facies mosaics across the persian gulf and around antigua stochastic and deterministic products of shallow water sediment accumulation abstract among broadly different types of sedimentary successions those that accumulate in nearshore settings are perhaps unique in that a very wide range of rock types recurs with high frequency over relatively short stratigraphic intervals this vertical lithofacies heterogeneity suggests that deposition of any sedimentary unit at any site was short lived that many different sediment types existed within a complex mosaic over the depositional surface and that this facies montage repeatedly moved across surfaces of accumulation in response to eustatic sedimentologic and or tectonic forcing data on numbers and thicknesses of lithofacies units from several dozen such sequences define the size frequency distribution expected if horizons of lithologic change occur randomly within sedimentary successions walther s law suggests that the amount of vertical lithologic heterogeneity manifest in a sedimentary sequence should reflect the degree of lateral heterogeneity in sediment composition that existed across depositional surfaces if so this repetition should also be manifest in sizes and areal distributions of sediment patches constituting the depositional mosaic in order to examine size frequency relations of sediment bodies across surfaces of sediment accumulation we tabulated numbers and areal extents of lithotopes across two rather dissimilar settings across the persian gulf and around the caribbean island of antigua although compositions and lateral extents of different sediment types exhibit broad lateral variation across interior to margin transects in either area lithotope abundances and areal extents define frequency distributions that are in excellent agreement with those anticipated for a facies mosaic of elements whose mean linear widths constitute an exponential frequency distribution these are the size frequency distributions one would expect if mosaic element boundaries occur randomly across regions of sediment accumulation and suggest that distributions of lithotope areas from holocene surfaces are directly analogous to lithofacies thickness frequencies from ancient successions in addition to the fact that both of the size frequency distributions attest to the importance of stochastic processes during sediment deposition they also afford numerical descriptors of abundances and areal extents of holocene lithosomes that can then be used as controlling parameters in computational models of sediment accumulation importantly results derived from such simulations are based not on inference of water depth varying in response to change in subsidence sea level and rate of sediment accumulation but on statistical attributes intrinsic to modern and ancient marginal marine successions

a new model for the emplacement of columbia river basalts as large inflated pahoehoe lava flow fields extensive flows of the columbia river basalt crb group in washington oregon and idaho are dominantly inflated compound pahoehoe sheet lavas early studies recognized that crb lavas are compound pahoehoe flows with textures suggesting low flow velocities but it was thought that the great thickness and extent of the major flows required very rapid emplacement as turbulent floods of lava over a period of days or weeks however small volume 1 km compound pahoehoe flows on kilauea hawai i demonstrate that such flows can thicken by at least an order of magnitude through gradual inflation and the same mechanism has been proposed for larger 10 20 km3 pahoehoe flows in iceland the vertical distribution of vesicles and other morphologic features within crb lava flows indicate that they grew similarly by inflation small pahoehoe lobes at the base and top of many crb pahoehoe lava flows indicate emplacement in a gradual piecemeal manner rather than as a single flood we propose that each thick crb sheet flow was active for months to years and that each group of flows produced by a single eruption a flow field was emplaced slowly over many years

volcanic vents rooted on extension fractures and their geodynamic implications in the ethiopian rift abstract most of the extension fractures located in the ethiopian rift are related to rift dynamics and they have consistently similar orientations for hundreds of kilometers the orientation of extension fracture gives the local extension direction which is perpendicular to its horns end segments of an extension fracture we have established clear geometrical relationships between tectonics and volcanism in the main ethiopian rift by interpreting high resolution images obtained from landsat tm and spot satellites and by quantitatively analyzing the geometry of extension fractures elongated vents and linear volcanic clusters applying the relationships obtained we show that extension fractures in the rift served as channels for magma rising to the surface and that extension fractures underlie most of the elongated volcanic vents and linear volcanic clusters the geometry of extension fractures beneath volcanic edifices can be deduced from the shape of elongated vents and pattern of linear volcanic clusters rooted on them utilizing the orientations of extension fractures directly observed and those inferred from elongated volcanic vents and linear clusters we found that the extension direction of the main ethiopian rift is northwest southeast and that the direction has been rotated clockwise for about 20 in the time interval 2 83 to 0 023 ma the recent axis of rift opening is oriented n40 and located closer to the southeastern escarpment giving an asymmetric geometry to the main ethiopian rift mer

