diagenesis of the hild brent sandstones northern north sea isotopic evidence for the prevailing influence of deep basinal water abstract the deeply buried 3 8 4 3 km brent reservoir sandstones of the hild field northern north sea have undergone intense diagenetic alteration fluid inclusion o c h sr isotope and k ar age data combined with petrography and burial history constrain the conditions and timing of the main diagenetic transformations as well as the nature and origin of diagenetic fluids non ferroan calcite cement formed at shallow depth the reconstructed diagenesis of the hild brent reservoirs displays notable differences with diagenetic models developed in many fields of the northern north sea in particular diagenesis in hild is characterized by the prevailing influence of deep basinal water a feature related to the immediate proximity of the viking graben this study further illustrates that diagenetic processes related to compaction derived fluids commonly reported in sediments located within rift basins should also be expected to occur in neighboring sub basins along rift margins

holocene rainfall variability in southern chile a marine record of latitudinal shifts of the southern westerlies geochemical and clay mineral parameters of a high accumulation marine sediment core from the chilean continental slope 41 s provide a 7700 yr record of rainfall variability in southern chile related to the position of the southern westerlies we especially use the iron content measured with a time resolution of ca 10 yr on average of 14 caccelerator mass spectrometry dated marine sediments as a proxy for the relative input of iron poor coastal range and iron rich andean source rocks variations in this input are most likely induced by rainfall changes in the continental hinterland of the core position based on these interpretations we find a pronounced rainfall variability on multicentennial to millennial time scales superimposed on generally more arid conditions during the middle holocene 7700 to 4000 cal yr b p compared to the late holocene 4000 to present this variability and thus changes in the position of the southern westerlies are first compared to regional terrestrial paleoclimate data sets from central and southern chile in order to derive possible wider implications and forcing mechanisms of the holocene latitudinal shifts of the southern westerlies we then compare our data to ice core records from both tropical south america and coastal antarctica these records show similar bands of variability centered at ca 900 and 1500 yr comparisons of band pass filters suggest a close connection of shifts of the southern westerlies to changes within the tropical climate system the correlation to climate conditions in coastal antarctica shows a more complicated picture with a phase shift at the beginning of the late holocene coinciding with the onset of the modern state of el nin o southern oscillation system the presented data provide further evidence that the well known millennial scale climate variability during the last glacial continued throughout the holocene fl 2001 elsevier science b v all rights reserved

kaolinitic meniscus bridges as an indicator of early diagenesis in nubian sandstones sinai egypt discussion j marcelo ketzer l fernando de ros and norberto daniuniversidade federal do rio grande do sul instituto de geocie ncias avenue bento gonc alves 9500 91501 970 porto alegre brazil e mail jm ketzer com br lfderos inf ufrgs br norberto dani ufrgs br keywords clay in ltration diagenesis kaolinite microtexture sandstone introductionthe recently published paper by du bernard c moraes de ros 1990 weibel 1998 salem et al 2000 fig 1a this is becausemechanical in ltration is most effective andextensive in semi arid climatic conditions kess ler 1978 walker et al 1978 moraes de ros 1990 under which smectitic clays are the mostcommon weathering products conversely kaoli nite is characteristically formed in humidclimatic conditions under which in ltration isuncommon or volumetrically insigni cant ketzer et al 2003a despite nding the occurrence described by dubernard carrio schaffhauser 2003 interesting we identi ed problems in their methodology anddiscussion the present discussion aims to com ment on these points and to suggest an alter native interpretation of the origin timing andeffects on compaction and reservoir quality of thedescribed clays in the nubian sandstones origin of kaolinitedu bernard carrio schaffhauser 2003 de scribed two types of kaolinite occurrence in thenubian sandstones i nely crystalline 1 5lm and ii coarsely crystalline aggregates 50lm the nely crystalline kaolinite consists of brown under uncrossed polarizers colour pore llingaggregates with meniscus shape a close inspec tion of the backscattered bse scanning elec tronic microscope sem images provided by dubernard and carrio schaffhauser their g 5cand d suggests that the meniscus aggregates arecomposed of several kaolinite booklets g 1b this morphology is typical of diagenetic authi genic kaolinite such evidence indicates an au thigenic origin for the nely crystalline kaolinite as opposed to the in ltrated origin proposed bydu bernard and carrio schaffhauser hence thiskaolinite most probably resulted from the in situreplacement of mechanically in ltrated possiblysmectitic clay minerals owing to active circula tion of meteoric water through the sandstones the origin of the uids responsible for thekaolinitization of the precursor in ltrated claysshould be constrained by o and h isotopicanalyses of the kaolinite morad et al 2003 the preservation of the meniscus morphology ofthe in ltrated clay aggregates after kaolinitizationresulted from the inheritance of the texture of theprecursor clay mineral by the kaolinite it is nosurprise that such preservation occurs as pseudo morphic replacement is rather common amongclay minerals e g in the chloritization or illiti zation of kaolinite morad et al 1998 de ros 1998 the variable in places random orientationof some kaolinite booklets is typical of authigenicaggregates and thus has no direct relationshipwith differences in water volume within themeniscus as suggested by du bernard andcarrio schaffhauser p 1227 additionally therelevance of the theoretical discussion on theaspects of the menisci geometry pp 1225 1227 to the interpretations of the authors is not clear x ray diffraction analysis from the 2 lmfraction revealed that kaolinite is the single claymineral present in the samples as shown in theprovided x ray diffractogram their g 4 thissedimentology 2005 52 213 217

accelerating shrinkage of patagonian glaciers from the little ice age ad 1870 to 2011 davies b j glasser n f 2012 accelerating shrinkage of patagonian glaciers from the little ice age similar to ad 1870 to 2011 journal of glaciology 58 212 1063 1084

the evolution of the patagonian ice sheet from 35 ka to the present day patice abstract we present patice a gis database of patagonian glacial geomorphology and recalibrated chronological data patice includes 58 823 landforms and 1 669 geochronological ages and extends from 38 s to 55 s in southern south america we use these data to generate new empirical reconstructions of the patagonian ice sheet pis and subsequent ice masses and ice dammed palaeolakes at 35 ka 30 ka 25 ka 20 ka 15 ka 13 ka synchronous with the antarctic cold reversal 10 ka 5 ka 0 2 ka and 2011 ad at 35 ka the pis covered of 492 6 x103 km2 had a sea level equivalent of 1 496 mm was 350 km wide and 2090 km long and was grounded on the pacific continental shelf edge outlet glacier lobes remained topographically confined and the largest generated the suites of subglacial streamlined bedforms characteristic of ice streams the pis reached its maximum extent by 33 28 ka from 38 s to 48 s and earlier around 47 ka from 48 s southwards net retreat from maximum positions began by 25 ka with ice marginal stabilisation then at 21 18 ka which was then followed by rapid irreversible deglaciation by 15 ka the pis had separated into disparate ice masses draining into large ice dammed lakes along the eastern margin which strongly influenced rates of recession glacial readvances or stabilisations occurred at least at 14 13 ka 11 ka 6 5 ka 2 1 ka and 0 5 0 2 ka we suggest that 20th century glacial recession a 1 is occurring faster than at any time documented during the holocene

the geomorphology and sedimentology of the tempanos moraine at laguna san rafael chile the geomorphology and sedimentology of the tempanos moraine at laguna san rafael chile journal of quaternary science 21 0 pp 1 15 sponsorship nerc rono ner b s 2002 00282

a record from lake cardiel of climate change in southern south america southern south america the only continental land mass lying between 38 s and the antarctic circle presents a rare opportunity to reconstruct terrestrial records of palaeoclimate in an area that is subject to shifts of polar and mid latitude wind and pressure belts in the bulk of this region patagonia are many hydrographically closed lakes which despite the palaeoclimatic significance of the region and the proven utility of lake level records in reconstructing past climates1 2 have escaped detailed study using sedimentary and geomorphic evidence together with 14c dating we present here a detailed lake level record for lake cardiel fig 1 the highest level of the past 21 000 years occurred at about 9 780 bp reminiscent of tropical lakes rather than those in northern mid latitudes1 2 the lake cardiel record corroborates and clarifies the timing of the wetness record inferred from pollen studies in patagonia

sandstone diagenesis in the pattani basin gulf of thailand history of water rock interaction and comparison with the gulf of mexico abstract in the pattani basin a failed rift basin extensive water rock interaction has occurred between subquartzose alluvial sandstones of miocene age and their pore fluids diagenetic rates and pathways have been strongly influenced by high geothermal gradients high co 2 fugacities and low pore water salinities depositional pore water was fresh to brackish depending on the depositional environment of the sediments chloride concentrations in modern formation water are believed primarily to reflect the proportions of river and sea water in the depositional environment however the concentration of other important solutes and the isotopic composition of the formation waters can not be explained by roportional mixing of these two end member waters dissolution of detrital plagioclase an 3 and k feldspar are reactions of major significance that are reflected chemically in the na cl and k cl ratios of the formation water despite the high temperature of the sandstones 120 200 c diagenetic albite does not occur geochemical calculations indicate the formation water is undersaturated with respect to both orthoclase and albite this style of feldspar diagenesis differs significantly from that of sandstones of similar composition in other basins and has probably influenced other aspects of silicate diagenesis important authigenic minerals are 1 locally abundant calcite cement 13 c 12 8 18 o 17 3 pdb an early diagenetic phase that formed at about 60 c 2 pore filling kaolinite 18 o 9 9 d 83 5smow that was closely associated with feldspar dissolution and formed over a range of temperatures and 3 fibrous pore lining and pore bridging illite 18 o 9 8 d 86 7 smow the last significant cement formed at temperatures of 120 to 150 c potassium argon dates on illite indicate that sandstone diagenesis took place during a period of rapid sedimentation in the first two thirds of the burial history comparison of pattani basin diagenesis with diagenesis of sandstones of similar age in other sedimentary basins demonstrates that chemical diagenesis relative to mechanical compaction has been especially rapid in the pattani basin this reflects the effect of high temperatures on reaction rates the net effect is a high average rate of porosity loss with burial 11 km

