discontinuity surfaces clinoforms and facies architecture in a wave dominated shoreface shelf parasequence abstract detailed outcrop analysis of a wave dominated shoreface shelf parasequence exposed in the book cliffs utah reveals minor stratigraphic discontinuities which define clinoforms two types of discontinuity are recognized each with a distinctive lithologic character and geometry nondepositional discontinuities are marked by an abrupt decrease in the thickness and amalgamation of storm generated event beds and are interpreted to record hiatuses in sedimentation these discontinuities define clinoforms with a concave upward geometry that dip gently 0 02 0 58 over distances of 800 6000 m down depositional dip erosional discontinuities are marked by an abrupt increase in event bed amalgamation grain size and sand content and are interpreted as enhanced storm wave scours these discontinuities define more steeply dipping 0 22 0 95 concave upward clinoforms that extend over 100 1600 m down depositional dip and 500 1500 m along depositional strike the distribution and amalgamation of minor stratigraphic discontinuities defines linear zones of distinctive facies architecture that are oriented parallel to the paleoshoreline trend using the simple assumption that the shoreface shelf equilibrium profile remained approximately constant for each type of discontinuity throughout shoreface migration the bruun rule intra parasequence facies architecture can be speculatively interpreted in terms of shoreline trajectory which reflects the balance between sediment supply and accommodation the resulting interpretations support the notion that shoreline trajectory exerts a strong control on intra parasequence facies architecture and preservation of the shoreface shelf profile

field and seismic images of sharp based shoreface deposits implications for sequence stratigraphic analysis abstract sharp based shoreface sandstones are of considerable interest because of their potential as hydrocarbon reservoirs and because they play an important role in the stratigraphic analysis of basin fills the sharp based shoreface sandstones studied herein are upper jurassic kimmeridgian tithonian and exposed along the coastal cliffs of the dover strait in northwestern france these series consist of tens of meter thick alternations of sandstones bodies and organic rich shales that can be correlated for over 30 km along coastal cliff exposures and tied to high resolution ca 1 m of sediment marine seismic profiles obtained several hundred meters offshore the units described here comprise two sharp based sandstone bodies each is composed of a basal progradational set of shoreface parasequences overlain by a progradational aggradational shoreface succession each sharp based sand body lies on a marine regressive surface of erosion and is truncated by a marine transgressive surface of erosion which in turn is overlain by a thin retrogradational ravinement lag or coarse grained planar laminated bedset the two progradational packages are separated by a third surface a subaerial exposure surface that is interpreted as a sequence boundary two distinct types of seismic units referred to as type a and type b have been identified in the study area seismic unit a has conformable upper and lower boundaries and parallel aggradational configurations seismic unit b is characterized by downlap and toplap boundaries and simple or compound sigmoid and oblique tangential progradational configurations a single sharp based shoreface sandstone body makes up the type b unit and typically consists of two compound superimposed progradational sets b1 b2 the lowermost set b1 corresponds in the field to the progradational set sensu stricto whereas b2 corresponds to a progradational aggradational set b1 and b2 are separated in outcrop by a sequence boundary these observations led us to reevaluate the sequence stratigraphic interpretation of sharp based shoreface sandstones it is proposed here that complete single sharp based shoreface sandstones bodies can be separated into two different systems tracts 1 a progradational set b1 seismic body at the base which corresponds to the forced regressive wedge systems tracts frwst of hunt and tucker 1992 and 2 a progradational aggradational set b2 at the top above the sequence boundary which corresponds to the lowstand systems tract lst of posamentier et al 1992 a complete sharp based shoreface sandstone body is bounded below the frwst by a regressive surface of marine erosion caused by the downward shift of wave base and by a transgressive surface of marine erosion or ravinement surface at the top of the lst

intra shoreface erosion in response to rapid sea level fall depositional record of a tectonically uplifted strand plain pacific coast of japan this study documents lowering of the surf zone i e the upper shoreface leading to intra shoreface erosion following two rapid relative sea level falls along a tectonically uplifted coast during the holocene and the characteristics of the resultant prograding shoreface deposits these findings are based on high resolution analysis and radiocarbon dating of three new drill cores obtained from the kujukuri strand plain pacific coast of eastern japan combined with previously published borehole data and information on modern shoreline profile adjustments a shallowing upward sandy succession composed of lower and upper shoreface facies foreshore and backshore facies was recognized in the drill cores two rapid falls in relative sea level at 2ae 3t o 2ae6 and 1ae 8t o 2ae0 ka are recorded by downstepping of the base of the foreshore facies and farther seawards by the lowering of an erosional boundary between the upper and lower shoreface facies superimposed bed profiles of an adjacent modern beach define an envelope the base of which reflects shore normal migration of longshore bars and troughs the base of the envelope represents an erosional surface that divides the surface mobile layer above from preserved deposits beneath the surface is concave upwards and steeper than the mean beach profile and exhibits a flat platform approximately at the lower limit of the upper shoreface equating to the storm surf zone the seaward transition of this surface rather than the mean equilibrium profile controls the metre scale to decimetre scale internal structure of the kujukuri shoreface deposits depositional models for sea level fall based on an exponential equilibrium profile do not adequately account for the presence and migration of longshore bars and troughs

environmental interpretation and a sequence stratigraphic framework for the terminal proterozoic ediacara member within the rawnsley quartzite south australia abstract fossils of the ediacara biota are confined to preservational windows in the ediacara member of the rawnsley quartzite pound subgroup from the flinders ranges south australia the base of the ediacara member is a type 1 sequence boundary incised into the partly lithified chace quartzite member of the rawnsley quartzite the ediacara member and the upper half of the rawnsley quartzite comprise the rawnsley depositional sequence bounded above by the early cambrian uratanna depositional sequence the rawnsley sequence developed over an erosional surface cut into the chace quartzite member with some 250 m of relief southeasterly directed palaeovalleys are filled with a sequence of massive sandstone and laminated siltstone passing up into well bedded sandstone at lowstand local channels were filled by massive sand the highstand systems tract consists of several parasequence sets of laminated siltstone and channelized amalgamated massive sandstone overlain by interbedded siltstone and sandstone grading up into well bedded clean sandstone impressions of soft bodied ediacaran organisms are preserved above the valley fill facies on sandstone partings within upward shoaling delta front environments between storm and fairweather wavebase the ediacara member is in places conformably overlain by up to 500 m of sandstone of the same lithofacies as those underlying the member distinctive microbial mat bound sand laminae described as petee structures are characteristic of the rawnsley quartzite above and below the ediacara member during deposition of the ediacara member colonization of the deeper substrates by microbial mat communities enabled preservation of the ediacara biota the erosional surface at the base of the ediacara member is one of at least four incision events recorded in the terminal proterozoic and early cambrian succession of the adelaide geosyncline the similarity of incision filling lithofacies of the rawnsley and uratanna sequences has in condensed sections led to confusion between the depositional sequences characteristic trace and body fossil assemblages provide the only clear distinction between depositional cycles spanning the proterozoic cambrian boundary

