the peraluminous aurumina granite suite in central brazil an example of mantle continental crust interaction in a paleoproterozoic cordilleran hinterland setting abstract peraluminous granites and tonalites granodiorites of the aurumina suite crop out in the external zone of the brasilia fold belt on the western margin of the sao francisco craton rocks of this suite intrude retrograde medium grade schists and paragneisses of the ticunzal formation and display a magmatic muscovite biotite garnet assemblage and discrete graphite lamellae the suite is divided into six members au1 through au6 which grade from synkinematic to post kinematic in character with ages spanning from 2 11 to 2 16 ga according to zircon u pb data compositional features of the aurumina suite and associated coeval metaluminous mafic to intermediate plutons suggest an origin by source hybridization processes characterized by reaction between metasedimentary rocks and basaltic melts that would have taken place at shallow depths pressure

ostracodes and paleoenvironments of the late quaternary don and scarborough formations toronto ontario type section exposures at the don valley brickyard and scarborough bluffs were studied for ostracode occurrences in all 12 species were identified from the don formation with candona rawsoni and

pb sr and nd isotope constraints on the archaean evolution of gneissic granitoid complexes in the southern sao francisco craton brazil abstract three archaean gneissic complexes bonfim belo horizonte and campo belo in the southern part of the sao francisco craton were studied by means of u pb zircon and titanite monazite and sm nd rb sr and pb pb whole rock methods in the bonfim metamorphic complex the period 2780 2700 ma is marked by in situ anatexis of gneisses intrusion of tonalites mafic dikes and late granites and deposition of the rio das velhas greenstone belt sm nd tdm model ages on its gneisses amphibolites and granites range from 2800 to 3000 ma indicating involvement of older sialic crust in the 2780 2700 ma event in the belo horizonte metamorphic complex u pb zircon geochronology has yielded ages of 2860 2776 and 2712 ma and rb sr whole rock isochrons on its gneisses and migmatites yielded ages in the range 2800 2750 ma with large uncertainties and 87sr 86sr initial ratios of 0 700 0 710 the highest initial ratio 0 710 obtained for the migmatites suggests that ensialic episodes participated in the tectonomagmatic evolution existence of older crust is suggested by u pb zircon ages of 3030 2920 and 2880 ma from inherited grains in metavolcanics and orthogneisses rb sr ages of 2250 2130 ma on granitoids and u pb titanite monazite ages from 2320 to 2030 ma on granitoids felsic veins and amphibolite enclaves indicate reworking of this complex in the palaeoproterozoic in the campo belo metamorphic complex granite and greenstone lithologies have yielded ages of 3380 3000 2900 and 2650 ma by u pb zircon and rb sr and pb pb whole rock methods tdm ages on its granites gneisses and granulites have yielded ages from 3070 to 2780 ma indicating involvement of older sialic material during the 2650 ma event these complexes indicate major events during the period 2860 2700 ma including reworking of established sialic crust with components up to 3380 ma old late granites were injected between 2700 2600 ma preceding final assembly and stabilization of the archaean crust

sedimentary and paleoclimatic controls on caddisfly insecta trichoptera assemblages during the last interglacial to glacial transition in southern ontario abstract southern ontario canada has late pleistocene deposits that contain evidence for climatic cooling during the last interglacial glacial transition and much of the succeeding wisconsin glaciation fossils of lacustrine and riverine caddisflies insecta trichoptera are abundant and well preserved in these deposits we examined 26 samples from the interglacial section exposed in the don valley brickyard and compared their caddisfly assemblages with those recovered from the overlying early wisconsin scarborough formation deposits at nearby scarborough bluffs fifty one caddisfly taxa in 16 families were recovered from the don valley site fossil abundance and species richness appear related to the storm or fair weather conditions inferred from the sedimentary facies caddisfly fossils were most abundant and species richness highest in fair weather peaty rippled sands highest proportions of river species as opposed to lake species were recovered from sands storm and fair weather assemblages from both sites indicate the presence of a large and productive river flowing into ancestral lake ontario however the river assemblage appeared to be far more sensitive to environmental change than the relatively stable assemblage representing the thermally buffered lake warm temperate river species such as hydropsyche bidens hydropsyche mississippiensis macrostemum carolina and potamyia flava are present in the lower don samples but absent from the scarborough bluffs deposits while indicators of cooler than present climatic conditions such as arctopsyche indogensis and hagenella canadensis are present in the scarborough bluffs sediments but absent from the lower don samples for the interval from about 80 000 to 55 000 yr b p we infer a climatic cooling from temperature about 2 c warmer than present to about 3 c cooler than present

implications of trace fossil assemblages from late paleozoic glaciomarine talchir formation raniganj basin india abstract the trace fossil assemblages of the ice marginal shallow marine sediments of the talchir formation permo carboniferous raniganj basin india record the adverse effect of extreme climatic conditions on biota the glaciomarine talchir succession starts with glacial sediments near the base and gradually passes to storm laid shallow marine sediments up section the fine grained storm sediments host abundant trace fossils although the studied ichnites characteristically show marginal marine affinity the ichnodiversity and bioturbation intensity suggest a lower than normal shallow marine trace fossil population further endobenthic annelids worms and crustaceans are identified as dominant trace makers sediment reworking near the ice grounding line extremely cold climate high energy storm sedimentation and anomalous water chemistry hindered organic colonization during the early phases of talchir sedimentation later climatic amelioration ushered in a favourable ambience for the benthic community to colonize within or beyond the storm weather wave base in the outer shoreface shelf environment fluctuating storm energy dominantly controlled the availability and influence of other environmental stimuli in the environment and thus governed the distribution abundance and association of the studied ichnites however impoverished ichnodiversity sporadic distribution of the traces overall smaller burrow dimensions absence of body fossils dominance of worms and annelids as trace makers all indicate a stressed environmental condition induced by cold climate and lowered marine salinity due to influx of glacier melt out freshwater during climatic amelioration in the permo carboniferous ice marginal sea

sole marks in storm event beds in the permo carboniferous talchir formation raniganj basin india abstract sole marks in storm event beds are described for the first time from talchir formation permo carboniferous of raniganj basin india gutters and grooves trending subparallel to wave ripple crests were formed by shore parallel geostrophic flow at the initial phase of storms during intensification of storms oscillation dominated shore normal current produced gutters grooves and bipolar bimodal prod marks and bounce marks at nearly perpendicular or highly oblique to the axis of major wave ripple crests superposition of shore normal oscillatory flow on shore parallel geostrophic current during peak storms is evident from curvilinear crosscutting and turnabout groove marks hydrodynamic interpretation of these sole marks interrelationship between palaeogeographic constraints governing the overall sediment dispersal pattern and the stratification architecture in storm event beds signify complex interplay of mutually perpendicular shore parallel and shore normal components of storm current in shallow marine setting

biological origin of tetracyclic diterpanes n alkanes and other biomarkers found in lower carboniferous gondwana coals niger abstract the saturated hydrocarbons of coal samples of the anou araren mine tim mersoi basin niger republic have been studied by gc and gc ms chromatograms revealed rather unusual n alkane distributions dominated by compounds in the c 20 c 23 range and showing a rapid and irregular decrease towards higher molecular weights these signatures appear to be typical of the paleozoic gondwana swamps flora unlike typical low maturity terrestrial organic matter characterized by a dominance of odd carbon number n alkanes in the c 27 c 33 range which could be attributed to angiosperms the presence of large amounts of polycyclic diterpanes ent beyerane phyllocladanes and kauranes is unexpected in samples of that age since these compounds are usually thought to be derived from conifers which supposedly had not yet evolved at the time a more likely explanation is that these diterpanes could be derived from biological precursors of the conifers

last interglacial sediments of the don valley brickyard toronto canada and their paleoenvironmental significance the don valley brickyard in toronto is an internationally designated type site in recognition of diverse faunal remains in the don beds of last sangamonian interglacial age pollen in overlying strata record the climatic deterioration marking the onset of the last wisconsinan glacial cycle new sedimentological descriptions show that the don beds about 8 m thick were deposited in a lacustrine lower shoreface environment subject to episodic storms storm deposited sand facies are interbedded with peaty muds that are extensively bioturbated water depths derived from wave formed ripples using linear wave theory appear to have increased during deposition of the don beds from about 2 m to about 18 m 12 28 m above the modern lake level a change that is recorded by an overall fining up sequence increasing water depths may have been the result of isostatic recovery of the lake outlet to the east the don beds overlie a thin bouldery deposit possibly a remnant of older illinoian glacial sediments yo

multi stage crustal accretion by magmatic flare up and quiescence intervals in the western margin of the sao francisco craton u pb hf and geochemical constraints from the almas terrane abstract the global plate tectonic regime in early paleoproterozoic times is highly debated the interval 2 45 2 2 ga is known for a minima in juvenile magmatism but this is not a global phenomenon new results of whole rock geochemistry and u pb hf analysis in igneous and detrital zircons allied with existing isotopic and geophysical data allow to identify and constrain the duration of magmatic flare up and quiescence events in the western sao francisco paleoplate igneous samples yield ages indicating three accretionary magmatic events an older with ages ca 2476 4 9 ma to 2462 13 ma an intermediate at 2390 14 ma and a younger from 2235 26 ma to 2201 5 ma all presenting magmatic arc geochemical signatures xenoliths of quartzite and volcanic tuff from the upper greenstone sequence morro do carneiro fm are hosted in the 2211 9 ma tonalite and the maximum depositional age of the morro do carneiro basin is dated 2234 12 ma indicating a syn orogenic setting for this basin detrital zircon u pb age distribution for quartzites of the greenstone sequence shows peaks at 2 65 2 47 2 39 2 27 and 2 23 ga altogether the studied rocks record an accretionary orogeny with four distinct episodes episode s1 2 52 2 46 ga hf t values from 0 57 to 6 36 episode s2 2 43 2 37 ga hf t values from 0 10 to 4 30 episode r1 2 32 2 26 ga hf t values from 1 61 to 7 23 from detrital zircons episode r2 2 24 2 20 ga hf t values from 0 39 to 2 73 these early paleoproterozoic accretionary orogenies mark the onset of amalgamation of the sao francisco continental paleoplate that surrounds the craton with accretions of an exotic micro block and continental magmatic arcs indicating evolution from dominant siderian juvenile magmatism to rhyacian crustal magmatism these patterns show striking similarities to the orogenies in the mineiro belt and north china craton

field and geochronological evidence for origin of the contendas mirante supracrustal belt sao francisco craton brazil as a paleoproterozoic foreland basin abstract the low grade contendas mirante meta volcano sedimentary belt cmb was previously interpreted as an archean greenstone belt with the uppermost formation deposited in the paleoproterozoic new zircon u pb la icp ms ages on sedimentary groups and granite sheets intrusive in the belt constrain the timing of basin development phyllites of the lower group and meta arenites of the upper group yielded similar young zircon populations at ca 2080 ma which are interpreted as the maximum deposition age for the entire sequence the unique exception is the 3273 3338 ma zircon bearing quartzite that occurs in spatial association with the 3300 ma rhyolite a granite sheet intrusive into metagraywacke of the lower group constrains the minimum deposition age of 2045 26 ma for the cmb altogether four main age clusters of detrital zircon grains were recognized namely 2075 2200 ma 2200 2440 ma 2500 2770 ma 3270 3380 ma these age intervals match the ages of igneous and metamorphic rocks in the different terranes that comprise the sao francisco craton maximum deposition age for both groups indicates that sedimentation occurred immediately prior the high grade metamorphism in the adjacent archean paleoproterozoic jequie block and itabuna salvador curaca orogen these observations along with coarsening upwards in the sediments indicate that the cmb represents a foreland basin developed along the eastern margin of the gaviao block during plate convergence paleoarchean basement rocks were reactivated and emplaced into the cmb during basin inversion and is timely correlated with the granitic intrusion recognition of older supracrustal fragments is ambiguous one main example is the 3273 3338 ma zircon bearing quartzite which correlates with the northern jacobina basin along the contendas mirante lineament e g bahia gold belt and may represent part of an archean intracontinental rift sequence