authigenic chlorites in sandstones as indicators of high temperature diagenesis arkoma foreland basin usa abstract abundant authigenic chamosite associated with higher than average porosities is present in a deep gas reservoir spiro sandstone of the arkoma basin east central oklahoma three types of chlorite can be distinguished petrographically all of which appear texturally to have formed early chlorite peloids diffuse matrix and grain coatings x ray diffraction scanning electron microscopy and electron microprobe studies show that most chlorites are composed of two distinct polytypes ib s 90 and iib a third structure ia polytype was identified in only one sample the relative percentage of the high temperature iib structure increases gradually with increasing thermal maturity from 40 at 3 5 r sub o iib chlorite forms rather thick blocky crystals distinct from the thin pseudohexagonal plates typical of low temperature ib chlorite temperature estimates based on data on vitrinite reflectance and fluid inclusions suggest that iib chlorite formed at burial temperatures 150 180 c higher contents of tetrahedral al3 and slightly higher fe fe mg ratios in iib chlorite are consistent with precipitation temperatures higher than those of the ib structure a higher temperature origin for the iib structure is also consistent with oxygen isotope data

evidence of early holocene glacial advances in southern south america from cosmogenic surface exposure dating cosmogenic nuclide surface exposure dating reveals that glaciers in southern south america 46 s advanced at ca 8 5 and 6 2 ka likely as a result of a northward migration of the southern westerlies that caused an increase in precipitation and or a decrease in temperature at this latitude the older advance precedes the currently accepted initiation of holocene glacial activity in southern south america by 3000 yr both of these advances are temporally synchronous with holocene climate oscillations that occurred in greenland and the rest of the world if there are causal links between these events then rapid climate changes appear to be either externally forced e g solar variability or are rapidly propagated around the globe e g atmospheric processes

climate change during the last deglaciation in antarctica greenland ice core records provide clear evidence of rapid changes in climate in a variety of climate indicators in this work rapid climate change events in the northern and southern hemispheres are compared on the basis of an examination of changes in atmospheric circulation developed from two ice cores high resolution glaciochemical series covering the period 10 000 to 16 000 years ago from a central greenland ice core and a new site in east antarctica display similar variability these findings suggest that rapid climate change events occur more frequently in antarctica than previously demonstrated

diagenesis and reservoir quality evolution of incised valley sandstones evidence from the abu madi gas reservoirs upper miocene the nile delta basin egypt abstract elucidation of the distribution of diagenetic alterations in incised valley sandstones within a sequence stratigraphic framework allows a better understanding of their reservoir quality evolution during burial gas reservoirs of the upper miocene abu madi formation present day depth 3350 m temperature 116 the nile delta basin egypt consist of lowstand systems tract lst fluvial and transgressive systems tract tst estuarine sandstones deposited in an incised valley these sandstones have a wide range of porosity 2 to 29 and permeability 0 01 to 6071 md which reflect both depositional facies and diagenetic controls diagenetic events that influenced the reservoir quality evolution include mainly the formation of extensive grain rimming fe mg chlorite mechanical compaction of ductile grains pressure dissolution of quartz and quartz cementation the chlorite rims distributions of which are not clearly related to sequence stratigraphy have preserved reservoir quality by inhibiting quartz cementation but have increased microporosity values in the reservoirs calcite cementation 18o 13 5 to 6 0 13c 14 3 to 1 0 and 87sr 86sr 0 707124 to 0 708181 has not influenced the overall reservoir quality evolution of the sandstones because of its localized occurrence other diagenetic events that have little influence on reservoir quality include the more frequent formation of kaolin in the lst fluvial sandstones and formation of pyrite in the tst estuarine sandstones this study demonstrates the possibility of constraining and evaluating the impact of diagenetic alterations on reservoir quality evolution in incised valley deposits and their sequence stratigraphic distribution and thus has an important impact on hydrocarbon exploration in such settings

holocene glacier fluctuations a global overview of glacier advances and retreats grouped by regions and by millennia for the holocene is compiled from previous studies the reconstructions of glacier fluctuations are based on 1 mapping and dating moraines defined by 14 c tcn osl lichenometry and tree rings discontinuous records time series and 2 sediments from proglacial lakes and speleothems continuous records time series using 189 continuous and discontinuous time series the long term trends and centennial fluctuations of glaciers were compared to trends in the recession of northern and mountain tree lines and with orbital solar and volcanic studies to examine the likely forcing factors that drove the changes recorded a general trend of increasing glacier size from the earlyemid holocene to the late holocene in the extra tropical areas of the northern hemisphere nh is related to overall summer temperature forced by orbitally controlled insolation the glaciers in new zealand and in the tropical andes also appear to follow the orbital trend i e they were decreasing from the early holocene to the present in contrast glacier fluctuations in some monsoonal areas of asia and southern south america generally did not follow the orbital trends but fluctuated at a higher frequency possibly triggered by distinct teleconnections patterns during the neoglacial advances clustered at 4 4e4 2 ka 3 8e3 4 ka 3 3e2 8 ka 2 6 ka 2 3e2 1 ka 1 5e1 4 ka 1 2e1 0 ka 0 7e0 5 ka corresponding to general cooling periods in the north atlantic some of these episodes coincide with multidecadal periods of low solar activity but it is unclear what mechanism might link small changes in irradiance to widespread glacier fluctuations explosive volcanism may have played a role in some periods of glacier advances such as around 1 7e1 6 ka coinciding with the taupo volcanic eruption at 232 5 ce but the record of explosive volcanism is poorly known through the holocene the compilation of ages suggests that there is no single mechanism driving glacier fluctuations on a global scale multidecadal variations of solar and volcanic activity supported by positive feedbacks in the climate system may have played a critical role in holocene glaciation but further research on such linkages is needed the rate and the global character of glacier retreat in the 20th through early 21st centuries appears unusual in the context of holocene glaciation though the retreating glaciers in most parts of the northern hemisphere are still larger today than they were in the early and or mid holocene the current retreat

environments of formation and controls on spatial distribution of calcite cementation in plio pleistocene fluvial deposits new mexico u s a abstract the sierra ladrones formation is the uppermost syn rift sedimentary unit of the rio grande rift in central new mexico in the vicinity of the study site it was deposited in a variety of fluvial subenvironments portions of the formation are strongly cemented by calcite forming resistant ledges in otherwise poorly consolidated sediment the calcite exhibits a wide range of macroscopic and microscopic textures and structures which formed in different hydrologic environments including vadose nonpedogenic vadose pedogenic and phreatic phreatic cements are characterized by sparite with uniform disseminated isopachous poikilotopic and drusy textures vadose nonpedogenic by micrite with meniscus textures and vadose pedogenic by textures similar to those in the vadose nonpedogenic environment plus macroscopic features such as root structures destruction of primary sedimentary textures and a red hue many of the cements are of mixed vadose phreatic origin with vadose micrite formation preceding phreatic sparite the calcite is near end member in composition with only minor substitution of trace elements sr mg mn and fe for ca in the calcite structure vadose micrite cements generally have a higher trace element content than phreatic sparite perhaps as a result of more rapid precipitation in the vadose zone carbon isotope values range from 4 7 to 3 5 pdb and 18o values range from 10 3 to 7 2 pdb cements that are dominantly vadose have a wider range of 13c values and are more 13c depleted overall than phreatic cements oxygen values are similar for both vadose and phreatic cements at large scales i e several meters to decameters vertical dimension calcite is present preferentially in coarse grained sediments that had high pre cementation saturated permeabilities relative to uncemented finer grained strata at smaller scales i e several meters or less vertical dimension however there is no clear relationship between degree of cementation and pre cementation permeability at these scales calcite cement is present preferentially in areas that contain early vadose calcite this suggests that at large scales cementation was controlled by pre cementation permeability perhaps due to a greater flux of ca2 and or hco3 in permeable horizons whereas at smaller scales within high permeability units the distribution of cementation was controlled by other factors such as the presence of nucleating material

younger dryas and early holocene age glacier advances in patagonia reliable dating of southern hemisphere glacier fluctuations since the last glacial maximum lgm is crucial to resolving debates about millennial scale climate change here we present be 10 dates f

holocene glacier fluctuations in south america and antarctica abstract glacial geologic evidence indicates that glaciers throughout the andes and antarctica fluctuated during the holocene radiocarbon dating and other age determinations suggest that glaciers readvanced significantly only during the last 5 ka reaching positions from several 100 m to a few kilometres beyond their present limits in south america tenuous evidence from radiocarbon dates with dendrochronological data and environmental interpretations from pollen analyses indicate four main periods of neoglacial advance culminating 5000 4000 bp 3000 2000 bp 1300 1000 bp and 15th late 19th centuries smaller advances may have occurred at ca 8400 bp ca 7500 bp and ca 6300 bp the meagre data are consistent in indicating broad synchrony throughout the andes during the last 5 ka suggesting response to global climatic changes anomalies exist in patagonia where some tide water glaciers reached their maximal holocene limits recently this century the broad spectrum of differing antarctic environments produces interesting contrasts some local glaciers in the mcmurdo sound area of the east artarctic continent are more extensive now than during the global glacial maximum ca 18 ka bp when they were starved of precipitation consistent agreement among 14 radiocarbon dates from the south shetland islands indicates two main holocene glacier advances the most extensive 2 3 km peaking in the 12th century the other culminating in the 18th 19th century glaciers in south georgia reached their most advanced holocene limits before 2200 bp moraine fjord glacier which culminated as a 6 km advance between 1460 1700 radiocarbon bp may have lagged 400 650 years behind the climatic forcing because it could only advance in its deep water fjord by building a moraine bank smaller advances in south georgia culminated in the 17th 19th centuries and during the 1920s 30s there is no firm evidence of glacier advances before 3 ka bp in the southern ocean sub antarctic domain but broad synchrony in glacier advances during the last ca 3000 years appears to have occurred throughout the andes antarctic transect caution is required in the interpretation and correlation of moraines associated with calving glaciers and of those with poorly constrained dating

jurassic deep water fans in the neo tethys ocean the kashafrud formation of the kopet dagh basin iran abstract the middle jurassic kashafrud formation of northeast iran was deposited in the kopet dagh basin linked to the neo tethys ocean the 2 km thick succession commences with fluvio marine boulder conglomerates that occupy bedrock valleys but the bulk of the formation comprises a deep water succession of interbedded sandstone and mudstone packages with trace fossils and sparse ammonites neogene collisional events deformed the strata to create the kopet dagh mountains the deep water succession represents channel lobe systems and associated levees and overbank areas on slope to basin floor fans northward paleoflow suggests that rivers drained uplands along the paleo tethys suture zone forming fan deltas on a narrow shelf with associated sediment transport to deeper water coarse sands extrabasinal pebbles and plant fragments are present throughout the formation and a thick boulder conglomerate unit lies within the turbidite succession these observations suggest proximity to terrestrial sources throughout deposition sandstone packages are mainly less than 10 m thick maximum 84 m and numerous lensoid packages of thick bedded sandstone tens of meters thick and up to 200 m wide represent submarine channel fills thick bedded lenses and sheets show a relatively narrow range of paleoflow direction and represent major submarine conduits whereas the more varied paleoflow direction of thin bedded packages suggests that many were deposited on levees the presence in the kashafrud formation of potential source rocks in the form of organic rich mudstones and abundant plant fragments suggests that the formation may have contributed to hydrocarbon fields within overlying formations sandstone sheets and channel fills could form local reservoirs

