climate and environment of a pliocene warm world the pliocene epoch 5 33 2 58 million years ago ma was a generally warmer and wetter interval with atmospheric co2 concentrations at or slightly above modern levels this paper provides an overview of pliocene vegetation sea surface temperatures and climate modelling outcomes most prominent changes in pliocene biome distribution compared to today include a northwards shift of temperate and boreal vegetation zones in response to a warmer and wetter climate as well as an expansion of tropical savannas and forests at the expense of deserts faunal analysis techniques and modelling experiments using the hadley centre climate model identified significantly higher pliocene sea surface temperatures at mid and high latitudes of the northern hemisphere with cooling or unchanged sea surface temperatures at low latitudes global mean annual surface temperatures mat are estimated to have been 2 to 3 c higher during the piacenzian 3 6 2 58 ma than today with a reduced equator to pole gradient the marine realm during the pliocene was characterised by a reconfiguration of ocean gateways particularly the narrowing of the indonesian seaway and closure of the central american isthmus which produced essentially a modern pattern of ocean circulation in the southern ocean a warm early pliocene gave way to late piacenzian cooling proxy data indicate a reduced east to west sea surface temperature gradient in the tropical pacific during the pliocene warmth the pliocene is one of the most intensively studied geological intervals of the pre quaternary no other warm period in the geological past yields such a unique combination of near modern atmospheric co2 concentrations palaeogeography and palaeobiology however this paper also identifies data gaps and shortcomings in the reconstruction of pliocene environments using proxy data and climate models on which future research should focus

core evidence of paleoseismic events in paleogene deposits of the shulu sag in the bohai bay basin east china and their petroleum geologic significance abstract the shulu sag located in the southwestern corner of the jizhong depression bohai bay basin of east china is a ne sw trending elongate cenozoic half graben basin the lowermost part of the third member of the shahejie formation in this basin is characterized by continental rudstone and calcilutite to calcisiltite facies based on core observation and regional geologic analysis seismites are recognized in these lacustrine deposits which include soft sediment deformation structures sedimentary dikes hydraulic shattering diapir structures convolute lamination load flame structures ball and pillow structures loop bedding and subsidence structures synsedimentary faults and seismoturbidites in addition mixed source rudstones consisting of the paleozoic carbonate clasts and in situ calcilutite clasts in the lowermost submember of shahejie 3 appear in the seismites suggesting an earthquake origin a complete representative vertical sequence in the lowermost part of the third member found in well st1h located in the central part of the shulu sag shows from the base to the top underlying undeformed layers synsedimentary faults liquefied carbonate rocks allogenetic seismoturbidites and overlying undeformed layers seismites are widely distributed around this well and there are multiple sets of stacked seismites separated by undeformed sediment the nearby nw trending taijiazhuang fault whose fault growth index is from 1 1 to 1 8 and the nne trending xinhe fault with a fault growth index of 1 3 1 9 may be the source of the instability to create the seismites these deformed sedimentary layers are favorable for the accumulation of oil and gas for example sedimentary dikes can cut through many layers and serve as conduits for fluid migration sedimentary faults and fractures induced by earthquakes can act as oil and gas migration channels or store petroleum products as well seismoturbidites and mixed source rudstones are excellent reservoirs due to their abundant primary or dissolved pores

sedimentary facies and evolution in the qiantang river incised valley eastern china abstract this paper deals with the sedimentary facies and evolution of the qiantang river qr estuary and the characteristics and formation of the incised valley sequences and the related shallow biogenic gas reservoir on the basis of analysis of over 500 cores the result shows that since the last glaciation the late quaternary formation of the qr estuary area underwent three stages 1 deep cutting stage 2 rapid filling stage and 3 burial stage the fall of global sea level during the last glacial maximum enhanced the fluvial gradient and river cutting resulting in the formation of the large scale qr and taihu incised valleys with the interfluve being exposed to air on both flanks of the incised valley fluvial terraces at the elevations are present near the present qr estuarine mouth corresponding to 60 70 90 100 and 115 125 m burial depths the valleys were filled rapidly with fluvial sediments during the post glacial period with the rise of sea level the river mouth migrated to landward and backwater and retrogressive aggradation was enhanced the qr and taihu incised valleys are associated with an early filling and transgressive channel infilling sequence formation and a late filling and transgressive floodplain estuary formation subsequently the qr valley was buried under estuarine marine and estuarine sand bar sediments from bottom to top the incised valley successions can be grouped into four sedimentary facies river channel floodplain estuary estuary shallow marine and estuary sand bar the thickness of the river channel infilling deposits is controlled mainly by base level rising backwater retrogressive aggradation and neotectonism further localized thickening took place where deeper scour pools were present in the incised valley or fluvial terraces were formed during the fall of elative sea level during the deposition of the floodplain estuary facies the conditions of sea level rise tidal regime sediment supply and accommodation space were suitable for the development of a tidal ridge system the sand lenses associated with this facies may represent a tidal ridge system in the incised valley at the later stage when the estuarine sand bars were formed the sedimentary conditions were no longer favourable resulting in absence of sand ridge deposits biogenic gas is stored in the floodplain estuary sand lenses of the incised valleys the changjiang river provides the major sediment supply for the qr estuary sand bar and the qr carried sediments constitute only a small portion of the deposits

sedimentary structures tentatively attributed to seismic events abstract fingerprints of earthquakes in the sedimentary record are as yet difficult to identify this is particularly true for failure phenomena dewatering slumping fault graded and turbidite structures that could have been triggered also by other kinds of energy input other promising candidates are strange biostratinomic features convex down stacking of shells current orientation in wave ripple accumulations as well as certain preservational features found in geosynclinal pelagic limestones but in every case verification of the seismic origin is still needed

a raised ois 3 sea level recorded in coastal sediments southern changjiang delta plain china abstract the distribution of marine influenced oxygen isotope stage ois 5 to ois 1 sediments was examined in several late quaternary boreholes from the southern changjiang yangtze delta plain china using different dating methods including osl u series ams 14c and paleomagnetism results demonstrate that coastal and estuarine deposition during ois 5 and ois 3 occurred throughout the study area however holocene transgressive sediments were absent on the taihu block the burial depth of intertidal to subtidal sediment deposited during ois 5e records 30 80 m subsidence caused by sediment compaction and tectonic movement since that time however coastal sediments formed during the late phase of ois 3 were buried to a depth of ca 6 15 m in the taihu lake area while the burial depth increased eastward to ca 45 60 m on the coastal plain this phenomenon combined with the distribution of holocene marine strata indicates at least 25 30 m uplift of the taihu block since the end of ois 3 we suggest that this uplift was mainly caused by the differential subsidence due to substantial amount of post glacial deposition by the changjiang and huanghe rivers on the continental shelf of east china marginal sea

