chemical evolution of magmas in the proterozoic terrane of the st francois mountains southeastern missouri 1 field petrographic and major element data major element chemical data for plutonic and volcanic rocks of the eastern st francois mountains indicates that ring plutons of the butler hill caldera are low silica granites and chemically distinct from the high silica butler hill granite and grassy mountain ignimbrite additionally the ring plutons silvermine stono knoblick and slabtown granites are characterized by abundant mafic inclusions whereas these are almost completely absent in butler hill granite silvermine granite is mostly of a medium grained variety but cliffs along the st francis river expose gradations upward to a high silica fine grained cap rock least squares mixing calculations indicate that the cap rock could have formed by the fractional crystallization of plagioclase hornblende biotite magnetite and sphene all of which are liquidus phases in the medium grained silvermine granite the chemical similarity of the fine grained cap rock to butler hill granite and grassy mountain ignimbrite suggested that silvermine granite might be a sample of the parental magma from which the high silica rocks were derived least squares mixing calculations indicate that butler hill granite magma could have been derived from the composition of the average medium grained silvermine by fractional crystallization of the same liquidus phases indicated above the major element composition of grassy mountain ignimbrite can be derived from the average butler hill granite magma by fractional crystallization of plagioclase alkalic feldspar quartz biotite and magnetite all of which are liquidus phases in butler hill granite textural and chemical variations in butler hill granite from northeast to southwest suggest that the body was internally differentiated and that the present distribution of rock types is due to tilting and erosion the internal zonation of butler hill granite can be accounted for by fractional crystallization of plagioclase alkalic feldspar quartz biotite sphene and magnetite the chemical data and calculations indicate that the primary magma emplaced at the beginning of igneous activity was of silvermine type the magma crystallized fractionally so that the magma chamber became compositionally zoned with high silica magma in the upper part the top most part of this material was erupted to form grassy mountain ignimbrite during formation of the butler hill caldera subsequently more of the high silica magma was emplaced into the volcanic material in the caldera during resurgent doming after formation and resurgent doming of the butler hill caldera some of the parental magma from deeper in the chamber leaked upward into the ring fracture or into arcuate faults within the caldera forming the ring plutons the abundant mafic inclusions in the ring plutons may be earlier crystallized magma carried upward during intrusion one of the ring plutons silvermine granite apparently formed a sill like intrusion and underwent in situ differentiation a body of foliated granodiorite exposed as a giant inclusion in granite at hawn state park east of the principal exposures of the st francois mountains has the mineralogy major element chemistry and trace element chemistry to be a sample of the cumulate resulting from the processes in the magma chamber

is the proterozoic ladoga rift se baltic shield a rift the southern part of the baltic shield hosts a series of mafic dykes and sills of mesoproterozoic ages including a ca 1 53 1 46 ga sheet like gabbro dolerite sills and the salmi plateau basalts from the lake ladoga region based on chiefly geochemical data the region is conventionally interpreted as an intracratonic ladoga rift graben we question the validity of this geodynamic interpretation by analyzing regional geophysical data crustal structure heat flow bouguer gravity anomalies magnetic anomalies and mantle vs velocities we provide a complete list of tectonic magmatic and geophysical characteristics typical of continental rifts in general and demonstrate that except for magmatic and perhaps some gravity signature the lake ladoga region lacks any other rift features we also compare the geophysical data from the lake ladoga region with similar in age midcontinent and valday rifts and provide alternative explanations for mesoproterozoic geodynamic evolution of the southern baltic shield we propose that mesoproterozoic mafic intrusions in southern fennoscandia may be associated with a complex deformation pattern during reconfiguration of a part of nuna columbia supercontinent which led to magma intrusions as a series of mafic dykes along lithosphere weakness zones and ponding of small magma pockets within the cratonic lithosphere consequent magma cooling and its partial transition to eclogite facies could have led to the formation of a series of basement depressions similar to intracratonic basins of north america while spatially heterogeneous thermo chemical subsidence with phase transitions locally speeded by the presence of subduction related fluids could have produced a series of faults bounding graben like structures

miocene pliocene boundary magnetostratigraphy at capo sopartivento calabria itlay a magnetostratigraphic study at capo spartivento calabria southern italy indicates that the miocene pliocene boundary lies in the lowest reversed interval chron 3r of the gilbert chron the magnetostratigraphic time frame gives an estimate close to 19 ka for the duration of individual limestone marl couplets that characterize the lithology the eight couplets within chron 3r indicate that the age of the miocene pliocene boundary is about 154 ka older than the age of the reversal at the top of chron 3r 4 78 ma we therefore estimate the age of this boundary as 4 93 ma which is 420 ka younger than that given by berggren et al and 100 ka older than that given by zijderveld et al the first appearance datums of globorotalia margaritae and globorotalia puncticulata are similarly estimated to have ages of 4 66 and 4 15 ma respectively the former being considerably younger than its first appearance in the open ocean

detrital blue sodic amphibole in recent sediments southern coast turkey detrital blue sodic amphibole sporadic lawsonite and pumpellyite occur in beach and river sediments between gazipasa and manavgat on the southern turkish coast this area lies s of the metamorphic alanya massif which contributes to the detritus but blueschists have not previously been recorded in the region the blue amphiboles have a provincial variation related to differing conditions during their formation in the eastern region in the vicinity of gazipasa and demirtas homogeneous glaucophanes sometimes with remnant ca amphiboles are characteristic in the western region the grains exhibit a considerable variation of optical and physical properties and are crossitic glaucophane crossite and occasionally magnesio riebeckite the efficacy of sedimentary mineralogy in reconstructing a hinterland is demonstrated

tectono sedimentary characteristics of late miocene quaternary extensional basins of the northern apennines italy abstract extensional and compressional regimes exist at the same time in adjacent parts of the northern apennines italy and the former regime succeeded the latter at the same place as the thrust mountain front moved eastward since miocene times numerous extensional basins have developed west of the present mountain divide the westernmost ones formed over attenuated continental crust since late miocene and have been subjected to several subsidence and uplift events with rates of subsidence generally faster than rates of sedimentation they contain continental deposits overlain by gypsum bearing upper miocene marine sequences and siliciclastic marine pliocene deposits these basins were affected by shallow magmatism and are still experiencing high geothermal gradient and late to post magmatic activities such as in the renowned thermal region of larderello to the east closer to the present mountain divide the extensional basins formed later from pliocene to quaternary contain continental fluvial and lacustrine deposits and have not experienced near surface magmatic activities the sedimentary fill architecture of the apennine extensional basins is similar to that of other european american and african extensional or transtensional systems for instance a common characteristic is the prevalence of large alluvial fan deposits at the hanging wall shoulder of half grabens coarser smaller alluvial fans at the footwall shoulder and some fluvial deposits introduced longitudinally unlike the african rifts though the sedimentary facies distribution of extensional basins which developed in active orogenic zones such as in the apennines may be strongly affected by uplifting steep mountain slopes and can have large thick coarse alluvial fans also on the footwall side of the half grabens

petrological geochemical and statistical analysis of eocene oligocene sandstones of the western thrace basin greece and bulgaria abstract the rhodopian orogen developed since the late cretaceous early eocene during accretionary processes following the closure of the vardar ocean basin a branch of neotethys through a multidisciplinary approach including sandstone petrology and geochemistry of the clastic and volcanoclastic sediments we reconstruct the unroofing history of the rhodopian orogen and characterize the formation and the evolution of the western portions of the thrace basin in greece and bulgaria between the late eocene and oligocene detrital modes of 127 sandstone samples provide evidence of three distinctive petrofacies quartzolithic quartzofeldspathic and volcanoclastic the petrographic composition gives evidence of contributions from three key source areas corresponding to the three main tectonic units the circum rhodope belt the variegated complex ultramafic complex and the gneiss migmatite complex the three petrofacies reflect multiple provenance from different tectonic settings as they evolve from quartzolithic to quartzofeldspathic to volcanoclastic corresponding to collisional orogen crustal block uplift and volcanic arc settings respectively geochemical data on major elements and trace elements are used to discuss the efficacy of tectonic setting discrimination diagrams and compare them to the dickinson model as well as to distinguish and characterize i petrographically homogeneous gneiss supplied subbasins and ii volcanic contributions to sandstone composition multivariate statistical techniques are used to unravel the complex web of factors controlling sediment composition biplot analysis highlights the influence of two independent processes 1 mixing between carbonate and silicate phases and 2 evolution from mafic to felsic source rocks the latter indicates progressively increasing supply rates from deeper crustal levels the compositional evolution of the sandstone suites of thrace basin in ne greece and se bulgaria is strictly related to various geodynamic stages of the rhodope region provenance analysis of thrace sandstones provide an example of the changing nature of orogenic belt sand associate basins through time and may contribute to the general understanding of similar geodynamic settings

inferring tectonic provenance of siliciclastic rocks from their chemical compositions a dissent abstract chemical compositions of siliciclastic sedimentary rocks are commonly used to infer their tectonic provenance we have tested the universal applicability of the underlying principle in a small but controlled study expecting 100 confirmation of the practice a comparison is made between the chemical composition of the 1480 ma butler hill granite in an uplifted cratonic block of the st francois mountain igneous complex and that of a small 1 m thick regolith body a weathered granite sample and the basal quartz arenites of the 520 ma lamotte formation immediately above the regolith the results show that in plots of k 2 o na 2 o vs sio 2 al 2 o 3 the regolith and sandstone samples correctly plot in the passive margin field although the weathered granite plots in the arc field in plots of th sc zr 10 and la th sc the results plot in the passive and active continental margins and their extensions in other common plots to discriminate tectonic provenance e g sio 2 vs k 2 o na 2 o fe 2 o 3 mgo vs al 2 o 3 sio 2 fe 2 o 3 mgo vs tio 2 sc cr vs la y a few points plot in the passive margin field but scatter into and outside of other fields of tectonic provenances the chondrite normalized ree distributions show variable degrees of negative eu anomalies with flat hree conforming to a felsic source the lree distributions show both positive and negative ce anomalies that can be ascribed to the variability of redox conditions during weathering and diagenesis of the original siliciclastic sediments the variability of the eu anomaly was likely affected by post erosion processes in addition to whatever was inherited from the parent rocks we conclude that chemical compositions can provide good clues but are neither strong indicators nor unique identifiers of their tectonic provenance rather they indicate a dominantly felsic or dominantly mafic or a mixed set of source rocks

geochemistry of shales from the archean 3 0 ga buhwa greenstone belt zimbabwe implications for provenance and source area weathering abstract phyllites from the archean 3 0 ga buhwa greenstone belt zimbabwe were deposited on a stable cratonic platform analyses of the phyllites generally define a single geochemical group based on major and trace element abundances the phyllites are strongly depleted in cao na2o and sr with respect to average archean upper crust by contrast k2o ba and rb are enriched several times relative to average archean upper crust reflecting basin scale k metasomatism transition metals are somewhat depleted whereas high field strength elements are typically enriched relative to average archean upper crust samples generally have fractionated lree patterns average cen smn 2 4 with small negative eu anomalies average eu eu 0 78 and generally flat hrees average gdn ybn 1 3 such geochemical characteristics suggest that the source dominantly consisted of tonalite with less common occurrences mafic volcanic rocks and granite mixing calculations which massbalance the rees and th sc suggest 70 tonalite 15 mafic volcanic rocks and 15 granite as possible proportions for the source of the phyllites a nearby early archean 3 5 ga continental nucleus preserves similar lithologies and is the probable source intense chemical weathering of the source terrane is indicated by premetasomatized chemical index of alteration values of 95 100 nearly complete depletion of cao and na2o and high al2o3 na2o ratios fine grained sediments of comparable age and presumed tectonic setting elsewhere in southern africa show similar geochemical characteristics implying that source area compositions and weathering intensities were similar these mature platformal deposits suggest a tectonically stable environment where intense chemical weathering took place at 3 0 ga across southern africa

