depositional history and sequence stratigraphy of the precambrian cambrian boundary stratotype section chapel island formation southeast newfoundland abstract facies relationshps in the vendian to lower cambrian chapel island formation of southeast newfoundland are used to establish a sequence stratigraphic framework for this important boundary stratotype section the formation consists of five members of sandstone mudstone and minor limestone deposited in a variety of shoreline to shelf environments peritidal sandstone and shale units in member 1 are overlain by sandstone and silstone deltaic and shelf deposits of member 2 these make up a transgressive system tract in which small scale changes in relative sea level are superimposed on autocyclic deltaic processes the thickness 400 m of nearshore and inner shelf sediments resulted from high sediment accumulation rates which for member 2 nearly kept pace with subsidence upper member 3 and member 4 consist of inner shelf mudstone and peritidal limestone that were deposited in a low energy oxygen stratified basin these deposits are arranged in three large scale shoaling cycles representing three foresteping parasequences of one highstand systems tract an extensive limestone bed at the tope of member 4 contains a sequence boundary associated with or shortly postdating development of this surface is a significant epeirogenic event that resulted in basin reorganization increased subsidence and progradation of a thick clastic sequence represented by member 5 the deposits of this upper member consist of an upward coarsening storm dominated shelf to shoreface succession of sandstone and silstone deposits of nearly identical character are also found in new brunswick and suggest that these sediments and the underlying sequence boundary could be significant for interregional correlation global correlation of the paleobathymetric curve developed for the chapel island formation is considered unfeasible given the long history of epeirogenic movements during the vendian and early cambrian in this region

experiments of dike induced deformation insights on the long term evolution of divergent plate boundaries the shallow transport of magma occurs through dikes causing surface deformation our understanding of the effects of diking at the surface is limited especially on the long term for repeated intrusive episodes we use analogue models to study the upper crustal deformation induced by dikes we insert metal plates within cohesive sand with three setups in setup a the intrusion rises upward with constant thickness and in setups b and c the intrusion thickens at a fixed depth with final rectangular setup b or triangular setup c shape in section setup a creates a doming delimited by reverse faults with secondary apical graben without close correspondence in nature in setups b and c a depression flanked by two uplifted areas is bordered by inward dipping normal faults propagating downward and for deeper intrusions in setup b also by inner faults reverse at the surface this deformation is similar to what is observed in nature suggesting a consistent physical behavior dikes in nature initially propagate developing a mode i fracture at the tip subsequently thickened by magma intrusion without any host rock translation in the propagation direction as in setup a the deformation pattern in setups b and c depends on the intrusion depth and thickness consistently to what is observed along divergent plate boundaries the early deformation in setups b and c is similar to that from a single rifting episode i e lakagigar iceland and dabbahu afar whereas the late stages resemble the structure of mature rifts i e krafla iceland confirming diking as a major process in shaping divergent plate boundaries

rainfall and recharge to a dolomite aquifer in a semi arid climate at kabwe zambia abstract rainfall at kabwe is stable over long periods of time but varies considerably in the short term over periods of approximately 8 and 4 years corresponding variations are present in the recharge to a dolomite aquifer using a slightly modified version of the penman grindley recharge model it is possible to make estimates of recharge from rainfall and evaporation data the validity of the model is verified by comparison with borehole hydrographs estimates of specific yield from the hydrographs agree closely with those determined by conventional pumping tests

reconstructing the avalonia palaeocontinent in the cambrian a 519 ma caliche in south wales and transcontinental middle terreneuvian sandstones an early cambrian caliche on the st non9s formation emended is the base of the caerfai bay formation unit term changed at caerfai bay south wales subaerial exposure and the caliche mean the two formations were not genetically related units the st non9s is an older sand sheet likely tidalitic not delta related referred to avalonian depositional sequence ads 2 and the caerfai bay is a shallow mud basin unit refered to ads 4a the similar random formation upper ads 2 in north american avalonia has a basal age of c 528 ma and is unconformably overlain by red mudstones or sandstones in fault bounded basins on the avalonian inner platform coeval british sandstones lower hartshill wrekin st non9s brand hills are unconformably overlain by latest terreneuvian ads 3 or epoch 2 ads 4a units dates of 519 ma on caerfai bay ashes give an upper bracket on the late appearance of avalonian trilobites and suggest an ads 2 4a hiatus of several million years post st non9s and post random basin reorganization led to abundant caerfai bay formation volcanic ashes and sparse brigus formation ashes in newfoundland the broad extent of erosional sequence boundaries that bracket lithologically similar to identical units emphasize that east and west avalonia formed one palaeocontinent the inner platform in southern britain was larger than the midlands craton a tectonically defined later palaeozoic area unrelated to terminal ediacaran early palaeozoic depositional belts the cool water successions of early palaeozoic avalonia were distant from coeval west gondwanan carbonate platforms