a retreating fan delta system in the neoproterozoic chattisgarh rift basin central india major controls on its evolution a thick wedge of immature siliciclastics characterizes the basal part of the basin fill succession in the eastern part of the neoproterozoic chattisgarh basin it comprises a mosaic of mass flow deposited conglomerate and pebbly sandstone coarse grained sandy braided stream deposits wave lag pebble sheets high energy wave dominated foreshore and upper shoreface facies and wave and tide dominated lower shoreface facies the succession is characterized by strong lateral and vertical facies variation the facies associations and stacking pattern point to the development of an alluvial fan to fan delta complex with outbuilding of delta lobes onto a high energy shallow marine shelf via a high gradient narrow delta plain the delta front deposits of coarse grained sand interfinger and grade into prodelta mud in the seaward direction the dominance of coarse grained sandy detritus with a high content of fresh feldspar grains points to mechanical weathering of granites and gneisses of the cratonic basement and a semiarid climate the sediment caliber and the climate exerted a major control on the facies and on processes of sediment transfer from the fan to the shelf a critical balance between progradation aggradation and retrogradation controlled the evolution of delta successions within an overall transgressive regime related to the extension of a cratonic rift basin repeated fault controlled uplift of the source followed by subsidence and transgression generated multiple fining upward cycles and a retreating fan delta system the marked variations in thickness of the delta succession and the stacking pattern in different measured profiles reflect the overriding tectonic controls on delta evolution the accumulated fault displacement in active sectors created higher accommodation and thicker delta sequences intermittent uplift of fault blocks exposed fresh bedrock to mechanical weathering generated a large amount of detritus and resulted in forced regressions repeatedly disrupting the fining upward pattern the controls of source rock lithology or climate were of secondary importance to tectonic effects retreating fan deltas are rarely reported and may be a stratigraphic response of marine connected rift basins at the early stage of extension the delta stratigraphy is analogous to the submarine fan stratigraphy in the case where basin shales act as hydrocarbon sources the fan deltas are potential hydrocarbon reservoirs the coarse grained lobes can be excellent reservoirs with the enclosing prodelta muds acting as seals to vertical migration of hydrocarbon the coarse grained deposits of the delta plain and proximal delta front occurring as laterally coalesced large sand bodies blanketed by transgressive prodelta mud might also form good reservoirs

sea level changes and the continental freeboard concept general principles and application to the precambrian abstract eustatic sea level changes reflect variation in ocean water or ocean basin volume or changes to the hypsometric curve which is in itself geographically and chronologically variable freeboard the elevation of a continent above mean sea level is closely related to changes in both sea level and this curve relative sea level change occurs due to tectonism sediment supply compaction and eustatic movements hydroisostatic compensation modifies first order sea level variation by about one third short term and localised change in sea level may be ascribed to waves and tides storm winds hurricanes tsunamis and catastrophic sediment slumps wide gently sloping shelves with more uniform circulation systems inferred for the precambrian may have enhanced tide and wave induced sea level changes salinity and water temperature mutually dependent affect eustatic and relative sea levels elevated water temperatures postulated for the early precambrian would have been offset partly by enhanced evaporation and increased salinity longer term changes in sea level regional or eustatic may result from orogenesis volcanism sediment supply compaction and loading isostasy and thermal mechanisms glacioeustatic changes compounded by related salinity variations moderated by glacioisostatic effects and modified by hydroisostasy reach ca 150 m isostatic rebound in interglacial episodes will produce rapid and marked sea level drops up to ca 250 m this is a localised effect and contrasts with the global enhancement of sea level during interglacials however evidence for glaciation in the geological record is limited also for most of the precambrian sea level oscillations in non glacial episodes may reflect flexure of tectonic plates change up to 100 m or changes to earth s geoid 250 m eustasy up to 350 m will result from change to ocean basin volume due to variation in mid ocean ridge volume and spreading rates also related to supercontinent amalgamation and breakup intra plate hot spots and oceanic plateaus will change eustatic sea level more slowly up to 100 m higher heat flow in the archaean and concomitant enhanced volcanism suggest that these were important influences on precambrian sea levels the exponential elevation age relationship observed for phanerozoic oceanic lithosphere may have been more significant in the precambrian as continental crust grew from ca 4 0 ga declining heat flow and concomitant deepening of the ocean basins maintained an approximately constant freeboard during the archaean although still hotly debated there is strong support for episodic growth models inferring rapid formation of continental crust near the archaean proterozoic boundary this would imply constant freeboard conditions after 2 5 ga as well the constant freeboard model however is one based on average global conditions freeboard was still subject to geographic and chronologic variation and these potential changes lie within the bounds of eustatic and relative sea level change continental crustal growth the freeboard concept and sea level changes are thus interdependent variables in precambrian geology

lowstand shorefaces transgressive incised shorefaces and forced regressions examples from the viking formation joarcam area alberta abstract in the joarcam beaverhill lake area of alberta there are three long 40 km narrow 5 km sandbodies in the late albian viking formation they are surrounded by offshore open marine mudstones and have previously been interpreted as offshore bars however the sandbodies are both underlain and overlain by erosion surfaces joarcam is the only field with abundant cores and the sandbody shows a sandier upward and coarsening upward succession all three fields have recently been reinterpreted in the literature as lowstand shoreface deposits but the order in which they formed remains controversial our well log cross sections suggest that the lindbrook shoreface was the first to form at a time of maximum lowstand of sea level it was truncated as sea level began to rise and the lindbr ok transgressive surface of erosion tse has been traced into the erosion surface that underlies joarcam joarcam can therefore be interpreted as a shoreface incised during a pause in an overall transgression both the lindbrook and joarcam shorefaces appear to be truncated by the regressive surface of erosion rse that underlies beaverhill lake this suggests that beaverhill lake is the youngest of the shorefaces and implies a second major fall of relative sea level the lowstand shorefaces tend to be thinner because of reduced accommodation space during sea level fall they tend to prograde farther beaverhill lake about 23 km because of abundant sediment supply at lowstand but consist largely of sandstone directly overlying the rse at beaverhill lake the shoreface sediments prograded at least 10 km before any mud in the offshore to shoreface transition was preserved by contrast the transgressive shorefaces tend to be thicker because of accommodation space created during transgression however they tend not to prograde so far joarcam up to 13 km possibly because of reduced supply of sediment to the shoreface during transgression the two proposed episodes of lowering of relative sea level are tentatively correlated with the two separate valley incisions documented at crystal about 90 km to the southwest these incisions represent type 1 sequence boundaries but the boundaries are not continuous regressive surfaces of erosion from crystal to the joarcam beaverhill lake area in both cases the falling stage rses have been eroded by the subsequent tses these tses are the only surfaces preserved between the incised valleys and the lowstand shorefaces

