automatic conversion of magnetic data to depth dip and susceptibility contrast using the spi tm method the source parameter imaging spi method computes source parameters from gridded magnetic data the method assumes either a 2 d sloping contact or a 2 d dipping thin sheet model and is based on the complex analytic signal solution grids show the edge locations depths dips and susceptibility contrasts the estimate of the depth is independent of the magnetic inclination declination dip strike and any remanent magnetization however the dip and the susceptibility estimates do assume that there is no remanent magnetization image processing of the source parameter grids enhances detail and provides maps that facilitate interpretation by nonspecialists the spi method tests successfully on synthetic profile and gridded data spi maps derived from aeromagnetic data acquired over the peace river arch area of northwestern canada correlate well with known basement structure and furthermore show that the ksituan magmatic arc can be divided into several susceptibility subdomains

tephrochronology of late wisconsin deglaciation and holocene glacier fluctuations near glacier peak north cascade range washington abstract tephra layers near glacier peak in the north cascade range provide limiting dates for four periods of alpine glacier advance field relations suggest that late wisconsin alpine glaciers last advanced prior to the eruption of tephra layers from glacier peak about 11 250 yr b p late wisconsin deglaciation in the central north cascades was complete prior to the glacier peak tephra eruptions glaciers again expanded in the early holocene about 8400 8300 yr b p soil formed in alpine meadows during an episode of mild climate in the middle holocene prior to at least two intervals of glacier expansion an older episode between 5100 and 3400 yr b p and a younger episode within the last 1000 yr

thrust tectonics of the dibba zone and the structural evolution of the arabian continental margin along the musandam mountains oman and united arab emirates in the northern oman mountains several major thrust sheets of tethyan oceanic rocks dibba zone and a 12km thick complete ophiolite sequence have been thrust westward onto the depressed arabian continental margin musandam zone during the turonian to campanian late cretaceous early thrusting was dominantly a downward foreland propagating sequence as the higher earlier thrust sheets are folded around structurally lower and later culminations breached roof thrusts where imbricate thrusts do not always converge with a major roof thrust but in places actually penetrate up into the overlying duplex are common at outcrop scale affecting adjacent thrust sheets late stage breakback or leap frog thrusts cut through the whole pile of duplexes on to previously higher earlier dulexes late thrusting in the musandam zone affects the deeper previously autochthonous permian cenomanian shelf carbonate sequence and probably also the pre permian basement thrusting these rocks at least 15 km over previously allochthonous hawasina rocks late stage oblique dorsal culmination collapse along the se margin of the musandam mountains has downfaulted dibba zone rocks up to 2 5 km to the se along a hinged listric normal fault strain is transferred from the ne sw trending late cretaceous dibba zone to the n s striking mid tertiary musandam culmination at a major pivot point or transfer zone sw of the shelf carbonate culmination

holocene tephrostratigraphy and glacial fluctuations in waterton lakes and glacier national parks alberta and montana waterton lakes national park in alberta and glacier national park in montana lie along adjacent sections of the continental divide in the rocky mountains in cirques or near divides there is evidence for two ages of glacial deposits younger deposits are generally well preserved poorly vegetated and bear no tephra and no or very small lichens older deposits are more poorly preserved better vegetated bear rhizocarpon sp lichens at least up to 92 mm in diameter and bear tephra the tephra often occurs in two different coloured horizons but both are compositionally equivalent to mazama tephra the older advance has a minimum age of about 6800 14c years bp and a probable maximum age of about 12 000 14c years bp it is correlated with the pre mazama crowfoot advance of the canadian rockies deposits of the younger advance are probably not too much older than mid 19th century because some glaciers began retreating from the deposits about then the younger advance is correlated to the cavell advance of t

multi proxy record of holocene glacial history of the spearhead and fitzsimmons ranges southern coast mountains british columbia abstract evidence from glacier forefields and lakes is used to reconstruct holocene glacier fluctuations in the spearhead and fitzsimmons ranges in southwest british columbia radiocarbon ages on detrital wood and trees killed by advancing ice and changes in sediment delivery to downstream proglacial lakes indicate that glaciers expanded from minimum extents in the early holocene to their maximum extents about two to three centuries ago during the little ice age the data indicate that glaciers advanced 8630 8020 6950 6750 3580 2990 and probably 4530 4090 cal yr bp and repeatedly during the past millennium little ice age moraines dated using dendrochronology and lichenometry date to early in the 18th century and in the 1830s and 1890s limitations inherent in lacustrine and terrestrial based methods of documenting holocene glacier fluctuations are minimized by using the two records together