itrf2000 a new release of the international terrestrial reference frame for earth science applications 1 for the first time in the history of the international terrestrial reference frame the itrf2000 combines unconstrained space geodesy solutions that are free from any tectonic plate motion model minimum constraints are applied to these solutions solely in order to define the underlying terrestrial reference frame trf the itrf2000 origin is defined by the earth center of mass sensed by satellite laser ranging slr and its scale by slr and very long baseline interferometry its orientation is aligned to the itrf97 at epoch 1997 0 and its orientation time evolution follows conventionally that of the no net rotation nnr nuvel 1a model the itrf2000 orientation and its rate are implemented using a consistent geodetic method anchored over a selection of itrf sites of high geodetic quality ensuring a datum definition at the 1 mm level this new frame is the most extensive and accurate one ever developed containing about 800 stations located at about 500 sites with better distribution over the globe compared to past itrf versions but still with more site concentration in western europe and north america about 50 of station positions are determined to better than 1 cm and about 100 sites have their velocity estimated to at or better than 1 mm yr level the itrf2000 velocity field was used to estimate relative rotation poles for six major tectonic plates that are independent of the trf orientation rate a comparison to relative rotation poles of the nuvel 1a plate motion model shows vector differences ranging between 0 03 and 0 08 m y equivalent to approximately 1 7 mm yr over the earth s surface itrf2000 angular velocities for four plates relative to the pacific plate appear to be faster than those predicted by the nuvel 1a model the two most populated plates in terms of space geodetic sites north america and eurasia exhibit a relative euler rotation pole of about 0 056 0 005 m y faster than the pole predicted by nuvel 1a and located about 10 n 7 e more to the northwest compared to that model

cardium formation u cretaceous at seebe alberta storm transported sandstones and conglomerates in shallow marine depositional environments below fair weather wave base as a result of detailed mapping at seebe alberta we have defined five coarsening upward sequences in the turanian cardium formation the sequences begin with bioturbated mudstones and coarsen int

crustal deformation measured by gps in the south iceland seismic zone due to two large earthquakes in june 2000 two large earthquakes struck the south iceland seismic zone in june 2000 the first on june 17 mw 6 5 and the second on june 21 mw 6 4 these are the largest earthquakes in the area in the past 88 years a network of gps stations was remeasured followingthe earthquakes the whole network was last measured in 1995 and partly in 1999 we correct for the interseismic motion from 1995 to 2000 to obtain the coseismic displacements the largest co seismic motion we observe is about 0 55 m in the epicentral area of the june 17 event we model the surface deforma tion for the two earthquakes usingrectang ular dislocations in an elastic half space best fit uniform slip models indi cate that the events occurred on two parallel n s vertical faults with right lateral strike slip motion this is the same style of faultingbelieved to have occurred in larg e historical earthquake sequences in south iceland

latest precambrian to early cambrian basin evolution fortune bay newfoundland fault bounded basin to platform uppermost precambrian and lowest cambrian sediments of the rencontre chapel island and random formations in the fortune bay area western avalon zone consist of conglomerates sandstones and shales deposited in fluvial marginal marine and open marine settings deposition began in a small fault bounded basin alternation between nonmarine and marine deposition resulted from pulses in fault activity uplift and coarse terrestrial clastics separated by quiescent periods of basinwide thermal subsidence transgressive fine grained marine units overstepping earlier basin margins the tectonic regime may have been extensional rift or transtensional strike slip pull apart a strike slip origin is easiest to defend and is consistent with current tectonic models for the avalon zone involving prolonged extension or transtension but little spreading the fortune bay basin persisted until the beginning of the cambrian period at which time eustatic sea level rise led to widespread transgression and d

rift transform kinematics in south iceland deformation from global positioning system measurements 1986 to 1992 crustal deformation in the plate boundary regions in south iceland is estimated from repeated global positioning system gps geodetic measurements in the period 1986 1992 we compare coordinate solutions for the 1986 and 1989 surveys with the results from the most recent survey in 1992 horizontal position uncertainty is about 2 cm for the 1986 and 1989 coordinates and about 4 mm for the 1992 coordinates little internal deformation is observed in the area west of the western volcanic zone within the north american plate and at the southern tip of the eastern volcanic zone within the eurasian plate the observed relative velocity of these two areas is 2 1 0 4 cm yr in direction n117 11 e 1 uncertainties compatible with the 1 94 cm yr widening in direction n 104 e across south iceland predicted from the nuvel 1 global plate motion model left lateral shear strain is developing across the intervening transform zone the e w trending south iceland seismic zone sisz strain is concentrated within a 20 to 30 km wide zone that correlates with seismic activity in the sisz about 85 15 of the relative plate motion is accommodated by this zone in such a way that the area south of the sisz is moving toward the east with the eurasian plate and the area north of the sisz is moving toward the west with the north american plate accordingly north of the sisz the western rift zone can accommodate a maximum of 15 15 of the relative plate motion within the sisz the shear strain results in an anticlockwise rotation of lineaments oriented north south at a rate of 0 5 1 rad yr the shear strain accumulation can be accommodated by bookshelf faulting on mapped recent north south faults in the sisz if the deformation is accommodated by an array of n s faults spaced 1 5 km apart an average slip rate of about 0 5 5 mm yr is required on each fault the rate of geometric moment release due to earthquakes averaged over centuries m 0 expected from such an array is about the same as expected from a simple transform fault 2vad where 2v is the relative plate motion a is the total length of the seismic zone and d is the thickness of the brittle crust if 2v 0 85 0 15 1 94 cm yr d 10 15 km ana a 75 85 km then m 0 1 0 2 5 107 m3 yr comparable to the rate of geometric moment release in large historical earthquakes in the sisz for the last several centuries we conclude that historical seismicity in the sisz can be attributed to left lateral shear accumulation across the seismic zone at a similar rate throughout historical times as during the years 1986 1992

