aptian albian palaeogeography of neo tethyan domain abstract the aptian albian interval 124 5 97 0 ma was a critical time both globally and for the tethyan domain in the tethyan domain it was the time when a united neo tethyan subduction zone became established between the future site of the alps and southeast asia and greatly accelerated the rate of north south convergence throughout the tethyan region a consequent widespread transgression on both laurasian and gondwanian margins deposited orbitolina limestones and associated clastics on wide continental shelf areas on the sea floor of the neo tethys ocean organic rich siliceous black shales radiolarites and turbidites with minor amounts of carbonates were deposited siliceous black shales accumulated under euxinic conditions of restricted small ocean basins of the neo tethyan realm and along their margins these areas received large amounts of organic debris from deltaic areas and coastal plains of the neighbouring continental shelves following the establishment of the north dipping subduction zone the laurasian passive margin was largely converted to an active one fringed by a large number of magmatic arcs that greatly influenced the sedimentation on the margin land areas and continental basins were widespread on this margin in northern tibet china and indo china this was a consequence of the late triassic to early jurassic continental collissions and accompanied intracontinental convergence that lasted well into the cretaceous a detailed aptian albian facies map and a crude palinspastic palaeogeographic map of the entire tethyan realm are prepared in order to express the contrasts in sedimentation on laurasian and gondwanian margins and to show the compatibility of the presented data with the most recent and reliable reconstructions of the major tectonic elements in tethysides

origin of the breno and esino dolomites in the western southern alps italy implications for a volcanic influence the esino limestone of the western southern alps represents a differentiated ladinian lower carnian carbonate platform comprised of margin slope and peritidal inner platform facies up to 1000 m thick a major regional subaerial exposure event lead to coverage by another peritidal lower carnian carbonate platform breno formation multiphase dolomitization affected the carbonate sediments petrographic examinations identified at least three main generations of dolomites d1 d2 and d3 that occur as both replacement and fracture filling cements these phases have crystal size ranges of 3 35 m dolomicrite d1 40 600 m eu to subhedral crystals d2 and 200 m to 5 mm cavity and fracture filling anhedral to subhedral saddle dolomite d3 respectively the fabric retentive near micritic grain size coupled with low mean sr concentration 76 37 ppm and estimated 18o of the parent dolomitizing fluids of d1 suggest formation in shallow burial setting at temperature 45 50 c with possible contributions from volcanic related fluids basinal fluids circulated in volcaniclastics or related to volcanic activity which is consistent with its abnormally high fe 4438 4393 ppm and mn 1219 1418 ppm contents the larger crystal sizes homogenization temperatures d2 108 9 c d3 111 14 c of primary two phase fluid inclusions and calculated salinity estimates d2 23 2 eq wt nacl d3 20 4 eq wt nacl of d2 and d3 suggest that they formed at later stages under mid to deeper burial settings at higher temperatures from dolomitizing fluids of higher salinity which is supported by higher estimated 18o values of their parent dolomitizing fluids this is also consistent with their high fe 4462 4888 ppm and 1091 1183 ppm respectively and mn 556 289 ppm and 1091 1183 ppm contents and low sr concentrations 53 31 ppm and 57 24 ppm respectively the similarity in shale normalized sn ree patterns and ce ce ce sn and la pr pr sn anomalies of the investigated carbonates support the genetic relationship between the dolomite generations and their calcite precursor positive eu anomalies coupled with fluid inclusion gas ratios n2 ar co2 ch4 ar he high f concentration high f cl and high cl br molar ratios suggest an origin from diagenetic fluids circulated through volcanic rocks which is consistent with the co occurrence of volcaniclastic lenses in the investigated sequence

the foreslope and toe of slope facies of the middle triassic latemar buildup dolomites northern italy abstract the latemar buildup was a circular carbonate buildup 4 km wide with a central platform core flat bedded interior platform and massive reef margin flanked on all sides by slope facies steeply dipping 30 35 foreslope breccias are present adjacent to the margin and flat lying graded grainstones at the toe of slope slope facies relate directly to depositional profile and slope angle the steeply dipping foreslopes consist of lobate breccia beds that are 25 m thick and a few tens of meters across and extend tens to hundreds of meters downslope some beds are conformably overlain by thinner 1 m thick beds of finer grained carbonate sediment the basal surfaces of the breccias are erosional and are anastamosing in both strike and dip views the breccia rains was derived principally from margin boundstones and deposited by rockfalls and avalanches planar clinoforms extend the entire height of the foreslope hundreds of meters and bracket depositional units clinothems tens of meters thick clinoforms appear to be shear surfaces formed during large slope failures avalanches graded grainstone beds less than 1 m thick are present at the nearly flat lying toe of slope these consist of redeposited shallow water platform interior and reef margin carbonate sands some with nodular limestone caps that are interpreted as proximal carbonate turbidites toe of slope breccias are the downdip extensions of foreslope breccias and pinch out abruptly basinward some slope depositional processes are related to high frequency fourth order and fifth order sea level changes toe of slope graded grainstones correspond to times of platform submergence in contrast foreslope breccia was deposited during both platform submergence and exposure the slope deposits do not record the high frequency cyclic rhythms identified in shallow water platform sections this is attributed to the nature of slope deposition downslope talus transport was episodic and localized graded grainstone beds reflect storm redeposition

large scale progradation demise and rebirth of a high relief carbonate platform triassic lombardy southern alps italy abstract the upper anisian to early carnian succession of the middle val brembana pegherolo massif central southern alps of italy records a complete depositional cycle from platform inception to growth demise and rebirth the depositional architecture of this system reflects different evolutionary stages an inception stage which postdates a previous drowning of an anisian carbonate platform with progradation of the carbonate platform from the nucleation areas an aggradational stage with increasing water depth in the basins a progradational stage where steep slopes composed of margin derived breccias develop and a final crisis corresponding to the subaerial exposure of the platform top followed by the deposition of shales in the basin before the rebirth of a different type of carbonate factory the record of this evolution reflects the effects of the change in accommodation space interplay of subsidence and eustacy which controls the type and storage sites of the sediments produced by the carbonate factory the effects of the changes in accommodation space are recorded in the shallow water platform as well as in the intraplatform basins where the sediments delivered at different rates from the platform top are stored as a consequence the aggradational stage corresponds to reduced sedimentation in the basins i e sediments are stored on the platform top whereas during progradation resedimented limestones are more common in the basin subaerial exposure rapidly halted the carbonate production on the platform top while a major input of shales probably reflecting a climate change and or lowering of the base level is recorded in the basin where shales onlap the slope of the previous carbonate system the rebirth of the carbonate factory after subaerial exposure of the platform top is characterized by a different composition of the carbonate factory probably reflecting changes of the environmental conditions the step by step recording of the evolution of the carbonate system represents a unique opportunity to record a seismic scale complete evolutionary cycle of a carbonate system in its different sub environments from the platform top to the basin

