melting of newly formed mafic crust for the formation of neoproterozoic i type granite in the hannan region south china abstract neoproterozoic magmatism in the hannan region at the northwestern margin of the yangtze block is characterized by numerous felsic plutons associated with minor mafic ultramafic intrusions the felsic plutons are either adakitic or normal arc granitic in composition the adakitic plutons are 735 ma in age and are interpreted as having formed by partial melting of a thickened lower mafic crust among the normal arc related felsic plutons the tianpinghe pluton is the largest and has a shrimp zircon u pb age of 762 4 ma older than the adakitic plutons in the region rocks from the tianpinghe pluton have relatively high sio2 67 1 70 1 wt and k2o na2o 7 8 8 6 wt and relatively low mgo 0 7 1 3 wt and al2o3 contents 14 5 15 6 wt with al2o3 cao k2o na2o a cnk values ranging from 0 95 to 1 08 they have arc affinity trace element compositions that are characterized by enrichment of large ion lithophile elements and depletion of high field strength elements nb ta with strong

tectonic evolution of the qinling orogenic belt central china new evidence from geochemical zircon u pb geochronology and hf isotopes abstract the qinling orogenic belt qob located between the north china craton ncc and the yangtze craton yzc is composed of the northern qinling belt nqb and the southern qinling belt sqb this study presents new geochemical data zircon u pb ages and hf isotopes from a suite of metamorphic rocks from the kuanping qinling danfeng douling and wuguan groups in the nqb and the sqb our results suggest that the qinling group in the nqb formed in an active continental margin related to the subduction of the songshugou ocean under the southern ncc during grenvillian period the kuanping group in the northern nqb was deposited in the within plate extension basin during late neoproterozoic to early paleozoic the detritus of sedimentary rocks of the kuanping group were mainly sourced from the nqb and subordinately from the basement rocks of the ncc the danfeng group in the southern nqb formed later than 827 ma with the sediments derived mainly from the qinling terrane the nqb witnessed multiphase tectono thermal events from mesoproterozoic to early paleozoic including several magmatic events and the early paleozoic metamorphic event the original douling group in the sqb represents the basement complex of the sqb which is composed of rocks with different formation ages the oldest rock in the complex is represented by 3 0 ga granitic gneiss which underwent at least two periods of metamorphism at 2 5 ga and 0 97 0 91 ga in this study the douling group is redefined as a suite of neoproterozoic 860 750 ma rocks formed in an extensional setting after the subduction of the songshugou ocean the wuguan group in the sqb formed in the middle late neoproterozoic later than 740 ma and was subjected to early paleozoic metamorphism our data indicate that the sqb experienced early neoproterozoic 970 865 ma and early paleozoic 444 ma metamorphism and strong middle neoproterozoic 870 730 ma magmatism the age spectra of zircons from the nqb trace major tectono thermal events at 1462 ma 927 ma and 412 ma which are different from those recorded in the southern ncc and northern yzc suggesting that the nqb had a distinct evolution during mesoproterozoic to early neoproterozoic grenvillian the hf isotopic compositions of zircons from the various rocks suggest that the nqb probably developed on the basement of the southern ncc the rocks in the sqb show zircon age spectra and hf isotope compositions similar to those in the northern yzc suggesting a close affinity we therefore interpret the sqb to have developed on the basement of the northern yzc integrating the new data in this study with those from previous works we propose a new tectonic model for the formation and evolution of the qob during late mesoproterozoic to early paleozoic involving the following major events 1 late mesoproterozoic to early neoproterozoic grenvillian northward subduction of the songshugou ocean 2 early middle neoproterozoic 870 800 ma bidirectional subduction and collision 3 middle neoproterozoic 800 710 ma post collision extension 4 middle late neoproterozoic 710 600 ma within plate extension 5 late neoproterozoic early paleozoic 600 520 ma opening of the shangdan ocean and 6 early paleozoic 520 420 ma subduction collision we thus trace at least two distinct wilson cycles in the qob

stable carbon isotopes of coal derived gases sourced from the mesozoic coal measures in china coal derived large scale gas fields derived from the mesozoic coal measures in china are mainly distributed in the middle lower jurassic coal measures in the tarim junggar and turpan hami basins in northwest china and the upper triassic xujiahe formation coal measure in sichuan basin central china in 2011 the annual production was 21 6 109 m3 and the proved geological reserves were 2485 109 m3 accounting for 21 and 30 of the total in china respectively based on analyses of gas composition and stable carbon isotopes ratios of 203 samples and stable carbon isotopes of 102 co2 samples the following conclusions were made a based on diagnostic plots using the stable carbon isotopic and molecular composition of gas samples alkane gas from the mesozoic coal measures in china is shown to be coal derived b according to the 13c2 vs c2h6 plot of a great number of oil derived and coal derived gases in china it is concluded that gases with 13c2 28 5 are coal derived and those with 13c2 28 5 are oil derived in most cases c among the natural gases from the mesozoic coal measures in china primary coal derived gases with normal carbon isotopic distribution pattern among the c1 c4 alkanes i e 13c1 13c2 13c3 13c4 are dominant d carbon isotopic pattern reversal mainly results from the mixing of coal derived gases having different maturities but the same source and secondly from microbial oxidation of propane e g mu 3 and mu 4 wells in the gumudi gas field junggar basin e co2 in the coal derived gases from the mesozoic coal measures in china has both biogenic and abiogenic origins the biogenic origin is dominant and the abiogenic co2 is mainly found in the kuqa depression in the tarim basin and western sichuan basin f isotopic differences between heavy hydrocarbon gases and methane become less with increasing maturity

