sedimentology and isotope geochemistry of carnian deep water marl limestone deposits from the sicani mountains sicily environmental implications and evidence for a planktonic source of lime mud abstract the upper triassic halobia bearing marl limestone deposits from the sicani mountains sicily record the sedimentary evolution of the sicanian basin through the middle and late carnian time dark marls and interbedded grey calcilutites of julian age are characterized by abundant pyrite sparse bioturbation and negative carbonate carbon 13c values they accumulated in a basin with dominantly anoxic to dysaerobic bottom waters lower tuvalian dark grey pyritic marls and calcilutites which contain carbonate minerals with relatively high mn contents and widely fluctuating 13c signatures were deposited under dysaerobic conditions middle and upper tuvalian cherty limestones show intense bioturbation and nearly invariable positive 13c values around 2 for calcite they form a thick and monotonous succession accumulated in a deeper and more oxygenated basin the halobia bearing deposits preserve some calcareous nannoplanktonic forms the nannofossils varying in size from 7 to 32 m are significantly abundant in the cherty limestones pointing to a notable role of the calcareous nannoplankton as a source of carbonate mud in the deep water basins of the southern tethys during the late triassic time

sedimentary pyrite formation an update sedimentary pyrite formation during early diagenesis is a major process for controlling the oxygen level of the atmosphere and the sulfate concentration in seawater over geologic time the amount of pyrite that may form in a sediment is limited by the rates of supply of decomposable organic matter dissolved sulfate and reactive detrital iron minerals organic matter appears to be the major control on pyrite formation in normal non euxinic terrigenous marine sediments where dissolved sulfate and iron minerals are abundant by contrast pyrite formation in non marine freshwater sediments is severely limited by low concentrations of sulfate and this characteristic can be used to distinguish ancient organic rich fresh water shales from marine shales under marine euxinic conditions sufficient h2s is produced that the dominant control on pyrite formation is the availability of reactive iron minerals calculations based on a sulfur isotope model indicate that over phanerozoic time the worldwide average organic carbon to pyrite sulfur ratio of sedimentary rocks has varied considerably high cs ratios during permo carboniferous time can be explained by a shift of major organic deposition from the oceans to the land which resulted in the formation of vast coal swamps at that time low cs ratios compared to today during the early paleozoic can be explained in terms of a greater abundance of euxinic basins combined with deposition of a more reactive type of organic matter in the remaining oxygenated portions of the ocean the latter could have been due to lower oceanic oxygen levels and or a lack of transportation of refractory terrestrial organic matter to the marine environment due to the absence of vascular land plants at that time

the modern carbonate ramp slope of central west florida abstract a holistic investigation of the modern carbonate ramp slope of central west florida has been completed via analysis of approximately 1 500 km of air gun seismic reflection profiles tied to two drillcores and bottom samples recovered at 92 stations our primary goal has been to characterize modern depositional processes and products to compare and contrast results with modern rimmed platform slopes and to develop a model for application to the rock record the modern depositional environment of the west florida ramp slope was initiated 12 15 ma when depositional style changed from seaward prograding clinoforms to a pelagic slope front fill system bound along the shelf margin by contour parallel flow of the loop current a seaward thickening wedge 0 250 m of late miocene to recent pelagic carbonate ooze has been deposited across antecedent mid miocene topography in general the sea floor dips 1 2 seaward from water depths of about 200 2 000 m and slopes are relatively smooth however contemporary submarine geomorphology is controlled in part by earlier slope failures the primary control of modern sedimentation along the west florida slope is loop current flow which acts as a dynamic oceanographic boundary between outer shelf and upper slope winnows bottom sediments catalyzes early submarine cementation and stimulates pelagic production of calcium carbonate the axis of loop current circulation has also migrated laterally in response to climatically controlled sea level fluctuations which has resulted in a relatively wide 25 km band of winnowed sands and hardgrounds along the shelf margin climatic oscillations have also resulted in cyclic deposition of pelagically derived aragonite pteropods on the ramp slope that is out of phase with bank derived aragonite cycles of rimmed platform slope there are three major facies belts that parallel modern isobaths 1 a hardground facies of intraclastic grainstones and rhodolith rudstones as well as algal ridges along the outer shelf at water depths of approximately 200 400 m 2 a winnowed sand facies of planktonic forams intraclasts glauconite and reworked phosphorite grains as well as deep water coral mounds along the shelf margin at depths of approximately 400 600 m and 3 a bioturbated pelagic ooze facies along the ramp slope at depths of approximately 600 2 000 m these facies patterns geometries and grain types along with a general paucity of sediment gravity flow deposits readily distinguish this carbonate ramp slope from better known rimmed platform slopes of the bahamas

paleomagnetism of jurassic to miocene sediments from the apenninic carbonate platform southern apennines italy evidence for a 60 counterclockwise miocene rotation abstract the tectonic evolution of the apennine belt southern tyrrhenian sea system is addressed through a paleomagnetic study of lias to langhian sediments from the apenninic carbonate platform southern apennines italy reliable paleomagnetic data gathered from 21 sites document a regional scale post langhian 80 counterclockwise ccw rotation since previous studies of the plio pleistocene clays spread over the orogen had shown a 20 ccw rotation we conclude that the southern apennines rotated by 60 during middle late miocene our data provide evidence that the southeastward drift of calabrian block and synchronous spreading of the southern tyrrhenian sea induced saloon door like deformation of the southern apennines and sicily which underwent similar magnitude although opposite in sign orogenic rotations a paleomagnetically derived paleogeographic reconstruction shows that at 15 ma late langhian the alpine apennine belt collided with a nne oriented carbonate platform corridor surrounded by oceanic basins we speculate that both the end of the corsica sardinia rotation and the eastward jump of the locus of back arc extension from the liguro provencal to the tyrrhenian sea may have been consequences of this event

origin dimensions and distribution of remobilized carbonate deposits in a tectonically active zone eocene thebes formation sinai egypt abstract determination of the distribution and mechanism for carbonate dominated mass transport sediments is often compromised by the scale and access to exposures consequently many studies lack the resolution to capture the heterogeneity and dimensions of mass transport deposits this study documents the size shape and stratal assemblage of remobilized carbonates in the eocene thebes formation in the hammam faraun fault block hffb of western sinai revealing the complexities of carbonate mass transport deposits at sub seismic scale present day pseudo three dimensional exposure of the thebes formation in a large fault block formed during the opening of the gulf of suez allowed for lateral and down dip measurement of slope and basinal facies in the field and from photos remobilized facies were digitized in the photos and evaluated using image analysis software a technique with a wide range of applications to outcrop studies of sedimentary architecture debris flow deposits in the lower section of the thebes formation comprises clasts with differing fossil assemblages a relative sea level rise at the start of upper thebes formation deposition resulted in basinal sediments comprising periodic incursions of high density turbidite grainstones encased within a background of planktonic foraminiferal wackestones foraminiferal assemblages of remobilized facies imply multiple sources on the carbonate platform demonstrating the effect of short lived tectonism on slope instability and deposition of mass transport deposits the results of the study confirm that tectonism associated with the syrian arc fold belt which altered the style of basin sedimentation between egypt and syria persisted into the eocene at least as far south as wadi araba in the western desert and hammam faraun in sinai in addition the shape size and extent of the two dominant remobilized facies debris flows and grainstone turbidites are influenced by their mud rich versus grainy compositions

controls on carbonate mineral accumulation in bahamian basins and adjacent atlantic ocean sediments abstract carbonate mineralogical studies of surface bahamian periplatform ooze containing pelagic calcite as well as bank derived aragonite and magnesian calcite were coupled with studies of the carbonate chemistry of the waters overlying these sediments the presence of metastable aragonite and magnesian calcite in the periplatform ooze presents a unique opportunity to assess the relation between the extent of carbonate saturation in the water column and the disappearance of metastable carbonate minerals in an area of the north atlantic ocean where intermediate and deep waters are saturated with respect to calcite aragonite is present in the fine fraction of the surface sediment to a water depth of 4 800 m but decreases sharply below 4 000 m this is also the depth limit of the occurrence of pteropod tests and fragments in the coarse fraction of the sediment the aragonite compensation depth should be by extrapolation between 5 000 and 5 200 m the saturation depth with respect to aragonite was estimated to be located between 3 800 and 4 500 m this corresponds fairly well with the depth of a sharp decrease of the fine aragonite as well as the depth of pteropod disappearance magnesian calcite in the fine fraction of the sediment decreases irregularly with depth and disappears between 3 700 and 4 000 m the calculated saturation depth with respect to magnesian calcite 13 mole mgco3 is between 900 and 1 500 m at this depth a significant drop in the concentration of magnesian calcite occurs this decrease of magnesian calcite from 25 to 15 percent could be caused by both dissolution and the increasing distance of deeper waters from the banks however the higher values of specific alkalinity of the waters ranging between 750 and 2 000 m when compared with the alkalinity values of the sargasso sea at the same latitude are interpreted to be indicative that some dissolution of magnesian calcite occurs in the bahamian basins at these water dept s our results show depressed levels by 500 m or more of the aragonite saturation depth in the water column as well as of the depth of aragonite disappearance in the surface sediment when compared with open ocean studies in the northwest atlantic in addition our results indicate that fine magnesian calcite 12 to 13 mole mgco3 disappears 1 200 to 1 500 m above the extrapolated disappearance depth of aragonite this observation is consistent with results for experimental studies showing that aragonite is more stable in seawater than a magnesian calcite of 12 to 13 mole mgco3

structures and mechanisms associated with development of a fold in the cantabrian zone thrust belt nw spain a detailed history of progressive fold development based on mesostructural analysis is provided for a metre scale fold in the cantabrian fold and thrust belt of northwestern spain the well exposed asymmetric syncline displays a wide variety of structures including extensional faults thrusts veins tectonic stylolites bedding plane faults drag folds and a main limb thrust that transects the entire fold important constraints on fold development are provided by the spatial distribution and style of deformation angular relations and cross cutting relations among the structures fold mechanisms varied as a function of structural position while the northwest limb was subjected to pure shear shortening in the form of contractional faults the southeast limb was bent under tangential longitudinal strain resulting in a combination of outer arc extensional faulting in

grain size variations in pelagic carbonate oozes from the walvis ridge se atlantic ocean odp site 1265 a low resolution miocene record of carbonate sedimentation and preservation abstract a record of variations in winnowing and dissolution was established for miocene 19 7 ma deep sea sediments at site 1265 from the walvis ridge south atlantic in this study we apply a new preservation index based on the abundance of coarse calcareous silt fraction 10 63 m the miocene record of this silt preservation index corresponds well with the conventional foraminiferal preservation index and variations in sand content preservation ranging from good to moderate during the miocene indicates that site 1265 is located above and close to the foraminiferal lysocline grain size mass accumulation rates of carbonate and organic carbon records indicate that changes in productivity and carbonate production play a minor role in variations of calcium carbonate concentration the miocene variation in carbonate content is caused mostly by a combination of winnowing and dissolution significant decreases of preservation at 17 3 16 3 13 8 13 0 11 6 and 10 4 ma coincide with miocene glacial events mi events suggesting that dissolution was caused by an increase of southern component water scw influence which occurred as a response to the intensification of antarctic ice sheet development the scw acts as the major deep water source during the global miocene cooling at 10 4 ma a change to overall better preservation points to a weakening of scw that occurred as a response to the initiation or strengthening of north atlantic deep water nadw

segmentation and configuration of subducted lithosphere in italy an important control on thrust belt and foredeep basin evolution the apennine foredeep basin system located on continental crust consists of four roughly parallel basin segments each containing a flexural outer rise and an inner trough that deepens continuously toward the thrust belt flexural modeling of subsidence data across the basin indicates that this foredeep basin results mainly from deep subsurface loads acting on the subducted slab from within the subduction zone rather than from the topographic load of the apennine mountains the geometry of the four basin segments observed within the apennine foredeep is thus inferred to reflect subduction of segmented lithosphere where each lithospheric segment corresponds to a segment of the foredeep basin beneath the basin and in the foreland the lithosphere is continuous segmentation occurs only at depth beneath the thrust belt this pattern olf segmentation of the subducted lithosphere at depth is reflected in the large scale geometry of the outer part of the apennine thrust belt and appears to control it similarly the pattern of segmentation also appears to control the position of the eastern limit of back arc type extension in western italy these relations strongly suggest a genetic relation between subduction zone processes foredeep basin geometry and thrust belt evolution in which the configuration of the subducted lithosphere largely controls the large scale surface deformation observed in the apennine system

