marine oxygenation lithistid sponges and the early history of paleozoic skeletal reefs abstract microbial carbonates were major components of early paleozoic reefs until coral stromatoporoid bryozoan reefs appeared in the mid ordovician microbial reefs were augmented by archaeocyath sponges for 15 myr in the early cambrian by lithistid sponges for the remaining 25 myr of the cambrian and then by lithistid calathiid and pulchrilaminid sponges for the first 25 myr of the ordovician the factors responsible for mid late cambrian microbial lithistid sponge reef dominance remain unclear although oxygen increase appears to have significantly contributed to the early cambrian explosion of marine animal life it was followed by a prolonged period dominated by greenhouse conditions as sea level rose and co2 increased the mid late cambrian was unusually warm and these elevated temperatures can be expected to have lowered oxygen solubility and to have promoted widespread thermal stratification resulting in marine dysoxia and hypoxia greenhouse conditions would also have stimulated carbonate platform development locally further limiting shallow water circulation low marine oxygenation has been linked to episodic extinctions of phytoplankton trilobites and other metazoans during the mid late cambrian we propose that this tendency to dysoxia hypoxia in shallow marine environments also limited many metazoan reef builders in contrast during the mid late cambrian the ability of lithistid sponges to withstand low oxygen levels allowed them to create a benthic association with microbial carbonates that dominated global reefs these conditions ameliorated during the ordovician as temperature decline promoted ocean ventilation the prolonged time gap occupied by low diversity reefs between the cambrian explosion and the great ordovician biodiversification event reflects elevated temperatures and reduced marine oxygenation that limited metazoan diversification in shallow marine environments

stromatolitic framework of carbonate mud mounds abstract mud mounds are an important phanerozoic reef type generally formed in deeper water on carbonate shelf to basin slopes they commonly contain radiaxial calcite spar filled depositional cavities stromatactis but lack abundant metazoan framebuilders mud mounds are often flanked by steeply dipping bioclastic grainstones and sometimes attained widths and depositional reliefs of over a hundred meters they occasionally occur as basal cores on which developed shallow water metazoan constructed reefs stromatactoid mud mounds are composed of a framework of submarine cemented crudely reticulate masses or a succession of laminar crusts surrounded by cement filled cavities these cavities developed when unconsolidated sediment around the framework was removed by winnowing mud mound frameworks of all ages show strong geometric and petrographic similarities to shallow water cryptalgal structures especially thrombolites unlaminated stromatolites which occur in many phanerozoic shallow water reefs both thrombolites and mud mound frameworks are largely composed of lime mudstone cemented on the sea floor and contain fenestral fabric and diagnostic cryptalgal microstructure their depositional surfaces were irregular not bored or burrowed and rarely encrusted stromatolitic lamina ion although commonly not well developed in the subtidal zone anyway occasionally occurs in mud mounds it is proposed that mud mounds accumulated from organic probably blue green algal binding of locally derived lime mud and bioclasts deposited relatively slowly from suspension patchy distribution of algal mats resulted in areas of both bound and unbound sediment sporadic floodlike episodes of rapid sedimentation however temporarily smothered the living algal mat and also left layers of unbound sediment periods of winnowing washed out unconsolidated unbound sediment and promoted synsedimentary cementation of resulting stromatactoid cavities and algal bound framework

organic buildups and reefs on the palaeozoic carbonate platform margin pechora urals russia abstract in the pechora urals palaeozoic organic structures are widespread and are represented by various types from small bioherms to large barrier reefs which can be observed throughout upper ordovician lower permian strata in the pre orogenic history of palaeozoic carbonate sedimentation and reef growth three stages are distinguished each stage is characterized by a distinct reef geometry growth rate and depositional setting 1 the reefs of the lower palaeozoic ashgillian lower emsian stage were restricted to the outer shelf margin and they were wave resistant stromatolite rich frameworks except for upper llandoverian knoll and patch reefs the total thickness of the lower palaeozoic reefs is 60 1200 m 2 the middle palaeozoic middle frasnian lower tournaisian organic buildups are quiet water carbonate bank type structures generally between 300 and 700 m thick they were formed on both the outer and the inner shelf margin however they are better developed and more characteristic of the latter setting stromatoporoid microbial and microbial associations form the main buildup facies separated by bedded interbuildup sediments the upper palaeozoic upper visean sakmarian organic structures are represented by both isolated wave resistant shelf margin reefs up to 200 m thick and quiet water carbonate banks up to 330 m thick these buildups were located in the outer and inner shelf margin framework builders were mainly branching and platy stromatoporoids associated with stromatolites in the reefs and calcified microbes and phylloid algae in the carbonate banks the distribution and geometry of the buildups was mainly determined by regional tectonic events caused by the passive to active margin transition of the northeastern european platform the size of the reefs depended on the magnitude and duration of sea level fluctuations

periplatform drift the combined result of contour current and off bank transport along carbonate platforms hydroacoustic and sedimentological data from the western leeward flank of the great bahama bank document the interplay of off bank sediment export along slope transport and erosion which together shape facies and thickness distribution of slope carbonates the integrated data set depicts the combined product of these processes and allows formulation of a comprehensive model of a periplatform drift that significantly amends established models of carbonate platform slope facies distribution and geometry the basinward thinning wedge of the periplatform drift at the foot of the bank escarpment displays along slope and downslope variations in sedimentary architecture sediments are muddy carbonate sands that coarsen basinward the drift wedge has a pervasive cover of cyclic steps in zones of lower contour current speed depth related facies belts develop whereas strike discontinuous sediment lobes scarps and gullies characterize areas with higher current speed this understanding of the impact of currents on carbonate slope sedimentation has wider implications for seismic and sequence stratigraphic interpretation of carbonate platforms and for applied aspects such as hydrocarbon exploration

ordovician cyanobacterial calcification a marine fossil proxy for atmospheric co2 abstract ordovician atmospheric co2 level was an important influence on climate and life however modelled estimates of ordovician co2 differ widely and in contrast to much of the subsequent phanerozoic they lack fossil proxy constraints in vivo cyanobacterial sheath calcification promoted by carbon dioxide concentrating mechanisms ccms creates distinctive microfossils these provide a direct ecophysiological link to ambient concentrations of co2 and to a lesser extent o2 cyanobacteria do not calcify at high co2 concentrations experiments show that ccms can be induced in present day cyanobacteria at co2 levels below 10 times present atmospheric level pal and that this promotes sheath calcification we compiled a global database of cyanobacterial calcification in marine environments throughout the ordovician 485 443 myr ago and compared it with modelled estimates of atmospheric co2 and o2 these data show that many genera of marine calcified cyanobacteria reappeared from cambrian series 2 or first appeared globally during the late middle to late upper ordovician late darriwilian to late katian in carbonate platform facies resulting in a previously unrecognized ten fold increase in global diversity such a large increase in calcification suggests widespread induction of ccm expression in cyanobacteria consistent with sustained decline in external co2 concentrations below 10 pal together with increase in dissolved o2 level during the late darriwilian sandbian and katian stages 460 445 myr ago these cyanobacterial calcification fossil proxy data provide a first order constraint on modelled estimates of atmospheric co2 for the ordovician estimated co2 outputs from copse and recent geocarb based models are broadly consistent with this cyanobacterial calcification proxy for the ordovician in view of the long history of cyanobacteria the calcified cyanobacterial proxy offers potential to assist interpretation of co2 deeper into geological time

microbial carbonates the geological record of the calcified bacterial algal mats and biofilms summary deposits produced by microbial growth and metabolism have been important components of carbonate sediments since the archaean geologically best known in seas and lakes microbial carbonates are also important at the present day in fluviatile spring cave and soil environments the principal organisms involved are bacteria particularly cyanobacteria small algae and fungi that participate in the growth of microbial biofilms and mats grain trapping is locally important but the key process is precipitation producing reefal accumulations of calcified microbes and enhancing mat accretion and preservation various metabolic processes such as photosynthetic uptake of co2 and or hco3 by cyanobacteria and ammonification denitrification and sulphate reduction by other bacteria can increase alkalinity and stimulate carbonate precipitation extracellular polymeric substances widely produced by microbes for attachment and protection are important in providing nucleation sites and facilitating sediment trapping microbial carbonate microfabrics are heterogeneous they commonly incorporate trapped particles and in situ algae and invertebrates and crystals form around bacterial cells but the main component is dense clotted or peloidal micrite resulting from calcification of bacterial cells sheaths and biofilm and from phytoplankton stimulated whiting nucleation interpretation of these texturally convergent and often inscrutable fabrics is a challenge conspicuous accumulations are large domes and columns with laminated stromatolite clotted thrombolite and other macrofabrics which may be either agglutinated or mainly composed of calcified or spar encrusted microbes stromatolite lamination appears to be primary but clotted thrombolite fabrics can be primary or secondary microbial precipitation also contributes to hot spring travertine cold spring mound calcrete cave crust and coated grain deposits as well as influencing carbonate cementation recrystallization and replacement microbial carbonate is biologically stimulated but also requires favourable saturation state in ambient water and thus relies uniquely on a combination of biotic and abiotic factors this overriding environmental control is seen at the present day by the localization of microbial carbonates in calcareous streams and springs and in shallow tropical seas and in the past by temporal variation in abundance of marine microbial carbonates patterns of cyanobacterial calcification and microbial dome formation through time appear to reflect fluctuations in seawater chemistry stromatolites appeared at 3450 ma and were generally diverse and abundant from 2800 to 1000 ma inception of a proterozoic decline variously identified at 2000 1000 and 675 ma has been attributed to eukaryote competition and or reduced lithification thrombolites and dendrolites mainly formed by calcified cyanobacteria became important early in the palaeozoic and reappeared in the late devonian microbial carbonates retained importance through much of the mesozoic became scarcer in marine environments in the cenozoic but locally re emerged as large agglutinated domes possibly reflecting increased algal involvement and thick micritic reef crusts in the late neogene famous modern examples at shark bay and lee stocking island are composite coarse agglutinated domes and columns with complex bacterial algal mats occurring in environments that are both stressed and current swept products of mat evolution ecological refugia sites of enhanced early lithification or all three

