lithospheric processes and products in the southern canadian cordillera a lithoprobe perspective analyses of lithoprobe and other data from southwestern canada provide new insights on how this portion of the cordillera formed during plate convergence along the western margin of north america crustal rocks are detached from their mantle lithosphere which must have been consumed during subduction detachment occurred at or near the base of the crust beneath the intermontane and or omineca belts probably along the tips of tectonic wedges while the rocks were still outboard of the relatively cool mechanically rigid north american craton during the late cretaceous and early tertiary rotation of detached rocks caught between the north american craton and the oceanic plates accounts for some apparently conflicting results between paleomagnetic data that indicate large northward translation of rocks in the western cordillera and regional geological features that appear to preclude comparable amounts of translation of rocks in the eastern cordillera during the same time interval transpression assoc

fault generated mountain fronts in southeast spain geomorphologic assessment of tectonic and seismic activity abstract tectonic activity of se spain is evaluated through the application of a general morphometric analysis over 17 different mountain fronts the selected fronts are distributed along the two most prominent crustal scale structures of the mediterranean sector of spain the eastern betic shear zone ebsz and the valencia trough geomorphic indexes used in this study are mountain front sinuosity index smf and valley floor width ratio vf this work is largely based on the smf vf regression analysis of the studied fronts together with previous available data from sw usa the development of mountain fronts in both different lithologies and tectonic contexts enabled characteristic morphometric signatures for different activity scenarios tectonic activity classes to be obtained this study thus indicates that variations of mountain front geomorphology triggered by different styles of faulting can be detected by morphometric analysis it is demonstrated that discrete uplift rates of 0 15 0 08 m ka are sufficient to keep relatively low smf values down to 1 4 in active fronts class 1 taking into account the reported uplift rates and preliminary palaeoseismic data for some of the class 1 studied fronts recurrence periods for surface rupture events can be theoretically bracketed for se spain recurrence periods for class 1 fronts could theoretically range between 10 000 and 12 500 years for maximum slip conditions and 1750 and 2600 years for minimum slip conditions inactive fronts class 3 develop under uplift rates down to 0 03 m ka and tested recurrence intervals for rupture events range between 25 000 and 50 000 years class 2 fronts of intermediate characteristics and activity display uplift rates between 0 07 and 0 03 m ka

the stability of gypsum in marine sediments using the entire odp iodp porewater composition database abstract the stability of gypsum in marine sediments has been investigated through the calculation of its saturation index at the sediment in situ temperature and pressure using the entire odp iodp porewater composition database 14416 samples recovered from sediments collected during 95 odp and iodp legs saturation is reached in sediment porewaters of 26 boreholes drilled at 23 different sites during 12 odp iodp legs as ocean bottom seawater is largely undersaturated with respect to gypsum the porewater ca content or its so4 concentration or both must increase in order to reach equilibrium at several sites equilibrium is reached either through the presence of evaporitic gypsum layers found in the sedimentary sequence and or through a salinity increase due to the presence of evaporitic brines with high concentrations of ca and so4 saturation can also be reached in porewaters of seawater like salinity 35 provided sulfate reduction is limited in this case saturation is due to the alteration of volcanogenic material which releases large amounts of ca to the porewaters where the ca concentration can reach 55 times its seawater value as for example at odp leg 134 site 833 at a few sites saturation is reached in hydrothermal environments or as a consequence of the alteration of the basaltic basement in addition to the well known influence of brines on the formation of gypsum these results indicate that the alteration of sediments rich in volcanogenic material is a major process leading to gypsum saturation in marine sediment porewaters therefore the presence of gypsum in ancient and recent marine sediments should not be systematically interpreted as due to hypersaline waters especially if volcanogenic material is present

alaska crustal deformation finite element modeling constrained by geologic and very long baseline interferometry data we compute crustal motions in alaska by calculating the finite element solution for an elastic spherical shell problem the method we use allows the finite element mesh to include faults and very long baseline interferometry vlbi baseline rates of change boundary conditions include pacific north american pa na plate motions the solution is constrained by the oblique orientation of the fairweather queen charlotte strike slip faults relative to the pa na relative motion direction and the oblique orientation from normal convergence of the eastern aleutian trench fault systems as well as strike slip motion along the denali and totschunda fault systems we explore the effects that a range of fault slip constraints and weighting of vlbi rates of change has on the solution this allows us to test the motion on faults such as the denali fault where there are conflicting reports on its present day slip rate we find a pattern of displacements which produce fault motions generally consistent with geologic observations the motion of the continuum has the general pattern of radial movement of crust to the ne away from the fairweather queen charlotte fault systems in se alaska and canada this pattern of crustal motion is absorbed across the mackenzie mountains in nw canada with strike slip motion constrained along the denali and tintina fault systems in south central alaska and the alaska forearc oblique convergence at the eastern aleutian trench and the strike slip motion of the denali fault system produce a counterclockwise pattern of motion which is partially absorbed along the contact and related fault systems in southern alaska and is partially extruded into the bering sea and into the forearc parallel the aleutian trench from the alaska peninsula westward rates of motion and fault slip are small in western and northern alaska but the motions we compute are consistent with the senses of strike slip motion inferred geologically along the kaltag kobuk trench and thompson creek faults and with the normal faulting observed in nw alaska near nome the nonrigid behavior of our finite element solution produces patterns of motion that would not have been expected from rigid block models strike slip faults can exist in a continuum that has motion mostly perpendicular to their strikes and faults can exhibit along strike differences in magnitudes and directions

upper limit of docking time for stikinia and terrane i paleomagnetic evidence from the eocene ootsa lake group british columbia the middle eocene ootsa lake group is exposed in the central portion of the stikine terrane where it was sampled along the shoreline of tahtsa reach and whitesail reach the group consists of dominantly subaerial flows which range in composition from basalt to rhyolite that unconformably overly the jurassic hazelton group detailed alternating field and thermal stepwise demagnetizations were done on all specimens from the 21 sites collected the presence of a normal and reversed polarity remanence a positive fold test and high coercivities and unblocking temperatures indicate that a prefolding primary remanence has been isolated the mean tilt corrected direction of d 002 2 i 69 2 95 7 4 from 13 sites for which paleohorizontal is well known yields a pole position at 354 6 e 88 0 n a95 11 5 which is statistically indistinguishable from published 50 ma reference poles for cratonic north america this evidence demonstrates that the proposed large scale northward displacement of stik

geomorphology of lake lisan terraces along the eastern coast of the dead sea jordan abstract lake lisan the lake that filled the jordan graben during the last glacial left behind a well developed sequence of erosional and depositional shore terraces in the south east of the current dead sea these terraces record a series of stillstands that were caused by small transgressions within an overall trend of falling lake levels the terraces were observed in places where they had not been identified previously the morphology of the terraces was investigated in six cross sections using differential gps altimetry the levels of the terraces range between 370 and 148 m a s l the high stand of lake lisan at 148 m correlates well with the high level of 150 m reported by bowman and gross bowman d gross t 1992 the highest stand of lake lisan 150 meters below msl israel journal of earth science 41 233 237 along the western coast of lake lisan the lake terraces are horizontal elongated and tectonically undisturbed and have a sub horizontal foreshore tread with an average slope of 8 2 and steep backshore cliff riser with an average slope of 17 7 the six cross sections show a good altitudinal correlation between their terraces moreover the terraces appear in undisturbed continuity on the aerial photos these morphological characteristics demonstrate that the retreat of the lake was a result of substantial climatic changes not of tectonic subsidence in situ stromatolites were found on most of the terraces reflecting a shallow water environment and emphasizing that these terraces are recessional well developed desert varnish and tafoni observed on blocks sitting on the terrace surfaces imply a long period of exposure and a low rate of post lacustrine erosion the formation of lisan terraces is constrained mainly by coastal slope water depth and underlying lithology the morphological analysis of these terraces allows identification of two kinds of pseudo terraces which were formed as a result of tread or riser destruction u th and osl dating allowed the dating of three events within the lake level curve more precisely the high level of 148 m occurred at 30 5 0 22 ka bp consistent with the heinrich event 3 and dansgaard oeschger stadial 5 the coldest period in the ngrip greenland ice core record the next lower terrace at 154 m was formed at 22 9 ka bp 0 29 and corresponds to the stadial 2c the final phase of the last high glacial the correlation between the lisan high stands and climatic stadials suggests that northern hemispheric cold periods led to periods with a more positive water balance in the near east at 10 0 8 ka bp lake lisan experienced a sharp drop to 200 m followed by a transgression between 9 5 to 7 ka bp

holocene climatic changes in the western mediterranean from south east france to south east spain abstract holocene climatic changes along coastal regions from south east france to south east spain were studied using pollen ratios comparing modern pollen rain vegetation and climate along selected transects from the atlantic ocean to the mediterranean we obtained threshold values of two different ratios corresponding to the different climatic conditions along the transects these pollen ratios and threshold values were employed to characterize the holocene climatic changes from nine mediterranean coastal sites the results were compared with data from marine and continental pollen sequences distributed in the western mediterranean basin and with additional regional data independent of human activity lake level fluctuations alpine glacier advance and retreat chronology 14 c anomaly and cooling phases in eastern france and central europe the role of anthropogenic activities and climate on the changes in vegetation is discussed six major changes in vegetation cover were identified they correspond to aridification phases that occurred around 9500 9000 yr bp 10 900 9700 cal bp 7500 7000 yr bp 8400 7600 cal bp 4500 4000 yr bp 5300 4200 cal bp 3700 3300 yr bp 4300 3400 cal bp 2600 1900 yr bp 2850 1730 cal bp and 1300 1000 yr bp 1300 750 cal bp these arid episodes were regional responses to more global climatic changes and determined the changes in the vegetation cover humans undoubtedly enhanced the vegetation changes but none the less had to adapt to these new climatic conditions

optical dating of a scroll bar sequence on the klip river south africa to derive the lateral migration rate of a meander bend problems are often encountered in accurately establishing the rates of processes associated with river channel change in this study optical dating was used to obtain the lateral migration rate of an abandoned meander bend on the klip river eastern free state south africa five samples were collected by augering along a transect across an approximately 200 m wide scroll bar sequence on the inner meander bend and an additional sample was collected from the channel fill of the related oxbow lake optically stimulated luminescence osl ages were derived for each sample using the single aliquot regenerative dose protocol on small aliquots of quartz incomplete bleaching was evident in some of the samples and thus the appropriate statistical analysis was performed using the finite mixture model for the scroll bar samples and the minimum age model for the channel fill sample the ages calculated were in the correct chronological order for the depositional sequence which was formed over the last 1000

paleomagnetic evidence for motion of the hawaiian hotspot during formation of the emperor seamounts the bend in the hawaiian emperor chain is the best example of a change in plate motion recorded in a fixed hotspot frame of reference alternatively the bend might record primarily differences in motion of the hawaiian hotspot relative to the pacific lithosphere new paleomagnetic data from the emperor chain support the latter view althouth the rate of motion is difficult to constrain because of uncertainties posed by true polar wander and limited sampling of the chain the best available paleomagnetic data suggest pacific hotspots may have moved at rates comparable to those of lithospheric plates 30 mm yr 1 in late cretaceous to early tertiary times 81 43 ma if correct this requires a major change in how we view mantle dynamics and the history of plate motions in the early to mid cretaceous 128 95 ma hotspots in the atlantic moved at similar rates these episodes during which groups of hotspots appear to move rapidly are separated by times of much slower motion such as the past 5 m y