formation processes of framboidal pyrite abstract pyrite framboid formation may be the result of four consecutive processes 1 nucleation and growth of initial iron monosulfide microcrystals 2 reaction of the microcrystals to greigite fe 3 s 4 3 aggregation of uniformly sized greigite microcrystals i e framboid growth and 4 replacement of greigite framboids by pyrite the uniform morphology uniform size range and ordering of the microcrystals in individual framboids as well as the range of observed framboid structures from irregular aggregates to densely packed spherical aggregates and polyframboids are consequences of these processes using dlvo theory derjaguin landau verwey and overbeek we have evaluated the stability of colloidal iron monosulfide suspensions with ionic strengths typical of marine and lacustrine waters in addition to van der waals attractive and double layer repulsive forces a term is included to account for the ferrimagnetic properties of greigite numerical models predict that magnetically saturated greigite particles 0 1 m in diameter will rapidly aggregate in either marine or fresh water the aggregation model is in agreement with the sequence of greigite formation followed by pyrite framboid formation established in a previous experimental study sweeney and kaplan 1973 and is consistent with the occurrence of framboids composed of other magnetic minerals e g greigite magnetite and magnesioferrite based on the temperature dependent magnetic properties of greigite and aging experiments in hydrothermal solutions this mechanism for framboid formation via precursor greigite could operate to temperatures of 200 c consistent with the occasional occurrence of pyrite framboids in the paragenesis of metalliferous ore deposits

deep water asymmetric cycles and progradation of carbonate platforms governed by high frequency eustatic oscillations triassic of the dolomites italy the basinal san cassiano formation triassic dolomites italy is interfingered with clinostratified megabreccia slope deposits of coeval carbonate platforms and to a large extent is composed of metre scale thickening coarsening upward cycles these asymmetrical cycles often representing bundles of five coarsening upward sequences are interpreted as platformbasin interactions governed by fourth and fifth order eustatic oscillations according to this model progradation of triassic platforms of the dolomites occurred mainly during fourthorder sea level lowstands

silica burp in the eocene ocean the eocene was a time of greatly increased silica accumulation in the ocean and the peak was in the early middle eocene at about 50 ma the responsible geohistorical configuration included the following elements extensive volcanism about 4 m y earlier as part of the chron 24 plate reorganization early eocene warming with deep weathering to high latitudes and accumulation of the released silica in a sluggish ocean and sharp cooling in the earliest middle eocene stimulating oceanic upwelling and biosilicification it is possible on the evidence of carbon and oxygen isotopic patterns that the trigger for the exhalation of silica was a reverse greenhouse effect

kinetics of pressure solution at halite silica interfaces and intergranular clay films pressure solution is widely regarded as a potentially important deformation mechanism along crustal faults and during aliagenesis yet the mechanisms and kinetics of this process remain highly controversial to better understand the fundamental factors controwing the rates of pressure solution at the grain to grain scale we conducted experiments in which convex halite lenses were pressed against fiats of fused silica in brine fluid pressures were maintained at 0 1 mpa temperatures and mean contact normal stresses ranged from 8 3 o to 90 2oc and 0 5 to 13 5 mpa respectively the geometry and growth rate of the contact spot between the two lenses and the rate at which the lenses approached one another convergence were monitored using reflected light interferometry and transmitted light photomicrography convergence occurred when halite and silica lenses were pressed together in brine halite silica experiments no undercutting was observed and dry control experiments indicated negligible dislocation creep convergence rates in experiments at 50 2oc ranged from 0 01 to 0 05 m d depending on mean normal stress and contact spot radius the data are consistent with intergranular pressure solution ips rate limited by diffusion through an intergranular film with a very high diffusion coefficient 10 5 10 7 cm2 s the data further suggest that the diffusion coefficient and or thickness of this film increases with decreasing normal stresses at least for normal stresses less than about 4 mpa as no island channel boundary structures were observed we propose that this film consists of a continuous layer of strongly adsorbed i e structured water that is maintained between the halite and silica lenses during deformation convergence rates in similar experiments conducted at a constant load of 0 11 n but at 8 3 o 50 2 o and 90 2oc were approximately constant at a given normal stress and contact spot size the cause of this temperature insensitivity is unknown but might result from changes in interphase boundary structure or thickness with increasing temperature that are sufficient to offset the expected thermal activation an experiment was also conducted in which a halite lens was pressed against a fused silica fiat coated with an 0 8 m thick film of na montmorillonite in brine this clay film produced an approximately fivefold increase in convergence rates over those observed in a halite silica experiment conducted without clay at the same load and temperature the strong sensitivity of ips rates both to contact spot radius and to the presence of second phases along grain boundaries suggests that fine grained clay rich fault gouges and multiphase granular aggregates should be particularly susceptible to pressure solution creep in the middle to upper crust

stress field fluctuations along the dead sea rift since the middle miocene the dead sea transform dst is the suture between the african and the arabian plates both of which subduct northward under the eurasian plate the collision of these plates with eurasia and their relative motion are the source for their internal deformation especially in the vicinity of the dead sea transform geological observations indicate that two distinct paleostrain regimes operated adjacent to the dead sea rift and in the sinai israel subplate 1 wnw shortening less than 10 and nne extension beginning in the turonian is associated with the development of the syrian arc fold belt and attributed to the syrian arc stress field sas and 2 middle miocene to recent nnw shortening and ene extension associated with the 105 km sinistral displacement along the dead sea transform and the opening of the red sea is attributed to the dead sea stress field dss it was originally suggested that the sas terminated during the middle miocene with initiation of the dss however trend and age analysis of many structures shows that formation of sas compatible structures continued after the middle miocene up to the recent in some middle miocene and younger rocks structures such as faults dikes volcanic lineaments and tectonic stylolites compatible with both stress fields were reported in a few locations structures compatible with both stress fields crosscut each other it is suggested that the movements which resulted in the development of the syrian arc and other sas compatible structures are continuing to the recent and that dss movements are superimposed upon them the overlapping of sas and dss structures adjacent to the dst results from spatial and temporal fluctuations in the overall stress state we propose that such variations could be caused by the superposition of large earthquake stress drops associated with movements along the dst on a steady background plate scale stress regime associated with the sas thus dss compatible structures should form in preseismic activity periods when dst related elastic strain is high on the other hand the sas compatible structures should form during interseismic activity times subsequent to large local stress release along the dst

a preliminary experimental study of turbidite fan deposits we present preliminary laboratory experimental results that demonstrate lobe switching in a turbidite fan after a significant number of individual event beds more than eight in both experimental fans made in this study the flow began to focus itself into a lobe at the center of which appeared a subtle channel form initial lobe switching occurred after nearly twenty event beds subsequent switching appeared to scale with lobe size and sedimentation rate the densest coarsest runs tended to initiate the switching of the depocenter instabilities within the turbidity current itself appear to be responsible for initial flow confinement to a lobe and ultimate switching events currently untreated scale effects and measurement difficulties limit quantitative extension of the results to natural settings though some general relationships are proposed

enhanced productivity led to increased organic carbon burial in the euxinic north atlantic basin during the late cenomanian oceanic anoxic event 1 three cenomanian turonian c t 93 5 ma black shale sections along a northeast southwest transect in the southern part of the proto north atlantic ocean were correlated by stable carbon isotope stratigraphy using the characteristic excursion in 13c values of both bulk organic matter om and molecular fossils of algal chlorophyll and steroids all three sites show an increase in marine organic carbon oc accumulation rates during the c t oceanic anoxic event oae the occurrence of molecular fossils of anoxygenic photosynthetic green sulfur bacteria lack of bioturbation and high abundance of redox sensitive trace metals indicate sulfidic conditions periodically reaching up into the photic zone before as well as during the c t oae during the c t oae there was a significant rise of the chemocline as indicated by the increase in concentrations of molecular fossils of green sulfur bacteria and mo al ratios the presence of molecular fossils of the green strain of green sulfur bacteria indicates that euxinic conditions periodically even occurred at very shallow water depths of 15 m or less during the c t oae however bottom water conditions did not dramatically change as indicated by more or less constant v al and zn al ratios at site 367 this suggests that the increase in oc burial rates resulted from enhanced primary productivity rather than increased anoxia which is supported by stable carbon isotopic evidence and a large increase in ba al ratios during the c t oae the occurrence of the productivity event during a period of globally enhanced organic carbon burial rates i e the c t oae points to a common cause possibly related to the formation of a deep water connection between north and south atlantic basins

carbonate apron models alternatives to the submarine fan model for paleoenvironmental analysis and hydrocarbon exploration sediment gravity flow deposition along the deep water flanks of carbonate platforms typically does not produce submarine fans rather wedge shaped carbonate aprons develop parallel to the adjacent shelf slope break the major difference between submarine fans and carbonate aprons is a point source with channelized sedimentation on fans versus a line source with sheet flow sedimentation on aprons two types of carbonate aprons may develop along relatively gentle 4 platform margin slopes aprons form immediately adjacent to the shallow water platform and are referred to as carbonate slope aprons along relatively steep 4 15 platform margin slopes redeposited limestones accumulate in a base of slope setting by passing an upper slope via a multitude of small submarine canyons and are referred to as carbonate base of slope aprons both apron types are further subdivided into inner and outer facies belts inner apron sediments consist of thick mud supported conglomerates and megabreccias facies f as well as thick coarse grained turbidites facies a interbedded with subordinate amounts of fine grained peri platform ooze facies g outer apron sediments consist of thinner grain supported conglomerates and turbidites facies a as well as classical turbidites facies c with recognizable bouma divisions interbedded with approximately equal proportions of peri platform ooze facies g seaward aprons grade laterally into basinal facies of thin base cut out carbonate turbidites facies d that are subordinate to peri platform oozes facies g carbonate base of slope aprons grade shelfward into an upper slope facies of fine grained peri platform ooze facies g cut by numerous small canyons that are filled with coarse debris as well as intraformational truncation surfaces which result from submarine sliding in contrast slope aprons grade shelfward immediately into shoal water platform margin facies without an intervening by pass slope the two carbonate apron models presented here offer alternatives to the submarine fan model for paleoenvironmental analysis and hydrocarbon exploration for mass transported carbonate facies

organic matter oxidation in deep sea sediments distribution in the sediment column and implications for calcite dissolution abstract this study uses pore water profiles of no3 and o2 from 34 deep sea study sites from five oceanic regions encompassing broad ranges of sediment composition and organic matter oxidation rate to analyze the depth distribution of organic matter oxidation within the sediment column while the results are consistent with those of hammond et al 1996 and hales 2003 the broader range of environmental variables considered in this study allows us to show that the depth of oxidation varies systematically with the integrated sedimentary organic matter oxidation rate the scale length for oxidation varies from large values of about 4 cm when the organic matter oxidation rate is 5 mol cm2 y to about 0 35 cm at oxidation rates above 20 mol cm2 y we have included this variability of organic matter oxidation depth in models of calcite dissolution our results show that variations in oxidation depth at a constant degree of supersaturation may result in changes in metabolic dissolution efficiency that are similar in magnitude to those resulting from basin wide variations in the degree of supersaturation with respect to calcite the model shows that when the ratio of sedimentary organic matter oxidation rate to calcite rain rate is held fixed at 0 8 mol mol metabolic dissolution is likely to be significant at all bottom water saturation levels and may result in dissolution of up to 50 of the calcite rain at the calcite saturation horizon

sand rich turbidite system of the late oligocene northern apennines foredeep physical stratigraphy and architecture of the macigno costiero coastal tuscany italy

carbonate turbidites in a mesozoic pelagic basin scaglia formation apennines comparison with siliciclastic depositional models abstract in the central apennines during most of the mesozoic a carbonate platform shed detrital material that was discharged by turbidity currents into an adjacent basin a sedimentological study of these detrital bodies has revealed that the depositional fan models largely applied to siliciclastic turbidites are not appropriate for carbonate turbidites the downslope succession of carbonate and siliciclastic facies and deposits are similar in a general way but carbonate turbidites do not appear to be organized into fan bodies apenninic calcarenite turbidites constitute sedimentary bodies 10 20 m thick are elongated more than 40 km along strike and are less than 10 km across such a shape is not consistent either with that of a hemicircular fan or with an ellipsoidal suprafan lobe morphology it suggests instead a kind of submarine piedmont debris sheet or a debris apron the different areal distribution of carbonate turbidites versus siliciclastic ones seems to be caused by a differences in composition scaglia turbidites are very poor in mud and the turbidity currents which had low transport efficiency deposited detritus abruptly at the end of the slope and had no opportunity to disperse sediments over wide areas b differences in feeding system carbonate detritus was not supplied by one large channel but rather from many small channels along the platform margin discrete turbidity currents deposited sediment at the base of the slope producing small deposits that coalesced to form a debris apron and c tectonic control a synsedimentary fault system occasionally rejuvenated the escarpment preventing the development of a large sedimentary body the final morphology was controlled more by tectonics than by sedimentation

