the late devensian periglaciation of upland scotland abstract a wide variety of late devensian periglacial landforms developed on scottish mountains both before ca 13 000 bp and during the loch lomond stadial of ca 11 000 10 000 bp nearly all such features are now inactive late devensian periglacial weathering produced three types of regolith mantle openwork block deposits sandy diamicts and silt rich frost susceptible diamicts each of which supports a characteristic assemblage of relict landforms on upper slopes these include large scale sorted circles and stripes earth hummocks and nonsorted relief stripes sorted and nonsorted solifluction features massive boulder sheets and lobes and nivation benches talus protalus ramparts rock glaciers and alluvial fans also developed at the base of mountain slopes the distribution of late devensian periglacial features on scottish mountains is locally controlled by topography the response of underlying rocks to periglacial weathering and the limits of former glaciers regional variations in the altitude of certain forms of loch lomond stadial age particularly protalus ramparts and rock glaciers indicate a decrease in former snowfall eastwards across the scottish highlands and northwards from the highland boundary fault several upland periglacial features are also diagnostic of former permafrost and complement palaeotemperature reconstructions based on ice wedge casts and the equilibrium firn line altitudes of stadial glaciers these suggest that under stadial conditions mean january temperatures at 600 m and 1000 m on mountains in the western grampians must have been no higher than 20 c and 23 c respectively and possibly several degrees lower

current scattered detrital remanence directions in the zn rich pennsylvanian stark black shale usa summary palaeomagnetic results are reported from the metalliferous stark black shale in the upper pennsylvanian missourian kasimovian kansas city group palaeomagnetic analysis of 400 specimens from 28 sites gives a characteristic remanent magnetization in 17 sites of the shale that yields a late mississippian to middle pennsylvanian palaeopole at 32 2 n 128 5 e dp 4 7 and dm 8 8 the observed palaeomagnetic age is slightly older than the host rock indicating that the mineralization of the stark shale has excluding recent alteration a primary sedimentary or syngenetic origin the reason for the slightly older age is likely due to trace modern hematite that slightly steepens the remanence inclination the large oval of 95 per cent confidence is interpreted to be caused by clay magnetite aggregates that formed during sediment transport and the biasing effect of the gentle palaeocurrent at each site acting on the large aggregates therefore the scattered distribution of the site mean remanence declinations found for the stark shale is evidence of a detrital remanent magnetization that is formed by primary sedimentary processes with an enriched metallic content and not remagnetization with mineralization by secondary hydrothermal processes

rapid localized glacio isostatic uplift at glen roy scotland many studies involving measurement of the altitudes of fossil marine and lacustrine shorelines have demonstrated glacioisostatic tilting particularly in north america fennoscandia and the british isles such studies are normally illustrated by height distance diagrams in which fossil shorelines are portrayed as straight lines in some studies the shoreline relation diagram is used to analyse and illustrate the altitudinal data1 3 before constructing such a diagram it is assumed that a simple pattern of glacioisostatic uplift has prevailed warping of shorelines as opposed to uniform tilting has been inferred in north america4 6 on the other hand harme7 envisaged block movements in fennoscandia sauramo8 also proposed dislocations but his interpretation was rejected by hyyppa9 more recently the concept of the scandinavian shield as a stable area has been dismissed10 11 here we provide evidence from scotland for shoreline dislocation by differential movement of blocks of the earth s crust

deglacial warming of the northeastern atlantic ocean correlation with the paleoclimatic evolution of the european continent abstract isotopic micropaleontologic and pollen analyses of deep sea cores from the bay of biscay and the northeastern atlantic ocean show that the deglacial warming of this oceanic area was closely correlated with the paleoclimatic evolution of the adjacent european continent temperatures were at least as warm as those of today in the bay of biscay between 13 300 and 11 000 b p coinciding with the combined bolling allerod warm continental events a major spread of polar water occurred between 11 000 and 10 000 b p during this event which coincides with the younger dryas continental cold event marine temperatures were almost as low as those of the last glacial maximum the final deglacial warming of the norteastern atlatntic ocean occurred during the following 3000 yr

reductive diagenesis magnetite dissolution greigite growth and paleomagnetic smoothing in marine sediments a new view abstract in many anoxic sedimentary environments the onset of sulfate reduction and pyritization of detrital iron bearing minerals leads to a precipitous decline in magnetic mineral concentration during early diagenesis the usefulness of the surviving paleomagnetic record in such environments is usually argued to depend on how much of the primary detrital magnetic assemblage survives diagenetic dissolution detailed rock magnetic and electron microscope analyses of rapidly deposited 7 cm kyr latest pleistocene holocene sediments from the continental margins of oman 22 22 4 n 60 08 0 e and northern california 38 24 8 n 123 58 2 w demonstrate that pyritization during early diagenesis also leads to the progressive down core growth of the ferrimagnetic iron sulfide greigite greigite growth begins with nucleation of large concentrations of superparamagnetic sp nanoparticles at the inferred position of the sulfate methane transition which can explain the apparently paradoxical suggestion that diagenetically reduced sediments contain enhanced concentrations of sp particles looping of hysteresis parameters on a day plot records the dissolution of single domain sd titano magnetite and the formation of sp greigite which then slowly and progressively grows through its sd blocking volume and acquires a stable paleomagnetic signal this looping trend is also evident in data from several published records oregon margin korea strait japan sea niger fan argentine margin and the ontong java plateau indicating that these processes may be widespread in reducing environments our observations have profound implications for paleomagnetic records from sulfate reducing environments the paleomagnetic signal recorded by greigite is offset from the age of the surrounding sediments by 10 s of kyr and ongoing growth of greigite at depth results in smoothing of the recorded signal over intervals of 10 s to 100 s of kyr we therefore expect the presence of greigite to compromise paleomagnetic records in a wide range of settings that have undergone reductive diagenesis

the role of diagenetic carbonate concretions in the preservation of the original sedimentary record the upper cretaceous organic rich limestones and marls of the tarfaya basin of southwest morocco contain numerous calcite concretions which formed during early diagenesis relative textural similarities are observed both in the concretions and in the host sediments however the biological content of the concretions is considerably higher than in the host marls and limestones evidence for fossil dissolution in the host marls and the absence of concretions in some fossil rich zones suggest that the difference in fossil abundance between the concretions and host rock is a function of dissolution rather than preferential precipitation in fossil rich areas consequently the carbonate concretions appear to represent the memory of the sediment and allow quantification of the original biological components and are potential tools for estimating the original biological material deposited in the soft sediments