pb sr and nd isotope systematics of metavolcanic rocks of the hutti greenstone belt eastern dharwar craton constraints on age duration of volcanism and evolution of mantle sources during late archean abstract the hutti greenstone belt hosting major gold mines is made up of tholeiitic basalts felsic volcanic rocks and sediments metamorphosed to amphibolite facies and surrounded by granitoid rocks predominantly of granodiorite in composition the granitoid rocks show intrusive contact relationship at places along the eastern and northern margins of the belt while such relationships could not be observed along the western margin as it is covered by soil the tholeiitic basalts have flat to moderately lree enriched chondrite normalized ree patterns and show depletion in nb relative to morb the hutti metabasalts define a collinear array in the rb sr isotope evolution diagram with a slope corresponding to an age of 2706 130 ma the higher uncertainty is due to scatter caused by mobility of rb and sr during metamorphism and low temperature hydrothermal alteration in the 206 pb 204 pb vs 207 pb 204 pb diagram the metabasalts define a collinear array corresponding to an age of 2637 150 ma with significant scatter indicating that pb was also mobilized by the post crystallization alteration processes the sm nd isotope system in the hutti metabasalts has been least disturbed giving an isochron age of 2662 81 ma which is suggested as the age of formation of their precursors combined with the published u pb shrimp ages on zircons from the felsic volcanic rocks it is inferred that the hutti greenstone belt formed over a period of 86 ma the major greenstone belts of the eastern dharwar craton have evolved coevally at ca 2700 ma ago and are older than the surrounding granitoid rocks the metabasalts have e nd values of 1 4 to 3 0 and e sr values of 23 4 to 2 0 and plot close to the mantle array they were derived from long term lree depleted mantle source the felsic volcanic rocks have e nd values of 1 3 and 1 4 and e sr values of 30 6 and 89 3 respectively their magmas were derived from older continental crustal sources

sea level changes an integrated approach sea level changes an integrated approach in october 1985 sepm sponsored a four day conference entitled sea level changes an integrated approach the purpose of the conference was to provide a forum for an interdisciplinary exchange of ideas on sea level changes and to provide an opportunity for integrating various types of evidence in approaching unresolved issues the conference was successful in bringing together scientists from industry academia and government representing all of the major geosciences disciplines presentations of many new papers plus significant releases of data that were previously held proprietary provided fertile ground for discussion this much cited volume represents the best of the material presented at the conference includes the early vail chart

paleogeographic setting and depositional architecture of a sand dominated shelf depositional system miocene utsira formation north sea basin abstract the middle late miocene utsira sandstone of the north sea basin contains a fully preserved regional marine sand deposit that records a stable paleogeographic setting of shelf sand transport and accumulation within an epeiric shelf sea which persisted for ca 8 myr the sediment dispersal system was defined by 1 sediment input through a prograding strandplain platform coast to shelf bypass and regional basin centered transport and deposition within an elongate seaway 2 a high energy marine regime 3 very low rates of sediment supply and accumulation in the accommodation dominated seaway 4 high sediment reworking ratio and consequent abundance of autochthonous sediment 5 regional along strike sediment transport and 6 local to subregional landward sediment transport shelf systems were primarily nourished by sediment reworked from the shetland strandplain which prograded eastward into the central viking trough the viking strait lay between the constructional platform and the nondepositional horda platform southward longshore transport on the high energy shoreface and shallow shelf platform constructed the mounded south viking shelf shoal southward building sandy banner banks that formed along the recurved arc of the platform margin nourished the shoal system low angle sigmoid clinoforms with downstepping aggradational tops are distinctive architectures of the strike fed sand bodies the combination of strong marine currents and slow but continual sand supply from the shetland strandplain created regional sandy shelf depositional systems that individually covered 3500 to 6000 sq km of basin floor defining elements of the shelf shoal systems include their location within the basin axis mounded morphology stratal architecture and construction by amalgamated marine sand facies

variations in atmospheric sulphate recorded in stalagmites by synchrotron micro xrf and xanes analyses abstract we report here the first speleothem time series of the variability of sulphate a species whose abundance in catchments is strongly influenced by atmospheric anthropogenic and volcanic sources annually resolved archives of s mg si and p were generated by applying synchrotron radiation micro x ray fluorescence xrf to two speleothems from different sites in northern italy x ray absorption edge spectrometry proves that the s is in the form of sulphate and xrf mapping demonstrates that s is within calcite and enriched zones are predominantly as layers a post 1850 a d record from the ernesto cave shows a substantial rise in sulphate interpreted as reflecting the largely anthropogenically forced variation of sulphate of the atmospheric boundary layer moderated by some ecosystem storage analysis of the circa 5 2 to circa 5 0 ka interval of a speleothem from savi cave where ecosystem retention of s is likely to have been minimal shows a spiky sulphate record resembling that of ice cores a series of sulphate peaks suggest that multiple volcanic sulphate aerosol emissions at that time this probably enhanced summer temperature cooling thus favouring the preservation of the human mummy of neolithic copper age the iceman on the watershed between italy and austria both examples illustrate the power of speleothems to record atmospheric sulphate variability

variability of lowstand wedges and their distinction from forced regressive wedges in the mesaverde group southeast wyoming the debate on the geometry and origin of shelf sandbodies has evolved from a discussion of how sands and gravels managed to move from shorelines far out onto muddy shelves to an acceptance that many of these sandbodies did not originate on the shelf but were simply resident there after a fall and subsequent rise of sea level in the efforts to reinterpret these sandstones there has been some tendency to underestimate how varied they can be data from eight such shelf sandstone tongues campanian in southeast wyoming are used to illustrate how variable lowstand prograding wedges can be and how these should in addition be distinguished from forced regressive wedges the depositional environments encountered in these two types of wedges are surprisingly different and the lowstand wedges which are frequently tidally influenced show a greater affinity with the overlying transgressive tract than with the preceding wave dominated forced regressive shoreface deposits

deposition and interpretation of long narrow sandbodies underlain by a basinwide erosion surface cardium formation cretaceous western interior seaway alberta canada abstract sand bodies of the cardium alloformation burnstick allomember occur in three parallel linear trends in the garrington caroline crossfield and lochend oilfields they are extremely long up to 100 km straight and narrow up to 4 km and are encased in marine mudstones suggesting their former interpretation as offshore bars our study of 189 cores and over 800 resistivity well logs shows that below the burnstick the hornbeck allomember consists entirely of dark mudstones deposited in quiet water the hornbeck burnstick contact where seen in cores is extremely sharp in cross sections resistivity well log markers are truncated by the lower surface of the burnstick and the sand bodies rest in asymmetrical one sided elongate scours with erosional relief of up to 7 m above he scoured surface there is a basal lag of mudstone intraclasts and chert pebbles overlain by a sandier upward succession of mudstones sandstones and conglomerates the sandstones are extensively burrowed but show some cross stratification the burnstick sandier upward succession is overlain by black mudstones of the raven river allomember the morphology of the scoured surface as defined in isopach maps does not indicate its formation in an open marine setting the long straight asymmetrical scours are parallel to regional strike and do not suggest subaerial erosion instead we suggest that a major relative lowering of sea level first exposed the hornbeck mudstones to subaerial erosion subsequently marine transgression of this surface removed evidence of its subaerial exposure pauses in transgression stillstands resulted in incised shoreface profiles the asymmetrical scours and at this time rivers supplied coarse sediment to the shoreface this sediment was reworked alongshore to form what are now the very long straight narrow sand bodies continued transgression resulted in the burial of the shoreface sand bodies by black mudstone basal part of the raven river allomember incised shoreface environments provide an alternative to the offshore bar settings suggested for other long linear sand bodies

