erosion of the laurentide region of north america by glacial and glaciofluvial processes collection of seismic reflection data from continental margins and ocean basins surrounding north america makes it possible to estimate the amount of material eroded from the area formerly covered by laurentide ice sheets since major glaciation began in north america a minimum estimate is made of 1 62 106 km3 or an average 120 m of rock physically eroded from the laurentide region this figure is an order of magnitude higher than earlier estimates based on the volume of glacial drift cenozoic marine sediments and modern sediment loads of rivers most of the sediment produced during laurentide glaciation has already been transported to the oceans the importance of continental glaciation as a geomorphic agency in north america may have to be reevaluated evidence from sedimentation rates in ocean basins surrounding greenland and antarctica suggests that sediment production sediment transport and possibly denudation by permanent ice caps may be substantially lower than by periodic ice caps such as the laurentide low rates of sediment survival from the time of the permo carboniferous and precambrian glaciations suggest that predominance of marine deposition during some glacial epochs results in shorter lived sediment because of preferential tectonism and cycling of oceanic crust versus continental crust

structural evolution of the la trocha fault zone oblique collision and strike slip basins in the cuban orogen 1 the la trocha fault zone acted as a major left lateral transfer zone and is bounded by the la trocha ltf zaza tuinicu ztf cristales ctf and taguasco tgf faults these faults were consistent with the clockwise rotation of convergence and shortening in central cuba from the paleocene to the early eocene 65 48 ma a ssw nne shortening produced transtension in the ltf and transpression in the ztf subsequently during the middle eocene 48 37 ma shortening shifted to a sw ne direction resulting in the normal component of the ltf and transpression in the ztf and ctf since the late eocene 37 ma central cuba has been welded to the north american plate the post welding deformation gave rise to transtension of the ltf and tgf this deformation is consistent with a wsw ene shortening and reflects activity in the transform boundary of the cayman trough both the normal and thrust displacements of these previous faults are corroborated by structural data whereas left lateral displacement is deduced from the concordance between oblique collision and structural features plate kinematics and the structural evolution of the la trocha fault zone indicate that the related central basin is a strike slip polygenetic basin and that the formation of this system i e fault zone strike slip basin was a consequence of the paleogene oblique collision between the caribbean volcanic arc and the bahamas borderland north american plate

evolution and mass accumulation of the cenozoic hoh xil basin northern tibet abstract this work reconstructs the depositional history and estimates the mass of sediments stored in the hoh xil basin northern tibet the largest cenozoic sedimentary basin in the hinterland of the tibetan plateau the mass estimate is derived from over 75 geologic sites and 21 measured stratigraphic sections with a total thickness of 13 478 m the results show that the hoh xil basin underwent six stages of development from the early eocene to the early miocene with a hiatus in sedimentation in the late oligocene the fenghuoshan group was deposited during the first four stages 56 0 52 0 52 0 43 0 43 0 38 2 and 38 2 31 5 myr the yaxicuo group comprises stage 5 31 5 30 0 myr the wudaoliang group covered the entire basin during the last stage 23 0 to 16 0 myr the strata of the fenghuoshan and yaxicuo groups were strongly deformed mainly during the late oligocene whereas only minor tilting has occurred since then in the wudaoliang group the depositional history indicates that the hoh xil basin could have been formed as a piggyback basin and that the onset of northeastward growth of the central tibet was from the early eocene about 56 myr to the late oligocene the analyses of subsidence history and mass accumulation indicate that both accelerated subsidence and sudden increases of accumulation rate occurred at the four periods of about 52 0 40 5 34 5 and 31 5 myr in three sub basins and over the entire basin from the early eocene to the early oligocene during the four periods the deposits were either lacustrine turbidite sandstone or fan delta conglomerate which resulted from the tectonic movement on the basis of the mechanism of northeastward growth of the piggyback basins and the consistency of accelerated subsidence depositional systems and mass accumulation we suggest the continental collision and early uplift of the tibetan plateau controlled the formation and evolution of the hoh xil basin the event that occurred at 52 0 myr could represent the continental collision between india and asia whereas the other three events that happened during about 40 30 myr could show the early uplift of the tibetan plateau this study on sedimentary records in the hoh xil basin along with widespread magmatic activity in eastern and western tibet suggests a diachronous uplift history for the tibetan plateau from east to west

three positive feedback mechanisms for ice sheet melting in a warming climate three positive feedback mechanisms that accelerate ice sheet melting are assessed in a warming climate using a numerical ice model driven by atmospheric climate models the greenland ice sheet gris is the modeling test bed under accelerated melting conditions the first feedback is the interaction of sea water with ice it is positive because fresh water melts ice faster than salty water owing primarily to the reduction in water heat capacity by solutes it is shown to be limited for the gris which has only a small ocean interface and the grounding line of some fast glaciers becomes land terminating during the 21st century the second positive feedback strain heating is positive because it produces further ice heating inside the ice sheet the third positive feedback granular basal sliding applies to all ice sheets and becomes the dominant feedback during the 21st century a numerical simulation of jakobshavn isbrae over the 21st century reveals that all three feedback processes are active for this glacier compared with the year 2000 level annual ice discharge into the ocean could increase by 1 4 km3 a 1 5 of the present annual rate by 2100 granular basal sliding contributes 40 of this increase

evolution of the transport direction of the carpathian belt during its collision with the east european platform the evolution of the carpathians is in its final stage with intermediate seismic activity 70 200 km mw 4 7 7 localized beneath its southeastern salient vrancea zone our analysis in the transition area between south carpathians and east carpathians reveals that the termination of convergence is characterized by a clockwise rotation of the carpathian belt transport direction using structural maps and cross sections we show that this change of convergence direction had several structural consequences including 1 the pliocene quaternary activation of out of sequence structures in the southern east carpathians and 2 the creation of dextral strike slip faults bounding the mobile belt to the west in the south carpathians our fracture analysis in syntectonic deposits allows us to distinguish and stratigraphically date two fanning stress patterns corresponding to the two last transport directions of the carpathian system 1 a burdigalian to early tortonian stress field with compression directions rotating along with the carpathian curved orogenic belt but with transpression nw se compression and a low strain partitioning along east trending internal strike slip faults in the south carpathians and 2 a late tortonian to pleistocene rotated and smaller radial stress pattern with n s compression in the south carpathians the rotation of the convergence direction is interpreted as the result of the miocene migration and progressive collision of the carpathian system with the thick crust of the nw trending tornquist teisseyre line and its prolongation in romania the area able to subduct determined by thickness of crust entering the subduction zone was progressively restricted to a foreland corner in front of the southeastern carpathians the progressive collision forced the convergence to slow down and rotate from eastward to southeastward in late miocene the dobrogea hills in front of the latest migrating system may represent the late neogene ne sw flexural bulge of the subducting foreland panel this clockwise rotation of the transport direction can be compared with the clockwise rotation that occurred in other subduction systems tyrrhenian subduction caribbean subduction etc which were controlled by the location of oceanic versus continental crust in front of the orogenic belt

incipient subduction of the ontong java plateau along the north solomon trench abstract the ontong java plateau ojp in the western central pacific is the largest and thickest oceanic plateau and one of a few oceanic plateaus converging on an island arc solomon island arc sia to better understand the evolution of the north solomon trench nst active oblique convergence between the ojp and sia and late neogene development of malaita accretionary prism map we present 850 km of multichannel seismic reflection data integrated with 7832 km 2 of izanagi side scan sonar coverage we have focussed the study at the transition area between the well defined northwestern end of the north solomon trench and a diffusely deformed area where the trench is actively propagating in a northwestward direction the deeper structure beneath the survey area is discussed by phinney et al oceanic plateau accretion in the malaita accretionary prism inferred from multi channel seismic reflection data this issue using deeper penetration multichannel seismic reflection lines the serial cross sections provided by multichannel seismic profiling combined with the izanagi backscattering imagery provides a time series evolution for the development of the north solomon trench the main evolutionary stages include 1 the incipient trench in the northern area marked by a diffuse zone of deformation above a broad arch in the crust deeper penetration profiles by phinney et al show the bulge is related to a deeper decollement fault that is propagating upward and seaward through the crust 2 the formation of a continuous thrust front in the central area deeper penetration profiles by phinney et al show this thrust front is surface expression of the same decollement present at depth to the north the boundary between the surface trace of the thrust and the diffuse area of deformation in the northern area is inferred as a vertical high angle tear fault with left lateral offset 3 the formation of a deep elongate trench which controls gravitationally related slumping and sedimentation around the steep edges of the trench fill basin the areas to the southeast are those that have undergone convergence for the longest period of time and therefore show better developed trench structures and a reduced width of the map areas to the northwest have undergone convergence for a shorter period of time and show less developed trench structures and a wide area of the map

late cenozoic uplift of mountain ranges and global climate change chicken or egg the high altitudes of most mountain ranges have commonly been ascribed to late cenozoic uplift without reference to when crustal thickening and other tectonic processes occurred deep incision and recent denudation of these mountain ranges abundant late cenozoic coarse sediment near them and palaeobotanical evidence for warmer climates where high mountain climates today are relatively cold have traditionally been interpreted as evidence for recent uplift an alternative cause of these phenomena is late cenozoic global climate change towards lower temperatures increased alpine glaciation a stormier climate and perturbations to humidity vegetative cover and precipitation

