glacial and syntectonic sedimentation the upper proterozoic kingston peak formation southern panamint range eastern california a sedimentological stratigraphic study of the upper proterozoic kingston peak formation in the southern panamint range shows that it was deposited under glacial conditions with contemporaneous volcanism and tectonic activity evidence for glaciation rests primarily upon 1 the homogeneity thickness and lateral extent of two diamictite units 2 the facies association of the diamictite and 3 presence of striated stones and dropstones within the formation elsewhere in the death valley area in the panamint range pillowed basalt interbedded with diamictite demonstrates synchronous subaqueous volcanism lower kingston peak units rest on a variable substrate and locally overlap faults indicating tectonism prior to deposition tectonism during kingston peak deposition is inferred from abrupt thickness changes and buried faults sedimentation was chiefly on a submerged continental platform and locally terrestrial during a period of incipient rifting two ice advances are recorded with associated sea level fluctuations the formation thickens northward from 40 to about 1 200 m over 40 km initial sediments were fine grained and in basins a few kilometres across nearby islands provided coarse debris overlying sandstone and conglomerate indicate regression predominantly massive diamictite as much as 450 m thick and interpreted as lodgment till or glacioma rine sediment records the first ice advance a northward increase in diamictite thickness decrease in clast size and facies change from diamictite to argillite and graywacke suggest a southern source overlying laminated limestone marks a transgression succeeding interbedded sandy limestone thick bedded graywacke and parallel laminated siltstone and sandstone double in thickness over a few kilometres demonstrating local subsidence and renewed terrigenous input trough cross laminated arkosic sandstone and conglomerate overlain by predominantly massive diamictite as much as 190 m thick with a locally erosive base represent glaciofluvial deposits and lodgment till and record the second ice advance

meteoric stabilization and preservation of limestone within the late proterozoic beck spring dolomite of eastern california petrographic and geochemical study of limestone silicified carbonate and dolostone indicates that meteoric diagenetic processes and paleogeographic position played important roles in the stabilization and preservation of limestone within the pervasively dolomitized beck spring dolomite the authors conclude that beck spring marine cement allochems precipitated as aragonite and high magnesium calcite in the vicinity of saratoga spring these metastable mineralogies were dissolved eroded stabilized to calcite and replaced by silica through interaction with meteoric waters early stabilization of limestone components along the margin of the amargosa basin apparently decreased susceptibility to subsequent dolomitization

soil gas survey for tracing seismogenic faults a case study in the fucino basin central italy soil gas he rn co2 and ch4 surveys were performed to test their sensitivity for locating fault or fracture systems when masked by unconsolidated lithologies and to investigate the gas bearing properties of seismogenic faults the fucino basin central italy was chosen as a test site because it displays a network of surface and shallow buried active faults within the valley floor which were partially reactivated during the 1915 avezzano earthquake ms 7 0 the highest radon values were found aligned along the most important faults especially along the san benedetto gioia dei marsi fault sbgmf to the east and in the northwestern sector where the avezzano celano fault acf meets the northwestern prolongation of the 1915 coseismic rupture moderately anomalous values of radon occur along the faults located in the depression of the historical lake trasacco fault tf and ortucchio fault of anomalous values of co2 rn and he were detected north of borgo ottomila in a zone where coseismic scarps and liquefaction phenomena were responsible for a pervasive brittle deformation during the 1915 earthquake highest helium values prevail in the western part of the plain in correspondence with a horst structure bounded by the tf and considered to be the extension of the vallelonga trasacco ridge results of this research confirm the possible usefulness of soil gas methods for locating some tectonic faults when covered by unconsolidated deposits the study provides some clues on the spatial influence of tectonics and geology on deeply seated gas migration toward the surface

an oscillating trend in phanerozoic non skeletal carbonate mineralogy textural and compositional data on ancient ooids and cements suggest the existence of an oscillating phanerozoic temporal trend in non skeletal carbonate mineralogy the trend shows good correlation with eustatic climatic oscillations proposed by others the most likely mechanism appears to be plate tectonically influenced oscillations in pco2 the vapour pressure of co2 rather than change in oceanic mg ca ratio

distal degassing of radon and carbon dioxide on galeras volcano colombia abstract diffuse degassing at galeras volcano colombia was studied during three consecutive field seasons from 1993 to 1995 measurements of222rn and co2 were made at 30 stations which were distributed on the volcano and on regional faults intersecting the edifice time series data show a decline of radon soil gas of up to 50 prior to a m 2 8 earthquake on 12 august 1993 at stations located near the epicenter and on the volcano near the location of earthquake swarms which occurred in april 1993 november december 1993 and march 1995 the onset of volcanic seismic activity tornillos on 9 august 1994 was preceded by anomalous soil gas increases at six stations located on the flanks of the volcano on the southwestern flank radon increased from 51 to 130 pci 1 between 7 and 14 august while on the northern flank radon concentrations began to increase 19 days before the appearance of tornillos in general stations close to the crater showed the largest radon increases soil gas distributions and carbon isotope data suggest that diffuse degassing on the volcano is structurally controlled and that the abundance of co2 in soil gas on the edifice cannot be taken as an indicator for the presence of magmatic gases radon soil gas concentrations and the222rn emanating226ra concentration increase near faults whereas co2 concentrations are more variable but commonly are higher on the volcano than near faults 13c values in soil co2 vary between 8 5 and 23 2 with 13c values more enriched than 15 found only in the vicinity of faults or sites prone to earthquake swarms this suggests a magmatic origin of co2 soil gas only near faults and an almost impermeable edifice in unfractured areas the observed correlations between seismic activity and soil degassing provide further evidence that soil gas studies especially when correlated to other methods of volcano surveillance such as seismicity and deformation may be useful in forecasting volcanic and seismic events

demise of ediacaran dolomitic seas marks widespread biomineralization on the siberian platform the trigger for biomineralization of metazoans in the terminal ediacaran ca 550 ma has been suggested to be the rise of oxygenation or an increase in seawater ca concentration but geochemical and fossil data have not been fully integrated to demonstrate cause and effect here we combine the record of macrofossils with early marine carbonate cement distribution within a relative depth framework for terminal ediacaran to cambrian successions on the eastern siberian platform russia to interrogate the evolution of seawater chemistry and biotic response prior to ca 545 ma the presence of early marine ferroan dolomite cement suggests dominantly ferruginous anoxic aragonite dolomite seas with a very shallow oxic chemocline that supported mainly soft bodied macrobiota after ca 545 ma marine cements changed to aragonite and or high mg calcite and this coincides with the appearance of widespread aragonite and high mg calcite skeletal metazoans suggesting a profound change in seawater chemistry to aragonite seas with a deeper chemocline by early cambrian stage 3 the first marine low mg calcite cements appear coincident with the first low mg calcite metazoan skeletons suggesting a further shift to calcite seas we suggest that this evolution of seawater chemistry was caused by enhanced continental denudation that increased the input of ca into oceans so progressively lowering mg ca which combined with more widespread oxic conditions facilitated the rise of skeletal animals and in turn influenced the evolution of skeletal mineralogy

field evidences from northern dead sea fault zone south turkey new findings for the initiation age and slip rate abstract the left lateral strike slip dead sea fault zone dsfz extends from the red sea in the south to the east anatolian fault zone eafz in the north this study examines the northern part of the dsfz around amik basin and presents surface and subsurface geological evidence for the quaternary activity and initiation age of the northernmost dsfz the dsfz extends n s in the south of the amik basin where clear geological and morphological evidence exists for faulting geological observations around amik basin analyses of borehole data and electrical resistivity profiles within the amik basin indicate that the activity of the northern dsfz started after pliocene in the amik basin subsurface data in the basin suggest that the dsfz offsets a pre quaternary basin sinistrally by about 7 9 km the offset pre quaternary basin suggests at least 4 94 0 13 mm year slip rate for the northern part of the dsfz the karasu fault zone kfz extends in an en echelon pattern along the western margin of the karasu valley and it transfers the significant amount of slip from dsfz to the eafz

kinematics of the amanos fault southern turkey from ar ar dating of offset pleistocene basalt flows transpression between the african and arabian plates

dolomite formation and biogeochemical cycles in the phanerozoic summary based on present knowledge of the purely chemical controls on the kinetics of massive dolomite formation the abundance and distribution of dolomite throughout the phanerozoic remains an enigma sometimes referred to as the dolomite problem comparing dolomite abundance to secular variation in seawater chemistry indicates that some changes in seawater chemistry are more likely to have resulted from extensive dolomitization rather than to have caused it the recently formulated microbial dolomite model provides the opportunity to view the geological history of dolomite formation from a new perspective a biogeochemical approach to the dolomite problem reveals a plausible connection between phanerozoic geochemical cycles and dolomite formation in particular periods of more extensive dolomitization broadly correlate with diverse indicators of decreased oxygen levels in the atmosphere and oceans lowered oxygen levels would have fostered a more active community of anaerobic microbes including sulphate reducing bacteria which in turn could have led to more extensive dolomitization of marine carbonates

soil gas method for tracing neotectonic faults in clay basins the pisticci field southern italy abstract two soil gas surveys were performed in 1991 and 1993 over an area of 95 km 2 at pisticci southern italy the research was aimed at assessing the relationship between soil gas distribution and fracture systems in a plio pleistocene clay basin located in the bradanic trough more than 400 samples were collected to measure the he co 2 and 222 rn concentration in soil atmosphere very large helium anomalies he up to 21 000 ppb above atmospheric reference were detected in 1991 in correspondence with the youngest fractures reported in the literature in order to verify the persistence of such soil gas anomalies a survey was conducted again in 1993 in subareas where major helium anomalies were previously detected the values of co 2 and 222 rn have shown about the same average as that in the 1991 survey while he values have revealed a sharp decrease with maximum values not exceeding 3000 ppb this considerable difference is tentatively related to the seismic activity that occurred just before the 1991 survey whereas no appreciable seismic activity was reported in 1993 the results of the soil gas surveys show that the shape and spatial distribution of the gas anomalies are related to the structural pattern of the area whereas the magnitude of gas leakage is controlled by the occurrence of deep gas bearing traps hydrocarbon reservoirs and possibly triggered by seismic activity

seismo geochemical variations in sw taiwan multi parameter automatic gas monitoring results gas variations of many mud volcanoes and hot springs distributed along the tectonic sutures in southwestern taiwan are considered to be sensitive to the earthquake activity therefore a multi parameter automatic gas station was built on the bank of one of the largest mud pools at an active fault zone of southwestern taiwan for continuous monitoring of co2 ch4 n2 and h2o the major constituents of its bubbling gases during the year round monitoring from october 2001 to october 2002 the gas composition especially ch4 and co2 of the mud pool showed significant variations taking the co2 ch4 ratio as the main indicator anomalous variations can be recognized from a few days to a few weeks before earthquakes and correlated well with those with a local magnitude 4 0 and local intensities 2 it is concluded that the gas composition in the area is sensitive to the local crustal stress strain and is worthy to conduct real time monitoring for the seismo geochemical precursors

