control of pre rift lithospheric structure on the architecture and evolution of continental rifts insights from the main ethiopian rift east africa we investigate the along axis variations in architecture segmentation and evolution of the main ethiopian rift mer east africa and relate these characteristics to the regional geology lithospheric structure and surface processes we first illustrate significant along axis variations in basin architecture through analysis of simplified geological cross sections in different rift sectors we then integrate this information with a new analysis of ethiopian topography and hydrography to illustrate how rift architecture basin symmetry asymmetry is reflected in the margin topography and has been likely amplified by a positive feedback between tectonics flexural uplift and surface processes fluvial erosion unloading this analysis shows that 70 of the 500 km long mer is asymmetric with most of the asymmetric rift sectors being characterized by a master fault system on the eastern margin we finally relate rift architecture and segmentation to the regional geology and geophysical constraints on the lithosphere we provide strong evidence that rift architecture is controlled by the contrasting nature of the lithosphere beneath the homogeneous strong somalian plateau and the weaker more heterogeneous ethiopian plateau differences originating from the presence of pre rift zones of weakness on the ethiopian plateau and likely amplified by surface processes the data provided by this integrated analysis suggest that asymmetric rifts may directly progress to focused axial tectonic magmatic activity without transitioning into a symmetric rifting stage these observations have important implications for the asymmetry of continental rifts and conjugate passive margins worldwide

u th ages obtained by mass spectrometry in corals from barbados sea level during the past 130 000 years the study of the sea level record during the last glacial cycle has primarily proceeded indirectly by means of oxygen isotope measurements on foraminifera from deep sea sediments1 2 the direct approach of dating sea level indicators stagnated during the past decade mainly because the samples required to complete our knowledge of the past glaciations are below the present day sea level3 7 using the 14c ages of acropora palmata samples collected by drilling offshore the island of barbados fairbanks8 presented the first detailed chronology for the last deglaciation this radiocarbon chronology is limited to the past 30 kyr because of the short half life of 14c 5 730 yr we must therefore rely on other dating methods to obtain information for the whole last glacial cycle during the past four years 230th 234u dating of corals by thermal ionization mass spectrometry has been shown to be significantly more precise and accurate than the classical counting method9 14 we have used this technique to measure u th ages in coral samples from the barbados collection and from subaerially exposed outcrops see also ref 15 here we present results bearing on the sea level record for the past 130 000 years we conclude that the last deglaciation started 3 000 years earlier than previously thought and confirm that there were two surges in melt water8 at about 11 kyr and 14 kyr bp before present

fault reactivation control on normal fault growth an experimental study field studies frequently emphasize how fault reactivation is involved in the deformation of the upper crust however this phenomenon is generally neglected except in inversion models in analogue and numerical models performed to study fault network growth using sand silicon analogue models we show how pre existing discontinuities can control the geometry and evolution of a younger fault network the models show that the reactivation of pre existing discontinuities and their orientation control i the evolution of the main fault orientation distribution through time ii the geometry of relay fault zones iii the geometry of small scale faulting and iv the geometry and location of fault controlled basins and depocenters these results are in good agreement with natural fault networks observed in both the gulf of suez and lake tanganyika they demonstrate that heterogeneities such as pre existing faults should be included in models designed to understand the behavior and the tectonic evolution of sedimentary basins

angular velocities of nubia and somalia from continuous gps data implications on present day relative kinematics abstract this study focuses on the break up of the african tectonic plate into separate nubian and somalian blocks based on recent global positioning system gps data a new unique velocity field has been obtained by processing all available observations of permanent gps stations on africa since 1996 the quantity and distribution of the stations and the length of the time series of observations exceed that of previous studies by a considerable margin allowing one to derive a reliable estimate of the differential motion between the nubia and somalian plates which are considered as a single african block in the prevailing global tectonic plate models the estimated relative pole of rotation of somalia with respect to nubia is located at 54 8 s 37 0 e with magnitude 0 069 ma implying distinct opening in the ethiopian rift of magnitude 7 mm year and azimuth n94 e whereas in southeastern south africa this value is reduced to 2 mm year in almost the same direction this is in accordance with some of the independent geological and geophysical tectonic models of the nubia somalia plate boundary region however the spatial density of the current tracking network is still not optimal to establish the exact location of the entire somalia nubia plate boundary in particular the possible branch east of lake victoria and heading towards the mozambique channel is impossible to confirm or reject at this moment

fault reactivation and rift localization northeastern gulf of aden margin 1 the gulf of aden and the sheba spreading ridge gulf of aden forms the southern boundary of the arabian plate its orientation 075 e and its kinematics about 030 e divergence are interpreted as the result of an oblique rifting in this contribution a field study in the northeastern gulf of aden allows us to confirm the oligo miocene synrift directions of extension and to precise the normal fault network geometry the synrift extensions are 020 e and 160 e possibly in this chronological order the normal faults strike 070 e 090 e and 110 e the results show that some characteristics are consistent with oblique rifting analogue models while some others are not especially fault reactivation of mesozoic structures is shown to have occurred significantly at the beginning and during rifting these data are therefore compared to analogue models of oblique reactivation and this comparison demonstrates that fault reactivation played a key role during the early stage of the gulf of aden rifting finally scenarios of the lithospheric evolution during the eastern gulf of aden opening preexisting weaknesses in the lithosphere or not are discussed to better constrain the deformation history of the northern margin especially we show that rift localization processes may imply stress rotations through time

paleogeographic and paleoclimatic significance of diatoms from middle pleistocene marine and glaciomarine deposits on baldwin peninsula northwestern alaska abstract a newly revised diatom biostratigraphic scheme for the north pacific ocean based on studies of the diatom flora of the cape blossom and hotham inlet formations of baldwin peninsula northwestern alaska provides new information on the paleoceanography of kotzebue sound alaska during middle pleistocene time sediments exposed along coastal bluffs of baldwin peninsula contain subarctic north pacific zonal index species including extinct proboscia barboi pr curvirostris actinocyclus ochotensis var fossilis thalassiosira nidulus var nidulus th jouseae th gravida var fossilis and stephanopyxis dimorpha which are correlated with the middle part of the proboscia barboi zone 0 43 0 36 ma based on the distribution of the zonal diatom species and on changes in the paleoecological structure of the diatom assemblages e g warm vs cold water assemblages we conclude that the marine deposits of the cape blossom formation and lower baldwin silt member of the hotham inlet formation formed under relatively warm high sea level conditions associated with the marine oxygen isotope stage ois 11 transgression glaciomarine sedimentation middle and upper baldwin silt and selawik gravel members of the hotham inlet formation initiated during relatively warm conditions at the end of the stage 11 transgression and continued into stage 10 high latitude glacier growth during a global interglacial period was likely facilitated by warm surface waters on flooded continental shelves and limited regional sea ice cover the biostratigraphic record at baldwin peninsula provides further evidence that high latitude ice growth is favored by increased moisture supply during warm climatic intervals and inhibited by arid conditions during full glacial intervals

oxygen isotope calibration of the onset of ice rafting and history of glaciation in the north atlantic region we report here that dsdp site 552a cored with the hydraulic piston corer on the west flank of rockall bank recovered an undisturbed sequence of alternating white deep sea carbonate oozes and dark coloured layers that are rich in glacial debris oxygen isotope analysis of the sequence together with detailed nannofossil and palaeomagnetic stratigraphy shows that the first major horizon of ice rafting occurred at about 2 4 myr and was preceded by a minor pulse of ice rafting at about 2 5 myr the carbon isotope record shows that the site has been bathed by a water mass of similar characteristics to present day north atlantic deep water at least since 3 5 myr

the progressive intensification of northern hemisphere glaciation as seen from the north pacific ocean drilling project odp site 882 50 22 n 167 36 e provides the first high resolution grape density magnetic susceptibility carbonate opal and foraminifera planktonic and benthic stable isotopes records between 3 2 and 2 4 ma in the northwest pacific we observed a dramatic increase in ice rafting debris at site 882 at 2 75 ma which is coeval with that found in the norwegian sea suggesting that the eurasian arctic and northeast asia were significantly glaciated from 2 75 ma onwards prior to 2 75 ma planktonic foraminifera 18o records indicate a warming or freshening trend of 4 c or 2 over 80 ka if this is interpreted as a warm pre glacial pliocene north pacific it may have provided the additional moisture required to initially build up the northern hemisphere continental ice sheet the dramatic drop in sea surface temperatures sst 7 5 c at 2 75 ma ended this suggested period of enhanced sst and thus the proposed moisture pump moreover at 2 79 and 2 73 ma opal mass accumulation rates mar decrease in two steps by five fold and is accompanied by a more gradual long term decrease in caco3 mars evidence from the southern ocean odp site 704 indicates that just prior to 2 6 ma there is a massive increase in opal mars the opposite to what is found in the north pacific this indicates that the intensification of northern hemisphere glaciation was accompanied by a major reorganisation of global oceanic chemical budget possibly caused by changes in deep ocean circulation the initiation of northern hemisphere glaciation occurred in the late miocene with a significant build up of ice on southern greenland however the progressive intensification did not occur until 3 5 3 ma when the greenland ice sheet expanded to include northern greenland following this stage we suggest that the eurasian arctic and northeast asia glaciated at 2 75 ma approximately 100 ka before the glaciation of alaska 2 65 ma and 200 ka before the glaciation of the north east american continent 2 54 ma

late cenozoic arctic ocean sea ice and terrestrial paleoclimate sea otter remains found in deposits of two marine transgressions bigbendian and fishcreekian of the alaskan arctic coastal plain which occurred between 2 4 and 3 ma suggest that during these two events the southern limit of seasonal sea ice was at least 1600 km farther north than at present in alaskan waters perennial sea ice must have been severely restricted or absent and winters were warmer than at present during these two sea level highstands paleomagnetic faunal and palynological data indicate that the later transgression fishcreekian occurred during the early part of the matuyama reversed polarity chron amino acid diagenesis in fossil mollusks suggests that since the later transgression the effective diagenetic temperature edt in the deposits has been about 16 c which is about 7 c colder than modern values and slightly colder than the edt calculated for the past 125 ka such a low edt suggests that permafrost and perennial sea ice have been present nearly continuously since this transgression permafrost probably was absent however during the earlier bigbendian transgression permafrost and extensive perennial sea ice may have been initiated during the late stages of climatic cooling that spanned the gauss normal matuyama reversed polarity chron boundary and led into the first major late cenozoic glaciation of the northern hemisphere

oxygen isotope mass balance constraints on pliocene sea level and east antarctic ice sheet stability the mid pliocene warm period mpwp 3 3 2 9 ma with reconstructed atmospheric p co2 of 350 450 ppm represents a potential analogue for climate change in the near future current highly cited estimates place mpwp maximum global mean sea level gmsl at 21 10 m above modern requiring total loss of the greenland and marine west antarctic ice sheets and a substantial loss of the east antarctic ice sheet with only a concurrent 2 3 c rise in global temperature many estimates of pliocene gmsl are based on the partitioning of oxygen isotope records from benthic foraminifera 18ob into changes in deep sea temperatures and terrestrial ice sheets these isotopic budgets are underpinned by the assumption that the 18o of antarctic ice 18oi was the same in the pliocene as it is today and while the sensitivity of 18ob to changing meltwater 18o has been previously considered these analyses neglect conservation of 18o 16o in the ocean ice system using well calibrated 18o temperature relationships for antarctic precipitation along with estimates of pliocene antarctic surface temperatures we argue that the 18oi of the pliocene antarctic ice sheet was at minimum 1 4 higher than present assuming conservation of 18o 16o in the ocean ice system this requires lower pliocene seawater 18o without a corresponding change in ice sheet mass this effect alone accounts for 5 20 of the 18ob difference between the mpwp interglacials and the modern with this amended isotope budget we present a new pliocene gmsl estimate of 9 13 5 m above modern which suggests that the east antarctic ice sheet is less sensitive to radiative forcing than previously inferred from the geologic record

