the carbonate factory of middle triassic buildups in the dolomites italy a quantitative analysis middle triassic carbonate buildups of the dolomites were high in relief 500 1000m and small in size one to a few square kilometres in area a paradox results from the carbonate platform model that invokes the platform top including reef rims as the carbonate factory and flanking beds as talus deposits most buildups consist largely of clinoforms inclined at 10 50 whereas massive reef rocks and stratified buildup interiors are poorly developed or absent facies and modal analysis of 323 thin sections from buildups of the marmolada indicate that clinoforms are i predominantly composed of in situ boundstones 56 of all samples ii primarily made up of early cements 37 vol microbial crusts 17 vol micritic intraclasts 10 vol and tubiphytes 8 vol and iii contain diagnostic shallow water grains dasyclads coated grains that are less abundant by 1 2 orders of magnitude compared with buildup interior facies these data suggest that the clinoforms themselves were the main carbonate factory of the triassic buildups stratified buildup interior rocks and massive reef rocks were apparently not a prerequisite for buildup growth and clinoform progradation

the latemar a flat topped steep fronted platform dominated by microbialites and synsedimentary cements abstract facies analyses on the latemar isolated carbonate platform suggest a higher proportion of microbial carbonates compared to literature this is evident especially in the margin upper slope zone where microbial boundstone associated with tubiphytes calcareous sponges botryoidal aragonite and radiaxial fibrous cements extended down to 250 m water depth the latemar flat topped high relief platform has been subdivided into five different facies belts inner and outermost platform margin upper and lower slope each facies belt represents subtidal environments except for the inner platform which is characterized by a peritidal facies association point counting analysis was carried out on ca 90 thin sections to quantify the different platform components microbialite and cements are most abundant they represent respectively ca 40 and ca 34 of the whole platform volume these results suggest that carbonate production at latemar occurred in a m factory microbial carbonates as well as early marine cements are most abundant on the upper slope margin and outermost platform although microbialites are found in all facies belts the presence of supratidal sedimentary facies restricted only to the inner platform and of a completely subtidal outermost platform suggests a new depositional profile for the latemar the central portion is occupied by the flat platform interior cyclically subaerially exposed facies of the subtidal outermost platform surround the inner platform and display a progressive increase in depth toward the margin the margin is submerged and essentially constituted by microbial and cement boundstone the slope is characterized by steep clinoforms 35 dominated by in situ microbialites in the upper middle portion 0 250 m depth evidently precipitated by non light dependent microbially influenced processes the lower slope is mostly detrital poor in platform top derived sediments and dominated by margin and upper slope derived rudstone and grainstone all these observations are in agreement with the slope shedding model observed in the pennsylvanian microbial margin in asturias n spain and allow the interpretation of the latemar as a flat topped steep fronted platform dominated by microbialites and cement boundstones

dolomitization of the latemar platform fluid flow and dolomite evolution abstract the anisian ladinian latemar platform northern italy presents a spectacularly exposed outcrop analogue for dolomitized carbonate reservoirs in relation to fracture controlled igneous intrusions although the latemar is one of the best studied carbonate platforms worldwide timing and evolution of dolomitization and the link to fractures and dikes have not been explored in detail previous dolomite observations are based on a stratigraphically limited portion of the platform this study extends observations to the complete exposed interval in which dolomite bodies occur including those within the less accessible valsorda valley numerous parallel mafic dikes crosscut the latemar platform and border several of its large dolomite bodies 50 m wide 100 m high within dikes and along dike carbonate contacts there are abundant dolomite veins that are geochemically related to surrounding dolomite bodies dolomitization is the result of limestone interaction with hydrothermal fluids delivered along these dikes at dike boundaries impermeable marble aureoles exist derived from contact metamorphism the marble aureoles have locally shielded surrounding limestone from dolomitizing fluid dolomite occurs only where the protective marble is missing or crosscut by fractures based on geometric relationships we conclude that dikes and their damage zones formed the pathways for the dolomitizing fluids and functioned as boundaries for dolomite bodies from field observations and petrography we established a detailed paragenesis dolomitization started shortly after dike emplacement there is an evolution in the fe content of matrix dolomite and dolomite veins from highly ferroan dolomite to non ferroan saddle dolomite alternating with episodes of silica cementation non ferroan calcite precipitation followed dolomitization possibly indicating concurrent depletion in mg this stage likely resulted in further limestone recrystallization rather than dolomitization stable and radiogenic isotopes suggest that the dolomitizing fluid comprised carnian seawater with elevated fe and mg from interaction with other lithologies possibly the nearby predazzo intrusion

grain growth kinetics in olivine aggregates abstract grain growth kinetics were studied in hot pressed fine grained olivine aggregates experimental conditions include pressures of 0 1 mpa 300 mpa and 1 gpa and temperatures of 1473 1573 and 1673 k with or without the presence of water at the initial stage of grain growth growth of larger grains occurs rapidly consuming smaller grains which results in significant pore entrapment almost homogeneous grain size distribution is established in this process after this stage grain size distribution remains almost homogeneous in most cases it was found that the presence of water enhances the grain growth kinetics when the amount of water is limited however when the amount of water is large the water containing pores significantly inhibit the grain boundary migration therefore the enhancement of grain growth due to the presence of water is due to the role of dissolved water in olivine rather than the mass transport through water abnormal grain growth was found in some samples in these cases normal grain growth was inhibited by the presence of a significant amount of water filled pores or grains with significantly larger size than the rest occurred in the starting materials in 0 1 mpa runs significant porosity developed and the grain growth rates were significantly lower than in those at high confining pressures these results show that both water and pores have important effects on grain growth kinetics in olivine when the effects of pores or secondary phases in inhibiting grain growth are unimportant the grain growth rate in olivine is very fast growth to 100 m size will occur in 102 to 103 hours at 1500 k thus fine grain size in olivine will be maintained only for a short geological time unless the grain boundaries are effectively pinned by secondary particles

upper triassic norian cephalopod limestones of the hallstatt type oman norian crinoidal brachiopod limestones and cephalopod limestones of the hallstatt type occur as blocks in a hettangian calcareous breccia of the haliw formation in the oman mountains crinoidal and brachiopod packstones up to 12 m thick prevail in the lower part of the sequence and were deposited on a substrate of norian forereef breccia the overlying cephalopod wackestones up to 4 9 m thick have a basal white bed followed by red limestones with abundant planar and scalloped corroded surfaces and local stromatolites upward red nodular wackestones and finally slumped grey wackestones follow the analysis of geopetal fabrics in orientated samples shows that bedding of these facies is in fact inclined bedding inclinations varied between 15 and 29 in addition the restored dip directions demonstrate rotation indicating deposition on a gliding block the preferred orientation of orthoconic cephalopods and imbrication of discoidal ammonoids coincide with the dip direction measured from geopetal fabrics such features generally interpreted as current induced are here interpreted as gravity induced the overall mud supported rock fabric thus indicates deposition under very low energy conditions the common mud supported texture of the rocks contrasts with evidence for current activity found in the scalloped surfaces and shell lags particularly in the crinoidal brachiopod facies and the lower stratigraphically condensed cephalopod limestones this indicates that deposition of lime mud alternated with periods of elevated current strength a comparison of the hallstatt type limestones and current influenced sediments on the northern slope of the little bahama bank suggests that condensed sequences of the hallstatt type are restricted to relatively shallow depths with strong fluctuation of contour following currents undersaturated with respect to aragonite along carbonate shelf margins facing the open ocean on steep slopes sediment bypassing may be an additional factor for stratigraphic condensation

