however the pattern of landforms now preserved at seabed e g convergent flow indicators cross cutting flow sets is more indicative of a thinning ice mass undergoing reorganization during overall ice sheet retreat during latter stages of late weischselian glaciation suites of moraines overprinting the streamlined landforms suggest partial stabilization of the his prior to the ice sheet retreating to more isolated topographically confined troughs and basins retreat from the shelf towards and back into the inner hebrides may have been rapid due the prevalence of overdeepened troughs within the near shore fjord like troughs and deeps basin aligned streamlined landforms indicate the subsequent flow of thinner topographically partitioned ice masses and overprinted moraines record further ice margin retreat potentially along tide water margins this work provides the first geomorphological constraints for this large marine influenced sector of the former biis we also shed new light on the glacial geomorphic record found at the transition from terrestrial to marine continental shelf settings and examine the interplay between substrate geology bed topography bathymetry and grounding line positions relationships which are important for characterizing contemporary marine ice sheet margins

a rapid and synchronous initiation of the wide spread cryogenian glaciations abstract the neoproterozoic glaciations represent a remarkable milestone in earth evolution due to their major influence on atmosphere biosphere and hydrosphere the early cryogenian sturtian glaciations evidence for which has been recorded worldwide may have lasted for about 50 million years but the precise timing and synchroneity of these glaciations have been disputed jiangkou glacigenic strata in south china can be attributed to the sturtian glacial episode as they share sedimentological stratigraphic and lithological similarities with sturtian strata in south australia as such dating the onset of the jiangkou glaciation would contribute to testing the synchroneity of the worldwide sturtian glaciation in this paper we demonstrate by means of sims u pb zircon dating that the jiangkou glaciation in south china was initiated at 715 9 2 8 ma the new age is within uncertainty synchronous with dates obtained from the lower parts of glacigenic successions in laurentia and oman thereby indicating thereby indicating a synchroneity and global extent to the sturtian glaciation the synchronous occurrence of the sturtian glaciation in mid to low latitude regions implies rapid ice sheet advancement in response to ice albedo feedback as supported by numerical climatic modeling

holocene coastal carbonates and evaporites of the southern arabian gulf and their ancient analogues abstract the holocene sediments of the coast of the united arab emirates in the southeastern arabian gulf are frequently cited in the literature as type examples for analogous assemblages of carbonates evaporites and siliciclastics throughout the geologic record this paper is intended as a convenient single source for the description of sediments of this region providing information on how to reach the classic localities and some of the analogs the holocene sediments of the region accumulate over an area that is 500 km long and up to 60 km wide the sediments collecting offshore are predominantly pelecypod sands mixed with lime and argillaceous mud with these latter fine sediments increasing as the water deepens the pelecypod rich sediments also collect east of abu dhabi island both in the deeper tidal channels between the barrier island lagoons and in deeper portions of the protected lagoons west of abu dhabi island the shallow water margin is the site of coral reefs and coralgal sands whereas to the east oolites accumulate on the tidal deltas of channels located between barrier islands grapestones accumulate to the lee of the reefs and the oolite shoals where cementation becomes more common they are particularly common on the less protected shallow water margins of the lagoons west of abu dhabi island pelleted lime muds accumulate in the lagoons in the lee of the barrier islands of the eastern abu dhabi lining the inner shores of the protected lagoons of abu dhabi and on other islands to the west are cyano bacterial mats and mangrove swamps landward of these a prograding north facing shoreline is formed by supratidal salt flats sabkhas in which evaporite minerals are accumulating this paper describes the localities associated with 1 the mangrove swamps of the west side of the al dhabaiya peninsula 2 the indurated cemented carbonate crusts cyanobacterial flats and sabkha evaporites on the shore of the khor al bazam south of qanatir island 3 the reef and oolitic sand flats on the coast just east of jebel dhana and 4 the marine travertine and aragonite coats associated with the beach sediments in a small bay south of jebel dhana and 5 the sabkha mutti between jebel barakah and al sila similar sedimentological associations of carbonate and evaporites to those of the holocene of the united arab emirates are to be found in the tertiary and mesozoic sedimentary rocks of the immediate subsurface in the arabian gulf other analogs to this setting include the paleozoic carbonates of the western usa europe and asia mesozoic carbonates of the gulf of mexico europe and middle east and tertiary sedimentary rocks in the middle east

dissolution methods for strontium isotope stratigraphy whole rock analysis the preparation of samples for strontium isotope stratigraphy sis by whole rock dissolution results in contributions of sr from contaminant phases as well as from the target carbonate phase here we highlight and quantify the errors in 87sr 86sr values that might result when calcium carbonate is dissolved using an inappropriate method we report the variation in 87sr 86sr value of sr released from four samples of differing calcite content and degrees of cementation when subject to different methods of dissolution we show that errors of up to 0 000076 in 87sr 86sr which correspond to errors of 3 68 ma in age can be avoided by careful preleaching of the samples

