magma degassing buffered by vapor flow through brecciated conduit margins obsidian pyroclasts a common component of rhyolitic tephra preserve a range of volatile contents which has been used to infer syneruptive conditions of magmatic degassing here we show that the textures of obsidian pyroclasts provide information on physical mechanisms of magma flow and degassing along conduit margins obsidian clasts often contain xenoliths sheared bands of lithic powder and textures consistent with magma autobrecciation these features suggest that pyroclastic obsidian primarily forms near conduit walls where magma fragments and reanneals during ascent we use these observations to develop a degassing model for pyroclastic obsidian from the a d 1340 mono craters california eruptions we suggest that degassing was buffered by continual flux of vapor through highly permeable brecciated magma along conduit walls continuous reequilibration of magma with vapor of relatively constant composition not only explains the co 2 h 2 o and d h 2 o data from mono craters pyroclastic obsidian but also requires much lower magmatic co 2 values than the commonly accepted model of closed system degassing taken together the chemical and physical evidence suggests that magma brecciation along conduit walls aids the degassing of ascending rhyolite

nature and origin of the nonsulfide zinc deposits in the sierra mojada district coahuila mexico constraints from regional geology petrography and isotope analyses the sierra mojada district comprises multiple types of near surface mineral concentrations ranging from polymetallic sulfide zones nonsulfide zn nsz deposits and a silver rich pb carbonate deposit hosted by lower cretaceous carbonate strata hypogene concentrations of fe zn pb cu ag sulfides and sulfosalts are locally preserved and are associated with hydrothermal dolomite and silica alteration mineralogy and sulfur isotope data suggest primary zn pb ag mineralization from circa 200 c hydrothermal fluids the nsz deposits dominantly consist of smithsonite and hemimorphite associated with local mn fe oxides the red zinc zone consists of strata bound zones dominantly of hemimorphite that fills pores in residual and resedimented fe oxides the white zinc zone shows local dissolution features including internal sediments interbanded with and cemented by smithsonite similar pb isotopic compositions of smithsonite hemimorphite and cerussite to sierra mojada galena document that the nsz deposits originated from polymetallic carbonate replacement sulfide deposits with flow of metal bearing groundwater being controlled by local topography and structural features in this extensional terrane oxygen isotope values for sierra mojada smithsonite are relatively constant 18ovsmow 20 9 to 23 3 but are unusually low compared to other supergene smithsonites using 18ovsmow 8 of modern groundwater at nearby cuatrocienegas smithsonite formational temperatures are calculated to have been between 26 to 35 c smithsonite precipitation was favored by near neutral conditions typical of carbonate terranes whereas hemimorphite precipitated by reaction with wallrock silica and locally or episodically more acidic conditions resulting from sulfide oxidation transition to and stabilization of the modern desert climate over the past 9000 years from the late pleistocene wetter cooler climate of northern mexico resulted in episodic drawdown of the water table and termination of local supergene metal mobilization

evolution of cupido and coahuila carbonate platforms early cretaceous northeastern mexico the cupido and coahuila platforms of northeastern mexico are part of the extensive carbonate platform system that rimmed the ancestral gulf of mexico during barremian to albian time exposures of cupido and coahuila lithofacies in several mountain ranges spanning an 80 000 km 2 area reveal information about platform morphology and composition paleoenvironmental relations and the chronology of platform evolution new biostratigraphic data integrated with carbon and strontium isotope stratigraphy significantly improve chronostratigraphic relations across the region these data substantially change previous age assignments of several formations and force a revision of the longstanding stratigraphy in the region the revised stratigraphy and enhanced time control combined with regional facies associations allow the construction of cross sections isopach maps and timeslice paleogeographic maps that collectively document platform morphology and evolution the orientation of the cupido barremianaptian shelf margin was controlled by the emergent coahuila basement block to the northwest the south facing margin is a highenergy grainstone shoal whereas the margin facing the ancestral gulf of mexico to the east is a discontinuous rudist coral reef a broad shelf lagoon developed in the lee of the cupido margin where as much as 660 m of cyclic peritidal deposits accumulated during middle to late aptian time a major phase of flooding forced a retrograde backstep of the cupido platform shifting the locus of shallow marine sedimentation northwestward toward the coahuila block this diachronous flooding event records both the demise of the cupido shelf and the consequent initiation of the coahuila ramp the backstepped coahuila ramp aptianalbian consisted of a shallow shoal margin separating an interior evaporitic lagoon from a low energy muddy deep ramp more than 500 m of cyclic carbonates and evaporites accumulated in the evaporitic lagoon during early to middle albian time restriction of the platform interior dissipated by middle to late albian time with the deposition of peloidal miliolid rich packstones and grainstones of the aurora formation the coahuila platform was drowned during latest albian to early cenomanian time and the deep water laminites of the cuesta del cura formation were deposited this study fills in a substantial gap in the cretaceous paleogeography of the eastern gulf of mexico coast improving regional correlations with adjacent hydrocarbon rich platforms the enhanced temporal relations and chronology of events recorded in the cupido and coahuila platforms significantly improve global correlations with coeval economically important platforms worldwide perhaps con

concurrence of folding and remagnetization events in the monterrey salient ne mexico abstract carbonate formations from many locations reveal magnetizations that are secondary attaching a numerical age to these remagnetizations would provide information on orogenic processes to contribute to the effort of assigning an age to remagnetization events lower cretaceous formations from the monterrey salient in northeast mexico were sampled individual fold tests reveal eight site pair synfolding remagnetizations set a of eocene age the remanence is a chemical remanent magnetization crm carried by magnetite the magnetization of set b is possibly due to an early carbonate alteration that produced a remanence significantly older than folding a complexity of set b is that the site pairs reveal k versus unfolding percentage diagrams with maximum unfolding peaks at 100 to 125 an explanation of multiple deformation phases with an earlier horizontal folding phase around a non plunging horizontal axis and a later vertical axis rotation is suggested for the past 100 peaks of the b sites the latter deformation rotation about a vertical axes is revealed by a declination strike test in set a sites and site means of the full collection that deviate counterclockwise from the reference declination by combining synfolding results with published 40ar 39ar illite ages of folding fitz diaz et al 2016 remagnetization ages in set a sites of 48 52 ma are obtained the magnetization in set b sites is likely older though not well constrained interestingly prior results from the central sierra madre oriental to the south show two remagnetization events late cretaceous and early eocene in age in a succession from w to e nemkin et al 2015 the age of folding and remagnetization acquisition in set a sites along the monterrey salient are concurrent with the frontal remagnetized folds in the central sierra madre oriental thus the timing of major remagnetization in the monterrey salient occurred in the eocene

geochemical and paleoenvironmental record of the early to early late aptian major episodes of accelerated change evidence from sierra del rosario northeast mexico abstract the lower to lower upper aptian succession of northern mexico documents the drowning of the shallow water cupido cupidito carbonate platform system followed by deposition of the deep water sediments of the la pena formation using 13 c stratigraphy geochemical and mineralogical information coupled with previous microfacies paleontological and total organic carbon toc data from a stratigraphic section which includes such lithological change this study identifies distinctive episodes of accelerated global environmental change and determines the paleoenvironmental conditions conducive to the deposition of toc rich intervals within the cupidito unit the oceanic anoxic event 1a oae 1a is recorded near the base of the section and the intra furcata negative excursion in the topmost beds of the unit the upper part of the section within the la pena formation is correlatable with the noire level organic carbon rich intervals occur in the lower and middle part of the oae 1a upper part of the cupidito unit base of the la pena formation and in the noire level equivalent reducing conditions within the sediment and oxic dysoxic at the seafloor locally controlled persisted both before and during oae 1a interval in the cupidito lagoon oxygen depleted conditions dysoxic anoxic were more permanent and stronger during the deposition of the base of the la pena formation and the noire equivalent level it is proposed here that deposition of the lower middle part of the oae 1a and the base of the la pena formation was influenced by climate controlled increases in detrital and accompanying nutrient influx that supplied especially biolimiting nutrients fe p fostering marine productivity and toc burial upwelling of nutrient rich deeper waters and minor arrival of nutrients from runoff both account for the domination of radiolaria and organic carbon burial during the noire level equivalent record of the oae 1a time equivalent facies in the cupidito lagoonal sediments confirms the diachronism of the cupidito la pena flooding heterozoan carbonate production in the cupidito ramp was uninterrupted during and after oae 1a periodic arrival of detrital components and nutrients during warmer humid periods accelerated platform drowning which peaked during the diachronic deposition of the la pena formation

reevaluation of the oxygen isotopic composition of planktonic foraminifera experimental results and revised paleotemperature equations cultured planktonic foraminifera orbulina universa symbiotic and globigerina bulloides nonsymbiotic are used to reexamine temperature 18o relationships at 15 25 c relationships for both species can be described by linear equations equations for o universa grown under low light ll and high light hl share a slope of 4 80 0 21 c 1 with a hl ll offset of 0 33 due to symbiont photosynthetic activity the effect of co32 on o universa is 0 002 mol 1 kg 1 and is insensitive to temperature for g bulloides ontogenetic effects produce size related trends in temperature 18o whereby larger shells are enriched in 18o relative to smaller specimens the o universa temperature 18o relationships are more accurate than previously published equations for describing plankton tow data our equations do not explain planktonic core top data with the same precision but provide a good fit to benthic cibicidoides data below 10 c temperature 18o relationships for g bulloides provide good agreement with field data for this species from the northeast pacific

black shale deposition and early diagenetic dolomite cementation during oceanic anoxic event 1 the mid cretaceous maracaibo platform northwestern south america thin laterally continuous organic rich dolomitic marlstones were deposited in the extended late aptian early albian epicontinental sea of northwestern south america these intervals are the proximal equivalents of thick hemipelagic black shale ammonitic floatstone couplets deposited in the distally stepped differentially subsiding part of the maracaibo platform the marlstones reflect the dynamic conditions resulting from orbital forcing mechanisms and can be genetically related to 1 minor sea level changes 2 proximal turnovers in marine productivity and 3 sudden climate shifts affecting mid cretaceous shoaling upward shallow marine carbonate cyclicity therefore the marlstones may well be linked to the multiple environmental perturbations collectively referred to as oceanic anoxic event 1 the interstitial euhedral dolomite has a medium crystallinity and exhibits unusual textural relations with framboidal pyrite and gypsum the authigenic mineral assemblage also includes quartz ca f apatite and barite which together with the chemical signals of dolomite point to an unsteady climate regime bulk rock biomarker parameters rare earth element geochemistry and iron speciation data point to widespread photic zone anoxia and transient shallow marine euxinia by the time of deposition with climatic instability driving the delivery of oxidized detritus from the hinterlands these conditions led to a schizohaline redox stratified environment favorable to dolomite precipitation in such a depositional setting the bio utilization of fe mn and sulfur for organic matter respiration sustained elevated pore water alkalinity and ph and allowed for the pre compactional growth of interstitial dolomite

stratigraphy and provenance of strata along the san marcos fault central coahuila mexico stratigraphic and petrologic studies supported by geologic mapping north of the san marcos fault central coahuila indicate that as much as 3 000 m of coarse upper jurassic and lower cretaceous detritus was derived from south of the fault two coarse jurassic submarine conglomerate units las palomas and sierra el granizo beds of the la casita formation reflect separate episodes of displacement younger jurassic eolianite and marine sandstone colorado and tanque cuatro palmas beds of the la casita formation record subsequent tithonian fault inactivity neocomian rejuvenation of the fault produced alluvial deposits san marcos formation finer grained paralic or marine strata that are distal and suprajacent and manifest the same faulting are the la mula formation interruption of neocomian displacement is indicated by a tongue of carbonate padilla and barril viejo formations that divides the san marcos into upper and lower members the principal source of this detritus was the wildflysch of the late paleozoic arcproximal las delicias basin and the plutonic rocks that cut it rb sr ages on clasts and from outcrops of granitic rocks are triassic and probably reflect late stage magmatism within the las delicias arc although this arc supplied most of the detritus to the las delicias basin devonian ages on some clasts reveal that an unknown source area lay somewhere nearby during the late part of the paleozoic era the san marcos fault may have served as part of the system of transform faults that connected sea floor spreading ridges of the atlantic with those of the pacific if so then the jurassic units record periods of jurassic activity and inactivity of that system neocomian displacment may have been caused by subsequent isostatic adjustment

