early carboniferous carbonate systems an alternative to the cainozoic paradigm abstract an alternative model for carbonate deposition is offered for the early carboniferous the major features of this interval are not explained using late cainozoic analogues early carboniferous low latitude shallow seas were apparently strongly influenced by upwelling and high nutrient levels these conditions favoured highly carbonate productive offshore systems but also resulted in the formation of extensive abiogenic carbonates as muds and ooids if correct the carboniferous serves to illustrate the dangers in extrapolating from present day systems to the geological record

an oscillating trend in phanerozoic non skeletal carbonate mineralogy textural and compositional data on ancient ooids and cements suggest the existence of an oscillating phanerozoic temporal trend in non skeletal carbonate mineralogy the trend shows good correlation with eustatic climatic oscillations proposed by others the most likely mechanism appears to be plate tectonically influenced oscillations in pco2 the vapour pressure of co2 rather than change in oceanic mg ca ratio

relative precipitation rates of aragonite and mg calcite from seawater temperature or carbonate ion control the temperature and degree of carbonate mineral supersaturation co3 2 ion concentration of seawater are the two most likely controlling variables on the compositions of recent marine carbonate cements the relative importance of these variables is difficult to assess in nature because they have similar trends with depth 0 1500 m and latitude in modern oceans we carried out laboratory experiments to investigate the relative growth rates of calcite mg calcite and aragonite in seawater as functions of both temperature 5 25 and 37 c and of carbonate ion concentration 2 5 to 15 times supersaturated with respect to calcite the precipitation rates of aragonite relative to those of calcite increase strongly with increasing temperature and are not affected greatly by changes in saturation state at 5 c calcite precipitation rates are nearly equivalent to those of aragonite regardless of the degree of saturation at both 25 and 37 c aragonite precipitation rates are much more rapid than those of calcite up to a factor of 4 except at very low saturation states calcite compositions vary from less than 5 mol mgco3 at 5 c to 14 mol mgco3 at 37 c our results suggest that the well documented shift toward precipitation of lower mol mg calcite and the decrease in abundance of aragonite cements with increasing oceanic depth and latitude can be attributed largely to lower temperatures

holocene carbonate sedimentation on the west eucla shelf great australian bight a shaved shelf the southern continental margin of australia is a cool water carbonate sedimentary province located in a high energy swell dominated oceanographic setting a vibrocore transect of 14c dated sediments across the centre of the eucla shelf is the first record of holocene shelf deposition in the great australian bight much of the seafloor shallower than 70 m water depth the base of wave abrasion is bare cenozoic limestone in some places encrusted by late pleistocene coral rich limestone that is cemented by high magnesium calcite 12 mole mgco3 the areally extensive 100 km wide hard bored substrate supports an epibiota of coralline algae minor bryozoans and soft algae or is covered by patches of holocene sediment up to 1 5 m thick generally a basal bivalve lag 3 ka overlain by quartzose bioclastic palimpsest sand this pattern of active carbonate production but little accretion on the wave swept mid to inner shelf is similar to that on other parts of the southern australian continental margin the term shaved shelf is proposed for this style of carbonate platform formed by alternating periods of sediment accretion cementation and erosion the palimpsest sand is typically rich in bivalves coralline algae and locally detrital dolomite outer shelf holocene sediment below the base of wave abrasion but inboard of the shelf edge is a metre thick unit of fine microbioclastic muddy sand with minor delicate bryozoans overlying a 9 13 ka rhodolith gravel some of this outer shelf sediment appears to have been resedimented the shelf edge is a sandy and rocky seafloor with active bryozoan growth and sediment production the holocene sediments are enriched in coralline algal particles and conspicuous large foraminifers cf marginopora and depleted in bryozoans as compared to coeval deposits on the lacepede and otway shelves off southeastern australia these differences are interpreted to reflect warmer waters of the leeuwin current and prevalent downwelling in this area as opposed to the general upwelling and colder waters in the east