stratigraphy and chronology of quaternary deposits of the puget lowland and olympic mountains of washington and the cascade mountains of washington and oregon in the southern puget lowland probably are correlative with salmon springs drift but farther north drift directly beneath vashon till is most likely correlative with much younger drifts such as the double bluff or possession drifts thus virtually all previouslymapped salmon springs drift needs to be re examined to determine if it is indeed correlative with salmon springs drift or is younger

regional significance of an early holocene moraine in enchantment lakes basin north cascade range washington abstract the upper enchantment lakes basin in the north cascade range of washington displays two moraine belts each recording an episode of glacier advance after the end of the last glaciation the inner belt the brynhild 0 1 to 0 5 km beyond existing glaciers postdates mount st helens wn tephra 450 yr old which lies only beyond the moraines the morainal surface is only slightly weathered is almost barren of lichens and is devoid of soil evidence suggesting that the brynhild moraines are no more than a century old the outer moraine the brisingamen 0 3 to 0 7 km beyond existing glaciers is weathered and is covered with large lichens on and behind the brisingamen moraine the mazama ash 6900 yr old is present beneath the mount st helens yn and wn tephras despite more than 7 millennia of weathering the rock surface behind the brisingamen moraine is measurably less weathered than the surface beyond which was last glaciated during the rat creek advance about 13 000 yr ago the age of the brisingamen moraine therefore is probably early holocene the brisingamen moraine evidently correlates with moraines near glacier peak near mount rainier in northeastern and central oregon in the southern canadian rockies and in the northern u s rocky mountains these regional effects suggest that a climatic episode of cooling or increased snowfall affected the entire region some time during the early holocene

uranium lead isotopic ages of the samail ophiolite oman with applications to tethyan ocean ridge tectonics plagiogranites are a minor but widespread component of the samail ophiolite plutonic member they crystallized from the most fractionated melts generated by magmatic crystallization and differentiation of a steady state magma chamber beneath the tethyan spreading ocean ridge and their ages are thought to mark the time of ocean crust formation isotopic u pb ages of zircons from 13 plagiogranites collected along a 270 km segment of the samail ophiolite subparallel to the regional trend of the sheeted dike complex the former spreading ridge axis direction define a narrow time interval of 93 5 97 9 m y with a pronounced clustering about 95 m y the zircon ages of the plagiogranites agree remarkably well with the early cenomanian to early turonian biostratigraphic ages of sediments that are intercalated within the ophiolite pillow lavas and that lie just above them tippit et al 1981 the agreement of radiometric and biostratigraphic ages provides strong support for the conclusion that the plagiogranite u pb ages closely date the time span of ocean crust formation no step changes in age patterns are observed along the ridge axis sheeted dike direction suggesting that there are no major internal offsets of the ophiolite by transform or other faults along most of the traverse one possible exception occurs at the southeastern end of the sampled interval ibra area where a 3 m y discontinuity might be caused by an unmapped fault assuming that the regional trend of the sheeted dikes n10 25 w marks the direction of the former spreading ridge axis the present array of sample localities spans a distance of 130 to 195 km normal to that axis i e in the spreading direction the data as a whole do not define a clear cut age trend normal to the spreading axis but by eliminating samples that may be aberrant due to faulting the data array suggests a pattern of increasing ages from east to west this would indicate that the samail ophiolite is derived from the western southwestern side of the tethyan spreading system a conclusion reached independently from geological evidence also the gentle age gradient in the spreading direction i e between 130 and 195 km of ocean crust were formed within an age span of no more than 2 m y suggests a very fast spreading rate this conclusion also is supported by independent geologic evidence

interpretation of magnetic and gravity surveys in the southern arabian gulf the strait of hormuz and the northwesternmost gulf of oman implications of pre permian basement tectonics abstract a 5 nt aeromagnetic chart and a 5 mgal bouguer gravity map of the area bounded by latitudes 25 30 27 10 n and longitudes 55 15 57 00 e in the southern arabian gulf the strait of hormuz and the entrance of the gulf of oman are collectively studied the total magnetic intensity map covering the coastal strip and the arabian side of the southern part of arabian gulf reveals three prominent anomalies of amplitudes ranging from 30 to 150 nt related to tectonically controlled igneous bodies emplaced in the deep seated pre permian basement of the arabian shield the bouguer gravity map indicates three well defined trends an effect duplicating a magnetic source in the basement a negative belt indicating an anomalous hormuz salt accumulation in the southern gulf salt basin and a continental margin gravity effect marking the transition from continental crust to the gulf of oman oceanic crust the magnetic and the gravity derived lineaments are shown to correlate with gemini interpreted strike slip basement faults in the iran s southeastern zagros fold zone

