oxygen isotope analyses and pleistocene ice volumes abstract the oxygen isotope record from fossil foraminifera in deep sea sediments is commonly used as a proxy for global ice volume the linkage between 18 o and ice volume however is probably nonlinear we have developed a simple numerical model of the isotopic response of the oceans to ice volume change the major features it simulates are 1 the changing mean isotopic composition of snow as a function of ice volume colder snow temperatures forced by climate change and higher elevation accumulation areas imply more negative mean 18 o 2 the nonequilibrium isotopic composition of ice sheets the past history of an ice sheet is integrated into its mean isotopic composition which introduces a lag of isotopic ice volume i e the measured 18 o record scaled to ice volume units behind true ice volume 3 selective preservation of isotopically more negative colder higher latitude ice this geographic effect can selectively amplify or dampen the isotopic response to the ice volume signal we illustrate the response of our model to simple hypothetical ice volume transitions of ice growth and ice decay sensitivity tests are illustrated for all model parameters the results suggest that oxygen isotope records reproduce the general patterns of ice volume change fairly accurately the foraminiferal isotope record however may misrepresent the true amplitude of the ice volume signal and lag true ice volume by 1000 to 3000 yr

history of stage 5 sea level in bermuda review with new evidence of a brief rise to present sea level during substage 5a abstract oxygen isotope substage 5e is represented by the devonshire formation in bermuda the occurrence of these coastal marine deposits to about 5 m indicates pleistocene sea level data in bermuda do not need tectonic corrections a few published u series coral dates suggest that a conglomerate spencer s point formation may have formed during substage 5c geologic mapping however indicates that the eolianite beneath the conglomerate is pre rather than post devonshire formation in age as was previously thought and the aminostratigraphy of marine sheels also confirms the correlation of the spencer s point and devonshire formations substages 5c and 5a are represented by the southampton formation large eolianites comprise the bulk of this formation they are onlapped by a few small younger marine 1 m and eolian deposits aminostratigraphy confirms that these late southampton age deposits are significantly younger than the devonshire formation and u series dates indicate a substage 5a age the setting of some of these deposits along a protected shoreline precludes discounting their position as anomalous due to large storms this evidence that sea level in bermuda was at about present datum late in substage 5a agrees with interpretations of neotyrrhenian deposits of mediterranean shorelines but not with inferences from the deep sea oxygen isotope record or with data from uplifted coral reefs

th u dating of strombus bubonius bearing marine terraces in southeastern spain single dates obtained on mollusk shells by the u series nuclides method are highly unreliable primarily because of the mobility of uranium isotopes however in several cases a statistical approach was demonstrated to yield coherent chronologies in both continental and marine environments the authors report on 34 new th and u isotope measurements on strombus bubonius and glycymeris glycymeris fossils from raised marine terraces in the almeria area southeastern spain the results yield a coherent chronology that indicates the presence of the warm water s bubonius fauna in the mediterranean basin reconsideration of the tyrrhenian stratigraphy based on the presence of s bubonius is thus required

the puglia uplift se italy an anomaly in the foreland of the apenninic subduction due to buckling of a thick continental lithosphere the apenninic foreland shows two distinct structural signatures comparing the central adriatic sea and the puglia region during the pliocene pleistocene the central adriatic underwent high subsidence rates due to the eastward rollback of the hinge of the west dipping apenninic subduction the puglia region and the bradanic foredeep are located southward along strike in the same foreland but in contrast with the central adriatic after pliocene early pleistocene subsidence they underwent uplift since the middle pleistocene the geometry and the kinematics of the frontal accretionary wedge and related foreland changed from that moment on between the two areas at the front of the central northern apennines off scraping and subsidence continued whereas the foredeep and foreland of the southern apennines were buckled those differences are interpreted as being due to the larger subduction hinge rollback rate since middle pleistocene of the central adriatic lithosphere 70 km thick with respect to the thicker puglia 110 km the different thicknesses of the continental crust and lithosphere were inherited from the mesozoic rifting that disrupted the adriatic plate the different thicknesses appear to have controlled the variable degree of flexure of the lithosphere and its asthenospheric penetration rate the tremiti e w alignment is the right lateral lithospheric transfer zone of those different tectonic regimes the consequent different dip of the subduction in the two sections steeper west of puglia could also explain the lower elevation of the southern apennines compared to their central northern sector

influence of late quaternary climatic changes on geomorphic and pedogenic processes on a desert piedmont eastern mojave desert california radiocarbon dating of late quaternary deposits and shorelines of lake mojave and cation ratio numerical age dating of stone pavements dorn 1984 on the adjacent soda mountains piedmont provide age constraints for alluvial and eolian deposits these deposits are associated with climatically controlled stands of lake mojave during the past 15 000 yr six alluvial fan units and three eolian stratigraphic units were assigned ages based on field relations with dated shorelines and piedmont surfaces as well as on soil geomorphic data all but one of these stratigraphic units were deposited in response to time transgressive climatic changes beginning approximately 10 000 yr ago increased eolian flux rates occurred in response to the lowering of lake mojave and a consequent increase in fine sediment availability increased rates of deposition of eolian fines and associated salts influenced pedogenesis stone pavement development and runoff infiltration relations by 1 enhancing mechanical weathering of fan surfaces and hillslopes and 2 forming clay and silt rich surface horizons which decrease infiltration changes in alluvial fan source areas from hillslopes to piedmonts during the holocene reflect runoff reduction on hillslopes caused by colluvial mantle development and runoff enhancement on piedmonts caused by the development of less permeable soils inferred increased in early to middle holocene monsoonal activity resulted in high magnitude paleo sheetflood events on older fan pavements this runoff triggered piedmont dissection which in turn caused increased sediment availability along channel walls thus runoff infiltration changes during the late quaternary have occurred in response to eolian deposition of fines pedogenesis increased sheetflood activity in the holocene and vegetational changes which are related to many complicated linkages among climatic change lake fluctuations and eolian hillslope and alluvial fan processes

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr

a new look at the structural geology of the southern side of the central and eastern high atlas mountains we give a general description of two evaporite basins discovered one under and the other south of the lower jurassic carbonate platform which fringes the atlas gulf in the south the larger of these basins lies in the triangle tazzouguert aoufouss tarda the smaller whose extent is difficult to determine it being considerably deformed and partially covered over by the southward sliding of the liassic carbonate platform lies north of tinerhir and ifer marl and evaporite middle liassic deposits from this smaller basin form a tectonic window in the massive limestones of the liassic carbonate platform at tisgui todrha gorges this window clearly shows that the zone in question was affected by southward sliding to the east of tazzouguert going towards bouanane the carbonate platform backs directly onto the african craton

range front fault scarps of the sierra el mayor baja california formed above an active low angle normal fault the canada david detachment a west dipping low angle normal fault juxtaposes pliocene and pleistocene sedimentary units over sheared bedrock in the sierra el mayor baja california along the west central range front the detachment is overlapped by quaternary alluvial fans that are in turn cut by fault scarps up to 7 m high map relationships suggest that scarp forming faults may sole into the detachment at very shallow depth 200 300 m palinspastic restoration of a topographic profile across 15 north striking scarps suggests that the ratio of net heave to net throw along scarp forming faults is 2 consistent with them soling into a low angle 30 fault these 15 scarps may have all formed in one earthquake with rupture propagation from depth to the near surface aided by clay gouge along the detachment the detachment is abandoned in the footwall east of the scarps

tims u series dating and stable isotopes of the last interglacial event in papua new guinea the extensive flight of uplifted reef terraces which occurs along the vitiaz strait on the northern flank of the huon peninsula in png papua new guinea contains a particularly good record of sea level changes in the last 250 ky the huon terraces were the target of an international expedition which took place in july august 1988 in particular we searched for suitable samples for u series dating in a reef complex designated as vii which is correlated with the last interglacial episode and high sea level stand this complex is composed of a barrier reef viib a lagoon and a fringing reef viia twelve corals from these terraces and two corals from the older reef complex viii were selected for analysis the petrography oxygen and carbon isotope compositions and magnesium and strontium concentrations were determined along with the concentrations and isotopic compositions of uranium and thorium 230 th 234 u ages of the corals with 99 aragonite having primary textures and which show u sr ratios around 0 4 10 3 and initial 234 u values close to that of present seawater appear to be reliable the most reliable ages from complex vii corals fall in two tight groups centered at 118 ky and 134 ky corals with 234 u t values higher than 160 and u sr ratios substantially lower than seawater are assumed to have undergone diagenetic alteration which appears to be common in this area the simplest model for sea level height for terrace vii is a continuous rise between 134 and 118 ky alternatively there may have been two periods of rapid sea level rise in contrast in the bahamas there is evidence that sea level remained rather constant over the time interval 132 to 120 ky the absence of ages between 132 and 120 ky in png could be the result of changes in the local tectonic uplift rates during that time or erosion that disrupted the continuous record in any event we find no basis for accepting a single brief time for the age of the last interglacial and applying this age as a precise chronometer for worldwide correlation or as a test of climatic models the older ages reported here precede the milankovitch solar insolation peak at 128 ky and the younger ages are 10 ky after this peak if the present high precision data are correct then it will be necessary to reassess the validity of the milankovitch theory of climatic changes the fundamental issue which must now be resolved is a means of identifying coral samples that have not been disturbed by diagenetic processes