the goias massif implications for a pre columbia 2 2 2 0 ga continent wide amalgamation cycle in central brazil abstract the goias massif is a collage of archean paleoproterozoic terranes that crop out in the central brazil northern brasilia belt and acted as the continental margin onto which neoproterozoic brasiliano orogenic events took place most belts in the massif formed from 2 2 to 2 0 ga a widespread age bracket in the sao francisco congo craton pericratonic areas and other terranes associated with the formation of the atlantica supercontinent however the genesis of the goias massif has always been a matter of debate due to a sharp crustal thickness contrast marked on surface by the trace of the rio maranhao thrust and widely hypothesized as a suture zone the hypothesis that this suture would have been formed when a microcontinent was accreted to the rest of the massif during the neoproterozoic brasiliano orogeny is tested in this paper through mapping and zircon geochronology of rocks along the rio maranhao thrust our study indicates that units contain paleoproterozoic ages have similar geological features to other goias massif 2 2 2 0 ga terranes and show no evidence of syn collisional neoproterozoic magmatism we therefore reinterpret the available data to propose instead that the amalgamation of the massif occurred fully in the paleoproterozoic first the gravimetric contrast marked by the rio maranhao thrust represents in fact a neoproterozoic lower crust delamination event that affected both the brasiliano orogen and the terrane it was accreted against the campinorte arc second serra da mesa suite mesoproterozoic granites intruded both sides of the rio maranhao thrust and thus indicate the two domains were amalgamated prior to the mesoproterozoic finally mesoproterozoic volcanic and plutonic rocks follow the trace of the rio maranhao thrust suggesting a reactivated intracontinental structure rather than an original product of brasiliano collision the goias massif also show important similarities to the sao francisco craton a orogen building and magmatism from 2 2 to 2 0 ga b metamorphic peaks from 2 11 to 2 08 ga c zircon age peaks at 1 76 ga 1 58 ga and 1 2 ga largely attributed to crustal extension events and d contiguous seismic signature from massif to craton these common features allied to our reassessment of central brazil geochronology and the nature of central brazil sharp crustal thickness contrast indicate that the goias massif was fully assembled during a 2 2 2 0 ga orogeny as part of the western border of the sao francisco congo paleocontinent a comprehensive understanding of this orogeny is vital to test the validity of atlantica and to infer the landmasses later involved in the assembly of columbia

isotopic and geochemical composition of marl lake waters and implications for radiocarbon dating of marl lake sediments radiocarbon dates on organic and calcareous fractions of sediment cores from marl lakes may yield anomalous ages due to the assumption of a constant hardwater correction factor along the sediment sequence a study of eight marl lakes in southern ontario that are actively precipitating calcium carbonate was conducted in order to assess those isotopic and aqueous geochemical parameters in modern lakes that may be utilized to estimate the history and extent of variations in the hardwater effect along such sediment sequences results show an increase in the 13c composition of lake dic dissolved inorganic carbon as approach to isotopic equilibrium with atmospheric co2 occurs differences in the extent to which this equilibrium is established also appear responsible for observed differences in the 14c activity of dic between lakes of as much as 20 pmc percent modern carbon these variations have been related to the relative residence times of water in each lake by examination of their corresponding seasona

no plate tectonic shutdown in the early paleoproterozoic constraints from the ca 2 4 ga granitoids in the quanji massif nw china abstract the global plate tectonic regime in the early paleoproterozoic period is highly debated granitoids bear key information to address such a debate petrological geochemical and geochronological studies are conducted on two post collisional granitoid plutons in the quanji massif northwestern china to investigate the tectonic regime during this period the granitoids are composed of syenogranite monzogranite and granodiorite with minor tonalite which intruded into the delingha and hudesheng regions at ca 2 39 2 37 ga these plutons are high k i type granitoids with variable ga al ratios showing some characteristics of a2 type granitoids they are characterized by enrichment of liles and lrees and depletion of sr p ti and eu they show depleted nd and hf isotope signatures with whole rock end t 0 7 to 4 8 and zircon ehf t 1 0 to 7 8 indicating a juvenile crustal growth event at ca 2 44 2 37 ga our new results together with other coeval post collisional granitoids in the quanji massif suggest that the protracted post collisional magmatism at ca 2 39 2 34 ga occurred just after a short interval of subduction and generation of juvenile magmas before or around ca 2 4 ga collectively the formation of these ca 2 4 2 3 ga granitoids in the quanji massif may correlate with coeval granitoids in the tarim and north china cratons and is broadly coeval with magmatism in several other cratons in the west african and canadian shields thus the globally well documented magmatism at early paleoproterozoic or siderian provides further information for filling up the age gap of the so called plate tectonic shutdown in the early paleoproterozoic period worldwide the geologic record therefore suggests no siderian shutdown of plate tectonics but instead continuous global subduction and generation of juvenile magmas from the archean through the paleoproterozoic

paleorift structure constrained by gravity and stratigraphic data the statherian arai rift case abstract gravimetric and stratigraphic data were used to investigate the paleoproterozoic arai paleorift a failed statherian continental rift located in the western margin of the sao francisco craton where basement and cover were affected by the neoproterozoic brasiliano orogeny euler deconvolution tilt total horizontal gradient amplitude and upward continuation technics were applied to terrestrial gravimetric data in order to investigate the rift s main faults location direction and depth allowing to identify its main horsts grabens volcanic and plutonic centers we found that rift faults occur to a maximum depth of ca 38 km but major fault throw occurs from 4 to 8 km deep and attenuates from 8 to 12 km probably the brittle ductile transition zone at the time of rifting practically disappearing at 20 km stratigraphic data and basement mapping were used in order to constraint gravimetric results we classify the arai rift as a passive three armed failed rift narrow to divergent type that produced preferably anorogenic rapakivi related magmas most of it still lodged in the crust from surface down to ca 19 km deep and subsidiary mafic magmatism the results indicate the deep occurrence of low density magmas beneath the rift s main axis detected up to 20 km deep correlation to other global statherian rifts show that the sao francisco craton was strongly affected by taphrogenesis during the statherian together with siberia north america and north china cratons finally by comparing our results to recent rifts we found that the ethiopian rift s morphology is quite similar to the arai surrounding the tanzanian craton the cenozoic east africa rift system morphology is compared to the arai espinhaco rift system which surrounds the sao francisco craton the major contribution of this paper is the recognition of arai paleorift surface and subsurface morphology up to now unknown over an area of ca 45 000 km2

paleoproterozoic accretionary orogenesis in the north china craton a shrimp zircon study abstract the inner mongolia suture zone imsz and the trans north china orogen tnco incorporate the major paleoproterozoic accretionary orogens in the north china craton ncc with the jiao liao ji belt jljb representing the third one here we investigate the paleoproterozoic tectonics of the imsz and tnco through zircon shrimp geochronology on a representative suite of rocks comprising metasediments and arc magmatic rocks shrimp analysis of zircons with textures indicating extreme recrystallization under ultrahigh temperature uht conditions from the metapelites at heling er in the southern domain of the imsz reveals a single population with a weighted mean 207 pb 206 pb age of 1913 17 ma the zircons in another uht granulite from this locality yield a weighted mean 207 pb 206 pb age of 1910 18 ma these data correlate with the ca 1 92 ga age reported from zircons in sapphirine bearing uht granulites further north and confirm the regional extent of the paleoproterozoic uht metamorphism within the imsz zircons in a charnockite from the southern margin of the khondalite belt fringing the uht granulites in the imsz show two distinct age groups an older population with a magmatic paragenesis and a weighted mean 207 pb 206 pb age of 1932 24 ma and a younger group of metamorphic zircons with an age of 1858 26 ma we also report zircon ages from charnockites in two localities around xing he in the huangtuyao belt belonging to the huai an complex within the westernmost domain of the tnco at the junction with the imsz the charnockite from first locality carries two distinct zircon populations with the older group yielding a weighted mean 207 pb 206 pb age of 2477 2 ma and the younger population showing an age of 1807 38 ma the internal structure as revealed from cl images and the overall high th u values up to 2 42 of the older zircons suggest their magmatic affinity whereas the younger group with extremely low th u 0 02 0 09 is of metamorphic origin zircons from the charnockite in the second locality also define two distinct age clusters with a dominant older magmatic group having a weighted mean 207 pb 206 pb age of 2147 11 ma and a minor younger group with an age of 1958 25 ma the range of ages from 2477 to 2147 ma from magmatic zircons in the charnockites from the eastern periphery of the imsz within the western margin of the tnco in combination with similar ages reported in recent studies from zircons in magmatic complexes within the imsz suggest a prolonged history of subduction related arc magmatism and accretionary tectonics analogous to those in some of the phanerozoic belts such as the central asian orogenic belt and the western pacific subsequent progressive collision and suturing of the continental blocks were accompanied by the exhumation of high pressure hp and uht metamorphic rocks the available data from the imsz and tnco suggest long lived convergent margins associated with the southward subduction of the yinshan block and westward subduction of the eastern block in a double sided subduction realm prior to the final amalgamation of the ncc and its incorporation within the columbia supercontinent in the late paleoproterozoic

a palaeoproterozoic tectono magmatic lull as a potential trigger for the supercontinent cycle the geologic record exhibits periods of active and quiescent geologic processes including magmatism metamorphism and mineralization this apparent episodicity has been ascribed either to bias in the geologic record or fundamental changes in geodynamic processes an appraisal of the global geologic record from about 2 3 to 2 2 billion years ago demonstrates a palaeoproterozoic tectono magmatic lull during this lull global scale continental magmatism plume and arc magmatism and orogenic activity decreased there was also a lack of passive margin sedimentation and relative plate motions were subdued a global compilation of mafic igneous rocks demonstrates that this episode of magmatic quiescence was terminated about 2 2 billion years ago by a flare up of juvenile magmatism this post lull magmatic flare up is distinct from earlier such events in that the material extracted from the mantle during the flare up yielded significant amounts of continental material that amalgamated to form nuna earth s first hemispheric supercontinent we posit that the juvenile magmatic flare up was caused by the release of significant thermal energy that had accumulated over some time this flux of mantle derived energy could have provided a mechanism for dramatic growth of continental crust as well as the increase in relative plate motions required to complete the transition to modern plate tectonics and the supercontinent cycle these events may also be linked to palaeoproterozoic atmospheric oxygenation and equilibration of the carbon cycle earth experienced a lull in magmatic and tectonic activity about 2 3 billion years ago followed by a flare up of magmatism according to a compilation of existing geologic data these events might mark the transition to the supercontinent cycle

