coseismic and postseismic slip distribution of the 2003 mw 6 5 chengkung earthquake in eastern taiwan elastic modeling from inversion of gps data abstract the chengkung earthquake with m l 6 6 occurred in eastern taiwan at 12 38 local time on december 10th 2003 based on the main shock relocation and aftershock distribution the chengkung earthquake occurred along the previously recognized n20 e trending chihshang fault this event did not cause human loss but significant cracks developed at the ground surface and damaged some buildings after 1951 taitung earthquake there was no larger m l 6 earthquake occurred in this region until the chengkung earthquake as a result the chengkung earthquake is a good opportunity to study the seismogenic structure of the chihshang fault the coseismic displacements recorded by gps show a fan shaped distribution with maximal displacement of about 30 cm near the epicenter the aftershocks of the chengkung earthquake revealing an apparent linear distribution helps us to construct the clear fault geometry of the chihshang fault in this study we employ a half space angular elastic dislocation model with gps observations to figure out the slip distribution and seismological behavior of the chengkung earthquake on the chihshang fault the elastic half space dislocation model reveals that the chengkung earthquake is a thrust event with minor left lateral strike slip component the maximum coseismic slip is located around the depth of 20 km and up to 1 1 m the slips are gradually decreased to less than 10 cm near the surface part of the chihshang fault the seismogenic fault plane which is constructed by the delineation of the aftershocks demonstrates that the chihshang fault is a high angle fault however the fault plane changes to a flat plane at depth of 20 km in addition a significant part of the measured deformation across the surface fault zone for this earthquake can be attributed to postseismic creep the postseismic elastic dislocation model shows that most afterslips are distributed to the upper level of the chihshang fault and most afterslips consist of both of dip and left lateral slip the model results show that the chihshang fault may be partially locked or damped near surface during coseismic slip after the mainshock the strain which cumulated near the surface was released by postseismic creep resulting in significant postseismic deformation

high resolution sequence stratigraphy of lower paleozoic sheet sandstones in central north america the role of special conditions of cratonic interiors in development of stratal architecture well known difficulties in applying sequence stratigraphic concepts to deposits that accumulated across slowly subsiding cratonic interior regions have limited our ability to interpret the history of continental scale tectonism oceanographic dynamics of epeiric seas and eustasy we used a multi disciplinary approach to construct a high resolution stratigraphic framework for lower paleozoic strata in the cratonic interior of north america within this framework these strata proved readily amenable to modern sequence stratigraphic techniques that were formulated based on successions along passive margins and in foreland basins settings markedly different from the cratonic interior parasequences parasequence stacking patterns systems tracts maximum flooding intervals and sequence bounding unconformities can be confidently recognized in the cratonic interior using mostly standard criteria for identification the similarity of cratonic interior and foreland basin successions in size geometry constituent facies and local stacking patterns of nearshore parasequences is especially striking this similarity indicates that the fundamental processes that establish shoreface morphology and determine the stratal expression of retreat and progradation were likewise generally the same despite marked differences in tectonism physiography and bathymetry between the two settings our results do not support the widespread perception that paleozoic cratonic interior successions are so anomalous in stratal geometries and constitute such a poor record of time that they are poorly suited for modern sequence stratigraphic analyses the particular arrangement of stratal elements in the cratonic interior succession we studied is no more anomalous or enigmatic than the variability in architecture that sets all sedimentary successions apart from one another thus paleozoic strata of the cratonic interior are most appropriately considered as a package that belongs in a continuum of variable stratigraphic packages reflecting variable controls such as subsidence and shelf physiography special conditions of exceptionally slow subsidence rate shallow bathymetry and nearly flat regional shelf gradient are manifest mostly by the presence of individual systems tracts of relatively long duration that extend for much greater distances across depositional strike than those that characterize successions deposited in more dynamic tectonic and physiographic settings these results suggest that if other cratonic interior successions are as anomalous as reported a low sediment supply may have played a primary role in development of their apparently condensed stratal architecture the results also lead us to suggest that a nonvegetated lower paleozoic landscape played a relatively insignificant role in the development of what are commonly perceived to be enigmatic stratigraphic features of sheet sandstones particularly their widespread yet thin geometry and a scarcity of shale and siltstone

cenozoic tectonism in the central basin and range magnitude rate and distribution of upper crustal strain a wealth of pre cenozoic geologic markers across the central basin and range province defined mainly by thrust faults developed within a miogeoclinal wedge makes it one of the best areas on earth to reconstruct large scale continental extension we use this 100 000 km 2 region bounded by the southern sierra nevada on the west and the colorado plateau on the east to illustrate the concepts of correlation and misalignment for regional strain markers and of strain compatibility and kinematic viability in palinspastic reconstructions the results indicate 250 to 300 km of west northwest motion of the sierra away from the plateau accommodated by both crustal thinning and north south shortening tertiary intermontane basin deposits and mineral cooling ages of deeply exhumed rocks constrain the overall kinematics of motion most of the westward motion occurred between 16 and 5 ma at rates near 2 cm yr slowing to 1 to 1 5 cm yr in the last 5 ma we have quantified the partitioning of strain between vertical crustal thinning via normal faults and map view plane strain via conjugate strike slip faults by placing a grid of 10 x 10 km elements on a retrodeformed map of the region and measuring the increase in area of grid elements between the undeformed and present day grids this analysis yields a maximum finite elongation of the basin and range at 36 n to 37 n of 3 4 oriented n73 w map view area balance shows that 20 percent of this elongation is compensated by north south shortening and 80 percent by crustal thinning this yields an average thinning factor for the upper crust of 2 7 between the sierra and plateau inconsistent with the hypothesis that neogene deformation in the central basin and range is predominantly dextral shear plane strain these results in concert with the observation that the southern sierra nevada has similar crustal thickness to the central basin and range support the hypothesis of large scale eastward flow of sierran deep crust during extension

anatomy of extremely thin marine sequences landward of a passive margin hinge zone neogene calvert cliffs succession maryland u s a abstract detailed examination of neogene strata in cliffs 25 35 m high along the western shore of chesapeake bay maryland reveals the complexity of the surviving record of siliciclastic sequences 150 km inland of the structural hinge zone of the atlantic passive margin previous study of the lower to middle miocene calvert plum point member and choptank formations documented a series of third order sequences 7 10 m thick in which lowstand deposits are entirely lacking transgressive tracts comprise a mosaic of condensed bioclastic facies and regressive highstand tracts are present but partially truncated by the next sequence boundary smaller scale fourth order cyclic units could not be resolved together these sequences constitute t e transgressive and early highstand tracts of a larger second order miocene composite sequence the present paper documents stratigraphic relations higher in the calvert cliffs succession including the upper miocene st marys formation which represents late highstand marine deposits of the miocene second order sequence and younger neogene fluvial and tidal inlet deposits representing incised valley deposits of the succeeding second order cycle the st marys formation consists of a series of tabular units 2 5 m thick each with an exclusively transgressive array of facies and bounded by stranding surfaces of abrupt shallowing these units which are opposite to the flooding surface bounded regressive facies arrays of model parasequences are best characterized as shaved sequences in which only the transgressive tract survives and are stacked into larger transgressive highstand and forced regression sets biostratigraphic analyses by others indicate that this onshore record contains the same number of third order 1 my duration units as present offshore and so thinning landward of the hinge zone was accomplished not by omission or erosion of entire cycles of deposition but instead by omission of some subsidiary elements e g lowstand tracts by erosional shaving of sequence tops removing the entire regressive tract in some sequences by a reduced number of component high order cycles surviving per larger set and by qualitative changes in the anatomy or composition of elements e g condensed transgressive tracts shaved sequences rather than parasequences all of these differences can be attributed to limited accommodation ut preservation of an onshore record of each baselevel cycle was probably also favored by the large amplitude and rapidity of eustatic fluctuations during the miocene