revised sequence stratigraphy of the upper katian stage cincinnatian strata in the cincinnati arch reference area geological and paleontological implications abstract the upper ordovician cincinnatian series is a critical upper katian reference succession previously six 3rd order depositional sequences c1 to c6 have been recognized and frequently used as regional time slices recent research however indicates a need for revision and additions including the recognition of additional 3rd and 4th order sequences we propose amendments based upon high resolution correlations using a combination of regional disconformities cycle stacking patterns bioevents marker beds and chemostratigraphy several disconformities including a large regionally angular mid richmondian unconformity are newly recognized or reinterpreted in addition distinctive depositional patterns aid in the recognition of systems tracts with a thick proximal laminated peritidal facies representing early transgressive systems tracts tsts or lowstands in part lsts b shell rich limestone packages representing later tsts and overlain by c more shale prone highstand systems tracts hsts themselves overlain locally by d siliciclastic dominated falling stage systems tract fsst deposits that are commonly removed beneath substantial unconformities sequence boundaries at present we recognize eight 3rd order cincinnatian sequences designated c1 through c8 and 16 4th order subdivisions and their component systems tracts a younger hirnantian sequence may be present at some localities as the enigmatic centerville formation and or basal belfast member of the brassfield formation the implications of these new correlations and sequence interpretations include a new standard for relative sea level changes and insights into basin dynamics this framework also permits a more nuanced history of biotic changes that include geologically brief pulses of immigration associated with the transgressions of the c1 lower kope formation c5c clarksville member of waynesville formation and c7a basal whitewater formation

analysis of sample level properties along a paleoenvironmental gradient the behavior of evenness as a function of sample size abstract the assessment of fossil biodiversity is influenced by a range of sampling effects such as sample size evenness and lithological character many paleontologists have worked to understand and mitigate for such biasing effects generating standardized assessments of local regional and global biodiversity however when assessing biodiversity among individual communities with small sample sizes such as those from lithified paleozoic samples it is important to understand how these properties relate to one another qualitatively and quantitatively here the properties of richness and evenness were investigated at the sample level along an ecological gradient within a stratigraphically and geographically constrained interval the fulton submember of the kope formation upper ordovician of kentucky and ohio using a replicate subsampling procedure analogous to rarefaction evenness values were generated using four metrics j pie ess and essmin simulations using real and simulated data revealed that the pie metric generates the most stable assessments of evenness at very small sample sizes and relative evenness can be assessed at any sample size provided that replicate subsampling is performed comparisons of richness evenness and lithology revealed no directional trend along the ecological gradient but two distinct groups of samples were identified by differences in evenness as well as the number of sampled individuals such differences in abundance structure influence perceptions of biodiversity when samples from low evenness and high evenness assemblages are aggregated increasing the sampling intensity in low evenness communities may help to mitigate for these differences and more thoroughly capture the richness contained within small samples

the use of faunal gradient analysis for intraregional correlation and assessment of changes in sea floor topography in the type cincinnatian abstract in paleobiology and stratigraphy there is a growing need to develop high resolution chronostratigraphic frameworks at regional scales which would permit unprecedented assessments of spatiotemporal variation in preserved biotas here we present an intraregional correlation for the kope and lower fairview formations of the type cincinnatian on the basis of detrended correspondence analysis dca of faunal census data we believe that the method also holds promise as a tool of correlation in other fossiliferous venues the data were collected directly in the field at closely spaced stratigraphic intervals but with relatively coarse taxonomic and quantitative data resolution this approach is independent of lithologic assessments and does not require the delineation of sequence stratigraphic architecture in the study area faunal curves were constructed for each locality on the basis of stratigraphic changes in sample scores for dca axis 1 the curves were smoothed to reveal a long term signal of

