facies architecture and depositional dynamics of the upper permian rangal coal measures bowen basin australia the upper permian rangal coal measures in the northern bowen basin australia accumulated during rapid basinal aggradation in a retroarc foreland basin setting they reflect peatland deposition towards the close of a long lived climatic regime that came to an abrupt termination at the permian triassic boundary which is well developed in the newlands mine highwall and adjoining borefield six lithofacies are represented in the newlands district 1 erosionally based vertically stacked ribbon and sheet like sandstone bodies up to 30 m thick and 1000 m wide 2 heterolithic lobes and wedges 3 interbedded siltstone and sandstone sheets 4 interlaminated claystone and coal stringers 5 laterally extensive bituminous coal sheets and 6 laterally extensive laminated carbonaceous siltstone sheets this facies assemblage is interpreted to correspond to six alluvial cold climate depositional environments 1 trunk river channels and crevasse feeder channels 2 levee bank proximal crevasse splay 3 distal splay overbank 4 marsh 5 peat mire and 6 floodbasin lake respectively the sequence architecture at newlands reveals that a prolonged period of peat deposition was progressively terminated by northward stepping lobes of fluvial sediment in the south and by lacustrine drowning in the north exceptionally well developed composite elongate crevasse splay microdeltas up to 26 m thick and 3000 m long indicate that crevassing was responsible for the localized emplacement of thick sediment packages on the proximal floodplain in the absence of active siliciclastic sedimentation peat mire environments expanded from the distal floodplain extending across abandoned depositional lobes the geometry of these deposits reflects in large part accommodation space developed by the compaction of the peat precursor of the thick and laterally extensive upper newlands seam sequential compaction of peat by clastic overburden controlled the nucleation and location of succeeding clastic packages the behavior of the peat under compactional load largely controlled the lateral facies mosaic and stacking pattern of depositional units on a district scale

tidal residual intertidal mudflat trim model and its applications to san francisco bay california abstract a numerical model using a semi implicit finite difference method for solving the two dimensional shallow water equations is presented the gradient of the water surface elevation in the momentum equations and the velocity divergence in the continuity equation are finite differenced implicitly the remaining terms are finite differenced explicitly the convective terms are treated using an eulerian lagrangian method the combination of the semi implicit finite difference solution for the gravity wave propagation and the eulerian lagrangian treatment of the convective terms renders the numerical model unconditionally stable when the baroclinic forcing is included a salt transport equation is coupled to the momentum equations and the numerical method is subject to a weak stability condition the method of solution and the properties of the numerical model are given this numerical model is particularly suitable for applications to coastal plain estuaries and tidal embayments in which tidal currents are dominant and tidally generated residual currents are important the model is applied to san francisco bay california where extensive historical tides and current meter data are available the model calibration is considered by comparing time series of the field data and of the model results alternatively and perhaps more meaningfully the model is calibrated by comparing the harmonic constants of tides and tidal currents derived from field data with those derived from the model the model is further verified by comparing the model results with an independent data set representing the wet season the strengths and the weaknesses of the model are assessed based on the results of model calibration and verification using the model results the properties of tides and tidal currents in san francisco bay are characterized and discussed furthermore using the numerical model estimates of san francisco bay s volume surface area mean water depth tidal prisms and tidal excursions at spring and neap tides are computed additional applications of the model reveal qualitatively the spatial distribution of residual variables

utility of coal petrology for sequence stratigraphic analysis abstract sequence stratigraphy seeks to predict the depositional architecture of sediments based on the principle that their superposition and lateral arrangement are largely determined by the rate at which accommodation is made below depositional base level relative to the supply rate of sediments depositional base level is generally correlated with sea level which in paralic peat coal deposits controls the position of the groundwater table above which oxidation ablation and erosion would occur the current late quaternary sequence is used to discuss some of the constraints on coal formation that stem from the interaction of short and long period modulations on sequence forming eustatic cycles the results show that the mid transgressive systems tract is unlikely to produce significant coal deposits which is supported by a survey of the relevant literature from eight different countries it reveals a bimodal distribution of coal deposits with the strongest mode being situated in the early transgressive systems tract while a broader secondary mode occurs in the early and mid highstand position this concentration contrasts with the complete absence of any significant coal deposits in the early and mid lowstand systems tract and only a low occupancy of the late highstand systems tracts the reasons for this distribution are briefly discussed and attention is drawn to the possible over stating of the coal forming potential of the late lowstand systems tract following a brief discussion of the sequence stratigraphic interpretation of coal measures emphasis is put on the application of sequence stratigraphy to the study of coal seams and their composition at various levels of petrographic detail while in low rank coals botanical affinities contribute much to the lithotype based analysis a genetic assessment of bituminous coal seams relies primarily on physical and chemical palaeo environmental signatures simple properties such as maximum coal thickness low detrital mineral content and maximum preservation of vitrinite particularly of telovitrinite define a good balance between the former rates of accommodation versus peat accumulation iso metamorphic variations in telovitrinite reflectance and its dispersion measured by the coefficient of variation have also contributed to the palaeo environmental interpretation this paper confirms the identification within coal seams of most of the sequence stratigraphically significant surfaces e g sequence and parasequence boundaries transgressive flooding and maximum flooding surfaces it also gives examples of some new ones referred to as accommodation reversal non marine flooding give up transgressive terrestrialisation and paludification surfaces some of these are specific to coal measures but the give up transgressive and accommodation reversal surfaces may have wider significance