widespread prolonged late middle to late ordovician upwelling in north america a proxy record of glaciation late middle to late ordovician subtidal ramp carbonates of new mexico texas and oklahoma contain abundant spiculitic chert to 70 chert by volume and phosphate 1 5 wt indicating that these rocks formed in an extensive upwelling zone upwelling began in the late middle ordovician ca 454 ma and persisted until the end of the ordovician late ordovician cherty carbonates also occur along the u s cordilleran margin in board of organic rich graptolitic shale and chert the widespread occurrence of late ordovician cherty and phosphatic carbonates on southern and western laurentia in addition to phosphate rich cool water carbonates over much of the north american midcontinent suggests vigorous thermohaline circulation related to prolonged 10 14 ma gondwana glaciation

palaeozoic stromatoporoid taphonomy ecologic and environmental significance abstract epibenthic sessile marine organisms such as the aspiculate stromatoporoids show a wide range of growth forms in different settings across palaeozoic carbonate banks and reefs making them useful taphonomic tools in palaeoenvironment analysis field observations of ordovician through late devonian stromatoporoid bearing biostromal and biohermal successions on different palaeocontinents have revealed three main post mortem tapho signatures that affect palaeoecologic analysis 1 variability of physical breakage and bioerosion prior to burial 2 loss of morphologic and taxonomic information due to post burial diagenesis and 3 minor localized reorientation during karstification physical fragmentation abrasion and lesser bioerosion and dissolution represent the main processes responsible for post mortem destruction hydrodynamic behaviour of stromatoporoid clasts was similar to other carbonate skeletal clasts in their rounding and sorting characteristics although bioerosion and bioturbation did not play an important role in palaeozoic stromatoporoid taphofacies characterization a marked increase in bioerosion of stromatoporoids is evident beginning in certain silurian wenlock morphotypes and in some devonian morphotypes stromatoporoids offer varying profiles to shelf currents and seasonal storm surges and apparently have different skeletal strength durability depending on skeletal architecture cyst dominated skeleton architecture appears to have been fairly resistant to fragmentation latilaminae a common skeletal feature in different families of calcified sponges represent inherent zones of weakness that appear to have enhanced equidimensional breakage away from latilaminae to oblate breakage along latilaminar surfaces fragmentation construction of lamina pillar architecture amongst the most common skeletal attributes of siluro devonian stromatoporoids gives the visual impression of varying robustness but this is supported by few data stromatoporoid response to increasing hydrodynamic energies varies greatly from no movement or simple overturning of skeletons to severe fragmentation and size sorting although such variation broadly reflects palaeogeographic setting and thus periodic disturbance by tropical storms familial and generic skeletal traits greatly influenced taphofacies characterization these differences in modularity and ontogeny in the stromatoporoid groups has hampered development of generalized taphofacies models as devised for shell rich deposits taphofacies are not comparable between modern coralgal reefs especially the highly specialized acroporid facies and palaeozoic stromatoporoid bearing reefs for the following reasons significant differences exist in diversity of observable growth strategies nature of attachment of skeletons to substrate and variety of morphotypes probable significant differences in life modes between these groups feeding strategies and positions and areal extent of clonal tissue within the skeletons and their subsequent susceptibility to infestation by microborers and palaeozoic macrobioeroders were fewer than modern representatives and apparently less effective in stromatoporoid taphofacies characterization than modern reef macrobioeroders are for coral taphofacies development

cyclostratigraphic calibration of the frasnian late devonian time scale western alberta canada until now the duration of the frasnian stage has remained very poorly constrained hampering a detailed understanding of sedimentation processes and environmental and evolutionary change in this study timeseries analyses of high resolution 10 20 k y magnetic susceptibility data identify sixteen 405 k y eccentricity cycles in the magnetic susceptibility stratigraphy of the frasnian late devonian derived from carbonate platform and surrounding slope and basin deposits in western alberta canada previous studies demonstrated the generally consistent pattern of magnetic susceptibility change across the alberta basin and thus demonstrated the utility of magnetic susceptibility stratigraphy as a refi ned regional correlation tool compared to biostratigraphy in the present study we show that the magnetic susceptibility stratigraphy of the frasnian interval in western alberta has been signifi cantly infl uenced by astro nomical forcing using the sixteen 405 k y eccentricity cycles as a geochronometer we constructed a frasnian astronomical time scale this time scale indicates a duration of 6 5 0 4 m y for the frasnian calibrating this duration to the best available devonian chronology the absolute age of the givetian frasnian boundary is recalculated to 383 6 3 0 ma and the age of the frasnian famennian boundary is recalculated to 376 7 3 0 ma these new absolute ages take into account the astronomically derived duration of the frasnian but they also yield a narrowing of the error margins of the absolute ages by several hundreds of thousands of years

comparative analysis of methods used to define eustatic variations in outcrop late cambrian interbasinal sequence development interbasinal correlation of late cambrian cyclic carbonates from the appalachian and cordilleran passive margins the texas craton and the southern oklahoma aulacogen defines six major third order depositional sequences graphic correlation of biostratigraphically constrained strata was used to establish equivalency of stratigraphic sequences between the individual sections relatively isochronous biomere boundaries were used as time datums for lithostratigraphic correlation although the individual sections are composed of different types of meter scale cycles and component lithofacies that reflect the various environmental settings of the localities the overall upward shallowing character of individual sequences is evident the sequences are late cedaria mid crepicephalus late crepicephalus aphelaspis to earliest elvinia elvinia to early saukia and saukia to the cambrian ordovician boundary interbasinal correlation of stratigraphic sequences permits an evaluation of quantitative techniques for determining accommodation history correlation of fischer plots of cyclic successions from separate basins supports a eustatic control of late cambrian sequence development r2 r3 curves derived from subsidence analysis of the late cambrian sections provide good resolution of the second and third order scales of accommodation change and interbasinal correlations of r2 r3 curves also support eustatic control on sequence development comparing the accomodation curves and subsidence analysis with paleobathymetric trends of late cambrian cyclic strata suggests that themore curves may approximate the form of the eustatic sealevel signal a composite eustatic sealevel curve for late cambrian time in north america was created by qualitatively combining the accommodation curves defined by the different techniques for each of the four localities 129 refs 16 figs 3 tabs less

calibrating the devonian time scale a synthesis of u pb id tims ages and conodont stratigraphy the recalibrated devonian time scale represents an important improvement of devonian chronology regarding two aspects firstly a data set of 13 biostratigraphically well bracketed u pb id tims zircon and monazite ages constitutes the framework of the scale secondly approximately time linear biostratigraphic scales have been used for the interpolation between the isotopic ages the new construction thus represents a biochronometric time scale which allows the assignment of numeric ages not only to stage boundaries but also to each biozone boundary the method of interpolation applied also enables the projection of the geochronological error onto the time scale according to the newly calibrated scale the devonian lasted 57 4 5 7 ma from 418 1 3 0 to 360 7 2 7 ma this is compared to previously published time scales the longest time span ever calculated for this period the age interpolations for the eight stage boundaries are famennian tournaisian devonian carboniferous 360 7 2 7 ma frasnian famennian 376 1 3 6 ma givetian frasnian 383 7 3 1 ma eifelian givetian 388 1 2 6 ma emsian eifelian 391 9 3 4 ma pragian emsian 409 1 3 8 ma lochkovian pragian 412 3 3 5 ma pridolian lochkovian silurian devonian 418 1 3 0 ma full size table table options view in workspace download as csv the duration of the middle devonian is calibrated here as quite short with 8 2 ma and the emsian and the famennian are the longest stages with interpolated durations of 17 2 and 15 4 ma respectively together all devonian stages contain 57 conodont zones including subzones according to the standard conodont zonation giving a mean duration of about 1 ma in the highly resolved part of the time scale mid eifelian to the devonian carboniferous boundary zonal resolution averages 0 6 ma in contrast the lowest resolution is shown in the early emsian to mid eifelian interval with zonal durations of up to 5 5 ma serotinus zone