the syrian arc system an overview abstract a comparison between the ne directed negev and palmyra foreland monoclines of the syrian arc shows strong similarity in both their statigraphy and late mesozoic and cenozoic tectonic history a first phase of simple folding in the senonian was followed by a phase of reverse faulting in the miocene and ended with a phase of post miocene uplift in the style of fault bend fold this triple deformation of the north arabian subplate was contemporaneous with the thrusting of the tauros zagros zone the ne sw direction of the syrian arc as well as many other structures on the african and arabian plates are an inherited ancient feature predating any contact with the eurasian plate the continental drift proposed for turkey and arabia is reviewed and rejected for both the amounts of horizontal displacement of the dead sea rift and the east anatolian fault are estimated to be 45 and 27 km respectively it is suggested that the stress system upon the levant has been nw directed since the late cretaceous to the present time the dead sea rift n s stress direction is a local post miocene response to limited regional shift and to intense uplift

evinosponges in the triassic esino limestone southern alps documentation of early lithification and late diagenetic overprint a carbonate buildup of middle triassic age the esino limestone outcrops in the southern calcareous alps of lombardy n italy along its margin and within the open subtidal facies the esino limestone contains calcite cement filled cavities of cm to m size these features known as evinosponges may form pervasive networks within the host rock the filling consists of concentric isopachous layers of fibrous low mg calcite crystals characterized by strong undulose extinction and bent cleavages the cement crusts are non luminescent under cathodoluminescence but both cements and host rock are cross cut by microfractures filled with bright luminescent calcite related to late void filling sparite mixing of different carbonates is reflected in stable isotope data on the hand specimen scale the oxygen and carbon isotope compositions of cements and host rock show little variation when compared on a regional scale the values cover a broad range from 6l80 pdb 5 to 12 and from 613c pdb o to 3 the linear covariant trends defined by the oxygen and carbon isotope data for different sampling regions reflect the admixture of late isotopically depleted calcite with an isotopically enriched non luminescent calcite of early diagenetic origin the esino limestone fibrous cements which were probably precipitated in the marine or marinemeteoric phreatic environment were affected by late diagenetic processes that caused mineral deformation and isotopic depletion through recrystallization and the admixture of a later calcite these later calcites precipitated from penetrative fluids possibly related to late triassic volcanic activity and or to the late cretaceous early palaeogene alpine orogeny

progradation geometries of carbonate platforms examples from the triassic of the dolomites northern italy various types of progradation of triassic carbonate platforms are described from the dolomites of the southern alps the internal and external geometric relationships are exposed in spectacular natural sections and moreover their scale 500 1000 m of thickness is such that they can be compared with features found in seismic profiles the different types of progradation are controlled by a number of factors which normally interact with each other these factors include rate of basinal sedimentation rate of subsidence width of the platform depth of the surrounding basin and eustatic variations of sea level progradation is not a continuous process but episodic moments of massive debris input during which the platform advances alternate with long periods of negligible progradation during which basinal sediments accrete and onlap the toe of slope upper boundary relationships of the prograding platforms include offlap toplap and erosional truncation lower boundary relationships are horizontal climbing and descending progradations a variety of phenomena and circumstances have caused the cessation of progradation of the triassic platforms they include volcanism collapse of margins drowning rapid relative rise of sea level subaerial exposure relative fall of sea level and probably a natural decay of the system in the triassic of the dolomites two main progradation models can be put forward in the ladinian model progradation took place simultaneously with aggradation relative rise of sea level whereas the characteristic feature of the carnian model is toplap relative stillstand of sea level

high stress paleoenvironment during the late maastrichtian to early paleocene in central egypt biostratigraphic mineralogical geochemical and isotopic analyses of the gebel qreiya section in the asyut basin of central egypt indicate a depositional environment interrupted by periods of erosion due to local tectonic activity exacerbated by eustatic sea level fluctuations and by high stress environmental conditions akin to those normally experienced during the cretaceous tertiary boundary transition during the late maastrichtian 66 8 65 4 ma this region experienced a breakdown of the biologically mediated surface to bottom gradient of the 13c 12c ratio with planktic 13c values 0 2 0 8 lighter than benthic values planktic foraminiferal species diversity was reduced by more than 50 with faunal assemblages dominated 75 90 by the opportunistic disaster species guembelitria cretacea which alternate with abundance of small low oxygen tolerant heterohelicids heterohelix navarroensis h dentata h globulosa this prolonged breakdown in ocean primary productivity occurred during a time of global climate cooling and sea level regressions at 66 8 and 65 5 ma though clay mineralogy suggests that locally low seasonality warm wet tropical and subtropical conditions prevailed the high detrital influx suggests that the biologically high stress environment was primarily linked to the existing shallow shelf conditions in southern egypt and possibly to local tectonic activity and restricted circulation a normal carbon isotope gradient was briefly re established during the short climate warming and rising sea level between 65 4 and 65 2 ma a time of increased species diversity peak abundance of rugoglobigerinids and common heterohelicids during the last 200 000 years of the maastrichtian increased precipitation and terrestrial runoff increased phyllosilicates and kaolinite and increasing total organic carbon values are associated with heterohelix dominated planktic foraminiferal assemblages the k t boundary is marked by a red clay layer and ir anomaly of 5 4 ppb during the early danian planktic foraminiferal populations and stable isotope data indicate that similarly fluctuating high stress conditions prevailed in central egypt as elsewhere in the marginal eastern tethys

growth mode of middle triassic carbonate platforms in the western dolomites southern alps italy abstract the correlation of carbonate platform and slope sediments with biostratigraphically and radiometrically dated basinal successions in the western dolomites allows the reconstruction of the growth of a middle triassic carbonate platform schlern rosengarten over a time interval of approximately five ammonoid zones reitzi secedensis curionii gredleri archelaus zones the whole platform evolution had a total duration of

