sequence stratigraphy in a mixed carbonate silicilastic depositional system middle miocene styrian basin austria the mixed carbonate siliciclastic weisenegg allo formation records three depositional sequences corresponding approximately to the tb 2 3 tb 2 4 and tb 2 5 global cycles sea level fluctuations were of the order of at least 30 m siliciclastic lowstand systems tracts comprise lignite deposits reworked basement and tidal siltstones above a tectonically enhanced sequence boundary as well as coastal sand bars coastal sands of the transgressive systems tract contain distinct layers of well cemented nodules they are interpreted as the first stage in hardground formation and record superimposed minor sea level fluctuations coral patch reefs and rhodolith platforms developed during transgressive phases and were subsequently drowned and or suffocated by siliciclastics during early highstand shallowing upwards siliciclastic parasequences each terminated by a bank of rhodolith limestone form the late highstand systems tract the limestone beds record superimposed fourth order transgressive pulses occasionally a carbonate highstand wedge developed lowstand carbonate shedding occurred where the top of a platform which suffered incipient drowning during highstand was near sealevel again during the following lowstand late highstand delta progradation is common

hierarchal genetic stratigraphy a framework for paleoceanography a detailed genetic stratigraphic framework for paleoceanographic studies can be derived by describing correlating interpreting and predicting stratigraphic sequences relative to a hierarchy of their constituent time stratigraphic transgressive regressive units t r units t r unit hierarchies are defined and correlated using lithostratigraphic and paleoecologic data but correlations can be enhanced or checked tested to confirm or deny with objective biostratigraphic magnetostratigraphic or chemostratigraphic data such chronostratigraphies can then be bracketed by radiometric ages so that average periodicities for t r units can be calculated and a hierarchal geochronology derived t r units are inferred to be the net depositional result of eustatic cycles of sea level change and can be differentiated from autocyclic deepening shallowing units because the latter are noncorrelative intrabasinally boundaries between t r units are conformable or unconformable genetic surfaces of two types transgressive surfaces and climate change surfaces the latter are useful for correlating minor transgressive phases through nonmarine intervals thereby deriving information linking paleoclimatic and paleoceanographic processes permo carboniferous sequences can be analyzed relative to a hierarchy of six scales of genetic t r units having periodicities of 225 300 m y first order 20 90 m y second order 7 13 m y third order 0 6 3 6 m y fourth order 300 500 10 years fifth order and 50 130 10 years or less sixth order paleogeographic maps for the time of maximum transgression transgressive apex of successive fifth order t r units 5 25 m thick in the glenshaw formation upper pennsylvanian northern appalachian basin delineate delta lobes embayments islands and linear seaways relative extent of marine inundation on the fifth order maps was used to delineate fourth order t r units and the fourth order t r units constitute the transgressive half of a third order t r unit this third fourth and fifth order hierarchy is correlated more than 1200 km 750 miles to the western interior basin and is confirmed with limited objective biostratigraphy

carbonate platform evolution from a bioconstructed platform margin to a sand shoal system devonian guilin south china the depositional organization and architecture of the middle late devonian yangdi rimmed carbonate platform margin in the guilin area of south china were related to oblique extensional faulting in a strike slip setting the platform margin shows two main stages of construction in the late givetian to frasnian with a bioconstructed margin evolving into a sand shoal system in the late givetian the platform margin was rimmed with microbial buildups composed mainly of cyanobacterial colonies mostly renalcis and epiphyton these grew upwards and produced an aggradational locally slightly retrogradational architecture with steep foreslope clinoforms three depositional sequences s3 s5 are recognized in the upper givetian strata which are dominated by extensive microbialites metre scale depositional cyclicity occurs in most facies associations except in the platform margin buildups and upper foreslope facies in the latest givetian at the top of sequence s5 relative platform uplift subaerial exposure and associated rapid basin subsidence probably a block tilting effect caused large scale platform collapse and slope erosion to give local scalloped embayments along the platform margin and the synchronous demise of microbial buildups subsequently sand shoals and banks composed of ooids and peloids and a little later stromatoporoid buildups on the palaeohighs developed along the platform margin from which abundant loose sediment was transported downslope to form gravity flow deposits another strong tectonic episode caused further platform collapse in the early frasnian at the top of sequence s6 leading to large scale breccia release and the death of the stromatoporoid buildups siliceous facies banded cherts and siliceous shales were then deposited extensively in the basin centre as a result of the influx of hydrothermal fluids the platform margin sand shoal bank system possibly with gullies on the slope persisted into the latest frasnian until the restoration of microbial buildups four sequences s6 s9 characterized by abundant sand shoal deposits on the margin and gravity flow and hemipelagic deposits on the slope are distinguished in the frasnian strata smaller scale depositional cyclicity is evident in all facies associations across the platform slope basin transect the distinctive depositional architecture and evolution of this yangdi platform are interpreted as having been controlled mainly by regional tectonics with contributions from eustasy environmental factors oceanographic setting biotic and sedimentary fabrics

geomorphic thresholds and complex response of fluvial systems some implications for sequence stratigraphy first generation sequence stratigraphic models have dealt in a very rudimentary fashion with the response of fluvial systems to eustasy a major element of presently accepted models is that rivers incise when sea level falls and aggrade during the ensuing rise well established geomorphic principles state that fluvial systems are complex process response systems that can adjust to internal and external changes in other ways besides incision and aggradation by modifying their stream patterns and channel geometries application of geomorphic principles to sequence stratigraphic models results in the following observations during eustatic lowstands rivers may adjust to lowered base levels and changes in slope by modifying channel patterns therefore not all lowstands produce type 1 sequence boundaries type 1 sequence boundaries characterized by fluvial valley incision are more likely to develop when sea level drops below the shelf slope break resulting in topological relief near the strandline in which headwardly eroding knickpoints form rates of eustatic change although rapid in a geological context are sufficiently low that geomorphic systems can easily maintain their equilibrium during eustatic changes and migrate back and forth across the shelf without major modifications finally und r conditions of relatively static sea level sequences and parasequences of the same scale in time and space as those which form during eustatic change can be deposited as the result of purely intrinsic causes and responses of a fluvial system in general eustasy controls the location of deposition and erosion but the resultant stratal geometry is controlled by sediment supply and processes acting on the sediments as the shoreline moves across the shelf in response to eustasy

the declining but non rejuvenating base level the lisan lake the dead sea area israel laboratory experiments investigating the effects of a lowering base level do not simulate natural eustatic lowering along concave river profiles the field data on this issue are also quite limited in evaluating the control exercised by lowering base level on a drainage network distinction must be made between its influence and those of other hydromorphological processes operating within the basin field data on morphological relations based on photogrammetric mapping and longitudinal profiling have been gathered in the dead sea area israel where a rapid fall in base level has occurred during the holocene the study area is an entrenched fan delta with a sequence of 14 unpaired fan terraces which die out at intersection points within an alluvial fan system the results suggest that the intersection points did not function as base levels the receding base level played only a passive role allowing entrenchment without transmitting a head cutting feedback basinwards the arid environment caused a delay in transmission of information through the system the results support the model of short episodic and discontinuous erosional events inherent in the evolution of drainage basins it is suggested that base level effects in temperate and humid regions are not transferrable to arid zones

1982 sepm presidential address episodic sedimentation how normal is average how rare is rare does it matter abstract do sedimentary rocks record mainly average continuous day to day processes or relatively rare large magnitude ones separated by long nondepositional intervals subtle legacies from lyellian uniformitarianism may still impose a subconscious abhorrence of unique events discontinuities and large deviations from average magnitudes where repeated sharp changes of sedimentation are inescapable periodic cycles are commonly invoked to preserve uniform orderly variations from some supposed norm the sedimentary record rarely reflects such uniformity however as sedimentologists have gradually realized magnitude versus frequency of processes has long been debated in geomorphology but has received less attention in sedimentology recurrence interval recovery time and preservation potential are critical factors for evaluating their significance for the sedimentary record large magnitude processes which represent positive deviations from the norm and are rare on the human time scale must be significant over geologic time but how significant could not everyday processes have obliterated much of the evidence flood deposits have relatively low preservation potential because they lie above base level marine gravel layers dispersed by abnormal waves have greater preservation potential because most ordinary processes are not competent to modify them sandy or shelly de osits formed by large waves and displaying either hummocky cross stratification or graded bedding have a moderate preservation potential especially if too thick for burrowing animals to homogenize them turbidites which provide exceptional records of episodicity have excellent preservation potential because they lie well below base level many bedding planes are important records of episodicity too some are surfaces of erosion others of nondeposition these represent negative deviations from average process magnitudes the sedimentological importance of rare events is difficult to assess because the record of such events may be very subtle this is especially true if a deposit has been thoroughly bioturbated or if the record of an event is simply an erosional surface it has now become possible to evaluate quantitatively ancient episodic sedimentation using modern process rates as well as refined biostratigraphic and isotopic dating i predict that such evaluation will necessitate revision of our favorite depositional models which have become so important for exploration as well as for research

facies architecture and sequence stratigraphy in glacially influenced basins basic problems and water level glacier input point controls with an example from the quaternary of ontario canada abstract sequence architecture is controlled by two fundamental factors the water level relative to the depositional surface which controls accommodation space and the points or areas of sediment injection which control how this space is filled in relative water level accommodation space and injection points normally vary together and various genetic terms are used to define systems tracts but in glacially influenced basins accommodation space is controlled not only by water level but also by the glacier injection points are similarly dually controlled by water level and by the terminus of the glacier during high lake levels the injection point of the glacier may be underwater at the base of the slope genetic terms like highstand and lowstand therefore are meaningless in successions controlled by sediment input points which are independent of water levels and accommodation space distinct water level and glacier input point systems can occur side by side the water level system controlled by lake level or sea level the glacier input point system controlled by the position of the subaqueous glacier front and both can form juxtaposed systems passing laterally into each other a bewildering and incompatible terminology is needed if the terms of genetic sequence stratigraphy are used for both water level and glacier input point systems because the sedimentary injection points and sequence boundaries of the two systems fluctuate out of phase with one another sequences developed by movement of the glacier are completely independent of those controlled by water levels if genetic sequence stratigraphy is applied to a basin with both lake level and glacier input point systems then each needs separate genetic terminologies to describe them which leads only to confusion however descriptive sequence stratigraphy allostratigraphy can be readily applied to successions like the quaternary of lake ontario we therefore suggest that genetic sequence terms be discarded and simpler allostratigraphic terminology used in glacially influenced basins