the paradox of drowned reefs and carbonate platforms shallow water carbonate platforms and reefs are drowned when tectonic subsidence or rising sea level outpaces carbonate accumulation and benthonic carbonate production ceases drowned platforms are common in the geologic record but they present a paradox if one considers rates of processes involved during the early holocene when sea level rose at rates of 6 000 to 10 000 m yr mm 1 000 yr most reefs and platforms were outpaced by the rising sea during the late holocene with sea level rising 500 to 3 000 m yr in the atlantic caribbean area reefs and platforms started to recover built to sea level and prograded seaward 1 000 m yr is thus a conservative estimate of the average growth potential of modern reefs and platforms independently accumulation rates of prograding platforms in the geologic record suggest growth potential in excess of several hundred microns per year the growth potential of 1 000 m yr exceeds any relative rise of sea level caused by long term processes in the geologic record newly formed ocean crust subsides at a maximum of 250 m yr basin subsidence averages 10 to 100 m yr and sea level rises due to increased sea floor spreading amount to less than 10 m yr rapid pulses of relative rise of sea level or reduction of benthic growth by deterioration of the environment remain the only plausible explanations of drowning the geologic record shows examples of both of these processes global mass extinctions of reefs and platforms occurred in the middle cretaceous eustatic rise due to submarine volcanism or desiccation of a small ocean basin and the late devonian global crisis of ocean environment extraterrestrial cause drowning controlled by regional tectonics prevailed in the jurassic and early cretaceous of the tethyan realm and the drowning of mesozoic platforms in the western north atlantic seems to have been dictated by plate tectonic drift to higher latitudes

quantification of high frequency sea level fluctuations in shallow water carbonates an example from the berriasian valanginian french jura abstract when quantifying sedimentary processes on shallow carbonate platforms it is important to know the high frequency accommodation changes through time accommodation changes in cyclic successions are often analysed by simply converting cycle thickness to fischer plots this approach is not satisfactory because it does not account for differential compaction possible erosion sea level fall below the depositional surface or subtidal cycles an attempt is made here to reconstruct a realistic high frequency accommodation and sea level curve based on a detailed facies and cyclostratigraphical analysis of middle berriasian to lower valanginian sections in the french jura mountains the general depositional environment was a shallow marine carbonate platform on a passive margin our approach includes the following steps 1 facies interpretation 2 cyclostratigraphical analysis and identification of milankovitch parameters in a well constrained chronostratigraphic framework 3 differential decompaction according to facies 4 estimation of depth ranges of erosion and vadose zone 5 estimation of water depth ranges at sequence boundaries and maximum flooding intervals 6 estimation of mean subsidence rate 7 classification of depositional sequences according to types of facies evolution catch up catch down give up or keep up 8 classification of depositional sequences according to long term sea level evolution rising stable falling 9 calculation of eustatic sea level change for each depositional sequence using the parameters inferred from these scenarios assuming that sea level cycles were essentially symmetrical which is probable in early cretaceous greenhouse conditions 10 calculation of a sea level curve for each studied section 11 comparison of these curves among each other to filter out differential subsidence 12 construction of a composite eustatic sea level curve for the entire studied platform 13 spectral analysis of the calculated sea level curves limitations of the method are those common to every stratigraphic analysis however the method has the potential to improve the original cyclostratigraphical interpretations and to better constrain the high frequency sea level changes that control carbonate production and sediment fluxes

time lapse changes of seismic velocity in the shallow ground caused by strong ground motion shock of the 2000 western tottori earthquake japan as revealed from coda deconvolution analysis abstract a large earthquake shock often drops the seismic velocity of the shallow ground however it is not clear whether the dropped velocity recovers shortly after the earthquake shock or not the purpose of this article is to report the time lapse changes of seismic velocity in the shallow ground after the 2000 western tottori earthquake japan we deconvolve the coda record of small earthquakes registered on the ground surface by that registered at the 100 m depth in a borehole at a station that experienced a strong shock from the mainshock because coda waves are mostly composed of randomly scattered s waves deconvolution of the two coda records enables us to obtain a robust image of the ground structure assuming that the shear modulus was reduced at the depth of 0 11 m we estimate the shear modulus change in each time period after the mainshock by fitting synthetic coda deconvolution to the observed one from 1 to 16 hz as a result the shear modulus dropped to 52 of the value obtained before the mainshock a few minutes after the strong earthquake shock this caused a decrease in the s wave velocity of 30 and an increase in s wave travel time of 17 msec the shear modulus continued to recover for over 1 yr following the logarithm of the lapse time it recovered to 69 83 87 and 97 of the value obtained before the mainshock in the periods of 0 to 1 week 1 week to 1 month 1 month to 1 yr and 1 to 4 yr after the mainshock respectively

cyclic ramp to basin carbonate deposits lower mississippian wyoming and montana a combined field and computer modeling study abstract the lower mississippian lodgepole lower madison formations 20 225 m thick developed along a broad 700 km storm dominated pericratonic ramp three types of fifth order upward shallowing cycles are recognized across the ramp to basin transition peritidal cycles consist of very shallow subtidal facies overlain by algal laminated tidal flat deposits which are rarely capped by paleosol breccia layers shallow subtidal cycles consist of stacked ooid grainstone shoal deposits or deeper subtidal facies overlain by ooid skeletal grainstone caps deep subtidal cycles located along the outer ramp consist of basal sub storm wave base limestone argillite overlain by storm deposited limestone which are capped by hummocky stratified to massive skeletal ooid grainstone deep subtidal c cles pass downslope into ramp slope facies composed to rhythmically interbedded limestone and argillite with local deep water mud mounds no upward shallowing cycles occur within the ramp slope facies average cycle durations calculated along the outer ramp are between 30 110 ky the fifth order cycles are stacked to form three third to fourth order depositional sequences which are recognized by regional transgressive regressive facies trends and cycles stacking patterns ramp margin wedges rmw developed during long term sea level fall and lowstand and consist of cyclic crinoidal bank and oolitic shoal facies which pass downdip into deep subtidal cycles transgressive systems tracts tst which onlapped the ramp during long term sea level rise include thick shallow and deep subtidal cycles peritidal cycles are restricted to the inner ramp highstand systems tracts hst developed during long term sea level highstand and fall and along the ramp are composed of early hst shallow subtidal cycles overlain by late hst peritidal cycles shallow through deep subtidal cycles characterize the hst along the ramp slope two dimensional computer modeling of the cyclic sequences suggests that for the assumed water depths of facies fifth order sea level oscillations of at least 20 25 m were required to generate deep subtidal cycles along the ramp slope synthetic sequences run with fifth order sea level amplitudes end page 1194 and tst deposition a feature not observed in the actual sequences other factors in addition to fifth order sea level oscillations likely played a role in generating synchronous peritidal and deep subtidal cycles during hst deposition these factors may include short term climatic changes which influenced the depths to storm wave reworking the moderate amplitude sea level oscillations suggested by the cyclic sequences may reflect the initial effects of carboniferous glaciation that was occurring in gondwana

scaling of sedimentation rates and drowning of reefs and carbonate platforms the rule that sedimentation rates decrease as the time interval increases has been examined by a procedure that avoids the mathematical problem of plotting a variable time against its inverse the test confirms that the scaling trend has real physical meaning in the time range of 10 1 108 yr sedimentation rates change roughly proportionally to the inverse of the square root of time this report proposes and evaluates the hypothesis that the growth potential of reefs and carbonate platforms follows the same scaling trend the trend implies that a growth of 104 m yr sustained over 103 yr an upper limit of reef growth in the holocene translates into 102 m yr sustained over 107 yr decrease of the growth potential with increasing time solves the paradox of drowned platforms if the decrease results largely from environmental factors and not simply from increase of the time fraction of subaerial exposure