oceanographic and climatic changes over the past 160 000 years at deep sea drilling project site 594 off southeastern new zealand southwest pacific ocean high resolution textural carbonate microfossil and oxygen 18o and carbon 13c stable isotopic analyses are presented for the late quaternary isotopic stages 1 to 6 interval of a core at deep sea drilling project site 594 situated just south of the present subtropical convergence in northernmost subantarctic surface waters on the southern flank of chatham rise in the southwest pacific downcore alternations of pelagic and hemipelagic oozes correspond to interglacial and glacial episodes respectively interglacial oozes contain a northern subantarctic assemblage of planktonic foraminifera with rare cool subtropical species while glacial oozes are characterized by species typical of southern most subantarctic waters and include radiolaria with affinity for antarctic waters the planktonic 18o record for the site supports a 3 6 c temperature change in near surface waters between interglacial and glacial stages and indicates that during stage 5e the near surface waters were about 1 c warmer than at present a pronounced cooling during stage 5d matches that of the vostok ice core d record and negative excursions at the end of stages 2 and 6 support a southern latitude warming preceding northern hemisphere deglaciation benthic foraminifera typical of cold intermediate to deep waters can increase dramatically in abundance in the hemipelagic ooze intervals when 18o results suggest a temperature drop in glacial stage bottom waters of 2 4 c possibly a result of upward displacement of antarctic intermediate water by circumpolar deep water at the site the foraminiferal 13c records support a reduced influence of north atlantic deep water in the southwest pacific during glacial stages when nutrient enhancement occurred in both bottom and surface waters despite the pronounced changes between interglacial and glacial conditions inferred at site 594 contributed to by a substantial northward shift by at least 5 of latitude in the position of the antarctic convergence south of new zealand during glacial episodes we conclude that the subtropical convergence remained locked to chatham rise approximately 44 s throughout stages 1 to 6 major compression of the intervening belt of subantarctic water during glacial episodes and the associated very steep thermal gradients and intensified atmospheric and oceanic circulation patterns that developed in this part of the southwest pacific account for the harsh frigid environment reported for on land southern new zealand at these times

oxygen and carbon isotope fields for temperate shelf carbonates from tasmania and new zealand abstract temperate latitude bryomol carbonates mantle significant areas of the modern tasmanian and new zealand shelves and bounding basins the isotope fields for the temperate skeletons and whole sediments are distinctly separated from their warm shallow marine counterparts because of their heavier 18o and narrow range of 13c values however the temperae isotope fields overlap with the deep sea carbonate isotope field and the seafloor diagenesis isotope trend linepasses through these fields tasmanian whole sediments and skeletal isotope fields are similar and are closely clustered along the diagenesis trend line because of intragranular cementation the new zealand skeletal isotope field is broader and scateerd possibly due to lack of cementation and some biochemical fractionation but its whole sediment isotope field is tighter and contained within the tasmanian whole sediment field in contrast to warm water carbonates the enrichement of 18o is mall

marine cements in mid tertiary cool water shelf limestones of new zealand and southern australia large areas of southern australia and new zealand are covered by mid tertiary limestones formed in cool water shelf environments the generally destructive character of sea floor diagenesis in such settings precludes ubiquitous inorganic precipitation of carbonates yet these limestones include occasional units with marine cements 1 within rare in situ biomounds 2 within some stacked cross bedded sand bodies 3 at the top of metre scale subtidal carbonate cycles and 4 most commonly associated with certain unconformities the marine cements are dominated by isopachous rinds of fibrous to bladed spar interstitial homogeneous micrite and interstitial micropeloidal micrite often precipitated sequentially in that order internal sedimentation of microbioclastic micrite may occur at any stage the paradox of marine cemented limestone units in an overall destructive cool water diagenetic regime may be explained by the precipitation of cement as intermediate mg calcite from marine waters undersaturated with respect to aragonite in some of the marine cemented limestones aragonite biomoulds may include marine cement sediment internally suggesting that dissolution of aragonite can at times be wholly marine and not always involve meteoric influences we suggest that marine cementation occurred preferentially but not exclusively during periods of relatively lowered sea level probably glacio eustatically driven in the mid tertiary at times of reduced sea level there was a relative increase in both the temperature and the carbonate saturation state of the shelf waters and the locus of carbonate sedimentation shifted towards formerly deeper shelf sites which now experienced increased swell wave and or tidal energy levels fostering sediment abrasion and reworking reduced sedimentation rates and freer exchange of sediment pore waters energy levels were probably also enhanced by increased upwelling of cold deep waters onto the southern ocean margins of the australasian carbonate platforms where water mass mixing warming and loss of co2 locally maintained critical levels of carbonate saturation for sea floor cement precipitation and promoted the phosphate glauconite mineralization associated with some of the marine cemented limestone units

platform drowning leading to cool water carbonate deposition evolution of a late ordovician turinian chatfieldian mixed sediment platform within the taconic orogen long point group newfoundland appalachians late ordovician turinian chatfieldian drowning of a mixed carbonate siliciclastic platform within the taconic orogen newfoundland appalachians is recorded by net deepening of an initial warm shallow water platform succession lourdes formation culminating in a metre scale thick condensed interval that characterizes a drowning succession punctuated by storm deposits composition of transported material suggests that seaward drowning was coupled with back stepping of a high energy carbonate factory related to hinterland uplift and erosion that would eventually lead to drowning of the outer platform beneath marine transported siliciclastic sediments winterhouse formation in the new offshore shelf setting a sparse reciprocal stratigraphy of fine to very coarse grained phosphatic carbonate and mixed sediment is interpreted to document gravity flow deposition downgradient from either a sustained or episodically developed high energy cool water carbonate source along the inner shelf transported carbo