anatomy of a submarine channel system and related fan in a foramol rhodalgal carbonate sedimentary setting a case history from the miocene syn rift sardinia basin italy abstract during aquitanian burdigalian times thick mixed carbonate siliciclastic successions were deposited in basins located on the grabens and half grabens along the oligo miocene sardinia rift basin locally active tectonics sea level variations and ecological factors combined to control the development and distribution of foramol carbonate factories as well as the remobilisation and the redeposition of carbonate sediments into the adjacent deeper areas in the isili basin foramol rhodalgal carbonate factories developed on submerged structural highs which resulted from pre and syn sedimentary tectonics these carbonate factories were periodically shaved mainly during negative sea level oscillations and the sediments removed were funnelled towards the basin through a complex submarine channel network which included a tributary belt one main channel isili channel and the related fan the isili channel is up to 1 km wide 60 100 m deep and includes two stacked channel complexes each built up by several minor order channel units complex strata geometries characterise the isili channel and its related architectural elements e g overbank levee margin and channel thalweg which also include up to 15 m high bedforms individual channel complexes were temporally related to individual fan systems whose spatial distribution and internal geometry were strongly controlled by the type and rate of sediment accumulation and in turn by relative sea level oscillations facies associations include sandy to cobble sized gravity flow and bottom current deposits as well as megabreccias characterised by impressive displaced and tilted blocks which resulted from major channel margin collapses detailed analysis has led to the reconstruction of the internal geometry and depositional architecture of these carbonate bodies and to the determination of the main controlling factors the dimension and distribution of channel and channel related depositional bodies have been accurately determined this information provides a useful tool to analyse less extensively exposed analogues and to model foramol shelf to basin transitions and related channel and fan systems

stratigraphy and depositional setting of slurry and contained reflected beds in the marnoso arenacea formation langhian serravallian northern apennines italy this work presents the stratigraphy and facies analysis of an interval of about 2500 m in the langhian and serravallian stratigraphic succession of the foredeep turbidites of the marnoso arenacea formation a high resolution stratigraphic analysis was performed by measuring seven stratigraphic logs between the sillaro and marecchia lines 60 km apart for a total thickness of about 6700 m the data suggest that the stratigraphy and depositional setting of the studied interval was influenced by syndepositional structural deformations the studied stratigraphic succession has been subdivided into five informal stratigraphic units on the basis of how structurally controlled topographic highs and depocentres a consequence of thrust propagation change over time these physiographic changes of the foredeep basin have also been reconstructed through the progressive appearance and disappearance of thrust related mass transport complexes and of five bed types interpreted as being related to structurally controlled basin morphology apart from bouma like type 4 beds type 1 tripartite beds characterized by an internal slurry unit tend to increase especially in structurally controlled stratigraphic units where intrabasinal topographic highs and depocentres with slope changes favour both mud erosion and decelerations type 2 beds with an internal slump type chaotic unit characterize the basal boundary of structurally controlled stratigraphic units and are interpreted as indicating tectonic uplift type 3 beds are contained reflected beds that indicate different degrees of basin confinement while type 5 are thin and fine grained beds deposited by dilute reflected turbulent flows able to rise up the topographic highs the vertical and lateral distribution of these beds has been used to understand the synsedimentary structural control of the studied stratigraphic succession represented in the marnoso arenacea formation by subtle topographic highs and depocentres created by thrust propagation folds and emplacements of large mass transport complexes

tectono sedimentary constraints to the oligocene to miocene evolution of the peloritani thrust belt ne sicily abstract the peloritani thrust belt belongs to the southern sector of the calabrian arc and is formed by a set of south verging tectonic units including crystalline basement and sedimentary cover from the top aspromonte u mela u mandanici u fondachelli u longi taormina u piled up starting from late oligocene at least two main terrigenous clastic formations lie with complicated relationships on top of the previous units the frazzano fm oligocene and the stilo capo d orlando fm late oligocene early miocene as syn to post tectonic deposits these clastic deposits have different characteristics in space and time representing or flysch like sequences involved in several thrust events frazzano fm or molassic like sequences stilo capo d orlando fm which unconformably overlie the tectonic units in the present paper we describe a kinematic model of the progressive foreland migration of the peloritani thrust belt starting from oligocene carrying piggy back basins and incorporating foredeep deposits recognised in the frazzano stilo capo d orlando terrigenous successions in general the facies and structural observations on the overall oligo miocene clastic sequences outcropping in the western peloritani mts indicate a the distal character of the frazzano fm b a complex group of terrigenous facies of the stilo capo d orlando fm with lateral to vertical organisation characterised by a distal to proximal to distal facies trend c facies analogies of the basal portions of the stilo capo d orlando fm with the frazzano fm d the involvement of the frazzano fm in lowermost and more external thrusting and of the basal late oligocene distal stilo capo d orlando facies in the higher and inner thrusting during the early stages of deformation e the involvement of the proximal stilo capo d orlando facies in the tectonic edifice during the early miocene deformation f the generally unconformable stratigraphical contacts of the higher proximal to distal early miocene stilo capo d orlando facies on the constructing mobile belt and g the presence of various thrust faults distinguished in a sequential order the collected data allow us to hypothesise that the oligo miocene tectono sedimentary history was characterised by a foredeep with a deforming internal flank probably lying in onlap on the constructing tectonic edifice frazzano lower stilo capo d orlando fms and then deformed and covered by a piggy back like sequence middle upper stilo capo d orlando fm which was subsequently also deformed the tectono sedimentary evolution of the peloritani belt has been probably developed through a progressive migration towards the foreland of a foredeep compressional front couple and the chain body the thrust stack progressively incorporates terrigenous foredeep deposits and in turn carried piggy back basins

paleomagnetic and structural evidence for neogene block rotations in the central apennines italy magnetic fabric and paleomagnetic analyses on sedimentary sequences in several structural units in the central apennines ranging from upper cretaceous pelagic carbonates to upper miocene turbidites provide evidence for at least two distinct phases of rotation the first counterclockwise ccw rotation is well recorded in eocene oligocene sediments and does not affect the lower middle miocene sequences the second phase is clearly recorded in lower middle and upper miocene sediments and shows both ccw and clockwise cw rotations in concordance with trends of the different thrust structures we detected three domains characterized by different rotation patterns the westernmost is the southern sabina area an arcuate thrust belt which underwent a cw rotation after the early miocene the second domain is the latium abruzzi carbonate platform where a ccw rotation occurred after the late miocene the third is the marsica area that underwent a cw rotation after the late miocene the magnetic fabric analyses confirm the existence of these different structural provinces and show a strong correlation between the present day strike of the anisotropy of magnetic susceptibility magnetic lineation and the rotations recorded in miocene sediments we attribute present day variations in orientation of the compressional structures in the central apennines to differential rotations about vertical axes due to strike slip faults and out of sequence thrust activity rather than to a change in the stress field orientation we also suggest that this deformation mechanism could be common in other collisional chains around the world

bio retexturing early diagenetic fabric modifications in outer ramp settings a case study from the oligo miocene of the central mediterranean abstract bioturbation is ubiquitous in cenozoic outer ramp settings the oligo miocene ramp carbonate sequences of se sicily and the maltese islands provide specific examples to illustrate the effects of sediment retexturing by burrowers and provide significant conclusions which must be taken into account by sedimentologists when interpreting palacoenvironments thalassinoidean burrow systems may penetrate several metres into the underlying beds with evidence of concentrated activity at selected levels the general intra bed process of this crustacean dominated bioturbation is well documented however the effects when several beds are involved can be dramatic 1 a buried homogeneous wackestone beds can be depleted in lime mud by gallery excavation the dumping of this mud at the sediment surface leads to lime mud enrichment of the contemporary accumulating layer and might be a major factor in the development of the tabular outer ramp bedforms 2 b vertical reworking of unlithified sediment between beds both upwards and down is capable of homogenising two distinctly dissimilar lithologies producing a third which in no way reflects the surface processes of the depositional setting 3 c bioturbation often continues during incipient near seafloor lithification this produces random lateral variations in lithology within single beds the degree of lateral dissimilarity is proportional to the intensity longevity of the bioturbation episode bio retexturing destroys primary depositional fabrics and masks inorganic process related structures it can be as effective a remodelling agent as tidal energy it can texturally remodel areas of high primary permeability into irregular interconnected zones of low permeability as the outer ramp provides a potential fluid migration route from basin to shallow water clearly bio retexturing must exert a major influence on longer term formation wide diagenetic processes

a point sourced calciclastic submarine fan complex eocene anotz formation western pyrenees facies architecture evolution and controlling factors a complete transect of a fossil carbonate ramp slope has been reconstructed using outcrop data from the lower middle eocene anotz formation in the western pyrenees the anotz formation contains four calciclastic mostly bioclastic members encased within hemipelagic marl limestone alternations each calciclastic member representing a submarine fan system individual fans are composed of a gullied upper slope a leveed feeder channel a channelized lobe area an unconfined lobe zone and a peripheral lobe fringe that grades downcurrent into basinal deposits quantitative data on the dimensions and degree of lateral continuity and vertical connectivity of the anotz calciclastic fan elements are presented these data provide information for a better understanding of the intrinsic nature of calciclastic submarine fans and to model their reservoir potential the long term evolution of the anotz carbonate slope was generally progradational as evidenced by the four discrete episodes of calciclastic fan development the location of the fans was controlled by the synsedimentary tectonic activity of the pamplona fault which created a slope valley along which the reworked shallow water calciclastic sediments were funnelled in addition episodic basinward tilting of the shallow water carbonate ramp linked to the development of the south pyrenean foreland basin switched on and off the process of calciclastic resedimentation and determined the growth or abandonment of the fan systems

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

a diagenetic study of intrabasaltic siliciclastics sandstones from the rosebank field abstract the rosebank field contains producible hydrocarbons from paleocene eocene intrabasaltic fluvial and shallow marine siliciclastic sandstone reservoirs despite close proximity to volcanic lithologies the siliciclastic sandstones display very good reservoirs properties with permeability in the darcy range and porosity values ranging from 19 to 23 preservation of high quality reservoir properties is the result of low quantities of volcanic minerals in the siliciclastic sandstones and limited element diffusion e g fe and mg from adjacent basalts into siliciclastic reservoir sandstones the low content of volcanic derived detritus is most likely a result of the main sediment source being situated outside the volcanic terrain the effect is that formation of clay minerals smectites and or chlorites reducing permeability and porosity is low in contrast to the siliciclastic sandstones the pore space of the volcaniclastics is occupied by authigenic clays chlorite smectite and carbonates calcite and mg calcite resulting in poor reservoir quality this paper demonstrates that high quality reservoirs can be found in intrabasaltic siliciclastic reservoirs in depth analyses of core samples show that authigenic phases formed during progressive burial with temperatures up to 120 c the suite of diagenetic phases in siliciclastic sandstones between wells and the different colsay units vary and are interpreted to result from differences in pore water chemistry and or detrital mineralogy laumontite was formed as a late stage authigenic mineral restricted to cored colsay 1 and 3 units in well 213 26 1z and has not been observed in the neighbouring 213 27 2 core which may be explained by differences in pore water ph or co2 partial pressure the occurrence of laumontite is often associated with poor reservoir quality but due to the patchy distribution of this mineral in the rosebank reservoir sands it appears not to have affected reservoir quality

influence of mica surfaces on pore water ph abstract the close spatial association of detrital biotite with diagenetic carbonate prehnite or laumontite is attributed to attraction of h to the mica surface resulting in an increase in pore water ph and stabilization of carbonate or calcium aluminosilicates in the adjacent pore space experimental results at 25 c with biotite and muscovite show that in the ph range of 10 4 biotite adsorbs h whereas muscovite does not adsorb h until ph is less than 6 5 for 0 01 m nacl solutions or less than 5 8 for 0 5 m nacl solutions increasing salinity reduces the h affinity of the micas at seawater type salinities 0 5 m nacl biotite is still capable of adsorbing from 1 10 5 mol h g ph 7 to 2 10 5 mol h g ph 6 during late stage diagenetic compaction if iotite pore fluid ratios are high this effect can substantially raise pore fluid ph biotite may also have an inherited net negative charge in the framework or develop such a charge by incongruent loss of k from cleavage surfaces the theoretical cation distribution adjacent to such a charged surface has been evaluated by the guoy chapman double layer theory calculations show that within 10 a of the biotite surface ph can be several orders of magnitude lower than in the bulk fluid and na ca 2 ratios may be more than three times higher than the bulk fluid