foraminiferal response to sea level change organic flux and oxygen deficiency in the cenomanian of the tarfaya basin southern morocco the mohammed plage coastal section and well s13 in the tarfaya basin southern morocco are key sections to investigate the subsidence of the basin and the cenomanian eustatic sea level history results from a canonical correspondence analysis cca based on benthic foraminiferal assemblage counts and additional proxies percent planktic foraminifera planktic foraminifera morphogroups total organic carbon content toc show a general deepening trend for the investigated sections the most important factor identified in the ordination of species and samples is water depth the cca identifies bolivina anambra globulina lacrima lenticulina spissocostata and spiroplactammina sp as typical shallow water species praebulimina nannina gavelinella dakotensis gavelinella sp saccammina alexanderi and valvulineria lenticula as deep water species and gabonita levis gabonita obesa neobulimina albertensis lingulogavelinella asterigerinoides lenticulina gaultina haplophragmoides gigas haplophragmoides bauchensis and trochammina taylorana as unrestricted or intermediate species the temporal succession of benthic foraminiferal assemblages indicates repeated periods of shallowing within the general deepening trend in particular within the lower portion of the sections rotalipora brotzeni and r reicheli planktic foraminiferal zones restricted assemblages occurred when intensification of the oxygen minimum zone inhibited a diverse benthic community abundant high organic flux indicators at the base of the mohammed plage section indicate that an upwelling cell off northwest africa was already active during the early cenomanian c 2004 elsevier b v all rights reserved

engineering properties of fibrous peats this state of the art paper presents an interpretation of the permeability compressibility and shear strength of fibrous peats using data from laboratory tests on undisturbed block samples of two fibrous peats as well as extensive laboratory and field data from the literature on fibrous peat deposits engineering properties of fibrous peats are significantly different from those of most inorganic soils however the same fundamental mechanisms and factors determine behavior of both inorganic soils and fibrous peats fibrous peat deposits possess very high initial permeability typically 1 000 times the initial permeability of soft clay and silt deposits upon compression the permeability of fibrous peats decreases dramatically with a ratio of permeability change index to in situ void ratio equal to 0 25 as compared to 0 50 for soft clay and silt deposits fibrous peats display extreme compressibility to the increase in effective vertical stress with compression index values right after preconsolidation pressure 5 to 20 times the corresponding compressibility of typical soft clay and silt deposits among geotechnical materials fibrous peats display the highest ratios of secondary compression index to compression index in the range of 0 05 to 0 07 the values of coefficient of earth pressure at rest for normally consolidated young fibrous peat deposits are in the range of 0 30 to 0 35 as compared to 0 45 to 0 65 for inorganic soils the values of friction angle from triaxial compression tests for fibrous peats are in the range of 40 to 60 as compared to less than 35 for soft clay and silt compositions for fibrous peats the ratios of undrained shear strength in compression to preconsolidation pressure are usually in the range of 0 50 to 0 75 as compared to 0 32 for soft clay and silt deposits for surficial fibrous peat deposits the ratio of vane shear strength to preconsolidation pressure is near 1 0 as compared to 0 12 to 0 35 for inorganic soft clay and silt deposits for fibrous peats the ratio of undrained young s modulus to undrained shear strength is in the range of 20 to 80

enhanced productivity led to increased organic carbon burial in the euxinic north atlantic basin during the late cenomanian oceanic anoxic event 1 three cenomanian turonian c t 93 5 ma black shale sections along a northeast southwest transect in the southern part of the proto north atlantic ocean were correlated by stable carbon isotope stratigraphy using the characteristic excursion in 13c values of both bulk organic matter om and molecular fossils of algal chlorophyll and steroids all three sites show an increase in marine organic carbon oc accumulation rates during the c t oceanic anoxic event oae the occurrence of molecular fossils of anoxygenic photosynthetic green sulfur bacteria lack of bioturbation and high abundance of redox sensitive trace metals indicate sulfidic conditions periodically reaching up into the photic zone before as well as during the c t oae during the c t oae there was a significant rise of the chemocline as indicated by the increase in concentrations of molecular fossils of green sulfur bacteria and mo al ratios the presence of molecular fossils of the green strain of green sulfur bacteria indicates that euxinic conditions periodically even occurred at very shallow water depths of 15 m or less during the c t oae however bottom water conditions did not dramatically change as indicated by more or less constant v al and zn al ratios at site 367 this suggests that the increase in oc burial rates resulted from enhanced primary productivity rather than increased anoxia which is supported by stable carbon isotopic evidence and a large increase in ba al ratios during the c t oae the occurrence of the productivity event during a period of globally enhanced organic carbon burial rates i e the c t oae points to a common cause possibly related to the formation of a deep water connection between north and south atlantic basins

palaeomagnetic evidence for early pleistocene in the central and northern north sea the palaeomagnetic evidence presented here refutes the earlier hypothesis that most of the quaternary succession in the central north sea area is of middle to upper weichselian age a study of the quaternary seismic stratigraphy has been tied to 11 cored boreholes which are being examined for their physical properties and faunal content initial palaeomagnetic studies show a major reversely magnetized zone which can be correlated from borehole to borehole and with the seismic stratigraphy this reversely magnetized zone is thought to represent the matuyama epoch which ended 790 000 yr bp consequently this suggests the presence of early pleistocene strata in the central and northern north sea

palaeosecular variation over the past 5 myr based on a new generalized database summary a generalized database of global palaeomagnetic data from 3719 lava flows and thin dykes of age 0 5 ma has been constructed for use with a relational database management system the database includes all data whose virtual geomagnetic poles vgp lie within 45 of the spin axis and can be used for studies of palaeosecular variation and for geomagnetic field modelling because many of these data were collected and processed more than 15 20 years ago each result has been characterized according to the demagnetization procedures carried out analysis of these data in terms of the latitude variation of the angular dispersion of vgps palaeosecular variation from lavas strongly suggests that careful data selection is required and that many of the older studies may need to be redone using more modern methods differences between the angular dispersions for separate normal and reverse polarity data sets confirm that many older studies have not been adequately cleaned magnetically therefore the use of the database for geomagnetic field modelling should be carried out with some caution using a vgp cut off angle that varies with latitude the best data set consists of 2636 results that show a smooth increase of vgp angular dispersion with latitude model g for palaeosecular variation which is based on modelling of the antisymmetric dipole and symmetric quadrupole dynamo families provides a good fit to these results

