geology and geochemistry of middle eocene maden complex ferromanganese deposits from the elazig malatya region eastern turkey abstract in the study region the puturge precambrian permian metamorphic rocks the upper jurassic lower cretaceous guleman ophiolites the upper cretaceous lower eocene hazar unit the campanian lower maastrichtian aged elazig magmatics and the middle eocene maden complex crop out extensively the maden complex containing ferromanganese mineralization unconformably overlies the puturge metamorphic rocks the guleman ophiolites and the hazar unit and is unconformably overlain by plio quaternary sediments the ferromanganese mn fe ores in the elazig malatya region eastern turkey are hosted in the mudstone member of the volcano sedimentary part of the middle eocene maden complex as lenses or interbedded layers in the elazig malatya region mn fe ores occur at eight localities namely beyhan palu sarikamis kockale germili hazar alihan and kom mn fe ores are found in the kockale and palu deposits as a single bed but in the hazar and kom deposits as two beds and in the sarikamis germili and alihan deposits in three levels the thickness of these mineralized levels ranges from 0 3 m to 10 m all the investigated mineralizations are conformable with the foot wall mudstones braunite bixbyite jacobsite pyrolusite manganite and psilomelane are the main manganese oxide minerals hematite barite and pyrite are also found in variable amounts in the ferromanganese ores the trace element content of all studied ferromanganese deposits is generally in low concentrations and tends to enrichment in the assemblage of ba sr v cu pb zn and as with a geochemical characteristic similar to hydrothermal deposits rare earth element ree patterns of the maden complex mn fe deposits support a hydrothermal origin with a slight enrichment in the middle ree 4 04 29 91 ppm average 16 49 and a slightly high concentration of total ree 92 40 738 23 ppm average 517 85 in all the investigated deposits ree patterns displayed negative ce 0 08 to 0 72 average 0 15 and eu 0 55 to 0 82 average 0 72 anomalies this shows that low temperature hydrothermal fluids played an important role in the formation of mineralization the ore deposition is similar to that of sedimentary exhalative mineralization deposited within the maden marginal basin

mineralogy geochemistry and the origin of high phosphorus oolitic iron ores of aswan egypt abstract the coniacian santonian high phosphorus oolitic iron ore at aswan area is one of the major iron ore deposits in egypt however there are no reports on its geochemistry which includes trace and rare earth elements evaluation texture mineralogy and origin of phosphorus that represents the main impurity in these ore deposits have not been discussed in previous studies in this investigation iron ores from three localities were subjected to petrographic mineralogical and geochemical analyses the aswan oolitic iron ores consist of uniform size ooids with snowball like texture and tangentially arranged laminae of hematite and chamosite the ores also possess detrital quartz apatite and fine grained ferruginous chamosite groundmass in addition to fe 2 o 3 the studied iron ores show relatively high contents of sio 2 and al 2 o 3 due to the abundance of quartz and chamosite p 2 o 5 ranges from 0 3 to 3 4 wt showing strong positive correlation with cao and suggesting the occurrence of p mainly as apatite x ray diffraction analysis confirmed the occurrence of this apatite as hydroxyapatite under the optical microscope and scanning electron microscope hydroxyapatite occurred as massive and structureless grains of undefined outlines and variable size 5 150 m inside the ooids and or in the ferruginous groundmass among trace elements v ba sr co zr y ni zn and cu occurred in relatively high concentrations 62 240 ppm in comparison to other trace elements most of these trace elements exhibit positive correlations with sio 2 al 2 o 3 and tio 2 suggesting their occurrence in the detrital fraction which includes the clay minerals ree ranges between 129 5 and 617 ppm with strong positive correlations with p 2 o 5 indicating the occurrence of ree in the apatite chondrite normalized ree patterns showed lree enrichment over hree la yb n 2 3 5 4 and negative eu anomalies eu eu 0 75 0 89 the oolitic texture of the studied ores forms as direct precipitation of iron rich minerals from sea water in open space near the sediment water interface by accretion of feo sio 2 and al 2 o 3 around suspended solid particles such as quartz and parts of broken ooliths the fairly uniform size of the ooids reflects sorting due to the current action the geochemistry of major and trace elements in the ores reflects their hydrogenous origin the oolitic iron ores of the timsha formation represent a transgressive phase of the tethys into southern egypt during the coniacian santonian between the non marine turonian abu agag and santonian campanian um barmil formations the abundance of detrital quartz positive correlations between trace elements and tio 2 and al 2 o 3 and the abundance mudstone intervals within the iron ores supports the detrital source of fe this prediction is due to the weathering of adjacent land masses from cambrian to late cretaceous the texture of the apatite and the ree patterns which occurs entirely in the apatite exhibits a pattern similar to those in the granite thus suggesting a detrital origin of the hydroxyapatite that was probably derived from the precambrian igneous rocks determining the mode of occurrence and grain size of hydroxyapatite assists in the maximum utilization of both physical and biological separation of apatite from the aswan iron ores and hence encourages the use of these ores as raw materials in the iron making industry

arsenic bearing manganese ore of the mukulu enrichment in the kalahari manganese field south africa a new discrimination scheme for kalahari manganese ore abstract the thrusted manganese ore above the blackridge thrust fault in the kalahari manganese field south africa has undergone three significant alterations events namely the wessels alteration event the newly identified mukulu enrichment and classic supergene alteration along the kalahari unconformity alteration during the mukulu enrichment is manifested in the precipitation of fluorapatite within the thrusted manganese ore resulting in a distinct supergene related enrichment in arsenic using the low grade diagenetic mamatwan type manganese ore from mamatwan mine in the south of the kalahari manganese field as a reference protolith ore a geochemical distinction has been established between the high vanadium bearing classic supergene altered ore below the kalahari unconformity the arsenic bearing ore of the mukulu enrichment and the high nickel and copper bearing high grade wessels type ore utilising these alteration specific geochemical signatures unique to the area a new method of ore discrimination has been established for the manganese ore types of the kalahari manganese field