accommodation and supply a dual control on stratigraphic sequences abstract it is widely accepted that both eustatic and tectonically controlled regional changes of sea level have contributed to the record of stratigraphic sequences i suggest that environmental change be added as a third autonomous control sedimentologic principles clearly indicate that sequences and their systems tracts are controlled by the interplay of two rates the rate of change in accommodation space available for sedimentation and the rate of sediment supply sea level has direct control on accommodation but its influence on sediment supply is remote and easily overshadowed by environmental factors for instance the record of the most recent sea level rise is a transgressive systems tract where supply is low it is a prograding highstand systems tract in deltas where the supply is high examples of sequence boundaries generated by changes in sediment supply include tectonically driven shifts in sediment input into basins changes in ocean currents pulsating supply from failure of submarine slopes and drowning of carbonate platforms by environmental stress furthermore the stratigraphic sequences in fluviatile continental basins are physically removed from sea level induced changes in accommodation and must have formed by changes in the rate and pattern of supply subaerial exposure of marine sediments at the sequence boundary is a most important criterion for recognizing sea level cycles as opposed to supply cycles other criteria include downstepping of shelf breaks and characteristic patterns in the spacing of time lines within sequences some third order cycles ca 0 5 3 ma duration meet these criteria others do not cycle stacking patterns and the shifting facies belts on cratons indicate that many second and third order cycles lack pronounced exposure unconformities and represent gradual changes superimposed on more rapid shorter oscillations seismic data yield poor images of these gradational changes because they lack resolution seismic models of outcrops show that near the limits of resolution the seismic tool tends to portray rapid changes in facies and bed thickness i e lateral variations in supply as unconformities seismic unconformities do not necessarily correspond to unconformities in outcrop the succession of stratigraphic sequences is best considered a composite record of sea level and environmental change separating the various controls requires carefully planned experiments work on the oxygen isotope curve another proxy for sea level has set an example in this respect

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

stratigraphic and oxygen isotope evidence for my scale glaciation driving eustasy in the early middle devonian greenhouse world article i nfo million year scale 3rd order depositional sequences few 10s to 100 m thick are common in the devonian marine record and are correlated between sedimentary basins and across widely separated continents implying a eustatic origin tectonically driven changes in mid ocean ridge spreading rates lengths are too slow to account for the calculated 3rd order rise fall rates and typical orbital frequencies 20 400 ky are too fast we analyzed oxygen isotopes from conodont apatite to evaluate if early middle devonian 3rd order sea level changes were controlled by paleoclimatically driven ice volume glacio eustasy and seawater temperature change thermo eustasy two successive depositional sequences in the western u s nevada and czech republic prague basin were sampled the 18 o values range from 17 8

macrostratigraphy of north america abstract the geological record is a three dimensional mosaic of gap bound rock bodies that at any given scale of temporal resolution were emplaced more or less continuously at any geographic location the irregular alternation of processes responsible for the formation and destruction of rock bodies results in the preservation of hiatus bound rock packages that have a distinct time of first occurrence base or oldest portion a time of last occurrence top or youngest portion and a suite of defining characters e g lithologies thickness fossils etc many important aspects of the geologic record can be quantified by compiling the stratigraphic ranges of such gap bound rock packages these include the quantity and spatial and temporal distribution of preserved rock rates of rock formation sequence stratigraphic architecture and area weighted rates of expansion and contraction erosional truncation of rock emplacement settings this approach to characterizing the rock record is scalable per

models for circulation patterns in epicontinental seas applied to paleozoic facies of north america craton circulation in epicontinental seas develops in response to thermohaline wind driven and tidal motions in various climatic geographic and bathymetric settings mass balance relations in a seaway are established by the relative rates of outflow inflow freshwater and ocean water and evaporation which constrain two contrasting styles of epicontinental circulation quasietuarine circulation qec is established where rates of freshwater influx exceeds evaporation surface outflow from a seaway with qec typically is balanced by inflow of oceanic water at depth a density stratification can be established below the limits of vertical mixing a bottom layer of oxygen poor or anoxic water may develop in a seaway with or without an entrance sill if the bottom waters are derived from the oxygen minimum zone of the open ocean or if organic productivity exceeds the limits of aerobic respiration upwelling may be promoted in specific epicontinental settings with qec antiestuarine circulation aec is developed in arid climates where evaporation exceeds freshwater influx evaporative concentration in the surface layer causes oxygenated water to sink bottom outflow of denser more saline water is balanced by surface inflow from the open ocean a sill or barrier may inhibit bottom circulation in seas with aec permitting development of a basal brine layer stagnation in the brine layer may lead to oxygen depletion seas with aec commonly are characterized by extensive carbonate evaporite facies geographic and stratigraphic syntheses of lithofacies and biofacies provide the empirical basis for interpretations of seaway dynamics in ancient epicontinental settings examples from the upper ordovician maquoketa formation and upper devonian lime creek sweetland creek formations of cratonic north america are interpreted in the context of stratified qec patterns in each case oxygen poor to anoxic waters appear to have impinged along the basin slope below the margin of an oxygenated carbonate shelf upwelling along the shelf margin in the maquoketa example helps explain the distribution of phosphatic sediments a stratified aec pattern is interpreted for the gower formation silurian of eastern iowa a barrier to bottom circulation at the mouth of an embayment in the epicontinental sea resulted in a basal layer of hypersaline water devoid of shelly benthos surface water salinities increased progresively shoreward within the embayment but benthic organisms flourished where carbonate mounds built upward into the oxygenated layer

fractal nature of stratigraphic sequences orders of stratigraphic sequences are being used loosely and with widely varying definitions the orders seem to be subdivisions of convenience rather than an indication of natural structure it is proposed that at least at time scales of 103 106 yr sequences and systems tracts are scale invariant fractal features in which units bounded by exposure surfaces and units bounded by flooding surfaces are about equally likely support for this conceptual model derives from the well known facts that 1 sediment architecture is largely scale invariant over a wide range of scales in time and space 2 first order trends of sea level movements and sedimentation rates are fractal on all geologically relevant time scales and 3 detailed studies in carbonates indicate approximately equal abundance of flooding surfaces and demonstrable exposure surfaces among unit boundaries finally traces of prograding shelf edges that step up and step down in response to sea level changes are demonstrated in this study to have a fractal nature

