shelf to basin temperate skeletal carbonate sediments three kings plateau new zealand abstract three kings plateau is 10 000 km2 in area less than 500 m deep and includes the mainland shelf and submarine ridges and banks centered on three kings islands 34 s off northernmost new zealand the plateau receives little input of terrigenous sediment and lies in a zone of active nutrient upwelling and vigorous wind wave and tidal current activity as a consequence surficial sediments on and about the margins of the plateau are dominantly pure skeletal carbonate sands and gravels which lack mud to depths of 1500 to 3000 m plateau top sediments include a bryozoan calcareous red algal barnacle lithofacies on coarse and rocky substrates and a bivalve bryozoan lithofacies associated with particulate bottoms plateau edge sediments include a bryozoan ahermatypic co al serpulid lithofacies in areas of rugged topography and a bivalve gastropod lithofacies on sandy substrates both grading down slope into a planktic foraminiferal lithofacies by 1500 to 3000 m depth depending on locality the carbonates are dominated by a high mg calcite and or low mg calcite mineralogy with only subordinate aragonite active skeletal production is presently restricted to only about 10 percent of the plateau area principally in regions of rough sea floor topography on submarine cliff faces on bank tops and in in shore portions of the mainland shelf about these areas modern carbonates occur down to depths of 50 to 200 m below which the sediments are mainly relict and include rare glauconite redeposition of plateau derived skeletal carbonates into surrounding basins was especially active during the last glacial low sea level s it is inferred that this is the ultimate fate of the bulk of the shallow marine sediment and that the plateau top itself preserves only a thin laterally discontinuous mixed age and highly condensed sequence of quaternary temperate skeletal carbonates

sedimentological and palaeoecological integrated analysis of a miocene channelized carbonate margin matese mountains southern apennines italy abstract lower middle miocene temperate marine carbonates occur in the matese mountains southern apennines italy these carbonates formed in an open shelf depositional system with an uneven margin 10 km long and up to 6 km wide shelf margin morphology shows multiple submarine channelized carbonate deposits which are dominated by coralline red algae and subordinate bryozoans two main channel networks pietraroia and regia piana channels with their sedimentary bodies were analysed the studied submarine channels grew by sediment accumulation as prograding bodies on a tectonic modelled substrate shallow water rhodalgal skeletal debris from moderately re mobilized up to significantly re worked built up the complex channel system fills in which sedimentary lenses overlapped and partially amalgamated one another when they were still unlithified the early channelized succession is characterized by parautochthonous bryozoan floatstone and rhodolith bryozoan floatstone representing soft muddy substrates in a low water turbulence and high turbidity setting the rhodoliths dominated by melobesioid coralline algae are sub discoidal and sub spheroidal in shape with a characteristic loosely packed inner arrangement these sediments whose latter portion underwent submarine diagenetic processes incipient to evoluted hard grounds were eroded and successively covered by shallower water gravitative deposits constituted by rhodolith floatstone rudstone their rhodoliths constituted by melobesioids mastophoroids and subordinate lithophylloids and sporolithaceans are mainly spheroidal sub spheroidal in shape with subordinate sub discoidal specimens with massive and laminar inner arrangements the lack in early lithification can be drawn back to the physiography of the channelized shelf margin to the active tectonic as well as to the temperate type carbonate dominant biogenic components the depositional surface profile and local hydrodynamic conditions were the major factors controlling sedimentary facies which differ in their relative proportions of dominant components their internal structures and sedimentary body geometries

constraints on provenance of the central european triassic using detrital zircon fission track data the type of provenance information obtained from dating detrital grains will depend upon the thermal sensitivity of the isotopic dating method for detrital zircon the two methods fission track and u pb in routine use have widely different thermal sensitivities and therefore may provide quite different provenance information zircon fission track data are sensitive to thermal overprinting in the temperature range 200 300 c and therefore have the unique ability to provide source thermal history data the purpose of this study is to evaluate the suitability of zircon fission track data for provenance studies of the triassic siliciclastic sediments of central europe with an emphasis on testing proposed sediment pathways zircon fission track data obtained during this study are consistent with a sediment pathway linking fennoscandia with the central german basin in addition during carnian times there must also have been a pathway linking the schilfsandstein formation of the german basin with the lunzersandstein of the tethyan realm pointing to a european wide fluvial transport system detrital zircon fission track data are therefore a useful means for discerning sediment source and reconstructing sediment pathways

surficial geology of the continental shelf northwestern vancouver island abstract the vancouver island continental margin lies along the convergent boundary between the explorer and juan de fuca plates and the america plate off northwestern vancouver island this tectonic regime is manifested in major thrust faults and folds which dislocate volcanic and sedimentary rocks of tertiary age beneath a relatively undeformed wedge of late neogene mudstones surficial sedimentation reflects both the tectonic and high latitude settings of the area predominance of lithic arenites and graywackes high wave and current energy restricting modern sedimentation to the outer shelf deeper than 110 m and resulting in the formation of large oscillation bedforms to depths of 100 110 m trapping of terrigenous sediments in fjords leading to low sediment accumulation rates on the shelf which in turn favor the formation of abundant glauconie gravel lags and extensive areas of biogenic sediments dominated by molluscs and bryozoa and the presence of pleistocene glaciomarine sandy muds and muddy sands beneath the mid and outer shelf

endolithic biodegradation of cool water skeletal carbonates on scott shelf northwestern vancouver island canada abstract biodegradation of shell material is widespread in the cool water skeletal carbonate deposits on scott shelf northwestern vancouver island and is especially evident in the large aragonitic bivalves glycymeris and humilaria major primary sediment contributors ten types of endolithic microborings have been identified in the shells including representatives of green algae e g ostreobium quekettii blue green algae e g plectonema terebrans scytonema sp fungi bacteria and clionid sponges as well as macroborings of phoronids polychaetes and naticid gatropods microcrystalline carbonate is not precipitated in vacated bores boring physically weakens the shells rendering them more prone to mechanical abrasion during sediment transport and bioturbation and to biological abrasion by grazing benthos tumbling experiments demonstrate that the rate of carbonate mud production is much greater for bored as compared to fresh bivalve shells and that mud production rates decrease with tumbling time because most endolithic microborings are confined to the periphery of grains boring also increases significantly the porosity and surface area of skeletal grains and destroys their organic matrix making them susceptible to maceration and dissolution on cool water shelves fostered by the generally low rates of carbonate production and accumulation many aragonitic bivalve shells on scott shelf have become thoroughly degraded through a combination of endolithic microboring maceration and dissolution within about 1000 years in ambient sea water in geologic terms such selective taphonomic loss of skeletal material may be considerable in ancient temperate shelf limestones and should be evaluated when interpreting their paleoecology and paleoenvironments

rethinking turbidite paleoseismology along the cascadia subduction zone a stratigraphic synthesis of dozens of deep sea cores most of them overlooked in recent decades provides new insights into deepsea turbidites as guides to earthquake and tsunami hazards along the cascadia subduction zone which extends 1100 km along the pacific coast of north america the synthesis shows greater variability in holocene stratigraphy and facies off the washington coast than was recognized a quarter century ago in a confluence test for seismic triggering of sediment gravity flows that test compared counts of holocene turbidites upstream and downstream of a deep sea channel junction similarity in the turbidite counts among seven core sites provided evidence that turbidity currents from different submarine canyons usually reached the junction around the same time as expected of widespread seismic triggering the fuller synthesis however shows distinct differences between tributaries and these differences suggest sediment routing for which the confluence test was not designed the synthesis also bears on recent estimates of cascadia earthquake magnitudes and recurrence intervals the magnitude estimates hinge on stratigraphic correlations that discount variability in turbidite facies the recurrence estimates require turbidites to represent megathrust earthquakes more dependably than they do along a flow path where turbidite frequency appears limited less by seismic shaking than by sediment supply these concerns underscore the complexity of extracting earthquake history from deep sea turbidites at cascadia

glauconitic sediments on the continental shelf off vancouver island british columbia canada abstract the tectonically active vancouver island continental margin is characterized by a very narrow 80 km continental shelf and an extremely steep continental slope the shelf is marked by high wave and current energies on the inner nondepositional shelf and very slow rates of sediment accumulation on the outer shelf within the muddy sands of the outer shelf and slope glauconitic grains are frequently an important constituent of the sand fraction occurring in four principal forms a locally abundant pale green infillings of benthic foraminifera b very abundant pale to moderately dark green dull grains displaying varying degrees of fracturing of the external surfaces c scarce moderately dark green altered and expanded mica grains and d scarce very dark green small 200 m grains with polished highly fractured surfaces mineralogically the grains mainly reflect their origins as detrital sediments they consist most commonly of quartz plagioclase minerals chlorite smectite and illite also a mixed layer mineral smectite illite occurs in significant amounts in glauconitic grams but is absent in unaltered mud fragments and in the clay fraction of sediments from the outer shelf the appearance of this mineral reflects the first stages of glauconite authigenesis bulk analyses of glauconitic grains yielded k2o values of less than 2 reflecting their very early stage of evolution but 19 28 fe2o3 several times the level in the surrounding matrix sediments microprobe analyses and scanning electron microscopy show that glauconitic smectite forms in the pores and along fractures in the host grains commonly as a boxwork arrangement or rosette clusters of blades fe2o3 and k2o values at these sites can reach 32 5 and 7 5 respectively several lines of evidence including radiocarbon age determinations on glauconitized foraminifera tests indicate a recent age for the vancouver island shelf glauconitic grains

cementation in oligo miocene non tropical shelf limestones otway basin australia abstract the oligocene to miocene heytesbury group of the otway basin southeastern australia is a non tropical carbonate shelf succession this subsurface stratigraphic succession consists of bioclastic grainstones to mudstones containing bryozoa benthonic and planktonic foraminifera echinoderms brachiopods and molluscs the basal bryozoa dominated clifton formation was deposited in relatively shallow waters the overlying gellibrand marl rich in planktonic foraminifera and bryozoa formed under deep waters the uppermost unit benthonic foraminifera dominated port campbell limestone was deposited in a moderately deep middle shelf environment cementation is limited and includes 1 scalenohedral calcite non luminescent to bright mn and fe poor in inter and intraparticle porosity 2 blocky equant calcite dull mn and fe rich in interparticle porosity 3 syntaxial calcite overgrowths on echinoderm particles non bright dull zoned 4 euhedral dolomite in the interparticle pore space of the port campbell limestone 5 bladed prismatic calcite ferroan in planktonic foraminifera 6 fibrous calcite non luminescent in intraparticle porosity and 7 glauconite and iron oxides only in intraparticle porosity all caco3 cements are low mg calcites the cements observed in the heytesbury group appear to have formed in three successive diagenetic environments 1 early shallow burial early fe and mn poor non luminescent syntaxial overgrowths and non luminescent scalenohedral calcite under oxidising conditions 2 late shallow burial bright more mn rich syntaxial overgrowth zone i e more than the initial non luminescent one and bright scalenohedral calcite under moderately reducing pore water conditions and 3 moderate burial ferroan dull blocky calcite and dull syntaxial overgrowth zone under reducing conditions pressure solution was the main cement producing mechanism although seawater and aragonite dissolution could account for the precipitation of the early non luminescent cements scarcity of early interparticle cements may have been caused by the calcite rich character of the original sediments the ferroan dully luminescent blocky equant calcite and syntaxial overgrowths typically interpreted to represent products of deep burial in ancient carbonate successions are observed in the shallow buried port campbell limestone

