magnetite authigenesis and diagenetic paleotemperatures across the northern appalachian basin the concentration of magnetite in the lower and middle devonian helderberg and onondaga carbonate formations varies in a distinct pattern along an east west profile across new york state magnetite concentrations are uniformly low in the western half of the profile increase sharply eastward to a peak value near syracuse and decrease farther east the pattern strongly resembles previously reported variations in the extent of clay mineral diagenesis that reflect differences in paleotemperatures along the profile previous paleomagnetic studies have documented that the magnetite carries a well defined magnetization of pennsylvanian permian age and magnetite authigenesis is therefore no younger than late paleozoic we attribute the correlation between high magnetite concentration and high illite content to temperature dependent diagenesis triggered by orogenic fluids the large proportion of secondary magnetite indicates that over most of the area the mechanism of late paleozoic remagnetization was principally chemical thermal effects played a less direct role in the remagnetization of the strata by controlling the extent of the chemical processes that resulted in overprinting of the original remanence

zur systematik der kohlenstoff schwefel eisen verhaltnisse in auftriebssedimenten abundances of organic carbon sulfur and reactive iron in sediments of three upwelling environments peru oman and benguela suggest that organic carbon reduced sulfur ratios c s ratios in this category of marine sediments deviate considerably from previously established empirical ratios in normal marine sediments to clarify the discrepancies we investigated those components of the diagenetic system that limit the formation of pyrite sulfate concentrations and reduction rates in pore waters availability of reactive iron and the quantity and quality of organic matter all three limitations are evident in our sample pools the results suggest that c s ratios in recent and fossil marine sediments rich in organic matter may be unsuitable as paleoenvironmental indicators

tectonic implications of finite strain variations in baraboo interval quartzites ca 1700 ma mazatzal orogen wisconsin and minnesota usa abstract variably deformed baraboo interval quartzites 1750 1630 ma are now correlated by detrital zircon ages holm d schneider d coath c d 1998 age and deformation of early proterozoic quartzites in the southern lake superior region implications for extent of foreland deformation during final assembly of laurentia geology 26 907 910 and were analyzed using finite strain techniques which document a se nw tectonic shortening orientation from the baraboo syncline south to the flambeau syncline north fabric interpretations using bedding and the principal strain axis orientations indicate there was a mix of layer parallel and layer normal synfolding shortening in the plane of tectonic transport se nw in the thrust belt finite strain magnitudes increase from the foreland barron sioux quartzites south toward the baraboo syncline electron backscatter device ebsd fabric diagrams pole figures of quartz optic axes also demonstrate an increasingly penetrative strain to the south anisotropy of low field ac magnetic susceptibility ams as a strain proxy preserve kmin measurements in the baraboo syncline quartzites that are sub horizontal e w and intersect bedding ams measurements in underlying rhyolite on opposite limbs of the baraboo syncline are clean appear to be primary magmatic as kmax intersects bedding but require a complex folding interpretation that is inconsistent with field kinematic indicators the flat lying foreland barron and sioux quartzites preserve a mix of results quartzites with no strain finite strain and ebsd measurements or small strains that preserve vertical shortening ams measurements in the foreland preserve kmin axes that are sub horizontal and parallel to the regional shortening orientation in the adjacent thrust belt the mazatzal orogen produced a thrust belt that is orders of magnitude wider 500 km and of higher metamorphic grade than most thrust belts where both the thrust belt and foreland are quartzites

3d model of the can sadurni cave abstract graphic and metric information about the site and its environment and about the different structures and artefacts located are indispensable for the optimal management of an archaeological excavation a geographic information system gis proves useful in managing and analysing information and data obtained from different sources two techniques of data capture terrestrial laser scanning tls and close range photogrammetry are used to generate accurate and high resolution 3d models of a cave the silos and a combustion structure at the can sadurni site begues ne spain this site is especially noteworthy on account of its complete stratigraphy of the catalonian holocene the capture and processing of the photogrammetric and tls data used to generate 3d models are discussed in detail these models cannot be obtained by classic archaeological techniques since the record is made layer by layer approximately one decimetre apart with the result that the information between the layers is lost our findings highlight the potential of these techniques for obtaining accurate and photorealistic models that facilitate a complete analysis of the available information at an archaeological site

sedimentary geochemical record of human induced environmental changes in the lake brunnsviken watershed sweden environmental changes in lake brunnsviken its watershed and the greater stockholm region since the middle of the nineteenth century have left interpretable geochemical imprints in the bottom sediments these humaninduced perturbations within the lake s watershed included agriculture urbanization sewage and industrial disposal and water column aeration smaller d 15 ntotal values high organic carbon mass accumulation rates low c n ratios and larger d 13 corg values identify periods of increased nutrient delivery and elevated primary productivity in the lake c s ratios that change from high to low trace the transition from an oxic hypolimnion to an anoxic one during the periods of high productivity accumulations of redox sensitive trace elements increase during the anoxic period and are further magnified during a time of industrial waste discharge into the lake a recent decrease in black carbon concentrations in sediments reflects the conversion from wood and coal to cleaner forms of energy

early diagenetic processes in deep labrador sea sediments reactive and nonreactive iron and phosphorus a sequential extraction procedure was applied to separate the oxides and lithogenous phases of iron and manganese and the organic and inorganic phosphorus phases in four box cores and one piston core from the slopes and rises of the labrador sea sedimentation rate rather than the location in the basin appears as a master variable of the diagenetic transformations of fe mn and p high sedimentation rate characteristic of two of the box cores led to the creation of zones near the redox boundary of partial reprecipitation of dissolved fe mn and p released in the deeper reducing portions of the sediments in contrast surficial sediments from box cores with 10 times lower sedimentation rate only have sufficient reductive capacity to remobilize mn hydroxides while leaving the fe oxyhydroxides intact under these conditions there is evidence for a redistribution of reactive inorganic p leading to the crystallization of carbonate fluorapatite in the top 30 cm of the cores gradual transformation of bur

magnetic fabric determined from arm and irm anisotropies in paleozoic carbonates southern appalachian basin we have undertaken a comparative study of arm and irm anisotropies in paleozoic carbonate rocks from the nashville and jessamine domes in the southern appalachian basin the arma ellipsoids differ markedly from the irma ellipsoids arma appears to reflect a pre deformation magnetic fabric due to deposition and or compaction with minimum axes near vertical and a weak lineation conversely irma has minimum axes near horizontal and oriented ne sw which is compatible with a tectonic fabric due to alleghanian deformation percent arma is consistently greater than irma arm was imparted at low alternating fields 30 mt and thus arma may reflect the fabric residing in low and intermediate coercivity coarse grained magnetite however the irm was imparted in saturating fields 300 mt and appears to be dominated by the single domain fraction which is believed to carry the observed kiaman superchron remagnetization

sedimentological characteristics heavy metal distribution and magnetic properties in subtidal sediments ria de pontevedra nw spain the rias of nw spain are coastal ecosystems of high biological productivity and great economic importance they are intensively exploited by man for fish and shellfish there are a number of important centres of population and industrial activity along their margins which serve as sources of contamination in this context it is desirable to achieve the best possible understanding of the physico chemical processes that control spatial and temporal variations in the geochemical mineralogical and sedimentological characteristics of near surface sediments in the ria de pontevedra and in particular the distribution and mobility of heavy metal contaminants thus adequate environmental planning can be achieved for this site and understanding gained for comparable contexts core samples were examined from the inner middle and outer parts of the ria grain size distributions reflect the presence of two main populations one dominated by silt and clay derived mainly from terrestrial sources and the other by fine sand to coarse silt which is derived mainly from continental shelf and ria mouth sources mineralogical analysis shows an abundance of terrestrial intensive weathering products near the ria head a dominance of shelf derived sediment towards the mouth and the presence of several diagenetic minerals whose nature varies with location within the ria in the inner ria the near surface sediments are slightly enriched in pb cu and zn from anthropogenic sources these sediments are fine grained and have a high organic content hence they have a higher potential to sorb contaminants than the coarser grained less organic rich sediments of the mid and outer ria the estimated sedimentation rates for the fine grained organic rich sediments from the inner part of the ria are about 1 mm year 1 the dominant authigenic minerals in the inner ria are iron sulphides whereas in the mid and outer ria iron silicates and oxyhydroxides are more important these differences in authigenic iron mineralogy are clearly reflected by the magnetic properties of the sediments

geochemical evidence for widespread euxinia in the later cambrian ocean it has been suggested that the cambrian ocean was oxygen deficient but physical evidence for widespread anoxia has been lacking gill et al present sulphur isotope data from cambrian rocks at six different locations around the world and find a positive sulphur isotope excursion in phase with a large excursion in the marine carbon isotope record which is thought to be indicative of a global carbon cycle perturbation at the time a prolonged period of anoxia during the cambrian may explain the previously enigmatic peculiarities seen in the fossil record it has been suggested that the cambrian ocean was oxygen deficient but physical evidence for widespread anoxia has been lacking now sulphur isotope data from cambrian rocks at six different locations around the world is presented with the finding of a positive sulphur isotope excursion in phase with a large excursion in the marine carbon isotope record which is thought to be indicative of a global carbon cycle perturbation at the time with the help of a box model these isotope shifts support the idea of large scale anoxic and sulphidic conditions in the later cambrian ocean widespread anoxia in the ocean is frequently invoked as a primary driver of mass extinction as well as a long term inhibitor of evolutionary radiation on early earth in recent biogeochemical studies it has been hypothesized that oxygen deficiency was widespread in subsurface water masses of later cambrian oceans1 2 possibly influencing evolutionary events during this time1 2 3 physical evidence of widespread anoxia in cambrian oceans has remained elusive and thus its potential relationship to the palaeontological record remains largely unexplored here we present sulphur isotope records from six globally distributed stratigraphic sections of later cambrian marine rocks about 499 million years old we find a positive sulphur isotope excursion in phase with the steptoean positive carbon isotope excursion spice a large and rapid excursion in the marine carbon isotope record which is thought to be indicative of a global carbon cycle perturbation4 5 numerical box modelling of the paired carbon sulphur isotope data indicates that these isotope shifts reflect transient increases in the burial of organic carbon and pyrite sulphur in sediments deposited under large scale anoxic and sulphidic euxinic conditions independently molybdenum abundances in a coeval black shale point convincingly to the transient spread of anoxia these results identify the spice interval as the best characterized ocean anoxic event in the pre mesozoic ocean and an extreme example of oxygen deficiency in the later cambrian ocean thus a redox structure similar to those in proterozoic oceans6 7 8 may have persisted or returned in the oceans of the early phanerozoic eon indeed the environmental challenges presented by widespread anoxia may have been a prevalent if not dominant influence on animal evolution in cambrian oceans