mapping basement structures in the northwestern offshore of abu dhabi from high resolution aeromagnetic data this paper presents a case study of mapping basement structures in the northwestern offshore of abu dhabi using high resolution aeromagnetic data lineament analysis was carried out on the derivatives of the reduced to the pole magnetic data along with supporting information from published geologic data the lineament analysis suggests three well defined basement trends in the north south northeast southwest and northwest southeast directions the reduced to the pole magnetic data reveal high positive magnetic anomalies hypothesized to be related to intra basement bodies in the deep seated arabian shield depth to basement was estimated using spectral analysis and source parameter imaging techniques the spectral analysis suggests that the intruded basement blocks are at the same average depth level around 8 5 km the estimated source parameter imaging depths from gridded reduced to the pole data are ranged between 4 km and 12 km with a large depth variation within small distances these estimated depths prevent a reliable interpretation of the nature of the basement relief however low pass filtering of the horizontal local wavenumber data across two profiles shows that the basement terrain is characterized by a basin like structure trending in the northeast southwest direction with a maximum depth of 10 km two dimensional forward magnetic modelling across the two profiles suggests that the high positive magnetic anomalies over the basin could be produced by intrusion of mafic igneous rocks with high susceptibility values 0 008 to 0 016 si

the maastrichtian transgression onto the northwestern flank of the proto oman mountains sequences of rudist bearing beach to open shelf facies

holocene glacier fluctuations in the american cordillera abstract in many areas of the american rocky mountains colorado wyoming utah idaho montana cascade range washington oregon and the sierra nevada california radiocarbon ages suggest that ice receded to near present limits before 10 ka bp a pre altithermal readvance or stillstand left moraines ca 1 3 km beyond and ca 50 300 m below present glacier margins at one locality on glacier peak in washington these deposits are perhaps dated to the early holocene but in general these deposits are probably at least 10 ka old glacial advances during the altithermal ca 8 to 5 ka bp elsewhere are rare radiocarbon evidence for altithermal glacial advances in the colorado front range is questionable the earliest radiocarbon dated neoglacial advances occurred about 5 ka bp in the washington cascades moraines and related deposits believed to be of early neoglacial age i e 5 to 3 ka bp elsewhere are poorly dated for example moraines believed to date to the early neoglacial in colorado triple lakes and wyoming temple lake are actually late pleistocene age based on radiocarbon ages derived from lake sediments at the type localities although relative age data i e lichens rock weathering soils from many areas suggest a three fold neoglacial sequence little supporting radiocarbon evidence is available however tephrochronology distinguishes three neoglacial advances near mount rainier in washington in most mountain ranges of the western united states fresh unweathered sharp crested moraines usually adjacent to present ice margins or near headwalls in empty cirques date to the little ice age of the last several centuries however detailed photographic or other historical records of glacial fluctuations during the last century are rare and detailed mass balance studies rarer still whether or not pre little ice age glacial fluctuations in the american cordillera are synchronous must await better radiometric dating of local moraine sequences

early holocene glacier advance in the north cascade range washington moraines and glacial drift of the white chuck advance were deposited in early holocene time in cirques near glacier peak washington these sediments overlie glacier peak tephra including layers g n f c m t and b which were erupted between about 12 500 and 11 250 yr b p white chuck drift is overlain by mazama tephra layer o deposited about 6 700 yr b p charcoal collected from till deposited during the white chuck advance is about 8 300 to 8 400 radiocarbon years old indicating that the glacial advance that deposited the till occurred about this time and that a previously unrecognized period of cooling and or increased precipitation of sufficient intensity to produce glacial advances comparable to or greater than those of the recent little ice age occurred in early holocene time in the north cascade range other pre altithermal moraines from the cascades the rocky mountains laurentide canada and baffin island may have been produced during this cool period

late quaternary vegetation in the southwestern columbia basin washington abstract a 33 000 yr pollen record from carp lake provides information on the vegetation history of the forest steppe border in the southwestern columbia basin the site is located in the pinus ponderosa zone but through much of late quaternary time the area was probably treeless pollen assemblages in sediments dating from 33 000 to 23 500 yr b p suggest a period of temperate climate and steppe coinciding with the end of the olympia interglaciation the fraser glaciation ca 25 000 10 000 yr b p was a period of periglacial steppe or tundra vegetation and conditions too dry and cold to support forests at low altitudes aridity is also inferred from the low level of the lake between 21 000 and 8500 yr b p and especially after about 13 500 yr b p about 10 000 yr b p chenopodiineae and other temperate taxa spread locally providing palynological evidence for a shift from cold dry to warm dry conditions pine woodland developed at the site with the onset of humid conditions at 8500 yr b p further cooling is suggested at 4000 yr b p when pseudotsuga and abies were established locally