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

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

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

submarine cementation and subaerial exposure in oligo miocene temperate carbonates torquay basin australia abstract at least four hardgrounds are present throughout the 27 m thick exposed oligo miocene cool water point addis limestone of the torquay basin in southeastern australia they range from thin a few centimeters thick incipient layers that have a nodular fabric to thick up to 1 m thick continuous hardgrounds the hardgrounds tend to be at the top of coarsening upward cycles and are typically overlain by low relief erosion surfaces the uppermost hardground is the best developed and most widespread in the point addis limestone and can be observed in all exposures of the succession at some localities it shows evidence of karstification such as dissolution pits clints and grikes and dissolution pinnacles whether karstified or not well developed hardgrounds are overlain by a lag c nglomerate that consists of hardground intraclasts with marine fe oxide crusts the hardgrounds are cemented by a first generation isopachous inclusion rich columnar and fibrous radiaxial calcite of marine origin with trace element compositions mg2 0 68 1 74 mole mgco3 fe2 800 4690 ppm sr2 0 260 ppm mn2 0 230 ppm and cathodoluminescence dull blotchy indicative of stabilized mg calcite the isopachous cements are invariably overlain by homogeneous peloidal or microbioclastic micrite having trace element compositions mg2 0 77 1 54 mole mgco3 fe2 760 10 030 ppm sr2 0 240 ppm mn2 60 340 ppm and cathodoluminescence dull blotchy again indicative of stabilized mg calcite this micrite is always closely associated wi h the isopachous cements and appears to be of marine origin perhaps being analogous to the micritic precipitates described from reefal settings clear calcite is the last cement generation in the hardgrounds and has attributes of meteoric cements nonluminescent mg2 0 12 0 87 mole mgco3 fe2 0 230 ppm sr2 and mn2 below detection limits the whole rock stable isotope compositions of the hardgrounds and host limestone indicate that the whole unit has been subjected to pervasive alteration by meteoric fluids the least altered carbonates analyzed from the point addis limestone are brachiopods d13c 1 5 to 2 2 pdb d18o 1 7 to 0 9 pdb and the unkarstified hardgrounds d13c 3 8 to 1 0 pdb d18o 0 6 to 0 6 pdb these hardground occurrences help promote the validity of a unique sea level driven model for the formation of hardgrounds in cool water settings we propose that the development of these hardgrounds was an entirely marine process produced by relative sea level drop and entry of the sea floor into the zone of wave reworking marine cementation may begin in the form of nodules at and below the seawater sediment interface and involves both slow sedimentation and shallowing of the cool waters the nodules can later merge to form continuous hardgrounds in such a high energy environment nondeposition and erosion are the dominant processes and marine cementation can occur further sea level drop would lead to subaerial exposure of the previously formed hardgrounds as found in one inst nce in the point addis limestone at coastal exposures

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

high resolution 104 years deep sea foraminiferal stable isotope records of the eocene oligocene climate transition we have constructed high resolution 104 105 years benthic foraminiferal 13c and 18o records for the upper eocene through lower oligocene of two pelagic sequences deep sea drilling project dsdp site 522 in the angola basin south atlantic ocean and ocean drilling program odp site 744 in the southern indian ocean these records provide improved constraints on both the timing and magnitude of marine oxygen and carbon isotope events from 30 to 35 ma the oxygen isotope records indicate that the ubiquitous 18o increase oi 1 which marks the rapid expansion of continental ice sheets and a minimum of 3 to 4 c of cooling of bottom waters in the earliest oligocene 33 6 ma occurred in 350 kyr more than half the transition occurred over the final 40 50 kyr this period of lower temperatures and widespread continental glaciation persisted for roughly 400 kyr i e the duration of magnetochron c13n these records also indicate that this interval was characterized by at least two 100 kyr waxing and waning cycles oi 1a and oi 1b and possibly several higher frequency events the benthic foraminiferal 13c records show a positive 0 8 excursion that is nearly isochronous with the oi 1 oxygen isotope increase similar magnitude 13c increases at other sites indicate this was a global phenomenon suggestive of an unusually large perturbation to the carbon cycle this excursion was followed by smaller amplitude 13c oscillations with periods of roughly 400 kyr we suspect that the ubiquitous oi 1 13c excursion resulted from a brief but substantial increase in export production and carbon burial