segmentation and coalescence of cenozoic carbonate platforms northwestern great bahama bank seismic profiles over the northwestern great bahama bank reveal that it is formed by the coalescence of three smaller platforms and significant lateral progradation this conclusion is contrary to previous models which assumed that the bank is the result of continuous accumulation on one huge buildup in late cretaceous to early tertiary time a north south trending depression the straits of andros separated an eastern platform andros bank from a western platform bimini bank initially the straits of andros had dimensions similar to the modem tongue of the ocean but was progressively filled from east to west in early to middle tertiary time a second depression the bimini embayment formed within bimini bank by folding it had a maximum depth of about 470 m this depression was also filled from east to west in addition prograding systems built the western margin of bimini bank more than 25 km westward into the straits of florida

depositional facies and stratal geometry of an upper carboniferous prograding and aggrading high relief carbonate platform cantabrian mountains n spain seismic scale continuous exposures of an upper carboniferous bashkirian moscovian carbonate platform n spain provide detailed information about the lithofacies and stratal geometries quantified with differential global positioning system measurements of microbial boundstone dominated steep prograding and aggrading platform margins progradational and aggradational platform to slope transects are characterized by distinct lithological features and stratal patterns that can be applied to the understanding of geometrically comparable high relief depositional systems the bashkirian is characterized by rapid progradation at rates of 415 970 m my 1 characteristic outerplatform facies are high energy grainstones with coated intraclasts ooids and pisoids moderate energy algal skeletal grainstones to packstones and lower energy algal packstone and boundstone units the moscovian aggradational phase is characterized by aggradation rates of 108 m my 1 coated grain shoals are less common whereas crinoidal bars nucleated in well circulated settings below wave base boundstones form a belt 30 300 m wide at the platform break and interfinger inwards with massive algal skeletal wackestones mud rich banks the progradational phase has divergent outer platform strata with basinward dips of 12 to 2 steep clinoforms with dips of 20 28 are 650 750 m in relief and possibly sigmoidal to concave in the lower part the basinward dipping outer platform strata might be depositional for less than 6 consistent with lithofacies deepening seaward the basinward dip is attributed to the downward shift of upperslope boundstone forced by late highstand and relative sea level fall and to compaction induced differential subsidence during progradation the aggradational phase is characterized by horizontally layered platform strata clinoforms steepen to 30 45 reaching heights of 850 m and are planar to concave the evolution from progradation to aggradation at the bashkirian moscovian boundary is attributed to increased foreland basin subsidence and decreased boundstone accumulation rates progradation was primarily controlled by boundstone growth rather than by highstand shedding from the platform top within the major phases aggradational progradational increments are produced by third to fourth order relative sea level

sedimentary dynamics and high frequency sequence stratigraphy of the southwestern slope of great bahama bank abstract new geophysical data from the leeward slope of great bahama bank show how contour currents shape the slope and induce re sedimentation processes along slope segments with high current control drift migration and current winnowing at the toe of slope form a deep moat here the slope progradation is inhibited by large channel incisions and the accumulation of large mass transport complexes triggered by current winnowing in areas where the slope is bathed by weaker currents the accumulation of mass transport complexes and channel incision is rather controlled by the position of the sea level large slope failures were triggered during the mid pleistocene transition and mid brunhes event both periods characterized by changes in the cyclicity or the amplitude of sea level fluctuations within the seismic stratigraphic framework of third order sequences four sequences of higher order were identified in the succession of the upper pleistocene these higher order sequences also show clear differences in function of the slope exposure to contour currents two stochastic models emphasize the role of the contour currents and slope morphology in the facies distribution in the upper pleistocene sequences in areas of high current influence the interplay of erosional and depositional processes form a complex facies pattern with downslope and along strike facies alterations in zones with lower current influence major facies alternations occur predominately in downslope direction and a layer cake pattern characterizes the along strike direction therefore this study highlights that contour currents are an underestimated driver for the sediment distribution and architecture of carbonate slopes

is there evidence for solar forcing of climate in the gisp2 oxygen isotope record abstract changes in solar constant over an 11 yr cycle suggest a certain but limited degree of solar forcing of climate the high resolution climate oxygen isotope record of the greenland gisp2 greenland ice sheet project 2 ice core has been analyzed for solar and volcanic influences the atmospheric14c record is used as a proxy of solar change and compared to the oxygen isotope profile in the gisp2 ice core an annual oxygen isotope profile is derived from centimeter scale isotope measurements available for the post a d 818 interval associated extreme summer and winter isotope ratios were found to yield similar climate information over the last millennium the detailed record of volcanic aerosols converted to optical depth and volcanic explosivity change was also compared to the isotope record and the oxygen isotope response calibrated to short term volcanic influences on climate this calibration shows that century scale volcanic modulation of the gisp2 oxygen isotope record can be neglected in our analysis of solar forcing the timing estimated order of temperature change and phase lag of several maxima in14c and minima in18o are suggestive of a solar component to the forcing of greenland climate over the current millennium the fractional climate response of the cold interval associated with the maunder sunspot minimum and14c maximum as well as the medieval warm period and little ice age temperature trend of the past millennium are compatible with solar climate forcing with an order of magnitude of solar constant change of 0 3 even though solar forcing of climate for the current millennium is a reasonable hypothesis for the rest of the holocene the century scale events are more frequent in the oxygen isotope record than in the14c record and a significant correlation is absent for this interval oceanic atmospheric circulation forcing of climate may dominate solar forcing during the surprisingly strong 1470 yr climate cycle of the 11 000 75 000 yr b p interval is rather hypothetical

carbonate delta drift a new sediment drift type based on high resolution reflection seismic and core data from iodp expedition 359 we present a new channel related drift type attached to a carbonate platform slope which we termed delta drift like a river delta it is comprised of several stacked lobes and connected to a point source the delta drifts were deposited at the exit of two gateways that connect the inner sea of the maldives carbonate platform with the open ocean the channels served as conduits focusing and accelerating the water flow entrained material was deposited at their mouth where the flows relaxed the lobe shaped calcareous sediment drifts must have formed under persistent water through flow sediment supply was relatively high and continuous resulting in an average sedimentation rate of 17 cm ka 1 the two delta drifts occupy 342 and 384 km2 respectively with a depositional relief of approximately 500 m they have a sigmoidal clinoform reflection pattern with a particular convex upward bending of the foresets in the maldives the drift onset marks the transition from a sea level controlled to a progressively current dominated depositional regime this major event occurred in the serravallian about 13 ma ago leading to the partial drowning of the carbonate platform and the creation of shallow seaways the initial bank enclosed topography resembles an empty bucket geometry which is rapidly filled by the drift sediments that aggrade and prograde into the basin thereby the depositional environment of the delta drifts changes from deep water 500 to shallow water conditions at their topsets indicated by the overall coarsening upward trend in grain size and the presence of shallow water large benthic foraminifers at their top

incipiently drowned facies within a cyclic peritidal ramp sequence early ordovician chepultepec interval virginia appalachians the chepultepec interval 145 to 260 m thick in virginia although dominated by peritidal carbonates contains thick subtidal sequences that formed during repeated incipient drowning of the early ordovician ramp cyclic peritidal sequences make up the lower member up to 150 m thick and upper member up to 85 m thick subtidal limestone and bioherms make up the middle member up to 110 m thick and pass landward into cyclic peritidal facies average long term subsidence rates were up to 4 cm 1 000 yr mature passive margin rates and ramp gradients commonly were extremely low 2 cm km computer modeling helped define mechanisms involved in formation of the stratigraphic sequence the peritidal sequences are upward shallowing cycles average period 140 000 to 200 000 yr of pellet and skeletal limestone pellet grainstone thrombolites intraclast grainstone and laminite caps these resulted from periodic sea level oscillations of several metres amplitude and possible slow long teim third order sea level fall superimposed on long term subsidence tidal flats were shifted far westward after each sea level rise but had sufficient time to prograde back across the ramp during sea level fall the middle number contains repeated sequences of subtidal skeletal limestone and pellet limestone with storm beds and burrowed units formed below fair weather wave base local rippled pellet limestone and thrombolite bioherms subwave base to wave agitated shoals that may have erosional tops overlain by thin grainstone sheets tidal flat facies are absent these sequences formed by periodic sea level rise more than 12 to 17 m amplitude which caused incipient drowning of the platform and migration of tidal flats several hundred kilometres back onto the platform these flats were unable to prograde onto the outer ramp during regression because of insufficient time and because seaward retreat of the shoreline outpaced progradation of tidal flats this left them abandoned on the inner ramp similar sequences reflecting incipient drowning are widespread in the geological record

