the masquerade of alkaline carbonatitic tuffs by zeolites a new global pathfinder hypothesis rapid and progressive reaction of alkaline carbonatitic tuffs with magmatic and crustal fluids disguises their initial character and origin this is collectively indicated from a the extensive literature on zeolite formation from volcanic glass precursors and alkaline fluids b mineralogical characteristics of specific zeolite species c a comparative review of global distributions of alkaline carbonatite suites and of zeolite minerals and d new trace element data from zeolite samples a unifying conceptual model based on tectonic and geological settings hydrological regime and mineralogy is presented that helps to explain the global distributions and current understanding of occurrences the model will assist in resource exploration by contributing deeper understanding of the economically important bedded zeolite deposits and further serve as a guide to the discovery of new alkaline carbonatitic suites potentially of economic significance metallic ores and rare earth elements it follows that future testing of the hypothesis will impact on models of natural carbon cycling as volcanic contributions of co2 are reviewed

influence of water column anoxia and sediment supply on the burial and preservation of organic carbon in marine shales abstract previous work has suggested that the laminated organic rich and bioturbated organic poor shales of the camp run member of the late devonian early mississippian new albany shale formed under anoxic and oxygenated bottomwater conditions respectively and that the interbedding of the two facies was due to the vertical oscillation of a water column anoxic oxic boundary where it impinged on the basin margin we have extended this analysis by examining the chemical and mineralogical differences between the two shale facies in a single borehole core by seeking evidence for deposition of the laminated shales under bottom water oxia or anoxia and by determining whether the laminated shales formed when the carbon supply to the sea floor was higher the results of this study show that the laminated and bioturbated shales are mineralogically and chemically distinct relative to al an index of the aluminosilicate content si ti fe p na ba co cr cu mo ni v zn and zr are all higher whereas mn ca mg and sr are lower in the laminated compared with the bioturbated shales the differences are due to a higher quartz feldspar titanite ilmenite and zircon content in the laminated shales probably indicating a coarser grain size and the greater abundance of manganoan calcite in the bioturbated shales dissolved oxygen was present in bottom waters during the deposition of some of the laminated shale intervals because of the presence of manganoan calcite a phase that can only form in sediments with an oxic surface in addition the organic matter preserved in the two shale types is isotopically different 13corganic values are 1 9z permil lighter on average in the laminated compared with bioturbated intervals possibly indicating a larger fraction of terrestrial organic matter in the latter 15n values are 1 9z permil lighter on average in laminated compared with bioturbated intervals possibly indicating a larger fraction of terrestrial organic matter in the latter 15n values are 1 9z permil lighter on average in laminated compared with bioturbated intervals suggesting that nutrient drawdown was less during the deposition of the organic rich laminated shales the chemical mineralogical and isotopic contrasts between the two shale facies of the camp run member indicate that the conditions of sedimentation were different during their deposition the difference was possibly related to variations in sea level which would have caused the camp run shoreline to move closer to and farther from the core site causing in turn the deposition of coarser and finer grained sediments that contained different mixtures of marine and terrestrial organic matter bottomwater conditions were anoxic during deposition of most laminated intervals bottom water anoxia or dysoxia led to decreased burial and preservation of the essential nutrient phosphorus in the laminated organic rich shales relative to the rocks deposited beneath better oxygenated bottomwaters increased availability of phosphorus in the water column on long timescales leads to increased productivity and a higher settling flux of organic matter causing bottom water oxygen levels to fall this is consistent with the nitrogen isotope evidence suggesting that production was probably higher during the deposition of the organic rich shales thus production variations coupled with enhanced sedimentary regeneration of phosphorus from sediments related to low oxygen bottom water concentrations provide a general mechanism for the formation of the alternating facies of this member of the new albany shale

sedimentology csfe relationships and stable isotopic compositions in devonian black mudrocks mackenzie mountains northwest territories canada abstract an integrated approach combining c s fe relationships stable isotopic compositions and lithofacies characterization was utilized to constrain the palaeoenvironmental and early diagenetic conditions of middle upper devonian eifelian frasnian mudrocks from the mackenzie mountains northwest territories canada these rocks include the hare indian formation informally subdivided into the lower bluefish member and the hare indian upper member carcajou marker and canol formation the bluefish member is dominated by black laminated organic rich shales toc 0 35 10 34 wt av 5 83 wt with moderate degrees of pyritization dop of 0 34 0 67 av 0 55 these mudrocks were deposited in dysoxic marine bottom waters that became progressively more oxygenated with time variations in toc dop and organic matter 13cpdb values 29 7 to 19 9 av 27 2 are attributed to repeated clastic dilution and increased input of terrestrial organic matter in association with shallowing upward ramp clinothem cycles pyrite 34scdt values 32 7 to 18 8 av 24 9 indicate an open system bacteriogenic seawater sulphate reduction conversely the overlying hare indian upper member characterized by clinothem facies is composed of grey to green mudstone with minor argillaceous limestones and considerably less organic matter contents toc 0 28 2 99 wt 13c 29 5 to 22 5 deposition occurred in oxic to slightly dysoxic waters dop 0 20 0 54 34s 23 0 to 20 9 depending on the palaeotopographic location along the depositional slope a rapid rise in sea level drowned the carbonate ramp member of the ramparts formation and produced the thin organic rich carcajou marker bottom water stagnation that resulted from subdued ramp palaeotopography produced anoxic sea bottom black laminated organic rich shales from the canol formation toc 1 37 6 68 wt are very similar to those of the bluefish member and are likewise basinal sediments however toc dop and organic matter 13cpdb values 29 1 to 20 8 av 26 2 do not show pronounced variations and indicate that low energy quietwater conditions persisted over relatively long uninterrupted periods of time high dop values 0 72 0 93 throughout the canol formation suggest that deposition occurred in anoxic bottom waters but as basin fill conditions continued there was a shift to a dysoxic environment dop 0 55 0 65 which grades into nearshore and offshore sequences of the overlying imperial formation in contrast with the hare indian formation much heavier 34scdt values of pyrite in canol mudrocks 11 1 to 5 3 av 3 1 point to bacterial sulphate reduction in a closed to semi closed system with respect to seawater sulphate

sequence stratigraphic and genetic aspects of the tournaisian liegender alaunschiefer and adjacent beds this study reports the results of interdisciplinary investigations of tournaisian deposits from the german rheinisches schiefergebirge and provides a genetic and sequence stratigraphic interpretation microfacies and geochemical data confirm normal marine outer shelf to slope environments for the lower tournaisian hangenberg formation in contrast data from the condensed phosphatic liegender alaunschiefer black shale indicate low current energy and anoxic conditions in the sediment and the water column we suggest that anoxia was caused by eutrophication and high organic productivity due to factors such as upwelling a climate related improvement of oceanic ventilation and volcanic nutrient input the hangenberg formation represents the lowstand through the early transgressive systems tract of a third order depositional sequence while the liegender alaunschiefer is a late transgressive systems tract and maximum flooding deposit the richrath limestone was deposited during the highstand systems tract thus quickly rising sea level and eutrophication may account for the peculiar and uniform facies of the liegender alaunschiefer

lack of evidence for enhanced preservation of sedimentary organic matter in the oxygen minimum of the gulf of california a test of the hypothesis that hydrogen rich organic matter accumulates preferentially in sediments under oxygen minima has been carried out by examining the composition of laminated and homogeneous diatomaceous sediments of the guaymas basin in the gulf of california the laminated sediments occur where an intense oxygen minimum intersects the slope around the margins of the basin above and below the depth of the oxygen minimum the sediments are homogenized by a burrowing infauna the two sediment types have very similar bulk chemical and mineral compositions and the organic matter is overwhelmingly marine the total organic carbon contents and rock eval parameters hydrogen and oxygen indices of the two sediment types are not significantly different whereas a road organic carbon maximum in the homogeneous sediments is centered at roughly 1200 m depth on the slope of the basin this maximum lies deeper than the core of the oxygen minimum thus both the concentration and the nature of the organic matter in the sediments of this highly productive marginal marine basin are not related to the concentration of dissolved oxygen in the bottom waters

occurrence of zeolites in sedimentary rocks an overview zeolites have been known since the mid 1750s but prior to the early 1950s most reported occurrences of zeolites were in fracture fillings and amygdules in igneous rocks particularly basaltic lava flows indeed most of the large attractive zeolite specimens in museum collections were obtained from lavas in recent years zeolites have been recognized as important rock forming constituents in low grade metamorphic rocks and in a variety of sedimentary rocks most zeolites in sedimentary rocks are finely crystalline that is they occur as microscopic or submicroscopic crystals and they are therefore of little appeal to mineral collectors however deposits of this type are voluminous and have great geologic significance and economic potential zeolites are among the most common authigenic silicate minerals that occur in sedimentary rocks and they form in sedimentary rocks of diverse lithology age and depositional environment about twenty species of zeolites have been reported from sedimentary rocks but only eight zeolites commonly make up the major part of zeolitic rocks these are analcime chabazite clinoptilolite erionite heulandite laumontite mordenite and phillipsite this chapter will consider chiefly the zeolites in sedimentary rocks with emphasis on volcaniclastic deposits which contain the largest concentrations of zeolites the occurrence of zeolites in lava flows is mentioned only briefly journal articles on the occurrence and origin of natural zeolites have multiplied at a rapid rate since the mineralogy and geology of natural zeolites was first published in 1977 as volume 4 of the mineralogical society of america s reviews in mineralogy the present review will highlight areas of more recent research on the occurrence and origin of zeolites and some of the coexisting minerals a wide variety of zeolites has been identified in sedimentary deposits with the most common being clinoptilolite analcime heulandite laumontite and phillipsite less abundant zeolites include chabazite erionite mordenite natrolite

