latest chesterian carboniferous initiation of gondwanan glaciation recorded in facies stacking patterns and brachiopod paleocommunities of the antler foreland basin idaho stacking patterns of facies and brachiopod communities of latest chesterian middle carboniferous units of east central idaho record an increase in the frequency and amplitude of sea level changes water depth as inferred from lithology and paleoecology provides the basis for quantifying sea level fluctuations the surrett canyon formation is dominated by thick sequences of subtidal carbonates the arco hills formation consists of thin parasequences of mixed carbonate and siliciclastic lithologies representing sea level changes up to 50 m in amplitude bounded by flooding surfaces overlying the arco hills the bluebird mountain formation very fine grained quartz arenite dolomite and unfossiliferous limestone records a major lowstand just below the mid carboniferous boundary increased amplitude and frequency of sea level changes in the antler foreland basin initiated at the c naviculus a unicornis conodont zone boundary which occurs at the base of the arco hills formation these are interpreted as 4th order glacio eustatic sea level changes related to the onset of gondwana glaciation comparable to those seen in the illinois basin alaska and elsewhere

oolitic sandbody depositional models and geometries mississippian of southwest britain implications for petroleum exploration in carbonate ramp settings abstract a 1000 m thick early mississippian carbonate supersequence the carboniferous limestone of southwest britain consists of three third order depositional sequences these comprise parasequences in various configurations and the whole forms a carbonate ramp stack within this framework five major oolitic carbonate sandbodies developed a castell coch limestone b stowe oolite c brofiscin oolite d gully oolite and e high tor limestone the depositional regime was storm and wave dominated throughout and the major sandbodies represent a range of progradational carbonate beaches barriers and detached subtidal shoals analysis of the three dimensional shapes and distribution of these five examples shows that they evolved to produce three major carbonate sandbody geometries a strings b sheets and c wedges these geometries are characterised using the five field examples and offered as a template which may assist in the exploration and reservoir modelling of petroleum rich high energy ramp systems progradation for up to 40 km of barrier islands stowe oolite and beach ridge plains gully oolite formation generated strings and thick sheets individually up to 10 20 m thick thin shoreface retreat carbonate packstone grainstone sheets up to 5 m thick high tor limestone developed during transgressions as veneers across flooding surfaces these are comparable with sheet sands developed in siliciclastic shelf depositional systems progradation for up to 30 km and vertical aggradation of shoreline detached oolite shoals castell coch limestone brofiscin oolite generated basinwards expanding or thinning wedges up to 30 m thick tectonically controlled stacking of strandplain sheets produced a composite carbonate sandbody up to 80 m thick gully oolite the intrinsic sedimentary and extrinsic eustacy tectonism climate factors which controlled these sandbody geometries are addressed establishing the positions of the sandbodies accurately within depositional sequences allows them to be located within inferred seismic sequence geometries and provides one possible solution to the difficult problem of predicting carbonate facies distribution in subtle stratigraphic plays in this ramp system the most homogeneous sandbodies up to 30 m grainstones with greatest reservoir facies potential are represented by shoal belt wedges potential grainstone reservoir facies in the prograding shorelines are limited to the upper parts of individual shoreface sequences max 10 m grainstones for shoreline carbonate sandbodies the greatest reservoir and stratigraphic trapping potential exists in the earliest ramp parasequences where enveloping offshore sediments are siliciclastic mudstones in later stages potential seals are likely to be less reliable low porosity outer ramp carbonates

a sedimentary prelude to marinoan glaciation cryogenian middle neoproterozoic keele formation mackenzie mountains northwestern canada abstract continental margin deposition between the sturtian and marinoan aged global glacial periods is represented in nw canada by a siliciclastic to carbonate grand cycle the keele formation a 300 600 m thick carbonate and siliciclastic deposit comprises the upper part of this interglacial cycle sedimentary facies in the lower carbonate dominated member of the keele span a broad spectrum of depositional environments from below storm wave base to peritidal to continental and are disposed across a relatively narrow paleogeographic belt lateral arrangement of facies and the gradual stratigraphic transitions between them suggest deposition in a ramp setting local slump structures and occasional debrites in deep water facies imply that the ramp was distally steepened fluvial facies are concentrated at a single locality indicating that terrigenous clastic sediment was derived from a point source or sources most strata of the carbonates are bahamian in character and similar to phanerozoic warm water carbonates in that they contain abundant calcite ooids of interpreted original aragonitic mineralogy and have well developed muddy peritidal facies nevertheless close juxtaposition of deep and shallow water facies in keele rocks indicates high amplitude sea level change during deposition on the order of 100 m suggesting accumulation in a climatic icehouse period this interpretation implies that although the globe possessed polar and high altitude glaciers at this time sea surface temperature at least at tropical latitudes warmed dramatically between neoproterozoic glacial episodes the onset of marinoan glaciation here is heralded by an abrupt shift to nearshore marine siliciclastic sedimentary rocks these deposits form the upper member of the keele formation informally called the keele clastic wedge and directly underlie ice brook formation diamictites carbonates are rare and are restricted to mudstones and flat pebble conglomerates that lack any indication of tropical conditions

oceanographic and eustatic control of carbonate platform evolution and sequence stratigraphy on the cretaceous valanginian campanian passive margin northern gulf of mexico an integrated sequence stratigraphic study based on outcrop core and wireline log data documents the combined impact of cretaceous eustacy and oceanic anoxic events on carbonate shelf morphology and facies distributions in the northern gulf of mexico the diverse facies and abundant data of the comanche platform serve as a nearly complete global reference section and provide a sensitive record of external processes affecting cretaceous platform development regional cross sections across the shoreline to shelf margin profile provide a detailed record of mixed carbonate siliciclastic strata for the hauterivian to lower campanian stages ca 136 to 80 ma the study window on the slowly subsiding passive margin allows the stratigraphic response to external forcing mechanisms to be isolated from regional structural processes three second order supersequences comprised of eight composite sequences are recognized in the valanginian barremian the aptian albian and the cenomanian campanian the valanginian barremian supersequence transitioned from a siliciclastic ramp to carbonate rimmed shelf and is a product of glacial ice accumulation and melting as well as variable rates of mid ocean ridge volcanism the aptian albian supersequence chronicles the drowning and recovery of the platform surrounding oceanic anoxic events 1a and 1b the cenomanian campanian supersequence similarly documents shelf drowning following oceanic anoxic event 1d after which the platform evolved to a deep subtidal system consisting of anoxic dysoxic shale and chalk in the time surrounding oceanic anoxic event 2 each period of oceanic anoxia is associated with composite sequence maximum flooding termination of carbonate shelf sedimentation and deposition of condensed shale units in distally steepened ramp profiles composite sequences unaffected by oceanic anoxic events consist of aggradational to progradational shelves with an abundance of grain dominated facies and shallow subtidal to intertidal environments because they are products of eustacy and global oceanographic processes the three supersequences and most composite sequences defined in the south texas passive margin are recognizable in other carbonate platforms and published eustatic sea level curves

holocene fire and vegetation changes in southeastern brazil as deduced from fossil charcoal and soil carbon isotopes abstract carbon isotopes of soil organic matter som and radiocarbon dating on charcoal from nine soil profiles collected under native forest vegetation in londrina state of parana anhembi botucatu and jaguariuna sao paulo and salitre minas gerais southeastern brazil were used to evaluate the vegetation changes and to establish the chronology 13 c and 14 c data in som and charcoal respectively indicate that c 4 plants were the dominant vegetation in londrina and jaguariuna during the late pleistocene until middle holocene probably associated with the presence of a drier climate in anhembi and botucatu c 3 plants dominate the landscape during the period a probable mixture of c 3 and c 4 plants occurred in salitre during the holocene this study is part of a main research program related to palaeoenvironmental reconstruction of vegetation and climate in distinct regions of brazil during the last 20 000 years

carbonate mounds from paradox to world heritage the recent marine carbonate world comprises two major compartments 1 the surface domain of the photozoan carbonates confined in space by water depth and by the penetration of light and 2 a deep domain where heterozoan mound builder guilds directly forage on fluxes of nutrients which primarily percolate from the photic zone and or are generated by in situ benthic processes locally giant cold water coral mounds tower up to heights of 150 to 250 m above the sea floor in general between 500 and 1300 m water depth and within sharply delineated provinces some 15 years of research on these giant mound provinces conveys a picture of their distribution in space and possibly sheds light on controls acting in concert globally there is no counterpart for the prolific north atlantic mound basin namb a chemical control is seen by an overlay of the mound provinces on a map of the aragonite saturation horizon ash an external physical control is inferred fromthe position of themound provinces girdling a vigorous north atlantic subtropical gyre systemand clustering close to the roof of the intermediate to deep water masses of a dynamically stratified ocean on the eastern boundary of the namb nutrient fluxes are enhanced by mixing processes driven either by internal waves between galicia and the shetlands or by the vast and heterogeneous eastern boundary upwelling system along the iberian african margins down to 10 n early diagenesis by carbonate dissolution and re precipitation driven by convecting or advecting internal fluids can contribute to stabilize such constructions facilitating an exuberant vertical accretion it is speculated that in thenorth atlantic ocean the deep water carbonate factory outclasses in size the shallow water coral reefs giant mound formation is a recurrent play of life since the dawn of the metazoans nama group upper neoproterozoic however with actors and plots varying from act to act remarkably literature reports only three occurrences of deep water mounds in the phanerozoic the modern ocean possibly the danian and the carboniferous some striking parallelisms in the development of the atlantic and the paleo tethys oceans combined with the developing insights in the controls on deep watermounds in the present ocean invite for a comparative study this has the potential to eventually shed light on the full circulation pattern of the paleo tethys ocean surface and deep comparative studies will build upon 1 modeling of ocean circulation constrained by the record of deep water carbonate systems and supported by advances in tracer and proxy tools and 2 field studies on representative and accessible continental locations the mound route that develops in morocco under the auspices of ioc unesco will provide tomulti disciplinary teams with marine and continental experience opportunities for confronting observations from the modern ocean and on key records of past oceanic basins it has the potential to eventually qualify for a unesco recognition as world heritage

a far field record of the end ordovician glaciation the ellis bay formation anticosti island eastern canada abstract the end ordovician was a critical period in earth history it was a time of global climatic change with large scale continental glaciations a wealth of recent work has documented the stratigraphical records from the near field areas i e from various gondwanan continental relics where glaciation was more severely felt there is an urgent need to re examine the stratigraphic record from the far field areas at greater levels of resolution than it has been hitherto possible in order to understand the timing duration and character at the glaciation centred around the ordovician silurian o s boundary one of the best exposed and most complete stratigraphic records from paleotropical areas near the boundary is on anticosti island in eastern canada the east west trending 200 km long ellis bay hirnantian outcrop belt with superb coastal exposures at both ends of anticosti island is slightly oblique to the paleoshoreline with near shore siliciclastic dominated facies restricted to the eastern part of the island and more offshore carbonate dominated facies present along the central and western parts these mixed carbonate siliciclastic facies accumulated along a storm dominated beach to offshore profile they are organized into a stacked set of shallowing upward offshore to shoreline facies successions typically coarsening upward separated by deepening upward facies successions typically fining upward formed during intervening transgressions high frequency glacio eustatic fluctuations were the dominant control on the development of tr sequences observed in the ellis bay succession of anticosti island although tectonic subsidence had a substantial secondary effect on thickness five tr sequences are recognized allowing for precise correlation along the ellis bay outcrop belt in the eastern sections relatively thin tr sequences are locally bounded by unconformities a typical sequence begins with thin transgressive limestone overlain by a maximum flooding calcareous shale grading up into regressive storm influenced proximal to transitional zone fine sandstone grainstone and shale which are sharply overlain by shoreface to foreshore sandstone grainstone in the central and western sections the thicker tr sequences have more symmetrical transgressive regressive components reflecting greater subsidence compensated by a higher carbonate sediment supply two discrete glacial periods are recognized during the deposition of the hirnantian ellis bay succession with the younger one recording large sea level changes 50 m in magnitude caused by the development of very large ice sheets over western gondwana abundant ice conditions on the globe during the end ordovician and the resulting high amplitude eustasy appear to have left distinctive stratigraphical imprints on mixed paleotropical siliciclastic carbonate ramps

a signal to noise index to quantify the potential for peak detection in sediment charcoal records article i nfo charcoal peaks in lake sediment records are commonly used to reconstruct fire histories spanning thousands of years but quantitative methods for evaluating the suitability of records for peak detection are largely lacking we present a signal to noise index sni that quantifies the separation of charcoal peaks signal from other variability in a record noise we validate the sni with simulated and empirical charcoal records and show that an sni n3 consistently identifies records appropriate for peak detection the sni thus offers a means to evaluate the suitability of sediment charcoal records for reconstructing local fires matlab and r functions for calculating sni are provided