the three dimensional geometry and growth of forced folds above saucer shaped igneous sills forced folds formed at the seabed immediately overlying shallow 1 km saucer shaped sills along the ne atlantic margin during the early paleogene examples of this sill fold relationship are exceptionally well imaged by high resolution 3d seismic datasets from the ne rockall basin the forced folds are domal in shape 2 4 km in diameter exhibit a structural relief of up to 350 m and comprise sediment volumes of ca 1 km3 a comparison of the thickness distribution across and volume of a saucer shaped sill with a high intrusion diameter to depth ratio and the structural relief and volume of its associated forced fold shows a remarkable equivalence this has the important implication that the structural relief on intrusion related forced folds can be used as an estimate of the thickness of the underlying sill the analysed forced folds are interpreted to have formed through three continual growth stages that are directly linked to the mechanical emplacement of the underlying saucer shaped sills their growth was associated with an increase in faulting of the overlying strata and influenced coeval or subsequent development of polygonal fault systems within the overburden these structures represent a new type of four way dip closed hydrocarbon trap

the etendeka igneous province magma types and their stratigraphic distribution with implications for the evolution of the parana etendeka flood basalt province detailed geochemical and field data for the volcanic sequence and intrusions of the etendeka igneous province are used to construct a stratigraphic framework for petrogenetic interpretation of the evolution of the etendeka parana continental flood volcanic event geochemical and petrographic characterization of over 1 000 analyzed samples allows 8 mafic and 17 silicic magma types to be recognized both silicic and mafic types can be grouped into high ti and low ti suites on the basis of elevated ti relative to other elements the mafic magmas are khumib high ti tafelberg kuidas horingbaai huab tafelkop albin and esmeralda all low ti amongst the silicic types the goboboseb springbok wereldsend grootberg and beacon low ti quartz latites and the nil desperandum high ti latite have been described previously in addition the hoas low ti nadas sechomib and hoarusib all high ti latites and the fria low ti sarusas ventura khoraseb naude and elliott all high ti quartz latites are described for the first time here there is a marked provinciality in the distribution of the high and low ti suites with the former concentrated in the northern etendeka region and the latter dominant in the southern etendeka stratigraphic distribution of magma types allows two new formations to be defined in the northern etendeka the khumib formation of basaltic flows and the skeleton coast formation dominated by silicic sheets the geochemical provinciality hampers precise correlations between northern and southern etendeka available evidence suggests that the lower part of the awahab formation in the southern etendeka is coeval with the lower part of the khumib formation and that the silicic units in the upper part of the tafelberg formation probably correlate with the skeleton coast formation the paucity of khumib dykes in relation to tafelberg dykes and their field relationships with regard to the volcanic sequence in the northern etendeka suggests that the main khumib eruptive centers lay further north consistent with southward thinning of the khumib basalts in the southern etendeka the doros complex is the eruptive center of the plume derived tafelkop basalts which probably built a shield volcano within the regional flood lava field this work indicates that the etendeka has a greater variety of both silicic and low ti mafic magma types than are known from the se parana detailed comparisons reveal that all the important silicic types in the parana have geochemical equivalents in the etendeka new correlations are santa maria fria ourinhos khoraseb guarapuava sarusas thus extending the previously recognized correlations between southern etendeka quartz latites and the caixas do sul and anita garibaldi rhyolites these correlations emphasize that very large volume silicic systems develop with pronounced lithospheric rifting in continental flood basalt provinces