microbial methane turnover at mud volcanoes of the gulf of cadiz the gulf of cadiz is a tectonically active area of the european continental margin and characterised by a high abundance of mud volcanoes diapirs pockmarks and carbonate chimneys during the r v sonne expedition gap gibraltar arc processes so 175 in december 2003 several mud volcanoes were surveyed for gas seepage and associated microbial methane turnover pore water analyses and methane oxidation measurements on sediment cores recovered from the centres of the mud volcanoes captain arutyunov bonjardim ginsburg gemini and a newly discovered mud volcano like structure called no name show that thermogenic methane and associated higher hydrocarbons rising from deeper sediment strata are completely consumed within the seabed the presence of a distinct sulphate methane transition zone smt overlapping with high sulphide concentrations suggests that methane oxidation is mediated under anaerobic conditions with sulphate as the electron acceptor anaerobic oxidation of methane aom and sulphate reduction sr rates show maxima at the smt which was found between 20 and 200 cm below seafloor at the different mud volcanoes in comparison to other methane seeps aom activity 383 mmol m 2 year 1 and diffusive methane fluxes 321 mmol m 2 year 1 in mud volcano sediments of the gulf of cadiz are low to mid range corresponding lipid biomarker and 16s rdna clone library analysis give evidence that aom is mediated by a mixed community of anaerobic methanotrophic archaea and associated sulphate reducing bacteria srb in the studied mud volcanoes little is known about the variability of methane fluxes in this environment carbonate crusts littering the seafloor of mud volcanoes in the northern part of the gulf of cadiz had strongly 13c depleted lipid signatures indicative of higher seepage activities in the past however actual seafloor video observations showed only scarce traces of methane seepage and associated biological processes at the seafloor no active fluid or free gas escape to the hydrosphere was observed visually at any of the surveyed mud volcanoes and biogeochemical measurements indicate a complete methane consumption in the seafloor our observations suggest that the emission of methane to the hydrosphere from the mud volcano structures studied here may be insignificant at present

geomorphological impacts of a flood event on ephemeral channels in se spain a flood event occurred on 30 september 1997 in three catchments torrealvilla salada and nogalte in se spain which were being monitored for morphological change peak discharges were high in the torrealvilla catchment moderate in the salada and low in the nogalte detailed topographic surveys were made before and after the flood and from these dems of difference were constructed the two sites with highest flow both underwent significant incision of the channel at other sites both scour and aggradation of the channel took place with scour holes of up to 1 m depth eroded elsewhere within the channels major erosion took place downstream of tracks and structures such as check dams that impeded sediment movement the pattern and amounts of change show little relationship to independent factors other than a scale effect of peak discharge behaviour of channels is closely related to local sediment supply sediment flux calculated from changes in volumes at the site is comparable with the other figures produced for ephemeral channels and much higher than for perennially flowing streams

palaeoflood and floodplain records from spain evidence for long term climate variability and environmental changes abstract palaeoflood chronologies from seven spanish river basins and floodplain aggradation chronologies from thirteen rivers are analysed these fluvial records were divided in to two sub sets namely atlantic 10 ka record and mediterranean 3 ka record river basins which represent distinct modern hydroclimatic conditions in atlantic basins floods result from intense widespread rainfalls associated with atlantic frontal systems transported by westerly airflow mediterranean river flooding is related to heavy rainfall induced by mesoscale convective systems mcss during autumn months evidence from radiocarbon dates in slackwater flood deposits shows six periods of flood clusters at 10 750 10 240 9550 9130 4820 4440 2865 2350 960 790 and 520 290 cal bp despite the different flood producing weather conditions in atlantic and mediterranean rivers the radiocarbon sample clusters overlap and indicate changes in large scale atmospheric circulation and climatic conditions in the iberian peninsula comparison with proxy records of mean temperature for the northern hemisphere demonstrates a relationship between the period of slackwater flood deposition and cold climatic phases e g the 2650 yr bp climatic event or ad 1590 1650 period of the little ice age radiocarbon dates from aggraded floodplain sediments were clustered at 2710 2320 2000 1830 and 910 500 cal bp the first cluster period is in phase with the timing of slackwater deposition whereas the third 910 500 cal bp occurs in between two periods of increased flood frequency as indicated by the palaeoflood and documentary flood records it is argued that the 910 500 cal bp floodplain aggradation period reflects the first post roman evidence of environmental change related to generalised land use changes at the catchment scale which produced high sediment load transported to overbank areas during high flows

the holocene and upper pleistocene pollen record from padul granada spain a new study two borings were made at the site of padul granada pollen analysis of 200 spectra from two successive sequences 14 8 and 8 m deep enables a description of the vegetational and climatic history of this region the most southern one in europe from early wurmian times the chronology is supported by twenty one 14c dates original equivalents are found for the great european prewurm interstadials a markedly arid though thermically not extreme episode exactly equivalent to stage 4 of the marine isotopic stratigraphy closes this relatively temperate period the middle part of the last glacial shows climatic fluctuations that are poorly characterized as is often the case in europe for this period a long section very probably corresponding to the complete last pleniglacial does not show any climatic amelioration towards 15 000 yr b p a change in the diagram is noted that can only be interpreted as reflecting a larger expansion of a regional steppe cover this event also reported on three occasions in southeast france marks the beginning of the oldest dryas the climatic amelioration of ca 13 000 yr b p is far more pronounced here than anywhere else in europe whereas that at 10 000 yr b p is not so clearly marked this unexpected result may be accounted for by the fact that padul is the first continental site so far south and so near pleniglacial refuges to be known on the other hand this result is consistent with what is known from oceanic isotopic stratigraphy a quite new late glacial and holocene vegetational history is revealed characterized by the early appearance and dominance of quercus ilex oak forests of a southern type and the early occurrence of quercus suber and olea it is the first account of a complete history of the postglacial reafforestation in a region with a modern semi arid mediterranean climate from the palaeoclimatic point of view it shows that the hot and humid holocene optimum was attained slightly before 8000 yr b p and that the holocene climatic fluctuations were of but small amplitude

climatic and human influence on river systems and glacier fluctuations in southeast spain since the last glacial maximum abstract the semi desert environments of the mediterranean region are most sensitive to climatic changes and human land exploitation this paper is focused on the late pleistocene and holocene geomorphic evolution of southeast spain one of the driest regions in europe late pleistocene and holocene chronosequences of river terraces were established for the antas and aguas valleys respectively the deposition of up to four fluvial terraces during isotope stage 2 points to important erosion and accumulation processes at the end of late pleistocene in the vera basin in contrast to the stage 2 deposits the holocene terraces are composed of point bar deposits accumulated by meandering rivers with less sediment discharge according to the obtained 14c dating and extracted pottery fragments holocene terrace deposition occurred during the atlantic period early middle ages little ice age lia and the 20th century the most outstanding site in southern spain for studying holocene glacier shifts up to five end moraines is the veleta cirque in sierra nevada where the southernmost glacier of europe persisted during the little ice age the climate changes of the lia probably are recorded by two glacier fluctuations as indicated by 210pb dating and historical data the reconstruction of the evolution of the aguas and antas valleys stress that the aggradations of the lower terraces is mostly climate induced although during the last 500 years human interference in the landscape christian conquest mining boom of the 19th century etc may have played an important role to river dynamics

high resolution fluvial record of late holocene geomorphic change in northern tunisia climatic or human impact abstract in northern tunisia the late holocene alluvial record of medjerda floodplain sediments indicates geomorphic changes due to fluctuations of past climate superimposed by the effects of human activity geomorphic activity occurred several times interrupting stable conditions enhanced fluvial dynamics occurred around 4 7 3 0 1 7 1 0 and 0 7 ka cal bp a peak of activity took place about 0 4 ka cal bp some periods of fluvial activity show event like phenomena in particular when an anthropogenic impact intensifies climatic aridification this has been the case around 1 7 1 0 0 7 and 0 4 ka cal bp with severe floods in the medjerda valley during antiquity as well as around 1 3 0 8 and 0 5 ka cal bp immature alluvial soils have developed the first one being the most distinct late holocene medjerda alluvial history shows that fluvial dynamics in northern tunisia were predominantly climate driven anthropogenic impact only intensified or weakened these processes

middle pleistocene to holocene geochronology of the river aguas terrace sequence iberian peninsula fluvial response to mediterranean environmental change abstract our results from the river aguas basin suggest that fluvial archives travertine and slope deposits provide sensitive resolution records of environmental changes during the last 170 kyr from the chronostratigraphic data sets we have established a model of middle and late pleistocene river response for littoral basins on the southern iberian peninsula u th and osl dating indicate the major periods of travertine formation of the alfaix travertine platform which range from 169 to 26 kyr at least four incision events interrupted this aggradation period between 167 and 148 kyr between 148 and 110 kyr around 95 kyr and at 71 kyr aggradation ceased after 26 kyr and incision occurred during ois 2 subsequently the terraces t4a and t4b were deposited osl dating of the t4a channel deposit provides maximum ages of 28 20 and 18 kyr however short climatic events such as the younger dryas produced two more river incision episodes during ois 2 nonetheless for river systems influenced by tectonics climate and sea level changes it is difficult to assess the weight of each controlling factor regarding the three mechanisms of pleistocene river dynamics in middle size catchment areas of the littoral region of southeastern spain our results support the hypothesis that large scale tectonics triggered the general downcutting trend whereas the main aggradation and incision phases occurred during periods of major sea level changes over short time scales the influence of climate variability as documented by pollen records plays a decisive role thus the river responses to the three cyclic mechanisms operate at different time scales although synergetic processes should be considered with respect to the magnitude of abrupt incision aggradation events

the impact of quaternary sea level and climatic change on coastal alluvial fans in the cabo de gata ranges southeast spain conventionally a fall in base level is seen as stimulating incision into the distal zones of alluvial fans in the cabo de gata ranges of southeast spain evidence exists to the contrary two sets of quaternary coastal alluvial fans demonstrate the interaction between climatically driven variations in the supply of sediment and eustatically driven changes in base level the fans are supplied from miocene volcanic terrain within which no evidence can be found for major tectonic deformation during the period of fan development the evolution of the east coast fans has been affected by variations in sediment supply and changes in sea level the west coast fans were buffered from the effects of changes in sea level by coastal barriers three phases of past sedimentation can be identified on the fans these can be differentiated on the basis of field observations of soil profiles particularly colour of the b horizons and accumulation of caco3 and laboratory analyses of sequential iron oxide extractions and magnetic mineral properties the two earlier major sedimentation phases were coincident with global glacials ca 135 ka and ca 85 10 ka based on the stratigraphy and uranium thorium dating of the coastal sediments high sea levels during the intervening interglacial and during the holocene caused erosion of the distal zones of the east coast fans which led to channel incision into the fan surfaces on the west coast fans no such incision occurred simply proximal incision by small fanhead trenches the youngest relatively minor phase of fan sedimentation has occurred during the holocene these contrasting contexts have produced differing styles of fans with telescopic fan morphology on the east coast and stacked morphology on the west coast fans the differences are reflected in the fan profiles with steeper gradients dominating the east coast fans and extensive lower gradient distal surfaces on the west coast fans fan morphometry based on analysis of the residuals from drainage area to fan area and gradient regressions also differentiates between the fan contexts the fan building phases appear to be controlled proximally by climatically driven pulses of sediment supplied to the fans these occurred during global glacials coincident with low sea levels and caused fan progradation onto the exposed foreshore the intervening global interglacials were times of little fan sedimentation and on the east coast where high sea levels were able to erode the fan toes deep through fan dissection ensued