palaeoenvironmental assessment of westphalian fluvio lacustrine deposits of lorraine france using a combination of organic geochemistry and sedimentology abstract the quality and the quantity of organic carbon preserved in modern and ancient terrestrial sediments is the result of a complex interactions of sedimentological factors such as in situ productivity allochtonous supply of organic matter oxidation processes biodegradation and sediment accumulation rates the study aims at utilizing multidisciplinary information in order to characterize the palaeoenvironment in westphalian fluvio lacustrine deposits of the lorraine coal basin ne france in this basin the lack of outcrops is the major difficulty to compensate for this problem sedimentology and molecular geochemistry are combined in order to significantly improve the palaeoenvironmental assessment of the area geochemical analyses and sedimentology have been carried out on several core samples of the saulcy drill hole to evaluate local palaeoenvironmental variability the lithofacies associations in the upper carboniferous of the lorraine basin suggest an alluvial plain environment without marine incursions sedimentological interpretations of the core as well as comparison with sedimentological models suggests the recognition of different depositional environments from braided and or meandering rivers to swamp and lakes the organic geochemistry is focussed on the recognition of aliphatic hydrocarbons and especially on molecular biomarkers which provide valuable information about the original organic matter and the transformations that took place during sedimentation and diagenesis in the lorraine basin the botanical variability is high and clearly related to the position of the vegetation communities in the fluvial system the biomarkers e g diterpanes steranes show variations which can be related to the diversity of this ecosystem in this study a reinterpretation of the environmental zonation in the sterane ternary diagram adapted to a fluvio lacustrine sedimentology is proposed the correlation between sedimentological and geochemical interpretation permits characterization of various depositional environments a palaeoenvironment model relating sediment deposition conditions and organic matter characteristics is proposed

the fernbank interglacial site near ithaca new york usa abstract the fernbank interglacial site on the west side of cayuga lake new york has been recently subjected to more detailed study to a lengthened mollusc list are added ostracodes insects fish pollen and plant macrofossils of these plants are well preserved and diverse whereas other groups are poorly preserved and incomplete nevertheless all support the interglacial assignment sangamon which is further supported by minimum age radiocarbon dates 50 000 14 c yr bp and a tl date of 81 11 ka in the plant record near the top of the sequence abundant tree charcoal indicates forest fires like the toronto interglacial record the plants show a declining july mean temperature from 24 to 18 c according to transfer functions through the sequence from mixed deciduous forest to boreal forest

biomarkers of holocene buried conifer logs from bella coola and north vancouver british columbia canada abstract the biomarker compositions of a holocene seep oil liquefied resin originating from a buried log of douglas fir pseudotsuga menziesii from bella coola bc canada and a holocene pine wood pinus sp sample from north vancouver bc canada were analyzed using gas chromatography mass spectrometry gc ms the total extract of the bella coola sample contains the sesquiterpenoid derivative calamenene and diterpenoids of the labdane abietane pimarane and phyllocladane classes a novel series of successively degraded labdane derivatives labdan 15 oic acid norlabdanoic acids drimenoic acid was detected in the polar fraction and a diagenetic pathway is proposed aromatic abietanes are the major components in the neutral fraction the neutral fraction of the pine wood contains two sesquiterpenoids calamenene cadalene diterpenoids of the abietane pimarane isopimarane and kaurane classes and a series of steroids 18 norabieta 8 11 13 triene dehydroabietin is the major component among the predominantly aromatic abietanes based on the compositions of the terpenoids it is concluded that the diagenesis of the pine and douglas fir logs probably occurred under anaerobic conditions leading to reductive reactions such as decarboxylation of resin acids with concurrent oxidation reactions to form the aromatic derivatives

interpreting paleoclimate from l8o and 2h in plant cellulose comparison with evidence from fossil insects and relict permafrost in southwestern ontario the oxygen isotope content of terrestrial plant cellulose is related to that of the source waters by a two step process involving evapotranspirative leaf water enrichment and equilibrium isotopic exchange between leaf water and atmospheric carbon dioxide a combination of two models that describe these steps yields consistent agreement between measured and predicted climatic and isotopic data humidity is the dominant influence on variations in the cellulose 18o enrichment relative to the source water a good first order approximation of the average daytime relative humidity during the growth season at a site can be based on the linear correlation that exists between humidity and cellulose enrichment without explicit consideration of factors such as temperature 18o of atmospheric vapour and leaf boundary layer dynamics the value of the combined model for paleoclimatic reconstruction has been tested using fossil wood from a late glacial site at brampton ontario estimates of the past relative humidity

the latest neoarchean paleoproterozoic evolution of the dunhuang block eastern tarim craton northwestern china evidence from zircon u pb dating and hf isotopic analyses abstract the dunhuang block in the easternmost segment of the tarim craton exposes precambrian mafic granulite and felsic gneiss to better understand the poorly known formation and evolution of the tarim craton we carried out detailed field based petrological and geochronological investigations on the major lithologies of the dunhuang block u pb dating and hf isotopic analyses on the mafic granulite and felsic gneiss ttg gneiss of the dunhuang block reveal two distinct age populations the latest neoarchaean 2 5 ga and the late palaeoproterozoic 1 82 1 85 ga the zircon magmatic cores and metamorphic rims of tonalitic gneisses yield similar ages of 2 5 ga supporting the existence of archean rocks in the dunhuang block the short time interval between latest neoarchean magmatism and high grade metamorphism suggests that they were related to the same latest neoarchean tectonothermal event the 2 5 ga zircons show hf depleted mantle model ages between 2 55 ga and 2 8 ga with a peak at 2 7 ga suggesting that 2 7 ga juvenile crust of the dunhuang block was reworked during a 200 300 m y period at the end of the neoarchean the age of 1 85 ga obtained from the mafic granulites and felsic gneisses is interpreted as the age of high pressure granulite facies metamorphism combined with the hf isotopic data these data suggest that the dunhuang block experienced 2 7 ga crustal growth a 2 5 ga magmatic metamorphic event and a 1 82 1 85 ga hp granulite facies metamorphic event this sequence of events is very similar to that of the north china craton implying that the evolutionary history of the dunhuang block was consistent with that of the north china craton from the neoarchean to paleoproterozoic

early paleoproterozoic magmatism in the yangtze block evidence from zircon u pb ages sr nd hf isotopes and geochemistry of ca 2 3 ga and 2 1 ga granitic rocks in the phan si pan complex north vietnam abstract our understanding of the early evolution of the yangtze block is limited by the sparsely dispersed nature of pre neoproterozoic exposures new integrated petrographic zircon u pb age and hf nd isotope analyses and whole rock geochemical data for early paleoproterozoic granites in the phan si pan complex provides new insights into the evolution of the yangtze block as well as its role in the pre nuna supercontinent la icp ms zircon u pb dating of magmatic zircons from quartz monzonite and gneissic granite yielded 207pb 206pb ages of 2306 12 ma and 2096 15 ma respectively zircons from the quartz monzonite have ehf t values ranging from 4 1 to 2 1 corresponding to tdm2 model ages of 3002 2890 ma whereas zircons in the gneissic granite have ehf t values between 0 95 and 1 72 and corresponding tdm2 model ages of 2660 2516 ma which are consistent with their whole rock nd isotope values geochemically the quartz monzonites are i type granites combined with their relatively high sr y ratios and low y concentrations as well as fractionated ree patterns with relatively high lree but low hree concentrations they were probably generated by partial melting of the thickened middle lower crust under elevated temperature geochemical and isotopic signatures suggest that the ca 2 1 ga gneissic granites are high k calc alkaline ferroan a type granites formed by partial melting of juvenile crustal source at high temperature and low pressure with little involvement of ancient crustal material the phan si pan complex has a distinct early paleoproterozoic crustal evolution history compared with the other crustal provinces of the yangtze block suggesting independent histories that were not unified until the late paleoproterozoic during the assembly of nuna moreover the magmatism and tectonic evolution of the north vietnam region is broadly similar to that of the arrowsmith orogen of the rae craton in laurentia suggesting a potential spatial linkage the geologic record of the yangtze block does not support an early paleoproterozoic shutdown of plate tectonics

neoproterozoic early cambrian biota and ancient niche a synthesis from molecular markers and palynomorphs from bikaner nagaur basin western india abstract the time frame of present study is neoproterozoic early cambrian an enigmatic and consequential time in the history of earth the present study elucidates the terminal proterozoic biota and palaeoenvironment by characterizing the soluble and insoluble fractions of organic matter extracted from sediment core samples recovered from marwar supergroup bikaner nagaur basin western india the normal alkanes range from c15 to c33 wherein c19 to c21n alkanes predominate and carbon preference index ranges from 1 12 to 1 19 pristane phytane ratio varies between 0 9 and 1 2 the kerogen matter occurs as homogenous laminae and discrete organic remains which are mostly derived from microbial mat triterpenoids include cheilanthanes and hopanes which are confirming evidences of microbial input algal presence has also been confirmed from palynological data green algae evolved to be a major biota during the neoproterozoic early cambrian time and this is validated by the appreciable abundance of c29 steranes in the bitumen fraction the amorphous pieces of kerogen residues lack any visibly distinct internal features however a very few simple ornamented acritarchs like micrhystridium sp lophosphaeridium sp and leiosphaeridia sp are observed in the organic residues micro ftir spectroscopy of the amorphous organic particles reveals the presence of long chain aliphatic components and unusually high c c aromatic ring stretching band the organic remains were deposited in restricted marine water and elevated saline condition as indicated by several salinity biomarkers the present study clearly demonstrates a microbial mat dominated niche with significant eukaryotic green algae that had been capable of surviving in the high salinity of the terminal proterozoic oceans

the pre late wisconsin stratigraphy of southern simcoe county ontario implications for ice sheet buildup decay and great lakes drainage evolution1 recent three dimensional mapping investigations in southern simcoe county ontario allow refinement of the existing regional stratigraphic framework analysis of 25 continuously cored boreholes ha

the oldest known rocks in south western china shrimp u pb magmatic crystallisation age and detrital provenance analysis of the paleoproterozoic dahongshan group abstract the paleoproterozoic dahongshan group outcrops along the present day southwest margin of the yangtze craton it is the oldest rock found in the region and forms the basement for the late mesoproterozoic sedimentary successions the dahongshan group is a sequence of volcanic and sedimentary rocks which have undergone structural deformation and metamorphism to upper greenschist lower amphibolite facies some of the original sedimentary features such as unimodal cross bedding in quartzite and rounded conglomerate clasts are still preserved suggesting deposition in a fluvial environment abundant carbonate rocks also found within the sedimentary sequence indicate periods of shallow marine or lagoonal conditions a weighted mean shrimp 206pb 207pb age of 1675 8 ma for a tuffaceous schist unit confirms the paleoproterozoic formation age of the group shrimp and lam icp ms u pb analysis of detrital zircon grains from metasedimentary units indicate a late archean to paleoproterozoic ca 2780 1860 ma source region the age spectrum of the detrital zircons is similar to that of the late archean and early paleoproterozoic basement rocks previously identified in the yangtze craton but includes a population of paleoproterozoic grains ca 2400 2100 ma which have no known source region in the exposed yangtze craton