depth and structural index from normalized local wavenumber of 2d magnetic anomalies recent improvements in the local wavenumber approach have made it possible to estimate both the depth and model type of buried bodies from magnetic data however these improvements require calculation of third order derivatives of the magnetic field which greatly enhances noise as a result the improvements are restricted to data of high quality we present an alternative method to estimate both the depth and model type using the first order local wavenumber approach without the need for third order derivatives of the field our method is based on normalization of the first order local wavenumber anomalies and provides a generalized equation to estimate the depth of some 2d magnetic sources regardless of the source structure information about the nature of the sources is obtained after the source location has been estimated the method was tested using synthetic magnetic anomaly data with random noise and using three field examples

methane gas release from the storegga submarine landslide linked to earlyholocene climate change a speculative hypothesis the 3000 km3 storegga submarine landslide occurred c 8150 years ago from an area rich in gas hydrates off the western coast of norway a synchronous increase of 80 100 ppb in atmospheric methane c

latest pleistocene and holocene glacier fluctuations on mount baker washington abstract glaciers on stratovolcanoes of the pacific northwest of north america offer opportunities for dating late pleistocene and holocene glacier advances because tephra and fossil wood are common in lateral moraines and in glacier forefields we capitalize on this opportunity by examining the holocene glacial record at mount baker an active stratovolcano in northwest washington earlier workers concluded that glaciers on mount baker during the early holocene were more extensive than during the little ice age and hypothesized that the explanation lay in unusual climatic or hypsometric effects peculiar to large volcanoes we show that the main argument for an early holocene glacier advance on mount baker namely the absence of ca 10 000 year old tephra on part of the south flank of the mountain is incorrect moreover a lake sediment core indicates that a small cirque moraine previously thought be of early holocene age is also likely older than the tephra and consequently of late pleistocene age lateral and end moraines and wood mats ca 2 km downvalley of the present snout of deming glacier indicate that an advance during the younger dryas interval was little more extensive than the climactic little ice age advance tephra and wood between tills in the left lateral moraine of easton glacier suggest that ice on mount baker was restricted in the early holocene and that neoglaciation began ca 6 ka a series of progressively more extensive neoglacial advances dated to about 2 2 1 6 0 9 and 0 4 ka are recorded by stacked tills in the right lateral moraine of deming glacier intervening retreats were long enough to allow establishment of forests on the moraine wood mats in moraines of coleman and easton glaciers indicate that little ice age expansion began before 0 7 ka and was followed by retreat and a readvance ca 0 5 ka tree ring and lichen data indicate glaciers on the south side of the mountain reached their maximum extents in the mid 1800s the similarity between glacier fluctuations at mount baker and those elsewhere in the cascades and in british columbia suggests a coherent history of holocene climate change over a broad area of the western cordillera we found no evidence that glaciers on stratovolcanoes behave differently than glaciers elsewhere

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

late quaternary climatic change on the american north pacific coast temporal changes in solar radiation caused by variations in the earth s orbit figure prominently in current quaternary climate theory1 4 experimental design of atmospheric circulation models emphasizes the importance of solar radiation in the heating of interglacial land and ocean surfaces at different seasons of the year whereby monsoon type circulation seasonal shifting of regional cyclonic and anticyclonic centres develops while during glacial ages seasonality is greatly modified by the influence of ice sheets5 7 we investigated the late quaternary climate of the north pacific where according to modelling solar radiation in the early holocene at the time of the summer solstice is high and in the late holocene is relatively low we compared quantitative temperature and precipitation estimates from southern alaska obtained by application of transfer functions to fossil pollen records with estimates from western washington8 and southern british columbia9 data extending over 10 000 years show a broadly consistent pattern of climatic change in general agreement with predicted variations in solar radiation and their effect on atmospheric circulation and seasonal duration of pressure systems over the north pacific ocean in the early holocene as monsoon type circulation became established with melting of glaciers the subtropical north pacific anticyclone annually regulated climate for a longer period at higher latitudes than at present so that warmth and dryness high summer radiation increased in southern alaska the aleutian low pressure centre locus of cyclonic storm activity intensified during the late holocene resulting in colder and more humid coastal climate low summer radiation over much of the year and increased frequency of glacier growth in the cordillera