measuring and adjusting the weathering and hydraulic sorting effects for rigorous provenance analysis of sedimentary rocks a case study from the jurassic ashikita group south west japan the present study examines the provenance of the jurassic ashikita group distributed in south west japan which is composed of the idenohana kyodomari and sakamoto formations two geochemical diagrams for provenance analysis were utilized which incorporate full consideration of compositional modifications resulting from weathering mfw diagram and hydraulic sorting processes sio2 al2o3 na2o k2o diagram the mfw diagram delineates weathering trends of sedimentary rocks and allows estimation of the original source rock composition by tracing the weathering trends backwards to an unweathered domain weathering trends of the idenohana and kyodomari formations extend backward to the domain of intermediate and felsic igneous rocks in contrast sediments of the sakamoto formation do not fit into a linear weathering trend indicating that the source rock cannot be approximated to igneous rocks on the sio2 al2o3 na2o k2o diagram sediments are organized into compositional trends in which the range reflects compositional variations induced by the hydraulic sorting effect on this diagram sediments derived from the igneous and recycled sedimentary provenances can be distinguished by reading the inclination of the trend by utilizing this principle source rocks of the idenohana and kyodomari formations are interpreted as igneous rocks and those of the sakamoto formation are interpreted as recycled sedimentary rocks therefore these diagrams concurrently estimate the source rock composition through quantifying and adjusting the weathering and sorting effects and reveal a systematic transition in the provenance of the ashikita group the idenohana and kyodomari formations were supplied chiefly from an igneous provenance which shifted from intermediate to felsic compositions in stratigraphic order whereas sediments of the sakamoto formation were sourced primarily from a recycled sedimentary provenance

provenance and weathering control on river bed sediments of the eastern tibetan plateau and the russian far east abstract we investigated the petrography and major trace and rare earth element compositions of the bed sediments from the large rivers draining the eastern tibetan plateau etp the huang he yellow chang jiang yangtze hong he red mekong and salween the combined drainage spans tropical temperate and arid climate zones in addition samples from the lena river draining the verkhoyansk and sette daban ranges in an arctic to sub arctic climate zone in siberia were also studied for their major and trace element composition the sub angular texture the quartz feldspar rock fragment classification in the lithic arenite field and the relatively low chemical index of alteration cia 42 79 indicate that these sediments are texturally petrographically and chemically immature and immobile trace elements can be used to obtain some information about the lithologic provenance the etp river sediments are felsic and similar to the upper continental crust with the salween most felsic and the lena most mafic the sediments show a gradation in maturity that is not clearly related to present climatic or physiographic regime this suggests that maturity itself is a relict feature inherited from previous sedimentary cycles the high physical erosion in such high energy and relief systems seems to inhibit intense weathering and manifests a provenance control from local rocks on the sediment compositions

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

migration of the carbonate ramp and sponge buildup driven by the orogenic wedge advance in the early stage carnian of the longmen shan foreland basin china abstract the marine carnian the maantang fm overlies a flexural forebulge unconformity and records the initial establishment drowning and migration of a carbonate ramp and sponge buildup along the forebulge margin of the longmen shan foreland basin the maantang fm is of wedge shaped geometry and is composed of oolitic and bioclastic limestones siliceous sponge reef and shale in an upward fining succession the formation shows the establishment and drowning of a distal margin carbonate ramp and sponge buildup deepening into offshore marine muds followed by progradation of marginal marine siliciclastics the formation also shows the transition from shale cratonward into carbonate rock southeastward the sponge reefs and shoal were deposited on a carbonate ramp on the distal margin of the early foreland basin the growth rate of sponge reefs is 0 04 mm yr equivalent to the rate of relative sea level rise of 0 01 0 05 mm yr the sponge buildup and oolitic shoal are divided into seven zones southeastward on the carbonate ramp along the basal unconformity their migration rate of 18 mm yr from nw to se coincides with the estimated orogenic wedge advance rate 5 15 mm yr li et al 2003 a clear indication that the advancing wedge controlled the migration rate of foreland oolitic shoal siliceous sponge reef we have inferred that the tectonic load of the longmen shan orogenic wedge led to flexural subsidence and rising relative sea level in the foreland basin located at the western margin of the yangtze craton driving the growth and subsequent drowning of the oolitic shoal sponge buildup in the early stage of the foreland basin we propose that the drowning and migration processes were the sedimentary response to the orogenic wedge advance toward the yangtze craton and to the rapid closure of the carnian songpan ganzi remnant ocean basin

an evaluation of geochemical weathering indices in loess paleosol studies abstract applying geochemical proxies as measure for the weathering intensity of paleosols and sediments such as loess the quaternary scientist is confronted with various element ratios that have been proposed in literature this paper gives an overview on the principle of geochemical weathering indices different types of indices are evaluated with respect to the suitability for loess paleosol sequences regarding the special characteristics of this type of sediments and paleosols case examples in this study are key sections in southeastern and eastern europe the loess paleosol sequences batajnica stari slankamen serbia mircea voda romania and stary kaydaky ukraine which represent archives of the late and mid pleistocene climate change of the region considering element behavior during weathering or diagenesis the chemical proxy of alteration cpa i e the molar ratio al2o3 al2o3 na2o 100 is proposed as the most appropriate index for silicate weathering the cpa was evaluated against commonly used weathering indices including the chemical index of alteration cia the chemical index of weathering ciw the plagioclase index of alteration pia the index b of kronberg and nesbitt and the ba sr and rb sr ratio depth profiles of sr type indices e g ba sr rb sr are likely to be influenced by the dynamics of secondary carbonate on the other hand common na type indices e g cia pia ciw may suffer from uncertainties in separating carbonate ca from silicate ca or from biases due to k fixation illitization the cpa is insensitive against such effects additionally using the cpa as with other na type indices provides the possibility to evaluate the homogeneity of the parent material regarding the relevant host minerals via the a cn k diagram