alteration characteristics of the archean golden grove formation at the gossan hill deposit western australia induration as a focusing mechanism for mineralizing hydrothermal fluids the archean golden grove formation is a 550 m thick rhyodacitic tuffaceous volcaniclastic succession that hosts the cu zn rich gossan hill volcanic hosted massive sulfide vhms deposit in the yilgarn craton western australia the golden grove formation consists of volcanic quartz and altered pumice and shards which were deposited during successive episodes of subaqueous mass flow coherent volcanics are absent from the golden grove formation at gossan hill but form the main rock type in the hanging wall scuddles formation a massive dacite dome that overlies its volcanic feeder dike is inferred to occupy a synvolcanic structure that focused mineralizing fluids during the formation of the gossan hill deposit the gossan hill deposit consists of two stratigraphically separate ore zones interconnected by stockwork the cu rich lower ore zone and the zn rich upper ore zone occur in the middle and upper parts of the golden grove formation respectively podiform zones of massive magnetite occur in the cu rich ore zone where the formation of magnetite predates massive sulfide the asymmetry of massive sulfide massive magnetite and alteration zones at the gossan hill deposit attest to synvolcanic structural control during mineralization the principal lithofacies of the golden grove formation are sandstone and pebble breccia which have a regionally extensive quartz fe rich chlorite and lesser muscovite alteration at gossan hill this alteration has resulted in near complete replacement of tuffaceous components causing substantial chemical modification of the primary lithologies quartz chlorite muscovite alteration is characterized by severe k2o na2o and cao depletion with rocks consisting principally of sio2 feo al2o3 and mgo along a quartz chlorite mixing trend widespread preservation of pumice and shard volcanic textures within the golden grove formation indicates that quartz chlorite muscovite alteration occurred soon after or possibly during sedimentation the absence of diagenetic compaction textures further suggests induration of the succession during this early alteration stage with the tuffaceous succession largely sealed from the texturally destructive effects of subsequent hydrothermal alteration except where mineralizing fluids were locally channeled along synvolcanic feeder conduits local intense hydrothermal alteration zones surround the gossan hill deposit and overprint earlier quartz chlorite muscovite alteration these local alteration zones have the same extent as the sulfide vein envelope and represent hydrothermal alteration formed during sulfide magnetite mineralization intense fe rich chlorite ankerite siderite alteration occurs as a strata bound envelope around massive magnetite cu rich veins and massive sulfide in the lower ore zone this chlorite rich alteration has strong feo and mgo enrichment with minor chloritoid and andalusite that reflect intense acid leaching during hydrothermal alteration iron chlorite ankerite siderite alteration grades upward into discordant to strata bound intense quartz alteration intense quartz alteration forms an envelope around zn rich veins and massive sulfide in the stockwork and upper ore zone the trend from fe chlorite ankerite siderite to quartz alteration toward the top of the deposit is consistent with the cooling of hydrothermal mineralizing fluids nearing the sea floor rhyodacite and dacite volcanics of the hanging wall scuddles formation have a pervasive muscovite calcite alteration muscovite calcite alteration led to na2o depletion and cao and k2o enrichment associated with burial of the gossan hill mineralizing system we propose that the gossan hill sulfide magnetite vhms deposit formed during an evolving archean hydrothermal system that began as part of a regional scale low temperature seawater convection alteration system initially this system caused extensive replacement of the golden grove formation by quartz and fe chlorite muscovite a process that sealed and indurated the volcaniclastic rocks by infilling of primary porosity and permeability structures due to subsequent impermeability of the host rock succession later and hotter mineralizing fluids that generated alteration and massive magnetite and sulfide at the gossan hill deposit were constrained to and focused upward along a synvolcanic feeder structure

zeolitic diagenesis of late quaternary fluviolacustrine sediments and associated calcrete formation in the lake bogoria basin kenya rift valley late quaternary fluviolacustrine siltstones mudstones and claystones loboi silts on the northern margins of the saline alkaline lake bogoria in the kenya rift valley contain up to c 40 authigenic analcime and minor natrolite the zeolitic sediments are reddish brown and up to 1 m thick the amount of analcime increases upward in the profile but decreases with distance from the lake the altered sediments show many pedogenic features including zeolitic root mats rootmarks concretions and carbonate rhizoliths residual patches of calcrete locally cap the zeolitic rocks the profile is interpreted as an exhumed palaeosol and land surface on the former margins of the lake the analcime occurs as submicroscopic 0 5 2 5 m subhedral and euhedral crystals which have an average si a 1 ratio of 2 33 as determined by x ray microanalysis or 2 18 d value of 639 analcime peak the analcime formed in lake marginal sediments soils by reaction of silicate detritus with na2co3 rich pore waters concentrated close to the land surface by evaporative pumping and evapotranspiration poorly ordered clay minerals were probably the main reactants authigenic illite may have been a by product of the reactions chemical analyses suggest that pore waters supplied some of na and possibly k and sio2 the associated calcrete and rhizoliths were formed during or shortly after the main period of zeolitic alteration the ca2 may have originated from infiltrating dilute runoff and groundwater authigenic smectite was precipitated in open porosity following analcime formation the zeolitic alteration at lake bogoria provides a relatively recent analogue for lake marginal zeolites found in many ancient saline alkaline lake sediments

were intercalated komatiites and dacites at the black swan nickel sulphide mine yilgarn craton western australia emplaced as extrusive lavas or intrusive bodies the significance of breccia textures and contact relationships intercalated archean komatiites and dacites sit above a thick footwall dacite unit in the host rock succession at the black swan nickel mine north of kalgoorlie in the yilgarn craton western australia both lithofacies occur in units that vary in scale from laterally extensive at the scale of the mine lease to localized thin irregular bodies from 100 m thick to only centimetres thick some dacites are only slightly altered and deformed and are interpreted to post date major deformation and alteration late porphyries however the majority of the dacites display evidence of deformation especially at contacts and metamorphism varying from silicification and chlorite alteration at contacts to pervasive low grade regional metamorphic alteration represented by common assemblages of chlorite sericite and albite texturally the dacites vary from entirely massive and coherent to partially brecciated to totally brecciated strangely some dacites are coherent at the margins and brecciated internally breccia textures vary from cryptically defined to blocky closely packed in situ jig saw fit textures with secondary minerals in fractures between clasts to more apparent matrix rich textures with round clast forms giving apparent conglomerate textures some clast zones have multi coloured clasts giving the impression of varied provenance strangely however all these textural variants have gradational relationships with each other and no bedding or depositional structures are present this indicates that all textures have an in situ origin the komatiites are generally altered and pervasively carbonate veined preservation of original textures is patchy and local but includes coarse adcumulate mesocumulate orthocumulate crescumulate harrisite and occasionally spinifex textures where original contacts between komatiites and dacites are preserved intact i e not sheared or overprinted by alteration the komatiites have chilled margins whereas the dacites do not the margins of the dacites are commonly silicified and inclusions of dacite occur in komatiite even at the top contacts of komatiite units but komatiite clasts do not occur in the dacites the komatiites therefore were emplaced as sills into the dacites and the intercalated relationships are interpreted as intrusive the brecciation and alteration in the dacites are interpreted as being largely due to hydraulic fracturing and alteration induced by contact metamorphic effects and hydrothermal alteration deriving from the intrusion of komatiites into the felsic pile the absence of autobreccia and hyaloclastite textures in the dacites suggest that they were emplaced as an earlier intrusive sill complex at a high level in the crust

continental shelf upwelling and benthic ostracoda in the benguela system southeastern atlantic ocean abstract the distribution of benthic ostracoda micro crustacea on the continental shelf off southwestern africa is controlled by sea floor physical and chemical parameters which in turn can be correlated with the positions of quasi permanent upwelling cells of the benguela system the linkage between benthic and surface physico chemical environments and consequently between benthos and surface parameters is not direct however being modulated by equatorward motion in the upper water column benthic poleward water motion fluvial input and cross shelf advection of off shelf water these phenomena and in particular the intensity of surface upwelling show a sharp distinction about 27 s so that the ostracod faunas in the northern benguela region are relatively sparse and dominated by palmoconcha walvisbaiensis hartmann and cytherella namibensis dingle while in the southern benguela region the faunas are more diverse and dominated by pseudokeijella lepralioides brady and ruggieria cytheropteroides brady when minor taxa are also considered each cell in the benguela upwelling system is shown to be associated with a unique ostracod fauna which can be related to its in particular environmental characteristics

sedimentary nitrogen isotopic ratio as a recorder for surface ocean nitrate utilization in two contrasting regions of the ocean the equatorial pacific and the southern ocean the 15n of core top sediments were strongly related to no3 in surface waters with distance from the equator in the equatorial pacific 15n increased from 7 to 16 as no3 decreased from 8 m to 0 1 m going from 60 to 30 s in the se indian ocean core top 15n increased from 5 to 11 as surface no3 decreased from 25 m to 0 1 m these results are strong evidence that sedimentary 15n in these regions is recording the increasing isotopic enrichment of near surface no3 with its depletion by phytoplankton in the case of the equatorial pacific 15n values for sinking particles collected at 150 m matched well the core top sediment values demonstrating little diagenetic alteration of the near surface generated isotopic signal these equatorial pacific data sets have variations with near surface no3 consistent with rayleigh fractionation kinetics for a fractionation factor u of 2 5 this value is substantially lower than previously found for temperate or polar regions perhaps as a result of differences in phytoplankton species assemblage or growth condition in the southern ocean south of the polar front comparison of 15n values for opal rich sediments south and sinking particles indicates an apparent 5 diagenetic enrichment relative to the surface generated signal that requires further investigation this exception aside our observations show that the surface water relationship of increasing 15n with increasing no3 depletion is generally transmitted to and preserved in the sediments an important requirement for further development and application of this important paleoceanographic tool

auriferous chert banded iron formation and related volcanogenic hydrothermal alteration atik lake manitoba small scale alteration pipes and stratiform alteration in archean glomeroporphyritic tholeiitic basalts at atik lake manitoba stratigraphically underlie silicate oxide banded iron formation bif and auriferous sulfide bearing chert the auriferous chert is locally interbedded with graphitic argillite indicating euxinic conditions during deposition cordierite gedrite rocks formed by recrystallization of alteration assemblages during the lower amphibolite facies metamorphism t 550 c p 2 5 kbar al2o3 tio2 zr and nb which were relatively immobile during alteration have been used to monitor igneous differentiation and alteration volcanogenic hydrothermal alteration resulted in depletion of ca si mg na and sr in the altered basalt and the addition of k fe rb and ba this was accompanied by mass and volume losses of up to 25 the mineralizing fluid was reducing and somewhat acidic rare earth element ree profiles of bif and graphitic argillite normalized to archean shale are less

genesis of zeolites in the neapolitan yellow tuff geological volcanological and mineralogical evidence the study proposes a model by which a thick succession of volcanic tuffs can be zeolitized by alteration of pyroclastic material in the presence of sufficient eruptive water and at temperatures close to water vapour condensation in the case of phreatomagmatic products the model simplifies interpretation of problematic deposits that exhibit pronounced vertical and lateral variation in lithification grade a major feature of the model is that thick zeolitized tuffs can be formed during emplacement of pyroclastic products in marked contrast to later alteration in an open hydrologic system geological volcanological and mineralogical data for the neapolitan yellow tuff a widespread trachytic pyroclastic deposit outcropping around campi flegrei southern italy have been used to infer the physico chemical conditions that determined mineral genesis this tuff shows a reduction in lithification grade towards the base top and with distance from the vent and very variable zeolitization within the lithified portion we suggest that during initial emplacement the erupted products chilled against the ground inhibiting zeolite crystallization during rapid deposition of the thick wet succession thermal insulation allowed the persistence of elevated temperatures for a time sufficient for enhancement of hydration dissolution processes in the volcanic glass the highly reactive alkali trachytic glass quickly buffered the acid ph of the system favouring phillipsite crystallization followed by chabazite nucleation the variable zeolite content reflects fluctuating emplacement conditions e g changes in water content and temperature cooling of the upper and relatively thin distal deposits inhibited the zeolitization process thereby preserving the primary unlithified deposit

late paleozoic depositional sequences are synchronous and worldwide more than fifty transgressive regressive depositional sequences are present in carboniferous and permian shallow marine successions on stable cratonic shelves worldwide these were synchronous depositional events resulting from eustatic sea level changes that generally ranged from 100 to 200 m each transgressive regressive sequence is correlatable using current fossil knowledge they average about 2 m y and range from 1 2 to 4 m y in length the presence within these strata of numerous synchronous unconformities of considerable duration and worldwide extent suggests that the fossil record is very incomplete and that we are studying a punctuated fossil record and not a punctuated evolution based on a highly irregular mutation rate these late paleozoic transgressive regressive depositional sequences facilitate correlations because depositional histories of a rock succession can support interpretations of faunal assemblages and faunal similarities in evaluating age relationships