quaternary slope development of the western leeward margin of the great bahama bank abstract to date work on the great bahama bank s western leeward margin has centred chiefly on seismic scale expressions of carbonate sequences and systems tracts however periplatform slope sediments also exhibit very well developed cyclicity on scales of decimetres to several metres it is these small scale high frequency cycles within the larger scale facies successions of the quaternary which form the main topic of this paper previous studies have shown that the small scale cycles correlate to the orbitally forced high frequency sea level changes therefore these cycles should indicate how sea level has affected the slope development and thus platform margin evolution during this period through detailed high resolution sequence stratigraphy of the great bahama bank s leeward margin obtained via 18o isotope and mineralogical xrd analyses confined by u th dating and nannofossil bioevents a greater understanding of the bedding geometries within the pleistocene holocene seismic sequences and clues as to the nature of the slope development has been achieved the high resolution seismic profiles indicate that since the plio pleistocene change in geometry in which the great bahama bank developed into a rimmed platform continued steepening and subsequent progradation of the leeward margin has typified slope development during the quaternary which is described as an accretionary slope however on the basis of our observations we conclude that only the early to lower middle pleistocene section isotope stages 45 20 and the holocene isotope stage 1 of the leeward margin is accretionary this indicates that a degree of erosion and or by passing has occurred on the leeward margin since the lower middle pleistocene isotope stage 19 during the first part of this period isotope stages 19 12 erosion and or by passing occurred in the middle to lower slope regions and toe of slope by the end of the upper middle to late pleistocene phase isotope stages 11 2 erosion also occurred on the upper slope this erosion by currents at the toe of slope and oversteepening of the upper and middle slopes have led to back cutting upslope and resulted in the progressive retreat of the toe of slope towards the platform to the east however the rise in sea level since the last glacial maximum to its present day level has allowed high productivity on the platform top during the holocene and the deposition of a thick sediment wedge on the slope and sedimentation across the entire leeward flanks this has led to the redevelopment of an accretionary slope and continued westward progradation of the great bahama bank s western leeward margin

forward modelling of carbonate platforms sedimentological and diagenetic constraints from an application to a flat topped greenhouse platform triassic southern alps italy abstract quantitative analysis of depositional systems using numerical models can provide insights into the interaction of sedimentological and diagenetic processes difficult to interpret from observation of the geological products alone numerical models can highlight the interactions between controlling parameters and generate best estimate simulations of case studies from the geological record different data sources e g outcrop data uniformitarian constraints paleogeography need to be considered in the process of defining the parameters required to produce models that honour individual case studies we present a best estimate forward model of a high relief triassic carbonate platform southern alps italy generated using carb3d a 3d process based forward modelling package able to simulate sedimentary facies geometries and early diagenesis of isolated carbonate platforms the parameters used for the presented forward model have been deduced by the study of architectural sedimentological and diagenetic features of the platform and by data from modern and ancient analogues sensitivity analysis is used to tune values of the parameters within ranges defined from field laboratory and uniformitarian constraints critical evaluation of the model allowed 1 verification of the validity of the used parameters 2 evaluation of the interaction between controlling parameters 3 development of a numerical model that can be used for quantitative elaborations furthermore the process of generating the numerical model required a detailed interpretation of field and laboratory data crucial to define the required input parameters modelling the studied carbonate platform also enabled evaluation of the effects of the interaction between productivity environmental energy and creation of accommodation space promoting the understanding of their role on the architecture of carbonate systems forward modelling also allows the integration of data from conventional data sets with data from present day observations and seismic geometries promoting a transition from a qualitative to a semi quantitative quantitative sedimentological approach forward models can further be used to parameterise petrophysical properties of complex geobodies with potential application for the management of georesources

association of tepees and palaeokarst in the ladinian calcare rosso southern alps italy the ladinian calcare rosso of the southern alps provides a rare opportunity to examine the temporal relationships between tepees and palaeokarst this unit comprises peritidal strata pervasively deformed into tepees repeatedly capped by palaeokarst surfaces mantled by terra rossa palaeokarsts characterized by a regional distribution across the southern alps occur at the base and at the top of the unit local palaeokarsts confined to this part of the platform occur within the calcare rosso and strongly affected depositional facies tepee deformation ranges from simple antiformal structures peritidal tepees to composite breccias floating in synsedimentary cements and internal sediments senile tepees peritidal tepees commonly occur at the top of one peritidal cycle in association with subaerial exposure at the cycle top while senile tepees affect several peritidal cycles and are always capped by a palaeokarst surface cements and internal sediments form up to 80 of the total rock volume of senile tepees the paragenesis of senile tepees is extremely complex and records several superimposed episodes of dissolution cement precipitation fibrous cements laminated crusts mega rays and deposition of internal sediments marine sediment and terra rossa petrographical observations and stable isotope geochemistry indicate that cements associated with senile tepees precipitated in a coastal karstic environment under frequently changing conditions ranging from marine to meteoric and were altered soon after precipitation in the presence of either meteoric or mixed marine meteoric waters stable isotope data for the cements and the host rock show the influence of meteoric water average 18o 5 8 while strontium isotopes average 87sr 86sr 0 707891 indicate that cements were precipitated and altered in the presence of marine triassic waters field relationships sedimentological associations and paragenetic sequences document that formation of senile tepees was coeval with karsting senile tepees formed in a karst dominated environment in the presence of extensive meteoric water circulation in contrast to previous interpretations that tepees formed in arid environments under the influence of vadose diagenesis tepees initiated in a peritidal setting when subaerial exposure led to the formation of sheet cracks and up buckling of strata this porosity acted as a later conduit for either meteoric or mixed marine meteoric fluids when a karst system developed in association with prolonged subaerial exposure relative sea level variations inducing changes in the water table played a key role in exposing the peritidal cycles to marine mixed marine meteoric and meteoric diagenetic environments leading to the formation of senile tepees the formation and preservation in the stratigraphic record of vertically stacked senile tepees implies that they formed during an overall period of transgression punctuated by different orders of sea level variations which allowed formation and later freezing of the cave infills

environmental control on the end of the dolomia principale hauptdolomit depositional system in the central alps coupling sea level and climate changes abstract the norian in the western tethys is characterised by the deposition of early dolomitised inner platform facies dolomia principale hauptdolomit dp hd bordered on the landward side by terrigenous coastal deposits keuper and on the seaward side by calcareous backreef and reefal facies dachstein limestone passing basinward to open sea sediments hallstatt facies the inner carbonate platform is locally lombardy basin carnic alps central austroalpine dissected by normal faults leading to the development of intraplatform troughs close to the norian rhaetian boundary sedimentation records an abrupt environmental change both on platform top and basins all over the western tethys e g western carpathians transdanubian range alps central apennine the top of the dolomia principale locally emerged reflecting a major eustatic sea level fall emersion is recorded in favourable settings by the development of polycyclic paleosols up to 30 m thick in the norian intraplatform basins the succession is capped by 4 to 8 m of thin bedded fine grained limestones yielding abundant remnants of fishes and terrestrial reptiles fossil concentration as well as sedimentological features is indicative of reduced sedimentation rates due to decreased carbonate production induced by the emersion of the platform top the sea level fall was followed by deposition of mixed fine grained siliciclastic carbonate successions e g riva di solto shale kossen beds rhaetavicula contorta beds fatra formation stratigraphic evidence indicates a dry climate in the western tethys during the norian as indicated by the presence of evaporites burano apennine and arid to semi arid coastal to playa settings upper keuper germany in contrast the basal layers of the basinal shales show evidence of wet climate the end of the norian depositional system records two different phenomena 1 an important sea level fall was responsible for the emersion of the platform top and deposition of a condensed horizon in the basins and 2 transition from dry to humid climate the observed evolution is explained with a global cooling which caused the rapid sea level fall responsible for the abrupt end of the dp hd depositional system and the shift of the boundary between arid and temperate climate belts which modified the distribution and amount of rainfall triggering the deposition of shales along the western tethys margin