foraminifera in elevated bermudian caves provide further evidence for 21 m eustatic sea level during marine isotope stage 11 abstract two hypotheses have been proposed to explain the origin of marine isotope stage mis 11 deposits in small bermudian caves at 21 m above modern sea level 1 a 21 m mis 11 eustatic sea level highstand and 2 a mis 11 mega tsunami event importantly the foraminifera reported in these caves have yet to be critically evaluated within a framework of coastal cave environments after statistically comparing foraminifera in modern bermudian littoral caves and the mis 11 calonectris pocket a 21 m cave to the largest available database of bermudian coastal foraminifera the assemblages found in modern littoral caves and calonectris pocket a cannot be statistically differentiated from lagoons this observation is expected considering littoral caves are simply sheltered extensions of a lagoon environment in the littoral zone where typical coastal processes waves storms homogenize and rework lagoonal reefal and occasional planktic taxa fossil protoconchs of the bermudian cave stygobite caecum caverna were also associated with the foraminifera these results indicate that the mis 11 bermudian caves are fossil littoral caves breached flank margin caves where the total mis 11 microfossil assemblage is preserving a signature of coeval sea level at 21 m brackish foraminifera polysaccammina pseudothurammina and anchialine gastropods 95 300 individuals indicate a brackish anchialine habitat developed in the elevated caves after the prolonged littoral environmental phase the onset of sea level regression following the 21 m highstand would first lower the ancient brackish ghyben herzberg lens

origin nature and world climate effect of arctic ocean ice cover during the cenozoic an open water arctic ocean changed to the modern permanently ice covered condition significant world climate modification accompanied this change but the precise role of the arctic ocean in major pleistocene climate events is controversial the present ice cover averages 3 m thickness but there are theories that during the pleistocene it was antarctic like several thousand metres thick the time of origin of the ice cover is placed as young as 0 7 myr ago and as old as the middle miocene any theory concerned with origin nature and climatic response of the arctic ice cover must consider the ocean s sediment record

some geological implications of average quaternary glacial conditions analyses of quaternary landscape evolution tend to focus on events associated with culminations of glacial and interglacial ages but for most of quaternary time environments were intermediate in character average quaternary glacial conditions based on assessment of the marine isotope record approximated those near the stage 2 stage 1 transition and during substages 5b and 5d isotope stages 3 and 4 and substages 5a d lie within one standard deviation of the mean value under average glacial conditions ice sheets lying over northern north america and europe were much more contracted than their full glacial counterparts and the distribution of mountain glaciers reflected a snowline depression of some 500 m geomorphic processes operating under average quaternary conditions contributed importantly to landscape evolution examples of landscapes that may represent such average conditions include cirques and fluvial deposits of the pacific northwest the fjords and strandflat of western norway and atolls of the tropical oceans by examining the geologic record from the perspective of average conditions rather than those of climatic extremes added insight can be gained regarding the evolution of quaternary landscapes

rift propagation in rotational versus orthogonal extension insights from 4d analogue models abstract in rift settings extension rates often vary along strike due to rotation about a vertical axis or euler pole yet tectonic modelers traditionally apply constant along strike deformation rates here we compare rift development and propagation under traditional orthogonal extension versus rotational extension conditions the set ups involve brittle viscous layering and localize deformation through structural weaknesses seeds our models provide first order insights into the differences in rift development between both boundary conditions orthogonal extension produces a rift basin with constant synchronous along strike features whereas rotational extension induces along strike structural gradients diachronous rift development causing rift propagation and the development of v shaped basins we observe important viscous flow associated with differential pressure gradients in rotational extension we also describe the important effects of strain partitioning between rift axis and model boundaries the quantifying of which is crucial to avoid incorrect model interpretations although our model results are first order only they are in good agreement with various natural examples and previous modeling studies and highlight the importance of considering the third dimension when studying tectonic systems

stratigraphy fossils and age of sediments at the upper pit of the lost chicken gold mine new information on the late pliocene environment of east central alaska abstract the upper pit at the lost chicken placer gold mine in east central alaska contains fossils that provide information on the flora and insect fauna of interior alaska just before the onset of global cooling at 2 5 myr fossils come from sediments interbedded with the lost chicken tephra dated at 2 9 0 4 myr early late pliocene and portray the floodplain and valley of a small creek within a region dominated by a coniferous forest richer in genera and species than the present one climate was wetter and less continental and there was probably little or no permafrost at least one other pliocene tephra the fortymile tephra occurs at the site and is also associated with plant and insect fossils among these fossils are extinct plants and insects like those found at other tertiary sites in northern canada and alaska the lost chicken sequence is the same age as the beaufort formation on meighen island more than 1000 km to the north like lost chicken meighen island sediments contain fossils representing a diverse boreal environment this shows that the latitudinal climate gradient during early late pliocene time was shallower than at present and the boreal forest had a far greater latitudinal span than now

marine isotope stage 11 palaeoclimates palaeoenvironments and its role as an analogue for the current interglacial abstract interglacials of the quaternary period are currently the focus of a great deal of attention within the scientific community this is primarily because they play a vital role in distinguishing between natural and human climate change in the current interglacial and in understanding how the holocene would evolve in the absence of anthropogenic greenhouse warming in this respect marine isotope stage 11 mis 11 ca 410 000 yr bp is one of the key interglacial stages of the past 450 000 yr the pattern of insolation variability that occurs during mis 11 matches that which occurs in the holocene more closely than in any other warm stage of the past half a million years in addition there is now an extensive range of evidence for mis 11 palaeoclimates and palaeoenvironments from marine ice core lacustrine and terrestrial sequences the aim of this paper is to provide a comprehensive review of the current state of our understanding of mis 11 this is the first paper to provide a detailed review of mis 11 that incorporates the wide range of marine ice core long lacustrine and terrestrial records that have been generated over the last ten years since the last major overview crucially it is the first review of mis 11 that incorporates a detailed synthesis of the high resolution terrestrial sequences of western and central europe this paper therefore provides a holistic integration of a diverse range of proxies and archives to provide a detailed understanding of the expression of mis 11 in the earth system in particular the review focuses on 1 the climatic background of mis 11 2 the robustness of the identification of mis 11 in a diverse range of sequences 3 the climatic structure of mis 11 4 the magnitude of warmth that occurred in this warm stage 5 mis 11 sea level magnitude and variability 6 the duration of mis 11 7 evidence for abrupt climatic events within the interglacial of mis 11 and 8 precipitation patterns and trends during this interglacial the paper concludes by considering how useful mis 11 is as an analogue for holocene climates and compares it with other proposed analogues such as mis 19 with particular reference to the early anthropogenic hypothesis

interactions between propagating rotational rifts and linear rheological heterogeneities insights from three dimensional laboratory experiments the lateral propagation of rifts is a consequence of the relative divergence of lithospheric plates about a pole of rotation modern and ancient examples of rifts are known to overprint pre existing linear anisotropies in the crust and lithosphere such as lithospheric boundaries crustal sutures and thermal anomalies here we investigate how propagating rifts interact with pre existing structures by using three dimensional analogue experiments with rotational extensional boundary conditions and variably oriented linear weak zones in the lithospheric mantle when linear weaknesses are oriented at low angles to the rift axis early strain localization occurs in narrow domains which merge at later stages resulting in continental break up by unzipping strong strain partitioning is observed when the linear heterogeneity is oriented at high angles with respect to the rift axis in these experiments early sub parallel v shaped basins propagate toward the pole of rotation until they are abandoned and strain is transferred entirely to structures developed in the vicinity of the strongly oblique weak lithosphere zone boundary the experimental results are characterized in terms of their evolution patterns of strain localization and surface topography as a function of the lithospheric heterogeneity obliquity angle comparison of the experiments to ancient and modern examples in nature may help to elucidate the common but still poorly understood process of propagating rift lithospheric heterogeneity interaction

middle pleistocene age of the nome river glaciation northwestern alaska abstract during the middle pleistocene nome river glaciation of northwestern alaska glaciers covered an area an order of magnitude more extensive than during any subsequent glacial intervals the age of the nome river glaciation is constrained by laser fusion 40 ar 39 ar analyses of basaltic lava that overlies nome river drift at minnie creek central seward peninsula that average 470 000 190 000 yr 1 milligram size subsamples of the lava were dated to identify and eliminate extraneous 40ar enrichments that rendered the mean of conventional k ar dates on larger bulk samples of the same flow too old 700 000 570 000 yr while the 40 ar 39 ar analyses provide a minimum limiting age for the nome river glaciation maximum ages are provided by a provisional k ar date on a basaltic lava flow that underlies the nome river drift at nearby lave creek by paleomagnetic determinations of the drift itself at and near the type locality and by amino acid epimerization analysis of molluscan fossils from nearshore sediments of the anvilian marine transgression that underlie nome river drift on the coastal plain at nome taken together the new age data indicate that the glaciation took place between 580 000 and 280 000 yr ago the altitude of the anvilian deposits suggests that eustatic sea level during the anvilian transgression rose at least as high as and probably higher than during the last interglacial transgression by correlation with the marine oxygen isotope record the transgression probably dates to stage 11 at 410 000 yr and the nome river glaciation is younger still analyses of floor altitudes of presumed nome river cirques indicate that the nome river regional snowline depression was at least twice that of the maximum late wisconsin the cause of the enhanced snowline lowering appears to be related to greater availability of moisture in northwestern alaska during the middle pleistocene

biostratigraphy and late cenozoic paleoceanography of the arctic ocean foraminiferal lithostratigraphic and isotopic evidence detailed studies of benthonic foraminifera stable isotopes and lithofacies in cores from the southeastern alpha ridge central arctic ocean reveal some new aspects of arctic ocean paleoceanography high ratios of benthonic to planktonic foraminifera are found in most of the quaternary sediment units and ratios of 1 1 appear to characterize the arctic deep water sediments benthonic foraminifera in the carbonate mud unit m show a succession of calcareous species reflecting increased influx of norwegian sea bottom water to the arctic ocean during the past 0 4 m y foraminiferal and lithological data indicate less uniform sedimentation during a warmer interval from 0 4 to 0 6 ma when most of the silty lutite unit l was deposited at the cesar site lower pleistocene units j to i contain less limestone and more dolomite and they contain a uniform faunal assemblage with low numbers of calcareous foraminifera upper pliocene units h to ab contain rare limestone and relatively large amounts of do lomite and quartz sand middle to upper pliocene units ab to a3 are marked by abundant sand sized ferromanganese coated particles which in many cases have a silt nucleus hence much of the coarse sand in these units does not indicate increased ice rafting the pliocene sediments mostly contain a low diversity assemblage of agglutinated foraminifera but a mixed calcareous arenaceous fauna occurs in a short interval above the matuyama gauss boundary 2 4 ma stable isotopic curves occur within sequences which broadly correspond to stages 1 9 of the global record below stage 9 the record is discontinuous strong vertical mixing apparently prevailed during most of the pliocene and early pleistocene then decreased during the past 0 4 m y owing to damping by a perennial ice cover isotopic and foraminiferal data however suggest that an interval of perennial sea ice also occurred during the late pliocene at the time of the earliest glacial event recorded in the north atlantic

nature and tectonic setting of the southern kermadec submarine arc volcanoes an overview abstract the 1000 km long kermadec subduction system northern new zealand and adjacent havre trough back arc basin associated with the pacific australian plate boundary is an archetypal example of an active island arc convergent margin although the position and tectonic setting of the frontal arc is critical to understanding tectonism and magmatism within an arc back arc system this has not been unequivocally established for the kermadec subduction system swath surveys from the 35 37 s segment of the kermadec system reveal that the frontal arc comprises seven large arc stratovolcanoes rumble ii iii iv silent ii rumble v tangaroa and clark the frontal arc continues south with the whakatane volcano sited at the northern extremity of the taupo volcanic zone of these eight volcanoes the latter four are newly identified and all have constructional volumes varying between 50 and 260 km 3 all of these arc edifices are sited 15 25 km west of the kermadec frontal ridge bathymetric data similarly indicate that other kermadec arc volcanoes between 32 and 35 s also lie west of the ridge axis within the back arc region while north of 32 s the arc volcanoes lie along the frontal ridge this apparent variation in the tectonic position of the frontal arc coincides with other changes in the morphology of the subduction system north and south of 32 s and as suggested by pelletier and dupont 1990 may reflect differences in the length of the underlying subducted slab the 35 37 s frontal arc segment is sited within 35 45 km of the present day back arc rift axis and may control the initial loci of rift graben evolution sidescan imagery and seafloor photography of the southern kermadec arc volcanoes reveal a complex volcanic stratigraphy with intertwined pillow lavas proximal pillow breccias highly vesicular scoriaceous lapilli and pervasively mass wasted volcaniclastic and epiclastic detritus all volcanic deposits interdigitate with pelagic sediments a single k ar dated andesite from whakatane volcano suggests that the history of the present frontal arc may extend back to at least 0 77 ma while rumble iii and v volcanoes are the major although not exclusive sites of geologically recent edifice construction the historical acoustic record of southern kermadec submarine eruptions since 1958 is now regarded as equivocal with the july 1986 eruption of rumble iii the only unambiguous volcanic activity recorded in modern times

