reply to the comments of d l pinti r mineau and v clement and of a o marshall and c p marshall on biogenicity of earth s earliest fossils a resolution of the controversy by j william schopf and anatoliy b kudryavtsev gondwana research 22 2012 761 771 abstract the abundant and diverse assemblage of filamentous microbial fossils permineralized in the 3465 ma apex chert of northwestern australia among the oldest records of life are arguably the best studied by the most workers using the most advanced techniques in the history of science despite the extensive body of data establishing the biogenicity of the demonstrably cellular carbonaceous apex fossils pinti et al 2013 and marshall and marshall 2013 have raised issues regarding the interpretation of their studies of the apex chert presented in our recent review article schopf and kudryavtsev 2012 we agree with the assessment of both of the relevant papers by pinti et al 2009 2013 the observations they report do not apply to the bona fide microscopic fossils of the apex chert similarly like the minute objects reported by pinti et al 2009 2013 the quartz and haematite filled fractures discussed by marshall and marshall 2013 are mineralic pseudofossils that are not relevant to interpretation of the apex fossil microbes and their suggestion that multiple populations of carbonaceous material may be a wide spread issue through out the precambrian is without merit

the early permian branchiosaurids amphibia of sardinia italy systematic palaeontology palaeoecology biostratigraphy and palaeobiogeographic problems the branchiosaurid fauna from the is alinus lake of rio su luda formation lithofacies c in the perdasdefogu basin of sardinia italy includes three species melanerpeton eisfeldi apateon kontheri and apateon flagrifer the same three species are known from gottlob lake in the thuringian forest basin of germany and are interpreted as valid in the sense of the biospecies concept not closely related to each other and most probably reproductive in the same lake that is a very surprising and convincing conformity of both branchiosaurid faunas parallel evolution of three different amphibian species in two different areas seems impossible gene flow must have existed between the populations of the northern and southern parts of the variscan mountain chain additional findings of three dimensionally preserved but isolated amphibian bones such as jaw fragments with pleurodent dentition have been discovered in limestone of the rio su luda formation lithofacies d from the ortu mannu section they belong very probably to those branchiosaurids occurrences in both sardinia and thuringia require corresponding migration routes for the branchiosaurs possibly via basins in southern france the french massif central and southern germany possibly all branchiosaurids of these three species are neotenic and referable to the ecomorphological stream type with favourable migration capabilities as in modern urodelans such as newts and salamanders the perdasdefogu basin of sardinia is presently the southernmost known occurrence of branchiosaurid amphibians in europe and its palaeo position is of special interest sardinia was obviously part of a hydrographical system at the southern flank of the variscides no insurmountable migration barrier such as a marine sound or seaway existed between sardinia and palaeo europe because the same species of obligatorily non marine amphibians are known from these two areas the sardinian occurrence widens significantly the amphibian migration routes described before on the basis of these amphibians it is possible to correlate the rio su luda formation of sardinia with the goldlauter to lower oberhof formation of the thuringian forest reference section by combined use of melanerpeton eisfeldi and apateon flagrifer as index speciesofphylo morpho geneticlineages insynthesiswithisotopicages thistimespanisequivalenttotheasselian sakmariantransition of the global scale most likely the rio su luda formation correlates directly with the upper goldlauter formation late asselian 2007 elsevier b v all rights reserved

sediment transport during recent cave flooding events and characterization of speleothem archives of past flooding abstract extreme precipitation events have a disproportionate impact on landscape evolution and on human constructions and the frequency and intensity of extreme events may vary with changes in mean climate in the past and in the future we document the potential for cave sediment archives to record past changes in the frequency of flooding events by characterizing the modern processes responsible for sediment deposition and mobilization during floods and linking these to their incorporation in speleothem deposits we focus on the cueva fria cave system in nw spain which like other caves in the region features abundant sandy sediments sourced from dominant sandstone lithologies in the catchment area in this case delineated by our dye trace study in this system the extreme flood conditions in june 2010 caused overflow of the cave stream and deposition of nearly 1 m of sand in sectors near the cave stream and resulted in burial of some stalagmites in 30 cm of sand in more distal sectors all sectioned stalagmites growing

microfabric analysis of mn carbonate laminae deposition and mn sulfide formation in the gotland deep baltic sea the manganese carbonate deposits of the anoxic littorina sediments of the gotland deep have been commonly related to the periodic renewal of deep water by inflowing saline water from the north sea the use of scanning electron microscopy based techniques allows identification of small scale sedimentary and geochemical features associated with mn carbonate laminae which has significant implications for models of mn carbonate formation varves occurring in the littorina sequence contain up to four laminae that may be placed in a seasonal cycle and kutnahorite laminae occur within varves only as a winter early spring deposit this kutnahorite laminae seasonality is in agreement with the seasonal distribution of major baltic inflow events recorded in historical records and a direct causal link between inflows and kutnahorite deposition is implied benthic foraminifera tests are found to be heavily encrusted in kutnahorite implying that benthic recolonization during oxidation events occurs concurrently with kutnahorite formation the relatively common occurrence of small 50 to 100 m hexagonal mn sulfide pseudomorphs associated with 13 of kutnahorite laminae studied is reported in gotland deep sediments for the first time although mn sulfide crystals are not usually preserved in the sediment the discovery of mn sulfide pseudomorphs suggests that initial formation of mn sulfide in the gotland deep may occur much more commonly during the process of kutnahorite formation than previous reports of mn sulfide occurrence have implied

marine os isotopic fluctuations in the early eocene greenhouse interval as recorded by metalliferous umbers from a tertiary ophiolite in japan abstract the mineoka umbers occur within the tertiary accretionary complex of central japan immediately overlying 53 7 ma tholeiitic basalts the associated tholeiitic basalts exhibit typical normal mid ocean ridge basalt n morb type geochemical signatures and are interpreted to be a remnant of tertiary oceanic crust centimeter resolution bulk rock chemical analyses were performed to cover the entire section of the 35 cm thick umber deposit there are striking similarities in major element trace element re and os contents between the umbers and modern metalliferous sediments along the east pacific rise these results demonstrate that the mineoka umbers are ancient counterparts of mor metalliferous sediments that are plume fall out ferromanganese precipitates scavenging various seawater derived elements including p v y rees and os and confirm that the umbers subaerially exposed in the accretionary complex generally preserve their primary geochemical signatures at the time of deposition the marine 187 os 188 os ratios inferred from the mineoka umbers gradually increase up section with moderate fluctuations the 187 os 188 os composition ranging from 0 47 to 0 54 is significantly higher than that of the prior period post paleocene eocene thermal maximum petm 187 os 188 os 0 38 this was probably the result of an increase in the chemical weathering rate of continental crust caused by the long duration of noticeably warm climate during the early eocene greenhouse interval several fluctuations observed in the marine 187 os 188 os record during this interval are most likely related to petm like brief hyperthermals supporting the suggestion that the intensity of continental crustal weathering controlled by climatic changes can fluctuate on timescales of 10 5 yr

recognition genesis and evolution of manganese ore deposits in southeastern china abstract manganese ore deposits are common in the falang formation of ladinian age middle triassic southeastern yunan china the deposits containing manganese oxide and manganese carbonate ores are not metamorphic in origin and they commonly contain bioclasts concentric ring structures are clearly observed in oolitic and pisolitic manganese ores an integrated approach using sedimentology and paleoenvironment analysis provides new insight into the genesis of these ores systematic research has been conducted on typical deposits dounan yanzijiao laowu tujichong using cathodoluminescence and scanning electron microscope techniques which allow elucidation of changes in laminated microtextures at the mm m scale preliminary results show that manganese enrichment in triassic deposits of this region may be related to microbial activity and mineralization was a consequence of bacterially mediated diagenetic reactions in addition findings of biodetritus in the manganese ore indicate that manganese ore is close to the redox level the concentration of manganese in solution and in precipitates in triassic is controlled by bacterial oxidation and redox conditions corresponding to sea level changes during the ladinian

stromatolites the challenge of a term in space and time abstract several definitions of stromatolites are discussed and kalkowsky s most important statements about stromatolites are translated from german to english a new definition for stromatolites is proposed namely stromatolites are laminated rocks the origin of which can clearly be related to the activity of microbial communities which by their morphology physiology and arrangement in space and time interact with the physical and chemical environment to produce a laminated pattern which is retained in the final rock structure unconsolidated laminated systems clearly related to the activity of microbial communities and often called recent stromatolites or living stromatolites are defined as potential stromatolites the main microbial activities which are important in the formation of potential stromatolites and stromatolites are described and examples of stromatolites of various types including iron stromatolites are also described

six decades of glacier mass balance observations a review of the worldwide monitoring network glacier mass balance is the direct and undelayed response to atmospheric conditions and hence is among the essential variables required for climate system monitoring it has been recognized as the largest non steric contributor to the present rise in sea level six decades of annual mass balance data have been compiled and made easily available by the world glacier monitoring service and its predecessor organizations in total there have been 3480 annual mass balance measurements reported from 228 glaciers around the globe however the present dataset is strongly biased towards the northern hemisphere and europe and there are only 30 reference glaciers that have uninterrupted series going back to 1976 the available data from the six decades indicate a strong ice loss as early as the 1940s and 1950s followed by a moderate mass loss until the end of the 1970s and a subsequent acceleration that has lasted until now culminating in a mean overall ice loss of over 20 m w e for the period 1946 2006 in view of the discrepancy between the relevance of glacier mass balance data and the shortcomings of the available dataset it is strongly recommended to 1 continue the long term measurements 2 resume interrupted long term data series 3 replace vanishing glaciers by early starting replacement observations 4 extend the monitoring network to strategically important regions 5 validate calibrate and accordingly flag field measurements with geodetic methods and 6 make systematic use of remote sensing and geo informatics for assessment of the representativeness of the available data series for their entire mountain range and for the extrapolation to regions without in situ observations and 7 make all these data and related meta information available

paleoclimate and paleoceanography over the past 20 000 yr in the mediterranean sea basins as indicated by sediment elemental proxies abstract marine sediments record paleoenvironmental changes over time through variations in major and trace element concentrations the main objective of this paper is to review such changes in the mediterranean sea basins over the last 20 ka using the inorganic chemistry and mineralogy of marine sediment records elemental ratio proxies that are mostly used are discussed and the uncertainties involved in using them for paleoclimate and paleoceanographic reconstructions are evaluated the focus on the mediterranean region is based on the sensitivity of this region to global climate changes due to its semi enclosed nature the elemental ratios that have been particularly useful for reconstructing terrigenous inputs into the mediterranean have been ti al and zr al ratios as proxies for eolian dust input and mg al k al and rb al ratios as proxies for fluvial input redox sensitive elements e g u mo v co ni cr have provided reliable reconstructions of oxygen conditions at the time of deposition some of these elements are also particularly susceptible to post depositional remobilization and record diagenetic processes instead of the original environmental signatures regarding productivity fluctuations most of the paleoproductivity reconstructions are based on the abundance of barite and ba excess algorithms the biogeochemistry of ba is however not fully understood and mechanisms for barite precipitation in the water column are not yet known two case studies are presented the eastern mediterranean sapropel s1 deposited between 10 8 and 6 1 cal ka bp and the westernmost mediterranean paleoclimate record over the last 20 ka

well documented travel history of mesozoic pelagic chert in japan from remote ocean to subduction zone the mino tanba belt in southwest japan a segment of the cordilleran type orogenic chain of jurassic east asia is composed mainly of a middle upper jurassic subduction accretion complex in which triassic and lower jurassic bedded radiolarian cherts occur as large allochthonous units structurally interlayered with middle upper jurassic clastic rocks high resolution microfossil conodont and radiolaria research has identified very low average sedimentation rates of about 0 5 g cm 1000 yr in the chert units similar to those of modern pelagic sediments accumulated in open ocean environments judging from the low average sedimentation rate high purity of biogenic silica long duration of continuous deposition 50 m y and wide along strike extent 1000 km the bedded radiolarian cherts in the mino tanba belt are best understood as ancient pelagic sediments that accumulated in open ocean environments accordingly the alleged origin in smaller marginal basins is untenable upward lithologic change from bedded chert to overlying siliceous mudstone in the uppermost portion of chert sequences suggests the gradual landward approach of the oceanic plate toward a trench the tectonic interlayering of these cherts and coarse grained terrigenous elastics is a secondary feature that was added through duplexing underplating in the subduction zone on the basis of the primary stratigraphy and field occurrence of triassic bedded chert in the mino tanba belt newly proposed are an idealized oceanic plate stratigraphy and a generalized travel history of a cordilleran type bedded chert from its birth at a mid oceanic ridge to its demise at a subduction zone