regional patterns of magnetite authigenesis in the appalachian basin implications for the mechanism of late paleozoic remagnetization we report paleomagnetic and rock magnetic data from sedimentary carbonates of the appalachian basin that have implications for the mechanism of widespread late paleozoic remagnetization in this rock type sampling was accomplished mostly along two across basin transects one in devonian carbonates of new york state and the other in ordovician and mississippian carbonates of tennessee and alabama paleomagnetic investigations of the new york devonian carbonates along a transect from albany to buffalo indicate that these rocks were completely remagnetized in alleghenian time rock magnetic studies show that magnetite concentration varies in a regular fashion along the transect with a local maximum near syracuse and decreasing gradually to the east and west this pattern shows a striking correlation with the degree of diagenetic alteration of clay minerals in a devonian bentonite horizon which took place during alleghenian time we conclude that most of the magnetite present in these carbonates is of authigenic origin and that clay mineral alteration and magnetite authigenesis were coeval late paleozoic events that were controlled by the same diagenetic factors thermoviscous remagnetization processes cannot be ruled out in this setting in light of the observed degree of thermal maturity however our results suggest that chemical factors played a critical role in remagnetization since they allow us to infer that magnetite authigenesis and remagnetization are about the same age we propose a geochemical model for magnetite authigenesis wherein the iron is derived from detrital smectites during diagenetic illitization which is triggered by the introduction of potassium rich brines results from the tennessee transect from nashville to chattanooga show a very different pattern paleomagnetic studies indicate that late paleozoic remagnetization has affected ordovician carbonates of the nashville dome paleozoic carbonates in the overthrust belt near chattanooga also carry the late paleozoic remagnetization however mississippian carbonates between the dome and the overthrust belt are very weakly magnetized and show no evidence for late paleozoic remagnetization samples show only a present field magnetization or at one locality in northwestern alabama a dual polarity magnetization of probable mississippian age rock magnetic studies indicate that higher concentrations of magnetite are present in the remagnetized rocks of the nashville dome and the overthrust belt than in the nonremagnetized mississippian carbonates we therefore conclude that magnetite authigenesis and remagnetization are related events in this setting and that the remagnetization must be due to chemical processes the presence of a remagnetization shadow in the younger rocks now exposed between the fold thrust belt and the flexural arch is attributed to westward flow of magnetite forming aqueous fluids through deep sub carboniferous aquifers during alleghenian time upward migration of the fluids through the mississippian carbonates may have been prevented by the devono mississippian chattanooga shale an impermeable stratum that is present throughout the region

palaeoenvironmental controls on the uranium distribution in an upper carboniferous black shale gastrioceras listeri marine band and associated strata england the mudrocks associated with the gastrioceras listeri g listeri marine band contain 0 to 200 ppm authigenic uranium several geochemical degree of pyritisation dop c s ratios and framboidal pyrite size distribution and palaeontological indicators oxygen restricted biofacies orb analysis suggest that the highest authigenic uranium concentrations are within marine sediments associated with the most oxygen restricted biofacies orbs 2 and 3 the uranium peaks tend to occur at the transition between biofacies rather than within the middle of more persistently anoxic intervals these horizons may have been deposited when the oxygen minimum zone impinged on the seafloor brief oxygenation of an otherwise anoxic environment was conducive to francolite precipitation which then scavenged dissolved uranium slow sedimentation rates are also important in concentrating uranium and francolite thus enriched u values are only encountered under specific conditions of low but fluctuating oxygen regime and extremely slow sedimentation rates truly euxinic facies lacking any fossils and a uniformly small framboid population do not contain high concentrations of francolite and are not u rich

coal weathering and the geochemical carbon cycle abstract the weathering rate of sedimentary organic matter in the continental surficial environment is poorly constrained despite its importance to the geochemical carbon cycle during this weathering complete oxidation to carbon dioxide is normally assumed but there is little proof that this actually occurs knowledge of the rate and mechanisms of sedimentary organic matter weathering is important because it is one of the major controls on atmospheric oxygen level through geologic time we have determined the aqueous oxidation rates of pyrite free bituminous coal at 24 and 50 c by using a dual cell flow through method coal was used as an example of sedimentary organic matter because of the difficulty in obtaining pyrite free kerogen for laboratory study the aqueous oxidation rate obtained in the present study for air saturated water 270 m o2 was found to be on the order of 2 10 12 mol o2 m2 s at 25 c which is fast compared to other geologic processes such as tectonic uplift and exposure through erosion the reaction order with respect to oxygen level is 0 5 on a several thousand hour time scale for both 24 and 50 c experiments activation energies determined under 24 and 50 c conditions were 40 kj mol o2 indicating that the oxidation reaction is surface reaction controlled the oxygen consumption rate obtained in this study is two to three orders of magnitude smaller than that for pyrite oxidation in water but still rapid on a geologic time scale aqueous coal oxidation results in the formation of dissolved co2 dissolved organic carbon doc and solid oxidation products which are all quantitatively significant reaction products

organic matter apatite pyrite relationships in the botneheia formation middle triassic of eastern svalbard relevance to the formation of petroleum source rocks in the nw barents sea shelf abstract the middle triassic botneheia formation of eastern svalbard edgeoya and barentsoya comprises an organic carbon rich fine grained clastic succession 100 m thick that makes the best petroleum source rock horizon in the nw barents sea shelf the succession records a transgressive regressive interplay between the prodelta depositional system sourced in the southern barents sea shelf black shale facies of the lower and middle parts of the muen member and the open shelf phosphogenic system related to upwelling and nutrient supply from the panthalassic ocean phosphogenic black shale facies of the upper part of the muen member and the blanknuten member the relationships between organic matter authigenic apatite and pyrite in these facies allow to characterize the relative roles of redox conditions and oceanic productivity in the organic carbon preservation the accumulation of terrestrial and autochthonous marine organic matter in the black shale facies occurred under dominating oxic conditions and increasing upward productivity related to early transgressive phase and retrogradation of the prodelta system the phosphogenic black shale facies deposited in an oxygen minimum zone omz of the open shelf environment during the late transgressive to regressive phases under conditions of high biological productivity suppressed sedimentation rates and changing bottom redox the phosphatic black shales occurring in the lower and upper parts of the phosphogenic succession reveal depositional conditions indicative of the shallower part of omz including high input of autochthonous organic matter into sediment oxic to dysoxic episodically suboxic and or anoxic conditions intense phosphogenesis and recurrent reworking of the seabed the massive phosphatic mudstone occurring in the middle of the phosphogenic succession reflects the development of euxinia in the deeper part of omz during high stand of the sea high input of autochthonous organic matter in this environment was coupled with mineral starvation and intermittent phosphogenesis in mature sections in eastern svalbard the petroleum potential of the botneheia formation rises from moderate to good in the black shale facies and from good to very good in the phosphogenic black shale facies attaining maximum in the massive phosphatic mudstone

time dependent changes for midcontinent pennsylvania black shales u s a abstract three types of midcontinent north american black shale types have been recognized based on metal content organic carbon contents sulfur isotopes and various other sedimentological and paleontological characteristics that may reflect fluctuations in bottom water oxygenation during deposition near shore middle pennsylvanian black shales exemplified by the mecca quarry shale member of indiana typically yield degree of pyritization dop values near 0 65 the highest measured in the study consistent with relatively but not fully anoxic conditions of sedimentation dop values for heebner type shales most prevalent in the upper pennsylvanian average 0 27 0 35 barely in the dysaerobic range which is difficult to reconcile with an origin for black shale dependent upon upwelling bottom water positive correlations exist between dop metal values and total organic carbon toc in black shale units through the pennsylvania these changes can be related to organic carbon production and published sea level fluctuations suggesting a change in black shale character in the midcontinent from the middle to late pennsylvanian consistently decreasing values for dop and toc through time suggest the likelihood of a progressive ventilation or improved bottom water oxygenation accompanied by a reduced rate of input from terrestrial organic matter during this time interval

regional trends in the timing of alleghanian remagnetization in the appalachians pole positions related to remagnetized components isolated in appalachian limestone and redbed rock units range over about 60 m y of the permian carboniferous apparent polar wander path for north america apparent ages of remagnetization are older in the southern appalachians and younger to the north if the remagnetizations are associated with fluids expelled during the alleghany orogeny then the apparent remagnetization age trend could describe the timing of thrust sheet emplacement

a genetic link between remagnetization and potassic metasomatism in the devonian onondaga formation northern appalachian basin whole rock chemical analyses indicate that the onondaga formation along a rochester syracuse new york transect has a marked eastward increasing trend in k al ratio which correlates with an increase in authigenic magnetite content and degree of diagenetic illitization an eastward increase in the content of some authigenic minerals including k feldspar quartz and fe rich chlorite in the rocks is indicated by petrographic and x ray diffraction studies these observations suggest a link between remagnetization and potassic alteration of fe bearing silicates in the onondaga two hypothetical reactions are proposed in which magnetite authigenesis is related to the breakdown of fe bearing smectite in the presence of potassium products of these reactions include authigenic k feldspar illite quartz and chlorite as well as magnetite our results suggest that remagnetization was triggered by a basin wide migration of k rich fluids during the alleghenian orogeny

paleosalinity determination in ancient epicontinental seas a case study of the t oae in the cleveland basin uk abstract the early jurassic toarcian oceanic anoxic event t oae was marked by deposition of organic rich sediments and a pronounced negative carbon isotope excursion across the northwest european sea nwes representing a signal that was stronger regionally than globally various models for the t oae have been proposed some focusing on general atmospheric oceanic controls to reflect its global character and others emphasizing local or regional factors to account for its strong expression in the nwes in this study we evaluate watermass dynamics of the early jurassic cleveland basin uk during the t oae using a combination of paleosalinity proxies b ga sr ba and s toc these proxies suggest that brackish conditions existed prior to onset of the t oae with a shift to nearly freshwater conditions during the t oae reflecting a large increase in terrestrial runoff due to a stronger hydrological cycle possibly combined with shallowing of the marginal sill of the cleveland basin through sea level fall following the t oae basinal salinity conditions first returned to brackish and then gradually shifted to fully marine this hydrographic history accounts for low mo concentrations in t oae sediments of the cleveland basin demonstrating control by watermass restriction and local rather than global aqueous mo drawdown these findings demonstrate the importance of local hydrographic controls on the sedimentary expression of the t oae the more general significance of this study is that it highlights the need for application of paired salinity and redox proxies in order to correctly interpret paleoenvironmental variations in marginal marine basins