onset of subduction as the cause of rapid pliocene quaternary subsidence in the south caspian basin backstripping a representative stratigraphic column from the northwest of the south caspian basin shows that 2 4 km of tectonic subsidence has occurred since ca 5 5 ma at 1 5 10 times the rate recorded in typical foreland basins roughly half the basin s sedimentary thickness of 20 km has accumulated in this time while the upper part of the succession has begun to deform by buckle folding the south caspian basement appears to be either thick oceanic crust or thinned high velocity continental crust seismicity and gravity data indicate that the basement is in the initial stages of subduction under the middle caspian region to the north we propose that basement subduction began ca 5 5 ma to create the major pliocene quaternary subsidence subduction may have been triggered by a regional reorganization in the arabia eurasia collision at that time possibly following the construction of the turkish iranian plateau

differential mobility of elements in burial diagenesis of siliciclastic rocks abstract mass balance calculations involving smectite rich siliciclastic mudstones sampled from boreholes show that significant k2o addition and cao loss correlate strongly with the progress of illitization of smectite and with the dissolution of calcite the calculations are based on the immobility of al2o3 and require a chemically homogeneous sediment at deposition such that the shallower samples represent protolith compositions of deeper samples constancy of ratios of tio2 al2o3 are used to 1 establish that both tio2 and al2o3 have similarly low differential mobilities and 2 identify stratigraphic sections available in the literature that are sufficiently homogeneous to allow the calcu ations our calculations show that most major oxide components are immobile at the 5 limit of resolution of the calculations exceptions are k2o which is almost universally added to mudstones and cao which is commonly removed from mudstones during diagenesis the addition of up to 50 k2o correlates with percent illite in mixed layer illite smectite indicating that illitization of smectite involves fixation of k2o from diagenetic fluids removal of 40 cao from some sections correlates with decreasing calcite mode and is attributed to dissolution of calcite together these reactions lead to a 10 15 loss of mineral volume a volume loss that must be added to porosity loss when modeling compaction illitization and carbonate dissolution may be linked because k fixation during illitization decreases the ph of the local fluid a reverse weathering reaction which enhances carbonate dissolution addition of up to 20 na2o in some rocks may be caused by albitization of plagioclase but na2o addition is not pervasive the apparent lack of mass transfer associated with dissolution of kaolinite and feldspars or precipitation of chlorite implies that these reactions are balanced by other reactions such that their oxide components in mudstones are conserved limited data from sandstone mudstone pairs are consistent with transfer of k2o from sandstones to mudstone via rising diagenetic fluids except for cao and the alkalis diagenesis of siliciclastic mudstones appears isochemical 5 relative for most major oxide components the much larger changes recorded in some reservoir sandstones are clearly exceptions and may not reflect changes occurring at the scale of kilometers

onset of neoglaciation in the southern hemisphere a review of evidence documenting an early neoglacial mid holocene advance of mountain glaciers in south america and new zealand reveals that of 16 glaciers for which radiocarbon age control exists only two have associated dates that may approximate the culmination of an advance advances of the remaining glaciers are controlled only by minimum or maximum limiting ages additional dates for several new zealand glaciers are based on weathering rind measurements having large potential errors twelve of the glaciers now terminate or have terminated in lakes or in tidewater and are subject to instabilities associated with calving termini an extensive debris cover in the ablation zone of nearly half of the glaciers makes their moraine succession potentially suspect as a record of detailed climatic variation the two glaciers with seemingly reliable age control are located in valleys where large rock avalanches could affect glacier mass balance and lead to random advances or where rock avalanche deposits might easily be mistaken for moraines and tills the early neoglacial interval has been defined primarily based on this set of data the ages taken at face value suggest that the early neoglacial advance culminated between ca 5400 and 4900 cal yr ago ca 4600 4400 14c yr bp this chronology however should remain provisional until improved age control is obtained for a large population of glaciers based on closely bracketing radiocarbon dates and or an adequate number of cosmogenic isotope ages data from calving glaciers and those subject to rock avalanche activity should be avoided or assessed critically copyright 2000 john wiley sons ltd

chronology of bathymetric variations of the pueyrredon posadas salitroso lacustrine system during the late pleistocene to early holocene abstract the pueyrredon posadas salitroso lacustrine system pps ls is located in the andean patagonia region of argentina 47 22 28 s 71 55 34 w and represents a series of lakes formed as glaciers retreated during the late pleistocene and early holocene these lakes began as proglacial lakes and later evolved into periglacial lakes this research presents the chronological evolution of the pps ls bathymetric variations based on the analysis of stratigraphic profiles surveyed at different locations and the dates obtained from lake sediments four paleogeographic sketches representing the chronological evolution of the pps ls between 23 580 bp and 5208 bp have been developed based on the integration of these data

evidence from the rio bayo valley on the extent of the north patagonian icefield during the late pleistocene holocene transition abstract this paper presents data on the extent of the north patagonian icefield during the late pleistocene holocene transition using cosmogenic nuclide exposure age and optically stimulated luminescence dating we describe geomorphological and geochronological evidence for glacier extent in one of the major valleys surrounding the north patagonian icefield the rio bayo valley geomorphological mapping provides evidence for the existence of two types of former ice masses in this area i a large outlet glacier of the north patagonian icefield which occupied the main rio bayo valley and ii a number of small glaciers that developed in cirques on the slopes of the mountains surrounding the valley cosmogenic nuclide exposure age dating of two erratic boulders on the floor of the rio bayo valley indicate that the outlet glacier of the icefield withdrew from the rio bayo valley after 10 900 1000 yr the mean of two boulders dated to 11 400 900 yr and 10 500 800 yr single grain optically stimulated luminescence osl dating of an ice contact landform constructed against this glacier indicates that this ice mass remained in the valley until at least 9700 700 yr the agreement between the two independent dating techniques osl and cosmogenic nuclide exposure age dating increases our confidence in these age estimates a date obtained from a boulder on a cirque moraine above the main valley indicates that glaciers advanced in cirques surrounding the icefield some time around 12 500 900 yr this evidence for an expanded north patagonian icefield between 10 900 1000 yr and 9700 700 yr implies cold climatic conditions dominated at this time

sedimentary record of late paleozoic to recent tectonism in central asia analysis of subsurface data from the turan and south kazak domains abstract the turan and south kazak domains tsk are in central asia between the caspian sea and the tien shan the area is covered by sediments deposited since the late permian during a series of tectonic events closely related to the history of two oceanic domains paleotethys and neotethys sedimentary basins on the tsk therefore provide constraints on the tectonic development of the southern margin of eurasia since the late permian our study is based on structure contour maps and isopach maps of five key stratigraphic markers of late permian to tertiary age isopach maps help locate major faults and delimit sedimentary basins providing information on vertical motions and in some instances horizontal motions subsidence associated with extension appears to have dominated the tsk from the late permian to the eocene the extension may have been of back arc type in southern eurasia next to the active margin where the paleotethys and neotethys successively subducted toward the north here sedimentary basins are both wide and deep up to 15 km during the mesozoic two compressional events of regional significance occurred in association with accretion of continental blocks at the southern margin of eurasia the first one at the end of the triassic led to strong selective inversion of basins over the turan domain the second one during the late jurassic early cretaceous had weaker effects since the oligocene following collision of both india and arabia with eurasia inversion has become more generalized and compressional basins have formed on the tsk throughout the entire history of development of the tsk from the late permian to the tertiary structures of paleozoic and early mesozoic age have exerted a strong control on sedimentation and especially on the location of depocenters the south kazak domain has registered little subsidence in comparison with the turan domain where some basins have become very deep

extrusion tectonics and subduction in the eastern south caspian region since 10 ma reply we examine active deformation of the region surrounding the eastern south caspian sea using a combination of seismic geological geodetic and geomorphological data global positioning system gps velocities indicate a westward component of motion of the south caspian basin relative to eurasia and central iran we identify major zones of shear the ashkabad and shahrud fault zones that accommodate this westward extrusion on either side of the south caspian block estimates of total strike slip motion could at present day slip rates derived from gps observations be achieved in 10 m y therefore the northwest extrusion of the south caspian region which is accommodated by subduction beneath the north caspian region stable eurasia along the apsheron balkan sill may also date from that time this suggests that the onset of subduction may be older than previous estimates ranging from 1 8 to 5 5 ma our results are summarized in a new kinematic model that significantly clarifies the active tectonics of this complicated region

patagonian glacier response during the late glacial holocene transition whether cooling occurred in the southern hemisphere during the younger dryas yd is key to understanding mechanisms of millennial climate change although southern hemisphere records do not reveal a distinct climate reversal during the late glacial period many mountain glaciers readvanced we show that the puerto bandera moraine 50 s which records a readvance of the southern patagonian icefield spi formed at or shortly after the end of the yd the exposure age 10 8 0 5 thousand years ago is contemporaneous with the highest shoreline of lago cardiel 49 s which records peak precipitation east of the andes since 13 thousand years ago absent similar moraines west of the andes these data indicate an spi response to increased amounts of easterly sourced precipitation reflecting changes in the southern westerly circulation rather than regional cooling

high frequency holocene glacier fluctuations in new zealand differ from the northern signature understanding the timings of interhemispheric climate changes during the holocene along with their causes remains a major problem of climate science here we present a high resolution 10be chronology of glacier fluctuations in new zealand s southern alps over the past 7000 years including at least five events during the last millennium the extents of glacier advances decreased from the middle to the late holocene in contrast with the northern hemisphere pattern several glacier advances occurred in new zealand during classic northern warm periods these findings point to the importance of regional driving and or amplifying mechanisms we suggest that atmospheric circulation changes in the southwest pacific were one important factor in forcing high frequency holocene glacier fluctuations in new zealand