sequence development of a latest devonian tournaisian distally steepened mixed carbonate siliciclastic ramp canning basin australia abstract the sequence development and evolution of latest devonian earliest carboniferous fairfield group in the canning basin have been established through integration of detailed sedimentological analysis of core petrophysical data existing biostratigraphic data and new seismic interpretations the fairfield group on the lennard shelf was deposited on a mixed carbonate siliciclastic distally steepened ramp with a broad inner ramp narrow mid ramp and steepened outer ramp the majority of facies associations fa1 fa8 were formed in intertidal shallow subtidal conditions in proximal to distal inner ramp including siliciclastic tidal flats fa1 carbonate intertidal flats fa2 tidal flats and channels fa3 lagoons fa4 fa5 and shallow subtidal fa6 backshoal fa7 and fore shoal areas fa8 bioclastic muddy sandstone fa9 and bioclastic mudstone fa10 are the dominant mid ramp facies recognition of turbiditic facies of middle to lower slope of the outer ramp fa11 fa13 led to the identification of a distally steepened ramp antecedent topography exerted a significant control on platform morphology and the development of the widespread inner ramp facies on the lennard shelf a sequence stratigraphic analysis reveals that the fairfield group ramp deposits consists of four third order sequences s1 s4 that were largely deposited during sea level highstands hst characterized by progradational trends and dominant shallow subtidal inner ramp facies associations transgressive systems tracts tst are well developed in s1 and s3 and have a retrogradational facies pattern with dominant deep subtidal mid outer ramp facies associations lowstand systems tracts characterized by lowstand wedges and turbiditic facies are identified in the lower parts of s2 and s3 coarse and fine grained siliciclastic facies are mixed with carbonate facies as a result of coeval deposition on the inner and mid ramp and reciprocal deposition on the outer ramp a temporal variation in the types of carbonate grains and the amount of siliciclastic facies from the mixed peloidal skeletal carbonate siliciclastic ramp in s1 and s2 to the mixed skeletal carbonate siliciclastic ramp in s3 and a siliciclastic dominated ramp in s4 is interpreted as the change from a greenhouse to an icehouse state

sediments and history of the rottnest shelf southwest australia a swell dominated non tropical carbonate margin abstract the rottnest shelf is a narrow wave dominated open shelf on the passive continental margin of southwest australia adjacent to a hinterland of low relief and sluggish drainage high physical energy low nutrients in cool subtropical waters and rapid postglacial transgression have limited carbonate productivity restricted grain types and reworked the transgressed surface to form only a thin given sufficient time the rottnest shelf could recover from drowning and form blanket like skeletal carbonates thin

digital reconstruction and stratigraphic evolution of a microbial dominated isolated carbonate platform terminal proterozoic nama group namibia abstract a terminal proterozoic ca 550 ma isolated carbonate platform developed downdip on a carbonate ramp of the nama group of southern namibia the stratigraphic evolution of the platform was reconstructed from an extensive dataset that was compiled by using digital surveying technologies and traditional outcrop observations digital field geology techniques enabled rapid and accurate mapping over the 10 km outcrop belt with spatial and geological information captured at scales ranging from centimeters to kilometers furthermore these digital geology techniques made the reconstruction and interpretation of the development of the carbonate platform considerably more efficient and quantitative the carbonate platform deposits encompass three accommodation cycles in which each subsequent cycle experienced progressively greater influence of a long term accommodation increase aggradation and progradation during the first cycle produced a flat topped sheet like platform deposits of the first cycle show a coarsening upward motif grading from dominantly columnar stromatolitic thrombolites and interbedded mudstone grainstone at the base to dominantly massive and cross bedded dolostones toward the top the second cycle features aggradation and is typified by the formation of a distinct margin and development of a bucket shaped geometry the margin contained thrombolite mounds and domes whereas columnar stromatolitic thrombolites dominated the platform interior the third and last cycle records a gradual deepening trend with initial aggradation and formation of well bedded thin deposits in the interior and microbial mounds at the margins while the interior drowned the platform margins kept up with rising sea level and complex pinnacle reefs formed which contained fused and coalesced thrombolite mounds flanked by bioclastic grainstones and collapse breccias the top of the unit consists of a set of isolated large thrombolite mounds flanked by shale and is interpreted to indicate the final stage of the carbonate platform before drowning the overall geometric evolution and spatial scale of this platform from flat topped to bucket shaped with elevated margins is recorded in many proterozoic and phanerozoic isolated carbonate platforms this study clearly illustrates that accommodation changes are a fundamental control on the development of carbonate platforms regardless of whether they are formed from microbial or metazoan components or are of precambrian or phanerozoic age significantly the architectural elements and spatial dimensions are comparable throughout earth history

speculations on the controls on cyclic peritidal carbonates ice house versus greenhouse eustatic controls abstract metre scale peritidal cyclothems which are distinctive components of lower palaeozoic and many mesozoic platform carbonates are not common in carboniferous sequences in their place the platform sequences are characterized by 5 10 m thick largely subtidal limestones with prominent exposure surfaces the former type of platform cyclothems developed during greenhouse phases when in the absence of major continental ice sheets sea level oscillations were caused by small scale obliquity and precession milankovitch rhythms under such conditions platforms rapidly aggraded with the deposition of peritidal cyclothems the carboniferous was an ice house phase when the waxing and waning of gondwanan ice sheets caused by eccentricity rhythm generated climatic changes created high amplitude rapid falls and rises in sea level the resulting carbonates reflect such changes with catch up subtidal dominated sequences and pronounced subaerial exposure surfaces capping the cyclothems

the origin of high frequency platform carbonate cycles and third order sequences lower ordovician el paso gp west texas constraints from outcrop data and stratigraphic modeling abstract the passive margin succession of the diablo platform lower ordovician west texas is represented by the second order sauk c supersequence set consisting of a basal transgressive clastic unit the bliss sandstone above the breakup unconformity marking the second order basal lowstand transgressive phase overlain by 750 m of drift related shallow marine platform carbonates the el paso group recording the second order highstand due to late paleozoic structuring of the gondwanan passive margin present exposures in texas are in an updip shelf position and lack internal stratal geometries across depositional strike so sequences and systems tracts are identified solely by the vertical stacking patterns of depositional subfacies and higher frequency fifth order cycles accommodation plots fischer plots of high frequency cycles gauge systematic shifts in third order accommodation of two complete third order sequences each about 2 m y long and 60 140 m thick within the el paso group this is expressed in the vertical succession of cycle types systematic changes in cycle thickness and variations in subfacies as revealed by histograms of subfacies types tied to fischer plots a complete el paso shelf sequence contains a thin lowstand systems tract of quartz arenite a thick transgressive systems tract dominated by upward thickening thrombolitic subtidal cycles and a highstand systems tract marked by dolomitic thinning upward peritidal cycles containing quartz sand the el paso third order depositional sequences have been correlated by biostrat graphy and cycle stacking pattern from the franklin mountains southeast to the diablo arch northeast into the ardmore basin and thence to the appalachian basin hence the third order sequences appear to be eustatic based on biostratigraphic correlation of accommodation plots around the periphery of gondwana time series analyses suggest that a strict allocyclic milankovitch driven glacio eustatic mechanism alone is insufficient to account for the higher frequency fifth order and lower frequency third order accommodation cycles we used a two dimensional forward computer simulation to compare allocyclic and autocyclic models for high frequency cycles the allocyclic simulation superimposes a deterministic milankovitch glacio eustatic driver on a lower frequency third order accommodation cycle and generates a two dimensional synthetic cross section composed of high frequency peritidal and subtidal cycles stacked into third order sequences the autocyclic simulation is generated by a ginsburg autocyclic mechanism for high frequency cyclicity triggered by third order accommodation changes the autocyclic simulation quantitatively replicates an autocyclic mechanism for fifth order cycle development linked to onshore sediment transport and seaward progradation of tidal flats the two dimensional internal facies architecture of a third order sequence and the high frequency cycle stacking patterns are simulated in both scenarios important differences in patterns of cycles and subfacies stacking in the simulations shed light on the interpretation of the diablo platform cycles and sequences as an alternative or a supplement to autocyclicity or milankovitch forced glacio eustasy we have studied stochastic models for driving high frequency changes in relative sea level these intriguing results maintain essentially all the features observed in the rock record our smoothed sto hastic simulations suggest that the cycle problem is much more complex than presently realized

depositional model for a prograding oolitic wedge upper jurassic iberian basin abstract facies architecture and bedding patterns of the kimmeridgian pozuel formation iberian basin evidence that this 50 70 m thick oolitic grainstone unit conforms to the infralittoral prograding wedge ilpw model instead of the classic models used for interpreting oolitic grainstones sandbodies on carbonate ramps or platforms i e bank margin shoal complexes beaches and beach ridges ten lithofacies have been distinguished in the pozuel formation 5 10 dipping clinobedded oolitic grainstone foresets passing to tabular oolitic packstones grainstones which interfinger the muddy basinal bottomsets landwards the clinobeds pass into subhorizontal topsets composed of trough cross bedded to structureless oolitic grainstones oolitic skeletal grainstones with stromatoporoids and coral stromatoporoid microbial mounds siliciclastic lithofacies and oncolitic peloidal packstones occur at the innermost position these lithofacies stack in strike elongated 5 20 m thick 0 5 2 km dip oriented wide aggradational progradational packages with complex sigmoid oblique geometries lithofacies depositional geometries and stacking pattern permit to summarize the main characteristic of such upper jurassic oolitic infralittoral prograding wedge potentially to be applied in other oolitic sandbodies both in outcrops and subsurface 1 sediment production within the wave action zone 2 grainstone dominated textures 3 prograding basinward onto basinal muds 4 laterally strike extensive paralleling the shoreline 5 variable thickness commonly of few tens of meters 6 broadly sigmoidal to oblique internal architecture with topsets foresets and bottomsets 7 dip of foresets close to the angle of repose 8 topsets deposited in shallow water extending through the shoreface from the shoreline down to the wave base 9 mounds either microbial or skeletal may occur in the topsets the coated grains factory was along the high energy wave dominated outer platform topset beds from where the mud was winnowed and the grains transported both landward to the platform interior and seaward to the platform edge from were the grains cascaded down the slopes as grain flows and mass flows forming clinobeds this genetic model can be applied to other grain dominated lithosomes some of them forming hydrocarbon reservoirs e g the jurassic hanifa formation and some arab d e g qatif field in arabia the smackover formation in northern louisiana and south arkansas the aptian shuaiba formation e g bu hasa field and the cenomanian mishrif formation e g umm adalkh field of the arabian gulf

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

sedimentology and basin evolution of the siluro devonian helderberg group central appalachians abstract the late silurian early devonian helderberg group central appalachians is a sequence of mixed siliciclastic carbonate sediments that was deposited during relative tectonic quiescence on a ramp that was built out from low relief tectonic highlands bordering the eastern side of the appalachian basin the helderberg group is a third order vail cycle that lasted about 8 10 m y three transgressive regressive sequences are also recognized each sequence was deposited over 2 3 m y subsidence rates during deposition were about 1 2 cm 1 000 yr lithofacies patterns resulted from eustatic sea level changes differential basin subsidence and varying sedimentation rates skeletal grainstone rudstone formed fringing skeletal banks that developed during regression and prograded away from the eastern side of the basin at rates of 35 50 m 1 000 yr quartz sandstone tongues in the helderberg group probably were reworked from underlying silurian sandstone and were introduced to the basin by rivers that nearly coincided with ancestral silurian drainage systems siliciclastic influx was never great enough to shut carbonate production off completely thick middle devonian siliciclastic sediments buried the helderberg group and updip subaerial exposures accompanying the onset of the acadian orogeny

storms in the deep tempestite and beach like deposits in pelagic sequences jurassic subbetic south of spain abstract fine peloidal to coarse oolitic bioclastic grainstones with hummocky cross stratification hcs occur interbedded in jurassic pelagic lime mudstone successions subbetic betic ranges southern spain these strata were deposited in pelagic troughs and swells away from continental areas in the southern iberian paleomargin of the western tethys selected examples presented in this study include a coarse oolitic grainstones encased in pelagic marls holding characteristics similar to the ridge berm swash zone of modern beaches b peloid grainstones with hcs interbedded with radiolarite marls deposited on the flanks of volcanic guyots the interbedded lime muds and marls contain filaments sponge spicules and radiolarians c peloid bioclastic radiolarians filaments etc grainstone beds with hcs interbedded with pelagic lime muds d crossbedded peloidal skeletal saccocoma grainstones with hcs and wave ripples on top interbedded with pelagic mudstones and wackestones with abundant bioturbation and ammonites ammonitico rosso facies all the examples here presented share 1 grainstone beds are interbedded with pelagic mudstones and marls 2 grainstone components were reworked by oscillatory flows superimposed to unidirectional tractive flows unidirectional ripple lamination and hcs 3 components either derived from shallow water environments e g ooids or produced in pelagic conditions e g radiolarians saccocoma filaments peloids etc were reworked by high energy processes unrelated to surface storm waves 4 internal waves iws propagating along a pycnocline and breaking against a sloping surface are the best candidates to induce the sedimentary structures and sediment organization that characterize these grainstone beds coarser sediments trapped at the breaker zone form sediment accumulations similar to the sediments caught by the littoral fence in the surface beach this scenario evidences the hcs not to be necessarily linked to the surface storms but to the pycnocline bathymetry solving the problem of having hcs in pelagic zones where the storm and hurricanes wave action can be considered out of context

sequence stratigraphy of the red river formation williston basin usa stratigraphic signature of the ordovician katian greenhouse to icehouse transition abstract the upper katian upper ordovician red river formation is a carbonate evaporite supersequence that formed in the epicratonic williston basin of western north america this study focuses on the upper part of the formation in the southern us part of the basin the studied succession is made up of three transgressive regressive sequences rr1 rr2 and rr3 each 0 5 1 m y in duration and composed of relatively few meter scale high frequency cycles parasequences sequence boundaries are characterized by intraclastic breccia laminated dolomite successions that have been truncated and capped by evaporite deposits subaqueous anhydrites within each sequence represent evaporite lowstand systems tracts lsts that formed during relative sea level lows that lead to the precipitation of gypsum later recrystallized into anhydrite in a quiet salina type environment transgressive tst and early highstand systems tracts hst are composed of subtidal facies of predominantly skeletal mudstone to wackestone packstone with abundant burrow mottling late hsts are predominantly composed of peritidal porous laminated dolomite the study illustrates how the sequence stratigraphic framework of carbonate evaporite deposits from the williston basin relates to the late ordovician glacio eustasy transitional climates and low basin subsidence in an arid setting