quaternary slope development of the western leeward margin of the great bahama bank abstract to date work on the great bahama bank s western leeward margin has centred chiefly on seismic scale expressions of carbonate sequences and systems tracts however periplatform slope sediments also exhibit very well developed cyclicity on scales of decimetres to several metres it is these small scale high frequency cycles within the larger scale facies successions of the quaternary which form the main topic of this paper previous studies have shown that the small scale cycles correlate to the orbitally forced high frequency sea level changes therefore these cycles should indicate how sea level has affected the slope development and thus platform margin evolution during this period through detailed high resolution sequence stratigraphy of the great bahama bank s leeward margin obtained via 18o isotope and mineralogical xrd analyses confined by u th dating and nannofossil bioevents a greater understanding of the bedding geometries within the pleistocene holocene seismic sequences and clues as to the nature of the slope development has been achieved the high resolution seismic profiles indicate that since the plio pleistocene change in geometry in which the great bahama bank developed into a rimmed platform continued steepening and subsequent progradation of the leeward margin has typified slope development during the quaternary which is described as an accretionary slope however on the basis of our observations we conclude that only the early to lower middle pleistocene section isotope stages 45 20 and the holocene isotope stage 1 of the leeward margin is accretionary this indicates that a degree of erosion and or by passing has occurred on the leeward margin since the lower middle pleistocene isotope stage 19 during the first part of this period isotope stages 19 12 erosion and or by passing occurred in the middle to lower slope regions and toe of slope by the end of the upper middle to late pleistocene phase isotope stages 11 2 erosion also occurred on the upper slope this erosion by currents at the toe of slope and oversteepening of the upper and middle slopes have led to back cutting upslope and resulted in the progressive retreat of the toe of slope towards the platform to the east however the rise in sea level since the last glacial maximum to its present day level has allowed high productivity on the platform top during the holocene and the deposition of a thick sediment wedge on the slope and sedimentation across the entire leeward flanks this has led to the redevelopment of an accretionary slope and continued westward progradation of the great bahama bank s western leeward margin

tectonic and sedimentary evolution of the korean peninsula a review and new view abstract this review focuses on the tectonics and sedimentation of major sedimentary basins and orogenic belts late proterozoic neogene in the korean peninsula the korean peninsula is part of the amuria plate and represents an important link between continental blocks of north and south china and the island arcs of japan the basement rocks exposed in the kyonggi and yongnam massifs consist of 2 7 to 1 1 ga high grade gneiss and schist these massifs are separated by the okchon fold belt which comprises metasedimentary rocks and bimodal meta volcanic rocks the stratigraphy of the okchon group is unclear at present the okchon basin was probably initiated as an intraplate rift prior to the late proterozoic the hwanggangri formation clast bearing phyllite most likely represents deposition by subaqueous debris flows in slope environments of an enclosed basin the stratigraphic relationship between the okchon group and the choson supergroup cambro ordovician of the taebaeksan basin is poorly constrained the choson supergroup unconformably overlies the yongnam massif and consists mainly of carbonate sequence that formed mostly in shallow marine and tidal environments reflecting numerous sea level fluctuations the sequence is disconformably overlain by siliciclastic sequence of pyongan supergroup carboniferous triassic which formed most likely in shallow marine deltaic and fluvial environments the imjingang belt is an east trending fold and thrust zone and consists of metasedimentary rocks and volcaniclastics devonian carboniferous underlain unconformably by proterozoic basement rocks late proterozoic amphibolites of oceanic affinity were metamorphosed at about 8 13 kbar and 630 740 c during the late permian to the early triassic the south vergent contraction and top down to the north normal faulting are suggestive of a suture belt between the north china block sino korea craton and the south china block yangtze craton an extension of sulu belt across the yellow sea entire peninsula experienced strong deformation and metamorphism during the suturing event namely songrim orogeny during this orogenic event the kyonggi massif and the okchon basin accreted to the yongnam massif and taebaeksan basin along the south korean tectonic line running northeast southwest a series of northward trending thrust formed along the boundary zone to the east kaktong and kongsuwon thrusts and others piggyback basins locally developed along the thrust faults forming the taedong group the crustal deformation resumed in the early to late jurassic daebo event under contractional setting dextral ductile shearing associated with thrusting and folding continued in the mid southern part of the peninsula it was due to orthogonal northwestward subduction of the izanagi plate under the asian continent the yongnam massif experienced continuous dextral offset along the honam shear zone in the early cretaceous the izanagi plate began to subduct northward and caused formation of strike slip basins in retroarc setting i e kyongsang basin in the southeastern part and a number of small scale basins in the mid southwestern part of the peninsula small scale alluvial fans and fluvial channel networks formed in the basin margin and were transitional to ephemeral lacustrine systems under semiarid to arid conditions extensive intrusion of granitoids occurred from triassic to early tertiary with a gap between 160 and 100 ma representing continental magmatic arc in the tertiary the southeastern margin of the korean peninsula experienced back arc opening pull apart basins formed in the miocene bounded by the yangsan and hupo faults the yonil group sedimentary fill of the pohang basin comprises more than 1 km thick siliciclastic sequence which represents deposition in fan delta systems on the hanging wall of the yangsan fault thick more than 10 km thick sediments in the ulleung basin margin were deformed in the late miocene due to the northward movement of kyushu block quarternary volcanic events in cheju island represent intraplate hot spots

wings mushrooms and christmas trees the carbonate seismic geomorphology of central luconia miocene present offshore sarawak northwest borneo central luconia is a geological province of the sarawak basin offshore northwest borneo characterized by extensive development of miocene to holocene carbonate buildups the buildups are up to 2 km 1 mi thick and reveal complex seismic geomorphologies including out building in building carbonate siliciclastic intercalations and coalescence of neighboring carbonate bodies intermittent carbonate and siliciclastic deposition is interpreted to have been governed by frequently oscillating sea level and variable siliciclastic input location of the buildups with respect to deltaic facies and the seismic expressions of marginal carbonate strata locally known as wings are used here to classify carbonate seismic geomorphologies buildups encompassed by deltaic topsets are said to reside onshelf and are flanked by marginal carbonate deposits conformable with the onlapping siliciclastics and interpreted as thin carbonate platforms deposited in situ over prominent erosional unconformities and flooding surfaces such marginal facies are described on the basis of their appearance as open wings in contrast buildups downlapped by prodelta foresets or bottomsets or those draped by pelagic sediments are said to reside offshelf and are characterized by high relief steeply dipping marginal carbonate strata discordant with respect to the relatively flat lying platform carbonates as well as the onlapping siliciclastics these marginal strata have an appearance of closed wings and are interpreted as slope aprons composed of carbonate material derived from the productive platform tops and deposited off platform in deeper water carbonate geometries range from contracting upward pinnacles to expanding upward platforms in onshelf settings whereas buildups located offshelf have mostly contracting upward or aggrading morphologies buildups deposited onshelf have generally maintained a similar height of depositional slopes as they evolved reflecting rates of background siliciclastic deposition approximating those of carbonate growth in contrast depositional slopes of offshelf buildups have become progressively higher owing to limited siliciclastic input observations presented here on carbonate geomorphology and adjacent siliciclastic stratigraphy provide important clues for the understanding of the geology of the province because carbonates and siliciclastics intercalate frequently siliciclastic biostratigraphy can be used to precisely date and correlate geographically remote carbonate reservoir intervals and intrareservoir depositional and diagenetic events such as marine transgressive or exposure surfaces or karst networks conversely basin paleobathymetry can be measured by the size of carbonate clinoforms and the thickness of buildups established over flooded siliciclastic surfaces deposition of low relief carbonate platforms over siliciclastic substrates indicates shallow marine conditions as opposed to the prevalent notion of kilometer scale paleobathymetry these interpretations have important implications for understanding of the sedimentology and lithology of the ambient basinal siliciclastics with fundamental applications to hydrocarbon exploration

role of climate in partial drowning of the queensland plateau carbonate platform northeastern australia abstract ocean drilling program leg 133 core data samples and geophysical data logs and seismics were analyzed to document late miocene early pliocene partial drowning of the queensland plateau carbonate platform off northeast australia the modern plateau consists of a mosaic of pinnacle reefs and larger 10 50 km reefs representing relicts of early to middle miocene buildups late miocene early pliocene floatstones packstones and mudstones rich in the larger benthic foraminifers lepidocyclina and cycloclypeus drilled in a transect of sites across the drowned margin of a middle miocene buildup show that the late pliocene partial drowning of the platform was preceded by 4 myr of neritic carbonate deposition without any reefs the carbonate factory was unable to aggrade to sea level during this period as indicated by the lack of any shallowing trend in the succession monitoring of the miocene to recent neritic shedding pattern on the windward and leeward side of a pinnacle reef on the queensland plateau supports this interpretation shedding on the leeward side of the reef which records periods of active reef growth played a minor role during the late miocene increased during the pliocene and reached very high values during the late pliocene and pleistocene shedding on the windward side of the reef which was active during lowstands of relative sea level occurred during the late middle early late miocene and during the pliocene quaternary the data presented here when combined with paleoceanographic data points to low surface water temperatures 17 19 c as a major factor which suppressed reef growth during the late miocene early pliocene period

the growth potential of a bypass margin great bahama bank abstract observations and sampling to 350 m from a two person submersible off chub cay berry islands bahamas suggest that accretion is occurring to varying degrees in all subdivisions of the platform margin profile at the chub cay dive site a nearly vertical wall extends to 140 m subsea below and extending to the limit of the dives is a low relief fore reef slope ca 50 of limestone veneered with sediment this study supports the idea that the upper portion of the wall from 30 to 85 m the brow or deep reef is a principal source of talus now cemented that foots the windward margins of great bahama bank we infer that the brow grows outward so rapidly that it calves periodically the resulting debris largely bypasses the deeper wall but some is perched on the steep fore reef slope below where it is soon incorporated into the slope by submarine cementation this model further explains the observation that carbonate platform margins tend to steepen through time and shows how those steepened slopes can be maintained during their continued growth

