characterization of quartzites in the southern korean peninsula abstract in the southern korean peninsula twelve quartzite strata occur in the gyeonggi massif and okcheon belt their geologic ages range from precambrian to upper paleozoic all quartzites in the gyeonggi massif are of precambrian in age and are characterized by high grade metaquartzites they are seosan anyang yongmunsan and uiam quartzites from west to east quartzite types occurring in the okcheon belt are diverse from orthoquartzite to medium grade metaquartzite orthoquartzites are all paleozoic in age and are distributed mainly in the eastern okcheon belt taebaeksan basin jangsan dongjeom and jeongseon quartzites with one in the central okcheon belt mungyeong quartzite low grade metaquartzite is hwasan quartzite in the western part and medium grade metaquartzites are daehyangsan and geumsusan quatzites in the central part and yongamsan quartzite in the southwestern part of the okcheon belt distribution of quartzite types in the southern korean peninsula is not related to the geologic age of quartzites as a case study quartzite characteristics were applied to a provenance study of quartzite clasts in the northwestern part of the cretaceous gyeongsang basin quartzite clasts in the study area are interpreted to have been mostly derived from source quartzites in the okcheon belt which is consistent with the results of previous studies

encrusting corals on a latest ordovician to earliest silurian rocky shore southwest hudson bay manitoba canada paleozoic tabulate corals are generally thought to have been free standing a flattened disc shaped to dome shaped morphology providing a degree of stability in shallow water high energy environments the ability to encrust has previously been suggested by patterns of competitive overgrowth in certain species definite proof of encrustation by favositid corals is exhibited in an extraordinary example of an ancient rocky shore exposed for 350 m on hudson bay near churchill manitoba carbonate strata attributed to the upper ordovician port nelson or lower silurian severn river formations locally transgress a massive precambrian quartzite an ancient shoreface is clearly marked by large smoothly eroded boulders of the dark quartzite commonly 2 10 m in diameter the boulders are buried in coarse carbonate debris but corals up to 20 cm in diameter are found cemented directly onto the surface of some boulders deep pitting of many boulders to a depth of 2 3 cm was contemporaneous and may have been promoted by unpreserved encrusters such as sponges or anemones

early middle paleozoic intraplate orogeny in the ogcheon belt south korea a new insight on the paleozoic buildup of east asia the polycyclic ogcheon belt of south korea represents the boundary between two precambrian blocks investigation on the timing and kinematics of the block agglomeration is of considerable bearing on the understanding of the constitution of the asian continent we report here structural evidence showing that the earlier tectonic event dates back to early middle paleozoic the ogcheon tectonism or orogeny the ductile piling up of nappes of the ogcheon belt corresponds to an intracontinental orogeny involving the opening and the subsequent closure of an aborted rift and not of a wide oceanic area the nappes contain unequivocal evidence for ductile shearing with a northwest over southeast sense of movement field evidence includes the presence of s1 and s1 2 foliations bearing an extensive stretching lineation perpendicular to the belt associated with a strongly noncoaxial deformation regime the f1 isoclinal folds are commonly a type and sheath folds whose axes are parallel to the stretching lineation whereas the southeast facing f2 recumbent folds have subhorizontal axes parallel to the belt all lines of evidence unconformity superposed deformations age of the metamorphism etc imply that the d1 2 ogcheon tectonism is pre middle carboniferous late silurian early devonian the subsequent indosinian middle triassic f3 upright synfolial folds that trend nne ssw and later structures clearly overprint the middle paleozoic ductile thrusts and isoclinal folds the early paleozoic ogcheon supergroup is formed of a thick volcanosedimentary pile deposited above an early platform sequence in a rift basin on the basis of the geochemical characteristics of the metavolcanics it appears that oceanization did not occur and ogcheon rift aborted soon after it was formed we suggest that middle paleozoic ductile nappe structures have been formed by the structural inversion of the rift extensional features during the ductile stacking episode the early formed foliation and isoclinal folds have been folded in a continuum during the same tectonic event middle carboniferous terrigenous formations have been deposited unconformably upon folded and thrust older rocks a tentative correlation with early paleozoic imjingang qinling and cathaysian belts within the asian continent reveals that ogcheon rift was emplaced within the south china plate and that imjingang belt should represent the limit between north and south china blocks in the korean peninsula

ordovician paleotopography as evidenced from original dips and differential compaction of dolostone and shale unconformably overlying precambrian basement on manitoulin island canada abstract the middle to basal upper ordovician lindsay formation unconformably overlies the paleoproterozoic bar river and lorrain formations on manitoulin island ontario canada representing a depositional hiatus of at least 1 7 billion years the paleoproterozoic inliers currently exposed as basement highs in the sheguiandah region comprised a 14 km2 area of quartz arenite archipelago during the middle to late ordovician inland sea transgression of north america the quartz arenite outcrop collectively covers an area of approximately 1 8 km2 high energy transport and reworking during wave and tropical storm activity along a high relief rocky shoreline is indicated by dolostone containing 2 5 m size rounded to subrounded quartz arenite boulders with percussion marks up to 4 5 m size subangular quartz arenite blocks consistent with mechanical breakage along joints fractures or bedding planes lenticular conglomerate beds and cracks in quartz arenite basement containing mixtures of dolostone quartz granules and fossiliferous debris with continued transgression organic rich carbonate muds were deposited under low energy conditions either on carbonate strata or directly on quartz arenite basement in restricted regions protected from the open sea clast size distribution in the dolostone clast rounding and the location of the shale quartz arenite unconformity relative to basement highs are all consistent with a longshore current running from the present northeast to southwest with the leeward sides of rocky islands protected from high wave and storm energy processes subsequent deposition of upper ordovician and silurian strata resulted in burial and differential compaction of the lindsay formation units the compaction may have been associated with fractures through which mg rich fluids migrated locally altering the lowermost lindsay formation to dolostone evidence for differential compaction is provided by bed thickening down dip of basement highs and boulder flanks and higher regional dips in shale beds proximal to basement highs compared with dolostone strata the relatively high angle strata of the lindsay formation are a result of the combined effects of paleotopography a high relief rocky shoreline and differential compaction

geodynamics of the ogcheon belt south korea abstract the ogcheon belt is a stack of synmetamorphic southeastward verging nappes resulting from the deformation of a volcanosedimentary sequence deposited in an early palaeozoic rift which was affected by polyphase tectonics its pre cretaceous structure results from three main orogenic events the ogcheon late silurian devonian indosinian late permian triassic and yenshanian middle jurassic early cretaceous tectonic phases the external autochthonous or para autochthonous units represent platform zones with shallow water deposits whereas rift facies characterize the internal domain the yeongweol sequence forming an outer shelf on the southeastern margin of the rift displays affinities with the jiangnan basin of south china it is in wrench fault contact with the easternmost duwibong sequence correlated with the north china north korea platform in the internal metamorphic units post cambrian early ordovician pelitic and turbiditic rift metasediments overlie a thin cambrian or cambrian ordovician early platform sequence two subdomains are distinguished the upper units chung ju and pibaryeong units representing the deep axial part of the basin contain distal flyshoids and large olistoliths derived from the northwestern narrow margin the lower units turung san poeun and iwharyeong are related to the wide margin located between the deep rift domain and the stable southeastern platform the latter transitional domain is characterized by thick submarine debris flows and volcanics of alkali or transitional tholeiitic affinity the volcanic activity and mass gravity flow sedimentation are closely related to the crustal thinning and subsequent rifting and tilting lithostratigraphic evidence allows the correlation of the unfossiliferous rift metasediments with the cambrian ordovician platform sequence in one single basin the post middle silurian pre mid carboniferous ogcheon ensialic orogeny resulted in the closure of the rift with relatively minor effects in the platform area it gave rise to an intracontinental fold thrust belt without ophiolites this tectonic event may have been contemporaneous with early palaeozoic tectonism in the quinling belt in central china and in the southeast china fold belt the definitive constitution of the sino korean craton took place before the mid carboniferous and molasse sedimentation was initiated on a single platform located on the western edge of the yakuno oceanic basin of southwest japan in late permian and early triassic times the closure of the oceanic area and the subsequent westward collision of the honshu block are marked in korea by the intracratonic indosinian tectonism since late triassic times predominantly transcurrent movements have occurred along nne ssw faults associated with syntectonic intermontane troughs and important granitization

late ordovician massive bedded thalassinoides ichnofacies along the palaeoequator of laurentia abstract massive bedded thalassinoides ichnofacies occurs pervasively in widely separated areas on the vast upper ordovician carbonate platforms along the palaeoequator of laurentia from the borglum river formation in north greenland through the red river formation and bighorn dolomite of the williston basin manitoba canada to wyoming usa to the ely springs dolomite and equivalent strata of the eastern great basin utah and nevada usa the late ordovician thalassinoides is characterised by complex three dimensional anastomosing or multi level galleries that are consistent in size pattern and density with preserved depth of 1 m or greater in addition to the similar thalassinoides burrows the ichnofacies across the palaeocontinent also contains typical taxa of the red river biota such as the soccer ball sized receptaculitid fisherites large shelled diverse and abundant nautiloids the distinctively planispiral gastropod maclurina as well as diverse tabulate and rugose corals the consistent characteristics of the red river biofacies and thalassinoides ichnofacies suggest a palaeogeographically homogeneous and temporally stable depositional environment along the palaeoequatorial belt of laurentia during the pre hirnatian late ordovician the thalassinoides ichnofacies marked the first phase of mega scale invasion of burrowers into relatively deep water platform and shelf environments by successively creating a well oxygenated deep burrow system for protection and deposit feeding such substrate tiering expansion constituted an important aspect of the great ordovician biodiversification event