fault and magmatic interaction within iceland s western rift over the last 9 kyr we present high resolution chirp sub bottom profiler data from thingvallavatn a lake in iceland s western rift zone these data are combined with stratigraphic constraints from sediment cores to show that movement on normal faults since 9 ka are temporally correlated with magmatic events indicating that movements were controlled by episodic dyke intrusion sediment depo centres and the focus of subsidence migrated westwards over 3 4 kyr towards the locus of subsequent brittle failure we interpret this subsidence as related to dyke intrusion a few km along strike originating from the hengill volcanic system which occurred prior to major dyking faulting and subsidence within the lake at 1 9 ka

tidal deposits of the lower cambrian random formation eastern newfoundland facies and paleoenvironments the avalon tectonostratigraphic zone occupies about 25 of the area of insular newfoundland late precambrian development of the avalon terrane is distinctly different than that of other parts of the appalachian orogen and cratonic north america late precambrian volcanism and tectonic instability gave way to deposition of about 2 km of cambrian and lower ordovician dominantly epiclastic sediments on a slowly subsiding relatively stable shelf platform the lower cambrian random formation is part of the platformal sequence and is bounded by regional disconformities over much of the newfoundland avalon zone except around fortune bay where it is underlain by older terrestrial and shallow marine sediments the random formation was deposited during a time of global sea level rise and consists of up to 250 m of shoreline nearshore and open shelf deposits that record macrotidal conditions and periodic storm activity cross bedded quartzarenites occur in units to about 50 m thick one exceptional unit is 110

methods of evaluating recent crustal movementsstatistical tests for detecting movements in repeatedly measured geodetic networks geodetic networks with two or more measuring epochs can be found rather frequently for example in connection with the investigation of recent crustal movements in the field of monitoring problems in engineering surveying or in ordinary control networks for these repeatedly measured networks the so called congruency problem has to be solved i e possible changes in the geometry of the net have to be found in practice distortions of bench marks and an extension or densification of the net differences in the 1st order design and or changes in the measuring elements or techniques differences in the 2nd order design can frequently be found between different epochs in this paper a rigorous mathematical procedure is presented for this congruency analysis of multiple measured networks taking into account these above mentioned differences in the network design as a first step statistical tests are carried out to detect the epochs with departures from congruency as a second step the individual points with significant movements within these critical epochs can be identified a numerical example for the analysis of a monitoring network with 9 epochs is given

groundwater recharge in the victoria nile basin of east africa support for the soil moisture balance approach using stable isotope tracers and flow modelling across equatorial africa increasing demand for groundwater has raised concerns about resource sustainability and has highlighted the need for reliable estimates of groundwater recharge recharge investigations in this environment are typically inhibited by a shortage of good quality meteorological and hydrogeological records moreover when recharge studies are attempted they tend to rely on a single technique and frequently lack corroborating evidence to substantiate recharge predictions in recent studies undertaken in the aroca catchment of the victoria nile basin in central uganda the timing and magnitude of recharge determined by a soil moisture balance approach are supported by stable isotope data and groundwater flow modelling the soil moisture balance study reveals that recharge averages in the order of 200 mm year 1 and is more dependent on the number of heavy more than 10 turn day 1 rainfall events than the total annual volume of rainfall stable isotope data suggest independently that recharge occurs during the heaviest rains of the monsoons and further establish that recharge stems entirely from the direct infiltration of rainfall an assumption implicit in the soil moisture balance approach deforestation over the last 30 years is shown to have more than doubled the recharge estimate aquifer flow modelling supports the recharge estimates but demonstrates that the vast majority over 99 of recharging waters must be transmitted by the aquifer in the regolith rather the underlying bedrock fractures which have traditionally been developed for rural water supplies

ediacaran events boundary relationships and correlation of key sections especially in armorica the transitional interval between the adelaidean and ediacaran systems in the central flinders ranges south australia comprises mainly basinal sediments with some tuff beds bunyeroo formation and a widespread thin dolomite bed which apparently evidences a brief regressive episode base of wonoka formation body imprints of metazoans trace fossils and probable faecal pellets are present at various levels in the ediacaran succession comparable assemblages occurring in key successions in southern africa northern russia siberia newfoundland and england promise a global biostratigraphy one ediacaran body fossil occurs in the yangtze gorges section china analysis of abundant late precambrian radiometric data for the present north atlantic margins suggests that the ediacaran may be dated between about 590 ma and 545 540 ma

an unusual mid cambrian faunule from st john s island fortune bay newfoundland three trilobites hypagnostus aff clipeus cotalagnostus sp nov and pagetides johannis sp nov not previously recorded in newfoundland are associated with onymagnostus cf hybridus h mammillatus peronopsis cf fallax minor paradoxides p davidis davidis p p cf abenacus brunswickia b cf jaculator b jincella sp agraulos sp and some hyolithids stenothecid molluscs and orthid acrotretid and lingulate brachiopods in a thin limestone within dark grey slaty mudstones of the young s cove formation on st john s island fortune bay a stratigraphical position within the cambrian punctuosus zone in the upper part of the drumian stage is indicated the presence of the oculate eodiscid pagetides in late mid cambrian rocks within the avalon tectonostratigraphical zone is highlighted because the genus was previously only known associated with the much earlier cambrian olenellid zones of laurentia paradoxides p cf abenacus and the species of brunswickia b close to peregrina