interpretation of marine and freshwater paleoenvironments in permo carboniferous deposits article i nfo the freshwater criteria of gray gray j 1988 evolution of the freshwater ecosystem the fossil record palaeogeogr palaeoclimatol palaeoecol 62 1 214 are discussed relative to north american permo carboniferous deposits the faunas of the permo carboniferous basins of north america are compared with those from europe they are very similar organisms which live or lived in the aquatic environment can only characterize this environment terrestrial animals and plants are extraneous to the aquatic environment the best way of interpreting the environment is to compare with contemporaneous aquatic faunas myxinids acritarchs polychaetes and some ostracodes are marine forms spirorbiform microconchids spirorbis and some foraminifers are brackish water indicators based on faunal comparison the permo carboniferous deposits of north america and europe are interpreted as either marine or marine influenced

challenges and recommendations in mapping of glacier parameters from space results of the 2008 global land ice measurements from space glims workshop boulder colorado usa on 16 18 june 2008 the us national snow and ice data center held a glims workshop in boulder co usa focusing on formulating procedures and best practices for operational glacier mapping using satellite imagery despite the progress made in recent years there still remain many cases where automatic delineation of glacier boundaries in satellite imagery is difficult error prone or time consuming this workshop identified six themes for consideration by focus groups 1 mapping clean ice and lakes 2 mapping ice divides 3 mapping debris covered glaciers 4 assessing changes in glacier area and elevation through comparisons with older data 5 digital elevation model dem generation from satellite stereo pairs and 6 accuracy and error analysis talks presented examples and work in progress for each of these topics and focus groups worked on compiling a summary of available algorithms and procedures to address and avoid identified hurdles special emphasis was given to establishing standard protocols for glacier delineation and analysis creating illustrated tutorials and providing source code for available methods this paper summarizes the major results of the 2008 glims workshop with an emphasis on definitions methods and recommendations for satellite data processing while the list of proposed methods and recommendations is not comprehensive and is still a work in progress our goal here is to provide a starting point for the glims regional centers as well as for the wider glaciological community in terms of documentation on possible pitfalls along with potential solutions

exceptional fossil preservation during co2 greenhouse crises abstract exceptional fossil preservation may require not only exceptional places but exceptional times as demonstrated here by two distinct types of analysis first irregular stratigraphic spacing of horizons yielding articulated triassic fishes and cambrian trilobites is highly correlated in sequences in different parts of the world as if there were short temporal intervals of exceptional preservation globally second compilations of ages of well dated fossil localities show spikes of abundance which coincide with stage boundaries mass extinctions oceanic anoxic events carbon isotope anomalies spikes of high atmospheric carbon dioxide and transient warm wet paleoclimates exceptional fossil preservation may have been promoted during unusual times comparable with the present co 2 greenhouse crises of expanding marine dead zones oceanic acidification coral bleaching wetland eutrophication sea level rise ice cap melting and biotic invasions

automated mapping of earth s annual minimum exposed snow and ice with modis global snow and ice have been diminishing during theanthropocenebutwestilllackacompletemappingofannualminimumexposedsnowandicewithaconsistent repeatablealgorithm the global land ice measurements from space glims project has compiled digital glacier outlines andrelated metadata for the majority of the world s glaciers butinconsistency among product algorithms and time periodsrepresented precludes the production of a consistentlyderived global data set here we present the modis persis tent ice modice algorithm that leverages the time seriesof fractional snow and ice cover from the modis snowcovered area and grain size modscag algorithm theend product of modice is a consistently derived map ofannual minimum exposed snow and ice comparisons ofmodice with glims glacier outlines derived from spot aster and landsat thematic mapper show strong agree ment with the higher resolution outlines subject to uncer tainties with spatial resolution deep mountain shadows andglims interpretation errors

primary braunite in triassic sedimentary manganese deposits of dounan yunnan china abstract this paper is concerned with the genesis of dounan braunite the study includes the precise determination of the mineral by 1 transmitted and reflected light microscopy 2 cathodoluminescence and scanning electron microscopy 3 x ray diffraction 4 x ray fluorescence and 5 electron microprobe besides determinations of the mineral the petrology and geologic environment of the samples are reviewed for an interpretation of its mode of origin in many descriptions even during recent years braunite has not been positively identified and the criteria by which the modes of origin are interpreted leave some doubt that conclusions are correct the study indicates that dounan braunite is primary sedimentary in origin although braunite elsewhere has usually been interpreted as either a metamorphic or hydrothermal or rarely a diagenetic product dounan braunite as accretionary ooliths pisoliths occurs conformably in the terrigenous clastic carbonate sediment in the transgressive regressive middle triassic marine sequence of the falang group southeastern yunnan china this sequence shows no evidence of volcanism or hydrothermal activity and is not metamorphosed examination of the mineralogical character and chemical composition of the important phases as well as their textures suggest that braunite occurs in two generations primary braunite probably grew as accretionary ooliths pisoliths precipitated as primary sediment within lagoonal and intertidal zones during sedimentation coarse or polycrystalline braunite resulting from recrystallization and replacement of earlier braunite is considered as a diagenetic product of primary manganese ores

distribution and mineral assemblages of bedded manganese deposits in shikoku southwest japan implications for accretion tectonics abstract numerous bedded manganese and manganese iron ore deposits occur in shikoku southwest japan the mineralogy wall rock characteristics and fossil age data of the deposits are synthesized in this paper their mineral assemblages correlate well with the progressive metamorphic grade of the accretionary complexes in shikoku based on the plate tectonic framework of subduction accretion process the deposits are considered to have formed by metamorphism of mn fe nodule bearing siliceous sediments on the ocean floor

tracing bottom water redox conditions during deposition of lower and upper jurassic organic rich sedimentary rocks in the lusitanian basin portugal insights from inorganic geochemistry abstract the lower jurassic agua de madeiros am fm and vale das fontes vf fm formations and the upper jurassic cabacos formation cab fm are considered the most important units with petroleum source rock potential in the lusitanian basin and the likely sources for its widespread hydrocarbon occurrences nonetheless the bottom water redox conditions during their deposition remain debatable to resolve this controversy we investigated whole rock inorganic geochemical data of the most significant organic rich levels of the am vf and cab fms cropping out at basin scale significant variations in toc ts and redox sensitive elements contents and their ratios are evident within and between the organic rich levels of the studied units a positive covariation between primary productivity proxies toc enrichment and paleo redox proxies for the lower jurassic units clearly suggest an interdependence between enhanced primary productivity organic matter accumulation and bottom water redox conditions for the am fm the paleo redox proxies indicate that the black shales deposition took place beneath bottom waters that ranged from suboxic to strongly euxinic conditions with a clear predominance of the latter a toc threshold of 6 7 wt clearly separates samples deposited under suboxic to anoxic conditions from those deposited under true euxinic conditions and is interpreted as the minimum amount of organic matter om accumulation within sediments required to sustain h2s production at rates that outpaced its consumption through precipitation of sulphides and or om sulphurization allowing the diffusion of h2s to the bottom waters for the vale das fontes fm the paleo redox proxies suggest a prevalence of suboxic to anoxic bottom waters despite all black shales displaying toc contents greater than the above threshold the less reducing conditions relative to the am fm euxinic black shales are attributed to i a larger proportion of continental om ii lower reactivity of the om reaching the sediment water interface decreasing oxygen consumption and iii higher availability of reactive iron increasing the buffer effect to h2s produced through om remineralization by sulphate reducing bacteria both units display mo ef vs u ef covariation patterns that deviate from the field of sediments deposited under unrestricted open marine conditions towards higher mo enrichment relative to that of u indicating an accelerated transport of aqueous mo to the sediments consistent with the operation of a metal oxyhydroxide particulate shuttle linked to mn and fe redox cycling within the water column in a weakly restricted basin the mo cot regression line slope indicates a moderate degree of bottom water mass restriction with mo aq concentration of 60 70 of the present day seawater value and bottom water renewal times of 10 20 years akin to the present day cariaco basin the redox conditions of the cab fm organic rich levels are dependent on the location of the depositional environment in the basin with deposition taking place beneath oxygenated bottom waters at cabo mondego and under suboxic conditions at vale de ventos and pedrogao the latter denoting a larger degree of oxygen depletion than the former in this context the overall potential for om preservation should increase from cabo mondego to vale de ventos and pedrogao

mineralogy of low grade metamorphosed manganese sediments of the urals petrological and geological applications abstract the paper describes mineralogy of the low grade metamorphosed manganese sediments which occur in sedimentary complexes of the pai khoi ridge and the polar urals and volcanosedimentary complexes of the central and south urals the degree of metamorphism of the rocks studied corresponds to pt conditions of the prehnite pumpellyite deposits of pai khoi and polar and south urals and green schist deposits of the central urals facies one hundred and nine minerals were identified in the manganese bearing rocks on the basis of optical and electron microscopy x ray diffraction and microprobe analysis according to the variations in the amount of major minerals of the manganese rocks of the urals they are subdivided on carbonate i oxide carbonate silicate ii and oxide silicate iii types carbonates various mn 2 bearing silicates associated with oxides and carbonates and braunite mn 3 bearing silicate are the major mn hosts in types i ii and iii respectively because of the different oxidation state of mn the rocks of types i and ii are termed as reduced and the rocks of type iii as oxidized the formation of a certain mineralogical type of metamorphic assemblage is controlled by the content of organic matter in the primary sediments the sequence type i type ii type iii reflects the decrease in the amount of organic matter in metalliferous sediments mineralogical data indicate that manganese in the primary sediments accumulated in a silicate form mn si gel glass etc during diagenesis the mn si phase was transformed to neotokite with subsequent formation of caryopilite and further crystallization of pyroxmangite rhodonite tephroite and other silicates due to reactions involving caryopilite the hydrated mn silicates caryopilite and or friedelite and the spatially associated parsettensite stilpnomelane and other minerals are the index minerals of the low grade metamorphism under pt conditions of prehnite pumpellyite facies nearly 70 of silicate minerals are hydrous the metamorphosed mn bearing sediments are characterized by the low temperature caryopilite or tephroite caryopilite pyroxmangite rhodonite and the high temperature caryopilite free or tephroite pyroxmangite rhodonite facies their pt conditions correspond to zeolite and prehnite pumpellyite the low temperature and green schist and higher grade the high temperature facies

basalt seawater interaction the plenus cold event enhanced weathering and geochemical change deconstructing oceanic anoxic event 2 cenomanian turonian late cretaceous oceanic anoxic event 2 cenomanian turonian ca 94 ma represents a major palaeoceanographic phenomenon that took place during an interval of extreme global warmth when large amounts of organic matter entered the marine burial record probably triggered by increased availability of nutrients for planktonic biota three sections eastbourne sussex uk raia del pedale campania italy and tarfaya morocco recording this event illustrate the influence on marine geochemistry of mafic volcanic rock seawater interaction anoxia to euxinia and re oxygenation and cooling during the so called plenus cold event the eastbourne section represents the organic lean epicontinental pelagic deposits of the english chalk the raia del pedale section represents a shallow water platform carbonate on the tethyan continental margin also largely devoid of organic matter and the tarfaya core represents an atlantic margin site where cyclically bedded organic rich sediments were well developed correlation between all three sections is readily achieved by biostratigraphy and carbon isotope stratigraphy 13ccarb and 13corg over the oceanic anoxic event 2 interval represented by a characteristic broad positive carbon isotope excursion the stratigraphic range of the plenus cold event defined by the presence in two discrete levels of boreal fauna and an excursion to heavier oxygen isotope values in the english chalk can be identified in raia del pedale and tarfaya by using the carbon isotope curve as a correlative tool similarly a section in southern france allows its co existing osmium isotope excursion to relatively unradiogenic values to be placed in the context of the oceanic anoxic event in all three analysed sections a fall to lower osmium isotope values clearly pre dated the onset of oceanic anoxic event 2 as defined by the initial rise in carbon isotope values allowing the putative magmatic mafic event as a trigger for the oceanic anoxic event an initial drop in sulphur isotope ratios 34scas at eastbourne correlates with the osmium isotope curve suggesting that isotopically light sulphur could have been derived from a mafic igneous source re oxygenation of sediments of all three investigated sections during the plenus cold event is variably illustrated by change in cerium calcium iodine calcium molybedenum calcium and uranium calcium ratios according to the redox behaviour of the elements in question and whether controls on seawater chemistry were local or global in nature changes in molybdenum isotope ratios from tarfaya and portions of the sulphur isotope curve from eastbourne and raia del pedale also indicate the probable presence of more oxygen rich bottom waters during the plenus cold event oxidation by such waters of previously deposited organic rich shales as well as loss of anoxic euxinic sinks is credited with temporarily enriching global seawater in a range of other redox sensitive trace metals for example v cr co ni cu zn and cd during ongoing basalt seawater interaction indicated by persistent relatively non radiogenic osmium isotope seawater values however early diagenetic enrichment of manganese in the english chalk over much of the oceanic anoxic event interval is broadly correlative in time with relatively low osmium isotope values in sections elsewhere a relationship that may be due to the lack of affinity of manganese with carbon rich shales hence allowing relatively elevated concentrations of the element in marine waters to persist during leaching of mafic rocks unlike other redox sensitive species the calcium isotope and lithium isotope ratios from eastbourne and raia del pedale indicate an increase in global weathering during the initial phase of oceanic anoxic event 2 and the shift in strontium isotopes and osmium isotopes to more unradiogenic values during the event suggests that not only construction but also destruction of one or more large igneous provinces was probably a proximal cause of this major palaeoceanographic phenomenon by elevating nutrient levels and planktonic productivity in large tracts of the world ocean globally widespread carbon burial and silicate weathering are both identified as important mechanisms for drawing down atmospheric carbon dioxide that in the absence of overwhelming volcanogenic replenishment of this greenhouse gas during the early phase of oceanic anoxic event 2 caused the plenus cold event