titan imagery with keck adaptive optics during and after probe entry 1 we present adaptive optics data from the keck telescope taken while the huygens probe descended through titan s atmosphere and on the days following touchdown no probe entry signal was detected our observations span a solar phase angle range from 0 05 up to 0 8 with the sun in the west contrary to expectations the east side of titan s stratosphere was usually brightest compiling images obtained with keck and gemini over the past few years reveals that the east west asymmetry can be explained by a combination of the solar phase angle effect and an enhancement in the haze density on titan s morning hemisphere while stratospheric haze was prominent over the northern hemisphere tropospheric haze dominated the south from the south pole up to latitudes of 45 s at 2 1 mm this haze forms a polar cap while at 1 22 mm it appears in the form of a collar at 60 s a few small clouds were usually present near the south pole at altitudes of 30 40 km our narrowband j h k images of titan s surface compare extremely well with that obtained by cassini iss down to the small scale features the surface contrast between dark and bright areas may be larger at 2 mm than at 1 6 and 1 3 mm which would imply that the dark areas may be covered by a coarser grained frost than the bright regions and or that there is additional 2 mm absorption there

origin of ooidal ironstones in relation to warming events cretaceous eocene bakchar deposit south east western siberia abstract an integrated study involving petrographical mineralogical and geochemical investigations proposes the origin of the bakchar ironstone deposit by upward migration of a mixture of fe rich brine and hydrothermal fluid through marine sediments trace element concentrations of the ironstone deposits rule out continental derivation of fe while high ree concentrations indicate mixed hydrogeneous and hydrothermal source three main types of ironstone within the bakchar deposit are characterized by distinct mineralogical assemblage of authigenic minerals corresponding to oxic methanic and weakly sulfidic dysoxic conditions changing redox conditions of the depositional environment methane seepage in warm seawater and availability of iron influx possibly determined the final mineralogy of three varieties of ironstones the association of siderite with ferrimagnetic sulfides like greigite and pyrrhotite in type 1 ore indicate anaerobic oxidation of methane with limited bacterial sulfate reduction the ironstone deposits of narym kolpashevo and bakchar are contemporaneous with geological events like ocean anoxic event 3 oae 3 cretaceous paleogene k pg boundary and palaeocene eocene thermal maximum petm respectively all corresponding to warm seawater conditions

submillimeter scale topography of the lunar regolith we have applied computer stereophotogrammetry to apollo lunar surface closeup camera alscc pictures of the lunar surface to construct the first ever digital topographic relief maps of undisturbed lunar soil over spatial scales from 85 m to 8 5 cm using elevation histograms fractal analysis and hapke s photometric roughness model we show that apollo 14 fra mauro imbrium ejecta is rougher than average apollo 11 mare tranquilitatis and apollo 12 oceanus procellarum mare surfaces at submillimeter to decimeter size scales we confirm the early result of k lumme et al 1985 earth moon planets33 19 29 that the cumulative distribution of elevations for lunar soil is typically well described by gaussian statistics however cumulative distributions are insensitive to asymmetries in the shapes of elevation histograms of 11 discrete elevation histograms we measured about half exhibit significant deviations from gaussian behavior we also confirm lumme et al s finding that the roughnesses of all lunar surfaces increase with decreasing size scale we further show that the scale dependence of roughness is well represented by fractal statistics the rates of change of roughness with size scale represented by fractal dimension d are remarkably similar among terrians after correcting for the contribution of large scale roughness our average value of d 2 31 0 06 falls within the range 2 0 d 2 4 reported from lunar radar studies the amplitude of roughness which we characterize with the rms slope angle at 1 mm scale varies significantly among terrains for lunar mare the average rms slope angle is 16 4 3 and that for fra mauro regolith is 25 1 by comparison to radar data we suggest that the roughness of fra mauro imbrium ejecta regolith is similar to that of lunar highland terrains we find that the gaussian slope distribution assumed in b w hapke s model 1984 icarus59 41 59 adequately describes typical lunar regolith surfaces a revised form of hapke s equation that models realistic particle phase functions and the coherent backscatter opposition effect was fitted to disk resolved lunar photometric observations and yields estimates of 27 1 for highland and 24 1 for mare regolith these values of as well as the implied relative highland mare photometric roughness ratio are best matched in our elevation data by the cummulative contributions of surface topography covering all scales greater than 0 1 mm less than 5 of the photometrically detected roughness of lunar regolith is contributed by surface relief at scales larger than 8 cm this conclusion implies that values of derived from whole disk and disk resolved photometry respectively may be taken to represent the same physical quantity in addition particulate samples used in goniophotometric measurements should not be assumed to be photometrically smooth i e 0 as is often done in laboratory applications of hapke s photometric model the predicted photometric roughness at size scales of 0 1 mm and less significantly exceed photometric estimates and suggests that there exists a measurable size scale below which topographic relief either is not photometrically detectable or is not represented in the hapke model as macroscopic roughness

recent mn ag deposits in coastal hydrothermal springs in the baja california peninsula mexico hot springs with associated mn ag mineralization were identified in the intertidal zone of the bahia concepcion bay of the central eastern baja california peninsula hot spring activity is related to a system of nw se faults that are associated with the opening of the gulf of california the hot springs are hosted by miocene volcanic and volcaniclastic units of the comondu group the maximum discharge temperature recorded is 72 c with the ph ranging from 6 2 to 6 5 and salinity values reaching up to 27 g kg veins stockworks breccias crusts and organosedimentary stromatolites of silica carbonate and mn oxides are associated with the hot springs the mn oxide and silica deposits show an association with ag as ba ca cu mg pb sb sr tl v w and zn acanthite and native silver occur along with pyrite in a mineral assemblage rich in opal a todorokite romanechite aragonite high mg calcite and barite three distinct mineral associations characterized by sulfides sulfates and oxides are recognized the silver minerals formed late in the paragenesis textural evidence suggests a microbial mediation for the mn mineral deposition pourbaix diagrams for mn and ag species were constructed for the physicochemical conditions of the coastal hot springs these diagrams show that both mn and ag minerals are stable at low temperature 65 c and near neutral ph under slightly reducing or oxidizing conditions the characteristics of the subaerial to shallow submarine hot springs and the results of the geochemical modeling suggest that the hydrothermal system in the bahia conception bay is formed through convection of meteoric waters intermixed with some saline fluids or seawater

