middle to late holocene palaeoenvironmental study of gialova lagoon sw peloponnese greece abstract the coastal areas of eastern mediterranean have long been the subject of research due to their rapid geomorphological changes but also because of their archaeological interest our study is focused on a shallow coastal lagoon of peloponnese gialova lagoon which for several years has attracted the scientific interest of archaeologists geomorphologists as well as sedimentologists gialova lagoon is located near the ancient city of pylos the kingdom of king nestor during the mycenaean period 1600 1100 bc the objectives of this study are a to reconstruct the middle to late holocene depositional environments of the lagoon and b to correlate our data to already existing publications in order to shed new light on the holocene evolution of the lagoon and the associated coastal palaeoenvironmental changes an 8 m deep vibracore was drilled and a multi proxy analysis was carried out on the sediment sequence including sedimentological grain size analysis and moment measures total organic carbon toc total nitrogen tn and total phosphorus tp high resolution geochemical xrf scanning and palaeontological micro and macro faunal analysis the chronological framework is based on five 14c datings forming the basis for an age depth model calculated using the oxcal software the radiocarbon dates from previous studies 6 cores 20 dates were also taken into account the data synthesis and interpretation provided robust and coherent indications regarding the palaeoenvironment shoreline changes and the rate of geomorphological changes of the coastal area of gialova lagoon as well as useful information about the palaeonvironmental and palaeoclimatic conditions that prevailed during the mycenaean period the interpretation reveal a transition from a shallow marine environment 6500 5800 yr b p to a brackish lagoonal 5800 3300 yr b p followed by a shift towards a freshwater marsh environment 3300 yr b p to present

mid silurian back arc spreading at the northeastern margin of gondwana the dapingzhang dacite hosted massive sulfide deposit lancangjiang zone southwestern yunnan china abstract the dapingzhang dacite hosted volcanogenic massive sulfide deposit is located in a late paleozoic collisional zone the sanjiang fold and thrust belt characterized by a collage of gondwana derived terranes at the southern margin of the south china yangtze block this area has experienced repeated paleozoic and mesozoic collisional and extensional events and is overprinted by himalayan strike slip and thrust movements the dapingzhang orebody is strongly sheared into discontinuous ore lenses and blocks and is hosted by a several hundred meter thick volcanic rock sequence of dacite with minor metabasalt spilite rhyolite and chert bulk rock nd isotope data give end 429 ma values of 2 to 5 and indicate a dominantly mantle source or origin from young continental crust tdm 800 1000 ma the dacites have distinctly low abundances of ti nb ta zr th and rees which is typical of subduction related volcanism the base metal mineralization occurs as polymetallic massive sulfide mineralization mainly pyrite sphalerite galena chalcopyrite tetrahedrite tennantite and locally barite and as pyrite chalcopyrite stockworks pervasive hydrothermal alteration is dominantly quartz sericite maximum enrichment in gold bismuth selenium and tellurium is at the interface between the stockwork and massive sulfide mineralization styles deeper parts of the stockwork zone are characterized by elevated molybdenum and rhenium whereas the distal parts to the massive sulfide mineralization have high mercury antimony zinc cadmium arsenic lead and silver the metal association and mineral assemblage are typical of volcanic rock hosted massive sulfides in back arc volcanic settings uranium pb dating on zircon by la icp ms defines an age of 429 3 ma 2 n 19 for the dacite sequence rhenium os isotope data on mo rich bulk ore samples define an isochron of 429 10 ma 2 n 9 mswd 0 21 initial 187os 188os 3 1 1 9 common os is very low and the absolute abundances of 187re and 187os define a model age of 429 4 ma n 9 95 confidence the mid silurian dacite sequence and associated massive sulfide mineralization identify a hitherto unknown early rifting and back arc seafloor spreading event at the northeastern gondwana margin related to the early evolution of the paleotethys ocean

the spacing of rift axis highs dependence upon diapiric processes in the underlying asthenosphere abstract detailed bathymetric mapping has revealed a near harmonic distribution of intermediate wavelength morphologic highs on slow to fast spreading centers one model suggests that the highs may result from the thermal instabilities generated by the interaction of cold fracture zone walls with the axial asthenosphere this may force a deepening of the isotherms near the fracture zone and an uplift of the isotherms midway between the fracture zones a preferred model based on newly accumulated data suggests that the highs may be a result of upwelling within the asthenosphere underlying the ridge axis where a linear region of instability develops at the base of a partial melting zone less dense material at depths of 40 80 km may penetrate the overlying material at discrete and ideally evenly spaced points harmonically spaced upwellings should generate excess magma at discrete points on the ridge axis creating volcanic highs the spacing between highs may depend upon the continuity and thickness of the deep axial instability layer the temperature and viscosity ratios within the magma and the distance between major transform faults instability of the diapirs may stimulate the migration of the highs through time

diffusion of osmium in pyrrhotite and pyrite implications for closure of the re os isotopic system abstract in order to better constrain the extent to which common sulfide minerals will retain their osmium isotopic composition subsequent to crystallization we have conducted experiments to quantify the diffusion behavior of osmium in pyrite and pyrrhotite experiments consisted of either 1 isothermal soaking of diffusion couples consisting of natural pyrite or pyrrhotite crystals packed against powdered os bearing fe sulfide or 2 relaxation of initially high near surface osmium concentrations produced in the latter experiments pyrite only osmium penetration into samples was characterized by depth profiling using rutherford backscattering spectroscopy rbs pyrite or electron microprobe analyses across sectioned run products pyrrhotite results of the first type of diffusion experiment involving pyrite show only limited osmium penetration into sample surfaces with the extent of penetration uncorrelated with run duration images of pyrite samples using atomic force microscopy show roughening of initially smooth surfaces as a consequence of step formation and suggest that osmium incorporation into the near surface occurred by solute uptake during step growth and not by volume diffusion prolonged 1000 h relaxation experiments revealed no additional osmium penetration into pyrite surfaces and based on the depth resolution for rbs a maximum diffusion coefficient of 2 5 10 23 m2 s at 500 c was calculated experiments involving pyrrhotite over the temperature range of 950 1100 c showed extensive osmium uptake and osmium concentration gradients that conform with fickian diffusion behavior we found that pyrrhotite fe s could be varied by changes in the composition of the starting material and osmium source and over the range of fe s produced in experiments molar fe s 0 83 0 90 we observed no systematic variation in the osmium diffusion coefficient diffusion coefficients measured parallel to the a crystallographic axis were on average 1 4 higher than values measured parallel to c and regression of the c axis data yielded the arrhenius relation d t 1 31 0 16 10 5 m 2 s exp 211 5 14 7 kj mol rt the application of these diffusion data to simple models of diffusive exchange during static or polythermal time temperature histories is used to assess the conditions under which radiogenic osmium will be retained during isothermal annealing calculations indicate that the cores of millimeter sized spherical pyrrhotite crystals undergoing diffusive exchange with an external osmium reservoir will have their initial compositions perturbed in 0 5 ma at temperatures exceeding 400 c pyrite undergoing the same process at 500 c requires in excess of 10 ma before crystal cores are affected the relatively short core retention time scales for pyrrhotite indicates that this mineral may be prone to isotopic resetting following relatively brief crustal thermal events thus possibly accounting for the scatter that commonly occurs in re os isochrons generated from massive sulfide samples calculated closure temperatures tc for osmium exchange in pyrrhotite yielded values of 300 400 c for grain sizes ranging from 10 to 1000 m these values of tc are similar to those calculated for ar retention in biotite and considerably lower than for sr in apatite and plagioclase for example such low closure temperatures for pyrrhotite suggest this mineral will date the final stage in the cooling of a magmatic system and possibly be susceptible to open system osmium exchange in the presence of late stage hydrothermal fluids this latter result infers that caution be applied when interpreting elevated initial osmium isotopic ratios as a product of crustal assimilation at the magmatic stage

