eocene climate record of a high southern latitude continental shelf seymour island antarctica a high resolution record of eocene paleotemperature variation is preserved within the high southern latitude marine shelf succession of the la meseta formation on seymour island off the ne side of the antarctic peninsula 87 sr 86 sr ratios of bivalve shell carbonate indicate that the la meseta formation spans virtually the entire eocene and suggest the presence of an early middle eocene unconformity paleoclimatic and paleoceanographic inferences are based on the stable oxygen and carbon isotope values of two genera of bivalves collected with a high degree of stratigraphic resolution within the formation and with multiple replicate samples from each horizon 18 o data indicate roughly 10 c of cooling from the early eocene climatic optimum 15 c through the end of the eocene minimum 5 c much of which took place in two comparatively short intervals at ca 52 and ca 41 ma many features of the isotope curves generated from this eocene shelf section are apparent in 18 o and 13 c data from the southern and global oceans including warm intervals that likely correspond to the early and middle eocene climatic optima eeco and meco a rapid middle eocene shift to much more positive values is the most signifi cant in the section and refl ects a drop to universally cooler temperatures in the late middle and late eocene that might also be associated with a short lived glacial advance however even using a somewhat depleted value for 18 o of seawater in the antarctic peninsular region average seymour island shelf water paleotemperatures did not reach freezing before the end of the eocene 13 c data similarly refl ect the documented middle eocene surface ocean enrichment followed by more negative values but depletion is much more pronounced on seymour island and persists for the remainder of the eocene suggesting a combination of upwelling metabolic effects and or atypical carbon cycling on the shelf in this region isotope data capture information about changes in the paleoenvironment that also had consequences for the biota as published paleontological records document marked change in the nature of terrestrial and marine biota at this time the fact that middle eocene cooling and biotic turnover in the peninsular region correspond well in time to the proposed initial opening of drake passage suggests that the formation of gateways in addition to changes in pco 2 had signifi cant consequences for the earth s climate system during the paleogene

seismic stratigraphy of baltimore canyon trough examination of approximately 3 000 km of multichannel seismic reflection profiles collected over the u s middle atlantic shelf cape hatteras to long island shows that the margin was rifted prior to the separation of africa and north america and that it broadly subsided after the separation major accumulation of sediment is centered in the baltimore canyon trough where more than 15 km of triassic and younger sedimentary rocks has been deposited the trough is asymmetric in that the thickest sedimentary section is beneath the outer part of the shelf seaward of a hinge zone further the trough is wider on the north off new jersey than it is seaward of virginia flanking the trough are two block fault platforms long island and carolina where thickness of the sedime tary cover is 1 to 4 km eight depositional sequences have been delineated in analysis of the profiles by use of the techniques vail and others have presented in aapg memoir 26 marked changes in reflection characteristics and unconformities are used to bound the sequences the oldest sequence late triassic early jurassic is thought to be nonmarine and restricted marine sediments associated with a complexly faulted crust the changing seismic facies of younger sequences chronicle the transition to more open marine shelf and slope paleoenvironments during the cretaceous and tertiary the thickest units accumulated during a phase of rapid basin subsidence in the jurassic sediment accumulation decreased substantially during the late cretaceous and cenozoic so that the sequences are thinner and unconformities re more evident the most conspicuous unconformities seismically are correlated with the albian turonian coniacian late cretaceous paleocene oligocene and late miocene early pliocene by correlation with cost continental offshore stratigraphic test and coastline wells several of these breaks coincide with pronounced fluctuations in the vail curve of relative sea level particularly during the tertiary when indications of falling sea level were widespread lastly the records confirm the presence of a carbonate platform along the seaward edge of the trough during the jurassic and early cretaceous the stages of formation of the continental margin here are similar to those of the margin off the canadian maritime provinces

three dimensional dynamic simulation of the 1992 landers earthquake the 1992 landers california earthquake magnitude 7 3 was modeled as the propagation of a spontaneous rupture controlled by a realistic prestress distribution with the use of a three dimensional finite difference method the dynamic rupture reproduces the general slip pattern used to compute the initial stress distribution and generates near fault ground motions at the surface similar to observations the simulated rupture propagates on the fault along a complex path with highly variable speed and rise time changing the magnitude and pattern of the stress significantly the method provides the framework to estimate earthquake rupture parameters from recorded seismic and geodetic data

quantitative constraints on the origin of stratigraphic architecture at passive continental margins oligocene sedimentation in new jersey u s a the oligocene of the new jersey continental margin is divisible into as many as eight sequences and 23 lithofacies associations documented in a series of seven boreholes across the modern coastal plain this paper summarizes the sequence architecture of these de posits interpreted from high resolution biostratigraphy and sr isotope chemostratigraphy and evaluates the factors that governed patterns of sedimentation making use of previously published quantitative es timates of water depth changes and eustasy from 2 d foraminiferal paleoslope modeling and flexural backstripping each sequence is markedly wedge shaped thinning both landward of the rollover in the underlying sequence boundary the point at which the surface steepens into a clinoform and seaward of the rollover in the overlying boundary each bounding surface is associated with ev idence for offlap onlap geometry and at least locally with benthic fo raminiferal evidence for abrupt upward shoaling most unconformities merge up dip into a single surface marking the oligocene miocene boundary earliest oligocene unconformities 33 5 31 6 ma merge downdip as a result of sediment starvation on the deep shelf conven tional lithostratigraphic units within the new jersey oligocene are highly diachronous for example the base of atlantic city formation at cape may a downdip borehole is at least 6 6 myr younger than the top of the same formation at acgs 4 an updip borehole factors controlling patterns of sedimentation include 1 a terraced physiography with gradients ranging from 1 1 000 0 06 al plain and shallow shelf and 1 500 0 118 on the deep shelf to 1 100 1 08 on an intermediate slope 2 generally low siliciclastic sed iment flux with in situ production of authigenic glauconite especially during times of transgression 3 a location landward of the hinge zone of the passive margin with slow tectonic subsidence augmented by compaction and sediment loading 4 low to moderate amplitudes and rates of eustatic change 10 50 m over spans of 1 2 myr and 5 an active wave climate that permitted efficient lateral transport and complete bypass of sediment at paleodepths of at least 20 6 10 m sequence architecture in the new jersey oligocene differs from that of the standard exxon model sequences are highstand dominated in spite of deposition and preservation largely seaward of the rollover in each underlying sequence boundary transgressive systems tracts are thin recognizable lowstand units did not form because efficient transfer of sediment across the shallow shelf combined with the ab sence of major river systems in the area of study prevented the re organization of sedimentation patterns commonly associated with point source development in spite of rates of eustatic fall considerably greater than the local rate of tectonic subsidence repeated eustatic rises and falls are expressed primarily by variations in paleo water depth although 65 80 of the shallow shelf that had been flooded during each rise became subaerially exposed during the subsequent fall well developed offlap at each sequence boundary is due primarily to marine bypassing and degradation rather than to forced regres sion sequence boundaries correspond in time at their correlative conformities not with the onset of falling relative sea level but with the start of eustatic rise

stable isotopic evidence for relative and eustatic sea level changes in eocene to oligocene carbonates baldwin county alabama eocene to oligocene marine carbonate shelf deposits in a continuous core in baldwin county alabama were evaluated within a sequence stratigraphic framework to determine characteristic stable isotopic responses to inferred fluctuations in sea level due to a greater sampling density per unit of time stable isotopes in this core reveal more defined trends than have previously been reported from dsdp odp deep sea drilling project ocean drilling project records and from more land ward sections that have undergone intense sub aerial alteration or erosion the 18 o signature records eustatic sea level 18 o becomes heavier as eustatic sea level falls and lighter as eustatic sea level rises 18 o records a secular shift to heavy from the early eocene to oligocene of 3 0 the 13 c signature records relative sea level change paleobathymetry 13 c generally becomes heavier in shallower water deposits and lighter in deeper water deposits however in planktonic oozes 13 c may shift to heavy 13 c also records a secular shift to heavy from the early eocene to the oligocene of 3 5 although minor diagenetic perturbations in the stable isotopes are present the depositional signal dominates the isotopic signal spar cements generally result in lighter 18 o and 13 c if the dolomite is 20 dolomitization results in heavier 18 o and 13 c

a two asperity fault model with wave radiation abstract we study the dynamics of a fault containing two asperities having different strengths and subject to a constant strain rate the fault is modeled by a discrete dynamical system with two degrees of freedom that are the slip deficits of the asperities the radiation of elastic waves during the slipping modes is taken into account by introducing a term proportional to slip rate in the equations of motion we give a complete analytical solution of the four dynamic modes of the system any seismic event can be expressed as a sequence of modes for which the moment rate the spectrum and the total seismic moment can be calculated we consider the energy budget of the event and calculate the seismic efficiency the presence of radiation may remarkably change the evolution of the system from a given state since it moves the boundaries between the different subsets of the sticking region in addition the slip amplitude in a seismic event is smaller while the slip duration is longer in the presence of radiation the shape of the moment rate function depends on the seismic efficiency and the seismic moment decreases with increasing efficiency at constant radiated energy as an application of the model we consider the 1964 great alaska earthquake and calculate the mode durations the slip distribution the moment rate function and the seismic moment of the earthquake obtaining values that are consistent with observations

complex events in a fault model with interacting asperities abstract the dynamics of a fault with heterogeneous friction is studied by employing a discrete fault model with two asperities of different strengths the average values of stress friction and slip on each asperity are considered and the state of the fault is described by the slip deficits of the asperities as functions of time the fault has three different slipping modes corresponding to the asperities slipping one at a time or simultaneously any seismic event produced by the fault is a sequence of n slipping modes according to initial conditions seismic events can be different sequences of slipping modes implying different moment rates and seismic moments each event can be represented geometrically in the state space by an orbit that is the union of n damped lissajous curves we focus our interest on events that are sequences of two or more slipping modes they show a complex stress interchange between the asperities and a complex temporal pattern of slip rate the initial stress distribution producing these events is not uniform on the fault we calculate the stress drop the moment rate and the frequency spectrum of the events showing how these quantities depend on initial conditions these events have the greatest seismic moments that can be produced by fault slip as an example we model the moment rate of the 1992 landers california earthquake that can be described as the consecutive failure of two asperities one of which has a double strength than the other and evaluate the evolution of stress distribution on the fault during the event

strontium isotope and sequence stratigraphy of the miocene kirkwood formation southern new jersey we use sr isotope stratigraphy to correlate the miocene kirkwood formation of the new jersey coastal plain to the geomagnetic polarity time scale gpts and to ascertain the age of miocene depositional sequences sr isotope stratigraphy confirms diatom biostratigraphy which delineates three kirkwood sequences corresponding to east coast diatom zone ecdz 1 ecdz 2 and ecdz 6 of andrews 1988 sr isotope age estimates of the lowermost sequence ecdz 1 range from 19 2 to 22 6 ma 0 5 m y the middle sequence ecdz 2 ranges from 15 5 to 17 4 ma 0 5 m y a disconformity within ecdz 2 at the belleplain state forest borehole and the wildwood 198a well separates it into two sequences with a possible hiatus from 17 to 16 ma sr isotope age estimates of the upper kirkwood sequence ecdz 6 are not as certain and range from 11 5 to 13 6 ma 0 8 ma a shorter age range of 12 2 13 6 ma for this sequence is supported by its assignment to the d stauracanthus silicoflagellate subzone sedimentation rates were as high as 40 m per million years during deposition of the kirkwood formation suggesting possible tectonic influences on depositional history the timing of lower to middle miocene sequence boundaries from the new jersey coastal plain compares well with other indicators of sea level change including oxygen isotopes miller and others 1991b the global sea level record of haq and others 1987 and the offshore new jersey sequence boundaries of greenlee and others 1992 thus both tectonic and eustatic changes influenced miocene depositional history of the new jersey coastal plain

stratigraphic sequences and their chronostratigraphic correlation abstract the exxon sequence models of posamentier and coworkers incorporate two concepts which i question they suggest that rivers grade to a bayline but evidence from modern major rivers indicates that they do not they also proposed that fluvial sedimentary accomodation space is generated by the seaward shift in equilibrium profiles during sea level fall but this is too simplistic a model based on the use of schematic continental margin configurations which do not incorporate real slope and relief data in most cases a fall in base level leads to deltaic progradation and upstream fluvial incision most coastal plain fluvial wedges result from two processes sea level rise with the drowning and filling of estuaries and active source area tectonism major tectonic events adjacent to foreland basins such as terrane collisions lead to the development of sequences of third order type duration approximately 1 15 m y changes in intraplate stress regimes resulting from changes in regional plate kinematics have a similar episodicity and can be shown to be responsible for some third order cycles on extensional continental margins examination of the chronostratigraphic basis of the mesozoic cenozoic cycle chart of haq and coworkers reveals internal inconsistencies and an unrealistic downplaying of the built in potential for error this chart is not an approved global standard and it should be used with extreme caution