an expanded shale δ98mo record permits recurrent shallow marine oxygenation during the neoarchean abstract multiple attempts have been made using the ancient shale record to track the molybdenum isotope composition 98mo of seawater during the final two hundred million years of the archean eon 2 7 to 2 5 billion years ago or ga this seawater 98mo value is important because it should have scaled with levels of ocean oxygenation during the runup to the great oxidation event goe unfortunately however it is difficult to tell if the majority of the existing late archean shale 98mo record tracks an ancient seawater value here we further attempt to track pre goe seawater 98mo using an expanded and well characterized shale sample set from western australia jeerinah wittenoom and mt sylvia formations and south africa nauga and klein naute formations most importantly and in contrast to most previous mo isotope studies of similarly aged shales local redox conditions for our shales have been independently constrained using the iron fe speciation proxy and bottom water mo contents at the time of deposition have been qualitatively estimated using mo toc ratios local redox conditions and bottom water mo availability are important parameters because transfer of the seawater 98mo to sediments today is shown to be dependent on these conditions according to our updated sedimentary 98mo record seawater 98mo commonly exceeded 1 0 between 2 69 ga and 2 50 ga in order to drive such a heavy seawater 98mo there must have been a marine sink with a strong preference for lighter mass mo isotopes frequently present over this timeframe the operation of some anaerobic processes in late archean marine settings could theoretically explain the heavier seawater 98mo such processes are known to promote the preferential retention of lighter mass mo isotopes in marine sediments today e g interactions between mo and organic matter or the formation of thio complexes alternatively or in addition adsorption of lighter mass mo isotopes to fe and mn oxide minerals formed in oxygenated marine environments can explain the heavier seawater 98mo a compilation of previous work suggests that oxygenated shallow marine environments were fairly common during the late archean and thus mo adsorption to fe mn oxides formed in these settings probably played an important role in driving heavy seawater 98mo over this timeframe

recognition of ocean plate stratigraphy in accretionary orogens through earth history a record of 3 8billion years of sea floor spreading subduction and accretion abstract ocean plate stratigraphy ops is a term used to describe the sequence of sedimentary and volcanic rocks deposited on oceanic crust substratum from the time it forms at a spreading center to the time it is incorporated into an accretionary prism at a convergent margin in this study we review the major geological characteristics of relict cenozoic to early archean oceanic crust and ops persevered in alaska japan california franciscan complex central asia british isles canada slave province australia pilbara craton and greenland isua and ivisaartoq belts an assessment of ops in accretionary orogens spanning the duration of earth s rock record shows remarkable similarities between ops of all ages in terms of structural style major rock components sequence of accretion and trace element geochemical signatures volcanic rocks preserved in the orogenic belts are characterized predominantly by oceanic island arc basalts island arc picrites mid ocean ridge basalts back arc basalts oceanic plateau basalts ocean island basalts and boninites with extremely rare komatiites this demonstrates that sea floor spreading lateral movement of oceanic plates with accompanying sedimentation over the oceanic substratum and accretion at convergent margins have been major earth processes since at least 3 8 ga ago there have been some secular changes in the rock types in ops such as changes in carbonates and radiolarian cherts whose sources were in the biota in existence in phanerozoic times but absent in the precambrian but overall there have been few changes in the style of ops accretion with time komatiites and banded iron formations occur predominantly in archean orogenic belts reflecting higher mantle temperatures and less oxic seawater composition respectively before 2 5 ga this is clear documentation that plate tectonics including the lateral movement of oceanic lithosphere has been a major heat loss mechanism on earth since the early precambrian

biogenicity of earth s earliest fossils a resolution of the controversy abstract the abundant and diverse assemblage of filamentous microbial fossils and associated organic matter permineralized in the 3465 ma apex chert of northwestern australia widely regarded as among the oldest records of life have been investigated intensively first reported in 1987 and formally described in 1992 and 1993 the biogenicity of the apex fossils was questioned in 2002 and in three subsequent reports however as is shown here by use of analytical techniques unavailable twenty years ago the apex filaments are now established to be bona fide fossil microbes composed of three dimensionally cylindrical organic kerogenous walled cells backed by a large body of supporting evidence of similar age other microfossils stromatolites and carbon isotopic data it seems clear that microbial life was present and flourishing on the early earth 3500 ma ago

a new species of dimetrodon synapsida sphenacodontidae from the lower permian of germany records first occurrence of genus outside of north america a new species of the sphenacodontid synapsid dimetrodon d teutonis is described on the basis of a single adult specimen consisting of a large portion of the presacral vertebral column the holotype was collected from the lower permian tambach formation lowermost formational unit of the upper rotliegend of the bromacker quarry locality in the midregion of the thuringian forest near gotha central germany this is the first record of the genus outside of north america and therefore provides not only additional biological evidence of a continuous euramerican landmass during the early permian but also the absence of any major physical or biological barrier to faunal interchange of terrestrial vertebrates an estimated weight of 14 kg for d teutonis is half that of the smallest previously recognized species d natalis sphenacodontid phylogeny indicates that the diminutive size of d teutonis represents an autapomorphy and is in general accord with the absence of large sized basal synapsid predators at this truly terrestrial upland locality it is speculated that the diminutive size of d teutonis was probably an adaptation to a truly terrestrial relatively uplands existence like that represented by the bromacker locality here it subsisted on small vertebrates and possibly large invertebrates of the bromacker assemblage in which the dominant members in both size and abundance were herbivorous diadectids and it was unlikely to encounter large predators

black shale formation during the latest danian event and the paleocene eocene thermal maximum in central egypt two of a kind abstract the paleocene eocene thermal maximum petm 55 8 ma is considered as the most severe of a series of transient warming events hyperthermals that occurred during the early paleogene however the extent and magnitude of environmental changes during the short lived warming events pre and post dating the petm are still poorly constrained in this study we focus on the latest danian event lde 61 7 ma and compare it to the petm we present high resolution micropaleontological geochemical and mineralogical data of the petm and the lde in two adjacent sections from the gebel qreiya area in egypt there both events are characterized by a distinct set of event beds overlying an unconformity they are associated with intense carbonate dissolution and substantial changes in the benthic foraminifera fauna moreover both show an abrupt drop of siliciclastic input sediment starvation correlative to the onset of black shale formation and a strong enrichment in redox sensitive trace elements the evidence for enhanced detrital input during the onset of the petm and a longer recovery phase with enhanced phosphorus sedimentation during the petm attests a stronger environmental impact of this event compared to the lde according to rock eval and elemental analysis the petm as well as the lde event beds have up to 4 wt organic carbon small amounts of volatile hydrocarbons but high amounts of highly weathered and inert organic matter black carbon during pyrolysis the extremely high temperatures for the maximum release of hydrocarbons of the petm and lde samples correspond to thermal heating of 170 c which is incompatible with the sediment burial history therefore we suggest that the organic matter in both event deposits does not reflect well preserved marine biomass but predominantly represents a mixture of heavily weathered autochthonous marine material and allochthonous combustion residues differences in preservation and or type of organic matter are also likely to account for the divergent stable isotope anomalies of organic carbon the well known negative carbon isotope anomaly at the petm and a positive anomaly at the lde although warming water column stratification and enhanced nutrient input may have promoted anoxic conditions on the shelf during the lde as well as during petm our results support rapid sea level rise and clastic starvation as one important mechanism for black shale formation and carbon sequestration for both events this result underlines the similarity of both hyperthermal events in terms of environmental changes recorded on the southern tethyan margin with the petm showing an additional early phase of strong detrital input not revealed at the lde

a multistage genetic model for the metamorphosed mesoproterozoic swartberg base metal deposit aggeneys gamsberg ore district south africa

geological and geochemical constraints on the cheshmeh frezi volcanogenic stratiform manganese deposit southwest sabzevar basin iran abstract the cheshmeh frezi mn deposit belongs to the southwest sabzevar basin to the north of the central iranian microcontinent this basin which hosts abundant mineral deposits including mn exhalative and besshi type cu zn volcanogenic massive sulfide deposits followed an evolution closely related to the subduction of the neo tethys oceanic crust beneath the central iranian microcontinent two major sedimentary sequences are recorded within this basin i the lower late cretaceous volcano sedimentary sequence llcvss and ii the upper late cretaceous sedimentary dominated sequence ulcss the cheshmeh frezi mn deposit is hosted within red tuff with interbeds of green tuffaceous sandstone of the llcvss mineralization occurs as stratiform blanket like and tabular orebodies psilomelane pyrolusite and braunite are the main minerals of the ore which display a variety of textures such as layered laminated disseminated massive replacement or open space fillings the footwall and hanging wall volcanic rocks are predominantly andesite and trachyandesite rocks footwall and hangingwall volcanic rocks at cheshmeh frezi are enriched in light rare earth elements lrees compared to chondrite have steep ree patterns and generally show ta and nb depletions relative to chondrite which are characteristic of back arc environments the significant geochemical characteristics of ore such as high mn content 12 41 33 14 wt average 19 41 wt low concentration of fe 0 64 2 27 wt average 1 63 wt high ba 49 7 9901 ppm average 2728 67 ppm lree hree and negative ce and eu anomalies reveal a primary distal hydrothermal exhalative source for mineralization cheshmeh frezi deposit in comparison with different types of volcanogenic manganese deposits shows broad similarities with the cuban type mn deposits such as tectonic host and associated rock types geometry textures structures mineralogy and lithogeochemistry

sedimentology of tufa facies and continental microbialites from the palaeogene of mallorca island spain abstract the middle eocene and oligocene basins in northwestern half of mallorca are filled by detrital rocks conglomerates calcarenites and lutites and carbonates deposited in alluvial fluvial palustrine and lacustrine settings the sediment supplied to these continental basins was transported by alkaline bicarbonate rich waters as a consequence these non marine carbonate deposits display extensive developments of diverse kinds of organosedimentary facies the sedimentary record from three localities peguera alaro and sineu enabled one to characterize well preserved eocene tufa deposits as well as eocene and oligocene stromatolites and oncolites a total of ten carbonate facies are described and interpreted the facies related to tufa deposits are diverse types of boundstones rudstones and packstones of bryophytes in situ stems s l phytoclasts etc and associated oncolite rudstones and bioclastic mudstones to packstones these facies deposited in littoral lacustrine and fluvio lacustrine environments oncolites and stromatolites present a great variety of shapes and sizes oncolites from centimetres to several meters in diameter that somehow were conditioned by environmental conditions within shallow lacustrine and fluvial settings three types of lamination apparently dependent on the type of microorganisms responsible for calcite precipitation are distinguished fan shaped and bush shaped grouped filaments and isolated to loosely grouped filaments the 13c and 18o composition of these deposits agrees with carbonate precipitation in freshwater hydrologically open systems with similar carbon sources throughout the eocene and oligocene however eocene and oligocene samples are set apart by the 18o oligocene facies present lower 18o values which might indicate deposition from isotopically less evolved waters perhaps under slightly greater precipitation evaporation conditions tufa facies have the highest 13c composition and show some positive covariation of 13c and 18o primarily reflecting the effects of physical and biological co2 outgassing and maybe also minor evaporation