subsidence compaction and gravity sliding implications for 3d geometry dynamic rupture and seismic hazard of active basin bounding faults in southern california in southern california high rates of measured geodetic shortening occur where active basin bounding faults thrust early cenozoic rocks over young uncon solidated sediments this implies that compaction subsidence and other nonelastic processes of footwall deformation may play an important role in contributing to the high rates of observed crustal strain even in the absence of active tectonic short ening sediment compaction alone can produce surficial motions that mimic deep fault slip or elastic strain accumulation differential compaction and subsidence of footwall sediments relative to hanging wall rocks can lead to increased vertical sep aration basinward collapse and fault rotation about horizontal axes such effects contribute to net horizontal and vertical motions in both geologic and geodetic data and if not properly accounted for result in incorrect estimates of the inferred seismic hazard subsidence and compaction also increase the potential for gravity sliding toward the basin and the development of significant nonplanar 3d fault geometry a prime example occurs along the san cayetano fault that bounds the eastern ventura basin at shallow levels a large thrust sheet the modelo lobe with low dip extends out in front of the more steeply dipping planar fault segment by over 4 km is nearly 2 km thick and occupies over 60 cubic km this geometry is strongly indicative of gravity driven failure resulting from hanging wall uplift basinward tilt and collapse enhanced by footwall subsidence and compaction failure of this mega slide off the hanging wall block most likely occurred within the rincon formation a thick ductile shale sequence that often accommodates detachment slip this 3d geometry has significant implications for how the fault may behave during dynamic rupture and implies that additional care should be taken in extrapolating near surface measure ments or estimates of fault slip and dip to seismogenic depths

near surface expression of the eastern part of the san cayetano fault a potentially active thrust fault in the california transverse ranges examined in this study are the near surface geometry late cenozoic geologic history and seismic potential of the eastern part of the san cayetano fault a major north dipping thrust fault of the transverse ranges california the fault generally dips with a low angle close to the surface but the dip increases up to 40 at about 5 km below sea level the fault may become nearly horizontal at depth and root into a midcrustal detachment surface of the transverse ranges the late cenozoic reverse movement along the san cayetano fault may have begun during the deposition of the lower part of the saugus formation the fault has also moved after the deposition of the saugus formation within the last 0 2 m y the san cayetano fault should be considered at least potentially active and may be capable of producing damaging earthquakes this conclusion is based collectively on 1 the presence of several surficial geological features suggestive of recent movement along the fault 2 the presence of microearthquakes on the fault plane and 3 the structural similarity of the fault to seismically active north dipping thrust faults of the region

deformation rates across the placerita northridge mw 6 7 aftershock zone and hopper canyon segments of the western transverse ranges deformation belt abstract aftershocks of the 1994 northridge m w 6 7 earthquake provide insights into the geometry of the seismic source faults in the san fernando valley and the east ventura basin and allow the calculation of deformation rates for the region the northridge thrust and santa susana faults dip in opposite directions with the northridge thrust entirely beneath the santa susana fault these opposing reverse faults interact resulting in a folded active santa susana fault and uplift in the footwall block of that reverse fault two balanced cross sections suggest thick skinned deformation of the western transverse ranges the western section across the modelo lobe segment of the north dipping san cayetano fault and the easternmost surface trace of the south dipping oak ridge fault is west of any aftershocks of the northridge earthquake and has been termed the hopper canyon segment of the deformation belt structural modeling predicts a dip of 46 s on the oak ridge fault at seismogenic depths horizontal shortening rates are calculated by adding the products of the dip slip displacements and the cosines of the dips of both faults the eastern cross section shows the northridge mainshock with a 45 south dipping nodal plane at a depth of 18 km aftershocks reach a depth of 20 km in a thin skinned paradigm a hinge should occur at the surface near the santa monica mountains due to rocks moving from a decollement at the brittle plastic transition and changing dip as they move up the ramp no hinge of that magnitude occurs there calculation of horizontal short ening rates across this part of the western transverse ranges must take into account the displacement on both the northridge thrust eastern extension of the oak ridge fault and the santa susana fault placerita segment horizontal shortening rates are 8 2 2 4 mm yr across the modelo lobe segment of the san cayetano fault and the oak ridge fault and 5 7 2 5 mm yr across the northridge thrust and the santa susana fault these rates are consistent with those based on tectonic geodesy using gps dip slip displacement rates on the faults are 1 7 mm yr for the northridge thrust since 2 3 ma 4 1 0 4 mm yr for the oak ridge fault since 500 ka 5 9 3 9 3 8 mm yr for the santa susana fault since 600 to 2300 ka and 7 4 3 0 mm yr for the modelo lobe segment of the san cayetano fault since 500 ka this indicates that the slip rates on the north dipping the eastern san cayetano and the santa susana faults are comparable but the slip rate on the south dipping faults decreases eastward the slip rate on the oak ridge fault in the ventura basin is more than double that of the northridge thrust

the effects of crack anisotropy on the hypocentral locations of local earthquakes summary exact modelling of the earthquake location process in regions of dilatancy anisotropy shows that failure to take account of the velocity anisotropy in the determination of local hypocentres can result in erroneous and misleading locations in particular the locations can indicate spurious migrations of foci from the true epicentral positions and the true depths of foci these spurious locations may indicate planes of hypocentres deviating from the true fault plane observations of such phenomena have been noted several times in the literature however once the anisotropic model is known a simple location program incorporating the anisotropic velocity variations permits accurate location of local earthquakes using p and first s wave arrival times

erosion and accretion processes in a muddy dissipative coast the chao phraya river delta thailand seasonal variation in seabed elevation in the muddy intertidal zone of the chao phraya river delta an area of serious coastal erosion for 40 years was assessed using information on waves and tides predicted by numerical simulations the study area is under the influence of the southeast asian monsoon climate and lies in the innermost part of a sheltered gulf across which a low gradient slope has developed observations aimed at evaluating the effectiveness of a prototype breakwater on mitigating coastal erosion indicated that the seasonal variation in the seabed elevation typically about 30 cm was caused primarily by seasonal changes in wave direction and height the breakwater seems to have contributed to a net rise in the seabed level at sites behind the structure seabed erosion was most apparent during the northeast monsoon when waves are weak erosion under this low wave energy state was attributed to the combined effect of wave breaking and the low tidal level a difference in the observed seabed accretion rate between the transitional intermonsoon period and the succeeding southwest monsoon period was attributed to the direction of the wave energy flux offshore sediments seem to have been supplied efficiently to the study area by waves during the transitional period another potential cause of seabed erosion and accretion during the wet southwest monsoon season was the discharge of water and sediments from local canals associated with intense tropical rainfall this discharge seems to be linked to land use in the coastal area the results of this study show the importance of monitoring across shore sediment transport for better understanding of coastal erosion processes copyright 2010 john wiley sons ltd

the 1994 northridge earthquake sequence in california seismological and tectonic aspects the m w 6 7 northridge earthquake occurred on january 17 1994 beneath the san fernando valley two seismicity clusters located 25 km to the south and 35 km to the north northwest preceded the mainshock by 7 days and 16 hours respectively the mainshock hypocenter was relatively deep at 19 km depth in the lower crust it had a thrust faulting focal mechanism with a rake of 100 on a fault plane dipping 35 to the south southwest and striking n75 w because the mainshock did not rupture the surface its association with surficial geological features remains difficult to resolve nonetheless its occurrence reemphasized the seismic hazard of concealed faults associated with the contractional deformation of the transverse ranges the northridge earthquake is part of the temporal increase in earthquake activity in the los angeles area since 1970 the mainshock was followed by an energetic aftershock sequence eight aftershocks of m 5 0 and 48 aftershocks of 4 m 5 occurred between january 17 and september 30 1994 the aftershocks extend over most of the western san fernando valley and santa susana mountains they form a diffuse spatial distribution around the mainshock rupture plane illuminating a previously unmapped thrust ramp extending from 7 10 km depth into the lower crust to a depth of 23 km no flattening of the aftershock distribution is observed near its bottom at shallow depths above 7 10 km the thrust ramp is topped by a dense distribution of aftershock hypocenters bounded by some of the surficial faults the dip of the ramp increases from east to west the west side of the aftershock zoae is characterized by a dense steeply dipping and north northeast striking planar cluster of aftershocks that exhibited mostly thrust faulting these events coincided with the gillibrand canyon lateral ramp along the east side of the aftershock zone the aftershocks also exhibited primarily thrust faulting focal mechanisms the focal mechanisms of the aftershocks were dominated by thrust faulting in the large aftershocks with some strike slip and normal faulting in the smaller aftershocks the 1971 san fernando and the 1994 northridge earthquakes ruptured partially abutting fault surfaces on opposite sides of a ridge both earthquakes accommodated north south contractional deformation of the transverse ranges the two earthquakes differ primarily in the dip direction of the faults and the depth of faulting the 1971 north northeast trend of left lateral faulting chatsworth trend was not activated in 1994