authigenic silicates and silica polymorphs in the miocene saline alkaline deposits of the karlovassi basin samos greece the lower neogene unit of the karlovassi basin samos island greece was deposited in a continental basin during miocene times and consists of four successions overlying a basal conglomerate the four successions are from the base upward carbonates tuffaceous rocks claystones and porcelanites volcanic glass was originally abundant in the tuffaceous succession but is now represented by its diagenetic products including boron bearing k feldspar the zeolites clinoptilolite analcite and mordenite smectite opal disordered tridymite cristobalite cristobalite and minor amounts of the zeolites erionite phillipsite and chabasite and tridymite evaporite minerals such as gypsum celestite and thenardite are present along with authigenic silicates in tuffaceous intervals into the claystone succession authigenic silica polymorphs represented by opal and chalcedony were identified in the uppermost succession of porcelaneous limestones to chert five irregular concentric zones related to the presence and kind of zeolites and k feldspar are recognized in the lower neogene unit 1 a marginal zone of carbonate and detrital silicate minerals nonauthigenic silicates 2 a clinoptilolite zone 3 a mixed clinoptilolite analcite zone 4 an analcite zone and 5 a central boron bearing k feldspar zone the general pattern of zonation and distribution of authigenic silicates as well as their chemical characteristics indicates the presence of a saline alkaline lake during miocene times this lake is analogous to those of the same age which existed in southern yugoslavia and western turkey where borate sulfate and double carbonate deposits were formed along with authigenic silicates it is possible that a large continental area in the eastern mediterranean underwent large scale dessication which took place during the miocene messinian salinity crisis resulting in the development of highly saline alkaline lacustrine environments

alteration history of mount epomeo green tuff and a related polymictic breccia ischia island italy evidence for debris avalanche this paper presents mineralogical chemical and textural data for the mount epomeo green tuff and an associated polymictic breccia on ischia island italy with the purpose of defining the alteration history of the two units and the emplacement origin of the polymictic breccia our results indicate that the green tuff trachytic ignimbrite experienced three alteration events that produced the following mineral assemblages 1 phillipsite randomly interstratified r0 illite smectite i s fe illite and smectite in situ green tuff 2 chabazite phillipsite r0 i s and fe illite proximal facies green tuff at scarrupata di barano and 3 analcime authigenic k feldspar fe illite r0 i s and smectite clasts of green tuff in polymictic breccia phillipsite chabazite and r0 i s within the in situ and proximal facies green tuff indicate low temperature alteration t 70 c alteration within a mostly closed chemical system these data suggest that the polymictic breccia represents a debris avalanche deposit created by a catastrophic volcanic collapse which was associated with low temperature hydrothermal alteration and thus structural weakening of the volcano the debris avalanche that produced the polymictic breccia on ischia may be related to nearby massive debris avalanche deposits recently discovered offshore of southern ischia the young age of the polymictic breccia 5 7 8 6 ka and the possibility of its catastrophic emplacement indicate an additional volcanic hazard for ischia island

relationship between altered pyroxene diorite and the magnetite mineralization in the chilean iron belt with emphasis on the el algarrobo iron deposits atacama region chile north of el algarrobo one of the four main deposits of the chilean iron belt the iron mineralization magnetite etrmolite actinolite apatite is related to clinoand orthopyroxene diorite intrusions which have crystallized at shallow depth 4km under increasing oxygen fugacities the supercritical fluid phase exsolved during cooling after the consolidation of the plutons 800 900 c results in a h cl and sodic enrichment and in the sequential leaching of fe at less than 700 c then ca and mg between 600 and 500 c from minerals of the primary magmatic diorite assemblage titanomagnetite ilmenite plagioclase an70 40 augite hypersthene as a consequence of the cationic leaching the lower mobility of silica and aluminium and the enrichment in sodium residual altered dioritic rocks present a retromorphic mineral assemblage evolving down to boundary conditions of the greenchist amphibolite facies 450 c fe mg and ca are carried in cationic form associated with cl anions toward cooler rocks where they are precipitated the deposition between 550 and 450 c of magnetite followed iron mineralization paragenesis and occurred in fractured zones located both in altered diorites and contact andesites

geologic consequences of globe encircling equatorial currents many black shales phosphorites and cherts that formed at low paleolatitudes on the north american continent during the late paleozoic were a direct consequence of equatorial upwelling and an equatorial undercurrent in an ocean that spanned much of the globe in equatorial parts of modern oceans wind stress divergence leads to high surface productivity sinking organic matter is remineralized in the strong eastward flowing equatorial undercurrent the undercurrent thus acts as a nutrient trap that becomes progressively oxygen poor and nutrient rich as it moves eastward the late paleozoic global ocean was 60 to 80 wider than the modern pacific ocean 24 000 km total width the nutrient trapping equatorial current system of this globe encircling ocean was probably anoxic and may have been sulfate reducing nutrient rich anoxic water from the undercurrent would have had direct consequences for the genesis of black shale facies in devonian and pennsylvanian epicontinental seaways as well as possibly providing the source water for coastal upwelling in settings such as the phosphoria sea

geochemistry of the mississippian delle phosphatic event eastern great basin u s a abstract the middle mississippian delle phosphatic event marks a significant change in depositional conditions in the devonian mississippian antler foreland basin of north america stratigraphic and petrographic studies show that deposition of delle event rocks ended a long period of open marine carbonate sedimentation when facies shifted to phosphorites cherts fine grained siliciclastics and lime mudstones from highly productive waters that may have been episodically anoxic this drastic change in lithology is reflected in the chemistry of the two suites of rocks 18o values of the delle event lime mudstones and phosphatized wackestones packstones affected by the delle event are 3 5o oo lighter than underlying and overlying open marine wackestones packstones sr concentrations of delle event lime mudstones and open marine wackestone packstone facies are low suggesting that both of these lithologies have undergone similar postdiagenetic alteration the uniform sr concentrations and variable 18o data suggest that either the younger delle event rocks were exposed to meteoric water during diagenesis or that the relatively light 18o values represent a primary brackish water depositional signal either interpretation is consistent with sedimentological evidence of the delle event occurring in a predominantly shallow water setting 13c values of delle event lime mudstones are also anomalously light indicating a high input of organic carbon during their formation mn concentrations of the delle event lime mudstones and stratigraphic equivalents are highly variable suggesting fluctuating oxygen concentrations during their deposition and diagenesis rare earth element data from phosphorites and cherts of the delle event indicate oxic to suboxic depositional conditions

hydrothermal alteration of felsic volcanic rocks at the helen siderite deposit wawa ontario within the footwall volcanic sequence five chemically and mineralogically distinct alteration types have been defined least altered sericite chlorite chloritoid and ankerite an alteration model is proposed in which shallow circulating seawater 1 3 km heated by a subvolcanic intrusion encountered rocks of felsic composition within the upper part of the volcanic succession seawater rock reactions evolved an acidic potassium rich solution which migrated upward reacting with overlying felsic rocks converting plagioclase to sericite and quartz porosity of the altered rocks decreased and a widespread sericitic alteration zone formed at depths greater than 3 km circulating seawater came into contact with basaltic rocks and ensuing reactions enriched the seawater in fe mg mn ca and co 2 this second hydrothermal solution moved upward and encountered sericite rich rocks near the sea floor boiling of the solution and or mixing with relatively cold seawater rapidly decreased co 2 solubility causing mass precipitation of iron carbonate this led to the formation of the ankerite assemblage in the immediate footwall rocks and the siderite iron formation on the sea floor modified journal abstract

palaeoenvironmental and palaeoceanographic controls on black laminated mudrock deposition example from devonian carboniferous strata alberta canada abstract sedimentological palaeontological and ichnological analyses indicate that heightened episodes of equatorial upwelling in tandem with an expanded and intensified oxygen minimum zone promoted deposition of upper famennian to lower tournaisian laminated organic rich mud rocks of the exshaw formation on the alberta cratonic platform exshaw mud rocks represent the culmination of an upper devonian transgression that commenced with deposition of open marine carbonates of the big valley formation the transgression was abruptly halted at the devonian carboniferous boundary by a rapid eustatic sea level fall and the consequent deposition of near shore marine to shelfal bioturbated siltstones and sandstones of the exshaw formation the siltstones grade into laminated organic lean mud rocks to the north in more distal offshore shelf settings these mudrocks reflect a period of low primary production but continued anoxia of bottom waters continuation of anoxic conditions resulted from development of restricted circulation in the epicontinental sea due to the establishment of a westward located physical barrier following this event was a relative sea level rise that led to deposition of black laminated mudrocks of the banff formation

occurrence composition and origin of analcime in sedimentary rocks of non marine petroliferous basins in china abstract natural analcime a highly brittle aluminosilicate mineral that dissolves easily during diagenesis occurs in the sedimentary rocks of eight main non marine petroliferous basins in china this mineral has been well documented for the past 30 years and has proved to be significant for the formation of high quality hydrocarbon reservoirs the present study fully reviews analcime occurrences chemical compositions si al ratios origin and controlling factors and influence on the hydrocarbon reservoir quality in permian to paleogene sedimentary rocks previous research has shown that analcime is commonly distributed within argillaceous laminae l type occurs as intergranular cement c type replacement r type and crack filling f type forms or is closely intergrown with other authigenic exhalative minerals a type analcime in lacustrine basins is slightly al rich and na poor and its si al ratios range from 1 95 to 2 80 the geochemical compositions of the analcime and ankerite bearing exhalites are characterised by enrichment in light rare earth elements and 13c and depletion in heavy rare earth elements and 18o with negative eu and positive ce anomalies diagenetic analcime forms by the alteration of volcanic glass clays or zeolite precursors in saline alkaline lakes or during buried diagenetic stages in sedimentary rocks in addition it coexists with other authigenic zeolite carbonate and clay minerals as well as albite hydrothermal analcime presumably precipitates from hydrothermal fluids and is not dependent on a local precursor mineral or volcanic glass this type is commonly related to exhalative mineralisation of hydrothermal springs the formation of natural analcime is controlled by various factors such as the composition of the parent material temperature prevalent during crystallisation chemistry of the fluid phase and thermodynamic characteristics of the geological environment as zeolites are formed in alkaline fluid phases they become unstable in acidic pore water secondary pores created by analcime mineral dissolution and intercrystalline micropores among analcime minerals are highly significant in hydrocarbon reservoirs analcime bearing mudstone siltstone dolostone and exhalite are favourable lithofacies for unconventional hydrocarbon accumulation owing to its high brittleness and selective dissolution of analcime and other associated minerals

trace element budgets in the ohio sunbury shales of kentucky constraints on ocean circulation and primary productivity in the devonian mississippian appalachian basin abstract the hydrography of the appalachian basin in late devonian early mississippian time is modeled based on the geochemistry of black shales and constrained by others paleogeographic reconstructions the model supports a robust exchange of basin bottom water with the open ocean with residence times of less than forty years during deposition of the cleveland shale member of the ohio shale this is counter to previous interpretations of these carbon rich units having accumulated under a stratified and stagnant water column i e with a strongly restricted bottom bottom water circulation a robust circulation of bottom waters is further consistent with the palaeoclimatology whereby eastern trade winds drove upwelling and arid conditions limited terrestrial inputs of siliciclastic sediment fresh waters and riverine nutrients the model suggests that primary productivity was high 2 g c m 2 d 1 although no higher than in select locations in the ocean today the flux of organic carbon settling through the water column and its deposition on the sea floor was similar to fluxes found in modern marine environments calculations based on the average accumulation rate of the marine fraction of ni suggest the flux of organic carbon settling out of the water column was approximately 9 of primary productivity versus an accumulation rate burial of organic carbon of 0 5 of primary productivity trace element ratios of v mo and cr mo in the marine sediment fraction indicate that bottom waters shifted from predominantly anoxic sulfate reducing during deposition of the huron shale member of the ohio shale to predominantly suboxic nitrate reducing during deposition of the cleveland shale member and the sunbury shale but with anoxic conditions occurring intermittently throughout this period