triassic latemar cycle tops subaerial exposure of platform carbonates under tropical arid climate the triassic latemar platform in the dolomites italy is the site of several ongoing controversies perhaps the most interesting debate focuses on apparent cyclic deposition within the latemar platform whose nature and duration are still open to debate further disagreement concerns the lack of meteoric diagenesis related isotope shifts at cycle tops that bear circumstantial petrographic evidence for subaerial emergence here an evaluation of the nature of latemar cycle tops is presented combining evidence from previous work and new field petrographic and geochemical data cycle tops are ranked according to increasing exposure duration and spatial extent type i surfaces lacking unequivocal evidence of prolonged supratidal conditions type ii dolomite caps formed in warm evaporitic intertidal lagoonal waters followed by exposure of perhaps intermediate duration type iii clastic rich red calcareous horizons with some showing platform wide extent representing prolonged supratidal conditions and type iv discontinuities in tepee belts genetically related to type ii and iii surfaces but likely representing shorter lived exposure stages petrographic and geochemical criteria indicate that most diagenesis occurred in the shallow marine and burial domain whilst an extensive meteoric overprint of cycle tops is lacking this is underlined by the scarcity of meteoric diagenetic fabrics such as gravitational cements that where present are here interpreted as marine vadose in origin the scarcity of carbon and oxygen isotope signatures commonly assigned to subaerial exposure stages is best explained in the context of mid triassic climate the low latitude tropical but arid setting of the latemar situated in the western extension of the tethys ocean its isolation from nearby continental areas and overall short term emergence episodes are in agreement with a limited degree of meteoric alteration of most cycle tops high amounts of aeolian clastic material beneath some cycle tops along with high fe and mn elemental abundances argue for intermittent subaerial conditions this study proposes an enhancement of the classical allan and matthews 1982 isotope model for subaerial exposure under strongly arid climates as the subaerial exposure nature of latemar cycle tops and therefore eustasy as the cause for cyclicity have been previously challenged due to the lack of meteoric induced isotopic signatures the outcome of this study is of significance for the ongoing latemar stratigraphic controversy

oldest scleractinian coral reefs on the north american craton upper triassic carnian northeastern british columbia canada abstract bioclastic accumulations composed of crinoids brachiopods molluscs spongiomorphs and scleractinian corals occur within upper triassic strata of the lower baldonnel formation at pardonet hill in northeastern british columbia canada these small buildups 100 to 500 m3 have planar bases and broadly convex tops these mounds are interpreted as small patch reefs composed of packstone bioclastic floatstone rudstone and carbonate breccia intercalated with mixed siliciclastic carbonate sediments deposited in a shallow subtidal setting i e above fairweather wave base amalgamated hummocky cross stratified to current ripple laminated quartz dominated sandstone beds and numerous sharp based normally graded bioclastic commonly encrinitic packstone grainstone quartz sandstone couplets characterize inter reef lithologies conodont biostratigraphy indicates that the pardonet hill patch reefs occur within strata dated as earliest upper carnian lower nodosus zone the pardonet hill patch reefs originated and developed during an interval of regional sea level lowstand strata within which these patch reefs occur represent the westernmost migration of the triassic shoreline in western canada disappearance of coral reefs in the study area may have been affected by rapid marine transgression and failure of reef faunas to recolonize the new shore zone further to the east the pardonet hill locality occurred on the western margin of the north american craton during the triassic prior to their discovery reef like structures dominated by corals in the western panthalassa were limited to allochthonous terranes now part of the cordillera the pardonet hill patch reefs occur at approximately 30 triassic paleolatitude in modern settings this is at the extreme latitudinal margin of subtropical zooxanthellate reef development the presence of benthic faunas characteristic of low paleolatitude settings on the northwestern coast of pangea has significant implications in paleotectonic and paleoenvironmental reconstructions

quantitative compositional analysis of a triassic carbonate platform southern alps italy abstract we have estimated abundance and distribution of automicrite marine cements and skeletal grains in the triassic sella massif an isolated platform flanked by steep 25 35 clinoforms 108 samples were taken at constant intervals from measured sections of the major zones of the platform edifice the platform top margin upper slope and lower slope in a first step carried out in the field and on hand specimen purely detrital deposits were separated from automicrite facies i e beds with automicrite cement filled primary vugs and admixtures of skeletal carbonate and lithoclasts in the second step samples with automicrite facies were thin sectioned and point counted the categories used for point counting were a automicrite b vugs and cement c microspar or neomorphic spar d skeletal grains and e internal sediments at the platform top 46 of samples are pure detrital deposits 27 consist of automicrite facies and 27 are too strongly altered by dolomitization to allow classification at the margin upper slope 68 of samples consist of automicrite facies 22 are pure detrital sediments and 10 are strongly altered at the lower slope 63 are detrital deposits 10 automicrite facies and 27 are extensively dolomitized the most important contributors to the automicrite facies are automicrite 41 on the platform top 29 on the margin upper slope 28 on the lower slope and early marine cement 35 on the platform top 48 on the margin upper slope 27 on the lower slope the amount of skeletal grains is less than 10 the automicrite facies stabilized the platform margin and upper slope automicrite abundant early marine cements and micro organisms such as tubiphytes formed a rigid framework thus substituting for the lack of a metazoan reef on the upper slopes the framework of automicrite facies stabilized the slope but intermittently the automicrite layers are frequently dissected by sediment filled fractures or are broken into clasts we assume that they slid on the layers of loose detritus bigger slides turned into rubbly debris flows that formed metre thick breccias at the lower slope and the proximal basin floor the planar shape and steep angle of the clinoforms indicate that the large scale geometry of the slope was not controlled by the automicrite but rather by non cohesive layers of sand and rubble piled up to the angle of repose the production mode of the sella is comparable of that of a mud mound factory this factory was highly productive in 1 ma the platform aggraded over 300 m and prograded over 2000 m in all directions

progradation geometries of carbonate platforms examples from the triassic of the dolomites northern italy various types of progradation of triassic carbonate platforms are described from the dolomites of the southern alps the internal and external geometric relationships are exposed in spectacular natural sections and moreover their scale 500 1000 m of thickness is such that they can be compared with features found in seismic profiles the different types of progradation are controlled by a number of factors which normally interact with each other these factors include rate of basinal sedimentation rate of subsidence width of the platform depth of the surrounding basin and eustatic variations of sea level progradation is not a continuous process but episodic moments of massive debris input during which the platform advances alternate with long periods of negligible progradation during which basinal sediments accrete and onlap the toe of slope upper boundary relationships of the prograding platforms include offlap toplap and erosional truncation lower boundary relationships are horizontal climbing and descending progradations a variety of phenomena and circumstances have caused the cessation of progradation of the triassic platforms they include volcanism collapse of margins drowning rapid relative rise of sea level subaerial exposure relative fall of sea level and probably a natural decay of the system in the triassic of the dolomites two main progradation models can be put forward in the ladinian model progradation took place simultaneously with aggradation relative rise of sea level whereas the characteristic feature of the carnian model is toplap relative stillstand of sea level

reef fabrics biotic crusts and syndepositional cements of the latemar reef margin middle triassic northern italy the latemar reef buildup of the central dolomites northern italy provides a rare opportunity to examine an in place middle triassic upper anisian to lower ladinian platform margin that is not strongly deformed or dolomitized the margin lies between the flat lying platform interior and steeply dipping foreslope clinoforms across this transition the depositional profile relates directly to a consistent lateral facies pattern 1 restricted biota grainstone of the platform interior 2 tubiphytes rich boundstone and 3 diverse biota grainstone that grades into 4 foreslope breccia beds the boundstone and diverse biota grainstone facies comprise the platform margin the boundstone facies consists of a framework of small 10 cm skeletal remains 10 by volume with associated biotic crusts internal sediments and syndepositional cements crusts and cements constitute most of the rock volume and created the boundstone fabric biotic crusts exhibit gravity defying geometries and range from a light grey structure grumeleuse rind to dark grey micritic laminae both cements and biotic crusts occur as redeposited talus in the foreslope talus deposits indicating a syndepositional origin the diverse biota grainstone facies primarily consists of skeletal peloidal grainstone with a diverse open marine biotic assemblage in contrast to the restricted biota grainstones of the platform interior that have a low diversity restricted marine biota metre scale hexacoral boundstone and centimetre scale sponge boundstone and microbial boundstone occur as isolated patches tens to hundreds of metres apart within the diverse biota grainstone facies the depositional profile facies zonation and biotic constituents all indicate that the latemar buildup had a shallow water reef margin in contrast to previous interpretations that these were upper slope reefs the syndepositional biotic crusts and inorganic cementation played key roles in stabilizing the boundstone fabric to form a wave resistant reef fabric

zoned minerals in garnet peridotite nodules from the colorado plateau implications for mantle metasomatism and kinetics some garnet peridotite nodules from the thumb a minette neck on the colorado plateau in the southwestern united states contain zoned minerals zoning does not exceed 1 5 wt for any oxide but some relative changes are large in one garnet tio2 and cr2o3 ranges are 0 05 0 65 and 3 5 5 0 wt respectively in two porphyroclastic nodules garnet rims are depleted in mg and enriched in fe ti and na compared to cores and one garnet is irregularly zoned in ti and cr olivine crystals in these rocks are unzoned and pyroxene zoning is slight yet matrix olivine and pyroxene contain more fe and ti and less mg and cr than inclusions of these phases in garnet in three coarse nodules garnet rims are ti rich compared to cores and ca fe mg and cr zoning patterns are complex several nodules appear to have partially equilibrated near 1200 c and 35 kb and under these conditions cation mobility in pyroxene was greater than in garnet