biomarkers and aromatic hydrocarbons in bituminous coals of upper silesian coal basin example from 405 coal seam of the zaleskie beds poland abstract this paper presents the geochemical characteristics of hard coals from the 405 coal seam found in several mines in the upper silesian coal basin poland the coals classifying as of medial coalification types d and c and as para and orthobituminous coals show variable technical chemical and petrographic properties vitrinite reflectance values range from 0 65 to 1 24 cdaf from 79 2 to 88 3 wt and vdaf from 23 7 to 37 4 wt maceral composition in all of the coals studied is dominated by vitrinite macerals 43 5 74 0 gas chromatography mass spectrometry was applied to assess organic matter sources and ranks using several biomarker and aromatic hydrocarbon parameters distributions of n alkanes acyclic isoprenoids diterpenoids steranes and triaromatic steroids indicate that the organic matter in the coals analysed is derived mostly from terrestrial vascular plants the biogenic organic matter was deposited mostly in an estuarine deltaic environment with a normal to low water level in a few cases a marine lagoonal or paludal environment is possible tetracyclic diterpanes such as phyllocladanes and kauranes indicators of the podocarpaceae and araucariceae families are explained by proposing input of organic matter deriving from voltziales plants which may have been able to synthesise these compounds biomarker and aromatic hydrocarbon parameters of thermal maturity in the coals show a clear correlation to vitrinite reflectance values and carbon content indicating degrees of thermal maturity in the range from early to advanced catagenesis frictional heat related to the klodnica fault movement caused aberrations in values of aromatic hydrocarbon maturity parameters in coals sampled

the raniganj coal basin an example of an indian gondwana rift abstract rifting occurred in peninsular india during permian triassic gondwana sedimentation the rocks of the paleozoic mesozoic indian gondwana supergroup succeed the mesoproterozoic vindhyan sedimentary rocks and the indian precambrian shield unconformably and are renowned for their coal resources the rocks of the gondwana supergroup occur mainly in trough like depressions arranged in a more or less en echelon fashion along distinct shear fault zones which are parallel to ancient structural lineaments in the indian peninsular shield thus the gondwana group of basins occurs along the three major directions a son narmada and damodar koel valley running east west b son mahanadi valley with a nw se trend and c rewa pranhita godavari valley which trends in a nnw sse direction the important common structural imprints in most of the above basins are i a half graben basin geometry with a strong master boundary fault on one side and a homoclinal tilt of the basin towards it ii a network of intrabasinal faults one set oriented along the basin axis and which formed during the tensional stage and another iii transverse to it basin marginal oblique faults and slips coincide with both the tensional and compressional stages and have different manifestations syndepositional subsidence of the basin floor through loss of support from below due to the lateral transport of sub crustal mantle materials caused faulting at the axial zones of the basins sub basins to accommodate a thick pile of sediments volcanic activities in the region or in adjacent areas provide further support for these inferred processes and are confined within comparatively narrow and linear zones defined by the crustal weaknesses of considerable antiquity all these stages have their signatures imprinted in the sediments which have been studied in detail this paper presents relevant data on the raniganj coalfield of eastern india in order to examine whether these linear depressions are of rift origin the process of rifting was a prelude to the rafting of gondwana continents after the early cretaceous fragmentation of gondwanaland thus the gondwana rift valleys flanked the periphery of the peninsular indian stable blocks to collide ultimately with the sino eurasian plate in the north

aliphatic and aromatic hydrocarbons in candiota coal samples novel series of bicyclic compounds abstract aliphatic and aromatic fractions obtained from nine samples taken from two different seams of five boreholes in the candiota coalfield lower permian were analysed by gas chromatography mass spectrometry the occurrence of the tetracyclic diterpenoids 16 h phyllocladane and ent 16 h kaurane among the aliphatic hydrocarbons and the tricyclic diterpenoids simonellite and retene in the aromatic hydrocarbon concentrates suggest an important input from conifers to the sedimentary biomass this may explain the origin of a novel series of saturated and aromatic bicyclic compounds detected in the extracts which may be structurally related to the same precursor possibly a conifer resin derived tricyclic diterpenoid

stratigraphic distribution of macerals and biomarkers in the donets basin implications for paleoecology paleoclimatology and eustacy abstract more than one hundred and thirty coal seams and coaly layers occur in the donets basin donbas twenty eight 52 samples of them ranging in age from serpukhovian late mississipian to gzhelian late pennsylvanian 33 clastics and three limestones were studied in terms of maceral composition sulphur contents and biomarker distribution diterpanes are used to estimate the contribution of different groups of plants and the height of the water table in the swamp hopanes are a measure of bacterial activity in the peat and steranes indicate the relative input of wood and algae stratigraphic trends in these parameters are discussed in relation to paleoenvironment climatic changes and eustacy a tropical climate prevailed in the donbas from serpukhovian to kasimovian times nevertheless periods with drier and wetter conditions can be distinguished based on maceral and biomarker data relatively dry conditions are observed during serpukhovian and vereian times whereas wetter climates with a maximum of coal deposition occurred during the late bashkirian most of the moscovian and the earliest kasimovian no economic coal seams are hosted in upper kasimovian and gzhelian deposits a result of a change to an arid climate our data also suggest climatic changes during sequences of different order for the second order third order and fourth order sequences relatively dry or wet conditions occurred during coal deposition in the lowstand systems tract an intermediate climate during the transgressive systems tract and the maximum flooding and a wet climate during the highstand systems tract the results for high frequency sequences support the cecil s paleoclimatic model an intermediate paleoclimate during lst sandstone and levee siltstone a wet climate during early tst coal and a dry climate during late tst limestone mfs claystone and hst deltaic siltstone coals deposited during maximum flooding periods are more enriched in c27 steranes derived from algae and contain lower proportions of c29 steranes derived from the wood of higher plants

biomarker signatures of permian gondwana coals from india and their palaeobotanical significance abstract coal samples belonging to the lower permian barakar formation and the upper permian raniganj formation collected from damodar valley basin of eastern india have been analysed for understanding their organic geochemical characteristics using rock eval pyrolysis gas chromatography mass spectrometry gc ms and comprehensive two dimensional gas chromatography coupled with time of flight mass spectrometry gc gc tofms the rock eval pyrolysis parameters suggest that the coals from both the formations contain a mixture of type ii and type iii kerogen the rock eval tmax values of the analysed coals vary from 417 to 451 c n alkanes ranging from c12 to c31 predominate the aliphatic hydrocarbons present in the coal extracts the carbon preference indices cpi as well as the odd to even preference oep values of the n alkanes are 1 suggesting input from higher vascular land plants c29 steranes predominate over c27 and c28 steranes which corroborates contribution from terrestrial higher plants aliphatic diterpanes like ent beyerane isopimarane abietane phyllocladanes and ent kaurane as well as aromatic diterpanes like simonellite bisnorsimonellite retene methylretenes and tetrahydroretene which are mainly known to originate from conifers are detected in the studied coals the lower gondwana floral assemblage of peninsular india is mainly represented by glossopteris flora pteridospermatophyta however some primitive conifers have also been reported from this succession we propose that the diterpanes detected in the studied coals were possibly derived from the primitive conifers this implies that the biosynthetic pathways to produce these diterpanes had evolved in the gondwana flora during the permian period

filling in the juvenile magmatic gap evidence for uninterrupted paleoproterozoic plate tectonics abstract despite several decades of research on growth of the continental crust it remains unclear whether the production of juvenile continental crust has been continuous or episodic throughout the precambrian models for episodic crustal growth have gained traction recently through compilations of global u pb zircon age frequency distributions interpreted to delineate peaks and lulls in crustal growth through geologic time one such apparent trough in zircon age frequency distributions between 2 45 and 2 22 ga is thought to represent a pause in crustal addition resulting from a global shutdown of magmatic and tectonic processes the 2 45 2 22 ga magmatic shutdown model envisions a causal relationship between the cessation of plate tectonics and accumulation of atmospheric oxygen over the same period here we present new coupled u pb hf and o isotope data for detrital and magmatic zircon from the western churchill province and trans hudson orogen of canada covering an area of approximately 1 3 million km2 that demonstrate significant juvenile crustal production during the 2 45 2 22 ga time interval and thereby argue against the magmatic shutdown hypothesis our data is corroborated by literature data showing an extensive 2 22 2 45 ga record in both detrital and magmatic rocks on every continent and suggests that the operation of plate tectonics continued throughout the early paleoproterozoic while atmospheric oxygen rose over the same time interval we argue that uninterrupted plate tectonics between 2 45 and 2 22 ga would have contributed to efficient burial of organic matter and sedimentary pyrite and the consequent rise in atmospheric oxygen documented for this time interval

quantifying the timing and rate of crustal evolution global compilation of radiometrically dated detrital zircon grains abstractmultiple models steady state episodic and early growth followed by crustal reworking have been postulated to explain the evolution of earth s continental crust an independent assessment of these models is now possible as a result of the massive numbers of detrital zircon grains that have been dated individually over recent years using u pb and hf isotopes a compilation of 200 000 published zircon dates reveals a global age distribution u pb with six prominent statistically significant peaks 3 2 3 0 2 7 2 5 2 0 1 7 1 2 1 0 0 7 0 5 and 0 3 0 1 ga in most cases these peaks are recorded on all seven continents most of the peaks are detectable also in modern sediments a comparison of grains with both u pb ages and hf isotope model ages available for 5100 detrital zircons suggests that the age frequency distribution of detrital grains reflects predominantly episodic crustal recycling rather than crustal growth the zircon age distributions and associated data provide consistent ev

u pb and sm nd constraints on the nature of the campinorte sequence and related palaeoproterozoic juvenile orthogneisses tocantins province central brazil

tectonic evolution of the paranoa basin new evidence from gravimetric and stratigraphic data abstract field gravimetric and stratigraphic surveys were conducted with the aim to constraint the mechanisms responsible for the initiation of the stenian tonian paranoa basin central brazil a subject not yet studied in detail the paranoa group crops out in the external zone of the brasilia belt a neoproterozoic orogen in the western margin of the sao francisco craton detailed geological mapping confirmed the existence of a regional scale fault that controlled sedimentation of the paranoa group during the deposition of its basal formations revealing important details about basin initiation and early evolution gravimetric modeling indicates the existence of paleorift structures beneath the paranoa sequence in the study area results from both stratigraphic and gravimetric surveys show strong evidence of mechanical subsidence by faulting during basin initiation unsorted angular clasts cut by quartz veins and brecciated boulders present in the basal conglomerate support this hypothesis basin initiation faults coincide with deeper paleorift faults and are thus interpreted as reactivations of the older statherian arai rift the reactivations favored an initial regime of mechanical subsidence dominated by the development of epirogenic arches subsiding at different rates apart from faulting activity the post basal sequence presents no evidence of rift environment in the strict sense besides the great lateral continuity and relatively constant thickness of facies indicate that an initial mechanic subsidence rapidly gave way to flexural subsidence during subsequent stages of basin evolution the paranoa group do not present reliable characteristics that would allow its strict classification as a passive margin its main stratigraphic characteristics tectonic location and basement architecture indicate that the paranoa group was deposited in a cratonic margin basin and may have been either connected to a passive margin basin at times of sea level rise or evolved to a passive margin later in time