timing of mid cretaceous carbonate platform depositional cycles northern sinai egypt abstract the northern sinai upper aptian to middle cenomanian succession represents an example of a carbonate platform where stratigraphic interpretations are mainly based on benthic foraminifera ostracods and rudists this paper presents a concept combining the stratigraphic study of benthic organisms with graphic correlation and sequence stratigraphy at a scale that determines the timing of sequence boundaries and quantification of sediment accumulation rates biostratigraphic analyses result in multibiostratigraphic zonations and contribute to a northern sinai fossil range chart for benthic larger and smaller foraminifera ostracods and rudists the age interpretation results from the careful comparison of the ages given in the literature and the distribution patterns in the northern sinai sections the northern sinai chart for many fossil ranges matches with other studies but also indicates some exceptions ostracods were grouped into assemblages characterised by short local ranges which enables the exact correlation of different sections the use of graphic correlation techniques within this framework improves the stratigraphic resolution and results in timing of the sequence boundaries these chronostratigraphic assignments allow comparison of the sinai sequence boundaries with those described from other regions furthermore graphic correlation measures long term sediment accumulation rates of the northern sinai based on their variations we calculate the relative sea level changes resulting in a detailed second order sea level curve in the upper aptian to middle cenomanian succession important changes in the long term sediment accumulation rate were measured they reflect three second order sea level cycles which subdivide a general relative sea level rise 18 sequences superimpose the second order sea level change 3 sequences in the upper aptian 11 sequences in the albian and 4 sequences in the lower middle cenomanian both sequence stratigraphic patterns and long term sea level changes were compared with those from the tethyan domain the african arabian plate and the western pacific abundance and distribution of the sinai sequence boundaries were similar to the patterns described from other regions we distinguish between sequence boundaries with regional extent correlating with examples from the north african arabian plate or the western pacific sequence boundaries of possibly global or tethyan extent and the few sequence boundaries of local extent the influence of the regional and global signals on the studied successions reflect the sinai location between the southeastern and southwestern tethyan realms local tectonics or changes in subsidence are only of subordinate importance for the creation of sequence boundaries the comparison of the chronostratigraphic assignments of the second order sea level curve with other descriptions indicates a second order relative sea level history of its own for sinai triggered by the interaction of subsidence sediment supply and eustasy

holocene fires in the northern amazon basin abstract the ubiquitous occurrence of charcoal in the forest soils of the upper rio negro region of colombia and venezuela indicates the presence of frequent and widespread fires in the amazon basin possibly associated with extremely dry periods or human disturbances charcoal ranged from 3 12 to 24 76 mg cm 3 in the upper 50 cm of soil and was more abundant in oxisols and ultisols than in other soil types charcoal dates range from 6260 yr b p to the present several dates coincide with dry phases recorded during the holocene ceramic shards were found at several sites and thermoluminescence analysis indicates that their ages range from 3750 to 460 yr b p the age of charcoal and shards confirms that this region has been subjected to fire and human disturbances during the past 6000 yr

3d computer simulation of carbonate depositional facies distribution and productivity rates using continuous set theory to mimic geologists reasoning abstract a new computer model predicts depositional facies distribution and productivity rates on a 3d carbonate platform using continuous set theory fuzzy logic which accepts complex linguistic data with large uncertainties earlier deterministic models have become valuable tools for stratigraphic interpretation but have a difficult time with linguistic concepts whose parameters are difficult to define for example deterministic models estimate depositional facies based solely on water depth the term depositional facies involves many more complex nonlinear processes including water energy circulation climate and distance from siliciclastic input the current model integrates water depth with such complex variables the user approximates parameters for each of the variables using linguistic terminology the model produces depositional facies including sabkha tidal flat reef shoal and subtidal carbonate productivity is controlled by many complex processes such as water depth temperature latitude turbidity climate and water energy deterministic models use either simple water depth dependent functions or apply a constant rate to model productivity within the shallow water zone both deterministic methods unrealistically apply the same productivity rates across a model s extent the current model integrates water depth with interrelated variables allowing variation in productivity depending on processes occurring at specific locations development of this model makes it possible to incorporate linguistic and imprecise geologic data into stratigraphic simulations and this allows visualization of the response of carbonate systems to interactions of complex processes this also allows greater potential for accurately predicting carbonate reservoir distribution

stratigraphic modelling of carbonate platform to basin sediments maastrichtian to paleocene in the eastern desert egypt abstract in the galala mountains of the eastern desert egypt carbonate platform and basin deposits have excellent exposure these exposures show a late campanian early paleocene rimmed platform evolving into a late paleocene distally steepened ramp we modelled the evolution of the platform basin transition from the maastrichtian to selandian 68 7 59 ma with the 2 d stratigraphic simulation program phil and compared the modelled results with outcrop sections stratigraphic facies and environmental data are summarized and operate as input and control parameters for the computer simulation the most important parameters that control the depositional geometries of the late cretaceous mixed carbonate siliciclastic platform and the paleogene carbonate platform are changes in relative sea level sediment flux and initial topography the simulation provides an understanding of platform growth and slope to basin deposition particularly in areas of the platform that are poorly exposed or have been eroded moreover the simulated geologic parameters like lithology overall thickness and palaeowater depth closely resemble field and laboratory measurements of the individual sections in an earlier study the maastrichtian slope angle was calculated to be 5 8 and this was confirmed in this study in this earlier study also the timing of the transition from a rimmed platform to a distally steepened ramp was established to be during latest maastrichtian early paleocene the present study shows that the rimmed platform persisted at least until the late paleocene 59 ma as indicated by the relatively high slope angle of 6

stratigraphic sedimentology of tertiary cool water limestones se australia abstract mid tertiary limestones exposed as sea cliffs along the coast of victoria southeastern australia accumulated on the inner part of a cool water distally steepened ramp or open shelf all sediments are bioclastic dominated by particles of bryozoans echinoderms benthic foraminifers brachiopods and molluscs shallow grainy facies also contain coralline algae quartz and glauconite while deep muddy facies include ahermatypic corals ostracodes sponge spicules planktic foraminifers and terrigenous clays the fundamental depositional unit is a meter scale subtidal cycle or rhythm shallow shelf cycles are shallowing upward cross bedded or burrowed grainstone capped by a marine cemented hardground or quartz granule lag while mid shelf cycles are upward coarsening and thickening proximal to distal tempestites such cycles are interpreted to form by eustatically driven climatically controlled oscillations in abrasion wave base and swell wave base deep shelf rhythms are interbedded bryozoan marl and calcareous clay thought to be generated by climatically influenced fluctuations in carbonate productivity and terrigenous dilution lowstand systems tracts are depositional or erosional sequence boundaries are complex multigeneration mostly submarine surfaces condensed cycle boundaries that can be traced offshore into multiple omission surfaces and conformable contacts basinward facies shifts result in deposition of condensed lowstand wedges of stacked shallowing upward grainstone cycles transgressive systems tracts are thick bryozoan marl calcareous clay rhythms associated with facies backstepping and abrupt deepening such rhythmites typically grade stratigraphically upward into tempestite cycles highstand systems tracts are highly progradational wedge shaped rock bodies of shallowing upward grainy cycles these limestones provide the critical link of stratigraphy between modern cool water carbonate shelf deposits and the older mesozoic and paleozoic record of similar sediments

depositional cycles composite sea level changes cycle stacking patterns and the hierarchy of stratigraphic forcing examples from alpine triassic platform carbonates carbonate platform deposits record a complex interplay of numerous geodynamic variables of which eustasy subsidence and sediment accumulation are prime factors in determining both the kilometer scale depositional sequence scale and meter scale depositional cycle scale stratigraphic packaging in this study we looked particularly at composite eustasy that is superimposed sea level fluctuations with different frequencies defined as orders and different amplitudes and the role it plays in the linkage between meter scale cyclic stratigraphy and kilometer scale sequence stratigraphy specifically we have investigated the relationship between low frequency third order 1 10 m y period depositional cycles and their component high frequency fourth 0 1 1 m y and fifth 0 01 0 1 m y order cycles through detailed stratigraphic analyses of alpine triassic platforms complemented by computer modeling on the basis of our results we suggest that in general there exists a hierarchy of stratigraphic forcing driven by composite eustasy that results in organized stacking patterns thickness subfacies character early diagenetic attributes of high frequency typically fourth and fifth order shallow water carbonate cycles dictated by low frequency third order relative sea level effects we suggest that systematic vertical changes in stacking patterns of high frequency cycles across a larger depositional sequence are due to systematic and predictable differences in depositional space available during the rising and falling stages of a relative third order sea level change we also suggest that these systematic variations in cycle stacking patterns will exist regardless of the mechanism responsible for generating the high frequency cycles be it an autocyclic or allocyclic mechanism this approach has major implications for the use of high frequency fourth and fifth order cycle characteristics to identify third order cycles in outcrops and cores of shallow water carbonates where stratigraphic control may be less than desirable this would constitute a valuable bridge between cyclic stratigraphy at the meter scale and sequence stratigraphy at the seismic scale we present two examples from triassic buildups of the alps the ladinian latemar buildup and the norian dolomia principale where a systematic succession of high frequency cycle stacking patterns and early diagenetic features exists within an overriding third order cycle sequence reflecting the interplay of short term high frequency fourth fifth order eustasy and long term low frequency third order eustasy in accordance with the hierarchy of stratigraphic forcing central to the interpretation of these examples is the demonstration that true eustatic rhythms are recorded in the high frequency cyclicity as verified by time series analyses and the use of fischer plots these examples can be modeled by computer under conditions of lag depth constrained sedimentation uniform subsidence and composite eustasy we also present two examples one from the alpine triassic the norian lofer cyclothems and one from the pleistocene of south florida that lack both a systematic succession of high frequency cycle stacking patterns and identifiable composite rhythms in the stratigraphic record despite the existence of composite high frequency eustasy in these examples we call upon 1 local tectonic forcing in the form of short term deviations in subsidence via faulting lofer example and 2 large differences in the relative amplitudes of different orders of high frequency sea level oscillations pleistocene example to explain the lack of composite rhythms and we present computer simulations to illustrate the concepts an understanding of composite relative sea level changes and the potential for a hierarchy of stratigraphic forcing provides the link between cyclostratigraphy and sequence stratigraphy and also has important implications regarding the stratigraphy of early diagenesis

sub wavebase cross bedded grainstones on a distally steepened carbonate ramp upper miocene menorca spain cross bedded grainstones on carbonate ramps and shelves are commonly related to the locus of major wave energy absorption such as shorelines shoals or shelf breaks in contrast on the early tortonian carbonate platform of menorca balearic islands coarse grained cross bedded grainstones are found at a distance from the palaeoshoreline where they were deposited below the wavebase excellent exposures along continuous outcrops on the sea cliffs of menorca reveal the depositional profile and three dimensional distribution of the different facies belts of the tortonian ramp depositional system basinward from the palaeoshoreline fan deltas and beach deposits pass into 5 km wide gently dipping bioturbated dolopackstone inner and middle ramp then into 12 20 dipping dolograinstone rudstone clinobeds ramp slope and finally into subhorizontal fine grained basinal dolowackestone to dolopackstone outer ramp in this miocene example coarse grained grainstones exist in five different settings other than beach deposits 1 on the middle ramp where cross bedded grainstones were deposited by currents roughly parallel to the shoreline at 40 70 m estimated water depth and are interbedded with gently dipping bioturbated dolomitized packstones 2 on the upper slope where clinobeds are composed mostly of in situ rhodoliths and red algae fragments 3 on the lower slope as small scale bedforms small three dimensional subaqueous dunes migrating parallel to the slope 4 at the transition between the lower slope and the outer ramp where mollusc rich and rhodolithic rudstones and grainstones interbedded in dolomitized laminated wackestones containing abundant planktonic foraminifera infill slide slump scars as upslope backstepping bodies backsets 5 at the toe of the slope where coarse skeletal grainstones indicate bedform migration parallel to the platform margin induced by currents at more than 150 m estimated water depth this late miocene example also illustrates how changes in intrabasinal environmental conditions nutrients and or temperature may produce changes in stratal patterns and facies architecture if they affect the biological system two depositional sequences compose the miocene platform on menorca where a reef rimmed platform prograded onto an earlier distally steepened ramp the transition from the ramp to the reef rimmed platform was effected by an increase in accommodation space caused by ecological changes promoting a shift from a grain to a framework producing biota

onset of the late paleozoic glacioeustatic signal a stratigraphic record from the paleotropical oil shale bearing big snowy trough of central montana u s a

southward movement of the pacific intertropical convergence zone ad 1400 1850 tropical rainfall patterns control the subsistence lifestyle of more than one billion people seasonal changes in these rainfall patterns are associated with changes in the position of the intertropical convergence zone which is characterized by deep convection causing heavy rainfall near 10 n in boreal summer and 3 n in boreal winter dynamic controls on the position of the intertropical convergence zone are debated but palaeoclimatic evidence from continental asia africa and the americas suggests that it has shifted substantially during the past millennium reaching its southernmost position some time during the little ice age ad1400 1850 however without records from the meteorological core of the intertropical convergence zone in the pacific ocean quantitative constraints on its position are lacking here we report microbiological molecular and hydrogen isotopic evidence from lake sediments in the northern line islands galapagos and palau indicating that the pacific intertropical convergence zone was south of its modern position for most of the past millennium by as much as 500km during the little ice age a colder northern hemisphere at that time possibly resulting from lower solar irradiance may have driven the intertropical convergence zone south we conclude that small changes in earth s radiation budget may profoundly affect tropical rainfall