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

uniquely extensive soft sediment deformation in the rhaetian of the uk evidence for earthquake or impact the lower part of the cotham member in the penarth group latest triassic rhaetian of the uk incorporates a uniquely extensive metre scale horizon of soft sediment deformation interpreted as a seismite it shows evidence for only a single seismic event even at its thickest development it is recorded from more than forty sites across at least eight discrete sedimentary basins covering n250 000 km 2 and originally must have covered a still larger area such a widespread horizon of soft sediment deformation unique for the uk phanerozoic and implying a seismic event of exceptional magnitude is difficult to account for by conventional terrestrial mechanisms contemporaneous volcanism in the central atlantic magmatic province camp was too far distant to cause the deformation and the tectonic setting of the region was not conducive to earthquakes on this scale slump fold long axes suggest an epicentre broadly in the southern irish sea or st george s channel impact of a km scale asteroid here potentially could produce the observed sedimentological effects across the uk but any late triassic impact structure would now be concealed by a km or more of younger strata at its thickest development in northern ireland the seismite is succeeded by a rip up breccia and hummocky and wave rippled cross stratification these facies and their position immediately above the seismite are consistent with the effects of a tsunami arising directly from the seismic event tentative evidence for a tsunamite of this age has also been reported from southern france the putative tsunamite in northern ireland is succeeded by a desiccation cracked hiatus which may correlate with a similar hiatus truncating the seismite at sites in southern england the hiatus in southern england correlates closely with a 13 c isotope excursion that has been traced from eastern europe across to western north america and is associated with significant biotic changes the ultimate cause of the seismite and associated tsunamite remains unclear no impact crater of appropriate age or location is currently known and other evidence for impact at this time is at best equivocal it is considered here that impact of a km scale asteroid may have caused the observed sedimentological effects in the lilstock formation across the uk area but was not necessarily a significant contributory factor in the generation of either the isotope excursion or of the biotic changes through the triassic jurassic boundary interval

a global synthesis of the marine and terrestrial evidence for glaciation during the pliocene epoch abstract the pliocene climate is globally warm and characterised by high atmospheric carbon dioxide concentrations yet the terrestrial and marine scientific communities have gathered considerable evidence for substantial glaciation events in both the northern and southern hemisphere prior to the quaternary evidence on land is fragmentary but marine records of glaciation present a more complete history of pliocene glaciation here we present a global compilation of the terrestrial and marine glacial evidence for the pliocene and demonstrate four glaciation events that can be identified in the southern and or northern hemisphere prior to the latest pliocene intensification of northern hemisphere glaciation there are two globally recognisable glacial events in the early pliocene c 4 9 4 8 ma and c 4 0 ma one event around the early late pliocene transition c 3 6 ma and one event during marine isotope stage m2 c 3 3 ma long term climate cooling decreasing carbon dioxide concentrations in the atmosphere and high climate sensitivity in the pliocene probably facilitated each glaciation event however the mechanisms behind the early pliocene glacial events are unclear the global glaciation at c 3 3 ma may be caused by changes in ocean gateways whereas the decline in carbon dioxide concentrations is important for the latest pliocene intensification of northern hemisphere glaciation

seismites from a well core of palustrine deposits as a tool for reconstructing the palaeoseismic history of a fault abstract the concud fault is located at the junction between the jiloca and teruel grabens central eastern iberian chain spain the late pleistocene activity of this fault has been well logged from structural and palaeoseismological trench studies but only scattered data of the late pliocene seismic activity exist the late pliocene early pleistocene syn tectonic infill consists of an endorheic continental succession in which a 75 m long continuous well was drilled near the concud fault along the entire well core several types of soft sediment deformation structures with variable morphology size and frequency have occurred including clastic dykes load structures and slumps the rigorous analysis of the deformation structures their relationships with the involved sedimentary facies and the discrimination of possible deformation mechanisms and trigger processes allow us to interpret part of them as seismically induced structures the recognition of 21 deformed beds seismites allow the late pliocene early pleistocene seismic history of the concud fault to be reconstructed therefore 21 seismic events with m 5 and an apparent recurrence period of about 45 ka have been inferred

sublacustrine precipitation of hydrothermal silica in rift lakes evidence from lake baringo central kenya rift valley abstract many lakes in volcanic regions are fed by hot springs that in some basins can contribute a large percentage of the annual recharge especially during times of aridity it is important to recognize any contemporary hydrothermal contribution in paleoenvironmental reconstruction of lake basins because recharge from thermal waters can potentially confuse paleoclimatic signals preserved in the lacustrine sedimentary record hot spring deposits travertine sinter provide the most tangible evidence for thermal recharge to lakes although subaerial spring deposits have been widely studied lacustrine thermal spring deposits especially sublacustrine siliceous sinters remain poorly known detailed field petrographic and scanning electron microscope sem studies have been made of fossil sublacustrine sinter exposed at soro hot springs along the northeastern shoreline of ol kokwe a volcanic island in lake baringo kenya modern hot springs at soro which discharge na hco3 cl waters from a deep reservoir 180 c have thin 1 10 mm friable microbial silica crusts around their subaerial vents but thicker 1 cm sinter deposits are not forming the fossil sinter which is present as intergranular cements and crusts in littoral conglomerates and sandstones is composed mainly of opaline silica opal a three types of fossil sinter are recognized 1 massive structureless silica which fills intergranular pores and forms crusts up to 5 cm thick 2 pore lining silica some of which is isopachous and 3 laminated silica crusts which formed mainly on the upper surfaces of detrital particles all three types contain well preserved diatoms including lacustrine planktonic forms microbial remains mainly filamentous and coccoid bacteria including cyanobacteria and extracellular polymeric gels are locally abundant in the opaline silica together with detrital clays and thin laminae composed of authigenic chlorite most of the hydrothermal silica precipitated when the thermal springs were submerged by fresh lake water silica precipitated upon rapid cooling of thermal 90 c waters at and just below their interface with the overlying cooler 25 c lake waters microbial mats locally acted as a filter that limited mixing and rapid dilution of the thermal fluids some of the silica originally may have been soft and partly gelatinous planktonic diatoms and detrital clay rained down then became incorporated in the amorphous silica following a fall in lake level the opal a lithified and partly altered to cristobalite opal c and chalcedony the lowest fossil sinters were later encrusted by calcite stromatolites with calcite and quartz forming late pore filling cements the age of the sublacustrine sinters is unknown but some of the deposits could date back to the late pleistocene similar conglomerates cemented by hydrothermal silica are present along fault lines at neighbouring lake bogoria such rocks may provide evidence for deep hot fluid recharge to lakes when encountered in the geological record

