climate change during the early paleogene in the bogota basin colombia inferred from paleosol carbon isotope stratigraphy major oxides and environmental magnetism abstract paleosols in the bogota basin colombia record an increase in chemical weathering across the paleocene eocene p e transition rock magnetic properties and major element geochemistry exhibit an abrupt change in an interval identified as including the p e boundary as established by previously published biostratigraphy and a u pb date on volcanic zircons 56 2 1 6 ma during the stratigraphic interval that contains the p e transition magnetic susceptibility increases significantly with an order of magnitude higher concentration of magnetite maghemite and hematite the preponderance of pure stoichiometric magnetite in the paleosols of this interval indicates that the increase in magnetic susceptibility is due to changes in the rate of pedogenesis rather than an increase in the erosion of nearby volcanic rocks which would contribute titanomagnetite pedogenic structures preserved within the paleosols a lack of iron oxides as cement friability of the sandstones and previously published thermochronologic data are not consistent with burial diagenesis as an explanation for the origin of the magnetic mineral assemblage these enhanced pedogenesis and related chemical weathering is also confirmed by increases in the concentration of fe 2 o 3 and al 2 o 3 and loss on ignition values an increase in mean precipitation across this interval is inferred by the lack of carbonate nodules and a decrease in sio 2 in paleosols thus we hypothesize that there was an intensification of chemical weathering during the interval that contains the p e transition

tracking exhumation of andean ranges bounding the middle magdalena valley basin colombia the shortening history of the andes is important for understanding retroarc deformation along convergent margins and forcing mechanisms of cenozoic climate however the timing of uplift in the northern andes is poorly constrained with estimates ranging from cretaceous to pliocene detrital zircon u pb ages from the middle magdalena valley basin in colombia reveal two provenance shifts during cenozoic time the fi rst shift occurs between early and late paleocene strata where u pb results show a switch from proterozoic dominated to phanerozoic dominated age spectra we attribute this change to uplift related exhumation of the central cordillera the second shift occurs between middle late eocene and late oligocene strata where increased grenville ages and diminished mesozoic ages can be linked to uplift of the eastern cordillera our results show that signifi cant pre neogene deformation affected the northern andes underscoring the potential importance of andean uplift on the dynamics of paleogene climate

geochronology geochemistry and tectonic evolution of the western and central cordilleras of colombia abstract autochthonous rocks of the pre cretaceous continental margin of nw south america the tahami terrane are juxtaposed against a series of para autochthonous rock units that assembled during the early cretaceous allochthonous oceanic crust of the caribbean large igneous province collided with and accreted onto the margin during the late cretaceous we present the first regional scale dataset of zircon u pb la icp ms ages for intrusive and metamorphic rocks of the autochthonous tahami terrane early cretaceous igneous para autochthonous rocks and accreted oceanic crust the u pb zircon data are complemented by multiphase 40ar 39ar crystallization and cooling ages the geochronological data are combined with whole rock major oxide trace element and ree data acquired from the same units to constrain the tectonic origin of the rock units and terranes exposed in the western cordillera cauca patia valley and the central cordillera of colombia the tahami terrane includes lower paleozoic orthogneisses 440 ma that may have erupted during the active margin stage of the rheic ocean basement gneisses were intruded by permian continental arc granites during the final assembly of pangea triassic sedimentary rocks were subsequently deposited in rift basins and partially melted during high t metamorphism associated with rifting of western pangea during 240 220 ma continental arc magmatism during 180 145 ma is preserved along the whole length of the central cordillera and was followed by an early cretaceous out board step of the arc axis and the inception of the quebradagrande arc that fringed the continental margin back stepping of the arc axis may have been caused by the collision of buoyant seamounts which were coeval with plateau rocks exposed in the nicoya peninsular of costa rica rapid westward drift of south america closed the quebradagrande basin in the late aptian and caused medium high p t metamorphic rocks of the arquia complex to exhume and obduct onto the continental margin subduction beneath hot spot derived rocks of the caribbean plateau 100 92 ma formed an intra oceanic arc 92 75 ma which collectively comprise the late cretaceous caribbean large igneous province the remnant ocean basin located between south america and the caribbean large igneous province was partly consumed via continental subduction forming the large antioquia batholith the caribbean large igneous province collided and accreted to south america during 75 70 ma along the cauca almaguer fault resulting in the cessation of both arcs and the paleocene onset of subduction beneath the accreted oceanic crust

tsunamigenic sources in an active european half graben gulf of corinth central greece abstract the gulf of corinth is an active half graben dissecting the mainland of greece along an east west axis the gulf is well known for its intense seismic activity and its rapid extension rates however published historical catalogues reveal that the gulf of corinth is also the site of frequent and relatively destructive tsunami occurrences this paper presents a comparative study of the potential of probable tsunami sources in the gulf of corinth by referring to published offshore geology data coseismic seafloor displacement along offshore faults and submarine mass failures are the active tsunamigenic sources the paper applies easy to use empirical and semi empirical equations that estimate the generated tsunami wave height just over the source area building upon the most probable worst case scenarios for both coseismic fault displacement and submarine mass failure generated tsunamis the tsunami potential of its case is explored a maximum probable 6 7 m w offshore earthquake would produce a rupture on the seafloor surface with a maximum displacement of 0 66 to 1 08 m in height in the gulf of corinth the tsunami which would be generated by the seafloor displacement would have a wave height of the same magnitude as the seafloor displacement furthermore existing evidence of submarine mass failures that took place over the last 3000 years in the eastern part of the corinth gulf had and would have the potential of generating tsunamis with a maximum wave height of 1 04 and 4 04 m and maximum wave length of 4 52 and 6 25 km

middle to late holocene palaeoenvironmental study of gialova lagoon sw peloponnese greece abstract the coastal areas of eastern mediterranean have long been the subject of research due to their rapid geomorphological changes but also because of their archaeological interest our study is focused on a shallow coastal lagoon of peloponnese gialova lagoon which for several years has attracted the scientific interest of archaeologists geomorphologists as well as sedimentologists gialova lagoon is located near the ancient city of pylos the kingdom of king nestor during the mycenaean period 1600 1100 bc the objectives of this study are a to reconstruct the middle to late holocene depositional environments of the lagoon and b to correlate our data to already existing publications in order to shed new light on the holocene evolution of the lagoon and the associated coastal palaeoenvironmental changes an 8 m deep vibracore was drilled and a multi proxy analysis was carried out on the sediment sequence including sedimentological grain size analysis and moment measures total organic carbon toc total nitrogen tn and total phosphorus tp high resolution geochemical xrf scanning and palaeontological micro and macro faunal analysis the chronological framework is based on five 14c datings forming the basis for an age depth model calculated using the oxcal software the radiocarbon dates from previous studies 6 cores 20 dates were also taken into account the data synthesis and interpretation provided robust and coherent indications regarding the palaeoenvironment shoreline changes and the rate of geomorphological changes of the coastal area of gialova lagoon as well as useful information about the palaeonvironmental and palaeoclimatic conditions that prevailed during the mycenaean period the interpretation reveal a transition from a shallow marine environment 6500 5800 yr b p to a brackish lagoonal 5800 3300 yr b p followed by a shift towards a freshwater marsh environment 3300 yr b p to present

la reunion island dunites as analogs of the martian chassignites tracking trapped melts with incompatible trace elements abstract fractional crystallization of basalts produces a variety of ultramafic cumulates poor in incompatible elements in order to discuss the effect of trapped liquids on the concentrations of incompatible elements in these cumulates we studied a series of dunites and pyroxenites from the piton de la fournaise la reunion island indian ocean these rocks have a high variability in the abundance of these elements which is only partially explained by their proportions of olivines and pyroxenes mass balance calculations indicate that 0 25 to 1 wt of trapped melts are required to account for the budget of the highly incompatible element abundances such as u rb nb or light rare earth elements ree using our results we revisited the ree geochemistry of chassignites a grouplet of martian meteorites chassignites are mineralogically texturally and chemically very similar to the dunites from la reunion island which can be seen as very close terrestrial analogs the variations of ree abundances and ratios in chassigny one of the three known chassignites can be explained by inhomogeneous distribution of trapped melts in this meteorite at the scale of the size of the fragments typically

multiproxy record for the last 4500 years from lake shkodra albania montenegro a multi proxy record is presented for approximately the last 4500 cal a bp from lake shkodra albania montenegro lithological analyses c n ratio and d 13 c of the organic and inorganic carbon component suggest that organic matter and bulk carbonate are predominantly authigenic the d 18 o record of bulk carbonate indicates the presence of two prominent wet periods one at ca 4300 cal a bp and one at ca 2500 2000 cal a bp the latter phase is also found in southern spain and central italy and represents a prominent event in the western and central mediterranean in the last 2000 years four relatively wet intervals occurred between ca 1800 and 1500 cal a bp 150 450 ad 1350 1250 600 700 ad 1100 800 850 1150 ad and at ca 90 cal a bp 1860 ad between ca 4100 and 2500 cal a bp d 18 o values are relatively high with three prominent peaks indicating drier conditions at ca 4100 4000 cal a bp ca 3500 and at ca 3300 cal a bp four additional drier events are identified at 1850 ca 100 ad 1400 ca 550 ad 1150 800 ad and ca 750 cal a bp 1200 ad the pollen record does not show changes in accordance with these episodes owing to the poor sensitivity of vegetation in this area which is dominated by an orographic rainfall effect and where changes in altitudinal vegetation belts do not affect the pollen rain in the lake catchment however since ca 900 cal a bp a significant decrease in the percentage arboreal pollen and in pollen concentrations suggest major deforestation produced by human activities copyright 2012 john wiley sons ltd

late holocene coastal depositional environments and climate changes in the gulf of corinth greece multidisciplinary studies in coastal systems of the eastern mediterranean region have proven to be excellent tools in understanding paleoenvironmental paleoecological and paleoclimatic changes th

mode and timing of terrane accretion in the forearc of the andes in ecuador the volcanic basement of the ecuadorian western cordillera pallatanga formation and san juan unit is made up of mafi c and ultramafi c rocks that once formed an oceanic plateau radiometric ages from these rocks overlap with a hornblende 40 ar 39 ar plateau age of 88 1 6 ma age obtained for oceanic plateau basement rocks of the pinon formation in coastal ecuador and with ca 92 88 ma ages reported for oceanic plateau sequences in the caribbean and western colombia these results suggest that the oceanic plateau rocks of the western cordillera and fl at forearc in ecuador are derived from the late cretaceous caribbean colombia oceanic plateau intraoceanic island arc sequences rio cala group overlie the plateau in the western cordillera and yield crystallization ages that range between ca 85 and 72 ma the geochemistry and radiometric ages of island arc lavas from the rio cala group combined with the age range and geochemistry of their turbiditic volcaniclastic products indicate that the arc was initiated by westward subduction beneath the caribbean plateau they are coeval with island arc rocks of coastal ecuador las orquideas san lorenzo and cayo formations and colombia ricaurte arc these island arc

annual to millennial record of sediment delivery to us virgin island coastal environments over 100 sediment cores were collected from us virgin island coastal marine and salt pond environments to document the record of sediment delivery to the coastal system on annual to millennial time