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

relation of eustasy to stacking patterns of meter scale carbonate cycles late cambrian u s a abstract an interbasinal study of late cambrian cyclic carbonate successions in the appalachian and cordilleran passive margins suggests that superimposed orders of eustasy controlled the development of large scale depositional sequences and the component peritidal to subtidal meter scale cycles that comprise them the focus of this paper is on the small scale cyclicity its probable control by milankovitch forced sea level oscillations and how stacking patterns of meter scale cycles can be used to define internal components of larger scale sequences and estimate variations in relative sea level fining upward peritidal cycles showing evidence of episodic emergence grade seaward into coarsening upward subtidal cycles which lack evidence of emergence and form a continuum across the cambrian carbonate platforms eustasy appears to exert the dominant control on the simultaneous development of peritidal and subtidal cycles on late cambrian carbonate platforms evidence for milankovitch forcing of glacio eustatic sea level oscillations is provided by a 4 1 bundling of fifth order meter scale cycles 96 ky within fourth order cycles spanning tens of meters 440 ky within the big horse member of the orr formation in the house range of utah the 4 1 bundling may manifest the short e centricity to long eccentricity ratio of the milankovitch astronomical rhythms systematic changes in the stacking patterns of meter scale cycles can be used in conjunction with fischer plots to define long term sea level cycles on fischer plots of peritidal cyclic successions long term relative sea level rises are characterized by thick subtidal dominated cycles with thin laminite caps long term relative sea level falls are defined by stacks of thin laminite dominated cycles that show brecciated cycle caps and quartz sands toward the relative sea level lowstand on fischer plots of dominantly subtidal cyclic successions long term sea level rise is characterized by storm dominated open marine carbonate cycles or thick deep ramp shale based cycles falling segments of the fischer plot are characterized by thin shallow subtidal cycles compos d of restricted lithofacies cycle stacking patterns parasequence sets provide the crucial link between the meter scale cycles parasequences and the larger scale sequences and their component systems tracts one and two dimensional models of peritidal and subtidal cycle development indicate that whereas peritidal cycle thickness is primarily controlled by accommodation space deeper subtidal cycle thickness is primarily controlled by sedimentation rate lithofacies within peritidal cycles reflect the sedimentologic response to fluctuations in sea level lithofacies within subtidal cycles may be related to fluctuations in the zones of fairweather and storm wave reworking that oscillated in harmony with sea level fluctuations and may have acted as a subtidal limit to upward aggradation the 2 d modelling illustrates how stacked peritidal to deep subtidal carbonate cycles with thicknesses compositions and stacking patterns similar to the late cambrian of north america can be generated by ilankovitch driven composite eustasy

the role of nutrient availability in bioerosion consequences to carbonate buildups abstract zooxanthellate organisms which are among the major carbonate producers on coral reefs are highly adapted to nutrient deficient conditions and tend to be outcompeted by filamentous or fleshy algae if nutrients are abundant reef dwelling bioeroding organisms on the other hand seem to increase in abundance with increasing availability of nutrient and food resources maximum rates of calcium carbonate production in a reef system are comparable in magnitude to maximum rates of bioerosion the dynamic interplay between accretion destruction of coral reefs is therefore likely to be strongly influenced by nutrient availability nutrient availability may also influence development of carbonate facies in reef systems that develop in oligotrophic waters skeletal sands and framework should dominate carbonate buildups in systems that develop in mesotrophic waters enhanced bioerosion should reduce much of the skeletal material to carbonate muds increasing the prevalence of mud rich facies eutrophic conditions should result in bioeroded hardgrounds and carbonate depositional hiatuses when carbonate accumulation rates fail to equal or exceed rates of local relative sea level rise reefs drown bored and lithified pavements with crusts of ferromanganese oxides phosphates or glauconite often separate shallow reef from overlying deeper water deposits nondeposition bioerosion and evidence for low redox potentials at the sediment water interface all implicate excess nutrient availability as a factor in reef drowning some carbonate depositional hiatuses and bioerosional surfaces are local phenomena evidence of responses to local increases in nutrient availability resulting from submergence of soils runoff or topographic upwelling others appear to reflect regional or worldwide events because many carbonate producing organisms have life history strategies specialized to nutrient deficient conditions they are unable to compete when nutrients become plentiful events that triggered ocean turnover or sharp increases in the rate of deep ocean circulation would have increased sea surface nutrient availability worldwide such eutrophication could have caused widespread extinctions in reef communities because eutrophication promotes bioerosion details of the fossil records of those events are probably lost in bioerosional hiatuses

discontinuity surfaces on a shallow marine carbonate platform berriasian valanginian france and switzerland discontinuities in sedimentation are commonly expressed as surfaces in outcrop sections and are due to rapid and substantial environmental changes on shallow marine carbonate platforms most such surfaces represent hiatuses below biostratigraphic resolution and detailed analysis is necessary to identify and evaluate the environmental change involved surfaces in nine sections of the lower cretaceous of the french and swiss jura platform are characterized on the basis of eight universally applicable criteria geometry lateral extent morphology biological activity mineralization facies contrast diagenetic contrast and biostratigraphy nine different surface types are distinguished by their common features and environment of formation all of them are related to environmental changes in the form of subaqueous erosion subaerial exposure subaqueous omission or changes in texture and facies the distribution of surface types in the studied sections shows that condensation and exposure related surfaces tend to occur repetitively in certain intervals calibrated by biostratigraphy these surface zones can be correlated across the platform from proximal to distal positions in comparison with the global sequence stratigraphic framework hardenbol et al 1997 most exposure zones correlate with third order sequence boundaries condensation zones fall in between in the studied sections third order eustatic sea level drops appear to be represented rather by zones of small scale discontinuities than by widespread and well marked single sequence boundaries this is explained by the superposition of high frequency low amplitude sea level fluctuations on a larger scale sea level trend under greenhouse conditions the lateral extent of the surface zones varies through time and indicates important changes in platform morphology changes in local subsidence rate indicated by variable thicknesses of the deposits in comparison with second and third order sea level trends suggest an evolution of the french jura platform from a ramp type morphology in the late middle berriasian to a flat topped platform in the late berriasian the early valanginian again is characterized by increased differential subsidence and well marked platform morphology this study demonstrates that 1 small scale and short lived discontinuities can reflect large scale variations of relative sea level 2 on shallow platforms characterized by small topographic variations and lateral facies changes third order sequence stratigraphic surfaces are not necessarily expressed by one widespread single surface but by zones of surfaces indicating repeated environmental changes surface zones can serve as an additional tool for correlation and interpretation of platform evolution and 3 small scale discontinuities form an integral part of the stratigraphic record and should receive the same attention as the sedimentary deposits they delimit

ecological control of sedimentary accommodation evolution from a carbonate ramp to rimmed shelf upper miocene balearic islands abstract stratal patterns and facies architecture develop in response to sediment flux and the available space for sediment accumulation accommodation in siliciclastic systems these two parameters are independent in carbonates however they are highly interdependent 1 sediment input production highly depends on biological systems and consequently on intrabasinal conditions nutrients temperature salinity etc 2 sediment dispersal depends on the production loci and on the interaction between the amount and type of sediment being produced and the hydraulic energy additionally biological processes binding baffling framework construction and even cementation frequently modify it 3 accommodation is not an independent factor with respect to sediment input type efficiency and area of the carbonate factory depend on sea level changes and sea floor morphology the base level for sediment to accumulate accommodation depends on the type and locus of sediment being produced the upper miocene carbonate platforms of the balearic islands illustrate how changes in intrabasinal environmental conditions nutrients and or temperature produce changes in stratal patterns and facies architecture if they affect the biological system during early tortonian carbonate production occurred both in the shallow euphotic zone foramol and in the deeper oligophotic zone rhodalgal originating a distally steepened ramp during late tortonian and early messinian carbonate production mainly occurred in the euphotic zone where framework producing biota coral reefs formed a rimmed platform although deposited under similar conditions of high frequency sea level fluctuations these two types of platforms exhibit different internal facies architecture and distribution of heterogeneities because of differences in base level in carbonates base level for sediment accumulation depends on the type and amount of sediment being produced on the production loci and on the processes controlling sediment dispersal base level for the loose foramol rhodalgal sediment associations of the ramp was controlled by wave and storm base and the associated currents whereas base level for the framework dominated reef complex was sea level furthermore the increase on effective accommodation space to allow the reef rimmed shelf to prograde onto the distally steepened ramp both platforms being depositional sequences resulted from an ecological change rather than significant relative sea level change namely by the shift from grain to framework producing biota the euphotic framework producing biota was able to fill the accommodation space existing between wave and storm base level and sea level that was not previously filled by the loose bioclasts

