sedimentary pyrite formation an update sedimentary pyrite formation during early diagenesis is a major process for controlling the oxygen level of the atmosphere and the sulfate concentration in seawater over geologic time the amount of pyrite that may form in a sediment is limited by the rates of supply of decomposable organic matter dissolved sulfate and reactive detrital iron minerals organic matter appears to be the major control on pyrite formation in normal non euxinic terrigenous marine sediments where dissolved sulfate and iron minerals are abundant by contrast pyrite formation in non marine freshwater sediments is severely limited by low concentrations of sulfate and this characteristic can be used to distinguish ancient organic rich fresh water shales from marine shales under marine euxinic conditions sufficient h2s is produced that the dominant control on pyrite formation is the availability of reactive iron minerals calculations based on a sulfur isotope model indicate that over phanerozoic time the worldwide average organic carbon to pyrite sulfur ratio of sedimentary rocks has varied considerably high cs ratios during permo carboniferous time can be explained by a shift of major organic deposition from the oceans to the land which resulted in the formation of vast coal swamps at that time low cs ratios compared to today during the early paleozoic can be explained in terms of a greater abundance of euxinic basins combined with deposition of a more reactive type of organic matter in the remaining oxygenated portions of the ocean the latter could have been due to lower oceanic oxygen levels and or a lack of transportation of refractory terrestrial organic matter to the marine environment due to the absence of vascular land plants at that time

40ar39ar dating of combustion metamorphism mottled zone israel tertiary surface combustion of cretaceous bituminous sediments in israel produced high t low p metamorphic assemblages which were dated by conventional k ar and 40ar39ar techniques meaningful ages were obtained from samples of high metamorphic grade and k content higher than 0 8 containing sanidine anorthite gehlenite and zeolites in these minerals the k ar system has been reset and equilibrated with atmospheric ar yielding a mean age of 3 1 ma 40ar39ar plateau and isochron ages for four whole rock samples range between 2 3 and 4 0 ma one gehlenite rock yielded an 40ar39ar age of 16 0 2 ma 1 these results indicate a major combustion metamorphic event around 3 ma probably preceded by an event around 16 ma the early event took place upon initial exposure of the protolith in the miocene whereas the second followed the removal of neogene sediments and re exposure of the bituminous rocks

development of incisions on a periodically emergent carbonate platform natih formation late cretaceous oman abstract subaerial exposure of carbonate platforms is generally recorded by karstification and pedogenesis whereas erosion features such as incisions along emersion surfaces have seldom been observed and studied however the recognition of incisions and the characterization of their fill may facilitate definition and hierarchy of sequence boundaries especially along exposure surfaces that do not otherwise present clear petrographic evidence for emersion in the natih formation late albian early turonian oman two successive incision surfaces are present in the upper part of the first third order depositional sequence seismic interpretation of regional subsurface data has allowed the quantification of progradational geometries within the natih sequence i carbonate platform and the correlation of incision surfaces with forced regressive prograding wedges on the margins of the intrashelf basin detailed geological sections and correlations have been made from three outcrop localities allowing a precise description of geometries and facies of incision fills morphology orientation and extent of these incisions have been assessed from detailed seismic interpretation coupled with forward seismic modeling the integration of outcrop and seismic data sets at the regional and local scales allows the interpretation and discussion of the origin and factors controlling the development of these incisions and a refinement of the stratigraphic model these two incisions record rapid sea level variations 500 ky with a magnitude of approximately 20 and 30 m that occurred during the early cenomanian this is probably not a unique case since for the same time interval incisions have been observed in siliciclastic systems in western canada and india and in carbonate systems on the arabian plate

a tale of shales the relative roles of production decomposition and dilution in the accumulation of organic rich strata middle upper devonian appalachian basin abstract a new consensus on the processes responsible for organic carbon burial in ancient epeiric seas has emerged more firmly grounded in the uniformitarian framework of modern oceanography and biogeochemistry this consensus recognizes the interdependent roles of sedimentation primary production and microbial metabolism in favor of earlier end member models e g production vs preservation in this study one of the classic stratigraphic sequences upon which the preservation end member was based is re interpreted in light of this new consensus the study employs an extensive new sedimentological biogeochemical database from cores drilled in western new york the database spans over 500 m and 15 my of devonian deposition in the appalachian basin and provides a framework for comparative study of organic matter burial the major conclusions are 1 few organic rich units were deposited under pervasive anoxic sulfidic water columns 2 establishment and breakdown of seasonal thermoclines on annual or longer timescales were the predominant mode of stratification and 3 under such conditions remineralization of bio limiting nutrients may have played a key role in organic matter burial by creating a eutrophication pump this pump may have augmented an already rising nutrient inventory such that productivity levels exceeded the threshold required for development of suboxic to anoxic conditions in sediments and episodically in bottom waters a final conclusion asserts that the master variable for organic matter accumulation was relative sea level change which exerted influence on clastic dilution preservation and production processes sea level rise events led to sediment starvation and organic carbon concentration in distal basin sediments as well as to decreased effectiveness of seasonal mixing and thus longer build up intervals for remineralized nutrients episodic mixing of nutrient enriched bottom waters led to enhanced production ultimately increased clastic sediment delivery and water column mixing during relative sea level fall diluted surface sediment organic content such that respiratory demand could be met by increased oxygen supply thus terminating deposition of strata enriched in organic carbon

