pliocene climate history of the western united states derived from lacustrine ostracodes abstract pliocene sediments from several sites in western north america contain ostracodes indicating deposition in lacustrine and wetland settings the ostracodes offer a means of reconstructing the aquatic paleoenvironment because water temperature chemistry and lake volume are coupled to climate reconstruction of these parameters provides a direct insight into pliocene climate the site ages were determined from tephrochronology paleomagnetics and associated mammals the morphology of many ostracode species also provides direct information about the paleoenvironment in which they lived during the pliocene about 3 5 2 5 ma some species have unusually ornate carapace morphology indicative of large geologically stable lakes which must have required a stable climate to sustain them north american pliocene climate changed from a modern like state 4 5 3 5 ma to a period with greater precipitation and less evaporation than today 3 5 2 5 ma this wetter period inferred from the large geologically long lived lakes implies a stable atmospheric circulation pattern the stable circulation pattern collapsed around 2 5 ma and climate returned to a modern like situation

facies architecture and depositional dynamics of the upper permian rangal coal measures bowen basin australia the upper permian rangal coal measures in the northern bowen basin australia accumulated during rapid basinal aggradation in a retroarc foreland basin setting they reflect peatland deposition towards the close of a long lived climatic regime that came to an abrupt termination at the permian triassic boundary which is well developed in the newlands mine highwall and adjoining borefield six lithofacies are represented in the newlands district 1 erosionally based vertically stacked ribbon and sheet like sandstone bodies up to 30 m thick and 1000 m wide 2 heterolithic lobes and wedges 3 interbedded siltstone and sandstone sheets 4 interlaminated claystone and coal stringers 5 laterally extensive bituminous coal sheets and 6 laterally extensive laminated carbonaceous siltstone sheets this facies assemblage is interpreted to correspond to six alluvial cold climate depositional environments 1 trunk river channels and crevasse feeder channels 2 levee bank proximal crevasse splay 3 distal splay overbank 4 marsh 5 peat mire and 6 floodbasin lake respectively the sequence architecture at newlands reveals that a prolonged period of peat deposition was progressively terminated by northward stepping lobes of fluvial sediment in the south and by lacustrine drowning in the north exceptionally well developed composite elongate crevasse splay microdeltas up to 26 m thick and 3000 m long indicate that crevassing was responsible for the localized emplacement of thick sediment packages on the proximal floodplain in the absence of active siliciclastic sedimentation peat mire environments expanded from the distal floodplain extending across abandoned depositional lobes the geometry of these deposits reflects in large part accommodation space developed by the compaction of the peat precursor of the thick and laterally extensive upper newlands seam sequential compaction of peat by clastic overburden controlled the nucleation and location of succeeding clastic packages the behavior of the peat under compactional load largely controlled the lateral facies mosaic and stacking pattern of depositional units on a district scale

block models of crustal motion in southern california constrained by gps measurements 1 we estimate slip rates on major active faults in southern california using a block model constrained by global positioning system measurements of interseismic deformation the block model includes the effects of block rotation and elastic strain accumulation consistent with a simple model of the earthquake cycle our estimates of the right lateral strike slip rate on the san andreas fault vary by at least a factor of 5 from a high of 35 9 0 5 mm yr in the carrizo plain to a low of 5 1 1 5 mm yr through the san bernadino segment shortening across the puente hills thrust and left lateral slip on the raymond hill fault are consistent with both thickening and escape tectonics in the los angeles basin discrepancies between geodetic and geologic slip rate estimates along the san andreas and san jacinto faults as well as in the eastern california shear zone may be explained by a temporal change in fault system behavior we find no substantial evidence for long term postseismic relaxation and infer that the viscosity of the lower crust upper mantle may be relatively high 1019 pa s

the relationship between arabian sea upwelling and indian monsoon revisited in a high resolution ocean simulation studies based on sediment records sea surface temperature and wind suggest that upwelling along the western coast of arabian sea is strongly affected by the indian summer monsoon we examine this relationship directly in an eddy resolving global ocean simulation storm driven by atmospheric reanalysis over the last 61 years with its very high spatial resolution 10 km storm allows us to identify characteristics of the upwelling system we analyse the co variability between upwelling and meteorological and oceanic variables from 1950 to 2010 the analysis reveals high interannual correlations between coastal upwelling and along shore wind stress r 0 73 as well as with sea surface temperature r 0 83 however the correlation between the upwelling and the monsoon is small we find an atmospheric circulation pattern different from the one that drives the monsoon as the main modulator of the upwelling variability in spite of this the patterns of temperature anomalies that are either linked to arabian sea upwelling or to the monsoon are spatially quite similar although the physical mechanisms of these links are different in addition no long term trend is detected in our modelled upwelling in the arabian sea

quaternary landscape evolution in the san jacinto fault zone peninsular ranges of southern california transient response to strike slip fault initiation well constrained case studies of transient landscape response to external forcing are needed to improve our understanding of erosion processes in tectonically active mountain belts the peninsular ranges portion of the san jacinto fault zone sjfz is an excellent location for such a study because it displays pronounced geomorphic disequilibrium resulting from initiation of a major strike slip fault in the past 1 0 to 2 5 million years we recognize two geomorphic domains in this region 1 a relict low relief upland domain consisting of broad flat valleys and low gradient streams and 2 very steep rough topography with deeply incised canyons and retreating erosional knickpoints pleistocene sediments exposed along and near the sjfz include fluvial conglomerate sandstone and mudstone with weak paleosols and west to nw directed paleocurrents these sediments accumulated in a lowgradient stream system represented by domain 1 during an early phase of slip in the sjfz prior to the modern phase of erosion and degradation domain 2 late pliocene or early pleistocene initiation of the sjfz triggered a wave of headward erosion and stream capture that is still migrating nw along the fault zone using the total distance that capture points have migrated along the fault zone and a range of possible ages for fault initiation the rate of knickpoint retreat is estimated at 12 to 44 km my to explore the signal of transient geomorphic response to fault initiation we analyzed 23 tributaries along an 20 km portion of the main fault valley within domain 2 the analysis reveals three zones with distinctive morphologies 1 strongly convex longitudinal profiles in the nw 2 a large ca 5 6 km 2 landslide in the central zone and 3 concave tributaries in the se with profile complexity decreasing and catchment area increasing from nw to se the distribution of these zones suggests close spatial and temporal association of active fault slip bedrock incision deep seated landslides and erosional modification the fundamental driving force behind these processes is profound geomorphic disequilibrium resulting from initiation of the sjfz we suggest that landslides may have played a significant role in shaping the morphology of this fault zone and that the influence of landslides may be underestimated in areas where characteristic landforms and deposits are obscured by later erosion and faulting d 2005 elsevier b v all rights reserved

spatial and temporal deformation along the northern san jacinto fault southern california implications for slip rates the san timoteo badlands is an area of uplift and erosional dissection that has formed as a result of late quaternary uplift along a restraining bend in the san jacinto fault of the san andreas fault system in southern california this bend currently is located in a region where late quaternary deposits and associated surfaces have formed in lower san timoteo canyon we have used morphometric analysis of these surfaces in conjunction with computer modeling of deformational patterns along the san jacinto fault to reconstruct spatial and temporal variations in uplift along the bend morphometric techniques used include envelope subenvelope map ping a gradient length index along channels and denudation values age control is determined using a combination of thermoluminescence tl and near infrared op tical simulation luminescence dating irosl and correlation of soil development indices these approaches are combined with an elastic half space model used to determine the deformation associated with the fault bend the region of modeled uplift has a similar distribution as that determined by morphometric techniques luminescence dates and soil correlation age estimates generally agree based on soil development surfaces within the study area were stabilized at approximately 300 700 ka for q3 43 67 ka for q2 and 27 5 67 ka for q1 luminescence ages both tl and irosl for the formation of the younger two surfaces are 58 to 94 ka for q2 and 37 to 62 ka for q1 ages reported to 1r uncertainty periods of uplift were determined for the surfaces in the study area resulting in approximate uplift rates of 0 34 to 0 84 m ka for the past 100 ka and 0 13 to 1 00 m ka for the past 66 ka comparison of these rates of uplift to those generated by the model support a higher rate of lateral slip along the san jacinto fault than commonly assumed greater than 20 mm yr as compared to 8 12 mm yr commonly cited this higher slip rate supports the proposal that a greater amount of slip has transferred from the san andreas fault to the san jacinto fault than generally held the san jacinto fault may have accommodated a significant portion of the plate boundary slip during the past 100 ka

stratigraphic record of pliocene pleistocene basin evolution and deformation within the southern san andreas fault zone mecca hills california abstract a thick section of pliocene pleistocene nonmarine sedimentary rocks exposed in the mecca hills california provides a record of fault zone evolution along the coachella valley segment of the san andreas fault saf geologic mapping measured sections detailed sedimentology and paleomagnetic data document a 3 5 myr history of deformation and sedimentation in this area sw side down offset on the painted canyon fault pcf starting 3 7 ma resulted in deposition of the mecca conglomerate southwest of the fault the lower member of the palm spring formation accumulated across the pcf from 3 0 to 2 6 ma during regional subsidence sw side up slip on the pcf and related transpressive deformation from 2 6 to 2 3 ma created a time transgressive angular unconformity between the lower and upper members of the palm spring formation the upper member accumulated in discrete fault bounded depocenters until initiation of modern deformation uplift and basin inversion starting at 0 7 ma some spatially restricted deposits can be attributed to the evolution of fault zone geometric complexities however the deformation events at ca 2 6 ma and 0 7 ma are recorded regionally along 80 km of the saf through coachella valley covering an area much larger than mapped fault zone irregularities and thus require regional explanations we therefore conclude that late cenozoic deformation and sedimentation along the saf in coachella valley has been controlled by a combination of regional tectonic drivers and local deformation due to dextral slip through fault zone complexities we further propose a kinematic link between the 2 6 2 3 ma angular unconformity and a previously documented but poorly dated reorganization of plate boundary faults in the northern gulf of california at 3 3 2 0 ma this analysis highlights the potential for high precision chronologies in deformed terrestrial deposits to provide improved understanding of local to regional scale structural controls on basin formation and deformation along an active transform margin

stratigraphic record of basin development within the san andreas fault system late cenozoic fish creek vallecito basin southern california the fish creek vallecito basin contains a 5 5 km thick section of late miocene to early pleistocene sedimentary rocks exposed in the hanging wall of the west salton detachment fault these deposits preserve a high fidelity record of late cenozoic subsidence and basin filling that resulted from deformation in the san andreas fault system of southern california existing and new paleomagnetic data combined with new u pb zircon ages of two tuffs high in the section show that the section ranges in age from ca 8 0 0 4 ma at the base to ca 0 95 ma at the top geohistory analysis reveals 1 moderate subsidence 0 46 mm yr from ca 8 0 to 4 5 ma 2 rapid subsidence 2 1 mm yr from 4 5 to 3 1 ma 3 moderate subsidence 0 40 mm yr from 3 1 to 0 95 ma and 4 rapid uplift and erosion that has exhumed the section since ca 1 ma onset of sedimentation at ca 8 0 0 4 ma records earliest extension or transtension in the area possibly related to localization of the pacific north america plate boundary in the salton trough and gulf of california alternatively marine incursion at 6 3 ma may be the earliest record of plate boundary deformation in the gulf of california salton trough region a thick interval higher in the section records progradation of the colorado river delta into and across the basin starting ca 4 9 ma progradation continued during an abrupt increase in subsidence rate at 4 5 ma and fluvial deltaic conditions persisted for 1 4 m y during the rapid subsidence phase indicating that delta progradation was driven by a large increase in rate of sediment input from the colorado river uplift and inversion of the basin starting ca 1 0 ma record initiation of strike slip faults that define the modern phase of dextral wrench tectonics in the western salton trough