influence of palaeoclimate and hydrothermal activity on organic matter accumulation in lacustrine black shales from the lower cretaceous bayingebi formation of the yin e basin china abstract the lacustrine black shales of the lower cretaceous bayingebi formation are an important hydrocarbon source rock in the yin e basin it is important to understand the mechanism of organic matter accumulation in these shales to reconstruct the palaeoenvironment and palaeoclimate in the early cretaceous in northwestern china and search for potential oil and gas resources based on petrological elemental geochemical and organic geochemistry analyses of typical field profile samples the influence of palaeoclimate and hydrothermal activity on organic matter accumulation in different sedimentary units unit i ii and iii is revealed unit ii has the highest total organic matter abundance tocavg 5 95 mainly type i kerogen lamalginite which is in the immature to low mature stage organic carbon isotope data 13corg element ratios sr cu and c value and weathering indexes including cia ciw and pia together revealed that the region experienced a semihumid to semiarid palaeoclimate in the middle of the early cretaceous the increase in rainfall in unit ii enhanced the abundance of lake algae and surrounding terrestrial vascular vegetation and elevated the lake level which contributed to adequate sources and favourable preservation conditions for organic matter accumulation several lines of evidence including high sulfur contents the combination of vein pyrite and micritic dolomite positive eu anomalies and element geochemical correlations confirm the existence of intermittent low temperature white smoker type hydrothermal activity the decrease of oxygen content in lake bottom water may be related to the input of hydrothermal fluid which provided necessary nutrient elements for biological productivity according to palaeontological and radioisotope dating data it can be inferred that the black shales of the bayingebi formation are the product of the combined effect of global palaeotemperature rise in the early aptian stage of the early cretaceous and intermittent low temperature hydrothermal activity

mineralogy geochemistry and genesis of the ferromanganese ores from hazara area nw himalayas northern pakistan abstract ferromanganese ores occur in hazara area near abbottabad within the hazira formation of the kalachitta margala thrust belt of the nw himalayas of the indo pakistan plate in pakistan the hazira formation of cambrian age is a relatively thin unit up to 150 m thick which consists of either thin ferruginous siltstone with variable amounts of clay shale ferromanganese ores phosphorite and barite or thicker evenly bedded reddish brown siltstone it has a conformable lower contact with the abbottabad formation cambrian and an unconformable upper contact with the samana suk limestone jurassic the ferromanganese ores of the hazara area were studied in terms of their mineral and geochemical composition mineralogically a variety of mn and fe phases have been noticed in kakul galdanian and chura gali ferromanganese ores bixbyite is the principal mn phase while pyrolusite hollandite partridgeite and braunite occur in lesser amounts hematite however is the only fe phase in these ores gangue minerals include carbonates cryptocrystalline quartz iron clay and variable amounts of apatite plumbogummite and barite glauconite occurs in traces textural features suggest remobilization and subsequent precipitation of early diagenetic mn and fe phases along the fractures and interstices of the gangue minerals during later metamorphism chemical analyses show that the mn fe ratio in the ores is highly variable and ranges from 0 46 to 5 25 these ores exhibit a line of descent from lree to hree with a small positive ce anomaly their ree is higher than the hydrothermal mn deposits and lower than the hydrogenous crust the petrochemical characteristics suggest a mixed hydrothermal hydrogenetic source for the ferromanganese ores which have formed in shallow water or continental shelf environment due to the upwelling of anoxic deep seated water

geochemistry and origin of mn deposits in the waziristan ophiolite complex north waziristan pakistan the waziristan ophiolite complex is located along the western margin of the indian plate in northwestern pakistan the mn deposits in the saidgi and shuidar areas are part of this ophiolite complex these deposits both banded and massive in nature are hosted by metachert and are generally overlying metavolcanics braunite and cryptocrystalline quartz are the main constituents of the manganese ores in both areas hematite occurs in the shuidar deposits as a minor phase metacherts are microcrystalline aggregates of microcrystalline quartz chalcedony and lesser hematite chemically the studied mn deposits and associated metacherts are very similar to those formed by submarine hydrothermal effusive processes the deposits originated along sea floor spreading centers mid ocean ridges within the neo tethys ocean and were later obducted as part of the waziristan ophiolite complex

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

origins and antiquity of the island fox urocyon littoralis on california s channel islands abstract the island fox urocyon littoralis is one of few reportedly endemic terrestrial mammals on california s channel islands questions remain about how and when foxes first colonized the islands with researchers speculating on a natural human assisted or combined dispersal during the late pleistocene and or holocene a natural dispersal of foxes to the northern channel islands has been supported by reports of a few fox bones from late pleistocene paleontological localities direct ams 14c dating of these fossil fox bones produced dates ranging from 6400 to 200 cal yr bp however postdating human colonization of the islands by several millennia although one of these specimens is the earliest securely dated fox from the islands these new data support the hypothesis that native americans introduced foxes to all the channel islands in the early to middle holocene however a natural dispersal for the original island colonization cannot be ruled out until further paleontological archaeological and genetic studies especially adna ancient dna are conducted

mineralogy and geochemistry of neoproterozoic siliceous manganese formations from ntui betamba cameroon pan african fold belt implications for mineral exploration the siliceous manganese formations from ntui betamba area have been studied with the aim to constrain their mineralogy geochemistry and genesis neoproterozoic manganese bearing rocks at ntui betamba include garnet galaxite bearing quartzite and galaxite bearing quartzite that besides a characteristic quartz spessartine garnet and galaxite mnal2o4 assemblage comprises also graphite and rutile galaxite crystals show chemical zoning from core to rim due to the change in composition from galaxite to cryptomelane bulk rock geochemistry reveals that the studied rocks are characterized by high sio2 content 52 83 wt they are enriched in fe2o3 and al2o3 and display mn fe ratio of 1 2 mno concentrations are high in galaxite bearing quartzite 16 wt and moderate 8 03 wt in garnet galaxite bearing quartzite the transition trace metal co cu and ni contents are lower with co and cu markedly depleted relative to ni and variable contents of zn the ree pattern of garnet galaxite bearing quartzite shows ce positive anomaly similar to the hydrogenous sediment but differs from the later with strong eu negative anomaly and the lack of weak positive anomaly in yb whereas the galaxite bearing quartzite is characterized by the lack of ce anomaly and the weak eu negative anomaly both rocks show hree content close to that of hydrothermal sediment and exhibit flat hree trend the high contents of silica iron and aluminum together with the co zn ratios 0 3 and the contrasting behavior of ree suggest that the studied manganese bearing rocks are of sedimentary origin probably derived from a mixed hydrothermal hydrogenous source the high content of mn bearing minerals in these rocks represents indicators of concealed or buried mineralization and could be used as exploration guide

