fertilizing potential of volcanic ash in ocean surface water the fertilization potential of newly erupted and well preserved ash from the 2000 hekla eruption in iceland was measured for the first time by flow through experiments as previously shown 1 the north atlantic ocean including the subarctic seas surrounding iceland is the largest net sink of the world s oceans for atmospheric co 2 owing to biological drawdown during summer 2 almost complete consumption of phosphate in chlorophyll rich areas of the north atlantic ocean might limit primary production and 3 in the southern pacific ocean and parts of the equatorial pacific ocean iron might limit primary production we found through laboratory experiments that volcanic ash exposed to seawater initially releases large amounts of adsorbed phosphate 1 7 mmol g 21 h 21 iron 37 0 mmol g 21 h 21 silica 49 5 mmol g 21 h 21 and manganese 1 7 mmol g 21 h 21 dissolution of acid aerosols adsorbed to the surface of the ash caused the high initial release of major and trace elements because of the instantaneous dissolution of adsorbed components when newly erupted volcanic ash comes in contact with the ocean surface water macronutrients and bioactive trace metals are released fast enough to become available to support primary production

did a katian large igneous province trigger the late ordovician glaciation a hypothesis tested with a carbon cycle model abstract the ordovician is known as a period with high temperatures and high sea levels and a cooling event at the end of the period leading to the hirnantian glaciation and the first of the big five mass extinctions of marine life the cause of this cooling event remains unclear several authors correlate it with a drop in atmospheric p co 2 to a threshold permitting the ice accumulation on the gondwana supercontinent however what are the reasons of the atmospheric p co 2 decrease here we follow the hypothesis initiated by barnes 2004 that an ordovician superplume event occurred during the middle to late ordovician such an event would not only have a large impact on the ordovician biodiversification barnes 2004 but it would also be responsible for the climatic upheaval during the late ordovician by the emplacement of a low latitudinal continental basaltic province that had an impact on the atmospheric p co 2 there is no direct evidence of a superplume event or of basaltic traps and the present study is therefore a hypothetical modelling approach where we demonstrate with a numerical box model including carbon alkalinity and phosphorus cycles coupled with a 1d climate model energy balance model ebm francois and walker 1992 that such a scenario allows to explain both the mid ashgill katian global warming event known as the boda event fortey and cocks 2005 and the subsequent late ordovician hirnantian glaciation because silicate weathering is enhanced upon warm and wet climate we try to constrain the size and the latitudinal emplacement of the basaltic province leading to a sufficient consumption of atmospheric p co 2 to the threshold proposed by herrmann et al 2004 a b to initiate a glaciation on gondwana

rapid releases of metal salts and nutrients following the deposition of volcanic ash into aqueous environments deposition of volcanic ash into aqueous environments leads to dissolution of adsorbed metal salts and aerosols increasing the bioavailability of key nutrients volcanogenic fertilization events could increase marine primary productivity leading to a drawdown of atmospheric co2 here we conduct flow through experiments on unhydrated volcanic ash samples from a variety of locations and sources measuring the concentrations and fluxes of elements into de ionized water and two contrasting ocean surface waters comparisons of element fluxes show that dissolution of adsorbed surface salts and aerosols dominates over glass dissolution even in sustained low ph conditions these surface ash leachates appear unstable decaying in situ even if kept unhydrated volcanic ash from recent eruptions is shown to have a large fertilization potential in both fresh and saline water fluorine concentrations are integral to bulk dissolution rates and samples with high f concentrations display elevated fluxes of some nutrients particularly fe si and p bio limiting micronutrients are released in large quantities suggesting that subsequent biological growth will be limited by macronutrient availability importantly acidification of surface waters and high fluxes of toxic elements highlights the potential of volcanic ash leachates to poison aqueous environments in particular large ph changes can cause undersaturation of caco3 polymorphs damaging populations of calcifying organisms deposition of volcanic ash can both fertilize and or poison aqueous environments causing significant changes to surface water chemistry and biogeochemical cycles

geochemistry and sedimentology of the lower silurian longmaxi mudstone in southwestern china implications for depositional controls on organic matter accumulation abstract spatial and temporal changes of lithofacies and abundance of organic matter in mudstones control distribution of prospective unconventional petroleum reservoirs in a sedimentary basin lithofacies characterization is an essential prerequisite to understanding of organic matter accumulation depositional processes and water column chemistry this research combines geochemical analyses and detailed sedimentologic observations in order to investigate the depositional controls on organic matter abundance in the prolific black mudstone of the long 1 member of the lower silurian longmaxi formation in southwestern china six primary lithofacies deposited at variable marine water depths and under differing water column chemistry were identified from an 83 m long core based on microscopic observations of sediment texture and structure and biota and analyses of total organic carbon toc content mineralogy and trace element abundances our results show that toc content is well correlated to biogenic quartz content and the non detrital components of v u mo ni and cu suggesting the accumulation of organic matter in the studied mudstone was controlled by high paleoproductivity and anoxic water conditions the good correlations also suggest that the abundant organic matter was produced by algal blooms which are typically associated with radiolarian thrive because of the symbiotic relationship between algal and radiolarian the low mo toc ratios of the three lithofacies formed in deep anoxic environments were similar to the ratios of modern sediments deposited in anoxic euxinic environments suggesting moderate basin restriction during deposition the mudstone in the lower longmaxi formation may be part of the globally abundant organic rich mudstones of early silurian age whose depositional mechanism have yet to be fully explored the distribution of lithofacies in the studied interval shows an overall trend from deep water to shallow water depositional environments we developed a detailed depositional model to interpret the evolution of depositional environments of the lower longmaxi formation this study provides an example to how better characterize unconventional hydrocarbon systems through coupling of rigorous geochemical and sedimentological analysis

carbon isotopes and event stratigraphy near the ordovician silurian boundary yichang south china abstract the organic carbon isotope data through the unweathered ordovician silurian boundary strata at the wangjiawan riverside section which is c 180 m southeast of the wangjiawan north section the gssp for the base of the hirnantian stage upper ordovician show that a positive 13 c org excursion begins just below the base of the hirnantian stage and peaks in the lower part of the n extraordinarius biozone this is followed by an interval of slightly reduced 13 c values and a second peak of 2 above pre hirnantian values which occurs in the lower part of the n persculptus biozone upper hirnantian the peaks in 13 c org values can be correlated well with episodes of glacial expansion described from africa and peri gondwanan europe evidence from sedimentological faunal and geochemical data from south china as well as the evidence of glacial sediments in north africa all suggests a short lived glaciation of 1 ma in the ordovician south pole region consisting of at least two major pulses the first phase of gradual glacial expansion began just before the hirnantian epoch and the second phase ended with rapid melting in the late hirnantian early n persculptus biozone

the fold test in palaeomagnetism summary the fold test suggested by mcelhinny is shown to be inappropriate more correctly one should determine whether the mean direction of a group of sites from one limb of a fold may be distinguished statistically from the mean direction of a group of sites from another limb details of the application of this test are given with examples it is shown that the test indicates significance under far less severe folding than does the test suggested by mcelhinny

productivity or preservation the factors controlling the organic matter accumulation in the late katian through hirnantian wufeng organic rich shale south china abstract the wufeng organic rich shale is widespread in the upper yangtze platform and it is one of the most advantageous shale gas producers in china its deposition commenced with the onset of the boda warming event in the late katian and terminated at the hirnantian glacial maximum the depositional mechanism of the wufeng formation was poorly understood owing to its relatively thin thickness being interpreted as the result of organic matter om accumulation in a shelf setting under anoxic conditions this study integrated detailed geochemical analyses based on the core samples from three boreholes which are located in the outer middle and inner shelf of the upper yangtze platform in order to investigate the depositional environments during the deposition of the wufeng formation geochemical redox proxies mo ef u ef and v cr and productivity proxies p baxs sixs indicate that the deposition of the wufeng formation was associated with four intervals wf1 to wf4 each characterized by its unique geochemical features related to sea level fluctuations black siliceous mudstones deposited during wf1 and wf2 are relatively organic lean due to low productivity less favorable preservation conditions and terrestrial dilution whereas black siliceous mudstone deposited during wf3 and wf4 is organic rich due to high paleoproductivity and conducive preservation conditions the geochemical proxies cd mo co x mn associated with the modern upwelling settings were replicated in the wufeng formation revealing that the outer shelf of the upper yangtze platform was dominated by persistent upwelling the upwelling driven primary productivity is considered as the first order control for the om enrichment at the outer shelf of the upper yangtze platform seasonal upwelling may influence the middle shelf of the upper yangtze platform where both primary productivity and preservation played essential roles in the om accumulation in contrast the om accumulation at the inner shelf was fundamentally driven by good preservation conditions