ambient redox and hydrothermal environment of the wolverine volcanogenic massive sulfide deposit yukon insights from lithofacies and lithogeochemistry of mississippian host shales the wolverine volcanogenic massive sulfide vms deposit is a polymetallic felsic siliciclastic deposit hosted by 352 to 347 ma volcanic and sedimentary rocks of the yukon tanana terrane yukon canada shales are located at various stratigraphic levels and in various mineralized zones within the wolverine deposit area e g fisher puck and sable zones shales present along the mineralized horizon near the immediate hanging wall and footwall were deposited under anoxic conditions e g low mn anoxic v cr mo u systematics whereas in the stratigraphically deeper footwall and uppermost hanging wall the redox signatures imply deposition under suboxic to oxic conditions the mo u systematics of the shales suggest that during the time of sulfide mineralization the ambient basin was periodically euxinic with aqueous h2s present in the water column that this h2s contributed to the sulfur budget of the deposit furthermore the mo u and corg ni systematics favor deposition in a restricted basin i e nutrient trap where restriction of the water column led to h2s formation via sulfate reduction associated with excess organic carbon preservation there is also evidence of a progressive shift upward in the stratigraphy to more oxygenated conditions in the uppermost hanging wall the shift from euxinic to oxic suboxic conditions is consistent with regional tectonic models that indicate a change from rifting during wolverine deposit formation where the basin was partially restricted with minimal circulation i e restricted depocenter to an incipient back arc basin accompanied by extension and likely ingress of oxygenated seawater the rare earth element and y rey systematics in wolverine shales illustrate that proximal to the mineralized horizon shales have higher y ho 27 and ce ce 1 and negative ce anomalies indicative of oxygenated seawater the ce ce values in the wolverine shales have an inverse correlation with p2o5 content and suggest partial control by detrital apatite it is envisioned that apatite formed in the upper oxygenated portion of the water column inherited the ree signature of oxygenated seawater i e ce ce 1 and was subsequently deposited into deeper waters as detrital grains the ce ce and y ho also correlate with co2 and carbonate content of the shales moreover the shales that have the strongest rey signature of oxygenated seawater also coincide with the strongest euxinic signatures this paradox can be reconciled by enhanced deposition of apatite coincident with deposit formation coupled with a late hydrothermal overprint on the shales from low temperature co2 rich oxygenated hydrothermal fluids i e high y ho and ce ce 1 in a vent proximal environment this model is consistent with the geology stratigraphy and hydrothermal alteration in the immediate footwall and hanging wall of the deposit prospective shales in the wolverine basin and similar sediment rich hydrothermal basins globally should exhibit evidence for deposition under anoxic conditions i e mn 1 000 ppm high v mo u uef moef hydrothermal fe al mn systematics i e high fe al and evidence for hydrothermal alteration i e high ciw values high molar sericite and chlorite identification of samples having these features is useful in targeting prospective vms environments in shale dominated successions and potential targets within shale rich basins

genetic relationship between granitic magmatism and w mineralization recorded in the nanling scientific drilling sp nlsd 2 in the pangushan w mining district south china abstract the nanling region in south china hosts numerous w dominated polymetallic deposits that are related to mesozoic granites although considerable amounts of age data have been obtained the genetic relationship between granitic magmatism and w mineralization remains unclear the nanling scientific drilling sp nlsd 2 in the pangushan w deposit has penetrated upper devonian sedimentary rocks 4 1 721 9 m sinian sedimentary rocks 721 9 1287 9 m and mesozoic granite 1287 9 2012 1 m the drill hole clearly reveals a zonation including exocontact w bearing quartz veins alkali autometasomatic zone and primary k feldspar granite the k feldspar granite at the depth of 1880 m and rocks of potassium autometasomatic zone at 1414 m and greisenized zone at 1288 m have magmatic zircon grains with u pb ages of 164 8 1 4 ma 161 7 1 6 ma and 153 8 1 2 ma respectively molybdenite re os ages of endocontact mineralization at the depths of 1302 m and 1291 m are 155 9 3 1 ma and 155 0 2 3 ma respectively muscovite ar ar ages of exocontact mineralization at the depths of 1050 and 885 m are 154 9 1 5 ma and 154 0 3 0 ma respectively and molybdenite re os age of exocontact quartz vein type mineralization at 860 m is 152 0 2 6 ma these new ages indicate that the granite emplacement potassium autometasomatism greisenization and w mineralization occurred at 164 8 ma 161 7 ma 153 8 ma and 155 9 152 ma respectively the w mineralization was approximately 9 13 myr younger than the hosting granite the whole rock and feldspar chemical compositions of k feldspar granite potassium autometasomatic zone greisenized zone and feldspar quartz veins indicate the sequence of metal transportation and concentration to form the zonation the granite crystallized from high k calcalkaline metaluminous to peraluminous highly differentiated magmas that were enriched in w and bi during crystallization the magmas underwent potassium autometasomatism caused by post magmatic fluids which were rich in k fe w and rare earth elements ree but poor in na and ca and formed the potassium autometasomatic zone the evolved post magmatic fluids became rich in k si ca ree and w but poor in na and fe and initiated greisenization to generate the greisenized zone which almost exhausted ca ree na and fe of the fluids the later crystallization of feldspar quartz veins exhausted k and caused the residual post magmatic fluids to be rich in si and w the fluids formed w bearing quartz veins with decreasing temperature and pressure the main reason for w enrichment in the hydrothermal fluids was due to the successive crystallization of minerals rather than autometasomatism