triassic climates state of the art and perspectives abstract the climate of the triassic period was characterized by a non zonal pattern dictated by a strong global monsoon system with effects that are most evident in the tethys realm this strong monsoonal regime is related to the aggregation of the pangaean supercontinent which by triassic time was already completed climate oscillations existed within this framework the harsh hot house climatic conditions that characterized the late permian and perhaps precipitated the end permian mass extinction were probably maintained during the early triassic and may account for the impoverished but distinctive faunal and floral lower triassic associations although metazoan reef builders were probably the most affected group carbonate production remained high at least in the western tethys realm the middle triassic was characterized locally by humid episodes although their geographical distribution has yet to be clarified the carnian pluvial event marks an episode of increased rainfall documented worldwide was the most distinctive climate change within the triassic different hypotheses have been proposed for its causes changes of atmospheric or ocean circulation driven by plate tectonics a peak of the global monsoon due to maximum continent aggregation or triggering by the eruption of a large igneous province subsequently the late carnian and norian seem to have been climatically stable although minor climatic changes have recently been described even from this time period finally the end triassic extinction event is also associated with climate change specifically warming and increased rainfall but this evidence comes mostly from the northern parts of the central atlantic magmatic province and the global pattern of climate change at the triassic jurassic boundary has still to be resolved many facets of triassic climate are intriguing and deserve further research however palaeoclimate studies on the triassic have so far been carried out only locally with different proxies those proxies will require inter calibration in order to depict correctly the temporal and geographical patterns of triassic climate

pioneer reef communities within a middle triassic anisian to upper triassic carnian mixed carbonate siliciclastic ramp system from the star peak group south canyon central nevada abstract reef patterns change drastically between the late paleozoic and early mesozoic due to the effects of the end permian mass extinction reef communities follow an ecological transition from the stabilization stage in the anisian to the colonization stage in the carnian through norian to the final diversification and domination stages in the norian through the rhaetian most eastern panthalassa reef studies focused on documenting framework supported reef structures elevated from the seafloor during the late triassic diversification stage however to fully understand reef development we also need to record the precursor stages here we examine field based and microfacies data using a sequence stratigraphic lens to develop a quantitative assessment of non skeletal and skeletal carbonate grains our results indicate that a reef mound and biostromes developed during an overall transgressive sequence due to substrate cementation caused by flooding events although taxonomic differences between biostromes and the reef mound change through time we conclude that these taxonomic changes do not record true first occurrence data instead these fossil accumulations probably occurred due to random chance of larval recruitment even though the reef types found here preserve similar taxa that have been shown to promote high reef growth e g calcified demosponges calcareous algae and bivalves low reef growth structures are found at our site thus reefs containing large amounts of micrite built by low growing binding and encrusting organisms typify this middle and upper triassic section confirming that this section records the colonization stage of reef recovery

quantification of input and compositional variations of calciturbidites in a middle triassic basinal succession seceda dolomites southern alps triassic calciturbidites were studied in a 100 m long core and nearby outcrops of the basinal buchenstein formation to determine composition and thickness variations the quantity of recognized turbidite sediment relative to background sediment changes from 15 by volume in the lower part to 60 in the upper part reflecting the steady progradation of nearby platforms the composition of the sand fraction of 214 turbidites was point counted in thin sections micrite peloids average 23 and lithoclasts 16 are by far the most dominant constituents they are interpreted as two different varieties of in situ precipitated micrite automicrite which probably formed under the influence of microbes and constitute the principal building material of the adjacent platforms platform derived skeletal grains amount to only 0 5 variations in turbidite composition were quantified using spearman s rank correlation and cluster analysis the most significant compositional variations seem to be related to hydrodynamic sorting in the turbidity currents and to the gradual shift from distal to more proximal turbidites in the core as the platforms prograded basinward cluster analysis of the 214 samples shows a major subdivision into micrite and sparite dominated turbidites clusters associated with micrite dominated turbidites are enriched in radiolaria and thin shelled bivalves whereas the clusters related to sparite dominated turbidites show an abundance of lithoclasts this subdivision seems strongly related to sorting effects in a turbidity current point counting of turbidites in nearby outcrops revealed a lateral variation in composition proximal turbidites are sparite dominated and enriched in lithoclasts distal portions are chiefly micrite with an open ocean biota thin shelled bivalves radiolaria this differentiation resembles the vertical change in composition of thick turbidite beds and is attributed to different settling rates of the various grains in the turbidity current there is no indication that turbidite composition fluctuated significantly under the influence of sea level fluctuations this is not surprising because the dominant automicrite facies of the platforms only migrates laterally but does not change much during sea level cycles

isolated stationary carbonate platforms the middle triassic ladinian of the marmolada area dolomites italy as a result of a phase of extensional tectonics in the western tethyan region a horst and graben topography formed during the middle triassic ladinian in northern italy horsts were sites of shallow water carbonate sedimentation while pelagic and volcaniclastic sediments were deposited in the grabens two carbonate platforms approximately 500 m thick can be distinguished in the marmolada area of the dolomites the marmolada platform proper which covered an area of 6 km2 and the costabella platform which extended for about 12 km in a nw se direction and was about 3 km across the facies of these isolated platforms reflect the influence of storms from the sw windward platform margins were characterized by a marine sand belt of skeletal and aggregate grainstones with a dominant platform directed cross stratification the central portions of the platforms were occupied by supratidal sand cays which are made up of storm washovers leeward parts of the platforms are composed of shallow subtidal sand flat deposits laterally discontinuous reefs chiefly composed of various calcareous algae are developed at the outer margins of the platforms along windward margins reefs may form a belt several hundred metres wide along leeward margins their width is commonly reduced to some tens of metres foreslope talus breccias surround the platforms clinoform bedding showing basinward dips of 30 40 is typical of this facies belt which is approximately 2 km wide basinal sediments only some tens of metres thick are radiolarian micrites abundant sediment gravity flow deposits expand the basinal sequence at the toes of windward margins and were probably triggered by storm return flows synsedimentary faults striking both nne ssw and nw se separate the bedded platform limestones from flank deposits and reefs they account for the stationary nature of the platforms neptunian dykes show preferred nne ssw and e w trends sinistral displacements are associated with nw se trending faults depressions in the basins filled with red turbiditic pelagic sediments show n s trends and are probably compressional in origin the structural pattern may have resulted from oblique nw se oriented extension of the e w trending middle triassic graben zone of the dolomites in the ladinian of the dolomites the stationary platform type can be distinguished from a retrograding type whereas continuously prograding platforms apparently did not develop

middle triassic strike slip tectonics and igneous activity of the dolomites southern alps abstract strike slip faults and south vergent thrusts deformed a rhomb shaped area measuring about 20 20 km in the dolomites during the late ladinian deformation was caused by a right stepover of a nne ssw trending sinistral strike slip fault strike slip displacement amounted to more than 10 km thrusting caused a relief shortening of more than 3 km and can be demonstrated by the matching of particular ladinian carbonate facies boundaries these tectonic movements may account for the termination of a transgressive depositional megacycle which had begun in permian times rupture of the crust of the deformed terrain caused the emplacement of a magma chamber beneath its evacuation in the latest ladinian and early carnian was associated with the collapse of its roof and the extrusion of shoshonitic lavas they filled a volcano tectonic depression which overlaps with the deformed and eroded area the orientation of volcanic dikes suggests the absence of tectonic strain during igneous activity provided that they formed contemporaneously