the effect of hot spots on the oceanic age depth relation hot spots located both midplate and on midocean ridges can bias the empirical age depth relation ocean floor bathymetry for seafloor greater than 80 m y b p in age has been previously used to determine if the oceanic lithosphere behaves as a cooling half space or as a cooling plate however large areas of the ocean basins do not fit a simple age depth relation anomalously shallow swells approximately 1000 km wide and 1 km high surround hot spots such as iceland the azores and the cape verde islands by sorting seafloor depth data by distance to the nearest hot spot track we show that the along isochron variation in depth in the north atlantic correlates with distance from a hot spot track due to the absence in the north atlantic of seafloor both old and far from hot spots we compare depth versus age at constant distance and do not observe flattening of the age depth relation in any distance range the age depth relation depth meters 2700 295 t m y 1 2 derived for seafloor 1200 to 1800 km from a hot spot track represents our best estimate of the age depth relation appropriate to seafloor unaffected by a hot spot track in the north atlantic the previously inferred flattening of the age depth relation appears to be caused by the inclusion of hot spot swells this implies that hot spots may be the primary means of heat transfer from the deeper mantle to the base of the lithosphere

the ups and downs of north america evaluating the role of mantle dynamic topography since the mesozoic the driving force for transient vertical motions of earth s surface remains an outstanding question a main difficulty lies in the uncertain role of the underlying mantle especially during the geological past here i review previous studies on both observational constraints and physical mechanisms of north american topographic evolution since the mesozoic i first summarize the north american vertical motion history using proxies from structural geology geochronology sedimentary stratigraphy and geomorphology based on which i then discuss the published physical models overall there is a progressive consensus on the contribution of mantle dynamic topography due to buoyancy structures associated with the past subduction at the continental scale a largely west to east migrating deformation pattern suggests an eastward translation of mantle dynamic effects consistent with models involving an eastward subduction and sinking of former farallon slabs since the cretaceous among the existing models the inverse model based on an adjoint algorithm and time dependent data constraints provides the most extensive explanations for the temporal changes of north american topography since the mesozoic at regional scales debates still exist on the predicted surface subsidence and uplift within both the western and eastern united states where discrepancies are likely due to differences in model setup e g mantle dynamic properties and boundary conditions and the amount of time dependent observational constraints toward the development of the next generation predictive geodynamic models new research directions may include 1 development of enhanced data assimilation capabilities 2 exploration of multiscale and multiphysics processes and 3 cross disciplinary code coupling

sediment cycling on continental and oceanic crust sedimentary rocks are often described as declining in quantity with increasing age due to the cumulative effects of crustal deformation and erosion one important implication of such a model is that the geological record becomes progressively less voluminous and less complete with increasing age here we show that the predictions of a model in which the destruction of sedimentary rock is the predominant process signal are borne out only among sediments deposited on oceanic crust and among sediments deposited above sea level in non marine environments most of the surviving volume of sedimentary rock 75 was deposited in and adjacent to shallow seas on continental crust and does not exhibit any steady decrease in quantity with increasing age instead shallow marine sediments exhibit large fluctuations in quantity that were driven by shifting global tectonic boundary conditions such as those that occur during the breakup and coalescence of supercontinents the accumulation of sediments on the continents has not been uniform in rate but it does record a primary signal of net growth that has many implications for the long term evolution of earth s surface environment

collisional model for rapid fore arc block rotations arc curvature and episodic back arc rifting in subduction settings 1 we review geophysical and geological data from 23 active and ancient plate boundaries to document a compelling spatial and temporal relationship between collision plate boundary curvature rapid tectonic rotations and the occurrence of back arc rifting our observations support a conceptual model where the change from subduction to collision causes rapid fore arc rotation when viewed in a reference frame relative to the bounding tectonic plates leading to marked plate boundary curvature our global compilation reveals that most active back arc rifts are associated with rapidly rotating fore arcs and nearby collisions thus we propose that collision and rapid fore arc rotations play a major role in the evolution and kinematics of back arc basins we conduct numerical modeling to better understand the physical processes behind these observed rapid tectonic rotations at convergent margins our results suggest that the presence of an indentor or choke point in the subduction system e g collision can generate rapid rotation of the fore arc about a nearby pole and lead to back arc rifting the rate of fore arc rotation and back arc rifting depends on the incoming indentor velocity and can be greatly enhanced by slab rollback and the presence of a low viscosity back arc where viscosity of the back arc is low fore arc rotation dominates where back arc viscosity is high the formation of strike slip faults and tectonic escape dominates our observational and model derived results illustrate that shallow crustal forces produced by the entry of buoyant features into subduction zones are a fundamental mechanism for the generation of fore arc block rotations plate boundary curvature back arc rift evolution and tectonic escape in subduction systems rollback of the subducting slab within the mantle will certainly enhance the processes we describe but it is not the only driving force

structural framework and deformation history of the western cyprus arc abstract an extensive grid of high resolution multichannel seismic reflection profiles complemented with wider spaced deep penetrating industry seismic profiles revealed that the pre messinian miocene structural architecture of the antalya basin and its southwestern extension into the florence rise is characterized by a very prominent broadly northwest southeast striking and largely southwest verging fold thrust belt with occasional northeast verging backthrusts during the messinian a number of prominent thrusts remained active however numerous thrusts which were active during the pre messinian miocene became inactive during the uppermost messinian quaternary the stain was partitioned into five broadly northwest southeast trending morphotectonic domains each delineated by a distinctive seafloor morphology a a domain across the inner and western antalya basin is dominated by extensional faults b a domain immediately south of the extensional faults is characterized by contractional structures c a halokinetic zone in southwestern antalya basin north of the foothills of the anaxagoras mountain is characterized by numerous positive flower structures beneath a corrugated seafloor d a domain characterized by fluid escape structures immediately southeast of the halokinetic zone and e a domain across the crestal portion of the florence rise is dominated by prominent inversion structures detailed mapping documented that several of these tectonic domains can be readily correlated with previously mapped tectonic elements in the eastern mediterranean as well as structures mapped across the adjacent landmass the change from ubiquitous pre messinian miocene contraction to partitioned strain of the latest messinian quaternary is likely related to the collision of the eratosthenes with cyprus and the resultant jostling of the tectonic blocks

late paleozoic ice age glaciers shaped east antarctica landscape abstract the erosion history of antarctica is fundamental to our understanding of interlinks between climate and glacier dynamics however because of the vast polar ice sheet covering more than 99 of antarctica land mass the continental surface response to glacial erosion remains largely unknown over the last decade the subglacial topography of antarctica has been imaged by airborne radar surveys these studies revealed high and complex sub glacial relief in the core of the east antarctic shield interpreted as resulting from rifting episodes and low long term erosion rates or repeated large scale glacial retreats and advances in east antarctica thermochronology studies have revealed a spatially localized cenozoic erosion starting after 34 ma with a maximum denudation of 2 km in the lambert trough low pre glacial erosion rates before 34 ma have been inferred since the permian period following a phase of significant 2 km erosion during the late paleozoic between 350 and 250 ma however the exact extent magnitude and significance of this late paleozoic erosion phase remain elusive here we show that homogeneous exhumation occurred at the scale of the terre adelie margin of east antarctica in response to major glacial erosion during the late paleozoic ice age lpia our data require homogeneous exhumation and 4 km erosion between 340 and 300 ma along a 600 km profile along the terre adelie george v land coast the data are inconsistent with either exhumation during permian rifting or with significant 1 5 km cenozoic glacial erosion which requires lpia glaciers to have been temperate promoting glacial sliding erosion and sediment transfer even at high latitudes unlike in the present situation

detrital sediment fluxes from continents to oceans abstract detrital sediment is carried from land to the sea by three agents rivers glaciers and winds the shoreline is an arbitrary boundary within the detrital sediment transport system which extends from a site of origin across areas of temporary storage to a site of long term deposition the most important of the agents moving sediment across the land is river transport estimated to be in the order of 20 10 12 kg of sediment annually at present analysis of drainage basins indicates that relief and runoff are the most important factors in determining the sediment load of rivers the competence of rivers to transport sediment is governed by the volume flow gradient and the sediment load itself today most large rivers are fed by snowmelt in highland areas runoff from rainfall in the drainage basin and groundwater inflow along the river course water is lost to evaporation and groundwater infiltration river courses can often be divided into two segments a degradational section in which the gradient is relatively steep and little temporary storage of sediment takes place and an aggradational section where the gradient is sharply reduced through meandering and where large scale temporary sediment storage forms a flood plain lakes trap sediment inland and prevent its transport to the sea today many high and mid latitude rivers are interrupted by lakes of glacial origin there are also some large areas of internal drainage that deliver no sediment to the sea the load carried by rivers has been markedly altered by human activity and may have doubled over the past few thousand years only to be reduced in the past century by the widespread construction of dams the ancient use of fire in hunting and its subsequent use in clearing land has increased erosion extensive deforestation and cultivation processes have also increased the sediment supply dam construction is a relatively new factor and affects the sediment transport system by trapping sediment before it can reach the sea the resulting lower sediment supply from rivers is at least in part compensated by increased coastal erosion glacial erosion is difficult to estimate there is an ongoing controversy whether ice sheets are effective erosive agents or not estimates of the present global flux of glacial detritus range from 0 8 50 10 12 kg annually with the lower value most probable the dust flux is in the order of 0 5 to 0 9 10 12 kg annually but may vary greatly with time

