sedimentology csfe relationships and stable isotopic compositions in devonian black mudrocks mackenzie mountains northwest territories canada abstract an integrated approach combining c s fe relationships stable isotopic compositions and lithofacies characterization was utilized to constrain the palaeoenvironmental and early diagenetic conditions of middle upper devonian eifelian frasnian mudrocks from the mackenzie mountains northwest territories canada these rocks include the hare indian formation informally subdivided into the lower bluefish member and the hare indian upper member carcajou marker and canol formation the bluefish member is dominated by black laminated organic rich shales toc 0 35 10 34 wt av 5 83 wt with moderate degrees of pyritization dop of 0 34 0 67 av 0 55 these mudrocks were deposited in dysoxic marine bottom waters that became progressively more oxygenated with time variations in toc dop and organic matter 13cpdb values 29 7 to 19 9 av 27 2 are attributed to repeated clastic dilution and increased input of terrestrial organic matter in association with shallowing upward ramp clinothem cycles pyrite 34scdt values 32 7 to 18 8 av 24 9 indicate an open system bacteriogenic seawater sulphate reduction conversely the overlying hare indian upper member characterized by clinothem facies is composed of grey to green mudstone with minor argillaceous limestones and considerably less organic matter contents toc 0 28 2 99 wt 13c 29 5 to 22 5 deposition occurred in oxic to slightly dysoxic waters dop 0 20 0 54 34s 23 0 to 20 9 depending on the palaeotopographic location along the depositional slope a rapid rise in sea level drowned the carbonate ramp member of the ramparts formation and produced the thin organic rich carcajou marker bottom water stagnation that resulted from subdued ramp palaeotopography produced anoxic sea bottom black laminated organic rich shales from the canol formation toc 1 37 6 68 wt are very similar to those of the bluefish member and are likewise basinal sediments however toc dop and organic matter 13cpdb values 29 1 to 20 8 av 26 2 do not show pronounced variations and indicate that low energy quietwater conditions persisted over relatively long uninterrupted periods of time high dop values 0 72 0 93 throughout the canol formation suggest that deposition occurred in anoxic bottom waters but as basin fill conditions continued there was a shift to a dysoxic environment dop 0 55 0 65 which grades into nearshore and offshore sequences of the overlying imperial formation in contrast with the hare indian formation much heavier 34scdt values of pyrite in canol mudrocks 11 1 to 5 3 av 3 1 point to bacterial sulphate reduction in a closed to semi closed system with respect to seawater sulphate

sequence stratigraphic and genetic aspects of the tournaisian liegender alaunschiefer and adjacent beds this study reports the results of interdisciplinary investigations of tournaisian deposits from the german rheinisches schiefergebirge and provides a genetic and sequence stratigraphic interpretation microfacies and geochemical data confirm normal marine outer shelf to slope environments for the lower tournaisian hangenberg formation in contrast data from the condensed phosphatic liegender alaunschiefer black shale indicate low current energy and anoxic conditions in the sediment and the water column we suggest that anoxia was caused by eutrophication and high organic productivity due to factors such as upwelling a climate related improvement of oceanic ventilation and volcanic nutrient input the hangenberg formation represents the lowstand through the early transgressive systems tract of a third order depositional sequence while the liegender alaunschiefer is a late transgressive systems tract and maximum flooding deposit the richrath limestone was deposited during the highstand systems tract thus quickly rising sea level and eutrophication may account for the peculiar and uniform facies of the liegender alaunschiefer

paleomagnetic evidence for dextral strike slip motion in the pyrenees during alpine convergence mauleon basin france abstract the paleomagnetic study of the aptian albian black marls from the inverted early cretaceous mauleon basin in the northern pyrenees reveals two components of magnetization that both yield negative fold tests the carriers of each component show different unblocking temperatures indicating that ferrimagnetic iron sulphides are the main carriers of the intermediate temperature component itc unblocks around 360 400 c and magnetite is the main carrier of the high temperature component htc unblocks around 460 500 c both components show a clockwise deviation in declination with respect to the reference field directions itc di and htc di both in in situ coordinates the reference direction for stable europe for the cenozoic is d i 001 50 d 5 i 3 however the reversal test for both of the magnetization components in situ is positive the structural evolution of the basin involves transtensional deformation during the main stage of basin formation and inversion during compression with migration of hydrocarbons and development of thrusts and folds with axial planar cleavage secondary magnetizations were acquired at the latest stages of the evolution of the inverted basin post folding as the result of a chemical mechanism and they were blocked during two different and likely close spaced in time polarity chrons the blocking of the two different magnetizations with different carriers implies chemical changes in the environment from anoxic sulphate reduction to oxic inferred clockwise rotation of the paleomagnetic vectors can be interpreted in terms of dextral shear across the north pyrenean zone during the tertiary probably eocene according to the plate tectonic scenario this distributed dextral shear was probably favored by discrete shear along cleavage planes as shown by geologic markers of consistent dextral strike slip motion in non competent units with strong cleavage development there is no evidence of such dextral movement in the south pyrenean zone thus indicating a strong partitioning of deformation during the pyrenean orogeny