a modern vs permian black shale the hydrography primary productivity and water column chemistry of deposition the sediment currently accumulating in the cariaco basin on the continental shelf of venezuela has an elevated organic carbon content of approximately 5 is accumulating under o2 depleted bottom water conditions so42 reduction is composed dominantly of foraminiferal calcite diatomaceous silica clay and silt and is dark greenish gray in color upon lithification it will become a black shale recent studies have established the hydrography of the basin and the level of primary productivity and bottom water redox conditions these properties are used to model accumulation rates of cd cr cu mo ni v and zn on the seafloor the model rates agree closely with measured rates for the uppermost surface sediment the model is applied to the meade peak phosphatic shale member of the phosphoria formation a phosphate deposit of permian age in the northwest united states it too has all of the requisite properties of a black shale although the deposit is a world class phosphorite it is composed mostly of phosphatic mudstone and siltstone chert limestone and dolomite it has organic carbon concentrations of up to 15 is strongly enriched in several trace elements above a terrigenous contribution and is black the trace element accumulation defines a mean primary productivity in the photic zone of the phosphoria basin as moderate at 500 g m 2 year 1 organic carbon comparable to primary productivity in the cariaco basin the source of nutrient enriched water that was imported into the phosphoria basin upwelled into the photic zone and supported primary productivity was an o2 minimum zone of the open ocean the depth range over which the water was imported would have been between approximately 100 and 600 m the mean residence time of bottom water in the basin was approximately 4 years vs 100 years in the cariaco basin the bottom water was o2 depleted but it was denitrifying or no3 reducing rather than so42 reducing

using detrital zircons from river sands to constrain major tectono thermal events of the cathaysia block se china abstract detrital zircons from the minjiang and zhujiang rivers in se china have been analyzed for u pb ages and lu hf isotopic compositions to constrain their provenance and the growth history of the continental crust of the cathaysia block zircon u pb ages show five major populations at 90 250 ma 400 500 ma 0 7 1 2 ga 1 6 2 0 ga and 2 3 2 6 ga proterozoic zircons have hf isotopic signatures consistent with the remelted ancient crust and the involvement of juvenile crust however phanerozoic zircons have hf isotopic signatures indicative of reworked or recycled ancient crust crustal growth rates based on the two stage hf model ages of the detrital zircons indicate that 30 and 90 of present crust in the northeastern cathaysia block was formed by 2 5 ga and 1 6 ga respectively whereas

the north lhasa terrane in tibet was attached with the gondwana before it was drafted away in jurassic evidence from detrital zircon studies abstract it was commonly accepted that the north lhasa terrane of the present day central tibetan plateau in asia came from the northern gondwana but the timing of its northward drifting away from the gondwana remains controversial here we present for the first time u pb age and hf isotope data on detrital zircons from the cambrian metasedimentary rocks in the north lhasa terrane the detrital zircons display age peaks at ca 505 548 926 and 1104 ma and are interpreted to have gondwanan source regions these metasedimentary rocks were probably deposited in a collisional tectonic setting e g foreland basin related to the cambrian collisional accretion of microcontinents along the gondwanan proto tethyan margin the cambrian and carboniferous late triassic sedimentary rocks in the north lhasa terrane share the similar precambrian cambrian detrital zircon age and ehf t distributions indicating constant source accretion during the cambrian triassic time by contrast the precambrian cambrian detrital zircon age distribution of the late jurassic early cretaceous sedimentary rocks in the north lhasa terrane is distinctive from that of the adjacent cambrian triassic sedimentary rocks suggesting that the northward drifting of this terrane occurred in the jurassic

prediction of some weathering trends of plutonic and volcanic rocks based on thermodynamic and kinetic considerations abstract the exposed crust consists mainly of plagioclase 35 quartz 20 k feldspar 11 volcanic glass 12 biotite 8 and muscovite 5 quartz is a resistate thus feldspars and glass represent approximately 75 percent of the labile minerals the weathering characteristics of these constituents are summarized in the context of thermodynamic mass balance and kinetic considerations experimentally determined release rate constants were used to predict the proportions of ca na and k released by feldspars of plutonic rocks granites to gabbros to weathering solutions the chemical weathering trends of the weathered residues calculated from the kinetic data conform closely to the initial trends observed in some recent weathering profiles demonstrating the accuracy of the predictions since the weathering of feldspars is controlled by processes that should not change through geological time the relative release rates of ca na and k from the feldspars of granitic rocks can be calculated for future and past episodes of continental weathering experimentally determined release rate constants are not available for a wide range of volcanic glass compositions but the limited data indicate that compositional trends are predictable in weathering profiles developed on volcanic rocks the kinetic data available for rhyolitic glasses accurately predict the initial weathering trends observed in a recent rhyolite weathering profile

middle upper ordovician radiolarians in hunan and jiangxi provinces south china implications for the sedimentary environment and nature of the nanhua basin abstract the yanxi and duiershi formations of the middle upper ordovician in south china are composed of black grayish black and dark gray thin bedded cherts and siliceous slates rich in carbonaceous materials and pyrite horizontal beddings are developed the strata contain randomly distributed fossils radiolarians are discovered in the loudi yongzhou hengyang ji an and ganzhou sections the radiolaria from two sections are identified as protoentactinia sp abundances of radiolarian in the central area of hunan and jiangxi provinces are higher than in the southern area the strata become thickened while the amounts of siliceous materials are decreased and argillaceous contents are increased from northwest to southwest for the yanxi and duiershi formations the lithology gradually changes from carbonate rocks in the north to clastic rocks in the south 30si values of chert and siliceous slate range from 0 6 to 1 18 with al2o3 al2o3 fe2o3 mno tio2 lan cen ce ce and la yb n ratios of 0 65 0 97 0 01 0 16 0 99 1 27 0 85 1 10 and 0 91 1 66 respectively the sio2 and tio2 average contents are 89 08 and 0 27 the sio2 contents decrease while the tio2 increase from northwest to southeast they have similar the ree concentration with no obvious eu anomalies the yanxi and duiershi formations were deposited predominately in a bathyal environment on the continental slope basin and the seawater was stagnant in the middle early late ordovician the nanhua basin occupied a rather large area and sedimentary rocks in the region around hengyang ji an were deposited in the basin center with terrigenous source derived from the southeast

