fluid inclusion studies of regionally extensive epigenetic dolomites bonneterre dolomite cambrian southeast missouri evidence of multiple fluids during dolomitization and lead zinc mineralization sources of basinal fluids that precipitated the dolomite hosted mississippi valley type orebodies of southeast missouri historically have been a subject of debate this study presents microthermometric data for fluid inclusions in the regionally extensive epigenetic dolomite at the base of the ore hosting bonneterre dolomite and in gangue dolomite of the viburnum trend pb zn district samples of epigenetic dolomite cover an area of more than 25 000 km 2 west of the st francois mountains and permit determination of regional variations of temperature and composition of the mineralizing fluids and possible fluid interactions homogenization temperature ice melting relationships temperature salinity among these inclusions document at least two end member fluid components a warmer less saline fluid 120 to 187 c 5 wt equiv nacl and a cooler more saline fluid 60 to 80 c 30 wt equiv nacl intermediate temperatures and fluid compositions indicate that the end member fluids likely mixed as they flowed through the region mixing was not confined to a stationary front but occurred throughout the study area comparison of homogenization temperatures to distance from possible basinal fluid sources indicates no discernible temperature gradient over the 25 000 km 2 study area the data are interpreted to indicate multiple basinal fluid interactions coeval with dolomitization and associated pb zn ore formation

seismic stratigraphy of waterton lake a sediment starved glaciated basin in the rocky mountains of alberta canada and montana usa abstract upper and middle waterton lakes fill a glacially scoured bedrock basin in a large 614 km2 watershed in the eastern front ranges of the rocky mountains of southern alberta canada and northern montana u s a the stratigraphic infill of the lake has been imaged with 123 km of single channel fm sonar chirp reflection profiles offshore sonar data are combined with more than 2 5 km of multi channel land based seismic reflection profiles collected from a large fan delta three seismic stratigraphic successions sss i to iii are identified in waterton lake resting on a prominent basal reflector bedrock that reaches a maximum depth of about 250 m below lake level high standing rock steps reigels divide the lake into sub basins that can be mapped using lake floor reflection coefficients a lowermost transparent to poorly stratified seismic succession sss i up to 30 m thick is present locally between bedrock highs and has high seismic velocities 1750 2100 m s typical of compact till or outwash a second stratigraphic succession sss ii up to 50 m thick occurs throughout the lake basin and is characterised by continuous closely spaced reflectors typical of repetitively bedded and rhythmically laminated silts and clays most likely deposited by underflows from fan deltas paleo depositional surfaces identify likely source areas during deglaciation intervals of acoustically transparent seismic facies up to 5 m thick are present within sss ii at the northern end of upper waterton lake sss ii has a hummocky surface underlain by collapse structures and chaotic facies recording the melt of buried ice sediment collapse may have triggered downslope mass flows and may account for massive facies in sss ii a thin holocene succession sss iii

seismic stratigraphy of shuswap lake british columbia canada abstract shuswap lake is a glacially overdeepened fiord lake located in the shuswap highlands of southern british columbia canada and consists of two sub basins each nearly 60 km long and up to 3 km wide single channel seismic reflection data collected along 218 km of track line identifies a tripartite infill stratigraphy up to 800 m thick preserved in bedrock basins eroded as much as 298 m below sea level a similar tripartite stratigraphy is exposed in nearby outcrops along the valley of the south thompson river and allows interpretation of age and depositional settings for the infill identified on seismic records in shuswap lake the lowermost seismic stratigraphic sequence sssi up to 407 m thick shows chaotic seismic facies with large scale diffractions and fills axial parts of v shaped bedrock basins outcrop data suggest that this sequence consists of subaqueously deposited ice contact silts sands and gravels deposited in a deep 1 km ice frontal lake during late wisconsin deglaciation ca 10 ka the overlying seismic stratigraphic sequence sssii up to 403 m thick shows continuous high frequency seismic facies that pass down basin into transparent reflection free facies high frequency facies are interpreted as rhythmically deposited silts and sands deposited by underflows varves such facies are well exposed along the south thompson river valley transparent distal facies likely record uninterrupted settling from suspended sediment transported down basin by interflow or overflow plumes and similar deposits are reported as currently forming in nearby kamloops lake a relatively thin deposition of very thick late glacial stratigraphic successions and an absence of older pre late wisconsin strata appears to be a characteristic shared by other narrow glacially overdeepened valleys and basins in central british columbia this may be the result of scour by subglacial meltwaters and sediment focussing during deglaciation of fiord like valleys occupied by deep ice frontal lakes and rapidly retreating ice margins

late quaternary evolution of a subantarctic paleofjord tierra del fuego lago roca lapataia valley 54 50 s 68 34 w is a paleofjord that was occupied by a valley glacier system during the glacial maximum of the late pleistocene estimated ca 18 20 ka bp deglaciation began before 10 080 270 bp the marine fauna in several marine terraces found in the area shows that early middle holocene climatic conditions were basically the same as at present species found are characteristic of cold and shallow waters although minor temperature fluctuations cannot be ruled out for this period a recent radiocarbon date of 7518 58 bp on chlamys patagonica nz 7730 confirms that lago roca was transformed into a fjord ca 7500 8000 bp the sea reached its maximum level of 8 10 m a s l around 6000 bp and at 4000 4500 bp was at least above 6 1 m a s l later when sea level fell lago roca was occupied by fresh water and was no longer tidal the relative land sea positions during this period are a consequence of combined eustatic and neotectonic processes