controls on facies architecture of a large triassic carbonate platform the great bank of guizhou nanpanjiang basin south china abstract the great bank of guizhou gbg is an exceptionally well exposed isolated triassic platform in the nanpanjiang basin of south china the platform is exhumed with its depositional profile preserved and is dissected by a faulted syncline that exposes a complete and uncomplicated cross section providing a unique opportunity to evaluate mechanisms involved in its birth evolution and demise the gbg formed near the southern margin of the yangtze platform during a deepening event that expanded the nanpanjiang basin and drowned the region surrounding the gbg in the latest permian initial accumulation of the gbg began in the latest permian with small reef mounds and open marine skeletal packstones following the end permian extinction cyanobacterial boundstones grew over the bank top during the early triassic the gbg developed a low relief bank profile with mobile oolite shoals at the margin shallow subtidal and peritidal deposits in the interior and gentle slopes dominated by pelagics debris flow deposits and turbidites at the basin margin in the middle triassic anisian the gbg developed a progressively steepening profile rimmed with massive tubiphytes reefs the platform was flat topped with tidal flat deposits across the interior basin margin deposition was dominated by turbidites and debris flow deposits but eventually shifted to avalanche and rock fall deposits as the slopes steepened to the angle of repose in the middle triassic ladinian an erosional escarpment up to 1700 m high developed at the margin platform margin strata are bedded packstones similar to interior strata whereas breccias at the basin margin contain coral boundstone clasts suggesting erosion of reefs from the escarpment a restricted subtidal lagoon formed in the interior producing an atoll like morphology later a flat topped profile was restored as tidal flats spread across the interior in the beginning of the late triassic deepening contributed to termination of the gbg before siliciclastic turbidites and shales were deposited over the platform in contrast with the well known platforms of the dolomites of northern italy the gbg contains abundant muddy carbonates and a progressively steepening bank to reef rimmed and escarpment architecture the italian platforms contain little mud and have angle of repose pinnacle geometries the gbg s larger size increased mud production and protected it from extensive winnowing of mud which in turn resulted in off bank shedding of muddy sediments that were stable on relatively gentle basin margin slopes which progressively steepened and ultimately led to avalanche deposits and a high relief erosional escarpment in contrast the lesser mud content of the dolomites platforms forced avalanche and talus deposition to dominate throughout deposition of basin margins which in turn produced their angle of repose geometries

sequence stratigraphy after the demise of a high relief carbonate platform carnian of the dolomites sea level and climate disentangled abstract sedimentary facies analysis aided by quantitative 3d georeferenced field data is applied to constrain the sequence stratigraphy of a complex stratigraphic interval in the late triassic of the dolomites this multidisciplinary approach was the key to disentangle the timing of climatic change vs sea level fluctuation and their effects on shallow water carbonate depositional systems the carnian pluvial event a global episode of climate change worldwide documented at low latitudes involved increased rainfall and possibly global warming this climatic event begins before a drop of sea level and caused the demise of microbial dominated high relief carbonate platforms that dominated the dolomites region and was followed by a period of coexistence of small microbial carbonate mounds and arenaceous skeletal oolitic grainstones a subsequent sea level fall brought to the definitive disappearance of microbialites and shallow water carbonates switched to ramps dominated by oolitic bioclastic grainstones the crisis of early carnian shallow water carbonate systems of the dolomites generated a geological surface similar to a drowning unconformity although no transgression occurred as the high relief microbial carbonate systems characterized by steep slopes switched to gently inclined oolitic skeletal siliciclastic ramps basins were rapidly filled the change of carbonate depositional systems was associated with an increase in siliciclastic input in turn triggered by the onset of a humid climatic event and only later to a sea level drop this evolution of carbonate systems cannot be interpreted in the light of sea level changes only climate change and consequent ecological changes in the main carbonate producing biotas induced significant modifications in depositional geometries this case study may serve as a conceptual model for the sedimentary evolution of carbonate systems subject to ecological crisis that do not evolve in platform drowning because despite a drop in shallow water carbonate production a combination of low subsidence and or sea level drop maintains the platform top at shallow depth

facies architecture of an isolated carbonate platform in the hawasina basin the late triassic jebel kawr of oman abstract in the oceanic realm of the southern tethys carbonate production of isolated platforms ceased after the end permian mass extinction and did not recover until the late triassic the misfah formation mf at jebel kawr in the oman mountains is interpreted as a relic of such an isolated late triassic platform of the hawasina ocean a part of the neo tethys correlation of three sections at jebel kawr points to a sequence architecture with four third order sequences mf1 mf4 the maximum flooding surface mfs of mf3 can be correlated to the attached arabian platform the shallow water carbonates of jebel kawr comprise a platform rim reef facies and bedded inner platform facies characterized by stacked high frequency cycles with subtidal to intertidal carbonate sequences the depositional profile of this late triassic isolated platform evolved during carnian and norian time from a low relief carbonate bank to a high relief platform rimmed by reefs the onset of the carbonate sedimentation is characterized by an initial phase with volcaniclastic interruptions followed by a carbonate bank stage with a shallow subtidal to peritidal interior and marginal oolite shoals in the norian vertical accumulation caused an increase of the platform height and developed a relief along the margins that progressively increased through the aggrading reef stage the possibility that a reef rim existed and was later removed by erosion is suggested by the sint reef and olistoliths of similar reef limestones in the surrounding areas

compositional variations during phases of progradation and retrogradation of a triassic carbonate platform picco di vallandro durrenstein dolomites italy in this paper data are presented on the composition of sediments deposited at the toe of slope during progradation or retreat of triassic carbonate platforms in the dolomites italy for this purpose a succession was studied from the toe of slope of a triassic carnian carbonate platform picco di vallendro durrenstein dolomites italy the microfacies analysis of selected calciturbidites sequences revealed a reduced input of oncolites and ooids during progradation and an increase in clasts the main input however was derived from the reefs on the platform retrogradation of the platform showed an increase of filaments and radiolarians open ocean biota as well as carbonate mud and a reduced input of grains that originated within the reefs on the platform both during progradation and retrogradation parts of the platform were flooded and could produce excess sediment that could be exported to the surrounding basins however the absence of platform interior biota documents that progradation occurred from sediments of the reefal belt probably during relative sea level lowstands carbonate composition varies systematically with toe of slope progradation retrogradation and thus argues for carbonate production as the main driver of the geometries observed at the toe of slope

alpujarride carbonate deposits southern spain marine sedimentation in a triassic atlantic abstract in the betic cordillera the westernmost of the alpine chains the alpujarride complex is the only one in which the middle upper triassic is represented predominantly by carbonate marine facies the correlation of various stratigraphic columns together with the position of the facies belts at different levels reveal that these carbonate deposits could only have originated in a basin which opened westwards to the sea in contrast to previous hypotheses the triassic alpujarride basin is thought to have opened towards an atlantic in the west and not towards the tethys in the east although some connection clearly existed between the alpujarride and tethys basins during the middle triassic when the extension of the alpujarride carbonate deposits was at its greatest the upper triassic saw a separation of the alpujarride basin from the tethys which is reflected in the very specific peculiarities in the endemic flora and differences in the types of bioconstructions which evolved in this and in coetaneous basins thus the alpujarride carbonate deposits originated in an early atlantic and were tectonically emplaced in the western mediterranean by transform movements and later by overthrust

grain boundary enrichment of incompatible elements in some mantle peridotites electron microprobe analyses sensitive to 15 40 ppm at 3 confidence have been made for minerals in a spinel dunite from san carlos arizona u s a and a spinel lherzolite from ichinomegata akita ken japan whereas both rocks contain an appreciable amount of k2o p2o5 and tio2 the constituent minerals contain only trace amounts of these elements microprobe analyses across the grain boundaries on polished sections and on mineral surfaces before and after acid leaching show that most of the incompatible elements in the rocks are contained within a surface film al k emission spectroscopy suggests that the surface film is neither an aggregate of fine grained intergranular minerals nor a quenched glass it could be an adsorbate on the irregular sites of crystal surfaces and was probably formed by any of diffusion from interiors of minerals i e segregation mantle metasomatism and partial melting the contribution of incompatible elements from the grain boundaries into partial melts has been documented by heating experiments on peridotite chips under controlled fo2 the spinel dunite yields at 1300 c a 4 5 vol partial melt with about 1 k2o 1 6 na2o 0 14 p2o5 0 8 tio2 210 ppm sr 140 ppm ba and 40 ppm ce along the grain boundaries grain boundaries are an important storage of incompatible elements in peridotites and they in turn can be the dominant source of these elements in magmas during partial melting of the upper mantle

the nature of grain boundaries in dunite and lherzolite xenoliths implications for magma transport in refractory upper mantle material using x ray photoelectron spectroscopy xps we have determined that the composition of intergranular regions on olivine crystals of unaltered dunite and lherzolite xenoliths from flows in hawaii australia and arizona are markedly different from the compositions of both the olivine and the host transporting lavas the boundaries are without low melting components such as alkalis but are rich in aluminum silicon magnesium and iron while xps spectra offer only semiquantitative analyses the compositions of the intergranular regions appear to be such that they would remain unmelted at temperatures existing in the xenolith source regions we infer that within their source regions refractory dunite bodies of which the hawaiian dunites are samples have solid mechanical contacts along the olivine grain boundaries furthermore we feel that the compositions of surface films are established so as to minimize the surface free energy along intergranular faces as melt is gradually removed this is consistent with the observed inability of the host lavas to penetrate these xenoliths during their ascent to the surface as such the parent refractory material within the mantle appears to be effectively nonporous to the magma and hence magma transport within the upper mantle would have to proceed by some mechanism other than the migration of melt along channels developed along wetted intergranular surfaces