toward reconciliation of late ordovician 440 ma glaciation with very high co2 levels although phanerozoic glaciations usually coincided with times of estimated low atmospheric co2 the late ordovician 440 ma glaciation is a significant exception co2 levels during that time may have been as much as 10 times greater than present in an earlier paper we suggested that the unique geographic configuration of gondwanaland may explain such a response as the edge of the supercontinent was essentially tangent to the south pole and the moderating effect of the nearby ocean may have suppressed the magnitude of summer warming on the landmass thereby allowing glacial inception one limitation to the earlier study was that it used a linear energy balance model ebm in this paper we further test the above hypothesis in a suite of experiments with a nonlinear ebm that allows for snow albedo feedback we also utilize updated estimates for co2 levels decreases in solar luminosity and variations in orbital forcing baseline experiments with no changes in luminosity or co2 resulted in an ice covered area of 6 3 106 km2 53 of the estimated area covered by the ordovician ice sheet additional experiments for different combinations of orbital forcing 7x 13x co2 and 3 5 5 0 luminosity yielded 0 35 of the estimated ice area in the late ordovician a crude estimate of possible topographic influences increased these numbers to7 47 of total estimated ice area additional factors related to ice sheet growth should increase these values somewhat these results provide additional support for the high co2 glaciation explanation with the caveat that even the partial success occurs only when parameters are at the extreme end of their permissible range the estimated duration of ordovician glaciation is also consistent with the migration of gondwanaland across the south pole with a centrally located pole yielding ice free conditions in the summer thus identical levels of external forcing yield either glaciated or ice free conditions with the solution dependent on location of the landmass although more work is required on this topic our experiments suggest that there may be a relatively parsimonious explanation for this perplexing paleoclimate paradox the results lend further support to the proposition that paleogeography significantly modifies the role of co2 in the long term evolution of climate

anatomy of a cyclically packaged mesoproterozoic carbonate ramp in northern canada abstract carbonates in the upper member of the mesoproterozoic victor bay formation are dominated by lime mud and packaged in cycles of 20 50 m these thicknesses exceed those of classic shallowing upward cycles by almost a factor of 10 stratigraphic and sedimentological evidence suggests high amplitude high frequency glacio eustatic cyclicity and thus a cool global climate ca 1 2 ga the victor bay ramp is one of several late proterozoic carbonate platforms where the proportions of lime mud carbonate grains and microbialites are more typical of younger phanerozoic successions which followed the global waning of stromatolites facies distribution in the study area is compatible with deposition on a low energy microtidal distally steepened ramp outer ramp facies are hemipelagic lime mudstone shale carbonaceous rhythmite and debrites mid ramp facies are molar tooth limestone tempestite with microspar intraclast lags in a marine environment where stromatolitic and oolitic facies were otherwise rare large stromatolitic reefs developed at the mid ramp coeval with inner ramp facies of microspar grainstone intertidal dolomitic microbial laminite and supratidal evaporitic red shale deep subtidal outer ramp cycles occur in the southwestern part of the study area black dolomitic shale at the base is overlain by ribbon nodular and carbonaceous carbonate facies all of which exhibit signs of synsedimentary disruption cycles in the northeast are shallow subtidal and peritidal in character shallow subtidal cycles consist of basal deep water facies and an upper layer of subtidal molar tooth limestone tempestite interbedded with microspar calcarenite facies peritidal cycles are identical to shallow subtidal cycles except that they contain a cap of dolomitic tidal flat microbial laminite and rarely of red shale sabkha facies or of sandy polymictic conglomerate a transect along the wall of a valley extending 8 5 km perpendicular to depositional strike reveals progradation of inner ramp tidal flats over outer and mid ramp facies during shoaling the maximum basinward progradation of peritidal facies coincides with a zone of slope failure that may have promoted the development of the stromatolitic reefs the sea level history of the victor bay formation is represented by three hectometre scale sequences an initial flooding event resulted in deposition of the lower victor bay shale member upper member carbonate cycles were then deposited during highstand mid ramp slumping was followed by late highstand reef development the second sequence began with development of an inner ramp lowstand unconformity and a thick mid ramp lowstand wedge a second transgression promoted a more modest phase of reef development at the mid ramp and shallow water deposition continued inboard a third and final transgressive episode eventually led to flooding of the backstepping ramp overall consistent cycle thickness and absence of truncated cycles as well as the high rate and amount of creation of accommodation space suggest that the periodicity and amplitude of sea level fluctuation were relatively uniform and point to a eustatic rather than tectonic mechanism of relative sea level change high amplitude high frequency eustatic sea level change is characteristic of icehouse worlds in which short term large scale sea level fluctuations accompany rapidly changing ice volumes affected by milankovitch orbital forcing packaging of cyclic upper victor bay carbonates therefore supports the hypothesis of a late mesoproterozoic glacial period as proposed by previous workers

the structure of the easter platform houtman abrolhos reefs pleistocene foundations and holocene reef growth abstract seismic reflection profiles have been used to expand an evolutionary model developed from a drilling and dating program of the easter platform one of three shelf edge coral reef platforms on the western margin of australia the houtman abrolhos reefs are surrounded by an open shelf which is mantled by cool water carbonate sediments and exist in a temperate tropical transition zone in conditions which are close to the limits for coral reef development the easter platform has distinct windward and leeward reefs and a lagoon divided by a central platform consisting of several small islands reef limestones of the central platform are calcretised and are last interglacial in age whilst the windward and leeward reefs and associated blue hole and reticulate reef terrains are holocene features seismic investigations indicate that holocene reef growth was strongly asymmetrical about the antecedent last interglacial reef platform the windward reef front is dominated by relict reef morphology and relatively thin ca 9 m or less holocene reefs have recolonised the windward margin of the antecedent platform at the site of the present day windward reef most holocene reef growth took place on the lee side of the antecedent platform and colonised an essentially flat surface at sl 40 m which has been seismically identified as the last interglacial surface up to 40 m of interpreted holocene reef overlies this monotonous surface throughout the leeward reef and associated blue hole and reticulate reef terrains demonstrating that the antecendent surface has had little influence on the processes and morphology of holocene reef construction in addition to the last interglacial reflector three deeper subparallel reflectors at sl 46 m 52 m and 60 m interpreted to represent calcrete horizons are present beneath the leeward lagoon and leeward reef terrains and are traceable to beneath the adjacent shelf surface the unconformity bound sequences so defined are thin 6 8 m and blanket like and are likely to be shelfal equivalents of pre holocene reef buildup phases found within the central platform

carbonate ramp depositional systems abstract the classification tectonic settings stratigraphy and early diagenesis of carbonate ramp systems are reviewed carbonate ramps are common in all geological periods but were dominant at times when reef constructing organisms were absent or inhibited ramps can be subdivided into inner mid and outer ramp environments the mid ramp zone extends from fair weather wave base to normal storm wave base although the water depths which these boundaries represent vary an additional outer slope environment occurs on distally steepened ramps as with siliciclastic shelves a range of wave storm and tide dominated ramps can be recognised and this forms the most convenient basis for ramp classification the carbonate productivity profile of ramps differs from that of rimmed shelves with the inner ramp showing lower production rates than comparable shallow water facies on rimmed shelves the zone of greatest organic carbonate sediment production appears to have shifted from the mid ramp to the inner ramp since the late jurassic carbonate ramps occur in most types of sedimentary basin but are best developed where subsidence is flexural and gradients are slight over large areas as in foreland and cratonic interior basins and along passive margins the featureless depositional profiles of many ramps means that sequence geometries are best observed on regional seismic lines some show low angle sigmoidal or shingled clinoforms suggesting that ramps may seldom be homoclinal but possess subtle slope geometries which reflect depositional environments because of their low angle slopes ramps respond differently to rimmed shelves during relative sea level changes although results seem to be strongly dependent on the rate of relative sea level change during a minor fall shallow ramp facies belts will simply shift basinwards in a forced regression in contrast the whole surface of a steep sloped flat topped rimmed shelf may be exposed so that sediment production ceases or is drastically reduced during a major fall shallow ramp bounded basins may empty completely conversely ramps also flood gradually whereas rimmed shelves do so more rapidly homoclinal ramps develop no resedimented lowstand deposits rimmed shelves and distally steepened ramps in contrast may develop lowstand talus or turbiditic wedges distally steepened ramps may behave more like homoclinal ramps during minor base level falls and like rimmed shelves during major base level falls many ramps consist of layered successions of several ramp sequences stacked one upon the other ramp stacks of this sort may show gross vertical accretion but individual ramp sequences seldom appear to develop in a keep up style apart from minor organic buildups as with many rimmed shelves steepening of the outer ramp margin due to tectonism slope inheritance or differential sedimentation may promote the development of a distally steepened ramp or rimmed shelf a wide variety of organisms have constructed buildups in mid and outer ramp environments isolated buildups may seed early in ramp development accrete to wave base or sea level and continue growth by stacking through successive ramp sequences so that depositional and diagenetic features within them are in concert with those of the shallow ramp the location of isolated buildups on ramps is governed by tectonism halokinesis antecedent topography or by the subtle slope geometry of the previous ramp sequence diagenesis on ramps shows some major variations compared with diagenesis on steep sloped flat topped carbonate platforms ramp bounded basins may form prolific petroleum sourcing and reservoiring systems and offer a range of subtle stratigraphic play types and lateral facies variations which determine reservoir quality and distribution isolated buildups in the mid and outer ramp environments represent one of the commonest petroleum reservoirs in ramp systems and tend to have their foundations in transgressive systems tracts grainstone and packstone reservoirs are widespread and range from shoreline carbonate sandbodies to major detached shoal complexes or shoals over offshore highs grainstone sandbodies occur in both highstand systems tracts and in prograding lowstand wedges

palaeofires in amazon interplay between land use change and palaeoclimatic events interpreting the geological record of amazon biomass combustion requires comparing charcoal accumulation rates in various biomes at different time scales charcoal accumulation rates a proxy for palaeofire records were obtained in sediment cores from amazon lakes surrounded by several vegetation types and from a reservoirs in an intense land use change region the records presented in this study were obtained in the following areas i a reservoirs in alta floresta region northern mato grosso state ii lago do saci southern para state a lake close to alta floresta and located at the southern border of para state iii a bog in an ecotone area in the humaita region southern amazonas state iv lakes in lateritic iron crust of the carajas hills southeastern para state v lago comprido a floodplain lake close to the amazon river and surrounded by tropical rain forest monte alegre para state vi lagoa da pata in the morro dos seis lagos alkaline complex sao gabriel da cachoeira amazonas state and vii lago caracarana a secluded lake in the northern amazon cerrado roraima state the highest charcoal accumulation rates were observed for modern records related to an intense change in land use at alta floresta which had no precedent during the holocene history of the amazon high charcoal accumulation rates that were observed in the carajas region during low lake level phases in the amazon in the mid holocene were comparable to those at the onset of the human settlement in alta floresta region an increase in charcoal accumulation rate was observed in the late holocene when the lake level was high suggesting an interaction between climates and human presence low charcoal accumulation rates are typical of modern high rainfall environments as observed in lagoa da pata where the environment is not susceptible to occurrences of wildfires even during relatively drier climatic phases low charcoal accumulation rates also exist in the relatively dry cerrado savanna type biome even during relatively dry phases in the caracarana region where the savanna type vegetation biomass is lower and thus generates less charcoal particles than forest ecosystems

vegetation dynamics during the late pleistocene in the barreirinhas region maranhao state northeastern brazil based on carbon isotopes in soil organic matter abstract the study place is in the barreirinhas region maranhao state northeastern brazil a vegetation transect of 78 km was studied among four vegetation types restinga coastal vegetation cerrado woody savanna cerradao dense woody savanna and forest as well as three forested sites around lagoa do caco located approximately 10 km of the transect soil profiles in this transect were sampled for 13c analysis as well as buried charcoal fragments were used for 14c dating the data interpretation indicated that approximately between 15 000 and 9000 14c yr b p arboreal vegetation prevailed in the whole transect probably due to the presence of a humid climate approximately between 9000 and 4000 3000 14c yr b p there was the expansion of the savanna probably related to the presence of drier climate from 4000 3000 14c yr b p to the present the results indicated an increase in the arboreal density in the area due to the return to a more humid and probably similar climate to the present the presence of buried charcoal fragments in several soil depths suggested the occurrence of palaeofires during the holocene the vegetation dynamic inferred in this study for northeastern brazil is in agreement with the results obtained in areas of amazon region based on pollen analysis of lake sediments and carbon isotope analysis of soil organic matter som implying than similar climatic conditions have affected these areas during the late pleistocene until the present

vegetational history of a site in the central amazon basin derived from phytolith and charcoal records from natural soils abstract analysis of phytoliths and macroscopic charcoal from natural soils near manaus brazil shows that the central amazonian terra firme forest has not been stable during the holocene phytolith taxonomic composition and radiocarbon ages indicate that a closed forest has continuously existed in the area since at least 4600 yr b p but that forest composition and species abundance changed significantly sometime during the holocene epoch there is no evidence that the vegetation experienced swidden cultivation the distribution and dates of the charcoal in the soils indicate that forest fires between 1795 and 550 yr b p burned an area of about 200 hectares vegetational changes and fires appear to be a result of climatic drying that may have affected large areas of the amazon basin over the past 5000 to 7000 years soil phytolith analysis is a promising tool for the study of environmental history in the humid tropics and may reduce the previous dependence on lake and swamp sediments at least for the holocene epoch