magnetic polarity stratigraphy of the tertiary igneous rocks of skye scotland summary palaeomagnetic results are given for 115 sites mainly from the central igneous intrusive complex and also radiometric dates by the 40ar 39ar step heating method these are combined with published dates and palaeomagnetic results for the lavas and regional dyke swarms with the aim of establishing the magnetic polarity stratigraphy igneous activity spanned at least the approximate interval 61 54 ma and a polarity sequence of at last r n r n r but could span seven polarity intervals r n r n r n r depending on the age of the loch ainort epigranite however these polarities cannot be identified with specific chrons of either the harland et al 1982 or berggren et al 1985 polarity time scales the skye igneous activity therefore spans more polarity intervals than in mull ardnamurchan or rhum and this is consistent with the radiometric ages interpretations of the results for the coire uaigneich and related granites and for the loch ainort epigranite present problems and partial solutions are offered

palaeomagnetic study of the late mesoproterozoic torridon group nw scotland age magnetostratigraphy tectonic setting and partial magnetic overprinting by caledonian orogeny abstract the late mesoproterozoic torridonian supergroup is a predominantly fluviatile 7 km thick succession of red sediments deposited onto palaeoproterozoic lewisian metamorphic terrane of the hebridean craton in nw scotland although a subject of investigation since the earliest days of palaeomagnetism the age and constitution of the remanent magnetisation in the upper torridonian torridon group have remained unclear in this study we undertake detailed statigraphically controlled sampling through the succession and conduct progressive thermal demagnetisation to resolve component structures rock magnetic analysis shows that magnetite although volumetrically small is a significant component of the ferromagnetism in these sediments in addition to specularite and pigmentary hematite unlike the lower torridonian stoer group which was fully lithified prior to late grenville deformation 1100 ma the torridon group was not influenced by tectonism until early palaeozoic times and records a complex history of partial and sometimes total later overprinting the a remanence is extensively overprinted by a b remanence with e to s directed intermediate to steep positive directions and subordinate reversed representatives and less commonly by a c remanence with ne direction b is resolved mainly in the magnetite spectrum and incorporates a swathe of directions coincident with mid ordovician palaeofields predicted from baltica and adjoining caledonian terranes it is therefore interpreted as a remanence residing in small amounts of authigenic magnetite acquired during burial of this margin of the hebridean craton by nappe stacking during the grampian orogeny 470 430 ma following final closure of the iapetus ocean due to the merging of the b population with the a direction a has not been defined as an antiparallel axis by former studies and can be inseparable by cleaning however defining a to include components with i d i 115 31 95 2 9 for a and d i 293 25 95 3 5 for a the poles at 238 e 1 s dp dm 2 0 3 8 and 235 e 1 n dp dm 1 8 3 3 are close to the laurentian apwp at 1039 1025 ma on the pre drift reconstruction and constrain sedimentation within the 1060 to 994 977 ma range of previous evidence only minor polar movement is detected through the entire thickness of the torridon group and suggests a sedimentation rate of the order of 0 5 m 1000 years for this clastic succession a magnetic stratigraphy in a suggested by early work is confirmed in at least 13 polarity zones and identifies a rapid reversal rate preserved in specular hematite fixed by post depositional mechanisms postdating slumping and sand volcano formation in wet sediment the palaeomagnetic age of the a remanence links torridonian sedimentation to rifting and subsidence accompanying break up of the laurentian and fennoscandian shields at 1050 950 ma following the grenville orogeny rifting between the two shields was followed by rotation and rewelding into a neoproterozoic configuration these events correlate with transition in torridon group palaeoenvironments from enclosed basin to open basin with river systems feeding onto a passive margin to marine transgression and finally return to enclosed basin conditions diagenesis continued in post palaeozoic times and a d remanence with n s shallow axis is sporadically preserved in authigenic hematite and interpreted as mainly a variscan acquisition

geologic consequences of globe encircling equatorial currents many black shales phosphorites and cherts that formed at low paleolatitudes on the north american continent during the late paleozoic were a direct consequence of equatorial upwelling and an equatorial undercurrent in an ocean that spanned much of the globe in equatorial parts of modern oceans wind stress divergence leads to high surface productivity sinking organic matter is remineralized in the strong eastward flowing equatorial undercurrent the undercurrent thus acts as a nutrient trap that becomes progressively oxygen poor and nutrient rich as it moves eastward the late paleozoic global ocean was 60 to 80 wider than the modern pacific ocean 24 000 km total width the nutrient trapping equatorial current system of this globe encircling ocean was probably anoxic and may have been sulfate reducing nutrient rich anoxic water from the undercurrent would have had direct consequences for the genesis of black shale facies in devonian and pennsylvanian epicontinental seaways as well as possibly providing the source water for coastal upwelling in settings such as the phosphoria sea