mineralogy and sedimentology of the miocene gocenoluk borate deposit kirka district western anatolia turkey the miocene boratiferous district of kirka in western anatolia turkey is the most important na borate borax resource in the world two separate deposits in the kirka district are located near the villages of sarikaya and gocenoluk eskisehir province borax is intensively exploited in open pit mines in the sarikaya deposit while only small quarries of colemanite are known in the gocenoluk deposit recent exploratory drilling in the gocenoluk area intersected a thick succession of dolostones tuffs and three borate bearing units lower intermediate and upper borate units in them the most abundant borate mineral is ulexite ca na borate passing at depth to probertite borax na borate is only present in the intermediate borate unit minor amounts of colemanite ca borate and hydroboracite ca mg borate occur at the base and or top of each mineralized unit pyroclastic layers within the borate units show intense alteration by alkaline boron bearing waters and formation of diagenetic clay minerals smectites zeolites analcime and borosilicates searlesite the gocenoluk succession is interpreted as a shallow ephemeral alkaline lake deposit in which carbonates formed as stromatolites and travertines borate precipitation in the gocenoluk area took place interstitially within muddy and carbonate sediments in a lateral progression from marginal ca borates towards na ca borates and rarely to na borates in the center of the lake authigenic silicate mineral distribution shows parallel changes toward the center of the lake that reflect increasing ph gradient

palaeoceanographic controls on geochemical characteristics of organic rich exshaw mudrocks role of enhanced primary production organic rich source rocks have generally been attributed to enhanced preservation of organic matter under anoxic bottom waters here geochemical analysis of kerogen and whole rock samples of organic rich lithofacies b1 and organic lean lithofacies b2 laminated mudrocks of the devonian carboniferous exshaw formation alberta highlight the importance of primary production in governing the quantity and quality of organic matter lower si al k al ti al and quartz clay ratios in lithofacies b2 similar maceral types and the laminated fabric of the two lithofacies indicate that the quality and quantity of organic matter are not related to grain size redox or organic matter source changes high total organic carbon toc and hydrogen index hi low oxidation index ox i ratio of oxygen functional groups to aliphatic groups derived by ftir lighter 15ntot and heavier 13corg isotopes indicate that kerogen of lithofacies b1 accumulated during periods of high organic carbon production and delivery of relatively fresh labile well preserved organic matter to the sea floor in contrast low toc hi high ox i heavier 15ntot and lighter 13corg isotopes indicate low primary productivity and delivery high recycling and poor preservation of organic matter during accumulation of lithofacies b2

concretion formation in volcaniclastic host rocks evaluating the role of organics mineralogy and geochemistry on early diagenesis abstract the upper part of the brushy basin member of the jurassic morrison formation in the four corners regions of the u s was deposited in an ephemeral alkaline saline lake system with copious input of volcanic ash that resulted in dynamic fluid rock interaction during early diagenesis three broad diagenetic facies defined by color and associated bioturbation features are interpreted red green and intermediate diagenetic facies reflect meter scale paleotopography red facies represent shallow water to subaerial oxidizing conditions green facies reflect saturated conditions and reducing pore water chemistry shortly after deposition and intermediate facies represent a combination of or rapid transition between the previous two conditions three categories of concretions are characterized based on mineralogy carbonate iron oxyhydr oxide and phosphate concretions variation in concretion mineralogy and morphology in the brushy basin member suggests that alkaline saline fluid chemistries created diagenetic microenvironments within a larger lake system to influence concretion precipitation however porosity and permeability are more important factors affecting concretion size morphology and mineralogy than host rock composition diagenetic fluid rock interactions in volcaniclastic sediments can be spatially variable even on tens of centimeters scale

organic rich transitional facies in silled basins response to sea level change high resolution profiles of organic carbon delta sup 13 c sub org sulfur delta sup 38 s and some trace elements in cores from two silled basins kau bay indonesia and the black sea allow division of the sedimentary record into three distinct units representing a pleistocene fresh water brackish water facies unit 3 a holocene transitional facies unit 2 and a modern fully marine facies unit 1 the geochemical characteristics of these units are strikingly similar for both basins the sediments form unit 3 are characterized by the predominance of terrestrial organic matter mo and u concentrations at crustal abundance and positive delta sup 34 s values the transitional sediments unit 2 are strongly enriched in marine organic matter and mo v and u and have intermediate delta sup 34 s values sediments from the modern marine facies unit 1 are moderately organic carbon rich and slightly enriched in mo and u and have negative delta sup 34 s values the organic carbon rich sediments from unit 2 were formed by increased production during the transition from the pleistocene isolated fresh water brackish water environment to the modern open marine facies this temporarily higher productivity was caused by displacement of nutrients from the deep water into the euphotic zone owing to the gradual infilling by marine waters

glacial to interglacial changes in surface nitrate utilization in the indian sector of the southern ocean as recorded by sediment δ15n we present a new approach for paleoceanographic reconstruction of surface nutrient utilization in the southern ocean it has been observed in the contemporary ocean that due to preferential uptake of 14no3 during photosynthesis the 15n of planktonic organic matter increases with increasing nitrate depletion in surface waters our results demonstrate that the 15n signal produced in surface waters is reflected in the underlying surface sediments core top 15n is inversely correlated with surface nitrate concentration along a transect across the subtropical convergence and the polar front in the southeast indian ocean these results are consistent with a four box model showing that the nitrogen isotopic composition of sinking organic matter depends on percent nitrate utilization in the euphotic zone by comparing the 15n of surface sediments with that measured in the glacial sections of several cores we infer changes in the intensity and latitudinal distribution of nitrate uptake in this region during the last glacial maximum these preliminary results argue against increased biological uptake of nutrients in southern polar waters as a major mechanism for glacial lowering of atmospheric co2 they also suggest that subantarctic waters in the se indian sector became more nutrient depleted as they migrated northward increased nitrate depletion might have also occurred slightly south of the glacial polar front we use a six box model to explore the possible impact of this observation on atmospheric co2

depositional mechanisms and alteration processes in different types of pyroclastic deposits from campi flegrei volcanic field southern italy the campi flegrei volcanic field southern italy is composed of a large variety of pyroclastic deposits related to both magmatic and hydromagmatic activity in spite of similarities of composition grain size age and pre eruptive environment the various deposits exhibit great differences in terms of degree and type of alteration of the juvenile components in particular detailed analyses of pyroclasts collected in the numerous monogenetic volcanic cones show the broad range of alteration from fresh glass to complete replacement of the glass by the zeolites the comparative analysis of 17 different deposits has allowed us to conclude that the eruptive and emplacement conditions were the major controls on the zeolitization processes the relationships between volcanological features of deposits and secondary mineralization are consistent with the glass fluid phase reaction in a near closed post depositional system eruptions characterised by separation of water vapour from the pyroclastic particles produce unaltered or poorly altered deposits in contrast eruptions characterised by mechanisms that permit the capture and retention of pore water and water vapour produce zeolitized deposits according to these lines of evidence the zeolitization of pyroclastic products of campi flegrei took place immediately after emplacement during the cooling of wet deposits

alteration processes of the roque nublo ignimbrites gran canaria canary islands abstract the non welded lithic rich ignimbrites of roque nublo are the most characteristic deposits of the second magmatic cycle pliocene in age on gran canaria they are very heterogeneous with 35 55 by volume of lithic clasts 15 30 of moderately vesiculated pumice 5 7 of crystals and 20 30 of ash matrix the juvenile components pumice fragments and ash matrix are largely altered the mineral assemblage that originated by the alteration of vitric components consists mainly of zeolites chabazite phillipsite and analcime and subordinate smectites the alteration does not show any lateral or vertical gradation in the deposits and does not change in intensity with respect to the distance from the emission center these alteration processes affect only the roque nublo ignimbrites their associated fall and surge deposits remain unaltered a geo autoclave mechanism is proposed to explain the alteration processes which devitrified the juvenile components of the roque nublo ignimbrites and gave the rocks their characteristic strong induration this implies that the eruptions which led to the formation of the roque nublo ignimbrites had an important phreatomagmatic component and that the resulting pyroclastic flows were too dense and too poorly expanded to permit the water vapour to be separated from the vitric fragments during transport the alteration took place in situ and immediately after the deposition of the deposits when they were still hot by the reaction between the vitric components and the condensed vapour and cannot be attributed to late diagenesis or weathering

carbon accumulation rates and the origin of the holocene sapropel in the black sea a detailed radiocarbon chronology obtained by accelerator mass spectrometry together with organic carbon and carbonate measurements on two black sea cores has been used to compare and contrast the burial fluxes of organic carbon in the holocene sapropel and the modern sediment at both deep water and eastern slope sites the sapropel is separated from the modern facies by a variable thickness of compositionally homogeneous sediment with low levels of organic carbon and anomalously old radiocarbon ages this homogeneous unit probably represents deposition by slumping or mudflow the age limits of the sapropel are 1600 6600 b p at the deep water site and 4000 6000 b p radiocarbon years before 1950 a d at the shallow water site the carbon accumulation rate in the deep water sapropel is higher than that in the modern deep water facies by a factor of 2 and is approximately the same as that in the modern sediment in shallow water the revised chronology of sapropel formation and the differences in the carbon accumulation rates probably indicate that the sapropel was formed by increased production during the transition from the premodern lake to the modern marine phases of the black sea this conclusion is consistent with the clear marine carbon isotope signal in the organic mattermore in the sapropel in both cores results to be reported elsewhere in contrast to the mixed source of carbon in the other facies less

jarosite in a pleistocene east african saline alkaline paleolacustrine deposit implications for mars aqueous geochemistry 1 jarosite occurs within altered tephra from the saline alkaline paleolake deposits of pliocene pleistocene olduvai gorge tanzania zeolites mainly phillipsite authigenic k feldspar and mg fe smectites dominate the mineral assemblage indicating saline alkaline diagenetic conditions ph 9 as jarosite is ordinarily an indicator of acidic conditions on earth and mars its association with such undisputed high ph indicators is unexpected of 55 altered tephra samples collected from the paleolake basin and margin deposits eleven contained jarosite detectable by x ray diffraction xrd 0 15 mossbauer spectroscopy fourier transform infrared reflectance ftir electron probe microanalysis epma x ray fluorescence xrf and scanning electron microscopy sem analyses confirm the presence and nature of the jarosite this paper documents this occurrence and presents mechanisms that could produce this unusual and contradictory mineral assemblage we favor a mechanism by which jarosite formed recently perhaps as modern ground and meteoric water interacted with and oxidized paleolacustrine pyrite providing local and temporary acidic conditions however local groundwater at modern springs has a ph 9 in recent studies of mars the presence of jarosite or other fe or mg sulfates is often used to indicate dominantly acidic conditions regardless the current study shows that jarosite can form in sediments dominated by alkaline minerals and solutions its coexistence with mg fe smectites in particular makes it relevant to recent observations of martian paleolakes