episodic deposition and preservation of eolian sands a late paleozoic example from southeastern utah the upper pennsylvanian and lower permian stratigraphic sequence in canyonlands national park contains about 40 flat topped eolian sand bodies rhizoliths burrows and traces of former evaporites abound at the tops of these tabular genetic units upper surfaces of units were created by eolian deflation to the level of the groundwater table analysis of cross stratification reveals that sands accumulated via migration and climb of relatively small dunes brief episodes of sand accumulation were triggered by regression and were terminated when upwind sand supplies were depleted upper surfaces of genetic units are diastems and represent much more geologic time than the rocks themselves

tidal channel levee and crevasse splay deposits from a cambrian tidal channel system a new mechanism to produce shallowing upward sequences abstract two cliff exposures 1 km and 0 7 km long and 10 m high of the middle upper cambrian waterfowl formation were mapped in detail on the costigan thrust in southwestern alberta the formation here comprises 5 rock types intraformational conglomerate cross stratified grainstone wavy bedded grainstone mudstone massive dolomite mudstone and prism cracked cryptmicrobial laminated mudstone these rock types form a grainstone body in the upper 7 m of the outcrops and 4 fining upwards sequences in the lower 3 m the grainstone body is divided into 5 storeys each of which has a basal erosion surface overlain by an intraformational conglomerate with interbedded thrombolites storeys contain lateral accretion bedding that is composed of decimeter thick bedsets which are inclined up to 12 d grees relative to the basal erosion surfaces the fining upwards sequences comprise basal cross stratified grainstone overlain by wavy bedded grainstone mudstone that is capped by prism cracked cryptmicrobial laminated mudstones three fining upwards sequences are laterally continuous however one fining upward sequence pinches out along the outcrop face we interpret the grainstone body as the deposits of laterally migrating sinuous tidal channels it is not clear whether the stacking of channel deposits into storeys represents superimposed channel bar and channel fill deposits from a single channel belt or superimposed channel belts the fining upwards sequences may be shallowing upwards sequences in the sense of james 1984 and represent aggrading prograding tidal flat deposits a ternatively these sequences may be crevasse splay and levee deposits analogous to fluvial overbank flood sequences in this case these sequences may not be related to eustatic sea level changes although they resemble classic shallowing upwards sequences and punctuated aggradational cycles

paleogeography as geological heritage developing geosite classification abstract geological heritage sites geosites are sites that contain information about the state and the dynamics of the earth paleogeographical paleoenvironmental geosites preserve paleoenvironments paleoecosystems and other relevant phenomena however the value of these sites can only be fully understood through professional interpretation of the observed features description of paleogeographical geosites in terms of the paleospace and the geologic time they encompass is challenging partially because of many uncertainties in the interpretations of a given geosite and in the paleogeographical paleobiogeographical and stratigraphical nomenclature these geosites can be classified on the basis of facies paleoecosystems ichnological value taphonomic patterns major events and catastrophes and geoarcheological potential that they exhibit some geosites comprise several subtypes and some are especially important for construction of paleogeographical maps moreover the paleogeographical geosite type always associates with other types of geosites 20 in total these combinations form complex geosites that contribute to geodiversity if information about the earth s past is especially valuable for a given complex geosite then the paleogeographical type is dominant

field and modelling studies of cambrian carbonate cycles virginia appalachians reply abstract field studies coupled with computer modelling of carbonate cycles in the elbrook conococheague formations middle to upper cambrian in the appalachians have helped define the mechanisms of formation the sequence is up to 1 6 km thick and composed of cyclic peritidal carbonates these formed on an aggraded rimmed shelf on a mature passive continental margin the cycles 1 7 m thick have lower parts of subtidal intertidal carbonate and caps of dolomitic laminite containing minor quartz arenite shale and breccia sedimentation rates for these peritidal carbonate environments exceeded long term subsidence of the platform 0 01 to 0 1 m 1 000 yr thus the shelf stayed near to sea level i e was aggraded milankovitch 20 000 to 100 000 yr low amplitude sea level fluctuations few meters superimposed on 3rd order sea level fluctuation of 1 to 3 m y duration and less than 20 m amplitude caused periodic submergence of the gently sloping platform less than 0 02 m km slopes resulting in deposition of over 400 peritidal cycles in about 26 m y cycles that formed during 3rd order sea level rise are thick and limestone rich whereas those formed during 3rd order fall are thin quartzose and highly dolomitized the modelling suggests that fewer and thinner cycles formed during the long term falls compared to the rises reflecting decreased accommodation cycle frequency decreases into areas of lower subsidence rate open marine cycles typical of the outer shelf and cycles formed during 3rd order sea level rise contain digitate bioherms grainstone and ribbon carbonates in lower parts they reflect high subsidence rate and an open marine setting inner shelf cycles and cycles that formed during 3rd order sea level fall commonly are thrombolitic or have thin subtidal parts grainstone conglomerate or stromatolite and reflec the low subsidence rates interior areas of quaternary carbonate shelves are characterized by incipiently drowned facies and pinnacle reefs and are punctuated by soil caliche horizons and karst surface that reflect 100 m glacio eustatic sea level fluctuations in contrast many ancient shelves like the cambro ordovician shelf of the appalachians were flat topped and dominated by cyclic peritidal sequences lacking evidence of high amplitude sea level fluctuations such aggraded shelves may represent the typical state of mature carbonate shelves that formed in response to low amplitude milankovitch sea level fluctuations as opposed to the large scale fluctuations that typified the quaternary

changes in fire regimes since the last glacial maximum an assessment based on a global synthesis and analysis of charcoal data fire activity has varied globally and continuously since the last glacial maximum lgm in response to long term changes in global climate and shorter term regional changes in climate vegetation and human land use we have synthesized sedimentary charcoal records of biomass burning since the lgm and present global maps showing changes in fire activity for time slices during the past 21 000 years as differences in charcoal accumulation values compared to pre industrial there is strong broad scale coherence in fire activity after the lgm but spatial heterogeneity in the signals increases thereafter in north america europe and southern south america charcoal records indicate less than present fire activity during the deglacial period from 21 000 to 11 000 cal yr bp in contrast the tropical latitudes of south america and africa show greater than present fire activity from 19 000 to 17 000 cal yr bp and most sites from indochina and australia show greater than present fire activity from 16 000 to 13 000 cal yr bp many sites indicate greater than present or near present activity during the holocene with the exception of eastern north america and eastern asia from 8 000 to 3 000 cal yr bp indonesia and australia from 11 000 to 4 000 cal yr bp and southern south america from 6 000 to 3 000 cal yr bp where fire activity was less than present regional coherence in the patterns of change in fire activity was evident throughout the post glacial period these complex patterns can largely be explained in terms of large scale climate controls modulated by local changes in vegetation and fuel load

reconstructing past fire temperatures from ancient charcoal material abstract charcoal abundance measurements are commonly used to estimate fire activity in palaeoecological studies however fire temperature is not directly measured reconstructing fire temperature is desirable because the ecological response to fire is in part a function of the temperature of the fire e g crown fires 500 c slash and burn agriculture the inferred chemistry of the reference charcoal from the ftir spectra was in broad agreement with previous studies and the model based clustering algorithms were able to distinguish clusters based on the temperature to which the material was heated the ftir spectra from the ancient charcoal fragments fell within the range of variability of the modern reference charcoal allowing for successful classification of the fragments created by fires in the long distant past we used a probability density function of each statistically significant cluster to infer combustion temperatures for the ancient charcoal fragments our results suggest that the use of ftir analysis of charcoal can differentiate low 200 c 300 c medium 400 c 600 c and high 600 c 700 c temperature fires our findings pave the way for generating a better understanding of the role of fire in earth s system through time

eustatic tectonic and climatic signatures in the lower cretaceous siliciclastic succession on the eastern russian platform abstract a methodical approach to identifying major abiotic events in the siliciclastic succession accumulated in the shallow epicontinental basin on the eastern russian platform during the early cretaceous is presented on the basis of a reliable chronostratigraphic framework a comparison between global and regional sea level curves was undertaken the intervals during which the global and regional sea level curve trends are similar correspond to a predominance of eustasy in the particular basin alternatively tectonic activity dominates during intervals when there is no similarity between the trends of the global and regional sea level curves three intervals of noncoincidences of trends of these two curves matched with major tectonic events that took place within the eastern russian platform in the early cretaceous the early hauterivian tectonic uplift subsequent late hauterivian subsidence and the late albian uplift the main consequences of the tectonic activity were two large regional unconformities and hiati the comparison of main global and regional sea level trends also reveals major climatic events the cold snaps that occurred during the early cretaceous greenhouse world hu et al 2012 coincided with simultaneous global and regional sea level lowstands peak shallowing of the basin and the almost complete absence of sediments the cold snap is identified in the late aptian sedimentary sequences on the eastern russian platform

discovery of permanent amazon lakes and hydraulic disturbance in the upper amazon basin we describe here the first autonomous permanent deep lakes found in the amazon lowlands permanent amazon lakes have hitherto been considered unlikely because the ubiquitous rivers meandering over flat terrain should obliterate ancient basins resulting in lakes subject to annual flooding the so called varzeas 1 4 the lakes described here are in the rain forests of ecuador in western amazonia within 100 km of the andes mountains but at elevations below 700 m fig 1 they occupy either deep abandoned channels of high energy rivers or closed volcanic basins sedimentary histories and pollen data over several millennia from these lakes record disturbance of the amazonian ecosystem by flooding encouraging the view that high amazonian species richness is maintained by non equilibrium processes5 6

pre columbian fire regimes in lowland tropical rainforests of southeastern peru abstract we document the fire history of the forests of a well studied ecological research station los amigos in western amazonia through soil charcoal analysis and compare results with data from a nearby lake district known to have supported pre columbian human populations we present novel methods of soil charcoal analysis that improve on its current limitations by accounting for variability in post fire charcoal deposition problematic age depth relationships and the presence of weathered or regionally deposited charcoal particles that allow statistical comparisons of fire history characteristics between regions the fire histories indicate that the research station experienced less intensive historical fire and pre columbian disturbance than the lake district dated charcoal particles indicated that while soil depth could not be used to predict fire age fragments below 20 cm depth were generally older than 500 years frequent fires have not occurred in either region during the last 1000 years but fire events in both regions were significantly synchronous from 1000 to 4000 cal yr bp the sampling design and methods that provide an ecologically and statistically valid avenue for comparing fire history characteristics between regions can be modified to suit other ecosystems the results presented here establish confidence that the patterns and processes of the lowland tropical rainforests studied at los amigos are not affected by intense or recurrent historical fires these data also suggest that forests of madre de dios peru are not post successional remnants of a cultural parkland as suggested by some amazonian archeologists

the history of south american tropical precipitation for the past 25 000 years long sediment cores recovered from the deep portions of lake titicaca are used to reconstruct the precipitation history of tropical south america for the past 25 000 years lake titicaca was a deep fresh and continuously overflowing lake during the last glacial stage from before 25 000 to 15 000 calibrated years before the present cal yr b p signifying that during the last glacial maximum lgm the altiplano of bolivia and peru and much of the amazon basin were wetter than today the lgm in this part of the andes is dated at 21 000 cal yr b p approximately coincident with the global lgm maximum aridity and lowest lake level occurred in the early and middle holocene 8000 to 5500 cal yr b p during a time of low summer insolation today rising levels of lake titicaca and wet conditions in amazonia are correlated with anomalously cold sea surface temperatures in the northern equatorial atlantic likewise during the deglacial and holocene periods there were several millennial scale wet phases on the altiplano and in amazonia that coincided with anomalously cold periods in the equatorial and high latitude north atlantic such as the younger dryas

biocalcarenite and mixed cool water prograding bodies of the mediterranean pliocene and pleistocene architecture depositional setting and forcing factors

investigating the origin of continual radio frequency impulses during explosive volcanic eruptions volcanic lightning studies have revealed that there is a relatively long lasting source of very high frequency radiation associated with the onset of explosive volcanic eruptions that is distinct from radiation produced by lightning this very high frequency signal is referred to as continual radio frequency crf due to its long lasting nature the discharge mechanism producing this signal was previously hypothesized to be caused by numerous small 10 100m leader forming discharges near the vent of the volcano to test this hypothesis a multiparametric data set of electrical and volcanic activity occurring during explosive eruptions of sakurajima volcano in japan was collected from may to june 2015 our observations show that a single crf impulse has a duration on the order of 160ns giving an upper limit on discharge length of 10m and is distinct from near vent lightning discharges that were on the order of 30m in length crf impulses did not produce discernible electric field changes and occurred in the absence of a net static electric field lightning mapping data and infrared video observations of the eruption column showed that crf impulses originated from the gas thrust region of the column these observations indicate that crf impulses are not produced by small leader forming discharges but rather are more similar to a streamer discharge likely on the order of a few meters in length plain language summary this paper investigates the origin of a radio frequency rf signal previously termed continual rf that has been detected from the ash plumes of explosive volcanic eruptions continual rf had been hypothesized to be caused by many very small lightning like discharges on the order of 100m in length occurring at the vent of the volcano to test this hypothesis we conducted a multiparametric observational experiment at sakurajima volcano in japan we measured continual rf during eruptions of sakurajima in 2015 and found that continual rf is a collection of short duration rf impulses on the order of 160ns in duration these rf impulses are distinct from those typically produced by lightning we also observed small 30 m lightning discharges occurring near the volcanic vent that were distinct from the source of continual rf our observations show that continual rf is caused by an electrical discharge that is more simple than even a very small approximate to 100m lightning discharge we conclude that continual rf is caused by numerous small electrical discharges similar to streamer discharges on the order of a few meters in length