geochemistry of the mississippian delle phosphatic event eastern great basin u s a abstract the middle mississippian delle phosphatic event marks a significant change in depositional conditions in the devonian mississippian antler foreland basin of north america stratigraphic and petrographic studies show that deposition of delle event rocks ended a long period of open marine carbonate sedimentation when facies shifted to phosphorites cherts fine grained siliciclastics and lime mudstones from highly productive waters that may have been episodically anoxic this drastic change in lithology is reflected in the chemistry of the two suites of rocks 18o values of the delle event lime mudstones and phosphatized wackestones packstones affected by the delle event are 3 5o oo lighter than underlying and overlying open marine wackestones packstones sr concentrations of delle event lime mudstones and open marine wackestone packstone facies are low suggesting that both of these lithologies have undergone similar postdiagenetic alteration the uniform sr concentrations and variable 18o data suggest that either the younger delle event rocks were exposed to meteoric water during diagenesis or that the relatively light 18o values represent a primary brackish water depositional signal either interpretation is consistent with sedimentological evidence of the delle event occurring in a predominantly shallow water setting 13c values of delle event lime mudstones are also anomalously light indicating a high input of organic carbon during their formation mn concentrations of the delle event lime mudstones and stratigraphic equivalents are highly variable suggesting fluctuating oxygen concentrations during their deposition and diagenesis rare earth element data from phosphorites and cherts of the delle event indicate oxic to suboxic depositional conditions

the north atlantic igneous province reconstructed and its relation to the plume generation zone the antrim lava group revisited summary large igneous provinces lips have recently been suggested to originate at the edges of low velocity zones on the core mantle boundary plume generation zones if true lips can potentially be used to constrain paleolongitude in plate tectonic reconstructions to validate the hypothesis it is essential to study lips of which the paleolongitude can be constrained by other methods such as hotspot reference frames an ideal candidate to this end is the early cenozoic north atlantic igneous province naip despite being the largest volcanic unit of the british tertiary igneous province btip part of the naip the age and paleoposition of the antrim lava group alg in northern ireland which is key to the naip as a whole was hitherto poorly constrained in this paper we therefore present an integrated high resolution paleomagnetic and geochronological study the alg is divided into three formations the lower basalt formation lbf interbasaltic formation ibf and the upper basalt formation ubf the ibf is mostly lateritic and encloses the tardree rhyolite we offer new age constraints from all three formations using the 40 ar 39 ar method and propose that 62 6 0 3 61 3 0 3 and 59 6 0 3 ma 1 internal uncertainties are sound estimates of the age of emplacement of the lbf tardree rhyolite ibf and ubf respectively this constrains the nominal duration of emplacement of the alg to 3 0 6 ma 1 this reevaluation of the magnetic signature in the alg revealed reverse polarity remanence in all three formations and an overall paleomagnetic north pole at latitude 78 9 n longitude 167 e a95 6 3 age 61 ma in the european reference system this appears consistent with paleomagnetic poles from the rest of the naip both in europe and greenland as well as predictions from modern apparent polar wander paths the new radiometric ages span magnetochron c26r c27n and c27r the normal polarity chron c27n most probably occurred during the ibf hiatus explaining why no normal polarity remanence was detected in the paleomagnetic investigation emplacement of the lbf falls in magnetochron c27r making this one of the oldest lava sequence in the naip older than the c27n lava pile in western greenland the 60 ma position of the naip in a paleomagnetic reference frame puts it close to the northern edge of the african large low shear wave velocity anomaly at the core mantle boundary and therefore in the line with the plume generation zone hypothesis however the back projected icelandic hotspot normally considered to have formed the naip is located 1500 km north of the latitude at which the naip erupted the northward motion of the north atlantic lithosphere since the late cretaceous challenging the existing correlation of the naip to the icelandic hotspot normally used to explain the observed pre and syn breakup north atlantic magmatism 63 55 ma and either an additional plume located further south in the north atlantic may be invoked to create the naip or the icelandic hotspot must have

