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

organic geochemical proxies of paleoceanographic paleolimnologic and paleoclimatic processes abstract organic matter constitutes a minor fraction of marine and freshwater sediments yet its important contribution to the sedimentary record can be used to reconstruct marine and continental paleoenvironments the organic matter content of sediments is the residue of past biota the amounts and types of organic matter present in sediments consequently reflect environmental conditions that impacted ecosystems at different past times general sources of the organic matter are inferred from bulk properties such as elemental compositions carbon and nitrogen stable isotope ratios rock eval pyrolysis data and organic petrography details of organic matter origins are refined by analyses of biomarker molecular compositions source changes are proxies for fluctuations in sea level oceanic surface currents and continental climates algal paleoproductivity rates are indicated by organic carbon mass accumulation rates and carbon and nitrogen stable isotopic compositions these parameters record past availability of nutrients and therefore are proxies of surface mixing in the oceans and amount of land runoff to lakes sea surface paleotemperatures are recorded by the number of carbon carbon double bonds in lipid biomarkers produced by marine algae larger proportions of the double bonds are proxies for the cooler surface waters that accompanied periods of global glaciation and intervals of enhanced upwelling the 13c and d values of plant organic matter record past concentrations of carbon dioxide in the atmosphere and changes in delivery of atmospheric moisture respectively diagenesis which causes the concentration and composition of organic matter in sedimentary settings to differ from those of the original biologically synthesized materials can bias organic geochemical paleoenvironmental records the magnitude of this potential source of misinformation must always be considered and evaluated comparison of multiple organic geochemical proxies of past conditions helps to compensate for the effects of diagenetic alterations and thereby to improve interpretations of paleoenvironmental change

history of the celebes sea basin based on its stratigraphic and sedimentological record abstract the stratigraphic and sedimentary history of the celebes sea basin provides the basis for a tectonic model for its evolution which is consistent with new regional plate reconstructions cores drilled on leg 124 of the ocean drilling program sites 767 and 770 form a stratigraphic record from the basement to the sea floor in just under 800 metres of sedimentary succession the basement itself is basalt with a strong morb affinity radiolaria in pelagic mudstones at the base of the succession indicate a late middle eocene age a very condensed pelagic sequence 90 m in 20 ma suggests a setting which was distal from sources of terrigenous clastics and volcaniclastics and below the ccd these characteristics are similar to the west philippine sea basin drilled on dsdp legs 31 and 59 which also has oceanic basement dated at 44 42 ma and paleogene pelagic strata these data are therefore consistent with any plate reconstruction model which has these two basins forming as part of the same ocean basin during the miocene quartz rich sandy turbidites were deposited in the celebes sea basin this influx of terrigenous clastics occurred for a brief period in middle to late miocene times c 10 ma the nearest large continental landmass which could have acted as the source of this mature siliciclastic detritus was the island of borneo and the onset of this clastic supply may be related to uplift caused by collision events on the island cessation of terrigenous clastic supply to the basin centre occurred as southward subduction of the underlying oceanic crust beneath the northern arm of sulawesi began it is speculated that the development of a trench along the southern margin of the basin acted as a trap for detritus coming from borneo diverting material from the basin centre

an exhumed palaeozoic underwater scenery the visean mud mounds of the eastern anti atlas morocco about one hundred carbonate mud mounds covering an area of 440 km 2 in the eastern anti atlas of morocco constitute one of the largest mound agglomerations known so far from lower carboniferous settings they occur within a 4000 m thick succession of shales with intercalated bedded limestones sandstones and siltstones according to conodont and goniatite biostratigraphy mound formation started in the early gnathodus texanus zone and terminated during the g bilineatus zone of the visean stage individual mounds are a few metres to 30 m high have base diameters of up to 300 m and are concentrated in several parallel wnw ese running belts from their lithology and facies relationships four types of mounds can be distinguished 1 massive crinoidal wacke or packstones without stromatactis 2 massive crinoidal wacke or packstones with rare stromatactis 3 similar to 2 but allochthonous and 4 biodetrital skeletal grainstone mounds while carbonate deposition in types 1 to 3 was probably triggered by microbial precipitation type 4 is the result of a predominantly mechanical accumulation of skeletal debris biota in the four types comprise a great variety of invertebrates among which crinoids sponges and bryozoans are most common diagenesis of the mound carbonates was dominated by recrystallization of micritic matrix and organic remains and late burial cementation oxygen and carbon isotope data of brachiopod and crinoid ossicles matrix and early marine cements plot in a large field and do not allow definite conclusions about the composition of the ambient seawater microbial activity and the absence or scarcity of green algae colonial corals and coralline sponges suggest deposition of the mounds in moderate water depth close to the lower limit of the photic zone d 2001 elsevier science b v all rights reserved