geodynamic controls on tertiary arc magmatism in ecuador constraints from u pb zircon geochronology of oligocene miocene intrusions and regional age distribution trends abstract we obtained u pb zircon ages of late tertiary intrusions in the northern andes to provide robust time calibration points for the intrusive geochronologic framework of ecuador which is mostly based on k ar data magmatism associated with intrusion emplacement ranges from 31 to 7 ma with ages mainly pooling in the late oligocene early miocene where both k ar and u pb data exist for a given intrusive system ages obtained by the different methods are usually concordant within 1 4 m y suggesting that k ar ages are accurate indicators for the timing of tertiary arc magmatism on a regional multi m y scale except for a single sample the investigated intrusions completely lack externally inherited zircons in agreement with dominantly zircon poor oceanic crustal basement domains spatio temporal distribution trends of tertiary arc magmatism inferred from screened u pb k ar and zircon fission track geochronologic data allow tracking of the progressive along arc broadening of a flat slab segment below southernmost ecuador in the mid to late miocene and of moderate slab shallowing in northern central ecuador in the late miocene these regional arc migration patterns correlate in time with the subduction of the buoyant inca plateau and the carnegie ridge seamount chain the temporal distribution of tertiary ecuadorian arc magmatism indicates a late oligocene early miocene arc magmatic flare up event comprising widespread ignimbrite eruption and batholith construction initiation of the flare up event coincides in time with accelerating less oblique farallon nazca south america plate convergence suggesting a positive feedback between convergence rates asthenospheric melt production mantle crust melt flux and upper crustal arc magmatic productivity in ecuador

geoscience of ancient mediterranean harbours abstract although much has been written on the subject of ancient mediterranean harbours the relatively new area of harbour geoarchaeology remains dispersed in the geoscience and archaeological literature over a decade of research has amassed rich and varied datasets of anthropogenically forced coastal evolution with a remarkable number of between site analogies this new research field also shows the rich potential of geoscience to reconcile important archaeological questions no single publication however has yet drawn on these geological patterns to yield a detailed overview suitable for geoscientists and environmental archaeologists the aim of this review article is to 1 discuss how ancient harbours have come to be preserved in the geological record 2 expound the basic principles and palaeoenvironmental tools underpinning ancient harbour geoarchaeology 3 outline some of the most significant research advances made and 4 discuss a new chrono stratigraphic model applicable to harbour sequences

the isotopic composition of yb and the precise and accurate determination of lu concentrations and lu hf ratios by isotope dilution using mc icpms 1 we report yb isotopic data for the purpose of accurately correcting measurements of lu and lu hf ratios during multicollector inductively coupled plasma mass spectrometer mc icpms analysis the yb isotopic ratios agree with recent results of chu et al 2002 and amelin and davis 2004 when corrected for mass fractionation to the same reference values protocols for lu measurement involving simultaneous subtraction of yb interference and application of a fractionation correction based on yb are described it is shown that lu concentrations and lu hf ratios determined by mc icpms using this methodology are more precise and potentially more accurate than results based on analysis of lu by thermal ionization mass spectrometry tims a number of mc icpms lu hf isotopic analyses of standard rocks and other geological samples previously analyzed by tims are presented these document reproducibility of lu hf within 0 2 where most discrepancies can be assigned to the unknown lu mass fractionation during tims analysis

magmatic affinity of modern and ancient subalkaline volcanic rocks determined from trace element discriminant diagrams when dealing with ancient subalkaline volcanic rocks the alkali total iron magnesium afm diagram is of limited use in assigning a tholeiitic versus calc alkaline affinity because these eleme

new geological and geochronological data from the colombian andes continental growth by multiple accretion the regional geology of colombia consists of a composite palaeozoic to cenozoic sedimentary basin overlying precambrian shield rocks which are exposed in the eastern cordillera magdalena valley and at least part of the extensive llanos plains a palaeozoic metamorphic schist belt with abundant post metamorphic igneous rocks comprises the central cordillera a mesozoic volcanic suite extends from the western flank of the central cordillera and accounts for the bulk of the western cordillera a cenozoic sedimentary sequence probably overlying a late cretaceous oceanic crust and fore arc complex forms the pacific coastal plain the continental edge of central and southern colombia is interpreted as a composite margin made up of successively accreted oceanic island arc related sequences of palaeozoic early mesozoic and late cretaceous ages the present day cycle which began in the miocene is not associated with island arc volcanism

from oceanic plateaus to allochthonous terranes numerical modelling abstract large segments of the continental crust are known to have formed through the amalgamation of oceanic plateaus and continental fragments however mechanisms responsible for terrane accretion remain poorly understood we have therefore analysed the interactions of oceanic plateaus with the leading edge of the continental margin using a thermomechanical petrological model of an oceanic continental subduction zone with spontaneously moving plates this model includes partial melting of crustal and mantle lithologies and accounts for complex rheological behaviour including viscous creep and plastic yielding our results indicate that oceanic plateaus may either be lost by subduction or accreted onto continental margins complete subduction of oceanic plateaus is common in models with old 40 ma oceanic lithosphere whereas models with younger lithosphere often result in terrane accretion three distinct modes of terrane accretion were identified depending on the rheological structure of the lower crust and oceanic cooling age frontal plateau accretion basal plateau accretion and underplating plateaus complete plateau subduction is associated with a sharp uplift of the forearc region and the formation of a basin further landward followed by topographic relaxation all crustal material is lost by subduction and crustal growth is solely attributed to partial melting of the mantle frontal plateau accretion leads to crustal thickening and the formation of thrust and fold belts since oceanic plateaus are docked onto the continental margin strong deformation leads to slab break off which eventually terminates subduction shortly after the collisional stage has been reached crustal parts that have been sheared off during detachment melt at depth and modify the composition of the overlying continental crust basal plateau accretion scrapes oceanic plateaus off the downgoing slab enabling the outward migration of the subduction zone new incoming oceanic crust underthrusts the fractured terrane and forms a new subduction zone behind the accreted terrane subsequently hot asthenosphere rises into the newly formed subduction zone and allows for extensive partial melting of crustal rocks located at the slab interface and only minor parts of the former oceanic plateau remain unmodified oceanic plateaus may also underplate the continental crust after being subducted to mantle depth u hp terranes are formed with peak metamorphic temperatures of 400 700 c prior to slab break off and subsequent exhumation rapid and coherent exhumation through the mantle along the former subduction zone at rates comparable to plate tectonic velocities is followed by somewhat slower rates at crustal levels accompanied by crustal flow structural reworking and syndeformational partial melting exhumation of these large crustal volumes leads to a sharp surface uplift

heavy mineral analysis and clinopyroxene geochemistry applied to provenance analysis of lithic sandstones from the azuero sona complex nw panama abstract the volcaniclastic sandstones of the middle eocene to lower miocene tonosi formation were deposited within the forearc realm of an island arc system which today is part of the southern central american landbridge both heavy mineral analyses and geochemical analyses of clinopyroxenes clearly reveal differences in the composition between sediments of the lower and upper tonosi formation indicating changes within the tectonic setting as well as island arc evolution during time of deposition based on characteristic heavy mineral suites three lithogroups can be determined and assigned to the lower and upper tonosi formation respectively provenance analyses indicate that the sandstones of the tonosi formation were generally derived from an island arc setting the abundance of a mafic heavy mineral suite relative to heavy minerals derived from metamorphic and sialic intrusive rocks indicates a convergent plate boundary setting for provenance of the lower tonosi formation this result is supported by the chemistry of clinopyroxenes within the heavy mineral suite which indicates evolved basaltic magma types sourced the detrital grains within the hb ol id cpxbrown opx cpxgreen diagram most samples of the upper tonosi formation plot in the field for divergent plate boundaries the geochemical analyses also show that clinopyroxenes of the upper tonosi formation additionally exhibit affinities to within plate alkaline magma types as an integration of our results we present a provisional two stage model for the tectono sedimentary evolution of the western panamanian forearc area during the deposition of the tonosi formation

vertical displacement trends in the aegean coastal zone ne mediterranean during the holocene assessed by geo archaeological data trends in the vertical displacement i e uplift or subsidence of the aegean sea coastal zone have been assessed by comparing observational data with those derived from the predictive glacio hydro isostatic model of lambeck and purcell 2005 for a period spanning from the mesolithic to the late roman times the data base comprises published studies that use both geomorphological with associated biological material and archaeological sea level indicators markers localities demonstrating uplift of high amplitude were detected in front of the hellenic arc antikythira crete rhodes nisyros and in the northeast aegean region thrace whilst areas experiencing tectonic subsidence were mainly observed in the central aegean region which is characterized by an extensional tectonic domain however regional scale tectonic particularities have caused uplift in parts of the west and east coast of central aegean tectonically stable sites can be found in the cyclades plateau however this is due to a bala

evidence for middle eocene and younger land emergence in central panama implications for isthmus closure the rise of the isthmus of panama linked to a number of climatic paleoceanographic and biological events has been studied mostly from indirect often distal geochemical and biotic evidence we have upgraded existing geologic mapping in central panama with more than 2000 field stations over 40 petrographic analyses and more than 30 new geochronological and thermochronological analyses this data set suggests that the isthmus was an uninterrupted chain above sea level from late eocene until at least late miocene times the basement complex of central panama is a folded faulted 3 km thick arc sequence intruded by granitoid bodies and onlapped by mildly deformed upper eocene and oligocene strata six u pb zircon ages in the granitoids along with published geochronological data reveal intense late paleocene to middle eocene magmatism 58 39 ma a temporary cessation of magmatic activity between 38 and 27 ma and renewed magmatism between 25 and 15 ma in a position 75 km south of the former magmatic axis thermochronological analyses in zircon eight u th he ages and in apatite crystals four u th he ages and nine fission track ages obtained from a subset of 58 54 ma granitoid bodies record a concordant lutetian age 47 42 ma cooling from 200 c to 70 c in 5 m y and cooling below 40 c between 12 and 9 ma cooling is linked to exhumation by an angular unconformity that separates the deformed basement complex below from mildly deformed upper eocene to oligocene terrestrial to shallow marine strata above exhumation and erosion of the basement complex are independently confirmed by lower miocene strata that have a detrital zircon signature that closely follows the central panama basement complex age distribution these results greatly restrict the width and depth of the strait separating southern central america from south america and challenge the widely accepted notion that the central american seaway closed in late pliocene time when the ice age began

benthic foraminiferal evidence and paleoenvironmental evolution of holocene coastal plains in the aegean sea greece abstract benthic foraminiferal composition of sedimentary successions during the last 7500 years was investigated from boreholes drilled in three rather tectonically stable coastal areas of the aegean sea alykes kitros lafrouda thrace and vravron attica the quantitative analysis of foraminiferal fauna enabled separation into two different groups that are supported by the analysis of modern benthic foraminiferal communities in the studied sites group a consists of ammonia tepida and haynesina germanica closed lagoon assemblage whereas the most common species of group b open lagoon assemblage are aubignyna perlucida miliolids elphidium spp and ammonia spp the foraminiferal composition integrated with radiometric dating provides information on holocene paleoenvironmental changes in the studied coastal plains related to sea land interaction alykes kitros and lafrouda thrace boreholes show a similar trend with an open lagoonal fauna in the lower part transitional upwards to closed lagoonal conditions this environmental change has taken place after 6500 cal bp in alykes kitros and around 3000 cal bp at lafrouda thrace the benthic communities of vravron attica borehole sediments seem to represent continuously an open lagoon shallow marine environment from 4700 to 400 cal bp