transfer of germanium to marine sediments insights from its accumulation in radiolarites and authigenic capture under reducing conditions some examples through geological ages in the geosphere germanium ge has a chemical behavior close to that of silicon si and ge commonly substitutes for si in small proportions in silicates studying the evolution of the respective proportions of ge and si through time allows us to better constrain the global si cycle the marine inventory of ge present as dissolved germanic acid is facing two main sinks known through the study of present sediments 1 incorporation into diatom frustules and transfer to sediments by these shuttles 2 capture of ge released to pore water through frustule dissolution by authigenic mineral phases forming within reducing sediments our goals are to determine whether such a bio induced transfer of ge is also achieved by radiolarian and whether ge could be trapped directly from seawater into authigenic phases with no intervention of opal secreting organisms shuttles to this end we studied two paleozoic radiolarite formations and geological formations dated of devonian jurassic and cretaceous deposited under more or less drastic redox conditions our results show that the ge si values observed for these radiolarites are close to slightly above those measured from modern diatoms and sponges in addition our results confirm what is observed with some present day reducing sediments the ancient sediments that underwent reducing depositional conditions are authigenically enriched in ge furthermore it is probable that at least a part of the authigenic ge came directly from seawater the recurrence and extent through time and space of anoxic conditions affecting sea bottoms have been quite important through the geological times consequently the capture of ge by reducing sediments must have impacted ge distribution and in turn the evolution of the seawater ge si ratio

time dependent changes for midcontinent pennsylvania black shales u s a abstract three types of midcontinent north american black shale types have been recognized based on metal content organic carbon contents sulfur isotopes and various other sedimentological and paleontological characteristics that may reflect fluctuations in bottom water oxygenation during deposition near shore middle pennsylvanian black shales exemplified by the mecca quarry shale member of indiana typically yield degree of pyritization dop values near 0 65 the highest measured in the study consistent with relatively but not fully anoxic conditions of sedimentation dop values for heebner type shales most prevalent in the upper pennsylvanian average 0 27 0 35 barely in the dysaerobic range which is difficult to reconcile with an origin for black shale dependent upon upwelling bottom water positive correlations exist between dop metal values and total organic carbon toc in black shale units through the pennsylvania these changes can be related to organic carbon production and published sea level fluctuations suggesting a change in black shale character in the midcontinent from the middle to late pennsylvanian consistently decreasing values for dop and toc through time suggest the likelihood of a progressive ventilation or improved bottom water oxygenation accompanied by a reduced rate of input from terrestrial organic matter during this time interval

lithospheric composition and thermal structure of the arabian shield in jordan abstract in this paper a unique set of samples from the uppermost crust down to the lithospheric mantle of jordan is analyzed for composition and petrophysical properties density thermal conductivity radiogenic heat production these data covering a vertical section of almost 65 km are used in conjunction with surface heat flow to generate a detailed and comprehensive lithospheric thermal model that reflects the conditions of the arabian shield as prior to the post oligocene onset of lithosphere thinning and voluminous basaltic volcanism the pre miocene model geotherms based on conductive surface heat flows of 55 and 60 mw m 2 a meet the range of lithosphere asthenosphere boundary depths of 110 160 km known from seismology b conform to results of thermomechanical models on the origin of the dead sea basin that started in miocene time and c are consistent with typical xenolith derived geotherms for terranes of similar age and lithospheric thickness moho temperatures at depths between 35 and 40 km of the as in pre miocene times were most likely in the order of 530 650 c with mantle heat flows averaging between 24 and 29 mw m 2 results contradict former views of the late proterozoic early cambrian stabilized as being an anomalously cold terrane a cold thermal structure inferred from previously measured low surface heat flows generally 45 mw m 2 is inconsistent with the thickness composition and petrophysical properties of the stable lithosphere of the shield

behavior of rare earth elements in seawater at the ocean margin a study along the slopes of the sagami and nankai troughs near japan using a flow injection icp ms method yttrium and all the lanthanides in seawater were determined in the coastal offshore mixing regime near japan marked enrichments in the trivalent rare earth elements rees in the surface waters are ascribed to the influence of coastal waters from tokyo bay in march and perhaps somewhere else in september and october to this region at less than half of the stations where the detailed vertical profiles were obtained throughout the water column we found marked excess ree iii concentrations near the bottom these bottom concentration anomalies are probably caused by resuspension of underlying sediments excluding those surface and bottom anomalous concentrations the distribution of ree iii s in the midwater column are very similar to those of the open ocean and are highly correlated with each other r2 0 95 this suggests that the boundary effects on the chemical fractionation of ree iii s are small we find no effect of the boundary scavenging known for 210pb and 231pa on the ree distribution whereas there may be preferential release of light and middle ree iii s over heavy rees from slope sediments to the seawater much like 227ac from the shale normalized ree patterns we obtained up to 90 negative ce and 10 positive gd anomalies in the water column

the trace metal content of recent organic carbon rich sediments implications for cretaceous black shale formation organic carbon rich sediments are enriched in several redox sensitive and stable sulfide forming trace metals tm and form an important sink in global tm cycles in today s ocean such sediments are deposited in coastal upwelling areas like those in the gulf of california off peru or off the namibian coast and euxinic basins like the black sea in an attempt to distinguish both environments by their specific tm patterns some important conclusions may be drawn 1 the tm enrichment seen in both environments broadly is rather similar 2 upwelling sediments are often enriched in cd and p and depleted in co and mn 3 sapropels have a tendency towards higher enrichments in ba and mo s re as cu ni sb and fe reflecting the strong sulfidation in an anoxic water column 4 upwelling systems cover a broad range of environmental settings where the steepness of the slope the proximity of h2s to the sediment seawater interface and the intensity of bio accumulation and regeneration play an important role for tm accumulation 5 the tm content of anoxic basins is mainly controlled by tm availability in the water column and sedimentation rate 6 enhanced bio productivity is the main switch turning an oxygenated into an anoxic environment cretaceous black shales oae 2 exhibit tm signatures of both coastal upwelling areas and sapropels the strong enrichments in cd mo tl v cu ni bi and sb demonstrate that bio accumulation and presence of h2s in the water column and associated sulfidation processes persisted during this time interval in large parts of the proto atlantic the usefulness of ba as a paleoproductivity proxy is obscured by diagenesis the extreme accumulation in ag and zn requires either an additional tm source for instance hydrothermal input or a different tm seawater composition during the cretaceous the geochemical data suggest that the major driving force for the widespread occurrence of c t black shales seems to be the increase in volcanic activity and associated co2 input throughout the cretaceous the ocean atmosphere system operated in a mode different from today during this time interval after conversion of the nutrient co2 into organic matter the system switched back into the normal operational mode