1 08 ga diabase sills in the pahrump group california implications for development of the cordilleran miogeocline u pb baddeleyite ages of 1087 3 and 1069 3 ma for twodiabase sills that intrude the crystal spring formation of the pahrump group southeastern california provide a minimum estimate for the depositional age of the crystal spring formation the new ages high light the potential range in deposition ages for the pahrump group from 1087 ma to possibly as young as 600 ma for kingston peak glaciogenic sediments consequently there probably are significant disconformities within the pahrump group that separate unrelated tectonically distinct episodes of basin subsidence the crystal spring and beck spring formations are considered to be platform cover rocks preserved as a result of block faulting during deposition of the upper kingston peak formation the age of the pahrump sills is in excellent agreement with the age of sills that intrude the apache group central arizona and the unkar group grand canyon and supports earlier correlations of those units

a palaeoproterozoic dolomite vempalle formation cuddapah basin india showing phanerozoic type dolomitisation abstract the palaeoproterozoic vempalle formation of the cuddapah basin india significantly adds to our understanding of the evolution of precambrian marine carbonate systems and the redox state of the earth s early oceans a facies microfacies diagenetic geochemical examination of samples from a 1000 m long exposure in a freshly cut canal section shows that 10 15 of precursor limestone is still preserved in the vempalle formation in the form of remnant patches of calcimicrite and ooids with calcite spar cement the ooids preserving primary radial and concentric fabrics and radial fractures are considered to have been originally precipitated as calcite which may have been low mg in places the preserved calcite spar that is partially replaced by fabric destructive dolomite shows type i calcite twin lamellae petrographic observations demonstrate that vempalle formation dolomite formed through very early precipitation which in stromatolites preserved microbial filaments as well as through fabric destructive dolomitization during shallow to moderate burial vempalle formation dolomite is characterized by micritic dolomite crystals which suggest rapid early dolomitization of lime mud and micritic calcite from a supersaturated mg ca rich solution probably near surface or during shallow burial depletion of na and sr contents of vempalle formation dolomite along with negative 18o values indicate dolomite recrystallisation during burial and further replacement dolomite 13c values of 0 5 to 2 are likely inherited original marine values geochemical proxies trace elements and rare earths imply that cuddapah basin seawater and dolomitizing fluids were anoxic and ferruginous but not euxinic geochemical analyses also indicate that the burial diagenetic fluids evolved from eu enriched seawater that probably resulted from continental rifting around 1 9 2 0 ga this probable ocean chemistry is in contrast with the anoxic ferruginous and extremely high mg ca dolomite oceans that prevailed during proterozoic time the vempalle dolomite shows more similarities with dolomitised phanerozoic platform carbonates than typical precambrian dolomite with its well preserved textures and burial dolospar cements

submarine hydrothermal weathering global eustasy and carbonate polymorphism in phanerozoic marine oolites abstract the age and fabric of 347 phanerozoic marine oolites have been compiled in order to evaluate secular variations in the original mineralogy of these physicochemically precipitated sedimentary carbonates variation in the abundance of oolite correlates with positions of global sea level ooids were common during transgressions and regressions but were rare during lowstands and highstands the rarity of oolite during continental emergence early cambrian permo triassic late tertiary quaternary probably relates to a diminished areal extent of shallow carbonate environments causes for a similar paucity during continental submergence silurian devonian late cretaceous are more problematic higher atmospheric co2 and lower hydrospheric co3 concentration during highstands may have inhibited a biotic carbonate precipitation ooids coeval with highstands display a preponderance of fabrics evincing a primary calcite mineralogy ooids formed during lowstands are more diverse but record dominance of aragonite variations in cortical mineralogy relate more closely to flooded continental areas than to sea level elevations supporting the suggestion of mackenzie and pigott 1981 that variations in hydrospheric carbonate concentrations were more important in determining phanerozoic ooid mineralogy than were magnesium calcium concentrations these data on oolite abundance and mineralogy demonstrate that abiotic phanerozoic marine carbonates have been responsive to secular changes in atmospheric hydrospheric chemistry and global eustasy and suggest that these changes are directly related to past rates of submarine weathering and sea floor hydrothermal activity

the east anatolian fault an oblique collisional belt abstract the tectonic setting for the area around the arabia africa anatolia triple junction is described from combined landsat spot satellite image analysis and field observations since the late miocene the motion along the east anatolian fault generated major structures corresponding to shortening with a sinistral slip component the 150 km wide area of the triple junction is highly deformed by folding and thrusting distributed mainly on the border of the anatolian block in addition kinematic reconstructions confirm that the arabia anatolia relative motion is both sinistral and convergent the sinistral strike slip faults of the east anatolian fault zone are of second order and local consequences of the n s arabia anatolia collision

hydrothermal methane fluxes from the soil at pantelleria island italy abstract chemical and isotopic analyses of the main gas manifestations of the island of pantelleria italy were used to gain insight on the origin of the released methane results indicate that the most probable origin is through abiogenic reactions within the hydrothermal system methane and co 2 flux measurements from the soils were made with the accumulation chamber method in an area of about 0 015 km 2 within the main fumarolic area of the island favara grande the 23 measurements range from 34 to 3550 mg m 2 d 1 for ch 4 and from 0 6 to 379 g m 2 d 1 for co 2 the relationships between ch 4 and co 2 fluxes and the ch 4 co 2 ratios in the gases collected between the depths of 25 and 100 cm provide evidence for methanotrophic processes within the soils methane output for the surveyed area was calculated to be 2 5 t a 1 and extrapolated to about 5 10 t a 1 for the entire volcanic hydrothermal system of the island previous higher estimates of the ch 4 output at pantelleria etiope et al 2007 j volcanol geotherm res 165 76 86 were based on soil co 2 output and ch 4 co 2 ratios in fumarolic gases the present work provides the first direct ch 4 flux data and it suggests that methanotrophic activity in the soil could be substantial in reducing the ch 4 emission to the atmosphere

the schwartzwalder uranium deposit ii age of uranium mineralization and lead isotope constraints on genesis u pb isotope analyses of ores from the schwartzwalder uranium mine colorado show that these ores have high amounts of initial common pb and that the initial pb was both variable and relatively radiogenic in its pb isotope ratios 206 pb 204 pb 26 30 as a result the only useful approach to dating these ores is with u pb isochrons and even so some means of dealing with the variable initial pb isotope ratios is required because the common pb in these ores was apparently derived from sources of similar age and th u the observed 208 pb 204 pb of these th free ores can be used either to identify sample suites with similar initial pb isotope ratios or to normalize for the variable initial pb isotope ratios the resulting u pb isochrons indicate an age of mineralization for both illinois vein and titan vein ores of 69 3 or 1 1 m y suggesting that the deposit was formed during the earliest stages of laramide uplift and under at least 3 km of phanerozoic cover the initial pb isotope systematics of the ores show that the metals in the schwartzwalder ores were derived from source s of 1 730 or 130 m y age with a th u of 2 2 or 0 2 and 238 u 204 pb of 30 to 60 these restrictions on the source s of the metals rule out the possibility that the deposit could have been formed by remobilization of a proterozoic uranium deposit and both the 69 3 m y age of the ores and their initial pb isotope ratios preclude any contribution of metals to the deposit by younger volcanics such as those in the denver formation

dolomite abundance and stratigraphic age constraints on rates and mechanisms of phanerozoic dolostone formation increasing dolomite abundance with age relative to limestone has long been accepted as one of the general truisms of sedimentary geology a relationship which suggests that dolomitization is a cumulative process occurring slowly over the full burial history of a carbonate sequence however reevaluation of data in support of this assumption indicates that although relative dolomite abundances do change significantly throughout phanerozoic carbonate sequences no data set demonstrates any direct correlation between dolomite content and age whereas tabulation of available data does suggest greater amounts of dolomite formation during periods of continental flooding global mass balance calculations of potential magnesium sources also indicate that most dolomite has formed from marine or marine derived fluids at the earth9s surface this conclusion is indirectly supported by significant short term period scale changes in phanerozoic dolomite abundance a variation which would be more attenuated if dolomitization were dominantly a burial process dolomitization may be enhanced during times of global transgression higher atmospheric pco 2 and lower calcite saturation state in shallow marine settings

reassessment of the basal sauk supersequence boundary across the laurentian craton margin hinge zone southeastern california abstractin the death valley and mojave desert regions of southeastern california the contact separating the lower and middle members of the wood canyon formation wcf is currently interpreted as a regional scale unconformity coincident with the base of the sauk sequence regional mapping of this surface however reveals a nonconformable contact with underlying crystalline basement in cratonic settings and a relatively conformable contact atop a northwest thickening wedge of off craton strata that is capped by the lower member of the wcf consistent with an unconformity the progressive loss of three carbonate units within the lower member of the wcf has been attributed to incision by the base of the middle member wcf however fossil evidence and correlation based on carbon isotope compositions of each lower member wcf dolostone unit reject top down erosion to describe their loss and overall cratonward thinning results from multiple detailed measured stratigraphic sections of a conglomerate at the b

deep valley incision in the terminal neoproterozoic ediacaran johnnie formation eastern california usa tectonically or glacially driven neoproterozoic sedimentary successions worldwide display evidence for multiple low latitude glacial events and continental rifting episodes related to the fragmentation of the supercontinent rodinia in death valley eastern california these events are represented by two intervals of glacial diamictite and two episodes of synsedimentary extensional faulting in the kingston peak formation deep incised valleys of uncertain origin in the upper johnnie formation approximately 1 km stratigraphically above the kingston peak formation may provide evidence either for a third glacial episode or for an additional tectonic event eleven measured sections indicate that one of these incised valleys is 120 m deep and approximately 2 5 km wide detailed mapping of the paleovalley has revealed the presence of numerous synsedimentary normal faults that offset underlying units but are capped by incised valley breccia abrupt incision occurs across buried normal fault scarps several large olistoliths up to 15 m in diameter are located near the fault scarps and the average clast size of the breccia decreases in general away from mapped normal faults incised valley clasts are derived exclusively from underlying neoproterozoic formations nearly entirely from the johnnie formation itself there is no evidence for direct glacial influence as no striated clasts or dropstones were observed the absence of glacial indicators coupled with the strong correlation between incision and synsedimentary normal faulting imply a primary tectonic control on valley formation the valley represents a significant tectonic reactivation of the neoproterozoic passive margin similar to early paleozoic extensional events in the northern cordillera of western north america 2005 elsevier b v all rights reserved