error analysis for the determination of tectonic rotation from paleomagnetic data appendix b is available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington d c 20009 document b83 001 2 50 payment must accompany order recent determinations of tectonic rotation and flattening from paleomagnetic data have exaggerated the size of the confidence limits or error bars by about 25 this has been caused by the misuse of conventional error propagation formulas to derive one degree of freedom error bars from a two dimensional cone of confidence 95 an analytical calculation which is valid when error bars are small shows that the correct error bars are 75 to 80 of the values derived in previous studies i have used numerical integration to check on the applicability of the analytical solution and to calculate error bars when the analytical approximation cannot be used the analytical approximation may be used whenever 95 is less than 10 and the mean inclination is not too close to vertical confidence limits given for tectonic rotation and flattening in recent literature are too large and should be reduced by 20 25 narrowing the error bars in this way permits a more accurate interpretation of paleomagnetic data

kinematics of orocline and arc formation in thin skinned orogens the regional traces of folds faults and foliations found in many fold thrust belts are bent in plan view it proves valuable to distinguish between two types of bent orogens based on their kinematic evolution oroclines or rotational arcs are bent orogens in which segments of the orogen change strike during the evolution of the bend and nonrotational arcs are bent orogens in which segments of the orogen do not change strike during development of the bend the kinematic evolution of a bend that forms in a thin skinned orogen can be described in terms of three parameters the displacement path trajectories followed by points along the strike of the orogen the magnitude and distribution of tangential extension along the strike of the orogen and the change in position of the endpoints of the orogen with respect to a reference line only slight differences in the displacement path trajectory pattern determine whether an orogen evolves as a nonrotational arc or as an orocline thus the distinction between these two types of bends is not always of major tectonic significance compressional deformation along irregular continental margins or the impact of indentors on continental margins during collisional orogenies more likely leads to formation of nonrotational arcs as can be simulated with a sand wedge model interaction between a fold thrust wedge with obstacles in the foreland or with a wrench fault more likely leads to orocline formation orocline formation is also associated with noncoaxial reactivation of thrust faults tangential extension is a necessary consequence of certain displacement path trajectory patterns and can accompany development of either nonrotational arcs or oroclines two examples one from the umbrian apennines and one from the makran range demonstrate how movement on cross strike fault arrays can accommodate tangential extension in thin skinned bends

multicomponent magnetizations from the mississippian mauch chunk formation of the central appalachians and their tectonic implications previous paleomagnetic study of mississippian red beds of the mauch chunk formation from the central appalachians reported shallow inclination directions a positive fold test was obtained after thermal demagnetization typically to only 550 c the near equatorial position for north america indicated by these results has been used to support the idea of a circa 15 latitudinal tectonic offset of the acadia displaced terrain in the northern appalachians the present study of 153 samples from 29 sites occupied in the mauch chunk formation of eastern and southern pennsylvania reveals multicomponent magnetizations a characteristic component declination d 161 0 inclination i 27 8 alpha95 a95 7 9 with unblocking temperatures usually concentrated above 650 c and with dual polarity 10 sites normal 13 sites reversed is isolated in 23 sites and passes a fold test at the 99 confidence level it is interpreted as an early acquired hematitic detrital or chemical magnetization of pre alleghanian orogeny and pre kiaman reverse polarity interval age a southern hemisphere paleolatitude of 15 for the sampling area is indicated another component has generally lower unblocking temperatures which however can extend up to 650 c or more and therefore is also likely to be carried by hematite this secondary magnetization d 170 6 i 5 3 a95 5 0 isolated in 25 sites is of uniform reverse polarity and application of fold tests suggests that it is of synfolding origin a near equatorial paleolatitude 3 n at the time of acquisition is obtained consistent with permo carboniferous kiaman directions from north america incomplete removal of the secondary component can explain the previous results from the mauch chunk comparison of the present paleomagnetic results with those from similar age rocks in the canadian maritimes does not support a latitudinal offset of acadia with respect to interior north america in the early carboniferous in fact according to these and other paleomagnetic data thought to be representative of this age the atlantic bordering continents already were near to a pangea configuration the alleghanian and particularly the hercynian orogenies therefore may not be associated with the closure of a large latitudinal ocean later in the carboniferous and permian alleghanian deformation however may have resulted in the partial bending of the pennsylvanian salient on the basis of apparently systematic deviations in paleomagnetic declinations

relationship between the origin of organic rich shale and geological events of the upper ordovician lower silurian in the upper yangtze area abstract based on detailed sedimentological observations and geochemical analyses four geological events have been identified and a genetic depositional model has been established within a sequence stratigraphic framework the organic rich siliceous shale interbedded with dense bentonite layers in the transgressive systems tract 1 tst 1 is attributed to the first stage of high frequency volcanism which started at 447 62 ma associated with the collision of the cathaysia and yangtze blocks the presence of the organic fair lime mudstone shelly limestone indicates that hirnantian glaciation in the highstand systems tract hst the occurrence of organic rich siliceous shale interbedded with scarce bentonite layers in the transgressive systems tract 2 tst 2 is attributable to the second stage of low frequency volcanism which started at 443 83 ma and to postglacial effects the formation of organic fair mixed shale with silty laminae is attributed to bottom current activity in the early highstand systems tract ehst the occurrence of organic poor clay rich shale is due to terrigenous input in the late highstand systems tract lhst our research also shows that the high marine productivity caused by volcanic ash and a high burial rate in an anoxic depositional setting led to organic matter and siliceous mineral enrichment in the tst 1 and tst 2 the favorable organic matter preservation conditions and the postglacial biotic recovery played significant roles in the formation of the organic rich shale in the tst 2

lithofacies and depositional mechanisms of the ordovician silurian wufeng longmaxi organic rich shales in the upper yangtze area southern china the ordovician silurian organic rich shales in the wufeng and longmaxi formations are widespread in southern china and are the most important shale gas producers in china the shales display varying total organic carbon content ranging from 0 2 to 6 and are composed of black siliceous mudstone shelly limestone siliceous clay rich mudstone gray silty shaly interlaminated mudstone gray argillaceous mudstone and calcareous or dolomitic mudstone detailed stratigraphic correlation of these formations was achieved and a high resolution sequence stratigraphy was constructed based on the integration of well log data mineralogical geochemical and petrophysical analyses the wufeng formation and the guanyinqiao bed were interpreted to be a condensed section with four cycles of sea level fluctuation the longmaxi formation consists of three members the long 1 member was interpreted to be a third order depositional sequence that can be subdivided into a transgressive systems tract an early highstand systems tract and a late highstand systems tract within the constructed isochronal stratigraphic framework the characteristics and genetic mechanism of different shale lithofacies were studied the deposition of black siliceous mudstone of high total organic carbon in the wufeng formation and the long 1 transgressive systems tract was likely influenced by volcanic activity the guanyinqiao shelly limestone or calcareous mudstone was associated with the ordovician silurian transition when glaciation and mass extinction took place the gray silty shaly interlaminated mudstone of moderate total organic carbon in the long 1 early highstand systems tract was the product of bottom flow intrusion the deposition of gray argillaceous mudstone and calcareous or dolomitic mudstone with low total organic carbon in the long 1 late highstand systems tract resulted from enhanced terrigenous input from peripheral uplifts the distribution pattern of different lithofacies varies greatly in the upper yangtze area and this difference is a result of dissimilar sediment provenances and variable hydraulic restriction levels that were controlled by basin geometry a better understanding of the distribution pattern and depositional history of the wufeng and longmaxi formations might provide guidance for future profitable shale gas exploration

synfolding and prefolding magnetizations in the upper devonian catskill formation of eastern pennsylvania implications for the tectonic history of acadia the upper devonian catskill formation was sampled for paleomagnetic study in east central pennsylvania 41on 76ow in one area the dominant component of magnetization se is revealed over a broad spectrum of demagnetization temperatures ranging to at least 660oc a conventional fold test is positive at the 99 confidence level however statistical analysis of dispersion with incremental bedding tilt correction shows a significant peak in the precision parameter after about 3 4 unfolding the magnetization is therefore secondary with a mean direction of d 166 6 o i 1 8 o the