migration of orogenic fluids through the siluro devonian helderberg group during late paleozoic deformation constraints on fluid sources and implications for thermal histories of sedimentary basins abstract fluid inclusion data and fracture filling cement fabrics in deformed but non overthrusted carbonate and siliciclastic rocks of the siluro devonian helderberg group central appalachians indicate post cementation late paleozoic migration of high pressure high temperature fluids void filling quartz and calcite cements contain secondary two phase fluid inclusions liquid vapor which occur in annealed microfractures most melting temperatures last occurrence of ice are 20 to 25 c which correspond to salinities of greater than 22 equivalent wt nacl pressure corrected liquid vapor homogenization temperatures are 200 to 300 c and greatly exceed maximum paleotemperatures 150 c given by conodont cai values vitrinite reflectance illite crystallinity or temperatures calculated from known sedimentary overburden completely cemented sandstone and limestone also have multiple crosscutting trains of secondary hydrocarbon inclusions hydrocarbon inclusions occur along deformation microstructures in cements some hydrocarbon inclusion trains crosscut cement filled fractures the nature of occurrence of the secondary inclusions suggests that fluids moved along intracrystalline deformation microstructures either during or after late paleozoic deformation rare fractures contain transported skeletal grains exotic clasts lithologies different from wall rock recemented clasts of fracture filling cement and mud cement clasts contain solid inclusions of mud and skeletal fragments and indicate several episodes of particle transport cementation and refracturing prior to final fracture filling and cementation these fracture fills locally crosscut stylolites coarse grained poorly sorted clastic fracture fills suggest migration of rapidly moving fluids which were capable of transporting clasts through fracture conduits under deep burial conditions conduction calculations place upper limits on size and duration of thermal anomalies which were caused by extrabasinal fluids these calculations indicate that hot fluid migration events most likely were short lived heat transfer by extraformational fluids moving along faults and fractures may have been the mechanism by which thermal anomalies developed in the helderberg group stratigraphic constraints suggest that likely sources for the hot brines are overthrusted terranes to the east of the study area possible stratigraphic horizons which were sources for the overpressured hot fluids may have been thick cambrian shales which are important detachment horizons for major late paleozoic thrust sheets in the eastern valley and ridge province east of the study area fluids may have migrated during thrusting along thrust faults which ramp upwards from east to west into stratigraphically higher units thrust faults ultimately die out in devonian units some of the dissolved ions in the secondary two phase inclusions may have been incorporated when shale derived fluids moved through silurian evaporites or cambro ordovician carbonates which contain evidence of cryptic evaporites potential source rocks for secondary hydrocarbon inclusions may have been lower silurian through lower devonian strata based on lopatin modeling and assuming that migration occurred during late paleozoic deformation this study may help to explain many apparently anomalous geologic phenomena in deformed foreland basin sediments it also has implications for tracking migration pathways for fluids which facilitate regional scale deformation in fold and thrust belts and how tectonic fluids may affect the rocks through which they move

diagenetic sources of stable remanence in remagnetized paleozoic cratonic carbonates a rock magnetic study hysteresis measurements lowrie fuller tests cisowski tests and low temperature demagnetization experiments on samples of the knox dolomite trenton limestone and onondaga limestone indicate that the remanence in these remagnetized carbonate units resides principally in single domain magnetite in contrast to previous interpretations volumetrically however a significant fraction of the magnetite is coarser grained as previous scanning electron microscopic work on magnetic extracts has shown these conclusions are based mainly on the characteristic wasp waisted shape of the hysteresis loops and on the anomalously high ratios of remanent coercivity to bulk coercivity both of which clearly indicate a bimodal distribution of coercivities grain sizes the magnetization is controlled mainly by cubic magnetocrystalline anisotropy consistent with the spheroidal particles commonly observed in extracts hysteresis trends show that especially the finest particles lack shape anisotropy in view of these conclusions the two components of natural remanence in these rocks are interpreted as 1 a late paleozoic kiaman chemical remanence carried by single domain diagenetic magnetite and 2 a cenozoic thermoviscous overprint residing principally in coarser pseudosingle domain and multidomain magnetite also of late paleozoic diagenetic origin

marine biodiversity through the late cenomanian early turonian palaeoceanographic controls and sequence stratigraphic biases changes in the marine macro and microfauna sedimentary geochemistry and surface water palaeoproductivity through the last 500 000 years of the cenomanian and first 300 000 years of the turonian are documented these are based on the succession at eastbourne the thickest and most complete section through the late cenomanian and early turonian in the anglo paris basin two levels of rapid faunal and geochemical change are identified one coincident with a significant increase in siliciclastic input at the base of the plenus marls member and the other with a marked drop in surface water productivity near the top of the same unit faunal change is demonstrated to be largely a pattern of immigration emigration rather than true extinction and our sequence stratigraphical analysis shows that it was coincident with major sea level changes no evidence is found to support the hypothesis that reduced bottom water oxygenation developed and was responsible for extinctions amongst the benthos in mid shelf environments the onset of pure chalk facies is interpreted to mark the breakdown of shelf break fronts and the spread of oligotrophic oceanic waters over much of the continental shelf initiated by rising sea level the cenomanian turonian event far from recording a mass extinction of shelf fauna is most probably an artifact caused by a significant switch in the nature of the surviving sedimentary record as a result of a major but perfectly ordinary oceanographic change

comprehensive evolution of a petroleum system in absolute time the example of brynhild norwegian north sea abstract petroleum systems are inherently complex comprising multiple components and processes which variably interact in space and time to form petroleum accumulations improved understanding of these complex systems requires a holistic approach of integrating diverse geological geophysical and organic and inorganic geochemical data here we present an applied and comprehensive re os geochronological and geochemical study on the brynhild petroleum system from the norwegian north sea essential components of this system include shale source rocks of the mandal and farsund formations reservoir sandstones of the ula formation and their bitumen extracts and produced brynhild crude oil rock eval trace metal and re os data reveal the excellent oil generation potential of the shaley source rocks high contents of organic matter containing large amounts of type i kerogens and constrain their depositional conditions anoxic bottom waters in a high productivity regime driven by enhanced supply of land derived nutrients seven re os shale ages between 146 and 134 ma are consistent with existing volgian ryazanian age estimates and constrain the initial 187os 188os of the shales to 0 52 in the lowermost farsund formation and 0 75 in the uppermost mandal formation solvent extracted reservoir rocks of the ula formation contain insoluble organic matter with type iii type iv kerogens likely supplied by erosion of older a precise 179 ma re os age with unrealistically low initial 187os 188os coal bearing sediments or organic rich shales the brynhild crude oil has relatively low 187os 188os and a generation age of 44 ma based on an asphaltene only re os isochron maltenes from the brynhild crude oil are isotopically affected by interaction with organic rich source rocks that represent the seal for the brynhild oil field compared with the crude oil bitumen from ula formation sandstones have contrasting re os properties high 187os 188os ratios and young generation ages between 8 and 0 ma based on asphaltene bitumen maltene re os triplets asphaltene only re os regressions and re os model ages for components with extremely high 187re 188os the 44 ma and 8 0 ma re os ages agree well with regional burial models that indicate oil generation from 44 ma to present day a genetic link between crude oil and bitumen is indicated by their similar alkane patterns v and ni contents and v ni and pristane phytane ratios modeling of 187os 188os for individual organic components through time shows that shales of the mandal formation developed 187os 188os ratios that match those of the crude oil and bitumen at 44 ma and 8 ma respectively and therefore confirm the source for both hydrocarbon phases we suggest that bitumen formed during in reservoir mixing of a 44 ma old early mature asphaltene poor oil brynhild crude oil with an 8 ma old asphaltene rich oil

organic accumulation in the lower chihsia formation middle permian of south china constraints from pyrite morphology and multiple geochemical proxies article i nfo the organic rich chihsia formation middle permian on the yangtze platform western hubei south china is considered to be the major hydrocarbon source rock in south china the lower part of the chihsia formation reported here was deposited in an intrashelf basin and is characterised by black laminated marlstones shales intercalated with dark grey limestones dolomites in which metre scale shallowing or cleaning upward cycles are ubiquitous each cycle is composed of basal marlstone shale and upper lime stone the organic matter is concentrated exclusively in the shaley bases of these cycles and shows system atic cyclic variations in abundance up through the succession an integrated approach of pyrite morphology and multiple geochemical proxies was used to determine the mechanism of organic accumulation in the organic rich sediments many redox proxies including pyrite framboid size distribution c s fe relation ships iron speciation and 34 s values of pyrite suggest deposition beneath the dysoxic bottom water which evolved into a more oxic water body when the organic poor limestones were deposited however the coincidence of increased abundance of total organic carbon toc with increased ba and mo contents in dicates that organic matter accumulation was controlled mainly by primary productivity these data indicate that increased organic accumulation resulted mainly from higher organic carbon export with increased nutri ent flux during superimposed sea level rises of different orders this in turn could have increased the oxygen consumption by respiration of microorganisms and organic matter decay leading to the depletion of oxygen in the water columns furthermore the rapid sedimentation rate further limited bioturbation and organic matter decomposition facilitating the preservation of buried organic matter

geochemistry of inorganic and organic sulphur in organic rich sediments from the peru margin abstract we have determined 1 the abundance and isotopic composition of pyrite monosulphide elemental sulphur organically bound sulphur and dissolved sulphide 2 the partition of ferric and ferrous iron 3 the organic carbon contents of sediments recovered at two sites drilled on the peru margin during leg 112 of the ocean drilling program sediments at both sites are characterised by high levels of organically bound sulphur obs obs comprises up to 50 of total sedimentary sulphur and up to 1 of bulk sediment the weight ratio of s to c in organic matter varies from 0 03 to 0 15 mean 0 10 such ratios are like those measured in lithologically similar but more deeply buried petroleum source rocks of the monterey and sisquoc formations in california the sulphur content of organic matter is not limited by the availability of porewater sulphide isotopic data suggest that sulphur is incorporated into organic matter within a metre of the sediment surface at least partly by reaction with polysulphides most inorganic sulphur occurs as pyrite pyrite formation occurred within surface sediments and was limited by the availability of reactive iron but despite highly reducing sulphidic conditions only 35 65 of the total iron was converted to sulphide 10 30 of the total iron still occurs as fe iii in surface sediments the isotopic composition of pyrite is similar to that of both iron monosulphide and dissolved sulphide either pyrite like monosulphide formed by direct reaction between dissolved sulphide and detrital iron and or the sulphur species responsible for converting fes to fes2 is isotopically similar to dissolved sulphide likely stoichiometries for the reaction between ferric iron and excess sulphide imply a maximum resulting fes2 fes ratio of 1 1 where pyrite dominates the pool of iron sulphides at least some pyrite must have formed by reaction between monosulphide and elemental sulphur and or polysulphide elemental sulphur s0 is most abundant in surface sediments and probably formed by oxidation of sulphide diffusing across the sediment water interface in surface sediments s0 is isotopically heavier than dissolved sulphide fes and fes2 and is unlikely to have been involved in the conversion of fes to fes2 polysulphides are thus implicated as the link between fes and fes2