neogene carbonate platform development in the nw south china sea litho bio and chemo stratigraphic evidence abstract the variations of lithostratigraphy foraminifera geochemical elements and organic biomarkers in well xk1 from the xisha paracel islands reveal the history of carbonate platform development since the early miocene in the south china sea our results indicate that reef growth was more active in the middle miocene than in any earlier periods decreased in the late miocene revitalized in the pliocene and active again in the pleistocene interglacial periods unlike those limestone rich intervals the late miocene succession in well xk1 is characterized by dolomitized limestones with a low deposition rate 30 60 m ma post compaction these late miocene rocks also contain relative high mgo 20 more ree abundant algae and some small sized foraminifera but rare larger benthic foraminifera very low land sourced brgdgts 0 0 5 ng 20 g low bit index 0 1 0 5 and low tex86 derived sea temperature 20 25 c indicating limited active reef growth in relative cooler mesophotic environments at 30 m water depths similar dolomitized limestones of late miocene age also occur in other carbonate platform areas including the nansha spratly islands in the southern south china sea together these south china sea records provide regional evidence of a recession in global carbonate platform development starting from the late miocene while carbonate platform reduction in other regions may have been triggered by global cooling and changing oceanic chemistry accelerated basin subsidence coupled with monsoon cooling are considered as the main factors causing the reef decline in the late miocene south china sea

climatic solar oceanic and geomagnetic influences on late glacial and holocene atmospheric 14c 12c change late glacial and holocene 14c12c ratios of atmospheric co2 vary in magnitude from a few per mil for annual decadal pertubations to more than 10 for events lasting millennia a data set illuminating 10 to 104 yr variability refines our understanding of oceanic climatic versus geomagnetic or solar forcing of atmospheric 14c12c ratios most of the variance in the holocene atmospheric 14c12c record can be attributed to the geomagnetic millennia time scale and solar century time scale influence on the flux of primary cosmic rays entering the atmosphere attributing the observed atmospheric 14c12c changes to climate alone leads to ocean circulation and or global wind speed changes incompatible with proxy records climate ocean related 14c redistribution between carbon reservoirs while evidently playing a minor role during the holocene may have perturbed atmospheric 14c12c ratios measurably during the late glacial younger dryas event first order corrections to the radiocarbon time scale 12 000 30 000 14c yr b p are calculated from adjusted lake sediment and tree ring records and from geomagnetically defined model 14c histories paleosunspot numbers 100 9700 cal yr b p are derived from the relationship of model 14c production rates to sunspot observations the spectral interpretation of the 14c12c atmospheric record favors higher than average solar activity levels for the next century minimal evidence was found for a sun weather relationship

the middle miocene climatic transition east antarctic ice sheet development deep ocean circulation and global carbon cycling abstract the middle miocene represents a major change in state in cenozoic climatic evolution following the climax of neogene warmth in the late early miocene at 16 ma the early stage of this climatic transition from 16 to 14 8 ma was marked by major short term variations in global climates east antarctic ice sheet eais volume sea level and deep ocean circulation in the later stage from 14 8 to 12 9 ma climatic developments included major growth of the eais and associated antarctic cooling a distinct increase in the meridional temperature gradient large fluctuations in sea level followed by a global sea level fall and important changes in deep water circulation including increased production of southern component water east antarctic ice sheet growth and polar cooling also had large effects on global carbon cycling and on the terrestrial biosphere including aridification of mid latitude continental regions increased stability of the eais after 14 8 ma represents a crucial step in the establishment of late neogene global climate systems what controlled these changes in polar climates and the east antarctic ice sheet deep ocean circulation changes probably played a major role in the evolution and variation in polar climates as they have throughout the cenozoic oxygen and carbon isotopic evidence for warm saline deep water production in the eastern tethyan northern indian ocean indicates that meridional heat transport to the antarctic inhibited cenozoic polar cooling and eais growth during the early middle miocene from 16 to 14 8 ma inferred competition between warm low latitude sources derived from the eastern tethyan northern indian ocean and a cold high latitude source southern component water from 16 to 14 8 ma may have been associated with instability in the antarctic climate and cryosphere reduction of warm saline deep water flow to the southern ocean at 14 8 ma may have decreased meridional heat transport to the antarctic cooling the region and leading to increased production of southern component water these middle miocene climatic and cryospheric changes in the antarctic had profound effects on marine and terrestrial climates as the meridional surface temperature gradient increased boundaries between climatic zones strengthened leading to increased aridification of mid latitude continental regions in australia africa and north and south america enhancing the development of grasslands and stimulating the evolution of grazing mammals

sulige field in the ordos basin geological setting field discovery and tight gas reservoirs abstract the sulige gas field in central ordos basin is one of the largest gas fields in china with about 860 7 billion cubic meters bcm of proven gas reserve this field covers an area of about 500 km 2 with largely tight clastic reservoirs the upper carboniferous lower permian deltaic sandstones and upper permian lacustrine mudstones deposited in a stable cratonic tectonic setting form an effective petroleum system that is favorable for gas accumulation in large scale stratigraphic lithologic traps based on wire line log response drilling stem test and core data a generalized classification system was developed for the gas reservoirs of the sulige field thus type i and ii rocks are capable of gas production without natural and or artificial fracturing type iii rocks are capable of gas production after artificial fracturing and type iv rocks are too tight to produce at commercial rates even with artificial fracturing the discovery of the sulige field not only adds large gas reserve in the ordos basin but strongly indicates the overlook potential of both tight sandstone reservoir rock and relatively porous and permeable sweet spots in it

microbial micritic carbonates in uppermost permian reefs sichuan basin southern china some similarities with recent travertines the uppermost permian chuenmuping reef formed on the western side of a carbonate platform situated in the eastern sichuan basin southern china contrasts exist between this western patch reef and the better known jiantianba barrier reef complex on the eastern platform margin in western hubei province 250 km to the east microbial micritic carbonates form significant components of the chuenmuping reef limestones three types of fabric can be identified irregular clotted and scalloped laminated an additional cuneiform fabric has been found only in fore reef facies at jiantianba irregular fabric is comparable with the surface of presently forming travertines at rapolano terme central italy which are produced by calcification of cyanobacteria clotted fabric shows indistinct peloids which tend to lack rims and are amalgamated into irregular masses some of which exhibit bush like arrangements where traces of filaments can be seen traces of filaments are observed in both dark and light layers in the scalloped laminated fabric again suggesting a microbial origin cuneiform fabric consists of peloids and filaments and closely resembles deposits in quaternary travertines which may have been caused by bacterial action chuenmuping reef shows a shallowing sequence in normal marine conditions the micritic fabrics interpreted here as microbial occur more commonly in the upper part of the reef this indicates that microbial micrites with a cementing role formed coevally with reef growth within the upper part of the photic zone

bahama carbonate platforms the deep and the past abstract carbonate deposition prevailed for 150 ma in the bahama florida segment of the west atlantic margin and provides an interesting test for actualism present day facies patterns on the banks are controlled by the backward decrease of waves and tides and the concomitant increase of temperature and salinity variation in the troughs influx of sand and rubble from gravity flows varies with topography and distance from shallow water sources and allows one to define facies belts a rhythmic sequence of ooze and graded beds on the basin floors subdivided into a basin margin belt of coarse thick turbidites and basin interior with fine turbidites slope facies change with increase in height and declivity from accretionary to by pass to erosional regimes stratigraphic history of the bahamas is not simply a projection of the holo scene back in time both long term natural evolution decrease in subsidence upbuilding of the banks submarine erosion and outside factors climate eustacy have caused significant changes since the jurassic the bahamas seem to have evolved from a clastics evaporite province to a single carbonate evaporite platform and finally to an array of platforms and troughs during the platform trough stage the rate of upbuilding of the platforms decreased submarine canyon erosion increased platform flanks steepened as they grew higher and changed from accretionary to by pass to erosional slopes a change imposed by extraneous factors occurred in the pliocene when the great bahama bank changed from a giant reef rimmed atoll to a flat platform covered by oolites and peloid sands the bahamas share both long term trends as well as random changes by extraneous factors with other platforms in the geologic record compared to ancient platforms however they are unusually long lived and at a more advanced stage of growth they are deeply dissected by erosion their flanks are unusually high and steep and the troughs very narrow the neogene platform sequence is strongly controlled by eustatic sea level fluctuations

relative control of paleoceanography climate and eustasy over heterozoan carbonates a perspective from slope sediments of the marion plateau odp leg 194 in this paper we explore the relative control of paleocean ography eustasy and water temperature over the evolution of a car bonate slope system deposited on the marion plateau northeastern australia growth of several carbonate platforms started in the early miocene on this plateau and although they occurred in low latitude subtropical waters they are composed mainly of heterozoan organisms we investigated an upper to distal slope transect drilled during odp leg 194 and located close to the northern marion platform we re constructed mass accumulation rates of carbonate as well as the evo lution in the ratios of carbon and oxygen stable isotopes power spec trum analysis of the carbon isotope record revealed the existence of cycles with main frequencies centered around 409 kyr and 1800 kyr we interpret the 409 kyr cycle as being paced by changes in the ec centricity of the earth orbit and we suggest that the 1800 kyr cycle could be linked to long term eustatic changes finally on the basis of the timing of changes in mass accumulation rates of carbonate we infer that the strength and direction of oceanic currents affected sedimen tation on the marion plateau by shifting depocenters of slope sedi mentation a process probably further modulated by sea level changes we argue that the evolution and demise of the heterozoan carbonate systems present on the marion plateau were controlled mainly by the evolution of strong benthic currents and that eustasy and water tem perature alone did not account for the drowning of the platforms in the mid miocene