upper neogene stratigraphy and tectonics of death valley a review abstract new tephrochronologic soil stratigraphic and radiometric dating studies over the last 10 years have generated a robust numerical stratigraphy for upper neogene sedimentary deposits throughout death valley critical to this improved stratigraphy are correlated or radiometrically dated tephra beds and tuffs that range in age from 3 58 ma to

oxygen isotopes and sea level from the time that detailed oxygen isotope records derived from foraminifera living in the constant temperature environment of the abyssal ocean became available there has been a discrepancy between the ice volume record that these records imply and that derived from the altitude of dated coral terraces around the world here we re examine the data and conclude that the temperature of the abyssal ocean has been an actively varying component of the climate system

late pleistocene paleoclimates and sea level change in the mediterranean as inferred from stable isotope and u series studies of overgrowths on speleothems mallorca spain abstract phreatic overgrowths on speleothems form at the surface of brackish pools which are present in many coastal caves of mallorca spain unlike common vadose speleothems formed in subaerial environments their occurrence directly identifies the height of the sea level at the time of the carbonate deposition because such pools are physically connected with the sea these deposits from the late pleistocene have recorded the same global variations in oxygen isotopes as planktonic and benthonic foraminifera corals and cave deposits a number of phreatic overgrowths on speleothems have been dated using the th u method in order to determine the position of the sea level during late quaternary the same samples as well as some subaerial speleothems have been analysed for 18 o 16 o and 13 c 12 c ratios the former samples allow the analysis of variations in sea water component in the brackish pools associated with glacio eustatic mediterranean fluctuations and the latter permit inferences concerning past continental climate changes some high sea stands have been recognized in correspondence with oxygen isotope stages ois 9 or older 7 5e 5c and 5a phreatic overgrowths on speleothems have also been formed during a colder phase ois 4 demonstrating that also in that period there were environmental conditions favourable for this kind of carbonate precipitation vadose crystallizations have recorded a cold period at 36 ka corresponding with the end of ois 3

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

luminescence ages for alluvial fan deposits in southern death valley implications for climate driven sedimentation along a tectonically active mountain front abstract controversy exists over whether alluvial fan sedimentation along tectonically active mountain fronts is driven by climatic changes or tectonics knowing the age of sedimentation is the key to understanding the relationship between sedimentation and its cause alluvial fan deposits in death valley and throughout the arid southwestern united states have long been the subjects of study but their ages have generally eluded researchers until recently most mapping efforts have recognized at least four major relative age groupings q1 oldest q2 q3 and q4 youngest using observed changes in surface soils and morphology relation to the drainage net and development of desert pavement obtaining numerical age determinations for these morphologic stages has proven challenging we report the first optically stimulated luminescence osl ages for three of these four stages deposited within alluvial fans along the tectonically active black mountains of death valley deposits showing distinct remnant bar and swale topography q3b have osl ages from 7 to 4 ka whereas those with moderate to poorly developed desert pavement and located farther above the active channel q3a have osl ages from 17 to 11 ka geomorphically older deposits with well developed desert pavement q2d have osl ages 25 ka using this osl based chronology we note that alluvial fan deposition along this tectonically active mountain front corresponds to both wet to dry and dry to wet climate changes recorded globally and regionally these findings underscore the influence of climate change on alluvial fan deposition in arid and semi arid regions

u series measurements in tyrrhenian deposits from mallorca further evidence for two last interglacial high sea levels in the balearic islands the campo de tiro type section for the tyrrhenian ecostratigraphic beds of the balearic islands shows four indurated littoral conglomerates and beach rocks unconformably superimposed the lower two units 1 and 2 are separated by a thin layer of reddish continental silts both contain a typical eutyrrhenian fauna whereas a neotyrrhenian fauna characterizes the overlying units 3 and 4 thu measurements by thermal ionisation mass spectrometry on mollusk shells from these deposits yielded ages of 135 ka unit 1 117 ka units 2 and 3 and a scatter of ages around 100 ka unit 4 the stratigraphic relationships and thu data indicate i that uranium was uptaken by mollusks shells but arca sp each time during a relatively short early diagenetic interval before cementation ensured a fair closure of the radioactive system ii two high sea stands characterized the last interglacial isotopic substage 5e of the balearic islands area iii the duration of this episode was 17 ka and iv the change in faunal assemblages and disconformity observed between units 2 and 3 are due to fluctuations in sea level and surface water conditions which occurred during the second high sea level episode of the last interglacial

holocene slip rates along the owens valley fault california implications for the recent evolution of the eastern california shear zone one of the largest historical earthquakes in california occurred in 1872 along the owens valley fault located along the western margin of the eastern california shear zone new paleoseismic and optically stimulated luminescence data are the first to bracket the timing of the pre 1872 rupture to between 3 3 0 3 and 3 8 0 3 ka these data yield an earthquake recurrence interval between 4100 and 3000 yr under the assumption of uniform return and indicate a holocene slip rate between 1 8 0 3 and 3 6 0 2 mm yr our data are broadly consistent with a model proposed for the space time evolution of the eastern california shear zone our holocene slip rate estimates for the owens valley fault are slower than present day slip rates determined from elastic half space models of geodetic data this discrepancy is reduced by using the recurrence interval estimated here and a viscoelastic model of geodetic data or by including geologic slip rates from adjacent faults

dating fluvial sediments by optically stimulated luminescence selection of equivalent doses for age calculation fluvial sediments are not an ideal material for optical dating because of insufficient or and uneven exposure to daylight prior to burial the equivalent doses for a sample obtained using the single aliquot regenerative dose method usually show a large scatter which may be attributed to many factors here we developed a technique to evaluate the contributions from each factor using this technique relatively well bleached aliquots were identified and the average of their equivalent doses was taken for age calculation

cosmogenic dating of fluvial terraces fremont river utah absolute dating of river terraces can yield long term incision rates clarify the role of climate in setting times of aggradation and incision and establish the rates of pedogenic processes while surface exposure dating using cosmogenic 10be and 26al would seem to be an ideal dating method the surfaces are composed of individual clasts each with its own complex history of exposure and burial the stochastic nature of burial depth and hence in nuclide production in these clasts during exhumation and fluvial transport and during post depositional stirring results in great variability in clast nuclide concentrations we present a method for dealing with the problem of pre depositional inheritance of cosmogenic nuclides we generate samples by amalgamating many individual clasts in order to average over their widely different exposure histories depth profiles of such amalgamated samples allow us to constrain the mean inheritance to test for the possible importance of stirring and to estimate the age of the surface working with samples from terraces of the fremont river we demonstrate that samples amalgamated from 30 clasts represent well the mean concentration depth profiles show the expected shifted exponential concentration profile that we attribute to the sum of uniform mean inheritance and depth dependent post depositional nuclide production that the depth dependent parts of the profiles are exponential argues against significant post depositional displacement of clasts within the deposit our technique yields 10be age estimates of 60 9 102 16 and 151 24 ka for the three highest terraces corresponding to isotope stages 4 5d and 6 respectively the mean inheritance is similar from terrace to terrace and would correspond to an error of 30 40 ka if not taken into account the inheritance likely reflects primarily the mean exhumation rates in the headwaters of order 30 m ma