cooling and uplift patterns in the lepontine alps south central switzerland and an age of vertical movement on the insubric fault line 96 new fission track ft apatite and zircon k ar and rb sr biotite and muscovite ages are presented for 19 samples mainly acid gneisses from a 40 km traverse through the lepontine alps in the maggia valley south central switzerland plotting measured mineral ages against assumed system closure temperatures yields cooling rates for each sample the entire profile shows a fairly uniform late neogene recent mean uplift rate of 0 5 mm a confirmed by a gradient of ft apatite age with elevation cooling from higher temperatures occurred earlier in the south where uplift rates of 2 2 mm a in the steep belt root zone indicate 9 km early miocene uplift of the northern pennine block this uplift started before 23 ma and is interpreted as resulting from a major phase of backthrusting along the insubric line and as dating the formation of the mylonite belt estimated cooling rates constrain the timing of lepontine mid tertiary metamorphism 3 schematic models are proposed which also consider published rb sr k ar mica and hornblende and u pb monazite ages slow cooling differential initial heating and subsequent cooling of different parts of the central alps and post 38 ma cooling with syntectonic metamorphism at 27 ma are postulated as alternative interpretations of isotopic data and geologic evidence from extrapolation between k ar and rb sr mica ages and apatite ft ages 240 50 c is proposed as the closure temperature for the retention of fission tracks in zircon

bioclastic carbonate sediments on the southwestern svalbard shelf the poleward continuation of one of the largest known arctic carbonate factories the western spitsbergenbank of the barents sea has been surveyed along the narrow sw svalbard shelf on this shelf formation of cold water carbonate sediments occurs under glaciomarine environmental conditions mya truncata and hiatella arctica colonized a soft glacio marine diamicton 3000 6000 years after the final retreat of the icedome from the sw svalbard shelf since 2600 yr b p an increase of along shelf bottom currents washed out the fine terrigenous deposits leaving behind a shelly lag deposit and winnowed boulders on a morainic shelf topography the most favourable depth interval promoting the establishment of an amalgamated bioclastic blanket is located in 50 80 m water depth in this interval strong bottom currents prevent sedimentation thus facilitating colonisation of filter feeding benthic communities dominated by balanus balanus and chlamys islandica additional skeletal components are supplied by echinoderms bryozoans serpulids brachiopods and gastropods in shallower water depths carbonate production is hampered by intense iceberg scouring and release of ice rafted debris from the still glaciated hinterland of svalbard in deeper water 80 m olive grey muds with dispersed pebbles rich in benthic foraminiferans clinocardium ciliatum and taxodont bivalves are present on all surveyed shelf banks the deepest unit is a blue mud in water depths 120 m with benthic foraminiferans taxodont bivalves and sipunculids compared to spitsbergenbank carbonate production is much more restricted and impoverished on the sw svalbard shelf but is still an instructive modern example for the formation of skeletal carbonates resting on tillites in the geological record

the role of fission track dating in discrimination of provenance determination of single crystal ages by fission track dating analysis of zircons and subordinately apatites within a detrital heavy mineral assemblage together with frequency distribution and radial plot analysis of the measured ages permits identification of different age modes synopses are presented of published fission track provenance studies in north central victoria northeastern tasmania barbados the rockall trough the english wealden mexico utah and the central alps from authors

chronological constraints on cordilleran ice sheet glaciomarine sedimentation from core md02 2496 off vancouver island western canada chronology based on 46 radiocarbon dates has been generated for md02 2496 western vancouver island canada subsequent correlation between glaciomarine sedimentary sequences within the core and the terrestrial stratigraphy of the cordilleran ice sheet for the last 50 ka provide new insight into cordilleran ice sheet processes glaciomarine sedimentation associated with the most recent advance fraser glaciation of the cordilleran ice sheet began at 30 5 cal kyr bp 25 14 c kyr bp extremely high sedimentation rates indicate the ice sheet became proximal to the site at 19 5 cal kyr bp 16 14 c kyr bp deposition of ice rafted detritus ird began at 17 cal kyr bp 14 14 c kyr bp and abruptly terminated at 16 2 cal kyr bp 13 5 14 c kyr bp indicating rapid regional ice sheet retreat a minor ird event followed at 14 7 cal kyr bp 12 5 14 c kyr bp glaciomarine sediment deposition abruptly ended at 10 2 cal kyr bp 8 8 14 c kyr bp with the resumption of biogenic sedimentation the olympia interstade is represented by an interval of hemipelagic sedimentation between 43 and 31 5 ka prior to 45 ka sediment deposition is controlled by glaciomarine processes with evidence for a significant ird event at 47 cal kyr bp 44171 06 14 c kyr bp

the fate of foramol temperate type carbonate platforms abstract on rimmed shelves of bahamian type characterized by chlorozoan associations and typical of tropical seas carbonate production keeps pace with normal sea level rise except when rapid rise or drastic environmental changes occurs on the other hand open temperate carbonate shelves are characterized by low carbonate production of the foramol association molluscs benthic foraminifera bryozoans coralline algae etc and generally show seaward relict sediments because carbonate production cannot keep pace with normal rate of sea level change several examples of recent drowning foramol carbonate platforms e g large areas of the mediterranean sea eastern northeastern yucatan shelf as well as analogous ancient drowned foramol type carbonate platforms e g early to middle miocene of the southern apennines miami terrace may support the idea that the drowning of many ancient carbonate platforms has been favoured by their biogenic foramol sensu lato constitution because of their typically low rate of growth foramol carbonate platforms are fated to be drowned even if the sea level rise is one with which the normal growth of chlorozoan platforms can keep pace similar conditions may also occur in tropical areas where variations in environmental conditions such as the presence of cold waters changes in salinity and increased nutrients preclude the development of chlorozoan associations

burial dominated cementation in non tropical carbonates of the oligocene te kuiti group new zealand abstract cementation of bryozoan echinoid benthic foraminiferal temperate shelf carbonates of the oligocene te kuiti group north island new zealand occurred mainly during subsurface burial the calcite cements in the limestones are dominated by equant and syntaxial rim spar which typically becomes ferroan given an iron supply and compared to the skeletal material with normal marine 18o values from 2 to 1 more depleted in 18o with depth of burial the 18o composition of bulk cement samples ranging from 1 to 7 these trends reflect the establishment in pore waters during sediment burial of reducing conditions and gradually increasing temperatures 20 50 c respectively the 13c values 0 to 3 of the cements remain the same as the host marine shells suggesting the source of carbon in the cements was simply redistributed marine carbonate derived from shell dissolution two gradational burial diagenetic environments influenced by marine derived porewaters are arbitrarily distinguished shallow burial phase and moderate burial phase during the shallow burial phase down to 500 600 m sub bottom depth the carbonates lost at least 25 of their original porosity by mechanical compaction and were selectively cemented by non ferroan or usually ferroan variably luminescent slightly 18o depleted sparry calcite cement 18o 2 to 4 mainly as syntaxial rims about echinoid grains these shallow burial cements form less than about 10 of total cement in the majority of the limestones and their source was probably mainly mild intergranular dissolution of calcitic skeletal fragments accompanying the onset of chemical compaction during the moderate burial phase between about 600 and 1100 m sub bottom depth porosity loss continued typically to about 70 of its original value as a result of pressure solution of calcitic bioclasts associated with more advanced stages of chemical compaction this involved development of a wide variety of non sutured and microstylolitic solution seams including both single and composite wispy or continuous bedding parallel types and non parallel reticulate forms the released carbonate was precipitated as ferroan or non ferroan where iron supply was negligible dull luminescent strongly 18o depleted 18o 4 to 7 mainly equant calcite spar cement occluding available pore space in the limestones

diagenetic comparisons between non tropical cenozoic limestones of new zealand and tropical mississippian limestones from indiana usa is the non tropical model better than the tropical model abstract mississippian limestones exposed in indiana u s a were deposited in a shallow tropical ocean however many properties of these limestones are more like those of modern and cenozoic non tropical limestones such as those found in new zealand the dominant skeletal grains in the indiana limestones are calcitic echinoderms bryozoans and brachiopods the dominant skeletal grains in most cenozoic limestones of new zealand are calcitic bryozoans echinoderms bivalve molluscs and foraminifera in contrast modern and cenozoic tropical limestones contain an abundance of aragonitic green algae corals and molluscs early in diagenesis the metastable aragonite dissolves and reprecipitates as calcite causing early cementation of the sediments originally aragonitic fossils that have dissolved can be identified as molds that are commonly filled with secondary calcite because they contained little aragonite most of the indiana and new zealand limestones did not have an abundant source of early cement except for local cases in which grains were cemented in contact with carbonate supersaturated seawater grainstones were relatively deeply buried with little cement between the grains this resulted in mechanical and chemical compaction of skeletal grains producing a fitted fabric with greatly reduced pore space either open or filled with cement between the grains cement in these aragonite poor grainstones comes largely from pressure dissolution between grains and along stylolitic seams in the rock features that are common only after burial beyond a few hundred meters the final product of deeply buried up to 2000 m cenozoic new zealand grainstones is similar to the mississippian grainstones of indiana in the indiana limestones we have only the final product of this extensive burial diagenesis however the new zealand sediments and rocks reveal all steps of formation of the final deeply buried limestone the reason for the scarcity of originally aragonitic fossil grains in paleozoic rocks worldwide is unknown organisms with aragonitic skeletons such as some molluscan groups and calcareous green algae were present but seldom in much abundance the aragonitic scleractinian corals had not yet evolved previous researchers have noted that non skeletal precipitates such as ooids and cements have at times during the paleozoic been predominantly aragonite and at other times calcite they have attributed this difference to secular variation in seawater chemistry icehouse vs greenhouse seas abundance of aragonitic and calcitic skeletal grains does not follow this pattern

geometry of the kapuskasing structure from a lithoprobe pilot reflection survey a short 10 km pilot seismic reflection profile recorded in the kapuskasing structural zone near foleyet ontario reveals reflections with travel times of at least 5 0 s about 16 km depth an event dipping west from about 1 7 to 3 4 s probably corresponds to the ivanhoe lake cataclastic zone the true geologic dip on this boundary is calculated to be about 35 38 west northwest and is consistent with interpretations of this zone as a west dipping crustal scale thrust fault east dipping reflections are observed with longer travel times than the fault zone arrival and are likely from within the greenstone terrane of the abitibi subprovince

