nd isotopic and geochemical constraints on the provenance and tectonic setting of the low grade meta sedimentary rocks from the trans north china orogen north china craton abstract in the trans north china orogen tnco of the north china craton low grade supracrustal successions extensively occur in the wutai luliang zanhuang zhongtiao and dengfeng complexes from north to south meta sedimentary samples from the wutai and zhongtiao complexes were collected for geochemical and nd isotopic studies and several samples from the zanhuang and dengfeng complexes were also analyzed for nd isotopic studies for comparative purpose most of the meta siltstones and meta sandstones from the wutai and zhongtiao complexes are characterized by depletions in mobile elements like cao sr and na2o high chemical index of weathering ciw values and strong positive correlation between al2o3 and tio2 indicating intense weathering conditions significant post depositional k metasomatism is indicated in the a cn k diagrams for most of the analyzed samples and the relatively high pre metasomatized chemical index of alteration cia values 43 87 also imply a high degree of source weathering depleted transitional trace elements ni cr co and sc fractionated light rare earth elements patterns mild negative eu anomalies in the majority of these meta sedimentary samples point toward felsic source rocks including the 2 5 ga granitics ttg gneisses and the paleoproterozoic granitics in the tnco minor contribution from mafic rocks is evidenced from relative high contents of mgo fe 2 o 3 t sc and lower la ybn ratios in some older sequence set samples from the zhongtiao complex our geochemical and nd isotopic data combined with previous studies in the lithostratigraphic sequence provenance and depositional age suggest that the older and younger sequence sets of the low grade supracrustal successions in the tnco were deposited in the different depositional environments the older sequence set was deposited in a back arc basin between the andean type continental margin arc and the eastern block after 2 1 ga whereas the younger sequence set formed in a foreland basin between 1 88 and 1 80 ga which is consistent with the model that the collision between the eastern and western blocks to form the trans north china orogen occurred at 1 85 ga

a basin redox transect at the dawn of animal life multiple eukaryotic clades make their first appearance in the fossil record between 810 and 715 ma molecular clock studies suggest that the origin of animal multicellularity may have been part of this broader eukaryotic radiation animals require oxygen to fuel their metabolism and low oxygen levels have been hypothesized to account for the temporal lag between metazoan origins and the cambrian radiation of large ecologically diverse animals here paleoredox conditions were investigated in the fifteenmile group ogilvie mountains yukon canada which hosts an 811 ma ash horizon and spans the temporal window that captures the inferred origin and early evolution of animals iron based redox proxies redox sensitive trace elements organic carbon percentages and pyrite sulfur isotopes were analyzed in seven stratigraphic sections along two parallel basin transects these data suggest that for this basin oxygenated shelf waters overlay generally anoxic deeper waters the anoxic water column was dominantly ferruginous but brief periods of euxinia likely occurred these oscillations coincide with changes in total organic carbon suggesting euxinia was primarily driven by increased organic carbon loading overall these data are consistent with proposed quantitative constraints on proterozoic atmospheric oxygen being greater than 1 of modern levels but less than present levels comparing these oxygen levels against the likely oxygen requirements of the earliest animals both theoretical considerations and the ecology of modern oxygen deficient settings suggest that the inferred oxygen levels in the mixed layer would not have been prohibitive to the presence of sponges eumetazoans or bilaterians thus the evolution of the earliest animals was probably not limited by the low absolute oxygen levels that may have characterized neoproterozoic oceans although these inferred levels would constrain animals to very small sizes and low metabolic rates

lithium saltworks of the salar de atacama a model for mgso 4 free ancient potash deposits abstract potash basins similar to those in the geological past no longer exist at present there are only hypersaline lakes such as those in the tibetan plateau where carnallite kcl mgcl2 6h2o precipitates given that the purpose of common saltworks is to obtain nacl the halitic stage is not exceeded by contrast saltworks extracting lithium by solar evaporation reach more advanced stages of brine evolution and saline precipitation in the salar de atacama saltworks with a relative humidity commonly below 30 monthly average salts precipitate following a sequence of halite nacl sylvite kcl carnallite and bischofite mgcl2 6h2o and display a useful model of evolution similar to that which gave rise to mgso4 free potash deposits in the past prismatic acicular gypsum caso4 2h2o the main accessory mineral is transformed into a less hydrated calcium sulfate probably anhydrite caso4 during carnallite precipitation mineral crystal size and annual sedimentary thickness of each paragenesis are compared with those in ancient potash deposits the behavior of sylvite and carnallite as cements is observed at the onset of their precipitation in ponds where both minerals coexist with previous halite millimeter cyclicity due to day night thermal variations is observed in these saltworks whereas cm and mm cyclicities have been interpreted in ancient sites as annual regular and intra annual irregular respectively conditions similar to those existing at the salar de atacama were necessary to preserve carnallite which is commonly the most evolved mineral in the ancient deposits the development of potash deposits in the south pyrenean foreland basin and the rhine graben near the eocene oligocene boundary is attributed to global aridity and cooling and to the basin restriction associated with a decrease in the ocean level caused by the spread of the antarctic ice cap

environmental implications of salt facies in the dead sea thick sequences of salt halite have been recovered in a 456 m long core drilled at the deepest floor of the dead sea by the dead sea deep drilling project and extending 200 k y back in time the salt sequences were precipitated in the ancient lake that occupied the dead sea basin during the last three interglacials during intervals of extreme aridity in the lake s watershed the salt layers alternate with mud layers that indicate wetter periods in the watershed when floods transported fine detritus matter to the lake the salt sources include brine discharge and freshwater runoff that dissolved halite units dissolved salts accumulated in the lake during glacials and relatively wet periods when the lake expanded and precipitated during interglacials when the lake levels dropped this study establishes for the first time the evaporite facies and sedimentological features of the deep dead sea brine during interglacial periods by using the modern precipitation of halite in the dead sea as an analogue for past halite depositional periods as recorded in the drill core the halite intervals provide a record of facies characterizing a deep water evaporitic environment the halite layers consist mainly of two types of crystals small cumulate crystals containing halite rafts which indicate precipitation from the surface brine of the lake epilimnion and bottom growth usually large halite crystals that precipitated on the lake floor hypolimnion the layers of small halite crystals formed during drier periods as compared to the bottom growth crystals the bottom growth halite crystals contain variable quantities of detritus and show mild dissolution structures at the contact between the mud and the halite crystals these two main types of halite in combination with muds and gypsum comprise seven categories of salt facies that reflect the hydrological conditions dry to wet and that display a cyclic decadal to millennial pattern along the sampled core intervals frequent alternation of these two salt crystal types suggests seasonal changes whereby the small cumulate crystals were formed during the summer and the bottom growth crystals were formed during the winter when the surface temperatures of the lake were low and the surface water was less saline and less likely to be saturated with respect to halite comparison of the last interglacial halite with the modern halite facies together with the absence of significant dissolution features within the halite and the cyclic nature of the facies indicates that the lake was continuously deep 100 m during the last 200 k y

chemistry of modern soils as a guide to interpreting precambrian paleosols precambrian paleosols are potentially one of our best sources of information about the composition of the atmosphere early in earth s history to be used this way however an alteration profile must be shown to be an in situ product of vadose processes data from modern soils show that the ratios of less mobile elements such as zr ti and al can be used as a preliminary screen to test for the in situ nature of a profile if the ti zr ratio departs from that of the host rock by more than 40 or the ti al ratio departs by more than 50 for moderate degrees of weathering then a significant allochthonous contribution to the profile is indicated this technique correctly separates in place from allochthonous horizons when applied to independent data from two modern profiles a review of published precambrian profiles identifies two often cited examples denison and pronto as suspect based on these criteria in the interpretation of paleoatmospheres it is also necessary to show that fe is controlled not b

molybdenum isotopes in late archean carbonate rocks implications for early earth oxygenation abstract we present carbonate mo isotope data of the 2 64 2 5 ga old ghaap group transvaal supergroup south africa to contribute to the debate on early earth oxygenation mo fractionation in carbonates has just recently been introduced as a potential new proxy for ocean redox chemistry and it was suggested that under favorable conditions non skeletal carbonates closely monitor the ambient seawater 98 95 mo composition the record presented here is characterized by three phases of moderately to strongly fractionated 98 95 mo with values of up to 1 6 interrupted by two shifts towards detrital levels this near continuous presence of heavy 98 95 mo suggests a quasi permanent availability of free atmospheric o 2 because fractionation relative to the continental background signature occurs exclusively when mo is present as dissolved molybdate ions moo 4 2 we compare our carbonate data to a previously published black shale mo record on samples from the same drill core the general interpretation of both records is identical a rise in o 2 preceded the commonly accepted transition to a consistently oxygenated atmosphere by 150 ma however in the ghaap group carbonates fractionated mo is found at a time when the coeval black shales still indicate detrital sedimentation a combination of detritus admixture and or redox controlled mo isotope fractionation during shale formation in suboxic to anoxic waters is suggested as cause for a period characterized by a persistent offset between lighter shale and heavier carbonate 98 95 mo the apparent offset can then be attributed to the different geochemical behavior of the two archives with respect to the local depositional conditions redox vs non redox dependent such changes in the sedimentary environment might also explain why the carbonates do not reproduce rapid fluctuations found throughout the shale record but show a continuous signature with scarce outliers thus by means of the combined archives the conspicuous 98 95 mo scatter found in the shale record could be attributed to variable depositional conditions during its formation rather than global oxic anoxic fluctuations simultaneously the carbonates provide a better approximation of the long term 98 95 mo seawater evolution this study introduces the mo isotopic composition of carbonates as a promising new tool for paleo redox studies in particular when combined with black shales