emplacement of the most recent lava flows on hualālai volcano hawai i a detailed field and petrologic study of the ca 1800 a d flows at hual lai volcano documents at least two eruptive episodes the hu ehu e flow field ending in 1801 and the ka p lehu flow several decades earlier the morphology and stratigraphy of the ka p lehu flow require an emplacement duration of several days to weeks based on a comparison with recent eruptive activity at mauna loa volcano the eruption cannot have occurred at the anomalously high rate 104 105 m3 s proposed by previous workers the hummocky flow surface of the later phase of the hu ehu e eruption suggests a duration of months based on a comparison with recent eruptive activity at k lauea volcano although none of the ca 1800 flows show evidence for extraordinarily fast emplacement or unusual fluid rheologies both flows show unusual features the abundant xenoliths for which the ka p lehu flow is famous were transported in numerous episodes of deposition and remobilization during which they eroded the channel systems through which they traveled lava transport in proximal and medial regions of both flow fields was probably through lava tubes as evidenced by preserved tubes and by the prevalence of p hoehoe lined channels that require thermally efficient transport of lava over great distances both flows also show abundant evidence for re occupation of older cones and lava tubes a characteristic that may typify infrequent eruptions of older volcanic systems although lava flows from hual lai volcano do not show anomalous eruptive behavior they pose a substantial hazard for coastal communities of kona

three dimensional lithofacies variations in hyaloclastite deposits analysis of the spatial lithofacies variability within lava fed delta formations in southern iceland has revealed complex three dimensional volcanic architectures in hyaloclastite deposits in non glacial settings two depositional environments are studied a lava entering a marine embayment stori nupur and b lava advancing into a body of water of the flanks of a surtseyan cone hjorleifshof i interaction between environmental factors such as shoreline geomorphology water depth wave energy levels the nature of the lava transport system lava supply rate all affect the resulting lava deltas creating complex lithofacies arrangements and stacking patterns recognised here are two types of hyaloclastite deltas one of syn sedimentary origin hjorleifshof i and one derived from primary fragmentation processes stori nupur syn sedimentary systems are dominated by destabilisation of the hyaloclastite pile leading to reworking downslope and share similarities to alluvial delta systems conversely primary fragmented systems are controlled by waxing and waning cycles in volcanic effusivity whereby the hyaloclastite unit recorded is not the product of one lava flow rather than one eruptive event

reply to comment by k thomson on the three dimensional geometry and growth of forced folds above saucer shaped sills by d m hansen and j cartwright

structural evolution beneath sakurajima volcano japan revealed through rounds of controlled seismic experiments abstract structural evolution beneath an active volcano is detected as the variation of seismic reflectivity through controlled seismic experiments which is interpreted as being associated with discharging magma the target of the present study is sakurajima volcano which is one of the most active volcanoes in japan six rounds of seismic experiments with controlled sources have been conducted annually at the volcano two seismic reflection profiles are obtained from the datasets for each successful round of experiments the experiments reveal clear annual variation in seismic reflectivity at a depth of 6 2 km in the northeastern part of sakurajima the reflectivity is maximum in december 2009 upon the first intrusion of magma and decreases gradually until december 2013 which coincides with the inflation and deflation cycle of sakurajima volcano reflectivity variation occurred in the embedded clear reflector at depth an evolving sandwiched structure in the intermediate layer is used as the reflector model lower velocity magma embedded in the intermediate layer and its succeeding velocity increment explain the variation range of reflectivity this is interpreted as a temperature decrease associated with discharging magma at depth the present study describes a new approach for instantaneously sensing magma properties and for monitoring active volcanoes

lava tubes terraces and megatumuli on the 1614 24 pahoehoe lava flow field mount etna sicily the 1614 1624 lava flow of mt etna was formed during a long duration flank eruption involving predominantly pahoehoe flows which produced unusual surface features including mega tumuli here defined and terraces detailed mapping of the flow units surface features and associated tubes reveals a complex sequence of emplacement for the field the stair stepped terraces appear to have been formed as a consequence of self damming of tube fed flows which developed perched ponds of lava surges of lava through tubes elevated sections of crusted lava at the distal ends of the flow to generate tumuli some as high as 130 m as a consequence of pressure via hydrostatic head conditions within the tube although pahoehoe lavas and the related features described here are atypical of mt etna they may reflect styles of eruption and lava emplacement found on volcanoes elsewhere