palaeoenvironmental evolution of the ancient harbor of lechaion corinth gulf greece were changes driven by human impacts and gradual coastal processes or catastrophic tsunamis abstract the corinth gulf central greece is one of the most rapidly widening tectonic rifts on earth where large earthquakes with magnitudes of up 7 0 have been documented not only by instrumental records but also assessed from historical reports extending back to the 5th century bce several of these earthquakes were associated with tsunamis particularly in the western part of the gulf of particular interest is the ancient harbor of lechaion in the eastern side of corinth gulf we reexamine the hypothesis that lechaion was hit by high energy tsunami waves in the 8th 6th century bce 1st 2nd century ce and during the 6th century ce on the basis of sedimentological seismotectonic archaeological and historical data completed with field observations we support that there is no evidence for tsunami impact in lechaion local stratigraphy and environmental changes are rather interpreted by human impacts and gradual coastal processes such interpretations confirm that the tsunami potential in the east corinth gulf is relatively low

paleoenvironmental changes since 3000 bc in the coastal marsh of vravron attica se greece abstract the coastal area of the vravron bay in the vicinity of the homonym archaeological site is a marshy plain located on the eastern part of the attica peninsula eastern greece in order to provide evidence for palaeoenvironmental changes and landscape evolution of the area detailed micropaleontological palynological and sedimentological analyses have been conducted at the underlying late holocene coastal deposits the recovered sediments lithostratigraphic units a d represent a continuous record of the environmental history of the area since the early bronze age covering all subsequent historical periods the base of the recovered deposits is older than the 3rd millennium bc until late medieval times the studied sequence contains plenty evidence for the existence of the natural port reported from the mycenaean lithostratigraphic unit a that infilled after repeated flooding events during the classic period lithostratigraphic unit b and gradually developed into a shallower marine environment lithostratigraphic unit c in the uppermost part of the sequence lithostratigraphic unit d a transition towards brackish environment with intense fresh water input is featured around 1540 ad signs of human agricultural activities in vravron appear since 3000 bc early bronze age and are linked to the history of inhabitation in the area

the subduction initiation rule a key for linking ophiolites intra oceanic forearcs and subduction initiation we establish the subduction initiation rule sir which predicts that most ophiolites form during subduction initiation si and that the diagnostic magmatic chemostratigraphic progression for sir ophiolites is from less to more hfse depleted and lile enriched composi tions this chemostratigraphic evolution reflects formation of what ultimately becomes forearc lithosphere as a result of mantle melting that is progressively influenced by subduction zone enrichment during si the magmatic chemostratigraphic progression for the izu bonin mariana ibm forearc and most tethyan ophiolites is specifically from morb like to arc like volcanic arc basalts or vab boninites or bon because si progressed until establishment of a mature subduction zone morb like lavas result from decompression melting of upwelling asthenosphere and are the first magmatic expression of si the contribution of fluids from dehydrating oceanic crust and sediments on the sinking slab is negligible in early si but continued melting results in a depleted harzburgitic residue that is progressively metasomatized by fluids from the sinking slab subsequent partial melting of this residue yields typical ssz like lavas in the latter stages of si if si is arrested early e g as a result of collision morb only ophiolites might be expected consequently morb and ssz only ophiolites may represent end members of the si ophiolite spectrum the chemostratigraphic similarity of the mariana forearc with that of ophiolites that follow the sir intimates that a model linking such ophiolites oceanic forearcs and si is globally applicable

geochemistry and tectonic setting of pre collision cretaceous and paleogene volcanic rocks of ecuador pre collision cretaceous lower tertiary volcanic rocks of western ecuador from the coastal area pinon and san lorenzo formations and western cordillera macuchi and celica formations consist of three rock suites the first suite includes tholeiites of ocean floor affinities that have distinct light ree depleted patterns and low la nb la hf and th hf ratios the island arc tholeiites of the second suite have lower contents of ti zr hf and nb the third suite comprises calc alkalic rocks mainly continental margin andesites and dacites the continental volcanic arc rocks crop out in an area east of the tholeiitic rocks the boundary between the two areas is the major suture separating continental south america from accreted terrenes to the west a model is suggested for the geodynamic evolution of what is now western ecuador during the late cretaceous it includes two east dipping subduction zones of turonian to santonian ages and the accretion of the oceanic island arc to the continent

geodynamic models of terrane accretion testing the fate of island arcs oceanic plateaus and continental fragments in subduction zones 1 crustal growth at convergent margins can occur by the accretion of future allochthonous terranes fats such as island arcs oceanic plateaus submarine ridges and continental fragments using geodynamic numerical experiments we demonstrate how crustal properties of fats impact the amount of fat crust that is accreted or subducted the type of accretionary process and the style of deformation on the overriding plate our results show that 1 accretion of crustal units occurs when there is a weak detachment layer within the fat 2 the depth of detachment controls the amount of crust accreted onto the overriding plate and 3 lithospheric buoyancy does not prevent fat subduction during constant convergence island arcs oceanic plateaus and continental fragments will completely subduct despite having buoyant lithospheric densities if they have rheologically strong crusts weak basal layers representing pre existing weaknesses or detachment layers will either lead to underplating of faulted blocks of fat crust to the overriding plate or collision and suturing of an unbroken fat crust our experiments show that the weak ultramafic layer found at the base of island arcs and oceanic plateaus plays a significant role in terrane accretion the different types of accretionary processes also affect deformation and uplift patterns in the overriding plate trench migration and jumping and the dip of the plate interface the resulting accreted terranes produced from our numerical experiments resemble observed accreted terranes such as the wrangellia terrane and klamath mountain terranes in the north american cordilleran belt

late postglacial paleoenvironmental change in the northeastern mediterranean region combined palynological and molecular biomarker evidence three gravity cores collected from the ne mediterranean nemr across a transect from the northern aegean sea north skyros basin to the south cretan margin scm were investigated for pollen and terrestrial biomarkers derived from epicuticular waxes of vascular plants during the last 20 ky pollen data show diversified mixed temperate forest in the northern borderlands and enhanced mediterranean vegetation in the southern areas documenting an n s climatic trend terrestrial plant biomarkers and their diagnostic geochemical indices exhibit latitudinal patterns which are interpreted in terms of the different delivery pathways fluvial runoff vs atmospheric transport resulting from the climate conditions during different periods during the late glacial and early deglaciation periods 20 14 ka bp relatively increased humidity h index is recorded in the north aegean sea while in the south drier climate was the limiting factor for vegetation development during this interval terrestrial n alkanes showed increased accumulation rates suggesting massive transport of terrestrial organic matter through runoffs and rivers followed by weaker input after 14 ka bp after 11 ka bp a major expansion of forest cover is evidenced in the nemr accompanied by a higher h index because of the climatic amelioration the forest vegetation exhibited regionally different characteristics with cool temperate taxa being more abundant in the aegean cores while the scm record is being featured by mediterranean elements at the onset of the holocene and throughout the holocene climatic optimum the delivery of terrestrial biomarkers increased and became more significant in the aegean sites compared to the scm site within the holocene the average chain length acl of long chain n alkanes exhibits lower values in the northern aegean than in the southeastern aegean and scm indicating the predominance of warmer species southwards finally the h index records a conspicuous humidity increase between 5 4 and 4 3 ka bp in the south aegean that coincides with an increase in the terrestrial biomarker supply and the deposition of a distinct sapropel like layer smh sapropel mid holocene similar trends in t temperature and h indices are slightly delayed and attenuated in the northern aegean and are accompanied by an increase in the acl index a noticeable increase in the accumulation rates ars of terrestrial biomarkers and the hpa index values during this period are clearly recorded in all three cores indicative of enhanced terrigenous inputs of organic matter along with higher in situ preservation

core top calibration of mg ca in tropical foraminifera refining paleotemperature estimation 1 optimal use of mg ca as a paleotemperature proxy requires establishing calibrations for different species of foraminifera and quantifying the influence of dissolution to achieve this goal we have measured mg ca and 18o in a series of tropical and subtropical core tops including four depth transects the ceara rise the sierra leone rise and the rio grande plateau in the atlantic and the ontong java plateau in the pacific focusing on spinose mixed layer dwelling species globigerinoides ruber and globigerinoides sacculifer and nonspinose thermocline dwelling neogloboquadrina dutertrei shell mg ca in g sacculifer is 5 15 lower than in g ruber while n dutertrei mg ca is 49 55 lower than in g ruber this statistically significant offset has allowed us to establish different calibrations for each species multilinear regression analysis was used to develop calibration equations that include a correction term for the dissolution effect on mg ca in foraminiferal calcite presented in this paper are two sets of calibrations one set using core depth as a dissolution correction and another using co32 as a dissolution parameter the calibrations suggest that g ruber is the most accurate recorder of surface temperature while g sacculifer records temperatures below the surface at 20 30 m the depth habitat of n dutertrei is more uncertain owing to the wide range in habitat depths depending on hydrographic conditions but on average mg ca and 18o data suggest it is at 50 m of the three species n dutertrei is the most sensitive to dissolution up to 23 decrease in shell mg ca per km while g sacculifer is the most resistant

tectonics basin subsidence mechanisms and paleogeography of the caribbean south american plate boundary zone abstract using a mega regional dataset that includes over 20 000 km of on and offshore 2d seismic lines and 12 wells we illustrate three different stages of fault formation and basin evolution in the caribbean arc south american continent collisional zone transpressional deformation associated with oblique collision of the caribbean arc migrates diachronously over a distance of 1500 km from western venezuela in paleogene time 57 ma to a zone of active deformation in the eastern offshore trinidad area each diachronous stage of pre syn and post collisional basin formation is accompanied by distinct patterns of fault families we use subsidence histories from wells to link patterns of long term basinal subsidence to periods of activity of the fault families stage one of arc continent collision initial collision is characterized by overthrusting of the south and southeastward facing caribbean arc and forearc terranes onto the northward subducting mesozoic passive margin of northern south america northward flexure of the south american craton produces a foreland basin between the thrust front and the downward flexed continental crust that is initially filled by clastic sediments shed both from the colliding arc and cratonic areas to the south as the collision extends eastward towards trinidad this same process continues with progressively younger foreland basins formed to the east on the overthrusting caribbean arc and forearc terranes north south rifting adjacent to the collision zone initiates and is controlled by forward momentum of southward thrusting arc terranes combined with slab pull of the underlying and subducting north dipping south american slab uplift of fold thrust belts arc continent suture induces rerouting of large continental drainages parallel to the collisional zone and to the axis of the foreland basins stage two this late stage of arc continent collision is characterized by termination of deformation in one segment of the fold thrust belt as convergent deformation shifts eastward rebound of the collisional belt is produced as the north dipping subducted oceanic crust breaks off from the passive margin inducing inversion of preexisting normal faults as arc continent convergence reaches a maximum strain partitioning also begins to play an important role as oblique convergence continues accommodating deformation by the formation of parallel strike slip fault zones and backthrusting southward subduction of the caribbean plate beneath the south caribbean deformed belt as subsidence slows in the foreland basins sedimentation transitions from a marine underfilled basin to an overfilled continental basin offshore sedimentation is mostly marine sourced by the collided caribbean terranes localized islands and carbonate deposition stage three this final stage of arc continent collision is characterized by 1 complete slab breakoff of the northward dipping south american slab 2 east west extension of the caribbean arc as it elongates parallel to its strike forming oblique normal faults that produce deep rift and half grabens 3 continued strain partitioning strike slip faulting and folding the subsidence pattern in the caribbean basins is more complex than interpreted before showing a succession of extensional and inversion events the three tectonic stages closely control the structural styles and traps source rock distribution and stratigraphic traps for the abundant hydrocarbon resources of the on and offshore areas of venezuela and trinidad