from greenhouse to icehouse nitrogen biogeochemistry of an epeiric sea in the context of the oxygenation of the late devonian atmosphere ocean system abstract the late devonian emergence of extensive arborescent terrestrial ecosystems produced changes in the earth s atmosphere and climate that resulted in substantial changes to the biogeochemistry of marine ecosystems the biogeochemistry of nitrogen in epeiric seas was particularly susceptible to alteration because of its dependence upon the series of redox mediated reactions that comprise the marine n cycle in order to explore the impact of climate change on n biogeochemistry in a late devonian epeiric sea we sampled a core from the appalachian basin that spans the interval from the greenhouse climate at the base of the famennian period to glacial conditions near its conclusion based upon stable isotope analysis of n c and s as well as elemental analysis of n c p s and fe we contend that two distinct biogeochemical regimes obtained during the contrasting climates the greenhouse regime featured low seawater o2 and ph that served to significantly curtail the oxidation of ammonia i e nitrification resulting in an ammonium dominated water column and low sediment 15n values the greenhouse also featured more extensive recycling of c n and p in contrast the higher seawater o2 and ph of the icehouse regime permitted nitrification in the water column resulting in a nitrate dominated system and higher sediment 15n values we conclude that nitrification was the key component of the n cycle that differentiated the two climate biogeochemical regimes

late folding related magnetic foliation in the active ferdows northeastern iran thrust fold system abstract in this work we present new ams and structural results from the ferdows active fold thrust system lut block central iran ams analyses show that the miocene units of the upper red formation have a well defined magnetic fabric of tectonic origin with both magnetic lineation and magnetic foliation oriented parallel to the regional fold axes in most of the cases the magnetic fabric acquired when the bedding was still horizontal is related to different degrees of lps shortening in some other cases the magnetic foliation is vertical and oblique to the bedding suggesting that in the ferdows thrust fold structure a cleavage system not visible at the outcrop scale has been developed as a consequence of later shortening related to the activity of the thrust system responsible of the recent earthquakes in the area results from this study establish a relationships between the recent tectonics of the area and the evolution of the magnetic fabric and demonstrate that a well defined magnetic fabric of pure tectonic origin can also develop in poorly deformed rocks lacking field evidence of pervasive internal deformation

strain variations across the proterozoic penokean orogen usa and canada abstract strata in the huron 2 5 2 0 ga and animikie 2 2 1 85 ga basins were deposited on the southern margin of the archean superior province these rocks were deformed during the penokean orogeny 1850 ma followed by subsequent accretionary orogens to the south at 1750 ma yavapai and 1630 ma mazatzal strain patterns are unique to each orogenic belt with no far field effect archean wawa terrane rocks in the penokean foreland preserve deformation associated with archean accretion with no younger penokean yavapai or mazatzal strain overprint the penokean orogeny deformed huron animikie basin sediments into a north vergent fold and thrust belt with no yavapai or mazatzal strain overprint yavapai orogen strains sw ne margin parallel shortening are unique when compared to the younger mazatzal shortening n20 w shortening with no strain overprint penokean deformation is characterized by shortening from the south including uplifted archean gneisses and a northerly thin skinned fold and thrust belt with north vergent nappes and a gently dipping foreland our study of finite and calcite twinning strains n 60 along 1500 km and across 200 km the penokean belt indicate that this orogeny was collisional as layer parallel shortening axes are parallel across the belt or parallel to the tectonic transport direction n s penokean nappe burial near the margin resulted in vertical shortening strain overprints some of which are layer normal the sudbury impact layer 1850 ma is found across the animikie basin and provides a widespread deformation marker with many local unique strain observations we also report new geochronology u pb zircon and apatite for the gneiss mafic dike rocks at wissota chippewa falls wi and arbutus black river falls wi dams respectively which bears on penokean yavapai deformation in the archean marshfield terrane which was accreted during the penokean orogen pseudotachylite formation was common in the superior province archean basement rocks especially along terrane boundaries reactivated by contemporaneous penokean trans hudson cape smith and new quebec deformation in the hinterland south the younger yavapai orogen 1750 ma n 8 deformation is preserved as margin parallel horizontal shortening sw ne in yavapai crust and up to 200 km to the north in the penokean thrust belt as a strain and barrovian metamorphic overprint mazatzal deformation 1630 ma n 16 is preserved in quartzites on yavapai and penokean crust with layer parallel and layer normal shortening strains oriented n20 w

relationship between remagnetization magnetic fabric and deformation in paleozoic carbonates abstract we have studied the magnetic fabric of paleozoic carbonates from numerous sites in the north american midcontinent for comparison with paleomagnetic behavior and calcite twinning strains sites carrying a kiaman remagnetization have significantly lower anhysteretic remanent magnetization arm anisotropy less than 3 than other sites minimum axes of arm ellipsoids are distributed in a vertical plane trending approximately se nw this trend is very similar to the orientation of alleghenian layer parallel shortening as inferred by mechanical twinning in calcite sites lacking a kiaman overprint invariably have steeply oriented minimum arm axes and relatively strong anisotropy whereas the most strongly remagnetized sites have nearly horizontal minima and weak anisotropy these observations suggest that diagenetic authigenic magnetites formed independently of any pre existing fabric of precursor sulphides and host rock and that the magnetic fabric of the whole midcontinent was at least partially affected by alleghenian syn orogenic activity

trace metal enrichments in lake tanganyika sediments controls on trace metal burial in lacustrine systems abstract we investigate the distributions of several key diagenetic reactants c s fe and redox sensitive trace metals mo cd re u in sediments from lake tanganyika east africa this study includes modern sediments from a chemocline transect which spans oxygenated shallow waters to sulfidic conditions at depth as well as ancient sediments from a longer core 2 m taken at 900 m water depth modern sediments from depths spanning 70 335 m are generally characterized by increasing enrichments of c s mo cd and u with increasing water depth but static fe distributions it appears that the sedimentary enrichments of these elements are to varying degrees influenced by a combination of organic carbon cycling and sulfur cycling these modern lake characteristics contrast with a period of high total organic carbon corg total sulfur stot and trace metal concentrations observed in the 900 m core a period which follows the most recent deglaciation 18 11 ky this interval is followed abruptly by an interval 11 6 ky that is characterized by lower c s u and mo consistent with other work we suspect that the low concentrations of s mo and u may indicate a period of intense lake mixing during which time the lake may have been less productive and less reducing as compared to the present an alternative but not mutually exclusive hypothesis is that changes in the lake s chemical inventory driven by significant hydrological changes could be influencing the distribution of sedimentary trace elements through time

the impact of organic fluids on the carbon isotopic compositions of carbonate rich reservoirs case study of the lucaogou formation in the jimusaer sag junggar basin nw china abstract the processes involved in the interaction between organic fluids and carbonates and the resulting effect on reservoir quality during the evolution and maturation of organic matter remain unclear despite the fact that these processes influence the carbon and oxygen isotopic compositions of carbonates here we provide new insights into these processes using data obtained from a detailed analysis of a mixed dolomitic clastic and organic rich sedimentary sequence within the middle permian lucaogou formation in the junggar basin of nw china the techniques used during this study include drillcore observations thin section petrography scanning electron microscopy sem and electron probe microanalysis and carbon and oxygen isotope analyses oil grades and total organic carbon toc contents represent the amount of oil charging and the abundance of organic fluids within a reservoir respectively and both negatively correlate with the whole rock 13c and 18o of the carbonates in the study area indicating that organic fluids have affected the reservoir rocks secondary carbonates including sparry calcite and dolomite overgrowths and cements are common within the lucaogou formation well developed sparry calcite is present within dark mudstone whereas the other two forms of secondary carbonates are present within the dolomite rich reservoir rocks in this formation comparing thin section petrology with 13c compositions suggests that the carbon isotopic composition of matrix carbonates varies little over small distances within a given horizon but varies significantly with stratigraphic height as a result of the development of secondary carbonates the net change in whole rock 13c as a result of these secondary carbonates ranges from 1 8 to 4 6 with the secondary carbonates having calculated 13c compositions from 18 6 to 8 5 that are indicative of an organic origin the positive correlation between the concentration of fe within matrix and secondary carbonates within one of the samples suggests that the diagenetic system within the lucaogou formation was relatively closed the correlation between 13c and 18o in carbonates is commonly thought to be strengthened by the influence of meteoric water as well as organic fluids however good initial correlation between 13c and 18o of whole rock carbonates within the lucaogou formation resulted from the evaporitic sedimentary environment was reduced by organic fluids to some extent consequently the 13c 18o covariations within these sediments are not always reliable indicators of diagenetic alteration by organic fluids or meteoric water the characteristics and 13c compositions of the sparry calcite within the formation is indicative of a genetic relationship with organic acids as a result of the addition of organic co2 to the reservoir further analysis suggests that both carbonate and feldspar were dissolved by interaction with organic co2 however dissolved carbonate reprecipitated as secondary carbonates meaning that the interaction between organic fluids and dolomites did not directly improve reservoir quality although this process did enhance the dissolution of feldspar and increase porosity this indicates that the 13c and 18o of secondary carbonates and their influence on whole rock carbonate isotopic values can be used to geochemically identify the effect of organic fluids on closed carbonate rich reservoir systems

minor changes in surface water fertility across the oceanic anoxic event 1d latest albian se france evidenced by calcareous nannofossils the latest albian sediments deposited in the vocontian basin in south eastern france record the oceanic anoxic event oae 1d locally named the breistroffer interval they are represented by argillaceous marls and marls containing organic matter total organic carbon varying from 0 8 to 1 changes in calcareous nannofossil abundance and assemblage composition as well as macrofauna abundance ichnofossil assemblage and bioturbation intensity were analysed in order to evaluate the main palaeoenvironmental factors controlling the deposition of the oae 1d sediments in this area the pelagic carbonate production is limited and the carbonate fraction is predominantly of nektonic benthic and of allochthonous origin from carbonate platforms the enrichment in organic carbon within the breistroffer interval is weak and not associated with high surface water productivity the organic matter is mainly terrigenous its record is due to 1 a good preservation under dysoxic conditions within the sediments and 2 a weak input of allochthonous carbonates eustatic fluctuations strongly influenced the variations of nannofossil and macrofauna abundances distinctive patterns in nannofossil assemblages and macrofauna abundances within the breistroffer interval are also recognized reflecting changes from mesotrophic to more oligotrophic conditions which are probably controlled by climate