the dynamic history of the trans mexican volcanic belt and the mexico subduction zone abstract the trans mexican volcanic belt tmvb is a 1000 km long neogene continental arc showing a large variation in composition and volcanic style and an intra arc extensional tectonics it overlies the rivera and cocos slabs which display marked changes in geometry geophysical studies indicate that lithospheric mantle is very thin or absent beneath the forearc and arc the fluids from the slab are released in a 40 to 100 km wide belt beneath the frontal part of the arc and the lower crust beneath the arc is partially molten east of 101 w the tmvb is built on a precambrian to paleozoic crust with thickness of 50 55 km west of 101 w the tmvb is underlain by jurassic to cenozoic marine and continental arcs with a 35 40 km thick crust the evolution of the tmvb occurred in four stages 1 from 20 to 10 ma the initial andesitic arc moved inland showing progressively drier melting and eventually slab melting suggesting flattening of the subducted slab 2 since 11 ma a pulse of mafic volcanism migrated from west to east reaching the gulf of mexico by 7 ma this mafic lavas marks the lateral propagation of a slab tear triggered by cessation of subduction beneath baja california 3 thereafter the volcanic front started moving trenchward with a marked phase of silicic volcanism between 7 5 and 3 ma local emplacement of small volume intraplate like basalts since 5 ma and development of extensional faulting these features are related to slab rollback enhancing asthenophere flux into the mantle wedge and promoting partial melting of the crust 4 the modern arc consists of a frontal belt dominated by flux and slab melting and a rear belt characterized by more differentiated rocks or by mafic lavas with little or no evidence of subduction fluids but higher asthenosphere fingerprint

aminostratigraphic correlations and paleotemperature implications pliocene pleistocene high sea level deposits northwestern alaska abstract multiple periods of late pliocene and pleistocene high sea level are recorded by surficial deposits along the coastal plains of northwestern alaska analyses of the extent of amino acid epimerization in fossil molluscan shells from the nome coastal plain of the northern bering sea coast and from the alaskan arctic coastal plain of the chukchi and beaufort sea coasts allow recognition of at least five intervals of higher than present relative sea level three late pliocene transgressions are represented at nome by the complex and protracted beringian transgression and on the arctic coastal plain by the colvillian bigbendian and fishcreekian transgressions these were followed by a lengthy period of non marine deposition during the early pleistocene when sea level did not reach above its present position a middle pleistocene high sea level event is represented at nome by the anvilian transgression and on the arctic coastal plain by the wainwrightian transgression anvilian deposits at the type locality are considerably younger than previously thought perhaps as young as oxygen isotope stage 11 410 000 bp finally the last interglacial pelukian transgression is represented discontinuously along the shores of northwestern alaska amino acid epimerization data together with previous paleomagnetic measurements radiometric age determinations and paleontologic evidence provide geochronological constraints on the sequence of marine deposits they form the basis of regional correlations and offer a means of evaluating the post depositional thermal history of the high sea level deposits provisional correlations between marine units at nome and the artic coastal plain indicate that the temperature difference that separates the two sites today had existed by about 3 0 ma since that time the effective diagenetic temperature was lowered by about 3 4 c at both sites and the mean annual temperature was lowered considerably more this temperature decrease was largely accomplished by the close of the fishcreekian beringian iii transgression ca 2 5 2 1 ma since then intervals of warm temperature must have been extremely brief these data suggest that the steep latitudinal temperature gradient and the frigid temperatures that characterize the high latitudes of alaska today are ancient features of arctic climate

extensional hard linkages eastern gulf of suez egypt the araba abu durba area on the eastern margin of the gulf of suez exhibits two superb outcrop examples of extensional hard linkages in a rift basin here three large domino style basement cored northeast dipping fault blocks are formed by a series of major northwest trending normal faults these are offset by two north northeast trending sinistral oblique slip transfer faults that terminate in horsetail normal fault splays the transfer faults do not extend across the entire rift basin detailed mapping and structural analysis show that they developed by breakage of initial low strain relay ramps along reactivated north northeast trending basement fabrics between overlapping northwest trending normal fault segments paleostrain analysis of fault slip indicators shows that both the normal and the sinistral oblique slip transfer faults were formed synchronously in response to northeast southwest extension perpendicular to the main northwest rift trend

the structural architecture of the los humeros volcanic complex and geothermal field abstract the los humeros volcanic complex lhvc is a large silicic caldera complex in the trans mexican volcanic belt tmvb hosting a geothermal field currently in exploitation by the comision federal de electricidad cfe of mexico with an installed capacity of ca 95 mw of electric power understanding the structural architecture of lhvc is important to get insights into the interplay between the volcano tectonic setting and the characteristics of the geothermal resources in the area the analysis of volcanotectonic interplay in lhvc benefits from the availability of subsurface data obtained during the exploration of the geothermal reservoir that allows the achievement of a 3d structural view of the volcano system the lhvc thus represents an important natural laboratory for the development of general models of volcano tectonic interaction in calderas in this study we discuss a structural model of lhvc based on morphostructural and field analysis integrated with well logs focal mechanism solutions and magnetotelluric imaging the structural analysis suggests that inherited regional tectonic structures recognized in the basement played an important role in the evolution of the magma feeding system caldera collapses and post caldera deformations these inherited weak planes have been reactivated by resurgence faults and post caldera magma driven hydrofractures under a local radial stress field generated by the shallow lhvc magmatic hydrothermal system the local stress field induced caldera resurgence and volcanotectonic faulting the results of this study are important to better constrain the structural architecture of large caldera complexes also our study is useful to understand the structure of the los humeros geothermal field and support the exploration of deeper super hot geothermal systems shgss and engineering of enhanced geothermal systems egss for electric power production in the lhvc and other active resurgent calderas

nw se pliocene quaternary extension in the apan acoculco region eastern trans mexican volcanic belt abstract the apan acoculco area is located in the eastern portion of the mexico basin and the trans mexican volcanic belt the area is transected by right stepping variably dipping ne sw normal faults the apan tlaloc fault system is a major discontinuity that divides the region into two contrasting areas with different structural and volcanic styles a the western area is characterized by a horst graben geometry with widespread quaternary monogenetic volcanism and scattered outcrops of miocene and pliocene rocks b the eastern area is dominated by tilted horsts with a domino like geometry with widespread miocene and pliocene rocks scattered quaternary monogenetic volcanoes and the acoculco caldera gravity data suggest that this structural geometry continues into the mesozoic limestones normal faulting was active since the pliocene with three stages of extension one of them an intense dilatational event began during late pliocene and continues nowadays contemporaneously with the emplacement of the apan tezontepec volcanic field and the acoculco caldera statistical analysis of cone elongation cone instability and the kinematic analysis of faults attest for a nw50 se 7 extensional regime in the apan acoculco area the activity in some portions of the apan tlaloc fault system continues today as indicated by earthquake swarms recorded in 1992 and 1996 that disrupted late holocene paleosols and holocene volcanism

analogue experiments of propagation of oblique rifts abstract we present the results of analogue models of oblique rifting which were carried out using a isostatically compensated two layered small scale models the experiments show that structures formed in the brittle layer under oblique extension comprise a series of lenticular rifted basins set en echelon along the axial zone of the experiment box in time the basins propagate lengthways to merge and form a unified composite rift however traces of the initial en echelon rifts expressed in deeper axial basins separated by shallower threshold zones are clearly discernible in the mature rifts both the basins and the threshold zones are located within the composite rift so that the rift margins are abrupt and steep along the basins and more diffuse along the threshold zones the thinning in the brittle layer along the rift is enhanced by diapirs that ascend from the ductile layer and penetrate the rift floor model experiments of nearly orthogonal extension showed a single unified rift which differed conspicuously from the composite oblique rifts the results of the experiments suggest that oblique extension forms en echelon rift segments the axes of which are perpendicular to the extension direction separated by threshold zones therefore there is ground to presume that occurrence of a series of alternating basins and threshold zones inside the axial section of a major rift could suggest a regime of oblique tectonic extension

quaternary sedimentation of the alaskan beaufort shelf influence of regional tectonics fluctuating sea levels and glacial sediment sources abstract the offshore stratigraphy of the quaternary gubik formation of arctic alaska has been studied on high resolution seismic profiles with a maximum sub seafloor penetration of about 100 m in general marine transgressive subunits of the gubik formation are wedge shaped on the shelf thickening slightly seaward to the shelf break beyond which they are offset by landslides and slumps beneath the eastern third of the alaskan beaufort shelf active folding has created two persistent structural depressions the eastern and western wedge terranes in which the wedge morphology is especially well developed the youngest transgressive marine wedge which was deposited in such a way as to fill these depressions leaving a generally flat present day shelf surface is inferred to be late wisconsin or younger in age because it overlies a prominent disconformity interpreted to have been formed during the late wisconsin glacial sea level minimum the thickness of this youngest wedge unit a locally exceeds 40 m on the outer shelf yet apparently relict gravel deposits collected from its seabed surface indicate that the depositional rate is presently quite low on the middle and outer shelf lithologies of the gravels are exotic to alaska but similar to suites exposed in the canadian arctic islands these observations suggest a depositional scenario in which the retreating laurentide ice sheet shed sediment laden icebergs from the canadian arctic islands into the arctic ocean following the late wisconsin glacial maximum these bergs were then rafted westward by the beaufort gyre and grounded on the alaskan shelf by northeasterly prevailing winds especially large numbers of bergs accumulated in the wedge terrane embayments created as sea level rose and melted there filling the embayments with their sedimentary cargo as glacial retreat slowed depositional rates on the shelf dwindled this mode of deposition in the alaskan beaufort wedge terranes may be typical of early post glacial transgressive phases throughout quaternary time it has resulted in the preservation of disconformities that apparently formed during glacioeustatic lowstands and whose seaward termination depths appropriately corrected may yield estimates of lowstand magnitudes knowledge of global sea level fluctuations back through the sangamon interglacial oxygen isotope stage 5e and possible correlations with dated onshore deposits have facilitated a tentative correlation of major disconformities in the beaufort sea record with major 18 o enrichment maxima in the oxygen isotope curve back through stage 8 in this tentative scheme close similarities between the two data sets occur both in magnitudes and in numbers of fluctuations intervening between major correlation points further testing of the quaternary depositional model suggested here and of the resulting sea level curve awaits the collection and dating of core samples from the beaufort wedge terranes

a refined age for the earliest opening of bering strait abstract biostratigraphically and chronostratigraphically important diatoms from the milky river formation alaska peninsula southwestern alaska imply an age range of 5 4 5 5 ma for the oldest north pacific cenozoic occurrence of the marine bivalve mollusk astarte which migrated from the arctic ocean into the north pacific when bering strait first flooded the data presented here are a refinement of the age range of 4 8 5 5 ma reported earlier and imply that bering strait first opened very near the end of the miocene at 5 32 ma