correlation and geochronology of middle eocene strata from the western united states abstract in this study i integrate marine and continental biostratigraphy magnetic polarity stratigraphy and radioisotopic chronology in a synthetic correlation of middle eocene strata from the western united states more than 2000 m of section were sampled from volcaniclastic deposits aycross and tepee trail formations northwestern wyoming lacustrine and fluviatile deposits washakie formation southwestern wyoming and intertonguing marine and continental strata la jolla and poway groups san diego area california detailed demagnetization studies on numerous pilot samples from all three field areas revealed moderately complex magnetizations most sample nrm s are dominated by a strong normal polarity magnetic component alternating field demagnetization does not consistently isolate the primary magnetization high blocking temperature hematite is frequently a significant carrier of remanence therefore most samples were subjected to detailed stepwise alternating field and thermal demagnetization to 600 650 c the east fork basin area northwestern wyoming magnetic polarity sequence consists of five major polarity intervals a to e the thick washakie formation sequence contains four a to d and the san diego area sequence has four polarity intervals a to d a new biochronologic interval the shoshonian land mammal subage earliest uintan is defined and characterized in all three field areas shoshonian earliest uintan faunas and the bridgerian uintan boundary occur within a single long reversed polarity interval correlation of marine biostratigraphy between the san diego area section and deep sea sections allows precise identification of san diego polarity interval b as chron c21n therefore the bridgerian uintan boundary and earliest uintan faunas occur within the reversed interval of chron c20r high temperature k ar dates bracketing this horizon in northwestern wyoming provide an age estimate of approximately 49 5 ma for the top of chron c21n and 49 ma for the bridgerian uintan boundary berggren et al 1985 use the age estimate of 49 5 ma for the top of anomaly 21 younger boundary of chron c21n as one calibration point for the generation of a paleogene geochronology the methodology and conclusions of this geochronology are compared to those of other recent geochronologies data from independent studies integrating high temperature radioisotopic dates biochronology and magnetochronology are used to test the validity of the berggren et al 1985 geochronology

a simulation model of morphological vegetation and sediment changes in ephemeral streams a model to simulate channel changes in ephemeral river channels and to test the effects of hydrological changes due to climate change and sol or land use change was developed under the auspices of the eu funded medalus programme mediterranean desertification and land use the model changism channel change gis simulation model is designed to simulate the effect of channel flow events and of climate conditions on morphology sediment and vegetation through sequences of events and conditions over periods of up to several decades the modelling is based on cellular automata but with calculations for water and sediment continuity process rules have both deterministic and stochastic elements an important feature of the model is that it incorporates feedback elements between each event the main aim of the model is to indicate the likely outcomes of events and combinations of conditions it is linked to gis for both input and output the modelling is based on a channel reach and state is input as gis layers of morphology dem sediment and vegetation cover and state other initial conditions of soil moisture groundwater level and overall gradient are input parameters for processes are read from tables and can be easily changed for successive runs of the model the bases for decisions on process specifications are discussed in this paper initial tests of the operation and sensitivity of the model were made on idealized reaches the model was then tested using data from monitored sites in se spain simulations using clearwater flow worked well but initial simulations using events with sediment loads showed some tendency for excess deposition further tests and modifications are taking place overall the model is one of the most sophisticated that simulates the interaction of flows with sediment and vegetation and the outcomes in terms of erosion deposition morphology sediment cover vegetation cover and plant survival over periods of up to 30 years for the scale of a channel reach copyright 2005 john wiley sons ltd

paleomagnetic and geobarometric study of the late cretaceous mount lorne stock southern yukon territory the 75 ma mount lorne monzodiorite stock has been studied paleomagnetically to estimate the tectonic motion of the northern canadian cordillera since the late cretaceous the stock is one of sever

a paleomagnetic test for northward tectonic transport of the eastern selwyn basin northern canadian cordillera data from the mid cretaceous ragged pluton ragged pluton is a member of the tungsten plutonic suite in the eastern selwyn basin this circular massive 97 ma granitic pluton is 5 km in diameter it intrudes deformed and metamorphosed clastic strata of the neoproterozoic to lower cambrian vampire formation thermal and alternating field step demagnetization data for 216 specimens from 21 plutonic sites isolated a stable characteristic remanent magnetization chrm direction at 20 sites of declination d 325 9 inclination i 80 4 95 2 7 k 142 thermal demagnetization and saturation remanence analysis show that the chrm is carried by both single domain pyrrhotite and magnetite ragged pluton s paleopole at 73 9 n latitude 191 4 e longitude dp 5 0 dm 5 2 is concordant with its co eval 97 ma north american reference paleopole showing at 95 confidence that the pluton has not been significantly rotated or translated relative to north america this paleomagnetic result favours tectonic models in which the eastern selwyn basin is

the coastal archives of the last 15 ka in the atlantic mediterranean spanish linkage area sea level and climate changes sea level and climate changes archived in various coastal environments during the last part of the last glacial and present interglacial periods are investigated by interpolating available geomorphology sedimentology palaeontology and geochronology data the coastal response to these changes depended on the environment and geographic location changes of sea level during the rising transgressive phase are well recorded in the sedimentary filling of the estuaries whereas during the phase of highstand they are best recorded in beach barrier environments the postglacial rise of sea level took place in two phases a rapid rise until 6500 cal bp and a second phase of near stability with minor oscillations of metric magnitude regarding climate changes there is no record of changing temperatures in the coastal zones of southern spain although there is in precipitation and wind intensity velocity after 7 5 cal ka bp the general climatic trend towards aridity was punctuated by several short lived centennial episodes of increased aridity that occurred with a millennial cycle often coincident with bond cool events and in some cases with decreases of sea surface temperatures the absence of human intervention in vegetation composition until 2000 bp suggests that most environmental coastal shifts were climatically driven

stratigraphy depositional environments and level reconstruction of the last interglacial lake samra in the dead sea basin in this paper we describe the stratigraphy and sediments deposited in lake samra that occupied the dead sea basin between 135 and 75 ka this information is combined with u th dating of primary aragonites in order to estimate a relative lake level curve that serves as a regional paleohydrological monitor the lake stood at an elevation of 340 m below mean sea level msl during most of the last interglacial this level is relatively higher than the average holocene dead sea 400 30 m below msl at 120 and 85 ka lake samra rose to 320 m below msl while it dropped to levels lower than 380 m below msl at 135 and 75 ka reflecting arid conditions in the drainage area lowstands are correlated with warm intervals in the northern hemisphere while minor lake rises are probably related to cold episodes during mis 5b and mis 5d similar climate relationships are documented for the last glacial highstand lake lisan and the lowstand holocene dead sea yet the dominance of detrital calcites and precipitation of travertines in the dead sea basin during the last interglacial interval suggest intense pluvial conditions and possible contribution of southern sources of wetness to the region

plate motions in the north pacific the 43 ma nonevent the hawaiian emperor seamount chain in the north pacific ocean is commonly considered to have been produced by motion of the pacific plate over a hotspot if the hotspot is assumed to have remained fixed in a mantle frame of reference the 60 change in trend between the hawaiian and emperor portions of the chain results from a change in motion direction of the pacific plate relative to the mantle at 43 ma during middle eocene time such a large and abrupt direction change should result in significant plate reorganizations and tectonic events in the pacific and surrounding plates but no evidence for these events can be found in addition in this paper it is shown that there were no changes in relative plate motions between pacific area plates that can be associated with the hawaiian emperor bend this is done by calculating motion of the pacific farallon and kula plates relative to asia and north america using the plate circuit farallon pacific antarctica africa north america asia with no major regional tectonic event at the time of the bend it is suggested that there was no plate reorganization at 43 ma and that the emperor portion of the seamount chain was formed by a nonstationary hotspot

tertiary paleomagnetism of the north cascade range washington we have obtained paleomagnetic data for the southern tip of the middle tertiary chilliwack composite batholith located on the canada united states border about 125 km e of vancouver b c thirty four separately oriented samples were collected along a road traverse 1 5 km long located along state highway 22 about 20 km ne of marblemount washington the mean direction after magnetic cleaning is d 182 8 i 65 0 95 1 5 this corresponds to a paleomagnetic pole at 87 5 n 267 5 e close to other poles for tertiary plutons from the north cascades and only slightly displaced from tertiary reference poles from the craton we conclude that the north cascades block has not been rotated or suffered major internal disruption since perhaps late eocene time in marked contrast to all the terranes that surround it

a magnetostratigraphic and secular variation study of level mountain northern british columbia summary palaeomagnetic results are reported from 50 flows erupted by level mountain which is a composite volcano in northern british columbia fourteen magnetic polarity zones are represented and these allow a magneto stratigraphy to be established which indicates that eruptive activity began about 6 5 myr ago and continued up to very recent times with several hiatuses of up to 1 myr or more most of the flows yield acceptable normal or reversed palaeopoles but two of them record the gauss matuyama polarity transition and a further four yield a tight group of divergent directions which are here interpreted as a geomagnetic excursion near the base of the gauss epoch this observation lends support to an earlier suggestion bingham stone that the geomagnetic field was abnormally disturbed about 3 5 myr ago at least locally in north western north america the overall average palaeopole obtained after filtering out flows with high internal variance and those yielding divergent virtual geomagnetic poles vgps lies at 256 e 85 n n 38 a 7 2 a more representative palaeopole is obtained by combining the results with those of souther symons from mount edziza a closely related contemporaneous volcano some 100 km away this pole lies at 292 e 87 n n 92 ag5 4 1 and again includes the geographic pole within its 95 per cent confidence limits how ever the mean itself is not far sided as wilson s model predicts neither is it left handed as the analysis by merrill mcelhinny predicts the slight near sidedness observed agrees with the global compilation of wilson mcelhinny who show that the north western region of north america is the only area out of 15 regions worldwide to yield a near sided pole the dispersion of the vgps angular standard deviation 22 is a little higher than would be expected from global summaries and secular variation models this was also found to be the case in data from alaska doell cox the angular dispersion the occurrence of geomagnetic excursions and the

multi process late quaternary landscape evolution modelling reveals lags in climate response over small spatial scales landscapes evolve in complex non linear ways over quaternary timespans integrated geomorphological field studies usually yield plausible hypotheses about timing and impact of process activity landscape evolution models lems have the potential to test and falsify these landscape evolution hypotheses despite this potential lems have mainly been used with hypothetical data and rarely to simulate the evolution of an actual landscape in this paper we use a lem lapsus landscape process modelling at multi dimensions and scales to explore if it is possible to test and falsify conclusions of an earlier field study on 50 ka landscape evolution in okhombe valley kwazulu natal south africa in this lem five landscape processes interact without supervision water driven erosion and deposition creep solifluction biological weathering and frost weathering calibration matched model results to three types of qualitative fieldwork observations individual process activity over time relative process activity over time and net landscape changes over time results demonstrate that landscape evolution of the okhombe valley can be plausibly simulated a particularly interesting and persistent feature of model results are erosional and depositional phases that lag climatic drivers both by decades and by several ka within a few hundred meters the longer lag has not been reported for this spatial scale before and may be an effect of slow landscape soil vegetation feedbacks the combined modelling and fieldwork results allow a more complete understanding of these responses to climate change and can fill in hiatuses in the stratigraphical record suggestions are made for methodological adaptations for future lem studies