structure and origin of terpenoid hydrocarbons in some german coals abstract hydrocarbon extracts of coal samples from major coal fields in west germany have been investigated by gas chromatography mass spectrometry gc ms the samples are of carboniferous and tertiary age and derive from limnic and paralic environments the saar district the ruhr area and the lower rhine basin differences in facies maturity and age reflected in the distribution patterns of the extracted alkylcyclohexanes an unexpected occurrence of cyclic diterpenoid hydrocarbons in some samples of carboniferous age has been found the tetracyclic compounds mainly show phyllocladane type structures and can serve as source indicators hydrocarbons obtained from chemical degradation of the macromolecular material of the samples also revealed phyllocladane type compounds which are normally associated to resins of modern and extinct familes of conifers origin and structural variations of this class of hydrocarbons are discussed in terms of maturity and palaeobotanical implications

metacraton nature genesis and behavior article i nfo in this paper we show with examples that cratons involved in intercontinental collisions in a lower plate position are often affected by orogenic events leading to the transformation of their margins in some cases craton interiors can also be shaped by intense collisional processes leading to the generation of intra cratonic orogenic belts we propose to call these events metacratonization and the resulting lithospheric tract metacraton metacratons can appear similar to typical orogenic belts i e active margin transformed by collisional processes but are actually sharply different their main distinctive characteristics not all are present in each metacraton are 1 absence of pre collisional events 2 absence of lithospheric thickening high pressure metamorphism being generated by subduction leading to high gradient in strain and meta morphic intensity 3 preservation of allochthonous pre collisional oceanic terranes 4 abundant post collisional magmatism associated with shear zones but not with lithospheric thickening 5 presence of high temperature low pressure metamorphism associated with post collisional magmatism 6 intraconti nental orogenic belts unrelated to subduction and oceanic basin closures reactivation of the rigid but fractured metacratonic lithosphere will cause doming asthenospheric volcanism emplacement and mineral izations due to repetitive mineral enrichments this paper provides several geological cases exemplifying these different metacratonic features in scandinavia sahara central africa and elsewhere a special focus is given to the saharan metacraton because it is where the term metacraton originated and it is a vastly ex panded tract of continental crust 5 000 000 km 2

initiation and development of the laurentide and cordilleran ice sheets following the last interglaciation abstract fossil records from sites overridden by or adjacent to the laurentide ice sheet indicate that the climate of the last interglaciation oxygen isotope substage 5e ca 130 116 ka was warmer than today following the last interglaciation the laurentide ice sheet first developed during stage 5 over keewatin quebec and baffin island along its northern margin the ice sheet reached its maximum extent of the last glaciation during stage 5 the ice sheet advanced across baffin island onto the continental shelf early during stage 5 5d whereas the advance into the western canadian arctic occurred late during stage 5 5b the ice sheet also may have advanced into the st lawrence lowland during substage 5b although this event may be younger stage 4 the hudson bay lowland became ice free during substage 5a retreat of the ice sheet on baffin island occurred during late stage 5 probably substage 5a the exact timing of retreat from the western canadian arctic is unknown but it occurred before 48 ka the southern sector including the st lawrence lowland was ice free during late stage 5 the hudson bay lowland may have remained ice free through stage 4 and much of stage 3 because of conflicting chronologies however it is more likely that this area was glaciated throughout stage 3 and perhaps stage 4 nevertheless the data demonstrate that the lowland was ice free during part of the last glaciation an independent ice cap developed over the appalachian uplands and advanced across nova scotia during stage 4 perhaps as far as the edge of the continental shelf the ice cap remained active over nova scotia as a setellite to the laurentide ice sheet throughout the remainder of the last glaciation the ice sheet advanced into the st lawrence lowland during stage 4 and subsequently overwhelmed the local ice cap in the appalachian uplands advancing perhaps into northern new england but not farther south the lowland remained covered by the ice sheet until late stage 2 the ice sheet may also have advanced into the lake ontario basin during stage 4 the position of the northern margin of the laurentide ice sheet during stage 4 is not known but it remained an unknown distance behind its maximum position reached during stage 5 cores from baffin bay indicate a substantial decrease in high latitude glaciation during stage 4 following retreat the keewatin sector of the ice sheet may have remained over much of northwestern canada as a quasi stable ice mass until it readvanced during stage 2 similarly the baffin island sector of the ice sheet may have remained largely intact the southern margin of the ice sheet may have advanced into the lake ontario basin and upper mississippi valley during the middle of stage 3 ca 50 ka reaching its maximum extent of the last glaciation during stage 2 ca 18 21 ka advance of the northern margin was younger ca 8 13 ka than that of the southern margin this advance was less extensive than the penultimate advance stage 5 paleoenvironmental records indicate that the last interglaciation in areas covered by and near the cordilleran ice sheet was as warm as or warmer than present the cordilleran ice sheet appears to have developed during stage 5 or 4 at that time it advanced over southern british columbia and into the northern puget lowland there is no record of this event in northern areas that were later covered by the ice sheet the ice sheet disappeared before 59 ka at the beginning of a lengthy nonglacial interval paleoenvironmental records indicate that climate was similar to the present during part of this interval the ice sheet was absent and glaciers probably were confined to mountain areas throughout stage 3 climatic deterioration marking the end of this nonglacial interval may have begun as early as 29 ka by 14 15 ka the ice sheet had achieved its maximum extent of the last glaciation because there are few suitable dating methods capable of resolving events beyond the radiocarbon limit and because sites that preserve a record of events from the last glaciation are spatially restricted we consider this synthesis as tentative and subject to significant revision as dating methods improve nevertheless this perspective of the north american ice sheets through the last glaciation demonstrates their complex and dynamic behavior and attendant rapid fluctuations in ice volume

gondwana lithostratigraphy of peninsular india abstract the controversy regarding the stratigraphic interpretation of the indian gondwana succession in the peninsular basins has continued for more than a century with the exception of the damodar and satpura basins while the stratigraphic reconstruction in damodar and satpur was based on the order of superposition of strata elsewhere the relative ages were based on paleontological evidence that disregarded various physical criteria including the order of superposition overlying the precambrian crystalline basement the gondwana succession of late permian to early jurassic age can be classified into four sedimentary facies a glaciogenic facies facies a a coal bearing facies facies b a red shale sandstone facies facies c and a hill forming coarse sandstone conglomeratic facies facies d the stratigraphic order of these four facies in ascending order from facies a at the bottom to facies d at the top is well established in the damodar and satpura regions in both areas facies d overlies the underlying older sediments as well as the crystalline basement with a pronounced unconformity however in the pranhita godavari and son basins and elsewhere the stratigraphic relations between facies b facies c and facies d are controversial one such enigma is where the sequence of facies c and facies d are repeated several times in the geological column this interpretation contrasts with the supposed genesis of climatically controlled lithic fill in gondwana basins overturning the standard stratigraphic relation between facies c and facies d was based on fragmentary fossil evidence where the lower gondwana flora seems to be present in upper gondwana rocks turning the stratigraphy upside down was done without establishing the order of superposition between strata throughout the 20 th century most stratigraphers working in the pranhita godavari and son basins worked within a fossil based stratigraphic paradigm this resulted in still more confusion the magnitude of which can be appreciated as one browses through various interpretations presented in innumerable publications in this paper we attempt to offer a lithostratigraphic interpretation of the peninsular gondwana basins based only on physical criteria such as lithological association their petrographical characteristics and the most fundamental tool of stratigraphy the order of superposition

isolation and structural characterisation of isopimarane in some new zealand seep oils abstract isopimarane a tricyclic diterpane was isolated from some new zealand late cretaceous seep oils and coals in which it occurs in abundance the structure and absolute stereochemistry of this terrigenous oil biomarker were determined by nmr spectroscopy cd and synthesis

a paleoenvironmental study of the molluscs from the don formation sangamonian don valley brickyard toronto ontario the don formation comprises 8 9 m of fossiliferous stratified sand and clay lying between glacial deposits of wisconsinan and presumed illinioan age it has yielded a diverse fossil flora and fauna indicating a climate as warm as or warmer than present and is considered to be of last or sangamonian interglacial age about 2 t of sediment were processed from the type section of the don formation at toronto ontario and yielded approximately 18 000 identifiable mollusc shells representing 45 taxa previously unpublished taxa include 11 freshwater gastropod species 12 pelecypod species sphaeriidae and 7 terrestrial gastropod species the molluscs are mainly concentrated in the lower two thirds of the formation and are dominated by valvata perdepressa with abundant valvata sincera probythinella lacustris amnicola limosa amnicola walkeri pleurocera acuta elimia livescens pisidium casertanum pisidium compressum pisidium fallax and sphaerium striatinum all the mollusc species are modern inhabitants of the great lakes region their known ecological tolerances suggest deposition in relatively shallow waters of a large temperate lake having substantial fluvial input nearby stratigraphic variations in the relative abundance of different aquatic taxa may reflect variations in water depth or fluvial activity stable isotope data from several mollusc species and a single wood specimen together with taxonomic paleoenvironmental interpretation are consistent with deposition during the climatic optimum of the sangamonian interglaciation environmental conditions and faunas are similar to those of the nipissing phase hypsithermal of the eastern great lakes

a routine high precision method for lu hf isotope geochemistry and chronology a method for chemical separation of lu and hf from rock meteorite and mineral samples is described together with a much improved mass spectrometric running technique for hf this allows i geo and cosmochronology using the176lu 176hf decay scheme and ii geochemical studies of planetary processes in the earth and moon chemical yields for the three stage ion exchange column procedure average 90 for hf chemical blanks are 0 2 ng for lu and hf from 1 g of hf a total ion current of 0 5 10 11 ampere can be maintained for 3 5 h yielding 0 01 0 03 precision on the ratio176hf 177hf normalisation to179hf 177hf 0 7325 is used extensive results for the johnson matthey hf standard jmc 475 are presented and this sample is urged as an international mass spectrometric standard suitable aliquots prepared from a single batch of jmc 475 are available from denver lu hf analyses of the standard rocks bcr 1 and jb 1 are given the potential of the lu hf method in isotope geochemistry is assessed

occurrence of retene in upper silurian lower devonian sediments from north africa origin and implications abstract the biomarkers retene cadalene tetrahydroretene and isohexylalkylnaphthalene have been identified in the extracts of silurian devonian clastic sediments from southern tunisia the occurrence of retene is unexpected as it is generally considered to be a diagenetic product of the conifer constituent abietic acid however conifers evolved only after the devonian the retene shows a strong correlation with the abundant terrestrial signal from bryophyte derived cryptospores in the palynofacies suggesting that it derives from a terrestrial source accordingly we propose that either abietic acid synthesis evolved prior to the appearance of conifers or retene is a diagenetic product of precursors other than abietic acid which were synthesized by the earliest land plants without excluding the first possibility it appears likely that retene derives here from the diagenesis of compounds with a kaurane type skeleton which were abundantly produced by the early palaeozoic bryophytes