natural mass dependent variations in the isotopic composition of molybdenum we present the first observations of natural mass dependent fractionation of the isotopic composition of molybdenum mo using multi collector inductively coupled plasma mass spectrometry variations in the isotopic composition of mo are reported as 97 95mo 97mo 95mo sample 97mo 95mo standard 1 1000 external analytical precision of 97 95mo is 1 between sediments deposited under anoxic conditions 97 95mo 1 02 to 1 52 relative to our in house standard and ferromanganese nodules 97 95mo 0 63 to 0 42 97 95mo of pacific ocean seawater 97 95mo 1 48 lies within the range of values for anoxic sediments closest to modern black sea anoxic sediments molybdenites from continental ore deposits have intermediate 97 95mo ranging from 0 26 to 0 09 variations in the abundances of 92mo 95mo 96mo 97mo and 98mo are consistent with mass dependent fractionation a sporadic unidentified interference occurs at mass 94 and 100mo is not measured we hypothesize that the 97 95mo offset between anoxic sediments and ferromanganese nodules results from mo isotope fractionation during inefficient scavenging of mo from seawater by mn oxides under oxic conditions the similarity in 97 95mo of anoxic sediments and seawater is consistent with the very efficient removal of mo from seawater under anoxic conditions in the presence of h2s the data can be interpreted in terms of a steady state mass balance between the mo flux into the oceans from the continents and the mo flux out of the oceans into oxic and anoxic sediments such an interpretation is quantitatively consistent with existing estimates of the removal fluxes of mo to anoxic and oxic sediments these findings suggest that 97 95mo in seawater may co vary with changes in the relative proportions of anoxic and oxic sedimentation in the oceans and that this variation may be recorded in 97 95mo of anoxic sediments hence the mo isotope system may be useful in paleoredox investigations

the composition of gases in fluid inclusions of late permian zechstein marine evaporites in northern germany abstract in order to understand the generation of gases in late permian marine evaporites and the migration of gases in salt domes 428 gas bearing fluid inclusions of the gorleben salt dome northern germany were analysed using laser raman spectrometry lrs the investigations were divided in two parts in the first part only gas rich inclusions were analysed involving samples from different stratigraphic layers of the zechstein 2 stasfurt serie and zechstein 3 leine serie and from different locations within the salt dome for the second part only the gaseous components in brines rich inclusions of the zechstein 2 were measured the compositional range of all inclusions investigated can be subdivided into two main groups with rare exceptions the first group of n 2 and n 2 o 2 inclusions reveals a n 2 o 2 ratios close to that of modern atmosphere thus indicating trapped paleoatmosphere the second group is represented by inclusions that contain mixtures of n 2 ch 4 occasionally h 2 and or h 2 s the most abundant subgroups are n 2 ch 4 and n 2 ch 4 h 2 mixtures these gas mixtures can be produced by the decomposition of organic material under anoxic conditions it is noted that n 2 in both main groups can also be generated by degassing of underlying early permian rotliegendes or carboniferous c org rich sedimentary rocks and an entrapment in early stages of the zechstein halokinesis the different origin of both main groups is supported by stratigraphic correlation in the stratigraphic layers which contain mainly mixtures of n 2 and o 2 or pure n 2 inclusions of the n 2 ch 4 h 2 h 2 s group are rare and vice versa layers which are rich in n 2 ch 4 h 2 h 2 s do not contain many n 2 o 2 inclusions the majority of layers investigated frequently contains inclusions of the n 2 o 2 group only two anhydrite rich layers of zechstein 3 main anhydrite and anhydrite intercalated salt contain mainly inclusions of the second group the zechstein 3 potash seam as well as secondary halites contain more or less the same population of inclusions from every main group a comparison of the gas rich inclusions and the gases in the brine rich inclusions of the zechstein 2 layer main rock salt 3 shows distinct differences whereas the gas rich inclusions are of the n 2 o 2 group the gases from the brine rich inclusions are of the n 2 ch 4 group emphasising different origins the latter is a product of anhydrite rich parts or potash seams that have migrated later into the overlying main rock salt 3

the remaking of the mengyejing potash deposit in yunnan china evidence from rb sr isotopic systematics abstract the mengyejing potash deposit mpd is the first significant ancient potash deposit ever found in china and it was considered to have formed during the middle to late cretaceous the 87 sr 86 sr ratios of potash bulk samples suggest that both bedded and veined potash orebodies of the mpd have been affected by igneous activity resulting from decompression melting of a metasomatically altered depleted mantle from 16 ma to present the rb sr isotopic systematics of the potash bulk samples define several apparent isochrons ranging from 0 609 0 026 to 14 23 0 63 ma with the maximum age being consistent with previous k ar ages of the k bearing minerals from the mpd such isotopic signatures imply that the mpd may have been affected by multiple stage fluid flow events since the mid miocene consisting of hydrothermal fluids continental fresh water and or hot spring water it is very likely that the mpd is still affected by fluid flow events in modern times the mineral assemblage of halite sylvite with minor amounts of carnallite was formed due to the recrystallization and diagenetic modification by hydrothermal fluids some characteristics of halite photomicrographs and inclusions and the lack of original halite chevron patterns are also supportive of the hypothesis that the deposit has undergone a diagenetic modification and dissolution recrystallization processes

initiation of leaking earth an ultimate trigger of the cambrian explosion abstract for life to have dramatically evolved and diversified during the so called cambrian explosion there must have been significant changes in the environmental conditions of earth a rapid increase in atmospheric oxygen which has been discussed as the key factor in the evolution of life cannot by itself explain such an explosion since life requires more than oxygen to flourish let alone survive the supply of nutrients must have played a more critical role in the explosion including an increase in phosphorus p and potassium k which are key elements for metabolisms to function so what happened at the onset of the cambrian to bring about changes in environmental conditions and nutrient supply and ultimately evolution of life an ultimate trigger for the cambrian explosion is proposed here the geotherm along subduction zones of a cooling earth finally became cool enough around 600 ma to allow slabs to be hydrated the subduction of these hydrated slabs transferred voluminous water from the ocean to the mantle resulting in a lowering of the sea level and an associated exceptional exposure of nutrient enriched continental crust along with an increase in atmospheric oxygen this loss of water at the surface of the earth and an associated increase in exposed landmass is referred to here as leaking earth vast amounts of nutrients began to be carried through weathering erosion and transport of the landmass rock fragments of the landmass would break down into ions during transport to the ocean through river providing life forms prokaryote sufficient nutrients to live and evolve also plume driven dome up beneath the continental crusts broadened the surface area providing a supply of nutrients an order magnitude greater than that produced through uplift of mountains by continental collision simultaneously atmospheric oxygen began to increase rapidly due to the burial of dead organic matter by enhanced sedimentation from the emergence of a greater landmass which ultimately inhibited oxidation of organic matter hence oxygen began to accumulate in the atmosphere which when coupled with a continuous supply of nutrients resulted in an explosion of life including an increase in the size an enhanced oxygen supply in the atmosphere resulted in the formation of an ozone layer providing life a shield from the uv radiation of the sun this enabled life to invade the land in addition to a change in the supply of nutrients related to a leaking earth the evolution of life was accelerated through mass extinction events such as observed during snowball earth possibly related to a starburst in our galaxy as well as mutation in the genome due to radiogenic elements sourced from carbonatite magma atomic bomb magma in rift valley there are two requirements to find a habitable planet 1 the initial mass of an ocean and 2 the size of a planet these two conditions determine the history of a planet including planetary tectonics and the birth of life this newfound perspective which includes the importance of a leaking planet provides a dawn of new planetary science and astrobiology

iron oxidation state of a 2 45 byr old paleosol developed on mafic volcanics the 2 45 byr old weathering profile developed on early proterozoic mafic volcanics located near cooper lake ontario canada was examined geochemically and mineralogically for a better understanding of the atmospheric oxygen evolution ferrous to ferric ion fe ii and fe iii respectively ratios of the bulk rock samples were analyzed by mossbauer spectrometry the total fe fe t and fe ii concentrations decrease from 12 0 and 11 2 wt to 1 85 and 0 89 wt respectively from the bottom to the top of the weathering profile the fe t and fe ii concentrations normalized to ti and zr as well as the fe ii fe iii ratio of raw data linearly decrease with depth toward the top while the fe iii concentration remains nearly constant throughout the profile the linear decrease of fe ii accompanied by the nearly constant distribution of fe iii is difficult to be explained by the scenario of oxidizing weathering and subsequent reducing hydrothermal alteration the behaviors of fe ii and fe iii can be simply explained by anoxic weathering the anoxic weathering suggests that the 2 45 ga atmosphere was anoxic the slight increase of fe fe mg in the octahedral sites of chlorite toward the top and no ce anomaly in the ree patterns are also consistent with anoxic weathering

a widespread positive 13ccarbanomaly at around 2 33 2 06 ga on the fennoscandian shield a paradox carbon isotope measurements carried out on 201 carbonate samples from the early proterozoic of the kola peninsula n karelia and norway yield 13c pdb spanning 20 5 to 11 a general 13c secular trend shows that prior to 2 33 ga values are typically normal marine averaging around 3 0 between 2 33 and 2 06 ga in jatulian time there follows a rapid excursion to positive 13c of around 6 post jatulian time is characterized by 13c of sedimentary carbonates fluctuating between 5 and 3 also it is remarkable for the first pronounced development of diagenetic carbonates which have 13c between 14 and 6 the c 6 positive 13c shift with a duration of about 270 myr coincides with a maximum in the diversity and abundance of stromatolites and with widespread development of red beds but does not coincide with the maximum of buried corg mass the fennoscandian shield represents the largest isotoically anomalous carbonate province yet reported and the positive 13c excursion together with a series of major global palaeoenviromental changes seems to be more intense than the precambrian cambrian transition events however it is still not clear what kind of mechanism this phenomenon could be attributed to an increase of the ronov ratio and or broecker ratio and other possible models are discussed as the target for future investigations