dissolution and relic textures in framework grains of holocene sediments from the brazos river and gulf coast of texas abstract holocene sediments from the brazos river point bar near wallis texas and from marginal marine settings along the gulf coast of texas between galveston and freeport were analyzed to document the surface texture of near surface framework grains the purpose was to determine whether or not textures exist that resemble textures formed during deeper burial the samples range from subarkoses and sublitharenites to quartz rich lithic arkoses and feldspathic arkoses many feldspar grains particularly k feldspars show extensive dissolution textures that either are inherited from the source area developed during transport or are forming at the present time also quartz grains with slightly abraded quartz overgrowths and detrital grains with clay coats and bridges were observed these eatures if observed in samples from deeply buried sandstones could be misintepreted to be the result of diagenesis during the current cycle of burial in light of these observations caution should be used in the interpretation of the time of formation of diagenetic textures particularly dissolution textures that are commonly categorized as contributing to secondary porosity the determination of exactly where and when these textures formed was beyond the scope of this study

southern patagonian glacial chronology for the last glacial period and implications for southern ocean climate the magellan region of southern south america is in a unique setting at 50 s on the equatorial side of the antarctic frontal zone to record in detail terrestrial glacial to interglacial events a 10be chronology shows growth and millennial fluctuations of a patagonian ice sheet between 25 and 17 6 17 0 cal ka in the strait of magellan the maximum ice margin position is dated to 24 6 0 9 ka and other moraine ages are 18 5 1 8 and 17 6 0 2 ka mean 1 standard deviation in bahia inutil dated moraine ages are 20 4 1 2 and 17 3 0 8 ka the chronology of the local last glacial maximum lgm reveals a record of atmospheric cooling that was broadly in phase with changes in southern ocean conditions such as sea ice fluctuations and surface water characteristics published modeling results indicate that a decline in temperature of 6 c and slight drying over southernmost patagonia could simulate the growth and sustained presence of an ice sheet to the mapped lgm limit the terrestrial record in southern patagonia and marine records in adjacent oceans indicate mean northward movement of the antarctic frontal zone which caused the last southern south american ice age the antarctic frontal zone at present lies only 3 5 to the south some significant changes in the magellan region occurred in step with north atlantic region and the northern hemisphere for example the overall time span of the last glaciation and the timing of maximum ice extent were similar between the hemispheres despite maximum local summer insolation intensity in southern south america other characteristics of the southern patagonian glacial history differ from the north atlantic region specifically an out of phase relationship during deglaciation which is more similar to that of southern ocean and antarctic records

history of quartz cementation in the lower cretaceous travis peak formation east texas abstract quartz is the most abundant authigenic mineral in sandstones of the travis peak formation in east texas but the extent of quartz cementation varies widely to determine major controls on quartz cement distribution this study used 431 thin sections from 1 100 m of core from 26 wells volume of detrital clay matrix is the main textural control on quartz cement in sandstones lacking detrital clay no significant correlation exists between quartz cement and grain size sorting bed thickness or sedimentary structure depositional facies was an indirect control on quartz cement distribution because facies controlled detrital matrix content but no significant difference exists between average quartz cement volume in matrix free paralic 16 7 and matrix free fluvial 17 1 sandstones quartz cement increases significantly with present depth from an average of 14 6 at 1 825 m to 20 0 at 3 050 m this trend of increasing quartz cement is interpreted to be the result of 1 an early episode of quartz cementation by meteoric water that resulted in relatively uniform distribution of quartz within the formation and 2 a later episode related to the development of stylolites that preferentially added quartz cement in the deepest sandstones approximately 10 to 20 of the authigenic silica in travis peak sandstones was derived internally from intergranular pressure solution and stylolitization the remaining 80 was imported from unknown sources outside the sandstones

the mid cimmerian tectonic event bajocian in the alborz mountains northern iran evidence of the break up unconformity of the south caspian basin

the geology and petroleum potential of the north afghan platform and adjacent areas northern afghanistan with parts of southern turkmenistan uzbekistan and tajikistan the north afghan platform has a pre jurassic basement unconformably overlain by a jurassic to paleogene oil and gas bearing sedimentary rock platform cover unconformably overlain by neogene syn and post orogenic continental clastics the pre jurassic basement has four units 1 an ordovician to lower devonian passive margin succession developed on oceanic crust 2 an upper devonian to lower carboniferous tournaisian magmatic arc succession developed on the passive margin 3 a lower carboniferous visean to permian rift passive margin succession 4 a triassic continental magmatic arc succession the mesozoic palaeogene cover has three units 1 a late triassic to middle jurassic rift succession is dominated by variable continental clastics thick coarse lenticular coal bearing clastics were deposited by braided and meandering streams in linear grabens while bauxites formed on the adjacent horsts 2 a middle to upper jurassic transgressive regressive succession consists of mixed continental and marine bathonian to lower kimmeridgian clastics and carbonates overlain by regressive upper kimmeridgian tithonian evaporite bearing clastics 3 a cretaceous succession consists of lower cretaceous red beds with evaporites resting unconformably on jurassic and older deposits overlain usually unconformably by cenomanian to maastrichtian shallow marine limestones which form a fairly uniform transgressive succession across most of afghanistan 4 a palaeogene succession rests on the upper cretaceous limestones with a minor break marked by bauxite in places thin palaeocene to upper eocene limestones with gypsum are overlain by thin conglomerates which pass up into shales with a restricted brackish water upper oligocene lower miocene marine fauna the neogene succession consists of a variable thickness of coarse continental sediments derived from the rising pamir mountains and adjacent ranges almost all the deformation of the north afghan platform began in the miocene oil and gas traps are mainly in upper jurassic carbonates and lower cretaceous sandstones across the entire north afghan block upper jurassic carbonate traps sealed by evaporites occur mainly north of the southern limit of the upper jurassic salt lower cretaceous traps consist of fine grained continental sandstones sealed by aptian albian shales and siltstones upper cretaceous palaeocene carbonates sealed by palaeogene shales are the main traps along the northern edge of the platform and in the tajik basin almost all the traps are broad anticlines related to neogene wrench faulting in this respect like similar traps along the san andreas fault hydrocarbon sources are in the mesozoic section the lower middle jurassic continental coal bearing beds provide about 75 of the hydrocarbons the callovian oxfordian provides about 10 the neocomian a meagre 1 and the aptian albian about 14 the coal bearing source rocks decrease very markedly in thickness southwards cross the north afghan platform much of the hydrocarbon generation probably occurred during the late cretaceous paleogene and migrated to structural traps during neogene deformation since no regional structural dip aids southward hydrocarbon migration and since the traps are all structural and somewhat small then there is little chance of very large petroleum fields on the platform nevertheless further studies of the north afghan platform should be rewarding because a the traps of strike slip belts are difficult to find without detailed exploration b the troubles of the last 20 years mean that almost no exploration has been done and c conditions may soon become more favorable there should be ample potential for oil and particularly gas discoveries especially in the northern and western parts of the north afghan platform

latest pleistocene and holocene glacial events in the colonia valley northern patagonia icefield southern chile the northern patagonia icefield npi is the primary glaciated terrain worldwide at its latitude 46 5 47 5 s and constraining its glacial history provides unique information for reconstructing southern hemisphere paleoclimate the colonia glacier is the largest outlet glacier draining the eastern npi ages were determined using dendrochronology lichenometry radiocarbon cosmogenic 10be and optically stimulated luminescence dated moraines in the colonia valley defined advances at 13 2 0 95 11 0 0 47 and 4 96 0 21 ka with the last being the first constraint on the onset of neoglaciation for the eastern npi from a directly dated landform dating in the tributary cachet valley which contains an ice dammed lake during periods of colonia glacier expansion defined an advance at ca 2 95 0 21 ka periods of advancement at 810 49 cal a bp and 245 13 cal a bp and retreat during the intervening periods recent colonia glacier thinning which began in the late 1800s opened a lower elevation outlet channel for lago cachet dos in ca 1960 our data provide the most comprehensive set of latest pleistocene and holocene ages for a single npi outlet glacier and expand previously developed npi glacial chronologies

material flux and porosity changes during sediment diagenesis understanding the changes in porosity that occur during burial of sediments is of importance both in modelling fluid flow in sedimentary basins and for prediction of petroleum reservoir quality when deposited up to 50 of the volume of sands is intergranular pore space porosity generally decreases with depth because of compaction and precipitation of diagenetic minerals but some sandstones retain an anomalously high porosity whether this is due to dissolution and removal of material or to its local redistribution is not clear we originally intended to quantify losses of major chemical components during burial of a complete sedimentary unit we have investigated ten reservoir sandstones of permian to tertiary age from oilfields worldwide these show consistent results and here we present detailed data from four of them we found that the silica content of these sandstones actually increased by 220 to 350 kg m 3 following compaction no statistically significant changes were observed for aluminium potassium or sodium the flux of silica cannot be modelled satisfactorily using currently accepted values of permeability silica solubility and flow rates posing a challenge for existing models of fluid flow and ore emplacement

composition porosity and reservoir potential of the middle jurassic kashafrud formation northeast iran abstract in the kopet dagh basin of iran deep sea sandstones and shales of the middle jurassic kashafrud formation are disconformably overlain by hydrocarbon bearing carbonates of upper jurassic and cretaceous age to explore the reservoir potential of the sandstones we studied their burial history using more than 500 thin sections supplemented by heavy mineral analysis microprobe analysis porosity and permeability determination and vitrinite reflectance the sandstones are arkosic and lithic arenites rich in sedimentary and volcanic rock fragments quartz overgrowths and pore filling carbonate cements calcite dolomite siderite and ankerite occluded most of the porosity during early to deep burial assisted by early compaction that improved packing and fractured quartz grains iron oxides are prominent as alteration products of framework grains probably reflecting source area weathering prior to deposition and locally as pore fills minor cements include pore filling clays pyrite authigenic albite and k feldspar and barite existing porosity is secondary resulting largely from dissolution of feldspars micas and rock fragments with some fracture porosity porosity and permeability of six samples averages 3 2 and 0 0023 md respectively and 150 thin section point counts averaged 2 7 porosity reflectance of vitrinite in eight sandstone samples yielded values of 0 64 0 83 in the early mature to mature stage of hydrocarbon generation within the oil window kashafrud formation petrographic trends were compared with trends from first cycle basins elsewhere in the world inferred burial conditions accord with the maturation data suggesting only a moderate thermal regime during burial some fractures iron oxide cements and dissolution may reflect cenozoic tectonism and uplift that created the kopet dagh mountains the low porosity and permeability levels of kashafrud formation sandstones suggest only a modest reservoir potential for such tight sandstones fractures may enhance the reservoir potential