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

depositional environment and organic matter accumulation of upper ordovician lower silurian marine shale in the upper yangtze platform south china abstract the main controlling factors of organic matter accumulation in the upper ordovician wufeng lower silurian longmaxi formations are complex and remain highly controversial this study investigates the vertical variation of total organic carbon toc content as well as major and trace element concentrations of four ordovician silurian transition sections from the upper yangtze platform of south china to reconstruct the paleoenvironment of these deposits and to improve our understanding of those factors that have influenced organic matter accumulation in these deposits the residual toc content of the wufeng formation averages 3 2 and ranges from 0 12 to 6 0 the overlying lower longmaxi formation displays higher toc content avg 4 4 followed upsection by consistent and lower values that average 1 6 in the upper longmaxi formation the concentration and covariation of redox sensitive trace elements mo u and v suggest that organic rich intervals of the wufeng formation accumulated under predominantly anoxic conditions organic rich horizons of the lower longmaxi formation were deposited under strongly anoxic to euxinic conditions whereas organic poor intervals of the upper longmaxi formation accumulated under suboxic conditions positive correlations between redox proxies and toc contents suggest that organic matter accumulation was predominantly controlled by preservation barium excess ba xs values indicate high paleoproductivity throughout the entire depositional sequence with an increase in the lower longmaxi formation increased productivity may have been induced by enhanced p recycling as evidenced by elevated c org p tot ratios mo u covariation and mo toc values reveal that the wufeng formation was deposited under extremely restricted conditions whereas the longmaxi formation accumulated under moderately restricted conditions during the late ordovician the extremely restricted nature of ocean circulation on the upper yangtze platform in tandem with enhanced stratification of the water column promoted anoxic conditions favorable for the preservation of organic matter during early silurian time organic matter accumulation was principally controlled by changes in sea level which affected terrigenous flux redox conditions and the degree of nutrition recycling

paleomagnetism and the orocline hypothesis eldredge s bachtadse v and van der voo r 1985 paleomagnetism and the orocline hypothesis in n l carter and s uyeda editors collision tectonics deformation of continental lithosphere tectonophysics 119 153 179 oroclines were originally defined by carey as curved mountain belts which initially were straight or at feast straighter than they are today in the last few years the definition has been broadened to include any curved mountain belt regardless of its original shape since the occurrence of oroclinal bending is best recorded in the change of declination as a function of tectonic setting paleomagnetic and structural data from six potential oroclines have been compiled and analyzed to determine the amount of rotation displayed by the change of paleomagnetic declination relative to the change in strike of the fold belt the arcuate belts investigated are the sicilian calabr n arc and the umbrian arc of italy the swiss portion of the jura mountains the central portion of the appalachian mountains from pennsylvania to virginia u s a the wyoming idaho overthrust belt of western north america and the hercynides of western and central europe the jura mountains and the pennsylvania virginia portion of the appalachians fail to show significant oroclinal bending the wyoming idaho belt shows a combination of rotated possibly oroclinai and unrotated thrust sheets in the sicilian calabrian arc significant oroclinat bending caused by the impingement of the calabria peloritani nappes in the late tertiary can be demonstrated while the umbrian arc of similar age in the northern apennines also shows oroclinal bending on a smaller scale hercynian europe the only belt included in which deformation of basement rocks can be demonstrated shows oroclinal bending at least so as well as a marked original curvature 70 in its western part common to all the orociines studied in this paper is the probable impingement of a rigid block or continental margin during the orogeny causing subsequent deformation and bending of the fold belt

palaeomagnetism of the early carboniferous deer lake group western newfoundland no evidence for mid carboniferous displacement of acadia early carboniferous visean to possibly earliest namurian sedimentary rocks of the deer lake group of western newfoundland rest unconformably on grenvillian basement rocks of the canadian shield which form the western border of the early palaeozoic appalachian orogen in addition to magnetically soft magnetizations directed along the present field three families of magnetization directions are found two of them referred to as n north and s south are antiparallel and prefolding and were probably acquired during the depositional process n and s are roughly of equal frequency they have a mean direction irrespective of sign of 0 7 35 2 k 40 95 8 9 and a palaeopole 21 5 n 121 8 e 10 3 6 0 corresponding to a palaeolatitude of 20 6 s this agrees with the palaeolatitude 17 5 s determined from the somewhat older early carboniferous tournaisian terenceville formation of the avalon platform on the eastern side of the appalachian orogen in newfoundland the third magnetization referred to as h roughly horizontal has a mean direction 156 8 13 3 k 37 95 10 1 and a palaeopole 45 4 n 140 3 e 10 3 5 3 corresponding to a palaeolatitude of 7 4 n we interpret this to be an early kiaman latest carboniferous to early permian overprint probably acquired chemically the palaeolatitude determined from the h overprint agrees with that determined from early carboniferous rocks of cratonic north america west of the appalachians therefore we argue early carboniferous palaeofield determinations for cratonic north america have been strongly biased by unremoved kiaman overprints because of this and because of the good agreement between early carboniferous palaeolatitudes obtained from opposite margins of the appalachian orogen we suggest that there is at present no palaeomagnetic evidence for the previously proposed 1500 km displacement from the south of an eastern portion of the appalachians acadia relative to cratonic north america during the carboniferous

calculating ice volumes and ice flux to constrain the dimensions of a 440 ma north african ice sheet abstract geological evidence indicates that the sahara was glaciated by a large ice sheet c 440 ma ago two end member theories have been proposed for the large scale configuration of this ice mass in the large ice sheet hypothesis the sahara was covered by a continuous ice sheet that straddled north africa arabia south africa and south america in the small ice sheet hypothesis it has been argued that separate ice sheets developed in each of these areas taking these end members and an ice sheet of intermediate dimensions we investigate this problem calculating likely ice volumes and the flux of ice to the ice margin we find that the small ice sheet adequately accounts for the estimated magnitude of post glacial transgression c 45 80 m associated with ice mass decay additionally the notion of a north african arabian ice sheet within the small ice sheet hypothesis is supported by an analysis of ice stream fluxes across the sahara accounting for widespread heterogeneous flow within the ice sheet this paper provides an independent check on the likely size and extent of late ordovician ice masses with potential application to other palaeozoic ice sheet reconstructions

paleoceanographic applications of trace metal concentration data abstract recent studies have identified a range of new applications of trace metal concentration data in the analysis of paleoceanographic systems in restricted anoxic marine systems trace metal toc ratios can provide insight into the degree of watermass restriction and estimates of deepwater renewal times in such systems secular changes in sediment trace metal ratios may provide evidence of the chemical evolution of basinal deepwaters in response to differential rates of trace metal removal to the sediment the degree of deepwater restriction in silled basins is generally controlled by eustatic elevations with higher lower sea levels resulting in lesser greater watermass restriction short term ca million year drawdown of the trace metal inventory of seawater has occurred repeatedly in conjunction with oceanic anoxic events which result in elevated rates of trace metal removal to widespread anoxic facies long term eon scale changes of the trace metal composition of seawater have occurred in response to secular changes in atmospheric oceanic redox conditions and their effects on trace metal cycling caution must be exercised in evaluating trace metal patterns in paleomarine systems however 1 hydrographic analyses based on trace metal toc relationships can be undertaken only on systems that had anoxic deepwaters and 2 the influence of redox variation on trace metal accumulation patterns outweighs that of hydrographic factors in some paleomarine systems

geochemical characteristics in the longmaxi formation early silurian of south china implications for organic matter accumulation abstract the organic rich early silurian sediments longmaxi formation on the yangtze platform are considered to be one of the main source rocks in south china in order to investigate the mechanism of organic accumulation multiple geochemical proxies including redox parameters s c and trace element ratios productivity indices p and ba contents and clastic influx indicator ti al ratios are presented here from the hehua section yichang hubei province the longmaxi sediments have high toc contents 3 00 10 85 avg 5 63 low pyrite sulfur contents 0 42 1 14 avg 0 59 high p 0 02 0 44 avg 0 12 and ba contents 576 65 2542 43 ppm avg 1592 17 ppm calculated s c th u ni co v cr and v v ni ratios are 0 05 0 24 avg 0 12 0 23 9 86 avg 2 30 2 65 46 24 avg 15 46 0 27 14 42 avg 3 75 and 0 36 0 96 avg 0 75 respectively s c and trace element ratios together with pyrite morphology suggest dysoxic anoxic conditions prevailed during deposition of the longmaxi intervals which was mainly caused by a worldwide marine transgression after the melting of gondwana glaciation productivity proxies indicate that the organic rich longmaxi sediments were deposited in moderate to high primary productivity water columns the consistent ti al ratios suggest a rather homogeneous nature for the detrital supply geochemical data provide a good constraint on the accumulation of organic matter and relevant oceanic environment anoxic conditions together with relatively high productivity were likely responsible for the accumulation of organic rich sediments during the longmaxi interval