hierarchy of high frequency orbital cycles in cretaceous carbonate platform strata abstract lower cretaceous valanginian hauterivian carbonate platform strata which are well exposed in the matese mountains of the southern apennines italy have been analyzed on a microstratigraphic cm scale to exemplify the high frequency cyclic nature of the mesozoic shallow water sedimentation in southern italy based on the vertical organization of lithofacies and their early diagenetic signature 46 metre scale cycles are recognized these elementary cycles are hierarchically organized into groups bundles and superbundles the elementary cycles are prevalently formed by subtidal deposits and show emersion related features at the top suggesting repeated sea level fluctuations the number of elementary cycles compared to time as constrained by biostratigraphy and their grouping into sets implying higher order complexity in the environmental oscillation suggest an orbital control on sedimentation spectral analysis of recurrent thickness in stratal features defines and quantifies the cyclicity which is characterized by lithofacies thickness periodicities of 1271 391 159 124 and 69 cm linear correlation of the relative ratio set rrs of these periodicities with the corresponding rrs of the orbital perturbation periodicities shows that 1271 and 391 cm fit the 404 220 and 94 890 year cycles of early cretaceous orbital eccentricity 159 and 124 cm fit the 49 010 and 38 030 year cycles of the earth s axial obliquity whereas 69 cm corresponds to the precession periodicity thus the san lorenzello section required not less than 1 6 ma to form at an average rate of 26 mm ka each 400 ka cycle can be viewed as a depositional sequence in which sequence boundaries maximum flooding surfaces and system tract equivalents have been recognized the microstratigraphic approach is very promising for understanding the fine structure of climate related environmental fluctuation recorded by the 3000 m thick carbonate platform successions of the southern apennines over a time span of about 150 ma upper triassic upper cretaceous and for deriving a more precise chronostratigraphy for global correlation

response of shallow marine carbonate facies to third order and high frequency sea level fluctuations hauptrogenstein formation northern switzerland abstract facies patterns in shallow marine carbonates of the hauptrogenstein formation of northern switzerland middle bajocian to early bathonian reflect small changes in sea level third order sea level fluctuations calculated from large scale facies patterns alternations of marl and carbonate dominated sedimentary units on the level of members and subsidence show two phases of sea level rise and fall in the late bajocian and a relative sea level rise in the early bathonian most of the sedimentary rocks were produced during phases of relative rise and highstand of sea level no periods of emergence during lowstands are preserved sea level changes of a higher order have been analyzed by facies changes at the outcrop scale thin shallowing up parasequences 0 5 6 m thick have been correlated across platform ramp and offshore sedimentary environments in each of these environments carbonates react differently to sea level fluctuations relative rises in sea level are represented by non deposition and biogenic sediments periods of stable or slightly falling sea level are dominated by oolitic sediments 1 in the offshoal environment marl layers at the base of thin shallowing up units are covered by increasingly proximal tempestites 2 in the ramp environment oblique stratified oolitic and bioclastic grainstones are bounded by marine flooding surfaces 3 on the platform marine flooding surfaces are overlain by beds deposited under moderate energy conditions coral beds oncoid beds platform tempestites which are in turn covered by high energy oblique stratified oolitic grainstones such parasequences deposited in response to small scale high frequency sea level changes can be correlated over distances of more than 100 km a model for evolution and response of carbonate facies to sea level changes is presented

cyclic sedimentation in the southern alpine rhaetic the importance of climate and eustasy in controlling platform basin interactions uppermost triassic rhaetic facies as developed in the southern alpine region of northern italy were deposited in a rapidly subsiding fault dissected trough the lombardy basin bounded by carbonate platforms the main part of the rhaetic succession consists of 10 m scale asymmetric cycles each divided into three parts a lower shale portion a central rhythmic portion consisting of repeated marl limestone couplets the limestone parts of which thicken upward and an upper wholly carbonate unit a study of the diagenetic history of the series demonstrates that both the major asymmetric cyclicity and the limestone marl couplets of the central rhythmic member together constituting a compound cyclic form are fundamentally depositional in nature it is suggested that this compound cyclicity resulted from the superposition of a low frequency approximately 100 000 year periodicity asymmetric carbonate mud signal with a higher frequency terrigenous mud signal field petrographic and geochemical investigations suggest that the basinal carbonate is predominantly allochthonous in origin having been derived as relatively pure aragonitic mud from adjacent carbonate platforms it is postulated that the asymmetric carbonate signal was linked to the ecological effects of eustatic fluctuation on platform carbonate systems repeated subaerial exposure of subtidal muds in shallow areas indicates that such sea level variations occurred a model is presented in which the basinward export of carbonate was negligible in the deepening phase increased to a maximum during shallowing and was finally halted by the emergence of large platform flats in contrast the higher frequency terrigenous mud signal of the basin is thought to have been climatically modulated fluctuations of a shorter period than those predicted by the milankovitch theory affected hinterland precipitation and runoff particularly rapid subsidence and high depositional rates may have allowed the preservation of this signal

onset of biotic and environmental recovery from the end permian mass extinction within 1 2 million years a case study of the lower triassic of the meishan section south china abstract paleontological sedimentary and geochemical data obtained from the lower triassic strata of the meishan section south china suggest that onset of biotic recovery coincided with amelioration of paleoceanographic conditions and an increase in ocean productivity the griesbachian meishanorhynchia association from meishan indicates biotic recovery between the recovery stages 1 and 2 both the initial biotic recovery and palaeoceanic environmental amelioration occurred within 1 2 myr after the end permian mass extinction in the late griesbachian

symmetrical and upward shallowing cycles in the middle devonian of new york state and their implications for the punctuated aggradational cycle hypothesis the middle devonian eifelian and givetian hamilton group in western and central new york composed largely of fossil rich marine shelf and slope facies is subdivisible into repetitive facies sequences of varying thicknesses minor cycles include 1 to 3 m thick upward coarsening shale to siltstone hemicycles resembling sixth order punctuated aggradational cycles pacs in central new york probably correlative 0 5 1 0 m shale to argillaceous nodular limestone couplets occur in western areas major cycles in western new york include subsymmetrical 3 to 5 m thick packages with medial limestone beds analogous to upper limestones of pennsylvanian cyclothems the center of each cycle marks a regressive maximum and grades vertically above and below into black shale or dark gray mudstone corresponding in a facies sense to cyclothemic core shales in the midcontinent pennsylvanian these widespread units appear to be allocyclic in nature and approximate fifth order transgressive regressive cycles based upon average unit thickness relative to the encompassing well zoned hamilton sequence correlations show that most key regressive events marked by limestones in western new york are expressed by equivalent siltstone or fine sandstone units in central new york most cycles which are nearly symmetrical in western new york grade eastward into 5 to 20 m upward coarsening pac motif hemicycles these asymmetric cycles apparently reflect rapid sediment aggradation to limits imposed by wave energy in a region of abundant sediment supply further minor shallowing was accompanied by winnowing and bypass of fine grained sediments generating condensed capping deposits of coarser silt and sand reworked shells and commonly phosphatic nodules ensuing sea level rises were accompanied by initial sediment starvation followed by sedimentation in deeper water hence asymmetrical upward shallowing hemicycles pacs appear to grade offshore into thin but symmetrical cycles both pac and symmetrical motifs are local responses to the same probably allocyclic sea level fluctuations we suggest that the pac motif is partially facies controlled being largely restricted to shallow shelf settings with relatively high rates of sediment accumulation

autocyclic perturbations of orbitally forced signals in the sedimentary record small scale cyclicity in stratigraphic sequences 1 mm 10 m is often attributed to regular orbital signals commonly however these signals are overprinted by other signals a dynamic forward model for clastic sedimentation in foreland basins suggests that this overprint can be caused by slope instability stress variations in the lithosphere and autocyclicity induced by climate change spectral analyses of predicted sedimentation rates with various external controls demonstrate the occurrence of autocyclic fluctuations in sediment flux on time scales smaller than the time scale of the variation of the original triggering external control this feature probably represents the response of the sedimentary system to external variations depending on the eigenfrequencies of this system because the eigenfrequencies are determined by the basin geometry changing through time a chaotic frequency distribution of sedimentation rates is expected this hypothesis explains the commonly observed absence of a significant number of frequencies of the orbital spectrum in a large number of sediment sequences

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

stratal thickness frequencies and the prevalence of orderedness in stratigraphic sequences assuming the existence of discernable hierarchies in the thickness and or temporal recurrence of stratal units within sedimentary sequences has become an increasingly important axiom of sequence and cyclostratigraphic studies and multiple orders of stratigraphic cyclicity are now commonly associated with inferred durations and magnitudes of rhythmic variation in global sea level beyond the desire to establish an informal nomenclature relating stratigraphic thickness to periodicity of eustatic change an assumption of stratigraphic orderedness also supports the inference that groups of sedimentary units with distinct modal dimensions in fact do occur with some generally distinct frequency in stratigraphic sequences in contrast to such perceived patterns of stratigraphic order many groupings of sedimentary units exhibit lognormal frequency distributions wherein most of the population has an exponentially increasing frequency of occurrence with linearly decreasing class size such thickness distributions

depositional environments and cyclicity of the early ordovician carbonate ramp in the western tarim basin nw china abstract during the early ordovician the tarim basin nw china was mainly occupied by an extensive shallow water carbonate platform on which a carbonate ramp system was developed in the bachu keping area of the western part of the basin three well exposed typical outcrop sections of the lower ordovician penglaiba formation were investigated in order to identify the depositional facies and to clarify origins of meter scale cycles and depositional sequences thereby the platform evolution thirteen lithofacies are identified and further grouped into three depositional facies associations peritidal restricted and open marine subtidal facies these lithofacies are vertically stacked into meter scale shallowing upward peritidal and subtidal cycles the peritidal cycles are mainly distributed in the lower and uppermost parts of the penglaiba formation deposited in the inner middle ramp and commonly start with shallow subtidal to intertidal facies followed by inter to supratidal facies in contrast the subtidal cycles occur throughout the formation mostly in the middle outer ramp and are dominated by shallow to relatively deep i e intermediate subtidal facies the dominance of asymmetrical and incomplete cycles suggests a dominant control of earth s orbital forcing on the cyclic deposition on the platform on the basis of vertical facies and cycle stacking patterns and accommodation changes illustrated by the fischer plots from all studied sections five third order depositional sequences are recognized in the penglaiba formation individual sequences comprise a lower transgressive part and an upper regressive one in shallow water depositional environments the transgressive packages are dominated by thicker than average subtidal cycles indicating an increase in accommodation space whereas regressive parts are mainly represented by thinner than average peritidal and subtidal cycles denoting a decrease in accommodation space in contrast in intermediate to deep subtidal environments transgressive and regressive packages display an opposite trend in accommodation space changes sequence boundaries except the basal and top boundaries of the penglaiba formation are usually represented by laterally traceable transitional boundary zones without apparent subaerial exposure features good correlation of the long term changes in accommodation space or sea level inferred from vertical stacking patterns of facies and cycles suggests an overriding eustatic control on the formation of meter scale cycles and third order depositional sequences as well as platform evolution superimposed with local and or regional tectonic influence during the early ordovician this study would help understand the controls on the tempo spatial facies distribution stratal cyclicity and carbonate platform evolution in the western tarim basin during the early ordovician facilitating prediction for favorable subsurface carbonate reservoirs and future hydrocarbon exploration and production in the penglaiba formation