melt depletion and subsequent metasomatism in the shallow mantle beneath koolau volcano oahu hawaii xenoliths from pali oahu hawaii include samples of the mantle lithosphere underlying koolau shield volcano most such xenoliths are spinel peridotites the remainder being plagioclase spinel peridotites and garnet free pyroxenites clinopyroxene separates from pali peridotite xenoliths have relatively depleted 87sr 86sr 0 70309 0 70346 and 143nd 144nd 0 512967 0 513206 the mantle lithosphere beneath the koolau volcano has a range of present day epsilonnd 6 9 11 on a 143nd 144nd versus 147sm 144nd diagram they define a 61 20 ma errorchron within error of the estimated age of 80 85 ma of the pacific lithosphere at oahu and an intercept of epsilonnd 6 8 we interpret the pali spinel peridotites as samples of the pacific lithosphere residual to melt extraction of the pacific crust these rocks were not metasomatized by melts having isotopic composition similar to the shield building koolau volcano but they could have been metasomatized by melts related to the honolulu volcanic series plagioclase mineral separates from two peridotites are in 87sr 86sr isotopic disequilibrium with coexisting clinopyroxenes the plagioclases are light rare earth element depleted and have enriched 87sr 86sr ratios 0 70436 and 0 70443 the delta18o of olivine 5 09 5 12 and clinopyroxene 5 32 5 33 from spinel peridotites are typical for oceanic upper mantle rocks in contrast delta18o of olivine pyroxene and plagioclase in plagioclase bearing peridotites are enriched by 0 5 relative to the spinel peridotites e g delta18o ratios of olivines from plagioclase peridotites are 5 4 5 5 it is here interpreted that the plagioclases represent phases that formed by reaction with or precipitation from a melt that intruded the pacific lithospheric mantle the pacific lithospheric isotopic composition is reflected in the clinopyroxene separates the high delta18o and 87sr 86sr of the plagioclase resemble koolau lavas and suggest that the melt passing through the lithosphere was plume related the elevated delta18o of the plagioclase indicates that the melt from which it fractionated had a component of recycled crustal material not acquired from local crustal contamination it is also estimated here that the duration of the porous melt flow of the koolau like melt though the mantle lithosphere was short lived 10 2 10 4 years

climate changes and human impact on the mistras coastal barrier system w sardinia italy abstract integrated archaeological and geological studies conducted on mistras coastal barrier system of central sardinia showed that it developed as transgressive systems during the final stages of the holocene sea level rise final stage of the holocene climate optimum about 6300 6000 cal y bp and become regressive prograding from about 2500 cal y bp when sea level reached the present elevation the regression of the coast was however not continuous but characterized by distinct transgressive regressive phases t r associated to precise climatic fluctuations tied with global eustatic and climatic phases the first regression occurred between 2500 and 1900 cal y bp this time interval known as roman warm coincides with the phoenician punic and roman attendance of the west sardinia coast at that time areas close to the coastal cities had to host landings and perhaps ports probably located at short distance from the shoreline archaeological excavations and findings have documented that in the mistras area punic constructed a long boulder structure probably dated from the 4th century bce to better protect an incipient lagoon used as the harbour of the city of tharros this had the effect to modify the normal behaviour of the beach system that transformed from spit to barrier lagoon during the second regressive phase the well established beach lagoon system developed quasi continuously for 1200 y 650 and 1850 ce this progradation started during a new warm period medieval and continued favoured by gentle sea level fall occurred during the cold little ice age time during this time after the abandonment of the city of tharros and of the sinis peninsula the mistras area was poorly populated as consequence there was no more an active harbour and large sandy dunes developed and nourished the shore allowing a no man influence progradation of the coast the third stage is the current one and begun about 165 y ago post 1850 ce after the relative sea level rise occurred after the end of the little ice age geological and archaeological data of western sardinia barrier lagoon systems revealed that the mistras barrier lagoon evolution was human influenced since the punic time the study pointed that little human activities on the coast could influence its natural behaviour and landscape and that little climatic changes both positive and negative can induce progradation or erosion of the system as well

submarine and coastal sediment failure triggered by the 1995 ms 6 1 r aegion earthquake gulf of corinth greece on june 15th 1995 a locally destructive earthquake of magnitude ms 6 1 on the richter scale occurred offshore 7 5 km nne of the town of aegion in the western gulf of corinth greece an offshore survey using 3 5 khz subbottom profiling system and a remote operated vehicle rov has shown that the earthquake caused small sized subaerial to submarine sediment failure in at least four sites in three fan delta deposits the rododafni the eliki and the tolofonas the fan deltas were located within a radius of about 9 km from the epicentre the areal size of the four sediment failure sites ranged from 2 104 m2 to 6 105 m2 whilst the volume of the failed masses ranged from 4 103 to 3 106 m3 the sediment deformation types identified at the failure sites consist of ground cracking rotational slides elongated slides sediment gravity flows and extrusion of mixtures of water and sand sand boils the sediment failure in the four sites affected the upper 5 6 m of well layered holocene topset and foreset fan delta deposits the failure occurred on slopes ranging from 0 2 to 23 and the slip planes were all bedding planes which have a gradient from 0 2 to 21 the dominant instability mechanism that caused the sediment failure in the rododafni and eliki fan deltas is considered to be liquefaction of a shallow sub surface horizon the liquefaction was caused by elevated pore pressure enhanced perhaps by the presence of gas resulting from the cyclic loading induced by the earthquake the liquefied layer is assumed to have temporarily provided a failure surface for sliding to take place on and caused movement of sand that was ejected onto the surface in the tolofonas fan delta the causative mechanism in the case of the multi block rotational slide is considered to be deformation of the underlying sediments caused by remoulding and or liquefaction while in the case of the elongated slide it is considered to be the result of a combination of shear stress increase and or strength degradation of the unconsolidated sediment both of these conditions could have been generated during the cyclic loading resulting from the aegion earthquake the study of historical documents reveals that sediment failure like those described above have also occurred at least four times during the past 2500 years in the same locations therefore it is suggested that they could be repeated in the future by any earthquake event with a magnitude greater than 6 r depending upon the proximity of the site to the earthquake epicentre

an overview of the petroleum system of maracaibo basin the geologically complex maracaibo basin in northwestern venezuela is one of the most prolific hydrocarbon basins in the world having a basinal area of 50 000 km2 19 300 mi2 the basin has produced more than 30 billion bbl of oil with estimated recoverable oil reserves of more than 44 billion bbl the central elements of the petroleum system of the basin include 1 a world class source rock upper cretaceous la luna formation deposited on a shelf to slope environment under anoxic conditions and modified by intermittent oxygenated periods and tectonic events 2 high quality clastic reservoir rocks deposited in eocene and miocene fluviodeltaic settings 3 two main periods of rapid tectonic subsidence responsible for two pulses of voluminous hydrocarbon generation first during paleogene caribbean south american oblique plate collision and second during the neogene uplift of the sierra de perij mrida andes and 4 lateral and vertical migration of oil along strike slip normal and inverted faults as well as a regional unconformity of late eocene oligocene age the maturation migration and trapping of hydrocarbons were closely controlled by the tectonic evolution of the maracaibo basin during the paleogene the development of a foredeep along the northeastern margin of the basin and the strike slip reactivation of the rift related jurassic faults on the maracaibo platform controlled the early structural setting of the source and reservoir rocks hydrocarbons migrated updip from source rocks beneath the north northeastern margin of the basin along north south strike slip faults and into overlying eocene clastic reservoirs in the south central parts of the basin the second period of the maracaibo basin petroleum system developed during subaerial exposure of most of the maracaibo basin during oligocene miocene uplift of the adjacent sierra de perij and mrida andes uplift of mountain ranges surrounding the basin folded and depressed the interior of the basin to form the extensive maracaibo syncline because of the formation of the maracaibo syncline oil generation began in the central and southern parts of the synclinal basin and migrated northward hydrocarbons migrated up the flanks of the maracaibo syncline along reactivated strike slip faults and into miocene rocks adjacent to the uplifted mountain ranges escaping oil has formed numerous surface seeps along the edges of the maracaibo basin

relative sea level changes and regional tectonic evolution of seven coastal areas in nw greece since the mid holocene abstract this study presents relative sea level rsl curves for seven coastal areas in akarnania and the northwestern peloponnese nw greece since the mid holocene rsl fluctuations are deduced from 48 14c ams dated sedimentological sea level markers from 27 vibracores drilled in near coast geological archives as well as from six geoarchaeological sea level indicators of known ages seven palaeo sea level curves including uncertainty bands are reconstructed for a coastal zone spanning a distance of 150 km considerable intra regional differences in sea level evolution exist these differences are mainly due to tectonic reasons in general rsl in northwestern greece has never been higher than today rates of local sea level rise were highest until 5500 5000 cal bc up to 12 3 m ka and lowest during 4000 500 cal bc 0 2 1 4 m ka during the past 2500 or so years rsl has accelerated anew 0 7 2 7 m ka calculating differences between local mean sea level curves provides quantitative information on intra regional differences of tectonic activity the coastal plains of palairos and elis show signs of uplift whereas the mytikas and boukka plains are strongly subsiding compared to other areas of the eastern mediterranean northwestern greece has been subject to significant net long term subsidence regional tectonic events rtes were detected for the time around 4000 2500 500 and 250 cal bc as well as around 250 and 1250 cal ad rtes are characterized by changes of uplift subsidence rates or by the redirection of local tectonic movements the question if some of the rtes were of a supra regional nature is still open from a geodynamic point of view the results presented show that akarnania s southwestern fringe is being downwarped while the tectonic block as a whole is moving towards the southwest strongest subsidence rates are observed for central akarnania at akarnania s fringes subsidence is reduced by the influence of strong uplift of adjacent areas such as around preveza and the northern peloponnese

the geology of the darien panama and the late miocene pliocene collision of the panama arc with northwestern south america the geology of the darien province of eastern panama is presented through a new geologic map and detailed biostratigraphic and paleobathymetric analysis of its upper cretaceous to upper miocene sediments the sequence of events inferred from the stratigraphic record includes the collision of the panama arc the southwestern margin of the caribbean plate and south american continent three tectonostratigraphic units underlie the darien region 1 precollisional upper cretaceous eocene crystalline basement rocks of the san blas complex form a series of structurally complex topographic massifs along the northeastern and southwestern margins of the darien province these rocks formed part of a 20 m y submarine volcanic arc developed in a pacific setting distant from the continental margin of northwestern south america the northerly basement rocks are quartz diorites granodiorites and basaltic andesites through dacites to rhyolites indicating the presence of a magmatic arc the southerly basement rocks are an accreted suite of diabase pillow basalt and radiolarian chert deposited at abyssal depths precollisional arc related rocks of eocene to lower miocene age consist of 4000 m of pillow basalts and volcaniclastics and biogenic calcareous and siliceous deep water sediments they consist of the eocene oligocene darien formation the oligocene porcona formation and the lower middle miocene clarita formation postcollisional deposits are mostly coarse to fine grained siliciclastic sedimentary rocks and turbiditic sandstone of upper middle to latest miocene age this 3000 m thick sedimentary sequence is deformed as part of a complexly folded and faulted synclinorium that forms the central chucunaque tuira basin of the darien the sedimentary package reveals general shallowing of the basin from bathyal to inner neritic depths during the 12 8 7 1 ma collision of the panama arc with south america the sediments are divided into the upper middle miocene tapaliza formation the lower upper miocene tuira and membrillo formations the middle upper miocene yaviza formation and the middle to upper miocene chucunaque formation the precollisional open marine units of late cretaceous middle miocene age are separated from the overlying postcollisional sequence of middle to late miocene age by a regional unconformity at 14 8 12 8 ma this unconformity marks the disappearance of radiolarians the changeover of predominantly silica deposition from the atlantic to the pacific the initiation of the uplift of the isthmus of panama and the onset of shallowing upward coarser clastic deposition this pattern is also recorded from the southern limon basin of caribbean costa rica to the atrato basin of northwestern colombia by the middle late miocene neritic depths were widespread throughout the darien region and a regional unconformity suggests completion of the central american arc collision with south america by 7 1 ma no pliocene deposits are recorded from either the darien or the panama canal basin and no sediments younger than 4 8 ma have been identified in the atrato basin of colombia suggesting rapid uplift and extensive emergence of the central american isthmus in the latest miocene northward movement of the eastern segment of the panama arc along a now quiescent panama canal zone fault during eocene oligocene time may have dislocated the pre collision arc since collision the portion west of this fault chorotega block has remained stable without rotation to the east in the darien region compression has been accommodated through formation of a panama microplate with convergent boundaries to the north north panama deformed belt and south south panama deformed belt and suturing with south america along the atrato valley deformation within the microplate has been accommodated in the darien province by several major left lateral strike slip faults that were active until the early pliocene since when the plate has behaved rigidly