facies model on the modern isolated carbonate platform in the xisha archipelago south china sea abstract the xuande atoll with a discontinuous reef rim caused by platform drowning is a typical ellipse isolated platform on the northern slope of the south china sea based on the data of drilling holes the analysis of surface sediments and high resolution acoustic data six sedimentary facies are identified in the xuande atoll including reef outer slope reef front reef flat aeolianite sand island back reef slope and lagoon facies map shows that the elevated reef rimmed margins with islands are more noticeable on the windward of the platform with an elevated and discontinuous reef rimmed margin as well as coarse grained sediment in the interior platform xuande can serve as a case of a leaky bucket atoll which is characterized by initially drowning scenarios the facies architecture of the xuande atoll is evidently influenced by complex and interacting parameters including antecedent topography sea level wind driven currents water depth and tectonic subsidence different controlling factors exist in the drowning of the windward and leeward sides of the platform margin the study of modern depositional settings in the xuande atoll will provide insight on predictions for ancient carbonate provinces

sedimentary patterns and geometries of the bahamian outer carbonate ramp miocene lower pliocene great bahama bank core logging and high resolution seismic data from odp leg 166 were used to analyse deposits of the neogene miocene lower pliocene bahamian outer carbonate ramp ramp sediments are cyclic alternations of light and dark grey wackestones packstones with interbedded calciturbidite packages and minor slumps cyclicity was driven by high frequency sea level changes light grey layers containing shallow water bioclasts were formed when the ramp exported material whereas the dark grey layers are dominantly pelagic calciturbidites are arranged into mounded lobes with feeder channels internal bedding of the lobes shows a north directed shingling as a result of the asymmetrical growth of these bodies calciturbidite packages occur below and above sequence boundaries indicating that turbidite shedding occurred during third order sea level highstands and lowstands highstand turbidites contain shallow water components such as green algal debris and epiphytic foraminifera whereas lowstand turbidites are dominated by abraded bioclastic detritus gravity flow depocentres shifted from an outer ramp position during the early miocene to a basin floor setting during the late miocene to early pliocene this change was triggered by an intensification of the strength of bottom currents during the tortonian which was also responsible for shaping the convex morphology of the outer ramp the miocene and lower pliocene of the leeward flank of great bahama bank provides an example of the poorly known depositional setting of the outer part of distally steepened carbonate ramps the contrast between its sedimentary patterns and the well known upper pliocene quaternary slope facies associations of the flat topped great bahama bank shows the strong control that the morphology of a carbonate platform exerts on the depositional architecture of the adjacent slope and base of slope successions

karst controlled diagenesis and reservoir development example from the ordovician main reservoir carbonate rocks on the eastern margin of the ordos basin china the ordovician majiagou formation contains the main reservoir of the ordos central gas field in the ordos basin the producing zone at the top of member 5 consists of carbonate rocks modified during a long period of subaerial exposure and karstification from the late ordovician to the middle carboniferous on the eastern margin of the ordos basin the porosity of the exposed carbonate rocks of this unit ranges from 0 5 to 15 1 and permeability ranges from 8 and permeability ranges from 0 1 to 5 md the main reservoir porosity is a dissolution enhanced vuggy porosity associated with dolomite the carbonate rocks show great heterogeneity reflecting the varying effects of karstification in creating and modifying porosity petrographic and geochemical analyses of various components in these carbonates provided evidence for depositional and diagenetic processes the reservoir carbonates were deposited in shallow and restricted hypersaline environments and were later modified by karstification and burial diagenesis dolomitization appears to have resulted from mixing of marine and meteoric waters and probably occurred in both shallow and deep burial settings cementation by calcite also occurred in both shallow and deep environments under different hydrodynamic conditions both depositional settings and diagenetic processes such as leaching by meteoric water paleokarstification dolomitization and cementation controlled reservoir development the outcrop and subsurface samples show similar petrographic features porosity types and geochemical characteristics but the exposed section of the formation shows evidence of more alteration by meteoric water

sequence sequence stratigraphy sea level changes and depositional systems in the cambro ordovician of the north china carbonate platform abstract the cambro ordovician strata in north china were deposited over a very extensive craton extending some 1500 km east west and 1000 km north south the dominantly shallow water carbonate succession reaches up to 2000 m in thickness and two megasequences transgressive regressive cycles can be distinguished lower cambrian through lower ordovician strata and middle through upper ordovician strata separated by a major palaeokarst the first megasequence consists of nine sequences which are generally 50 150 m in thickness the lower cambrian sediments consist of phosphorites and phosphatic sandstones deposited during the flooding of the craton carbonates mudrocks and evaporites were deposited in the early cambrian under an arid climate laying the foundation for the subsequent long period of shallow water carbonate deposition which lasted some 70 m y the middle and lower upper cambrian sequences consist predominantly of mudrocks and storm deposits tempestites in the lower part and oolitic grainstones and tidal flat lime mudstones in the upper part these represent outer mid and mid inner ramp depositional systems respectively of the transgressive and highstand systems tracts these sequences have strong similarities with the grand cycles in the cambro ordovician successions of north america in the upper cambrian there is a distinctive unit of glauconitic purple red mudstone several metres thick which is interpreted as the deposits of the maximum flooding of the first megasequence in the upper cambrian there was a phase of tilting of the north china carbonate platform to the north and storm deposits especially intraclastic conglomerates and hummocky cross stratified grainstones packstones were very common at this time also common in upper middle and lower upper cambrian strata are stromatolitic thrombolitic bioherms several metres in diameter the upper upper cambrian through lower ordovician strata are dominantly fine grained limestones and dolomites deposited in shallow subtidal and inter to supra tidal environments on a low energy epeiric sea platform this part of the succession is the regressive part of the first megasequence so that overall the platform shows an evolution from platform initiation to platform foundation to a ramp depositional system and then an extensive epeiric platform on a small scale the succession is composed of metre scale shallowing upward cycles parasequences arranged into cycle sets of 10 30 m thick the middle upper ordovician megasequence consists mostly of shallow water carbonates with several thick evaporite units minor palaeokarsts and palaeosoils separate the sequences which are composed of metre scale cycles regional uplift affected the north china platform in the ordovician and sedimentation did not resume until the carboniferous there is a good correlation of the two transgressive regressive megasequences described here with the global 2nd order relative sea level curve for the cambro ordovician

middle to late miocene stepwise climate cooling evidence from a high resolution deep water isotope curve spanning 8 million years 1 we present high resolution 2 3 kyr benthic foraminiferal stable isotopes in a continuous well preserved sedimentary archive from the west pacific ocean ocean drilling program site 1146 which track climate evolution in unprecedented resolution over the period 12 9 to 8 4 ma we developed an astronomically tuned chronology over this interval and integrated our new records with published isotope data from the same location to reconstruct long term climate and ocean circulation development between 16 4 and 8 4 ma this extended perspective reveals that the long eccentricity 400 kyr cycle is prominently encoded in the 13c signal over most of the record reflecting long term fluctuations in the carbon cycle the 18o signal closely follows variations in short eccentricity 100 kyr and obliquity 41 kyr in particular the obliquity cycle is prominent from 14 6 to 14 1 ma and from 9 8 to 9 2 ma when high amplitude variability in obliquity is congruent with low amplitude variability in short eccentricity the 18o curve is additionally characterized by a series of incremental steps at 14 6 13 9 13 1 10 6 9 9 and 9 0 ma which we attribute to progressive deep water cooling and or glaciation episodes following the end of the miocene climatic optimum on the basis of 18o amplitudes we find that climate variability decreased substantially after 13 ma except for a remarkable warming episode at 10 8 10 7 ma at peak insolation during eccentricity maxima 100 and 400 kyr this transient warming associated with a massive negative carbon isotope shift is reminiscent of intense global warming events at eccentricity maxima during the miocene climatic optimum

the importance of microbial binding in neogene quaternary steep slopes abstract the geometry and inclination of carbonate platform slopes are typically described as the result of the sediment texture components and grain size occurring in the slope three carbonate slopes from the holocene of the tongue of the ocean bahamas and three slopes from an upper miocene carbonate platform in se spain are investigated to identify the factors controlling dip angles although platforms differ in size and elevation with regard to the surrounding basin both locations present slopes with linear profiles and steep angles over 35 the slope facies in both locations are very similar with the matrix and some bioclasts presenting microfabrics that evidence microbial activity during deposition these include 1 clotted micrite patches locally connecting bioclasts or infilling primary pores 2 porostromate structures in the micrite 3 dense micritic masses 4 binding structures 5 micritic crusts and 6 peloidal textures the holocene and miocene depositional geometries and facies distribution are the response to various sedimentary processes including rockfalls gravity flows and in situ carbonate production extensive microbial binding is identified as the controlling factor for early stabilization of the slope which in combination with subsequent rapid cementation produces and maintains the steep slope angles consequently microbial induced stabilization of modern and neogene slopes is as significant as in paleozoic and triassic examples