paleogeography an earth systems perspective abstract paleogeography is the subdiscipline within the geosciences that studies the physical and biological geography of the geologic past including the configuration and latitudinal distribution of continental landmasses their topographic relief climate and biota in recent years the study of paleogeography has evolved from simple continental reconstructions to more sophisticated paleocontinental maps that form the basis of paleoclimactic modeling by incorporating elements of oceanic and atmospheric circulation and their interactive relationship with landmasses a broad range of geologic elements can be reconstructed through paleogeographic studies such as mountain belts climate zones emergent land and continental configurations many of which impact directly on understanding the driving forces behind geochemical signals contained in the rock record which are used as a proxy for biogeochemical processes in earth history paleogeography is thus an essential component of an earth systems approach to interpreting the geologic past paleoconfigurations of continents and ocean basins are determined by a variety of techniques paleomagnetic studies are the most common but additional constraints are provided by faunal provincialism biogeography and abiotic continental linkages such as pre break up magmatism recent developments within paleogeography include the use of various forms of climate models to analyze the relationships between global continental reconstructions and the rock record of past climates in order to test more directly feedback between paleogeography and paleoclimate development of an extended gis database for the geological past promises new insights into quantitative analysis of earth system evolution

the geology mineralogy petrography and geochemistry of the miocene dursunbey coal within fluvio lacustrine deposits balikesir western turkey abstract the dursunbey coalfield a typical example of coalfields in the western anatolia hosts a mineable coal seam about 9 0 m coal thickness with altered tuff layers within early miocene fluvio lacustrine sequences the aim of this study is to identify peat accumulation conditions and factors controlling the mineralogy and geochemistry of this seam the standard coal features and petrographical mineralogical and elemental compositions display changes throughout the seam ash yields display decreasing trends towards to the upper parts of seam while total c contents and gross calorific values are increasing furthermore the coal facies patterns evidence changes of depositional conditions and vegetation in the palaeomires during initial stages of peat accumulation the contribution of herbaceous peat forming plants were more common and palaeomires were open to detrital inputs whereas woody peat forming were becoming predominant and the water table was stable and high which caused development of anoxic conditions during late stages therefore the content of detrital minerals such as quartz and clay minerals illite smectite and chlorite increases in the lower parts of seam while that of pyrite increases in the upper parts in addition the sem edx data show that matrices of clay mineral aggregates are illitic in composition in the lower parts of seam while those of smectite prevalence are more common below and above altered tuff layers interestingly authigenic rhomboid k feldspar grains are observed within smectite clay aggregates in the samples from the upper parts of seam framboidal pyrite grains and clusters were also commonly identified from these samples as well this data shows that synchronous volcanic inputs were altered within a hydrologically closed system under slight acidic to neutral conditions during late syngenetic stages the enriched elements such as cr ni cs and v display moderate to strong positive correlations with ash yields while al2o3 and k2o indicate an aluminosilicate affinity clay mineral and feldspar considering the presence of metamorphic and ophiolitic rocks in the basement and the adjacent areas clastic inputs into the palaeomire seems to be controlling aluminosilicate affiliated elements additionally the sem edx analyses denoted that ni and as are associated with pyrite the ni and as bearing epigenetic pyrite infillings are mostly identified in coal samples below altered tuff layers hence as and ni enrichments are controlled by precipitation of leached pore waters from altered tuff layers nevertheless as and ni bearing syngenetic pyrite grains and clusters are related with the development of anoxic conditions within palaeomires this could also favour a mo and u enrichment which is another testimony for synchronous volcanic inputs altered under anoxic conditions overall high detrital input ratios from adjacent areas during initial stages of peat accumulation in the study area controlled by enrichments of aluminosilicate affiliated elements whereas during late stages of peat accumulation the development of a hydrologically closed system and redox conditions within the palaeomire caused as ni mo and u enrichments and the formation of smectite and authigenic k feldspars

zeolites in tertiary coal from the cayirhan mine beypazari turkey the study focuses on the mineralogy of the upper coal seam accumulated at the top of the coraklar formation miocene beypazari turkey this coal seam is laterally extensive and averages 3 0 m thick varying from 1 0 to 4 9 m analcime and clinoptiolite comprise up to 80 of the mineral matter which also includes feldspars quartz and pyrite and traces of dolomite clay minerals and apatite in the coal from the cayirhan mine zeolites were formed when sodium rich solutions altered aluminosilicate epiclastic material derived from contemporaneous volcanic activity the allocthonous organic matter accumulated as a result of detrital plant and epiclastic material from an adjacent fresh water environment being washed into a saline lake in sufficient quantities to form peat with a high mineral matter content 29 7 mean mineral matter content in raw coal subsequent syngenetic alteration of the volcanic glass incorporated into the peat resulted in zeolite formation alteration of sodium rich epiclastic material by sodium rich solutions resulted in the formation of analcime whilst alteration of calcium rich epiclastic material by sodium rich solutions resulted in the formation of clinoptilolite

44ca 42ca and 143nd 144nd isotope variations in cretaceous eocene tethyan francolites and their bearing on phosphogenesis in the southern tethys measurements of 4 4 ca 4 2 ca and 1 4 3 nd 1 4 4 nd isotope ratios in carbonate fluorapatite cfa through the aptian eocene section of the negev israel together with quantified rates of p and ca accumulation and bulk sedimentation permit an examination of the relationships of these five factors to tethyan phosphogenesis the data provide an aptian eocene ca 70 ma record of the ca isotope composition of 35 cfa samples 24 of which were also analyzed for nd isotopes representing 11 time stratigraphic phosphate horizons within the sequence the 4 4 ca values are significantly lower in the aptian albian samples 4 4 ca 0 11 to 0 06 than in the campanian eocene samples 4 4 ca 0 22 to 0 42 whereas the e n d values increase from continental crust like in the aptian albian e n d t 10 9 to more radiogenic pacific like e n d t 6 6 to 6 1 in the campanian both peaks of 4 4 ca and e n d t in the campanian coincide with the peak of tethyan phosphogenesis in the negev which is marked by a sharp increase of p accumulation rates from 200 mol cm 2 k y 1 in pre campanian time to 1700 mol cm 2 k y 1 in the campanian and a decrease in rates of ca accumulation and bulk sedimentation the coincident increases of 4 4 ca and e n d t values and p accumulation rates in the negev area during the campanian suggest that they are related in this time interval and were induced by the global late cretaceous sea level rise and increasing circumequatorial tethyan flow

the key tuffite matagami camp abitibi greenstone belt canada petrogenesis and implications for vms formation and exploration the key tuffite is a stratigraphic marker unit for most of the zinc rich volcanogenic massive sulfide deposits of the matagami camp in the abitibi greenstone belt this 2 to 6 m thick unit was previously interpreted as a mixture of ash fall andesitic to rhyolitic tuffaceous components and volcanogenic massive sulfide vms related chemical seafloor precipitate exhalative component previous attempts to develop geochemical exploration vectoring tools using metal content within the key tuffite were mostly inconclusive due to the complex nature of the key tuffite unit and a poor understanding of its composition origin and relationship with the vms forming hydrothermal systems detailed mapping and thorough lithogeochemistry of the key tuffite in the vicinity of the perseverance and bracemac mcleod deposits indicate that the key tuffite is a homogeneous calc alkaline andesitic tuff that was deposited before the vms deposits were formed the unit is mostly devoid of exhalative component but it is strongly hydrothermally altered close to orebodies this is characterized by a strong proximal chloritization and a distal sericitization which grades laterally into the unaltered key tuffite neither the key tuffite nor the ore was formed by seafloor exhalative processes for the two studied deposits this probably explains why previously proposed exploration models based on metal scavenging proved unsuccessful and suggests that a re evaluation of the exhalative model should be done at the scale of the mining camp however as shown in this study hydrothermal alteration can be used to vector towards ore along the key tuffite

evidence for voluminous bimodal pyroclastic volcanism during rifting of a paleoproterozoic arc at snow lake manitoba the thrust bounded mcleod road birch lake mb sequence occurs within the paleoproterozoic snow lake arc sla assemblage of the flin flon belt stratigraphic correlation of volcanic strata of the mb sequence with strata of the thrust bounded chisel sequence indicates that distinctive submarine eruption fed pyroclastic flow deposits are more extensive and voluminous than previously recognized 10 km3 these voluminous felsic pyroclastic deposits define a distinct magmatic and explosive volcanic event during bimodal volcanism that accompanied rifting of the sla the felsic pyroclastic deposits define the remnants of a basin or of nested basins that formed during arc rifting and subsidence and their eruption immediately preceded formation of the chisel sequence volcanogenic massive sulfide vms deposits although the chisel sequence ore interval is recognized in the mb sequence the lack of vms related alteration indicates that vms hydrothermal activity was restricted to the chisel portion of the

erosion and deposition from bottom currents during the givetian and frasnian response to intensified oceanic circulation between gondwana and laurussia abstract calcareous bottom current deposits in otherwise pelagic and hemipelagic successions of the harz mountains in germany herzyn limestone formation the eastern moroccan central massif ziar mrirt nappe and the carnic alps in austria italy valentin and pal limestone formation show strong evidence of bottom current reworking of carbonate ooze during givetian and early frasnian associated phosphates confirm that higher hydraulic energy temporarily prevailed the bottom current deposited facies builds up strongly condensed and reduced successions with stratigraphic gaps which also occur with similar features in other areas of central europe and northwest africa at the same stratigraphic interval the widespread current induced reworking of calcareous sediments and phosphate formation during the givetian and early frasnian as well as the associated erosional processes marked by pronounced hiatuses all signal a major circulation event the temporal and spatial positions of these fossil calcareous contourites in the devonian are discussed research concluded that thermohaline currents were intensified by the acceleration of flows constricted in the narrow oceanic passages between the approaching continental plates laurussia and gondwana areas affected were the southeastern rhenish sea shelf the disintegrated northern continental margin of gondwana and deep marginal plateaus of the noric terrane in the western part of the prototethys the disposition of the fossil calcareous contourites and faunal data corroborate palaeogeographic reconstructions that show an advanced convergence between gondwana and laurussia and the smaller continental plates such as the armorican and noric terranes during givetian and frasnian times

characterisation and potential economic interest of authigenic zeolites in continental sediments from nw mexico in nw mexico zeolite deposits of potential economic interest occur in continental sediments related to mid tertiary basin and range tectonism in central sonora where the stratigraphic column is thicker e g in the moctezuma basin two superposed sequences of sediments are distinguished on the basis of their lithology and stratigraphy they are known as the baucarit formation the lower sequence miocene in age and 300 to 400 m thick is indurated and consists mainly of sandstones and conglomerates the upper one of variable thickness consists of clays zeolites occur in both sequences as alteration products of volcanic glass in beds of white intercalated rhyolitic tuff previously known outcrops of zeolitites from rio batepito erionite tetuachi and san pedro ures heulandite group divisaderos chabazite and several other newly discovered occurrences are described in this work in terms of mineral association physical properties porosity thermal behaviour and chemical characteristics major and trace elements for individual crystals and bulk rock heulandite group minerals are also present as cement 30 by volume of the sandstones from the lower sequence amygdales and veins from basaltic flows intercalated within the lowest sediments contain a large variety of zeolite species chabazite stilbite phillipsite mesolite erionite thomsonite heulandite and analcime zeolites in the pyroclastic beds intercalated in the upper sequence represent the highest economic potential because they are essentially monomineralic and constitute up to 80 in volume of the whole rock because of the inhomogeneous distribution of amygdales zeolites in the basaltic flows have a low economic interest