stable isotopes 14c dating and geochemical characteristics of carbonate nodules and sediment from an active vent field northern juan de fuca ridge northeast pacific abstract a record of early uplift events foreshadowing development of an active vent field in middle valley on northern juan de fuca ridge is preserved in a core taken on the margin of the field by a near surface mud fragment breccia dated 8 300 to 11 500 yr b p cementation of the breccia with low mn methanogenic calcite at 5 c formed a carbonate nodule layer by 6 800 yr b p recent hydrothermal overprinting at 6 m in the same core resulted in formation of carbonate nodules with late stage high mn calcite cements oxygen isotopic temperatures of 55 85 c and more positive 13 c values reworked vent detritus suggests that surface venting began by at least 2 900 yr b p localized lateral flow of hydrothermal fluid tens of cm below the seafloor is suggested by a barite rich zone in a permeable interval bounded sharply below by relatively impervious mud clast breccia carbonate and barite cementation near the seabed could eventually result in localized ponding or redirection of fluid flow in the shallow subsurface near the center of the active field a barite zone originating from reaction of hydrothermal ba with residual highly fractionated seawater sulfate barite 34 s 44 5 is found at 6 m below the seafloor

carbonate lithofacies as paleolatitude indicators problems and limitations abstract detailed study of miocene carbonates in the mediterranean region and their analogues on modern carbonate shelves in the mediterranean sea brazil and other areas reveals at least three major types of carbonate platform lithofacies in addition to the classic tropical coral reef chlorozoan lithofacies a chloralgal lithofacies similar to the chlorozoan but without hermatypic corals b rhodalgal lithofacies characterized by abundant encrusting coralline algae and c molechfor lithofacies consisting of benthic foraminifers molluscs echinoids bryozoans and barnacles these carbonate lithofacies present complex distribution patterns seemingly related primarily to latitude and depth that control water temperature although other factors e g water circulation river discharge suspended sediment controlling water salinity and temperature nutrient content light penetration etc also play important roles chloralgal and rhodalgal lithofacies can be considered two transitional terms between the two end members the chlorozoan lithofacies which characterizes shallow tropical shelves and the molechfor lithofacies which characterizes colder and or deeper areas detailed textural and sequential analysis are required for satisfactory interpretation of these lithofacies in ancient rocks

carbonate basaltic sediments from cobb seamount northeast pacific zonation bioerosion and petrology abstract six dives were made with pisces iv at depths of 30 to 700 m and sediments collected by scoop bathymetrically zoned bioclastic carbonates rim the seamount they reflect the zonation of the living fauna but are complicated by relic mytilus gravels from the wisconsin low stand successive faunal zones contain prominent echinoderms echinoid bivalve bryozoan 30 to 90 m crinoid brachiopod 90 to 180 m coralbrachiopod ophiuroid 180 to 500 m hydrocoral crinoid gorgonian ophiuroid 500 to 700 m sediments down to 360 m average over 80 caco3 within the photic zone down to 185 m they are dominated by bivalves and bryozoans below this by benthic and planktonic foraminifera bioerosion occurs within the photic zone by algal boring and echinoid limpet grazing but at lower rates than during the low stand wave base is 150 m a conspicuous belt of ahermatypic reefs occurs on pillowed dykes at 310 to 360 m gorgonian coral bases perform a rapid secondary encrusting role e g lining eunicid polychaete tubes associated with the coral lophelia basaltic granules hyalotuff of basaltic composition feldspar crystal fragments and hyaloclastite grains dilute the carbonate particularly in deeper water manganese nodules occur in the sample at 385 m these nodules are small and could have formed in 20 000 yrs high mn fe ratios indicate their formation in an environment of high productivity a poorly lithified hyalotuff beach believed to have originated intertidally is now seen at 310 m well rounded basaltic granules occur down to 537 m and make up the bulk of the sediment at this depth

early diagenesis of carbonates on a cool water carbonate shelf southern australia abstract the southern australian continental margin is an immense cool water carbonate factory the high energy open shelf is blanketed by heterozoan carbonates of both holocene and late pleistocene age three distinct grain types have been identified and radiocarbon dated these include 1 relict grains highly abraded iron stained intraclasts formed during the intermediate sea level stands of marine isotope stages 3 and 4 2 stranded grains gray and buff colored abraded biofragments and intraclasts marooned during the sea level rise associated with marine isotope stage 2 and 3 holocene grains unaltered biofragments formed during marine isotope stage 1 optical mineralogical and chemical characterization of grains of each age has revealed pathways of early diagenesis in this realm both calcitic and aragonite biogenic grains undergo dissolution while dissolution of calcitic components is minor and incomplete relict sediments are predominantly mg calcite aragonitic skeletons undergo significant dissolution within 30 000 years in contrast to early dissolution of aragonite micritic calcite cement with 12 mol mgco3 is a significant diagenetic phase in these sediments infilling many stranded and most relict skeletons similar cement precipitates between grains forming small numbers of cemented grain aggregates in most samples microprobe and icp ms analysis demonstrates fe oxides mn oxides and associated clay minerals discolor stranded and relict grains by coating grain surfaces and infesting micropores such coatings begin to form on holocene grains during or soon after formation the oxides scavenge trace elements including v ti cr and ree altering the elemental compositions of biogenic carbonate

modern heterozoan carbonates from a eutrophic tropical shelf mauritania abstract heterozoan or foramol production is typical in extratropical carbonate sedimentary systems however under mesotrophic to eutrophic conditions heterozoan carbonates also form in tropical settings but such heterozoan tropical sedimentary systems are poorly understood nevertheless distinction between tropical and extratropical heterozoan carbonates in ancient successions is crucial for accurate paleoenvironmental and paleoclimate reconstructions here surficial holocene and pleistocene sediments of the northern mauritanian shelf are studied as an example of a tropical eutrophic carbonate depositional system 11 g l 1 chl a chlorophyll a upwelling nutrient rich waters push onto the wide mauritanian shelf where they can warm up to in excess of 25 c this condition favors production of heterozoan carbonates dominated by bivalves and foraminifers even in this tropical setting in addition sediments are provided by eolian input from the desertic hinterland the resulting sediments are carbonate and mixed carbonate siliciclastic facies in which the carbonates are characterized by a mixture of tropical and cosmopolitan taxa benthic photosynthetic biota are absent while suspension feeding organisms are dominant this foramol grain association on a shelf scale is reminiscent of cool water carbonates therefore recognition of warm water heterozoan carbonates relies on key taxa related to tropical waters within the biota assemblages associated with a highly productive environment

diagenetic alterations in temperate shelf carbonates from southeastern australia abstract temperate shelf carbonates form in cool marine waters and have skeletal and mineralogical compositions which are different from their tropical counterparts they commonly lack non skeletal grains and are often composed of low and high magnesium calcite with subordinate aragonite many of the aragonitic components found in tropical carbonates such as corals ooids blue green algae and lime mud are absent temperate shelf carbonates undergo diagenesis in marine waters with lower carbonate saturation than do tropical carbonates and are exposed to cool climates with moderate to low rainfall marine cementation is rare because of low carbonate saturations in the surrounding waters however aragonite and high magnesium calcite cements have been reported forming under specialized conditions associated with biogenic precipitation submarine methane and sulphate reducing bacteria and more commonly in the intertidal environment where evaporation has increased carbonate concentrations in pleistocene and tertiary temperate shelf carbonates from southeastern australia evidence of marine diagenesis is rare to absent diagenetic stabilization of aragonite and high magnesium calcite has taken from 80 000 y to 1 my or longer during subaerial exposure this is slower than rates reported from tropical climates a general lack of aragonite in some facies within these temperate carbonates leads to a lack of secondary porosity and only sparse low magnesium calcite cement even after prolonged fresh water diagenesis however with lengthy exposure and under the right climatic conditions karstic solution and calcrete precipitation can occur in sequences containing siliciclastic clays pyrite and glauconite abundant iron is present in interstitial waters leading to the precipitation of ferroan calcite cements in the phreatic and shallow burial environments and to the substitution of iron for magnesium in stabilizing high magnesium calcite skeletal material a unique void filling micritic internal sediment occurs in discrete layers in many of the tertiary temperate shelf carbonate sequences in southeastern australia this internal sediment is localized as a pore filling material above permeability barriers such as fine grained sediments or volcanics and above paleo water tables which formed during periods of subaerial exposure it is a feature of the vadose zone and lithifies to form a dense micritic low magnesium calcite cement with characteristic pink brown coloration often associated with erosion surfaces and nodule beds dolomite is uncommon in the southeastern australian temperate shelf carbonates it forms associated with preferential fluid pathways or mixing zones ferroan dolomite forms in siliciclastic clay rich carbonates in the shallow burial environment the ubiquitous fine evaporite related dolomite so common in tropical carbonates is absent

paleoenvironments of the mid ordovician upper caradocian trenton limestones of southern ontario canada storm sedimentation on a shoal basin shelf model abstract the mid ordovician caradocian limestones of southern ontario were deposited on a shelf undergoing collision with a magmatic arc within the general deepening upwards sequence shoals and islands complicate the facies patterns around these shoals and islands carbonate sediments can be divided into nine lithotypes reflecting shallow agitated to deep quiet marine environments many of these lithotypes show good evidence of storm deposition the lithotypes can be grouped into natural associations which define shoal intershoal slope and basinal facies though the basins were probably less than 100 m deep the closest recent analogues of these ordovician environments occur on the arabian shelf of the persian gulf and on the sahul shelf of northern australia which is undergoing collision with the banda arc in both these environments local shoal basin shelf topography controls the detailed carbonate shelf sedimentation which on a large scale is controlled by storm and tsunami effects on a seaward sloping ramp such shoal basin and ramp models now seem more suitable in explaining carbonate facies in epeiric seas than the flat slope models previously proposed glacio eustatic sea level changes may have controlled the larger aspects of carbonate sedimentation on the ordovician shelf as they did and continue to do now on the recent shelves such changes may explain the localization of the variety of ordovician hardgrounds which we previously described