cyclicity in pleistocene upper slope cool water carbonates unravelling sedimentary dynamics in deep water sediments great australian bight odp leg 182 site 1131a abstract ocean drilling program site 1131 located in the central great australian bight recovered an expanded series of pleistocene cool water carbonates three distinct facies are arranged in repeating sedimentary cycles omission intervals form the base of the cycles and are overlain by laminated deposits the upper part of the cycles consists of bioturbated sediments facies cyclicity parallels glacial interglacial sea level changes firmground hardground surfaces formed during latest stages of sea level falls laminated sediments were deposited during later sea level fall and or early phases of the sea level lowstand and the bioturbated intervals are related to interglacial sea level highstands bottom current activity is interpreted to play an important control on facies and cycle development during the late stages of sea level fall upwelling currents winnowed the slope sediments leading to hardground formation during latest sea level falls and early sea level lowstands a relative increase in the ramp sediment supply to the slope leading to the formation of the laminated facies was also a response to the continued action of the near bottom upwelling currents that reworked previously deposited sediments along the slope during the early sea level rises laminated upwelling influenced facies were progressively covered by the bioturbated facies the adopted approach to decipher sedimentary cyclicity involving the integrated use of wireline logs geochemical data fms images and sedimentological analysis of the lithofacies has allowed to recognise subtle facies changes in upper slope settings of a distally steepened carbonate ramp and their relationship with the sea level as well as to unravel the importance of the oceanic current regime in the deposition style on the ramp that otherwise would remain unsolved this integrated method could be applied to study more precisely apparently homogeneous fine grained calcareous sediment successions of distal ramp outcrops

carbonate cement fabrics displayed a traverse across the margin of the bahamas platform near lee stocking island in the exuma cays abstract consolidated to friable carbonate rocks found in the lee stocking island area in the exuma cays include 1 reef rock 2 channel stromatolites 3 shallow water hardgrounds 4 beachrock rimming the islands and 5 pleistocene bedrock the most common cement fabrics observed are aragonitic fibers which include acicular fan druse and square tipped coarse fibers cementing beachrock and stromatolites and an isopachous needle fiber rim cementing hardgrounds and stromatolites less common are high mg calcite bladed textures of the reef rock and stromatolites two types of blades are present the more common stubby variety of either high mg or low mg calcite and an elongated variety of high mg calcite which was found in only three beachrock samples aragonitic micrite envelopes usually surround grains in beachrock hardgrounds and stromatolites but only in association with fibrous cement an aragonitic crust cements the surfaces of lime mud beds of the tidal channel while a high mg calcite cryptocrystalline cement occurs in all the rock types calcified algal filaments of high mg calcite from the abundant green and blue green algae in the area are a primary cement in stromatolites and a secondary cement in hardgrounds and beachrock a low mg calcite equant spar cements the pleistocene samples and is associated with meteoric diagenesis and cementation of the pleistocene surface cement precipitation coincides with the path of the cool oceanic water from exuma sound as it warms and loses co 2 and moves up onto the bank near lee stocking with the incoming tide cryptocrystalline cement is the first and commonest cement forming to the seaward while platformward fibrous cements become predominant as suggested by their crystal size and location on the shelf margin we think that the reef rock cryptocrystalline material are the fastest forming of the cements where the incoming oceanic water is more saturated with respect to calcium carbonate and undergoes the most significant warming the rate of the warming and degassing process is thought to increase in the tidal channel though the cementation rate is thought to fall slightly in response to a reduced availability of calcium carbonate on the platform interior further warming and degassing are believed to cause cement precipitation and the development of hardgrounds but these may form at a slower rate than that of the margin though this rate is still quite high cementation gradients occur from the tidal channel to the intertidal zones of 1 west norman s pond cay where cement fabric suggests a reduced calcium carbonate availability and 2 west lee stocking island where a change in mineralogy suggests a change in water chemistry thus a sequence of cement fabrics and mineralogies can be traced micritic textures occur in a more seaward position fine fibrous aragonite fibers in a more lagoonal and levee position and coarser aragonite fibers and mg calcite cements in the intertidal and supratidal position this sequence is thought to track the evolution of the water mass