compositional evolution of siliciclastic sediments recording the tectonic stability of a pericratonic rift mesozoic kutch basin western india abstract this study presents a combined petrographical and geochemical investigation to track the compositional changes in the mesozoic sedimentary record during the evolution of the pericratonic rift basin of kutch the mesozoic sequence of the proven petroliferous basin of kutch representing 3000 m thick siliciclastic and carbonate deposition within a time frame of 70 ma consists of jhurio jhumara jhuran and bhuj formations in ascending order of succession the dominance of arkosic sandstones and the abundance of zircon and monazite indicate predominantly felsic source rocks the concentration of individual trace elements such as th sc zr v ni and ratios like th sc cr v y ni th co la sc support the predominantly felsic source rock the lree enrichment and the negative eu anomaly corroborate the predominantly felsic source however concentrations of v ni and ti reveal the mafic input in older stratigraphic units while gdn ybn indicates dominant post archean source across the mesozoic succession younger stratigraphic units reveal contributions from the archean rocks from nagar parkar and aravalli highland regions the cia values suggest intermediate to intense weathering while the icv data record a shift from immature sediments in the older formations to mature and recycled types in the younger formations the high value of zr sc as well a high content of hf reflects the addition of zircon by recycling or by erosional unroofing of older continental rocks major oxide sio2 na2o and k2o and trace elements la th and hf bear the passive margin setting for the kutch basin during the mesozoic the decrease in feldspar content in sandstones increase in the concentration of zr and hf in shale and a decrease in values of icv from older to younger stratigraphic units corresponds to the compositional evolution related to increased stability of the kutch basin during the transition from early syn rift to post rift

cerium anomaly and th u fractionation in the 1 85 ga flin flon paleosol clues from ree and u rich accessory minerals and implications for paleoatmospheric reconstruction the 1 85 ga paleosol at flin flon manitoba canada was one of the first paleoweathering profiles taken as evidence for a dramatic rise in the oxygen content of the paleoproterozoic atmosphere diagenesis and greenschist facies metamorphism have modified the abundances of some major elements e g k and fe in the flin flon paleosol inductively coupled plasma mass spectrometry icp ms analyses reveal a positive ce anomaly on both chondrite and amisk basalt normalized ree patterns and marked th u fractionation in the uppermost maroon paleosol the ce anomaly is confirmed by the occurrence of cerianite and by the compositions of other ree and u rich accessory minerals i e secondary monazite and uraninite in the uppermost maroon paleosol th u fractionation is supported by the presence of uraninite in both the paleosol and overlying missi sedimentary rocks chemical ages of uraninite 1 85 to 1 0 ga suggest that this mineral might have formed during weathering or diagenesis but was susceptible to disturbance although igneous monazite and zircon are well preserved in even the uppermost maroon paleosol primary fluorapatite exhibits variable degrees of weathering in the basal green paleosol and has been obliterated completely in the upper maroon paleosol published paleomagnetic data suggest a tropical paleolatitude for the flin flon region at the time of formation of the paleosol the positive ce anomaly in the flin flon paleosol confirms previous studies for an oxic atmosphere p o 2 10 1 5 to 10 2 pal at 1 85 ga however extreme caution must be exercised in the interpretation of th u fractionation in paleosols moreover this study demonstrates the advantage of a detailed characterization of ree and u rich accessory minerals in the application of trace element geochemistry of paleosols for paleoatmospheric reconstruction eh ph diagrams for the stabilities of cerianite and uraninite in their respective systems ce p c h o and up c h o at 25 c and 1 bar reveal the importance of phosphate complexes in the formation of ce anomalies and th u fractionation in both modern and ancient weathering environments

the source and origin of terrigenous sedimentary rocks in the mesoproterozoic ui group southeastern russia abstract arenites wackes and associated shales and siltstones of the ui group of riphcan age in southeastern siberia have been analyzed for petrographic major element and selected trace element compositions including the ree petrographic results suggest that the arenites may have been derived from granites and that the wackes may have been derived from more plagioclase rich rocks like tonalites or granodiorites the high quartz relative to other materials in many sandstones suggest that they may have been derived from intense chemical weathering or diagenesis so the mineralogic ratios may have been changed during these processes the shales and siltstones are composed mostly of illite and quartz in addition a cn k diagrams indicate that the wackes and associated shales and siltstones underwent k metasomatisim extrapolation of the shales and siltstones associated with the wackes back to the plagioclase alkali feldspar line in the a cn k diagram suggests a high average plagioclase to alkali feldspar ratio in the provenance tonalite to granodiorite extrapolation of shales and siltstones associated with the arenites suggest a low plagioclase to alkali feldspar ratio in the provenance granite in addition the index of compositional variability icv and chemical index of alteration cia parameters of the shales and siltstones suggest the weathering of the first cycle material was intense trace element ratios suggest all the sedimentary rocks were derived from mostly granitoids shales and siltstones were plotted as elemental ratios e g th sc vs eu eu these plots suggest a mix of a granodiorite tonalite source for the source of the shales and siltstones associated with the wackes with a granite source for the shales and siltstones associated with the arenites the arenites also contain lower eu eu and higher th co and th sc ratios than the wackes this as is consistent with the petrography suggests that the arenites were derived from a source with more granite and less granodiorite tonalite than the wackes

palaeoweathering composition and tectonics of provenance of the proterozoic intracratonic kaladgi badami basin karnataka southern india evidence from sandstone petrography and geochemistry abstract petrographic and geochemical data on the sandstones of the proterozoic intracratonic kaladgi badami basin southern india are presented to elucidate the palaeoweathering pattern and composition and tectonics of their provenance the kaladgi badami basin hosting the kaladgi supergroup occupies an e w trending area the supergroup unconformably overlies archaean basement ttg gneisses granites and greenstones comprises a cyclic arenite pelite carbonate association and is divided into the bagalkot and badami groups the immature arkosic character of the basal saundatti quartzite member bagalkot group containing fresh and angular feldspars along the northern margin of the basin suggests that during the initial stage of deposition this part of the basin received sediments from a restricted uplifted and less weathered source dominated by k rich granites occurring to the north in contrast the saundatti quartzite along the southern margin displays a mostly mature quartz rich character with less abundant but severely weathered feldspars and higher sio2 and cia but lower al2o3 tio2 rb sr ba k2o k2o na2o zr ni and zr cr this is interpreted in terms of a tectonically stable considerably weathered mixed source archaean gneisses granites and greenstones along the southern fringe of the basin the highly mature quartz arenite muchkundi quartzite member also of the bagalkot group occurring higher up in the succession exhibits minor but severely altered feldspars and higher sio2 na2o cia cr and ni with lower k2o al2o3 tio2 and k2o na2o this reflects that with the passage of time the source evolved to a uniform extensively weathered tectonically stable peneplained provenance which consisted of less evolved ttg gneisses and greenstones this was followed by closure deformation and upliftment of the basin hosting the bagalkot group and subsequent deposition of the badami group sandstone members of this younger group cave temple arenite and belikhindi arenite range widely in mineralogy quartz arenite to arkose and chemistry including cia and point to a source that varied from uplifted less weathered k rich granites to less evolved peneplained ttg gneisses and greenstones or even bagalkot sediments variable alteration of feldspars in the kaladgi sandstones and severe depletion of ca na and sr in the associated shales indicate a humid tropical tropical and subtropical climate facilitating chemical weathering

basement unconformity control on alteration st francois mountains se missouri the basement lamotte formation unconformity in southeastern missouri shows evidence of several distinctive alteration events some of which may be related to migration of ore forming fluids or k rich basinal brines the alterations are spatially related to the unconformity suggesting that the unconformity was a preferred pathway for fluid migration unconformity related rocks in five cores penetrating both the lamotte formation and the basement have been characterized by bulk chemistry mineralogy textures and paleotopographic position the alteration history along the unconformity includes 1 pre lamotte hydrothermal alteration affecting basement 2 pre lamotte weathering and 3 post lamotte hydrothermal and diagenetic events the third group is particularly complex including early diagenetic hematite and calcite cementation later quartz cementation secondary biotite growth k metasomatism that generated adulaira and k leaching that left a narrow dickite rich zone along the unconformity sev

climate and biomes in the west mediterranean area during the pliocene a new pollen derived method of climatic quantification based on the mutual climatic range of plant taxa has been applied to 17 pliocene pollen sequences in the west mediterranean area the latitudinal gradient observed in the pollen data was confirmed by the climatic reconstructions there is a gradient from north to south both for temperatures and precipitation at the beginning of the pliocene 5 32 5 ma the climate in the north mediterranean area was on average warmer and more humid than today respectively 1 4oc and 400 700 mm in the south mediterranean region the climate was both warmer and drier than today respectively equal to or 5oc higher and drier or equal humidity the pollen based climate estimates were then used to reconstruct biomes for the region the results show the occurrence of three biomes the broad leaved evergreen warm mixed forest the xerophytic woods scrub biome and the warm grass shrub biome these biomes are still represented today in the mediterranean region despite different thermic and water conditions

petrology and geochemistry of cretaceous sedimentary rocks of the monte soro unit sicily italy constraints on weathering diagenesis and provenance abstract the mineralogy and chemical compositions of shale and sandstone alternations of cretaceous age of the monte soro unit sicily have been determined the clay minerals in the shales are mostly illite and i rich mixed layer i s reflected by enrichment in al2o3 k2o and chemically similar elements the sandstones are subarkose to quartz arenite the shales and sandstones have upper crustal rare earth element patterns and except for k2o they are depleted in alkaline and alkaline earth elements as a result of intense weathering the sandstone and shale mineralogy suggests a diagenetic history in which the sediments were subjected to temperatures in excess of 100 c during which interaction between some minerals in the shales and sandstones took place thus diagenetic quartz cementation and feldspar alteration in the sandstones and smectite illitization in the shales occurred together with the shales being a sink for potassium and the sandstones a sink for silicon negative europium anomalies bet

sedimentary rocks and crustal evolution tectonic setting and secular trends a significant change in the composition of turbidites deposited at active tectonic settings is seen at the archean post archean transition in comparison to post archean active margin turbidites archean greenstone turbidites exhibit more uniform th sc ratios but with a similar average greater hree depletion gd n yb n 2 less eu depletion eu eu mostly 0 85 and an absence of low th u ratios th u 3 these data indicate that differing mantle sources and or conditions of mantle melting existed during the archean and that intracrustally differentiated rocks older cratons or young differentiated arcs were relatively unimportant as provenance components for archean turbidites in contrast some sedimentary rocks preserved in archean platformal sequences of high grade terranes display significant negative eu anomalies similar to the majority of post archean shales indicating that the general process of cratonization including intracrustal differentiation has taken place since at least 3

petrological and geochemical evidence of the paleoproterozoic and the meso neoproterozoic sedimentary rocks of the bastar craton indian peninsula implications on paleoweathering and proterozoic crustal evolution the petrology and geochemistry of the sandstones and shales of the meso neoproterozoic chattisgarh and indravati basins and the pelites and quartzites of the paleoproterozoic sakoli and sausar basins of the bastar craton have been studied for the paleoweathering tectonic setting and to delineate sediment source components and finally to trace the proterozoic crustal evolution in the bastar craton indian peninsula the geochemical data shows decrease in the abundance of mafic major elements and transition elements and an increase in the large ion lithophile elements liles from the paleoproterozoic pelites to the meso neoproterozoic shales this suggests partial exposure of granitoids in the paleoproterozoic and unroofing of the granitoids by the complete removal of mafic rocks in the provenance as the meso neoproterozoic sedimentation progressed overall the study of the meso neoproterozoic sandstones and shales show homogeneity in the source rock composition with strong felsic component however the paleoproterozoic pelites and quartzites show heterogeneity in the source rock composition with mixture of the felsic and mafic components geological geochemical and petrographic evidences indicate that the sediments in the paleoproterozoic sakoli and sausar basins and the meso neoproterozoic chattisgarh and indravati basins have been deposited in passive margin tectonic settings cratonic basins or intra cratonic rifts the relationship among alkali and alkaline earth elements cia pia and the th u ratio indicate that the source area was affected by moderate to intense weathering history