late quaternary vegetation and climate of southern tierra del fuego vegetation and climate over approximately the past 13 000 yr are reconstructed from fossil pollen in a 9 4 m mire section at caleta robalo on beagle channel isla navarino 54 56 s 67 38 w southern tierra del fuego fifty surface samples reflecting modern pollen dispersal serve to interpret the record chronologically controlled by nine radiocarbon dates fossil pollen assemblages are empetrum gramineae gunnera tubuliflorae zone 3b 13 000 11 850 yr b p gramineae empetrum assorted minor taxa zone 3a 11 850 10 000 yr b p nothofagus gramineae tubuliflorae polypodiaceae zone 2 10 000 5000 yr b p nothofagus empetrum zone 1b 5000 3000 yr b p and empetrum nothofagus zone 1a 3000 0 yr b p assemblages show tundra under a cold dry climate zone 3 followed by open woodland zone 2 as conditions became warmer and less dry and later with greater humidity and lower temperatures by closed forest and the spread of mires zone 1 comparisons drawn with records from antarctica new zealand tasmania and the subantarctic islands demonstrate broadly uniform conditions in the circumpolar southern hemisphere the influences of continental and maritime antarctic air masses were apparently considerable in tierra del fuego during cold late glacial time whereas holocene climate was largely regulated by interplay between maritime polar and maritime tropical air

regional dolomitization of the waulsortian limestone in southeastern ireland evidence of large scale fluid flow driven by the hercynian orogeny the lower carboniferous waulsortian limestone has been affected by late diagenetic regional burial dolomitization over an area of 7000 km 2 extending 170 km northeastward from the hercynian front the dolostone is composed of two components 1 a very fine crystalline replacive component and 2 a coarse crystalline baroque component that fills vuggy porosity developed within the replacive dolostone fluid inclusions within the coarse crystalline component of the regional dolostone indicate that the dolomitizing solutions were warm 100 c and moderately saline 10 13 wt nacl equivalent the replacive dolomite displays systematic decreases in crystal size and degree of xenotopic texture northward both components of the regional dolostone display a regular northward increase in mean 18 o values the replacive dolomite has 87 sr 86 sr values that decrease northward these laterally variable characteristics suggest that regional dolomitization resulted from large scale north directed fluid flow of heated brines developed in response to topographic uplift associated with collapse of the continental margin south of ireland during the hercynian variscan orogeny

impact of the 1960 major subduction earthquake in northern patagonia chile argentina abstract the recent sedimentation processes in four contrasting lacustrine and marine basins of northern patagonia are documented by high resolution seismic reflection profiling and short cores at selected sites in deep lacustrine basins the regional correlation of the cores is provided by the combination of 137cs dating in lakes puyehue chile and frias argentina and by the identification of cordon caulle 1921 22 and 1960 tephras in lakes puyehue and nahuel huapi argentina and in their catchment areas this event stratigraphy allows correlation of the formation of striking sedimentary events in these basins with the consequences of the may june 1960 earthquakes and the induced cordon caulle eruption along the liquine ofqui fault zone lofz in the andes while this catastrophe induced a major hyperpycnal flood deposit of ca 3 106 m3 in the proximal basin of lago puyehue it only triggered an unusual organic rich layer in the proximal basin of lago frias as well as destructive waves and a large sub aqueous slide in the distal basin of lago nahuel huapi a very recent mega turbidite in the two distal basins of reloncavi fjord located close to the lofz suggests that 1960 co seismic movements in this area may have triggered the remobilization of ca 187 106 m3 of marine sediments

detailed seismic stratigraphy of lago puyehue implications for the mode and timing of glacier retreat in the chilean lake district lago puyehue is a glacigenic lake in the chilean lake district 40 s with a complex deglaciation history a detailed seismic stratigraphic study of its sedimentary infill indicates a much earlier retreat of the glacier from the lago puyehue basin than the neighbouring glacier from the lago rupanco basin because of their close proximity rupanco meltwater streams played an important part in the depositional processes of lago puyehue a timing discrepancy between the in lake ages of a sediment core and the outer lake ages of moraine deposits re opens the discussion on the timing of deglaciation in the southern hemisphere copyright 2011 john wiley sons ltd

prehistoric earthquake history revealed by lacustrine slump deposits five strong paleoseismic events were recorded in the past 15 k y in a series of slump deposits in the subsurface of lake lucerne central switzerland revealing for the first time the paleoseismic history of one of the most seismically active areas in central europe although many slump deposits in marine and lacustrine environments were previously attributed to historic earthquakes the lack of detailed three dimensional stratigraphic correlation in combination with accurate dating hampered the use of multiple slump deposits as paleoseismic indicators this study investigated the fingerprint of the well described a d 1601 earthquake i vii viii mw 6 2 in the sediments of lake lucerne the earthquake triggered numerous synchronous slumps and megaturbidites within different subbasins of the lake producing a characteristic pattern that can be used to assign a seismic triggering mechanism to prehistoric slump events for each seismic event horizon the slump synchronicity was established by seismic stratigraphic correlation between individual slump deposits through a quasi three dimensional high resolution seismic survey grid four prehistoric events dated by accelerator mass spectrometry 14c measurements and tephrochronology on a series of long gravity cores occurred at 2420 9770 13 910 and 14 560 calendar yr ago these recurrence times are essential factors for assessing seismic hazard in the area the seismic hazard for lakeshore communities is additionally amplified by slump induced tsunami and seiche waves numerical modeling of such tsunami waves revealed wave heights to 3 m indicating tsunami risk in lacustrine environments

