chemistry of modern soils as a guide to interpreting precambrian paleosols precambrian paleosols are potentially one of our best sources of information about the composition of the atmosphere early in earth s history to be used this way however an alteration profile must be shown to be an in situ product of vadose processes data from modern soils show that the ratios of less mobile elements such as zr ti and al can be used as a preliminary screen to test for the in situ nature of a profile if the ti zr ratio departs from that of the host rock by more than 40 or the ti al ratio departs by more than 50 for moderate degrees of weathering then a significant allochthonous contribution to the profile is indicated this technique correctly separates in place from allochthonous horizons when applied to independent data from two modern profiles a review of published precambrian profiles identifies two often cited examples denison and pronto as suspect based on these criteria in the interpretation of paleoatmospheres it is also necessary to show that fe is controlled not b

geochemical signature of provenance tectonics and chemical weathering in the quaternary flood plain sediments of the hindon river gangetic plain india abstract the ganga basin in the himalayan foreland is a part of the world s largest area of modern alluvial sedimentation flood plain sediments of the hindon river of the gangetic plain have been analyzed for sediment texture major and trace elements including rare earth elements rees the results have been used to characterize the source rock composition and to understand the intensity of chemical weathering tectonics and their interplay in the hindon flood plain the sediments of the hindon flood plain dominantly consist of sand sized particles with little silt and clay the geochemistry of the hindon sediments has been compared to the siwalik mudstone of the siwalik group siwaliks the siwalik sedimentary rocks like sandstones mudstones and conglomerates are the known source rocks for the hindon flood plain sediments mudstone geochemistry has been considered best to represent the source rock characteristics the ucc upper continental crust normalized major and trace elements of the hindon flood plain sediments are very similar to the siwalik mudstone except for th and cr furthermore the average chondrite normalized ree pattern of the hindon flood plain sediments is similar to the siwalik mudstone textural immaturity k rb ratios and the average cia chemical index of alteration and pia plagioclase index of alteration values of the hindon flood plain sediments indicate that the sediments have not been affected by chemical weathering our study suggests that the active tectonics of the himalayas and monsoon climate enhances only physical erosion of the source rocks siwaliks rather than the chemical alteration these factors help the hindon sediments to retain their parental and tectonic signature even after recycling

provenance and tectonic setting of the proterozoic turbidites in hunan south china geochemical evidence the geochemical composition of the middle upper proterozoic turbidites in hunan south china is related to provenance and tectonic setting of the sedimentary basin the turbidites are characterized by moderate sio 2 contents al 2 o 3 sio 2 typically 0 1 0 3 and moderate k 2 o na 2 o ratios generally 0 1 0 3 but relatively high fe 2 o 3 mgo contents 5 10 wt and unusually low contents of cao typically 1 wt abundances of ferromagnesian trace elements and incompatible elements are moderate the ree patterns are uniform and similar to the upper continental crust and typical post archean shales with lree enrichment flat hree and significant negative eu anomalies in general the slates show higher contents of fe 2 o 3 mgo and ferromagnesian trace elements and lower ratios of la sc and th sc than the associated graywackes suggesting that more mafic materials were incorporated into the clay size fraction compared to the upper proterozoic banxi group the middle proterozoic lengjiaxi group has higher concentrations for most ferromagnesian trace elements and lower la sc ratios implying more mafic components in the provenance of the latter the relationship among alkali and alkaline earth elements the chemical index of alteration cia and the th u ratios indicate that the source area was affected by a moderate weathering history the main source was old continental crust the yangtze craton dominated by felsic rocks of magmatic origin with a variable admixture of mafic components from continental island arcs e g the fangjingshan dayong and the sibao yiyang island arc chains the flysch deposition took place in a back arc basin rather than a failed intracontinental rift as proposed by some workers we suggest that suturing between the yangtze and cathaysia blocks did not occur until late proterozoic time and that the final assembly of the supercontinent rodinia in south china was probably marked by the jingning orogeny at 0 8 ga

