comparative stratigraphy and subsidence history of mesozoic rift basins of north atlantic mesozoic rift basins around the north atlantic all possess many of the following upper jurassic to lower cretaceous oxfordian to albian stratigraphic elements 1 an early oxfordian hiatus 2 backfill deposits in upper jurassic paleovalleys 3 multiple tithonian transgressive regressive sequences 4 early berriasian regressive sequences 5 a sub valanginian unconformity overlain by coarse siliciclastic sandstones and conglomerates 6 valanginian to hauterivian fining upward sequences 7 condensed barremian sequences and 8 prominent aptian unconformities more local features include abrupt kimmeridgian deepening lusitanian basin portugal albian deepening cantabrian and aquitaine basins northern spain and southern france and late albian early cenom nian source rejuvenation cantabrian basin northern iberia decompaction and backstripping of sediments from well and outcrop sections in six basins also reveal broad similarities in trends of rates of apparent basement subsidence relatively high rates 50 100 m m y characterize onset of rift phases in the triassic and the kimmeridgian locally in the lusitanian basin of portugal kimmeridgian rates reach about 250 m m y in the cantabrian and aquitaine basins a third phase of rapid subsidence characterizes the aptian albian interval after the main phase of continental breakup around iberia this phase may be due to transtensional stresses as iberia continued to rotate relative to europe tensional intraplate stresses or gravity driven partial collapse of the new continental marg n the north atlantic mesozoic basins share many features because they had a common origin controlled by intracontinental rifting and subsequent separation of europe and north america pulses of extension generally are reflected in the stratigraphy of all of the basins superimposed on this record are the effects of eustatic sea level variations the main difference between the canadian jeanne d arc basin and iberian basins is the significantly greater early and middle jurassic basement subsidence rate in the former about 40 m m y vs 0 10 m m y this difference may result from prolonged extension on the canadian side perhaps due to northward transfer of shear stress from left lateral transform motion between the grand banks and northwestern africa

the apparent paradox of abundant foramol facies in low latitudes their environmental significance and effect on platform development recent studies of low latitude carbonates from se asia and australia have revealed deposits and platform types that do not fit easily into the perceived view of warm water tropical carbonates the sediments are classified as a foramol or foralgal facies and are dominated by non framework building light dependent biota such as perforate larger benthic foraminifera coralline algae and sometimes halimeda although ancient foramol deposits are often interpreted as an indication of non tropical conditions foramol facies have long been known from the tropics yet the environmental conditions in which they form are poorly known the aims of this paper are to evaluate how these deposits are best classified and more importantly whether there are any overriding controls that influence their common development in low latitude areas and if resultant platform development is affected the deposits are all best grouped within the photozoan association james n p 1997 the cool water depositional realm in james n p clarke j a d eds cool water carbonates sepm special publication 56 1 20 an assignment synonymous with warm water conditions the facies were also found to develop in conditions of limited light or oligophoty all the platforms described are characterised by having extensive areas of oligophotic facies generally in water depths extending down from 20 m but sometimes in shallower waters platforms types vary from land attached rimmed shelves homoclinal and distally steepened ramps to isolated banks and platforms but all have extensive moderate to deep photic zone development of oligophotic facies some workers might assign these platforms to the incipiently drowned platform type read j f 1985 carbonate platform facies models american association of petroleum geologists bulletin 69 1 21 however a morphological assignment is preferred here to signify that many of the deposits did not or may not form through drowning limited light in moderate to deeper depths of the photic zone often in regions with a reduced depth euphotic high light zone is seen as key to the extensive development of these deposits and the resultant platforms these conditions are often developed in humid low latitude areas of high terrestrial runoff and therefore regions of reduced water salinity or in areas of nutrient upwelling reduced water clarity due to nutrients plankton blooms suspended particulate matter upwelling and strong currents all promote the development of oligophotic conditions and facies on a regional scale time periods of relative rises in sealevel can also promote oligophotic facies development the findings of this study have broader implications for the development of low latitude platforms beyond australasia and during time periods when non framework building oligophotic biota are dominant sediment contributors the reconstruction of past climatic conditions based on study of foramol grain assemblages requires careful study to distinguish warm water deposits from those formed in cool waters

oolitic sandbody depositional models and geometries mississippian of southwest britain implications for petroleum exploration in carbonate ramp settings abstract a 1000 m thick early mississippian carbonate supersequence the carboniferous limestone of southwest britain consists of three third order depositional sequences these comprise parasequences in various configurations and the whole forms a carbonate ramp stack within this framework five major oolitic carbonate sandbodies developed a castell coch limestone b stowe oolite c brofiscin oolite d gully oolite and e high tor limestone the depositional regime was storm and wave dominated throughout and the major sandbodies represent a range of progradational carbonate beaches barriers and detached subtidal shoals analysis of the three dimensional shapes and distribution of these five examples shows that they evolved to produce three major carbonate sandbody geometries a strings b sheets and c wedges these geometries are characterised using the five field examples and offered as a template which may assist in the exploration and reservoir modelling of petroleum rich high energy ramp systems progradation for up to 40 km of barrier islands stowe oolite and beach ridge plains gully oolite formation generated strings and thick sheets individually up to 10 20 m thick thin shoreface retreat carbonate packstone grainstone sheets up to 5 m thick high tor limestone developed during transgressions as veneers across flooding surfaces these are comparable with sheet sands developed in siliciclastic shelf depositional systems progradation for up to 30 km and vertical aggradation of shoreline detached oolite shoals castell coch limestone brofiscin oolite generated basinwards expanding or thinning wedges up to 30 m thick tectonically controlled stacking of strandplain sheets produced a composite carbonate sandbody up to 80 m thick gully oolite the intrinsic sedimentary and extrinsic eustacy tectonism climate factors which controlled these sandbody geometries are addressed establishing the positions of the sandbodies accurately within depositional sequences allows them to be located within inferred seismic sequence geometries and provides one possible solution to the difficult problem of predicting carbonate facies distribution in subtle stratigraphic plays in this ramp system the most homogeneous sandbodies up to 30 m grainstones with greatest reservoir facies potential are represented by shoal belt wedges potential grainstone reservoir facies in the prograding shorelines are limited to the upper parts of individual shoreface sequences max 10 m grainstones for shoreline carbonate sandbodies the greatest reservoir and stratigraphic trapping potential exists in the earliest ramp parasequences where enveloping offshore sediments are siliciclastic mudstones in later stages potential seals are likely to be less reliable low porosity outer ramp carbonates

oceanographic and eustatic control of carbonate platform evolution and sequence stratigraphy on the cretaceous valanginian campanian passive margin northern gulf of mexico an integrated sequence stratigraphic study based on outcrop core and wireline log data documents the combined impact of cretaceous eustacy and oceanic anoxic events on carbonate shelf morphology and facies distributions in the northern gulf of mexico the diverse facies and abundant data of the comanche platform serve as a nearly complete global reference section and provide a sensitive record of external processes affecting cretaceous platform development regional cross sections across the shoreline to shelf margin profile provide a detailed record of mixed carbonate siliciclastic strata for the hauterivian to lower campanian stages ca 136 to 80 ma the study window on the slowly subsiding passive margin allows the stratigraphic response to external forcing mechanisms to be isolated from regional structural processes three second order supersequences comprised of eight composite sequences are recognized in the valanginian barremian the aptian albian and the cenomanian campanian the valanginian barremian supersequence transitioned from a siliciclastic ramp to carbonate rimmed shelf and is a product of glacial ice accumulation and melting as well as variable rates of mid ocean ridge volcanism the aptian albian supersequence chronicles the drowning and recovery of the platform surrounding oceanic anoxic events 1a and 1b the cenomanian campanian supersequence similarly documents shelf drowning following oceanic anoxic event 1d after which the platform evolved to a deep subtidal system consisting of anoxic dysoxic shale and chalk in the time surrounding oceanic anoxic event 2 each period of oceanic anoxia is associated with composite sequence maximum flooding termination of carbonate shelf sedimentation and deposition of condensed shale units in distally steepened ramp profiles composite sequences unaffected by oceanic anoxic events consist of aggradational to progradational shelves with an abundance of grain dominated facies and shallow subtidal to intertidal environments because they are products of eustacy and global oceanographic processes the three supersequences and most composite sequences defined in the south texas passive margin are recognizable in other carbonate platforms and published eustatic sea level curves