a 1 25 ga depositional age for the paleoproterozoic mapedi red beds kalahari manganese field south africa new constraints on the timing of oxidative weathering and hematite mineralization the great oxidation event goe is marked by the loss of readily oxidizable detrital minerals and the onset of oxidative weathering one of the oldest post goe weathering surfaces which extends for almost 350 km along strike occurs in griqualand west south africa it is best preserved east of the blackridge thrust where oxidized paleoweathering profiles are developed below the unconformity at the base of mapedi gamagara red beds in the maremane dome the red beds preserve pisolitic hematite laterites which indicate a highly oxygenated atmosphere and suggest hot and humid climatic conditions the mapedi and gamagara formations are undated east of the blackridge thrust but were thought to be lithological correlatives of the 1 91 ga mapedi red bed sequence to the west here we report a u pb zircon age of 1 25 ga for a felsic tuff in red beds of the mapedi formation in the kalahari manganese field the new tuff age shows that the mapedi red beds east of the thrust were deposited 650 m y after the mapedi formation to the west and therefore they are part of a distinct mesoproterozoic sequence based on lithologic and sedimentological similarities the mapedi east and gamagara formations are likely to be correlatives that were deposited on an ancient weathering surface at ca 1 25 ga our findings suggest that key evidence for a highly oxygenated atmosphere during the early paleoproterozoic actually formed at ca 1 25 ga during a major episode of mesoproterozoic oxidative weathering

effects of mass transfer compaction and secondary porosity on hydrothermal upgrading of paleoproterozoic sedimentary manganese ore in the kalahari manganese field south africa in the northwestern part of the kalahari manganese field low grade carbonate rich mamatwan type ore is altered to high grade oxide rich wessels type ore in association with normal faults mass balance calculations based on the assumption that manganese was geochemically immobile suggest that upgrading of the manganese ore can be attributed to leaching of mg ca co2 and sio2 from the sedimentary ore with residual enrichment of mn hydrothermal alteration resulted in development of about 10 to 20 of secondary porosity in the ores and the orebed was compacted to two thirds of its original stratigraphic thickness

origin of polyhalite deposits in the zechstein upper permian zdrada platform northern poland polyhalite deposits in the zechstein upper permian of northern poland occur in the lower werra anhydrite in the zdrada sulphate platform the polyhalite appears to be a very early replacement of anhydrite the replacement was caused by the halite precipitating brines which contained potassium and magnesium ions the formation of polyhalite was preceded by the syndepositional anhydritization of the original gypsum deposit which has often preserved its primary textures this anhydritization on the platform and its slopes was a reaction of the precipitated gypsum in a hydrologically open evaporite basin with brines of salt basins adjacent to the sulphate platform these brines when nearly saturated with respect to halite and potassium and magnesium rich reacted with anhydrite to precipitate polyhalite along the slopes of the zdrada platform the oxygen and sulphur isotopic compositions of sulphate evaporites indicate that marine solutions were the only source of sulphate ions supplied to the zechstein basin and that anhydrite was transformed to polyhalite by reaction with marine brines more concentrated than those that precipitated precursor calcium sulphate minerals

marine like potash evaporite formation on a continental playa case study from chott el djerid southern tunisia abstract an exceptional flood in january 1990 led to the formation of a large ephemeral lake on the chott el djerid a salt playa in southern tunisia repeated observations made during 1990 show that the ephemeral lake underwent four evolutionary stages 1 initial flooding 2 evaporative concentration of lake waters 3 the movement of concentrated brine pools over the playa surface as a result of wind action and 4 total desiccation of the lake by september 1990 during all four stages the brine chemistry of the lake was monitored water inflow into the chott el djerid basin was found to have a consistent ca so 4 cl rich and hco 3 co 3 poor chemistry reflecting the recycling of homogeneous assemblages of cretaceous mio pliocene and quaternary evaporites within the catchment as the ephemeral lake shrank these waters produced an na mg k cl so 4 brine which was similar to modern sea water mineral saturation data show that during the desiccation of the lake saturation with respect to both gypsum and halite was achieved and that the most concentrated brines were ultimately saturated with respect to potash phases after the desiccation of the lake the main mineral phases found on the chott included gypsum and halite in addition ephemeral deposits of carnallite observed as carnallitite 3kmgcl 3 6h 2 0 nacl were found this assemblage is that which would be expected to form if the waters had undergone salt norm evaporation at 1 bar pressure at 25 c snorm in the evaporation model proposed by jones and bodine 1987 the nature of both the brine chemistry and evaporite mineralogy provides a new and rare example of marine like potash bearing evaporites being formed in a contemporary continental playa

chemical and boron isotope compositions of non marine brines from the qaidam basin qinghai china the general chemistry and boron isotope composition were investigated in fresh waters and hypersaline brines from the qaidam basin northern qinghai xizang tibet plateau china this basin is a large tectonically active system isolated from the ocean and composed of thick clastic and evaporite sediments the modern playas are subject to intense evaporation and are characterized by hypersaline brines as well as potash and borate evaporites the chemical composition of the dissolved solutes in the modern brines and waters reveals three main sources 1 inflow of hot springs enriched in sodium sulphate and boron evaporation of these waters leads to a high na cl ratio 1 a na cl so4 brine and an evaporite mineral assemblage of halite mirabilite borate lakes daqaidam and xiaoqaidam 2 inflow surface river waters which are modified by preferential dissolution of halite and potassium and magnesium salts characterized by a na mg cl solute type with low na cl 1 brcl licl and bcl ratios and 3 ca chloridic subsurface brines which are controlled by both salt dissolution and dolomitization processes evaporation and salt crystallization of mixtures of the latter two types leads to a marine like brine e g na mg cl type nacl ratio 1 and mineral assemblages similar to that predicted for progressive evaporation of seawater e g qarhan playa halite sylvite carnallite bischofite the 11 b values of the input waters to the qaidam basin range of 0 7 to 10 9 vs nbs 951 and brines from salt lakes 0 5 to 15 0 are similar to those of associated granitic rocks 11b 2 3 to 3 7 n 3 and hence indicate the non marine origin of these fluids the highest 11b values are associated with fluids with low bli ratios indicating selective removal of elemental boron and 10b by adsorption onto clay minerals the magnitude of 11b enrichment due to adsorption is 15 20 and thus non marine brines are well distinguished from marine derived brines 11b of 39 to 59 preserving the large isotopic difference 40 of their source waters it is proposed to use this distinctive isotopic signature for tracing the origin of ancient evaporite environments

pb pb age of earliest megascopic eukaryotic alga bearing rohtas formation vindhyan supergroup india implications for precambrian atmospheric oxygen evolution abstract though considered to be the earliest known well preserved megascopic body fossil of an eukaryotic alga grypania spiralis has not yet been dated directly and reliably in any of its four known locations in the world we report a pb pb isochron age of 1599 48 ma for the grypania bearing rohtas formation of the vindhyan supergroup central india besides being about 500 myears older than the previously inferred age for this formation this pb pb age together with close age constraints on the same fossil bearing horizons in jixian china and montana usa indicates that grypania bloomed on a global scale between 1 6 and 1 5 ga being an obligate aerobe the appearance of a much older grypania within one of the principal bif deposits near michigan usa has been linked to a significant jump in atmospheric oxygen between 2200 and 1900 ma inferred from geochemical evidence the long gap of 400 myears between the older and younger grypania occurrences could be due to reduction of atmospheric oxygen below the grypania survival threshold as a result of extensive bifs between about 1950 and 1850 ma

late archean initiation of manganese metallogenesis its significance and environmental controls abstract manganese metallogenesis was initiated in a modest scale during the late archean time selectively in india and brazil sedimentary deposits occur in both greenstone belts and high grade granulite terranes in shallow water shelf regimes only and are often intimately associated with stromatolites the changes in the rates of continental crustal growth mantle heat flux and outgassing along with the evolution of tectonic regimes sedimentary environments the state of the biosphere and finally the compositions of interacting atmosphere hydrosphere system from the early to the late archean time have been traced as interdependent parameters and interpreted to explain the first appearance of sedimentary manganese deposits promoted by possibly localized oxygenated environments compared to the spectacular manganese event represented by the giant paleoproterozoic kalahari deposit south africa which is interpreted to have been formed as a consequence of the rapid increase in atmospheric oxygen level ca 2 5 2 4 ga ago the modest initiation of the late archean manganese depositions was triggered by localized photosynthetic oxygen supply forming basin margin oxygen oases as a prologue for the succeeding stratified ocean system the dissolved manganese in the basin water that was oxidized to form shelf type shallow water deposits is suspected by analogy with contemporary banded iron formations bifs but not proved to be of hydrothermal ancestry the initiation of concentrated manganese sedimentation during the late archean by itself provides an evidence for an increase in the oxygen content in the contemporary atmosphere hydrosphere system compared to that in the earlier period supporting the geochemical indications from paleoweathering profiles

the effect of land plants on weathering rates of silicate minerals abstract land plants and their associated microbiota directly affect silicate mineral weathering in several ways by generation of chelating ligands by modifying ph through production of co2 or organic acids and by altering the physical properties of a soil particularly the exposed surface areas of minerals and the residence time of water in laboratory experiments far from equilibrium 1 mm oxalate a strong chelator of al has a negligible effect on the dissolution rate of alkali feldspars but some effect on calcic feldspars and olivine by analogy to oxalate the overall effect of organic ligands on the weathering rate of silicate minerals in nature is likely to be small except perhaps in microenvironments adjacent to roots and fungal hyphae the effect of ph on silicate mineral dissolution rate depends on ph below ph 4 5 the rate increases with decreasing ph in the circumneutral region the rate is ph independent and at ph values above around 8 the rate increases with increasing ph vegetation should thus cause an increase in weathering rate through the ph effect only where the ph is below 4 5 as an overall generalization the effect of plants on weathering rate through changes in soil solution chemistry is probably small for granitic rocks it may be greater for more mafic rocks it is the release of ca and mg from mafic rocks that has the greatest influence on the global co2 budget the effect of changes in soil physical properties on weathering rate can be major by binding fine particles plants can greatly increase weathering rates in areas of high physical erosion where erosion rates are lower the effect of plants is less clear on long timescales plants may decrease chemical weathering by binding secondary products and isolating unweathered minerals from meteoric water a major unknown in estimating the effect of the advent of land plants on weathering rates is the nature thickness particle size distribution permeability of the regolith on the pre silurian continents the indirect effect of vegetation through changing the regional distribution of precipitation may be as important as the direct effects