downdip segmentation of strike slip fault zones in the brittle crust outcrop scale field evidence from the southern san jacinto fault zone in southern california indicates that bedding parallel slip may be an important mechanism for transferring and accommodating slip within strike slip fault zones that cut across heterogeneous stratigraphy steeply dipping strike slip fault segments exposed in conglomeratic sandstones abruptly terminate at weaker shale layers where slip occurs on bedding parallel planes cross sections of fault related seismicity within the southern san jacinto fault zone reveal that events generally cluster within tabular steeply dipping fault parallel streaks that are limited in extent in the downdip direction the depths of the downdip terminations of shallow streaks tend to be roughly coincident with the depths of the updip terminations of deeper streaks these configurations define stepover geometries that range in character from sharp to diffuse the examples described herein provide evidence that downdip segmentation within strike slip fault zones may be common over a wide range of scales

block kinematics of the pacific north america plate boundary in the southwestern united states from inversion of gps seismological and geologic data 1 the active deformation of the southwestern united states 30 41 n is represented by a finite number of rotating elastic plastic spherical caps gps derived horizontal velocities geologic fault slip rates transform fault azimuths and earthquake derived fault slip vector azimuths are inverted for block angular velocities creep on block bounding faults permanent strain rates within the blocks and the rotations of 11 published gps velocity fields into to a common north american reference frame gps velocities are considered to be a combination of rigid block rotations recoverable elastic strain rates resulting from friction on block bounding faults and nonrecoverable strain rates resulting from slip on faults within the blocks the resulting pacific north america angular velocity is similar to some published estimates and satisfies transform azimuths and one spreading rate in the gulf of california earthquake slip vectors in the gulf of california and alaska and gps velocities along coastal california and within the pacific basin published fault slip rates are satisfied except in the southern mojave desert where the motion of the mohave block relative to north america is faster than can be explained by mapped faults the largest blocks the sierra nevada great valley and the eastern basin and range show permanent strain rates after removing elastic strain of only a few nanostrain per year demonstrating approximately rigid behavior observed horizontal strain rates correlate strongly with predicted strain rates from known faults suggesting that the short term strains evident in gps velocities are largely elastic in only about 20 of the region is distributed deformation needed to match the data indicating that a plate tectonic style description of the deformation of the western united states is plausible most blocks rotate about vertical axes at approximately the same rate as the pacific relative to north america suggesting that locally spin rates are communicated from block to block arguing against both floating block and ball bearing mechanisms of block rotation the similarities of the blocks spin rates to that of the pacific suggests that the pacific strongly influences their motions through edge tractions however it is shown that the blocks cannot rotate about the pacific north america pole without spinning counter to the sense of pacific north america shear unlike some other broad plate boundaries in the western united states vertical axis rotations take up very little of the slip rate budget across the region

remotely sensed features in the us jgofs arabian sea process study abstract topex poseidon altimeter data and wind data are used to calculate the geostrophic transport and ekman transport in the northern arabian sea within the upper 500 m in the summer the upper 500 m layer in the northern arabian sea is horizontally divergent with a transport going out of the northern arabian sea across 15 75 n reaching a maximum of 10 106 m3 s 1 in late june in the winter it is horizontally convergent with a transport within the upper 500 m layer across 15 75 n reaching about 5 106 m3 s 1 into the northern arabian sea the mean net transport for 1993 1995 out of the northern arabian sea across 15 75 n within the upper 500 m is estimated to be 0 74 106 m3 s 1 most of the deep water upwelling across the 500 m depth which compensates for the loss of waters in the upper 500 m layer occurs in the eastern part of the northern arabian sea the north equatorial current is found to deflect into the arabian sea during the ne monsoon and the spring intermonsoon periods in addition estimates are made of the net transport into and out of the region encompassed by the us joint global ocean flux study jgofs arabian sea process study the total transport out of the us jgofs region is approximately 3 5 4 0 106 m3 s 1 in july of 1995 in the upper 500 m analysis of the mean sea surface height for the arabian sea shows a periodic change with the seasonal monsoon with a typical depression of the ocean surface during the summer indicative of arabian sea cooling the yearly change of the averaged sea surface height at 15 75 n is of the order of 15 cm rossby wave propagation also was observed at 15 75 n in the sea surface height fields

seasonal variation of hydrographic and nutrient fields during the us jgofs arabian sea process study abstract between september 1994 and december 1995 the us jgofs arabian sea process experiment collected extensive high quality hydrographic data temperature salinity dissolved oxygen and nutrients during all seasons in the northern arabian sea an analysis of this unique data suite suggests the presence of many features that are described in the canonical literature but these new data provided the following insights 1 although the seasonal evolution of mixed layer depths was in general agreement with previous descriptions the deepest mixed layer depths in our data occurred during the late ne monsoon instead of the sw monsoon 2 the region exhibits considerable mesoscale variability resulting in extremely variable temperature salinity ts distributions in the upper 1000 db this mesoscale variability is readily observed in satellite imaging in the high resolution data taken by a companion onr funded project and in underway adcp data 3 the densest water reaching the sea surface during coastal upwelling appeared to have maximum offshore depths of 150 m and s close to the core value 25 for the saline arabian sea water asw but salinities in these upwelling waters were relatively low the densest water found at the sea surface during late ne monsoon conditions has s 24 8 and relatively high salinities suggesting that they are a source for the asw salinity maximum 4 persian gulf water pgw with a core of 26 6 forms a widespread salinity maximum despite the considerable extent of this feature persian gulf outflow water with a salinity 4 of 39 at its source can only be a minor contributor within the standard us jgofs sampling grid maximum salinities on this surface are 36 8 at stations near the gulf falling to values as low as 35 3 at the stations farthest removed from its influence even at our standard stations closest to the gulf n 1 and n 2 the high salinity low nutrient persian gulf water has only a modest direct effect on nutrient concentrations this pgw salinity maximum is associated with the suboxic portions of the arabian sea s oxygen minimum zone 5 the salinity maximum associated with red sea water rsw core 27 2 in the jgofs study region is clearly evident at the southermost sampling site at 10 n s 15 elsewhere this signal is weak or absent and salinity on the 27 2 surface tends to increase towards the persian gulf suggesting that the disappearance of this salinity maximum is due at least in part to the influence of the persian gulf outflow 6 inorganic nitrogen to phosphate ratios were lower frequently much lower than the standard redfield ratio of 15 1 16 1 by atoms at all times and all depths suggesting that inorganic nitrogen was more important than phosphate as a limiting nutrient for phytoplankton growth and that the effects of denitrification dominated the effects of nitrogen fixation 7 the water upwelling off the omani coast during the sw monsoon has inorganic nitrogen to silicate ratios that were higher 2 1 than the 1 1 ratio often assumed as the ratio of uptake during diatom growth 8 the temporal evolution of inorganic nitrogen to silicate ratios suggests major alteration by diatom uptake only during the late sw monsoon cruise tn050 in august september 1995 9 widespread moderate surface layer nutrient concentrations occurred during the late ne monsoon 10 a zone of high offshore nutrient concentrations was encountered during the sw monsoon but instead of being associated with offshore upwelling it may represent offshore advection from the coastal upwelling zone the influence of an eddy or both 11 although our data do not contradict previous suggestions that the volume of subtoxic water may be reduced the sw monsoon they suggest a weaker re oxygenation than indicated by some previous work similarly they do not confirm results suggesting that secondary nitrite maxima may be common in waters with oxygen concentrations 5 m

inter monsoonal changes in the t s properties of the near surface waters of the northern arabian sea the arabian sea experiences extremes in atmospheric forcing that lead to the greatest seasonal variability in any ocean during 1995 6 cruises were carried out within the northern arabian sea the data collected represent the first consistent dataset covering an entire monsoonal cycle ocean soundings of temperature and salinity from these cruises are used to characterize variability of water masses in the surface layers associated with monsoonal forcing this paper documents the role of advection versus local water mass modification on seasonal extremes in t s in near surface waters of the arabian sea seasonal changes are associated with seasonal heating advection of waters from the oman upwelling zone varying of mixed layer depth due to ekman pumping in the central basin and mixing of high salinity waters from persian gulf

glacial origin of the cryogenian nantuo formation in eastern shennongjia area south china implications for macroalgal survival abstract the cryogenian period was characterized by global glaciations imposing extreme environmental stresses on early multicellular organisms globally distributed diamictite deposits are the major evidence for these glaciation events but the glacial origin of at least some of these diamictite deposits has been disputed complicating interpretations of the environmental conditions influencing the evolution of life in the cryogenian 720 635 ma in this study we conducted a systematic sedimentological investigation of the marinoan age 650 635 ma nantuo formation in six sections representing a 20 km long east west transect in the eastern shennongjia area of south china the nantuo formation which ranges in thickness from 2 m in the east to 300 m in the west comprises diamictite conglomerate lonestone bearing sandstone green siltstone and black shale facies the eastern sections e g longxi and wushanhu consist mainly of diamictite facies exhibiting micro scaled rotation structures microshear grain stacking grain to grain contacts and water escape structures supporting their deposition in a subglacial setting in contrast the western sections shijiahe liziping and songluo consist of massive and graded diamictite and conglomerate facies consistent with an origin as glacially induced submarine debris flows furthermore the lonestone bearing sandstone facies in these sections contain abundant dropstones and mud pellets within finely laminated turbidites indicating an ice rafted origin with locally reworking by turbidity currents the green siltstone and black shale facies lack glacigenic features and may represent late deglacial deposits based on thickness and facies variations among the study sections we infer that the nantuo formation records glacial sedimentation on a complex paleotopographic surface that was incised into the underlying bedrock with subglacial deposits to the east transitioning into glaciomarine deposits to the west of study area the distal songluo section likely records three cycles of glacial advance and retreat in the form of a facies alternation between diamictite and black shale consistent with a dynamically fluctuating ice margin in summary our sedimentological investigation supports a glacial origin for the nantuo formation in the eastern shennongjia area the occurrence of the benthic macroalgal dominated songluo biota in the black shale facies at songluo suggests that strong glacial retreats provided niches for macroalgal survival in the cryogenian glacial ocean

lonestones as indicators of tsunami deposits in deep sea sedimentary rocks of the miocene morozaki group central japan abstract lonestones are isolated larger clasts enclosed in muddy fine grained deposits and are usually interpreted as iceberg rafted dropstones this interpretation implies the existence of glaciers continental ice sheets and consequently a cool climate however alternative interpretations are possible as lonestones may also be deposited by non glacial processes therefore clarification of the depositional processes associated with lonestones is fundamental for studies based on lonestone bearing deposits a field survey of lonestone bearing deposits from early miocene deep sea sedimentary rocks found around the chita peninsula of central japan suggests that tsunami induced flows on the sea bottom may also form lonestones these lonestones are associated with sandy to gravelly deposits and were deposited by high energy episodic currents the main features of these deposits are the multiple stacking of normally graded units and the laterally discontinuous distribution of coarse grained clastic material sands and gravels such features are consistent with deposition by tsunamis and suggest that lonestone bearing depositional successions must be carefully interpreted especially where lonestones are used as glacial indicators as some lonestones were probably put in place by ancient tsunami events