geochemistry and pb pb geochronology of the neoarchean nkout west metamorphosed banded iron formation southern cameroon the nkout west iron deposit of the northern edge of the congo craton in southern cameroon forms part of the northwest plunging isoclinal mega fold composed of metamorphosed banded iron formations bifs which have been deformed and metamorphosed resulting in recrystallized magnetite quartz and silicates here we present whole rock geochemistry together with pb pb isotopic compositions and dating of metamorphosed bif with the aim to constrain the genesis and elucidate the metamorphic resetting age based on the mineral composition two types of bif magnetite bif garnet bif have been distinguished the magnetite bif shows high sio2 and fe2o3 and low al2o3 tio2 hfse and ree contents similar to detritus free chemical sediments in contrast their high concentrations in garnet bif indicate clay rich contaminated input the co zn ratios are consistent with trace metals of hydrothermal sources 0 14 for magnetite bif or with minor hydrogenous component 0 27 for garnet bif the paas normalized ree y patterns of the studied metamorphosed bifs show lree depletion relative to hree and positive eu anomalies the magnetite bif exhibits positive y anomaly y y paas 1 3 which is the signature inherited from sea water but its y ho 39 93 ratio suggests a mixture of hydrothermal solution with sea water the garnet bif shows positive eu negative y anomalies and chondritic y ho ratio 27 49 which is consistent with hydrothermal solution with significant clastic contamination whole rock pb concentration is roughly on average of 2 0 6 0 ppm suggesting a hydrothermal pb source the pb pb dating yielded an age of 2679 ma interpreted as the neoarchean metamorphic event in the ntem complex

earliest record of sinicuon in zanda basin southern tibet and implications for hypercarnivores in cold environments abstract the out of tibet hypothesis envisions late cenozoic tibetan mammals acquiring adaptations to cold environments and being ancestral to several eurasian megafaunal species in the pleistocene here we report an early record of a hypercarnivorous canid sinicuon cf sinicuon dubius from zanda basin in the himalaya range although the new record is recovered from reworked sediments in a pleistocene alluvium we can constrain the fossil to within a narrow age range of 3 8 3 4 ma in the middle pliocene presence of this hypercarnivorous canid in the pliocene of tibet along with the recently described pantherine cat and arctic fox suggests a predator guild with predominately carnivorous diet characteristic of modern arctic carnivorans such as the arctic fox and polar bear wintering in extremely cold climates may have been the cause of such adaptations sinicuon shows transitional morphology to modern hypercarnivorous hunting dogs in southern asia cuon suggesting linkage of the high tibetan plateau to the southern continents

geochemistry and depositional environment of mn oxide deposits in the tokoro belt northeastern hokkaido japan numerous early cretaceous mn oxide and mn fe deposits are distributed in the tokoro belt northeastern hokkaido japan the mn oxide deposits usually occur in the southwestern part of the belt and within bedded cherts whereas the mn fe deposits are restricted to the northeastern part of the belt and occur between bedded cherts and underlying basaltic pillow lava the mn oxide ores are characterized by low fe mn ratios and the trace element concentrations and rare earth element ree patterns are similar to those of the submarine hydrothermal mn deposits distribution patterns of trace elements co ni cu and zn and ree in the mn oxide ores determine two types of deposits hydrogenous deposits which have relatively high concentrations and submarine hydrothermal deposits which have low concentrations these compositional trends and geologic evidences of the tokoro mn deposits suggest that the fe phases precipitated first closer to their source whereas the mn phases deposited later at a distance from their source some hydrogenous effects on the mn oxide deposits are due to the adsorption of trace elements from seawater trace element concentrations of tokoro mn oxide deposits show that they formed within 40 km from their source

insular dwarfism in canids on java indonesia and its implication for the environment of homo erectus during the early and earliest middle pleistocene abstract several canid fossils which were originally discovered and described in the early 20th century are known from early and earliest middle pleistocene of java indonesia here we revise the taxonomy and relative age of the javanese canid fossils in light of recent developments in the taxonomy and phylogeny of canidae and new insights in the evolution of island mammals results show that cuon was absent during the early and earliest middle pleistocene while the large sized xenocyon previously megacyon was present in the early pleistocene and replaced by the small sized xenocyon previously mececyon during the earliest middle pleistocene the latter is probably an anagenetic dwarf derived from the larger form of the preceding period the change in body size of xenocyon on java over time is likely the effect of increased competition within the carnivore guild within the restricted boundaries of the island simultaneously with a pronounced body size shift a dietary shift from large sized prey to much smaller prey must have taken place in order to meet energetic constraints the degree of endemism of terrestrial mammals of the earliest middle pleistocene horizon of the site trinil which has also yielded homo erectus fossils indicates that during this period java was marginally isolated which allowed for a corridor dispersal to the island with subsequent vicariance the nature and degree of isolation may have been similar to that of late pleistocene sicily but of a longer duration given the higher degree of dwarfism of the stegodon antilope and canid the following continentalisation enabled the invasion by mainland terrestrial mammals as is seen in younger layers at trinil and eventually by homo sapiens and cuon in the late pleistocene holocene

landscape development preceding homo erectus immigration into central java indonesia the sangiran formation lower lahar abstract the sangiran dome is the primary stratigraphic window for the solo basin a coastal feature on the pliocene pleistocene sunda subcontinent south margin in the dome the lower lahar unit llu is a lahar type debris flow overlying near shore marine sediments the event that emplaced the llu likely originated from sector collapse on a neighboring volcanic edifice freshwater mollusc fossils in the llu indicate that swamps or shallow lakes lay between the edifice and the current dome area 40ar 39ar analyses on hornblende separates from six pumice lenses suggest that the llu was deposited as early as 1 90 0 02 ma the event resulting in deposition of the llu transformed late pliocene near shore marine environments into estuarine and marsh settings shortly thereafter glacioeustatic sea level falls completed the local transition to fully terrestrial environments that attracted homo erectus to southernmost sunda in the early pleistocene