postconstruction settlement of an expressway built on peat by precompression this paper presents the analysis of 18 years of settlement observations of two expressway embankments built on a peat deposit with an initial depth of 3 0 5 8 m using the precompression technique observations show that upon removal of the temporary surcharge the highway embankments heaved for about 1 year by a total of 4 3 7 9 cm this foundation movement was followed by slow rate settlement for a few years and subsequently by additional secondary settlement occurring at a greater rate of settlement versus logarithm of time eighteen years after construction settlements range from 2 7 to 11 9 cm it is concluded that precompression has been effective in reducing postconstruction settlement by about 65 and its effectiveness on the long term settlement was experienced for years after that the rate of settlement became identical to that of the normally consolidated peat key words peat precompression technique secondary compression long term settlement field observation swelling surcharge

upper cretaceous palaeoenvironments and benthonic foraminiferal assemblages of potential source rocks from the western african margin central atlantic abstract upper cretaceous benthonic foraminiferal assemblages clay minerals kerogen types and carbonate microfacies are examined in organic rich sediments from western african coastal basins along a latitudinal transect extending from southern morocco to nigeria samples from onshore sections of the tarfaya basin southern morocco from dsdp site 369 from offshore commercial wells on the casamance shelf senegal from dsdp site 367 from odp site 959 and from onshore sections of the benue trough in nigeria are analysed organic rich sediments from these sites are characterized by smectiterich clay mineral assemblages high amounts of marine organic matter and a typical benthonic foraminiferal biofacies dominated by buliminids and bolivinids benthonic foraminifera provide robust proxy indicators of palaeoproductivity and organic matter flux to the seafloor the palaeobiogeographic distribution of benthonic foraminiferal biofacies can be used to identify areas and stratigraphic intervals of hydrocarbon accumulation lower turonian benthonic foraminiferal assemblages exhibit extremely low diversity and are strongly dominated by a gabonita biofacies in contrast to coniacian to maastrichtian assemblages which display higher diversity and contain numerous species of buliminella praebulimina afrobolivina bolivina and orthokarstenia the palaeobathymetric distribution of these high productivity benthonic foraminiferal biofacies reflects the establishment of a productivity driven oxygen minimum zone along the western african shelf associated with an upwelling system active off coastal africa during most of the late cretaceous the extent of the high productivity equatorial belt appears to have shifted latitudinally during the late cretaceous as sea level and circulation patterns changed the zone of highest productivity was broadest in the early turonian when it coincided with the maximum sea level rise and highest atmospheric temperature in the late cretaceous

differential glacio isostatic uplift of crustal blocks at glen roy scotland abstract detailed measurements of the altitudes of the shorelines of former ice dammed lakes in glen roy and vicinity in the scottish highlands prove erroneous the conventional view that former shorelines in areas affected by glacio isostatic uplift are uniformly tilted and or gently warped the measurements demonstrate differential uplift of blocks of the earth s crust the surfaces of some blocks have no detectable tilt whereas others have gradients up to at least 4 6 m km and are tilted in different directions in three areas 0 7 2 0 km long shorelines are distorted by crustal movements all these areas have landslides attributed to earthquakes that accompanied the release of stress in the area of greatest local distortion three shorelines rose about 3 m above their average altitudes for the immediately surrounding area and a fault scarp was produced possibly these local distortions accompanied catastrophic lake drainage by jokulhlaup analogous to crustal movements associated with man made lakes a relationship between crustal movement and the limit of a glacial advance is demonstrated these findings have implications for other parts of the world affected by glacioisostatic uplift

a new geomagnetic polarity time scale for the late cretaceous and cenozoic we have constructed a magnetic polarity time scale for the late cretaceous and cenozoic based on an analysis of marine magnetic profiles from the world s ocean basins this is the first time since heirtzler et al 1968 published their time scale that the relative widths of the magnetic polarity intervals for the entire late cretaceous and cenozoic have been systematically determined from magnetic profiles a composite geomagnetic polarity sequence was derived based primarily on data from the south atlantic anomaly spacings in the south atlantic were constrained by a combination of finite rotation poles and averages of stacked profiles fine scale information was derived from magnetic profiles on faster spreading ridges in the pacific and indian oceans and inserted into the south ariantic sequence based on the assumption that spreading rates in the south atlantic were smoothly varying but not necessarily constant a time scale was generated by using a spline function to fit a set of nine age calibration points

evidence for two pre flandrian palaeosols in buchan north east scotland evidence is presented for the existence of two distinct pre flandrian palaeosols at a single site kirkhill quarry in buchan north east scotland this is the first such site reported from scotland and it is possible that the two palaeosols represent interglacial episodes which are equivalent in age to last interglacial compare with ipswichian and the penultimate interglacial compare with hoxnian a combination so far unknown in the british isles the stratigraphy also demonstrates that the part of the buchan plateau under study may have been glaciated on at least three separate occasions

new faunal and isotopic evidence on the late weichselian holocene oceanographic changes in the norwegian sea downcore studies of planktonic and benthonic foraminifera and 18o and 13c in the planktonic foraminifer neogloboquadrina pachyderma sin in two piston cores from the southern part of the norwegian sea suggest large changes in the oceanic circulation pattern at the end of oxygenisotope stage 2 and in the early part of stage 1 prior to oxygen isotope termination ia 16 000 13 000 yr b p an isolated watermass with lower oxygen content and temperature warmer than today existed below a low salinity ice covered surface layer in the norwegian sea close to termination ia well oxygenated deep water probably with positive temperatures was introduced this deep water which must have had physical and or chemical parameters different from those of present deep water in the norwegian sea could have been introduced from the north atlantic or been formed within the basin by another mechanism than that which forms the present deep water of the norwegian sea a seasonal ice cover in the southern part of the norwegian sea is proposed for the period between termination ia and the beginning of ib close to 10 000 yr b p the present situation with strong influx of warm atlantic surface water and deep water formation by surface cooling was established at termination ib