sedimentary succession and evolution of the mediterranean ridge western sector as derived from lithology of mud breccia clasts abstract rock fragments from mud breccia extruded by mud volcanoes discovered during the ttr 4 cruise of the r v gelendzhik on the western mediterranean ridge are represented by a number of different lithologies they provide important information on the composition genesis and age of the deep seated sedimentary series of the basin lithological description and age determination of the main rock types obtained as clasts from mud breccia were made on the basis of a study of ninety seven samples depositional processes and environments of their accumulation were determined using sedimentological criteria the sedimentary section through which mud volcanoes erupted on the western mediterranean ridge includes aptian albian claystones late cretaceous limestones paleogene siliciclastic rocks and a variety of miocene limestones and mudstones the rock clasts studied throw insight into the evolution of the western sector of the eastern mediterranean basin from at least aptian time the aptian albian clayey series have been deposited in the marine conditions of a relatively narrow basin with a high input of terrigenous clayey material during the late cretaceous the basin enlarged terrigenous input into deep parts of the basin decreased and carbonate pelagic sedimentation became prevalent regression in paleogene time led to the deposition of thick terrigenous siliciclastic series of deltaic prodeltaic sediments extensive turbidite systems were emplaced in the western sector of the eastern mediterranean during the miocene along with predominantly carbonate pelagic sedimentation

facies and paleogeographic importance of the pre rift limestones from ne egypt sinai the depositional environments of the phanerozoic limestones of northeastern egypt were reconstructed based on microfacies and fossil content of the following limestonedominated sequences late carboniferous late anisian ladinian carnian bajocian kimmeridgian aptian albian late cenomaman early turonian late coniacian maastrichtian late paleocene early eocene the african craton in the south and the tethyan sea in the north mainly controlled the sedimentation of most phanerozoic strata they increase in thickness towards the north due to the gentle north northwest dip of the precambrian cratonal basement different subsiding areas enabled the filling of different depocenters since jurassic times with a maximum during the cretaceous

facies analysis of lofer cycles upper triassic in the argolis peninsula greece abstract the upper triassic carbonate sediments of argolis peninsula are part of the upper triassic lower jurassic extensive and thick neritic carbonate formations pantokrator facies that formed at the passive pelagonian margin and are considered as dachstein type platform carbonates facies analysis of the upper triassic lofer type lagoonal peritidal cycles in the dhidimi area proved that cycles although mostly incomplete were regressive shallowing upward the ideal elementary cyclothems are meter scale in thickness and begin with a subtidal bed member c represented by a peloidal dolostone with megalodonts wackestone or packstone being followed by a stromatolitic intertidal dolomitic mudstone and or fenestral intertidal dolomitic mudstone member b that is overlain by dolocrete terrestrial stromatolites or pisoidic dolomite or a supratidal soil conglomerate in red micritic matrix member a lofer cycle boundaries are defined at the erosional surfaces and accordingly the lofer cyclothems are unconformity bounded units due to common post depositional truncation of the subtidal and intertidal facies the supratidal members prevail being developed in places directly upon subaerial exposure surfaces erosionally reduced cyclothems peritidal layers are characterized by a well expressed lamination sheet cracks tepee structures fenestral pores and karst dissolution cavities the studied lagoonal peritidal cycles are considered to have been deposited in a tidal flat setting inner platform repeatedly exposed under subaerial conditions in the context of a broader tropical rimmed platform although the studied area was tectonically active due to rift activity and the autocyclic processes should also be taken in consideration the great lateral correlatability of cycles the facies shifting and the widespread erosion that resulted in superposition of supratidal pedogenic facies directly upon subtidal members subaerial erosional unconformity indicating a sea level drop reflect allocyclic control via high frequency eustatic sea level oscillation orbital forcing sediment deposition occurred during low stand system tract lst that probably continued also in the transgressive system tract tst and reflects an overall sea level fall under these conditions dissolution and cement precipitation episodes as well development of paleosols and karsts were triggered during a relatively less arid interval

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

carbonate platform flanks slope angle and sediment fabric more than 20 examples of fossil carbonate platform systems were compared for slope angle and sediment fabric plots of slope angle versus sediment fabric show that grainy non cohesive mud free sediments build steeper slopes than muddy cohesive sediments examples near the end members of grainy and muddy carbonate platform flanks are found in the triassic of the dolomites in northern italy and in the bahamas respectively they document the flank geometry and the processes readjusting the slope profile once the limiting slope angle is exceeded the grainy flank sediments in the dolomites modified by shearing and avalanching produce straight slope profiles with declivities up to 35 whereas the muddy bahamian flank sediments modified by large scale creep and rotational to translational sliding and slumping produce a concave upwards slope profile inclined at less than 4 the comparison between slope angle and sediment fabric indicates that the physical behaviour of sediments in the gravity field angle of shearing and mode of readjustment processes is linked to the composition of the slope sediment among the variables such as sea level subsidence climate plate motion and oceanographic setting windward leeward sediment fabric is suggested to be a major if not the major control on slope angle and slope curvature of carbonate platform flanks besides the recently documented tendency of carbonate sediments to build steeper slopes than siliciclastics this proposed relation sheds new light on the analysis and quantification of the variables influencing the geometry and depositional evolution of carbonate systems furthermore it provides an opportunity to deduce sediment composition from seismic lines and predict lithology prior to drilling

