geophysical constraints on crustal structure in the dalradian region of scotland the crust in the region of the dalradian outcrop in scotland is 25 35 km thick and may be divided into two areas separated by the nw se cruachan lineament to the ne the crust is dominated by late caledonian granites which give rise to surface topography isostatically compensated at shallow depth to the sw thick dalradian sediments formed in an extensional basin later subjected to crustal shortening of 70 100 km achieved by zigzag obduction physical parameters of the deep crust are compatible with metamorphic grade increasing downwards except that the basic lower crust may be partly retrogressed and contain free water

pedogenic carbonate carbon isotopic constraints on paleoprecipitation evolution of desert in the pacific northwest usa in response to topographic development of the cascade range abstract the cascade range in the northwestern u s acts as an orographic barrier to the easterly movement of humid air masses from the pacific ocean producing a massive rain shadow with arid to semi arid climate conditions on the leeward side of the range pedogenic carbonates formed in the c3 dominated landscapes east of the range have 13ccarbonate that is enriched by approximately 4 relative to carbonates formed in sub tropical c3 dominated ecosystems we measured stable isotopic compositions of pedogenic carbonates preserved in the quaternary and neogene sedimentary rock units in the inland pacific northwest and examined the impact of long term aridification and paleohydrology on their isotopic compositions the determined 13ccarbonate record shows a gradual increase of 5 from approximately 10 in older pedogenic carbonates to 5 in younger ones whereas 18ocarbonate record indicates a decrease of approximately 4 in the late neogene in addition the quaternary 13ccarbonate and 18ocarbonate records indicate the highest 13c and 18o among the samples during the pleistocene and significant fluctuation over the time period the gradual increase in the 13ccarbonate and the decrease in the 18ocarbonate in the late neogene are interpreted by the development of the rain shadow as a result of topographic development of the cascade range changes in the quaternary isotope records suggest a decrease in regional precipitation and isotopically depleted winter precipitation resulting from changes in large scale atmospheric circulation patterns due to advance and retreat of northern hemisphere continental ice sheet the isotope record from pedogenic carbonates provides a direct record of climatic change suggesting that long term carbon isotope data can provide useful constraints on timing and intensity of regional desertification and its associated climate and topographic interaction

stable isotopic investigation of clay minerals and pedogenesis in an interfluve paleosol from the cenomanian dunvegan formation n e british columbia canada abstract mineralogical and stable hydrogen and oxygen isotopic compositions have been obtained for clay minerals comprising an interfluve paleosol clayhurst ch 2 from the early to middle cenomanian dunvegan formation british columbia canada this paleosol provides a special opportunity to determine the stable isotopic composition of early late cretaceous paleoprecipitation on the western coast of the western interior seaway at a very northerly paleolatitude 65 detrital kaolinite and illite and complex dioctahedral mixed layer clay minerals of pedogenic origin are abundant throughout the paleosol in the d values of 93 to 81 and 18 o values of 12 9 to 11 6 were generally obtained for the ancient soil water and hence paleoprecipitation for one thin interval near the top of the paleosol higher values are indicated for the ancient soil water these results may indicate processes arising from a westward transgression of the western interior seaway

palaeomagnetic properties of a precambrian metamorphic terrane the lewisian complex of the outer hebrides nw scotland abstract the palaeomagnetism of a large area of precambrian metamorphic basement comprising the outer hebrides archipelago in nw scotland is described a stable magnetite held imprint characterises much of the complex dispersed easterly steep a1 and ne intermediate c components are present in the northern sector but are subordinate to nw positive to nw negative a2 a5 b components nw shallow a4 components predominate in the south of the outcrop area a1 a2 and c components are confined largely to areas which have escaped tectonism since scourian 2650 ma times and are probably a relict record the a4 components are most prominent in areas profoundly affected by the laxfordian episode and record the peak of a later magnetising event by correlation with apw from the laurentian and fennoscandian shields relict components are interpreted as a possible acquisition at 1820 1750 ma close to the peak of laxfordian tectonism the younger components are linked to retrogressive amphibolite facies metamorphism and rapid crustal uplift at 1700 1630 ma anisotropy of susceptibility is variable in magnitude and predominantly foliated it appears to be controlled mainly by laxfordian strain although the effect of the earlier scourian episode is also recorded a younger lamprophyre dyke suite yields a palaeomagnetic pole from nine sites 349 e 47 s dated as mid permian by reference to the eurasian apw path the spatial distribution of magnetisations in the outer hebrides basement mirrors the distribution observed in the mainland outcrop comprising the nw foreland to the caledonian orogen but is displaced laterally the two distributions can be matched by adjustment for ca 95 km of sinistral strike slip on the site of the minches basin between the two outcrops this fault zone is the nw member of a suite of ne sw trending transcurrent faults active in late caledonian times and possesses the largest strike slip offset

a paleoclimate interpretation derived from pedogenic clay minerals from the piedmont province virginia abstract oxygen isotope ratios of pedogenic kaolinites were measured to estimate the ambient climate conditions during the formation of a saprolite in the piedmont province woodbridge va kaolinite is the predominant pedogenic clay mineral in this saprolite it is formed mostly from weathering of muscovite and to a lesser extent from weathering of microcline a dioctahedral smectite vermiculite phase formed by weathering muscovite is present in minor amounts the 18o 16o ratios indicate that most if not all the kaolinite formed in a cooler climatic regime in which meteoric waters were more depleted in 18o than most present meteoric waters it is possible that the pedogenic kaolinite formed shortly after or during the pleistocene glacial stage in north america this interpretation is consistent with the age of this saprolite derived from 10be dating methods the oxygen isotopic signatures of these kaolinites are not consistent with an older middle or early miocene age for this saprolite

cocorp seismic profiling of the appalachian orogen beneath the coastal plain of georgia a southeastward extension onto the coastal plain of an earlier cocorp traverse which confirmed large scale thin skinned thrusting of crystalline rocks of the southern appalachians has provided some of the most spectacular reflections yet seen in crustal seismic data most of the reflectors can be interpreted as either fault surfaces or as metamorphosed strata of late precambrian early paleozoic age they are consistent with the hypothesis that a major detachment extends eastward beneath this part of the orogen although other interpretations with a more complex pattern of detachments or sutures are also possible large scale overthrusting provides a mechanism for incorporating sedimentary rocks into the lower crust and may help to explain many of the layered features on crustal seismic data reflections from deep beneath the coastal plain indicate that the structural configuration of the rocks is complex and that the remains of a collision zone are being observed several east dipping horizons which bear strong similarities to thrust faults in valley and ridge sedimentary rocks are seen in the basement at shallow and mid crustal levels beneath the coastal plain the augusta fault for example displays a reflection which extends at a low angle some 80 km or more southeast of its surface position in conjunction with surface geologic information these new data demonstrate that late paleozoic compressive deformation was pervasive and resulted in lateral movements in the upper crust extending from the valley and ridge to the crystalline rocks beneath the coastal plain a distance of 400 km or more a large antiform cresting at about 2 3 sec or about 6 km below the surface and other structures beneath the coastal plain of georgia deserve further consideration for petroleum exploration although metamorphism may have eliminated petroleum from these rocks refracted arrivals and fault geometries indicate two triassic rift basins beneath coastal plain sedimentary rocks one of which has apparently not been recognized previously

palaeoclimate of the late jurassic of portugal comparison with the western united states investigation of the palaeoclimatic conditions associated with upper jurassic strata in portugal and comparison with published palaeoclimate reconstructions of the upper jurassic morrison formation in western north america provide important insights into the conditions that allowed two of the richest terrestrial faunas of this period to flourish geochemical analyses and observations of palaeosol morphology in the informally named upper jurassic lourinhaformation of western portugal indicate warm and wet palaeoclimatic conditions with strongly seasonal precipitation patterns palaeosol profiles are dominated by carbonate accumulations and abundant shrink swell vertic features that are both indicative of seasonal variation in moisture availability the d 18 osmow and ddsmow values of phyllosilicates sampled from palaeosol profiles range from 22ae4 to 22ae7 and 53ae0 to 37ae3 respectively these isotope values correspond to temperatures of formation between 32 c and 39 c 3 with an average of 36 c which suggest surface temperatures between 27 c and 34 c average 31 c on average these surface temperature estimates are 1 c higher than the highest summer temperatures modelled for late jurassic iberia using general circulation models elemental analysis of matrix material from palaeosol b horizons provides proxy chemical index of alteration minus potassium estimates of mean annual precipitation ranging from 766 to 1394 mm year with an average of approximately 1100 mm year palaeoclimatic conditions during deposition of the lourinhaformation are broadly similar to those inferred for the morrison formation except somewhat wetter seasonal variation in moisture availability does not seem to have negatively impacted the ability of these environments to support rich and relatively abundant faunas the similar climate between these two late jurassic terrestrial ecosystems is probably one of the factors which explains the similarity of their vertebrate faunas

cocorp profiling across the southern oklahoma aulacogen overthrusting of the wichita mountains and compression within the anadarko basin cocorp consortium for continental reflection profiling deep reflection profiles recorded across the wichita mountains and anadarko basin suggest that significant crustal shortening occurred in the final stages of the evolution of the southern oklahoma aulacogen the crystalline rocks of the wichita mountains were thrust in pennsylvanian time northeastward over sedimentary rocks of the anadarko basin along a series of faults with moderate average 30 to 40 and southwesterly dips these faults can be traced possibly as deep as 20 to 24 km listric thrust faults and hanging wall anticlines developed in the sedimentary rocks of the basin these features contrast with conventional interpretations of pennsylvanian structures as the result of predominantly vertical movements along high angle faults and they suggest that pennsylvanian downwarping of the anadarko basin was at least partially due to thrust loading truncations of reflections from cambrian ordovician rocks in the deepest part of the basin suggest normal faulting which would support ideas of an early extensional stage in the aulacogen cycle the distinctive precambrian layering seen on earlier cocorp data recorded south of the wichita mountains cannot be recognized under the anadarko basin and the proterozoic basin containing that layering may have been bounded on its north side by a precambrian fault this inferred fault was probably twice reactivated during formation of the southern oklahoma aulacogen once during late precambrian early cambrian extension and again during pennsylvanian compression the popular view that aulacogens originated from radial rifting of updomed homogeneous continental crust is probably too simplified and a more important constraint on their location and development may be the nature of pre existing lines of weakness

caledonian plutonism and major lineaments in the sw scottish highlands within the sw grampian highlands several ne sw trending shear zones and faults related to the caledonian transpressional collision are recognized as being distinct from an intersect ing set of nw se trending pre caledonian crustal lineaments which were reactivated during caledonian orogenesis the geochemical and isotopic characteristics of the 425 400 ma granitoids of this region show that they were derived by anatexis of the lower crust associated with a mantle component which provided an influx of mantle heat and or metasomatic fluids their spatial distribution suggests a close genetic relationship with caledonian shear zones having made the fundamental distinction between ascent transport and emplacement arrival configurations possible for granitoid magmas new data are presented for these plutons which show that i a common modal sequence of intrusive phases can be recognized ii these phases are all sited at shear zone or lineament intersections where transtensional zones allowed and facilitated ascent iii emplacement was often by a process of localized in situ ballooning the existence of such lineaments in these orientations in the sw highlands may indicate that the structure of the lower crust can be regarded as a series of blocks bounded by intersecting ductile zones of high strain the establishment of such a pattern of structural interactions within the lower crust could provide a mechanistic framework within which the location of anatectic zones siting and ascent pathways and any subsequent emplacement phenomena can be explained in orogenic belts