geochemical characteristics of chilean upwelling sediments at 36 s abstract we examined the cycling of c s fe and the trace elements te ag cd mo mn re and se in chilean upwelling sediments from water depths of 127 2744 m at 36 s the sediments are clay rich with moderate total organic carbon toc and low biogenic caco3 contents for the shallow site within oxygen minimum zone omz which shows some thioploca biomass highest observed toc contents correspond to highest productivity induced toc flux and or enhanced preservation under o2 deficient conditions pyrite formation may be restricted by the concurrent presence of elemental s in thioploca and or the availability of reactive iron in the other sediments 370 m water depth pyrite formation is strongly restricted due to the low availability of metabolizable toc for sulfate reduction calculations of the degree of bacterially mediated remineralization suggest that more nitrogen than toc was remineralized by sulfate reduction than expected from redfield c n relationship manganese is significantly depleted due to reductive dissolution of mn hydr oxides within all sediments mo is only significantly enriched vs the lithogenic background in the shallow core implying anoxic conditions contents of re and mo as well as re mo ratios indicate suboxic conditions for the other cores cd and re contents decrease with increasing water depth reflecting decreasing reducing conditions in contrast authigenic ag contents increase with water depth suggesting enrichment controlled by seawater availability and or opaline input and not redox conditions elevated se contents in all cores may be either due to bio detrital input or diffusion from seawater accumulation rates of toc ts and te off chile are in the same order as those from the gulf of california and lower than those off peru distinct seasonality in upwelling and dilution of chilean sediments with terrigenous material lead to rather low metabolizable toc contents and lower te trapping capacity

coupling between sedimentary dynamics early diagenetic processes and biogeochemical cycling in the amazon guianas mobile mud belt coastal french guiana coastal french guiana lies within the vast mobile mudbelt that characterizes much of the s american inner shelf downdrift of the amazon river approximately 15 20 of the amazon sediment outfall moves nw along the guianas in part as a series of 20 25 coastal mud waves seasonal studies of a representative migrating mudwave located between kourou and sinnamary french guiana demonstrate that diagenetic properties and biogeochemical cycling are closely coupled to sedimentary dynamics and the refluxing of reduced components between the seabed coastal facies and well oxygenated overlying water an unsteady two zone diagenetic regime is typically present in the shallow subtidal and low intertidal regions a surficial layer usually 0 5 1 m thick is nonsulfidic highly reactive and dominated by fe mn cycling this suboxic layer unconformably overlies more consolidated sediment in which net so42 reduction is often observed and contracts shoreward toward the mangrove fringe as sediments stabilize and become bioturbated the relatively stable intertidal flats are also sites of significant benthic primary production despite suboxic conditions over extensive intervals anaerobic remineralization rates are high co2 0 2 0 6 mm day 1 and often show little evidence of attenuation with depth integrated co2 fluxes are 20 235 mmol m 2 day 1 wet dry season average 120 far exceeding diffusive o2 fluxes into the bottom high reactivity 0 08 day 1 and low c n remineralization release ratios 5 3 of decomposing material imply fresh substrate of marine origin most reduced solid phase fe is present as nonpyritic authigenic fe minerals 20 fe ii is in pyrite and low sedimentary c s ratios 6 8 reflect the generally nonsulfidic conditions a broad range of tracers e g 234th t1 2 24 days 210pb t1 2 22 years seasonal cl profiles and nonsteady state diagenetic models of pore water concentrations and oxidant reductant relationships demonstrate that the upper 0 1 1 m of deposits are reworked and exchanged with overlying water on timescales of 10 days to seasonally thus the seafloor acts as a massive suboxic batch reactor entraining and processing reactive marine plankton regenerating fe mn oxides exchanging metabolites and nutrients with the oxygenated water column and generating suites of nonsulfidic authigenic minerals the apparent paradoxical properties of high remineralization rate low reductant content corg 630 mol g 1 and dominance of suboxic metal cycling are a direct consequence of frequent entrainment of highly reactive organic substrate and simultaneous regeneration of the major fe oxidants in oxygenated water the amazon guianas mobile mudbelt is a zone of extraordinarily intense sedimentary and biogeochemical recycling greatly exceeding stable coastal systems such as salt marshes in material exchange with the sea

degree of pyritization of iron as a paleoenvironmental indicator of bottom water oxygenation abstract a new method is presented for recognizing the degree of bottom water oxygenation in organic carbon bearing rock the method uses the parameter degree of pyritization dop which is the ratio of pyritic fe to pyritic fe acid soluble fe sediments with ages ranging from devonian to cretaceous have been classified on paleoecological and sedimentological criteria as having been deposited in aerobic conditions deposited in fully oxygenated bottom waters restricted marine conditions deposited in waters with low oxygen concentrations or inhospitable bottom conditions where little or no oxygen is present and h2s may be continually or intermittently present aerobic dop

sulphur incorporation in jurassic marine mudrocks and their bitumens at low thermal maturity cleveland basin england abstract the distribution of sulphur between pyrite kerogen elemental sulphur and the aromatic fraction of mudrock bitumens has been quantitated in two cored sections of immature marine kimmeridgian strata which have experienced different levels of thermal stress strata in the two boreholes ebberston and reighton were deposited in different basinal settings basinal marine and platform respectively and occasional euxinic laminated horizons are present at ebberston otherwise dysoxic deposition was the norm at both localities pyrite the dominant sulphur carrier in all the mudrocks has a sulphur isotopic composition consistent with mineralisation in a system mainly open to sulphate diffusion kerogens are mostly low sulphur atomic s c and account for between 5 and 10 of rock sulphur although occasionally up to 30 kerogen sulphur is closely correlated with toc and highest in laminated mudrocks consistent with most effective sulphurization of kerogen under anoxic conditions although kerogen compositions in both cores vary with organic richness no systematic differences in organic input between the borehole localities are recognised geochemically some thermal effects on sulphur geochemistry are therefore interpreted from a comparison of stratigraphically equivalent sections from the two cores bitumen yields and abundances of aromatic sulphur in the more thermally stressed ebberston section although variable are generally much higher than in the reighton section and are partly related to kerogen sulphur content this is tentatively attributed to thermal release of additional extractable bitumen from macromolecules elemental sulphur s0 in bitumen is unrelated in abundance to other sulphur species and isotopically heavier than coexisting pyrite overprinting of minor preserved diagenetic s0 by secondary oxidation of pyrite appears likely the distributions of individual sulphur aromatic compound classes have features related both to maturity and stratigraphy

major element analysis of cyclic black shales paleoceanographic implications for the early cretaceous deep western tethys lower cretaceous sediments are frequently characterized by a well expressed cyclicity while the processes influencing environments above the carbonate compensation depth ccd are reasonably well understood almost nothing is known about the deep ocean cretaceous sub ccd sediments from the tethys and atlantic oceans typically show rhythmic black green shale successions to gain insight into the nature of these black green shale cycles we performed detailed geochemical analyses x ray fluorescence rock eval and reactive iron analysis on a 3 m long section of latest aptian age the major element distribution of the analyzed shale sequence indicates a periodic change from a high productivity and well oxygenated green shale mode to a low productivity oxygen deficient black shale mode it is proposed here that the preservation of organic matter was dependent on the strength of salinity driven deepwater generation furthermore the data show that the corg content covaries with changes in the detrital composition therefore we hypothesize that tethyan deepwater circulation was sensitive to changes in the monsoonal system time series analysis suggests that these changes are periodic in nature although we are currently unable to prove that the dominant periodicity is related to the precession component of the milankovitch frequencies

smartfauna a microscale gis based multi dimensional approach to faunal deposition at the ness of brodgar orkney recent technological advances in survey and computing are opening up new opportunities for the accurate spatial recovery and recording of archaeological materials during excavation these have the potential to revolutionise understanding of depositional practices and other such taphonomic processes which create the deposits and sites that archaeologists explore this article summarises a new methodological approach to the recovery and analysis of faunal remains which enables a highly accurate 3d spatial analysis of any patterning in bone deposited within archaeological layers using a combination of high resolution survey techniques for the recovery of animal bones bridging software and a high end gis package application of this methodology to archaeological deposits from the ness of brodgar in orkney has provided evidence for deliberate placement of selected cattle and red deer remains suggesting that these species were of central importance in late neolithic society

quantifying the effects of erosion on archaeological sites with low altitude aerial photography structure from motion and gis a case study from southern jordan abstract cutting edge photogrammetric techniques combined with traditional methods are a boon for archaeologists interested in performing spatial analyses low altitude aerial photography laap combined with photogrammetric image based modeling ibm comprise a workflow that allows for precise and accurate recording of both photographic and elevation data of archaeological sites with a great deal of speed and efficiency through these techniques the researcher can create spatially referenced orthophotos and digital elevation models dems which can serve as the basis for investigations into site formation processes due to the rapidity of the creation of these datasets analysis of site formation processes can be completed over the course of hours or days the results of such site formation studies can inform and guide further archaeological investigations of sites this paper presents the application of a combined laap ibm method to acquire gis data which serves as the basis for a case study of a new model of the effects of erosion on archaeological sites a key factor in understanding site formation processes these methods are applied to khirbat nuqayb al asaymir a middle islamic site in southern jordan as a case study

scanning electron microscopy and rock magnetic studies of magnetic carriers in remagnetized early paleozoic carbonates from missouri this study was supported by nsf ear 90 05075 and 92 19616 institute for rock magnetism irm contribution 9303 the irm is funded by the keck foundation the national science foundation and the university of minnesota

organic geochemistry and palynofacies of the early middle frasnian transition late devonian of the holy cross mountains southern poland abstract geochemical and palynological investigation of the lower to middle frasnian reef to basin succession at the well known kowala quarry holy cross mountains demonstrates the variable character of organic matter om deposited in different oxidative reductive conditions during sedimentation of the basinal deposits anoxic conditions in the water column prevailed in the organic rich sediments deposited during the palmatolepis punctata zone set d anoxia occurred in the photic zone as inferred from the presence of isorenieratane aryl isoprenoids and gammacerane in the same kind of deposits but occurring during the palmatolepis hassi zone set f anoxia apparently occurred mainly in the deeper parts of the basin and only sporadically reached the photic zone this interpretation is based on the lack of isorenieratane traces of aryl isoprenoids and the presence of gammacerane in the investigated samples the basinal clay enriched sediments of sets d and f are divided by an organic poor set e typical for the carbonate platform fore reef environment characterized by oxic conditions a palynostratigraphical study of the frasnian section from the kowala quarry allowed recognition of two miospore zones geminospora semilucensa perotrilites donensis sd and archaeoperisaccus ovalis verrucosisporites grumosus og relatively small quantitative and qualitative changes of the organic particles miospores tracheids prasinophytes and acritarchs are interpreted primarily in terms of sea level fluctuations and enhanced productivity in particular the appearance of abundant abnormally large mature leiospheres in set d can be the result of progressive eutrophication related to environmental changes recorded in the recently detected major positive carbon isotope anomaly as during the frasnian famennian mass extinction interval this eutrophication could have been stimulated by a rapid increase in primary production and subsequently expanding anoxic conditions but it is evident only in the early phase of the middle frasnian 13 c excursion the processes of the secondary hydrothermal fluid migration taking place after the lithification of the sediments caused partial om oxidation the products of these processes are such phenyl derivatives of aromatic hydrocarbons as phenylphenanthrenes terphenyls phenyldibenzothiophenes and phenyldibenzofurans moreover an oxygen compound rarely described from sedimentary om dibenzo p dioxin and its methyl and dimethyl derivatives seems to be the additional product of hydrothermal om oxidation