magnetostratigraphy and biochronology of the san timoteo badlands southern california with implications for local pliocene pleistocene tectonic and depositional patterns the san timoteo badlands expose nearly 2000 m of nonmarine sedimentary rocks ideally situated temporally and spatially to address questions regarding major tectonic events that occurred in southern california from latest miocene to medial pleistocene time these events include development of the san andreas san jacinto fault system and uplift of the transverse ranges the badlands sequence also spans three of the four most recent north american land mammal ages and therefore coincides with important trans beringian and neotropical mammal dispersal events no other terrestrial sequence in north america records relatively continuous deposition over this interval of time magnetostratigraphy and mammalian biochronology provide a temporal framework that allows greater resolution of the geologic and biotic events recorded within the sequence than previous studies on this region data show that the sequence extends from chron c3an 2n ca 6 3 ma at the lowest part of the section in the study area to within the brunhes chron or younger than 0 78 ma near the top refined age estimates for geologic and biotic events recorded within the sequence indicate that 1 a peninsular ranges basement source south of the badlands region dominated deposition from before 6 3 ma to about 4 6 ma after which time the provenance shifted to a san gabriel mountains basement source from the north 2 deposition of san gabriel mountains type material continued until as recently as ca 0 70 ma although sediments from the san bernardino mountains appeared in the northwesternmost area of the badlands ca 1 5 ma 3 the late hemphillian mount eden local fauna is dated as 5 6 ma compared with previous estimates of 5 0 5 4 ma 4 the early irvingtonian el casco local fauna is 1 3 1 4 ma and 5 the shutt ranch local fauna is ca 0 7 0 99 ma paleomagnetic data show that the badlands region may be slightly rotated in a counterclockwise direction contrary to previous models predicting clockwise rotation in right lateral shear zones

sequence stratigraphy in active extensional basins implications for the interpretation of ancient basin fills abstract systematic variations in sequences their component units and their stacking patterns exist within rift basins these variations can be related to displacement gradients associated with the large scale 12 50 km segmentation of normal fault zones which control accommodation sediment supply and basin physiography sediment supply is also strongly influenced by the nature of pre rift drainage networks and variations in bedrock lithology high rates of hangingwall subsidence close to the centre of normal fault segments may cancel out the effects of glacio eustatic sea level fall so that accommodation development is normally characterized by the continual addition of new space the resulting sequences lack type 1 sequence boundaries and lowstand systems tracts and stack into aggradational sequence sets the adjacent footwall is subject to uplift which may lead to subaerial exposure and incision generating a composite type 1 sequence boundary away from the fault zone and near segment boundaries slip rates are much lower and hence relative sea level change is dominated by eustasy here falls in relative sea level are important resulting in type 1 sequences sequence stacking patterns reflect not only eustasy and local fault controlled subsidence but also the interaction of these with adjacent uplifting footwalls and or regional uplift tectonic influence on sequence development will be more pronounced during greenhouse times than icehouse times

variable rates of late quaternary strike slip on the san jacinto fault zone southern california three strike slip displacements of strata with known approximate ages have been measured at two locations on the san jacinto fault zone minimum horizontal offset between 5 7 and 8 6 km in no more than 0 73 m y northeast of anza indicates 8 12 mm yr average slip rate since late pleistocene time two measures of more recent displacement are based on trenching studies of stratigraphic offsets on the coyote creek fault in western imperial valley horizontal slip of 1 7 m has been calculated for the youngest sediment of lake cahuilla since its deposition 275 510 yr b p the corresponding slip rate is 2 8 5 0 mm yr right lateral offset of 10 9 m measured on a buried stream channel older than 5060 yr b p but younger than 6820 yr b p yields average slip rates for the intermediate time periods 400 to 6000 yr b p of 1 2 mm yr the average rates of slip for these three time intervals suggest a relatively quiescent period for the san jacinto fault zone from about 4000 b c to about 1600 a d to the extent that long term variations in seismic activity of major strike slip faults elsewhere are known fluctuations in slip rate for the san jacinto fault would not appear to be abnormal if the san jacinto and adjacent segments of the san andreas fault alternately assume dominant roles in absorbing motion between the pacific and american plates perhaps even more recently than 400 yr ago the san andreas fault south of the transverse ranges expressed most of the motion but has since become relatively inactive

the santa rosa event 40ar 39ar and paleomagnetic results from the valles rhyolite near jaramillo creek jemez mountains new mexico the jaramillo event was originally defined by doell and dalrymple in 1966 on the basis of k ar ages from sanidine in the normally transitionally and reversely magnetized rhyolite domes named cerro del abrigo cerro santa rosa i and cerro santa rosa ii respectively that erupted following collapse of the archetypal valles caldera new mexico we have collected new paleomagnetic data from the three domes and new 40 ar 39 ar laser fusion and furnace incremental heating experiments on sanidine crystals from the cerro santa rosa i rhyolite step wise alternating field and thermal demagnetization techniques applied to 52 samples from seven sites indicate that the original paleomagnetic results of doell and dalrymple science 152 1966 1060 1061 are valid cerro del abrigo is normally magnetized whereas the santa rosa i dome is transitional with an inclination of 363 toward the east and the santa rosa ii dome is of reversed polarity twenty five laser fusion experiments on sanidine crystals from the the cerro santa rosa i dome together with the saddle shaped spectrum obtained by incrementally heating the sanidine in a furnace reveal that this rhyolite contained a small but significant component of excess argon prior to eruption our preferred age of 936 8 ka 2c for the santa rosa i rhyolite is based on the concordant laser fusion isochron and incremental heating plateau ages this age is significantly older than was inferred on the basis of earlier laser fusion 40 ar 39 ar results that suggested a trapped component characterized by a 40 ar 36 ar ratio lower than the atmospheric value of 295 5 our new age distinguishes the santa rosa i dome by 65 kyr from the termination of the jaramillo normal subchron 1001 10 ka and by 37 kyr from basaltic lavas at haleakala and tahiti which record the kamikatsura event 899 6 ka moreover this determination is a factor of three more precise than the best previous estimate for a proposed geomagnetic event in this time period the cerro santa rosa i rhyolite dome once intimately linked with the end of the jaramillo event and the acceptance of plate tectonic theory now defines a highly resolved feature the santa rosa event in a terrestrial geomagnetic reversal time scale that is consistent with the global record of magnetic field intensity from marine sediments fl 2002 elsevier science b v all rights reserved

zooplankton spatial distributions in coastal waters of the northern arabian sea august 1995 abstract the spatial distribution of zooplankton biomass was surveyed in coastal waters of the northern arabian sea during the 1995 southwest monsoon august on cruise mb 95 06 of the noaa ship malcolm baldrige vertical patterns of displacement volumes from a limited set of paired day night mocness tows suggest there was little diel vertical migration in the coastal waters off the southern arabian peninsula zooplankton biomass varied from 5 2 to 15 1 g dw m 2 178 517 mm c m 2 in the upper 200 300 m of omani coastal waters distributions of acoustic backscatter were mapped in eight daytime acoustic doppler current profiler transects in coastal waters off oman and somalia several transects contained maxima in acoustic backscatter that coincided with cool fresh surface features that were several tens of kilometers wide although there was considerable scatter in the relationship between acoustically determined biomass adb of zooplankton and surface temperature there was a trend of increased biomass in the cool surface temperatures of the omani upwelling zone acoustic transects crossed two filaments that extended seaward from upwelling centers off oman and somalia estimated zooplankton adb exported from the upwelling zones in the surface features was on the order of 300 kg dw s 1 the physical and biological characteristics of filaments maintain zooplankton associated with upwelling areas such as calanoides carinatus as they are advected offshore from coastal upwelling zones

pleistocene brawley and ocotillo formations evidence for initial strike slip deformation along the san felipe and san jacinto fault zones southern california abstract we examine the pleistocene tectonic reorganization of the pacific north american plate boundary in the salton trough of southern california with an integrated approach that includes basin analysis magnetostratigraphy and geologic mapping of upper pliocene to pleistocene sedimentary rocks in the san felipe hills these deposits preserve the earliest sedimentary record of movement on the san felipe and san jacinto fault zones that replaced and deactivated the late cenozoic west salton detachment fault sandstone and mudstone of the brawley formation accumulated between 1 1 and 0 6 0 5 ma in a delta on the margin of an arid pleistocene lake which received sediment from alluvial fans of the ocotillo formation to the west southwest our analysis indicates that the ocotillo and brawley formations prograded abruptly to the east northeast across a former mud dominated perennial lake borrego formation at 1 1 ma in response to initiation of the dextral oblique san felipe fault zone the 25 km long

paleomagnetism of the ocotillo badlands southern california and implications for slip transfer through an antidilational fault jog abstract the right lateral coyote creek fault is the southernmost segment of the san jacinto fault zone in california at the ocotillo badlands an anticlinorium of locally updomed material is exposed at a step over between echelon segments of the fault here uplift and deformation most probably result from multiple slip increments transferred across the antidilational fault jog under the assumption that material away from the jog region deforms by rigid body translation within the 2 km wide fault jog contraction has occurred by folding of the quaternary sedimentary strata about east west trending hinge lines structural analysis of this deformation shows that folding has accommodated 800 m of fault slip transferred through the antidilational jog by comparison total right slip on the coyote creek fault is 2 5 km measured 25 km to the northwest at coyote ridge a magnetostratigraphic study of the deformed strata was undertaken to determine the longevity of this fault discontinuity at the ocotillo badlands the eroded core of the updomed material at the ocotillo badlands exposes a 325 m thick sequence of sedimentary rock made up by the lacustrine borrego formation 200 m and the overlying conglomeratic ocotillo formation 125 m stepwise thermal demagnetization of samples from the exposed strata suggests that the formation boundary also marks a magnetic polarity reversal of reversed field to normal field as one travels upwards through the composite section the inferred primary magnetization is probably produced by a detrital remanent magnetization drm and is often overprinted with a weak viscous present field component comparison with magnetostratigraphy of the borrego badlands 10 km to the northwest indicates that the reversal sampled is the onset of the jaramillo event 0 97 ma the presence of a 20 angular unconformity within the upper portion of the exposed stratigraphy shows that deformation within the ocotillo badlands began during deposition of the ocotillo formation shortly after the time of the field reversal if total slip on the coyote creek fault at the ocotillo badlands is greater than 800 m it appears that the fault jog has been a transitory feature within the fault zone with slip alternately bypassing it or being transferred across it such switchyard behavior of slip transfer through the fault jog has important implications for understanding structural controls on earthquake rupture