phytoliths pollen and microcharcoal from the baringo basin kenya reveal savanna dynamics during the plio pleistocene transition abstract as part of the hominin sites and paleolakes drilling project hspdp phytoliths pollen and microcharcoal were examined from the 228 m 3 29 to 2 56 ma baringo tugen hills barsemoi drill core btb13 a total of 652 samples were collected at 10 to 32 cm intervals corresponding to sub millennial to millennial scale temporal resolution microcharcoal was well preserved throughout the core and often peaked in abundance 5 kyr before and after insolation peaks phytolith preservation varied between excellent to total dissolution in alternating intervals throughout the core pollen was rarely preserved these combined datasets indicate that prior to 3 1 ma woody cover fluctuated between open savanna 80 cover at typically precessional 19 23 kyr periodicities during the mid piacenzian warm period mpwp 3 26 3 01 ma intervals with exceptionally high microcharcoal abundance suggest that regional turnover from wooded to open habitats was driven in part by fire after 3 1 ma low elevation woody cover likely never exceeded 40 with oscillations between mesic tall grass vs xeric short grass savanna at precessional periodicities mesic c4 tall grass panicoideae peaked in abundance during insolation maxima whereas xeric c4 short grass chloridoideae peaked during insolation minima the onset of northern hemisphere glaciation nhg at 2 75 ma coincided with the appearance of deep lake phases and increases in grass density and fire frequency spectral analysis and intervals with well preserved phytoliths indicate that precession and interhemispheric insolation gradients influenced vegetation via their effects on equatorial precipitation and fire this study fills a crucial gap in pliocene vegetation reconstructions from the east african rift valley and its associated hominin localities it also provides orbitally resolved regional vegetation data useful in paleodata model comparisons for the onset of the mpwp which is often used as an analog for future warming and nhg

extensive soft sediment deformation structures in the early darriwilian middle ordovician shallow marine siliciclastic sediments formed on the baltoscandian carbonate ramp northwestern estonia abstract the nearshore middle ordovician early darriwilian deposits of the baltoscandian basin formed on the flank of tectonically stable fennoscandian shield comprise numerous soft sediment deformation structures the areal extent of the deformed interval extends up to 9000 km 2 from nw estonia to se sweden the deformation structures occur within a meter scale sandstone horizon that includes load casts flame structures ball and pillow morphologies up to 2 m wide sedimentary dykes autoclastic breccias sand volcanoes and other related soft sediment deformation structures evidently these deformation structures formed during a single seismic event that caused liquefaction and fluidization of the water saturated unconsolidated shallow marine sediments within almost the entire sandstone unit pakri formation probably a unique catastrophic earthquake of magnitude 7 or higher occurred in this region penecontemporaneously with the deposition of these sediments the ultimate cause of seismic event of such magnitude in the tectonically stable baltoscandian basin is unclear however deposition and deformation of the pakri formation fall within the middle ordovician meteoritic bombardment period which resulted from the disruption of a large parent body in the asteroid belt approximately 470 ma ago this in turn suggests a potential impact origin for the single catastrophic earthquake in the tectonically stable study region although impact crater of suitable age is currently not known from the region then previous studies have documented some impact metamorphic shock lamellae i e pdfs and abundant extraterrestrial chromite grains from the deformed sediments

mid to late holocene geomorphological and hydrological changes in the south taihu area of the yangtze delta plain china abstract the taihu plain of the lower yangtze valley china was a centre of rice agriculture during the neolithic period reasons for the rapid development of rice cultivation during this period however have not been fully understood for this coastal lowland which is highly sensitive to sea level change to improve understanding of the geomorphological and hydrological context for evolution of prehistoric rice agriculture two sediment cores dtx4 and dtx10 in the east tiaoxi river plain south taihu plain were collected and analysed for radiocarbon dating diatoms organic carbon and nitrogen stable isotopes 13c and 15n grain size and lithology these multiproxy analyses revealed that prior to ca 7500 cal yr bp the east tiaoxi river plain was a rapidly aggrading high salinity estuary the palaeo taihu estuary after ca 7500 cal yr bp low salinity conditions prevailed as a result of strong yangtze freshwater discharge subsequently seawater penetration occurred and saltmarsh developed between ca 7000 and 6500 cal yr bp due to accelerated relative sea level rise this transgression event influenced a large area of the taihu plain during the holocene as shown by multiple sediment records from previous studies persistent freshwater marsh or subaerial land formed due to dramatic shrinkage closure of the palaeo taihu estuary after ca 5600 cal yr bp when sea level was relatively stable we speculate that geomorphological and hydrological changes of the east tiaoxi river plain played an important role in agricultural development across the taihu plain during the neolithic period the closure of the palaeo taihu estuary and the formation of stable freshwater marsh or subaerial land after ca 5600 cal yr bp were critical preconditions encouraging the rapid rise of rice productivity in the liangzhu period 5500 4500 cal yr bp this development changed the landscape and river systems and thus provided adequate freshwater supply to the taihu plain

cation exchange capacity and water content of opal in sedimentary basins example from the monterey formation california surface characteristics of sedimentary opal a and ct were investigated for a large collection of samples from the monterey formation california based on the bulk rock mineral and chemical analysis cation exchange capacity cec and water content two approaches were used 1 modeling bulk cec and adsorbed water content for the entire data set using the contents of opal and clay minerals measured by xrd and 2 correcting the chemical composition and cec of the most pure opal samples for the mineral impurities quantified by xrd modeling indicates that the bulk rock data can be best explained by mixing an illite smectite cec 59 meq 100 g 7 8 h2o consistent with the xrd characteristics of the clay fraction with opal a 8 meq 100 g 3 4 h2o and opal ct 13 meq 100 g 3 7 h2o correcting the chemical composition of the most pure opal samples leaves a large excess of cations al fe na k ca and mg iron is suspect to form traces of separate oxy hydroxide phases not detected by xrd while al for si substitution in the opal structure produced local negative charge which was compensated by na k ca and mg exchange cations a perfect balance of positive and negative charges is observed if the clay admixture in pure opals has the composition of montmorillonite the concentration of heterogeneous impurities in silica network in opal leads to smectite formation on or within the diatom frustules these dispersed smectite particles perhaps monolayers can be missed during the bulk rock mineral quantification the recalculated cec of the opal assuming the occurrence of dispersed smectite particles varies from 3 to 11 meq 100 g which is slightly less than that evaluated by modeling all the rock samples in the set and corresponds to 10 50 of the total opal charge quantified by the degree of al for si substitution the remaining charge of the opal structure represents non exchangeable cations as opposed to smectite opal cec may depend on the size of cation used for the cec measurement for opals in the monterey formation the content of water removable at 200 c can be modeled as a sum of a constant value and a variable value dependent on cec the latter component is similar to the h2o cec relationship that is typical for smectite the combined system of a constant h2o variable h2o in opal can potentially be applied for mineral modeling programs in wireline log formation evaluation in diatomaceous hydrocarbon reservoirs