multi scale three dimensional distribution of fracture and igneous intrusion controlled hydrothermal dolomite from digital outcrop model latemar platform dolomites northern italy abstract in recent years fracture controlled hydrothermal dolomitization in association with igneous activity has gained interest in hydrocarbon exploration the geometry and distribution of dolomite bodies in this setting are of major importance for these new plays the latemar platform presents a spectacularly exposed outcrop analogue for carbonate reservoirs affected by igneous activity and dolomitization light detection and ranging lidar scanning and digital outcrop models doms of outcrops offer a great opportunity to derive geometrical information only a few analysis methods exist to quantitatively assess huge amounts of georeferenced three dimensional lithology data this study presents a novel quantitative approach to describe three dimensional spatial variation of lithology derived from doms this approach is applied to the latemar platform to determine dolomite body geometry and distribution in relation to crosscutting dikes a high resolution photorealistic dom of the latemar platform allows description of dolomite occurrences in three dimensions with high precision at platform scale this results in a unique lithology dataset of limestone dolomite and dike positions this dataset is analyzed by true three dimensional variography for the geospatial description of dolomite distribution in most studies three dimensional geostatistics is the combination of two dimensional horizontal and one dimensional vertical variation in this study the dolomite occurrences are extensive in three dimensions and cannot be reduced to a two dimensional one dimensional case therefore the concept of two dimensional variogram maps is expanded to a three dimensional description of lithology variation three dimensional anisotropy detection is used to derive principal directions in the occurrence of dolomite two small scale

the latemar a middle triassic polygonal fault block platform controlled by synsedimentary tectonics abstract detailed field mapping of a middle triassic carbonate buildup the latemar in the western dolomites northern italy has been carried out the latemar is an isolated carbonate buildup that nucleates on a fault bounded structural high horst cut into the underlying late anisian carbonate bank of the contrin fm this study demonstrates that extensional synsedimentary tectonics is the main factor controlling its geometry and provides an age for this tectonic phase in an early phase slopes were mostly composed of well bedded clinostratified grainstones and rudstones in a later stage the deposition of grainstones was accompanied by the emplacement of clinostratified megabreccias the upper portion of slopes is a microbial boundstone with abundant tubiphytes and patches or lenses of grainstone boundstones may occasionally expand into the platform interior and downward to the base of the slope the depositional profile was that of a mounded platform the buildup is dissected by a dense framework of high angle fractures and faults and by magmatic and sedimentary dikes exhibiting two principal directions trending nnw sse and ene wsw faults trending wnw ese were also observed magmatic dikes are related to the emplacement of the nearby predazzo intrusion and are thus upper ladinian kinematic indicators of strike slip activity were observed on fault planes trending nne ssw and nnw sse that can be attributed to cenozoic alpine tectonics faults magmatic dikes and sedimentary dikes show systematic cross cutting relationships with strike slip faults cutting magmatic dikes and magmatic dikes cutting sedimentary neptunian dikes ene wsw and wnw ese faults are cut by all other structures and record the oldest tectonic activity in the region structural analysis attributes this tectonic phase to an extensional stress field with a direction of maximum extension oriented ca n s several lines of evidence including sealed faults and growth wedge geometries allow us to recognize this old tectonic phase as syndepositional and to date it to the latest anisian avisianum and crassus ammonoid biochronozones the horse shoe shape of the platform and its margins rectilinear for long tracts are explained by the existence of a network of extensional faults whose activity lasted for part of the growth of the platform the latemar is thus a polygonal fault block platform controlled by synsedimentary tectonics the resulting sedimentary architecture is that of a growth wedge deposited probably on the uplifted side of a submerged half graben continuous reactivation of faults at platform margins locally determined anomalous facies transitions with well layered platform interior directly in contact with the clinostratified slopes

multicyclic history of the northern india continental margin northwestern himalaya 1 the geologic evolution of northern india is best recorded in the stratigraphic succession of the zanskar range northwestern himalaya which represents the most complete transect through this ancient continental margin sedimentary history began in the late proterozoic and recorded a late pan african orogenic event around the cambrian ordovician boundary when the gondwana supercontinent was eventually assembled the following long period of epicontinental deposition in shallow seas linked to palaeo tethys lasted until the early permian when a neo tethyan rift began to open between paleo india and the cimmerian microcontinents neo tethyan history can be subdivided into two sedimentary megasequences both recording a major tectonic and magmatic event in the lower part the first one began with breakup in the late permian and lasted until the end of the jurassic the second one started in the early cretaceous with the final detachment of india from gondwana and the opening of the indian ocean and ended with the india eurasia collision in the early eocene the two megasequences can be in turn subdivided into six transgressive regressive supersequences bounded by tectonically enhanced unconformities basal sandstone units of early permian late permian norian callovian early cretaceous and paleocene age are invariably associated with oolitic ironstones or reworked glauco phosphorites and mark the transgre sive part of each supersequence next condensed nodular carbonates or shales with pelagic fauna are typically overlain by thick shallowing upward marly units capped by regressive platformal carbonates the six tectono eustatic supercycles reflect successive rifting episodes which punctuated the progressive separation of india from the rest of gondwana and document the combination of plate microplate reorganizations and eustatic climatic and oceanographic changes in the tethyan domain after the onset of collision between india and asia close to the paleocene eocene boundary obduction of the remnants of the neo tethys ocean floor onto the indian margin began and the latter underwent multiphase deformation with fold thrust shortening followed by heating and extension after the main metamorphic event ophiolitic nappes were re thrusted and finally emplaced with their sedimentary sole on top of the passive margin succession

middle triassic orbital signature recorded in the shallow marine latemar carbonate buildup dolomites italy a new time frequency analysis of sea level controlled carbonate platform cycles in the middle triassic latemar massif dolomites italy reveals a strong depositional signature with characteristics of dominant forcing by climatic precession modes corresponding to long and short precession components at 1 21 7 k y and 1 17 6 k y underwent amplitude modulations matching earth9s orbital eccentricity with major frequency components at 1 400 k y 1 125 k y and 1 98 k y obliquity appears as a minor component at 1 35 4 k y the latemar signature thus constitutes the oldest pristine milankovitch signature yet observed in the geologic record its fidelity rivals that of the pliocene pleistocene record originally used to confirm the theory of orbitally forced climates this evidence deepens a widely noted disagreement between radiometric and cyclostratigraphic time scales for the latemar buildup the latemar cycles indicate that orbitally forced sea level oscillations were operative in the ice free middle triassic hothouse world

facies architecture of an isolated carbonate platform tracing the cycles of the latemar middle triassic northern italy the 720 m thick succession of the middle triassic latemar massif dolomites italy was used to reconstruct the lagoonal facies architecture of a small atoll like carbonate platform facies analysis of the lagoonal sediments yields a bathymetric interpretation of the lateral facies variations which reflect a syndepositional palaeorelief based on tracing of lagoonal flooding surfaces the metre scale shallowing upward cycles are interpreted to be of allocyclic origin short term sea level changes led to subaerial exposure of wide parts of the marginal zone resulting in the development of a tepee belt of varying width occasional emergence of the entire lagoon produced lagoon wide decimetre thick red exposure horizons the supratidal tepee belt in the backreef area represented the zone of maximum elevation which circumscribed the sub to peritidal lagoonal interior during most of the platform s development this tepee rim the subtidal reef and a sub to peritidal transition zone in between stabilized the platform margin the asymmetric width of facies belts within individual metre scale cycles was caused by redistribution processes that reflect palaeowinds and storm paths from the present day south and west the overall succession shows stratigraphic changes on a scale of tens of metres from a basal subtidal unit overlain by three tepee rich intervals separated by tepee poor units composed of subtidal to peritidal facies this stacking pattern reflects two third order sequences during the late anisian to early middle ladinian