reply to mega highstand or megatsunami discussion of mcmurtry et al elevated marine deposits in bermuda record a late quaternary megatsunami sed geol 200 2007 155 165 by paul j hearty and storrs l olson our recent paper mcmurtry g m tappin d r sedwick p n wilkinson i fietzke j and sellwood b 2007a elevated marine deposits in bermuda record a late quaternary megatsunami sedimentary geol 200 155 165 critically re examined elevated marine deposits in bermuda and concluded that their geological setting sedimentary relations micropetrography and microfaunal assemblages were inconsistent with sustained intertidal deposition instead we hypothesized that these deposits were the result of a large tsunami that impacted the bermuda island platform during the mid pleistocene hearty and olson hearty p j and olson s l in press mega highstand or megatsunami discussion of mcmurtry et al elevated marine deposits in bermuda record a late quaternary megatsunami sedimentary geology 200 155 165 2007 aug 07 sedimentary geol 200 155 165 in their response attempt to refute our conclusions and claim the deposits to be the result of a 21 m eustatic sea level highstand during marine isotope stage mis 11 in our reply we answer the issues raised by hearty and olson hearty p j and olson s l in press mega highstand or megatsunami discussion of mcmurtry et al elevated marine deposits in bermuda record a late quaternary megatsunami sedimentary geology 200 155 165 2007 aug 07 sedimentary geol 200 155 165 and conclude that the bermuda deposits do not provide unequivocal evidence of a prolonged 21 m eustatic sea level highstand rather the sediments are more likely the result of a past megatsunami in the north atlantic basin

successive orthogonal and oblique extension episodes in a rift zone laboratory experiments with application to the ethiopian rift small scale modeling was performed to examine the effects of the superposition of two successive extensional phases from orthogonal to oblique type 1 and from oblique to orthogonal type 2 in both the type 1 and type 2 models faults produced during the first stage strongly control fault development during the second stage in type 1 models the oblique faults developed during the second oblique phase are confined within a first phase graben whereas in type 2 models the oblique faults produced during the first phase continue to develop during orthogonal extension and connect with each other to give sigmoidal fault blocks type 1 models are compared with the structural setting of the ethiopian rift the evolution of the rift is related to a recent extensional event whose principal direction of stretching trends at around 50 to preexisting major normal faults type 1 laboratory models are fairly comparable to the northern sector of the ethiopian rift referred to here as mer they account for both the development of the en echelon oblique faults of the wonji fault belt and the sinistral shear gradient running parallel to the eastern border of the mer which formed during an oblique rifting extension the statistical analysis of the whole ethiopian rift fault pattern by reference to the experimental data allows the determination of a n100 n110 mean direction of stretching

controls of inherited lithospheric heterogeneity on rift linkage numerical and analog models of interaction between the kenyan and ethiopian rifts across the turkana depression inherited rheological structures in the lithosphere are expected to have large impact on the architecture of continental rifts the turkana depression in the east african rift connects the main ethiopian rift to the north with the kenya rift in the south this region is characterized by a nw se trending band of thinned crust inherited from a mesozoic rifting event which is cutting the present day n s rift trend at high angle in striking contrast to the narrow rifts in ethiopia and kenya extension in the turkana region is accommodated in sub parallel deformation domains that are laterally distributed over several hundred kilometers we present both analog experiments and numerical models that reproduce the along axis transition from narrow rifting in ethiopia and kenya to a distributed deformation within the turkana depression similarly to natural observations our models show that the ethiopian and kenyan rifts bend away from each other within the turkana region thus forming a right lateral stepover and avoiding a direct link to form a continuous n s depression the models reveal five potential types of rift linkage across the pre existing basin three types where rifts bend away from the inherited structure connecting via a 1 wide or 2 narrow rift or by 3 forming a rotating microplate 4 a type where rifts bend towards it and 5 straight rift linkage the fact that linkage type 1 is realized in the turkana region provides new insights on the rheological configuration of the mesozoic rift system at the onset of the recent rift episode

environmental changes at final warming of middle pleistocene mis 7 in south kurils abstract entirely new data have been obtained on the south kuril environments at the time of the middle pleistocene warming these data are correlatable with mis 7 the data show climatic rhythms and shed new light on paleo oceanologic conditions and the evolution of environments at that time paleo environmental reconstructions are based on multidisciplinary studies of the marine deposit sequence exposed in a sea cliff in the eastern part of tanfiliev island including a buried oyster reef in the course of the studies analyses of mollusc fauna diatoms and pollen were performed benthic foraminifera were first found in the middle pleistocene sediments of the south kurils the sediments were dated using the 230 th u method and by the presence of the zonal diatom species thalassiosira nidulus the warming process was not unidirectional two warmer intervals were separated by a slight cooling a complicated process of climatic fluctuation is reflected in the succession of diatom assemblages the latter also being influenced by the warm current and the solar heating of coastal water in the first stage of warming there existed an oyster reef composed of densely packed shells of crassostrea gigas nineteen associated species were found 11 percent of them extra limital warm water species the presence of these species suggests the summer surface sea water temperature was 6 c 8 c above that of today on the tanfiliev coast at the time of the reef growth the warming coincided with marine transgression the latter was once interrupted with a limited regression which coincided with a short period of cooling the sequence of deposition environments is reconstructed as follows a shallow bay a coastal lake an open bay the adjacent land was covered with cool temperate broadleaf and coniferous broadleaf forests the coniferous species gaining in importance during cooling during the second warm phase the proportion of coniferous and small leaved species in plant communities was drastically reduced

quaternary history of sea ice in the western arctic ocean based on foraminifera sediment cores from the northwind ridge western arctic ocean including uniquely preserved calcareous microfossils provide the first continuous proxy record of sea ice in the arctic ocean encompassing more than half of the quaternary the cores were investigated for foraminiferal assemblages along with coarse grain size and bulk chemical composition by combination of glacial cycles and unique events reflected in the stratigraphy the age of the foraminiferal record was estimated as ca 1 5 ma foraminiferal abundances diversity and composition of benthic assemblages especially phytodetritus and polar species were used as proxies for sea ice conditions foraminiferal assemblage zone 2 in the lower pleistocene indicates diminished mostly seasonal sea ice probably facilitated by enhanced inflow of pacific waters a gradual decrease in ice free season with episodes of abrupt ice expansion is interpreted for the mid pleistocene transition consistent with climatic cooling and ice sheet growth in the northern hemisphere a principal faunal and sedimentary turnover occurred near the earlyemiddle pleistocene boundary ca 0 75 ma with mostly perennial sea ice indicated by the overlying assemblage zone 1 two steps of further increase in sea ice coverage are inferred from foraminiferal assemblage changes in the glacial pleistocene by ca 0 4 and 0 24 ma possibly related to hemispheric mid brunhes event and laurentide ice sheet growth respectively these results suggest that year round ice in the western arctic was a norm for the last several 100 ka in contrast to rapidly disappearing summer ice today

reactivation of intrabasement structures during rifting a case study from offshore southern norway abstract pre existing structures within crystalline basement may exert a significant influence over the evolution of rifts however the exact manner in which these structures reactivate and thus their degree of influence over the overlying rift is poorly understood using borehole constrained 2d and 3d seismic reflection data from offshore southern norway we identify and constrain the three dimensional geometry of a series of enigmatic intrabasement reflections through 1d waveform modelling and 3d mapping of these reflection packages we correlate them to the onshore caledonian thrust belt and devonian shear zones based on the seismic stratigraphic architecture of the post basement succession we identify several phases of reactivation of the intrabasement structures associated with multiple tectonic events reactivation preferentially occurs along relatively thick c 1 km relatively steeply dipping c 30 structures with three main styles of interactions observed between them and overlying faults i faults exploiting intrabasement weaknesses represented by intra shear zone mylonites ii faults that initiate within the hangingwall of the shear zones inheriting their orientation and merging with said structure at depth or iii faults that initiate independently from and cross cut intrabasement structures we demonstrate that large scale discrete shear zones act as a long lived structural template for fault initiation during multiple phases of rifting

aminostratigraphy of european marine interglacial deposits molluscan fossils collected from shallow water marine sediment across nw europe and nearby arctic regions have been analysed for the extent of isoleucine epimerization dl ratio in indigenous protein residues the dl ratios confirm that essentially all classical eemian sites from nw europe are of the same age and are correlative with the type locality near amersfoort in the netherlands shells from interglacial marine sediment beneath the type weichselian till in poland also correlate with the type eemian site dl ratios in holsteinian marine shells 0 29 are substantially higher than in their eemian counterparts 0 17 late cromerian shells yield even higher ratios 0 46 dl ratios in late glacial shells 0 06 and middle weichselian shells 0 09 permit differentiation from modern 0 01 and last interglacial material based on the position of the matuyama brunhes boundary and the differences in dl ratios the eemian must correlate with isotope substage 5e whereas the holsteinian is most likely substage 7c possibly stage 9 but certainly younger than stage 11 intra saalian warm periods may be terrestrial equivalents of the younger substages of stage 7 extensive pre eemian marine sediments along the sw coast of denmark previously correlated with the holsteinian are shown to be of late cromerian age the underlying till there is the first widespread evidence of a pre elsterian till in nw europe dl ratios in molluscs from last interglacial sites along the arctic coast of the ussr the arctic islands and eastern greenland are substantially lower than in their european counterparts due to their low thermal histories the combined mid and high latitude data are used to develop a predictive model for the expected dl ratio in any of several moderate epimerization rate taxa for last interglacial sites with mean temperatures between 20 and 15 c not all sites could be unambiguously assigned to an established interglacial the fjosanger norway and margareteberg sweden sites previously thought to be eemian yield dl ratios higher than in secure nearby eemian material it is yet unresolved whether these are aberrant sites or if they predate the last interglacial in situ shoreline deposits encountered in borings in sw belgium and in exposures on the belgium coastal plain contain molluscs that yield dl ratios intermediate between secure eemian and late weichselian ratios raising the possibility that a late stage 5 high sea level event attained near modern levels in the southern north sea basin resolution of these uncertainties is the focus of future work

tectonic inheritance and continental rift architecture numerical and analogue models of the east african rift system 1 the western branch of the east african rift is composed of an arcuate succession of elongate asymmetric basins which differ in terms of interaction geometry fault architecture and kinematics and patterns of uplift subsidence and erosion sedimentation the basins are located within proterozoic mobile belts at the edge of the strong tanzanian craton surface geology suggests that the geometry of these weak zones is an important parameter in controlling rift development and architecture although other processes have been proposed in this study we use lithosphere scale numerical models and crustal scale analogue experiments to shed light on the relations between preexisting structures and rift architecture results illustrate that on a regional scale rift localization within the mobile belts at the curved craton s western border results in an arcuate rift system which implies that under a constant extensional stress field part of the western branch experienced orthogonal extension and part oblique extension largest depocenters are predicted to form mostly orthogonal to the extension direction and smaller depocenters will form along the oblique parts of the rift the varying extension direction along the rift zone furthermore results in lengthwise varying rift asymmetry segmentation characteristics and border fault architecture trend length and kinematics analogue models predict that discrete upper crustal fabrics may influence the location of accommodation zones and control the architecture of extension related faults at a local scale models support that fabric reactivation is responsible for the oblique slip kinematics on faults and for the development of z shaped or arcuate normal faults typically documented in nature

constraints on geological strain rates arguments from finite strain states of naturally deformed rocks a summary of known finite strain states is presented longitudinal strains 1 e as measured in many rocks often range from 1 to 40 and 1 to 0 025 the time span available to produce such measureable strains in young orogenic zones seems to be less than 10 m y possibly less than 1 m y which constrains conventional strain rates into the range of 10 sup 13 s sup 1 to 10 sup 15 s sup 1 for both pure and simple shear the most efficient way and much less efficient way to accumulate incremental strains respectively the ellipticity of the finite strain ellipse increases in a nonlinear manner finite strain variations in adjacent layers which give rise to features such as cleavage refraction arise with only slight differences in the strain rates within these layers

forested arctic evidence from north greenland shallow water marine sediments of the kap kabenhavn formation at lat 82 30 n perry land north greenland contain an abundance of well preserved remains of terrestrial vegetation and invertebrate fauna indicative of a mosaic of forest tundra environments having similarities to present conditions in labrador the presence of foraminifera faunas marine molluscs and one mammal species supported by studies of paleomagnetism and amino acid diagenesis suggests an age of 2 ma at the pliocene pleistocene transition at this time the arctic tree line was located 2500 km to the north of its present position in the northwest atlantic region and forest tundra vegetation existed in lowland areas bordering on an arctic ocean without perennial sea ice cover