the arabian infracambrian extensional system abstract during the late precambrian and early cambrian about 600 540 ma extensive left lateral faulting along the complex nw se trending najd fault system cut across the arabian shield this tectonic episode was accompanied by nw se directed extension in northern egypt and the sinai peninsula based on these relationships stern 1985 interpreted the najd fault system as a set of transform faults emanating from a rift basin in ne egypt contemporaneous to this system in the western part of the arabian plate and northern egypt extensive evaporitic basins developed in northern pakistan southern oman and the arabian gulf and zagros mountains these basins are generally bounded by nw trending faults such as the najd hawasina and zagros faults and ne trending faults such as the ghudun khasfah and dibba faults these evaporitic basins are interpreted as rift basins such that stern s 1985 extensional model in northern egypt may be expanded regionally to include the eastern part of the arabian plate and the indian subcontinent this broader interpretation implies that after the e w directed collisional tectonics of the late precambrian in western arabia and africa which terminated around 640 600 ma the arabian plate experienced nw se directed crustal extension and continental break up

hydrologic variation during the last 170 000 years in the southern hemisphere tropics of south america despite the hypothesized importance of the tropics in the global climate system few tropical paleoclimatic records extend to periods earlier than the last glacial maximum lgm about 20 000 years before present we present a well dated 170 000 year time series of hydrologic variation from the southern hemisphere tropics of south america that extends from modern times through most of the penultimate glacial period alternating mud and salt units in a core from salar de uyuni bolivia reflect alternations between wet and dry periods the most striking feature of the sequence is that the duration of paleolakes increased in the late quaternary this change may reflect increased precipitation geomorphic or tectonic processes that affected basin hydrology or some combination of both the dominance of salt between 170 000 and 140 000 yr ago indicates that much of the penultimate glacial period was dry in contrast to wet conditions in the lgm our analyses also suggest that the relative influence of insolation forcing on regional moisture budgets may have been stronger during the past 50 000 years than in earlier times d 2003 university of washington all rights reserved

early holocene glaciation on mount baker washington state usa abstract the relation between radiocarbon dated tephras and glacial moraines on the south flank of mount baker washington records evidence of an early holocene glacier advance scoria that erupted from a local cinder cone 8420 70 14 c yr bp 9450 100 cal yr occurs immediately in front of but not on a complex of moraines overlain by mazama ash radiocarbon ages of 7670 130 14 c yr bp 8415 110 cal yr and 7045 65 14 c yr bp 7890 90 cal yr were obtained from charred wood below the mazama ash and above till of the moraines bracketing the age of the glacial advance between 7700 and 8400 14 c yr bp 8400 and 9450 cal yr well preserved little ice age moraines occur proximal to the maximum holocene positions assuming that precipitation regimes were similar depression of former equilibrium line altitudes suggests that climate during the early holocene event was at most 2 c cooler than present and 0 5 c cooler than the little ice age

interpretation of aeromagnetic data from the norwegian sector of the north sea total magnetic intensity contour maps for the study region between 2 e to 10 e and 56 n to 60 n were digitized and converted to a regular grid of 285 285 points the study area measures approximately 444 km 444 km and the grid spacing is thus 1 56 km the international geomagnetic reference field for 1975 was gridded for the above used net and from the two data sets a further grid of the t field was generated a large number of profiles were constructed which were suitable for depth determinations the regular grid t data is also convenient for the computation of the second vertical derivative using the method of vertical prisms of vacquier et al 1963 a large suite of curvature depth indices was measured to complement the depths obtained from the intensity slopes and from boreholes which reach the crystalline basement the depth to the magnetic basement has been contoured and the resulting map is shown to be in good agreement with what is known about the deeper geology of the study area the work reported here is part of a research project supported by amoco norway bp petroleum development ltd elf aquitaine esso exploration and production norwegian gulf norsk hydro mobil exploration norway norwegian petroleum directorate royal norwegian council for scientific and industrial research ntnf norske shell and statoil

oman exotics oceanic carbonate build ups associated with the early stages of continental rifting the so called oman exotic limestones form isolated masses from boulder size to 1 000 m thick of middle to upper permian and upper triassic fossiliferous limestones and crop out within imbricated thrust slices beneath the semail ophiolite in the oman mountains permian exotics are of dominantly reef and forereef facies whereas triassic exotics are more typically of back reef and lagoonal facies they are commonly associated with a substrate of alkalic and transitional tholeiitic basalts and are interpreted as a series of reef associated carbonate buildups deposited in part on oceanic islands or seamounts close to the site of initial rifting of the oman continental margin