climate variability and socio environmental changes in the northern aegean ne mediterranean during the last 1500 years abstract we provide new evidence on sea surface temperature sst variations and paleoceanographic paleoenvironmental changes over the past 1500 years for the north aegean sea ne mediterranean the reconstructions are based on multiproxy analyses obtained from the high resolution decadal to multi decadal marine record m2 retrieved from the athos basin reconstructed ssts show an increase from ca 850 to 950 ad and from ca 1100 to 1300 ad a cooling phase of almost 1 5 c is observed from ca 1600 ad to 1700 ad this seems to have been the starting point of a continuous sst warming trend until the end of the reconstructed period interrupted by two prominent cooling events at 1832 15 ad and 1995 1 ad application of an adaptive kernel smoothing suggests that the current warming in the reconstructed ssts of the north aegean might be unprecedented in the context of the past 1500 years internal variability in atmospheric oceanic circulations systems as well as external forcing as solar radiation and volcanic activity could have affected temperature variations in the north aegean sea over the past 1500 years the marked temperature drop of approximately 2 c at 1832 15 yr ad could be related to the 1809 d unknown and the 1815 ad tambora volcanic eruptions paleoenvironmental proxy indices of the m2 record show enhanced riverine continental inputs in the northern aegean after ca 1450 ad the paleoclimatic evidence derived from the m2 record is combined with a socio environmental study of the history of the north aegean region we show that the cultivation of temperature sensitive crops i e walnut vine and olive co occurred with stable and warmer temperatures while its end coincided with a significant episode of cooler temperatures periods of agricultural growth in macedonia coincide with periods of warmer and more stable ssts but further exploration is required in order to identify the causal links behind the observed phenomena the black death likely caused major changes in agricultural activity in the north aegean region as reflected in the pollen data from land sites of macedonia and the m2 proxy reconstructions finally we conclude that the early modern peaks in mountain vegetation in the rhodope and macedonia highlands visible also in the m2 record were very likely climate driven

the seismicity geomorphology and structural evolution of the corinth area of greece in the eastern gulf of corinth geological structure is closely reflected in the topography in the 1981 corinth earthquakes ground deformation accentuated existing geomorphological patterns we explore the relationship between seismicity and landforms in space and time the area examined extends beyond the epicentral region of the 1981 events and its evolution is traced over the last 40000 years to understand the relation between deep and superficial structures we discuss processes that occurred in the 1981 earthquakes and go on to propose that surface faulting appears only above linear faults at depth that move in earthquakes with magnitudes m s greater than six where faults at depth intersect or bend the faulting becomes distributed and prim ary faulting does not reach the surface here the surface manifestation of faulting at depth is surface folding and secondary faulting such regions are identified in maps of the eastern gulf of corinth evidence for the evolution of the fault systems is provided by eyewitness accounts of shoreline changes following the recent earthquakes historical and archaeological data pertaining to old sea levels and 14 c dates for molluscs collected from fossil shorelines the results of these studies broadly confirm an earlier view of j a jackson et al earth planet sci lett 57 377 397 1982 that motion has shifted from faulting south of the city of corinth to faulting in the perachora peninsula but the transfer is not complete areas lying between the two fault systems have moved up and down in historical and archaeological times indicating that both systems are still active the evidence for activity of the northern system points to a repeat time of 300 years for earthquakes com parable with those of 1981 the work discussed in this paper suggests that some of the features previously described as m arine terraces are fault controlled continental surfaces furtherm ore beach deposits at a num ber of different levels long regarded as successive shorelines are in fact contemporaneous the critical ages were obtained by radiocarbon dating of shell carbonate a technique which yields dependable results if applied to samples which have been carefully selected and pretreated palaeontological dating of the terraces in contrast is found to be misleading because the faunas are environm entally controlled and consequently diachronous

neogene stratigraphy paleoceanography and paleobiogeography in northwest south america and the evolution of the panama seaway abstract the atrato basin in the pacific coastal region of nw south america colombia exhibits stratigraphic and biostratigraphic characteristics similar to other neogene pacific coastal basins of southern central america and northern south america an evaluation of the neogene stratigraphy and foraminiferal biostratigraphy with emphasis on paleoceanographic and paleobiogeographic phenomena indicate the following 1 previous to the middle miocene well aerated deep and open oceanic conditions and free and active water circulation prevailed along the steep continental margins of nw south america 2 during the early middle miocene right after the neogene hiatus nh 2 15 2 ma tectonic disturbances triggered the initial uplift of the panama sill bottom water circulation foraminiferal and sedimentation changes are observed in both the pacific and caribbean coastal areas of nw south america 3 during the middle miocene coinciding with the neogene hiatus nh 3 12 9 11 8 ma an abrupt paleobathymetric change from lower to middle bathyal depths indicates a major uplift of the panama sill to about 1000 m reflecting the middle miocene tectonic disturbances in nw south america 4 during the late middle miocene immediately following this uplift a distinctive pacific benthic foraminiferal fauna abruptly appeared and extended from ecuador to california because these assemblages do not occur in the adjacent caribbean region a circulation barrier between the atlantic and pacific oceans as a result of intensification of the cool marginal california current is proposed anoxic middle to upper bathyal environments prevailed under well aerated cool surface waters in the pacific coastal areas of nw south america 5 during the latest miocene immediately following the neogene hiatus nh 6 7 0 6 3 ma surface water circulation between the caribbean and the pacific was re established and the previous influence of the california current disappeared a rapid filling and shallowing of the basin to mostly neritic depths is indicated along the pacific and caribbean coastal basins of colombia as well as a progressive increase in similarity between the coastal pacific and caribbean benthic biotas this shallowing in the early late miocene also appears to have been associated with the earliest terrestrial interchange of ground sloths to north america and raccoons and their allies to south america 6 immediately following early pliocene time the panamanian isthmus became completely emergent providing a terrestrial environment favourable for intermingling of terrestrial faunas and floras between north and south america i correlate this pliocene uplift with the neogene hiatus nh 8 3 7 3 1 ma four regional unconformities associated with tectonic disturbances in the nw corner of south america have also been recognized and correlated with neogene hiatuses recorded from the oceans early middle miocene middle miocene late miocene and early pliocene

controls on architecture of the late cretaceous to cenozoic southern middle magdalena valley basin colombia the maastrichtian cenozoic southern middle magdalena valley basin of colombia contains a unique record of unconformities strata and structure from which we extract the histories of exhumation of the central cordillera to the west and evolution of the eastern cordillera fold and thrust belt to the east this study integrates field based analyses of stratigraphy laboratory analyses of provenance fission track thermochronology vitrinite reflectance data volcanic ash geochronology and studies of synorogenic geometries and structure displayed in seismic data a major unconformity the middle magdalena valley unconformity formed by eastward migration of central cordillera uplift during late cretaceous to early eocene time which transformed a maastrichtian marine basin into a paleocene depositional piedmont area this transformation is recorded by a coarsening upward sequence of marine shales to alluvial fan conglomerates which was partly eroded during further early eocene propagation of central cordillera deformation cessation of this phase of uplift led to formation of a pediment surface the middle magdalena valley unconformity which was buried by westward onlapping middle eocene to neogene alluvial deposits middle eocene to neogene facies paleoflow and unconformities were controlled by eastern cordillera deformation in the eastern cordillera foot hills growth strata and thermal history reveal two phases of folding of middle eocene oligocene and late miocene ages prior to intense pliocene pleistocene uplift two unconformities of early late miocene and pliocene pleistocene ages occur to the west of the eastern cordillera and record flexural tilting related to episodes of eastern cordillera loading

geometrical control of subduction related magmatism the mesozoic and cenozoic plutonic history of western colombia radiometric age data from western colombia combined with geological evidence allow five main plutonic episodes ranging in age from triassic to tertiary to be recognized it is suggested that variation in the convergence angle of the oceanic plate relative to the continental edge was an important factor affecting the timing and spatial distribution of plutonic activity on a regional scale major breaks in activity are probably best attributed to either low angle parallel convergence or periods of accretion along the convergent margin

the holocene sea level story since 7500 bp lessons from the eastern mediterranean the black and the azov seas abstract this paper addresses the obvious controversy between the so far published sea level curves of the black sea and the mediterranean it starts with a discussion of the methods of reconstructing sea level curves the evaluation of sea level indicators and the application of the radiocarbon dating method at least since 7500 bp when the black sea and the mediterranean were connected both water bodies must have reacted synchronously on glacio eustatic changes it is documented that none of the mediterranean sea level curves shows the major wiggles postulated for the black sea which are supposed to reflect trans and regression cycles the very shallow bathymetric condition of the azov sea and the northern black sea should have led to considerable and traceable shoreline displacements there is neither archaeological nor historical evidence of mid and late holocene regressions of several meters the tectonic setting of the black and azov seas implicates that the tectonic signal often overrides the eustatic one therefore only local sea level curves can be established in this paper based on vibracores a locally valid sea level curve for the taman peninsula is demonstrated layers of paralic peat were used as sea level indicators and for 14 c dating the shape of this curve follows the one known from the mediterranean this study also revealed that the present peninsula of taman evolved out of a former archipelago

some first order observations on magma transfer from mantle wedge to upper crust at volcanic arcs the viscosity of lavas erupted at volcanic arcs varies over orders of magnitude a comparison of the relative abundance of viscous lava dome eruptions indicates that the average viscosity of arc lavas also varies considerably between arcs it is shown that for continental or transitional arcs with little within arc crustal deformation and without underlying slab windows or tears average lava viscosity is anti correlated with average surface heat flux the latter may be influenced by crustal thickness and crustal magma throughput to constrain the relative contributions of these parameters variations of average lava viscosity with average crustal thickness and plate convergence rate are assessed while crustal thickness appears to have little effect on average lava viscosity a good anticorrelation exists between average lava viscosity and plate convergence rate with the exception of two arcs that show significant intra arc crustal deformation if plate convergence rate is a good proxy of the rate of melt generation within the mantle wedge cf cagnioncle et al 2007 these first order observations indicate that where the rate of mantle melting is high crustal magma throughput is rapid and efficient resulting in low viscosity melts migrating through a hot overriding crust in contrast where the rate of mantle melting is low crustal magma transfer is slow and inefficient resulting in high viscosity melts that may frequently stall within a cool overriding crust prior to eruption uranium series geochemical evidence from dome lavas is presented and lends support to this interpretation finally some explanations are offered for the observed average viscosity variations of arcs with underlying slab windows or tears and or significant intra arc crustal deformation