paleoproterozoic arc magmatism in the north china craton no siderian global plate tectonic shutdown abstract arc magmatism in convergent plate margins has been a major contributor to continental growth following arc arc and arc continent collisions in the archean leading to the amalgamation of micro blocks the north china craton ncc witnessed major pulses of continental arc magmatism during the paleoproterozoic in this study we present geochemistry zircon u pb geochronology and lu hf isotope data from a suite of magmatic rocks sampled from the region of confluence of two major paleoproterozoic suture zones in the ncc the inner mongolia suture zone imsz and the trans north china orogen tnco our zircon u pb geochronological data indicate new zircon growth during multiple tectonothermal events as displayed in the 207pb 206pb weighted mean ages of 2410 41 ma for metagranite 2480 12 ma 2125 18 ma 1946 8 ma 1900 15 ma and 1879 12 ma from metagabbros 2446 11 ma from charnockite and 1904 6 ma and 1901 9 ma from metatuffs the 207pb 206pb upper intercept age of zircons in the khondalite shows 2102 76 ma which is identical to the age obtained from the magmatic zircons in one of the metagabbros the khondalites also carry a group of concordant metamorphic zircons with 207pb 206pb mean age of 1881 20 ma metamorphic zircons in the gabbros and charnockites also yield similar ages of 1890 14 ma and 1852 19 ma respectively the age data suggest prolonged arc magmatism in a convergent margin setting during ca 2 48 to 1 9 ga followed by metamorphism at ca 1 89 1 85 ga associated with the final collision lu hf analyses reveal that the dominant populations of zircons from all the rock types are characterized by positive ehf values 1 9 to 6 8 mean 1 8 the ehf and tdmc data suggest that the magmas were mostly derived from neoarchean and paleoproterozoic juvenile components the salient geochemical features of these rocks attest to magma generation from heterogeneous sources involving subduction derived arc components with minor input from continental crust the results presented in this study together with those from previous investigations in different domains of the imsz and tnco suggest major paleoproterozoic arc magmatic events in the ncc lasting for nearly 600 million years associated with the final assembly of the crustal blocks into a coherent craton construction of the final cratonic architecture of the ncc thus witnessed not only the arc continent amalgamations at 2 7 2 5 ga but also major crust building events in the paleoproterozoic through melts generated from juvenile and recycled components in continental magmatic arc systems along an active convergent margin followed by intense deformation and metamorphism during the final collision at 1 85 1 80 ga the prominent paleoproterozoic magmatic records in the ncc do not support the proposal of global plate tectonic shutdown in the siderian and confirm vigorous convergent margin magmatism and crust building processes throughout the paleoproterozoic

a u pb zircon paleoproterozoic age for the metasedimentary host rocks and gold mineralization of the crixas greenstone belt goias central brazil abstract the crixas greenstone belt central brazil consists of a greenschist to low amphibolite facies metamorphic volcanosedimentary sequence that contains the sixth largest gold reserve 70 t au in the average 12 g t of brazil and the largest gold only deposit of central brazil the gold orebodies are hosted by low angle thrust faults within the stratigraphically upper metasedimentary rocks and are crosscut by a set of post mineralization mafic dykes for decades the sequence has been interpreted as a typical archean greenstone belt of the brazilian shield and the gold mineralization considered either archean or neoproterozoic this study shows the results of in situ u pb shrimp and la icp ms dating of detrital zircon grains from graywacke and mafic dyke samples as well as pb and nd isotopic signatures of the ores the oldest detrital zircon grains of the graywacke samples yielded u pb ages of 3354 40 ma and the youngest between 2209 28 ma and 2222 30 ma which indicates a mixture of archean and paleoproterozoic rhyacian source area and that the maximum depositional age is of ca 2 2 ga magmatic zircon of the post mineralization mafic dykes yielded the u pb age of 2170 17 ma which suggests that the basin stage its deformation metamorphism and mineralization were restricted to the rhyacian and took place during a time span of about 30 40 m y the paper thus provides a new insight into the age of the crixas greenstone belt rocks and of its gold only deposits and reveals that mid paleoproterozoic was a more widespread metallogenetic epoch related to greenstone belts of the brazilian precambrian platform then previously interpreted the observed pb and nd isotopic signatures of the ores suggest that metabasalts carbonaceous schist and metagraywackes could provide the adequate sources for the ore bodies and that the initiation of fluid circulation may have resulted by the emplacement of a high level granite

a late pleistocene to holocene record of precipitation reflected in margaritifera falcata shell δ18o from three archaeological sites in the lower salmon river canyon idaho oxygen 18 18o concentrations in margaritifera falcata shells preserved in three archaeological sites in the lower salmon river canyon of idaho are compared with modern mussel shells shell 18o records show that late pleistocene and early holocene climates were drier with occasional periods of increased precipitation after c 4000 years bp precipitation is higher in the salmon river basin than at present and trends toward modern conditions after c 1800 years bp the climatic conditions reflected by fluctuations in shell 18o are matched by regional palaeoenvironmental records including pollen glacial and palaeohydraulic proxy sources and are compared with major changes in plateau prehistoric cultural patterns studies of late quaternary records of freshwater bivalve shell 18o are useful for reconstructing climatic conditions and complement geoarchaeological studies in riparian contexts

pre late wisconsinan pleistocene biota from southeastern michigan u s a abstract fossiliferous sediments underlie the late wisconsinan mill creek and fisher road tills at the mill creek site northwest of port huron michigan fragmentary remains of 5 fish and 11 mammal taxa occur with 39 taxa of molluscs 6 of ostracodes and a pine spruce pollen assemblage while the fish are wide ranging the mammals include distinctly northern elements such as dicrostonyx sp lemmus sp mictomys borealis and microtus xanthognathus the molluscs include a mixture of cold vertigo alpestris oughtoni and v modesta and warm lioplax sulculosa taxa none of the vertebrates have been found at michigan sub till sites before and lioplax is new to michigan fossil or living vertigo hannai is known only as a pleistocene fossil at present the age of the biota is indeterminate the stratigraphy indicates a middle wisconsinan or greater age a finite 14c age of 48 3 0 8 ka ql 1215 was later supplemented by a tl date of 57 9 ka but perhaps as old as 300 ka two clusters of amino acid allo isoleucine isoleucine values obtained from six genera of molluscs are interpreted to represent the co occurrence of early sangamonian aile ile values ranging from approximately 0 15 to 0 25 and illinoian aile ile values ranging from approximately 0 25 to 0 35 mollusc fossils at the mill creek site these results highlight the need for more reliable quaternary dating methods

u pb geochronology of the 2 0 ga itapecerica graphite rich supracrustal succession in the sao francisco craton tectonic matches with the north china craton and paleogeographic inferences abstract la icpms u pb isotopic studies are conducted for key samples from the itapecerica graphite rich supracrustal succession and the crystalline basement in the southern sao francisco craton sfc the detrital zircon analyses in paragneiss indicated a maximum deposition age of 2080 ma the age spectra in the relative probability diagrams suggested the precursor basin was essentially fed with detritus from the accretionary complexes of the mineiro belt 2470 2000 ma which is the most preserved segment of the minas orogen the basement rocks yielded zircon u pb crystallization ages between 2753 81 and 2679 61 ma whereas the metamorphic overprint gave 2069 84 ma one nearby charnockitic gneiss yielded a sm nd garnet whole rock linear array with an age of 2086 19 ma the youngest ages estimate the timing of the regional prograde granulite facies metamorphism that also overprinted the itapecerica rocks given our upper intercept zircon u pb ages of 1997 20 ma and 1971 40 ma in paragneiss and quartzite respectively these ages also constrained the timing of the conversion of carbonaceous material into graphite in the itapecerica mine the second largest graphite mine in brazil the high grade metamorphism was associated with the final docking of the mineiro belt against the neoarchean foreland the minas orogen has geologic matches with the jiao liao ji orogen located in the present eastern margin of the north china craton where khondalites uht granulites anatectic charnockites as well as large graphite deposits are documented such as in the 1 97 1 88 ga korean arc the tectonic similarities between the two cratons support a relatively close position at the time frame the dynamic scenario considers broadly coeval accretionary collisional belts along the active margins of archean blocks the progressive closure of the paleoproterozoic ocean and final docking of the sao francisco congo paleocontinent against the active continental margin of the north china craton the work model allows new insights into the paleogeography of the core of supercontinent columbia at 1 90 ga and the subsequent 1 78 1 50 ga intraplate activity

assessing meteoric water composition and relative humidity from18o and2h in wood cellulose paleoclimatic implications for southern ontario canada abstract an empirical model is presented that derives the initial isotopic composition of water used by terrestrial plants and the relative humidity that prevailed during photosynthesis from the isotopic composition of oxygen and carbon bound hydrogen in the plant cellulose the model uses fixed values for the fractionation factors that describe the evapotranspirative isotopic enrichment of leaf waters and the biochemical fractionations occurring during cellulose synthesis when applied to cellulose extracted from fossil plant matter the model can be used to generate quantitative estimates of the temperature and moisture regimes of the past the application of the model is demonstrated by consideration of 18o and 2h results on cellulose from fossil wood collected at brampton ontario the brampton data yield records of systematic changes in the temperature and moisture regimes of the eastern great lakes region over the past 11 500 a both mean annual temperature and photosynthetic humidity increased substantially from values much lower than the present at the end of the wisconsin stage to values higher than the present in the mid holocene the phase relation of the paleotemperature and paleohumidity curves engenders differentiation of the climatic history at brampton into four characteristic zones i a period of ameliorating climate predominantly much colder and drier than now lasting until about 7400 b p ii an early hypsithermal period of warm and dry conditions that transformed after 6000 a b p into iii the main hypsithermal time of warmth and pronounced moistness subsequent climatic detrioration led to establishment of iv cool moist conditions like the present sometime within the last few thousand years

continental outbuilding along the margin of an archean cratonic nucleus in the north china craton abstract the history of crustal growth in the early earth formation of cratonic nuclei and the building of large continents have important implications in understanding the secular evolution of our planet the north china craton ncc is envisaged in recent models as a collage of several archean microblocks which were amalgamated along multiple zones of ocean closure during the late neoarchean and offers window to gain insights on the origin of cratonic nuclei and their subsequent outbuilding here we investigate a suite of magmatic rocks developed at the periphery of one of these microblocks the qianhuai block we present petrological geochemical and zircon u pb geochronological and lu hf isotopic data on a suite of rocks ranging from hornblendite through gabbro and dioritic gabbro to ttg tonalite trondhjemite granodiorite and granitoids exposed in the miyun area and representing the cross section of the lower to mid segments of a continental magmatic arc geochemically the felsic units of the suite straddle from monzonite through granodiorite to granite with dominantly metaluminous affinity magnesian composition and arc related features the metagranites and ttg gneisses are characterized by negative nb ta anomalies and positive k and pb anomalies the diorite gabbros and hornblendite display negative anomalies of th u nb ta and zr hf and positive anomalies at ba pb and sm with negative eu anomalies and minor positive ce anomalies attesting to arc related origin in the tectonic discrimination diagrams the rocks plot in the volcanic arc field indicating formation within a subduction related setting the oldest magmatic population with ages of ca 2560 and 2529 ma from the hornblendite and the ttg gneiss represent the magma emplacement ages with fractional crystallization of underplated basalts derived from slab melts leaving hornblendite as the cumulate magmatic zircon grains from the metagranite and granodiorite show upper intercept ages of 2457 21 ma and 2475 12 ma whereas those from the ttg gneisses yield ages of 2529 19 ma and 2522 38 ma younger age groups of 2444 4 8 3 ma 2418 16 ma and 2161 31 ma also occur in these rocks indicating multiple thermal events the zircon grains from diorite and gabbros show 207pb 206pb weighted mean ages of 2411 11 ma 2486 13 ma with younger ages of 2 0 2 37 ga these rocks also carry older xenocrystic grains of ca 2 51 2 65 ga the zircons in hornblendite show an upper intercept age of 2560 33 ma and a lower intercept age of 1947 54 ma young groups of ca 2 2 ga and 1 8 ga are also found in this rock the ca 1 9 to 1 8 ga ages correspond to the timing of metamorphism the hf isotopic data on zircons from the various rock types of the miyun magmatic suite show both negative and positive ehf t values ranging from 9 64 to 7 04 with hf model ages in the range of 2606 2844 ma tdm1 and 2635 3147 ma tdm2 suggesting crustal growth through both juvenile magmas from depleted mantle sources and reworked meso to neoarchean crustal components our study reveals that the ca 2 7 3 0 ga core of the qianhuai microcontinent represents one of the ancient cratonic nuclei in the ncc that underwent extensive continental outbuilding during late neoarchean early paleoproterozoic through multiple magmatic events mostly related to convergent margin arc type processes it is possible that similar processes operated around the other archean microcontinents in the ncc in the process of building the major crustal blocks which were finally amalgamated at the end of the paleoproterozoic