geology and geochemistry of paleosols developed on the hekpoort basalt pretoria group south africa the hekpoort paleosols comprise a regional paleoweathering horizon developed on 2 224 0 021 ga basaltic andesite lavas at the top of the hekpoort formation of the pretoria group transvaal supergroup south africa in five separate profiles from outcrops along road cuts near waterval onder and the daspoort tunnel and in three drill cores from the bank break area bb3 bb8 and bb14 the top of the paleosol is a sericite rich zone the sericite zone grades downward into a chlorite rich zone in core bb8 and in the road cut at the daspoort tunnel we sampled the underlying or parent basaltic andesite into which the chlorite zone grades we did not obtain samples of the parent material at waterval onder and in cores bb3 and bb14 but chemical analyses indicate that the chlorite and sericite zones in these profiles derive from underlying lavas similar to the ones we sampled in core bb8 and at the daspoort tunnel the presence of apparent rip up clasts of the paleosol in the overlying ironstones of the strubenkop formation in the cores from bank break makes it very unlikely that most of the alteration was a result of interactions with hydrothermal fluids desiccation cracks at the top of the paleosol that were filled with sand during the deposition of the overlying sediments at waterval onder point to a subaerial weathering origin very little if any al ti zr v or cr moved a discernible distance during weathering of any of the five profiles the vertical distribution of fe mg mn ni and co indicates that these elements were largely removed from the top of the soil during weathering the overall abundance of these elements in each of the profiles indicates that a significant fraction of the complement lost from the top subsequently reprecipitated in the lower portion of the soil as constituents of an fe 2 rich smectite the loss of fe from the top of the soil during weathering of the hekpoort paleosols indicates that atmospheric p o 2 was less than 8 x 10 4 atm about 2 22 ga fe 2 rich smectite should only precipitate during soil formation if atmospheric p co 2 is less than or equal to 2 x 10 2 atm rye kuo and holland 1995 ca and na were largely lost during weathering some na was apparently added to the sericite zone in cores bb3 bb8 and bb14 after weathering all five profiles are enriched in k and rb and most are enriched in ba the distribution of these elements indicates that they all were added during post weathering hydrothermal metasomatism rb sr analysis of the paleosol at the daspoort tunnel indicates that metasomatism last affected that profile 1 925 0 032 ga macfarlane and holland 1991

a paleoweathering profile from griqualand west south africa evidence for a dramatic rise in atmospheric oxygen between 2 2 and 1 9 bybp a core drilled near wolhaarkop in griqualand west south africa intersected highly oxidized kuruman iron formation below red beds of the gamagara formation the lateral equivalents of the kuruman iron formation in this drill hole consist largely of siderite ankerite magnetite greenalite and quartz the oxidation of the kuruman iron formation in wol 2 occurred almost certainly during weathering prior to the deposition of the gamagara formation the date of this weathering episode is bracketed between about 2 2 and 1 9 bybp by the age of the ongeluk lavas in the transvaal sequence below the unconformity and by the age of the hartley lavas in the olifantshoek group above the unconformity the ratio of iron to sio2 in the several facies of the weathered kuruman iron formation in wol 2 is nearly the same as that in their unweathered equivalents since sio2 loss during weathering was almost certainly minor the similarity of the fe sio2 ratio in the weathered and unweathered bif indicates that nearly all the feo in the kuruman iron formation was oxidized and retained as feo3 during weathering such a high degree of iron retention is best explained by an o2 content of the atmosphere or 0 03 atm at the time of weathering such an o2 pressure is very much greater than that suggested by the composition of paleosols developed on basalt or 2 2 bybp but is consistent with the highly oxidized nature of the 1 85 by flin flon paleosol the new data suggest that po2 rose dramatically from about 1 percent pal present atmospheric level to or 15 percent pal between 2 2 and 1 9 bybp

carbon and sulfur isotopic compositions of organic carbon and pyrite in sediments from the transvaal supergroup south africa abstract sedimentary organic matter and pyrite from parts of the lower transvaal supergroup and few samples from the olifantshoek group have been studied for their carbon and sulfur isotopic compositions respectively carbon isotopic compositions for minimally altered organic matter range from 43 to 31 sulfur isotope values for sedimentary pyrite display values between 1 3 to 23 6 results from this and previously published work are being interpreted with respect to past biochemical pathways carbon isotope data indicate autotrophic carbon fixation as the process of primary production in addition products of secondary biological reworking contributed to the total organic carbon content sulfur isotope data indicate bacterial sulfate reduction as the main process however changes in sulfate availability and or the rate of sulfate reduction may have caused the observed range in isotopic compositions

sediment and basalt hosted regoliths in the huronian supergroup role of parent lithology in middle precambrian weathering profiles weathering profiles developed side by side on sandstone and a mafic dike provide an unusual opportunity to examine the role of parent rock bulk composition in the chemical evolution of middle precambrian regoliths because the profiles are adjacent to one another differences in topography can be eliminated in accounting for differences in the chemical evolution of the two profiles both profiles show upward increases in al ti k and rb and decreases in mg ca and na in addition the mafic regolith increases upward in zr and nb and decreases in zn and ni total fe decreases upward in both profiles but the sandstone profile retains significantly more of its initial fe than does the mafic dike this difference in fe loss is consistent with weathering in a low oxygen atmosphere of rock types with very different initial fe contents and therefore different atmospheric requirements for complete oxidation of the fe present the fe in the sandstone was mostly oxidized and retained within the profile whereas

permian paleoclimate data from fluid inclusions in halite abstract this study has yielded surface water paleotemperatures from primary fluid inclusions in mid permian nippewalla group halite from western kansas a cooling nucleation method is used to generate vapor bubbles in originally all liquid primary inclusions then surface water paleotemperatures are obtained by measuring temperatures of homogenization to liquid homogenization temperatures ranged from 21 c to 50 c and are consistent along individual fluid inclusion assemblages indicating that the fluid inclusions have not been altered by thermal reequilibration homogenization temperatures show a range of up to 26 c from base to top of individual cloudy chevron growth bands petrographic and fluid inclusion evidence indicate that no significant pressure correction is needed for the homogenization temperature data we interpret these homogenization temperatures to represent shallow surface water paleotemperatures the range in temperatures from base to top of single chevron bands may reflect daily temperatures variations these permian surface water temperatures fall within the same range as some modern evaporative surface waters suggesting that this permian environment may have been relatively similar to its modern counterparts shallow surface water temperatures in evaporative settings correspond closely to local air temperatures therefore the permian surface water temperatures determined in this study may be considered proxies for local permian air temperatures

the chemical and hydrological evolution of an ancient potash forming evaporite basin as constrained by mineral sequence fluid inclusion composition and numerical simulation the chemical evolution of the brine in a potash evaporite basin has been investigated by x ray microanalysis of frozen primary inclusions trapped in halite a computer program based on thermodynamic equilibrium and mass balance principles has been used to simulate evaporation paths the comparison between the results of calculations the observed mineralogy and mineral sequence and the solute content in fluid inclusions has placed constraints on the hydrological evolution of the basin the upper eocene basin of navarra southern pyrenees spain began as a marine basin evolving from a moderate to a high degree of restriction depositing first a basai anhydrite horizon and then a thick sequence of massive halite an additional inflow of cacl2 in the basin during seawater evaporation is proposed as the process responsible for the sulfate depletion required for sylvite instead of mg sulfates to form mixing of seawater with continental waters bacterial sulfate reduction and in situ dolomitization are discarded the basin subsequently closed to the sea and evolved with decreasing volume alternating bands of clays halite sylvite and then clays halite carnallite were deposited under the influence of seasonal continental recharge before reaching total desiccation the residual brine was diluted by continental water the basin then evolved under an endoreic regime where continental recharge and the recycling of previously formed halite led to deposition of alternating beds of clays and halite

surface crusts on soils sediments of the southern aral sea basin uzbekistan soils and sediments of the southern aral sea basin of central asia are commonly covered by salt bearing surface crusts these crusts represent a potential source of salt rich dust that can contribute to salinisation of soils in a large area crust types include takyric crusts surface crusts on solonchaks and salt crusts covering dry parts of the lake bed the takyric crusts are structural crusts showing features related to flooding and shrinkage gypsum formed within the sediment matrix is the only evaporite mineral they contain one studied solonchak crust is fine grained with a thin thenardite and bloedite coating along the irregular surface and halite coatings along the sides of pores all salts in this crust formed by evaporation of solutions contained in the groundmass a solonchak crust with a sandy texture contains prismatic gypsum crystals that formed in a water saturated surface layer as well as bloedite eugsterite and halite formed by evaporation of interstitial brines the lake bed crust is a pure accumulation of salt minerals bloedite hexahydrite halite kainite with synsedimentary and diagenetic features salt mineral assemblages in the three crust types are those that form during successive stages of evaporation of aral sea waters in agreement with published theoretical predictions