cool kaolins in finland we use d h and 18o 16o ratios to explore the age of kaolins on the fennoscandian shield sub cretaceous kaolins in southern scandinavia have isotopic compositions indicative of weathering under warm mean annual temperatures mats of 15 c deep kaolins on the shield surface in finland previously also have been regarded as products of humid tropical weathering of mesoproterozoic to eocene age new oxygen and hydrogen isotope ratios indicate however weathering by cool groundwater under mats of 13 15 c isotope ratios are also not consistent with deep 1 km burial by cover rocks indicating that a very old age for the weathering is unlikely palaeotemperatures are below cretaceous mats yet substantially above plio pleistocene mats comparisons with palaeotemperatures in n europe and around the arctic ocean indicate that the finnish kaolins developed on the shield surface in the palaeogene or alternatively miocene deep weathering was selectively developed in highly fractured shield rocks and took place in response to latest cretaceous and palaeogene uplift and after stripping of palaeozoic cover rocks the cool kaolins in finland indicate that previous routine attributions of kaolinitic weathering products in the geological record to humid tropical environments should be closely scrutinised

hydrogen and oxygen stable isotope signatures of goethite hydration waters by thermogravimetry enabled laser spectroscopy abstract the hydrogen and oxygen stable isotope composition 2h and 18o values of mineral hydration waters can give information on the environment of mineral formation here we present and validate an approach for the stable isotope analysis of mineral hydration waters based on coupling a thermogravimetric analyzer with a laser based isotope ratio infrared spectroscopy instrument picarro l 2130i which we abbreviate as tga iris tga iris generates 2h and 18o values of liquid water samples with precision for 2h of 1 2 and for 18o of 0 17 for hydration waters in goethite precision for 2h ranges from 0 3 to 1 6 and for 18o ranges from 0 17 to 0 27 the ability of tga iris to generate detailed water yield data and 2h and 18o values of water at varying temperatures allows for the differentiation of water in varying states of binding on mineral surfaces and within the mineral matrix tga iris analyses of hydrogen isotopes in goethite yields 2h values that reflect the hydrogen of the oh phase in the mineral and are comparable to that made by irms and found in the literature in contrast 18o values on goethite reflect the oxygen in oh groups bound to fe fe oh group and not the oxygen bound only to fe fe o group in the mineral crystal lattice and may not be comparable to literature 18o values made by irms that reflect the total o in the mineral tga iris presents the possibility to isotopically differentiate the various oxygen reservoirs in goethite which may allow the mineral to be used as a single mineral geothermometer tga iris measurements of hydration waters are likely to open new avenues and possibilities for research on hydrated minerals

lineaments and basement domains an alternative view of dalradian evolution this paper examines the evidence for basement structures of predominantly non caledonoid trend which appear to have influenced the development of the dalradian belt in scotland a number of domains or blocks separated by dominantly trans caledonoid lineaments are recognized on the basis of geophysical stratigraphical and geochemical patterns these are thought to reflect fault bounded depositional basins controlled by basement lineaments during the extensional phases of the caledonian 9orogeny9 in addition the recognition of a number of these domains and lineaments in the structural metamorphic and igneous data sets for the dalradian belt shows the continuing influence of these basement controlled features throughout the compressional and uplift phases of the orogenesis a possible tectonic model is proposed which envisages the depositional basins forming in a setting dominated by caledonoid trending transcurrent faults and a major pull apart basin forming on a trans caledonoid axis

empirical relationships between elevation and the stable isotope composition of precipitation and surface waters considerations for studies of paleoelevation change a compilation of 68 studies from throughout many of the world s mountain belts reveals an empirically consistent and linear relationship between change in elevation and change in the isotopic composition of precipitation along altitudinal transects the isotopic composition of precipitation decreases linearly with increasing elevation in most regions of the world except in the himalayas and at elevations 5000 m there are no significant differences in isotopic lapse rates from most regions of the world 0 28 permil 100 m except at the extreme latitudes where isotopic lapse rates are higher given information on past changes in the isotopic composition of precipitation preserved in pedogenic or authigenic minerals this global isotopic lapse rate can be used to place numerical constraints on the topo graphic development of some ancient mountain belts or plateaus there are many complicating factors that can confound interpretation of paleoel evation change based on stable isotopes and many of these are unique to specific mountain belts or time periods relevant to all stable isotope based paleoelevation change studies is the temperature dependent isotope fractionation between a pedo genic or authigenic mineral and the water from which it forms in cases where isotopic proxy minerals are sampled from localities where temperature will change simulta neously with elevation change the apparent change in the isotopic composition of precipitation may be dampened by several permil this suggests that samples taken from the rainshadow side of an emerging orographic barrier may be more likely to preserve isotopic changes resulting from mountain uplift than samples taken from atop a rising mountain range or plateau

stable isotope composition of bentonites from the swiss and bavarian freshwater molasse as a proxy for paleoprecipitation abstract the hydrogen and oxygen isotope compositions of bentonites and smectite rich tuffs from the north alpine foreland basin were measured for samples dated between 9 and 21 ma assuming clay mineral formation shortly after the deposition of the volcanic ash layers and at surface temperatures estimated from paleoclimatic studies the h and o isotope composition of water in equilibrium with the clay minerals can be calculated a comparison with values derived from other proxies of paleoprecipitation in the molasse basin such as pedogenic carbonates and mammal remains and 18 o values of carbonate in the bentonite beds suggests that the 18 o values of water estimated by this method are typical for foreland precipitation at this time and for this region therefore the 18 o value of smectite in bentonites and altered tuff layers can be a useful tool for studies of paleoclimate and topography there are however indications that the clay minerals did not retain their initial hydrogen isotopic composition but that a postformational exchange of h isotopes has occurred

stable isotopic evidence for neogene surface downdrop in the central basin and range province authigenic calcite and smectite stable isotopic records were determined for five neogene terrestrial stratigraphic sections from the central basin and range province and surrounding regions we recognized a general pattern of increasing authigenic mineral 18 o values with decreasing age since the middle miocene throughout the region we suggest this pattern results from regional elevation decrease and associated changes in atmospheric circulation patterns an anomalous pattern of decreasing 18 o values with decreasing age is observed in the miocene horse spring formation exposed in the lake mead basin which is contemporaneous with local magmatic activity we suggest this pattern results from surficial uplift of local highlands feeding water into the horse spring depositional system the topographic histories suggested here provide insight into the response of the land surface to crustal processes neogene extensional deformation in the central basin and range province resulted in a net regional elevation decrease

18o 16o and d h ratios of pedogenic kaolinite in a north american cenomanian laterite paleoclimatic implications abstract kaolinite gibbsite and quartz are the dominant minerals in samples collected from two outcrops of a cenomanian 95 ma laterite in southwestern minnesota a combination of measured yields and isotope ratios permitted mass balance calculations of the d and 18 o values of the kaolinite in these samples these calculations yielded kaolinite d values of about 73 and 18 o values of about 18 7 the d and 18 o values appear to preserve information on the ancient weathering system if formed in hydrogen and oxygen isotope equilibrium with water characterized by the global meteoric water line gmwl the kaolinite d and 18 o values indicate a crystallization temperature of 22 5 c a nominal paleotemperature of 22 c implies a 18 o value for the corresponding water of 6 3 the combination of temperature and meteoric water 18 o values is consistent with relatively intense rainfall at that mid paleolatitude location 40 n on the eastern shore of the north american western interior seaway the inferred cenomanian paleosol temperature of 22 c is in general accord with published mid cretaceous continental mean annual temperatures mat estimated from leaf margin analyses of fossil plants when compared with results from a published gcm based cenomanian climate simulation which specifies a latitudinal sea surface temperature sst gradient that was either near modern or smaller than modern the kaolinite paleotemperature of 22 c is closer to the gcm predicted mat for a smaller equator to pole temperature difference in the mid cretaceous moreover the warm kaolinite derived mid paleolatitude temperature of 22 c is associated with proxy estimates of high concentrations of atmospheric co 2 in the cenomanian the overall similarity of proxy and model results suggests that the general features of cenomanian continental climate in that north american locale are probably being revealed

post laxfordian magnetic imprint in the lewisian metamorphic complex and strike slip motion in the minches nw scotland the palaeomagnetic imprint in the lewisian metamorphic basement was acquired during early post laxfordian times and resides in magnetite filled microfractures an early magnetizing event dated c 1820 1750 ma was largely overprinted by a second event between 1700 and 1500 ma which was probably linked to retrogressive amphibolite fades metamorphism it reaches its greatest intensity in the south of the outcrop while the relict remanence survives most prominently in scourian terranes populations of magnetic components are offset by c 95 km of presumed caledonian sinistral strike slip in the minches intensities and susceptibilities of magnetization are enhanced in zones of laxfordian reworking relative to the relict scourian zones their distributions in the outer hebrides are reproduced in the mainland outcrop and can be matched following correction for the same sinistral strike slip a third line of evidence suggesting this motion is the offset of the deep crustal contribution to the aeromagnetic anomalies the fault zone accommodating this motion may now be represented by one or more of the low angle detachments bordering the western margin of the minches basin post laxfordian remanences in the outer hebrides are rotated by an average of 4 with respect to equivalent vectors on the mainland and may record later block rotations a mid proterozoic reconstruction of the lewisian complex derived from the magnetic evidence is presented

tectonic framework of the celtic sea and adjacent areas with special reference to the location of the variscan front abstract structural trends in the celtic sea area indicate that variscan deformation patterns were inherited from caledonian basement structures and that the regional fold alignment is arcuate with a regional wsw ene direction rather than wnw ese armorican there is no lateral structural continuity between southern ireland and south wales southwest england three major structural provinces arranged en echelon across the variscan foldbelt are recognised a southwest england where there was complex deformation of a major basin b the south wales mendips foreland area with strong basement cover interaction and c the southern ireland graben and flanking platform province late palaeozoic depositional patterns indicate that southern ireland and southwest england were separated by a wsw ene trending platform bounded on the north by the inherited wexford boundary lineament and to the south by a previously unidentified major palaeozoic fault zone here termed the bristol channel lineament the south wales mendips variscan successions accumulated on this intervening wales celtic sea platform and were partly influenced by rejuvenated caledonian fault lines it is suggested that the northern margin of the rheno hercynian foldbelt the variscan front be taken along the bristol channel lineament which can be traced for some 400 km southwestwards towards the goban spur on the continental margin this permits a rationalisation of both tectonic and major facies boundaries in locating the front it is also suggested that the structurally localised nature of the southern ireland basin be recognised by designating it as the southern ireland zone of the variscan foldbelt the sites of mesozoic rifting in the celtic sea and adjacent areas although complex in detail appear to have been located along the wexford boundary and bristol channel lineaments

paleoenvironmental reconstruction from chemical and isotopic compositions of permo pennsylvanian pedogenic minerals mineralogical and chemical analysis of late pennsylvanian and early permian paleosols from the eastern shelf of the midland basin north central texas usa are used to test hypothesized climate change in late paleozoic western equatorial pangea previously defined independently on the bases of sedimentologic and paleontologic proxies and climate models the 0 2 m size phyllosilicate fraction in the studied paleosols exhibits down profile trends in mineralogy and chemical composition that are consistent with modern weathering profiles suggesting a dominantly pedogenic origin a stratigraphic trend from kaolinite dominated profiles in upper pennsylvanian paleosols to profiles dominated by smectite and hydroxy interlayered 2 1 phyllosilicates in lower permian paleosols indicates a relatively rapid decrease in soil weathering and leaching in the latest pennsylvanian followed by a more gradual decrease in leaching throughout the early permian the chemical composition cation ratios and exchange capacity of these phyllosilicates further corroborates this shift toward less intensive leaching presumably in response to climate change from humid to progressively more arid conditions the phyllosilicates in the 0 2 m size fraction and contemporaneous pedogenic calcites from the permo pennsylvanian paleosols exhibit a long term stratigraphic increase in their 18o values of as much as 3 2 and 5 2 respectively this long term trend is consistent with a transition throughout the latest pennsylvanian through early permian toward progressively more evaporatively enriched soil waters superimposed on the long term trend is an apparent rapid enrichment 1 5 to 2 in phyllosilicate 18o values immediately above the pennsylvanian permian boundary observed oxygen isotope fractionation between the phyllosilicates and calcites within individual paleosols indicate isotopic disequilibrium between mineral pairs this is attributed to a minor detrital component in the pedogenic clay dominated phyllosilicate fraction coupled with the effects of seasonality of mineral formation inferred 18o compositions of late paleozoic meteoric water 2 to 4 are compatible with less intensive soil leaching under conditions of increasing aridity possibly coupled with a shift in local precipitation from a continental source to a marine source