craton derived alluvium as a major sediment source in the himalayan foreland basin of india within the himalayan foreland basin the axial yamuna river with himalayan headwaters lies along the northern margin of the indian craton giving the impression that cratonic rivers have contributed little to the basin compared with himalayan drainages however the betwa chambal and other rivers which drain northward into the yamuna are vigorous monsoonal rivers with large catchments stratigraphic and petrographic evidence shows that sediment derived largely from these rivers extends north of the axial yamuna river red feldspathic sand and gravel underlie much of the southern foreland basin at shallow depth 25 m where its topmost strata are dated at ca 119 ka ago and extend at deeper levels 500 m to about one third of the distance across the foreland basin petrographic analysis confirms a match with modern betwa river sands which derive their feldspar from granitic gneisses of the bundelkhand complex along the yamuna valley the red alluvium is overlain by gray alluvium dated at 82 35 ka ago which also yields a cratonic signature with large amounts of smectite derived from the deccan traps cratonic contributions are evident in alluvium as young as 9 ka ago in a section 25 km north of the yamuna this gray cratonic sediment was probably deposited in part by the chambal river which transports high grade metamorphic minerals from the banded gneiss complex of the aravalli belt cratonic sediment appears to interfinger with himalayan detritus farther north below the ganga yamuna interfluve with its headwaters in the tectonically unstable indus ganga watershed area the yamuna river may have occupied its present course late in the quaternary and if so cratonic rivers may have provided the basin9s axial drainage for prolonged periods the penetration of himalayan sediment to the distal foreland basin may reflect avulsion of orogenic rivers along the craton margin in addition to dynamic transverse drainage systems from the himalaya that pushed the axial drainage to the basin9s feather edge the wide spread of cratonic sediment would have been enhanced by slow subsidence in the distal foreland basin and focusing of rivers into a basin reentrant

holocene glacier fluctuations in patagonia are modulated by summer insolation intensity and paced by southern annular mode like variability abstract alpine glaciers are sensitive indicators of changes in climate and their ubiquity in mountainous regions make them valuable proxies for terrestrial climate reconstructions worldwide however the timing and extent of glacier change across the south american mid latitudes through the holocene are still poorly constrained relative to their counterparts in the northern hemisphere here we report a new 10be surface exposure based chronology of moraines recording a series of progressively less extensive glacier advances of glaciar torre argentina 49 3 s 73 0 w since the last glacial maximum with expansions culminating at 17 600 900 13 500 500 9700 400 6900 200 6100 300 4500 200 and 530 60 yr bp the declining magnitude of holocene glacier expansions parallels a gradual rise in local summer insolation intensity during the holocene while individual advances occurred during inferred negative southern annular mode sam like states at centennial to millennial timescales these observations suggest that i summer insolation intensity modulated antiphased trends in glacier extent in the polar hemispheres during the holocene and that ii centennial scale sam like temperature and precipitation anomalies paced glacier fluctuations throughout patagonia given the persistence of the inferred sam like anomalies throughout the holocene the modern measured trend towards positive sam index conditions could mark the onset of a fundamental shift in the climate of the southern hemisphere midlatitudes that warrants consideration in projections of future climate

the last glacial holocene transition in southern chile warming at the last glacial termination in the north atlantic region was interrupted by a period of renewed glacial activity during the younger dryas chronozone ydc the underlying mechanism of this cooling remains elusive but hypotheses turn on whether it was a global or a north atlantic phenomenon chronological sedimentological and palaeoecological records from sediments of small lakes in oceanic southern chile demonstrate that there was no ydc cooling in southern chile it is therefore likely that there was little or no cooling in southern pacific surface waters and hence that ydc cooling in the north atlantic was a regional rather than global phenomenon

compaction and porosity evolution of pliocene sandstones ventura basin california sandstones of the pico and repetto formations were studied to quantify the processes involved in compaction and to determine the porosity evolution of the beds during burial the sandstones are mineralogically immature and except for local carbonate cemented beds have insufficient cement to have prevented compaction stratigraphic studies and graphic porosity depth plots suggest that the samples maximum burial depths were approximately 10 000 ft 3 048 m deeper than the present day depths of 850 13 000 ft 259 3 962 m compaction produced closer grain packing as measured by the contact index ci average number of contacts per grain and tight packing index tpi average number of long sutured and embayed contacts per grain for samples with less than 10 cement the ci depth gradient is 0 21 1 000 ft 0 69 1 000 m and tpi depth gradient is 0 27 1 000 ft 0 89 1 000 m assuming sands had 40 initial porosity the sandstones that are at present most deeply buried lost a total absolute porosity of 26 by all compactional processes which includes 14 by grain rearrangement and 6 each by pressure solution and ductile grain deformation porosity loss by nondeformational grain rearrangement was complete by a present day depth of 5 000 ft 1 524 m but in uncemented sandstones pressure solution plus associated grain rearrangement and ductile grain deformation continued to the maximum depths sampled compaction is most abrupt in sands with abundant micas and ductile rock fragments the ci gradient is 0 14 1 000 ft 0 46 1 000 m for samples with ess than 10 ductile grains but 0 22 1 000 ft 0 72 1 000 m for samples with more than 10 ductile grains compaction was almost entirely the result of overburden pressure and was not noticeably retarded in overpressured zones suggesting that overpressures developed after maximum burial was achieved for samples with less than 10 cement the ci is a better depth predictor than the tpi r2 0 58 vs 0 45 but the tpi is a better predictor of pre cement porosity than the ci r2 0 54 vs 0 31 secondary porosity averages 20 40 of the total thin section porosity secondary porosity is present at all depths but makes up the greatest percentage of total porosity between present depths of 6 000 and 9 500 ft 1 829 and 2 896 m except for grain fracturing secondary porosity formed only by dissolution of framework grains fractured grain porosity contributes up to 29 of total porosity 5 absolute porosity in some samples fractures formed during pleistocene tectonic episodes

plate tectonic evolution of the southern margin of eurasia in the mesozoic and cenozoic abstract thirteen time interval maps were constructed which depict the triassic to neogene plate tectonic configuration paleogeography and general lithofacies of the southern margin of eurasia the aim of this paper is to provide an outline of the geodynamic evolution and position of the major tectonic elements of the area within a global framework the hercynian orogeny was completed by the collision of gondwana and laurussia whereas the tethys ocean formed the embayment between the eurasian and gondwanian branches of pangea during late triassic early jurassic times several microplates were sutured to the eurasian margin closing the paleotethys ocean a jurassic cretaceous north dipping subduction boundary was developed along this new continental margin south of the pontides transcaucasus and iranian plates the subduction zone trench pulling effect caused rifting creating the back arc basin of the greater caucasus proto south caspian sea which achieved its maximum width during the late cretaceous in the western tethys separation of eurasia from gondwana resulted in the formation of the ligurian penninic pieniny magura ocean alpine tethys as an extension of middle atlantic system and a part of the pangean breakup tectonic system during late jurassic early cretaceous times the outer carpathian rift developed the opening of the western black sea occurred by rifting and drifting of the western central pontides away from the moesian and scythian platforms of eurasia during the early cretaceous cenomanian the latest cretaceous paleogene was the time of the closure of the ligurian pieniny ocean adria alcapa terranes continued their northward movement during eocene early miocene times their oblique collision with the north european plate led to the development of the accretionary wedge of the outer carpathians and its foreland basin the formation of the west carpathian thrusts was completed by the miocene the thrust front was still propagating eastwards in the eastern carpathians during the late cretaceous the lesser caucasus sanandaj sirjan and makran plates were sutured to the iranian afghanistan plates in the caucasus caspian sea area a north dipping subduction zone jumped during paleogene to the scythian turan platform the shatski terrane moved northward closing the greater caucasus basin and opening the eastern black sea the south caspian underwent reorganization during oligocene neogene times the southwestern part of the south caspian basin was reopened while the northwestern part was gradually reduced in size the collision of india and the lut plate with eurasia caused the deformation of central asia and created a system of nw se wrench faults the remnants of jurassic cretaceous back arc systems oceanic and attenuated crust as well as tertiary oceanic and attenuated crust were locked between adjacent continental plates and orogenic systems

diagenesis and reservoir quality of the sherwood sandstone triassic corrib field slyne basin west of ireland abstract the triassic sherwood sandstone in the corrib field slyne basin west of ireland on the european continental margin is a dry gas reservoir with a mercia mudstone top seal petrographic analysis combined with x ray diffraction stable isotope fluid inclusion and core analysis have been used to assess timing of growth and origin of mineral cements whether sandstone diagenesis involved mass flux the controls on reservoir quality and how reservoir quality is likely to vary in more deeply buried sections depositional and early diagenetic characteristics of the sherwood in corrib are typical of a semi arid fluvial environment containing groundwater of meteoric origin early diagenesis included the development of copious dolomite cement in the form of dolocrete as well as the formation of abundant clay while less volumetrically important grain coating haematite and k feldspar cement also grew burial diagenesis witnessed the initial growth of minor chlorite and albite quartz overgrowths and ankerite followed and are the most important burial cements growing over a temperature interval between 100 and 1165 c albite commenced growth at about 90 c quartz cement at 100 c and ankerite at 110 c these cements reached the zenith of their development at 105 110 c for albite 125 130 c for quartz and 135 145 c for ankerite siderite and anhydrite are relatively minor late stage cements the formation water has been consistently highly saline during burial and in terms of mineral cement derived oxygen stable isotope values is likely to be a diagenetically evolved version of the initial depositional water suggesting long term stagnation of the pore fluids the diagenetic reactions that formed burial cements all seem to be essentially isochemical including the ankerite that has carbon isotope characteristics of the cannibalisation of dolocrete reservoir quality is mainly controlled by early diagenetic dolomite and clay although grain size is also important because only sandstones with 200 m grain size have 50 md permeability both shallower and deeper sections than corrib may have similar porosity and permeability since temperature dependent diagenetic controls on reservoir quality e g quartz and illite cement are peripheral

tectonic versus chemical weathering controls on the composition of fluvial sands in tropical environments the compositions of fluvial sands collected in mountainous regions along the volcanic front in central america and along the andean front in venezuela and colombia correlate with the tectonic setting of their source terrains the sands derived from the central american volcanic arc are compositionally distinct from those derived from the andean terrains and minor variations in tectonic style can also be discriminated subtle differences in tectonic setting and source rock composition are recognizable only when modification by chemical weathering is slight they are strongest in sands from low order streams draining mountainous areas with modest alluvial plain development sands that have been exposed to weathering for extended periods during alluvial storage are progressively enriched in chemically stable phases with increased weathering sands from continental terrains converge toward a supermature quartz arenite end member and the imprint left by source rock composition and tectonic setting is obscured in intraoceanic terrains a similar but much less pronounced enrichment in stable phases relative to less stable phases is observed similarly overprinting the tectonic signal although detailed tectonic information is easily lost sands derived from intraoceanic terrains are distinguishable from those derived from continental terrains even after long exposure to intense chemical weathering conditions