sedimentation and diagenesis along open and island protected windward carbonate platform margins of the cretaceous el abra formation mexico abstract the windward margin of the mid cretaceous valles san luis potosi carbonate platform in northeastern mexico included open and island protected segments depositional environments and diagenesis vary markedly with margin type sand shoals near the windward open margin are composed of oncoid bioclastic and cross laminated carbonates increasingly restricted and finer lagoonal and tidal flat environments occurred bankwards recording gradually decreasing wave and current energy lithofacies include peloid miliolid cryptalgal laminite lime mudstone and molluscan carbonates islands along the windward margin are composed of rudistid skeletal debris from adjacent reefs lagoonal to tidal flat sediments were deposited bankwards similar lithofacies occur as in these environments along the open margin but they are muddier and contain less diverse fauna the different energy regimes along the margin influenced the distribution and packaging of banktop sediments the bankward transition to low energy restricted environments was gradual across the open margin in contrast muddy sediments with restricted fauna accumulated in close proximity to the island protected margin non cyclic vertical lithofacies successions characterized the open platform margin whereas asymmetric shoaling upward sequences characterized the island protected margin early diagenesis along the open margin was minor burial diagenesis was of major importance thin rinds of marine cement are widespread but meteoric diagenesis was minor burial promoted extensive compaction mg rich connate brines expressed from guaxcama gypsum resulted in dolomitization and lithification thereby precluding further compaction pore fluids resulting from dehydration of guaxcama gypsum to anhydrite yielded pore filling and replacement anhydrite in the el abra formation burial and laramide deformation maastrichtian paleocene resulted in stylolitization and extensive fracturing uplift produced widespread meteoric diagenesis for the first time resulting in dissolution of anhydrite calcitization of dolomite and equant calcite cementation early diagenesis along the windward protected margin was extensive prolonged subaerial exposure resulted in calcrete cementation and secondary porosity subsequent marine cementation and internal sedimentation reduced porosity equant calcite cement precipitated during local upper cretaceous exposure burial diagenesis was limited to traces of dolomite anhydrite and late stage equant calcite cement suggesting similar pore fluids as in the open margin depositional environment determined the type and degree of early diagenesis which strongly influenced subsequent diagenetic events subtidal sediments of the open margin underwent minimal early diagenesis and entered the burial realm much as they were deposited they were subjected to intensive compaction and alteration by brines in contrast sediments exposed to meteoric diagenesis and marine cementation on near backreef islands and tidal flats entered the mesogenetic realm as stabilized lithified rocks much as they are at present

a review of the occurrence form and origin of c bearing species in the khibiny alkaline igneous complex kola peninsula nw russia abstract the khibiny complex hosts a wide variety of carbon bearing species that include both oxidized and reduced varieties oxidised varieties include carbonate minerals especially in the carbonatite complex at the eastern end of the pluton and na carbonate phases reduced varieties include abiogenic hydrocarbon gases particularly methane and ethane dispersed bitumens solid organic substances and graphite the majority of the carbon in the khibiny complex is hosted in either the carbonatite complex or within the so called central arch the central arch is a ring shaped structure which separates khibinites coarse grained eudialite bearing nepheline syenites in the outer part of the complex from lyavochorrites medium grained nepheline syenites and foyaites in the inner part the central arch is petrologically diverse and hosts the major ree enriched apatite nepheline deposits for which the complex is best known it also hosts zones with elevated hydrocarbon dominantly methane gas content and zones of hydrothermally deposited na carbonate mineralisation the hydrocarbon gases are most likely the product of a series of post magmatic abiogenic reactions it is likely that the concentration of apatite nepheline deposits hydrocarbon gases and na carbonate mineralisation is a function of long lived fluid percolation through the central arch fluid migration was facilitated by stress release during cooling and uplift of the khibiny complex as a result carbon with a mantle signature was concentrated into a narrow ring shaped zone

multiple episodes of dolomitization in the arbuckle group arbuckle mountains south central oklahoma field petrographic and geochemical evidence abstract the cambro ordovician arbuckle group in the arbuckle mountains south central oklahoma had a complex history of dolomitization that resulted in two different geometries of dolomite bodies stratal dolomite of stratigraphically consistent widespread distribution and non stratal dolomite of stratigraphically inconsistent local occurrence stratal dolomite includes the royer and butterly units in the lower arbuckle group most stratal dolomite samples are coarsely crystalline and have 87sr 86sr ratios 0 70890 0 70919 similar to late cambrian limestone and coeval seawater 0 7089 0 7092 all stratal dolomite and arbuckle limestone samples have low 18o values 5 3 to 11 9 the cross platform distribution of stratal dolomite coupled with dominant 87sr 86sr ratios similar to coeval seawater suggests that stratal dolomite formed during early diagenesis however the low 18o values indicate that all stratal dolomite and arbuckle limestone samples suffered postdepositional modification probably as the result of infiltration of meteoric water during development of the ordovician unconformities nonstratal dolomite is present in two areas the tishomingo anticline and the arbuckle anticline in the tishomingo anticline area massive bodies 10 km2 of nonstratal dolomite are present in a paleokarst system of pre middle ordovician age some of the nonstratal dolomite bodies were displaced by pennsylvanian faults whereas many dolomite bodies are related to the faults petrographically nonstratal dolomite is finely to medium crystalline and has replaced recrystallized limestone the dolomite has lower 87sr 86sr ratios 0 70772 0 70900 average 0 70834 and higher 18o values 0 6 to 5 8 average 2 9 relative to associated lower ordovician limestone 87sr 86sr 0 70878 0 70898 average 0 70887 18o 6 1 to 8 9 average 7 4 the petrographic and isotopic characteristics suggest that the nonstratal dolomite probably resulted from dolomitization of recrystallized limestone by post early ordovician seawater the relation of the nonstratal dolomite bodies to pennsylvanian faults may indicate that the dolomite originated from multiple times of seawater circulatio through a paleokarst system in the arbuckle anticline area nonstratal dolomite is present as small 1 km2 irregular bodies that are related to pennsylvanian faults and are associated with the margins of stratal butterly dolomite the nonstratal dolomite medium to coarsely crystalline and brightly luminescent is characterized by high radiogenic 87sr 86sr ratios 0 70951 0 70974 18o values average 1 1 and fe and mn concentrations average 1 32 mol and 0 65 mol respectively relative to all arbuckle carbonates such compositions suggest that this type of dolomite probably originated from fluids that were derived from the adjacent basin s duri g late paleozoic time

excess methane in continental hydrothermal emissions is abiogenic thermogenic hydrocarbons entirely deriving from the thermal degradation of organic matter usually exhibit methane to ethane plus propane ratios smaller than 100 we present hydrocarbon distribution data of continental hydrothermal gases whose methane has been independently identified to derive from the abiogenic reduction of co2 we find that excess amounts of methane with respect to thermogenic hydrocarbon distributions are characteristic for the investigated gases a similar pattern is observed for well discharges whose temperatures are too high to support any microbially mediated methanogenesis these findings strongly suggest that abiogenic methane production in continental hydrothermal systems is a more widespread process than previously assumed the maximum contribution of such emissions to the modern atmospheric ch4 budget is estimated at 1

copper deposition during quartz dissolution by cooling magmatic hydrothermal fluids the bingham porphyry abstract scanning electron microscope cathodoluminescence imaging is used to map successive generations of fluid inclusions in texturally complex quartz veinlets representing the main stage of ore metal introduction into the porphyry cu au mo deposit at bingham utah following conventional fluid inclusion microthermometry laser ablation inductively coupled plasma mass spectrometry la icpms is applied to quantify copper and other major and trace element concentrations in the evolving fluid with the aim of identifying the ore forming processes textures visible in cathodoluminescence consistently show that the bulk of vein quartz q1 characterized by bright luminescence crystallized early in the vein history cu fe sulfides are precipitated later in these veins in a microfracture network finally filled with a second generation of dull luminescing q2 quartz mapping of brine and vapor inclusion assemblages in these successive quartz generations in combination with la icpms microanalysis shows that the fluids trapped before and after cu fe sulfide precipitation are very similar with respect to their major and minor element composition except for copper copper concentrations in inclusions associated with ore formation drop by two orders of magnitude in a tight pressure temperature interval between 21 and 14 mpa and 425 350 c several hundred degrees below the temperature of fluid exsolution from the magma copper deposition occurs within a limited p t region in which sulfide solubility shows strong normal temperature dependence while quartz solubility is retrograde this permits copper sulfide deposition while secondary vein permeability is generated by quartz dissolution the brittle to ductile transition of the quartz feldspar rich host rocks occurs in the same temperature range which further enhances vein reactivation and promotes cooling and expansion of fluids ascending across the transition from lithostatic to hydrostatic conditions

u pb and re os geochronological evidence for the jurassic porphyry metallogenic event of the xiongcun district in the gangdese porphyry copper belt southern tibet prc abstract two large copper gold porphyry deposits no i and no ii were discovered in the last decade within the xiongcun district which is located along the south margin of the gangdese porphyry copper belt these two deposits are hosted by two porphyries that were emplaced into the early jurassic volcano sedimentary rock sequences of the xiongcun formation the porphyries are both quartz diorite bodies with one of these distinguished by its large quartz eyes our new molybdenite re os and zircon u pb dates for no i and no ii deposits and host intrusions reveal the presence of two middle jurassic ore forming episodes in the xiongcun district the no ii deposit is related to the 181 175 ma quartz diorite porphyry and formed ca 172 6 2 1 ma the no i deposit is related to the 167 161 ma quartz diorite porphyry with large quartz eyes and formed ca 161 5 2 7 ma geochronological and geochemical features of the jurassic ore bearing porphyries in the xiongcun district indicate that the porphyry copper gold mineralization formed in an island arc setting which is related to the northward subduction of the neo tethys oceanic plate these observations in combination with geochronological data reported at gangdese porphyry copper belt indicated four major metallogenic events existed in the gangdese porphyry copper belt at 172 161 ma 65 48 ma 40 23 ma and 20 12 ma we have identified two mineralization episodes comprise middle jurassic metallogenic event 172 161 ma in the xiongcun district which provides new constrains for the middle jurassic metallogenic event in the gangdese porphyry copper belt

diversity of primary cl textures in quartz from porphyry environments implication for origin of quartz eyes porphyry style mineralization is related to the intrusion and crystallization of small stocks which can be of different compositions from intermediate to felsic and can intrude into different host rocks from magmatic to sedimentary we used cathodoluminescence and electron probe microanalysis to study the internal textures of more than 300 quartz eyes from six porphyry deposits panguna papua new guinea far southeast porphyry philippines batu hijau indonesia antapaccay peru rio blanco chile and climax usa significant diversity of the internal textures in quartz eyes was revealed sometimes even within a single sample quartz grains with ti rich cores surrounded by ti poor mantles were found next to the grains showing the opposite ti distribution or only slight ti fluctuations we propose that diversity of the internal patterns in quartz eyes can actually reflect in situ crystallization history and that prolonged crystallization after magma emplacement under conditions of continuous cooling can account for the observed features of internal textures formation of quartz eyes begins at high temperatures with crystallization of high titanium quartz 1 which as the melt becomes more and more evolved and cooler is overgrown by low ti quartz 2 subsequent fluid exsolution brings about dramatic change in the melt composition oh alkalis and other cl complexed elements partition into the fluid phase whereas ti stays in the melt contributing to a rapid increase in ti activity separation of the fluid and its further cooling causes disequilibrium in the system and the quartz 2 becomes partially resorbed exsolution of the fluid gradually builds up the pressure until it exceeds the yield strength of the host rocks and they then fracture this pressure release most likely triggers crystallization of quartz 3 which is higher in ti than quartz 2 because ti activity in the melt is higher and pressure of crystallization is lower as a result of the reaction between the exsolved fluid and quartz a new phase a so called heavy fluid forms from this phase quartz 4 crystallizes this phase has extremely high metal carrying capacity and may give a rise to mineralizing fluids finally on the brink of the subsolidus stage groundmass quartz crystallizes prolonged crystallization under conditions of continuous cooling accounts better for the diversity of cl textures than crystallization in different parts of a deep magma chamber it is also in a better agreement with the existing model for formation of porphyry style deposits

magnetostratigraphy of mid cretaceous limestones from the sierra madre of northeastern mexico we present the results of a palaeomagnetic study of four mid cretaceous limestone sections exposed in northeastern mexico the limestones are weakly magnetized and exhibit two to three component magnetizations these magnetization components appear to be carried by both a sulphide mineral and a magnetite titanomagnetite mineral the sulphide mineral carries a reverse polarity overprint that often makes it difficult to isolate definitively the higher unblocking temperature component the high unblocking temperature component is well defined in the upper portion of the santa rosa canyon section and in the cienega del toro section and passes the fold test the characteristic remanent magnetization chrm inclinations agree well with predicted mid cretaceous inclinations for these sites although the declinations differ by more than 100 the relative rotation between these two sites probably occurred as the thrust sheets were emplaced during laramide deformation at two of the sections namely cienega del toro and the overturned los chorros sections only normal polarity directions are observed the la boca canyon and santa rosa canyon sections exhibit zones of both normal and reverse polarity magnetization correlation of these polarity zones with the geomagnetic polarity timescale provides a time framework for lithostratigraphic and palaeoceanographic studies of these sections