alluvial fan to storm dominated shelf transition in the mesoproterozoic singhora group chattisgarh supergroup central india abstract mesoproterozoic siliciclastic strata at the basal part of the singhora group central india provide an example of a pre vegetation alluvial fan and braid delta depositional system detailed process based facies and paleoenvironmental analysis have led to the identification of 15 facies types grouped under four different facies associations which record paleoenvironmental settings ranging between continental alluvial fan and distal marine shelf two formations investigated are the rehtikhol formation formed in a conglomeratic or coarse arenaceous alluvial fan braid plain and delta setting and the overlying saraipalli formation which preserved the sedimentation record of a storm infested inner to distal shelf setting the preponderance of granular and sandy sediment gravity flow products with subordinate rock fall deposits within the alluvial fan system together with a pervasive west northwesterly paleocurrent is suggestive of a gently sloping beveled source area in the east southeast distal to the inferred fan a braid plain system developed with the decrease in the depositional slope streams within the braid plain had widths up to several hundred meters the braid plain system at the margin of the marine basin developed a delta with the deposition of wave reworked fluvial dominated sediments the crest trends of wave generated bedforms within the inferred delta sediments depict the northeast southwest shoreline interpreted for the singhora sea the prodeltaic basinal part of the singhora braid delta was storm infested the inner shelf acted as a zone of throughput with high velocity storm flows eroding deep narrow scours gutter casts and is interpreted as a zone of bypass operation of geostrophic currents on the singhora shelf has been inferred from the directional relationship of gutters with the inferred orientation of the shoreline a proximal distal relationship has been established within the shelf products based on the relative dominance of erosional and depositional features the singhora alluvial fan and braid delta facies are arranged in a fining upward sequence denudation of the source area increasing bathymetry with relative rise in sea level or a combination of both is inferred both extrabasinal and intrabasinal forcings possibly contributed to the deepening upward trend

basal tuffs and contemporaneity of the chattisgarh and khariar basins based on new dates and geochemistry abstracttime bracketing of thousands of meters thick unmetamorphosed fossil free sedimentary successions is a long standing challenge in indian proterozoic stratigraphy limited geochronologic ages from either the basal or the upper part of the successions prevent workers from constraining the precise age interval for individual basin fill leaving aside the issue of correlatability between different basin sequences this article deals with silicic tuff units from the basal part of two areally separated proterozoic sedimentary successions of central india the singhora group of the chattisgarh supergroup and the khariar group the singhora tuff is enriched in large ion lithophile rb ba th etc elements and light rare earth elements and in a discrimination diagram falls within the volcanic arc granite field u th pb electron probe microanalyzer geochronology of monazite and zircon grains from the singhora tuff revealed several age data clusters namely 2500 2100 1800 1500 and 1000 ma in c

basement control on flexural profiles and the distribution of foreland facies the dwyka group of the karoo basin south africa flexural partitioning of a foreland system into foredeep forebulge and backbulge is the result of the interplay of lithospheric deflection under orogenic loading flexural tectonics and the structure of the underlying basement flexural tectonics is commonly invoked as the sole control on flexural profiles which are modeled as dampened sine curves with wavelengths and magnitudes controlled by a number of physical parameters of the lithosphere and the applied loads basement tectonics is shown here to be an equally important control on the scale and shape of flexural provinces by controlling the location of flexural hinge lines and the tilt directions within the foreland system the case study for this paper shows that basement heterogeneity coupled with the selective reactivation of major crustal faults may lead to distortion of the ideal flexural profile by modifying the wavelength and shape of individual flexural provinces

a reassessment of the archean mesoproterozoic tectonic development of the southeastern chhattisgarh basin central india through detailed aeromagnetic analysis abstract we constrained the geological framework over polydeformed paleoproterozoic sonakhan greenstone belt and addressed the tectonic evolution of singhora basin in the fringes of bastar craton central india by utilizing aeromagnetic data interpretation 2 5d forward modelling and 3d magnetic susceptibility inversions the sonakhan greenstone belt exposes volcano sedimentary sequences of the sonakhan group within nnw sse to nw se trending linear belts surrounded by granite gneisses which are unconformably overlain by sedimentary rocks of chhattisgarh basin the orientations of aeromagnetic anomalies are coincident with geological trends and appear to correlate with lithology and geologic structure regional magnetic anomalies and lineaments reveal both nnw sse and ne sw trends prominent e w trending linear high amplitude magnetic anomalies are interpreted as the trans chhattisgarh aeromagnetic lineament tcal nw se trending aeromagnetic signatures related to sonakhan greenstone belt extends below the singhora sedimentary rocks and forms the basement in the west the analysis suggests that tcal is a block fault with northern block down thrown and affected the basement rocks comprising the sonakhan greenstone belt and samblapur granitoids the episode of faulting represented by the tcal is pre singhora sedimentation and played a vital role in basin evolution the basement configuration image generated by estimates of depth to magnetic basement suggests a complex pattern of nne ssw to ne sw trending depressions separated by a linear n s trending basement ridge it is inferred from the 3d magnetic susceptibility inversion that the thickness of sediments is more towards the eastern basin margin and the n s ridge is a manifestation of post sedimentary faulting results of 2 5d modelling of a wnw ese profile across the singhora basin combined with results from 3d inversion suggest suggests the basin subsidence was controlled by ne sw trending regional faults in an active system the basin geometry evolved by e w block faulting overprinted by ne sw trending pre to syn depositional normal faults generating ne sw depression which are affected by n s trend post sedimentary faulting though the present work relates the basin evolution with the initiation of rift basin it warrants further work to establish the deformation within the basin pertaining to the proximal thrust and uplift along the craton fringe

forced regressions in a sequence stratigraphic framework concepts examples and exploration significance sequence stratigraphic concepts suggest that stratal geometries develop and are largely controlled by changes in relative sea level on the shelf lowstand deposits which form during falls and subsequent stillstands of relative sea level can be recognized by the presence of an unconformity at the base the isolated and basinward position relative to the previous shoreline and the abrupt seaward translation of shallow water and shoreline facies into the basin across an unconformity surface this seaward translation of facies and shoreline regression in response to relative sea level lowering is termed a forced regression a forced regression is independent of variations of sediment flux and is in contrast with normal regressions that occur in response to excess sediment flux relative to space available on the shelf i e accommodation forced regressions commonly are associated with a zone of sedimentary bypass subaerial exposure and possible fluvial erosion between the newly formed and preceding shorelines certain shelf sands previously interpreted as offshore or mid shelf sand bodies thus can be reinterpreted as stranded lowstand shorelines associated with forced regressions this alternative interpretation has economic significance insofar as it suggests different subsurface correlations and reservoir geometries with the potential for development of new play types and enhanced recovery in o der fields examples of forced regression can be observed at a variety of scales and ages several such examples include the modern east coulee fan delta and the lower cretaceous viking formation in alberta canada the quaternary rhone delta and the quaternary hudson valley system