sedimentary record of seismic events in the eocene green river formation and its implications for regional tectonics on lake evolution bridger basin wyoming abstract outcrops and cores from the top of the lacustrine tipton member and the base of the wilkins peak member 51 5 ma of the eocene green river formation bridger basin in southwestern wyoming yield a wide variety of sedimentary deformation features many of which are laterally extensive for more than 50 km they include various types of folds load structures pinch and swell structures microfaults breccias and sedimentary dikes in most cases deformation is represented by hybrid brittle ductile structures exhibiting lateral variation in deformation style these occur in low energy profundal organic rich carbonate mudstones oil shales trona beds tuffs and profundal to sublittoral silty carbonate deposited in paleolake gosiute the deformation is not specific to the depositional environment because sedimentary units stratigraphically higher with similar facies show no deformation the studied interval lacks any evidence for possible trigger mechanisms intrinsic to the depositional environment such as strong wave action rapid sediment loading evaporite dissolution and collapse or desiccation so endogenic causes are ruled out thus the deformation features are interpreted as seismites and change in deformation style and inferred increase in intensity towards the south suggest that the earthquakes were sourced from the nearby uinta fault system the 22 levels exhibiting seismites recognized in cores indicate earthquakes with minimum magnitudes between 6 and 7 minimum epicentral intensity mcs of 9 and varying recurrence intervals in the seismic history of the uinta fault system with a mean apparent recurrence period of 8 1 k y using average sedimentation rates and dated tuffs in detail however there are two noticeably active periods followed by relative quiescence the stratigraphic position of these deformed intervals also marks the transition between two distinct stages in lake evolution from the balanced filled tipton member to the overlying underfilled wilkins peak member thus these seismites are evidence for regional scale changes in lacustrine sedimentation of eocene lake gosiute in response to syndepositional tectonic activity analysis of synsedimentary deformation features is therefore a promising yet under utilized tool to trace the tectonic evolution of lacustrine deposits of the green river formation and other tectonically active marine and non marine basins

ecosystem and paleohydrological response to quaternary climate change in the bonneville basin utah we report the results of a detailed paleoecological study of the bonneville basin covering the last 280 000 yr our study used fossil ostracodes and a sedimentological record obtained from the august 2000 glad800 drilling operation at great salt lake we analyzed 125 samples taken at 1 m intervals from site 4 gsl00 4 for ostracodes and other paleoecologic and sedimentologic indicators of environmental change multivariate analyses applied to the ostracode data and qualitative analyses of fossil and sedimentological data indicate an alternation between three major environments at the core site over the cored interval 1 shallow saline or hypersaline lakes 2 salt or freshwater marshes and 3 occasional deep freshwater lakes these environmental changes are consistent with shoreline studies of regional lake level fluctuations but provide considerable new detail on both the timing and environmental conditions associated with the various lake phases our age model using 14 c useries tephra and biostratigraphic chronologies allowed us to associate the core s record of regional paleohydrology with the marine oxygen isotope stages of global climate change the core contains continuous records for the last four glacial interglacial sequences salt freshwater marshes were common during the interglacials and deep freshwater conditions correspond with maximum global ice volume in ois 2 and before a maximum in global ice during ois 6 immediately following deep lake phases crashes in lake level from rapid desiccation resulted in the deposition of thick evaporite units our study suggests that the climate of the great salt lake catchment appears to have been drier during ois 6 than during ois 2 we compare our record of environmental change during ois 6 glaciation with other records from the western united states and find that the overall

seismically triggered soft sediment deformation structures close to a major strike slip fault system in the eastern alps hirlatz cave austria abstract we investigate episodic soft sediment deformation structures cross cut by normal faults preserved in unlithified finely laminated calcite rich sediments in the hirlatz cave in the northern calcareous alps austria these sediments comprise varve like alternations of brighter carbonate quartz rich layers and darker clay mineral rich layers the deformed sediments contain abundant millimeter to centimeter scale soft sediment structures load casts ball and pillow structures sheet slumps thrust faults and folds erosive channels filled with slides and chaotic slumps after deposition and soft sediment deformation normal faults developed within the entire sedimentary succession an event that probably correlates with an offset of c 10 cm of the passage wall above the outcrop our major conclusions are i the sediments have a glacial origin and were deposited in the hirlatz cave under phreatic fluvio lacustrine conditions the deposition and the soft sediment deformation occurred most likely during the last glaciation i e around 25 ka ago ii the liquefaction and formation of the soft sediment structures in water saturated stratified layers was triggered by episodic seismic events iii the internally deformed sediments were later displaced by normal faults iv a possible source for the seismic events is the active sinistral salzach ennstal mariazeller puchberger semp strike slip fault which is located about 10 km south of the outcrop and plays a major role in accommodating the extrusion of the eastern alps towards the pannonian basin to our knowledge the described structures are the first report of liquefaction and seismically induced soft sediment deformations in quaternary sediments in the eastern alps

features and sealing mechanism of shallow biogenic gas in incised valley fills the qiantang river eastern china a case study abstract late quaternary shallow biogenic gas reservoirs have been discovered and exploited in the qiantang river qr estuary area eastern china the fall of global sea level during the last glacial maximum resulted in the formation of the qr incised valley from bottom to top the incised valley successions can be grouped into four sedimentary facies river channel facies floodplain estuarine facies estuarine shallow marine facies and estuarine sand bar facies all commercial biogenic gas pools occur in floodplain estuarine sand bodies of the qr incised valley and its branches the deeply incised valleys provided favorable conditions for the generation and accumulation of shallow biogenic gas the clay beds that serve as the direct cap beds of the gas pools are mostly restricted within the qr incised valley with burial depths ranging from 30 to 80 m remnant thicknesses of 10 30 m and porosities of 42 2 62 6 in contrast the mud beds cover the whole incised valley and occur as indirect cap beds with burial depths varying from 5 to 35 m thicknesses of 10 20 m and porosities of 50 6 53 9 the pore water pressures of clay and mud beds are higher than that of sand bodies and the difference can be as much as 0 48 mpa the pore water pressures of clay or mud beds can exceed the total pore water pressure and gas pressure of underlying sand reservoirs shallow biogenic gas can be completely sealed by the clay and mud beds which have higher pore water pressure the direct cap beds have better sealing ability than the indirect cap beds generally the pore water pressure dissipation time of clay and mud beds is conspicuously longer than that of sand beds this indicates that the clay and mud beds have worse permeability and better sealing ability than the sand beds however once the gas enters the sand lenses the pore water pressure cannot release efficiently

seismic influence on the last 1500 year infill history of lake sapanca north anatolian fault nw turkey article i nfo lake sapanca is located on the north anatolian fault zone in nw turkey it occupies a pull apart basin at the junction between the izmit sapanca fault segment the sakarya segment and the westernmost end of the mudurnu valley fault multiproxy analyses lithology loss on ignition geochemistry magnetic susceptibility and palynology of a 586 cm long sediment core taken in the centre of the lake revealed a complex history of at least five mass movement events the radiocarbon chronology suggests that the sediment sequence spans approximately the last 1500 years the bottom metre of the sequence before c ad 580 is a gley soil resulting from a large sublacustrine landslide whose origin is a collapse of the floodplain between the lake and river sakarya sedimentation related to this eastern floodplain decreases progressively until c ad 910 sedimentological and palynological indicators from sediments younger than c ad 910 document four major episodes of mass movement originating most likely from the southern slopes of the lake the landslide and the following four mass movement events are suggested to be linked to earthquakes