progradational sequences in miocene shoreline deposits southeastern caliente range california abstract an exceptionally well exposed marine nonmarine transition in middle miocene strata exists in the southeastern caliente range california about 50 individual progradational sequences form a succession that ranges in thickness from approximately 1000 m where predominantly nonmarine to more than 2500 m where predominantly marine paleogeographic evidence in basalt flows near the top of the succession and in overlying fluvial deposits indicates that these middle miocene strata were deposited across a north northwest trending shoreline a complete progradational sequence typically is several meters to a few tens of meters thick and includes strata that represent three intertonguing stratigraphic units individual sequences generally rest on a thin gravel deposit interpreted as a transgressive lag on an erosional surface the gravel is overlain by structureless siltstone or fine grained sandstone deposited at water depths where the rate of faunal mixing exceeded that of production of structures by physical processes these rocks grade upward into bedded fine sandstone deposited closer to shore where physical processes exceeded bioturbation crossbedded lenses of coarse sand or fine gravel in the upper part of this facies suggest the presence of fairly long period surface waves the bedded fine sandstone is sharply ove lain by a cross bedded coarse sandstone facies that is interpreted as a combined offshore bar rip channel surf zone assemblage cross strata dip dominantly offshore suggesting substantial deposition from rip currents a secondary shoreparallel mode of cross strata direction suggests longshore currents produced by surface waves from the northwest the crossbedded coarse grained sandstone grades upward into planar bedded medium grained sandstone that is interpreted as a beach foreshore this facies grades upward through structureless medium grained sandstone into nonmarine or lagoonal red and green mudstone of the caliente formation the middle miocene succession was deposited in a subsiding basin that was otherwise remarkably stable tectonically the position of the strand line differed no more than a few kilometers through a period of 1 to 3 m y the average duration of the transgressive regressive cycles a few tens of thousands of years together with their distribution in groups of three or four in the lower two thirds of the succession is consistent with the pattern of long term climatic cycles produced by periodicity of the earth s solar orbit and may be related to eustatic sea level changes attendant to the development of the antarctic ice cap changes in the pattern of progradation in the upper part of the succession and nearby basaltic eruptions may have been precursors to the onset of movement along th san andreas fault in this area 12 14 m y ago

sedimentologic observation and stratigraphic interpretation of the lower devonian lochkovian manlius formation along the mohawk river valley in upstate new york a discussion

organic accumulation in the lower chihsia formation middle permian of south china constraints from pyrite morphology and multiple geochemical proxies article i nfo the organic rich chihsia formation middle permian on the yangtze platform western hubei south china is considered to be the major hydrocarbon source rock in south china the lower part of the chihsia formation reported here was deposited in an intrashelf basin and is characterised by black laminated marlstones shales intercalated with dark grey limestones dolomites in which metre scale shallowing or cleaning upward cycles are ubiquitous each cycle is composed of basal marlstone shale and upper lime stone the organic matter is concentrated exclusively in the shaley bases of these cycles and shows system atic cyclic variations in abundance up through the succession an integrated approach of pyrite morphology and multiple geochemical proxies was used to determine the mechanism of organic accumulation in the organic rich sediments many redox proxies including pyrite framboid size distribution c s fe relation ships iron speciation and 34 s values of pyrite suggest deposition beneath the dysoxic bottom water which evolved into a more oxic water body when the organic poor limestones were deposited however the coincidence of increased abundance of total organic carbon toc with increased ba and mo contents in dicates that organic matter accumulation was controlled mainly by primary productivity these data indicate that increased organic accumulation resulted mainly from higher organic carbon export with increased nutri ent flux during superimposed sea level rises of different orders this in turn could have increased the oxygen consumption by respiration of microorganisms and organic matter decay leading to the depletion of oxygen in the water columns furthermore the rapid sedimentation rate further limited bioturbation and organic matter decomposition facilitating the preservation of buried organic matter

jurassic sequence stratigraphy in the hebrides basin nw scotland abstract stratigraphical analysis of the triassic jurassic succession outcropping in the hebrides in terms of genetic sequences has identified seven major sequences and seven minor sequences the major sequence boundaries are defined at abrupt facies changes which usually represent deepening events often associated with a hiatus they are dated as 1 late triassic 2 mid sinemurian birchi subzone turneri zone diachronous to oxynotum zone 3 early toarcian exaratum subzone falciferum zone 4 latest toarcian aalensis subzone levesquei zone 5 late bajocian dichotoma subzone garantiana zone 6 late bathonian discus zone 7 early callovian medea subzone jason zone integrating stratigraphical with subsidence history analyses enables identification of basin tectonics as the causal mechanism for sequence boundaries 1 2 4 and 5 eustatic rises of sea level during toarcian and callovian phases of relative tectonic quiessence were the causes of sequence boundaries 3 6 and 7 late jurassic tectonic events are not reflected in the sequence stratigraphy on the basis of available data

stress induced changes in plate density vail sequences epeirogeny and short lived global sea level fluctuations the stratigraphic record contains clear evidence that broad regions have experienced rapid changes in sea level unrelated to changes in glacial ice volume e g third and higher order vail sea level variations continental foundering we propose that many of these changes can be caused by stress induced changes in plate density stress changes produce significant changes in the density of the crust and lithosphere a point missed in previous investigations and propagate across even the largest plates in less than 30 000 years lithospheric plates interacting at existing boundaries can produce stress related density changes sufficient to cause several meters change in plate elevation these may account for many of the regressions and transgressions seen in the stratigraphic record the creation of new rifts could increase plate compression enough to cause 50 m of plate subsidence plate elevation changes of up to 200 m could result from increased plate compression during continental collisions a particularly enigmatic kind of rapid nonglacial global ngg sea level change is a coupled 50 m sea level fall regression and roughly equal rise transgression occurring in less than 106 years these couplets associated with black shales and marine extinctions can be explained by the elastic snapback attending the rapid formation of a new rift isostatic disequilibria along the new rift depresses the seafloor sufficiently to cause a 50 m fall in sea level mantle flow restores isostatic equilibrium along the rift axis and erases the fall in 60 000 years unusually intense hydrothermal circulation along the new rift during the snapback promotes anoxic bottom water conditions and deposition of black shales a rapid drop in global sea levels reduces the area of ocean bottom within the photic zone causing overpopulation food exhaustion and extinctions the connections between changes in plate stress and density have many implications perhaps the most far reaching is that tectonic events on the 3 4 of the globe that is covered by oceans as well as the 1 4 that is subaerial are recorded in sedimentary strata

outcrop analog for cyclic shelf reservoirs san andres formation of permian basin stratigraphic framework permeability distribution geostatistics and fluid flow modeling vertical and horizontal transects were sampled from core and outcrop of the san andres formation at lawyer canyon guadalupe mountains new mexico to assess permeability variation in a geologic framework of upward shallowing carbonate cycles and to show the potential effect these variations have on viscous dominated flow behavior in analogous reservoirs these cycles occur in a ramp crest facies tract are 3 13 m 10 45 ft thick and contain both vertical and lateral variation of lithofacies thicker cycles consist of a basal dolomudstone which is overlain by burrowed dolopackstone and capped by bar flank ooid peloid dolograinstone and bar crest ooid dolograinstones in vertical transects permeability is extremely variable about the mean yet upward increasing trends coinciding with the succession of lithofacies typify a given cycle semi variance analysis shows permeability to be uncorrelated vertically at distances greater than 5 5 m 18 ft which is the average cycle thickness suggesting that the cycles may equate to a fluid flow unit in a reservoir semi variance analysis of measurements collected along a horizontal transect within bar crest dolograinstones of a single cycle shows permeability is uncorrelated at distances greater than 3 6 m 12 ft this correlation distance appears to be controlled by alternating porous and tightly cemented zones that formed during dolomitization vertical and lateral variogram models were fit to the spatial parameters to generate a variety of conditionally simulated permeability fields fluid flow simulations show viscous dominated flow behavior is compartmentalized by both the individual cycles and groups of cycles the basal dolomudstones are potential baffles to flow crossover between cycles but poorly developed cycles i e those that are mud rich and lack well developed bar flank and bar crest facies result in the greatest compartmentalization of fluid flow within a succession of cycles

stratigraphical and palaeoenvironmental analysis of the permian triassic transition in the badia valley souther alps italy abstract a sedimentological palynological and microfaunal integrated analysis was carried out across the permian triassic transition in a 35 m thick section near seres badia valley northern italy this section includes the uppermost part of the bellerophon formation and the base of the werfen formation tesero horizon and the lowermost mazzin member the bellerophon formation badiota facies displays a general shallowing upward trend it has been subdivided into three intervals on the basis of facies microfacies biofacies and palynofacies associations the bellerophon werfen formation boundary was located at the boundary between a thin black organic rich layer and a 50 cm thick limestone bed containing in the upper part the first oolitic beds the palynological assemblages show throughout the bellerophon formation a gradual decrease of exclusive permian palynomorphs and a concomitant increase of triassic ranging forms triassic palynomorphs were found in the lower part of the tesero oolitic horizon toh where the permian triassic transition can be recognized foraminifers with triassic affinity appear just above the proposed permian triassic transition this multidisciplinary approach led to evidence the palaeoenvironmental evolution which was characterized by variations in the water column oxygenation from dysoxic to oxic conditions related to climatic and or physiographic changes influencing the water layering palynofacies studies show a shift from relatively distal to more proximal conditions which reached the maximum during the deposition of the black organic rich level at the upper boundary of the bellerophon formation the overlying shallowing upward cycle at the base of the toh starts with an anoxic transgressive layer and ends with the oolitic beds

the cyclic hierarchy of the purbeckian sierra del pozo section lower cretaceous berriasian southern spain the lowermost cretaceous berriasian sierra del pozo formation is divisible into metre scale cycles that are bundled in a four tiered hierarchy of cycles and cyclic sequences at the smallest scale sixth order cycles thought to be the product of precessionally forced sea level fluctuations c 20 ka average less than a metre in thickness shallow upward and are bounded by surfaces where deeper facies abruptly overlie shallower facies bundles of sixth order cycles called fifth order sequences are recognized by two types of asymmetric patterns in facies distribution first more pronounced facies changes occur at sixth order cycle boundaries lower in a sequence whereas smaller facies changes occur at cycle boundaries higher in a sequence secondly subtidal marine limestones i e biomicrites and biosparites are the dominant facies lower in a cyclic sequence whereas more restricted or shallower water facies i e mud cracked microbial laminites dolomites shale and clay are more predominant higher in a cyclic sequence the bundling of sixth order cycles is explained as a product of periodic change 100 ka in the eccentricity of the earth s orbit the degree of orbital eccentricity modulates the magnitude of precessional sea level fluctuations which in turn determine the relative facies contrasts at sixth order cycle boundaries larger scale fourth and third order sequences are defined by similar patterns in facies contrast at successive sequence boundaries and by a change in predominant facies type from bottom to top these patterns are explained as the product of 400 ka and 2 ma periodic variations in the eccentricity of the earth s orbit in summary the strength of the precessional signal varies in consort with periodic changes in orbital eccentricity at three time scales producing a stacked hierarchy of cycles and sequences of cycles change in obliquity of the earth s axis may modulate the effects of the precessional signal and thereby modify patterns of preserved cyclic structure this interpretation of cyclicity in the sierra del pozo section is markedly different from that of