late paleozoic sedex deposits in south china formed in a carbonate platform at the northern margin of gondwana abstract sedex sulfide deposits hosted in black shale and carbonate are common in the south china block the dajiangping pyrite deposit is the largest of these deposits and is made up of stratiform orebodies hosted in black shales sandstone interlayered with stratiform orebodies contains detrital zircon grains with the youngest ages of 429 ma pyrite from the orebodies has a re os isochron age of 389 62 ma indicative of formation of the hosting strata and syngenetic pyrite ores in the mid late devonian the hosting strata is a transgression sequence in a passive margin and composed of carbonaceous limestone in the lower part and black shales in the upper part the ore hosting black shales have high toc total organic carbon mo as pb zn and cd indicating an anoxic euxinic deep basin origin the high redox proxies v v ni 0 6 and v cr 1 and the positive correlations of toc with mo and v in black shales are also consistent with an anoxic depositional environment the dajiangping deposit is located close to the ne trending wuchuan sihui fault which was active during the devonian the mid late devonian mineralization age and the anoxic euxinic deep basinal condition of this deposit thus imply that the formation of this deposit was causally linked to hydrothermal fluid exhalation in an anoxic fault bounded basin that developed in a carbonate platform of the south china block the regional distribution of many devonian stratiform carbonaceous sediment hosted sulfide deposits along the ne trending fault bounded basins in south china similar to the dajiangping deposit indicates that these deposits formed at a basin developed in the passive margin setting of the south china block during the devonian this environment was caused by the break up and northward migration of the south china block from gandwana

redox controls on arsenic enrichment and release from aquifer sediments in central yangtze river basin abstract more than 100 million people in asia are presently exposed to groundwater with arsenic as concentrations exceeding the world health organization standard of 10 g l 1 arsenic contaminated groundwater within basins of the central portion of the yangtze river has recently been reported but the processes controlling arsenic concentrations have yet to be resolved we examined the hydrologic and geochemical factors controlling arsenic within the jianghan plain an inland sedimentary basin of the yangtze river where arsenic concentrations exhibit strong seasonal variability driven by surface and groundwater mixing schaefer et al 2016 hydrologic fluctuations alter redox conditions in the aquifer leading to oscillations between arsenic iron reduction and oxidation here we investigate the depth distribution of solid and aqueous phase iron and arsenic species and through a series of laboratory manipulations constrain the biogeochemical processes controlling seasonal changes in groundwater arsenic concentrations in sediment incubations from 20 m below the surface where solid phase arsenic concentrations exceed 100 mg kg 1 both unamended and glucose amended sediment samples result in arsenic release to the aqueous phase in situ carbon was capable of promoting as release in the sediment in contrast sediment batch incubations from other depths resulted in limited as release solid phase arsenic in the enriched zone was relatively oxidized but may become reduced over short time periods in sediments below the as enriched zone glucose amendment resulted in arsenic reduction but arsenic release to the aqueous phase was restricted by the subsequent formation of arsenic sulfide minerals buried sedimentary arsenic coupled with anaerobic microbial respiration of subsurface organic carbon within the jianghan plain aquifer leads to rapid release of as to groundwater arsenic release from sediments at 20 m depth is sufficient to explain arsenic concentrations throughout the aquifer and provides a mechanism to explain how shifts in hydrology result in seasonally variable arsenic concentrations in groundwater

historical and pre historical tsunamis in the mediterranean and its connected seas geological signatures generation mechanisms and coastal impacts abstract the origin of tsunamis in the mediterranean region and its connected seas including the marmara sea the black sea and the sw iberian margin in the ne atlantic ocean is reviewed within the geological and seismotectonic settings of the region a variety of historical documentary sources combined with evidence from onshore and offshore geological signatures geomorphological imprints observations from selected coastal archeological sites as well as instrumental records eyewitnesses accounts and pictorial material clearly indicate that tsunami sources both seismic and non seismic e g volcanism landslides can be found in all the seas of the region with a variable tsunamigenic potential local regional and basin wide tsunamis have been documented an improved map of 22 main tsunamigenic zones and their relative potential for tsunami generation is presented from west to east the most important tsunamigenic zones are situated offshore sw iberia in the north algerian margin in the tyrrhenian calabria and messina straits in the western and eastern segments of the hellenic arc in the corinth gulf of central greece in the levantine sea offshore the dead sea transform fault and in the eastern side of the marmara sea important historical examples including destructive tsunamis associated with large earthquakes are presented the mean recurrence of strong tsunamis in the several basins varies greatly but the highest event frequency 1 96 years is observed in the east mediterranean basin for most of the historical events it is still unclear which was the causative seismic source and if the tsunami was caused by co seismic slip by earthquake triggered submarine landslides or by a combination of both mechanisms in pre historical times submarine volcanic eruptions i e caldera collapse massive pyroclastic flows volcanogenic landslides and large submarine landslides caused important tsunamis although little is known about their source mechanisms we conclude that further investigation of the tsunami generation mechanisms is of primary importance in the mediterranean region inputs from tsunami numerical modeling as well as from empirical discrimination criteria for characterizing tsunami sources have been proved particularly effective for recent well documented aseismic landslide tsunamis e g 1963 corinth gulf 1979 cote d azur 1999 izmit bay 2002 stromboli volcano since the tsunami generation mechanisms are controlled by a variety of factors and given that the knowledge of past tsunami activity is the cornerstone for undertaking tsunami risk mitigation action future interdisciplinary research efforts on past tsunamis are needed

environmental analysis of paleoceanographic systems based on molybdenum uranium covariation abstract modern low oxygen marine systems exhibit patterns of molybdenum uranium covariation that can be linked to specific attributes and processes of the depositional system including 1 variation in benthic redox conditions 2 the operation of particulate shuttles within the water column and 3 the evolution of watermass chemistry the importance of these factors in each depositional system can be assessed both from the degree of enrichment of authigenic molybdenum mo auth and uranium u auth and from the mo u auth ratio of the sediment relative to the seawater mo u molar ratio of 7 5 7 9 in open ocean systems with suboxic bottomwaters u auth enrichment tends to exceed that of mo auth owing to onset of u auth accumulation at the fe ii fe iii redox boundary resulting in sediment mo u auth ratios less than that of seawater as bottomwaters become increasingly reducing and at least occasionally sulfidic the rate of accumulation of mo auth increases relative to that of u auth and sediment mo u auth ratios equal or exceed that of seawater in restricted marine systems with permanently sulfidic deepwaters the relative enrichment of mo auth and u auth depends on additional factors in the cariaco basin which has an aqueous mo u ratio similar to that of seawater the operation of a particulate mn fe oxyhydroxide shuttle serves to accelerate the transfer of mo to the seafloor leading to strong enrichments in mo auth relative to u auth in the black sea the chemistry of the deep watermass has evolved to the point where its aqueous mo u ratio is only 0 04 that of seawater as a consequence of which sediments deposited under deepwater influence are depleted in mo auth relative to u auth these mo u covariation patterns can be used to gain a better understanding of the watermass attributes and processes of ancient low oxygen marine systems analysis of anoxic facies from two north american paleomarine systems the late pennsylvanian midcontinent sea lpms and the late devonian seaway lds reveals authigenic mo u relationships similar to those of the modern marine environments above implying similar redox and hydrographic controls the observed patterns are consistent with laterally unconfined circulation and strong watermass exchange within the lpms and with markedly restricted deepwater circulation in silled basins of the lds patterns of authigenic mo u covariation may prove useful in analysis of other paleoceanographic systems to reveal aspects of watermass composition and environmental dynamics