anatomy of a submarine channel system and related fan in a foramol rhodalgal carbonate sedimentary setting a case history from the miocene syn rift sardinia basin italy abstract during aquitanian burdigalian times thick mixed carbonate siliciclastic successions were deposited in basins located on the grabens and half grabens along the oligo miocene sardinia rift basin locally active tectonics sea level variations and ecological factors combined to control the development and distribution of foramol carbonate factories as well as the remobilisation and the redeposition of carbonate sediments into the adjacent deeper areas in the isili basin foramol rhodalgal carbonate factories developed on submerged structural highs which resulted from pre and syn sedimentary tectonics these carbonate factories were periodically shaved mainly during negative sea level oscillations and the sediments removed were funnelled towards the basin through a complex submarine channel network which included a tributary belt one main channel isili channel and the related fan the isili channel is up to 1 km wide 60 100 m deep and includes two stacked channel complexes each built up by several minor order channel units complex strata geometries characterise the isili channel and its related architectural elements e g overbank levee margin and channel thalweg which also include up to 15 m high bedforms individual channel complexes were temporally related to individual fan systems whose spatial distribution and internal geometry were strongly controlled by the type and rate of sediment accumulation and in turn by relative sea level oscillations facies associations include sandy to cobble sized gravity flow and bottom current deposits as well as megabreccias characterised by impressive displaced and tilted blocks which resulted from major channel margin collapses detailed analysis has led to the reconstruction of the internal geometry and depositional architecture of these carbonate bodies and to the determination of the main controlling factors the dimension and distribution of channel and channel related depositional bodies have been accurately determined this information provides a useful tool to analyse less extensively exposed analogues and to model foramol shelf to basin transitions and related channel and fan systems

application of bryozoan zoarial growth form studies in facies analysis of non tropical carbonate deposits in new zealand abstract the fragmental remains of bryozoan colonies are the dominant skeletal contributor in many modern and ancient occurrences of non tropical shelf carbonate deposits the taxonomic complexity of the bryozoa the difficulties of systematic classification except by specialists the wide range of particle sizes and of preservation state in the carbonate deposits and the often well cemented nature of host limestones all limit the sedimentological interpretation of the commonly diverse bryozoan component however following the pioneer work of stach in the 1930 s the potential exists for sedimentologists to obtain useful paleo environmental information about the deposits by recording simply the nature and relative abundances of the various growth shapes of the bryozoan material known as their zoarial colonial growth forms here we propose a simple descriptive terminology covering both cheilostome and cyclostome bryozoans that involves four main growth forms encrusting erect rigid erect flexible and free living and a selection of subcategories based on shape identification of these habitat related growth form types is aided by reference to line drawings specimen photographs and photomicrographs of thin section slices the scheme is illustrated by examining briefly some possible environmental controls on the spatial and or time variations in the nature and distribution of colonial growth forms in several examples of modern and tertiary bryozoan dominated carbonate deposits in new zealand we anticipate that the routine description and quantification of bryozoan colonial growth types in non tropical carbonates generally will facilitate the recognition and interpretation of contrasting sub facies within the global foramol bryomol group of carbonate deposits

evaluation of cold water carbonates as a possible paleoclimatic indicator abstract the common belief currently shared by many geoscientists concerning the climatic interpretation of limestones is that a warm water environment is essential this concept is not necessarily true because the rate and extent of terrigenous sediment dilution rather than water temperature is the primary factor determining whether or not a limestone forms at nearshore or continental shelf depths because carbonate productivity is lowest in cold climates however caco3 abundance and the thickness of carbonate accumulations tend to be least at high latitudes in this regard present day continental shelves and beaches offer a poor model for comparing cold water and warm water carbonates because of the generally emergent continental tectonic framework recent eustatic sea level changes and the presence of ice caps at the modern poles typically the influence of climate on non reef continental shelf and beach environments cannot be clearly distinguished by the presence or absence of major taxonomic groups faunal diversity and equitability are more sensitive in this regard the absence of shelf depth inorganic carbonate precipitates micrite envelopes and peloids may also point to the cold water origin of a rock skeletal mineralogy and oxygen isotopes of certain unrecrystallized carbonates may be good paleoclimatic indicators however trace elements and physical textural attributes of the carbonate fraction are probably temperature insensitive previous studies of high latitude continental shelves have concentrated merely on the abundance of calcareous material and there is seemingly a disproportionate amount of information with respect to low latitude carbonate studies further research on cold water carbonates may open up new avenues for alternative paleoenvironmental and paleoclimatic interpretations

fission track dating of phosphate minerals and the thermochronology of apatite several phosphate minerals have been investigated for their usefulness in geochronology and thermochronology by the fission track method of these apatite ca5 po4 3 f cl oh has proved pre eminently suitable for this purpose for reasons discussed below apatite was one of the first minerals amongst many others to be investigated for fission track dating by fleischer and price 1964 and has subsequently become by far the most important of all the minerals used for dating by this method the usefulness of apatites for fission track dating arises from their near universal tendency to concentrate uranium within their structure at the time of crystallization and their widespread occurrence in all of the major rock groups price and walker 1963 first recognized the possibility that the accumulation of radiation damage tracks in natural minerals from the spontaneous nuclear fission of 238u within their lattices could be used for geological dating they also demonstrated that a simple chemical etching procedure served to enlarge these fission tracks to optical dimensions so that they could be observed and measured under an ordinary optical microscope price and walker 1962b 1963 this simple procedure quickly opened the way for a wide range of nuclear particle track studies in natural minerals and glasses e g fleischer et al 1975 the most important of which was fission track dating fleischer et al 1964 also showed that spontaneous or fossil fission tracks provided an explanation for various anomalous etch pits in apatite which had puzzled crystallographers over many years the essence of a fission track age determination involves measuring the number of tracks that have accumulated over the lifetime of the mineral along with an estimate of the amount of uranium that is present knowing the rate of spontaneous fission decay a geological age can be calculated detailed

temperate skeletal carbonate sediments on scott shelf northwestren vancouver island canada abstract scott shelf 2000 km 2 centred at scott islands northwestern vancouver island is mainly shallower than 150 m topographically diversified and floored by bedrock outcrops and terrigenous lithic gravels and sands left stranded following the post glacial rise in sea level 13 000 yrs b p it lies in a zone of vigorous wind wave currents and strong tidal flows but is largely starved of modern terrigenous sediment as a consequence it is slowly accumulating a thin discontinuous blanket of clean skeletal carbonate sands and gravels admixed to varying degrees with the underlying terrigenous deposits principal skeletal contributors are infaunal bivalves on coarse sandy and gravelly substrates barnacles on low amplitude gravelly ridges bryozoans on bedrock outcrops and boulders and benthic foraminifera on fine sands in deep 100 m waters south of the scott islands living carbonate benthos are scattered and generally sparse occupying specific ecologic niches and the shelf wide rate of carbonate production is low skeletons are fragmented transported and mixed during storms and are concentrated within bedrock hollows and crevices and shallow depressions between gravel ridges where infaunal bivalves are abundant the carbonates are dominated by aragonite but otherwise the skeletal hashes are predominantly calcitic many grains and especially aragonitic ones are corroded and weakened by epilithic and endolithic bioerosion and probably also by marine and dissolution the most corroded shells have ages of only about 1000 yrs so that their preservation potential is low the character of scott shelf skeletal carbonate deposits reflects their temperate latitude cold water heritage

carbonate dissolution in nearshore terrigenous muds the role of physical and biological reworking because shallow marine sediments generally underlie waters which are saturated with respect to arago nite and calcite physical chemical dissolution of carbonate in these environments is sometimes discounted the present investigation as well as others before it show such an assumption to be unwarranted in this case study of terrigenous mud deposits from long island sound u s a demonstrates extensive dissolution of molluscan shell debris near the sediment water interface net buildup of carbonate varies significantly between different regions of the sound despite fairly uniform production of shell debris and similar total sedimentation rates aside from this apparent discrepancy between rate of supply and net carbonate sedimentation evidence for carbonate dissolution comes from the pitting of shells elevated ca levels in pore water and calculated undersaturation of pore waters with respect to carbonate minerals models of pore water distributions and carbonate supply imply dissolution ra

bioerosion and carbonate mud production on high latitude shelves low latitude carbonate muds often are composed either of entire units of skeletons e g algal muds or of precipitates whereas high latitude carbonate muds are bioerosional or result from maceration bioerosion at high latitudes is most intense in the photic zone particularly down to 25 m depth shelly substrata may be crushed bitten drilled bored or scraped clionid sponges endolithic algae acmaeid gastropods and regular echinoids are the most significant agents clionids produce distinctive facetted carbonate silt chips when boring which have been described from both high and low latitudes faecal pellets break down to yield mud sized carbonate particles that are more irregular than those produced by maceration exhumed infaunal bivalves are often preferred to epifaunal organisms as substrata bioerosion occurs very rapidly shells may be totally infested with boring algae in three months a moth eaten appearance therefore does not denote a relict grain reliable rates of fine sediment production are not yet available the mud fraction of northwest european shelf sediment generally contains 10 20 caco3 though an inshore and offshore belt with higher values may be identified some holocene supratidal mud flats exceed 50 caco3 much of the shelf represents a modern day equivalent of the calcareous shale facies common in the geological record instances of synsedimentary cementation are not uncommon particularly in association with heavily burrowed muds

a collision boundary imaged by magnetotellurics hidaka mountains central hokkaido japan magnetotelluric mt data were acquired across the hidaka mountains which are thought to have formed by collisional orogenic processes a regional electrical strike of n18 w consistent with surficial geology was derived from impedance tensor decomposition two dimensional resistivity models were constructed by forward model fitting with preference for reducing the misfit of transverse magnetic mode the final modeling imaged a collision boundary between cretaceous forearc basin rocks and continental crust the major features of the model are 1 a 5 km thick surficial conductive layer corresponding to cretaceous forearc basin and the underlying resistive basement that shallows and is exposed to the east where sorachi formations characterized by oceanic crustal rocks crop out therefore we interpret the underlying resistive layer as oceanic crust 2 a thin 500 m thick conductive 3 m anomaly corresponds to serpentinite exposure in the kamuikotan metamorphic belt 3 exposed deep crustal rocks in the hidaka belt showed high resistivity 1000 2000 m at the surface the subsurface westward extension inferred from the mt data is supported by seismic refraction data 4 in the hidaka mountains a relatively conductive 500 1000 m layer implying accretionary prism sequences was inferred at 2 to 10 km depth beneath a more resistive 1000 2000 m surface layer 5 a wedge shaped resistivity anomaly was found at 5 to 50 km depth beneath the hidaka belt the resistivity of this wedge decreases eastward from 30 000 m to 2000 m consistent with the surface decrease of metamorphic grade the spatial distribution is also consistent with a seismic high velocity anomaly 6 the western side of the resistive wedge is fringed by a dipping conductor correlations with a low velocity anomaly and high seismicity suggest that this conductor is an enhanced porosity region and that it may be working as a detachment zone at the collision boundary the high resistivity contrast between oceanic crust and high temperature metamorphosed continental crust permitted us to image the interfingered complex structure beneath the hidaka mountains from 300 m to 50 km depth