introduction to and classification of manganese deposits of china abstract manganese mn ore deposits are widely distributed in china and can be divided into six types based on origin and subsequent modifications 1 sedimentary 2 volcanic sedimentary 3 metamorphosed 4 hydrothermally modified 5 hydrothermal and 6 supergene sedimentary and supergene mn ore deposits are economically the most important mn ore deposits and ore bearing sequences are distributed temporally from the proterozoic through the quaternary but they principally are middle proterozoic sinian cambrian ordovician devonian carboniferous permian triassic and quaternary ages the largest mn metallogenic periods in china are sinian and devonian in contrast to the widespread proterozoic cretaceous and oligocene mn deposits found elsewhere in the world mn bearing stratigraphic successions in china can be divided into six types of lithologic associations 1 black shale series 2 chert mudstone limestone 3 carbonate 4 mudrock carbonate 5 volcanic sedimentary and 6 epeirogenic clastic rock types the most important mn metallogenic regions in china are 1 yanliao 2 border of hunan sichuan guizhou hubei provinces 3 southern shaanxi and northeastern sichuan 4 middle guizhou and eastern yunnan 5 southwestern guangxi 6 southeast yunnan 7 hunan guangxi guangdong fujian and 8 xinjiang the most striking characteristics of mn ore deposits in china are the wide distribution in geological ages and variety of compositional types of ores such as fe mn b mn p mn co mn ca mn ca mg mn among others the primary mn ores of china are mainly mn carbonates

u pb ages of magmatic and detrital zircon of the dohlen basin geological history of a permian strike slip basin in the elbe zone germany the post orogenic evolution of variscan central europe is characterized by the formation of numerous basins the early permian dohlen basin is located in the elbe zone germany and is bordered by metamorphic rocks of the erzgebirge and numerous variscan magmatic complexes the nw se oriented basin is evidence for a major rearrangement of stress fields during the post variscan reactivation of fault zones in central europe eleven samples of magmatic rocks and sediments have been analyzed with respect to their u th pb isotope ratios and geochemical composition of three magmatic samples two tuffs one trachyandesite we analyzed 170 zircon grains the unkersdorf tuff of the unkersdorf formation gave an age of 294 3 ma upper asselian to sakmarian whereas a trachyandesite of the same formation was dated at 293 5 ma lower artinskian to lower asselian the wachtelberg ignimbrite upper bannewitz formation showed an age of 286 4 ma artinskian to lower kungurian as the first study we also analyzed 984 detrital zircon grains of nine late paleozoic central european sandstone and conglomerate samples of the niederhaslich formation and the bannewitz formation with respect to their u pb age composition all sediments but two yielded two distinct age groups between 295 and 340 ma and 530 750 ma as well as a minor amount of precambrian zircon ages geochemical data points to an active margin setting with developing strike slip basins the data suggests a c 10 ma lasting basin formation during the second culmination of volcano tectonic activity with basic to intermediate melts the second youngest formation niederhaslich formation consists predominantly of pre permian basement material which implies only minor volcanic activity and erosion from adjacent basement blocks on the contrary the uppermost and youngest bannewitz formation features strong evidence for volcanic activity in the neighboring area of the basin the present study strongly suggests a rapid basin development and further shows how the evolution of the dohlen basin is proof for several post variscan tectonic reactivation phases in sakmarian and lower kungurian of central europe finally our results exemplarily show how basin evolution may be characterized by radiometric data of detrital zircon grains

a geochemical constraint on the formation process of a manganese carbonate nodule in the siliceous mudstone of the jurassic accretionary complex in the mino belt japan abstract manganese mn carbonate nodules which differ from seafloor mn nodules mainly composed of mno 2 are occasionally embedded in the form of a lens shape in the jurassic accretionary complexes such as the mino belt in japan the interpretation of the formation process of mn carbonate is still controversial particularly concerning whether the mn carbonate was formed primarily or secondarily in this study a fresh mn carbonate nodule incorporated into the red siliceous mudstone was collected for geochemical and sedimentological analysis the optical observation of thin sections indicates that the mn carbonate nodules are composed of abraded grains of rhodochrosite spherule with radiolarians and are sedimentary embedded in siliceous mudstone microfossil radiolarians from the mn carbonate nodules and the host red siliceous mudstone are dated as the bajocian but the radiolarians in the nodules are somewhat older than those in the host red siliceous mudstone geochemical analysis using the x ray absorption near edge structure on ce indicates the dominance of trivalent ce at present despite the observation of a positive ce anomaly in the paas normalized ree pattern of mn carbonate the ree adsorption experiment on synthesized mnco 3 does not show any distinctive positive ce anomaly and a thermodynamic calculation suggests the possible coexistence of rhodochrosite and spontaneous oxidation of ce a leaching experiment that can selectively decompose the carbonate phase demonstrated no ce anomaly in the carbonate phase of the mn carbonate and a poor contribution to the bulk ree concentration the carbon isotope data of mn carbonate nodule implied the dominance of inorganic marine carbonate origin with small contribution of organic decomposition the most plausible account of all of the observational and geochemical results is that the rhodochrosite grains were primarily formed on the depositional site and subsequently transferred to a different site where siliceous mudstone was deposited

carboniferous permian volcanic evolution in central europe u pb ages of volcanic rocks in saxony germany and northern bohemia czech republic nine shrimp u pb ages on zircon and two pb pb single zircon ages have been determined from late paleozoic volcanic rocks from saxony and northern bohemia samples came from the teplice altenberg volcanic complex the meissen volcanic complex the chemnitz basin the dohlen basin the brandov olbernhau basin and the north saxon volcanic complex the teplice altenberg volcanic complex is subdivided into an early namurian phase mikulov ignimbrite 326 8 4 3 ma thus older than assumed by previous studies and a late caldera forming phase teplice ignimbrite 308 8 4 9 ma the age of the latter however is not well constrained due to a large population of inherited zircon and possible hydrothermal overprint the leutewitz ignimbrite product of an early explosive volcanic episode of the meissen volcanic complex yielded an age of 302 9 2 5 ma stephanian a volcanic rocks intercalated in the brandov olbernhau basin bob 302 2 8 ma chemnitz basin cb 296 6 3 0 ma dohlen basin db 296 3 0 ma and the north saxon volcanic complex nsvc c 300 290 ma yielded well constrained stephanian to sakmarian ages the largest late paleozoic ignimbrite forming eruption in central europe the rochlitz ignimbrite has a well defined middle asselian age of 294 4 1 8 ma ages of palingenic zircon revealed that the namurian westphalian magmatism assimilated larger amounts of crystalline basement that formed during previous paleozoic geodynamic phases the precambrian inherited ages support the chronostratigraphic structure assumed for the saxo thuringian zone of the variscan orogen the present results help to improve the chronostratigraphic allocation of the late paleozoic volcanic zones in central europe at the same time the radiometric ages have implications for the interbasinal correlation and for the geodynamic evolution of the variscan orogeny

a new glacier inventory for the svartisen region norway from landsat etm data challenges and change assessment glaciers are widely recognized as key indicators of climate change and their meltwater plays an important role in hydropower production in norway since the last glacier inventory was compiled in northern norway in the 1970s marked fluctuations in glacier length and mass balance have been reported for individual glaciers and the current overall glacier state is thus not well known within the framework of the global land ice measurements from space glims initiative we have created a new inventory for 489 glaciers in the svartisen region northern norway using a landsat enhanced thematic mapper plus etm satellite scene from 7 september 1999 and automated multispectral glacier mapping thresholded band ratios in addition visual inspection and correction of the generated glacier outlines has been applied adverse snow conditions and uncertain drainage divides made glacier mapping challenging in some regions of the study site glacier outlines from 1968 as digitized from a topographic map were used for a quantitative change assessment for a selection of 300 glaciers the overall area change of this sample from 1968 to 1999 was close to zero but with a strongly increasing scatter towards smaller glaciers large area gains 50 for small glaciers 1 km 2 and an unexpected stronger relative area loss towards the wetter coast the overall size changes are small 1 for the three largest ice masses in the study region vestisen ostisen and blamannsisen

sedimentology of triassic dounan type manganese deposits western margin yangtze platform china abstract manganese mn deposits formed during the ladinian middle triassic are widely distributed along the western margin of the yangtze platform all the mn deposits occur in condensed sections cs and are formed in similar depositional and structural settings related to late stage incipient spreading of the tethys seaway differences in the degree of development and sedimentary facies in different areas determined the size ore body strike and dip and ore composition four sedimentary facies occur 1 dolomite rich mn rocks 2 glauconite bearing oolitic mn rocks 3 phosphatic fe rich mn rocks and 4 silica rich mn rocks type 1 formed along the margin of a passive stable margin type 2 formed on basin slopes with relatively low topography and deep water and types 3 and 4 formed mainly in the ma erkang basin a deep depression on the shelf ore constituents partly derived from a western source area formed medium to low grade ores in offshore areas during the ladinian maximum sea level rise ocean currents and lower cycle sea level changes produced composite ore beds seafloor hydrothermal systems typical of tethyan rifting may have provided mn bearing fluids that ascended along faults and mixed with bottom currents those fluids and or diagenetic oxidation reformed and concentrated the previously formed medium to low grade ore bodies

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

sedimentary geochemistry of manganese implications for the environment of formation of manganiferous black shales the sedimentary geochemistry of manganese is dominated by the redox control of its speciation higher oxidation states mn super 3 and super 4 occurring as insoluble oxyhydroxides in well oxygenated environments and the lower oxidation state mn super 2 being much more soluble in oxygen deficient settings its geochemical behavior is therefore quite different in oxic and anoxic environments and where oxic and anoxic conditions are juxtaposed mn is recycled between the two environments in modern marine sediments mn is present above its crustal abundance as an oxyhydroxide in all slowly accumulating pelagic sediments of the deep ocean and in surficial deposits of continental margin environments diagenetic recycling of mn in the latter causes surficial deposits to have larger mn enrichments than in many pelagic sediments bottom sediments of permanently anoxic basins show no enrichments and have mn concentrations that are controlled solely by the aluminosilicate fraction manganese carbonates kutnohorite and calcic rhodochrosite are found only in anoxic sediments accumulating beneath surface oxic horizons and therefore under oxygenated bottom waters in many nearshore environments such enrichments are due to delivery of mn by burial of surface oxyhydroxides into the subsurface anoxic environment where they are dissolved pore water mn levels can reach saturation with respect to a mixed mn ca carbonate phase in such sediments the diagenetic origin for these phases is shown by their carbon isotope compositions which typically indicate a carbon source from decomposing organic matter the presence of mn carbonates therefore signifies that the host sediment must have accumulated under oxygenated bottom waters on the basis of this information it is proposed that in contrast to several current explanations for the formation of mn carbonates kutnohorite and rhodochrosite in ancient organic rich shales limestone and marl sequences and in many mn ore deposits the occurrence of these mineral phases indicates that the sediments originally accumulated beneath oxygenated bottom waters by analogy with the present mn carbonates could not have formed in the bottom waters of anoxic basins these diagenetic phases however did form where mn was supplied at a high rate namely by the burial of oxyhydroxide enriched surface sediments to a subsurface anoxic environment this situation could only have occurred under oxygenated bottom waters the presence of mn carbonates in ancient black shales and in some carbonate rich rocks lends strong support to the notion that these rocks did not necessarily form in anoxic basins but owe their carbon richness to a high supply of organic matter to sediments deposited under oxygenated bottom waters probably in continental margin settings

assembling north china craton within the columbia supercontinent the role of double sided subduction abstract an evaluation of recent s wave receiver functions s wave velocities and two versions of p wave tomographic images along various transects in the north china craton provides some clues on the subduction collision history of the different crustal blocks and their final amalgamation within the paleoproterozoic columbia supercontinent interpretation of a n s seismic section of the craton suggests thick slab debris sinking to various depths in the mantle the w e seismic corridors show the preservation of a thick 200 km lithospheric root tectosphere beneath the ordos block and its variable and extensive erosion towards the yanliao block eastern block this zone is characterized by layers with marked velocity contrast and suggests repeated stacking of the remnants of underplated and accreted paleoproterozoic oceanic lithosphere the present day lithosphere asthenosphere boundary beneath this region probably marks the erosional plane along which decratonization occurred through subduction erosion from the east and thermal and material erosion by upwelling asthenosphere from below resulting in the partial destruction of the tectosphere and its thinning towards the east within the asthenosphere below the yanliao block younger and thinner slabs predominate in the absence of any prominent thick high velocity layers these younger slabs define a westward polarity and constitute a mega scale duplex formed by underplating through phanerozoic subduction process particularly the pacific plate subduction from the east the lithologic associations within the inner mongolia suture zone dividing the yinshan block to the north and ordos block to the south correspond to an accreted ocean plate stratigraphic sequence with the tonalite trondhjemite granodiorite ttg gneisses charnockites and calc alkaline granites representing a continental arc built up through subduction from the north the seismic transects bring out a contrasting polarity in the subduction regime with an oblique east to southward subduction of the yinshan block and a westward subduction of the yanliao block here i propose a double sided subduction history for the ncc similar to the ongoing subduction process in the western pacific such double sided subduction is considered to promote rapid amalgamation of continental fragments within supercontinents and the subduction polarities and mantle dynamics of ncc are therefore considered to be critical in evaluating the final assembly of the paleoproterozoic supercontinent columbia