origin of the extreme polymetallic enrichment cd cr mo ni u v zn of the late cretaceous early tertiary belqa group central jordan abstract the sedimentary formations of the late cretaceous to early tertiary belqa group correspond to pure to slightly clayey limestones and minor black shales characterized by a remarkable enrichment in phosphorous and various redox sensitive elements cd cr mo ni u v zn phosphorous enrichment is related to the great phosphorite deposition event that has occurred at the southern margin of the tethys ocean during this period the very low organic matter contents in the limestones despite their strong enrichment in redox sensitive elements is attributed to a deposition in anoxic water but under shallow water conditions permitting the bacterial degradation of a large part of the organic matter most of the elements constituting the belqa group sediments have been deposited from the sea water either directly by chemical precipitation most ca and redox sensitive elements or indirectly through biogenic activity p part of ca and u except for the minor detritial contribution presents in some limestones and more significantly in the shales such an origin is also supported by the ree patterns of the limestones which are similar to that of the present sea water the anomalously high concentrations of some redox sensitive trace metals cr ni and probably cd compared to worldwide black shales is explained by an exogenic metal flux corresponding to the leaching of the huge amounts of ophiolites obducted during the collision between the african arabian and eurasian plates at the same time as the deposition of the belqa group sediments uranium is substituted for calcium in biogenic apatite in the limestones but was also directly precipitated from sea water in the black shales in relation with the suboxic environment with the periodic anoxia developed during their deposition in restricted deeper basins the pyrometamorphism resulting from the burning of organic rich levels in clayey limestones has created a further enrichment of redox sensitive elements in the resulting marbles by a volume loss resulting from decarbonatation reactions and the combustion of the organic matter

sedimentological and geochemical interpretation of a transgressive sequence the late cretaceous qahlah formation in the western oman mountains united arab emirates abstract the stratigraphic and palaeogeomorphologic conditions of the qahlah formation deposition in the united arab emirates are related to the geotectonic evolution of the western oman mountains during the late cretaceous the qahlah formation ranges from a few metres to more than 70 m in thickness it is the first sedimentary deposit to onlap the obducted semail ophiolite which was subjected to extensive weathering in a tropical environment during the maastrichtian erosion accompanied the transgression of the maastrichtian sea across the region the sedimentary sequence can be divided into four facies ophiolitic breccia ophiolitic conglomerate lateritic ferruginous silstone and lithic sandstone these sediments were probably formed in a shallow marine to beach setting adjacent to a retreating cliff line of the ophiolite a comparative analysis of the principal chemical and mineralogical components of the different facies indicates a genetic relationship between them the nickel content 0 85 1 1 16 wt in the laterite facies is of economic interest as a low grade ore provided that larger reserves can be identified

vanadium accumulation in carbonaceous rocks a review of geochemical controls during deposition and diagenesis abstract published data relevant to the geochemistry of vanadium were used to evaluate processes and conditions that control vanadium accumulation in carbonaceous rocks reduction adsorption and complexation of dissolved vanadium favor addition of vanadium to sediments rich in organic carbon dissolved vanadate v v species predominate in oxic seawater and are reduced to vanadyl ion v iv by organic compounds or h 2 s vanadyl ion readily adsorbs to particle surfaces and is added to the sediment as the particles settle the large vanadium concentrations of rocks deposited in marine as compared to lacustrine environments are the result of the relatively large amount of vanadium provided by circulating ocean water compared to terrestrial runoff vanadium rich carbonaceous rocks typically have high contents of organically bound sulfur and are stratigraphically associated with phosphate rich units a correspondence between vanadium content and organically bound sulfur is consistent with high activities of h 2 s during sediment deposition excess h 2 s exited the sediment into bottom waters and favored reduction of dissolved v v to v iv or possibly v iii the stratigraphic association of vanadiferous and phosphatic rocks reflects temporal and spatial shifts in bottom water chemistry from suboxic phosphate concentrated to more reducing euxinic conditions that favor vanadium accumulation during diagenesis some vanadium organic complexes migrate with petroleum out of carbonaceous rocks but significant amounts of vanadium are retained in refractory organic matter or clay minerals as carbon in the rock evolves toward graphite during metamorphism vanadium is incorporated into silicate minerals

mineralogical and chemical variation of francolites with geological time francolites carbonate fluorapatites occur in temporally and spa tially related sedimentary phosphorite deposits that range in age from the proterozoic to the neogene previous mineralogical studies of francolites have established that systematic relationships exist between chemical composition and crystdlographic data the unit cell dimensions and indices of refraction of francolites decrease with increasing substitution of co for pot3 in the francolite structure accompanying cation substitutions of na and mg for ca also are significant fluorine contents of more than 2 moles unit cell also are typical of francolites and the excess fluorine is related to the basic co for po substitution francolites are thermodynamically metastable with respect to fluorapatite studies of francolites from deposits of various geologi cal ages demonstrate systematic trends in chemical composition and crystallographic properties with time francolites in rocks of palae ozoic or older ages usually have compositions close to fluorapatite mesozoic and younger francolites have wide range of compositions that vary with the type and intensity of post depositional alteration these alteration processes can result in mobilization of cations and anions decarbonation of the francolite and changes in crystal lographic properties the extent and intensity of alteration proc esses often are restricted by variations in francolite composition and associated accessory minerals

atmospheric circulation upwelling and organic rich rocks in the mesozoic and cenozoic eras abstract by using the basic principles of atmospheric circulation and analogies from present circulation patterns it is possible to construct qualitative atmospheric circulation models on paleogeographic maps the wind patterns predicted by these models then serve as the basis for predicting the locations of ancient upwelling zones atmospheric circulation and upwelling models for seven geologic stages in the mesozoic and cenozoic were constructed and the distribution of the upwelling zones compared with the distribution of organic rich rocks for all time periods together the correlation was statistically significant when the individual time periods were analyzed separately the following pattern emerged significant correspondence between upwelling zones and organic rich rocks in the triassic middle early cretaceous to late cretaceous and middle paleogene to neogene no significant correspondence was found for the intervening times upwelling does not account for all organic rich rocks so called anoxic oceanic events and transgressions play an important role in their deposition it is suggested that upwelling contributes significantly to the pattern of organic rich rock distribution and is important in determining organic facies