production and accumulation of calcium carbonate in the ocean budget of a nonsteady state present day production of caco3 in tne world ocean is calculated to be about 5 billion tons bt per year of which about 3 bt accumulate in sediments the other 40 is dissolved nearly half of the carbonate sediment accumulates on reefs banks and tropical shelves and consists largely of metastable aragonite and magnesian calcite deep sea carbonates predominantly calcitic coccoliths and planktonic foraminifera have orders of magnitude lower productivity and accumulation rates than shallow water carbonates but they cover orders of magnitude larger basin area twice as much calcium is removed from the oceans by present day carbonate accumulation as is estimated to be brought in by rivers and hydrothermal activity 1 6 bt suggesting that outputs have been overestimated or inputs underestimated that one or more other inputs have not been identified and or that the oceans are not presently in steady state one missing calcium source might be groundwater although its present day input is probably much smaller than that of rivers if as seems likely caco3 accumulation presently exceeds terrestial and hydrothermal input this imbalance presumably is offset by decreased accumulation and increased input during lowered sea level shallow water accumulation decreases by an order of magnitude with a 100 m drop in sea level while groundwater influx increases because of heightened piezometric head and the diagenesis of metastable aragonite and magnesian calcite from subaerially exposed shallow water carbonates

the lutetian bartonian transition middle eocene at the oyambre section northern spain implications for standard chronostratigraphy abstract with the aim of finding a potential global stratotype section and point gssp for the base of the bartonian stage an integrated stratigraphic study was carried out in the acebosa fm exposed at the cape of oyambre cantabria spain while the oyambre section does comply with the majority of the requirements of the international commission on stratigraphy several shortcomings were also found which apparently make it unsuitable for the gssp for the base of the bartonian stage an unexpected finding was that the chronostratigraphic calibration of the oyambre planktonic foraminiferal events revealed major discrepancies with the standard timescale the lowest occurrence of globigerinatheka index was found in the upper part of chron c20r and not in the upper part of c20n as depicted in the standard chart being dated at 43 68 ma and not at 42 64 ma the lowest occurrences of turborotalia pomeroli and globigerinatheka euganea were found in the upper part of calcareous nannofossil zone cp14a 40 92 ma and not in the upper part of zone cp13c 42 21 ma finally the highest occurrences of guembelitrioides nuttalli and morozovelloides bandyi were also found in the upper part of zone cp14a 40 68 ma and not in the upper part of zone cp13c 42 07 ma the accuracy of these anomalous results was further substantiated with data from other areas strongly suggesting that the standard eocene chronostratigraphy was in need of amendment the oyambre findings if proven significant at a global scale would have two important chronostratigraphic outcomes firstly the standard eocene planktonic foraminiferal biostratigraphy would need revision as there would be practically no space to accommodate zones e9 and e11 secondly an array of sound biostratigraphic markers would now be defined around chron c19n which has been considered the best marker for the lutetian bartonian boundary thus facilitating correlation of a potential gssp

an introductory perspective on non tropical shelf carbonates abstract this brief account introduces the topic of non tropical shelf carbonate deposits both modern and ancient specific aspects of which are described and discussed in the 22 accompanying papers in this special issue of sedimentary geology non tropical shelves are loosely defined as lying poleward of the present limit of development of hermatypic coral reefs or beyond the mean annual surface water isotherm of about 20 c typically near 30 latitude most geoscientists have traditionally regarded shallow water carbonate formation as a low latitude phenomenon however wherever the rate and extent of terrigenous sediment dilution is small the potential exists for extensive deposits of skeletal carbonate to accumulate on shelves beyond the sub tropics the facies attributes of the modern non tropical carbonates are distinctive and contrast significantly with the structural lithological faunal floral mineralogical and diagenetic character of their tropical counterparts in the rock record non tropical limestones probably occur throughout the phanerozoic but generally remain to be identified and or interpreted as such they are presently described mainly from the ordovician permian and tertiary quaternary periods of major continental glaciations and accentuated latitudinal thermal gradients a uniformitarian approach to the recognition and interpretation of ancient shallow marine limestones requires acceptance of both tropical and non tropical carbonate facies models