tidal deposition in the basal upper cambrian mt simon formation in wisconsin the upper cambrian mt simon formation 0 65 m thick is a basal quartz arenite exposed in westcentral wisconsin a detailed field investigation of the physical and biogenic sedimentary structures of the mt simon has led to the recognition of three distinct lithofacies the lower one unconformably overlies precambrian basement rocks it consists of medium to very large scale sets of tabular and trough cross bedded medium to very coarse grained sandstone and pebbly sandstone with minor intercalated horizontal beds of very fine to medium grained sandstone siltstone and shale sparse examples of skolithos and arenicolites are present this facies consists of a very thin sequence of possible braided fluvial and marine foreshore deposits overlain by probable marine shoreface and tidal channel deposits much of the facies seems to represent shallow subtidal deposition in a relatively high energy regime the middle lithofacies consists of two distinctly different subfacies which probably were deposited in a low tidal flat setting the higher energy subfacies consists of small to medium scale sets of tabular and trough crossbedded fine to coarse grained sandstones containing distinct zones dominated by skolithos and arenicolites this subfacies probably represents deposition in meandering tidal channels the lower energy subfacies consists of thinbedded horizontally laminated and ripple cross laminated very fine to medium grained sandstone siltstone and shale with common specimens of cruziana rusophycus and planolites this subfacies probably represents deposition on lower energy tidal flats adjacent to the tidal channels the upper lithofacies consists predominantly of structureless densely bioturbated very fine to coarse grained sandstone containing abundant specimens of skolithos the upper few meters of the facies consists of small to medium scale sets of trough cross bedded very fine to coarse grained sandstone with layers of disarticulated valves of the brachiopod obolus the upper facies probably represents deposition on tidal flats perhaps in a midtidal flat setting characterized by slower sedimentation rates a correspondingly higher degree of bioturbation persistent reworking of shelled macrobenthos and periodic subaerial exposure the mt simon formation is interpreted as a largely progradational regressive shoaling and fining upward tidal sequence a marine interpretation is supported by the widespread occurrence of marine trace fossils within this unit evidence for a tidal origin is seen in the presence of unimodal cross strata associated with reactivation surfaces compound cross strata numerous scour and truncation surfaces lined with intraformational conglomerates common clay drape laminae separating sets of cross strata interference and flat topped ripple marks and desiccation cracks sedimentation continued without apparent interruption as the overlying eau claire formation was deposited also under tidal influence recent reinterpretations of other basal cambrian cratonic quartz arenites together with this new interpretation for the mt simon formation suggest that the long held concept of basal transgressive sandstones deposited as blankets across the craton may be too simplistic for deposition in braided fluvial marginal marine tidal flat tidal channel and marine foreshore and shoreface environments seems indicated

throw rate variations within linkage zones during the growth of normal faults case studies from the western volcanic zone iceland abstract this work investigates how throw rates vary within fault bends and sites of fault linkage during the process of normal fault growth in the western volcanic zone iceland through detailed field mapping and field measurements of fault throws normal faults are mapped and along strike throw profiles are constructed in order to understand how the throw rates relate with the local fault geometry along faults at different stages of linkage the results show that throw rates increase within linkage zones and propagating fault bends independently from the stage of maturity of the fault bend this implies that 1 the relationship between the local fault geometry and the along strike distribution of throw rate is driven by the deeper part of the fault where established fault bends start propagating to the surface 2 faults grow first by linkage and coalescence of separate faults and then by accumulation of slip on the resultant fault in agreement with models of fault growth by linkage and coalescence 3 incipient fault bends can produce uncertainty associated with palaeoseismological results if fault bends remain unrecognised moreover this work demonstrates that existing models showing increased co seismic and throw rates within fault bends and sites of fault linkage found in continental extensional settings are valid in a geodynamic context of a mid oceanic rifts

a candidate stratotype for the precambrian cambrian boundary fortune head burin peninsula southeastern newfoundland the burin peninsula exhibits an exceptionally thick and essentially continuous succession of marine strata through the precambrian cambrian transition fossils are abundant and include trace fossils small shelly fossils vendotaenid algae soft bodied megafossils and microfossils the burin peninsula is readily accessible and has long been considered a potential area for a precambrian cambrian boundary stratotype a continuous section through the upper part of member 1 and all of member 2 of the chapel island formation is exposed at fortune head and this section is herein proposed as a global stratotype for the precambrian cambrian boundary the boundary horizon is located 2 4 m above the base of member 2 of the chapel island formation this horizon marks the base of the basal cambrian phycodes pedum ichnofossil zone and immediately overlies the top of the late precambrian harlaniella podolica ichnofossil zone shelly fossils sabelliditids first appear a few metres below the proposed boundary sof

an integrated global model of present day plate motions and plate boundary deformation summary in this paper we present a global model gsrm 1 of both horizontal velocities on the earth s surface and horizontal strain rates for almost all deforming plate boundary zones a model strain rate field is obtained jointly with a global velocity field in the process of solving for a global velocity gradient tensor field in our model we perform a least squares fit between model velocities and observed geodetic velocities as well as between model strain rates and observed geological strain rates model velocities and strain rates are interpolated over a spherical earth using bi cubic bessel splines we include 3000 geodetic velocities from 50 different mostly published studies geological strain rates are obtained for central asia only and they are inferred from quaternary fault slip rates for all areas where no geological information is included a priori constraints are placed on the style and direction but not magnitude of the model strain rate field these constraints are taken from a seismic strain rate field inferred from normalized focal mechanisms of shallow earthquakes we present a global solution of the second invariant of the model strain rate field as well as strain rate solutions for a few selected plate boundary zones generally the strain rate tensor field is consistent with geological and seismological data with the assumption of plate rigidity for all areas other than the plate boundary zones we also present relative angular velocities for most plate pairs we find that in general there is a good agreement between the present day plate motions we obtain and longterm plate motions but a few significant differences exist the rotation rates for the indian arabian and nubian plates relative to eurasia are 30 13 and 50 per cent slower than the nuvel1a estimate respectively and the rotation rate for the nazca plate relative to south america is 17 per cent slower on the other hand caribbean north america motion is 76 per cent faster than the nuvel 1a estimate while crustal blocks in the india eurasia collision zone move significantly and self consistently with respect to bounding plates only a very small motion is predicted between the nubian and somalian plates by integrating plate boundary zone deformation with the traditional modelling of angular velocities of rigid plates we have obtained a model that has already been proven valuable in for instance redefining a no net rotation model of surface motions and by confirming a global correlation between seismicity rates and tectonic moment rates along subduction zones and within zones of continental deformation