palaeozoic and mesozoic tectonic evolution and palaeogeography of east asian crustal fragments the korean peninsula in context east and southeast asia comprises a complex assembly of allochthonous continental lithospheric crustal fragments terranes together with volcanic arcs and other terranes of oceanic and accretionary complex origins located at the zone of convergence between the eurasian indoaustralian and pacific plates the former wide separation of asian terranes is indicated by contrasting faunas and floras developed on adjacent terranes due to their prior geographic separation different palaeoclimates and biogeographic isolation the boundaries between asian terranes are marked by major geological discontinuities suture zones that represent former ocean basins that once separated them in some cases the ocean basins have been completely destroyed and terrane boundaries are marked by major fault zones in other cases remnants of the ocean basins and of subduction accretion complexes remain and provide valuable information on the tectonic history of the terranes the oceans that once separated them and timings of amalgamation and accretion the various allochthonous crustal fragments of east asia have been brought into close juxtaposition by geological convergent plate tectonic processes the gondwana derived east asia crustal fragments successively rifted and separated from the margin of eastern gondwana as three elongate continental slivers in the devonian early permian and late triassic late jurassic as these three continental slivers separated from gondwana three successive ocean basins the palaeo tethys meso tethys and cenotethys opened between these and gondwana asian terranes progressively sutured to one another during the palaeozoic to cenozoic south china and indochina probably amalgamated in the early carboniferous but alternative scenarios with collision in the permo triassic have been suggested the tarim terrane accreted to eurasia in the early permian the sibumasu and qiangtang terranes collided and sutured with simao indochina east malaya in the early middle triassic and the west sumatra terrane was transported westwards to a position outboard of sibumasu during this collisional process the permo triassic also saw the progressive collision between south and north china with possible extension of this collision being recognised in the korean peninsula culminating in the late triassic north china did not finally weld to asia until the late jurassic the lhasa and west burma terranes accreted to eurasia in the late jurassic early cretaceous and proto east and southeast asia had formed palaeogeographic reconstructions illustrating the evolution and assembly of asian crustal fragments during the phanerozoic are presented d 2005 international association for gondwana research published by elsevier b v all rights reserved

hydrothermal venting and basin evolution devonian south china constraints from rare earth element geochemistry of chert this paper presents rare earth element ree geochemistry of siliceous deposits from which hydrothermal activity and basin evolution are elucidated in the late devonian in the yangshuo basin south china where siliceous deposits widely occurred as nodular chert in the deep water limestones and bedded chert interbeded with tuffaceous chert in the early late devonian both nodular and bedded cherts are characterized by very low la abundances avg 2 07 and 2 49 ppm respectively intermediate negative ce anomalies ce ce avg 0 69 and 0 61 slight to intermediate positive eu anomalies eu eu avg 1 33 and 1 57 and low to intermediate shale normalized lan ybn values avg 0 86 and 0 52 and intermediate lan cen values avg 1 61 and 1 72 these suggest both nodular and bedded cherts formed in the open marine basin of south china rather than in the intracontinental rift basin as previously assumed with involvement both with seawaters as indicated by intermediate negative ce anomalies and generally lree depleted patterns and hydrothermal vent fluids as indicated by convex less lree depleted patterns with apparent positive eu anomalies in comparison with nodular and bedded chert the tuffaceous chert has the highest la abundances avg 17 11 ppm similar ranges of ce anomalies avg 0 63 and lan cen values avg 1 77 but lower lan ybn values avg 0 48 and no apparent positive eu anomalies avg 0 97 this suggests that the tuffaceous fallouts were also significantly modified by the hydrothermal fluid and seawater rapid spatial variations of eu eu values and degree of lree depletions in the studied basin are recognized characterizing a spatially differential hydothermal activity that is not well discriminated by major element features such a difference in hydrothermal activity is interpreted as having been related to the intensity and depth of syndepositional tectonic activity reconciling the structural pattern unraveled by stratigraphic packages d 2005 elsevier b v all rights reserved

use of the geochemical and biological sedimentary record in establishing palaeo environments and climate change in the lake ngami basin nw botswana sediment samples from a continuous 4 6 m profile in the dry bed of lake ngami in nw botswana were analysed for geochemistry and dated using both 14c and tl methods certain units in the profile were found to be diatom rich and these with the geochemical results were used as indicators of high and low lake levels within the basin the lake ngami sediments contain a high proportion of sio2 51 92 5 wt avg 72 4 wt and variable levels of al2o3 2 04 17 2 wt avg 8 88 wt based on elevated al2o3 and organic matter loiorgc results lacustrine conditions occurred at ca 42 ka until 40 ka and diatom results suggest that relatively deep but brackish conditions prevailed at 40 ka the lacustrine sedimentary record was terminated abruptly possibly by tectonic activity at ca 19 ka shallow aerobic turbulent conditions were prevalent but lake levels were at this time increasing to deeper water conditions up until ca 17 ka this period coincides with the late glacial maximum a period of increased aridity in the central southern africa region generally increasing sr ca ratios and decreasing loiorgc and al2o3 from ca 16 to 5 ka suggest decreasing inflow into the basin and declining lake levels based on the enrichment of lree results slightly alkaline conditions prevailed at ca 12 ka diatom results also support shallow alkaline conditions around this time these lake conditions were maintained primarily by local rainfall input as the region experienced a warmer wetter phase between 16 and 11 ka lake levels rose rapidly by 4 ka probably in response to enhanced rainfall in the angolan catchment these results indicate that lake levels in the lake ngami basin are responding to rainfall changes in the angolan catchment area and local rainfall the results confirm that the present day anti phase rainfall relationship between southern africa and regions of equatorial africa was extant during the late quaternary over the angolan highlands and nw botswana

the holocene sea level story since 7500 bp lessons from the eastern mediterranean the black and the azov seas abstract this paper addresses the obvious controversy between the so far published sea level curves of the black sea and the mediterranean it starts with a discussion of the methods of reconstructing sea level curves the evaluation of sea level indicators and the application of the radiocarbon dating method at least since 7500 bp when the black sea and the mediterranean were connected both water bodies must have reacted synchronously on glacio eustatic changes it is documented that none of the mediterranean sea level curves shows the major wiggles postulated for the black sea which are supposed to reflect trans and regression cycles the very shallow bathymetric condition of the azov sea and the northern black sea should have led to considerable and traceable shoreline displacements there is neither archaeological nor historical evidence of mid and late holocene regressions of several meters the tectonic setting of the black and azov seas implicates that the tectonic signal often overrides the eustatic one therefore only local sea level curves can be established in this paper based on vibracores a locally valid sea level curve for the taman peninsula is demonstrated layers of paralic peat were used as sea level indicators and for 14 c dating the shape of this curve follows the one known from the mediterranean this study also revealed that the present peninsula of taman evolved out of a former archipelago