metamorphic alteration of a precambrian 2 2 ga paleosol from south africa revealed by backscattered electron imaging abstract like many precambrian paleosols the 2200 ma old waterval onder clay has been metamorphosed to the greenschist facies of regional metamorphism the extent of metamorphic alteration of the fine grained uppermost horizons of the paleosol is assessed here using optical and backscattered electron microscopy in hand specimens and under low power optical examination the paleosol shows surficial lamination cumulic horizon of soil terminology rounded clasts coated with opaque sesquioxides manganoferriargillans cracks defining a fitted breccia of blocks that were evidently soft in places blocky angular peds cracks filled with multiple generations of material from above illuviation argillans and zones of unusually highly birefringent clay climobimasepic plasmic fabric with backscattered electron microscopy however at a resolution of less than about 10 m the fine structure of originally colloidal parts of the paleosol mangans argillans matrix and plasma separations is shown to be extensively recrystallized to illite and berthierine original soil structure has been obscured at this resolution by crystal growth at random across original microscopic discontinuities preferred orientation of metamorphic crystals can still be seen along what are presumed to be highly birefringent zones of oriented clay similar to those in modern soils but the matrix itself shows random clusters of crystals suggestive of an advanced stage of illitization by ostwald ripening the style of recrystallization of laminae in the surface horizon is similar to that seen lower in the profile where recrystallized beds are thicker and coarser grained thus the paleosol probably formed on an upward thinning and fining sequence of sandstone and shale rather than on basalt on this assumption the profile has gained iron compared with its shaly parent material rather than lost iron compared with basalt this may be an indication of greater oxygenation of the atmosphere than previously thought possible microbial traces can be seen in thin section but because of pervasive recrystallization these remain dubiofossils

isotopic evidence for iron mobilization during paleoproterozoic lateritization of the hekpoort paleosol profile from gaborone botswana abstract the isotopic composition and elemental abundance of fe in a lateritic weathering profile drillcore strata 1 formed on the 2 2 ga hekpoort basalt of the pretoria group in gaborone botswana document open system behavior for fe during paleosol formation the 56 fe values of the profile increase from 0 at the bottom parental basalt to 1 in the mid depth mottled fe depleted zone then decrease to 0 3 at the top of the laterite fe enriched zone the reworked ferricrete and red beds that overlie the laterite have high 56 fe values of 0 2 to 0 4 which are comparable to those of the underlying laterite because of the absence of a complementary low 56 fe zone these results are not compatible with a model of simple internal redistribution closed system of fe within the paleosol column instead these results are well explained through fluid rock interaction involving transport of aqueous fe 2 through the system during paleosol evolution production of positive 56 fe values for fe 3 oxides were simulated through oxidation of low 56 fe fe 2 aq using experimentally determined fe 3 oxide fe 2 aq fractionation factors the increased quantities of fe 2 involved in formation of the hekpoort paleosol relative to previous estimates based on a closed system model require a commensurate increase in the abundance of an oxidant such as atmospheric o 2 to explain the fe 3 fe 2 ratios in the paleosol therefore previous estimates of atmospheric o 2 levels of 2 5 10 4 to 9 10 3 atm based on this section w yang h d holland the hekpoort paleosol profile in strata 1 at gaborone botswana soil formation during the great oxidation event american journal of science 303 2003 187 220 are too low by an order of magnitude or more these results demonstrate that fe isotopes can provide important constraints on open versus closed system behavior of fe in ancient weathering profiles a distinction that is critical when calculating fe mobility as a means for inferring surface redox conditions in the past

stable isotopic compositions of carbonates from the mesoproterozoic bangemall group northwestern australia marine carbonate rocks from the mesoproterozoic bangemall group of northwestern australia show little deviation 1 3 in whole rock delta 13c carb values about a mean of 0 5 this narrow range persists despite close sampling every 10 20 m through long sections up to 2500 m that are geographically widespread up to 250 km apart over many depositional environments supralittoral to outer shelf sediment sources stromatolitic bioherms to detrital calcilutites and rock types pure limestones to dolomitic shales the only major excursions from the norm seem related to unusual environmental or post depositional processes as they are correlated with large enrichments to 3 or depletions to 16 in 18o relatively heavy delta 13c values up to 2 5 occur in a single bed of brecciated ferruginous dolostone at a single locality these abnormal values may result from local evaporitic conditions limey and shaley nodular dolostones have delta 13c values as low as 4 3 probably caused by remineralization of organic matter during late and patchy dolomitization most notably sharp negative excursions in delta 13c up to 8 4 occur in bleached kerogen free rocks with mineral assemblages of dolomite quartz calcite tremolite talc reflecting isotopic re equilibration in thick metamorphic aureoles around dolerite intrusions general environmental variations are minor with delta 13c values of peritidal facies tending to be slightly positive whereas those of subtidal facies are slightly negative there are no strong secular trends but subtle fluctuations within the range 2 to l can be correlated along the northwestern margin of the basin this resembles the pattern seen in other mesoproterozoic successions but is markedly unlike the heavy background 5 and extreme variations up to l0 in delta 13c evident in neoproterozoic successions of similar thickness and environmental setting hence in contrast to the neoproterozoic the global rate of organic carbon burial was probably fairly constant during deposition of the bangemall group and perhaps generally during the mesoproterozoic as was the redox state of the atmosphere and hydrosphere

ree chemistry and sm nd systematics of late archean weathering profiles in the fortescue group western australia two weathering profiles each consisting of an upper sericite rich zone and a lower chlorite rich zone are preserved between flows of the mt roe basalt in the fortescue group hamersley basin western australia ree concentrations in samples from these two profiles which originally developed ca 2 760 ma show large variations depending on stratigraphic position lree abundances and la yb n are greatest at depths of 3 6 m below the paleosurface of the mt roe 1 profile and are somewhat lower in samples above this level the lrees reach concentrations 6 9 times greater than in the underlying basalt and thus appear to have been mobilized downward in the paleosol and concentrated in its middle part lree concentrations in the 2 profile show a similar distribution but with a sharp increase in all ree concentrations within 50 cm of the paleosurface the distinction between the ree profiles in the two paleosols may be related to the difference in the overlying material the 1 paleosol is overlain by a few meters of sediments and then by basalt whereas the 2 paleosol is directly overlain by basalt the lrees appear to have been mobilized both during chemical weathering of the parental basalt and during later lower greenschist facies metamorphism and metasomatism of the paleosols remobilization of the rees during the regional metamorphism of the fortescue group is confirmed by a whole rock sm nd reference isochron of mt roe 1 samples with an age of 2 151 360 ma variable initial 143nd 144nd values of unweathered basalt samples which may represent the paleosol protolith prevents a confident determination of the magnitude of lree mobility both the initial mobilization of the rees during weathering and the metasomatic remobilization appear to have taken place under redox conditions where ce was present dominantly as ce3 because ce anomalies are not developed within the sericite zone samples regardless of concentration europium anomalies in the paleoweathering profile are somewhat variable and were probably modified by mobilization of eu2 at metamorphic conditions in all samples the hrees appear to have been relatively immobile and correlate with al ti cr v zr and nb sm nd systematics and ree patterns of four unweathered basalt samples indicate derivation of the mt roe basalts from a heterogeneous and enriched source having epsilon nd between 4 0 and 7 4 initial 143nd 144nd values of these basalts are even lower than those reported by nelson et al 1992 for fortescue group basalts and indicate a substantial crustal component in the generation of mt roe basalts

reconstructed ancestral enzymes suggest long term cooling of earth s photic zone since the archean paleotemperatures inferred from the isotopic compositions 18o and 30si of marine cherts suggest that earth s oceans cooled from 70 15 c in the archean to the present 15 c this interpretation however has been subject to question due to uncertainties regarding oceanic isotopic compositions diagenetic or metamorphic resetting of the isotopic record and depositional environments analyses of the thermostability of reconstructed ancestral enzymes provide an independent method by which to assess the temperature history inferred from the isotopic evidence although previous studies have demonstrated extreme thermostability in reconstructed archaeal and bacterial proteins compatible with a hot early earth taxa investigated may have inhabited local thermal environments that differed significantly from average surface conditions we here present thermostability measurements of reconstructed ancestral enzymatically active nucleoside diphosphate kinases ndks derived from light requiring prokaryotic and eukaryotic phototrophs having widely separated fossil based divergence ages the ancestral environmental temperatures thereby determined for these photic zone organisms shown in modern taxa to correlate strongly with ndk thermostability are inferred to reflect ancient surface environment paleotemperatures our results suggest that earth s surface temperature decreased over geological time from 65 80 c in the archean a finding consistent both with previous isotope based and protein reconstruction based interpretations interdisciplinary studies such as those reported here integrating genomic geologic and paleontologic data hold promise for providing new insight into the coevolution of life and environment over earth history

sulfate minerals in evaporite deposits evaporite deposits preserve a wealth of information on earth s past surface conditions the deposits are sensitive indicators of depositional environment and climate recorded in a wide variety of mechanically and chemically produced sedimentary structures and fabrics unique to evaporite deposits is the record they carry of the hydrochemistry of surface waters including seawater sulfate minerals are important components in understanding the hydrochemistry of ancient surface waters sedimentological aspects of evaporite deposits were compiled by melvin 1991 in the compilation sedimentology specific to ca bearing sulfates was described by warren 1991 lowenstein and hardie 1985 handford 1991 and smoot and lowenstein 1991 discussed the sedimentology of evaporites in general these general principles can be applied specifically to the sulfate minerals in evaporite deposits sedimentological aspects of sulfate minerals in evaporite deposits are not discussed here for this information the reader is referred to the above references hardie et al 1985 and spencer and lowenstein 1988 discussed the petrography of evaporites and the interpretation of fabrics of evaporite minerals examples of petrographic aspects of sulfate minerals in evaporites are presented here along with references specific to the sulfate minerals for a more complete understanding of these aspects the reader is referred to the above references the major focus of this chapter is on the chemical aspects of the common sulfate minerals that occur in evaporite deposits the discussion begins with an explanation of the concept of chemical divides and the determination of evaporation paths and the evolution of brines in accordance with mineral solubility and the composition of dilute inflow waters determination of the precipitation pathways of the more soluble salts is more complex examples of sulfate mineral assemblages in evaporation systems calculated via thermochemical modelling are given for both marine and non marine systems the mineralogy of evaporite deposits is