structural development of the lower paleozoic belt of south china genesis of an intracontinental orogen abstract an extensive structural study of wuyishan and surrounding areas south china brings data on the structures formed prior to the devonian unconformity building the lower paleozoic belt an ordovician tectonic event was responsible for i south directed structures in the wuyishan proper and its southern border related to both thin and thick skinned tectonics accompanied by metamorphism and crustal thickening ii north directed structures to the west of ganjiang fault and north of jiangshan shaoxing fault where only thin skinned tectonics is visible the southward deformation accommodating the shortening includes emplacement of thrust sheets involving deep crustal material and some mantle peridotite and likely repetition of continental material both responsible for crustal thickening the orogeny was due to the underthrusting of the southern part of the south china block beneath the northern part of this block closing the pre existing nanhua rift created at around 850 800 ma and involving the rift sedimentary fill in the southward thrusting the syn metamorphic tectonic piling was followed by anatexis and granite emplacement at around 440 390 ma our new u th pb epma monazite dating gives ages of 433 9 ma and 437 5 ma early silurian for the main anatectic event and a younger age of 412 5 ma late silurian early devonian for a late re heating process the lower paleozoic belt is an intracontinental orogen without oceanic suture record it shows some similarities with the cenozoic european pyrenees chain with a strong asymmetry

bathymetric and isotopic evidence for a short lived late ordovician glaciation in a greenhouse period the end ordovician glaciation is distinct among phanerozoic glaciations in that co 2 levels were generally high yet major continental ice sheets accumulated on the gondwana supercontinent new oxygen isotopic data indicate substantial changes in sea water temperatures and ice volume coinciding with glacio eustatic changes in sea level reflecting the growth and decay of the gondwana ice cap major glaciation was apparently confined to the hirnantian and was 0 5 1 m y long rather than the 35 m y of earlier estimates carbon isotope values indicate significant changes in carbon cycling as the oceans changed from a state with warm saline bottom waters to a state with cold deep water circulation and then back again we believe that the changes in the carbon cycle effected a reduction in p co 2 levels in the oceans and atmosphere and thus promoted glaciation but were unable to sustain icehouse conditions in a greenhouse world

a review of paleomagnetic results from the carboniferous of north america the concept of carboniferous geomagnetic field horizon markers results from the east coast carboniferous basin contain an important time stratigraphic horizon of possible global significance late carboniferous units are found to have mostly reversed magnetizations while older carboniferous units may have normal reverse or most frequently dual polarity magnetizations this feature records the change in geomagnetic field from a period of common polarity changes to a period of mainly reversed polarity the kiaman magnetic interval recognition of the stratigraphic position of this polarity feature provides a time line for correlation of units within and among carboniferous basins in the east coast carboniferous basin of atlantic canada this horizon has now been located at the riversdale group level early pennsylvanian namurian westphalian boundary since remanence acquisition of red sediments is often a lengthy process possibly spanning field reversal time scales red bed units pre dating and post dating this time line can in most instances be readily distinguished the former generally recording both polarities and the latter just one reverse polarity a polar displacement of at least 16 is recorded in the results from the east coast carboniferous basin paleolatitude maps show that the area was located near the equator and was displaced northwards by about 8 during the pennsylvanian it cannot be ascertained if those observations are representative of the whole of north america or merely the atlantic seaboard poles derived from other areas of north america do not all fit the regular pattern observed on the atlantic coast using the horizon marker as a tool it is suggested that those poles are post time line in age so that none of them is representative of the position of north america prior to the time line

the role of salt in fold and thrust belts davis d m and engelder t 1985 the role of salt in fold and thrust belts in n l carter and s uycda editors collision tectonics deformation of continental lithosphere tectonophysics 119 67 88 the style of deformation in thin skinned fold and thrust belts is critically dependent upon the resistance to sliding along the detachment between the mass of deforming sediments and the underlying rocks evaporites can provide an extremely weak horizon within which a basal detachment can form and along which only a relatively small shear traction can be supported fold and thrust belts that form atop a salt layer such as the appalachian plateau the franklin mountains in northwestern canada and the jura of the alps among others share several readily observable characteristics as predicted by a simple mechanical model for fold and thrust belts a detachment in salt permits a thrust belt to have an extremely narrow cross sectional taper in addition predicted orientations of the principal stress axes over a salt dtcollement are consistent with the commonly observed lack of a consistently dominant vergence direction of structures within the thrust belt other common attributes of salt basal thin skinned deformation include the presence of several widely but regularly spaced folds and abrupt changes in deformational style at the edge of the salt basin

a middle late silurian paleomagnetic pole from limestone reefs of the wabash formation indiana u s a a middle late silurian paleomagnetic pole has been obtained from reefal limestones in north central indiana eleven of 25 collected sites yielded well clustered characteristic directions after stepwise alternating field demagnetization one additional site gave the same characteristic direction after great circle analysis these 12 site level directions were used to calculate the mean paleomagnetic pole reef flank beds dip steeply about 38 away from reef centers field and petrographic studies demonstrate that part of this dip is a primary depositional dip and that part is due to a tilt caused by early postdepositional differential compaction of underlying mudstone beds present attitudes of geopetal surfaces indicate that the postdepositional component of the observed bedding dip is about 12 a 12 tilt correction to paleomagnetic directions from oppositely dipping flank beds brings the mean directions into significantly better agreement indicating that the magnetization was acquired early the presence of both normal and reversed polarities also suggests early acquisition of the characteristic remanence the mean of the site paleomagnetic poles with sites from steeply inclined flank beds corrected for 12 of tilt is 16 8 n 124 9 e k 74 a95 5 1 in good agreement with the middle silurian rose hill pole for north america

multiscale petrographic heterogeneity and their implications for the nanoporous system of the wufeng longmaxi shales in jiaoshiba area southeast china response to depositional diagenetic process

the end ordovician glaciation and the hirnantian stage a global review and questions about late ordovician event stratigraphy abstract this paper proposes a global review of hirnantian event stratigraphy the hirnantian gssp in south china is tentatively correlated with latest ordovician strata from the peri gondwanan glacial regions problems of biostratigraphical correlation are highlighted at a worldwide scale the major biostratigraphically useful fossil groups graptolites chitinozoans brachiopods conodonts acritarchs are analysed and their limits for global correlation of the uppermost ordovician are discussed palaeobiogeographical disparities are invoked as the primary cause of the difficulty in establishing an effective late ordovician global biostratigraphical scheme as an alternative correlative tool the hice hirnantian isotopic curve excursion event is often put forward in the literature however carbon isotope chemostratigraphy shows like biostratigraphy some limits to the present state of knowledge no good independent biostratigraphical control of the hice exists in both shallow carbonate deposits and deeper shaly ones recent studies have also demonstrated inconsistencies between carbon isotopic signals obtained from organic 13corg and inorganic 13ccarb carbon species further complicating the use of the hice as an isochronous benchmark all of these difficulties for hirnantian event stratigraphy are discussed in detail in order to enable them to be overcome in the future precise late ordovician and early silurian event stratigraphies are essential for the understanding of the mechanisms linked to the first of the big five extinctions

lithofacies and sequence stratigraphy of the barnett shale in east central fort worth basin texas ten barnett shale lithofacies have been recognized in a 223 ft 68 m long core from johnson county texas eight of these lithofacies match those previously identified in the main producing area of the newark east barnett shale field in the northern part of the fort worth basin but two new lithofacies have been identified in this core resedimented spiculitic mudstone lithofacies and lag deposits both of which are indicative of a relatively higher energy environment and downslope resedimentation of shallower water deposits the recognition of cyclical stacking patterns of the lithofacies condensed sections css and transgressive surfaces of erosion were the keys to establishing the sequence stratigraphic framework in these fine grained rocks which consists of seven stratigraphic intervals in the lower barnett shale and nine stratigraphic intervals in the upper barnett shale spectral gamma ray uranium and thorium logs aided in this objective and are recommended for future sequence stratigraphic studies of these and other shales the sequence stratigraphic framework reveals that the lower barnett shale in this area was deposited mainly in a low energy relatively deep water environment somewhat far from a terrigenous source area which probably lies to the northwest by contrast the upper barnett shale was deposited in an oxygenated shallower water environment which had a source area from the west and southwest sides of the basin the higher frequency of sea level fluctuation during development of the upper barnett shale most probably indicates periodic tectonic activity perhaps associated with a structural high that was susceptible to sea level fluctuations alternatively it could have resulted from the onset of glaciations in gondwanaland during this time this higher frequency may indicate that the upper barnett is chesterian in age because cyclicity was higher than during the osagean and meramecian stages if so there may be more high frequency cycles than recognized in this core siliceous sponge spicules are more common in this core than in more northerly cores so more brittle facies might prevail in the southern part of the fort worth basin high gamma ray log responses which are caused by a high total organic carbon and or in situ phosphate minerals are commonly found in css and can be used for regional correlations however high gamma ray phosphatic deposits that have been resedimented to downslope positions by sediment gravity flows are an exception to the previous statement correlation of the barnett stratigraphic intervals now provides a north to southeast stratigraphic framework along the fort worth basin relative hydrocarbon potential rhp is an organic geochemical parameter applied to this core and found to provide an indicator of marine transgressions and regressions we recommend continued testing and use of the rhp parameter for high frequency sequence stratigraphic analysis of unconventional gas shales