barnacle dominated limestone with giant cross beds in a non tropical tide swept pliocene forearc seaway hawke s bay new zealand abstract pliocene non tropical widespread and locally thick up to 100 m limestones occur in hawke s bay eastern north island where they are intimately associated with very thick 5 km terrigenous dominated neogene sequences that formed in a tectonically active convergent margin setting the non tropical character of the limestones is shown unequivocally by 1 the complete dominance of skeletal calcarenites and calcirudites 2 the occurrence of oyster banks as the only in situ organic structures 3 the dominance of barnacles epifaunal molluscs bryozoans echinoderms foraminifers brachiopods and calcareous red algae as skeletal components and 4 the preponderance of calcite over aragonite in the mineralogy of the skeletal grains and cements the abundance of barnacle fragments in the limestones and the related exclusive occurrence of only one major organic association a barnacle epifaunal bivalve bryozoan assemblage is striking and unusual given the extent of the limestones pecten and oyster valves acted as substrates for barnacle attachment and their growth was promoted by strong tidal paleocurrents that swept the depositional setting a long 450 km narrow 30 50 km forearc basin seaway which formed between an actively deforming subduction complex to the east and an uplifting structural ridge to the west synsedimentary deformation promoted limestone formation on the margins of the seaway by creating current swept clastic free submarine ridges that acted as the sites of carbonate production tidal flows dispersed the carbonate constituents and organised them into a wide spectrum of tide influenced cross bedded and horizontal structures most spectacular are occurrences of giant tabular cross beds with sets 10 40 m thick and foreset dips of 7 36 some interpreted as the deposits of major sand bars on carbonate deltas marginal to the mouths of saddles traversing the rising antiforms and others analogous to modern linear sand ridges the small to large scale planar and trough cross beds and the horizontal and lenticular beds that are invariably associated with the giant cross beds and dominate most sections represent mainly the deposits of sand waves and sand sheets at inner to mid shelf depths in the seaway

archean crust as revealed in the kapuskasing uplift superior province canada in the central superior province of the canadian shield a 120 km wide transition from the low grade michipicoten greenstone belt to the high grade kapuskasing structural zone represents an oblique section through some 20 km of archean crust uplifted along a northwest dipping thrust fault the restored vertical section through the upper and middle crust consists of three megalayers with undulating boundaries 1 0 to 25 km a high grade heterogeneous gneissic assemblage in part older than the upper supracrustal succession

exhumation of an accretionary prism results from fission track thermochronology of the shimanto belt southwest japan abstract the along arc variation of the thermal history of the shimanto accretionary prism was studied with fission track thermochronology to investigate tectonic factors that control the exhumation of an accretionary prism twelve apatite and 35 zircon ages were analyzed on sandstone and granite samples from the kii and kyushu regions southwest japan and the samples are interpreted in combination with the previously reported data from the shikoku region zircon samples show various degrees of age resetting after deposition that are dependent on their position within the prism some of the zircon samples constrain the time of maximum heating within or cooling through the zircon partial annealing zone two lines of observation i e simultaneous exhumation revealed along across arc transect with relatively high maximum burial at the rear part of the prism and along arc coeval rebound from burial to exhumation indicate that the exhumation of the entire wedge was probably caused by a progressive accretionary process such as underplating at depth because the driving force for this type of exhumation is the growth of the wedge this exhumation process is probably a general exhumation process that occurs in all accretionary complexes apatite samples record cooling at 10 ma except for samples from sites in the north of the kii region whose ages are 35 ma suggesting the effect of the southwest japan block obduction onto the subducting young philippine sea plate this implies along with the distribution of locally reset zircon ages that the exhumation of the prism was also forced by local episodic events for example collision of blocks during differential rotational movement change of the subduction parameters and possible accelerated underplating beneath a narrow region probably caused by the increased material influx from the igneous activities

the conductivity of the crust and mantle beneath the kapuskasing uplift electrical anisotropy in the upper mantle summary kapuskasing uplift has been interpreted as an oblique cross section of up to 25km of crust and thus provides the opportunity to examine the properties of exposed mid to lower crustal material a magnetotelluric mt survey mapped a remarkably uniform upper crust and provided no evidence for upper crustal conductive zones that could be related to the often observed increase in mid and lower crustal conductivity the only shallow conductive anomaly is related to the ivanhoe lake cataclastic zone but its electrical signature does not appear to extend more than one kilometer in depth a regional apparent resistivity curve was determined from mt data and confirmed by subsequent controlled source electromagnetic surveys regional curves are essential for proper structural interpretation but are often difficult to determine because of electric field distortions the data show a decrease in resistivity at depths below 15 km which is typical of continental crust in many areas of the world there is a clear difference in orthogonal apparent resistivity and phase curves at periods greater than 10s which is most pronounced in a n65 e and n25 w coordinate frame two different models are proposed to explain the data the first consists of a conducting 2 d slab of approximately 50 km width in the lower crust and striking n65 e the strike direction is consistent with a number of regional structural trends but there is no other direct supporting evidence for it the second model invokes either micro or macro electrical anisotropy in the upper mantle there is considerable evidence for seismic anisotropy in the region the electrical anisotropy could be the result of preferential conduction along the c axis of olivine crystals hydrogen dissolved in the olivine lattice with preferential conduction along the a axis or possible alignment of dykes joints and faults in the upper mantle if the anisotropy is related to strain induced orientations of crystals or fabric it will provide evidence for the motions of the mantle associated with plate tectonics

a magnetotelluric survey over the east bull lake gabbro anorthosite complex tensor and scalar magnetotelluric and audiomagnetotelluric mt amt data have been acquired on a gabbro anorthosite pluton in northern ontario about 100 km west of sudbury the scalar data from 102 sites were used to map resistivity contrasts associated with near surface geology and overburden data from stations located away from possible geological inhomogeneities provided a structural interpretation which was subsequently confirmed by tensor mt soundings and by drilling the scalar data also provided a means of interpreting the bedrock structure associated with a major fault that bisects the pluton the apparent resistivity curves from the eight tensor stations ranged from nearly isotropic to strongly anisotropic with large shifts in apparent resistivity between the different locations however the measured impedances both modulus and phase strongly reflected the predominant northwest southeast trend of faulting and diabase dykes in the region modelling indicates the presence of an anisotropic subhorizontal conducting layer beginning at a depth of about 800 m the direction of fluid transport within this layer is expected to be parallel to the structural trends and to the e polarization axis of the impedance tensor the presence of this conductor has been confirmed by borehole resistivity measurements a conductive zone in the lower crust has also been detected commencing at a depth of about 18 km finally the tensor measurements at the longest periods are consistent with an increase in conductivity in the upper mantle suggesting the existence of an electrically conducting asthenosphere in this part of the canadian shield

the application of fission track analysis to the dating of barren sequences examples from red beds in scotland and thailand in continental red beds facies which often contain little or no organic material for biostratigraphic dating fission track ft analysis of detrital zircon crystals represents one method by which a maximum stratigraphic age may be determined in addition ft analysis of detrital apatite provides a means of palaeotemperature estimation especially in areas where there is insufficient or unsuitable organic matter for vitrinite reflectance two examples of the application of ft analysis to the solution of stratigraphic problems in red bed sequences are described from scotland and thailand from authors

the electrical resistivity of canada s lithosphere and correlation with other parameters contributions from lithoprobe and other programmes over the last 30 years through lithoprobe and other programmes modern high quality magnetotelluric mt measurements probing deep into the lithosphere and underlying asthenosphere have been made at over 6000 sites across canada in all provinces and territories except nova scotia some regions are well covered particularly alberta southern british columbia and western ontario whereas others remain poorly covered such as quebec and large swaths of nunavut prior publications from individual studies have added significantly to the wealth of canada s geoscience knowledge and have demonstrated that mt can contribute significantly to understanding of the tectonic processes that have shaped canada however to date no continent scale maps of lithospheric electrical parameters have been constructed from the extensive mt database herein we review the contributions made by the mt components of lithoprobe and present new continental scale maps of various electrical parameters at crustal and upper mantle

a late oligocene tectono volcanic event in east kalimantan and the implications for tectonics and sedimentation in borneo new apatite fission track data k ar radiometric ages and major and trace element geochem istry from the northern part of the kutai basin borneo document a major regional tectono volcanic episode apatite fission track data from late cretaceous sandstones indicate a period of rapid cooling in the late oligocene cooling initiated by a rapid temperature drop of over 40 c within c 2 ma might have been caused by increased denudation associated with tectonic movements rapid cooling is also concomitant with a phase of igneous activity new k ar radiometric ages of andesitic dacitic high level intrusive rocks and associated volcanic rocks give ages of 23 18 ma which correlate with the regionally extensive late oligocene miocene sintang intrusives suite these andesitic dacitic high level intrusive rocks also have geochemical characteristics of arc related rocks the sedimentary response to this tectono volcanic event is the eastwards shift of the western basin margin and the inception of deltaic deposition around the newly re defined basin margins up to 9 km of sediment was deposited in the basin during miocene delta progradation covering thick sequences of palaeogene bathyal shales providing an excellent decollement surface for later inversion elsewhere in borneo and adjacent areas of se asia major events recorded in the late oligocene to early miocene include major thrust imbrication and volcanic arc activity the cause of which is unclear possibilities include the collision of australia with the philippine sea plate the counter clockwise rotation of borneo in the neogene and the initial impingement of blocks of south china origin with northern borneo south palawan

biogenic facies in the antarctic glacimarine environment basis for a polar glacimarine summary abstract the association of glacial deposits diamicts or tillites with biogenic and or chemically derived sedimentary rocks in the ancient record is one which continues to challenge interpretation an analogous association can be found on portions of the east antarctic continental shelf where relict glacial and glacimarine diamictons are overlain by a varied and complex suite of modern biogenic deposits carbonate bioclastic material can be found in two distinct zones and its deposition may have been contemporaneous with partial glacial expansion onto the shelf a nearshore carbonate facies consists of in situ and partially reworked barnacles bryozoans ostracods pelycepods gastropods planktonic and benthonic foraminifera a siliceous biogenic component is intermixed within the shallow water 500 m siliceous facies of pelagic hemipelagic and sediment gravity flow origin is found within inner shelf depressions and consists predominantly of diatom frustules and radiolaria these accumulations of siliceous ooze and mud clearly post date glacial recession from the shelf and contain laminated cross laminated and massive interbeds which are accumulating at rates of 0 3 cm yr the extreme polar climate inhibits meltwater production and terrigenous influx into marine basins this allows for the accumulation of biogenic rich material which is also favored by the high seasonal productivity inherent in the south polar oceans ancient analogs to these modern deposits exist and their association with glacimarine strata could be used to infer polar climatic settings and glacial retreat that is related to eustatic sea level rather than regional warming