petrogenesis and tectonic significance of the baoxing granitic and mafic intrusions southwestern china evidence from zircon u pb dating and lu hf isotopes and whole rock geochemistry abstract voluminous neoproterozoic gabbros gabbro diorites and granites are exposed in the baoxing area along the western margin of the yangtze block we present here zircon u pb and lu hf isotope data as well as whole rock geochemical data for these rocks which help constrain the tectonic characteristics and evolution of the western margin of the yangtze block zircons from these rocks have high th and u contents and th u ratios 0 2 and show striped absorption patterns growth striations or zoning indicating a typical magmatic origin zircon u pb dating and lu hf isotope results show that the gabbros formed at ca 850 ma with e hf 5 44 to 11 94 and a single stage model age t hf of 1 04 ga suggesting a depleted mantle derived source the gabbro diorites formed at ca 800 ma with major e hf 3 99 to 14 62 and t hf 0 97 ga and minor e hf 0 68 to 5 66 and t hf 1 27 ga again suggesting a depleted mantle derived source the granites were emplaced at ca 770 ma with e hf 2 53 to 10 58 and t hf 1 07 ga indicating that they were derived from the partial melting of juvenile crust the geochemical data show that the gabbros and gabbro diorites are characterized by low sio 2 contents high mg values and cr co and ni contents significant enrichment in light rare earth elements and large ion lithophile elements depletion in high field strength elements e g nb ta zr and hf and relatively high nb u ta u and ce pb ratios these data suggest that the rocks were derived from the partial melting of depleted lithospheric mantle that had been metasomatized by subduction derived fluids or melts and which underwent very minimal crustal contamination during magma evolution and ascent the granites have high sio 2 and k 2 o and low mgo contents exhibit enrichment in rb ba th and pb and depletion in nb ta and ti and have low sr y and la yb n ratios and high y and yb contents which together with their hf isotopic compositions imply a juvenile crust source taking into account regional pre 750 ma arc related magmatism and the subsequent extensional setting it is proposed that a long lived active continental margin setting may have evolved along the western margin of the yangtze block during the neoproterozoic and that the coeval granitic and mafic rocks in the baoxing area were formed by the subduction of the western yangtze block

the applicability of the chemical index of alteration as a paleoclimatic indicator an example from the permian of the parana basin brazil abstract the chemical index of alteration cia was expressed as cia molar to become a more sensitive measure of the degree of chemical weathering the cia molar has the value of 1 for fresh feldspars and for unweathered non peraluminous igneous rocks but increases towards infinity as chemical weathering progresses the utility of this index as a humidity indicator for both modern and ancient muds was tested a database comprising 281 entries with chemical data for modern and ancient sediments deposited under arid semi arid semi humid and humid climate was assembled from the literature and used to calibrate the relationship between humidity and cia molar values for both modern and ancient sediments the histograms display a shift towards higher values with increasing geological indicators of humidity whereas sediments deposited under conditions inferred to be arid from other geological indicators show values tightly clustered around 1 the permian of the parana basin was then used as an example of the applicability of the cia molar for paleoclimatic studies major element analyses al2o3 k2o na2o cao were performed on 55 claystones and shales from three drill cores in a stratigraphic succession spanning the early to late permian the cia molar for these rocks accorded with expectations based on sedimentologic and paleontologic evidence discriminating well between arid and humid conditions in the basin independently determined from sedimentological and paleontological indicators the use of the cia molar as a paleo humidity indicator however can be limited by the presence of carbonate rich sediments the occurrence of post depositional k addition metasomatism metamorphism diagenetic illitization as well as by inheritance of clays from sedimentary rocks in the source area nevertheless with appropriate caution the cia molar is a useful tool for the assessment of the humidity conditions in the rock record

the trace metal content of recent organic carbon rich sediments implications for cretaceous black shale formation organic carbon rich sediments are enriched in several redox sensitive and stable sulfide forming trace metals tm and form an important sink in global tm cycles in today s ocean such sediments are deposited in coastal upwelling areas like those in the gulf of california off peru or off the namibian coast and euxinic basins like the black sea in an attempt to distinguish both environments by their specific tm patterns some important conclusions may be drawn 1 the tm enrichment seen in both environments broadly is rather similar 2 upwelling sediments are often enriched in cd and p and depleted in co and mn 3 sapropels have a tendency towards higher enrichments in ba and mo s re as cu ni sb and fe reflecting the strong sulfidation in an anoxic water column 4 upwelling systems cover a broad range of environmental settings where the steepness of the slope the proximity of h2s to the sediment seawater interface and the intensity of bio accumulation and regeneration play an important role for tm accumulation 5 the tm content of anoxic basins is mainly controlled by tm availability in the water column and sedimentation rate 6 enhanced bio productivity is the main switch turning an oxygenated into an anoxic environment cretaceous black shales oae 2 exhibit tm signatures of both coastal upwelling areas and sapropels the strong enrichments in cd mo tl v cu ni bi and sb demonstrate that bio accumulation and presence of h2s in the water column and associated sulfidation processes persisted during this time interval in large parts of the proto atlantic the usefulness of ba as a paleoproductivity proxy is obscured by diagenesis the extreme accumulation in ag and zn requires either an additional tm source for instance hydrothermal input or a different tm seawater composition during the cretaceous the geochemical data suggest that the major driving force for the widespread occurrence of c t black shales seems to be the increase in volcanic activity and associated co2 input throughout the cretaceous the ocean atmosphere system operated in a mode different from today during this time interval after conversion of the nutrient co2 into organic matter the system switched back into the normal operational mode