cocorp and the continental crust this is a speculative paper on the continental crust a major frontier of modern earth science seismic reflection profiling data from the cocorp project coupled with other kinds of geophysical and geological observations suggest some fresh perspectives on the crust for example there is evidence for great differences within the basement at a single site and from one cocorp site to another a simple layered model is surely not an adequate representation of the crust in most areas there is however the puzzling and rather common occurrence of limited zones of parallel though not always flat layered features at various depths in certain parts of the crust are the corresponding rocks metasedimentary or igneous or both there are transparent zones from which little or no coherent reflected seismic energy is detected are the corresponding rocks intrusions or highly deformed metasediments can degree of deformation suggest whether rocks were deformed in the hanging wall or footwall of a thrust there is evidence for large scale thrusting and related features that emphasizes the great importance of the wilson cycle to continental tectonics and that raises the possibility that water and rocks of sedimentary origin are trapped deep in the crust by the thrusting process and remain there for long periods with a variety of possible rheological and petrological consequences in some places the modern moho and adjacent rocks may correspond to parts of former oceanic or continental margin sections that have been emplaced at depth as a result of thrusting the widely held concept of the moho as a consistent boundary that is everywhere similar and that always separates the same kinds of rocks may be a major barrier to further progress in understanding the continental crust

evidence for extensional shear zones in the mantle offshore britain and their implications for the extension of the continental lithosphere deep seismic profiles recorded in the seas around the british isles have revealed bands of seismic reflections in the uppermost mantle on the basis of their appearance geophysical characteristics and association with major crustal faults these features are best interpreted as mantle shear zones furthermore in the north sea the mantle reflectors appear to follow an extensional trend and when interpreted as extensional shear zones help explain the regional stratigraphy of the overlying basin the crosscutting relationships between mantle reflections to the west of scotland and a major strike slip fault the great glen fault ggf suggest that the mantle structure postdates the ggf and hence is probably related to subsequent extension furthermore kinematic analysis of lithospheric deformation to the north of scotland is consistent with the structure observed on the seismic data if the flannan mantle reflection is an extensional shear zone reconstruction of the lithosphere prior to permian extension restores the flannan to the edge of the rockall trough a rift probably initiated in the carboniferous thus the flannan fault may have developed during carboniferous rifting it is concluded that most of the mantle reflections are some form of extensional shear zone in the mantle and the role of such structures during lithospheric extension is considered

stable isotopic evidence for a pre middle miocene rain shadow in the western basin and range implications for the paleotopography of the sierra nevada 1 a recently proposed method for approximating the paleorelief of mountain belts makes use of the predictable relationship between the isotopic depletion of precipitation and the net elevation of an orographic barrier over which an air mass rises this rain shadow effect often creates desert regions on the lee side of mountain belts in which precipitation is isotopically light changes in the isotopic composition of precipitation can be estimated from the isotopic composition of authigenic or pedogenic minerals which can then be used to infer both the development of relief during orogenesis as well as the stability of a rain shadow formed by developing mountains the 18o of smectites formed from the weathering of middle miocene to late pliocene volcanic ashes currently exposed in the rain shadow of the modern sierra nevada of california show no indication of large scale late cenozoic surface uplift of the sierra and corresponding regional rain shadow development rather smectite isotope data tentatively suggest that elevations may have decreased over this time by as much as 2000 m toward the southern end of the range and 700 m in regions farther north this suggests that the modern rain shadow cast over the western basin and range has been in existence since pre middle miocene and that the sierra nevada have been a prominent orographic barrier since before this time these interpretations are in accord with several recent studies also suggesting a possible cenozoic elevation loss of an already developed sierra nevada mountain range

the isotopic composition of meteoric water along altitudinal transects in the tian shan of central asia abstract the tian shan in central asia are a unique mountain range in that they are in the world s most continental location seasonal precipitation in the northern tian shan is segregated into distinct elevation bands where high elevations receive precipitation primarily during summer and low elevations to the north receive precipitation primarily during the late winter and spring in this study we sampled stream water along multiple altitudinal transects to determine the effect unique seasonal patterns of precipitation have on the isotopic composition of surface water our results suggest that the northern tian shan exhibits an isotopic lapse rate for waters sampled in late spring but not for those sampled in late summer when stream water budgets are dominated by high elevation precipitation and snow melt deuterium excess results suggest that subcloud evaporation significantly affects the isotopic composition of precipitation at low elevations in spring and that sublimation of snow has a minor impact on 18o values of summer melt water because high and low elevation 18o values are similar conventional paleoaltimetry based on rayleigh distillation of an air mass is not applicable to the kyrgyz tian shan stream water proxies from the rock record are likely to reflect changes in the seasonal distribution of precipitation which occur on the same spatial scale as altitudinal changes these results highlight the need to understand modern controls on local stable isotopes of meteoric water in reconstructions of past climate or topography using geologic proxy materials

oxygen isotope perspective on crustal evolution on early earth a record of precambrian shales with emphasis on paleoproterozoic glaciations and great oxygenation event abstract we present stable isotope and chemical data for 206 precambrian bulk shale and tillite samples that were collected mostly from drillholes on all continents and span the age range from 0 5 to 3 5 ga with a dense coverage for 2 5 2 2 ga time interval when earth experienced four snowball earth glaciations and the irreversible rise in atmospheric o2 we observe significant downward shift of several and a smaller range of 18 o values 7 to 9 in shales that are associated with the paleoproterozoic and potentially neoproterozoic glaciations the paleoproterozoic samples consist of more than 50 mica minerals and have equal or higher chemical index of alteration than overlying and underlying formations and thus underwent equal or greater degrees of chemical weathering their pervasively low 18 o and d down to 85 values provide strong evidence of alteration and diagenesis in contact with ultra low 18 o glacial meltwaters in lacustrine deltaic or periglacial lake sikussak type environments associated with the paleoproterozoic glaciations the d silicate values for the rest of precambrian shales range from 75 to 50 and are comparable to those for phanerozoic and archean shales likewise these samples have similar ranges in 13 c org values 23 to 33 pdb and corg content 0 0 to 10 wt to phanerozoic shales precambrian shales have a large range of 18 o values comparable to that of the phanerozoic shales in each age group and formation suggesting similar variability in the provenance and intensity of chemical weathering except for the earliest 3 3 3 5 ga archean shales which have consistently lower 18 o values moreover paleoproterozoic shales that bracket in age the great oxidation event goe overlap in 18 o values absence of a step wise increase in 18 o and d values suggests that despite the first order change in the composition of the atmosphere weathering cycle was not dramatically affected by the goe at 2 4 2 3 ga shales do not show comparable 18 o rise in the early phanerozoic as is observed in the coeval 18 o trends for cherts and carbonates there is however a sharp increase in the average 18 o value from the early archean to the late archean followed by a progressively decelerating increase into the phanerozoic this decelerating increase with time likely reflects declining contribution of mantle extracted normal 18 o crust and lends support to crustal maturation and increasing 18o sequestration into the crust and recycling of high 18 o and 87sr 86sr sedimentary rocks this secular increase in the 18 o composition of the continental crust could have also had a mild effect on seawater 18 o composition

deep structure of the scottish caledonides revealed by the moist reflection profile the moine and outer isles seismic traverse moist is a deep crustal reflection profile shot at sea off the north coast of scotland in 1981 spectacular reflections are observed from the moho and from thrust zones within the caledonian fold belt and foreland deep reflection profiling of the continental crust of the united states under the direction of the cocorp group has amply demonstrated the value of this technique when applied to suitable geological problems see for example refs 1 2 a similar group the british institutes reflection profiling syndicate birps has now been set up in the uk to organize such projects funds are provided by the natural environment research council nerc through the core group based at cambridge university however a preliminary experiment of which moist is the result was organized through the institute of geological sciences igs

calculation of oxygen isotope fractionation in metal oxides abstract a theoretical model calculating the thermodynamic isotope factors of oxygen in metal oxides of geochemical interest is presented for temperatures between 0 and 1200 c on the basis of the modified increment method the following order of 18o enrichment is obtained cassiterite rutile magnetite ilmenite ulvospinel hematite uraninite chromite corundum spinel the results are expressed as 103 in a 106 t2 b 103 t c which compare well with existing theoretical experimental and empirical calibrations on quartz oxides and oxides water systems the present calculations enable not only estimation of the oxygen isotope composition of fluids from which the metal oxides were precipitated when independent temperature information is available but can also be applied as oxygen isotope geothermometers to igneous and metamorphic rocks

permo pennsylvanian palaeotemperatures from fe oxide and phyllosilicate δ18o values abstract the oxygen isotope composition of fossil roots that have been permineralized by hematite are presented from eight different stratigraphic levels spanning the upper pennsylvanian and lower permian strata of north central texas hematite 18o values range from 0 4 to 3 7 the most negative 18o values occur in the upper pennsylvanian strata and there is a progressive trend toward more positive 18o values upward through the lower permian strata this stratigraphic pattern is similar in magnitude and style to 18o values reported for penecontemporaneous authigenic palaeosol phyllosilicates and calcites suggesting that all three minerals record similar paragenetic histories that are probably attributed to temporal palaeoenvironmental changes across the late pennsylvanian and early permian landscapes palaeotemperature estimates based on paired 18o values between penecontemporaneous hematite and phyllosilicate samples suggest these minerals co precipitated at relatively low temperatures that are consistent with a supergene origin in a low latitude soil forming environment hematite phyllosilicate 18o pairs indicate 1 relatively low soil temperatures 24 3 c during deposition of the upper pennsylvanian strata followed by 2 a considerable rise in soil temperatures 35 37 3 c during deposition of the lowermost permian strata significantly d and 18o values of contemporaneous phyllosilicates provide single mineral palaeotemperature estimates that are analytically indistinguishable from temperature estimates based on hematite phyllosilicate oxygen isotope pairs the results between the two temperature proxy methods suggest that the inferred large temperature change across the upper pennsylvanian lower permian boundary might be taken seriously if real such a significant climate change would have undoubtedly had far reaching ecological effects within this region of pangaea notably there are important lithological and palaeobotanical changes such as disappearance of coal and coal swamp floras across the upper pennsylvanian early permian boundary of north central texas that may be consistent with major climatic change toward warmer conditions

tomographic study of crustal velocity structure in southern finland abstract an inverse tomographic problem of the construction of a 3 d velocity structure has been solved for depths of 10 20 30 and 40 km using the p wave arrivals registered by the seismic array in southern finland and on the dss lines sveka 1981 and baltic 1982 the interpreted results verify and enlarge dss data obtained earlier for a high velocity structure of the crust and explain some small lateral velocity variations the concordant tomographic and dss data specify a 3 d model for a complex geological structure in the region