geochemical and mineralogic effects of contact metamorphism on banded iron formation an example from the transvaal basin south africa intrusion of a diabase sill into the paleoproterozoic kuruman iron formation transvaal basin south africa makes it possible to distinguish between effects of contact and regional metamorphism on mineralogic elemental and isotopic compositions of banded iron formation bif lithofacies temperatures within the aureole of contact metamorphism likely did not significantly exceed 450 c as suggested by the presence of early diagenetic carbonates greenalite and stilpnomelane formed prior to intrusion in chert rich facies as close as 4 m from the sill in sediments 32 m away from the intrusion a temperature of 280 c is indicated by the magnitude of 18o fractionation between successive chert and siderite microbands in unmetamorphosed equivalents similar isotopic analyses on whole rock samples yield temperature estimates between 150 and 230 c in comparison with samples of similar lithofacies from the underlying campbellrand kuruman transition zone carbonates from within the metamorphic aureole are depleted in 13c and 18o the abundance and c isotopic composition of total organic c toc in whole rock samples is lower and more enriched in 13c than those in samples outside of the zone of contact metamorphism within 5 m of the diabase sill the abundance of fe increases dramatically and the oxidation state of the sediments fluctuates considerably more than in sediments outside of the metamorphic aureole isotopic and mineralogic systematics in the zone of contact metamorphism in the kuruman iron formation are similar to those in siliceous dolomites and limestones altered by similar thermal processes as the most distinct isotopic and elemental variations occur within 10 m of the diabase sill it is suggested that volatilization and fluid infiltration associated with the intrusion were the main processes of alteration consideration of the effects of metamorphism both contact and regional as well as early diagenesis on the mineralogy and isotopic chemistry of bif sediments may be a key to our understanding of primary mineralogies and oxidation state of these enigmatic deposits

the use of environmental markers to distinguish marine vs continental deposition and to quantify the significance of recycling in evaporite basins abstract environmental markers namely the bromine content of halite samples the electrolyte content of primary fluid inclusions in halite and the isotopic composition of sulphates from two tertiary evaporite sequences provide complementary information on the depositional environment marine vs continental the use of these markers together with lithofacies and thicknesses of precipitated evaporites enable the detection and quantification of evaporite recycling within evaporite basins the information provided by the isolated use of each of these geochemical markers should be used with caution as this could lead to erroneous interpretations of the depositional environment or may not detect significant evaporite recycling processes the complementary information provided by geochemical markers enable quantification of solute input from recycling of previous precipitates within the basins themselves or from older evaporites the input of recycled evaporites increases progressively together with evaporite basin restriction to the open ocean

the antiquity of oxygenic photosynthesis evidence from stromatolites in sulphate deficient archaean lakes the tumbiana formation about 2700 million years old was largely deposited in ephemeral saline lakes as judged by the unusual evaporite paragenesis of carbonate and halite with no sulfate stromatolites of diverse morphology occur in the lacustrine sediments some with palimpsest fabrics after erect filaments these stromatolites were probably accreted by phototropic microbes that from their habitat in shallow isolated basins with negligible sulfate concentrations almost certainly metabolized by ozygenic photosynthesis

pore structure characterization in rock salt abstract the pore space of rock salt from the lower salt unit of the cardona saline fm spain was characterized using three independent methods mercury injection porosimetry saturation in a low viscosity isoparaflin and gas adsorption the total porosity in the studied samples ranged from 0 97 to 3 09 pores may be present as macropores 7 5 m micropores between 7 5 m and 100 nm and infrapores

pge re os and mo isotope systematics in archean and early proterozoic sedimentary systems as proxies for redox conditions of the early earth abstract re os data and pge concentrations as well as mo concentrations and isotope data are reported for suites of fine clastic sediments and black shales from the barberton greenstone belt south africa fig tree and moodies groups 3 25 3 15 ga the belingwe greenstone belt zimbabwe manjeri formation ca 2 7 ga and shales from the witwatersrand ventersdorp and transvaal supergroups south africa ranging from 2 95 to 2 2 ga moderately oxidizing conditions are required to mobilize re and mo in the environment mo fractionation only occurs in solution and these parameters thus have potential use as paleoredox proxies for the early earth pge re abundance patterns of barberton greenstone belt sediments are uniform and very similar in shape to those of komatiites this indicates 1 that the pge came from a source of predominantly ultramafic composition and 2 that pge were transported and deposited essentially in particulate form sediments from the younger belingwe greenstone belt show more fractionated pge re patterns and have re os ratios 10 to 100 higher than those of barberton sediments their pge abundance patterns and re os ratios are intermediate between those of the mid archean shales and neoproterozoic to recent black shales they reflect scavenging of re from solution in the sedimentary environment 98 95 mo values of black shales of all ages correlate with their concentrations the barberton greenstone belt samples have 1 3 ppm mo similar to a granitoid basaltic source this mo has 98 95 mo between 1 9 and 2 4 relative to present day mean ocean water molybdenum momo and is thus not isotopically fractionated relative to such a source similar to the pge this indicates transport in solid form sediments from the belingwe greenstone belt show in part enhanced mo concentrations up to 6 ppm and mo isotope fractionation 98 95 mo up to 1 4 relative to momo the combined pge re and mo data show mainly reducing conditions in the mid archean and suggest that by 2 7 ga the atmosphere and oceans had become more oxidizing substantially younger samples from the transvaal supergroup to ca 2 2 ga surprisingly have mainly low mo concentrations around 1 ppm and show no significant mo isotope fractionation relative to the continental source among possible explanations for this are a return to reducing atmospheric conditions after 2 7 ga reservoir effects or mo removal by sulfide precipitation following sulfate reduction in early proterozoic oceans

the geochemical evolution of the catalan potash subbasin south pyrenean foreland basin spain over the last decade our studies in ancient evaporitic basins have been based on a detailed study of a single borehole record the detailed findings in medium to large sized evaporitic basins were shadowed with a relevant question can interpretations from a representative evaporitic record in a single borehole be extended to the whole evaporitic basin this paper addresses that question the results obtained are compared with results from another distant point within the basin the general methodology not only proves its reliability in interpreting the evolution of evaporitic basins from a single borehole but reveals its capability to obtain detailed palaeoenvironmental interpretations the chemical evolution of an upper eocene evaporitic sequence from the south pyrenean foreland basin spain has been investigated along the suria 19 borehole record detailed petrographic and mineralogical study x ray microanalysis of frozen primary inclusions trapped in halite cryo sem eds systematic isotopic analysis d 34 s and d 18 o in sulphates and computer based evaporation models have been integrated in a multi proxy methodology this study revealed that a variable amount of ca excess is required throughout different parts of the marine lower halite unit lhu for sylvite instead of k mg sulphates to form this ca excess is in turn different from that required for the western sector of the same evaporitic basin navarrese subbasin quick and variable changes in ca rich brines or equivalent dolomitization required are explained as internal processes within the basin rather than secular variations in seawater chemistry the general hydrological evolution of the catalan subbasin is explained as a restricted subbasin with a first marine stage in which continental input up to 50 of total input had an important control on the geochemistry of the subbasin a second stage was determined during potash precipitation in which the subbasin was cut from any seawater input to end up in its last stage as a purely continental evaporitic basin coupling evaporation models and analytical results we have obtained the proportions of recycling and their sources estimated to change from a 100 total mass of sulphate eocene source to 20 eocene and 80 triassic keuper towards the latest stage of potash precipitation the results obtained have been compared with results from the navarrese subbasin allowing an integrated interpretation of the hydrological evolution of the whole upper eocene south

tracking physicochemical conditions of evaporite deposition by stable magnesium isotopes a case study of late permian langbeinites magnesium isotopic compositions of evaporite deposits may record information concerning brine evolution during deposition we report mg isotopic values delta mg 26 dsm3 measured from an evaporite deposit of langbeinite k2mg2 so4 3 found in the permian salado formation we used these data to model mg isotope fractionation between langbeinite and its parent brine in addition both measured and theoretical results are used to estimate precipitation temperature and interpret depositional environment the salado langbeinite delta mg 26 values are relatively low and fall within a relatively narrow range 4 12 0 03 parts per thousand to 3 81 0 07 parts per thousand equilibrium fractionation factors between langbeinite and aqueous mg2 solutions were calculated using quantum chemical density functional theory all computations were performed at the b3lyp 6 31 g d p level solvation effects were addressed using a solvent model water droplet approach and mineral structures were investigated using volume variable cluster models vvcm the equilibrium mg isotopic fractionation factors a between langbeinite and model brine solution we obtained are 1 0005 1 0004 and 1 0003 delta mg 26 langb water approximate to 10 3 ln alpha 0 473 parts per thousand 0 390 parts per thousand and 0 322 parts per thousand at 10 degrees c 25 degrees c and 40 degrees c respectively these relatively large equilibrium fractionation factors indicate significant mg isotope fractionation between langbeinite and its parent brine during precipitation as langbeinite preferentially incorporates the heavier mg 26 and mg 25 isotopes rayleigh distillation modeling of the salado langbeinite s relatively light mg isotopic composition requires delta mg 26 dsm3 values of 4 parts per thousand for the parent brine models favor a precipitation temperature as high as 40 degrees c under equilibrium conditions potential disequilibrium precipitation conditions suggested by mg isotopic data also imply rapid deposition in a hot arid sedimentary environment prevailing in the southwestern u s during the late permian