mantle fluids in the karakoram fault helium isotope evidence abstract the karakoram fault kkf is the 1000 km long strike slip fault separating the western himalaya from the tibetan plateau from geologic and geodetic data the kkf is argued either to be a lithospheric scale fault with hundreds of km of offset at several cm a or to be almost inactive with cumulative offset of only a few tens of kilometers and to be just the upper crustal localization of distributed deformation at depth here we show 3he 4he ratios in geothermal springs along a 500 km segment of the kkf are 3 100 times the normal ratio in continental crust providing unequivocal evidence that a component of these hydrologic systems is derived from tectonically active mantle mantle enrichment is absent along the indus yarlung suture zone isz just 35 km southwest of the kkf suggesting that the mantle fluids flow only within the kkf within the last few ma the kkf must have accessed tectonically active tibetan mantle northeast of the mantle suture which we therefore locate vertically beneath the kkf very close to the surface trace of the isz hence in southwestern tibet indian crust may not now be underthrusting substantially north of the isz even though miocene underthrusting may have placed indian crust north of the isz in the lower half of the tibetan plateau crust this is in significant contrast to central and eastern tibet where underthrust indian material not only forms the lower half of the tibetan crust but is also currently underthrusting for 200 km north of the isz our new constraint on kkf penetration to the mantle allows an improved description of the continuously evolving karakoram fault as a tectonically significant yet perhaps geologically ephemeral lithospheric structure

comparison of differential diagenesis of two oolites on the lower triassic platform margin ne sichuan basin implications for the co evolution of rock structure and porosity abstract two oolites of the lower triassic feixianguan formation on the margins of the kaijiang liangping k l trough in the ne sichuan basin were deposited in the upper parts of similar shallowing upward sequences and are capped by a subaerial exposure surface however they have contrasting diagenetic histories and reservoir qualities the sour oolitic dolostone reservoirs on the eastern side of the k l trough have significantly higher porosities than the sweet oolitic limestone reservoirs on the western side a petrologic and geochemical comparison of the two oolites was carried out so as to investigate the role of diagenetic processes on the co evolution of oolite structure and pore network on both sides of the k l trough eogenetic meteoric digenesis led to an inversion of texture with ooid dissolution and interparticle cementation in the oolite layers close to the exposure surface the layers relatively far from the exposure surface mostly underwent recrystallization in association with connate seawater resulting in neomorphic fabrics in the ooid cortices and less interparticle calcite cement during the subsequent dolomitization the early formed oolite structure were mostly inherited by the dolostones on the eastern side with fabric retentive textures in the layers close to the exposure surface and fabric destructive textures in the layers far from the exposure surface during deeper burial the oolitic limestones were subjected to extensive calcite cementation and porosity loss whereas the dolostones generally retained more porosity and have better connectivity of the micropore network the higher porosity of the dolostones is ascribed to lesser chemical compaction and associated cement precipitation rather than the creation of new pores porosity enhancement is closely dependent on the absence of the calcite cement related to pressure solution the heterogeneity of the dolostone fabrics and the porosity was further enhanced by the subsequent recrystallization and the dissolution reprecipitation process induced by thermochemical sulfate reduction during which small amounts of net porosity are calculated to have been created the oolitic limestones are the best reservoirs close to the exposure surface whereas the most porous dolostones with the highest degree of fabric destruction are commonly some distance from the exposure surface these results provide some insights into the diagenetic controls on oolite structure and porosity and have implications for predicting the porosity of deeply buried oolitic reservoirs so have global theoretical and practical significance

continental paleoclimates from δd and δ18o of secondary silica in paleokarst chert lags approximate continental paleotemperatures can be inferred from oxygen and hydrogen isotopic analyses of authigenic silica that precipitated within chert lags on paleokarst surfaces data for two proterozoic examples suggest continental weathering temperatures that ranged from 30 to 43 c quantitative results appear possible for rocks at least as old as 1 1 ga

reconstructing paleoceanographic conditions during the middle ediacaran evidence from giant ooids in south china abstract the ediacaran was a period of intense environmental change in earth history transient pulses of oxygenation and shifts in ocean chemistry have been interpreted from a range of geochemical proxies including rare earth elements and yttrium rey but it is still a challenge to reconstruct paleoceanographic conditions due to the scarcity of reliable recorder in this study we explore the possibility that a newly discovered deposit of giant ooids in the nanshanping outcrop in south china contains a relatively intact record of the ree composition of ediacaran seawater providing an important window into the redox state of the surface ocean at this time these ooids are relatively large in size 1 6 mm and exhibit densely banded laminae a regional chemostratigraphic correlation shows that the giant ooid bearing succession in south china is in the upper part of the second ediacaran positive carbon isotopic shift ep2 and thus its occurrence was not associated with the shuram excursion additionally the occurrences of giant ooid bearing oolites in different blocks were not synchronous during the middle ediacaran in situ laser ablation analysis of giant ooid cortices reveals that the shale normalized rey patterns are similar to those of modern seawater including depleted light rees superchondritic y ho ratios and positive la anomalies yet no ce anomalies 1 0 0 15 in numerous ooid cortices seems to indicate a suboxidized condition of surface ocean in south china at that time the petrographic and geochemical evidence support the weak diagenetic alteration of the pure giant ooids during burial they formed in open ocean settings with energetic hydrodynamic environments and were affected by early dolomitization that might preserve mostly original petrographic fabrics and rey signatures from further diagenetic overprinting the characteristics of ce anomalies and rey compositions acquired from the giant ooids indicate that the surface ocean was suboxidized in south china during the late stage of ep2 implying the very low atmospheric o2 level at that time our results suggest that giant ooids may be a reliable analytical target that provide a snapshot into palaeoceanographic conditions during this crucial period of dynamic changes in early earth history

secular changes in the amount and texture of dolomite the amount of dolomite in cenozoic carbonates is lower than throughout most of the paleozoic a difference that could be due to changes in either chemical conditions or physical conditions that lead to extensive dolomitization the abundance of mimetic texturally retentive dolomites in the cenozoic suggests that chemical conditions were unusually favorable for dolomite formation and therefore it must be physical conditions that explain the paucity of cenozoic dolomites one reasonable explanation for the paucity of cenozoic dolomites is that glacio eustatic sea level fluctuations reduced the amount of time carbonate sediments were in contact with dolomitizing solutions

on the secular variations in the composition of phanerozoic marine potash evaporites in a recent paper l a hardie proposed that the secular changes in the mineralogy of marine nonskeletal limestones and in the mineralogy of marine potash evaporites during the phanerozoic are the result of changes in the composition of seawater caused primarily by fluctuations in the flux of seawater through mid ocean ridges he suggested that even quite small variations 25 in this flux have a profound effect on the composition of seawater we show that the effects of changes in the hydrothermal flux are much smaller than he proposed nevertheless a doubling of the hydrothermal flux could probably alter the composition of seawater sufficiently to affect the mineralogy of marine potash evaporites an alternative explanation for the variations in the mineralogy of these deposits invokes differences in the degree of dolomitization during the evaporation of seawater the apparent near constancy of the k sup content of seawater during the phanerozoic supports this hypothesis it seems likely that during periods of rapid seafloor spreading the rate of seawater cycling is greater than today that sea level is higher that very large carbonate platforms are more abundant and that changes in seawater chemistry together with increases in dolomitization during the evaporation of seawatermore lead to mgso sub 4 free potash deposits the relative importance of these several effects can probably be determined with certainty only when we have analyses of relatively unaltered seawater from the several phanerozoic periods 27 refs 1 fig 1 tab less

geochemical characteristics of soil radon and carbon dioxide within the dead sea fault and karasu fault in the amik basin hatay turkey abstract the study area is close to the boundary of three tectonic plates anatolian arabian and african plates and is characterized by important tectonic lineaments which consist mainly of the dead sea fault dsf the karasu fault and the east anatolian fault eaf systems to understand the origin of soil gas emanation and its relationships with the tectonics of the amik basin hatay a detailed soil gas sampling was systematically performed together with co2 flux measurements 220 soil gas samples were analyzed for rn and co2 concentrations the distribution of soil rn kbq m3 co2 concentration ppm and co2 flux g m2 day in the area appears as a point source spot and or diffuses halo anomalies along the buried faults fractures due to crustal leaks the results revealed that rn and co2 concentrations in the soil gas show anomalous values at the specific positions in the amik basin the trace of these anomalous values is coincident with the n s trending dsf co2 is believed to act as a carrier for rn gas based on the rn and co2 concentrations of soil gases at least three gas components are required to explain the observed variations in addition to the atmospheric component two other gas sources can be recognized one is the deep crust component which exhibits high rn and co2 concentrations and is considered the best indicator for the surface location of fault fracture zones in the region the other component is a shallower gas source with high rn concentration and low co2 concentration moreover he isotopic compositions of representative samples vary from 0 94 to 0 99 ra illustrating that most samples have a soil air component and may have mixed with some crustal component without significant input of the mantle component based on the repeated measurements at a few sites soil gas concentrations at the same site were observed to be higher in 2014 than in 2013 which may be associated with the activity of the dsf in 2013 2014 this suggests that soil gas variations at fault zone are closely related to the local crustal stress and hence are suitable for monitoring fault activities

the stratigraphic expression of a large negative carbon isotope excursion from the ediacaran johnnie formation death valley the rainstorm member of the ediacaran johnnie formation of the southern basin and range us records a large negative excursion in carbon isotope ratios of carbonate strata 13 c vpdb 6 the character of the excursion raises fundamental questions about whether this isotopic pattern is accurately capturing the time series behavior of marine dissolved inorganic carbon dic or is a product of diagenesis to explore this issue we examined the expression of this isotopic excursion within the johnnie oolite a 2 m thick marker bed which records the highest rate of change in 13 c sedimentologically the oolite unit is thought to be time transgressive if the isotopic excursion reflects time series behavior of the carbon cycle its expression in the oolite across the basin should systematically align the sections according to their slight diachroneity detailed carbon and oxygen isotopic stratigraphy of the oolite at seven different locations indicates the magnitude of the excursion at the base of the oolite is spatially variable such that after a palinspastic reconstruction the sections align along a systematic north to south gradient in the isotopic data the oolite preserved in the old dad mountains the most southerly section measured is an outlier to this trend and the most difficult to ordinate accurately in the reconstruction showing the largest isotopic range between the onset of carbonate deposition and top of the oolite several hypotheses are congruent with these data but the sum of observations is best explained by a scenario wherein the oolite is time transgressive and deposited in a north to south manner throughout the onset of the isotopic excursion if correct this implies that the stratigraphic 13 c pattern reflects time series behavior of marine dic