proterozoic paleomagnetism in the nipigon embayment of northern ontario pillar lake lava waweig troctolite and gunflint formation tuffs abstract by using unusual combinations of demagnetization techniques proterozoic paleomagnetic vectors and paleopoles are provided for two recently discovered post tectonic proterozoic units near armstrong northern ontario and also for well dated gunflint formation which by previous techniques yielded problematical paleomagnetic data the first paleomagnetic data are provided also for the seagull pluton and inspiration sills characteristic remanent magnetizations chrm for the pillar lake lavas indicate a keweenawan age more specifically 1000 1040 ma by comparison with the well established apwp for the late proterozoic superior craton four combinations of demagnetization techniques yield declinations in the range 108 133 and inclinations in the range 65 to 70 n 100 which define paleopoles near 200 w 48 n corresponding to a location on the keweenawan apwp near 1040 ma in the underlying basement a recently discovered proterozoic igneous complex the waweig troctolitic complex yields new paleomagnetic data with declination and inclination 42 54 n 14 defining a paleopole at 238 w 09 n its ages may be 1400 1600 or 2000 ma by comparison with the presently available ambiguous and sparsely populated apwp the first paleomagnetic results for the seagull pluton u pb age 1113 ma yield a mean declination of 87 4 75 7 n 32 corresponding to a keweenawan paleopole near 233 42 n consistent with other paleopoles near 1200 ma tuffs of the oft studied but problematical gunflint formation u pb age1878 ma yielded stable and presumably primary vectors using several different demagnetization techniques on the same specimens their mean primary declination and inclination 303 48 8 n 17 yields a paleopole now located near 178 w 42 n comparable with the published locations of paleopoles of 2000 ma of broader interest we recognized that low temperature demagnetization preceding conventional demagnetization techniques enhanced the isolation of characteristic vectors combining the conventional techniques thermal and af demagnetization also improved the resolution of characteristic vectors not achieved by other means low grade metamorphism affected the non tectonized proterozoic cover to the canadian shield due to burial or hydrothermal effects obfuscating or erasing primary vectors in some lithologies and especially at certain sites

the occurrence and origin of late paleozoic remagnetization in the sedimentary rocks of north america although it has been known for 25 years that some paleozoic sedimentary rock units in europe and north america were remagnetized during pennsylvanian or permian time it is only very recently that the complex and widespread nature of the late paleozoic remagnetization phenomenon has been generally acknowledged it is now recognized that many paleozoic paleomagnetic poles for north america that were once considered reliable are in fact the result of remagnetization and as a consequence the paleomagnetic data base for the paleozoic is undergoing rapid and drastic revision the causes of late paleozoic remagnetization in north america are currently the focus of much interest and active research the remagnetization can reside in either hematite or magnetite and different remagnetization mechanisms have been important in different settings chemical remagnetization processes some related to specific diagenetic events are dominant in hematite bearing sandstones and carbonates in magnetite bearing carbonates both chemical and thermoviscous remagnetization processes appear to have been important but it is difficult to determine which process is the dominant one in some settings some of the observed remagnetizations can be linked to the migration of chemically active and perhaps hot fluids during the mountain building events that affected much of the continent during the late paleozoic paleomagnetic studies promise to be important in assessing the role of orogeny in driving fluid migrations within sedimentary basins and in constraining the age of the migrations and the nature of the fluids

redox sensitivity of p cycling during marine black shale formation dynamics of sulfidic and anoxic non sulfidic bottom waters abstract a high resolution geochemical record of a 120 cm black shale interval deposited during the coniacian santonian oceanic anoxic event 3 odp leg 207 site 1261 demerara rise has been constructed to provide detailed insight into rapid changes in deep ocean and sediment paleo redox conditions high contents of organic matter sulfur and redox sensitive trace metals cd mo v zn as well as continuous lamination point to deposition under consistently oxygen free and largely sulfidic bottom water conditions however rapid and cyclic changes in deep ocean redox are documented by short term 15 20 ka intervals with decreased total organic carbon toc s and redox sensitive trace metal contents and in particular pronounced phosphorus peaks up to 2 5 wt p associated with elevated fe oxide contents sequential iron and phosphate extractions confirm that p is dominantly bound to iron oxides and incorporated into authigenic apatite preservation of this fe p coupling in an otherwise sulfidic depositional environment as indicated by fe speciation and high amounts of sulfurized organic matter may be unexpected and provides evidence for temporarily non sulfidic bottom waters however there is no evidence for deposition under oxic conditions instead sulfidic conditions were punctuated by periods of anoxic non sulfidic bottom waters during these periods phosphate was effectively scavenged during precipitation of iron oxyhydr oxides in the upper water column and was subsequently deposited and largely preserved at the sea floor after 15 25 ka sulfidic bottom water conditions were re established leading to the initial precipitation of cds zns and pyrite subsequently increasing concentrations of h2s in the water column led to extensive formation of sulfurized organic matter which effectively scavenged particle reactive mo complexes thiomolybdates at site 1261 sulfidic bottom waters lasted for 90 100 ka followed by another period of anoxic non sulfidic conditions lasting for 15 20 ka the observed cyclicity at the lower end of the redox scale may have been triggered by repeated incursions of more oxygenated surface to mid waters from the south atlantic resulting in a lowering of the oxic anoxic chemocline in the water column alternatively sea water sulfate might have been stripped by long lasting high rates of sulfate reduction removing the ultimate source for hs production

diagenetic magnetite carries ancient yet secondary remanence in some paleozoic sedimentary carbonates many sedimentary carbonate rocks carry stable magnetizations that can be shown to reside in magnetite when such magnetizations are observed it is often argued or demonstrated that the magnetite was incorporated into the sediment during deposition however paleomagnetic and rock magnetic studies in conjunction with analyses of magnetic extracts from the helderberg and bonneterre carbonates united states indicate that the magnetite present in these rocks is most likely of diagenetic i e postdepositional origin

a comprehensive numerical chronology for the pre columbian cultures of the palpa valleys south coast of peru before the arrival of the spaniards in peru in 1532 many different societies flourished in the coastal desert of southern peru of these one of the best known is the nasca culture living in the area between about 260 cal bc and 640 cal bc which created the famous geoglyphs on the desert floor in this paper we present a numerical chronology for the cultural development in the valleys of palpa in the northern part of the nazca region which spans the time from the archaic period starting there around 3760 cal bc to the late intermediate period terminating with the arrival of the spaniards in 1532 ad the chronology is based on more than 150 14 c samples collected by our project from well documented

disentangling magnetic subfabrics and their link to deformation processes in cleaved sedimentary rocks from the internal sierras west central pyrenees spain abstract here we present a detailed study of the magnetic fabrics and subfabrics of remagnetized upper cretaceous limolites that crop out in the internal sierras west central pyrenees affected by a penetrative pressure solution cleavage the bulk magnetic fabrics of these rocks rt ams show variable orientations that do not conform to what is typically reported for cleaved sedimentary rocks in contrast the paramagnetic subfabrics lt ams show remarkably constant directional properties so that their k max and k min axes cluster parallel to the intersection lineation and to the poles to bedding respectively these lt ams subfabrics indicate a preferred orientation of phyllosillicates that is consistent with a syn sedimentary late cretaceous period of nne oriented layer parallel shortening noticeably these phyllosillicate subfabrics are not further altered by the subsequent formation of cleavage in the late eocene early oligocene the ferrimagnetic subfabrics aarm also show remarkably constant orientation so that their k max axes are strikingly parallel to the shortening direction in the area we interpret this preferred orientation of ferrimagnetic grains as being caused by subhorizontal shear associated to cleavage formation which is consistent with the age and mechanisms authigenic growth and rotation of pre existing magnetite grains proposed for the pervasive remagnetization that affects the studied rocks

magnetic anisotropy in the trenton limestone results of a new technique anisotropy of anhysteretic susceptibility a new method for determining magnetic anisotropy using anhysteric remanence susceptibility is described the magnetic fabric of a collection of trenton limestone specimens has been determined using this method as well as by conventional anisotropy of magnetic susceptibility the results demonstrate the usefulness of the new method for finding the magnetic fabric of rock units such as the trenton in which the bulk magnetic susceptibilities are low a model is proposed to explain the observed foliated and lineated fabric as a consequence of overburden compaction and regional horizontal stresses the original fabric is inferred to have been isotropic the anisotropy resides in secondary magnetite of late paleozoic age it is argued that the observed magnetic fabric must therefore be alleghenian or younger in age our method has the potential to determine paleostress directions in carbonates elsewhere provided our assumptions are correct

strain partitioning of deformation mechanisms in limestones examining the relationship of strain and anisotropy of magnetic susceptibility ams abstract in order to investigate the relationship between rock strain and anisotropy of magnetic susceptibility ams strain partitioning and ams analysis was conducted at 35 sites from two stratigraphically adjacent paleozoic limestone units in the patterson creek and wills mountain anticlines in the central appalachian orogen of west virginia in addition anisotropy of anhysteretic remanent magnetization aarm was conducted on selected samples to examine the role of preferentially oriented magnetite on the ams fabric strain is partitioned into bed normal shortening due to compaction solution strain 35 0 shortening bed parallel shortening due to tectonic solution strain 13 3 shortening calcite twinning strain 5 8 shortening and grain boundary sliding 26 7 shortening the ams fabrics in the rocks were found to be a result of a complex interaction between rock lithology deformation mechanisms and strain magnitude although all the rocks have experienced the same deformation conditions six different ams fabrics are exhibited each of the different ams fabrics is a composite fabric resulting from the overprinting of three components 1 an inherent primary depositional ams fabric that is attributed to preferentially oriented phyllosilicates in the rock matrix 2 a diagenetic and or compaction ams fabric formed during burial that is due to preferentially oriented phyllosilicates in solution structures and in the rock matrix and 3 a tectonic ams fabric that was imparted on the rocks by layer parallel shortening deformation prior to folding and is also attributed to preferentially oriented phyllosilicates in solution structures and in the rock matrix as well as twinning of ferroan calcite