cenomanian turonian facies succession in the guerrero morelos basin southern mexico abstract the cenomanian turonian succession of southern mexico is characterized by an abrupt change from shallow marine to pelagic facies the drowning of the platform coincides with the widely documented cenomanian turonian oceanic anoxic event ctoae a proper understanding of the drowning event and the effects of the oae requires as an essential first step the construction of a detailed stratigraphic framework this has been achieved and utilizes sedimentological data as well as a combination of benthic and planktonic biostratigraphic schemes deposition of the cenomanian turonian sedimentary rocks of the guerrero morelos basin was controlled by tectonic and oceanographic factors resulting in depositional environments ranging from a semi restricted shelf ramp pelagic and prodelta deposits facies analysis indicates that shallow marine limestones of the morelos formation lower upper cenomanian were deposited in intertidal shallow supratidal and subtidal environments in a semi restricted shelf peloidal bioclastic packstone wackestones with minor grainstones are the predominant texture of these rocks abundant large benthic foraminifers calcareous algae dasycladacean and mollusks gastropods and rudists characterize the fossil assemblage the cuautla formation uppermost cenomanian turonian represents sedimentation on a low energy wave dominated carbonate ramp the inner ramp accumulated bioclastic banks and shoals composed of peloidal benthic foraminifer grainstone calcareous red and green algae rudists and minor solitary corals the middle ramp is represented by nodular packstones with a diverse assemblage of echinoderms green and red algae bryozoan rudists solitary corals roveacrinids calcisphaerulids and non keeled planktonic foraminifers the outer ramp is dominated by argillaceous wackestone packstone characterized by calcisphaerulids roveacrinids and non keeled planktonic foraminifers an increase in terrigenous clastic material towards the eastern part of the area indicates progradation of a deltaic system while the mexcala formation uppermost cenomanian turonian was deposited in a pelagic setting the drowning of the platform is at the contact between the morelos and cuautla or mexcala formations and is dated as latest cenomanian the drowning is a hiatus in most sections and it began before the end of the cenomanian by a minimum of 150 ky if the top of the morelos is not eroded

stratigraphic architecture palaeogeography and sea level changes of a third order depositional sequence the late turonian early coniacian in the northern iberian ranges and central system spain abstract this paper reports a high resolution stratal palaeogeographical and quantitative analysis of a late turonian early coniacian carbonate ramp the northern iberian ranges and its siliciclastic coastal margin the central system the analyzed succession comprises a complete 3rd order depositional sequence with a shelf margin wedge a transgressive systems tract and a highstand systems tract based on the existence of a subaerial exposure evidences and early diagenetic overprints b stratal relationships onlap offlap toplap regarding underlying and overlying sequences and c changes in the vertical facies evolution the depositional sequence was bounded by two major sequence boundaries these indicate that a major fall in relative sea level occurred in these boundaries the comparative study of the internal stratal surfaces and the vertical facies succession allowed the identification of superimposed higher order depositional parasequences sets and parasequences 4th to 5th order which record short term changes in the relative sea level thus when vertical facies trends in the parasequences are arranged in the framework of a parasequence set a clearer palaeogeographic picture is obtained and palaeogeographic maps can more clearly show the evolutionary trend of the basin each parasequence set was composed of a basal lowstand transgressive systems tract in turn composed of fringing siliciclastic shoreface deposits and offshore muds older sequences were partially exposed further landwards the sedimentation of these sands resulted in the progradation of the coastal systems during times of low relative sea level during which the basal parasequence set boundary was also generated subsequent transgression remobilised underlying lowstand sands the early highstand was composed of carbonate sediments in platform areas and mixed siliciclastic carbonate sediments landwards separated by a narrow fringe of muddy marl offshore sediments the late highstand showed a progressive shallowing trend with carbonate littoral and tidal sediments covering broad areas of the basin and lagoon facies were restricted to the northern outcrops during late highstand underlying transgressive systems tract and older highstand deposits were exposed landwards sea level and accommodation curves have been obtained from paleogeographical sedimentological and sequence stratigraphical data the mean sea level curve for the entire 3rd order sequence shows a rise of the sea level and then an overall stillstand but accommodation curve shows a positive trend along the sequence the 3rd order sea level cycle has a mean amplitude of 52 m and high frequency cycles have amplitudes of 20 40 m 4th order and about 1 5 4 m 5th order the mean final rise in the sea level 46 6 m is quite similar to the total accommodation deduced from fischer plot 45 75 m the sea level cycles are considered to be eustatic in origin and driven by orbital forcing in the milankovitch band based on the estimated 4th order 400 kyr and 5th order cycle lengths 80 kyr

temporal and spatial correlations between changes in plate motions and the evolution of rifted basins in africa we present the results of a backstripping study incorporating over 200 wells in 14 different basins or groups of basins located on the african interior or continental margins these results presented as mean tectonic subsidence rates averaged over appropriate periods are compared with the opening histories and changes in plate motions of the atlantic and indian oceans and the tethys mediterranean area for seven time steps from the late jurassic until present the results indicate a temporal and spatial correlation between phases of rapid subsidence in african basins and changes in plate motions and therefore are promising in terms of applicability of large scale plate motions in the studies of paleo stresses in sedimentary basins especially at times of initial rifting and formation of subduction zones reactivation of the basins appears to be primarily controlled by the orientation of the basin and underlying basement structures with respect to the stress direction the basins are preferably formed within weaker zones mostly pan african shear zones and the distance from the active plate boundary to the weak zone plays a minor role in whether or not it will be reactivated the presence of three important hot spots which were active during the early stages of break up of gondwana may have been important in preweakening the lithosphere at their sites this may have played an additional role in the localization of the basin deformation

pinch out style and position of tidally influenced strata in a regressive transgressive wave dominated deltaic sandbody twentymile sandstone mesaverde group nw colorado the upper cretaceous twentymile sandstone of the mesaverde group in nw colorado usa has been analysed with respect to its pinch out style and the stratigraphic position of tidally influenced facies within the sandstone tongue detailed sedimentological analysis has revealed that the twentymile sandstone as a whole is a deltaic shoreface sandstone tongue up to 50 m thick proximally facies change character vertically from very fine grained storm wave dominated shelf sandstones and mudstones to fine grained wave dominated sandstones and finally to fine to coarse grained tidally dominated sandstones the pinch out style is characterized by a basinward splitting of the massive proximal sandbody into seven coarsening upward fourth order sequences consisting of a lower shaly part and an upper sandy part sandstone tongue these are stacked overall to reflect the regressive to transgressive development of the tongue each of the lower sandstone tongues 1 3 are gradationally based very fine grained and dominated by hummocky cross stratification and were deposited on the lower to upper shoreface sandstone tongues 4 and 5 prograded further basinwards than the underlying tongues are erosively based fine to coarse grained and mainly hummocky herringbone and trough cross stratified especially in tongue 5 tidal indicators such as bipolar foresets and double mud drapes are common these tongues were deposited as upper shoreface and tidal channel sandstones respectively sandstone tongues 6 and 7 retrograded in relation to tongue 5 are very fine to fine grained and hummocky cross stratified these tongues were deposited in lower shoreface to offshore transition environments the two lower fourth order sequences were deposited during normal regressions during slowly rising or stable relative sea level and represent the highstand systems tract the three succeeding fourth order sequences which show succeedingly increasing evidence of tidal influence were deposited during falling and lowstand of relative sea level and represent the falling stage forced regressive and lowstand systems tracts the uppermost two fourth order sequences were deposited during rapidly rising sea level in the transgressive systems tract the maximum tidal influence occurred during lowstand progradation in contrast to most other published examples reporting maximum tidal influence during transgression

the magnitude and cause of short term eustatic cretaceous sea level change a synthesis abstract no consensus currently exists regarding the magnitude of cretaceous short term less than 3 ma in duration eustatic sea level change the lack of a consensus limits the ability to predict sedimentary facies and architecture and to assess the potential drivers of eustasy during a period of earth history considered as significantly warmer than today consequently this review documents weighs synthesises and summarises records of short term relative sea level change and evaluates the observed trends in magnitude within the context of potential climatic drivers and their eustatic expression although cretaceous sea level change is addressed in many publications estimates of absolute values are relatively limited often cover short time intervals and use different methods based upon integrated geological and statistical analyses four broad episodes of magnitude change have been identified three of these episodes reflect trends of increasing magnitudes of sea level change from the berriasian to early hauterivian late hauterivian to aptian and santonian to maastrichtian the fourth episode reflects a decreasing magnitude trend from the albian to coniacian in addition the maximum magnitude of sea level change at an approximate stage level has been identified and categorised as slight less than 10 m modest 10 to 40 m or significant 41 to 65 m significant magnitudes are inferred for the valanginian aptian albian and maastrichtian exclusively slight magnitudes are restricted to the berriasian such an assessment casts doubt on the repeated and stratigraphically widespread episodes of very large magnitudes more than 75 m advocated by some workers and instead defines distinct periods and magnitudes of sea level change that should be globally reflected in sedimentary facies patterns for example intervals of sea level fall of significant magnitude are commonly associated with the increased delivery of sediment into basinal settings including the marked progradation of shallow marine sediments whilst up systems tract there can be enhanced development of karst and erosional features because climatically driven eustasy is the likely cause of short term sea level change an assessment of the characteristic maximum magnitude limits of the principal climatic drivers thermo aquifer and glacio eustasy has been made such a comparison argues for glacio eustasy as the driver of significant short term sea level change in addition climate proxy data demonstrates that the valanginian aptian albian and maastrichtian are intervals of cooling within the cretaceous thereby supporting the link between significant magnitudes and glacio eustasy