plate reorganization a cause of rapid late neogene subsidence and sedimentation around the north atlantic subsidence analysis of wells in the central north sea and labrador grand banks and oft the west greenland scotian shelf and united states atlantic margin shows distinct quantitative stratigraphic correlation patterns of circum north atlantic sites a significant departure from the overall decrease in subsidence for the pliocene occurs in many wells when the rate is found to have increased one or more orders of magnitude from oligocence miocene rates wells were selected along transects from shore to basin to find if relative basin position is influenced by differential basin subsidence although stratigraphic resolution is not detailed more basinward sites experienced up to four times larger subsidence rates in the late neogene than in the oligocene miocene with a peak in the pliocene wells at the basin edge experienced much less subsidence or showed uplift the observations are consistent with a rapid change of intraplate stress at the cause for this observed transition in neogene subsidence major reorganizations of spreading direction and rate occurred during the pliocene along the entire atlantic spreading system possibly in conjunction with more global changes in plate motions we propose that the associated changes in intraplate stress caused the excess margin subsidence relative uplift along basin edges is consistent with this mechanism of relative movement and may explain apparent eustatic changes in sea level

cenozoic uplift and subsidence in the north atlantic region geological evidence revisited abstract the topographic evolution of the passive margins of the north atlantic during the last 65 myr is the subject of extensive debate due to inherent limitations of the geological geomorphological and geophysical methods used for studies of uplift and subsidence we have compiled a database of sign time and amplitude where possible of topographic changes in the north atlantic region during the cenozoic 65 0 ma our compilation is based on published results from reflection seismic studies aft apatite fission track studies vr vitrinite reflectance trends maximum burial sediment supply studies mass balance calculations and extrapolation of seismic profiles to onshore geomorphological features the integration of about 200 published results reveal a clear pattern of topographic changes in the north atlantic region during the cenozoic 1 the first major phase of cenozoic regional uplift occurred in the late palaeocene early eocene ca 60 50 ma probably related to the break up of the north atlantic between europe and greenland as indicated by the northward propagation of uplift it was preceded by middle palaeocene uplift and over deepening of some basins of the north sea and the surrounding areas 2 a regional increase in subsidence in the offshore marginal areas of norway the northern north sea the northern british isles and west greenland took place in the eocene ca 57 35 ma 3 the oligocene and miocene 35 5 ma were characterized by regional tectonic quiescence with only localised uplift probably related to changes in plate dynamics 4 the second major phase of regional uplift that affected all marginal areas of the north atlantic occurred in the plio pleistocene 5 0 ma its amplitude was enhanced by erosion driven glacio isostatic compensation despite inconclusive evidence this phase is likely to be ongoing at present

the northern caribbean plate boundary in the jamaica passage structure and seismic stratigraphy multibeam bathymetry data and multichannel seismic reflection profiles have been collected at the end of 2012 along the enriquillo plantain garden fault zone epgfz in the jamaica passage between jamaica and hispaniola analysis of the data set reveals the tectonic evolution and the stratigraphic complexity of the northern caribbean boundary stratigraphic correlations with previous marine and on land studies are proposed to place the identified seismic sequences in their regional tectonic history two distinct crustal domains are interpreted typical stratigraphic sequences for the rifted blocks of the eastern cayman trough margin are identified in five basins of the jamaica passage highlighting the eastward limit of the cayman trough margin these inherited basins are deformed and folded during a first phase of compression that could correspond to the regional tectonic rearrangement recorded in the early miocene about 20 ma a distinct crustal domain that we propose to relate to the carib beds caribbean typical reflectors a b and v is identified in the southern part of the jamaica passage indicating that the caribbean large igneous province could extend up to the extreme northeast part of the lower nicaragua rise the left lateral epgfz currently cuts across two pre existing basins the morant and matley basins during the activity of the epgfz these basins are deformed and folded indicating a second phase of compression in contrast the navassa basin located in the middle of the jamaica passage results from the strike slip motion of the epgfz and is interpreted as an asymmetrical basin bordered by the epgfz only on its northern side

continental erosion and large scale relief a worldwide investigation of continental erosion is carried out by the study of large drainage basins on the basis of hydrological data environmental factors and basin relief distribution inside each basin mean geochemical and mechanical denudation rates are defined a multicorrelation analysis shows that the mechanical denudation rates ds are uncorrelated with environmental factors and correlated with mean basin elevation h while chemical denudation rates dd are insensitive to relief but correlated with mean annual precipitation furthermore two linear relationships between h and ds are detected 1 ds m 10 yr 419 10 6 h m 0 245 with v explained variance 95 1 this law concerns basins related to orogenies younger than 250 ma the negative intercept is interpreted as a continental sedimentation rate of 245 m m y an alternative model in which one invokes a critical elevation separating erosion from sedimentation is equally successful and leads to lower sedimentation rates 60 110 m m y for both models one derives from the slope of the adjustments erosion time constants on the order of 2 5 m y 2 ds m 10 yr 61 10 6 h m with v 86 5 this law concerns basins related to older orogenies the null intercept suggests the lack of continental storage because of the more important dispersion of the data the erosion time constant is calculated separately for each basin it ranges from 15 to 360 m y the tectonic implications of these results are discussed in particular the short time constant 2 5 m y agrees with orogenic uplift rates on the order of 1 mm yr observed in active mountain chains

earth s surface responses during geodynamic evolution numerical insight from the southern east china sea continental shelf basin west pacific abstract the interaction between the earth s surface and deep geodynamic processes has a great influence on sedimentary patterns and characteristics of sedimentary systems especially in the continental margin such as the southern part of the east china sea continental shelf basin ecscsb however the exact processes and dynamics are poorly understood the numerical tool badlands was adopted to simulate the geological evolution of the southern ecscsb during the mesozoic transitional regime of the west pacific continental margin between 200 and 100 ma the numerical model involving four dimensional 4d sequence stratigraphy was validated by comparing with the tectono morphology sedimentary environments and sediment distribution according to our findings the transition was mainly controlled by three structural stages the first transitional stage of the southern ecscsb was mainly controlled by lithospheric scale tectonic evolution in the second stage the dynamic topography contributed to slow regional uplift while the last stage showed mantle induced dynamic subsidence the model results on 4d geomorphic characteristics sediment distribution of basin evolution and deep dynamic topography provided a quantitative image for geological evolution of the west pacific continental margin in the mesozoic

mass accumulation rates in asia during the cenozoic summary this work establishes estimates of mass accumulation rates in 18 mostly offshore sedimentary basins in asia since the beginning of the cenozoic 66 ma the estimates were derived from isopach maps cross sections and drill holes or stratigraphic columns assuming regional similarity of the strata average solid phase volumes and accumulation rates were calculated for nine epochs approximately corresponding to geological periods palaeocene 66 58 ma eocene 58 37 ma oligocene 37 30 and 30 24 ma miocene 24 17 17 11 and 11 5 ma pliocene 5 2 ma and quaternary 2 0 ma these rates shed new light on the geological history of asia since the onset of the collision of india with asia 50 ma the overall average accumulation rates curve for asian sedimentary basins since the beginning of the tertiary shows an exponential form with slow accumulation rates less than 0 5 106 km3 myr 1 until the beginning of the oligocene more than 15 myr after the onset of the collision from the oligocene onwards rates increase quickly in an exponential manner reaching their maximum values in the quaternary more than 1 5 106 km3 myr 1 from these observations we suggest that extrusion and crustal shortening are complementary processes that have been successively dominant throughout the india eurasia collision history at smaller scales one may distinguish between independent histories at the subcontinental and basin scales this permits a comparison of the relative importance of tectonic and climatic erosion processes affecting the different mountain belts of asia during the cenozoic

mass transfer between eastern tien shan and adjacent basins central asia constraints on regional tectonics and topography summary using depths and ages derived from isopachs drill holes or cross sections it is possible to reconstruct the space time depositional history of a sedimentary basin drill holes and cross sections give the local sedimentation history while isopachs allow the definition of the spatial distribution of the sediments assuming several simple hypotheses such as similarity of the strata and regional applicability of results derived from local analyses one can reconstruct balanced maps of the solid or grain volumes and hence the mass of sediments deposited during several time intervals since the palaeogene applying this method to the tarim and dzungar basins nw china we estimate the total cenozoic solid phase volume and mass of sediments stored to be 1358 f 520 x lo3 km3 36 7 f 14 x 1017 kg and 172 f 56 x lo3 km3 4 6 f 1 5 x 1017 kg respectively the reconstruction also enables us to detect two main pulses in the sedimentation the first around 17 ma affected only the northern part of the tarim basin also known as the kucha or kuche depression at the foot of the tien shan mountains and supports the idea that the presently active shortening regime in that range started at that time the second 5 to 6 ma affected most of the depositional areas of the region and may have an even greater geographical extent assuming local isostasy we estimate the volume of shortening induced by the rotation of the tarim block relative to siberia and stored in the range and adjacent basins to be between 1 15 x lo6 and 4 23 x lo6 km3 this correspbnds to a clockwise rotation of between 2 5 and 8 7 we use these results in two simple models of self similar growth of pyramidal topographies that approximately fit the eastern tien shan