a new middle ordovician reef assemblage from north central china and its palaeobiogeographical implications abstract a new middle ordovician microbial boundstone incorporating the problematic coralline fossil amsassia is reported from the jinghe formation of north central china sino korean block the reefs are dominated by microbial masses composed of aggregated peloids and micrites the subordinate small module favositoid coral like organism amsassia characterized by phacelocerioid forms and module increase involving fission was surrounded by peloidal layers a few amsassia are preserved in growth position and are occasionally attached to each other the peloidal masses that make up these reefs are considered to be microbialite acting as a primary reef builder and binder whereas amsassia was a limited framework builder in these reefs the jinghe reefs have been previously described as coral stromatolite reefs because of the superficial resemblance of amsassia to lichenaria though their growth characteristics are fundamentally different amsassia and lichenaria show markedly different patterns of palaeobiogeographical initiation and distribution and all middle ordovician lichenaria and lichenaria bearing reefs reported from north central china apparently occur outside of the main palaeobiogeographical province of lichenaria this study demonstrates the need for re evaluation of such reports of early corals from the middle to late ordovician of the western margin of gondwana to clarify the palaeobiogeographical distributions of early coralline organisms

the maldives a giant isolated carbonate platform dominated by bottom currents abstract the maldives a 900 km north south trending paired chain of atolls that surround a ca 100 km wide central basin the inner sea represent a giant isolated carbonate platform in the indian ocean new reflection seismic multibeam and acoustic doppler current profiler data show that its development exhibits a distinct change from sea level to mainly bottom current controlled sedimentation at the end of the middle miocene the post middle miocene intra basinal fill consists of 9 mega units that have been formed and shaped by strong bottom currents entering the inner sea between the inter atoll passages at the end of the middle miocene the maldives represent a rimmed platform with the inner sea forming an empty bucket a connection to the indian ocean existed only in the northeastern part of the platform namely the kardiva channel probably concomitant with the onset of the indian monsoon the current pattern around the maldives changed significantly resulting in the formation of channels in the rimmed platform margin the latter process was encouraged by local drowning of large platform parts and additionally by bottom current forced submarine erosion that widened the channels to passages disintegrating the platform into separated atolls of different sizes the reworked material was dumped into the inner sea where it formed large contourite fans along slope bottom currents entering the inner sea from the north further redistributed the material leading to a southward shift of these sedimentary bodies in this way the inner sea was filled from west to east mega units 1 5 starting with mega unit 6 the opening of a southern gateway introduced a prominent northward flow of bottom waters in the inner sea it leads to the deposition of giant elongated drifts at the eastern flank of the basin filling it from east to west because the current swept away most of the material around the atolls the system was not able to prograde and the steady subsidence was compensated by aggradation accordingly a fundamental characteristic of a current controlled carbonate system is that aggradation occurs irrespective of platform sediment export or differently worded the rate of change in accommodation is always positive and greater than the rate of sediment supply adcp measurements in the winter monsoon season show two water masses in the inner sea one at the surface 0 150 m and a second below it that reaches its sea floor by the use of the grain size distribution of odp leg 716 located in the inner sea as proxy for the flow intensity of the bottom water we recognized an inverse proportional relationship to the monsoon strength from late upper miocene to present some of the current controlled deposits form sigmoidal prograding clinoforms preferably at the edges of the atolls adjacent to the passages where the velocity of the current entering the inner sea is high the anatomy of these prograding wedges is similar to sea level controlled clinoforms described for large isolated carbonate platforms in the sequence stratigraphic concept however our results document that they are not influenced by sea level fluctuations because of the high current velocities involved in their deposition they predominately consist of coarse sand sized carbonate fragments exhibiting large pore space and high permeability therefore these drift deposits comprise a possible exploration target

neogene overflow of northern component water at the greenland scotland ridge in the north atlantic ocean flow of north atlantic deep water nadw and of its ancient counterpart northern component water ncw across the greenland scotland ridge gsr is thought to have played an important role in ocean circulation over the last 60 ma the iceland plume has dynamically supported an area which encompasses the gsr consequently bathymetry of the gsr has varied with time due to a combination of lithospheric plate cooling and fluctuations in the temperature and buoyancy within the underlying convecting mantle here we reassess the importance of plate cooling and convective control on this northern gateway for ncw flow during the neogene period following wright and miller 1996 to tackle the problem benthic foraminiferal isotope data sets have been assembled to examine 13c gradients between the three major deep water masses i e northern component water southern ocean water and pacific ocean water composite records are reported on an astronomical timescale and a nonparametric curve fitting technique is used to produce regional estimates of 13c for each water mass confidence bands were calculated and error propagation techniques used to estimate ncw and its uncertainty despite obvious reservations about using long term variations of 13c from disparate analyses and settings and despite considerable uncertainties in our understanding of ancient oceanic transport pathways the variation of ncw through time is consistent with independent estimates of the temporal variation of dynamical support associated with the iceland plume prior to 12 ma 13c patterns overlap and ncw cannot be isolated significant long period variations are evident which are consistent with previously published work from 12 ma when lithospheric cooling probably caused the gsr to submerge completely long period 13c patterns diverge significantly and allow reasonable ncw estimates to be made our most robust result is a dramatic increase in ncw overflow between 6 and 2 ma when dynamical support generated by the iceland plume was weakest between 6 and 12 ma a series of variations in ncw overflow have been resolved

the transient nature of the empty bucket model of reef sedimentation abstract the geometry of modern reefs has been likened to an empty bucket with the narrow reef rim comprising the container pail that encloses the water filled bucket while the analogy is valid the assumption that this constitutes a final geometry is not examples from the indian pacific and atlantic oceans individually and collectively demonstrate current filling of the lagoons by reef perimeter sand aprons since sea level only approximated its present position 3 to 6 ky ago it follows that the observed extent of modern highstand lagoon filling is minimal if the filling process was to continue unabated the result would be a flat topped bank but during the pleistocene low stands of sea level aborted the filling process extrapolating these relationships to the geologic record suggests that the empty bucket model of unfilled reef lagoon space is greatest during icehouse high frequency glacial fluctuations of sea level alternatively filled buckets in which cycle thickness approximates accommodation space are probably largely restricted to greenhouse time intervals the co occurrence of quaternary high amplitude frequency sea level changes with rapidly growing scleractinian corals probably enhanced the occurrence of empty bucket morphologies

a model for solar constant secular changes although the direct influences of sunspots upon the solar constant leads to short term decreases an opposite nearly in phase 11 year variation in the solar constant can be modelled this opposite behavior results primarily from global faculae polar network and active region the model attributes the observed variations in the solar constant entirely to magnetic features in the solar atmosphere hence the model does not require any indirect effect of the magnetic cycle on the brightness of non magnetic areas of the sun the model uses the well studied active region influences upon the solar constant together with the influences of global faculae associated with polar and general solar magnetism studied by sheeley using the present model together with the sunspot prediction of schatten and sofia 1987 we predict the average solar constant to the year 1997 normalized to the mean active cavity radiometer acrim and earth radiation budget erb observations the model also provides a relation so 0 007 rm max for the very long term solar constant variations due to the secular changes in solar activity we obtain a change of 1 w m for the difference between the late twentieth century solar constant and the 17th century solar constant this supports eddy s view that this difference could give rise to the glacial increase during the little ice age of the 17th century

bypass margins basin restricted wedges and platform to basin correlation upper devonian canadian rocky mountains implications for sequence stratigraphy of carbonate platform systems abstract carbonate platforms can commonly keep up with relative sea level rise because of high rates of sediment accumulation and platform aggradation surrounding basinal environments are commonly starved but can receive variable extrabasinal siliciclastic input and episodically deposited carbonate sediment if accumulation rates in basinal settings lag behind those of the platform a bypass or erosional margin can develop under these circumstances platform and basin depositional sequences become physically detached and direct correlation of basinal and platform sequences is hindered we report here the results of high resolution stratigraphic analyses of two upper devonian isolated carbonate platforms in western alberta that provide insight into the sequence stratigraphy of bypass margins and criteria for accurate correlation of platform and basinal sequences the slope and basin sequences surrounding the miette and ancient wall platforms consist of basin restricted onlapping wedges of fine grained background sediment deposited dominantly from suspension and coarse grained platform derived sediment redeposited by a variety of gravity flow mechanisms sequence boundaries are identified within the redeposited carbonate intervals identification of sequence boundaries and differentiation of highstand and lowstand slope and basinal facies was based on the geometry mineralogy and clast content of redeposited carbonate units highstand carbonates contain sheet like debris flows and turbidites with abundant slope derived clasts and background facies with high total carbonate content lowstand carbonates contain sheet like and channelized debris flows and turbidites with abundant platform derived clasts and background facies with low carbonate content and locally high amounts of organic carbon transgressive facies are dominated by initially carbonate poor and organic rich background sediments that display a progressive increase in carbonate content and decrease in organic carbon content these patterns are interpreted to record abundant background carbonate sedimentation during late transgression and highstand when the carbonate factory was robust highstand redeposited carbonates record slope erosion due to oversteepening and slope readjustment processes lowstand redeposited carbonates indicate platform and platform margin erosion and low background carbonate sedimentation when the platform was either exposed or under very shallow peritidal conditions high siliciclastic and organic contents during lowstand and early transgression may partly be the result of reciprocal sedimentation but alternatively may represent continuous siliciclastic supply during times with little dilution by fine grained carbonate sediment successive stages of platform development at miette and ancient wall were controlled by accommodation changes driven by relative sea level fluctuations backstripping analyses of strata from both platforms confirm that significant differential subsidence was a major control on variations in platform thickness and patterns of slope development greater subsidence at ancient wall fostered the development of a steeper bypass margin and different slope evolution compared to miette slope oversteepening also initiated a process of slope readjustment that eventually reduced the platform to basin gradient and facilitated regressive platform progradation in conventional siliciclastic sequence stratigraphy basin restricted wedges are interpreted as lowstand deposits on the basis of their geometry and position relative to an updip margin wedge shaped basinal units along the miette and ancient wall bypass margins contain both highstand and lowstand facies that straddle sequence boundaries the results of this study provide objective criteria for differentiating systems tracts in carbonate slope and basin environments through mineralogic and compositional analyses providing more accurate correlation of detached platform and basin sequences interpretation of carbonate basin restricted wedges as purely highstand or lowstand deposits may lead to erroneous conclusions regarding sequence stratigraphy platform to basin correlation and the volumetric partitioning of sediments deposited in different systems tracts