the sedimentary record of glacial retreat marinelli fjord patagonia regional correlations and climate ties abstract the inland passage of chile comprises the most continuous latitudinal transect of ice fields ice caps and alpine glaciers in the southern hemisphere providing an excellent natural laboratory for the study of glacial response to climate change during the holocene here we report results from a marine geological investigation of marinelli fjord tierra del fuego 54 25 s 69 35 w and ainsworth fjord which merges with marinelli fjord data acquired during july 2005 onboard the rv ib nathaniel b palmer include high resolution seismic data multibeam swath bathymetry data and sediment cores post cruise analyses include detailed seismic facies and lithofacies analysis and radiocarbon dating the results indicate that a major transition in the glacimarine record from ice proximal facies to ice distal facies occurred in the outer basins of the fjord at 15 5 kyr to 12 5 kyr the ice proximal facies consists of pebbly mud with abundant laminations and is characterized by high average sedimentation rates 28 mm yr in contrast an ice distal facies is dominantly bioturbated mud with low average sedimentation rates 0 56 mm yr this transition marks the retreat of marinelli glacier from the outer basins with no evidence for glacial re advance subsequently during the mid to late holocene ainsworth glacier retreated and exposed ainsworth fjord our results are consistent with the climatic trends for southern south america where the final deglaciation of the region ended at 12 5 ka during the holocene stable ice conditions persisted until the mid 1960s when marinelli glacier began rapidly retreating to its modern day position

dolomitization of the waulsortian limestone lower carboniferous in the irish midlands the waulsortian limestone lower carboniferous of the southern irish midlands is dolomitized pervasively over a much larger region than previous studies have documented this study indicates a complex multistage multiple fluid history for regional dolomitization partially and completely dolomitized sections of waulsortian limestones are characterized by finely crystalline 0 01 0 3 mm planar dolomite planar replacive dolomite is commonly followed by coarse 0 5 mm nonplanar replacive dolomite and pervasive void filling saddle dolomite cement is frequently associated with zn pb mineralization planar dolomite has average 18o and 13c values pdb of 4 8 and 3 9 respectively these are lower oxygen and slightly higher carbon isotope values than averages for marine limestones in the waulsortian 18o 2 2 13c 3 7 mean c and o isotope values of planar replacive dolomite are also distinct from those of nonplanar and saddle dolomite cement 7 0 and 3 3 7 4 and 2 4 respectively fluid inclusions indicate a complex history involving at least three chemically and thermally distinct fluids during dolomite cementation the petrography and geochemistry of planar dolomites are consistent with an early diagenetic origin possibly in equilibrium with modified carboniferous sea water where the waulsortian was exposed to hydrothermal fluids 70 280 c planar dolomite underwent a neomorphic recrystallization to a coarser crystalline planar and nonplanar dolomite characterized by lower 18o values void filling dolomite cement is isotopically similar to nonplanar replacive dolomite and reflects a similar origin from hydrothermal fluids this history of multiple stages of dolomitization is significantly more complex than earlier models proposed for the irish midlands and provides a framework upon which to test competing models of regional vs localized fluid flow

palaeoenvironmental conditions during the early peopling of southernmost south america late glacial early holocene 14 8 ka b p abstract environmental conditions in southernmost south america the patagonian andes and the extra andean plains during the early peopling of the region in late glacial early holocene times are herein described different glacial advances or stabilization phases in valley glaciers occurred several millennia after the last glacial maximum lgm as a consequence of regional cold climatic episodes according to clapperton 1993 two advances during the late glacial took place ca 15 14 14 c ka and 12 10 14 c ka b p a cold event during this last period probably correlative with the younger dryas episode in the northern hemisphere has been observed in the palynological record a tundra environment dominated until ca 13 10 14 c ka b p afterwards a gramineous steppe with forest refuges developed the transition steppe forest lasted to the middle holocene when the nothofagus forest took over the arrival of man in southernmost south america ca 13 14 c ka b p or even before probably took place while glaciers were still present in most andean valleys sea level was much lower than today and tundra environments dominated the extra andean plains moreover peopling in the isla grande de tierra del fuego would have occurred not later than 11 8 14 c ka b p when the present magellan straits valley was still occupied by a meltwater discharge braided stream fed by the receding magellan glacier

pine point orebodies and their relationship to the stratigraphy structure dolomitization and karstification of the middle devonian barrier complex mississippi valley type ore field on the south side of great slave lake pine point has produced 58 2 million tons of 3 0 percent pb and 6 7 percent zn with present reserves of 25 7 million tons of 2 7 percent pb and 6 3 percent zn most pine point orebodies were deposited in interconnected paleokarst networks that developed at the lower limits of coarse dolomite alteration of upper barrier limestones karstic structures which exhibit the largest cavity development and consequently the greatest amounts of infilling internal sediments host the best grades of mineralization the following conclusions are suggested the barrier developed due to subtle epeirogenic crustal movements and or eustatic sea level changes affecting normal sedimentary processes deformation of the barrier is possibly due to differential sediment compaction or warping of underlying evaporites coarse dolomitization and paleokarstification metals introduced by chloride rich brines brines expelled by overburden pressures migrated eastward along the barrier and precipitated metals in paleokarst structures upon encountering reduced sulfur species modified journal abstract