new evidence for the age of the gubik formation alaskan north slope abstract at several alaskan north slope localities south of the shore of the arctic ocean the gubik formation herein regarded as latest pliocene and pleistocene in age contains a marine unit at its base near ocean point and near teshekpuk lake this basal unit or the lowest exposed marine unit of the gubik contains unusual relatively warm water marine mammals although these mammals have poorly known fossil histories consideration of what is known suggests that the basal marine unit near ocean point is of latest pliocene age between 2 2 and 1 7 my old and that the marine unit near teshekpuk lake is probably late pleistocene most likely correlating with the sangamon interglaciation and about 120 000 yr old

middle pliocene vegetation reconstructions paleoclimatic inferences and boundary conditions for climate modeling abstract the general characteristics of global vegetation during the middle pliocene warm period can be reconstructed from fossil pollen and plant megafossil data the largest differences between pliocene vegetation and that of today occurred at high latitudes in both hemispheres where warming was pronounced relative to today in the northern hemisphere coniferous forests lived in the modern tundra and polar desert regions whereas in the southern hemisphere southern beech apparently grew in coastal areas of antarctica pliocene middle latitude vegetation differed less although moister than modern conditions supported forest and woodland growth in some regions now covered by steppe or grassland pliocene tropical vegetation reflects essentially modem conditions in some regions and slightly cooler than or warmer than modern climates in other areas changes in topography induced by tectonics may be responsible for many of the climatic changes since the pliocene in both middle and lower latitudes however the overall latitudinal progression of climatic conditions on land parallels that seen in the reconstruction of middle pliocene sea surface temperatures pliocene paleovegetational data was employed to construct a 2 2 global grid of estimated mid pliocene vegetational cover for use as boundary conditions for numerical general circulation model simulations of middle pliocene climates continental outlines and topography were first modified to represent the pliocene landscape on the 2 2 grid a modern 1 1 vegetation grid was simplified and mapped on this pliocene grid and then modified following general geographic trends evident in the pliocene paleovegetation data set

emergent marine record and paleoclimate of the last interglaciation along the northwest alaskan coast the last interglacial high sea level stand the pelukian transgression of isotope substage 5e is recorded along the western and northern coasts of alaska by discontinuous but clearly traceable marine terraces and coastal landforms up to about 10 m altitude the stratigraphy indicates that sea level reached this altitude only once during the last interglacial cycle from the type area at nome to st lawrence island in the bering sea to the eastern limit of the beaufort sea pelukian deposits contain extralimital faunas indicating that coastal waters were warmer than present amino acid ratios in molluscs from these deposits decrease to the north toward barrow consistent with the modern regional temperature gradient fossil assemblages at nome and st lawrence island suggest that the winter sea ice limit was north of bering strait at least 800 km north of its present position and the bering sea was perennially ice free microfauna in pelukian sediments recovered from boreholes indicate that atlantic water may have been present on the shallow beaufort shelf suggesting that the arctic ocean was not stratified and the arctic sea ice cover was not perennial for some period in coastal regions of western alaska spruce woodlands extended westward beyond their modern range and in northern alaska on the arctic coastal plain spruce groves may have entered the upper colville river basin the flaxman member of the gubik formation on the alaskan arctic coastal plain was deposited during marine isotope substage 5a and records the breakup of an intra stage 5 ice sheet over northwestern keewatin

stable isotope profiles of last interglacial pelukian transgression mollusks and paleoclimate implications in the bering strait region abstract the marine paleoclimate during the last interglaciation in the bering strait region is inferred from the stable oxygen and carbon isotope profiles of fossil bivalve mollusks specimens were collected from the marine highstand deposits of the pelukian transgression from the arctic alaskan coastal plain the nome coastal plain st lawrence island and the val katlen suite on the chukotka peninsula as a calibration modern mollusks were obtained from the major water masses in the bering chukchi seas system and from coastal environments near the fossil localities the 18 o composition of the modern mollusks accurately reflects the seawater 18 o differences among the water masses and the ambient temperature range at each site seasonal paleotemperature ranges are estimated from the 18 o profiles of the fossils by comparison with those of the modern specimens a simple model is developed to correct the paleotemperature ranges for the influence of differences in seawater 18 o between water masses and seasonal variations caused by freshwater discharge paleotemperatures calculated for the skull cliff site alaskan arctic coastal plain are close to but slightly cooler than those of modern specimens from peard bay and icy cape the isotopic composition of a pelukian specimen collected near wainwright shows the obvious influence of locally reduced salinities with a correction for lower seawater 18 o this profile yields a summer temperature of 13 c which is 3 c warmer than that from the modern icy cape specimen the isotope records of two specimens from the nome coastal plain suggest salinities that were 3 5 psu lower than the modern eastern bering shelf the paleotemperature range of 0 15 c is consistent with modern conditions in norton sound the character of the isotope profiles of the pelukian specimens from st lawrence island is very different than that of modern specimens near the island but matches the 18 o values of shells from deeper sites in anadyr water this suggests that the fossil mollusks were living in anadyr strait and were transported by a glacial advance from the chukotka peninsula the last interglacial specimens from the val katlen suite have isotope profiles with large seasonal 18 o ranges and the clear influence of a reduced salinity coastal water mass calculated paleotemperatures from the val katlen specimens range from 0 to 13 c differences in the 13 c of shell carbonate between sites appears to reflect the regional distribution of the 13 c of sedimentary organic matter som which is a mixture between terrestrial organic matter mean 13 c of 24 and marine phytoplankton 21 partitioning of 13 c between shallow and deep waters by phytoplankton productivity and remineralization may also affect the regional distribution differences in shell 13 c between taxa may relate to feeding mode and the type and isotopic composition of ingested particles the filter feeders mya and astarte typically have 13 c values 1 2 more positive than the deposit feeders macoma and serripes this effect is attributed to a 13 c difference between marine phytoplankton and som with a component of terrestrial organic carbon

the role of co2 decline for the onset of northern hemisphere glaciation the pliocene pleistocene transition ppt from around 3 2 to 2 5 million years ago ma represented a major shift in the climate system and was characterized by a gradual cooling trend and the appearance of large continental ice sheets over northern eurasia and north america paleo evidence indicates that the ppt was accompanied and possibly caused by a decrease in atmospheric co2 but the temporal resolution of co2 reconstructions is low for this period of time and uncertainties remain large therefore instead of applying existent co2 reconstructions we solved an inverse problem by finding a schematic co2 concentration scenario that allows us to simulate the temporal evolution of key climate characteristics in agreement with paleoclimate records to this end we performed an ensemble of transient simulations with an earth system model of intermediate complexity from which we derived a best guess transient co2 scenario for the interval from 3 2 to 2 4 ma that gives the best fit between the simulated and reconstructed benthic 18o and global sea surface temperature evolution our data constrained co2 scenarios are consistent with recent co2 reconstructions and suggest a gradual co2 decline from 375 425 to 275 300 ppm between 3 2 and 2 4 ma in addition to a gradual decline the best fit to paleoclimate data requires the existence of pronounced co2 variability coherent with the 41 kyr 1 kyr 1000 years obliquity cycle in our simulations the long term co2 decline is accompanied by a relatively abrupt intensification of northern hemisphere glaciation at around 2 7 ma this is the result of a threshold behaviour of the ice sheets response to gradual co2 decrease and orbital forcing the simulated northern hemisphere ice sheets during the early pleistocene glacial cycles reach a maximum volume equivalent to a sea level drop of about 40 m both ice volume and benthic 18o are dominated by 41 kyr cyclicity our simulations suggest that before 2 7 ma greenland was ice free during summer insolation maxima and only partly ice covered during periods of minimum summer insolation a fully glaciated greenland comparable to its present day ice volume is modelled only during glacial maxima after 2 7 ma and more continuously after 2 5 ma

the influence of structural inheritance and multiphase extension on rift development the northern north sea the northern north sea rift evolved through multiple rift phases within a highly heterogeneous crystalline basement the geometry and evolution of syn rift depocentres during this multiphase evolution and the mechanisms and extent to which they were influenced by pre existing structural heterogeneities remain elusive particularly at the regional scale using an extensive database of borehole constrained 2d seismic reflection data we examine how the physiography of the northern north sea rift evolved throughout late permian early triassic rp1 and late jurassic early cretaceous rp2 rift phases and assess the influence of basement structures related to the caledonian orogeny and subsequent devonian extension during rp1 the location of major depocentres the stord and east shetland basins was controlled by favorably oriented devonian shear zones rp2 shows a diminished influence from structural heterogeneities activity localises along the viking sogn graben system and the east shetland basin with negligible activity in the stord basin and horda platform the utsira high and the devonian lomre shear zone form the eastern barrier to rift activity during rp2 towards the end of rp2 rift activity migrated northwards as extension related to opening of the proto north atlantic becomes the dominant regional stress as rift activity in the northern north sea decreases through documenting the evolving syn rift depocentres of the northern north sea rift we show how structural heterogeneities and prior rift phases influence regional rift physiography and kinematics controlling the segmentation of depocentres as well as the locations styles and magnitude of fault activity and reactivation during subsequent events

fracpaq a matlab toolbox for the quantification of fracture patterns abstract the patterns of fractures in deformed rocks are rarely uniform or random fracture orientations sizes and spatial distributions often exhibit some kind of order in detail relationships may exist among the different fracture attributes e g small fractures dominated by one orientation larger fractures by another these relationships are important because the mechanical e g strength anisotropy and transport e g fluids heat properties of rock depend on these fracture attributes and patterns this paper describes fracpaq a new open source cross platform toolbox to quantify fracture patterns including distributions in fracture attributes and their spatial variation software has been developed to quantify fracture patterns from 2 d digital images such as thin section micrographs geological maps outcrop or aerial photographs or satellite images the toolbox comprises a suite of matlab scripts based on previously published quantitative methods for the analysis of fracture attributes orientations lengths intensity density and connectivity an estimate of permeability in 2 d is made using a parallel plate model the software provides an objective and consistent methodology for quantifying fracture patterns and their variations in 2 d across a wide range of length scales rock types and tectonic settings the implemented methods presented are inherently scale independent and a key task where applicable is analysing and integrating quantitative fracture pattern data from micro to macro scales the toolbox was developed in matlab and the source code is publicly available on github and the mathworks fileexchange the code runs on any computer with matlab installed including pcs with microsoft windows apple macs with mac os x and machines running different flavours of linux the application source code and sample input files are available in open repositories in the hope that other developers and researchers will optimise and extend the functionality for the benefit of the wider community

amino acid geochronology resolution and precision in carbonate fossils changes in indigenous proteins preserved in carbonate skeletons can be used to estimate the time elapsed since death of the organism racemization the most widely used reaction in amino acid geochronology refers to the inversion of l amino acids to their d configuration for the protein amino acid l isoleucine racemization occurs about only one of the two chiral carbon atoms this reaction epimerization proceeds from an initial dl ratio near zero to an equilibrium ratio of about 1 30 the reaction rate is controlled primarily by temperature and to a lesser degree by the nature of the proteins themselves a variable related to taxonomy and the extent of protein degradation analyzing monospecific samples minimizes the taxonomic variable the resolving power of dl ratios as relative age indices is a function of the reaction rate degree of natural variability and analytical uncertainty natural variability is defined as the spread in ratios in five well preserved shells of the same age from a single stratum and is primarily related to taxonomy it can range from 20 or more in taxa of low reliability to 1 in taxa of greatest integrity 5 to 10 is to be expected analytical uncertainty within a single laboratory is relatively insignificant amounting to no more than 2 but interlaboratory comparisons suggest caution in comparing ratios determined at different laboratories or by different techniques sampling appropriate portions of a shell is essential to minimize variability in dl ratios site temperature exerts the greatest control on reaction rate hence resolving power for tropical sites 25 c age differences 1 ka can be resolved within the holocene and ca 5 to 10 ka for older samples as the rate decreases equilibrium is attained after 150 to 300 ka the reaction rate is substantially lower at mid latitude sites ca 10 c where equilibrium requires about 2 ma and resolution within the last glacial cycle is no better than 10 to 20 ka arctic sites 10 c show almost no measurable racemization within the holocene and in extreme cases even within the last 100 ka equilibrium is not attained in 10 ma the extent of amino acid racemization epimerization in carbonate fossils provides chronological information for the critical time period beyond radiocarbon dating dl ratios can be used directly as relative age indices and with suitable calibration can provide reasonable estimates of absolute age and or effective diagenetic temperature improving the accuracy of racemization based age estimates requires a better understanding of racemization kinetics in carbonate systems