quaternary alluvial fan development climate and morphologic dating of fault scarps in laguna salada baja california mexico article i nfo late quaternary slip across the canada david detachment has produced an extensive array of quaternary scarps cutting alluvial fans along nearly the entire length 60 km of the range bounding detachment eight regional alluvial fan surfaces q1 youngest to q8 oldest are defined and mapped along the entire sierra el mayor range front terrestrial cosmogenic nuclide 10 be concentrations from individual boulders on alluvial fan surfaces q4 and q7 yield surface exposure ages of 15 5 2 2 ka and 204 11 ka respectively formation of the fans is probably tectonic but their evolution is strongly moderated by climate with surfaces developing as the hydrological conditions have changed in response to climate change on milankovitch timescales systematic mapping reveals that the fault scarp array along active range bounding faults in sierras cucapa and el mayor can be divided into individual rupture zones based on cross cutting relationships with alluvial fans quantitative morphological ages of the laguna salada fault scarps derived from linear diffusive degradation modeling are consistent with the age of the scarps based on cross cutting relationships the weighted means of the maximum mass diffusivity constant for all scarps with offsets b 4 m is 0 051 and 0 066 m 2 ka for the infinite and finite slope solutions of the diffusion equation respectively this estimate is approximately an order of magnitude smaller than the lowest diffusivity constants documented in other regions and it probably reflects the extreme aridity and other microclimatic conditions that characterize the eastern margin of laguna salada

strain accumulation along the laguna salada fault baja california mexico strain accumulation observed over the 1978 1991 interval in a 30 100 km aperture trilateration network spanning the laguna salada fault is described by the principal strain rates 0 101 0 012 strain yr n80 e 2 and 0 021 0 012 strain yr n10 w 2 extension reckoned positive these strain accumulation rates have been corrected to remove coseismic effects of the nearby 1979 imperial valley m 6 5 1980 victoria baja california m 6 4 1987 superstition hills m 6 5 and 1987 elmore ranch m 5 9 earthquakes the observed strain rates indicate extension at a rate of about 0 08 strain yr perpendicular to the trend n35 w of the salton trough as well as a right lateral tensor shear strain rate 0 05 strain yr across it the extension perpendicular to the trough is observed neither farther north near the salton sea nor farther south across the gulf of california however holocene slip on the laguna salada fault about equal parts right lateral and normal slip is consistent with the observed strain accumulation a simple dislocation model intended to explain the observed strain accumulation as a product of slip at depth on the laguna salada fault would require that the fault be listric

late quaternary activity of the laguna salada fault in northern baja california mexico faulted alluvial fans and bajadas along the central laguna salada fault zone in northernbajacaliforniarecordarecurrent history of oblique slip holocene earthquakes alluvialsurfaces whichrangefrom late pleistocene to historic in age have been progressively displaced along the base of the crystalline rangefront as well as along more basinward fault splays in alluvium the recurrence interval determined from displacedalluvialdepositsthataredatedby soil profile development is in the range of 1 2 ka with a corresponding right lateral slip rate of 2 3 mm yr similar to that of thesouthernelsinorefaultinsoutherncalifornia the most recent event along the fault zone is probably the widely felt earthquake of february 23 1892 at least 22 km ofthefaultzonerupturedduringthisevent along both an oblique dextral section of the northwest strikinglagunasaladafaultand

response of alluvial fan systems to the late pleistocene to holocene climatic transition contrasts between the margins of pluvial lakes lahontan and mojave nevada and california usa abstract dated shorelines of late pleistocene pluvial lakes lahontan great basin desert northwest nevada and mojave mojave desert eastern california provide timelines for the assessment of alluvial fan sedimentation at the lake margins during the late pleistocene to early holocene two sets of alluvial fan systems have been mapped the stillwater fans feeding lake lahontan and the zzyzx fans feeding lake mojave their contrasting morphologies suggest different responses of the two fan systems to late pleistocene to early holocene climatic change at the time the stillwater fan systems underwent minimal sedimentation with the catchment hillslopes apparently stable the zzyzx fans experienced major changes in water and sediment supply from the catchment hillslopes there was a major phase of hillslope debris flow activity followed by fanhead trenching and distal fan progradation both areas were wetter and colder in the late pleistocene than they are today but during the transition to the holocene the zzyzx area was more likely to experience intense rains associated with the monsoonal penetration of warm moist tropical air into the southwest vegetation reconstructions for the late pleistocene to the early holocene suggest that catchment hillslopes in the mojave supported a desert shrub vegetation but those in the stillwaters supported juniper woodland and grasses at low elevations and pine at higher elevations contrasts in hillslope vegetation cover together with storm activity may account for the different responses of the alluvial fans to climatic change during the pleistocene to holocene climatic transition after the falls in lake levels of lakes lahontan and mojave in the early holocene both areas underwent aridification resulting in reductions in hillslope vegetation cover increased storm runoff led to fanhead trenching and distal progradation of the alluvial fans variations in fan style at that time may relate primarily to base level conditions resulting from different gradients on the exposed lake shores

late pleistocene holocene alluvial stratigraphy of southern baja california mexico abstract a late pleistocene to holocene alluvial stratigraphy has been established for the basins of la paz and san jose del cabo in the southern tip of the baja california peninsula mexico six discrete alluvial units qt1 through qt6 were differentiated across the region using a combination of geomorphologic mapping sedimentological analysis and soil development these criteria were supported using radiocarbon optically stimulated luminescence and cosmogenic depth profile geochronology major aggradation started shortly after 70 ka qt2 and buildup of the main depositional units ended at 10 ka qt4 after deposition of qt4 increasing regional incision of older units and the progressive development of a channelized alluvial landscape coincide with deposition of qt5 and qt6 units in a second incisional phase all units consist of multiple 1 3 m thick alluvial packages deposited as upper flow stage beds that represent individual storms main aggradational units qt2 qt4 occurred across broad 2 km channels in the form of sheetflood deposition while incisional stage deposits are confined to channels of 0 5 2 km width continuous deposition inside the thicker 10 m pre qt5 units is demonstrated by closely spaced dates in vertical profiles in a few places disconformities between these major units are nevertheless evident and indicated by partly eroded buried soils the described units feature sedimentological traits similar to historical deposits formed by large tropical cyclone events but also include characteristics of upper regime flow sedimentation not shown by historical sediments like long 10 m wavelength antidunes and transverse ribs we interpret the whole sequence as indicating discrete periods during the late pleistocene and holocene when climatic conditions allowed larger and more frequent tropical cyclone events than those observed historically these discrete periods are associated with times when insolation at the tropics was higher than the present day conditions determined by precessional cycles and modulated by the presence of el nino like conditions along the tropical and northeastern pacific the southern baja california alluvial record is the first to document a precession driven alluvial chronology for the region and it constitutes a strong benchmark for discrimination of direct tropical influence on any other alluvial record in southwestern north america

cosmogenic 10be and 36cl geochronology of offset alluvial fans along the northern death valley fault zone implications for transient strain in the eastern california shear zone the northern death valley fault zone ndvfz has long been recognized as a major right lateral strike slip fault in the eastern california shear zone ecsz however its geologic slip rate has been difficult to determine using high resolution digital topographic imagery and terrestrial cosmogenic nuclide dating we present the first geochronologically determined slip rate for the ndvfz our study focuses on the red wall canyon alluvial fan which exposes clean dextral offsets of seven channels analysis of airborne laser swath mapping data indicates 297 9 m of right lateral displacement on the fault system since the late pleistocene in situ terrestrial cosmogenic 10 be and 36 cl geochronology was used to date the red wall canyon fan and a second correlative fan also cut by the fault beryllium 10 dates from large cobbles and boulders provide a maximum age of 70 22 20 ka for the offset landforms the minimum age of the alluvial fan deposits based on 36 cl depth profiles is 63 8 ka combining the offset measurement with the cosmogenic 10 be date yields a geologic fault slip rate of 4 2 1 9 1 1 mm yr 1 whereas the 36 cl data indicate 4 7 0 9 0 6 mm yr 1 of slip summing these slip rates with known rates on the owens valley hunter mountain and stateline faults at similar latitudes suggests a total geologic slip rate across the northern ecsz of 8 5 to 10 mm yr 1 this rate is commensurate with the overall geodetic rate and implies that the apparent discrepancy between geologic and geodetic data observed in the mojave section of the ecsz does not extend north of the garlock fault although the overall geodetic rates are similar the best estimates based on geology predict higher strain rates in the eastern part of the ecsz than to the west whereas the observed geodetic strain is relatively constant