punctuated aggradational cycles implications for stratigraphic analysis application of the hypothesis of punctuated aggradational cycles pacs a model of episodic stratigraphic accumulation has yielded results fundamentally in conflict with those predicted and generated by gradualistic models the assumption that stratigraphic accumulation is controlled principally by rapid small scale base level fluctuations in the milankovitch band leads to the adoption of the pac a thin time stratigraphic unit as the fundamental unit of stratigraphic description and interpretation the thicker generally diachronous formation is inadequate for stratigraphic analysis because it is an artifact of stratigraphic gradualism correlation of stratigraphic sections is accomplished by matching patterns of facies change particularly the abrupt changes at the synchronous surfaces that mark pac boundaries this kind of physical event correlation is far more accurate than traditional biostratigraphic methods focus on synchronous pac boundaries separating environmentally disjunct facies reveals discontinuities that preclude application of walther s law across those surfaces when viewed from this episodic perspective the manlius formation of the helderberg group in new york state becomes a highly ordered set of time stratigraphic cycles rather than a disordered mosaic of facies representing short term autogenic processes in a single nearshore environment not only was manlius deposition episodic with no gradual upward deepening as is predicted by stratigraphic gradualism but also the manlius coeymans formational boundary is interpreted as a small scale unconformity rather than a paleoenvironmental boundary created by gradual transgression each of these interpretations is the direct result of assuming and applying a model of episodic stratigraphic accumulation

building the 3 d jigsaw puzzle applications of sequence stratigraphy to 3 d reservoir characterization permian basin reservoir characterization involves the quantification integration reduction and analysis of geological petrophysical seismic and engineering data this is no small task a principal goal of reservoir characterization is to derive a spatial understanding of interwell heterogeneity traditionally geologic attempts to characterize interwell heterogeneity have been done using hand drawn or computer generated two dimensional 2 d maps and cross sections results can be improved dramatically using three dimensional 3 d interpretation and analysis techniques three dimensional reservoir characterization requires the same input data used in 2 d approaches and the cost is equal to and commonly lower than traditional 2 d methods the product of 3 d reservoir characterization is a 3 d reservoir model the language used to communicate the results of a 3 d reservoir model is visualization i e visual images of numerical data all of the available log and core data in a model area are incorporated in a 3 d model but the data are depicted as colored cells rather than as log traces the integrity of the 3 d reservoir model is largely a function of the stratigraphic framework interpreting the correct stratigraphic framework for a subsurface reservoir is the most difficult and creative part of the 3 d modeling process sequence and seismic str tigraphic interpretation provide the best stratigraphic framework for 3 d reservoir modeling the purpose of this paper is to discuss the process of 3 d deterministic reservoir modeling and to illustrate the advantages of using a sequence stratigraphic framework in 3 d modeling mixed carbonate and siliciclastic sediment outcrop and subsurface examples from the permian basin of west texas and new mexico will be used as examples but the concepts and techniques can be applied to reservoirs of any age three dimensional reservoir modeling results in an improved geologic interpretation provides a means of integrating geological petrophysical geophysical and engineering data and allows for immediate model updates as new data are acquired as a result of 3 d reservoir characterization reservoir management decisions data quality control volumetric calculations numerical sim lation input and communication between disciplines are improved

shallowing upward carbonate cycles in the belingwe greenstone belt zimbabwe a record of archean sea level oscillations abstract shallowing upward carbonate cycles in the 2650 ma cheshire formation belingwe greenstone belt zimbabwe closely resemble their proterozoic and phanerozoic counterparts the cycles form part of a karstified carbonate ramp sequence that is overlain by and grades basinward into siliciclastic turbidites a single section of 74 cycles 1 5 m average thickness was studied in detail two basic cycle types are recognized both with an asymmetric facies stacking pattern one cycle type contains open marine subtidal shale at the base shale is intercalated with storm generated sandstone and grainstone beds that become more common and thicken upward indicating progressive shallowing wave rippled ooid intraclast grainstone beds and bedsets overlie shale or form the base of the second cycle type grainstone formed at or above fair weather wave base as shoreface sand sheets in an agitated shallow subtidal setting microbial laminites constitute the top of both cycle types and are interpreted as peritidal deposits in the upper part of the studied section microbial boundstones with aragonite pseudomorphs are intercalated with or overlie laminites and formed in a supratidal environment the vertical facies distribution within a cycle is indicative of rapid submergence followed by gradual shallowing of relative sea level high frequency eustatic sea level changes are favored over an autocyclic mechanism and tectonically induced allocyclicity as the controlling mechanism for the cyclicity hierarchies of stratigraphic cyclicity occur on different scales and may be a result of the combined effects of several orders of sea level oscillations cycle recurrence ratios correspond well to the milankovitch frequencies calculated for the late archean suggesting that orbital climatic forcing may have been in operation in archean times

stromatolites and associated facies in shallowing upward cycles from the middle proterozoic altyn formation of glacier national park montana abstract the approximately 1450 ma old altyn formation is the oldest stratigraphic unit exposed in glacier national park montana the lower part of the formation informally called member a contains at least 17 shallowing upward cycles with an average cycle thickness of 4 2 m each cycle rests on an erosional surface and has subtidal quartz microcline dolarenites in the basal part the subtidal rocks pass upward into stratiform stromatolites interbedded with dolarenites similar to those in the basal layers the stromatolites formed on tidal flats during calm periods and the dolarenites were transported from subtidal areas to the tidal flats by storm driven waves and currents domal and columnar stromatolites grew in relatively higher energy conditions particularly in tidal channels in the lower tidal flats the upper parts of some cycles have sparse dolarenites and are dominated by stratiform stromatolites desiccation features and complete dolomitization of subtidal and intertidal carbonate sediments occur in member a many cycles within this member contain evidence of the diagenetic formation of gypsum and anhydrite in sediments deposited in subtidal and intertidal zones the carbonate sediments in each cycle accumulated up to sea level causing progradation of tidal flats into a shallow subtidal area this led to the development of a supratidal zone analogous to a modern sabkha member a is overlain by quartz microcline dolarenites of informal member b which were deposited in subtidal environments informal member c overlies member b and contains shallowing upward cycles similar to those of member a but with an average cycle thickness of 2 5 m member c cycles also differ in containing mud cracked shales and terrigenous arenites these terrigenous sediments were derived by mechanical weathering in the source area they were transported into the supratidal and upper intertidal zones during flash flooding the change from member a to member b represents an overall transgressive trend this was followed by an overall regression giving the change from member b to member c the repeated shallowing upward cycles are due to smaller transgression progradation events that were superimposed on these larger trends the altyn formation was deposited in an epicontinental basin each shallowing upward cycle was produced by sediment aggradation and progradation following rapid subsidence resulting from vertical tectonic activity the paleoclimate was arid with occasional storms flooding the tidal flats with subtidal sediments and the upper tidal flats with terrestrial sediments such a paleoclimate is consistent with the subtropical to tropical paleolatitudes indicated by paleomagnetic data for the altyn formation depositional area

shallowing upward sequences in purbeckian peritidal carbonates lowermost cretaceous swiss and french jura mountains purbeckian carbonates in the swiss and french jura goldberg formation lower berriasian comprise shallow subtidal intertidal supratidal low energy high energy marine brackish freshwater and hypersaline facies these facies are arranged in small 0 2 1 5 m thick sequences which display a dominant shallowing upward component and which form the fundamental units of the highly structured purbeckian sedimentary record six types of small scale sequences can be recognized a intertidal to supratidal overprinting of shallow lagoonal facies b algal marsh sequence with frequent dolomitization c sabkha sequence often associated with collapse breccia d tidal flat sequence with desiccation features e lacustrine sequence f terrestrial overprinting of subtidal or intertidal facies episodic event deposits such as tempestites are superimposed thin transgressive beds which rework elements of the underlying facies are frequently found at the base of the sequences green marls and black pebbles are common at the top and indicate long subaerial exposure the sequences are often incomplete as subtidal facies may be absent or their upper part can be eroded lateral facies changes are common which is due to the very shallow and partly emergent purbeckian platform where various depositional environments were juxtaposed however many sequence boundaries are well developed and can be correlated over large parts of the study area the purbeckian shallowing upward sequences were generated by climatically controlled sea level changes autocyclic processes occurred locally but were overprinted by drops of sea level affecting the entire platform the small scale sequences are most probably related to the 20 000 year cycle of the precession of the equinoxes larger sequences with usually well developed emersion surfaces are attributed to the 100 000 and 400 000 year eccentricity cycles of the earth s orbit identification and correlation of sequence boundaries makes it possible to set up a framework of isochronous surfaces which often cut across facies boundaries and thus to interpret in detail the palaeogeographic sedimentological and diagenetic evolution of the purbeckian peritidal carbonate environments

reef geometries erosion surfaces and high frequency sea level changes upper miocene reef complex mallorca spain the upper miocene reef complex of mallorca is a 20 km prograding unit which crops out in sea cliffs along the southern side of the island these vertical and exceptionally clean outcrops permit i identification of different facies lagoon reef front reef slope and open platform and their geometries and boundaries at different scales ranging from metre to kilometre and ii construction of a 6 km long high resolution cross section in the direction of reef progradation this cross section shows vertical shifts of the reefal facies and erosion surfaces linked to a general progradational pattern that defines the accretional units four hierarchical orders of magnitude 1 m to 4 m of accretional units are identified by consideration of the vertical facies shifts and by which erosion surfaces are truncated by other erosion surfaces all these orders show similar patterns horizontal beds of lagoonal facies in the upper part landward reefal and slope facies with sigmoidal bedding in the central part and open platform facies with subhorizontal bedding in the lower part basinwards the boundaries are erosion surfaces horizontal over the lagoon facies dipping basinwards over the reef front facies and connecting basinwards with their correlative conformities over the reef slope and open platform facies the four orders of accretional units are interpreted in terms of four 1 m to 4 m hierarchies of sea level cycles because i there is a close relation between the coral growth and the sea surface ii there are vertical shifts in the reefal facies and their relation to the erosion surfaces and iii there was very little tectonic subsidence in the study area during the late miocene additionally all these units can be described in terms of their position relative to the sea level cycle i the reefs prograde on the open platform sediments during low stands of sea level ii aggradation of the lagoon reef and open platform facies dominates during sea level rises and the lagoonal beds onlap landwards upon the previous erosion surface iii reefal progradation occurs during high stands of sea level and iv the 2 m sea level fall produces an off lapping reef and there is progradation with downward shifts of the reefal facies and erosion landward on the emerged older reefal units a erosion surfaces the 3 m and 4 m sea level falls produce only erosion b and c erosion surfaces although precise age data do not exist at present some speculations upon the frequency of these miocene relative sea level cycles can be made by comparisons with pleistocene cyclicity there is a good correlation between the miocene 2 m cycles and the 100 ka pleistocene cycles consequently the 1 m cycles can be assigned to a fourth order in relation to previously proposed global cycles and the 2 m to fifth order cycles all these accretional units could be defined as sequences according to the definition as commonly used in sequence stratigraphy however they represent higher than third order sea level cycles but are not parasequences the term subsequence therefore is suggested to define a part of a sequence bounded by erosion surfaces mostly subaerial and their correlative conformities basinwards a hierarchy of subsequences can be established