the start up of the dolomia principale hauptdolomit carbonate platform upper triassic in the eastern southern alps wide carbonate platform environments developed on the western passive margin of the tethys during the late triassic after a major climate change carnian pluvial episode that produced a crisis of high relief microbial carbonate platforms the peritidal succession of this epicontinental platform dolomia principale hauptdolomit dachstein limestone is widespread in the mediterranean region however the start up stage is not fully understood the original platform to basin depositional geometries of the system have been studied in the north eastern southern alps close to the italian slovenian boundary where they are exceptionally preserved sedimentological features have been investigated in detail by measuring several stratigraphic sections cropping out along an ideal depositional profile the analysis of the facies architecture allowed reconstruction of the paleoenvironments of the dolomia principale platform during its start up and early growth stages in the late carnian the carbonate platform was characterized by an outer platform area connected northward to steep slopes facing a relatively deep basin southward the outer platform was connected to inner sheltered environments by a narrow often emerged shelf crest behind this zone carbonate sedimentation occurred in shallow lagoons and tidal flats passing inward to a siliciclastic mudflat the dolomia principale platform was initially aggrading and able to keep pace with a concomitant sea level rise and then prograding during the late carnian this stratigraphic interval was correlated to the tuvalian succession of the dolomites allowing depiction of the depositional system on a wide scale of hundreds of kilometrew this large scale depositional system presents features in common with some palaeozoic and mesozoic carbonate buildups fo example the permian capitan reef complex anisian latemar platform both in terms of architecture and prevailing carbonate producers a microbial dominated carbonate factory is testified in the outer platform and upper slope the recovery of high relief microbial carbonate platforms marks the end of the carnian pluvial episode in the tuvalian of tethys this article is protected by copyright all rights reserved

hybrid carbonates in situ abiotic microbial and skeletal co precipitates abstract abiotic bioinduced and biocontrolled carbonates are process based sediment categories they successively reflect increasing levels of biotic control over carbonate precipitation from aqueous solutions are often closely linked to depositional environment and change with time hybrid carbonates are intimate in situ combinations of two or more of these categories hybrid carbonates are widespread and diverse in the marine geological record and reflect large scale changes in carbonate precipitation through time they also occur in fluvial and lacustrine carbonates marine and non marine reef systems and methane seep deposits plots of hybrid carbonate composition in time and space reveal complex backtracking and looping patterns that reflect changes in environmental conditions and biological processes of carbonate production recognition of hybridity emphasizes the importance of distinguishing abiotic and bioinduced precipitates until they were diversified by skeletal carbonates in the late proterozoic precambrian hybrid carbonates were abiotic bioinduced combinations during the phanerozoic hybrid carbonates were conspicuous during periods of overlap or transition between intervals of microbial and skeletal carbonate abundance microbial skeletal dual hybrids are common during the cambrian mid ordovician late devonian mississippian and late jurassic early cretaceous abiotic microbial skeletal triple hybrids were common from late pennsylvanian to mid triassic shallow marine hybrid carbonates declined in abundance after the mid cretaceous although late cenozoic reefs contain some striking examples of microbial skeletal hybrids recognition of hybrid carbonates draws attention to fundamental processes underlying carbonate sedimentation and their patterns and drivers of change in time and space

magnetostratigraphic confirmation of a much faster tempo for sea level change for the middle triassic latemar platform carbonates new magnetostratigraphic data for the 470 m thick latemar carbonate platform which includes 600 shallowing upward bedding cycles are consistent with litho and biostratigraphic correlations of the section to a 10 m thick interval in the basinal buchenstein beds that most likely represents only 1 m y of deposition according to published u pb single crystal zircon dates a reappraisal of reported cycle stratigraphic analyses of the latemar suggests that the visibly obvious meter scale bedding is not due to milankovitch precessional forcing but rather reflects tempos an order of magnitude faster that may involve millennial scale tidal amplitude variations d 2004 elsevier b v all rights reserved

the changing climate framework and depositional dynamics of triassic carbonate platforms from the dolomites abstract the triassic of the dolomites offers a valuable opportunity to investigate the relationships between climate fluctuations and the changing depositional dynamics of carbonate platforms the reconstruction of the large palaeoclimatic modification is based on the synthesis of multiple sedimentological palaeobotanical pedological and geochemical proxies the triassic climate fluctuations were generally fast in nature and were probably associated with a latitudinal shift of the monsoon belts during the triassic the dolomites were placed at an intertropical northern latitude of about 16 18 and were generally dominated by dry climate and elevated temperature at least five pulses toward moister climate are however documented dated to early olenekian middle anisian late ladinian middle carnian and late norian times within this variable climatic scenario the carbonate systems record a global evolutionary trend from late permian early triassic regional shelves rich in loose micrites and bio calcarenites to anisian ladinian synsedimentary cemented steep sided 35 40 high relief platforms and back to carnian low angle ramps moist transgressive episodes were surprisingly prone to the spreading of corals and other colonial reef organisms probably because of the reduced space competition by syndepositional cementation structures the permo triassic boundary extinction dramatically impacted on the calcified organism communities but the carbonate depositional architecture nevertheless stayed almost unaffected through the boundary the early triassic and earliest anisian were commonly associated with hyperhaline sometimes evaporitic conditions intervals of moister climate and efficient river discharge are however documented by earliest induan and early olenekian sediments the latter terrigenous deposits matched a crisis in the carbonate production after a return to arid conditions during the anisian a fluctuation toward moister climate developed associated to a massive continental vegetation cover the anisian tectonic activation of the region fragmented the previous carbonate shelf triggering the development of three generations of fast prograding but globally backstepping isolated platforms recording an increasing role of the synsedimentary cementation a dry climate dominated the late anisian and early ladinian interval at the time a fast subsidence pulse was associated with platform drowning and basinal anoxia only a few aggrading pinnacles were able to survive providing the nuclei for larger prograding platforms during a dry climate interval massive syndepositional cementation generated a major source of carbonate carbonate production stayed active through the ladinian magmatic phase but the onset of volcanism was associated with a large modification in the platform carbonate facies which became dominated by automicrites moist climate phases are well documented again during the late ladinian followed by a return to dry conditions the late ladinian early carnian platforms prograded toward the eastern dolomites depocentre eventually infilling almost the whole of the accommodation space the middle portion of the carnian recorded renewed sharply moist phases associated with the demise of the rimmed platforms and with the return to loose sediment ramps at least four separated humid fluctuations can be identified in this carnian interval alone climate then returned to persistent aridity until the late norian moist phase

calciturbidite composition related to exposure and flooding of a carbonate platform triassic eastern alps the compositional variation of calciturbidites pedata potschen formation deposited adjacent to the dachstein formation carbonate platform in the triassic hallstatt basin was analysed using detailed field measurements and point counting of thin sections the 35 m long section is located in the northern calcareous alps of austria six point count groups were distinguished separating basinal from platform derived input summary statistics cluster and correspondence analysis of the point count data reveals a close relationship between the biota present on the dachstein carbonate platform and the calciturbidite composition the variations in turbidite composition are attributed to fluctuations in sea level and resulting flooding and exposure of the platform which alternately created and destroyed shallow water habitats on the platform top

nature and evolution of middle triassic carbonate buildups in the dolomites italy during the middle triassic an evolution from carbonate bank to buildup highly elevated in respect of the adjacent basins is observed in the alps the dolomites in the southern alps italy are here considered as an example during the anisian subtidal banks of the upper serla fm with rare peritidal cycles show only a limited biologic density and diversity with the late anisian contrin fm a gradual development of binding and framework building communities can be observed the sinking of wide areas of the contrin carbonate bank into anoxic conditions plattenkalke fm allowed the birth of isolated buildups their increased carbonate production due to a greater diversity and density of organisms was able to keep up with the rate of subsidence the latemar buildup with additional data for the slope taken from mt coldai civetta and sass da putia is used to illustrate the main character of a lower ladinian buildup the restricted platform sediments display peritidal cycles prevalent in the subtidal portion is dasycladacean packstone grainstone associated with gastropods ammonoids and blue green algae in the supratidal portion desiccation and tepee structures are present scleractinian and sphinctozoan frameworks are rare on the upper part of the slope which is bound predominantly by encrusting organisms mainly blue green algae porifers and tubiphytes the prevailing sediments on the upper part of the slope are bindstones whilst packstones and rudstones are in the lower part of the slope the latter carbonates were cemented early under submarine conditions mostly by isopachous palisade cement polyphasic internal sediments with phreatic vadose influence are present and can in the middle lower part of the slope replace most of the original sediment