deglacial and postglacial climate history in east central isla grande de chiloe southern chile 43 s abstract palynologic and stratigraphic data from laguna tahui 42 50 s 73 30 w indicate cool temperate and humid conditions there between 14 000 and 10 000 14c yr b p followed by warmer and drier than present conditions between 10 000 and 7000 14c yr b p and subsequent cooling and rise in precipitation over the last 5800 14c yr the thermophilous valdivian trees eucryphia cordifolia and caldcluvia paniculata reached their maximum abundance during the early holocene warm dry phase 10 000 7000 14c yr b p followed by a rise in lake levels and reexpansion of north patagonian conifers starting at 7000 and 5800 14c yr b p respectively variations in the stratigraphic and geographic distribution of temperate rainforests in southern chile suggest multimillennial trends in temperature and westerly activity which are spatially and temporally coherent with paleoclimate records from neighboring regions climate variability at millennial and submillennial time scales may account for the establishment and persistence of fine scale mosaics of valdivian and north patagonian rainforest species in low to mid elevation communities since 5800 14c yr b p

the glacial geomorphology and pleistocene history of south america between 38 s and 56 s abstract this paper presents new mapping of the glacial geomorphology of southern south america between latitudes 38 s and 56 s approximately the area covered by the former patagonian ice sheets glacial geomorphological features including glacial lineations moraines meltwater channels trimlines sandur and cirques were mapped from remotely sensed images landsat 7 etm pan sharpened landsat 7 and aster the landform record indicates that the patagonian ice sheets consisted of 66 main outlet glaciers together with numerous local cirque glaciers and independent ice domes in the surrounding mountains in the northern part of the mapped area in the chilean lake district 38 42 s large piedmont glaciers developed on the western side of the andes and the maximum positions of these outlet glaciers are in general marked by arcuate terminal moraines to the east of the andes between 38 s and 42 s outlet glaciers were more restricted in extent and formed alpine style valley glaciers along the eastern flank of the andes south of 45 s a series of large fast flowing outlet glaciers drained the ice sheet the location of these outlet glaciers was topographically controlled and there was limited scope for interactions between individual lobes west of the andes at this latitude there is geomorphological evidence for an independent ice cap close to sea level on the taitao peninsula the age of this ice cap is unclear but it may represent evidence of glacier growth during the antarctic cold reversal and or younger dryas chronozone maximum glacier positions are difficult to determine along much of the western side of the andes south of 42 s because of the limited land there and it is assumed that most of these glaciers had marine termini in the south east of the mapped area in the fuegan andes cordillera darwin the landform record provides evidence of ice sheet initiation by adding published dates for glacier advances from the literature we present maps of pre last glacial maximum lgm glacier extent lgm extent and the positions of other large mapped moraines younger than lgm in age a number of large moraines occur within the known lgm limits the age of these moraines is unknown but since many of them lie well outside the established maximum neoglacial positions the possibility that they reflect a return to glacial climates during the younger dryas chronozone or antarctic cold reversal cannot be discounted

high and low latitude climate control on the position of the southern peru chile current during the holocene 1 we reconstructed changes of temperature salinity and productivity within the southern peru chile current during the last 8000 years from a high resolution sediment core recovered at 41 s using alkenones isotope ratios of planktic foraminifera biogenic opal and organic carbon paleotemperatures and paleosalinities reached maximum values at 5500 years ago and thereafter declined to modern values whereas paleoproductivity continuously increased throughout the last 8000 years we ascribe these long term holocene trends primarily to latitudinal shifts of the antarctic circumpolar current acc the concurrence with shifts in the position of the southern westerlies points to a common response of atmospheric and oceanographic circulation patterns off southern chile millennial to centennial scale fluctuations of paleotemperatures and paleosalinities on the other hand lag displacements in the position of the southern westerlies but reveal a significant correlation to short term temperature changes in antarctica indicating a high latitude control of the acc at these timescales

deglacial holocene environmental changes at the pacific entrance of the strait of magellan abstract we show environmental and nitrogen cycle changes between 13 and 2 5 kyr bp from the latest deglaciation to the holocene based on biogeochemical records in a sediment core from the pacific entrance of the strait of magellan organic carbon total nitrogen and c 37 alkenone contents were low during 13 9 kyr bp but increased rapidly at 8 kyr bp the relative contribution of tetra unsaturated c 37 alkenone used as a salinity proxy suggests low salinity during 13 9 kyr bp changing to high salinity at 8 kyr bp planktic foraminifer data showed that globigerina bulloides was more abundant during the deglacial early holocene than in the mid late holocene whereas abundances of neogloboquadrina pachyderma showed the opposite pattern this evidence plus biogenic opal data suggest that sea level rose surface waters were relatively stratified and in situ productivity was low except for organisms with opal tests from 13 to 9 kyr bp bulk 15 n values were high 9 11 relative to present day values during the deglacial early holocene with consistently lower values 7 after 8 kyr bp these relatively high 15 n values most likely reflect increased nutrient utilization in the southern ocean which resulted in high 15 n water being advected to the patagonian fjords although local denitrification caused by the delivery of copious terrestrial materials and organic matter to the ocean cannot be ruled out by 8 kyr bp continental influences and surface stratification were reduced and characteristic holocene conditions were established with increased influence of southern ocean water in the western strait of magellan sea surface temperatures showed millennial scale changes during the deglaciation and early holocene with relatively warm temperatures 11 12 c corresponding to the antarctic counterpart of the younger dryas cooling event of the northern hemisphere the longer term pattern 10 kyr time scale in alkenone derived sea surface temperatures generally follows orbital changes in insolation during austral spring suggesting a controlling influence of austral spring insolation on southern patagonian climate

cosmogenic nuclide exposure ages for moraines in the lago san martin valley argentina at several times during the quaternary a major eastward flowing outlet glacier of the former patagonian ice sheet occupied the lago san martin valley in argentina 49 s 72 w we present a glacial chronology for the valley based on geomorphological mapping and cosmogenic nuclide 10be exposure ages n 10 of boulders on moraines and lake shorelines there are five prominent moraine belts in the lago san martin valley associated with extensive sandar glaciofluvial outwash plains and former lake shorelines cosmogenic nuclide exposure ages for boulders on these moraines indicate that they formed at 14 3 1 7 ka 22 4 2 3 ka 34 4 3 4 ka to 37 6 3 4 ka and possibly 60 3 5 ka and 99 11 ka 1 these dated glacier advances differ from published chronologies from the lago san martin valley based on 14c age determinations from organic sediments and molluscs in meltwater channels directly in front of moraines or in kettleholes within end moraine ridges the moraine boulder ages also point to possible pre lgm glacial advances during the last glacial cycle and a key observation from our data is that the lgm glaciers were probably less extensive in the lago san martin valley than previously thought

characterization of organic matter in the fine grained siliciclastic sediments of the shemshak group upper triassic middle jurassic in the alborz range northern iran

early and mid holocene age for the tempanos moraines laguna san rafael patagonian chile data about the nature and timing of holocene events from the southern hemisphere especially in southern south america are required to provide insight into the extent and nature of past climate change in a region where land based records are restricted here we present the first use of single grain optically stimulated luminescence osl dating of a moraine sequence recording glacial advance along the western side of the patagonian icefields dates from the tempanos moraines at laguna san rafael lsr show that the san rafael glacier srg advanced to maximum holocene positions during the period 9 3 to 9 7 ka and at 5 7 ka outwash lying beneath the moraine in its northern portion dated to 7 7 ka indicates that the glacier front was also advanced at this time since these advances span both the regional early holocene warm dry phase 11 5 ka to 7 8 ka and the subsequent cooling and rise in precipitation in the mid late holocene since 6 6 ka we infer that the advances of the srg are not simply climate driven but that the glacier has also probably responded strongly to non climatic stimuli such as internal ice dynamics and the transition between calving and non calving many westwards flowing glaciers in patagonia were probably calving during much of the late pleistocene and holocene so we conclude that establishing robust glacial chronologies where climatic and non climatic factors cannot be distinguished is likely to remain a challenge

diagenetic history of eocene wilcox sandstones south central texas abstract sandstones and shales of the lower eocene wilcox group extend from outcrop to depths greater than 5 km where temperatures exceed 200 c eight authigenic minerals have been identified quartz kaolinite calcite ankerite and albitized plagioclase are volumetrically significant whereas chlorite illite albite overgrowths and dolomite are present only in trace amounts quartz kaolinite and ankerite cements are present over the entire depth range sampled 1528 to 4446 m calcite cement occurs only in sandstones shallower than 3300 m albitized plagioclase is the predominant feldspar in samples deeper than 2600 m whereas detrital potassium feldspar has been completely dissolved out of sandstones deeper than about 3200 m no systematic variations in the chemical composition of calcite with depth no zoning within calcite or ankerite and no compositional differences between pore filling and grain replacing calcite or ankerite were found calcite cements have 87 sr 86 sr ratios generally less than 0 708 whereas ankerite cements are significantly enriched in 87sr the oxygen isotopic composition of carbonate cement ranges between 9 and 14 pdb for calcite and between 8 and 12 for ankerite with no systematic variation with depth calculated 18o values for authigenic quartz and kaolinite range from 22 to 31 smow and from 14 to 17 respectively volumetrically important amounts of authigenic quartz and kaolinite precipitated during early burial before calcite cementation secondary porosity generation or smectite to illite transformation in encasing shales the isotopic composition of strontium in calcite cement shows most of it to be of eocene or older marine carbonate origin ankerite cementation followed the generation of secondary porosity and occurred after the products of organic maturation and shale diagenesis plagioclase albitization or potassium feldspar dissolution significantly affected the sandstone pore water system