utility of coal seams as genetic stratigraphic sequence boundaries in nonmarine basins an example from the gunnedah basin australia concepts of genetic sequence stratigraphy evolved in marginal marine basin settings where widespread episodic marine flooding events provide readily recognizable correlative surfaces that bound successive progradational clastic wedges however application of these concepts to nonmarine aggradational basins has been limited in cases where marine flooding surfaces are absent different criteria for sequence recognition are necessary this paper addresses the utility of regionally extensive coal seams as one type of sequence boundary peat accumulation and preservation as coal can only occur in the absence of significant clastic deposition formation of coal seams of regional extent requires processes capable of interruption in sediment supply at a basin wide scale and can define times of major reorganization in basin tectonics or climate regionally extensive coals can exhibit the essential attributes of sequence boundaries in many cases they are readily recognized and correlated by their unique seam signature or profile which is a function of the original peat forming plants and the physical and chemical conditions imposed during peat swamp evolution the unique seam profile also records numerous isochronous events further emphasizing their time equivalence and potential for accurate dating the concept that regionally extensive coals can serve as genetic stratigraphic sequence boundaries is well illustrated by coal seams from the gunnedah basin australia the hoskissons seam marks the initial change to nonmarine conditions in the basin from underlying deltaic and shallow marine depositional systems the stratigraphically higher breeza seam divides the nonmarine sequence into an underlying quartzose lacustrine bed load fluvial complex and an overlying volcanic lithic mixed load fluvial alluvial fan complex

depositional environments of lower pennsylvanian coal bearing siliciclastics of southeastern tennessee northwestern georgia and northeastern alabama u s a abstract in the cumberland plateaus of southeastern tennessee northwestern georgia and northeast alabama pennsylvanian strata are siliciclastics containing discontinuous coal seams above some of these coal seams the shale deposits contain fossils of marine or brackish fauna the entire sequence was deposited in an asymmetric foreland basin and is thickest in the southeast within this general trend there are locally thick deposits of lowermost pennsylvanian gizzard group sequences that mark subbasins conglomeratic sandstone members of the gizzard group are discontinuous and tend to be thicker in the subbasins in contrast conglomeratic to sandy units are more laterally continuous in the overlying crab orchard mountains group the pennsylvanian sequence overlies paleosols with subjacent freshwater neomorphosed shallow marine carbonates or siliciclastics of the uppermost mississippian pennington formation a provenance discrimination diagram indicates that pennsylvanian siliciclastics were derived from an orogenic source profile analysis of thick quartzose sandstone sequences indicates facies architectural elements and bounding surfaces characteristic of braided stream deposits a dominant southwest paleoflow direction is inferred from paleocurrent indicators in sandy braided and meandering stream deposits

a storm surge prediction model for the northern bay of bengal with application to the cyclone disaster in april 1991 abstract a numerical model for simulating and predicting tides and storm surges in regions that include areas of open sea combined with estuarine channels and intertidal banks is described the model makes use of modified depth averaged equations with a numerical scheme in which the solution of 1d equations for narrow channels 2d equations for the open sea and an approach to modeling inundation are combined within a unified framework this simplifies the construction of realistic models for complex coastal areas and deltas the model is applied to the northern shelf of the bay of bengal and the ganges delta including the coast of bangladesh devastated by a cyclone surge in april 1991 in which about 140 000 people died hindcast and forecast simulations of this event using forcing derived from a semianalytical cyclone model with data supplied by the joint typhoon warning center jtwc are described it is shown that the timing of cyclone landfall and its coincidence with high tide determine the area