joining forces combined biological and geochemical proxies reveal a complex but refined high resolution palaeo oxygen history in devonian epeiric seas abstract two devonian black shale intervals were analysed using a carefully integrated palaeontological geochemical approach to interpret relative bottom water oxygen levels at a resolution and sensitivity possible only through the combined approach biological data presented as both trace and body fossil abundance and size suggest generally low bottom water oxygen conditions the frequently laminated sediments would be viewed traditionally as recording appreciable intervals of anoxic and or euxinic anoxic and h 2 s containing bottom waters the inclusion of parallel geochemical results however refines this perspective well established iron proxies for depositional redox tell us that anoxic and euxinic conditions were intermittent and short lived if present at all manganese and molybdenum data point to conditions with a likelihood of very low oxygen in bottom waters during intervals with high pore water concentrations of hydrogen sulphide near the sediment water interface these elevated sulphide concentrations under iron limited diagenetic conditions varied with organic content and may have further inhibited benthic colonization and an active infaunal community more specifically the combined palaeontological and geochemical data sets point to depleted bottom water oxygen contents with evidence for hydrogen sulphide limited dominantly or exclusively to the pore waters anoxia and euxinia if present occurred only intermittently and lasted only briefly perhaps on seasonal time scales tied to primary productivity cycles or climatically induced variation in water column stratification the time scales and mechanisms of rapid redox variation remain to be studied the details of such transitional and dynamic settings are best viewed from a multi proxy biogeochemical and palaeoecological perspective as an important byproduct geochemical methods refined in multi proxy studies of phanerozoic shales can then be extended with greater utility to precambrian strata without trace and body fossils

sulphur and iron geochemistry of holocene coastal peats nw germany a tool for palaeoenvironmental reconstruction abstract a drill core from the marshlands of nw germany covering the entire holocene was analysed at high resolution by geochemical xrf cirm ms and microfacies methods diatoms thin sections sem in order to provide information about the palaeoenvironmental development in addition microbial experiments were carried out with sulphate reducing bacteria srb and cellulose fermenting fungi in seawater using peat as substrate the core contains an intercalated reed peat layer 2 73 3 02 m and a basal peat 5 78 6 42 m the basal peat consists in the lowest part of fen woodland and raised bog peat while the upper part is formed by a reed peat bed the peat layers are characterised by a distinct enrichment of pyrite with negative bulk sediment 34 s values av 11 5 range 2 6 to 26 7 reflecting microbial sulphate reduction in some peat intervals under almost open system conditions with respect to the input of seawater sulphate pyrite occurs exclusively with framboidal texture in close vicinity to the organic matter which indicates localised pyrite formation at the decay site in microenvironments with high concentrations of dissolved fe microbial experiments reveal that peat does not represent an appropriate substrate for srb and that srb have to rely on the preceding decomposition of peat by other microorganisms in microenvironments the total sulphur content of the peat layers averages to 7 8 wt with a maximum value of 28 2 wt unusually found within the basal peat at the transition of fen woodland and raised bog peat the pyrite enrichments can be explained by two different scenarios which are related to the intensity of the sea level rise the first scenario applies to a moderate sea level rise and is decisive for the reed peats where pyrite formation coincides with peat growth a brackish zone is assumed for the peat forming environment which is influenced by iron rich freshwater and sulphate rich seawater as the freshwater forms the major fe source the amounts of pyrite increase to a certain degree with decreasing salinity in this environment the palaeosalinity is estimated by the investigation of littoral and pelagic diatoms the second scenario applies to the extensive pyrite formation within the basal peat at the transition of fen and bog peat this pyrite was likely formed after peat growth favoured by a steep sea level rise thin sections of this peat interval reveal clastic layers 1 3 mm with completely pyritised interfaces as these clastic layers contain marine pelagic diatoms e g paralia sulcata we propose that they are caused by tidal channel activities during a phase of a steep sea level rise the marine incursion led to a partial buoyancy of the basal peat at weak transition zones i e the transition from fen to bog peat as a result of the bouyancy marine suspended particulate matter can be introduced laterally in between the peat sections when the peat settles down a clastic layer remains whose interface with the peat may have favoured the inflow of waters of higher salinity therefore an enhanced formation of pyrite was possible due to the combination of sulphate rich ground water and iron rich peatland waters

characteristics of magnetic carriers responsible for late paleozoic remagnetization in carbonate strata of the mid continent u s a magnetic analysis of carbonate strata of the mid continent region of the united states indicates that the late paleozoic remagnetization already recognized in the appalachians also affects almost the entire mid continent magnetic intensity is regionally variable with more intense magnetizations occurring on intracratonic arches magnetization is carried predominately by magnetite which often occurs in tiny hollow spheroids composed of well formed octahedral microcrysts spheroid chemistry and morphology suggests that the magnetite is authigenic composed of iron extracted from pre existing pyrite or clay the timing of the remagnetization the character of the magnetite and the regional variation in magnetic intensity support the idea that the remagnetization is a diagenetic consequence of tectonically driven brine migration

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 rock magnetic fingerprint of chemical remagnetization in midcontinental paleozoic carbonates supported by nsf ear 90 05075 contribution number 9203 of the institute for rock magnetism the irm is supported by grants from the keck foundation the national science foundation and the university of minnesota

combining photogrammetry and laser scanning for the recording and modelling of the late intermediate period site of pinchango alto palpa peru this paper describes the 3d modelling of pinchango alto peru based on a combination of image and range data digital photogrammetry and laser scanning allow archaeological sites to be recorded efficiently and in detail even under unfavourable conditions in 2004 we documented pinchango alto a typical site of the hitherto poorly studied late intermediate period on the south coast of peru with the aim of conducting spatial archaeological analyses at different scales the combined use of a mini helicopter and a terrestrial laser scanner both equipped with a camera allowed a fast yet accurate recording of the site and its stone architecture in this paper we describe the research background the 3d modelling based on different image and range data sets and the resulting products that will serve as a basis for archaeological analysis 2006 elsevier ltd all rights reserved

organic carbon sulphur and iron in recent semi euxinic sediments of kau bay indonesia kau bay island of halmahera eastern indonesia is a 470 m deep basin separated from the pacific ocean by a sill that is at present only 40 m below sea level during weichselian time the sea level dropped below the depth of the sill and freshwater sediments were deposited these sediments are rich in organic matter corg 2 6 wt with terrigenous isotope characteristics 13corg 28 to 30 and are also rich in sulphur s 4 wt this sulphur enrichment is interpreted to be a late diagenetic feature related to diffusion of dissolved sulphate and sulphide from the marine sediments into the freshwater sediments the sulphur in these sediments has a 34s value of 15 the overlying holocene sediments consist of marine muds deposited in alternating low oxygen and h2s bearing bottom waters the marine sediments are also rich in organic matter corg 2 6 wt but of mixed terrigenous and marine origin 13c 25 to 19 moreover the sulphur content of these holocene sediments is lower s 1 2 wt and isotopically lighter 34s 20 in addition to pyrite large amounts of acid volatile sulphur avs compounds accumulate in kau bay the reactive iron content of the sediment limits the amount of iron that is sulphidized while the supply of oxidants controls the limited conversion of avs to pyrite total and reactive iron contents are strongly correlated with the amount of terrigenous organic matter as a consequence of their common provenance and depositional histories the marine sediments in kau bay show no simple relation between organic carbon and sulphur

late paleozoic deformation of the cratonic carbonate cover of eastern north america paleozoic carbonates that cover the eastern half of the north american craton preserved a bedding parallel shortening fabric up to 800 km away from the appalachian ouachita orogenic front as recorded by mechanical twins in calcite a strain fabric is present in 29 of 31 samples from three traverse within the flat lying cratonic cover sequence jasper arkansas to minneapolis bluefield west virginia to madison wisconsin and albany new york to hamilton ontario twinning is found only in paleozoic carbonates and is absent in cretaceous limestones in the two southernmost traverses the orientation of the principal shortening axis e1 is perpendicular to the thrust front and parallel to the thrusting direction of the southern appalachians and the ouachitas the magnitude of calcite shortening strain 6 and the calculated differential stress 90 mpa decrease exponentially away from the orogenic front until twinning is absent the northernmost traverse shows greater complexity probably because of its location in the bend of the appalachian trend the authors conclude that the regional strain fabric preserved in the cratonic cover sequence of eastern north american was produced by late paleozoic orogenic stresses of the appalachian ouachita orogeny and that compressive stresses were transmitted over distances greater than 1200 km awaymore from the active plate margin less

geochemical and multi isotopic 87sr 86sr 143nd 144nd 238u 235u perspectives of sediment sources depositional conditions and diagenesis of the marcellus shale appalachian basin usa abstract we investigate sediment sources depositional conditions and diagenetic processes affecting the middle devonian marcellus shale in the appalachian basin eastern usa a major target of natural gas exploration multiple proxies including trace metal contents rare earth elements ree the sm nd and rb sr isotope systems and u isotopes were applied to whole rock digestions and sequentially extracted fractions of the marcellus shale and adjacent units from two locations in the appalachian basin the narrow range of end values from 7 8 to 6 4 at 390 ma is consistent with derivation of the clastic sedimentary component of the marcellus shale from a well mixed source of fluvial and eolian material of the grenville orogenic belt and indicate minimal post depositional alteration of the sm nd system while silicate minerals host 80 of the ree in the shale data from sequentially extracted fractions reflect post depositional modifications at the mineralogical scale which is not observed in whole rock ree patterns limestone units thought to have formed under open ocean oxic conditions have 238u values and ree patterns consistent with modern seawater the 238u values in whole rock shale and authigenic phases are greater than those of modern seawater and the upper crust the 238u values of reduced phases the oxidizable fraction consisting of organics and sulfide minerals are 0 6 greater than that of modern seawater bulk shale and carbonate cement extracted from the shale have similar 238u values and are greater than 238u values of adjacent limestone units we suggest these trends are due to the accumulation of chemically and more likely biologically reduced u from anoxic to euxinic bottom water as well as the influence of diagenetic reactions between pore fluids and surrounding sediment and organic matter during diagenesis and catagenesis

effects of sources and diagenesis on the isotopic and chemical composition of carbon and sulfur in cretaceous shales abstract the cretaceous lea park formation of south central saskatchewan contains organic matter from marine and terrestrial sources in proportions that vary as a result of deposition during the campanian claggett transgressive regressive cycle in the western interior seaway of north america the relative proportions of organic matter from these sources were determined using a terrestrial index ti that compares n alkanes considered to be of terrestrial origin n c25 to n c59 to those considered to be of marine origin n c15 to n c22 the c isotopic composition of cretaceous marine organic matter is found to be near 32 o while terrestrial organic matter is near 24 the lower 13c values of marine organic matter from the lea park formation as compared with those of recent marine organic matter are similar to the relation observed in other cretaceous rocks 13c values of terrestrial organic matter however are similar to those of the present during the miocene 13c values of marine organic matter became similar to recent values and this change in isotopic composition may be related to the development of deep cold water associated with the formation of antarctic ice sheets consequences of the formation of deep cold water may include improved exchange of co2 between atmosphere and oceans reduced pco2 levels and co2 concentrations in the photic zone of the oceans and environmental changes sufficient to produce an alternate metabolic pathway in phytoplankton all of these processes potentially result in higher 13c values in marine organic matter pyrite formation in the lea park mudstones was limited by the availability of metabolizable organic matter with the greatest amount of pyrite typically associated with organic matter having the lowest ti values 34spy values range nearly 30 and vary directly with the composition of associated organic matter variations in the supply of metabolizable organic matter were more important than differences in sedimentation rate in producing the range of 34spy values a34s values 534sseawater 34spyrite vary with the composition of organic matter and become larger when associated with more metabolizable organic matter