arsenic incorporation into authigenic pyrite bengal basin sediment bangladesh abstract sediment from two deep boreholes 400 m approximately 90 km apart in southern bangladesh was analyzed by x ray absorption spectroscopy xas total chemical analyses chemical extractions and electron probe microanalysis to establish the importance of authigenic pyrite as a sink for arsenic in the bengal basin authigenic framboidal and massive pyrite median values 1500 and 3200 ppm as respectively is the principal arsenic residence in sediment from both boreholes although pyrite is dominant ferric oxyhydroxides and secondary iron phases contain a large fraction of the sediment bound arsenic between approximately 20 and 100 m which is the depth range of wells containing the greatest amount of dissolved arsenic the lack of pyrite in this interval is attributed to rapid sediment deposition and a low sulfur flux from riverine and atmospheric sources the ability of deeper aquifers 150 m to produce ground water with low dissolved arsenic in southern bangladesh reflects adequate sulfur supplies and sufficient time to redistribute the arsenic into pyrite during diagenesis

geochronology and petrogenesis of the early paleozoic i type granite in the taishan area south china middle lower crustal melting during orogenic collapse abstract the early paleozoic wuyi yunkai orogeny represents the first extensive tectonothermal event in south china since the neoproterozoic break up of the rodinia supercontinent the early paleozoic igneous rocks in the south china block scb are important for understanding the processes responsible for the orogeny the taishan batholith in the inner cathaysia block consists dominantly of granodiorite and hornblende bearing granite zircon u pb dating of four samples gives a consistent crystallization age of ca 436 ma synchronous with widespread late orogenic s type granitic intrusions in the wuyi yunkai orogen the taishan granitoid rocks are metaluminous or peraluminous a cnk 0 94 1 15 and have variable sio 2 61 5 74 9 wt mgo 0 4 2 4 wt fe 2 o 3 1 8 7 4 wt and cao 1 1 5 5 wt with gradually decreasing p 2 o 5 from mafic to felsic components thus the taishan batholith displays the petrological and geochemical characteristics of i type granites additionally all samples have strongly negative e nd t values 11 to 9 suggesting an overall ancient source the early paleozoic i type granitoid rocks in the taishan area were derived from partial melting of ancient middle to lower crust at a high thermal gradient 35 c km and underwent extensive fractional crystallization of hornblende plagioclase and biotite the wuyi yunkai orogenic collapse may have been responsible for middle to lower crustal melting of the cathaysia block the early paleozoic i and s type granitoid magmatism lack significant input of a juvenile component indicating that the processes accompanying orogenic collapse such as asthenosphere upwelling and basaltic underplating contributed heat to trigger widespread early paleozoic felsic magmatism in the scb an intraplate orogenic event instead of continental or arc collision may be the preferred model for the wuyi yunkai orogeny

crustal contamination versus an enriched mantle source for intracontinental mafic rocks insights from early paleozoic mafic rocks of the south china block abstract several recent studies have documented that the silicic rocks sio 2 65 wt comprising silicic large igneous provinces are derived from partial melting of the crust facilitated by underplating intraplating of hidden large igneous province scale basaltic magmas the early paleozoic intracontinental magmatic rocks in the south china block scb are dominantly granitoids which cover a combined area of 22 000 km 2 in contrast exposures of mafic rocks total only 45 km 2 these mafic rocks have extremely heterogeneous isotopic signatures that range from depleted to enriched whole rock initial 87 sr 86 sr 0 7041 0 7102 e nd t 8 4 to 1 8 weighted mean zircon e hf t 7 4 to 5 2 show low ce pb and nb u ratios 0 59 13 1 and 3 5 20 9 respectively and variable th la ratios 0 11 0 51 the high mgo mafic rocks mgo 10 wt tend to have lower e nd t values nd t values 4 and sm nd ratios 0 255 the differences in geochemistry between the high mgo and low mgo mafic rocks indicate greater modification of the compositions of high mgo mafic magmas by crustal material in addition generally good negative correlations between e nd t and initial 87 sr 86 sr ratios mgo and k 2 o along with the presence of inherited zircons in some plutons indicate that the geochemical and isotopic compositions of the mafic rocks reflect significant crustal contamination rather than an enriched mantle source the results show that high mgo mafic rocks with fertile isotopic compositions may be indicative of crustal contamination in addition to an enriched mantle source and it is more likely that the lithospheric mantle beneath the scb during the early paleozoic was moderately depleted than enriched by ancient subduction processes

basement structures underneath the northern south yellow sea basin east china implications for the collision between the north china and south china blocks abstract the south yellow sea basin sysb as the eastern part of the yangtze block has undergone multiple tectonic events since the formation of its basement the north china south china collision affected intensely the structures of the basin the relationship between the deep structures in the basement and collisional orogeny has long been a matter of debate in this paper 2d seismic magmatic gravity and drilling data were integrated to unravel the basement structures in the interpreted seismic sections the basement can be subdivided into three seismic facies the seismic facies i and iii correspond to two basement layers the seismic facies ii is interpreted as shear zones that were formed during the mesozoic collision and exhumation the influence of the north china south china collision propagated from north to south in the sysb according to observations from drill holes and seismic sections the northern part of the basin the yantai depression uplifted during the earlier stage of the collision resulting in the erosion of the upper paleozoic and triassic strata in the middle and southern parts the laoshan uplift and qingdao depression the compression was obviously after that in the yantai depression the exhumation of the qianliyan basement metamorphic complex of the yangtze block occurred gradually the shear zones were initially developed during the collision during early mesozoic the exhumation process of metamorphic rocks lasted till late mesozoic and the jurassic cretaceous strata were deposited in the hanging wall of the northern boundary fault

