early tertiary paleo thermal effects in northern england reconciling results from apatite fission track analysis with geological evidence abstract the paleozoic lake district block in northwest england has traditionally been thought of as tectonically stable since the late paleozoic receiving only small thicknesses of late paleozoic to mesozoic cover although some workers have put forward different views apatite fission track analysis afta data from outcrop samples across the region reveal early tertiary paleotemperatures around 100 c requiring kilometre scale late paleozoic and mesozoic cover removed during tertiary uplift and erosion with no evidence for elevated basal heat flow in nw england during the early tertiary and no a priori justification for invoking it earlier studies favoured an explanation involving burial by up to 3 km of overburden removed during tertiary uplift and erosion this conclusion was met with scepticism by many workers and provoked a range of comments and criticisms with a variety of alternative interpretations put forward although these are also open to criticism results from the west newton 1 hydrocarbon exploration well on the northern flank of the lake district gave the first indication of a possibly more realistic interpretation involving a combination of elevated heat flow and more restricted burial but some aspects of the interpretation of these data were equivocal more detailed sampling was therefore undertaken in order to shed more light on the origin of the elevated early tertiary paleotemperatures observed across nw england new afta data in outcrop samples from different elevations around sca fell characterised by the highest elevations in the lake district with the summit of scafell pike at 978 m asl define an early tertiary paleogeothermal gradient of 61 c km and require around 700 m of section removed from the summit during tertiary uplift and erosion these results together with those from the west newton 1 well provide strong support for an interpretation involving early tertiary paleogeothermal gradients between 50 and 100 higher than present day values providing clear evidence of elevated basal heat flow during the early tertiary contrary to earlier assumptions combined with amounts of section removed during tertiary exhumation varying between 0 7 km from mountain peaks and 1 5 2 km from coastal plains and glacial valleys near sea level over the region this interpretation finally provides a geologically plausible mechanism for the origin of the observed early tertiary paleo thermal effects in nw england

tertiary compressional structures on the faroe rockall plateau in relation to northeast atlantic ridge push and alpine foreland stresses abstract a number of compressional anticlinal structures are identified in the western and northern part of the faroe rockall plateau these structures occur on that part of the faroe rockall plateau which was above sea level during the latest phase of paleocene plateau basalt extrusion three post basalt compressional phases have affected the plateau most of the compressional structures in the northern part of the plateau are related to ne sw to ene wsw oriented stress which we date to late paleocene early eocene the oligocene phase is interpreted as resulting from n s directed compressional stress which also mainly affected the compressional structures on the northern part of the plateau compressional stress from the northwest seemed to affect the whole of the faroe rockall plateau and we suggest it to be of miocene age it is proposed that during the late paleocene early eocene phase of compression local structure and anomalously oriented gravitational ridge push from the now extinct aegir axis contributed to a local ne sw compressional stress system the two later deformation phases were apparently connected to the regional northwest european stress system with small local modifications

mesozoic cover over northern england interpretation of apatite fission track data whether a significant thickness of mesozoic cover rocks once rested upon the palaeozoic rocks which form the structural highs of the english lake district and the northern pennines is a subject of long debate which has been revived recently by apatite fission track analysis afta studies evidence from adjacent basins suggests that 1200 1750 m of mesozoic cover was probably formerly present on the highs prior to cenozoic erosion higher estimates c 3000 m of cover thickness based on such fission track derived palaeotemperatures result from underestimation of early cenozoic surface temperatures and from not allowing for the relatively low thermal conductivity of the eroded cover rocks for similar reasons apatite fission track estimates of eroded cover rocks elsewhere in britain may also prove to be overestimates

unusual biomarker maturation ratio changes through the oil window a consequence of varied thermal history abstract saturated and aromatic biomarker ratios continue to change systematically through the oil window and into the gas condensate window to high vitrinite reflectances r o 1 16 in mature marine and lacustrine mesozoic clastic samples from a south african basin two of the ratios reverse above r o 0 9 these unusual maturation effects result from isolated periods of high rates of maturation increase the basin cooled regionally after the break up of gondwana but high heating rates prevailed during the late cretaceous early tertiary as africa moved across a hotspot and again in the late tertiary as a result of a possible hotspot and hydrothermal event