quaternary climates and sea levels of the u s atlantic coastal plain uranium series dating of corals from marine deposits of the u s atlantic coastal plain coupled with paleoclimatic reconstructions based on ostracode marine and pollen continent data document at least five relatively warm intervals during the last 500 000 years on the basis of multiple paleoenvironmental criteria we determined relative sea level positions during the warm intervals relative to present mean sea level were 7 5 meters at 188 000 years ago 7 5 1 5 meters at 120 000 years ago 6 5 3 5 meters at 94 000 years ago and 7 3 meters at 72 000 years ago the composite sea level chronology for the atlantic coastal plain is inconsistent with independent estimates of eustatic sea level positions during interglacial intervals of the last 200 000 years hydroisostatic adjustment from glacial interglacial sea level fluctuations lithospheric flexure and isostatic uplift from sediment unloading due to erosion provide possible mechanisms to account for the discrepancies alternatively current eustatic sea level estimates for the middle and late quaternary may require revision

a sustained 21 m sea level highstand during mis 11 400 ka direct fossil and sedimentary evidence from bermuda abstract a small protected karstic feature exposed in a limestone quarry in bermuda preserved abundant sedimentary and biogenic materials documenting a transgressive phase still stand and regressive phase of a sea level in excess of 21 3 m above present during marine isotope stage mis 11 400 ka as determined by u th dating and amino acid racemization cobbles and marine sediments deposited during the high energy transgressive phase exhibit rim cements indicating a subsequent phreatic environment this was succeeded stratigraphically by a still stand deposition of fine calcareous lagoonal sediments containing bioclasts of red algae and benthic and planktonic foraminifera that was intensely burrowed by marine invertebrates probably upogebiid shrimp that could not be produced under any condition other than sustained marine submergence overlying this were pure carbonate beach sands of a low energy regressive phase containing abundant remains of terrestrial and marine vertebrates and invertebrates the considerable diversity of this fauna along with taphonomic evidence from seabird remains indicates deposition by high run up waves over a minimum duration of months if not years the maximum duration has yet to be determined but probably did not exceed one or two thousand years the most abundant snails in this fauna are two species indicative of brackish water and high tide line showing that a ghyben herzberg lens must have existed at 20 m the nature of these sediments and fossil accumulation is incompatible with tsunami deposition and given the absence of evidence for tectonic uplift of the bermuda pedestal or platform provide proof that sea level during mis 11 exceeded 20 m a fact that has widespread ramifications for geologists biogeographers and human demographics along the world s coastlines

pleistocene raised marine deposits on wrangel island northeast siberia and implications for the presence of an east siberian ice sheet two previously undocumented pleistocene marine transgressions on wrangel island northeastern siberia question the presence of an east siberian or beringian ice sheet during the last glacial maximum lgm the tundrovayan transgression 459 000 780 000 yr b p is represented by raised marine deposits and landforms 15 41 m asl located up to 18 km inland the presence of high sea level 64 000 73 000 yr ago the krasny flagian transgression is preserved in deposits and landforms 4 7 m asl in the krasny flag valley these deposits and landforms were mapped dated and described using amino acid geochronology radiocarbon optically stimulated luminescence electron spin resonance oxygen isotopes micropaleontology paleomagnetism and grain sizes the marine deposits are eustatic and not isostatic in origin all marine deposits on wrangel island predate the lgm indicating that neither wrangel island nor the east siberian or chukchi seas experienced extensive glaciation over the last 64 000 yr

sea level variation during mis 11 constrained by stepwise osaka bay extensions and its relation with climatic evolution abstract marine oxygen isotope stage mis 11 has been described as a super interglacial because of its long duration more than 30 ka but this view is often refuted by the observation that the peak sea level and maximum temperature did not surpass other interglacials including the last interglacial we address this problem using data from coastal sediments we conducted diatom and sulfur analyses on two cores of high accumulation rate 0 52 m ka sediments from osaka bay japan a linear age model applied to the diatom data shows that sea level variations with precession cycles are correlated with oxygen isotopic events 11 3 11 24 11 23 11 22 and 11 1 diatom abundances reveal sea level increases and falls because of environmental changes caused by stepwise extension of the bay this extension can be verified and mapped using data from 15 other drill cores sea level was above the sill for osaka bay during the marine interval in osaka bay spanning 60 ka it was above the sill for kawachi bay during the marine interval in kawachi plain for a duration of 44 ka including events 11 3 and 11 23 the highest sea level was above the sill for kyoto bay during an interval of 16 ka centered at event 11 3 estimates of sill elevations together with geological data suggest that the sea level of mis 11 changed within a range from 60 m to 20 m palynological data from the same core show that the mis 11 climate around osaka bay was divided into early warm temperate and late cool temperate times with a boundary between events 11 3 and 11 24 during the marine interval in kyoto the climate was an extremely warm hypsithermal almost coincided with the warmest interval in antarctica where temperatures are 0 c

departures from eustasy in pliocene sea level records estimates for sea level three million years ago a period with similar atmospheric co2 levels to today vary from 10 to 40 m above present glacial isostatic adjustment modelling suggests that variations in the height of palaeoshorelines result from the residual adjustment of continental flexure following recent glaciations

history of the greenland ice sheet paleoclimatic insights abstract paleoclimatic records show that the greenland ice sheet consistently has lost mass in response to warming and grown in response to cooling such changes have occurred even at times of slow or zero sea level change so changing sea level cannot have been the cause of at least some of the ice sheet changes in contrast there are no documented major ice sheet changes that occurred independent of temperature changes moreover snowfall has increased when the climate warmed but the ice sheet lost mass nonetheless increased accumulation in the ice sheet s center has not been sufficient to counteract increased melting and flow near the edges most documented forcings and ice sheet responses spanned periods of several thousand years but limited data also show rapid response to rapid forcings in particular regions near the ice margin have responded within decades however major changes of central regions of the ice sheet are thought to require centuries to millennia the paleoclimatic record does not yet strongly constrain how rapidly a major shrinkage or nearly complete loss of the ice sheet could occur the evidence suggests nearly total ice sheet loss may result from warming of more than a few degrees above mean 20th century values but this threshold is poorly defined perhaps as little as 2 c or more than 7 c paleoclimatic records are sufficiently sketchy that the ice sheet may have grown temporarily in response to warming or changes may have been induced by factors other than temperature without having been recorded

temperature and precipitation history of the arctic as the planet cooled from peak warmth in the early cenozoic extensive northern hemisphere ice sheets developed by 2 6 ma ago leading to changes in the circulation of both the atmosphere and oceans from not vert similar2 6 to not vert similar1 0 ma ago ice sheets came and went about every 41 ka in pace with cycles in the tilt of earth s axis but for the past 700 ka glacial cycles have been longer lasting not vert similar100 ka separated by brief warm interglaciations when sea level and ice volumes were close to present the cause of the shift from 41 ka to 100 ka glacial cycles is still debated during the penultimate interglaciation not vert similar130 to not vert similar120 ka ago solar energy in summer in the arctic was greater than at any time subsequently as a consequence arctic summers were not vert similar5 c warmer than at present and almost all glaciers melted completely except for the greenland ice sheet and even it was reduced in size substantially from its present extent with the loss of land ice sea level was about 5 m higher than present with the extra melt coming from both greenland and antarctica as well as small glaciers the last glacial maximum lgm peaked not vert similar21 ka ago when mean annual temperatures over parts of the arctic were as much as 20 c lower than at present ice recession was well underway 16 ka ago and most of the northern hemisphere ice sheets had melted by 6 ka ago solar energy reached a summer maximum 9 higher than at present not vert similar11 ka ago and has been decreasing since then primarily in response to the precession of the equinoxes the extra energy elevated early holocene summer temperatures throughout the arctic 1 3 c above 20th century averages enough to completely melt many small glaciers throughout the arctic although the greenland ice sheet was only slightly smaller than at present early holocene summer sea ice limits were substantially smaller than their 20th century average and the flow of atlantic water into the arctic ocean was substantially greater as summer solar energy decreased in the second half of the holocene glaciers re established or advanced sea ice expanded and the flow of warm atlantic water into the arctic ocean diminished late holocene cooling reached its nadir during the little ice age about 1250 1850 ad when sun blocking volcanic eruptions and perhaps other causes added to the orbital cooling allowing most arctic glaciers to reach their maximum holocene extent during the warming of the past century glaciers have receded throughout the arctic terrestrial ecosystems have advanced northward and perennial arctic ocean sea ice has diminished here we review the proxies that allow reconstruction of quaternary climates and the feedbacks that amplify climate change across the arctic we provide an overview of the evolution of climate from the hot house of the early cenozoic through its transition to the ice house of the quaternary with special emphasis on the anomalous warmth of the middle pliocene early quaternary warm times the mid pleistocene transition warm interglaciations of marine isotope stages 11 5e and 1 the stage 3 interstadial and the peak cold of the last glacial maximum

mid brunhes century scale diatom sea surface temperature and sea ice records from the atlantic sector of the southern ocean odp leg 177 sites 1093 1094 and core ps2089 2 abstract diatom assemblages from odp leg 177 sites 1093 1094 and core ps2089 2 from the present antarctic sea ice free zone and close to the polar front were analyzed in order to reconstruct the climate development around the mid brunhes event 400 000 yr ago as reflected by summer sea surface temperature ssst and sea ice distribution dense sample spacing allows a mean temporal resolution during marine isotope stage mis 11 423 362 ka of 300 400 yr ssst values were estimated from diatom assemblages using a transfer function technique the distribution pattern of sea ice diatoms indicates that the present day ice free antarctic zone was seasonally covered by sea ice during the cold mis 12 and mis 10 these glacial periods are characterized by sea ice fluctuations with a periodicity of 3 and 1 85 kyr suggesting the occurrence of dansgaard oeschger style millennial scale oscillations in the atlantic sector of the southern ocean during the glacial stages mis 12 and mis 10 termination v mis 12 11 is characterized by a distinct temperature increase of 4 6 c intersected especially at the southern site 1094 and core ps2089 2 by two distinct cooling events reminiscent of the younger dryas which are associated with a northward shift of the winter sea ice edge in the antarctic zone the ssst record is characterized by distinct temperature intervals bounded by stepwise rapid changes maximum temperatures were reached during termination v and the early mis 11 exceeding modern values by 2 c over a period of 8 kyr this pattern indicates a very early response of the southern ocean to global climate on milankovitch driven climate variability the ssst optimum is marked by millennial scale temperature oscillations with an amplitude of ca 1 c and periodicities of ca 1 85 and 1 47 kyr probably reflecting changes in the ocean circulation system the sssts during the mis 11 temperature optimum do not exceed values obtained from other interglacial optima such as the early periods of mis 5 or mis 1 from the antarctic zone however the total duration of the warmest period was distinctly longer than observed from other interglacials the comparison of the south atlantic climate record with a high resolution record from odp leg 162 site 980 from the north atlantic shows a strong conformity in the climate development during the studied time interval

faulting and block rotation in the afar triangle east africa the danakil crank arm model several domains of contrasted extensional deformation have been identified in the southern afar triangle east africa from fault patterns analyzed with panchromatic stereoscopic spot systeme probatoire d9observation de la terre images stretching directions and statistical orientation and offset variations of faults fit with the danakii crank arm model of sichler a 10 sinistral rotation of the danakil block explains the fault geometry and dextral block rotation in the southern part of the afar triangle as well as the oblique extension in the tadjoura gulf analogue modeling supports this interpretation

new evidence for the age of bering strait abstract the earliest known opening of bering strait in signaled by the presence in southern alaskan neogene strata of the marine bivalve mollusk astarte which had dwelled throughout the cenozoic in the arctic and north atlantic oceans astarte occurs with age diagnostic marine diatoms in the middle and upper miocene bear lake formation of the alaska peninsula southwestern alaska the diverse diatom flora of more than 100 taxa contains species characteristic of subzone b of the neodenticula kamtchatica zone of the north pacific diatom biochronology which has an age range of 4 8 5 5 ma this inferred age for an early opening of bering strait predates the generally cited ages of 3 1 4 1 ma stratigraphic data suggest that the first opening of the strait may have occurred even earlier