glacial trinity neoproterozoic earth history within the british irish caledonides two distinct neoproterozoic glacial episodes are known for the dalradian supergroup in the british irish caledonides the port askaig formation and the inishowen loch na cille ice rafted debris ird beds here we describe a third intermediate between those two the stralinchy reelan formations composed of diamictite and ird developed directly above these rocks is the cranford limestone which consists of a basal 1 6 m thick tan gray dolostone overlain by a variably developed but as much as 340 m thick sequence of thin bedded limestone and dolostone this unit exhibits a c isotopic trend that begins negative in the basal dolostone reaches a nadir of 7 and then rises to 0 2 these characteristics match strikingly those of marinoan style cap carbonates consequently we interpret the port askaig formation the stralinchy reelan units and the inishowan loch na cille beds as equivalents of the ca 700 ma sturtian the 635 ma marinoan and the ca 580 ma gaskiers glacials respectively two additional observations are noteworthy carbonate rocks below the port askaig formation record a 13c decline to 6 that implies that such downturns may occur in both pre sturtian and pre marinoan strata in addition the bonahaven dolomite is not a cap carbonate to the port askaig formation but exhibits a 13c rise to 12 which we correlate with the inferred global keele peak these data further document the utility of neoproterozoic glacial cap carbonate sequences in global correlations and denote the base of the cranford linestone as the cryogenian ediacaran boundary

giant cross beds in the neoproterozoic port askaig formation scotland implications for snowball earth abstract the neoproterozoic port askaig formation is a thick succession of interbedded diamictite conglomerate sandstone and mudstone that records glacially influenced marine sedimentation in the extensional dalradian basin giant cross beds individual units up to 11 m thick are observed in sandstone at the base of member iii of the port askaig formation the cross bedded sandstones are closely associated with other sandstone diamictite and conglomerate facies and are characterized by both planar and trough shaped foreset laminae with an average maximum dip angle of 14 the cross bedding has compound internal structure and indicates a predominant paleocurrent direction towards the south the sandstone is medium grained well sorted and quartzitic the giant cross beds are interpreted to have formed as a result of the migration of large subaqueous simple and compound dunes in a marine setting based on sedimentological analysis of the sandstone and associated facies as well as the tectonic setting of the port askaig formation the giant dunes are thought to have formed under the influence of tidal currents and indicate open marine ice free depositional conditions the sedimentology of the cross bedded sandstone and its close association with diamictite and conglomerate indicate repeated ice margin advance and withdrawal with periods of both ice free and ice influenced conditions the environmental conditions recorded in these port askaig deposits appear inconsistent with deep freeze or rapid meltback associated with a snowball earth

a cryogenian chronology two long lasting synchronous neoproterozoic glaciations the snowball earth hypothesis predicts globally synchronous glaciations that persisted on a multimillion year time scale geochronological tests of this hypothesis have been limited by a dearth of reliable age constraints bracketing these events on multiple cratons here we present four new re os geochronology age constraints on sturtian 717 660 ma and marinoan 635 ma termination glacial deposits from three different paleocontinents a 752 7 5 5 ma age from the base of the callison lake formation in yukon canada confirms nonglacial sedimentation on the western margin of laurentia between ca 753 and 717 ma coupled with a new 727 3 4 9 ma age directly below the glacigenic deposits of the grand conglomerate on the congo craton africa these data refute the notion of a global ca 740 ma kaigas glaciation a 659 0 4 5 ma age directly above the maikhan uul diamictite in mongolia confirms previous constraints on a long duration for the 717 660 ma sturtian glacial epoch and a relatively short nonglacial interlude in addition we provide the first direct radiometric age constraint for the termination of the marinoan glaciation in laurentia with an age of 632 3 5 9 ma from the basal sheepbed formation of northwest canada which is identical within uncertainty to u pb zircon ages from china australia and namibia together these data unite re os and u pb geochronological constraints and provide a refined temporal framework for cryogenian earth history

petrography and carbonate chemistry of some dalradian dolomitic metasediments preservation of diagenetic textures the bonahaven formation of northern islay scotland despite having undergone high pressure greenschist facies metamorphism contains many relics of its diagenetic history early diagenetic dolomite textures calcite and clay mineral cements are well preserved locally burial diagenetic compactional and pressure solution features are recognizable together with quartz and feldspar overgrowths and variable styles of replacement by and recrystallization of dolomite calcite pyrite quartz and albite the imprint of deformation and metamorphism is variable probably as a result of differences in the degree of pressure solution and the co 2 content of pore fluid typically some solution transfer phenomena occur accompanied by growth of cleavage defining phengite and sporadic phlogopite locally abundant phlogopite or biotite is present in lithologies with fully developed metamorphic textures dolomite shows good preservation of pre metamorphic textures and minor element zonation but calcite does not metamorphic re equilibration was insufficient to allow the derivation of maximum temperatures by calcite dolomite geo thermometry