abrupt deep sea warming palaeoceanographic changes and benthic extinctions at the end of the palaeocene a remarkable oxygen and carbon isotope excursion occurred in antarctic waters near the end of the palaeocene 57 33 myr ago indicating rapid global warming and oceanographic changes that caused one of the largest deep sea benthic extinctions of the past 90 million years in contrast the oceanic plankton were largely unaffected implying a decoupling of the deep and shallow ecosystems the data suggest that for a few thousand years ocean circulation underwent fundamental changes producing a transient state that although brief had long term effects on environmental and biotic evolution

cretaceous to eocene sea level fluctuations on the new jersey margin abstract the new jersey margin contains an extensive record of cretaceous to eocene sea level fluctuations these events have been documented on the basis of sedimentology benthic foraminiferal paleobathymetry paleoslope biostratigraphic recognition of unconformities and their associated hiatuses and on seismic reflection records the record of sea level change for the new jersey margin shows a long term second order rise beginning in the upper albian that is punctuated by numerous third order cycles of change in the upper cretaceous paleocene and eocene the sequences deposited during these cycles that are most readily recognizable are separated by type 1 unconformities sequences bracketed by one or two type 2 unconformities are more difficult to resolve although many have been identified sequences shown on the cycle chart of haq et al 1987 of less than 1 ma duration are the most difficult to recognize and many have not been identified in the new jersey section benthic foraminiferal paleoslope studies indicate that relative sea level rise on the new jersey margin varied on the order of 10 120 m above present sea level much of the preserved record in the coastal plain consists of sediments deposited during rising sea level this has led to a stacked record of sea level rise events separated by unconformities

long term dynamics of a fault with two asperities of different strengths summary a fault made of two segments or asperities having different strengths and subject to a constant strain rate is considered the fault is modelled by a discrete dynamical system made of two blockscoupledbyaspringandpulledatconstantvelocityonaroughplane wegiveacomplete analytical solution for the evolution of the system the long term behaviour of the fault is studied by calculating the orbits of the system in the phase space the dynamics of the system has four different modes and produces a variety of behaviours the asperities may slip one at a time originating a medium size earthquake or simultaneously originating a large earthquake in the latter case the focus may be at one asperity or at the other in some cases the weaker asperity may slip twice both before and after the failure of the stronger asperity the time pattern of the seismic events generated by the fault is controlled by the stress distribution on the asperities and may include many different behaviours we devise suitable correspondence rules allowing application of the discrete model to real fault systems as an example the model is applied to the 1964 great alaska earthquake which was originated by the failure of two asperities and a possible evolution of this fault system is discussed

oligocene glacio eustasy and erosion on the margins of the north atlantic oligocene foraminiferal 18 o records suggest the development of ice caps inferred glacio eustatic falls at ca 36 31 and 25 ma biostratigraphic analyses of wells from the united states east coast and irish continental margins consistently show that upper oligocene sediments overlie a diachronous erosional surface underlain by lower oligocene to eocene strata at the minimum the hiatus extends between ca 34 and 30 ma we speculate that erosion during a glacio eustatic fall near the early late oligocene boundary ca 32 31 ma developed 1 an unconformity on the margins 2 numerous canyons noted in seismic profiles from the margins of the north atlantic and 3 a coastal offlap event using 18 o data we apply a model for eustatic changes and margin response that explains the relationships of sea level unconformities and coastal onlap offlap events

tertiary oxygen isotope synthesis sea level history and continental margin erosion tertiary benthic and planktonic foraminiferal oxygen isotope records are correlated to a standard geomagnetic polarity time scale making use of improved chronostratigraphic control and additional oligocene isotope data synchronous changes in both benthic and planktonic 18o values which occurred in the oligocene to miocene 36 5 2 ma are interpreted in part to represent ice growth and decay the inferred ice growth events correlate with erosion on passive continental margins as interpreted from seismic and chronostratigraphic records this association is consistent with a link between oligocene to miocene erosional events and rapid 15 m m y glacioeustatic lowerings of about 50 m high benthic foraminiferal 18o values suggest the presence of continental ice sheets during much of the oligocene to recent 36 0 ma substantially ice free conditions probably existed throughout the paleocene and eocene 66 36 ma the mechanisms and rates of sea level change apparently were different between the early and late tertiary with glacioeustatic changes restricted to the past 36 m y pre oligocene erosion on passive continental margins was caused by eustatic lowerings resulting from global spreading rate changes we apply a model which suggests that large areas of the continental shelves were subaerially exposed during such tectonoeustatic lowstands stimulating slope failure and submarine erosion the different mechanisms and rates of eustatic change may have caused contrasting erosional patterns between the early and late tertiary on passive continental margins this speculation needs to be confirmed by examination of data from several passive margins

stratigraphy petrography and correlation of late cenozoic middle atlantic coastal plain deposits implications for late stage passive margin geologic evolution regional chronostratigraphic correlation of middle atlantic upper coastal plain and fall zone fluvial deposits long thought to represent the updip proximal facies of a well dated post oligocene marine sequence in the salisbury embayment remains incomplete in part because of the paucity of biostratigraphic data petrography based lithostratigraphic correlations provide an opportunity to extend age control present in downdip marine deposits updip to fluvial deposits thus establishing the means for a regional chronostratigraphic correlation previous stratigraphic studies in new jersey delmarva southern maryland virginia and the central appalachian piedmont are linked by a crucial sequence of fluvial deposits at the head of chesapeake bay here petrography based lithostratigraphic correlations demonstrate 1 late oligocene late miocene susquehanna river dominated polygenetic quartzose fluvial aggradation bryn mawr formation 2 pliocene heterolithic but quartz dominated fluvial terrace and alluvial fan deposition perryville formation 3 pliocene early pleistocene paleo delaware hudson river dominated lithic and feldspathic rich fluvial aggradation pensauken formation and 4 the initiation of estuarine conditions turkey point beds by early pleistocene time these results are synthesized to propose a new late cenozoic regional chronostratigraphic correlation and depositional history for the salisbury embayment the correlation elucidates a complex interaction between passive margin isostasy tectonics eustasy and sediment source

coseismic and postseismic slip of the 2004 parkfield earthquake from space geodetic data we invert interferometric synthetic aperture radar insar data jointly with campaign and continuous global positioning system gps data for slip in the coseismic and postseismic periods of the 2004 parkfield earthquake the insar dataset consists of eight interferograms from data collected by the envisat and radarsat satellites spanning the time of the earthquake and variable amounts of the postseismic period the two datasets complement each other with the insar providing dense sampling of motion in the range direction of the satellite and the gps providing more sparse but three dimensional measurements of ground motion the model assumes exponential decay of the postseismic slip with a decay time constant of 0 087 years determined from time series modeling of continuous gps and creepmeter data we find a geodetic moment magnitude of m 6 2 for a 1 day coseismic model and m w 6 1 for the entire postseismic period the coseismic rupture occurred mainly in two slip asperities one near the hypocenter and the other 15 20 km north postseismic slip occurred on the shallow portions of the fault and near the rupture areas of two m 5 0 aftershocks a comparison of the geodetic slip models with seismic moment estimates suggests that the coseismic moment release of the parkfield earthquake is as little as 25 of the total this underlines the importance of aseismic slip in the slip budget for the parkfield segment online material complete data tables and supplemental tables

reconstruction of tertiary progradation and clinoform development on the new jersey passive margin by 2 d backstripping we have reconstructed the oligocene to middle miocene paleobathymetry and stratigraphy of the new jersey margin using a modified backstripping technique by analyzing the geometry of the margin through time we investigate its response to fluctuating sea level changing climate and variable sediment supply during the tertiary the reconstructions reveal a change in the margin morphology from a more steeply dipping 1 300 to 1 500 carbonate ramp in the eocene to a flatter shelf with a sharp shelf edge at present this was accomplished by an increase in the terrigenous sediment supply that filled available accommodation and caused progradation across the margin we link the increase in sediment flux with climatic cooling rather than tectonic processes the progradation is evidenced by a series of clinoforms whose formation was modulated by sea level and which extend over 100 km across the shelf the height and dip of the clinoforms increased as they extended onto the deeper parts of the earlier ramp the miocene clinoform rollovers at the new jersey margin had water depths of60 130 m and are interpreted as the edge of a new continental shelf built over the older ramp sea level fall was probably insufficient to drive the miocene shorelines past the shelf breaks thus measurements of sea level amplitude based upon coastal onlap over the clinoforms are not reliable 1999 elsevier science b v all rights reserved

integrated late eocene oligocene stratigraphy of the alabama coastal plain correlation of hiatuses and stratal surfaces to glacioeustatic lowerings we integrated strontium and oxygen isotopic biostratigraphic and magnetostratigraphic studies of two upper eocene oligocene boreholes drilled near bay minette and st stephens quarry ssq alabama continuous coring provided fresh unweathered material for magnetostratigraphic studies minimizing problems reported from nearby outcrops difficulties with each technique were encountered because of diagenesis absence of marker fossils and the presence of unconformities however by integrating results from isotopic stratigraphy biostratigraphy and magnetostratigraphy we correlated these relatively shallow water deposits to the geomagnetic polarity time scale gpts at the ssq borehole the upper eocene to lower oligocene section is apparently complete within our stratigraphic resolution 0 2 0 5 m y allowing us to estimate the ages of several stratal surfaces late eocene sr isotope age estimates are as expected at the ssq borehole but oligocene ages are 1 m y older than expected due to diagenesis at the bay minette borehole a latest eocene earliest oligocene and a late early oligocene hiatus were detected we correlate these two hiatuses and stratal surfaces at ssq with global 18o increases inferred to represent glacioeustatic lowerings and with evidence for hiatuses on other continental margins 1 a distinct disconformity at the base of the chickasawhay limestone at both boreholes and a hiatus at bay minette correlates with a global 18o increase we revise the age of this surface equivalent to the tb 1 1 sequence boundary making it 2 m y older than previously reported and 2 a surface at the top of the shubuta member lowermost oligocene has been interpreted both as a condensed section and a disconformity this surface at ssq and a hiatus at bay minette correlate with a sharp global 18o increase and with hiatuses on the new jersey and irish margins the timing of the hiatuses and stratal surfaces correlates with the inflection of the 18o increases and not with the maximum values supporting models that indicate that unconformities form during the maximum rates of sea level fall

the role of the sediment load in sequence stratigraphy the influence of flexural isostasy and compaction simplified physically based models are utilized in order to examine the effects of sea level sedimentation tectonic subsidence isostatic compensation and compaction on development of unconformities unconformities divide volumes of relatively conformable sediments defining the time and spatial extent of sedimentary sequences the model parameters are varied both individually and in concert in order to isolate their contributions to sequence architecture these models reveal the importance of sedimentation and subsidence rates as well as sea level amplitude and rate in determining the type and extent of sequence boundary formed sedimentation and subsidence rate can vary significantly within and between margins producing different sequence boundaries given an identical eustatic sea level fall it is shown that sea level amplitude plays an important role in determining which systems tracts are present and sequence boundary timing for type 1 sequences and that sea level rate controls the same attributes in type 2 sequences isostatic compensation and compaction which have been described as secondary effects are shown to have considerable influence on sequence architecture these two processes due to isostatic response to sediment loading and sediment self loading initiate feedback by enhancing and partitioning accommodation space these additional effects invalidate application of the equilibrium point as a guide to where and how all accommodation space is created the manner in which flexure distributes accommodation space is a function of lithospheric rigidities higher rigidities partition space laterally producing wide shelves which favor type 1 sequence boundaries whereas lower rigidities partition space vertically forming narrow shelves which favor type 2 sequence boundaries compaction generates a net landward shift of the shelf edge and favors type 2 sequence development both isostatic compensation and compaction introduce time delays in sequence development one consequence of compaction is to rotate sedimentary packages generating growth and leakage of anticlinal structures as fluids are driven from the underlying section this process has important implications for hydrocarbon migration in compaction dominated systems such as the gulf of mexico margin