the magmatic hydrothermal transition evidence from quartz phenocryst textures and endoskarn abundance in cu zn skarns at the empire mine idaho usa information about the magmatic to hydrothermal transition is preserved in late stage features of quartz phenocrysts and endoskarn alteration in some cu zn skarn deposits such as the empire mine in idaho important features include 1 quartz phenocrysts with strong resorption textures such as vermicular zones of igneous groundmass cutting primary quartz cathodoluminescence banding 2 anomalous amounts of endoskarn more than 50 of mineralized rock 3 high f activities as evidenced by fluorite as an accessory mineral in igneous rocks in alteration assemblages and in fluid inclusions and by high f in hydroxyl sites in igneous biotite and amphibole and 4 direct association of zn which normally is deposited distally at low temperature with cu in proximal locations and in endoskarn these features are explained by the following model 1 f lowers the solidus temperature of the magma thus changing the timing temperature and duration of hydrothermal fluid exsolution 2 upon magmatic vapor saturation the f rich hydrothermal fluids form bubbles that adhere to quartz phenocrysts and chemically corrode tunnel into the quartz forming vermicular resorption textures 3 f rich hydrothermal fluids also promote the formation of endoskarn silicic rocks are attacked by f rich fluids in the same sense that carbonate wall rocks are dissolved by weakly to moderately acidic hydrothermal fluids 4 low fluid exsolution temperature facilitated by high f activity promotes high zn cu ratios in proximal locations due to the solubility of zn relative to cu at lower temperatures this model may be applicable at other localities such as the world class cu zn skarn antamina mine as well as some tin and rapakivi granites

regional stratigraphy and distribution of epigenetic stratabound celestine fluorite barite and pb zn deposits in the mvt province of northeastern mexico northeastern mexico hosts numerous epigenetic stratabound carbonate hosted low temperature hydrothermal deposits of celestine fluorite barite and zinc lead which formed by replacement of mesozoic evaporites or carbonate rocks such deposits can be permissively catalogued as mississippi valley type mvt deposits the deposits studied in the state of coahuila are associated with granitic and metasedimentary basement highs horsts marginal or central to the mesozoic sabinas basin these horsts controlled the stratigraphy of the mesozoic basins and subsequently influenced the laramide structural pattern the sabinas basin consists of 6 000 m thick jurassic to cretaceous siliciclastic carbonate and evaporitic series the mvt deposits are mostly in barremian and in aptian albian to cenomanian formations and likely formed from basinal brines that were mobilized during the laramide orogeny although earlier diagenetic replacement of evaporite layers barite and celestine deposits and lining of paleokarstic cavities in reef carbonates zn pb deposits is observed fluid inclusion microthermometry and isotopic studies suggest ore formation due to mixing of basinal brines and meteoric water homogenization temperatures of fluid inclusions range from 45 c to 210 c salinities range from 0 to 26 wt nacl equiv and some inclusions contain hydrocarbons or bitumen sulfur isotope data suggest that most of the sulfur in barite and celestine is derived from barremian to cenomanian evaporites regional geology and a compilation of metallogenic features define the new mvt province of northeastern mexico which comprises most of the state of coahuila and portions of the neighboring states of nuevo leon durango and perhaps extends into zacatecas and southern texas this province exhibits a regional metal zonation with celestine deposits to the south fluorite deposits to the north and barite and zn pb deposits mostly in the central part

combined raman microprobe spectrometry and microthermometry of fluid inclusions in minerals from igneous rocks of the gardar province south greenland abstract raman microprobe spectrometry has been applied to analysis of the gaseous phase in individual fluid inclusions in minerals from alkalic igneous rock types and associated hydrothermal veins from the gardar province south greenland quantitative analyses are given for co2 ch4 c2h6 h2 and h2s traces of co were observed in one co2 inclusion in conjunction with data from microthermometry the results permit calculation of the bulk chemical composition of entrapped fluids and evaluation of the possible pressure temperature oxygen fugacity and sulphur fugacity during entrapment of the individual fluid inclusions calculated oxygen fugacity values correspond to those of the nno and qfm buffer reactions at temperatures of 300 400 c and pressures of 0 5 1 0 kbar calculated sulphur fugacity values are within the range of normal ore forming solutions log fs2 6 to 10

methane origin and oxygen fugacity evolution of the baogutu reduced porphyry cu deposit in the west junggar terrain china most porphyry copper deposits worldwide contain magnetite hematite and anhydrite in equilibrium with hypogene copper iron sulfides chalcopyrite bornite and have fluid inclusions with co2 ch4 that are indicative of high fo2 in contrast the baogutu porphyry cu deposit in the west junggar terrain xinjiang china lacks hematite and anhydrite contains abundant pyrrhotite and ilmenite in equilibrium with copper iron sulfides chalcopyrite and has fluid inclusions with ch4 co2 that are indicative of low fo2 the mineralized intrusive phases at baogutu include the main stage diorite stock and minor late stage diorite porphyry dikes the main stage stock underwent fractional crystallization and country rock assimilation contamination and consists of dominant diorite and minor gabbro and tonalite porphyry the country rocks contain organic carbons 0 21 0 79 wt the 13cvpdb values of the whole rocks 23 1 to 25 8 in the wall rocks suggest a sedimentary organic carbon source the 13cvpdb values of ch4 28 2 to 36 0 and co2 6 8 to 20 0 in fluid inclusions require an organic source of external carbon and equilibration of their 13cco2 ch4 values 8 2 25 0 at elevated temperatures 294 830 c suggesting a significant contribution of thermogenic ch4 mineral composition data on the main stage intrusions such as clinopyroxene hornblende biotite magnetite ilmenite sphene apatite and pyrrhotite suggest that the primary magma at baogutu was oxidized and became reduced after emplacement by contamination with country rocks mineral compositions and fluid inclusion gas compositions suggest that the redox state of the system evolved from logfo2 fmq 1 in the magma stage to logfo2 fmq in the hydrothermal stage though oxidized magma was emplaced initially assimilation contamination of carbonaceous country rocks decreased its fo2 such that exsolved fluids contained abundant ch4 and deposited a reduced assemblage of minerals

sulfur bearing magmatic accessory minerals almost all magmas contain sulfide or sulfate bearing phases in most natural samples the sulfur bearing phase is a sulfide which typically is pyrrhotite fe1 x s or pyrite fes2 although chalcopyrite cufes2 pentlandite fe ni 9s8 sphalerite zns or molybdenite mos2 may be present as well sulfate minerals are rare at magmatic conditions and anhydrite caso4 is the most common other magmatic so4 bearing minerals include the sodalite group minerals hauyne simplified formula na ca 4 8 al6si6 o s 24 so4 cl 1 2 scapolite minerals silvialite ca na 4al6si6o24 so4 co3 and s bearing apatite ca5 po4 3 f cl oh barite baso4 has been mentioned in rare cases marchev 1991 sulfur bearing minerals usually constitute a negligible fraction of the mineral assemblage in magmatic rocks and thus can be classified as accessory minerals the crystallization of sulfide sulfate and s bearing minerals strongly depends on melt composition temperature and pressure and the s speciation in melt which in turn is strongly dependent on the prevailing oxygen fugacity baker and moretti 2011 this volume wilke et al 2011 this volume irrespectively of the low abundance of s bearing minerals the evolution of sulfur in magmas may be evaluated from the occurrence of sulfides and sulfates these minerals are critical for estimating the activity of various sulfur bearing species in magmas and can be used to constrain the oxygen fugacity and the s concentration in the melt e g pre eruptive sulfur concentration in melts the presence of either sulfide or sulfate in silicate melt indicates that the predominant dissolved sulfur species in the melt are s2 or s6 respectively typically one of these species is dominant but there are conditions where s2

cycle stacking and long term sea level history in the lower cretaceous gavrovo platform nw greece abstract the stacking pattern of peritidal shallowing upward cycles of a continuously exposed barremian to upper albian section from an isolated carbonate platform in the gavrovo tripolitza zone nw greece has been analyzed the 541 m thick succession is located in an intraplatform setting with an overall mud dominated facies development it comprises 252 peritidal cycles which show a systematic increase in cycle thickness from the barremian to albian comparison of the cycle stacking pattern of the section which spans 35 m y and several published curves of long term eustatic sea level history show striking similarities comparison of cycle stacking pattern in greece with a time equivalent section measured near potrero garcia in mexico suggests preservation of similar trends in fischer pl ts in the two areas even though a difference in mean cycle thickness indicates different rates of subsidence in greece and mexico this implies that the shallow water carbonates of the gavrovo platform are recording second order eustatic sea level variations closely spaced samples throughout the section allow evaluation of the degree of early diagenetic alteration of depositional facies within the shallowing upward cycles the degree of vadose diagenetic overprinting of intertidal and subtidal facies and multiple overprinting of individual cycles support a predominantly allocydic control of deposition by low amplitude high frequency sea level fluctuations during early cretaceous greenhouse climate however expected time gaps of different lengths in the succession during sea level lows ands may bias the direct translation of cycle stacking pattern into third order sea level curves

xiongcun tibet a telescoped system of veinlet disseminated cu au mineralization and late vein style au ag polymetallic mineralization in a continental collision zone abstract the xiongcun cu au deposit occurs in the western part of the gangdese porphyry and skarn cu au mineralization belt in the himalayan tibetan orogen and was formed in an intracontinental orogenic environment related to the india asia collision sericite 40 ar 39 ar dating of the xiongcun deposit indicates that ore formation occurred around 38 11 0 90 ma much earlier than the main ore forming ages 20 to 14 ma of the gangdese cu au metallogenic belt the potassium feldspar k ar age of the sulfide bearing pegmatoid dyke in the xiongcun district is 47 62 0 70 ma these ages indicate that the mineralization in xiongcun is related to relaxation ca 52 to 40 ma and subsequent uplift 40 to 38 ma of the orogen in the xiongcun deposit mineralization hosted by jurassic pyroclastic rocks and controlled by nw striking faults can be divided into two styles i e veinlet disseminated cu au mineralization and vein style au ag polymetallic mineralization the former is associated with local remnant k silicate alteration extensive phyllic alteration and peripheral widespread propylitization the latter overprinting the former is associated with strong silicification chloritization and kaolinization the early veinlet disseminated cu au mineralization is similar to porphyry type mineralization and has a mineral assemblage of quartz sericite pyrite chalcopyrite bornite magnetite pyrrhotite sphalerite rutile anhydrite the late vein style au ag polymetallic mineralization characterized by a mineral assemblage of quartz pyrite pyrrhotite sphalerite rich in fe chalcopyrite galena native gold electrum chlorite kaolinite barite calcite siderite hematite belongs to a sulfide rich low sulfidation type epithermal system the h o and s isotopic compositions and high salinities of fluid inclusions indicate a magmatic contribution and increasing contents of meteoric water in the mineralized system from early to late stage the wide range of homogenization temperatures 380 to 120 c homogenization pressures 45 92 to 1 94 bar and salinities 36 61 to 1 23 wt nacl equiv suggest rapid uplift and are consistent with the geological setting because of uplift the hydrothermal system of xiongcun evolved from a porphyry system to an epithermal system resulting in an immature porphyry system and the telescoping of late vein style au ag polymetallic mineralization onto the early veinlet disseminated cu au mineralization

phosphogenesis carbon isotope stratigraphy and carbonate platform evolution along the lower cretaceous northern tethyan margin we distinguish three different stages in the evolution of the tithonian late jurassic to aptian early cretaceous northern tethyan carbonate platform 1 carbonate production in the coral oolite mode late tithonian to early valanginian early barremian to early aptian 2 carbonate production in the crinoid bryozoan mode early valanginian haute rivian late aptian and 3 platform retrogradation and destruction condensation and phosphogenesis that is platform drowning early valanginian to early hauterivian middle hauterivian late hauterivian to early barremian early to early late aptian and latest aptian to earliest albian transitions from the coral oolite mode to the crinoid bryozoan mode and consequently to platform drowning may have been driven by increases in nutrient levels on the shelf phases of relative sea level rise in times of carbonate production in the coral oolite mode are named constructive because of the observed platform regeneration following phases of widespread emersion during late sea level highstands in contrast phases of relative sea level rise in times of platform drowning are termed destructive the 13 c stratigraphies obtained from valanginian hauterivian and aptian albian hemipelagic successions beyond the platform correlate well with the early cretaceous pelagic 13 c record positive excursions in the pelagic 13 c record correspond in time to episodes of platform drowning this suggests the existence of a coupling mechanism between changes in the global carbon cycle and platform drowning in our view the early cretaceous crises in carbonate platform growth were the consequence of reinforced greenhouse conditions which may have been triggered by episodes of extensive flood basalt volcanism strong greenhouse conditions may have induced the following chain of feedback mechanisms enabling the biosphere to return to normal conditions climate warming sea level rise accelerated water cycle intensified weathering nutrient mobilization platform destruction increased productivity increased phosphogenesis and carbon burial weakened greenhouse conditions