late holocene high frequency east asia winter monsoon variability inferred from the environmentally sensitive grain size component in the distal shelf mud area east china sea the b2 b2g and i4 sediment cores recovered from the centre of the distal mud area of the east china sea ecs were analysed for grain size distribution proxies for environmentally sensitive grai

why are ancient rocky shores so uncommon the geologic history of rocky shore biotas has been neglected by paleontologists under present conditions of high continentality rocky shores account for more than 33 of the world s coastline they are generally located on shores facing narrow continental shelves where the pattern of global plate tectonics exerts much influence over their regional concentration the highest frequency of rocky shores occurs on islands associated with hot spots island arcs and convergent plate margins associated with subduction rocky shores situated in these settings are subject to recycling so their remains are rare in the stratigraphic record some passive continental margins including those along newly rifted oceans and those with low rates of sedimentation exhibit frequencies of rocky shores as high or higher than those found on many convergent plate margins these have a good chance of being retained in the stratigraphic record for geologically significant periods of time epicontinental flooding reduces the

the santa barbara california earthquake of 13 august 1978 the 5 1 m l santa barbara earthquake of 13 august 1978 occurred at 22h54m 52 8s utc the epicenter was located 3 km southeast of santa barbara at 34 23 9 n latitude and 119 40 9 w longitude with a focal depth of 12 7 km the main shock was followed between 13 august and 30 september by 373 aftershocks that were located with the caltech usgs array the aftershock zone extended 12 km wnw from the epicenter and was 6 km wide in the n s direction and it had a very clear temporal development during the first 20 min of activity all the aftershocks were located in a cluster 7 km wnw of the main shock epicenter during the next 24 hr the aftershock zone grew to 11 km in the wnw direction and 4 km in the n s direction during succeeding weeks the zone extended to 12 by 6 km this temporal spatial development relative to the main shock epicenter may indicate that the initial rupture propagated 7 km unilaterally to the wnw and the initial rupture plane may have been considerably smaller than the eventual aftershock zone this smaller area suggests that the stress drop may have been significantly greater than that derived from the final aftershock zone in cross section the aftershock hypocenters outline a nearly horizontal plane dipping 15 or less at 13 km depth the main shock focal mechanism indicates nne ssw compression and vertical extension the preferred fault plane strikes n80 w and dips 26 nne indicating north over south thrusting with a component of left lateral movement focal mechanisms for 40 aftershocks also indicate compression in the general n s direction for most of these events the north dipping nodal plane dips between 7 and 45 with most dipping 25 or more which is significantly steeper than the plane delineated by the hypocenters themselves these observations are consistent with a tectonic model in which much of the slip during the santa barbara earthquake occurred on a nearly horizontal plane the after shocks then might represent movement on a complex series of imbricate thrust faults that flatten into the plane of primary slip hence the santa barbara earthquake may be taken as evidence for mid crustal horizontal shearing in the western transverse ranges

a high resolution record of rare earth element compositional changes from the mud deposit on the inner shelf of the east china sea implications for paleoenvironmental changes abstract a paleoenvironmental reconstruction of the east china sea ecs is presented using rare earth element ree analysis of sediments from core mz02 which was retrieved from the inner continental shelf s mud area the analytic results show that the total rees in the fine sediment vary between 137 76 g g and 231 53 g g with an average value of 187 69 g g obvious changes were found during the process of sedimentation by comparing with the ree compositions from the potential provenances the ratios of la sm ucc and gd yb ucc revealed that the sediments were mainly derived from river detrital outputs of the changjiang yangtze river minjiang and mountainous rivers from western taiwan island the contributions of terrestrial materials from these three main provenances were controlled by sea level change and the taiwan warm current twc chinese coastal current ccc system which is mainly driven by the east asian monsoon the high sedimentation rate during the transgression period between the late pleistocene and early holocene 13000 9800 a b p was caused by a well proportioned mixed provenance from changjiang western taiwanese rivers and minjiang sediments due to the lower sea level and the location of the foreshore nearshore face because of the stronger sediment reworking and erosion at the shelf edge during the early holocene 9800 7300 a b p the strengthening summer east asian monsoon transported the minjiang and western taiwanese river material northeastward and it became the main sediment source for fine sediments in the shallow sea region of the ecs while the changjiang provided a relatively minor amount of detrital sediment to the shelf the increasing strength of the twc might have played an important role in sediment dispersal and deposition on the ecs inner shelf during the period 7300 3500 a b p thus mountainous river material became the dominant sediment on the shelf of the ecs furthermore the results indicate that the east asian monsoon and the weakening of the twc were linked to an abrupt increase in changjiang derived terrigenous detritus material since 3500 a b p the source and sink pattern during this period is consistent with the modern sedimentation environment

comments on papers about shear wave splitting in dilatancy induced anisotropy by i n gupta and by a ryall and w u savage

geomorphology and coastal erosion of a quartzite island hongdo in the yellow sea off the sw korean peninsula abstractas a dense metamorphic rock with silica grains that are strongly fused quartzite exposed on rocky shores is generally resistant to marine erosion the longevity of quartzite coasts compared to those formed by other rock types is underscored by the preservation of many former islands that retain notable topographic relief as inliers of archean and proterozoic quartzite surrounded by paleozoic marine strata in north america and western australia among the few places where modern rocky shores composed principally of quartzite may be studied with regard to marine erosion hongdo in the yellow sea off the southwestern korean peninsula is a natural laboratory where intersection of structural geology coastal geomorphology oceanography sedimentology and climate converge to demonstrate how a quartzite island evolves through time although small in size 6 87 km2 hongdo is open to the ocean on all sides the island s structure as an asymmetrical anticline permits a wide range of attack angles for se

ironstones and green marine clays in the dongjeom formation early ordovician of korea abstract in the sino korean north china block the occurrence of ironstone is reported for the first time from the lower ordovician dongjeom formation korea the dongjeom formation comprises much quartzose sediment deposited on the extensive carbonate platform and is composed of three coarsening upward sequences ironstone beds are distributed on the tops of the lower two sequences suggesting that they mark approximately maximum flooding events during the relative lowstand of sea level when the dongjeom formation was deposited extensive weathering in the source areas coupled with higher order sea level rises resulted in the formation of the dongjeom ironstones the dongjeom ironstones include much green marine clays ironstones of the lowest sequence are characterized by glaucony facies and those of the middle sequence by chamosite facies chemical compositions of dongjeom glauconies reveal that they were originally nascent to slightly evolved 3 to 5 k 2 o wt and that they were affected by illitization after burial their immature compositions suggest that glauconies were formed in about 10 3 to 10 4 years or less on the seafloor the substrates for glauconitization are interpreted as detrital mineral grains regressions after glauconitization introduced iron oxides to the green grains eventually forming the iron oxide rich band under the most oxidizing conditions the distribution of glauconies in limited horizons suggests that the dongjeom glauconies are autochthonous in origin chamosites have granular shapes and are mixed with quartzose sand grains suggestive of reworking during storms the dongjeom chamosites were transformed from the precursor berthierines the occurrence of glauconies in correlative horizons in korea and north china may indicate that glauconitization in the host sediments which were deposited in far northern gondwana occurred under the influence of a coeval transgressive event

inversion of arrival times in a region of dilatancy anisotropy shear wave splitting has been identified in many three component seismograms from two separate field experiments on a section of the north anatolian fault in north west turkey these observations are consistent with shear wave propagation through a zone of extensive dilitancy anisotropy a preliminary attempt has been made to confirm this interpretation by simultaneously inverting suites of arrival times for hypocentral locations and for parameters describing an anisotropic halfspace although the inversion procedure is not globally convergent it is possible to recognize the true solution by systematically varying the initial conditions applied to selected data sets the inversion defines several anisotropic models that fit the data significantly better than a simple isotropic model and display the anisotropy required by the shear wave splitting however most of these anisotropic models are not superior when they are used to individually locate events in a much larger data set however for each experiment there is a single model that produces clearly superior locations for the larger data sets than those of other anisotropic or simple isotropic models both models display similar velocity variations which are characteristic of propagation through distributions of biplanar cracks displaying orthorhombic symmetry the principal axes of the two models are oriented in similar directions and are within 20 of the principal axis of regional stress derived from fault plane solutions the solutions indicate low velocities close to the tensional axis as would be expected in extensive dilatancy anisotropy