anoxia vs productivity what controls the formation of organic carbon rich sediments and sedimentary rocks discussion the prevailing explanation for the origin of organic rich sediments and rocks invokes deposition under conditions of anoxia however recent research suggests that high primary production and not water column anoxia provides the first order control on the accumulation of organic rich facies in the modern oceans oxygen minima do not appear to have any direct effect on carbon accumulation in continental margin or marginal sea environments sediments accumulating in the modern black sea the type euxinic basin are not particularly enriched in organic matter despite the presence of an anoxic water column although a sapropel containing extremely high carbon concentrations was deposited during the holocene at a time when the basin was oxic results of a recently published co pled ocean atmosphere model indicate that during the cretaceous thermohaline and surface circulation in the oceans was similar to or more intense than modern conditions despite the overall equable climate such conditions confound the idea that circulation in the cretaceous atlantic for example was punctuated by oceanic anoxic events brought about by more sluggish circulation sporadic temporal and spatial increases in primary production reflecting changes in the behavior and or state of the ocean atmosphere system constitute a more tenable explanation for the occurrence of modern and quaternary carbon rich sediments and cretaceous black shales consequently the fundamental control on the accumulation of carbon rich facies in the oceans and marginal seas is not the presence or absence of anoxia

zeolitization of volcaniclastic sediments the role of temperature and ph abstract this paper addresses the question of why some volcanic ashes are zeolitized and others are not the ph of interstitial water is the most important control on zeolitization surface water and groundwater in volcanic areas is acidic but zeolitization requires neutral to alkaline conditions therefore acidic interstitial water must be removed or neutralized before zeolitization can take place conditions favoring zeolitization are deposition or redeposition under water or reheating of ash after acidic interstitial water has been removed or influx of slightly alkaline bicarbonate bearing groundwater from overlying or neighboring limestones

the relation between iron formation and low temperature hydrothermal alteration in an archean volcanic environment abstract the uppermost section of the hunter mine group hmg 2728 ma a bimodal volcanic complex in the abitibi greenstone belt contains both oxide and carbonate facies banded iron formation bif this paper explores the relationship between volcanic activity and the development of the two types of iron formation the oxide facies represented by chert jasper magnetite iron formation is widespread and recurs at several stratigraphic levels field evidence suggests it deposited directly on the sea floor during periods of volcanic quiescence and is most probably derived from fluids seeping from volcaniclastic sediments and the compaction of felsic shard rich tuffs seeping occurred along synsedimentary and synvolcanic faults and then along bedding planes carbonate siderite facies iron formation in contrast formed locally below a silica cap rock by in situ low temperature hydrothermal replacement of chert tuff beds and even of the oxide formation thus the two types of iron formation although spatially and stratigraphically juxtaposed are not the result of the same process and only the carbonate facies appears to be directly related to a low temperature hydrothermal volcanic process the contrasting genesis of oxide and carbonate iron formations indicates that current simplistic models relating banded iron formation to volcanic massive sulphide deposits need to be re evaluated the notion that oxide iron formation represents a distal manifestation of volcano generated hydrothermal activity may be the exception and not the rule because as indicated by this study bif occurs in the central part of a volcanic edifice rather than on the flanks

a genetic model for na carbonate mineral precipitation in the miocene beypazari trona deposit ankara province turkey abstract the miocene beypazari trona deposit in central anatolia turkey with estimated reserves of 250 million of tons of soda ash sodium carbonate is the second largest na carbonate deposit in the world petrographic observations of sodium carbonate evaporites from basin center cores show that the evaporites and associated minerals underwent significant early diagenetic mineral transformations in the beypazari basin trona pirssonite and nahcolite are the major evaporite minerals with subordinate bradleyite shortite and thenardite pirssonite occurs in organic rich muds oil shales pirssonite is not a primary mineral but rather appears to have formed diagenetically from displacive gaylussite trona precipitated subaqueously in lake waters and as interstitial phase in playa muds nahcolite is a later diagenetic mineral replacing both trona and pirssonite beds evaporite minerals are closely related to pyrite in oil shales and are also associated with diagenetic silicates mg rich smectites zeolites k feldspar searlesite and idiomorphic quartz formed by reaction of alkaline brines with pyroclastic deposits the proposed sedimentary model involves an alkaline lake in which water depth fluctuated from deep perennial meromictic stratified stages to shallow ephemeral playa lake stages lake margin clastic deposits are absent in the center of the basin wherein na carbonate minerals were formed suggesting the prevalence of a groundwater regime during drawdown events

clay mineral assemblages and analcime formation in a palaeogene fluvial lacustrine sequence maiz gordo formation palaeogen from northwestern argentina abstract the palaeogene maiz gordo formation is one of the main lacustrine events recorded in northwestern argentina it consists of sandstone mudstone and limestone beds 200 m thick deposited in a brackish alkaline lake and braided alluvial systems the maiz gordo lake evolved mainly as a closed system with brief periods as an open one x ray diffraction xrd and scanning electron microscopy sem were used to study samples from seven sites corresponding respectively to proximal intermediate and transitional positions of the fluvial environment and marginal and inner lake environment focusing on the clay mineralogy and analcime formation the basinward zonation of diagenetic minerals identified in the maiz gordo lake was mordenite analcime k feldspar although not a typical zonation of saline alkaline lakes it does indicate an increase in salinity and alkalinity towards the centre in proximal fluvial settings smectite predominates at the base of the sequence with scarce kaolinite towards the top a striking increase in kaolinite content suggests a change from a relatively arid climate with alternating humid and dry seasons towards a warm and humid climate kaolinite content clearly decreases in a basinward direction such a variation is attributable to changes in hydro geochemistry denoting the progressive influence of the brackish and alkaline lake water on interstitial pores sem images of intermediate fluvial samples reveal authigenesis of illite at the expense of kaolinite booklets in littoral and inner lake settings the clay fraction is composed of muscovite sometimes with subordinate smectite analcime occurs in variable amounts in all sedimentary facies in rock pores or filling veins it forms subhedral square to hexagonal or anhedral rounded crystals denoting that they coarsened at low to moderate degrees of supersaturation although the mordenite identified in a fluvial level would have been the precursor of analcime in the maiz gordo basin no textural evidence of analcime formation through replacement of mordenite or other precursor zeolite was found hence it is more probable that analcime formation took place by direct authigenic precipitation or through the reaction between interstitial brines and clay minerals or plagioclase

age and tectonic setting of the jingangku besshi type volcanogenic massive sulfide deposit from the northern shanxi north china craton abstract the jingangku volcanogenic massive sulfide deposit is one of the largest archean deposits in china it is located in the wutai greenstone belt in the northern part of the central orogenic belt in the north china craton the deformed deposit is hosted in a suite of neoarchean metamorphosed volcano sedimentary rocks mica quartz schist plagioamphibolite plagioclase schist and bif the orebodies are characterized by massive pyrite and contain varied amounts of chalcopyrite pyrrhotite and sphalerite the country rock of the jingangku vms ores shows intense chloritization silicification sericitization and carbonation the vms hosted pyrite and copper deposit is represented by the jingangku deposit that yielded a la icp ms zircon age of 2500 15 ma mswd 0 87 the other two vms hosted pyrite and copper deposits are represented by the houping and haoditang deposits that formed between 2494 ma and 2507 ma the late neoarchean vms deposits can be interpreted to have formed in a forearc setting and subsequently tectonically transported in melange belts during continental collision quite similar to the younger besshi type deposits in japan analyses of fluid inclusions from ore bearing magnetite quartzite showed the composition of metamorphic fluid to be h2o nacl co2 ch4 n2 h2 the analysis also showed that during the peak of metamorphism the fluid was characterized by medium high temperature 322 473 and low salinity 2 2 6 74 sulfide orebodies are closely associated with the magnetite quartzite and therefore it is proposed that both the sulfide and magnetite quartzite were derived from the same material source and have the same formation age and underwent the same history of deformation and metamorphism consequently the jingangku deposit most likely formed from submarine exhalative sedimentation and later superimposed and transformed by metamorphic fluid

climatic signals in lacustrine deposits of the upper yacoraite formation western argentina evidence from clay minerals analcime dolomite and fibrous calcite

low productivity and slow deep water circulation in mid cretaceous oceans paleofertility estimates are derived from organic carbon accumulation rates determined in nonbioturbated mid cretaceous deep sea deposits using organic carbon preservation factors observed in laminated sediments from anoxic holocene environments the estimated mid cretaceous primary production rates are as much as an order of magnitude lower than those measured in today s oceans an evaluation of dissolved oxygen budgets using a simple oceanic circulation model indicates very low deep water renewal rates in mid cretaceous oceans 28 references 2 tables 4 figures

mineral precipitation sequence and formation of the lacustrine hydrothermal sediments in the lower cretaceous tenggeer formation in the baiyinchagan sag china abstract cores from the lower cretaceous tenggeer formation in the baiyinchagan sag of the erlian basin present dolomitic mudstones and argillaceous dolostone with white grains and laminae thin section x ray diffraction xrd electron microprobe empa and scanning electron microscopy sem analyses show that in addition to terrigenous clastics dolomite analcime natrolite pyrite pistomesite fluorite talc barite etc are abundant compared with the conventional lacustrine sediments these rocks contain highly abundant exhalative textures and structures such as laminae and banded textures disseminated textures mesh vein structures breccia structures and contemporaneous deformations these types of mineral associations rock textures and structures are specific and uncommon previous works indicate that these rocks are of hydrothermal origin in this study we provide supplementary evidence and recognition to support the lacustrine hydrothermal sediment origin and further study the mineral precipitation sequence and formation conditions and processes with the use of 3d seismic data the magmatic intrusions hydrothermal ducts and hydrothermal vents are first identified on seismic sections the ni co zn and fe mn cu ni co 10 ternary diagrams confirm the hydrothermal origin of these sediments the sr ba ratio v v ni ratio oxygen and carbon isotope values of carbonate ph and eh values suggest anoxic reducing and alkaline sedimentary conditions based on the analysis of fluid inclusions rock textures and structures we find that the precipitation of minerals occurred in a specific sequence pyrite pistomesite analcime natrolite dolomite the nature of the magmatic intrusions the changes in environmental variables and fluid energy and the flow distance may be the controlling factors of this specific sequence a mode of lacustrine white smoker type hydrothermal sedimentation is presented in this study as the hydrothermal fluid sourced from the intermediate basic magmatic basement enriched in fe2 mg2 al3 si4 ca2 na and co32 rose and mixed with cool lake water ferromagnesian aluminosilicate and carbonate minerals formed successively from the ducts to the vicinity of the vents pulsing exhalation and overflow formed alternating deposits of hydrothermal sediments and lacustrine mudstones