constraints of detrital zircon u pb ages and hf isotopes on the provenance of the triassic yidun group and tectonic evolution of the yidun terrane eastern tibet abstract eastern tibet to the west of the yangtze block consists of the yidun and songpan ganzi terranes separated by the ganzi litang suture zone the yidun terrane includes the zhongza massif to the west but the eastern part of the yidun terrane is covered by the yidun group extending from the south shangri la region to the north changtai region the yidun group from the base upward includes the lieyi qugasi tumugou and lanashan formations which are mainly composed of volcanic flysch successions based on the ages of volcanic interlayers and plutonic intrusions depositional ages of the qugasi and tumugou formations are considered to be slightly older than 230 ma and ca 220 230 ma respectively which are prominently older than the previous estimates the yidun group in the changtai region has two prominent detrital zircon age peaks at 400 480 and 880 980 ma and a minor peak at 2 45 2 50 ga this pattern suggests a detritus source from the zhongza massif which was a micro continent separated from the western yangtze block in contrast the yidun group in the shangri la region has various zircon age spectra among different formations the qugasi formation in this region has detrital zircon age patterns similar to the yidun group in the changtai region however the overlying tumugou formation shows distinct age peaks at triassic 220 240 ma neoproterozoic 720 880 ma and paleoproterozoic 1 75 1 90 ga this age pattern is similar to that of the xikang group of the songpan ganzi terrane to the east the detrital zircon age difference between the qugasi and tumugou formations in this region indicates a transition of sedimentary sources from the zhongza massif to locally distributed triassic magmatic rocks at 230 ma it is thus suggested that the songpan ganzi terrane may have been connected to or collided with the southern part of the yidun terrane during the late triassic whereas the songpan ganzi terrane and the northern part of the yidun terrane were still separated by the ganzi litang ocean

climate of the supercontinent pangea numerous climate models predict that the geography of the supercontinent pangea was conducive to the establishment of a megamonsoonal circulation in general geologic evidence supports the hypothesis of a megamonsoon that reached maximum strength in the triassic pangea in the late carboniferous had widespread peat formation in what is now central and eastern north america and europe and relatively dry conditions on the colorado plateau the equatorial region of the continent became drier through the end of the carboniferous by the permian the equatorial region of pangea was dry and indicators of aridity and rainfall seasonality became more widespread wind directions from colorado plateau eolian sandstones are consistent with an increasing influence of monsoonal circulation at this time in the triassic climate in the colorado plateau region became relatively wet though still seasonal and the few eolian sandstones indicate a major shift in wind direction at that time in addition sedimentation

triassic diorites and granitoids in the foping area constraints on the conversion from subduction to collision in the qinling orogen china abstract the western qinling is characterized by triassic granitic plutons which are keys to constrain the timing of subduction and collisional processes between the north china and south china blocks this paper presents a set of new la icpms u pb zircon geochronology major and trace element geochemistry for several representative diorite and granitoid plutons in the foping area the diorites are characterized by high mgo al2o3 y and yb contents but low sio2 sr y and la yb ratios as well as depletion of nb ta p and ti suggesting derived from a subduction related setting la icpms zircon u pb age of 216 9 1 5 ma mswd 0 69 from the diorite constrains the time of the subduction event the medium and fine grained monzogranites as well as the biotite granites exhibit relative high sio2 mgo and rb low y and yb contents and low sr y and la yb ratios as well as various depletions of nb ta p and ti these features indicate a derivation from lower continental crust but had been influenced by slab released fluids in a syn collisional setting the medium grained monzogranite and biotite granite yield la icpms zircon u pb ages of 207 3 2 1 ma mswd 1 8 and 201 6 1 2 ma mswd 1 04 respectively proposing the syn collision during ca 207 201 ma geochemical and geological evidences suggest that the granodiorites intruding in the syn collisional monzogranites were related to the post orogenic collapse after the collision between the north china and south china blocks the la icpms u pb zircon age of 189 3 2 9 ma mswd 5 6 for the granodiorite constrains the time of the post orogenic collapse our geochronological and geochemical data provide important constraints on the triassic evolution from subduction to collision then up to post collisional collapse along the qinling orogen

increasing chemical weathering in the himalayan system since the last glacial maximum continental chemical weathering is central in earth s surface biogeochemical cycles as it redistributes elements across reservoirs such as the crust and the oceans however the evolution of weathering through time and its response to external forcing such as changes in climate remain poorly constrained in this work a composite sediment record from the bay of bengal is used to document the evolution of chemical weathering in the himalayan system himalayan range and indo gangetic floodplain the world largest sediment conveyor to the oceans since the last glacial maximum lgm the degree of weathering of the sediments is documented using mobile to immobile ratios such as k si and h2o si as well as detrital calcite abundance robust weathering proxies are derived by correcting the chemical composition of sediment for sorting effects that occur during transport and deposition the bay of bengal record is also further compared to the chemical composition of modern river sediments from the ganga and brahmaputra basin weathering proxies all indicate that the sediments exported by the ganga and brahmaputra rivers became increasingly weathered over the past 21 kyr whereas sr nd and major elements suggest a constant sediment provenance in the system over the last 21 kyr these changes in the degree of weathering of the sediments show that the weathering flux exported by the system to the indian ocean during the lgm was significantly lower than at present and demonstrate that chemical weathering in continental scale basins such as the ganga and brahmaputra responds to late quaternary climate changes

tectonic control on coarse grained foreland basin sequences an example from the cordilleran foreland basin utah newly released reflection seismic and borehole data combined with sedimentological provenance and biostratigraphic data from upper cretaceous paleocene strata in the proximal part of the cordilleran foreland basin system in utah establish the nature of tectonic controls on stratigraphic sequences in the proximal to distal foreland basin during campanian time coarse grained sand and gravel were derived from the internally shortening charleston nebo salient of the sevier thrust belt a rapid regional campanian progradational event in the distal foreland basin 200 km from the thrust belt in 8 m y can be tied directly to active thrust generated growth structures and an influx of quartzose detritus derived from the charleston nebo salient eustatic sea level variation exerted a minimal role in sequence progradation