sequence paleogeography and coal accumulation of the early middle jurassic in central qilian mountain belt muli basin qinghai province northwestern china the muli basin in the qinghai province located at the northeastern margin of the tibetan plateau is a jurassic coal bearing basin and is an important area for coal production in china recent explorations have revealed the presence of unconventional types of gases such as coalbed methane and gas hydrates we have investigated the sedimentology sequence stratigraphy and lithofacies paleogeography of this basin based on data from outcrop and borehole sections the coal bearing strata include the lower jurassic reshui and the middle jurassic muli and jiangcang formations lithofacies including conglomerates sandstones mudstones and coal were identified and have been interpreted to be formed in environments ranging from braided fluvial braided fluvial delta to lacustrine the preferred sites of coal accumulation are the interdistributary bays of lower delta plain and upper delta plain environments three types of sequence boundaries are recognized including regional unconformities between the lower jurassic and underlying triassic the basal surface of incised valley fills of thick bedded sandstones in the muli and jiangcang formations and the surfaces that mark abrupt depositional facies shifts four third order sequences were subdivided namely s1 s2 s3 and s4 in ascending order which correspond to the reshui formation the muli formation the lower member of the jiangcang formation and the upper member of the jiangcang formation respectively each sequence consists of a lowstand systems tract a transgressive systems tract tst and a highstand systems tract a series of sequence specific basin wide paleogeographic maps have been constructed based on contour maps of several lithological parameters including stratal thickness sandstone to mudstone ratio and mudstone thickness from s1 to s4 the muli basin experienced an evolution from a braided fluvial system to braided fluvial delta then to a lacustrine system showing a gradual deepening process thick coal seams with thickness greater than 3 5 m 11 5 ft were primarily developed in the delta plain environment where the rate of peat accumulation can be easily balanced by the rate of accommodation generation a five stage coal accumulation model has been summarized and the major coal seams mainly developed in the early and late tst of sequences s1 and s2

sequence stratigraphy of paralic coal bearing strata an overview abstract sequence stratigraphy arose in the late 1980s to fundamentally change the science of stratigraphy former practice of labeling formations and erecting stratigraphic columns gave place to a dynamic genetic stratigraphic analysis where the main concern is about understanding the history of sedimentation and to establish models able to predict facies born and mainly applied to an environment of petroleum prospecting and exploration sequence stratigraphy has gained entrance to other branches of sedimentary geology the present paper gives a short introduction to sequence stratigraphic concepts and shows an overview of its application on coal bearing strata two case studies one from the early permian coals of the parana basin brazil and one from the lower cretaceous coals of the western canada sedimentary basin illustrate the concepts

tidal circulation pattern on a tidal flat minas basin canada abstract although tidal flats have been studied extensively from the geomorphologic sedimentologic and stratigraphic standpoints there is little information related to the actual water circulation over them and its consequences on sediment transport and the corresponding changes in the geomorphology and sediment distribution the circulation induced by tidal forcing over a macrotidal flat in the minas basin bay of fundy canada is addressed while the geomorphologic and wind influences on the currents are also assessed tidal currents are reversible although the main axis orientation depends on the local morphology since a linear ridge runs along the main axis of the flat differences among sites are evidently associated with their position in relation to the ridge and also to the length of the inundation time forcing for the observed minor rotation to the right may originate in the surface water slope developed by the differential water filling of the area since wind was mostly calm and rarely exceeded 10 m s the observed circulation was the result of the interaction of the tidal wave and the general morphology of the intertidal flat

abrasion of detrital grain coating clays during sediment transport implications for diagenetic clay coats abstract detrital grain coating clay minerals have been identified as precursors of diagenetic grain coating clay minerals that inhibit quartz cementation and preserve good reservoir quality properties in deeply buried sandstone reservoirs between initial and final deposition detrital grain coats are likely to be affected by sediment transport processes to date it has not been demonstrated that detrital grain coating clays are able to survive sediment transport flume experiments simulating open channel flow conditions were performed using sediments from the ravenglass estuary cumbria uk where the distribution and characteristics of modern detrital grain coating clays is well established scanning electron microscopy and automated mineralogy techniques were employed to study the sediment before and after transport to determine the stability of the detrital grain coating clays the experimental results show that detrital grain coating clays are still present after sediment transport in turbulent flows with velocities up to 0 5 m s 1 the stability of the detrital grain coating clays was enhanced by 1 high initial clay coat coverage 2 turbulence characteristics of the flow and 3 entrapment of the detrital grain coating clays in bedforms this work documents the first quantifiable evidence that estuary derived detrital clay coats are routinely preserved after sediment transport clay coat rich estuarine sediments can therefore act as the source of clay coated grains found in cleaner estuarine sandstones and may even survive transport out into open marine settings