depositional facies and stratal geometry of an upper carboniferous prograding and aggrading high relief carbonate platform cantabrian mountains n spain seismic scale continuous exposures of an upper carboniferous bashkirian moscovian carbonate platform n spain provide detailed information about the lithofacies and stratal geometries quantified with differential global positioning system measurements of microbial boundstone dominated steep prograding and aggrading platform margins progradational and aggradational platform to slope transects are characterized by distinct lithological features and stratal patterns that can be applied to the understanding of geometrically comparable high relief depositional systems the bashkirian is characterized by rapid progradation at rates of 415 970 m my 1 characteristic outerplatform facies are high energy grainstones with coated intraclasts ooids and pisoids moderate energy algal skeletal grainstones to packstones and lower energy algal packstone and boundstone units the moscovian aggradational phase is characterized by aggradation rates of 108 m my 1 coated grain shoals are less common whereas crinoidal bars nucleated in well circulated settings below wave base boundstones form a belt 30 300 m wide at the platform break and interfinger inwards with massive algal skeletal wackestones mud rich banks the progradational phase has divergent outer platform strata with basinward dips of 12 to 2 steep clinoforms with dips of 20 28 are 650 750 m in relief and possibly sigmoidal to concave in the lower part the basinward dipping outer platform strata might be depositional for less than 6 consistent with lithofacies deepening seaward the basinward dip is attributed to the downward shift of upperslope boundstone forced by late highstand and relative sea level fall and to compaction induced differential subsidence during progradation the aggradational phase is characterized by horizontally layered platform strata clinoforms steepen to 30 45 reaching heights of 850 m and are planar to concave the evolution from progradation to aggradation at the bashkirian moscovian boundary is attributed to increased foreland basin subsidence and decreased boundstone accumulation rates progradation was primarily controlled by boundstone growth rather than by highstand shedding from the platform top within the major phases aggradational progradational increments are produced by third to fourth order relative sea level

carbonate slopes and gravity deposits in this special volume a series of papers are presented that concentrate on sedimentation patterns observed on the slopes and within the basins surrounding shallow water carbonate depositional systems four papers discuss depositional patterns on the slope to basin transect of the cainozoic sedimentary system of the bahamas four other papers examine gravity deposits of jurassic and cretaceous carbonate depositional systems

paleoenvironmental reconstruction of microbial mud mound derived boulders from gravity flow polymictic megabreccias visean sw spain abstract the upper visean outcrops from the guadiato valley cordoba sw spain provide a well preserved record of the mud mound factory which was developed in a mainly siliciclastic synorogenic foreland basin during the oblique sinistral collision of two terranes ossa morena and central iberian blocks the first onset of mud mound development has been recorded as microbial mud mound derived boulders in polymictic megabreccias as result of strong tectonic activity the upper visean record from the mississippian central band at guadiato valley starts with lower heterolithic units up to 180 m thick and shows two major tectonically controlled cycles a fining upwards interval fu followed by a coarsening upwards interval cu these cycles are linked to two active margins with gravelly fan delta development and different source areas mud mound derived boulders occur in the cu interval and are formed by peloidal primary and secondary reworked automicrites and allomicrites showing a diverse faunal and floral assemblage although never as the main skeletal framebuilders however the observed coeval richness in sponges lyssacinose hexactinellids and non lithistid demosponges and the diverse calcareous algae assemblage in mud mound derived boulders are not common in other visean buildups the growth cavities display changes in the geopetal relationships between fillings and the secondary cavities containing sand to gravel fillings reflecting a complex pre boulder and mud mound derived boulder history detailed mapping sampling stratigraphic and microfacial analyses have allowed the reconstruction of the mud mounds sedimentary environment prior to the collapse transport and emplacement as boulders with polymictic gravels

active slivering of oceanic crust along the molucca ridge indonesia philippine implication for ophiolite incorporation in a subduction wedge a recent marine geophysical survey in the northern molucca sea revealed the structure to be that of a classical active convergent margin we observe from west to east a volcanic arc sangihe a forearc basin resting on an outer ridge the molucca ridge which serves as a buttress for an accretionary wedge and a composite downgoing plate snellius ridge and philippine sea basin gravity modeling indicates a strong negative anomaly above the wedge which cannot be explained with reasonable density values modeling imposes a basement deepening and a rupture of the 700 km long subducting lithosphere this process individualized the lithospheric slab from the snellius ridge which in turn was separated recently from the south philippine basin by the incipient philippine trench this induces a deformation of the forearc region with backthrusting of the outer ridge and forearc basin visible on bathymetry and seismic data we extrapolate the tectonic emplacement of such oceanic blocks to the oligocene times in order to explain the origin of the pujada miangas outer ridge as a sliver previously incorporated to the margin and we discuss the possibility of this deformation process being fabric for terrane accretion