evaluating trace elements as paleoclimate indicators multivariate statistical analysis of late mississippian pennington formation paleosols kentucky u s a abstract the temporal and spatial distributions of trace elements in paleosols in relation to soil forming processes and climate have received little attention primarily due to their generally low concentrations 100 ppm and a fundamental lack of knowledge of their behavior in soil systems trace element concentrations of pennington formation paleosols spanning an 8 ma interval in the late mississippian chesterian were analyzed using linear and multivariate statistics of whole rock elemental data linear statistics of the elemental data set show that ti zr nb cs la hf ta w ce and th have the highest correlation through time with r values 0 75 nb served as the proxy trace element for comparison temporal trends in nb closely match trends in lessivage clay formation and accumulation by feldspar weathering mean annual precipitation map and chemical weathering map effectively controls soil hydrology and the accumulation of organic matter and clay map in conjunction with chemical we

sedimentary fractionations between al ti and zr and the genesis of strongly peraluminous granites sedimentary sorting produces alternating shales and sandstones with complementary chemistries the preferential partitioning of quartz and zircon in the coarse grained fraction of the sediments results in a strong fractionation between sio 2 zr and other components al 2 o 3 tio 2 as a consequence shales may be defined chemically as having higher al 2 o 3 sio 2 and tio 2 zr ratios than their source rocks sandstones have the opposite characteristics and vary in composition according to the maturity of their source and the intensity of sorting processes most sedimentary suites display a good correlation between al 2 o 3 sio 2 and tio 2 zr this result is used to evaluate an average bulk composition for recent clastic materials and to model their composition on a ternary al ti zr diagram because the al 2 o 3 tio 2 ratio of igneous rocks is highly sensitive to magmatic differentiation igneous and sedimentary trends crosscut in the al ti zr di

sediment sources and dispersion as revealed by single grain 40ar 39ar ages of detrital muscovite from carboniferous and cretaceous rocks in mainland nova scotiageological survey of canada contribution 20090289 single grain ages of detrital muscovite from 15 sand stone samples from the lower carboniferous horton group and the lower cretaceous chaswood formation of central nova scotia were used to infer the nature of the early carboniferous unroofing of the meguma terrane and the reworking of carboniferous rocks in the early cretaceous in the western windsor basin a sample from the oldest horton group rocks yielded ages principally between ca 400 and 380 ma suggesting that most of the muscovite present came from the metamorphic rocks of the meguma terrane but was variably reset by the intrusion of the south mountain batholith at ca 380 ma other samples in this part of the basin show partial post depositional resetting younger horton group metamorphic rocks in the eastern windsor basin contain many grains with ages of ca 370 360 ma suggesting derivation from the central core of the south mountain batholith or the musquodoboit pluton horton group sandstones from the western part of the st marys basin co

the influence of source rock type chemical weathering and sorting on the geochemistry of clastic sediments from the quetico metasedimentary belt superior province canada abstract the geochemistry of clastic sediments is controlled by at least four factors source rock composition weathering of the source rocks sorting of the weathered detritus and post depositional alteration during diagenesis and metamorphism in order to evaluate the relative importance of these factors major trace and rare earth element contents were determined for distal and proximal clastic turbidites from the archaean quetico metasedimentary belt the degree of metamorphism of the samples ranges from middle greenschist to upper amphibolite facies simple mixing of archaean mafic and acidic rocks of similar composition to those found in the adjacent granite greenstone terrains will account for the tio2 feot mgo cr sc y and hree contents of the clastic turbidites the metasediments are enriched in lree relative to the mafic acidic rock mixing line indicating that the acidic source was enriched in the lree compared to archaean terrains from other parts of the world some quetico turbidites have an additional fe rich source component possibly a chemical sediment incorporated at the time of turbidite slumping cao na2o k2o rb and sr form trends on bivariant plots that are oblique to the mafic acidic rock mixing line and hence cannot be accounted for by simple mixing of the source rocks chemical weathering of feldspars prior to deposition can account for cao na2o k2o rb and sr trends since cao na2o and sr are lost to the weathering solutions and k2o and rb are retained on the product clays the higher na 2 o cao k 2 o na 2 o rb k 2 o and sr cao ratios but lower cao content of the distal samples suggest that they were derived from a bulk sediment that had experienced a greater degree of chemical weathering than the proximal sediments sorting is the factor that most strongly influences the composition of individual samples within the proximal sample group the coarse grained metagraywackes with their higher quartz feldspar and heavy mineral contents are enriched in sio2 cao na2o sr lree zr and hf relative to the fine grained clay rich metapelites metapelites are enriched in tio2 al2o3 feot mgo k2o cr zn sc y hree cs and rb as a result of their higher clay contents thus the use of clastic sediment compositions in determining average crustal compositions e g for the ree can only give satisfactory results when all grain size fractions are sampled in their correct relative proportions the chemical differences observed between the high and low grade samples can be accounted for by source rock type chemical weathering of the source rocks or sorting post depositional element mobility does not appear to be an important factor in determining the composition of the quetico metasediments