sedimentologic observation and stratigraphic interpretation of the lower devonian lochkovian manlius formation along the mohawk river valley in upstate new york a reply abstract observations from nine measured sections through the lower helderberg group across upstate new york suggest that component rock units within the manlius formation extend laterally over 150 km across upstate new york the most notable being a meter thick zone of microbial bioherms at the base of the formation overlying this zone of microbial bioherms is a 5 10 m thick zone of wavy and lenticular bedded ribbon rocks that grade up into microbial laminated mudstones that are in turn overlain by disrupted dolomitic mudstones deposited in playalike supratidal flats the upper 10 15 m of the manlius formation comprises meter thick cycles of nodular bedded stromatoporoid bearing thin sets that grade up into microbial laminated mudstones much of this succession of rock types is traceable across nearly the entire basin and strongly suggests that lower beds of the manlius formation do not pass laterally westward into nor are they coeval with the underlying rondout formation this in turn necessita

upward shallowing platform cycles a response to 2 2 billion years of low amplitude high frequency milankovitch band sea level oscillations shallow water carbonate platforms characterized by sequences of small scale upward shallowing cycles are common in the phanerozoic and proterozoic stratigraphic record proterozoic small scale cycles are commonly 1 to 10 m thick have asymmetrically arranged facies and are strikingly similar to phanerozoic platform cycles in some platform sequences eg rocknest wallace and helena formations of early to middle proterozoic age it can be demonstrated that the lateral distribution of facies within cycles relates to systematic variations in platform paleogeography and topography in the rocknest formation cycles with intervals of tepees and pisolitic breccia formed on a topographic high shoal complex near the shelf edge rim and provide evidence for eustatic falls in sea level at the end of each cycle the presence of these facies in other proterozoic cyclic platforms also suggests that eustatic sea level falls may have been important in the development of each cycle proterozoic upward shallowing cycles appear to have had periods of between 20 000 and 100 000 years and probably formed during eustatic oscillations in sea level with amplitudes of less than 10 m this suggests that cyclicity may have been regulated by milankovitch band climatic forcing perhaps influencing global sea level through minor changes related to small scale continental or alpine glaciation it is possible then that milankovitch band climatic forcing has occurred for at least the last 2 2 billion years of earth history

a proposed integrated multi signature model for peritidal cycles in carbonates abstract a new integrated multi signature model for meter scale peritidal carbonate cycles presented here is relevant to the interpretation of these cycles in the stratigraphic record meter scale shallowing upward micro facies cycles are the most common type of peritidal parasequence peritidal parasequences are a fundamental component of carbonate sequence stratigraphic models however the existence of meter scale cycles in the geological record has been questioned owing to the failure to prove statistically the existence of these cycles using data on micro facies and stacking pattern taken from previous studies nevertheless the shallowing upwards micro facies interpretive template remains widely used to identify these cycles and parasequences we propose that the sedimentary signatures of meter scale peritidal cycles vary systematically during the various phases of an underlying 3rd order relative sea level cycle although during specific phases of a 3rd order relative sea level cycle meter scale peritidal cycles may be characterized by shallowing upward units e g early transgressive systems tract during other periods the stratigraphic signal of cyclicity may be more cryptic and complex causing them to be overlooked e g late transgressive systems tract and highstand systems tract we also propose that there is a half cycle phase shift in periods of deposition and the formation of drowning surfaces relative to 4th to 5th order relative sea level cycles over the course of a 3rd order relative sea level cycle these points have ramifications for defining parasequences and using stacking patterns to determine peritidal cycle periodicity specifically parasequences defined using flooding surfaces identify sedimentary units that inconsistently partition 4th to 5th order relative sea level cycles at different stages of a 3rd order relative sea level cycle we propose testable new physical stratigraphic signatures for identifying meter scale cycles that have consistent genetic significance each cycle recording a relative sea level cycle characterized by a 4th to 5th order relative sea level rise and fall meter scale peritidal cycles are recorded by an ordered pattern of systematically varying micro facies signatures related to their position within a 3rd order relative sea level cycle the integrated multi signature model of meter scale peritidal carbonate cycles we propose here may assist in explaining the apparently contradictory evidence both for and against their existence in the geological record as a result of the detailed consideration in this paper of the nature of parasequences and their variations with 3rd order relative sea level changes a redefinition of parasequence is required and one is presented here

out of our depth on the impossibility of fathoming eustasy from the stratigraphic record the evolution of a sedimentary basin s gross morphology depends upon 1 basement movement 2 sediment accumulation and compaction and 3 variations of eustasy with time thus if an accurate history of eustasy could be derived it would aid in our understanding of basin stratigraphy and help in the prediction of sediment geometry from described areas techniques which attempt to determine the magnitude of eustatic sea level excursions include the measurement of 1 the amount of sedimentary onlap onto the continental margins with and without the use of hypsometric curves 2 the thickness of marine sedimentary cycles and the elevation and distance between indicators of old strandlines 3 the perturbations on individual thermo tectonic subsidence curves and stacked crustal subsidence curves 4 the variations in deep ocean oxygen isotopes found in sediments and 5 the size of variables used in graphical and numerical simulations of basin fill in terms of tectonic behavior rates of sediment accumulation and eustasy which invert the problem to date a combination of the use of relative sea level charts derived from sediment onlap of the continental margin with dimensioning by oxygen isotopes responding to glacial events offers the best potential for relative tectono eustatic sea level curves but even this method can not produce a unique solution for absolute eustatic variations mathematical modelling shows that at best it is possible to obtain only the sum of tectonic basement subsidence and sea level variations from the above methods and at worst not even that simple a combination thus every proposed scheme to measure eustatic sea level excursions assumes some behavior for two of the three underlying processes tectonic movement of the basement sedimentary accumulation and eustatic sea level each scheme then determines the third process relative to the assumed model behavior of the other two it would seem that like king canute we cannot command the sea though we can still use undifferentiated relative tectono eustatic sea level curves to generate a family of solutions which are the product of a variety of absolute sea level curves and tectonic models each solution has then to be assessed in terms of geologic setting and the hypotheses it generates

time stratigraphic aspects of a formation interpretation of surficial pleistocene deposits by analogy with holocene paralic deposits southeastern delaware pleistocene shoreline deposits in close spatial and temporal proximity to holocene deposits permit detailed interpretation of the development of pleistocene coastal deposits when a modern ancient analog approach is used peak sea levels during the past 1 m y or more have allowed the preservation of transgressive shoreline systems here referred to as paralic units along the inner continental margin these pleistocene paralic units are similar to holocene coastal deposits now forming on delmarva peninsula the omar formation early to late pleistocene age incorporates at least four juxtaposed transgressive paralic units of different ages each containing deposits of lagoonal sands and muds tidal marsh barrier sands and gravels tidal delta sands and silty sands and tidal channel sands and gravels the successive paralic units become younger in the seaward direction thus although the omar formation in the study area is almost entirely made up of transgressive deposits produced during rising sea levels in a longer time frame it forms a progradational sequence only about 2 to 5 of the elapsed time during the deposition of the studied part of the omar formation is represented by sedimentary units the internal time stratigraphy of the omar formation is extremely complex this makes the time stratigraphic interpretation of any one outcrop or drill hole difficult any lithologic change may represent a wide variety of time gaps from minutes to tens of thousands of years the analog approach in which sedimentary lithosome mapping is used allows one to infer a time stratigraphic framework of the deposits these concepts can aid in the interpretation of depositional history of older paralic deposits and the nature of the development of certain types of clastic formations

holocene evolution of the canet st nazaire lagoon golfe du lion france as determined from a study of sediment properties the sedimentation in the lagoons of the golfe du lion coast mediterranean sea france records their post holocene evolution the canet st nazaire lagoon provides an example of such an evolution eight cores ranging from 13 5 to 19 7 m in length from a transect of the lagoon provide a cross section of the late quaternary stratigraphy the sedimentary sequence comprises mud and sand layers the two sand formations are identified as parts of two distinct shelf sedimentary prisms stratigraphic analysis defines three stages in the recent muddy infilling corresponding to the last divisions of the holocene sedimentation rates of the muds related to climatic and palaeogeomorphological events largely determine their geotechnical and geochemical properties it appears indeed to be the most important factor in determining the compressibility index the saturated bulk density and the organic and water contents of the deposits subboreal muds poorly consolidated and rich in organic matter correspond to a high rate of deposition in the subatlantic muds in contrast the sedimentation rate is lower whilst there is a decrease in the organic matter and an increase in the degree of cohesion

anoxia as a cause of the permian triassic mass extinction facies evidence from northern italy and the western united states facies faunal and geochemical evidence from the permian triassic boundary sediments of the dolomites and idaho indicates a major anoxic event in the earliest triassic in both regions the basal beds consist of finely laminated micrites with common syngenetic pyrite the only fauna consists of occasional bedding plane assemblages of lingula or clacaria a typical lower dysaerobic assemblage this is a level where previous studies have shown a major negative carbon isotope excursion and a cerium anomaly in the dolomites the pyritic micrite directly overlies strata containing a diverse and typically permian marine fauna of algae foraminifers including fusulinids and articulate brachiopods implying an abrupt extinction in contradiction to many previous views sequence stratigraphic analysis of the dolomite boundary sediments reveals a minor sequence boundary in the late permian followed by extremely rapid transgression leading to the development of the relatively deep water pyritic micrite a maximum flooding surface at the permo triassic boundary a further pulsed deepening in the lower griesbachian recorded in both the dolomites and idaho lead to the widespread establishment of dysaerobic facies it is clear that most of the extinctions occurred at the erathem boundary although the subsequent failure of the marine benthos to fill the empty ecospace in the ensuing griesbachian may have been due to the widespread development of dysaerobic conditions

correlation of carboniferous strata using a hierarchy of transgressive regressive units carboniferous strata can be described interpreted and correlated using six scales of allocyclic transgressive regressive t r units these t r units are inferred to be the net result of deposition during cycles of sea level change all pennsylvanian and lower permian strata constitute one second order t r unit or synthem the pennsylvanian system contains third fourth fifth and sixth order t r units that can be correlated across both marine and nonmarine facies in the appalachian basin this permits differentiation of allocyclic t r units from autocyclic t r units or fluvial autocyclic units the hierarchical approach is also useful for predicting the location of marine horizons coals claystones and various types of stratigraphic breaks a hierarchical scheme of allocyclic t r units could be combined with biostratigraphic radiometric and magnetostratigraphic data to form a practical chronostratigraphic framework for the carboniferous

unravelling the influence of water depth and wave energy on the facies diversity of shelf carbonates carbonate sequence stratigraphy is founded on the principle that changes in relative sea level are recorded in the rock record by the accumulation of sediment with relative water depth dependent attributes while at the scale of a shelf to basin transect facies clearly arrange by water depth the relation blurs for depths 40 m the most vigorous zone of carbonate production the reason for this change in behaviour is two fold firstly in shallow water the intrinsic processes of storm and wave reworking influence the seabed through submarine erosion and sediment redistribution secondly facies diversity tends to be greater in shallow water than deep water because of a greater diversity in grain producers remote sensing imagery field observations and hydrodynamic models for two reef rimmed shore attached carbonate platforms in the red sea show neither water depth nor energy regime to be reliable indicators of facies type when considered in isolation considered together however the predictive power of the two variables rises significantly the results demonstrate it to be an oversimplification to assume a direct link between palaeo water depth and depositional diversity of subtidal lithofacies while highlighting the importance of hydrodynamics in directing the accumulation of carbonate sediments in the shallow photic zone while the size distributions of facies extents in the two focus areas follow power laws no direct relation between the lateral continuity of the facies belts and water depth or wave height is reported the work is relevant for the interpretation of metre scale subtidal carbonate cycles throughout the geological record by demonstrating how caution must be applied when inferring palaeowater depths from depositional facies