the yukon tanana terrane part of north america at 215 ma from paleomagnetism of the taylor mountain batholith alaska abstract the massive unmetamorphosed 212 ma taylor mountain batholith underlies 648 km2 of the yukon tanana terrane ytt in east central alaska and intrudes klippen thrust sheets of the fortymile river assemblage and the chicken metamorphic complex structural evidence indicates that the batholith is neither tilted nor rotated about a vertical axis paleomagnetic analysis of 295 specimens from 24 sites in the batholith and cross cutting mafic dikes isolates a stable primary characteristic remanent magnetization in magnetite with unblocking temperatures of 500 to 585 c that places the batholith s paleopole at 61 4 n 102 2 e n 17 95 5 2 on the north american apparent polar wander path apwp at 215 5 ma 1 the taylor mountain paleopole alone and all ytt paleopoles together show that the ytt has been a para autochthonous part of the north american margin since the late triassic further the intermontane belt imb paleopoles are distinct from the north american and ytt paleopoles prior to the mid eocene and provide two apwp segments one imb segment includes the quesnel cache creek eastern coast belt and northern stikine terranes and the second more speculative imb segment includes the central and southwestern stikine and methow terranes this analysis supports tectonic models for the northern cordillera in which the imb terranes were obducted onto north america during the late cretaceous to mid eocene co eval with the laramide orogeny

evolution of the late pleistocene holocene dead sea basin from sequence statigraphy of fan deltas and lake level reconstruction patterns of sediment transport to the dead sea basin during late pleistocene and holocene times were evaluated by comparing previously established lake levels with patterns of transgressions and regressions in fan deltas at the lake margins while the lake level history reflects the hydrological regime in the drainage basin the transgression regression patterns reflect the response of the clastic sediment transport to the regional hydrology and morphology of the basin by using the two techniques we are able to demonstrate the time relationship between the factors controlling the deposition six sequences are exposed at the western margins of the basin their chronology was obtained by u th radiocarbon and luminescence ages on aragonite and quartz sand from the samra lisan and ze elim formations which cover the past 160 ka our data shows a lag between periods of high water inflow and clastic sediment flux to the basin during highstands the sediments were stored in deep 100 200 m long estuaries that formed in incised canyons into the east and west bounding escarpments during lake level falls the stored sediments were flushed out forming prograding lowstand fan deltas this leads to a high sediment flux during early stages of arid conditions following extreme high lake levels

major dextral transcurrent displacements along the northern rocky mountain trench and related lineaments in north central british columbia the northern rocky mountain trench and a number of other prominent lineaments along and east of the eastern margin of the intermontane belt mark faults along which dextral transcurrent movements have been dominant offsets of shelf to off shelf facies boundaries in lower paleozoic rocks indicate a cumulative displacement of at least 750 km and probably 900 km within the system of faults related to those in the northern rocky mountain and the tintina trenches farther west another system of faults appears to offset plutons and stratigraphic assemblages along the eastern margin of the intermontane belt by as much as 300 km these faults including the kutcho and the pinchi connect in part with the teslin suture zone in yukon territory and probably with the fraser river straight creek fault zone in southern british columbia although dextral transcurrent faulting may have taken place between the middle jurassic and early cenozoic the most convincing evidence points to middle cretaceous and particularly to early cenozoic eocene displacements the eocene movements were temporally related to plutonism volcanism lamprophyre dike emplacement high heat flow sedimentation in grabens and rapid uplift of northwesterly trending elongate ranges climactic episodes of granite emplacement particularly in and near the northern omineca crystalline belt at 100 m y 70 m y and 50 m y ago may have been facilitated by changes from dominantly compressional to dominantly transcurrent and related tensional strain

anthropogenic and climatic impact on holocene sediment dynamics in se spain a review the climatic and anthropogenic control on holocene sediment dynamics was not well constrained for the western mediterranean basin the paucity of high resolution palaeoenvironmental records long hampered a detailed understanding of the human impact on erosion rates this paper analyses holocene sediment dynamics in the context of regional climatic conditions land cover and human occupation based on an extended compilation of recently published high resolution paleoenvironmental proxy data from both terrestrial and marine environments the palaeoenvironmental reconstruction identified four main aridification episodes a at 5600 4700 a4 4100 3400 a3 2800 2500 a2 and 1900 1300 1200 a1 cal bp most of the severe aridification phases were climatically induced not human driven and well correlated with a large dataset of paleoenvironmental records from the western mediterranean basin and north atlantic ocean the phases of enhanced aridity are generally associated with enhanced sediment dynamics independent of the intensity and type of human occupation in contrast wet climatic conditions are found to be associated with both high and low sediment dynamics dependent on the human impact on the environment the mid late phoenician phoenician ii republican rome civilizations and the christian reconquest are all associated with high human impact on the environment and high erosion rates are reported for the vera basin and ne spain despite the improved hydrological conditions human occupation is not necessarily associated with geomorphic instability as shown by the post argaric omeya and nazarene periods that are characterized by low erosion rates and geomorphic stability

paleomagnetic results for eocene volcanic rocks from northeastern washington and the tertiary tectonics of the pacific northwest the direction of remanent magnetization for 102 sites in eocene volcanic and volcaniclastic rocks of the o brien creek formation sanpoil volcanics and klondike mountain formation suggests approximately 25 of clockwise rotation of a 100 by 200 km area in northeastern washington the volcanic rocks consist chiefly of rhyodacite and quartz latite flows with intercalated ash flow tuff and volcaniclastic layers these rocks have been sampled at 102 sites distributed among five volcanotectonic depressions the toroda creek republic keller and first thought grabens and the spokane enterprise lineament the volcanic rocks probably range in age from 55 m y to about 48 m y and the 50 to 48 m y old volcanic rocks within this suite appear to be rotated as much as the older rocks previous investigators have shown that 40 m y old and younger plutonic rocks of northwestern washington are not rotated hence we infer that the north central washington rocks were rotated to their present declination between 48 and 40 m y b p during the middle and or late eocene during early eocene time this region was extended in a westward direction through crustal necking gneiss doming diking and graben formation internal deformation of the region related to this crustal extension was extreme but most bedrock units that were formed concurrent with the crustal extension were probably in place prior to the rotation hence we infer that the rotation was chiefly accommodated by movement on faults peripheral to the sampled area faults active during paleogene time appear to define boundaries of a triangular crustal block the sanpoil block encompassing much of northeastern washington northern idaho northwestern montana and adjacent parts of british columbia the faults include the laramide thrusts of the rocky mountain thrust belt the strike slip faults of the lewis and clark line and strike slip faults of the straight creek fraser zone we suggest that during early eocene time the sanpoil block was extended westward through crustal necking and dilation and then during the middle eocene was rotated clockwise and thrust over the craton in a final stage of laramide thrusting the motor driving these deformations presumably was interaction of north america with oceanic lithosphere off its western margin such interaction probably involved right oblique underthrusting and dextral shear

yellowstone in yukon the late cretaceous carmacks group the late cretaceous carmacks group a thick subaerial volcanic succession that once covered much of southwest yukon was deposited on an uplifted terrane and is divisible into a lower fragmental unit and an upper flood basalt unit coeval hydrothermal activity resulted in widespread alteration and gold mineralization the lavas are shoshonites enriched in large ion lithophile and light rare earth elements but depleted in high field strength elements ankaramitic absarokite flows in the upper carmacks group range up to 15 wt mgo requiring a high liquidus temperature 1400 c at 1 bar dry high k 2 o contents 3 of these magnesian lavas indicate that the potassic character of the volcanic suite was established in the mantle although previously interpreted as subduction related the carmacks group was erupted during a cordilleran wide magmatic lull and lacks coeval calc alkalic batholiths the lavas are petrologically similar to plume related eocene to pliocene potassic lavas of the western united states new paleomagnetic collections combined with previous work place the carmacks group 17 2 6 5 1900 700 km south of its present position relative to the craton during deposition near the paleolocation of the yellowstone hotspot the spatial coincidence similarity of tectonic setting and lithologic similarity of the carmacks group and yellowstone volcanic successions suggest that the carmacks group is the 70 ma effusion of the yellowstone hotspot subsequent northward displacement of the carmacks group is attributed to coupling with the kula plate correlation of the carmacks group and the yellowstone hotspot fixes the paleolatitude and the paleolongitude of the terranes of the northern intermontane belt at 70 ma

diagenetic nonevaporative origin for gypsum paleoenvironmental interpretations commonly cite the occurrence of gypsum associated with nonfossiliferous redbeds as evidence for arid conditions and high evaporation rates such interpretations ignore the common occurrence of gypsum in gossan on weathered black shale surfaces and especially in pleistocene glacial deposits glaciolacustrine deltaic sequences in ohio contain abundant large gypsum crystals that formed diagenetically as a result of oxidation of sulfides by calcium rich oxidizing ground water crystals display two forms related to the host sediment euhedral tabular crystals occur in pliable prodelta mud whereas bladed dovetail gypsum sand crystals occur in grain supported delta front sand the diagenetic non evaporative model could explain the formation of gypsum in numerous sedimentary sequences dune tidal flat beach lagoon reef lagoon deltaic and barrier bar lagoon massive extensive sulfate accumulations probably formed under arid conditions however the nonevaporative diagenetic model should be considered in the interpretation of scattered gypsum crystals and thin gypsum crusts

are post middle miocene tilts present in the southern coast belt of british columbia a case study of present earth s magnetic field overprints tectonic tilt is a possible explanation for the discordant cretaceous paleomagnetic poles obtained from intrusions in the coast belt of the canadian cordillera if tilting of these intrusions has taken place post cretaceous intrusions may have been similarly tilted paleomagnetism of the middle miocene rogers creek pluton 16 ma in the central southern coast belt was utilized to test the tilt hypothesis well grouped stable primary magnetizations have been isolated in 11 sites with both normal and reverse polarities the mean remanence component directed at d 000 7 i 67 9 95 3 9 paleolatitude 50 9 9 n paleopole 88 3 n 257 5 e a95 5 7 was likely acquired upon emplacement at 16 ma this direction agrees with the middle miocene reference direction d 357 i 68 calculated from the updated miocene 10 20 ma cratonic reference pole for north america this concordant result when combined with concordant data from other mid tertiary intrusions to the south defines a southern co