controls on regional variability in marine pore water diagenesis below the seafloor in upper jurassic lower cretaceous prodeltaic sandstone and shales scotian basin eastern canada abstract diagenesis in the uppermost jurassic to lower cretaceous deltaic sandstones and shales of the scotian basin is an important control on reservoir quality ferruginous zone sub oxic marine pore water diagenesis controls the initial formation of fe2 silicates that are the precursors of grain rimming chlorite that preserves porosity this study assesses the regional controls on the type of marine pore water diagenesis by studying the sedimentology mineralogy and geochemistry of the retrogradational units and underlying progradational units in parasequences from conventional cores in two wells in different parts of the basin coated grains preserve a record of whether marine pore water diagenesis below the seafloor was dominantly in the ferruginous or sulphidic geochemical zone four types of coated grain were distinguished each with a different mineral paragenesis mineralogical and chemical evidence of ferruginous zone diagenesis includes the presence of diagenetic chlorite and siderite and the correlation of p with fe or ti pyrite and fe calcite are found where the sulphidic zone is more significant than the ferruginous zone ferruginous zone diagenesis was common in low sedimentation rate retrogradational sediments with low organic carbon and in delta front turbidites and river mouth sandstones estuarine tidal flat and prodeltaic facies that are directly supplied by riverine sediments have a lower fe ti ratio than do fully marine shoreface and open shelf facies as a result of input of detrital ilmenite and its alteration products the relative contribution of colloidal iron hydr oxides appears greater in distal low sedimentation rate environments where large changes in sedimentation rate occurred at ravinement surfaces the underlying progradational rocks have evidence of ferruginous zone diagenesis whatever their facies rapid upward migration of the pore water profile resulting from the change in sedimentation rate reduced the time available for mineral products to form in the deeper pore water zones this study has shown that the availability of fe and organic carbon varying in a complex manner in marine deltaic sediments but that the resulting diagenesis by marine pore water can be predicted from facies and paleogeographic setting

karst rivers particularity an example from dinaric karst croatia bosnia and herzegovina the very complex system of sinking losing and underground transboundary karst rivers lakes and aquifers in the central part of the deep and bare dinaric karst in croatia and bosnia and herzegovina is analysed the groundwater and surface water are hydraulically connected through numerous karst forms which facilitate the exchange of water between the surface and subsurface a complex underground conduit system is an inherent characteristic karst system analysed groundwater and surface water exchange with both adjacent and distant aquifers through underground routes or inflows from surface streams and artificial reservoirs because of a complex surface and underground karst features which strongly influenced its hydrological and hydrogeological regime the main open stream flow with a longitude of about 106 km undergoes eight name changes in this paper it is noted as the eight name river in fact it represents one river with losing sinking and underground stream sections different surface and underground karst forms play crucial roles in the way the water flowing over the surface and on the underground sections of its catchment the analysed area is full of varied and often spectacular surface landforms including for example the blue and red lakes and the kravice waterfall the analyses made in the paper show the existence of a decreasing trend of mean annual discharges on the eight name river which can cause numerous problems in the regional water resource management of this transboundary river and catchment

