eight centuries of north atlantic ocean atmosphere variability climate in the tropical north atlantic is controlled largely by variations in the strength of the trade winds the position of the intertropical convergence zone and sea surface temperatures a high resolution study of caribbean sediments provides a subdecadally resolved record of tropical upwelling and trade wind variability spanning the past 825 years these results confirm the importance of a decadal 12 to 13 year mode of atlantic variability believed to be driven by coupled tropical ocean atmosphere dynamics although a well defined interdecadal mode of variability does not appear to be characteristic of the tropical atlantic there is evidence that century scale variability is substantial the tropical atlantic may also have been involved in a major shift in northern hemisphere climate variability that took place about 700 years ago

palynofacies analysis of the late holocene san nicolas terrace of the cauca paleolake and paleohydrology of northern south america abstract the detailed palynofacies analysis of the late holocene laminated succession of the san nicolas terrace in the middle cauca valley northern colombia is interpreted as the product of sedimentation in a lacustrine to fluvial dominated setting radiocarbon analyses reveal that the succession was deposited between 3500 and a few hundreds of years with sedimentary rates in excess of 600 cm ka the milimetric laminae and the high frequency fluctuations in the content of the palynodebris of terrestrial origin i e the high altered ligno cellulosic debris amorphous organic matter ratio together with diatoms typical of fluvial conditions such as aulacoseira granulata do suggest an intermittent and continuous hydrological and biological connectivity with the cauca river akin to a varzea lacustrine environment drier to wetter conditions appear to occur moving upward in the succession this might reflect regional precipitation conditions all along the cauca valley and the southern migration of the intertropical convergence zone

source receiver two way wave extrapolation for prestack exploding reflector modelling and migration most modern seismic imaging methods separate input data into parts shot gathers we develop a formulation that is able to incorporate all available data at once while numerically propagating the recorded multidimensional wavefield forward or backward in time this approach has the potential for generating accurate images free of artiefacts associated with conventional approaches we derive novel high order partial differential equations in the source receiver time domain the fourth order nature of the extrapolation in time leads to four solutions two of which correspond to the incoming and outgoing p waves and reduce to the zero offset exploding reflector solutions when the source coincides with the receiver a challenge for implementing two way time extrapolation is an essential singularity for horizontally travelling waves this singularity can be avoided by limiting the range of wavenumbers treated in a spectral based extrapolation using spectral methods based on the low rank approximation of the propagation symbol we extrapolate only the desired solutions in an accurate and efficient manner with reduced dispersion artiefacts applications to synthetic data demonstrate the accuracy of the new prestack modelling and migration approach

a 350014c yr high resolution record of water level changes in lake titicaca bolivia peru abstract sediment cores collected from the southern basin of lake titicaca bolivia peru on a transect from 4 6 m above overflow level to 15 1 m below overflow level are used to identify a new century scale chronology of holocene lake level variations the results indicate that lithologic and geochemical analyses on a transect of cores can be used to identify and date century scale lake level changes detailed sedimentary analyses of subfacies and radiocarbon dating were conducted on four representative cores a chronology based on 60 accelerator mass spectrometer radiocarbon measurements constrains the timing of water level fluctuations two methods were used to estimate the14c reservoir age both indicate that it has remained nearly constant at 25014c yr during the late holocene core studies based on lithology and geochemistry establish the timing and magnitude of five periods of low lake level implying negative moisture balance for the northern andean altiplano over the last 3500 cal yr between 3500 and 3350 cal yr b p a transition from massive inorganic clay facies to laminated organic matter rich silts in each of the four cores signals a water level rise after a prolonged mid holocene dry phase evidence of other significant low lake levels occurs 2900 2800 2400 2200 2000 1700 and 900 500 cal yr b p several of the low lake levels coincided with cultural changes in the region including the collapse of the tiwanaku civilization

climate drying and associated forest decline in the lowlands of northern guatemala during the late holocene abstract palynological studies document forest disappearance during the late holocene in the tropical maya lowlands of northern guatemala the question remains as to whether this vegetation change was driven exclusively by anthropogenic deforestation as previously suggested or whether it was partly attributable to climate changes we report multiple palaeoclimate and palaeoenvironment proxies pollen geochemical sedimentological from sediment cores collected in lake peten itza northern guatemala our data indicate that the earliest phase of late holocene tropical forest reduction in this area started at 4500 cal yr bp simultaneous with the onset of a circum caribbean drying trend that lasted for 1500 yr this forest decline preceded the appearance of anthropogenically associated zea mays pollen we conclude that vegetation changes in peten during the period from 4500 to 3000 cal yr bp were largely a consequence of dry climate conditions furthermore palaeoclimate data from low latitudes in north africa point to teleconnective linkages of this drying trend on both sides of the atlantic ocean