mineralogy and origin of surficial uranium deposits hosted in travertine and calcrete from central jordan abstract secondary uranium encrustations are hosted in thick travertine and calcrete deposits of pleistocene recent age in central jordan the central jordan varicolored marble and travertine are equivalent to the active metamorphic area in maqarin north jordan more than 100 samples were collected from the outcrops of the varicolored marble travertine calcrete and the yellow uranium encrustations the secondary yellow encrustations are mainly composed of uranyl vanadate complexes tyuyamunite ca uo 2 2 v 2 5 o 8 3 h 2 o strelkinite na2 uo2 2v2o8 6 h2o solid solution series are the major components and their composition reflects changes in the ca na ratio in solution potentially new vanadium free calcium uranate phases restricted to the varicolored marble were identified with cao uo3 ratios different from the known mineral vorlanite cau6 o4 carbon and oxygen isotope data from calcite in the varicolored marble are characterized by rayleigh type enrichment in light isotopes associated with release of 13c and 18o enriched co2 by high temperature decarbonation during combustion of the bituminous marl stable isotope results from uranium hosted travertine and calcrete varieties exhibit a wide range in isotopic values between decarbonated and normal sedimentary carbonate rocks the depleted 13c and 18o values in the travertine are related to the kinetic reaction of atmospheric co2 with hyperalkaline ca oh 2 water the gradual enrichment of 13c and 18o values in the calcrete towards equilibrium with the surrounding environment is related to continuous evaporation during seasonal dry periods uranium mineralization in central jordan resulted from the interplay of tectonic climatic hydrologic and depositional events the large distribution of surficial uranium occurrences hosted in travertine and calcrete deposits is related to the artesian ascending groundwater that formed extensive lakes along nnw sse trending depressions fresh groundwater moved upward through the highly fractured phosphate bituminous marl and varicolored marble to form unusual highly alkaline water hydroxide sulfate type enriched with sensitive redox elements among which were u and v

the ophiolite related mersin melange southern turkey its role in the tectonic sedimentary setting of tethys in the eastern mediterranean region the mersin melange underlies the intact mersin ophiolite and its metamorphic sole to the south of the mesozoic tauride carbonate platform in southern turkey the melange varies from chaotic melange to broken formation in which some stratigraphic continuity can be recognized based on study of the broken formation four lithological associations are recognized 1 shallow water platform association dominated by upper palaeozoic lower cretaceous neritic carbonates 2 rift related volcanogenic terrigenous pelagic association mainly upper triassic andesitic acidic volcanogenic rocks siliciclastic gravity flows basinal carbonates and radiolarites 3 within plate type basalt radiolarite pelagic limestone association interpreted as upper jurassic lower cretaceous seamounts with associated radiolarian sediments and upper cretaceous pelagic carbonates 4 ophiolite derived association including fragments of the upper cretaceous mersin ophiolite and its metamorphic sole locally the ophiolitic melange includes granite that yielded a k ar radiometric age of 375 7 10 5 ma late devonian this granite appears to be subduction influenced based on immobile element composition the mersin melange documents the following history 1 triassic rifting of the tauride continent 2 jurassic cretaceous passive margin subsidence 3 oceanic seamount genesis 4 cretaceous supra subduction zone ophiolite genesis 5 late cretaceous intra oceanic convergence metamorphic sole formation and 6 latest cretaceous emplacement onto the tauride microcontinent and related backthrusting regional comparisons show that the restored mersin melange is similar to the beysehir hoyran nappes further northwest and a northerly origin best fits the regional geological picture these remnants of a north neotethys inner tauride ocean were formed and emplaced to the north of the tauride carbonate platform they are dissimilar to melanges and related units in northern syria western cyprus and southwestern turkey which are interpreted as remnants of a south neotethys early high temperature ductile transport lineations within amphibolites of the metamorphic sole of the mersin ophiolite are generally orientated e w possibly resulting from vertical axis rotation of the ophiolite while still in an oceanic setting by contrast the commonly northward facing later stage brittle structures are explained by backthrusting of the ophiolite and melange related to exhumation of the partially subducted northern leading edge of the tauride continent

anoxic sediments an important environment for pge an overview anoxic sediments and metasediments have been recently recognized as important host environments for the platinum group elements pge economically significant pge concentrations have been reported from marine metal rich black shales in china yukon canada and poland these ore bearing horizons are characterized by extremely restricted vertical and sometimes larger horizontal extents they are associated with the evolution of intracontinental rifting structures without any magmatic activity suggesting a possible driving mechanism for mineralization processes complex pge associations including a significant relationship of pd and pt with ni bi se y and also with sb cu co au u and f are suggested using the results of a new statistical evaluation of available geochemical data these occurrences show more common features with other hydrothermal pge deposits the rift volcanic related marine metal rich black shales of the czech republic and finland however display lower pge values the mineralized layers are much thicker with a typically limited horizontal extent showing a close association with volcanic centres pd reveals a strong correlation with ni zn au and v pt exhibits a highly significant link with the cu and mo phases low average nicu ratios and pge au chondrite normalized patterns are similar to those of some magmatic pge deposits hosted in mafic and ultramafic rocks it is very likely that organic matter played an important role in the genesis of pge accumulations in metal rich black shales in both rift and rift volcanic related environments