cold climatic episode of younger dryas age in tierra del fuego pronounced climatic change during the last glacial maximum is recognized as global in extent and has been attributed to orbital forcing1 not readily explained in a global context because of the equivocal nature of the evidence are the late glacial climatic events of short 100 1 000 yr duration the cold climate of the younger dryas chron 11 000 10 000 yr bp for example is known to have been particularly pronounced over the north atlantic and parts of europe and north america2 3 whereas in the southern hemisphere cold conditions for that time are not well established here we present evidence for late glacial climatic cooling in southernmost south america from studies of radiocarbon dated glacial and pollen stratigraphy at sites along the beagle channel in tierra del fuego where a forest tundra tension zone in the region is especially sensitive to shifting climate we conclude that the cold episode corresponds with the time of the younger dryas in europe when a drop in temperature ascribed most recently to colder sea surface temperatures and production rate of deep water in the north atlantic4 5 apparently occurred worldwide

latest pleistocene and holocene glacier fluctuations in southernmost tierra del fuego argentina abstract some researchers propose that summer insolation controls long term changes in glacier extent during the holocene if this hypothesis is correct the record of glacier fluctuations at high latitudes in the southern hemisphere should differ from that in the northern hemisphere although the chronology of holocene glacier fluctuations in the northern hemisphere is well established much uncertainty remains in the ages of holocene glacier fluctuations in the southern hemisphere especially south america here we report on latest pleistocene and holocene glacier fluctuations at the southern end of the andes north and west of ushuaia argentina surface exposure ages 10 be from glaciated bedrock beyond cirque moraines indicate that alpine areas were free of ice by ca 16 9 ka one and in some cases two closely spaced moraines extend up to 2 km beyond little ice age moraines within many of the cirques in the region the mean age of five 10 be ages from two pre little ice age moraines is 14 27 12 67 ka whereas a minimum limiting radiocarbon age for a smaller recessional moraine in one cirque is 12 38 12 01 ka our ages imply that following glacier retreat beginning about 18 52 17 17 ka cirque glaciers first advanced during the antarctic cold reversal 14 5 12 9 ka and may have later advanced or stabilized in the younger dryas chronozone 12 9 11 7 ka based on the distribution of thick geochemically distinct and well dated hudson tephra no holocene moraines appear to be older than 7 96 7 34 ka at some sites there is evidence for one or more advances of glaciers sometime between 7 96 7 34 ka and 5 29 5 05 ka to limits only tens of meters beyond little ice age maximum positions taken together the data 1 do not support the summer insolation hypothesis to explain holocene glacier fluctuations in southernmost patagonia 2 confirm paleobotanical evidence for a warm dry early holocene and 3 suggest that some glaciers in the region reached extents comparable to those of the little ice age shortly before 5 29 5 05 ka

holocene sea level changes along the strait of magellan and beagle channel southernmost south america abstract radiocarbon dated marine sediments from five coastal sites along the strait of magellan and beagle channel in southernmost chile permit construction of a curve of relative sea level fluctuations during the holocene morphologic and stratigraphic data point to coastal submergence during the early holocene as the sea rose to a maximum level at least 3 5 m higher than present about 5000 yr ago progressive emergence then followed during the late holocene data from widely separated localities define a smooth curve the form of which is explainable in terms of isostatic and hydroisostatic deformation of the crust resulting from changing ice and water loads apparently anomalous data from one site located more than 100 km behind the outer limit of the last glaciation may reflect isostatic response to deglaciation the sea level curve resembles one derived by clark and bloom 1979 in proceedings of the 1978 international symposium on coastal evolution in the quaternary sao paulo brasil pp 41 60 sao paulo using a spherical earth model both in amplitude and in the timing of the maximum submergence

geomorphological evidence of different glacial stages in the martial cirque fuegian andes southernmost south america abstract the geomorphological features of a cirque partially occupied by receding ice bodies are presented as evidences of different glacial stages in the fuegian andes summits since the last glaciation ios 2 a glacierization scheme involving i regional glacier accumulation basin ii glacier individualization from a main regional ii a stillstand during the general retreat and iii two advancing stages are suggested geomorphic and sedimentary units named martial i ii iii and iv have been distinguished as a consequence of the glacial scheme unfortunately the lack of datable materials has impeded establishment of an absolute chronology recognized glacier advances in the region are discussed the palaeoclimatic framework for the surroundings based on previous studies is presented