description and dating of a submerged beach in the northern north sea abstract an assumed submerged beach bordering the northern part of the north sea plateau towards the norwegian trench at 130 to 160 m waterdepth has previously been described based on interpretation of seismic profiling the seismic unit is parallel to the edge of the plateau for at least 50 km with an eastward dipping bedding soil borings and vibrocorer samples reveal that a stiff to hard clay is overlain by a thin lag deposit of coarse material on the plateau by an up to 40 m thick coarsening upwards sequence of sand and gravel on the upper part of the slope and by gradually finer material further eastwards in deeper water a low sea level is also indicated by the foraminiferal faunas and abundant littoral and aeolian textures on quartz sand grains nine radiocarbon datings of shell material found in sand and gravel from about 1 to 23 m below the sea bed gave ages from 10 800 to 12 500 yrs b p we thus consider the interpretation of the edge of the plateau and the top of the slope as a submerged beach built out in late weichselian time to be confirmed by the sample evidence

the submerged landforms of the st kilda archipelago western scotland abstract a detailed bathymetric map of the area around the st kilda archipelago has been prepared with a 10 m isobath vertical interval the map reveals two major submerged erosional surfaces that culminate in clifflines the lower surface at ca 120 m covers at least 40 km2 and is thought to have been produced during low sea levels coincident with periods of maximum northern hemisphere glaciation the upper surface is complex in origin varying between 80 and 40 m it is thought to have been produced during periods of partial northern hemisphere glaciation the last such period the loch lomond younger dryas stadial being responsible for the production of the ca 40 m cliff platform junction the last 40 m relative rise of sea level has been accompanied by very little marine erosion despite the very exposed situation of the islands and this sea level rise is thought to have taken place during the flandrian

laboratory testing and in situ behaviour of peat as embankment foundation reply intact block samples of fibrous peat have been obtained using special equipment from two different sites in the james bay territory in quebec instrumented test fills were subsequently built at those two sites and the observed behaviour was used to check the laboratory data the laboratory testing program has included standard 24 h incremental tests and stage creep tests where constant loads were applied for periods of about 30 d pore pressure and direct permeability measurements were conducted in most of the tests the tests have been interpreted using the classical e log p curves or the tangent modulus approach the evaluation of compression with time under a constant load has allowed the distinction between primary and secondary consolidation a certain lag in pore pressure response has been observed and related to incomplete saturation the coefficient of permeability decreases rapidly with compression as indicated by direct measurements and pore pressure dissipation the comparison with field observ

geomagnetic secular variation in the cretaceous normal superchron and in the jurassic abstract it is now widely thought that geomagnetic polarity reversals occur spontaneously as a result of normal dynamo action rather than being externally triggered if this is the case then it may well be that periods of time in which the geomagnetic reversal frequency was dramatically different were characterised by different styles of secular variation two such periods were the cretaceous normal superchron cns 84 125 ma when the field was dominantly of a single polarity for 40 myr and the jurassic period 145 200 ma when reversals occurred at an average rate of as much as 4 6 myr 1 here we analyse a database of new and published palaeomagnetic directions from lavas emplaced during these periods in order to obtain first order descriptions of the palaeosecular variation psv during these times we then compare these records with one another and with that produced for the period 0 5 ma with average reversal frequency of 4 0 myr 1 our results are more equivocal than those obtained in a previous similar study mcfadden p l merrill r t mcelhinny m w lee s h 1991 reversals of the earths magnetic field and temporal variations of the dynamo families journal of geophysical research solid earth and planets 96 3923 3933 we demonstrate that this is probably a result of the previous study being affected by an artefact of their correction for within site scatter the usefulness of our jurassic record is severely limited by the restricted palaeolatitudinal span of the available data however our record for the cns is sufficient to allow us to conclude that it was likely that secular variation then was different from that in the 0 5 ma period this supports the hypothesis of a link between psv and reversal frequency and therefore endorses psv analysis as a first order tool for determining geomagnetic stability in the past

lower pleistocene dinoflagellate cyst foraminiferal and pollen assemblages in four boreholes in the southern north sea neogene and lower pleistocene stratigraphy in the southern north sea has been investigated in four i g s boreholes between east anglia and the netherlands the foraminifera of the red crag formation in borehole 81 51 are closely similar to upper pliocene assemblages in holland the overlying succession is clearly punctuated by unconformities in seismic profiles separating four early pleistocene formations in the boreholes and indicating intervals of significant stratigraphic hiatus offshore the westkapelle ground and smith s knoll formations correlate with thurnian and antian stage deposits in east anglia pollen spectra in the winterton shoal and yarmouth roads formations are similar to baventian and bramertonian assemblages in britain the autochthonous marine and allochthonous terrestrial microfauna and flora provide conflicting evidence of early pleistocene palaeoclimate the dinoflagellate cysts and foraminifera indicate that each formation was deposited in a warm temperate neritic environment the pollen record containing evidence of fluctuation between boreal and mixed coniferous deciduous regional forest cover suggests alternation between cool and warm temperate palaeoclimate

nitrate reduction sulfate reduction and sedimentary iron isotope evolution during the cenomanian turonian oceanic anoxic event onset of the oae in italy have unusually low bulk d 57 fe values unlike those found in the black shale livello bonarelli deposited during the oceanic anoxic event itself these latter conform to the phanerozoic norm for organic rich sediments pyrite formation in the pre oae black shales has apparently taken place via dissimilatory iron reduction dir within the sediment a suboxic process that causes an approximately 2 fractionation between a lithogenic fe iii oxide source and fe ii aq in contrast bacterial sulfate reduction bsr at least partly in the water column characterized the oae itself and was accompanied by only minor iron isotope fractionation this change in the manner of pyrite formation is reflected in a decrease in the average pyrite framboid diameter from 10 to 7 mm the gradual albeit irregular increase in fe isotope values during the oae as recorded in the italian section is taken to demonstrate limited isotopic evolution of the dissolved iron pool consequent upon ongoing water column precipitation of pyrite under euxinic conditions given that evidence exists for both nitrate and sulfate reduction during the oae it is evident that redox conditions in the water column were highly variable in both time and space