manganese methane iron zinc and nickel anomalies in hydrothermal plumes from teahitia and macdonald volcanoes abstract hydrothermal vents discharging turbid water have recently been discovered at teahitia and macdonald seamounts which are situated at the southeast ends of two south pacific hotspot systems mixtures of the plumes with ambient seawater were sampled during the 1989 cyapol cruise and found to contain significant amounts of ch4 mn fe zn and ni which are comparable in concentration to those found over hydrothermal fields on the epr and in megaplumes over the juan de fuca ridge above teahitia volcano ch4 shows maximum concentrations of 8 nmol kg mn concentrations of 19 nmol kg and fe concentrations of 125 nmol kg the concentrations were much higher during an earlier so 47 cruise in 1987 reaching maximum values of 14 nmol ch4 kg and 60 nmol mn kg by contrast the macdonald seamount plume shows an opposite trend reaching very high concentrations of 350 nmol kg ch4 250 nmol mn kg and 3920 nmol fe kg during the cyapol cruise when the volcano was at an eruptive stage with high seismic activity the fe mn ratio of the plume is variable between the two active volcanoes and at different hydrocast stations reflecting the balance between input and removal of these two elements mapping of the element concentrations in the water column shows the plume ceiling or anomaly maxima to occur to several hundred metres above the seafloor and up to several kilometres 5 km from the vents on macdonald seamount multiple maxima in hydrocast profiles indicate the presence of several distinct hydrothermal vents at different water depths on teahitia and on the western flank of macdonald seamount ree data from a single hydrocast over the active macdonald summit indicate a mobility of the ree which probably results from high temperature basalt seawater interaction

the cr th ratio in precambrian pelites from the kaapvaal craton as an index of craton evolution the cr th ratio in precambrian pelites from the kaapvaal craton in southern africa correlates with pelite th sc and co th ratios and appears to monitor changes in source composition it is a more sensitive indicator of provenance than other commonly used ratios including eu eu la yb and th u pelite cr th ratios are controlled most strongly by the effects of local provenance and local tectonics secular decreases in this ratio the most prominent of which occurred at 2 4 2 3 ga in pelites of the kaapvaal craton record rapid uplift exposing granite decreases in the ratio reflect increases in the abundance of komatiite basalt in sediment sources in response to arc collisions rift hotspot volcanism or intracratonic uplift of older greenstones relatively constant cr th ratios appear to require widespread uplift or and efficient sediment mixing during tectonic stability changes in cr th ratio of kaapvaal pelites reflect a complex tectonic history of the craton from about 3 3 ga to 1 8 ga and do not favor single stage cratonization in the late archean

seawater as the source of minor elements in black shales phosphorites and other sedimentary rocks many of the minor elements in seawater today have a concentration depth profile similar to that of the biologically essential nutrients no 3 and po3 4 they show a relative depletion in the photic zone and enrichment in the deep ocean the difference between their surface and deep ocean values normalized to the change in po3 4 approaches the average of measured minor element p ratios in marine plankton although individual analyses of the latter show extreme scatter for a variety of reasons despite this scatter in the minor element analyses of plankton agreement between the two sets of data shows unequivocally that an important marine flux of many minor elements through the ocean is in the form of biogenic matter with a composition approaching that of plankton this interpretation is further supported by sediment studies particularly of sediments which accumulate in shelf slope environments where biological productivity in the photic zone is exceptionally high and organic carbon contents of the underlying sediment elevated the interelement relations observed for some of these sediments approach the average values of plankton these same interelement relations are observed in many marine sedimentary rocks such as metalliferous black shales and phosphorites rocks which have a high content of marine fractions e g organic matter apatite biogenic silica and carbonates many previous studies of the geochemistry of these rocks have concluded that local hydrothermal activity and or seawater with an elemental content different from that of the modern ocean was required to account for their minor element contents however the similarity in several of the minor element ratios in many of these formations to minor element ratios in modern plankton demonstrates that these sedimentary rocks accumulated in environments whose marine chemistry was virtually identical to that seen on continental shelf slopes or in marginal seas of the ocean today the accumulation of the marine fraction of minor elements on these ancient sea floors was determined largely by the accumulation of organic matter settling from the photic zone and with a composition of average plankton a second marine fraction of minor elements in these rocks accumulated through precipitation and adsorption from seawater the suite of elements in this fraction reflects redox conditions in the bottom water as determined by bacterial respiration for example high mn high cr v and high mo concentrations above those which can be attributed to the accumulation of planktonic matter characterize accumulation under bottom water oxidizing denitrifying and sulfate reducing conditions respectively

a review of the tectonics of the northern middle east region the structure of the northern part of the arabian platform is reviewed in the light of hitherto unpublished exploration data and the presently accepted kinematic model of plate motion in the region the palmyra and sinjar zones share a common history of development involving two stages of rifting one in the triassic jurassic and the other during late cretaceous to early tertiary times deformation of the palmyra zone during the mio pliocene is attributed to north south compression on the eastern block of the dead sea transcurrent system which occurred after continental collision in the north in southeast turkey the asymmetry of the palmyra zone is believed to result from northward underthrusting along the southern boundary facilitated by the presence of shallow triassic evaporites an important nw se cross plate shear zone has been identified which can be traced for 600 km and which controls the course of the river euphrates over long distances in syria and iraq transcurrent motion along this zone resulted in the formation of narrow grabens during the late cretaceous which were compressed during the mio pliocene to a large extent present day structures in the region result from compressional reactivation of old lineaments within the arabian plate by the transcurrent motion of the dead sea fault zone and subsequent continental collision