geochemical relationships of late paleozoic carbon rich shales of the midcontinent usa a compendium of results advocating changeable geochemical conditions abstract previous studies have shown that pennsylvanian black shales of the midcontinent us possess a more complex geochemical history than was once thought vine and tourtelot econ geol 65 1970 253 and coveney and glascock appl geochem 4 1989 347 note that the widespread nature of metalliferous pennsylvanian black shales and the diverse geological environments across the midwestern us pose the likelihood that metals contained in the black shales are of complex origins detailed geochemical and statistical representations using characteristics of numerous black shale members have shown that water depth may not have been uniformly deep as previously inferred by numerous workers earlier suggestions that these black shales were associated exclusively with anoxic depositional conditions have been challenged by a more realistic theory of multifaceted fluctuating environmental conditions a wide range of major and trace element concentrations combined with widely varying characteristics and diverse types of organic matter indicate the presence of fluctuating geochemical settings the presumption is that numerous associated chemical reactions occurred syngenetically one geochemical index degree of pyritization dop suggests a dysaerobic to aerobic setting for many of the shales whereas some other geochemical proxies i e v v ni indicate punctuated episodes of bottom water anoxia schieber abstr programs geol soc am 33 6 2001 a102 notes that in some black shales pyrite enrichment due to intermittent organic reworking explains the high dop values once thought to equate with extreme euxinic depositional conditions it seems likely therefore that even during apparent euxinic periods as indicated by bulk geochemistry oxygen deprived events were apparently short lived the seemingly euxinic fingerprint as shown by geochemical characteristics may result through time averaging abstr programs geol soc am 33 6 2001 a102 of intermittent euxinic events providing a misleading indication of dominant euxinic conditions thus detailed microstratigraphic sampling is necessary to delineate short punctuated occurrences of intermittent sub oxic episodes the midcontinent pennsylvanian shales may reflect a complex array of bottom water oxygenation variations and water depth fluctuations in response to climatic and localized events hatch j r and leventhal j s 1992 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 usa in meyers p a pratt l m nagy b eds geochemistry of metalliferous black shales chem geol 99 65 82 complicated by post depositional events appl geochem 4 1989 347 this research examines the previous exclusively anoxic origin for midcontinent pennsylvanian black shales from a geochemical perspective and offers an alternative supported by detailed statistical presentations with the hypothesis that events of anoxia were punctuated by short lived dysaerobic or even near oxic events

geochemical response on redox fluctuations in holocene lake sediments lake steisslingen southern germany abstract holocene sediments of lake steisslingen record sedimentation under different redox conditions this is proven by the changing depth of the chemocline and the resulting varying extension of laminated sediments from the deepest part of the lake to shallower water depths redox fluctuations are additionally reflected by colour changes between red and green and the quality of the nonglacial varves major and trace elements were analysed on bulk sediment samples period between 8200 6200 and 2650 2000 cal a bp to test their response to the observed changes in past depositional environments mn mo u fe and s were found to be redox sensitive elements in lake steisslingen fe and s are almost entirely fixed in pyrite because pyrite formation is limited by fe availability a parallel distribution of mo u fe and s between 8200 7200 cal a bp is interpreted as a signal for syngenetic pyrite formation from anoxic and sulfidic hypolimnetic waters since bioproductivity was low this must have been caused by conditions favouring a longterm stable stratification of the lake i e high water level high summer temperatures ice cover wind protection and or low storm activity between 6000 2000 cal a bp frequently changing redox conditions from anoxic to dysoxic are assumed mo and u curves are mirror images of the fe s and mn variations this is interpreted as showing diagenetic pyrite formation from pore waters which is enhanced during times of high fe availability under rather oxygenated conditions i e when high input of fe oxy hydroxides is possible but when u and mo cannot necessarily be fixed in the sediments changes from slightly disturbed lamination dysoxic restricted mixis to homogenous sediments oxic conditions holomixis cannot be traced within the geochemical record the observed redox fluctuations between 6000 and 2000 cal a bp are not correlated to changes in bioproductivity detrital input or cultural influences and must therefore be of a natural probably climatic origin the north atlantic oscillation is discussed as a possible cause

synergic use of satellite and ground based remote sensing methods for monitoring the san leo rock cliff northern italy abstract the historic town of san leo emilia romagna region northern italy is located on top of an isolated rock massif above the marecchia river valley hillside on february 27th 2014 a northeastern sector of the massif collapsed minor structural damages were reported in the town and a few buildings were evacuated as a precautionary measure although no fatalities occurred and the san leo cultural heritage suffered no damage minor rock fall events kept taking place on the newly formed rock wall worsening this hazardous situation in this framework a monitoring system based on remote sensing techniques such as radar interferometry both spaceborne and ground based and terrestrial laser scanning was planned in order to monitor the ground deformation of the investigated area and to evaluate the residual risk in this paper the main outlines of a 1 year monitoring activity are described including a pre event analysis of possible landslide precursors and a post event analysis of the displacements of both the collapse affected rock wall sector and the rock fall deposits

predominance of stratified anoxic yangtze sea interrupted by short term oxygenation during the ordo silurian transition abstract the ordo silurian transition was a critical interval in geological history during which profound biotic climatic and oceanic changes occurred in order to explore the oceanic palaeoredox changes multiple geochemical proxies including ratios of s c fehr fet fep fehr and dop values are presented here from three sections wangjiawan western hubei sanjiaguan northern hunan and nanbazi northern guizhou across the ordo silurian boundary on the yangtze platform these palaeoredox data indicate a predominance of stratified anoxic ferruginous ocean on the yangtze block during this transition which was interrupted by a brief episode of oceanic oxygenation in the early hirnantian this oxygenation temporally coinciding with the end ordovician glaciation and global glacio eustatic sea level fall likely resulted from enhanced circulation of polar cold dense oxygen rich water onto the low latitude shelf the prior and subsequent longer term episodes of anoxic ocean particularly the later one which started in the late hirnantian occurred in parallel with the rapid climatic warming and sea level rise which could have slowed down oceanic circulation thereby enhancing oceanic stratification anoxia and organic preservation oceanic redox changes together with rapid climatic and sea level fluctuations were likely responsible for the stepwise massive demise of the ordo silurian biotic crisis

ediacaran cambrian ordovician silurian and permian shales of the upper yangtze platform south china deposition thermal maturity and shale gas potential abstract for many years the yangtze platform has been successfully explored and exploited for petroleum the lower silurian longmaxi shale proved to contain commercial quantities of gas but several other formations might also have a high potential for shale hosted gas exploration this paper comprises of geochemical petrographical petrophysical and mineralogical information on the major proterozoic and paleozoic gas shales in the upper yangtze area which provides insights on the depositional environment the thermal maturity of organic matter shale gas storage capacity and the fracability of these rocks the total organic carbon toc content varies from 0 1 to 22 5 with an average value of 2 7 and most of these shales were deposited in an oxygen depleted marine environment equivalent vitrinite reflectance vrr values range from 2 20 to 4 25 indicating that all samples are in the gas generation window and lost a large amount of primary organic carbon porosity varies between 1 5 and 13 6 with an average value of 5 8 while the excess sorption capacity ranges from 0 10 to 0 22 mmol g rock minerology data show that quartz is the predominant mineral except for the upper permian longtan formation in which clay minerals account for 29 to 84 new data were combined with those from other publications and compared to information on other well studied shale hosted gas systems

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

anomalous enrichments of iron monosulfide in euxinic marine sediments and the role of h 2 s in iron sulfide transformations examples from effingham inlet orca basin and the black sea it is well documented that sedimentary pyrite formation proceeds through an iron monosulfide fes precursor laboratory studies have tradition ally indicated that intermediate s species such as elemental sulfur s 0 or polysul fides sx 2 are responsible for the transformation of fes to pyrite fes2 recent experimental work however has suggested that h2s may also be responsible for the transformation the present study extrapolates reaction pathways respon sible for pyrite formation in the laboratory to two fundamentally different modern anoxic marine systems we hypothesize that on decadal timescales h2s or hs is responsible for transformations of fes into fes2 in natural systems where intermediate s species are isolated from fes production the possibility of prolonged coexistence of high levels of h2s and fes however challenges recent experimental predictions of extremely rapid transformations that is timescales of hours or less of fes to fes2 via the h2s pathway sediments of effingham inlet a fjord on vancouver island and the orca basin an intraslope brine pool in the northern gulf of mexico are both charac terized by atypically high concentrations of fes but contrasting levels of h2s and fes2 production in both systems fes formation is spatially decoupled from intermediate s species as a consequence of either rapid deposition burial or extreme water column stratification within settings that promote this separa tion h2s may be the principal species responsible for pyrite formation fes to fes2 transformations are favored by the high concentrations of h2s in sediments of effingham inlet additional results from the margin of the anoxic black sea corroborate the effingham model for iron sulfide transformation h2s concentrations are controlled by the amount of bacterial sulfate reduc tion and the availability of reactive fe h2s concentrations will be buffered to low levels via the production of fes in systems with appreciable amounts of reactive fe and therefore be unavailable to transform fes to fes2 under conditions where h2s is the only species available for fes to fes2 transformations some degree of fe limitation may promote pyrite formation by allowing h2 st o accumulate in the pore waters ultimately this balance between h2s production and reactive fe availability may strongly influence the amount of pyrite formed in anoxic systems

oxidation of detrital pyrite as a cause for marcasite formation in marine lag deposits from the devonian of the eastern us late devonian black shale successions in the eastern us contain numerous discontinuities that are characterized by lags containing variable amounts of quartz sand mixed with reworked pyritic and phosphatic debris these lags can be partially cemented by iron sulfides with a radial fibrous to massive morphology examination of iron sulfide cements via electron backscatter diffraction ebsd shows that these cements can consist entirely or partially of marcasite it is proposed here that oxidation and dissolution of reworked pyrite debris led to favorable conditions for intermittent rapid marcasite formation by forcing a substantial ph drop in the surface sediment and by raising dissolved iron concentrations in the pore waters