pore water profiles and numerical modelling of biogeochemical processes in peru basin deep sea sediments abstract an extensive set of pore water profiles including o 2 no 3 no 2 nh 4 po 4 3 fe 2 mn 2 so 4 2 sio 4 4 ph and alkalinity as well as solid phase data on organic carbon content and porosity in 18 sediment cores obtained from five areas in the peru basin rv sonne 106 expedition in 1996 is presented the pore water profiles indicate that early diagenesis progresses through oxygen respiration denitrification and manganese iv reduction while the subsequent redox states iron iii reduction sulphate reduction and methanogenesis cannot be observed from the dissolved phase in these deep sea sediments a numerical diagenetic model was applied to the data in order to derive parameters such as the depositional flux of metabolizable organic matter or the bioturbation intensity that control the geochemical conditions in the deep sea floor and could not be obtained directly by measurements moreover the numerical simulations show that even those pore water no 3 profiles that decline non linearly to zero concentration are not compatible with a steady state assumption they can be explained only by transient downward progression of a nitrate front

new gps constraints on the motion of the yakutat block global positioning system gps measurements were made at yakutat on the yakutat terrane of southern alaska to investigate the motion of the yakutat block with respect to the north american plate and to help constrain motion along the fairweather fault the velocity of yakutat derived from the gps data is 44 1 1 9 mm yr toward n37 4 w relative to stable north america the magnitude of this velocity is similar to that of the pacific plate predicted by nuvel1a although there is a significant difference in the azimuth of these two vectors the motion of yakutat relative to north america is almost exactly parallel to the strike of the fairweather fault suggesting that most deformation inboard of yakutat is right lateral strike slip on the fairweather fault or faults parallel to it and that significant motion normal to the fairweather fault occurs offshore of yakutat the gps velocity at yakutat is also used to help constrain the slip rate and locking depth of the fairweather fault

revised and synthetic apparent polar wander paths of the african eurasian north american and indian plates and true polar wander since 200 ma we have reviewed paleomagnetic data available for the eurasian african north american and indian plates over the last 200 ma selection criteria are those generally accepted with an emphasis on evidence for lack of remagnetization accurate dating and proper structural analysis this results in 23 35 51 and 2 poles for eurasia africa north america and india respectively we believe that this limited set of higher quality data is more likely to reveal key features of apparent polar wander apw paths than averaging of larger data sets involving less stringent selection criteria we propose and describe revised apw paths but more importantly we next use relative motion models to transfer all data in a common reference frame we find good agreement between transferred data when they are averaged separately for each plate in independent 20 ma windows this is a check on consistency of paleomagnetic data kinematic models and of the geocentric dipole hypothesis transferred data from all plates are averaged in 20 ma windows to generate synthetic apw paths for all plates studied these synthetic paths are in agreement with the original revised apw paths that use only data from a single plate moreover both geographic and time resolution are improved spatial confidence intervals are of the order of 5 the synthetic paths display interesting features such as a previously ill recognized apw loop for eurasia paleomagnetic and hotspot apw are next compared and a determination of true polar wander tpw is derived we find significant tpw amounting to over 20 in the last 200 ma tpw appears to be episodic with a standstill between 180 and 110 ma there is general agreement with a previous study of livermore et al 1984 the tpw standstill appears to correlate with a time of decreasing reversal frequency ending with the cretaceous long normal superchron other periods of fast tpw would seem to correspond to increasing reversal frequency however it is suggested that the major tpw hairpin at 50 ma might correspond to the collision of india with eurasia tentative correlations with core or mantle indicators can be understood as a result of couplings between the core mantle and lithosphere we believe primarily related to episodic evolution of the d layer

the time averaged paleomagnetic field 0 5 ma persistent departures from the geocentric axial dipole field model of the time averaged paleomagnetic field over the past 5 myr have been analyzed using oceanic data from deep sea cores and continental data from igneous rocks and sediments the data set comprises the equivalent of 9490 spot readings of the field 5831 normal and 3659 reverse from 930 groups of data variations in declination anomalies between groups of data strongly suggest the existence of second order tectonic effects small rotations that make it difficult if not impossible to identify any nonzonal terms that might exist inclination anomalies have therefore been modeled in terms of low degree zonal harmonics the calculated inclination anomalies within 10 latitude bands are widely scattered for both oceanic and continental data and do not appear to have been drawn from distributions with common means we attribute this large scatter to previously undetected or uncorrected second order tectonic effects in the continental data or in the oceanic data to small departures from the vertical in deep sea cores if it is assumed that these effects are random between groups of data and without a systematic bias they can be averaged out to a large extent if there are sufficient numbers of groups within each latitude band this method also has the major advantage that it maximizes time averaging of the field when this is done an acceptable fit to the inclination anomaly data is found using a zonal harmonic model although the point estimates for the reverse polarity zonal quadrupole term are consistently larger than those for the normal polarity zonal quadrupole term the difference is not significant and is likely due to contamination effects this finding is true for a combination of all the data or for separate combinations of continental igneous rocks and ocean sediments this conclusion differs from all previous analyses the major differences occur in model estimates of the zonal octupole term the estimates varying widely depending on the particular data combination we show that false octupole terms can be introduced by several factors including inclination errors in sediments and lavas the use of unit vectors in the analyses and incomplete magnetic cleaning particularly of reversely magnetized rocks thus we cannot impute a geomagnetic significance to the estimates of a zonal octupole term we suggest that the best estimates for the zonal quadrupole g2 g20 g10 are obtained from the combined brunhes age igneous rocks and oceanic normal data 0 033 0 019 and for the combined matuyama age igneous rocks and oceanic reverse data 0 042 0 022 when these two sets are combined the overall best estimate of g2 is 0 038 0 012

quantification of non ideal effects on diagenetic processes along extreme salinity gradients at the mercator mud volcano in the gulf of cadiz abstract we present a transport reaction model traction specifically designed to account for non ideal transport effects in the presence of thermodynamic e g salinity or temperature gradients the model relies on the most fundamental concept of solute diffusion which states that the chemical potential gradient maxwell s model rather than the concentration gradient fick s law is the driving force for diffusion in turn this requires accounting for species interactions by applying pitzer s method to derive species chemical potentials and onsager coefficients instead of using the classical diffusion coefficients electrical imbalances arising from varying diffusive fluxes in multicomponent systems like seawater are avoided by applying an electrostatic gradient as an additional transport contribution we apply the model to pore water data derived from the seawater mixing zone at the submarine mercator mud volcano mmv in the gulf of cadiz two features are particularly striking at this site i ascending halite saturated fluids create strong salinity nacl gradients in the seawater mixing zone that result in marked chemical activity and thus chemical potential gradients the model predicts strong transport driven deviations from the mixing profile derived from the commonly used fick s diffusion model and is capable of matching well with the profile shapes observed in the pore water concentration data even better agreement to the observed data is achieved when ion pairs are transported separately ii the formation of authigenic gypsum several wt occurs in the surface sediments which is typically restricted to evaporitic surface processes very little is known about the gypsum paragenesis in the subseafloor and we first present possible controls on gypsum solubility such as pressure temperature and salinity pts as well as the common ion and ion pairing effects due to leaching of deep diapiric salt rising fluids of the mmv are saturated with respect to gypsum as well as celestite and barite several processes that could drive these fluids towards gypsum supersaturation and hence precipitation were postulated and numerically quantified in line with the varied morphology of the observed gypsum crystals gypsum paragenesis at the mmv is likely a combination of two temperature related processes gypsum solubility increases with increasing temperature especially in strong electrolyte solutions and the first mechanism involves the cooling of saturated fluids along the geothermal gradient during their ascent secondly local temperature changes i e cooling during the transition from mmv activity towards dormancy results in the cyclic build up of gypsum the model showed that the interpretation of field data can be majorly misguided when ignoring non ideal effects in extreme diagenetic settings while at first glance the pore water profiles at the mercator mud volcano would indicate strong reactive influences in the seawater mixing zone our model shows that the observed species distributions are in fact primarily transport controlled the model results for so4 are particularly intriguing as so4 is shown to diffuse into the sediment along its increasing concentration gradient also a pronounced gypsum saturation peak can be observed in the seawater mixing zone this peak is not related to the dissolution of gypsum but is simply a result of the non ideal transport forces acting on the activity profile of so4 and ca profiles

eocene 51 ma end to northward translation of the coast plutonic complex paleomagnetism and k ar dating of the white pass dikes abstract the white pass mafic dikes are located in the coast belt inboard of the coast shear zone denali fault system east of skagway alaska astride the alaska british columbia border the dikes intrude eocene felsic plutons in the coast plutonic complex three k ar analyses date the dikes at 51 9 0 8 ma biotite 50 1 1 0 ma and 45 0 0 8 ma both whole rock structural analysis on these vertical dikes indicates that the study area has not been tilted significantly since dike emplacement conventional alternating field and thermal step demagnetization and saturation remanence paleomagnetic methods were used to analyse 407 specimens from 27 dike and five host rock sites three contact tests show that the specimens retain a primary thermoremanent magnetization trm carried in pseudosingle to multidomain magnetite although some magnetization in a few dikes is carried by pyrrhotite the dual polarity trm is mostly reversed and the 24 accepted dike sites give a pole position of 245 7 e 76 3 n dp 4 2 dm 4 4 indicating a paleolatitude discordance of 8 4 south and a clockwise rotation of 40 9 with respect to the north american craton these data along with other paleomagnetic data on eocene rocks indicate that the allochthonous eastern coast and intermontane belt terranes had halted their northward translation by about 51 ma but continued to be rotated clockwise by an average of 24 10 thereafter probably on underlying sole faults

late pleistocene and holocene alluvial archives in the southwestern mediterranean changes in fluvial dynamics and past human response abstract cohesive floodplains from the semiarid southwestern mediterranean morocco tunisia exhibit excellent preservation toward lateral erosion and present a continuous record of late pleistocene and holocene flood dynamics holocene mean sedimentation rates and 14 c cumulative probability plots from cohesive tunisian floodplain sequences reveal a coupling with north atlantic bond events short term periods of fluvial activity match well with north atlantic coolings the findings indicate a strong climatic link from 4 8 ka until today unlike fluvial archives from the humid mid latitudes semiarid southwest mediterranean alluvial archives exhibit phases of increased fluvial dynamics under generally drier conditions the 14 c cumulative probability plot of archeological sites in mediterranean north africa indicates correlations with alluvial records therefore prehistoric societies seemed to be very sensitive to past shifts in landscape dynamics

abrupt temperature changes in the western mediterranean over the past 250 000 years a continuous high resolution western mediterranean sea surface temperature sst alkenone record spanning the past 250 000 years shows that abrupt changes were more common at warming than at cooling during marine isotope stage mis 6 sst oscillated following a stadial interstadial pattern but at lower intensities and rates of change than in the dansgaard oeschger events of mis 3 some of the most prominent events occurred over miss 5 and 7 after prolonged warm periods of high stability climate during the whole period was predominantly maintained in interglacial interstadial conditions whereas the duration of stadials was much shorter