the origin of a mississippi valley type deposit in the viburnum trend southeast missouri petrologic and isotopic studies of the base metal sulfide mineralization in the buick mine have established the following paragenesis an early stage of fine grained pyrite and marcasite replaced the dolostone host rock the iron disulfides and dolostone were replaced by sphalerite during the main stage of sphalerite precipitation delta 34 s sp 16 5 to 19 0ppm following the sphalerite two main stages of galena were precipitated a cuboctahedral stage delta 34 s gn 21 3 to 10 0ppm during which galena replaced dolostone and sphalerite and grew in vugs in the dolostone and in the sphalerite and a cubic stage delta 34 s gn 10 5 to 0 9ppm the two stages of galena precipitation were separated by a period during which the main stage of sphalerite and the cuboctahedral galena were partially dissolved and bladed marcasite delta 34 s mc 2 3 to 4 1ppm was precipitated and followed by a period of mild etching of the cubic galena minor amounts of pale sphalerite delta 34 s sp 14 0 to 16 5ppm were then precipitated white and colorless rhombs of dolomite were precipitated at the same time as some of the main stage of sphalerite the cubic galena and the pale sphalerite after the pale sphalerite was precipitated chalcopyrite quartz and siegenite were precipitated followed by calcite and finally kaolinite the paragenetic and textural data for both galena and sphalerite in the buick mine strongly suggest that these minerals were precipitated and dissolved repetitively during ore formation similar textural evidence for galena reported by other workers for different mines in the viburnum trend implies that repetitive precipitation and dissolution of galena was probably an important process during the formation of the entire viburnum trend fluid inclusions in late quartz crystals coprecipitated with chalcopyrite have filling and freezing temperatures within the ranges reported for sphalerite from other parts of the viburnum trend demonstrating that the ore forming solutions in the viburnum trend were probably at temperatures in the range 105 degrees to 141 degrees c assuming a maximum pressure correction of about 11 degrees c and were extremely saline containing about 4 0 to 5 0 molal chloride consideration of typical chemical analyses of fluid inclusions from other mississippi valley type deposits suggests that the maximum likely concentration of dissolved co 2 in the ore forming solutions was about 0 05 molal at these concentrations the ore forming solutions that travelled to the site of deposition could have had ph9s about two units less than neutral and still have been in equilibrium with dolomite or calcite the ranges of sulfur and lead isotopic compositions of galena from the buick mine are very similar to those established by earlier studies of the old lead belt and adjacent subdistricts however the correlation of isotopically lighter sulfur with more radiogenic lead is much stronger for the viburnum trend suggesting that galena was precipitated from many solutions each of which carried lead and sulfur together and had different lead and overall sulfur isotopic compositions the textural paragenetic and isotopic data for the buick mine cannot be easily explained either by a sulfate reduction model in which sulfate was reduced by organic matter or methane or mixing models in which base metals and reduced sulfur were transported separately to the site of deposition instead the data strongly support a reduced sulfur model for ore formation according to which the base metals were transported together with reduced sulfur as h 2 s in the same solutions to the sites of deposition the reduced sulfur model is also supported by a theoretical calculation of the solubilities of galena and sphalerite which demonstrate that low but economically significant concentrations of lead or zinc could have been transported as chloride complexes together with equivalent concentrations of reduced sulfur at temperatures of 100 degrees to 150 degrees c and ph9s of one to two units less than neutral and could have been precipitated by ph increases cooling or dilution at the sites of deposition

minor and trace element distributions in the bonneterre dolomite cambrian southeast missouri evidence for possible multiple basin fluid sources and pathways during lead zinc mineralization the sources and flow paths of basinal fluids that precipitated the dolomite hosted mississippi valley type orebodies of southeast missouri have historically been a subject of debate this study presents geochemical data for epigenetic dolomites of the bonneterre dolomite directly above the lamotte sandstone aquifer and from the viburnum trend orebodies samples of epigenetic replacement dolomite were collected at the bonneterre dolomite lamotte sandstone contact from 35 drill cores covering an area of more than 25 000 km 2 west of the st francois mountains there are distinct aerial trends in fe mn and sr contents of the dolomite from values of 3 47 wt 0 38 wt and 27 ppm in the south to 0 82 wt 0 12 wt and 54 ppm in the north respectively in and near the viburnum trend lead zinc subdistrict the distributions of fe mn and sr are reversed from values of 0 50 wt 0 10 wt and 105 ppm in the south to 3 15 wt 0 55 wt and 40 ppm in the north respectively fe and mn contents of gangue dolomite cement in the viburnum trend orebodies show a similar south to north enrichment ranging from 1 41 mole feco 3 and 0 11 mole mnco 3 in the south to 2 34 mole and 0 23 mole in the north respectively on the basis of fractionation of minor and trace elements between fluids and dolomites the data are interpreted to indicate a regional south to north flow of water from the arkoma basin through the lamotte sandstone a second fluid flow system with a northern source possibly the illinois basin precipitated the late phases of gangue dolomite cement in the viburnum trend and may have been active during the earlier precipitation of the dolomite at the lamotte bonneterre contact the inferred fluid flow paths suggest a more complex multiple basin fluid involvement than previously suggested for the mississippi valley type pb zn mineralization of southeast missouri

post last glacial maximum evolution of a fjord type lake based on high resolution seismic data the lago roca acigami southern tierra del fuego argentina chile

bedrock response to llanquihue holocene and present day glaciation in southernmost south america 1 modern geodetic techniques such as precise global positioning system gps measurements and high resolution space gravity mapping make it possible to measure the present day rate of viscoelastic gravitational earth response to present and past glacier mass change patagonia is a rapidly evolving glacial environment over the past decade the local rate of surface stress unloading may be the largest anywhere on the planet we compute the present day land uplift rate that could be observed using bedrock gps measurements the little ice age lia of the past half millennium generates large vertical rates since the underlying mantle material is likely to have anomalously low viscosity owing to late neogene ridge subduction