geometry and growth of sill complexes insights using 3d seismic from the north rockall trough doleritic sill complexes which are an important component of volcanic continental margins can be imaged using 3d seismic reflection data this allows unprecedented access to the complete 3d geometry of the bodies and an opportunity to test classic sill emplacement models the doleritic sills associated with basaltic volcanism in the north rockall trough occur in two forms radially symmetrical sill complexes consist of a saucer like inner sill at the base with an arcuate inclined sheet connecting it to a gently inclined commonly ragged outer rim bilaterally symmetrical sill complexes are sourced by magma diverted from a magma conduit feeding an overlying volcano with an elongate concave upwards trough like geometry bilaterally symmetrical sills climb away from the magma source from which they originate both sill complex types can appear as isolated bodies but commonly occur in close proximity and consequently merge producing hybrid sill complexes radial sill complexes consist of a series of radiating primary flow units with dimensions up to 3 km each primary flow unit rises from the inner saucer and is fed by primary magma tube primary flow units contain secondary flow units with dimensions up to 2 km each being fed by a secondary magma tube branching from the primary magma tube secondary flow units in turn are composed of 100 m scale tertiary flow units a similar branching hierarchy of flow units can also be seen in bilaterally symmetrical sill complexes with their internal architecture resembling an enlarged version of a primary flow unit from a radial sill complex this branching flow pattern as well as the interaction between flow units of varying orders provides new insights into the origin of the structures commonly seen within sill complexes and the hybrid sill bodies produced by their merger the data demonstrate that each radially symmetrical sill complex is independently fed from a source located beneath the centre of the inner saucer grows by climbing from the centre outwards and that peripheral dyking from the upper surface is a common feature these features suggest a laccolith emplacement style involving peripheral fracturing and dyking during inner saucer growth and thickening the branching hierarchy of flow units within bilaterally symmetrical sill complexes is broadly similar to that of primary flow units within a radially symmetrical sill complex suggesting that the general features of the laccolith emplacement model also apply

mid jurassic volcanic structures in the outer moray firth basin uk 3d seismic mapping in the southern part of quadrant 15 in the outer moray firth basin reveals an array of circular to oval downthrown blocks bound by steep ring faults these lows affect triassic and older strata are approximately 1 5 2 km in diameter and 0 5 1 km deep the footwall crests of the structures now lie at a depth of c 2 5 km several alternative causal mechanisms for these circular fault blocks are examined including salt dissolution strike slip pull apart and impact cratering but in terms of geological and geometrical criteria the most likely mechanism appears to be small calderas or diatreme conduit collapse seismic data indicates that the circular structures cut triassic permian and devono carboniferous strata and are infilled with pre upper oxfordian sediments therefore they are broadly synchronous with mid jurassic volcanism local well control demonstrates the presence of several thousand feet of basalt tuffs and lavas the model proposed here to account for the circular structures consists of an initial phase of diatreme maar cratering as magmas associated with the rattray volcanics member intruded shallow aquifers in the pentland formation fluviodeltaic rocks these maars enlarged and deepened via conduit wall collapse supplemented by downsag faulting due to magma withdrawal the post volcanic evolution of the structures included 1 differential erosion creating accommodation space which may have been infilled with oxfordian reservoir sands and 2 local reactivation by underlying basement faults in the kimmeridgian

stratigraphic resolution and perceptions of cycle architecture variations in meter scale cyclicity in the type cincinnatian series previous analyses of meter scale cyclicity have de emphasized thin beds within investigated stratigraphic intervals here we analyze the effect of excluding relatively thin beds on cycle delineation and interpretation in the type cincinnatian series whereas inclusion of all strata suggests wide variation in cycle architecture systematic culling of thin beds decreases this variability considerably in part by removing much of the evidence for intervals of deepening that are important components in more than half the meter scale cycles recognized here thus cycles in the culled data conform more easily to a parasequence model in that a greater plurality exhibit a simple shallowing upward motif raising the concern that the exclusion of thin beds in other analyses might similarly oversimplify the perceived signal of cyclicity