provenance signatures recorded in transgressive sandstones of the upper cretaceous iberian seaway abstract maximum mesozoic transgressions flooded many continental areas worldwide forming a wide and shallow seaway on the iberian microplate during the late cretaceous several siliciclastic and mixed siliciclastic carbonate units developed along the iberian massif cratonic area while at the same time epeiric carbonate platforms spanned iberia these siliciclastic deposits unconformably cover the variscan basement as well as the permian and triassic deposits this study focuses on sandstone provenance in central spain in a transgressive relatively quiet tectonic setting with a wide rock variety in the potential source areas results shown in this paper can be applied in analogue systems transgressive sandstones often form important hydrocarbon reservoirs due to their high primary porosity the cretaceous siliciclastic deposits are included in four formations ranging in age from the cenomanian to the early coniacian the deposits were initially of fluvial origin followed by a coastal tidal setting quantitative petrographic analysis of sandstones from these formations reveals compositional variations related to provenance and weathering degree the oldest formation utrillas fm was deposited on a paleorelief surface sandstone composition changes from arkosic sandstones in the depressed area petrofacies p1a to younger quartzarenites when sediments were deposited on top of the paleotopographic high petrofacies p1b quartz grains in both sub petrofacies are angular to subangular and the framework is poorly sorted intense weathering conditions are deduced for petrofacies p1b manifested by grain infiltration clay coatings and the absence of plagioclase grains and alteration features on k feldspars all these observations have been related to wetter conditions during p1b deposition main source areas of the utrillas fm were ordovician metasediments and orthogneisses permian volcanic rocks and triassic buntsandstein facies petrofacies 2 encompasses the three coastal tidal formations constituted mainly by subarkoses generally showing a subangular and poorly sorted framework the deduced source areas are mainly associated with variscan granitoids pre ordovician schists and paragneisses and ordovician metasediments glauconite and carbonate grains support intrabasinal inputs the low degree of sorting of this petrofacies related to a low energy sedimentary environment produced lower values of original porosity compared to transgressive sandstone hydrocarbon reservoirs also intrabasinal inputs promoted carbonate cementation and contribute to almost occlude the porosity

late aptian palaeoclimatic turnovers and volcanism insights from a shallow marine and continental succession of the apennine carbonate platform southern italy abstract this study reports an integrated facies analysis carried out on a new section from the upper aptian of the se matese mts civitella licinio northern campania s italy which includes several decimeter to meter scale lacustrine intervals straddling a meter scale plant rich plattenkalk these intervals are assigned to the late gargasian early clansayesian by their stratigraphic relationship with the upper salpingoporella dinarica acme as well as lithologic and biostratigraphic supra regional key markers found in the apennine carbonate platform apcp including the orbitolina level we infer that the monogeneric parautochthonous plant remains frenelopsis sp were deposited in a supratidal to paralic coastal mudflat close to a restricted shallow marine lagoon at the verge of an arid semiarid climatic phase the plattenkalk was rapidly replaced by persistent lacustrine lithofacies at the onset of a major climatic turnover glacial trigger the overlying shallow marine deposits are capped by a deeply incised palaeokarstic surface and in turn by unconformable middle clansayesian transgressive shallow marine deposits interlayering of reliable lithologic indicators of palaeoclimate and high resolution event stratigraphic hires correlation of the civitella licinio succession with the astrochronologically tuned mt faito reference section of the apcp bring evidence of rapidly fluctuating hydroclimatic conditions wet and arid phases in the short 100 ky and long 400 ky eccentricity time band hires and astrochronological age assignment to crucial key markers and humid arid phases at civitella licinio permit to further refine the detailed stratigraphy of the mt faito reference section and to assign the upper s dinarica acme of the apcp to a numerical age of 118 55 118 50 my sem and eds analyses document common to abundant windblown volcanic particles glass shards and sanidine crystals throughout the frenelopsis rich plattenkalk 118 3 to 118 2 my and the encasing units especially in the overlying brackish lacustrine deposits palaeogeographic and palaeoclimatic reconstructions suggest that the pyroclastic material was probably transported by northeasterly trade winds from orogenic volcanic centers located within the dinaridic carpatho balkan arc trench system and have been supplied to the apcp for a time span of 3 my during the late aptian a preliminary tephrostratigraphic correlation of the upper aptian volcaniclastic levels of the apcp with the bentonite levels of the vocontian basin is proposed

internal anatomy of a mixed siliciclastic carbonate platform the late cenomanian mid turonian at the southern margin of the spanish central system the late cenomanian mid turonian succession in central spain is composed of siliciclastic and carbonate rocks deposited in a variety of coastal and marine shelf environments alluvial plain estuarine lagoon shoreface offshore hemipelagic and carbonate ramp three depositional sequences third order are recognized the atienza patones and el molar sequences the patones sequence contains five fourth order parasequence sets while a single parasequence set is recognized in the atienza and el molar sequences systems tracts can be recognized both in the sequences and parasequence sets the lowstand systems tracts only recognized for atienza and patones sequences are related to erosion and sequence boundary formation transgressive systems tracts are related to marine transgression and shoreface retreat the highstand systems tracts are related to shoreface extension and progradation and to carbonate production and ramp progradation sequences are bounded by erosion or emergence surfaces whose locations are supported by mineralogical analyses and suggest source area reactivation probably due to a fall in relative sea level transgressive surfaces are subordinate erosion and or omission surfaces with a landward facies shift interpreted as parasequence set boundaries the co existence of siliciclastic and carbonate sediments and environments occurred as facies mixing or as distinct facies belts along the basin mixed facies of coastal areas are composed of detrital quartz and clays derived from the hinterland and dolomite probably derived from bioclastic material siliciclastic flux to coastal areas is highly variable the maximum flux postdates relative sea level falls carbonate production in these areas may be constant but the final content is a function of changing inputs in terrigenous sediments and carbonate content diminishes through a dilution effect carbonate ramps were detached from the coastal system and separated by a fringe of offshore fine grained muds and silts as distinct facies belts the growth of carbonate ramp deposits was related to the highstand systems tracts of the fourth order parasequence sets during the growth of these ramps some sediment starvation occurred basinwards progradation and retrogradation of the different belts occur simultaneously suggesting a sea level control on sedimentation in the study area the co existence of carbonate and siliciclastic facies belts depended on the superimposition of different orders of relative sea level cycles and occurred mainly when the second order third order and fourth order cycles showed highstand conditions

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

facies and depositional sequence evolution controlled by high frequency sea level changes in a shallow water carbonate ramp late kimmeridgian ne spain the outcrops of the sierra de albarracin ne spain allow a precise reconstruction of the shallow sedimentary domains of a late kimmeridgian carbonate ramp developed in western marginal areas of the iberian basin the sedimentary record shows a hierarchical sequence stratigraphic organization which implies sea level changes of different frequencies the studied succession is arranged in a long term transgressive regressive sequence which is likely to reflect local variation in the subsidence rates this sequence includes four higher order sequences a to d which have variable thickness from 3 to 21 m the similar sedimentary evolution observed in distant localities suggests the existence of high frequency sea level fluctuations controlling the sequence development the average amplitude of these cycles would range from 5 to 10 m the precise estimation of their duration some few hundreds of kyr and their possible assignment to any of the long term orbital cycles the 100 or the 400 kyr eccentricity cycles is uncertain sequences a and b formed during the long term transgressive interval are relatively thin from 3 to 9 m give up sequences that were never subaerially exposed these sequences are locally formed by five shallowing upward elementary sequences sequences c and d are catch down sequences with evidence of emersion of subtidal facies sequence c formed during the stage of maximum gain of long term accommodation is the thickest sequence from 13 to 21 m and includes coral microbial reefs pinnacles up to 16 m in height the increased production rates were able to fill part of the accommodation created during the early stage of high frequency sea level rise and the shallow platform was eventually exposed to subaereal erosion and meteoric cementation