deglacial paleoclimate of the american sector of the southern ocean late glacial holocene records from the latitude of canal beagle 55 s argentine tierra del fuego abstract paleoclimate at the time of deglaciation 14 000 10 000 14 c yr b p in different sectors of the southern ocean has followed a continuous warming trend but also warming broken by a transitory episode the younger dryas stadial event during which on the order of a millennium colder conditions prevailed evidence is from antarctic ice cores deep sea cores glacier fluctuations and pollen and beetle records reasons for the apparent nonuniformity include differential sensitivity of each sector to climatic change uneven dating control and the variable forcing response nature of biota used as climatic indicators establishing the late glacial paleoclimate of the southern ocean is of significance as it bears on comprehending the character of deglaciation in a global context with the object of investigating further the sequence of deglacial climatic events pollen stratigraphic studies at canal beagle at the southern extremity of south america were extended westward to the vicinity of ushuaia and lapataia supplementing work done previously at caleta robalo puerto harberton and bahia moat at ushuaia pollen frequency and influx records of the late glacial as well as the holocene chronologically controlled by 25 14 c age determinations are from four sphagnum empetrum mires results obtained at sites dating from 12 500 to 12 000 yr b p show late glacial climatic variability most indicative among tundra communities of grass and dwarf shrub heath is a drop both in frequency and influx of the singular arboreal component nothofagus at the time of the younger dryas when estimated summer january temperature was 3 c lower than at present at ushuaia in general terms the late glacial pattern is not unlike the northwestern european sequence sensu walker 1995 which exhibits a late glacial interstadial 13 000 11 000 yr b p followed by a younger dryas stadial 11 000 10 000 yr b p within limits of the chronology in the american sector there is no indication as shown by marine cores from the southern ocean and by antarctic ice cores that deglacial climatic events at higher latitudes of the southern hemisphere exemplified by the younger dryas lead similar events in the northern hemisphere uninterrupted warming evident in the marine and ice cores occurred after 11 600 11 500 yr b p at canal beagle in contrast the trend toward steadily milder climate indicated by continuous expansion of nothofagus frequency followed in the early holocene after 10 000 yr b p early holocene nothofagus woodland containing grass and composites replaced tundra under a warmer and drier set of conditions coupled with burning estimated summer temperature averaged 1 c higher than today and annual precipitation 100 mm less pollen influx remained generally low until about 5000 yr b p when the rate of nothofagus greatly increased together with increase in the rate of empetrum a characteristic mire component the implication is of late holocene spread of both closed forest and mire the result of greater precipitation and lower temperatures while burning abated summer temperatures evidently varied within about 0 5 c and precipitation by 100 mm compared with the present renewed albeit fluctuating glacial activity is recorded after 5000 yr b p under a variable cooler and more humid late holocene climatic regime

holocene raised beaches along the northern coast of the beagle channel tierra del fuego argentina abstract raised beaches developed during holocene times along the northern beagle channel coast these deposits contain a rich marine fauna especially shelled organisms such as mollusks four holocene marine sites along the northern coast of the beagle channel have been analysed from west to east they are bahia ensenada playa larga bahia brown and cutalataca airfield they were studied in relation to relative altitude sediment type faunal composition and radiocarbon dates the area is characterized by several discontinuous terraces with elevations varying from about 1 5 to 10 m above sea level their possible origin 1 due to tectonic uplifting in comparison with raised beaches of the northern part of tierra del fuego and 2 resulting from glacio isostatic recovery taking into account the ice retreat is discussed seventeen species of mollusks eight bivalves nine gastropods were collected from the study sites all of them are living species from the beagle channel and have been interpreted as representative of holocene paleocommunities in this channel these species show no evidence of substantial climatic changes during the holocene although minor temperature fluctuations cannot be ruled out yet

dolomite fronts and associated zinc lead mineralization usa this paper provides previously unpublished drill core and mapping evidence of the spatial relationship between regional dolomitization and mississippi valley type mvt mineralization in the midcontinent of the united states dolomitization is discussed for several key carbonate units and their contained mvt mineralization this more complete picture of the relationship between regional dolomitization and mineralization provides constraints on models for mvt mineralization and serves as an exploration guide for new deposits

na cl br systematics of mineralizing brines in mississippi valley type deposits new and published analyses of fluid inclusion leachates from mississippi valley type mvt deposits can be divided into two groups on the basis of na br and cl br ratios mvt leachates from the illinois kentucky and cincinnati arch districts and from cubic galena in the viburnum trend have na br and cl br ratios that extend to values significantly above that of seawater which are characteristic of evaporite dissolution brines mvt leachates from polaris and octahedral galena in the viburnum trend have na br and cl br ratios that plot below seawater and along the compositional trend formed by evaporation solubility volume constraints require that brines formed by seawater evaporation had high dissolved metal contents preliminary correlation of leachate compositions allows delineation of two brine provinces in the midcontinent united states 1 an early high br province found only in southeastern missouri and 2 a later low br province of probable permian age that extended from the cincinnati arch to the tri state district these observations along with na cl br data for modern brines from the illinois basin argue against models for single stage midcontinent mvt brine flow based on recharge from late paleozoic arkoma foreland basins to the south

middle late holocene palynology and marine mollusks from archipielago cormoranes area beagle channel southern tierra del fuego argentina abstract the palynology and marine mollusks of a marine sequence from rio ovando 54 51 s 68 35 w archipielago cormoranes beagle channel has been studied in order to reconstruct paleoenvironmental conditions during the middle late holocene the dinoflagellate cyst assemblages from rio ovando sequence reflect fjord estuarine environments close to terrestrial ice field affected by glacier meltwater discharge and characterized by short term oscillations of sea surface water parameters the base of the section which is dated at about ca 4160 14 c yr b p 4736 cal yr b p palynological subzone ro 2c is characterized by a high species diversity of dinocyst and mollusks and it is immediately followed by an interval palynological subzone ro 2b characterized by the presence of the echinidinium islandinium complex and the monospecific mytilus mollusk assemblage this subzone registers an inverse correlation between nothofagus dombeyi type and echinidinium islandinium complex concentration values during ca 4160 14 c yr b p 4736 cal yr b p 4064 14 c yr b p 4540 cal yr b p suggesting a variable climatic condition probably related to neoglacial episodes occurred in the southern patagonia andes during this interval the pollen assemblages permit direct correlations with the onshore palynostratigraphy from southern of tierra del fuego the high percentages of nothofagus dombeyi type recorded throughout most of the profile strongly suggest the presence of a closed forest confirming the existence of a variable cool and wet climate for the archipielago cormoranes area during the middle late holocene