thermal evolution of monte blanco dome low angle normal faulting during gulf of california rifting and late eocene denudation of the eastern peninsular ranges footwall rocks of the canada david detachment fault northeastern baja california record late eocene earliest oligocene and late neogene cooling events previously unrecognized in the region biotite 40 ar 39 ar ages of 65 ma reflect slow cooling through 350 c 5 to 10 m y later than is typical in the region multiple diffusion domain modeling of k feldspar 40 ar 39 ar release spectra shows very slow cooling 1 c m y from 65 to 45 ma accelerated cooling from 315 c to 215 c between 45 and 33 ma records at least 3 4 km of denudation that we relate to east side up reactivation of late cretaceous structures that generally follow the oceanic continental suture previously established rivers flowing west from mainland mexico apparently became further entrenched during this uplift and continued to supply distinctive rhyolitic detritus to the coast ultimately surface uplift disrupted and rerouted the extraregional rivers some 2 to 6 m y before the cooling event ended footwall rocks remained nearly isothermal from 30 to 15 10 ma when renewed rapid cooling 33 17 c m y began in response to footwall exhumation by top to the west low angle normal faulting that accommodated rift related extension in what finally became the gulf of california apatite fission track and u th he ages of 5 ma and 4 ma respectively record final detachment related cooling through 110 c to 70 c thermal kinematic modeling suggests that 5 7 km of late neogene tectonic denudation and 10 12 km of horizontal extension were necessary in order to unroof the samples by 2 ma additional extension of unknown magnitude has probably occurred subsequently geodetically measured horizontal extension rates are considerably higher than the long term extension rate that can be attributed to detachment faulting

uranium concentration and isotope ratio profiles within mercenaria shells geochronological implications shells of nineteen specimens of mercenaria from unconsolidated sediments of the southeastern usa coast ranging in age from alive to pliocene were each separated into three to six sections parallel to the shell surface the uranium concentration and isotope ratio of each subsample was determined the results confirm those of previous studies that whole fossil shells have about 8 times as much uranium 300 vs 40 ppb and considerably higher 234u 238u ratios than do whole live collected shells however it was also found that uranium concentrations fall very steeply by factors of 300 and 15 in live and fossil shells respectively from the exterior of the shell to about two thirds of the shell thickness between this depth and the interior surface the uranium concentrations of live shells increase by about a factor of 5 while fossils have gradients which vary from moderately positive to moderately negative the most surprising finding of the study is that the interior portions of the shells become closed chemical systems by no more than about 15 ka after their death this is known from the observation that these portions of late pleistocene shells still have oceanic uranium isotope ratios while the exterior portions of the same shells have ratios which reflect an uptake of uranium from continental groundwaters the water the shells have been in contact with for the vast majority of their existence thus the u series ages of the interior portions of mercenaria shells may be valid after a small correction though shells older than about 200 ka seem less promising firm conclusions cannot be drawn regarding them because of the great scatter in the data

seismically induced mass movements and volumetric fluxes resulting from the 2010 mw 7 2 earthquake in the sierra cucapah mexico the observation that sediment flux from mountain ranges struck by high magnitude earthquakes can be strongly influenced by coseismic mass movements brings into question the nature of coseismic deformation as a net contributor to mountain building to better constrain the role of high magnitude earthquakes in orogenesis high resolution data of earthquake induced mass wasting is required for areas of differing tectonic morphological and climatic settings here we compare the erosional flux to the tectonic flux associated with the 2010 mw 7 2 sierra el mayor earthquake in mexico and examine the landslide patterning of coseismic mass movements associated with this event the ruptured fault system has a significant strike slip component with subsidence along the eastern flank and uplift on the western flank of the range peak ground acceleration was highest along the steepest sections of the range such that the frequency of landslide occurrence was strongly correlated to slope gradient both vertical and horizontal coseismic displacement demonstrated a strong control over landslide initiation this result suggests that strike slip systems experience very different landslide patterning to thrust faults during earthquakes based on interferometric analysis of synthetic aperture radar images the earthquake resulted in a total uplifted volume of 41 6 106 m3 and a loss of 95 2 106 m3 due to subsidence this suggests a net tectonic volumetric flux of 53 6 106 m3 sediment mobilisation by coseismic landslides is estimated at 2 7 106 m3 derived from a manually mapped inventory using spot 5 multispectral imagery thus the net volume loss through coseismic subsidence of the mountain range generated a strongly negative mass flux which was only marginally enhanced by mass wasting

the reliability of uranium series mollusc dates from the western mediterranean basin abstract fossil mollusc shells from western mediterranean raised beach deposits have been dated using u series techniques sub sampling has allowed intra shell isotopic variability to be assessed although most of the calculated ages appear plausible and some internal consistency exists closer scrutiny of the data reveals that the shells have behaved as geochemically open systems and all the ages therefore must be considered suspect some previously published u series mollusc data from the same region may also contain evidence of open system behaviour and are considered equally unreliable simple modelling suggests considerable variation in isotopic uptake behaviour both within and between shells

the age of late pleistocene shorelines and tectonic activity of taranto area southern italy abstract the results of isoleucine epimerization ratios in pelecypods glycymeris sp arca sp and cerastoderma sp and u series dating of bivalves and cladocora caespitosa sampled from different late pleistocene units in the cheradi islands and in the coastal areas of mar piccolo and mar grande near taranto apulia region italy are presented u series measurements on pelecypods and on corals directly associated with mollusc samples provide an independent calibration of amino acid data the d l ratios of isoleucine show a strong correlation with age and thus may be considered as a predictive dating technique this correlation also supports the reliability of u series ages obtained for molluscs these results including the stratigraphic position the lithological lateral continuity the morphological evidence and the palaeontological characteristics of the various units made it possible to attribute them to different marine trangressive phases referable to oxygen isotope stages ois 5e c 5a and 3 no evidence of land emersion between ois 5e and 5c has been found in the area pinkish red sands deposits located above present sea level 1 m have been referred to ois 3 the late pleistocene morphological evolution and uplift of a complex area between the apulian foreland and the bradanic foredeep have been reconstructed due to the lack of incontestable indicators of past sea level stands the facies analysis has been performed on u series dated 89 8 ka ois 5c shoreline north of mar piccolo and an uplift rate ranging from 0 21 0 27 mm yr has been calculated

beryllium 10 terrestrial cosmogenic nuclide surface exposure dating of quaternary landforms in death valley quaternary alluvial fans and shorelines spits and beach bars were dated using 10 be terrestrial cosmogenic nuclide tcn surface exposure dating in death valley the 10 be tcn ages show considerable variance on individual surfaces samples collected in the active channels date from 6 ka to 93 ka showing that there is significant inheritance of 10 be tcn within cobbles and boulders that were dated which suggests that slopes erode and sediment is transferred very slowly in most regions within death valley comparisons of 10 be tcn ages on alluvial fan surfaces with chronostratigraphies based on soil development and optically stimulated luminescence dating show that minimum 10 be tcn ages within sample sets on individual surfaces most closely approximate to the age of landforms that are younger than 70 ka alluvial fan surfaces older than 70 ka have begun to undergo significant erosion so that the majority of 10 be tcn ages for data sets on individual surfaces underestimate the true age of the surface due to erosion and exhumation of fresh cobbles and boulders the spread of 10 be tcn ages for beach bars near beatty junction and shorelines 8 km south of furnace creek is large ranging from 119 ka to 385 ka and 109 ka to 465 ka respectively however new and previously published luminescence ages soil development and geomorphic context suggest that these landforms formed during high lake level stands in marine isotope stage 2 22 18 ka but these younger ages my reflect soil development and material elluviated into the bar deposit long after deposition this suggests that the cobbles and boulders dated with 10 be methods have inherited 10 be tcns which have been derived from older shorelines or associated landforms these results highlight the problems associated with using surface cobbles and boulders to date quaternary surfaces in death valley and other similar dryland settings moreover this study emphasizes the need to combine multiple different dating methods to accurately date landforms in death valley and similar settings

luminescence chronology of incision and channel pattern changes in the river ganga india the river ganga in the central gangetic plain shows the incision of 20 m of late quaternary sediments that form a vast upland terrace t2 the incised ganga river valley shows two terraces namely the river valley terrace t1 and the present day flood plain terrace t0 terrace t1 shows the presence of meander scars oxbow lakes scroll plains which suggests that a meandering river system prevailed in the past the present day river channel flows on terrace t0 and is braided sensu stricto it is thus inferred that the river ganga experienced at least two phases of tectonic adjustments 1 incision and 2 channel metamorphosis from meandering to braided optical dating of samples from three different terraces has bracketed the phase of incision to be 6 and 4 ka different ages of the top of terrace t2 show that this surface experienced differential erosion due to tectonic upwarping in the region which also caused the river incision river metamorphosis occurred some time during 4 and 0 5 ka