are holocene wood charcoal fragments stratified in alpine and subalpine soils evidence from the alps based on ams 14c dates the possible stratification of charcoal particles buried in well drained soil in the subalpine and alpine belts in an inner valley of the northwestern alps savoy france is examined radiocarbon dating and quantification of charcoal fragments more than 400mm in diameter were used to analyse the soil depth distri bution of charred wood particles between 1700 and 2600 m a s l in two study areas 10 km apart in the same valley above 2100 m a s l in both study areas charcoal concentrations are low and mainly contained in the upper horizons and all dated charcoal fragments are older than 2300 cal yr bp below 2100 m the greatest charcoal concentration is located in the topmost 30 cm of the soil profiles and the 14c dates yield late holocene ages 1600 to 75 cal yr bp when profiles have an elevated charcoal concentration in deeper horizons the charcoal dates are mid holocene 6360 2770 cal yr bp radiocarbon dates of charcoal fragments do not reveal an age depth relationship although charcoal mass concentrations suggest a coarse stratification of char coal particles in the soils below 2100 m at forested sites this difference may be due to the charcoal dating on a single fragment which is not representative of the charcoal assemblage containing a few tens to thousands of fragments the lack of stratification probably results from soil bioturbation by soil fauna soil reworking by uprooted trees and freeze thaw processes at higher elevation in the alpine belt charcoal is concentrated in the topmost soil due to a low bioturbation rate from a pedological point of view the 14 c dating and the quantification of charcoal concentration per soil level provides a time range estimate for soil particle reworking by anecic earthworms dung beetles and other biota this has application in pedogenesis studies to estimate the rapidity of processes of soils dynamics these data suggest that soils in the alps have limited potential for palaeoecological studies based on a stratigraphic assumption but have more applications in precise spa tial studies

stratigraphic completeness of carbonate dominated records from continental interiors versus continental margins stratigraphic thinning occurs via condensation and omission at multiple scales abstract over phanerozoic time scales stratigraphic records from continental interiors or cratons are dramatically thinner and are generally assumed to be relatively incomplete with more numerous and longer duration hiatuses compared to records from more rapidly subsiding continental margins however this assumption need not be true for the shorter time scales i e several 106 years and shorter over which accumulation of the preserved stratigraphic record on the continental interior actually takes place this study compares carbonate dominated sedimentary records from the devonian continental interior iowa and continental margin nevada to evaluate whether the continental interior record is 1 miniaturized i e thinner but equally complete 2 comparable in thickness and quality where the sedimentary record is preserved but certain portions of the record are notably absent i e omitted or truncated or 3 so invariably preserved that equivalent stratigraphic packages cannot be recognized compared to the continental margin record this study finds that fourth to fifth order cycles in iowa are on average approximately half as thick and half as numerous compared to the continental margin of nevada moreover the stratigraphic record on the continental margin of nevada is dominated by cycles that are composed of tidal flat and shallow subtidal lithofacies capped by simple flooding surfaces and exhibit catch up or keep up depositional styles the continental interior record in iowa is dominated by cycles that are composed of subtidal lithofacies capped by a range of bounding surfaces and exhibit catch down or give up depositional styles these findings suggest that the thin record in iowa is largely a result of low sedimentation rates associated with suppressed carbonate production in this epeiric sea setting rather than minimal subsidence rates and an increased potential for subaerial exposure and associated loss of record

vegetation development in an amazonian peatland recent investigations of wetlands in western amazonia have revealed the presence of extensive peat deposits up to 7 5 m thick developing under a variety of vegetation types we report the first attempt to establish the long term centennial to millennial scale vegetation history of one of these peatland sites quistococha a palm swamp close to iquitos in northern peru pollen and sedimentological analyses show that peat formation began at the core site under sedge fen or floating mat vegetation c 2200 calendar years before present cal yr bp a seasonally flooded woodland developed c 1880 cal yr bp the permanently waterlogged palm swamp which persists today began to form c 1000 cal yr bp with the present vegetation community established by c 400 years ago the vegetation at this site has undergone continuous change throughout the period of peat formation with several abrupt transitions and reversals and repetitions in the apparent trajectory of change the pollen data combined with sedimentary evidence suggest that the dominant control on ecosystem functioning and development is the flooding regime there appears to have been a decrease in fluvial influence over time there is no clear evidence of direct climatic or anthropogenic influence although we cannot rule out the possibility of climatically driven hydrological changes our results caution against adopting a simple model of peatland vegetation succession in this region

facies heterogeneity at interwell scale in a carbonate ramp upper jurassic ne spain abstract the well exposed upper kimmeridgian carbonate ramp near arroyo cerezo iberian basin eastern spain provides an excellent analog to stratigraphically equivalent subsurface reservoirs such as the carbonate ramps of the arab d of the middle east and the smackover of the gulf of mexico critical questions regarding interwell scale heterogeneity and correlation motifs for low angle ramp systems can be addressed using continuous exposures that encompass a full range of inner to outer ramp facies outcrops in this area provide a complete exposure of the ramp succession in depositional dip direction at arroyo cerezo a 40 m thick and 1 3 km long dip oriented continuous outcrop has been studied lithofacies and bounding surfaces have been mapped on a continuous photomosaic to build a detailed 2d cross section complemented by five stratigraphic sections 300 m apart and petrographic analysis the reconstructed section shows the facies transition from relative proximal to distal carbonate ramp settings carbonate facies associations are grouped according to the dominant carbonate types buildup dominated systems and coated grain dominated systems detailed mapping of facies and bounding surfaces documents distinct ramp depositional units with downdip facies changes occurring within the 1 3 km length of the outcrop the arroyo cerezo outcrop indicates that the ramp facies continuity when based on a 5 10 km distance well log correlation is mostly apparent use of detailed spatial and temporal analysis of high quality outcrop analogs promotes more realistic models for understanding the interwell meter scale heterogeneity and the scale of these depositional heterogeneities although being below resolution of subsurface tools governs in fact along with diagenetic modifications the fluid flows within a reservoir the scale of these stratigraphic heterogeneities needs to be considered in order to optimize and enhance hydrocarbon production and last recovery

a paleotropical carbonate dominated archive of carboniferous icehouse dynamics bird spring fm southern great basin usa abstract much of our far field knowledge of glaciation and climate during the late paleozoic ice age is built on decades of study of mixed carbonate siliciclastic cyclothemic successions from paleotropical euramerica far fewer carbonate dominated successions have been studied despite their high sensitivity to changes in accommodation space and environmental conditions here we present a sequence stratigraphic framework for the carbonate dominated bird spring formation southern great basin u s a and infer from it a relative sea level history for the latest mississippian through latest pennsylvanian correlation of four successions across the paleo platform documents changes in the lithofacies composition of meter scale cycles their cycle stacking patterns and cycle bounding surfaces that record substantial variation in relative sea level at several temporal scales during the pennsylvanian ten genetic sequences bounded by intervals of restricted peritidal lithofacies karst terra rossa rooted caliche and or protosols are recognized within sequences 126 parasequences stack into parasequence sets that in turn define lowstand transgressive and highstand systems tracts the stratigraphic cycle stacking patterns and across platform architecture of systems tracts suggest a mid carboniferous lowstand in relative sea level followed by a middle morrowan middle bashkirian highstand as previously suggested bishop et al 2010 subsequent progradation of the platform occurred during a gradual long term fall through the late morrowan and atokan late bashkirian early moscovian upon which repeated higher frequency events were superimposed culminating in widespread exposure across the platform proximal to the atokan desmoinesian boundary long term sea level increased into the mid desmoinesian end moscovian after which progradation late desmoinesian and aggradation missourian virgilian of shallow water and peritidal carbonates occurred across the bird spring platform the progradational to aggradational phase involved an abrupt shift from ramp to rimmed shelf geometry in the missourian kasimovian likely in response to progressively increasing sea level dampened high frequency sea level fluctuations and or to regional faulting along the bird spring platform margin inferred magnitudes of short term 105 yr fluctuations superimposed on the longer term rises and falls range from 20 to 70 m during the early to mid pennsylvanian and are substantially reduced 20 m during the late pennsylvanian the early to middle pennsylvanian sea level history inferred from the carbonate dominated bird spring platform corresponds well with a recently published pennsylvanian onlap offlap history defined from the cyclothemic succession of the donets basin and with independent near field reconstructions of glaciation during the pennsylvanian

eustatic control on early dolomitization of cyclic peritidal carbonates evidence from the early ordovician upper knox group appalachians the early ordovician upper knox group is characterized by stacked meter scale peritidal cycles that repeat at high frequencies 10 4 to 10 5 yr stacking patterns stratigraphic trends in lithofacies and cycle thickness of meter scale cycles define five depositional sequences that in conjunction with fischer plots delineate five long term relative sea level fluctuations during upper knox deposition intrabasinal and interbasinal correlation of upper knox fischer plots suggests that the third order sea level events were eustatic meter scale peritidal cycles likely formed in response to high frequency fourth and fifth order eustatic sea level fluctuations superimposed on these third order sea level events upper knox cyclic carbonates are extensively dolomitized as much as 85 of all dolomite is stratiform and consists of early dolomite exhibiting minor to extensive modification by burial dolomite synsedimentary dolomitization likely occurred in modified sea water during tidal flat progradation governed by high frequency sea level events this is suggested by the common association of dolomite with mud cracked laminites and silicified evaporite nodules the systematic decrease in dolomite abundance below laminite cycle caps and the presence of dolomite clasts in regoliths veneering high frequency cycle tops or in transgressive limestones of the overlying cycle dolomite distribution within depositional sequences shows a strong relationship to third and fourth order eustatic sea level events indicating that long term eustasy also strongly controlled early dolomitization of upper knox carbonates mass balance calculations show that the proposed sabkha model of dolomitization in concert with composite eustasy could generate stratiform dolomite of considerable vertical and lateral extent in peritidal cyclic carbonates this reflects the duration of progradation and supratidal exposure 10 4 to 10 5 yr available for dolomitization to proceed and the broad zone of active dolomitization that would develop during continued progradation throughout each cycle period

a model for atmospheric co 2 over phanerozoic time a new model has been constructed for calculating the level of atmospheric co sub 2 over phanerozoic time which is much simpler mathematically than the blag model but more complex geologically and biologically results suggest that there has been a notable pattern of varying atmospheric co sub 2 level over the past 570 my with high levels during the mesozoic and early paleozoic and low levels during the permo carboniferous and late cenozoic sensitivity analysis shows that within reasonable limits of the principal governing parameters this qualitative trend of varying co sub 2 is relatively insensitive to the actual values chosen for these parameters causes of the co sub 2 variation are multiple and no single geological or biological process can be called upon to explain all co sub 2 variation for all time the calculated trend of co sub 2 over time agrees well with independent estimations of paleoclimates thus the greenhouse theory of paleoclimate on a long geological time scale is supported by the results of the present study

sea level control of mixed carbonate siliciclastic gravity flow deposition lower part of the keeler canyon formation pennsylvanian southeastern california depositional cycles present in a mixed carbonate and quartz gravity flow sequence exposed in the death valley owens valley of southeastern california may record the response of this system to third order 0 7 1 4 m y sea level changes during late pennsylvanian time time equivalent outer shelf and basin margin deposits elucidate the following key elements of this depositional system 1 a distally steepened ramp profile 2 an unchanneled basin margin sequence which accumulated as a line sourced apron system and 3 penecontemporaneous deposition of carbonate and fine grained quartz sediment in both the shallow and deep water regimes basin margin facies consist of mudstones turbidites debris flows and megabreccias organized into thickening and coarsening upward packages lime mudstone intervals 3 7 m thick alternate with mixed carbonate siliciclastic gravity flow intervals 10 30 m thick time equivalent outer ramp facies show a similar organization of alternating silty bioclastic wackestones grainstones 10 40 m thick containing a diverse open marine fauna and rhythmically bedded lime mudstone 15 60 m thick which is barren of fauna an upward increase in debris flows and megabreccias within basin margin cycles indicates the involvement of large scale ramp processes and cannot be explained by simple progradation and abandonment of depositional lobes the absence of megabreccia caps on many of the cycles argues against autocyclic progradation and collapse of the platform although larger scale coarsening and thickening upward trends within the basin margin succession are attributed to autocyclic processes instead we propose that cycles develop in both the shallow and deep water regimes by changes in relative sea level drowning of the outer shelf during relative highstands rhythmically bedded lime mud stone would yield starved basin deposits lime mudstone as sea level falls both carbonates and siliciclastics prograde closer to the shelf edge silty bioclastic wackestones grainstones thus activating the mass transport system mixed clastic gravity flow packages increased storm and wave influence on the outer ramp upper slope triggers debris flows and occasional large scale collapses producing megabreccias most models of turbidite deposition have stressed reciprocal sedimentation with sea level change bioclastic turbidites during highstands and silicilclastic turbidites during lowstands instead our model for mixed clastic deposition emphasizes the importance of the build up profile the position of sea level relative to the shelf margin and the rate of change of sea level