integrated magnetostratigraphy and biostratigraphy of the upper pliocene lower pleistocene from the monte singa and crotone areas in calabria italy the results of a detailed magnetostratigraphic and biostratigraphic study of late pliocene to early pleistocene marine marl sequences from the monte singa and crotone areas in calabria italy are presented the magnetostratigraphy from the monte singa sequence ranges from below the gauss matuyama boundary up to and including the lower olduvai boundary normal polarities at a level corresponding to isotope stage 81 most probably represent the r union subchron from the lower olduvai boundary upward a reliable magnetostratigraphy could not be established due to increased weathering of the marls resulting in mainly secondary magnetizations the magnetostratigraphy from the composite sequence of the crotone area belongs to a large part of the matuyama chron and includes the olduvai subchron the position of the lower and upper boundaries of the olduvai subzone could be established more precisely than from earlier results moreover the upper boundary of the olduvai subzone poses an ambiguity a relatively long normal polarity interval representing the main olduvai subchron and corresponding to a duration of 115 ka is followed by a short 30 ka reversed subchron and the short 15 ka normal vrica subchron another option and more in accordance with the duration of the olduvai subchron in literature would be to consider the complete n r n polarity succession with a total duration of 160 ka as representing the olduvai subchron implying that this olduvai subchron has a short reversed interval in its upper part linear interpolation and extrapolation yield ages for the most important late pliocene early pleistocene biostratigraphic datum levels an age of 1 69 ma is found for the pliocene pleistocene boundary using the conventional polarity time scale dated with radiometric results however hilgen 1 in correlating the sapropel groups and patterns to the precession curve of the earth s orbit obtained significantly different ages for the polarity transitions of the present study according to this astronomically calibrated polarity time scale the age of the pliocene pleistocene boundary is 1 81 ma

provenance tectonic setting and age of the sediments of the upper disang formation in the phek district nagaland abstract integrated petrographic and geochemical studies of sandstones and geochemical studies of shales of turbidites from the upper disang formation phek district nagaland have been carried out to determine their provenance weathering conditions and tectonic setting paleomagnetic studies were carried out for magnetostratigraphic purposes studies indicate that most of these sediments were derived from felsic and mafic sources with minor contribution from low to medium grade metamorphic rocks most of the felsic components have been transported from distant sources as evidenced from extensive reworking of grains the most likely source rocks are the granite granite gneiss of the karbi anglong crystalline complex to the west of the study area however the bulk of the sediments have been contributed from nearby basic and ultrabasic sources this would correspond to the fast rising naga ophiolite which probably emerged above sea level during the mid eocene prevailing high temperatures and humid climate caused intense chemical weathering of the source rocks the sediments from the west were transported great distances by turbidity currents into an easterly deepening basin sediments from the nearby east were rapidly dumped on the seafloor causing rapid mixing leading to textural and chemical immaturity paleomagnetic studies endorse published paleontological evidence to indicate that most of the sediments of the upper disang formation were deposited during the late eocene deposition took place in a westward migrating accretionary prism complex in an active margin setting at the convergence of the indian and burma plates this was a rapidly closing basin where anoxic conditions prevailed towards the end of the eocene this basin closed completely with the destruction of the tethyan ocean

geochemical evolution of the tertiary succession of the nw shelf bengal basin bangladesh implications for provenance paleoweathering and himalayan erosion abstract whole rock major trace and rare earth element ree compositions of paleogene to neogene sedimentary rocks of the nw shelf succession province 1 of bangladesh contain a record of interaction of the india and asian plates himalayan tectonism and climatic development analyses of 66 sandstones and mudrocks from the tertiary succession of bangladesh were made to examine provenance source weathering and the influence of paleoclimate and tectonism the sediments display linear geochemical trends due to quartz dilution and varying quartz clay ratios produced by hydrodynamic sorting chondrite normalized ree patterns for both sandstones and mudrocks from different groups are similar to upper continental crust with moderate to high lree enrichment lithotypes within formations average lan ybn 5 31 11 41 and marked negative eu anomalies eu eu 0 51 0 69 based on geochemical criteria the succession can be divided into three parts jaintia barail surma and dupi tila very high silica contents in jaintia tura sandstones and high chemical index of alteration cia indices in kopili mudrocks fe shales suggest derivation from a deeply weathered and stable cratonic source india the tura sandstones are interpreted as first cycle quartz arenites produced while the indian plate drifted across equatorial regions during the paleocene eocene thermal maximum petm the barail surma and dupi tila sediments were derived from a felsic orogen the himalaya the barail surma sediments were mainly derived from the trans himalayan batholith and associated granitoids with significant contribution from the lesser himalaya mafic input is also evident probably from intraoceanic arc material within the himalaya barail mudrocks have uniformly high cia values 92 95 suggesting intense steady state weathering of their proto himalayan source and warm and humid climate in contrast cia values of surma mudrocks range from 66 to 93 average 84 suggesting non steady state weathering related to active uplift in the himalaya the dupi tila sediments were derived from a more felsic lesser himalaya source with significant contribution from the trans himalaya and very little or no ophiolitic or arc material dupi tila mudrocks have cia ratios of 62 99 average 72 also indicating non steady state weathering in the rising himalayan source geochemical compositions of the nw shelf sediments are comparable to coeval successions in the surma basin province 2 of bangladesh and the siwaliks india indicating similar source evolution of the indian monsoon and associated high precipitation caused intense chemical weathering of the surma and dupi tila source despite rapid uplift the surma group thus bears the signature of evolution of the asian monsoon in the bengal basin at 21 ma simultaneous with the development of the east asian monsoon this supports proposals that both monsoon systems developed at the same time

chemical evolution of magmas in the proterozoic terrane of the st francois mountains southeastern missouri 2 trace element data the st francois mountains igneous complex of proterozoic age consists of hypabyssal granite plutons intruded into the overlying rhyolites of similar age melting and crystallization models of these rocks suggested by the field petrographic and major element contents are further refined using rb ba sr ree rare earth element th sc and co contents there are two groups of relatively undifferentiated plutons associated with the butler hill caldera and taum sauk area that could have formed by partial melting of lower crustal rocks the plutons associated with the butler hill caldera knoblick and silvermine granites could have formed by about 30 aggregate melting of a quartz diorite graywacke or subgraywacke the plutons associated with the taum sauk area could have formed by about 30 equilibrium melting of a subarkose or arkose more silicic rocks of the butler hill caldera could have formed by fractional crystallization the silvermine granite is internally zoned crystallization of plagioclase biotite hornblende magnetite apatite zircon sphene in a ratio of 0 70 0 10 0 15 0 04 0 005 0 003 0 007 from the least differentiated portion of the silvermine granite could have formed intermediate portions of the silvermine further crystallization of the silvermine requires more biotite ba begins to decrease and less hornblende zircon and sphene hree increase to precipitate and form the most differentiated portions also fractional crystallization of undifferentiated silvermine type magmas could have produced the sequence of butler hill breadtray graniteville granites as residual liquids respectively the early crystallizing mineral assemblage is dominated by plagioclase and biotite while the late crystallizing mineral assemblage is dominated by quartz k feldspar and lesser plagioclase the gneissoid granodiorite in the hawn park area has the mineral assemblage and composition of a cumulate derived from the silvermine granite type differentiation sequence the associated volcanic rocks could not have formed from melts of exactly the same composition of any of the associated intrusive rocks rather the volcanic rocks formed from melts of slightly different chemistry

diagenetic constraints on the use of cerium anomalies as palaeoseawater redox proxies an isotopic and ree study of cambrian phosphorites seawater rare earth element ree distributions show heavy ree enrichment and cerium depletion but these characteristics are only rarely found in ancient marine authigenic minerals such as carbonate fluorapatite and calcite this enigma may be due to changing ree distributions in seawater through time or to post depositional redistribution of ree differentiating between these two factors is however far from straightforward as their relative importance is likely to vary and evidence is often ambiguous in this article we present ree as well as strontium and sulphur isotope data for basal cambrian phosphorites of south china which confirm the emerging rule of thumb that granular phosphorites seldom reveal extreme departures from the seawater norm and tend to undergo therefore less diagenetic alteration of ree spectra than skeletal apatites and other phosphate types this study reveals stratigraphic trends in ce anomalies ce ce that could be taken to imply the preservation of a palaeoenvironmental signal however further investigation of our data shows that such trends in phosphorites can also be caused by post depositional alteration which tends to 1 increase ree contents 2 reverse ce depletion 3 alter eu anomalies and 4 concentrate preferentially the middle ree mree further alteration which may be due to weathering has led to hree depletion and positive la and y anomalies tetrad effect this is the first study where ceanom and phosphate bound sulphate s isotope values could be compared for one particular stratigraphic section which provides us with an additional tool for the interpretation of diagenetic redox conditions least altered phosphorites from meishucun that yield a strongly negative ceanom constrain early cambrian seawater 34s to about 33 we conclude that phosphorite ceanom primarily records variations in the local conditions of diagenesis while outlining some special cases in which diagenetic redox conditions may broadly reflect local bottom water redox conditions

geochemistry and provenance of the altendorf feldspathic sandstone in the middle bunter of the thuringian basin germany an integrated mineralogical and geochemical study of the altendorf feldspathic sandstone in the middle bunter of the thuringian basin germany was carried out to obtain more information on its provenance sedimentological history and geochemistry the fine to coarse grained sandstone has an average composition of 66 63 71 quartz 30 27 35 feldspar and a fine grained illitic matrix the heavy mineral assemblage consists mainly of tourmaline zircon rutile apatite and opaque fe ti minerals it is inferred that this terrigenous material was laid down at the margin of the bunter basin high abundances of igneous quartz grains determined by cathodoluminescence cl the lack of metamorphic heavy minerals as well as alkali feldspar with an average k2o na2o ratio of 14 9 point to material of mostly granitic origin regional geologic and paleogeographic observations suggest that granites of the older and younger intrusive complex of the western erzgebirge are possible source rocks of the feldspathic sandstone the geochemical signature of the alkali feldspar k2o na2o ratio bao content points to the bergen and kirchberg granites as possible parent rocks comparing the mineralogical and geochemical data of the presumed source granites with those of the altendorf sandstone provides information on the sedimentation processes weathering fluvial transport and sedimentation under arid climatic conditions have caused complete decomposition and removal of plagioclase and biotite lowered the bulk ree content and led to the development of a positive eu anomaly the immobile trace elements e g ta th zr sc co ti are best suited for provenance determination because of their relatively low mobility during sedimentary processes elemental ratios such as la sc th sc co th and th ta have inherited the signature of the parent rocks and thus may be particularly useful for provenance studies to evaluate the control of specific minerals and grain size fractions on the distribution of trace elements in the sandstone separated fractions of quartz feldspar the 20 m fraction and heavy minerals were additionally analyzed the concentration densities elemental concentration in the fraction fraction weight reveal that with exception of hf the influence of the heavy mineral fraction on the whole rock geochemistry is insignificant although this fraction generally plays the most important role as carrier of trace elements quartz feldspar and the 20 m fraction have similar concentration densities between 20 and 40 for the ree with exception of eu which is mainly hosted in feldspar strong positive eu anomaly the influence of the 20 m fraction on the distribution of the ree and the elements u th sc ta strongly depends on the abundance of this fraction in the sediment alkali feldspar contains most of the ba sr rb and cs in the samples concentration densities of up to 97 thus differences in the abundances of these elements in whole rock samples can be related to changes in the mineralogical composition quartz feldspar ratio of the sediment