modern pollen rain characteristics of tall terra firme moist evergreen forest southern amazonia the paucity of modern pollen rain data from amazonia constitutes a significant barrier to understanding the late quaternary vegetation history of this globally important tropical forest region here we present the first modern pollen rain data for tall terra firme moist evergreen amazon forest collected between 1999 and 2001 from artificial pollen traps within a 500 x 20 m permanent study plot 14 degrees 34 50 s 60 degrees 49 48 w in noel kempff mercado national park ne bolivia spearman s rank correlations were performed to assess the extent of spatial and inter annual variability in the pollen rain whilst statistically distinctive taxa were identified using principal components analysis pca comparisons with the floristic and basal area data of the plot stems 10 cm d b h enabled the degree to which taxa are over under represented in the pollen rain to be assessed using r rel values moraceae urticaceae dominates the pollen rain 64 median abundance and is also an important constituent of the vegetation accounting for 16 of stems 10 cm d b h and ca 11 of the total basal area other important pollen taxa are arecaceae cf euterpe melastomataceae combretaceae cecropia didymopanax celtis and alchornea however 75 of stems and 67 of the total basal area of the plot 10 em d b h belong to species which are unidentified in the pollen rain the most important of which are phenakospermum guianensis a banana like herb and the key canopy emergent trees erisma uncinatum and qualea paraensis

environmental controls on clay mineralogy of an early jurassic mudrock blue lias formation southern england we present a dataset including clay mineralogy gamma ray spectrometry organic matter content and magnetic susceptibility of the hettangian to lowest sinemurian successions of dorset and somerset southern uk blue lias formation bristol channel and wessex basins in both areas the clay assemblages comprise predominantly detrital illite kaolinite and illite smectite mixed layers clays probably originated from the erosion of the hercynian massifs the relative proportions of kaolinite and illite being modulated by arid humid climatic fluctuations the organic matter om content types ii to iv ranges up to 12 in both areas a clear stratigraphical trend in clay mineral assemblages is apparent in somerset whereas in dorset sharp contrasts between adjacent horizons and a greater dilution by carbonate mask the long term evolution correlations between both areas based on similar vertical trends in clay mineral abundance support the suggestion of a hiatus within the angulata zone of the dorset succession as expected the kaolinite illite ratio correlates with the th k ratio deduced from gamma ray spectrometry however significant departures from the correlation occur in om rich intervals suggesting that th may be partly adsorbed on to om particles surprisingly high magnetic susceptibility correlates with abundant kaolinite not with fe rich clays indicating either that kaolinite is accompanied by a soil inherited magnetisable phase possibly iron oxide or that illite rich rocks are more strongly diluted by carbonate than are kaolinite rich strata

the lower cretaceous chaswood formation in southern new brunswick provenance and tectonics the most northwesterly outcrop of lower cretaceous chaswood formation is in a pit at vinegar hill south of sussex new brunswick new mapping and boreholes show thick fluvial loosely lithified conglomerates and lesser sandstones unconformably overlying 12 m of mudstone in a 1 km2 basin bounded to the northwest by the clover hill fault sparse paleocurrent indicators to the southwest parallel this fault the tectonic setting is similar to that of the chaswood formation in the fault bounded elmsvale basin in nova scotia in both cases a basal unit is paraconformable on underlying upper mississippian rocks was folded into a syncline within which a middle unit accumulated and was further deformed and is capped by thin flat lying sandstone and conglomerate the tectonic style of the chaswood formation at vinegar hill demonstrates that early cretaceous deformation was widespread in the southern maritimes gravel clasts consist overwhelmingly of vein quartz but sparse lithic clasts match source rocks in s