geophysical evidence of multiple glacier advances in lago fagnano 54 s southernmost patagonia the island of tierra del fuego at the southernmost extreme of patagonia is located in one of the most extensively glaciated areas of the southern hemisphere outside antarctica during the late pleistocene the lago fagnano region at w54 30 0 s and w68 w has experienced several phases of glacier growth and retreat since the last glacial maximum lgm we illustrate these phases using combined geomorphological geophysical and coring surveys in lago fagnano itself a w105 km long e w oriented glaciotectonic basin we identify and map a complex set of submerged frontal central and lateral moraines covered by lacustrine sediments using seismic stratigraphic analysis of multi channel profiles imaging the sub lake floor we then combine these geophysical data with field observations and regional maps of similar structures around the lake to reconstruct the spatial behavior of the fagnano paleo glacier since the lgm we interpret the preserved frontal moraines as having formed during at least 20 re advance stages of the glacier within a long term deglaciation interval post lgm preliminary tephrochronological dating of a w7 5 m long core indicates a step wise deglaciation pattern comprising a final glacier re advance stage at w11 2 ka bp

magallanes fagnano continental transform fault tierra del fuego southernmost south america 1 multichannel seismic reflection profiles gravity measurements and bathymetric soundings in conjunction with field geological reconnaissance and remote sensing images reveal with unprecedented detail the morphostructure of a major segment of the south america scotia plate boundary in the tierra del fuego region this segment known as the magallanes fagnano fault system is a continental transform margin arranged in an en echelon geometry along which prominent asymmetric basins were developed data acquired off the atlantic coast of isla grande the main island of tierra del fuego in its central and eastern part and in the central and western magallanes strait image the surface and subsurface structure of the transform fault and its associated basins the magallanes fagnano fault system is composed of distinct tectonic lineaments that are segments of the transform system and are represented by mostly near vertical faults in the atlantic sector the fault system trends broadly n70 e and seems to be composed by a single master fault along which a highly asymmetric basin has formed at around 63 w the fault terminates by splaying into secondary normal faults that dissipate the horizontal displacement along the system in the central eastern part of isla grande the fault segments have been principally identified from analyses of remote sensing images on the basis of their morphological expression these segments are located within river valleys and are generally associated with localized gravity minima lago fagnano a 105 km long e w trending depression is a large mostly asymmetric pull apart basin developed within the principal displacement zone of the magallanes fagnano fault system restraining bends and overlapping step over geometry characterize the central part of the magallanes strait along the western part of the fault system in the vicinity of the pacific entrance of the magallanes strait asymmetric sedimentary basins have also developed the sedimentary architecture of the basins formed within the principal displacement zone of the fault in which the thick end of the depositional wedge abuts the transform segment suggest simultaneous strike slip motion and transform normal extension a common feature found in other continental transtensional environments strike slip faulting in the tierra del fuego region is also documented along other prominent lineaments which parallel the magallanes fagnano fault system along at least two of these lineaments characterized by a remarkable morphological expression widespread quaternary activity occurs the present day motion between the south america and scotia plates is slow 5 mm yr also the modern seismicity monitored in the tierra del fuego region is low individual events 3 5 in magnitude the low seismicity may be explained by the slow relative motion between plates and may be further affected by slip partitioning along the different segments which make up the magallanes fagnano fault array and along the subsidiary wrench lineaments that traverse the region

the ore forming process of the maoping pb zn deposit northeastern yunnan china constraints from cathodoluminescence cl petrography of hydrothermal dolomite abstract most mississippi valley type mvt pb zn deposits have a common host rock lithofacies sequence known as the hydrothermal dolomite htd facies however the spatial and temporal relationships between dolomitization and pb zn mineralization remain unclear in this paper we report a detailed cathodoluminescence cl study on the htd facies of the no ii orebody in the maoping pb zn deposit in northeastern yunnan province southwestern china the results indicate that the dolomite in the carboniferous limestone is part of a spectrum of hydrothermal mineral deposits and the diagenesis and mineralization processes in which the acidity of fluids played an important role can be divided into six steps a dolomite prototype formed during the first and second steps in the third step acid fluids produced by sulfide precipitation interacted with the dolomite prototype resulting in dissolution and alteration thus forming cavities the fluid that formed during the first three steps flowed along open tensional faults dolomitization in the first step covered most of the region of later mineralization and gradually extended toward the center of the orebody in the fourth and fifth steps vugs and fractures were the main pathways for fluids with only a small volume of fluid in the fifth step dedolomitization occurred in the sixth step and vugs were filled mostly by calcite however the fact that voids are present in only a small number of vugs is indicative of fluid exhaustion dolomite with growth zoning is characteristic of precipitation by ore forming fluids accompanied by pulsed filling there is no significant correlation between vugs and the locus of mineralization rather the vugs indicate that the ore forming fluids had passed through them and the locus of massive ore formation was the center of the migrating fluid body the saddle dolomite was deposited during pauses in sulfide precipitation cathodoluminescent zonation of htd can be used as an aid in understanding the ore forming process and for mineral prospecting in the maoping deposit and other mvt deposits