spatial variation in fluid flow and geochemical fluxes across the sediment seawater interface at the carlos ribeiro mud volcano gulf of cadiz submarine mud volcanism is an important pathway for transfer of deep sourced fluids enriched in hydrocarbons and other elements into the ocean numerous mud volcanoes mvs have been discovered along oceanic plate margins and integrated elemental fluxes are potentially significant for oceanic chemical budgets here we present the first detailed study of the spatial variation in fluid and chemical fluxes at the carlos ribeiro mv in the gulf of cadiz to this end we combine analyses of the chemical composition of pore fluids with a 1 d transport reaction model to quantify fluid fluxes and fluxes of boron lithium and methane across the sediment seawater interface the pore fluids are significantly depleted in chloride but enriched in lithium boron and hydrocarbons relative to seawater pore water profiles of sulphate hydrogen sulphide and total alkalinity indicate that anaerobic oxidation of methane occurs at 34 180 cm depth below seafloor clay mineral dehydration and in particular the transformation of smectite to illite produces pore fluids that are depleted in chloride and potassium profiles of boron lithium and potassium are closely related which suggests that lithium and boron are released from the sediments during this transformation pore fluids are expelled into the water column by advection fluid flow velocities are 4 cm yr 1 at the apex of the mv but they rapidly decrease to 0 4 cm yr 1 at the periphery the associated fluxes of boron lithium and methane vary between 7 301 0 5 6 and 0 806 mmol m 2 yr 1 respectively we demonstrate that fluxes of li and b due to mud volcanism may be important on a global scale however release of methane into the overlying water column is suppressed by microbial methanotrophy

isotope ratios of nonexchangeable hydrogen in soils from different climate zones abstract the fractionation of h isotopes in global precipitation leads to a continuous decrease in 2 h concentrations of precipitation with increasing latitude altitude and continentality thus the local precipitation soil and ground water used by plants for photosynthesis or consumed during neoformation of pedogenic clay minerals often have a spatially diagnostic 2 h value we hypothesize that the 2 h value of isotopically nonexchangeable h in bulk soil composed of c bonded h in soil organic matter som and the nonexchangeable fraction of o bonded h in pedogenic clay minerals is correlated with the mean 2 h value of local precipitation water at the place and time of biomass production and clay mineral neoformation respectively we equilibrated soil samples with water of known isotopic composition prior to 2 h analysis with an elemental analyzer isotope ratio mass spectrometer ea irms to determine the 2 h value of isotopically nonexchangeable h in soil we analyzed 12 topsoil samples from different climate zones temperate zone subarctic zone and tropics the 2 h values of nonexchangeable h in soil ranged from 75 to 167 the 2 h values of nonexchangeable h in soil were highly correlated with predicted average annual 2 h values of local precipitation at the sampling sites r 0 89 p 2 h values of nonexchangeable h in soils from siberia were up to 80 depleted in 2 h compared to soils from central europe which directly corresponds to the difference in average annual 2 h values of precipitation from central europe and siberia our study supports the hypothesis that the average h isotope composition of local precipitation is the primary control of the isotopic composition of nonexchangeable h in bulk soils since 2 h values of nonexchangeable h in som and pedogenic clay minerals are both primarily determined by 2 h values of global precipitation 2 h analyses of bulk soil samples are meaningful irrespective of the precise fractions of som and clay minerals in soil

climatic implications of surface domains in arrays of δd and δ18o from hydroxyl minerals goethite as an example abstract paired d h and 18o 16o analyses of natural goethites range from 224 to 93 for d and from 15 5 to 2 8 for 18o the isotopic systematics of these goethites seem to be most closely mimicked by the goethite water d h and 18o 16o fractionation curves of yapp 1987 yapp 1990 most of these goethites are of unknown age but the large range of their isotopic compositions illustrates the possible paleoenvironmental significance of surface domains calculated for hydroxyl minerals a modern surface domain msd for goethite in coordinates of d and 18o was calculated from the following information a scatter in the modern relationship between surface temperatures and 18o of meteoric water rozanski et al 1993 b average annual surface air temperatures from 0 c to 30 c for the meteoric water sample sites c the meteoric water line mwl of craig 1961 and d the goethite water isotopic fractionation factors of yapp 1987 yapp 1990 goethites that had formed in continental environments in approximate thermal equilibrium with the earth s modern atmosphere would be expected to lie within the msd and 16 of 31 goethites do so the remaining 15 are outliers of the 16 msd samples 12 including the three samples from active soil or bog environments are concordant the calculated isotopic temperatures of the concordant goethites range from 6 c to 27 c and are the same within analytical uncertainty as the modern average surface air temperatures at the respective sites calculated temperatures of the four discordant msd samples range from 7 c to 25 c and are higher than corresponding modern surface temperatures a warm earth surface domain wesd was calculated with an assumed temperature of 35 c for the tropics eight of the 15 outlier samples plot within the portion of the wesd that does not overlap the msd thus these eight goethites may have formed at times when the earth s global climate was warmer than at present temperatures calculated from the eight wesd samples range from 20 c to 33 c and suggest lower latitudinal temperature gradients as predicted by climate models of a warmer earth calculated temperatures of the seven samples that lie outside both the msd and the wesd non sd samples range from 19 c to 69 c the non sd status of these seven samples suggests that they formed in environments dominated by subsurface heat sources surface domains can be calculated for any hydroxyl mineral for which both the hydrogen and oxygen isotope mineral water fractionation factors are known the concept of surface domains provides a criterion for assessing the likelihood that a particular sample records information on ancient climatic temperature

late jurassic paleoclimate of central africa abstract paleopedology and geochemical analysis of upper jurassic deposits in the stanleyville group of central africa indicate harsh late jurassic paleoclimates in the interior of gondwana subsurface samples collected from the samba borehole near the center of the congo basin show only weak morphological evidence of pedogenesis but are characterized by an abundance of shrink swell vertic features and rare calcium carbonate nodules indicating seasonal variations in moisture availability and net soil moisture deficiency respectively x ray diffraction analysis of paleosol matrix material reveals the presence of analcime and the clay mineral palygorskite strong indicators of hot arid climatic conditions the 18 o and d values of clay minerals from paleosol profiles range from 22 3 to 25 4 and 44 4 to 39 6 smow respectively and correspond to crystallization temperatures between 25 c and 40 c these crystallization temperatures compare favorably with austral summer surface temperature estimates for central africa that result from late jurassic global circulation models calculations of soil co 2 production using the 13 c values of pedogenic carbonates and plant derived organic matter produce lower co 2 production estimates for the stanleyville group relative to the roughly contemporary morrison formation of the western u s these low soil co 2 production estimates provide further support for arid late jurassic climate conditions in the congo basin the paleoclimatic conditions inferred here from the stanleyville group are similar to those reconstructed from other upper jurassic african continental localities between 5 s and 20 s paleolatitude however penecontemporaneous terrestrial coastal sites within this latitudinal belt of gondwana retain evidence of generally wetter conditions suggesting that those regions may have received more rainfall than the continental interior the paleoclimatic setting reconstructed here from geologic indicators and geochemical proxies suggests that general circulation models accurately predict unique paleoenvironmental conditions that lack modern analogs

triple oxygen isotope investigation of fine grained sediments from major world s rivers insights into weathering processes and global fluxes into the hydrosphere abstract continental weathering is accompanied by formation of clays and other secondary minerals and their 18 o and 17 o values should hence reflect to some extent signatures of meteoric water 18 o mw and mean annual temperatures mat our ability to extract climate information from weathered products across the geologic history relies on analytical methods tested and calibrated against modern climate conditions we here present triple oxygen isotope analyses of clay size sediments from 45 rivers worldwide as well as 18 o analyses of corresponding silt and sand rich detrital fractions which altogether cover about 25 of the continental area that drained into the oceans extending from the tropics to polar regions the majority of studied clays closely approximate weathering products always having high 18 o signatures regardless of the bedrock type and in equilibrium with local meteoric waters silts are only 1 9 lighter on average due to greater detrital dilution overall bulk clays from across different climatic regions do not vary much isotopically an observation which we attribute to opposing effects of temperature on clay water fractionation and hydrologic relationship between temperature and 18 o mw mathematical inversion of measured clay 18 o and 17 o values corrected for detrital contribution into mat and 18 o mw compiled for each studied watershed returns satisfactory estimates globally triple o isotopes in clays appear to be water dominated being controlled almost exclusively by 18 o mw at respective temperature of weathering with minor effects related to evaporation using sand from rivers correlation of 18 o silts with detrital proportions and estimated surface outcrop of different rock types we additionally arrive at a 11 5 estimate for the exposed silicate crust undergoing weathering globally averaged sediment flux weighted clay 18 o and 17 o values are 14 80 and 0 164 respectively these values are significantly skewed toward o isotope signatures for the southeast asia and western pacific regions characterized by very high sediment fluxes to the ocean using both clay and silt size fractions the total weighted silicate weathering 18 o signature exported to the world s ocean is 2 59 almost 50 higher the previous estimate yielding an ice free world hydrosphere estimate of 0 78 overall the modern river clays represent a snapshot of modern weathering conditions on continents and associated first order climatic signatures related to mat and 18 o of the hydrosphere this implies that measured increase in 18 o and stepwise decrease in 17 o in shales in the geologic record capture evolving global hydrologic cycle upon continental emergence decrease in global mat or diagenetic conditions and decreasing ocean mass via rehydrating of the mantle by subduction of hydrated low 18 o high 17 o slabs

intensification of monsoon microclimate and asynchronous c4 appearance isotopic evidence from the indian siwalik sediments article i nfo analysis of the d h ratio of pedogenic clay and the 18 o 16 o ratio of carbonate nodules collected from siwalik sediments in india indicates three episodes of monsoon intensification at 11 ma 6 ma and 3 ma these episodes coincide with major pulses of tectonic uplift in the himalayas suggesting causal link between monsoon intensity and uplift in addition variation in the carbon isotope ratio of carbonate nodules and residual organic matter indicates a change in vegetation regime from pure c3 type to a mix of c3 c4 type during this time span isotopic analysis of samples collected from different locations of the himalayan siwalik shows that the late miocene c4 appearance was locally asynchronous by 3 ma similar to what is seen on a global scale the lack of synchronous emergence of c4 plants in various parts of siwalik probably indicates a combined effect of microclimate e g varying monsoon intensity and habitat disturbance e g forest fire in contrast subsequent expansion of c4 plants during the late miocene pliocene time could be entirely due to monsoon intensification that favoured c4 respiration in a warm and seasonally variable rainfall regime 2010 elsevier b v all rights reserved

spatial and temporal variation of cenozoic surface elevation in the great basin and sierra nevada the surface uplift of mountain belts caused by tectonism plays an important role in determining the long term climate evolution of the earth however the general lack of information on the paleotopography of mountain belts limits our ability to identify the links and feedbacks between topography tectonics and climate change on geologic time scales here we present a 1 8 o and d record of authigenic minerals for the northern great basin that captures the timing and magnitude of regional surface uplift and subsidence events in the western united states during the cenozoic authigenic calcite smectite and chert 1 8 o values suggest the northern great basin region experienced 2km of surface uplift between the middle eocene and early oligocene followed by 1 to 2km of surface subsidence in the southern great basin and or sierra nevada since the middle miocene these data when combined with previously published work show that the surface uplift history varied in both space and time surface uplift migrated from north to south with high elevations in southern british columbia and northeastern washington in the middle eocene and development of surface uplift in north and central nevada in the oligocene this pattern of north to south surface uplift is similar to the timing of magmatism in the western cordillera a result that supports tectonic models linking magamtism with removal of mantle lithosphere and or a subducting slab