sedimentological and geoarchaeological evidence of multiple tsunamigenic imprint on the bay of palairos pogonia akarnania nw greece abstract this paper presents evidence of multiple tsunami impact on the bay of palairos pogonia nw greece during the holocene based on detailed geo scientific studies altogether 41 vibracores were drilled to detect high energy influence in the stratigraphical record layers of coarse grained allochthonous marine deposits were found intersecting autochthonous fine grained back beach sediments in the palairos coastal plain on top of beach or marly bedrock units at pogonia beach and along the pogonia cliff section high energy deposits are associated with specific sedimentary structures such as fining upward sequences rip up clasts basal erosional contact bi to multimodal grain size distribution lamination and co existence of both well rounded and angular sharply edged components all of them typical of tsunami impact macro and microfaunal analyses revealed tsunami related input of numerous ex situ marine species and mostly angular shell debris into quiescent fresh to brackish water environments by high energy and long distance transport geophysical methods helped to find subsurface structures and to seize the lateral extent of tsunami layers ca fe ratios derived from xrf measurements were used to trace tsunami influence inland most important is the widespread spatial distribution of the tsunamites with a lateral extent between 70 m at the pogonia cliff section 200 m at pogonia beach and 1 km in the central palairos plain and overall tendencies of fining and thinning towards inland highest elevations of tsunamites were found around pogonia village at ca 7 5 m a s l vibracore data give evidence that the overall coastal evolution has been strongly affected locally even controlled by multiple high energy impact a conspicuous geoarchaeological tsunamite up to 1 5 m thick was found at pogonia cliff consisting of mixed marine sand pebbles bio erosively altered stones shell debris foraminifers and terrigenous material abundant ceramic fragments bones building material it is directly associated with the submerged remains of an ancient mole which was destroyed and its building material partly dislocated by the same event dating of tsunamites was accomplished by archaeological age determination of diagnostic sherds and by radiocarbon and luminescence dating techniques strong tsunami events were dated to the beginning of the 6th the mid 5th the 4th 3rd and the late 2nd millennia bc as well as to the 4th 3rd century bc on a regional scale the recurrence interval for large events is ca 500 1000 years at least twice during the late holocene the palairos coastal plain was flooded quasi contemporaneously from both the northern and southern side

paleoenvironmental evolution and prehistoric human environment in the embayment of palamari skyros island greece during middle late holocene abstract palamari bay is located on the northeastern coast of skyros island sporades islands aegean sea at the northern edge of the bay a fortified prehistoric settlement is found dated between 2800 and 1700 bc early bronze age ii middle bronze age i detailed geomorphological mapping of the coastal alluvial plain and paleontological micropaleontological palynological sedimentological and micromorphological studies of the holocene coastal deposits have been conducted in order to reconstruct the palaeoenvironment and the landscape evolution of the broader area of palamari bay three main sedimentary units were recognized a b and c from oldest to youngest the lowermost sedimentary unit a deposited between before 7500 and 3500 cal bp consists of sediment deposited from high to moderate energy fresh water flows with some suspended load fallout in established water bodies the microfauna indicates a shallow fresh water environment however a tendency to oligohaline conditions was established gradually during the same period the palamari area was characterized by open mixed deciduous forests that gradually retreated as a possible consequence of the intensification of anthropic activity associated with the settlement of palamari indications of cultivating and grazing activities in the vicinity of the lagoon were identified pointing to a strong human presence since the neolithic between about 6000 and 3500 cal bp the embayment was a lagoon southeasterly connected to the sea therefore sheltered and protected from northeastern winds the overlying unit b ca 3500 800 cal bp is characterized by the dominance of brackish water microfauna indicating a brackish stagnant shallow water depositional environment which was periodically supplied with fresh water from the surrounding springs as the result of the continuous sea level rise during the late holocene part of the northern headland was submerged the decline of the palamari settlement at the time of the establishment of unit b might be related to the observed changes that rendered the embayment a restricted body of water the uppermost sedimentary unit c corresponds to a backshore environment dominated by aeolian activity modified by fluvial processes

chemical weathering since the little ice age recorded in lake sediments a high resolution proxy of past climate because of the different geochemical behaviour of rubidium and strontium in earth surface processes variations of the rb sr ratios in lake sediments were used as a geochemical proxy of chemical weathering and past climate in a single watershed low magnetic susceptibility low caco3 low sr concentration and hence high rb sr ratio in the lake sediments indicate weak chemical weathering under a cold but wet climate during the little ice age lia in the closed daihai lake watershed the concordant change in both sr and caco3 concentrations with 18o values in the dunde ice core suggests that weak chemical weathering during the wet lia was controlled by air temperature after the lia however precipitation played a dominant role in chemical weathering copyright 2001 john wiley sons ltd

geochemical discrimination of clastic sedimentary rock sources abstract factors controlling the geochemistry of a clastic sedimentary rock can include 1 composition of source terrain 2 chemical weathering 3 hydraulic sorting 4 diagenesis 5 metamorphism and 6 hydrothermal alteration a linear solution inferring source terrain composition from geochemistry of the sediment is impossible in this multivariate system as several unknowns will commonly be present the use of graphical analysis of element pairs circumvents the problem chemically immobile elements will maintain invariant ratios during rock mass change caused by either addition or depletion of mobile elements this results in chemically immobile element scattergrams exhibiting linear trends along radians extending from the origin if the major mineral phases of the immobile elements have behaved in a hydrodynamically similar manner as chemically mobile element plots will produce a scatter of points this relationship can be used to test chemical immobility and similarity in hydrodynamic sorting history the constraint on analysis is that the source area must be compositionally uniform or the sediment well mixed prior to delivery to the basin a second technique using sio2 plots has also been developed to investigate element mobility and hydrodynamic behaviour of the mineral phases containing the elements sio2 immobile element plots result in a linear arrangement of points extending towards either 0 or 100 sio2 the 0 intercept position occurs for elements with major mineral phases concentrated in sand the 100 intercept for those concentrated in clays plotting chemically mobile elements produces different patterns and this can be used to gain information on alteration and sorting history elemental ratios for chemically immobile elements with similar hydrodynamic behaviour will be the same as those for the weighted average composition of the source material this provides a powerful tool for deducing source terrain from sediment geochemistry techniques outlined above were tested on archaean metasandstones from superior province canada immobile element ratio diagrams for nb al ti and zr al ti indicate that a calc alkaline extrusive intrusive suite lying to the north of the study area was the source and not five other volcanic suites in the region this conclusion agrees with previous clast lithology studies and accentuates the applicability of the geochemical techniques

trace element behavior and redox facies in core shales of upper pennsylvanian kansas type cyclothems the black shale submember of core shales of pennsylvanian kansas type cyclothems is highly enriched in redox sensitive trace elements tes relative to the overlying gray shale submember as well as to many other modern and ancient organic rich deposits controls on trace element behavior in the black shale can be inferred from trace element enrichment factors efs relative to gray shale and the relationship of tes to total organic carbon toc most tes conformed to one of two patterns 1 mo u v zn and pb exhibited moderate efs and strong covariation with toc in samples having 10 wt toc and 2 cu ni cr and co exhibited low efs and moderate to strong covariation with toc in all samples these patterns are inferred to represent different responses to benthic redox conditions the first pattern is characteristic of tes of strong euxinic affinity i e those taken up in solid solution by fe sulfide or involved in other reactions catalyzed by free h2s and resident mainly in authigenic phases whereas the second pattern is characteristic of tes of weak euxinic affinity i e those not strongly influenced by the presence of free h2s and resident mainly in the organic carbon or detrital fractions of the sediment these inferences allowed development of a multiproxy technique for assessing redox facies in black shale samples euxinic conditions were considered to have existed if at least two of four redox indicator trace elements mo u v zn showed euxinic levels of enrichment and nonsulfidic anoxic conditions were inferred otherwise the validity of the procedure is indicated by 1 agreement among all four redox indicators for a large majority of samples 69 of 185 2 among samples yielding a mixed redox signal a systematic sequence of te enrichment v zn mo u and 3 for tes of weak euxinic affinity reduced variance among samples representing each redox facies sequential enrichment may be a response to differential redox thresholds for accumulation e g v or postdepositional remobilization of trace elements e g u and may provide a basis for finer assessment of redox conditions in low oxygen paleoenvironments than permitted by simple classification schemes the multiproxy procedure for redox facies analysis developed in this study is likely to be more reliable than widely used single proxy indicators based on trace elements e g mo authigenic u or v v ni or c s fe systematics e g s toc or dop d 2004 elsevier b v all rights reserved