production and preservation of organic matter during deposition of the bakken formation late devonian and early mississippian williston basin abstract the organic rich up to 35 toc lower and upper black mudstone members of the bakken formation late devonian and early mississippian accumulated in response to both increased productivity and enhanced preservation that resulted from unique palaeogeographic palaeoceanographic and palaeoclimatic conditions during bakken deposition the semi isolated williston basin was located close to the equator 5 to 10 n in a zone of prevailing east to west winds a pattern of estuarine like marine circulation between the williston basin and open ocean conditions at the western craton edge of north america is proposed surface water discharged from the basin was replaced by nutrient rich deeper water sourced from the equatorial undercurrent in the pacific basin undercurrent flow into the williston basin upwelled providing a potentially sustainable source of nutrients to enhance productivity in the surface photic zone during black mudstone deposition in response to increased productivity that led to a high rate of organic sedimentation and quiescent deep water conditions due primarily to the geographic isolation of the basin and the restriction of estuarine like circulation to the upper water column anoxic bottom water developed on the basin floor as sea level rose during lower and upper black mudstone deposition anoxic bottom water expanded across the basin enhancing organic matter preservation conditions in the williston basin demonstrate that both increased productivity and improved preservation can be essential and complementary factors affecting organic rich mud deposition these results have potentially important implications for the accumulation of similarly organic rich deposits across the north american interior during late devonian and early mississippian time

outflow ignimbrite sheets from late carboniferous calderas currabubula formation new south wales australia regionally mappable silicic outflow ignimbrite sheets are interbedded with fluvial volcanogenic conglomerates and sandstones of the late carboniferous currabubula formation of north eastern n s w four of the most widespread of these ignimbrites are described and defined as members the oldest member is comprised of many thin originally non welded flow units interbedded accretionary lapilli horizons may indicate phreatomagmatic activity at vent during the eruption in addition to local rain flushing of co ignimbrite ash clouds of the three other members two are multiple flow unit sheets 160 180 m in aggregate thickness substantial portions of these sheets were originally welded the remaining member is a simple welded ignimbrite characterized by abundant spherulites and lithophysae irregular pre eruption topography and contemporaneous erosion were responsible for thickness variations of the ignimbrite sheets some palaeovalleys now delineated by the ignimbrites persisted in spite of repeated pyroclastic influxes relic pumice shards and crystal fragments are ubiquitous components of the sedimentary facies of the currabubula formation and were probably derived from originally poorly consolidated pyroclastic deposits such as airfall ash layers and non welded ignimbrites no surface trace of the sources of these ignimbrites exists however internal facies thickness variations and volumes of the ignimbrites indicate that they periodically emanated from a multiple caldera terrain which was continuously active during the late carboniferous and located several kilometres to the west of present exposures

jurassic lake t oo dichi a large alkaline saline lake morrison formation eastern colorado plateau a large alkaline saline lake lake t9oo9dichi9 occupied the entire eastern part of the colorado plateau region during deposition of the brushy basin member of the upper jurassic morrison formation the lake extended from near the site of albuquerque new mexico to near the site of grand junction colorado and occupied a region that encompassed the san juan and ancestral paradox basins making it the largest ancient alkaline saline lake known the lake was typically shallow and frequently evaporated to dryness although the water table was probably never far beneath the surface intermittent streams carried detritus from source areas to the west and southwest far out into the lake basin a reflection of a low depositional gradient and the ephemeral nature of the lake prevailing westerly winds carried silicic volcanic ash to the lake basin from an arc region to the west and southwest a lateral hydrogeochemical gradient characterized by increasing salinity and alkalinity from the margin of the lake to the center developed in pore waters of the lacustrine sediments and resulted in alteration of the ash to a variety of authigenic minerals that define concentric zones within the lake basin the basinward progression of diagenetic mineral zones is smectite clinoptilolite analcime potassium feldspar albite a concomitant lateral zonation of mixed layer illite smectite developed from highly smectitic in the outermost zones to highly illitic in the central zone authigenic albite and illitic mixed layer clay minerals previously thought to require elevated temperatures for formation crystallized during early diagenesis at syndepositional temperatures in the lacus trine sediments of lake t9oo9dichi9 this study presents evidence for a syndepositional origin for both of these minerals these findings have important implications in terms of limiting the use of these minerals as geothermometers recognition of alkaline saline lake deposits in the morrison formation significantly alters interpretations of depositional environments of this formation and it also has important implications for paleoclimatic interpretation late jurassic climate was apparently much more and than had previously been thought in fact sedimentologic evidence suggests that the lake basin was typically dry for extended periods and enjoyed only brief wet intervals this conclusion has important consequences for environmental interpretation of the habitat that was favorable for large herbivorous dinosaurs which thrived in the late jurassic

chloritoid hornblende assemblages in quartz muscovite pelitic rocks of the central metasedimentary belt grenville province canada abstract chloritoid hornblende occurs in quartz muscovite pelitic schist derived from sediment in a volcaniclastic sequence of the grenville supergroup and from reworked sedimentary and regolithic material above the unconformity at the base of the flinton group comparison of these samples with other pelitic rocks on triangular composition diagrams and in the acnf and acfm tetrahedra indicates that the presence of hornblende cannot be explained by unusually high cao content the rare assemblage is attributed to a combination of relatively low al2o3 and high k2o with high cao cao na2o and feo feo mgo on two qualitative reaction grids derived from afm diagrams projected through cao and plagioclase respectively the p t stability field of chloritoid hornblende overlaps the first appearance of staurolite biotite in normal pelitic rocks in the kyanite field staurolite hornblende overlaps chloritoid hornblende and extends to the higher temperatures and pressures of the kyanite hornblende field the phase relations in these rocks provide a link between the conventional hornblende absent grids for pelitic rocks and those for k2o poor muscovite absent pelitic and mafic amphibolitic rocks

original sediment composition of the lower cretaceous lacustrine tight oil mudstone and influences on diagenesis and organic matter content the erennaoer sag in erlian basin ne china abstract the original sediment composition is of great value to providing an understanding of depositional environment and hydrocarbon generation potential but it is easily altered by diagenesis and difficult to recognize in this study we examine carbonate rich tight oil mudstones of the lower cretaceous arshan formation in the erennaoer sag of the erlian basin as an example based on analyses of mineralogy stable carbon and oxygen isotopes and trace rare earth elements the original composition of the arshan mudstones has been reconstructed results show that the original arshan mudstone composition was mainly siliciclastic detritus tuffaceous and clay matrix which has a major impact on diagenesis and organic matter content the erupted volcanic ashes were beneficial to the introduction of nutrients an increase in biomass and an associated increase in to the preservation of organic matter which has been suggested by an improvement of toc of arshan tuffaceous mudstones with average contents of 2 82 the volcanic ashes in the studied mudstones had also enhanced methanogensis during the shallow burial additionally the early alteration products of authigenic minerals include analcime or zeolite most of which is entirely altered to analcime and chlorite the formation of major eogenetic carbonate cements include early dolomite and calcite which were related to volcanic materials and methanogenesis at shallow depths

evolution of tethyan phosphogenesis along the northern edges of the arabian african shield during the cretaceous eocene as deduced from temporal variations of ca and nd isotopes and rates of p accumulation abstract the evolution of tethyan phosphogenesis during the cretaceous eocene is examined to try to explain fluctuations of phosphogenesis through time and whether or not they reflect long term changes in ocean circulation or in continental weathering twenty seven time stratigraphic phosphate levels in various tethyan sites covering a time span of about 90 myr from the hauterivian to the eocene were analyzed for 44 ca 42 ca and 143 nd 144 nd in their carbonate fluorapatite cfa fraction p and ca accumulation rates and bulk sedimentation rates were quantified throughout the cretaceous eocene negev sequence to examine how changes in 44 ca 42 ca and 143 nd 144 nd are reflected in the intensity of phosphogenesis a clear cut change occurs in e nd t and 44 ca and in the rates of p and ca accumulation and bulk sedimentation through the time analyzed e nd t is much lower in the hauterivian lower cenomanian 12 8 to 10 9 than in the upper cenomanian eocene 7 8 to 5 9 much lower 44 ca values occur in the hauterivian turonian 0 22 to 0 02 than in the coniacian eocene 0 23 to 0 40 p accumulation rates in the negev steeply increase from 2 k yr 1 in the albian coniacian to 1500 mol cm 2 k yr 1 in the campanian whereas a strong decrease is concomitantly recorded in the rates of ca accumulation and bulk sedimentation in addition distinct e nd t values are shown by the phosphorites of the negev 6 7 to 6 4 and egypt 9 1 to 7 6 during the campanian and by those of the negev 7 8 to 6 3 and north africa 10 1 to 8 9 during the maastrichtian eocene the culmination of p accumulation rates in the negev during the campanian occurring with a high in e nd t and 44 ca and a low in sedimentation rates indicates that paleoceanographic and paleogeographical factors mostly governed phosphorite accumulation in this area the abrupt e nd t rise after the cenomanian is attributed to increased incursion of pacific radiogenic water masses into the tethys driven by the late cretaceous global sea level rise the connection between north and south atlantic the global post santonian cooling and the progressive widening of the caribbean threshold all acting in combination to significantly intensify the tethyan circumglobal current tcc it also reflects a weakening of the continental nd signal due to a reduction of exposed landmasses caused by increased flooding of continental shelves high 44 ca values at those times also point to a decrease in weathering ca 2 fluxes and expansion of carbonate sedimentation in shelves both enriching seawater with isotopically heavy ca 2 deep ocean circulation intensified by the post santonian cooling of high latitudes increased p inventory in the tethys basin whereas the strengthened tcc and the folded shelf likely resulted in coastal and topographically induced upwelling supplying p rich intermediate waters to southeastern tethys shelves only in the paleocene eocene following major changes in global circulation produced by narrowing of tethys and widening of the atlantic did phosphogenesis shifts its locus of high intensity to the western atlantic tethys and west african atlantic coasts this change in paleocirculation is expressed by distinctly differing e nd t in the middle east and the north and west african phosphorites suggesting different oceanic p sources and current systems for these two major groups of phosphorites our nd isotope results further suggest a weaker tcc during the mid cretaceous becoming more intense in late cretaceous times they also point to the north pacific ocean as major source of deep water formation for the intermediate deep waters in the tethys basin during the late cretaceous

the mineral chemistry of hydrothermally altered and metamorphosed wall rocks at the stollberg fe pb zn mn ag deposit bergslagen sweden the c 1 9 ga old stollberg sulphide and mnrich skarn iron ores and sulphide ores in bergslagen south central sweden are hosted by hydrothermally altered and metamorphosed felsic volcanic and volcaniclastic rocks the ores are underlain by comformable alteration zones characterized by albite gedrite quartz and biotite muscovite plagioclase k feldspar quartz garnet assemblages the present mineralogies are interpreted as medium grade metamorphic equivalents to the original alteration mineral assemblages pt conditions during prograde regional metamorphism are semiquantatively determined to be 510 to 560 c at approximately 3 kbar with increasing modal content of gedrite and biotite in the alteration zones the mg fe ratios and xmg s in octahedral positions of these minerals also increase in the gedrite bearing strata whole rock mg fe ratios remain constant whereas in the biotite rich unit the wholerock mg fe trend is parallel to that of the biotites