u pb zircon and titanite systematics of the fish canyon tuff an assessment of high precision u pb geochronology and its application to young volcanic rocks a large data set of single and multi grain zircon and titanite analyses from a sample of the oligocene fish canyon tuff fct a voluminous ash flow from the san juan mountains of colorado and widely used 40ar 39ar geochronological standard has been used to evaluate the influence of various sources of analytical and geological uncertainty on the calculated age of this tuff by the isotope dilution u pb zircon method twenty three single zircon grains and seven small multi grain fractions of the fct yield an inverse variance weighted mean 206pb 238u date of 28 402 0 023 ma 2 mswd 0 93 and a slightly older weighted mean 207pb 235u date of 28 529 0 030 ma mswd 0 74 which are insensitive to common pb corrections initial 230th disequilibria calculated from a newly measured th u 2 2 for fct pumice shards indicate th deficiency for these zircons its correction brings the weighted mean 206pb 238u date to 28 478 0 024 mswd 0 97 minimizing the discordance of the fct zircon analyses these calculations culminate in concordia ages ludwig 1998 for the crystallization of the fct zircons of 28 476 0 029 ma mswd 1 50 without propagating decay constant errors or 28 498 0 035 ma mswd 1 03 with propagated decay constant errors these results are in close agreement with a previous single grain 206pb 238u zircon date of 28 41 0 05 ma for the fct oberli et al 1990 however they do not corroborate the discordia lower intercept date of 27 52 0 09 put forth by lanphere and baadsgard 2001 the 28 476 0 064 ma concordia age for fct zircons including systematic decay constant errors and uncertainty in pb u tracer calibration is substantially older than all published 40ar 39ar sanidine ages which range from 27 5 to 28 05 ma lanphere and baadsgaard 1997 renne et al 1998 a lengthy period 400 k y of zircon residence in the magma chamber before eruption is commonly called upon to explain the age discrepancy however fct titanite which may remain open to pb diffusive exchange until quenching upon eruption yield a minimum 230th disequilibrium corrected weighted mean 206pb 238u age of 28 395 0 049 ma 0 078 with tracer uncertainty weakening residence time arguments and supporting recent calls for re evaluation of the 40k decay constant and the accepted ages for commonly used 40ar 39ar mineral standards the fct zircon concordia age also provides an empirical constraint on the decay constants of the u isotopes indicating the relative accuracy of the currently accepted decay constants to within the original counting statistic errors of jaffey et al 1971

fluvial architecture of the upper permian raniganj coal measure in the damodar basin eastern india abstract the upper permian raniganj formation of the damodar basin consists of an interbedded assemblage of sandstone shale carbonaceous shale and coal facies the trough cross bedded sandstone bodies st facies formed by migration of dunes in sand bar point bars are widely developed in the lower part of raniganj formation the planar cross bedded facies sp of transverse and diagonal bars and massive sandstone of longitudinal bars abound in the upper part of the eastern raniganj and jharia coalfields the succeeding ripple cross laminated sr facies with or without reactivation surface alternating with thick beds of fine clastics suggestive of flood deposits is widespread in the western bokaro and north karanpura coalfields markov chain statistics reveals a fining upward cyclical order of superposition throughout the raniganj sequence the integrated results of paleocurrent channel morphology texture and petrography suggest that the raniganj sedimentation was brought about in an extensive unified alluvial plain drained by a system of west northwest flowing streams whose channel sinuosity increased and depth decreased progressively in a downcurrent direction from east to west post gondwana faulting and subsequent erosion account for the disconnected disposition of the coalfields

a petrological and organic geochemical study of permian coal seams east of maracaja south santa catarina parana basin brazil abstract coal samples from the permian rio bonito formation collected from borehole mml 09 east of maracaja south santa catarina parana basin brazil were characterized by petrological vitrinite reflectance measurements maceral analyses and geochemical rock eval total organic carbon toc and gc ms methods the mean vitrinite reflectance values range from 0 73 to 0 87 rrandom indicating a rank level of high volatile b a bituminous the maceral composition showed predominance of vitrinite 49 4 to 61 2 vol and inertinite 9 to 24 5 vol the rock eval analysis presented the following values s1 and s2 ranging from 0 74 to 2 51 mg hc g coal and 34 1 to 108 87 mg hc g coal respectively hydrogen indices between 158 and 240 mg hc g toc and tmax c between 440 and 448 c the toc contents of the coal samples present values ranging from 18 85 to 45 31 wt vitrinite reflectance and rock eval tmax values indicate that the coals are in the beginning of the oil generation window the potential for the formation of liquid hydrocarbons is rather low due to the nature of the humic coal whereas the rank level indicates that generation of gas from the coal has occurred the biomarker analysis using gc ms and gc ms ms allowed the interpretation of the depositional environment and provided another way of determining the degree of maturity of the coals besides vitrinite reflectance and tmax the pristane phytane pr ph ratio is 1 mainly controlled by organic matter type implied suboxic conditions during sedimentation the vitrinite reflectance measurements tmax values and 20s 20s 20r and ratios for c29 regular steranes revealed the marginally mature stage of the organic matter although the distribution of hopanes indicated a mature stage of the organic matter due to the absence of hopanes and predominance of the 22s epimer over the 22r epimer for the hopanes from c 31 to c 35

early eocene equatorial vegetation and depositional environment biomarker and palynological evidences from a lignite bearing sequence of cambay basin western india abstract an investigation of palaeofloral distribution with depositional environment and palaeoclimatic condition of western indian subcontinent during early eocene period has been carried out from a lignite bearing succession of cambay basin western india the study of biomarkers palynological remains and petrography is taken as proxies for providing supportive evidence for our inference the petrographic results reveal that the sediments are thermally immature and coalification was extended up to the lignitic stage low rank b the palynological results show the dominance of angiosperms mainly members belonging to the arecaceae family throughout the studied section triterpenoids with oleanane ursane and lupane structure in extractable organic matter are derived from angiosperm wax pollen grains spinizonocolpites proxapertites dipterocarpuspollenites albertipollenites retipollenites arengapollenites lakiapollis and longapertites with pteridophyte spores and fungal fruiting bodies confirm the prevalence of tropical to subtropical climate during the deposition of the sediments sesquiterpenoids like longifolene 12 methanoazulene cadinane and selinene together with amyrin derivatives are the indicator of dipterocarpaceae family that grows in the extant tropical rain forests in se asia appearance of dinoflagellate cysts and the predominance of lower molecular weight part in n alkane series with the signature of submerged floating vegetation in the shale horizon indicate marine influence in the younger part of the mine section the presence of mangrove pollen such as spinizonocolpites proxapertites and acanthotricolpites further suggests that the lignite bearing sequence was deposited in marshy marginal marine environment

terpenoid composition and botanical affinity of cretaceous resins from india and myanmar abstract fossil resins from the cretaceous sediments of meghalaya india and kachin myanmar burma were analysed using curie point pyrolysis gas chromatography mass spectrometry and thermochemolysis gas chromatography mass spectrometry to help elucidate their botanical source the major pyrolysis products and methyl esterified thermochemolysis products of both the resins were abietane and labdane type diterpenoids with minor amount of sesquiterpenoids the thermochemolysis products also included methyl 16 17 dinor callitrisate methyl 16 17 dinor dehydroabietate and methyl 8 pimaren 18 oate the latter two from just the myanmarese resin the exclusive presence of both labdane and abietane diterpenoids and the lack of phenolic terpenoids may suggest that the studied cretaceous resins were derived from pinaceae pine family conifers

bizarre geochemistry of komatiites from the crixas greenstone belt brazil komatiite lava flows in the crixas greenstone belt goias brazil have textures and volcanic structures typical of archean komatiites but are geochemically most unusual the flows are porphyritic and massive or layered with spinifex upper parts and olivine cumulate lower parts mgo contents range from 18 to 40 in such lavas only olivine and minor chromite can have crystallized but neither major nor trace elements fall on olivine control lines in mgo variation diagrams cao and sr fall on lines with slopes steeper than olivine control lines sio2 feo na2o k2o and y show little systematic variation zr shows a large variation that does not correlate with mgo and al2o3 decreases markedly with decreasing mgo the aberrant behaviour is highlighted by the ree rare earth elements in spinifex and olivine cumulate layers from three flows in the spinifex layers chondrite normalized ree patterns are hump shaped with maxima at nd or sm la sm n 0 6 gd yb n 1 6 2 3 whereas cumulate zones in the same flows have steadily sloping patterns with lree enriched relative to hree la sm n 1 3 gd yb n 1 4 neither normal magmatic processes acting during emplacement of the komatiites nor thermal erosion and wall rock assimilation can explain these effects and we speculate that elements commonly thought of as immobile e g al zr ree migrated during hydrothermal alteration or metamorphism a pb pb whole rock isochron gave an age of 2 728 140 ma and selected sm nd analyses an apparent isochron age of 2 825 98 ma nd 0 the pb pb age is believed to be the approximate time of emplacement interpretation of the sm nd data is complicated by the evidence of mobility of ree

pleistocene glacio lacustrine deltaic deposits of the scarborough formation ontario canada abstract the late pleistocene scarborough formation of the lake ontario basin represents a lacustrine deltaic sequence strongly affected by a nearby glacier it shows gradual upward coarsening and thickening of layers from varve like clay rich rhythmites at the base to channelized cross bedded sands at the top thick lensing massive layers cm of silty sand are found interstratified with thin layers of silt and clay in the lower and middle parts of the sequence these massive layers were probably formed by subaqueous gravity flows of material in part derived directly from a glacier absence of pebbles and of other features such as glacial silt pellets suggests dispersal away from the foot of the glacier rather than deposition under floating ice varve like rhythmites pollen and insect fauna indicate subarctic to arctic climatic conditions at the time of sediment deposition the large amount of sand in the upper part of the formation is best explained as derived from active outwash fans similar fans were formed during the last deglaciation in southern ontario and can be observed on the landscape