helium neon and argon systematics of the european subcontinental mantle implications for its geochemical evolution in this study we present a comprehensive noble gas study of mantle xenoliths from various european cenozoic volcanic provinces the main body of samples is from the massif central france and the eifel germany smaller subsets of samples are from spitsbergen and the graz basin austria in all the helium neon and argon isotopic abundances of a total of forty five mantle xenoliths phenocrysts and xenocrysts were determined the 3he 4he ratios within each volcanic province are very uniform irrespective of the diverse lithologies and p t conditions which are represented by our sample suite mean 3he 4he ratios of the massif central eifel spitsbergen and kapfenstein are 6 53 25 6 03 14 6 65 25 and 6 1 7 1 times the atmospheric ratio ra respectively the strontium and neodymium isotopic composition of some of the cpx separates are highly variable and therefore in contrast to the uniform he signature we thus conclude that he and probably also the other noble gases in the xenoliths are effectively decoupled from the non volatile elements therefore the he signature that is preserved in the xenoliths is actually that of their host magmas published strontium neodymium and lead isotope data of the unevolved host magmas of the xenoliths correlate well with our xenolith he data the position of the fields of the investigated volcanic provinces in hesr hend and hepb variation diagrams depict ternary mixtures between dmm em himu endmembers as the source the host magmas and their volatiles the neon isotopic composition of the gases released from the xenoliths is in most cases atmospheric and probably reflects atmospheric contamination only a few samples reveal indications for morb type ne or evidence of mass fractionation the 40ar 36ar ratios of the xenoliths are mostly radiogenic with the highest ratio being 17 000 however all samples have suffered a certain degree of atmospheric contamination we calculate that the uncontaminated 40ar 36ar ratio of the european subcontinental mantle is 30 000 the4he 40ar ratios have been fractionated since with values around 0 25 they are below both the current production ratio and the morb ratio they cannot be explained by atmospheric contamination as the samples with high 40ar 36ar ratios also have low 4he 40ar ratios helium and ar were probably fractionated during initial closed system degassing of the host magma we calculate the original unfractionated 4he 40ar ratios of the massif central and eifel magma source which are 2 56 18 and 2 71 17 respectively the noble gas systematics are compatible with the notion that addition of crustal material has modified a former morb source signature we use our mean 3he 4 he ratios and reconstructed 4he 40ar ratios to model the time and degree of contamination of a morb like source with crustal material combining our model with evidence from published oxygen strontium neodymium and lead isotope data we judge that the source of the massif central and eifel magmas became enriched in k u and th shortly prior or during the variscan orogeny pre collisional collisional in this case the enrichment in these elements is therefore most probably related to subduction of crustal material in a destructive continental margin setting

strontium isotopic variations in jurassic and cretaceous seawater a high resolution seawater strontium isotope curve has been generated through the analysis of well dated and well preserved belemnites and oysters from the middle and upper jurassic and the lower cretaceous of great britain analysis of fe and mn concentrations in these fossils has yielded criteria for eliminating samples that are diagenetically altered the strontium isotope curve remains relatively flat through the aalenian and early bajocian rapidly descends through the late bajocian and bathonian and reaches a minimum in the callovian and oxfordian it then begins a rapid increase in the kimmeridgian and portlandian that continues through much of the early cretaceous the curve levels off in the barremian suddenly dips downwards in the aptian and recovers gradually through the albian the strontium isotopic variations are sufficiently large and the data are presented with sufficient stratigraphic detail to allow precise correlation to the classic ammonite zones and lithologic sections of great britain using the techniques of strontium isotope stratigraphy model results indicate that much of the variation in seawater 87sr86sr between 120 and 40 ma can be explained by changing the intensity of mid ocean ridge hydrothermal fluxes proportionally to estimated mid ocean ridge crustal generation rates it is also possible that the variations during the rest of the mesozoic and the permian are primarily reflections of changing hydrothermal inputs the model results have several important implications first they provide an example in which the variations in the strontium isotope curve are not necessarily driven by changes in fluvial inputs second they suggest that from at least the aptian through the eocene variations in continental weathering were minimal this heightens the importance of the rapid rise in seawater 87sr86sr beginning 40 ma as a significant transition to an extended period of increasing fluvial 87sr fluxes continuing to the present finally the results suggest that several documented short term excursions towards lower 87sr86sr in the latest triassic pliensbachian toarcian callovian oxfordian aptian albian and cenomanian turonian are interpretable as pulses of seafloor hydrothermal activity if so the strontium isotope record offers a means of constraining the timing duration and magnitude of known or proposed hydrothermal events in the geological record

major palaeoenvironmental perturbation in an early aptian carbonate platform prelude of the oceanic anoxic event 1a the early aptian oceanic anoxic event oae 1a was characterized by intensified greenhouse climate conditions widespread accumulation of organic deposits in open marine settings major perturbations in the c cycle and a generalized increase in terrestrial runoff sedimentological diagenetic and chemostratigraphic analyses of lower aptian platform carbonates from the north cantabrian basin n spain illustrate the regional impact and effects of those global conditions on shallow marine environments the studied interval outlines four stages of platform evolution stage 1 earliest bedoulian is defined by an initial rapid marine transgression that led to deposition of shallow water oligotrophic photozoan skeletal assemblages and by a later interval of subaerial exposure stage 2 early bedoulian starts with a rapid transgression followed by deposition of grainstones that yield heterozoan assemblages more typical of mesotrophic conditions along with ferruginized oolites stage 3 early bedoulian is defined by the drowning of the carbonate platform and subsequent deposition of open marine marls which are thought to represent the local expression of the oae 1a finally stage 4 shows the return of shallow water photozoan carbonate sedimentation the carbonate o and c stable isotope records have revealed prominent negative excursions during deposition of the marly interval of the stage 3 which may be associated with the important global changes that occurred at the onset of the oae 1a the change in skeletal assemblages that preceded the isotopic excursions and the platform drowning documents conditions of environmental stress caused by a combination of local and global factors the global change coupled with increased basin subsidence triggered the drowning of the platform by progressive reduction of the growth potential of the carbonate factory

reduced fluids in porphyry copper gold systems reflect the occurrence of the wall rock thermogenic process an example from the no 1 deposit in the xiongcun district tibet china abstract high fo2 conditions characterize the majority of global porphyry copper deposits and contain highly oxidized minerals such as magnetite and anhydrite in contrast the no 1 porphyry cu au deposit in the xiongcun district tibet china has abundant pyrrhotite reduced fluids ch4 co2 and a relative lack of highly oxidized minerals which are indicative of low fo2 conditions scanning electron microscopy fluid inclusion c h o he ar isotopes and whole rock organic carbon contents and isotope analysis were used to constrain the evolution of ore forming fluid the origin of ch4 and metal deposition mechanisms for the no 1 deposit the he ar isotopic compositions 3he 4he 0 11 0 96 ra 40ar 36ar 418 7 2920 2 suggest that the ore forming fluids predominantly derived from crust source with minor mantle input the h o isotopic analysis results 18oh2o 1 8 to 5 2 d 106 to 89 9 indicate that the ore forming fluids were derived from a magmatic source that mixed with some meteoric waters the element compositions of zircons and fluid melt inclusions from the mineralized middle jurassic quartz diorite porphyry reveal that the primary magma was characterized by high log fo2 nno conditions the quartz diorite porphyry intruded into the carbon bearing wall rocks produced abundant ch4 by thermal decomposition of organic matter 13cch4 26 3 to 28 5 which changed the redox state of the porphyry copper system from oxidized to reduced condition ore elements were deposited via fluid boiling as a consequence of the rapid decrease in temperature and pressure

control of regional structural styles and faulting on northeast mexico spring distribution groundwater dependent spring fed ecosystems of the cuatrocienegas basin coahuila mexico host 70 endemic species these desert springs occur primarily aligned along the base of an anticline that bisects the cuatrocienegas basin but the hydrogeologic controls of the springs are poorly understood the hypothesis that spring locations are controlled by subsurface geology such as buried anticlines or faulting versus stratigraphic controls is tested by evaluating 1 regional structural styles 2 fracture models of analogous structures 3 hydrogeologic data and 4 geophysical surveys jurassic and cretaceous siliciclastic and carbonate rocks deposited on the coahuila block west of the cuatrocienegas basin have dips 10 and lack faults because of a structurally rigid granodiorite basement to the east of the coahuila block and around the cuatrocienegas basin the coahuila folded belt has anticlines associated with basement involved faults 10 25 backlimb dips and forelimb dips up to vertical or slightly overturned springs in the western sub basin that represent 85 of total basin discharge are located on zones of highest anticipated fracture density predicted by fracture models of analogous anticlines spring waters reveal elevated temperature 32 35 c and low tritium 1 tritium unit gravimetry and time domain electromagnetic surveys correspond with a best fit cuatrocienegas basin hydrogeologic model of fractures associated with reverse faulting controlling spring locations in the western cuatrocienegas basin springs in the eastern sub basin are located where ephemeral streams have eroded through confining beds along the base of alluvial fans and lack faulting regional variations in structural style are an important control on the location of springs in the cuatrocienegas basin

a physically based interpolation method for fluvially eroded topography 1 interpolation of elevation data from fluvially eroded topography is difficult for available methods because of the inherent roughness and drainage properties of the fine scale surface we propose a new method that produces an interpolation surface by adapting a simulated topography to a given set of point elevation data the simulated surface is produced by a simple model that rapidly simulates topography in dynamic equilibrium including the effects of tectonic uplift fluvial incision and hillslope diffusion agreement between the simulated topography and the elevation data is improved by iteratively adjusting a spatially varying erodability parameter when the iterative procedure terminates the simulated surface is in close but not in exact agreement with the observations exact agreement can usually be produced by distorting the simulated surface in a way that does not introduce local depressions interpolation surfaces generated by the proposed method have realistic drainage patterns without unrealistic depressions in addition the textural properties of the interpolation surfaces including the distributions of slopes and curvatures are better than those generated by other interpolation methods

multiple origins of methane in the earth methane occurrences in the earth s crust are predominantly of biogenic origin i e their ultimate source is biologically formed organic matter methane can also form through inorganic reactions and is consequently termed abiogenic biogenic methanes can either form through bacterial or thermogenic processes bacterial processes follow a co2 reduction and or fermentation pathway the fermentation processes are quantitatively more important in recent fresh sediments and swamps methane formed by co2 reduction however is most common in older sediments and commercial gasfields temperature organic substrate and age may be the major factors controlling the relative importance of the two pathways stable isotope concentrations in thermogenic methanes seem to be controlled by the extent of conversion of organic matter the timing of gas expulsion and trapping the different character of methane in individual sedimentary basins may be a result of the geologic history geothermal methanes are most likely derived from pyrolysis of organic matter abiogenic methane occurs in hydrothermal vents and ophiolite complexes inorganic reactions either surficial or deep seated are the likely source of such methanes a uniform mantle origin of methane is not supported by the observed isotope variations in naturally occurring methanes