provenance analysis of lower cretaceous sindong group sandstones in the gyeongsang basin korea using integrated petrography quartz sem cathodoluminescence and zircon zr hf analysis the sindong group aptian albian in southeastern korea is a 2 3 km thick fluvio lacustrine sedimentary package deposited in an elongated basin the nakdong trough which was formed by extension in an active continental margin setting the provenance of the sindong group was studied to understand spatial and temporal variation in composition in three different parts of the basin by using integrated data on petrography quartz sem cathodoluminescence cl analysis and zircon zr hf analysis although sindong group sandstones display wide variation in the composition of framework grains they generally have increasing amounts of feldspar and decreasing amounts of quartz up sequence significant amounts of volcanic rock fragments and volcanic quartz are observed in the late stage sediments metamorphic quartz is predominant in all sindong group sandstones indicative of the exposure of metamorphic rocks in the source terrane mostly from precambrian basement and triassic granites the occurrence of significant amounts of plutonic quartz from early stage sediments suggests that jurassic granites were widely exposed in the source terranes in addition the episodic increase in volume of plutonic quartz content in the sequence especially in the northern part of the basin suggests that episodic tectonic activity occurred in the catchment the increasing feldspar content up sequence could support the occurrence of tectonic activity in the catchments the zr hf analysis of detrital zircons revealed that the majority of zircons are of continental crust origin formed in orogenic settings but zircons in the lowest strata in the northern part of the basin were derived largely from anorogenic magmatic rocks of mantle origin our results demonstrate that source terranes for the sindong group have heterogeneous spatial and temporal distribution and were composed mainly of precambrian basement and triassic to jurassic granitic rocks with minor meta sedimentary rocks and syndepositional volcanic rocks the detritus derived from syndepositional volcanic rocks became significant in the late stage of basin filling representing the transition from extensional tectonism to continental arc magmatism the differences in characteristics of quartz sem cl and zircon zr hf ratios in different parts of the basin are best explained by deposition on different alluvial fans and river systems

structural transect of the western transverse ranges california implications for lithospheric kinematics and seismic risk evaluation a retrodeformable cross section that integrates surface and subsurface data across the western transverse ranges california illustrates an actively developing fold and thrust belt that began forming at 2 3 ma high level thrusts are interpreted to root in a mid crustal detachment at 12 15 km depth which coincides with the maximum depth of earthquakes the cross section documents 53 km of convergence above the mid crustal detachment dividing this by the time since onset of deformation yields convergence rates of 17 6 26 5 mm yr the high density lithospheric anomaly beneath the transverse ranges is related to subduction of lower crust and lithosphere below the mid crustal detachment to balance the shallow crustal shortening thrust ramps coincide with zones of high seismicity in the transverse ranges this suggests that ramp regions have the highest potential for compressive earthquake events e g the recent whittier narrows earthquake of october 1 1987 m sub l 5 9 occurred along the eastern part of a ramp zone

modelling the compliance of crustal rock ii response to temporal changes before earthquakes summary there have been several claims that seismic shear waves respond to changes in stress before earthquakes the companion paper develops a stress sensitive model ape for the behaviour of low porosity low permeability crystalline rocks containing pervasive distributions of fluid filled intergranular microcracks and this paper uses ape to model the behaviour before earthquakes modelling with ape shows that the microgeometry and statistics of distributions of such fluid filled microcracks respond almost immediately to changes in stress and that the behaviour can be monitored by analysing seismic shear wave splitting the physical reasons for the coupling between shear wave splitting and differential stress are discussed in this paper we extend the model by using percolation theory to show that large crack densities are limited at the grain scale level by the percolation threshold at which interacting crack clusters lead to pronounced increases in rock matrix permeability in the simplest formulation the modelling is dimensionless and almost entirely constrained without free parameters nevertheless ape modelling of the evolution of fluid saturated rocks under stress reproduces the observed fracture criticality and the narrow range of shear wave azimuthal anisotropy in crustal rocks it also reproduces the behaviour of temporal variations in shear wave splitting observed before and after the 1986 m 6 north palm springs earthquake southern california and several other smaller earthquakes the agreement of ape modelling with a wide range of observations confirms that fluid saturated crystalline rocks are stress sensitive and respond to changes in stress by critical fluid rock interactions at the microscale level this means that the effects of changes in stress and other parameters can be numerically modelled and monitored by appropriate observations of seismic shear waves

sequence stratigraphy of the red river formation williston basin usa stratigraphic signature of the ordovician katian greenhouse to icehouse transition abstract the upper katian upper ordovician red river formation is a carbonate evaporite supersequence that formed in the epicratonic williston basin of western north america this study focuses on the upper part of the formation in the southern us part of the basin the studied succession is made up of three transgressive regressive sequences rr1 rr2 and rr3 each 0 5 1 m y in duration and composed of relatively few meter scale high frequency cycles parasequences sequence boundaries are characterized by intraclastic breccia laminated dolomite successions that have been truncated and capped by evaporite deposits subaqueous anhydrites within each sequence represent evaporite lowstand systems tracts lsts that formed during relative sea level lows that lead to the precipitation of gypsum later recrystallized into anhydrite in a quiet salina type environment transgressive tst and early highstand systems tracts hst are composed of subtidal facies of predominantly skeletal mudstone to wackestone packstone with abundant burrow mottling late hsts are predominantly composed of peritidal porous laminated dolomite the study illustrates how the sequence stratigraphic framework of carbonate evaporite deposits from the williston basin relates to the late ordovician glacio eustasy transitional climates and low basin subsidence in an arid setting

stress induced temporal variations in seismic anisotropy observed in microseismic data summary in situ stress monitoring of crustal rocks is desirable as it yields insights into earthquake mechanisms volcanic eruptions and changes in hydrocarbon reservoirs shear wave splitting induced by stress controlled cracks in the shallow crust provides a way to infer this stress temporal variations in these observations can be difficult to quantify due to scatter in the data and discontinuous observations here we present evidence of temporal variations in shear wave splitting from a continuous time series with a high occurrence of microseismic events recorded in a borehole we interpret these observations in terms of stress controlled cracks and are able to infer changes in stress and via modelling suggest the cause of the anisotropy possible origins of the temporal variation in per cent anisotropy are tidal or oil field production processes our results suggest that shear wave splitting is a viable probe for inferring changes in crustal stress in cracked rock

an inverse method for determining three dimensional fault geometry with thread criterion application to strike slip and thrust faults western alps and california abstract in order to draw geological structures such as faults interpolation is generally needed between scattered data the use of an approximation criterion integrating the kinematic properties of the faults helps to document the fault surfaces by adding a compatibility criterion to the data set assuming that two jointed blocks of rocks slipping on each other generate a thread surface an approximation method has been developed which integrates a thread criterion this approximation method is used to solve an inverse problem with least squares criteria including proximity to data points smoothness and thread criteria the aim is to find a smooth surface which is as close as possible to a thread and as close as possible to the observed data set applications to two corrugated fault surfaces with a dense data set located in the western alps france and in the transverse ranges california confirm the validity of the thread assumption despite their difference in mean corrugation wavelength 5 m and 10 km respectively in the type of fault strike slip and thrust fault respectively and in the nature of the faulted rocks limestones and sandstones respectively very similar results are obtained in both cases the observed data fit well with a thread surface and the computed fault displacement fits well with the measured displacement on the fault striae seismic focal mechanism geodetic data restoration the conclusion is that treating a fault as a thread is a valid physical description which gives the slip direction independently of other kinematic indicators the advantage of using a thread criterion in addition to classical proximity and smoothness criteria is that this physical insight allows information from areas where data are relatively dense to help constrain areas where data are relatively sparse these last areas being those that are usually not well constrained by proximity and smoothness criteria

a synchronously coupled tide wave surge model of the yellow sea abstract a coupled wave tide surge model has been established in this study in order to investigate the effect of tides storm surges and wind waves interactions during a winter monsoon on november 1983 in the yellow sea the coupled model is based on the synchronous dynamic coupling of a third generation wave model wam cycle 4 and the two dimensional tide surge model the surface stress generated by interactions between wind and waves is calculated using the wam cycle 4 directly based on an analytical approximation of the results obtained from the quasi linear theory of wave generation the changes of bottom friction factor generated by waves and current interactions are calculated by using simplified bottom boundary layer model the model simulations showed that bottom velocity and effective bottom drag coefficient induced by combination of wave and current were increased in shallow waters of up to 50 m in the yellow sea during the wintertime strong storm conditions

continental island from the upper silurian ludfordian stage of inner mongolia implications for eustasy and paleogeography an unconformity between the silurian xibiehe formation and ordovician igneous rocks marks the perimeter of a small paleoisland near bater obo in north central inner mongolia 180 km northwest of the provincial capital of hohhot the stratigraphic position of the lower part of the xibiehe formation is correlated by means of conodonts with the upper part of the ancoradella ploeckensis zone in the basal ludfordian stage corresponds to mid ludlovian epoch ca 421 ma elongate in plan 610 m 200 m the exhumed diorite core rises 30 m above the lowest elevations of surrounding silurian strata paleoshores along the principal axis of the inlier delineate contrasting facies robust stromatoporoids are in growth position within silty limestones some directly encrusting the unconformity surface of the sheltered southeast margin a basal conglomerate of diorite cobbles and boulders characterizes the high energy northwest margin the depositional constraints and timing of transgressive facies associated with this continental paleoisland have implications for the eustatic and paleogeographic history of the parent sino korean plate burial of the island corresponds to the beginning of a global rise in sea level that peaked in late ludlovian time our interpretation of windward and leeward facies requires an approximate 90 clockwise rotation of the parent plate to accommodate the dominant pattern of low latitude trade winds and storms