storm effects on siliciclastic and carbonate shelf sediments in the medial silurian succession of pennsylvania abstract upper llandoverian through wenlockian strata in the pennsylvania part of the northern appalachian basin formed on a gentle epeiric ramp that extended from marginal tidal flats through coarser grained mid shelf shoals to a muddy basin center over approximately 10 million years the composition of the accumulating sediment evolved from siliciclastic to carbonate while the ramp maintained a relatively similar configuration and position below sea level and while storm generated processes continued as the major producers of sediment characteristics in both siliciclastic and carbonate parts of the succession sedimentary structures and their sequences are generally similar with only a small number of dissimilar features resulting from the differences in composition small scale coarsening and shallowing upward sequences are present in both mid shelf bar and basin transition deposits although specific sequence characteristics are different in siliciclastic and carbonate parts such sequences record cyclic fluctuations of relative sea level while the composition of the sediment evolved over this extended period the gentle ramp gradient was maintained largely by the processes generated by storms such processes were more effective because of the fluctuations of relative sea level

the significance of metre scale allocycles in the quest for a fundamental stratigraphic unit the major transgressive sequence in the lower helderberg group devonian of new york state and a regressive sequence of similar scale in the first courceyan mesothem carboniferous of south wales are entirely divisible into metre scale allocycles the boundaries of these cycles are produced by non sedimentological processes larger scale stratigraphic events associated with relative sea level fluctuations the existence of these boundaries as basin wide discontinuities precludes the application of walther s law except within cycles thus palaeogeographic reconstructions based on the assumption of contemporaneity of large scale fades tracts formations and members must be abandoned instead stratigraphic interpretation requires the recognition and application of a genetic unit of analysis consistent with the actual internal allogenic fabric of such sequences application of the metre scale allocycle the smallest allogenic unit of stratigraphic accumulation results in fundamentally different interpretations of the helderberg and courceyan sequences rather than being continuously and unidirectionally transgressive or regressive both sequences were discontinuously generated by episodes of rapid deepening and gradual shallowing at more than one scale

palaeosols in microtidal carbonate sequences sierra de utiel formation upper cretaceous se spain abstract the sierra de utiel formation upper coniacian to lowermost campanian of the prebetic and iberian ranges consists of a thick 70 120 m carbonate series of stacked thin shallowing up cycles 0 4 0 6 m average that were developed in an extensive shallow epeiric sea control was mainly by a humid climate and by the virtual absence of tides each of these cycles basically consists of a shallow subtidal unit capped by a supratidal unit characterized by calcrete development by considering the maturity of the soils as a guide to its formation time palaeosol analysis emerges as a useful tool for the analysis of these monotonous peritidal series a statistical study of the variations of degree of calcrete maturation and of other variables such as cycle thickness and subtidal facies up through the sierra de utiel formation allows the recognition of three transgressive regressive sequences that correspond to three successive 3rd order cycles further each small cycle could be the result of 5th order sea level changes in tune with milankovitch orbital rhythms the available data however do not allow the rejection of a sedimentary autocyclical origin for the smaller cycles

lithofacies diagenesis and cyclicity of the lower member of the khuff formation late permian al qasim province saudi arabia abstract the lower member of the khuff formation exposed along the western margin of the arabian basin al qasim province saudi arabia comprises seven carbonate and two siliciclastic lithofacies the carbonate lithofacies include laminated lime mudstone ostracode wackestone foraminiferal wackestone intraclastic wackestone burrowed dolostone lithoclastic grainstone and caliche the clastic lithofacies are represented by claystone and quartzarenite these lithofacies are arranged vertically into shallowing upward or emergence cycles the boundaries between which were delineated by field observations peritidal as well as subtidal cycles built up the lower member of the khuff formation the peritidal cycles consist of laminated lime mudstone or subtidal claystone overlain by intertidal burrowed dolostone which is capped in most cases by supratidal lithoclastic grainstone and locally by subaerial caliche deposits these cycles were probably formed by allocyclic mechanism due to the effect of sea level changes and intrabasinal tectonics the subtidal cycles comprise laminated lime mudstone claystone foraminiferal wackestone and ostracode wackestone capped by intertidal burrowed dolostone or intraclastic wackestone these cycles may be formed due to internal factors e g carbonate production changes in water circulation salinity depth chemistry energy temperature and nutrient content diagenetic studies on the depositional cycles show that the basal part of cycle subtidal zone includes micrite cementation micritization and silicification the middle part intertidal zone was affected by early dolomitization while the upper part supratidal zone was subjected to dedolomitization aggrading neomorphism sparry calcite cementation and evaporite carbonate replacement

regional to global correlation of lower cretaceous hauterivian barremian shallow water carbonates of the southern apennines italy and dinarides montenegro southern tethyan margin abstract we propose a high resolution regional to global scale correlation of two hauterivian barremian shallow water carbonate platform sections belonging to different palaeogeographic domains of the southern margin of the tethys these successions are now located more than 500 km apart and are represented by 137 m of core drilled at monte raggeto southern apennines italy and by 80 m of well stratified rocks cropping out in the podgorica mountains dinarides montenegro they display three superimposed orders of stratigraphic cyclicity defined by elementary cycles grouped into bundles and superbundles and attributed to orbitally induced composite sea level fluctuations elementary cycles are interpreted as the precession and the obliquity periodicities 20 40 ky while bundles and superbundles correspond to the short 100 ky and long 400 ky eccentricity cycles respectively as both the ratios between the elementary cycles and the bundles and between the bundles and the superbundles do not always reflect the classical 5 1 and 4 1 relationship the sedimentary record of both the studied sections is likely to include omission of bundles or their portion the general evolution of depositional and diagenetic facies the vertical change in thickness of the cyclic units and the interpretation of superbundles as small scale depositional sequences suggest that elementary cycles and their groups are superimposed on lower frequency environmental oscillations these display an upward transgressive regressive trend t rt of the facies and testify to larger scale variations of accommodation potential on the shelf t rts sequence stratigraphic interpretation of the superbundles as well as the common occurrence of the biostratigraphic dated hauterivian barremian boundary in the studied sections support the long distance regional correlation between the successions to be carried out on the 100 ky scale moreover by assuming the maximum flooding intervals of time equivalent superbundles as virtually isochronous intervals we have detected stratigraphic gaps of 1200 and 600 ky in the monte raggeto and in the podgorica mountains sections respectively both sections are formed of 10 complete superbundles each of them testifying to the 400 ky long eccentricity hence the monte raggeto and podgorica mountains successions represent a duration of at least 4 0 my in terms of elapsed time regardless of gaps within the stratigraphic record finally a correlation between the orbitally induced compared sections and both the 3rd order tethyan stratigraphic cycles and the global cycle chart is suggested our study confirms that cyclically organized shallow marine carbonate platform deposits controlled by orbitally induced sea level fluctuations represent a powerful tool for high precision regional and global correlations this can be of fundamental importance for quantification of sedimentary diagenetic and evolutionary processes as well as for the understanding of autocyclic versus allocyclic control on sequence development

tectonic settings of archaean 3325 2775 ma crustal supracrustal belts in the west pilbara block abstract the archaean pilbara block comprises six fault bounded tectonostratigraphic domains the west pilbara block contains from east to west domains 4 5 and 6 review of stratigraphic magmatic structural and geochronologic data and new field mapping indicates that the crustal and supracrustal rock records correlate to three megacycles megacycle ivu 3325 3135 ma is recorded by an intra arc basin and arc granitoids in domain 6 and a back arc basin in domains 4 and 5 the domains were an arc continent orogen from 3200 3155 ma during which the outboard are setting was accreted to the back arc continental margin although domain 6 is allochthonous with respect to domains 5 and 4 it was not exotic with respect to the tectonic settings of the pilbara continent megacycle vl 3135 2955 ma is recorded by in decreasing age i a back arc basin and arc granitoids in domain 5 ii a deep marine retroarc or remnant ocean basin in domain 4 and a plutonic belt in domain 5 iii a plutonic belt in domains 5 and 6 and possibly also in domain 4 and iv craton wide deformation belts coeval with the whim creek basin and granitoid plutons in domain 5 the whim creek basin was a half graben that developed at a releasing bend or overstep along the boundary fault to domains 4 and 5 and to the northeast domains 4 and 6 the basin was closed by sinistral transpression as the boundary fault between domains 4 and 6 propagated to the southwest from the releasing bend and thereby generating a restraining bend geometry fundamental strike slip faults which are interpreted to have been tectonic escape responses to a cause external to the preserved pilbara block juxtaposed domains craton wide the initial stage of megacycle vu 2955 2775 ma is recorded by the eroded remnants of a rift province preserved elements include the negri basin domain 5 only mafic ultramafic sub volcanic layered intrusions and granitic plutons and related high level sills two periods of granitoid intrusion are preserved base metal sulphide deposits hosted by the whim creek basin were probably sourced from extensional geofluids in the rift province a plume origin is likely for the komatiitic parent magmas to sub volcanic intrusions and to basalts of the negri basin plume magmatism is interpreted to have been coincident with but not the cause of lithospheric extension because plumerelated volcanism post dates the first period of plutonic intrusion by 25 million years extension was followed by orogenic deformation that converted domains 4 5 and 6 to a hinterland fold thrust belt deformation is interpreted to have been caused by collision orogeny during terrane accretion along the western pilbara margin collision orogeny was the last event of a long history of pacific type tectonics along the margins of the archaean pilbara continent

sedimentary evolution and drowning of a passive margin shelf giumal group zanskar tethys himalaya india palaeoenvironmental changes during final break up of gondwanaland

carbonate platform lagoon and delta high frequency cycles from the carnian of lombardy southern alps italy abstract the early and middle carnian succession of the bergamasc alps southern alps italy was deposited in three different environments a deltaic depositional system passing seaward to a lagoon or bay and then to a carbonate platform the corresponding lithofacies sandstones and siltstones shales and limestones are organized in high frequency cycles fining upward trends are typical of the subaerial delta plain cycles and shallowing upward trends are widespread in the lagoon and platform cycles the genesis of the lagoonal and carbonate platform cycles is possibly accounted for by sea level changes mainly controlled by small scale eustatic oscillations sea level changes are interpreted as exerting a major control also in the development of the deltaic cycles

polyphase erosion of subaerial omission surfaces in the late dinantian of anglesey north wales the lower carboniferous of anglesey consists of bioclastic carbonates and subsidiary terrigenous siliciclastics built as a cyclic succession against the northern flank of the contemporary welsh landmass cycle boundaries are marked by subaerial erosive features that are unlike the normal late dinantian palaeokarst association and one such surface at red wharf bay shows remarkable evidence of polyphase erosion indicating at least three distinct periods of karstification and one of fluvial channelling each erosive period was succeeded by an interval of lithification during which newly arrived siliciclastic sediment was stabilized diagenetic textures in the underlying limestones reveal no evidence of this complex surface history and seen in cathodoluminescence the earliest pore filling cements evidently post date the entire emergent episode the karsts occupy positions adjacent to channels and are attributable to overbank flooding rather than atmospheric weathering autocyclic mechanisms may be responsible for the polyphase development but the overall control of sedimentary cyclicity is considered to have been eustatic