late mesozoic and cenozoic tectonic history of south central california the late mesozoic cenozoic history of south central california is punctuated by at least five major tectonic events the oldest of these involves late cretaceous drag folding and thrusting of epizonal shelf sediments westward over and to the north along the rising eastern margin of the peninsular ranges batholith these overthrusts with associated drag folds and nappes form imbricate stacks of metasediments slices of plutons and mylonites which overlie a regional core of cretaceous granitic plutons of the peninsular ranges batholith a second distinct kind of epizonal low temperature crustal displacement includes an episode of mid tertiary detachment faulting and folding this represents the westerly extension of the detachment terrane of eastern california and western arizona and utah superimposed upon the cretaceous structural features the mid tertiary motions involve major e w extension and n s compressive strain with formation of east trending antiformal core complexes remarkably parallel to a pervasive set of fold axes and b lineations formed in the cretaceous thrusting and folding all of these features are repeatedly segmented and displaced by step faulting as sial in the salton trough is fragmented and depressed 5 to 10 km below sea level at intervals throughout the cenozoic the irregular step faulted interface of the peninsular ranges batholith and salton trough is accentuated by a series of ne to se striking left lateral and dipslip faults with displacements of several to 10 kilometers these appear to both predate and occur during movements along the san andreas system pliocene pleistocene right lateral faulting a younger extension of the san andreas displacements north of the transverse ranges has broken and displaced all older structural features with total net slip in south central california of perhaps 300 km total right lateral slip along the several strands of the san andreas system are measurable via reconstruction of the mosaic of numerous older predominantly e w trending linear elements mid tertiary antiforms and cretaceous and older rocks right lateral strain on the san andreas appears to either alternate with or to be a byproduct of n s compressional strain from the pleistocene to the present a resultant effect is a large family of e w trending folds and fault scarps in plio pleistocene sediments

fluctuations of gulf stream frontal position between cape hatteras and the straits of florida low frequency variations in the onshore offshore position of the gulf stream thermal front have been examined at 10 cross isobath transects spaced along the south atlantic bight between the straits of florida and cape hatteras the data were obtained from the u s navy s frontal analysis charts for the 12 year period 1976 1988 a time domain empirical orthogonal function eof analysis revealed two modes of fluctuation about the mean gulf stream position which together explain the well known open quotes weakly and strongly deflected close quotes frontal position states which occur on timescales of a few months in the vicinity of the charleston bump analyses of fluctuations at the annual period revealed a 3 month phase lag between frontal position as shown by the most significant time domain eof mode and volume transport through the straits of florida in addition frequency domain eof and cross spectral analysis of frontal position revealed annual waves which appear to propagate to the south north in the region south north of the bump for transect pairs having significant coherence and nonzero phase estimates the phase speed and wavelength were about 10 cm s southward 7 cm s northward and 3000 km 2000 km in the southern northern region this suggests an annual generation of amore perturbation in the vicinity of the bump which radiates away as a long annual wave and which may be related to or part of the mechanism which produces the annual modulation of gulf stream transport 11 refs 9 figs 1 tab less

late quaternary rate of slip along the san jacinto fault zone near anza southern california the anza section of the san jacinto fault southern california has not experienced a groundbreaking earthquake since at least 1918 and probably since before 1899 leading previous workers to designate this 20 km long fault segment as a seismic gap study of displaced pleistocene and holocene alluvial fan and fluvial deposits across the san jacinto fault near anza california dated using 14c and soil development age control indicates a minimum right lateral slip rate of 9 2 2 mm yr since 9 5 ka and a slip rate of 11 9 5 mm yr since 14 ka 12 9 5 mm yr since 17 ka and 13 10 6 mm yr since 50 ka these estimates agree with a previously determined 700 ka to present minimum slip rate of 10 2 mm yr based on an estimated average slip rate of 12 mm yr from the longer term slip rate estimates about 0 8 m of potential slip has accumulated if the 1918 earthquake broke the anza segment over 1 1 m of potential slip has accumulated if the last earthquake occurred prior to 1899 these data attest to the potential for an earthquake m6 5 for this section of the fault

paleohydrologic regimes in the southwestern great basin 0 3 2 my ago compared with other long records of gobal climate abstract nine distinct paleohydrologic regimes in the southwestern great basin over the last 3 2 my are recorded by the lacustrine deposits in km 3 a 930 m core from searles lake california these are characterized as being wet intermediate or dry like today excepting the present incomplete regime each lasted 0 12 to 0 76 my major regime changes 0 01 0 13 0 6 and 2 5 my ago appear to coincide with recognized changes in global ice sheet histories as represented by 18 o and other records from marine sediments but comparable changes 0 3 1 0 1 3 and 2 0 my ago do not appear to coincide closely with comparable perturbations in ice sheet histories however all regime boundaries during the last 1 75 my coincide closely in time with changes in sea surface temperatures in the tropical atlantic and many coincide with other deep sea and continental paleoclimatic boundaries the average duration of these paleohydrologic regimes was about 0 4 my standard deviation 0 2 my or less depending on assumptions and it is suggested that the regime boundaries reflect times of change in global sea surface temperatures possibly controlled in part by the earth s 413 000 yr orbital eccentricity cycle during the wettest and driest regimes in the searles lake area lake levels were not sufficiently affected by the 23 000 to 42 000 or 100 000 yr climate cycles related to high latitude ice sheet fluctuations to produce changes in the lacustrine sediment character during intermediate regimes however when lacustrine sedimentation in this area was more sensitive to climate the sediments in km 3 record lake fluctuations with average frequencies near those of the ice sheets this seems to indicate that the high latitude ice sheet fluctuations caused local climatic perturbations but did not dominate the hydrologic component of climate in this area other lacustrine deposits in the southwestern great basin of california and nevada have ages comparable in part to those of the wet to intermediate regimes indicated by km 3 and they may all be products of finite periods when lake expansion alluvial fan growth increased spring discharge and fluvial deposition were promoted in this area by widespread wet climates glacier expansion in the sierra nevada may also have been primarily an expression of and in phase with these wet regimes

relict sheetflood bed forms on late quaternary alluvial fan surfaces in the southwestern united states late pleistocene and early holocene alluvial fan surfaces in southeastern california are locally mantled by narrow widely spaced transverse to slope bands of fine gravel and coarse sand these features are interpreted to be relict bed forms of high magnitude sheetfloods that inundated abandoned alluvial fan surfaces the majority of these sheetflood events apparently occurred in the latest pleistocene to middle holocene and produced meso bed forms with wavelengths of 2 6 m these flood events mobilized sediment with mean grain sizes of 2 8 mm on inactive fan surfaces under calculated velocities of 30 60 cm s and may be responsible for increased dissection of upper piedmonts and widespread alluvial fan deposition in the lower piedmont regions an older sheetflood event produced macro bed forms with wavelengths of 20 80 m on a pedogenic caco 3 cemented piedmont in southwestern arizona both scales of bed forms display characteristics of confined flow fluvial bed forms which form under diverse flow regimes that cause either megaripples or transverse ribs

seepage analysis in a fractured rock mass the upper reservoir of pushihe pumped storage power station in china abstract a numerical simulation model of seepage in a fractured rock mass was constructed based on the hydrogeological conditions of the upper reservoir of pushihe pumped storage power station in china which is currently under construction in addition an analysis was conducted of groundwater movement in the reservoir rock system and calculations were made of the leakage rate and distribution of seepage under various operating conditions during the simulation the most important but most difficult problem was the determination of the hydraulic conductivity tensor of a fractured rock mass this paper modifies the method of determining the hydraulic conductivity tensor so that it not only reflects the permeability characteristics of the fractured rock mass but also improves the calculation precision the principal values and directions of the hydraulic conductivity tensor were first determined with a statistical method based on measurements of the spatial spreading of the fractures and were then modified using estimates of isotropic hydraulic conductivity that were calculated by the babushkin formula according to the water permeability rate from a field water pressure test and finally were verified using an inversion analysis with a mathematical model the simulation results show that the total leakage rate is estimated to be 5832 92 m3 d under the operating conditions of a normal pool level and no anti seepage treatment results of the analysis of various seepage control scenarios suggest that the preferred scenario is grouting curtain only in the dam foundation with the curtain depth 5 m below the line where the water permeability rate equals 3 lu thus reducing the leakage rate by 3571 27 m3 d the above results provide a basis and reference for designing seepage control structures and facilitating decision making

segmentation of the northern san jacinto fault zone southern california accurate forecasting of large earthquakes in the san jacinto fault zone depends on the correct determination of fault segmentation we have searched for discontinuities in the fault zone using as data geological maps of the fault traces relocated earthquake hypocenters focal mechanisms slip rates and historic large earthquake rupture zones we identify nine principal discontinuities in the northern san jacinto fault zone these are characterized as structural discontinuities bends steps branches intersections geodetic discontinuities slip rate and lithologic discontinuities most of the discontinuities have more than one defining characteristic we also analyzed the local strain field orientation along the fault zone significant lateral discontinuities in the strain field orientation are coincident with many of the structural and geodetic discontinuities we identify segment lengths defined from the data vary from about 7 to 35 km this range of segment lengths is consistent with the lengths of large historical earthquake ruptures however evidence from small earthquake hypocenter patterns suggests the possibility that in some areas large earthquakes may rupture multiple adjacent segments in these cases maximum magnitudes may be larger than those observed historically because of the short historic record and the sparse paleoseismic record probabilistic estimates of earthquake recurrence for this fault zone have depended heavily on assumed characteristic lengths of individual rupture segments ours and previous delineations of segment lengths have varied considerably indicating that assumed segment length is a major source of uncertainty in the recurrence calculations this source of uncertainty should be taken into account in calculations of the reliability of the probabilistic hazard estimates

new kinematic models for pacific north america motion from 3 ma to present i evidence for steady motion and biases in the nuvel 1a model we use velocities derived from 2 4 5 years of continuous gps observations at 21 sites on the pacific and north american plates along with a subset of the nuvel 1a data to examine the steadiness of pacific north america motion since 3 16 ma the transfer of baja california to the pacific plate and the magnitude of biases in the nuvel 1a estimate of pacific north america motion we find that pacific north america motion has remained steady since 3 16 ma but at rates significantly faster than predicted by nuvel 1a in the vicinity of baja california our gps derived model and recent seafloor spreading rates in the southern gulf of california both indicate that the nuvel 1a model underestimates pacific north america rates by 4 2 mm yr 1 steady pacific north america motion since 3 16 myr and increasing seafloor spreading rates since 3 58 myr in the gulf of california imply that pacific north america motion was partitioned between seafloor spreading in the gulf of california and decelerating slip along faults in or offshore from the baja peninsula

the sawqirah contourite drift system in the arabian sea nw indian ocean a case study of interactions between margin reactivation and contouritic processes the relationships between oceanic circulation in the arabian sea and late cenozoic climate changes including variations in monsoon intensity at the million year time scale remain poorly investigated using multibeam and seismic data we provide the first description of a contourite drift in the arabian sea along the south eastern oman margin this contourite drift is referred as the sawqirah contourite drift system late miocene reactivation of the south eastern oman margin resulted in the formation of a complex anticline system which shaped the seafloor topography above which the sawqirah drift subsequently developed the drift resulted from the circulation of bottom currents within the north intermediate indian water major seismic unconformities identified within the sawqirah drift were tied to ocean drilling program odp drill holes and allowed defining distinct episodes of drift construction at least two of these unconformities record reorganizations of the oceanic circulation at 4 5 4 8 ma and 2 4 ma the 4 5 4 8 ma old unconformity is coeval with the onset of upwelling of deep and cold waters in the owen basin the 2 4 ma old unconformity records a major episode of indian monsoon intensification at the million year time scale over the arabian sea indicating strong coupling between oceanic and atmospheric circulation processes