dating offset fans along the mojave section of the san andreas fault using cosmogenic 26al and 10be analysis of cosmogenic 1 0 be and 2 6 al in samples collected from exposed boulders n 20 and from buried sediment n 3 from offset fans along the san andreas fault near little rock california yielded ages ranging from 16 to 413 ka which increase with dis lance from their source at the mouth of little rock creek in order to determine the age of the relatively younger fans the erosion rate of the boulders and the cosmogenic nuclide inheritance from exposure prior to deposition in the fan were established cosmogenic nuclide inheritance values that range between 8 5 x 10 3 and 196 10 3 atoms 1 0 be g 1 quartz were determined by measuring the concentrations and ratios of 1 0 be and 2 6 al in boulders n 10 and fine sediment n 7 at the outlet of the present active stream boulder erosion rate ranging between 17 and 160 mm k y 1 was estimated by measuring 1 0 be and 2 6 al concentrations in nearby bedrock outcrops n 8 since the boulders on the fans represent the most resistant rocks in this environment we used the lowest rate for the age calculations monte carlo simulations were used to determine ages of 16 5 and 29 7 ka for the two younger fan surfaces older fans older than 100 ka were dated by analyzing 1 0 be and 2 6 al concentrations in buried sand samples the ages of the three oldest fans range between 227 242 and 413 185 ka although fan age determinations are accompanied by large uncertainties the results of this study show a clear trend of increasing fan ages with increasing distance from the source near little rock creek and provide a long term slip rate along this section of the san andreas fault slip rate along the mojave section of the san andreas fault for the past 413 k y can be determined in several ways the average slip rate calculated from the individual fan ages is 4 2 0 9 cm yr 1 a linear regression through the data points implies a slip rate of 3 7 1 0 cm yr 1 a most probable slip rate of 3 0 1 0 cm yr 1 is determined by using a 2 test these rates suggest that the average slip along the mojave section of the san andreas fault has been relatively constant over this time period the slip rate along the mojave section of the san andreas fault determined in this study agrees well with previous slip rate calculations for the quaternary

millennial scale varnish microlamination dating of late pleistocene geomorphic features in the drylands of western usa abstract varnish microlamination vml dating is a climate based correlative age determination technique used to correlate and date various geomorphic features in deserts in this study we establish a generalized late pleistocene 18 74 ka millennial scale microlamination sequence in fine grained fast accumulating rock varnish for the drylands of western usa radiometrically calibrate the sequence and correlate it with the 18 o record in the gisp2 greenland ice core we then use this climate correlated varnish microstratigraphy to estimate surface exposure ages for radiometrically dated late pleistocene geomorphic features in the study region the vml dating of debris flow deposits on the sehoo recessional shorelines of lake lahontan at the jessup embayment of central nevada yields a minimum limiting age of 14 95 15 95 ka in good agreement with a calibrated 14 c age of 15 22 0 12 ka for the timing of the lake recession the vml dating of a giant ejecta block on the rim of meteor crater in northern arizona yields a minimum limiting age of 49 15 ka closely matching a thermoluminescence tl age of 49 3 ka and slightly younger than a recently updated cosmogenic 36 cl age of 56 0 2 4 ka for the meteor impact event the vml dating of distal q2c fan surfaces on hanaupah canyon alluvial fan in death valley california yields a minimum limiting age of 73 55 ka in accord with cosmogenic 36 cl depth profile ages of 66 22 14 ka and 72 24 20 ka for the same fan deposits the close agreement between the vml age estimates and the independently derived radiometric ages for these geomorphic features attests to the validity and reliability of millennial scale vml dating to further assess its potential in desert geomorphological research we use the vml method to study alluvial fan responses to millennial scale climatic changes the vml dating of a small tributary fan in death valley reveals two episodes of fan aggradation one ceasing at 73 55 86 75 ka during the dry period of the last interglacial mis 5a and the other finishing at 66 15 ka during the wet period of the last glacial mis 4 the vml and 36 cl dating of the distal q2c fan surfaces on hanaupah canyon fan reveal two episodes of large scale fan aggradation ended at 72 24 20 ka and 73 55 ka during the wet period of mis 4 fanhead incision and associated within channel or fantoe aggradation are found to take place during the relatively dry period of the glacial to interglacial climatic transition 12 24 ka and the holocene interglacial dry period 0 12 ka these data indicate that on the millennial to sub milankovitch timescale 10 3 10 4 years fan aggradation is a discrete sedimentational process under various climatic conditions because fan aggradation is ultimately controlled by the intensity and frequency of precipitation events which in turn are modulated by major climatic oscillations such as heinrich events dansgaard oeschger do events and glacial interglacial shifts these major climatic changes could be the pacemaker of regionally contemporaneous large area fan segmentation

a test of uranium series dating of fossil tooth enamel results from tournal cave france abstract a series of well preserved mammal bones and horse teeth was analyzed from archaeological levels of tournal cave magdalenian aurignacian and mousterain to test the hypothesis that well crystallized enamel behaves more as a closed system than does whole bone the isotopic composition of bones and tooth enamels from this deposit meet criteria for confidence and gave no reasons to suspect contamination or open system behavior two samples for which231pa could be analyzed showed internal concordance with the respective230th ages in spite of the favourable isotopic criteria however comparison of the u series ages of the bones and the tooth enamel with stratigraphic position and14c control indicated the dates were not meaningful in general both bones and tooth enamels gave ages too young although some were clearly too old neither group showed any systematic increase of age with stratigraphic depth tooth enamel therefore shows no advantage over bone for u series dating for this site in tournal cave both bones and enamel are apparently open to u which is probably cycling as a consequences of post depositional groundwater movement

new data on the pleistocene of mallorca abstract stratigraphic geomorphologic and isoleucine epimerization studies at 15 sites in mallorca define four aminozones a c e and f g of increasing age that are related to transgressive regressive marine cycles from the holocene to the mid pleistocene calibration of aminozone e glycymeris aile ile mean from all sites 0 41 0 03 n 38 is provided by a 129 7 ka u series coral age on cladocora caespitosa from son grauet of the younger aminozones a relates to the holocene transgression and aminozone c to a mid to late isotopic stage 5 event 90 15 ka revealed only by supralittoral eolianites assigning an age to the older poorly resolved aminozones f and g called f g in this case is uncertain without supporting radiometric data but an age of 180 ka can be assigned to these aminozone s f g based on a kinetic model and other examples in the mediterranean several deposits previously dated u series molluscs between 75 and 300 ka appear to belong to the last interglacial complex stage 5 and aminozone e a proposed revision of the positive sea level history of mallorca shows multiple minor oscillations during the major last interglacial cycle stage 5 and two mid pleistocene sea levels one lower than present and the other at about 14 m a s l

paleoseismology of the johnson valley kickapoo and homestead valley faults clustering of earthquakes in the eastern california shear zone paleoseismic data from 11 trenches at seven sites excavated across the southern johnson valley kickapoo and homestead valley faults that ruptured in the 1992 landers earthquake as well as the northern johnson valley fault which did not fail in 1992 indicate that the return period for large surface rupturing events in this part of the eastern california shear zone is in the range of 5 15 ka the inferred slip rates based on their respective recurrence intervals are in the range of 0 2 0 6 mm yr for each of the faults studied a previous large earthquake ruptured the southern johnson valley and kickapoo faults about 5 ka b p the northern johnson valley fault also failed at about this time at 5 8 ka b p and may have been part of the same rupture in contrast the penultimate large earthquake that we identify on the homestead valley fault occurred about 15 ka b p much earlier than other faults involved in the 1992 rupture from these observations combined with paleoseismic work by others after the 1992 earth quake it appears that previous events along the southern johnson valley and kick apoo faults were different than those of 1992 and may have involved other fault segments it has been over 5 ka since the most recent rupture on the northern johnson valley fault therefore it is surprising that it did not fail in the 1992 rupture from our observations dextral shear appears to be distributed across the entire eastern california shear zone with individual faults taking only a small proportion of the overall slip release of this regional strain appears to occur in temporal clusters of large earthquakes with the 1992 event apparently the most recent of a sequence of late holocene 0 1 ka earthquakes that have ruptured the nine faults we have trenched in the southwestern mojave desert previous clusters of earthquake activity occurred in the early 8 9 ka and middle 5 6 ka holocene and possibly the latest pleistocene 15 ka