reach scale channel sensitivity to multiple human activities and natural events lower santa clara river california usa abstract understanding the cumulative impact of natural and human influences on the sensitivity of channel morphodynamics a relative measure between the drivers for change and the magnitude of channel response requires an approach that accommodates spatial and temporal variability in the suite of primary stressors multiple historical data sources were assembled to provide a reach scale analysis of the lower santa clara river lscr in ventura county california usa sediment supply is naturally high due to tectonic activity earthquake generated landslides wildfires and high magnitude flow events during el nino years somewhat typically for the region the catchment has been subject to four reasonably distinct land use and resource management combinations since european american settlement when combined with analysis of channel morphological response quantifiable since ca 1930 reach scale and temporal differences in channel sensitivity become apparent downstream reaches have incised on average 2 4 m and become narrower by almost 50 with changes focused in a period of highly sensitive response after about 1950 followed by forced insensitivity caused by structural flood embankments and a significant grade control structure in contrast the middle reaches have been responsive but are morphologically resilient and the upstream reaches show a mildly sensitive aggradational trend superimposing the natural and human drivers for change reveals that large scale stressors related to ranching and irrigation have been replaced over time by a suite of stressors operating at multiple spatial scales lower reaches have been sensitive primarily to local scale impacts urban growth flood control and aggregate mining whereas upstream catchment scale influences still prevail including flow regulation and climate driven sediment supply factors these factors illustrate the complexity inherent to cumulative impact assessment in fluvial systems provide evidence for a distinct anthropocene fluvial response and underpin the enormity of the challenge faced in trying to sustainably manage and restore rivers

possible eastward extension of chinese collision belt in south korea the imjingang belt structural petrological and geochronological data from the middle korean peninsula indicate that the qinling dabie sulu collisional belt of east central china crosses the yellow sea and extends into the imjingang belt the yeoncheon complex first identified as the western imjingang belt comprises primarily north dipping metamorphic sequences 1 the northern jingok unit consisting of barrovian type metapelites and 2 the southern samgot unit consisting of calc silicate and amphibolitic rocks south vergent structures with reverse sense shearing are dominant in the jingok unit whereas late normal sense shearing is pervasive in the samgot unit and the deformed granitoid to the south these structural patterns are interpreted to correspond to extensional deformation associated with uplift following compression in a collisional belt pressure temperature p t estimates from the amphibolites suggest a high p amphibolite facies metamorphism 8 13 kbar and 630 790 c possibly evolving from eclogite facies conditions along a clockwise p t path sm nd and rb sr geochronological data suggest that the amphibolites emplaced in late proterozoic time were metamorphosed during permian triassic time

uniformitarianism as a guide to rocky shore ecosystems in the geological record literature on pleistocene and neogene rocky shores is reviewed from a uniformitarian perspective to assess the fidelity of physical and biological information entrained in the geological record through present day processes coverage by latitude spans tropical to subarctic shores variations in paleotopography are illustrated by unconformities between sedimentary accumulations and rocks of igneous or non igneous origin former rocky shores occur across a range of geographic scales that include i spot localities ii embayments with continuous transition from exposed outer to protected inner shores and iii entire islands with windward and leeward shores differences in rate and mag nitude of sea level change affect rocky shore physiography terrace deposits characterize the pleistocene but ramp de posits typify older neogene shores on average species with hard parts account for about 50 of the modern rocky intertidal fauna on a regional basis regardless of latitude biodiversity is highest in mid latitudes fixed organisms with encrusting wedging or boring habits corals barnacles oysters other bivalves and vermetid gastropods show high potential for fossilization in growth position mobile organisms that cling to rocks gastropods crabs and echinoids suffer post mortem transport but may be immured within neptunian dikes or interstices among cobbles and boulders at best localized fossil deposits from the pleistocene reflect 30 of the biodiversity of skeletonized organisms tabulated from modern rocky shores on a regional basis uniformitarianism provides little insight into the diversity of soft bodied organisms excluding stromatolites that joined the ecosystem in precambrian times and the extent to which soft bodied organisms dominated shore life through later times

fault slip rates and interseismic deformation in the western transverse ranges california to better constrain fault slip rates and patterns of interseismic deformation in the western transverse ranges of southern california we present results from analysis of gps and interferometric synthetic aperture radar insar data and three dimensional mechanical and kinematic models of active faulting anthropogenic motions are detected in several localized zones but do not significantly affect the vast majority of continuous gps site locations gps measures contraction rates across the ventura basin of 7 mm yr oriented west northwest with rates decreasing to the west and east the santa barbara channel is accommodating 6 5 mm yr in the east and 2 5 mm yr in the western portions of n s contraction inversion of horizontal gps velocities highlights a zone of localized fast contraction rates following the ventura basin using a mechanical model driven by geodetically calculated strain rates we show that there are no significant discrepancies between short term slip rates captured by geodesy and longer term slip rates measured by geology mechanical models reproduce the first order interseismic velocity and strain rate patterns but fail to reproduce strongly localized contraction in the ventura basin due to the inadequate homogeneous elastic properties of the model existing two dimensional models match horizontal rates but predict significant uplift gradients that are not observed in the gps data mechanical models predict zones of fast contraction in the santa barbara channel and offshore near malibu suggesting that offshore faults represent a significant seismic hazard to the region furthermore many active faults throughout the region may produce little to no interseismic deformation making accurate seismic hazard assessment challenging 2013 american geophysical union all rights reserved

neotectonics of the san cayetano fault transverse ranges california study of late quaternary alluvial deposits cut by the san cayetano reverse fault indicates that the dip slip rate of faulting increases from 1 05 0 2 mm yr at sisar creek near the western end of the fault eastward to 1 35 0 4 mm yr at bear canyon and 2 35 0 55 to 4 15 0 85 mm yr at mud creek at timber canyon near the central part of the fault a minimum slip rate of 3 6 0 4 mm yr is suggested by fanhead segmentation however a higher slip rate of 8 75 1 95 mm yr is suggested by stratigraphic evidence stratigraphic separation of 7 5 km in less than 1 m y across the fault between fillmore and piru indicates a slip rate of at least 7 5 mm yr for the eastern section of the fault recent activity is shown by faulted holocene or latest pleistocene fan alluvium and colluvium at bear canyon and the silverthread oil field respectively and inferred at timber canyon by fanhead deposition active folding of the footwall is demonstrated by tilted and faulted holocene and pleistocene alluvial fans present tilt rates approach 1 10 ka yr and associated bedding plane faulting rates are about 0 5 to 1 5 mm yr the hanging wall however does not appear to be involved in active deformation inasmuch as pleistocene deposits as old as several hundred thousand years are not tilted or affected by bedding plane faulting the only exception is in the silverthread field area where hanging wall deformation is directly relatable to fault geometry not folding of the hanging wall rocks the lack of documented moderate to large magnitude historical earthquakes on this fault is in strong contrast with its demonstrated late quaternary activity based on its length slip rate overall geometry and segmentation into two parts a recurrence interval of between 200 and 600 yr for the western segment and about 230 yr for the eastern segment is suggested

the 1987 whittier narrows earthquake in the los angeles metropolitan area california the whittier narrows earthquake sequence local magnitude m l 5 9 which caused over 358 million damage indicates that assessments of earthquake hazards in the los angeles metropolitan area may be underestimated the sequence ruptured a previously unidentified thrust fault that may be part of a large system of thrust faults that extends across the entire east west length of the northern margin of the los angeles basin peak horizontal accelerations from the main shock which were measured at ground level and in structures were as high as 0 6g where g is the acceleration of gravity at sea level within 50 kilometers of the epicenter the distribution of the modified mercalli intensity vii reflects a broad north south elongated zone of damage that is approximately centered on the main shock epicenter

geodetic measurement of deformation in the ventura basin region southern california we have measured the deformation in the ventura basin region southern california with global positioning system gps measurements carried out over 4 6 years between 1987 and 1992 the deformation within our network is spatically variable on scales of tens of kilometers with strain rates reaching 0 6 1 micro rad yr in the east central basin blocklike rotations are observed south and northwest of the basin where the maximum shear strain rates are an order of magnitude lower 0 06 1 micro rad yr to the south we also observed clockwise rotations of 1 deg 7 deg m y shear strain rates determined by comparing angle changes from historical triangulation spanning several decades and gps measurements give consistent though less precise results the geodetic rates of shortening across the basin and western transverse ranges are lower than those estimated from geological observations but the patterns of deformation from the two methods agree qualitatively