mo total organic carbon covariation in modern anoxic marine environments implications for analysis of paleoredox and paleohydrographic conditions 1 sedimentary molybdenum mo s has been widely used as a proxy for benthic redox potential owing to its generally strong enrichment in organic rich marine facies deposited under oxygen depleted conditions a detailed analysis of mo s total organic carbon toc covariation in modern anoxic marine environments and its relationship to ambient water chemistry suggests that 1 mo s while useful in distinguishing oxic from anoxic facies is not related in a simple manner to dissolved sulfide concentrations within euxinic environments and 2 patterns of mo s toc covariation can provide information about paleohydrographic conditions especially the degree of restriction of the subchemoclinal water mass and temporal changes thereof related to deepwater renewal these inferences are based on data from four anoxic silled basins the black sea framvaren fjord cariaco basin and saanich inlet and one upwelling zone the namibian shelf representing a spectrum of aqueous chemical conditions related to water mass restriction in the silled basin environments increasing restriction is correlated with a systematic decrease in mo s toc ratios from 45 5 for saanich inlet to 4 5 1 for the black sea this variation reflects control of mo s by mo aq which becomes depleted in stagnant basins through removal to the sediment without adequate resupply by deepwater renewal the basin reservoir effect the temporal dynamics of this process are revealed by high resolution chemostratigraphic data from framvaren fjord and cariaco basin sediment cores which exhibit long term trends toward lower mo s toc ratios following development of water column stratification and deepwater anoxia mo burial fluxes peak in weakly sulfidic environments such as saanich inlet owing to a combination of greater mo aq availability and enhanced mo transport to the sediment water interface via fe mn redox cycling and are lower in strongly sulfidic environments such as the black sea and framvaren fjord these observations demonstrate that at timescales associated with deepwater renewal in anoxic silled basins decreased sedimentary mo concentrations and burial fluxes are associated with lower benthic redox potentials i e more sulfidic conditions these conclusions apply only to anoxic marine environments exhibiting some degree of water mass restriction e g silled basins and are not valid for low oxygen facies in open marine settings such as continent margin upwelling systems

hydrothermal chert and associated siliceous rocks from the northern pacific their geological significance as indication od ocean ridge activity adachi m yamamoto k and sugisaki r 1986 hydrothermal chert and associated siliceous rocks from the northern pacific their geological significance as indication of ocean ridge activity sediment geol 47 i25 148 analyses of 42 cretaceous rock samples from deep sea drilling project dsdp leg 32 in tile northern pacific show that chert and porcellanite are enriched in fe mn p cu ba mo ni and pb relative to both triassic biogenic cherts of central japan and cretaceous dsdp cherts of leg 62 the iron enrichment up to 6 68ve fe20 as total iron is most prominent in chert immediately overlying basal basah which is the only chert free of radiolarians and veined by megaquartz containing many fluid inclusions chemical features characterized by a low ratio for a1 ai fe mn and ai z tio 2 and a high ratio for total fe2oj tio 2 mno tio 2 and mo tio 2 as well as petrological evidence indicatc that the cherts formed in an intense submarine hydrothermal environment on or near the cretaceous japanese spreading center which separated the kula plate from the pacific plate the spreading rate of the cretaceous japanese spreading center estimated from the chemical composition of the cherts was about 3 7 cm r i the rate is comparable to that inferred from the geomagnetic data

paleomagnetism of the upper devonian catskill formation from the southern limb of the pennsylvania salient possible evidence of oroclinal rotation multiple components of magnetization were isolated in the natural remanent magnetiza tion of samples of the upper devonian catskill formation red beds taken from the southern limb of the pennsylvania salient the dominant ther mally distributed component sf previously thought to predate folding is demonstrably syn folding in origins the mean direction for sf based on data from the current study and a pre vious study is declination inclination 161 6o 7 9 o a95 3 9 o pole position 127 3oe 43 1on a95 3 1 o n 14 sites although the remagnetization is clearly synfolding in most areas the relative ages of folding and remagne tization vary locally a subordinate high unblocking temperature component ht has a mean tilt corrected direction of 160o 36 o a95 16 o pole position 123 5oe 26 ion a95 15 4 o s n m 7 samples comparison of ht with the prefolding magnetization isolated in the northern limb of the salient suggests that the paleolatitude of this part of north america was about 16os and that part of the curvature of the salient was acquired during orogenesis

fracture development in paleozoic shale of chongqing area south china part one fracture characteristics and comparative analysis of main controlling factors abstract natural macro and micro fractures in the longmaxi shale lower silurian from yuye 1 well and the niutitang shale lower cambrian from yuke 1 well are characterized regional geological structural evolution and shale geochemistry including toc and mineral composition etc are analyzed the controlling factors of natural fractures in palaeozoic shale in the southeast of chongqing have been confirmed which have been analyzed qualitatively or semi quantitatively the results show that fractures are abundant in both the longmaxi shale and niutitang shale due to the multiphase strong tectonic movement in the southeast of chongqing therefore tectonic factors are the principal factors that control fracture development in the paleozoic shale of this region followed by the mineral composition of the shale vertically the mineral composition of shale in yuke 1 well has a high dispersion degree and a strong heterogeneity the dispersion coefficients of quartz and dolomite were 0 48 and 1 respectively therefore the development and distribution of fractures are controlled by quartz and dolomite content in the niutitang shale moreover the quartz content shows positive correlation with the fractures quantity and fractures are most abundant where dolomite content up to 64 7 while the mineral composition of shale in yuye 1 well has a low dispersion degree and a strong homogeneity in a vertical position the dispersion coefficients of quartz and plagioclase were 0 15 and 0 26 respectively which shows unconspicuous control effect for fractures therefore the development and distribution of fractures are mainly controlled by the toc content moreover the toc content shows positive correlation with the fractures quantity fractures are sealed by calcite quartz and pyrite although sealed fractures do not contribute to the permeability of the reservoir they are important planes of weakness that tend to be reactivated by hydraulically induced fractures sem images show that intergranular pore is connected by microfractures thereby the validity of porosity has been improved the mixed network of microfractures and micropore provide enhanced permeability or storage capacity for the reservoir

statistical significance of the fold test in palaeomagnetism summary the significance of the change in direction dispersion on applying the fold test in palaeomagnetism is used as the criterion for deciding whether or not the fold test has statistical significance a set of tables is compiled which can be used for quick application of the test

subduction zone volcanic ash can fertilize the surface ocean and stimulate phytoplankton growth evidence from biogeochemical experiments and satellite data volcanoes confront earth scientists with new fundamental questions can airborne volcanic ash release nutrients on contact with seawater thereby excite the marine primary productivity mpp and most notably can volcanoes through oceanic fertilization affect the global climate in a way that is so far poorly understood here we present results from biogeochemical experiments showing that 1 volcanic ash from subduction zone volcanoes rapidly release an array of nutrients co limiting algal growth in vast oceanic areas 2 at a speed much faster minute scale than hitherto known and that marine phytoplankton from low iron oceanic areas can swiftly within days utilize iron from volcanic sources we further present satellite data possibly indicating an increase of the mpp due to the seaward deposition of volcanic particulate matter our study supports the hypothesis that oceanic iron fertilization with volcanic ash may play a vital role for the development of the global climate

changes in marine productivity and redox conditions during the late ordovician hirnantian glaciation abstract changes in marine productivity and redox conditions during the end ordovician hirnantian glaciation and ordovician silurian transition were investigated through mo isotope and major and trace element analyses of the wangjiawan hubei province and nanbazi guizhou province sections from the yangtze platform of south china katian shales of the wufeng formation which yield the graptolites dicellograptus complanatus dicellograptus complexus and paraorthograptus pacificus were deposited under euxinic conditions at both localities as shown by high mo ef u ef and 98 mo values a major sea level regression during the hirnantian glaciation resulted in shallowing and a shift toward better oxygenated conditions within the yangtze sea as well as deposition of thin bedded siliceous sediments calcirudite debris flows and limestone turbidites of the kuanyinchiao formation the base of which correlates with the first phase of the end ordovician mass extinction the termination of the hirnantian glaciation at the top of the kuanyinchiao formation was associated with a major sea level transgression a rapid expansion of euxinia in the yangtze sea as documented by a return of high mo ef u ef and 98 mo values and the second phase of the mass extinction during which the cool adapted hirnantian fauna went extinct the long term cooling trend of the middle and late ordovician which culminated in the hirnantian glaciation was driven by enhanced burial of organic carbon as documented by 13 c carb 13 c org and 34 s py records increased organic carbon burial was linked to high rates of marine productivity as shown by high toc and biogenic ba concentrations especially at the deeper less restricted wangjiawan locale producing the hice hirnantian isotopic curve excursion 13 c carb excursion the locus of organic carbon burial during the hirnantian crisis shifted to deeper water environments that were located outside the study region the relatively rapid onset and termination of the hirnantian glaciation were probably due to crossing of tipping points in the late ordovician climatic oceanic system