eustatic control of calciclastic turbidites abstract global changes in sea level can be recognized in seismic sections by establishing the relationship between sea level changes and the timing of potential deep sea carbonate reservoir facies of turbidity current and debris flow origin their occurrence may be predicted prior to drilling compilation of published data suggests that throughout the phanerozoic most calciclastic turbidites tend to correspond to lowering episodes of sea level calciclastic turbidites therefore should occur primarily in association with major uncorformities caused by lowstands of sea level the data also suggest a possible lowstand of sea level during the late cretaceous campanian maastrichtian

influence of pore fluid chemistry on the state of stress in sedimentary basins in order to accommodate growth of a grain an equivalent volume of the surrounding material must be removed by deformation displacement or diffusion under certain conditions of stress fluid pressure and pore fluid saturation the process known as pressure solution can occur in reverse the grains moving apart as solute diffuses into the grain contacts and precipitates there in this paper the horizontal stress required to prevent lateral spreading of a rock due to reverse pressure solution is shown to be equal to the fluid pressure plus an extra term dependent on the saturation level of the pore fluid results of numerical modeling suggest that the contribution of this term can be significant equivalent to the horizontal stress required to resist expansion due to overpressure such interaction between chemistry and stress may have significant consequences for the stress state within sedimentary basins

an analysis of the roles of stress temperature and ph in chemical compaction of sandstones discussion in a recent article on chemical compaction of sandstones sheldon et al 2003 claim that models of quartz cementation based upon the diffusional transport of dissolved silica originating from the clay induced dissolution cid of quartz at stylolites are untenable because no chemical driving force is available to drive silica diffusion in the aqueous phase as examples of such untenable models they cite a number of our papers oelkers et al 1992 1996 walderhaug 1994 bjorkum 1996 bjorkum and nadeau 1998 bjorkum et al 1998 walderhaug et al 2001 in the following discussion of their paper we will demonstrate that there is indeed a driving force for aqueous silica diffusion within the cid quartz cementation model and point out several flaws in the sheldon et al 2003 treatment of quartz dissolution at stylolites contrary to the claims of sheldon et al 2003 the quantitative models of quartz cementation presented in oelkers et al 1992 1996 walderhaug 1994 1996 and bjorkum et al 1998 do not claim to present nor do they depend upon a detailed understanding of the mechanisms of quartz dissolution at stylolites these models are based upon an overwhelming number of petrographic observations indicating that 1 quartz dissolution in quartzose sandstones occurs predominately at quartz clay and quartz mica interfaces clay induced dissolution cid and 2 this enhanced quartz dissolution requires negligible stress see bjorkum 1996 the actual mechanism which increases quartz solubility at these interfaces is unclear it may result from an electrostatic interaction between quartz and clay mineral mica surfaces but this has yet to be demonstrated unambiguously nevertheless just as newton s law of gravitation enables useful calculations without providing insight into the underlying causes of gravity these quartz cementation models provide accurate predictions of quartz cement volumes in quartzose

stratigraphic architecture and gamma ray logs of deeper ramp carbonates upper jurassic sw germany abstract the objective of this paper is to contribute to the development of sequence stratigraphic models for extensive epicontinental carbonate systems deposited over cratonic areas epicontinental carbonates of the sw german upper jurassic were analysed in terms of microfacies sedimentology and sequence stratigraphy based on 2 5 km of core 70 borehole gamma ray logs and 24 quarries facies analysis revealed six major facies belts across the deeper parts of the carbonate ramp situated generally below fair weather wave base and mostly below average storm wave base but in the reach of occasional storm events observed stratigraphic patterns differ in some aspects from widely published sequence stratigraphic models 1 elementary sedimentary cycles are mostly more or less symmetrical and are thus referred to as genetic sequences or genetic units aaapg bull 55 1971 1137 frazier d e 1974 depositional episodes their relationship to the quaternary stratigraphic framework in the northwestern portion of the gulf basin university of texas austin bureau of economic geology geologicalo circular 71 1 aapg bull 73 1989 125 galloway w e hobday d k 1996 terrigenous clastic depositional systems 489 pp springer cross t a baker m r chapin m s clark m s gardner m h hanson m s lessenger m a little l d mcdonough k j sonnenfeld m d valasek d w williams m r witter d n 1993 applications of high resolution sequence stratigraphy to reservoir analysis edition technip 1993 11 33 bull cent rech explor prod elf aquitaine 16 1992 357 homewood p mauriaud p lafont f 2000 best practices in sequence stratigraphy elf ep mem 25 81 pp homewood p eberli g p 2000 genetic stratigraphy on the exploration and production scales elf ep mem 24 290 pp in contrast to the asymmetrical shallowing upward parasequences of the exxon approach 2 neither sequence boundaries nor maximum flooding surfaces could be clearly delineated cycle boundaries are generally not represented by sharp stratal surfaces but are always transitional and thus referred to as turnarounds nor pet soc spec publ 8 1998 171 several types of genetic sequences were delineated both major types of facies and sequences show characteristic gamma ray log signatures based on the cycle stacking and the gamma ray patterns a hierarchy of sequences was recognized probably driven in part by 100 000 and 400 000 year milankovitch signals the cyclicity allowed regional correlations across various depositional environments such as sponge microbial bioherms and coeval basins the basin wide correlation revealed evidence for a subtle clinoform type stratigraphic architecture along very gentle slopes rather than a so far assumed simple layer cake pattern

effects of ocean chemistry sea level and climate on the formation of primary sedimentary manganese ore deposits the mineralogy geochemistry and in some cases the mode of origin of many phanerozoic sedimentary manganese orebodies are fairly well known but the effects of the important variables represented by changing ocean chemistry sea level and climate on ore formation are only recently being considered the high degree of mobility of manganese particularly through redox processes insures that it can change phase during weathering transport deposition and diagenesis during chemical weathering manganese is solubilized in acid reducing conditions and carried in surface and subsurface waters to the coastal zone where many of the exploitable deposits can form in slightly reducing carbonate ores to oxidizing conditions oxide ores rainfall controls ground water acidity through fostering vegetation growth major deposits at groote eylandt australia and the extensive deposits of the paratethys seaway in eastern europe and the soviet union accumulated as a result of large scale delivery of dissolved mn to restricted black shale basins during marine transgressions the deposits show compositional zoning and display evidence of having been deposited in shallow marine environments following accumulation of a dilute ore solution in the basin interiors manganese was precipitated when the environments of the basin became oxidized apparently during the early stages of marine regressions during the phanerozoic the concentrations of dissolved oxygen and carbon in the oceans varied significantly in response to large changes in the burial rate of organic carbon when the rate was high there was a drawdown of atmospheric co 2 which led to global reverse greenhouse cooling later upon oxidation of sea floor organic matter co 2 was released and greenhouse warming eventuated manganese is now known to have precipitated rapidly as crusts in the oceans late in the glacial and early in the interglacial stages of the quaternary probably as a result of extensive sea floor oxidation accompanying the release of co 2 this same set of processes operating over geologic time may have played a significant role first in generating large reservoirs of dissolved manganese in intracratonic basins and in the oceans and second by providing the metal for the formation of ore deposits when conditions changed

tertiary extensional tectonics in tuscany northern apennines italy abstract two extensional events have been recognized in the tertiary evolution of tuscany the first event occurred in the period between the late oligocene and late tortonian and caused a stretching of 120 or greater the second event occurred between the late tortonian and quaternary periods and caused a stretching not greater than 10 the first event is characterized by the exhumation of middle crust rocks and therefore by the development of core complexes the most significant structures of the first event are low angle normal faults which characterize the upper plate of the core complexes and ductile shear zones which characterize the lower plate the low angle normal faults tend to die out in the late triassic evaporite level which constitutes the main detachment of the core complexes the main structures of the second extensional event are high angle normal faults which dissect all the previous tectonic features these faults border tectonic depressions which were the site of clastic sedimentation from late tortonian to quaternary time these normal faults may tend to flatten in a seismic lozenge shaped band explained as an active extensional shear zone which is located at the brittle ductile boundary a similar explanation is given for the detachment located in the late triassic evaporite level during the first extensional event while the first extensional event is in the framework of the northern apennine post collisional evolution the second extensional event because it affects an already stretched crust could be attributed to the southern tyrrhenian opening which began during late tortonian

origin of manganese giants sea level change and anoxic oxic history inversely graded pisolites of manganese oxide in the mid cretaceous manganese giant at groote eylandt australia were deposited during a regional fall in sea level as indicated by their relationships to wave cut benches dissolved manganese was concentrated in relatively anoxic waters of the intracratonic basin during a marine transgression and precipitated as oxides and carbonates during a regression ore bodies ultimately formed by concentration of abundant particulate manganese by a tidal lag mechanism

an outer ramp to basin plain transect interacting pelagic and calciturbidite deposition in the eocene oligocene of the tuscan domain adria microplate italy abstract the interaction of ramps basin plains and turbidite systems on the scale of tens of km has been rarely observed in fossil examples deep marine eocene oligocene beds are exposed in the axial zone of the chianti mountains italy and compose a regionally continue stratigraphic succession known as the scaglia toscana formation the formation was deposited in the tuscan domain of the adria microplate this research aims at depicting its depositional architecture and evolution in the type area stratigraphic and sedimentologic analyses were performed on a ca 25 km long transect that includes depositional systems sectioned both in the down and along dip directions shaly carbonate deposits compose a complex of interacting ramps basin plains and turbidite floor fan systems ramp deposits accumulated above the lysocline and in oxic conditions basin plain beds were deposited below the lysocline and were subject to episodes of oxygen depletion turbidity flows fed elongate fan lobes characterized by poor channelisation the basin palaeogeography hampered the development of slope apron turbidite systems the eocene oligocene geodynamic setting of the tuscan domain was characterized by the evolution of a peripheral bulge and by the early structuring of a foredeep basin syn sedimentary tectonism acted a primary role in the basin scale arrangement however other mechanisms also contributed to the local facies distribution including the disposition of sediment source areas and intrabasinal confinement morphologies as well as relative oscillations of the depositional surface with respect to the lysocline and oxycline

eocene oligocene ocean de acidification linked to antarctic glaciation by sea level fall one of the most dramatic perturbations to the earth system during the past 100 million years was the rapid onset of antarctic glaciation near the eocene oligocene boundary some 34 million years ago this climate transition was accompanied by a deepening of the calcite compensation depth the ocean depth at which the rate of calcium carbonate input from surface waters equals the rate of dissolution but the mechanism linking glaciation to the deepening of calcite compensation depth remains unclear merico et al use a global biogeochemical box model to test competing hypotheses put forward to explain the eocene oligocene transition they find that only shelf to deep sea carbonate partitioning can explain the observed changes in both carbon isotope composition and calcium carbonate accumulation at the sea floor this work sheds new light on the mechanisms linking glaciation and ocean acidity change during this important climate transition a global biogeochemical box model is used to test competing hypotheses put forward to explain the eocene oligocene transition it is found that only shelf to deep sea carbonate partitioning is capable of explaining the observed changes in both carbon isotope composition and calcium carbonate accumulation at the sea floor this work sheds new light on the mechanisms linking glaciation and ocean acidity change across the climate transition of the cenozoic one of the most dramatic perturbations to the earth system during the past 100 million years was the rapid onset of antarctic glaciation near the eocene oligocene epoch boundary1 2 3 34 million years ago this climate transition was accompanied3 by a deepening of the calcite compensation depth the ocean depth at which the rate of calcium carbonate input from surface waters equals the rate of dissolution changes in the global carbon cycle4 rather than changes in continental configuration5 have recently been proposed as the most likely root cause of antarctic glaciation but the mechanism linking glaciation to the deepening of calcite compensation depth remains unclear here we use a global biogeochemical box model to test competing hypotheses put forward to explain the eocene oligocene transition we find that of the candidate hypotheses only shelf to deep sea carbonate partitioning is capable of explaining the observed changes in both carbon isotope composition and calcium carbonate accumulation at the sea floor in our simulations glacioeustatic sea level fall associated with the growth of antarctic ice sheets permanently reduces global calcium carbonate accumulation on the continental shelves leading to an increase in pelagic burial via permanent deepening of the calcite compensation depth at the same time fresh limestones are exposed to erosion thus temporarily increasing global river inputs of dissolved carbonate and increasing seawater 13c our work sheds new light on the mechanisms linking glaciation and ocean acidity change across arguably the most important climate transition of the cenozoic era