distribution paleoenvironmental implications and stratigraphic architecture of paleosols in lower permian continental deposits of western kansas u s a abstract cumulic paleosols in core from the lower permian asselian sakmarian council grove group of western kansas contain a diverse suite of pedogenic features including carbonate nodules gleying fossil burrows rhizoliths peds and cutans abundant gleying burrowing by organisms with a high soil moisture requirement and extensive plant growth are evidence of at least intermittently high soil moisture during this time paleosol character was strongly influenced by regional topography and paleogeographic position as well as the climate changes accompanying hierarchical glacioeustatic cycles the distribution of pedogenic features across formations also indicates a shift toward more humid conditions during a larger 3rd order regression climatic variability during the interval of soil formation resulted in overprinting and close stratigraphic juxtaposition of both humid and arid climate indicators variability is likely the result of exposure to multiple 5th order eustatic and climatic cycles during the lowstands of 4th order cycles fifth order cycles are expressed as lithologic changes in stratigraphically equivalent outcrops across the state but lack of accommodation space prevented cycles from being expressed as differing lithologies in the study area biologic activity assisted in consolidation and stabilization of eolian and alluvially deposited sediments this study emphasizes that detailed quantitative study of pedogenic features can reveal important paleoclimatic and paleoenvironmental information in otherwise lithologically similar paleosols close juxtaposition of opposing climatic indicators over intervals of known sea level change adds evidence to the hypothesis of a link between sea level change and climate change in the early permian pedogenic features thus support a semiarid or wetter climate for the midcontinent during the early permian

late archaean foreland basin deposits belingwe greenstone belt zimbabwe abstract the c 2 65 ga old sedimentary cheshire formation of the belingwe greenstone belt bdb central zimbabwe has been studied in detail for the first time to shed some light on the much debated evolution of this classical belt the cheshire formation rests sharply on a mafic volcanic unit zeederbergs formation and comprises a basal eastward sloping carbonate ramp sequence built of shallowing upward metre scale sedimentary cycles the cycles strongly resemble proterozoic and phanerozoic carbonate cycles and might have formed by small scale eustatic sea level changes the top of the carbonate ramp is represented by a karst surface the carbonates are overlain by and grade laterally to the east into deeper water sub wave base siliciclastic facies conglomerate shale and minor sandstone were deposited by high to low density turbidity currents and were derived from the erosion of zeederbergs like volcanic rocks from the east shortly after deposition the cheshire formation and underlying volcanics were affected by a northwest directed thrusting event thrusting gave rise to the deformation of semi consolidated sediments and resulted in the juxtaposition of a thrust slice of zeederbergs basalts onto cheshire sediments the stratigraphy asymmetric facies and sediment thickness distribution palaeogeographic constraints and evidence for an early horizontal tectonic event suggest that the cheshire formation formed in a foreland type sedimentary basin

cyclicity in the middle eocene yamak turbidite complex of the haymana basin central anatolia turkey the haymana basin in central anatolia turkey formed on a late cretaceous to middle eocene fore arc accretionary wedge a sequential model is proposed for the 1 km thick lutetian yamak turbidite complex ytc which is the youngest paleotectonic unit of the basin the ytc represents a prograding submarine fan subdivided into three depositional sequences ds each several hundred meters thick each depositional sequence consists of a turbidite system ts with sandstone and conglomeratic sandstone beds alternating with mudstones overlain by basin plain mudstones in each turbidite system the sandstone and mudstone sequential organization allows the distinction of smaller subdivisions namely basic sequences bs and basic units bu with each basic sequence being composed of several basic units this subdivision associated with a two dimensional geometric reconstruction of the ytc leads to a better understanding of the evolution in time and space of the submarine fan system lower to middle fan depositional lobes and upper fan and slope channels are represented as a whole the ytc progressed from a sand poor to a sand rich system depositional sequences ds of the ytc may correspond to third order sea level cycles of tectonic origin accordingly fourth and fifth order cycles might be proposed for the bs and bu respectively however partly because of the limited extent of exposures the allocyclic origin of these finer subdivisions remains problematic

was the oligocene miocene a time of fire and rain insights from brown coals of the southeastern australia gippsland basin abstract lithotype cycles ranging from 10 to 30 m thick in the brown coals of the latrobe valley gippsland basin australia display well developed lightening upward trends cycle tops are characterized by abrupt and unconformable boundaries with the overlying cycle geological geochemical palynological and macrofossil evidence is consistent with a relative drying terrestrialization upward depositional model for the cycles the abundance of charcoal in dark lithotypes near the cycle bases is explained by the fire prone and highly flammable nature of the herbaceous reed wetlands in common with similar modern wetlands in modern australasia in which the dark lithotypes are suggested to have formed this together with the greater preservation potential of charcoal in subaqueous environments results in the wettest facies of the latrobe valley coals having the highest charcoal contents despite prevailing warm wet climate conditions and the predominance of rainforests that are suggested to have characterized the cenozoic of southern australia some swamp taxa were clearly already pre adapted to tolerate fire and are likely to have been the ancestors of the fire adapted floral communities of modern arid australia

sedimentologic framework of late devonian oolitic iron formation shatti valley west central libya abstract late devonian paralic to shallow marine shatti formation exposed along the northern margin of murzuk basin in west central libya is in the upper part of an essentially continuous paleozoic detrital succession iron bearing shatti deposits a maximum of 90 m thick comprise five coarsening upward regressive sequences that record intermittent detrital influx along a low energy coast quartz arenite sandbodies include long breaker bars on a chenier coast thin storm generated littoral sheet sands wave dominated delta front sands thin crevasse splays and minor deeply scoured channel fill processes and products along the shatti shoreline ranged from those characteristic of the low energy shelf of southwestern louisiana to those of fluvial wave interaction on the rhone delta shatti seq ences are marked by the absence of large well winnowed shoreface sandbodies and other evidences of major transgressive nearshore sedimentation and also of any associated platform carbonate facies as many as 10 beds of ferric oxide chamosite ooids are present in the iron bearing section most of the thicker oolitic ironstones overlie coarsening upward deltaic sequences where they accumulated during episodes of delta abandonment some interfinger laterally with sheeted shoreline sandbodies the ooids were formed on low energy mudflats and then concentrated in thick nearshore bars by local currents interruptions in accretion produced burrowed ferruginous horizons when building ceased the ooid bars were deeply penetrated by large vertical burrowers commonly an ooid bar was succeeded by or graded laterally into a thin ferruginous phosphatic intraclast lag deposit that developed when relatively higher coastal energy of storms or renewed transgression winnowed the sediment star ed mudflats then the oolite and intraformation conglomerate were buried under marine mud that accumulated during the succeeding transgression

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

the record of density induced underflows in a glacial lake as part of an overall study of sedimentation processes in a proglacial lake an effort was made to compare field results with some of the general equations for density flows the results suggest that in relatively small glacial lakes the occurrence of underflows with lower sediment loads involves a complex interplay between thermal and sediment effects which is extremely sensitive to varying hydrologic and climatic conditions in terms of actual transport mechanics the results i indicate that a higher value of 0 6 or 0 7 gives a closer agreement between the measured velocity values and the established equations on moderately shallow slopes ii provide field support for the experimentally derived relationship of britter linden 1980 for the velocity of underflows and suggest the equation may be applicable in situations below 5 slopes and iii support the relationship between velocity of the front and body of a continuous underflow for moderate slope situations suggested by middleton 1966b finally the velocity values measured by electromagnetic current meters stationed in the lake the grain size data obtained from mapping core data and the application of other criteria support the concept that in this environment the underflows are capable of erosion

storm features of siliciclastic shelf sedimentation in the mid cretaceous epeiric seaway of northern australia abstract late aptian to early cenomanian strata were deposited in a large epeiric seaway which covered much of the northern australian landmass during mid cretaceous time the seaway stretched from the carpentaria basin in the north to the eromanga basin in the south during this period siliciclastic sediments accumulated on a gently sloping epeiric shelf which formed the western margin of the carpentaria basin the shelf maintained a relatively similar configuration throughout the mid cretaceous with water depths rarely exceeding 50 m and the seafloor was apparently within the influence of storm waves over much of the area the shelf was storm and wave dominated and most early formed or fair weather sedimentary structures were destroyed or extensively modified during episodic storms storm features include hummocky cross stratification shelly lags erosional conglomeratic lags gutter casts lenticular micro hummocky sand beds megaripples characteristic low diversity and opportunistic ichnofacies various styles of wave ripple lamination and poorly preserved event beds most storm influenced units are preserved as coarsening and shallowing upwards facies successions which aggraded during high relative sea level and prograded during falling relative sea level some of these successions were subsequently eroded during further cyclic fluctuations of relative sea level

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

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

episodic accumulation and the origin of formation boundaries in the helderberg group of new york state at any single locality in the helderberg group of new york state most formation and member boundaries coincide with boundaries of punctuated aggradational cycles in each case of coincidence the boundary is a discontinuity that was produced by a rapid rise of relative base level rather than a facies contact representing gradual migration of contiguous paleoenvironments apparently diachronous formation boundaries in the sequence are not single continuous surfaces instead each diachronous boundary is actually a stratigraphic series of isochronous surfaces that are separate punctuated aggradational cycles pac boundaries produced by distinct geologically instantaneous base level rises these conclusions about the origin of formation boundaries suggest that the concept of the formation as a fundamental unit of stratigraphic description and interpretation may need revision if the stratigraphic record accumulated episodically on a small scale

dynamics of cyclic carbonate deposition and biotic recovery on platforms during the famennian of late devonian in guangxi south china constraints from high resolution cycle and sequence stratigraphy to better understand the dynamics of platform carbonate deposition evolution and biotic recovery during the famennian high resolution cycle and sequence stratigraphic analyses were carried out upon three platform sections one in ramp and two in rimmed platforms along with a biostratigraphically well constrained basinal section in guangxi south china four main facies and fourteen lithofacies are identified in the three isolated platforms these are vertically arranged into decimetre to metre scale shallowing upward peritidal and subtidal cycles or parasequces in which the peritidal cycles predominate over the lower middle famennian six third order sequences s1 to s6 are identified based on the cycle stacking patterns as illustrated by fischer plots and vertical facies changes these sequences are temporally calibrated through correlation with basinal sequences constrained with conodont zonation and match well the six main famennian transgressive regressive cycles t1 to t6 in euramerica and elsewhere indicating a eustatic control however an opposite longer term trend in accommodation change s3 to s4 between platform interior and deeper open shelf to basin settings during the middle famennian suggests a differential subsidence across the platform basin section likely driven by block tilting thus both eustatic fluctuations and local tectonism had played an important role in platform development and evolution after the frasnian famennian biotic crisis main marine benthos preferentially recovered in the normal marine niches on the nearshore open shelves and radiated gradually into offshore restricted platforms brachiopods notably rhychonellides were the taxa recovering the earliest s1 in the normal or near normal marine conditions then echinoderms s3 stromatoporoids upper s3 and corals s5 stepped in episodically however these benthos generally appeared later in the restricted platform interiors only as if the ecological conditions were improved well enough for their colonization therefore the biotic recovery processes were diachronous both taxonomically and ecologically specified