low latitude glacial cooling in the southern hemisphere from amino acid racemization in emu eggshells the record of natural climate variability over glacial interglacial timescales provides a framework from which a better mechanistic understanding of the climate system may be derived but this approach is limited by the number and distribution of well dated and reliable palaeoenvironmental archives particularly vexing is the conflicting evidence for low latitude cooling during the last glacial maximum and the apparent synchrony in glacial activity between the hemispheres despite out of phase insolation forcing1 4 here we utilize the temperature dependent amino acid racemization reaction in radiocarbon dated emu eggshell fragments from the continental interior of australia to reconstruct low altitude subtropical temperatures for the past 45 kyr racemization rate changes indicate that millennial scale average air temperatures were at least 9 c lower between 45 and 16 kyr bp than since 16 kyr bp a temperature change of this magnitude coupled with other low latitude palaeotemperature records that indicate substantial cooling3 4 must reflect global processes which we speculate involved glacial age reduction in atmospheric water vapour content

the age and extent of tropical alpine glaciation in the cordillera blanca peru based on new 10 be data for moraines in the cordillera blanca of central peru we have calculated model ages of three sets of pleistocene glacial moraines in order of decreasing age these are the cojup rurec and laguna baja moraines the oldest moraines occur at the lowest elevations and yield dates of 400 ka pre dating the last interglacial and demonstrating that maximum ice volumes occurred during previous glacial periods and not at the end of the last glacial our new data from the younger moraines indicate that the end of the last glacial cycle comprised two separate advances at ca 29 ka and ca 16 5 ka each reflecting significant 4 c tropical of cooling at 10 s these data combined with published records from the laurentide ice sheet indicate that climate instabilities associated with the close of the last glacial were likely global and synchronous in nature copyright 2005 john wiley sons ltd

evaluating the life expectancy of a desert pavement abstract this paper integrates prior scholarship on desert pavements with a case study of pavements on stream terraces in the sonoran desert to analyze the processes and site conditions that facilitate the survival of ancient desert pavements this synthesis identifies vital factors key factors and site specific factors promoting pavement stability hyperaridity is the vital factor in pavements surviving for 106 years or more aided by minimal bioturbation and clast size reduction three key factors aid in pavements surviving for 104 to 105 years accumulation of allochthonous dust underneath pavement cobbles a flat topography and a lack of headward retreating swales or gullies a unified explanation for pavement longevity however did not emerge from a literature review because a variety of site specific factors can also promote pavement antiquity including resistant bedrock beneath the pavement disk shaped cobbles to promote dust accumulation and microclimatological and ecological reasons for minimal bioturbation both key and site specific explanations for pavement longevity apply well to a case study of pavements on stream terraces in the sonoran desert central arizona the buildup of cosmogenic 10be and in situ 14c optically stimulated luminescence and varnish microlamination ages reveal stable pavements range in age between 30 and 332 ka with conditions for longevity including flat surface topography pavements underlain by consolidated granitic bedrock a lack of headward retreating gullies and swales 87sr 86sr analyses indicating the infiltration of allochthonous dust floating disk shaped pavement cobbles and a quartzite lithology resistant to disintegration however 10be ages also indicate evidence for the instability of desert pavements on stream terraces underlain by unconsolidated playa clays and unconsolidated fanglomerate these weaker materials allowed the growth of headward retreating swales that in turn promoted exposure of newer gravels by surface erosion

the lower colorado river valley a pleistocene desert abstract a chronological sequence of plant macrofossil assemblages from twenty five pack rat middens provides a record of desert scrub vegetation for most of the last 13 380 yr b p from a hyperarid portion of the lower colorado river valley at the end of the late wisconsin and probably during much of the quaternary the picacho peak area imperial county california supported a typical mohave desert association of larrea divaricata creosote bush coleogyne ramosissima blackbrush yucca brevifolia joshua tree and y whipplei whipple yucca recent arrivals of sonoran desert plants such as olneya tesota ironwood and fouquieria splendens ocotillo suggest that the area supported relatively modern sonoran desert scrub species for relatively short periods during interglaciations

episodic late quaternary slopewash deposition as recorded in colluvial aprons southeastern wyoming abstract colluvial aprons found along fluvial terraces of the laramie river and sybille creek in southeastern wyoming are interpreted as late quaternary slopewash deposits each apron studied contained multiple buried soils interpreted to indicate that slopewash activity was episodic and short lived and was followed by relatively long periods of landscape stability and soil development apron deposits were described and subsequently correlated based on their internal stratigraphy and their relative degree of soil development optical dating was used to chronologically constrain periods of slopewash deposition and based on 17 optical ages taken from five aprons aggradation occurred at 65 56 16 0 12 9 11 8 8 1 7 3 5 0 and 1 7 ka several of these events correspond with climatic transitions such as the termination of heinrich event 1 the onset and termination of the younger dryas and the 8 2 ka event suggesting that apron aggradation was driven by changes in climatic regime although either increased aridity or a change in precipitation regime could result in increased erosion of terrace scarps apron aggradation events do not correlate with regional records of aridity instead periods of increased precipitation intensity and or frequency that occur during climatic transitions most likely drive apron aggradation events

late quaternary stratigraphy and luminescence geochronology of the northeastern mojave desert abstract the chronology of the holocene and late pleistocene deposits of the northeastern mojave desert have been largely obtained using radiocarbon ages our study refines and extends this framework using optically stimulated luminescence osl to date deposits from valjean valley silurian lake playa red pass and california valley of particular interest are eolian fine silts incorporated in ground water discharge gwd deposits bracketed at 185 140 and 20 50 ka alluvial fan deposits proved amenable for osl by dating both eolian sand lenses and reworked eolian sand in a matrix of gravel that occurs within the fan stratigraphy lacustrine sand in spits and bars also yielded acceptable osl ages these osl ages fill gaps in the geochronology of desert deposits which can provide data relevant to understanding the responses of several depositional systems to regional changes in climate this study identifies the most promising deposits for future luminescence dating and suggests that for several regions of the mojave desert sediments from previously undated landforms can be more accurately placed within correct geologic map units

luminescence dating applications in geomorphological research abstract chronological control remains critical to the interpretation of environmental change and to establishing long term rates of geomorphological processes radiocarbon dating will continue to be the central technique for age assessment of carbon bearing sediments deposited in the last ca 40 ka but alternative absolute dating strategies are required for older or non carbon bearing sediments they include uranium series dating of precipitated sediments k ar and ar ar dating of primary volcanic materials and cosmogenic isotopic dating of surface exposure ages an additional family of methods collectively termed luminescence techniques is increasingly providing a basis for the age assessment of detrital sedimentary deposits these methods directly date the deposition of detrital mineral grains typically quartz and feldspar and have been demonstrated to provide accurate deposition chronologies for up to 800 ka although 150 ka is more typical in the past decade a subset of luminescence techniques which employ optical sample stimulation methods called optical dating has made it possible to date samples from a much wider range of depositional systems given that the methods directly date sedimentation they allow direct assessment of depositional dynamism in numerous terrestrial and subaqueous including marine sedimentary systems and have demonstrated particular potential in the elucidation of chronologies from aeolian dune and loess fluvial colluvial coastal and volcaniclastic environments this paper provides a summary of the principles of the luminescence especially optical dating methods and shows how recent developments specifically single aliquot dating procedures have dramatically enhanced the scope and potential of the method the luminescence techniques are increasingly being incorporated into a wide range of geomorphological studies which seek to establish the nature of landscape changes over the past interglacial glacial cycle and beyond

deformation of the 125 ka marine terrace in italy tectonic implications in peninsular italy marine terraces and shorelines created during oxygenisotope substage 5e known historically as the tyrrhenian highstand provide a reliable and homogeneous datum of vertical motions during the past 125 000 years published accounts of 121 locations on the tyrrhenian inner edge were reinterpreted and used to calculate both local and regional uplift rates the data show arching of southern italy between the tyrrhenian and the adriatic coasts and of the calabrian arc between the sangineto and the longi taormina tectonic lineaments at rates of up to 1 2 mm yr for the past 125 ka they also suggest that the present configuration of the southern apennines is the product of post early pleistocene regional uplift superimposed on tortonian to early pleistocene thrusting uplift patterns are characterised by different wavelength in different geodynamic settings suggesting a close link with the depth of the causative tectonic sources