organic carbon variations of the eastern mediterranean holocene sapropel a key for understanding formation processes abstract this work reports on the organic carbon content of the s1 holocene sapropel the youngest and most extensively researched of the eastern mediterranean sapropels the peak organic carbon percentage of the s1 sapropel varies between 1 2 and 3 4 at varying locations these variations could not be correlated with sapropel thickness or with spatial location in contrast there was a close linear correlation with water depth the deeper samples containing the highest values of organic carbon within the s1 layer the highest values were found in the top of the sapropel even if primary productivity increased during the s1 sapropelic period the main factors responsible for sapropel deposition were changes in the degradation and preservation of organic matter in the water column and at the sediment water interface water column stratification created an oxygenated surficial layer 0 350 400 m thick and a stagnant deep water layer the majority of the organic material escaping the surficial layer was remineralised either at the sediment water interface or just below it organic matter preserved in sapropelic sediments can be assumed to have remained for a significantly longer time 1000 years within the benthic boundary layer than in the water column organic flux decreased with depth through the stagnant deep water layer when stagnation was established water exchanges either did not exist or were limited vertical oxidant transport depended on eddy diffusion while oxidant fluxes at the sediment water interface decreased with depth the organic matter mineralisation rate also decreased and the burial efficiency increased the linear relationship between sapropel organic content and depth was reflected in a linear decrease in oxidant flux regardless of location the same organic carbon percentage was preserved at the same depth in contrast in the same area but at different depths organic carbon content ranges between 1 2 and 3 4 this observation suggests that primary productivity was of the same order of magnitude basinwide the organic carbon concentration of sediment should be used with caution as a quantitative record of palaeoproductivity

44ca 42ca and 143nd 144nd isotope variations in cretaceous eocene tethyan francolites and their bearing on phosphogenesis in the southern tethys measurements of 4 4 ca 4 2 ca and 1 4 3 nd 1 4 4 nd isotope ratios in carbonate fluorapatite cfa through the aptian eocene section of the negev israel together with quantified rates of p and ca accumulation and bulk sedimentation permit an examination of the relationships of these five factors to tethyan phosphogenesis the data provide an aptian eocene ca 70 ma record of the ca isotope composition of 35 cfa samples 24 of which were also analyzed for nd isotopes representing 11 time stratigraphic phosphate horizons within the sequence the 4 4 ca values are significantly lower in the aptian albian samples 4 4 ca 0 11 to 0 06 than in the campanian eocene samples 4 4 ca 0 22 to 0 42 whereas the e n d values increase from continental crust like in the aptian albian e n d t 10 9 to more radiogenic pacific like e n d t 6 6 to 6 1 in the campanian both peaks of 4 4 ca and e n d t in the campanian coincide with the peak of tethyan phosphogenesis in the negev which is marked by a sharp increase of p accumulation rates from 200 mol cm 2 k y 1 in pre campanian time to 1700 mol cm 2 k y 1 in the campanian and a decrease in rates of ca accumulation and bulk sedimentation the coincident increases of 4 4 ca and e n d t values and p accumulation rates in the negev area during the campanian suggest that they are related in this time interval and were induced by the global late cretaceous sea level rise and increasing circumequatorial tethyan flow

phases of activity and geochemistry of basaltic dike systems in northeast jordan parallel to the red sea abstract k ar dates petrographic and chemical data were obtained from representative samples from three nw se trending basaltic dikes in the harrat ash shaam volcanic field northeast jordan compared with other ne sw trending dikes in jordan three phases of activity were determined for the studied dikes starting from the oldest around 23 ma to the youngest at around 1 7 ma three dominant petrotypes of basalt were distinguished and related to the three phases during the early miocene there was emplacement of a pyroxene iddingsite basalt 23 which is characterized by a tholeiitic composition later in the middle to late miocene the composition was that of pyroxene olivine basalt 34 with an increase in the alkaline character of the magma chamber in the final stage the dikes comprised olivine basalt 22 with a basanite composition it is reasonable to assume that the emplacement of the dikes was part of the same volcanic phase and regional tectonic regime associated with the phases of volcanic activity of the red sea system

structure of the earth s crust in jordan from potential field data abstract gravity and magnetic data were collected and used to study the crustal structure of jordan three new geophysical maps of jordan were created a moho discontinuity map a crystalline basement surface map and a map showing the lowest limit of magnetic blocks depths of the curie isotherm were also calculated results indicate that the depth to the moho discontinuity in jordan varies from 32 to 33 km in the northwest to 38 km in the southeast the basement complex rocks outcrop on the surface in the southwest but lie at about 8 km in the northeast the curie isotherm 585 c lies at a depth of about 10 km in the area east of the dead sea and dips southeastward towards the al sirhan wadi sirhan southeast jordan where it is located at 35 km depth local isostasy of rock masses blocks in jordan does not occur nevertheless this does not rule out the possible existence of isostasy in a regional scale at greater depths within the mantle

rhyolitic volcanism in extension zone associated with strike slip tectonics in the taxco region southern mexico abstract the taxco volcanic field tvf is part of a broad magmatic province in southern mexico it constitutes an isolated zone of deeply dissected volcanic rocks encircled by outcrops of mesozoic sedimentary and volcano sedimentary units a thick unit of rhyolitic lava flows associated with domes and at least two ignimbrite units forms the tvf this volcanic sequence is distributed within a well defined zone it overlies and is in part contemporaneous with continental sedimentary beds limited by major faults geochronologic data indicate that most rhyolitic volcanism in the area is oligocene in age and synchronous with episodes of strike slip faulting we document two successive phases of strike slip faulting for the late eocene early oligocene interval the first with nnw extension and the second with ne extension in both cases pre existing structures were reactivated and sedimentary basins were developed in response to displacement along major faults the stratigraphic sequence gives evidence that the tvf is located in an extensional basin associated to strike slip faults the evolution of the basin underwent a change from sedimentary deposition with subsidence to piling up by volcanism the result of this change was the development of a volcanic pile with elevations higher than the surrounding mesozoic rocks according to the fault kinematics stratigraphy and the volume of volcanic rocks the rhyolitic volcanism was emplaced in the area of maximum extension showing that magma flowed into low pressure zones the small number of faults within the oligocene volcanic sequence suggests that volcanism inhibited normal faulting and that magma partially filled the space generated in the extended zone produced by the strike slip faulting