palaeoenvironmental and palaeoceanographic controls on black laminated mudrock deposition example from devonian carboniferous strata alberta canada abstract sedimentological palaeontological and ichnological analyses indicate that heightened episodes of equatorial upwelling in tandem with an expanded and intensified oxygen minimum zone promoted deposition of upper famennian to lower tournaisian laminated organic rich mud rocks of the exshaw formation on the alberta cratonic platform exshaw mud rocks represent the culmination of an upper devonian transgression that commenced with deposition of open marine carbonates of the big valley formation the transgression was abruptly halted at the devonian carboniferous boundary by a rapid eustatic sea level fall and the consequent deposition of near shore marine to shelfal bioturbated siltstones and sandstones of the exshaw formation the siltstones grade into laminated organic lean mud rocks to the north in more distal offshore shelf settings these mudrocks reflect a period of low primary production but continued anoxia of bottom waters continuation of anoxic conditions resulted from development of restricted circulation in the epicontinental sea due to the establishment of a westward located physical barrier following this event was a relative sea level rise that led to deposition of black laminated mudrocks of the banff formation

reassembling the paleogene eocene north atlantic igneous province new paleomagnetic constraints from the isle of mull scotland abstract the paleomagnetic data sets from the british tertiary igneous province btip have recently been criticized as being unreliable and discordant with data from elsewhere in the north atlantic igneous province naip riisager et al earth planet sci lett 201 2002 261 276 riisager et al earth planet sci lett 214 2003 409 425 we offer new paleomagnetic data for the extensive lava flow sequence on the isle of mull scotland and can confirm the paleomagnetic pole positions emanating from important earlier studies our new north paleomagnetic pole position for eurasia at 59 0 2 ma has latitude 73 3 n longitude 166 2 e dp dm 5 2 7 0 a re evaluation and an inter comparison of the paleomagnetic database emanating from the naip were carried out to test for sub province consistency we find a general agreement between the eurasian part of naip btip and faeroes and east greenland data however a compilation of west greenland data displays a large and unexplained dispersion we speculate on if this is related to different sense of block rotation of the tertiary west greenland constituents combining all data from the naip constituents give a pole position at 75 0 n 169 9 e n 25 k 84 3 a95 3 2 in eurasian reference frame

palaeomagnetism and radiometric dating of the british tertiary igneous province muck and eigg summary the lavas dykes and other intrusive bodies of muck and eigg have been sampled for palaeomagnetic purposes all the bodies are reversely magnetized except for four dykes of muck which are normally magnetized the lavas show variations of direction of magnetism believed to be a record of secular variation the radiometric dates support the geological evidence that the lavas of eigg and muck predate parts of the rhum central igneous complex the lavas of rhum and canna and some of those of skye the combined evidence shows that most of the activity took place during an r n r n sequence between 63 and 58 ma the younger r n sequence is the same as the first part of the r n r sequence found in mull but the sgurr pitchstone of eigg and parts of the eastern redhills of skye belong to later reversed intervals and correspond to chron 26r and chron 26 the igneous activity occurred over a 10 myr period from about 63 ma and can probably be associated with chrons 27r to 23r of the harland et al time scale

trace element budgets in the ohio sunbury shales of kentucky constraints on ocean circulation and primary productivity in the devonian mississippian appalachian basin abstract the hydrography of the appalachian basin in late devonian early mississippian time is modeled based on the geochemistry of black shales and constrained by others paleogeographic reconstructions the model supports a robust exchange of basin bottom water with the open ocean with residence times of less than forty years during deposition of the cleveland shale member of the ohio shale this is counter to previous interpretations of these carbon rich units having accumulated under a stratified and stagnant water column i e with a strongly restricted bottom bottom water circulation a robust circulation of bottom waters is further consistent with the palaeoclimatology whereby eastern trade winds drove upwelling and arid conditions limited terrestrial inputs of siliciclastic sediment fresh waters and riverine nutrients the model suggests that primary productivity was high 2 g c m 2 d 1 although no higher than in select locations in the ocean today the flux of organic carbon settling through the water column and its deposition on the sea floor was similar to fluxes found in modern marine environments calculations based on the average accumulation rate of the marine fraction of ni suggest the flux of organic carbon settling out of the water column was approximately 9 of primary productivity versus an accumulation rate burial of organic carbon of 0 5 of primary productivity trace element ratios of v mo and cr mo in the marine sediment fraction indicate that bottom waters shifted from predominantly anoxic sulfate reducing during deposition of the huron shale member of the ohio shale to predominantly suboxic nitrate reducing during deposition of the cleveland shale member and the sunbury shale but with anoxic conditions occurring intermittently throughout this period

the british tertiary igneous province palaeomagnetism of the dyke swarm along the sleat coast of skye summary a palaeomagnetic investigation has been made of a swarm of more than 400 dykes along the south coast of skye scotland by the sound of sleat seven red lamprophyre dykes have palaeomagnetic directions inconsistent with tertiary age and not inconsistent with their previously held caledonian age the remaining 409 dykes have palaeomagnetic directions that are consistent with a lower tertiary age we present evidence suggesting that the tertiary dykes might have been emplaced during a short time over which the geomagnetic polarity occupied as few as three polarity intervals nrn or rnr certain intermediate directions of magnetization have also been found and are presented here