bacterially induced dolomite precipitation in anoxic culture experiments to study the process of microbial mediated dolomite formation growth experiments were carried out with selected bacterial cultures under anoxic environmental conditions simulating those found in lagoa vermelha a hypersaline lagoon in brazil where dolomite precipitation occurs specifically we report the isolation of a particular strain of sulfate reducing bacteria lvform6 from lagoa vermelha sediment which apparently promotes the formation of nonstoichiometric dolomite sulfate reducing bacteria grown in a synthetic liquid medium produced dolomite during 30 days incubation at 30 c the precipitates have morphologies similar to those observed in lagoa vermelha sediment our results demonstrate that sulfate reducing bacteria can influence dolomite precipitation under controlled lowtemperature anoxic conditions and imply that anaerobic microorganisms can play an important role in carbonate sedimentation they may have been particularly significant in earth s earliest history when a more reducing atmosphere existed

gas geochemistry and seismotectonics a review abstract publications on soil and spring gases have been examined regarding their relationships with both tectonic and seismic activities the main sources behaviours and uses of species detected in soils and springs are displayed and their mode of sampling and analysing briefly described the main patterns of degassing in soils are described and we outline the wide range of geochemical signatures as the result of both permeability and mineralogical contrasts because thermomineral waters have been in contact with great volumes of crustal rocks at various depths spring gases might be more representative of the local environment than soil gases moreover gas signature comparisons show that spring gases are much more enriched with deep gases and slightly contaminated by atmospheric gases therefore they can be considered as better samples for identifying precursors of earthquakes environmental perturbations are examined and it is shown from divergent cases that pressure temperature soil moisture or earth tides may generate very high perturbations of the degassing process such effects demonstrate that no systematic correction law can be proposed and that removing external contributions from gas concentrations must be performed case by case this demonstrates therefore the need for the simultaneous measurement of external parameters during gas monitoring a qualitative examination of about 150 claimed precursors proposed in the literature has been reviewed as noted by previous authors anomalies appear at distances sometimes much greater than typical source dimensions and occur in the field of strain higher than 10 9 most of them being in the field of strain higher than 10 8 taking into account the very high heterogeneity of such a set of data we can suggest that amplitudes of gas anomalies are independent of both magnitudes and epicentral distances of related earthquakes suggesting local conditions to control amplitudes on the contrary precursory time and duration of anomalies seem to increase both with magnitudes and epicentral distances abundant evidence demonstrates the major role of crustal fluids in the earthquake cycle many works have outlined the fact that crustal instabilities can appear as the result of low stress strain perturbations during loading it has been suggested that motion of fluids may occur at various scales from microcrack fluid transfer up to changes of hydraulic levels of water tables the study of subsequent anomalies is expected to supply a tool for earthquake prediction following previous authors we outline the need for further methodological improvements including the setting up of multiparameter station networks and the simultaneous recording of the main external parameters atmospheric pressure water and air temperature soil moisture for signal processing

interpretation of radon anomalies in seismotectonic and tectonic gravitational settings the south eastern crati graben northern calabria italy the study area is located in the south eastern part of the crati valley northern calabria italy which is a graben bordered by n s trending normal faults and crossed by nw se normal left lateral faults numerous severe crustal earthquakes have affected the area in historical time present day seismic activity is mainly related to the n s faults located along the eastern border of the graben in this area much seismically induced deep seated deformation has also been recognised in the present paper radon concentrations in soil gas have been measured and compared with a lithology b quaternary faults c historical and instrumental seismicity and d deep seated deformation the results highlight the following a there is no evidence of a strong correlation between lithology and the radon anomalies b a clear correlation between the n s geometry of radon anomalies and the orientation of main fault systems has been recognised except in the southernmost part of the area where the radon concentrations are strongly affected by the superposition of the n s and the nw se fault systems c epicentral zones of instrumental and historical earthquakes correspond to the highest values of radon concentrations probably indicating recent activated fault segments in particular high radon values occur in the zones struck by earthquakes in 1835 1854 and 1870 d deep seated gravitational deformation generally coincides with zones characterised by low radon concentrations in the studied area the anisotropic distribution of radon concentrations is congruent with the presence of neotectonic features and deep seated gravitational phenomena the method used in this study could profitably contribute towards either seismic risk or deep seated gravitational deformation analyses

role of sulfide oxidation in dolomitization sediment and pore water geochemistry of a modern hypersaline lagoon system dolomite precipitation has been reported in sediments of marginal marine hypersaline lagoons near rio de janeiro brazil and has been related to microbial sulfate reduction our field study of pore water and sediment geochemistry in two lagoons reveals only modest degrees of so4 reduction and even h2s oxidation significant differences in dolomite contents salinity and carbon sulfur cycling occur in the two lagoons pore waters from the most dolomite rich sediments exhibit significantly elevated so4 cl ratios relative to seawater moreover the o isotope composition of so4 in all lagoonal waters has evolved significantly from seawater values this suggests active sulfur recycling via h2s oxidation which provides acid that decreases pore water saturation state for high mg calcite and aragonite thermodynamically favoring the precipitation of dolomite the open hydrogeochemical nature of these lagoons maintains so4 concentrations below gypsum saturation allowing dolomite to form from fluids with normal marine mg ca

did anoxia terminate ediacaran benthic communities evidence from early diagenesis abstract the ediacaran oceanic redox landscape was heterogeneous where many basins had a shallow and highly dynamic chemocline above anoxic ferruginous or euxinic or low oxygen manganous waters seawater mmg ca ratio was also high promoting early diagenetic dolomitisation how the benthos responded to these conditions is fundamental to understanding their ecological dynamics here we utilise redox sensitive elements in early marine carbonate cements to investigate possible water column redox controls on the distribution and growth of the oldest metazoan communities skeletal communities in the zaris sub basin of the nama group namibia 550 547 ma grew in shallow waters where fine grained carbonate sediment often shows evidence of early dolomitisation mid ramp cloudina reefs are composed of open highly porous structures that formed multiple successive assemblages each assemblage is terminated by thin reef cements show a paragenetic sequence from synsedimentary to early marine cement and final burial which we infer were precipitated under dynamic redox conditions first acicular pseudomorphed aragonite cement formed under oxic conditions low fe and mn next the presence of iron rich dolomicrite sediment often associated with a recrystallised ferroan dolomite crust suggests that originally aragonitic or calcitic sediment and a high mg precursor cement were preferentially dolomitised dolomitisation may have been enhanced either via upwelling of deeper water anoxic ferruginous seawater or by later fluid remobilisation from adjacent shales a following mn rich calcite cement is inferred to be early marine due to its inclusion rich fibrous form and well preserved cl zonation the final blocky cement precipitated under oxic conditions probably during shallow burial the cements likely record a general shallow to deeper water transect from oxic shallow waters to low oxygen manganous waters then to oxic shallow burial conditions we hypothesize that cloudina reef communities were terminated by episodic sediment incursions during short term transgressive cycles possibly accompanied by upwelled anoxic ferruginous and dolomitising waters although the timing for this is poorly constrained more generally such incursions may have terminated ediacaran benthic communities that grew close to the chemocline

subsoil co2 and ch4 and their advective transfer from faulted grassland to the atmosphere measurements of co2 and ch4 in 3 m deep groundwater soil gas and soil atmosphere fluxes were completed in two grasslands in central italy having the same soil conditions but different subsoil fault linked secondary permeability unfaulted grassland displays gas phase equilibrium between soil air and groundwater typical soil gas diffusion profiles and diffusive soil to atmosphere gas transfer on the basis of oxygen depletion assessment assuming a ratio of 1 1 between biogenic o2 consumption and co2 production the measured soil co2 concentrations are consistent with a normal production in the soil by biologic activity the faulted grassland instead has higher co2 and ch4 concentrations up to 6 and 10 ppmv in soil air and flux 1 2 ml m 2 s 1 and 1 3 l m 2 s 1 resulting from a combination of soil biologic and endogenous components with evidence of gas transfer from the saturated to the unsaturated zone and advective gas transfer from soil to the atmosphere the extra soil source in the faulted zone which is about 0 3 4 times the background soil biologic production is likely related to migrating crustal gas whatever the c gas origin and depth may be biogenic or abiogenic shallow or deep the present results demonstrate that the subsoil derived component occurring in the soil in areas with active tectonics cannot be ignored a priori in the assessment of the c terrestrial sources in particular the assumption that dryland soils are sinks for methane owing to methanotrophic consumption may be not true in areas affected by active and gas bearing faults accordingly it would be very important to assess at global scale the actual role in the carbon dioxide and methane cycle of soils within the active tectonic bounds

local δ34s variability in 580ma carbonates of northwestern mexico and the neoproterozoic marine sulfate reservoir abstract many 34s records have been produced from carbonate associated sulfate cas in order to understand the oxidation state of the neoproterozoic oceans but interregional correlation is complicated by the absence of robust chronostratigraphic markers here a globally correlatable stratigraphic interval containing the wonoka shuram w s 13c excursion was analyzed to explore variability in the sulfur isotope record in the excursion containing units the local 34s record from multiple closely spaced sections in sonora mexico was examined to explore potential heterogeneities and then these were compared to more distant sections elsewhere in sonora the inception and isotopic minimum of the w s excursion is located in the clemente formation and coincides with an extensive oolite marker bed five sections containing this marker bed span 25 km of lateral distance exhibit significant variability in 34scas range 18 6 to 27 6 vcdt and high variability in cas concentration range 1200 ppm unlike the 34scas values cas concentrations show strong negative correlation with mn sr ratios and fecarb concentrations consistent with cas removal upon diagenetic recrystallization and an absence of an accompanying sulfur isotopic fractionation indeed samples containing low cas concentrations exhibit petrographic characteristics consistent with diagenetic recrystallization including fabric destructive neomorphism and relatively coarse crystalline textures coeval w s strata in death valley oman and the least altered sonora samples record a decrease in 34scas and an increase in cas concentration however the magnitude of the changes are distinct perhaps reflecting differential response to a transient oxidation event in contrast time equivalent facies of south china do not exhibit a decrease in 34scas nor a relative increase in cas concentrations the variability in geochemical characteristics likely developed from local and or regional marine 34ssulfate heterogeneity although neoproterozoic oceanic heterogeneity in 34ssulfate has been proposed it has not been reported on such close spatial scales in addition the existence of variability among the sonora sections in which strata were all deposited at similar depth indicates that heterogeneity could have occurred laterally finally these findings demonstrate that while cas concentrations may be drastically affected by diagenesis 34scas may retain primary signatures