silicon isotopes in allophane as a proxy for mineral formation in volcanic soils abstract weathering of basaltic ash in volcanic areas produces andosols rich in allophane and ferrihydrite since the rate of mineral formation is very useful in climate and geochemical modelling this study investigates si isotope compositions of allophane as a proxy for mineral formation allophane formed in contrasting conditions in five icelandic soil profiles displays silicon isotope signatures lighter than the basalt in less weathered soils 0 64 0 15 and heavier in more weathered organic rich soils 0 23 0 10 the fate of the dissolved si in those volcanic soils strongly depends on al availability in organic rich soils most of al is humus complexed and the results support that si precipitates as opaline silica by super saturation leaving an isotopically heavier dissolved si pool to form allophane with uncomplexed al this study highlights that si isotopes can be useful to record successive soil processes involved in mineral formation which is potentially useful in environmental paleo reconstruction

correlation between the oxygen isotope record from dasuopu ice core and the asian southwest monsoon during the last millennium long high resolution proxy records are valuable for understanding asian southwest monsoon asm dynamics on decadal to centennial timescales a millennium long d 18 o ice core record from the central himalayas provides an opportunity to study the asm variability on decadal to centennial timescales the dasuopu ice core d 18 o record indicates that a relatively warm period corresponding with the medieval warm period lasted from ad 1140s to 1390s a notable warming trend is apparent from 1800s to 1990s and several cool periods occurred between ad 1010 1130s 1290 1330s 1400 1460s 1520s 1590 1630s 1740s and 1770 1790s comparisons with other high resolution monsoon proxy records from the arabian sea south oman and southern china reveal a high correspondence between temperature changes in the central himalayas and the asm variability during the last 1000 years a pronounced warming trend since ad 1670 coincides with an abrupt transition from a weak to a strong intensity of the asm the thermal conditions in the himalayas and on the tibetan plateau and associated glacial boundary conditions may have been predominantly responsible for variations of the asm intensity and for a latitudinal movement in the mean position of the itcz on decadal to centennial timescales r 2007 elsevier ltd all rights reserved

a latest cretaceous hotspot and the southeasterly tilt of britain the southeasterly regional dip of england and wales is usually ascribed to miocene movements loss of up to 2 km of cover from northern england shown by apatite fission track analysis has been related to uplift and erosion induced by a mantle hotspot but its effects were far more widespread than considered hitherto outcrop patterns throughout much of england wales and eastern ireland can be related to a hotspot beneath the irish sea uplift occurred within the late maastrichtian and erosion continued into the late palaeogene after post oligocene down faulting of the irish sea the modern drainage was initiated on the eroded surface unconformities provide the best means of dating orogenic movements in some localities the time interval between the youngest rocks preserved beneath the unconformity and the oldest preserved above may be small enough to enable the dating of fold movements to be determined with some precision thus in southeastern britain the major e w structures of the hampshire basin the weald and the london basin can be dated as miocene as rocks of oligocene age are involved in the folding in the hampshire basin and pliocene sands rest in erosional pockets of the chalk of se england because fold movements tend to affect large areas of the crust at discrete intervals of time the southeasterly tilt of britain evident from the fact that a nw se transect from anglesey to london crosses outcrops of rocks getting progressively younger from the precambrian of anglesey to the tertiary of the london basin has