early pleistocene 40ar 39ar ages for bapang formation hominins central jawa indonesia the sangiran dome is the primary stratigraphic window for the plio pleistocene deposits of the solo basin of central jawa the dome has yielded nearly 80 homo erectus fossils around 50 of which have known findspots with a hornblende 40 ar 39 ar plateau age of 1 66 0 04 mega annum ma reportedly associated with two fossils swisher c c iii curtis g h jacob t getty a g suprijo a widiasmoro 1994 science 263 1118 1121 the dome offers evidence that early homo dispersed to east asia during the earliest pleistocene unfortunately the hornblende pumice was sampled at jokotingkir hill a central locality with complex lithostratigraphic deformation and dubious specimen provenance to address the antiquity of sangiran h erectus more systematically we investigate the sedimentary framework and hornblende 40 ar 39 ar age for volcanic deposits in the southeast quadrant of the dome in this sector bapang kabuh sediments have their largest exposure least deformation and most complete tephrostratigraphy at five locations we identify a sequence of sedimentary cycles in which h erectus fossils are associated with epiclastic pumice from sampled pumice eight hornblende separates produced 40 ar 39 ar plateau ages ranging from 1 51 0 08 ma at the bapang sangiran formation contact to 1 02 0 06 ma at a point above the hominin bearing sequence the chronological sequence of 40 ar 39 ar ages follows stratigraphic order across the southeast quadrant an intermediate level yielding four nearly complete crania has an age of about 1 25 ma

titan s meridional wind profile and huygens orientation and swing inferred from the geometry of disr imaging abstract the altitude and zonal motion of the huygens probe descending through titan s atmosphere was determined early under the assumption of no meridional motion bird et al 2005 nature 438 800 802 by comparing images taken during the descent karkoschka et al karkoschka et al 2007 planet space sci 55 1895 1935 determined the meridional motion of huygens which was generally much smaller than its zonal motion here we present a comprehensive geometrical analysis of all images taken during the descent that is four times more accurate than the previous study the result is a meridional wind profile across titan s troposphere with northward winds by up to 0 4 m s with an average of 0 1 m s above 1 km altitude and southward winds below peaking at 0 9 m s near 0 4 km altitude the imaging data extend down to 0 22 km altitude although additional information came from the horizontal impact speed near 0 8 m s southward schroder et al 2012 planet space sci 73 327 340 there is a region between 5 and 8 km altitude with no significant meridional wind in the stratosphere the average meridional wind was 1 2 1 5 m s northward and zero meridional motion is possible down to 15 km altitude we present the difference between the zonal speeds of huygens and the wind that was ignored in previous publications and amounts to up to 7 m s we determined the three rotational angles of huygens for the times of each exposure that showed surface features during 26 exposures the swing speed of huygens was fast enough to smear images inferred swing speeds were up to 20 s during the calm phase of the descent consistent with up to 40 s swings reported before during the rough phase the improved geometric calibration of images allowed identification of many features also seen in cassini radar images this comparison yields the location of the huygens landingsite as 192 34 02 west and 10 47 0 02 south

paleo sedimentary environment in relation to enrichment of organic matter of early cambrian black rocks of niutitang formation from xiangxi area china abstract early cambrian organic rich black rocks are extensively distributed in the southern china in this study we have discussed the relation of paleo sedimentary environments with enrichment of organic matter based on toc data we divided the niutitang formation into three parts upper middle and lower the amount of total organic carbon in the lower 1 55 wt and the upper part 1 35 wt of niutitang formation is significantly smaller than the middle part 8 0 wt which suggest initial transgression and regression stages of the sea level respectively the middle part from both sections longbizui and sancha contains higher toc content which is a clue of intense transgression stage of sea level with high bio productivity kerogen type index kti using different macerals specify the organic matter in these black rock series is mainly type i with a minor amount of type ii1 moreover these black rocks were deposited in weak to moderately restricted hydrographic conditions the heterogenic mineral composition was also observed in these black rocks including quartz clay gypsum pyrite barite dolomite and plagioclase quartz content in the middle part is relatively higher than the upper and the lower part displays a strong positive relation with toc which suggests the main source of quartz during deposition of the middle part was biogenic quartz during early cambrian period due to extension between the yangtze and the cathaysian plate the hydrothermal fluids rich in uranium vanadium molybdenum zinc barium etc from the deeper part of the earth crust and entered the ocean basin through extensional remnant fissures and cracks and due to upwelling phenomena entered to the shelf area these nutrient rich deep crustal fluids at the surface of the sea enhanced the evolution and breeding of planktons and other marine life meanwhile it upsurges the bio productivity additionally it creates bottom water hypoxia which is favourable for the preservation of organic matter in the sedimentary rocks the main factors responsible for the enrichment of organic matter in these early cambrian black rock series of niutitang formation were a hydrographic restriction hydrothermal activities and paleo redox conditions respectively

titan s surface revealed by hst imaging we present for the first time relative albedo maps of titan s surface the maps were made from images taken by the hubble space telescope s planetary camera 295 km per pixel through atmospheric windows at 940 and 1080 nm coverage at all longitudes and between 45 s and 60 n was obtained with 14 orbits from 4 18 october 1994 each image is characterized by haze with both limb effects brightening and a large north south contrast subtracting an averaged image from each frame removes haze effects and reveals surface features of 10 maximum contrast many features are clearly visible in multiple images and in both filters but the surface map is dominated by a large bright roughly rectangular feature centered at 110 w 10 s and elongated in an east west direction 4000 2500 km2 this feature and others indicate the diversity of titan s surface we consider the origin of the bright feature in an otherwise dark landscape and suggest that highland washing by methane rainfall is a likely mechanism