molybdenum isotope evidence for widespread anoxia in mid proterozoic oceans how much dissolved oxygen was present in the mid proterozoic oceans between 1 8 and 1 0 billion years ago is debated vigorously one model argues for oxygenation of the oceans soon after the initial rise of atmospheric oxygen 2 3 billion years ago recent evidence for h 2 s in some mid proterozoic marine basins suggests however that the deep ocean remained anoxic until much later new molybdenum isotope data from modern and ancient sediments indicate expanded anoxia during the mid proterozoic compared to the present day ocean consequently oxygenation of the deep oceans may have lagged that of the atmosphere by over a billion years

numerical modeling of ooid size and the problem of neoproterozoic giant ooids temporal variation in ooid size reflects important changes in physical and chemical characteristics of depositional environments two numerical models are used to evaluate the effects of several processes influencing ooid size the first demonstrates that low supply of new ooid nuclei and high cortex growth rate each promote growth of large ooids the second model demonstrates that high average water velocity and velocity gradient also enhance ooid growth several neoproterozoic oolites contain unusually large ooids some reaching diameters of up to 16 mm while lower nuclei supply and higher ooid growth rate may have prevailed prior to the evolution of carbonate secreting organisms neither difference can explain the presence of giant ooids in neoproterozoic deposits because archean through mesoproterozoic ooids rarely exceed 5 mm in diameter in the presence of lower nuclei supply and higher growth rate high average water velocity may have allowed growth of such large ooids higher average water velocity could have been due to a prevalence of carbonate ramps over rimmed shelves during neoproterozoic time

cavity filling dolomite speleothems and submarine cements in the ediacaran dengying microbialites south china responses to high frequency sea level fluctuations in an aragonite dolomite sea speleothems mostly composed of calcium carbonate are widely present in modern karst originated caves but have rarely been reported in palaeokarst systems this study presents a novel type of dolomite speleothem and subsequent submarine dolomite cement which are widely present in the upper ediacaran dengying formation in the upper yangtze area these precipitated materials occur in the cavity system that cuts across several peritidal cycles the interconnected cavity networks with irregular shapes embayed walls internal breccias on cavity floor and their preferential development in the shallower cycle tops for example tepee deformed beds suggest that they were initially generated by subaerial dissolution as the earliest infills the hemispherical protrusions icicle like pendants and ground up columns show similar morphological features and occurrence patterns to the cave popcorn stalactites and stalagmites respectively thus these earliest infills are speleothems resulting from associated meteoric precipitation during subaerial exposure the isopachous growth pattern of subsequent more extensive fibrous dolomite cements points to a submarine diagenetic environment in which they were precipitated microscopically the micritic to micro crystalline dolomite acicular dolomite in speleothems and the subsequent fibrous dolomite share similar crystal fabrics to metastable precursors for example mg calcite meanwhile the carbon oxygen isotope compositions of the speleothem and fibrous dolomite although partly altered by burial diagenesis share a large overlap with host rock and coeval marine carbonates all over the yangtze platform for these reasons these speleothems and fibrous cements are considered to have been initially precipitated as metastable carbonate precursors in meteoric and submarine environments respectively and stabilized during submarine mimetic dolomitization the cyclic occurrence of cavity systems filled with speleothems and submarine cements reflects periodic subaerial exposure and marine flooding of broad tidal flat in the upper yangtze area driven by high frequency sea level fluctuations furthermore the neoproterozoic seawater chemistry that favoured early dolomitization of carbonate precursor mineralogies was an advantage for the preservation of fabrics from metastable precursor minerals

recent volcanism tectonics and plate kinematics near the junction of the african arabian and anatolian plates in the eastern mediterranean abstract in the eastern mediterranean plate convergence occurs between africa arabia and anatolia the africa arabia motion is a strike slip displacement along the dead sea fault the africa anatolia motion is taken up by subduction south of cyprus the convergence between arabia and anatolia is taken up along the east anatolian fault the analysis of the regional fault surfaces reveals the presence of two major tectonic phases that affected southeastern turkey near the junction of these three plates the older deformations are related to a n s compression the more recent movements are directed mainly westward and associated with strike slip and extension tectonics near the triple junction since 2 ma a fissure volcanism produced tholeiite followed by alkali basalt along the amanos fault the northern end segment of the dead sea fault in addition reconstruction of rigid plate kinematics between arabia africa and anatolia using recent plate motion parameters and space geodesy data suggest for the east anatolian fault a slip rate of 7 8 9 mm year the maximum finite displacement recognised for this structure being around 15 km we have obtained 1 9 ma as the maximum age for the fault formation the volcanic tectonic and kinematic data converge to propose a ca 2 ma age for the change of local tectonic regime in the junction area the structural mapping the geometry of the fractures used by the magma to reach the surface and the presence of alkali basalt of mantle source suggest that the deformation along the northern end of the dead sea transform i e the amanos fault was modified by the formation of the east anatolian fault zone in this region apparition of the east anatolian fault accommodating westward motion of the anatolian plate resulted in oblique slip tension along the amanos segment of the dead sea transform giving rise to a fissure fed mantle derived alkaline volcanism at ca 2 ma which lasted until recent times 0 4 ma

the effects of diagenesis on geochemical paleoredox proxies in sedimentary carbonates abstract metal and metal isotope records in carbonates have the potential to provide novel insights into ancient ocean atmosphere redox conditions paleoenvironmental conditions and biogeochemical cycling however trace element geochemical signatures in carbonates can record either diagenetic or depositional signatures here we explore the variability in uranium isotopes trace metal and rare earth element yttrium rey concentrations in carbonate successions that have undergone several common types of diagenetic alteration case studies include the cryogenian balcanoona reef australia marine dolomitization neomorphism the devonian canning basin reefs australia burial dolomitization karstification the paleozoic of the great basin usa high temperature and regional burial dolomitization and the carboniferous waulsortian limestone ireland pb zn mineralization in all of the examined cases there are significant heavier and or lighter shifts in u isotope values between the most petrographically pristine marine depositional components and altered or late stage diagenetic phases although we also found that rey patterns can be overprinted during diagenesis normalized rey profiles appear to be commonly retained through diagenetic recrystallization consistent with previous studies the direction and magnitude of the change in metal isotope systems during diagenesis cannot be generalized between case studies consistent with carbonate alteration being controlled by a wide range of factors including the composition and source of the alteration fluids in this light we build on framework developed from traditional isotope systems and support the view that future work on metal and metal isotope compositions of carbonates should include integrated sedimentological and petrographic analysis petrographic work not only represents a screening procedure for sedimentary geochemical work but can also significantly enhance the paleo environmental interpretation of metal isotope data

soil gas profiles as a tool to characterise active tectonic areas the jaut pass example pyrenees france a new method to investigate active tectonic structures using soil gas composition at faults suggests relevant information about regional stress conditions which can be obtained rapidly and at relatively low cost in 1995 we carried out geochemical profiles around the epicentre of the m 5 1 1980 earthquake near arudy in the french pyrenees where the presence of minor fractures is evident in the field and confirmed using satellite spot imagery fractures are conduits facilitating fluid migrations in the crust and are also pathways for the release of deep seated gases to the atmosphere in order to investigate the implication of these fractures in the present deformation i e if they are connected to the hercynian substratum at a depth of about 1800 m soil gases were measured along four traverses crossing the observed structures gases determined were 222rn co2 and 4he each of them for their characteristic source 222rn has essentially a shallow origin due to its short half life whereas co2 is the major soil gas component with a mainly surficial biogenic source however there could additionally be co2 from crustal or mantle degassing which would also be the principal sources of he data analysis clearly reveals anomalous values for each gas at specific positions along the traverses two sets of fractures corresponding to different observed trends are distinguished the one characterised by he anomalies accompanied by other gases and the second with few identified he anomalies the agreement between the geochemical data and the field observations leads us to propose a deformation model for the area studied analogous to a pull apart system located in a right lateral shear zone

sedimentology and sequence stratigraphy of neoproterozoic and cambrian units across a craton margin hinge zone southeastern california and implications for the early evolution of the cordilleran margin abstract neoproterozoic basal cambrian strata exposed in eastern california represent the deposits of a craton margin hinge zone that formed in response to the fragmentation of the neoproterozoic supercontinent rodinia one unresolved question regarding the late neoproterozoic stratigraphy in the southwestern united states has been the interpretation of paleotectonic affinity for rocks deposited above the glaciogenic kingston peak formation of central concern has been attempts to identify the position in this stratigraphy where rift related sediments give way to passive margin deposits subsidence analyses suggest that rifting occurred near the start of the cambrian perhaps coincident with the feldspathic middle member wood canyon formation it rests on a disconformity that represents the base of the sauk supersequence and would likely represent the break up unconformity in subsidence analysis models middle member wood canyon and overlying lower middle cambrian strata extend far into the craton detailed sedimentary facies and sequence stratigraphic analysis of post kingston peak pre middle wood canyon rocks indicate that depositional facies in this succession distal alluvial through shallow subtidal are similar to units deposited on the stable craton further these pre sauk units which can be divided into multiple principally eustatically driven depositional sequences are correlated across long distances and even lap onto the edge of the stable craton we suggest the kingston peak formation is the principal rift generated deposit and the overlying thick predominantly siliciclastic section represents the basal deposits of the cordilleran passive margin kingston peak strata consist of thick coarse diamictites interbedded with turbidites such facies are unique in the overall stratigraphy but are similar to other known rift deposits although the age of the kingston peak formation is not well constrained and may be as young as 590 ma it may correlate with the rapitan sturtian glaciation 720 ma which would place middle wood canyon strata some 150 ma younger than the start of rifting