early mid holocene sea level change and coastal environmental response on the southern yangtze delta plain china implications for the rise of neolithic culture abstract we used a series of holocene sediment cores with ams 14c dated basal saltmarsh peat and supratidal sediment to reconstruct early mid holocene sea level change on the southern yangtze delta plain we also synthesized results for ca 150 late quaternary cores as well as archeological data to reveal the unique interplay between coastal evolution and neolithic cultural response relative sea level was ca 16 5 to 14 5 m from 8600 to 8500 cal bp and ca 6 to 4 m from 7400 to 7200 cal bp reflecting the rate of eustatic sea level rise but being ca 10 m higher possibly because of the effect of hydro istostasy three late pleistocene interfluve terraces t3 to t1 were revealed at burial depths of

geochemical characteristics of granulite facies rocks in the archean varpaisjarvi area central fennoscandian shield abstract archean lower crustal granulites are exposed as fault bounded blocks in the varpaisjarvi area central finland the prevailing rock types in these blocks are igneous enderbites tonalitic trondhjemitic granodioritic migmatites and mafic granulites although metamorphosed at moderate pressures 8 10 kbar the varpaisjarvi granulites are not in a geochemical sense good representatives of depleted restitic lower crust having invariably negative or negligible eu anomalies only the enderbites have k rb ratios showing depleted granulite trends the enderbites are orthopyroxene bearing igneous rocks ranging in composition from diorite to tonalite they have distinctive flat lree patterns with la sm from 2 03 2 86 which may be due to the removal of a lree rich phase during fractionation if not the result of infiltration by a co 2 rich fluid mafic granulites occur as intercalations within the tonalitic trondhjemitic granodioritic gneisses and while all are tholeiitic in composition they fall into two groups on the basis of major and trace element abundances the group 1 tholeiites are mostly basaltic with steeply increasing alkali contents over a short range in sio 2 ti zr ratios are close to the chondritic value of 110 the group 2 tholeiites vary from picrobasaltic to andesitic in composition with the latter being dominant ti zr ratios lie below the chondritic value the group 1 rocks have higher ni and cr and lower zr y ratios than their group 2 counterparts the varpaisjarvi area represents at least two accreted blocks or terranes that exhibit marked lithological and geochemical differences with the jonsa block being the most distinctive the main differences are the two contrasting groups of tholeiitic mafic granulites the jonsa block having only the group 2 metatholeiites and the presence of quartz cordierite and cordierite orthoamphibole orthopyroxene rocks only in the jonsa block where they are found as interlayers amongst the group 2 tholeiites the ti zr and zr y ratios of these latter lithologies are closely comparable with those of the group 2 tholeiites the jonsa block cordierite orthoamphibole orthopyroxene rocks have high mgo mgo feo tot ratios compared to most cordierite orthoamphibole rocks produced by seawater basalt interaction their major and trace element geochemistry nevertheless indicates that they were derived from a mafic igneous precursor

clastic dykes of the devono carboniferous horton bluff formation nova scotia storm related structures in shallow lakes abstract clastic dykes are common in the late devonian to early carboniferous horton bluff formation of nova scotia where they occur in wave dominated shoreline deposits of lacustrine shoaling upward cycles the dykes typically less than 25 cm wide and 40 cm in vertical extent project downward into clayshale from broad loads at the base of elongate isolated lenses of hummocky cross stratified siltstone ptygmatic folding of the dykes reflects a shale siltstone compaction ratio of 2 3 times and maximum depth of dyke penetration prior to compaction was 1 m dyke orientation parallels the orientation of wave ripple crests and the elongation direction of the siltstone lenses dyke formation was penecontemporaneous with sedimentation dyke and load formation was probably initiated in shallow water during storms which promoted sediment failure through cyclic wave loading microseisms and rapid deposition of hcs bearing siltstone lenses reversed density gradient and uneven sediment loading from silt lenses probably promoted downward emplacement loads reflect ductile failure of surficial water rich mud whereas dykes reflect downward injection of silt following brittle failure of underlying more compacted mud the depositional slope provided a tensional stress that controlled the fracture direction orthogonal to the slope of the failed sediment

seismites as a tool in the palaeoenvironmental reconstruction of fluvial deposits the cambrian guarda velha formation southern brazil abstract soft sediment deformation ssd is widely described in the literature but there is no clear consensus regarding its origin and significance existing models for ssd in fluvial sediments do not clearly demonstrate a relationship between the structures preserved facies expression and larger scale depositional architecture in this study several types of ssd structures are recorded in cambrian fluvial deposits and these occur interbedded with undeformed strata throughout the entire stratigraphic interval the random distribution of these features in relation to primary facies types and fluvial forms indicates that they have neither a direct nor indirect relationship with any depositional processes or bedform type we propose that the relationship of ssd at the bed set scale to larger scale depositional architecture combined with tectono stratigraphic analysis allows the determination of both short term fluvial hydraulic conditions in ancient stream systems such as the nature of the flow regime responsible for depositing ancient fluvial stream successions and the long term subsidence rates in the form of mean recurrence interval of the seismic events responsible for triggering the generation of ssd in tectonically active basins

marine sediment records and relative sea level change during late pleistocene in the changjiang delta area and adjacent continental shelf abstract optically stimulated luminescence osl dating and microfossil analysis were conducted on late quaternary samples from two boreholes in the changjiang delta area successions from 12 collected boreholes revealed lithology stratigraphy and sedimentary facies of the changjiang delta area and continental shelf of the east china sea ecs these data were used to determine the chronology of two transgressions during marine isotope stage mis 5 and mis3 interpret the sedimentary facies and mechanisms of the distinctive transgression pattern and reconstruct relative sea level of the study area during late mis3 fluvial gravelly sediment deposition prevailed with limited marine influence during mis5 while muddy and sandy deposition occurs along with widespread coastal facies during mid and late mis3 in the changjiang delta area this suggests that the study area was dominated by high relief and local rivers developed with large freshwater and sediment discharge during mis5 therefore marine micro faunas may not have survived due to dominant freshwater process or strong erosion has scoured away the marine records of mis5 tectonic subsidence is indicated to occur at a rate of 1 m ka since mis5 and lower the changjiang coastal area to be invaded by seawater during mis3 the altitude of late mis3 transgressive sediments decreases from the inner delta plain seaward gradually reflecting differential tectonic subsidence of the study area abrupt sea level rise occurred and relative sea level is proposed as 5 m during late mis3

earthquake induced soft sediment deformation structures in upper jurassic open marine microbialites neuquen basin argentina penecontemporaneous decimetre scale soft sediment deformation structures are reported from the basal part of the upper jurassic lower cretaceous vaca muerta formation in the malargue las lenas area of the back arc neuquen basin mendoza province central andes the deformed interval amarillas bed is only 0 3 to 0 9 m thick but occurs in a wide area larger than 1500 km2 its age determined by ammonite biostratigraphy is early tithonian the soft sediment deformation structures were generated in finely laminated partially consolidated organicrich carbonate microbialites that were deposited in open marine poorly oxygenated settings apparently devoid of any significant slope those structures include boudins of different sizes and complexity a variety of folds normal listric dm scale faults sub horizontal detachment surfaces and other features which are part of several larger scale complex slump structures deformation was dominantly plastic but near to the ductile brittle field transition on the basis of the observed soft deformation structures their geographic distribution their lateral homogeneity and the geodynamic framework of the basin in which it was generated the amarillas bed can be tentatively attributed to a large intermediate depth earthquake that occurred within the plate that subducted beneath the andean continental margin and the neuquen back arc basin