chronology of miocene pliocene deposits at split mountain gorge southern california a record of regional tectonics and colorado river evolution late miocene to early pliocene deposits at split mountain gorge california preserve a record of basinal response to changes in regional tectonics paleogeography and evolution of the colorado river the base of the elephant trees formation magnetostratigraphically dated as 8 1 0 4 ma provides the earliest well dated record of extension in the southwestern salton trough the oldest marine sediments are ca 6 3 ma the nearly synchronous timing of marine incursion in the salton trough and northern gulf of california region supports a model for localization of pacifi c north america plate motion in the gulf ca 6 ma the fi rst appearance of colorado river sand at the miocene pliocene boundary 5 33 ma suggests rapid propagation of the river to the salton trough and supports a lake spillover hypothesis for initiation of the lower colorado river

steady 10be derived paleoerosion rates across the plio pleistocene climate transition fish creek vallecito basin california rates of erosion over time provide a valuable tool for gauging tectonic and climatic drivers of landscape evolution here we measure 10be archived in quartz sediment from the fish creek vallecito basin to resolve a time series of catchment averaged erosion rates and to test the hypothesis that aridity and increased climate variation after ca 3 ma led to an increase in erosion rates in this semi arid ice free setting the fish creek vallecito basin located east of the peninsular ranges in southern california is an ideal setting to derive a plio pleistocene paleo erosion rate record the basin has a rapid sediment accumulation rate a detailed magnetostratigraphic age record and its stratigraphy has been exposed through recent rapid uplift and erosion a well defined source region of uniform lithology and low erosion rate provides a high reproducible 10be signal we find that paleo erosion rates were remarkably consistent between 1 and 4 ma averaging 38 24 m myr 2 modern catchment averaged erosion rates are similar to the paleo erosion rates the uniformity of erosion over the past 4 myr indicates the landscape was not significantly affected by late pliocene global climate change nor was it affected by a local long term increase in aridity

the oman upwelling zone during 1993 1994 and 1995 abstract satellite derived sea surface temperature topex poseidon t p sea level anomalies slas model wind data and hydrographic data are used to characterize the upwelling along the oman coast during the us joint global ocean flux study us jgofs arabian sea process study asps in 1995 as well as to look at interannual variability in the upwelling over the period 1993 1995 empirical orthogonal function eof analysis of the satellite derived sea surface temperature sst at the locations of the us jgofs standard stations shows the first mode which represents a biannual variability contributes 67 of the total variance in addition the sst shows the upwelling front moving offshore with the development of southwest sw monsoon in early june 1995 reaching a maximum distance of approximately 120 km by late august 1995 finally sst shows the persistence of cold upwelling waters for nearly a month after the end of the sw monsoon within the bays along the oman coast topex poseidon slas indicate that with the onset of the sw monsoon a 30 cm drop in steric height is observed along the oman coast associated the presence of the cool upwelled waters this drop in steric height sets up a horizontal pressure gradient and results in a compensating along shore northeastward flowing geostrophic current east arabian current eac during the sw monsoon similarly the altimeter data slow an offshore decrease in steric height during the northeast ne monsoon indicating a seasonal reversal in direction of the eac with flow to the southwest subsurface temperature data indicate that the actual uplifting of isotherms associated with the upwelling can be found to a distance of approximately 260 km from the shore and to a depth of 150 200 m using along track altimetry data we estimate that for a region 260 km in offshore distance and 600 km alongshore 2 2 10 6 1 4 10 6 and 0 55 10 6 m 3 s 1 were upwelled through the 100 m level with upwelling velocities o 2 0 10 5 m s 1 during the sw monsoons of 1993 1994 and 1995 respectively the reduced upwelling in the summer of 1995 is attributed to a reduction in wind stress curl along the arabian coast when compared to 1993 and 1994

plio pleistocene climate change and timing of peninsular ranges uplift in southern california evidence from paleosols and stable isotopes in the fish creek vallecito basin article i nfo abundant plio pleistocene paleosols in the fish creek vallecito basin record the effects of late neogene global climate change on inland southern california analysis of 82 paleosol horizons ranging in age from 3 9 to 0 7 ma reveals two primary populations vertic paleosols with abundant mud cracks and calcic paleosols with pronounced calcite accumulation zones vertic paleosols are dominant in older deposits but disappear from the stratigraphic record by 2 8 ma after which point calcic paleosols are nearly the only paleosol type present pedogenic carbonate nodules from 47 horizons were analyzed for oxygen and carbon isotopic compositions in late pliocene time carbonate 13 c values become depleted from an average of 5 1 between 3 9 and 3 5 ma to 7 3 vpdb between 2 75 and 2 25 ma recording an increase in c3 plants at the expense of c4 grasses this finding suggests that summer precipitation decreased in the study area from 3 8 to 2 5 ma possibly due to a weakening of the summer monsoon the absence of vertic paleosols in post 2 8 ma deposits supports this hypothesis the increase in abundance of calcic paleosols through time suggests a long term increase in aridity a gradual enrichment of about 2 in 18 o values from 3 9 to 0 7 ma also likely resulted from increased aridification and evaporative enrichment of soil water our findings suggest that global cooling in late pliocene time resulted in increased aridity in southern california due to decreased monsoonal activity and the end of persistent el nino conditions in the pacific ocean the observed enrichment in

advection of upwelled waters in the form of plumes off oman during the southwest monsoon abstract advanced very high resolution radiometer avhrr imagery of sea surface temperature topex poseidon measurements of sea level anomaly sla and modeled surface winds and wind stress fields are used in concert with other ancillary data to describe the influence of the 1995 southwest monsoon on the distribution of upwelled waters off the coast of oman the oman upwelling zone is characterized by the entrainment of cold upwelled waters into plumes extending from the coast into the deep ocean unaffected by the steep bottom gradients the most prominent of these plumes is found offshore of ras al madraka a mechanism for the entrainment of upwelled water into plumes is hypothesized and validated by observational data it is proposed that the location of the plume is primarily governed by the sea level structure away from the coast and that coastally upwelled water is passively advected offshore through regions of low sea level analysis of the surface wind stress fields show significant spatial variability associated with the predominantly cyclonic mean wind stress curl with relatively weak curl observed in the region south of ras al madraka and north of ras marbat decomposition of the surface wind stress fields through principal component analysis shows that at certain periods the development of strong along shore winds and cyclonic wind stress curl in the region north of ras al madraka this information combined with concurrent observations of topex poseidon sea level anomalies slas satellite derived sea surface temperatures sst and surface current measurements shows that the combined effects of a strong along shore wind field and positive wind stress curl forces a depression in sea level in the region north of ras al madraka the sea level gradient caused by the presence of a sustained high sea level to the south of ras al madraka causes geostrophic advection of coastally upwelled waters away from the shelf acoustic doppler current profiler adcp velocity measurements along with sst maps further prove that the upwelled water is geostrophically advected offshore as opposed to being an offshore deflection of a wind driven coastal current comparison of interannual features in the topex poseidon slas suggest that the plumes coming off coast in the oman upwelling zone may not be directly linked to the coastal topography or bathymetry but are a result of interaction between mesoscale variations in the wind field and the underlying ocean the strong along shore winds and cyclonic wind stress curl to the north of ras al madraka becomes enhanced when the findlater jet moves closer to the oman coast than its mean position

tectonic control on facies distribution of the camp rice and palomas formations pliocene pleistocene in the southern rio grande rift the pliocene pleistocene camp rice and palomas formations in the rio grande rift of southern new mexico provide an excellent test of the role of basin symmetry in the distribution of piedmont and axial fluvial facies in the asymmetrical palomas and northern mesilla basins the axial fluvial facies is characterized by multistory channel sands and sandstones and is concentrated near the locus of maximum subsidence within a few kilometers of the footwall scarp fanglomerate derived from the footwall uplift extends only a few kilometers or less from the footwall scarp whereas alluvial fan and alluvial flat conglomerate sand and mudstone deposited on the hanging wall dip slope occupy a much wider outcrop belt in the symmetrical hatch rincon basin the axial fluvial facies extends to within a few kilometers of both the northern and southern basin margins and has a much higher percentage of fine grained overbank deposits some of which contain calcareous paleosols in all three basins a tongue of fanglomerate as much as 30 m thick prograded over the axial fluvial facies near the end of camp rice and palomas deposition the distribution of facies of the camp rice and palomas formations supports previously published models that predict a two stage history of asymmetrically subsiding basins during tectonically active periods axial river channels preferentially avulse into the topographically lowest area of the alluvial plain which is directly above the axis of maximum subsidence during the postorogenic stage when erosion rate exceeds subsidence rate coarse transverse dispersed sediment progrades toward the center of the basin

linked sequence stratigraphic and structural evolution of propagating normal faults two distinct phases in the structural evolution of normal faults can be identified in the miocene gulf of suez rift 1 an initial growth fold stage when the fault is a buried structure and 2 a subsequent surface faulting stage during the growth fold stage strata thin and become truncated toward the fault zone and are rotated and diverge away from the buried fault into growth synclines in contrast once the fault breaks surface strata form a divergent wedge which is rotated and thickens into the fault the two tectono stratigraphic styles also occur contemporaneously along the length of a single fault segment growth folding characterizes deformation around the ends of fault segments where the fault is blind whereas the center of fault segments are characterized by surface faulting these observations suggest that marked along strike variation in stratal surfaces and facies stacking patterns will occur in depositional sequences in areas of normal faulting

lacustrine to fluvial floodplain deposition in the eocene bridger formation abstract the depositional systems and sedimentology of lithofacies sequences in the bridger formation unit b are described a lithofacies association is determined and includes from base to top limestone claystone thin bedded sandstone and siltstone and a cross bedded sandstone facies the limestone facies is generally composed of a dense resistant limestone that may contain fossil plant impressions tufa and or stromatolites gastropods bivalves and other fossils the claystone facies contains abundant fossil turtles gar crocodiles gastropods and plants desiccation cracks plant roots and soil features are lacking extremely abundant turtles may occur in this facies sometimes associated with abundant coalified plant fragments the thin bedded sandstone and siltstone facies is composed of silty clay to medium sand at a few localities it grades laterally into medium to course grained sandstone channels up to 3 m thick fossil turtles are present but are much less abundant than in the claystone facies the cross bedded sandstone facies is composed of thick laterally extensive channel sandstones associated laterally with silty claystone beds the lithofacies association is interpreted as a shallowing upward sequence it started with a basal limestone facies deposited in a widespread shallow carbonate precipitating lake the lake was rapidly filled by episodic volcaniclastic deposition delivered via air fall and or prograding fluvial deltaic systems deltaic deposition may have been similar to the infilling of the northern portion of lake turkana in africa by the omo river delta the claystone facies is interpreted as a short lived fluvial lacustrine system that prograded out over the limestone facies and or was deposited as air fall ash into the entire lake the sharp upper contact of the limestone facies with the claystone facies suggests that an abrupt paleoenvironmental change may have taken place with a large influx of volcaniclastics an organic rich unit the organic turtle bed within the black mountain turtle layer a claystone facies contains abundant plant material and turtles and is interpreted as representing an episodic depositional event probably storm related as volcaniclastic deposition continued to dominate the system the thin bedded sandstone and siltstone facies sequence was deposited it is interpreted as distributary and crevasse splay sheet sands uniformly deposited laterally correlative over large areas this depositional system was ultimately replaced by a well established fluvial floodplain environment with large fluvial channels representing major meandering rivers development of the succeeding lake system occurred when siliciclastic deposition significantly slowed relative to the rate of basin subsidence deposition in the bridger formation unit b suggests a delicate balance between a closely interacting lacustrine and fluvial system although fluvial processes and clastic sedimentation dominated depositional patterns lacustrine depositional regimes frequently returned