depositional and compositional controls on sandstone diagenesis the tetori group middle jurassic early cretaceous central japan abstract the tetori group is a representative middle jurassic to lower cretaceous deposit in the northern central part of honshu japan the tetori group is divided into the kuzuryu itoshiro and akaiwa subgroups with decreasing age it consists mainly of a marine sequence in the lower part kuzuryu subgroup and non marine sequence in the upper part akaiwa subgroup with transitional sequence in the middle part itoshiro subgroup diagenesis of tetori group sandstones comprises compaction cementation and replacement early diagenetic events include mechanical compaction and pore filling cementation of calcite siderite dolomite and formation of kaolinite late diagenesis includes formation of quartz cement and albitization of feldspar and formation of illite chlorite calcite ankerite and pyrite among the diagenetic minerals carbonate forms the major cement in tetori group sandstones calcite of each subgroup is subdivided into two or three types based on cathodoluminescence tetori group sandstones of marine fresh water and mixed depositional environments are characterized by distinct chemical compositions of early diagenetic calcites late diagenesis seems to have been mainly influenced by detrital compositions of the sequence burial temperatures and partially hydrothermal processes especially late diagenetic carbonate and authigenic clay minerals seem to have formed mainly from ions released from clay mineral transformations in the adjacent shales based on the illite crystallinity ic the kuzuryu subgroup exhibits higher diagenetic grades than the overlying itoshiro and akaiwa subgroups indicating that the diagenesis of the tetori group was mainly affected by depth of burial

variations in sediment yield over the advance and retreat of a calving glacier laguna san rafael north patagonian icefield abstract bathymetric and sub bottom acoustic data were collected in laguna san rafael chile to determine sediment yields during the little ice age advance and subsequent retreat of san rafael glacier the sediment volumes and subaqueous landforms imaged are used to interpret the proglacial dynamics and estimate erosion rates from a temperate tidewater glacier over a complete advance retreat cycle sediment yields from san rafael glacier averaged 2 7 107 m3 a since the end of the little ice age circa ad 1898 corresponding to average basin wide erosion rates of 23 9 mm a the highest erosion rates 68 23 mm a occurred at the start of the retreat phase and have since been steadily decreasing erosion rates were much lower during glacial advance averaging at most 7 mm a than during retreat such large glacial sediment yields over two centuries of advance and retreat suggest that the contribution of sediments stored subglacially cannot account for much of the sediment being delivered to the terminus today the detailed sub bottom information of a proglacial lagoon yields important clues as to the timing of erosion deposition and transfer of glacigenic sediments from orogens to the continental shelves and the influence of glacier dynamics on this process

characteristics of tide water calving at glaciar san rafael chile glacial calving is a poorly understood process this study tests the influence of local environmental variables on the magnitude and frequency distributions of calving behaviour at glaciar san rafael chile near the terminus of the glacier surface speeds average 17 m d 1 in summer and calving is profuse and continual the size location and characteristics of over 7000 calving events were recorded during 32 d in 1991 and 1992 together with meteorological bathymetric and oceanographic data mean daily calving exceeds 400 events per day and the mean calving flux is more than 2 mm 3 d 1 mean annual calving speed and calving flux are about 4500 m a 1 and 2 0 km 3 a 1 respectively this calving speed is higher than that predicted by the established empirical relationship between tide water calving speed and water depth this is surprising given the low salinity of laguna san rafael and that fresh water calving speeds are commonly much lower than those in tide water daily patterns of calving frequency and flux correlate poorly or not at all with meteorological variables but tidal stage may have some control over the timing of large submarine calving events submarine calving produced the largest bergs however the relatively small total flux recorded from the submerged part of the ice cliff may imply unusually rapid melt rates

diagenesis and pore water evolution in permian sandstones gharif formation sultanate of oman abstract shallow marine coastal plain and fluvial sediments of the lower permian gharif formation in the interior oman sedimentary basin presently range in depth from outcrop in the huqf haushi area to almost 5000 m in the northwest this large depth range results from a varied subsidence history with only minor uplift during the late triassic to early jurassic the degree of diagenetic overprint varies depending on burial history sandstone at shallow depth 2600 m is highly compacted and tightly cemented by quartz carbonate and sulfate minerals this varied diagenesis is caused by increasing temperature with burial by surface water infiltration during the late triassic to early jurassic basin inversion and uplift in the late cretaceous along the southeastern basin margin and obduction of the oman mountains in the late cretaceous depositional pore water was initially of low salinity 50 g l with 18osmow values of 0 5 to 1 5o oo in the marine lower gharif and 2o oo in the arid middle and upper gharif during shallow burial late triassic to early jurassic pore water in the three gharif members changed to high salinity brines 180 g l with 18osmow values of 4 to 7o oo highly saline deep burial pore water with a heavy 18o signature 0 5 5o oo is the result of rock water interactions in a rock dominated system present pore water compositions mainly reflect subsurface dissolution of ara group evaporites precipitation of late diagenetic carbonates and sulfates and recharge of surface water along the uplifted southeastern basin margin

oblique to orthogonal convergence across the turan block in the post miocene the 2 17 km thick post triassic sediments of the turan continental block accumulated in a south dipping basin characterized by fault controlled facies and thickness variations since the late miocene the thickest part of the basin fill on the southern margin of the turan block has been folded and uplifted as the kopet dag range in response to the iran turan convergence the apsheron sill which separates the northern continental from the southern oceanic caspian sea basins links the kopet dag greater balkan ranges turkmenistan to the caucasus azerbaijan the large scale east west to west northwest east southeast oriented arrays of periclinal folds of the kopet dag range which indicate a north south oriented compression were generated by a fault propagation mechanism the migration and accumulation of hydrocarbons has been controlled by the deformation pattern the 75 km of north south shortening in the western kopet dag greater balkan area can be resolved into 70 km of pure compression orthogonal to the n120 oriented ashgabat fault and 35 km of dextral slip along this fault the north south iran asia relative motion has produced the oblique convergent northwest southeast structures along the dextral ashgabat fault and the pure convergent east west structures in the western kopet dag greater balkan region the orientation of the structures has been controlled by the angular relationship between the relative motion of two blocks and the orientation of their boundaries the ashgabat fault as a major crustal anisotropy has concentrated the deformation into a narrow fold and thrust belt whereas in the west the deformation is distributed over a wider area the pattern of deformation has been controlled by the iran turan boundary conditions

quartz cementation and related sedimentary architecture of the triassic solling formation reinhardswald basin germany abstract the olenekian solling formation of the reinhardswald basin was studied with the aim to examine the dependency of the degree of silica diagenesis on the sedimentary architecture the solling formation is composed of stacked sandstone clay siltstone cycles deposited by braided i e subarkoses and meandering i e subarkosic wackes river systems the sand dominated braided rivers of the lower solling formation are characterized by channels and downstream accretion whereas mixed load meandering rivers of the upper solling formation are represented by lateral accretion and laminated sands diagenetic processes which modified the sandstone siltstone successions include compaction feldspar alteration and cementation sandy clay poor successions are highly quartz cemented i e silica importers whereas clay and mica rich successions are more compacted i e silica balanced or silica exporters three quartz cement generations with a total volume of up to 18 indicate that silica from several different sources cemented the sandy fluvial architectural elements of the lower solling formation cementation includes silica supply from internal and external to the sandstone layers which are silica from grain margin dissolution from feldspar alteration silica released from clay siltstones and silica precipitated from basinal brines this cementation history is supported by cathodoluminescence observations and fluid inclusion studies and a consistent burial history was successfully modeled by simulation of the thermal subsidence in contrast to the lower solling formation the fluvial architectural elements of the mixed load systems of the upper solling formation contain only one quartz cementation phase with a total volume up to 8 the reinhardswald basin shows a dependency of the fluvial architecture and the diagenetic features for that we define the term diagenetic architecture

coastline changes nearby harbour structures comparative analysis of one line models versus field data abstract the coastline changes at wladyslawowo harbour in poland characterised by distinct longshore sediment transport were analysed using available field data the computations of shoreline evolution were made using four models genesis litpack unibest and ibw pan software called sand94 the model results for shoreline changes were compared with respective field data the comparison of the models results versus measurements and inter comparisons of the models were the main objectives of the study an attempt was also made to assess the models with respect to user friendliness sensitivity and efficiency

petrographic and isotope constraints on the origin of authigenic carbonate minerals and the associated fluid evolution in late permian coal measures bowen basin queensland australia authigenic carbonate minerals are ubiquitous throughout the late permian coal measures of the bowen basin queensland australia in the northern bowen basin carbonates include the following assemblages siderite i delta o 18 smow 11 4 to 17 delta c 13 pdb 5 3 to 120 fe mg calcite ankerite siderite ii mineral association delta o 18 smow 7 2 to 10 20 delta c 13 pdb 10 9 to 1 80 for ankerite and a later calcite delta o 18 smow 5 9 to 14 60 delta c 13 pdb 11 4 to 4 40 in the southern bowen basin the carbonate phase consists only of calcite delta o 18 smow 12 5 to 14 80 delta c 13 pdb 19 4 to 0 80 where it occurs extensively throughout all stratigraphic levels siderite i occurs in mudrocks and sandstones and predates all other carbonate minerals this carbonate phase is interpreted to have formed as an early diagenetic mineral from meteoric waters under cold climate and reducing conditions fe mg calcite ankerite siderite il occur in sandstones as replacement of volcanic rock fragments clay minerals illite smectite chlorite and kaolinite postdate ca fe mg carbonates and precipitation of the later calcite is associated with clay mineral formation the ca fe mg carbonates and later calcite of the northern bowen basin are regarded as having formed as a result of hydrothermal activity during the latest triassic extensional tectonic event which affected this part of the basin rather than deep burial diagenesis during the middle to late triassic as previously reported this hypothesis is based on the timing relationships of the authigenic mineral phases and the low delta o 18 values of ankerite and calcite together with radiometric dating of illitic clays and recently published regional geological evidence following the precipitation of the ca fe mg carbonates from strongly o 18 depleted meteoric hydrothermal fluids continuing fluid circulation and water rock interaction resulted in dissolution of these carbonate phases as well as labile fragments of volcaniclastic rocks subsequently the later calcite and day minerals precipitated from relatively evolved o 18 enriched fluids the nearly uniform delta o 18 values of the southern bowen basin calcite have been attributed to very low water rock ratio in the system where the fluid isotropic composition was buffered by the delta o 18 values of rocks c 2000 elsevier science b v all rights reserved