the chronostratigraphic significance of seismic reflections along the bahamas transect abstract continuous cores drilled during the bahamas drilling project bdp and the ocean drilling program odp leg 166 along a transect from the top of great bahama bank to the basin in the straits of florida provide a unique data set to test the assumption in seismic stratigraphy that seismic reflections are time lines and thus have a chronostratigraphic significance seismic reflections that are identified as seismic sequence boundaries ssbs were dated by means of biostratigraphy in the five odp sites and by a combination of biostratigraphy magnetostratigraphy and sr isotope stratigraphy in the two bdp sites the seismic reflection horizons are carried across a variety of facies belts from shallow water carbonates over slope carbonates to drift deposits in the straits of florida within this system 17 ssbs were identified and dated despite the fact that the seismic reflections cross several facies belts their ages remain remarkably constant the average offset in all sites is 0 38 myr in no cases do the seismic reflections cut across time lines the age differences are the combined result of the biostratigraphic sampling frequency the spacing of marker species that required extrapolation of ages and the resolution of the seismic data in addition uncertainties of age determination in the proximal sites where age diagnostic fauna are rare add to the age differences between sites therefore it can be concluded that the seismic reflections which mark the ssbs along the bahamas transect are time lines and can be used as stratigraphic markers this finding implies that depositional surfaces are preferentially imaged by reflected seismic waves and that an impedance contrast exists across these surfaces facies successions across the sequence boundaries indicate that the sequence boundaries coincide with the change of deposition from times of high to low sea level in the carbonate setting of great bahama bank sea level changes produce changes in sediment composition sedimentation rate and diagenesis from the platform top to the basin the combination of these factors generates differences in sonic velocity and thus in impedance that cause the seismic reflection the impedance contrasts decrease from the proximal to the distal sites which is reflected in the seismic data by a decrease of the seismic amplitude in the basinal area

solar modulation of cosmogenic nuclide production over the last millennium comparison between 14c and 10be records for about the last 30 years it has been recognized that the high frequency component of the tree rings 14c 12c record is dominated by the modulation of the cosmic ray flux by the solar wind in particular it has been demonstrated that the three most recent periods of low sunspot occurrence were characterized by high values of atmospheric 14c 12c during the last millennium other periods of high 14c 12c values were observed but their solar origin is still debatable in the present work we compare these fluctuations with an independent record of cosmogenic 10be measured in ice from the south pole to check the solar origin of the observed 14c 12c variations in order to compare quantitatively the results obtained on 10be and 14c it is necessary to take into account the different behaviour of these two cosmogenic isotopes and especially the damping effect of the carbon cycle in the case of 14c as an input to a 12 box numerical model we used the relative fluctuations of the 10be concentrations record measured in south pole ice and converted it into a synthetic 14c record we took into account the fact that 10be modulation is enhanced in polar regions due to the orientation of the geomagnetic field as expected the fluctuations of the modelled 14c record are much smaller a factor of 20 than those observed for the raw 10be record in addition the variations are smoother and shifted in time by a few decades the 10be based 14c variations closely resemble the 14c measurements obtained on tree rings r 0 81 in particular it is easy to identify periods of maximal 14c 12c which correspond to solar activity minima centred at about 1060 1320 wolf 1500 sporer 1690 maunder and 1820 dalton yr a d cross correlation calculations suggest that there is no significant lag between the 10be based 14c and the tree ring 14c records our study strongly suggests the dominance of the solar modulation on the cosmonuclide production variations during the last millennium

middle cambrian siliceous sponge calcimicrobe buildups daegi formation korea metazoan buildup constituents in the aftermath of the early cambrian extinction event abstract numerous decimetre to metre scale carbonate buildups dominated by siliceous sponges and the calcimicrobe epiphyton are reported from the middle cambrian series 3 daegi formation of korea these siliceous sponge epiphyton buildups consist predominantly of grey micritic boundstones with dark clots and or white clumps the boundstones contain sponge spicule networks interpreted as the calcified remains of siliceous sponges the white clumps and dark clots in the boundstones represent variously preserved epiphyton siliceous sponges form constructional pore space and are commonly encrusted by epiphyton the sponges were probably the primary frame builders providing substrates for the attachment and subsequent growth of epiphyton epiphyton is considered to be a binder when covering the surface of siliceous sponges and a subordinate frame builder when filling depositional voids created by siliceous sponges or growing on top of other epiphyton growth bundles the siliceous sponge epiphyton buildups of the daegi formation show similarities to previously described late cambrian furongian anthaspidellid calcimicrobe buildups from iran and the usa together with recently reported examples from the zhangxia formation of eastern china the sponge epiphyton buildups from korea represent some of the oldest metazoan calcimicrobe buildups after the extinction of most archaeocyaths at the end of the early cambrian series 2 this implies that the incorporation of metazoans in middle cambrian series 3 carbonate buildups occurred much earlier than previously known the buildup forming siliceous sponges described in this study demonstrate that their role in early phanerozoic carbonate buildups has been grossly underestimated

marine peloids a product of bacterially induced precipitation of calcite high magnesian calcite peloids are a common constituent of cemented marine carbonate accumulations they are abundant and well developed within both isolated microcavities and surface crusts the nuclei of marine peloids are composed of fossil bacterial clumps encased within anhedral submicron to micron sized high magnesian calcite crystals the marine peloids are similar to silt sized particles found in travertine deposits that also are composed of fossil bacterial clumps and their surrounding calcite coronas these similarities include size 20 60 mu m a cloudy brown nucleus and rims of clear euhedral crystals in addition previous studies have established the presence of fatty acids of bacterial origin within peloidal deposits and enriched stable isotopic signatures have been interpreted as recording organic fractionation concomitant with calcite precipitation these characteristics all indicate that the nuclei of many peloids originate as calcite precipitates within and around clumps of bacteria and that this precipitation was induced by the vital activity of bacterial colonies

construction of the earliest stromatoporoid framework labechiid reefs from the middle ordovician of korea abstract the great ordovician biodiversification event gobe involved a remarkable rise of skeletal reefs during the late middle ordovician a new type of skeletal patch reef built by labechiid stromatoporoids is reported from the yeongheung formation darriwilian of the korean peninsula part of the eastern north china block a hot spot for late middle ordovician diversification of early labechiids the attachment of laminar labechiids subordinate peloidal micritic crusts and spiculate sponges and minor bryozoans on peloidal intraclastic packstone to grainstone substrates and upward growth of these organisms by repeated encrustation resulted in the construction of centimeter scale domal tight frame structures these skeletal frames were in turn veneered by larger labechiids forming sub meter scale laminar skeletal reefs with primary cavities such skeletal reefs that formed by the encrustation and binding of labechiid stromatoporoids are analogous to the bindstone frameworks of coeval laurentian reef mounds and skeletal reefs though they differ markedly in composition as is apparent in the absence of tabulate corals and markedly lower contribution of bryozoans both of which were key elements of the chazy reefs of laurentia the yeongheung reefs described herein represent some of the oldest labechiid skeletal reefs known to date and formed mainly by the aggregation of early stromatoporoids prior to the arrival of corals and other robust constructors in the region this discovery provides new information on the evolutionary trends of early skeletal reefs in response to the appearance of new reef building organisms and their regional distributions during the ordovician radiation

carbonates and relative changes in sea level abstract in the geologic record some of the most accurate gauges of changes in sea level are the sediment type geometry and diagenesis of carbonate shelves and platforms this is because carbonates frequently occur at or very near sea level and are usually less compacted than siliciclastics world wide changes in relative sea level the sum of eustatic sea level changes sedimentation and crustal movements have occurred repeatedly and cyclicly through geologic time producing characteristic responses in carbonates 1 1 relative rises in sea level usually caused by the cumulative effect of tectonic subsidence and eustatic rise may result in the following 1 1 a drowned carbonate reefs or platforms here carbonate growth potential is exceeded by relative sea level rise and is characterized by shallow water sediments overlain by hardgrounds and or deep water sediments some of which may be condensed sequences 1 2 b platforms where only the fast growing rim and patches of the interior are able to match sea level rise while the remainder of the platform is drowned temporarily 1 3 c platforms which keep up and maintain a flat top at sea level and contain shallow water sediments whose thickness at the least matches the height of the sea level rise if terrigenous supply is limited prograding sheets of shelf carbonate occur frequently capped by supratidal evaporites with prograding shelf margin carbonate clinoforms and turbidites if terrigenous supply is high the shelf carbonates encroach on deltaics 2 2 relative drops in sea level caused by crustal uplift or by subsidence being outpaced by a eustatic drop in sea level cause karst and soil development over shelves and platforms deposition of deep water evaporites in adjacent semi enclosed basins and in open marine basins the deposition of deltaic and aeolian clastics that bypassed the shelf falls are accompanied by platform wide fresh water diagenesis during relative sea level rises marine diagenesis is common in the subtidal portions of the shoaling upward carbonates and fresh water diagenesis and dolomitization and sulphate deposition is common in their intertidal and supratidal portions the stratigraphic significance of these reponses to relative sea level change is that many are tied to eustatic events and so are predictable within a basin of deposition