long term tidal cycle influences on a late holocene clay mineralogy record from the cariaco basin abstract recent analyses of coastal mudbank dynamics along northeastern south america indicate significant sediment remobilization associated with the 18 6 y lunar nodal tide over the last 20 y we present a near annually resolved record of quartz and illite illite smectite abundances spanning the last 800 y from the cariaco basin venezuela that suggests effects of the lunar nodal tide have played an important role in coastal processes over the last 8 centuries spectral analysis results of the clay and fine silt data include a statistically significant peak at 18 3 y in both the quartz and illite illite smectite records that is identified with the 18 6 y lunar nodal tide remobilization of shelf sediments by mean high water line variations driven by the lunar nodal tide is presented as the probable explanation of this signal in the cariaco basin mineral content since the period of this astronomically determined signal is constant with time it can be used to calibrate high resolution age models we modify our existing age model by tuning the 18 3 y component of the illite data to the 18 6 y period and explore its impact on the age depth relationship we suggest that the 18 6 y signal can be used to refine existing chronologies where detected

late holocene paleoenvironmental change at mid elevation on the caribbean slope of the cordillera central dominican republic a multi site multi proxy analysis abstract high resolution proxy records from the circum caribbean region indicate significant variation in late holocene climate especially precipitation attributed primarily to shifts in the mean annual position of the intertropical convergence zone itcz the paleoenvironmental and cultural impacts of this late holocene climate variability have been analyzed intensively in the western caribbean and to a lesser extent in the southern caribbean however the occurrence and impacts of late holocene climate shifts in the eastern caribbean especially in island interiors has not been well documented here we present sediment records of late holocene paleoenvironmental change from two lakes located on the caribbean slope of the cordillera central in the dominican republic that span the last 3000 years sediment characteristics pollen charcoal biogenic carbonate assemblages and isotopic composition and bulk sedimentary carbon isotope values in laguna castilla and laguna de salvador indicate extreme shifts in hydrology vegetation and disturbance regimes in response to climate change and human activity in the lake watersheds close correspondence between the hydrological histories of the lakes and trace metal concentrations in sediments of the cariaco basin indicate that precipitation variability here responds to the same controls and may similarly reflect shifts in the mean annual position of the itcz human occupation of the watersheds appears to be closely linked to severe dry periods and may indicate larger scale cultural responses to precipitation variability on the island of hispaniola prehistoric human populations strongly affected vegetation and disturbance regimes in the lake watersheds impacts may have lasted several centuries and may have been more severe than impacts of modern populations

mid to late holocene changes in tropical atlantic temperature seasonality and interannual to multidecadal variability documented in southern caribbean corals proxy reconstructions of tropical atlantic sea surface temperature sst that extend beyond the period of instrumental observations have primarily focused on centennial to millennial variability rather than on seasonal to multidecadal variability here we present monthly resolved records of sr ca a proxy of sst from fossil annually banded diploria strigosa corals from bonaire southern caribbean sea the individual corals provide time windows of up to 68 years length and the total number of 295 years of record allows for assessing the natural range of seasonal to multidecadal sst variability in the western tropical atlantic during snapshots of the mid to late holocene comparable to modern climate the coral sr ca records reveal that mid to late holocene sst was characterised by clear seasonal cycles persistent quasi biennial and prominent interannual as well as inter to multidecadal scale variability however the magnitude of sst variations on these timescales has varied over the last 6 2 ka the coral records show increased seasonality during the mid holocene consistent with climatemodel simulations indicating that southern caribbean sst seasonality is induced by insolation changes on orbital timescales whereas internal dynamics of the climate system play an important role on shorter timescales interannual sst variability is linked to ocean atmosphere interactions of atlantic and pacific origin pronounced interannual variability in the western tropical atlantic is indicated by a 2 35 ka coral possibly related to a strengthening of the variability of the el nino southern oscillation throughout the holocene prominent inter to multidecadal sst variability is evident in the coral records and slightly more pronounced in the mid holocene we finally argue that our coral data provide a target for studying holocene climate variability on seasonal and interannual to multidecadal timescales when using further numerical models and high resolution proxy data