the lower palaeozoic of oman and its context in the evolution of a gondwanan continental margin the lower palaeozoic haima group of the sultanate of oman comprises a sequence dominated by siliciclastic rocks up to several kilometres thick and broadly divisible into two groups the sequence is known in outline from subsurface exploration but recent field work on outcrops in the isolated huqf area in east central oman has allowed a more detailed environmental interpretation of the succession at the base coarse continental deposits of the lower haima group rest unconformably on precambrian lower cambrian huqf group sediments mainly carbonates and evaporites the overlying upper haima group comprises from base to top the aeolian dominated amin formation the non marine coastal plain to shallow marine intertidal subtidal sediments of the andam formation the non marine to marginally marine ghudun formation and the complex cyclical deep to shallow water deposits of the safiq formation correlation of the haima group of oman with the lower palaeozoic of the arabian peninsula north africa and iran allows the evolution of the gondwanan margin to be modelled a widespread lower cambrian sequence of coarse alluvium resting on peneplained upper precambrian infracambrian huqf group strata represents the final stage of uplift and basin fill associated with the late proterozoic suturing of arabia and adjacent plates which resulted in the formation of the gondwanan continent the overlying thick sequence of continental fluvial and aeolian sediments was deposited in a series of stable intracratonic basins across the gondwanan landmass in the mid and late cambrian an overall sea level rise led to the repeated development of shallow marine shelf carbonates across the margin the subsequent replacement of this marginal carbonate sequence with a thick marginal to non marine sand dominated sequence may reflect the interplay of several events the drift of gondwana towards more southerly latitudes a phase of strong tectonic rejuvenation during the latest cambrian early ordovician and or a eustatic fall in sea level organic rich marine mudrocks were deposited over much of the gondwanan platform during a series of marked eustatic sea level rises during the mid late ordovician and early silurian in oman no evidence has yet been found for the significant late ordovician glacial event recorded from north africa and saudi arabia

strain accumulation 1986 1992 across the reykjanes peninsula plate boundary iceland determined from gps measurements gps geodetic observations 1986 1992 spanning the oblique plate boundary on the reykjanes peninsula sw iceland show that left lateral shear strain is accumulating in the area the principal strain rates are 1 0 255 0 055 strain yr extension at n121 6 e and 2 0 190 0 053 strain yr contraction at n31 6 e the principal axis of extension is perpendicular to the strike of fractures within volcanic systems on the peninsula the direction of maximum left lateral shear strain is n76 6 e the same as the trend of the seismic zone on the peninsula tensor shear strain in this direction is 0 222 0 054 strain yr continuous aseismic slip of the north american eurasian plates below a 5 11 km locking depth on the peninsula can explain the observed depth of earthquakes the width of the deformation zone determined from recent fissuring and faulting and the gps measurements of strain

the influence of tectonic setting on the hydrological characteristics of deeply weathered terrains evidence from uganda abstract deeply weathered landscapes occur throughout equatorial regions and are transformed by cycles of deep weathering and stripping these processes are driven by rainfall that infiltrates the subsurface as groundwater recharge or runs across the landsurface recent work in uganda demonstrates that long term 10 5 10 6 a cycles of deep weathering and stripping are tectonically controlled the influence of tectonics on the present day hydrological regime and hence contemporary geomorphic process is examined in this study the hydrological characteristics of two humid basins in uganda were determined using soil moisture balance techniques hydrograph separation methods borehole hydrographs and stable isotope 2 h 18 o tracers these were in turn related to the dominant geomorphic process deep weathering or stripping suggested by the local tectonic history in central uganda where deep weathering of the landsurface has occurred since the miocene soil moisture balance calculations monitoring well records and stable isotope data show that groundwater recharge is derived from monsoon rainfall is in the order of 120 mm a 1 and greatly exceeds surface runoff of 3 4 mm a 1 basin output occurs as evapotranspiration from a wetland that runs centrally through the catchment consistency in this discharge despite highly seasonal rainfall reflects a large basin storage that is permitted by a thick weathered mantle in south western uganda where stripping of the landsurface has occurred since the mid pleistocene soil moisture balance calculations and hydrograph separation techniques indicate groundwater recharge is restricted to years of exceptionally high rainfall annual surface runoff 34 mm a 1 generated primarily from monsoon rainfall events exceeds the recharge flux 8 15 mm a 1 streamflow discharge varies considerably from 0 2 to 14 m 3 s 1 and occurs along well incised drainage channels the comparatively smaller basin storage results from a thinner partially stripped weathered mantle the influence of tectonics is indicated by the conclusion that deep weathering associated with prolonged tectonic stability in central uganda is facilitated by a recharge dominated hydrological regime whereas stripping prompted by mid pleistocene tectonic uplift in south western uganda continues to occur under a runoff dominated regime