landslides in rio de janeiro the role played by variations in soil hydraulic conductivity landslides are natural processes triggered by complex relationships between many conditioning factors in rio de janeiro city intense rainstorms combined with steep slopes usually occupied by slums create favourable conditions for landslide generation in general slope failures are related to high positive pore pressures inside soil mantles which are associated with topographic hollows and hydraulic discontinuities inside the deep weathered profile this study aims to characterize the role played by spatial variations in saturated soil hydraulic conductivity ksat on landsliding in the papagaio basin 2 5 km2 triggered by intense rainstorms 250 mm in less than 2 days in february 1996 field measurements using the guelph permeameter were conducted along soil profiles up to 5 0 m depth around and inside landslide scars representing different geomorphological domains also soil physical properties grain size total porosity macroporosity microporosity etc were evaluated at the 87 sites where ksat was measured despite the many geological and pedological variations inside the basin including changes in lithology fracture density vegetation type and succession stage soil characteristics and weathering stage and human activities 94 of the ksat values varied by only two orders of magnitude 1 0 10 6 9 0 10 5 m s 1 however abrupt changes in ksat were observed along some of the soil profiles studied e g an increase of two orders of magnitude in only 0 30 m these hydraulic discontinuities may contribute locally to the development of high pore pressures during intense rainstorms leading to landsliding the results also suggest that different ksat variation patterns coexist inside the basin which should be considered in mathematical models of landslide prediction copyright 2004 john wiley sons ltd

coal in a carbonate sequence stratigraphic framework the upper permian heshan formation in central guangxi southern china microfacies and sedimentological analyses of the upper permian coal bearing heshan formation in the heshan coalfield of central guangxi suggest that these coal measures formed in a marine carbonate platform setting low volatile bituminous coals with very high organic sulphur overlie either palaeosols or locally developed cherts the petrography and geochemistry of the coals suggest formation in low lying mires in which marine influence increased upwards in the heshan and overlying dalong formations four third order sequences are described based on the recognition of four sequence boundaries higher order sequences within each of these third order sequences are also documented and within sequence iii coal seams are developed above higher order transgressive surfaces representing the deposits formed during the lag time between initial flooding of the platform and the onset of carbonate production in the heshan formation the coals with greatest thickness occur immediately above third order transgressive surfaces it is argued that in some coal bearing siliciclastic free marine carbonate platform settings accommodation creation rates and peat accumulation rates are balanced hence greater coal accumulation can be achieved at the transgressive surface rather than at the maximum flooding surface

universal similarity and the thickness of the viscous sublayer at the ocean floor experiments conducted on the oregon continental shelf in june 1979 indicate that the boundary layer flow at the seafloor was hydrodynamically smooth fine resolution velocity profiles are used to test the assumption that the flow behaved like a universally similar neutrally buoyant flow over a smooth wall the non dimensional thickness of the viscous sublayer is far more variable than has been observed in laboratory studies over perfectly smooth walls this variability may conceivably be related to upstream changes of surface roughness or to the presence of distributed roughness elements laboratory results indicate that the near bed flow adjusts extremely slowly to upstream roughness changes and suggests that flow near the sublayer in the ocean may be influenced by roughness changes as far as tens of meters upstream

facies relationships and cyclicity of high latitude late permian coal measures bowen basin australia the late permian moranbah coal measures are developed throughout the northern and central bowen basin eastern australia and are subject to large scale opencut coal mining activity they were deposited in a rapidly subsiding retroarc foreland basin during frequent base level changes contemporaneous compressive deformation and volcanism facilitated the supply of abundant volcanoclastic sediments resulting in rapid but punctuated basinal aggradation to the south and east transgressive regressive cycles were marked by the inter digitation of paralic shallow marine and alluvial strata lonestones dropstones are common within the marine deposits and are attributed to ice rafting indicative of a cold climate depositional regime two basin wide chronostratigraphic units the p tuff bed and the harrow creek superseam have been used to evaluate the facies architecture of the stratigraphic interval they enclose the lithofacies mosaic of the 25 75 m thick sequence has been examined by means of 26 widely distributed coreholes and two detailed district scale studies based around the moranbah goonyella and german creek minesites eight alluvial shallow marine facies associations have been recognised their architectural and temporal relationships allow the accurate reconstruction of the coal bearing depositional system two dissimilar stacked depositional systems tracts a organics and b clastics are recognised the p tuff bed is enclosed by facies of tract a forming a thick low ash coal bearing interval which was emplaced essentially synchronously across the basin it represents a time of clastic sediment starvation when basin wide peat mire accumulation prevailed four similar extensive coal bearing intervals within the moranbah coal measures are also considered to represent basin wide episodes of peat accumulation this pattern is in strong contrast to traditional views of coal measure development which argue that coals formed within a contemporary facies mosaic in which fluvial channels levees and crevasse splays were also represented the second depositional systems tract b is characterised by clastic packages dominated by large scale up to 4 km wide and 50 m thick sandstone bodies deposited by low sinuosity trunk river systems flanked by substantial crevasse splay deposits up to 3 km wide and 30 m thick it represents the product of catastrophic flooding events the cyclothemic succession of systems tracts a and b is interpreted in terms of eustatic sealevel cycles the tract a coal bearing intervals represent relative sealevel lowstands systems tract b represents relative sea level highstand with its lower interval at german creek to the south consisting of paralic and marine facies the cycles had durations in the order of 400 to 600 ky and are considered to represent 4th order sealevel cycles of the permian period