u pb and 40ar 39ar geochronology of the saint urbain and lac allard havre saint pierre anorthosites and their associated fe ti oxide ores quebec evidence for emplacement and slow cooling during the collisional ottawan orogeny in the grenville province abstract intrusive suites containing anorthosite mangerite charnockite granite amcg are a characteristic feature of mesoproterozoic magmatic activity in the grenville province of eastern north america in this study the u pb and 40ar 39ar geochronology of two amcg suites saint urbain and havre saint pierre and associated rutile bearing hemo ilmenite deposits within the allochthonous polycyclic belt of the grenville province in quebec are used to constrain their crystallization ages and cooling histories and to assess their tectonic setting both amcg suites separated by 700 km along the st lawrence river have similar crystallization ages ca 1050 1060 ma and durations of magmatism 10 15 million years the 450 km2 saint urbain anorthosite is a composite intrusion with a distinctly younger central leuconorite 1046 2 3 1 ma compared with anorthosite to the north and south 1055 0 2 4 ma and 1053 6 2 6 ma respectively the age of a deformed oxide apatite gabbronorite 1057 4 1 5 ma along the northwest margin of the intrusion is within analytical uncertainty of the anorthosites whereas the oldest intrusion in the saint urbain area is the regionally extensive saint anne du nord orthopyroxene granodiorite 1060 8 2 8 ma the large 11 000 km2 havre saint pierre anorthosite suite comprises a number of intrusive phases including the 2700 km2 lac allard anorthosite which contains the giant lac tio ilmenite deposit and big island ilmenitite dyke u pb zircon ages of three anorthosites from the lac allard intrusion including the host to the lac tio deposit overlap within error 1061 6 3 0 ma 1060 5 1 9 ma 1057 4 8 4 ma and the crosscutting big island dyke yields an age of 1052 9 6 5 ma these results indicate that the havre saint pierre anorthosite should be divided into an older geon 11 part ca 1129 ma and a younger geon 10 part ca 1060 ma average cooling rates of 3 4 c million years were estimated for the two amcg suites by combining crystallization ages u pb zircon and cooling ages u pb rutile 40ar 39ar biotite plagioclase and reflect emplacement of the intrusions into a hot long duration orogen emplacement of these two amcg suites at ca 1050 1060 ma is related to regional extensional tectonics near the end of peak metamorphism associated with the collisional ottawan orogenic phase of the grenville orogeny the results of this study provide strong support for proposals that link amcg magmatism associated with the grenville orogeny to convective thinning or delamination of the lithosphere and subsequent melting of upwelling asthenospheric mantle

relationship of diagenetic chlorite rims to depositional facies in lower cretaceous reservoir sandstones of the scotian basin the relationship between diagenetic chlorite rims and depositional facies in deltaic strata of the lower cretaceous missisauga formation was investigated using a combination of electron microprobe bulk geochemistry and x ray diffraction data the succession studied comprises several stacked parasequences the delta progradational facies association includes i fluvial or distributary channel sandstones some with tidal influence ii thick bedded delta front graded beds of sandstone interpreted as resulting from fluvial hyperpycnal flow during floods and storms and iii more distal muddier delta front and prodeltaic facies the transgressive facies association includes lag conglomerate siderite cemented muddy sandstone and mudstone and bioclastic sandy limestone chlorite rims are absent in the fluvial facies and best developed in thick sandstones lacking mudstone baffles good quality chlorite rims are well correlated with ti in bulk geochemistry ti is a proxy for fe availability principally from the breakdown of abundant detrital ilmenite fetio3 under conditions of sea floor diagenesis the abrupt decrease in sedimentation rate at transgressive surfaces caused progressive shallowing of the sulphate depletion level and of the overlying eh controlled diagenetic zones resulting in conditions suitable for diagenetic formation of berthierine to migrate upwards through the packet of reservoir sandstones this early diagenetic berthierine suppressed silica cementation and later recrystallized to chlorite thick euhedral outer chlorite rims were precipitated from formation water in sandstone lacking muddy baffles on this chlorite substrate and inhibited late carbonate cementation this study thus shows that the preservation of porosity by chlorite rims is a two stage process rapidly deposited delta front turbidite facies create early diagenetic conditions that eventually lead to the formation of chlorite rims but the best quality chlorite rims are restricted to sandstones with high permeability during burial diagenesis

statistical empirical index of chemical weathering in igneous rocks a new tool for evaluating the degree of weathering abstract chemical weathering indices are useful tools in characterizing weathering profiles and determining the extent of weathering however the predictive performance of the conventional indices is critically dependent on the composition of the unweathered parent rock to overcome this limitation the present paper introduces an alternative statistical empirical index of chemical weathering that is extracted by the principal component analysis pca of a large dataset derived from unweathered igneous rocks and their weathering profiles the pca analysis yields two principal components pc1 and pc2 which capture 39 23 and 35 17 of total variability respectively the extent of weathering is reflected by variation along pc1 primarily due to the loss of na 2 o and cao during weathering in contrast pc2 is the direction along which the projections of unweathered felsic intermediate and mafic igneous rocks appear to be best discriminated therefore pc1 and pc2 represent independent latent variables that correspond to the extent of weathering and the chemistry of the unweathered parent rock subsequently pc1 and pc2 were then mapped onto a ternary diagram mfw diagram the m and f vertices characterize mafic and felsic rock source respectively while the w vertex identifies the degree of weathering of these sources independent of the chemistry of the unweathered parent rock the w index has a number of significant properties that are not found in conventional weathering indices first the w index is sensitive to chemical changes that occur during weathering because it is based on eight major oxides whereas most conventional indices are defined by between two and four oxides second the w index provides robust results even for highly weathered sesquioxide rich samples third the w index is applicable to a wide range of felsic intermediate and mafic igneous rock types finally the mfw diagram is expected to facilitate provenance analysis of sedimentary rocks by identifying their weathering trends and thereby enabling a backward estimate of the composition of the unweathered source rock