geochemical identification of clastic sediment provenance from known sources of similar geology the cretaceous scotian basin canada abstract this study tests the effectiveness of a geochemical approach in identifying provenance in a basin where different sources do not show strongly contrasting geology petrological studies indicate that at least three distinct rivers draining reactivated horsts of the appalachian orogen supplied sediment to the lower cretaceous deltaic sandstones and mudrocks in the offshore scotian basin ninety five samples mostly from conventional core were analyzed for 44 major and trace elements the data were first screened for variability unrelated to provenance including changes in elemental abundance due to weathering and diagenesis and the effects of grain size and sorting on element variation the effect of hydraulic sorting was distinguished from the effects of concentration of ultrastable heavy minerals from polycyclic sources multivariate statistical analysis by principal component analysis pca was used to test the hypothesis of three discrete sources suggested by the petrologic model major element pca on sandstones discriminated the sources but results from trace element pca required further investigation using element biplots to understand their significance only a few elements were found to be diagnostic of different sources namely k rb sr u th nb and ti with the latter two of value only for sandstones all of these are elements that are abundant in the granites of the appalachians most published geochemical discrimination diagrams did a poor job of distinguishing the three petrographically recognized sources in other basins with quite different hinterland geology other elements are known to be of value in discriminating provenance thus it is unlikely that a globally applicable set of elemental discriminants can identify terrigenous sediment sources rather systematic investigation is needed that evaluates processes such as diagenesis and sorting and then tests geographic and stratigraphic variability in bulk geochemistry informed by at least semiquantitative petrographic data

geochemistry of permo triassic mudstone of the satpura gondwana basin central india clues for provenance abstract major and trace element data of the permo triassic mudstones from the intracratonic satpura gondwana basin central india have been used to investigate provenance the satpura succession 5 km thick unconformably overlies the precambrian basement sediment dispersal pattern suggests that the precambrian rocks straddling the southern margin of the satpura basin were the most probable source for the sediments the lowermost unit of the satpura succession comprises glacio marine and glacio fluvial deposits the rest of the succession largely represents a variety of fluvial depositional systems with some records of fluvio deltaic and fluvio lacustrine sedimentation under a climatic spectrum of temperate humid to warm semi arid the present study is confined to the lower six formations namely talchir barakar motur bijori pachmarhi and denwa arranged in that order from bottom to top the oldest rocks of this sequence the talchir formation are enriched in mobile elements such as na ca and mg depleted in alumina and have high icv 0 93 1 29 and lower cia values 61 82 74 89 compared to those of the younger mudstones k 2 o al 2 o 3 ratios of the talchir mudstones 0 24 0 28 are higher than the younger mudstones in this sequence these results suggest that the talchir mudstones were weathered less intensely and are thus more immature than the younger mudstones this is consistent with the prevailing cold climate and relatively higher rate of basin subsidence in contrast the majority of the mudstones from the younger formations are depleted in mobile elements have relatively low icv 0 18 0 87 and k 2 o al 2 o 3 values 0 07 0 26 higher cia values 76 99 92 86 and appear compositionally more mature reflecting moderate to high intensity source rock weathering among them the barakar mudstones likely have been more intensely weathered than mudstones from any of the other formations the trace element compositions and ratios are consistent with most mudstones being derived from a felsic source with some mudstones being derived from a more mafic source for example la sc 0 805 and 0 114 la th 6 245 5 072 7 418 6 245 and 5 072 and eu eu 1 431 0 868 and 0 805 of some mudstones indicate mafic source bivariate plot of th sc and zr sc indicates considerable enrichment of zircon that suggests recycling from meta sedimentary rocks prominent negative eu anomaly high lree hree and flat hree pattern reflect sediment derivation from predominantly felsic rocks of the old upper continental crust sio 2 al 2 o 3 versus k 2 o na 2 o plot for the mudstones suggests that they formed in a passive margin also total ree content of most of the mudstones is conformable with passive margin tectonic setting and craton interior type of provenance plotting in la th sc th sc zr 10 and la sc versus ti zr diagrams largely indicates continental margin settings for majority of the mudstones but fails to differentiate between active and passive continental margins

magnetic stratigraphy and biostratigraphy of pliocene argille azzurre northern apennines italy abstract an integrated biomanetostratigraphic chronology for the mediterranean pliocene has been developed in the last five years mainly from land sections in southern italy calabria and sicily and odp leg 107 tyrrhenian sea cores in this paper the chronology is applied to terrigenous sediments from the northern apennine foredeep where reworking as well as sedimentation rate and facies variations limit the resolution of biostratigraphy and physical stratigraphy the integrated chronology gives improved stratigraphic control for a messinian to upper pliocene section exposed on the banks of the stirone near parma northern italy and for a short lower pliocene section located nearby at sant andrea bagni the sections are in the vicinity of stratotype sections for the tabianian lower pliocene and piacenzian upper pliocene and the chronology gives new insights into the complex pliocene sedimentation history in the northern apennine foredeep at this time at the stirone section the base of the pliocene record is in a normal polarity chronm correlated to the thvera subchron indicating a hiatus at the miocene pliocene boundary and the absence of the mpl1 foraminiferal zone at sant andrea bagni mpl1 is also missing in contrast to previous reports we conclude that this biozone is probably absent throughout the northern apennines where post messinian flooding appears to have occurred at the onset of mpl2 time during the gilbert chron sedimentation rates at stirone reached 104 cm kyr as nearly 300 m of argille azzurre blue clay were deposited in less than 0 5 myr very sporadic sedimentation is apparent from the late nunivak to the top of the section late gauss chron with a number of hiatuses being recognized within chron 2ar late gilbert and in the early gauss this interruption of sedimentation at about 4 1 ma is associated with a widely recognized early pliocene tectonic event involving thrusting and migration of the depocenter of the northern apennine foredeep

mesoproterozoic trans laurentian magmatism a synthesis of continent wide age distributions new sims u pb ages zircon saturation temperatures and hf and nd isotopic compositions abstract the origin and tectonic setting of the mesoproterozoic 1 50 1 34 ga granite rhyolite provinces of the midcontinent region of the united states and the coeval a type granite plutons of the southwestern united states have been an enigma for decades in this paper we review the history of this problem examine the significance of a wealth of previously published u pb zircon and whole rock sm nd data and present new u pb zircon age and lu hf isotopic data from selected zircon samples our data show that the initiation of this magmatism spans the interval 1 50 1 40 ga across the continent but there is a general younging westward younger 1 39 1 34 ga magmatism also occurred across the continent but forms a major magmatic event only in the south central mid continent there is generally a good correlation between sm nd and lu hf isotopic compositions and inferred mantle derivation model ages except possibly in southeastern oklahoma the absence of older cores in zircons is compatible with calculated zircon saturation temperatures of ca 850 c and supports mantle driven basaltic underplating and resulting crustal partial melting as a petrogenetic model for the a type magmatism our new data compilation refines the existence of the nd line that extends from southwestern texas into southeastern michigan and the western grenville province in canada it marks an isotopic boundary between granites and rhyolites of cratonal origin to the northwest 1 8 1 6 ga model ages and those of more juvenile origin to the southeast 1 5 1 4 ga model ages our suggested tectonic model for the mesoproterozoic a type magmatism across eastern and southern laurentia involves the development of an active laurentian margin extending from eastern canada across what is now the midcontinent region of the united states and at least into the current southwestern united states magmatism along this margin was likely related to asthenosphere lithosphere interactions associated with the accretion of outboard arcs and possible exotic terranes that caused complex deformational and magmatic responses in the continental interior this activity evidently spread from northeast to southwest over a period of ca 70 million years the occurrence of the younger ca 1 39 1 34 ga event indicates that similar processes occurred some 130 million years later suggesting a long lived convergent plate margin and recurring basaltic underplating in some locations perhaps due to inboard lithospheric delamination and or mantle upwelling

extension of the astronomically calibrated polarity time scale to the miocene pliocene boundary the early pleistocene to late pliocene astronomically calibrated time scale of shackleton et al 1 and hilgen 2 is extended to the miocene pliocene boundary this is done by correlating the detailed record of caco3 cycles in the trubi and the lower part of the overlying narbone formation rossello composite section sicily to the astronomical record using 1 inferred phase relations between these caco3 cycles and the corresponding orbital cycles of precession and eccentricity and 2 calibration points provided by the previously established astronomical calibration of sapropelitic layers which occur in the topmost part of the caco3 record 2 this correlation allows all small scale caco3 cycles in the rossello composite section to be coded after the correlative precession peak and to be dated astronomically with an accuracy of 1 ky in combination with the available high resolution magnetostratigraphy it further allows the construction of an astronomically calibrated geomagnetic polarity time scale for the major part of the gilbert and gauss chrons this new time scale gives ages for the reversal boundaries of the kaena 3 04 3 11 ma and mammoth 3 22 3 33 ma the gilbert gauss chron boundary 3 58 ma and the reversal boundaries of the cochiti 4 18 4 29 ma nunivak 4 48 4 62 ma sidufjall 4 80 4 89 ma and thvera 4 98 5 23 ma these ages are significantly older than the ages given by conventional time scales age discrepancies gradually increase with increasing age the age of 5 32 ma for the miocene pliocene boundary as defined by the base of the trubi on sicily is almost 0 5 m y 9 5 older than the presently accepted age of 4 86 ma 3 these considerable discrepancies with the conventional time scale can either be explained by an consistent error in the decay constants used in k ar radiometric dating or more likely by diffusional loss of radiogenic argon

oxygenation of the archean atmosphere new paleosol constraints from eastern india it is widely believed that atmospheric oxygen saturation rose from 5 present atmospheric level pal in the archean to 10 2 pal at the great oxidation event goe at ca 2 4 ga but it is unclear if any earlier oxygenation events occurred here we report u pb zircon data indicating that a pyrophyllite bearing paleosol from keonjhar in the precambrian singhbhum craton of eastern india formed between 3 29 and 3 02 ga making it one of very few known archean paleosols globally field and geochemical evidence suggests that the upper part of the paleosol was eroded prior to unconformable deposition of an overlying sequence of shallow marine siliciclastic sediments a negative cerium anomaly within the currently preserved level of the paleosol indicates that ancient oxidative weathering occurred in the original upper soil profile the presence of redox sensitive detrital uraninite and pyrite together with a complete absence of pyrophyllite in the overlying sediments indicate that the mineralogical and geochemical features of the paleosol were established prior to the unconformable deposition of the sediments and are not related to subsequent diagenetic or hydrothermal effects we suggest that a transient atmospheric oxygenation event occurred at least 600 m y prior to the goe and 60 m y prior to a previously documented archean oxygenation event we propose that several pulsed and short lived oxygenation events are likely to have occurred prior to the goe and that these changes to atmospheric composition arose due to the presence of organisms capable of oxygenic photosynthesis

classification of paleosols despite increased interest in paleosols during the past decade no satisfactory classification is in current use presented here is a largely descriptive classification system that utilizes those pedogenic features that have the highest preservation potential in the rock record emphasized in the classification are morphological and mineralogical features that are easily recognizable in the field and through the petrographic microscope the classification is based on evaluation of the relative prominence in a paleosol of six pedogenic features or processes organic matter content horizonation redox conditions in situ mineral alteration illuviation of insoluble minerals compounds and accumulation of soluble minerals the most prominent of these six features processes provides the key to classifying a paleosol into one of nine orders four of the order names are borrowed from soil taxonomy histosol spodosol oxisol vertisol whereas the other five order names are presented here for the first time calcisol gypsisol gleysol argillisol protosol the orders may be preceded by one or more subordinate modifiers that describe other important features of the paleosol the classification is relatively easy to apply to the rock record and should enhance communication and aid in the standardization of terminology