sedimentology and sequence stratigraphy of the lopingian late permian coal measures in southwestern china the lopingian coal measures of southwestern china were deposited within a range of facies associations spanning a spectrum of settings from fluvial to marine carbonate platform the transitional to terrestrial coal measures are dominated by siliciclastics but they also contain fifteen laterally extensive marine bands limestone beds and mudstone these bands act as marker horizons that enable correlation between fully marine and terrestrial facies examination of this range of facies and their sedimentology has enabled the development of a high resolution sequence stratigraphic framework set against the established backdrop of second order lopingian transgression sixteen fourth order sequences and three composite sequences third order are recognized results show that in the composite sequences peat accumulation in the seaward parts of the study area predominantly correlates with early transgressive sequence sets tss while in more landward areas it correlates with the middle tss to late highstand sequence sets hss differences in peat accumulation regimes within the sequence stratigraphic framework are attributed to variations in subsidence and background siliciclastic input rates in different depositional settings with these combining to produce differences in the rate of accommodation change the preservation of coal resources in the middle to late hss in this area was most likely related to the rise of the regional base level throughout the lopingian

deltaic depositional systems coal distribution and quality and petroleum potential permian gunnedah basin n s w australia abstract upper permian sediments of the lower black jack formation were deposited as a major delta system in the gunnedah basin a foredeep of the rising new england fold belt two principal depositional units are recognized in the lower black jack formation the lower delta plain facies and the shallow marine facies a third but minor depositional unit the western bed load fluvial facies is correlative with the upper part of the shallow marine facies geometry of the framework sandstones indicates that the lower delta plain facies was deposited in a combination of fluvial dominated and wave modified delta systems and that the shallow marine facies was deposited in a tide dominated system sediment source was predominantly from the northeast except for the western bed load fluvial facies which was derived from the lachlan fold belt region to the west the lower delta plain facies was deposited during a major episode of delta construction principal components recognized in drillcore are distributary channel crevasse splay and splay subdelta interdistributary bay lagoon and marsh deposits transgression of the delta possibly initiated by a major eustatic sea level rise led to deposition of the shallow marine facies this facies consists chiefly of beach barrier beach tidal sand ridge and tidal channel fill deposits subsequent lowering of sea level was accompanied by deposition of the western bed load fluvial facies this facies consists predominantly of upward fining fluvial channels which display considerable marine reworking toward the basin centre a vast coal swamp was established rapidly after the marine conditions regressed and is represented by the hoskissons coal member coals of commercial interest are developed within the lower delta plain facies and above the shallow marine facies the lobate geometry of the coal deposits in the lower delta plain facies mirrors the geometry of the framework sandstones and indicates a deltaic origin for coal formation two mechanisms for coal formation are recognized in the lower delta plain facies thick laterally extensive coals such as the melvilles coal member are thought to have originated as blanket peats following delta abandonment thin discontinuous coals formed in interdistributary depressions during active deltaic progradation coal above the shallow marine facies is contained in one major seam the hoskissons coal member this seam probably formed mostly as a back barrier or lagoonal peat depositional setting strongly influenced coal quality isoash trends for the melvilles coal member suggest a marginal marine influence during peat accumulation ash content of the hoskissons coal member has a similar distribution to the percentage of sandstone in the underlying shallow marine facies potential exists for petroleum accumulation in the lower black jack formation suitable reservoir rocks are present in the lower delta plain and shallow marine facies underlying prodelta facies are potential source rocks

origin of large scale crossbeds in the late permian coal measures of the sydney and bowen basins eastern australia abstract theories proposed for the origin of large scale crossbeds may be generalised into two main categories the first suggests the large sigmoidal shape of the sediment layers results from variable differential compaction during and after deposition whereas the second infers that the high angle of the crossbeds is the result of primary depositional processes britten 1983 has proposed that large scale inclined strata may be produced according to his cide model whilst mallett 1983 has suggested that such structures are produced by channel automigration parbury 1976 and conaghan 1981 both proponents of the primary depositional model interpret the large scale inclined strata as foreset beds of a gilbert type delta prograding into deep 50 m water depth lakes within which floating islands produce allochthonous deposits from hydroponic vegetation marchioni 1976 1982 however envisages that the large scale inclined strata are epsilon crossbeds which have tilted during differential subsidence of peat swamps over which active channel systems have encroached nine kilometers of almost continuous high wall exposures have been studied in the moura kianga coal mine of the southeastern bowen basin and it is concluded that none of the above mentioned processes can explain the present configuration of sedimentary layering observed in these high walls at the moura kianga coal mine it is proposed that there the high angle large scale inclined strata have originated as primary features associated with a crevasse sub delta subsidence in excess of vegetation accumulation within the peat swamp provides the mechanism whereby a shallow lake developed and into which a crevasse sub delta was deposited similar processes have been described by coleman and prior 1980 from the mississippi delta