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

an upper turonian fine grained shallow marine stromatolite bed from the munecas formation northern iberian ranges spain abstract a fine grained stromatolite bed laterally continuous on the kilometer scale and with small synoptic relief crops out in the munecas formation in the northern iberian ranges the munecas fm was deposited during the late turonian on a shallow water platform in the upper cretaceous intracratonic iberian basin the stromatolite bed has a tabular to domed biostromal macrostructure its internal mesostructure consists of planar wavy to hemispherical stromatoids that display a broad spectrum of microstructures including dense micrite bahamite peloids peloidal to clotted microfabrics irregular micritic wall tubes which are suggestive of algae and filamentous microframeworks which are suggestive of filamentous cyanobacteria various stromatolite growth stages have been linked to the dominance of different accretion processes the accretion of the entire fine grained stromatolite involves a complex mosaic of processes trapping and binding of quartz silt grains and bahamites which form the agglutinated parts of some laminae and microbially induced precipitation which forms spongiostromic and micritic laminae tubiform and filamentous microframeworks resembling porostromatate or skeletal stromatolitic growth were also recognized laser icp ms measurements of al si mg mn sr s and fe were analyzed to detect the influence of siliciclastic inputs and major trends during stromatolite accretion carbon and oxygen isotopic compositions from the stromatolite and associated facies were used to identify possible microbial signatures these data describes a unique and well preserved example of a shallow marine upper turonian fine grained stromatolite

evidence of widespread cretaceous remagnetisation in the iberian range and its relation with the rotation of iberia a palaeomagnetic investigation has been carried out at 13 sites of jurassic age in the iberian range northern spain two components of remanent magnetisation have been found at each site a primary high temperature component shows an average counterclockwise rotation with respect to the north of 33 2o clockwise about a vertical axis corresponding to the absolute rotation of the iberian plate since the jurassic a secondary low temperature component shows a systematic declination difference of 16 4o with respect to the primary component this indicates that a rotation of iberia must have occurred between the two acquisition times comparison of the magnetisation directions with previous palaeomagnetic data and with sea floor spreading data constrains the age of the remagnetisation between 95 and 125 ma the remagnetisation may be associated with the extensional phases in the iberian basin in the early cretaceous barremian early albian or late cretaceous cenomanian a principal characteristic of the remagnetisation is its widespread character in the iberian range 1998 elsevier science b v all rights reserved

cyclic sedimentation in the shallow marine upper permian kennedy group carnarvon basin western australia abstract the upper permian kennedy group of the carnarvon basin western australia was deposited while the merlinleigh sub basin was undergoing thermal subsidence and the global climate was warming from the carboniferous permian glaciation to the mesozoic greenhouse conditions the kennedy group comprises siliciclastic sedimentary rocks dominated by sandstones in the lower part with coarsening up cycles from mudstones to very coarse sandstones and granule conglomerates in the upper part cycles were observed and logged in the field and although many types of cycles were found three main motifs describe most of the cycles cycle motifs are defined based on the dominance of the various facies mooka motif cycles are dominated by fine grained and bioturbated facies interpreted as deposition during relative sea level highstand with only thin laminated or cross bedded sandstones interpreted as deposited during relative sea level fall binthalya motif cycles are dominated by laminated and cross bedded sandstones and coolkilya motif cycles consist of alternating laminated and bioturbated beds a hierarchy of cycles was observed in the field and this correlated well with spectral analysis of logged parameters spectral analysis of section log data and data sets corrected for the effects of compaction and sedimentation rates detected regular cyclicity geochronology of the kennedy group is not well enough constrained to allow the cycle periods in time to be calculated but ratios of the different scale cycle thicknesses correlate well with ratios of the milankovitch orbital cycles that have been calculated for the permian the presence of regular cyclicity and even bed thicknesses across large distances are not consistent with tectonic or autocyclic models of cycle formation the cycles are more likely to have been caused by fluctuating eustatic sea levels perhaps enhanced by changing amounts or seasonality of precipitation both sea levels and climatic fluctuations would ultimately be controlled by the milankovitch orbital cycles

syndepositional shallow water precipitation of glauconitic minerals abstract numerous studies have demonstrated that glauconitic minerals predominantly form in water depths of mid shelf to upper slope in modern oceans these areas tend to have slow sedimentation rates another commonly cited requisite for glauconitic mineral precipitation cambro ordovician strata from the southwestern us are rich in glauconitic minerals stratigraphic sedimentological and petrographic constraints indicate that the glauconitic minerals are autochthonous in marked contrast to the modern environments of deposition these cambro ordovician strata formed under very shallow water to tidal flat conditions the trough cross stratified deposits of the most glauconitic mineral rich accumulations glaucarenites indicate a high energy environment and probably a normal to high rate of sedimentation the presence of fibroradiated rims of glauconitic minerals on glauconitic mineral pellets echinoderm fragments and quartz grains demonstrates that the cambro ordovician glauconitic minerals precipitated on or in close proximity to the sea floor and prior to calcite precipitation consequently glauconitic minerals must have formed under markedly different conditions in the lower paleozoic than they do today thus the occurrence of glauconitic minerals in the rock record cannot be used a priori as an environmental indicator of either mid shelf and deeper water and or a slow rate of sedimentation

carbonate cycle stacking patterns and hierarchies of orbitally forced eustatic sealevel change ordered stacking of meter scale upward shallowing cycles manifested as repeated thickness hierarchies within cratonic carbonate sequences has been considered primary evidence for causal relations between orbitally forced climate change and eustatic sealevel variation explicit in this argument is the assumption that each individual cycle represents a single sealevel rise sensitivity testing of one dimensional forward models incorporating a depth threshold of carbonate accumulation indicates that multiple upward shallowing cycles may originate during any single rise in sealevel variation in resultant cycle stacking pattern is sensitive to changes in sealevel amplitude sedimentation rate and subsidence rate with highest stacking ratios ratio of number of cyclic units to number of eustatic periods produced by low sealevel amplitudes and high sedimentation and subsidence rates these relations indicate that direct correlation between multiple frequency eustatic sealevel variations and meter scale cycle stacking hierarchies is unwarranted thus prevalent interpretations regarding the stacking record of orbital forcing in ancient carbonate rock sequences should be reevaluated

sub wavebase cross bedded grainstones on a distally steepened carbonate ramp upper miocene menorca spain cross bedded grainstones on carbonate ramps and shelves are commonly related to the locus of major wave energy absorption such as shorelines shoals or shelf breaks in contrast on the early tortonian carbonate platform of menorca balearic islands coarse grained cross bedded grainstones are found at a distance from the palaeoshoreline where they were deposited below the wavebase excellent exposures along continuous outcrops on the sea cliffs of menorca reveal the depositional profile and three dimensional distribution of the different facies belts of the tortonian ramp depositional system basinward from the palaeoshoreline fan deltas and beach deposits pass into 5 km wide gently dipping bioturbated dolopackstone inner and middle ramp then into 12 20 dipping dolograinstone rudstone clinobeds ramp slope and finally into subhorizontal fine grained basinal dolowackestone to dolopackstone outer ramp in this miocene example coarse grained grainstones exist in five different settings other than beach deposits 1 on the middle ramp where cross bedded grainstones were deposited by currents roughly parallel to the shoreline at 40 70 m estimated water depth and are interbedded with gently dipping bioturbated dolomitized packstones 2 on the upper slope where clinobeds are composed mostly of in situ rhodoliths and red algae fragments 3 on the lower slope as small scale bedforms small three dimensional subaqueous dunes migrating parallel to the slope 4 at the transition between the lower slope and the outer ramp where mollusc rich and rhodolithic rudstones and grainstones interbedded in dolomitized laminated wackestones containing abundant planktonic foraminifera infill slide slump scars as upslope backstepping bodies backsets 5 at the toe of the slope where coarse skeletal grainstones indicate bedform migration parallel to the platform margin induced by currents at more than 150 m estimated water depth this late miocene example also illustrates how changes in intrabasinal environmental conditions nutrients and or temperature may produce changes in stratal patterns and facies architecture if they affect the biological system two depositional sequences compose the miocene platform on menorca where a reef rimmed platform prograded onto an earlier distally steepened ramp the transition from the ramp to the reef rimmed platform was effected by an increase in accommodation space caused by ecological changes promoting a shift from a grain to a framework producing biota