inorganic geochemical indicators of glacial interglacial changes in productivity and anoxia on the california continental margin abstract evidence from sediments in cores collected from within the present oxygen minimum zone omz 600 1200 m on the central and northern california margins record several episodes during the last interstadial ois 3 ca 60 24 ka of deposition of laminated sediments containing elevated concentrations of several trace elements indicative of anoxic conditions e g mo ni zn and cu the presence of abundant well preserved organic matter as well as lack of bioturbation and the presence of elevated concentrations of mo and other trace elements all support the theory that the omz in the northeastern pacific ocean was more intense possibly anoxic at several times during the late pleistocene sediments of all ages in cores from the southern california margin contain elevated concentrations of mo suggesting that this area has always had higher rates of sulfate reduction than either the central or northern california areas most of the ba in sediments in all cores collected on the upper continental slope 200 2700 m off california and southern oregon is derived from detrital clastic material and this source did not change much in time however the amount of biogenic ba did vary with time and these variations closely follow the temporal variations in organic c corg mass accumulation rate using ba and corg mass accumulation rates as proxy variables for productivity all cores show that organic productivity under the california current upwelling system was highest during ois 3 and the holocene and lowest during the last glacial interval lgi ca 24 10 ka all paleoproductivity proxy variables indicate that the southern california area has always experienced higher productivity than other areas under the california current at least over the last 50 ky

subduction related origin of the 750 ma xuelongbao adakitic complex sichuan province china implications for the tectonic setting of the giant neoproterozoic magmatic event in south china abstract the xuelongbao plutonic complex in the eastern margin of the tibetan plateau is dated at 748 7 ma using the shrimp zircon u pb method and represents part of the neoproterozoic igneous assemblage of south china rocks in the complex include tonalite and granodiorite and have sio2 ranging from 62 0 to 74 8 wt and al2o3 from 14 3 to 20 9 wt their na2o contents range from 4 2 to 6 7 wt and k2o from 0 47 to 1 96 wt indicating that they belong to the na series these rocks show chondrite normalized ree patterns depleted in hree and variably enriched in lree they have positive sr and negative nb and ti anomalies in the primitive mantle normalized trace elemental spider diagram their sr contents range from 320 to 780 ppm and y contents are lower than 10 ppm resulting in high sr y ratios 52 320 characteristic of typical adakites their end t and initial sr isotopic compositions range from 0 36 to 2 88 and from 0 7033 to 0 7054 respectively the geochemical features of the xuelongbao plutonic complex are consistent with an origin from adakitic magmas that were likely derived from partial melting of a subducted oceanic slab together with arc signatures of other granites and mafic intrusions in the region the 750 ma xuelongbao adakitic complex provides evidence for a major subduction related neoproterozoic magmatic event of south china

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

multiple controls on the preservation of organic matter in devonian mississippian marine black shales geochemical and petrographic evidence geochemical and petrographic analysis of an interval of black shales between the huron shale member of the new albany shale upper devonian famennian and the sunbury shale lower mississippian tournaisian suggests that multiple controls influenced the accumulation of organic matter stratigraphic trends were determined following detailed analysis of a core from the central appalachian basin d6 montgomery county ky specifically c s fe relationships mo v v ni ni co and v cr were used to assess paleo redox conditions during sediment accumulation the role of clastic input was evaluated using ti al k al and si al and c p was used as a proxy for paleoproductivity the terrestrial to marine maceral ratio t m vitrinite plus inertinite alginite plus bituminite was used to evaluate changes in om source c s fe relationships and trace element ratios suggest anoxic conditions prevailed during deposition of much of the upper part of this interval however bottom water conditions were intermittently dysoxic during accumulation of the huron shale member and possibly dysoxic to marginally oxic during accumulation of the lowermost huron shale member productivity appears to have been an important factor in the accumulation of corg and high c p ratios are consistent with a productivity anoxia feedback mechanism in addition nutrients from increased terrestrial weathering may have contributed to enhanced productivity variations in sediment influx may also have influenced corg concentrations through sediment starvation one of the more significant observations in this work is an increase in terrestrial om inertinite and vitrinite up section which may reflect vegetative changes occurring on land during this time interval most of this increase is due to inertinite much of which appears to be fusinitic in origin and hence may be fossil charcoal this latter observation has implications for the expansion of land plants into drier niches and for late devonian atmospheric oxygen levels introduction of more resistant terrestrial om to anoxic basins may have been an important factor in the preservation of high carbon 10 intervals especially in the cleveland member of the new albany shale upper devonian famennian and the sunbury shale lower mississippian tournaisian

crustal thickening or isostatic rebound of orogenic wedge deduced from tectonostratigraphic units in indosinian foreland basin longmen shan china abstract longmen shan is located at the boundary between the sichuan basin and tibetan plateau representing the steepest gradient of any edges of the plateau three endmember models of uplift process and mechanism have been proposed including crustal thickening crustal flow and crustal isostatic rebound here we use tectonostratigraphic units in the late triassic foreland basin to restraint uplift process and mechanism in the longmen shan during indosinian orogeny the late triassic foreland basin developed as a flexural foredeep on the yangtze passive continental margin during the indosinian orogeny the basin fill includes the maantang formation the xiaotangzi formation and the xujiahe formation and it is divided into four tectonostratigraphic units with wedge shaped or tabular cross sectional geometry by unconformities and flooding surfaces in this paper the first and third ones are wedge shaped tectonostratigraphic units and correspond to underfilled condition with basal unconformities or major flooding surfaces the high rate of subsidence and sediment accumulation coarsening upward succession and a dual sediment supply and them may link to strong active thrust loading events or the rapidly advance rate of the orogenic wedge the second and fourth ones are tabular tectonostratigraphic units and correspond to overfilled condition with the unconformity the low rate of subsidence and sediment accumulation fining upward succession a single sediment supply the mass emergence of conglomerate layers and they may be related to isostatic rebound and erosion unloading two endmember models of uplift process and mechanism in the longmen shan during indosinian cycle have been proposed by coeval late triassic sedimentary sequences in the foreland basin here 1 crustal thickening during the wedge shaped tectonostratigraphic units 2 crustal isostatic rebound during the tabular tectonostratigraphic units this two endmember models proposed in this paper may be helpful to understand the mechanism of the wenchuan earthquake