intraplate stresses and the subsidence history of the sirte basin libya abstract results of quantitative analysis of subsidence data from 20 wells covering six major basement blocks from the sirte basin libya are presented following the late cretaceous onset of extension and associated collapse of the sirte arch the tectonic history post dating this event can be separated into four distinct phases 1 1 minor subsidence during the late cretaceous 2 2 differential fault tectonics and reactivation of basement faults during latest cretaceous to paleocene 3 3 regional uplift and subsidence during the eocene 4 4 minor subsidence during the early oligocene and early miocene a late cretaceous paleocene stretching phase of finite duration can explain the overall patterns of observed tectonic subsidence during the syn and post rift evolution of the sirte basin strong short term deviations from thermally induced long term subsidence observed during the eocene can be explained by intraplate compression and subsequent stress release related to changes in atlantic flowline geometry modelling of the observed tectonic subsidence for the sirte basin yields estimates of extension in excess of estimates inferred from displacements along high angle normal faults the effect of late stage intraplate compression on tectonic subsidence may cause part of the observed discrepancy between estimates of crustal extension

dinosaurs re write the geodynamics of the eastern mediterranean and the paleogeography of the apulia platform abstract evidence of a sizeable population of large dinosaurs on the apulia carbonate platform calls for a revision of the current paleotectonic and paleogeographic scenario of the eastern mediterranean area a review of geophysical and geological data of the ionian sea and surrounding areas leads to envisage the late jurassic early cretaceous ionian sea region as a cul de sac type basin enclosed by shallow water carbonate banks connecting the apulia carbonate platform to peloponnesus northern cyrenaica cyrene seamount and medina ridge these banks were repeatedly and periodically exposed to subaerial conditions and offered vast land areas for migration of dinosaurs as regards the nature of the mesozoic ionian basin interpretations are quite controversial the continental vs oceanic crust debate will likely be solved only when the ionian basin crust will be reached by drilling the conclusion of the present review leads to consider adria as a true african promontory and the apulia platform as a sort of florida peninsula attached to north africa cyrenaica spur subdividing the oceanic mesozoic mediterranean into a western ionian basin and an eastern levantine basin

messinian subaerial erosion of the proto nile delta abstract the evaporitic drawdown and subsequent dessication of the mediterranean basins during the messinian salinity crisis has been confirmed by detailed seismic mapping of the ensuing erosion surface in the nile delta region the basal messinian unconformity determined by seismic analysis and borehole correlation extends from almost sea level in the southern delta area to depths of at least 5 km in the nile cone the onlap of the contemporaneously deposited fluvio deltaic clastics of the qawasim formation occurs at between 2 5 to 4 km below present gradual initial drawdown of the mediterranean sea with occasional sudden sporadic falls is implied by the presence of entrenched meanders and impaired rejuvenation terraces in the nile canyon formed as the proto nile river cut down into the pre existing tortonian delta complex the former tortonian delta slope became an extensive linear erosional front with over 3 km of vertical relief the uppermost levels of which were protected by tabular oligocene basalt flows preserved as mesas and buttes the lower slopes were the site of coalescing piedmont fans fed by upper slope wadi systems the piedmonts merged into the qawasim fluvio deltaic deposits of the proto nile fluvial flood plain the subcrop beneath the basal messinian unconformity reveals a remarkable diversity of rock type each with its own distinctive control on the geomorphology and geometry of the ensuing messinian erosional surface fracture patterns within the oligocene basalts produced a trellis drainage network which became later captured by a dendritic system developed on less resistant prodelta shales of the former tortonian delta slope close study of seismic profiles clearly demonstrates that the basal messinian erosional disconformity can be traced northwards to depths of at least 2 5 3 0 km before becoming affected by later pliocene faulting this validates a deep dessication model for the evolution of the messinian evaporites

calciturbidites and calcidebrites sea level variations or tectonic processes abstract the compositional variation of pleistocene carbonate gravity deposits from the exuma sound basin bahamas and of turonian conacian deposits from the southern provence basin france was determined the bahamian carbonate platform is located in a tectonically stable passive margin setting and the gravity deposits were deposited in an environment controlled by eustatic sea level fluctuations in contrast the southern provence basin sediments were deposited in a tectonic active regime two types of gravity deposits were present in the cores of odp leg 101 site 632a i e calciturbidites and calcidebrites in analogy with earlier studies haak and schlager 1989 the compositional variations in the calciturbidites could be linked to different sources on the carbonate margin i e platform interior platform edge platform slope interglacial sea level highstands calciturbidites show a dominance of non skeletal grains derived from the platform interior while glacial sea level lowstands calciturbidites show a dominance of skeletal platform edge to platform slope derived grains hence the calciturbidite composition can be used to reconstruct the position in relative sea level in contrast the composition of the calcidebrites remained unaltered through time and showed a clear dominance of platform edge derived sediments in addition it was shown that the calcidebrites were deposited during regressions in the southern provence basin spb the gravity deposits were deposited during episodes of sea level rise coinciding with a series of earthquakes associated with the opening of the spb the spb megabreccias show a mix of sediment grains derived from the platform interior the platform edge and the upper slope thus in contrast to the exuma sound calcidebrites with their platform margin domain specific composition the spb megabreccias have a composition that could not be assigned to a single domain on the platform margin and comprise a total mix of platform margin domains in conclusion this study shows that the composition of calciturbidites calcidebrites and megabreccias can be used to determine which processes eustatic variations or tectonic events triggered the redeposition of these gravity deposits

calcareous nannofossil biostratigraphy and paleoecology of the cretaceous tertiary transition in the central eastern desert of egypt abstract the gebel qreiya and nearby wadi hamama sections of the central eastern desert are among the most complete k t boundary sequences known from egypt the two sections were analyzed spanning an interval from l 83 myr below to about 3 myr above the k t boundary a 1 cm thick red clay layer at the k t boundary at gebel qreiya contains an ir anomaly of 5 4 ppb the high resolution study and well preserved nannoflora provide good age control and the first quantitative records of calcareous nannofossil assemblages for paleoecological interpretations across the k t transition in egypt four zones micula murus micula prinsii np1 and np2 were distinguished and correlated with other nannofossil and planktonic foraminiferal zonations that are broadly applicable for the eastern tethys region latest maastrichtian assemblages are abundant and diverse though cretaceous species richness progressively decreased across the k t boundary dominant species include arkhangelskiella cymbiformis micula decussata and watznaueria barnesae with high abundance of dissolution resistant m decussata reflecting periods of high environmental stress thoracosphaera blooms mark the k t boundary and are followed by an acme of the opportunistic survivor braarudosphaera bigelowii the first appearance of the new tertiary species cruciplacolithus primus and an acme of coccolithus cavus pelagicus these successive abundance peaks provide the basis for subdivision of the early danian zones np1 and np2 into five subzones correlation of selected nannofossil taxa from the egyptian sections with those from various onshore marine and deep sea sections provides insights into their paleoenvironmental and paleoecological affinities