sedimentary and botanical factors influencing peat accumulation in the mississippi delta the holocene mississippi delta system consists of six cyclic deltaic packages associated peat deposits are planar and eutrophic and accumulate in areas abandoned by deltaic sedimentation peats that formed in large scale interlobe basins are the subject of this paper true peats 75 organic matter average 81 7 organic matter on a dry weight basis controls on quality and lateral distribution of peat deposits are botanical parent material the balance between subsidence and accretion rates detrital clastic influx and marine inundation botanical parent material inferred from 13 c signatures and microtome sections is always freshwater originating either in forested swamps or under herbaceous floating mats sphagnum spp is essentially absent in order for peat to accumulate rates of accretion and subsidence must balance long term subsidence rates in the study area increase from about 0 10 to 0 30 cm a 1 over a distance of 40 km from upper to lower delta plain subsurface accretion rates for true peats at a depth of 2 3 m however average about 0 05 cm a 1 renewed coarse detrital clastic influx terminates peat accumulation the largest quantities of true peat are found together with relatively large amounts of organic poor clastic sediments mostly clays delta lobe abandonment and consequent coastal erosion causes salt water intrusion into freshwater environments resulting saline marsh sediments have maximum organic matter contents of 35 in a transgressive setting these may overlie older high quality low ash freshwater peats leaching experiments reveal the presence of water soluble salts in both transgressed and fresh peats leaching reduces ash values by 1 5 to 1 3 suggesting that such losses may occur during early diagenesis it is possible that some commercial coal seams originated in analogous interlobe environments where leaching and possibly silica mobilization reduced the originally high ash contents to acceptable levels

maastrichtian paleocene foreland basin stratigraphies western canada a reciprocal sequence architecture palynological and magnetostratigraphic chronostratigraphic correlations of lower maastrichtian to paleocene strata along an east west western canada basin transect allow for the recognition of a reciprocal sequence architecture in nonmarine strata reference sections include three canadian continental drilling program cretaceous tertiary boundary project core holes and outcrops in alberta southern saskatchewan and north central montana the spatial and temporal position of the third order sequences provides evidence for the correlation of proximal sector regional disconformities and sedimentary wedges with distal sector sedimentary wedges and regional disconformities respectively the boundary between the two sectors is represented by a hingeline which separates the foreland basin syncline from the peripheral bulge the stratigraphies defined by reciprocal third order sequences are complicated by fourth order boundaries developed within proximal sedimentary wedges and with no correlative distal strata these results support tectonic control on foreland basin sedimentation a model for interpreting the various types of sequences in terms of foreland basin evolution vertical tectonics and orogenic cycles is provided it is argued that nonmarine sequence boundaries times of maximum uplift in the foreland region may be expressed as disconformities incised valleys top of mature paleosol levels or base of fluvial channels whereas nonmarine equivalents of marine maximum flooding surfaces times of maximum basinal subsidence may be indicated by extensive coal seams and or lacustrine sediments resume les correlations palynologiques magnetostratigraphiques et chronostratigraphiques des strates echelonnees du maastrichtien inferieur au paleocene le long du transect est ouest du bassin de la cordillere occidentale au canada permettent la reconnaissance d une ordonnance architecturale de sequences reciproques dans les strates continentales les coupes de reference incluent trois trous de forage carottes du canadian continental drilling program cretaceous tertiary boundary project et des affleurements localises en alberta dans le sud de la saskatchewan et dans le centre nord du montana la position spatiale et temporelle des sequences de troisieme ordre plaide pour la mise en correlation des discordances regionales et des depots sedimentaires en coin dans le secteur proximal avec les depots sedimentaires en coin et les discordances regionales dans le secteur distal respectivement une ligne de jonction represente la limite entre les deux secteurs qui separe le bassin d avant pays en forme de cuvette du bombement peripherique les stratigraphies definies par les sequences de troisieme ordre reciproques sont embrouillees par les limites de quatrieme ordre developpees au sein des depots sedimentaires en coin proximaux sans la presence de strates distales correlatives ces resultats appuient la these d un controle tectonique sur le bassin sedimentaire d avant pays on presente ici un modele interpretant les divers types de sequences en termes d evolution d un bassin d avant pays de tectonique verticale et de cycles orogeniques nous tentons de demontrer que les discordances les vallees entaillees les horizons sommitaux de paleosols matures ou la base des chenaux fluviaux peuvent aider a definir les limites des sequences continentales periodes de soulevement maximum dans la region de l avant pays tandis que les couches de charbon etendues et ou les sediments lacustres representent plutot les equivalents continentaux des aires d inondation maximale periodes de subsidence maximum du bassin traduit par la redaction catuneanu and sweet 703