initial investigation of the landers california earthquake of 28 june 1992 using terrascope the 1992 landers earthquake m s 7 5 m w 7 3 was recorded at six terrascope stations in southern california peak accelerations ranged from 0 16 g at svd 63 km to 0 0092 g at isa 245 km decreasing with distance away from the fault zone the peak velocity showed a different pattern reflecting the rupture directivity from south to north the largest peak velocity 19 cm sec was observed at gsc 125 km moment tensor inversion of long period surface waves yielded a mechanism with m 0 1 1 10 27 dyne cm m w 7 3 dip 74 rake 176 and strike 340 inversion of teleseismic p and s waves revealed two distinct sub events of 6 and 8 sec duration and about 10 sec apart the source parameters for the first and second events are m 0 1 9 10 26 dyne cm dip 83 rake 179 strike 359 and m 0 6 1 10 26 dyne cm dip 87 rake 178 strike 333 respectively the radiated wave energy e s was estimated as 4 3 10 23 ergs the ratio e s m 0 3 9 10 4 corresponds to a stress drop of 280 bars and suggests that the landers earthquake belongs to the group of high stress drop earthquakes and occurred on a fault with a long recurrence time the rupture directivity can be seen clearly in the records from pfo 68 km located to the south and gsc located to the north of the epicenter the maximum displacement at pfo is only 13 of that at gsc despite the shorter epicentral distance to pfo than to gsc the slip distribution determined with the empirical green s function method indicates that the landers earthquake consists of two distinct sub events about 30 km apart with the second sub event to the north being about twice as large as the first one this slip distribution is consistent with the teleseismic data and the surface offsets mapped in the field

evidence for iceberg armadas from east antarctica in the southern ocean during the late miocene and early pliocene abstract sediments from ocean drilling program site 1165 in the indian ocean sector of the southern ocean off prydz bay contain a series of layers that are rich in ice rafted debris ird here we present evidence that ird rich layers at site 1165 at 7 4 8 and 3 5 ma record short lived massive discharges of icebergs from wilkes land and adelie land more than 1500 kilometers to the east of the depositional site this distant source of icebergs is clearly defined by the presence of ird hornblende grains with 40ar 39ar ages of 1200 1100 ma and 1550 1500 ma ages that are not found on the east antarctic continent in locations closer to site 1165 this observation requires enormous amounts of detritus carrying drifting icebergs most likely in the form of large icebergs these events probably reflect destabilization surge and break up of ice streams on the wilkes land and adelie land margins of the east antarctic ice sheet in the vicinity of the low lying aurora and wilkes basins they occurred under warming conditions but each coast seems to have produced ice rafting events independently at different times the data presented here constitute the first evidence of far traveled icebergs from specific source areas around the east antarctic perimeter launch of these icebergs may have happened during quite dramatic events perhaps analogous to heinrich events in the north atlantic

paleocene to eocene benthic foraminiferal isotopes and assemblages implications for deepwater circulation early paleogene warm climates may have been linked to different modes and sources of deepwater formation warm polar temperatures of the paleocene and eocene may have resulted from either increased atmospheric trace gases or increased heat transport through deep and intermediate waters the possibility of increasing ocean heat transport through the production of warm saline deep waters wsdw in the tethyan region has generated considerable interest in addition general circulation model results indicate that deepwater source regions may be highly sensitive to changing basin configurations to decipher deepwater changes we examined detailed benthic foraminiferal faunal and isotopic records of the late paleocene through the early eocene 60 to 50 ma from two critical regions the north atlantic bay of biscay site 401 and the pacific shatsky rise site 577 these records are compared with published data from the southern ocean maud rise site 690 islas orcadas rise site 702 during the late paleocene similar benthic foraminiferal 18o values were recorded at all four sites this indicates uniform deepwater temperatures consistent with a single source of deep water the highest 13c values were recorded in the southern ocean and were 0 5 more positive than those of the pacific we infer that the southern ocean was proximal to a source of nutrient depleted deep water during the late paleocene upper paleocene reflector ab was cut on the western bermuda rise by cyclonically circulating bottom water also suggesting a vigorous source of bottom water in the southern ocean a dramatic negative excursion in both carbon and oxygen isotopes occurred in the latest paleocene in the southern ocean this is a short term 100 kyr globally synchronous event which also is apparent in both the atlantic and pacific records as a carbon isotopic excursion of approximately 1 faunal analyses from the north atlantic and pacific sites indicate that the largest benthic foraminiferal faunal turnover of the cenozoic was synchronous with the isotopic excursion lending support to the hypothesis that the extinctions were caused by a change in deepwater circulation we speculate that the southern ocean deepwater source was reduced or eliminated at the time of the excursion during the early eocene southern ocean 13c values remained enriched relative to the north atlantic and pacific however the southern ocean was also enriched in 18o relative to these basins we interpret that these patterns indicate that although the southern ocean was proximal to a source of cool nutrient depleted water the intermediate to upper deep water sites of the north atlantic and pacific were ventilated by a different source that probably originated in low latitudes i e wsdw

onshore offshore correlations of cretaceous fluvial deltaic sequences southern baltimore canyon trough we evaluate cretaceous depositional sequences on approximately 4400 km 2700 mi of newly released multichannel seismic profiles and five wells on the continental shelf in the southern baltimore canyon trough and tie the data to three wells drilled onshore in the maryland coastal plain seismic geometries coupled with facies and biostratigraphy from the wells are used to delineate mid cretaceous aptian turonian depositional sequences and paleogeography beneath these sequences 400 1000 m 1300 3300 ft of lower cretaceous sedimentary rocks underlie the modern shelf they thicken along strike to the southwest implying a southern sediment source aptian to cenomanian sediments were deposited in shelf to nearshore settings a landward movement of the depocenter and a shift toward facies indicative of deeper paleodepths marks a 107 yr mid cretaceous transgression within which we identify five sequences a composite maximum flooding surface mfs within the uppermost of these retrogradational units is associated with the cenomanian turonian boundary and ocean anoxic event 2 shingled lower turonian seismic reflections prograde across the outer shelf downlapping onto the composite mfs and are truncated by a mid turonian sequence boundary the upper cretaceous section thickens seaward and along strike to the northeast implying a northern source and little late cretaceous accommodation beneath the modern shelf mid cretaceous strata offshore maryland are likely sand prone considering their proximity to the correlative fluvial facies of the onshore potomac group these potential reservoir sands are capped by regional confining units generated by 107 yr global mean sea level flooding events and are excellent targets for supercritical carbon storage

the middle miocene climatic transition east antarctic ice sheet development deep ocean circulation and global carbon cycling abstract the middle miocene represents a major change in state in cenozoic climatic evolution following the climax of neogene warmth in the late early miocene at 16 ma the early stage of this climatic transition from 16 to 14 8 ma was marked by major short term variations in global climates east antarctic ice sheet eais volume sea level and deep ocean circulation in the later stage from 14 8 to 12 9 ma climatic developments included major growth of the eais and associated antarctic cooling a distinct increase in the meridional temperature gradient large fluctuations in sea level followed by a global sea level fall and important changes in deep water circulation including increased production of southern component water east antarctic ice sheet growth and polar cooling also had large effects on global carbon cycling and on the terrestrial biosphere including aridification of mid latitude continental regions increased stability of the eais after 14 8 ma represents a crucial step in the establishment of late neogene global climate systems what controlled these changes in polar climates and the east antarctic ice sheet deep ocean circulation changes probably played a major role in the evolution and variation in polar climates as they have throughout the cenozoic oxygen and carbon isotopic evidence for warm saline deep water production in the eastern tethyan northern indian ocean indicates that meridional heat transport to the antarctic inhibited cenozoic polar cooling and eais growth during the early middle miocene from 16 to 14 8 ma inferred competition between warm low latitude sources derived from the eastern tethyan northern indian ocean and a cold high latitude source southern component water from 16 to 14 8 ma may have been associated with instability in the antarctic climate and cryosphere reduction of warm saline deep water flow to the southern ocean at 14 8 ma may have decreased meridional heat transport to the antarctic cooling the region and leading to increased production of southern component water these middle miocene climatic and cryospheric changes in the antarctic had profound effects on marine and terrestrial climates as the meridional surface temperature gradient increased boundaries between climatic zones strengthened leading to increased aridification of mid latitude continental regions in australia africa and north and south america enhancing the development of grasslands and stimulating the evolution of grazing mammals

sequence stratigraphy eustasy or tectonic imprint sequence stratigraphy is viewed by many geologists as the expression in the stratigraphic record of the history of sea level changes sequence boundaries are its most distinctive elements and are used for global correlations until now correlations between unconformities and postulated lowerings of sea level have been seen primarily in terms of cause and effect relationships the postulated fall providing an explanation for the presence of an unconformity they have not been truly perceived in terms of stratigraphic correlations which would imply the establishment of synchrony between the cause and the effect to decipher the presence of a global sea level signal in the stratigraphic record the synchrony of sea level related unconformities in widely separated basins must be established which can be achieved by comparing the degree of overlap between hiatuses in different stratigraphic sections outcrop sections wells and the deep sea record reveal an apparently worldwide unconformity ies across the lower middle eocene boundary characterized by intensive reworking and or relatively rapid shallowing in some areas e g cyrenaica ne libya california egypt the lower middle eocene intervals in sections on the north atlantic margins have been correlated through magnetobiostratigraphy and the durations of the hiatuses have been precisely determined this record is compared with that in sections in other basins where shallowing and intensive reworking occur this study shows that there are two groups of unconformities and associated hiatuses around the lower middle eocene boundary the older hiatuses in the latest early eocene are generally short even on the shelf 1 m y the younger hiatuses in the early middle eocene are somewhat longer 2 m y the stratigraphic record around the lower middle eocene boundary suggests that there may be two mechanisms acting simultaneously to produce unconformities unconformities of a given age on the shelf may result from a global fall in sea level while their stratigraphically correlative unconformities on the slope and rise may result from tectonic instability unconformities related to the third order cycles in sea level changes in vail s model primarily may reflect tectonoeustasy

late paleocene to eocene paleoceanography of the equatorial pacific ocean stable isotopes recorded at ocean drilling program site 865 allison guyot an expanded and largely complete upper paleocene to upper eocene section was recovered from the pelagic cap overlying allison guyot mid pacific mountains at ocean drilling program odp site 865 18o26 n 179o33 w paleodepth 1300 1500 m reconstructions show that the site was within a few degrees of the equator during the paleogene because no other paleogene sections have been recovered in the pacific ocean at such a low latitude site 865 provides a unique record of equatorial pacific paleoceanography detailed stable isotopic investigations were conducted on three planktonic foraminiferal taxa species of acarinina morozovella and subbotina we studied benthic foraminiferal isotopes at much lower resolution on species of cibicidoides and lenticulina nuttallides truernpyi and gavelinella beccariiformis because of their exceptional rarity the 5180 and 513c stratigraphies from site 865 are generally similar to those derived from other paleocene and eocene sections the planktonic foraminiferal records at site 865 however include significantly less short term single sample variability than those from higher latitude sites indicating that this tropical oligotrophic location had a comparatively stable water column structure with a deep mixed layer and less seasonal variability low amplitude 0 1 0 8 o oscillations on timescales of 250 000 to 300 000 years correlate between the 513c records of all planktonic taxa and may represent fluctuations in the mixing intensity of surface waters peak sea surface temperatures of 24o 25oc occurred in the earliest eocene followed by a rapid cooling of 3 6oc in the late early eocene temperatures remained cool and stable through the middle eocene in the late eocene surface water temperatures decreased further vertical temperature gradients decreased dramatically in the late paleocene and were relatively constant through much of the eocene but increased markedly in the late eocene intermediate waters warmed through the late paleocene reaching a maximum temperature of 10oc in the early eocene cooling in the middle and late eocene paralleled that of surface waters with latest eocene temperatures below 5oc extinction patterns of benthic foraminifera in the latest paleocene were similar to those observed at other pacific sites and were coeval with a short term very rapid negative excursion in 513c values in planktonic and benthic taxa as at other sites during this excursion benthic foraminiferal 5180 values decreased markedly indicating warming of 4 to 6oc for tropical intermediate waters while planktonic taxa show slight warming 1 oc followed by 2oc of cooling convergence of 5180 values of planktonic and benthic foraminifera suggests that thermal gradients in the water column in this tropical location collapsed during the excursion these data are consistent with the hypothesis that equatorial pacific surface waters were a potential source of warm higher salinity waters which filled portions of the deep ocean in the latest paleocene oxygen isotopic data indicate that equator to high southern latitude sea surface thermal gradients decreased to as little as 4oc at the peak of the excursion suggesting some fundamental change in global heat transport