accommodation sedimentation development and massive early marine cementation latemar vs concarena middle upper triassic southern alps abstract massive early marine cementation mec is a major diagenetic feature of some carbonate platforms the comparison of two triassic buildups of similar size and preservation but contrasting degree of mec latemar dolomites and concarena lombardic alps allows for the investigation of differential cementation on carbonate platforms the assessment of the response of platform cementation to changes in accommodation sedimentation led to the identification of fundamental boundary conditions for mec 1 the time interval available i e a low rate of creation in accommodation space and 2 low carbonate production other important factors are 3 margin topography e g walled reefs and 4 effective fluid flow e g wave energy open and connected cavities provided by rigid frameworks the latemar mainly aggrading and locally retrograding lacks mec due to a high a s ratio i e creation destruction of accommodation in time a d a d t vs changes in sediment supply in time s d s d t and a low relief of the reefal margin in contrast the concarena in the beginning slowly and later rapidly prograding indicates mec owing to a low a s ratio and a distinct topography of the reef particular features of the concarena are cement arrangements of lenticular shape and considerable size in the back reef domain up to 3 m in diameter and 2 m in height these arrangements consist of botryoids and isopachous crusts of radiaxial fibrous calcite cements they represent one of the main components of the platform margin at concarena cathodoluminescence analyses of cements from both platforms quantifies the influence of shallow and deep burial diagenesis and shows that the majority 60 90 of all cements are of early marine origin

plate tectonic evolution of the mediterranean middle east region abstract an interpretive model for the mesozoic cenozoic plate tectonic evolution of the mediterranean and adjacent areas is illustrated by a series of paleoposition maps at selected intervals between the late triassic and recent this interval witnessed an important period of tensional development during the triassic and jurassic that fragmented pangea after its late paleozoic consolidation a number of oceanic areas evolved through jurassic time all of which have since been consumed during the alpine orogeny during the cretaceous and tertiary sea floor spreading geometry in the north and south atlantic resulted in convergence between africa and eurasia that controlled the evolution of the mediterranean and adjacent middle east areas from the late mesozoic to recent the interpretation departs from several previous ones in the following respects 1 1 the eastern mediterranean and adjacent middle east area are interpreted to have developed as two seaways with an intervening continental sliver derived from africa that now comprises central turkey and west iran these seaways persisted from the late triassic to late cretaceous by which time they were largely consumed by northward subduction 2 2 spreading that produced the present eastern mediterranean sea developed during the late cretaceous driving the tripolitza eratosthenes iskenderun continental fragments northward from africa to collision with central turkey as the preceding southern arm of the mesozoic tethys sea floor was entirely consumed initial block faulting in this zone occurred during the jurassic and early cretaceous but without subsidence reaching clearly bathyal depths until the cenomanian turonian this differs from the timing of events in the ionian sequence of the pindic nappe of crete which shows a change from shallow carbonate shelf in the triassic to deep basin in the liassic to the north of equivalent platform facies of the tripolitza nappe 3 3 moesia and rhodope are concluded to have been a single plate until a rifting event that started during the late jurassic the balkan mountains are interpreted to represent an alpine inversion of this mesozoic rift system that extended west from the black sea basin 4 4 the eastern carpathian microcontinental sliver is concluded as continuing southward as the serbo macedonian massif that separates rhodope from the vardar zone rather than as rhodope itself 5 5 the scutari pec lineament is considered as representing a major discontinuity between the apulia pannonian plate and adjacent greece and turkey ophiolites to the northwest of this lineament originated in a single oceanic area the vardar zone ophiolites to the southeast of this lineament evolved from two oceanic areas those of interior greece and northern anatolia and the associated ankara melange relating to the vardar zone the former north arm of tethys and the pindos southern anatolia zagros oman ophiolites relating to a former south arm of mesozoic tethys 6 6 based on the history of development of various elements of the alpine system there is a strong suggestion that important dextral movement took place along a major strike slip fault system reaching from the middle east to the central alps between late cretaceous and middle eocene times

influence of sea level and basin physiography on emplacement of the late pleistocene herodotus basin megaturbidite se mediterranean sea radiocarbon 14c dates from pelagic intervals above a megaturbidite in the herodotus basin give direct evidence of emplacement at the beginning of the last glacial period approximately 27 125 calendar years before present as sea level lowered rapidly and entered a low stand phase the herodotus basin megaturbidite is a basinwide deposit that forms a recognisable acoustically transparent layer on 3 5 khz high resolution seismic profiles and covers an area of approximately 40 000 km2 it thins from about 20 m in thickness proximally to some 10 m distally over a basin length in excess of 400 km the total volume is estimated at around 400 km3 which is significantly more than the volume of sediment that could have been displaced from its most likely source area the funnel shaped marginal embayment of the gulf of salum to the west of the nile cone the additional material may have been derived in part from synchronous failures on other parts of the libyan egyptian shelf and slope but most is believed to have come from large scale erosion at the base of the very large volume turbidity current that was generated from the original slide detailed sedimentary analyses of cores recovered from the megaturbidite show its distinctive characteristics graded sand silt mud and bioturbated mud units poorly developed structures proximally becoming more distinct and ordered distally variation in grain size and structures that suggest either flow separation reflection around topographic highs and or an inherently unstable flow and a mixed source bioclastic terrigenous composition these features together with its size and lateral extent would make any similar megabed an excellent marker horizon in basin analysis a combination of factors was responsible for triggering the initial slide debris flow event that evolved downslope into this mega turbidity current these include lowered sea level that destabilised the outer shelf upper slope sediments tectonic oversteepening of the margin relatively high rates of sedimentation and seismic activity

growth and demise of late carboniferous carbonate platforms in the eastern cantabrian zone asturias northwestern spain abstract geometric relationships of seismic scale stratal patterns observed on aerial photographs of late carboniferous carbonate platforms in the cuera region in asturias northwestern spain allow the identification of two discrete stages of platform development with different styles of deposition the first phase represented by the bashkirian valdeteja formation is characterized by progradation of more than 10 km with steep clinoforms of up to 35 and slope heights up to 650 m during the second phase corresponding to the moscovian picos de europa formation the platform aggraded mainly vertically nearly 850 m both phases of platform growth were terminated by major relative sea level lowstands in conjunction with local filling of the adjacent basins by shales and mudstones that onlap the platform flanks calibration with outcrops suggests a subdivision into the following lithofacies directly related to the depositional profile 1 platform interior parallel well to thick bedded skeletal pack to grainstones 2 margin algal and sponge dominated bioherms with little internal structure 3 slope clinothems of medium to thick bedded margin derived breccia beds 4 toe of slope alternating grain and packstones with spiculites and 5 basin marly shales shales sandstones and calcareous mudstones relative sea level changes caused by regional tectonic movements are suggested to be responsible for the generation of the two platform phases sea level highstands triggered the nucleation and growth of the platforms whereas major sea level lowstands in combination with terrigenous infill of the basins terminated the platform growth in addition it is proposed that the termination of late carboniferous carbonate platforms is caused by the combined effect of a sea level fall subaerial exposure and erosion and finally a rapid transgression that drowned and polluted the platform with shales and mudstones local variations in the infilling of the basins controlled the variations in the style of progradation the subsidence rates for the vertically aggrading phase picos de europa formation were approximately twice that for the progradational phase valdeteja formation and may explain the aggradational versus progradational character