the little ice age and medieval warm period in the sargasso sea sea surface temperature sst salinity and flux of terrigenous material oscillated on millennial time scales in the pleistocene north atlantic but there are few records of holocene variability because of high rates of sediment accumulation holocene oscillations are well documented in the northern sargasso sea results from a radiocarbondated box core show that sst was approximately 1 degree c cooler than today approximately 400 years ago the little ice age and 1700 years ago and approximately 1 degree c warmer than today 1000 years ago the medieval warm period thus at least some of the warming since the little ice age appears to be part of a natural oscillation 39 refs 4 figs 1 tab

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

does a monsoon climate exist over south america the climatology and the basic state of the summertime circulation and rainfall over south america are studied using assimilation products from the data assimilation system of goddard earth observing system 1 geos1 and satellite derived rainfall results indicate the existence of a regional summer monsoon circulation regime induced by strong diabatic heating over the subtropical south american highland centered at the altiplano plateau sensitivity of the results to the assimilation scheme is tested by comparing that with the national centers for environmental prediction ncep reanalysis and with satellite rainfall estimates results show general agreement between the model produced rainfall anomaly and the satellite estimates as well as consistency between the basic circulation features in the geos 1 and the ncep reanalyses a case study of 1989 90 south american summer monsoon sasm reveals the following characteristics 1 in late spring the onset of sasm is signaled by an abrupt merging of the upper tropospheric double westerly jets one in the subtropics and the other in the subpolar region into a single jet in the midlatitudes this is followed by the establishment of a vortex to the southeast of altiplano and occurrence of heavy precipitation over subtropical eastern brazil 2 during the mature phase of sasm the heavy rainfall zone moves over the altiplano plateau and the southernmost brazilian highland the fully established sasm features are the following a an enhancement of equatorial north atlantic trade wind which emanates from the sahara high and crosses the equator over the south american continent b a buildup of strong northwesterlies along the eastern side of the tropical andes and c development of the south atlantic convergence zone in the southernmost position with strong convective activity meanwhile the upper tropospheric return flow emerges from an anticyclone formed over the altiplano plateau crosses the equator and sinks over northwestern africa 3 the withdrawal of sasm in late summer is signaled by the resplitting of the midlatitude westerly jet at the same time the low level northwest monsoon flow diminishes reducing the moisture supply and leading to the termination of heavy precipitation over the subtropical highland results also show that the above mentioned characteristics of sasm are clearly linked to the tropospheric temperature changes over the central south american highland sensible versus latent heating over the highland are bound to play an important role in the evolution of sasm to provide further support of presence of a monsoon climate over south america sasm is compared and contrasted to the classic east asian summer monsoon easm many similar features including evolution characteristics between the two systems have been identified contrasting aspects of the sasm from the easm are also discussed it is pointed out that a number of monsoonal characteristics of the climate of south america such as the seasonal reversal of the low level wind become apparent only when the strong annual mean wind is removed based on the characteristic features and their evolution the authors conclude that a monsoon climate does exist over south america

the oxygen isotope composition of planktonic foraminifera from the cariaco basin venezuela seasonal and interannual variations material collected during a three year sediment trapping experiment in the cariaco basin venezuela january 1997 to december 1999 is used to examine both temporal and inter species variability in the oxygen isotope composition of planktonic foraminifera specifically this study compares the oxygen isotope composition of six species of planktonic foraminifera globigerinoides ruber pink globigerina bulloides neogloboquadrina dutertrei orbulina universa globorotalia menardii and globorotalia crassaformis with the climatology and hydrography of the region and evaluates the application of each species for use in paleoceanographic reconstructions the isotope results are consistent with known depth habitats for all six species the lowest 18 o values 1t o 2 were measured on g ruber pink and g bulloides two species that live in the surface mixed layer values for deeper dwelling species such as n dutertrei g menardii and g crassaformis are higher predominantly ranging from 0 to 0 5 temperature estimates derived using species specific paleotemperature equations indicate that g ruber pink accurately estimates sea surface temperatures ssts throughout the year while g bulloides temperature estimates are similar to measured surface temperatures only during the upwelling season january april for the remainder of the year the 18 o derived temperatures for g bulloides typically are lower than the measured sst although the maximum flux of all species occurs during upwelling the flux weighted annual mean isotopic composition of the six species indicates that only g bulloides is biased towards this season therefore we conclude that the sediment 18 o record of g ruber pink is most suitable for estimating past values of mean annual sst while g bulloides provides information on conditions during spring upwelling the depth of calcification of n dutertrei varies seasonally in response to changes in the depths of the thermocline and chlorophyll maximum as a result the 18 o difference between g ruber pink and n dutertrei provides an estimate of the annual surface to thermocline temperature gradient in the basin 2006 elsevier b v all rights reserved