geochemistry of asara shale member of karaj formation central alborz iran provenance source weathering and tectonic setting abstract the asara shale member of the karaj formation middle to upper eocene in age includes mixed volcaniclastic siliciclastic and carbonate strata in the alborz mountains northern iran these strata have been geochemically analyzed to constrain their source area provenance most of the major and trace element contents of asara shale samples are generally similar to the upper continental crust ucc values and their chemical index of alteration cia values 31 7 50 9 suggesting a semi arid climate in a weathering limited source area moreover correlation of major element oxides suggests the controlling effect of plagioclase and clay minerals on these data when xrd analysis and sem images indicate clastic sourced illite and chlorite in the samples probably due to the weathering of volcanic ash and glass in an aqueous transport and depositional environment however the chondrite normalized ree plot of mudrocks of the asara shale show a similarity with the ucc composition mineral composition and geochemistry of the asara shale mudrocks reveal the rapid reworking of penecontemporaneous volcaniclastic deposits which had covered the surrounding areas instead of their epiclastic genesis related to erosion and transport major trace and rare earth element ree data imply a felsic composition of the volcanic source related to an active continental margin continental island arc and most probably back arc tectonic setting for the depositional basin inferring a mid upper eocene extensional volcanism in a subduction complex

petrogenesis of metaluminous a type rhyolites from the st francois mountains missouri and the mesoproterozoic evolution of the southern laurentian margin abstract predominantly acid volcanic and intrusive rocks of the approximately 1 48 ga eastern granite rhyolite province are exposed only in the st francois mountains inlier missouri combined nd isotopic major and trace element analyses are presented for the predominantly acid volcanic rocks of the st francois mountains they are metaluminous to mildly peraluminous a type compositions with positive initial e nd values of 3 1 5 0 they are interpreted to be the result of crystal fractionation of partially melted calc alkaline igneous rocks formed at a recently active subduction zone the likelihood of a juvenile calc alkaline subduction generated protolith for the st francois mountains rhyolites leads to a hypothesis in which dacitic parental magmas resulted from partial melting in a continental back arc setting basaltic magmatism due to decompression melting of the mantle resulted from lithospheric extension and thinning and provided the heat source for melting in the middle or lower crust penecontemporaneous magmatism elsewhere in laurentia included subduction related calc alkaline rocks in the pinware terrane of labrador some felsic igneous rocks of uncertain plate tectonic setting within the grenville province also have 1 5 1 6 ga t dm ages these are interpreted as magmatic products of approximately 1 5 ga northward dipping subduction beneath much of the length of the southern margin of laurentia the eastern granite rhyolite province is consequently seen as an integral inboard expression of this subduction related igneous activity petrogenetic models involving a mantle plume or the development of a continental rift are not required to explain this granite rhyolite terrane and evidence against their involvement is discussed

rb sr and u pb geochronology and distribution of rock types in the precambrian basement of missouri and kansas most of what we know about basement rocks in kansas and missouri is derived from cores and cuttings from deep drilling these rocks may be divided into a northern terrane underlain by rocks consisting of abundant granite commonly showing cataclastic textures and by metavolcanic to metasedimentary rocks and a southern terrane underlain almost exclusively by rhyolitic flows and ash flow tuffs and epizonal granite plutons the northern terrane is interrupted in central kansas by mafic igneous rocks and flanking arkosic sedimentary rocks of the central north american rift system data from 63 rb sr whole rock analyses yield ages ranging from 1 153 to 1 748 m y but these are considered to represent only the minimum ages of the rocks ages derived from u pb analyses of suites of cogenetic zircons from 22 rock samples indicate that some rocks of the northern terrane were formed 1 610 to 1 650 m y ago these are apparently intruded by younger granite plutons formed 1 450 1 470 m y and 1 340 1 380 m y ago rocks of the southern terrane were formed 1 460 1 480 m y ago in the st francois mountains terrane of southeastern missouri and its buried equivalents but these are about 1 380 m y old in southwestern missouri and southern kansas rocks of the central north american rift system in kansas are assumed to be about 1 100 m y old by geophysical and drill hole extension to their outcrop in the lake superior region where they have been dated both the northern and southern terranes are notable for the great abundance of granitic rocks and the scarcity of intermediate to mafic igneous rocks quartzite is the most abundant metamorphic rock although the decrease in ages from north to south in the mid continent region suggests their sequential accretion at the edges of a pre existing continent the rock assemblages are not consistent with convergent plate margin suites of the andean type the great volumes of rhyolite and epizonal granite of the southern terrane may represent melting of thickened somewhat older crust following accretion at the continental margin major element chemical data are presented for basement rocks from kansas oklahoma and texas and these are compared with the compositions of similar rocks from the st francois mountains names and locations are given for wells from which samples were obtained

fingerprinting and tracing the sources of soils and sediments earth and ocean science geoarchaeological forensic and human health applications abstract fine grained sediment is perhaps the most widespread and pervasive contaminant in aquatic systems reflecting its role in influencing the quality of the water e g turbidity vector of chemicals and other pollutants and its detrimental effect on infrastructure e g dams turbines and aquatic habitats e g salmonid spawning grounds through sedimentation determining the sources of fine grained sediment thus represents an important requirement for watershed and coastal management as well as for understanding the evolution of landscapes and ocean basins sediment source fingerprinting utilizes the diagnostic physical chemical and biological properties i e tracers of source materials to enable samples of collected sediment to be apportioned to these sources this review examines the development of the technique within the earth and ocean sciences focusing mainly on agricultural landscapes however the development of new tracers such as compound specific stable isotopes has allowed the technique to be applied in a growing number of environmental settings including forested including wildfire impacted forests urban and estuarine coastal settings this review also describes other applications of the fingerprinting approach such as geoarchaeological e g archaeological site formation forensic e g identifying the sources of soil sediment particles in criminal investigations and human health e g identifying the sources of airborne particulate matter pm 2 5 applications identifying commonalities in methods and approaches between environments and disciplines should foster collaboration and the exchange of ideas furthermore refinement of the sediment source fingerprinting technique requires that several methodological issues be addressed these methodological issues range from the initial sampling design to the interpretation of the final apportionment results this review also identifies and assesses these methodological concerns

another look at rare earth elements in shales linear correlation and mass balance considerations indicate that clays are more important than zircon or other heavy minerals in hosting both light and heavy ree in cratonic shales considering the uniformity of the eu anomaly and ree distributions in cratonic shales it seems likely that detritus is thoroughly mixed during weathering and sediment transport and that the ree patterns in shales reflect the average ree pattern of the sources regardless of the ratio of clays to heavy minerals in the shales shales suspended river loads and near shore marine sediments all have broadly similar ree patterns and reported hree depletions in the latter two groups may reflect incomplete dissolution of heavy minerals during sample preparation ree distributions in shales and suspended river loads determined by inna are similar to those in average upper continent crust and ree distributions in shale averages nasc and paas seem to be reasonably representative of the average composition of post archean upper continental crust

geochemistry of sandstones from the upper miocene kudankulam formation southern india implications for provenance weathering and tectonic setting abstract petrographic major trace and rare earth element compositions of sandstones from the upper miocene kudankulam formation southern india have been investigated to determine their provenance tectonic setting and weathering conditions all sandstone samples are highly enriched in quartz q but poor in feldspar f and lithic fragments l the major element concentrations of these sandstones reveal the relative homogeneity of their source geochemically the kudankulam sandstones are classified as arkose subarkose litharenite and sublitharenite the cia values chemical index of alteration mean value 44 5 for these sandstones and the a cn k diagram suggest their low weathering nature similarly their fe2o3 mgo mean 2 7 al2o3 sio2 0 09 k2o na2o 2 2 ratios and tio2 contents 0 3 are consistent with a passive margin setting the eu eu 0 5 la lu cn 21 la sc 5 9 th sc 1 9 la co 5 7 th co 1 8 and cr th 5 3 ratios support a felsic source for these sandstones chondrite normalized ree patterns with lree enrichment flat hree and negative eu anomaly also are attributed to felsic source rock characteristics for kudankulam sandstones total ree concentrations of these sandstones reflect the variations in their grain size fractions the source rocks are probably identified to be proterozoic gneisses charnockites and granites of the kerala khondalite belt which must have been exposed at least since the late miocene finally the unusual ni enrichment in the kudankulam sandstones unaccompanied by a similar enrichment in cr co and v may be related to either the presence of pyrite in the sandstones or more likely the fractionation of garnet from the source rocks during transportation

seasonality intensification and long term winter cooling as a part of the late pliocene climate development abstract a mutual climatic range method is applied to the mediterranean marine pollen record of semaforo vrica section calabria italy covering the period from 2 46 ma to 2 11 ma the method yields detailed information on summer annual and winter temperatures and on precipitation during the nine obliquity and precession controlled glacial periods marine isotope stages 96 to 80 and eight interglacial periods marine isotope stages 95 to 81 characterising this time interval the reconstruction reveals higher temperatures of at least 2 8 c in mean annual and 2 2 c in winter temperatures and 500 mm in precipitation during the interglacials as compared to the present day climate in the study area during the glacials temperatures are generally lower as compared to the present day climate in the region but precipitation is equivalent along the consecutive interglacials a trend toward a reduction in annual and winter temperatures by more than 2 3 c and toward a higher seasonality is observed along the consecutive glacials a trend toward a strong reduction in all temperature parameters of at least 1 6 c is reconstructed climatic amplitudes of interglacial glacial transitions increase from the older to the younger cycles for summer and annual temperatures the cross spectral analyses suggest obliquity related warm humid cold dry interglacial glacial cycles which are superimposed by precession related warm dry cold humid cycles a time displacement in the development of temperatures and precipitation is indicated for the obliquity band by temperatures generally leading precipitation change at 4 kyr and on the precession band of 9 6 kyr in maximum

the influence of sediment recycling and basement composition on evolution of mudrock chemistry in the southwestern united states this paper reports systematic changes in mudrock composition through time on a single con tinental cmstal block the changes reflect both sediment recycling processes and changes through time in the composition of crystalline material being added to the sedimentary system and are related to tectonic evolution as the block matures from a series of accreted arc terranes to a stable craton the major and trace element distributions reflect different aspects of the provenance of the mudrocks in this study major elements record sediment recycling processes as well as changing proportions of sedi mentary and first cycle source rocks with the exceptions of kzo which tends to increase and sioz and a o3 which show no trend most major oxides tend to decline in relative abundance in younger mud rocks patterns shown by the index of compositional variability fe03 kro naao cao mgo mno tiojialro and by k20 a1203 indicate that the major oxide trends are due to decreasing proportions of nonclay silicate minerals and a concomitant increase in the proportion of clay minerals probably due to decreasing input of first cycle detritus coupled with recycling of sedimentary material excursions from progressive trends marked by increases in mgo k20 and cao reflect episodes of large scale input of nonclay first cycle minerals from crystalline source rocks due to large scale basement uplift the chemistry of low solubility trace elements in contrast is not sensitive to recycling effects and reflects the composition of first cycle input incompatible elements are progressively enriched relative to compatible elements in younger mudrocks and values for chondrite normalised rare earth elements also increase in addition the eu anomaly becomes systematically more negative in younger samples these trends cmnot be explained by diagenetic or weathering processes and therefore indicate that the proportion of fnc tionated granitic first cycle detritus being added to the sedimentary system becomes greater with time these results confirm the importance of tectonic setting in controlling mudrock chemistry and also demonstrate that there is a dynamic relationship between the tectonic evolution of a continental block and the composition of its sedimentary mantle

thermal evolution and geometry of the descending lithosphere beneath the se carpathians an insight from the past abstract mantle heterogeneities imaged by seismic tomography in the se carpathians contain information on the present thermal state of the mantle based on p wave seismic velocity anomalies we develop a model of the present mantle temperature beneath the region and combine the model with a model of crustal temperature constrained by heat flow data the modeled temperatures are assimilated into the geological past using the information on the regional movement in the early and middle miocene prominent thermal states of the lithospheric slab descending in the region are restored from its diffuse present state in miocene times the slab geometry clearly shows two portions of the sinking body the northwest southeast oriented portion of the body is located in the vicinity of the boundary between the east european and scythian platforms and this portion of the sinking body may be a relic of cold lithosphere that has traveled eastward another portion has a northeast southwest orientation and is related to the present descending slab above a depth of 60 km the slab had a concave thermal shape confirming the curvature of the carpathian arc and a convex surface below that depth the slab maintained its convex shape until it split into two parts at a depth of about 220 km we propose that this change in the slab geometry which is likely to be preserved until the present can cause stress localization due to the slab bending and subsequent stress release resulting in large mantle earthquakes in the region also we hypothesize that either the processes of dehydration and partial melting of the descending lithospheric slab or dragging down of hotter rocks from the adjacent uppermost mantle by the slab are possible causes of the reduction in seismic velocities beneath the transylvanian basin