marine to fluvial transition proterozoic upper rewa sandstone maihar india abstract the proterozoic upper rewa sandstone in central india is generally interpreted as entirely marine a detailed study in maihar madhya pradesh however reveals upward transition from marine to fluvial through a mixed facies association also bearing eolian imprints facies associations differ in stratal geometry and arrangement palaeocurrent direction and pattern as well as in grain size and sorting the fine grained marine association is dominated by tidal sheet deposits with characteristic rhythmic changes in thickness and style of cross stratification and their packages as well as local evidence of current reversals subordinate beach deposits are also present the major palaeocurrent direction is highly consistent and westward the coarse grained often granule rich sandstones of the fluvial association are embodied by four facies correlatable with flow stages and relative bed shear these braided stream deposits are preserved in vertical stacks of tabular sandbodies in response mainly to basin subsidence the palaeocurrent pattern is unimodal and northwestward but its dispersion covers 180 the rocks are poorly sorted and at places incorporate sand clasts although they are virtually mud free and mineralogically mature as in two other associations the medium to fine grained sandstones at the intermediate interval between the marine and fluvial associations are of distinct lensoid geometry they incorporate representatives from the previous two associations as well as translatent strata interdune erg deposits and possibly aeolian cross strata consequently the palaeocurrent pattern is polymodal with a spread over 270 an overall coarsening up trend in the fluvial part and thinning up trend in the tidal part imply progradation in spite of evidence of basin subsidence a high rate of sediment discharge from a perennial river system in a humid climate is suggested

shannon sandstone in wyoming a shelf ridge complex reinterpreted as lowstand shoreface deposits abstract the shannon sandstone campanian of wyoming was formerly interpreted as two stacked shelf ridge complexes sand was believed to have been transported from a time equivalent shoreline 110 150 km to the west and reworked or molded into ridges at the depositional site we show that this time equivalent shoreline section at lucerne wyoming consists of not one shoreface sandbody but two superimposed they are both storm dominated and the lower one terminates in beach facies capped by root traces there must have been a rise in relative sea level of at least 14 m to make accommodation space for the second shoreface sandbody in the salt creek area and the adjacent subsurface teapot dome there are two sandier upward facies successions in the lower succession there are abrupt vertical acies contacts between offshore bioturbated sandstones thicker hummocky cross stratified sandstones and coarser cross bedded sandstones there is also evidence that the cross bedded sandstones rest erosively on underlying facies the trace fauna in the sandstones includes macaronichnus segregatis rosselia socialis and ophiomorpha the m segregatis suggests a foreshore or upper shoreface depositional environment and r socialis indicates a lower to middle shoreface neither are characteristic of a shelf ridge complex the abrupt and probably erosive facies contacts along with the trace fauna suggest that the cross bedded sandstones in this succession represent a shoreface deposit that formed during a stage of actively falling relative sea level overlyi g muddy bioturbated sandstones indicate that shoreface deposition was terminated by a transgression the upper sandier upward succession contains facies and trace fauna similar to those of the lower succession and is also interpreted as a prograding shoreface rather than the sand moving 110 150 km from the shoreline and then being molded into shelf ridge complexes at salt creek we suggest that the shoreline moved into the salt creek area as the result of a fall in relative sea level it was transgressed and moved back westward a second fall of relative sea level moved the shoreline back to salt creek and a final transgression terminated shannon deposition

forced regressive wedge in the mesoproterozoic koldaha shale vindhyan basin son valley central india abstract the present paper highlights the sequence development within the mesoproterozoic koldaha shale member of the kheinjua formation vindhyan supergroup which records the occurrence of a forced regressive wedge and associated discontinuity surfaces at the base of the wedge nine lithofacies have been identified within the study area that are grouped into three lithofacies associations varying in depositional setting from outer shelf through shoreface foreshore beach to continental braidplain the outer shelf sediments are aggradational to slightly progradational representing highstand systems tract the rapidly progradational wedge shaped shoreface to foreshore beach succession occurs sharply or erosively above the outer shelf sediments and is bounded by a regressive surface of marine erosion rsme at the base and by a subaerial unconformity at the top this along with its downstepping trajectory supports deposition of this sedimentary wedge during falling sea level a laterally extensive soft sediment deformation zone occurs at the base of the wedge the forced regressive wedge is incised by fluvial braidplain deposits that rest on an erosive surface representing a sequence boundary the thin braidplain deposits are the product of aggradation during a subsequent early rise in relative sea level and thus they are inferred to represent a lowstand systems tract the constituent architectural elements that characterize the braidplain deposits are downstream accretion elements and small channel elements further landward the base and top of the shoreface wedge merge to form an unconformity across deposits that rest directly on the outer shelf sediments the identification of forced regressive wedges has significant economic importance in view of the potential occurrence of hydrocarbons within the proterozoic formations

determining the channel sinuosity of ancient fluvial systems from paleocurrent data abstract the classification of modern river channels is based primarily on their sinuosity values which can be determined directly from aerial photographs ancient channel systems are seldom sufficiently exposed to allow direct measurement of thalweg and valley lengths but paleocurrent directions can be used to calculate fairly accurate sinuosity values aerial photographs of four modern meander belts were studied to determine the relationship between local current directions within the meander belts and the actual sinuosity of the active river channels a value of 3 2 times the standard deviation gave the best approximation of the operational channel range resulting in a close correspondence between calculated and actual sinuosity values this method can therefore be used to estimate the s nuosity of ancient fluvial systems

geometry and facies of stacked shallow marine sandier upward sequences dissected by erosion surface cardium formation willesden green alberta willesden green field is a long narrow sandstone body completely encased in marine mudstones the field is late cretaceous turonian in age and contains as many as seven stacked sandier upward sequences the sequences are as much as 12 m 39 3 ft thick are stratigraphically distinct and do not offlap systematically each sequence begins with marine bioturbated mudstones and passes upward into storm dominated shallow marine sandstones each sequence shows a lateral shaling out from hummocky cross stratified sandstone into bioturbated mudstone isopach maps show that the sequences thin basinward at a rate of 15 67 cm km 9 45 42 21 in mi and suggest dispersal directions ranging from north northeast to southeast the stack of marine sequences is dissected by a basin wide erosion surface that initially formed subaerially following a major relative lowering of sea level during ensuing transgression a series of stepped shorefaces was cut into the stack of sequences removing all evidence of subaerial exposure the shorefaces in most places are overlain by a thin pebble veneer which in turn is buried by thick transgressive marine mudstones in places the pebble veneer thickens into conglomerates as much as 20 m 65 6 ft thick that form reservoirs at carrot creek pembina and ferrier as well as willesden green these conglomerates are interpreted to have been deposited at river mouths and locally reworked along the shoreface by waves during continued transgression the stacked sequences a d shoreface conglomerates were buried by marine mudstones overall reservoir characteristics are determined by the geometry and stacking of the sequences stratigraphic traps have been formed partly by lateral shaling out and partly by mud draped incised shorefaces locally shoreface gravels are good reservoirs and the overlying transgressive mudstones form the traps we believe that the long narrow geometry of the field represents an erosional remnant of a formerly continuous sand sheet the field is not an offshore bar

high resolution sequence stratigraphy of early transgressive deposits viking formation joffre field alberta canada the lower cretaceous viking formation of the joffre field is characterized by complex reservoir architecture deposits of three discrete sequences were delineated using high resolution sequence stratigraphy the coarse grained deposits of sequence 3 lying between bd 2 and an overlying open marine flooding surface comprise the main reservoir interval within the viking formation of the joffre field this succession has previously been interpreted as an incised conglomeratic shoreface stranded in a basinal position during transgression however sequence 3 displays characteristics difficult to reconcile with a shoreface interpretation including an abundance of brackish mudstone interbeds and rip up clasts dominance of trough cross stratification in the coarse clastics and large scale interfingering of the coarse clastics with fine grained marginal marine deposits despite the incised basal contact and brackish water characteristics of the deposits the succession does not reflect an estuarine incised valley complex as conventional sequence stratigraphic wisdom might suggest the shore parallel orientation of the deposit the lack of a convincing valley margin to the northeast and parasequence orientations lying parallel to the strike of the deposit are inconsistent with an incised valley interpretation instead the succession is interpreted as a broad brackish water embayment of the shoreline into which coarse clastic bayhead delta and distributary channel complexes were deposited during incremental transgression such lagoonal or brackish bay complexes are ubiquitous in modern transgressive shorelines but previously have been recognized only rarely in the ancient record