implications of early devonian poles from the canadian arctic archipelago for the north american apparent polar wander path lower devonian red beds from the upper member of the peel sound formation at prince of wales island canadian arctic yield two different paleopoles at 25n 099e and at 01n 091e the first one being

global and regional controls on marine redox changes across the ordovician silurian boundary in south china abstract the ordovician silurian o s transition coincided with significant environmental and biological changes in south china the yangtze platform experienced both global and regional events at this time including sea level fluctuations tectonic movements volcanic eruptions mass extinction and widespread anoxia the o s transitional strata of the yangtze platform comprise organic rich black shales that are an important oil source rock to explore the evolution of watermass chemistry and its relationship to organic matter accumulation we conducted an integrated fe s c geochemical study i e fe speciation 13corg 34spy pyrite s and toc of the o s boundary sections at datianba chongqing municipality and shuanghe sichuan province these sections were located in the restricted inner yangtze sea in contrast to the previously studied wangjiawan section which was deposited in a more open setting of the outer yangtze sea in contrast to the well oxygenated conditions at wangjiawan the datianba and shuanghe sections record persistently anoxic and episodically euxinic conditions during the hirnantian which can be explained by the unique paleogeography and restricted hydrography of the inner yangtze sea we propose that the regional kwangsian orogeny which was driven by collision of the yangtze and cathaysia blocks played a key role in basin development watermass chemistry changes and accumulation of wufeng formation black shales within the yangtze sea the more widespread black shales of the lower silurian lungmachi formation were linked to the post hirnantian global marine transgression

quantifying vertical axis rotation in curved orogens correlating multiple data sets with a refined weighted least squares strike test 1 map scale curvature is a fundamental feature of most contractional orogenic belts and is central to understanding the kinematic and dynamic evolution of mountain systems paleomagnetic analysis combined with detailed structural studies is the most robust means of quantifying vertical axis rotations that produce curvature over a range of temporal and spatial scales this paper explores how vertical axis rotations can best be evaluated for multiple data sets by applying a weighted least squares method to the classic strike test this refined method provides measures of best fit slope confidence interval and goodness of fit between map scale structural trend paleomagnetic rotations and deformation fabric orientations structural trend is estimated by averaging fold axial trace formation contact and bed strike data over kilometer scale areas paleomagnetic and deformation fabric site mean orientations and measurement uncertainties are estimated using vector and bootstrap statistics weighting factors are estimated from combined measurement uncertainty structural noise related to small scale block rotation and stress strain refraction and variations in restoration paths the number of sites needed to obtain a significant confidence interval in strike test slope is a function of combined uncertainty in paleomagnetic or deformation fabric directions and the total range in structural trend around a curved orogen improved estimates of strike test slope and rotation thus require systematic sampling with a wide distribution of sites evaluation of appropriate weighting factors and statistical analysis a case study is presented that highlights application of this refined method to paleomagnetic and deformation fabric data sets from the wyoming salient of the sevier thrust belt paleomagnetic data yield a strike test slope of 0 76 0 11 indicating that the wyoming salient is a progressive arc with 3 4 secondary curvature related to vertical axis rotation synchronous with large scale thrusting and 1 4 initial curvature finite strain anisotropy of magnetic susceptibility and mesoscopic structural orientations which are related to early layer parallel shortening all yield strike test slopes of 0 9 0 1 comparing these slopes with paleomagnetic results indicates that deformation fabrics had initial curvature and thus cannot be used alone to accurately estimate rotations by integrating systematic paleomagnetic and structural data using statistical analysis curvature models for the wyoming salient are closely constrained

paleomagnetic evaluation of the orocline hypothesis in the central and southern appalachians the axial traces of the major appalachian folds change azimuthal direction from a ne sw orientation to a n s orientation in the area of the pennsylvania salient and swing back to a ne sw orientation in the vicinity of the virginia reentrant all available paleomagnetic data from the folded appalachians have been examined to test the appalachian orocline hypothesis pre deformational site mean directions from suitable studies were rotated by the amount required to bring the strike of the sampled beds into coincidence with an average trend of the central and southern appalachians n35e a comparison of clustering of site means before and after this correction reveals that in all cases unbending of the arc causes site mean directions to disperse this dispersal demonstrates that the curvature of the appalachian orogen is to a very large degree a primary feature rather than a feature which resulted from the bending of initially straight fold axes

a weathering hypothesis for glaciation at high atmospheric pco2 during the late ordovician new paired carbonate and organic carbon isotope analyses from nevada usa together with a consideration of the effects of mountain building and ice sheet coverage of the continents on atmospheric pco2 lead to a new hypothesis for the cause of the late ordovician glaciation we suggest that the taconic orogeny which commenced in the late middle ordovician caused a long term decline in atmospheric pco2 through increased weatherability of silicate rocks ice sheet growth was triggered when pco2 decreased to a threshold of 10 present atmospheric level and proceeded by positive ice albedo feedback in the midst of glaciation atmospheric pco2 began to rise as continental silicate weathering rates declined in response to coverage of weathering terrains by ice sheets at first this enhanced greenhouse effect was overcompensated for by ice albedo effects ultimately however atmospheric pco2 reached a level which overwhelmed the cooling effects of ice albedo and the glaciation ended the isotope results can be interpreted to indicate that atmospheric pco2 rose during the glaciation consistent with other proxy information although alternative interpretations are possible the large positive carbonate isotope excursion observed in late ordovician rocks around the world is explained as the expected response to increased carbonate platform weathering during glacioeustatic sea level lowstand rather than as a response to increased organic carbon burial

facies patterns and geography of the yangtze region south china through the ordovician and silurian transition abstract lithofacies and biofacies changes through the ordovician and silurian transition on the yangtze platform are coincident with stepwise mass extinctions recovery events global sea level changes and regional palaeogeographic configurations facies patterns through three intervals the late mid ashgill hirnantian and early rhuddanian indicate that black shale occupied most of the yangtze platform region during the late mid ashgill and early rhuddanian while the hirnantian possesses more diverse facies types the black shale was replaced by carbonate facies during the hirnantian coincident with a global sea level low stand biofacies changes from the late mid ashgill graptolitic to the hirnantian shelly facies were apparently signalled by gradual and diachronous existence of a mixed facies the manosia facies in the yangtze region however the biofacies change was abrupt from the hirnantian to the early rhuddanian when graptolitic facies occupied most areas on the yangtze platform leaving only a very narrow limited belt of shelly facies along the southern margin of the platform in northern guizhou the early rhuddanian unified biofacies pattern is a result of a global sea level rise which may be synchronized with a recovery bioevent of graptolites after hirnantian mass extinction

a chronology of paleozoic sea level changes sea levels have been determined for most of the paleozoic era 542 to 251 million years ago but an integrated history of sea levels has remained unrealized we reconstructed a history of sea level fluctuations for the entire paleozoic by using stratigraphic sections from pericratonic and cratonic basins evaluation of the timing and amplitude of individual sea level events reveals that the magnitude of change is the most problematic to estimate accurately the long term sea level shows a gradual rise through the cambrian reaching a zenith in the late ordovician then a short lived but prominent withdrawal in response to hirnantian glaciation subsequent but decreasingly substantial eustatic highs occurred in the mid silurian near the middle late devonian boundary and in the latest carboniferous eustatic lows are recorded in the early devonian near the mississippian pennsylvanian boundary and in the late permian one hundred and seventy two eustatic events are documented for the paleozoic varying in magnitude from a few tens of meters to 125 meters

late ordovician mass extinction a new perspective from stratigraphic sections in central nevada integrated sequence stratigraphic biostratigraphic and chemostratigraphic analyses of three stratigraphic sections in central nevada indicate that late ordovician glaciation induced sea level fall produced diachronous stepwise faunal turnover in graptolites conodonts chitinozoans and radiolarians and also triggered a strong but transient positive 13c excursion this pattern is very different from that described for most mass extinction events