characteristics of manganese ore deposits in china abstract manganese ore deposits are widely distributed in china based on features of regional tectonics and sedimentary environments as well as genetic characteristics seven important metallogenic provinces can be classified the commercial manganese ore deposits are distributed mainly on platforms and their marginal areas especially those of relatively mobile platforms the main metallogenic epochs of manganese ore deposits of china are sinian and devonian in contrast with the famous proterozoic cretaceous and oligocene manganese deposits elsewhere in the world based on their modes of origin manganese ore deposits in china can be divided into six types among them sedimentary and supergene deposits are the main types accounting for commercial manganese deposits according to the lithological association of the ore bearing series sedimentary manganese ore deposits can be classified into 1 mud rock type 2 black shale type 3 carbonate rock type in addition eight element association types can also be identified among which b mn s mn ca mg mn and p mn types are quite special for manganese ore deposits in china

growth history of manganese nodules and crusts of the peru basin abstract in the nodule field of the peru basin situated south of the zone of high bioproductivity a relatively high flux of biogenic matter explains a distinct redox boundary at about 10 cm depth separating very soft oxic surface sediments from stiffer suboxic sediments maximum abundance 50 kg m 2 of diagenetic nodules is found near the calcite compensation depth ccd currently at 4250 m there the accretion rate of nodules is much higher 100 mm ma 1 than on ridges 5 mm ma 1 highest accretion rates are found at the bottom of large nodules that repeatedly sink to a level immediately above the redox boundary there distinct diagenetic growth conditions prevail and layers of dense laminated mn oxide of very pure todorokite are formed the layering of nodules is mainly the result of organisms moving nodules within the oxic surface sediment from diagenetic to hydrogenetic environments the frequency of such movements is much higher than that of climatic changes two types of nodule burial occur in the peru basin large nodules are less easily moved by organisms and become buried consequently buried nodules generally are larger than surface nodules this type of burial predominates in basins at ridges where smaller nodules prevail burial is mainly controlled by statistical selection where some nodules are not moved up by organisms

permo carboniferous climate early pennsylvanian to late permian climate development of central europe in a regional and global context a well justified stratigraphical correlation of continental successions and new palaeogeographic reconstruction of pangaea reveal new insights into the northern pangaean climate development influenced by palaeogeography palaeotopography glacio eustatic sealevel changes and ocean currents the overall permo carboniferous aridization trend was interrupted by five wet phases these are linked to the gondwana icecap the aridization and weakening of wet phases over time were not only caused by the drift of northern pangaea to the arid climatic belt but also by the successive closure of the rheic ocean which caused the expansion of arid semi arid environments in the lower middle permian the end of the gondwana glaciation rearranged ocean circulation leading to a cold coast parallel ocean current west of northern pangaea blocking moisture coming with westerly winds the maximum of aridity was reached during the roadian wordian the trans pangaean mountain belt was non existent its single diachronous parts never exceeded an average elevation of 2000 m the maximum elevation shifted during time from east to west the hercynian orogen never acted as an orographic east west barrier and the inter tropical convergence zone was widely displaced causing four seasons dry summer winter wet spring autumn at the equator and a strong monsoon system the climate history of the european realm during the late carboniferous pennsylvanian and permian is stored in many solitary basins fig 1 within the hercynian orogen and the foreland basin the story of westphalian climate is well known because of the numerous investigations of the coal bearing variscan foredeep the younger westphalian is characterized by a slight aridization abbink van kronijnenburgvan cittert 2003 oplustil 2004 which was accompanied by an increase of seasonality nevertheless the environment was strongly influenced by the ocean and epi continental seas with multiple transgression events the last extensive marine ingression was the aegir mansfield band westphalian b c the post westphalian climate development is more differentiated and

major and trace element characterization of oceanic anoxic event 1d oae 1d insight from the umbria marche basin central italy abstract the pialli level in the umbria marche basin central italy correlates with the lowermost part of the positive carbon isotopic excursion characterizing the late albian early cenomanian oceanic anoxic event 1d oae 1d high resolution litho bio and chemostratigraphic data from the monte petrano and le brecce sections allow for a bed by bed comparison of the two successions and discriminate local from basin scale signals we present new x ray fluorescence icp ms and toc data for both the limestones and the pialli level shales integrated with available carbonate carbon isotopes and nannofossil temperature and nutrient indices data indicate a homogenous background sedimentation dominated by pelagic carbonates biogenic silica with little contribution by clays the limited variation in lithogenic elements points to an essentially homogeneous detrital source area with limited fluvial terrigenous input higher mn concentrations coupled with low enrichments in redox sensitive elements such as u fe s re mo ag suggest that the pialli level shales represent temporary suboxia without reaching anoxia furthermore p authigenic ba cd and ni enrichments together with nannofossil nutrient index indicate generally low primary productivity conditions along the entire succession with only minor increases for some of the black to dark grey shales of the pialli level the nannofossil temperature index highlights a warm climate during the oae 1d with the warmest conditions experienced during the deposition of the pialli level shales during the late albian the warm and humid climate was interrupted by brief episodes of relatively warmer and less saline surface waters ensuring slower rates of bottom water renewal and producing temporary suboxic conditions such paleoceanographic dynamics would be the continuation of episodic warmer and humid pulses characterizing the late albian interval in the umbria marche basin as such the pialli level can be considered the result of a last episode closing a cycle before the establishment of a steadier climate during the early cenomanian

evidence of archean life stromatolites and microfossils abstract fossil evidence of the existence of life during the archean eon of earth history 2500 ma is summarized data are outlined for 48 archean deposits reported to contain biogenic stromatolites and for 14 such units that contain a total of 40 morphotypes of described microfossils among the oldest of these putatively microfossiliferous units is a brecciated chert of the 3465 ma apex basalt of western australia the paleoenvironment carbonaceous composition mode of preservation and morphology of the apex microbe like filaments backed by new evidence of their cellular structure provided by two and three dimensional raman imagery support their biogenic interpretation such data together with the presence of stromatolites microfossils and carbon isotopic evidence of biological activity in similarly aged deposits indicate that the antiquity of life on earth extends to at least 3500 ma

mineralogical and geochemical investigations of the middle eocene ironstones el bahariya depression western desert egypt abstract the middle eocene ironstone succession is located in the northeastern part of el bahariya depression western desert egypt this succession is subdivided into lower and upper sequences and consists of two main shallow marine ironstone facies associations the first is a lagoonal manganiferous mud and fossiliferous ironstone facies association and consists mainly of goethite and hematite detrital minerals quartz rutile and feldspars manganese minerals todorokite psilomelane pyrolusite birnessite aurorite and manjiroite and authigenic clay minerals kaolinite and illite the second is a peritidal microbially mediated stromatolitic and nummulitic ooidal oncoidal ironstone facies association consists of goethite apatite and secondary minerals that include quartz jarosite psilomelane and pyrolusite organic materials such as proteinaceous compounds lipids cellulose and carotenoids were detected in the cortices of the ferruginous ooids and oncoids the marine ironstone facies were exposed to subaerial weathering and subsurface alteration processes the weathering resulted in the formation of lateritic iron ores and paleosols during humid climatic periods the lateritic iron ores consist mainly of colloform goethite hematite and psilomelane the identification of cavity filling sulfate nitrate carbonate and silicate minerals in the marine ironstones and the lateritic iron ore may indicate more recent alteration under arid climatic conditions the subsurface alteration is attributed to the oxidation of sulfides primarily pyrite and weathering of glauconitic clastic rocks in the underlying cenomanian bahariya formation during the interaction with acidic heated groundwater the formation of ferrous and ferric sulfate and silicate minerals and mobilization of trace metals are the products of the alteration process enrichments in ba co k pb and sr are correlated with manganese oxides whereas anomalous p v cr ni zn as mo and u are correlated with iron oxyhydroxides

genetic diversity of manganese deposition in the terrestrial geological record terrestrial manganese deposits formed by hydrothermal sedimentary and supergene processes ancient analogues of modern oceanic hydrothermal deposits formed in spreading centre and subduction related settings and those deposited from terrestrial hot springs are discussed sedimentary mn oxide deposits formed in shallow water at the margins of stratified oceans above the redoxcline during sea level changes mn carbonate deposits probably formed by diagenesis through mn oxyhydroxide reduction coupled with organic matter oxidation climatic variation and basin water stratification responsible for mn concentration were manifestations of atmospheric coz content prompted by tectonism supergene manganese enrichment in continental weathering profiles was mainly dictated by climate topography and drainage systems manganese deposits of diverse genetic types occur in the terrestrial geological record roy 1981 these were produced by direct hydro thermal activity sedimentary processes and continental weathering although the processes may be interrelated each involves distinct mechanisms that place the deposits into specific genetic types some of these processes are best understood in preset day depositional sites the ancient environments were determined by the intensity and style of tectonism volcanism and hydrothermal activity the composition of the atmosphere and the hydrosphere and the development of the biosphere which all varied with time it is my intention to unfold the total panorama of the environmental evolution during different time envelopes that produced a variety of manganese deposits in the past only major deposits and those providing distinctive evidence of their environment of deposition will be considered here

climate forcing of fine grained deep marine systems in an active tectonic setting middle eocene ainsa basin spanish pyrenees abstract a multi proxy approach to understand environmental change in deep time was undertaken on about 150 m of core from a 230 m long middle eocene core from the ainsa basin spanish pyrenees representing deep marine siliciclastic sediments using detailed sedimentary logging high resolution multi element xrf geochemistry total organic carbon and stable carbon isotopes the well a6 was drilled as part of an industry university consortium through siltstones fine very fine grained sandstone turbidites and hemipelagic structureless mudstones that were deposited as overbank and off axis deposits from a sandy submarine fan and interfan deposits for comparative mineralogy between the sandstone turbidites and siltstones scanning electron microscopy sem and x ray diffraction xrd were undertaken on selected samples the sandstone turbidites show enrichment of detrital elements such as si zr and ti that can be linked to greater quartz and heavy mineral content compared with adjacent siltstones structureless hemipelagic mudstones comprise mainly clay minerals and carbonate we interpret the sandstone turbidites as from hyperpycnal flows during high river sediment discharge whilst hemipelagic mudstones resulted from the suspension fall out of hypopycnal flows cyclostratigraphic analysis of the core reveals milankovitch cyclicity at frequencies of 0 03 cycles m short eccentricity 0 09 cycles m obliquity 0 15 cycles m precession couplet and 0 19 cycles m precession couplet orbital parameters appear to have controlled the cyclic delivery of coarser grained sediment by turbidity currents two equally plausible depositional models both as milankovitch driven can explain the cyclical changes in the deep marine sediments 1 climatic cycles with humid periods of enhanced chemical weathering increased storminess and greater riverine run off leading to high sediment flux to the deep basin as sandstone turbidites 2 climatic cycles with cooler conditions linked to high frequency small scale eustatic sea level fluctuations with lowstand shelf edge delta progradation resulting in greater volumes of coarse detrital sediment to the seafloor by hyperpycnal flows this study provides an insight into the likely depositional effects of orbitally induced climate change on the nature and delivery of terrigenous sediment into deep marine environments

inorganic geochemistry of the type caradoc series sandbian to middle katian upper ordovician onny valley shropshire uk the geochemistry and petrology of the type section of the caradoc series in the onny valley indicate that it was deposited on a marginal basin continental shelf similar to the western side of the present sea of japan the lower beds form a transgressive regressive sequence in which the rocks become less mature upwards all the coarser sediments above the basal quartzites and conglomerates are greywackes in which the apparent muddy and ferrous matrix is due to the breakdown of unstable minerals and particles higher values of na 2 o and na k ratios are found in the coarser shallow water sandstones of the horderley sandstone formation and decrease markedly in the succeeding beds accompanied by an increase in k 2 o higher values of carbonate corrected and hence related other major and minor elements like sio 2 cao p 2 o 5 mno and most trace elements correlate with the transgressive systems and maximum flooding surfaces of the three sequences recognized where they are related to condensation at those horizons chemical indices of alteration cia suggest that the horderley sandstone formation underwent greater predepositional physical weathering than lower and higher beds which is compatible with the petrography and were deposited during a cool phase within overall warm sandbian katian times trace element ratios suggest an oxic to suboxic depositional environment