palaeoenvironmental evolution of the late cretaceous sequence in the tarfaya basin southwest of morocco abstract the late cretaceous sedimentary evolution of the tarfaya basin is reviewed based on late albian campanian outcrops and two cored exploration wells s13 and s75 with a stratigraphic range from the early cenomanian to the late turonian standard sedimentological and micropalaeontological methods were used together with clay mineralogy and organic geochemistry two distinct depositional environments were found the first is late albian early middle cenomanian in age and dominated by terrigenous silici and bioclastic sediments containing primarily terrestrial organic matter with a low organic content abundant illite and chlorite eroded from crystalline rocks outcropping in the anti atlas mountain and mauritanides is present as is abundant kaolinite reworked from soils surrounding the tarfaya basin the second environment comprises late cenomanian campanian sediments characterized by pelagic marls and limestones with a high organic content and a abundant pelagic macro and microfauna these sediments which were probably deposited in an upwelling system are characterized by higher contents of smectite

palaeomagnetic and ams study of the tarfaya coastal basin morocco an early turonian palaeopole for the african plate abstract an early turonian c 93 ma anoxic cyclic marine deposition is registered in the unfolded outcrops from the tarfaya coastal basin where very high sedimentation rates enable the investigation of past geomagnetic field record at high temporal resolution one hundred and fourteen samples have been sampled along a 10 5 m vertical profile c 200 500 ka of orbital scale forced sedimentation rock magnetic investigations reveal mineralogy principally controlled by diamagnetic and paramagnetic behaviour along with very low concentrations of low coercivity ferromagnetic material which is probably magnetite a well defined magnetic fabric can be seen with the minimum susceptibility axis perpendicular to the foliation plane and magnetic lineation compatible with nw african palaeostress since sedimentation times and or the palaeocurrent associated with upwelling system deposition magnetic signature has the potential for performing reliability checks of reversed tiny wiggles which were found in four samples not considered for the tectonic analysis alternating field demagnetization shows a single stable low coercivity directional component the new palaeopole n 88 plat 64 3 plon 256 3 a 95 2 5 k 38 7 obtained after moderate f 0 8 inclination flattening correction is the first early turonian palaeopole for the nw african craton it can contribute to the 90 ma centred sliding window of the different proposed synthetic apparent polar wander paths

pseudo ice wedge casts of connecticut northeastern united states since 1965 ice wedge casts have been reported in deposits of sand and gravel in connecticut these are wedge forms up to 1 1 m wide and many meters high most are single forms not in polygonal array they are found in adjoining states as well their distribution dimensions structure and fabric and an assessment of the former physical environment preclude their origin as permafrost features they appear to be tension fractures produced by the loading of coarse clastics on fine clastics near and below the water table where sediments creep toward a stream or depression locally movement started with kettle formation during deglaciation however some wedges cut horizontal layers of iron coated sand and gravel and must be younger than those distinctly postglacial phenomena moreover modern b horizons of the overlying soil have moved down into some wedges more than 2 m indicating that fracturing is still active today complex fracture fillings in bedrock also have been attributed to a permafrost origin but this too seems unlikely

the mode and mechanism of the last deglaciation oceanic evidence changes in ocean temperature carbonate productivity and ice rafted detritus in the north atlantic suggest that half of the northern hemisphere ice volume at the last glacial maximum had disappeared by 13 000 yr b p despite the still extensive limits of the ice sheets this early thinning of the ice sheets occurred during a time when summer insolation values were slowly rising but when pollen evidence south of the ice margins indicates cold dry air masses we infer that this rapid early ice disintegration 16 000 13 000 yr b p was caused by oceanic mechanisms 1 rising sea level causing increased calving along ice margins 2 the chilling of the sea surface by icebergs and meltwater reducing moisture extraction by the atmosphere and transport to the ice sheets and 3 winter freezing of the low salinity meltwater layer suppressing local moisture extraction and the regional influx of moisture bearing storms from lower latitudes in winter and hence starving the ice sheets these oceanic feedback mechanisms were strongest from 16 000 to 13 000 yr b p and weaker but still active from that date until the end of deglaciation at 6000 yr b p

reversed polarity characteristic magnetizations in the albian contessa section umbrian apennines italy implications for the existence of a mid cretaceous mixed polarity interval paleomagnetic and paleontologic data from the valle della contessa umbrian apennines italy span a 14 m y gap in previous magnetostratigraphic sections and reveal several intervals of reversed characteristic remanent magnetization chrm in limestones and marls of the albian marne a fucoidi rock magnetic data indicate that the reversed chrm is carried by hematite having high unblocking temperatures 625 690 c hematite with these unblocking temperatures also carries a normal polarity chrm in other intervals a potential bias towards the identification of normal polarity is present since at every horizon measured a normal polarity component carried by magnetite and hematite is isolated at lower unblocking temperatures 300 600 c bulk magnetic properties vary throughout the measured section in the portion containing most of the reversed chrm intervals hematite is the dominant carrier of natural remanent magnetization while magnetite is the dominant carrier stratigraphically above and below these changes correspond approximately with lithology the zone of dominant hematite magnetization is marked by reddish bands pigmentary hematite which can be correlated throughout umbria and are thought to record changes in the oxidation state of the seafloor during deposition two models may account for the observed magnetization directions the reversed magnetizations may record a remagnetization which occurred at least 18 m y after deposition while the beds were still flat lying in reversed polarity chron 33r 83 79 ma or later if the reversed chrm represents a remagnetization the process is potentially of great importance since it can produce magnetization patterns which resemble polarity intervals alternatively the reversed magnetizations may have been acquired during intense seafloor oxidation episodes during the mid albian 107 104 ma and may record unrecognized intervals of reversed geomagnetic field polarity milankovitch like bedding cyclicity can be used to tune the sedimentation rate and obtain estimates of the duration of the potential reversed intervals using these estimates two of the potential reversed polarity intervals are of sufficient duration 100 kyr to be recognizable in both detailed stratigraphic sections and marine magnetic anomaly surveys a primary magnetization model predicts that several intervals of reversed magnetization should be found near the boundary of the biticinella breggiensis and ticinella primula foraminiferal zones and within the prediscosphaera cretacea nannofossil zone on a worldwide basis