behavior of major and trace elements including ree during paleoproterozoic pedogenesis and diagenetic alteration of an archean granite near ville marie quebec canada abstract this paper presents a complete set of chemical data from a pre 2 0 ga weathering profile that formed on the archean granite near ville marie quebec examination of data from two sections of the paleosol indicates that na ca p and sr were lost from the paleosol whereas ti nb th zr hf and ta remained immobile during chemical weathering and all subsequent alteration rare earth mobility during genesis of the ville marie paleosol closely follows the pattern of early stages of chemical weathering in modern profiles average concentration of ree in both profiles is 20 40 lower than what is found in the fresh granite suggesting mobilization during pedogenesis hrees seem to be less mobilized than the lrees la sm n ratios gradually decrease toward the top of the paleosol but the values remain very close to that of the protolith gd yb n values remain unchanged in the weathering profile la yb n values in the weathering profile are quite variable and generally lower than that of the protolith eu eu and ce ce values are essentially the same as those of the protolith but two samples from the uppermost part of the profile have developed positive cerium anomaly of 0 3 relative to the protolith

provenance determined by ree th and sc analyses of metasedimentary rocks boyden cave roof pendant central sierra nevada california abstract ree th and sc analyses of metasedimentary rocks collected from the western sequence of the boyden cave roof pendant when compared with similar analyses of uppermost precambrian to cambrian miogeoclinal mudstones from the nopah range support the idea that rocks from the former area are a part of a large tectonically displaced fragment of the cordilleran miogeocline as proposed by r a schweickert and m m lahren for example ree distribution diagrams for samples from the western sequence of the boyden cave pendant show parallel light ree enrichment trends and negative eu anomalies that range from 0 61 to 0 86 and average 0 69 likewise ree distribution patterns for samples from the uppermost precambrian to cambrian cordilleran miogeoclinal section in the nopah range also show p rallel light ree enrichment trends and eu anomalies that range from 0 65 to 0 75 and average 0 68 on a la th se diagram samples from the boyden cave pendant cluster with specimens from the nopah range finally sediments from both areas have broadly similar th sc and th u ratios these results suggest that samples from the western sequence of the boyden cave pendant are composed of detritus like that shed from differentiated western north american upper continental crust during the early development of the cordilleran miogeocline such an interpretation is consistent with 1 the quartz rich to slightly feldspathic character of sandstones in the boyden cave pendant which implies a continental to transitional continental block provenance 2 a precambrian u pb age for detrital zirco extracted from a single sandstone bed and 3 the complete absence of volcanic material in the western sequence of the boyden cave pendant our results support the regional correlations and tectonic model proposed by r a schweickert and m m lahren and further suggest that although underutilized ree th and sc analyses are useful in evaluating stratigraphic sedimentologic and tectonic problems in complexly metamorphosed and deformed metaclastic terranes

slab behaviour and its surface expression new insights from gravity modelling in the se carpathians abstract we use lithosphere scale gravity models to calculate gravity anomalies resulting from oceanic subduction continental collision slab steepening delamination and break off local isostasy was assumed for determining vertical movements caused by mass changes related to these tectonic processes our results show that subduction is accompanied by basin subsidence on the upper plate caused by the heavy lithospheric root of the subducting slab the basin evolution goes parallel with the slab evolution and shows considerable modifications when the processes at depth change slab steepening delamination break off characteristic gravity anomaly curves were acquired for the different tectonic scenarios these curves together with other data e g basin evolution on the upper and the lower plate were used for the reconstruction of the tectonic evolution of the se carpathians which includes tertiary subduction and collision followed by slab steepening and delamination

three dimensional numerical modeling of contemporary mantle flow and tectonic stress beneath the earthquake prone southeastern carpathians based on integrated analysis of seismic heat flow and gravity data the principal purpose of the study is to understand the interplay between intermediate depth large earthquakes in the southeastern carpathians vrancea and tectonic stress induced by a high velocity body lithospheric slab descending into the mantle beneath the region to analyze processes of stress generation and localization in and around the descending slab we develop a three dimensional 3d numerical model of contemporary mantle flow and stress beneath the vrancea region the input data of the model consist of i temperatures derived from seismic p wave velocity anomalies and surface heat flow ii crustal and uppermost mantle densities converted from p wave velocities obtained from seismic refraction studies iii geometry of the vrancea crust and slab from tomography and refraction seismic data and iv the estimated strain rate in the slab as a result of earthquakes to constrain the model viscosity we find that major crustal uplifts predicted by the model coincide with the east carpathian orogen and surround the transylvanian basin and that predicted areas of subsidence are associated with the moesian and east european platforms we show a correlation between the location of intermediate depth earthquakes and the predicted localization of maximum shear stress modeled tectonic stresses predict large horizontal compression at depths of about 70 220 km beneath the vrancea region which coincides with the stress regime defined from fault plane solutions for the intermediate depth earthquakes this implies that buoyancy driven descent of the lithospheric slab beneath the vrancea region is directly linked to intermediate depth seismicity 2004 elsevier b v all rights reserved

geochemical characteristics and organic matter enrichment mechanism of black shale in the upper triassic xujiahe formation in the sichuan basin implications for paleoweathering provenance and tectonic setting abstract the first third and fifth members henceforth referred to as t 3 x 1 t 3 x 3 and t 3 x 5 respectively of the upper triassic coal bearing xujiahe formation black shale are among the most significant hydrocarbon source rocks in the sichuan basin here we present geochemical data for the upper triassic black shales from core from well ld 1 to determine their paleoenvironmental conditions paleoweathering provenance transitions and tectonic setting the v v ni vs u th v cr vs u th and ni co vs u th bivariate plots and the tfe toc ts total fe total organic carbon total sulphur ternary diagram indicate that the synsedimentary redox regime of almost all the shale samples was oxidizing ba al sr al and p ti data combined with quantitative biogenic ba data indicate that moderate high primary paleoproductivity levels prevailed during deposition the sr cu ratio and c value combined with the sedimentary features are indicative of warm humid climate conditions the ti al deposition rate proxy and decompacted sedimentation rate are positively correlated with the total organic carbon toc content according to our multiproxy approach black shale development in the xujiahe formation was mainly controlled by the primary productivity level foreland basin setting high tectonic subsidence and sedimentation rate and exhibited a limited correlation with water column redox conditions through the compilation and calculation of various weathering indices for the xujiahe black shale we suggest that caution must be taken when inferring paleoclimate characteristics based on the chemical index of alteration cia because of the influence of multiple nonweathering factors provenance sensitive elemental ratios th sc vs zr sc and co th vs la sc indicate that the clastic contribution to xujiahe black shales was of a predominantly felsic character the black shales exhibit a transition from t 3 x 1 to t 3 x 3 to t 3 x 5 whereby t 3 x 1 was primarily sourced from the proterozoic to early paleozoic strata of the qinling orogeny t 3 x 3 was primarily sourced from the neoproterozoic complex in the longmen shan and t 3 x 5 was primarily sourced from the songpan ganzi flysch strata which contributed recycled material because of folding and strong southeastward thrusting

a method for climatic reconstruction of the mediterranean pliocene using pollen data pollen data from numerous sites around the mediterranean sea indicate that several important vegetation and climatic changes occurred during the pliocene these data are in good agreement with pollen records from northwest europe and with 18o curves from mediterranean and atlantic deep sea cores quantitative palaeoclimatic reconstructions from pliocene pollen data of the mediterranean region cannot be based on conventional modern analogue techniques as individual pliocene pollen spectra contain taxa representing temperate warm temperate and subtropical plants that do not grow together today instead we propose a new method that uses a climatic amplitude method modified to take partially into account the relative abundances of the taxa we applied this method to the pliocene garraf 1 palynological sequence from catalonia which provides a long continuous record of climatic change from 5 3 ma to the early pleistocene we estimate that annual temperatures were 1 to 5 c higher than today and the annual precipitation 400 to 1000 mm higher than today prior to the beginning of the late cenozoic glacial interglacial cycles in contrast temperature and precipitation both fell sharply during the glacial phases of the earliest glacial interglacial cycles

impact of short term climatic events on latest pliocene land settings and communities in central italy upper valdarno basin abstract the upper valdarno italy plio pleistocene continental deposits record the latest uniform subtropical humid conditions and the successive climatic signature of glacial interglacial cycling the palynological and sedimentological analyses on the poggio rosso alluvial plain sediments reveal two major climatic fluctuations correlated to a glacial interglacial cycle just before the plio pleistocene boundary the glacial phase indicated by the expansion of herbs as well as by ephemeral streams associated with calcareous palaeosols extends from the base of the succession and culminates close to an impressive mammalian bone accumulation dated at 1 87 ma the associated increasing aridity had severe consequences on the faunal communities inducing the migration of open plain dwellers and the trapping of other residents around a few residual shrinking water bodies a cooperative pachycrocuta brevirostris clan acted as regulator of game populations debilitated by drought previous research indicates that hyenas were also the major bone accumulators the following moister and warmer interglacial phase ca 1 83 ma is documented by arboreal taxa and hydromorphic palaeosols in a floodplain crossed by migrating perennial sinuous streams the climatic amplitude method calculated mean annual temperatures around 12 5 14 c and mean annual precipitation around 800 mm with a minimum of 400 mm during the glacial phase and 15 16 19 c and 750 1200 mm during the interglacial phase the reconstruction reveals higher mean annual temperatures and precipitation during the interglacial as compared to the present day climate during the glacial conditions were similar to today s in all but lower precipitation values were reached during the acme drought phase just above the fossiliferous bed poggio rosso documents the ecological consequences the buildup of the apennine chain had under the effects of the latest pliocene global climatic changes it therefore represents one of the first signals of the patchiness that since then gradually increased leading to the eventual habitat fragmentation typical of the late pleistocene landscapes

sediment chemistry and detrital zircon record in the bosque and paseo del mar coastal areas from the southwestern gulf of mexico abstract in this study we analyzed the mineralogy and bulk chemical composition of 20 sediment samples as well as trace rare earth element ree concentrations and u pb ages of 400 detrital zircons retrieved from the bosque pb and paseo del mar pm coastal sediments southwestern gulf of mexico to investigate the provenance the xrd study revealed that the pb sediments are associated with quartz muscovite cordierite albite and anorthite the pm sediments are associated with calcite aragonite and biogenic materials which derived probably within the coastal environment the weathering indices like chemical index of alteration cia chemical index of weathering ciw and plagioclase index of alteration pia revealed a moderate intensity of weathering for the pb sediments the chondrite normalized ree patterns of the pb and pm sediments are with negative and positive europium anomalies eu eu suggesting that the sediments were derived by the combination of felsic and mafic source rocks the th u ratios 0 3 of the pb and pm zircons indicated an igneous origin the chondrite normalized ree patterns of the pb and pm zircons are depleted in low ree lree and enriched in heavy ree hree with positive cerium and negative europium anomalies a wide variation in chondrite normalized ree patterns of zircons with respect to ages was observed the pb is dominated by proterozoic 551 2500 ma and paleozoic zircons 445 480 ma ordovician whereas pm is dominated by cenozoic zircons 5 21 ma miocene indicating that the zircons were derived from different source terranes the chiapas massif cmc and chuacus complexes are identified as the potential source areas which contributed proterozoic zircons to pb on the other hand cuicateco terrane cui and tuxtla volcanic field tvf are considered as the potential source areas which supplied significant number of cenozoic zircons to the pm coastal area the zircon u pb ages and the bulk sediment geochemistry together indicate that the source terranes which supplied sediments to the pb and pm coastal areas consist of mafic and felsic rocks the results of this study further illustrated the importance of littoral currents in distributing sediments although rivers are considered as a carrier and agent of distributing sediments along the coastal areas