plate tectonics radiogenic isotopic tracers and paleoceanography the case of the manganese crusts in the pacific abstract hydrogenous ferromanganese crust deposits on seafloor and volcanic seamounts are archives of past isotopic compositions of the ocean isotopic compositions of long life radiogenic isotopes that are dissolved in the ocean such as nd and pb are mixtures of different erosion products continents volcanics arcs ridges etc transported by oceanic currents or winds isotopic studies on mn crusts are thus potential paleogeographic and paleoceanographic tracers however global paleogeography can drastically evolve over the period of growth of crust as well as the latitude longitude and water depth of the mn crust thus each crust sampled a succession of geographic sites related to its spatial evolution through time for this reason valid information about the past ocean isotopic composition can only be extracted from mn crust under the condition that the successive paleogeographic and paleodepth positions can be reconstructed for each mn crust we followed this approach for six hydrogenous mn crusts from the pacific ocean that have recorded pb and nd isotopic signals for the past 80 myr the evolution of the isotopic data was considered within a proper geodynamical framework that takes into account the paleopositions of the pacific plate and surrounding continents of the hot spots and ridges as well as the paths of the six crusts the differences and similarities between the pb and nd revealed by our analysis emphasize their complementarity as paleoceanographic tracers the nd isotopes are strongly influenced by the exchange between indian and pacific waters specifically by the progressive closure of the indonesian gateway the closed central pacific characteristics are defined from the extrapolation of the isotopic trend this highlights the important role played by erosion of volcanic arcs in the nd isotopic value of seawater our approach also stresses the influence of local volcanic activity ridges or active hot spot for lead isotopes

early diagenesis of foraminiferal calcite under anoxic conditions a case study from the landsort deep baltic sea iodp site m0063 abstract the chemical composition of foraminiferal calcite is widely used for studying past environmental conditions and biogeochemistry however high rates of microbial organic matter degradation and abundant dissolved metal sources in sediments and pore waters may impede the application of foraminifera based proxies due to formation of secondary carbonates or other authigenic minerals on and or inside of foraminiferal tests secondary carbonate precipitation severely alters the bulk foraminiferal geochemistry and can be difficult to eliminate through standard foraminiferal trace element cleaning procedures we present results showing the mineral composition and formation sequence of diagenetic coatings on foraminiferal tests formed under extreme anoxic conditions in the baltic sea s deepest basin the landsort deep iodp exp 347 site m0063 our study focuses primarily on the diagenetic carbonates present on and in the tests of the low oxygen tolerant benthic foraminiferal species elphidium selseyensis and elphidium clavatum we applied various geochemical and imaging methods to ascertain the diagenesis processes and the authigenic mineral formation sequence on foraminifera the authigenic carbonates were enriched in mn mg fe and ba depending on the environmental redox conditions when the authigenic carbonates were precipitated concentrations of redox sensitive elements such as mn and fe were particularly elevated in bottom waters and sedimentary pore waters under oxygen depleted conditions in the landsort deep resulting in formation of carbonates with highly elevated mn and fe contents in addition to mn and fe carbonates several other types of authigenic minerals also formed on and in the foraminiferal chambers including authigenic calcite and non carbonate accessory minerals the formation sequence reveals the redox sensitivities of different elements and the preferential sequence of oxidants used by the microbes during organic matter oxidation and secondary redox reactions this study provides a case study of extreme early diagenesis of foraminiferal calcite and may serve as a valuable guide when interpreting foraminiferal trace element records from low oxygen environments

metallogeny and temporal spatial distribution of manganese mineralizations in iran implications for future exploration abstract there are a lot of manganese mn deposits and numerous mineral occurrences of this type of mineralization in iran the major tectonic structural zones of iran that host manganese deposits are 1 urumieh dokhtar magmatic assemblage udma 2 the central iran ci 3 the sabzevar zone sz 4 the alborz magmatic belt amb and 5 the cretaceous ophiolites these manganese deposits were formed during discrete time periods 1 late neoproterozoic early cambrian narigan and halab deposits in the ci 2 jurassic halalan deposit in the sz 3 cretaceous mn mineralizations in the late cretaceous volcano sedimentary sequence of southwest sabzevar basin in the sz nasirabad abadeh tashk alashtar sorkhvand esfandagheh benvid gugher kamar talar sardasht and safou manganese deposits in the southeast of birjand dehoo and north of sabzevar deposits which occur in the upper cretaceous ophiolites and 4 eocene miocene e g venarch jalal shahrestanak boznein garab menamin robat karim qaleh mohammad khan rabiei zarashlou narkan sarikand jokandy gharaeh tavaragh and barout aghaji deposits in the udma and amb magmatic arcs intra arc rifts and back arc basins are the principal plate tectonic settings for iranian manganese deposits all of the manganese deposits of the udma and amb formed within tertiary arc and back arcs respectively that developed during subduction of the neo tethyan crust beneath the iranian plate intra oceanic or continental back arc spreading settings are recognized in the neo tethys domain in iran and these host several manganese deposits in the sz and ophiolites the trace element content of all studied manganese deposits is generally low in concentrations and tends to enrichment in the assemblage of v cu pb zn and as with geochemical characteristics similar to hydrothermal deposits rare earth element ree patterns of the iranian manganese deposits support a hydrothermal origin the main time period of formation of manganese mineralization in iran was from cretaceous to miocene the udma and sz are the most favourable metallogenic provinces in iran for manganese exploration because these zones host the most and the largest manganese deposits including venarch and shahrestanak deposits in the udma and manganese mineralizations in the late cretaceous volcano sedimentary sequence of the southwest sabzevar in the sz

the central india tectonic zone a geophysical perspective on continental amalgamation along a mesoproterozoic suture abstract the central india tectonic zone citz is a prominent divide and a major suture zone between the north indian and south indian crustal blocks the resistive upper crust as modeled in the magnetotelluric data from citz suggests a dominant tonalite trdondhjemite granodiorite composition associated with an accretionary complex characterized by mainly felsic rock components the highly conductive bodies in this zone might represent mafic ultramafic layered intrusives derived from a deeper reservoir of underplated basaltic magma related to the formation of the cretaceous deccan flood basalts the uniformly thick mafic lower crust below the cratons on both sides of the suture is interpreted as the accreted remnants of archaean and paleoproterozoic subducted slabs we redefine the nature of deep faults traversing the citz which were described as steep and penetrating the moho by previous workers and classify them as listric faults with gentle dips at depth seismic reflection data from the eastern side of the suture suggest a northwestward subduction of the bhandara craton reflection data from the central part of the citz show northerly dip in the southern part suggesting northward subduction of the dharwar craton however an opposite trend is observed in the northern part of the suture with a southward dip of the bundelkhand craton based on these features and in conjunction with existing magnetotelluric models we propose a double sided subduction history along the citz this would be similar to the ongoing subduction accretion process in the western pacific region which possibly led to the development of paired collision type and pacific type orogens one important feature is the domal structure along the central part of the suture with a thick felsic crust occurring between mafic and intermediate crust the high resistivity felsic domain suggests underplated sediments felsic crust that would have caused the doming our model also accounts for the extrusion of regional metamorphic belts at the orogenic core and the occurrence of high pressure ultrahigh temperature paired metamorphic belts within the suture

transition between terrestrial submerged walking and swimming revealed by early permian amphibian trackways and a new proposal for the nomenclature of compound trace fossils abstract exceptionally preserved early permian tetrapod trackways from the orobic basin central western southern alps offer a unique opportunity to investigate in detail locomotion in fossil vertebrates that lived on continental european landmasses herein are reported the results of a study on several tetrapod trackways that display a large variety of behavioral gait and substrate related extramorphologies they clearly document the transition from terrestrial underwater walking to swimming and are assigned to the compound ichnotaxon batrachichnus c lunichnium the use of the c symbol is here introduced for the first time as nomenclatural indication of a compound trace producers were probably small sized temnospondyl or lepospondyl microsaurs amphibians comparisons with living urodelan anatomy and mechanics provide evidence for conservatism of locomotor mechanics in evolutionary history among amphibians the derived model for locomotor kinematics in early permian amphibians provides a reference for interpreting transitional land to water trackways the shift from walking to swimming behavior in early tetrapods as in extant urodelan amphibians is described as a complex balance between different dynamics

origin and environment of manganese rich sediments within black shale basins abstract sediments with unusually high manganese contents occur in anoxic basins of the central baltic sea we present a new model for the enrichment of manganese which is based on sedimentological and geochemical analyses of holocene sediments from the gotland deep and on published hydrographic data due to salinity stratification and high primary production bottom waters of the central baltic sea are anoxic and rich in dissolved mn 2 episodically bottom waters become oxygenated by inflows of denser water from the north sea mixing results in oxidation of mn 2 to fine grained particulate oxides which accumulate in the deepest parts of the basins where currents are mostly absent here anoxic conditions are re established within a few months or years and manganese oxides are again dissolved causing high concentrations of mn 2 in the near bottom layer alkalinity is high as a consequence of bacterial reduction of manganese oxides and sulphate under these conditions manganese is reprecipitated and forms a layer of ca rich rhodochrosite on the top of laminated sapropels occasionally periods of such extremely and rapidly changing redox conditions are followed by long term oxygenation of bottom waters in that case a layer rich in manganese oxides forms on the top of a bioturbated layer due to dissolution of rhodochrosite and oxidation of manganese in the near surface sediment return of anoxic conditions results again in the transformation of manganese oxides into rhodochrosite varying rhodochrosite contents in the basinal sediments therefore record a detailed history of redox conditions in bottom waters the manganese rich sediments of the baltic sea share many features with some occurrences of lower jurassic and lower carboniferous manganese ores in western and central europe we therefore suggest that these manganese enrichments were formed by similar processes

sedimentary manganese metallogenesis in response to the evolution of the earth system abstract the concentration of manganese in solution and its precipitation in inorganic systems are primarily redox controlled guided by several earth processes most of which were tectonically induced the early archean atmosphere hydrosphere system was extremely o2 deficient thus the very high mantle heat flux producing superplumes severe outgassing and high temperature hydrothermal activity introduced substantial mn2 in anoxic oceans but prevented its precipitation during the late archean centered at ca 2 75 ga the introduction of photosystem ii and decrease of the oxygen sinks led to a limited buildup of surface o2 content locally initiating modest deposition of manganese in shallow basin margin oxygenated niches e g deposits in india and brazil rapid burial of organic matter decline of reduced gases from a progressively oxygenated mantle and a net increase in photosynthetic oxygen marked the archean proterozoic transition concurrently a massive drawdown of atmospheric co2 owing to increased weathering rates on the tectonically expanded freeboard of the assembled supercontinents caused paleoproterozoic glaciations 2 45 2 22 ga the spectacular sedimentary manganese deposits at ca 2 4 ga of transvaal supergroup south africa were formed by oxidation of hydrothermally derived mn2 transferred from a stratified ocean to the continental shelf by transgression episodes of increased burial rate of organic matter during ca 2 4 and 2 06 ga are correlatable to ocean stratification and further rise of oxygen in the atmosphere black shale hosted mn carbonate deposits in the birimian sequence ca 2 3 2 0 ga west africa its equivalents in south america and those in the francevillian sequence ca 2 2 2 1 ga gabon are correlatable to this period tectonically forced doming up attenuation and substantial increase in freeboard areas prompted increased silicate weathering and atmospheric co2 drawdown causing glaciation on the neoproterozoic rodinia supercontinent tectonic rifting and mantle outgassing led to deglaciation dissolved mn2 and fe2 concentrated earlier in highly saline stagnant seawater below the ice cover were exported to shallow shelves by transgression during deglaciation during the sturtian glacial interglacial event ca 750 700 ma interstratified mn oxide and bif deposits of damara sequence namibia was formed the varangian marinoan ca 600 ma cryogenic event produced mn oxide and bif deposits at urucum jacadigo group brazil the datangpo interglacial sequence south china liantuo nantuo varangian event contains black shale hosted mn carbonate deposits the early paleozoic witnessed several glacioeustatic sea level changes producing small mn carbonate deposits of tiantaishan early cambrian and taojiang mid ordovician in black shale sequences china and the major mn oxide carbonate deposits of karadzhal type central kazakhstan late devonian the mesozoic period of intense plate movements and volcanism produced greenhouse climate and stratified oceans during the early jurassic oae organic rich sediments host many mn carbonate deposits in europe e g urkut hungary in black shale sequences the late jurassic giant mn carbonate deposit at molango mexico was also genetically related to sea level change mn carbonates were always derived from mn oxyhydroxides during early diagenesis large mn oxide deposits of cretaceous age at groote eylandt australia and imini tasdremt morocco were also formed during transgression regression in greenhouse climate the early oligocene giant mn oxide carbonate deposit of chiatura georgia and nikopol ukraine were developed in a similar situation thereafter manganese sedimentation was entirely shifted to the deep seafloor and since ca 15 ma b p was climatically controlled glaciation deglaciation assisted by oxygenated polar bottom currents aabw nadw the changes in climate and the sea level were mainly tectonically forced