morphological patterns of aptian lithocodium bacinella geobodies relation to environment and scale lithocodium aggregatum and bacinella irregularis are now extinct shallow marine life forms of unknown taxonomic origin forming part of the tropical platform biota during much of the mesozoic these organisms experienced bloom periods and temporarily replaced rudist coral assemblages during parts of the early aptian within the limitations of time resolution this out of balance facies is coeval with the oceanic anoxic event 1a related black shale deposition in oceanic basins but the triggering factors remain poorly understood here a platform wide comparison of lithocodium bacinella geobodies and morphotypes from the sultanate of oman is presented and placed in its environmental bathymetric and physiographic context lithocodium bacinella geobodies reach from kilometre scale superstructures to delicate centimetre sized growth forms clearly scale matters and care must be taken when drawing conclusions based on spatially limited observational data whilst the factors that cause lithocodium bacinella expansion should probably be considered in a global context regional to local factors affected growth patterns in a more predictable manner here the unresolved taxonomic relationship remains the main obstacle in any attempt to unravel the response of lithocodium bacinella to specific or interlinked environmental parameters as different organisms respond differently to changing environment acknowledging these limitations the following tentative patterns are observed i lithocodium bacinella tolerated a wide range of hydrodynamic levels and responded to differences in energy level or physiographic settings margin intrashelf basin inner platform by obtaining characteristic growth forms ii lithocodium bacinella favoured low sediment input but had the ability to react to higher sedimentation rates by enhanced upward growth a feature perhaps pointing to a phototrophic metabolism circumstantial evidence for continuous growth within the upper sediment column is debated iii the availability of accommodation space had a direct influence on the maximum size of geobodies formed iv fluctuating nutrient levels and sea water alkalinity may have affected the growth potential of lithocodium bacinella understanding the relationship between lithocodium bacinella morphogenesis on a wide range of scales and local environmental parameters allows for better prediction of the spatial distribution of reservoir properties and also results in an improved interpretation of palaeoenvironments this study might represent a useful first step in this direction

jurassic u pb and re os ages for the newly discovered xietongmen cu au porphyry district tibet prc implications for metallogenic epochs in the southern gangdese belt the gangdese belt in southern tibet includes the cretaceous to early eocene gangdese continental magmatic arc a newly recognized middle jurassic magmatic arc and post gangdese arc magmatism of miocene age that is well known for its association with important copper molybdenum deposits although the tectonic history of the gangdese continental arc is relatively well constrained the tectonomagmatic setting of the jurassic and miocene magmatic events was poorly constrained previously geochronological analysis of samples from the xietongmen copper gold porphyry district has identified a previously unknown metallogenic event related to middle jurassic arc magmatism the occurrence of several metallogenic epochs within the southern gangdese belt highlights the importance of systematic metallogenic studies of this belt

toward an orbital chronology for the early aptian oceanic anoxic event oae1a 120 ma abstract the early aptian oceanic anoxic event oae1a 120 ma represents a geologically brief time interval in the mid cretaceous greenhouse world that is characterized by increased organic carbon accumulation in marine sediments sudden biotic changes and abrupt carbon isotope excursions indicative of significant perturbations to global carbon cycling the brevity of these drastic environmental changes

collision related genesis of the sharang porphyry molybdenum deposit tibet evidence from zircon u pb ages re os ages and lu hf isotopes article i nfo sharang is a low fluorine calc alkaline porphyry mo deposit hosted mainly in a granite porphyry of a multi stage plutonic complex in the northern gangdese metallogenic belt largely with stockwork and ribbon textured mineralization the observed age estimates suggest that the formation of the magmatic host complex 52 9 51 6 ma and the ore deposit itself 52 3 ma occurred during the main stage of the india asia collision the host rocks are characterized by lower zircon ehf t values than those of the pre ore and post ore rocks this suggests that the lhasa terrane basement might play an important role in the formation of sharang ore forming intrusions in view of the framework of magmatic metallogenic events we suggest that slab roll back may have induced melting of juvenile crust and ancient continental complexes during the india asia collision this proposal focuses exploration for additional molybdenum deposits on the collision zone

geological characteristics and genesis of the jurassic no i porphyry cu au deposit in the xiongcun district gangdese porphyry copper belt tibet abstract the xiongcun district located in the western segment of the gangdese porphyry copper belt gpcb hosts the only known jurassic mineralization in the gpcb tibet prc the no i deposit in the xiongcun district is related to the middle jurassic quartz diorite porphyry 167 161 ma and the mineralization was formed at ca 161 5 2 7 ma ore bearing middle jurassic quartz diorite porphyry emplaced into the early jurassic volcano sedimentary rock sequences of the xiongcun formation veinlets and disseminated mineralization developed within the middle jurassic quartz diorite porphyry and the surrounding metamorphosed tuff hosting a measured and indicated resource of 1 04 mt copper 143 31 t gold and 900 43 t silver with an average grade of 0 48 copper 0 66 g t gold and 4 19 g t silver the mineralization can be assigned to four stages including three main stages of hypogene mineralization and one epigenetic stage the main alteration associated with mineralization is potassic seven mineralization related hydrothermal veins have been recognized including quartz sulfide biotite sulfide magnetite sulfide quartz molybdenite sulfide chalcopyrite pyrite pyrrhotite pyrite and polymetallic veins the s and pb isotopic compositions of the ore sulfides and the re contents of the molybdenite suggest a mantle source for the ore forming materials with minor contamination from the subducted sediments hydrogen and oxygen isotope compositions of quartz in the ores suggest that both magmatic and meteoric waters were involved in the ore forming process the ore bearing porphyry 167 161 ma and ore forming 161 5 2 7 ma ages of the no i deposit correspond to the time of northward subduction of neo tethys oceanic slab the geochemical data of the ore bearing porphyry indicate that the no i deposit formed in an intra oceanic island arc setting and the ore bearing porphyry originated from the partial melting of mantle with limited contribution of subducted sediments the genesis of the ore bearing porphyry and no i deposit is interpreted as being related to northward intra oceanic subduction of neo tethys oceanic slab in the middle jurassic time 167 161 ma

fluid inclusion noble gas and halogen evidence on the origin of cu porphyry mineralising fluids the naturally occurring noble gas isotopes 40ar 36ar 84kr and 129xe and halogens cl br i have been determined simultaneously in irradiated quartz vein samples by noble gas mass spectrometry quartz vein samples were collected from the potassic and propylitic alteration zones of six porphyry copper deposits pcd bingham canyon utah and silverbell ray mission pinto valley and globe miami in arizona in addition analyses of 3he 4he have been obtained from sulphide minerals hosted by the quartz veins at silverbell ray pinto valley and globe miami the majority of pcd fluids studied have br cl and i cl ratios that overlap those of fluids included in mantle diamond suggesting that the salinity had a juvenile origin the high i cl 121 10 6 mole m in samples from the propylitic zone of silverbell is attributed to the presence of sedimentary formation water 3he 4he ratios have r ra values in the range 0 3 to 1 72 and provide evidence for the involvement of a crustal component in addition to mantle volatiles 40ar 36ar ratios vary from meteoric values of 317 in the propylitic zone of bingham canyon and 323 in the skarn alteration of mission up to 3225 in the potassic zone of pinto valley fluids in both the potassic and propylitic alteration zones of every deposit are a mixture of a low salinity end member comprising meteoric water and air and a high salinity end member consisting of a mixed mantle and crustal fluid the 40ar cl ratio of fluid inclusions at pinto valley 10 4 m is similar to values obtained previously for mantle fluids the 40ar cl value is two orders of magnitude lower at bingham canyon where a depleted 36ar concentration 0 2 10 6 cm3 g below that of air saturated water asw and a range of highly fractionated noble gas compositions f84kr 13 and f129xe 160 indicate that boiling and pulsed fluid flow have occurred

eocene neotethyan slab breakoff in southern tibet inferred from the linzizong volcanic record abstract formation of the linzizong volcanic successions in the lhasa terrane southern tibet has long been related to northward subduction of the neotethyan oceanic slab under asia here we report new 40ar 39ar age results for the volcanic rocks recovered from a large area 29 n to 32 n and 85 e to 93 e that together with literature data delineate two discrete stages of volcanism these are a widespread cretaceous stage and an intense but spatially confined paleogene stage the latter occurring only in the southern part of the lhasa terrane resulted in the linzizong volcanic successions our data furthermore suggest southward migration and intensification of the volcanism in the lhasa terrane with magmatic flare ups at ca 50 ma while the volcanic successions consist dominantly of calc alkaline rocks typical of arc lava geochemistry those formed during the flare up period show significant compositional variations from low k tholeiitic through calc alkaline to shoshonitic magma suites these observations enable us to interpret the volcanic southward migration and following flare ups as the consequences of rollback and breakoff of the subducted neotethyan slab that occurred ahead and in the early stage respectively of the india asia collision our interpretation that involves a major eocene tectonomagmatic activity and concomitant topographic uplift in southern tibet is consistent with himalayan metamorphic constraints regional sedimentary records and seismic tomography

oxidation of ch4 to co2 and h2o by chloritization of detrital biotite at 270 5 c in the external part of the central alps switzerland abstract the upper end of the ch 4 zone in the external part of the central alps of switzerland results from an oxidation reaction of methane into water and carbon dioxide at 270 5 c tarantola a mullis j vennemann t dubessy j de capitani c 2007 oxidation of methane at the ch 4 h 2 o co 2 transition zone in the external part of the central alps switzerland evidences from stable isotope investigations chemical geology 237 329 357 petrographic investigations of the north helvetic flysch revealed the presence of detrital biotite muscovite and chlorite in the ch 4 zone at the transition from the methane to the water zone the sudden increase of co 2 in the fluid is associated with the formation of chlorite and muscovite in replacement of detrital biotite in the h 2 o zone biotite is entirely replaced by chlorite muscovite interlayered stacks mossbauer spectroscopy showed a minimum decrease of x fe 3 from 0 18 to 0 09 within the sheet silicate fraction at the transition from the ch 4 to the h 2 o co 2 dominated fluid zone detrital biotite of the investigated host rocks incorporates at the same conditions larger amounts of fe 3 than chlorite in its structure and x fe 3 biotite x fe 3 new chlorite x fe 3 detrital chlorite the reaction of chloritization of detrital biotite is interpreted as a fluid controlled mineralogical isograde at 270 5 c marking the transition from the low to the high grade anchizone and allowing the oxidation of up to 36 moles of ch 4 per cubic meter of rock

facies sequence of triassic jurassic red beds in the sierra madre oriental ne mexico and its relation to the early opening of the gulf of mexico abstract the configuration of upper triassic grabens in the gulf of mexico rift system is pointed out by the suture zones of late palaeozoic plate convergence rifting particularly started on both sides of the ancient magmatic arc the taphrogenic red beds of the huizachal formation in the sierra madre oriental represent the western parts of this system the early syn rift sediments are characterized by fining upward cycles of a fluvial environment with a low sinuosity channel pattern later on decreasing of relief intensity caused the change to a rather meandering system climate was evidently semiarid during that time the petrographic composition of the clastic rocks suggests a nearby sedimentary metamorphic basement the transition to early post rift sediments is marked by an angular unconformity its formation approximately coincides with the first emplacement of oceanic crust in the central parts of the gulf basin the early post rift sediments of the la joya formation show within a single fining upward megacycle the transition from terrestrial to marine conditions that persisted up to the beginning of cenozoic time

sequence stratigraphy of lower cretaceous barremian albian carbonate platforms of northeastern mexico regional and global correlations abstract the lower cretaceous cupido and coahuila platforms of northeastern mexico form part of the extensive carbonate platform system that surrounded the ancestral gulf of mexico a sequence stratigraphic model for these barremian to albian platforms was constructed from regional correlations of vertical cycle stacking patterns constrained by newly acquired biostratigraphic data and c and sr isotope stratigraphy the cupido shelf lagoon barremian aptian is composed of up to 150 peritidal cycles which stack into high frequency sequences that are correlated across the shelf cupido high frequency sequences build into a lower partial composite sequence cu1 an overlying full composite sequence cu2 and the transgressive base of a third composite sequence cu co3 related to backstepping of the cupido platform the highstand part of cu co3 is recorded in evaporite and carbonate facies of the coahuila platform aptian albian more than 80 meter scale evaporite to carbonate cycles characterize the restricted interior of the coahuila platform and stack into two full composite sequences co4 co5 the coahuila platform was drowned in the latest albian or earliest cenomanian terminating shallow water carbonate sedimentation in the region regional correlations of the depositional sequences in northeast mexico with coeval platforms in texas and the northern gulf coast indicate that the lower two composite sequences of the cupido shelf correlate with the lower part of the sligo hosston platform in texas the transgressive systems tract of the third composite sequence of the cupido la pena is recorded in texas by the upper sligo and pearsall formations the highstand systems tract and the disconformable top of the third composite sequence coahuila platform is likely coeval with the upper glen rose platform in texas the fourth and fifth composite sequences are correlative with the fredericksburg platform and the washita devils river platforms of texas respectively we conservatively correlated our sequence stratigraphic framework with composite global sequences and eustatic curves derived from several other basins given the available time resolution results are variable but sequence boundaries at the top of cu co3 and co5 appear to have clear interbasinal equivalents