secular oscillations in the carbonate mineralogy of reef building and sediment producing organisms driven by tectonically forced shifts in seawater chemistry the primary mineralogy of oolites and early marine carbonate cements led sandberg nature 305 1983 19 22 to divide the phanerozoic eon into three intervals of aragonite seas and two intervals of calcite seas hardie geology 24 1996 279 283 has shown that these oscillations together with synchronous oscillations in the mineralogy of marine potash evaporites can be explained by secular shifts in the mg ca ratio of seawater driven by changes in spreading rates along mid ocean ridges the hardie model also predicts that high mg calcite should precipitate along with aragonite as it does in today s aragonite sea we have uncovered oscillations in the carbonate mineralogy of hypercalcifying organisms ones that have produced massive skeletons large reefs or voluminous bodies of sediment that correspond to sandberg s aragonite seas and calcite seas and that are predicted by the hardie model particular groups of corals sponges and algae appear to have been dominant reef builders only when favored by an appropriate mg ca ratio in seawater in early and middle paleozoic calcite seas calcite i reefs were dominated by calcitic tabulate heliolitid and rugose corals and calcitic stromatoporoids in contrast during the period of late paleozoic early mesozoic aragonite seas aragonite ii aragonitic groups of sponges scleractinian corals and phylloid algae as well as high mg calcitic red algae were principal reef builders during late cretaceous time at the acme of calcite ii massive rudists displaced aragonitic hermatypic corals in today s aragonite sea aragonite iii scleractinian corals are again dominant reef builders along with high mg calcitic coralline algae major sediment producing algae exhibit temporal patterns similar to those of reef builders calcitic receptaculitids flourished during calcite i whereas aragonitic dasycladaceans did not become dominant rock formers until aragonite ii during calcite ii calcitic nannoplankton formed massive coccolith chalks in warm shallow seas of the late cretaceous after the mg ca ratio of seawater had reached a very low value and calcium concentration a very high value as the mg ca ratio of seawater rose and calcium concentration fell during the cenozoic era individual coccoliths on average became less massive and encrusted cells less thickly by pliocene time during aragonite iii the prominent genus discoaster secreted only narrow rayed coccoliths that covered less than 25 of the cell surface also during aragonite iii the aragonitic green alga halimeda emerged as the dominant skeletal sediment producer in reef tracts the influence of seawater chemistry on skeletal secretion appears to have been especially strong for morphologically simple taxa that exert relatively weak control over their own calcification such groups include algae sponges corals and bryozoans morphological simplicity also permits these groups to adopt vegetative or colonial modes of growth that confer success in competition for space on reefs this linkage in addition to the basic chemical demands of hypercalcification has given the mg ca ratio of seawater strong control over the success of individual reef building taxa more generally this ratio appears to have strongly influenced evolutionary changes in the skeletal mineralogy of sponges and cheilostome bryozoans throughout their history we conclude that throughout phanerozoic time a chain of causation has extended from mid ocean ridge processes via seawater chemistry to the mineralogical and biological composition of reef communities and bioclastic carbonate deposits

constraints on arabian plate motion and extensional history of the red sea analysis of the geologic and geophysical data from the western and northern margin of the arabian plate combined with data from the red sea gulf of aden leads to an interpretation of arabian plate motion that supports an episodic extensional history in the red sea and gulf of aden phase 1 extension began in medial to late eocene and was caused by the nw propagation of the reoriented central indian ridge spreading center it stretched and thinned continental crust along numerous wrench and normal faults that reactivated preexisting structures first phase extension stopped when the arabian plate terminally sutured to eurasia in the medial miocene and halted northward movement of arabia relative to africa the combined african arabian plates moved north more slowly constricting and thickening continental crust in the bitlis zagros sutures while the red sea remained technically quiescent and accumulated salt by the early pliocene continued northward movement was accommodated by lateral extrusion of large continental wedges north of the bitlis zagros sutures this allowed arabia to move northward faster than africa and reopen the red sea where phase 2 extension was expressed by seafloor spreading extension within the red sea gulf of aden rift system has been controlled by the interactions and effects of two factors 1 convergent processes between the north margin of the arabian plate and the eurasian plate to the north and 2 northwest propagation of extension associated with the medial eocene reorganization of the central indian spreading center

petrological and geochemical characteristics of the botryoidal dolomite of dengying formation in the yangtze craton south china constraints on terminal ediacaran dolomite seas abstract recent studies suggest that the massive precambrian dolomite successions were likely the products of specific seawater conditions known as dolomite seas however whether these so called dolomite seas existed in the terminal ediacaran ocean has not yet been constrained the widespread botryoidal dolomite with well preserved sedimentary fabrics from the upper ediacaran dengying formation ca 551 to 545 ma south china can be potentially an ideal target to constrain this issue results showed that within the botryoidal dolomite fibrous dolomite cements are the dominant constituent part and either grew upward from microbialite layers or occurred in sheet cracks within the microbialites implying a syn sedimentary diagenesis two different types of fibrous cements are newly redefined fascicular and radial slow dolomite well preserved chemical and cathodoluminescent zonations and length slow optical characters are direct evidence for syn sedimentary primary dolomite precipitation different with the previous alternative interpretations of mimetic dolomitization of aragonite or high mg calcite precursors in contrast microbialite matrix consists of finely crystalline dolomicrite and preserved microbial fabrics reveling an early mimetic dolomitization of aragonitic precursors the dolomite precipitation and mimetic dolomitization likely occurred in coeval seawater or seawater type fluids as indicated by comparable 13c and 87sr 86sr data with global changes in particular the presence of primary dolomite cement precipitates within botryoidal dolomite can reflect that the specific dolomite seas associated with anoxic or even euxinic shallow water conditions inferred by redox sensitive trace elements and rees and increased microbial activity also prevailed in the terminal ediacaran ocean however the occurrence of dolomite seas was not one occasional event but common even if not persistent in the early to terminal neoproterozoic oceans this study helps to improve the understanding of dolomite problem and ubiquitous distribution of precambrian dolomite worldwide

sedimentary characteristics and origin of dolomitic ooids of the terminal ediacaran dengying formation at yulin chongqing south china abstract the ediacaran was a crucial transition period in the evolutionary history of the earth ediacaran ooids in the dengying formation from the yulin section in southwestern china are important archives of paleoenvironmental information although these ooids have been totally dolomitized the cortical fabric characteristics are locally preserved well indicating that these ooids were mimetically replaced the common occurrence of concentric radial fabrics and low level of sr concentrations 60 3 8 8 ppm in the studied ooid cortex is more likely suggestive of a primary low mg calcite mineralogy and that a calcite sea might exist during deposition of the second member of the dengying formation in situ geochemical data for the ooid cortices obtained by laser ablation inductively coupled plasma mass spectrometry show that these ooids have middle rare earth element enrichment prn smn 0 7 0 1 and smn ybn 1 5 0 4 and high fe contents 8200 1800 ppm this suggests ferruginous pore waters which were related to the selective or preferential absorption and release of rees by fe mn oxyhydroxides

stratigraphic investigations of carbon isotope anomalies and neoproterozoic ice ages in death valley california an unusual richness of biogeochemical events is recorded in neoproterozoic cambrian strata of the death valley region california united states eight negative carbon isotope d13c excursions are found in carbonate units between 1 08 ga and the precambrian cambrian boundary four of these excursions occur in carbonates that contain textural features similar to those found globally in postglacial cap carbonates including one or more of the following laminite with rollup structures apparent tube rocks seafloor precipitates and sheet crack cements however only two of these units the sourdough limestone member of the kingston peak formation and the noonday dolomite rest directly upon glacial strata the basal beck spring dolomite and the rainstorm member of the johnnie formation each contain negative excursions and cap carbonate like lithofacies but do not rest on known glacial deposits if the negative d13c excursions are assumed to record depositional processes two equally interesting hypotheses are possible 1 the death valley succession records four glacial pulses in neoproterozoic time but glacial units are not preserved at two stratigraphic levels 2 alternatively other global oceanographic processes can cause negative excursions and cap carbonate like facies in addition to or independent of glaciation

trends in oolite dolomitization across the neoproterozoic cambrian boundary a case study from death valley california abstract changes in dolomite fabric within the neoproterozoic cambrian stratigraphic succession in death valley california preserve evidence for a first order biogeochemical change in early diagenetic environments through the neoproterozoic cambrian transition oolite forms the primary focus of the study so that the general paleoenvironmental setting and presumed susceptibility to early diagenesis and fluid flow can be kept relatively constant across geologic time two key generalizations can be made 1 late neoproterozoic dolomitization in death valley occurred very early in the paragenetic sequence was volumetrically significant and preserved fine detail of the original aragonite or calcite precursor and 2 early cambrian dolomitization in death valley occurred late in the paragenetic sequence with burial was commonly incomplete and obliterated details of the calcite or aragonite precursor early diagenetic dolomitization of any kind was absent the dolomitization fabrics in death valley parallel the presumed pattern of seawater mg ca with respect to mimetic dolomitization in the paleozoic low mg ca little no mimetic dolomitization and cenozoic higher mg ca more common mimetic dolomitization however the volume of neoproterozoic mimetic dolomitization is immense compared to the cenozoic examples we speculate that a fundamental shift in the early diagenetic environment occurred in late neoproterozoic time perhaps in association with secular variation in the sulfate concentration of seawater and the advent and proliferation of penetrative bioturbation that destroyed sediment capping microbial mats an oscillatory trend in the fabric and volume of dolomite through the phanerozoic has been suggested but the termination of volumetrically significant mimetic dolomitization across the neoproterozoic cambrian transition a critical time in earth history for many reasons dwarfs the oscillatory trends noted in the phanerozoic

origin and interactions of fluids circulating over the amik basin hatay turkey and relationships with the hydrologic geologic and tectonic settings abstract we investigated the geochemical features of the fluids circulating over the amik basin se turkey syria border which is crossed by the northern extension of the dsf dead sea fault and represents the boundary area of three tectonic plates anatolian arabian and african plates we collected 34 water samples thermal and cold from natural springs and boreholes as well as 8 gas samples bubbling and gas seepage besides the gases dissolved in the sampled waters the results show that the dissolved gas phase is a mixture of shallow atmospheric and deep components either of mantle and crustal origin coherently the sampled waters are variable mixtures of shallow and deep ground waters the latter being characterised by higher salinity and longer residence times the deep groundwaters from boreholes deeper than 1000 m have a ch 4 dominated dissolved gas phase related to the presence of hydrocarbon reservoirs the very unique tectonic setting of the area includes the presence of an ophiolitic block outcropping in the westernmost area on the african plate as well as basalts located to the north and east on the arabic plate the diffuse presence of co 2 enriched gases although diluted by the huge groundwater circulation testifies a regional degassing activity fluids circulating over the ophiolitic block are marked by h 2 dominated gases with abiogenic methane and high ph waters the measured 3 he 4 he isotopic ratios display contributions from both crustal and mantle derived sources over both sides of the dsf although the serpentinization process is generally independent from mantle type contribution the recorded helium isotopic ratios highlight variable contents of mantle derived fluids due to the absence of recent volcanism over the western side of the basin african plate we argue that co 2 rich volatiles carrying mantle type helium and enriched in heavy carbon are degassed by deep rooted regional faults rather than from volcanic sources