neoproterozoic chuar group 800 742 ma grand canyon a record of cyclic marine deposition during global cooling and supercontinent rifting abstract chuar group sediments were deposited in a marine cratonic basin synchronously with marine deposition in other basins of western north america and australia the top of the chuar group is 742 ma thus this succession offers a potentially important record of global climatic and tectonic changes during the mid neoproterozoic a critical time leading to possible global glaciation during supercontinent rifting chuar group cycles and sequences may record glacioeustatic fluctuations during the climatic transition into the sturtian ice age 750 700 ma as well as extension related to the dispersal of rodinia the mid neoproterozoic chuar group 1600 m thick is predominantly composed of mudrock with subordinate meter scale beds of dolomite and sandstone facies analysis leads to the interpretation of a wave and tidal influenced marine depositional system diagnostic marine features include 1 marine fossils and high local pyrite content in the mudrock facies 2 mudcracked mud draped symmetric ripples and reverse flow indicators in the sandstone facies 3 facies associations between all facies and 4 no unequivocal terrestrial deposits chuar facies stack into 320 dolomite and sandstone capped meter scale cycles 1 20 m thick and non cyclic intervals of uniform mudrock facies 20 150 m thick nearly all cycles have mudrock bases indicating subtidal water depths dolomite capped cycles shallow to peritidal environments peritidal cycles some indicating subaerial exposure of varying degrees exposure cycles sandstone capped cycles shallow to peritidal environments with no evidence of prolonged exposure peritidal cycles non cyclic intervals represent the deepest water depths 10s of meters peritidal cycles and non cyclic intervals dominate the lower and middle chuar group in the upper chuar group the percentage of exposure cycles increases as does the thickness of individual cycles and non cyclic intervals and the degree of subaerial exposure in the cycle caps correlation of cycles across 10 km shows that many cycles are laterally continuous and some vary in thickness some thickness changes are coincident with local and regional extensional structures these cycle trends reflect a resolvable mixture of tectonic and climatic controls cycles are interpreted to be high frequency and glacioeustatically controlled based on comparison of cycle character and thickness to phanerozoic examples and lateral continuity of many cycles respectively cycles in the lower and middle chuar group show characteristics suggestive of low amplitude sea level changes similar to meter scale cycles from global greenhouse climates in the phanerozoic upper chuar group cycles show characteristics suggestive of moderate amplitude sea level changes similar to phanerozoic greenhouse icehouse transition climates indicating an increase in continental ice volume variability in cycle thickness and lateral pinching of some cycle caps is controlled by variable tectonic subsidence evidenced by thickening trends coincident with active rift related structures and also by variability in sediment supply the presence of dolomite caps in this otherwise siliciclastic succession is interpreted to be due largely to rapid changes in climate related to short term glacioeustatically controlled sea level changes four crude lithostratigraphic sequences 150 775 m thick are defined based on dolomite poor to dolomite rich stratigraphic intervals long term changes in cycle cap lithology may be driven by long term changes in climate similar to short term glacioeustatic controls on meter scale cycle cap lithology large scale thickness variability in these sequences is due to local differential tectonic subsidence

a user friendly one dimensional model for wet volcanic plumes 1 this paper presents a user friendly graphically based numerical model of one dimensional steady state homogeneous volcanic plumes that calculates and plots profiles of upward velocity plume density radius temperature and other parameters as a function of height the model considers effects of water condensation and ice formation on plume dynamics as well as the effect of water added to the plume at the vent atmospheric conditions may be specified through input parameters of constant lapse rates and relative humidity or by loading profiles of actual atmospheric soundings to illustrate the utility of the model we compare calculations with field based estimates of plume height 9 km and eruption rate 4 105 kg s during a brief tephra eruption at mount st helens on 8 march 2005 results show that the atmospheric conditions on that day boosted plume height by 1 3 km over that in a standard dry atmosphere although the eruption temperature was unknown model calculations most closely match the observations for a temperature that is below magmatic but above 100 c

use of fischer plots to define third order sea level curves in ordovician peritidal cyclic carbonates appalachians fischer plots in which cumulative cycle thickness corrected for linear subsidence is plotted against time were originally used in the study of triassic peritidal sequences to define short duration departures in relative sea level in the milankovitch range 104 to 105 yr however they also provide a means of assessing magnitude of third order 1 to 10 m y fluctuations in sea level which on the basis of their regional correlatability we ascribe to eustatic events

use of insolation as a proxy for high frequency eustasy in forward modeling of platform carbonate cyclostratigraphy a promising approach abstract eustatic oscillations driven by milankovitchian astronomical forcing have been interpreted as sea level drivers for high frequency carbonate depositional cycles in studies dating from the mid 1960s forward modeling of these oscillations with respect to their recorded effects on cyclical stacking patterns has only been attempted using generalized parameters for milankovitchian forcing the development of increasingly advanced forward modeling software coupled with the availability of formulas quantifying insolation incoming solar radiation as a function of composite orbital variations allows for the testing of milankovitchian insolation against measured stratigraphy in this case a series of milankovitchian insolation curves were calculated and used to generate proxy sea level curves for use in the carb3d forward modeling package in order to synthesize a series of stacked carbonate strata these synthetic successions are compared against that of the latemar platform middletriassic northern italy which has been interpreted to contain a record of orbital forcing within its stratigraphy while the timing and nature of periodic drivers that affected latemar stratigraphy have stirred a vigorous debate results from this study indicate that use of milankovitchian insolation as a proxy for high frequency sea level oscillations was successful in modeling latemar like stratigraphy with both pure milankovitchian and mixed milankovitchian sub milankovitchian temporal frameworks

a guide to phanerozoic cold polar climates from high latitude ice rafting in the cretaceous the high latitude extent of warm climate indicators at certain times in earth history has been considered as evidence that the globe was ice free for long intervals despite theoretical considerations and results from numerical modelling experiments1 2 indicating that this was unlikely one of the warmest periods the cretaceous displays faunal and floral evidence for cool temperate to sub tropical conditions very near to the poles however our studies of lower cretaceous mudstones of central australia that contain outsized exotic blocks have led to the conclusion that the blocks were emplaced by ice rafting implying that high latitude ice was present at sea level strata of a similar origin of mid jurassic to mid cretaceous age occur on other continents that were positioned between 65 and 78 palaeolatitude indeed there is a record of high latitude ice rafting throughout the phanerozoic suggesting that ice was present on earth for much of its history and that ice free conditions could have been at most only episodic over the past 600 myr

waulsortian type bioherm development and response to sea level fluctuations upper visean of bechar basin western algeria abstract an exceptionally well developed and well preserved upper visean succession rich in sponge bryozoan crinoid mounds in the foreland carboniferous bechar basin northwestern algerian sahara is described and discussed the succession is composed of recurrent facies mosaics forming individual superposed members an ideal member is made up of two distinct fades assemblages the lower assemblage forms the actual mounds and is composed of sponge bafflestone wackestone at the base overlain by massive sponge fenestellid bafflestone wackestone and capped by massive crinoid wackestone with bedded flanks of lithoclastic wackestone in contrast to massiveness of the mounds the upper facies assemblage is composed of well bedded crinoid packstone grainstone and ooid grainstone with local rugose coral and algal foraminiferal banks on the basis of benthic assemblages and nature of substrate seven bathymetric zones are defined and indicate that each member of the bioherm rich formations is a shallowing upward parasequence controlled by an asymmetrical transgressive regressive cycle the local curve of relative sea level for the late visean shows 13 cycles interpreted as fourth order eustatic sea level changes each cycle averaging half a million years in duration third order cycles could not be identified the platform model proposed is a distally steepened ramp 15 20 km wide that developed in a rapidly subsiding foreland basin lateral distribution of facies on the ramp depended strongly on local tectonic setting whereas vertical development was controlled by sea level fluctuation the deep water mud rich sponge bryozoan crinoid mounds developed in 100 150 m water depths during phases of sea level highstand whereas deposition of shallow water facies occurred on top of the mounds in less than 70 80 m water depths during regressive phases the bechar mounds share similarities with the classical lower carboniferous waulsortian mounds but they differ in two aspects the abundance of large sponges which is unique and their vertical zonation wherein basal facies consist of sponge dominated assemblages the proposed model can serve as a tool in developing exploration strategies in the search for hydrocarbon reservoirs in the bechar basin because the peculiar architecture of the platform may provide suitable plumbing systems for fluid migration and the depositional signature of the mounds and associated facies is possibly recognizable on seismic profiles

transgressive oversized radial ooid facies in the late jurassic adriatic platform interior low energy precipitates from highly supersaturated hypersaline waters dark gray oolitic units characterized by oversized ooids with primary radial calcite fabrics occur in the interior of the late jurassic late tithonian adriatic platform a large mesozoic tethyan isolated platform in croatia they differ from open marine platform margin ooid grainstones in their dark color cerebroid outlines broken and recoated grains abundant inclusions highly restricted biota and lack of cross stratifithey have been interpreted as being of vadose origin vadoids at tops of upward shallowing parasequences however detailed sections show that most oolitic units occur at bases of precessional parasequences overlying erosional surfaces on fenestral carbonates the oolitic units are similar to quiet water ooids that form today in low energy settings they developed in an arid climate during initial transgression of supratidal fl ats along lowenergy shores seaward of tidal fl ats and along the margins of restricted lagoons and intertidal ponds superimposed fenestral fabrics meniscus micrite cements and grain breakage occurred as they aggraded to high tide level and were subjected to wetting and drying thermal expansion and contraction and wind transport they migrated landward with transgression forming extensive sheets and were overlain by subtidal lagoonal facies that shallow up into fenestral carbonates these distinctive facies may have been overlooked in the geological record or their geological distribution requires juxtaposition of calcite seas high calcite supersaturation states arid climate and presence of fl at topped carbonate platforms in a greenhouse world

microbial laminite versus rooted and burrowed caps on peritidal cycles salinity control on parasequence development early cretaceous isolated carbonate platform croatia some parasequences in the interior of the early cretaceous isolated carbonate platform croatia which formed under a greenhouse climate lack the typical regressive tidal flat laminites instead these bioturbated emergent parasequences have burrowed and rooted upper parts capped with thin greenish paleo sols and are reminiscent of triassic lofer cycles we propose that the bioturbated cycle tops reflect coastal salinities that are normal marine brackish or metahaline whereas the transgressive rare and abundant regressive tidal flat laminites formed under hypersaline coastal waters thus these features may be used to track gross salinity changes of coastal waters on the platform through time in addi tion we suggest ways to evaluate whether the salinity changes relate to hypersaline embay ments on the platform or changes in the cli mate at the parasequence scale we propose that the bioturbated emer gent parasequences could have formed under semiarid conditions seaward of subtle shallow embayments on the platform con temporaneously in the bayheads micro bial laminites developed these would require time equivalent updip and downdip laminate capped and bioturbated emer gence capped parasequences however the para sequences could also have been con trolled by climate changes the laminite capped parasequences could have resulted from salinity increase with shallowing of the platform interior under semiarid condi tions stable climate in contrast the bio turbated emergence capped parasequences could have formed during times of more humid climate punctuating the overall semi arid climate the humid phase would have favored brackish to normal marine salinities in the coastal zone along with macrophytes and intense animal and plant bioturbation which would suppress development of lami nite caps thus these parasequences provide a means of tracking gross salinity of coastal waters and if climate induced then they have implications for fluctuating climates in greenhouse worlds

on the labeling length and objective basis of fischer plots abstract fischer plots of the accumulation of shallow marine carbonate cycles track the cumulative departure from mean cycle thickness through a vertical sequence of contiguous upward shallowing units this is a simple objective treatment of residuals in a time series and is applicable to other stratigraphic phenomena to reflect the noninterpretive construction of fischer plots the vertical axis should be labeled cumulative departure from mean cycle thickness and the horizontal axis cycle number the typical fischer plot is an erratic bridge that begins and ends at the same elevation but has the form of an irregular train of asymmetric waves which rise steeply and fall gradually the asymmetry of the individual waves arises because thinner than average cycles typically outnumber thick r cycles two to one the overall form of the wave train is sensitive to mean cycle thickness but can guide correlation and may have considerable interpretive potential provided that enough cycles are included to ensure a robust estimate of mean thickness runs tests demonstrate that fischer bridges for peritidal carbonates are unlikely to be the result of random stacking processes since this anticipated result does not emerge unequivocally for fischer plots of less than 50 cycles however we recommend against plotting such short sections

cyclostratigraphy of middle devonian carbonates of the eastern great basin abstract middle devonian carbonates 250 430 m thick of the eastern great basin were deposited along a low energy westward thickening distally steepened ramp four third order sequences can be correlated across the ramp to basin transition and are composed of meter scale upward shallowing carbonate cycles or parasequences peritidal cycles shallow subtidal facies capped by tidal flat laminites constitute 90 of all measured cycles and are present across the entire ramp the peritidal cycles are regressive and transgressive prone upward deepening followed by upward shallowing facies trends approximately 80 of the peritidal cycle caps show evidence of prolonged subaerial exposure including sediment filled dissolution cavities horizontal to vertical desiccation cracks rubble and ka st breccias and pedogenic alteration locally these features are present down to 2 m below the cycle caps subtidal cycles capped by shallow subtidal facies are present along the middle outer ramp and ramp margin and indicate incomplete shallowing submerged subtidal cycles 64 of all subtidal cycles are composed of deeper subtidal facies overlain by shallow subtidal facies exposed subtidal cycles are composed of deeper subtidal facies overlain by shallow subtidal facies that are capped by features indicative of prolonged subaerial exposure dissolution cavities and brecciation average peritidal and subtidal cycle durations are between approximately 50 and 130 k y fourth to fifth order the combined evidence of abundant exposure capped peritidal and subtidal cycles transgressive prone cycles and subtidal cycles correlative with updip peritidal cycles indicates that the cycles formed in response to fourth to fifth order glacio eustatic sea level oscillations sea level oscillations of relatively low magnitude 10 m are suggested by the abundance of peritidal cycles the lack of widely varying water depth dependent facies within individual cycles and the presence of noncyclic stratigraphic intervals within intrashelf basin slope and basin facies noncyclic intervals represent missed subtidal beats when the seafloor lay too deep to record the effects of the short term sea level oscillations exposure surfaces at the tops of peritidal and subtidal cycles represent one or more likely several missed sea level oscillations when the platform lay above fluctuating sea level but the amplitude of fourth to fifth order sea level oscillation s were not high enough to flood the ramp the large number of missed beats exposure capped cycles specifically in sequences 2 and 4 results in fischer plots that show poorly developed rising and falling limbs subdued wave like patterns consequently the fischer plots are of limited use as a correlation tool for these particular depositional sequences the abundance of missed beats also explains why milankovitch type cycle ratios 5 1 or 4 1 are not observed and why such ratios would not be expected along many peritidal cycle dominated carbonate platforms