oxygen and hydrogen isotope compositions of permian pedogenic phyllosilicates development of modern surface domain arrays and implications for paleotemperature reconstructions abstract mineralogic chemical and oxygen and hydrogen isotope compositions of 15 different phyllosilicate samples from permo pennsylvanian age paleosols of the eastern shelf of the midland basin of texas and the southern anadarko basin are presented mixtures of 2 1 phyllosilicates and kaolinite dominate most samples although some samples consist of relatively pure 2 1 phyllosilicates chemical and mineralogic data are used in conjunction with published thermodynamic data to calculate hydrogen and oxygen isotope fractionation factors for each sample in turn application of measured oxygen and hydrogen isotope compositions of the phyllosilicates to temperature dependent fractionation equations are used to calculate paleotemperatures of crystallization the d values of the phyllosilicates range from 69 to 55 the 18 o values range from 19 5 to 22 7 if these samples preserve a record of equilibrium with paleo meteoric waters the isotopic compositions of the phyllosilicates correspond to paleotemperatures of phyllosilicate crystallization ranging from 22 3 c to 35 3 c in particular the stratigraphic trend of calculated temperatures from midland basin samples suggests that early permian surface temperatures may have been up to 10 c warmer than those of the latest pennsylvanian

isotopic evidence for cooler and drier conditions in the tropical andes during the last glacial stage documentation of paleoclimatic conditions during the last glacial stage in the tropical andes is sparse despite the importance of understanding past climate changes in the tropics to reconstruct paleoenvironmental conditions in the alpine neotropics we measured the oxygen 18o and hydrogen d isotopic composition of authigenic kaolinite within weathering profiles of the bogota basin colombia because of the strong dependence of isotopic values on both surface temperature and rainfall while kaolinite isotope data from holocene soils in the basin reflect modern mean annual temperature and mean weighted rainwater isotopic composition of the basin kaolinite isotope data from paleosols developed during the last glacial stage suggest 6 2 c cooler temperatures moreover the isotope data indicate higher isotopic values of paleorainwater interpreted to reflect drier conditions the combination of reduced rainfall temperature and p co2 significantly affected the distribution of tropical montane flora during the last glacial stage

paleocene eocene climatic variation in western north america evidence from the δ18o of pedogenic hematite reconstruction of the pre pleistocene climate of continental interiors has been hampered by a lack of climatic proxies and limited temporal resolution we developed a new approach based on the oxygen isotope composition 18 o of hematite which occurs as a coating on fossil vertebrates and used this method to study climatic change across the paleocene eocene boundary in the bighorn basin wyoming hematite coatings form in soils or shallow sediments and therefore may be used to monitor near surface conditions hematite 18 o values are measured by combining selective leaching laser fluorination and mass balance calculation these values in conjunction with 18 o values for co occurring carbonates are used to assess the plausibility of published hematite water oxygen isotope fractionation relations though uncertainty remains as to the appropriate fractionation all are relatively insensitive to temperature variations thus differences in hematite 18 o values most likely reflect shifts in surface water 18 o values analysis of hematites spanning the paleocene eocene transition reveals a roughly 4 decrease in the 18 o of surface water in very early eocene time this episode probably reflects a cooling event perhaps as great as 6 c that started 0 7 m y after the terminal paleocene 13 c excursion which corresponds to a pulse of extreme marine warming following the cooling which lasted 0 6 m y temperatures rebounded to values close to those for late paleocene time the cooling episode coincides remarkably well with other indicators of environmental and climatic change from the basin such as mammalian turnover events and mean annual temperatures estimated from leaf physiognomy

unraveling climatic changes from intraprofile variation in oxygen and hydrogen isotopic composition of goethite and kaolinite in laterites an integrated study from yaou french guiana an integrated study of o and h isotopes in the lateritic profile of yaou french guiana was undertaken to investigate the usefulness of stable isotopes as tracers of climatic changes in continental environments the studied profile is composed of a 27 m thick saprolite mostly developed in the past under wet and dry tropical climate in association with a duricrust overlain by a 3 m thick yellow latosol formed more recently under present equatorial hot and humid climate 18o d values determined for weathering goethite pseudomorphs after pyrite and kaolinite microcrystalline clay groundmass throughout the 30 m deep profile reflect formation temperatures consistent with present 25 c and realistic past climatic temperatures 20 c 30 c indicating that weathering minerals formed in isotopic equilibrium with their genetic environment and were not subjected to significant isotope exchange after formation a distinct shift downward 2 for 18o 15 for d from low to high 18o d values occurs around 20 m depth in the saprolite it is interpreted as recording the change from the past tropical to the present equatorial climate goethite and kaolinite in the 5 10 m thick saprolite interval immediately above the active basement weathering front are in isotopic equilibrium with modern water and must have formed under present equatorial humid conditions in contrast goethite and kaolinite found higher up in the saprolite and in the duricrust formed in the past under tropical wet and dry climate from waters distinctly depleted in 18o and d relative to modern water the marked depletion of paleo meteoric water at yaou most likely reflects a more contrasted or monsoonal character of the ancient tropical climate the present study shows that ancient weathering minerals in lateritic profiles preserve their 18o d values and carry a time signal the time signal is best expressed in minerals formed rapidly at the weathering front and not subjected to post formational remobilization such as the goethite pseudomorphs after pyrite occurring at yaou groundmass kaolinite is more susceptible to partial remobilization through successive dissolution precipitation reactions which may obliterate the paleoclimatic signal unraveling the climatic record carried by weathering minerals in old soil systems is greatly enhanced by studying both oxygen and hydrogen isotopic compositions

shifts in late paleozoic atmospheric circulation over western equatorial pangea insights from pedogenic mineral δ18o compositions the d 18 o values of pedogenic calcites phyllosilicates and iron oxyhydr oxides from fossil soils throughout the southwestern united states show systematic paleolatitudinal and temporal trends that indicate a significant change in soil moisture conditions and atmospheric circulation patterns over southwestern euramerica throughout latest pennsylvanian and early permian time a progressive depletion of as much as 6 in mineral 18 o values with increasing distance northward to 108 of the paleoequator indicates a weakening or disruption of zonal easterly flow over the study area by latest pennsylvanian time furthermore elevated d 18 o values suggest a proximal source of paleoprecipitation over the study area perhaps due to initiation of reversed equatorial flow over tropical southwestern euramerica coupling of the geographic and temporal trends defined by pedogenic mineral d 18 o values with those defined by climatically sensitive paleosol pedotypes in the study area along with overall elevated mineral d 18 o values provides some of the strongest evidence that northern hemisphere monsoonal circulation was well established over pangea by early permian time

the hydrogen and oxygen isotope geochemistry of pedogenic clay minerals principles and theoretical background abstract the 18 o 16 o and d h ratios of the structural oxygen and hydrogen of naturally occurring clay minerals carry information about the conditions under which the minerals formed clays generally form in isotopic equilibrium with the environment and hence have isotopic compositions that reflect the temperature of formation and the 18 o 16 o and d h ratios of water in the micro environment the isotopic signature of water in the weathering environment is a reflection of the climate once formed clays are resistant to isotopic alteration under surface and near surface conditions except when they undergo subsequent mineralogical alteration in some instances this alteration may be subtle as in the case of conversion of kaolinite with a high degree of crystalline order as measured by the hinckley index to kaolinite of low crystalline order in a pedogenic profile isotopic studies of pedogenic clays may be expected to yield more information about pedogenesis and paleoclimate when both 18 o 16 o and d h ratios of the clays are measured however few studies have incorporated the use of the two isotope ratios

quantitative paleoenvironmental and paleoclimatic reconstruction using paleosols abstract paleosols fossil soils are preserved throughout the geologic record in depositional settings ranging from alluvial systems to between basalt flows until recently paleosols were studied using primarily qualitative methods in recent years paleopedology has shifted from a largely qualitative field based on comparisons with modern analogues to an increasingly quantitative endeavor some of this change has been a result of applying existing techniques to new materials but many of the innovations have been the result of applying new techniques to new materials including thermodynamic modeling of soil formation isotope geochemistry and applications of empirical relationships derived from modern soils a variety of semi quantitative and quantitative tools has been developed to examine past weathering and pedogenesis and to reconstruct both paleoenvironmental and paleoclimatic conditions at the time that the paleosols formed though it is often not possible to achieve the same temporal resolution as with marine records for paleoclimatic reconstructions proxies based on paleosols are potentially a much more direct means of making paleoclimatic reconstructions because soils form at the earth s surface in direct contact with the atmospheric and climatic conditions at the time of their formation paleoclimatic and environmental properties that may be reconstructed using the new proxies include provenance weathering intensity mean annual precipitation and temperature during pedogenesis nutrient fluxes into and out of the paleosols the atmospheric composition of important gases including co2 and o2 the moisture balance during pedogenesis the soil gas composition reconstructed vegetative covering and paleo altitude

late paleozoic continental warming of a cold tropical basin and floristic change in western pangea abstract an increase in mineral crystallization temperatures of 13 3 c is preserved in paleosol profiles ancient soils within a stratigraphic interval of cooler than soil temperatures observed in the modern lowland tropics to permian age soil mineral crystallization temperatures which are equivalent to or slightly exceed soil temperatures observed in modern lowland tropics this record of mineral crystallization temperatures occurs at a time when some sources indicate the onset of the largest single glaciation of the late paleozoic ice age the temperature change indicated by these paleosol minerals is accompanied by a unidirectional irreversible change in the composition of tropical lowland vegetation this transition delineates the magnitude and characteristics of vegetational changes in the modern tropics that might accompany continued atmospheric warming times of low surface temperatures coincide with a typical late pennsylvanian tropical pangean wet biome dominated by sigillaria macroneuropteris other pteridosperms and marattialean ferns this plant assemblage is replaced spatially by a xeromorphic biome dominated by conifers callipterids and other seed plants characteristic of the tropical permian across western and central pangea the fully xeromorphic flora appears initially in sub meter scale beds within outcrops otherwise characterized by wet flora and becomes predominant once peak surface temperatures were reached in the earliest permian a narrow stratigraphic interval 20 m separates these two biomes in the region marking what was to be a permanent floristic change in western pangea the lower diversity floras of seasonally dry habitats apparently migrated from drier extrabasinal areas into increasingly dry landscapes formerly dominated by the wet biome this study documents the regional disappearance of an entire tropical biome with a net reduction of biodiversity accompanying rapid environmental warming

fractal analysis of seismic and geological data abstract continental lithosphere is a highly organised physical medium which can be investigated by seismic methods to obtain objective information the use of fractal representation offers new possibilities to determine quantitative parameters of the structural arrangement of the lithosphere and to compare tectonic structures composed of a similar set of participants i e structural complexes with a relatively homogeneous range of rocks fractals as a universal property of continental crust are shown to be an important tool for a comparative study of geological and seismic sections on a quantitative basis and also in reassessing many of the previous interpretations of seismic and geological structures

does the great glen fault really disrupt moho and upper mantle structure many previous interpretations of deep seismic reflection profiles across the great glen strike slip fault system have postulated that the fault penetrates the crust and upper mantle as a vertical plane that sharply offsets the moho discontinuity such an interpretation has become a general feature of more recent regional syntheses of the deep geology of the british isles reprocessing of portions of four profiles across the fault improves the resolution of lower crustal and upper mantle structure and calls into question the moho step interpretation diffraction analysis and seismic migration applied to reflection data north of shetland across the northward continuation of the great glen fault walls boundary fault indicate a narrow synform or keel developed on the moho directly beneath the fault this keel is itself underlain by a possible mantle reflection that is cut off by the downward projection of the fault north and west of ireland analyses of amplitudes frequencies and the geometrical behavior of reflections upon migration show that structures previously interpreted as moho steps may be better explained as distinct packages of reflectivity that are uppermost mantle or possibly out of the plane in origin in one location north of ireland where some three dimensional control exists the vertically downward projection of the great glen fault intersects without disrupting dipping structure in the upper mantle this observation leads to a model for displacement on the fault system in which motion is laterally transferred along a dipping ramp or blind thrust in the uppermost mantle somewhat analogous to models developed for the san andreas fault that indicate displacement along the fault to be laterally offset within the middle crust one of the principal conclusions of this study that major vertical steps on the moho beneath the great glen fault are difficult to support from the available seismic data is consistent with theologically based studies which predict that moho topography such as vertical steps is unlikely to be preserved over long periods of geologic time