quantitative models of sedimentary basin filling summary quantitative modelling of the filling of sedimentary basins was begun in earnest in the 1960s dozens of themes and variations have been proposed since then and have yielded an abundance of idealized stratigraphic patterns as functions of both imposed changes and basin properties post plate tectonic modelling began with rigid lid models which show the stratigraphic signature of subsidence variation this work introduced the connection between stratigraphy and the rheology of the lithosphere rigid lid models are the simplest type of geometric model in which the sediment surface is assigned prescribed geometries usually corresponding to different depositional environments these can reproduce many aspects of overall stratal geometry but are formally restricted to relatively long timescales for which quasi steady surface topography can be assumed so called dynamic models attempt to represent the morphodynamics of the sediment surface by abstracting and averaging short term transport processes most of the dynamic models proposed to date can be seen as special cases of a single general morpho dynamic equation the most important result of the first wave of quantitative basin filling models is that even relatively simple models can produce reasonable stratal patterns we now have a wide array of tools for exploring scenarios searching for general behaviours and effects and making initial quantitative predictions we have also learned that basin response to external forcing as recorded in stratigraphy can be as sensitive to the characteristics of the basin as to the forcing the main brake on the development of basin modelling is not computing power but lack of methods and data for testing the models we have already developed physical experiments which are only just beginning are one means of doing this experimental stratigraphy is a bridge to quantitative field tests which will require collaboration among academic researchers from a wide range of areas and between academia and industry on projects of greater scale and degree of integration than we have seen so far the advancement of quantitative sedimentary geology will also require significant changes in the way the subject is taught at all levels

climatic influences on continental deposition during late stage filling of an extensional basin southeastern arizona climatic rather than tectonic influences on continental deposition are recorded in the late stage fill of a neogene extensional basin in south eastern arizona regional geomorphic relations low sedimentation rates and stratigraphic overlap of the principal basin bounding structures identified in a gravity anomaly profile indicate that the plio pleistocene st david formation accumulated in the san pedro valley during a period of tectonic quiescence stable isotopic composition of paleosol calcite is placed within a magnetostratigraphic framework that provides an interpretive record of variable arid to semiarid climate in the valley before 3 4 ma the valley was hydrologically closed and experienced an arid climate with seasonal precipitation drainage integration at ca 3 4 ma corresponds with a transition to wetter conditions less seasonally variable precipitation and a rising water table indicated by hydromorphic paleosols and pond deposits gradually increasing seasonality of precipitation after 2 8 ma and further decrease in winter rainfall after 2 2 ma led to establishment of a dry monsoonal climate between 1 6 and 0 6 ma the change in climate at ca 1 6 ma coincides with abrupt appearance of sheet flood dominated fan gravels above earlier vertically aggraded fluvial channel and interfluve flood plain deposits this change in facies is interpreted as the result of climatic change rather than an example of subsidence driven gravel progradation sedimentation rates were greatest when climate was relatively wet with dominant winter rainfall and about equally low for relatively dry with dominant summer rain and relatively wet but nonseasonal conditions contrary to past model simulations channel flood plain facies ratios and sedimentation rate varied directly ribbon as opposed to sheet channel bodies were favored by relatively wet climatic conditions and were less commonly formed during dry strongly seasonal times precise process response interpretation of this correlation of sedimentological variability to changing climate is limited by the restricted interpretation of paleosolisotope paleoclimate data and the poor understanding of sedimentological response to climate change during 10 5 to 10 6 yr time intervals the results of this study suggest however that caution be applied to a priori interpretations of stratigraphic variations within thick syntectonic basin fills as responses to varying subsidence rates only

the role of waterfalls and knickzones in controlling the style and pace of landscape adjustment in the western san gabriel mountains california bedrock rivers set the pace of landscape adjustment to tectonic and climatic forcing by transmitting signals of base level change upstream through the channel network and ultimately to hillslopes river incision is typically modeled as a monotonic function of bed shear stress or stream power modulated by sediment tools and cover effects but these models do not apply in channels with steep or vertical bedrock reaches due to changes in flow dynamics hydraulic geometry and bed cover here we investigate how such knickzones oversteepened channel reaches often containing waterfalls influence the propagation of slope break knickpoints that separate relict from adjusting topography and thus the response times of landscapes to external forcing we use a conceptual long profile model to explore the consequences of waterfalls and knickzones on channel response and compare predictions to light detection and ranging lidar topography field observations and cosmogenic radionuclide data from big tujunga creek a 300 km2 watershed in the san gabriel mountains california three prominent knickzones along big tujunga creek characterized by numerous waterfalls show contrasting behavior for the upper knickzone waterfalls align with bands of harder rock exposed on adjacent hillslopes and between waterfalls the channel is mantled by large 2 m boulders indicating knickzone retreat is slow compared to predictions of slope break knickpoint retreat from stream power models enhancing the preservation of an upstream relict landscape the middle knickzone shows evidence for both fast and slow knickzone retreat as well as significant deviations from predictions of uniform tributary knickpoint elevations derived from stream power models the lower knickzone is characterized by a waterfall and knickzone within an incised inner gorge that provide evidence of rapid retreat relative to background channel incision overall we find a pattern of decreasing knickzone and waterfall retreat rate with distance upstream of the range front beyond decreases predicted by simple area dependent celerity models our results highlight that waterfalls and knickzones can both enhance and inhibit landscape adjustment leading to divergent controls on the pace of landscape evolution

theory and validation of the multiple window sea surface temperature technique the development of the split window approach for correcting satellite measurement of radiance for atmospheric attenuation is reviewed then the theoretical results are compared to results from actual measurements which consist of satellite measurements in the three infrared windows of the avhrr ground truth for the comparisons comes from buoys the satellite measurements were screened for clouds and the remaining ones were used in the analysis using this data set several statistical analyses were performed these showed that when the two channels that are truly a split window are used the result of the statistical model agrees with the one derived from theoretical considerations when the 3 8 m channel is combined with one in the 10 12 m region the result of the statistical model does not take the split window form results show that the method is capable of producing sea surface temperatures with a standard deviation of 1 k or less

the wind field in the western indian ocean and the related ocean circulation abstract monthly wind stress contoured for the western indian ocean clearly shows the southwest monsoon from may through september with values over 4 dyn cm 2 during july to be considerably stronger than the northeast monsoon with a maximum in january maps of wind stress curl during the southwest monsoon show a large region of negative curl over 4 10 8 dyn cm 3 to the northeast off the somali coast whereas a region of high positive curl occurs off the arabian coast and in a small band off the somali east coast north of 5 n sverdrup mass transports of up to 40 10 12 g s 1 to the north off the somali coast are in rough agreement with observed values

did the indo asian summer monsoon decrease during the holocene following insolation a few studies from the western arabian sea indicate that the indian summer or southwest monsoon ism after attaining its maximum intensity at ca 9 ka declined during the holocene as did insolation in contrast earlier and later observations from both the eastern and the western arabian sea do not support this inference analysis of multiple proxies of productivity in a new sediment core from the western arabian sea fails to confirm the earlier single proxy e g abundance of globigerina bulloides based inference of the holocene weakening of ism following insolation the reason for the observed decreasing trend in foraminiferal abundance the basis for the earlier inference could be the favouring of silicate rather than carbonate productivity by the increased ism wind strength although ism exhibits several multi millennial scale fluctuations there is no evidence from several multi proxy data to conclude that it declined during the holocene this is consistent with the phase lag analysis of longer time series of monsoon proxies thus on sub milankovitch timescales ism did not follow insolation highlighting the importance of internal feedbacks a comparison with east asian summer monsoon easm records suggests that both ism and easm varied in unison implying common forcing factors on such longer timescales copyright 2010 john wiley sons ltd

mesoscale eddies coastal upwelling and the upper ocean heat budget in the arabian sea estimation of the terms in the upper ocean heat budget from a moored array in the central arabian sea shows periods when a rough balance between the temperature trend and the horizontal advection of heat exists altimetry and sea surface temperature imagery are used to demonstrate that these episodes of strong horizontal advection are associated with mesoscale features during the wintertime northeast ne monsoon these are capped off mesoscale eddy features generated during the previous summertime southwest sw monsoon and have little horizontal transport of heat within the mixed layer during the sw monsoon the major contribution is strong offshore export of coastally upwelled water in a filament with a strong surface presence temperature and salinity properties from the moored array and a seasoar survey during the formation of the coastal filament confirm the offshore transport of the upwelled water mass to the site of the moored array more than 600 km offshore estimates of the filament section heat flux are several percent of the total estimated heat flux due to upwelling along the arabian peninsula and remote sensing data show that similar mesoscale variability along the coast is enhanced during the sw monsoon this points to the importance of mesoscale modulated transports in not only the observed heat budget at the moored array but in the overall upper ocean heat budget in the arabian sea

oxygen isotopic evidence for late triassic monsoonal upwelling in the northwestern tethys the oxygen isotopic composition of conodonts from the pizzo mondello section in the sicani basin sicily italy on the northwestern tethys margin has been used to reconstruct regional paleoseawater conditions the 18 o phos values 21 21 9 measured by sensitive high resolution ion microprobe shrimp ii are consistent with previously published 18 o phos data from the contemporaneous marginal hallstatt meliata basin 20 3 22 5 located farther north but are distinctly higher than those previously reported from the open ocean setting of the nearby lagonegro basin 18 7 20 0 this 2 offset represents a temperature differential of 8 c suggesting that sea surface temperatures along the northwestern margin sicani and hallstatt meliata basins of the tethys ocean were lower than in the open ocean lagonegro basin during the late carnian tuvalian 2 to early norian lacian we interpret the cooler waters of the marginal basins to reflect coastal upwelling driven by strong monsoonal systems as predicted by existing paleoclimate models for this region

chapter 5 extension and contraction within an evolving divergent strike slip fault complex the san andreas and san jacinto fault zones at their convergence in southern california