lateral flow and ponding of starting plume material many mantle plumes started with voluminous heads of hot material that ascended as diapirs through the mantle flood basalts radial dike swarms and frequently continental breakup are associated with the impingement of starting plume heads on the base of the lithosphere the buoyant plume head material ponds at the base of the lithosphere and then flows laterally relief on the base of the lithosphere acts as an upside down drainage pattern with enclosed catchments for this flow that is plume material preferentially collects beneath regions where the lithosphere is locally thin such as thermally subsiding sedimentary basins an example is uplift associated with the iceland starting plume which inverted the mesozoic irish sea basin additional relief at the base of the lithosphere is associated with rifting and seafloor spreading in the case of the northern north sea material from the iceland starting plume ponded beneath a basin with locally thin lithosphere rifting breached the enclosed catchment allowing the ponded plume material to drain across the new passive margin toward very thin lithosphere produced by seafloor spreading rifting also creates a conduit for the flow of plume material away from the region underlain by the starting plume head an example is the volcanic passive margin off nova scotia which is 2000 km from the center of the bahama starting plume head numerical and analytical calculations indicate that lateral flow of plume material consistent with this observation is expected if its viscosity is around 1018 pa s

an analysis of cotswold topography insights into the landscape response to denudational isostasy we have used the nextmap britain digital terrain model dtm to determine the lithospheric response to erosional unloading and the contribution of tectonics in the form of elastic plate flexure to the cotswold scarp and vale landscape the calculations take into account lithology variations and along strike changes in escarpment retreat we show that flexural rock uplift as a result of erosional unloading varies spatially and may contribute up to 50 of the relief in the cotswold region this is supported by morphometric analysis of concavity and steepness for 66 longitudinal river profiles that drain the scarp and dip slope of the escarpment viscoelastic plate models suggest that the uplift is initially rapid up to 8 m ka 1 and essentially complete within 50 ka these initial rates are compatible with an early post anglian incision rate inferred from the thames terraces the staircase terrace pattern suggests however that there have been a number of denudational isostatic events each associated with a climate cycle finally the analysis reveals an inherited proto landscape that has a subdued relief when compared with the modern dtm such a relief is consistent with an early extension of the river thames through the vale of moreton to the north of the present day cotswold hills

a new approach to the relief of great britain i the machine readable database abstract we describe a simple if fairly large database of relief and geology for great britain and the surrounding shelf based on the kilometre squares of the national grid the area covered is 560 000 km 2 319 490 km 2 classified as sea and 240 510 km 2 as land squares which included the coastline were classed as land the database affords a new approach to establishing the importance of rock resistance to erosion as a factor affecting the form of the present land surface the legacy of older tectonic movements and the role of neotectonics it can be used to test existing hypotheses or propose new ones which can then be tested against other evidence initial data on land shelf contrasts are presented the current coastal zone is found to be a sector of relatively abrupt transition from shelf depths between 60 and 70 m to land elevations exceeding an average of over 100 m even within a few kilometres of the coast this transition zone is attributed to the isostatic buoyancy of a land area steadily unloaded by denudation and attacked by the transgressing sea as water levels rise after each glacial stage the database is a novel and powerful way to tackle some fundamental aspects of the evolution of the relief of great britain and further papers will explore issues such as relative rock resistance and evidence for neotectonic movement

the bytham river reconsidered abstract the english midlands is one of the most important regions for british pleistocene geology the middle pleistocene glacial sediments of the region termed the wolston formation overlie deposits of a pre existing river system the baginton formation the latter are characteristically composed of quartz rich sediment derived from underlying triassic bedrock this sw ne aligned proto soar system was overridden by the wolstonian ice its lack of terraces or discrete sedimentary units implies that the river can only have existed for a limited period the deposits accumulated during a period of climate change from boreal interstadial to subarctic conditions a reinterpretation of these sediments as the headwaters of a pre anglian bytham river aligned towards east anglia across the fenland where they were linked to the ingham formation deposits found favour for two decades this was especially so when the wolston formation sediments were reassigned to the earlier anglian stage however recent work has shown that the bytham river could not have existed in the form suggested by some authors since pre anglian age fluvial sediments are absent from the eastern fenland margin except possibly certain deposits at high lodge suffolk therefore a re examination of the evidence is required it is concluded that the wolstonian glaciation late saalian marine isotope stage mis 6 indeed post dates that during the anglian stage elsterian mis 12 in addition it appears that the baginton proto soar stream as originally conceived almost certainly did not exist before the early wolstonian early saalian stage following a significant period of fluvial incision rather than being aligned towards east anglia the substantial proto soar flowed into south lincolnshire and thence potentially to the north sea via the wash and the silver pit depression by contrast the pre anglian ingham formation deposits of central east anglia were almost certainly deposited by a separate proto trent river that drained the east midlands over an extended period as a left bank thames tributary together these conclusions reinforce the view that the main drainage alignment in southern england during the pre anglian period was nw to se parallel to the regional tilt of the landmass