palaeoceanographic controls on geochemical characteristics of organic rich exshaw mudrocks role of enhanced primary production organic rich source rocks have generally been attributed to enhanced preservation of organic matter under anoxic bottom waters here geochemical analysis of kerogen and whole rock samples of organic rich lithofacies b1 and organic lean lithofacies b2 laminated mudrocks of the devonian carboniferous exshaw formation alberta highlight the importance of primary production in governing the quantity and quality of organic matter lower si al k al ti al and quartz clay ratios in lithofacies b2 similar maceral types and the laminated fabric of the two lithofacies indicate that the quality and quantity of organic matter are not related to grain size redox or organic matter source changes high total organic carbon toc and hydrogen index hi low oxidation index ox i ratio of oxygen functional groups to aliphatic groups derived by ftir lighter 15ntot and heavier 13corg isotopes indicate that kerogen of lithofacies b1 accumulated during periods of high organic carbon production and delivery of relatively fresh labile well preserved organic matter to the sea floor in contrast low toc hi high ox i heavier 15ntot and lighter 13corg isotopes indicate low primary productivity and delivery high recycling and poor preservation of organic matter during accumulation of lithofacies b2

quantitative paleoclimate reconstruction based on a 130 ka pollen record from the c9001c core off ne japan abstract although monsoons are an important climatic factor in the indo pacific region the mechanism responsible for monsoon variations is not fully understood particularly at the 10 5 year scale which includes the milankovitch orbital cycles here we provide a palynological result from the c9001c marine core drilled in the nw pacific off the shimokita peninsula eastern japan based on the parallel 18 o record the pollen record covers the past 130 000 years during the interglacial periods mis1 and 5e the c9001c core is dominated by cool temperate pollen of fagus beech and quercus subgenus lepidobalanus deciduous oak that is similar to the present day shimokita vegetation however during the glacial periods mis2 4 the pollen spectra are dominated by subarctic elements of betula birch and picea spruce similar to the vegetation of sakhalin and northern hokkaido these fossil pollen data are converted into quantitative climate variables by using the modern analog technique of the reconstructed paleoclimate variables the mean annual temperature tann correlates with the parallel 18 o record by contrast reconstructed precipitation in the summer psum shows a similar pattern to the northern insolation variations particularly during mis5 though the phase relation between the two curves requires further studies

palaeomagnetic and anisotropy of magnetic susceptibility data bearing on the emplacement of the western granite isle of rum nw scotland the western granite is the largest of several granitic bodies around the margin of the rum central igneous complex we report palaeomagnetic and anisotropy of magnetic susceptibility ams data that bear on the emplacement and deformation of the western granite the collection includes samples from 27 sites throughout the western granite five sites in adjacent feldspathic peridotite and two sites in intermediate to mafic hybrid contact aureole rocks palaeomagnetic data from 22 of the 27 sites in the granite provide an in situ group mean d 213 2 i 69 5 95 5 5 that is discordant to an early paleocene reverse polarity expected field about 184 66 95 4 3 the discrepancy is eliminated by removing an inferred 15 of northwest side down tilting about a best fit horizontal tilt axis trending 040 data from the younger peridotite and hybrid rocks of the rum layered suite provide an in situ group mean of d 182 6 i 64 8 95 4 0 which is statistically indistinguishable from an early paleocene expected field and imply no post emplacement tilting of these rocks since remanence acquisition the inferred tilt recorded in the western granite which did not affect the younger layered suite suggests that emplacement of the ultrabasic rocks resulted in roof uplift and associated tilt of the western granite to make space for mafic magma emplacement magnetic fabric magnitude and susceptibility parameters yield two subtle groupings in the western granite ams data set group 1 data defined by rocks from exposures to the east and south have comparatively high bulk susceptibilities kmean 29 51 10 3 in si system stronger anisotropies pj 1 031 and oblate susceptibility ellipsoids group 2 data from rocks in the west part of the pluton have lower values of kmean 15 89 10 3 si and pj 1 014 and triaxial susceptibility ellipsoids magnetic lineations argue for emplacement of the granite as a tabular sheet from the south southeast toward the north and west moderate to steeply outward dipping magnetic foliations together with deflection of the country rock bedding in the north are consistent with doming accompanying magma emplacement