quaternary evolution of the corinth rift and its implications for the late cenozoic evolution of the aegean summary we present geological and morphological observations at different scales to constrain rates of faulting and the distribution of deformation in the seismically active aegean region we focus first on the 130 km long corinth rift an asymmetric graben where a flight of terraces of marine origin are uplifted we show that the edges of the terraces lie in the footwall of the normal fault bounding the corinth rift and correspond to sea level highstands of laic pleistocene age using a detailed analysis of aerial and spot imagery supported by field observations we have mapped 10 terrace platforms and strandlines ranging in elevation from 10 to 400 m over distances of 2 to 20 km from the fault the elevation of the terraces inner edges was estimated at 172 sites with an error of 5m this data set contains a precise description of the uplift and flexure of 10 different palaeohorizontal lines with respect to the present sea level to date the deformation we correlate the corinth terraces with late pleistocene oxygen isotope stages of high sea level stands and with global sea level fluctuations using a thick elastic plate model consistent with our current understanding of the earthquake cycle and a boundary element technique we reproduce the geometry of the shorelines to constrain both mechanical parameters and the slip on the fault we show that the seismogenic layer behaves over the long term as if its elastic modulus were reduced by a factor of about 1000 all the terraces are fitted for fault slip increasing in proportion to terrace age and the component of regional uplift is found to be less than 0 3 mm yr 1 the best fits give a slip rate of 11 3 mm yr 1 on the main rift bounding fault over the last 350 kyr other geological and morphologic information allows us to estimate the total age of the main fault 1 ma and to examine the mechanical evolution of the corinth rift the minimum observed sediment thickness in the gulf places an extreme check on the results of the modelling and a lower bound on slip rate of 6 7 mm yr 1 40 per cent less than estimated with modelling even this slip rate is nearly 10 times higher than for comparable features in most of the aegean and elsewhere in the world at a larger scale the spacing and asymmetry of the rift systems in the aegean suggest strain localization in the upper mantle with slow extension starting 15 myr ago or earlier the more recent 1 myr rapid phase of rifting in corinth partly reactivated this earlier phase of extension the younger faulting in corinth appears to result from its present location in the inhomogeneous stress field process zone of the south westward propagating tip of the southern branch of the north anatolian fault we extend these relations to propose a mechanical model for the late cenozoic evolution of the aegean as the arabia europe collision progressed in eastern turkey it caused anatolia to move to the west and the north anatolian fault to propagate into the aegean where the early slow extension started to be modified about 5 ma ago the process of propagation dramatically increased the activity of some but not all of the earlier rifts the model we present is compatible with tectonic observations as well as with the seismicity the palaeomagnetic rotations and the displacement field now observed with gps and slr

holocene palaeoenvironmental changes in agia paraskevi prehistoric settlement lamia central greece abstract holocene palaeoenvironmental changes in the area of the prehistoric settlement of megali vrysi close to the village of agia paraskevi in central greece 5 km east of lamia city were investigated the area is situated in the low flat alluvial plain on the outskirts of sperchios valley that is bordered nnw to ene by a rocky hilly ridge of the othrys mountain foothills 5 5 km away from the present coastline the megali vrysi site is considered to be an important mediterranean prehistoric commercial centre reconstruction of the palaeoenvironmental changes of the broader area adds new information concerning the general palaeogeographical setting of the settlement multidisciplinary research involved a detailed geomorphological survey combined with stratigraphical palaeontological and geophysical studies the penetrated strata differentiated into 4 units from top to bottom the first represents the archaeological strata the second consists of the freshwater marshy sediments while the third is the transition layer between the second and the deeper fourth group of marine lagoonal sediments the holocene stratigraphy data was combined with the 14 c ams dating results and showed a marine palaeoenvironment 5500 bc gradually having shifted to a coastal lagoonal one 3500 bc and finally changed to a freshwater marshy environment 2500 bc the comparison between ages and depths of the relative sea level points allowed the estimation of the sea level rise rate for the agia paraskevi area which is considerably lower than the one proposed for the aegean sea in the same time period this considerable offset is attributed to the intensive tectonic uplift of the study area due to the tectonic deformation of the sperchios valley and this is probably why the prehistoric coastal settlement remained on the surface and unaffected from the sea transgression for more than 7000 yrs during holocene

tracking mid to late holocene depositional environments by applying sedimentological palaeontological and geochemical proxies amvrakikos coastal lagoon sediments western greece mediterranean sea abstract this study presents sedimentological palaeontological geochemical mineralogical and organic petrography data from a 30 m deep core representing a mid to late holocene lagoonal depositional environment of a coastal area of amvrakikos gulf western greece three horizons were dated using 14c the sedimentological palaeontological and geochemical interpretations of the lagoonal sediments reveal three major lithological units deposited between around 5200 and 1600 bp the upper lithological unit extended to a depth of 11 20 m the middle from 11 20 to 21 30 m and the lower one from 21 30 to 30 00 m a mean rate of sedimentation of 5 7 mm y and a maximum rate of 12 6 mm y were estimated the mineralogical analysis and the magnetic susceptibility of the core points to a constant sediment source supply the mid to late holocene depositional environment mainly reflects inundation by the braid plain of the arachthos and secondarily by the louros river the reconstruction of the depositional environments corresponds to a shallow marine and deltaic brackish lagoon and specifically to an environment proximal to river supply the high rates of sedimentation as well as the interpretation of depositional environments indicate that the coastal sedimentological processes during the mid to late holocene were mainly controlled by the progradation of river deltas moreover the geochemical proxies the recovered molluscs and the microfauna as well as the organic petrography analyses indicate periods of dysoxic and hypoxic conditions these holocene dysoxic and hypoxic events indicate that the recent dystrophic crises in the amvrakikos gulf are not only the result of human activities but also the contribution of natural processes

microseismicity and faulting geometry in the gulf of corinth greece summary during the summer of 1993 a network of seismological stations was installed over a period of 7 weeks around the eastern gulf of corinth where a sequence of strong earthquakes occurred during 1981 seismicity lies between the alepohori fault dipping north and the kaparelli fault dipping south and is related to both of these antithetic faults focal mechanisms show normal faulting with the active fault plane dipping at about 45 for both faults the aftershocks of the 1981 earthquake sequence recorded by king et al 1985 were processed again and show similar results in contrast the observations collected near the western end of the gulf of corinth during an experiment conducted in 1991 rigo et al 1996 and during the aftershock studies of the 1992 galaxidi and the 1995 aigion earthquakes hatzfeld et al 1996 bernard et al 1997 show seismicity dipping at a very low angle about 15 northwards and normal faulting mechanisms with the active fault plane dipping northwards at about 30 we suggest that the 8 12 km deep seismicity in the west is probably related to the seismic aseismic transition and not to a possible almost horizontal active fault dipping north as previously proposed the diverence in the seismicity and focal mechanisms between east and west of the gulf could be related to the diverence in the recent extension rate between the western gulf of corinth and the eastern gulf of corinth which rotated the faults dipping originally at 45 as in the east of the gulf to 30 as in the west of the gulf

fracturing of the panamanian isthmus during initial collision with south america tectonic collision between south america and panama began at 23 25 ma the collision is significant because it ultimately led to development of the panamanian isthmus which in turn had wide ranging oceanic climatic biologic and tectonic implications within the panama canal zone volcanic activity transitioned from hydrous mantle wedge derived arc magmatism to localized extensional arc magmatism at 24 ma and overall marks a permanent change in arc evolution we interpret the arc geochemical change to result from fracturing of the panama block during initial collision with south america fracturing of the panama block led to localized crustal extension normal faulting sedimentary basin formation and extensional magmatism in the canal basin and bocas del toro synchronous with this change both panama and inboard south america experienced a broad episode of exhumation indicated by u th he and fission track thermochronology coupled with changing geographic patterns of sedimentary deposition in the colombian eastern cordillera and llanos basin such observations allow for construction of a new tectonic model of the south america panama collision northern andes uplift and panama orocline formation finally synchroneity of panama arc chemical changes and linked uplift indicates that onset of collision and isthmus formation began earlier than commonly assumed

a rb sr record of catchment weathering response to holocene climate change in inner mongolia variation in the rubidium to strontium rb sr ratio of the loess palaeosol sequences has been proposed to reflect the degree of pedogenesis and weathering in the northwestern region of china to characterize the rb sr ratio of the dissolved loads of a single catchment we analysed a 12 08 m sediment core from daihai lake in inner mongolia north china dating control was provided by 210pb 137cs and ams 14c sequential extraction experiments were conducted to investigate the concentrations of rb and sr on various chemical fractions in the lake sediments down core variation in the rb sr ratios provides a record of holocene weathering history from 9 to 3 5 ka bp accelerated chemical weathering was experienced throughout the daihai catchment under mainly warm and humid conditions and this reached a maximum at c 5 ka bp however weathering was reduced between c 8 25 and 7 90 ka bp which may reflect the global 8 2 ka cooling event after c 2 5 ka bp increased rb sr ratios with higher frequency of fluctuations indicate reduced weathering within the daihai catchment the highest rb sr ratios in the little ice age lake sediments indicate the weakest phase of holocene chemical weathering resulting from a marked reduction in sr flux into the basin the rb sr record also shows an enhancement of chemical weathering under today s climate but its intensity is less than that of the medieval warm period increased rb sr in lake sediment corresponding to reduced catchment weathering is in striking contrast to rb sr decrease in the glacial loess layers in the loess palaeosol sequence copyright 2005 john wiley sons ltd

a late holocene record of environmental changes from the aliki lagoon egion north peloponnesus greece abstract aliki lagoon is a small lagoon located on the micro tidal south coast of the gulf of corinth greece the sediments of the lagoon recovered in three cores provide a record of late holocene environmental change including tectonic subsidence tsunami layers and change in local vegetation and sedimentation four periods of rapid environmental changes were identified over a 5000 yr long record these date from about 4700 3000 2500 and 2000 yr bp each change is linked to activity on the egion fault a deepening of the lagoonal bottom and a rise in relative sea level six tsunami events are recorded and have been caused by earthquakes on the egion fault three events 4700 3000 and 2500 bp eliki fault 2350 40 yr bp and two more distal fault ruptures the vegetation history and pollen zones are similar to those recognised by jahns vegetation hist archaebot 2 1993 187 on the argive plain 100 km southeast of the lagoon five successive sedimentological configurations are established in relation to the time frame provided by the tectonic activity 1 crevasse splay 2 fresh to brackish water marsh 3 and 4 brackish to hypersaline blind lagoon and 5 brackish to hypersaline blind lagoon or brackish open lagoon

model for late neogene deformation in panama previous workers mostly using earthquake data have postulated both discrete faults and complex diffuse zones for the caribbean nazca plate boundary in panama we have better resolved the location and character of late neogene plate boundary structures by using satellite imagery and a compilation of existing geologic map data on the basis of these results we propose that panama is moving northwestward away from a zone of active convergence along the continental margin of south america toward more easily subducted areas of the colombian basin movement is accommodated across a diffuse zone by a complex interaction of oroclinal bending left lateral strike slip faulting and subduction