two neoarchean supercontinents revisited the case for a rae family of cratons abstract a variety of early paleoproterozoic supercontinents or supercratons have been proposed including kenorland superia and vaalbara improved geologic knowledge of the churchill province canadian shield suggests that the classical kenorland configuration with linked rae and hearne cratons is invalid and represents a younger ca 1 9 ga nuna configuration we review the early paleoproterozoic tectonic history of the rae craton and propose that the ca 2 55 2 50 ga macquoid and 2 50 2 28 ga arrowsmith orogens represent critical piercing points for supercontinent reconstruction utilizing the stratdb and dateview databases we have identified nearly two dozen regions worldwide that show effects of these orogenic events including the rae gawler mawson peninsular india west africa amazonia north china and sask crustal blocks we propose that these cratonic blocks form a distinct rae family lineage utilizing new time space plots for the rae family and components of the superia and vaalbara supercratons we demonstrate that the rae family lacks the distinctive early paleoproterozoic depositional and glaciogenic record characteristic of superia and vaalbara but has an important contemporaneous record of juvenile crust formation and contractional orogenesis we propose the collective history of the rae family is best reconciled if it represents the now dispersed blocks of a third earliest paleoproterozoic supercraton that we term nunavutia in this model the magmatic and tectonometamorphic record of these cratons includes an early 2 55 2 45 ga period of interior collisional orogenesis in which the supercraton amalgamated and a later phase of long lived peripheral orogenesis 2 45 2 28 ga prior to its partial break up at ca 2 05 ga forming within an otherwise globally quiescent period the history of the rae family is important for assessment of constrasting models of early paleoproterozoic geodynamic activity

three detailed radiocarbon dated holocene tufa and alluvial fan mollusc successions from southern ontario the first in northeastern north america abstract fossil mollusc remains particularly those of land snails provide a wealth of detailed information concerning local quaternary paleoenvironments and regional paleoclimatic conditions however this important resource is generally overlooked in north america and consequently quantitative well dated terrestrial mollusc successions are extremely rare here in an attempt to redress this imbalance a project examining the holocene molluscan faunal history of northeastern north america has been initiated thus far detailed mollusc successions and associated radiocarbon age determinations have been obtained from three sites in southern ontario two alluvial fans chine drive fan and cudia park fan both from the scarborough bluffs east of toronto and a tufa west river road near cambridge the observed land snail successions to provide an initial view of the molluscan faunal history of this region during the period from the late glacial to the mid holocene between approximately 10 500 and 5000 radiocarbon years bp yr bp the molluscan data have also been used to reconstruct the paleoenvironmental history of southern ontario during this time documenting the progression from exposed open habitats characterised by species such as vertigo modesta vallonia albula columella columella and vitrina angelicae limpida to closed woodland biotopes indicated by the presence of taxa including carychium nannodes nesovitrea binneyana paravitrea multidenta and helicodiscus parallelus this study has already demonstrated the potential of this technique in the study of quaternary climatic and environmental change in eastern north america and represents a strong foundation for extending the analysis of fossil land snail successions to other sites throughout this region it has also provided new and important insights into the establishment of the modern molluscan fauna which are essential to the understanding of present day distributional patterns and environmental associations

paleoclimate reconstruction from petrography and biomarker geochemistry from permian humic coals in sydney coal basin australia abstract the character of the coal in tomago and greta coal measures are similar to other coals from the sydney coal basin with variation from vitrinite rich to inertinite rich coal a type iii organic matter om linked to continental higher plants and a perhydrous type iii similar to type ii were found by rock eval analysis the coexistence of inertinite with algae botryococcus in the greta coals explains the high hi in the perhydrous type the gangamopteris flora that is reported in the greta coal measures grew after plants in a taiga like the recent birch forests in russia retallack 1980 the glossopteris flora that is reported in the tomago coal measures grew in a swamp forest based upon the botanic zonation this flora was located in the cold temperate biome that was located in gondwanaland except for antarctica which was in the glacial biome diterpane analysis results reveal alternation of wet and dry periods existed during the deposition of lewis coals in the greta coal measures during the kungurian and an increase of dryness is noted from upper donaldson to beresfield in the tomago coal measures during the capitanian based on analysis of aromatics and diterpanes the same periods of dryness and wetness alternate during the coal deposition in the sydney coal basin these climatic changes correspond to high frequency cycles n alkanes naphtalenes and phenanthrenes and does not alter the paleoenvironmental and paleoclimatic interpretation the comparison between biomarkers from coals and isotopes from marine birgenheier et al 2010 and terrestrial retallack et al 2011 deposits allow us to identify precise dry wet climate and glacial interglacial periods during the permian

illinoian to late wisconsinan stratigraphy at woodbridge ontario near woodbridge northwest of toronto ontario a 15 metre high railroad cut and associated borrow pit first excavated in 1962 exposed a multiple till sequence and intervening fossiliferous sediments work over the next 35 years revealed that illinoian york till early wisconsinan sunnybrook till and late wisconsinan humber till halton till and wildfield till are interbedded with fossiliferous sediments equivalent to the sangamonian don formation early wisconsinan scarborough formation 50 ka bp and middle wisconsinan thorncliffe formation 45 ka bp a complex periglacial record displays multistage fossil frost wedges indicating intervals of severe climate in late illinoian and early wisconsinan time cored boreholes indicate deep gravel below and a till on ordovician shale bedrock georgian bay formation vertebrates molluscs ostracodes insects and plants diatoms wood seeds pollen indicate mostly cool conditions boreal to tundra for interstadial sediments interglacial conditions a

sesqui and diterpenoid biomarkers preserved in taxodium rich oligocene oxbow lake clays weisselster basin germany several diterpenoids of the abietane pimarane and phyllocladane type and three cadalanetype sesquiterpenoids have been identified in the organic solvent extracts of lower oligocene clay sediments haselbach strata saxony germany the sediment contains needles and cone scales of a fossil taxodium species which represents the only conifer in the samples a clear correlation between the observed conifer biomarkers and taxodium is evident apart from diterpenoids detected previously in other sediments a new diaromatic totarane diterpenoid is reported in isolated fossil and recent taxodium needles and cone scales as well as in the haselbach clays a phenolic diterpenoid of the abietane type ferruginol has been identified the results indicate that the taxodium rich clay samples contain several diterpenoids which so far have been used as biomarkers for other conifer families and thus the chemotaxonomical use of diterpenoid biomarkers for the differentiation of fossil conifer families has to be revised

stable isotope paleoclimate records for southern ontario canada comparison of results from marl and wood profiles of 18o in two marl cores from southern ontario canada are compared in detail with the records of meteoric water isotopic composition and photosynthetic humidity obtained from previous isotopic studies using wood cellulose at brampton ontario by accounting for the inferred changes in meteoric water composition and temperature the changes in the oxygen isotope content of the marl arising from fluctuations in the evaporative enrichment of the lakewater can be estimated the resulting synthetic profiles of relative evaporative enrichment from both marl cores exhibit strong correspondence to the photosynthetic humidity profile generated from the studies at brampton which substantiates the importance of evaporation in the water budgets of these two lakes a striking analogy exists between the isotopic evaporative enrichment response of such lakewaters and that of the waters in terrestrial plants both of the marl lakes approach close to isotopic steady state during the summer season when carbon

vascular plant biomarkers as proxies for palaeoflora and palaeoclimatic changes at the dogger malm transition of the paris basin france abstract vascular plant biomarkers are used here as a chemostratigraphic tool for tracing both palaeoflora and palaeoclimatic changes during the callovian and oxfordian in the paris basin the retene cadalene ratio shows low values in claystones from the middle callovian to the end of the lower oxfordian then increases drastically from the end of the lower oxfordian cordatum zone synchronously with the progressive development of the oxfordian carbonate platform the relative proportion of retene a conifer biomarker is strongly correlated with the abundance of some of its diagenetic precursors and with saturated diterpanes some of these are very common and abundant in the pinaceae family while specific markers for non pinaceae conifers are not detected thus the increase in the retene cadalene ratio around the cordatum zone reflects the rising proportion of pinaceae on the london brabant massif which was the nearest land from the locations studied as pinaceae show many morphological adaptations to dry climate compared to the other plants reported in the jurassic taphofloras of the paris basin their increasing proportion indicates an increasing aridity this climatic change is also supported by published geochemical palaeobiogeographical palynological palaeobotanical and mineralogical data a comparable increase in the relative proportion of retene was also described for the oxfordian of western australia which could be an argument for a worldwide increase in aridity at the end of the lower oxfordian

occurrence and palaeoenvironmental significance of aromatic hydrocarbon biomarkers in oligocene sediments from the mallik 5l 38 gas hydrate production research well canada abstract the aromatic hydrocarbon biomarker distributions of thirty oligocene sediment samples with different lithology lignite clay and sand from the japex jnoc gsc et al mallik 5l 38 gas hydrate production research well canada were analyzed using gas chromatography mass spectrometry gc ms the compositions vary with lithology indicating a change in palaeoenvironmental conditions at the time of deposition aromatic diterpenoids of the abietane type are more abundant in the lignite samples than in the clay samples and represent a gymnosperm e g conifer dominated palaeovegetation in contrast in the clay samples aromatic triterpenoids are generally preserved as major constituents indicating angiosperm dominated vegetation the sand samples contain only minor amounts of aromatic terpenoids but show a preference for diterpenoid gymnosperm markers to recognise gymnosperm versus angiosperm dominated palaeoenvironments a new ratio termed the angiosperm gymnosperm aromatic ratio agar has been developed thus the terpenoid distribution in the deltaic sediments provides information on the compositional changes in the plant community at the mallik site lignites and the hinterland clays over time concomitantly the changing dominance in the plant communities allows an insight into varying climatic conditions during the late oligocene in the area additionally the aromatic biomarker composition has been used to assess the level of thermal maturity of the organic matter in the mallik samples and indicates a prevailing immature character

molecular composition and chemosystematic aspects of cretaceous amber from the amazonas araripe and reconcavo basins brazil amber occurrences in brazil are rare in this regard the molecular composition of three such fossil resin samples from brazilian cretaceous sedimentary basins has been analyzed to determine the botanical origin of the resins the samples were collected from the amazonas alter do chao formation araripe santana formation crato member and reconcavo maracangalha formation caruacu member basins the mono sesqui and diterpenoids in the extracts were used as chemosystematic markers when compared with terpenoids in extant conifers the compounds were mainly diterpenoids and their degradation products from the labdane podocarpane pimarane and isopimarane classes in addition to paraffins methoxyphenols and carboxylic acids tetracyclic diterpenoids such as phyllocladane kaurenol and kauranol were also present the biomarker compositions are certainly typical for conifers and given the absence of triterpenoids and diterpenoids such as ozic acid angiosperms can be excluded as a botanical source the absence of phenolic diterpenoids ferruginol totarol and their derivatives excludes podocarpaceous affinities for the ambers from the amazonas and araripe basins the fossil records of the embedding sediments e g araucariaceae pollen and leaves support the proposal of an araucariacae origin for these ambers but cupressaceae and cheirolepidiaceae cannot be excluded on the other hand the presence of phyllocladane and kaurane derivatives is evidence for araucariaceae or podocarpaceae origins for the amber from the reconcavo basin but cupressaceae cannot be excluded