sedimentary environment and diagenesis of the lower cretaceous chaswood formation southeastern canada the origin of kaolin rich mudstones abstract the lower cretaceous fluvial sandstone mudstone succession of the chaswood formation is the proximal equivalent of offshore deltaic rocks of the scotian basin that are reservoirs for producing gas fields this study interprets the mineralogical consequences of cretaceous weathering and early diagenesis in a 130 m core from the chaswood formation in order to better understand detrital and diagenetic minerals in equivalent rocks offshore mineralogy was determined by x ray diffraction electron microprobe analysis and scanning electron microscopy the rocks can be divided into five facies associations light gray mudstone dark gray mudstone silty mudstone and muddy sandstone sorted sandstone and conglomerate and paleosols facies transitions in coarser facies are related to deposition in and near fluvial channels in the mudstones they indicate an evolutionary progression from the dark gray mudstone facies association swamps and floodplain soils to mottled paleosols well drained oxisols and ultisols following syntectonic uplift facies transitions and regional distribution indicate that the light gray mudstone facies association formed from early diagenetic oxidation and alteration of the dark gray mudstone facies association probably by meteoric water principal minerals in mudstones are illite muscovite kaolinite vermiculite and quartz illite muscovite is of detrital origin but variations in abundance show that it has altered to kaolinite in the light gray mudstone facies association and in oxisols vermiculite developed from the weathering of biotite and is present in ultisols the earliest phase of sandstone cementation in reducing conditions in swamps and ponds produced siderite nodules and framboidal pyrite which were corroded and oxidized during subsequent development of paleosols kaolinite is an early cement coating quartz grains and as well crystallized pore filling booklets that was probably synchronous with the formation of the light gray mudstone facies association later illite and barite cement indicate a source of abundant k and ba from formation water this late diagenesis of sandstone took place when the chaswood formation was in continuity with the main scotian basin prior to oligocene uplift of the eastern scotian shelf findings of this study are applicable to other mid latitude cretaceous weathering and early diagenetic environments

oligocene uplift of the western greater caucasus an effect of initial arabia eurasia collision the greater caucasus is europe s largest mountain belt significant uncertainties remain over the evolution of the range largely due to a lack of primary field data this work demonstrates that depositional systems within the oligocene early miocene maykop series on either side of the western greater caucasus wgc display a similar provenance and divergent palaeocurrents away from the range constraining a minimum age for the subaerial uplift of the range as early early oligocene an eocene oligocene hiatus basal oligocene olistostromes and a marked increase in nannofossil reworking also point to initial deformation in the earliest oligocene the initial uplift of the wgc occurred during the final assembly of the tethysides to its south uplift commenced after the late eocene final suturing of northern neotethys and during the initial collision of arabia with the southern accreted margin of eurasia this suggests that compressional deformation was rapidly transferred across the collision zone from the indenting arabian plate to its northern margin

diagenesis of eolian and fluvial feldspathic sandstones norphlet formation upper jurassic rankin county mississippi and mobile county alabama norphlet sandstones in seven cores from mississippi and alabama are arkoses and subarkoses deposited in eolian dune interdune and fluvial environments similar to the deeply buried 5 km tertiary feldspathic sandstones of the gulf basin all detrital plagioclase that survived dissolution has been albitized however some k feldspar instead of dissolving was stabilized by k rich brines derived from adjacent evaporites this k feldspar then developed extensive overgrowths fluvial red sandstone lost all initial porosity by the introduction of preburial pedogenic calcite and compaction initial porosity of eolian sands was reduced by compaction to an average of 29 and later by cementation by quartz carbonates anhydrite halite k feldspar and illite quartz and anhydrite cements precipitated between 90 and 100 c approximately 2 3 km deep carbonates and halite cements formed below 120 c 3 km and late stage illite cement formed between 130 and 150 c 4 5 km deep cements are patchy and some especially quartz and anhydrite are texture selective being more abundant in coarser laminae secondary porosity which makes up approximately half the porosity in thin sections formed by dissolution of detrital grains f ldspar rock fragments and cements anhydrite carbonate halite reservoir bitumen records an early phase of oil entrapment reservoir quality is influenced by the abundance of reservoir bitumen and thread like illite both of which bridge pores the radiometric age of illite approximately 55 ma probably reflects its cementation age but may also record a later recrystallization event depleted oxygen and carbon isotopic values for ferroan dolomite reflect the progressive replacement of earlier more enriched carbonate phases by higher temperature phases isotopic data suggest that during the first 30 to 40 m y of burial subsurface diagenesis of the norphlet formation was dominated by deep circulating hot meteoric water this phenomenon may be characteristic of the early diagene ic history of rifted basins

geohistory analysis and petroleum reservoir characteristics of lower cretaceous neocomian sandstones eastern kopet dagh basin northeastern iran the eastern part of the kopet dagh basin of northeastern iran contains over 4000 m of upper jurassic through tertiary strata deposited in a variety of shallow marine and terrestrial environments geohistory diagrams from well and outcrop data provide a useful mechanism with which to relate the stratigraphic framework of this part of the basin to the tectonic history of the region during some episodes of regional tectonic uplift e g episodes occurring 99 95 ma 74 70 ma and 63 54 ma sediment accommodation space continued to be created in the basin due to sediment loading and compaction of increased amounts of fine grained sediments in some cases concomitant with eustatic sea level rises much of the post jurassic subsidence in this part of the kopet dagh basin was aused by sediment loading rather than tectonism the effects of basin geohistory on petroleum reservoir properties were studied using the lower cretaceous neocomian shurijeh formation as an example detailed petrologic sedimentologic and geohistory analyses done on this formation show that the petroleum reservoir properties of shurijeh sandstones were affected by their depositional settings and the subsequent subsidence of these units through meteoric and compactional hydrogeologic regimes in this part of the kopet dagh basin these rocks consist mostly of sublitharenitic red beds deposited during a regressive phase of sedimentation dominated by rapid siliciclastic sediment supply the lower and middle parts of the interval studied were deposited in low sinuosity braided fluvial systems and the upper part was deposited in high inuosity meandering systems by relating the paragenetic sequence of the shurijeh sandstones to the geohistory of this formation we determined the timing of both porosity destroying and porosity enhancing diagenetic processes and related these processes to the timing of petroleum generation

climatic depositional and burial controls on diagenesis of appalachian carboniferous sandstones qualitative and quantitative methods abstract carboniferous quartz lithic and feldspar rich sandstones from different stratigraphic intervals within the central appalachian basin contain evidence for eogenetic and mesogenetic diagenesis important eogenetic products include fe oxide oxyhydroxide siderite kaolinite chlorite and calcite whereas quartz albite illite sericite fe carbonate and secondary porosity are the most important mesogenetic components correspondence and detrended correspondence analysis of the framework grain and diagenetic mineral data set has guided diagenetic interpretations and leads to two major conclusions first minerals that formed early appear to have been influenced by stratigraphic position the distribution of siderite and iron oxide oxyhydroxide is considered to reflect a second order paleoclimatic signature recognized throughout the carboniferous where siderite formed during everwet periods and iron oxide oxyhydroxide during semi arid conditions reflecting differences in redox second framework grain composition controlled the distribution of diagenetic products in the burial environment lithic arenites are deficient in authigenic quartz yet have undergone various degrees of illitization quartz deficiency is attributed to compaction related loss of primary porosity relatively early which inhibited sufficient fluid flow to account for much higher concentrations of quartz cement in the more competent quartz rich sandstones

diagenesis and reservoir potential of permian triassic fluvial lacustrine sandstones in the southern junggar basin northwestern china the junggar basin is one of the largest oil producing areas in china and contains upper permian lacustrine oil shales with some of the greatest hydrocarbon potental in the world in this study we present the diagenetic characteristics of permian triassic sandstones from the southern junggar basin and evaluate their reservoir potential the uppermost permian and lower triassic cangfanggou group in the southern junggar basin is characterized by alternating fluvial and lacustrine deposits whereas the middle upper triassic xiaoquangou group was deposited predominantly in a lacustrine environment fluvial and deltaic sedimentation was subordinate the sandstones of the cangfanggou and xiaoquangou groups are volcanic litharenites their detrital modes and textures of volcanic fragments suggest a primarily andesitic basaltic volcanic arc provenance early diagenesis of the sandstones is characterized by nonferroan calcite cementation grain coating pore lining clay minerals and the initial dissolution of detrital grains authigenic quartz pore filling phyllosilicates pore filling grain replacive zeolites albitized detrital plagioclase authigenic k feldspar copyright 1997 the american association of petroleum geologists all rights reserved 1manuscript received april 15 1996 revised manuscript received november 4 1996 final acceptance may 2 1997 2department of earth sciences university of western ontario london ontario n6a 5b7 canada 3school of geosciences queen s university of belfast belfast bt7 1nn united kingdom this work was done at the queen s university of belfast with funding from exxon bhp mobil and itotal which we gratefully acknowledge the karamay institute of petroleum exploration and development generously provided borehole samples geng ansong at the institute of geochemistry guangzhou academia sinica and zhou yisheng at the xinjiang institute of petroleum are thanked for assistance with field work and for valuable discussions special thanks go to the staff of the electron microscopy unit at the queen s university of belfast we also thank a h ruffell and s r lawrence for their constructive comments on an earlier version of the manuscript stable isotope analysis and ongoing research concerning the junggar basin at the university of western ontario have been supported by the natural science and engineering research council of canada the manuscript benefited substantially from critical commentary by kevin t biddle suzanne kairo w r kaiser and an anonymous reviewer

glaciar leon chilean patagonia late holocene chronology and geomorphology harrison s glasser n f winchester v haresign e warren c duller g a t bailey r ivy ochs s jansson k kubik p 2008 glaciar leon chilean patagonia late holocene chronology and geomorphology the holocene 18 4 pp 643 652 sponsorship nerc university of st andrews american alpine club british geomorphological research group dudley stamp memorial trust royal scottish geographical society quaternary research association carnegie trust for the universities of scotland

fluctuations of outlet and valley glaciers in the southern andes argentina during the past 13 000 years abstract in the southern argentine andes ten advances of valley glaciers were used to reconstruct the late glacial and holocene glacier history the accumulation areas of these glaciers lie in the precordillera and are thus independent of fluctuations of the south patagonian icefield like the viedma outlet glacier the valley glaciers advanced three times during late glacial time 14 000 10 000 yr b p the youngest advance correlates with the younger dryas stade based on two minimum ams 14 c dates of 9588 and 9482 yr b p the second oldest advance occurred before 11 800 yr b p during the first half of the holocene ca 10 000 5000 yr b p advances culminated about 8500 8000 7500 and 5800 5500 yr b p during the second half of the holocene advances occurred between ca 4500 and 4200 yr b p as well as between 3600 and 3300 yr b p in the rio condor valley three subsequent advances have been identified