orbital scale record of the late cenomanian turonian oceanic anoxic event oae 2 in the tarfaya basin morocco high sedimentation rates up to 12 cm kyear of laminated organic carbon rich biogenic limestones in the tarfaya basin provide an unusually high millennial resolution record of the late cenomanian oceanic anoxic event oae 2 the global positive carbon isotope excursion across the cenomanian turonian corresponds to 11 light dark sedimentary cycles we interpret these cycles as a response to orbital obliquity variation and estimate the duration of the complete excursion as 440 kyear or one long eccentricity cycle on this time scale the main increase in delta 13 c values occurred over a short time interval of less than 20 kyear in the late cenomanian and reached a first maximum approximately 15 kyear prior to the bulk mainly coccoliths delta 18 o derived sea surface maximum temperature that occurs coeval to the extinction of rotalipora cushmani organic carbon accumulation rates follow obliquity cycles reaching a maximum approximately 10 kyear after the last occurrence of r cushmani then slowly decreasing during the early turonian thus the maximum temperature and the maximum organic carbon accumulation in the tarfaya basin lagged by at least 15 kyear behind the global carbon isotope shift and a proposed reduction of atmospheric co 2 content the climate change across the cenomanian turonian boundary probably occurred independent of co 2 levels and may have been controlled by different greenhouse gases water vapour and methane and changes in ocean circulation i e opening of the equatorial atlantic gateway

the quaternary deposits and landforms of scotland and the neighbouring shelves a review abstract a thick sequence of quaternary sediments up to 1000 m has been deposited in the north sea basin and perhaps five major glacial episodes the first occurring prior to ca 1 8 2 1 ma bp and the last during the late devensian can be recognised between the glacial events periods of low salinity arctic marine or glacio marine sedimentation have been dominant although episodes of ameliorated climate when north atlantic drift waters had access to the north sea have been identified a number of horizons in separate boreholes have been correlated with the last interglacial oxygen isotope stage 5e and a sequence of water mass movements around the scottish coasts can be reconstructed for the last ca 125 ka on land sequences of quaternary deposits relating to several glacial and non glacial terrestrial and marine events occur in different areas but due to poor dating correlation between these sequences cannot yet be achieved in particular north east scotland has a complex glacial history with evidence for ice sheet glaciation on at least four occasions evidence from the outer hebrides north east scotland and the north sea basin indicates that the late devensian scottish ice sheet had a rather restricted extent only reaching a short distance offshore along much of the east and west coasts at this time ice free areas existed in north east scotland on the isle of lewis and probably in caithness and orkney whilst part of the outer shelf around st kilda was dry land a marine embayment extended down the east coast of scotland between the scottish and scandinavian ice sheets and independent ice caps existed on the outer hebrides and probably on shetland deglaciation of the greater part of the country took place prior to ca 13 ka bp whilst the climate was still very cold the ice retreat appears to have been orderly with stagnant ice masses being trapped only in topographically suitable locations a number of retreat stages or minor readvances occurred during the general deglaciation the firth of clyde was one of the last areas outside the highlands to be deglaciated and this occurred in a rapid possibly catastrophic fashion shortly prior to ca 13 ka bp despite the mild climate at the start of the lateglacial interstadial it is not known if there was complete deglaciation prior to the loch lomond readvance the readvance glaciers however may have started to advance during the latter part of the interstadial when declining terrestrial temperatures coincided with a period of mild marine conditions the loch lomond readvance maximum can only be dated to some time after ca 10 9 ka bp and it is likely that final ice free conditions were not achieved until the earliest holocene

integrated depositional model for the cenomanian turonian organic rich strata in north africa abstract during the late cenomanian early turonian c t oceanic anoxic event oae2 organic rich strata was deposited in rift shelf basins and slopes across north africa and in deep sea basins of the adjacent oceans based on a review of published and unpublished information this paper documents the distribution and organic richness of c t strata across the whole region within a palaeogeographic framework and systematically analyses the conditions and processes which controlled their deposition previously the c t in north africa has been most intensively studied in southern morocco tarfaya and tunisia only little data is availabe for other parts of north africa namely algeria libya and egypt because distribution of c t corg strata there becomes more patchy a general decrease in peak organic richness and black shale thickness occurs from west to east partly as a result of upwelling along the moroccan atlantic coast and the absence of upwelling in the eastern mediterranean area furthermore in the confined central atlantic the oxygen minimum zone omz in many places reached down to the deep sea floor 3 4 km while the lower limit of the omz along the north african tethys was much shallower and underlain by oxic water masses as documented by high resolution biostratigraphic and chemostratigraphic data c t black shale deposition in most areas outside the upwelling zone are restricted to a strong eustatic latest cenomanian transgressive phase triggered by this sea level rise the omz impinged onto the north african continental shelf and the margins of intrashelf basins which mostly formed during the early cretaceous as halfgrabens important units containing c t organic rich strata in the region are the atlantic tarfaya black shales morocco western sahara black shales and phtanites in the moroccan and algerian atlas the bahloul fm in the se constantine basin and in northern and central tunisia the etel fm in the sirte basin the al hilal fm in cyrenaica libya the abu roash fm in the abu gharadig and fayium basins western desert egypt the daliyya fm along the ne sinai palestine isreal coast and the shueib fm in west central jordan

precompression design for secondary settlement reduction a large water treatment plant is to be built on soft deltaic deposits precompression has been selected as the method for achieving the required ground improvement an instrumented preload test has been carried out to obtain reliable information on precompression performance distributions of displacements throughout the foundation depth obtained using sliding micrometer extensometers have proved extremely useful for identifying the mechanisms of behaviour controlling ground deformation the magnitudes of displacements are largely dependent on the overconsolidation state of the soil as primary consolidation settlements take place rather quickly they can be largely controlled by applying a preload over a limited period the main design criterion therefore concerns secondary settlements laboratory and field data indicate clearly that overconsolidating the soil even in moderate amounts significantly reduces the secondary compression rate the performance of an unloading stage in the preload test provi

cenomanian sequence stratigraphy and sea level fluctuations in the tarfaya basin sw morocco we investigated the sequence architecture of two expanded cenomanian successions along a depth transect in the tarfaya basin sw morocco and correlated these successions to published records from northwest europe and india changes in terrigenous material carbonate and organic carbon content carbonate microfacies and foraminiferal biofacies as well as nondepositional and erosional surfaces were used to define depositional sequences and systems tracts we identified two main transgressive cycles in the lower and middle upper cenomanian separated by a major regression at the early middle cenomanian transition sequence boundary ce 3 this regressive interval is characterized by lagoonal low stand deposits indicating an overall sealevel fall of more than 30 m superimposed on the two main transgressive cycles there are 11 third order depositional sequences that correlate to globally recognized sealevel fluctuations and appear to be paced by long eccentricity variations 400 ka period positive carbon isotope excursions in the middle cenomanian 96 0 ma and latest cenomanian 94 0 ma following sealevel lowstands together with planktonic foraminiferal and ammonite datums provide a robust framework for stratigraphic correlation we suggest that the onset of these excursions was triggered by eccentricity minima during periods of low variability in obliquity nodes which probably coincided with glacioeustatic lowstands