extension of the astronomically calibrated polarity time scale to the miocene pliocene boundary the early pleistocene to late pliocene astronomically calibrated time scale of shackleton et al 1 and hilgen 2 is extended to the miocene pliocene boundary this is done by correlating the detailed record of caco3 cycles in the trubi and the lower part of the overlying narbone formation rossello composite section sicily to the astronomical record using 1 inferred phase relations between these caco3 cycles and the corresponding orbital cycles of precession and eccentricity and 2 calibration points provided by the previously established astronomical calibration of sapropelitic layers which occur in the topmost part of the caco3 record 2 this correlation allows all small scale caco3 cycles in the rossello composite section to be coded after the correlative precession peak and to be dated astronomically with an accuracy of 1 ky in combination with the available high resolution magnetostratigraphy it further allows the construction of an astronomically calibrated geomagnetic polarity time scale for the major part of the gilbert and gauss chrons this new time scale gives ages for the reversal boundaries of the kaena 3 04 3 11 ma and mammoth 3 22 3 33 ma the gilbert gauss chron boundary 3 58 ma and the reversal boundaries of the cochiti 4 18 4 29 ma nunivak 4 48 4 62 ma sidufjall 4 80 4 89 ma and thvera 4 98 5 23 ma these ages are significantly older than the ages given by conventional time scales age discrepancies gradually increase with increasing age the age of 5 32 ma for the miocene pliocene boundary as defined by the base of the trubi on sicily is almost 0 5 m y 9 5 older than the presently accepted age of 4 86 ma 3 these considerable discrepancies with the conventional time scale can either be explained by an consistent error in the decay constants used in k ar radiometric dating or more likely by diffusional loss of radiogenic argon

effect of stress perturbations on the dynamics of a complex fault a plane fault containing two asperities subject to a constant strain rate by the motion of tectonic plates is considered the fault is modelled as a discrete dynamical system where the average values of stress friction and slip on each asperity are considered the state of the fault is described by the slip deficits of the asperities we study the behaviour of the system in the presence of stress perturbations that are supposed to be due to dislocations of neighbouring faults the fault complexity entails consequences that are not present in the case of a homogeneous fault a stress perturbation not only changes the occurrence time of the following earthquake but may also sensitively change the slip amplitude and area hence the seismic moment of the earthquake as well as the position of its hypocentre the greatest changes take place when simultaneous slip of asperities is involved a coulomb stress value can be assigned to each asperity the change in the difference between the coulomb stresses of the two asperities is a measure of how much the system gets closer to or farther from the condition for simultaneous slip as an example we consider the effect of the 1960 great chilean earthquake on the two asperity fault that produced the 2010 maule earthquake and calculate the changes in the moment rate and in the total seismic moment it results that in the absence of the 1960 earthquake the maule earthquake would have occurred several decades later and would have involved a different sequence of modes so that the moment rate function would have been very different with a longer duration and a greater seismic moment

the rupture process and tectonic implications of the great 1964 prince william sound earthquake we have determined the rupture history of the march 28 1964 prince william sound earthquake m w 9 2 from long period wwssn p wave seismograms source time functions determined from the long period p waves indicate two major pulses of moment release the first and largest moment pulse has a duration of approximately 100 seconds with a relatively smooth onset which reaches a peak moment release rate at about 75 seconds into the rupture the second smaller pulse of moment release starts at approximately 160 seconds after the origin time and has a duration of roughly 40 seconds because of the large size of this event and thus a deficiency of on scale digitizable p wave seismograms it is impossible to uniquely invert for the location of moment release however if we assume a rupture direction based on the aftershock distribution and the results of surface wave directivity studies we are able to locate the spatial distribution of moment along the length of the fault the first moment pulse most likely initiated near the epicenter at the northeastern down dip edge of the aftershock area and then spread over the fault surface in a semi circular fashion until the full width of the fault was activated the rupture then extended toward the southwest approximately 300 km ruff and kanamori 1983 the second moment pulse was located in the vicinity of kodiak island starting at 500 km southwest of the epicenter and extending to about 600 km although the aftershock area extends southwest past the second moment pulse by at least 100 km the moment release remained low we interpret the 1964 prince william sound earthquake as a multiple asperity rupture with a very large dominant asperity in the epicentral region and a second major but smaller asperity in the kodiak island region

the history of post miocene sea level change inferences from stratigraphic modeling of enewetak atoll the history of post miocene sea level change has been investigated using a quantitative one dimensional stratigraphic forward model the stratigraphic model produces synthetic stratigraphies including mineralogy and sediment age versus depth in response to changes in sea level subsidence sedimentation and diagenesis model outputs using sea level curves inferred from passive margin sequence stratigraphy and deep sea foraminiferal oxygen isotope stratigraphy were compared to the post miocene stratigraphy of enewetak atoll modeling results support high frequency 104 to 105 years fluctuations of post miocene sea level post miocene sea level elevations significantly greater than modern sea level elevation are not easily reconciled with the stratigraphy of enewetak atoll model data fit is maximized when a rapid subsidence rate for enewetak atoll is used alternatively model data fit may be maximized using a lower subsidence rate for enewetak and having post miocene sea level elevations significantly lower than modem sea level elevation given the present state of knowledge much work is still needed to accurately decipher the record of post miocene sea level change

orbitally paced climate oscillations across the oligocene miocene boundary the late oligocene and early miocene periods some 21 to 27 million years ago have generally been viewed as times of moderate global warmth and ice free conditions yet several lines of evidence suggest that this interval was punctuated by at least one and possibly several episodes of high latitude cooling and continental glaciation1 2 3 here we present stable isotope and per cent coarse fraction data from an equatorial western atlantic deep sea sediment core that provide high resolution records of the climate variability across the oligocene miocene transition 22 5 25 7 million years ago a strong 40 kyr periodicity in the oxygen isotope record is consistent with a high latitude orbital obliquity control on ice volume and temperature orbital influences are also apparent at precession and eccentricity frequencies including a series of 400 kyr oscillations that culminate in distinct maxima at the oligocene miocene boundary about 23 7 million years ago covariance between the carbon and oxygen isotope records suggests that the oceanic carbon cycle may have contributed to global cooling during the 400 kyr cycles particularly at the oligocene miocene boundary

a record of appalachian denudation in postrift mesozoic and cenozoic sedimentary deposits of the u s middle atlantic continental margin abstract the complex interplay between source terrain uplift basin subsidence paleoclimatic shifts and sea level change left an extensive sedimentary record in the contiguous offshore basins of the u s middle atlantic margin salisbury embayment baltimore canyon trough and hatteras basin isopach maps of 23 postrift lower jurassic to quaternary a allostratigraphic units coupled with a revised stratigraphic framework reveal that tectonism by regulating sediment supply accumulation rate dominated the interplay of forcing mechanisms tectonic pulses are evidenced by abruptly accelerated sediment accumulation marked latitudinal shifts in the location of depocenters and regional changes in lithofacies relatively rapid tectonic subsidence during the early and middle jurassic history of the basins may have enhanced sediment accumulation rates beginning in the late jurassic however subsidence rates decreased significantly though occasional short pulses of subsidence may have effected relative sea level rises sea level change heavily influenced the distribution and redistribution of sediments one they reached the basins and paleoclimate regulated the relative abundance of carbonates and evaporites in the basins we conclude that source terrains of the central appalachian highlands were tectonically uplifted intensely weathered and rapidly eroded three times since the late triassic 1 early to middle jurassic aalenian to callovian 2 mid early cretaceous barremian and 3 late cenozoic middle miocene intervals of tectonic quiescence following these three tectonic pulses provided conditions suitable for the formation of regional erosion surfaces geomorphic features commonly reported to characterize the central appalachian highlands this series of three irregularly spaced tectonic quiescent cycles does not however match the traditional four cycle concept of post triassic appalachian peneplanation

strontium isotopes and miocene sequence stratigraphy across the northeast florida platform abstract a preliminary assessment of miocene sea level fluctuations is presented based on the integration of sr derived ages and sequence stratigraphic concepts applied to subsamples of 12 cores that transect the hawthorn group on the northeast florida platform the hawthorn group section includes phosphorite nodules peloids and crusts as well as dolosilt and dolostone nodules and beds formed during early burial diagenesis of organic rich sediments deposited during periods of intensified and persistent upwelling associated with rising and maximum sea level the 87sr 86sr composition of phosphorite and dolomite is used to determine the age of in place phosphorite crusts and dolostone beds condensed sections and reworked phosphorite and dolostone sand and gravel unconformities and transgressive surfaces regional correlation of unconformities and condensed sections provides the basis for a sequence stratigraphic framework from which the age and relative amplitude of sea level fluctuations are constructed seven depositional sequences are identified from the data depositional sequences correspond to local sea level fluctuations with maximum water depths at approximately 25 24 21 20 19 18 17 15 14 12 11 9 and 8 6 ma greatest water depth apparently occurred at 17 15 ma

cenozoic global sea level sequences and the new jersey transect results from coastal plain and continental slope drilling the new jersey sea level transect was designed to evaluate the relationships among global sea level eustatic change unconformity bounded sequences and variations in subsidence sediment supply and climate on a passive continental margin by sampling and dating cenozoic strata from coastal plain and continental slope locations we show that sequence boundaries correlate within 0 5 myr regionally onshore offshore and interregionally new jersey alabama bahamas implicating a global cause sequence boundaries correlate with 18o increases for at least the past 42 myr consistent with an ice volume glacioeustatic control although a causal relationship is not required because of uncertainties in ages and correlations evidence for a causal connection is provided by preliminary miocene data from slope site 904 that directly link 18o increases with sequence boundaries we conclude that variation in the size of ice sheets has been a primary control on the formation of sequence boundaries since 42 ma we speculate that prior to this the growth and decay of small ice sheets caused small amplitude sea level changes 20 m in this supposedly ice free world because eocene sequence boundaries also appear to correlate with minor 18o increases subsidence estimates backstripping indicate amplitudes of short term million year scale lowerings that are consistent with estimates derived from 18o studies 25 50 m in the oligocene middle miocene and 10 20 m in the eocene and a long term lowering of 150 200 m over the past 65 myr consistent with estimates derived from volume changes on mid ocean ridges although our results are consistent with the general number and timing of paleocene to middle miocene sequences published by workers at exxon production research company our estimates of sea level amplitudes are substantially lower than theirs lithofacies patterns within sequences follow repetitive predictable patterns 1 coastal plain sequences consist of basal transgressive sands overlain by regressive highstand silts and quartz sands and 2 although slope lithofacies variations are subdued reworked sediments constitute lowstand deposits causing the strongest most extensive seismic reflections despite a primary eustatic control on sequence boundaries new jersey sequences were also influenced by changes in tectonics sediment supply and climate during the early to middle eocene low siliciclastic and high pelagic input associated with warm climates resulted in widespread carbonate deposition and thin sequences late middle eocene and earliest oligocene cooling events curtailed carbonate deposition in the coastal plain and slope respectively resulting in a switch to siliciclastic sedimentation in onshore areas oligocene sequences are thin owing to low siliciclastic and pelagic input and their distribution is patchy reflecting migration or progradation of depocenters in contrast miocene onshore sequences are thicker reflecting increased sediment supply and they are more complete downdip owing to simple tectonics we conclude that the new jersey margin provides a natural laboratory for unraveling complex interactions of eustasy tectonics changes in sediment supply and climate change

a revised and improved age model for the middle miocene part of iodp site u1318 porcupine basin offshore southwestern ireland integrated ocean drilling program leg 307 site u1318 is one of the few relatively complete middle miocene drillcores from the north atlantic porcupine basin offshore southwestern ireland using benthic foraminiferal stable carbon and oxygen isotopes the existing age model for site u1318 was improved the stable isotope record displays globally recognized isotope events used to revise the existing magnetostratigraphy based age model two intervals contained misidentified magnetochrons which were corrected the sampled interval now has a refined age of 12 75 16 60 ma with a temporal resolution of c 29 ka