provenance of quartzite clasts in the eocene oligocene sespe formation paleogeographic implications for southern california and the ancestral colorado river quartzite clasts in fluvial sespe formation conglomerates of the santa monica mountains were compared petrographically with potential source rocks in the basin and range and transition zone provinces to determine their provenance modal analysis indicates that sespe orthoquartzite clasts are mainly quartzofeldspathic and derived from source rocks with craton interior provenance such clasts were probably derived from stirling quartzite and wood canyon formation sources in the northern mojave desert the mazatzal peak quartzite of central arizona is the probable source of quartzolithic orthoquartzite clasts containing abundant detrital jasper grains sespe metaquartzite clasts are mainly from sources in the southern mojave desert but some may be from the yavapai terrane of central arizona the dual provenance of orthoquartzite clasts suggests that the sespe paleoriver was a bifurcating system tapping both mojave desert and sonora desert sources after compensating for neogene displacement along the san andreas fault a paleogeographic reconstruction shows that there is a general spatial coincidence between sespe and other cenozoic paleodelta deposits around los angeles that contain exotic clasts and the inferred location of the mouth of the colorado river assuming that it existed during the eocene thus the colorado river may be much older than previously thought as old as late paleocene and perhaps was once part of an ancient fluvial connection with the mojave desert interior

palaeoecology and evolution of marine hard substrate communities abstract marine organisms have occupied hard substrates since the archaean shells rocks wood and sedimentary hardgrounds offer relatively stable habitats compared to unconsolidated sediments but the plants and animals which inhabit them must develop means to gain and defend this premium attachment space hard substrate communities are formed by organisms with a variety of strategies for adhering to and or excavating the substrates they inhabit while mobile grazers organically attached and even soft bodied organisms may leave evidence of their former presence in ancient hard substrate communities a superior fossil record is left by sessile encrusters with mineralised skeletons and by borers which leave trace fossils furthermore encrusters and borers are preserved in situ retaining their spatial relationships to one another and to the substrate spatial competition ecological succession oriented growth and differential utilisation of exposed vs hidden substrate surfaces can all be observed or inferred hard substrate communities are thus excellent systems with which to study community evolution over hundreds of millions of years here we review the research on modern and ancient hard substrate communities and point to some changes that have affected them over geological time scales such changes include a general increase in bioerosion of hard substrates particularly carbonate surfaces through the phanerozoic this is at least in part analogous to the infaunalisation trends seen in soft substrate communities encrusting forms show an increase in skeletalisation from the palaeozoic into the mesozoic and cenozoic which may be a response to increasing levels of predation hard substrate communities considering borers and encrusters together show a rough increase in tiering through the phanerozoic which again parallels trends seen in soft substrate communities this extensive review of the literature on living and fossil hard substrate organisms shows that many opportunities remain for large scale studies of trends through time at the community and clade levels palaeontologists will especially benefit by closer integration of their work with that of neontologists particularly in aspects of ecology such as larval recruitment competition and succession

fluvial plain lacustrine facies transition in the cretaceous sindong group south coast of korea abstract along the south coast of korea a 250 m stratigraphic interval corresponding to the uppermost hasandong and lowermost jinju formations of the cretaceous sindong group has been studied in terms of facies transition the interval displays a passage from a fluvial plain facies association consisting of floodplain levee crevasse splay and channel facies to a lacustrine facies association composed of crevasse splay channel overbank sheet splay marginal lake open lake and stream mouth bar facies between these two associations a transitional facies association occurs in which some facies of both associations alternate in the lacustrine association shallow marginal lake deposits including channel facies are gradually replaced upwards by deeper open lake deposits made up of open lake and stream mouth bar facies during the hasandong jinju period small channels which originated in the uplifted areas beyond the fault s bounded western margin of the gyeongsang basin flowed through alluvial fans developed along the fault s and a fluvial plain to a lake which occupied the central part of the basin as a result the lake shoreline was non coincident with the basin margin sinuosity of the streams increased downstream reaching a maximum near the shoreline but decreased in the marginal lake areas the fluvial plain was progressively submerged by the transgression of a non deltaic shoreline resulting in a deepening of the depositional sites from a fluvial plain through a marginal lake to an open lake setting intermittent channel overflows deposited levee and crevasse splay facies in the fluvial plain and crevasse splay and overbank sheet splay facies in the marginal lake stream mouth bars were developed at the ends of the sublacustrine channels by hyperpycnal density flows operated mainly during floods the non deltaic shoreline was formed due to 1 maintenance of shallow and wide marginal lake areas 2 dispersal of sediments by small channels 3 continuous shifting of the channels and their mouths and 4 direct transport of coarser sediments to the open lake and their subsequent wide dispersions

reconciling rapid strain accumulation with deep seismogenic fault planes in the ventura basin california global positioning system measurements across the east central ventura basin transverse ranges southern california before the nearby 1994 northridge earthquake show high strain rates interpreting this rapid strain accumulation using the usual model of deep slip on a dislocation in a uniform elastic half space requires slip to extend to within 5 km of the surface such shallow slip is difficult to reconcile with the substantial coseismic displacement at depths from 7 to 19 km during the northridge earthquake here we model the displacement and velocity fields throughout the earthquake cycle using a two dimensional finite element model with a viscoelastic rheology displacements are driven by far field and basal velocity boundary conditions and by imposed periodic earthquakes on the thrust faults bounding the basin the thrust faults rupture through an elastic upper crust to a depth of 15 km after a transient stage during which stresses and strains build up to quasi equilibrium values the behavior of the model becomes periodic the sum of the coseismic displacement divided by the repeat interval plus the average interseismic velocity is equal to the geologic velocity the temporal variation in surface velocity depends mainly on the elsasser relaxation time proportional to the product of the maxwell time of the lower crust and the ratio of the thicknesses of the entire crust and viscoelastic lower crust we are able to match the observed high strain rate only if we include the observed variations in elastic modulus associated with the deep basin sediments the model reconciles geologic geodetic and seismological observations of deformation there are trade offs among the far field convergence rate the elsasser time the earthquake repeat time and the time into the earthquake cycle acceptable convergence rates range from 8 mm yr for a relaxation time of the lower crust of 300 years to 12 mm yr for a 30 year relaxation time

effects of nonplanar fault topology and mechanical interaction on fault slip distributions in the ventura basin california to assess the control of fault geometry and mechanical interactions on fault slip distributions in a complex natural system we present results from three dimensional mechanical models incorporating both nonplanar and rectangular planar representations of active faults within the ventura basin region of southern california we find that the incorporation of geologically constrained nonplanar fault surfaces into numerical models of active deformation results in a better match to available geologic slip rate data than models utilizing rectangular planar fault surfaces the model results demonstrate that nonplanar fault geometry and mechanical interactions exert a strong control on resultant slip distributions additionally we find that slip rates at most locations along the surface trace of ventura faults are not likely to rep resent average values for the entire fault surface we propose that results from three dimensional mechanical models using realistic i e nonplanar fault geometry can be used to both predict slip rates at specific locations and determine whether existing site specific slip rate estimates are representative of average fault slip rates although geo metric irregularities along fault surfaces should resist slip planar faults can have lesser slip than nonplanar faults due to the differing mechanical interactions among nearby faults in the two representations this suggests that models using simplified or planar fault geometry are likely to inaccurately simulate regional deformation we assert that detailed knowledge of three dimensional fault shape as well as the geometry and con figuration of deep fault intersections is essential for accurate seismic hazard char acterization of regions of complex faulting such as the ventura basin of southern california

the chemical signature of source rocks in size fractions of holocene stream sediment derived from metamorphic rocks in the wet mountains region colorado u s a eight stream sediments draining primarily mixed silica rich and silica poor metamorphic rocks in the wet mountains colorado were analyzed at their source for their mineralogic and selected elemental composition the low silica source rocks include amphibolite hornblende schist and muscovite biotite schist the high silica source rocks include granodioritic to leucocratic granitic gneisses the high silica source rocks tend to contain higher concentrations of ree th hf and ba lower concentrations of fe sc and cr higher la sc and thsc ratios and more negative eu anomalies than the low silica source rocks especially those low silica source rocks derived from basic sources rather than weathered silicic sources the stream sediments draining this mixed metamorphic rock terrain are dominated by sands and gravels and they are composed of feldspar quartz and 25 heavy minerals the silts contain more total biotite hornblende pyroxene and opaque minerals and less quartz and feldspar than the sands and gravels sediment especially the silts derived from mixed low and high silica sources tends to be intermediate in elemental composition between those of the end member sources so there is some hope that source rock signatures may be preserved in the sediment elemental ratios of la sc th sc la co th co and ba co and th la sc plots most clearly distinguish sediment derived from the most silicic and most basic source rocks in addition finer sediment near the source can potentially distinguish silicic sources higher ree and more negative eu anomalies from those of basic sources the clay and silt fractions contain negative eu anomalies normalized to the mcps north american mid continent platform sediment and the sands and gravels have positive eu anomalies normalized to the mcps most size fractions are similar to more enriched in la sc th sc la co and th co ratios than the mcps this suggests local sources in the wet mountains are on the average more silica rich than those that formed the mcps

exceptionally preserved late ordovician biotas from manitoba canada there are few body fossil biotas known from early paleozoic accretionary shorelines and very few examples of ordovician soft bodied assemblages this study documents two recently discovered biotas from separate sedimentary basins in manitoba canada that provide unique information about tropical shoreline communities shortly before the late ordovician extinction event each site represents a distinct depositional environment but they share biotic elements including eurypterids xiphosurids and large problematic tubes the william lake biota representing more restricted conditions includes jellyfish that are among the best hydromedusan body fossils known rocks at the airport cove site deposited under more open circulation contain scolecodonts and noncalcified algae these biotas have some parallels with the recently described middle ordovician winneshiek lagerstatte but are also similar to some late silurian assemblages considered together early paleozoic marginal marine deposits are a rich but as yet poorly known source of paleobiodiversity data