the late quaternary palaeogeography of mammal evolution in the indonesian archipelago abstract the quaternary faunal evolution for the indonesian archipelago reflects the unique relationship of each island with se asian mainland the recent sub faunas of sundaland kalimantan sumatra java and bali preserved broad connections with the se asian mainland during the latest glacial they are all balanced and show many mainland components alternatively wallacea sulawesi and the lesser sunda islands has always been geographically isolated from the mainland wallacea faunas thus remain unbalanced they lack large carnivores and endemic a significant turnover arrives throughout the region with pronounced global sea level recessions around 0 8 ma during the transition from early pleistocene ep to the middle pleistocene mp by way of comparison the palaeontological records of japan and taiwan also preserve this turnover with ep mp recessions bringing east asian mainland immigrants on java the earliest late pliocene to early pleistocene satir fauna indicates island conditions java became connected to the se asian mainland towards the end of the early pleistocene global cooling brought open woodlands on java an environment evidently preferred by homo erectus in the ci saat fauna and trinil h k fauna as ep mp sea level recessions created a wide corridor across the sunda shelf siwaliks and the se asian mainland terrestrial mammals invaded as is seen in the kedung brubus fauna the succeeding ngandong fauna maintains an open woodland character but shows some endemism homo erectus and stegodon trigonocephalus among others can be distinguished on a subspecies level the late pleistocene marks the earliest known tropical rainforest and the corresponding punung fauna is of chinese affinity with pongo hylobates and elephas maximus homo sapiens probably arrives at this point as well the youngest fossil faunas known from java are the still poorly known cipeundeuy fauna ca 30 ka and the holocene faunas from wajak and sampung while sulawesi and flores remained isolated throughout the quaternary only a limited number of terrestrial vertebrates arrived by crossing sea barriers endemic island faunas with pygmy elephantoids and giant tortoises were present during the early pleistocene ep mp sea level recessions allowed large to medium sized elephantoids to replace the dwarf species around the same time homo erectus appears on the island of flores modern faunas eventually replaced the middle pleistocene island faunas but the time frame has yet to be pinpointed sulawesi presents a unique case its current fauna holds no walanae representatives apart from the phalangers which must have come from the east the ancestors of all other large sulawesi land vertebrates fossil and extant reached the island by crossing the sunda sea as the south sulawesi fauna was stable until the middle pleistocene this area must have constituted a separate palaeo island some localized developments can be observed e g shortening of the metapodials in celebochoerus increasing hypsodonty in stegodon

a mixed seawater and hydrothermal origin of superior type banded iron formation bif hosted kouambo iron deposit palaeoproterozoic nyong series southwestern cameroon constraints from petrography and geochemistry abstract the kouambo iron deposit contains banded iron formations bifs and is located in the northwestern margin of the congo craton the bifs are hosted in palaeoproterozoic nyong series a dominantly metasedimentary formations which were metamorphosed into greenschist to granulite facies the kouambo bifs are medium to coarse grained banded rocks consisting of alternation of si rich and fe rich mesobands and belong to oxide facies iron formations geochemistry analyses reveal that these iron formations are composed of 96 wt fe2o3 and sio2 and have low concentrations of al2o3 tio2 and trace hfse suggesting chemical precipitates of silica and iron moreover these bifs have low concentrations of al2o3 tio2 and trace hfses high field strength elements e g zr hf ta pb and th suggesting that terrigenous detrital materials contributed insignificantly to the sedimentation the post archean australian shale paas normalized ree y patterns display seawater like profile minor lree depletion and hree enrichment positive y anomalies however they display positive eu and negative ce anomalies and low y ho ratio average 29 which suggest the influence of the hydrothermal fluids the weak positive eu eu paas ratio average 1 5 associated with the low v 17 5 ppm co 6 1 ppm and ni 27 5 ppm contents similar to other superior type bifs worldwide are consistent with the deposition of the kouambo bifs in continental marginal sea or back arc basin environment in summary the kouambo bifs show a seawater like ree y signature however the positive eu anomalies and reduced y ho ratios relative to seawater indicates a possible mixing with hydrothermal fluids 0 5

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

ni cu co rich hydrothermal manganese mineralization in the wallis and futuna back arc environment sw pacific abstract the wallis and futuna back arc system is a complex area composed of at least two active oceanic spreading centers the futuna and alofi spreading centers and young volcanic zones characterized by diffuse magmatism locally affected by the samoan hotspot this geological setting is favorable to the establishment of hydrothermal systems in the form of either high temperature ht hydrothermal venting or low temperature lt diffuse flow during the 2010 futuna cruise aboard the r v l atalante three remarkable inactive lt fe si mn deposits were discovered utu uli anakele and utu sega some of the mn rich precipitates discovered exhibit the highest base metals concentrations so far recorded in ferromanganese rocks including in the well documented hydrogenetic crusts and polymetallic nodules the deposits lie on top of volcanoes and formed in close association with the volcanic facies the manganese mineralization occurs in the form of massive layered crusts and mn rich cements within strongly altered basaltic pyroclastic rocks brecciated lavas and more rarely in sediments field observations and mineralogical and chemical studies support a hydrothermal origin for the mineralization and show that nickel cobalt and copper enrichments are controlled by the precipitation of 7 a and 10 a manganates the conventional geochemical classifications e g bonatti et al 1972 used to decipher the origin of mn mineralization cannot be used for this new type of deposit and new robust discrimination diagrams need to be established we suggest that the unusual enrichment of metals recorded in our samples is due to i a lack of precipitation of high temperature massive sulfides at depths that would have retained metals e g cu ni co ii isolation of the hydrothermal system thereby avoiding ni co and cu losses in the water column and iii the ability of birnessite and buserite todorokite to scavenge co ni and cu from aqueous fluids the utu uli and anakele deposits share certain characteristics with the active hydrothermal system at loihi seamount e g the depth of mineralization relationships with pyroclastic volcanoes and the influence of a mantle plume source and thus might represent late stage products of this specific type of hydrothermal activity elsewhere the co rich mineralization of the calatrava volcanic field cvf in spain may be a potential analog of the utu sega deposit the mn co deposits of the cvf formed in close proximity to pliocene volcanic rocks metals were transported by epithermal hydrothermal solutions with high fo 2 and cobalt was scavenged by mn oxides together with the well documented stratabound mn deposits gonzalez et al 2016 hein et al 2008 hein et al 1996 the mn deposits discovered in the wallis and futuna back arc provide crucial insights into lt hydrothermal activity in the deep ocean the metal rich character of this lt hydrothermal activity may be of major importance for future research on the net flux of hydrothermally derived metals e g ni co cu to the open ocean