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

fluctuations in epeiric sea carbonate production during silurian positive carbon isotope excursions a review of proposed paleoceanographic models positive excursions in the carbon isotopic ratio of marine carbonates 13ccarb are commonly attributed to an increase in the burial ratio of organic versus carbonate carbon in the global oceans regardless of whether this increased deposition of organic carbon was oceanographically or biologically induced the fact that high carbon isotope values are most often attributed to the sequestration and burial of organic carbon remains the notion that high 13ccarb values should be the result of organic rich deposition in epeiric sea settings is not surprising considering that the overwhelming majority of organic carbon burial in the modern oceans occurs in continental shelf and margin settings what is surprising is that major positive carbon isotope excursions during the silurian are recorded in clean carbonate successions with little to no appreciable black shale deposition in epeiric seas in fact silurian 13ccarb excursions occurred during intervals of prolific reef development and an overall expansion of carbonate platform environments globally this discrepancy has sparked considerable debate among silurian carbon isotope specialists but has offered a valuable opportunity to re examine the intricate connections among nutrients primary productivity carbonate sedimentology and the global carbon cycle in the lower paleozoic here we consider several sedimentological and geochemical features of one of these silurian positive carbon isotope 13ccarb excursions and discuss the broader implications of current silurian 13ccarb models to the interpretation of lower paleozoic carbonate sequences

plate tectonics and basin subsidence history tectonic setting exerts fi rst order control on basin formation as refl ected in basin subsidence history while our approach ignores the effects of fl exural loading and eustatic sea level change consistency of backstripped subsidence histories i e with local loading effects of sediment removed suggests consistent tectonic driving mechanisms in each tectonic setting with the possible exception of forearc basins based on published subsidence curves and open fi le stratigraphic data we show the subsidence characteristics of passive margins strike slip basins intracontinental basins foreland basins and forearc basins passive margin subsidence is characterized by two stages rapid initial synrift subsidence and slow post rift thermal subsidence with increasing subsidence rates toward the adjacent ocean basin subsidence of intracontinental basins is similar in magnitude to that seen in passive margin settings but the former is generally slower longer lived and lacks initial subsidence long lived subsidence for many intracontinental basins is consistent with cooling following thermal perturbation of thick lithosphere found beneath old parts of continents basins associated with strike slip faults are usually short lived with very rapid subsidence changes in local stress regimes as strike slip faults evolve and migrate over time coupled with three dimensional heat loss in these small basins likely explain this subsidence pattern foreland basin subsidence rates refl ect the fl exural response to episodic thrust loading resultant subsidence curves are punctuated by convex up accelerating segments forearc basins have the least consistent subsidence patterns subsidence histories of these basins are complex and may refl ect multiple driving mechanisms of subsidence in forearc settings second order deviations in subsidence suggest reactivation or superimposed tectonic events in many basin settings the effects of eustatic sea level change may also explain some deviations in curves for many of these settings subsidence histories are suffi ciently distinctive to be used to help determine tectonic setting of ancient basin deposits

genesis of unusual lithologies associated with the late middle devonian taghanic biocrisis in the type taghanic succession of new york state and pennsylvania abstract the middle devonian late middle givetian tully formation in new york state is the type regional expression of the global taghanic biocrisis it is marked by anomalous development of massive to rhythmically bedded micritic limestone deposits within a vastly thicker acadian foreland basin clastic succession lower medial tully carbonates record the incursion of tropical old world realm owr taxa tully fauna and the outage of the long standing higher diversity cooler water endemic eastern americas realm ear biota hamilton fauna succeeding tully strata record a return of the hamilton fauna followed by its demise due both to replacement by the lower diversity cosmopolitan genesee fauna and by the overspread of widespread anoxic bottom conditions coupled with the onset of drastically increased sediment input following tully group deposition massive micritic limestones yielding modest diversity tully fauna assemblages are particularly characteristic of the lower medial tully succession on the western new york tully platform these are coeval with nearly barren ribbon limestone and siltstone deposits in the adjacent new berlin east central new york and central pennsylvania basins these depocenters trapped terrigenous sediment and helped to create sediment starved conditions on the platform anomalous tully carbonate deposition is believed to be coincident with strong super estuarine water mass stratification in offshore tully shelf and basin settings where a warmer denser more saline water mass flowed northward shoreward across the study area beneath a counter flow of oxygenated river influenced surface water dysoxic conditions would have developed below the pycnocline favoring the tully fauna incursion precipitation of carbonate mud and possibly promoting the formation of ooidal chamosite at least five thin 1 30 cm thick mappable beds of black ooidal chamosite are observed in taghanic shelf margin slope and basin deposits these beds are typically intensely bioturbated variably rich in associated siderite contain corroded low diversity fossil assemblages and are regionally associated with condensed lag deposits above unconformities work by others suggests that chamosite formation occurs under minimally reducing post oxic interstitial conditions which are followed in turn by more strongly reducing conditions which allow for variable siderite and pyrite formation terrestrial pedogenic alteration of silicates by evolving land plant communities under warm humid conditions led to an increased supply of kaolinite as well as iron oxides and hydroxides that served as precursors to chamosite formation in the new berlin basin the transgressive top hamilton base taghanic succession is marked by a succession of diastems associated with basin deepening and upward increasing chamosite occurrence in dysoxic facies occurrence of ooidal chamosite in upper medial tully platform deposits smyrna bed may reflect water mass stratification and extreme sediment starvation at the shelf margin eastward spectral transformation of sparsely fossiliferous smyrna ooidal chamosite in the western new berlin basin into richly fossiliferous non chamositic equivalent neritic deposits east of that basin suggests that the counter flow of oxygen and nutrient rich lower salinity water had blocked the denser restricted water layer from advancing over the eastern tully clastic shelf closer to shore

on the interpretation of shallow shelf carbonate facies and habitats how much does water depth matter abstract many stratigraphic studies of ancient shallow water carbonate platforms focus interpretation on the primacy of changes in accommodation inferred by assuming a direct and deterministic link between depositional facies and water depth the purpose of this study is to test this assumption explicitly and quantitatively by exploring relations between substrate type classified on the basis of both habitats and facies and the water depth at which they occur on a modern well studied shallow rimmed shelf margin gis analysis of digital benthic habitat and bathymetry maps of the shallow 8 m south florida shelf illustrate that most substrate types occur across a range of water depths similarly at greater water depths habitats and facies are more constrained more dominance of one class more deterministic with generally decreasing dominance more diversity at shallower water depths at a scale of shelf to basin transects facies and habitats clearly are related to water depth yet on this narrower 10 km shallow shelf margin at the scale of this study water depth and habitats and facies are not uniquely related or linked this general lack of correspondence between bottom type and water depth may be a manifestation of landscape disequilibrium a state in which habitats and facies do not fully reflect ambient environmental conditions perhaps recording the influence of rapid change in sea level alternatively it may reflect the impact of variables other than water depth although more general consequences of these results for other depositional settings remains to be evaluated they do emphasize the fact that variables other than bathymetry may significantly influence the ecological and sedimentologic attributes of depositional surfaces they do allow for the quantification of some of the potential uncertainties inherent in the interpretation of analogous ancient platforms and can serve to focus future observations on the causes and consequences of vertical and lateral heterogeneity in ancient stratigraphic sequences

discontinuities in carbonate successions identification interpretation and classification of some italian examples abstract the growing use of unconformities as bounding surfaces for new types of stratigraphic units seems not to be matched by a corresponding effort on process oriented researches on unconformities themselves this paper aims at giving a contribution to classification and understanding of discontinuities in carbonate successions from the outcrop perspective based on some italian examples a number of integrated criteria geometry sedimentology diagenesis biostratigraphy is proposed to recognise stratigraphic breaks old terms are discussed and sometimes redefined while some new terms are introduced the term discontinuity surface ds is proposed as a general one to indicate any stratigraphic interface where an interruption of sedimentation can be proved a ds can be characterized as a firm ground or a rock ground depending on its coherence at the moment of the renewal of sedimentation polygenic and simple omission surfaces are separated within firm grounds if a recognizable gap is either present or not a third kind of firm ground revealed only by biostratigraphy has been called hidden discontinuity surface two categories of rock grounds are also distinguished hard grounds and inherited rock grounds if respectively generation of the ds and or deposition of the overlying sediments took place in the same environment of the underlying sediments or not a genetic interpretation for each type of discontinuity is proposed the largest variety of ds s occurs in pelagic sediments some discontinuities hard grounds and simple omission surfaces are attributed to increased bottom current activity during sea level falls others polygenic omission surfaces and hidden ds s are interpreted as submarine slide scars either with or without the overprint due to exposure on the seafloor the ds s separating different facies e g platform and pelagic ones are interpreted to be due to tectonics the relevance of the recognized ds s to sequence stratigraphy is briefly discussed