stable isotope variations in the neoproterozoic beck spring dolomite and mesoproterozoic mescal limestone paleokarst implications for life on land in the precambrian proterozoic karst events lowered 13c values by as much as 11 for the 800 ma beck spring dolomite california and as much as 8 5 for the 1 1 ga mescal limestone central arizona relative to the originally deposited carbonate the 13c changes are attributed to input of 13c depleted organic co2 derived from photosynthetic organisms that colonized the ancient land surface the large isotopic shift and its presence at two separate localities suggest that proterozoic karst surfaces were colonized by significant photosynthetic communities with phytomasses possibly approaching those of today

a survey of paleozoic microbial fossils in chert abstract non acritarch microbial fossils from paleozoic marine cherts exhibit generally poor preservation with rare exceptional preservation microbial microfossils were discovered in 11 out of 17 stromatolitic and non stromatolitic paleozoic units containing replacement cherts from the continental united states many microfossils likely have a cyanobacterial affinity having both coccoid and filamentous morphotypes examined units range in age from middle cambrian to late permian and were deposited in peritidal open shelf and basinal settings all of which have preserved microbial assemblages cherts from the examined units generally formed during early diagenesis and the quality of microbial preservation does not seem to have changed during the paleozoic which is a period that experienced significant secular changes in the mode of marine silica formation

microbial fossilization in carbonate sediments a result of the bacterial surface involvement in dolomite precipitation recent dolomitic sediment samples from lagoa vermelha brazil were examined microscopically to study the process of bacterial fossilization in carbonate sediments bacteria like bodies were intimately associated with carbonate mineral surfaces and coatings on the former demonstrate the calcification of single bacterial cells the bacterial fossilization process in lagoa vermelha sediments was simulated in the laboratory by cultivation of mixed and pure cultures of sulphate reducing bacteria which were isolated from the lagoa vermelha sediments these cultures produced carbonate minerals that were studied to provide insight into the initiation of the fossilization process in mixed culture experiments bacterial colonies became calcified whereas in pure culture experiments single bacterial cells were associated with dolomite surfaces dolomite nucleated exclusively in bacterial colonies intimately associated with extracellular organic matter and bacterial cells electrophoretic mobility measurements of the bacterial cells in electrolyte solutions demonstrated the specific adsorption of ca 2 and mg 2 onto the cell surfaces indicating the role of the bacterial surface in carbonate nucleation and bacterial fossilization the affinity of the cells for mg 2 was related to the capability of the strains to mediate dolomite formation combined with sulphate uptake which dissociates the mgso 4 o ion pair and increases the mg 2 availability the concentration of mg 2 ions in the microenvironment around the cells where the conditions are favourable for dolomite precipitation may be the key to overcome the kinetic barrier to dolomite formation these results demonstrate that bacterial fossilization is a consequence of the cell surface involvement in carbonate precipitation implying that fossilized bacterial bodies can be used as a tool to recognize microbially mediated carbonates

the tonian beck spring dolomite marine dolomitization in a shallow anoxic sea abstract the reason for the abundance of dolomite lithologies in earth s early geological record compared to modern environments remains contentious this study provides new insight into this precambrian dolomite problem by revisiting one of the most controversial dolomite localities the beck spring dolomite of death valley usa consistent with some previous studies petrographic evidence indicates that although the beck spring dolomite now consists almost entirely of dolomite it was originally precipitated largely as aragonite and high mg calcite depositional constituents microbialites and ooids were likely originally aragonitic and early marine length fast cements now dolomite are suggested to have precipitated as high mg calcite then replaced syntaxially by dolomite based on petrographic and geochemical evidence we suggest that marine dolomitization was the dominant synsedimentary diagenetic process in the unit and for the most part involved syntaxial and mimetic replacement further a length slow fibrous dolomite generation was precipitated during the later stages of marine diagenesis as a primary marine dolomite cement this is indicated by the length slow crystallographic structure of the cement and from its preserved geochemical and cathodoluminescence growth zonation this new evidence for tonian marine dolomite precipitation reinforces the idea of precambrian marine environmental conditions including the chemical composition of seawater promoting dolomite formation at this time the trace metal geochemical composition of well preserved marine components especially dolomite marine cements reveals information about redox conditions in this tonian shallow seawater in terms of rare earth element geochemistry the beck spring dolomite has no significant ce anomaly and a ubiquitous positive eu anomaly consistent with widespread oceanic anoxia during deposition furthermore the relatively low levels of iron and chalcophile elements co cu pb and zn in marine components compared to other neoproterozoic carbonates suggest euxinic conditions both anoxic and sulphidic prevailed during deposition of the beck spring dolomite

helium isotope variations in turkey relationship to tectonics volcanism and recent seismic activities the distribution of helium isotope ratios in the various tectonic provinces of turkey is examined through a synthesis of previously published data and the results of a recent survey along the north anatolian fault zone nafz following the catastrophic 1999 earthquakes the r ra values where r sample 3he 4he and ra air 3he 4he cover a wide range from 0 05 to 7 87 and the mantle derived helium is clearly identified in most locations the mantle derived component is high 50 of total he in a regions of central and eastern anatolia both of which are associated with historically active volcanoes and b the seismically active west to central segment of nafz while the mantle contribution reaches a maximum at nemrut volcano in eastern anatolia a region of dominantly compressional tectonics and with moderate enthalpy geothermal fields it is relatively low 50 in the western anatolian extensional province even though this region has the highest geothermal potential the average 3he enthalpy ratios estimated for the different provinces suggest lithospheric stretching and rise of the geotherm as the major mechanism of high heat flow yet limited intrusive activity in western anatolia is suggested as the reason for the comparatively low he additions and consequently low 1 7 106 atoms j 3he enthalpy ratios a more extensive magmatic activity appears to be responsible for the greater input of both heat and helium in eastern and central anatolia with intra province 3he enthalpy variations from 3 1 106 atoms j in eastern to 0 25 106 atoms j in central anatolia reflecting the ageing of hydro magmatic systems the relatively high 3he concentrations in low enthalpy waters of northern anatolia 2 8 106 atoms j are particularly significant since there is no evidence of volcanic activity associated with the strike slip motion along the seismically active segment of nafz continuous monitoring of he isotope compositions along nafz should lead to a better understanding of this apparent anomaly as well as the relationship if any between he isotope variations and seismic activities in this region

causes and consequences of extreme permo triassic warming to globally equable climate and relation to the permo triassic extinction and recovery permian waning of the low latitude alleghenian variscan hercynian orogenesis led to a long collisional orogeny gap that cut down the availability of chemically weatherable fresh silicate rock resulting in a high co2 atmosphere and global warming the correspondingly reduced delivery of nutrients to the biosphere caused further increases in co2 and warming melting of polar ice curtailed sinking of o2 and nutrient rich cold brines while pole to equator thermal gradients weakened wind shear and associated wind driven upwelling lessened further diminishing productivity and carbon burial as the earth warmed dry climates expanded to mid latitudes causing latitudinal expansion of the ferrel circulation cell at the expense of the polar cell increased coastal evaporation generated o2 and nutrient deficient warm saline bottom water wsbw and delivered it to a weakly circulating deep ocean warm deep currents delivered ever more heat to high latitudes until polar sinking of cold water was replaced by upwelling wsbw with the loss of polar sinking the ocean was rapidly filled with wsbw that became increasingly anoxic and finally euxinic by the end of the permian rapid incursion of wsbw could have produced 20 m of thermal expansion of the oceans generating the well documented marine transgression that flooded embayments in dry hot pangaean mid latitudes the flooding further increased wsbw production and anoxia and brought that anoxic water onto the shelves release of co2 from the siberian traps and methane from clathrates below the warming ocean bottom sharply enhanced the already strong greenhouse increasingly frequent and powerful cyclonic storms mined upwelling high latitude heat and released it to the atmosphere that heat trapped by overlying clouds of its own making suggests complete breakdown of the dry polar cell resulting rapid and intense polar warming caused or contributed to extinction of the remaining latest permian coal forests that could not migrate any farther poleward because of light limitations loss of water stored by the forests led to aquifer drainage adding another 5 m to the transgression non peat forming vegetation survived at the newly moist poles climate feedback from the coal forest extinction further intensified warmth contributing to delayed biotic recovery that generally did not begin until mid triassic but appears to have resumed first at high latitudes late in the early triassic current quantitative models fail to generate high latitude warmth and so do not produce the chain of events we outline in this paper future quantitative modeling addressing factors such as polar cloudiness increased poleward heat transport by deep water and its upwelling by cyclonic storms and sustainable mid latitude sinking of warm brines to promote anoxia warming and thermal expansion of deep water may more closely simulate conditions indicated by geological and paleontological data

soil gas distribution in the main coseismic surface rupture zone of the 1980 ms 6 9 irpinia earthquake southern italy soil gas measurements of different gas species with different geochemical behaviors were performed in the area of the pecore plain a 200 m 300 m sized fault bounded extensional basin located in the northern mount marzano massif in the axial belt of the southern apennine chain the pecore plain area was affected by coseismic surface faulting during the ms 6 9 1980 irpinia earthquake the strongest and most destructive seismic event of the last 30 years in southern italy the collected data and their geostatistical analysis provide new insights into the control exerted by active fault segments on deep seated gas migration toward the surface the results define anomalies that are aligned with the nw se trending coseismic rupture of the 1980 earthquake along the western border of the plain as well as along the southern border of the plain where a hidden e w striking fault is inferred geospatial analysis highlights an anisotropic spatial behavior of 222rn along the main nw se trend and of co2 along the e w trend this feature suggests a correlation between the shape and orientation of the anomalies and the barrier conduit behavior of fault zones in the area furthermore our results show that gas migration through brittle deformation zones occurs by advective processes as suggested by the relatively high migration rate needed to obtain anomalies of short lived 222rn in the soil pores