cryptalgal metazoan bioherms of early ordovician age in the st george group western newfoundland bioherms are common in the st george group a sequence of shallow water carbonate rocks deposited on the western continental shelf of iapetus ocean they range from small heads and metre sized mounds to extensive banks and complexes many metres thick and hundreds of metres in lateral extent the cores of these bioherms are principally composed of thrombolites unlaminated branching columnar stromatolites structures quite distinct from laminated stromatolites which are common in intertidal beds associated with thrombolites is a diverse fauna of burrowing invertebrates trilobites nautiloids pelmatozoans brachiopods gastropods rostroconchs and archaeoscyphiid sponges on the basis of framework building components three main bioherm types are distinguished 1 thrombolite mounds 2 thrombolite lichenaria or sponge mounds and 3 thrombolite lichenaria renalcis reef complexes the framework of the last is the most complex with abundant cavities and a demonstrably uneven growth surface of thrombolites corals and free standing renalcis heads walls and roofs some cavities were active sediment conduits while others were protected their roofs draped with renalcis and their walls coated by cryptalgal laminites these bioherms possess the attributes of shallow water ecologic reefs they span a critical time gap in the development of reefs the transition period from algal dominated bioherms of the precambrian and cambrian to the metazoan dominated bioherms of the middle ordovician and remaining phanerozoic

the intrinsic effect of shape on the retrogradation motif and timing of drowning of carbonate patch reef systems lower frasnian bugle gap canning basin western australia the evolution and architecture of a set of retreating lower frasnian patch reef outcrops in the canning basin of western australia were evaluated and their depositional and stratigraphic contacts spatially recorded using digital surveying tools the geological data together with high resolution digital elevation models were assembled in three dimensional visualization and modelling software and subsequently used for building two dimensional surface models and three dimensional volumetric models numerical data on geometry and shape were extracted from these models and used to quantitatively assess the retrogradation motif of patch reef development the development of the patch reefs comprises three stages during stages 1 and 2 the patch reefs exhibited an overall retrogradational escarpment type configuration displayed by on average 60 steep reef margin walls that lacked the support of coeval slope deposits the subdivision between stages 1 and 2 is based on minor backstepping reducing less than 10 of the platform top area the onset of stage 3 is recognized by stromatolite development fringing reef margin walls during stage 3 an aggrading accretionary reef margin developed comprising allochthonous and autochthonous slope deposits both types of slope deposit onlap the previous stages and are distributed unevenly with allochthonous slope deposits being noticeably absent around the smaller and more elongate patch reefs the variation in distribution of slope sediment type can be explained by the amount linked to platform size of platform top shedding small patch reefs were unable to fill the available accommodation adjacent to escarpments with allochthonous slope sediments and were thus encroached by autochthonous slope sediments the variation which cannot be explained by the size difference in the platform top factory has been related to the difference in perimeter length for patch reefs with similar platform top production areas a more elongate patch reef inherits a longer perimeter and a proportionally smaller volume of allochthonous slope sediment per margin length will be transported to the flanks thus the more elongate patch reef intrinsically contained more sites within which autochthonous slope sediments developed digital outcrop modelling and numerical evaluation of the evolution of the patch reefs revealed the major differences in retrogradation motif the quantified variations in progressive decline of platform top area with height were confirmed by hypothetical decline curves for ellipse shaped carbonate systems for which aspect ratio ratio between length and width varied this mathematical model demonstrates that the progressive decline of the production area is highly sensitive to shape and can be used to numerically assess and predict the relative timing of drowning i e when the platform top production area becomes nil of retrogradational isolated carbonate platforms that are controlled by high accommodation wider implications can be surmised for highstand systems tracts and prograding carbonate systems for example for equally sized platforms with hypothetically similar carbonate factories and identical external forces the potential to prograde by platform top shedding is higher with a smaller aspect ratio because the shorter perimeter implies less accommodation space needing to be filled up to commence slope progradation clearly there are intrinsic effects of shape on the development of carbonate platform systems

peloidal fabrics in upper jurassic reefal limestones weald basin southern england abstract coraliferous limestones from the corallian group upper jurassic of subsurface of the weald basin southern england record the localized development of superimposed patch reefs and banks the reefal limestones exhibit a variety of peloidal fabrics in particular well sorted peloids 10 60 m in diameter with a well developed euhedral rim of fibrous sparry calcite around a micritic anhedral nucleus they occur in confined intraskeletal pores corals molluscs and borings growth cavities between framebuilders and as stromatolitic crusts the peloids in interskeletal cavities and as crusts resemble microbial precipitates and merge into spongiostromate fabrics the distribution of these peloidal fabrics seems to be facies related and is best developed in zones which had relatively low framework growth rates low sedimentation rates and moderate energy levels the peloids are identical in form and occurrence to those in some ancient and quaternary reefs the association of the peloids with stromatolitic coatings and spongiostromate fabrics leads us to interpret the peloids as microbial precipitates either by direct precipitation or by induction the abundance of microbial carbonate in these reefal limestones places them in an intermediate category between frame built reefs and microbial mud mounds

carbonate mounds in the santaren channel bahamas a current dominated periplatform depositional regime abstract new hydroacoustic data high resolution multichannel seismic reflection data ctd casts and sampling document the dominance of bottom currents and the occurrence of carbonate mounds in the santaren channel off great bahama bank and cay sal bank based on these data sets three types of carbonate mounds have been identified in water depths between 285 and 685 m their distribution is strongly related to the present current regime bank driven sediments are caught up by the currents and redeposited mainly in the channel center resulting in the accumulation of giant confined drifts flanked by moats the moats at the banks toe of slope are formed by a southward and northward flowing water mass respectively mainly antarctic intermediate water and subtropical underwater the observed carbonate mounds are concentrated in these moats mound type 1 has an elongated shape parallel to the prevailing bottom current direction a gently inclined flank facing the water flow and a steep flank in its current shadow its upstream flank is covered by a thin sediment wedge whereas the lee side is marked by a parabolic scour type 1 occurs at both bank margins but mainly off great bahama bank consisting of cold water coral rubble floating in a sediment matrix and is thus interpreted as cold water coral mound by contrast type 2 mounds are restricted to the cay sal margin and have a predominately conical outline bottom samples including living sessile crinoids show that its surface must be lithified and colonized by macroepibenthos except corals the mounds are situated in pockmark like depressions that are underlain by fluid escape structures like pipes and chimneys these fluid pathways are generated by a network of fractures mound type 2 is probably formed by abiotic carbonate precipitation however a chemoherm nature cannot be ruled out mound type 3 has a conical to polygonal shape and occurs off cay sal bank and great bahama bank it is surrounded by a scour which is elongated in downcurrent and crescent in upcurrent direction a sediment bulge formed at its front this type is consistent with blocks and boulders colonized by macroepibenthos and related to gravity controlled mass movements at the steep bank slopes principally two habitats can be distinguished the great bahama bank periplatform deep water province dominated by mound type 1 and the cay sal bank slope to basin province occupied by mound type 2 that is associated with pockmark like structures mound type 3 occurs in both habitats physical water mass properties for the existence of cold water corals are limited to a depth range of ca 430 to 685 m with seawater densities of 26 93 to 27 29 kg m and temperatures below 13 c their dominance off great bahama bank might be addressed to a more effective food supply induced by local downwelling

assessing controls on isolated carbonate platform development in central luconia nw borneo from a regional 3d seismic facies and geomorphology investigation

from the great bahama bank into the straits of florida a margin architecture controlled by sea level fluctuations and ocean currents high resolution multichannel seismic data collected across the great bahama bank margin and the adjacent straits of florida indicate that the deposition of neogene quaternary strata in this transect are controlled by two sedimentation mechanisms 1 west dipping layers of the platform margin which are a product of sea level controlled platform derived downslope sedimentation and 2 east or north dipping drift deposits in the basinal areas which are deposited by ocean currents these two sediment systems are active simultaneously and interfinger at the toe of slope the prograding system consists of sigmoidal clinoforms that advanced the margin some 25 km into the straits of florida the foresets of the clinoforms are approximately 600 m high with variable slope angles that steepen significantly in the pleistocene section the seismic facies of the prograding clinoforms on the slope is characterized by dominant partly chaotic cut and fill geometries caused by submarine canyons that are oriented downslope in the basin axis seismic geometries and facies document deposition from and by currents most impressive is an 800 m thick drift deposit at the confluence of the santaren channel and the straits of florida this santaren drift is slightly asymmetric thinning to the north the drift displays a highly coherent seismic facies characterized by a continuous succession of reflections indicating very regular sedimentation leg 166 of the ocean drilling program odp drilled a transect of five deep holes between 2 and 30 km from the modern platform margin and retrieved the sediments from both the slope and basin systems the neogene slope sediments consist of peri platform oozes intercalated with turbidites whereas the basinal drift deposits consist of more homogeneous fine grained carbonates that were deposited without major hiatuses by the florida current starting at approximately 12 4 ma sea level fluctuations which controlled the carbonate production on great bahama bank by repeated exposure of the platform top controlled lithologic alternations and hiatuses in sedimentation across the transect both sedimentary systems are contained in 17 seismic sequences that were identified in the neogene quaternary section seismic sequence boundaries were identified based on geometric unconformities beneath the great bahama bank all the sequence boundaries could be traced across the entire transect into the straits of florida biostratigraphic age determinations of seismic reflections indicate that the seismic reflections of sequence boundaries have chronostratigraphic significance across both depositional environments