shallow water gravity flow deposits chapel island formation southeast newfoundland canada a remarkable suite of shallow water gravity flow deposits are found within very thinly bedded siltstones and storm generated sandstones of member 2 of the chapel island formation in southeast newfoundland medium to thick siltstone beds termed unifites range from non graded and structureless type 1 to slightly graded with poorly developed lamination type 2 to well graded with lamination similar to that described for fine grained turbidites type 3 unifite beds record deposition from a continuum of flow types from liquefied flows type 1 to turbidity currents type 3 calculations of time for pore fluid pressure dissipation support the feasibility of such transitions raft bearing beds consist of siltstone with large blocks or rafts of thinly bedded strata derived from the underlying and adjacent substrate characteristics suggest deposition from debris flows of variable strength estimates of debris strength and depositional slope are calculated for a pebbly mudstone bed using measurable and assumed parameters an assumed density of 2 0 g cm 1 and a compaction estimate of 50 gives a strength estimate of 79 7 dyn cm 2 and a depositional slope estimate of 0 77 the lithologies and sedimentary structures in member 2 indicate an overall grain size distribution susceptible to liquefaction inferred high sediment accumulation rates created underconsolidated sediments metastable packing types of sediment failure included in situ liquefaction disturbed bedding sliding and slumping raft bearing debrites resulted from sliding and incorporation of water locally hummocky cross stratified sandstone directly overlies slide deposits and raft bearing beds linking sediment failure to the cyclical wave loading associated with large storms the gravity flows of the chapel island formation closely resemble those described from the surfaces of modern mud rich marine deltas details of deltaic gravity flow deposition from this and other outcrop studies further our understanding of modern deposits by adding a third dimension to studies primarily carried out with side scan sonar

distinguishing eustatic and epeirogenic controls on lower middle cambrian boundary successions in west gondwana morocco and iberia major eustatic fall has been invoked to explain lower middle cambrian boundary sandstones and faunal replacements on a number of cambrian palaeocontinents this proposal has been tested on the moroccan and spanish margins of west gondwana and found to be inadequate to explain stratigraphical developments in these regions sandstone intervals long presumed to be regressive and late early cambrian in age are now shown to be early middle cambrian and composed of a lower regressive and an overlying transgressive sandstone separated by a regional unconformity only the lower tidalites i e tazlaft formation in morocco and lower daroca sandstones in spain record the hawke bay eustatic regression in west gondwana the tazlaft is overlain by a newly recognized unconformably overlying sandstone talelt formation that onlapped southern morocco with reactivation of a pull apart or transcurrent regime up to 150 m of erosion on uplifted blocks in the high atlas range and foundering of the souss basin to the south preceded onlap and deposition of the volcanic rich tatelt the correlative and depositional analogue of the upper daroca and lower valdemides formations in northern spain with folding and erosion a type 1 depositional sequence boundary also caps the tatelt at its contact with an overlying lower middle cambrian mudstone dominated succession this unconformity probably occurs in spain within the valdemiedes formation and corresponds to a faunal discontinuity called the valdemiedes geoevent the iberian daroca regression and moroccan asrir regression are misnomers as the sandstones on which they are based are composite units with a lower regressive interval that records eustatic fall and an upper transgressive unit that records epeirogenically driven onlap

the 1994 1995 seismicity and deformation at the hengill triple junction iceland triggering of earthquakes by minor magma injection in a zone of horizontal shear stress since july 1994 an unusually persistent swarm of earthquakes m 4 0 has been in progress at the hengill triple junction sw iceland activity is clustered around the center of the hromundartindur volcanic system geodetic measurements indicate a few centimeters uplift and expansion of the area consistent with a pressure source at 6 5 3 km depth beneath the center of the volcanic system the system is within the stress field of the south iceland transform zone and the majority of the recorded earthquakes represent strike slip faulting on subvertical planes we show that the secondary effects of a pressure source modeled as a point source in an elastic half space include horizontal shear that perturbs the regional stress near the surface shear stress is enhanced in quadrants around the direction of maximum regional horizontal stress and diminished in quadrants around the direction of minimum regional stress the recorded earthquakes show spatial correlation with areas of enhanced shear the maximum amount of shear near the surface caused by the expanding pressure source exceeds 1 strain sufficient to trigger earthquakes if the crust in the area was previously close to failure

loading of a seismic zone to failure deforms nearby volcanoes a new earthquake precursor the south iceland seismic zone sisz was loaded to failure in june 2000 resulting in two m6 6 earthquakes the sisz is an e w trending zone with an overall sinistral movement numerical models indicate that when the sisz is loaded to failure there are stress concentrations at its ends tensile in the north east and south west quadrants and compressive in the north west and south east quadrants these model predictions fit well with observations geodetic measurements indicate considerable compression uplift and associated intense seismicity in recent years in the volcanoes of hengill and eyjafjallajokull located in the quadrants of compression whereas there have been unusually frequent eruptions in the past decades in the hekla volcano located in one of the quadrants of extension the models predict that following the large june 2000 earthquakes stress relaxation within the sisz should lead to stopping of the intense seismicity and deformation in the volcanoes of hengill and eyjafjallajokull again in agreement with observations however when similar episodes of deformation and seismicity start again particularly in the hengill volcano a large earthquake would be expected within several years in the sisz the numerical models and the deformation and seismic data indicate that monitoring of soft inclusions such as volcanoes many with magma chambers in the vicinity of a seismic zone may serve as precursors to large earthquakes