the importance of subsurface lithology in controlling magma storage v eruption an example from offshore southern australia the volumetric relationship between the intrusive and extrusive components of volcanic fields is difficult to constrain this is because either the erupted products are commonly eroded or the intrusions are concealed by overburden three dimensional seismic data therefore offer a unique opportunity to study ancient volcanic provinces as these datasets can image both components without the need for erosional dissection this study is based on 3d seismic data from the bight basin igneous complex bbic a volcanic province constructed within a sedimentary basin offshore southern australia we demonstrate that the bbic contains abundant sills and laccoliths emplaced within deltaic sediments the intrusions have a total volume of 92 111 km 3 and the lava flows and volcanoes have a combined volume of 66 76 km 3 dense rock equivalent this indicates that the ratio of intrusive extrusive products for the bbic is between 1 1 and 2 1 the architecture of the bbic contrasts markedly with the neighbouring newer volcanics province nvp which lacks abundant sills and laccoliths because lava flows and volcanoes in the nvp were dominantly fed by dykes hosted in basement rock we suggest that subsurface lithology plays an important role in causing sill formation and determining the total volume of magma stored in the subsurface

the north atlantic igneous province stratigraphy tectonic volcanic and magmatic processes the north atlantic igneous province has been the subject of extensive scientific investigation over the past thirty years with a wide field of knowledge being accumulated recently recognition of the potential role of large igneous provinces in affecting ocean and atmosphere systems and biotic evolutionary pathways has lead to increased interest in this province this has been further stimulated by the expansion in the search for oil and gas in mesozoic and tertiary sediments along the ne atlantic margin an improved understanding of the interaction between igneous and sedimentary processes is vital for the identification of potential hydrocarbon resources the regions covered include continental margin norway east and west greenland the faroe shetland basin and the faroe islands themselves the papers in this book contain new data and interpretations of north atlantic igneous province magmatic processes rift evolution tectonics stratigraphy chemostratigraphy biostratigraphy seismic and isotope stratigraphy and sediment dispersal many of the papers adopt a multidisciplinary approach to tha analysis and interpretation of complex volcanic and sedimentary sequences these new data and the reviews and compilations of existing data provide the reader with access to current research directions in north atlantic igneous province geology

structure and origin by injection of lava under surface crust of tumuli lava rises lava rise pits and lava inflation clefts in hawaii tumuli are positive topographic features that are common on hawaiian pahoehoe lava flow fields particularly on shallow slopes and 75 measured examples are presented here to document the size range tumuli form by up tilting of crustal plates without any crustal shortening and are thus distinguished from pressure ridges which are up buckled by laterally directed pressure the axial or star like systems of deep clefts that characterize tumuli are defined here as lava inflation clefts their tips advanced into red hot lava and they widened as uplift proceeded and while the lava crust was thickening flat surfaced uplifts formed like tumuli by injection of lava under a surface crust were previously called pressure plateaus but lava rise is proposed instead the pits that abound among lava rises previously attributed to collapse or subsidence are generally formed because the lava around them rose and the name lava rise pit is proposed unique examples of tumuli and lava rises from which lava drained out under a surface crust 1 5 to 2 5 m thick are described from kilauea caldera these examples show that in tumuli and lava rises the crust floats on considerable bodies of fluid lava and is able to do so because of its higher vesicle content the fluid lava loses many of its gas bubbles during residence beneath the crust the bulk densities of samples from tumuli show a general downward increase the form of the density profile is consistent with the relationship that for any given crustal thickness the density of fluid lava closely matched the average density of that crust suggesting that the lava was stably density stratified it is inferred that stable stratification was regulated by out flows of the more vesicular lava fractions loss of bubbles through the lava inflation clefts and entry of injected lava at its level of neutral buoyancy below the uppermost meter the downward decrease in vesicularity closely conforms with that expected by compression of a uniform mass of gas per unit mass of lava