a multiproxy study distinguishes environmental change from diagenetic alteration in the recent sedimentary record of the inner cadiz bay sw spain in this study we reconstruct the recent environmental evolution of the inner cadiz bay using sedimentary records reaching back as far as ad 1700 we report lithological descriptions of the sedimen

constraining paleo latitude of a biogeographic boundary in mid panthalassa fusuline province shift on the late guadalupian permian migrating seamount abstract the guadalupian paleo atoll limestone iwato formation in sw japan was primarily formed in low latitude mid panthalassa and was later tectonically accreted to south china japan margin during the jurassic the present biostratigraphic study clarified that the iwato formation consists of 5 biostratigraphical intervals i e four fusuline assemblage zones assemblage zones 1 to 4 and a barren interval on the top assemblage zones 1 to 4 correspond to the neoschwagerina craticulifera zone n margaritae zone yabeina globosa zone and lepidolina multiseptata zone of the conventional tethyan fusuline stratigraphy respectively the present study newly clarified the following significant aspects of paleobiogeography of the permian fusulines as to the extinction of large tested taxa in the latest guadalupian 1 the long unknown stratigraphic relationship was documented for the first time between the yabeina dominant interval and the overlying lepidolina dominant one within a single limestone unit 2 the occurrence of lepidolina cf kumaensis kanmera the unique last runner of large tested fusuine was detected for the first time in mid oceanic paleo atoll limestones 3 with respect to the northbound migration history of the paleo seamount capped by the iwato formation the development of the two coeval fusuline biogeographic territories in the low latitude panthalassa i e the yabeina territory on the south and the lepidolina territory on the north was confirmed 4 the paleo latitude of the biogeographic boundary between the yabeina and lepidolina territories is constrained around 12 in the southern hemisphere on the basis of the latest geomagnetic data from the same limestone this new approach utilizing biostratigraphy on ancient migrating seamounts coupled with geomagnetic paleo latitude data is applicable to other cases in different time space co ordinates and of other fossil groups for constraining position of ancient biogeographic boundaries within lost oceanic domains of deep past

geochemistry and origin of piemontite quartz schists in the sanbagawa metamorphic belt central shikoku japan abstract in the sanbagawa metamorphic belt of central shikoku geochemical characteristics are used to demonstrate that piemontite quartz schists had a manganiferous sedimentary protolith the sanbagawa metamorphic belt was formed during a cretaceous regional intermediate high pressure type of metamorphism which is present throughout southwest japan based on a detailed mineralogical study of the asemi gawa and besshi areas in central shikoku the sanbagawa piemontite quartz schists can be divided into talc bearing and talc free types phlogopite occurs only in talc bearing assemblages and the modal percentage of piemontite in talc bearing types is higher than in talc free types plotting analyses of piemontites and garnets from talc bearing and talc free types in the al2o3 fe2o3 mn2o3 mno al fe3 mn3 mn2 diagram for the asemi gawa and besshi areas separately shows that the piemontite which accompanies talc is richer in mn3 and poorer in fe3 also garnets from talc bearing assemblage contain a slightly higher amount of mn2 and a lower amount of al than talc free types the al2o3 sio2 fe2o3 feo plot shows that sanbagawa piemontite quartz schists have a composition between deep sea pelagic clay and pure silica by the use of pearson s product moment correlation coefficient method and plotting elements against each other after removing silica and volatiles it is possible to distinguish four components which are able to explain the variance of the samples these components are first component al2o3 tio2 mgo na2o k2o zr rb y nb and to lesser degree fe2o3 feo ni th ba second component sio2 third component mno and fourth component cao al2o3 tio2 zr and other elements with positive coefficient relations with them have a detrital origin biogenic origins are considered for cao and sio2 and it was concluded that mno was derived from an hydrothermal source because the sanbagawa metamorphic belt has been subjected to much detailed research and also contains talc bearing and talc free piemontite quartz schists it provides the best opportunity to find an explanation for the occurrence of talc in some types of piemontite schist and its absence from others mineralogical and geochemical evidences show that the oxygen fugacity for talc bearing and talc free types is similar oxygen fugacity is so high that almost all of the iron is present as fe3 in hematite pressure and temperature is considered to have been constant for talc bearing and talc free types in each locality because the samples were collected from a known metamorphic context the talc absent present problem is discussed using phase relations of the samples with the greatest number of phases in each locality consideration of talc clinochlore piemontite and garnet in the system al2o3 mn2o3 mno mgo cao acmmn with excess phases albite quartz hematite phengite and water shows that talc coexists with piemontite and garnet which are richer in the piemontite and spessartine end members respectively

decadal changes in glacier parameters in the cordillera blanca peru derived from remote sensing we present spatial patterns of glacier fluctuations from the cordillera blanca peru glacier area terminus elevations median elevations and hypsography at decadal timescales derived from 1970 aerial photography 2003 spot5 satellite data geographic information systems gis and statistical analyses we derived new glacier outlines from the 2003 spot images and ingested them in the global land and ice measurements from space glims glacier database we examined changes in glacier area on the eastern and western side of the cordillera in relation to topographic and climate variables temperature and precipitation results include 1 an estimated glacierized area of 569 6 21 km 2 in 2003 2 an overall loss in glacierized area of 22 4 from 1970 to 2003 3 an average rise in glacier terminus elevations by 113 m and an average rise in the median elevation of glaciers by 66 m showing a shift of ice to higher elevations especially on the eastern side of the cordillera and 4 an increase in the number of glaciers which indicates disintegration of ice bodies annual air temperature showed a significant upward trend in the last 30 years with larger temperature increases at lower elevations there was a slight but not significant decrease in precipitation our results are consistent with glacier retreat and warming trends noted in the last three decades in the tropics

geochemical evidence for the paleoproterozoic arc back arc basin association and its importance in understanding the evolution of the central indian tectonic zone abstract the central indian tectonic zone citz is considered to be one sector in a series of paleoproterozoic orogens that stitched together the supercontinent columbia the paleoproterozoic mahakoshal belt forms the foundation of the citz metabasalts and metaclastic rocks of the mahakoshal belt have been studied for major elements and trace elements including the rare earth elements ree metabasalts of the lower saleemanabad formation are grouped into two types however both types of metabasalt depict a back arc basalt character by showing enrichments in large ion lithophile elements liles like k rb cs and ba and light rare earth elements lrees but show depletions in high field strength elements hfses like nb ta y and ti and hree heavy rare earth elements in comparison to the n morb this is further supported by some key elemental ratios like ba nb nb ta la nb eu eu nb nb and ree patterns the geochemistry of the metaclastic rocks of the lower saleemanabad middle parsoi and upper dudhmaniya formations of the mahakoshal belt show an arc signature rather than the cratonic signature in the bundlekhand ttg and n morb normalised diagrams the arc signature calc alkaline series of metaclastic rocks is further supported by various tectonic discrimination diagrams the overall study indicates that the mahakoshal belt was formed as a back arc rift basin very close to continental arcs on the hinterland of the bundelkhand craton at the initial stage of subduction as a result of trench rollback followed by thermal relaxation and basin inversion the sediment supply started from the continental arcs lying south of the mahakoshal basin furthermore the present study strengthens the mechanism of subduction related outgrowth of columbia along its continental margins and implies that the citz is a major precambrian crustal boundary that began as a mahakoshal back arc rift by northward subduction

combining sedimentological trace metal mn mo and molecular evidence for reconstructing past water column redox conditions the example of meromictic lake cadagno swiss alps here we present sedimentological trace metal and molecular evidence for tracking bottom water redox state conditions during the past 12 500 years in nowadays sulfidic and meromictic lake cadagno switzerland a 10 5 m long sediment core from the lake covering the holocene period was investigated for concentration variations of the trace metals mn and mo xrf core scanning and icp ms measurements and for the presence of anoxygenic phototrophic sulfur bacteria carotenoid pigment analysis and 16s rdna real time pcr our trace metal analysis documents an oxic intermediate sulfidic redox transition period beginning shortly after the lake formation similar to 12 5 kyr ago the oxic period is characterized by low sedimentary mn and mo concentrations as well as by the absence of any remnants of anoxygenic phototrophic sulfur bacteria enhanced accumulation preservation of mn up to 5 6 wt in the sediments indicates an intermediate mn enriched oxygenation state with fluctuating redox conditions during a similar to 2300 year long transition interval between similar to 12 1 and 9 8 kyr bp we propose that the high mn concentrations are the result of enhanced mn2 leaching from the sediments during reducing conditions and subsequent rapid precipitation of mn oxyhydr oxide minerals during episodic and short term water column mixing events mainly due to flood induced underflows at 9800 130 cal yr bp a rapid transition to fully sulfidic conditions is indicated by the marked enrichment of mo in the sediments up to 490 ppm accompanied by an abrupt drop in mn concentrations and the increase of molecular biomarkers that indicate the presence of anoxygenic photosynthetic bacteria in the water column persistently high mo concentrations 80 ppm provide evidence that sulfidic conditions prevailed thereafter until modern times without any lasting hypolimnetic ventilation and reoxygenation hence lake cadagno with its persistently stable chemocline offers a framework to study in great temporal detail over similar to 12 kyr the development of phototrophic sulfur bacteria communities and redox processes in a sulfidic environment possibly depicting analogous conditions in an ancient ocean our study underscores the value of combining sedimentological geochemical and microbiological approaches to characterize paleo environmental and redox conditions in lacustrine and marine settings

high precision u pb zircon ages for explosive volcanism calibrating the nw european continental autunian stratotype volcanism was intense in western european basins during the late carboniferous early permian transition related to the late variscan extension and associated magmatism in the autun basin explosive eruptions expressed as highly weathered distal ashfall deposits tonsteins were preserved in lacustrine to swamp environments the analysis of eleven tonsteins confirmed as non reworked volcanic horizons indicates a highly explosive acidic calc alkaline volcanism with active volcanic centres probably linked to massif central or vosges black forest magmatism new accurate ca id tims u pb ages are obtained from four of these tonsteins recorded within the lower autunian igornay and muse fms which defines the lower part of the autunian stratotype in the autun basin the middle part of the igornay fm is dated at 299 9 0 38 ma the lally oil shale bed is dated at 298 91 0 08 ma and the upper part of the muse oil shale bed is dated between 298 05 0 19 and 298 57 0 16 ma for the first time a numerical calibration of the regional continental autunian stage in its stratotype is proposed thus allowing correlation with global marine stages defined in the urals and highlighting a late gzhelian early asselian age for the lower autunian the tonstein in the lally oil shale appears to demarcate the carboniferous permian boundary within the 100 kyr resolution of the u pb ages in both the autun and southern uralian basins comparison with other european domains confirms that these new ages are consistent with well known macrofloral assemblages characteristic of the autunian