shale tectonic processes field evidence from the parras basin north eastern mexico abstract major decollements located within buried overpressured shale commonly develop in thrust fronts accretionary prisms and sedimentary deltas controlled by gravity tectonics in seismic data it is possible to observe only large scale deformation of what is commonly designed as mobile shale but the precise geometry and the dynamic evolution of these bodies remains poorly understood it is often difficult to define if we are dealing with ductile or brittle deformation and to understand the role of the fluids in time and space during deformation for this reason large scale outcrops were studied in the parras basin mexico which makes possible a direct observation of the shale tectonic processes this work suggests changes in space and time of the deformation processes which occurred within the shale formation hosting the decollement distributed deformation was observed within the shale formation hosting the decollement compared to more localized deformation above also a change of the rheology of the shale over time occurred progressively toward brittle processes in the whole sedimentary pile xrd and microscopic studies have shown that diagenetic processes are favored in the shear zones of penetrative deformation leading notably to reverse gradient of illitization the isotopic analysis of cements in veins and the study of associated fluid inclusions have shown that fluid dynamics also evolved during time showing notably evidence for widespread fluid migration issued from rocks located below the decollement during the beginning of the deformation progressively the tectonic system located above the decollement tends to be preserved from fluid migration coming from below the decollement and to be influenced only by local fluid migration closed system

baogutu an example of reduced porphyry cu deposit in western junggar abstract classic oxidized porphyry copper deposits opcd are characterized by high tonnage and elevated f o 2 and contain highly oxidized minerals including primary anhydrite and hematite in contrast the baogutu deposit contains abundant hypogene pyrrhotite and methane rich fluid inclusions characteristic of lower tonnage reduced porphyry copper deposits rpcd mineral paragenesis and mineral chemistry studies reveal two mineralization periods magmatic and hydrothermal with the hydrothermal period further subdivided into three paragenetic stages including ca na alteration potassic alteration and propylitization locally overlapped by phyllic alteration several independent geothermometers indicate that the temperatures of the magma potassic and propylitization alteration are estimated to be 600 900 c 200 400 c and 200 300 c respectively multiple indicators including mineral assemblages apatite so 3 content whole rock fe 2 o 3 feo ratios and fluid compositions indicate the f o 2 of the magma and hydrothermal fluid to be nno and nno nno 2 respectively hydrothermal fluids associated with primary biotite yield log f h 2 o f hcl fluids values of 4 8 6 2 for diorite and 4 1 4 5 for granodiorite porphyry the log f s2 of the magmatic and potassic alteration are estimated to be 0 7 to 3 0 and 5 5 to 11 0 respectively based on pyrrhotite and sulfide assemblages mineral assemblage and hessite composition suggest the log f te2 of the potassic alteration is 8 5 to 14 5 the low tonnage baogutu deposit displays significantly lower f o 2 than opcds nno 2 and on this basis could be classified as a rpcd other physicochemical conditions including t f s2 log f h2o f hcl fluid do not show obvious differences to those of opcds we deduce that the low f o 2 of baogutu metallogenic granitoids and aqueous fluids likely produced the unusual pyrrhotite arsenopyrite mineral assemblage and the nacl h 2 o ch 4 co 2 ore forming fluids and small tonnage typical of rpcds previous obtained fluid inclusion h o isotope data and sulfide s pb isotope data suggest the methane rich ore forming fluids were derived from deep mantle source with little contamination from sedimentary components however detailed studies are needed to clarify the origin of the ch 4

microbial foraminiferal episodes in the early aptian of the southern tethyan margin ecological significance and possible relation to oceanic anoxic event 1a two regionally significant microbial foraminiferal episodes 150 kyr each occur within the early aptian shallow marine platform in oman and throughout eastern arabia the stratigraphically lower of these two intervals is characterized by isolated or coalescent domes that share similarities with modern open marine stromatolites from the exuma cays bahamas the upper interval is predominantly built by a problematic lithocodium bacinella consortium in buildup and massive boundstone facies based on highresolution chemostratigraphy these shoalwater intervals are coeval with oceanic anoxic event 1a oae1a livello selli field evidence demonstrates that the buildup episodes alternate with stratigraphic intervals dominated by rudist bivalves this biotic pattern is also recognized in other coeval tethyan sections and is perhaps a characteristic shoalwater expression of the oae1a the short lived regional expansions of this microbial foraminiferal out ofbalance facies cannot be explained by local environmental factors salinity and oxygen level alone and the buildup consortia do not occupy stressed refugia in the absence of grazing metazoans judging from recent analogues the main fossil groups i e microbial assemblages macroalgae larger sessile foraminifera and rudist bivalves all favoured elevated trophic levels but with different tolerance limits the implication of this is that the influence of palaeofertility events possibly related to oae1a on carbonate platform community structures must be investigated the observations made in these coastal sections are a significant first step for the improved understanding of the early aptian period of biotic oceanic and climatic change

lithofacies relations and palaeoecology of a late jurassic to early cretaceous fan delta to shelf depositional system in the sierra madre oriental of north east mexico the la casita formation in north eastern mexico represents a period of increased terrigenous clastic supply that is characteristic for the entire northern and western margins of the gulf of mexico basin during latest jurassic and earliest cretaceous time a prograding delta complex developed at the south eastern margin of the coahuila peninsula delta plain delta front prodelta and shelf areas show distinct lithofacies associations some of the most characteristic elements are fining upward and coarsening upward grain size trends syndepositional deformational features storm layers phosphorites fossiliferous carbonate concretions and an anaerobic biofacies a possible break in sedimentation is inferred for parts of the valanginian this may be interpreted as a sequence boundary between second order cycles the kimmeridgian berriasian cycle appears to correlate with the cotton valley cycle of the texas gulf coast

evidence from fluid inclusions for microbial methanogenesis in the early archaean era methanogenic microbes may be one of the most primitive organisms although it is uncertain when methanogens first appeared on earth during the archaean era before 2 5 gyr ago methanogens may have been important in regulating climate because they could have provided sufficient amounts of the greenhouse gas methane to mitigate a severely frozen condition that could have resulted from lower solar luminosity during these times nevertheless no direct geological evidence has hitherto been available in support of the existence of methanogens in the archaean period although circumstantial evidence is available in the form of approximately 2 8 gyr old carbon isotope depleted kerogen here we report crushing extraction and carbon isotope analysis of methane bearing fluid inclusions in approximately 3 5 gyr old hydrothermal precipitates from pilbara craton australia our results indicate that the extracted fluids contain microbial methane with carbon isotopic compositions of less than 56 per thousand included within original precipitates this provides the oldest evidence of methanogen 3 46 gyr ago pre dating previous geochemical evidence by about 700 million years

mid cretaceous strontium isotope stratigraphy of deep sea sections large variations exist between published mid cretaceous late barremian to early turonian stages seawater sr isotope stratigraphies this has resulted in disparate interpretations of crustal production rates we report on a detailed investigation of seawater sr isotope stratigraphy based on foraminifers and where available on inoceramid bivalves from 12 mid cretaceous deep sea drilling project and ocean drilling program sections the effects of diagenesis are assessed using scanning electron microscope observations and traceelemental analyses but are best distinguished by comparing the 87 sr 86 sr values of similarage samples from different sites strontiumisotope analyses compiled from 9 of 12 sites that have detailed age control define one band of common values this band is used as a composite curve which presumably represents seawater 87 sr 86 sr values the composite curve shows a trough of markedly lower 87 sr 86 sr values in the aptian and early albian stages higher but constant values for the middle albian cenomanian stages followed by a decrease in 87 sr 86 sr values in the early turonian

evolution of the marine stable carbon isotope record during the early cretaceous a focus on the late hauterivian and barremian in the tethyan realm abstract in order to improve our understanding of the relationships between the late hauterivian oceanic anoxic faraoni event contemporaneous platform drowning along the northern tethyan margin and global environmental change in general we established high resolution 13 c and 18 o curves for the late hauterivian and the entire barremian stage these data were obtained from whole rock carbonate samples from the veveyse de ch tel saint denis section switzerland the fiume bosso section and the nearby gorgo a cerbara section central italy and the angles section barremian stratotype france we observe an increase of 0 3 in mean 13 c values within sediments from the middle hauterivian subsaynella sayni ammonite zone to the hauterivian barremian boundary 13 c values remain essentially stable during the early barremian during the latest early barremian and most of the late barremian 13 c values increase slowly until the imerites giraudi zone and the latest barremian is characterized by a negative trend in 13 c values with minimal values at the barremian aptian boundary during the earliest aptian 13 c mean values start to rise again and attain 2 25 we interpret the evolution of the 13 c record as resulting from the interaction between changes in the carbon cycle in the tethyan basin and the adjacent platforms and continents in particular changes towards warmer and more humid conditions on the continent and coeval phases of platform drowning along the northern tethyan margin may have contributed to enhance the oceanic dissolved inorganic carbon dic reservoir which may have pushed the 13 c record towards more negative values and exerted a general attenuation on the 13 c record from this may have come the general change from a heterozoan to a photozoan carbonate platform community which influenced the evolution in 13 c values by increasing the export of aragonite and diminishing export of dissolved organic carbon into the basins

vapor phase exsolution as a controlling factor in hydrogen isotope variation in granitic rocks the notch peak granitic stock utah abstract the notch peak granitic stock western utah is comprised of three concentric sequentially intruded rock types from granite at the rim to quartz monzonite i to quartz monzonite ii at the core the 18 o values of whole rocks vary about an average of 9 4 smow irrespective of the rock type and position relative to contact suggesting that the three magmas had the same parent the whole rock d values in the stock range from 100 to 55 d values increase toward the cores of both quartz monzonite i and quartz monzonite ii resulting in concentric contours the d contours of quartz monzonite ii cross cut those of quartz monzonite i suggesting little isotopic interaction between these bodies and the absence of a late pervasive fluid phase there is a positive correlation between d values and water content of the samples where samples from each body define a distinct field the positive correlation is explained by isotopic fractionation attendant on vapor exsolution from the crystallizing magma an observed increase in d with the degree of chloritization a trend opposite to that observed in systems where participation of meteoric water has been demonstrated is the result of subsolidus interaction with the exsolved fluids these results show that large variations in the hydrogen isotope ratios of a granitoid can arise by exsolution of a vapor phase from the melt on crystallization in general magmas with larger modal amount of primary hydrous phases will tend to have higher d values than those with small amounts of hydrous phases furthermore the relatively high d values of chlorites at notch peak confirm the applicability of classical concepts of closed system deuteric alteration to some granitoid bodies thus meteoric water interaction need not be always invoked to explain hydrogen isotope variation and deuteric alteration in granitoids

tectono stratigraphic evolution of eastern mexico during the break up of pangea a review abstract the lower jurassic cenomanian successions of mexico can be grouped into two different tectono stratigraphic systems that were developed under the influence of two distinct geodynamic processes 1 the mesozoic atlantic system of mexico which occupies the eastern two thirds of the country and was dominantly influenced by the break up of pangea and consequent opening of the atlantic ocean and 2 the mesozoic pacific system of mexico which is exposed along its western margin and was controlled by the subduction of the farallon plate beneath the pacific margin of north america the mesozoic atlantic system of mexico can be subdivided into two tectono stratigraphic subsystems representing the two main tectonic stages of the break up of pangea the early middle jurassic rift subsystem was developed during the initial stage of lithospheric attenuation of western equatorial pangea which is evidenced by the opening of a number of right lateral transtensional troughs that were opened according to the nw se regional extension imposed by north america south america divergence rift related troughs were progressively infilled by continental to marginal marine deposits and locally by volcanic lava flows that display a geochemical signature typical of supra subduction settings based on these characteristics the rift subsystem is interpreted in this work as a hybrid tectono stratigraphic domain that displays characteristics that are typical both of the mesozoic atlantic system of mexico and mesozoic pacific system of mexico reflecting the superposition of the atlantic and pacific tectonic processes during the initial phase of north america south america divergence by late callovian time most of intra continental extension in western equatorial pangea had occurred and was followed by anticlockwise rotation of the yucatan block to its present position and initial seafloor spreading in the gulf of mexico the opening of the gulf of mexico promoted the incursion of marine waters in eastern mexico and the onset of carbonate basins and platforms that make up the late jurassic cenomanian drift and cooling subsystem the lack of arc like igneous rocks in the drift and cooling subsystem suggests that by the late callovian the mesozoic atlantic system of mexico was developed independently of the tectonic processes related to subduction along the pacific margin according to our synthesis the mesozoic atlantic system of mexico represents a unique stratigraphic record that was developed at least in part under the combined influence of two main tectonic processes that are 1 the divergence between north america and south america and 2 the subduction of the farallon plate in light of this the mesozoic atlantic system of mexico can be considered a natural laboratory to explore the evolution of complex geodynamic settings related to the interaction of plate tectonic boundaries