manganese and ferromanganese ores from different tectonic settings in the nw himalayas pakistan abstract in pakistan manganese and ferromanganese ores have been reported from the hazara area of north west frontier province waziristan agencies in the federally administered tribal areas and the lasbela khuzdar regions of baluchistan this study is focused on comparison of mineralogy and geochemistry of the continental ferromanganese ores of hazara and the ophiolitic manganese ores of the waziristan area of pakistan in the hazara area ferromanganese ores occur at kakul galdanian and chura gali near abbottabad within the hazira formation of the kalachitta margala thrust belt of the nw himalayas of the indo pakistan plate the cambrian hazira formation is composed of reddish brown ferruginous siltstone with variable amounts of clay shale ferromanganese ores phosphorite and barite in waziristan manganese ores occur at shuidar mohammad khel and saidgi within the waziristan ophiolite complex on the western margin of the indo pakistan plate in nw pakistan these banded and massive ores are hosted by metachert and overlie metavolcanics the ferromanganese ores of the hazara area contain variable amount of bixbyite partridgeite hollandite pyrolusite and braunite bixbyite and partridgeite are the dominant mn bearing phases hematite dominates in fe rich ores gangue minerals are iron rich clay alumino phosphate minerals apatite barite and glauconite are present in variable amounts in both fe rich and mn rich varieties the texture of the ore phases indicates greenschist facies metamorphism the waziristan ores are composed of braunite with minor pyrolusite and hollandite hematite occurs as an additional minor phase in the fe rich ores of the shuidar area the only silicate phase in these ores is cryptocrystalline quartz the chemical composition of the ferromanganese ores in hazara suggests that the mn fe was contributed by both hydrogenous and hydrothermal sources while the manganese ores of waziristan originated only from a hydrothermal source it is suggested that the fe mn ores of the hazara area originated from a mixed hydrothermal hydrogenetic source in shallow water in a ontinental shelf environment due to the transgression and regression of the sea while the mn ores of waziristan were formed at sea floor spreading centers within the neo tethys ocean and were later obducted as part of the waziristan ophiolite complex

mineral precipitation sequence and formation of the lacustrine hydrothermal sediments in the lower cretaceous tenggeer formation in the baiyinchagan sag china abstract cores from the lower cretaceous tenggeer formation in the baiyinchagan sag of the erlian basin present dolomitic mudstones and argillaceous dolostone with white grains and laminae thin section x ray diffraction xrd electron microprobe empa and scanning electron microscopy sem analyses show that in addition to terrigenous clastics dolomite analcime natrolite pyrite pistomesite fluorite talc barite etc are abundant compared with the conventional lacustrine sediments these rocks contain highly abundant exhalative textures and structures such as laminae and banded textures disseminated textures mesh vein structures breccia structures and contemporaneous deformations these types of mineral associations rock textures and structures are specific and uncommon previous works indicate that these rocks are of hydrothermal origin in this study we provide supplementary evidence and recognition to support the lacustrine hydrothermal sediment origin and further study the mineral precipitation sequence and formation conditions and processes with the use of 3d seismic data the magmatic intrusions hydrothermal ducts and hydrothermal vents are first identified on seismic sections the ni co zn and fe mn cu ni co 10 ternary diagrams confirm the hydrothermal origin of these sediments the sr ba ratio v v ni ratio oxygen and carbon isotope values of carbonate ph and eh values suggest anoxic reducing and alkaline sedimentary conditions based on the analysis of fluid inclusions rock textures and structures we find that the precipitation of minerals occurred in a specific sequence pyrite pistomesite analcime natrolite dolomite the nature of the magmatic intrusions the changes in environmental variables and fluid energy and the flow distance may be the controlling factors of this specific sequence a mode of lacustrine white smoker type hydrothermal sedimentation is presented in this study as the hydrothermal fluid sourced from the intermediate basic magmatic basement enriched in fe2 mg2 al3 si4 ca2 na and co32 rose and mixed with cool lake water ferromagnesian aluminosilicate and carbonate minerals formed successively from the ducts to the vicinity of the vents pulsing exhalation and overflow formed alternating deposits of hydrothermal sediments and lacustrine mudstones

the disr imaging mosaic of titan s surface and its dependence on emission angle abstract the disr descent image spectral radiometer imagers took about 300 images during the descent of the huygens probe in titan s atmosphere we combined them into a photometrically calibrated mosaic of titan s surface within 100 km of the huygens landing site with a resolution ranging from 1 km at 100 km distance from the landing site to 50 cm near the landing site we analyzed how the reflectivity of each location varies with the changing phase angle and emission angle during the descent we found strong variations with the emission angle but no significant variation of the surface phase function the latter is possibly obscured by the diffuse nature of illumination by titan s sky at visible wavelengths we constructed a map of this emission angle dependence which represents a measure of surface reflectivity and roughness of the terrain titan s surface probed by the images shows various terrain types with a small correlation between reflectivity and roughness we propose that variations in the emission angle dependence might be correlated with average tilt angles of the surface we detected elevated terrain in the bright highland north of the landing site as published by soderblom et al soderblom l a et al 2007 planet space sci 55 2015 2024 but their high ridges in the lakebed appear mostly flat in our analysis we integrated the color information from the disr spectrometers into our mosaic to create a color map we also compared the features seen in maps of the reflectivity the emission angle dependence and color to features seen in cassini radar images finally we provide a refined version of the images from huygens after landing down to a resolution of 2 mm

characteristics of pleistocene megafauna extinctions in southeast asia the extinction of large bodied taxa from the pleistocene in southeast asia is examined although the chronological resolution of these extinctions is poor and number of excavations in the region relatively few broad characteristics of these extinctions can be described many taxa which became extinct appear to have been endemic to regions within southeast asia while some taxa which experienced extinction or severe range reduction occurred in several regions members of the latter group include proboscideans stegodon and palaeloxodon the pygmy hippopotamus hexaprotodon the orangutan pongo hyenas crocuta and hyaena the giant panda ailuropoda tapirs tapirus and megatapirus rhinoceroses rhinoceros and the giant asian ape gigantopithecus the loss of these species cannot be assigned to a single cause rather their disappearance is likely tied to both climatic and human agents unlike other regions which experienced megafauna extinctions eustatic changes in sea level in southeast asia seems to have been an important factor