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

cross stratified calcarenites from new zealand subaqueous dunes in a cool water oligo miocene seaway cross bedded cool water bioclastic limestones of the te kuiti group on the north island of new zealand are composed primarily of bryozoans echinoderms and benthic foraminifers their prominent large scale unidirectional cross stratification is interpreted as produced by migrating subaqueous dunes on the floor of a 50 100 km wide north east trending seaway in water depths of 40 60 m these dunes are thought to have developed in response to strong seaway parallel tidal currents combined with a north east directed set up or oceanic current cross stratification is organized into four hierarchical levels 1 cross lamination 2 first order sets 3 second order sets and 4 cross stratified successions the levels are based on increasing degrees of internal complexity distinct attributes such as internal organization cross set thickness foreset shape and lower bounding surface shape are used to describe and interpret the cross stratification all these attributes are here integrated in a new and expanded classification of unidirectional cross stratification that emphasizes flow and bedform dynamics rather than overall set shape individual cross stratified successions are interpreted to have formed by dunes with varying sinuosity superposition and flow history under conditions of different current strength but constant sediment production horizontally bedded successions are the result of robust active dune fields that grew during times of vigorous sediment transport formset successions were produced from large compound dunes and are the expression of languid and decaying dune fields that developed during times of decreasing sediment transport these decaying dunes were gradually smothered by continuously and locally produced bioclastic sediment formset cross stratified successions are most likely to develop in carbonates where the sediment is produced in place than in terrigenous clastics where the sediment is imported

late eocene early oligocene integrated isotope stratigraphy and biostratigraphy for paleoshelf sequences in southern australia paleoceanographic implications abstract a late eocene early oligocene planktonic foraminiferal oxygen isotope stratigraphy derived for two overlapping sections browns creek and castle cove through paleoshelf sequences in southern victoria australia contains a pronounced late eocene depletion warm peak 1 2 pdb centred at about 41 ma followed by a two stage enrichment cooling pattern the later one coinciding with the well known terminal eocene event 37 ma exhibiting 1 0 pdb erinchment the early oligocene isotope stratigraphy shows fluctuations of about 1 0 pdb with prominent depletion peak immediately following the terminal eocene 18 o enrichment the start of the terminal eocene 18 o enrichment coincides with the lad of the nannofossil indicator of the eo oligocene boundary discoaster saipanensis early np21 zone on this basis the traditional southern australia planktonic foraminiferal eocene oligocene boudary markers lad globigerapsis index lad subbotina linaperta subbotina linaperta locally survived into zone np22 well into the early oligocene sea surface paleotemperature estimates derived from the 18 o data assuming a w value of 1 2 pdb show that the late eocene ingression of the tropical planktonic foraminiferal genus hankenina coincided with peak surface water tempertures of 24 c the temperature decline in the southern australia shelf waters associated with the terminal eocene event may have been as much as 7 c reaching a minimum value of 13 c the later survival of g index and s linaperta coincides with a rapid recovery of water temperatures over the south australian shelf following the terminal eocene event this is attributed to the local warming of waters in shallow broad embayments where circulation patterns were decoupled from the developing circum antartic current to the south

the random redistribution of sediment by wind in a lake the total sedimentation rate was measured fortnightly for a year in a large shallow lake lough neagh northern ireland surface area 383 km2 mean depth 8 9 m at five sites using 10 sediment traps the total sedimentation rate included both primary and secondary sedimentation as the annual average total sedimentation rate 53 2 44 1 g m 2 d 1 is more than 25 times the primary value secondary sedimentation due to wind induced resuspension is very important the average of the largest 30 of wave mixed layer wml values a function of wind speed and effective fetch strongly correlates with the total sedimentation rate r2 values of 0 69 and 0 98 at two westerly sites at most of the sites as the wml value approaches the water depth then the orbital motion of the waves and the associated turbulence cause sediment disturbance and resuspension changing wml values then provide a basis to describe the random redistribution rr of sediment in lakes and these resuspension events can occur as frequently as 2 3 times every two weeks this study provides for the first time clear results and a description of the process of rr of sediment in a lake particularly the link between wind and sediment resuspension

origin of a cool water oligo miocene deep shelf limestone eucla platform southern australia the abrakurrie limestone is an areally extensive bryozoan rich unit within the eucla platform a tertiary carbonate shelf which caps the central part of the southern australian continental margin the onshore portion the topic of this study has been exposed since middle miocene time and lies beneath the nullarbor plain the rocks are fine sand to granule sized calcarenites composed of bryozoans bivalves benthic foraminifera and echinoids with lesser numbers of brachiopods solitary corals and serpulids they conspicuously lack significant numbers of planktonic foraminifera and coralline algae most bryozoan remains are from delicate branching cyclostomes although delicate branching robust branching foliose fenestrate multilaminar encrusting and free living cheilostomes are variably abundant in specific units the poorly lithified sequence is punctuated by well cemented layers with erosional tops which are interpreted as hardgrounds the limestone is interpreted as a cool water deep shelf deposit which accumulated in water depths generally greater than 50 m on the inner part of the eucla platform a model which involves deposition and cementation on a carbonate shelf swept by open ocean swells is proposed to explain the style of sedimentation the shelf is envisaged as partitioned by the depth of the zone of wave abrasion sediments were produced throughout but accumulated only below this depth when the seafloor was above this depth it was an environment of cementation and erosion the vertical sequence correlates in a general way with the global sea level model for the mid cenozoic while accumulation rates for southern australian carbonates are similar to rates of cool water carbonate deposition elsewhere c 2 5 cm kyr 1 the rate of abrakurrie accumulation is much less suggesting that significant time periods are represented by the hardgrounds