the expected duration of upward shallowing peritidal carbonate cycles and their terminal hiatuses meter scale accommodation cycles which dominate the stratigraphic record of peritidal carbonate accumulation might provide a time scale of unusually high resolution but the duration of the hiatuses that cap the resulting cyclothems is difficult to determine thousands of rates of peritidal accumulation from many different carbonate sections have been combined according to the length of the time span of measurement to describe a hypothetical average section because all sections are interrupted by hiatuses the average accumulation rate falls progressively with increasing time span and most steeply at the time spans that capture the highest proportion of hiatuses the process of combining rates from many sections cancels local differences in the distribution of hiatuses only hiatuses that have similar spacing and duration in a majority of sections will stand out after compilation the size and position of a pronounced inflection in the combined plot of accumulation rates against time span identifies a dominant cycle period of 100 000 yr of which the terminal hiatus accounts for 80 90 the expected cyclothem is 10 m thick because peritidal accommodation cycles begin and end with the sediment surface at sea level the expected cycle period can be estimated by finding the time span at which accommodation and accumulation rates balance the maximum duration of the hiatus is the time span at which rates of subsidence and sea level fall balance compilations of many empirical measurements were again employed to determine the relationship between time span and the rates of subsidence sea level change and net accommodation this second method confirms the results of the first and can be modified to predict the expected cyclothem in different climatic tectonic and depositional settings because quaternary data dominate short term rates the hypothetical average section best describes a passive margin in an icehouse climate with strong glacio eustatic fluctuations in sea level after modification for an extreme greenhouse climate devoid of ice caps the second method predicts that 20 000 yr accommodation cycles will be preferentially recorded the expected cyclothem is 2 m thick and accounts for about 50 of the cycle period increased subsidence rates whether on active margins in the initial phase of passive margin formation or at the seaward edge of a platform tend to extend the limit of cycle duration increase cyclothem thickness and partition less time to the bounding hiatus increased subsidence however raises the risk that the sediment surface will drown

depositional bias and environmental change important factors in sequence stratigraphy abstract differences among depositional systems here called depositional bias strongly influence sequence patterns siliciclastics and shallow water carbonates for instance shed most of their sediment during opposite phases of a sea level cycle lowstand shedding and highstand shedding respectively furthermore the two systems generate their own system specific relief on the sea floor disperse their sediment load along different avenues and differ in the way they are deactivated reefs and carbonate platforms can be drowned whereas siliciclastic deposition can be shut off and renewed at any depth as a consequence of these differences pronounced unconformities drowning unconformities develop where carbonate platforms are terminated and buried by siliciclastics the siliciclastic to carbonate transition tends to be more gradual drowned platforms and drowning unconformities appeared world wide in great abundance in the miocene cretaceous valanginian turonian jurassic toarcian and devonian frasnian famennian examples of drowning unconformities interpreted as sequence boundaries include those of the early cretaceous platforms off new jersey and off morocco the mid cretaceous unconformity in the gulf of mexico and miocene unconformities on top of reefs in the far east the eustatic cycles postulated from sequence stratigraphy are a very unlikely cause for the mass drownings of reefs and platforms either the rates of rise are an order of magnitude lower than the growth potential of platforms or cycle amplitudes are too small or the cycles are too short and subsidence too slow to remove platforms permanently from the photic zone the critical element in the mass drowning seems to be environmental stress that reduces the growth potential of carbonate systems thus drowning unconformities demonstrate the importance of environmental change as a control on sequence development other examples of dominantly environment controlled sequences include slope deposits shaped by shifting currents e g florida and blake plateau and basin fills that were controlled by changes in sediment input related to tectonic alteration of the drainage in the hinterland e g gulf of mexico environmental change must be considered as a third independent factor that competes with eustatic and tectonically driven regional changes of sea level for control of sequences the definition of sequences and sequence boundaries should be broad enough to include the possibility of non sea level controls

sequence stratigraphy and a revised sea level curve for the middle devonian of eastern north america abstract the well exposed middle devonian rocks of the appalachian foreland basin onondaga formation hamilton group tully formation and the genesee group of new york state preserve one of the most detailed records of high order sea level oscillation cycles for this time period in the world detailed examination of coeval units in distal areas of the appalachian basin as well as portions of the michigan and illinois basins has revealed that the pattern of high order sea level oscillations documented in the new york pennsylvania section can be positively identified in all areas of eastern north america where coeval units are preserved the persistence of the pattern of high order sea level cycles across such a wide geographic area suggests that these cycles are allocyclic in nature with primary control on deposition being eustatic sea level oscillation as opposed to autocylic controls such as sediment supply which would be more local in their manifestation there is strong evidence from studies of cyclicity and spectral analysis that these cycles are also related to milankovitch orbital variations with the short and long term eccentricity cycles 100 kyr and 405 kyr being the dominant oscillations in many settings relative sea level oscillations of tens of meters are likely and raise considerable issues about the driving mechanism given that the middle devonian appears to record a greenhouse phase of phanerozoic history these new correlations lend strong support to a revised high resolution sea level oscillation curve for the middle devonian for the eastern portion of north america recognized third order sequences are eif 1 lower onondaga formation eif 2 upper onondaga and union springs formations eif giv oatka creek formation giv 1 skaneateles giv 2 ludlowville giv 3 lower moscow giv 4 upper moscow lower tully and giv 5 middle tully geneseo formations thus in contrast with the widely cited eustatic curve of johnson et al 1985 which recognizes just one major transgressive regressive t r cycle in the early mid givetian if prior to the major late givetian taghanic unconformity iia upper tully geneseo shale we recognize four t r cycles if restricted ig ih and ii we surmise that third order sequences record eustatic sea level fluctuations of tens of meters with periodicities of 0 8 2 myr while their medial scale fourth order subdivisions record lesser variations primarily of 405 kyr duration long term eccentricity this high resolution record of sea level change provides strong evidence for high order eustatic cycles with probable milankovitch periodicities despite the fact that no direct evidence for middle devonian glacial sediments has been found to date

carbonates and relative changes in sea level abstract in the geologic record some of the most accurate gauges of changes in sea level are the sediment type geometry and diagenesis of carbonate shelves and platforms this is because carbonates frequently occur at or very near sea level and are usually less compacted than siliciclastics world wide changes in relative sea level the sum of eustatic sea level changes sedimentation and crustal movements have occurred repeatedly and cyclicly through geologic time producing characteristic responses in carbonates 1 1 relative rises in sea level usually caused by the cumulative effect of tectonic subsidence and eustatic rise may result in the following 1 1 a drowned carbonate reefs or platforms here carbonate growth potential is exceeded by relative sea level rise and is characterized by shallow water sediments overlain by hardgrounds and or deep water sediments some of which may be condensed sequences 1 2 b platforms where only the fast growing rim and patches of the interior are able to match sea level rise while the remainder of the platform is drowned temporarily 1 3 c platforms which keep up and maintain a flat top at sea level and contain shallow water sediments whose thickness at the least matches the height of the sea level rise if terrigenous supply is limited prograding sheets of shelf carbonate occur frequently capped by supratidal evaporites with prograding shelf margin carbonate clinoforms and turbidites if terrigenous supply is high the shelf carbonates encroach on deltaics 2 2 relative drops in sea level caused by crustal uplift or by subsidence being outpaced by a eustatic drop in sea level cause karst and soil development over shelves and platforms deposition of deep water evaporites in adjacent semi enclosed basins and in open marine basins the deposition of deltaic and aeolian clastics that bypassed the shelf falls are accompanied by platform wide fresh water diagenesis during relative sea level rises marine diagenesis is common in the subtidal portions of the shoaling upward carbonates and fresh water diagenesis and dolomitization and sulphate deposition is common in their intertidal and supratidal portions the stratigraphic significance of these reponses to relative sea level change is that many are tied to eustatic events and so are predictable within a basin of deposition