digital photogrammetry as a tool in analogue modelling applications to volcano instability abstract three techniques of digital photogrammetry have been applied successfully to laboratory analogue models to study surface displacements caused by various volcano deformation types firstly side perspective videos are used to differentiate profile displacements between cryptodome intrusion models and models deforming by ductile inner core viscous flow both models show similar morphologic features including a bulged flank and an asymmetric upper graben however differences in displacement trajectories of the bulge crest reflect upward intrusion push contrasting with essentially downward displacement vectors of weak core models the other two techniques use vertical views correlated automatically either as time sequence monoscopic views or as coeval stereoscopic pairs this exploits to a maximum the method s potential by imaging surface displacements over the whole model successive monoscopic photograms because they suffer only moderate numerical processing for topographic effect removal can detect very small displacements occurring early in deformation processes as illustrated by analysis of intrusion models the monoscopic method allows prediction of fault locations and main displacement locations it can also anticipate the principal strain directions and separate different deformation stages on the other hand the stereo photogrammetry technique although more complicated provides topography and volume changes as well as pictures of surface displacements in three dimensions results are presented for the spreading of volcano models on a ductile substratum and viscous cored cones we have found digital photogrammetry to be a useful tool for analogue modelling because it provides quantitative data on surface displacements including movement invisible to the eye as well as topographic changes it is a good method for investigating and comparing different deformation mechanisms it is especially useful for interpretation of displacement patterns obtained from monitoring of natural active volcanoes in fact results of the methods used in the laboratory can be directly compared with field data from geodetic or photogrammetric surveys as at mount st helens in 1980

impact of pre existing fabrics and multi phase oblique extension on cenozoic fault patterns wichianburi sub basin of the phetchabun rift thailand abstract cenozoic fault patterns associated with rift development in the wichianburi sub basin show a wide range of controls at different scales including influence by the margin of a permian basin and nw se to ne sw trending triassic folds and faults during the late oligocene early miocene phase 1 normal faults nnw sse to nne ssw trends developed in response to e w extension faults predominantly trend nnw sse to n s during this phase during the middle miocene pliocene the extension direction rotated to a more nw se orientation the old fault orientations were reactivated and new faults also developed with predominantly nne ssw to ne sw orientations many new faults nucleated within the syn rift section and were not directly influenced by pre existing fabrics in the pre rift section four types of phase 2 fault can be identified type 1 newly formed faults that strike sub orthogonal to the phase 2 extension direction type 2 newly formed faults that strike between the phase 1 fault orientations and type 1 faults type 3 newly formed faults that strike at angles greater than 90 with respect to the phase 2 extension direction type 4 reactivated phase 1 faults local stress rotations and fault linkage rotations explain many of the type 2 and 3 fault orientations the stress rotation in the middle miocene is observed in other basins in central thailand notably the suphan buri and phitsanulok basins where a range of fault patterns are produced by the effects of inherited fabrics plus multi phase rifting

pollen analysis of a late pliocene and early pleistocene section from the gubik formation of arctic alaska abstract a 14 m thick section of marine and nonmarine sediments of the gubik formation of northern alaska exposed in bluffs near ocean point on the colville river has been studied by means of pollen analysis pollen from the marine sediments of probable late pliocene age records a boreal forest of spruce and birch with minor amounts of alder in the adjacent terrestrial vegetation pine and perhaps true fir were probably at or near their northern limit here but hemlocks and hardwoods were absent the suggested environment for the arctic slope during the time represented by the marine sediments is similar to that of present day anchorage pollen floras from the overlying fluvial strata of early or middle pleistocene age record predominantly herbaceous taxa indicating tundra conditions probably more severe than those of the present day these deposits were most likely contemporaneous with glacial conditions in the brooks range to the south pollen of woody taxa spruce alder birch heaths is rare through most of the section although birch and alder percentages similar to those found in modern river sediments indicate an interstadial or interglacial warming in midsection inland climates during glacial episodes may have been similar to those of the present arctic coast

marine plio pleistocene of iceland and problems of its correlation abstract the marine pliocene pleistocene sequence of iceland contains four main assemblages of mollusks 1 venerupis rhomboides et al 2 serripes groenlandicus et al 3 portlandia arctica et al and 4 recent species analysis of the stratigraphic distribution of 100 species shows that the percentage of extinct species in the assemblages decreases from 40 in the oldest to 4 8 in the youngest there is also a change from south boreal affinities in the oldest assemblage to north boreal in the youngest the molluskan assemblages of iceland can be correlated with pliocene pleistocene assemblages of england and north europe 1 coralline crag 2 red crag lower part of the icenian strata 3 upper part of the icenian cromerian strata the upper boundaries of the pliocene and eopleistocene are defined by paleomagnetic data and radiological dating the upper boundary of the pliocene presumably should be established in the basalts lying between the tjornes and the breidavik deposits by changes between the second and third mollusk assemblages and by the gilsa paleomagnetic event

pliocene warmth polar amplification and stepped pleistocene cooling recorded in ne arctic russia understanding the evolution of arctic polar climate from the protracted warmth of the middle pliocene into the earliest glacial cycles in the northern hemisphere has been hindered by the lack of co

new perspectives on beringian quaternary paleogeography stratigraphy and glacial history abstract aspects of the paleogeography stratigraphy and glacial history of beringia have been greatly revised over the past 15 20 yr access to north east russia in particular has provided the opportunity to evaluate the beringia landscape as a contiguous subcontinent during the quaternary for the first time new research has made clearer the connection between tectonic forces and the submergence of the bering strait during the middle pliocene revisions in the regional stratigraphy of glacial and interglacial deposits in northwest alaska and northeast russia provide a new foundation for assessing the causes for differences in glacial ice extent through time the consensus of all field workers verifies that glacial ice throughout most of beringia was of very limited extent during the last glacial maximum the onset of regional glaciation during the waning stages of the last interglaciation is clearly out of phase with glaciation at lower latitudes despite the lack of much glacial activity during the early holocene alaska contains a rich record of late holocene glacial response to neoglacial cooling changes in the holocene environment of beringia likely had a profound affect on early inhabitants the curiosity driven vision and spirit of both david hopkins and the late troy pewe have had a profound influence on arctic paleoenvironmental research

mega highstand or megatsunami discussion of mcmurtry et al elevated marine deposits in bermuda record a late quaternary megatsunami sed geol 200 2007 155 165 abstract graded sorted rounded and ponded marine sand and conglomerate deposited in caves and on an erosional terrace at 20 m on bermuda previously interpreted as originating in a eustatic highstand of sea level during the middle pleistocene were reinterpreted by mcmurtry et al 2007 as the result of a great 20 m megatsunami at sea propagating out across the north atlantic from the canary islands cresting and rolling up and over the bermuda platform however no middle pleistocene tsunami deposits have been reported elsewhere on bermuda or anywhere else around the north atlantic rim the tsunami origin is unsupportable whereas the available evidence unequivocally establishes a 21 m eustatic sea level during the middle pleistocene mis 11 interglacial

age of pre late wisconsin glacial estuarine sedimentation bristol bay alaska pleistocene glacial estuarine sediment deposited in an intertidal environment of northeastern bristol bay southwestern alaska was dated using a variety of approaches including infrared stimulated and thermoluminescence irsl and tl techniques analysis of modern and14c dated holocene tide flat mud demonstrates that the bulk of sediment in this environment is reset by solar radiation thereby lending confidence to ages obtained from similar pleistocene deposits by luminescence techniques irsl seems to be especially well suited for dating with resolution on time scales of 10 000 yr the ages of tide flat mud of the nushagak formation derived from the ahklun mountains to the northwest of bristol bay and of halfmoon bay drift derived from the alaska peninsula to the southeast suggest contemporaneous glacial estuarine deposition related to independent glacial source areas about 75 000 80 000 yr ago this age is consistent with other geochronological data that indicate a pre late wisconsin and post substage 5e age including nonfinite14c ages a lack of interglacial indicators and old crow tephra 140 000 yr atop the drift normal paleomagnetic inclinations and amino acid isoleucine epimerization ratios aile ile aile ile ratios inportlandia arctica 0 052 0 003 from a marine lag horizon at south naknek beach which separates halfmoon bay drift above from older glacial estuarine drift below are only slightly higher than inmya truncata 0 041 0 007 from last interglacial pelukian deposits at nome as laboratory heating experiments show that the two genera epimerize at similar rates these data imply correlation of the marine lag at south naknek beach with pelukian deposits hence glaciers on the alaska peninsula experienced major pre late wisconsin advances both before and after the last interglaciation shells reworked into halfmoon bay drift yield aile ile ratios of 0 028 0 005 forportlandiaat second point and 0 027 0 001 forhiatella arcticaat etolin point together with assumptions about the postdepositional temperature history these ratios indicate that the shells are at least 55 000 yr and probably closer to 90 000 yr although the uncertainty in this age estimate is broad the amino acid and luminescence data converge on an age between about 75 000 and 90 000 yr late during oxygen isotope stage 5 for a major ice advance far beyond late wisconsin limits

extralimital senegalese species during marine isotope stages 5 5 and 11 in the canary islands 29 n sea surface temperature estimates abstract the presence of harpa doris roding 1798 in marine deposits of the last interglacial period 130 120 ka marine isotope stage or mis 5 5 in the canary islands gran canaria lanzarote and fuerteventura enabled us to compare this occurrence with its present habitat in the gulf of guinea and the cape verde islands well to the south this comparison leads to the conclusion that sea surface temperatures ssts in the waters around the canary islands during the last interglacial period were at least 3 3 c higher than today h doris is found in association with the large gastropod persististrombus latus gmelin 1791 as well as the coral siderastrea radians pallas 1766 the presence of these extralimital southern warm water species in the canary islands during the last interglacial period also implies a northward expansion of plankton feeding larvae in seawater with a high chlorophyll a content such conditions would require a shortening of the southern arm of the cool canary current that dominates the waters around the canary islands at present marine deposits dating to 400 ka mis 11 are also found on the canary islands in these deposits the presence of saccostrea cucullata born 1778 allows a comparison with its present habitat in the gulf of guinea in this analysis we conclude that ssts in waters around the canary islands during this major interglacial period were at least 4 2 c higher than today middle pleistocene fossils of s cucullata have also been found in the western mediterranean sea and morocco as well as the cape verde islands if these deposits also date to mis 11 sst warming could have been a regional phenomenon including much of the eastern atlantic ocean and mediterranean sea

rift segment interaction in orthogonal and rotational extension experiments implications for the large scale development of rift systems abstract during extension of the continental lithosphere rift basins develop these are often initially offset and must interact and connect in order to create a continuous rift system that may ultimately achieve break up when simulating extensional tectonics and rift interaction structures analogue and numerical modellers often apply a continuous extension rate along the strike of a rift or rift system yet in nature significant extension velocity variations occur along rifts and plate boundaries as a natural consequence of tectonic plates moving apart about a pole of rotation resulting in rotational extension and associated rift propagation and structural gradients here we present various analogue tectonic experiments to assess rift interaction structures forming in orthogonal extension settings versus rotational extension settings our modelling efforts show that rotational extension and orthogonal extension produce significantly different large scale structures rotational extension can cause important variations in rift maturity between rift segments delay rift interaction zone development and make rift segments propagate in opposite directions still local features in a rotational extension system can often be regarded as evolving in an orthogonal extension setting furthermore we find that various degrees of rift underlap produce three basic modes of rift linkage structures low underlap distance high angle experiments develop rift pass structures with increasing underlap distance ca 40 transfer zone basins develop high degrees of underlap 30 tend to result in en echelon sub basins our results match with data from previous modelling efforts and natural examples we furthermore propose a large scale tectonic scenario for the east african rift system based on rotational extension and associated rift propagation these insights may also be applicable when studying other large scale rift systems