the effects of solar irradiation changes on the migration of the congo air boundary and water levels of paleo lake suguta northern kenya rift during the african humid period 15 5 ka bp abstract the water level record from the 300 m deep paleo lake suguta northern kenya rift during the african humid period ahp 15 5 ka bp helps to explain decadal to centennial intensity variations in the west african monsoon wam and the indian summer monsoon ism this water level record was derived from three different sources 1 grain size variations in radiocarbon dated and reservoir corrected lacustrine sediments 2 the altitudes and ages of paleo shorelines within the basin and 3 the results of hydro balance modeling providing important insights into the character of water level variations abrupt or gradual in the amplifier paleo lake suguta the results of these comprehensive analyses suggest that the ahp highstand in the suguta valley was the direct consequence of a northeastwards shift in the congo air boundary cab which was in turn caused by an enhanced atmospheric pressure gradient between east africa and india during a northern hemisphere insolation maximum rapidly decreasing water levels of up to 90 m over less than a hundred years are best explained by changes in solar irradiation either reducing the east african indian atmospheric pressure gradient and preventing the cab from reaching the study area or reducing the overall humidity in the atmosphere or a combination of both these effects in contrast although not well documented in our record we hypothesize a gradual end of the ahp despite an abrupt change in the source of precipitation when a decreasing pressure gradient between asia and africa prevented the cab from reaching the suguta valley the abruptness was probably buffered by a contemporaneous change in precession producing an insolation maximum at the equator during october whether or not this is the case the water level record from the suguta valley demonstrates the importance of both orbitally controlled insolation variations and short term changes in solar irradiation as factors affecting the significant water level variations in east african rift lakes

seismically induced soft sediment deformation structures in the palaeogene deposits of the liaodong bay depression in the bohai bay basin and their spatial stratigraphic distribution abstract soft sediment deformation structures ssds have been identified from well cores in the palaeogene deposits of the liaodong bay depression in the bohai bay basin china these deposits formed as interbedded sand and mud at a delta front or on the slope toe of the prodelta according to criteria proposed by previous research we established that these ssds were induced by earthquakes and that they can be divided into two groups ductile deformation structures plastic intrusions ball and pillow structures flame structures boudinage structures irregular convolute stratifications and synsedimentary faults and folds and brittle deformation structures sand dykes and autoclastic breccias based on their level of deformation size and complexity the ssds were divided into three groups from weak to strong to reflect the intensity of palaeo earthquakes with consideration of the palaeo sedimentary environment we proposed a model to account for the production and preservation of these ssds according to the classification adopted in this study and the spatial stratigraphic distribution of the ssds the tectonic activities of the tan lu faults in the bohai bay basin were investigated the a and b oilfields assumed names are located in the tectonically active zones of the west and east branches of these faults respectively the extension tectonic activities in the a oilfield region exhibit a sharply decreasing trend from e2s3 to e2s1 and increase again in e3d2 whereas the strike slip tectonic activities in the b oilfield region exhibit an increasing trend from e2s3 to e2s1 and finally reach a maximum to e3d3 the results of this study show that the method of analysis of the spatial stratigraphic distribution of ssds is suitable for determining the evolution of tectonic activity and thus it can provide a new perspective for basin analysis

early diagenesis of biogenic silica in the amazon delta alteration authigenic clay formation and storage deltaic environments are commonly assumed to be relatively minor sites of biogenic silica burial because of the small quantities of opaline silica detected by most operational analytical techniques rapid conversion of biogenic silica into authigenic silicates is also often discounted as a significant control on oceanic silica budgets a variety of evidence for extensive early diagenetic alteration of biogenic silica in rapidly accumulating amazon delta sediments indicates that both of these general assumptions are unjustified apparent lack of significant biogenic silica storage in deltaic environments particularly in the tropics may be largely an artifact of operational definitions that do not include early diagenetic products of biogenic silica biogenic silica particles buried in suboxic amazon delta deposits can be unaltered partially dissolved covered with aluminosilicate or metal rich coatings or completely reconstituted into authigenic k fe rich aluminosilicate minerals pore water k mg f si and solid phase distributions direct observations of particles laboratory experiments and depositional context indicate that authigenic clays form rapidly 1 yr in the seasonally reworked surface layer 0 5 2 m of the delta topset and are disseminated during sediment remobilization fe al oxide rich debris derived from the tropical drainage basin is an abundant reactant and thus the supply of biogenic silica is a major control on the amount of clay formed the mild 1 na2co3 alkaline leach procedure commonly used to estimate biogenic silica was modified to include an initial mild leach step with 0 1n hcl to remove metal oxide coatings and to activate poorly crystalline authigenic phases for alkaline dissolution well crystallized clays are not significantly affected by this modification nor is bulk amazon river bed sediment the two step procedure indicates that 90 of the biogenic silica originally present in deposits is converted to clay or otherwise altered raising the effective quantity of biogenic silica stored from 33 to 296 mol si g 1 1 8 sio2 biogenic si stored in the delta increases away from the river mouth across shelf and along the dispersal system where primary production is highest the k si ratio of labile authigenic material is 0 19 mol mol 1 far higher than amazon river suspended matter 0 07 mol mol 1 diagenetic models indicate formation rates in the mobile sediment layer of 2 8 mol k g 1 yr 1 16 mol si g 1 yr 1 inclusion of authigenic alteration products of biogenic silica in estimates of reactive si burial increases the deltaic storage of riverine si to 22 of the amazon river input the rapid formation of aluminosilicates from biogenic sio2 seawater solutes and remobilized fe al oxides represents a form of reverse weathering rapid reverse weathering reactions in tropical muds and deltaic deposits the largest sediment depocenters on earth confirms the general importance of these processes in oceanic elemental cycles

early cretaceous slumps and turbidites with peculiar soft sediment deformation structures on lingshan island qingdao china indicating a tensional tectonic regime abstract some sections on lingshan island in the yellow sea close to the city of qingdao show the early cretaceous lingshandao formation the exposed succession consists mainly of turbidites some of which show uncommon soft sediment deformation structures and contains well developed large scale slumps that consist of sets of turbidites the sediments were deposited as part of lobes of turbidites and hyperpycnites deposits of flood generated sediment laden bottom currents derived from an estuary in a deep sea environment that formed part of an inter arc basin with a tensional tectonic regime some of the slumps have dimensions of the order of metres to tens of metres they consist of the turbidites that build most of the succession the soft sediment deformation structures in the turbidites represent a wide variety of types most of which are common in subaqueous environments with a high accumulation rate the most interesting are however structures that indicate active tectonic tension these structures are boudins which are present with two subtypes the most common are pinch and swell structures sometimes leading to isolated parts of the affected sandy layer enveloped by shales of the under and overlying shale layers the second type consists of domino boudins which have as far as we are aware of not earlier been described from sediments that were still unlithified during their formation the presence of the boudins and associated structures which indicate synsedimentary stretching related to an extensional tectonic setting form an additional argument in the long lasting debate about the question of whether a compressional or an extensional tectonic regime dominated in the area during the early cretaceous