a summary of electromagnetic studies on the abitibi grenville transect electromagnetic surveys on the abitibi grenville lithoprobe transect have elucidated a number of conductivity signatures that can be genetically linked to precambrian tectonic processes some major fault zones are moderately conductive possibly signalling graphite deposition from a mantle co2 flux along crust penetrating fault systems however conductive graphitic metasedimentary rocks characteristic of foreland basins are apparently absent from the transect area a weak inverse correlation between metamorphic grade and electrical conductivity was observed by following rock units across the grenville front into high grade equivalents within the parautochthonous belt a uniformly conductive mid crustal layer extends across the grenville front apparently without change in character the existence of this ubiquitous mid crustal conductor has been interpreted to mean that electrical conductivity is controlled by the present day pressure temperature and fluid saturation of the lower crust independent o

non tropical carbonate deposits on the modern new zealand shelf abstract extensive ca 50 000 km 2 shallow marine platforms 70 caco 3 despite proximity to a tectonically active plate margin in these regions the terrigenous sediment supply is presently low and growth of epibenthos is fostered by firm substrates rock gravels shells seaweeds and the generally energetic nature and high nutrient levels of open shelf waters rapid transition into adjacent terrigenous dominated facies is characteristic irrespective of water depth the carbonates are coarse grained and fragmental carbonate mud is rare calcite dominates over aragonite high mg calcite widespread off northern new zealand is rare in the south skeletal material is dominated by bryozoans and bivalve molluscs with significant local contributions from foraminifers barnacles calcareous red algae and echinoderms the name bryomol is suggested for this distinctive temperate region skeletal carbonate facies which can be usefully subdivided based on dominant zoarial growth forms of the bryozoan component known to be habitat related bioerosion is an important mechanism of skeletal fragmentation and degradation many grains especially aragontic bivalves are infested by endolithic borers and have low preservation potential ages of skeletal material in the surficial deposits range from more than 20 000 years b p to modern which is consistent with both low rates of carbonate production and sediment accumulation and the wide range in preservation state of grains some data suggest that the skeletal carbonates are dispersed and mixed mainly during infrequent movement of sand ribbons sand waves and sand sheets driven by storm assisted tidal flows tracts of modern palimpsest and relict carbonates can occur in juxtaposition the facies characteristics of the new zealand shelf carbonate deposits contrast significantly with those of the classical bahaman type carbonate model however they are similar to those reported from many other mid to high latitude carbonate shelves and afford good analogues for most onland occurrences of new zealand cenozoic limestones

a controlled source time domain electromagnetic survey over an upthrust section of archean crust in the kapuskasing structural zone summary a pilot controlled source electromagnetic survey was conducted in the kapuskasing structural zone to test the application of the utem technique for determining the electrical conductivity structure of the earth s crust to depths of up to 10 km in general the data are consistent with the results of an earlier broadband magnetotelluric mt survey and indicate a quasi layered earth below a variable overburden zone with conductances between 0 1 and 0 5 s at some depth below 10 km conductivity appears to increase in agreement with the mt interpretation and provides confidence that the static shift of the mt data was corrected a weakly conductive layer located at depths greater than 2 km is possibly associated with a feature of the ivanhoe lake cataclastic zone ilcz a major fault zone along which up to 30 km of the earth s crust has been thrust to the surface there was no clear evidence in the utem data for a conductive zone extending to the proposed surface strike location of the ilcz a conductive anomaly at depths of 1 2 km may extend east of the present survey area and suggested that a subsequent utem survey must expand the coverage to the east

criteria for recognition of cold water carbonate sedimentation berriedale limestone lower permian tasmania australia abstract the permian berriedale limestone is an alternating sequence of limestone and calcareous shale associated with marine glacial terrigenous sediments it was deposited at a paleolatitude near 80 s during the gondwanan permo carboniferous ice age dropstones commonly disrupt laminae range widely in size and composition and reveal glacially derived shapes and textures under the sem there is a lower diversity of fauna mostly bryozoans brachiopods and pelecypods and non skeletal grains mostly intraclasts than in warm water limestones the vertical variation in depositional microfacies through shale limestone shale beds indicates that the shallow marine limestones formed during the lowering of sea level in colder periods as the sea level rose during warmer periods a shower of dropstones preceded shale deposition for this mason dropstones are more numerous around the contacts between limestone beds and overlying shale beds but rare in the middle or base of limestone beds icebergs calved from adjacent glaciers were floating and the surface water temperature was near freezing during limestone deposition upwelling cold currents provided nutrients and maintained calcium carbonate at saturation well developed rhombs in micrite microspar and spar and length slow elongate rhombs and poikilotopic rhombic plates both formed by accretion of rhombohedra indicate low mg calcite precipitated from seawater at a temperature of 3 c these cements are overlain by micrite marine mud dropstones and geopetal fillings of well sorted internal sediments and are cut by borings all proving both synsedimentary ages and submarine origin of these cements the calcium carbonate content in these cold marine waters fluctuated ranging from undersaturated destructive diagenesis pits etchings rhombic pores and dissolution features to saturated constructive diagenesis as the sea level rose during warmer periods large volumes of melt waters mixed with marine waters the mixing zone cements succeeding marine cements are cloudy inclusion rich coarse plates up to a few mm these crystals grew embedding or nucleating over early formed crystals and previously cemented both fillings and encrustations bioclasts the mixing zone cementation is preceded by erosion of early formed crystals the eroded crystals now occur as inclusions in mixing zone cements the field microfacies and diagenetic criteria evolved in this study might be used for recognition of a wide spectrum of cold water carbonates temperate subpolar and glacio marine

pliocene sedimentation in a shallow cool water estuarine gulf murray basin south australia the pliocene norwest bend formation is a well preserved succession of terrestrial and shallow marine deposits in the murray basin south australia sediments in this unit consist of two discrete terrigenous clastic rich decametre scale sequences or informal members which record episodes of marine incursion during the early and late pliocene respectively the base of each sequence is a transgressive lag and or strandline deposit that is transitional upwards into a highstand subtidal terrigenous clastic and cool water carbonate sediment accumulation the top of each sequence is incised by fluvial channels that are filled by river deposits which formed as relative sea level fell and terrestrial environments prograded basinward sedimentological data suggest that gross stratigraphic architecture was primarily determined by glacioeustasy differences in sedimentary style between these two sequences however reflect a major climatic change that took place in southern australia during the mid pliocene the lower quartzose sand member is formed of siliciclastic sediment derived from prolonged deep subaerial weathering and contains a bivalve dominated cool temperate open marine mollusc assemblage these sediments accumulated under an equitable relatively warm humid climate the murray basin during this time because of high fluvial discharge was a salt wedge estuary with typical estuarine circulation in contrast the upper oyster rich member is typified by large monospecific oyster buildups that grew in restricted coastal environments strandline deposits contain a warm temperate skeletal assemblage contemporaneous aeolian sediments accumulated under warm semi arid climatic conditions well developed ferricrete silcrete and calcrete horizons reflect cyclic conditions of rainwater infiltration and evaporation in the seasonally dry climate that typifies southern australia today highly seasonal rainfall produced an estuary that fluctuated annually from being well to partially mixed these pliocene sediments support the notion that mollusc rich facies are the signature of cool water carbonate accumulations in inboard neritic environments unlike bryozoans that dominate the outer parts of cenozoic cool water carbonate shelves molluscs evolved to exploit an array of coastal ecosystems with wide salinity variations and variable sedimentation rates

pleistocene glacimarine sedimentation on the continental slope off vancouver island british columbia abstract cordilleran ice sheet activity has had a significant influence on glacimarine sediment transport and deposition on the western canadian continental slope resulting in distinct sediment facies here we present lithogenic sediment grain size distributions grains 250 m g 1 63 m 10 to 60 m and 2 to 4 m and mass accumulation rates mar from a marine core md02 2496 collected 50 km offshore of vancouver island british columbia the lithogenic fraction of sediment deposited on the slope increased as grain size decreased and sediment sorting increased at 30 ka when the cordilleran ice sheet grew into southern british columbia during the fraser glaciation as the ice sheet advanced onto the continental shelf near core md02 2496 between 19 and 17 ka the proximal ice margin dramatically increased lithogenic sediment mars glacimarine sedimentation at this time was associated with cyclic deposition of generally coarse poorly sorted sediment an 80 year cyclicity suggests the influence of 1 outburst floods 2 lunar or 3 solar cycles on tidewater outlet glacier discharge rapid ice sheet retreat at 17 ka is indicated by ice rafted debris ird deposition followed by the deposition of fine well sorted silt suggestive of iceberg discharge followed by rock flour in a meltwater plume lithogenic sediment mars decreased dramatically at the bolling with a brief return to coarse poorly sorted sediments during the younger dryas glacimarine sedimentation decreased by 10 ka as the cordilleran ice sheet extent diminished to the areal extent of modern ice fields

late quaternary deglaciation and sea level history of eastern juan de fuca strait cascadia abstract eastern juan de fuca strait of southwestern british columbia northwestern washington state is near the western and southern terminus of late wisconsinan glaciation in north america seismic reflection profiles bathymetric data sediment core data and 41 new radiocarbon dates provide insight into the history of ice retreat and sea level change in the eastern portion of the strait the retreating ice margin appears to have passed through the area between 14 460 200 and 13 595 145 14c yr glacial marine sediments date between 12 889 50 and 11 110 50 14c yr bp wave eroded unconformities drowned prograded deposits and a partially isolated low stand basin are evidence attributed to low stand sea levels following deglaciation and five new control points on the local eustatic sea level curve are assigned based on radiocarbon dating of these features sea level change was rapid from 75 m immediately after deglaciation to possibly 60 4 m at 9920 60 14c yr bp after this time gradual sea level transgression took place relative sea level reached its approximate present position by 5470 115 14c yr bp since then relative sea level has remained constant suggesting eustatic rise is balanced by crustal uplift

biodegradation of temperate water skeletal carbonates by boring sponges on the scott shelf british columbia canada abstract boring sponges are a major agent of shell destruction and in the process an important contributor of fine grained carbonate detritus in temperate skeletal carbonate deposits on scott shelf northwestern vancouver island intensive boring is encouraged by the generally low rates of carbonate production and sedimentation skeletal grains become considerably weakened by sponge boring and break preferentially along the directions of sponge excavated tunnels and galleries within the shell boring also facilitates shell dissolution by significantly increasing the surface area weight ratio of shells and by breaking down the organic matrix of shells the large aragonitic bivalves glycymeris and humilaria appear especially susceptible to sponge biodegradation and have become thoroughly bored and corroded within about 1000 years in ambient shelf waters thus their preservation potential is low selective loss of aragonitic biota from ancient cool water shelf skeletal carbonate deposits is anticipated and is evident in many temperate latitude occurrences of new zealand cenozoic limestones