the role of inherited crustal and lithospheric architecture during the evolution of the red sea insights from three dimensional analogue experiments abstract the red sea represents an incipient ocean basin that is in transition from continental rifting to ocean initiation in this paper we assess how pre existing mantle and crustal heterogeneities within the african and arabian lithospheres influenced rift development and propagation using three dimensional 3d brittle ductile analogue laboratory experiments with a rotational boundary condition here we investigate the effect of three different configurations i pre existing rheological heterogeneities in the crust ii in the lithospheric mantle and iii in both the experimental outcomes show that a linear weak zone in the lithospheric mantle layer exerts a first order control on the overall mechanical behaviour of extending lithosphere rift architecture and style of rifting crustal heterogeneities control second order features such as the trends of the main boundary escarpments along the rift axis our experiments reproduce the geological history of the red sea and provide key insights on its deformation history in space and time we provide for the first time 3d dynamic constraints on how pre existing weak zones in the lithosphere have controlled the temporal evolution of the red sea and determined its distinctive present day morphology the results find that certain morphological elements of the red sea can only be explained by the combined effects of crustal and mantle lithosphere heterogeneities when applied to other natural examples our findings provide significant new insights on the role of crustal and lithospheric heterogeneities during continental rifting

pre late wisconsin glacial history coastal ahklun mountains southwestern alaska new amino acid thermoluminescence and 40ar 39ar results abstract new stratigraphic and geochronologic data from the togiak bay area of southwestern alaska indicate that glaciers advanced from the southern ahklun mountains at least three and as many as six times prior to the late wisconsin the oldest glaciations are represented by glacial marine sediment in coastal exposures on hagemeister island the extent of amino acid isoleucine epimerization in fossil molluscs indicates that at least one and possibly four older middle pleistocene glacial intervals are represented with age estimates spanning 500 280 ka and averaging 400 100 ka the youngest glacial marine drift on hagemeister island may correlate with the eruption of the togiak tuya a new 40 ar 39 ar age on basalt that overlies pillow lava indicates that the volcano erupted through glacial ice at least 300 m thick 263 22 ka the youngest drift in the region overlies the old crow tephra 140 10 ka and a 70 10 ka basaltic lava flow dated by thermoluminescence analysis of underlying baked sediment the drift delimits flat piedmont lobes that spread out onto the continental shelf and terminated 100 km from their source areas during the early wisconsin sensu lato the glacial geologic evidence suggests that major expansions of glaciers were out of phase with global ice volume

cave fills in miocene pliocene strata on cayman brac british west indies implications for the geological evolution of an isolated oceanic island abstract an 8 m high wall in a quarry on the west end of cayman brac exposes the upper part of the cayman formation miocene the lower part of the overlying pedro castle formation pliocene and the cayman unconformity which is a karstic unconformity that separates these formations the modern day karst surface caps the pedro castle formation this exposure also includes cross sections through two filled caves the lower cave 8 m long up to 2 5 m high and upper cave 23 m long up to 2 m high that are housed in the cayman formation and pedro castle formation respectively the lower cave is filled with caymanite which is formed of laminated varicolored dolomitized mudstones and grainstones that contain scattered marine fossils e g foraminifera red algae this cave connected to the cayman unconformity by a small diameter tunnel evolved as part of the karst system that developed during the messinian lowstand 7 3 5 3 ma the cave was filled and dolomitized prior to deposition of the pedro castle formation the upper cave is filled with a wide spectrum of lithotypes including dolostones calcareous mudstones terra rossa gastropod coquina coated grains and speleothems u th dating indicates that some of the flowstones are 500 000 years old whereas others are only 21 000 years old dolostones and mudstones in the basal part of the upper cave contain marine fossils foraminifera red algae whereas the younger deposits are devoid of such fossils the upper cave and its deposits developed after the sediments of the pedro castle formation had been deposited and lithified development of the cave filling deposits which includes a clear transition from marine to non marine influences was controlled by eustatic sea level changes and or westward tectonic tilting of cayman brac that occurred after the pedro castle formation became exposed probably during the late pliocene

aminostratigraphy of pliocene pleistocene high sea level deposits nome coastal plain and adjacent nearshore area alaska amino acid epimerization ratios aile ile measured in 295 fossil molluscan shells of 3 genera provide a basis to evaluate the number and relative timing of high sea level events represented by deposits blanketing the nome coastal plain and adjacent nearshore area northwestern alaska frequency distribution analysis along with a new approach that relies on the ranked data distribution was used to identify clusters aminozones in the aile ile data each of which presumably represents a discrete period of marine inundation of the study area six periods of high relative sea level were distinguished some are recognized only by redeposited shells rather than in situ bio or lithostratigraphic units the oldest period is represented by shells recovered from the deepest sections of two offshore boreholes aile ile ratios in these shells 1 0 are much higher than in any found onshore and probably date to the late miocene early pliocene the oldest aminozone lies below nonfossiliferous sediments which in turn are overlain by glacigenic and marine deposits containing largely fragmented shells with aile ile ratios ranging from 0 35 to 0 65 this range coincides with aile ile ratios from various onshore deposits previously ascribed to the middle pliocene 3 m y beringian transgression ratios in this range can be subdivided into three evenly spaced aminozones each of which may represent multiple short duration 10 4 yr high sea stands separated by a longer period 10 5 yr sea level oscillation on the basis of a new empirical model of parabolic epimerization kinetics and an assumed age of 3 2 m y for the oldest beringian aminozone the approximate age of the initial submergence of bering strait the estimated length of time represented by the three beringian aminozones is between 0 5 and 1 7 m y the youngest beringian highstand was followed in the late pliocene or early pleistocene by a lengthy period of nonmarine deposition during which local valley glaciers advanced onto the coastal plain at least once relative sea level apparently did not again surpass that of today until the middle pleistocene anvilian transgression the oldest higher than present stand of the pleistocene yet considerably younger than previously thought glaciers overran the nome coastal plain at least once following the anvilian transgression incorporating abundant shells into their drift the drift is notched by a shoreline formed during the pelukian transgression of the last interglaciation although well represented onshore no pelukian deposits have been found offshore

enhanced age resolution of the marine quaternary record in the arctic using aspartic acid racemization dating of bivalve shells abstract aspartic acid asp racemization occurs at a significantly higher rate than isoleucine epimerization and consequently provides better temporal resolution of arctic marine deposits from alaska spitsbergen and baffin island heating experiments at 100 c on the bivalvesmyaandhiatellashow the asp racemization rate decreases with increasing d l values as is typical for biogenic carbonates based on these experimental racemization rates and rates determined from racemization of samples radiocarbon dated to ca 10 000 12 000 yr b p activation energies formyaandhiatellaare estimated to be 30 6 and 30 0 kcal mol respectively for asp racemization and 29 0 and 29 5 for isoleucine epimerization analysis of a time series of plio pleistocenehiatellafrom the north coast of alaska shows that last interglacial mollusks can be readily distinguished from modern samples by asp but not by isoleucine d l asp values indicate a younger age for the fishcreekian transgression than does isoleucine epimerization for spitsbergen d l asp shows a slight age difference ca 12 000 yr between two units of the episode b interstadial and suggests that the age of these units may be closer to 65 000 than to 80 000 yr b p two possible ages suggested by other evidence the age of the loks land interstadial on baffin island is likely to be greater than that indicated by radiocarbon ages within deposits from each region d l asp values are less variable among individual shells than isoleucine epimerization values this may indicate better reliability of asp for geochronology

using different grain size granular mixtures quartz and k feldspar sand in analogue extensional models abstract we have performed a series of sandbox models addressing the influence of sand mixtures quartz and feldspar sand in different proportions with different grain size on the development of normal faults the overall model evolution suggests that fault orientation width of the deformed area and average subsidence are not significantly influenced by the different sand mixtures conversely the number of secondary structures mean fault length and average fault dip are strongly dependent on the material and grain size modelling results suggest that a log normal distribution of fault length and segment length distribution betst describes the experimental fault populations particularly when the amount of fine grained k feldspar sand is 30 the length distribution and the number of faults are related specifically with increasing the amount of the k feldspar sand i e higher the amount of fine grained material the shorter the minimum detectable fault length this behavior is described by a log normal distribution with a few long faults and many intermediate to short faults we thus suggest that for length ratios of 10 5 to 2 10 6 a sand mixture composed of 70 quartz sand and 30 k feldspar sand is the one among those we have tested that provides the best compromise in terms of frictional properties density structural detail number and length distribution of the faults easiness of use and general behavior

structural characteristics of the suez rift margins field study of the hadahid block the eastern margin of the central half graben of the suez rift indicates two listric normal faults at its eastern and western boundaries the rift bounding fault and the hadahid fault respectively these faults were affected by two episodes of movement the earlier movement at the initial neogene rift opening led to equal displacements on the two faults whereas the later movement at the mid clysmic event l7 ma ago caused the hadahid fault to bound the deep part of the central half graben a similar conclusion is also reached for the western margin of the southern half graben of the rift esh el mellaha and zeit blocks the two listric faults bounding the margin blocks in these two oppositely tilted half grabens hadahid and esh el mellaha blocks join at depth into a ramp flat detachment this geometry of the rift bounding faults represents an intermediate stage in the evolution of rift basins it is preceded by the early rifting stage where extension is less and oppositely tilted half grabens are formed e g the ancestral red sea gulf of suez rift increased extension at later stages leads to the prevailance of one system of detachment instead of oppositely dipping detachments of adjacent half grabens the central and southern red sea have perhaps had this geometry before the onset of seafloor spreading

sensitivity of pliocene ice sheets to orbital forcing the stability of the earth s major ice sheets is a critical uncertainty in predictions of future climate and sea level change one method of investigating the behaviour of the greenland and the antarctic ice sheets in a warmer than modern climate is to look back at past warm periods of earth history for example the pliocene this paper presents climate and ice sheet modelling results for the mid pliocene warm period mpwp 3 3 to 3 0 million years ago which has been identified as a key interval for understanding warmer than modern climates jansen et al 2007 using boundary conditions supplied by the united states geological survey prism group pliocene research interpretation and synoptic mapping the hadley centre coupled ocean atmosphere climate model hadcm3 and the british antarctic survey ice sheet model basism we show large reductions in the greenland and east antarctic ice sheets gris and eais compared to modern in standard mpwp experiments we also present the first results illustrating the variability of the ice sheets due to realistic orbital forcing during the mid pliocene while gris volumes are lower than modern under even the most extreme cold mid pliocene orbit losing at least 35 of its ice mass the eais can both grow and shrink losing up to 20 or gaining up to 10 of its present day volume the changes in ice sheet volume incurred by altering orbital forcing alone means that global sea level can vary by more than 25 m during the mid pliocene however we have also shown that the response of the ice sheets to mpwp orbital hemispheric forcing can be in anti phase whereby the greatest reductions in eais volume are concurrent with the smallest reductions of the gris if this anti phase relationship is in operation throughout the mpwp then the total eustatic sea level response would be dampened compared to the ice sheet fluctuations that are theoretically possible this suggests that maximum eustatic sea level rise does not correspond to orbital maxima but occurs at times where the anti phasing of northern and southern hemisphere ice sheet retreat is minimised

slab detachment control on mafic volcanic pulse and mantle heterogeneity in central mexico seismic tomography studies and plate reconstructions suggest that the farallon slab broke off shortly before subduction ended off southern baja california however the progress of detachment in time and space and its consequences on the volcanism of central mexico have not so far been considered here i use the neogene geologic record of central mexico to propose a lateral propagation of slab detachment beneath the trans mexican volcanic belt during the late miocene i suggest that the trace of the detachment is expressed by a short 2 3 m y eastward migrating pulse of mafic volcanism that took place from ca 11 5 to ca 6 ma to the north of the pliocene quaternary volcanic arc as hot subslab material flowing into the slab gap produced a transitory thermal anomaly in the mantle wedge slab detachment of the deeper and denser part of the plate was initiated in the southern gulf of california area by the incoming of progressively younger oceanic lithosphere at the paleotrench that produced an increasing coupling between the magdalena microplate and the overriding north american plate the tear in the slab propagated eastward from the gulf of california to the gulf of mexico paralleling the southern mexico trench system the decrease in the rivera north america convergence rate between ca 9 and 7 ma appears to be related to the loss of slab pull after the detachment sparse oceanic island type basalts emplaced since the end of the miocene in the trans mexican volcanic belt are located above a trench parallel slab window between the inferred detachment trace and the leading edge of the present slab which has been detected seismically in this context the occurrence of these unusual intraplate magmas is easily explained by the infiltration of enriched asthenosphere into the subarc mantle