field investigation of ridge runnel dynamics on an intertidal mudflat flow parallel linear ridge runnel r r bedforms composed of mainly cohesive sediments have been investigated at an intertidal site located at hills flats in the severn estuary uk it is argued that the sequences of sand mud laminae in the ridge sediments indicate strongly that r r are depositional bedforms faint r r topography scoured in the underlying soft bedrock and parallel rows of coarser particle now found at the base of ridges are evidence of secondary vortices that may have provided a catalyst for mud ridge growth bed shear stress remains below the erosion threshold for all but the most recent and weak surficial mud deposits which are removed by evorsion mechanical erosion by turbulent flows that may also carry sand and or gravel during spring tidal flow ca 60 cm s differences in flow characteristics between ridges and runnel are minor corrasion to erode or be eroded by abrasion by sparse coarse sediment largely prevents net deposition in the runnels over time a slight imbalance between mud deposition and erosion rates allows slow growth of the ridges suggesting that these mudflats may be especially sensitive to slight changes in the local hydrodynamic regime and or sediment supply

fluvial sequence stratigraphy the wapiti formation west central alberta canada abstract outcrop exposures and high resolution subcrop data allow the description and mapping of four stratigraphic discontinuities in the fully nonmarine strata of the campanian maastrichtian wapiti formation western interior foreland basin alberta canada this framework defines four unconformity bounded depositional sequences a d based on sequence stratigraphic methodology well log patterns and facies analysis in ascending order sequence a records the transition from the underlying marine facies of the puskwaskau formation into the wapiti fluvial facies and consists of strongly progradational and aggradational stacking patterns sequences b and c show a similar pattern of basal amalgamated channel fill deposits that grade upwards into floodplain dominated strata finally sequence d is dominated by channelized sediments and extensive overbank facies an aggradational stacking pattern suggests deposition under high accommodation conditions maximum flooding surfaces are interpreted within fine grained deposits in the upper portions of sequences c and d they are tied to regionally extensive coals that accumulated more than 250 km away from the coeval shoreline this study provides new evidence that major coal seams may represent the extension of marine maximum flooding surfaces into the downstream controlled fluvial realm furthermore the new stratigraphic framework of subaerial unconformities and maximum flooding surfaces provides the means of subdividing the previously undifferentiated fully nonmarine wapiti formation into depositional sequences and component systems tracts

linked sequence stratigraphy and tectonics in the sichuan continental foreland basin upper triassic xujiahe formation southwest china abstract intracontinental subduction of the south china block below the north china block in the late triassic resulted in formation of the transpressional sichuan foreland basin on the south china block the upper triassic xujiahe formation was deposited in this basin and consists of an eastward tapering wedge of predominantly continental siliciclastic sedimentary rocks that are up to 3 5 km thick in the western foredeep depocenter and thin onto the forebulge and into backbulge depocenters five facies associations a e make up the xujiahe formation and these are interpreted respectively as alluvial fan transverse and longitudinal braided river meandering river overbank or shallow lacustrine and deltaic deposits this study establishes a sequence stratigraphic framework for the xujiahe formation which is subdivided into four sequences sq1 2 3 and 4 sequence boundaries are recognized on the basis of facies tract dislocations and associated fluvial rejuvenation and incision and systems tracts are identified based on their constituent facies associations and changes in architectural style and sediment body geometries typical sequences consist of early to late transgressive systems tract deposits related to a progressive increase in accommodation and represented by facies associations a b and c that grade upwards into facies association d regionally extensive and vertically stacked coal seams define maximum accommodation and are overlain by early highstand systems tract deposits represented by facies associations d e and c late highstand systems tract deposits are rare because of erosion below sequence boundaries sequence development in the xujiahe formation is attributed to active and quiescent phases of thrust loading events and is closely related to the tectonic evolution of the basin the sichuan basin experienced three periods of thrust loading and lithospheric flexure sq1 lower sq2 and sq3 two periods of stress relaxation and basin widening upper sq 2 and sq3 and one phase of isostatic rebound sq4 paleogeographic reconstruction of the sichuan basin in the late triassic indicates that the longmen mountains to the west consisting of metamorphic sedimentary and pre neoproterozoic basement granitoid rocks was the major source of sediment to the foredeep depocenter subordinate sediment sources were the xuefeng mountains to the east to backbulge depocenters and the micang mountains to the northwest during the late history of the basin this study has demonstrated the viability of sequence stratigraphic analysis in continental successions in a foreland basin and the influence of thrust loading on sequence development