metamorphism of magnesium altered felsic volcanic rocks from bergslagen central sweden a transition from mg chlorite to cordierite rich rocks abstract the ca 1 9 ga old felsic volcanic rocks of the bergslagen province have been affected by synvolcanic hydrothermal mg metasomatism a spatial relationship exists between mg alteration zones and calc silicate carbonate banded iron mineralizations and a genetic link is suggested this is supported by the occurrence of the mg rich tourmaline dravite which exists in the mg alteration zones as well as in the wall rocks to iron oxide mineralizations following later regional metamorphism and deformation these rocks occur as large zones of mg rich schists parallel to sub parallel with the regional foliation s1 the dravite crystals have been affected by this regional deformation a second deformational episode folded s1 along steeply dipping fold axes locally this resulted in a crenulation cleavage and the development of a new generation of micas s2 crosscutting s1 in the westernmost areas the mg schists contain a fine grained network of mg chlorite and muscovite with little or no preferred orientation indicating low pressures and low grade metamorphic conditions the grade of recrystallization and deformation increase towards the east and a boundary between low and medium grade metamorphic terrains is crossed the metamorphic boundary is marked by the disappearance of chlorite and the appearance of cordierite in the mg schists porphyroblasts of mg chlorite or cordierite grew across s1 and cordierite porphyroblasts are transected by s2 micas this indicates that the peak of regional metamorphism occurred between the two deformational episodes retrogression of cordierite to chlorite and muscovite is confined to the vicinity of crosscutting s2 micas

devonian carboniferous transition containing a hangenberg black shale equivalent in the pho han formation on cat ba island northeastern vietnam abstract on cat ba island in northeastern vietnam the devonian to carboniferous d c transition consists mainly of ramp carbonates intercalated with black shale beds beds 1 to 176 in the pho han formation and is one of the few records of the d c transition of the eastern paleotethys the three main facies of the sequence are facies 1 alternations of whitish gray to gray limestone and marl facies 2 calcirudite bed 115b and facies 3 alternations of dark gray limestone and organic carbon rich black shale beds 115c 120 and 126 129 the latest famennian siphonodella praesulcata subzone conodont assemblage of s praesulcata palmatolepis gracilis palmatolepis sigmoidalis and rhodalepis polylophodontiformis was recognized in beds 113 115c beds 105 112 commonly contain palmatolepis expansa p gracilis and p sigmoidalis bed 119 yielded a basal carboniferous index conodont siphonodella sulcata in beds 116 118 solenoporids such as pseudochaetetes elliotti and parachaetetes sp were characteristic species in organic carbon rich dark gray limestone facies 1 is characterized by bioclastic peloidal and intraclastic grainstone and packstone containing massive normal grading and cross laminations and is interpreted to represent deep ramp carbonates above storm wave base facies 2 is represented by typical lag deposits overlying a transgressive surface facies 3 comprises organic carbon rich black shale and minor scour filling bioclastic peloidal and intraclastic packstone and may represent a marginal basin plain environment surrounding a carbonate ramp the alternations of organic carbon rich black shale and dark gray packstone facies 3 show no evidence of bioturbation and have high toc contents 0 18 5 73 wt a minor succession within the transgressive lag deposits from bed 115b of facies 2 to beds 115c 120 in the lower part of facies 3 is equivalent to the hangenberg black shale s l in the middle part of the siphonodella praesulcata to siphonodella sulcata zones because beds 115b 120 characterized by no evidence of bioturbation and high toc contents are interpreted to be accumulated in anoxic to dysoxic conditions

zeolites in closed hydrologic systems zeolites were first described from vugs and fissures in basaltic flows in the mid eighteenth century cronstedt 1756 and they are now known to be widespread in a variety of geological environments more zeolite species occur in vesicles and fractures of basaltic rocks than in any other geologic setting however zeolites from sedimentary rocks in particular represent the most important occurrences both in terms of aerial extent of deposits and in terms of the abundance of certain zeolite species the introduction of new analytical techniques in the latter part of the 20th century provided a significant stimulus to zeolite research these techniques allowed identification of large quantities of zeolites in widespread deposits of sedimentary rocks and in particular in sediments from saline alkaline lakes of the western united states sheppard and gude 1968 1969a 1973 based on geological and hydrologic environments zeolite occurrences in sedimentary rocks can be classified in the following framework a saline alkaline lakes b alkaline soils and land surfaces c deep sea sediments d open hydrologic systems e as products of hydrothermal alteration and f burial diagenetic or low metamorphic environments from a broader perspective zeolite deposits can be classified into two main groups namely closed hydrologic systems and open hydrologic systems the work of sheppard and gude 1968 1969a 1973 and later surdam 1977 discussing not only the mineralogy of the deposits but also the geology hydrology and chemistry of the depositional basins represent milestones in the study of closed hydrologic system formation of zeolites surdam 1977 considered closed hydrologic basins in two different tectonic settings a block faulted regions in arid and semiarid regions and b trough valleys associated with rifting examples of the first setting are the closed lakes of the basin and range province of the western united states whereas the

crystal chemistry of diagenetic zeolites in volcanoclastic deposits of italy zeolites from the most important volcanoclastic deposits of italy include 1 phillipsite and heulandite from the cinerite of the central northern apennines 2 chabazite and phillipsite from the phonolitic tephritic ignimbrite with black pumices 3 phillipsite from the tufo lionato of vulcano laziale 4 chabazite and phillipsite from the campanian ignimbrite 5 phillipsite from the neapolitan yellow tuff and 6 chabazite and phillipsite from the pyroclastics of monte vulture compared with sedimentary phillipsites and chabazites described in the literature the chabazites and phillipsites studied here have lower si al ratios and higher k contents these chemical peculiarities are correlated with both the k rich vesuvitic leucititic latitic phonolitic and potassic alkali trachytic chemistry of the ash from which they were derived and very likely with the character of the hydrologically open system environment in which they formed the zeolite of the heulandite clinoptilolite group from the cinerite of the central northern apennines is classified as a true heulandite on the basis of its chemical composition and thermal behavior

diatom paleolimnology of late pliocene baringo basin kenya paleolakes abstract kenya s baringo tugen hills barsemoi drill site is one of six localities across kenya and ethiopia from which the hominin sites and paleolakes drilling project has obtained sediment cores in an effort to investigate the role of environmental forcing in shaping human evolution the baringo basin site features extensive exposures of the chemeron formation which contains 100 fossil vertebrate localities including five hominin sites the 228 m drill core dating from 3 29 to 2 56 ma is characterized by fluvio lacustrine sediments including multiple diatomites with evidence of variable degrees of later pedogenic modification in the lower part of the core 3 29 3 04 ma diatoms were preserved only in very low abundance consistent with predominantly fluvial or lake marginal environments in contrast five diatomites and two additional diatom rich intervals were deposited after 3 04 ma reflecting a major shift in the basin hydrology planktonic freshwater species dominated these diatom rich intervals whereas periphytic taxa were present in proportions less than 2 suggesting that these intervals represent open water deposition during lake highstands littoral or saline assemblages are largely absent throughout the core instead we observed a pattern of increasing diatom frustule dissolution at the tops and bottoms of diatomite units indicating increased alkalinity during the transgressive regressive phases a na bearing zeolite analcime indicative of saline waters precipitated in clastic dominated intervals between diatomites suggesting extreme environmental variability between lake highstands and lowstands diatom assemblages were consistently dominated by a few species belonging to the genera aulacoseira and stephanodiscus which were at times co dominant we infer that assemblages dominated by aulacoseira represent a well mixed lake with abundant supply of silica when stephanodiscus was dominant which occurred more frequently in the later freshwater phases we infer incomplete mixing and reduced silica flux to the epilimnion upper water layer

paleozoic paleogeography of north america gondwana and intervening displaced terranes comparisons of paleomagnetism with paleoclimatology and biogeographical patterns new paleomagnetic data have become available in the past 5 yr that require modifications in previously published paleogeographic reconstructions for the silurian and devonian in this paper the new paleopoles are compared to published paleogeographic models based on paleoclimatologic and biogeographic data the data from the three fields of paleomagnetism paleoclimatology and biogeography are generally in excellent agreement and an internally consistent paleogeographic evolutionary picture of the interactions between north america gondwana and intervening displaced terranes is emerging during the interval of the ordovician silurian and devonian north america stayed in equatorial paleoposition while rotating counter clockwise the northwest african part of gondwana was in high southerly latitudes during the late ordovician and was fringed by peri gondwanide terranes such as southern europe armorica and avalonian basement blocks now found in eastern newfoundland nova scotia the boston basin the appalachian piedmont and northern florida subsequently gondwana and the peri gondwanide terranes displayed rapid drift with respect to the pole this drift translates into the following pattern of movement for northwest africa during the latest ordovician early silurian this area moved rapidly northward from polar to subtropical latitudes followed by equally rapid southward motion from subtropical to intermediate about 50 s paleolatitudes during the late silurian middle devonian it is likely that significant east to west motion accompanied the latter shift in paleolatitudes with the caledonian acadian orogeny the result of silurian to early devonian convergence and collision between gondwana and north america this collision sandwiched several of the intervening displaced terranes between gondwana and north america subsequent to this collision gondwana was separated in the late devonian by a medium width ocean from north america and the avalonian and southern european blocks which were left behind adjacent to north america this new ocean closed during the carboniferous and the resulting convergence and collision were the cause of the hercynian alleghanian orogenic belt problems remaining for future research besides the further gathering of reliable paleopoles involve the uncertain pre devonian position of the southern british isles in this scenario and the very rapid velocity with respect to the pole that results from the rapid late ordovician silurian apparent polar wander for gondwana

volcanic reconstruction of the paleoproterozoic stroud breccia understanding the transition from a primitive to mature arc and its impact on vms ore formation snow lake manitoba canada abstract the stroud breccia is a 400 m thick package of dominantly felsic volcaniclastic rocks within the paleoproterozoic snow lake arc assemblage it stratigraphically overlies the ore interval for the anderson stall and rod volcanogenic massive sulfide vms deposits at snow lake manitoba canada and occupies the stratigraphic interval between the underlying primitive arc anderson sequence and the overlying mature arc chisel sequence the stroud breccia is interpreted to be a product of subaqueous pyroclastic and effusive dominantly rhyolitic volcanism and concomitant subsidence it consists of felsic tuff to lapilli tuff crystal rich felsic tuff felsic lapillistone felsic tuff breccia mafic tuff to lapilli tuff heterolithic tuff breccia to breccia and rhyolite the finer felsic volcaniclastic units are characterised by angular or broken quartz crystals angular lithic rhyolite lapilli and pumice fine ash broken crystals and pumice suggest they were deposited by eruption fed density currents associated with a phreatomagmatic eruption the coarser felsic volcaniclastic units are characterized by blocks of strongly quartz feldspar porphyritic rhyolite and pumice and are interpreted to have been deposited during the reworking of pyroclastic debris flow deposits on the seafloor during mass wasting events at fault scarps planar and cross laminations graded beds and bomb sag structures suggest the mafic tuff to lapilli tuff unit was deposited by a combination of subaqueous eruption fed density currents and eruption driven ballistically emplaced ejecta likely through subaqueous tephra jetting lithofacies analyses and geochemistry has allowed comparison between the felsic volcanic rocks of the stroud breccia and those that host the anderson stall and rod vms deposits detailed mapping has led to the identification of synvolcanic faults defining basins and volcanic vents that indicate that the process of incipient rifting of the anderson sequence primitive arc continued during emplacement of the stroud breccia these structures also define magma and fluid pathways critical in controlling the formation of the anderson vms deposits meaning they represent deep seated and long lived structures that can be used as vectors to mineralization at depth