wind reworked carbonates permo pennsylvanian of arizona and nevada several workers have suggested that calcareous wind blown dunes are genetically related to rapid glacio eustatic fluctuations of sea level although such pleistocene and holocene deposits are widespread along low latitude coasts older eolian limestones are either extremely rare or have been misinterpreted as subaqueous in origin medium to large scale cross laminated limestones of the callville limestone pennsylvanian of southern nevada the correlative manakacha and wescogame formations supai group and the pakoon limestone permian of western grand canyon although considered marine by earlier workers contain several diagnostic structures indicative of an eolian origin cross strata are dominantly composed of thin inverse graded laminae produced by the migration and climb of wind ripples sets of cross strata commonly have irregular upper surfaces produced by differential wind erosion of damp or lightly cemented laminae southward dipping cross strata in these rocks are the earliest record of a paleowind system that persisted in this region well into jurassic time mechanical breakage of shells fitted fabrics and microstylolites indicate that marine beds that are cyclically interbedded with the eolian deposits did not undergo early lithification echinoderm grains with abraded over growths within eolian deposits indicate however that some wind transported grains were reworked from beds that had previously undergone fresh water phreatic diagenesis gravel lags composed of macrofossils and hardground lithoclasts at the contacts between marine and eolian beds and between eolian coasts give further evidence for deflation of subaerially exposed marine deposits where marine units underwent extensive early lithification there are no gravel lags or interbedded eolian deposits subaerially exposed marine strata were the primary source of eolian sediment during eustatic highstands onshore winds probably drove beach sediment landward but in contrast to quaternary examples the eolian deposits of this study do not cap shallowing upward sequences beach facies are rare during lowstands uncemented beach facies were first to be removed by deflation material too coarse to be wind transported accumulated as gravel lags deflation was facilitated by the lack of widespread sea floor cementation hardgrounds and by an arid paleoclimate which limited the extent of meteoric diagenesis

heterozoan carbonates when where and why a synthesis on parameters controlling carbonate production and occurrences abstract in modern and phanerozoic times heterozoan carbonates group a large array of depositional environments from the poles to the tropics this global assessment reviews the critical parameters and controlling factors of heterozoan carbonates i stratigraphic and global distributional trends ii oceanographic and trophic relationships and iii biological and sedimentary processes well documented case studies n 129 have been investigated when facies and stratigraphic attributes were available and when environmental settings such as oceanography climate and paleogeography were clearly identified these case studies occur during specific periods of time in the sedimentary record e g late ordovician early carboniferous early permian and neogene while they are absent during others e g triassic and jurassic periods during greenhouse to icehouse transitions and those with active thermohaline circulation are particularly conducive for heterozoan carbonates based on global oceanographic patterns and existing ecological and hydrodynamic regime classifications hallock 2001 pedley and carannante 2006 james and jones 2015 a process based classification scheme is proposed that distinguishes two main heterozoan carbonate systems i a highly productive system characterized by suspension feeding biota and ii an oligo mesotrophic warm temperate system characterized by red algal and seagrass derived biota eight depositional models are proposed that combine i the source of energy for metabolic activities that allow the carbonate producing biota to thrive and ii hydrodynamics and physiography of the depositional system that control the sediment accumulation the local and platform scale based profiles can be used to complement the facies approach of james and jones 2015

deepening upward subtidal cycles murray basin south australia abstract decimeter scale deepening upward cycles are the basic depositional motif of oligocene miocene murray supergroup limestones in the murray basin southeastern australia cycles formed in this large intracratonic basin on a centripetal temperate water epeiric ramp they reflect generation by trophic resource influenced carbonate production under mostly transgressive conditions listed from the base up each cycle is ideally composed of five parts part a biotically depauperate carbonates reflecting relatively shallow water restricted variably stressed highly mesotrophic environments part b increasingly biotically diverse limestones recording progressively more physical energy and less mesotrophic conditions upward om1 a conspicuous hardground to firmground surface formed during late transgression to stillstand during which wave sweeping and reworking contributed to omission and lithification part c relatively biotically diverse epifauna dominant sediments that were highly abraded during periods of condensed sedimentation under marginally oligotrophic conditions and om2 cycle boundary a rarely conspicuous surface representing arrested sedimentation and variable cementation as trophic resources increased and conditions for carbonate production deteriorated ten cycle types are grouped into four major styles clay cycles mollusc cycles echinoid cycles and bryozoan cycles these are interpreted to form a lithological continuum from inner restricted terrigenous locales to outer open marine bryozoan colonized environments deepening upward cycles were profoundly sensitive to autogenic factors such as nutrient influx terrigenous content and turbidity hydrodynamic energy water temperature salinity and water depth manifested in this intracratonic setting although these cycles share a similar sedimentological motif and hydrodynamic energy based cycle capping process with open shelf epicratonic shallowing upward subtidal cycles of tertiary age they formed in a very different way reflecting the distinctive intracratonic environment in which they formed murray basin cycles preserve a record of relative sea level rise whereas open shelf cycles accumulated mostly during relative sea level fall

radiocarbon calibration curve spanning 0 to 50 000 years bp based on paired 230 th 234 u 238 u and 14 c dates on pristine corals abstract radiocarbon dating is the most widely used dating technique in the world recent advances in accelerator mass spectrometry ams and sample preparation techniques have reduced the sample size requirements by a factor of 1000 and decreased the measurement time from weeks to minutes today it is estimated that more than 90 percent of all measurements made on accelerator mass spectrometers are for radiocarbon age dates the production of 14 c in the atmosphere varies through time due to changes in the earth s geomagnetic field intensity and in its concentration which is regulated by the carbon cycle as a result of these two variables a radiocarbon age is not equivalent to a calendar age four decades of joint research by the dendrochronology and radiocarbon communities have produced a radiocarbon calibration data set of remarkable precision and accuracy extending from the present to approximately 12 000 calendar years before present this paper presents high precision paired 230 th 234 u 238 u and 14 c age determinations on pristine coral samples that enable us to extend the radiocarbon calibration curve from 12 000 to 50 000 years before present we developed a statistical model to properly estimate sample age conversion from radiocarbon years to calendar years taking full account of combined errors in input ages and calibration uncertainties our radiocarbon calibration program is publicly accessible at http www radiocarbon ldeo columbia edu along with full documentation of the samples data and our statistical calibration model

testing for astronomical forcing of cycles and gamma ray signals in outer shelf upper slope mixed siliciclastic carbonates upper oligocene new zealand abstract we evaluate whether outer shelf upper slope settings preserve a record of astronomical forcing using gamma ray logs from the upper oligocene upper chattian tikorangi formation onshore taranaki basin north island new zealand the formation is a siliciclastic carbonate succession deposited in outer neritic to upper bathyal depths at paleolatitudes of c 45os gamma ray and sonic logs calibrated to core indicate four lithofacies based on percent carbonate these are calcareous siliciclastic mudrock highest gamma ray values highly calcareous siltstones high gamma ray values very fine to fine siliciclastic muddy packstones intermediate gamma and winnowed very fine to medium grain dominated packstones and grainstones low gamma detrended gamma ray logs were tuned using minimal tuning methods 405 kyr long eccentricity cycle or where this was poorly developed the 100 kyr short eccentricity cycle with sedimentation rates tested statistically against astronomical forcing the tuned data show well developed long and short term eccentricity obliquity and a weak precessional forcing obliquity modulation is observed at the 1 2 myr scale one well and 175 kyr scale two wells the floating time scale was tied to the absolute time scale via published biostratigraphy the la2004 eccentricity solution the atlantic odp site 1264 18o record and the mi 1 isotope event at c 23 ma sea level fluctuations typically were moderate 20 to 40 m estimated from the 18o record the high gamma siliciclastic prone units formed during warmer and wetter phases and possibly slightly higher sea levels whereas the cleaner carbonates with abundant inner shelf derived fine carbonate developed during cooler drier phases and possibly slightly lower sea levels gamma ray logs from outer shelf upper slope settings provide valuable data sets for documenting the effects of astronomical forcing on the sedimentary record the study supports climate models for new zealand which predict generally increased precipitation with warming over the next 100 years the study appears to be the first to record astronomical forcing in the oligocene marine record of new zealand

the role of climate in stratigraphic patterns exhibited by late palaeozoic rocks exposed in kansas abstract late palaeozoic cyclothems of the midcontinental u s cannot be represented by a single ideal facies sequence rather they encompass a wide range of cycle types depending on their stratigraphic position the exposed late palaeozoic pennsylvanian and permian rocks of kansas as compiled by zeller 1968 can be divided into nine major lithofacies these lithofacies were ordered based on their times of greatest abundance through the section from oldest to youngest they attain their peak abundance in the following order 1 coal 2 gray mudrocks and sandstones 3 black mudrocks 4 limestones 5 cherty limestones 6 fossiliferous mudrocks 7 variegated mudrocks 8 evaporites and 9 variegated dolomitic siliciclastics climatically these nine lithofacies suggest a change from generally wetter at the base to generally drier at the top of the section this climatic trend was probably generated by a complex interaction of factors primarily driven by global tectonics climatic changes can be used to explain the five generally recognized types of lithofacies cyclothems in kansas and thus are a potential explanation for the changing stratigraphic patterns of the entire late palaeozoic time interval of kansas and perhaps elsewhere

punctuated aggradational cycles a general hypothesis of episodic stratigraphic accumulation according to the hypothesis of punctuated aggradational cycles presented here the stratigraphic record consists of small scale 1 5 m thick shallowing upward cycles pacs separated by surfaces marked by abrupt change to deeper facies this motif pervasive in time and environment is produced by relatively long periods tens of thousands of years of base level stability punctuated by geologically instantaneous relative base level rises of at least basin wide extent as basin wide lithologic time stratigraphic units pacs are fundamental to all aspects of stratigraphic analysis including correlation paleoenvironmental interpretation and paleogeographic reconstruction of several possible allogenic mechanisms for a pervasively cyclic stratigraphic record glacial eustasy driven by orbital perturbations is preferred the pac hypothesis is presented as a comprehensive model to be tested and modified by examination of the stratigraphic record from an episodic perspective

sea level and climatic controls on aptian depositional environments of the eastern russian platform abstract on the basis of a high resolution chronostratigraphic framework of the eastern russian platform a comparison between late barremian aptian global and regional sea level trends was performed the detailed evaluation of the long term 3rd order aptian sea level cycle results in the recognition of sea level and climate as controlling factors on depositional environments in the basin the rising part of the aptian sea level cycle lasted from the deshayesites tenuicostatusis zone to the deshayesites deshayesi zone and transgression is responsible for the local development of anoxia on the eastern russian platform the lower aptian bituminous shales and sheeted calcite concretions associated with the eastern russian platform are interpreted as being a regional manifestation of oceanic anoxic event oae 1a the late aptian cold snap that occurred during the early cretaceous greenhouse world coincided with a simultaneous global and regional sea level lowstand peak shallowing of the basin and the almost complete absence of sediments due to subaerial exposure in the studied region the global distribution of the lowstand gives clear evidence for sea level fluctuations and intrinsic climate control on sequences in the study area

paleoclimate controls on stratigraphic repetition of chemical and siliciclastic rocks climate is a primary control on sediment flux from continental sources into sedimentary systems in warm climates siliciclastic input is greatest under highly seasonal rainfall nonseasonal conditions favor formation of end member chemical rocks perennially wet climates are conducive to coal formation whereas dry climates produce carbonates and or evaporites stratigraphic repetition of siliciclastic and chemical rocks therefore appears to be related to paleoclimate cycles as well as to transgressive regressive events and tectonics

shallow marine record of orbitally forced cyclicity in a late triassic carbonate platform hungary abstract well preserved examples of milankovitch driven cyclicity in the triassic sedimentary record include triassic jurassic lake sedimentary cycles marine cyclic carbonates on small middle triassic platforms in the dolomite alps and off shelf facies equivalent to late triassic large passive margin platforms in contrast the late triassic hungarian shallow marine carbonate platform that formed on the southern margin of tethys records a far from perfect milankovitch eustatic signal these carbonate cycles contain subtidal skeletal wackestone packstone tidal laminites and paleosols the cycles include not only transgressive laminites the classic lofer cycles some cycles contain regressive laminites whereas other cycles have both transgressive and regressive laminites the stratigraphic successions do not show the clear bundling of five precessional cycles into larger eccentricity cycles the poor record of milankovitch sea level changes is interpreted to be due to many missed beats in the platform stratigraphy missed beats are evidenced by 1 caliches and paleosols and 2 thick amalgamated subtidal carbonates and may result from precessional sea level fluctuations either not flooding the platform or flooding it too deeply to allow shallowing up to sea le el in one precessional beat fourth order bundling of the cycles is weak with fewer than the typical 5 cycles 100 k y bundle and far less than 20 cycles for inferred 400 k y eccentricity bundles fischer plots of the hungarian cycles show third order bundling that matches aigner s 1992 sea level curve from the german muschelkalk basin but is less similar to the haq et al 1987 global sea level curve