fluvial responses to climate and sea level change a review and look forward summary fluvial landforms and deposits provide one of the most readily studied quaternary continental records and alluvial strata represent an important component in most ancient continental interior and continental margin successions moreover studies of the long term dynamics of fluvial systems and their responses to external or allogenic controls can play important roles in research concerning both global change and sequence stratigraphy as well as in studies of the dynamic interactions between tectonic activity and surface processes these themes were energized in the final decades of the twentieth century and may become increasingly important in the first decades of this millennium this review paper provides a historical perspective on the development of ideas in the fields of geomorphology quaternary geology vs sedimentary geology and then summarizes key processes that operate to produce alluvial stratigraphic records over time scales of 103 106 years of particular interest are changes in discharge regimes sediment supply and sediment storage en route from source terrains to sedimentary basins as well as changes in sea level and the concept of accommodation late quaternary stratigraphic records from the loire france mississippi usa colorado texas usa and rhine meuse the netherlands rivers are used to illustrate the influences of climate change on continental interior rivers as well as the influence of interacting climate and sea level change on continental margin systems the paper concludes with a look forward to a bright future for studies of fluvial response to climate and sea level change at present empirical field based research on fluvial response to climate and sea level change lags behind a the global change community s understanding of the magnitude and frequency of climate and sea level change b the sequence stratigraphic community s desire to interpret climate and especially sea level change as forcing mechanisms and c the modelling community s ability to generate numerical and physical models of surface processes and their stratigraphic results a major challenge for the future is to catch up which will require the development of more detailed and sophisticated quaternary stratigraphic sedimentological and geochronological frameworks in a variety of continental interior and continental margin settings there is a particular need for studies that seek to document fluvial responses to allogenic forcing over both shorter 102 103 years and longer 104 106 years time scales than has commonly been the case to date as well as in larger river systems from source to sink studies of quaternary systems in depositional basin settings are especially critical because they can provide realistic analogues for interpretation of the pre quaternary rock record

interglacial sea levels abstract isotopic curves have been used as approximative estimators of global sea level calculations of the amplitude of sea level variations during interglacials especially for the last interglacial are based on the study of emerged coral terraces the application of different dating methods shows great uncertainty about the length of each interglacial and also about the number chronology and altitude of the different highstands that occur during each interglacial data of raised marine terraces from areas with different geodynamic behaviour bermudas bahamas peru chile italy and spain are summarized in order to analyze the relationships between sea level and interglacial stages two interglacials have been identified for the early pleistocene represented by two marine terraces with different highstands during the early middle pleistocene an interglacial with several highstands is recorded in uplifted areas during isotopic stage 11 at least one highstand with sea level equal or higher than present has been recorded similar sea level behaviour can be suggested for isotopic stage 9 all the analyzed areas record two highstands during isotopic stage 7 when warm equatorial fauna migrate into the mediterranean during isotopic substage 5e at least two highstands took place with evidence of lowstands between them and at least one highstand during substage 5c with similar sea level height above present msl except in barbados and bermuda during substage 5a at least one highstand has been recorded

late pleistocene records of littoral processes at the tyrrhenian coast central italy depositional environments and luminescence chronology two cliff sites on the tyrrhenian coast of central italy have been investigated in order to investigate late pleistocene depositional environments by microfacies analysis and chronostratigraphy by luminescence age estimations both sections cover the period from the last interglacial to the end of the last glaciation in the buca dei corvi site an increasing rate of uplift is recognised which is responsible for significant environmental change and formation of the modern coastal fault scarp at around 9 ka in the golfo di baratti site the vertical succession of three marine horizons previously recognised by cortemiglia et al 1983 is attributed to the ois stages 5c 5a and 3 respectively this cliff section is affected by nne ssw orientated normal faults confirming that extentional structural processes are still active the coastal deposit of stage 3 today located at 7 m a s l suggests abnormal high uplift rate if the position of the palaeo shoreline was assumed at 40 to 50 m both central mediterranean coastal records strongly suggest that the eustatic sea level has dropped to a smaller amount than that of the open oceans

explicit treatment of inheritance in dating depositional surfaces using in situ 10be and 26al we describe a new strategy for dating depositional landscape surfaces using in situ produced cosmogenic radionuclides crns that removes the complication of nuclide inheritance by clasts prior to depositon two amalgamated samples each consisting of 30 clasts one from the surface and one from a fixed depth in the subsurface constrain this crn inheritance and date the surface the inheritance may be used to estimate minimum exhumation rates and maximum transport times within the geomorphic system we test the technique using sup 10 be and sup 26 al to date the third fr3 of five terraces along the fremont river utah and the third wr3 of 15 along the wind river wyoming whereas effective ages based solely upon the surface samples yield 118 138 ka fr3 and 93 ka wr3 the subsurface samples reveal that inheritance accounts for 22 wr3 to 43 fr3 of the total crn concentration taking this into account yeilds terrace ages of nearly 61 81 ka for fr3 and nearly 67 76 ka for wr3 we explore the dependence of age estimates on the accumulation history of the terrace silt caps 22 refs 3 figs 1 tab

late quaternary alluvial fans at the eastern end of the san bernardino mountains southern california abstract alluvial fans at the eastern end of the san bernardino mountains in southern california provide a record of climate modulated sediment transfer and erosion and are deformed and displaced in places by active faults alluvial fans within two study areas the mission creek and the whitewater river drainages were examined using geomorphic sedimentological and 10be terrestrial cosmogenic nuclide tcn surface exposure methods to define the timing of alluvial fan formation and erosion and to examine the role of climatic tectonic and autocyclic processes these alluvial fan complexes were studied because they are amongst the best preserved successions of alluvial fans in southern california and they are located at the mouths of two of the largest drainages whitewater river and mission creek in the san bernardino mountains and traverse major faults the mission creek and banning the alluvial fans comprise bouldery debris deposits that represent deposition dominated by flash flood and debris flow events tcn surface exposure dating indicates that abandonment incision of alluvial fan surfaces date to early in the last glacial or more likely the penultimate glacial cycle to marine isotope stage mis 4 and to the holocene the lack of alluvial fan ages during the latter part of the last glacial mis 2 and 3 suggests that there has been little alluvial fan lobe deposition incision during that time this is similar to findings for many other alluvial fans throughout the american southwest and supports the view that there is a strong climatic control on alluvial fan formation throughout this region furthermore the oldest alluvial fan surfaces in the mission creek region are beheaded by the whitewater river drainage showing that the oldest alluvial fans in the mission creek region underwent significant capture by the whitewater river drainage this shows the autocyclic controls are also important on alluvial fan evolution in this region but the importance of these processes to alluvial fan development in other regions of the american southwest needs to be more fully assessed the alluvial fans in the mission creek area traverse the mission creek fault but are not deformed by it which suggests that there may have been little if any movement along this fault since at least mis 4 in contrast alluvial fans in the whitewater river study are displaced by active faults highlighting the influence of tectonism on alluvial fan development in this region in addition to illustrating the importance of climatic controls on the development of alluvial fans in the american southwest a classic region for alluvial fan studies this study illustrates the complex mixture of autocyclic and allocyclic factors that force alluvial fan development in tectonically active settings

isotopic insights into smoothening of abandoned fan surfaces southern california cosmogenic nuclide concentrations measured on abandoned fan surfaces along the mojave section of the san andreas fault suggest that sediment is generated transported and removed from the fans on the order of 30 40 kyr we measured in situ produced cosmogenic 10 be and in some cases 26 al in boulders n 15 surface sediment n 15 and one depth profile n 9 nuclide concentrations in surface sediments and boulders underestimate fan ages suggesting that 10 be accumulation is largely controlled by the geomorphic processes that operate on the surfaces of the fans and not by their ages field observations grain size distribution and cosmogenic nuclide data suggest that over time boulders weather into grus and the bar sediments diffuse into the adjacent swales as fans grow older the relief between bars and swales decreases the sediment transport rate from bars to swales decreases and the surface processes that erode the fan become uniform over the entire fan surface the nuclide data therefore suggest that over time the difference in 10 be concentration between bars and swales increases to a maximum until the topographic relief between bars and swales is minimized resulting in a common surface lowering rate and common 10 be concentrations across the fan during this phase the entire fan is lowered homogeneously at a rate of 10 15 mm kyr 1