structural elements of the sulu sea philippines the structure and tectonic history of the sulu sea are described on the basis of seismic reflection data combined with the findings of onshore and offshore geological studies and the results of odp leg 124 drilling closing of a hypothetical mesozoic proto south china sea associated with the formation of oceanic crustal splinters in the late eocene followed by southward subduction and in turn progressive collision of the north palawan continental terrane with the micro continental borneo plate since the middle miocene resulted in the formation of the structurally complex sulu borneo collision belt the latter comprises north sabah southern and central palawan and the northwest sulu basin fracturing of the borneo micro continental plate into the sulu and cagayan ridges initiated the opening of the southeast sulu basin during the late oligocene through the early miocene collision of the north palawan continental terrane with cagayan ridge in the late early miocene and oblique collision of these blocks with the central philippines resulted in the still ongoing closing of the southeast sulu basin since the middle or late miocene closing of the southeast sulu basin began with the formation of an oceanic crustal slab

neogene sediment thickness and miocene basin floor fan systems of the celebes sea abstract in the celebes sea basin the middle miocene turbidites were correlated from odp site 767 throughout the studied area differences in their regional thickness variations and distribution indicate two source areas the middle miocene turbidite fan complexes of the central and southern celebes sea basin are controlled by the paleo tarakan delta system the tectonic events and the basin floor morphology respectively the main source area for the time correlative turbidites along the southern sulu arc is assumed to be mindanao the correlation of the middle miocene to pleistocene sequences exhibit tentative ages for the development of the accretionary wedges along the cotabato trench and along the north sulawesi subduction a post middle miocene to pre pliocene age is inferred for the cotabato wedge and a plio pleistocene age is assumed for the north sulawesi wedge

sequence development of a latest devonian tournaisian distally steepened mixed carbonate siliciclastic ramp canning basin australia abstract the sequence development and evolution of latest devonian earliest carboniferous fairfield group in the canning basin have been established through integration of detailed sedimentological analysis of core petrophysical data existing biostratigraphic data and new seismic interpretations the fairfield group on the lennard shelf was deposited on a mixed carbonate siliciclastic distally steepened ramp with a broad inner ramp narrow mid ramp and steepened outer ramp the majority of facies associations fa1 fa8 were formed in intertidal shallow subtidal conditions in proximal to distal inner ramp including siliciclastic tidal flats fa1 carbonate intertidal flats fa2 tidal flats and channels fa3 lagoons fa4 fa5 and shallow subtidal fa6 backshoal fa7 and fore shoal areas fa8 bioclastic muddy sandstone fa9 and bioclastic mudstone fa10 are the dominant mid ramp facies recognition of turbiditic facies of middle to lower slope of the outer ramp fa11 fa13 led to the identification of a distally steepened ramp antecedent topography exerted a significant control on platform morphology and the development of the widespread inner ramp facies on the lennard shelf a sequence stratigraphic analysis reveals that the fairfield group ramp deposits consists of four third order sequences s1 s4 that were largely deposited during sea level highstands hst characterized by progradational trends and dominant shallow subtidal inner ramp facies associations transgressive systems tracts tst are well developed in s1 and s3 and have a retrogradational facies pattern with dominant deep subtidal mid outer ramp facies associations lowstand systems tracts characterized by lowstand wedges and turbiditic facies are identified in the lower parts of s2 and s3 coarse and fine grained siliciclastic facies are mixed with carbonate facies as a result of coeval deposition on the inner and mid ramp and reciprocal deposition on the outer ramp a temporal variation in the types of carbonate grains and the amount of siliciclastic facies from the mixed peloidal skeletal carbonate siliciclastic ramp in s1 and s2 to the mixed skeletal carbonate siliciclastic ramp in s3 and a siliciclastic dominated ramp in s4 is interpreted as the change from a greenhouse to an icehouse state