accommodation and supply a dual control on stratigraphic sequences abstract it is widely accepted that both eustatic and tectonically controlled regional changes of sea level have contributed to the record of stratigraphic sequences i suggest that environmental change be added as a third autonomous control sedimentologic principles clearly indicate that sequences and their systems tracts are controlled by the interplay of two rates the rate of change in accommodation space available for sedimentation and the rate of sediment supply sea level has direct control on accommodation but its influence on sediment supply is remote and easily overshadowed by environmental factors for instance the record of the most recent sea level rise is a transgressive systems tract where supply is low it is a prograding highstand systems tract in deltas where the supply is high examples of sequence boundaries generated by changes in sediment supply include tectonically driven shifts in sediment input into basins changes in ocean currents pulsating supply from failure of submarine slopes and drowning of carbonate platforms by environmental stress furthermore the stratigraphic sequences in fluviatile continental basins are physically removed from sea level induced changes in accommodation and must have formed by changes in the rate and pattern of supply subaerial exposure of marine sediments at the sequence boundary is a most important criterion for recognizing sea level cycles as opposed to supply cycles other criteria include downstepping of shelf breaks and characteristic patterns in the spacing of time lines within sequences some third order cycles ca 0 5 3 ma duration meet these criteria others do not cycle stacking patterns and the shifting facies belts on cratons indicate that many second and third order cycles lack pronounced exposure unconformities and represent gradual changes superimposed on more rapid shorter oscillations seismic data yield poor images of these gradational changes because they lack resolution seismic models of outcrops show that near the limits of resolution the seismic tool tends to portray rapid changes in facies and bed thickness i e lateral variations in supply as unconformities seismic unconformities do not necessarily correspond to unconformities in outcrop the succession of stratigraphic sequences is best considered a composite record of sea level and environmental change separating the various controls requires carefully planned experiments work on the oxygen isotope curve another proxy for sea level has set an example in this respect

geomorphic tectonic control of sediment discharge to the ocean the importance of small mountainous rivers analysis of data from 280 rivers discharging to the ocean indicates that sediment loads yields are a log linear function of basin area and maximum elevation of the river basin other factors controlling sediment discharge e g climate runoff appear to have secondary importance a notable exception is the influence of human activity climate and geology on the rivers draining southern asia and oceania sediment fluxes from small mountainous rivers many of which discharge directly onto active margins e g western south and north america and most high standing oceanic islands have been greatly underestimated in previous global sediment budgets perhaps by as much as a factor of three in contrast sediment fluxes to the ocean from large rivers nearly all of which discharge onto passive margins or marginal seas have been overestimated as some of the sediment load is subaerially sequestered in subsiding deltas before the proliferation of dam construction in the latter half of this century rivers

quantifying denudation and sediment accumulation systems open and closed lakes basic concepts and first results abstract the quantitative aspects of denudation in the drainage areas and sediment accumulation in the corresponding closed or open lakes are approached using two methods 1 from known mean rates of mechanical and chemical denudation and the ratio of the drainage lake area average terrigenous and potential chemical biogenic and evaporites sedimentation rates in the lake are determined or 2 from known sedimentation rates the average denudation rate is found in closed systems the total mass denuded during a certain unit of time is deposited in the lake as terrigenous biogenic and evaporitic sediments whereas open lake systems lose a major part of the dissolved river input derived from chemical denudation applying elementary equations describing these relationships and using ratios between mechanical and chemical denudation weathering ratio established in other regions e g chemical weathering in the lake drainage can be estimated likewise the knowledge of the bio index ratio of biogenic sediment total dissolved mass allows the calculation of the loss of dissolved matter through the outflow from the lake etc in a first step existing data from modern lake systems are evaluated later idealized lake systems in various climatic and morphotectonic zones can be simulated and the results utilized to better understand ancient lake systems modern alpine lakes reflect increased mechanical denudation rates 100 to 300 mm ka in highly elevated drainage areas of the central alps mainly crystalline rocks and high chemical denudation up to ca 100 mm ka in carbonate rocks of the northern calcareous alps mechanical denudation is significantly enhanced by glaciation but transport of the detritus into lakes may be delayed until the time immediately after glacial retreat average rates of terrigenous lake sedimentation amount to 5 to 15 mm a crystalline rocks high relief or are 5 mm a carbonate rocks delta outbuilding was a main factor in the filling of many alpine lakes lakes draining low altitude semi arid parts along the eastern margin of the alps lake balaton in hungary have low sedimentation rates and reflect the influence of increased temperature and vegetation in east africa the transition from the late pleistocene arid to the early holocene humid and again back to somewhat drier conditions caused substantial rises in lake levels and changes from closed to open lake systems in such cases the calculation of denudation from accumulation rates is biassed as a result of intermittent sediment storage at the lake margins low sedimentation rates in the lake centre during lake highstands or redeposition of sediment during lowstands lowstand shedding the modern denudation rates of east african rift lake systems vary by a factor of 15 lake tanganyika crystalline rocks and more dense vegetation cover total denudation rate ca 4 mm ka lake turkana young volcanic rocks and tephra sparse vegetation mechanical denudation rate ca 60 mm ka

model for the formation of large transtensional basins in zones of tectonic escape tectonic escape is strike slip dominated motion of colliding continental or arc crust in the direction of subductable oceanic crust i describe four examples of large transtensional basins in cenozoic zones of tectonic escape and propose that these basins formed along newly formed transtensional faults formed between the collided and escaping parts of the plate the reoriented direction of the escaping plate split along the new transtensional fault zone is determined by the presence of a free face or subductable oceanic crust continued subduction toward the free face is driven by the force of gravity acting on dense oceanic crust slab pull the four examples presented here show that a variety of transtensional deformational styles can be generated within this specific type of divergent tectonic setting these transtensional styles include pull apart basins at fault stepovers more asymmetrical rift like basins thought to be formed under conditions of fault normal extensional stresses and single or multiple short spreading ridges transtensional styles may be controlled more by the type and age of crust present than the angle of reorientation of the escaping plate

paleogeodynamics world base maps and paleobathymetry for the last 70 ma an explanatory note abstract a short description of global paleogeodynamic maps for the last 70 ma at 5 ma intervals is presented two paleobathymetric maps for 70 and 35 ma b p are also presented

global tectonics and eustasy for the past 2 billion years abstract continental freeboard and eustasy as gauged by the relative position of the world shelf break with respect to sea level have varied by 250 m from today s ice free shelf break depth of 200 m during the past 600 ma assuming constant or uniformly accreting continental crust and ocean water volume in an ice free world sea level fluctuations can be attributed to variation in the world ocean basin volume caused by changes in either its area or its depth relative to the world shelf break an increase in volume and lowering of sea level occur as 1 the world ocean floor ages cools and subsides 2 accreting continents collide thicken and decrease in area and 3 poorly conductive continental platforms become thermally elevated due to a size induced stasis over the mantle conversely a decrease in the age of the world ocean floor attenuation of continental crust during rifting and an increase in continent number and mobility will reduce the world ocean basin volume and raise sea level theoretical sea level calculated from these principles correlates well with calibrated first order cycles of eustatic sea level change for the phanerozoic the record closely fits a simple model of retardation and acceleration of terrestrial heat loss during alternating periods of supercontinent accretion and fragmentation calibrated to sea level highstands successive first order marine transgressions and orogenic pangea regressions characterize a self sustaining 440 ma plate tectonic cycle for the late precambrian and phanerozoic the cycle can be recognized as far back as 2 ga from the tectonic evidence of continental collision and rifting recorded in global orogenic peaks and mafic dike swarms and may be related to major episodes of glaciation and evolutional biogenesis