paleogeography an earth systems perspective abstract paleogeography is the subdiscipline within the geosciences that studies the physical and biological geography of the geologic past including the configuration and latitudinal distribution of continental landmasses their topographic relief climate and biota in recent years the study of paleogeography has evolved from simple continental reconstructions to more sophisticated paleocontinental maps that form the basis of paleoclimactic modeling by incorporating elements of oceanic and atmospheric circulation and their interactive relationship with landmasses a broad range of geologic elements can be reconstructed through paleogeographic studies such as mountain belts climate zones emergent land and continental configurations many of which impact directly on understanding the driving forces behind geochemical signals contained in the rock record which are used as a proxy for biogeochemical processes in earth history paleogeography is thus an essential component of an earth systems approach to interpreting the geologic past paleoconfigurations of continents and ocean basins are determined by a variety of techniques paleomagnetic studies are the most common but additional constraints are provided by faunal provincialism biogeography and abiotic continental linkages such as pre break up magmatism recent developments within paleogeography include the use of various forms of climate models to analyze the relationships between global continental reconstructions and the rock record of past climates in order to test more directly feedback between paleogeography and paleoclimate development of an extended gis database for the geological past promises new insights into quantitative analysis of earth system evolution

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

erosion and deposition from bottom currents during the givetian and frasnian response to intensified oceanic circulation between gondwana and laurussia abstract calcareous bottom current deposits in otherwise pelagic and hemipelagic successions of the harz mountains in germany herzyn limestone formation the eastern moroccan central massif ziar mrirt nappe and the carnic alps in austria italy valentin and pal limestone formation show strong evidence of bottom current reworking of carbonate ooze during givetian and early frasnian associated phosphates confirm that higher hydraulic energy temporarily prevailed the bottom current deposited facies builds up strongly condensed and reduced successions with stratigraphic gaps which also occur with similar features in other areas of central europe and northwest africa at the same stratigraphic interval the widespread current induced reworking of calcareous sediments and phosphate formation during the givetian and early frasnian as well as the associated erosional processes marked by pronounced hiatuses all signal a major circulation event the temporal and spatial positions of these fossil calcareous contourites in the devonian are discussed research concluded that thermohaline currents were intensified by the acceleration of flows constricted in the narrow oceanic passages between the approaching continental plates laurussia and gondwana areas affected were the southeastern rhenish sea shelf the disintegrated northern continental margin of gondwana and deep marginal plateaus of the noric terrane in the western part of the prototethys the disposition of the fossil calcareous contourites and faunal data corroborate palaeogeographic reconstructions that show an advanced convergence between gondwana and laurussia and the smaller continental plates such as the armorican and noric terranes during givetian and frasnian times

a palaeomagnetic study of recumbently folded and thermally metamorphosed torridon group sediments eishort anticline skye scotland two geologically significant palaeomagnetic components have been isolated in samples of torridon group sandstones from the kishorn nappe of nw scotland the samples were collected from the eishort anticline a large recumbent fold of caledonian age the softer component which is demagnetized by low temperatures and weak magnetic fields when in situ displays a steep upward direction typical of reversed tertiary magnetizations both polarities of the harder component which is demagnetized by high temperatures only are present and when dip corrected display either northwesterly upward or southeasterly downward directions characteristic of torridonian remanences it is suggested that the tertiary component is of chemical origin and the result of alteration of magnetite titanomagnetite grains the geographical distribution of these grains is irregular and as a result the distribution of the tertiary overprint is irregular the torridonian palaeomagnetic components from both limbs of the fold can be restored by rotation about the fold axis to internally consistent directions which lie close to previously published data from the caledonian foreland no correction is necessary for finite strain which suggests that the eishort anticline formed by a flexural slip mechanism however an anticlockwise rotation of 26 is required to reconcile the torridonian directions from the kishorn nappe with those of the caledonian foreland which suggests that during emplacement the thrust sheet rotated on the underlying fault surface

production and preservation of organic matter during deposition of the bakken formation late devonian and early mississippian williston basin abstract the organic rich up to 35 toc lower and upper black mudstone members of the bakken formation late devonian and early mississippian accumulated in response to both increased productivity and enhanced preservation that resulted from unique palaeogeographic palaeoceanographic and palaeoclimatic conditions during bakken deposition the semi isolated williston basin was located close to the equator 5 to 10 n in a zone of prevailing east to west winds a pattern of estuarine like marine circulation between the williston basin and open ocean conditions at the western craton edge of north america is proposed surface water discharged from the basin was replaced by nutrient rich deeper water sourced from the equatorial undercurrent in the pacific basin undercurrent flow into the williston basin upwelled providing a potentially sustainable source of nutrients to enhance productivity in the surface photic zone during black mudstone deposition in response to increased productivity that led to a high rate of organic sedimentation and quiescent deep water conditions due primarily to the geographic isolation of the basin and the restriction of estuarine like circulation to the upper water column anoxic bottom water developed on the basin floor as sea level rose during lower and upper black mudstone deposition anoxic bottom water expanded across the basin enhancing organic matter preservation conditions in the williston basin demonstrate that both increased productivity and improved preservation can be essential and complementary factors affecting organic rich mud deposition these results have potentially important implications for the accumulation of similarly organic rich deposits across the north american interior during late devonian and early mississippian time