temperature seasonality control on modern halite layers in the dead sea in situ observations layered halite sequences are found in deep basins throughout the geological record however analogs for such sequences are commonly studied in shallow environments here we studied active precipitation of halite layers from the only modern analog for deep halite precipitating basins the hypersaline dead sea in situ observations in the dead sea link seasonal thermohaline stratification halite saturation and the characteristics of the actively forming halite layers the spatiotemporal evolution of halite precipitation in the dead sea was characterized by means of monthly observations of 1 lake thermohaline stratification temperature salinity and density 2 degree of halite saturation and 3 textural evolution of the active halite deposits we present the observed relationships between the textural characteristics of layered halite deposits i e grain size consolidation and roughness and the degree of saturation which in turn reflects the limnology and hydroclimatology the lake floor is divided into two principal environments a deep hypolimnetic lake floor and a shallow epilimnetic lake floor in the deeper hypolimnetic lake floor halite continuously precipitates with seasonal variations 1 during summer consolidated coarse halite crystals form rough surfaces under slight supersaturation 2 during winter unconsolidated fine halite crystals form smooth lake floor deposits under high supersaturation these observations support interpretations of the seasonal alternation of halite crystallization mechanisms the shallow epilimnetic lake floor is highly influenced by the seasonal temperature variations and by intensive summer dissolution of part of the previous year s halite deposit which results in thin sequences with annual unconformities this emphasizes the control of temperature seasonality on the characteristics of the precipitated halite layers in addition precipitation of halite on the hypolimnetic floor at the expense of the dissolution of the epilimnetic floor results in lateral focusing and thickening of halite deposits in the deeper part of the basin and thinning of the deposits in shallow marginal basins

fluid inclusions in sedimentary and diagenetic systems abstract some of the major problems in sedimentary geology can be solved by using fluid inclusions in sedimentary and diagenetic minerals important fluids in the sedimentary realm include atmospheric gases fresh water of meteoric origin lake water seawater mixed water evaporated water formation waters deep in basins oil and natural gas preserving a record of the distribution and composition of these fluids from the past should contribute significantly to studies of paleoclimate and global change research is essential for improving understanding of diagenetic systems and provides useful information in petroleum geology applications of fluid inclusions to sedimentary systems are not without their complexities some fluid inclusions exposed to natural conditions of increasing temperature may be altered by thermal reequilibration which results in stretching or leakage and refilling of some fluid inclusions similarly overheating in the laboratory can also cause reequilibration of fluid inclusions so fluid inclusions from the sedimentary realm must be handled carefully and protected from overheating natural overheating of fluid inclusions must be evaluated through analysis of the most finely discriminated events of fluid inclusion entrapment fluid inclusion assemblages fia consistency in homogenization temperatures within a fluid inclusion assemblage consisting of variably sized and shaped inclusions is the hallmark of a data set that has not been altered through thermal reequilibration in contrast fluid inclusion assemblages yielding variable data may have been altered through thermal reequilibration if a fluid inclusion assemblage has not been altered by thermal reequilibration its fluid inclusions may be useful as geothermometers for low and high temperature systems or useful as geobarometers applicable throughout the sedimentary realm if a fluid inclusion assemblage has been altered partially by thermal reequilibration techniques for distinguishing between altered and unaltered fluid inclusions may be applied in studies of global change fluid inclusions can be used as sensitive indicators of paleotemperature of surface environments fluid inclusions also preserve microsamples of ancient seawater and atmosphere the analysis of which could figure prominently into discussions of past changes in chemistry of the atmosphere and oceans in petroleum geology fluid inclusions have proven to be useful indicators of migration pathways of hydrocarbons they can delineate the evolution of the chemistry of hydrocarbons and they remain important in understanding the thermal history of basins and relating fluid migration events to evolution of reservoir systems in studies of diagenesis fluid inclusions can be the most definitive record most diagenetic systems are closely linked to temperature and salinity of the fluid thus fluid inclusions are sensitive indicators of diagenetic environments

origin and diagenetic evolution of gypsum and microbialitic carbonates in the late sag of the namibe basin sw angola abstract ephemeral evaporitic conditions developed within the uppermost part of the transgressive late sag sequence in the namibe basin sw angola leading to the formation of extensive centimetre to metre thick sulphate bearing deposits and correlative microbialitic carbonates rich in pseudomorphs after evaporite crystals the onshore pre salt beds examined in this study are located up to 25 m underneath the major mid aptian evaporitic succession which is typified at the outcrop by gypsiferous bambata formation and in the subsurface by the halite dominated loeme formation carbonate evaporite cycles mostly occur at the top of metre thick regressive parasequences which progressively onlap and overstep landward the former faulted rift topography or fill major pre salt palaeo valleys the sulphate beds are made up of alabastrine gypsum associated with embedded botryoidal nodules dissolution related gypsum breccia and are cross cut by thin satin spar gypsum veins nodular and fine grained fabrics are interpreted as being diagenetic gypsum deposits resulting from the dissolution and recrystallisation of former depositional subaqueous sulphates whereas gypsum veins and breccia result from telogenetic processes the carbonates display a broader diversity of facies characterised by rapid lateral variations along strike thin dolomitic and calcitic bacterial mediated filamentous microbialitic boundstones enclose a broad variety of evaporite pseudomorphs and can pass laterally over a few metres into sulphate beds dissolution related depositional breccias are also common and indicate early dissolution of former evaporite layers embedded within the microbialites sulphate and carbonate units are interpreted as being concomitantly deposited along a tide dominated coastal supra to intertidal sabkha and constitute high frequency hypersaline precursor events prior to the accumulation of the giant saline mid aptian bambata and loeme formations petrographic and geochemical analyses reveal successive dissolution recrystallisation and cementation phases that occurred during burial uplift and exhumation implying a complex diagenetic evolution of both gypsum and carbonates influenced by pore fluids of diverse composition which distinctly varied from meso to telogenetic domains

service life of a high density polyethylene geomembrane under simulated landfill conditions at 85 c abstractthe time to rupture of a 1 5 mm thick high density polyethylene geomembrane aged in a typical landfill composite liner configuration is investigated under a pressure of 250 kpa at 85 c the geomembrane was underlain with a geosynthetic clay liner and had a 560 g m2 needle pinched nonwoven geotextile protection layer separating it from 50 mm of drainage gravel containing leachate seventeen 0 6 m diameter tests were conducted in addition to 9 months required to deplete antioxidants stage i the tests indicated a lag period stage ii of 5 5 months and a time from the start of degradation to rupture stage iii of 20 months giving a total inferred time to rupture of 34 5 months 2 9 years there were up to 61 brittle ruptures per sample i e 2 million cracks per hectare the ruptures were predominately oriented in the machine direction and located 1 directly beneath a gravel contact 2 at the side of a gravel indentation or 3 between gravel indentations the ruptures between gravel

geology and major and trace element chemistry of late archean weathering profiles in the fortescue group western australia implications for atmospheric po2 abstract we have identified two thick weathering profiles between flows of the mt roe basalt unit of the fortescue group in the pilbara area of western australia the age of weathering is constrained by u pb zircon dating to lie between 2765 and 2715 ma the profiles herein referred to as the mt roe 1 and 2 paleosols were mapped in detail for 1500 m and 760 m along strike respectively samples were collected along traverses across both profiles where they were well developed and well exposed the profiles which may be structurally offset parts of the same weathering horizon have well developed upper sericite zones 1 15 m thick these grade downward into chlorite rich zones which are chemically and physically heterogeneous the chlorite zones grade downward into unweathered basalts the mt roe 1 profile is overlain by 2 6 m of bedded probably lacustrine sediments these in turn are covered by succeeding lava flows evidence of a surficial origin for the paleosols includes mud cracks ripple marks and rip ups of the paleosol material in the post paleosol sediments soft sediment deformation and probable dewatering structures are present along the paleosol sediment contact the mt roe 2 profile is overlain directly by the succeeding lava flow with little or no intervening sediments some brecciation and pillowing is observed along the base of the overlying basalt flow in both cases probably due to emplacement of lava into a shallow lake or onto wet soil in the sericite zones of both profiles nearly all of the fe mn mg and zn and a substantial fraction of the ca pb na ni and si have been leached the chlorite zones have elevated fe pb ni and zn contents and appear to be repositories of elements lost from the sericite zone al ti zr and th were immobile in the mt roe 1 paleosol and are concentrated by factors of 2 5 2 6 over the unweathered basalt v u and cr were also nearly immobile major element and trace element data indicate that weathering took place under conditions of low atmospheric oxygen k is strongly enriched toward the upper contact of the sericite zone and was introduced during post weathering metasomatism together with rb and sr na and ca are also enriched near the top of each profile and small amounts of each may have been introduced during regional low grade metamorphism of the hamersley basin at 2168 10 ma

a master of the earth h d holland and his contributions to geochemistry abstract h d holland was one of the great geochemists of modern times as a professor at princeton university for 22 years and at harvard for 33 he mentored 24 graduate students and 24 postdoctoral researchers he was a member of the u s national academy of sciences and a president of the geochemical society he co authored 179 publications in 64 years from 1949 to 2012 including four books he edited one other book and with karl turekian co edited the ten volume treatise on geochemistry his contributions to geochemistry were mainly in economic geology hydrothermal processes and especially the chemistry and evolution of the earth s atmosphere and oceans a topic to which he devoted nearly half of his publications his most significant contributions documented changes in the composition of seawater through geologic time and the rise of oxygen in earth s atmosphere he pioneered the use of mineral sequences in marine evaporite deposits and fluid inclusions in evaporite minerals to determine the composition of ancient seawater he collected extensive data on paleosols and used them to calibrate the oxygen content of the ancient atmosphere documenting its rise in the great oxidation event that peaked between 2 41 and 2 32 ga and writing extensively about the causes of this event one of the most significant in earth history