varietal heavy mineral analysis of sediment provenance lower cretaceous scotian basin eastern canada abstract the origin of a major increase in sand supply in the early cretaceous of the scotian basin offshore eastern canada has been investigated by analysis of heavy mineral varieties the chemistry of detrital minerals from the scotian basin was compared with that of minerals from potential source rocks sampled from older sedimentary successions river sands and glacial tills on land heavy mineral varieties were established based on 1000 high quality electron microprobe emp analyses and used to classify heavy mineral types by mineral liberation analysis mla which uses a rapid scanning electron microscope particle analyser heavy mineral varieties were compared between the cretaceous quartz arenites and subarkoses and samples from potential source areas different chemical varieties of the same mineral group have different grain size distributions so that their relative modal abundances may be influenced by hydraulic sorting but modal abundance of different varieties of tourmaline garnet and spinel provides useful information widely used provenance sensitive mineral ratios are difficult to interpret because of the abundance of polycyclic sources comparisons of the shape parameters of the individual mineral types are also useful for provenance identification aspect ratio in elongate grains such as tourmaline and zircon is a measure of polycyclic reworking but is influenced by the initial shapes of minerals from different source rocks uniformity of varietal heavy minerals over a large area and stratigraphic range and the covariance of spinel and zircon with quite different crystalline sources indicate predominance of polycyclic sources to the central scotian basin probably principally from carboniferous and lower paleozoic sandstones in part sourced from western newfoundland ophiolites heavy mineral varieties in the west scotian basin can be closely matched to sources in the adjacent meguma terrane of the appalachians all the data show that the sands of the scotian basin were derived from reworking of crystalline basement of the appalachian orogen and its paleozoic sandstone cover uplifted during rifting of iberia from the grand banks there is no evidence of a significant supply of sand to the scotian basin from a proto st lawrence river

geochemistry of late middle jurassic early cretaceous igneous rocks on the eastern north american margin geochemical analyses have been made of late middle jurassic to early cretaceous volcanic rocks on the eastern north american margin from baltimore canyon northeastward to the newfoundland seamounts samples from the newfoundland seamounts were obtained from dredge hauls from the new england seamounts from deep sea drilling project holes and from the grand banks scotian shelf georges bank and baltimore canyon area from exploratory oil wells all of the rocks analyzed are alkali basalts and related mafic rocks the analytical data allow the rocks to be divided into two distinct igneous suites the new england suite includes the baltimore canyon georges bank and new england seamounts rocks from these areas show marked enrichment in light ree and many incompatible trace elements the eastern canadian suite consisting of rocks from the scotian shelf and grand banks show slightly convex ree spectra and less enrichment in incompatible elements the rocks from the new england suite contain high pressure clinopyroxene phenocrysts some of which show complex zoning these are absent in rocks from the eastern canadian suite the data available from these offshore areas is limited and does not permit a unique petrogenetic explanation for the geochemical differences between the two suites the eastern canadian suite resembles early formed alkali rocks from loihi seamount interpreted as the products of a low degree of partial melting of a morb type mantle source this source was slightly depleted in lree in order to produce the observed convex lree spectra the new england suite closely resembles many ocean island basalt suites our data do not allow discrimination between various current hypotheses for the origin of relative enrichment in incompatible elements of alkali olivine basalts variations in element ratios for geochemically very similar element pairs such as la ce and zr hf suggest that the mantle beneath the two suites may have different compositions the mantle composition inferred for the new england suite is similar to that postulated by many authors as resulting from mantle plumes the localization of the volcanism in the early cretaceous however is related to the development of fractures some of which resulted from reactivation of old fracture zones