the detection of concealed faults in the ofanto basin using the correlation between soil gas fracture surveys abstract an integrated geochemical morphological and structural analysis was applied to a basin filled with clayey sediments in southern italy ofanto valley to delineate tectonic features more than 100 soil gas samples were collected and analysed for co2 rn and he and the resulting distribution was compared with the location and orientation of field observed brittle deformations faults and fractures and air photo interpreted morphotectonic features the results show that the highest helium radon and co2 values occur preferentially along elongated zones similar to the most representative trends obtained by geomorphological and mesostructural analyses i e anti apennine apennine and secondarily n s orientations furthermore the development of geostatistical techniques has allowed the semi quantitative evaluation of the anisotropic soil gas distribution the gas distribution pattern is considered to result from the combination of the anisotropic distribution of fracture traces and the randomly distributed background field the correspondence between soil gas distribution and geomorphological mesostructural features as well as the results from the geostatistical analysis suggest that gas leakage towards the surface is controlled by the same structural pattern which also created some morphological features this technique has been shown to be a useful tool for neotectonic studies this is especially true in basins filled with clayey sediments as soil gas is even able to define the leakage of deep seated gases along tectonic discontinuities which have no surface expression

diagenesis of late proterozoic carbonates the beck spring dolomite of eastern california abstract petrographic and compositional attributes of limestone and dolostone in the beck spring dolomite of eastern california indicate that late proterozoic mineralogies isotopic compositions and diagenetic processes were similar to those inferred for younger phanerozoic marine carbonate sequences allochems in limestones include strontium rich ooids with well preserved concentric banding and cortices of equant neomorphic calcite that commonly exhibit dissolution and compaction features cements include microdolomite rich columnar marine calcite and equant spar calcites are depleted relative to dolomites and become enriched with stratigraphic depth acicular and columnar marine cement and allochems in dolostones display fabrics identical to those in limestones but are isotopically distinct dolomite ooids columnar and acicular cement crystal silt and early luminescent spar cement from four stratigraphic sections define overlapping positive oxygen carbon covariant fields that trend toward depleted calcite compositions early luminescent dolomite spar cement is unconformably overlain by depleted ferroan dolospar fabric data suggest that marine cement and ooids were precipitated as magnesian calcite and aragonite isotopic data suggest that metastable components locally stabilized to calcite during subaerial exposure while laterally dolomitization took place in mixed marine meteoric waters early dolospar precipitation began during replacive dolomitization and late ferroan dolospar precipitated during burial lack of evidence for hypersaline conditions suggests that late proterozoic normal marine carbonate isotopic composition was 0 5 2 018o and 5 3 0 5913c

tectonic subsidence of the early paleozoic passive continental margin in eastern california and southern nevada quantitative analysis of tectonic subsidence in cambrian and ordovician platform carbonates and associated strata exposed in the spring mountains nevada and the nopah funeral and inyo ranges california indicates that subsidence associated with this segment of the early paleozoic passive continental margin is exponential in form consistent with thermal contraction of the lithosphere following extension as in other parts of the north american cordillera continental separation in the southern great basin appears to have taken place between 590 and 545 ma these results are not sensitive to uncertainties in stratigraphic thickness biostratigraphic age control or paleobathymetry uncertainties in the cambrian time scale lead to predictable variations in the inferred time of onset of thermal subsidence but they have no effect on the inferred stratigraphic position of the rift to post rift transition a younger age for the base of the middle cambrian results in a younger inferred age of onset of thermal subsidence accompanied by greater rates of subsidence during the cambrian whereas a significantly older estimate of the onset of thermal subsidence can be obtained only if the base of the middle cambrian is substantially older than 540 ma a possibility that is inconsistent with available data results of the subsidence analysis are particularly significant because this is one of the few regions along the length of the north american cordillera where they can be compared directly to the geologic evidence for syn rift and post rift deposition basement involved faulting associated with the amargosa basin aulacogen ceased during deposition of the noonday dolomite which is thought to be older than 700 680 ma on the basis of stromatolites of late riphean affinity the overlying johnnie formation contains supposed vendian stromatolites younger than 700 680 ma if it is assumed that our results indicate the timing of the final rift to post rift transition then either the ages inferred from stromatolites are incorrect or the lithosphere was thinned regionally after deposition of the noonday the latter possibility is supported by limited geologic evidence for extension in latest proterozoic and early cambrian time the lack of appreciable physical evidence for crustal extension after deposition of the noonday however may imply that 1 a uniform extension model for lithospheric thinning is inappropriate for this part of the margin or that 2 some or all of the localities studied are continentward of the hinge zone and that the observed subsidence is exaggerated by flexural loading in a deeper basin to the west

gps constraints on continental deformation in the africa arabia eurasia continental collision zone and implications for the dynamics of plate interactions 1 the gps derived velocity field 1988 2005 for the zone of interaction of the arabian african nubian somalian and eurasian plates indicates counterclockwise rotation of a broad area of the earth s surface including the arabian plate adjacent parts of the zagros and central iran turkey and the aegean peloponnesus relative to eurasia at rates in the range of 20 30 mm yr this relatively rapid motion occurs within the framework of the slow moving 5 mm yr relative motions eurasian nubian and somalian plates the circulatory pattern of motion increases in rate toward the hellenic trench system we develop an elastic block model to constrain present day plate motions relative euler vectors regional deformation within the interplate zone and slip rates for major faults substantial areas of continental lithosphere within the region of plate interaction show coherent motion with internal deformations below 1 2 mm yr including central and eastern anatolia turkey the southwestern aegean peloponnesus the lesser caucasus and central iran geodetic slip rates for major block bounding structures are mostly comparable to geologic rates estimated for the most recent geological period 3 5 myr we find that the convergence of arabia with eurasia is accommodated in large part by lateral transport within the interior part of the collision zone and lithospheric shortening along the caucasus and zagros mountain belts around the periphery of the collision zone in addition we find that the principal boundary between the westerly moving anatolian plate and arabia east anatolian fault is presently characterized by pure left lateral strike slip with no fault normal convergence this implies that extrusion is not presently inducing westward motion of anatolia on the basis of the observed kinematics we hypothesize that deformation in the africa arabia eurasia collision zone is driven in large part by rollback of the subducting african lithosphere beneath the hellenic and cyprus trenches aided by slab pull on the southeastern side of the subducting arabian plate along the makran subduction zone we further suggest that the separation of arabia from africa is a response to plate motions induced by active subduction

secular variations in precambrian seawater chemistry and the timing of precambrian aragonite seas and calcite seas an extension of the seawater secular variation model that successfully predicted the observed timing of phanerozoic mgso 4 vs kcl marine evaporites and aragonite seas vs calcite seas has been applied to the prediction of the secular variations in the major ion chemistry of seawater and aragonite seas vs calcite seas during the precambrian testing of the predictions was based on those precambrian seafloor carbonate precipitates that have been interpreted by others to have formed originally as aragonite of 16 examples of precambrian seafloor aragonite 14 fall within the 6 periods of aragonite seas predicted for the late archean proterozoic by the model 1 falls on the transition between an aragonite sea and calcite sea and 1 falls in a period of calcite seas this strong correlation supports the following predictions of the model 1 precambrian seawater was a saline nacl water with ca hco 3 since at least the late archean 2 the major ion compositions of precambrian seawater chemistry and their secular variations are in the same ranges as those of phanerozoic seawater 3 the mg ca mole ratio in seawater has controlled the types of caco 3 polymorphs that have precipitated from earth9s oceans throughout the phanerozoic and most if not all of the precambrian

environmental and diagenetic variations in carbonate associated sulfate an investigation of cas in the lower triassic of the western usa an integrated stable isotope elemental and petrographic analysis of early triassic spathian carbonates and evaporites along a proximal to deep environmental transect reveals significant variations in 34s composition of carbonate associated sulfate cas the variations in the 34s of cas are strongly correlated with the ca mg composition of carbonates suggesting that the variations are driven by the degree of dolomitization the 34s of dolostones and evaporites are similar to one another and exhibit lower 34s values than limestones from all localities three hypotheses may explain the differences in 34s between proximal dolostones evaporites and inner middle shelf limestones 1 limestones experienced anaerobic sulfate reduction and subsequent incorporation of 34s enriched sulfate into cas during diagenesis while dolostones did not this is unlikely because of the lack of correlation between 34scas and toc as well as other indicators of diagenesis 2 dolomitization controlled the 34scas in proximal paleoenvironments where the source of the 34s depleted fluids was either continentally derived or the result of rayleigh distillation during evaporite formation and 3 a 34s depth gradient existed during the early triassic such that limestones formed in distal waters are more enriched in 34s versus evaporites and dolostones formed in proximal settings we do not favor this hypothesis because the strong correlation between ca mg and 34scas implies that dolomitization controls the 34scas in these samples results from subtidal well preserved non dolomitized limestones suggest that the 34s of spathian seawater sulfate may have been heavier than previously suggested from analyses of evaporite deposits alone

high spatial resolution radon measurements reveal hidden active faults on mt etna radon emissions are frequently monitored in volcanically and tectonically active areas in order to reveal changes in soil degassing as radon acts a tracer for the more abundant co2 degassing commonly observed in such areas between july 2002 and may 2003 a series of discrete measurements of radon concentrations in soil were made with high spatial resolution similar to5 100 m in the santa venerina area on mt etna these measurements revealed well defined linear anomalies that we interpret as being caused by active faults whose higher porosity than surrounding soils allows an increased co2 flux carrying radon from beneath these faults were not visible at the surface and were therefore revealed at high spatial resolution by our radon survey our hypothesis that the positive anomalies are attributable to active faults was strengthened by the observation of concentrated damage along this geometry during the earthquakes that struck this area in late october 2003

precambrian cambrian transition death valley united states the death valley region contains one of the best exposed and often visited precambrian cambrian successions in the world but the chronostratigraphic framework necessary for understanding the critical biologic and geologic events recorded in these sections has been inadequate the recent discovery of treptichnus phycodes pedum within the uppermost parasequence of the lower member of the wood canyon formation allows correlation of the precambrian cambrian boundary to this region and provides a necessary global tie point for the death valley section new carbon isotope chemostratigraphic profiles bracket this biostratigraphic datum and record the classic negative carbon isotope excursion at the boundary for the first time biostratigraphic chemostratigraphic and lithostratigraphic information from pretrilobite strata in this region can be directly compared with similar data from other key sections that record the precursors of the cambrian explosion few precambrian cambrian boundary sections contain both the facies restricted boundary fossil t pedum and carbon isotope data as found in death valley thus the death valley succession provides a critical link toward our understanding of the correlation between siliciclastic dominated and carbonate dominated precambrian cambrian transition sections