experimental soft sediment deformation structures formed by the liquefaction of unconsolidated sands and some ancient examples the effects of liquefaction in saturated sand bodies under a variety of driving forces are described from shaking table experiments and structures from the geological record are presented which are analogous to the experimental structures the collapse of sloping heaps of cross bedded sand under a gravitational body force generates low angle essentially uncontorted stratification a basal zone of shearing may be present with steepened and folded foresets stretching of foresets may be accommodated on normal faults and bottomsets may be contorted into inclined folds in natural systems the substrate may also liquefy causing deformation driven by an unevenly distributed confining load stratification in the surface bedform is flattened and stratification in the substratum contorted experiments failed to produce relative displacement at the interface between stacked sand bodies liquefaction of gravitationally unstable systems in sands generates load structures comparable to those from sand mud systems recumbent folded deformed cross bedding is formed by current shear over a liquefied bed as has been inferred from field and theoretical analyses shear of nonliquefied sand forms angular folds other deformation mechanisms such as fluidization or seepage may generate structures similar to all of these local water escape structures driven by fluidization occur in the upper parts of some liquefied sand bodies they include cusps sand volcanoes and clastic dykes transient cavities formed in some experiments and seemed to be preserved as breached cusps although the experiments tried to isolate individual driving forces driving forces may operate together and there may be a continuum between deformation driven by water escape and deformation driven by loading different structures from those described here may form where liquefaction develops in a buried layer as opposed to at the sediment surface

documentation of earthquake induced disturbance of lake sediments using subbottom acoustic profiling subbottom acoustic profiling in lakes on the canadian shield and in the canadian cordillera has revealed disruptions in deltaic and lacustrine sediments that can be attributed to large historical earthquakes the timiskaming earthquake of 1935 magnitude 6 25 and the vancouver island earthquake of 1946 magnitude 7 2 triggered extensive slumping and flow of postglacial sediments in lakes located within a few tens of kilometres of the epicentres of these events there is some evidence in one of the surveyed lakes for in situ mobilization of sediment on relatively gentle slopes with minimal horizontal displacement this may be a product of liquefaction induced by coseismic shaking or displacements along faults beneath the basin in another lake widespread coseismic slumping resuspended large amounts of fine sediment which then settled out onto the lake floor to produce a texturally anomalous layer features similar to those produced by the 1935 and 1946 earthquakes can also result from a variety of non

sedimentary records of paleoseismic events in the late pleistocene sediments of the southern yangtze river deltaic plain east china and their implications for differential subsidence of the taihu block abstract drilling cores from the hangjiahu coastal plain in the southwestern corner of the southern yangtze river deltaic plain east china contain a variety of soft sediment deformation structures in the late pleistocene lacustrine and tidal sediments they include load flame structures ball and pillow structures diapir structures liquefied sand veins liquefied breccias syn sedimentary fault seismo cracks and brittle breccias sedimentary facies assessment of host deposits and development features rule out an exogenic origin of the soft sediment deformation structures such as gravity flow storm activity wave action or flood these soft sediment deformation structures in the study area are interpreted as seismites their spatial distribution suggest that the earthquakes were sourced from the intersection of the majin wuzhen fault and the huzhou jiashan fault seismites recognized in cores indicate three episodes of short and sudden seismicity magnitude 5 which are interpreted as a response to syn depositional tectonic activity and differential subsidence of the taihu block during the late pleistocene period systematic study of spatial and temporal distribution of these seismites improves the understanding of the tectonic context and evolutionary history of sedimentary basement

the potential of lake ohrid for long term palaeoenvironmental reconstructions abstract lake ohrid at the macedonian albanian border was likely tectonically formed during the tertiary and therefore is one of the oldest lakes in europe however only a few studies exist concerning the potential of lake ohrid sediments for long term palaeoenvironmental reconstructions within the scope of future potential deep drilling campaigns therefore as a first step a transect of short surface sediment cores was investigated for chronology physical properties grain size and biogeochemistry the results were compared with information derived from a shallow hydro acoustic seismic survey the investigations indicate a rather uniform and bioturbated sedimentation in the central part of the lake basin with mean sedimentation rates of ca 0 5 1 mm year the sediment composition is dominated by authigenetic carbonates diatom frustules or fragments form the major part of biogenic matter deposits as indicated by the relatively high contents of biogenic opal and low contents of total organic carbon and total nitrogen the shallow hydro acoustic seismic survey indicates that horizons of sediment redeposition occur sporadically towards the shore of the lake the sedimentation rate increases and sedimentation is increasingly influenced by local inflows or mass movement processes triggered by tectonic activities thus lake ohrid has a high potential for palaeoenvironmental reconstructions on a multi decadal scale and provides additional information concerning tectonic activity in the region

seismites an attempt at critical analysis and classification abstract the main types of seismites are reviewed following the proposed classification and are illustrated by our own case studies the large variety of seismites depends on the sedimentologic hydrodynamic and diagenetic characters of the deposits subject to seismic shocks on a given site generally different types of seismites cane be related to the same seismic event these peculiar but widespread sedimentary structures are not always univocal and may often be related to different causes therefore the structures discussed must necessarily be placed in a detailed geological context

recognition of trigger mechanisms for soft sediment deformation in the pleistocene lacustrine deposits of the santʻarcangelo basin southern italy seismic shock vs overloading abstract the lacustrine deposits of the san lorenzo cycle belong to the infill succession of the sant arcangelo basin a pliocene to pleistocene satellite basin developed close to the front of the south apennines thrust belt the lower to middle pleistocene lacustrine succession is made up of siltstone and claystone interbedded with sandstone carbonate and volcaniclastic beds arranged in fining upward sequences the upper to middle part about 50 m thick of the succession about 200 m thick has been investigated in detail in the depocentral sector of the lacustrine basin here soft sediment deformation structures occur in fine grained sandstone and claystone alternations and show a wide morphological variability deformed laminations slumps load structures large vertical water escape structures and neptunian dykes their formation occurred during and after sedimentation with different mechanisms of deformation some structures are related to liquefaction and fluidization processes viscous fluid behaviour while others occurred when sediment had already undergone lithification and its behaviour was plastic and or brittle facies analysis and detailed morphologic study of the soft sediment deformation structures indicate that the main trigger agents for deformation were seismic shocks and overloading induced by sudden deposition of coarser sediments on clays due to the arrival of density currents thus the soft sediment deformation structures provide a continuous record of the tectonic and sedimentary processes that acted in the lacustrine basin from sedimentation until diagenesis