recognizing oib and morb in accretionary complexes a new approach based on ocean plate stratigraphy petrology and geochemistry abstract we present a new approach for recognizing the origin of accreted basaltic rocks based on ocean plate stratigraphy ops and on the petrology and geochemistry of basalts from mid oceanic ridges morb and oceanic islands oib using examples from four accretionary complexes ac in sw japan akiyoshi mino tamba chichibu and shimanto the key to the problem is the model of ops which includes an association of igneous and sedimentary rocks that form on an oceanic plate during its travel from a mid oceanic ridge to a subduction zone we propose the reconstruction of the tectonic settings of basalts according to their relationships with associated ops sediments their petrogenesis and their geochemical features five types of ops are recognized in the accretionary complexes of sw japan 1 sandstone shale 2 sandstone shale and chert 3 sandstone shale chert and morb 4 sandstone shale chert morb and gabbro peridotite 5 seamount ops including oib cap carbonates slope clastics and basal shale chert the alkaline tholeiitic or calc alkaline composition of basaltic melts which are typical of oceanic islands mid oceanic ridges and island arcs respectively can be identified by the sequence in crystallization of their major phenocrysts i e olivine ol clinopyroxene cpx and plagioclase pl and by their compositions alkaline and calc alkaline mafic lavas are characterized by an ol cpx pl succession whereas tholeiitic melts by their ol pl cpx succession titanium rich minerals e g ti augite kaersutite ti biotite are typical of alkaline lavas the application of geochemistry based tectonic discrimination diagrams is also a powerful tool if not supported by geological and petrological data may result in confusion due to magma contamination post magmatic alteration and secular change of mantle thermal conditions we propose that a direct comparison of normalized multi element patterns and key binary plots from older volcanic rocks with their modern analogues provides a more viable and reliable method of basalt discrimination our ops petrology geochemistry method allows us to confirm the above conclusions that the lavas of the akiyoshi mino tamba and southern chichibu ac formed in oceanic islands because they are associated with seamount ops sediments crystallized from ol to cpx and pl contain ti augite and kaersutite and are enriched in tio2 lree and nb in this paper we present geochemical data from the inuyama basalts of the mino tamba ac and from the toba complex in the huge mikabu greenstone belt of the chichibu ac the inuyama basalts are in contact with jurassic pelagic cherts but their geochemical features are confusing they contain phenocrysts of ol ti augite and kaersutite and therefore probably formed in seamounts the toba volcanic rocks are a part of the huge ophiolite belt they have flat to slightly lree enriched ree patterns are characterized by an ol cpx succession of phenocrysts and they plot in the oib field in binary plots suggesting they formed in an oceanic plateau

seymouria sanjuanensis amphibia batrachosauria from the lower permian cutler formation of north central new mexico and the occurrence of sexual dimorphism in that genus questioned six specimens of the amphibian seymouria preserved in a single block of matrix from the lower permian cutler formation of north central new mexico are described and referred to seymouria sanjuanensis vaughn they are the only seymouria specimens known from new mexico and provide a more extensive definition of the species it is interpreted that the specimens from new mexico were collected from an early to middle wolfcampian horizon and therefore represent the earliest known members of the genus evidence is presented that challenges previous explanations for the variability of several features of the skull and axial skeleton in specimens of seymouria baylorensis and s sanjuanensis as an indication of sexual dimorphism differences in the number of maxillary teeth depth of the maxilla and development of the maxillary dentition particularly in the canine region are interpreted as closely related morphological trends in seymouria although no satisfactory explanation is offered for differences in th

biogenic signature and ultra microfossils in ferromanganese nodules of the central indian ocean basin abstract theories related to the precipitation mechanism of the metallic elements in marine manganese nodules have remained controversial between two schools of thoughts 1 chemical oxidation abiotic origin and 2 deposition of the metals through microbial enzymatic processes biogenic origin one of the most important evidence in support of the biogenic origin is the occurrence of fossilized microbes however well documented literature in this regard is either lacking or very scanty in case of indian ocean nodules using high resolution feg sem we have recorded various biogenic signatures and ultra microfossils in the ferromanganese nodule samples from central indian ocean basin ciob that are presented in this paper the microfossils are mostly protozoans belonging to varieties of bacteria diatoms and foraminifera some of the features recorded in this study have perhaps never been reported before from any manganese nodules the chemical compositions of these ultra microfossils indicate a high level of manganese precipitation in and around them in comparison to the distant surrounding areas while clumpy microbes are enriched with nickel the rod shaped bacteria are rich in copper up to 4 70 wt nickel and 5 31 wt cu have been recorded in the fossilized microbe bodies the high abundance of biogenic features as well as microfossils in the ferromanganese nodules and their chemical compositions support arguments in favor of a dominant role of the microorganisms in the construction of the nodules of the ciob

geochemistry of istrian lower palaeogene bauxites is it relevant to the extent of subaerial exposure during cretaceous times abstract investigation of the origin and occurrence of istrian lower palaeogene bauxites discussed in this work relies on adoption of the recent perspectives on development of the collision induced diachronous discontinuity surface in the istrian part of the adriatic dinaric carbonate platform this process related to the forebulge uplift at the latest stages of alpine orogenesis is amply recorded in the geochemical signature of contemporaneous bauxites in order to elucidate the patterns of bauxite formation a discriminant function model based on the compositional data analysis major and trace elements is constructed providing the solid ground for separation of the bauxite groups deposited in the subaerially exposed istrian palaeoenvironment complete distinction between the four a priori defined istrian lower palaeogene bauxite groups achieved by the analysis demonstrates the highest degree of efficiency in characterizing environmental conditions marked by the unique suite of geochemical variables compositions

planimetric and volumetric glacier changes in the khumbu himal nepal since 1962 using corona landsat tm and aster data multitemporal space imagery from 1962 corona kh 4 1992 landsat tm 2001 and 2005 terra aster was used to investigate the glacier changes in the khumbu himal nepal the ice coverage in the investigation area decreased by about 5 between 1962 and 2005 with the highest retreat rates occurring between 1992 and 2001 the debris coverage increased concomitantly with the decrease in total glacier area the clean ice area decreased by 10 digital terrain model dtm generation from the early corona kh 4 stereo data in this high relief terrain is time consuming and the results still contain some elevation errors however these are minor in the snow free areas with gentle slopes thus comparison of the surfaces of the debris covered glacier tongues based on the corona dtm and an aster dtm is feasible and shows the downwasting of the debris covered glaciers the highest downwasting rates more than 20 m 0 5 m a 1 can be found near the transition zone between the active and the stagnant glacier parts of the debris covered glacier tongues the downwasting is lower but still evident in the active ice areas and at the snout with thick debris cover all investigated debris covered glaciers in the study area show similar behaviour the estimated volume loss for the investigated debris covered glacier tongues is 0 19 km 3

recent contributions of glaciers and ice caps to sea level rise satellite measurements of earth s gravity field show that the mass loss of glaciers and ice caps contributed to sea level rise by approximately 0 4 millimetres per year between 2003 and 2010 the extent to which mass loss from ice covered land areas contributes to sea level rise is not known accurately in part because previous global estimates use different techniques for glaciers ice caps and ice sheets the gravity recovery and climate experiment grace satellite has provided monthly measurements of the global gravity field since 2002 using grace data jacob et al assess regional mass loss between 2003 and 2010 and conclude that mass loss from ice covered land areas contributed almost 1 5 mm per year to the sea level rise estimated mass loss from the high mountains of asia was negligible in contrast to some other reports glaciers and ice caps gics are important contributors to present day global mean sea level rise1 2 3 4 most previous global mass balance estimates for gics rely on extrapolation of sparse mass balance measurements1 2 4 representing only a small fraction of the gic area leaving their overall contribution to sea level rise unclear here we show that gics excluding the greenland and antarctic peripheral gics lost mass at a rate of 148 30 gt yr 1 from january 2003 to december 2010 contributing 0 41 0 08 mm yr 1 to sea level rise our results are based on a global simultaneous inversion of monthly grace derived satellite gravity fields from which we calculate the mass change over all ice covered regions greater in area than 100 km2 the gic rate for 2003 2010 is about 30 per cent smaller than the previous mass balance estimate that most closely matches our study period2 the high mountains of asia in particular show a mass loss of only 4 20 gt yr 1 for 2003 2010 compared with 47 55 gt yr 1 in previously published estimates2 5 for completeness we also estimate that the greenland and antarctic ice sheets including their peripheral gics contributed 1 06 0 19 mm yr 1 to sea level rise over the same time period the total contribution to sea level rise from all ice covered regions is thus 1 48 0 26 mm 1 which agrees well with independent estimates of sea level rise originating from land ice loss and other terrestrial sources6

accreted oceanic materials in japan abstract the phanerozoic circum pacific orogenic belts contain numerous ocean derived materials accreted through plate converging processes japanese islands in particular display various kinds of oceanic materials of different origins including fragments of seamounts oceanic reef limestone morb like rocks and oceanic mantle and pelagic sediments the compilation of these rocks in many subduction complexes of late permian to the present led to following conclusions accretion processes work effectively only for materials primarily composing the upper portion of subducting oceanic crust i e layer 1 and layer 2 many fragments of seamount with alkali basalt 600 hot spot seamount 26 oceanic reef limestone 291 morb like basalt 200 and numerous cherts more than 1000 are recognized as ancient oceanic materials accreted to the japanese islands however gabbros and mantle materials of layer 3 and lower parts of the oceanic lithosphere scarcely occur in subduction accretion complexes except for a few examples of back arc basin or fore arc origin accretion occurs episodically in southwest japan oceanic materials were accreted intermittently in 1 a end permian 2 b middle late jurassic 3 c late cretaceous times 4 d at ca 50 ma and 5 e in miocene times while in northeast japan and hokkaido this occurred in b middle late jurassic c late cretaceous and f early cretaceous times in contrast to the general belief on accretion of younger oceanic plates the majority of japanese subduction accretion complexes were formed during the subduction of plates up to 160 ma old the accretionary events in end permian and middle late jurassic times coincide with northward collision of ancient island arcs oceanic rises or seamount chains of hot spot origin with the asian continent accretion relevant to subduction of older plates may be controlled by the collision subduction process of these topographic reliefs on an oceanic plate in addition the chronological coincidence with the continent collision amalgamation between the sino korean and siberian platforms and between the sino korean and yangtze blocks also implies collision induced voluminous supply of elastics from back arc regions and its contribution to the formation of huge accretionary complexes accreted fragments of ancient seamounts are much smaller than the average size of modern seamounts this implies that most parts of a colliding seamount are not accreted but subducted together with the underlying oceanic crust to much deeper levels with respect to the metamorphic grades for japanese subduction complexes oceanic materials have less than 1 vol in the zeolite facies 15 20 in the prehnite pumpellyite metagraywacke facies and ca 30 in the greenschist glaucophane schist facies and albite epidote amphibolite fades this relationship indicates that the major process for landward accretion of oceanic materials is not off scraping or sedimentary mixing at the trench but underplating subcretion at much deeper levels of a subduction zone

bacterially mediated diagenetic origin for chert hosted manganese deposits in the franciscan complex california coast ranges numerous manganese deposits in the franciscan complex california occur as conformable lenses within bedded radiolarian chert argillite sequences that are in turn intercalated within thicker sections of sandstone and shale the field relations composition and petro graphic and isotopic characteristics indicate that the manganese was concentrated by diagenetic reconstitution of siliceous and hemipelagic sediment during burial the ore lenses are mn rich and fe poor assemblages consisting largely of rhodochrosite manganese silicates opal ct disordered cristobalite tridymite and quartz highly negative 13 c values for the carbonate carbon in rhodochrosite indicate that co 2 likely originated from oxidation of methane less negative values result from mixing of methanogenic carbon and co 2 derived from bacterial degradation of organic matter the 18 o values for the carbonate of rhodochrosite indicate temperatures of formation between 12 and 100 c the oxidation of methane prior to carbonate precipitation may have used the minor 0 4 0 5 mn and fe oxyhydroxides and oxides deposited with the sediment the mobilization of manganese from biogenic and terrigenous sources in the sediment column into discrete horizons and the fractioriation of manganese from iron reflect the presence of oxidation reduction boundaries and gradients in the sediment column fluids derived from compaction and silica dehydration reactions in the transformation of opal a x ray amorphous biogenic silica to quartz were involved in transportation of principal components sedimentary and geochemical attributes suggest that the deposits formed in a deep water environment in a zone of oceanic upwelling near a continental margin

manganese formations in the accretionary belts of japan implications for subduction accretion process in an active convergent margin abstract in the accretionary complexes of japan many bedded manganese and iron manganese ore deposits occur especially in the jurassic complexes such as the chichibu tamba mino ashio and northern kitakami belts the manganese ores in these jurassic accretionary complexes probably formed from manganese nodule crust bearing siliceous sediments on deep sea floor and were subsequently converted to the manganese ores by metamorphism during the subduction accretion process some of the deposits also show the signatures of younger granitic intrusions the manganese formations now incorporated within these belts are marker beds of accretionary tectonics associated with plate tectonic processes in convergent margins

earliest record of exophytic insect oviposition on plant material from the latest pennsylvanian gzhelian stephanian c of the saale basin germany abstract the late palaeozoic fossil record of plant insect interactions contains few records of oviposition here we report the earliest evidence of exophytic oviposition where eggs are laid directly on the outer surface of plants the fossil structures consist of small circular impressions on plant fossils from the late pennsylvanian gzhelian stephanian c of the saale basin in germany their interpretation as exophytic insect eggs is supported by the oviposition pattern their three dimensional preservation and the undamaged nature of the plant host tissue the tight arrangement of the eggs in curved arcs suggests a producer with a short abdomen such as roachoids the ancestral group of the dictyoptera sensu stricto a diagnostic feature of roachoids is their long ovipositor which was well suited for deposition of single eggs in a distinct pattern