evolution of tethyan phosphogenesis along the northern edges of the arabian african shield during the cretaceous eocene as deduced from temporal variations of ca and nd isotopes and rates of p accumulation abstract the evolution of tethyan phosphogenesis during the cretaceous eocene is examined to try to explain fluctuations of phosphogenesis through time and whether or not they reflect long term changes in ocean circulation or in continental weathering twenty seven time stratigraphic phosphate levels in various tethyan sites covering a time span of about 90 myr from the hauterivian to the eocene were analyzed for 44 ca 42 ca and 143 nd 144 nd in their carbonate fluorapatite cfa fraction p and ca accumulation rates and bulk sedimentation rates were quantified throughout the cretaceous eocene negev sequence to examine how changes in 44 ca 42 ca and 143 nd 144 nd are reflected in the intensity of phosphogenesis a clear cut change occurs in e nd t and 44 ca and in the rates of p and ca accumulation and bulk sedimentation through the time analyzed e nd t is much lower in the hauterivian lower cenomanian 12 8 to 10 9 than in the upper cenomanian eocene 7 8 to 5 9 much lower 44 ca values occur in the hauterivian turonian 0 22 to 0 02 than in the coniacian eocene 0 23 to 0 40 p accumulation rates in the negev steeply increase from 2 k yr 1 in the albian coniacian to 1500 mol cm 2 k yr 1 in the campanian whereas a strong decrease is concomitantly recorded in the rates of ca accumulation and bulk sedimentation in addition distinct e nd t values are shown by the phosphorites of the negev 6 7 to 6 4 and egypt 9 1 to 7 6 during the campanian and by those of the negev 7 8 to 6 3 and north africa 10 1 to 8 9 during the maastrichtian eocene the culmination of p accumulation rates in the negev during the campanian occurring with a high in e nd t and 44 ca and a low in sedimentation rates indicates that paleoceanographic and paleogeographical factors mostly governed phosphorite accumulation in this area the abrupt e nd t rise after the cenomanian is attributed to increased incursion of pacific radiogenic water masses into the tethys driven by the late cretaceous global sea level rise the connection between north and south atlantic the global post santonian cooling and the progressive widening of the caribbean threshold all acting in combination to significantly intensify the tethyan circumglobal current tcc it also reflects a weakening of the continental nd signal due to a reduction of exposed landmasses caused by increased flooding of continental shelves high 44 ca values at those times also point to a decrease in weathering ca 2 fluxes and expansion of carbonate sedimentation in shelves both enriching seawater with isotopically heavy ca 2 deep ocean circulation intensified by the post santonian cooling of high latitudes increased p inventory in the tethys basin whereas the strengthened tcc and the folded shelf likely resulted in coastal and topographically induced upwelling supplying p rich intermediate waters to southeastern tethys shelves only in the paleocene eocene following major changes in global circulation produced by narrowing of tethys and widening of the atlantic did phosphogenesis shifts its locus of high intensity to the western atlantic tethys and west african atlantic coasts this change in paleocirculation is expressed by distinctly differing e nd t in the middle east and the north and west african phosphorites suggesting different oceanic p sources and current systems for these two major groups of phosphorites our nd isotope results further suggest a weaker tcc during the mid cretaceous becoming more intense in late cretaceous times they also point to the north pacific ocean as major source of deep water formation for the intermediate deep waters in the tethys basin during the late cretaceous

devonian carboniferous transition containing a hangenberg black shale equivalent in the pho han formation on cat ba island northeastern vietnam abstract on cat ba island in northeastern vietnam the devonian to carboniferous d c transition consists mainly of ramp carbonates intercalated with black shale beds beds 1 to 176 in the pho han formation and is one of the few records of the d c transition of the eastern paleotethys the three main facies of the sequence are facies 1 alternations of whitish gray to gray limestone and marl facies 2 calcirudite bed 115b and facies 3 alternations of dark gray limestone and organic carbon rich black shale beds 115c 120 and 126 129 the latest famennian siphonodella praesulcata subzone conodont assemblage of s praesulcata palmatolepis gracilis palmatolepis sigmoidalis and rhodalepis polylophodontiformis was recognized in beds 113 115c beds 105 112 commonly contain palmatolepis expansa p gracilis and p sigmoidalis bed 119 yielded a basal carboniferous index conodont siphonodella sulcata in beds 116 118 solenoporids such as pseudochaetetes elliotti and parachaetetes sp were characteristic species in organic carbon rich dark gray limestone facies 1 is characterized by bioclastic peloidal and intraclastic grainstone and packstone containing massive normal grading and cross laminations and is interpreted to represent deep ramp carbonates above storm wave base facies 2 is represented by typical lag deposits overlying a transgressive surface facies 3 comprises organic carbon rich black shale and minor scour filling bioclastic peloidal and intraclastic packstone and may represent a marginal basin plain environment surrounding a carbonate ramp the alternations of organic carbon rich black shale and dark gray packstone facies 3 show no evidence of bioturbation and have high toc contents 0 18 5 73 wt a minor succession within the transgressive lag deposits from bed 115b of facies 2 to beds 115c 120 in the lower part of facies 3 is equivalent to the hangenberg black shale s l in the middle part of the siphonodella praesulcata to siphonodella sulcata zones because beds 115b 120 characterized by no evidence of bioturbation and high toc contents are interpreted to be accumulated in anoxic to dysoxic conditions