deglacial changes in ocean circulation from an extended radiocarbon calibration temporal variations in the atmospheric concentration of radiocarbon sometimes result in radiocarbon based age estimates of biogenic material that do not agree with true calendar age this problem is particularly severe beyond the limit of the high resolution radiocarbon calibration based on tree ring data which stretches back only to1 2 about 11 8 kyr before present bp near the termination of the younger dryas cold period if a wide range of palaeoclimate records are to be exploited for better understanding the rates and patterns of environmental change during the last deglaciation extending the well calibrated radiocarbon timescale back further in time is crucial several studies attempting such an extension using uranium thorium dated corals3 4 5 and laminae counts in varved sediments6 7 8 9 show conflicting results here we use radiocarbon data from varved sediments in the cariaco basin in the southern caribbean sea to construct an accurate and continuous radiocarbon calibration for the period 9 to 14 5 kyr bp nearly 3 000 years beyond the tree ring based calibration a simple model compared to the calculated atmospheric radiocarbon concentration and palaeoclimate data from the same sediment core suggests that north atlantic deep water formation shut down during the younger dryas period but was gradually replaced by an alternative mode of convection possibly via the formation of north atlantic intermediate water

vertical distribution and isotopic fractionation of living planktonic foraminifera from the panama basin a model1 2 which explains the vertical and seasonal distribution of planktonic foraminifera was developed using data from the western north atlantic and is comprised of three tenets 1 the conditions in the photic zone upper 80 100 m exclusively dictate planktonic foraminifera species composition and abundance throughout the water column 2 species are vertically stratified within the photic zone according to their temperature preference depth distribution according to temperature preference has been proposed by several authors3 based on isotope analyses of sediments due to seasonal temperature variations seasonal variations in the 18o composition of seawater and species specific isotope fractionation rigorous proof of this hypothesis cannot be provided from sediment analyses alone 3 the chlorophyll maximum is a major food source zone which is preferentially exploited by foraminifera our data from the panama basin which are presented here are confirmation of this model the panama basin in the eastern equatorial pacific which has a shallow and steep thermocline was sampled for living planktonic foraminifera a multiple opening closing net and environmental sensing system mocness 4 was used to collect 13 sets of eight vertically stratified oblique samples we report here the quantitative distribution and stable isotopic composition of planktonic foraminifera from four mocness tows taken over 5 days during august 1979 rv knorr cruise 73 at 5 20 n 8 50 w each tow consisted of eight samples which integrated 12 5 m intervals from 0 to 100 m for moc 126 25 m intervals from 0 to 200 m for moc 127 100 150 m intervals from 0 to 1 000 m on moc 128 and 250 m intervals from 0 to 2 000 m on moc 131

increased northeast pacific climatic variability during the warm middle holocene 1 we use a pair of decadally resolved planktonic foraminiferal 18o records from santa barbara basin sbb to show that the warmest interval of the current interglacial the middle holocene was characterized by increased decadal to centennial scale climatic variability modern relationships between the pacific decadal oscillation pdo the el nino southern oscillation enso and upper water conditions in sbb also suggest a preference of the northeast ne pacific climate during the warm mid holocene toward the warm phase of the pdo and more intense enso warm events el ninos in the context of future climate this study suggests increasing decadal to centennial scale climatic variability in a globally warmed world