accommodation and sedimentary architecture of isolated icehouse carbonate platforms insights from forward modeling with carb3d abstract a fundamental control on the evolution of carbonate platforms is accommodation the space available for sediment deposition here we adopt a sensitivity analysis approach using the process based forward model carb3d to quantitatively investigate the sedimentary response of isolated carbonate platforms to individual accommodation drivers of eustasy subsidence and surface dissolution sediment production the mechanism invoked to fill accommodation is also investigated fourth order milankovich driven sea level cycles dominate icehouse carbonate sedimentology with 400 ky cycles modulating the effect of 100 ky cycles of comparable magnitude when both cycles are present both overwhelm higher frequency lower amplitude fifth order cycles which are rarely preserved on the platform top subsidence is a fundamental control on sedimentary stacking patterns sequence boundary frequency sbf and platform geometry with rapid subsidence increasing the preservation of platform top sequences most icehouse platforms are subject to extended periods of platform top exposure missed beats when the platform top remains emergent at a sea level maximum are common and create non milankovich sbfs furthermore during platform emergence surface lowering via surface dissolution also creates accommodation for the subsequent platform flooding event with surface dissolution rates in humid climates comparable to moderate rates of subsidence however accommodation generation by surface dissolution is self limiting in as much as accommodation generated by dissolution is rapidly refilled on flooding sediment production is a key control on unfilled accommodation which our simulations suggest is considerable on icehouse platforms increased shallow water 3 m depth sediment production enhances intra platform bathymetric relief between the margin and interior this is driven in large part by a higher sedimentation rate at the margin than in the interior platforms can be flooded to depths up to 45 m during marine transgressions and accommodation often remains unfilled there are two distinct phases of platform top sedimentation during the transgression and early highstand platform margins accumulate at a greater rate than interior sediments generating differential intra platform bathymetry subsequently accommodation in the interior fills by forced regression and progradation from the margins into the platform interior numerical forward models can augment our understanding of icehouse carbonate platform evolution by identifying the nature of the sedimentary response to individual controls they can thus contribute to improving characterization of carbonate reservoirs in icehouse platforms such as the large hydrocarbon fields in the north caspian and s e asia

dynamic modeling of the 1992 landers earthquake we have used observed band pass filtered accelerograms and a previously determined slip distribution to invert for the dynamic rupture propagation of the 1992 landers earthquake in our simulations dynamic rupture grows under the simultaneous control of initial stress and rupture resistance by friction which we modeled using a simple slip weakening law we used a simplified landers fault model where the fault segments were combined into a single vertical planar fault by trial and error we modified an initial stress field inferred from the kinematic slip distribution proposed by wald and heaton 1994 until dynamic rupture generated a rupture history and final slip distribution that approximately matched those determined by the kinematic inversion we found that rupture propagation was extremely sensitive to small changes in the distribution of prestress and that a delicate balance with energy release rate controls the average rupture speed for the inversion we generated synthetic 0 5 hz ground displacements using an efficient green s function propagator method axitra this method enables us to propagate the radiation generated by the dynamic rupture to distances greater than those feasible using the finite difference method the dynamic model built by trial and error inversion provides a very satisfactory fit between synthetics and strong motion data we validated this model using records from stations used in the slip inversion as well as some which were not included we also inverted for a complementary model that fits the data just as well but in which the initial stress was perfectly uniform while rupture resistance was heterogeneous this demonstrates that inversion of ground motion is nonunique

visions of ice sheets in a greenhouse world abstract backstripped eustatic estimates from new jersey and the russian platform show large 25 m and rapid 18 o record highlights the enigma this was the warmest interval of the past 200 my yet it was bracketed by two inferred eustatic falls of 25 m that were associated with two large 0 75 deep sea 18 o increases 92 93 ma mid turonian and 96 ma mid cenomanian we reconcile records of warm high latitudes with glacioeustasy by proposing that late cretaceous early eocene ice sheets generally reached maximum volumes of 8 12 10 6 km 3 20 30 m glacioeustatic equivalent but did not reach the antarctic coast hence coastal antarctica hence deep water remained relatively warm even though there were significant changes in sea level as the result of glaciation unlike the oligocene and younger icehouse world these ice sheets only existed during short intervals of peak milankovitch insolation leaving antarctica ice free during much of the greenhouse late cretaceous to middle eocene these results highlight the need to re evaluate the paradigm that polar ice sheets did not exist during times of warm high latitude climates

stable creeping fault segments can become destructive as a result of dynamic weakening faults in earth s crust accommodate slow relative motion between tectonic plates through either similarly slow slip or fast seismic wave producing rupture events perceived as earthquakes these types of behaviour are often assumed to be separated in space and to occur on two different types of fault segment one with stable rate strengthening friction and the other with rate weakening friction that leads to stick slip the 2011 tohoku oki earthquake with moment magnitude m w 9 0 challenged such assumptions by accumulating its largest seismic slip in the area that had been assumed to be creeping here we propose a model in which stable rate strengthening behaviour at low slip rates is combined with coseismic weakening due to rapid shear heating of pore fluids allowing unstable slip to occur in segments that can creep between events the model parameters are based on laboratory measurements on samples from the fault of the m w 7 6 1999 chi chi earthquake the long term slip behaviour of the model which we examine using a unique numerical approach that includes all wave effects reproduces and explains a number of both long term and coseismic observations some of them seemingly contradictory about the faults at which the tohoku oki and chi chi earthquakes occurred including there being more high frequency radiation from areas of lower slip the largest seismic slip in the tohoku oki earthquake having occurred in a potentially creeping segment the overall pattern of previous events in the area and the complexity of the tohoku oki rupture the implication that earthquake rupture may break through large portions of creeping segments which are at present considered to be barriers requires a re evaluation of seismic hazard in many areas

cenozoic record of δ 34 s in foraminiferal calcite implies an early eocene shift to deep ocean sulfide burial understanding the changes in and drivers of isotopic variability of sulfur in seawater sulfate 34sso4 sw over geological time remains a long standing goal particularly because of the coupling between the biogeochemical sulfur and carbon cycles the early cenozoic has remained enigmatic in this regard as the existing seawater sulfate isotopic records appear to be decoupled from the well defined carbon isotope composition of the ocean here we present a new cenozoic record of sulfur isotopes using carbonate associated sulfate hosted in the calcite lattice of single species foraminifera the vastly improved stratigraphy afforded by this record demonstrates that carbon and sulfur cycles as recorded by their isotopes are not fully decoupled in the early cenozoic with a model driven by partial coupling of the carbon and sulfur cycles we demonstrate that a change in sulfur isotopic fractionation of the pyrite burial flux best explains the large increase in 34sso4 sw 53 million years ago ma and the subsequent long steady state we suggest that the locus of pyrite burial changed from shallow epicontinental seas and shelf environments to more open ocean sediments around 53 ma loss of extensive shelf environments corresponds to cretaceous palaeogene sea level changes and tectonic reorganization occurring as the himalayan arc first collided with asia a cenozoic reconstruction of the 34s of marine sulfate suggests a shift in the locus of pyrite burial from shallow seas to the open ocean during the early eocene

response of the lithosphere to in plane force variations the earth s lithosphere deforms when subjected to vertical and horizontal tectonic forces because it is not perfectly rigid the deformation has both elastic flexural and inelastic brittle and ductile creep components we use the yield strength envelope formulation of a depth dependent rheology to predict how the lithosphere will deform in response to applied in plane force brittle deformation of the upper lithosphere is influenced by the distribution of existing faults and fractures in the crust and their orientation with respect to the applied tectonic force the sense of fault reactivation indicates the sign of the applied in plane force the induced flexural deformation is governed by the pre existing lithospheric deflection the effective elastic thickness of the lithosphere when the force was applied and the magnitude of the applied force using this framework we compare the predicted response of the lithosphere to in plane force variations with that observed in the central indian ocean and the jeanne d arc basin offshore newfoundland the brittle deformation in both regions is readily observed in seismic reflection data the upper oceanic crust in the central indian ocean is broken into blocks bounded by high angle reverse faults the dip of these basement faults and their orientation parallel to the marine magnetic lineations suggest that they represent a reactivated crustal fabric imparted during the formation of oceanic crust the reverse sense of fault reactivation is consistent with the north south compression determined from earthquake focal mechanisms in the jeanne d arc basin episodes of northwest southeast extension reactivated the basin bounding faults in a normal sense during late barremian early aptian and late aptian time in the late albian the same crustal blocks were reactivated and uplifted in response to north northeast in plane compression flexural deformation due to applied in plane force is observed only in the central indian ocean case where the oceanic crust and most of the overlying bengal fan sediments were deformed into broad east west trending undulations with wavelengths of 100 300 km and amplitudes up to 2 km in the jeanne d arc basin the flexural deformation which should accompany the fault reactivation is difficult to recognize from the preserved stratigraphy consequently brittle deformation within extensional basins which appears to be the most recognizable response of the lithosphere to in plane force variations obscures the effects of the flexural deformation however it is this flexural deformation that has been postulated as a tectonic alternative to glacial eustasy in explaining the 3rd order sea level cycles because it is difficult to recognize the effects of the flexural deformation in the preserved stratigraphy we surmise that it is not a viable alternative to glacial eustasy in generating either regional or global unconformities instead we propose that the flexural and brittle deformation due to applied in plane force may locally enhance or diminish the effects of other processes responsible for unconformity generation

the 1992 landers earthquake sequence seismological observations the m w 6 1 7 3 6 2 1992 landers earthquakes began on april 23 with the m w6 1 1992 joshua tree preshock and form the most substantial earthquake sequence to occur in california in the last 40 years this sequence ruptured almost 100 km of both surficial and concealed faults and caused aftershocks over an area 100 km wide by 180 km long the faulting was predominantly strike slip and three main events in the sequence had unilateral rupture to the north away from the san andreas fault the m w6 1 joshua tree preshock at 33 n58 and 116 w19 on 0451 ut april 23 was preceded by a tightly clustered foreshock sequence m 4 6 beginning 2 hours before the mainshock and followed by a large aftershock sequence with more than 6000 aftershocks the aftershocks extended along a northerly trend from about 10 km north of the san andreas fault northwest of indio to the east striking pinto mountain fault the m w7 3 landers mainshock occurred at 34 n13 and 116 w26 at 1158 ut june 28 1992 and was preceded for 12 hours by 25 small m 3 earthquakes at the mainshock epicenter the distribution of more than 20 000 aftershocks analyzed in this study and short period focal mechanisms illuminate a complex sequence of faulting the aftershocks extend 60 km to the north of the mainshock epicenter along a system of at least five different surficial faults and 40 km to the south crossing the pinto mountain fault through the joshua tree aftershock zone towards the san andreas fault near indio the rupture initiated in the depth range of 3 6 km similar to previous m 5 earthquakes in the region although the maximum depth of aftershocks is about 15 km the mainshock focal mechanism showed right lateral strike slip faulting with a strike of n10 w on an almost vertical fault the rupture formed an arclike zone well defined by both surficial faulting and aftershocks with more westerly faulting to the north this change in strike is accomplished by jumping across dilational jogs connecting surficial faults with strikes rotated progressively to the west a 20 km long linear cluster of aftershocks occurred 10 20 km north of barstow or 30 40 km north of the end of the mainshock rupture the most prominent off fault aftershock cluster occurred 30 km to the west of the landers mainshock the largest aftershock was within this cluster the m w6 2 big bear aftershock occurring at 34 n10 and 116 w49 at 1505 ut june 28 it exhibited left lateral strike slip faulting on a northeast striking and steeply dipping plane the big bear aftershocks form a linear trend extending 20 km to the northeast with a scattered distribution to the north the landers mainshock occurred near the southernmost extent of the eastern california shear zone an 80 km wide more than 400 km long zone of deformation this zone extends into the death valley region and accommodates about 10 to 20 of the plate motion between the pacific and north american plates the joshua tree preshock its aftershocks and landers aftershocks form a previously missing link that connects the eastern california shear zone to the southern san andreas fault

onlap offlap and the origin of unconformity bounded depositional sequences christie blick n 1991 onlap ofttap and the origin of unconformity bounded depositional sequences mar geol 97 35 56 unconformity bounded depositional sequences represent the fundamental building blocks of sedimentary successions they are typically characterized by onlap at the base and by offlap at the top and they tend to be markedly asymmetrical with onlap accounting for a larger part of any cycle of sedimentation than offlap offlap cannot be attributed solely to erosional truncation but instead implies that sequence boundaries develop over a finite interval of time depositional sequences are commonly associated with a cyclic arrangement of facies but transgressive regressive cycles are out of phase with respect to sequence boundaries which in down dip locations are both overlain and underlain by progradational deposits and hence form during times of regression of the shoreline these observations are used to develop some ideas about the origin of unconformity bounded sequences with reference to the inter related roles of changes in depositional base level and sediment supply in particular it is shown than onlap and offlap are due to lateral migration of a line of critical bypassing defined so as to incorporate the effects of sediment loading and compaction as well as the rate of change of elevation with respect to sea level downward shifts in onlap may be achieved by either an increase in the rate of eustatic fall or a decrease in the rate of tectonic subsidence and it is premature to assume that eustatic and tectonic controls on sea level may be distinguished solely on the basis of the frequency of depositional cyclicity small shifts in the position of onlap can also be produced by changes in sediment supply and more attention needs to be paid to the influence of sediment supply in the development of minor boundaries unconformities related to eustatic fluctuations are thought to correspond approximately to times of relatively rapid sea level fall inflection points but questions remain about the existence of possible leads and lags of up to cycle and hence about the degree to which sequence boundaries of eustatic origin may vary in age both within a given basin and from one basin to another