core concepts of paleopedology abstract the current renaissance of scientific interest in paleosols has brought a variety of views and approaches to paleopedology two main approaches have emerged for the description and labelling of paleosols geosols are ancient land surfaces consisting of laterally connected suites of paleosols used for stratigraphic subdivision of sedimentary deposits pedotypes are individual kinds of paleosols named after localities like geosols pedotypes are used for mapping and describing individual profiles usually for the purpose of paleoenvironmental interpretation both pedotypes and geosols are field based labels for which genetic or interpretive considerations are at a minimum they can be interpreted using at least three distinct approaches taxonomic uniformitarianism is based on the assumption that a paleosol is formed in a similar environment to a surface soil of the same type the factor function approach interprets specific aspects of paleoenvironments from measured features of paleosols by comparison with paleoenvironmentally related variation of that feature in surface soils finally the process model approach seeks to recreate soil forming processes mathematically with input from measurable features of paleosols each approach has limitations such as the need for proxy features to classify paleosols in systems designed for surface soils the attainment of similar appearance of a paleosol by different pathways and the mathematical uncertainty of model assumptions the approaches of classification experimentation and modelling are not unique to paleopedology being widespread among other sciences fundamental to paleopedology however are the concepts of profiles and soilscapes of the past

structure of the lower atmosphere over the northern california coast during winter abstract the structure of the lower atmosphere over the northern california coastal ocean upwelling area was studied during the shelf mixed layer experiment in the winter of 1989 surface data were collected at seven automated coastal stations and six buoys boundary layer soundings were made using balloons at the coast and a research aircraft over the ocean the aircraft was also used to map the low level 30 m mean and flux fields over the 80 km 120 km shelf area the wintertime coastal weather conditions were more variable than in summer and were observed to fit into three categories strong northerly downcoast winds strong southerly upcoast winds and weak winds the variability was caused by the passage of wintertime cyclones interspersed with periods of small pressure gradients the strong wind cases had small diurnal variations whereas the diurnal variations were large for the weak wind case the vertical structure of the coastal boundary layer was more uniform compared to that in summer

halite cementation and carbonate diagenesis of intra salt reservoirs from the late neoproterozoic to early cambrian ara group south oman salt basin late neoproterozoic to early cambrian carbonates of the ara group form important intra salt stringer reservoirs in the south oman salt basin differential loading of thick continental clastics above the six carbonate to evaporite cycles of the ara group led to the formation of salt diapirs encasing a predominantly self charging hydrocarbon system within partly highly overpressured carbonate bodies stringers these carbonates underwent a complex diagenetic evolution with one stage of halite cementation in a shallow early and another in a deep late burial environment early and late halite cements are defined by their microstructural relationship with solid bitumen the early phase of halite cementation is post dated by solid reservoir bitumen this phase is most pervasive towards the top of carbonate stringers where it plugs nearly all available porosity in facies with initially favourable poroperm characteristics bromine geochemistry revealed significantly higher bromine contents up to 280 p p m in the early halite compared with the late halite 173 p p m the distribution patterns and the high bromine contents of early halite are consistent with precipitation caused by seepage reflux of highly saturated brines during deposition of the overlying rock salt interval later in burial history relatively small quantities of early halite were dissolved locally and re precipitated as indicated by inclusions of streaky solid bitumen within the late halite cements late halite cement also seals fractures which show evidence for repeated reopening initially these fractures formed during a period of hydrothermal activity and were later reopened by a crack seal mechanism caused by high fluid overpressures porosity plugging by early halite cements affects the poroperm characteristics of the ara carbonates much more than the volumetrically less important late halite cement the formation mechanisms and distribution patterns of halite cementation processes in the south oman salt basin can be generalized to other petroliferous evaporite basins

soil slip debris flow localized by site attributes and wind driven rain in the san francisco bay region storm of january 1982 abstract gis analysis at 30 m resolution reveals that effectiveness of slope destabilizing processes in the san francisco bay area varies with compass direction nearly half the soil slip debris flows mapped after the catastrophic rainstorm of 3 5 january 1982 occurred on slopes that face s to wsw whereas fewer than one quarter have a northerly aspect azimuthal analysis of hillside properties for susceptible terrain near the city of oakland suggests that the skewed aspect of these landslides primarily reflects vegetation type ridge and valley alignment and storm wind direction bedrock geology soil expansivity and terrain height and gradient also were influential but less so the role of surface curvature is not wholly resolved normalising soil slip aspect by that of the region s nnw striking topography shifts the modal azimuth of soil slip aspect from sw to se the direction of origin of winds during the 1982 storm but opposite that of the prevailing wnw winds wind from a constant direction increases rainfall on windward slopes while diminishing it on leeward slopes generating a modelled difference in hydrologically effective rainfall of up to 2 1 on steep hillsides in the oakland area this contrast is consistent with numerical simulations of wind driven rain and with rainfall thresholds for debris flow activity we conclude that storm winds from the se in january 1982 raised the vulnerability of the bay region s many s facing hillsides most of which are covered in shallow rooted shrub and grass that offer minimal resistance to soil slip wind driven rainfall also appears to have controlled debris flow location in a major 1998 storm and probably others incorporating this overlooked influence into gis models of debris flow likelihood would improve predictions of the hazard in central california and elsewhere

high resolution real time modeling of the marine atmospheric boundary layer in support of the aosn ii field campaign abstract the navy s coamps atmospheric model has been used to provide twice daily real time forecasts of 72 h duration in support of the aosn ii field campaign during august 2003 the model was configured with four grid meshes with a minimum horizontal grid increment of 3 km a statistical analysis of the model forecasts using available buoy observations demonstrates the skill of the atmospheric model predictions with characteristic wind speed rms and bias errors of 1 3 m s 1 and less than 0 5 1 0 m s 1 respectively and temperature rms errors of 1 2 c and biases typically less than 1 0 c the highest resolution mesh provides more accurate wind speed variances during the upwelling periods in the nearshore region where the wind speed gradients and diurnal variations are the largest persistent and strong low level winds from a northwesterly direction were associated with a mid tropospheric trough and jet stream that was substantially stronger than the overall mean monthly conditions during the relaxation periods which were relatively infrequent during august 2003 the trough was weaker than the mean conditions with a closed low west of the coast that resulted in southerlies near the coast during upwelling favorable conditions the mean marine inversion was substantially stronger than during the relaxation periods with the surface stress field exhibiting maxima in the lee of prominent coastal capes and topography particularly during the periods of strong larger scale low level flow the persistent mean stress pattern that is topographically locked yields maxima in the stress curl pattern that induce favorable regions of coastal upwelling near and downwind of the coastal promontories and headlands

oxygen overshoot and recovery during the early paleoproterozoic abstract during the lomagundi event ca 2 22 to 2 06 ga marine carbonates recorded the largest and longest uninterrupted positive carbon isotope excursion the earliest extensive marine sulfate evaporites were deposited and the average ferric iron to total iron expressed as fe 2 o 3 fe fe2o3 ratio of shales increased dramatically at the end of the lomagundi event the first economic sedimentary phosphorites were deposited and the carbon isotope values of marine carbonates returned to 0 vpdb thereafter marine sulfate evaporites and phosphorites again became scarce while the average fe 2 o 3 fe fe2o3 ratio of shales decreased to values intermediate between those of the archean and lomagundi age shales we propose that the large isotopic and chemical excursions during the lomagundi event were caused by a positive feedback between the rise of atmospheric o 2 the weathering of sulfides in the pre 2 3 ga continental crust and the flux of phosphate to the oceans cf holland 2002 the rise in the terrestrial phosphate flux led to an increase in the burial rate of organic carbon and a major transfer of oxygen from the carbon to the sulfur cycle the end of the lomagundi event was probably caused by a decrease in the terrestrial phosphate flux related to the weathering of low pyrite sediments that were deposited during the lomagundi event the rate of deposition of organic matter and the precipitation of sulfate evaporites decreased the isotopic and chemical excesses of the lomagundi event were eliminated and the ocean atmosphere system entered the period frequently called the boring billion

burial evolution of evaporites with implications for sublacustrine fan reservoir quality a case study from the eocene es4x interval dongying depression bohai bay basin china abstract eocene sublacustrine fan sandstones that developed in a rift basin are important tight gas reservoirs in the dongying depression bohai bay basin northeastern china two units of evaporites developed at the top and bottom of the lower unit of the es4 interval es4x consist predominantly of anhydrite with subordinate gypsum evaporite and related diagenetic processes greatly influenced reservoir quality 13 c values for micritic dolomite cements in es4x are depleted 7 45 to 2 57 due to microbial sulfate reduction msr under shallow burial conditions and this interpretation is supported by large 34 s fractionation between anhydrite and framboidal pyrite precipitation temperatures for micritic dolomite are calculated as 57 5 72 8 c anhydritization of gypsum probably occurred at 100 5 145 2 c during progressive burial as evidenced by homogenization temperatures of aqueous inclusions within anhydrite cements this process resulted in dehydration fractures within anhydrite cements that increased reservoir permeability by connecting isolated pores thermochemical sulfate reduction tsr probably resulted in dissolution of gypsum and anhydrite cements under relatively deep burial conditions ankerite cements are replaced by anhydrite cements and are enclosed by solid bitumen in es4x ankerite cements likely were derived from tsr as reflected in negative 13 c values 7 12 to 3 70 and high calculated temperatures 121 3 185 1 c dissolution by products e g saddle dolomite ankerite nodular pyrite related to tsr precipitated in adjacent pores a lack of significant 34 s fractionation between parent sulfate and nodular pyrite indicates that tsr occurred in a relatively closed system therefore dissolution of gypsum and anhydrite related to tsr contributed little to reservoir quality middle fan lithofacies with better sorting porosity and permeability than inner and outer fan lithofacies constitute high quality reservoirs in es4x