paleoenvironmental evolution and prehistoric human environment in the embayment of palamari skyros island greece during middle late holocene abstract palamari bay is located on the northeastern coast of skyros island sporades islands aegean sea at the northern edge of the bay a fortified prehistoric settlement is found dated between 2800 and 1700 bc early bronze age ii middle bronze age i detailed geomorphological mapping of the coastal alluvial plain and paleontological micropaleontological palynological sedimentological and micromorphological studies of the holocene coastal deposits have been conducted in order to reconstruct the palaeoenvironment and the landscape evolution of the broader area of palamari bay three main sedimentary units were recognized a b and c from oldest to youngest the lowermost sedimentary unit a deposited between before 7500 and 3500 cal bp consists of sediment deposited from high to moderate energy fresh water flows with some suspended load fallout in established water bodies the microfauna indicates a shallow fresh water environment however a tendency to oligohaline conditions was established gradually during the same period the palamari area was characterized by open mixed deciduous forests that gradually retreated as a possible consequence of the intensification of anthropic activity associated with the settlement of palamari indications of cultivating and grazing activities in the vicinity of the lagoon were identified pointing to a strong human presence since the neolithic between about 6000 and 3500 cal bp the embayment was a lagoon southeasterly connected to the sea therefore sheltered and protected from northeastern winds the overlying unit b ca 3500 800 cal bp is characterized by the dominance of brackish water microfauna indicating a brackish stagnant shallow water depositional environment which was periodically supplied with fresh water from the surrounding springs as the result of the continuous sea level rise during the late holocene part of the northern headland was submerged the decline of the palamari settlement at the time of the establishment of unit b might be related to the observed changes that rendered the embayment a restricted body of water the uppermost sedimentary unit c corresponds to a backshore environment dominated by aeolian activity modified by fluvial processes

cenozoic paleogeography of the andean foreland and retroarc hinterland of colombia new biostratigraphic zonations core descriptions sandstone petrography facies analysis and seismic information are compared with published detrital and bedrock geo and thermochronology to build a cenozoic paleogeographic reconstruction of the andean retroarc region of colombia encompassing the ancestral central cordillera middle magdalena valley eastern cordillera and llanos basin we identify uplifted sediment source areas provenance domains depositional environments and thickness changes to propose a refined paleogeographic evolution of eastern colombia we conclude that cenozoic evolution of the northernmost andes includes 1 a period of contractional deformation focused in the central cordillera and middle magdalena valley that may have started by the late cretaceous although thermochronological data points to maximum shortening and exhumation during the late paleocene 2 a period of slower deformation rates or even tectonic quiescence during the middle eocene and 3 a renewed phase of contractional deformation from the late eocene to the pleistocene holocene expressed in provenance bedrock thermochronology and increased subsidence rates in the llanos foreland the sedimentary response in the llanos foreland basin is controlled by source area proximity exhumation and shortening rates relationships between accommodation and sediment supply as well as potential paleoclimate forcing this new reconstruction changes the picture of cenozoic basin evolution offered by previous reconstructions providing an updated chronology of deformation which is tied to a more precise understanding of basin evolution

chemical weathering since the little ice age recorded in lake sediments a high resolution proxy of past climate because of the different geochemical behaviour of rubidium and strontium in earth surface processes variations of the rb sr ratios in lake sediments were used as a geochemical proxy of chemical weathering and past climate in a single watershed low magnetic susceptibility low caco3 low sr concentration and hence high rb sr ratio in the lake sediments indicate weak chemical weathering under a cold but wet climate during the little ice age lia in the closed daihai lake watershed the concordant change in both sr and caco3 concentrations with 18o values in the dunde ice core suggests that weak chemical weathering during the wet lia was controlled by air temperature after the lia however precipitation played a dominant role in chemical weathering copyright 2001 john wiley sons ltd

piraeus the ancient island of athens evidence from holocene sediments and historical archives the famous greek geographer strabo wrote in the fi rst century a d that piraeus was formerly an island and lay over against the mainland from which it got its name to validate strabo s hypothesis cartographic and historical data were compiled with multiproxy paleoenvironmental analyses and radiocarbon dating from a series of boreholes drilled in the cephissus coastal plain southwest of athens greece the results of this interdisciplinary geoarchaeological research demonstrate the reliability of strabo s text by revealing that piraeus was indeed an island in early holocene time the rocky hill of piraeus was linked to the mainland of attica during the late to fi nal neolithic period 4850 3450 b c piraeus became an island in a shallow marine bay due to sea level rise in the holocene between 2850 and 1550 b c in the early and middle bronze age piraeus was separated from the mainland by a wide lagoon in the fi fth century b c themistocles cimon and then pericles connected athens to piraeus by building two long walls partly built on a residual coastal marsh called the halipedon this study reveals an impressive example of past landscape evolution

motion on the kaparelli fault greece prior to the 1981 earthquake sequence determined from 36cl cosmogenic dating in february and march 1981 three successive destructive earthquakes occurred at the eastern end of the gulf of corinth the third shock march 4 ms 6 4 ruptured the kaparelli fault about 40 cm of a limestone fault scarp was exhumed by the earthquake each major prehistoric earthquake has added new surface to this cumulative scarp exposing fresh material to cosmic ray bombardment using 36cl cosmic ray exposure dating we have obtained the continuous exposure history for this 4 5 m high limestone surface at two sites about 50 m apart the results suggest that the kaparelli fault has ruptured three times prior to 1981 at 20 3 ka 14 5 0 5 ka and 10 5 0 5 ka with slip amplitudes between 0 6 m and 2 1 m the kaparelli fault appears to have been inactive for 10 thousand years prior to the 1981 event

episodic orogenic front migration in the northern andes constraints from low temperature thermochronology in the eastern cordillera colombia 1 new thermochronometric data from the eastern cordillera of the colombian andes reveal diachronous exhumation associated with cenozoic contractional deformation in this sector of the northern andes we present a comprehensive account of exhumation patterns along a 150 km long across strike transect between 4 and 6 n by integrating 29 new apatite fission track aft ages and 17 new zircon fission track zft ages with sparse published thermochronological data from this area our data reveal episodic eastward migration of the orogenic front at an average rate of 2 5 2 7 mm a during the late cretaceous cenozoic we identify three major stages of orogen propagation 1 slow propagation 0 5 3 1 mm a until early eocene 2 rapid orogenic advance 4 0 18 0 mm a during middle late eocene which accounts for 86 of the orogen s present width and 3 slow orogen propagation 1 2 2 1 mm a from oligocene to holocene times our data demonstrate that in the course of changes in plate kinematics the presence of inherited crustal anisotropies such as the former rift bounding faults of the eastern cordillera favor a nonsystematic progression of foreland basin deformation through time by preferentially concentrating accommodation of slip and thrust loading along these zones of weakness

cretaceous basaltic terranes in western colombia elemental chronological and sr nd isotopic constraints on petrogenesis accreted terranes comprising mid to late cretaceous picrites basalts and dolerites occur in three north south trending belts in western colombia in the central cordillera western cordillera and along the pacific coast the geochemistry of these rocks is consistent with an oceanic plateau plume related origin and they most probably formed in the pacific as part of the caribbean oceanic plateau these igneous rocks display small but significant inter cordillera variations being younger and more depleted in incompatible trace element ratios and with more positive end values to the west the igneous rocks of the pacific coast serrania de baudo are dated at 73 78 ma 40ar 39ar and those of the western cordillera at 90 ma whereas the volcanics of the central cordillera are believed to be older than 100 ma most of the igneous rocks are basaltic and it is suggested that they have fractionated from picritic primary magmas generated by partial melting within a hot mantle plume variable and positive end values reveal that the plume must have been heterogeneous originating from a mantle source with a long term history of depletion partial melt modelling suggests that the composition of the basalts requires at least some input from a mantle source region containing garnet and that the extent of partial melting required to reproduce the composition of the erupted basalts is of the order of 20 mixing of melts from different depths either in the mantle melting column or during fractionation in lithospheric magma chambers can explain the relative homogeneity of basaltic lavas erupted to form this and other oceanic plateaux the caribbean colombian oceanic plateau may have formed at an oceanic spreading centre and valuable comparisons can be made between iceland and the caribbean colombian plateau

regional provenance from southwestern colombia fore arc and intra arc basins implications for middle to late miocene orogeny in the northern andes andean orogenic processes controlled the spatial and temporal distribution of the magmatic and sedimentary record this contribution integrates new u pb zircon ages heavy mineral analyses and biostratigraphic constraints from the neogene sedimentary record of the fore arc and intra arc basins and volcano plutonic rocks of southwestern colombia to reconstruct these orogenic processes the results reveal continuous arc magmatism since the late oligocene with a major post middle miocene magmatic peak and exhumation when integrated with other geological constraints the tectonic evolution of the margin includes eocene oligocene oblique convergence with limited magmatic activity followed by the initiation of a late oligocene early miocene arc that migrated to the east in the middle miocene when it experienced a major increase in magmatic activity crustal deformation exhumation and thickening this orogenic evolution is related to the shallowing of the slab dip due to the subduction of the neogene nazca plate

seismicity and associated strain of central greece between 1890 and 1988 summary we examined the seismicity of central greece between 1890 and 1988 using macroseismic and instrumental data to ask two questions 1 does the seismicity of this period reveal all the major tectonic structures that are known to be active and 2 what are the likely strains associated with the seismicity over this period many known active structures have been effectively aseismic for the last hundred years and even the inclusion of all known large events earlier than 1890 reveals no activity associated with the ne coast of evia gulf of argos or graben ne of mt parnassos it is clear that even 100 years data are inadequate for either a reasonable assessment of seismic risk or for a confident estimation of maximum magnitude however we are aware of no earthquakes in central greece during the last 200 yr that were larger than ms 7 0 it is probable that the maximum magnitude is restricted by the maximum length of fault segments which appears to be around 15 20 km the earthquakes of ms 5 8 during 1890 1988 can account for a n s displacement of around 45 70 cm with maximum and minimum estimates a factor of two greater and smaller than this across part of a 1890 1900 triangulation network in central greece that was resurveyed in 1988 the contribution of smaller events may increase this displacement by about 50 per cent this cumulative seismic displacement is similar to that estimated from the geodetic work about 100 cm but a detailed comparison of the two sets of observations will be reported elsewhere a re evaluation of all the important earthquakes of 1890 1988 in central greece is presented in the appendix which summarizes information of use to both earth scientists and engineers

early subduction related orogeny in the northern andes turonian to eocene magmatic and provenance record in the santa marta massif and rancheria basin northern colombia terra nova 23 26 34 2011 abstract the timing of orogeny in the northern andes and the mechanism driving it are still debated we have studied the age composition and provenance of granitoids and sandstones of the santa marta massif and rancheria basin northern colombia to relate deep seated and surface tectonic processes attending the late cretaceous palaeogene history of the northern andes our results indicate the development of five tectonic episodes 1 collision of northwestern south america with a 92 80 ma caribbean arc 70 ma 2 late collisional to early subduction metamorphism and magmatism 65 ma 3 distal accumulation of a thick siliciclastic sequence 60 58 ma 4 renewed arc magmatism 58 50 ma and 5 magmatic quiescence and block uplift post 50 ma the first episodes are related to the onset of subduction and the last episode is related to shallow subduction and oblique convergence similar events in colombia and ecuador reveal that the late cretaceous eocene orogeny of the northern andes was influenced by the collision and subduction of the caribbean oceanic plate

tectonic evolution of the caribbean the development of the caribbean is discussed in terms of modern tectonic theory the nature of the site on which the caribbean formed is examined and the development of the rifted margins of the caribbean is described constraints on caribbean evolution from the relative motions of north and south america are briefly examined and the caribbean oceanic plateau is discussed the great island arc system of the caribbean is addressed in detail emphasizing the way the great arc of the caribbean was segmented the role of central america in caribbean history is briefly considered