tectonostratigraphic evolution of the labrador margin atlantic canada abstract the labrador continental margin provides a rich source of data with which to study the relationships between stratigraphy tectonics and paleoenvironment we have completed a regional seismic interpretation and integrated this with new biostratigraphic data based on analyses of palynomorphs from wells in the hopedale and saglek basins which occur on this margin our results are summarized in a tectonostratigraphic chart which displays new and consistent age control for the major lithostratigraphic units and provides more precise evaluation of their depositional and paleoenvironmental history we have identified and dated six regional unconformities in the wells and we can recognize several others on the seismic data the older unconformities cretaceous are related to the tectonics of rifting and seafloor spreading and may delineate the onset of different stages of the rift process in the paleocene early eocene unconformity development was influenced by episodic volcanism due to the passage of the proto iceland hotspot to the north and to a major change in spreading direction in the labrador sea many of these unconformities are also identified in offshore southwest greenland and the grand banks suggesting widespread controlling mechanisms during the post seafloor spreading stage the effects of mass wasting and slumping and of paleoenvironmental controls on the stratigraphy were more pronounced we discuss the petroleum potential of the hopedale basin in terms of the structures we see on the seismic data and highlight the bjarni formation which likely contains the most prospective source and reservoir rocks in this basin

controls on diagenesis of lower cretaceous reservoir sandstones in the western sable subbasin offshore nova scotia abstract lower cretaceous deltaic sandstones of the scotian basin offshore eastern canada are important gas reservoirs the influence of several factors on diagenesis has been investigated depositional lithofacies sea level changes chemistry of basinal sediments and basinal fluid flux during burial the distribution and chemistry of diagenetic minerals was determined from nine wells located along a dip section of the sable subbasin mineral type and paragenesis were characterized using a combination of optical petrography back scattered electron images and electron microprobe analyses siderite is unusually abundant in marine sediments of the scotian basin and has thus been studied in detail siderite occurs in several generations early and late siderites are similar in chemical composition suggesting buffering by pre existing siderite but rare low mg siderite is related to a greater contribution of meteoric water siderite has locally dissolved to create microporosity and has suppressed quartz overgrowths siderite is most common in those muddy prodeltaic lithofacies where there is the highest availability of detrital ilmenite reactive fe released by breakdown of this ilmenite is responsible for the unusual presence of early siderite in marine sediments with the ca and mg content of the siderite indicating fully marine waters lithofacies have a strong influence on early diagenetic mineral assemblages lithofacies deposited in the transgressive system tract have abundant early fe calcite and siderite early kaolinite occurs principally in proximal fluvial and river mouth lithofacies where meteoric water was most likely available during the deposition contrary to other studies we find little impact of sequence stratigraphy on diagenetic minerals except in the transgressive system tract mesogenetic minerals are related to flux of formation water and maturing hydrocarbon products resulting first in pyrite and siderite and later in ankerite and ferroan calcite the principal controls are interpreted to be high fe 2 and low ca 2 of formation waters and vertical movement of the waters along faults overall the bulk chemical composition of terrigenous sediments and the depositional lithofacies are the most important factors controlling diagenetic minerals in the lower cretaceous of the scotian basin

sediment geochemistry as a provenance indicator unravelling the cryptic signatures of polycyclic sources climate change tectonism and volcanism interpretation of bulk sediment geochemistry is one of several approaches for determining sediment provenance this study investigates the value added by bulk sediment geochemical analysis in interpreting provenance in a passive margin clastic basin the upper jurassic lower cretaceous deltaic sediments of the scotian basin provenance studies in this basin are challenging because source tectonic terranes are parallel to the basin margin and polycyclic sediment sources are abundant more than 400 samples of mudstone and sandstone representing the geographical and stratigraphic range of interest were analysed for 57 elements diagenetic processes added calcium to many samples and removed potassium in rocks buried below 3 km thus impacting principal component analysis and published weathering indices however multiple geochemical approaches to assessing the degree of weathering showed climatically controlled changes in weathering in the tithonian and barremian and changes in supply from major tectonic events such as the top aptian uplift in the labrador rift covariance of elements in heavy minerals demonstrates the varying magnitude of polycyclic supply and stratigraphic changes in sources geochemical analyses revealed a previously unsuspected tithonian alkali volcanic sediment source characterized by high niobium and tantalum the lack of highly contrasting sources means that geochemistry alone is inadequate to determine sediment provenance published discrimination diagrams are of limited value statistical analysis of geochemical data is strongly influenced by diagenetic processes episodic volcanic inputs and polycyclic concentration of resistant heavy minerals in sandstones single indicator elements for particular sources are generally lacking nevertheless careful consideration of geochemical variability on a case by case basis integrated with detrital mineral studies provides new insights into palaeoclimate sediment provenance and hence regional tectonics although there is no simple template for such analysis this study demonstrates an approach that can be used for other basins