the sequence stratigraphic concept and the precambrian rock record an example from the 2 7 2 1 ga transvaal supergroup kaapvaal craton abstract sequence stratigraphic concepts are applied to the 2 7 2 1 ga transvaal supergroup which constitutes the sedimentary floor to the bushveld igneous complex the transvaal succeeds the foreland fill of the witwatersrand supergroup and in its lowermost portions is partly synchronous with the ventersdorp supergroup lavas that followed upon the witwatersrand sediments in the stratigraphic record the unconformable contacts at the base and the top of the transvaal supergroup mark significant changes in the overall tectonic setting which qualifies them as first order sequence boundaries sedimentation within the transvaal basin was controlled by cycles of extensional and or thermal subsidence resulting in the accumulation of sequences separated by stages of base level fall generating sequence bounding subaerial unconformities the transvaal first order sequence is subdivided into five second order unconformity bounded depositional sequences i e the protobasinal black reef chuniespoort rooihoogte timeball hill and boshoek houtenbek sequences the span of time of these second order sequences averaging 130 ma is much longer than the duration of the second order phanerozoic cycles which is explained by the less evolved and thus slower plate tectonic processes that dominated the late archaean early proterozoic times each transvaal second order sequence preserves a variable number of systems tracts mainly as a function of the strength of the erosional processes associated with the ravinement surfaces and subaerial unconformities in a complete succession a sequence would include a basal lowstand systems tract lst followed by transgressive tst highstand hst and falling stage fsst systems tracts the protobasinal and rooihoogte timeball hill sequences only preserve the lst and tst due to the strong post depositional erosion the black reef sequence is composed of lst tst and hst the chuniespoort sequence preserves the tst hst and fsst but lacks the lst due to ravinement erosion the boshoek houtenbek sequence develops the complete succession of systems tracts common features may be emphasized between the same types of systems tract developed within different sequences the lst includes high energy coarse prograding facies such as alluvial fans and fan delta systems that fill the irregularities of the pre existing topography and lead to the peneplanation of the depositional areas the tst may be recognized from retrogradational stacking patterns that are associated with the transgression of marine environments the hst marks the normal regression of the previous marine environments which assumes coeval aggradation of fluvial and basinal facies within an overall progradational framework the fsst would normally include only basinal facies age equivalent with the correlative subaerial unconformities in our case study the stages of base level fall resulted invariably in fully nonmarine environments within the transvaal area generally leading to the development of subaerial unconformities in particular circumstances the nonmarine environment may still accumulate and preserve fluvial alluvial fan or lacustrine sediments as a function of the relative position between topography and local equilibrium profiles and base levels the interpretations of base level rise and fall resulting from the application of the sequence stratigraphic concept to the 2 7 2 1 ga transvaal supergroup enable estimation of sea level changes during deposition of this succession with an understanding of local tectonic conditions on the kaapvaal craton and of coeval sedimentation elsewhere in africa eustatic and relative sea level changes and variation in continental freeboard conditions may be suggested for the transvaal supergroup

sequence stratigraphy and coal accumulation of lower cretaceous coal bearing series in erlian basin northeastern china the detailed depositional systems and basin evolution of lower cretaceous coal bearing strata in the erlian basin of northeastern china were analyzed based on extensive borehole and outcrop data a total of 7 facies associations are interpreted and consist of 14 distinct lithofacies with lithologies including conglomerates sandstones siltstones mudstones shales and coals five third order sequences were recognized and their internal lowstand transgressive and highstand systems tracts were defined based on six key sequence stratigraphic boundaries these boundaries were represented by regional unconformities basal erosional surfaces of incised valley fills interfluvial paleosols and abrupt depositional facies reversal surfaces sequences i v correspond to the rift initiation stage the early rift climax stage the late rift climax stage the immediate postrift stage and the late postrift stage of the basin respectively the preferred sites for coal accumulation were braided fluvial delta plain meandering fluvial delta plain and littoral shallow lake environments the major coal seams formed during the early and late transgressive systems tract of sequences iii iv and v which were well developed in the eastern northeastern and northeastern parts of the erlian basin respectively three coal depositional models were summarized in the sequence stratigraphic framework including types 1 2 and 3 corresponding to the newark type newark richmond type and richmond type respectively these coal depositional models were closely related to the basin evolution these results could provide preferred depositional environments and favorable areas of coal and coalbed methane cbm for the exploration and development of coal and cbm in the erlian basin with the jiergalangtu huolinhe baiyinhua and a nan sags recommended as the key sags