depositional history of the chhattisgarh basin central india constraints from new shrimp zircon ages a reply abstract the indian shield includes the singhbhum bastar and east and west dharwar cratons proterozoic sedimentary basins formed on these cratons have preserved rocks with a range of degrees of metamorphism and deformation in the chhattisgarh basin within the bastar craton the ca 2200 2500 m thick chhattisgarh supergroup has been preserved in nearly pristine condition previous work has shown that the sukhda tuff located about 2200 m from the base of the section was formed ca 1007 ma new u pb shrimp age determinations show that the singhora tuff located about 100 m above the base of the basin is not older than ma thus most of the chhattisgarh supergroup was deposited between 1400 and 1000 ma age data for detrital zircons from sandstones show that regardless of their stratigraphic position there is a unimodal age peak near 2500 ma the typical age of adjacent granitic and rhyolitic basement rocks indicating that these constituted the principal provenance of the sediments in the chhattisg

how and where do incised valleys form if sea level remains above the shelf edge sequence stratigraphic models predict that during relative sea level fall rivers will cut incised valleys across the exposed continental shelf incision is driven by the exposure of convex up topography and consequent downstream increases in stream power modern shelf profiles from passive margin and foreland basin settings show that profile convexities occur at the shelf edge and at the current highstand coastline the coastal prism in nonglacial times which form much of earth9s history it is unlikely that the shelf edge was subaerially exposed during such periods patterns of incision would have been primarily determined by the shape of the coastal prism on the basis of modern shelf profiles from passive margin and foreland basin settings river incision of as much as 20 to 70 m would be centered upon the preceding highstand coastline and would be restricted to the inner part of the shelf deeper incised valleys would only result from exposure of the shelf edge or from the processes involved in the formation of submarine canyons

the architecture of precambrian high energy tidal channel deposits an example from the lyell land group eleonore bay supergroup northeast greenland abstract within the 2 5 km thick late proterozoic lyell land group of the eleonore bay supergroup in east greenland numerous successions of stacked sheet sandstone bodies 10 70 m thick occur each succession consists of several 5 50 m thick multistorey sand sheets separated from each other by 0 2 2 m thick heterolithic mudstone or sandstone beds individual sand sheets are 0 2 3 0 m thick they have highly erosive lower contacts show a rough fining upward trend and are capped by a thin mudstone veneer containing desiccation cracks dominant sedimentary structures within the sand sheets are sets of planar cross bedding showing a range of characteristic tidal features such as successive bundles of foresets herringbone cross stratification ebb and flood caps and numerous reactivation surfaces horizontal lamination is abundant and may in some instances comprise more than half of the structures within a sand sheet the sand sheets represent high energy tidal channels with the multistorey sand sheets constituting larger tidal channel complexes the heterolithic beds represent mixed tidal flat sediment deposited during periods of tidal channel complex abandonment probably caused by channel aggradation and changing drainage patterns the tidal channels were wide shallow and very sandy with a very poorly developed channel morphology caused by lack of fine grained sediments and vegetation most likely they evolved within a meso to microtidal sandy back barrier setting where the channels migrated swiftly across tidal flats and reworked most interchannel sediment an architecture was developed consisting of stacked sand sheets interbedded with rare heterolithic mudstone beds the model presented incorporates sedimentary parameters and processes characteristic of a pre vegetative landscape and it has no direct modern analogue

braided stream and flood plain architecture the rio vero formation spanish pyrenees early to middle miocene fluvial sandstones of the rio vero formation were studied in an area around the town of barbastro south central pyrenees spain the outstanding quality of outcrops in this area allows a three dimensional study of architectural elements six architectural elements are recognised described in detail and interpreted from three key localities seven main lithofacies were identified and sub divided into gravelly sandy and fine grained lithofacies the architectural elements and lithofacies have been combined with a hierarchy of depositional bounding surfaces to fully interpret the evolution of the depositional system at the meso and macro scale not only the different architectural elements and lithofacies of the complete braided fluvial system but also the lateral variation of the architectural elements were emphasised in this study differential tectonic movements seasonal climate change and their effect on vertical and lateral evolution of the area were the main control on basin sedimentation channel interconnection palaeocurrent patterns and consequently the fluvial architecture the presence of lateral ramp anticlines caused the fluvial system to be laterally restricted with the main channel belts being located in the areas of highest subsidence and lowest topography intervening topographic highs acted as both flood plains and lateral barriers between the main channel systems the proposed depositional model comprises broad low sinuosity perennial but seasonal moderate energy streams the sandstone architecture is dominated by channel fill and sheet sands and associated simple and more complex bars adjacent to the main channel belts fine grained sandstones siltstones and immature paleosols occur the along strike relationship between major fluvial systems and their outlets into a foreland basin has important implications for the infill of the basin and the modelling of fluvial systems along mountain belt fronts

shannon sandstone in hartzog draw heldt draw fields cretaceous wyoming usa reinterpreted as lowstand shoreface deposits abstract the lower campanian shannon sandstone at hartzog draw heldt draw powder river basin wyoming is interpreted in the literature as a shelf ridge complex deposited 160 km from the contemporaneous shoreline this interpretation poses difficult problems and does not discuss the significance of bounding discontinuities preserved in the sandbodies cross sections show that the shannon sandstone is present at several stratigraphic horizons and is bounded by regionally extensive discontinuities the presence of these bounding discontinuities suggests that fluctuations in relative sea level were important in controlling geometry of sandbodies on the shannon shelf in the hartzog draw heldt draw area of wyoming the base of the shannon is a planar surface with respect to a lower bentonite marker and is characterized by the abrupt appearance of bioturbated sandstone on top of black basinal mudstone siderite pebbles 1 cm in diameter are common at this contact in hartzog draw the bioturbated sandstone interval has an average thickness of 10 m and is separated from an overlying unit of cross bedded fine to medium sandstone up to 20 m thick by a ubiquitous 50 cm thick horizon of mud clasts in a cross bedded highly glauconitic medium sandstone these three units are laterally continuous in hartzog draw except where removed by erosion the top of the shannon is marked by an abrupt change from the cross bedded sandstone or bioturbated medium sandstone to laminated black mudstone mud clasts siderite pebbles chert grains and glauconite mark this abrupt contact suggesting erosional transgression this surface can be traced westward where in many areas it is a mud on mud contact marked by a lag of shell debris this transgressive surface which terminates shannon deposition is characterized by at least one regionally extensive onlapping marker in the hartzog draw heldt draw area the presence of depositional discontinuities in the shannon sandstone is suggested by 1 the sharp basal contact 2 the lateral continuity of individual facies 3 the abrupt vertical facies changes and the association of mud clasts siderite pebbles and glauconite accompanying these abrupt juxtapositions of facies 4 the stratigraphic variability and 5 the termination of shannon deposition by erosive transgression marked by onlapping markers these depositional discontinuities are the bounding discontinuities these bounding discontinuities have asymmetrical one sided scour morphologies with steeper landward margins that flatten basinward these geometries and the linearity of the overlying sandstone and the troughs defined by these scoured surfaces suggest incised shoref ce profiles truncated by erosive transgression thus the shannon sandstone in hartzog draw heldt draw is reinterpreted as a lowstand shoreface deposit