late archean manganese mineralization and younger supergene manganese ores in the anmod bisgod region western dharwar craton southern india geological characterization palaeoenvironmental history and geomorphological setting abstract the field setting mineralogical geochemical genetic and depositional features of late archean metasedimentary manganese as well as cenozoic supergene manganese and ferromanganese ores along the 75 km long linear tract of the anmod bisgod region in the western dharwar craton southern india are described the 2700 ma metasedimentary manganiferous formation is underlain by stromatolitic limestone dolomite and quartzite arenite and also occurs within the former the older quartzite arenite which contains redox sensitive detrital pyrite and uraninite as well as thucolite indicates sedimentation under anoxic to oxic transitional palaeoenvironmental condition whereas the younger stromatolitic limestone dolomite indicates development of oxygen in the depositional environment the manganese ore types have been classified into three categories one of which is a mn rich duricrust once capping the late archean manganiferous formation it formed during a cenozoic lateritic weathering event and was eroded in response to crustal uplift perhaps uniquely clastic deposits of the eroded mn duricrust occur in mineable quantities in the form of fluvial palaeochannel fills these cryptomelane rich supergene ores are also suitable for radiometric dating knowing their age would help to constrain the timing of mn duricrust formation and indirectly the regional weathering event responsible for the extensive laterite occurrences of southern india

the palaeoenvironmental context of the palaeolithic of java a brief review abstract the earliest palaeolithic implements found in java island are older than 1 ma postdating the oldest homo erectus fossils the archaeological record subsequently documents acheulean like tools in early middle pleistocene deposits a diversity of flake tools assemblages found in late middle early upper pleistocene sites and the conspicuous development of cave occupations during the end of the pleistocene and the early holocene the environment mostly forested during the lower pleistocene underwent important changes during the setup of mid pleistocene climatic conditions then at the beginning of the upper pleistocene and at the boundary between mis 2 and 1 its reconstructions must also consider more local factors e g the repetitive effects of the tectonic and volcanic activities which had severe consequences on local climate on the palaeogeography and the vegetal formations or even isolation of faunistic and floristic groups examples presented here broach the context of ancient human settlements and adaptation from a multidisciplinary viewpoint that includes the study of the vegetal cover and the availability of lithic raw material the associated vertebrate faunas considered both as an environmental proxy and as a subsistence resource reflect the contrasts between periods of contact with the mainland increased biodiversity and periods of isolation favouring endemism and also the impact of local environmental constraints

titan s diverse landscapes as evidenced by cassini radar s third and fourth looks at titan abstract cassini s third and fourth radar flybys t7 and t8 covered diverse terrains in the high southern and equatorial latitudes respectively the t7 synthetic aperture radar sar swath is somewhat more straightforward to understand in terms of a progressive poleward descent from a high dissected and partly hilly terrain down to a low flat plain with embayments and deposits suggestive of the past or even current presence of hydrocarbon liquids the t8 swath is dominated by dunes likely made of organic solids but also contain somewhat enigmatic probably tectonic features that may be partly buried or degraded by erosion or relaxation in a thin crust the dark areas in t7 show no dune morphology unlike the dark areas in t8 but are radiometrically warm like the dunes the huygens landing site lies on the edge of the t8 swath correlation of the radar and huygens disr images allows accurate determination of its coordinates and indicates that to the north of the landing site sit two large longitudinal dunes indeed had the huygens probe trajectory been just 10 km north of where it actually was images of large sand dunes would have been returned in place of the fluvially dissected terrain actually seen illustrating the strong diversity of titan s landscapes even at local scales

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

petrography mineralogy and geochemistry of the late eocene oolitic ironstones of the jebel ank southern tunisian atlas abstract the oolitic ironstones ore deposit of jebel ank central tunisia is a simply folded stratiform ore body of about 2 5 8 m thickness located in the upper part of the epicontinental souar formation late eocene and is covered by the continental segui formation mio pliocene the deposit contains about 20 mt of ore with an average grade of 50 fe generally oolitic iron deposition occurs in shallow water lagoonal environments the jebel ank deposit lies between two regional disconformities late eocene and miocene and is evidence of a transitional stage at the end of regional regression before renewed transgression the footwall of the oolitic iron ore bearing bed consists of a fine grained sandstone bed 10 20 cm thick pinching out laterally westward into green clays the hanging wall is composed of thin bedded limestone and clay alternations 2 3 5 m thick iron occurs in the form of cryptocrystalline goethite with limited al fe substitution the goethite contains around 48 fe 5 al and up to 1 5 p jarosite alunite and manganese minerals cryptomelane psilomelane and manjiorite are supergene secondary minerals probably related to descending surface fluids these manganese minerals occur as accessory minerals with the goethite and are most abundant at the lowermost part of the succession showing varied morphologies local cement space filling and free centimeter sized nodules fe oolites in the deposit are similar to those documented in many other oolitic ironstone deposits the dominant fe oolite type 90 has a concentrically laminated cortex with no nucleus the nuclei of the oolites that do have a nucleus are most commonly detrital quartz grains major elements in high grade samples fe 2 o 3 65 vary within a limited range and show higher concentrations of sio 2 average 7 85 and al 2 o 3 average 5 1 with minor tio 2 mno mgo na 2 o k 2 o and so 3 less than 1 paas normalized trace elements of bulk samples and fe oolite generally show similar behavior both are enriched in v co ni mo as zn and y and are depleted in cu rb zr nb ba and hf anomalous v cr ni zn and ree y are correlated with goethite paas normalized ree y patterns of both bulk samples and fe oolite show slight hree enrichment positive ce with negative y anomalies the mineralogy goethite and cryptomelane along with the geochemistry si vs al as cu mo pb v zn vs ni co binary plots zn ni co triangular diagram ree y content and patterns and ce ce vs nd and ce ce vs y n ho n binary plots of the studied oolitic ironstone are congruent with a hydrogenetic type while two possible sources of iron for jebel ank ironstone can be proposed i submarine weathering of glauconite rich sandstone and ii detrital iron from adjacent continental hinterland the later is the more plausible source of iron based on paleogeographic setting the occurrence of fine sandstone underlying the iron level occurrence of mn ores in the lower part of the fe ores succession high phosphorous zinc ree y concentrations and y ho ratios and low la ce ratios