timing and magnitude of miocene eustasy derived from the mixed siliciclastic carbonate stratigraphic record of the northeastern australian margin article eustasy is a key parameter to understand sedimentary sequences on continental margins and to reconstruct continental ice volume in the cenozoic but timing and magnitude of global sea level changes remain controversial especially for the miocene epoch we analyzed sediment cores recovered from the marion plateau offshore northeastern australia during ocean drilling program odp leg 194 to define the mechanisms and timing of sequence formation on mixed carbonate siliciclastic margins and to estimate the amplitude of miocene eustatic adjustments we identified sequence boundaries on seismic reflection lines significantly revised the existing biostratigraphic age models and investigated the sedimentary response to sea level changes across the marion plateau we subdivided the miocene sediments into three sequence sets comprising a set of prograding clinoforms a muddy prograding carbonate ramp evolving into an aggrading platform and a lowstand ramp evolving into a backstepping ramp we recognized eight individual sequences dated at 18 0 ma 17 2 ma 16 5 ma 15 4 ma 14 7 ma 13 9 ma 13 0 ma and 11 9 ma we demonstrate that sequences on the marion plateau are controlled by glacio eustasy since sequence boundaries are marked by increases in 18 o deep sea miocene isotope events mi1b mbi 3 mi2 mi2a mi3a mi3 mi4 and mi5 respectively which reflects increased ice volume primarily on antarctica our backstripping estimates suggest that sea level fell by 26 28 m at 16 5 ma 26 29 m at 15 4 ma 29 38 m at 14 7 ma and 53 81 m at 13 9 ma combining backstripping with 18 o estimates yields sea level fall amplitudes of 27 1 m at 16 5 ma 27 1 m at 15 4 ma 33 3 m at 14 7 ma and 59 6 m at 13 9 ma we use a similar approach to estimate eustatic rises of 19 1 m between 16 5 and 15 4 ma 23 3 m between 15 4 and 14 7 ma and 33 3 m between 14 7 and 13 9 ma these estimates can be combined into a eustatic curve that suggests that sea level fell by 53 69 m between 16 5 and 13 9 ma this implies that at least 90 of the east antarctic icesheet was formed during the middle miocene the new independent amplitude estimates are crucial as the miocene is the geologic epoch for which the new jersey margin sea level record is poorly constrained

long term and short term global cenozoic sea level estimates backstripping analysis of three continuously cored well dated boreholes from the new jersey coastal plain ocean drilling program odp leg 150x indicates a long term 10 8 n10 7 yr eustatic fall of 100 m since 55 ma early eocene and suggests short term 0 5n3 m y eustatic falls of less than 70 m eustatic estimates are calculated from residuals between the decompacted unloaded and paleodepth corrected records and tectonic subsidence assuming a cooling lithospheric plate because the residuals are similar among the three sites we interpret them as an approximation of the eustatic signal

upper eocene to oligocene isotope 87sr 86sr δ18o δ13c standard section deep sea drilling project site 522 we improved upper eocene to oligocene deep sea chronostratigraphic control by integrating isotope 87sr 86sr 18o 13c stratigraphy and magnetostratigraphy most previous attempts to establish the timing of isotope fluctuations have relied upon biostratigraphic age estimates which have uncertainties of 0 5 to over 4 0 m y deep sea drilling project dsdp site 522 contains the best available upper eocene to oligocene magnetostratigraphic record which allows first order correlations of isotope records 87sr 86sr 18o 13c to the geomagnetic polarity time scale gpts empirical calibrations between the 87sr 86sr of foraminifera and magnetochronology at site 522 allow more precise correlation of unknown samples with the gpts for example shallow water and high latitude sections may be tied into the deep sea record sr isotope stratigraphic resolution for the latest eocene to oligocene is approximately 2 m y

effects of fault heterogeneity on seismic energy and spectrum abstract we study the effects of friction heterogeneity on the dynamics of a seismogenic fault to this aim we consider a fault model containing two asperities with different static frictions and a rate dependent dynamic friction we consider the seismic events produced by the consecutive failure of the two asperities and study their properties as functions of the ratio between static frictions in particular we calculate the moment rate the stress evolution during fault slip the average stress drop the partitioning of energy release the seismic energy the far field waveforms and the spectrum of seismic waves these quantities depend to various extent on the friction distribution on the fault in particular the stress distribution on the fault is always strongly heterogeneous at the beginning of the seismic event seismic energy and frictional heat decrease with increasing friction heterogeneity while seismic efficiency is constant we obtain an equation relating seismic efficiency to the parameters of the friction law showing that the efficiency is maximum for smaller values of dynamic friction the seismic spectrum depends on the friction distribution as to the positions and the values of the minima however under the model assumption that the slip durations are the same for both asperities the corner frequency is independent of the friction distribution but it depends on the friction law and on the coupling between asperities the model provides a relation between the total radiated energy and the seismic moment that is consistent with the empirical relation between the two quantities the fault model with one asperity is also considered as a particular case the model is applied to the 1965 rat islands alaska earthquake and shows the role of fault heterogeneity in controlling the spatial distribution of stress drop as well as the time dependence and the final amount of radiated energy

spatial and temporal distribution of slip for the 1992 landers california earthquake we have determined a source rupture model for the 1992 landers earthquake m w 7 2 compatible with multiple data sets spanning a frequency range from zero to 0 5 hz geodetic survey displacements near field and regional strong motions broadband teleseismic waveforms and surface offset measurements have been used explicitly to constrain both the spatial and temporal slip variations along the model fault surface our fault parameterization involves a variable slip multiple segment finite fault model which treats the diverse data sets in a self consistent manner allowing them to be inverted both independently and in unison the high quality data available for the landers earthquake provide an unprecedented opportunity for direct comparison of rupture models determined from independent data sets that sample both a wide frequency range and a diverse spatial station orientation with respect to the earthquake slip and radiation pattern in all models consistent features include the following 1 similar overall dislocation patterns and amplitudes with seismic moments of 7 to 8 10 26 dyne cm seismic potency of 2 3 to 2 7 km 3 2 very heterogeneous unilateral strike slip distributed over a fault length of 65 km and over a width of at least 15 km though slip is limited to shallower regions in some areas 3 a total rupture duration of 24 sec and an average rupture velocity of 2 7 km sec and 4 substantial variations of slip with depth relative to measured surface offsets the extended rupture length and duration of the landers earthquake also allowed imaging of the propagating rupture front with better resolution than for those of prior shorter duration strike slip events our imaging allows visualization of the rupture evolution including local differences in slip durations and variations in rupture velocity rupture velocity decreases markedly at shallow depths as well as near regions of slip transfer from one fault segment to the next as rupture propagates northwestward along the multiply segmented fault length the rupture front slows as it reaches the northern limit of the johnson valley landers faults where slip is transferred to the southern homestead valley fault an abrupt acceleration is apparent following the transfer this process is repeated and is more pronounced as slip is again passed from the northern homestead valley fault to the emerson fault although the largest surface offsets were observed at the northern end of the rupture our modeling indicates that substantial rupture was also relatively shallow less than 10 km in this region

slip distribution of the february 27 2010 mw 8 8 maule earthquake central chile from static and high rate gps insar and broadband teleseismic data 1 the shallow depth underthrust earthquake of february 27 2010 mw 8 8 ruptured the subduction plate interface in central chile between 34 s and 38 s we retrieve the spatial and temporal distribution of slip during this mega earthquake through a joint inversion of teleseismic records insar and high rate gps hrgps data additionally our model is shown to agree with broadband surface waves rupture initiated at about 32 km depth and propagated bilaterally resulting in two main slip zones located ssw and nne of the hypocenter nucleation did not take place within or at the edge of one of these main asperities but in between during the first 30s slip propagated predominantly southwards later on the rupture evolved more slowly and more symmetrically eventually the northern asperity became predominant with maximum slip reaching about 20 m most of the seismic moment was released within 110s a relatively short time explained by the bilateral propagation the overall average rupture velocity is 2 6 km s but propagation occurred initially faster towards the south 3 2 km s large slip did not reach the trench a result consistent with the moderate size of the tsunami down dip rupture stopped at about 50 km depth in agreement with the lower limit of the locked zone inferred by ruegg et al 2009 from pre seismic gps data

correlating miocene sequences in onshore new jersey boreholes odp leg 150x with global δ18o and maryland outcrops recent onshore new jersey drilling ocean drilling program leg 150x provided excellent recovery of lower to middle miocene sequences that we dated with sr isotopic stratigraphy sequence boundaries correlate with deep sea 18 o increases inferred glacioeustatic lowerings indicating a primary control by global sea level change maryland miocene outcrops appear to correlate with new jersey sequences and the 18 o record although diagenesis and intense bioturbation limit sr isotopic age resolution in maryland the early miocene is not well represented in maryland due to regional tectonics in contrast early miocene accommodation in new jersey was provided by flexural effects due to sediment loading

evolution of early cenozoic marine temperatures the equator to high southern latitude sea surface and vertical temperature gradients are reconstructed from oxygen isotope values of planktonic and benthic foraminifers for the following five time intervals late paleocene early eocene early middle eocene late eocene and early oligocene paleotemperatures are calculated using standard oxygen isotope temperature equations with adjustments to account for 1 variations in sea water 18o related to changes in global ice volume over time and 2 latitudinal gradients in surface water 18o these reconstructions indicate that sea surface temperatures sst of the southern oceans in the early eocene were as high as 15 c whereas temperatures during the late paleocene and early middle eocene reached maximum levels of 10 12 c by the late eocene and early oligocene high latitude sst had declined to 6 and 4 c respectively for most of the early paleogene low latitude sub tropical temperatures remained constant and well within the range of holocene temperatures 24 ndash 25 c but by the late eocene and early oligocene declined to values in the range of 18 to 22 c the late paleogene apparent decline in tropical temperatures however might be artificial because of dissolution of near surface foraminifera tests which biased sediment assemblages toward deeper dwelling foraminifera moreover according to recent plate reconstructions it appears that the majority of sites upon which the late eocene and early oligocene tropical temperatures were previously established were located either in or near regions likely to have been influenced by upwelling global deepwater temperature on average paralleled southern ocean sst for most of the paleogene we speculate based on the overall timing and character of marine sea surface temperature variation during the paleogene that some combination of both higher levels of greenhouse gases and increased heat transport was responsible for the exceptional high latitude warmth of the early eocene

oligocene miocene strontium isotopes stratigraphic revisions and correlations to an inferred glacioeustatic record this study tests and improves on previously published early and middle miocene 87sr 86sr marine correlations presents sr isotopic age correlations for this interval using the new timescale of cande and kent 1992 and evaluates sr isotopic changes against an inferred glacioeustatic proxy we generated a latest oligocene to early late miocene 87sr 86sr isotope record from ocean drilling program odp hole 747a this site provides an excellent magnetostratigraphic record during most of this interval for independent age estimates very good foraminiferal preservation and excellent core recovery comparisons of new 87sr 86sr data from hole 747a with previously published data from deep sea drilling project dsdp sites 608 miller et al 1991a and 588 hodell et al 1991 yield the following results 1 confirmation and refinement of the early miocene sr isotope changes 2 improved definition of the timing of the changes in slope of 87sr 86sr near 15 4 ma and 22 8 ma 3 improved sr isotopic age resolution for the middle miocene with resolution as good as 0 7 m y and 4 identification of an inflection in the sr isotope record at 28 0 ma based on the combined records from dsdp site 522 miller et al 1988 and odp hole 747a we have been unable to determine the cause of middle miocene offset between site 588 and hole 747a data although we believe it may be attributed to problems in the age assignments for hole 588a for the interval 14 11 ma and site 747 for the interval 11 8 ma because hole 747a results provide a better chronology than site 588 for most of the miocene and a better middle miocene sr isotope record than site 608 we propose that hole 747a serves as the best reference section for miocene 87sr 86sr variations from ca 23 to 11 ma using 87sr 86sr data from sites 522 608 and 747a we relate late eocene to early miocene inflections in the 87sr 86sr isotope record to oxygen isotope increases and decreases inferred to represent glacioeustatic events the decreases deglaciations observed in the 18o record apparently lead the 87sr 86sr inflections by 1 to 1 5 m y