seismic volcanostratigraphy of large volume basaltic extrusive complexes on rifted margins large volume extrusive basaltic constructions have distinct morphologies and seismic properties depending on the eruption and emplacement environments the presence and amount of water is of main importance while local rift basin configuration erosion and resedimentation determine the overall geometry of the volcanic constructions we have developed the concept of seismic volcanostratigraphy a subset of seismic stratigraphy to analyze volcanic deposits imaged on seismic reflection data the method places special focus on identification and mapping of seismic facies units and the volcanological interpretation of these units interpretation of seismic reflection data along the atlantic and western australia rifted margins reveals six characteristic volcanic seismic facies units named 1 landward flows 2 lava delta 3 inner flows 4 inner seaward dipping reflectors inner sdr 5 outer high and 6 outer sdr these units are interpreted in terms of a five stage tectonomagmatic volcanic margin evolution model comprising 1 explosive volcanism in a wet sediment broad basin setting 2 subaerial effusive volcanism forming gilbert type lava deltas along paleoshorelines 3 subaerial effusive volcanism infilling a fairly narrow rift basin 4 shallow marine explosive volcanism as the injection axis is submerged below sea level and finally 5 deep marine sheet flow or pillow basalt volcanism further erosion and resedimentation processes are particularly important during the shallow marine stages seismic volcanostratigraphy provides important constraints on rifted margin development in particular on the prevolcanic basin configuration relative timing of tectonomagmatic events total amount of volcanic rocks location of paleoshorelines and margin subsidence history these parameters give key boundary conditions for understanding the processes forming volcanic margins and other large volume basaltic provinces

stratigraphic architecture of the proterozoic succession in the eastern chattisgarth basin india tectonic implications abstract the basin fill succession of the proterozoic eastern chattisgarth basin comprises a sandstone shale conglomerate dominated shallow marine assemblage and an assemblage of limestone shale pyroclastics deposited in off shelf slope base of slope environments the proximal and distal lithologic assemblages developed as lateral equivalents and show signatures of sea level fluctuations amenable to chronostratigraphic correlation the stratigraphic architecture of the proximal assemblage is characterized by cyclic deposition on different scales the largest order cyclicity is represented by alternating sandstone sequences and mudstone dominated sequences of the order of several tens of metres the smallest order cyclicity is represented by metre scale units punctuated aggradation cycles pac bounded by isochronous surfaces the lowermost large scale sandstone sequence the lohardih sandstone unconformably overlies the highly deformed rocks of the gneissic basement complex the sequence was deposited as alluvial fan fan delta complexes controlled by basin margin faulting the upper two sandstones the daihan sandstone and the kansapathar sandstone represent two different phases of major sand accumulation in fan or river deltas their rapid emplacement over muddy shelf deposits along erosional surfaces signaled abrupt sea level fall and basinward migration of facies belts generation and accumulation of very large volumes of sand and their rapid influx into the basin accompanied by major changes in depositional motif and in the circulation system in the basin collectively indicate that larger order sand depositing cycles were caused by tectonic uplift of the cratonic basement the smallest order cycles the pacs on the other hand may be attributed to glacioeustacy though tectonic control cannot be ruled out the sand deficient mud dominated large scale sequences are attributed to major transgression during periods of relative tectonic quiescence and subsidence of the cratonic hinterland episodic tectonic uplift and derivation of sands from similar quartzo feldspathic sources suggest repeated rifting of the cratonic basement and expansion of the rift into a major marine basin