discussion on lithospheric flexure uplift and landscape evolution in south central england scientific editing by alex maltman j c w cope writes the paper by watts et al contains interesting ideas on landscape evolution but by concentrating their observations locally and by overestimating post anglian erosion they may have lost sight of more widespread effects that could have been major contributors to the features they describe and thus their causative mechanisms may need re examination cope 1994 suggested that uplift centred in the irish sea explained the loss of 2 km of mesozoic cover there explaining apatite fission track analyses from the eastern irish sea and northwestern england the southeasterly regional dip of the mesozoic outcrop of the english midlands could be attributed to this uplift although a mantle plume was suggested as the cause the same effect could be attributed to mantle underplating substantial igneous activity is known around the irish sea region before the earliest antrim basalts the fleetwood dyke in the eastern irish sea is dated at 65 5 ma arter fagin 1993 and similar ages are known from dykes in north wales evans et al 1973 pre basalt dykes exist in northern ireland whence simms 2000 records dykes cutting chalk and truncated by the basal palaeogene lavas cope s 1994 reconstruction of the missing mesozoic cover of the area from the cheshire basin southwards led him to suggest that the resultant average gradient imparted over the midlands from the cheshire basin to the chiltern scarp was 1 87 5 what was incorrectly calculated from this figure by cope 1994 was the angle of dip represented by that figure which is 0 7 and not 2 the former is close to that recorded by watts et al for the area of oxfordshire they considered and this suggests that they may have overestimated the uplift caused by lithospheric flexuring there may be

upper cretaceous feldspars in the cenozoic limagne basin a key argument in reconstructing the palaeocover of the massif central france abstract the northern part of the n s trending basin of the limagne graben located in the northern part of the massif central france contains oligocene and miocene calcareous lacustrine deposits the area is known for its stromatolite reefs surrounded by marl clay and uncemented carbonate sand with oncolites because the origin of the carbonate accumulated by cyanobacteria has long been debated the clayey deposits associated with the stromatolites were analysed using xrd sem and k ar dating methods the results show a monotonous assemblage of carbonates dioctahedral smectite illite smectite reichweite r 0 glauconitic illite and abundant orthoclase detrital minerals such as quartz and detrital illite are found near the basin s borders but are very scarce in its central part indicating a lack of detrital input from the regional basement hence the abundant orthoclase found in all the clayey deposits of the limagne basin cannot be linked to erosion of the surrounding hercynian basement the sem analysis showed the orthoclase crystals to have a tabular morphology with sharp boundaries and to be embedded within a clay matrix whilst the k ar dating of the orthoclase and glauconitic illite yielded ages ranging from 90 to 66 2 ma i e turonian to maastrichtian these two results clearly indicate that the fill of the limagne basin composed mainly of carbonate clay and orthoclase must have been partly due to the erosion of an upper cretaceous sedimentary blanket once covering the massif central basement this cover was probably constituted of chalk dioctahedral smectite i s and glauconitic illite associated with authigenic orthoclase and flint flints are found reworked in the alluvial formations of the late pliocene lower bourbonnais sands and clays sables et argiles du bourbonnais and in the pleistocene terraces moreover relicts of the upper cretaceous cover were preserved during the sedimentary filling of the cenozoic limagne basin authigenic orthoclase of similar shape has been described in the chalk group of the paris basin and from localities in northern france and belgium the mineral is rare in the turonian chalk but increases rapidly at the base of the coniacian to campanian chalk it has also been noted that the number of orthoclase crystals increases as the quantity of clastic components decreases similar orthoclase crystals were found associated with dioctahedral smectite in the decarbonated residues of the coniacian to santonian chalk from fecamp and etretat northern france moreover our results are consistent with other data from within and around the paris basin such as the palaeogeography and facies distribution of the chalk formations the residual flints in the clay with flints of the southern paris basin and around the morvan and apatite fission track thermochronology data from the hercynian basement of the massif central and the morvan all these data indicate a major connection between the paris basin and the tethys and an extensive palaeocover on the massif central and morvan basement