an allostratigraphic approach to a non marine basin the north western part of cretaceous kyongsang basin se korea the north western part of the cretaceous kyongsang basin south east korea comprises alluvial deposits of conglomerate gravelly sandstone sandstone and mudstone which can be grouped into four allomembers bounded by stratigraphic discontinuities the discontinuities trend nw se and are marked by distinct facies transitions abrupt emplacement of conglomerate and thin but persistent mudstone beds sedimentary facies and architectural analyses reveal that each allomember formed a depositional system of fluvial channel networks draining toward the south east with alluvial fans on the northern margin each allomember can be characterized by distinctive architecture of channel fills clast composition of conglomerate and sandstone mudstone ratio successive units show an eastward shift in the locus of deposition suggesting basinward relocations of alluvial systems such variations with time and space are interpreted to reflect changes in accommodation space and sediment supply during basin evolution probably caused by fault movements this study shows that detailed mapping combined with architectural analysis and the establishment of alluvial allostratigraphy can help assess changes in alluvial systems and structural development of the basin

geomorphic evidence for the geometry and slip rate of a young low angle thrust fault implications for hazard assessment and fault interaction in complex tectonic environments abstract we present surface evidence and displacement rates for a young active low angle 20 reverse thrust fault in close proximity to major population centers in southern california usa the southern san cayetano fault sscf active faulting along the northern flank of the santa clara river valley displaces young landforms such as late quaternary river terraces and alluvial fans geomorphic strain markers are examined using field mapping high resolution lidar topographic data 10be surface exposure dating and subsurface well data to provide evidence for a young active sscf along the northern flank of the santa clara river valley displacement rates for the sscf are calculated over 103 104 yr timescales with maximum slip rates for the central sscf of 1 9 1 0 0 5 mm yr 1 between 19 7 ka and minimum slip rates of 1 3 0 5 0 3 mm yr 1 since 7 ka uplift rates for the central sscf have not varied significantly over the last 58 ka with a maximum value of 1 7 0 9 0 6 mm yr 1 for the interval 58 19 ka and a minimum value of 1 2 0 3 mm yr 1 since 7 ka the sscf is interpreted as a young active structure with onset of activity at some time after 58 ka the geometry for the sscf presented here with a 20 north dip in the subsurface is the first interpretation of the sscf based on geological field data our new interpretation is significantly different from the previously proposed model derived geometry which dips more steeply at 45 60 and intersects the surface in the middle of the santa clara river valley we suggest that the sscf may rupture in tandem with the main san cayetano fault additionally the sscf could potentially act as a rupture pathway between the ventura and san cayetano faults in large magnitude multi fault earthquakes in southern california however given structural complexities including significant changes in dip and varying holocene displacement rates along strike further work is required to examine the possible mechanism likelihood and frequency of potential through going ruptures between the ventura and san cayetano faults confirmation of the sscf in a previously well studied area such as southern california demonstrates that identification of young faults is critical for accurate seismic hazard assessment we suggest that many young active faults remain undetected in other structurally complex and tectonically active regions globally and that significant seismic hazards can be overlooked

provenance of quartzarenite clasts in the tetori group middle jurassic to early cretaceous japan paleogeographic implications abstract there are many strata containing quartzite clasts in the japanese islands but the on land geology of the japanese islands has no candidate for the source rocks of the quartzite clasts this study deals with the provenance of quartzite clasts of the tetori group middle jurassic and early cretaceous distributed in northern central japan quartzarenite clasts from conglomerate beds of the tetori group are texturally subdivided into three types the most abundant is matrix bearing quartzarenite type 3 followed by poorly sorted feldspar bearing quartzarenite type 2 and by well sorted pure quartzarenite type 1 to identify the provenance of quartzarenite clasts in the tetori group characteristics of quartzarenite sequences distributed in north china and korea were studied and compared with those of the tetori quartzarenite clasts texturally and geochemically the quartzarenite clasts of the tetori group are very similar to pre mesozoic quartzarenites distributed in the south central and east central korean peninsula considering the previous results of depositional environments paleomagnetism and paleocurrent studies on the tetori group this study suggests that during deposition of the tetori group the northern part of central japan was probably land connected with the central region of eastern korea

ecological zonation during the carbonate transgression of a late ordovician rocky shore northeastern manitoba hudson bay canada late ordovician ashgillian carbonates belonging to the port nelson formation transgress a resistant rocky shore near churchill manitoba on the southwest flank of the hudson bay basin in canada examples of ancient rocky shores are very rare and this locality offers the first opportunity to document extensive offshore biological zonation with spatial reference to a well defined shoreline five biofacies zones are parallel to a 350 m long shoreface carved into the precambrian churchill quartzite eroded boulders of the dark quartzite blanket the shoreface and clast size is observed to decrease dramatically up section through 4 5 m of tan colored carbonates from an onshore to offshore position the ecological zones include 1 boulder encrusting favositid corals and a related high energy fauna 2 a shell pavement dominated by the inarticulate brahciopod monomerella 3 large free standing tabulate corals including palaeophyllum calapoecia and catenipora 4 tunneled trace fossils including chondritid thalassinoid and less common vertical volcano burrows and 5 surface cruziana burrows associated with rare large isotelid asaphacean trilobites siphuncular debris from aminocerid cephalopods abundantly scattered through zones 2 3 provides data on current orientation consistent with long shore drift a wide field of ripple marks preserved near the top of the stratigraphic sequence confirms that wave trains advanced shoreward at an indirect angle of about 45 although currents deflected by natural groin fields may have swept coarse clastics more seaward at some spots than others the biological zones are remarkably linear and persistent the churchill site is a comparatively simple case of landward migration by shore parallel biofacies primarily controlled by factors related to water depth and distance from shore this interpretation does not preclude the possibility that more random facies patterns may have existed in protected embayments or along more irregularly cliffed sectors of the ancient churchill coast

extent and bathymetry of north american platform seas in the early silurian the north american craton is 25 covered by lower silurian llandovery rocks based strictly upon the geographic area of surviving marine strata preserved in outcrop and the subsurface this figure does not take into account extensive post silurian tectonics and erosion isolated structural basins in which these strata are found today were not necessarily defined as corresponding topographic basins in the silurian analysis of interbasin structural arches and outliers provides important clues as to the actual extent of early silurian seas information on the age of tectonic origin for 15 prominent arches is reviewed the placement and significance of 11 key outliers is also discussed evidence of this kind indicates early silurian platform seas were among the most extensive of the paleozoic probably more than 65 of the north american craton was then flooded nothing on so vast a scale serves as a recent guide to the past the pliocene holocene bahamian banks do provide however worthy models for the role of bathymetry and water circulation as related to the changeover from laterally monotonous blanket deposits to a more complex mosaic of facies the original bathymetry of early silurian environments may be determined correlated and mapped on the basis of widespread carbonate cycles linked to sea level fluctuations the range of fully integrated facies patterns includes 1 coral stromatoporoid stromatolite paleosol cycles williston basin 2 pentamerid brachiopod coral stromatoporoid stromatolite cycles michigan basin and 3 stricklandiid brachiopod pentamerid brachiopod coral stromatoporoid cycles east iowa basin with shallow bathymetries of 0 30 m the williston class tends to represent mosaic facies while with bathymetries of 0 60 m and 10 90 m the deeper water michigan and iowa classes typically involve blanket deposits bathymetry of other basin deposits generally fits one of these three classes maximum and minimum stands in sea level during late llandovery time are represented by bathymetric maps

late quaternary evolution of the yellow east china sea tidal regime and its impacts on sediments dispersal and seafloor morphology the evolution of a tidal current field in the yellow sea and east china sea yecs in response to the sea level rise since the last glacial maximum lgm was investigated using a two dimensional tidal model with special attention to changes in the sedimentary environment of the continental shelf region it was found that tidal currents on the yecs shelf have generally been semi diurnal throughout the post glacial stages with f ratio index of diurnal inequality and s2 m2 ratio index of spring neap cycle remaining similar to present on the other hand the spatial distribution of the tidal bottom stress associated with m2 and m4 tidal currents changed greatly during the transgression as the sea level rose two core regions showing high bottom stress values migrated shoreward from cheju island toward the west coast of korea and along the retreat path of the paleo changjiang estuary distribution of extremely intense tidal bottom stress suggested that intense tidal reworking may have occurred at sea levels from 90 to 45 m in the southeast yellow sea and at 75 to 60 m off the paleo changjiang estuary the latter of which agreed with the timing of a large terrigenous organic c flux observed on the shelf slope distribution of slightly weaker bottom stress indicated that the sand ridges off the changjiang estuary and in the southeast yellow sea also might have formed at during those periods on the other hand when the sea level was between 45 and 15 m the tidal bottom stress was generally not strong enough to invoke significant reworking even though the stress intensity may be stronger than present correlation with modern and relict sedimentary features suggested that the tidal process have played a significant role on the reworking and deposition of sediments on the yecs shelf