out of our depth on the impossibility of fathoming eustasy from the stratigraphic record the evolution of a sedimentary basin s gross morphology depends upon 1 basement movement 2 sediment accumulation and compaction and 3 variations of eustasy with time thus if an accurate history of eustasy could be derived it would aid in our understanding of basin stratigraphy and help in the prediction of sediment geometry from described areas techniques which attempt to determine the magnitude of eustatic sea level excursions include the measurement of 1 the amount of sedimentary onlap onto the continental margins with and without the use of hypsometric curves 2 the thickness of marine sedimentary cycles and the elevation and distance between indicators of old strandlines 3 the perturbations on individual thermo tectonic subsidence curves and stacked crustal subsidence curves 4 the variations in deep ocean oxygen isotopes found in sediments and 5 the size of variables used in graphical and numerical simulations of basin fill in terms of tectonic behavior rates of sediment accumulation and eustasy which invert the problem to date a combination of the use of relative sea level charts derived from sediment onlap of the continental margin with dimensioning by oxygen isotopes responding to glacial events offers the best potential for relative tectono eustatic sea level curves but even this method can not produce a unique solution for absolute eustatic variations mathematical modelling shows that at best it is possible to obtain only the sum of tectonic basement subsidence and sea level variations from the above methods and at worst not even that simple a combination thus every proposed scheme to measure eustatic sea level excursions assumes some behavior for two of the three underlying processes tectonic movement of the basement sedimentary accumulation and eustatic sea level each scheme then determines the third process relative to the assumed model behavior of the other two it would seem that like king canute we cannot command the sea though we can still use undifferentiated relative tectono eustatic sea level curves to generate a family of solutions which are the product of a variety of absolute sea level curves and tectonic models each solution has then to be assessed in terms of geologic setting and the hypotheses it generates

the late cenozoic uplift climate change paradox the geologic evidence for worldwide uplift of mountain ranges in the neogene is ambiguous estimates of paleoelevation vary according to whether they are based on the characteristics of fossil floras on the masses and grain sizes of eroded sediments or on calculations of increased thickness of the lithosphere as a result of faulting detrital erosion rates can be increased both by increased relief in the drainage basin and by a change to more seasonal rainfall patterns the geologic record provides no clear answer to the question whether uplift caused the climatic deterioration of the neogene or whether the changing climate affected the erosion system in such a way as to create an illusion of uplift we suggest that the spread of c4 plants in the late miocene may have altered both the erosion and climate systems these changes are responsible for the apparent contradictions between data supporting uplift and those supporting high elevations in the past

the cause of the late cenozoic northern hemisphere glaciations a climate change enigma the ultimate cause of the onset of glaciations remains elusive but in the case of northem hemisphere glaciation it is probable that several factors acted in combination general global cooling resulted from reduction of atmospheric c02 by weathering of silicate rocks exposed by erosion of late cenozoic uplifts uplifts in south asia southwestern north america and scandinavia occurred at distances appropriate for the generation of quasi permanent rossby waves in the atmosphere the resulting winds given suitable moisture sources were favourable for causing large scale precipitation at mid latitudes on the northern continents moisture sources were provided by the closure of the central american isthmus gulf stream flow increased carrying warm subtropical waters to high latitudes the denmark strait deepened permitting greater outflow of deep water from the norwegian greenland sea the relative importance of each of these factors should be investigated by additional atmospheric and ocean climate model sensitivity studies

river history and tectonics the analysis of crustal deformation by tectonic processes has gained much from the clues offered by drainage geometry and river behaviour while the interpretation of channel patterns and sequences benefits from information on earth movements before or during their development the interplay between the two strands operates at many scales themes which have already benefited from it include the possible role of mantle plumes in the breakup of gondwana the cenozoic development of drainage systems in africa and australia himalayan uplift in response to erosion alternating episodes of uplift and subsidence in the mississippi delta buckling of the indian lithospheric plate and changes in stream pattern and sinuosity along individual alluvial channels subject to localized deformation developments in remote sensing isotopic dating and numerical modelling are starting to yield quantitative analyses of such effects to the benefit of geodymamics as well as fluvial hydrology

numerical modelling of subglacial erosion and sediment transport and its application to the north american ice sheets over the last glacial cycle abstract present day sediment distribution offers a potentially strong constraint on past ice sheet evolution glacial system models gsms however cannot address this constraint while lacking appropriate representations of subglacial sediment production and transport incorporating these elements in gsms is also required in order to quantify the impact of a changing sediment cover on glacial cycle dynamics towards these goals we present a subglacial process model hereafter referred to as the sediment model that incorporates mechanisms for sediment production entrainment transport and deposition bedrock erosion is calculated by both hallet s and boulton s abrasion laws separately and by a novel quarrying law parametrized as a function of subglacial cavity extent these process oriented erosion laws are compared against a simple empirical relationship between erosion rate and the work done by basal stress sediment entrainment is represented by philip s law for regelation intrusion and soft bed deformation is included as a subglacial sediment transport mechanism the model is driven by the data calibrated mun 3d gsm and a newly developed subglacial hydrology module the sediment model is applied to the last north american glacial cycle and predicts sediment thickness and cumulative erosion patterns results are obtained in the context of a sensitivity analysis and are compared against the present day distribution of glacigenic sediment and geological estimates of laurentide ice sheet erosion given plausible ranges for the sensitivity parameters chosen a priori based on available literature or on heuristic arguments the calculated erosion depths overlap with the geological estimates of laurentide erosion most of the runs in the sensitivity set produce unrealistically thick and continuous moraines along the eastern southern and western margins of the north american ice complex which suggests that the model overestimates sediment entrainment and thus englacial transport a realistic sediment distribution is only obtained when the entrainment rate is capped at the average basal melting rate which suggests that modelled entrainment and basal melting rates should be of the same order of magnitude

relation of selected mineral deposits to the mass age distribution of phanerozoic sediments the global mass age distribution of phanerozoic sediment shows maxima in the middle paleozoic at the paleozoic mesozoic boundary and in the late mesozoic all of these total sediment mass maxima are also maxima of masses of volcanogenic sediment and non marine sediment and represent times of maximum sediment flux on the surface of the earth the middle paleozoic and late mesozoic maxima correspond to the great marine inundations of the continents and the late paleozoic early mesozoic maximum to the time of transfer of a large number of terranes across the tethys from gondwanaland to eurasia all three maxima of sedimentary mass correspond to times of rapid sea floor spreading and orogeny

cenozoic sediment accumulation on drifts in the northern north atlantic the northern north atlantic sediment drifts have a much greater areal extent than has previously been indicated the northern north atlantic extends from the east greenland to european continental shelves and from the charlie gibbs fracture zone to the greenland scotland ridge within this region are seven major sediment drifts containing some of the best clues for pre quaternary bottom water circulation in the north atlantic feni drift is the oldest in the region originating near the eocene oligocene boundary it was followed by accumulation of bjorn gardar hatton and snorri drifts from the late early to middle miocene eirik drift may have started to accumulate in the late miocene and gloria drift in the early pliocene through analysis of the cenozoic sediment mass age distribution and the change in area of seafloor for the study area through time it can be concluded that there is a deficit of oligocene to miocene sediment in the region this could be explained by sediment cycling the erosion of older sediment to produce young sediment the mass of pliocene to quaternary sediment is much larger than that of the older sediment and may have been derived primarily through the erosion of eocene and oligocene sediment by deepwater currents the sediment drift portion of the total regional sediment mass increased significantly three times during the cenozoic each of these drift growth phases lasted between 3 and 4 m y the first two growth phases from the late eocene to early oligocene and from the early to middle miocene were accompanied by northward shifts of depocenters to the newly forming sediment drifts the third and largest growth phase occurred between 7 and 3 ma and may have been preceded by the initiation of accumulation on eirik drift 8 7 ma this most recent growth phase was accompanied by high apparent accumulation rates over southern gardar drift as it expanded to the east erosion rates over reykjanes ridge may have been higher during the mid pliocene than in the quaternary there are two main sites where dense water could have formed and flowed south through the rockall trough to start the accumulation of feni drift if the atmosphere were cool enough dense water could have formed in the norwegian sea or on the faeroe shelf dense water may also have formed on the rockall plateau due to salinity increase through evaporation in an arid climate as an alternative to the hypothesis of arctic ocean water overflowing the iceland faeroe ridge in the early middle miocene it is suggested that dense water formed along shallow segments of the iceland faeroe ridge and then flowed into the south iceland basin to begin accumulation of bjorn gardar and snorri drifts the initiation of sediment drift formation in the south iceland basin may have been caused by a decreased rate of deep water production combined with a higher rate of detrital input due to a middle miocene uplift event along the iceland faeroe ridge a second uplift event along the greenland scotland ridge and a decreased production of northern component water in the early pliocene may be responsible for increased sediment accumulation in bjorn gardar and eirik drifts

john hardcastle looks at the timaru loess climatic signals are observed and fragipans abstract john hardcastle 1847 1927 made several important loess related observations in new zealand in 1889 and 1890 he is best known for his invention of loess stratigraphy his observations of loess as a climate register but he made significant contributions in other areas he outlined the event sequence approach to loess deposit formation in 1889 well before the better known exposition in 1966 the basic sequence for loess deposit formation p1t1d1t2d2 could well be named the hardcastle sequence he pointed out the problem of silt particle production as an important question emphasizing the role of glacial action and he drew attention to the occurrence of bird crop stones in loess deposits as possible markers for deposition stages moa stones in particular may give useful information about new zealand deposits the timaru loess investigated by hardcastle has been proposed by j d raeside as the type section for new zealand loess jh was probably the first person to describe fragipans characteristic hard layers in loess the fragipan was not properly defined and named until the guy smith proposals c 1948 but hardcastle offered detailed descriptions in 1890 as the site of important loess investigation and possessing impressive stratigraphy the timaru loess could be proposed as an international loess section for new zealand hardcastle s stratigraphic observations were probably among the first relatively sophisticated palaeoclimatological observations made the inqua loess focus group could recognize the timaru loess the dashing rocks section as the representative loess section for new zealand a reference section for studies of loess stratigraphy and chronology hopefully preserved and curated by the local government authorities and other interested parties