groundwater exploitation and recharge rate estimation of a quaternary sand aquifer in dar es salaam area tanzania dar es salaam city gets water supply from surface water and groundwater the groundwater is used to supplement surface water supply and has increasingly become a major source of water supply in the city the study area comprises three major parts the central coastal plain with quaternary fluvial deltaic sediments the deltaic mio pliocene clay bound sands and gravels in the northwest and southeast and the lower miocene fluviatile sandstones of pugu hills in the west of the study area the main objective of this study was to quantify the integrated water balance the major source of renewable groundwater in the aquifer is rainfall hence the average recharge of 256 2 mm year for the year 2006 to the aquifer was estimated using the balance method of thornthwaite and mather which is equal to 99 4 hm3 year for the whole alluvial aquifer this value was balanced with total groundwater abstraction of 8 59 hm3 year baseflow to rivers of 75 7 hm3 year and discharge into the sea 15 11 hm3 year

distributed deformation in an oceanic transform system applying statistical tools to structural and paleomagnetic data near the husavik flatey fault northern iceland

temperature and melting of a ridge centred plume with application to iceland part ii predictions for electromagnetic and seismic observables summary the dynamic and melting processes of a ridge centred plume have been investigated in a companion paper by ruedas et al hereafter referred to as paper i in a set of 3 d numerical fluid dynamic models with varying plume excess temperatures and melt extraction thresholds in paper i the modelled thickness of the generated crust has been compared to observations of the icelandic crust using the results of those plume models magnetotelluric mt transfer functions and seismic velocity anomalies are predicted in this paper together with paper i a dynamically consistent set of geophysical observables of a ridge centred plume is presented and applied to iceland temperature partial melting and the connectivity of the melt phase influence the electrical conductivity of crust and mantle rocks the temperature and melt fraction of our plume models are used to calculate 3 d conductivity models for mt modelling for the melt geometry ellipsoidal inclusions with appropriate aspect ratios were assumed to control melt connectivity the resulting transfer functions are compared to each other and to models not including a plume to separate signals from the ridge and the plume they may be applied to observed mt measurements if the plume head contains only 1 per cent of melt the plume signal cannot be distinguished from the ridge signal at least 3 per cent melt is needed for such distinction the other predicted observables calculated from the different numerical models are seismic velocity anomalies the temperature induced vp and vs anomalies were estimated including anharmonic and anelastic effects as well as the water induced increase of dislocation mobility that lowers seismic velocities realistic melt geometries as observed in laboratory experiments were used to calculate the effect of partial melts on the seismic velocities vs anomaly distributions are synthesized from the different plume models and compared to seismic observations to reconcile seismic anomalies of the plume head and plume stem a wet plume stem overlain by a partially molten dehydrated plume head is favoured the combined interpretation of available observations crustal thicknesses paper i and seismic results with our dynamic plume models paper i leads to a favoured plume model with 135 k excess temperature and a vertical velocity of approximately 13 cm yr 1 at 200 km depth with 1 per cent melt extraction threshold and a melting zone of approximately 500 km width and 100 km depth extent

wrinkle marks an intertidal sedimentary structure due to aseismic soft sediment loading abstract the structures have a wide distribution intertidally in the macrotidal severn estuary and inner bristol channel occurring on the active sedimentary surface chiefly in association with a millimetre scale sand over mud doublet the sand surface is marked by depressions and ridges of a wide variety of shapes and orientations relative to slope that are matched antithetically by ridges and depressions on the mud sand interface below the sand layer consequently takes the form of a series of touching to detached pillow shaped masses whose centres lie 2 4 sand layer thicknesses apart wrinkle marks originate soon after the emergence of the sedimentary surface into the atmosphere and are considered to be soft sediment deformation structures on account of their 1 occasional displacement and or severance of early emergence surface organic trails and feeding marks 2 similarity in shape and internal structure to pseudo nodules recorded from the field and produced experimentally and 3 association with gravitationally unstable sediment layers in settings that favour the vigorous seepage of pore water through water logged sediments owing to their origin at the sedimentary surface wrinkle marks appear to be preserved mainly as surface markings on eroded and discordantly reburied mud sand interfaces

statistical tests for detecting movements in repeatedly measured geodetic networks abstract niemeier w 1981 statistical tests for detecting movements in repeatedly measured geodetic networks in p vyskocil r green and h malzer editors recent crustal movements 1979 tectonophysics 71 335 351 geodetic networks with two or more measuring epochs can be found rather frequently for example in connection with the investigation of recent crustal movements in the field of monitoring problems in engineering surveying or in ordinary control networks for these repeatedly measured networks the so called congruency problem has to be solved i e possible changes in the geometry of the net have to be found in practice distortions of bench marks and an extension or densification of the net differences in the lst order design and or changes in the measuring elements or techniques differences in the 2nd order design can frequently be found between different epochs in this paper a rigorous mathematical procedure is presented for this congruency analysis of multiple measured networks taking into account these above mentioned differences in the network design as a first step statistical tests are carried out to detect the epochs with departures from congruency as a second step the individual points with significant movements within these critical epochs can be identified a numerical example for the analysis of a monitoring network with 9 epochs is given