a 10 300 14c yr record of climate and vegetation change from haiti abstract pleistocene and holocene vegetation dynamics in the american tropics are inferred largely from pollen in continental lake sediments maritime influences may have moderated climate and vegetation changes on caribbean islands stable isotope 18 o study of a 7 6 m core from lake miragoane haiti provided a high resolution record of changing evaporation precipitation e p since 10 300 14 c yr b p the miragoane pollen record documents climate influences and human impacts on vegetation in hispaniola the 18 o and pollen data near the base of the core indicate cool dry conditions before 10 000 14 c yr b p lake miragoane filled with water in the early holocene as e p declined and the freshwater aquifer rose despite increasing early holocene moisture shrubby xeric vegetation persisted forest expanded 7000 14 c yr b p in response to greater effective moisture and warming the middle holocene 7000 3200 14 c yr b p was characterized by high lake levels and greatest relative abundance of pollen from moist forest taxa climatic drying that began 3200 14 c yr b p may have driven some mesophilic animal species to extinction the pollen record of the last millennium reflects pre columbian taino and european deforestation long term holocene vegetation trends in southern haiti are comparable to trends from continental lowland circum caribbean sites suggesting a common response to regional climate change

pore fluid constraints on the temperature and oxygen isotopic composition of the glacial ocean pore fluids from the upper 60 meters of sediment 3000 meters below the surface of the tropical atlantic indicate that the oxygen isotopic composition 18 o of seawater at this site during the last glacial maximum was 0 8 0 1 per mil higher than it is today combined with the 18 o change in benthic foraminifera from this region the elevated ratio indicates that the temperature of deep water in the tropical atlantic ocean was 4 c colder during the last glacial maximum extrapolation from this site to a global average suggests that the ice volume contribution to the change in 18 o of foraminifera is 1 0 per mil which partially reconciles the foraminiferal oxygen isotope record of tropical sea surface temperatures with estimates from barbados corals and terrestrial climate proxies

the history of south american tropical precipitation for the past 25 000 years long sediment cores recovered from the deep portions of lake titicaca are used to reconstruct the precipitation history of tropical south america for the past 25 000 years lake titicaca was a deep fresh and continuously overflowing lake during the last glacial stage from before 25 000 to 15 000 calibrated years before the present cal yr b p signifying that during the last glacial maximum lgm the altiplano of bolivia and peru and much of the amazon basin were wetter than today the lgm in this part of the andes is dated at 21 000 cal yr b p approximately coincident with the global lgm maximum aridity and lowest lake level occurred in the early and middle holocene 8000 to 5500 cal yr b p during a time of low summer insolation today rising levels of lake titicaca and wet conditions in amazonia are correlated with anomalously cold sea surface temperatures in the northern equatorial atlantic likewise during the deglacial and holocene periods there were several millennial scale wet phases on the altiplano and in amazonia that coincided with anomalously cold periods in the equatorial and high latitude north atlantic such as the younger dryas

century scale movement of the atlantic intertropical convergence zone linked to solar variability 1 the abundance of the planktic foraminifer globigerinoides sacculifer in gulf of mexico gom sediments is a proxy for the influx of caribbean surface waters the loop current into the gom penetration of the loop current into the gom is related to the position of the intertropical convergence zone itcz northward migration of the itcz results in increased incursion of the loop current into the gom southward migration of the itcz results in decreased penetration of the loop current into the gom abundance variations of g sacculifer in a sediment core from the pigmy basin in the gom show distinct century scale cyclicity over the last 5 000 years the periodicity of these abundance variations is similar to the century scale periodicity observed in proxy records of solar variability which suggests that the average position of the itcz and thus holocene century scale variability in the caribbean gom region is linked to solar variability

arctic north atlantic oscillation signature in holocene sea surface temperature trends as obtained from alkenone data 1 the variability in alkenone derived sea surface temperatures ssts in the north atlantic realm shows that a continuous sst decrease in the northeast atlantic from the early to the late holocene was accompanied by a persistent warming over the western subtropical atlantic the eastern mediterranean sea and the northern red sea based on the analysis of the instrumental data and of atmospheric general circulation model experiments we show that this variation in ssts during the holocene can be attributed to a continuous weakening of a northern hemisphere atmospheric circulation pattern similar to that of the arctic north atlantic oscillation

coherent high and low latitude climate variability during the holocene warm period a faunal record of sea surface temperature sst variations off west africa documents a series of abrupt millennial scale cooling events which punctuated the holocene warm period these events evidently resulted from increased southward advection of cooler temperate or subpolar waters to this subtropical location or from enhanced regional upwelling the most recent of these events was the little ice age which occurred between 1300 to 1850 a d when subtropical ssts were reduced by 3 to 4 c these events were synchronous with holocene changes in subpolar north atlantic ssts documenting a strong in phase link between millennial scale variations in high and low latitude climate during the holocene