subsidence and sedimentation on jurassic passive continental margin southern alps italy the southern alps of italy preserve a tectonically intact array of jurassic facies that record the evolution of a part of the margin of the apulian plate from its ancestral beginnings in a complex of permian and triassic rifted continental basins through the initial stages of breakup and stepwise foundering of a carbonate platform breakup was accompanied first by the rapid accumulation of thick prisms of carbonate turbidites in newly formed fault troughs then as the new ligurian oceanic basin began to open farther west and as subsidence gradually slowed accumulation of a succession of slowly deposited biogenous pelagic sediments recorded not only the increasing depths of the seafloor but also fluctuations in oceanographic conditions of fertility carbonate dissolutio levels and the strength of bottom currents estimates of the history of seafloor depths based on a simple subsidence law of the form subsidence k age 12 provide a basis for the construction of a set of curves showing the changing depths of significant carbonate dissolution surfaces during the jurassic in this region the rapid 1 km deepening of the compensation depth for calcite during the late jurassic may be due to a change in regional oceanic vertical circulation patterns from upwelling fertile silica rich carbonate dissolving to downwelling less fertile silica poor carbonate preserving

synsedimentary tectonics in the late cretaceous early tertiary pelagic basin of the northern apennines italy the sequence of upper cretaceous lower tertiary pelagic limestones in the umbria marches apennines of italy have recorded with remarkable continuity the geologic history of an epeiric sea on the eastern continental margin of the ligurian ocean during a time of widespread tectonism in the western tethys domain sedimentary facies and paleocurrent analyses indicate that intrabasinal depocenters and structural highs have formed in response to extensional tectonic movements which started to affect the central part of the paleobasin in the early turonian the topography of the paleobasin was probably controlled by a complex pattern of buried fault blocks formed during the passive margin phase of the western tethys and then reactivated in the turonian after a prolonged time aptian to cenomanian of tectonic quiescence calcareous turbidites essentially made of remobilized pelagic mud were generated on the newly formed intrabasinal slopes and deposited in the adjacent depocenters conspicuous sedimentary events such as maxima in turbiditic deposition and soft sediment slumps in these intrabasinal depocenters are attributed to major syndepositional earthquakes of regional extent a detailed event stratigraphy based on these sedimentary features indicates that the level of syndepositional tectonic activity reached a peak in the late maastrichtian early paleocene and rapidly diminished in the eocene

on the use of multicomponent streamer recordings for reconstruction of pressure wavefields in the crossline direction three component measurements of particle motion would bring significant benefits to towed marine seismic data if processed in conjunction with the pressure data we show that particle velocity measurements can increase the effective nyquist wavenumber by a factor of two or three depending on how they are used a true multicomponent streamer would enable accurate data reconstruction in the crossline direction with cable separations for which pressure only data would be irrecoverably aliased we also show that conventional workflows aimed at reducing these aliasing effects such as moveout correction applied before interpolation are compatible with multicomponent measurements some benefits of velocity measurements for deghosting data are well known we outline how the new measurements might be used to address some long standing deghosting challenges of particular interest specifically we propose methods for recovering de ghosted data between streamers and for 3d deghosting of seismic data at the stream

carbonate ramp to deeper shale shelf transitions of an upper cambrian intrashelf basin nolichucky formation southwest virginia appalachians the nolichucky formation 0 300 m thick formed on the cambrian pericratonic shelf in a shallow intrashelf basin bordered along strike and toward the regional shelf edge by shallow water carbonates and by nearshore clastics toward the craton lateral facies changes from shallow basinal rocks to peritidal carbonates suggest that the intrashelf basin was bordered by a gently sloping carbonate ramp peritidal facies of the regional shelf are cyclic upward shallowing stromatolitic carbonates these grade toward the intrashelf basin into shallow ramp cross bedded ooid and oncolitic intraclast grain stones that pass downslope into deeper ramp subwave base ribbon carbonates and thin limestone conglomerate ribbon limestones are layers and lenses of trilobite packstone parallel and wave ripple laminated quartzose calcisiltite and lime mudstone arranged in storm generated fining upward sequences 1 5 cm thick that may be burrowed shallow basin facies are storm generated upward coarsening and upward fining sequences of green calcareous shale with open marine biota parallel to hummocky laminated calcareous siltstone and intraformational flat pebble conglomerate there are also rare debris flow paraconglomerate 10 60 cm thick and shaly packstone wackestone with trace fossils glauconite horizons and erosional surfaces hardgrounds a 15 m thick tongue of cyclic carbonates within the shale package contains subtidal digitate algal bioherms which developed during a period of shoaling in the basin understanding the nolichucky facies within a ramp to intrashelf basin model provides a framework for understanding similar facies which are widely distributed in the lower palaeozoic elsewhere the study demonstrates the widespread effects of storm processes on pericratonic shelf sedimentation finally recognition of shallow basins located on pericratonic shelves is important because such basins influence the distribution of facies and reservoir rocks whose trends may be unrelated to regional shelf edge trends

calcareous nannoplankton response to surface water acidification around oceanic anoxic event 1a ocean acidification induced by atmospheric co2 may be a major threat to marine ecosystems particularly to calcareous nannoplankton we show that during the aptian 120 million years ago oceanic anoxic event 1a which resulted from a massive addition of volcanic co2 the morphological features of calcareous nannofossils traced the biological response to acidified surface waters we observe the demise of heavily calcified nannoconids and reduced calcite paleofluxes at the beginning of a pre anoxia calcification crisis ephemeral coccolith dwarfism and malformation represent species specific adjustments to survive lower ph whereas later abundance peaks indicate intermittent alkalinity recovery deepwater acidification occurred with a delay of 25 000 to 30 000 years after the dissolution climax nannoplankton and carbonate recovery developed over 160 000 years under persisting global dysoxia anoxia

phosphogenesis and active phosphorite formation in sediments from the arabian sea oxygen minimum zone in this study porewater chemistry solid phase analysis and microscopic observations were combined to evaluate phosphogenesis in three boxcores located within the intensive oxygen minimum zone of the arabian sea three parameters namely a decrease of the dissolved phosphate and fluoride concentrations with depth saturation with respect to carbonate fluorapatite and the presence of a solid phase ca phosphate mineral all indicate that phosphogenesis is currently taking place at all three sites authigenic apatite precipitation rates vary between 0 076 and 1 04 molp cm 2 yr 1 and are of the same order of magnitude as reported for other high productivity areas precipitation of an intermediate precursor precedes francolite formation in the continental slope sediments on the karachi margin results of a diagenetic p model indicate that phosphogenesis is induced by high rates of organic matter degradation dissolution of fish debris is likely to provide a substantial additional source of phosphate redox iron cycling does not influence phosphogenesis in these environments model results suggest that sediment mixing is essential in promoting early diagenetic phosphogenesis the highest rate of francolite formation was observed in a boxcore taken on the oman margin where it contributes to the formation of a holocene phosphorite deposit this observation contrasts with previous reports of only old phosphorites in this area phosphorites are presently forming on the oman margin as a result of a deposition of older reworked material from the continental shelf which has undergone an earlier phase of phosphogenesis b a high input of reactive p fish debris and degradable organic matter c a relatively low sediment accumulation rate and d the absence of winnowing on this location holocene phosphorite deposits may be less common on the oman margin than in other coastal upwelling areas because of the narrowness of the shelf and the steepness of the slope which limit the area where phosphorite formation may occur

the corsica sardinia massif as source area for the early northern apennines foredeep system evidence from debris flows in the macigno costiero late oligocene italy large isolated gravity flows debrites are widely present in the stratigraphic record of the northern apennines foreland basin system these strata may be useful for provenance signals and dispersal pathways during foreland evolution this paper examines a cohesive debris flow bed interbedded with turbidite strata of the macigno formation late oligocene tuscany italy in order to obtain new data on the provenance of the clastic material clasts in the debris flow are predominantly plutonic granodiorite tonalite and s granite and subordinately metamorphic gneiss and schist and sedimentary calcareous clasts the composition of the clasts within the debris flow is similar to the clastic composition of the interbedded turbidite sandstones of the macigno costiero the depositional features of the debris flow suggest that it traveled for a short distance within the basin before it was deposited not far from the slope the absence of a high pressure low temperature hp lt paragenesis in the plutonic and metamorphic clasts of the debris flow indicates a provenance from a crystalline basement not involved in the high pressure phases of the alpine orogenesis previous studies have indicated the central western alps as potential source areas for the macigno formation sediments the lack of hp lt metamorphic signatures in our studied samples excludes the pennidic and austroalpine nappes of the western alps as possible sources for the debris flows of the macigno costiero these new data sedimentological petrographical and microstructural suggest that the corsica sardinia hercynian basement lacking a hp lt paragenesis is the more accredited source area of the debris flow and of the related turbidite sandstones of the macigno costiero succession these foredeep feeding sediments were probably before deposited within an episutural basin developed close to the northern apennines orogenic wedge

depositional environments along a carbonate shelf to basin transect in the silurian of nevada u s a abstract during the llandovery silurian in central nevada foundering of the shelf margin and drowning of a homoclinal carbonate ramp produced a rimmed carbonate shelf westward the shelf was bordered by a slope which passed into a deep water basin at the shelf margin carbonate sand shoals lone mountain dolomite aggraded and prograded westwards over the slope the spatial and temporal facies variation in a transect across the slope roberts mountains formation records the history of a prograding shelf margin initial slope sedimentation adjacent to the carbonate shelf margin was lime mudstone hemipelagically derived from the shelf westwards and downslope dilute carbonate turbidites and hemipelagic lime mudstone laminated facies were deposited contemporaneous slope rise sediments fourmile canyon formation consist primarily of siliciclastic mudstone with minor dilute carbonate turbidites and turbiditic siliciclastic siltstone the latter essentially being part of the deep water basin subsequent shelf margin progradation and increasing slope differentiation is reflected in the downslope introduction of calcarenite and conglomerate derived from the shelf margin slope sedimentation records an overall coarsening and thickening upwards cycle superimposed on this in some areas are small scale coarsening and thickening upwards cycles reflecting deposition on carbonate debris aprons abandonment and subsequent build out of the aprons reflects the pulsatory and uneven progradation of the outer shelf margin simultaneous with these depositional patterns the immediate shelf margin periphery top of slope received hemipelagic lime mudstone sediments many rotational slides some generating debris flows indicate upper slope instability most allochthonous carbonate debris from the shelf margin by passed the top of slope and was deposited further downslope with the westward progradation of the shelf margin the fringing facies migrated basinward

compaction rock physics and rock properties of sandstones of the sto formation case study of five wells from the south western barents sea norway abstract five wells containing lower middle jurassic sandstones of sto formation from the hammerfest basin 7120 9 1 7121 7 1 the ringvassoy loppa fault complex 7119 12 1 7119 12 4 and the troms finnmark fault complex 7019 1 1 in the barents sea area are considered in this study the sto formation sandstones contain dominantly very fine to medium grained quartz arenites with occasional coarse grained sandstone layers feldspathic and quartz wackes are also present the effect of compaction and exhumation on reservoir properties porosity and permeability and seismic property p wave velocity of these sandstones have been investigated source of quartz cement has also been investigated forty polished thin sections embedded in blue epoxy were studied using optical microscopy scanning electron microscopy and cathodoluminiscence bulk mineralogy was also analysed using x ray diffraction the studied sandstones have experienced cenozoic exhumation ranging between 820 and 1050 m p wave velocity is higher porosities and permeabilities are lower in the western wells 7019 1 1 7119 12 1 and 7119 12 4 compared to the eastern wells 7120 9 1 and 7121 7 1 rock physics models and diagnostics show that the western wells are diagenetically more mature stiffer more compacted and more cemented than the eastern wells these trends are attributed largely to difference in burial history from the east to the west and less to textural variations quartz cement is the most important authigenic mineral in these sandstones quartz cement in the western well 7119 12 1 is predominantly derived from clay induced dissolution at macrostylolites whereas the eastern wells 7120 9 1 and 7121 7 1 are mostly sourced from clay induced dissolution at grain contacts or microstylolites while cementational porosity loss dominates in the western wells compactional porosity loss dominates in the eastern wells compaction can reduce porosities down to 26 and this might be the reason for better porosity preservation and reservoir quality in the eastern wells than in the western wells