the isotopic record of ocean chemistry and diagenesis preserved in non luminescent brachiopods from mississippian carbonate rocks illinois and missouri fossil brachiopod shells are commonly used as a faithful record of the chemical and isotopic composition of the ancient ocean water in which they grew owing to their stable mineralogy and their presence in marine strata throughout phanerozoic time the utility of these fossils for preserving ocean water compositions is evaluated through analyses of multiple specimens that grew in contemporaneous sea water at individual stratigraphic horizons in the mississippian age burlington keokuk formation of mid continent north america significant variations in sr c and o isotopic compositions are observed in contemporaneous non luminescent shells indicating that apparently pristine brachiopod shell material has been altered by post depositional processes of diagenesis the least altered compositions at each horizon are used to estimate secular variations of 87 sr 86 sr in early mississippian ocean water the estimated rates of change of ocean water 87 sr 86 sr are comparable in magnitude to the rapid sr isotopic changes documented for cenozoic ocean water for which high frequency glacial cycles are inferred as a driving mechanism the rigorous assessment of diagenetic effects on the isotopic signatures of marine phases is requisite for the advancement of high resolution reconstructions of paleo ocean chemistry

geochemistry of hydrothermal fluids from an intraplate ocean island everman volcano socorro island mexico abstract socorro island mexico still volcanically active is an alkaline and peralkaline volcanic island in the eastern pacific ocean located on a mid ocean ridge spreading center that was abandoned at 3 5 ma gas and water samples collected on the island in 1999 from the dome fumaroles and hot springs of everman volcano have been analyzed for major components h o c s he and ar isotopic composition and noble gas abundances the boiling point temperature steam vents and low salinity thermal springs discharge cl free meteoric water and are typical surface manifestations of a high temperature hydrothermal system high h 2 and ch 4 contents up to 14 and 3 5 vol in dry gas respectively and an enrichment of ch 4 in 13 c 13 c ch 4 18 may suggest that these reduced gases were at least partially produced by the interaction of ultramafic rocks with water inside volcanic edifice due to serpentinization of olivine the 3 he 4 he ratios 6 0 6 6 r a which are lower than the morb values and the high he ne ratios 4000 and he ar ratios up to 4 indicate a contribution of radiogenic he from the oceanic crust or shallow magma chamber like at a low 3 he hot spot the maximum of the 40 ar 36 ar values 311 is close to the maximum value found in the socorro volcanic rocks noble gas abundances are close to values for the partially degassed air saturated water however with some excess ne concentrations an enrichment in 132 xe or depletion in 84 kr of the least air contaminated gas sample he ne 4000 relative to air saturated water can be related to the contribution of noble gases from a non atmospheric source probably oceanic crustal component assimilated in a shallow magma reservoir

geological setting and genesis of stratabound barite deposits at muzquiz coahuila in northeastern mexico abstract the opening of the gulf of mexico during the mesozoic led to the formation of the sabinas basin large carbonate platforms were developed throughout the lower and middle cretaceous the basin provided ideal conditions for the formation of a suite of carbonate hosted stratabound deposits such as barite celestine fluorite and lead zinc of barremian aptian age these deposits resemble mississippi valley type mvt and associated deposits the mining district of sierra de santa rosa is located approximately 7 km se from melchor muzquiz in the state of coahuila mexico barite is the economic mineral and the shape of the ore bodies is considered mantos the gangue minerals are calcite local gypsum traces of celestine silica and iron oxy hydroxides the barite deposits show relict textures such as rhythmic alternating black and white bands due to the presence of organic matter and globular clusters similar to the chicken wire anhydrite typical of evaporites a fluid inclusion and stable isotope analysis s from barite c and o from carbonates were conducted the lower manto yielded a melting ice temperature between 26 c and 5 c salinities of 7 9 to 27 wt nacl equiv and a homogenization temperature ranged between 59 c to 155 c the eutectic temperature was 51 c 2 c denoting a primary calcic brine the upper manto yielded a melting ice temperature between 22 c and 15 c salinities of 18 6 and 24 wt nacl equiv and a homogenization temperature was ranging from 60 c to 126 c isotopic analysis of barite showed 34svcdt ranges from 14 9 to 19 5 average of 16 9 sulfur isotope data for barite from the sierra de santa rosa is consistent with a sulfur source formed during the lower cretaceous which coincides with the age of the cupido formation the carbon isotope analysis of the host limestone yielded a 13cvpdb range from 0 01 to 0 11 the 13c values for clear and gray calcites ranged from 0 15 to 1 5 and 1 41 to 2 3 respectively the oxygen isotope analysis showed a range between 18ovsmow 4 55 and 10 04 fluid inclusion microthermometry and isotopic measurements lead us to conclude that brines from the sabinas basin led to the replacement of the evaporite strata gypsum by barite in the cupido formation and thus classify these deposits within the category of mvt and associated deposits

carbon isotope stratigraphy of cenomanian turonian platform carbonates from the southern apennines italy a chemostratigraphic approach to the problem of correlation between shallow water and deep water successions the carbon isotope record of three sections of shallow water carbonates from the upper cretaceous sequences of the southern apennines italy shows a pronounced positive excursion of about 4 5 using the upper cenomanian cisalveolina fraasi level as a biostratigraphic tie point we correlate this excursion to the oae 2 isotopic event comparison with the standard reference 13 c curve of eastbourne england shows that the overall character of the excursion is clearly reproduced in the shallow water curves chemostratigraphic correlation allows definition of the age of some important shallow water biostratigraphic events to the precision of an ammonite zone using the well established bio chronostratigraphic framework defined in the eastbourne section the onset of the cenomanian turonian isotopic excursion coincides with a transgressive trend recorded by the occurrence of more open marine facies and culminating with an incipient drowning in one of the sections studied our data suggest that the open ocean isotopic signal is most faithfully recorded and preserved in shallow water platform carbonates during transgressive periods when the effects of meteoric diagenesis and seawater ageing are less severe

the evolution of middle america and the gulf of mexico caribbean sea region during mesozoic time a plate tectonic model for the evolution of middle america and the gulf of mexico caribbean sea region is presented the model which is based upon the existence of the mojave sonora megashear incorporates into the triassic pangea reconstruction three microplates between north and south america thus avoiding the overlap of the bullard fit these plates are the yaqui bounded on the north by the mojave sonora megashear the east and west maya plates bounded on the north by the mexican volcanic zone and on the south by a predecessor of the motagua fault zone and the chortis plate parts of guatemala and honduras during late jurassic time as north america split away from europe africa and south america shear with left lateral sense of displacement occurred along the transform faults that bounded the micro plates if 800 km of left lateral displacement along the mojave sonora megashear 300 km along the mexican volcanic belt and 1 300 km along a proto motagua megashear are restored and if yucatan and cuba are rotated to fit against northern south america then 1 a curvilinear belt of late paleozoic rocks that show lithologic as well as paleontologic similarities extends across the reconstruction and links outcrops in texas eastern mexico nuclear central america and colombia 2 a mediterranean like sea is delineated that was a precursor of most of the present gulf of mexico 3 correlation is implied between the distinctive quartzose san cayetano formation of cuba and the caracas and juan griego groups of venezuela geometric constraints suggest that probably shear initially occurred along the mexican volcanic zone near the end of the middle jurassic subsequently probably about 160 m y ago displacements that total 800 km began along the mojave sonora megashear contemporaneously yucatan and fragments of pre cretaceous rocks that compose parts of central and western cuba migrated northward toward their present positions rotation of yucatan was facilitated by considerable displacement along the proto motagua zone and along a zone that is probably coincident with the modern salina cruz fault accumulation of widespread major salt units of late jurassic callovian to early oxfordian age in the gulf basin probably occurred contemporaneously with the arrival of these blocks at their present positions clastic units that interfinger with some of the youngest salt units and rim the gulf of mexico have not recorded major recognized translations since their accumulation clockwise rotation of south america and the chortis plate occurred during early cretaceous time this movement which was manifested by subduction of jurassic ocean floor against the previously rifted precursor of the island of cuba and under parts of hispaniola and puerto rico is recorded by circum caribbean orogeny abrupt changes in the relative motions between north and south america during late cretaceous time may have resulted in extension and outpourings of basalt upon the jurassic rocks of the ocean floor of the venezuelan basin west of beata ridge sea floor spreading formed the colombian basin related subduction occurred as the chortis plate including part of central america the nicaraguan rise and southeastern cuba was sutured against the maya east plate along the present motagua fault and cayman trench our model is constrained by published geologic data the relative positions of north and south america from atlantic sea floor magnetic anomalies and the requirement that the major transform faults be compatible with the poles of rotation for the appropriate relative motions between north and south america paleomagnetic data from middle america are sparse but do not conflict with the predicted motions of some of the microplates especially chortis

mid cretaceous basin margin carbonates east central mexico isolated high relief carbonate platforms developed in the intracratonic basin of east central mexico during albian cenomanian time relief on the platforms was of the order of 1000 m and slopes were as steep as 20 43 basin margin debris aprons adjacent to the platforms comprise the tamabra formation in the sierra madre oriental at the eastern margin of the valles san luis potosi platform an exceptionally thick 1380m progradational basin to platform sequence of the tamabra formation can be divided into six lithological units basinal carbonate deposition that preceded deposition of the tamabra formation was emphatically punctuated by an allochthonous reef block 1 km long by 0 5 km wide with a stratigraphic thickness of 95 m it is encased in tamabra formation unit a approximately 360 m of peloidal skeletal wackestone and lithoclastic skeletal packstone that includes some graded beds unit b is 73 m of massive dolomite with sparse skeletal fragments and intraclasts unit c 114m thick consists of structureless skeletal wackestone passing upward into graded skeletal packstone interlaminated lime mudstone and fine grained bioclastic packstone with prominent horizontal burrows are interspersed near the top unit d is 126 m of breccia with finely interbedded skeletal grainstone and burrowed or laminated mudstone the breccias contain a spectrum of platform derived lithoclasts and basinal intraclasts up to 10 m in size the breccias are typically grain supported rudstone with a matrix of lightly to completely dolomitized mudstone or skeletal debris beds are up to several metres thick unit e is 206 m of massive sucrosic dolomite that replaced breccias unit f is approximately 500 m of thick bedded to massive skeletal packstone with abundant rudists and a few mudstone intraclasts metre scale laminated lime mudstone beds are interspersed the section is capped by el abra formation platform margin limestone consisting of massive beds of caprinid packstone and grainstone with many whole valves depositional processes within this sequence shift from basinal pelagic or peri platform sedimentation to distal platform derived muddy turbidity currents with a large slump block unit a through more proximal coarser and cleaner turbidity currents unit b c to debris flows incorporating platform margin and slope debris units d e finally a talus of coarse reef derived bioclasts unit f accumulated as the platform margin prograded over the slope sequence interspersed basinal deposits evolved gradually from largely pelagic to include influxes of dilute turbidity currents units containing turbidites with platform derived bioclasts reflect flooding of the adjacent platform breccia blocks and lithoclasts were probably generated by erosion and collapse of the platform during lowstands laminated black pelagic carbonates locally cherty are interbedded with both breccias and turbidites at least those interbedded with turbidites may have been deposited within an expanded mid water oxygen minimum zone during relative highstands of sea level they are in part coeval with mid cretaceous black shales of the atlantic ocean

reduced porphyry copper gold deposits a new variation on an old theme it is a widely accepted fact that porphyry cu au deposits form from highly oxidized ore fluids despite this assertion several otherwise typical porphyry cu au deposits exhibit clear evidence of having formed from relatively reduced ore fluids these reduced porphyry cu au deposits lack primary hematite magnetite and sulfate minerals i e anhydrite but contain abundant hypogene pyrrhotite commonly have carbonic rich ore fluids with substantial ch 4 and are associated with ilmenite bearing reduced i type granitoids based on a synthesis of theoretical experimental and field data a variation on the classic porphyry cu model is proposed to explain the formation of reduced porphyry cu au deposits and their relatively cu poor but au rich nature the proposed reduced porphyry cu au model does not contradict the current understanding of porphyry cu au formation rather it adds yet another variation on the theme of porphyry cu au genesis