subglacial erosion and englacial sediment transport modelled for north american ice sheets abstract reconstructions of north american glacial history have either been based on interpretation of the geologic record or on numerical models of continental ice dynamics because such models make no explicit reference to the geological products of glaciation the full potential of a combined approach has not been realized we present the results of a process based model of sediment production entrainment transport and deposition that represents a first step toward uniting these two lines of investigation in this model basal ice processes are dependent on ice sheet geometry hydrology and dynamics a three dimensional thermomechanical ice sheet model yields the ice geometry flow and thermal conditions that are used by a model of subglacial hydrology together these drive the basal process model comparisons of simulation results with mapped debris distributions of the hudson bay paleozoic carbonates and of the distinctive dubawnt group are used to test the validity of the transport model dispersion of debris radially out of hudson bay is greatly overestimated by the model and dispersion toward the bay equally underestimated this is because the modelled ice sheet has a single dome over hudson bay at glacial maxima including last glacial maximum rather than a saddle separating ice domes over quebec labrador and keewatin estimated rates of glacial erosion for the cordilleran and laurentide ice sheets are compared against those predicted by the model the model underestimates these rates because it underestimates the vigour of the quarrying process

mass balanced paleogeographic reconstructions paleogeography paleotopography and paleobathymetry of a closed erosion depositional system can be reconstructed by restoring sedimentary masses to elevated surfaces in a drainage basin based on the inverse of present erosion equations and adjusting for isostasy sea level changes sediment compaction and thermal subsidence the erosion deposition history of the northwestern gulf of mexico margin and its western central north american source area during the cenozoic is used to explore the sensitivity of mass balance reconstructions and changes in assumptions concerning erosion rate parameters and sea level

glacial interglacial variation in denudation rates from interior texas usa established with cosmogenic nuclides abstract the brazos colorado and trinity rivers of texas drain a tectonically quiescent non glaciated and low relief landscape inland from the gulf of mexico where long term 10 3 10 5 a changes in denudation rates are probably driven largely by climate change here we use cosmogenic 10be to obtain spatially averaged denudation rates for these river catchments primarily from terrace deposits associated with glacial or interglacial intervals over the past half million years the denudation rates are 30 35 higher during interglacial periods than during glacial periods and correlate broadly with temperature the results are consistent with predictions from the bqart sediment flux model and support the hypothesis that increased weathering rates associated with warmer climates will accelerate landscape erosion furthermore by analyzing 26al 10be in these deposits we can estimate the bed load sourced from up catchment surfaces the stored coastal plain fraction varies from 10 to 30 and is greater during times of relatively lower sea level the results indicate that although sediment flux is moderated by coastal plain storage increased up catchment flux during warmer interglacial periods outpaces evacuation of stored sediment during glacial periods resulting in a net increase in sediment flux to the ocean during warm intervals if this temperature sediment flux relationship is valid beyond the plio pleistocene transition then global sediment flux to the ocean from passive non glaciated and low relief landscapes would have been greater during the pliocene than in the cooler quaternary

thermal origin of the hawaiian swell heat flow evidence and thermal models the lithospheric reheating hypothesis for the origin of the hawaiian swell has been tested by heat flow measurements along the swell between hawaii and midway ninety five measurements at eight carefully selected sites show that the heat flux on the swell increases systematically from near normal values 52 2 mw m 2 near hawaii to values near midway 59 2 mw m 2 about 20 25 higher than normal for lithosphere of that age 110 m y this heat flow pattern is qualitatively consistent with a deep seated thermal anomaly created in a lithospheric plate moving across a fixed heat source modeling of the heat flow and bathymetry data on the hawaiian swell strongly suggest that the swell is caused by a rapid heating within 40 to 50 km depth of normal 90 m y old lithosphere over a relatively broad 500 1000 km region near hawaii this model is also consistent with gravity and geoid anomalies associated with the swell which require a low density region in the lower lithosphere and with flexure studies of seamounts in the hawaiian chain which indicate that the rigidity of the lithosphere is not significantly reduced by the reheating appendices a c are available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington d c 20009 document j82 005 1 00 payment must accompany order

rates and patterns of late cenozoic denudation in the northernmost atlantic coastal plain and piedmont topography of a 2800 km 2 section of the u s atlantic coastal plain and piedmont is reconstructed at five times from the late miocene to the holocene the reconstructions are based on mapping of fluvial colluvial and marginal marine deposits that are dated by radiocarbon palynostratigraphy and correlation to adjacent glacial and marine units denudation rates and patterns are calculated by subtracting successive topographies with 60 m horizontal resolution and 6 m vertical resolution the overall late miocene to holocene denudation rate of 10 m m y is similar to other estimates of long term denudation in the region the overall rate resolves spatially into a wide range of local rates varying from a minimum of 0 2 m m y on residual uplands to as high as 600 m m y in glacially rerouted stream channels the distribution of local rates shows that denudation is accomplished by stream incision in response to long term glacio eustatic decline followed by slope retreat into residual uplands from the incised channels slope retreat replaces the uplands with pediments and straths pediment landforms and sediments and observation of modern scarps and valley heads indicate that groundwater seepage from the base of residual uplands is an important mechanism of slope retreat this process is self limiting because as the volume of residual upland is reduced seepage diminishes and slope retreat slows until small residuals undergo little or no further reduction thus relict topography is preserved even as most of the landscape actively erodes

continental size eustasy and sediment yield sediment yield from modern continental blocks is a function of the area dissolved load and hypsometry mechanical load of the blocks hypsographic curves for modern continental blocks show that the change in the percentage area flooded for any change in eustatic sea level depends on the size of the block and the absolute sea level this allows predictions of changes in sediment yield around different sized blocks for any given eustatic change the range in size of continental blocks is such that for any given sea level change the blocks will show different percentage changes in yield data from modern continental blocks are compared with theoretical results assuming that the rules governing modern hypsometries applied in the past and a constant volume of continental crust it is possible to estimate the hypsographic curves of former continental blocks the implications of suggested past continental configurations and sea levels for sediment yield are discussed

late ordovician extinctions and sea level change abstract if ordovician continental blocks had similar hypsometries to modern continental blocks glacially induced regressions would have increased shallow water areas thus species area effects cannot be invoked to explain extinctions during these regressions because late ordovician sea level was so high glacially induced regressions of similar magnitudes to quaternary regressions would have dramatically increased the input of dissolved load into the shallow sea this pollution effect may have been one cause of the extinctions

late cenozoic increase in accumulation rates of terrestrial sediment how might climate change have affected erosion rates abstract accumulation rates of terrestrial sediment have increased in the past few million years both on and adjacent to continents although not everywhere apparently erosion has increased in elevated terrain regardless of when last tectonically active or what the present day climate in many regions sediment coarsened abruptly in late pliocene time sparser data suggest increased sedimentation rates at 15 ma approximately when oxygen isotopes in benthic foraminifera imply high latitude cooling if climate change effected accelerated erosion understanding how it did so remains the challenge some obvious candidates such as lowered sea level leading to erosion of continental shelves or increased glaciation account for increased sedimentation in some but not all areas perhaps stable climates that varied slowly allowed geomorphic processes to maintain a state of equilibrium with little erosion until 3 4 ma when large oscillations in climate with periods of 20 000 40 000 years developed and de

tectonic and climatic significance of a late eocene low relief high level geomorphic surface colorado new paleobotanical data suggest that in the late eocene the erosion surface which capped the front range colorado was 2 2 3 3 km in elevation which is similar to the 2 5 km present elevation of surface remnants this estimated elevation casts doubt on the conventional belief that the low relief geomorphic surface was formed by lateral planation of streams to a base level not much higher than sea level and that the present deeply incised canyons must represent neogene uplift of colorado description of the surface calculations of sediment volume and isostatic balance and fluvial landsculpting models demonstrate that while the high elevation of the erosion surface was due to tectonic forces its smoothness was mostly a result of climatic factors a sediment balance calculated for the front range suggests that from 2 to 4 km of material were eroded by the late eocene consistent with fission track ages this amount of erosion would remove a significant portion of the 7 km of laramide upper crustal thickening isostatic modeling implies that the 2 2 3 3 km elevation was most likely created by lower crustal thickening during the laramide a numerical model of fluvial erosion and deposition suggests a way that a late eocene surface could have formed at this high elevation without incision a humid climate with a preponderance of small storm events will diffusively smooth topography and is a possible mechanism for formation of low relief high level surfaces paleoclimate models suggest a lack of large storm events in the late eocene because of cool sea surface temperatures in the equatorial region return to a drier but stormier climate post eocene could have caused the incision of the surface by young canyons by this interpretation regional erosion surfaces may represent regional climatic rather than tectonic conditions