oxygen isotope geochemistry of kaolinite in laterite forming processes manaus amazonas brazil abstract mineralogic crystallographic and oxygen isotopic analyses were made of kaolinites from a 20 m thick lateritic profile developed on the detrital sands and clays of the mid cretaceous to tertiary alter do chao formation central amazon basin brazil a detailed 18o profile of soil water from the upper 4 m of the same section was also measured kaolinite separates were prepared from different pedogenic facies of small hand specimens most of these kaolinite separates exhibit polymodal size distributions the separates were further divided into individual particle size modes for subsequent isotopic and crystallographic analysis in general hinckley index and 18o values of different size fractions of the same sample differ hinckley index values decrease strongly and fe content increases in the upward direction in the profile we conclude that 1 the kaolinite in the profile has progressively evolved in response to changing microenvironments as weathering fronts have moved progressively downward 2 different kaolinite fractions even within a single facies of a single sample a few cm3 in size typically formed under somewhat different conditions 3 the bulk of the fine grained kaolinite in the lateritic profile does not constitute a continuous inverted time record that is lower levels do not represent more recent kaolinite formation and higher levels do not represent older kaolinite formation and 4 isotopic compositions of kaolinites from lateritic paleosols should provide an indication of mean climatic conditions and some measure of seasonality during the interval preceding the removal of the laterite from the active weathering environment we speculate that the different conditions under which the different kaolinite fractions have formed may be related at least in part to variations in soil microenvironments that are ultimately derived from seasonal and year to year variations in the chemistry and isotopic composition of infiltrating rainfall

birps deep seismic reflection studies of the british caledonides the western isles north channel winch traverse fig 1 an extension of the successful moist profile1 was recorded in 1982 at sea along the west coast of britain for birps british institutions reflection profiling syndicate by the geophysical company of norway geco the purpose of the winch traverse was to study crustal structure of the caledonian foreland to cross the caledonian orogen and to establish the three dimensional geometry of mantle reflectors originally seen on moist we describe here the data first emphasizing british caledonian structures and then discussing features of the deep crust of wider significance the data are of very good quality and contain clear moho and upper mantle reflections the lower crust is surprisingly reflective deeply penetrative thrusts are observed and there is firm evidence that several of the mesozoic basins round the shores of the united kingdom were formed by reactivation of older features

hydrogen and oxygen isotopic compositions of sedimentary kaolin deposits egypt paleoclimatic implications abstract the clay fractions of sedimentary kaolin deposits representing different ages carboniferous and cretaceous types pisolitic flint and plastic and localities sinai and aswan from egypt were analyzed for their h and o isotopic compositions to examine the paleoclimate conditions during their formation the d values of the carboniferous deposits in sinai range between 67 and 88 while the values for the cretaceous deposits in sinai range between 59 and 75 the 18 o values of the carboniferous deposits range from 17 9 to 19 4 and the values for the cretaceous deposits range between 19 2 and 20 4 the relatively low d and 18 o values of the carboniferous deposit at the abu natash area 67 and 17 9 respectively compared to other carboniferous deposits averages of 83 3 and 18 8 for d and 18 o respectively could be due to isotopic exchange between this deposit and the adjacent dolomite and or the enclosed hydrothermally formed mn ores of the carboniferous um bogma formation the d and 18 o values of the cretaceous pisolitic flint kaolin deposit from aswan averages of 65 and 20 3 respectively and plastic kaolin from the same area averages of 66 and 19 5 respectively are almost identical the differences in the 18 o values between the clay fractions of the pisolitic flint kaolin 20 3 and the previously analyzed bulk kaolin of the same deposit average of 17 5 suggest a significant effect of non clay minerals on the isotopic compositions of the kaolin deposits the h and o isotopic compositions plot close to the kaolinite line that marks the isotopic composition of kaolinite in equilibrium with meteoric water at 20 c this indicates that the kaolinite from both the carboniferous and cretaceous deposits in egypt formed by meteoric water weathering of the source rock s the d and 18 o values also suggest that kaolinite of these deposits formed under warm temperate to tropical conditions the slight deviations of some samples from the kaolinite line suggest post depositional modifications of the isotopic compositions of studied deposits probably due to the interaction between earlier formed kaolinite and downward percolating meteoric water the d and 18 o values of the cretaceous and carboniferous deposits from all localities suggest that both deposits formed under similar climatic conditions due to the location of egypt at almost the same distance from the equator either to the south during the carboniferous or to the north during the cretaceous

multicomponent magnetizations in the foyers old red sandstone northern scotland and their bearing on lateral displacements along the great glen fault summary the foyers sandstone a constituent of the old red sandstone of northern scotland located on the eastern flank of the great glen fault has yielded a multicomponent palaeomagnetic structure the principal magnetization called the b component with in situ mean direction d i 185 8 ag5 2 7 post dates the local mid devonian acadian tectonic event but this direction corresponds well with characteristic directions displayed by devonian and lower carboniferous rocks of scotland the most significant overprinted component the a2 magnetization with in situ mean direction d i 194 27 ag5 4 lo has a more patchy occurrence than the b remanence the strongest development of a2 being observed at sites that are situated close to the great glen fault zone the a2 direction is consistent with a hercynian age a third magnetization the a1 component of suggested lower tertiary age has been found at one of the sites close to the fault zone the a2 and b remanences support previously proposed declination discordances in corresponding magnetizations across the great glen fault it is concluded that the foyers sandstone developed its multicomponent magnetization through repeated tectonic events on the great glen fault in acadian hercynian and alpine times respectively

thermodynamics and lattice vibrations of minerals 5 applications to phase equilibria isotopic fractionation and high pressure thermodynamic properties in previous papers in this series a model that uses available elastic structural and spectroscopic data on minerals has been used to predict the thermodynamic functions cv heat capacity s entropy e internal energy and f helmholtz free energy in this paper four applications to problems of current geochemical and geophysical interest are presented 1 interpretation of complex trends of calorimetric data 2 calculation of phase equilibria 3 calculation of oxygen isotopic fractionation factors and 4 estimation of the effect of pressure on thermodynamic functions the model demonstrates that trends in high temperature thermodynamic properties of silicates are determined by the position and relative numbers of high frequency modes generally antisymmetric si al o stretching modes the position of these modes varies systematically with degree of polymerization of tetrahedra and therefore high temperature calorimetric behavior is relatively systematic as a function of crystal structure and mineral composition trends at low frequency are much more complex because the low frequency optic modes that most strongly influence the low temperature thermodynamic functions depend in a complex way on the size coordination and mass of cations and various polyhedra in the minerals the heat capacity curves of kyanite andalusite and sillimanite and of quartz coesite and stishovite show crossovers that cannot be explained by debye theory which accounts only for acoustic mode behavior but can be explained by the model spectra proposed because proper account is taken of the changing low and high frequency optic modes upon polymorphic transformations the proposed model is sufficiently accurate that phase equilibrium problems can be addressed the quartz coesite stishovite equilibrium curves the kyanite andalusite sillimanite triple point and the breakdown of albite to jadeite plus quartz are cited as specific examples for each example predicted slopes of equilibrium curves agree moderately well to excellently with slopes determined experimentally the calculated slopes are sensitive to spectroscopic parameters particularly to the distribution of optic modes in the far infrared this sensitivity is discussed in detail for the albite breakdown reaction the model can be used for prediction of isotopic fractionation factors if spectra of the isotopic forms of the mineral are known or postulated a simple set of rules for generating hypothetical spectra of 18o minerals from measured spectra of the 16o forms is given reduced partition functions are calculated for 13 minerals at 298 k the model values of reduced partition function 1000 ln of these minerals decrease in the order quartz calcite albite muscovite clinoenstatite anorthite diopside pyrope grossular zircon forsterite andradite rutile in good agreement with experimental data at 1000 k the first six minerals show small crossovers so that the order becomes calcite muscovite albite quartz anorthite and clinoenstatite the differences in 1000 ln at high temperature for these minerals are so small that the model probably cannot address the deviations from experimental trends the model clearly defines the region in which the fractionation factors do not follow a 1 t trend and should be useful for extrapolation of experimental data to low temperatures finally a modified gruneisen parameter model is proposed for shift of the lattice vibrational frequencies under compression and thermodynamic properties to 1000 kbar 1000 k are given for nine minerals at 1 mbar the predicted decrease in entropy at 298 k ranges from 54 of the 1 bar value for periclase to 25 for stishovite

calculation of oxygen isotope fractionation in hydroxyl bearing silicates abstract the modified increment method has been applied to the calculation of oxygen isotope fractionation factors for hydroxyl bearing silicate minerals the order of 18o enrichment obtained in common rock forming minerals is pyrophyllite kaolinite tourmaline talc prehnite topaz illite phengite lepidolite muscovite staurolite epidote glaucophane serpentine chlorite tremolite hornblende phlogopite biotite humite norbergite ilvaite hydroxyl bearing silicates are enriched in 18o relative to hydroxyl groups but depleted in 18o relative to anhydrous counterparts three sets of self consistent fractionation factors between quartz and the hydroxyl bearing silicate minerals between calcite and the silicate minerals and between the silicate minerals and water have been calculated for a temperature range of 0 1200 c the fractionation factors calculated for mineral pairs are applicable to isotopic geothermometry in igneous metamorphic and sedimentary petrology they can be used as a test of isotopic equilibrium or disequilibrium in natural mineral assemblages over all temperature ranges of geological interest the difference in oxygen isotope composition between the hydroxyl bearing mineral and the oh group is quantitatively demonstrated to be temperature dependent and therefore can be used as a single mineral geothermometer

paleoenvironmental and paleoclimatic reconstruction of cretaceous aptian cenomanian terrestrial formations of texas and oklahoma using phyllosilicates abstract clay mineralogy chemistry and stable oxygen and hydrogen isotope compositions of 11 phyllosilicate samples from cretaceous paleosol profiles were determined in order to evaluate early to late cretaceous paleoenvironments and paleoclimates around north central texas and southern oklahoma samples consist of mineralogical mixtures of illite smectite and kaolinite samples from the albian antlers formation in southern oklahoma and the cenomanian woodbine formation are dominated by kaolinite while the remaining samples are dominated by smectite and illite major element compositions of paleosol matrix materials are used to calculate calmag weathering values that range from 31 to 84 and correspond to cretaceous paleoprecipitation estimates ranging from 270 to 1490 mm yr paleosol phyllosilicate hydrogen and oxygen stable isotope values range from 50 to 67 to 18 5 to 21 7 respectively and in conjunction with their respective mineral and chemical compositions correspond to in situ soil crystallization temperatures ranging from 26 3 c to 31 c paleoprecipitation trends exhibit two marked increases in precipitation from the early to late cretaceous in the albian antlers formation and cenomanian woodbine formation stratigraphic intervals with phyllosilicates that yield cooler temperature estimates coincide with stratigraphic intervals with markedly higher precipitation estimates based on calmag values importantly cool high precipitation intervals correlate with periods of extensive shallow seas upon the north american craton comparison of cretaceous temperature precipitation and meteoric water estimates to modern analogs supports the presence of climates similar to modern tropical climates during the cretaceous at subtropical or temperate paleolatitudes in what is now texas and oklahoma consistent with general circulation models and energy balance models suggesting a pervading cretaceous greenhouse