geochemical signature of provenance in sand size material in soils and stream sediments near the tobacco root batholith montana u s a abstract trace element geochemistry of sandstones are being used to determine provenance we have conducted preliminary and limited experiments to determine to what extent daughter sands retain the geochemical signature of parent rocks six sets of first order stream sediments soils from adjacent slopes and a variety of parent rocks were collected from southwestern montana u s a sampling in a low relief area ensured that climate and residence time of soils on slopes could be eliminated as variables sand size fractions of stream sediments and soils and the corresponding parent rocks granodiorite quartz monzonite granite gneiss biotite tonalite gneiss and amphibolite were analyzed for most major elements and selected trace elements petrologic modal analysis of the parent rocks and the 0 25 0 50 mm fraction of each sand was done to monitor major mineralogic control if any on chemical compositions of the samples our data show that the abundances of the si and al in sediments do not discriminate provenance abundances of ca mg fe and ti may broadly distinguish between sands derived from metamorphic and igneous source rocks at least in the area studied differences in abundances of the ba and th and the ratio of la lu between granitic tonalitic and amphibolitic parent rocks are preserved in the daughter sediments that we studied however the size of the eu anomaly in the ree patterns of different daughter sediments is not diagnostic of parent rocks abundances of co and sc distinguish between sediments derived from felsic and mafic rocks a better provenance discrimination is obtained if the ratios la sc th sc la co ba sc and ba co are used petrologic modal data show that mineral contents and chemical compositions of parent rocks are compatible with each other the chemical composition of the sands may be roughly correlated to the petrological modal data but the abundances of some minor and trace elements of sediments cannot be inferred from modal mineralogy this is expected because these elements may concentrate in accessory minerals and or may weather out into aqueous or clay mineral fractions it is also compatible with conclusions of previous studies that some of these elements do not reside in sand size fractions of siliciclastic sediments

europium redox equilibria in aqueous solution thermochemical data and recent advances in theoretical aqueous solution chemistry enable prediction of the relative stabilities of aqueous eu2 and eu3 over a wide range of temperatures and pressures at low temperatures near earth surface conditions the aqueous geochemistry of europium should be dominated by the trivalent state except possibly in the most reducing alkaline pore waters of anoxic marine sediments however at temperatures greater than about 250 c and elevated pressures divalent europium should predominate even with significant amounts of complexing trivalent europium is not stable at elevated temperatures and pressures consequently under most hydrothermal and metamorphic conditions europium in aqueous solution should be divalent at intermediate temperatures around 100 c significant activities of both eu2 and eu3 and related complexes can occur in aqueous solutions depending on the oxidation state and the ph of the solutions and the activities of potential ligands such as sulfate carbonate and chloride the predicted stability of divalent europium in aqueous solution at elevated temperatures is consistent with the large positive europium anomalies in rare earth element patterns of high temperature barites of hydrothermal and metamorphic origin reported by guichard et al 5 and with the observed depletion of europium as a result of high temperature sericitization of feldspar bearing assemblages discovered by alderton et al 1 it is suggested that significant fractionation of europium relative to the other rare earth elements may take place during high temperature hydrothermal alteration processes such as in the mid oceanic ridge systems because of the expected stability of divalent europium during these processes

calderas in the precambrian terrane of the st francois mountains southeastern missouri precambrian igneous rocks in the st francois mountains of southeastern missouri consist of silicic volcanic rocks mostly ash flow tuff which crop out mostly in the western and southwestern part of the region and epizonal granitic plutons which are mostly exposed in the northeastern part of the area these relations suggest that the exposures in the northeast are of a somewhat deeper part of the crust and that rocks there are now exposed because of west southwesterly tilting and beveling by erosion in the eastern st francois mountains the occurrence of a thick rhyolitic ash flow tuff grassy mountain ignimbrite and its distribution relative to a large high silica pluton butler hill granite suggest that the ash flow is the principal eruptive material of a caldera the butler hill caldera and that butler hill granite is the frozen magma chamber that was originally beneath it structural relations indicate that butler hill granite was emplaced into the volcanic rocks of the caldera during resurgent doming four small low silica plutons silvermine stono knoblick and slabtown granites are distributed peripherally to the butler hill granite and are interpreted as ring plutons emplaced along the ring fracture of the caldera or along arcuate intracaldera faults after resurgent doming and emplacement of butler hill granite more than 3 km of silicic volcanic rocks occupy a basinal structure in the western st francois mountains these rocks lie with angular unconformity upon up domed older rocks of the butler hill caldera along an arcuate zone of megabreccia and disturbed structure on the western margin of the older caldera this feature is interpreted as the topographic wall of a second caldera which lies to the west the occurrence of the thick taum sauk rhyolite stratigraphically about 3 km higher than the rocks involved in the megabreccias may indicate that there was yet another caldera formed in this western part of the st francois mountains

trace element geochemistry and sedimentary provinces a study from the tasman geosyncline australia abstract the abundances of la th u and hf have been determined in flysch sequences of the tasman geosyncline australia the arc derived graywackes differ from those of rifted continental margins and marginal basins in containing low abundances of la th u and hf la 9 2 1 7 ppm th 1 4 0 6 ppm u 0 52 0 2 ppm hf 2 1 0 6 ppm reflecting similar low abundances in the andesitic source rocks graywackes of rifted continental margins and marginal basins in contrast are mature and characterised by high abundances of la th u and hf la 39 9 9 ppm th 16 0 6 ppm u 3 40 0 5 ppm hf 7 9 ppm mirroring increased abundances in the granitic and sedimentary source rocks sedimentary rocks deposited in inter arc basins show wide dispersion but have characteristics intermediate between these two types the th u ratio for magmatic arc sediments is 2 7 for most other sedimentary rocks it remains uniform at 4 5 0 3 for sediments having andesitic and dacitic rocks as provenance the la th ratios are 6 7 and 4 5 respectively this ratio remains constant at 2 6 for most quartzose sedimentary rocks

biochronology and biochron boundaries a real dilemma or a false problem an example based on the pleistocene large mammalian faunas from italy abstract reconstructing the neogene quaternary biostratigraphy in continental environments and recognising boundaries between successive mammalian faunal complexes is a problematic task the definition and application of biochronology has been often tainted by references to and inferences from biostratigraphy actually the discontinuities in the continental sedimentary record environmental conditions taphonomic and sampling biases are responsible for the fact that the stratigraphical order of the lowest and highest occurrences of fossil remains stratigraphic datum does not necessarily reflect the temporal order of actual first last appearances of taxa palaeobiological events in time nonetheless the first last appearance bioevents recorded by lowest highest occurrences of fossil remains in fossiliferous levels of different continental stratigraphical successions have been the principal foundation for establishing the biochronological setting of continental mammal faunas therefore from a theoretical point of view boundaries should be defined by the oldest and or youngest historical occurrence of one or more taxa what about an operational approach some examples of the italian faunas are presented focusing on the transition from the villafranchian to the galerian and from the galerian to the aurelian land mammal ages the results obtained indicate the difficulty of defining a stable scheme that can be applied for correlation by the international scientific community

tectonic influence on sedimentation along the southern flank of the late paleozoic magdalen basin in the canadian appalachians geochemical and isotopic constraints on the horton group in the st marys basin nova scotia the late devonian early carboniferous st marys basin in mainland nova scotia canada consists of horton group intracontinental clastic rocks that were deposited along the avalon meguma terrane boundary during the waning stages of the acadian orogeny and prior to terminal collision in the appalachian orogen these rocks represent the earliest stages of deposition along the southern flank of the composite magdalen basin late devonian to permian that extends over much of maritime canada and oversteps terrane boundaries in the canadian appalachians as such the horton group represents deposition in an episutural basin the horton group in the st marys basin predominantly consists of 3000 4000 m of clastic sedimentary rocks deposited in fluviatile and lacustrine nearshore environments geochemical analyses of clastic rocks reveal a range of sio2 content 60 94 wt high total rare earth elements and initial 87sr 86sr and strongly negative nd t t 360 ma the signature of the passive margin to active continental margin implied by standard discrimination diagrams probably is inherited largely from rocks in the source region and is not an indication of the setting in which the basin formed although the data indicate that some lithologies contain a minor avalonian basement component the geochemical and isotopic signatures of the sedimentary rocks reveal mixed sources that can be attributed largely to uplift and erosion of meguma terrane metasedimentary and granitoid rocks immediately to the south of the st marys basin regional syntheses indicate that this uplift occurred before and during horton group deposition and was coeval with dextral ramping of the meguma terrane over the avalon terrane along the southern flank of the magdalen basin

late pliocene northern hemisphere glaciations the continental and marine responses in the central mediterranean abstract detailed pollen analyses and oxygen isotope records of three foraminiferal species globigerina bulloides uvigerina peregrina and cibicides pachyderma from the semaforo and vrica composite sections crotone southern italy have been compared to the global climatic changes depicted by late pliocene early pleistocene foraminiferal 18o records of site 607 in the north atlantic and hole 653a in the tyrrhenian basin west mediterranean major overturns in the mid altitude vegetation are shown near isotopic stages 82 60 58 and 50 at about 2 03 ma 1 6 ma and 1 37 ma according to the raymo et al 1989 and ruddiman et al 1989 timescales at the same dates glacial 18o maxima either became higher or display step increases in the western mediterranean or in the open ocean as well this suggests that size increases of northern hemisphere ice sheets were the driving factor for regional or local marine and continental environmental changes within the mediterranean basin near isotopic stages 62 60 close to the conventional plio pleistocene boundary the climatic conditions severed enough within the mediterranean basin to modify the continental environment as depicted by a sudden increase of artemisia percentages while the first significant southward migration of the north polar front may have been recorded by an influx of left coiling neogloboquadrina pachyderma in the central mediterranean it also appears that boreal guests entered the mediterranean during phases of 18o enrichment of foraminiferal calcite there does not seem to be any discrepancy between the climatic concept of the pliocene pleistocene boundary and its chronostratigraphic definition

an integrated study of geochemistry and mineralogy of the upper tukau formation borneo island east malaysia sediment provenance depositional setting and tectonic implications abstract an integrated study using bulk chemical composition mineralogy and mineral chemistry of sedimentary rocks from the tukau formation of borneo island sarawak malaysia is presented in order to understand the depositional and tectonic settings during the neogene sedimentary rocks are chemically classified as shale wacke arkose litharenite and quartz arenite and consist of quartz illite feldspar rutile and anatase zircon tourmaline chromite and monazite all of them are highly matured and were derived from a moderate to intensively weathered source bulk and mineral chemistries suggest that these rocks were recycled from sedimentary to metasedimentary source regions with some input from granitoids and mafic ultramafic rocks the chondrite normalized ree signature indicates the presence of felsic rocks in the source region zircon geochronology shows that the samples were of cretaceous and triassic age comparable ages of zircon from the tukau formation sedimentary rocks granitoids of the schwaner mountains southern borneo and tin belt of the malaysia peninsular suggest that the principal provenance for the rajang group were further uplifted and eroded during the neogene additionally presence of chromian spinels and their chemistry indicate a minor influence of mafic and ultramafic rocks present in the rajang group from a tectonic standpoint the tukau formation sedimentary rocks were deposited in a passive margin with passive collisional and rift settings our key geochemical observation on tectonic setting is comparable to the regional geological setting of northwestern borneo as described in the literature