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

long term accumulation of carbonate shells reflects a 100 fold drop in loss rate shells in modern seabeds can be thousands of years old far older than would be extrapolated from the rapid rates of shell loss detected in short term experiments an extensive shelldating program on the southern california usa shelf permits rigorous modeling of the dynamics of shell loss in the mixed layer discriminating the key rates of carbonate disintegration and sequestration for the first time we find that bivalve shells experience an initially high disintegration rate l 1 decadal half lives but shift abruptly within the first 500 yr postmortem to a 100 fold lower disintegration rate l 2 millennial half lives at sequestration rate t burial and or diagenetic stabilization this drop permits accrual of a long tail of very old shells even when sequestration is very slow and allows only a minority 1 of all shells to survive the first phase these high rates of disintegration and low rates of sequestration are consistent with independent measures of high carbonate loss and slow sedimentation on this shelf our two phase model thus reveals significant spatial and temporal partitioning of car bonate loss rates within the mixed layer and shows how shell age frequency distributions can yield rigorous and realistic estimates of carbonate recycling on geological time scales

maceration of calcareous skeletons in the december issue of sedimentology 1979 26 two papers on the disintegration of calcareous skeletons appeared in both articles the authors alexandersson 1979 fitzgerald parmenter milliman 1979 describe skeletal degradation producing fragments and even single calcium carbonate crystallites in the present marine environment at least part of this maceration alexandersson 1978 is attributed to the breakdown of the skeletal organic matrix on the sea bottom both studies were carried out on samples from the sediment surface of marine cold water regions there another destructive process is active etching and dissolution of the calcareous particles by the ambient carbonate under saturated water e g alexandersson 1975 1978 the possible coexistence of these biological and physicochemical destructive processes and the lack of information from cores have left open questions in the above mentioned two studies some of these questions were discussed by me lewy 1975 my observations and conclusions may now have a wider significance

evolution of early cenozoic marine temperatures the equator to high southern latitude sea surface and vertical temperature gradients are reconstructed from oxygen isotope values of planktonic and benthic foraminifers for the following five time intervals late paleocene early eocene early middle eocene late eocene and early oligocene paleotemperatures are calculated using standard oxygen isotope temperature equations with adjustments to account for 1 variations in sea water 18o related to changes in global ice volume over time and 2 latitudinal gradients in surface water 18o these reconstructions indicate that sea surface temperatures sst of the southern oceans in the early eocene were as high as 15 c whereas temperatures during the late paleocene and early middle eocene reached maximum levels of 10 12 c by the late eocene and early oligocene high latitude sst had declined to 6 and 4 c respectively for most of the early paleogene low latitude sub tropical temperatures remained constant and well within the range of holocene temperatures 24 ndash 25 c but by the late eocene and early oligocene declined to values in the range of 18 to 22 c the late paleogene apparent decline in tropical temperatures however might be artificial because of dissolution of near surface foraminifera tests which biased sediment assemblages toward deeper dwelling foraminifera moreover according to recent plate reconstructions it appears that the majority of sites upon which the late eocene and early oligocene tropical temperatures were previously established were located either in or near regions likely to have been influenced by upwelling global deepwater temperature on average paralleled southern ocean sst for most of the paleogene we speculate based on the overall timing and character of marine sea surface temperature variation during the paleogene that some combination of both higher levels of greenhouse gases and increased heat transport was responsible for the exceptional high latitude warmth of the early eocene

tectonic architecture of the mountain front foreland basin transition south island new zealand assessed by fission track analysis oblique continental convergence across the alpine fault since the mid miocene has loaded the australia plate with the leading edge of the pacific plate and formed a foreland basin the basin occurs mostly offshore beneath the continental shelf but remnants of the marine basin fill overlie ordovician basement in a narrow coastal strip 10 20 km wide in westland between the tasman sea and the alpine fault the results of fission track analyses of apatite and zircon separates from this basement integrated with the regional structure and stratigraphy indicate that the foreland basin formerly extended across the whole of westland and that its succession increased in thickness eastward toward the alpine fault reaching a maximum of about 4 km continuing covergence across the main thrust alpine fault has caused its footwall to thicken by reverse fauting in a transitional zone 10 20 km wide immediately west of the mountain front southern alps consequently the inner margin of the foreland basin has been inverted and the succession almost completely eroded in the southern part of westland upper crustal shortening in the australia plate amounted to about 2 km associated uplift started about 5 m y ago and involved only one major fault bounded block in northern westland upper crustal shortening amounted to about 12 km two major fault bounded blocks were involved and uplift was underway by 10 ma assuming a preuplift geothermal gradient of 25 c km the long term rate of uplift ranged between 0 8 and 2 0 mm yr in southern westland and between 0 4 and 1 2 mm yr in different parts of northern westland