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

investigating carbonate platform types multiple controls and a continuum of geometries abstract current classifications of carbonate platforms use depositional gradient as the main criterion for separating systems into two end member types ramps and flat topped platforms ftps however many examples do not conform to this simple classification to investigate why this is and to better understand probable controls on platform development we have used a series of 2d numerical forward model runs to investigate how sediment production diffusional sediment transport and other controls such as tectonic subsidence antecedent topography and relative sea level oscillation interact to determine platform geometry modeling results reaffirm that rates of down dip sediment transport relative to rates of autochthonous production are a critical factor in maintaining a ramp profile in stable cratonic settings under a constant rate of relative sea level rise type of carbonate production versus water depth curve for example euphotic versus oligophotic is not a significant control in our model cases both euphotic and oligophotic production profiles produce ftps when diffusion coefficients are low relative to production rates and ramps when diffusion coefficients are relatively high these results suggest a continuum of platform types ranging from transport dominated low gradient systems at one end of the spectrum to in situ accumulation dominated systems at the other a system may be transport dominated because high energy processes are able to break down and transport even bound sediment or because carbonate factories produce only sediment that is easily transportable under even low energy conditions time evolution is also probably important initially low gradient systems will in the absence of sufficiently high sediment transport rates tend to evolve towards high gradient flat topped steep margined platforms many observed or inferred platform geometries are therefore likely to be transient forms and this could complicate interpretation investigating how basin bathymetry and style of subsidence control platform geometry suggests that in transport dominated systems strata simply drape the underlying topography and that pre existing breaks of slope and differential fault subsidence are a stronger control on platform geometry in in situ accumulation dominated systems rotational subsidence tends to create transport dominated systems during rotation as the topographic gradient increases and transport rate increases and outpaces in situ production rate relative sea level oscillations tend to move the locus of sediment production laterally along any slope present on the platform distributing the sediment accumulation across the whole width of the platform suppressing progradation and steepening and so favoring development of low gradient systems based on all these results we suggest that a simple cutoff classification into ramp and flat topped platform types can still be useful in some circumstances but a more meaningful approach may be to describe and predict platform strata in terms of a multiple dimension platform parameter space containing a continuum of geometries controlled by sediment production sediment diffusion coefficient antecedent topography differential subsidence effects relative sea level oscillations and perhaps other as yet unappreciated controls

characterization lateral variability and lateral extent of discontinuity surfaces on a carbonate platform barremian to lower aptian oman hiati of various duration in carbonates are commonly expressed as discontinuity surfaces the understanding of processes that form and affect these surfaces leads to an improved sequence stratigraphic interpretation a reliable outcrop correlation and better models for reservoir compartmentalization various intraformational discontinuities were analysed and interpreted in a well exposed study window 2 5 km in lateral length and 60 m in height comprising the barremian aptian qishn formation haushi huqf area central oman this study focuses on the lateral extent and morphology of the surfaces the petrography of the underlying rocks and the facies changes and geochemical trends across these discontinuities furthermore the lateral variability of discontinuity surfaces was documented three genetic types of discontinuities are differentiated i erosion surfaces ii omission surfaces hard and firmgrounds and iii composite surfaces with evidence for both subaerial exposure and submarine boring field observations combined with petrographic and geochemical data suggest that 17 surfaces are laterally extensive for at least 20 km and record relative sea level fluctuations of regional scale in contrast a large number of laterally limited surfaces 1 km are related to locally active processes such as waves and current erosion the lateral variability along extensive surfaces is the result of the depositional environment below the discontinuity the sea floor topography waves and currents and differential erosion the most pronounced lateral variability is present along six laterally extensive composite surfaces that record terrestrial exposure and subsequent flooding of a tidal flat environment this variability is caused by spatial variability in the tidal flat environment meteoric alteration and differential erosion this study emphasizes the spatial and temporal complexity of processes that form and modify discontinuity surfaces this variability must be kept in mind when interpretations and correlations are based on one dimensional sections or cores 2005 international association of sedimentologists

sequence stratigraphic hierarchy of the upper devonian foreknobs formation central appalachian basin usa evidence for transitional greenhouse to icehouse conditions abstract the foreknobs formation upper devonian upper frasnian to basal famennian comprises the uppermost marine strata of the progradational catskill clastic wedge of the south central appalachian mountains virginia west virginia usa the foreknobs formation consists of 14 lithofacies arranged in four facies associations which record the following depositional settings 1 storm dominated distal to proximal offshore to shoreface facies association a 2 sharp based conglomeratic shoreface facies association b 3 fluvial redbed facies association c and 4 incised valley fill ivf facies association d vertical juxtaposition and stacking patterns of lithofacies and facies associations permit recognition of a hierarchy of three scales of cyclicity up to 70 short term 5th order cycles each averaging 65 kyr consist of coarsening upward parasequences of storm dominated offshore marine facies in the distal setting which correspond to high frequency unconformity bound sequences hfs of fluvial redbed strata overlain by offshore marine strata in the proximal setting these facies relationships are a consequence of 10 15 m of sea level fluctuations up to 12 intermediate term 4th order cycles each averaging 375 kyr consist of stacked 5th order cycles the 4th order cycles are bounded by regressive surfaces of marine erosion rsme at the base of sharp based conglomeratic shoreface sandstones in the distal setting that correspond with paleosols in the proximal setting in some cases the 5th order cycles within each 4th order cycle exhibit stacking patterns indicative of increasing or decreasing accommodation space these facies relationships are a consequence of 25 35 m of sea level fluctuations three complete and portions of two additional 3rd order cycles each averaging 1 12 myr consist of stacked 4th order cycles the 3rd order sea level trends reflected in the foreknobs formation are nearly identical to published eustatic sea level curves incised valley fills are present at one of the 3rd order cycle boundaries and are a consequence of a 35 45 m sea level fluctuation the amplitudes of the inferred sea level fluctuations are comparable to the expansion and contraction of ice volumes within the current greenland and antarctic ice sheets which suggests glacioeustasy was the primary control on sea level fluctuations and cyclicity within the foreknobs formation such an interpretation is consistent with knowledge of devonian climate transitioning from middle devonian greenhouse to late devonian icehouse as indicated by evidence of glaciation during parts of the late devonian in south america and the appalachians

generic types of stratigraphic cycles controlled by eustasy thought experiments imply that stratigraphic cycles controlled directly by eustasy include keep up catch up catch down foreshortened or truncated and give up variants different patterns of thick ness and facies being governed by the interplay of sedimentation rate and accommodation space most examples of these types are in addition base cutout cycles wherever lowstands of sea level dropped below the top of the underlying cycle overall thicknesses of multiple cycles at any locale are controlled ultimately by net subsidence rate accordingly even keep up and catch up cycles can faithfully record full accommodation only where tectonic subsidence during cycle formation paced eustatic fluctuation paradoxically however only condensed cycles that fortuitously compensate for syncycle tectonic subsidence can accurately record the eustatic amplitude as adjusted for water loading