detrital zircon u pb ages of the jangsan formation in the northeastern okcheon belt korea and its implications for material source provenance and tectonic setting abstract the jangsan formation distributed in the taebaeksan basin central eastern korea is unfossiliferous and is composed of quartz arenite this formation is conventionally believed to be the lowermost stratigraphic unit of the lower paleozoic sequence deposited on the yeongnam massif in south korea corresponding to early cambrian in age u pb dating of detrital zircon grains using a laser ablation inductively coupled mass spectrometer yields ages ranging from archean to middle proterozoic 1738 67 ma to 3058 53 ma detrital zircons show no ages younger than 1 8 ga suggesting that the jangsan formation was deposited at some time after this age but much prior to ca 520 ma the depositional age of the immediately overlying myobong formation this interpretation is supported by the recent report on the presence of the unconformity between the jangsan and the myobong formations kim and lee 2006 zircon ages from jangsan sandstones define two major groups archean age grains with a maximum frequency at about 2 5 ga and paleoproterozoic age grains with maximum frequencies at about 2 1 and 1 8 ga the observed zircon age distribution in the jangsan sandstones may represent that of the yeongnam massif on which the jangsan formation was deposited such an age distribution of the yeongnam massif matches well with that the north china block suggestive of the yeongnam massif being a part of the sino korean craton during the precambrian

large scale quaternary detachments in ventura basin southern california the ventura basin is an east north east trending trough in the california transverse ranges which records major quaternary detachment faulting at three levels the earliest thrusting occurred along weak siltstone interbeds in a sequence dominated by competent basin plain turbidite sandstone because sedimentation continued during thrusting the age rate and direction of thrusting can be worked out faulting began 1 3 m y ago and ceased 0 65 m y ago with a maximum slip rate of 2 8 mm yr to the southeast the fault set moved up a 45 ramp and ended as a blind thrust the ramp had topographic expression on the seafloor diverting turbidites around the ramp and preserving ash beds along with other hemipelagic sediments on its crest following the end of deposition 0 2 m y ago the competent basin plain turbidites underwent flexural slip folding over an incompetent miocene sequence dominated by shale underlying competent paleogene strata were not folded the south flank of the ventura avenue anticline tilted at 3 4 rad yr the anticlinal crest rose at a rate of 15 16 mm yr decelerating to 4 3 5 2 mm yr and the anticline and an adjacent syncline shortened at a rate of 20 mm yr the high rate of folding in the ventura avenue oil field resulted in overpressured sandstone reservoirs and oil water interfaces which have not had time to reach gravity equilibrium the red mountain san cayetano and santa susana faults mark the surface expression of a seismically active midcrustal detachment which produced convergence across the ventura basin at rates as high as 23 mm yr total convergence across the eastern san cayetano fault near fillmore is 11 600 2000 m in the last million years

storm generated surface waves and sediment resuspension in the east china and yellow seas abstract surface winds derived from atmospheric pressure fields are used as input to a finite depth wind wave model to predict the sea state during a cold air frontal passage over the yellow and east china seas which occurred 15 18 november 1983 the predicted maximum wave stress field near the bottom is used to examine the concept of turbulent wave intensities causing sediment resuspension the temporal variability of the wave field at three sites is used to illustrate the dependence of the bottom response on depth within the yellow sea maps of the temporal and spatial distribution of index for initiation of sediment movement are computed for different noncohesive sediment materials during this storm period and compared to sedimentological results for this region this study demonstrates that wave action is a mechanism which can significantly influence the sediment transport pattern induced by the regional circulation existing in this marginal sea the results also identify regions where winter storm g

active tectonic studies in the united states 1987 1990 the techniques and instrumentation used in active tectonic studies are discussed and recent results are reviewed it is suggested that a critical mass of data on several particular regions has been accumulated making possible critical debates and attempts to assess earthquake hazards particular attention is given to studies of the pacific northwest region basin and range deformation studies and distributed deformation and hidden earthquake sources also included is a comprehensive bibliography for the period

jens munk archipelago ordovician silurian islands in the churchill area of the hudson bay lowlands northern manitoba abstract the name jens munk archipelago is proposed for a cluster of small monadnocks that rise a maximum of 45 m above present sea level on the shores of hudson bay in the churchill area of northern manitoba resistant precambrian quartzite formed shoals and islands during the late ordovician and early silurian periods outcrop control in the present tundra environment of the hudson bay lowlands is spotty at best but the quartzitic monadnocks are fringed by upper ordovician and lower silurian ramp deposits mainly carbonate in composition five isolated outliers of ordovician silurian strata are described and the location of four other potential outliers is indicated ramp dip at any one site generally ranges from 10 to 15 and the surviving ramps on opposite flanks of paleoislands suggest preservation of near synsedimentary conditions extensive conglomerates of reworked quartzite are most abundant on a northern exposure within the islands ripple marks and oriented cephalopod debris are related t

outer rocky shores of the mowanbini archipelago devonian reef complex canning basin western australia abstract the oscar range in western australia s canning basin features inliers of folded paleoproterozoic quartzite quartzitic conglomerate and phyllite that formed islands during the late devonian undisturbed strata of the pillara limestone upper devonian frasnian stage surround individual paleoislands that rise above the former seabed with a maximum topographic relief of 90 m on average the mowanbini archipelago aboriginal name for the oscar range lies 15 km off the granitic and metamorphic mainland represented by the kimberley block to the north devonian facies on outer rocky shores were studied at three localities near the southeast end of the oscar range at the west end of the study area a devonian reef margin sits unconformably on paleoproterozoic phyllite but to the east the reef is separated from rocky shores by a wide lagoon massive clast supported conglomerate and sandstone beds interfinger with backreef carbonates where the reef is closest to land across the lagoon 2 5 km eastw

paleoseismologic evidence for a very large mw 7 post a d 1660 surface rupture on the eastern san cayetano fault ventura county california was this the elusive source of the damaging 21 december 1812 earthquake the first paleoseismologic data from the san cayetano fault a major reverse fault that extends along the northern edge of the ventura basin northwest of los angeles reveal that the most recent event on the eastern part of the fault generated at least 4 3 m of surface slip age determinations from detrital charcoal recovered from the faulted section indicate that this surface rupture occurred after a d 1660 the faulted deposits are overlain by unfaulted historical alluvium containing abundant metal fragments and a leather glove comparison of the large surface slip in this event with data from other earthquakes indicates that the most recent eastern san cayetano surface rupture was larger than m w 7 and was probably of the order of magnitude 7 5 much larger than any earthquakes that have occurred on los angeles metropolitan region faults during the past 150 yr such a large event almost certainly would have been recorded had it occurred during the historical period even if it had occurred during the earliest part of the historical era between ca a d 1780 and 1850 although this surface rupture could have occurred during the century immediately preceding the historic era the location and large size of the event lead us to suggest that the trench exposed evidence for the damaging earthquake of 21 december 1812 whether the most recent surface rupture on the eastern san cayetano fault was the 21 december 1812 event these paleoseismologic data add to a growing body of evidence that shows that large earthquakes have occurred on faults within and adjacent to the los angeles metropolitan region reemphasizing the need to include such large events on urban faults in future seismic hazard analyses of the region

records of late holocene east asian winter monsoon in the east china sea key grain size component of quartz versus bulk sediments abstract quartz isolated from bulk sediments taken from a core obtained from the distal mud area in the outer shelf of the east china sea was used as a proxy in order to determine the strength of the east asian winter monsoon eawm this data was compared with the grain size of bulk sediment from the same core it was found that the content of the key quartz based indicator fraction 15 2 65 6 m correlated well with the eawm strength with reference to current conditions high content of quartz in the selected fraction reflected strong eawm and vice versa the core record spanned 2100 years and three periods of change in eawm strength were identified a period of increased eawm strength prior to 1520 cal bp was followed by a period of weakened eawm strength from 1520 to 720 cal bp which is consistent with the sui tang warm period and the medieval warm period this is followed by a period of slightly increased eawm between 720 and 220 cal bp which corresponds to what is called the little ice age the history of eawm revealed by the quartz based proxy is in striking agreement with results from a previous study on bulk sediment based proxy however the quartz based proxy showed much higher sensitivity and resolution to the eawm strength and displayed much more distinct and sharper boundaries of transition across the three intervals of eawm change compared to the bulk sediment records eleven short eawm strengthening periods were found compared with four by the bulk sediment based proxy therefore this suggests that the quartz grain size proxy is a superior indicator of the winter monsoon strength in the study area

the effect of wind wave enhancement of bottom stress on the circulation induced by tropical cyclones on continental shelves the effect of increased bottom friction due to wind wave current interaction on continental shelves is examined with a two dimensional shallow water numerical model using an adaptation of the grant and madsen 1979 bottom boundary layer theory in our formulation we allow for the wind wave amplitude to depend on the wind stress and bottom topography we find that under strong tropical cyclones the grant and madsen theory may break down in very shallow water where the wind wave amplitudes can become quite large since this is a region where the wind generated waves are particularly likely to be breaking we introduce a wave breaking criterion into our bottom friction formulation the effects of this wind wave induced bottom friction law on the wind driven circulation are then examined