high resolution tropical climate record for the last 6 000 years 1200 800 cal yrs b p the initial d 18 oi ncrease centered at 5 500 years ago is coincident with the development of arid conditions in the caribbean region and the end of the african humid period indicating a global drying of the northern tropics at this time synchronous with the aridification of the caribbean region are the onset of wetter conditions in the south american altiplano and the reoccupation of this region by humans this combination of contrasting climate conditions is attributed to a southward displacement of the intertropical convergence zone itcz that would have resulted in decreased precipitation and increased trade wind intensity in the caribbean region and increased rainfall over the altiplano index terms 4267 oceanography general paleoceanography 4231 oceanography general equatorial oceanography 4870 oceanography biological and chemical stable isotopes 4802 oceanography biological and chemical anoxic environments citation tedesco k and r thunell high resolution tropical climate record for the last 6 000 years geophys res lett 30 17 1891 doi 10 1029 2003gl017959 2003

isotopic evidence for late quaternary climatic change in tropical south america the tropical hydrologic cycle affects atmospheric trace gases and global climate change and thus records of hydrologic change encompassing a variety of time scales from the low latitudes are important in paleoclimatology isotopic analysis of calcite from lake junin peru provides a record of hydrologic variability that spans the last glacial interglacial transition in the southern tropics the record reveals a 6 enrichment in 18 o calcite during the late glacial followed by a gradual depletion during the holocene which can be interpreted as a decrease followed by a long term increase in effective moisture close agreement between 18 o calcite and rainy season insolation indicates that long term changes in tropical hydrology were linked to orbital variations furthermore hydrologic change was out of phase in the northern and southern tropics over this time period

southward migration of the intertropical convergence zone through the holocene titanium and iron concentration data from the anoxic cariaco basin off the venezuelan coast can be used to infer variations in the hydrological cycle over northern south america during the past 14 000 years with subdecadal resolution following a dry younger dryas a period of increased precipitation and riverine discharge occurred during the holocene thermal maximum since approximately 5400 years ago a trend toward drier conditions is evident from the data with high amplitude fluctuations and precipitation minima during the time interval 3800 to 2800 years ago and during the little ice age these regional changes in precipitation are best explained by shifts in the mean latitude of the atlantic intertropical convergence zone itcz potentially driven by pacific based climate variability the cariaco basin record exhibits strong correlations with climate records from distant regions including the high latitude northern hemisphere providing evidence for global teleconnections among regional climates

miocene extension and fault related folding in the highland range southern nevada a three dimensional perspective abstract the highland range of southern nevada contains a major anticline and syncline that constitute the westernmost segments of the black mountains accommodation zone in the highly extended colorado river extensional corridor the folds are defined by thick tilted sections of miocene volcanic and sedimentary strata that accumulated immediately prior to and during regional extension the folds are generally symmetrical with interlimb angles that exceed 90 subhorizontal hingelines and steeply inclined axial surfaces east and west dipping normal faults dominate the west and east tilted limbs of the folds respectively the limbs of the folds are parts of major half grabens tilt fanning within these half grabens and 15 new 40ar 39ar dates bracket major extension between about 16 5 and 11 ma tilting of the opposing fold limbs occurred simultaneously and was contemporaneous with extension the anticline and syncline are therefore interpreted as fault related extensional folds produced by the partial along strike overlap of oppositely dipping normal fault systems and attendant tilt block domains the anticline developed between overlapping listric normal faults that dip toward one another including the east dipping mccullough range and west dipping keyhole canyon faults each limb of the anticline is a rollover fold developed in the hanging wall of the inwardly dipping listric normal faults the syncline formed between overlapping outwardly dipping listric faults as adjacent fault blocks were tilted toward one another the dominant folding style was fault bend folding with drag folding and displacement gradient folding playing subsidiary roles the anticline and syncline significantly affected depositional patterns with synextensional units including two major ash flow tuffs thinning toward the anticlinal hinge and thickening toward the synclinal hinge the black mountains accommodation zone is largely composed of intersecting northwest trending anticlines and northeast trending synclines both occurring at a variety of scales depending on the amount of overlap between the opposing normal fault systems this three dimensional geometry contrasts with the typical style of folding in contractional settings and may characterize extensional accommodation zones that include the partial along strike overlap of multiple oppositely dipping normal faults the folds in the highland range serve as well exposed analogues of similar features in hydrocarbon rich areas of submerged continental margins