geodynamics and intermediate depth seismicity in vrancea the south eastern carpathians current state of the art abstract the vrancea region of the south eastern carpathians is a remarkable site of intra continental intermediate depth seismicity a large set of geological geophysical and geodetic observations has been accumulated for the last few decades and utilised to improve our knowledge of the shallow and deep structures beneath vrancea the crustal and mantle dynamics and the linkage between deep and surface processes in the region in this article we review geology and tectonics of the vrancea region including post collisional to recent deformations syn to post collisional magmatism and orogenic exhumation along the east and south carpathians the regional seismicity is analysed and the recent seismic studies including reflection refraction body and surface wave tomography are reviewed we discuss new geodetic measurements of horizontal and vertical movements in the region geoelectric studies density gravity and thermal modelling qualitative and quantitative including retrospective geodynamic models developed for vrancea are analysed the knowledge of regional tectonics geodynamics seismicity lithospheric deformation and stress regime in the vrancea earthquake prone region assists in an assessment of strong ground motion seismic hazard and risk the earthquake simulation seismic hazard and earthquake forecasting models have also been reviewed providing a link between deep geodynamic processes and their manifestation on the surface finally we discuss unresolved problems in vrancea in order to improve our understanding of the regional evolution present tectonics mantle dynamics intermediate depth seismicity and surface manifestations of the lithosphere dynamics and to enhance our ability to forecast strong earthquakes in the vrancea region the problems to be solved include i the origin of the high velocity body revealed by seismic tomography studies oceanic versus continental ii the lithospheric scale mechanism driving the miocene subsidence of the transylvania basin iii sub crustal structure between 40 and 70 km iv contemporary regional horizontal and vertical movements and v a comprehensive seismic hazard assessment in the region

pollen record from colle curti and cesi early and middle pleistocene mammal sites in the umbro marchean apennine mountains central italy the palynological record from the colle curti and cesi continental deposits has been examined in order to identify the main palaeofloristic and vegetational changes between 0 99 and 0 6 0 7 ma these data show a progressive increase in aridity as well as a progressive decrease in temperature which are associated with the transition in dominance from the 41 to 100 ka cyclicity in the milankovitch orbital record during the middle pleistocene the disappearance of tsuga recorded during the lower part of the brunhes chron also has been related to a shift in global aridity during the successive open vegetational phases glacials chenopodiaceae and artemisia progressively increase whereas cyperaceae decrease forest phases interglacials are successively dominated by tsuga abies with picea and finally pinus but all lack significant expansion of broad leaved deciduous taxa palynological and sedimentological data in addition to taphonomic interpretations demonstrate the occurrence of several hiatuses in the lower parts of the interglacials these hiatuses are considered to represent the palaeoenvironmental response to climatic changes affecting local sedimentological and geomorphological conditions copyright 2000 john wiley sons ltd

geochemistry of 1 8 1 67 ga mudstones and siltstones from the mount isa inlier queensland australia provenance and tectonic implications abstract sedimentary and volcanic rocks overlying basement in the mount isa inlier australia are subdivided into three cover sequences the upper two sequences range in age from 1800 to 1670 ma and each consist of rift and overlying sag phases of sedimentation fine grained siliciclastic sedimentary rocks in the upper two sequences define two distinct geochemical groups samples from groups i and ii are mainly from the lower and upper rift and upper thermal phases respectively one sample from the lower rift phase has affinities with group ii whereas samples from the lower thermal phase belong to both groups i and ii eu eu values are 0 70 to 0 85 for group iand 0 55 to 0 70 for group ii group i samples are characterized by lower la sc and th sc ratios and higher cr th ratios than group ii cr niand co concentrations are greater in group i than group ii groups i and ii also are distinguished on plots of eu eu vs lan smn and eu eu vs gdn ybn two samples from group i have elevated lree hree and lan ybn ratios that are attributed to intense weathering as revealed by their high chemical index of weathering values the geochemical data reflect a combination of local and more distant regional provenances and can be related to the tectonic evolution of the mount isa inlier group i samples are attributed to dilution of a mature post archean source by addition of recycled mafic volcanics group ii samples are typical post archean sediments derived from differentiated upper continental crust with no dilution by local sources the lower rift phase displays great geochemical variability samples from both groups that is typical of active tectonic settings such as rifts the great variability of samples from the lower sag phase both groups is surprising but probably reflects the diverse rock types beneath this basin stable tectonic conditions during this phase of sedimentation are indicated instead by major element geochemistry that records severe weathering similarity of the upper rift phase sample with some samples from the lower sag phase reflects recycling of the latter samples from the upper sag phase are remarkably uniform in composition group ii and reflect the stable tectonic conditions under which this basin developed

arid climate 2 5 ma in the plio pleistocene valdarno basin northern apennines italy abstract distinctive eolian dominated sandy deposits 35 m thick exposed along the sw margin of the plio pleistocene valdarno basin in the northern apennines italy reflect an unusually arid period in the region paleomagnetic investigation and 40 ar 39 ar dating of a tephra layer 10 m above the eolian sand suggest that the sand was deposited between about 2 7 and 2 4 ma this age is coeval with the global climatic deterioration that occurred at the middle upper pliocene transition eolian sediments are represented by cross bedded sand rippled sand and horizontal bedded sand the alluvial deposits associated with the eolian sediment consist of sheet like beds of coarse sand and erosively based pebbly sand bodies eolian sand together with fluvial sandy deposits was formed in the medial distal portion of an alluvial system and represents the rena bianca sand unit the eolian and alluvial deposits are arranged into sedimentary cycles 2 6 m thick displaying a wetting drying wetting upward trend recording second order climatic oscillations of ca 40 ka each cycle is enclosed between major bounding surfaces defined by iron mineral encrustations these bounding surfaces represent periods of reduced eolian sand accumulation caused by a rising water table during the 2 5 ma global cooling the valdarno basin experienced a period of arid conditions owing to the influence of cold and dry easterly and northeasterly winds in contrast during the pleistocene the uplift of the pratomagno ridge protected the valdarno basin from easterly and northeasterly winds giving rise to relatively warm and wet conditions and mitigating the regional and global climatic changes

implications of elemental concentrations for provenance redox conditions and metamorphic studies of shales and limestones near pueblo co usa abstract major element and some trace element compositions including the ree of shales carbonate rich shales and limestones of late cretaceous age have been analyzed at two outcrops near pueblo co elemental ratios that are characteristic of the provenance of terrigenous debris that are the least variable with changing percent acid insoluble residue vs percent calcite are th cr la co la lu cn and eu eu the ce ce la sc and la cr ratios however are only constant when greater than 30 of a sample is composed of acid insoluble residue at less than 30 acid insoluble residue these elemental ratios increase markedly the th co and th sc ratios are fairly constant from nearly 0 to about 60 acid insoluble residue above 60 residue these ratios increase due to the high concentration of th in the graneros to hartland shales at everhart ranch the average of the th co th sc th cr la co la sc and la cr ratios are similar to those of the mcs mid continent shales and paas post archean australian shales thus these carbonate rich to carbonate poor rocks analyzed in this study contain terrigenous debris that has been derived from granitoids similar to those that supplied debris to the mcs and paas the ce ce ratios are lower and the mn mn log mn sample mn shales fe sample fe shales values are more positive in the more calcite rich bridge creek and ft hays limestones than in the other units suggesting that they formed in an oxidizing environment the ce ce are the highest and the mn values are the most negative in the graneros to hartland shales suggesting that they formed under more reducing conditions the elemental concentration of one sample relative to that of another sample over a few meters distance usually vary in small amounts e g medians of the ratios of the same elements between adjacent samples ranges from 1 06 to 1 70 however the ratio of elemental concentrations between adjacent samples can sometimes be quite large the least variation of elemental ratios between adjacent samples often occurs within the more carbonate poor shales the greatest variation occurs within the limestones thus trying to decipher local movement of elements due to metamorphism in similar carbonate shale limestone sequences should be done cautiously since local elemental variation due to sedimentary processes can be large

introduction to the special issue actualistic models of sediment generation conceptual models in sedimentary petrology that relate verticaland lateral compositional signatures during the lling of sedimentarybasins to their internal and external control factors have beendeveloped in the 80 ies and 90 ies of the last century althoughre ned petrographic and geochemical analyses have focussed ondeciphering complex events in time and space such as tectonic evo lution of source terranes changes in sediment dispersal patterns orpalaeoclimate uctuations quantitativemodelsarestillintheirinfancy despite a long history of research one reason for this state of affairs isthe strong interdisciplinary nature of the subject matter another isthe lack of appropriate modelling tools capable of dealing with thecomplex nature of sediment properties the recent proliferation ofquantitative data acquisition techniques coupled with progress indata processing and modelling approaches has led to the emergenceof a new eld of study aimed at solving the fundamental problem ofreconstructing mass transfer from source areas to sedimentary basins the term sediment generation acts as a convenient umbrella for thecomplex web of processes acting between source and sink quantitative models of sediment generation aim at providing anassessment of the type amount and rateof supplyof detritalmaterialfrom identi able parent rock assemblages to a basin ll in order toful l this objective two key questions must be addressed i how much sediment is being delivered ii what are the compositional and textural characteristics of thesediment the rst question is intimately connected to sediment budget as sessments and their derivative with respect to time i e erosion ordenudation and sedimentation rates the second one refers to the

major and trace element characterization of oceanic anoxic event 1d oae 1d insight from the umbria marche basin central italy abstract the pialli level in the umbria marche basin central italy correlates with the lowermost part of the positive carbon isotopic excursion characterizing the late albian early cenomanian oceanic anoxic event 1d oae 1d high resolution litho bio and chemostratigraphic data from the monte petrano and le brecce sections allow for a bed by bed comparison of the two successions and discriminate local from basin scale signals we present new x ray fluorescence icp ms and toc data for both the limestones and the pialli level shales integrated with available carbonate carbon isotopes and nannofossil temperature and nutrient indices data indicate a homogenous background sedimentation dominated by pelagic carbonates biogenic silica with little contribution by clays the limited variation in lithogenic elements points to an essentially homogeneous detrital source area with limited fluvial terrigenous input higher mn concentrations coupled with low enrichments in redox sensitive elements such as u fe s re mo ag suggest that the pialli level shales represent temporary suboxia without reaching anoxia furthermore p authigenic ba cd and ni enrichments together with nannofossil nutrient index indicate generally low primary productivity conditions along the entire succession with only minor increases for some of the black to dark grey shales of the pialli level the nannofossil temperature index highlights a warm climate during the oae 1d with the warmest conditions experienced during the deposition of the pialli level shales during the late albian the warm and humid climate was interrupted by brief episodes of relatively warmer and less saline surface waters ensuring slower rates of bottom water renewal and producing temporary suboxic conditions such paleoceanographic dynamics would be the continuation of episodic warmer and humid pulses characterizing the late albian interval in the umbria marche basin as such the pialli level can be considered the result of a last episode closing a cycle before the establishment of a steadier climate during the early cenomanian

vegetation response to upper pliocene glacial interglacial cyclicity in the central mediterranean abstract new detailed pollen analysis of the lower part of the upper pliocene semaforo section crotone italy documents cyclic behavior of vegetation at the beginning of the northern hemisphere glaciations the competition between four vegetation units subtropical humid forest deciduous temperate forest altitudinal coniferous forest and open xeric assemblage probably reflects modifications of vegetation belts at this montane site several increases in herbaceous open vegetation regularly alternate with subtropical humid forest which expresses rapid climatic oscillations the complete temporal succession deciduous forest rich in quercus followed by subtropical humid forest taxodiaceae and cathaya then altitudinal coniferous forest tsuga cedrus abies and picea and finally herbaceous open vegetation graminae compositae and artemisia displays the climatic evolution from warm and humid interglaciation to cold and dry glaciation it also suggests an independent variation of temperature and humidity the two main climatic parameters the vegetation history of southern calabria recorded in the semaforo section have been correlated with the 18o signal established in the atlantic ocean