stratigraphic organization of carbonate ramps and organic rich intrashelf basins natih formation middle cretaceous of northern oman the middle cretaceous carbonate deposits in the middle east are among the most productive oil bearing stratigraphic intervals in the world containing numerous giant fields in for instance the united arab emirates mauddud and mishrif formations iran sarvak formation and oman natih formation one of the main reasons for this concentration of hydrocarbons is a geological factor the coexistence of both reservoir facies and source rocks in the same depositional sequences due to the repeated creation of organic rich intrashelf basins this is demonstrated in a high resolution sequence stratigraphic study of the natih formation in oman which shows distinct and predictive patterns in the distribution and geometries of reservoir source rock and seal facies the sequence stratigraphic model presented here may serve as a reference for time equivalent deposits in the middle east the sedimentological analysis showed that the natih formation was formed by the alternation of two types of depositional systems 1 a flat bedded mixed carbonate clay ramp dominated by benthic foraminifera and 2 a carbonate dominated ramp bordering an intrashelf basin with abundant rudists in the mid ramp environment and organic rich basinal facies three fully developed third order sequences are distinguished showing a similar evolution of the depositional system with a mixed carbonate clay ramp system at the base followed by a carbonate dominated ramp system in the upper part variations occur on this pattern however depending on the relative influence of eustasy environmental factors and tectonism the late albiannearly cenomanian sequence i shows an evolution from a mixed flat ramp to a carbonate dominated ramp and organic rich intrashelf begin page 22 basin and sedimentation is predominantly controlled by eustatic sea level in the middle cenomanian sequence ii the evolution from a mixed ramp to a carbonate ramp is also observed but no intrashelf basin topography was developed in the studied area this may be due to the high influx of clay that influenced the environment in this sequence inhibiting the carbonate production probably in combination with the lack of sufficient creation of accommodation space the late cenomaniannearly turonian transgressive part of sequence iii shows a similar evolution to that observed in sequence i with the development of an organic rich intrashelf basin during highstand however a tectonically controlled sedimentation pattern is observed with the development of forced regressive wedges due to the flexural bulge of the foreland basin intrashelf basin formation occurred twice in the transgressive part of the third order depositional sequences of the natih formation our study shows that this is mainly the result of differential sedimentation rates that is the dynamics of the carbonate sedimentary system itself in response to rapid rises in relative sea level probably of eustatic origin tectonism was only a minor factor in the creation of the basin topography possibly through the creation of small initial relief the accumulation of the organic matter is not only a result of the creation of a sufficiently deep water column to guarantee dysaerobic conditions for its preservation the late albian and late cenomaniannearly turonian were also periods of generally favorable conditions worldwide for high organic matter productivity the time lines and stratigraphic architecture of the third order sequences presented here have an application potential at the scale of the arabian plate the general sedimentation pattern is predicted by our model but modifications due to different local conditions are likely to occur

maastrichtian to early tertiary stratigraphy and palaeogeography of the central and northern oman mountains abstract maastrichtian to tertiary sedimentary rocks outcrop extensively around the periphery of the oman mountains they form part of a geologically distinct suite of strata deposited after obduction of the semail ophiolite and thrusting of the hawasina and sumeini imbricates onto the eastern edge of the arabian plate the lithostratigraphy of maastrichtian and early tertiary rocks of the central and northern oman mountains is revised and a number of new formations are erected the proto oman mountains were emergent in the early maastrichtian and were subject to subaerial erosion and weathering nw and w of the mountains gradual subsidence followed during the maastrichtian allowing for formation of a transgressive onlapping sequence represented by the qahlah fluviatile to shallow marine terrigenous clastics and simsima shallow shelf carbonate formations more rapid subsidence ne of the mountains produced fan delta and submarine debris flow turbidite apron sequences comprising the al khawd and thaqab formations respectively a low angle unconformity separates tertiary strata from older units during the palaeogene basinal and slope facies with debris flows and turbidite sequences were deposited directly upon the unconformity surface in rapidly subsiding basins nw muthaymimah formation and nne ruwaydah formation of the oman mountains elsewhere shallow carbonate shelf facies were extensively developed in less rapidly subsiding areas during the palaeogene the palaeocene and early eocene is represented by the jafnayn limestone formation this is succeeded and overlapped by a variety of later eocene units ene and e of the mountains early eocene regression is marked by restricted facies of the rusayl formation overlying the rusayl formation are shallow open shelf limestones of the seeb formation which is rich in alveolinid and nummulitic foraminifera on the arabian side of the mountains the rusayl formation is not developed and the jafnayn formation is succeeded either by the seeb formation or fine grained faunally restricted limestones and marls of the fahud beds which represent intra shelf facies

enhanced trapping of molybdenum by sulfurized marine organic matter of marine origin in mesozoic limestones and shales there have been many studies devoted to trace metals and their value in assessing the paleoredox conditions of ancient marine deposition among them molybdenum mo is frequently cited as an effective proxy for sediments and sedimentary rocks recently helz et al helz g r miller c v charnock j m mosselmans j l w pattrick r a d garner c d vaughan d j 1996 mechanisms of molybdenum removal from the sea and its concentration in black shales exafs evidences geochim cosmochim acta 60 3631 3642 and adelson et al adelson j m helz g r miller c v 2001 reconstructing the rise of recent coastal anoxia molybdenum in chesapeake bay sediments geochim cosmochim acta 65 237 252 suggested that mo does not behave conservatively in the water column when h2s reaches a threshold concentration above this concentration a switch operates and mo is scavenged by forming bonds with metal rich notably iron particles sulfur rich organic molecules and pyrite in this paper mo trapping by sulfur rich organic matter om in ancient marine deposits is emphasized the following mesozoic geological formations were selected for study because of their relatively high concentration of sulfurized om the akkuyu formation turkey the calcaires d orbagnoux france and kimmeridge clay uk and its timeequivalent in boulonnais france the kashpir oil shales russia and the la luna formation venezuela the sulfur rich om is identified by either measured organic s abundance or kerogen microscope observation our results show that mo is systematically more enriched relative to the other redox sensitive sulfide forming elements studied u v ni cu zn cr and mo enrichment is positively correlated with the amount of sulfurized om but not with pyrite abundance these results illuminate the role played by sulfurized om in geologic scale mo capture and retention but they also underline the role played by reactive iron significant om sulfurization is only possible when reactive iron is limited nevertheless pyrite formation though limited could act as an initial mo trap prior to mo uptake by om that is sulfurized after the pyritization step in future paleoenvironmental reconstructions attention must be paid to this enhanced mo enrichment in the presence of sulfurized organic matter in such cases the use of mo could lead to overestimation of the reducing conditions of the depositional environment