process controls on the development of stratigraphic trap potential on the margins of confined turbidite systems and aids to reservoir evaluation stratigraphic trapping at pinch out margins is a key feature of many turbidite hosted hydrocarbon reservoirs in systems confined by lateral or oblique frontal slopes outcrop studies show that there is a continuum between two geometries of pinch out configuration in type a turbidites thin onto the confining surface although the final sandstone pinch out is commonly abrupt and individual beds tend not to erode into earlier deposits in type b turbidite sandstones commonly thicken toward the confining slope and beds may incise into earlier deposits these two types may occur in combination to give a wide spectrum of pinch out characteristics our analysis suggests the principal control in determining pinch out character is flow magnitude with smaller flows producing type a and larger flows producing type b in areas of poor seismic control it can be difficult to assess either pinch out character or the proximity of wells to confining slopes because estimates of paleoflow magnitude can be made from core or high quality log image data however it is possible to make reasonable estimates of pinch out character even from wells such as exploration wells which may be placed conservatively away from the field margins furthermore systematic paleoflow variations and thickness trends are commonly seen in individual turbidite sandstones as they approach confining slopes for example dispersal directions indicate flow deflection parallel with the strike of confining topography beds thin toward type a onlaps and thicken toward type b onlaps these relationships can be exploited via analysis of vertical successions to constrain well position with respect to the slope similarly the presence location and frequency of locally derived debrites can provide information on the presence and proximity of confining slopes begin page 972

sumeini group oman evolution of a mesozoic carbonate slope on a south tethyan continental margin abstract deposition of the mostly mesozoic sumeini group occurred on the slope between the shallow marine arabian carbonate platform and the deep oceanic hawasina basin or south tethys sea these strata record the evolution of the northeast arabian continental margin from permian and triassic rifting to ocean basin closing with the late cretaceous obduction of the semail ophiolite platform margin type and its evolution can be inferred from exposures of these slope sediments at jebel sumeini in the western oman mountains in the lower permian base of the sequence bedded spicular limestones suggest deep marine conditions this is followed by an enigmatic thick sequence of bedded dolomite in the early to middle triassic small carbonate submarine fans formed along a distally steepened slope a subsequent interval of terrigenous clastic sedimentation was followed by development of a steep escarpment margin during ladinian to norian time with coralgal reefs at the shelf break and a debris apron at the base of the scarp the late triassic is marked by another influx of terrigenous sediment which accompanied widespread emergence of the platform in the jurassic a thick apron of thin bedded limestone formed on the slope this apron was cut by channelized gullies that now include blocks of older reefal material and oolitic sands a well documented submergence of the platform during the tithonian and early cretaceous led to the deposition of radiolarian cherts on the slope and basin upper lower cretaceous megabreccias up to 200 m thick suggest an interval of localized slope instability and or tectonism continued deposition of bedded limestone and marl with lesser calcirudite marks the top of stratigraphic sequence at jebel sumeini the early to middle triassic carbonate submarine fan deposits occur as discrete lenticular sequences of bedded calciturbidite modified grain flow and debris flow deposits which were derived from mostly slope sources the ladinian to norian base of slope debris apron deposits were derived from both slope and shallow marine sources including reefs and appear to form a laterally extensive but narrow belt of thick lenticular to sheet like beds of debris which accumulated over a long interval of time coarse limestones in the jurassic gullied slope deposits are distinct in that they occur randomly as individual channelized beds in a sequence dominated by thin bedded lime mudstones thick lower cretaceous megabreccias are distinguished by their great lateral distribution and general lack of matrix

marine biotic signals across a late eocene impact layer at massignano italy evidence for long term environmental perturbations the eocene oligocene transition marks the passage from greenhouse conditions to an icehouse state with progressive global cooling starting in the early middle eocene the late eocene presents substantial evidence for extraterrestrial impacts whose effects on living organisms and climatic changes are still not completely clear a high resolution microfloral and faunal investigation has been carried out in a 4 m thick segment of the massignano global stratotype section and point for the eocene oligocene boundary the studied interval includes a late eocene 35 7 0 4 myr old impactoclastic layer containing several cosmic signatures the impact event recorded at massignano had no abrupt dramatic effects on marine biota in terms of extinction however significant quantitative changes in the calcareous plankton and dinoflagellate cyst assemblages occurred 60 kyr after the impact event the observed pattern is intepreted as reflecting a long term re organization of water structure

evolution of the adriatic carbonate platform palaeogeography main events and depositional dynamics abstract the adriatic carbonate platform adcp is one of the largest mesozoic carbonate platforms of the perimediterranean region its deposits comprise a major part of the entire carbonate succession of the croatian karst external or outer dinarides which is very thick in places more than 8000 m and ranges in age from the middle permian or even upper carboniferous to the eocene however only deposits ranging from the top of the lower jurassic toarcian to the top of the cretaceous can be attributed to the adcp defined as an isolated palaeogeographical entity although the entire carbonate succession of the karst dinarides was deposited within carbonate platform environments there were different types of carbonate platforms located in different palaeogeographical settings carboniferous to middle triassic mixed siliciclastic carbonate deposits were accumulated along the gondwanian margin on a spacious epeiric carbonate platform after tectonic activity culminating by regional middle triassic volcanism recorded throughout adria the african promontory a huge isolated carbonate southern tethyan megaplatform abbreviated as stm was formed with the area of the future adcp located in its inner part tectonic disintegration of the megaplatform during the middle to late early jurassic resulted in the establishment of several carbonate platforms including the adriatic apenninic and apulian separated by newly drowned deeper marine areas including the adriatic basin as a connection between the ionian and belluno basins lagonero basin and the area of the slovenian and bosnian troughs the adcp was characterised by predominantly shallow marine deposition although short or long periods of emergence were numerous as a consequence of the interaction of synsedimentary tectonics and eustatic changes also several events of temporary platform drowning were recorded especially in the late cretaceous when synsedimentary tectonics became stronger leading up to the final disintegration of the adcp the thickness of deposits formed during the 125 my of the adcp s existence is variable between 3500 and 5000 m the end of adcp deposition was marked by regional emergence between the cretaceous and the palaeogene deposition during the palaeogene was mainly controlled by intense synsedimentary tectonic deformation of the former platform area some carbonates mostly eocene in age were deposited on irregular ramp type carbonate platforms surrounding newly formed flysch basins and the final uplift of the dinarides reached its maximum in the oligocene miocene the adriatic carbonate platform represents a part although a relatively large and well preserved one of the broader shallow water carbonate platform that extended from ne italy to turkey although its continuity is somewhat debatable in the area near albanian greece boundary this large carbonate body which was deformed mostly in the cenozoic including a significant reduction of its width needs a specific name and the central mediterranean carbonate platform is proposed abbreviated to cmcp although the local names such as adcp for its nw part should be kept to enable easier communication and to facilitate description of local differences in platform evolution

a model for the palaeoenvironmental distribution of larger foraminifera based on late middle eocene deposits on the margin of the south pyrenean basin ne spain abstract on the margin of the south pyrenean basin the late middle eocene sediments represent a well preserved regressive system permitting determination of the distribution of larger foraminifera along the depth gradient eocene deposits are compared with distribution patterns of recent larger foraminifera based on taxa occupying comparable positions along similar ecological gradients eocene taxa reveal by their test morphology a similar response to specific ecological conditions to that recorded for recent foraminifera four assemblages characterise an open marine shelf they range from the lower limit of the photic zone to the lower part of the upper photic zone two assemblages characterise the upper part of the upper photic zone and indicate respectively two different substrates firm or soft below the photic zone no larger foraminifera exist and the foraminiferal assemblages are dominated by smaller benthic foraminifera

overpressure preventing quartz cementation comment to stricker et al 2016 abstract there is increasing evidence that quartz cementation can be viewed as a process controlled by temperature and insensitive to effective stress this view of quartz cementation in sandstones is often referred to as the illite mica induced dissolution model imid which assumes quartz dissolution to occur along stylolites and clay laminae rather than at quartz quartz grain contacts in the present comment it is argued that the exceptional reservoir quality in the skagerrak formation of the heron cluster north sea is due to grain coatings and rapid cenozoic burial limiting the exposure to quartz cementation this line of reasoning implies overpressure has had neglectable porosity preserving effect in the heron cluster

multicomponent ocean bottom and vertical cable seismic acquisition for wavefield reconstruction in ocean bottom seismic and vertical cable surveying receiver stations are stationary on the sea floor while a source vessel shoots on a predetermined x y grid on the sea surface to reduce exploration cost the shot point interval often is so coarse that the data recorded at a given receiver station are undersampled and thus irrecoverably aliased however when the pressure field and its x and y derivatives are measured in the water column the nonaliased pressure field can be reconstructed by interpolation likewise if the vertical component of the particle velocity or acceleration and its x and y derivatives are measured then this component can also be reconstructed by interpolation the interpolation scheme can be any scheme that reconstructs the field from its sampled values and sampled derivatives in the case that the two fields first order derivatives are recorded the total number of components is six when also their second order derivatives are measured the number of components is

an analysis of the roles of stress temperature and ph in chemical compaction of sandstones abstract chemical compaction also known as pressure solution involves dissolution along grain contacts and transport of solute to the adjacent pore space by diffusion the driving force for diffusion is a gradient in chemical potential therefore chemical compaction requires persistent gradients in chemical potential along grain contacts in order to drive diffusion continuously such gradients exist in porous rocks because of the heterogeneous distribution of stress over the grain surfaces the rate of chemical compaction depends on stress fluid pressure temperature and the composition of the pore fluid which itself depends on various processes that add or remove solute an alternative model of chemical compaction invokes the effect of sheet silicates on ph to account for localized dissolution of grains adjacent to stylolites or where sheet silicates are present along grain contacts in this model the rate of chemical compaction is independent of stress and fluid pressure depending only on temperature this model is untenable because the proposed mechanism cannot give rise to the persistent gradient in chemical potential required to drive diffusion however sheet silicates may increase the rate of chemical compaction because of their influence on dissolution and diffusion rates the development of anisotropic fabrics as a result of chemical compaction and the widespread occurrence of stylolites in carbonates as well as sandstones are inconsistent with the ph model and provide strong support for the role of stress in chemical compaction

distribution patterns of benthic foraminifera across the ypresian lutetian gorrondatxe section northern spain response to sedimentary disturbance article we present a study of benthic foraminiferal assemblages from an ypresian lutetian distal submarine fan system in the lower bathyal gorrondatxe section basque cantabrian basin northern spain the objective of our study is to analyze the benthic foraminiferal distribution patterns and their response to sedimentary disturbance and related factors assemblages contain a high percentage of allochthonous taxa such as asterigerinids and other shallow water taxa which were transported downslope by turbidity currents detailed quantitative analyses supported by r mode cluster and detrended correspondence analyses after removing allochthonous taxa from the foraminiferal counts allowed us to identify 6 assemblages that are divided into two groups related to the turbidite content in the gorrondatxe section assemblages 1 characteristic of the turbidite poor intervals with low sedimentary disturbance include assemblage 1a with highly diverse common middle lower bathyal calcareous taxa assemblage 1b with common agglutinated taxa mainly trochamminids and assemblage 1c characterized by calcareous taxa that are also common in the turbidite rich interval assemblages 2 characterized by a high dominance prevail in the turbidite rich interval and include assemblage 2a characterized by the dominance of infaunal bolivinids and epifaunal cibicids assemblage 2b typified by moderate to low diversity and dominated by deep infaunal globobulimina species and assemblage 2c typified by very abundant suspension feeding astrorhizids the high abundance of bolivinids and globobulimina species may be related to an enhanced input of low quality organic matter transported by turbidity currents to the seafloor representing different stages of recolonisation after disturbance and different energy regimes high current activity was probably responsible for the abundance of cibicids while moderate to low diverse and high dominance assemblages characterize the recolonisation of the substrate after disturbance we conclude that sedimentary disturbance and other related factors such as current activity resuspension of sediments at the seafloor and supply of organic matter and its quality played an important role in the distribution of benthic foraminifera inthe gorrondatxesection the identification of allochthonous taxa emerges as an essential aspect of the study of environments with sedimentary disturbance