resolving apparent conflicts between oceanographic and antarctic climate records and evidence for a decrease in pco2 during the oligocene through early miocene 34 16 ma abstract an apparent mismatch between published oxygen isotopic data and other paleoclimate proxies for the span from 26 16 ma is resolved by calibration against global sea level estimates obtained from backstripping continental margin stratigraphy ice volume estimates from calibrated oxygen isotope data compare favorably with stratigraphic and palynological data from antarctica and with estimates of atmospheric pco2 throughout the oligocene to early miocene 34 16 ma isotopic evidence for an east antarctic ice sheet eais as much as 30 larger than its present day volume at glacial maxima during that span is consistent with seismic reflection and stratigraphic evidence for an ice sheet covering much of the antarctic continental shelf at the same glacial maxima palynological data suggest long term cooling during the oligocene with cold near tundra environments developing along the coast at glacial minima no later than the late oligocene a possible mechanism for this long term cooling is a decrease in atmospheric pco2 from the middle eocene to oligocene reaching near pre industrial levels by the latest oligocene and remaining at those depressed levels throughout the miocene

seismic coupling and uncoupling at subduction zones seismic coupling has been used as a qualitative measure of the interaction between the two plates at subduction zones kanamori 1971 introduced seismic coupling after noting that the characteristic size of earthquakes varies systematically for the northern pacific subduction zones a quantitative global comparison of many subduction zones reveals a strong correlation of earthquake size with two other variables age of the subducting lithosphere and convergence rate the largest earthquakes occur in zones with young lithosphere and fast convergence rates while zones with old lithosphere and slow rates are relatively aseismic for large earthquakes results from a study of the rupture process of three great earthquakes indicate that maximum earthquake size is directly related to the asperity distribution on the fault plane asperities are strong regions that resist the motion between the two plates the zones with the largest earthquakes have very large asperities while the zones with smaller earthquakes have small scattered asperities this observation can be translated into a simple model of seismic coupling where the horizontal compressive stress between the two plates is proportional to the ratio of the summed asperity area to the total area of the contact surface while the variation in asperity size is used to establish a connection between earthquake size and tectonic stress it also implies that plate age and rate affect the asperity distribution plate age and rate can control asperity distribution directly by use of the horizontal compressive stress associated with the preferred trajectory i e the vertical and horizontal velocities of subducting slabs are determined by the plate age and convergence velocity indirect influences are many including oceanic plate topography and the amount of subducted sediments all subduction zones are apparently uncoupled below a depth of about 40 km and we propose that the basalt to eclogite phase change in the down going oceanic crust may be largely responsible this phase change should start at a depth of 30 35 km and could at least partially uncouple the plates by superplastic deformation throughout the oceanic crust during the phase change

asperity distributions and large earthquake occurrence in subduction zones abstract ruff l j 1992 asperity distributions and large earthquake occurrence in subduction zones in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 61 83 plate tectonics and the seismic gap hypothesis provide the framework for long term earthquake forecasting of plate boundary earthquakes unfortunately detailed examination reveals that earthquake recurrence times and rupture length vary between successive earthquake cycles in the same subduction zone furthermore larger coseismic slip is commonly associated with larger rupture length hence large earthquake occurrence in subduction zones is characterized by variability in 1 recurrence times 2 rupture length and 3 coseismic slip these facts plus many other observations indicate that there are significant spatial variations in the strength of the plate interface one simple description of these variations and their role in the earthquake cycle is the asperity model where the large strong regions of the plate interface are called asperities and the large earthquakes occur when the large asperities break the asperity model of earthquake occurrence is able to qualitatively explain several features of large plate boundary earthquakes to go beyond general qualitative notions i pose the following scientific test are the observed asperity distributions and a simple model of their interaction self consistent with the above three observed features of large earthquake occurrence the distribution of the major asperities along plate boundary segments has now been determined for several subduction zones rupture process studies of adjacent large and great earthquakes have provided reliable estimates of the along strike asperity lengths and separations for several adjacent asperities in the kurile islands colombia and peru subduction zones the simplest mechanical model for asperity interaction is to idealize two adjacent asperities as frictional sliders that are connected by main springs to the upper plate by a coupling spring to each other and maintain frictional contact with a conveyer belt the lower plate that moves with a constant velocity an earthquake occurs when the net force on the asperity frictional slider reaches some specified level the failure force and spring constants are determined by the observed asperity distribution and simple models of elastic interaction two different macroscopic failure criteria are used this simple mechanical model displays a remarkable range of behavior from simple to complex when the two asperities are identical in all their properties sequences of identical earthquakes are produced for the more realistic case of non identical asperities earthquake sequences show great variety using system variables from the observed asperity distributions the earthquake sequences typically display 1 variable recurrence times 2 variable rupture length i e a combination of single asperity and double asperity failures and for one of the failure criteria 3 larger coseismic slip for double asperity failures statistical summaries of thousands of simulated earthquake sequences for asperity pairs in the kuriles colombia and peru subduction zones are broadly consistent with the observed features of large earthquake occurrence in these subduction zones the main conclusion is that the asperity model provides a self consistent explanation for fault zone heterogeneity the rupture process and recurrence times and rupture mode of large earthquake sequences via a simple model for adjacent asperity interaction in addition a conclusion independent of any particular model for fault zone heterogeneity is that simple deterministic models of fault zone interaction can explain complex patterns of large earthquake occurrence in subduction zones

unlocking the ice house oligocene miocene oxygen isotopes eustasy and margin erosion oxygen isotope records and glaciomarine sediments indicate at least an intermittent presence of large continental ice sheets on antarctica since the earliest oligocene circa 35 ma the growth and decay of ice sheets during the oligocene to modern ice house world caused glacioeustatic sea level changes the early eocene was an ice free greenhouse world but it is not clear if ice sheets existed during the middle to late eocene doubt house world benthic foraminiferal 18o records place limits on the history of glaciation suggesting the presence of ice sheets at least intermittently since the earliest oligocene the best indicator of ice growth is a coeval increase in global benthic and western equatorial planktonic 18o records although planktonic isotope records from the western equatorial regions are limited subtropical planktonic foraminifera may also record such ice volume changes it is difficult to apply these established principles to the cenozoic 18o record because of the lack of adequate data and problems in stratigraphic correlations that obscure isotope events we improved oligocene to miocene correlations of 18o records and erected eight oxygen isotope zones oi1 oi2 mi1 mi6 benthic foraminiferal 18o increases which are associated with the bases of zones oil circa 35 8 ma oi2 circa 32 5 ma and mil circa 23 5 ma can be linked with 18o increases in subtropical planktonic foraminifera and with intervals of glacial sedimentation on or near antarctica our new correlations of middle miocene benthic and western equatorial planktonic 18o records show remarkable agreement in timing and amplitude we interpret benthic planktonic covariance to reflect substantial ice volume increases near the bases of zones mi2 circa 16 1 ma mi3 circa 13 6 ma and possibly mi5 circa 11 3 ma possible glacioeustatic lowerings are associated with the 18o increases which culminated with the bases of zone mi4 circa 12 6 ma and mi6 circa 9 6 ma although low latitude planktonic 18o records are required to test this these inferred glacioeustatic lowerings can be linked to seismic and rock disconformities for example we link 12 oligocene early late miocene inferred glacioeustatic lowerings with 12 of the sequence boundaries inferred eustatic lowerings of haq et al 1987

glacioeustatic fluctuations the mechanism linking stable isotope events and sequence stratigraphy from the early oligocene to middle miocene one of the most difficult challenges of sequence stratigraphy is the establishment of synchronism between events observed in widely separated basins problems arise because the resolution of the best stratigraphic methods is not good enough to establish the synchronism of similar aged events on a global scale unless a common mechanism affecting global eustasy is assumed such as variations in the ice volume there is no a priori reason to expect that sequences of similar age in widely separated basins are indeed synchronous the stable oxygen isotope composition of marine carbonates is a proxy for sea level which has been underutilized in sequence stratigraphy identification of isotope events is based on d sup 18 o data from dsdp and odp sites 522 529 563 608 and 747 drilled in the atlantic and indian oceans these records were used to define oligocene and miocene oxygen isotope zones in addition we present isotope data from petrobras well a drilled in the campos basin brazil ages of isotope events correspond well with the ages of sequence boundaries and maximum flooding surfaces because of the good correlation between the isotope and sequence stratigraphic records we reconfirm that ice volume change is the common mechanism driving sea level fluctuations from the oligocenemore to present less

late cenozoic phosphogenesis on the western shelf of south africa in the vicinity of the cape canyon abstract the strontium isotope 87 sr 86 sr composition of phosphorite carbonate fluorapatite cemented grains pcg phosphate cemented limestone pcl skeletal phosphorite grains spg and biogenic calcite mollusc shell benthic foraminifera and echinoid spines from sediment on the outer continental shelf in the vicinity of the cape canyon ranges from 0 707981 to 0 709167 and corresponds to an age range of late early oligocene to late pleistocene most biogenic carbonate sr ages agree with biostratigraphic ages but some samples contain significantly older and reworked robust 250 m benthic foraminifera although the sr ages of biogenic and phosphorite grains indicate that sedimentation was fairly continuous most sediment is reworked with only lower miocene upper pliocene and upper pleistocene successions generally preserved in the study area the initial phosphogenic episode from the latest oligocene to early early miocene 21 26 ma was the largest with additional phosphogenic episodes in the late early miocene 16 19 ma and middle miocene 10 15 ma most phosphorite occurs as pcg that formed during marine transgressions and highstands from the late oligocene warming event until the mid miocene climatic optimum a period of episodic antarctic glaciation and several positive marine 13 c excursions upper oligocene to lower miocene pcg have been extensively reworked and are associated with major erosional unconformities pcg vary from peloidal sands to gravel mollusc moulds and contain variable amounts of quartz glauconite and pyrite inclusions pcl formed from 9 to 17 ma by cementation and replacement of older calcareous sediment during the middle to late miocene marine regression phosphorite as well as associated glauconite and pyrite indicate that periods of rapid accumulation of organic rich terrigenous muds derived from the focusing of the suspended load of rivers and organic matter produced in areas of coastal upwelling have occurred episodically on the margin since the late oligocene the relative paucity of phosphorite younger than the middle miocene may result from frequent erosional events as documented by pronounced unconformities on the shelf that reflect lowered eustatic sea level tectonic uplift and high frequency high amplitude quaternary sea level fluctuations

integrated sequence stratigraphy of neogene deposits new jersey continental shelf and slope comparison with the exxon model we have evaluated the neogene stratigraphic succession beneath the continental shelf off new jersey using high quality seismic and well data to 1 construct geologic cross sections that relate seismic geometries to lithofacies in a prograding tectonically quiescent setting 2 apply a sequence stratigraphic approach to subdivide the stratigraphic section and relate the characteristics of the deposition observed sequences to the published exxon model and 3 determine the resolution of the available biostratigraphy in the correlation of the offshore new jersey depositional sequences to the published eustatic cycle chart in the offshore new jersey area the well developed progradational geometries in the neogene section the high quality seismic data and the relatively abundant lithologic information from wells allow us to use the results of this study to predict lithofacies distribution in similar but less geologically constrained settings depositional sequences are characterized by similar overall stacking patterns within component systems tracts however the new jersey sequences are different in several ways these differences include the lack of type 2 unconformities an absence of leveed channel deposits within lowstand wedges very poorly developed transgressive systems tracts and sandstone rich high regressive highstand systems tracts these differences are explained in terms of the limited neogene accommodation on the newmore jersey shelf that resulted from slow subsidence rates and a second order miocene eustatic fall paleontologic data bracket the ages of the individual sequences but are not detailed enough at present to correlate precisely to the time scale and inferred global sea level records based on the available biostratigraphy however neogene depositional sequences from offshore new jersey have a cyclicity consistent with interpreted third order eustatic fluctuations on the global cycle chart 18 refs 6 figs 1 tab less