use of insolation as a proxy for high frequency eustasy in forward modeling of platform carbonate cyclostratigraphy a promising approach abstract eustatic oscillations driven by milankovitchian astronomical forcing have been interpreted as sea level drivers for high frequency carbonate depositional cycles in studies dating from the mid 1960s forward modeling of these oscillations with respect to their recorded effects on cyclical stacking patterns has only been attempted using generalized parameters for milankovitchian forcing the development of increasingly advanced forward modeling software coupled with the availability of formulas quantifying insolation incoming solar radiation as a function of composite orbital variations allows for the testing of milankovitchian insolation against measured stratigraphy in this case a series of milankovitchian insolation curves were calculated and used to generate proxy sea level curves for use in the carb3d forward modeling package in order to synthesize a series of stacked carbonate strata these synthetic successions are compared against that of the latemar platform middletriassic northern italy which has been interpreted to contain a record of orbital forcing within its stratigraphy while the timing and nature of periodic drivers that affected latemar stratigraphy have stirred a vigorous debate results from this study indicate that use of milankovitchian insolation as a proxy for high frequency sea level oscillations was successful in modeling latemar like stratigraphy with both pure milankovitchian and mixed milankovitchian sub milankovitchian temporal frameworks

computational modeling of fine sediment relocation within a dam reservoir by means of artificial flood generation in a reservoir cascade an edited version of this paper was published by agu copyright 2019 american geophysical union

sea level changes versus hydrothermal diagenesis origin of triassic carbonate platform cycles in the dolomites italy abstract the triassic platform carbonate cycles of the dolomites best developed and studied at the latemar have been considered key examples for the documentation of eustatic sea level changes the cycles appear to reflect a low energy lagoonal environment which is however difficult to reconcile with the small platforms lacking marginal energy barriers in a tropical stormy climate an alternative interpretation to eustatically controlled cyclicity and repeated subaerial exposure is provided by diagenesis in a hydrothermal field elevated heat flow 0 2 ma before the onset of the mafic igneous activity triggered the circulation of diagenetic fluids with a composition similar to seawater by intermittent opening of fractures through some platforms this caused tepee formation by precipitation of displacive cement pendant cement and pisolite formation and favoured cyanobacterial mat formation and their early dolomitization the abundance of cycles correlates with that of the somewhat younger volcanic dikes crosscutting some platforms diffuse venting or seeping in the upper unconsolidated sediment layers explains the stratiform occurrence of the diagenetic features and alternation with normal marine deposition in deep but photic water at the wave base

triassic carbonate development and reefbuilding in western north america the cordilleran region of western north american contains numerous examples of middle to upper triassic carbonate sequences many of these developed as broad shallow water platforms associated with island arcs these platforms however were not characterized by extensive reef structure shallow water facies in many sequences contain abundant corals spongiomorphs sponges and a variety of rich invertebrate faunas most of these are endemic with the exception of the corals which show much similarity with the tethyan faunas small local reefoid buildups occur within many sequences especially those of norian age and contain local organic framework

triassic carbonate buildup flanks in the dolomites northern italy breccias boulder fabric and the importance of early diagenesis the flanks of middle triassic carbonate buildups in the dolomites show well developed clinostratification with typical angles of 30 40 this paper focuses on the metre scale fabric of these clinoforms and sets these within the context of their large scale and microscopic features clinoform stratification is caused by fibrous cement crusts by stylolites paralleling a vague stratification and by pelagic limestone interbedded with the lower portions of the clinoforms these parts of the clinoforms locally exhibit a boulder fabric a fracture system subvertical to clinostratification is filled by fibrous cements and marine internal sediment the analysis of clinoform fabric indicates that parts consist of in situ automicrite other parts of the clinoforms are made up of breccia the breccias occur as isolated pockets and lenses with random orientation and dimensions ranging from a few square decimetres to hundreds of square metres the breccias have gradual contacts with the unbrecciated host rock breccia components are mostly angular show a microfacies similar to that of the unbrecciated host rock and are composed of millimetre to decimetre sized particles that generally float in radiaxial fibrous cement matching grain boundaries are common calcite cement typically makes up 20 and 40 vol of the brecciated areas clinostratification the fracture system brecciation and boulder fabric point to gravity induced deformation of in situ flank deposits rather than gravity induced depositional processes brecciation appears to result from translational sliding millimetres to metres on the steep buildup flanks which caused fracturing of the vaguely stratified automicrite followed by displacive growth of fibrous cement cementation occurred in a shallow burial marine phreatic environment because cement clasts are virtually absent from the flank derived gravity flows in the adjoining basinal sediments displacive cement growth indicates a volume increase of the clinoforms during diagenesis of up to 20 40 vol and can account for the local drag of buildup interior limestones similarly the boulder fabric appears to be a diagenetic feature which resulted from differential settling of incompletely lithified boundstone and grainstone and the interbedded pelagic limestone

meso cenozoic basin and carbonate platform development in the sw dolomites unraveled by basin modelling and apatite ft analysis rosengarten and latemar northern italy abstract the rosengarten and latemar middle triassic carbonate platforms indicate similar subsidence patterns during equivalent times of platform evolution as calculated by numerical basin reverse modelling in the case of rosengarten and latemar thermo tectonic subsidence is the most significant among all three subsidence components thermo tectonic s flexural s compaction induced s hence the influence of differential tectonics as recorded in the formation of structural highs and lows in the dolomites during the lower to middle anisian almost ceases in late anisian times basin modelling of rosengarten and latemar requires the correlation and integration of two sets of chronostratigraphic data from buchenstein fm basin and schlern dolomite fm 1 platform subsidence modelling argues for a microcycle i e a single shallowing upward cycle duration of less than 1 97 ka in the cyclic succession at latemar however previous time series analyses identify milankovitch cyclicities in larger order cycle stacking patterns and thus indicate a microcycle duration of 4 2 ka according to each model total subsidence reaches values of 650 700 m ma 4 2 ka model or 780 850 m ma 1 97 ka model during the first stage of platform evolution as both platforms successfully keep up with this subsidence peak it is evident that the carbonate factory despite its low diversity must have recovered from the p t faunal crisis after this regionally observed peak subsidence drops and triggers fast progradation at rosengarten subsidence in the study area is controlled by active strike slip tectonics and the subsequent formation of a magmatic chamber predazzo monzoni above the deep reaching truden stava line the area close to this tectonic line and to the volcanic centre of predazzo monzoni undergoes a higher heat flow pulse during the late ladinian and is possibly buried at shallower levels than the rosengarten area as shown by fission tracks in apatites the heat flow pulse almost disappears laterally underlining the localised thermal influence of the late ladinian volcano thermal event of predazzo monzoni

unraveling the origin of carbonate platform cyclothems in the upper triassic durrenstein formation dolomites italy abstract facies analysis of the durrenstein formation central eastern dolomites northern italy indicates that this unit was deposited on a carbonate ramp as evidenced by the lack of a shelf break slope facies or a reef margin together with the occurrence of a molechfor biological association its deposition following the accumulation of rimmed carbonate platforms during the ladinian and early carnian marks a major shift in growth mode of the triassic shallow marine carbonates in the dolomites the durrenstein formation is characterized by a hierarchical cyclicity with elements strongly suggestive of an allocyclic origin including a subaerial exposure features directly above subtidal facies within meter scale cyclothems b purely subtidal carbonate cyclothems c symmetric peritidal carbonate cyclothems and d continuity of cyclothems of different orders through facies boundaries the durrenstein cyclothems are usually defined by transgressive and regressive successions and so most of them probably originated from sea level oscillations their allocyclic origin allows their use for high resolution correlations over distances up to 30 km a stratigraphic section in the tre cime di lavaredo area encompassing the upper part of the durrenstein formation and the lower part of the overlying raibl formation upper carnian was studied using time frequency analysis a strong milankovitch signal appeared when interference arising from a variable sedimentation rate was estimated and removed by tuning the short precession line in a spectrogram all of the principal periodicities related to the precession index and eccentricity calculated for 220 ma are present p1 21 9 ky p2 17 8 ky e1 400 ky e2 95 ky and e3 125 ky along with a peak at a frequency double that of the precession which is a predicted feature of orbitally forced insolation at the equator components possibly related to earth s obliquity at ca 35 ky and ca 46 ky are present as well the recovery of milankovitch periodicities allows reconstruction of a high resolution timescale that is in good agreement with published durations of the carnian based on radiometric ages the recognition of a milankovitch signal in the durrenstein and lower raibl formations as well as in other mesozoic carbonate platforms strongly supports a deterministic and predictable rather than stochastic control on the formation of carbonate platforms carbonate platforms might thus be used in the future for the construction of an astronomical time scale for the mesozoic