evidence for kilometre scale neogene exhumation driven by compressional deformation in the irish sea basin system simon p holford paul f green jonathan p turner gareth a williams richard r hillis david r tappin ian r duddy

evidence for post early eocene tectonic activity in southeastern ireland the role played by cenozoic deformation in denudation and landscape development in ireland has historically been difficult to assess because of the lack of widespread pre glacial cenozoic deposits onshore here we combine analysis of apatite fission track data and geomorphic observations to place constraints on the timing kinematics and magnitude of onshore deformation in southeastern ireland relationships between apatite fission track central age and elevation for samples from the wicklow and blackstairs mountains and tullow lowland suggest that these rocks record an exhumed apatite partial annealing zone which after cooling was dismembered by differential vertical displacements of up to several hundred metres we use inverted models of sample thermal history to show that samples across the region experienced very similar thermal histories up to and including a cooling event in late paleocene or early eocene time this effectively rules out strongly spatially heterogeneous denudation and implies that differential rock uplift occurred in post early eocene time the central age elevation relationships define at least three spatial domains with internally consistent apatite fission track data separated by known faults or topographic escarpments geomorphic analysis of these structures shows that patterns of catchment incision and sinuosity as well as the presence of antecedent drainage are best explained by differential vertical displacements at or near the domain boundaries the kinematics and magnitudes of these displacements are consistent with those implied by the apatite fission track results and are compatible with other examples of known cenozoic deformation from ireland and the adjacent continental margin

episodic cenozoic tectonism and the development of the nw european passive continental margin the north atlantic margins are archetypally passive yet they have experienced post rift vertical movements of up to kilometre scale the cenozoic history of such movements along the nw european margin from ireland to mid norway is examined by integrating published analyses of uplift and subsidence with higher resolution tectono stratigraphic indicators of relative movements including results from the stratagem project three episodes of epeirogenic movement are identified in the early mid and late cenozoic distinct from at least one phase of compressive tectonism two forms of epeirogenic movement are recognised referred to as tilting coeval subsidence and uplift rotations 1 over distances of 100s of kilometres and sagging strongly differential subsidence rotations up to 4 over distances 100 km each epeirogenic episode involved relatively rapid 10 ma km scale tectonic movements that drove major changes in patterns of sedimentation to find expression in regional unconformity bounded stratigraphic units early cenozoic tilting late paleocene to early eocene c 60 50 ma caused the basinward progradation of shelf slope wedges from elongate uplifts along the inner continental margin and from offshore highs mid cenozoic sagging late eocene to early oligocene c 35 25 ma ended wedge progradation and caused the onset of contourite deposition in deep water basins late cenozoic tilting early pliocene to present 4 0 5 ma again caused the basinward progradation of shelf slope wedges from uplifts along the inner margin including broad dome like features and from offshore highs the early mid and late cenozoic epeirogenic episodes coincided with atlantic plate reorganisations but the observed km scale tectonic movements are too large to be accounted for as flexural deflections due to intra plate stress variations mantle lithosphere interactions are implied but the succession of epeirogenic episodes of differing form are difficult to reconcile with the various syn to post rift mechanisms of permanent and or transient movements proposed in the hypothetical context of a plume beneath iceland the epeirogenic movements can be explained as dynamic topographic responses to changing forms of small scale convective flow in the upper mantle tilting as coeval upwelling and downwelling above an edge driven convection cell sagging as a loss of dynamic support above a former upwelling the inferred cenozoic succession of epeirogenic tilting sagging and tilting is proposed to record the episodic evolution of upper mantle convection during ocean opening a process that may also be the underlying cause of plate reorganisations the postulated episodes of flow reorganisation in the ne atlantic region have testable implications for epeirogenic movements along the adjacent oceanic spreading ridge and conjugate continental margin as well as on other atlantic type passive margins