isotopic evidence 87sr 86sr δ7li for alteration of the oceanic crust at deep rooted mud volcanoes in the gulf of cadiz ne atlantic ocean the chemical and isotopic composition of pore fluids is presented for five deep rooted mud volcanoes aligned on a transect across the gulf of cadiz continental margin at water depths between 350 and 3860 m generally decreasing interstitial li concentrations and sr 87 sr 86 ratios with increasing distance from shore are attributed to systematically changing fluid sources across the continental margin although highest li concentrations at the near shore mud volcanoes coincide with high salinities derived from dissolution of halite and late stage evaporites clayey terrigenous sediments are identified as the ultimate li source to all pore fluids investigated light delta li 7 values partly close to those of hydrothermal vent fluids delta li 7 11 9 parts per thousand indicate that li has been mobilized during high temperature fluid sediment or fluid rock interactions in the deep sub surface intense leaching of terrigenous clay has led to radiogenic sr 87 sr 86 ratios similar to 0 7106 in pore fluids of the near shore mud volcanoes in contrast non radiogenic sr 87 sr 86 ratios similar to 0 7075 at the distal locations are attributed to admixing of a basement derived fluid component carrying an isotopic signature from interaction with the basaltic crust this inference is substantiated by temperature constraints from li isotope equilibrium calculations suggesting exchange processes at particularly high temperatures 200 degrees c for the least radiogenic pore fluids of the most distal location advective pore fluids in the off shore reaches of the gulf of cadiz are influenced by successive exchange processes with both oceanic crust and terrigenous fine grained sediments resulting in a chemical and isotopic signature similar to that of fluids in near shore ridge flank hydrothermal systems this suggests that deep rooted mud volcanoes in the gulf of cadiz represent a fluid pathway intermediate between mid ocean ridge hydrothermal vent and shallow marginal cold seep due to the thicker sediment coverage and slower fluid advection rates the overall geochemical signature is shifted towards the sediment diagenetic signal compared to ridge flank hydrothermal environments c 2009 elsevier ltd all rights reserved

paleomagnetism of the eocene kamloops group and the cratonization of terrane i of the canadian cordillera the lower middle eocene 49 4 2 4 ma kamloops group is exposed in the middle of the quesnellia subterrane of terrane i the group consists of the siliciclastic tranquille beds and the overlying dewdrop flats plateau basalts and andesites detailed alternating field af and thermal step demagnetization was carried out on 282 specimens from 26 flow sites and one conglomerate site and saturation isothermal remanent magnetization sirm tests were performed to examine the remanence carriers the petrology of the gently dipping flows the presence of antiparallel normal and reverse remanence the conglomerate test and the fold test all indicate that a primary remanence has been isolated it resides in both magnetite and hematite over a broad range of af coercivities blocking temperatures and domain sizes its mean direction of 355 0 73 4 95 6 9 gives a pole position of 138 4 w 81 4 n dp 11 0 dm 12 3 that is statistically indistinguishable from the 50 ma reference pole for the north a

climate controls on late pleistocene landscape evolution of the okhombe valley kwazulu natal south africa hillslopes in central and western parts of kwazulu natal south africa are often mantled by colluvial sediments of the masotcheni formation these sediments have accreted in response to several cycles of deposition pedogenesis and incomplete erosion climatic controls on these cycles are incompletely known results from fieldwork micromorphology stable carbon isotope analysis and optically stimulated luminescence dating of masotcheni formation sediments from okhombe valley in the drakensberg foothills are combined deposition in the area had at least 11 phases starting before 42 ka and ending before 0 17 ka the first six deposits from before 42 ka to after 29 ka resulted from the interplay between slope processes and fluvial redistribution under cold conditions solifluction was the most important slope process no deposits have been found from the last glacial maximum arguably because this period was too dry the last five deposits from about 11 ka to before 0 17 ka resulted from fluvial redistribution of upslope material and older deposits under increasing precipitation current extreme gully erosion in the masotcheni formation indicates a lack of available upslope material leaving downslope deposits as the only sediment source for fluvial redistribution this model for landscape response to climate change may be able to explain how climate controlled landscape processes in other masotcheni formation sites in kwazulu natal in the research area and elsewhere this proposition may be tested with numerical landscape evolution models

paleomagnetism of eocene rocks of the kelowna and castlegar areas british columbia studies in determining paleohorizontal the middle eocene marron volcanics mean age 52 2 ma of the kelowna outlier form the upper part of the hanging wall of the westerly dipping okanagan valley fault ovf in south central british columbia they overlie quesnellia the ovf is currently interpreted as the westernmost member of a network of low angle extension faults in the southern omenica belt the ovf was active in the middle eocene at much the same time that the marron volcanics were cooling relative to present horizontal the magnetizations are widely scattered fisher s precision parameter k 8 and after correction for bedding attitudes there is no significant improvement k 9 evidently some magnetizations were acquired before referred to as category 1 and others after category 2 tilting that is the horizontal plane at the time of magnetization sometimes did and sometimes did not coincide with the bedding plane partial unfolding experiments carried out on the two categories separately yield a precision comparable to t

sources of mud volcano fluids in the gulf of cadiz indications for hydrothermal imprint mud volcanism in the gulf of cadiz occurs over a large area extending from the shelf to more than 3500 m water depth and is triggered by compressional stress along the european african plate boundary affecting a deeply faulted sedimentary sequence of locally more than 5 km thickness the investigation of six active sites shows that mud volcano mv fluids on average are highly enriched in ch4 li b and sr and depleted in mg k and br the purity of the fluids is largely controlled by the intensity of upward directed flow flow rates could be constrained by numerical modelling and vary between 0 05 and 15 cm yr 1 application of d 18o systematics identifies clay mineral dehydration most likely within mesozoic and tertiary shales and marls as the major source of fluids hence cl and na in the pore fluids are mostly depleted below seawater values following a general trend of dilution however deviations from this trend occur and are likely caused by the dissolution of halite in evaporitic deposits other secondary processes overprinting the original fluid composition may occur along the flow path such as dissolution of anhydrite or gypsum and or the formation of calcite and dolomite different sources of fluids are also indicated by variations in 87sr 86sr which range from 0 7086 to 0 7099 at the different sites dehydration may be induced primarily by overburden and tectonic compression however very high concentrations of li and b specifically at captain arutyunov mv camv indicate additional leaching at temperatures above 150 c which could be explained by the injection of hot fluids along deep penetrating major e w strike slip fault systems this hypothesis is supported by the occurrence of generally thermogenic but significantly ch4 enriched light volatile hydrocarbon gases at camv which cannot be explained by shallow microbial methanogenesis li and li b ratios from different types of hot and cold vents are used to infer that high temperature signals seem to be preserved at various cold vent locations and indicate a closer coupling of both systems in continental margin environments than outlined in previous studies

diagenetic formation of gypsum and dolomite in a cold water coral mound in the porcupine seabight off ireland authigenic gypsum was found in a gravity core retrieved from the top of mound perseverance a giant cold water coral mound in the porcupine basin off ireland the occurrence of gypsum in such an environment is intriguing because gypsum a classic evaporitic mineral is undersaturated with respect to sea water sedimentological petrographic and isotopic evidence point to diagenetic formation of the gypsum tied to oxidation of sedimentary sulphide minerals i e pyrite this oxidation is attributed to a phase of increased bottom currents which caused erosion and enhanced inflow of oxidizing fluids into the mound sediments the oxidation of pyrite produced acidity causing carbonate dissolution and subsequently leading to pore water oversaturation with respect to gypsum and dolomite calculations based on the isotopic compositions of gypsum and pyrite reveal that between 21 6 and 28 6 of the sulphate incorporated into the gypsum derived from pyrite oxidation the dissolution of carbonate increased the porosity in the affected sediment layer but promoted lithification of the sediments at the sediment water interface thus authigenic gypsum can serve as a signature for diagenetic oxidation events in carbonate rich sediments these observations demonstrate that fluid flow steered by environmental factors has an important effect on the diagenesis of coral mounds

petrology and geochemistry of rhizoliths from plio pleistocene fluvial and marginal lacustrine deposits east lake turkana kenya abstract recent studies of rhizoliths from the koobi fora formation plio pleistocene of east lake turkana kenya indicate that their shapes vary with the depositional environment of their host sediment vertical rhizoliths are associated with channel bar and overbank deposits of fluvial origin these rhizoliths represent the tap roots of phreatophytes that lived in well drained upland settings horizontal rhizoliths predominate in facies ascribed to beaches lagoons and floodplains associated with ancient lake turkana they are produced by water emergent aquatic macrophytes and coastal grasses that grow in saturated or poorly drained soil environments the rhizoliths consist of sparry and micritic calcite cements whose petrography and geochemistry reflect differences in diagenesis between the two types of root systems the vertical roots contain little organic debris and have poorly developed meniscus and microstalactitic cements these attributes reflect precipitation of the calcite in well oxygenated well drained vadose conditions in contrast the cements of the horizontal root systems lack textures indicative of vadose conditions contain abundant clay and plant debris and display mn concentrations as high as 4 5 cation percent these features confirm that the horizontal rhizoliths developed in chemically reduced water saturated conditions bacterial decay of the plant debris maintained reduced eh conditions while also supply ng abundant mn2 to the pore solutions groundwater that had moved through volcanic strata may have also contributed mn2 the mn may have been incorporated in the calcite cements through a combined process of chemisorption and ionic substitution of mn2 as well as by inclusion of manganese oxides

variability of the western mediterranean sea surface temperature during the last 25 000 years and its connection with the northern hemisphere climatic changes sea surface temperature sst profiles over the last 25 kyr derived from alkenone measurements are studied in four cores from a w e latitudinal transect encompassing the gulf of cadiz atlantic ocean the alboran sea and the southern tyrrhenian sea western mediterranean the results document the sensitivity of the mediterranean region to the short climatic changes of the north atlantic ocean particularly those involving the latitudinal position of the polar front the amplitude of the sst oscillations increases toward the tyrrhenian sea indicating an amplification effect of the atlantic signal by the climatic regime of the mediterranean region all studied cores show a shorter cooling phase 700 years for the younger dryas yd than that observed in the north atlantic region 1200 years this time diachroneity is related to an intra yd climatic change documented in the european continent minor oscillations in the southward displacement of the north atlantic polar front may also have driven this early warming in the studied area during the holocene a regional diachroneity propagating west to east is observed for the sst maxima 11 5 10 2 kyr b p in the gulf of cadiz 10 9 kyr b p in the alboran sea and 8 9 8 4 kyr b p in the thyrrenian sea a general cooling trend from these sst maxima to present day is observed during this stage which is marked by short cooling oscillations with a periodicity of 730 40 years and its harmonics

fluid evolution and authigenic mineral paragenesis related to salt diapirism the mercator mud volcano in the gulf of cadiz the formation of mud volcanoes in the gulf of cadiz is closely linked to diapirism in the deep subsurface the mercator mud volcano mmv is a rare example where diapiric emplacement in addition to being key for upward fluid migration is also an important zone for fluid and mineral diagenesis the most intriguing findings in the near surface muds of the mmv are extremely high salinities of up to 5 2 m of nacl from diapiric and evaporitic halite dissolution and the occurrence of authigenic gypsum and anhydrite crystals both of which have not been observed to date in the gulf of cadiz employing a thermodynamic model we elucidate how the interplay of temperature pulses strong salinity gradients and fluid flow dynamically drive mineral dissolution and re formation the strong increase in salinity in the pore fluids has important implications for thermodynamic equilibria by significantly lowering the activity of water thereby raising the gypsum anhydrite transition zone from 1 km to about 400 m sediment depth at the mmv this transition is further shifted to immediately below the seafloor during intervals of active mud and fluid expulsion when the mv surface temperature is heated up to at least 30 c as a consequence precipitation of authigenic gypsum near the sediment surface 1 2 mbsf has been linked to the dissolution of evaporites below the mmv more precisely the mechanisms generating supersaturation in the ascending gypsum saturated mmv fluids are 1 the slow and constant cooling of these fluids along the geothermal gradient during their ascent leading to formation of ubiquitous micro crystals and 2 the more rapid cooling after a heat pulse or transport from greater and warmer depth during an active mud volcano phase leading to the precipitation of cm scale gypsum crystals or even fist size concretions the mmv fluids approaching the salt diapir from farther below have experienced a genesis similar to those of other mud volcanoes in the gulf of cadiz located above deep rooted faults these processes include clay mineral dewatering thermogenic degradation of organic matter and deep high temperature leaching of terrigenous sediments or continental crust