controls on cyclostratigraphy of lower cretaceous carbonates and evaporites cupido and coahuila platforms northeastern mexico the lower cretaceous cupido barremian aptian and coahuila albian carbonate platforms of northeastern mexico exhibit thick successions of meter scale cycles deposited in three unique paleoenvironmental settings 1 the cupido shelf lagoon is composed of peritidal carbonate cycles deposited in the protected lee of a reef rimmed to barrier shoal margin 2 the restricted coahuila ramp interior consists of cyclic alternations of subtidal evaporites and peritidal carbonates 3 the deep water parts of both the cupido and coahuila platforms are composed of foraminiferal wackestones and lime mudstones interspersed with firmgrounds and hardgrounds in a cyclic arrangement vertical successions of meter scale evaporitic cycles and peritidal cycles exhibit systematic stacking patterns that build into intermediate scale high frequency sequences tens to hundreds of meters thick and large scale composite sequences hundreds of meters thick that can be correlated across the cupido and coahuila platforms these large scale stacking patterns are interpreted to reflect longterm accommodation events and when combined with the scale independent architecture of all genetic units permit the inference that all three meter scale cycle types on the cupido and coahuila platforms are also governed by relative sea level change the composition thickness and number of meter scale cycles within individual high frequency sequences can be highly variable across the cupido and coahuila platforms however even though the overall upward shallowing patterns are evident the lateral complexity of cycle architecture and distribution is interpreted to be a natural response to fluctuations in regional climate interacting with autogenic processes such as variations in carbonate production and dispersal intensity and frequency of tropical storms and monsoons thermohaline circulation patterns and ambient ocean chemistry and temperature these interacting processes created laterally variable physiographic and oceanographic conditions across the cupido and coahuila platforms complicating the sedimentary record generated by the composite sea level signal well documented evidence from barremian cenomanian pelagic cycles throughout the tethyan seaway strongly indicates that milankovitch driven climatic changes operated during the early cretaceous contemporaneous shallow marine cyclicity in several locations suggests that these climatic changes may have had globally widespread effects in an effort to link the shallow water and deep water realms we propose a model whereby milankovitch driven global climatic changes generated low amplitude high frequency eustatic fluctuations through some combination of thermal expansion and contraction of ocean water waxing and waning of small ice caps and alpine glaciers and changes in the storage capacity of aquifers and lakes to produce meter scale cycles across lower cretaceous shallow marine platforms

marine carbonate factories a global model of carbonate platform distribution platform carbonates are a major component of the earth system but their spatial distribution through geological times is difficult to reconstruct due to the incompleteness of geological records sampling heterogeneity and their intrinsic complexity beyond this complexity carbonates are not randomly distributed in the world oceans neither in the modern nor in the past and thus global trends exist in the present review we focus on the understanding of the spatial distribution of carbonate production at a global scale we use a deterministic approach which focuses on discriminating components stratigraphic architectures and environmental features to relate shallow water carbonate production to oceanographic parameters the work is based on extensive literature reviews on carbonate platforms ecological niche modelling coupled with deep time general circulation models is used to calibrate a predictive tool of carbonate factory distribution a carbonate factory function is set up that is based on sea surface oceanographic parameters temperature salinity and primary productivity the model was tested using remote sensing and in situ oceanographic data of modern times while outputs of paleoceanographic models are utilized for lower aptian cretaceous modelling the approach allows determining four neritic carbonate factories that are called the marine biochemical photozoan photo c and heterozoan factories the model finely simulates the global distribution of lower aptian and modern carbonate platforms carbonate factories appear to thrive for specific ranges along the environmental gradient of carbonate saturation this conceptual scheme appears to be able to provide a simple universal model of paleoclimatic zones of shallow water marine carbonates

the origin and pre cenozoic evolution of the tibetan plateau different hypotheses have been proposed for the origin and pre cenozoic evolution of the tibetan plateau as a result of several collision events between a series of gondwana derived terranes e g qiangtang lhasa and india and asian continent since the early paleozoic this paper reviews and reevaluates these hypotheses in light of new data from tibet including 1 the distribution of major tectonic boundaries and suture zones 2 basement rocks and their sedimentary covers 3 magmatic suites and 4 detrital zircon constraints from paleozoic metasedimentary rocks the western qiangtang amdo and tethyan himalaya terranes have the indian gondwana origin whereas the lhasa terrane shows an australian gondwana affinity the cambrian magmatic record in the lhasa terrane resulted from the subduction of the proto tethyan ocean lithosphere beneath the australian gondwana the newly identified late devonian granitoids in the southern margin of the lhasa terrane may represent an extensional magmatic event associated with its rifting which ultimately resulted in the opening of the songdo tethyan ocean the lhasa northern australia collision at similar to 263 ma was likely responsible for the initiation of a southward dipping subduction of the bangong nujiang tethyan oceanic lithosphere the yarlung zangbo tethyan ocean opened as a back arc basin in the late triassic leading to the separation of the lhasa terrane from northern australia the subsequent northward subduction of the yarlung zangbo tethyan ocean lithosphere beneath the lhasa terrane may have been triggered by the qiangtang lhasa collision in the earliest cretaceous the mafic dike swarms ca 284 ma in the western qiangtang originated from the panjal plume activity that resulted in continental rifting and its separation from the northern indian continent the subsequent collision of the western qiangtang with the eastern qiangtang in the middle triassic was followed by slab breakoff that led to the exhumation of the qiangtang metamorphic rocks this collision may have caused the northward subduction initiation of the bangong nujiang ocean lithosphere beneath the western qiangtang collision related coeval igneous rocks occurring on both sides of the suture zone and the within plate basalt affinity of associated mafic lithologies suggest slab breakoff induced magmatism in a continent continent collision zone this zone may be the site of net continental crust growth as exemplified by the tibetan plateau c 2012 international association for gondwana research published by elsevier b v all rights reserved

paleogeographic evolution of early deep water gulf of mexico and margins jurassic to middle cretaceous comanchean the paleobathymetric configuration of the early gulf of mexico is inferred from 1 cretaceous carbonate shelf margins interpreted from seismic profiles and other stratigraphic data 2 distribution of jurassic and cretaceous platform and basinal facies and 3 hindcasting of subsidence history in the central basin substantial paleogeographic ambiguity results from uncertainty about 1 kinematics and timing of late triassic to jurassic extensional opening of the gulf basin which probably involved major strike slip faulting 2 the magnitude of subsequent compressive deformation on the western and southern basin margins and 3 possible accretion of allochthonous terranes the initial sub sea level topographic depression created by crustal extension is manifested by the distribution of callovian pre marine salt and oxfordian basinal marine facies late jurassic sea floor spreading split the main salt body and created a central deep water 1 km trough from the oxfordian to early neocomian ramp like platform margins generally underwent net retreat except in the northern gulf where major clastic progradation took place carbonate platform margins with sufficient paleorelief for geometric expression on seismic profiles developed early in the cretaceous these cretaceous carbonate margins exhibit a variety of architectural styles including 1 in the northwestern gulf two cycles of progradation coahuilan and comanchean terminated by drowning events 2 in the southwestern gulf a single cycle of progradation 3 continuous aggradation along the florida and campeche escarpments paleobathymetric relief across cretaceous carbonate margins ranges from high and steep to low relief to ramplike the close of comanchean drowning event greatly and permanently reduced the extent of circum gulf carbonate platforms and especially rimmed margins locations of cretaceous carbonate margins were influenced by basement hinge zones and paleohighs developed on attenuated continental crust by the distribution of salt and by clastic progradation eustacy is commonly invoked to explain behavior and architecture of carbonate margins in the gulf but other paleoenvironmental variables such as nutrient abundance are probably important as well

origin of terrestrial gypsum dunes implications for martian gypsum rich dunes of olympia undae abstract the estancia white sands guadalupe and cuatrocienegas dune fields are among the largest known aeolian gypsum sand dune accumulations on earth and occupy closed drainage basins within the rio grande rift high sedimentation rates of lacustrine gypsum occur in topographic depressions within the closed basins the gypsum accumulations result from long term complex interaction between tectonism climate and a hydrologic cycle that involves geochemical recycling of sulfur from older sedimentary rocks flanking and underlying the basins gypsum precipitation in lacustrine environments is strongly controlled by local groundwater bedrock interaction the ranges of 34s values per mil vs vcdt for gypsum sand in the white sands dune field 12 1 to 13 9 guadalupe dune field 10 2 to 12 5 and cuatrocienegas dune field 14 6 to 15 9 indicate that the main sources of dissolved sulfate are evaporite strata of lower permian middle permian and cretaceous ages respectively a spatial increase of 34s values across the white sands dune field in the direction of prevailing winds matches well with a stratigraphically upward increase of 34s values recorded in lake otero an ancient lake in the basin strata this finding supports previous suggestions that white sands dune field evolved as a result of the step wise deflation of previously stored sediments in lake otero the modern gypsum dune fields are primarily wet eolian systems in which dune accumulation is controlled by a near surface groundwater table which promotes early cementation of the dune accumulations early cementation in the interdune surfaces and to a lesser degree on the dune surfaces reduces the amount of sand available for transport and slows rates of dune migration based on an average migration rate of 2 m year the time needed for a dune at white sands to migrate the downwind distance of the dune field is approximately 6500 years which matches well with other estimates of the initiation of the dune field at approximately 7000 years ago and indicates that white sands likely evolved as a wet aeolian system as on earth gypsum rich dune fields apparently are rare on mars gypsum has been identified only within the olympia undae dune field which encircles a portion of the martian north polar residual ice cap analogous to terrestrial gypsum dunes the gypsum within the olympia undae gypsum rich dunes might have originated from transport and deposition via aeolian processes in this model gypsum rich source sediment could have been formed by confined groundwater or surface water activity and later transported by the wind any subsequent gypsum precipitation in the source area could have been initiated by episodic melting of the martian polar ice cap it is likely that the gypsum was deposited in the olympia undae dunes after the main deflation events that led to formation of the siliciclastic components of the dune field

global milankovitch cycles recorded in rock magnetism of the shallow marine lower cretaceous cupido formation northeastern mexico rock magnetic cyclostratigraphy was measured in the barremian aptian cupido cupidito formation northeastern mexico the goal was to develop an objective evaluation of palaeo environmental variability recorded in the formation that is independent of facies analysis and interpretation anhysteretic remanent magnetization arm was used to estimate magnetic mineral concentration variations for the upper 143 m of the formation which is characterized by metre scale carbonate cycles representative of innerand middle shelf marine environments isothermal remanent magnetization acquisition experiments and scanning electron microscope sem examination indicate that micron sized detrital magnetite from eolian dust carries the arm signal at the sampled sections from garcia and chico canyons 25 km apart arm records a synchronous 30 35 m oscillation with maxima coinciding with fourth order sequence boundaries superimposed with prominent high frequency variability calibrating the 30 35 m oscillation to a 405 kyr period long eccentricity cycle focuses the high frequencies into short eccentricity obliquity and precession index bands the precession band signal modulates with an eccentricity signature the arm signal is correlated between sections but decoupled from the interpreted fifthorder depositional cycles arm amplitudes diminish up section with facies suggesting deepening conditions that diluted magnetite concentration this probably signals a warming increasingly humid climate changing global circulation and or greater dispersal of magnetite grains earth s ancient shallow marine carbonate platforms are important archives of past global change their in situ biological genesis makes them sensitive indicators of physical conditions in shallow marine environments including temperature circulation and sea level wilson 1975 the accommodation space afforded by water depth is thought to govern the amount and type of sediment that accumulates at a given location water depth in turn is controlled by a combination of tectonic subsidence near shore deposition and global sea level which vary significantly through time schlager 2005 the commonly observed stacking of metrescale shallowing upward cycles in carbonate platform deposits has led to proposals of allocyclic v autocyclic forcing mechanisms the most widely cited allocyclic hypothesis is astronomically controlled eustasy fischer 1964 hardie et al 1986 autocyclic mechanisms involve infilling and oceanward progradation of sedimentation without eustatic change ginsburg 1971 to this day the allocycle v autocycle debate remains unresolved in understanding the origin of 10 10 year scale lithologic cyclicity in shallow marine carbonates schwarzacher 2000 burgess 2006 schlager 2010 full shallowing to sea level may not develop in response to every sea level oscillation subtidal missed beats resulting in amalgamated cycles conversely prolonged episodes of subaerial exposure may occur in inner platform settings that are only briefly or never flooded with every sea level oscillation leading to condensed or peritidal missed beats goldhammer et al 1990 ultimately facies analysis of shallow marine sections is limited in teasing apart the interplay of eustasy owing to climate change and subsidence arising from local tectonics this is in large part owing to the relatively subjective interpretation of lithofacies that is required from the stratigrapher therefore we need to develop facies independent from jovane l herrero bervera e hinnov l a housen b a eds 2013 magnetic methods and the timing of geological processes geological society london special publications 373 325 340 first published online april 25 2013 http dx doi org 10 1144 sp373 20 the geological society of london 2013 publishing disclaimer www geolsoc org uk pub ethics by guest on july 5 2013 http sp lyellcollection org downloaded from