erosion in the western alps dora baltea basin 2 quantifying sediment yield abstract the present work shows how sediment composition can be used to constrain bed load sediment budgets in mountain catchments a database of high resolution petrographic and dense mineral analyses of detritus carried by the dora baltea river and its tributaries allowed us to partition bed load sediment budgets obtained from data available from a public authority between two different sets of sediment sources major tributaries and major geological units relative and absolute budgets of sediment bed load thus obtained are more robust than those derived from traditional empirical methods alone total detrital flux in the dora baltea drainage basin is 1 000 000 ton year bed load 590 000 ton year suspended load 410 000 ton year with denudation rates of 0 12 mm year data from italian public authority progetto di piano stralcio per l assetto idrogeologico pai parma supplemento straordinario della gazzetta ufficiale 166 more than 75 of the dora baltea total bed load 453 000 9000 ton year is derived from tributaries dora di ferret dora di veny savara grand eyvia buthier lys sourced from the highest granitoid peaks 4000 m a s l m bianco m rosa m cervino gran paradiso massifs which drain 36 of the whole catchment the m bianco massif with its granitoid lithology extreme relief and heavily glaciated drainage basins occupies only 3 of total basin area but it produces 294 000 6000 tons of arkosic sands per year which represents 50 of total dora baltea bed load the dora di veny 2 of total dora baltea mountain catchment exhibits the highest denudation rate of the whole dora baltea mountain basin 0 73 mm year the values calculated in this study compare well with measured modern river loads of partly glaciated mid latitude mountain regions

late orogenic strike slip faulting and escape tectonics in frontal dinarides hellenides croatia yugoslavia albania and greece the frontal zone of the dinarides and its foreland are characterized by the presence of major late orogenic northwest southeast faults trending parallel to and locally dissecting the leading edge of the thin skinned thrust belt on the basis of their geometry and regional distribution these structures are interpreted as right lateral strike slip faults and are related to the formation of en echelon compres sional structures in the split dubrovnik area of the central adriatic region and to the opening of the post messinian pull apart albanian foredeep south adriatic basin in the pliocene holocene these strike slip faults represent the last stage of the mountain building process in the pliocene and holocene when the forelandward prop agation of the dinaric thrust belt was inhibited by stacking of thrust sheets and by overall thickening of the colliding continental crust in that respect the dinaric side of the apulia adria differs from the apenninic side where the thin skinned thrusting progressed normally toward the foreland until the pliocene on a regional scale these northwest southeast trending strike slip faults in the frontal dinarides and their apparent continuation to the hellenides of western greece as well as the dextral vardar fault system indicate the existence of escape tectonics in the di naric hellenic region during the last stage of orogeny the strike slip faults provided a means of tectonic transport from the collision zone of apulia with europe toward the subduction zone of the hellenic trench in southern greece the southeastward moving dinaric hellenic blocks apparently interfered with the westward moving anatolian plate and deflected it southwestward the albanian foredeep in terms of tectonic setting resembles the pull apart vienna basin which formed within the attenuated southwest northeast trending transfer zone of the west carpathi ans during the last stages of the alpine orogeny the late orogenic strike slip faulting may have breached seals and thus negatively affected the hydrocarbon potential of the dinaric hellenic side of the peri adriatic region as contrasted with that of the more prolific apenninic side which was not significantly disrupted by the late orogenic strike slip faulting

miocene to recent tectonic evolution of the eastern mediterranean new pieces of the old mediterranean puzzle the mediterranean sea and its surrounding land mass fig 1 have long been recognized as an excellent bnatural laboratoryq for the study of fundamental plate tectonic processes including rifting passive margin development contraction and associated subduction ophiolite emplacement and orogenesis and as such it is one of the most extensively studied regions of the world e g hsu et al 1975 dixon and robertson 1984 kastens et al 1990 emeis et al 1996 comas et al 1996 robertson 1998 mcclusky et al 2000 the late cretaceous to holocene tectonic evolution of the eastern mediterranean region is extremely complex and controversial and several commonly conflicting hypotheses have been proposed the scope of this special issue does not permit a full discussion of these hypotheses we refer the reader to robertson 1998 for a review however there is general agreement that the eastern mediterranean evolved as a small ocean basin during the late triassic robertson and dixon 1984 robertson et al 1991 this embryonic ocean achieved its maximum

evidence of quaternary and recent activity along the kyaukkyan fault myanmar abstract cenozoic right lateral shear between the eastern indian margin and eurasia is expressed by numerous n s trending fault systems inboard of the sunda trench including the sagaing fault the most easterly of these fault systems is the prominent 500 km long kyaukkyan fault on the shan plateau myanmar s largest recorded earthquake mw 7 7 on 23rd may 1912 focused near maymyo has been attributed to the kyaukkyan fault but the area has experienced little significant seismicity since then despite its demonstrated seismic potential and remarkable topographic expression questions remain about the kyaukkyan fault s neotectonic history in this study we document robust geologic evidence of fault activity along the kyaukkyan fault field investigation and interpretation of satellite imagery reveal deformation features developed along a fault system mostly indicative of quaternary dextral strike slip faulting clearly defined tectonic geomorphology including fault scarps and linear valleys are used to trace the northernmost and southernmost part of the fault the fault s central section is characterised by a complex pull apart system whose normal border faults show signals of relatively slow recent activity dextral transtensional activity along the kyaukkyan fault is recorded by geomorphic features such as sag ponds shutter ridges offset and beheaded streams triangular facets and low sinuosity mountain fronts the quaternary age of activity is demonstrated by short lived geomorphic features such as wind gaps offset and deformed alluvial fans and even offset of man made structures in the inle basin alluvial fan successions along the easternmost mountain front reveal a vertical transition from faulted and folded alluvial fan sequences adjacent to pre cenozoic flanking ranges to overlying gravels that appear less deformed conversely a locally buried cross basin fault system has fresh geomorphic expression even within the uppermost parts of the lacustrine fluvial basin fill this may indicate quaternary migration of dominant fault deformation from sidewall faults to a cross basin fault system which is indicative of a mature strike slip fault system and has been observed in other active strike slip faults around the world and in analogue models

new data on the vrancea nappe moldavidian basin outer carpathian domain romania paleogeographic and geodynamic reconstructions a study has been performed on the cretaceous to early miocene succession of the vrancea nappe outer carpathians romania based on field reconstruction of the stratigraphic record mineralogical petrographic and geochemical analyses extra basinal clastic supply and intra basinal autochthonous deposits have been differentiated appearing laterally inter fingered and or interbedded the main clastic petrofacies consist of calcarenites sub litharenites quartzarenites sub arkoses and polygenic conglomerates derived from extra basinal margins an alternate internal and external provenance of the different supplies is the result of the paleogeographic re organization of the basin margins system due to tectonic activation and exhumation of rising areas the intra basinal deposits consist of black shales and siliceous sediments silexites and cherty beds evidencing major environmental changes in the moldavidian basin organic matter rich black shales were deposited during anoxic episodes related to sediment starvation and high nutrient influx due to paleogeographic isolation of the basin caused by plate drifting the black shales display relatively high contents in sub mature to mature type ii lipidic organic matter good oil and gas prone source rocks constituting a potentially active petroleum system the intra basinal siliceous sediments are related to oxic pelagic or hemipelagic environments under tectonic quiescence conditions although its increase in the oligocene part of the succession can be correlated with volcanic supplies the integration of all the data in the progressive reorientation of convergence direction carpathian model and their consideration in the framework of a foreland basin led to propose some constrains on the paleogeographic geodynamic evolutionary model of the moldavidian basin from the late cretaceous to the burdigalian

accelerating late quaternary uplift of the new georgia island group solomon island arc in response to subduction of the recently active woodlark spreading center and coleman seamount abstract the new georgia island group of the solomon islands is one of four places where an active or recently active spreading ridge has subducted beneath an island arc we have used coral reef terraces paleobathymetry of neogene sedimentary rocks and existing marine geophysical data to constrain patterns of regional quaternary deformation related to subduction of the recently active woodlark spreading center and its overlying coleman seamount these combined data indicate the following vertical tectonic history for the central part of the new georgia island group 1 subsidence of the forearc region tetepare and rendova islands to water depths of 1500 m and deposition of marine turbidites until after 270 ka 2 late quaternary uplift of the forearc to sea level and erosion of an unconformity 3 subsidence of the forearc to 500 m bsl and deposition of bathyal sediments and 4 uplift of the forearc above sea level with holocene uplift rates up to at least 7 5 mm yr on tetepare and 5 mm yr on rendova in the northeastern part of the new georgia island group our combined data indicate a slightly different tectonic history characterized by lower amplitude vertical motions and a more recent change from subsidence to uplift barrier reefs formed around new georgia and vangunu islands as they subsided 300 m by 50 100 ka subsidence was replaced by uplift that accelerated to holocene rates of 1 mm yr on the volcanic arc compared with rates up to 7 5 mm yr in the forearc area of tetepare and rendova uplift mechanisms such as thermal effects due to subduction of spreading ridges tectonic erosion or underplating of deeply subducted bathymetric features are not likely to function on the 270 ka period that these uplift events have occurred in the new georgia island group a more likely uplift mechanism for the post 270 ka accelerating uplift of the forearc and volcanic arc of the new georgia island group is progressive impingement of the coleman seamount or other topographically prominent features on the subducting plate regional effects we relate to this ongoing subduction related process include 1 late quaternary post 270 ka accelerating uplift of the rendova tetepare forearc area in response to initial impingement of the coleman seamount followed by exponentially increasing collisional contact between the forearc and seamount 2 later quaternary propagation of uplift arcward to include the volcanic arc as the area of collisional contact between the forearc and seamount increased and 3 large wavelength folding that has produced regional variations in late holocene uplift rates observed in both forearc southern rendova tetepare and volcanic arc new georgia island areas we propose that the dominant tectonic effect of coleman seamount impingement is horizontal shortening of the forearc and arc crust that is produced by strong coupling between the subducting seamount and the unsedimented crystalline forearc of the new georgia island group the horizontal forces due to mechanical resistance to subducting rugged ridge and seamount topography may have terminated spreading of the woodlark spreading center entering the trench ghizo ridge and converted it to a presently active strike slip fault zone