carbonate ramp depositional systems abstract the classification tectonic settings stratigraphy and early diagenesis of carbonate ramp systems are reviewed carbonate ramps are common in all geological periods but were dominant at times when reef constructing organisms were absent or inhibited ramps can be subdivided into inner mid and outer ramp environments the mid ramp zone extends from fair weather wave base to normal storm wave base although the water depths which these boundaries represent vary an additional outer slope environment occurs on distally steepened ramps as with siliciclastic shelves a range of wave storm and tide dominated ramps can be recognised and this forms the most convenient basis for ramp classification the carbonate productivity profile of ramps differs from that of rimmed shelves with the inner ramp showing lower production rates than comparable shallow water facies on rimmed shelves the zone of greatest organic carbonate sediment production appears to have shifted from the mid ramp to the inner ramp since the late jurassic carbonate ramps occur in most types of sedimentary basin but are best developed where subsidence is flexural and gradients are slight over large areas as in foreland and cratonic interior basins and along passive margins the featureless depositional profiles of many ramps means that sequence geometries are best observed on regional seismic lines some show low angle sigmoidal or shingled clinoforms suggesting that ramps may seldom be homoclinal but possess subtle slope geometries which reflect depositional environments because of their low angle slopes ramps respond differently to rimmed shelves during relative sea level changes although results seem to be strongly dependent on the rate of relative sea level change during a minor fall shallow ramp facies belts will simply shift basinwards in a forced regression in contrast the whole surface of a steep sloped flat topped rimmed shelf may be exposed so that sediment production ceases or is drastically reduced during a major fall shallow ramp bounded basins may empty completely conversely ramps also flood gradually whereas rimmed shelves do so more rapidly homoclinal ramps develop no resedimented lowstand deposits rimmed shelves and distally steepened ramps in contrast may develop lowstand talus or turbiditic wedges distally steepened ramps may behave more like homoclinal ramps during minor base level falls and like rimmed shelves during major base level falls many ramps consist of layered successions of several ramp sequences stacked one upon the other ramp stacks of this sort may show gross vertical accretion but individual ramp sequences seldom appear to develop in a keep up style apart from minor organic buildups as with many rimmed shelves steepening of the outer ramp margin due to tectonism slope inheritance or differential sedimentation may promote the development of a distally steepened ramp or rimmed shelf a wide variety of organisms have constructed buildups in mid and outer ramp environments isolated buildups may seed early in ramp development accrete to wave base or sea level and continue growth by stacking through successive ramp sequences so that depositional and diagenetic features within them are in concert with those of the shallow ramp the location of isolated buildups on ramps is governed by tectonism halokinesis antecedent topography or by the subtle slope geometry of the previous ramp sequence diagenesis on ramps shows some major variations compared with diagenesis on steep sloped flat topped carbonate platforms ramp bounded basins may form prolific petroleum sourcing and reservoiring systems and offer a range of subtle stratigraphic play types and lateral facies variations which determine reservoir quality and distribution isolated buildups in the mid and outer ramp environments represent one of the commonest petroleum reservoirs in ramp systems and tend to have their foundations in transgressive systems tracts grainstone and packstone reservoirs are widespread and range from shoreline carbonate sandbodies to major detached shoal complexes or shoals over offshore highs grainstone sandbodies occur in both highstand systems tracts and in prograding lowstand wedges

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

cyclic deposits and hummocky cross stratification of probable storm origin in upper cretaceous rocks of the cape sebastian area southwestern oregon abstract cyclic deposits containing hummocky cross stratification occur in the upper part of the cape sebastian sandstone of bourgeois 1980 a shallow marine transgressive sandstone of late cetaceous age on the southern oregon coast the cycles average 1 6 m in thickness and consist where complete of a lower hummocky cross stratified sandstone a middle planar and ripple bedded sandstone with a shale bed in its middle part and an upper bioturbated sandstone noteworthy features of the hummocky cross stratification include the presence of depositional domes in addition to scoured depressions the absence of significant bedform migration and the presence of a small proportion of dip angles greater than the angle of repose 34 in addition to the large proportion of low 15 deg dip angles the lower stratified fining upward part of the cycle up to the top of the shale bed is interpreted as having accumulated under conditions of initially great but gradually decreasing current velocity and deposition rate the currents probably had a strong oscillatory component and the depositional event is inferred to have been a storm the part of the planar and ripple bedded sandstone above the shale bed was probably deposited during relatively fair weather after the storm but before re establishment of a normal benthic fauna the bioturbated sandstone is interpreted to have been deposited during fair weather or during minor storms separated by long intervals of fair weather

modelling tidal current induced bed shear stress and palaeocirculation in an epicontinental seaway the bohemian cretaceous basin central europe lower to middle turonian deposits within the bohemian cretaceous basin central europe consist of coarse grained deltaic sandstones passing distally into fine grained offshore sediments dune scale cross beds superimposed on delta front clinoforms indicate a vigorous basinal palaeocirculation capable of transporting coarse grained sand across the entire depth range of the clinoforms ca 35 m bi directional alongshore oriented trough cross set axes silt drapes and reactivation surfaces indicate tidal activity however the bohemian cretaceous basin at this time was over a thousand kilometres from the shelf break and separated from the open ocean by a series of small islands the presence of tidally influenced deposits in a setting where co oscillating tides are likely to have been damped down by seabed friction and blocked by emergent land masses is problematic the imperial college ocean model a fully hydrodynamic unstructured mesh finite element model is used to test the hypothesis that tidal circulation in this isolated region was capable of generating the observed grain size distributions bedform types and palaeocurrent orientations the model is first validated for the prediction of bed shear stress magnitudes and sediment transport pathways against the present day north european shelf seas that surround the british isles the model predicts a microtidal to mesotidal regime for the bohemian cretaceous basin across a range of sensitivity tests with elevated tidal ranges in local embayments funnelling associated with straits increases tidal current velocities generating bed shear stresses that were capable of forming the sedimentary structures observed in the field the model also predicts instantaneous bi directional currents with orientations comparable with those measured in the field overall the imperial college ocean model predicts a vigorous tide driven palaeocirculation within the bohemian cretaceous basin that would indisputably have influenced sediment dispersal and facies distributions palaeocurrent vectors and sediment transport pathways however vary markedly in the different sensitivity tests accurate modelling of these parameters in this instance requires greater palaeogeographic certainty than can be extracted from the available rock record

morphological patterns of aptian lithocodium bacinella geobodies relation to environment and scale lithocodium aggregatum and bacinella irregularis are now extinct shallow marine life forms of unknown taxonomic origin forming part of the tropical platform biota during much of the mesozoic these organisms experienced bloom periods and temporarily replaced rudist coral assemblages during parts of the early aptian within the limitations of time resolution this out of balance facies is coeval with the oceanic anoxic event 1a related black shale deposition in oceanic basins but the triggering factors remain poorly understood here a platform wide comparison of lithocodium bacinella geobodies and morphotypes from the sultanate of oman is presented and placed in its environmental bathymetric and physiographic context lithocodium bacinella geobodies reach from kilometre scale superstructures to delicate centimetre sized growth forms clearly scale matters and care must be taken when drawing conclusions based on spatially limited observational data whilst the factors that cause lithocodium bacinella expansion should probably be considered in a global context regional to local factors affected growth patterns in a more predictable manner here the unresolved taxonomic relationship remains the main obstacle in any attempt to unravel the response of lithocodium bacinella to specific or interlinked environmental parameters as different organisms respond differently to changing environment acknowledging these limitations the following tentative patterns are observed i lithocodium bacinella tolerated a wide range of hydrodynamic levels and responded to differences in energy level or physiographic settings margin intrashelf basin inner platform by obtaining characteristic growth forms ii lithocodium bacinella favoured low sediment input but had the ability to react to higher sedimentation rates by enhanced upward growth a feature perhaps pointing to a phototrophic metabolism circumstantial evidence for continuous growth within the upper sediment column is debated iii the availability of accommodation space had a direct influence on the maximum size of geobodies formed iv fluctuating nutrient levels and sea water alkalinity may have affected the growth potential of lithocodium bacinella understanding the relationship between lithocodium bacinella morphogenesis on a wide range of scales and local environmental parameters allows for better prediction of the spatial distribution of reservoir properties and also results in an improved interpretation of palaeoenvironments this study might represent a useful first step in this direction

alternating braidplain and lacustrine deposition in a strike slip setting the pennsylvanian boss point formation of the cumberland basin maritime canada abstract the boss point formation was deposited in the cumberland basin of southeastern new brunswick and northern nova scotia during the early pennsylvanian the basin is bounded to the northwest and south by strike slip faults active during the pennsylvanian the boss point comprises two main fades associations sandy braidplain bfa and muddy lacustrine lfa the abrupt alternation of which allows 16 depositional megacycles to be defined the lfa forms units 50 m thick that rest sharply but nonerosively on braidplain sandstone in some instances the contact can be traced for over 12 km perpendicular to paleoflow commonly dunes and ripples are preserved in relief beneath lacustrine mudstone implying rapid but very low energy flooding of t e braidplain the bfa comprises multistory channel sandbodies 90 m thick separated from the underlying lfa by sixth order surfaces with up to 15 m of erosional relief the erosion surfaces are commonly overlain by spectacular mudstone breccias and boulders that reflect deep erosion and rotational slumping into channels cut into and sometimes right through lacustrine deposits bfa packages are internally partitioned by fifth order erosion surfaces into individual channel fill units commonly about 5 m thick the bfa is dominated by trough cross bedded fine to lower medium sandstone conglomerate pebbly sandstone and ripple laminated and planar laminated sandstone are minor components rare mud filled abandoned channels suggest a mean width and de th of 160 m and 4 8 m respectively the dominance of trough cross bedding suggests relatively deep channels whose banks may have been maintained by a dense vegetation cover repeated channel avulsion and flood related erosion resulted in a rock record dominated by deep channel and flood stage deposits bartop facies were rarely preserved channel dimensions lateral consistency of facies paucity of muddy channel plugs and regionally consistent paleoflow suggest deposition on a braidplain the distribution of conglomerates indicates a local gravel source area in the caledonia highlands to the northwest but much of the sand is likely to have been sourced far to the southwest the boss point falls into two sharply disjunct paleoflow domains one directed to the north and northeast and the other to the east and southeast separated by the harvey hopewell fault zone the absence of an adequate watershed between the two domains strongly suggests tectonic juxtaposition involving several tens of kilometers of sinistral offset