paleoreef maps evaluation of a comprehensive database on phanerozoic reefs to get a better understanding of controls on reef development through time we created a comprehensive database on phanerozoic reefs the database currently comprises 2470 reefs and contains information about geographic position paleoposition age reef type dimensions environmental setting paleontological and petrographical features and reservoir quality of each buildup reef data were analyzed in two qualitatively different ways the first type of analysis was by visualization of paleogeographic reef distribution maps five examples late devonian early permian late triassic late jurassic middle miocene are presented to show the potential of paleoreef maps for paleogeographic and paleoclimatological reconstructions the second type of analysis was a numerical processing of coded reef characteristics to realize major trends in reef evolution and properties of reef carbonates the analysis of paleolatitudinal reef distributions through time shows pronounced asymmetries in some time slices probably related to climatic asymmetries rather than controlled by plate tectonic evolution alone the dominance of particular reef builders through time suggests that there are seven cycles of phanerozoic reef development first curves for the phanerozoic distribution of bioerosion in reefs bathymetric setting and debris potential of reefs are presented the observed pattern in the temporal and spatial distribution of reefs with reservoir quality may assist in hydrocarbon exploration statistical tests on the dependencies of reefal reservoir quality suggest that large size high debris potential low paleolatitude high amount of marine aragonite cement and a platform shelf edge setting favor reservoir quality reefal reservoirs are significantly enhanced in times of high evaporite sedimentation elevated burial of organic carbon low oceanic crust production low atmospheric co2 content and cool paleoclimate as well as when they are present in aragonite oceans

tectonic and climate control of oil shale deposition in the upper cretaceous qingshankou formation songliao basin ne china oil shales were deposited in the songliao basin ne china during the upper cretaceous period representing excellent hydrocarbon source rocks high organic matter om contents a predominance of type i kerogen and a low maturity of om in the oil shales are indicated by bulk geochemical parameters and biomarker data a major contribution of aquatic organisms and minor inputs from terrigenous land plants to om input are indicated by n alkane distribution patterns composition of steroids and organic macerals strongly reducing bottom water conditions during the deposition of the oil shale sequences are indicated by low pristane phytane ratios high c14 aryl isoprenoid contents homohopane distribution patterns and high v ni ratios enhanced salinity stratification with mesosaline and alkaline bottom waters during deposition of the oil shales are indicated by high gammacerane index values low mttc ratios high carotene contents low toc s ratios and high sr ba ratios the stratified water column with anoxic conditions in the bottom water enhanced preservation of om moderate input of detrital minerals during the deposition of the oil shale sequences is reflected by titanium concentrations in this study environmental conditions in the paleo lake leading to om accumulation in the sediments are related to sequence stratigraphy governed by climate and tectonics the first member of the qingshankou formation k2qn1 in the songliao basin containing the oil shale sequence encompasses a third order sequence that can be divided into three system tracts transgressive system tract tst highstand system tract hst and regressive system tract rst enrichment of om changed from low values during tst i to high moderate values during tst ii iii and hst i ii low om enrichment occurs during rst i and rst ii therefore the highest enrichment of om in the sediments is related to stages of mid late tst and early hst

the ciw index a new chemical index of weathering abstract a new chemical index of weathering that can be applied to modern soils and precambrian paleosis is proposed ciw al2o3 the value of this index increases as the degree of weathering increases and the difference between ciw index values of the silicate parent rock and soil or sediment reflects the amount of weathering experienced by the weathered material

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

critical evaluation of six tectonic setting discrimination diagrams using geochemical data of neogene sediments from known tectonic settings abstract an attempt is made to evaluate 6 tectonic setting discrimination diagrams 1 discriminant function and 5 bivariate diagrams frequently used by many researchers for this purpose an extensive database was established for major element geochemistry derived from miocene to recent sand and sandstone medium to fine grained samples collected from a variety of tectonic settings including 1 passive margin pm setting 2 active continental margin acm setting and 3 oceanic island arc oia setting our results suggest that the discrimination fields proposed to infer tectonic settings for six commonly used discrimination diagrams do not work properly for the analyzed miocene to recent sediments the success for these diagrams varies from 0 to about 62 we therefore recommend that these diagrams be used with prudence

estimating rill erosion process from eroded morphology in flume experiments by volume replacement method abstract rills are commonly found on the sloped farm fields in the loess regions worldwide especially on chinese loess plateau the erosion process along a rill provides information for understanding the rill erosion mechanism this study uses a volume replacement method to estimate the rill erosion processes by refilling the eroded rill segments the sediment concentration was calculated by summering the eroded soil mass and divided by the total water volume during the erosion period a flume that was 0 6 wide and 12 m long was subdivided into strips of 0 1 m wide and 12 m long to imitate eroding rills a typical silty loam soil from the loess plateau of china was used for the experiments the commutative eroded rill volumes along the rills under five slopes and three flow rates were measured at 11 rill segments all the sediment laden runoff was harvested at the rill outlet to measure the average sediment concentration the sediment concentrations at locations higher than that at the outlet were caused by sediment deposition and removed from the data set the computed sediment concentration processes increased with slope gradient and flow rate they also increase with rill length exponentially with all the coefficients of determination above 0 95 the results were about the same of the previous studies with sampling method this demonstrates that the proposed method is a feasible approach to estimate rill erosion distribution the data set is applicable to the estimation of rill erosion model parameters this study will provide a basis for estimating rill erosion model parameters

two phase stratigraphic model of foreland basin sequences application of flexural models to nonmarine foreland basin evolution indicates that two different stratigraphic styles of basin fill may develop over time basin subsidence is most rapid during times of thrust load emplacement associated sedimentation is coarse grained immediately adjacent to the thrust front and grades rapidly into fine grained deposits that cover most of the basin the distal part of the basin may also contain deposits derived from streams that flow from beyond the basin toward the thrust belt subsequent removal of the thrust load by erosion and other processes results in flexural rebound of the thrust belt and adjacent foreland basin during this postorogenic phase of adjustment a regional unconformity develops in the proximal part of the foreland basin proximal deposits along with thrust derived sediment are redeposited in the distal foreland basin and beyond this two phase model of foreland sedimentation predicts that coarsening upward sequences in the proximal and distal parts of the basin have reciprocal significance the proximal sequence represents thrust belt advance whereas the distal sequence represents thrust belt cessation