triassic carbonate buildup flanks in the dolomites northern italy breccias boulder fabric and the importance of early diagenesis the flanks of middle triassic carbonate buildups in the dolomites show well developed clinostratification with typical angles of 30 40 this paper focuses on the metre scale fabric of these clinoforms and sets these within the context of their large scale and microscopic features clinoform stratification is caused by fibrous cement crusts by stylolites paralleling a vague stratification and by pelagic limestone interbedded with the lower portions of the clinoforms these parts of the clinoforms locally exhibit a boulder fabric a fracture system subvertical to clinostratification is filled by fibrous cements and marine internal sediment the analysis of clinoform fabric indicates that parts consist of in situ automicrite other parts of the clinoforms are made up of breccia the breccias occur as isolated pockets and lenses with random orientation and dimensions ranging from a few square decimetres to hundreds of square metres the breccias have gradual contacts with the unbrecciated host rock breccia components are mostly angular show a microfacies similar to that of the unbrecciated host rock and are composed of millimetre to decimetre sized particles that generally float in radiaxial fibrous cement matching grain boundaries are common calcite cement typically makes up 20 and 40 vol of the brecciated areas clinostratification the fracture system brecciation and boulder fabric point to gravity induced deformation of in situ flank deposits rather than gravity induced depositional processes brecciation appears to result from translational sliding millimetres to metres on the steep buildup flanks which caused fracturing of the vaguely stratified automicrite followed by displacive growth of fibrous cement cementation occurred in a shallow burial marine phreatic environment because cement clasts are virtually absent from the flank derived gravity flows in the adjoining basinal sediments displacive cement growth indicates a volume increase of the clinoforms during diagenesis of up to 20 40 vol and can account for the local drag of buildup interior limestones similarly the boulder fabric appears to be a diagenetic feature which resulted from differential settling of incompletely lithified boundstone and grainstone and the interbedded pelagic limestone

the chronostratigraphic significance of seismic reflections along the bahamas transect abstract continuous cores drilled during the bahamas drilling project bdp and the ocean drilling program odp leg 166 along a transect from the top of great bahama bank to the basin in the straits of florida provide a unique data set to test the assumption in seismic stratigraphy that seismic reflections are time lines and thus have a chronostratigraphic significance seismic reflections that are identified as seismic sequence boundaries ssbs were dated by means of biostratigraphy in the five odp sites and by a combination of biostratigraphy magnetostratigraphy and sr isotope stratigraphy in the two bdp sites the seismic reflection horizons are carried across a variety of facies belts from shallow water carbonates over slope carbonates to drift deposits in the straits of florida within this system 17 ssbs were identified and dated despite the fact that the seismic reflections cross several facies belts their ages remain remarkably constant the average offset in all sites is 0 38 myr in no cases do the seismic reflections cut across time lines the age differences are the combined result of the biostratigraphic sampling frequency the spacing of marker species that required extrapolation of ages and the resolution of the seismic data in addition uncertainties of age determination in the proximal sites where age diagnostic fauna are rare add to the age differences between sites therefore it can be concluded that the seismic reflections which mark the ssbs along the bahamas transect are time lines and can be used as stratigraphic markers this finding implies that depositional surfaces are preferentially imaged by reflected seismic waves and that an impedance contrast exists across these surfaces facies successions across the sequence boundaries indicate that the sequence boundaries coincide with the change of deposition from times of high to low sea level in the carbonate setting of great bahama bank sea level changes produce changes in sediment composition sedimentation rate and diagenesis from the platform top to the basin the combination of these factors generates differences in sonic velocity and thus in impedance that cause the seismic reflection the impedance contrasts decrease from the proximal to the distal sites which is reflected in the seismic data by a decrease of the seismic amplitude in the basinal area

sea level fall carbonate production rainy days how do they relate insight from triassic carbonate platforms western tethys southern alps italy the interplay of sea level fall climate and sedimentological changes is recorded across two sequence boundaries at the top of two triassic carbonate platform systems in the western tethys earliest carnian and norian rhaetian boundary in age paleolatitude 18 25 n the sea level falls caused subaerial exposure of the platform top and decreased carbonate production leading to starvation in the intraplatform basins followed by deposition of shale evidence of freshwater input indicates that the change in sedimentation was driven by increased rainfall on the previously arid european hinterland and tethys coast a uniformitarian approach holocene sea level changes and global warming are coupled with changes in the distribution of precipitation implicates global cooling as the probable cause of the observed sea level climate and sedimentological changes global cooling likely triggered the sea level fall by increased storage of fresh water in continental settings and change in seawater density probably coupled with ephemeral ice sheet development possible even during greenhouse intervals such as the triassic furthermore global cooling caused a shift toward the equator of the poleward boundary of the arid belt this model is supported by the traceability of the sequence boundaries and climate sensitive facies from the tethys shelf up to the european continent the observed association of global climate changes sea level fall sedimentological changes and shift toward humid climate documents how climate sensitive facies record the control exerted by global changes on local sedimentation