rare earth geochemistry of phosphorites abstract the abundance of rare earth elements ree s in francolite increases with increasing age as a result of post depositional enrichment abundances are higher in pelletal samples than in non pelletal ones because the higher surface mass ratio of pelletal francolite promotes enrichment during diagenesis onshore francolite has higher ree abundances than that found offshore distribution patterns in francolite may be similar to those reported for open ocean water or shale depending upon the dominant source of the ree s different patterns result from weathering and deep burial diagenetic modification of the original patterns and abundances negative ce anomalies occur in francolites containing structural sulphur that is isotopically indistinguishable from seawater of the same age zero or positive anomalies occur in francolites which contain sulphur that is isotopically lighter than seawater

structural controls on orogenic gold mineralisation in the klondike goldfield canada the klondike schist that forms the basement rocks for the famous klondike placer goldfield was emplaced as km scale thrust slices in early jurassic time along with some thin 10 to 30 m scale slices of greenstone and ultramafic rocks permian metamorphic fabrics in the schists were deformed during thrust emplacement by structures formed as the rocks passed through the brittle ductile transition early formed thrust related structures were almost pervasive recumbent folds that affected both the schist and greenstone ultramafic slices and imposed a spaced cleavage with minor recrystallisation of micas these structures gave way to shallow dipping phacoidal cleavage near within 100 m of thrust structures thrust related structures have been overprinted locally by well defined steeply dipping reverse fault fold zones and associated upright folding on regional km to mesoscopic m scales the fold fault zones occur as two orthogonal sets of structures oriented nw to n and ne to e some of these steeply dipping fault zones have been reactivated by late cretaceous normal faulting orogenic mesothermal gold bearing veins were emplaced in local sites of extension during or after formation of the compressional fault fold zones and before normal fault reactivation over 400 veins m to cm scale observed in this study imply a general nw strike for mineralised structures w to n but with a broad scatter of orientations vein emplacement was controlled principally by fold axial surfaces of kink folds of the fault fold generation however some other local extension sites have opened along preexisting structures to host veins locally including metamorphic foliation and spaced cleavage planes in addition irregular extensional fractures with no obvious structural control host some veins the klondike mineralised veins formed as swarms with broad regional structural control but represent relatively diffuse mineralised zones with numerous scattered small veins compared to most orogenic vein systems these diffuse vein swarms appear to be sufficient sources for the rich and geographically localised placer gold deposits that formed in overlying gravels during erosion of the klondike schist basement

upper cretaceous campanian phosphorites in jordan implications for the formation of a south tethyan phosphorite giant a record of sedimentary authigenic and biological processes are preserved within the upper cretaceous campanian alhisa phosphorite formation ap in central and northern jordan the ap formed near the eastern extremity of the south tethyan phosphorite province stpp a carbonate dominated upper cretaceous to eocene phosphorite giant that extends from colombia north africa to the middle east multidisciplinary research of the ap and associated cherts chalks and oyster buildups indicate that phosphatic strata formed on a highly productive storm dominated east west trending epeiric platform along the south tethyan margin the onset of phosphogenesis and the accumulation of economic phosphorite coincided with a rise in relative sea level that onlapped peritidal carbonates of the ajlun group pristine phosphates are associated with well developed micrite concretionary horizons and contain abundant non keeled spiral planktic foraminifera and a low diversity benthic assemblage of buliminacean foraminifera suggesting that pristine phosphates are a condensed facies and phosphogenesis was stimulated by the effects of a highly productive surface ocean and the suboxic diagenesis of sedimentary organic matter the bulk sediment composition and absence of fe bearing authigenic phases such as glauconite pyrite including pyrite molds siderite and goethite within pristine phosphates suggests that deposition and authigenesis occurred under conditions of detrital starvation and that iron pumping played a minimal role in phosphogenesis authigenic precipitation of phosphate occurred in a broad array of sedimentary environments herein termed a phosphorite nursery that spanned the entire platform this is a non uniformitarian phenomenon reflecting precipitation of sedimentary apatite across a wide depositional spectrum in a variety of depositional settings wherever the conditions were suitable for phosphogenesis sedimentologic data indicate that pristine phosphates were concentrated into phosphatic grainstones through storm wave winnowing and storm generated shelf parallel geostrophic currents economic phosphorites formed through the amalgamation of storm induced event beds stratigraphic packaging of phosphatic strata indicates that temporal variations in storm frequency were a prerequisite for the formation of economic phosphorite syndepositional phosphogenesis reworking and amalgamation to form phosphorites contrasts sharply with the principles of baturin cycling a transgressive systems tract coupled with high surface productivity created detritally starved settings favourable for phosphogenesis storm reworking of pristine

source rock potential of the phosphorite bituminous chalk marl sequence in jordan abstract the phosphorite and the overlying oil shale succession in central and eastern jordan has been studied for its organic matter composition maturation hydrocarbon potential and sedimentological implications pristine phosphorite was authigenically precipitated from interstitial solutions in ventilated environments later they were reworked and winnowed to produced the granular phosphorites possibly as wave or storm sand bodies the oil shale was deposited in the same basins where restricted water circulation and subsequent hypersalinity led to more reducing conditions and better organic matter preservation both facies represent a high bio productivity regime associated with paleo upwelling on the shallow southern epicontinental shelf of the tethys ocean the organic matter is dominantly amorphous and the extractable part is high kerogen is type ii s to type iii all maturity parameters investigated proved it to be immature e g r0