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

marine red staining of a pennsylvanian carbonate slope environmental and oceanographic significance abstract red stained platform facies are a common feature of many carbonate settings throughout the geological record although the mechanisms involved in red staining of subaerially exposed or argillaceous peri platform limestones are reasonably well understood the environmental and oceanographic significance of red carbonates often remains uncertain here sedimentological sequence stratigraphic geochemical paleontological and quantitative bathymetric data from pennsylvanian red intervals across a well exposed carbonate platform top and slope are documented and interpreted in a process oriented context on the upper slope 80 350 meters below the shelf break red intervals alternate with gray mainly microbial algal boundstones on the lower slope 350 600 meters below the shelf break redeposited red stained mud builds matrix supported breccia tongues interbedded with predominantly redeposited clast supported carbonate debris the presence of large volumes of fibrous calcite biocementstones as well as firmgrounds point to low sedimentation rates or omission in terms of sequence stratigraphy red intervals occur within maximum flooding intervals and reflect near platform drowning elevated 18o values 2 3 and an essentially cool water heterotrophic biotic association in red intervals on platform top and slope suggest deposition during sea level highs associated with colder water masses and high nutrient levels the most likely drivers are an elevated thermocline and upwelling the red staining is the result of iron oxidation which occurred during early diagenesis likely by iron bacteria these red intervals provide an important bathymetric benchmark against which other mainly paleozoic red facies can be tested and calibrated

borrego springs santa rosa mylonite zone a late cretaceous west directed thrust in southern california the borrego springs shear zone section of the eastern peninsular ranges mylonite zone eprmz contains unequivocal evidence for ductile shearing with an east over west sense of movement field evidence includes the presence of s and c planes and shear bands all lines of microstructural evidence are internally consistent and support the field observations it appears that the data are compatible only with post mid cretaceous west directed thrusting on the eprmz

carbon and oxygen isotope time series records of planktonic and benthic foraminifera from the arabian sea implications on upwelling processes abstract oxygen and carbon isotopic analyses have been performed on the tests of globigerina bulloides and pulleniatina obliquiloculata planktonic foraminifera and uvigerina excellens benthic foraminifer to study the evolution of surface and bottom water hydrographic changes associated with summer monsoon upwelling process at the oman margin over the last 19 kyr globigerina bulloides p obliquiloculata and u excellens show sharp depleted 18o excursions around 9 ka ascribed to the distribution of melt water flux of termination ib in this region a synchronous 18o shift in surface subsurface and bottom water living foraminifera around 9 ka reveals a rapid transfer of the termination ib signal through the vertical circulation of the arabian sea in response to peak monsoon intensity a steep increase in 13c values of u excellens between 9 and 8 ka reveals advection of red sea intermediate water into the arabian sea during peak monsoon intensity for the first time a drastic climatic shift at 4 ka is noticed in the arabian sea as evidenced by the lowest 18o values of both p obliquiloculata 1 10 and g bulloides 2 29 this points to reduced upwelling strength both planktonic foraminifer species 18o records suggest the establishment of modern surface water conditions after 3 ka at the oman margin

shallow low velocity zone of the san jacinto fault from local earthquake waveform modelling summary we developed a method to determine the depth extent of low velocity zone lvz associated with a fault zone fz using s wave precursors from local earthquakes the precursors are diffracted s waves around the edges of lvz and their relative amplitudes to the direct s waves are sensitive to the lvz depth we applied the method to data recorded by three temporary arrays across three branches of the san jacinto fz the fz dip was constrained by differential traveltimes of p waves between stations at two side of the fz other fz parameters width and velocity contrast were determined by modelling waveforms of direct and fz reflected p and s waves we found that the lvz of the buck ridge fault branch has a width of 150 m with a 30 40 per cent reduction in vp and a 50 60 per cent reduction in vs the fault dips 70 5 to southwest and its lvz extends only to 2 1 km in depth the lvz of the clark valley fault branch has a width of 200 m with 40 per cent reduction in vp and 50 per cent reduction in vs the coyote creek branch is nearly vertical and has a lvz of 150 m in width and of 25 per cent reduction in vp and 50 per cent reduction in vs the lvzs of these three branches are not centred at the surface fault trace but are located to their northeast indicating asymmetric damage during earthquakes

response of deformation patterns to reorganization of the southern san andreas fault system since ca 1 5 ma abstract between 1 5 and 1 1 ma the southern san andreas fault system underwent a major reorganization that included initiation of the san jacinto fault zone and termination of slip on the extensional west salton detachment fault the southern san andreas fault itself has also evolved since this time with several shifts in activity among fault strands within san gorgonio pass we use three dimensional mechanical boundary element method models to investigate the impact of these changes to the fault network on deformation patterns a series of snapshot models of the succession of active fault geometries explore the role of fault interaction and tectonic loading in abandonment of the west salton detachment fault initiation of the san jacinto fault zone and shifts in activity of the san andreas fault interpreted changes to uplift patterns are well matched by model results these results support the idea that initiation and growth of the san jacinto fault zone led to increased uplift rates in the san gabriel mountains and decreased uplift rates in the san bernardino mountains comparison of model results for vertical axis rotation to data from paleomagnetic studies reveals a good match to local rotation patterns in the mecca hills and borrego badlands we explore the mechanical efficiency at each step in the modeled fault evolution and find an overall trend toward increased efficiency through time strain energy density patterns are used to identify regions of incipient faulting and support the notion of north to south propagation of the san jacinto fault during its initiation

sedimentary processes vertical stratification sequences and geomorphology of the roaring river alluvial fan rocky mountain national park colorado abstract the roaring river alluvial fan formed on 15 july 1982 in rocky mountain national park colorado by a catastrophic flood that was generated by a dam failure the fan covers an area of 0 25 square km has a radial length of 0 7 km and is up to 14 m thick sedimentation occurred in three phases each producing a distinct fan lobe initial sedimentation was by a noncohesive sediment gravity flow which deposited two levees on the proximal boundaries of lobe i the levees consist of a poorly sorted mixture of logs sand pebbles cobbles and boulders the first two lobes were built primarily by sheetflooding which deposited imbricated boulders in trains behind obstacles that formed as jams between boulders or logs and upright trees horizontally laminated granule and sand sedimentation took place down fan from the boulders due to deceleration of the expanding sheetflood thin to medium interbedded sand and cobble pebble gravel couplets were deposited by sheetflooding on the third lobe gravel was transported as bedload by supercritical flow and deposited locally where antidunes broke sand was transported as suspended load and deposited where flood velocity locally decreased due to destruction of antidunes increased roughness or flow separation around the low amplitude gravel bed forms the flood rechannelized at the distal end of lobe iii due to constriction between the fan and the valley margin deposits in the upper rechannelized reaches consist of crudely bedded cobble and pebble gravel and interstratified pebble gravel and backset bedded sand deposition was by supercritical flow in the lower reaches planar cross bedded sandy pebble gravel and climbing ripple horizontal trough cross bedded and backset bedded sand were deposited by supercritical and subcritical flow the flood deposit was modified during waning flood stage and during the three years following the flood by noncatastrophic discharge events these events formed braided distributary channels by erosion into the top of the sheet flood deposits fan building took place mostly by catastrophic unconfined discharge whereas much of the present fan surface consists of braided channels that formed by erosion into the sheetflood deposits by noncatastrophic discharge

tectonic and hydrologic controls on cyclic alluvial fan fluvial and lacustrine rift basin sedimentation jurassic lowermost cretaceous todos santos formation chiapas mexico abstract the nonmarine upper jurassic lowermost cretaceous todos santos formation of central chiapas mexico was deposited in half graben basins formed during the early rifting stage of the southern gulf of mexico basin this formation consists of alluvial fan fluvial and lacustrine sequences that were deposited under arid climatic conditions alluvial fans were built outwardly from the elongate basin margins by runoff that flowed transverse to the basin axis whereas fluvial units were deposited by rivers that flowed parallel to the basin axis lacustrine deposition took place in a topographic depression adjacent to the basin margin the presence of alluvial fan and fluvial or lacustrine deposits in vertically stacked cyclic megasequences hundreds of meters thick indicates that the basin opography changed through time this cyclicity denotes that periodically fluvial or lacustrine environments occupied the basin margin position and at other times alluvial fan sedimentation occurred there cyclicity was caused by periodic changes from high to low rates of basin subsidene the response of these three depositional environments to basin subsidence differed due to the unique hydrologic controls on sediment transport and deposition in each environment lakes were maintained by springs that emanated from the fractured fault margin and by fluvial discharge fluvial discharge and deposition resulted from precipitation or annual snowmelt anywhere in the river s expansive drainage basin whereas alluvial fan sedimentation occurred only when there was infrequent significant precipi ation in the small drainage basin from which fan sediment was derived as a result of these hydrologic controls the lacustrine or fluvial environments responded more quickly to periods of active tectonic subsidence and migrated over the fans to occupy the basin margin depression aided by a decrease in basin subsidence alluvial fans eventually prograded and displaced the fluvial or lacustrine environments away from the basin margin

buried rhyolites within the active high temperature salton sea geothermal system abstract previously unrecognized pulses of rhyolite volcanism occurred in the salton trough between 420 8 ka and 479 38 ka 2 based on high spatial resolution u pb zircon geochronology presently these rhyolite lavas tuffs and shallow subvolcanic sills are buried to depths between 1 6 and 2 7 km at ambient temperatures between 200 and 300 c and are overprinted by propylitic to potassic hydrothermal alteration mineral assemblages consisting of finely intergrown quartz k feldspar chlorite epidote and minor pyrite alteration resistant geochemical indicators whole rock nd isotopes zircon oxygen isotopes reveal that these rhyolites are derived from remelting of morb type crust that was chilled and hydrothermally altered by deep circulating hydrothermal waters u pb zircon dating confirms the presence of bishop tuff in well state 2 14 at 1 7 km depth approximately 5 km ne of the geothermal wells that penetrated the buried rhyolites these results indicate accelerated subsidence towards the center of the salton trough increasing from 2 2 mm a to 3 8 mm a based on these results the present day salton sea geothermal field is identified as a focus zone of episodic rhyolitic volcanism intense heat flow and metamorphism that predates present day geothermal activity and holocene volcanism by at least 400 ka

late quaternary slip rate gradient defined using high resolution topography and 10be dating of offset landforms on the southern san jacinto fault zone california 1 recent studies suggest the san jacinto fault zone may be the dominant structure accommodating pa na relative plate motion however because the late quaternary slip history of the southern san andreas fault system is insufficiently understood it is difficult to evaluate the partitioning of deformation across the plate boundary and its evolution landforms displaced by the clark fault of the southern san jacinto fault zone were mapped using high resolution airborne laser swath topography and selected offset landforms were dated using cosmogenic 10be beheaded channels at rockhouse canyon displaced by 500 70 m and 220 70 m have been dated to 47 8 ka and 28 9 ka respectively farther south near the southern santa rosa mountains an alluvial deposit displaced by 51 9 m has been dated to 35 7 ka from these sites the slip rate of the clark fault is determined to diminish southward from 8 9 2 0 to 1 5 0 4 mm yr this implies a slip rate decrease along the clark fault from anza southeastward to its surface termination near the salton trough where slip is transferred to the coyote creek fault and additional deformation is compensated by folding and thrusting in the basin these data suggest that since 30 to 50 ka the slip rate along the southern san jacinto fault zone has been lower than or equivalent to the rate along the southernmost san andreas fault accordingly either the slip rate of the san jacinto fault has substantially decreased since fault initiation or fault slip began earlier than previously suggested