reconnaissance electromagnetic induction study of the kapuskasing structural zone implications for lower crustal conductivity abstract a large scale electromagnetic induction study has been carried out over the kapuskasing structural zone ksz an upthrust section of lower crustal rocks in north central ontario the absence of an overall anomalous response from the ksz even though the lower crust in this region of the canadian shield is known to be anomalously conductive implies that enhanced lower crustal conductivity is related to intrinsic conditions at lower crustal depths and not to mineralogical composition

dissolution behaviour of bryozoan sediments taphonomic implications for nontropical shelf carbonates abstract diagenesis of carbonate sediments on temperate marine shelves is commonly destructive in contrast to a dominantly constructive regime in tropical waters in some cases dissolution can be important in temperate shelf waters particularly affecting the metastable carbonate minerals if dissolution does occur it can be an important taphonomic process reducing skeletal remains available for fossilization and biasing fossil assemblages the dissolution behaviour of bryozoans has been investigated in an acid bath laboratory experiment using nontropical carbonate sediments from the new zealand shelf bryozoans of various shapes growth forms and compositions low to high mg calcite and aragonite were extracted and their weight loss over time was measured results show that variations in stability of carbonate mineralogies are insufficient to predict relative dissolution rates if shelf dissolution occurs even if only periodically one might anticipate that the less stable aragonite and high mg calcite skeletons would dissolve first in fact this experiments shows that small delicate skeletons with non compact morphologies dissolve most rapidly apparently with little regard for mineralogy fossil bryozoan assemblages from temperate marine shelf environments may therefore not only reflect the preferential loss of certain aragonitic species but also the loss of small delicate species new zealand s nontropical tertiary bryomol limestones often lack aragonitic skeletons they may also be relatively depleted in small delicately branched bryozoans in contrast tropical shelf carbonate sediments can retain more delicate skeletons through early cementation and lack of dissolution a difference in character between tropical and temperate carbonate shelf deposits may therefore be in the proportion of small delicate bryozoan colonies

grain boundary graphite in kapuskasing gneisses and implications for lower crustal conductivity surface electromagnetic measurements commonly reveal that the intermediate and lower continental crust has an appreciable electrical conductivity much higher than that found for laboratory analogues of deep crustal rocks or for upper crustal rocks either formed at shallow depths or uplifted from deeper levels conducting films at grain boundaries are thought to play an important part in enhancing deep crustal conductivity with brines and graphite being the main candidates1 at present however there is a lack of direct evidence for such films frost et al 2 have reported an enhancement in conductivity of igneous lower crustal rocks from the la ramie complex apparently owing to the presence of graphite films but the possible role of brines was not clear from this work here we present a study of the grain surface composition of metamorphic and one igneous rocks exhumed from 20 km depth by the kapuskasing uplift of the canadian shield3 we expect these samples to be representative of metamorphic and igneous rocks of the deep archaean crust auger spectroscopy provides evidence for graphite films at grain boundaries which can account for the present electrical signature of the kapuskasing crust4 6 we also detect traces of chlorine sulphur and iron which suggest that brines and solid conductors other than graphite may have helped to enhance the conductivity but their abundance suggests at best a minor role relative to graphite

origin of modern heavy mineral deposits northern british columbia continental shelf abstract bottom sediments of the northern british columbia continental shelf contain on average 10 of heavy minerals by weight within the dominant sand fraction anomalous concentrations occur within selected sand samples from queen charlotte sound 25 and hecate strait 18 the heavy mineral suite here is dominated by amphibole and the titanium minerals ilmenite sphene and titaniferous magnetite dynamic modelling of the present oceanographic and sedimentary environment in queen charlotte sound suggests that the anomalous offshore concentrations of heavy minerals result from continuous differential sorting during extreme yearly storms the deposits are not considered to be relict

imaging of deep fluids in archaean crust despite the importance of aqueous fluids in tectonic metamorphic and magmatic activity in the earth s crust few techniques are available for directly observing their distribution at depth even in stable continental crust such observations as have been made electromagnetic deep sounding which by inference1 2 images saline fluids and super deep drilling3 suggest that fluids are present in varying amounts throughout the crust in direct conflict4 with the normal petrological inference of a very dry deep crust here we report the results of an unusually high resolution electromagnetic sounding method to image the deep electrical conductivity structure below a 30 km profile in ontario which crosses archaean lower crustal material of high metamorphic grade exposed by a proterozoic thrust fault the ivanhoe lake cataclastic zone the electrical resistivity image obtained shows embedded in very resistive crystalline crust two nearly continuous sub horizontal zones of enhanced electrical conductivity at depths of 2 3 and 5 6 km below this the commonly observed2 5 7 mid crustal rise in conductivity is seen at depths of 15 20 km the image does not correlate well with the structure inferred from surface geology suggesting that the transport and distribution of fluids was not strongly controlled by lithological boundaries or the thrust fault itself

correlation of sandstones using heavy minerals an example from the statfjord formation of the snorre field northern north sea correlation of sandstones using heavy minerals is dependent on the recognition and quantification of provenance sensitive parameters suitable criteria include ratios of minerals that have similar hydraulic and diagenetic behaviour and properties of populations of individual mineral species sandstones of the statfjord formation in the snorre field display marked variations in their heavy mineral assemblages although hydraulic and diagenetic processes have played some part in generating these variations major changes in the nature of the source material can be detected on the basis of heavy mineral ratio and varietal data these changes in sand provenance can be used to produce a detailed stratigraphic breakdown of the sequence and to correlate from well to well eleven heavy mineral zones have been recognised on the basis of variations in monazite zircon garnet zircon and rutile zircon ratios on the incoming of chloritoid and on the composition of garnet populations the marked changes in provenance result from the proximity of the depositional location to the hinterland and it is considered unlikely that the detailed correlation made in the snorre field area applies to statfjord sandstones in other parts of the northern north sea however there is evidence for some degree of allogenic control on the heavy mineral variations and therefore some events may have regional significance

mineralogical and biogenic composition of the zanzibar channel sediments tanzania sediments from the zanzibar channel have been analysed for mineralogical and biogenic composition the main objective of the study was to describe the depositional environment of the sediments based on these parameters the study was also conducted to give an insight into sediment provenance of the sediments quartz feldspar both microcline and plagioclase and hornblende are the main mineralogical components while zircon muscovite biotite and augite occur as accessory minerals the quartz grains are generally angular to sub angular and highly strained indicative of immature sediments probably derived from highly metamorphosed rocks the presence of hornblende also supports the conclusion that the sediments are immature a possible source is the metamorphic rocks of the mozambique belt located about 25 50 km from the coastline benthic foraminifera are the dominant biogenic constituents other common biogenic constituents are molluscs pelecypods and gastropods and corals bryozoans and ostracods are relatively less common while sea urchins are accessory biogenic components the composition and abundance of these biogenic components and morphological sedimentological and mineralogical data permit construction of a simple model which distinguishes between three bio physiographic settings in the zanzibar channel using depth contours 1 the coastal zone 0 10 m depth 2 the reef platform patch reefs zone 10 20 m depth and 3 the central channel zone 20 cm depth in the coastal zone the sediments are dominated by fine sand sized with a very prominent fine sand mode the proportion of benthic foraminifera is lower than in the other two zones 25 two lithogenic mineral components quartz and feldspar occur in significant proportions in the reef platform patch reefs zone the sediments are coarse to medium sand sized with no distinct mode the proportion of benthic foraminifera is highest 80 85 there and so is the biogenic quartz ratio 10 but that of lithogenic components is lowest 5 in the central channel zone the sediments are medium to fine sand sized and often bimodal with a prominent fine mode and a less prominent coarse mode the proportion of benthic foraminifera 70 75 is also higher than in the coastal zone but slightly lower than in the reef zone the proportion of lithogenic components 5 20 is higher than in the reef zone but lower than in the coastal zone and the biogenic quartz ratios is intermediate

glaciation and post glacial history of the continental shelf off southwestern vancouver island british columbia abstract bathymetry sediment distribution and seismic stratigraphy are used to interpret the pattern of glaciation of the continental shelf off southwestern vancouver island canada four seismostratigraphic units are distinguished and mapped in relation to sediments and sedimentary rocks present on the shelf they are 1 undivided tertiary bedrock 2 a unit composed mainly of pleistocene outwash 3 pleistocene morainal deposits and 4 holocene marine sediments a large piedmont glacier is envisaged formed by the coalescence of glaciers emanating from juan de fuca strait and barkley sound it cut a system of deep troughs into the tertiary bedrock built up a complex of morainal ridges and built out an extensive outwash plain on the unglaciated shelf to the northwest during glacial maxima the piedmont glacier extended right across the shelf particularly high discharge of debris from the seaward ends of the glacial troughs may have caused the erosion of adjacent submarine canyons during the final deglaciation the ice withdrew somewhat faster than the sea advanced although masses of downwasting ice may have persisted in many of the troughs the glacial topography including moraines and tertiary bedrock were levelled by the advancing sea but many of the troughs were preserved from burial perhaps because they were still ice filled or because the coastal system was sediment starved strong currents sweep the present shelf redistributing sand and mud winnowed from the tops of the truncated moraines into low lying areas and leaving concentrations of gravel behind

deep crustal structure and tectonic history of the northern kapuskasing uplift of ontario an integrated petrological geophysical study the northeast trending kapuskasing uplift transects the east west belts of the central superior province over a distance of some 500 km granulite to upper amphibolite facies rocks of the uplift form three distinct geological geophysical entities from south to north the chapleau groundhog river and fraserdale moosonee blocks uplift of the granulites along a moderately northwest dipping crustal scale thrust fault is attributed to an early proterozoic compressional event major northeast striking faults that bound the kapuskasing zone on the west were examined by modelling of geophysical anomalies to determine dip and by geobarometry of garnet orthopyroxene plagioclase quartz assemblages to determine vertical displacement granulites in the kapuskasing zone have 7 to 9 kbar signatures whereas those in the quetico belt to the west indicate metamorphic pressure of 4 6 kbar individual calibrations of the barometer yield consistent pressure differences of 2 3 kbar suggesting 7 10 km of west side down movement on the faults modelling of gravity and aeromagnetic gradients indicates westerly dips of 60 65 with west side down offset of up to 14 km these major normal faults probably formed as collapse structures in response to crustal thickening which occurred during the preceding compressional uplift stage differences in the configuration of individual blocks of the kapuskasing zone can be related to variable fault slip and intersection angles between normal and reverse faults thus the groundhog river and southern fraserdale moosonee blocks are perched thrust tips analogous to the sangre de cristo range of the laramide uplift province whereas the southern chapleau block is a tilted slab with similar configuration to the laramide wind river range pop up geometry deduced for the northern fraserdale moosonee block resembles the structure of the laramide uinta mountains a normal fault crosses the surface trace of the basal thrust fault between the groundhog river and fraserdale moosonee blocks and causes a 65 km gap without granulites this article contains supplementary material