reconstructions of the continents around the north atlantic at about the 60th parallel abstract late carboniferous early tertiary apparent polar wander apw paths 300 40 ma for north america and europe have been tested in various reconstructions these paths demonstrate that the 500 fathom bullard et al fit is excellent from late carboniferous to late triassic times but the continental configuration in northern pangea changed systematically between the late triassic ca 214 ma and the mid jurassic ca 170 ma due to pre drift extension best fit north atlantic reconstructions minimize differences in the late carboniferous early jurassic and late cretaceous tertiary segments of the apw paths but an enigmatic difference exists in the paths for most of the jurassic whereas for the early cretaceous the data from europe are nearly non existent greenland s position is problematic in a bullard et al fit because of a late triassic early jurassic regime of compression 300 km that would be inherently required for the norwegian shelf and the barents sea but which is geologically not defensible we suggest a radically new fit for greenland in between europe and north america in the early mesozoic this fit keeps greenland locked to europe for the late paleozoic early mesozoic and maintains a reconstruction that better complies with the offshore geological history of the norwegian shelf and the barents sea pre drift a24 extension amounted to approximately 450 km on the mid norwegian shelf but with peak extension in the late cretaceous

differences in hillslope runoff and sediment transport rates within two semi arid catchments in southeast spain this paper focuses on hillslope runoff and sediment transport within two catchments in southeast spain five monitoring sites were established on hillslope concavities throughout the two catchments the techniques used were mini crest stage recorders spray painted lines sediment traps and tipping bucket rain gauges established during previous research results show that a storm event in the rambla nogalte on 30 june 2002 of 83 0 mm was responsible for a maximum runoff depth of 12 cm and a maximum hillslope sediment transport of 1886 cm3 m 1 the same storm in the rambla de torrealvilla produced 53 4 mm of rainfall on the 1 july 2002 had a maximum runoff depth of 26 cm and resulted in 2311 cm3 m 1 of sediment transport there is evidence to suggest that measured sediment transport is related to runoff and a qualitative estimate of morphological runoff zones mrz sediment transport and depth of runoff varied dramatically with lithology marl sites produced most runoff and sediment transport followed by the sites of mixed red and blue schist then blue schist these results are important for understanding the behaviour of slopes and show that for short lived storms with high but not rare rainfall intensities and total rainfall amounts runoff can cause significant hillslope sediment transport in semi arid areas

modern sediment yield compared to geologic rates of sediment production in a semi arid basin new mexico assessing the human impact an erratum has been published for this article in earth surface processes and landforms 29 13 2004 1707 in the semi arid arroyo chavez basin of new mexico a 2 28 km2 sub basin of the rio puerco we contrasted short term rates 3 years of sediment yield measured with sediment traps and dams with long term geologic rates 10 000 years of sediment production measured using 10be examination of erosion rates at different time scales provides the opportunity to contrast the human impact on erosion with background or geologic rates of sediment production arroyo chavez is grazed and we were interested in whether differences in erosion rates observed at the two time scales are due to grazing the geologic rate of sediment production 0 27 kg m 2 a 1 is similar to the modern sediment yields measured for geomorphic surfaces including colluvial slopes gently sloping hillslopes and the mesa top which ranged from 0 12 to 1 03 kg m 2 a 1 the differences between modern sediment yield and geologic rates of sediment production were most noticeable for the alluvial valley oor which had modern sediment yields as high as 3 35 kg m 2 a 1 the hydraulic state of the arroyo determines whether the alluvial valley oor is aggrading or degrading arroyo chavez is incised and the alluvial valley oor is gullied and piped and is a source of sediment the alluvial valley oor is also the portion of the basin most modi ed by human disturbance including grazing and gas pipeline activity both of which serve to increase erosion rates copyright 2004 john wiley sons ltd

reply to comment on paleomagnetism of the upper cretaceous strata of mount tatlow evidence for 3000 km of northward displacement of the eastern coast belt british columbia by p j wynne et al and on paleomagnetism of the spences bridge group and northward displacement of the intermontane belt british columbia a second look by e irving et al

modelling sediment dynamics due to hillslope river interactions incorporating fluvial behaviour in landscape evolution model lapsus landscape evolution models lems simulate the three dimensional development of landscapes over time different lems have different foci e g erosional behaviour river dynamics the fluvial domain hillslopes or a combination lem lapsus is a relatively simple cellular model operating on timescales of centuries to millennia and using annual timesteps that has had a hillslope focus our objective was to incorporate fluvial behaviour in lapsus without changing the existing model equations the model should be able to reproduce alternating aggradation and incision in the floodplains of catchments depending on simulated conditions testing was done using an artificial digital elevation model dem and a demonstration of the ability for fluvial simulation was performed for a real landscape torrealvilla catchment southeast spain model equations to calculate sediment dynamics and water routing were similar for both hillslope and fluvial conditions but different parameter values were used for these domains defined based on annual discharge parameters changing between the domains are convergence factor p which is used in the multiple flow algorithm to route water and discharge and gradient exponents m and n used in transport capacity calculations erodibility and sedimentability factors k and p were changed between cold little vegetation high erodibility and warm conditions more vegetation lower erodibility results show that the adapted parameters reproduced alternating aggradation due to divergent flow in the floodplain and sediment supply under cold conditions and incision due to reduced sediment supply and resulting clean water erosion during simulated warm conditions the simulated results are due to interactions between hillslopes and floodplains as the former provide the sediments that are deposited in the latter similar behaviour was demonstrated when using the real dem sensitivity and resolution analysis showed that the model is sensitive to changes in m n and p and that model behaviour is influenced by dem resolution copyright c 2012 john wiley sons ltd

cretaceous tertiary geodynamics a north atlantic exercise summary new reconstructions are presented for the cretaceous early tertiary north atlantic using a combination of palaeomagnetic hotspot and magnetic anomaly data we utilize these reconstructions in an analysis of previously described misfits between the north atlantic plate elements at successive intervals during this time period we are able to achieve reasonable overlap between the hotspot and palaeomagnetic reconstructions between 40 and 95 ma and thus are able to support the idea that the indo atlantic hotspots are relatively stationary small but systematic discrepancies for this time interval can readily be modelled with a long term octopole non dipole field contribution g3 g30 g10 0 08 however hotspot and palaeomagnetic reconstructions for the early cretaceous north atlantic show substantial differences that cannot be explained by constant non dipole fields and we favour an explanation for these discrepancies in terms of true polar wander tpw triggered by mantle instabilities between 125 and 95 ma this constitutes the only identifiable event of significant tpw since the early cretaceous taken in the context of available geochronological and geological data and seismic tomography from the region the 95 40 ma reconstructions and their time consequent geological products are interpreted in terms of specific conditions of mantle crust coupling and global plate motions tectonic activity highlights from these reconstructions show uniform ne movement of the coupled north american greenland and eurasian plates from 95 to 80 ma a marked cusp in the paths for all three elements at 80 ma where the three plates simultaneously change direction and follow a uniform nw directed motion until c 20 ma when eurasia diverges ne away from the still nw moving greenland and north american elements positioning of the iceland plume beneath the spreading ridge at 20 ma may have increased upwelling below the ridge increased the ridge push and caused a ne shift in the absolute direction of eurasia

late cenozoic landscape development and its tectonic implications for the guadalhorce valley near alora southern spain abstract landscape evolution is the result of a variety of geomorphological processes and their controls in time in southern spain tectonics climate and sea level fluctuations have been some of the main variables controlling long term late cenozoic landscape evolution in the guadalhorce valley malaga geomorphological reconstructions can be undertaken using sedimentary evidence from marine and fluvial deposits as well as erosional evidence such as terrain form and longitudinal profile analysis data are obtained and analysed from the upper miocene to present these allow reconstructions which add information and constraints to the uplift history and landscape development of the area main sedimentation phases are the late tortonian early pliocene and pleistocene important erosional hiatus are found for the middle miocene messinian and late pliocene to early pleistocene these phases of erosion and sedimentation resulted in a relative large and elongated tortonian marine valley filled with complex sedimentary structures next a prolonged stage of erosion of these deposits and incision of the major valley system took place during the messinian in the pliocene a short palaeo guadalhorce in a narrow and much smaller valley existed this valley was partly filled with marine sediments and prograding fan delta complexes during the pleistocene a wider and larger incising river system resulted in rearrangements of the drainage network evaluating the uplift history of the area we found that rates of tectonic activity were higher during the tortonian messinian and upper pleistocene while tectonic activity was lower during the pliocene relative uplift rates for the study area range for the messinian between 160 and 276 m ma 1 for the pliocene between 10 and 15 m ma 1 and for the pleistocene between 40 and 100 m ma 1

rethinking yellowstone in yukon and baja british columbia paleomagnetism of the late cretaceous swede dome stock northern canadian cordillera 1 paleomagnetic results obtained from the 69 8 ma swede dome stock emplaced into the pericratonic yukon tanana terrane ytt west of dawson yukon indicate a minimal northward translation of 360 575 km and a clockwise rotation of 20 23 with respect to north america in accord with the displacement of 425 km along the nearby tintina fault coeval carmacks group volcanics in contrast have previously indicated 1900 km northward translation and minimal rotation and have been proposed to be a displaced manifestation of the fixed yellowstone hot spot thus providing an independent estimate of the late cretaceous paleoposition of the baja british columbia terranes of western north america a compilation of recent mid and late cretaceous paleomagnetic results from the ytt and intermontane belt imb terranes reveals that the carmacks group paleomagnetic result is anomalous the ytt and imb terranes which form the bulk of baja british columbia appear instead to have experienced 1000 km northward translation with respect to north america since 70 ma consistent with geological estimates of motion along plausible accommodating faults in addition past mobility of the hawaii emperor hot spot implies that the pacific hot spots may have experienced 1200 km of southward motion from 81 to 47 ma if so then the paleoposition of the yellowstone hot spot if it existed at 70 ma would likely have produced the carmacks magmatism 1000 km north of yellowstone s current latitude consistent with a moderate 1000 km post 70 ma northward translation of the ytt and imb terranes to their present position in north america

climatically controlled river terrace staircases a worldwide quaternary phenomenon a comparison of fluvial terrace sequences from around the world based on data collected as part of international geoscience programme igcp project no 449 has revealed significant patterns river terraces provide important records of uplift which is essential for their formation and of landscape evolution their cyclic formation however almost invariably seems to have been a response to climatic fluctuation sequences in the european core area of igcp 449 which has the longest and most extensive research history have been used as templates for worldwide comparison there is evidence for a global acceleration of uplift at the time of and perhaps in response to the mid pleistocene revolution when climatic fluctuation switched to 100 kyr milankovitch cycles terraces formed prior to this generally consist of wide aggradational sheets that probably each represent formation over several 41 kyr cycles subsequently river valleys became more steeply entrenched and terraces formed in response to the stronger 100 kyr climatic forcing in many cases at approximately one per cycle this paper uses the new data resource to explore differences between records in different climate zones between sequences with variable numbers of middle late pleistocene terraces and between systems in which the all important incision event has occurred in different parts of climatic cycles key records discussed include european examples from the rhine thames somme dniester dnieper don volga and aguas from asia the gediz turkey and orontes syria from north america the south platte and colorado from south africa the vaal and sundays from australia the shoalhaven and from south america the amazon paraguay and tributaries of the colorado and negro