high resolution x ray fluorescence core scanning analysis of les echets france sedimentary sequence new insights from chemical proxies the les echets sediment sequence has recently been the subject of a high resolution multi proxy study which revealed shifts in lake productivity linked to greenland stadials and interstadials over the last 40 ka wohlfarth et al 2008 rapid ecosystem response to abrupt climate changes during the last glacial period in western europe 40 16 ka geology 36 407 410 here we present new elemental data for this sequence as acquired using an x ray fluorescence core scanning system which provides in situ high resolution continuous multi element analyses it was found that the strength of associations between the studied elements ti rb k zr si ca sr mn and fe varied over time with changes in lake status which are ultimately driven by changes in climate increases in fine grained detrital input as indicated by ti rb k and zr rb overlap with independently established periods of lower lake productivity and are interpreted to represent more arid conditions several of these arid periods are coincident with low diatom concentrations and the timing of heinrich events h4 h3 and h2 the duration of the environmental impacts linked to the h events varied by proxy with elemental data ti and zr rb estimating shorter events than the diatom data periods of lower detrital input and coarser grain sizes agreed in time with periods of higher lake productivity the elemental data provide new insights into hydrological changes and related sediment processes within the catchment and highlight the need for multi element and multi proxy approaches when reconstructing climate change using lacustrine sediment sequences copyright 2011 john wiley sons ltd

arc continent collision and orocline formation closing of the central american seaway closure of the central american seaway was a local tectonic event with potentially global biotic and environmental repercussions we report geochronological six u pb la icp ms zircon ages and geochemical 19 xrf and icp ms analyses data from the isthmus of panama that allow definition of a distinctive succession of plateau sequences to subduction related protoarc to arc volcaniclastic rocks intruded by late cretaceous to middle eocene intermediate plutonic rocks 67 6 1 4 ma to 41 1 0 7 ma paleomagnetic analyses 24 sites 192 cores in this same belt reveal large counterclockwise vertical axis rotations 70 9 6 7 and moderate clockwise rotations between 40 4 1 and 56 2 11 1 on either side of an east west trending fault at the apex of the isthmus rio gatun fault consistent with isthmus curvature an oligocene miocene arc crosscuts the older deformed and segmented arc sequences and shows no significant vertical axis rotation or deformation there are three main stages of deformation 1 left lateral strike slip offset of the arc 100 km and counterclockwise vertical axis rotation of western arc segments between 38 and 28 ma 2 clockwise rotation of central arc segments between 28 and 25 ma and 3 orocline tightening after 25 ma when this reconstruction is placed in a global plate tectonic framework and published exhumation data is added the central american seaway disappears at 15 ma suggesting that by the time of northern hemisphere glaciation deep water circulation had long been severed in central america

the paleogene arcs of the northern andes of colombia and panama insights on plate kinematic implications from new and existing geochemical geochronological and isotopic data abstract the northern andes of colombia comprise two non cogenetic paleogene arcs formed in contrasting geodynamic settings including continental and oceanic domains new whole rock geochemistry and isotopic constraints together with a review of 332 geochemical 76 isotopic and 204 geochronological data from paleocene to eocene volcanic and plutonic rocks exposed in central and western colombia and panama are used to evaluate cause effect relations between regional plate kinematics and the spatio temporal distribution of the circum caribbean magmatic arcs short lived 60 45 ma arc like magmatism in the central cordillera of colombia was emplaced in a thickened continental crust due to the oblique subduction of the caribbean oceanic plate underneath south america as suggested by the high sr y ratios conversely the panama arc and its poorly explored extension in the northwestern segment of the western cordillera of colombia document a major phase of tholeiitic to calc alkaline arc magmatism between 71 ma and 34 ma mostly derived from a hydrated mantle wedge and emplaced in an oceanic plateau crust this arc record a major phase of magmatic activity between 40 ma and 50 ma that can be associated to changes in the convergence direction and subduction rates of the farallon plate farther to the south in the pacific region of colombia eocene arc related rocks from the timbiqui complex show a geochemical signature that suggests a magmatic origin from melting of both a subduction modified mantle and lower tectonically thickened crust a possible interpretation for the pacific and western colombia panama arc systems and its analogous in ecuador recall an aleutian type convergent margin in which the continental arc laterally switches to a purely oceanic system along the trailing edge of the caribbean plate as consequence of eastward subduction of the farallon plate

the socio environmental history of the peloponnese during the holocene towards an integrated understanding of the past published archaeological palaeoenvironmental and palaeoclimatic data from the peloponnese in greece are compiled discussed and evaluated in order to analyse the interactions between humans and the environment over the last 9000 years our study indicates that the number of human settlements found scattered over the peninsula have quadrupled from the prehistoric to historical periods and that this evolution occurred over periods of climate change and seismo tectonic activity we show that societal development occurs both during periods of harsh as well as favourable climatic conditions at some times some settlements develop while others decline well known climate events such as the 4 2 ka and 3 2 ka events are recognizable in some of the palaeoclimatic records and a regional decline in the number and sizes of settlements occurs roughly at the same time but their precise chronological fit with the archaeological record remains uncertain local socio political processes were probably always the key drivers behind the diverse strategies that human societies took in times of changing climate the study thus reveals considerable chronological parallels between societal development and palaeoenvironmental records but also demonstrates the ambiguities in these correspondences and in doing so highlights some of the challenges that will face future interdisciplinary projects we suggest that there can be no general association made between societal expansion phases and periods of advantageous climate we also propose that the relevance of climatic and environmental regionality as well as any potential impacts of seismo tectonics on societal development need to be part of the interpretative frameworks

holocene sedimentology and coastal geomorphology of zakynthos island ionian sea a history of a divided mediterranean island the island of zakynthos is one of the most seismically active areas in the mediterranean region because it is located very close to the convergent boundary between the african and eurasian plates its evolution during the holocene has been influenced by tectonic activity catastrophic events and relative sea level changes the scope of the present paper is to examine the holocene palaeoenvironmental changes of the coastal areas of zakynthos island using a multidisciplinary approach combining sedimentological and palaeontological data with 14c and osl dating from four cores of a maximum depth of 30 m the integrated results reveal that sea level and tectonic activity have brought significant modifications in the coastal geomorphic settings of the island during the past 10 000 yr b p the depositional environments and the palaeontological biofacies document four main geomorphological evolutionary stages of the island we identified fully marine and lagoonal deposits with marine influence before 4100 yr b p as well as brackish and freshwater limnic depositional environments around 4100 yr b p to present the interpretation of our data indicates that zakynthos island was separated into two main parts before the middle neolithic period around 7500 yr b p with vasilikos peninsula in the se being isolated from the main island the fact that zakynthos island was a divided mediterranean island for a significant period of time in its prehistory is of great importance to understand better the archaeological landscapes of zakynthos and the other ionian islands

water saturated magmas in the panama canal region a precursor to adakite like magma generation amphibole while uncommon as a phenocryst in arc lavas is increasingly recognized as a key constituent in the petrogenesis of arc magmas fractional crystallization of water saturated arc magmas in the lower crust can yield substantial volumes of amphibole cumulates that depending on the pressure of crystallization may also contain garnet fractionation of this higher pressure assemblage has been invoked as a possible mechanism in the production of magmas that contain an adakitic signature this study examines newly dated late oligocene 25 37 0 13 ma hypabyssal amphibole rich andesites from cerro patacon in the panama canal region these andesites contain nodules of amphibole cumulates that are 4 6 cm in diameter and are almost entirely composed of 5 10 mm amphibole crystals dominantly ferri tschermakite geochemical variations optical and chemical zoning of the cerro patacon amphiboles are consistent with their evolution in a crystal mush environment that had at least one recharge event prior to entrainment in the host andesite amphiboles hosted within the cumulate nodules differ from those hosted in the cerro patacon andesite and contain consistently higher values of ti we suggest these nodules represent the early stages of fractionation from a water saturated magma cerro patacon andesites have ree concentrations that plot at the most depleted end of central american arc magmas and exhibit a distinctive depletion in the middle ree these geochemical and petrographic observations strongly support significant amphibole fractionation during formation of the cerro patacon andesite consistent with the petrographic evidence fractionation of water saturated magmas is a mechanism by which adakitic compositions may be produced and the cerro patacon andesites do exhibit adakite like geochemical characteristics e g elevated sr y 28 34 however the relatively elevated concentrations of y and hree indicate garnet was not stable in the fractionating assemblage during this early stage of arc development

seismic stratigraphy and structure of the caribbean igneous province multichannel seismic reflection profiles reveal the tectonic and stratigraphic complexity of the caribbean province a smooth reflector b forms the top of widespread cretaceous volcanic flows drilled during dsdp leg 15 and odp leg 165 in addition we also show other seismic evidence of volcanism sills and dipping horizons the southern parts of the venezuela and colombia basins are underlain by rough basement that shows many characteristics of oceanic crust several thick volcanic plateaus separated by deep basins with thin crust comprise the caribbean volcanic province in the venezuela basin only normal oceanic crust is present but in other basins this crust is underlain by underplated volcanic material the crust of the venezuela basin is less than 5 km thick and was probably formed in the pacific during the jurassic refraction data indicate that a thin layer 2v is formed by original oceanic crust overlain by a thin volcanic layer an intra basement reflection sub b marks the top of original oceanic crust that is sandwiched between an upper volcanic layer and lower underplated material this underplated layer forms a very thick layer 3v beneath the beata and nicaragua volcanic plateaus the upper part of layer 3v is gabbroic and outcrops on the beata ridge the thickening occurs mainly in the high velocity lower part of layer 3v and is attributed to the presence of magnesian rocks picrites or ultramafic cumulates a highly reflective horizon r is located at the top of this layer we present a model where the galapagos plume is 2500 km wide but has narrow heads that formed the caribbean volcanic plateaus separated by deep basins the caribbean igneous province is compared to similar volcanic features in the indian ocean kerguelen plateau and in the western pacific ocean ontong java plateau nauru and pigafetta basins the thick plateaus of the caribbean province resemble the kerguelen and ontong java plateaus whereas the deep basins present some similarities with the nauru and pigafetta basins the caribbean igneous province is younger 90 75 ma than the indian and pacific plateaus 110 130 ma however several geological evidences from land and geophysical offshore observations indicate that the onset of volcanic activity in the caribbean province could be as old as 115 ma

foraminiferal biodiversity and holocene evolution of the phetchaburi coastal area thailand gulf abstract twenty three surface sediments were collected in may 2002 in the phetchaburi coastal area thailand gulf starting from the outer margin of the vegetated zone to a depth of about 20 m covering an area of about 800 km 2 one core was taken in the north eastern area of the mae khlong delta plain to investigate the recent paleoenvironmental evolution of this zone thirteen core levels were collected for micropaleontological foraminifers investigation this highly populated area is characterized by the inflow of the mae khlong the second major river in thailand and the khlong ban labun river empty tests pertaining to the thanathocoenosis are dominant and as for the few living specimens are most frequently represented by ammonia spp the collected species are typically of brackish water settings foraminiferal diversity is rather low and increases from the northern part to the central southern part of the studied area where taxa typical of the indo pacific realm such as miliolids and schackoinella globosa are more abundant than the cosmopolitan species such as ammonia tepida and gaudryina exilis the geographic distribution of the four foraminiferal assemblages defined on the basis of the cluster analysis indicates that the northern sector is affected by severe environmental conditions since this area is affected by the mae khlong river input the salinity fluctuation is probably a controlling factor on the foraminifers distribution ammonia tepida a inflata murrayinella murrayi and miliolinella sp 1 are the most opportunistic species able to tolerate wide environmental variability as regards to the holocene data the study carried out on the core located on the mae khlong delta plain indicates that the tidal flat paleoenvironment has been subject to different fresh water influence with a general prograding trend