a late devensian ice free area and possible interglacial site on the isle of lewis scotland at the time of the last glacial maximum the last scottish ice sheet has been considered by some1 2 to have extended to the continental shelf edge fig 1a whilst others3 4 have suggested that there were ice free areas in northern scotland no radiocarbon dated strati graphical evidence has been published to support either interpretation we present here data from the isle of lewis establishing that the shelly deposits from the north of that island are of late devensian age but which also show that a late devensian ice margin lay across northern lewis leaving part of the island ice free a peat possibly of interglacial status has been found in the ice free area the last scottish ice sheet therefore did not pass beyond the outer hebrides and may not even have reached the north of the island chain this evidence is also of interest to the debate on the relative expansions of the northern and southern margins of the laurentide and scandinavian ice sheets at the last glacial maximum5 6 for it suggests a restricted glacial expansion of the northern margin of the last british ice sheet at the time of its greatest southerly extent

carbon isotope stratigraphy recorded by the cenomanian turonian oceanic anoxic event correlation and implications based on three key localities we present new detailed carbon isotope records for bulk carbonate total organic carbon toc and phytane from three key sections spanning the cenomanian turonian boundary interval eastbourne england gubbio italy tarfaya morocco with the purpose of establishing a common chemostratigraphic framework for oceanic anoxic event oae 2 isotope curves from all localities are characterized by a positive carbon isotope excursion of c 4 for toc and phytane and c 2 5 for carbonate although diagenetic overprinting appears to have obliterated the primary carbonate carbon isotope signal in at least part of the tarfaya section stratigraphically peak 13 c values for all components are followed by intervals of high near constant 13 c in the form of an isotopic plateau recognition of an unambiguous return to background 13 c values above the plateau is however contentious in all sections hence no firm chemostratigraphic marker for the end point of the positive isotopic excursion can be established the stratigraphically consistent first appearance of the calcareous nannofossil quadrum gartneri at or near the cenomanian turonian boundary as established by ammonite stratigraphy in conjunction with the end of the 13 c maximum characteristic of the isotopic plateau provides a potentially powerful tool for delimiting the stratigraphic extent and duration of oae 2 this oceanic anoxic event is demonstrated to be largely if not wholly confined to the latest part of the cenomanian stage

widespread cretaceous secondary magnetization in the high atlas morocco a common origin for the cretaceous remagnetizations in the western tethys in this paper we present the first palaeomagnetic data 51 sites for mesozoic lower middle jurassic sediments of the moroccan central high atlas and address the study of a widespread remagnetization the remagnetization is characterized by a very stable component with systematic normal polarity carried by magnetite the relationship between the magnetic properties and location within the basin suggests that the acquisition of the remagnetization is controlled by basin geometry fold tests indicate that the overprint acquisition is syn folding in some structures but clearly predates the tertiary compressional stage using the small circle intersection method we have calculated the remagnetization direction d 336 4 i 29 2 comparison with the global apparent polar wander path indicates that the remagnetization was acquired during the late cretaceous probably cenomanian considering both the basinal confinement of remagnetization and the connection with other remagnetization events in the western tethys we propose a scenario explaining widespread remagnetizations in the region concerning both basin scale conditions mainly related to sediment thickness and a regional scale thermal event acting as catalyst of remagnetizations in those sedimentary basins that satisfy the basin scale conditions

global plate motion frames toward a unified model 1 plate tectonics constitutes our primary framework for understanding how the earth works over geological timescales high resolution mapping of relative plate motions based on marine geophysical data has followed the discovery of geomagnetic reversals mid ocean ridges transform faults and seafloor spreading cementing the plate tectonic paradigm however so called absolute plate motions describing how the fragments of the outer shell of the earth have moved relative to a reference system such as the earth s mantle are still poorly understood accurate absolute plate motion models are essential surface boundary conditions for mantle convection models as well as for understanding past ocean circulation and climate as continent ocean distributions change with time a fundamental problem with deciphering absolute plate motions is that the earth s rotation axis and the averaged magnetic dipole axis are not necessarily fixed to the mantle reference system absolute plate motion models based on volcanic hot spot tracks are largely confined to the last 130 ma and ideally would require knowledge about the motions within the convecting mantle in contrast models based on paleomagnetic data reflect plate motion relative to the magnetic dipole axis for most of earth s history but cannot provide paleolongitudes because of the axial symmetry of the earth s magnetic dipole field we analyze four different reference frames paleomagnetic african fixed hot spot african moving hot spot and global moving hot spot discuss their uncertainties and develop a unifying approach for connecting a hot spot track system and a paleomagnetic absolute plate reference system into a hybrid model for the time period from the assembly of pangea 320 ma to the present for the last 100 ma we use a moving hot spot reference frame that takes mantle convection into account and we connect this to a pre 100 ma global paleomagnetic frame adjusted 5 in longitude to smooth the reference frame transition using plate driving force arguments and the mapping of reconstructed large igneous provinces to core mantle boundary topography we argue that continental paleolongitudes can be constrained with reasonable confidence

british shore platforms and ice sheets during the past few years views about the relative ages and modes of formation of fossil rock platforms and cliffs in scotland have changed considerably1 3 i suggest further changes here and present a model of rock platform relationships which involves an interglacial set of platforms a glacial set and a late glacial feature interpretations of the glaciation of the outer hebrides have recently been completely revised this revision has major implications for the glaciation of the inner hebrides which in turn has wider implications

comments on the quaternary deposits and landforms of scotland and the neighbouring shelves a review by d g sutherland quaternary science reviews 3 157 254