volcanic features of the north rockall trough application of visualisation techniques on 3d seismic reflection data understanding the volcanic processes operating during continental break up is hampered by the subsequent burial of the majority of the volcanic pile beneath thick sedimentary sequences currently located in bathymetrically deep offshore regions although portions of these volcanic systems are currently exposed on land a full understanding of the volcanic structure the eruptive styles and their evolution is not possible as these localities have been partially eroded furthermore as the onshore exposure represents a volumetrically minor part of the entire system the documented eruptive styles may not be representative the increasing availability of 3d seismic reflection data has the potential to significantly enhance our understanding of break up related volcanism as it allows direct access to detailed information from the buried volcanic succession however conventional seismic interpretation methodologies cannot determine lava flow morphologies and as a result eruptive styles and their evolution are still largely based on extrapolation from the accessible onshore outcrop data new 3d seismic volume visualisation techniques allow the buried basalt morphologies to be examined for the first time in a manner similar to outcrop aerial photographic or satellite based observations applying this new approach for 3d seismic data to the north rockall trough u k atlantic margin demonstrates that a range of volcanic features indicative of eruptive style can be determined the data reveal a complex terrain containing lava flows originating from discrete volcanic centres contemporaneous normal faults linear fissures a few kilometres long radial fissures and inflation ridges lava flow morphologies that are indicative of tube fed inflated sheetflows intracanyon flows and elongate subaerial flows that enter water downslope to produce a large hyaloclastite delta are observed

the snake river plain idaho representative of a new category of volcanism studies of the volcanic geology of the snake river plain idaho and comparison with other basaltic regions suggest a new category of volcanic activity termed basaltic plains volcanism typified by the snake river plain this style of volcanism is intermediate between basaltic flood or plateau eruptions and hawaiian volcanism characteristics that are common to both hawaiian and plains volcanism are multiple lava flow units which erupt primarily from point sources formation of low shields and frequent emplacement through lava tubes or channels characteristics that are common to both flood basalts and plains volcanism are high volume flows vents aligned along rift zones and planar surfaces the recognition of plains volcanism in other areas provides a means to interpret the style of eruption and volcanic history

decomposing observations of high frequency radar derived surface currents by their forcing mechanisms locally wind driven surface currents 1 the wind impulse response function and transfer function for high frequency radar derived surface currents off southern san diego are calculated using several local wind observations the spatial map of the transfer function reflects the influence of the coast on wind current dynamics near the coast within 20 km from the shoreline the amplitudes of the transfer function at inertial and diurnal frequencies are reduced due to effects of coastline and bottom bathymetry meanwhile the amplitude of low frequency currents increases near the coast which is attributed to the local geostrophic balance between cross shore pressure gradients against the coast and currents locally wind driven surface currents are estimated from the data derived response function and their power spectrum shows a strong diurnal peak superposed on a red spectrum similar to the spectra of observed winds current magnitudes and veering angles to a quasi steady wind are typically 2 5 of the wind speed and vary 50 90 to the right of the wind respectively a wind skill map is introduced to present the fractional variance of surface currents explained by local winds as a verification tool for wind data quality and relevance moreover the transfer functions in summer and winter are presented to examine the seasonal variation in ocean surface current response to the wind associated with stratification change

tumuli and associated features from the western deccan volcanic province india whale back shaped uplifts called tumuli are common in the pahoehoe flows of the western deccan volcanic province dvp although they usually occur in hummocky flows they are also associated with thicker sheet lobes they have been subjected to a detailed morphometric and petrographic study for the first time the tumuli are characterised by positive relief and lava inflation clefts occupied by squeeze ups they display elongate as well as equant forms some are constituted of a single flow lobe whereas others display multiple flow lobes some tumuli appear to have developed along anastomosing tube systems the detailed study of one of the tumuli reveals considerable petrographic and textural variations among the constituent flow units some of these such as the enrichment of phenocrysts in squeeze ups and breakouts could be related to the emplacement dynamics of the tumulus all the observed tumuli display much evidence of inflation or endogenous growth field observations and measurements reveal that the tumuli and associated pahoehoe features display a close similarity with their hawaiian counterparts this is a very significant observation since it points out to a similarity in nature and style of eruptions in hawaii and at least in the western part of the dvp this has an important bearing on determining the short medium and long term effusion rates in the deccan however any concrete inference will have to await systematic volcanological studies of the lava features in the dvp