sedimentation rate dilution preservation and total organic carbon some results of a modelling study abstract a modelling exercise was undertaken to evaluate the positive preservational and negative diluent effects of sedimentation rate sr on the total organic carbon toc content of marine sediments and to use multiple regression analysis of modern data to predict toc data presented show the predicted marine toc using the carbon burial efficiency be versus sr relationship of betts and holland betts j n holland h d 1991 the oxygen content of ocean bottom waters the burial efficiency of organic carbon and the regulation of atmospheric oxygen palaeogeography palaeoclimatology palaeoecology global and planetary change section 97 5 18 calculated for a range of sr water depths primary productivities and four fixed be values the results suggest that the preservation effect of sr only enhances toc at 5 cm ka in oxic regimes after which dilution occurs if carbon supply is held constant above 35 cm ka there is no appreciable difference in toc regardless of whether the sea floor is anoxic or not below 10 cm ka there is a strong divergence in oxic and anoxic toc values observed positive correlations of sr and toc at 5 cm ka are largely an artefact of including sites from shallower depths and or higher productivities multiple regression analysis mra of modern marine sediment data suggests that once re scaled to allow for their non linear effect dissolved oxygen values may be a significant additional variable in determining the toc predicting an approximately 2 5 4 0 times higher toc in anoxic facies compared with fully oxic ones 4 ml l dissolved oxygen all other things being equal the mra also indicates a generally negative partial correlation between carbon delivery flux and be in modern sediments producing a significant moderating effect on the predicted toc

recurring patterns of total organic carbon and source rock quality within a sequence stratigraphic framework sequence stratigraphy has been combined with total organic carbon toc analysis from well logs core and cuttings to develop a model of toc accumulation in marine source rocks routine well profiling of toc in marine source rocks has revealed that recurrent patterns in the vertical distribution of toc occur that can be explained with sequence stratigraphic concepts the model assumes that the principle controls on organic carbon accumulation are 1 the presence of low oxygen conditions at the sediment water interface and 2 sedimentation rate under these circumstances toc will vary inversely with terrigenous clastic influx if accommodation is high clastic influx is low in distal locations and the resulting weight percent toc in basinal sediments is increased th maximum toc in a vertical profile through a single marine sequence probably correlates to the maximum flooding surface toc decreases above this surface due to increasing sediment dilution during highstand progradation and decreases below it with the higher sedimentation rate of the older transgressive systems tract commensurate with toc increase towards the maximum flooding surface the organic matter type becomes more marine and therefore increasingly oil prone several marine source rock examples are presented as well as a lacustrine example which also conforms to the marine model

marine productivity changes during the end permian crisis and early triassic recovery abstract the latest permian mass extinction lpme coincided with major changes in the composition of marine plankton communities yet little is known about concurrent changes in primary productivity earlier studies have inferred both decreased and increased productivity in marine ecosystems immediately following the end permian crisis here we assess secular and regional patterns of productivity variation during the crisis through an analysis of the burial fluxes of three elemental proxies total organic carbon toc phosphorus p and biogenic barium babio primary productivity rates appear to have increased from the pre crisis late permian through the early triassic in many parts of the world although the south china craton is unusual in exhibiting a pronounced decline at that time most of the 14 permian triassic study sections show concurrent increases in sediment bulk accumulation rates suggesting two possible influences linked to subaerial weathering rate changes 1 intensified chemical weathering resulting in an increased riverine flux of nutrients that stimulated marine productivity and 2 intensified physical weathering leading to higher fluxes of particulate detrital sediment to continental shelves thus enhancing the preservation of organic matter in marine sediments an additional factor especially in the south china region may have been the intensified recycling of bacterioplankton derived organic matter in the ocean surface layer reducing the export flux rather than primary productivity per se the ecosystem stresses imposed by elevated fluxes of nutrients and particulate sediment as well as by locally reduced export fluxes of organic matter may have been important factors in the 2 to 5 million year long delay in the recovery of early triassic marine ecosystems

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

stable carbon and hydrogen isotopes of natural gases sourced from the xujiahe formation in the sichuan basin china abstract the compound specific hydrogen and carbon stable isotope ratios of alkanes in natural gases from the xujiahe and jurassic formations in the western sichuan basin were investigated to distinguish between coal derived and oil associated gases all gases were determined to be coal derived and sourced from the xujiahe formation thermal maturities of the source rocks are expected to vary from 0 8 1 8 vitrinite reflectance ro according to the empirical relationship between the measured 13cch4 values and ro which is within the scope of the maturities of source rocks 0 7 2 1 in particular c1 3 alkanes of primary coal derived gases which have not undergone any secondary alteration become more enriched in deuterium with increasing molecular mass and the dch4 values increase with increasing thermal maturity of source rocks in the sichuan basin d values of coal derived gases sourced from terrigenous source rocks of the xujiahe formation are more negative than those of oil associated gases sourced from marine organic matter of the sinian permian and triassic formations

spatial variation in sediment fluxes redox conditions and productivity in the permian triassic panthalassic ocean abstract two permian triassic boundary sections in central japan provide a rare window into environmental conditions within the panthalassic ocean which encompassed more than half the earth s surface at 252 ma integration of petrographic geochemical and time series data provides new insights regarding the fluxes of major and trace components to the sediment as well as environmental conditions in both the deep and intermediate water masses at each study site the ubara section was located in a high productivity peri equatorial location whereas the gujo hachiman section was located in a moderate productivity location at some distance from the paleoequator an upward transition from gray organic poor cherts to black siliceous mudstones at both sites occurred in conjunction with increased primary productivity intensified euxinia within the oxygen minimum zone omz and decimation of the radiolarian zooplankton community euxinia in the omz of the equatorial panthalassic ocean developed episodically for a 200 250 kyr interval during the late permian followed by an abrupt intensification and lateral expansion of the omz around the permian triassic boundary throughout the study interval bottom waters at both sites remained mostly suboxic a finding that counters hypotheses of development of a superanoxic permo triassic deep ocean as a consequence of stagnation of oceanic overturning circulation