architectural elements from lower proterozoic braid delta and high energy tidal flat deposits in the magaliesberg formation transvaal supergroup south africa abstract three architectural elements are identified in the lower proterozoic magaliesberg formation pretoria group transvaal supergroup of the kaapvaal craton south africa 1 medium to coarse grained sandstone sheets 2 fine to medium grained sandstone sheets and 3 mudrock elements both sandstone sheet elements are characterised by horizontal lamination and planar cross bedding with lesser trough cross bedding channel fills and wave ripples as well as minor desiccated mudrock partings double crested and flat topped ripples due to the local unimodal palaeocurrent patterns in the medium to coarse grained sandstone sheets they are interpreted as ephemeral braid delta deposits which were subjected to minor marine reworking the predominantly bimodal to polymodal palaeocurrent trends in the fine to medium grained sandstone sheets are inferred to reflect high energy macrotidal processes and more complete reworking of braid delta sands the suspension deposits of mudrocks point to either braid delta channel abandonment or uppermost tidal flat sedimentation the depositional model comprises ephemeral braid delta systems which debouched into a high energy peritidal environment around the margins of a shallow epeiric sea on the kaapvaal craton braid delta and tidal channel dynamics are inferred to have been similar fine material in the magaliesberg formation peritidal complexes indicates that extensive aeolian removal of clay does not seem applicable to this example of the early proterozoic

climatic and morphologic relationships of rivers implications of sea level fluctuations on river loads the characteristics of 279 rivers that discharge into the world oceans are analyzed in terms of their basin hydrology river discharge morphometry basin slope and area river length extension of the continental shelf seaward of the river mouth and climate precipitation statistically reliable relationships are found between discharge and basin area and between sediment load and a combined function of basin area and slope these functions are used to demonstrate how river hydrologic features would be strongly influenced by sea level fluctuations particularly under the influence of continental shelf emergence a fall in sea level toward a glacioeustatic lowstand would induce the merging of rivers on the subaerial continental shelf thereby allowing giant rivers to form for example rivers of western europe would reorganize themselves into two or three very large rivers sediment concentration carried by these mega rivers would decrease and thus the number of hyperpycnal plumes generated at river

architectural elements and bounding surfaces in fluvial deposits anatomy of the kayenta formation lower jurassic southwest colorado abstract three well exposed outcrops in the kayenta formation lower jurassic near dove creek in southwestern colorado were studied using lateral profiles in order to test recent regarding architectural element analysis and the classification and interpretation of internal bounding surfaces examination of bounding surfaces within and between elements in the kayenta outcrops raises problems in applying the three fold classification of allen 1983 enlarging this classification to a six fold hierarchy permits the discrimination of surfaces intermediate between allen s second and third order types corresponding to the upper bounding surfaces of macroforms and internal erosional reactivation surfaces within the macroforms examples of the first five types of surface occur in the kayenta outcrops at dove creek the new classifications is offered as a general solution to the problem of description of complex three dimensional fluvial sandstone bodies the kayenta formation at dove creek consists of a multistorey sandstone body including the deposits of lateral and downstream accreted macroforms the storeys show no internal cyclicity neither within individual elements nor through the overall vertical thickness of the formation low paleocurrent variance indicates low sinuosity flow whereas macroform geometry and orientation suggest low to moderate sinuosity the many internal minor erosion surfaces draped with mud and followed by intraclast breccias imply frequent rapid stage fluctuation consistent with variable seasonal monsonal ephemmeral flow the results suggest a fluvial architecture similar to that of the south saskatchewan river through with a three dimensional geometry unlike that interpreted from surface studies of that river

regressive depositional architecture on a mesoproterozoic siliciclastic ramp sequence stratigraphic and nd isotopic evidences from bhalukona formation singhora group chhattisgarh supergroup central india abstract a paleo environmental and sequence stratigraphic study of the mesoproterozoic bhalukona formation singhora group central india provides new interpretations applicable to understanding sedimentation and stratigraphic architecture in the proterozoic siliciclastic ramp settings under falling and lowstand sea level conditions beside delineation of two diachronous surfaces process based facies analysis identified fourteen facies types that are grouped under five different facies associations paleo environments range among continental fluvial beach foreshore upper shoreface lower shoreface and wave dominated delta front from the paleocurrent measurement within the fluvial channel sandstones and measurement of crest line orientations of wave generated swash bedforms it is inferred that the bhalukona sea had nne ssw shoreline trajectory and the south easterly flowing river system carried sediment on the shoreline from a source in the west northwest such inference though in clear discordance with the earlier proposed south southeastern sediment source for the singhora basin finds support in the shift in e nd t t 1 42 ga values from 3 5 3 3 to 9 3 2 2 indicating change in sediment provenance at the early bhalukona sedimentation history sediments in the bhalukona formation derived from more evolved or older continental crustal sources in comparison to those of the underlying saraipalli formation a tectonic forcing behind the shift in sediment provenance and fall in relative sea level is inferred that established the forced regressive and lowstand shoreline in the singhora basin during the bhalukona time abrupt basin ward shift of facies tract and incision on shelf is exhibited by the occurrence of poorly sorted coarse granular bhalukona fluvial system carrying rip up mud clasts directly above the argillaceous highstand saraipalli shelf with 10 m incision and is inferred as the signal for forced regression and development of type i sequence boundary in low gradient proterozoic ramp settings without shelf slope break we interpret that the bhalukona fluvial system incised the coastal prism developed on the saraipalli highstand coastline the low gradient of the ramp however prompted long distance 15 km regression represented by the offlapped and detached delta front lobe away from the shoreline the slow steady rise in sea level onset of lowstand and establishment of a wave dominated coastline caused reworking of fluvial sediments in the basinal part within the wave base and resulted development of ravinement deposit basin ward the surface grades into correlative conformity with aggradational and weak retrogradational stacking the beach foreshore upper and lower shoreface in order of superposition record the lowstand depositional history the basin scale transgression is witnessed with formation of transgressive surface of erosion tse and establishment of the chuipalli shelf system dominantly beyond storm wave base taking into consideration 23 m preserved shoreface succession 1 m per year eustatic rise consistent with present day rate and average rate of shoreface retreat 0 5 m per year 11 5 km retreat for the bhalukona shoreline is estimated in its lowstand history