quaternary of tierra del fuego southernmost south america an updated review abstract the quaternary of tierra del fuego is represented by glacial glaciofluvial glaciolacustrine marine and aeolian deposits six drift units have been described the oldest dating from the late pliocene these are starting from the oldest the rio grande sierra de los frailes cabo virgenes punta delgada primera angostura and segunda angostura drifts neoglacial and little ice age events are represented in cirques and higher mountain valleys marine deposits and raised beaches were formed during middle pleistocene late pleistocene and holocene interglacial stages after the definitive ice retreat 10 ka ago vegetation changed from tundra and cold steppe to subantarctic forest environments marine deposits reflect also colder conditions than the present ones aeolian processes prevailed in northern tierra del fuego where semiarid conditions and the frequent westerlies favoured the retransportation of finer materials coming from pre existing deposits before the opening of the magellan straits earliest human colonization occurred in northern tierra del fuego ca 11 ka bp in tundra like environmental conditions pedestrian hunters of camelids and foxes co existed with pleistocene fauna that became extinct during late glacial earliest holocene times the steppe area inland and atlantic coast was successively occupied since then until recent times on the other hand the beagle channel coasts were occupied since 6 ka bp by hunter gatherer groups adapted to maritime littoral conditions finally the easternmost area of the island was inhabited at least since 1 5 ka bp the human settlements in these latter areas occurred under environmental conditions similar to the present ones when the fuegian forest was definitively established

a model of subaqueous sedimentation at the margin of the late midlandian irish ice sheet connemara ireland and its implications for regionally high isostatic sea levels abstract the geomorphology and sedimentology of a series of late midlandian glacigenic sites in connemara western ireland are described and a set of commonly occurring sedimentary assemblages identified these form components of a simple model of ice contact subaqueous sedimentation involving progressive down current transition from subglacial esker tunnel fill through proximal tunnel mouth fans proximal and distal subaqueous fans into basin floor sediments in two of the sites aggradation to the water line passes into fan delta topsets and foresets all sites abut into inferred water bodies to their west and imply minimum water surface heights of between 35 and 65 m irish od or in the case of the two deltaic sites shoreline heights of between 75 and 80 m these high water levels very close to and facing directly into the immediately adjacent open atlantic ocean are difficult to explain as ice dammed glaciolacustrine water bodies without invoking improbable ice sheet marginal geometries they may however be explained as a set of successive fjord head grounding line depositional systems that trace temporary still stands in the phased retreat of the irish ice sheet from its offshore maximum this possibility not yet confirmed by the discovery of in situ marine fauna implies a degree of late midlandian isostatic depression and subsequent response unexplained by currently applied crustal response models but supported by previously constructed glacio sedimentary models

multiple volcano deformation sources in a post rifting period 1989 2005 behaviour of krafla iceland constrained by levelling tilt and gps observations abstract the krafla rifting episode which occurred in north iceland in 1975 1984 was followed by inflation of a shallow magma chamber until 1989 at that time gradual subsidence began above the magma chamber and has continued to the present at a declining rate pressure decrease in a shallow magma chamber is not the only source of deformation at krafla as other deformation processes are driven by exploitation of two geothermal fields together with plate spreading in addition deep seated magma accumulation appears to take place with its centre 10 km north of the krafla caldera the relative strength of these sources has varied with time new results from a levelling survey and gps measurements in 2005 allow an updated view on the deformation field deformation rates spanning 2000 2005 are the lowest recorded in the 30 year history of geodetic studies at the volcano the inferred rate of 2000 2005 subsidence related to processes in the shallow magma chamber is less than 0 3 cm yr whereas it was 5 cm yr in 1989 1992 currently the highest rate of subsidence takes place in the leirbotnar area within the krafla caldera and appears to be a result of geothermal exploitation

porosity evolution of the cambrian bonneterre dolomite south eastern missouri usa the cambrian bonneterre dolomite of south eastern missouri usa hosts the large mississippi valley type mvt lead zinc copper ore deposits of the region the bonneterre dolomite consists of dolomitized algal bioherms oolitic grainstone and associated lithologies that were deposited on a carbonate platform surrounding the precambrian age st francois mountains porosity was determined by point counting thin sections from cores and mines in the bonneterre dolomite and by gas porosimetry volumes of epigenetic cements were estimated by point counting cement filling micro and mesoporosity using cathodoluminescence cement volumes were added to present porosity to estimate porosities during various stages of mineralization prior to the onset of mineralization micro and mesoporosity in the bonneterre dolomite averaged approximately 19 precipitation of early dolomite cement roughly concurrent with the main period of sulphide deposition reduced average porosity to approximately 7 and closed off much of the intercrystalline pore space later cementation by dolomite prior to late stage sulphides reduced porosity to approximately 5 and late cementation by quartz further reduced porosity to the present average value of 4 periods of carbonate dissolution during mvt mineralization enhanced large scale megaporosity associated with fractures and breccias but did not significantly increase smaller scale porosity dolomite cementation associated with mvt mineralization porosity and permeability were facies controlled today as a result of mineralization large scale fractures and breccias control porosity and permeability this study indicates that dolomite porosity may undergo significant change during basinal brine migrations associated with mvt mineralization