unravelling late pleistocene and holocene landscape dynamics the upper guadalentin basin se spain abstract landscapes in se spain have developed in response to tectonics climate fluctuations and more recently human activity fluvial and colluvial sediments such as river terraces and slope deposits found in the valleys reflect a complex interplay between landscape forming processes investigating these sediment archives we reconstructed landscape evolution for the upper guadalentin basin se spain placing recent erosion processes in a landscape evolution context palaeo lake sediments dated between 17 and 13 8 ka evidence that a late glacial lake existed in the area probably formed by a sudden blockage of the guadalentin river differences in relative height above the floodplain and age between the river terraces of parts of the guadalentin river indicate that they have not been in equilibrium in the late quaternary deposition of river terraces along the upstream part of the river is recorded at 13 and 9 5 ka whereas no evidence of deposition is found for that period along the lower part of the river there episodes of sedimentation occur at 7 5 5 ka 3 4 1 6 0 7 and 0 4 ka this discrepancy is explained by the palaeo lake and its influence on erosion and sedimentation processes through base level changes combining these processes we propose a schematic model of late pleistocene and holocene landscape evolution from the model we can conclude that i the influence of the palaeo lake on deposition and erosion processes both upstream and downstream is evident and for the younger river terraces that ii episodes of deposition seem to coincide in time but iii episodes of erosion in between terrace level aggradation do not coincide and neither do terrace level heights and iv no evidence of deposition is found for the upstream part of the river correlation of erosion and sedimentation episodes with climate change and human impact is discussed although some correlations can be made there is strong evidence that climate was not the main driver of landscape processes we suggest that internal dynamics and local processes are more important drivers for landscape dynamics in the upper guadalentin basin than external and regional factors

the little ice age in iberian mountains abstract the little ice age lia is known as one of the coldest stages of the holocene most records from the northern hemisphere show evidence of significantly colder conditions during the lia which in some cases had substantial socio economic consequences in this study we investigated the magnitude and timing of climate variability during the lia in the mountains of the iberian peninsula based on a wide range of natural records including from glacial periglacial and lacustrine peatland areas fluvial alluvial deposits speleothems and tree rings historical documents and early instrument data the onset of the lia commenced in approximately ce 1300 and cold conditions with alternating moisture regimes persisted until approximately ce 1850 the environmental responses ranged from rapid e g tree rings to delayed e g glaciers the colder climate of the lia was accompanied by severe droughts floods and cold heat waves that showed significant spatio temporal variation across the iberian mountains several phases within the lia have been detected including a 1300 1480 increasing cooling with moderate climate oscillations b 1480 1570 relatively warmer conditions c 1570 1620 gradual cooling d 1620 1715 coldest climate period of the lia particularly during the maunder minimum with temperatures approximately 2 c below those at present e 1715 1760 warmer temperatures and a low frequency of extreme events f 1760 1800 climate deterioration and more climate extremes i e cold and heat waves floods and droughts g 1800 1850 highly variable climate conditions alternating with stability 1800 1815 extreme events 1815 1835 and a slight trend of warming associated with intense hydrometeorological events 1835 1850 h since 1850 a gradual staggered increase in temperature of approximately 1 c post lia warming has led to substantial changes in geo ecological dynamics mainly through shrinking of the spatial domain affected by cold climate processes

response of quaternary fluvial systems to differential epeirogenic uplift aguas and feos river systems southeast spain the geomorphic expression of two fluvial systems the rio de aguas and the rambla de los feos in southeast spain reflects their adjustment to differential epeirogenic uplift and local tectonic activity during the quaternary regional uplift of a depositional marine surface resulted in the development of a southward flowing drainage network during late pliocene early pleistocene time disruption of this consequent drainage began as the alhamilla cabrera sierras and the sorbas basin were differentially uplifted relative to the surrounding basins the ancestral feos drainage responded by incision across the uplift through a combination of superimposition and antecedence differential uplift of the sorbas basin enhanced headward erosion of strike oriented drainages and promoted capture of the ancestral feos drainage by the rio de aguas during the late pleistocene stratigraphic relations and soil development indicate that epeirogenic uplift and local tectonics together with climatic fluctuations have influenced the development of the drainage systems throughout the quaternary

transition from alluvial to fluvial systems in the guadalentin depression se spain during the holocene lorca fan versus guadalentin river abstract the lorca alluvial fan se spain constitutes an excellent example of transition from alluvial to fluvial sedimentary environments in a semiarid region the fan body represents a large gently sloping alluvial fan of mainly sandy silty composition it is presently dissected throughout its length by the guadalentin river which worked as the main fan channel and still operates as a torrential rambla type channel responsible for historic large flood events three different outcrops are analysed at fan apex mid fan and distal fan locations taking also into account the different inset terrace levels developed within the main fan trench at 8 9 m 5 6 m 3 4 m and 1 2 m above the present thalweg available radiocarbon data and archeological remains collected in fan sediments and inset terraces enable the construction of a preliminary hypothesis about the progressive incision of the fan body from pre historical to historical times proximal fan aggradation took place during the early holocene before 7900 7700 cal yr bp and continued until the late neolithic to calcolithic period 5500 4200 cal yr bp when the fan surface stabilised and channel incision generated a first fanhead trench subsequent infilling of the fan trench led to the development of the upper terrace level 8 9 m which merged with the palustrine environments 23 km downstream of lorca feeding distal fan lobes during late bronze age and post roman times the second terrace level 5 6 m is a cut fill episode of about 5 m thickness developed from roman times and dated to 1700 to 950 cal yr bp the geometry and altimetry of the upper terrace level together with the occurrence of different steps in the longitudinal profile of the river at mid to distal fan locations strongly suggest that the incision of the ancient fan channel was assisted by intersection point headcut development sensu harvey a m 1978 dissected alluvial fans in southeast spain catena 5 177 211 at proximal mid fan locations but by headward erosion exerted by neighbouring drainage basins at distal palustrine environments therefore the lorca fan exemplifies the behaviour of large sized fans in its transition from pure alluvial environments to fluvial ones and its eventual incipient integration into a regional drainage network subject to a dynamic base level during the historic period

new 42 ma cratonic north american paleomagnetic pole from the yukon underscores another cordilleran paleomagnetism geology conundrum eocene posttectonic plutons of the beaver river alkalic complex in southeastern yukon intruded devonian mississippian and triassic sandstones in the foothills of the canadian cordillera a paleomagnetic collection of 27 sites from three separate plutons produced 326 specimens that were analyzed using alternating field and thermal step demagnetization methods the a component characteristic remanent magnetization chrm resides in magnetite with normal polarity in the 42 6 0 8 ma beaver river pluton reversed polarity in the 42 1 0 7 ma larson creek east pluton and both polarities in the 41 3 0 4 ma larson creek west pluton corresponding with magnetic polarity chrons 20n 19r and the boundary between chron 19r and 18n respectively the chrms of the plutons are indistinguishable 2 with a mean for the 42 0 0 5 ma complex of d 158 8 i 73 1 n 21 sites 95 3 0 k 116 8 a positive paleomagnetic contact test shows the a component to be primary and the poorly isolated b component

eocene rotation of the coast plutonic complex and intermontane belt paleomagnetism of eocene plutons along the klondike highway paleomagnetic results are reported for the 59 ma skagway 54 ma fraser 53 ma summit lake and 48 ma clifton felsic plutons of the eastern coast plutonic complex cpc that outcrop along the south klondike highway in alaska and british columbia thermal and alternating field step demagnetizing methods yielded stable characteristic remanent magnetization chrm directions for all 29 sites of normal reversed and mixed polarity the chrm resides in single or pseudosingle domain magnetite and or pyrrhotite that is shown to be primary by contact tests with the 47 ma vertical white pass mafic dikes paleopoles from six 56 to 50 ma mean 52 2 ma intermontane belt yukon tanana terrane imb ytt units that cannot be explained by tectonic tilt are compared with nine clustered 59 to 46 ma mean 52 4 ma eastern cpc paleopoles both paleopole populations show nonsignificant poleward northward translation relative to north america imb ytt 3 7 5 3 n cpc 4 3 6 4 s overall 1 2 4 9 s ind

interpreting the response of a dryland river system to late quaternary climate change abstract a u series calcrete chronology has been constructed for three late quaternary terrace units termed the d1 d2 and d3 terraces in age descending order from the rio aguas river system of the sorbas basin southeast spain the d1 terrace formed between 30 300 4400 year bp and 12 140 360 year bp correlating well with the last glacial maximum when rates of sediment supply would have increased greatly because of higher rates of weathering reduced vegetation cover and weak soil development the d2 terrace formed between 12 800 1100 year bp and 9 600 530 year bp correlating well with the younger dryas event the d3 terrace could only be poorly constrained to the early holocene and no unequivocal cause could be assigned to this period of aggradation the sedimentology and geomorphology of the d2 terrace suggests however that the aggradation of this unit was a response to diapirism karstic processes occurring within the underlying messinian gypsum strata and the subsequent damming of the aguas system therefore despite its coincident occurrence with the younger dryas aggradation of the d2 terrace is unrelated to climate change the style of this response controlled predominantly by the characteristics of the underlying bedrock makes correlating the terrace record of the aguas with other systems in the mediterranean unreliable this study therefore highlights the problems of correlating fluvial sequences in regions of variable tectonics climatic history and bedrock geology and emphasises the need to properly understand the main controls on individual fluvial systems before any attempt is made to correlate their depositional histories

testing terrane transport an inclusive approach to the baja b c controversy the baja british columbia hypothesis holds that a large segment of the western edge of northern north america baja b c was situated alongside california and northern mexico in middle cretaceous time was displaced northward in the late cretaceous and paleocene by north oblique convergence of the kula plate with north america and arrived near its present location by the early eocene a consistent body of paleomagnetic data supports this hypothesis however doubt persists and various crucial tests of a geologic nature have been proposed one such test concerns the provenance of zircons in cretaceous sedimentary basins of baja b c in this paper we use both paleomagnetic data and zircon occurrences to reconfirm the baja b c hypothesis we first argue that the only truly crucial tests yet performed have been paleomagnetic and that all such tests have been positive second we show that detrital zircon data from the upper cretaceous nanaimo group although not a crucial test provide valuable paleogeographic information available data demonstrate a change in detrital zircon provenance in the nanaimo group that closely matches the position of these rocks predicted by the baja b c hypothesis detrital zircons in the nanaimo group suggest a change from a southwestern north american source rich in grenville and 1 4 1 5 ga rocks to an increasing contribution from older parts of the craton such as the wyoming province together detrital zircons and paleomagnetic inclinations allow us to assemble a detailed schedule of northward tectonic transport of the baja b c terranes