unlocking the ice house oligocene miocene oxygen isotopes eustasy and margin erosion oxygen isotope records and glaciomarine sediments indicate at least an intermittent presence of large continental ice sheets on antarctica since the earliest oligocene circa 35 ma the growth and decay of ice sheets during the oligocene to modern ice house world caused glacioeustatic sea level changes the early eocene was an ice free greenhouse world but it is not clear if ice sheets existed during the middle to late eocene doubt house world benthic foraminiferal 18o records place limits on the history of glaciation suggesting the presence of ice sheets at least intermittently since the earliest oligocene the best indicator of ice growth is a coeval increase in global benthic and western equatorial planktonic 18o records although planktonic isotope records from the western equatorial regions are limited subtropical planktonic foraminifera may also record such ice volume changes it is difficult to apply these established principles to the cenozoic 18o record because of the lack of adequate data and problems in stratigraphic correlations that obscure isotope events we improved oligocene to miocene correlations of 18o records and erected eight oxygen isotope zones oi1 oi2 mi1 mi6 benthic foraminiferal 18o increases which are associated with the bases of zones oil circa 35 8 ma oi2 circa 32 5 ma and mil circa 23 5 ma can be linked with 18o increases in subtropical planktonic foraminifera and with intervals of glacial sedimentation on or near antarctica our new correlations of middle miocene benthic and western equatorial planktonic 18o records show remarkable agreement in timing and amplitude we interpret benthic planktonic covariance to reflect substantial ice volume increases near the bases of zones mi2 circa 16 1 ma mi3 circa 13 6 ma and possibly mi5 circa 11 3 ma possible glacioeustatic lowerings are associated with the 18o increases which culminated with the bases of zone mi4 circa 12 6 ma and mi6 circa 9 6 ma although low latitude planktonic 18o records are required to test this these inferred glacioeustatic lowerings can be linked to seismic and rock disconformities for example we link 12 oligocene early late miocene inferred glacioeustatic lowerings with 12 of the sequence boundaries inferred eustatic lowerings of haq et al 1987

internal precipitation of microcrystalline carbonate a fundamental problem for sedimentologists abstract recent studies of submarine lithification have shown that microcrystalline carbonate or carbonate mud traditionally thought to represent ooze deposited in quiet water commonly forms as an internal precipitate below the sediment water interface this internally precipitated micrite alters the mud grain ratio of pre existing sedimentary deposits and invalidates classifications that relate the amount of micrite matrix in limestones to the degree of water energy associated with the environment of deposition

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

shallow burial dolomitization and dedolomitization of mid cenozoic cool water calcitic deep shelf limestones southern australia abstract oligocene to mid miocene deep shelf bryozoan rich limestones across southern australia are variably altered to gray to orange ca rich medium crystalline sucrosic dolomite degree of replacement ranges from scattered rhombs to complete dolostone units several tens of meters thick and many kilometers in areal extent the locale and timing of dolomitization are tightly constrained to shallow burial and mid to late miocene dolostone varies from friable to dense and well lithified dolomitization is fabric specific muddy sediments are preferentially replaced calcite bryozoans and brachiopods form biomolds geochemistry suggests that dolomitization was predominantly by seawater limestone interaction but admixing of continental possibly meteoric groundwater is required by data on stable and radiogenic isotopes and trace elements sr isotopes confirm a mid miocene age for the dolomite if precipitated from seawater with no inherited limestone values dolomite crystals have undergone variable degrees of dissolution and meteoric calcite cement has locally filled the resultant rhombic voids dissolution began in the crystal cores implying some sort of metastability and expanded outward until in some ins ances the whole dolomite crystal was dissolved leaving dolomolds in otherwise unaffected limestone this dolomite occurrence well constrained by regional geology shows that widespread porous and permeable fabric destructive medium crystalline sucrosic dolostone can form in the shallow subsurface soon after sediment deposition such dolomite however may be metastable in the presence of variably mixed continental marine waters and newly formed crystals can undergo dedolomitization soon after precipitation