delta plain coal deposits from the than formation of the early cretaceous saurashtra basin gujarat western india abstract the than formation of the early cretaceous saurashtra basin consists of an interbedded assemblage of sandstone claystone carbonaceous shale and coal facies small scale crossbedded and laminated mudstone siltstone sr lm facies are considered to have formed by down current migration of small scale subaqueous bedforms and overbank deposits of distributary channels the planar and trough crossbedded sandstone lithofacies sp st formed by migration of sand dunes and transverse bars in distributary channels laminated to ripple laminated siltstone f1 facies with or without coaly stringers alternate with fine clastics are suggestive of flood deposits and abandoned interchannel plain of delta distributaries the muddy carbonaceous shale fm facies represents deposition largely in low lying interchannel plains and backswamps peat coal pc facies are interpreted as in situ deposits in quiet water conditions of sedimentation across a lake the integrated results of lithofacies texture and palaeocurrent analysis suggest that than strata were deposited in a prograding major delta distributary complex in lower and upper delta plain environments

sequence stratigraphy and architecture of a late early middle aptian carbonate platform succession from the western maestrat basin iberian chain spain abstract the attributes of a four systems tract sequence are at times difficult to identify in outcrop scale carbonate successions poor exposure conditions variable rates of sediment production erosion and or superposition of surfaces that are intrinsic to the nature of carbonate systems frequently conceal or remove its physical features the late early middle aptian platform carbonates of the western maestrat basin iberian chain spain display facies heterogeneity enabling platform platform margin and slope geometries to be identified and provide a case study that shows all the characteristics of a quintessential four systems tract based sequence five differentiated systems tracts belonging to two distinct depositional sequences can be recognized the highstand systems tract hst and forced regressive wedge systems tract frwst of depositional sequence a and the lowstand prograding wedge systems tract lpwst transgressive systems tract tst and subsequent return to a highstand stage of sea level hst of depositional sequence b an extensive carbonate platform of rudists and corals stacked in a prograding pattern marks the first hst the frwst is constituted by a detached slightly cross bedded calcarenite situated at the toe of the slope in a basinal position the lpwst is characterized by a small carbonate platform of rudists and corals downlapping over the frwst and onlapping landwards the tst exhibits platform backstepping and marly sedimentation resumed carbonate production in shelf and slope settings characterizes the second hst a basal surface of forced regression a subaerial unconformity a correlative conformity a transgressive surface and a maximum flooding surface bound these systems tracts and are well documented and widely mappable across the platform to basin transition area analyzed moreover the sedimentary succession studied is made up of four types of parasequence that constitute stratigraphic units deposited within a higher frequency sea level cyclicity ten lithofacies associations form these basic accretional units each facies assemblage can be ascribed to an inferred depositional environment in terms of bathymetry hydrodynamic conditions and trophic level the architecture of the carbonate platform systems reflects a flat topped non rimmed depositional profile furthermore these carbonate shelves are interpreted as having been formed in low hydrodynamic conditions the long term relative fall in sea level occurred during the uppermost early aptian which subaerially exposed the carbonate platform established during the first hst and resulted in the deposition of the frwst is interpreted as one of global significance moreover a possible relationship between this widespread sea level drop and glacio eustasy seems plausible and could be linked to the cooling event proposed in the literature for the late early aptian because of the important implications in sequence stratigraphy of this study the sedimentary succession analyzed herein could serve as an analogue for the application of the four systems tract sequence stratigraphic methodology to carbonate systems

tectono depositional pattern and evolution of the middle yangtze platform south china during the late ediacaran abstract the depositional environments and evolution of the yangtze block during the ediacaran cambrian transition remain uncertain preventing a thorough understanding of the coeval ocean stratification redox heterogeneity and organism distribution in this study detailed facies and sequence stratigraphic analyses were carried out on the dengying formation and its correlatives to better constrain the tectono depositional pattern and evolution of the middle yangtze area in the late ediacaran twenty five lithofacies were identified in nineteen sections and grouped into six depositional facies intrashelf basin intrashelf shoal restricted platform interior platform margin upper middle slope and lower siliceous slope basin the spatiotemporal distributions of these depositional facies reveal an isolated rimmed middle yangtze carbonate platform embayed with a westward opening intrashelf basin this intrashelf basin gradually became wider and deeper westwards linking to a nne trending basinal seaway that separated the middle yangtze platform from its upper yangtze counterpart the enclosure of the marginal shoal reef complex with an intrashelf shoal chain formed a large scale restricted lagoon and associated tidal flat in the platform interior based on key sequence boundaries and cycle stacking patterns two and a half transgressive regressive sequences were distinguished in the dengying formation and its correlatives in the twelve representative sections furthermore these sequences can be correlated well with those identified in other upper ediacaran successions elsewhere in upper yangtze namibia india and oman indicating a eustatic origin for these sequences however the complex platform basin configuration with significant facies and thickness variations reflects a transtensional tectonic regime in the middle yangtze area during the late ediacaran the abrupt changes in lithofacies and thickness across the southern principal platform margin and those from sandy shoals banks to storm influenced shelf along the northern portion of the intrashelf basin in the three gorges western hubei suggest synthetic extensional faulting across the margins during deposition the two synthetic extensional fault zones might have been induced by nne trending transtensional faulting along the eastern margin of the upper yangtze platform this structural pattern fundamentally controlled the depositional differentiation of the middle yangtze platform during the late ediacaran and also laid the foundation for the subsequent facies distribution and depositional evolution during the early cambrian terreneuvian epoch

the interaction of tectonics climate and eustasy in controlling dolomitization a case study of cenomanian turonian shallow marine carbonates of the iberian basin

field and modelling studies of cambrian carbonate cycles virginia appalachians reply abstract field studies coupled with computer modelling of carbonate cycles in the elbrook conococheague formations middle to upper cambrian in the appalachians have helped define the mechanisms of formation the sequence is up to 1 6 km thick and composed of cyclic peritidal carbonates these formed on an aggraded rimmed shelf on a mature passive continental margin the cycles 1 7 m thick have lower parts of subtidal intertidal carbonate and caps of dolomitic laminite containing minor quartz arenite shale and breccia sedimentation rates for these peritidal carbonate environments exceeded long term subsidence of the platform 0 01 to 0 1 m 1 000 yr thus the shelf stayed near to sea level i e was aggraded milankovitch 20 000 to 100 000 yr low amplitude sea level fluctuations few meters superimposed on 3rd order sea level fluctuation of 1 to 3 m y duration and less than 20 m amplitude caused periodic submergence of the gently sloping platform less than 0 02 m km slopes resulting in deposition of over 400 peritidal cycles in about 26 m y cycles that formed during 3rd order sea level rise are thick and limestone rich whereas those formed during 3rd order fall are thin quartzose and highly dolomitized the modelling suggests that fewer and thinner cycles formed during the long term falls compared to the rises reflecting decreased accommodation cycle frequency decreases into areas of lower subsidence rate open marine cycles typical of the outer shelf and cycles formed during 3rd order sea level rise contain digitate bioherms grainstone and ribbon carbonates in lower parts they reflect high subsidence rate and an open marine setting inner shelf cycles and cycles that formed during 3rd order sea level fall commonly are thrombolitic or have thin subtidal parts grainstone conglomerate or stromatolite and reflec the low subsidence rates interior areas of quaternary carbonate shelves are characterized by incipiently drowned facies and pinnacle reefs and are punctuated by soil caliche horizons and karst surface that reflect 100 m glacio eustatic sea level fluctuations in contrast many ancient shelves like the cambro ordovician shelf of the appalachians were flat topped and dominated by cyclic peritidal sequences lacking evidence of high amplitude sea level fluctuations such aggraded shelves may represent the typical state of mature carbonate shelves that formed in response to low amplitude milankovitch sea level fluctuations as opposed to the large scale fluctuations that typified the quaternary