global implications of lower to middle eocene sequence boundaries on the new jersey coastal plain the icehouse cometh wedocumentninelower middleeocenesequencesonthenewjerseycoastalplainand comparethemwithglobal d 18 oandhaqetal records earlyeocenehiatusesdonotmatch d 18 ochanges anditisunlikelythattheyaretheresultofglacioeustasy consistentwithan ice free early eocene early middle eocene 49 43 ma evidence for a link between sequencesand d 18 oisequivocal andthepresenceoflargeicesheetsisuncertain beginning in the late middle eocene 43 42 ma concomitant increases in planktonic and benthic d 18 o records coincide with the timing of hiatuses on the new jersey coastal plain and a change from carbonate dominated to siliciclastic dominated sedimentation these represent the development of the antarctic ice cap and the beginning of the icehouse world of the 14 sequences predicted by haq et al for this interval 9 are resolvable on the new jersey margin and the other 5 appear to be combined with others we conclude that although ice volume changes controlled sequences since at least 42 ma mechanisms for sea level change prior to then are still not fully understood

uppermost campanian maestrichtian strontium isotopic biostratigraphic and sequence stratigraphic framework of the new jersey coastal plain firm stratigraphic correlations are needed to evaluate the global significance of unconformity bounded units sequences we correlate the well developed uppermost campanian and maestrichtian sequences of the new jersey coastal plain to the geomagnetic polarity time scale gpts by integrating sr isotopic stratigraphy and biostratigraphy to do this we developed a maestrichtian ca 73 65 ma sr isotopic reference section at deep sea drilling project hole 525a in the southeastern atlantic ocean maestrichtian strata can then be dated by measuring their 87 sr 86 sr composition calibrating to the gpts of s c cande and d v kent 1993 personal commun and using the equation age ma 37 326 894 52 639 89 87 sr 86 sr sr stratigraphic resolution for the maestrichtian is estimated as 1 2 to 2 m y at least two unconformity bounded units comprise the uppermost campanian to maestrichtian strata in new jersey the lower one the marshalltown sequence is assigned to calcareous nannofossil zones cc20 21 nc19 and cc22b nc20 it ranges in age from 74 1 to 69 9 ma based on sr isotope age estimates the overlying navesink sequence is assigned to calcareous nannoplankton zones cc25 26 nc21 23 it ranges in age from 69 3 to 65 ma based on sr isotope age estimates the upper part of this sequence the tinton formation has no calcareous planktonic control sr isotopes provide an age estimate of 66 1 2 ma latest maestrichtian sequence boundaries at the base and the top of the marshalltown sequence match boundaries elsewhere in the atlantic coastal plain owens and gohn 1985 and the inferred global sea level record of haq et al 1987 they support eustatic changes as the mechanism controlling depositional history of this sequence however the latest maestrichtian record in new jersey does not agree with haq et al 1987 we attribute this to correlation and time scale differences near the cretaceous paleogene boundary high sedimentation rates in the latest maestrichtian of new jersey shrewsbury member of the red bank formation and the tinton formation suggest tectonic uplift and or rapid progradation during deposition of the highstand systems tract

the alkali soils of the middle niger valley origins formation and present evolution in niger republic the regional development of irrigation along the river niger is confronted with a large extent of alkali soils for a sound management of the irrigated area it appears necessary to understand the present evolution of these alkali soils the study of one of these areas located on the liptako bedrock reveals a concentric soil distribution within a zone of brown soil with abrupt textural change and alkaline in depth stagnic solonetz appears a ring of brown steppe soils cambic calcisol around zones of alkali soils solonetz these alkali soils are not saline but their soil solution is more concentrated than in brown steppe soils the abrupt boundary between the brown steppe soils and the alkali soils is related with morphological and geochemical changes resulting from calcite and fluorite precipitation in the soil solution the detailed study of this contact demonstrates the current transformation of alkali soils into brown steppe soils therefore it appears that soil alkalization is no longer in process on the terraces of the river niger the formation of brown steppe soils and alkali soils may be explained by the juxtaposition of two contrasted hydrological regimes in a former pond this hypothesis is supported by aerial pictures and microscopic observations it is also consistent with a recent study of the hydrology of sahelian ponds and with considerations on the chemical quality of the runoff

the eocene oligocene transition changes in sea level temperature or both abstract the eocene oligocene transition eot 34 ma reflects the onset of major antarctic glaciation the primary geochemical signature of the eot is two 300 kyr spaced shifts in increasing deep sea oxygen isotope values possibly reflecting both global cooling and or increasing ice volume a way to assess the respective contribution of continental ice is to quantify concomitant glacio eustatic sea level change this is usually expressed in relatively shallow marine depositional settings one potentially suitable region is in the vicentinian alps ne italy where marginal marine deposits document sea level changes during the eot by correlating stable isotope bio and magnetostratigraphic information between three distant regions we are able to relate the shallow marine sections to the pacific oxygen isotope record from ocean drilling program odp site 1218 of coxall et al 2005 microfacies sedimentological and biotic analysis suggests that associated with the first isotope shift eot 1 sea level fell 20 m and with the ultimate shift the oligocene isotope event 1 oi 1 sea level fell some 50 60 m distribution patterns of temperature sensitive dinoflagellates from a coeval central italian section reveal that the early stages of the eot were accompanied by sea surface cooling whereas no sustained cooling is noted in association with the oi 1 this suggests that the initial eot shift s reflect a mixed signal of ice volume and temperature whereas the oi 1 primarily reflects expansion of the antarctic cryosphere

northwestern european paleogene magnetostratigraphy biostratigraphy and paleogeography calcareous nannofossil evidence global calcareous nannofossil biostratigraphy is used to correlate the paleogene chronostratigraphic units of northwestern europe and standard nannofossil biozones such biostratigraphic correlations show that the lithostratigraphic sequence is discontinuous and allows interpretation of the paleogeography of northwestern europe during the paleogene and evaluation of the influence of global sea level eustatic changes on northwestern european stratigraphy a well documented unconformity occurs near the lower middle eocene boundary in the paris basin this unconformity which also can be traced in the london hampshire basin and in belgium correlates with a coastal offlap event presumed sea level of vail et al on the basis of magnetostratigraphic biostratigraphic correlations the duration of the hiatus associated with this unconformity can be estimated to be 0 6 to 1 5 m y in the hampshire basin and 2 to 4 m y in the paris basin

episodic cenozoic tectonism and the development of the nw european passive continental margin the north atlantic margins are archetypally passive yet they have experienced post rift vertical movements of up to kilometre scale the cenozoic history of such movements along the nw european margin from ireland to mid norway is examined by integrating published analyses of uplift and subsidence with higher resolution tectono stratigraphic indicators of relative movements including results from the stratagem project three episodes of epeirogenic movement are identified in the early mid and late cenozoic distinct from at least one phase of compressive tectonism two forms of epeirogenic movement are recognised referred to as tilting coeval subsidence and uplift rotations 1 over distances of 100s of kilometres and sagging strongly differential subsidence rotations up to 4 over distances 100 km each epeirogenic episode involved relatively rapid 10 ma km scale tectonic movements that drove major changes in patterns of sedimentation to find expression in regional unconformity bounded stratigraphic units early cenozoic tilting late paleocene to early eocene c 60 50 ma caused the basinward progradation of shelf slope wedges from elongate uplifts along the inner continental margin and from offshore highs mid cenozoic sagging late eocene to early oligocene c 35 25 ma ended wedge progradation and caused the onset of contourite deposition in deep water basins late cenozoic tilting early pliocene to present 4 0 5 ma again caused the basinward progradation of shelf slope wedges from uplifts along the inner margin including broad dome like features and from offshore highs the early mid and late cenozoic epeirogenic episodes coincided with atlantic plate reorganisations but the observed km scale tectonic movements are too large to be accounted for as flexural deflections due to intra plate stress variations mantle lithosphere interactions are implied but the succession of epeirogenic episodes of differing form are difficult to reconcile with the various syn to post rift mechanisms of permanent and or transient movements proposed in the hypothetical context of a plume beneath iceland the epeirogenic movements can be explained as dynamic topographic responses to changing forms of small scale convective flow in the upper mantle tilting as coeval upwelling and downwelling above an edge driven convection cell sagging as a loss of dynamic support above a former upwelling the inferred cenozoic succession of epeirogenic tilting sagging and tilting is proposed to record the episodic evolution of upper mantle convection during ocean opening a process that may also be the underlying cause of plate reorganisations the postulated episodes of flow reorganisation in the ne atlantic region have testable implications for epeirogenic movements along the adjacent oceanic spreading ridge and conjugate continental margin as well as on other atlantic type passive margins

late cretaceous chronology of large rapid sea level changes glacioeustasy during the greenhouse world we provide a record of global sea level eustatic variations of the late cretaceous 99 65 ma greenhouse world ocean drilling program leg 174ax provided a record of 11 14 upper cretaceous sequences in the new jersey coastal plain that were dated by in tegrating sr isotopic stratigraphy and biostratigraphy backstripping yielded a late cre taceous eustatic estimate for these sequences taking into account sediment loading com paction paleowater depth and basin subsidence we show that late cretaceous sea level changes were large 25 m and rapid k1 m y suggesting a glacioeustatic control three large d 18 o increases are linked to sequence boundaries others lack sufficient d 18 o data consistent with a glacioeustatic cause and with the development of small 10 6 km 3 ephemeral ice sheets in antarctica our sequence boundaries correlate with sea level falls recorded by exxon production research and sections from northwest europe and russia indicating a global cause although the exxon record differs from backstripped estimates in amplitude and shape

a constitutive law for rate of earthquake production and its application to earthquake clustering seismicity is modeled as a sequence of earthquake nucleation events in which the distribution of initial conditions over the population of nucleation sources and stress ing history control the timing of earthquakes the model is implemented using solutions for nucleation of unstable fault slip on faults with experimentally derived rate and state dependent fault properties this yields a general state variable constitutive formulation for rate of earthquake production resulting from an applied stressing history to illustrate and test the model some characteristics of seismicity following a stress step have been explored it is proposed that various features of earthquake clustering arise from sensi tivity of nucleation times to the stress changes induced by prior earthquakes the model gives the characteristic omori aftershock decay law and interprets aftershock parameters in terms of stress change and stressing rate earthquake data appear to support a model prediction that aftershock duration defined as the time for rates to return to the back ground seismicity rate is proportional to mainshock recurrence time observed spatial and temporal clustering of earthquake pairs arises as a consequence of the spatial depen dence of stress changes of the first event of the pair and stress sensitive time dependent nucleation applications of the constitutive formulation are not restricted to the simple stress step models investigated here it may be applied to stressing histories of arbitrary complexity the apparent success at modeling clustering phenomena suggests the possibil ity of using the formulation to estimate short to intermediate term earthquake probabil ities following occurrence of other earthquakes and for inversion of temporal variations of earthquake rates for changes in driving stress

evidence for glacial control of rapid sea level changes in the early cretaceous lower cretaceous bulk carbonate from deep sea sediments records sudden inputs of strontium resulting from the exposure of continental shelves strontium data from an interval spanning 7 million years in the berriasian valanginian imply that global sea level fluctuated about 50 meters over time scales of 200 000 to 500 000 years which is in agreement with the exxon sea level curve oxygen isotope measurements indicate that the growth of continental ice sheets caused these rapid sea level changes if glaciation caused all the rapid sea level changes in the cretaceous that are indicated by the exxon curve then an antarctic ice sheet may have existed despite overall climatic warmth

sequence stratigraphic framework and application to the precambrian abstract sequence stratigraphy highlights stratal stacking patterns and changes thereof within a time frame each stratal stacking pattern defines a particular genetic type of deposit with a unique geometry and sediment dispersal pattern within the basin common genetic types of deposit are referred to as forced regressive lowstand normal regressive transgressive and highstand normal regressive these genetic units are the basic building blocks of the sequence stratigraphic framework at any scale of observation and are bounded by sequence stratigraphic surfaces the recurrence of the same types of sequence stratigraphic surface through geologic time defines cycles of change in accommodation or sediment supply which correspond to sequences in the rock record depending on the scale of observation sequences and sequence stratigraphic surfaces may be ascribed to different hierarchical orders the concept of accommodation which defines the space available for sediments to fill is central to sequence stratigraphy changes in accommodation are in part controlled by regional to local tectonism and therefore are location specific the construction of accommodation curves is based on wheeler diagrams the preserved thickness of sequences and the paleodepositional environment accommodation curves may or may not correlate between different sedimentary basins or even between different sub basins of the same sedimentary basin depending on the interplay of local versus global controls on sedimentation the offset between the accommodation curves that characterize different depozones tends to increase for cycles of increasingly lower rank while the workflow and principles of sequence stratigraphy remain the same irrespective of the age of strata under analysis the differences and similarities between the phanerozoic and the precambrian rock record provide significant clues to improving our approach to the application of the sequence stratigraphic method