palaeoclimate and palaeoenvironmental responses in the western mediterranean over the last 140 ka evidence from mallorca spain climatic change in the western mediterranean basin over the last 140 ka has been investigated from sediment and soil sequences along the coast of the northeastern part of mallorca spain palaeoclimate and palaeoenvironments are reconstructed from sediment and soil structures marine and terrestrial molluscan fauna grain size distributions mineral magnetics sediment and soil chemistry sem and oxygen isotope values dating is by osl and amino acid geochronometry along with marine molluscan faunal assemblages all oxygen isotope stages and substages from ois 6 to 1 are recorded mean annual temperatures m a t of c 19 2 c for the climatic optimum of the last interglacial compare with c 17 3 c for the present and are associated with high sea level extensive woodland and stable soils although wide temperature ranges are detected during this stage with values as low as c 10 3 c through ois 5d to 5a m a t fluctuated from 8 2 c to 17 9 c low sea level open vegetation effective river activity and aeolian sand and dust deposition characterize 5d and 5b while relatively high sea level and soil development on stable landscapes dominate ois 5c and 5a ois 4 is represented by m a t of c 4 9 c with aeolian sand and loess deposition limited river activity and weak soil development loess deposition persisted into ois 3 but at this time the m a t was c 13 c and with higher humidity and vegetation growth during the lgm ois 2 m a t was c 8 1 c and effective river slope and aeolian processes along with associated with limited vegetation cover were responsible for the most extensive changes in the landscape major rates of change occur during periods of climatic deterioration when the high levels of geomorphic energy were imposed on a landscape undergoing a breakdown of vegetation cover

rapid sea level fall and deep ocean temperature change since the last interglacial period we have dated huon peninsula papua new guinea and barbados corals that formed at times since the last interglacial period applying both 230 th and 231 pa dating techniques as a test of age accuracy we show that marine isotope stage mis 5e ended prior to 113 1 8 0 7 kyr when sea level was 319 m during mis 5b sea level was 357 m at 92 6 8 0 5 kyr having dropped about 40 m in approximately 10 kyr during the mis 5c 5b transition sea level then rose more than 40 m during the mis 5b 5a transition also in about 10 kyr mis 5a lasted until at least 76 2 8 0 4 kyr at a level of 324 m at that time combined with earlier data that places mis 4 sea level at 381 m at 70 8 kyr our late mis 5a data indicate that sea level fell almost 60 m in less than 6 kyr 10 6 m kyr during the mis 5 4 transition the magnitude of the drop is half that of the glacial interglacial amplitude and approximatelyequivalent to the volume of the present dayantarctic ice sheet during this interval the minimum average rate of net continental ice accumulation was 18 cm yr likely facilitated by efficient moisture transport from lower latitudes at three specific times 60 6 8 0 3 50 8 8 0 3 and 36 8 0 2 kyr during mis 3 sea level was between 385 and 374 m sea level then dropped to 3107 m at 23 7 8 0 1 kyr early in mis 2 before dropping further to last glacial maximum lgm values and then rising to present values during the last deglaciation times of rapid sea level drop correspond to times of high winter insolation at low northern latitudes and high winter latitudinal gradients in northern hemisphere insolation supporting the idea that these factors mayhave resulted in high water vapor pressure in moisture sources and efficient moisture transport to high latitude glaciers therebycontributing to glacial buildup we combined our sea level results with deep sea n 18 o records as a means of estimating the temperature and ice volume components in the marine n 18 o record this analysis confirms large deep ocean temperature shifts following mis 5e and during termination i deep ocean temperatures changed bymuch smaller amounts between mis 5c and 2 maximum temperature shift in the deep pacific is about 2 whereas the shift at a site in the atlantic is 4 under glacial conditions temperatures at both sites are near the freezing point the shift in the atlantic is likelycaused bya combination of changing proportions of northern and southern source waters as well as changing temperature at the sites where these deep waters form

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

late neogene stratigraphy and tectonic control on facies evolution in the laguna salada basin northern baja california mexico abstract the laguna salada basin lsb in northeastern baja california records late neogene marine incursions in the salton trough and progradation of the colorado river delta early subsidence and subsequent tectonic erosion are related to evolution of the sierra el mayor detachment fault during late miocene time

an enhanced role for the tropical pacific on the humid pleistocene holocene transition in southwestern north america abstract climate effects on landscape evolution during the late pleistocene holocene transition 14 6 8 ka in southwestern north america traditionally are linked to the activity of the north american monsoon and to vegetation change related to a decrease in winter precipitation acting in response to orbital cyclicity we performed an integrated analysis of regional alluvial fan lacustrine and paleobotanical records for the area comparing them with hemispheric and regional paleoclimate proxies our focus was on the potential role the tropical pacific has as a synoptic pattern modulator and moisture source for hydrogeomorphic activity in the region our analysis indicates that the onset of alluvial fan aggradation in most of the region at 13 5 ka could have been a response to semi permanent el nino like conditions in the tropical pacific which enhanced the frequency of winter frontal storms as well as increased penetration of tropical cyclones in the region the north american monsoon was restricted in extent and intensity until 7 ka and probably was not a major factor in alluvial fan aggradation a second stage of alluvial fan aggradation from 11 5 to 9 ka was dominated by hyper concentrated flows and sheet flood sedimentation along with deposition in fluvial settings storms were probably were linked to landfall of enhanced water vapor bands in the leading edge of winter extra tropical cyclones with moisture advected directly from the tropical pacific at 8 ka favorable conditions for the occurrence of these storms waned and storm tracks shifted northward analysis of modern analogs for storm types described above as prevalent during this period indicates that changes in circulation patterns across the tropical pacific can affect storm properties enough to explain the observed geomorphic effects regardless of other factors traditionally considered of large impact like vegetation change our results suggest that the tropical pacific plays a larger role than currently thought in landscape evolution of the region

timing and controls on late quaternary landscape development along the eastern sierra el mayor range front in northern baja california mexico abstract the sierra el mayor sierra cucapa mountain range in northern baja separates the colorado river delta from the laguna salada basin and is important in terms of understanding the structural transition from the northern gulf extensional province to the san andreas system one of the principal quaternary landscape features of the eastern sierra el mayor sierra cucapa is a prominent surface that slopes 1 2 eastward towards the colorado river delta along the eastern side of the sierra el mayor and facing the colorado river delta but not along other piedmont mountain fronts that face the delta this surface is terminated by a series of stepped terrace surfaces the terrace surfaces are cut into fluvial deltaic deposits from the colorado river delta system and are capped by 1 m thick gravels optically stimulated luminescence ages from interbedded coarse sands in the capping gravels of the upper surface and two of the inset terraces range from 17 to 31 ka average 24 3 ka but lack a systematic age trend from upper to lower surface the underlying fluvial deltaic deposits have older optically stimulated luminescence ages of 31 to 39 ka and suggest colorado river delta deposition during the relatively stable interstadial of the middle wisconsinan substage marine isotope stage 3 when sea level was ca 60 to 80 m samples from depth profiles in the capping gravels and from the top of the upper surface have a mean 10 be terrestrial cosmogenic nuclide age of 59 5 ka when corrected for inheritance an average age of 21 ka is computed for exposure of the capping gravels on the upper surface and inset terraces which is in the range of the optically stimulated luminescence burial ages both the upper surface and inset terraces formed 17 30 ka at a transition time from dry to relatively wet climate when increased aggradation caused alluvial fan development on the upper surface regionally these surfaces correlate with the q2c q3a age deposits of the southwestern north america alluvial fan and terrace deposits sea level was also falling rapidly at this time which may have caused the colorado river to become entrenched near the range front thus allowing rapid response and down cutting to form the inset terraces on the east side of the sierra el mayor facing the delta assuming the 34 ka delta deposits graded to a base level that was 60 to 80 m during marine isotope stage 3 the computed surface uplift rate for the eastern side of the sierra el mayor is 2 1 2 7 mm yr this uplift may be accommodated on a fault or fault system that is a southward extension of the mexicali spreading and seismic zone that is buried beneath the colorado river delta east of the sierra el mayor the uplift rates from this study are consistent with geologic and geodetic data for the sierra el mayor and sierra cucapa and account for much of the missing extensional strain across the area

reconciliation of late quaternary sea levels derived from coral terraces at huon peninsula with deep sea oxygen isotope records a major discrepancy between the late quaternary sea level changes derived from raised coral reef terraces at the huon peninsula in papua new guinea and from oxygen isotopes in deep sea cores is resolved the two methods agree closely from 120 ka to 80 ka and from 20 ka to 0 ka ka 1000 yr before present but between 70 and 30 ka the isotopic sea levels are 20 40 m lower than the huon peninsula sea levels derived in earlier studies new high precision u series age measurements and revised stratigraphic data for huon peninsula terraces aged between 30 and 70 ka now give similar sea levels to those based on deep sea oxygen isotope data planktonic and benthic 18o data using the sea level and deep sea isotopic data oxygen isotope ratios are calculated for the northern continental ice sheets through the last glacial cycle and are consistent with results from greenland ice cores the record of ice volume changes through the last glacial cycle now appears to be reasonably complete