crustal deformation at the oblique spreading reykjanes peninsula sw iceland gps measurements from 1993 to 1998 in 1993 and 1998 a 38 point gps network was surveyed on the reykjanes peninsula sw iceland according to the nuvel 1a plate motion model the spreading rate of the north american and eurasian plates in sw iceland is 18 9 0 5 mm yr toward n102 7 1 1 e highly oblique to the plate boundary instead of oblique spreading the measurements indicate left lateral shear strain accumulation parallel to the reykjanes peninsula seismic zone n76 e at the rate of about eyx 0 2 strain yr tensor shear strain subsidence is generally observed toward the seismic zone a local maximum subsidence of 60 mm was measured in the svartsengi geothermal area subsidence in this area has previously been detected with geodetic measurements and is considered a result of geothermal usage expansion was observed in the area of the hengill triple junction this is probably a result of magma accumulation beneath mount hromundartindur as previous seismic and geodetic measurements have indicated using a simple screw dislocation model we fit the majority of the data assuming a left lateral shear zone at depth along the seismic zone we estimate locking depth of 6 5 km and deep slip rate of 16 5 mm yr the maximum left lateral displacement predicted by the screw dislocation model 11 85 0 06 mm yr is consistent with the observed value of 11 9 0 5 mm yr if the hengill area is excluded little extension is observed across the peninsula the discrepancy between the nuvel 1a oblique spreading and the observed transcurrent motion is thought to be caused by lack of magma intrusion into the crust during this time period

gyrolithes from the ediacaran cambrian boundary section in fortune head newfoundland canada exploring the onset of complex burrowing abstract the beginning of the cambrian explosion is characterized by the onset of infaunalization and the appearance of systematic patterns of burrowing the trace fossil gyrolithes is common in the ediacaran cambrian global stratotype section and point where it shows a higher diversity and burrow depth than previously reported from any cambrian spiral vertical burrows two ichnospecies are present g scintillus isp nov exhibits a small burrow radius to whorl radius ratio whereas g gyratus hofmann exhibits an exceptionally large ratio that formerly led to its identification as an aberrant ichnospecies of skolithos the helical morphology of these cambrian gyrolithes is interpreted as having served two purposes as an anchor in a relatively high energy environment and as an optimal shape for maximizing surface area for bacterial gardening these shallow marine gardening burrows share a similar feeding strategy as graphoglyptids suggesting that shallow early cambrian sediments may have been relatively poor in organics and thus further supporting the model for onshore offshore migration of gardening burrows

the continental margin in iceland a snapshot derived from combined gps networks abstract the tectonical setting in iceland is quite complex due to the interaction of the iceland hot spot and the mid atlantic ridge while in the north of the island one active spreading zone exists the divergent motion in the centre and the south is distributed over at least two volcanic rift zones the spreading rate increases linearly along the western volcanic zone from north to south up to 8 mm yr at the hengill triple junction on the contrary the spreading rate of the parallel eastern volcanic zone decreases from 16 mm yr down to 6 mm yr at the island s southern coast the hreppar microplate between the two predominant rift zones has an independent motion which is distinct from that of the eurasian and north american plates a new detected feature is the spreading activity around the hofsjokull volcanic zone located in the centre of iceland with a significant rate of 6 mm yr during this investigation the coordinate sets of nearly 20 years of gps data acquisition on iceland were combined to get a velocity field for the surface of iceland this velocity field is based on a linear kinematic model with the consideration of local non linear effects like volcano up doming and displacements due to major earthquakes

revel a model for recent plate velocities from space geodesy 1 we present a new global model for recent plate velocities revel describing the relative velocities of 19 plates and continental blocks the model is derived from publicly available space geodetic primarily gps data for the period 1993 2000 we include an independent and rigorous estimate for gps velocity uncertainties to assess plate rigidity and propagate these uncertainties to the velocity estimates the velocity fields for north america eurasia and antarctica clearly show the effects of glacial isostatic adjustment and australia appears to depart from rigid plate behavior in a manner consistent with the mapped intraplate stress field two thirds of tested plate pairs agree with the nuvel 1a geologic 3 myr average velocities within uncertainties three plate pairs caribbean north america caribbean south america and north america pacific exhibit significant differences between the geodetic and geologic model that may reflect systematic errors in nuvel 1a due to the use of seafloor magnetic rate data that do not reflect the full plate rate because of tectonic complexities most other differences probably reflect real velocity changes over the last few million years several plate pairs arabia eurasia arabia nubia eurasia india move more slowly than the 3 myr nuvel 1a average perhaps reflecting long term deceleration associated with continental collision several other plate pairs including nazca pacific nazca south america and nubia south america are experiencing slowing that began 25 ma the beginning of the current phase of andean crustal shortening

kinematic model of the south icelandic tectonic system summary due to the hot spot ridge interaction the tectonical situation in the southern part of iceland is quite complex within this investigation it is shown that the western volcanic zone is in spite of missing recent volcanic activity still an active spreading zone its annual widening of 8 1 1 0 mm yr 1 represents more than 45 per cent of the spreading of the southern part of iceland the full spreading rate of the investigated region amounted to 17 1 3 0 mm yr 1 these are the results of a constrained linear multiepoch deformation analysis of six gps measurement campaigns which have been carried out between 1986 and 1999 in the southwest of iceland the presented solution combines the motion information of 79 stations to yield a linear velocity field which is a snapshot of the medium term motion the used gps measurement campaigns had changing network geometries with a lack of point identities