relative sea level fall since the last interglacial stage are coasts uplifting worldwide the growing interest in quantification of vertical ground motion stems from the need to understand in detail how the earth s crust behaves for both scientific and social reasons however only recently has the refinement of dating techniques made possible the use of paleoshorelines as reliable tools for tectonic studies although there are many local studies of quaternary vertical motions of coastlines we know of no comprehensive worldwide synthesis here we provide a compilation of 890 records of paleoshoreline sequences with particular emphasis on the last interglacial stage marine isotopic stage mis 5e 122 ka the quality of dating mis 5e makes it a reliable marker to evaluate vertical ground motion rates during the late quaternary on a global scale the results show that most coastal segments have risen relative to sea level with a mean uplift rate higher than 0 2 mm yr i e more than four times faster than the estimated eustatic drop in sea level the results also reveal that the uplift rate is faster on average for active margins than for passive margins neither dynamic topography nor glacio hydro isostasy may explain sustained uplift of all continental margins as revealed by the wide distribution of uplifted sequences of paleoshorelines instead we suggest that only plate tectonic processes reconcile all observations of quaternary coastal uplift we propose that long term continental accretion has led to compression of continental plates and uplift of their margins therefore this study concludes that plate tectonics processes impact all margins and emphasizes the fact that the notion of a stable platform is unrealistic these results therefore seriously challenge the evaluation of past sea levels from the fossil shoreline record

a new variscan deformation map of england and wales collections of bedding orientations from subareas of 550 km 2 are used to define bedding fabrics from the variscan fold belt and foreland in england and wales the bedding fabrics constructed from data taken from published geological maps 1 50 000 scale are analysed in terms of the scheidegger watson orientation tensor the calculated eigenvalues of the orientation tensor define the average structural trends including the best fit fold axis for each subarea the eigenvectors of the tensor allow the original sedimentary fabrics to be distinguished from those modified by deformation the progressive tectonic modification of these fabrics leads to the concept of fabric evolution paths and the extent of the modification is expressed by a deformation parameter although it is emphasised that this parameter is not solely a function of finite strain magnitude its variation is represented on a map which brings out different degrees of variscan tectonic modification of bedding fabrics this map delineates a variscan bedding fabric front corresponding to the northern boundary of a zone of pervasive and strong deformation in the foreland this new analysis allows the variation of variscan trends to be mapped and the significance of these trends to be quantified in terms of deformation magnitude 1999 elsevier science b v all rights reserved

structural trends in central britain from images of gravity and aeromagnetic fields digital image processing techniques have been used to analyse the regional gravity and aeromagnetic datasets in central britain colour and shaded relief images have been generated which convey information on both anomaly amplitude as colour and anomaly gradient as relief and highlight structural trends lineaments and textural contrasts not easily discernible on standard contour maps we have identified some of the more important features and have tried to relate these to the evolution of the crust in each region on a broad scale the images emphasize caledonoid ene trends to the north of the solway line and both tornquist se and caledonoid ne to ene trends to the south the pattern of magnetic anomalies over central england seems to define the extent of the shallow late precambrian early palaeozoic basement of the midlands microcraton and delineates crustal elements and characteristic trends within it magnetic lineaments and the grain of gravity anomalies trending in northeasterly and northwesterly directions on either side of the microcraton seem to relate to structures which originated during the evolution of the welsh and eastern english caledonides respectively where lower palaeozoic and precambrian rocks form the concealed basement as in most of england the gravity lineaments tend to reflect the influence of basement fractures on the subsequent pattern of sedimentation whereas many of the features on the magnetic images are more directly related to structures within the basement itself