black shale deposition on the northwest african shelf during the cenomanian turonian oceanic anoxic event climate coupling and global organic carbon burial high resolution geochemical records from a depth transect through the cenomanian turonian c t tarfaya basin northwest african shelf reveal high amplitude fluctuations in accumulation rates of organic carbon oc redox sensitive and sulphide forming trace metals and biomarkers indicative of photic zone euxinia these fluctuations are in general coeval and thus imply a strong relationship of oc burial and water column redox conditions the pacing and regularity of the records and the absence of a prominent continental signature suggest a dynamic depositional setting linked to orbital and higher frequency forcing determining the dominant frequency depends on the definition of the most pronounced oceanic anoxic event oae2 and its duration we propose that eccentricity is the main forcing factor at tarfaya and controlled fluctuations in wind driven upwelling of nutrient rich oxygen depleted intermediate waters from the adjacent atlantic and the periodic development of photic zone and bottom water euxinia on the mid cretaceous northwest african shelf accumulation records clearly identify the basin center as the primary site of sediment deposition with highest temporal variability and an up to six fold increase in oc burial from similar to2 g m 2 yr prior to the oae2 to similar to12 g m 2 yr during the oae2 photic zone and bottom water euxinia alternated with periods of greater oxygenation of the water column in response to climate forcing mass balance calculations imply that similar to2 of the overall global excess oc burial associated with the oae2 was deposited in the tarfaya basin an area that represented only similar to0 05 of the total global c t ocean floor in fact the lateral extent of similar black shales along the african continental margin indicates that this part of the ocean contributed significantly to the global increase in organic carbon burial during the oae2

physical interpretation of hysteresis loops micromagnetic modeling of fine particle magnetite 1 hysteresis measurements have become an important part of characterizing magnetic behavior of rocks in paleomagnetic studies theoretical interpretation is often difficult owing to the complexity of mineral magnetism and published data sets demonstrate remanence and coercivity behavior that is currently unexplained in the last decade numerical micromagnetic modeling has been used to simulate magnetic particles such simulations reveal the existence of nonuniform remanent states between single and multidomain known as the flower and vortex configurations these suggest plausible explanations for many hysteresis measurements yet fall short of explaining high saturation remanence high coercivity data such as those commonly observed in fine grained submarine basalts in this paper we review the theoretical and experimental progress to date in understanding hysteresis of geological materials we extend numerical simulations to a greater variety of shapes and sizes including random assemblages of particles and shapes more complex than simple rods and cubes our simulations provide plausible explanations for a wide range of hysteresis behavior

glacial erosion in an ice divide zone it is widely accepted that glacial erosion and therefore deposition are insignificant at the centres of ice sheets1 4 although a few authors have argued for extensive glacial erosion in those areas5 6 here i argue from the detailed study of erratics trains from three distinctive bedrock sources from striae and from ice moulded landforms that the two views need not be mutually exclusive the presence of large quantities of lodgement till in the vicinity of a former ice divide in south west scotland is explained by debris emplacement during ice sheet build up when conditions for erosion obtained the till was protected from subsequent removal by the superimposition of an ice divide across the area

magnetic properties of sedimentary greigite fe3s4 new data are presented here that document the previously poorly known magnetic characteristics of sedimentary greigite fe3s4 several diagnostic magnetic properties can be used in conjunction to rapidly screen sediments to detect the presence of greigite such discriminants are necessary because greigite displays a similar or higher range of coercivities compared to most ferrimagnetic minerals and the commonly used method of alternating field demagnetization cannot be used to distinguish between palaeomagnetic remanence components due to greigite and other ferrimagnetic minerals sedimentary greigite has high ratios of the saturation isothermal remanent magnetization to magnetic susceptibility mrs which are accompanied by hysteresis ratios of mrsms 0 5 and bcr bc 1 5 ms is the saturation magnetization bc is the coercive force and bcr is the coercivity of remanence greigite has no low temperature phase transition whereas the ferrimagnetic iron sulphide pyrrhotite undergoes a major phase transition at about 34 k and unoxidized magnetite displays the verwey transition at 118 k low temperature measurements may therefore prove valuable in distinguishing between magnetite pyrrhotite and greigite although the absence of a low temperature transition cannot be taken as definitive evidence for the presence of greigite greigite also displays characteristic high temperature behaviour with a major drop in magnetization between 270 and 350 c determination of the mrs ratio is an excellent means of rapidly screening sediments to identify stratigraphic intervals that may contain greigite subsequent low and high temperature analyses can then provide unambiguous identification of greigite and enable the evaluation of the presence of other magnetic minerals

lateglacial and early flandrian chronology of the isle of mull scotland the isle of mull which lies off the west coast of scotland fig 1 was partially over ridden by ice from the mainland during the build up of the late devensian ice sheet1 but in common with the adjacent islands of rum2 and skye3 supported smaller ice masses including independent valley and cirque glaciers during the loch lomond stadial4 5 approximately equivalent with the younger dryas of scandinavia6 7 however although the recent glacial history of mull is understood at least in general terms little is known about the nature and timing of the major environmental changes that preceded and succeeded the loch lomond stadial on the island we present here pollen stratigraphical evidence supported by 15 radiocarbon dates which provide new information on landscape changes on the isle of mull from the wastage of the last scottish ice sheet to the early part of the flandrian period the radiocarbon dates are of particular significance as they form the basis for the first lateglacial and early flandrian chronology for the islands of the scottish inner hebrides

enhanced productivity rather than enhanced preservation led to increased organic carbon burial in the euxinic southern proto north atlantic ocean during the cenomanian turonian oceanic anoxic event three cenomanian turonian c t 93 5 ma black shale sections along a northeast southwest transect in the southern part of the proto north atlantic ocean were correlated by stable carbon isotope stratigraphy using the characteristic excursion in c values of both bulk organic matter om and molecular fossils of algal chlorophyll and steroids all three sites show an increase in marine organic carbon oc accumulation rates during the c t oceanic anoxic event oae the occurrence of molecular fossils of anoxygenic photosynthetic green sulfur bacteria lack of bioturbation and high abundance of redox sensitive trace metals indicate sulfidic conditions periodically reaching up into the photic zone before as well as during the c t oae during the c t oae there was a significant rise of the chemocline as indicated by the increase in concentrations of molecular fossils of green sulfur bacteria and mo al ratios the presence of molecular fossils of the green strain of green sulfur bacteria indicates that euxinic conditions periodically even occurred at very shallow water depths of 15 m or less during the c t oae however bottom water conditions did not dramatically change as indicated by more or less constant v al and zn al ratios at site 367 this suggests that the increase in oc burial rates resulted from enhanced primary productivity rather than increased anoxia which is supported by stable carbon isotopic evidence and a large increase in ba al ratios during the c t oae the occurrence of the productivity event during a period of globally enhanced organic carbon burial rates i e the c t oae points to a common cause possibly related to the formation of a deep water connection between north and south atlantic basins