genesis and evolution of a syn orogenic basin in transpression insights from petrography geochemistry and sm nd systematics in the variscan pedroches basin mississippian sw iberia abstract the pedroches basin is an outstanding syn orogenic variscan mississippian depocenter located in the vicinity of and overstepping onto the neoproterozoic cadomian suture between the ossa morena and central iberian zones of the sw iberian massif its formation appears to be related to transtensional processes at a major releasing bend in the reactivated suture during sinistral escape of the ossa morena zone from the zone of frontal variscan collision between northern gondwana and laurussia subsequent basin inversion resulted in compartmentalization and internal deformation and was probably related to transpression at a restraining bend along the reactivated suture badajoz cordoba shear zone basin fill consists of both igneous and metasedimentary rocks generally deposited in a shallow marine storm dominated platform environment by using new petrographic geochemical and sm nd isotopic data we attempt to characterize 1 the sources and geological evolution of the pedroches basin fill and 2 the processes involved in basin development and sediment supply and dispersal sampling was carried out in both sedimentary and igneous rocks belonging to three major structural units within the central part of the basin guadiato unit guadalbarbo unit and south pedroches valley unit the combined nd isotopic and geochemical data from the pedroches mississippian metasedimentary rocks indicate an upper continental crust provenance and a high degree of sedimentary recycling of these materials throughout the basin i e they are derived from old recycled upper crust without any significant juvenile component despite the presence of interbedded basaltic rocks the igneous rocks in turn correspond to submarine basalts and trachy andesitic basalts plus some hybrid rocks including crust derived components concerning the mafic rocks major element compositions reveal a tholeiitic and transitional tholeiitic character for the guadalbarbo unit rocks morb type and an alkaline affinity for those of the guadiato unit trace element analyses along with sm nd isotopic ratios suggest two kinds of provenance sources for the pedroches basin syn sedimentary igneous rocks 1 an important crust contaminated and or old enriched mantle source for the guadiato unit and the pedroches batholith and 2 a time integrated depleted mantle source for the guadalbarbo rocks in which no significant interaction with continental crust components is discernible these latter rocks suggest that a strong attenuation or even almost complete tectonic and or thermal erosion of the continental lithosphere was reached at least locally in this region

sequence stratigraphy and the interpretation of neoproterozoic earth history abstract the application of sequence stratigraphy to neoproterozoic successions is important for improving the resolution of time correlation within individual sedimentary basins and potentially at a global scale the methodology is illustrated in this paper by reference to two contrasting examples from the flinders ranges adelaide geosyncline of south australia where the younger part of the neoproterozoic to earliest cambrian succession 770 ma to 540 ma has been divided into thirteen unconformity bounded depositional sequences one of the most prominent sequence boundaries at or near the base of the wonoka formation is characterized by a series of buried canyons as much as 1 km deep high resolution sequence stratigraphic studies at umberatana syncline continue to support the view that the canyons were cut subaerially and filled by fluvial and shallow water sediments in contrast to the wonoka canyons sequence boundaries interpreted at the base of the nuccaleena formation seacliff sandstone and near the top of the abc range quartzite are relatively subtle with only limited evidence for erosion and valley incision four sequence boundaries at the level of the sturtian and marinoan varanger glacial deposits and in the vicinity of the precambrian cambrian boundary are thought to correlate with surfaces in the amadeus basin of central australia other prominent sequence boundaries including the wonoka canyons and surfaces within the upper part of the wonoka formation and at the base of the ediacara member of the rawnsley quartzite correspond with a relatively condensed section in the amadeus basin and their lateral persistence beyond the adelaide geosyncline is therefore difficult to evaluate given the lack of precision in biostratigraphy and isotope geochemistry in neoproterozoic rocks and in a marked departure from phanerozoic practice we recommend placement of a terminal proterozoic gssp at a sequence boundary a prime candidate in australia is the sequence boundary at the base of the nuccaleena formation seacliff sandstone immediately above the marinoan glacial rocks in the adelaide geosyncline and its likely correlative at or near the base of the gaylad sandstone in the amadeus basin

rates and mechanisms of shoreface progradation and retreat downdrift of the amazon river mouth field surveys of the 350 km shoreline adjacent to the amazon river mouth reveal three distinct types erosional mud accretionary sand and accretionary mud formation of these zones is controlled by the delivery of amazon suspended sediment mediated by the hydrodynamic regime erosional mud shorelines extend from rio araguari near the amazon river mouth northwestward 280 km to 3 5 n near cabo cassipore shoreface 5 m water depth retreat annually yields 1 4 106 tons of fine grained sediment deposited during an earlier phase of shoreface progradation sandbodies up to 5 m thick overlie erosional mud shorefaces for 10 30 km downdrift of small rivers the sand is supplied from these rivers and released by shoreline retreat of the river mouth areas amazon river sand is restricted in the coastal zone from its mouth north to the cabo norte shoal area where it mixes with sand carried by rio araguari from the guiana highlands north of 3 5 n mud aggradation and progradation is taking place on underconsolidated low gradient tidal flats backed by mangrove swamps 210pb and 14c geochronology of vibracores from the mudflats indicate that sediment accumulation is rapid 0 24 2 0 cm yr landward of the 2 m isobath supplied from a thick 50 150 cm seasonal surface layer shoreface progradation is episodic separated by decadal hiatuses fine grained suspended sediment flux from the amazon and minor amounts of sand and mud from the local rivers supply sediment to the mudflats shore normal tidal currents and solitary waves rework the surface mud layer preferentially transporting available sand landward into the mangrove fringe and producing very fine grained accumulation on the tidal flat 10 12 mean grain size lateral accretion of features 10 100 km long termed mudcapes produces tens of kilometers of seaward coastal plain addition along the northern coast similar features are identified downdrift along the guianas coast as far as the orinoco river 1600 km the northern amapa shoreface deposits are a locus of modern sediment accumulation which progrades over subaqueous deltaic strata

forced regressive wedges on a neoproterozoic siliciclastic shelf chandarpur group central india abstract outcrop based sequence analysis across the transition from the chaporadih to the kansapathar formation of chandarpur group chattisgarh supergroup central india resolved a long standing uncertainty on occurrence of depositional discontinuity through undoubted identification of a forced regressive wedge and associated intraformational unconformity process based facies analysis identified eleven different facies types that are grouped into five different facies associations paleoenvironments range from shelf shoreface foreshore and beach tide influenced estuary and delta bounded between the surface of marine erosion at its base and subaerial unconformity marked by paleosol development at its top the coarse grained wedges of shoreface sandstone is interpreted as forced regressive in origin the basinward downstepping of two such regressive wedges bears evidence for lowering of wavebase in connection with relative fall in sea level the valley created during the falling sea level was filled by sediments in lowstand transgressive and highstand depositional motif the aggradational to weakly progradational bedsets of foreshore beach sediments record the history of early slow rise in base level with steepening in the rate of relative sea level rise the coastline transformed from wave dominated to tide dominated wide variability in the balance between sediment supply and accommodation is recorded in the facies types and stacking motif of transgressive estuarine sections at different studied locations the highstand tidal delta is a supply driven normal regressive product at stable or marginally rising base level

distribution of fault slip in outcrop scale fault related folds appalachian mountains abstract current kinematic models of ramp related folds predict a direct relationship between ramp angle and fold shape and imply specific sequences of deformation analyses of outcrop scale structures in the valley and ridge province of the appalachians reveal configurations that depart from model predictions the models fail to account for the presence of footwall synclines and are inconsistent with measured displacement distributions on some natural faults observations support the interpretation that faults can grow by propagation both up and down dip from a nucleation point fault propagation in either direction may result in the formation of folds primarily on the side of the fault that is displaced in the direction of fault propagation