spatial analysis of mineral deposit distribution a review of methods and implications for structural controls on iron oxide copper gold mineralization in carajas brazil abstract mineral deposits are formed by interaction of various geological processes and conditioned by controls that favor their formation and preservation the understanding of mineralization controls is critical for mineral exploration because it allows focusing exploration on regions where these controls are concentrated the analysis of the spatial distribution of mineral deposits particularly on a regional scale can provide information relevant to the understanding of regional scale processes involved during their formation here we present a review of fry and fractal methods for spatial analysis of mineral deposit distribution and an application using the iron oxide copper gold iocg deposits of the carajas mineral province brazil results show that different iocg mineralization structural controls acted in scales of 40 km the iocg deposits cluster at scales of

the crust as a heterogeneous optical medium or crocodiles in the mist abstract based on petrophysical data geologic maps and a well log we present statistical descriptions of likely upper middle and lower crustal rocks to characterize the fine scale heterogeneity observed in crustal exposures and inferred from deep crustal seismic data the statistical models developed for granitic and metamorphic upper crust and for an extended metamorphic lower crust are used to construct whole crustal models of seismic velocity heterogenity we present finite difference synthetic cmp data from several models which compare favorably with field data the statistical models also permit classification of the seismic reflection experiment and the crustal heterogeneity according to scattering regime the optical or scattering properties of importance for classification are the velocity fluctuation intensity the horizontal and vertical correlation lengths of the medium the correlation function of the medium and the velocity population function for the crustal properties we measured the bandwidth of a typical deep crustal experiment overlaps from the weak to the strong scattering regime with implications for crustal seismic data processing and imaging notably deep crustal signals are likely to have experienced multiple scattering making common seismic imaging techniques of questionable value moreover the details of the unmigrated cmp stacked section bears little resemblance to the underlying medium

application of environmental isotope tracers to modeling in hydrology advances in nuclear science and computer development have made practicable chemical transport models employing the environmental isotopes found in natural waters the heavy isotopes of hydrogen deuterium stable and tritium radioactive forming part of the water molecule are the most conservative tracers of water known the heavy stable oxygen isotope 18o circulates in tandem with deuterium in the hydrologic cycle tritium fallout varies seasonally and annually in a systematic fashion and due to its property of radioactive decay is highly useful for dating time of recharge of soil moisture and groundwater 14c is valuable for tracing old groundwater owing to its relatively long half life of 5568 yr but detailed knowledge of the hydrochemistry of the system is required for successful modeling deuterium and 18o are of principal value because they reflect the temperature at which precipitation condensed thus they show pronounced seasonal variability and also the effects of altitude latitude distance from the sea amount of precipitation history of evaporation and long period climatic cycles principal areas of application of environmental isotopes to hydrologic modeling have been in soil moisture transport modeling of mixing and evapotranspiration in large lakes and swamps glacial ice movement groundwater flow and transport of contaminants in groundwater

oxygen and hydrogen isotope compositions of paleosol phyllosilicates differential burial histories and determination of middle late pennsylvanian low latitude terrestrial paleotemperatures abstract the clay mineralogy chemistry and stable hydrogen and oxygen isotope compositions were measured from 20 phyllosilicate samples representing 11 pennsylvanian age paleosol profiles taken from three cores in the illinois basin in order to assess their utility as proxies of low latitude terrestrial paleotemperatures the majority of the samples are mineralogical mixtures of illite smectite i s kaolinite and rarely discrete illite samples from a shallowly buried locality in the northern part of the basin are dominantly composed of smectite rich i s with variable amounts of kaolinite and no discrete illite samples from deeply buried interior parts of the basin are composed of illite rich i s variable amounts of kaolinite and discrete illite these phyllosilicate mixtures have 18 o v smow and d v smow values that range from 17 2 to 23 0 and 56 to 27 respectively assuming that the phyllosilicates preserve a record of isotopic equilibrium with pennsylvanian meteoric waters these oxygen and hydrogen isotope values correspond to crystallization temperatures ranging from 22 3 c to 55 3 c the clay mineralogy phyllosilicate 18 o and d values and calculated crystallization temperatures of 44 c to 55 c from deeply buried localities in the interior of the basin are not consistent with a pedogenic origin instead these trends are considered to be the result of diagenetic recrystallization of pedogenic minerals in response to greater depths of burial by 1 5 to 3 km in the southerly basin center localities as well as an interval of middle permian elevated heat flow associated with magmatic intrusions in the southern part of the basin phyllosilicate mineralogy 18 o and d values and calculated phyllosilicate crystallization temperatures from a shallowly buried northern locality in the illinois basin are consistent with a pedogenic origin and reveal a long term warming trend from an average temperature of 23 3 c in the lower desmoinesian to an average temperature of 32 3 c in the missourian this temperature change is coincident with a significant change in the composition of wetland vegetation in euramerica which has been attributed to a shift in low latitude pennsylvanian climate towards warmer and drier conditions in the late pennsylvanian this study reveals the presence of a dynamic late paleozoic paleoequatorial icehouse climate characterized by significant low latitude temperature variability unprecedented on modern earth

stable isotope paleoaltimetry a critical review stable isotope paleoaltimetry makes use of systematic trends in the distribution and isotopic composition of modern precipitation with climate and topography and of the potential to estimate the isotopic composition of paleoprecipitation from authigenic in situ formed minerals to illustrate the usefulness as well as potential limitations of this method we review 1 processes controlling the isotopic composition of modern precipitation 2 stable isotope data from modern precipitation across regions of high topography and 3 stable isotope data from authigenic minerals that have been used to infer paleotopography from this we conclude that stable isotope studies of authigenic minerals can permit useful inferences on paleotopography with uncertainties that critically depend on a detailed understanding of local to global scale paleoclimate during the time interval of interest

the subseafloor thermal gradient at iheya north knoll okinawa trough based on oxygen and hydrogen isotope ratios of clay minerals abstract we measured the oxygen and hydrogen isotope ratios of smectite chlorite and illite in hydrothermally active sediments at the iheya north knoll okinawa trough obtained by seafloor drilling of active hydrothermal fields during the integrated ocean drilling program iodp expedition 331 formation temperatures calculated from oxygen isotope data were compared to the downhole temperatures that were measured during the same expedition the 18o values ranged from 9 9 to 13 3 for smectite 1 3 to 3 0 for chlorite or chlorite smectite mixed layer mineral and 2 1 to 5 1 for illite or illite smectite mixed layer mineral with minor chlorite for samples of illite that contained minor chlorite 18o values for illite or illite smectite mixed layer mineral of 4 4 to 6 1 were calculated based on the proportion of the two clay minerals calculated from chemical composition of the individual mineral and the mixture determined by tem eds and epma we estimated the formation temperatures of the minerals using oxygen isotope fractionation data and assumed values of 0 to 1 2 for the fluid that was equilibrated with the minerals based on the reported values of the seawater and vent fluid measured in previous studies the temperature range calculated was 111 175 c for a shallow layer less than about 25 m below seafloor mbsf that contained smectite and a minor kaolinite component 177 297 c for a deeper layer between about 25 and 40 mbsf that was dominated by chlorite or chlorite smectite mixed layer mineral and 220 314 c for the deepest layer between about 40 and 120 mbsf that contained illite or illite smectite mixed layer mineral with less chlorite the temperatures of mineral formation calculated from the oxygen stable isotope data were slightly higher at some depths but both calculated and measured temperatures demonstrated a steep step wise thermal gradient below the active hydrothermal field where temperatures of 200 c were determined at as little as 50 mbsf hydrogen isotope values mostly ranged between 40 and 55 and did not vary significantly or systematically between the layers except in the clay fractions containing smectite above 25 mbsf that had relatively low values between 65 and 72 hydrogen isotope results of the clay minerals were problematic to interpret and not consistent with interpretation of the oxygen data calculated temperatures from illite and smectite were mostly negative whereas temperatures calculated from chlorite were more positive average 145 c but lower than those from the oxygen isotope data additional work is still required to determine the hydrogen isotope fractionation between clay minerals and water with respect to temperature

geophysical lineaments and deep continental structure lineaments may be detected remotely by imaging electromagnetic radiation both inside and outside the visible spectrum and by examining the natural force fields particularly the magnetic and gravitational most electromagnetic imagery shows shallow structure which is readily correlated with surface geology gravimetry and magnetometry may show much deeper structure which is unrelated to surface structure or incompatible with its most obvious downward extrapolation seismology then offers scope for the high resolution study of buried lineaments revealed in this way from such examinations it is clear than many lineaments do not traverse the entire vertical extent of the lithosphere internal horizontal detachment may cause once through going structures to become segmented a number of examples will be given including local scottish examples the great glen fault and the cruachan lineament

stable isotope geochronology of the australian regolith australian regolith profiles can be assigned to one of three post palaeozoic age groups on the basis of the oxygen isotope composition of authigenic clay minerals developed in the profile systematic variations in the isotopic composition of meteoric waters and therefore of the authigenic regolith minerals that formed in equilibrium with them are a result of the continent s drift from high to low latitudes and changes in global climate residual clays collected in situ from regolith profiles of post mid tertiary age have 18o values between 17 5 and 21 3 with the exception of samples from northern australia north of approximately 20 s which have anomalously low values because meteoric waters in northern australia are largely derived from monsoonal rain the high 18o values of post mid tertiary residual clays are consistent with australia s northward drift to low warm latitudes during this time compared with the much higher latitudes it occupied for most of its post palaeozoic history late tertiary residual clays have 18o values that are indistinguishable from all other post mid tertiary clays indicating that further subdivision of the sample groups is not feasible on a continent wide scale comparison with hypothetical modern clays in equilibrium with modern meteoric waters confirms that there has been very little change in the isotopic composition of meteoric waters in australia since the mid tertiary pre mid tertiary clays have lower 18o values between 10 0 and 17 5 which are consistently lower than post mid tertiary clays 18o values of less than 14 to 15 are thought to reflect weathering events during much earlier geologic periods perhaps early or mid mesozoic when australia was at high latitude and the australian climate was humid and cool to cold several workers have documented the existence of very old regolith profiles and land surfaces in australia and support for the above hypothesis comes from three analyses of clays from profiles of stratigraphically demonstrable pre late mesozoic age which have 18o values between 10 2 and 12 3 regolith profiles composed of low 18o clays 15 are widespread in australia and it is possible that a much greater part of the modern landscape than previously recognized developed in the early or mid mesozoic the 18o values of transported i e sedimentary kaolinites reveals that the major source for many tertiary kaolinitic sediments was this postulated pre late mesozoic low 18o regolith the stableisotope evidence that much of the australian regolith formed in comparatively cold conditions suggests that contrary to some traditional interpretations lateritization and deep weathering phenomena are not solely the result of weathering in tropical or sub tropical climates the hydrogen isotope composition of the clays range from 115 to 50 however it is inferred that the majority of clays have undergone some post formational hydrogen isotope exchange which renders their d composition unsuitable for dating purposes