authigenic smectite on diatom frustules in bolivian saline lakes abstract observation under the electron microscope of diatom frustules from bolivian altiplano saline lakes shows that many of these are coated with particles occurring as tiny sheets the frustules can be found to be almost completely replaced by these sheets isolated sheet aggregates seem to have resulted from completely transformed frustules section observations of altered frustules bear out that the sheets have grown from biogenic silica through replacement selected area diffraction dark field observation microdiffraction and elemental microanalysis show that the particles on the diatom frustules consist of a poorly crystallized mg smectite the unambiguous localisation of this authigenesis allows us to reconstruct its hydrochemical and sedimentological environment observation of the most recent lake sediments has pointed out that at least two main conditions are required for this authigenesis at 5 c saturation with respect to amorphous silica and a ph above 8 2 variations in the mg concentration have no significant effect

recurrence pattern of holocene earthquakes along the dead sea transform revealed by varve counting and radiocarbon dating of lacustrine sediments abstract a high resolution holocene seismic history of the dead sea transform dst is established from laminated sedimentary cores recovered at the shores of the dead sea radiocarbon dating and annual laminae counting yield excellent agreement between disturbed sedimentary structures identified as seismites and the historical earthquake record all recent and historical strong events of the area were identified including the major earthquakes of a d 1927 1837 1212 1033 749 and 31 b c the total of 53 seismites recognized along the entire holocene profile indicate varying recurrence intervals of seismic activity between a few and 1000 years with a conspicuous minimum rate at 2100 31 b c and a noticeable maximum during the past six to eight centuries most of the epicenters of the correlated earthquakes are situated very close to the dead sea within 150 km or up to 400 km north of it along the dst between 1000 b c and a d 1063 and from a d 1600 to recent time the epicenters are all located on the northern segment of the dst whereas prior to 1000 b c and between a d 1000 and 1600 they appear to scatter along several segments of the dst we establish how the local intensity exerts a control on the formation of seismites at historically estimated intensities greater than vii all well documented earthquakes are correlated whereas at intensities smaller than vi none are matching the periods with enhanced earthquake rate along the dst correlate with those along the north anatolian fault as opposed to the intervening east anatolian fault this may indicate some elastic coupling on plate boundary scale that may also underlie escape and extrusion tectonics typical of continental collision

influence of the local environment on lacustrine sedimentary phytolith records abstract fossil phytolith assemblages from soils and lake sediments are widely used to reconstruct past vegetation patterns and dynamics especially in tropical environments where a phytolith index has been quantitatively calibrated to estimate tree cover most calibration studies have focused on comparing phytolith assemblages in modern soil with the present aboveground vegetation however little is known about phytolith taphonomy and the representativeness of phytolith assemblages and indices in lake sediments the aim of this study is to improve the understanding of the composition of phytolith assemblages and their influx into recent lake sediments by comparing them with local land cover assessments this study focused on three lakes in the central african republic located in savanna forest savanna mosaic and forest it appears that the local environment surrounding the lake was critical for interpreting current and past assemblages and the ratio of dicotyledon to poaceae diagnostic phytoliths the d p index the presence of a riparian forest in an open environment had no impact on phytolith assemblages or the d p index which instead reflected both the local and regional landscapes conversely contributions from a marsh if present in a forested environment completely dominated the phytolith records which consequently reflected only the local environment of the lake a high correlation between the poaceae phytoliths influxes and the charcoal accumulation rates for the two lakes surrounded by a riparian forest has also been found this finding which was associated with a high proportion of burned poaceae phytoliths provides evidence that poaceae phytoliths are mainly transported by wind in ash clouds produced by fires

soft sediment deformation structures interpreted as seismites in lacustrine sediments of the prebetic zone se spain and their potential use as indicators of earthquake magnitudes during the late miocene lacustrine formations of late miocene age in the prebetic area se spain show several types of deformational structures that are interpreted as seismites they are present in both marginal and deep lacustrine facies seismites formed in marginal lake environments comprise sand dikes pillows and intruded and fractured gravels in deep lacustrine facies the seismites are represented by pseudonodules mushroom like silts protruding into laminites mixed layers disturbed varved lamination and loop bedding the measured orientations of these structures are consistent with the orientations of the main faults limiting the basins showing that their origin is clearly related to the tectonic stress field that prevailed in the region during the late miocene the magnitudes of the earthquakes that deformed the sediments have been estimated after published data from both ancient and recent lake deposits accumulated in tectonic active regions elsewhere a rank of earthquake magnitudes with two end members i e the lowest magnitudes recorded by loop bedding in laminites and the highest magnitudes represented by intruded and fractured gravels is proposed

interstratal dewatering origin for polygonal patterns of sand filled cracks a case study from late proterozoic metasediments of islay scotland sand filled cracks from the lower fine grained quartzite of dalradian late proterozoic age on the island of islay western scotland may be divided into two main types both of which form orthogonal and non orthogonal closed patterns on bedding surfaces type 1 cracks are short and lenticular in cross section contain sand which had been injected downwards and are found on the bottoms of cross laminated sandstone beds type 2 cracks cut several beds and preserve evidence of upward flow of water saturated sand both types of crack developed through the interstratal intrusion of water saturated sand into shrinkage cracks in mud or muddy sand not as previously thought as a result of sub aerial desiccation or sub aqueous cracking of the sediment surface synaeresis these cracks likely resulted from layer parallel contraction caused by compaction of mudstone layers during burial seismic shock may have provided the trigger for the preferential development of polygonal crack patterns in these layers instead of the more usual small scale dewatering structures from a detailed comparison with published descriptions of filled cracks from a number of different geological environments it is concluded that interstratal cracking is a mechanism which rivals sub aerial desiccation in importance and is more common in the geological record than is currently realized

biogenic silica dissolution in the oceans reconciling experimental and field based dissolution rates 1 on average 50 60 of diatomaceous opal produced in the euphotic zone redissolves within the upper 100 m of the water column high specific silica dissolution rates in the surface ocean contrast with order of magnitude lower values in deep sea sediments the lack of a mechanistic understanding of these large variations in dissolution kinetics is a major source of uncertainty in models of nutrient silicon cycling in the oceans here we show that the observed variability in biogenic silica reactivity is consistent with results of experimental dissolution studies differences in aluminum content and specific surface area of the diatom skeletons plus differences in temperature and degree of undersaturation all contribute to lowering silica dissolution rates in deep sea sediments relative to the euphotic zone when variations in these material and environmental properties are accounted for the predicted specific opal dissolution rate in average surface ocean water is over 2 orders of magnitude faster than the rate measured in recently deposited biosiliceous oozes of the southern ocean the predicted specific dissolution rate however is approximately 5 times higher than the value obtained from global estimates of the depth integrated dissolution rate and biogenic silica concentration in the upper water column this discrepancy likely reflects the inhibitory effect of protective organic coatings on fresh diatom shells in surface waters the experimental data further imply that aluminum incorporation in the silica matrix during biomineralization or after death of the organisms enhances the preservation efficiency of biogenic opal in marine sediments