sequential and climatic framework of the growth and demise of a carbonate platform implications for the peritidal cycles late jurassic north eastern france the middle oxfordian of the eastern paris basin constitutes a remarkable example of the growth and demise of a carbonate platform fischer plots sedimentary and diagenetic features allow the identification of four depositional cycles s5 to s8 in the transversarium zone they are inserted in a lower frequency cycle of increased decreased accommodation space soiii the long term period of accommodation creation occurred during the older s5 and s6 cycles the maximum accommodation zone being located in the lower part of the s6 cycle this high accommodation period was tectonically controlled and was coeval with local distensive activity of a hercynian fault a major minimum accommodation zone exists during the s8 cycle at that time the platform was isolated and presented both a windward and a leeward margin the growth of the platform was favoured by a warm and arid climate oligotrophic conditions and reduced siliciclastic input during a highstand in relative sea level these palaeoenvironmental features favoured the proliferation of phototrophic organisms producing carbonate material the death of the platform was generated by a reduction in the carbonate production surface during a lowstand in relative sea level and by the appearance of mesotrophic conditions induced by the increase in siliciclastic inputs at the beginning of a period with a cooler and more humid climate in the eastern paris basin during the middle oxfordian the parasequences are ordered and present greenhouse characteristics in contrast at the beginning of the s8 cycle the randomness in the thickness of contiguous parasequences increased decreased carbonate production during the lowstand caused by a transition from photozoan to heterozoan benthic communities certainly favoured this randomness and the appearance of catch down parasequences

carbonate platform facies models various types of carbonate platforms are characterized by distinctive profiles facies and evolutionary sequences ramps may be homoclinal or distally steepened and may have fringing or barrier shoal water complexes of ooid pellet sands or skeletal banks homoclinal ramps pass seaward into deeper water without major break in slope and lack deep water breccias distally steepened ramps may be low energy and characterized by widespread shallow subwave base mud blankets or high energy with coastal beach dune complexes and widespread skeletal sand blankets slope facies may contain abundant breccias of slope derived clasts rimmed shelves have relatively flat tops and marked break in slopes at the high energy shallow shelf edge where they pass into deep water such shelves may be aggraded with peritidal facies extending over much of the shelf or incipiently drowned depending on magnitude of sea level fluctuations they may be accretionary or bypass types that include gullied slope escarpment and high relief erosional forms intrashelf basins occur on some shelves controlling distribution of reservoir and source beds isolated platforms are surrounded by deeper water and may be located on rifted continental margins or on submarine volcanoes most have high relief rimmed margins platforms that have been subjected to rapid sea level rise may be incipiently drowned and characterized by raised rims elevated patch or pinnacle reefs and widespread subwave base carbonate or fine clastic blankets completely drowned shelves develop where the shelf is submerged to subphotic depths terminating shallow water deposition and commonly resulting in blanketing of the shelf by deeper water facies some margins show extensive down to basin faulting that is contemporaneous with carbonate deposition or associated with thick prograding clastic sequences the various types of platforms change in response to variations in sedimentation subsidence or sea level rise and may form distinctive evolutionary sequences the relatively few models presented appear to accommodate most geological examples some of which contain major reservoir facies

sequences cycles and hiatuses in the upper albian cenomanian of the iberian ranges spain a cyclostratigraphic approach abstract the upper albian cenomanian deposits in the iberian ranges are composed of a complex alternation of continental sandstones coastal lime sandstones and marls and marine carbonates facies facies are arranged mainly in transgressive and deepening upward sequences and parasequences but deepening shallowing upwards sequences and parasequences also exist depositional sequences and parasequences are bounded by subaerial erosive surfaces or ferruginous crusts and by their correlative conformities it is evident from the facies alternation that deposition reflects a cyclic process in which is superimposed several orders of cycles of relative sea level rise and fall the cycles are preserved as 3rd order depositional sequences and 4th and 5th order discontinuity bounded parasequences the latter being the basic blocks of the field record a cyclostratigraphic model for sedimentation shows that each of the 3rd order cycles is composed of five 4th order cycles a 4th order cycle is also composed of five 5th order cycles this 1 5 5 ratio reflects the maximum number of parasequences observed in the most complete and marine sections the ratio remains unchanged throughout the basin except by onlap caused by relative sea level rises or truncations caused by relative sea level falls a detailed correlation of sections separated by more than 200 km shows that thickness differences are caused mainly by parasequence disappearance not parasequence thinning cycles are mainly eustatic in origin controlled by accommodation space increased accommodation generates thick parasequences of wider regional extension they contain the more marine facies in any section only some sequences with a restricted regional distrubution are recorded if the accommodation is low the average duration of 3rd order cycles was 1 95 ma ranging from 1 33 to ma an average 4th order cycle was 390 ka 266 533 ka and a 5th order cycle was 78 ka 53 106 ka

depositional sequences in shallow carbonate dominated sedimentary systems concepts for a high resolution analysis abstract oxfordian and berriasian sections representing shallow water carbonate dominated sedimentary systems have been studied in the swiss and french jura in spain and in normandy they all display a hierarchical stacking of depositional sequences facies evolution and stacking pattern allow to define elementary small scale medium scale and large scale sequences some depositional sequences display well marked sequence boundaries others are limited by transgressive or maximum flooding surfaces the hierarchical organisation of such sequence stratigraphic elements implies that sea level fluctuations were an important factor in their formation and that these fluctuations had different frequencies the superposition of high frequency sea level changes on a long term sea level trend leads to repetition of diagnostic surfaces defining sequence boundary and maximum flooding zones wherein the corresponding high frequency surfaces are well developed chronostratigraphic tie points permit us to estimate the duration of large scale sequences this time control and the observed hierarchical stacking suggest that the high frequency sea level changes were controlled by climatic cycles in the milankovitch frequency band the variability of stacking pattern and facies evolution between sections illustrates the complexity of the studied environments furthermore because of the minimal accommodation space available in these shallow water settings much of the geologic time is not recorded nevertheless detailed analysis of the depositional sequences allows the interpretation of the evolution of the sedimentary system with a high time resolution thus there is a potential to monitor sedimentological ecological and diagenetic processes on a time scale of 20 to 100 ka

misuse of fischer plots as sea level curves fischer plots are graphic representations of cyclic carbonate deposits showing cumulative departure from average cycle thickness plotted against cycle number and corrected for assumed subsidence during each cycle observed cycle thicknesses in excess of subsidence have been interpreted to represent depositional accommodation space formed by eustatic sea level rise however implicit in this interpretation is the assumption that preserved cycle thickness is a proxy for accommodation to test this assumption a survey of carbonate sediment accumulation patterns i e cycle thicknesses developing during a single transgressive event the holocene postglacial sea level rise was conducted on a shallow carbonate platform great bahama bank where accommodation was created primarily by sea level rise over the platform margin i e subsidence was minimal this survey demonstrates that holocene sediment cycle thickness and accommodation are uncorrelated r 2 0 03 consequently fischer plots constructed by using holocene cycle thicknesses are poor representations of the holocene transgression in extreme examples holocene fischer plots would be interpreted to show relative sea level fall during the holocene on great bahama bank because holocene subsidence currently exceeds sediment thickness in addition a simple sensitivity test shows that eustatic sea level interpretations based on interbasinal correlation of fischer plots are equivocal the gross form of fischer plots appears so overly robust as to be insensitive to broad variations in stratigraphic completeness cycle duration or subsidence because cycle thickness apparently is uncorrelated with accommodation and the gross form of fischer plots is relatively invariant it seems prudent to reevaluate the practice of interpreting fischer plots as sea level curves per se in the analysis of ancient carbonate cycles

braidplain evolution in the pennsylvanian south bar formation sydney basin nova scotia canada abstract the south bar formation is a 1 km thick alluvial succession in the pennsylvanian morien group of the sydney basin nova scotia that fines upward from conglomerate to pebbly sandstone to sandstone facies assemblages the conglomerate assemblage comprises mainly massive to horizontally stratified conglomerate and planar cross stratified sandstone attributed to deposition in proximal braided rivers confined between bedrock ridges the sandstone assemblage shows uniformity of facies and paleocurrents across the basin and is interpreted as a distal braidplain deposit the pebbly sandstone assemblage is transitional between the other two both sandstone assemblages are dominated by trough cross stratified sandstone formed by dune migration in channel tracts about 4 m deep this succession differs markedly from platte river and icelandic sandy braidplain deposits which are mainly planar cross stratified sands formed by broad shallow flow the south bar sandstones are more like south saskatchewan river deposits but differ in 1 greater abundance of trough sets and 2 rarity of planar sets and other components of shallow water channel fill these features are ascribed to 1 inheritance of relatively deep channels from confined upstream reaches 2 maintenance of deep flow in active tracts by local confinement between temporary banks and 3 rapid avulsive abandonment of active tracts which inhibited development of channel fill sequences evidence for local temporary confinement is preserved as in situ and slumped channel margin mudrock units lateral and vertical transitions from the upper south bar formation to the mud rich waddens cove and sydney mines formations are ascribed to changes in channel pattern from braided to meandering the former is attributed to decreased slope the latter to eustatic rise in sea level