triassic carbonate submarine fans along the arabian platform margin sumeini group oman the sumeini group formed along the passive continental margin slope that bounded the northeastern edge of the arabian carbonate platform with the initial development of this passive continental margin in oman during early to middle triassic time possibly permian small carbonate submarine fans of the c member of the maqam formation developed along a distally steepened slope the fan deposits occur as several discrete lenticular sequences of genetically related beds of coarsegrained redeposited carbonate calciclastic sediment within a thick interval of basinal lime mudstone and shale repeated pulses of calciclastic sediment were derived from ooid shoals on an adjacent carbonate platform and contain coarser intraclasts eroded from the surrounding slope deposits sediment gravity flows primarily turbidites with lesser debris flows and grain flows transported the coarse sediments to the relatively deep submarine fans channel erosion was a major source of intraformational calcirudite two small submarine fan systems were each recurrently supplied with calciclastic sediment derived from point sources submarine canyons the northern fan system retrogrades and dies out upsection the southern fan system was apparently longer lived calciclastic sediments in it are more prevalent and occur throughout the section the proximal portions of this fan system are dominated by channelized beds of calcirudite which represent inner to mid fan channel complexes the distal portions include mostly lenticular unchannelized beds of calcarenite apparently mid to outer fan lobes carbonate submarine fans appear to be rare in the geological record in comparison with more laterally continuous slope aprons of coarse redeposited sediment the carbonate submarine fans of the c member apparently formed by the funnelling of coarse calciclastic sediment into small submarine canyons which may have developed due to rift and or transform tectonics the alternation of discrete sequences of calciclastic sediment with thick intervals of background sediment resulted from either sea level fluctuations or pulses of tectonic activity

controls on modern carbonate preservation in the southern florida straits abstract the water masses in the florida straits and bahamas region are important sources for the northern atlantic surface ocean circulation in this study we analyse carbonate preservation in surface sediments located above the chemical lysocline in the florida straits and bahamas region and discuss possible reasons for supralysoclinal dissolution calcite dissolution proxies such as the variation of the foraminiferal assemblage fragmentation index benthic foraminifera index and resistance index displayed a good preservation in both areas the pteropod species limacina inflata showed very good preservation in sediments of inter platform channels from the great bahama bank providence channel exuma sound above the aragonite lysocline supralysoclinal aragonite dissolution however was observed at two water depth levels 800 1000 m and below 1500 m in the florida straits our observations suggest that the supralysoclinal dissolution in the florida straits is due to the degradation of organic material the presence of antarctic intermediate water aaiw may be a contributing factor for the significant aragonite dissolution in 800 1000 m the comparison of modern preservation patterns of the surface sediments with hydrographical measurements shows that the l inflata dissolution index ldx might be an adequate proxy to reconstruct paleo water mass conditions in an area which is highly saturated with respect to calcium carbonate

silica diagenesis origin of inorganic and replacement cherts abstract silicification of originally non siliceous sediments affects a wide variety of rock types and materials and ranges from minor to pervasive partial and minor chertification occur mostly in phanerozoic carbonates carbonate bearing sandstones evaporites and fossil wood the source of the silica is predominantly biogenic in petrified wood the silicification mechanism is a permeation or void filling process not a replacement in this example the sequence of silica phase transformation is the same as that in deep sea siliceous sediments in many silicified rocks particularly in certain carbonates the transformation sequence is different from that in radiolarites or diatomites the chemical environment and conditions of early diagenetic chert formation in shallow water carbonates are delineated by the general mixing model of knauth 1979 but remain unknown for most other types an exception are the flint nodules and bands of the english chalk a detailed geochemical study of the paramoudra flint structures by clayton 1986 provided remarkable insight into the replacement process seven different recurring silica fabrics have been recognized in chert replaced carbonates including equigranular microcrystalline quartz or microquartz and megaquartz and fibrous types chalcedony quartzine or length slow chalcedony lutecite zebraic chalcedony and microflamboyant quartz among the latter quartzine and microflamboyant quartz are common in but by no means restricted to chert replaced evaporites for which milliken 1979 recognized a sequence of seven quartz fabrics as a single criterion only anhydrite inclusions in megaquartz quartzine or microflamboyant quartz provide unequivocal evidence for an evaporite precursor the relative timing between silicification and well established diagenetic carbonate reactions shows that virtually all theoretically possible sequences occur chertification of carbonate host sediment thus may take place during early intermediate or late diagenesis and even during anchimetamorphism pervasive to complete silicification has been described in lacustrine pedogenic and hydrothermal volcanogenic rocks and occurs on the scale of individual beds members or entire formations it may affect some of the aforementioned rock types too for example carbonates the source of the silica is predominantly inorganic chert formation in these environments includes direct chemical silica precipitation from solution through a gel stage magadi type cherts result from the conversion of the hydrous sodium silicate magadiite into microcrystalline quartz which has occurred in east african rift valley lakes such as lake magadi in late pleistocene time they are closely related to directly precipitated inorganic cherts which have been observed in alkaline environments of playa lakes silcretes originate from weathering and soil forming processes under climatic and environmental conditions conducive to the formation of duricrusts and laterites in more humid climates however non weathering profile silcretes occur which have been distinguished from weathering profile silcretes four to five different silcrete fabric types have been established including the 1 grain supported or quartzitic 2 floating terrazzo 3 matrix albertinia and opaline and 4 conglomeratic types in volcanic edifices silicification related to hydrothermal activity occurs 1 along the ascent routes of the fluids vents within the volcanic complexes 2 in isolated ponds and depressions on the sea floor where the fluids discharge mostly in the median rift valley of mid ocean ridges and 3 in geothermal areas on land associated with spreading lineaments volcanic islands arcs transform faults or continental hot spots attention has focussed on the associated base metal concentrations and less on the silicification and accompanying iron enrichment processes the precambrian banded iron formations may be indirectly or directly related to hydrothermal volcanic processes the origin of these cherty iron formations certainly requires more than one genetic model and at present remains a major unresolved problem despite massive efforts to tackle it

outer ramp cycles in the upper muschelkalk of the catalan basin northeast spain the upper muschelkalk triassic of the catalan basin eastern spain was deposited upon a carbonate ramp of homoclinal type located in an intracratonic setting the rasquera unit in the upper muschelkalk mostly consists of outer ramp carbonates arranged in upward shallowing cycles five cycles from 1 5 to 12 m thick are recognised each cycle shows an upward coarsening of grain size an upward increase in bed thickness and an upward change in fossil content reflecting an upward shallowing of the environment in the complete cycle marlstone and shale pass up into marlstone with thin bedded line mudstones containing pelagic bivalves the succeeding thin bedded and nodular limestones with shaley partings contain a more varied fauna and are bioturbated they pass up into thick bedded skeletal wackestones packstone coquinas locally cap the cycles and have a diverse benthic fauna as well as the alga tubiphytes occurring as bioclasts encrustations around skeletal grains and forming microbuildups although some of the thin beds were deposited during weak storms there is little evidence of intense storm activity petrological sedimentological and palaeontological criteria and the geological setting allow the recognition of distal intermediate and proximal facies on a relatively deepwater carbonate ramp

deposition of upper jurassic fine grained limestones in the western subalpine basin france abstract the fine grained carbonate sequence on the western margin of the french subalpine basin provides information about the depositional conditions of the late jurassic nodular lithofacies which closely resemble the age equivalent ammonitico rosso of the mediterranean and central atlantic domains a variety of rock textures can be distinguished including lumpy nodular restricted sense and conglomeratic the formation of these textures is referred to different sedimentological processes cyclic marl limestone deposition bioturbation winnowing early lithification gravity displacement etc in addition the development of deep water cryptalgal carbonate constructions which include stromatolites and small mud mounds is noted outer shelf deep marine palaeoenvironments 100 s m are inferred from the sedimentary structures biotic associations and facies distributions the callovian oxfordian discontinuity is believed to have resulted from a sediment starved environment part of the overlying fine grained carbonate material was then presumably derived from an adjacent platform oscillations in nature and quantity of carbonate and clay input onto the margin probably reflect cyclic climatic and sea level changes

a survey of multi stage diagenesis and dolomitization of jurassic limestones along a regional shelf to basin transect in the ziz valley central high atlas mountains morocco abstract petrographic and geochemical data from five localities in the ziz valley of morocco indicate that jurassic limestones have undergone early diagenesis that varied with location from shelf to basinal settings burial diagenesis that was most pronounced in basinal settings and late diagenesis caused by compression and uplift of the high atlas mountains marine cements occur at all five localities from shelf to basin center although cement types vary from peloidal microcrystalline cements updip on the shelf to equant calcite in basinal settings presence of moldic grains and or mg poor fe poor blocky cements suggest that meteoric waters influenced early diagenesis at all shelf localities and on an upturned fault block in the basinal region leaving only one locality unaffected by early meteoric processes 87 sr 86 sr ratios of 0 70810 0 70895 greater than 87 sr 86 sr of coeval limestones mg contents that decrease upward from 47 5 to 43 0 mol mgco 3 presence of dolomitized marine cements and dolomite cements that postdate marine cements but predate meteoric to burial cements suggest that dolomitization and dolomite cementation at two shelf localities took place in mixed meteoric and marine waters early in diagenesis however poorer preservation of depositional fabrics lower 18 o values and larger and more anhedral crystals suggest that dolostones downdip underwent later modification during burial whereas those updip did not compaction during diagenesis generated numerous concavo convex and sutured intergranular contacts at updip shelf downdip shelf and basinal localities where earlier meteoric cementation was not extensive compaction was insignificant in more extensively cemented mid shelf settings high sr 1200 3800 ppm and fe 1000 2300 ppm contents in brachiopod grains suggest that lmc components underwent some modification during burial in basinal settings in sr rich reducing waters fe contents of late intergranular cements increase from 2000 ppm at the basin s edge to as much as 6000 ppm in the basin s center bedding parallel stylolites occur at all localities the most negative 18 o values of sparry dolomites near the tizi n firest fault 6 2 vs pdb imply diagenetic temperatures of 65 85 c assuming water 18 o values of 0 0 2 0 vs smow those temperatures are much less than previous estimates of burial temperatures in the high atlas basin an isotopic gradient extrapolating to roughly 5 km in diagenetically modified dolostones likewise suggests a geothermal gradient less than gradients previously proposed for at least parts of the area comparison of morphologies of transverse stylolites which are found at all localities with morphologies of bedding parallel stylolites suggests that transverse stylolites formed due to compression during late diagenesis uplift accompanying that compression allowed influx of low mg waters that along with other factors caused calcitization of dolomites the fe concentration of calcite that fills late fractures increases from less than 2000 ppm at the basin center to values in excess of 3000 ppm at the basin edge opposite trends in earlier cements and reflecting uplift of the high atlas mountains and resultant changes in patterns of groundwater flow

models for the deposition of mesozoic cenozoic fine grained organic carbon rich sediment in the deep sea the widespread occurrence of organic carbon rich strata black shales in certain portions of jurassic cretaceous and cenozoic sequences has been well documented from deep sea drilling project sites in the atlantic and pacific oceans and from sequences now exposed on land originally deposited in the tethyan ocean these ancient black shales usually have been explained by analogy with examples of modern deep sea sediments in which organic matter locally is preserved by 1 increasing the supply of organic matter 2 increasing the rate of sedimentation and or 3 decreasing the oxygen content of the bottom water however detailed examination of many black shales reveals characteristics that cannot be explained by simple local models including their approximate coincidence in time globally their occurrence in a variety of different environments including open oxygenated oceans restricted basins deep and shallow water their interbedding with organic carbonpoor strata which often dominate a so called black shale sequence their deposition by pelagic hemipelagic turbiditic and other processes and the variations in type and amount of organic matter that occur even within the same sequence a more complex model for the origin of black shales therefore appears most appropriate in which the cyclic preservation of organic matter depends on the interplay of the three main variables namely supply of organic matter sedimentation rate and deep water oxygenation each of which varies independently to some extent the variation and relative importance of these parameters in individual basins and widespread black shale deposition in general are linked globally and temporally by changes in global sea level climate and related changes in oceanic circulation an important and often overlooked factor for the supply of organic matter to deep basin sediments is the frequency and magnitude of redepositional processes the interplay of these variables is discussed in relation to the middle cretaceous and cenozoic organic carbon rich strata in particular which show marked differences in the relative importance of the different variables