deglacial ocean warming and marine margin retreat of the cordilleran ice sheet in the north pacific ocean abstract a new high resolution planktonic foraminiferal mg ca based ocean temperature record has been generated for deep sea core md02 2496 sited offshore of vancouver island western canada during the last deglaciation 21 12 ka the relationship between cordilleran ice sheet cis retreat and changing regional ocean temperatures has been reconstructed through glaciomarine sediments in md02 2496 that capture tidewater glacier response to surface ocean thermal forcing at cis maximum extent the marine margin of the ice sheet advanced onto the continental shelf during this interval ocean temperatures recorded by surface dwelling globigerina bulloides remained a relatively constant 7 5 c while subsurface dwelling neogloboquadrina pachyderma s recorded temperatures of 5 c these ocean temperatures were sufficiently warm to induce significant melt along the tidewater ice terminus similar to modern alaskan tidewater glacial systems during the deglacial retreat of the cis the n pachyderma temperature record shows two distinct warming steps of 2 and 2 5 c between 17 2 16 and 15 5 14 ka respectively coincident with ice rafting events from the cis while g bulloides records an 3 c warming from 15 to 14 ka we hypothesize that submarine melting resulting from relatively warm ocean temperatures was an important process driving ice removal from cis tidewater glaciers during the initial stages of deglaciation

ice streams of the late wisconsin cordilleran ice sheet in western north america abstract the late wisconsin cordilleran ice sheet cis of western north america is thought to have reached its maximum extent 2 5 106 km2 as late at c 14 5 ka most 80 of the ice sheet s bed consists of high mountains but its core zone sited on plateaux of the intermontane belt of british columbia and coterminous parts of the usa shows broad swaths of subglacially streamlined rock and sediment broad scale mapping from new digital imagery data identifies three subglacial bed types 1 hard beds of variably streamlined bedrock 2 drumlinized soft beds of deformation till reworked from antecedent sediment and 3 mixed beds of variably streamlined bedrock protruding through drumlinized sediment drumlins on soft beds appear to be erosional features cut into till and antecedent sediments and identify the catchment areas of paleo ice streams expressed downglacier as flow sets of megascale glacial lineations msgls grooved and cloned drumlins appear to record the transition from drumlins to msgls the location of paleo ice streams reflects topographic funneling of ice from plateau surfaces through outlet valleys and a soft bed that sustained fast flow rock cut msgls are also present locally on the floors of outlet valleys cis disintegrated in

effects of early sea floor processes on the taphonomy of temperate shelf skeletal carbonate deposits abstract cool water shelf carbonates differ from tropical carbonates in their sources modes and rates of deposition geochemistry and diagenesis inorganic precipitation marine cementation and sediment accumulation rates are absent or slow in cool waters so that temperate carbonates remain longer at or near the sea bed early sea floor processes occurring between biogenic calcification and ultimate deposition thus take on an important role and there is the potential for considerable taphonomic loss of skeletal information into the fossilised record of cool water carbonate deposits the physical breakdown processes of dissociation breakage and abrasion are mediated mainly by hydraulic regime and are always destructive impact damage reduces the size of grains removes structure and therefore information and ultimately may transform skeletal material into anonymous particles abrasion is highly selective amongst and within taxa their skeletal form and structure strongly influencing resistance to mechanical breakdown dissolution and precipitation are the end members of a two way chemical equilibrium operating in sea water in cool waters inorganic precipitation is rare there is conflicting opinion about the importance of diagenetic dissolution of carbonate skeletons on the temperate sea floor but test maceration and early loss of aragonite in particular are reported dissolution may relate to undersaturated acidic pore waters generated locally by a combination of microbial metabolisation of organic matter strong bioturbation and oxidation of solid phase sulphides immediately beneath the sea floor in otherwise very slowly accumulating skeletal deposits laboratory experiments demonstrate that surface to volume ratio and skeletal mineralogy are both important in determining skeletal resistance to dissolution biological processes on the sea floor include encrustation and bioerosion encrustation a constructive process may be periodic or seasonal and can be reversed it produces both information and material bioerosion in contrast is destructive and permanent in temperate areas bioerosion may destroy even very large shells during their long residence at the sea floor on the order of hundreds to thousands of years overall processes on the temperate sea floor may combine to destroy more carbonate than they produce and the preservation potential of temperate shelf carbonate into the rock record may be significantly affected where preservation does occur in such a destructive regime the effects of early sea floor processes will be key determinants of the deposit resulting in a taphofacies characteristic of temperate shelf carbonate sediments

sedimentary model and high frequency cyclicity in a mediterranean shallow shelf temperate carbonate environment uppermost miocene agua amarga basin southern spain uppermost tortonian to lower messinian temperate carbonates crop out in the agua amarga basin se spain they consist of four units the lower three units can be tentatively assigned to the lowstand systems tract of a fourth order sequence constituting in turn the lowstand megatrough unit transgressive breccia unit and highstand bedded unit stages of a higher order cycle all these materials were deposited in a small pull apart basin related to the sinistral carboneras strike slip fault system the best represented is the bedded unit up to 25 m thick which consists of bioclastic bryozoan bivalve dominated calcarenites calcirudites with abundant fragments of echinoids barnacles benthic foraminifers coralline algae brachiopods and solitary corals facies trends within this unit are roughly arranged in an e w direction with the coastline to the north of the basin the depositional model is that of a gentle ramp with prograding beaches and shoals in its higher parts seaward of the shoals was the factory area where most organisms lived and maximum carbonate production took place from this area some of the skeletons were washed landwards by waves and or currents during storms and incorporated into the shoals and beaches and others moved downslope along the ramp as mass flows accumulating to form the fan bedded zone the factory area and fan bedded sediments intercalate five well defined thick beds of calcarenites fine grained calcirudites they show bar morphologies single or amalgamated or make up sand waves with very consistent tabular cross bedding pointing landwards these beds formed in a very shallow wave current influenced coastal environment the bars and sand waves in the fan bedded zone developed during lowstands while those located higher up in the ramp interbedded with the factory facies are related to transgressive stages prograding beaches shoals factory facies and fan bedded layers developed during the highstands net skeletal production occurred mainly during the highstands sediment accretion values of these sediments are similar to those of present and ancient shallow marine temperate carbonates considering that the whole bedded unit was deposited in a 100 000 year interval equivalent to the short eccentricity cycle the five cycles inside the bedded unit would therefore correspond to the c 20 000 year precession cycles of the milankovitch band

magnetotelluric interpretation of crustal and mantle structure in the grenville province summary accurate determinations of depths and conductivities of electrical structures in shield regions are often difficult because of the inhomogeneity of the uppermost crust a magnetotelluric mt station bat in the grenville province of the precambrian shield in eastern canada has been in operation since 1975 for time dependency studies of electrical resistivity changes related to earthquakes the mt response of the station displays low skew with small to moderate anisotropy one dimensional inversion of the apparent resistivity and phase reveals two well defined conductors in the crust one at 10 km and the second at the base of the crust the latter has a resistivity less than 50 m these results are substantiated by three additional mt stations located up to 40 km distant data from other new mt stations and from stations previously published in the literature are compared with two dimensional computer model results and with the three dimensional analogue scale model results of dosso et al while additional data for periods less than 100 s would be desirable the results from a number of the mt stations are not inconsistent with a widespread occurrence of a conducting zone at the base of the crust in the grenville the inversion analysis also indicates the existence of a conductor at some depth greater than 100 km with a resistivity less than 30 m this may coincide with a seismic low velocity zone observed in the mantle under the canadian shield

a review of electromagnetic investigations in the kapuskasing uplift and surrounding regions electrical properties of key rocks electromagnetic investigations of the kapuskasing uplift show that the gross electrical conductivity structure of the present crust is subhorizontal contrary to the lithology as defined by seismic experiments with increasing conductivity with depth a feature common to most continental crusts the current upper crust of the chapleau block includes zones of reduced resistivity the near surface expression of the ivanhoe lake cataclastic zone 40 k m these include a subhorizontal layer at 5 km and a subhorizontal to dipping layer at 2 km the deeper layer is interpreted as imaging deep fluids porosities 0 5 postdating the uplift the shallower feature possibly related to the seismically detected detachment zone dipping at 15 could be imaging conductors s

petrophysical model of deep electrical conductors graphite lining as a source and its disconnection due to uplift petrophysical information including stress release data recently made available for low porosity 0 1 0 4 crystalline rocks has been used to develop a broken conductor model that may explain the origin of enhanced electrical conductivity of the intermediate to lower continental crusts of shields and its disappearance when the rocks are uplifted average pore size and pore density of their fluid flow paths are 0 1 0 4 m and 1 400 m respectively the model assumes that these paths are filled or lined with interconnected electrical conducting minerals such as graphite resulting in the rocks having resistivities as low as 40 to 800 m in situ graphite film thicknesses required to produce these resistivities are 5 20 nm 50 200 a the model also assumes that electrical conducting paths break up during uplift due to stress release resulting in a poorly conducting rock petrophysical data of granites and observations from deep drill holes suggest a porosity increase of the order of 3 from an uplift of 10 km or more however the newly formed pore space would fill with deposits or intruded material so that surface rock porosities would not be much larger than at depth electrical resistivities of rock samples containing disconnected grain boundary graphite presently exposed by the kapuskasing uplift of the canadian shield are in the range of 3000 12000 m for the direction of foliation these values are 10 100 times larger than the estimates for similar rocks containing interconnected graphite but are 10 100 times smaller than usually observed in the canadian shield for similar rocks absent of grain boundary graphite these observations are in good agreement with the results predicted by the broken conductor model for an uplift of 10 km or more if a gross linear relationship is assumed between crack porosity and uplift for the upper 10 km of the crust

the origin of major incisions within the pleistocene deposits of the north sea a seismic survey to resolve the geometry of major incisions within the upper pleistocene has been run over an area of 1600 km2 in the mid north sea twelve separate incisions have been identified ranging up to 5 km wide and 25 km long with incised depths from 100 to 350 m deposits categorised into four recurring types infill the incisions to form a flat sea bed the surveyed features are comparable to others widely found beneath the northern continental shelves and lowlands of europe asia and america such incisions have a similar range of sizes and shapes were cut during at least three separate periods in the pleistocene and are down cut into substrates of various lithologies ranging from precambrian to pleistocene in age the major incisions are believed to be the product of a singular mechanism the outburst of intra ice sheet lakes forming jokulhlaup plunge pools except for late stage hollow infills which have interglacial temperate deposits the incision infills are periglacial the former deposits are similar to the sediments accumulating in the present day bathymetric enclosed deeps such as the lambay deep and devil s hole found on continental shelves it is suggested that the enclosed deeps are large kettle holes which resulted from the thawing of ice formerly buried in the incision infills