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

sedimentation in shallow to deep water carbonate environments across a sequence boundary effects of a fall in sea level on the evolution of a carbonate system ladinian carnian eastern lombardy italy in the concarena pizzo camino massif lombardy basin southern alps italy the lateral transition from ladinian carnian carbonate platforms to coeval intraplatform basins is preserved the succession records the sedimentological evidence of a sea level fall on a flat topped platform with a narrow marginal reef rim and its effects in the adjacent deeper water basin repeated high frequency exposures of the platform top are recorded by a peritidal supratidal succession that overlies subtidal inner platform facies of the former highstand system tract hst on the slope and in the basin the sea level fall is recorded by a few metre thick succession of bioclastic packstones these facies directly lie on coarse clinostratified breccia bodies slope facies of the former hst or on resedimented well bedded dark laminated limestones basinal facies of the hst this facies distribution indicates that during the sea level fall carbonate production on the platform top decreased rapidly and that sedimentation in the basin was mainly represented by condensed facies microfacies record an enrichment during low stand in pelagic biota packstones with radiolarians and spiculae whereas the occurrence of platform derived shallow water materials is limited to thin lenses of reworked and micritized fe rich oolites and bioclasts mainly pelecypods and echinoderms the facies association in the concarena pizzo camino massif demonstrates that a highly productive carbonate factory was almost completely turned off during the emergence of the platform top at a sequence boundary leading to low stand starvation in the basin the reconstruction of the stratigraphic evolution of the concarena pizzo camino carbonate platform therefore represents a significant case history for the study of the behaviour of ancient carbonate systems during a fall in sea level independent of its origin eustatic or tectonic

the geology of the kuh e dalneshin area of southern iran and its bearing on the evolution of southern tethys the kuh e dalneshin area lay close to the northern margin of the arabian continent during mesozoic and palaeogene times recent mapping has shown that except perhaps in the late cretaceous it was inactive until it collided with central iran in the miocene the collision represented by a neogene melange zone in the ne resulted in the zagros orogeny and is expressed in the shelf sediments by folding parallel faulting and a possible arcuate sinistral shear in the late cretaceous a localized deepening of the shelf dates from the cenomanian a narrow trough in the w subsided to abyssal depths in the turonian following a period of faulting a more wide spread subsidence affected the shelf in the coniacian and santonian autochthonous cherts and associated sediments accumulated basaltic volcanics were erupted in the ne part of this basin and permian to cenomanian neritic exotic blocks were derived presumably from an uplift at the shelf edge the rocks from the outer edge of this basin slid westwards over their autochthonous counterparts probably in the campanian accompanied by further gliding of masses of earlier mesozoic cherts which had previously been emplaced on the continental margin a sheet of mantle peridotite partly serpentinized and enclosing neritic and metamorphic exotics in turn slid into the basin shelf sedimentation was renewed in the late campanian or maestrichtian but the transgression did not reach the area until the eocene the derivation and emplacement of the allochthonous rocks in the late cretaceous are still imperfectly understood alternative models are discussed one involving gliding from an aborted spreading ridge along the continental margin the other more conventionally based on subduction processes a preference is expressed for the former

genesis of limestone megabreccias and their significance in carbonate sequence stratigraphic models a review a re appraisal of the factors controlling the deposition of carbonate megabreccias and their sequence stratigraphic significance is presented based on an examination of the mechanisms for instigating carbonate seafloor slope instability and a review of the depositional settings of these distinctive rock deposits limestone megabreccias have classically been interpreted as formed by the catastrophic collapse of high angle metastable oversteepened carbonate platform margins however a review of megabreccia occurrence shows that these deposits formed on a broad range of carbonate slope angles and that metastable oversteepened slopes are not necessary for their genesis a re evaluation constructed from first principles of mechanisms promoting submarine gravitational instability indicates that pore water overpressure of confined aquifer horizons beneath the seafloor rather than slope oversteepening is the critical control on megabreccia deposition catastrophic release of overpressure may initiate gravitational instability of previously kinematically stable slopes the relative importance of endogenic processes intrinsically linked to the depositional system and exogenic processes operating independently in generating megabreccias is assessed two particularly important mechanisms in generating megabreccias are endogenic processes causing overpressure at discrete hydrologically confined horizons beneath the seafloor during relative sea level falls and increases in stress as pore fluid drains from the sediment when the platform top becomes subaerially exposed during relative lowstands of sea level the increased likelihood of megabreccia genesis during relative sea level falls is supported by an empirical trend identified from a review of the stratigraphic distribution of documented megabreccias exogenic causes of gravitational instability with inherently random periodicity especially seismicity may account for the small number of documented megabreccias that do not conform to this underlying trend the proposed endogenic pattern favouring megabreccia deposition during relative sea level falls is important in a sequence stratigraphic context megabreccia deposits may build volumetrically significant toe of slope wedges and aprons during relative lowstands of sea level partially compensating for the decrease loss in the supply of fresh granular sediment as the platform top carbonate factory contracts lowstand wedges and aprons in carbonate systems therefore generally differ in composition from equivalent highstand deposits in being composed not of calciturbidite deposits but of megabreccias cannibalized from the upper slope

the role of early lithification in development of chalky porosity in calcitic micrites upper cretaceous chalks egypt abstract petrological and geochemical examination of upper cretaceous chalks from the abu roash area and bahariya oasis egypt provide insights into factors which control porosity development in fine grained calcitic carbonates petrological studies indicate that primary skeletal fabrics of coccoliths and foraminifera in micrites of abu roash are well preserved in contrast primary skeletal fabrics of the bahariya oasis chalks are pervasively altered geochemical analysis of these chalks reveals a striking contrast in composition the high porosity chalks at bahariya oasis have depleted isotopic values 13 c 5 0 18 o 8 9 pdb and low concentrations of trace elements sr and na in contrast the low porosity chalks at abu roash are less depleted in terms of their isotopic values 13 c 1 0 18 o 4 0 and possess elevated concentrations of sr na fe and zn importantly fracture and collapse veins present only at abu roash are filled with calcite whose 18o value is coincident with that of altered micrites at bahariya oasis the lithic fragments cemented by this calcite however retain compositions identical to other lithified limestones at abu roash differences in fabric and chemistry of the pelagic marine micrites observed between abu roash and bahariya oasis reflect the degree of early lithification and compaction prior to exposure and meteoric diagenetic alteration associated with regional late cretaceous pre eocene subaerial unconformity

exact expression for the effective acoustics of patchy saturated rocks seismic effects of a partially gas saturated subsurface have been known for many years for example patches of nonuniform saturation occur at the gas oil and gas water contacts in hydrocarbon reservoirs open pore boundary conditions are applied to the quasi static biot equations of poroelasticity to derive an exact analytic expression of the effective bulk modulus for partially saturated media with spherical gas patches larger than the typical pore size the pore fluid and the rock properties can have different values in the central sphere and in the surrounding region an analytic solution prevents loss of accuracy from ill conditioned equations as encountered in the numerical solution for certain input for a sandstone saturated with gas and water we found that the p wave velocity and attenuation in conventional models differ as much as 15 from the exact solution at seismic frequencies this makes the use of present exact theory necessary to describe patchy saturation although more realistic complex patch shapes and distributions were not considered we found that despite earlier corrections the white conventional model does not yield the correct low frequency asymptote for the attenuation