plate motions and the geomagnetic field ii jurassic to tertiary summary the analysis of the time averaged geomagnetic field is extended back to 200ma palaeomagnetic poles from the major plates have been carefully selected from recent compilations of reliable results for each region these were returned with their corresponding sampling sites to their locations at the estimated dates of magnetization in a fixed hotspots framework the corrected results were then grouped into 20ma windows at intervals of 10ma representing the past 100ma and 40ma windows at 30ma intervals for the more sparse 100 200ma data global means and fisher statistics were calculated for each window having included the axial quadrupole in the calculation the value of this coefficient which gave the maximum value for the fisher precision parameter tightest grouping of poles was taken as representative of each interval the results indicate that a small axial quadrupole of the same sign as the axial dipole may have persisted throughout the cenozoic this is equivalent to a northward offset axial dipole field far sided effect during the late cretaceous this component appears to have changed sign with respect to the dipole negative values seem to have obtained throughout the cretaceous long normal polarity interval corresponding to a southward offset dipole near sided effect the data distribution is inadequate for the resolution of the quadrupole at earlier times and zero values cannot be discounted little relative motion is implied between the hotspots and the geomagnetic axis for the past 90 ma the global mean polar path curving around the predicted fixed hotspots pole at a distance of typically 5 latitude with little sign of rapid tertiary polar wander as implied by studies of pacific data alone between 100 and 200 ma however there is a clear difference between the two reference frames amounting to 17 19 in the jurassic this may reflect motion of the mantle relative to the geomagnetic axis but may also include errors due to inaccurate determination of hotspot tracks and inter hotspot motion

palaeomagnetic dating of sub torridon group weathering profiles nw scotland verification of neoproterozoic palaeosols a palaeoplain that cuts across lewisian gneiss in the cape wrath area northwest scotland is weathered to depths of 1 6 m beneath fluvial red conglomerates and sandstones of the applecross formation of the early neoproterozoic torridon group weathered lewisian rocks are enriched in k 2 o and fe 2 o 3 and contain hematite as an alteration product of biotite and magnetite palaeomagnetic analysis of the weathering profiles has been carried out to constrain the age of alteration thermal step demagnetization of 87 oriented core specimens of biotite gneiss and amphibolite spanning four profiles at poll a mhurain and sheigra reveal a stable high temperature component with a mean direction of remanence of d 149 1 i 57 2 95 5 0 corrected for dip of the overlying applecross strata that gives a pole at 9 8 s 199 2 e dp 5 3 dm 7 3 this direction differs significantly from that for little weathered lewisian at those two localities and also from directions for the late mesoproterozoic stoer group the remanence direction for the weathered rocks is however near the dip corrected high temperature remanence direction d 122 3 i 50 5 95 10 8 obtained by us from the thermal step demagnetization of 39 sandstone specimens of the applecross formation in the cape wrath area furthermore the direction for the weathered rocks agrees closely with other dip corrected results for the torridon group such as the detrital remanent magnetization drm mean direction d 148 3 i 59 9 95 13 8 for the applecross formation on rum and that for the main outcrop of the aultbea formation d 139 7 i 52 6 95 14 5 the concordance of palaeomagnetic results for the sediments and weathered rocks implies that the weathering profiles in the cape wrath area acquired their remanence penecontemporaneously with deposition of the applecross and aultbea formations the palaeomagnetic results therefore argue strongly that the weathering profiles are palaeosols of applecross age c 980 ma that formed at a palaeolatitude of 38 and constitute the oldest known palaeosols in the british isles views that the weathering is substantially older or younger than applecross deposition cannot be sustained our findings carry implications for applecross palaeoclimate and source and strengthen the conclusion that atmospheric oxygen was a substantial fraction of its present abundance by early neoproterozoic time