hummocky cross stratified deposits and turbidites in some sequences of the umbria marche area central italy during the toarcian abstract some sections of the umbria marche basin central italy were characterized during the toarcian by alternately thicker and thinner organic rich marls and well oxygenated red and nodular marly limestones these sequences exhibit sharp based hummocky cross stratified hcs deposits and turbidites ranging in thickness from several centimetres to 200 cm palaeocurrent measurements of hcs beds and turbidites indicate the same se nw direction hcs deposits that show wavelengths mostly from 70 to 140 cm are grainstones and matrix poor packstones a complete sequence consists of three divisions a a lower coarse grained bivalve and echinoderm lag from 0 5 to 40 cm thick the lag is generally erosive and discontinuous and probably represents a proximal material deposited during a high energy phase of a storm event b a middle well sorted calcarenite calcisiltite division from 20 to 100 cm thick that exhibits well preserved hummocky cross stratification bioclastic calcareous sands transported by offshore currents from storm surges were organized into hcs beds under an oscillatory unidirectional flow regime near the bottom c an upper oscillatory ripple bedded calcisiltite division from 0 5 to 25 cm thickness ripples were probably formed during a dominant oscillatory regime wave action after the sand sedimentation had stopped locally a pervasive bioturbation is common in the upper part of this bed turbidites 10 200 cm thick are packstones and rudstones with abundant muddy matrix and generally show the classical bouma bc sequence the lower and middle interval of the studied sequences from the late domerian to the early toarcian is dominated by fining upward turbidites on the contrary the upper part of the sequence middle late toarcian in age is dominated by sharp based hcs beds the vertical transition from turbidites to sharp based hcs deposits is indicative of a general regressive trend the causes of the sea bottom depth changes can be related respectively to a sea level rise documented for the early toarcian and to the sea level fall of the middle toarcian lateral and vertical distribution frequency grain size structures and composition of detritic beds and microfaunal assemblages confirm the differentiated topography of the umbria marche basin during toarcian time

calciclastic submarine fans an integrated overview abstract calciclastic submarine fans are rare in the stratigraphic record and no bona fide present day analogue has been described to date possibly because of that and although calciclastic submarine fans have long intrigued deep water carbonate sedimentologists they have largely been overlooked by the academic and industrial communities to fill this gap we have compiled and critically reviewed the existing sedimentological literature on calciclastic submarine fans thus offering an updated view of this type of carbonate slope sedimentary system calciclastic submarine fans range in length from just a few to more than 100 km three different types can be distinguished 1 coarse grained small sized most calciclastic submarine fans were formed on low angle slopes and were sourced from distally steepened carbonate ramps subjected to high energy currents under these conditions shallow water loose grainy sediments were transferred to the ramp slope and eventually funnelled into the submarine fan by sediment gravity flows these conditions seem to have been more easily met on leeward margins in which the formation of reefs was hampered by cool waters nutrient enrichment or oligophoty another circumstance that contributes to the transfer of shallow water sediments to the distal ramp slope is a low sea level forcing the carbonate factory closer to the slope break and destabilizing sediments by increased pore water pressure however the most important factor controlling the development of calciclastic submarine fans was the existence of an efficient funnelling mechanism forcing sediment gravity flows to merge downslope and build up a point sourced sedimentary accumulation in most cases this occurred through a major slope depression associated with tectonic structures an inherited topography or large scale mass failures

environments and processes of manganese deposition concentration of manganese in solution and its deposition takes place by redox controlled processes in a variety of modern and ancient geologic and geochemical environments modern mn deposition occurs predominantly in deep sea areas rather than shallow water domains although deep sea sedimentary deposits dominate hydrothermal contribution of mn to the ocean system may be substantial mn deposition from hydrothermal solutions at or near sea floor spreading centers and less commonly in island arc areas is known in addition near and far field dispersion of mn from vent sites is also substantial such distributions are controlled by the flow rate and egress temperature of the solution and the residence time of mn in seawater thus even in sedimentary deposit domains at least partial derivation of mn from a hydrothermal source is possible sedimentary fe mn crusts on older volcanic substrates on seamounts form by hydrogenous deposition of metal concentrated from terrigenous sources in the mid water column oxygen minimum zones thus the presence or absence of volcanic rocks is not a clear indication of whether sedimentary mn deposits particularly in the ancient geologic record are the result of a totally terrigenous or a totally volcanogenic source abyssal fe mn nodules are considered to form from a basin water hydrogenous and or pore water early diagenetic supply of metals but in most cases the extent of supply from either of the sources is unknown the metal incorporation mechanisms of free moving nodules is little understood and it is possible that in most cases both sources contribute to the nodule composition therefore no nodule should be considered as totally hydrogenous or totally early diagenetic based only on its bulk composition the determined growth rate giving only an average value cannot by itself reveal the growth history of the nodules biological participation directly or indirectly controls mn deposition the stratified black sea demonstrates the concentration of mn in solution in an anoxic zone its advection toward the redox interface and its precipitation in an oxygenated condition similar stratified basins are contemplated for ancient mn deposition in shallow water basin margin areas geologic and geochemical signatures indicate that during sea level highstands stratified basins formed in which mn was concentrated in solution in the anoxic part corresponding transgression led to the impingement of the redox interface on the continental shelf and precipitation of mn oxides could take place across the interface during transgression regression cycles offshore in anoxic or dysaerobic conditions mn carbonate could form by early diagenetic reaction of mn super 2 with co 2 or hco 3 super produced by organic carbon oxidation critical mn deposits occurring in transgressive glaciogenic and black shale bearing ancient sequences support this paleoenvironmental model for mn deposition

paragenesis of cretaceous to eocene carbonate reservoirs in the ionian fold and thrust belt albania relation between tectonism and fluid flow this paper examines the diagenetic history of dual i e matrix and fracture porosity reservoir lithologies in cretaceous to eocene carbonate turbidites of the ionian fold and thrust belt close to the oil producing centre of fier ballsh central albania the first major diagenetic event controlling reservoir quality was early cementation by isopachous and syntaxial low mg calcite these cements formed primarily around crinoid and rudist fragments which acted as nucleation sites in sediments in which these bioclasts are the major rock constituent this cement can make up 30 of the rock volume resulting in low effective porosity in strata in which these bioclasts are mixed with reworkedmicrite isopachous syntaxial cements stabilized the framework and matrixporosity is around 15 the volumetric importance of these cements their optical and luminescence character distribution and dull orange luminescence and stable isotopic signal 18o and 13c averaging respectively 0 5 vpdb and 2 vpdb all support a marine phreatic origin within these turbidites and debris flows several generations of fractures alternated with episodes of cementation a detailed reconstruction of this history was based on cross cutting relationships of fractures and compactional and layer parallel shortening lps stylolites the prefolding calcite veins possess orange cathodoluminescence similar to that of the host rock their stable isotope signatures 18o of 3 86 to 0 85 vpdb and 13c of 0 14 to 2 98 vpdb support a closed diagenetic rock buffered system a similar closed system accounts for the selectively reopened and subsequently calcite cemented lps stylolites 18o of 1 81 to 1 14 vpdb and 13c of 1 52 to 2 56 vpdb within the prefolding veins brecciated host rock fragments and complex textures such as crack and seal features resulted from hydraulic fracturing they reflect expulsion of overpressured fluids within the footwall of the frontal thrusts after folding and thrust sheet emplacement some calcite veins are still rock buffered 18o of 0 96 to 0 2 vpdb and 13c of 0 79 to 1 37 vpdb whereas others reflect external i e extraformational and thus large scale fluid fluxes some of these veins are linked to basement derived fluid circulation or originated from fluid flow along evaporitic decollement horizons 18o around 3 0 vpdb and 13c around 1 5 vpdb others are related to the maturation of hydrocarbons in the system 18o around 7 1 vpdb and 13c around 9 3 vpdb an open joint system reflecting an extensional stress regime developed during or after the final folding stage this joint system enhanced vertical connectivity this open joint network can be explained by the high palaeotopographical position and the folding of the reservoir analogue within the deformational front the joint system is pre burdigalian in age based upon a dated karstified discordance contact sediment filled karst cavity development is linked to meteoric water infiltration during emergence of some of the structures despite its sediment fill the karst network is locally an important contributor to reservoir matrix porosity in otherwise tight lithologies development of secondary porosity along bed parallel and bed perpendicular i e layer parallel shortening stylolites is interpreted as a late stage diagenetic event associated with migration of acidic fluids during hydrocarbon maturation development of porosity along the lps system enhanced the vertical reservoir connectivity

sequence stratigraphy and bedding rhythms of an outer ramp limestone succession late kimmeridgian northeast spain facies stratal and spectral analyses of an outer ramp lime mudstone succession aguilon north iberian ranges spain are presented in this work the studied succession is late kimmeridgian eudoxus and beckeri zones in age and comprises the transgressive and highstand deposits of a third order depositional sequence a number of higher order sequences bundles and sets of bundles have been identified based on the comparative analysis of the bedding planes the bundles and sets of bundles show a well defined stratal pattern spectral analysis has provided further independent confirmation of the cyclical nature of the bundles and sets of bundles defined from field analysis the bundles have variable thickness from 1 to 2 m and are formed by up to 10 micritic beds they have been related to sea level changes controlled by the orbital precession cycle affecting the shallow productivity area a significant amount of the lime mudstones accumulated in outer ramp settings were derived from resedimentation of the shallow carbonate production areas many of the bundles show a lower interval with a thinning and fining up trend indicating a progressive decrease of the carbonate production and carbonate export during periods of high frequency sea level rise the late transgressive and highstand deposits show sets of bundles groups of five bundles from 5 to 8 m probably related to sea level changes controlled by the short eccentricity cycle the overall thickness and the stacking pattern observed in the sets of bundles are controlled by the long term sea level variation the sets of bundles located in the late transgressive deposits show thinner micritic beds in their lower or middle part the sets of bundles found in the highstand deposits are thinner and show a thickening up and thinning up trend on the studied carbonate ramp during periods of long term sea level rise the overall carbonate production and carbonate export is high although the superposition of the high frequency sea level rises may result in episodic flooding and drowning of the shallow ramp areas during periods of long term early highstand of sea level the overall carbonate production and carbonate export is more reduced but it has maximum peaks during the transgressive and early highstand intervals of the high frequency sea level cycles sedimentation during the long term sea level fall late highstand was scarce and discontinuous in the outer ramp area and resulted in the overall thickness reduction of the sets of bundles d 2003 elsevier science b v all rights reserved

composition and provenance of the macigno formation late oligocene early miocene in the trasimeno lake area northern apennines abstract sandstone petrography and mudstone mineralogy and geochemistry of the late oligocene early miocene terrigenous deposits of the macigno fm of the trasimeno lake area central italy provide new information on provenance paleoenvironment palaeoclimate and geodynamics during the early stages of the northern apennines foreland basin setting sandstones are rich in trace fossils and are quartzofeldspatic with various crystalline phaneritic mostly granitoids and medium low grade metamorphic rock fragments volcanic and sedimentary lithic fragments are rare the mudstone mineralogy contains a large amount of phyllosilicates quartz and feldspars and small amount of calcite which increases in the mid part of succession palaeoweathering indices chemical index of alteration with and without cao value cia and cia respectively suggest a source area that experienced low to moderate weathering and low recycling processes on average cia 66 4 and cia 69 7 furthermore very low and homogeneous values of rb k ratios the sandstone and mudstone composition reflects a provenance derived from uplifted crystalline rocks the different amount in feldspars the variety of lithic fragments the occurrence of mafic and carbonate input coupled with evidence of multi directional flows suggest a provenance from different source areas the geochemical proxies indicate a provenance from both felsic and mafic sources predominantly for the maesta section that shows cr v values ranging from 1 15 to 3 36 typical of source areas composed of both felsic and mafic rocks the western central alps are inferred to be the main source area of the macigno foreland system but significant signals from the mesomediterranean microplate are also testified these new data suggest that the macigno fm was probably located in a peculiar area which received either distal fine turbidite flows from the northernmost alpine area and residual sandy debris flows coming from the westernmost alps

oxidation of detrital pyrite as a cause for marcasite formation in marine lag deposits from the devonian of the eastern us late devonian black shale successions in the eastern us contain numerous discontinuities that are characterized by lags containing variable amounts of quartz sand mixed with reworked pyritic and phosphatic debris these lags can be partially cemented by iron sulfides with a radial fibrous to massive morphology examination of iron sulfide cements via electron backscatter diffraction ebsd shows that these cements can consist entirely or partially of marcasite it is proposed here that oxidation and dissolution of reworked pyrite debris led to favorable conditions for intermittent rapid marcasite formation by forcing a substantial ph drop in the surface sediment and by raising dissolved iron concentrations in the pore waters