deep structure of the foreland to the caledonian orogen nw scotland results of the birps winch profile the winch marine deep seismic reflection profile crosses the hebridean shelf the proterozoic foreland to the caledonian orogen west of scotland the data quality is very good the upper crust is largely devoid of coherent seismic reflections although this may in part be due to acquisition techniques being inappropriate for this problem in contrast the middle and lower crust 10 25 km depth exhibits good reflections the mid crust contains reflectors which may be relics of early palaeozoic caledonian or earlier grenvillian eastward dipping thrust zones which pass into an acoustically strongly layered lower crust the outer isles thrust is mapped from the surface to the mid crust and tied into its land outcrop on north lewis reactivation of this thrust offshore in a normal sense in mesozoic times caused the formation of the minch and north lewis basins the mono is defined by a strong band of reflections at about 27 km depth which correlates well with results from the hmse explosion seismic survey moho depth is apparently rather uniform in the area of the foreland crossed by winch winch and hmse results together suggest a mean crustal velocity for the hebridean shelf of 6 4 0 1 km s 1 the eastward dipping flannan thrust can be mapped into the upper mantle on three lines from about 15 to 45 km depth well into the upper mantle neither the flannan thrust nor the outer isles thrust appear to pass straight through the reflective lower crust suggesting that the lower crust is a region of high strain the outer hebrides is a positive block probably formed as an isostatic response to mesozoic normal faulting which reactivated the outer isles thrust

rare earth element and stable isotope signatures of kaolin from a pliocene lateritic weathering profile at mid latitude region andalusia spain implications for paleoweathering and paleoclimatic reconstructions abstract this study reports the impact of weathering on behavior of rare earth elements ree in a coastal lateritic profile developed on pliocene sediments at mid latitude location 37 n in the guadalquivir basin spain it also explores the stable isotope signature of kaolinite providing constraints on paleotemperature and isotopic composition of the ancient meteoric water the paleoweathering profile 20 m thick comprises a white sandy clayey saprolite overlain by a red mottled clay zone which in turn is capped by a pisolitic ferricrete the kaolinitic regolith was practically reduced to a mixture of kaolinite and quartz by intense chemical weathering under warm and seasonally humid climate the kaolinized material is markedly depleted in total ree mean value of 77 30 mg kg 1 in the white saprolite and 72 70 mg kg 1 in the mottled zone relative to the parent rock 168 96 mg kg 1 development of acidic and oxidizing conditions promoted a suitable soil environment for ree release and leaching with percolating rainwater leading to an apparent loss of ree from the profile up to 87 the parent rock normalized ree patterns display concave upward shapes tracing a remarkable depletion in middle ree mree with no significant anomalies the ree concentrations normalized against the north american shale composite nasc showed consistently similar fractionation patterns the mree depleted signature nasc normalized ratios of la sm up to 3 32 and gd lu as low as 0 45 probably arises from reductive dissolution of iron oxyhydroxide phases due to seasonal water saturation as indicated from redoximorphic features the the lateritic weathering profiles evolved during the mid pliocene warm period in the southwestern iberian margin could be useful for predicting potential future environmental effects of increased atmospheric co2 on the earth s critical zone

a deep seismic reflection transect across the irish caledonides new reflection profiles recorded to 18s c 60km along a 600 km north south transect west of ireland wire lines provide a cross section of the irish caledonides from lewisian basement in the north to the variscan fold and thrust belt in the south and constrain the offshore extrapolations of major caledonide structures we interpret the profiles as showing the great glen fault and associated ne trending strike slip faults as near vertical structures which cut the whole crust and the uppermost mantle beneath the surface trace of the fair head clew bay line we image a north dipping zone which soles into horizontal layers just above the reflection moho the north dipping zone separates south dipping reflections above and to the north from north dipping reflections below and to the south from the fair head clew bay line as far south as the iapetus suture the lower crust contains north dipping packages of reflectors possibly related to acadian accretionary underplating the iapetus suture zone can be identified as a zone more than 50 km wide dipping north at 30 from 5 km depth offshore dingle peninsula to sole into the moho at c 30 km depth west of the shannon estuary in the upper crust the shallow part of the iapetus suture zone appears to be transported to the north by late caledonian retrocharriage or by variscan thrusting the iapetus suture does not penetrate through the present day reflection moho but there are scattered reflectors in the mantle not continuous with crustal reflectors perhaps relics of a subducted slab we recognize lower crustal reflectivity and the reflection moho along almost all the wire profiles regionally the travel time to the reflection moho varies from 9 s c 28 km offshore donegal northwest of ireland to 12 s c 35 km offshore kerry and cork southwest of ireland apparent moho offsets rapid lateral changes in the travel time to the reflection moho north of donegal and north of mayo are probably due to the great glen fault and associated faults the lower crustal reflectivity varies considerably in thickness and prevalent dip direction along the wire profiles in donegal bay this reflectivity is observed at depths less than 5 km c 1 5s whereas west of kerry prominent reflectivity is only observed beneath 6s c 17 km though the age of crustal reflectors cannot in general be determined beneath central ireland from donegal to dingle the lower crustal reflectors mimic in dip direction the structural vergence of the exposed dalradian and early palaeozoic rocks so that the lower crustal reflectivity patterns and probably much of the crust must be caledonian in age

oxygen and hydrogen isotopes in pedogenic minerals implications for paleoclimate evolution in amazonia during the cenozoic stable isotopes in gibbsite and kaolinite were analyzed to reconstruct the amazonia palaeoclimate during the cenozoic and to investigate the environmental conditions of the weathering process and the origin of the oxisol that cover the lateritic bauxite crust at least two types of kaolinite were identified in the oxisol near the surface the kaolinite is less fractionated and was developed at a higher temperature 35 c this is probably due to the effect of vegetation and or evapotranspiration or is a consequence of surface microenvironmental conditions or allochthonous inputs the other kaolinite samples ranged in formation temperatures from 21 c to 26 c and developed under conditions similar to the pleistocene and the modern climate of amazonia at least two types of gibbsite were found one type developed in the modern amazonia climate in a way similar to most kaolinite samples whereas the samples of the other type are more fractionated this is because they may have been formed in low recycling rainwater and or under a low amount of precipitation these two conditions indicate a seasonal climate for bauxite development that can be linked to the low exhumation of the andes cordillera and its geographical position relative to the trombetas region during the period ranging from the late oligocene to the early miocene at the end of the cenozoic the climate was less seasonal and wetter and the temperature was lower in addition there was the probable inland position of the trombetas region which allowed oxisol development the gibbsite developed earlier than the kaolinite of the oxisol but there is a partial inheritance or temporal equivalence among the bauxite horizon and the oxisol as well as multiple generations of gibbsite and kaolinite which is to be expected for materials developing over long periods in hard leaching conditions

the fractal nature of structural controls on ore formation the case of the iron oxide copper gold deposits in the carajas mineral province brazilian amazon the formation of ore minerals in hydrothermal deposits is the result of a complex interplay between physical and chemical processes that are conditioned by the geologic environment in which they occur in the last decades research has increasingly indicated that many of these processes display different forms of scale invariance i e they show fractal geometry this suggests that behind the apparent disorder and irregularity of the geometry of mineral deposits at different scales an underlying regular pattern is present if properly understood this regular geometrical pattern could be useful in a variety of theoretical and applied fields a great portion of this scale invariance is given by the structural framework during mineralization because structures are a dominant factor controlling fluid flow here we assess the geometry of iron oxide copper gold iocg mineralization in the world renowned carajas mineral province focusing on one of the largest and most economically important orebodies the sossego deposit the geometry of mineralization is evaluated at the microscale ore minerals in thin sections local scale orebodies in mine maps and regional scale deposit distribution on regional maps we show that the spatial distribution and shape of ore minerals at the microscale is largely nonrandom presents fractal geometry and displays defined trends in spatial distribution and anisotropy additionally the geometric trends observed at the microscale mimic those of the local scale geometry of orebodies as well as the regional scale distribution of mineralization the main property controlling the observed scale invariance is permeability which is intrinsically associated with structures at multiple scales these results contribute to further understanding the fractal nature of processes controlling mineral deposit formation and revealing new multiscale approaches to investigate structural controls on ore deposition

a stable isotope study of recharge processes in the english chalk the 2h and 18o values of water contained in unsaturated chalk have been measured in drillcore profiles taken over a period of 28 months on arable land in cambridgeshire eastern england the isotopic composition of rainfall and lysimeter drainage on the same site has also been monitored over a period of four years the distribution of isotope values in the upper few metres of soil and unsaturated chalk shows that the mechanism of infiltration is not simple piston like downward displacement since the scale of vertical fluctuations is incompatible with estimated annual infiltration and the apparent rates of movement of matrix water derived from thermonuclear tritium studies lysimeter drainage is not isotopically identical to matrix water at the same depth suggesting that different routes to water table are associated with consistently different isotopic content although there is an apparent difference between matrix water beneath arable and permanent grassland these differences appear to cancel out in the composition of bulk recharge beneath these land types the regional aquifer has a uniform isotopic composition similar in value to weighted average rainfall and lysimeter drainage suggesting that the recharge abstraction system has been in isotopic equilibrium for many years despite changes in pumping rates and land use two other chalk sites in southern england have been investigated in less detail but indicate clear difference in infiltration behaviour from that seen in cambridgeshire this seems to be related to a higher matrix conductivity and annual rainfall amount

formation of a rain shadow o and h stable isotope records in authigenic clays from the siwalik group in eastern bhutan we measure the oxygen and hydrogen stable isotope composition of authigenic clays from himalayan foreland sediments siwalik group and from present day small stream waters in eastern bhutan to explore the impact of uplift of the shillong plateau on rain shadow formation over the himalayan foothills stable isotope data from authigenic clay minerals 2 m suggest the presence of three paleoclimatic periods during deposition of the siwalik group between 7 and 1 ma the mean 18o value in paleometeoric waters which were in equilibrium with clay minerals is 2 5 lower than in modern meteoric and stream waters at the elevation of the foreland basin we discuss the factors that could have changed the isotopic composition of water over time and we conclude that a the most likely and significant cause for the increase in meteoric water 18o values over time is the amount effect specifically a decrease in mean annual precipitation b the change in mean annual precipitation over the foreland basin and foothills of the himalaya is the result of orographic effect caused by the shillong plateau s uplift the critical elevation of the shillong plateau required to induce significant orographic precipitation was attained after 1 2 ma c by applying scale analysis we estimate that the mean annual precipitation over the foreland basin of the eastern bhutan himalayas has decreased by a factor of 1 7 2 5 over the last 1 3 million years 2018 american geophysical union all rights reserved

a hot and high eocene sierra nevada despite broad interest in determining the topographic and climatic histories of mountain ranges the evolution of california s sierra nevada remains actively debated prior stable isotope based studies of the sierra nevada have relied primarily on hydrogen isotopes in kaolinite hydrated volcanic glass and leaf n alkanes here we reconstruct the temperature and elevation of the early eocene sierra nevada using the oxygen isotope composition of kaolinitized granite clasts from the ancestral yuba and american rivers that drained the windward pacific flank of the sierra nevada first we evaluated the possible contributions of hydrogen isotope exchange in kaolinite by direct comparison with oxygen isotope measurements next we utilized differences in the hydrogen and oxygen isotope fractionation in kaolinite to constrain early eocene midlatitude weathering temperatures oxygen isotope geochemistry of in situ kaolinites indicates upstream eastward depletion of 18o in the northern sierra nevada the 18o values ranging from 11 4 to 14 4 at the easternmost localities correspond to paleoelevations as high as 2400 m when simulating the orographic precipitation of moisture from a pacific source using eocene boundary conditions this result is consistent with prior hydrogen isotope studies of the northern sierra but oxygen isotope based paleoelevation estimates are systematically 500 1000 m higher than those from hydrogen based estimates from the same samples kaolinite geothermometry from 16 samples produced early eocene weathering temperatures of 13 0 36 7 c with an average of 23 2 6 4 c 1 these kaolinite temperature reconstructions are in general agreement with paleofloral and geochemical constraints from eocene california localities and climate model simulations our results confirm prior hydrogen isotope based paleoelevation estimates and further substantiate the existence of a hot and high eocene sierra nevada