the geochemistry of redox sensitive trace metals in sediments abstract we analyzed the redox sensitive elements v mo u re and cd in surface sediments from the northwest african margin the u s northwest margin and the arabian sea to determine their response under a range of redox conditions where oxygen penetrates 1 cm or less into the sediments mo and v diffuse to the overlying water as mn is reduced and remobilized authigenic enrichments of u re and cd are evident under these redox conditions with the onset of sulfate reduction all of the metals accumulate authigenically with re being by far the most enriched general trends in authigenic metal accumulation are described by calculating authigenic fluxes for the 3 main redox regimes oxic reducing where oxygen penetrates 1 cm and anoxic conditions using a simple diagenesis model and global estimates of organic carbon rain rate and bottom water oxygen concentrations we calculate the area of sediments below 1000 m water depth in which oxygen penetration is 1 cm to be 4 of the ocean floor we conclude that sediments where oxygen penetrates 1 cm release mn v and mo to seawater at rates of 140 260 60 150 and 5 10 of their respective riverine fluxes using the authigenic metal concentrations and accumulation rates from this work and other literature these sediments are sinks for re cd and u with burial fluxes of 70 140 30 80 and 20 40 respectively of their dissolved riverine inputs we modeled the sensitivity of the response of seawater re cd and v concentrations to changes in the area of reducing sediments where oxygen penetrates 1 cm our analysis suggests a negligible change in seawater re concentration whereas seawater concentrations of cd and v could have decreased and increased respectively by 5 10 over 20 kyr if the area of reducing sediments increased by a factor of 2 and by 10 20 if the area increased by a factor of 3 the concentration variations for a factor of 2 increase in the area of reducing sediments are at about the level of uncertainty of cd ca and v ca ratios observed in foraminifera shells over the last 40 kyr this implies that the area of reducing sediments in the ocean deeper than 1000 m 4 has not been greater than twice the present value in the recent past

enhanced trapping of molybdenum by sulfurized marine organic matter of marine origin in mesozoic limestones and shales there have been many studies devoted to trace metals and their value in assessing the paleoredox conditions of ancient marine deposition among them molybdenum mo is frequently cited as an effective proxy for sediments and sedimentary rocks recently helz et al helz g r miller c v charnock j m mosselmans j l w pattrick r a d garner c d vaughan d j 1996 mechanisms of molybdenum removal from the sea and its concentration in black shales exafs evidences geochim cosmochim acta 60 3631 3642 and adelson et al adelson j m helz g r miller c v 2001 reconstructing the rise of recent coastal anoxia molybdenum in chesapeake bay sediments geochim cosmochim acta 65 237 252 suggested that mo does not behave conservatively in the water column when h2s reaches a threshold concentration above this concentration a switch operates and mo is scavenged by forming bonds with metal rich notably iron particles sulfur rich organic molecules and pyrite in this paper mo trapping by sulfur rich organic matter om in ancient marine deposits is emphasized the following mesozoic geological formations were selected for study because of their relatively high concentration of sulfurized om the akkuyu formation turkey the calcaires d orbagnoux france and kimmeridge clay uk and its timeequivalent in boulonnais france the kashpir oil shales russia and the la luna formation venezuela the sulfur rich om is identified by either measured organic s abundance or kerogen microscope observation our results show that mo is systematically more enriched relative to the other redox sensitive sulfide forming elements studied u v ni cu zn cr and mo enrichment is positively correlated with the amount of sulfurized om but not with pyrite abundance these results illuminate the role played by sulfurized om in geologic scale mo capture and retention but they also underline the role played by reactive iron significant om sulfurization is only possible when reactive iron is limited nevertheless pyrite formation though limited could act as an initial mo trap prior to mo uptake by om that is sulfurized after the pyritization step in future paleoenvironmental reconstructions attention must be paid to this enhanced mo enrichment in the presence of sulfurized organic matter in such cases the use of mo could lead to overestimation of the reducing conditions of the depositional environment

reappraisal of the ages of neoproterozoic strata in south china no connection with the grenvillian orogeny the jiangnan fold belt separates the yangtze and cathaysia blocks in south china and has long been considered grenvillian in age in order to place south china in central rodinia it consists of deformed early neoproterozoic strata that are unconformably overlain by undeformed late neoproterozoic strata and intruded by undeformed and unmetamorphosed granitic plutons zircons from the early neoproterozoic strata yield u pb ages as young as 830 ma and one granitic pluton has a zircon u pb age of ca 827 ma the 830 ma mafic rocks along the southeastern margin of the yangtze block have arc affinity geochemical characters whereas mafic rocks younger than 830 ma have typical ocean island basalt oib like compositions thus we suggest that the early neoproterozoic strata were deposited on an active continental margin prior to amalgamation of the yangtze and cathaysia blocks at ca 830 ma the overlying late neoproterozoic strata were deposited in the intracontinental rifted nanhua basin at 820 730 ma and probably reflect backarc spreading above the long lived 950 735 ma oceanic subduction zone along the northern and western margin of the yangtze block this model is consistent with the secular tectonic evolution of south china during the neoproterozoic the jiangnan fold belt is therefore not a grenvillian feature as previously suggested and there is no evidence to place south china in central rodinia instead we believe that south china was located in a marginal position relative to this supercontinent

climate variability over the last two millennia in the north american monsoon region recorded in laminated lake sediments from laguna de juanacatlan mexico high resolution titanium ti data obtained using an itrax xrf core scanner from a laminated sediment core from the laguna de juanacatlan western central mexico yield a unique high resolution record of runoff precipitation change for the last 2000 years in the absence of reliable long term meteorological records comparison of the ti data with information from the rich spanish colonial period archives and the post independence period confirms that ti is a proxy for runoff this interpretation is supported by comparison with other high resolution archives from the surrounding region primarily tree rings and other lake sediment sequences the juanacatlan ti record is therefore a proxy for summer monsoonal rainfall the record provides new evidence from the pacific margin of tropical north america of the occurrence of dry conditions through much of the classic period c ad 300 900 and wetter conditions during the later medieval period c ad 1200 1350 the period commonly known as the little ice

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