remagnetization of the tonoloway formation and the helderberg group in the central appalachians testing the origin of syntilting magnetizations summary palaeomagnetic rock magnetic geochemical and strain studies of the helderberg group and the tonoloway formation in the valley and ridge province of west virginia were performed to test the origin of syntilting magnetizations and to test the mechanisms of chemical remanent magnetization crm acquisition the test for a connection between strain and remagnetization was performed by comparing the types and levels of strain with the magnetic properties between the generally coarse grained thickly bedded helderberg and the thinly bedded and finer grained tonoloway standard tilt tests as well as optimal differential untilting from two transects on the wills mountain anticline indicate that the helderberg contains a pervasive late syntilting 30 per cent untilting characteristic remanent magnetization chrm whereas the tonoloway contains a well defined early syntilting chrm 1 76 per cent untilting as well as a chrm 2 which is similar to the chrm in the helderberg the chrms reside in magnetite the rock magnetic results from the two units are similar although the helderberg samples have a finer apparent grain size perhaps as a result of magnetic hardening strain data reveal an apparent correlation between the syntilting magnetizations and types degrees of pressure solution strain pressure solution strain is higher in the helderberg and lower in the tonoloway strain may have caused rotation of magnetic minerals but it not clear that the differences in strain between the units were high enough to cause the rotations that are needed to explain the tilt test results several other viable hypotheses were also investigated one hypothesis is a strain enhanced chemical process that caused dissolution and precipitation of new magnetite in solution structures during folding a preliminary test of this hypothesis produced inconclusive results another hypothesis consistent with some of the characteristics of the magnetizations in the helderberg and tonoloway units is that the rocks were partially to completely remagnetized by a piezoremanent remagnetization process geochemical results show that origin of the remanence carrying grains cannot be attributed to orogenic type fluids but were probably caused by a burial diagenetic process

paleo environmental cyclicity in the early silurian yangtze sea south china tectonic or glacio eustatic control abstract the yangtze sea of the south china craton experienced strong environmental perturbations during the first 5 6 myr of the silurian the lower silurian lungmachi formation in the jiaoye 1 drillcore chongqing china records three sea level cycles stratigraphic sequences characterized by rapid deepening at the base of each cycle followed by slow shallowing each deepening event was associated with shifts toward higher marine productivity more intensely reducing bottomwater conditions reduced watermass restriction lower detrital input and enhanced siliciclastic weathering intensity we infer control by glacio eustasy in which deglacial sea level rises and concurrent climatic warming triggered the observed environmental changes shallowing was associated with renewed glaciation and characterized by the opposite set of conditions the results of this study thus provide evidence in support of continued continental glaciation during the early silurian i e following the termination of the major end ordovician hirnantian glaciation the study core also exhibits a long term shallowing trend through the entire lower silurian the origin of which may have been tectono epeirogenic uplift of the south china craton during the kwangsian orogeny

a preliminary global map of the vector lunar crustal magnetic field based on lunar prospector magnetometer data processing and mapping of the lunar prospector magnetometer data is supported by the nasa discovery data analysis program

mechanisms of shale gas storage implications for shale gas exploration in china this article reviews the mechanisms of shale gas storage and discusses the major risks or uncertainties for shale gas exploration in china at a given temperature and pressure the gas sorption capacities of organic rich shales are primarily controlled by the organic matter richness but may be significantly influenced by the type and maturity of the organic matter mineral composition especially clay content moisture content pore volume and structure resulting in different ratios of gas sorption capacity gsc to total organic carbon content for different shales in laboratory experiments the gsc of organic rich shales increases with increasing pressure and decreases with increasing temperature under geologic conditions assuming hydrostatic pressure gradient and constant thermal gradient the gsc increases initially with depth due to the predominating effect of pressure passes through a maximum and then decreases because of the influence of increasing temperature at greater depth this pattern of variation is quite similar to that observed for coals and is of great significance for understanding the changes in gsc of organic rich shales over geologic time as a function of burial history at an elevated temperature and pressure and with the presence of moisture the gas sorption capacities of organic rich shales are quite low as a result adsorption alone cannot protect sufficient gas for high maturity organic rich shales to be commercial gas reservoirs two models are proposed to predict the variation of gsc and total gas content over geologic time as a function of burial history high contents of free gas in organic rich shales can be preserved in relatively closed systems loss of free gas during postgeneration uplift and erosion may result in undersaturation the total gas contents lower than the sorption capacity and is the major risk for gas exploration in marine organic rich shales in china

further paleomagnetic evidence for oroclinal rotation in the central folded appalachians from the bloomsburg and the mauch chunk formations renewed paleomagnetic investigations of red beds of the upper silurian bloomsburg and the lower carboniferous mauch chunk formations were undertaken with the objective of obtaining evidence regarding the possibility of oroclinal bending as contributing to the arcuate structural trend of the pennsylvania salient these formations crop out on both limbs of the salient and earlier but less definitive paleomagnetic studies on these units indicate that early acquired magnetizations can be recovered oriented samples were obtained from nine sites on the southern limb of the salient and eight sites from the northern limb in the bloomsburg the natural remanent magnetizations are multivectorial dominated by a component b with a distributed spectrum of unblocking temperatures ranging up to 670 c and a component c with a higher and very discrete distribution of unblocking temperatures the b component is uniformly of reverse polarity shows a statistically significant synfolding character and represents a late paleozoic remagnetization the c component passes fold tests with normal and reverse polarity site means the c component directions from the southern limb 345 1 31 6 and the northern limb 359 3 29 7 are significantly different in declination 14 2 10 4 but not in inclination 1 9 9 samples were also analyzed from seven additional sites in the mauch chunk on the southern limb of the salient inclusion of these new data gives a revised estimate of the difference between southern and northern limb mean directions of prefolding magnetizations in the mauch chunk of 23 3 12 5 in declination and 4 8 11 in inclination paleomagnetic data from the bloomsburg mauch chunk and revised results recently reported for the upper devonian catskill formation together indicate 22 8 11 9 of relative rotation accounting for approximately half the present change in structural trend around the pennsylvania salient the oroclinal rotation can be regarded as a tightening of a less arcuate depositional package that developed across a basement reentrant to achieve a curvature closer to that of the earlier zigzag continental margin outline

merging sequence stratigraphy and geomechanics for unconventional gas shales the recent revelation of vast global quantities of potentially gas and oil productive shales has paved the way for rapid advancements in understanding their geological properties many of which affect their geomechanical properties and ultimately reservoir operations and performance because of shale s unique and very intricate geological physical and mechanical properties at all scales from nano to macro scale abousleiman et al 2010 compared with sandstones and carbonates the ad jective unconventional has often been applied to their characterization although many shale characteristics are different than those of sandstones and carbonates and require new technologies to measure them other characteristics mentioned below are similar as such customized conventional methodologies and concepts can be applied to exploration and production of shale gas and oil

a sulfidic driver for the end ordovician mass extinction the end ordovician extinction consisted of two discrete pulses both linked in various ways to glaciation at the south pole the first phase starting just below the normalograptus extraordinarius zone particularly affected nektonic and planktonic species while the second pulse associated with the normalograptus persculptus zone was less selective glacially induced cooling and oxygenation are two of many suggested kill mechanisms for the end ordovician extinction but a general consensus is lacking we have used geochemical redox indicators such as iron speciation molybdenum concentrations pyrite framboid size distribution and sulfur isotopes to analyze the geochemistry in three key hirnantian sections these indicators reveal that reducing conditions were occasionally present at all three sites before the first pulse of the end ordovician extinction and that these conditions expanded towards the second pulse even though the n extraordinarius zone appears to have been a time of oxygenated deposition pyrite is significantly enriched in 34s in our sections as well as in sections reported from south china this suggests a widespread reduction in marine sulfate concentrations which we attribute to an increase in pyrite burial during the early hirnantian the s isotope excursion coincides with a major positive carbon isotope excursion indicating elevated rates of organic carbon burial as well we argue that euxinic conditions prevailed and intensified in the early hirnantian oceans and that a concomitant global sea level lowering pushed the chemocline deeper than the depositional setting of our sites in the n persculptus zone an interval associated with a major sea level rise our redox indicators suggests that euxinic conditions and ferruginous in some places encroached onto the continental shelves in our model the expansion of euxinic conditions during the n extraordinarius zone was generated by a reorganization of nutrient cycling during sea level fall and we argue overall that these dynamics in ocean chemistry played an important role for the end ordovician mass extinction during the first pulse of the extinction euxinia and a steepened oxygen gradient in the water column caused habitat loss for deep water benthic and nektonic organisms during the second pulse the transgression of anoxic water onto the continental shelves caused extinction in shallower habitats