rejuvenation of appalachian topography caused by subsidence induced differential erosion topographic relief continued to develop in the appalachian mountains eastern usa long after the tectonic forces that created the range had become inactive numerical modelling and reconstructions of sediment deposition in the gulf of mexico suggest that the topographic relief was rejuvenated by subsidence induced differential erosion caused by sinking of the subducted farallon slab in the underlying mantle in ancient orogens such as the appalachian mountains in the eastern united states the difference between the high and low points topographic relief can continue to increase long after the tectonic forces that created the range have become inactive climatic forcing1 and mantle induced dynamic uplift2 3 could drive formation of relief but clear evidence is lacking in the appalachian mountains here i use a numerical simulation of dynamic topography in north america combined with reconstructions of the sedimentation history from the gulf of mexico4 to show that rejuvenation of topographic relief in the appalachian mountains since the palaeogene period could have been caused by mantle induced dynamic subsidence associated with sinking of the subducted farallon slab specifically i show that patterns of continental erosion and the eastward migration of sediment deposition centres in the gulf of mexico closely follow the locus of predicted dynamic subsidence furthermore pulses of rapid sediment deposition in the gulf of mexico4 and western atlantic5 correlate with enhanced erosion in the appalachian mountains during the miocene epoch caused by dynamic tilting of the continent the model predicts that such subsidence induced differential erosion caused flexural isostatic adjustments of appalachian topography that led to the development of 400 m of relief and more than 200 m of elevation i propose that dynamically induced continental tilting may provide a mechanism for topographic rejuvenation in ancient orogens

dramatic pliocene quaternary subsidence of the southern rhodes basin and concomitant north tilting and uplift of the anaximander mountains the junction of hellenic and cyprus arcs eastern mediterranean sea abstract the anaximander mountains and the rhodes basin at the junction of cyprus and hellenic arcs are one of the tectonically most complex regions in the eastern mediterranean harmonically tilted messinian and the uppermost messinian pliocene successions across the northern and eastern margins of the rhodes basin showed that these regions experienced dramatic subsidence exceeding 1500 2500 ms 1125 1875 m 1500 m s 1 during the upper pliocene quaternary tilted upper pliocene quaternary growth strata wedges showing apparent north directed downlap along the northern foothills of the anaximander mountain suggested that this region experienced 1000 2500 ms 750 1125 m concomitant uplift the absence of faults showing extensional stratigraphic separations and the relative subsidence rates calculated using amount of tilting collectively suggest that the rhodes basin experienced sagging of its deeper basinal regions which is attributable to the loading effect of the building of the tauride mountains modified by the vertical axis rotations of the beydaglari block and the island of rhodes and the horizontal axis rotation of the anaximander mountain messinian and uppermost messinian pliocene were tectonically relatively quiet as shown by the harmonically structured and isopachous successions across the rhodes basin and anaximander mountain this interval coincides with the paleomagnetically determined 9 counterclockwise vertical axis rotation of the island of rhodes the dramatic subsidence observed within the rhodes basin and the concommitant uplift of the anaximander mountain and its western extension occurred broadly coincident with southeast tilting of the island of rhodes and its associated 500 600 m subsidence between 2 5 and 1 8 ma the northwest tilting between 1 5 and 1 1 ma and the associated re emergence of the southeastern coast the large counterclockwise rotation of the island of rhodes since 0 8 ma corresponds with the enormous subsidence observed across the northeastern sector of the rhodes basin which brought the shelf edge deltas from the near sea level to their present day depth of 1200 1500 m

kinematic reconstruction of the caribbean region since the early jurassic abstract the caribbean oceanic crust was formed west of the north and south american continents probably from late jurassic through early cretaceous time its subsequent evolution has resulted from a complex tectonic history governed by the interplay of the north american south american and paleo pacific plates during its entire tectonic evolution the caribbean plate was largely surrounded by subduction and transform boundaries and the oceanic crust has been overlain by the caribbean large igneous province clip since 90 ma the consequent absence of passive margins and measurable marine magnetic anomalies hampers a quantitative integration into the global circuit of plate motions here we present an updated quantitatively described kinematic reconstruction of the caribbean region back to 200 ma integrated into the global plate circuit and implemented with gplates free software our reconstruction includes description of the tectonic units in terms of euler poles and finite rotation angles our analysis of caribbean tectonic evolution incorporates an extensive literature review to constrain the caribbean plate motion between the american continents we use a novel approach that takes structural geological observations rather than marine magnetic anomalies as prime input and uses regionally extensive metamorphic and magmatic phenomena such as the great arc of the caribbean the clip and the caribbean high pressure belt as correlation markers the resulting model restores the caribbean plate back along the cayman trough and major strike slip faults in guatemala offshore nicaragua offshore belize and along the northern andes towards its position of origin west of the north and south american continents in early cretaceous time we provide the paleomagnetic reference frame for the caribbean region by rotating the global apparent polar wander path into coordinates of the caribbean plate interior cuba and the chortis block we conclude that formation of the caribbean plate west of the north and south americas as a result of panthalassa pacific spreading leads to a much simpler plate kinematic scenario than proto caribbean atlantic spreading placing our reconstruction in the most recent mantle reference frames shows that the clip originated 2000 3000 km east of the modern galapagos hotspot and may not have been derived from the corresponding mantle plume finally our reconstruction suggests that most if not all modern subduction zones surrounding the caribbean plate initiated at transform faults two of these along the southern mexican and nw south american margins evolved diachronously as a result of migrating trench trench transform triple junctions

on the use of sedimentation rates in deciphering global change 1 the amount of sediment deposited through time at a given place is controlled by both tectonic and climatic factors that change over several length and time scales for these reasons the sedimentary record is commonly exploited to study global change to understand this record most studies have relied on assembling data from a few localities within a given reservoir and have extrapolated those data to whole of the reservoir here it is shown not only that this approach has very large inherent uncertainties but also that the use of extrapolating sedimentary records has little physical significance a much better approach although much more difficult is via a full three dimensional mass balance calculation

erosion in the western alps dora baltea basin 1 quantifying sediment provenance abstract sourced in the m bianco the highest mountain of the alps the dora baltea river cuts across the arc of the western alps drains all major alpine tectonic units from the helvetic domain to the south alpine domain and finally joins the po river petrographic composition of clastic detritus carried by the dora baltea river and its tributaries faithfully mirrors the complex geology of the western alps high resolution modal analysis of dora baltea sands allowed us to distinguish seven end member metamorphoclastic provenances river sands from the m bianco external massif are dominated by quartz feldspars and hornblende detritus from basement and cover rocks of the brianconnais zone includes low grade metasedimentary lithic fragments epidote chloritoid and garnet sands from the internal penninic massifs include quartz and subordinate feldspars garnet and epidote abundant metabasite and serpentine schist lithic grains along with epidote actinolite and few pyroxenes characterize detritus from the calcschists and meta ophiolites of the oceanic piemonte zone sands from the austroalpine zone include quartz abundant metamorphic lithic fragments garnet and locally significant sillimanite dent blanche kinzigites the relative contribution of each end member to the dora baltea sediment flux was assessed with forward modelling of end member mixing our estimates calculated from the entire petrographic and mineralogical data set indicate that the main sources of bed load in the dora baltea mountain basin are the granitoid to gneissic rocks exposed in the m bianco massif and in the austroalpine zone in order to make allowance for the contribution of a particular bedrock constituent in a compound source area to the derivative sand the original concept of sand generation index sgi was modified to assess the relative contribution of the seven end member sources of detritus the highest total basin sgi indices are calculated for the m bianco massif sgi 16 4 and austroalpine domain sgi 1 4 the m bianco massif which represents only 3 of the whole catchment has the highest capacity of sand sized bed load production owing to its granitoid lithology and extreme relief this actualistic provenance study demonstrates that sediment composition can be markedly influenced by source rocks that occupy only a minor portion of the drainage area