an alternative stratigraphic scheme for the sarawak basin abstract the present stratigraphic scheme for the tertiary of sarawak ho k f 1978 stratigraphic framework for oil exploration in sarawak bulletin of the geological society of malaysia 10 1 14 which subdivides the entire sedimentary succession into eight sedimentary cycles is based on the genetic sedimentary cycle concept each cycle starts with a transgressive basal part followed by a regressive unit which is in turn overlain by the basal transgressive unit of the next cycle the limitation of the present scheme is however in its general applicability for instance when one tries to identify the equivalents of marine surfaces within non marine sediments this is critical for some areas in sarawak where the sediments were deposited predominantly within lower coastal plain to upper coastal plain environments normally barren of foraminifera among other inadequacies of the scheme is the lack of basin wide association between the cycle boundaries and seismic reflectors in practice cycle boundaries picked on the composite well logs often do not agree with the seismic pick the scheme is however well accepted and continues to be used the alternative stratigraphic scheme for the sarawak basin which will be discussed in this paper is based on sequence stratigraphic concepts with the utilisation of unconformity or its correlative conformity as the stratigraphic boundary this scheme has been generated as the result of a programme of basin wide seismic mapping of the sarawak basin seven regional unconformities within the tertiary sedimentary sequences have been mapped the sedimentary units between the unconformities can be recognised as sequences the oldest unconformity is that between the basement belaga formation and the overlying tertiary sediments mainly of late oligocene age since the sediments in the basin are mainly of tertiary age the oldest unit of the succession is referred to as the tertiary one sequence t1 s the next younger sequence is called tertiary two sequence t2 s and so on the proposed scheme which is based on a more conventional and multi disciplinary approach can be understood and appreciated not only by palaeontologists but by all members of exploration and production teams the scheme should be able to facilitate prediction of stratigraphic levels not only after the well has been drilled but also prior to drilling

sequences cycles and basin dynamics in the silurian of the appalachian foreland basin abstract field stratigraphic analysis of the early and medial silurian strata of ontario new york and pennsylvania permits recognition of six major sequences reflecting 3rd order cycles in the niagaran llandoverian ludlovian of new york and adjacent regions these sequences correspond approximately to the medina lower clinton middle clinton upper clinton two sequences and lockport groups each is bounded by widespread unconformities produced by the interplay of eustatic sea level drop and local tectonic uplift in general erosional sequence boundaries and transgressive surfaces are merged with no record of the lowstand wedge each sequence is subdivisible into two to five sub sequences that are marked by sharp though generally non erosional basal discontinuities investigation of the clinton and lockport groups corroborates earlier suggestions that carbonate and siliciclassic tongues extended basinward from opposite margins synchronously in response to sea level drops analysis of the thickness and basinward extent of the progradational tongues reveals the existence of multi scale sedimentary cycles sequences and component sub sequences are correlative basinwide and are synchronous within the resolution of bio and event stratigraphy major drops in relative sea level are represented by the sequence bounding discontinutiies these surfaces are overlain by siliciclastic wedges near terrigenous source areas or winnowed carbonate pack and grainstones on the tectonically passive margin overlying highstand deposits typically shales calcareous mudstones and limestones are separated from lowstand or transgressive deposits by thin condensed intervals commonly marked by phosphatic or glauconitic material and or surfaces of maximum sediment starvation the relative highstand deposits of sequences and sub sequences are developed in relatively deep water facies and are at most slightly progradational hence most sequences and sub sequences are sharply bounded roughly upward deepening to slightly shallowing successions of strata in turn sub sequences are further divisible into widespread minor parasequences and parasequence sets probably corresponding to 6th and 5th order cycles respectively the smaller scale units 0 2 5 mthick commonly display an upward shallowing motif the nested relationship of these cycles supports the hierarchical model of transgressive regressive allocycles proposed by busch and rollins 1984 niagaran cycles discussed herein are equivalent to third fourth and fifth order cycles and are traceable circumbasinally depocenters of successive sequences and sub sequences display a pattern of eastward westward eastward basin axis migration through the silurian during early llandoverian the taconic queenston deltaic complex began to subside and the basin axis depocenter and eastern shoreline shifted eastward approximately 200 km over a 6 million year period as the basin axis migrated eastward the western basin ramp forebulge was repeatedly upwarded and eroded resulting in the generation of regionally angular unconformities at the bases of sequences ii iv and vi the pattern of unconformity greatest to the west suggests rise of the algonquin arch concomitant with eastward basin axis migration during the late llandoverian to early wenlockian the algonquin arch subsided slightly concurrently with a reversal in direction of basin axis migration during deposition of upper clinton and lockport vernon strata sequences v vi the basin axis shifted approximately 300 km back to the west eastward migration of the basin axis corresponds with a time of tectonic quiescence and probable thrust load relaxation the abrupt reversal of migration in the late llandoverian may be a signal of renewed thrusting in the hinterland at the onset of the salinic disturbance

milankovitch cyclicity in purbeck peritidal limestones of the prebetic berriasian southern spain peritidal carbonate rinks purbeck facies of the uppermost portlandian to berriasian in the type section of the sierra del pozo formation in the prebetic zone southern spain are divisible into 141 shallowing upward cycles averaging 2 m in thickness the subtidal facies in these cycles consist of micritic or marly limestones with dasycladacean algae and lituolids the intertidal facies are micritic limestones containing birdseyes and miliolids the supratidal facies comprise laminated algal limestones the tops of which display desiccation cracks and rhizocretions or more locally palaeosols calcretes or palaeokarst surfaces a statistical study using power spectra of the fast fourier transform demonstrates that the periodicity of these cycles is in the milankovitch frequency band

accelerating seismicity of moderate size earthquakes before the 1999 chi chi taiwan earthquake testing time prediction of the self organizing spinodal model of earthquakes summary seismic activation of moderate size earthquakes for the 1999 chi chi taiwan earthquake has been found a self organizing spinodal sos model can explain some observations concerning seismic activation but the equal time durations of the mid and precursory periods during an earthquake cycle conjectured in the original published sos model have not been supported in this case the chi chi test presented here shows unequal time durations of the mid and precursory periods of an earthquake cycle this in turn makes the possibility of time prediction of a characteristic earthquake impossible in the context of the sos model in addition comparisons with numerical simulations of the sliding block model suggest the change in the system s stiffness is a potential mechanism of seismic activation

climatic significance of natric horizons in permian asselian palaeosols of north central kansas usa columnar structured horizons have been recognized in ancient coastal palaeosols of several lower permian asselian stratigraphic units of north central kansas these strongly developed columnar polygonal shaped peds are characteristic of sodium influenced natric argillic horizons and are commonly indicative of semi arid to arid environments evaporite features above and below these palaeosols support the conclusion for a dry palaeoclimate the columnar peds are typically 3 15 cm in diameter and exhibit domed tops fine clay fills the cracks between the columnar peds and is generally of a darker colour than the peds each natric horizon has a low value and chroma colour apparently the result of carbonate accumulation the natric horizons in these permian palaeosols appear to have been partially influenced by sodium rich groundwaters root traces and root moulds are found between peds in all natric horizons indicating plant succession after columnar ped formation these sodium influenced palaeosol profiles occur as part of a spectrum of palaeosol types that indicate cyclical climate change associated with glacioeustatic sea level fluctuations

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

cyclostratigraphy of a carbonate platform as a tool for high precision correlation abstract mesozoic carbonate platforms of southern italy are thick 3000 m and well stratified bodies uplifted by the late tertiary quaternary deformation of the northern gondwanian continental margin they formed mostly in the shallow ramp open to restricted lagoon and peritidal supratidal settings and show a prevailingly cyclic organization consisting of m scale shallowing upward units we think that this cyclicity is demonstrably controlled by the earth s orbital perturbations individual cycle duration hierarchical organization numerical analysis of their sedimentological and petrophysical features the genetic mechanisms of the cyclicity have a climatic dictator allocyclicity that is coupled with eustatic oscillations evidenced by features related to subaerial exposure ranging from microkarst to more mature karst and paleosoils exposure features are widespread at the top of the cycles even when these units are formed by only subtidal deposits suggesting eustatic control this paper presents a study of three sections of the aptian in the campania region of southern italy here a total of 250 m has been studied at a cm scale sections include serra sbregavitelli central matese mountains 160 m upper aptian lower albian monte faito sorrento peninsula 55 m upper aptian lower albian and monte tobenna picentini mountains 35 m upper aptian the latter two outcropping 100 km sse of the former the three sections have a hierarchical organization composed of elementary cycles in turn grouped in bundles and superbundles that have been related respectively to the earth s short and long orbital eccentricity oscillation while the elementary cycles mostly appear to correspond to the precession or to a combination of precession and obliquity periodicities in these successions the stratal pattern shows a dominant aggradational configuration the thickness of the cycles and their groups appears environmentally controlled the thicker cycles being those formed in more open marine settings and vice versa if analysed in terms of sequence stratigraphy we may recognize in the superbundles a transgressive and a highstand system tract that together with maximum flooding surfaces and sequence boundaries was used to develop chronostratigraphic diagrams and to identify cycle omissions at the bundle and superbundle level the number and amplitude of omissions in the successions appear proportional to the environmental conditions the more restricted the water circulation in their original depositional sites the more prone they were to cycle omissions the sections of monte tobenna and monte faito were punctuated by omissions one of them at the superbundle level while in serra sbregavitelli we recognize a smaller number of gaps not reaching the superbundle level lower frequency oscillations 800 2000 k y are also evident and suggest a long term eustatic oscillation of the same periodicity during the lower cretaceous based on the hierarchical organization of the cyclic successions analysed and taking into account the recognized omissions we have correlated the serra sbregavitelli section sss with the two distant sections of monte tobenna corresponding to the lower sss and of monte faito corresponding to the upper sss using appropriate biostratigraphic markers a correlation appears possible at the scale of bundles of cycles 100 k y and sometimes also at the elementary cycle level 50 k y

shell beds as tools in basin analysis the jurassic of kachchh western india skeletal concentrations are ubiquitous in bathonian oxfordian shallow water sediments of the pericratonic basins of kachchh and rajasthan western india by analysing the biofabric of the concentrations and the taphonomic signatures of individual components it is possible to distinguish between the final concentration process recorded by the biofabric and events taking place prior to final deposition recorded by taphonomic signatures the skeletal concentrations are grouped in nine genetic types ranging from fair weather wave concentrations to storm concentrations and condensed concentrations they mainly reflect biological and hydraulic processes and in some instances permit estimates of their duration and show a rough zonation along a bathymetric gradient plotted against the stratigraphic sections the skeletal concentrations show in accordance with other sedimentological data three orders of bathymetric trends the first two orders are shallowing deepening cycles which possibly correspond to eustatic changes in sea level the third order represents parasequences with a strongly asymmetric sedimentary record skeletal concentrations are a useful additional tool in basin analysis but are best used in combination with other data