sequence stratigraphy and depositional environments of the shamokin union springs member marcellus formation and associated strata in the middle appalachian basin organic carbon rich shales of the lower marcellus formation were deposited at the toe and basinward of a prograding clinothem associated with a mahantango formation delta complex centered near harrisburg pennsylvania distribution of these organic carbon rich shales was influenced by shifts in the delta complex driven by changes in rates of accommodation creation and by a topographically high carbonate bank that formed along the findlay algonquin arch during deposition of the onondaga formation specifically we interpret the union springs member shamokin member of the marcellus formation and the onondaga formation as comprising a single third order depositional sequence the onondaga formation was deposited in the lowstand to transgressive systems tract and the union springs member was deposited in the transgressive highstand and falling stage systems tract the regional extent of parasequences systems tracts and the interpreted depositional sequence suggest that base level fluctuations were primarily caused by allogenic forcing eustasy climate or regional thermal uplift or subsidence instead of basement fault reactivation as argued by previous workers paleowater depths in the region of marcellus formation black mudrock accumulation were at least 330 ft 100 m as estimated by differences in strata thickness between the northwestern carbonate bank and basinal facies to the southeast geochemical analysis indicates anoxic to euxinic bottom water conditions these conditions were supported by a deep stratified basin with a lack of circulation

paleomagnetism of the silurian devonian andreas redbeds evidence for an early devonian supercontinent two components of magnetization were isolated in the silurian devonian andreas redbeds of the central appalachians of pennsylvania lat 40 75 n long 75 78 w a thermally distributed synfolding b component and a thermally discrete pre alleghenian age folding c component the c component mean direction and associated pole position correspond to a silurian devonian paleolatitude for the andreas location of about 35 s which in conjunction with early devonian results from gondwana is consistent with an early devonian supercontinent configuration

cyanobacterial blooms tied to volcanism during the 5 m y permo triassic biotic crisis widespread but episodic deposition of cyanobacterial mats occurred during the 5 m y permo triassic biotic crisis providing a critical record to decipher the long term stressful environmental conditions and thus a linkage with the killer here we document the timing and duration of these blooms indicated by lipid biomarkers and microbialites throughout south china and compare them to the timing of volcanic activity the initial cyanobacterial bloom has the longest duration and is associated with a prominent eu anomaly in southwestern china where the most intensive volcanism has been proposed to occur suggesting a causal relationship subsequent cyanobacterial blooms in the early triassic are associated with known volcanic events in south china and also with the most voluminous siberian flood basalts and with the largest negative carbon isotope excursions thus it appears that volcanic activity has had a significant impact on microbial development in south china south china volcanism around the permian triassic boundary ptb could have played a much larger role in biotic changes of both bacterial and calcified faunal ecosystems than previously thought the well known siberian volcanism is proposed herein on the basis of the current compilation of dating data to protract the early triassic faunal recovery rather than to cause the end permian extinction

the geochemical characteristics and factors controlling the organic matter accumulation of the late ordovician early silurian black shale in the upper yangtze basin south china abstract organic rich black shale of the upper yangtze basin from the late ordovician and early silurian is considered an excellent source rock in south china the formation and preservation conditions of this resource are revealed by its geochemical characteristics in this study geochemical indices including redox indices v v ni v cr v sc and ni co and primary productivity indices p ti and ba al and paleoclimate clastic flux and sedimentary rate analyses are presented to investigate the accumulation mechanism of organic matter redox indices suggest that a stagnant anoxic environment predominated in the upper yangtze basin during accumulation of wufeng and longmaxi formations in contrast ventilated and oxygenated marine conditions pervaded the upper yangtze basin during deposition of linxiang and guanyinqiao formations the concentrations of v and u demonstrate that accumulation of organic matter was mainly controlled by redox conditions besides such factors as clastic fluxes fresh water inflows or a mixed deposition with a rapid sedimentary rate cannot be ignored due to their influences on organic matter enrichment and preservation however weak co variance relationship of toc content and productivity proxies including p ti and ba al demonstrates that the accumulation of organic matter was not controlled by primary productivity results of the present study suggest a depositional model that stresses the importance of tectonic movements and glacial events on the accumulation and preservation of organic matter the model shows that the upper yangtze basin was a semi restricted basin system influenced by the isolation of xuefeng but also it implies that oxygen depleted bottom water of the basin favored the accumulation and preservation of sedimentary organic matter resulting in the formation of organic rich black shale

factors controlling organic matter accumulation in the upper ordovician lower silurian organic rich shale on the northeast margin of the upper yangtze platform evidence from petrographic and geochemical proxies abstract organic rich shales are widespread in the upper ordovician lower silurian wufeng longmaxi formations on the northeastern margin of the upper yangtze platform and these shales have been recognized to be the hydrocarbon source rocks and shale gas reservoirs with the greatest development potential in china however organic matter accumulation in these shales needs further research especially in the areas which experienced an extensive upwelling and volcanism here this work integrates detailed petrographic and geochemical proxies namely redox sensitive trace elements rstes and ratios of si al ti al from two ordovician silurian sections on the northeast margin of upper yangtze platform in order to understand the depositional environment and identify the major factors controlling the organic matter accumulation during the ordovician silurian transition data of si al and ti al ratios indicate that the deposition of black gray siliceous mudstones in the lower wufeng formation commenced with a transgression triggered by the boda warming event which led to a reduced detrital input based on rstes the black carbonaceous shales of the upper wufeng formation are organic rich owing to an elevated primary productivity caused by seasonal upwelling driven by the vigorous thermohaline circulation abundant nutrients supplied by the post glacial transgression and a mass biotic recovery of marine microorganisms stimulated productivity and further strengthened the depletion of oxygen in the water column which lead to high concentrations of organic matter in lower longmaxi formation although the water column conditions were not conducive to the accumulation of organic matter it was possible that the increased productivity from upwelling resulted in relatively high organic matter contents in the middle longmaxi formation the rstes especially cd mo co mn reveal that the organic matter accumulation of the wufeng longmaxi formation during ordovician silurian transition may have been primarily controlled by the preservation conditions and also influenced by the marine primary productivity and the detrital input

tracking silurian eustasy alignment of empirical evidence or pursuit of deductive reasoning abstract sea level is not static but liable to fluctuations due to addition or subtraction of water in the world s oceans as well as changes to the shape and holding capacity of ocean basins relative changes in sea level are well supported by the rock record on a regional scale whether or not global eustatic changes are evident and how frequently they occurred during any given interval of time is a matter of contention among stratigraphers opinions have evolved over the last century with arguments based on refinements in biostratigraphy chemostratigraphy radiometric dating and conceptual advances in sequence stratigraphy derived from technological advances in seismic stratigraphy the pulsation theory of a w grabau 1936 attributed to paleozoic strata a global history of 11 highstands distributed through a sequence with 21 subdivisions in 1977 peter vail and associates from the exxon production research company independently interpreted a similar paleozoic history showing 10 second order highstands but distributed over 19 subdivisions vail s approach was model based and followed a deductive path while grabau s was based on inductive reasoning recent refinements in a paleozoic sea level curve by haq and schutter 2008 are based on the same deductive approach taken by the vail group but pinned to patterns in sequence stratigraphy drawing on the silurian system as a paleozoic sample the timing frequency and magnitude of sea level highstands deduced by haq and schutter are compared with those promulgated by the author from the mid 1980s onward using empirical evidence more in line with grabau s methodology both apply the concept of geographic reference areas but haq and schutter identify 50 more silurian highstands over an interval lasting 27 7 million years eight out of 10 silurian highstands identified by this author match or overlap 8 out of 15 highstands recognized by haq and schutter at issue is which if any qualify as eustatic signals with respect to current databases for biostratigraphic correlation evaluation is based on evidence reviewed from iowa new york norway estonia and austria in the paleogeographic context of three independent silurian continents

negative δ13ccarb shifts in upper ordovician hirnantian guanyinqiao bed of south china linked to diagenetic carbon fluxes abstract the late ordovician hirnantian glaciation coincided with a major perturbation of the global carbon cycle characterized by large positive excursions of 13ccarb and 13corg known as the hirnantian carbon isotopic excursion hice previous studies from south china have reported a positive shift in 13corg but ambiguous trends in carbonate carbon isotopes to better define 13ccarb variation through the ordovician silurian o s transition in south china we investigated multiple components brachiopods micritic matrix and microspar cement in five study sections representing shallow shelf to deep basin facies across the yangtze block all sections exhibit negative 13ccarb shifts near the base of the hirnantian stage with small shifts in two sections to between 2 and 1 and large shifts in three sections mostly