late jurassic kimmeridgian tithonian stable isotopes δ18o δ13c and mg ca ratios new palaeoclimate data from helmsdale northeast scotland abstract the data presented here provide the first detailed stable isotope 18 o 13 c and geochemical mg ca investigation of kimmeridgian tithonian belemnites from the helmsdale coast scotland uk oxygen and carbon stable isotope values from well preserved specimens range from 2 8 to 0 3 and from 2 3 to 2 8 respectively the oxygen isotope data are consistent with palaeotemperatures of up to 24 c in the early kimmeridgian cymodoce zone and down to 11 c in the mid tithonian rotunda fittoni zones these estimates are strongly supported by the mg ca data which also indicate a cooling episode and very similar palaeotemperatures 11 22 c at this time the cooling event is associated with an approximately 5 decline in 13 c ratios this shift towards more negative 13 c values has also been recorded in the tethys and on the russian platform confirming that this event was of global origin such globally synchronous records can provide a valuable tool for stratigraphic correlation the helmsdale 13 c data are therefore combined here with other published belemnite isotope data from the jurassic of scotland from the callovian kimmeridgian of the isle of skye and the toarcian aalenian of raasay the resultant belemnite 13 c curve provides a detailed record of the toarcian tithonian british boreal realm that can be compared with coeval records to investigate regional differences in jurassic carbon isotope stratigraphy

sedimentary environment and diagenesis of the lower cretaceous chaswood formation southeastern canada the origin of kaolin rich mudstones abstract the lower cretaceous fluvial sandstone mudstone succession of the chaswood formation is the proximal equivalent of offshore deltaic rocks of the scotian basin that are reservoirs for producing gas fields this study interprets the mineralogical consequences of cretaceous weathering and early diagenesis in a 130 m core from the chaswood formation in order to better understand detrital and diagenetic minerals in equivalent rocks offshore mineralogy was determined by x ray diffraction electron microprobe analysis and scanning electron microscopy the rocks can be divided into five facies associations light gray mudstone dark gray mudstone silty mudstone and muddy sandstone sorted sandstone and conglomerate and paleosols facies transitions in coarser facies are related to deposition in and near fluvial channels in the mudstones they indicate an evolutionary progression from the dark gray mudstone facies association swamps and floodplain soils to mottled paleosols well drained oxisols and ultisols following syntectonic uplift facies transitions and regional distribution indicate that the light gray mudstone facies association formed from early diagenetic oxidation and alteration of the dark gray mudstone facies association probably by meteoric water principal minerals in mudstones are illite muscovite kaolinite vermiculite and quartz illite muscovite is of detrital origin but variations in abundance show that it has altered to kaolinite in the light gray mudstone facies association and in oxisols vermiculite developed from the weathering of biotite and is present in ultisols the earliest phase of sandstone cementation in reducing conditions in swamps and ponds produced siderite nodules and framboidal pyrite which were corroded and oxidized during subsequent development of paleosols kaolinite is an early cement coating quartz grains and as well crystallized pore filling booklets that was probably synchronous with the formation of the light gray mudstone facies association later illite and barite cement indicate a source of abundant k and ba from formation water this late diagenesis of sandstone took place when the chaswood formation was in continuity with the main scotian basin prior to oligocene uplift of the eastern scotian shelf findings of this study are applicable to other mid latitude cretaceous weathering and early diagenetic environments