stratigraphic record of pleistocene faulting and basin evolution in the borrego badlands san jacinto fault zone southern california sedimentary rocks in the borrego badlands southern california contain a record of pleistocene crustal deformation during initiation and evolution of the san jacinto fault zone we used detailed geologic stratigraphic and paleomagnetic analysis to determine the age and geometry of the deposits and reconstruct the history of fault controlled sedimentation in this area the base of the 300 to 500 m thick ocotillo formation is a paraconformity to abrupt conformable contact that records a brief hiatus followed by rapid progradation of coarse alluvial sediment over lacustrine facies of the borrego formation at 1 05 0 03 ma this coincides with regional scale progradation of ocotillo formation sand and gravel and appears to record initiation of strike slip faults in the southwestern salton trough at ca 1 1 ma thickness trends clast compositions paleocurrents and distribution of paleosols provide evidence for initiation of the east coyote mountain fault at ca 1 05 ma followed by onset of nne ward basin tilting obliquely toward the santa rosa segment of the clark fault at ca 1 0 ma stratigraphic omission of the ocotillo formation and progressively older units southwest of the coyote creek fault beneath the fonts point sandstone provides evidence that tilting to the northnortheast was related in part to growth of the san felipe anticline during deposition of the ocotillo formation map and stratigraphic data suggest that the coyote creek fault in the western borrego badlands postdates ocotillo deposition and thus appears to have propagated southeast into the study area at ca 0 6 ma the fonts point sandstone is a thin sheetlike alluvial deposit that records the end of deposition and onset of transpressive deformation in the borrego badlands the base of the fonts point sandstone changes from a conformable contact in a narrow belt southeast of the inspiration point fault where it is dated at 0 6 0 02 ma to an angular unconformity on the folded ocotillo formation northwest of the fault the pattern of stratal truncation records initiation of the inspiration point fault at ca 0 6 ma this coincides with a major structural reorganization in the san jacinto fault zone that initiated the modern phase of north south shortening and erosion in the southwestern salton trough

latest pleistocene and holocene slip rate for the san bernardino strand of the san andreas fault plunge creek southern california implications for strain partitioning within the southern san andreas fault system for the last 35 k y an alluvial succession on the northeast side of the san bernardino strand of the san andreas fault includes distinctive aggradational and degradational features that can be matched with correlative features on the southwest side of the fault key among these are 1 a terrace riser on the northeast side of the fault that correlates with an offset channel wall on the southwest side of the fault and forms a basis for slip estimates for the period ca 35 ka to the present and 2 a small alluvial fan on the southwest side of the fault that has been matched with its most likely source gullies on the northeast side of the fault and forms a basis for slip estimates for the last 10 5 k y slip rate estimates for these two separate intervals are nearly identical the rate for the older feature is most likely between 8 3 and 14 5 mm yr with a 95 confidence interval of 7 0 15 7 mm yr the rate for the younger feature is most likely between 6 8 and 16 3 mm yr with a 95 confidence interval of 6 3 18 5 mm yr these rates are only half the previously published slip rate for the san andreas fault 35 km to the northwest in cajon pass a rate that traditionally is extrapolated southeastward along the san bernardino section of the fault results from plunge creek suggest that about half of the 25 mm yr rate at cajon pass transfers southeastward to the san jacinto fault as proposed by other workers on the basis of regional geologic relations these results indicate that the discrepancy between latest quaternary slip rates and present day rates of strain accumulation across the san bernardino section of the san andreas fault from geodesy can be largely explained by slip transfer between faults leading to spatial variation in rate along the san andreas fault nonetheless the latest pleistocene and holocene slip rate at plunge creek is still somewhat faster than rates inferred for the san bernardino section of the san andreas fault based on elastic block modeling of geodetic data and may be more appropriate than those rates for hazard estimation

initiation of the southern elsinore fault at 1 2 ma evidence from the fish creek vallecito basin southern california 1 strike slip faults west of the san andreas fault saf accommodate more than half of the modern pacific north america plate motion in southern california yet their age kinematic evolution and long term slip rates are incompletely understood the southern elsinore fault is part of this zone and occupies the boundary between mesozoic crystalline rocks of the peninsular ranges and late cenozoic sedimentary rocks of the salton trough depocenter the fish creek vallecito basin a recently inverted western sub basin of the salton trough contains a thick succession of plio pleistocene sedimentary rocks that preserve a record of crustal subsidence and uplift in response to evolving tectonic controls deposits older than 1 2 ma accumulated during transtension and subsidence in the hanging wall of the low angle west salton detachment fault a fanning dip interval high in the section dated at 1 2 1 0 ma accumulated during tilting caused by earliest motion on the elsinore and earthquake valley faults total offset of 1 2 km yields a lifetime slip rate of about 1 2 mm yr for the southern elsinore fault similar to a late pleistocene rate in the coyote mountains but slower than published estimates for the northern elsinore fault this difference likely results from long term transfer of slip from the northern elsinore fault to the san felipe and san jacinto fault zones farther east initiation of the elsinore fault at 1 2 ma coincides with a major tectonic reorganization that terminated slip on the detachment fault and formed the modern network of strike slip faults west of the saf

mesoscale dynamics in the arabian sea and a focus on the great whirl life cycle a numerical investigation using roms the great whirl gw is a persistent anticyclonic mesoscale eddy that is observed seasonally in the arabian sea during a period embedding the 3 months of the southwest monsoon june july august at a quasi steady location its dynamics remain unclear despite it being one of the largest coherent vortices in the world ocean realistic regional numerical experiments using roms are performed to investigate the life cycle of the gw which is not well resolved by sparse available in situ measurements in the region using a set of sensitivity experiments and an accurate temporal characterization of the eddy properties including position radius depth and vorticity we i confirm the role of basin scale downwelling rossby waves in the gw generation ii clarify the role of the monsoonal strong anticyclonic wind in its maintenance and barotropization and iii suggest a connection between basin scale rossby wave dynamics and gw collapse

the ras al hadd jet remotely sensed and acoustic doppler current profiler observations in 1994 1995 abstract the existence of a surface barotropic front jet system at the confluence region off the eastern tip of oman ras al hadd or rah is documented for 1994 1995 through advanced very high resolution radiometer avhrr and acoustic doppler current profiler adcp observations the thermal signature of this confluence is visible in 1995 between early may and the end of october i e throughout the sw monsoon and into the transition period between sw and ne monsoons the thermal characteristics are those of a ne oriented front between cooler water of southern upwelled origin and warmer waters of northern gulf of oman origin during the period when the thermal front is absent adcp data suggest that the confluence takes a more southward direction with gulf of oman waters passing rah into the southeastern oman coastal region the thermal gradient is initially small june july but later increases august october into a front that exhibits small scale instabilities surface current velocities within the jet estimated by tracking these features in consecutive satellite images are 0 5 0 7 m s 1 and in remarkable agreement with concurrent adcp retrievals in which the seasonal maximum in velocity is 1 m s 1 adcp observations collected during several us jgofs cruises reveal a weakly baroclinic current in the confluence region that drives the waters into the offshore system the fully developed jet describes a large meander that demarcates two counter rotating eddies cyclonic to the north and anticyclonic to the south of the jet of approximately 150 200 km diameter the southern eddy of this pair is resolved by the seasonally averaged sea level anomaly derived from topex poseidon observations during the sw monsoon the rah jet advects primarily cold waters along its path but as soon as the wind system reverses with the transition to the intermonsoonal period a warm current is rapidly established that advects the surface coastal waters of the gulf of oman offshore in accordance with the interannual variation of the wind forcing phase the reversal of the currents from ne to sw occurred earlier in 1994 than in 1995 confirming that the rah jet is integral part of the east arabian current the transport of the jet estimated by combining sst information on the width with adcp data on the velocity s vertical structure is found to fluctuate between 2 8 106 m3 s 1 and its thickness between 150 400 m these significant fluctuations are due to the time variable partition of horizontal transport between eddies and the rah jet and are potentially important to the nutrient and phytoplankton budgets of the arabian sea

global positioning system constraints on fault slip rates in southern california and northern baja mexico we use global positioning system gps estimates of horizontal site velocity to constrain slip rates on faults comprising the pacific north america plate boundary in southern california and northern mexico we enlist a simple elastic block model to parameterize the distribution and sum of deformation within and across the plate boundary we estimate a pacific north america relative plate motion rate of 49 3 mm yr one standard deviation consistent with nuvel 1a estimates we are able to resolve robust slip rate estimates for the southernmost san andreas san jacinto and elsinore faults 26 2 9 2 and 6 2 mm yr respectively and for the imperial and cerro prieto faults 35 2 and 42 1 mm yr respectively accounting for about 86 of the total plate motion the remaining 14 appears to be accommodated to the west of these fault systems probably via slip along the san clemente fault and or the san miguel vallecitos rose canyon and newport inglewood fault systems these results are highly consistent with paleoseismic estimates for slip rates implying that off fault strain accumulation within the deforming zone of the plate boundary is largely elastic we estimate that the seismically quiescent southernmost san andreas fault has incurred about 8 2 m of slip deficit over the last few hundred years presumably to be recovered during a future large earthquake

location of largest earthquake slip and fast rupture controlled by along strike change in fault structural maturity due to fault growth earthquake slip distributions are asymmetric along strike but the reasons for the asymmetry are unknown we address this question by establishing empirical relations between earthquake slip profiles and fault properties we analyze the slip distributions of 27 large continental earthquakes in the context of available information on their causative faults in particular on the directions of their long term lengthening we find that the largest slips during each earthquake systematically occurred on that half of the ruptured fault sections most distant from the long term fault propagating tips i e on the most mature half of the broken fault sections meanwhile slip decreased linearly over most of the rupture length in the direction of long term fault propagation i e of decreasing structural maturity along strike we suggest that this earthquake slip asymmetry is governed by along strike changes in fault properties including fault zone compliance and fault strength induced by the evolution of off fault damage fault segmentation and fault planarity with increasing structural maturity we also find higher rupture speeds in more mature rupture sections consistent with predicted effects of low velocity damage zones on rupture dynamics since the direction s of long term fault propagation can be determined from geological evidence it might be possible to anticipate in which direction earthquake slip once nucleated may increase accelerate and possibly lead to a large earthquake our results could thus contribute to earthquake hazard assessment and earthquake early warning

variability of water properties heat and salt fluxes in the arabian sea between the onset and wane of the 1995 southwest monsoon abstract we investigate the variability of the circulation water masses heat and salt fluxes in the arabian sea over the course of the southwest monsoon two zonal sections taken along 8 30 n in 1995 as part of the indian ocean woce hydrographic program are used the first was occupied in early june at the onset of the southwest monsoon winds the second in late september at the wane of the monsoon the september section was found to be generally warmer 0 32 c and saltier 0 04 than in june despite a 50 mm drop in mean sea level therefore the common assumption that an increase in sea surface height follows an increase in heat content the hydrostatic response does not hold instead we conclude that the heat content increases due to the advection of arabian sea surface water and red sea water onto the section from the north and the drop in sea level is due to a loss of mass rather than heat from the water column there are large uncertainties involved in diagnosing the heat flux divergence across the arabian sea because the seasonal variability of the water masses and circulation in the basin mean that our data are not representative of a steady state we treat each section separately and find an oceanic heat export of 0 72 pw in june and 0 19 pw in september implying a basin cooling rate of about 0 36 pw in june and a slight heating of 0 12 pw in september in june the mass and heat balances are dominated by the ekman transport and the somali current with very flat density surfaces resulting in a small interior geostrophic transport by september the ekman transport has reduced and it is primarily the interior transport that balances a strong somali current there are two main overturning cells in june and september a shallow one of approximate magnitude 15 sv in june and 0 sv in september which reaches depths of no more than 500 m and is driven by ekman divergence at the surface and a deep cell of magnitude 1 sv representing a weak inflow and subsequent upwelling of circumpolar deep water the deep cell implies a basin averaged upwelling velocity of 3 2 10 5 cm s 1 through 2200 m