carbonates and relative changes in sea level abstract in the geologic record some of the most accurate gauges of changes in sea level are the sediment type geometry and diagenesis of carbonate shelves and platforms this is because carbonates frequently occur at or very near sea level and are usually less compacted than siliciclastics world wide changes in relative sea level the sum of eustatic sea level changes sedimentation and crustal movements have occurred repeatedly and cyclicly through geologic time producing characteristic responses in carbonates 1 1 relative rises in sea level usually caused by the cumulative effect of tectonic subsidence and eustatic rise may result in the following 1 1 a drowned carbonate reefs or platforms here carbonate growth potential is exceeded by relative sea level rise and is characterized by shallow water sediments overlain by hardgrounds and or deep water sediments some of which may be condensed sequences 1 2 b platforms where only the fast growing rim and patches of the interior are able to match sea level rise while the remainder of the platform is drowned temporarily 1 3 c platforms which keep up and maintain a flat top at sea level and contain shallow water sediments whose thickness at the least matches the height of the sea level rise if terrigenous supply is limited prograding sheets of shelf carbonate occur frequently capped by supratidal evaporites with prograding shelf margin carbonate clinoforms and turbidites if terrigenous supply is high the shelf carbonates encroach on deltaics 2 2 relative drops in sea level caused by crustal uplift or by subsidence being outpaced by a eustatic drop in sea level cause karst and soil development over shelves and platforms deposition of deep water evaporites in adjacent semi enclosed basins and in open marine basins the deposition of deltaic and aeolian clastics that bypassed the shelf falls are accompanied by platform wide fresh water diagenesis during relative sea level rises marine diagenesis is common in the subtidal portions of the shoaling upward carbonates and fresh water diagenesis and dolomitization and sulphate deposition is common in their intertidal and supratidal portions the stratigraphic significance of these reponses to relative sea level change is that many are tied to eustatic events and so are predictable within a basin of deposition

role of autochthonous versus detrital micrite in depositional geometries of middle triassic carbonate platform systems middle triassic platforms formazione di contrin upper anisian in the italian dolomites southern alps record large changes in carbonate production and depositional geometry the changes include variation in the abundance of detrital micrite i e allochthonous calcareous mud relative to the autochthonous micrite which formed in situ and was syndepositionally lithified carbonate factory dynamics controlled the geometry of the clinostratified slope units and were probably associated with changes in oxygenation early anisian low relief platforms were followed by late anisian high relief buildups associated with basinal dysoxic anoxic environments the geometric evolution of the platform slopes records a progressive increase in the dip angle of clinostratifications matched by a deepening evolution of the basinal environments at the same time the slope sediments record a gradual change from loose detrital micrite characterizing the lower portion to autochthonous micrite dominating the upper part and recording massive syndepositional lithification the development of the autochthonous micrite was associated with the preservation of significant amounts of organic matter this sharp increase in automicrite formation was probably induced by a rapid change from oxic to suboxic conditions in the carbonate slope and margin environments while anoxic conditions developed in the adjacent organic rich basin moena formation the low oxygen level promoted the preservation of organic matter and the activity of sulfate reducing bacteria which in turn induced in situ deposition of autochthonous micrite through biomediated processes this pervasive early cementation and lithification induced the development of steep platform slopes the conceptual model distilled from this middle triassic case can support the interpretation of analogous buildups where the skeletal framework is subordinate to the micrite component

windward leeward effects on triassic carbonate bank margin facies of the dolomites northern italy abstract triassic carbonate bank margins of the dolomites show compared to modern carbonate margins relatively low energy narrow facies belts distinctive facies depend on the geographical margin orientation and suggest windward leeward effects low energy deposits such as algal stabilized sand flats and tepee pisolite facies occur along margins facing deeper water in the north and east higher energy deposits such as algal reefs and cross bedded sand bars characterize margins facing southwest and west locally clinoforms show asymmetric distribution being thick at the eastern bank margin and thin or absent at the western bank margin while the overall low energy conditions could have been caused by the small size and in the late anisian the shallowness of the basins facies differentiations suggest a net energy flux of surface waters caused by storms and possibly consistent winds from the southwest to west in the triassic of the dolomites

sub milankovitch and milankovitch forcing on a model mesozoic carbonate platform the latemar middle triassic italy basic shallowing upward cycles shu cycles and five bundled megacycles in the latemar platform have been widely regarded as a model example for precessional and eccentricity forcing in the mesozoic based on bio chronostratigraphic data recent studies questioned this particular type of milankovitch forcing on the latemar cyclic series we present an integrated model that incorporates i new cyclostratigraphic data ii new and existing bio chronostratigraphic data and iii new spectral analyses the basic shu cycles in the latemar reflect sub milankovitch control cycle bundles of 1 4 5 megacycles shu cycles indicate precessional forcing they do not reflect eccentricity superimposed on precessional forcing spectral analyses reveal highly significant ratios in the large scale cycle bundlings stacking patterns of 1 9 9 and 1 24 0 shu cycles represent obliquity and short eccentricity forcing both sub milankovitch and milankovitch forcing potentially controlled shallow subtidal carbonate deposition in mesozoic greenhouse times cyclostratigraphic models require an integrated approach including bio and chronostratigraphic data

distributed fracturing affecting isolated carbonate platforms the latemar platform natural laboratory dolomites north italy abstract isolated carbonate platforms are highly heterogeneous bodies and are typically composed of laterally juxtaposed first order domains with different sedimentological composition and organization i e a well stratified platform interior a massive margin and a slope with steeply dipping and poorly organized layers once subjected to overburden and tectonics forces directions and magnitudes of principal stresses inside such heterogeneous bodies are expected to deviate significantly from the regional trends potentially resulting in non obvious fracture patterns in addition characteristics such as fracture height and spacing distances are likely to change moving from one domain to the other as well as through time the middle triassic latemar platform dolomites n italy is affected by ubiquitous fractures typically joints orientation and height of more than 1500 fractures from 33 outcrops have been measured and their spatial characteristics were assessed with dedicated software fractures are organized in two directional sets nnw sse and ene wsw the orientation of each set is constant throughout the platform showing that the trajectories of causative stresses were not influenced by the platform architecture fracture spacings and heights of each set change moving from one domain to the other in the well bedded platform interior fractures are generally there are also significant differences in the characteristics of fractures of the two sets in all platform domains fractures of nnw sse set are less tall and more narrowly spaced than those of the ene wsw set in the platform interior fractures of the first set have a higher tendency to be confined to fracture units than those of the second set these differences are associated with diagenesis driven changes in bulk mechanical properties of the platform during its subsidence to maximum burial depth

behaviour of rare earth elements during high pressure metamorphism abstract the behaviour of rare earth elements ree during high pressure metamorphism has been studied to estimate their possible use in determining the geodynamic settings of eclogite procoliths eclogites exhibiting various degrees of amphibolitization have been studied in a number lf metamorphic complexes in the urals mongolian fold belt the kokchetav massif in northern kazakhstan and the atbashi range in the central tien shan all in the u s s r in addition an eclogitized metagabbro from the koralpe austrian alps and gabbroids transformed into garnet amphibolites from the kokhchetav massif have been investigated the analytical data suggest that about 30 60 of the light rare earth elements lree in eclogites is present in the intergranular space the results of the investigation demonstrate that the ree were virtually immobile during eclogite formation their low mobility can be explained either by absence of complex formers in the fluid phase or by low fluid rock ratio

repeated subaerial exposure of subtidal carbonate platforms triassic northern italy evidence for high frequency sea level oscillations on a 104 year scale triassic carbonate platforms in northern italy ladinian latemar carnian durrenstein norian dolomia principale consist of hundreds of stacked meter scale cycles each made of a subtidal unit with a cap rock that carries vadose cements pisoids and tepee structures these diagenetic caps are interpreted to be due to subaerial exposure of the subtidal sediments the absence of peritidal deposits rules out progradation as the cause of the exposure i e these are not ginsburg autocycles thus the repeated exposure must be the result of relative sea level oscillations which based on the number of cycles and time intervals involved occurred with an average frequency in the 104 year range we postulate a combination of small scale high frequency eustasy and local tectonic movements e g differential subsidence in the norian and infrequent pulses of uplift in the ladinian to explain the cyclicity and its internal variations