an estimate of albian sea level amplitudes and its implication for the duration of stratigraphic hiatuses abstract carbonate platform tops are reliable but incomplete recorders of past sea level fluctuations as they are riddled with hiatuses of various durations basinal sections represent a more complete record but fail to register regressive transgressive events with small to moderate amplitudes we seek to avoid these problems by combining information on past sea level fluctuations from coeval platform top slope and basinal sections the outcome of this study is a semiquantitative albian sea level curve from the southern tethyan margin in oman in subaerial exposure surfaces the northern oman margin recorded 4 high amplitude 50 m 6 intermediate amplitude 30 m and 26 low amplitude 10 m regressive transgressive cycles hiatuses that cap the platform top depositional sequences might account for between 30 to 70 of the cycle duration the resulting platform top depositional sequences have frequencies in the order of 230 20 kyr i e they are in the time range of orbital eccentricity cycles it appears that at least some of these albian regressive transgressive cycles were rapid and punctuated as opposed to sinus shaped milankovitchian sea level oscillations

trace fossil model for reconstruction of paleo oxygenation in bottom waters recognition of fluctuations in the degree of paleo oxygenation of bottom waters recorded in fine grained pelagic strata is important for interpretation of paleoceanographic and paleoclimatologic conditions general sedimentary fabric composition of trace fossil assemblages and burrow size and crosscutting relationships have been incorporated into a trace fossil tiering model that permits detailed reconstruction of changes in paleo oxygenation of bottom waters applications of this model to the miocene monterey formation california and the cretaceous niobrara formation colorado indicate that the ichnologic approach is more sensitive to both magnitude and rates of change in oxygenation levels compared to macrobenthic body fossil information

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

quantitative meso cenozoic development of the eastern central atlantic continental shelf western high atlas morocco abstract the well exposed late paleozoic to cenozoic succession in the western high atlas morocco documents the early rift to mature drift development of the eastern central atlantic continental shelf basin vertical sections depositional geometries and unconformities have been used to reconstruct the basin architecture prior to atlasian inversion two dimensional reverse basin modeling has been performed to quantitatively analyze the development of the continental shelf between the latest paleozoic to early cenozoic basin evolution stages include i early rift late permian to anisian ii rift climax ladinian to carnian iii sag norian to early pliensbachian iv early drift late pliensbachian to tithonian v mature drift berriasian to cenomanian vi mature drift with initial atlasian deformation turonian to late eocene vii atlasian deformation late eocene to early miocene viii atlasian uplift and basin inversion early miocene to recent the late permian to late cretaceous basin development comprises eight subsidence trends of 10 35 myr duration trends were initiated by changes in thermo tectonic subsidence which in turn triggered positive and negative feedback processes between sediment flux flexural and compaction induced subsidence plate tectonic reconfigurations in the atlantic domain controlled the thermo tectonic subsidence history and the basin development of the agadir segment of the northwest african passive continental margin 1 major shifts in the sea floor spreading axis 2 significant decreases in sea floor spreading rates 3 the stepwise migration of crustal separation and sea floor spreading in and beyond the central atlantic 4 african eurasian relative plate motions and convergence rates during the early pliensbachian toarcian to cenomanian the first three plate tectonic reconfigurations triggered changes in ridge push forces and modulated the extensional stress field of central atlantic plate drifting since the turonian african eurasian relative plate motions and convergence rates represented the dominant control on the thermo tectonic subsidence history in the agadir basin major variations in sediment flux and total subsidence characterize the development of the northwest african passive continental margin the explanation of typical stratigraphic sequences as caused predominantly by sea level fluctuations and rough assumptions on sediment input production and subsidence is not necessarily applicable to passive continental margins the methodology applied in this study including the newly developed tool of compositional accommodation analysis allows to develop more rigorous genetic models for the development of continental shelf basins

sequence stratigraphy in the upper cretaceous of the basco cantabrian basin northern spain the sedimentary cycles of the cenomanian to maastrichtian were investigated in the basco cantabrian basin bcb in northern spain provinces of alava vizcaya and burgos the depositional area was a distally steepened carbonate ramp which extended from catalonia northwestwards to the basque country the investigated sediments range from calciturbidites and pelagic marls to marl limestone alternations deposited on a distal carbonate ramp shallow marine limestones marls and intertidal clastics and carbonates were deposited on the proximal part of the carbonate ramp the establishment of a regional sequence analysis is based on the investigation of seismic profiles well logs and outcrop sections examples of outcrop sections are interpreted in terms of sequence stratigraphy unconformities of third and second order cycles depositional geometries systems tracts the sequence stratigraphic interpretation of outcrop sections is based on facies analysis interpretation of observed depositional geometries and correlation of unconformities and marine flooding surfaces through the basin a biostratigraphic framework is established based on ammonites inoceramids planktonic and benthic foraminifera as a result a regional sequence stratigraphic cycle chart is presented and compared with published global cycle charts the correlation of the regional cycle chart with published cycle charts is good in the cenomanian and turonian several sequence boundaries in the bcb are shifted by up to one biozone compared with the global chart some type 1 boundaries of the standard chart are only type 2 in the bcb important type 1 boundaries in the bcb are top geslinianum zone with a 100 m lowstand wedge at the basis of the sequence sequence boundary 92 2 base petrocoriense zone with a 250 m shallowing upwards lowstand wedge at the basis sequence boundary 89 2 and within the syrtale zone sequence boundary 85 0

a review of the geodynamic setting of large scale late mesozoic gold mineralization in the north china craton an association with lithospheric thinning abstract abundant gold deposits are distributed along the margins of the north china craton ncc occurring throughout the precambrian basement and located in or proximal to mesozoic granitoids these deposits show a consistent spatial temporal association with late jurassic early cretaceous magmatism and are characterized by quartz lode or disseminated styles of mineralization with extensive alteration of wall rock their ages are mainly early cretaceous 130 110 ma and constrain a very short period of metallogenesis sr nd pb isotopic tracers of ores minerals and associated rocks indicate that gold and associated metals mainly were derived from multi sources i e the wall rocks precambrian basement and mesozoic granites and associated mafic rocks previous studies including high surface heat flow uplift and later basin development slow seismic wave speeds in the upper mantle and a change in the character of mantle xenoliths sampled by paleozoic to cenozoic magmas have been used to suggest that ancient cratonic mantle lithosphere was removed from the base of the ncc some time after the ordovician and replaced by younger less refractory lithospheric mantle the geochemistry and isotopic compositions of the mafic rocks associated with gold mineralization 130 110 ma indicate that they were derived from an ancient enriched lithospheric mantle source whereas the mafic dikes and volcanic rocks younger than 110 ma were derived from a relatively depleted mantle source i e asthenospheric mantle according to their age and sources relation to magmatism and geodynamic framework the gold deposits were formed during lithospheric thinning the removal of lithospheric mantle and the upwelling of new asthenospheric mantle induced partial melting and dehydration of the lithospheric mantle and lower crust due to an increase of temperature the fluids derived from the lower crust were mixed with magmatic and meteoric waters and resulted in the deposition of gold and associated metals

orbital cycles in a late cretaceous shallow platform iberian ranges spain abstract the late turonian to early coniacian 3rd order sequence in the northern iberian range is composed of a thin bedded inner platform carbonate succession based on the vertical facies trend and on the recognition and correlation of internal discontinuities up to 27 meter scale 6th order parasequences are recognised each showing shallowing upwards trends these parasequences are hierarchically grouped into 5th order and 4th order parasequences this stratigraphical arrangement suggests the presence of cyclic processes that controlled the sedimentary record the vertical lithofacies distribution is analysed in three different sections the spectral analysis of these data using the lomb scargle algorithm indicates the presence of three orders of cycles 12 76 to 14 05 m 3 11 to 3 28 m and 1 32 to 1 53 m very close to the mean thicknesses of the 4th 5th and 6th order parasequences respectively there is also a fourth prominent peak of 3 91 to 4 14 m but it is not represented in the field successions as a distinct order of parasequence the correlation with the orbital periodicities in the milankovitch frequency band using relative ratio sets shows that the spectral periodicities can be related to the long eccentricity cycle of 400 ka the short eccentricity cycle of 95 ka and the obliquity cycles of 39 and 50 6 ka respectively whereas the 3 91 to 4 14 m spectral periodicites can be related to the short eccentricity cycles of 123 ka thus it is suggested that orbital forcing acted as a major factor that controlled climate and sea level which in turn influenced the depositional environments in the late turonian to early coniacian of the iberian ranges these high frequency changes were superimposed on a long term 3rd order evolution of the relative sea level

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

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