main genetic types and geological characteristics of iron rich ore deposits in china the proven total reserves of iron ores in china are relatively abundant but the iron ores mainly belong to low grade ores the reserves of high grade iron ores are rare and only possess 4 6 of the total proven reserves of iron ores among them the high grade ores for steelmaking and for iron smelting are even rarer and only amount to 1180 million tones which make up 2 27 of the proven reserves of iron ores in china the main genetic types of iron deposits of high grade ores in china include hydrothermal reformed type in sedimentary metamorphosed iron deposits bif weathered leaching type in sedimentary metamorphosed iron deposits bif iron deposits related to continental volcano intrusive activities iron deposits related to marine vo l canic intrusive activities skarn iron deposits hydrothermal iron deposits among these iron deposit types of high grade iron ores the skarn iron deposits and iron deposits related to marine volcanic intrusive activities are relatively important and have favorable ore prospecting potential

a new paleothermometer for forest paleosols and its implications for cenozoic climate climate is a primary control on the chemical composition of paleosols making them a potentially extensive archive applicable to problems ranging from paleoclimate reconstruction to paleoaltimetry however the development of an effective widely applicable paleosol temperature proxy has remained elusive this is attributable to the fact that various soil orders behave differently due to their respective physical and chemical properties therefore by focusing on an individual order or a subset of the 12 soil orders whose members exhibit similar process behavior a better constrained paleothermometer can be constructed soil chemistry data were compiled for 158 modern soils in order to derive a new paleosol paleothermometry relationship between mean annual temperature and a paleosol weathering index pwi that is based on the relative loss of major cations na mg k ca from soil b horizons the new paleothermometer can be applied to clay rich paleosols that originally formed under forest vegetation including inceptisols alfisols and ultisols and halves the uncertainty relative to previous approaches a case study using cenozoic paleosols from oregon united states shows that paleotemperatures produced with this new proxy compare favorably with paleobotanical temperature estimates global climatic events are also evident in the oregon paleosol record including a 2 8 c drop across the eocene oligocene transition comparable to marine records and a neogene peak temperature during the mid miocene climatic optimum

relationship between inferred redox potential of the depositional environment and geochemistry of the upper pennsylvanian missourian stark shale member of the dennis limestone wabaunsee county kansas u s a analyses of 21 samples collected from a core of the 52 8 cm thick stark shale member of the dennis limestone in wabaunsee county kansas demonstrate four cycles with two orders of magnitude variations in contents of cd mo p v and zn and order of magnitude variations in contents of organic carbon cr ni se and u the observed variability in amounts and or ratios of many metals and amounts and compositions of the organic matter appear related to the cause and degree of water column stratification and the resulting absence presence of dissolved o2 or h2s high cd mo u v zn and s contents a high degree of pyritization dop 0 75 0 88 and high high v v ni 0 84 0 89 indicate the presence of h2s in a strongly stratified water column intermediate contents of metals and s intermediate dop 0 67 0 75 and intermediate v v ni 054 0 82 indicate a less strongly stratified anoxic water column whereas low metal contents and low v v ni 0 46 0 60 indicate a weakly stratified dysoxic water column high p contents at the top of the organic matter rich intervals within the stark shale member indicate that phosphate precipitation was enhanced near the boundary between anoxic and dysoxic water compositions relatively abundant terrestrial organic matter in intervals deposited from the more strongly stratified h2s bearing water column indicates a combined halocline thermocline with the fresher near surface water the transport mode for the terrestrial organic matter the predominance of algal organic matter in intervals deposited from a less strongly stratified water column indicates the absence of the halocline and the presence of the more generally established thermocline relatively low amounts of degraded hydrogen poor organic matter characterize intervals deposited in a weakly stratified dysoxic water column the inferred variability in chemistry of the depositional environments may be related to climate variations and or minor changes in sea level during the general phase of deeper water deposition responsible for this widespread shale member

sediment generation in humid mediterranean setting grain size and source rock control on sediment geochemistry and mineralogy sila massif calabria abstract grain size control on sediment composition is investigated in modern proximal sediment from the sila massif where basic to felsic intrusive rocks are exposed in a mediterranean humid temperate upland climate samples were taken from small creeks and weathering profiles from three areas reflecting different bed rock compositions samples were separated into eleven grain size fractions from very coarse sand to clay and analyzed by i x ray fluorescence for chemical composition and ii x ray diffraction and mineral liberation analysis for mineralogical composition the chemical composition vs grain size relations were modeled by compositional linear regression mineralogical composition of selected samples is used to substantiate the interpretations based on geochemistry results reveal a high degree of chemical weathering with chemical index of alteration cia up to 92 high cia values are restricted to the fine grained fractions while sand sized sediment average at low to moderate cia values 60 although strongly weathered the three sample suites reflecting basic to felsic plutonic bed rock can be effectively discriminated across all grain size classes using trace elements such as v rb and sr linear trend modeling and mineralogical data reflect similar patterns for all sample suites implying similar processes independent of source rock composition this includes overall decrease of quartz and k feldspar over the full grain size range from very coarse sand to clay which is contrasted by overall increase of sheet silicates from coarse to fine among the latter increase of clay minerals strongly outpaces the increase of micas in silt to clay fractions a more complex behavior is shown by plagioclase which is most abundant in intermediate grain size fractions for all sample suites this is likely caused by initial hydrolysis along cleavage and twinning planes and subsequent breakage of plagioclase crystals into smaller fragments towards finer grain size intense hydrolysis has destroyed most feldspars