intensified oceanic circulation during early carboniferous cooling events evidence from carbon and nitrogen isotopes abstract the early carboniferous was a climatic transition interval from a mid paleozoic greenhouse world into the late paleozoic ice age it was marked by a long term cooling trend that was punctuated by short glaciations in the tournaisian and visean early to mid early carboniferous here we generated organic carbon and nitrogen isotope profiles for two widely separated lower carboniferous sections arrow canyon range nevada and namur dinant basin belgium in order to assess the global nature and timing of changes in the carbon nitrogen cycles linked to oceanic productivity and redox conditions during this climatic transition interval the carbon and nitrogen isotope profiles of both study sections record major perturbations during the mid tournaisian and visean a mid tournaisian event tice is marked by increases in 13ccarb 13corg and 15nbulk at arrow canyon from 0 6 to 7 0 25 2 to 23 7 and 0 6 to 8 9 respectively and namur dinant from 0 3 to 4 7 27 9 to 22 2 and 5 7 to 5 2 respectively an early visean event vice named herein is marked by increases in 13ccarb 13corg and 15nbulk at arrow canyon from 0 6 to 3 1 28 4 to 23 6 and 1 4 to 9 4 respectively and namur dinant from 2 1 to 4 3 26 7 to 25 0 and 1 4 to 3 3 respectively the positive excursions in all three isotopic records during these events are consistent with increased fractional burial of organic carbon and enhanced denitrification implying intensification of marine productivity and expansion of hypoxia in the global ocean given that each event coincided with lowering of sea surface temperatures and increased glaciation as documented from published conodont 18o and sea level records we hypothesize that global cooling led to intensified oceanic circulation and upwelling on continental margins triggering increased marine productivity and attendant redox changes within the affected upwelling zones our results provide new insights into changes in early carboniferous oceanic conditions in response to the initial stages of cooling leading into the late paleozoic ice age

new paleomagnetic constraints on the cenozoic tectonic evolution of the north arm of sulawesi indonesia abstract extensive paleomagnetic sampling 34 sites was carried out in cenozoic formations of the north arm of sulawesi between 120 and 124 e consistent results obtained between 120 and 122 e suggest the existence of a unique post miocene clockwise rotation of about 20 25 of the western part of the north arm this rotation probably occurred during the northward drift of the north arm along the palu matano sinistral transcurrent fault between 122 5 and 124 e both clockwise and counterclockwise rotations with various amplitudes from 6 to 85 are encountered and these very likely correspond to individual microblock rotations due to pervasive deformation along shear zones this result is consistent with the complex fault system of the gorontalo and kotamobagu shear zones that have been recognized on radar imagery and by spot image analyses

devonian carboniferous boundary glacioeustatic fluctuations in a platform to basin direction a geochemical approach of sequence stratigraphy in pelagic settings abstract we investigated high resolution stratigraphic distribution of selected major and trace elements and gamma ray spectra of fourteen devonian carboniferous d c boundary sections of europe located in the late palaeozoic laurussia and gondwana the aim was to trace the geochemical signature of a marked forced and normal regressive interval which was associated with rapid progradation of siliciclastics into the marine carbonate systems rhenish massif and a prominent hiatus in shallow water ramp settings namur dinant basin this interval represents the late devonian hangenberg event hbe sensu lato middle praesulcata conodont zone as defined by previous authors this regressive interval fsst to lst correlates with thin shale layers hbe shale sandwiched between monotonous nodular calcilutite calcisiltite successions at five pelagic sections of moravia carnic alps montagne noire and pyrenees in all sections with continuous d c sedimentation i e except those of the namur dinant basin the hbe s l interval is accompanied by elevated percentages of detrital proxies al k rb zr and changes in their ratios zr rb k al rb k which are normally interpreted as indicators of increased siliciclastic input provenance and grain size zr rb and other proxies are traceable even without apparent lithological evidence and can therefore facilitate stratigraphic correlation paleoredox and productivity proxies u th and ni rb enrichment factors only rarely show elevated values in the hangenberg black shale interval indicating that the associated water dysoxia anoxia was a local rather than global phenomenon global correlations based on the hbe black shales should therefore be dropped in favor of the hbe s l interval moreover analysis of sedimentation rates in the upper expansa to kockeli zone interval using the published radiometric ages suggests that the hbe s l was a time of significant increase in the rate of siliciclastic supply into the ocean even in the most distal pelagic sections consequently the previous interpretation of the hbe black shale as a condensed succession deposited during rapid sea level rise seems unlikely we interpret the hbe s l i e including the hbe black shale as a marine record of glacioeustatic sea level drop and increased aeolian transport in connection with late devonian climatic cooling and glaciation the set of geochemical markers related to the late devonian sea level fluctuation can be used for super regional to global correlations from platform to basin settings moreover they can facilitate current efforts to determine a new d c boundary definition

drainage network analysis and tectonics of mindanao southern philippines abstract mindanao southern philippines is the site of an active arc continent collision which began in the late pliocene the principal tectonic features are faults and blind folds and duplexes which are not easily detectable in this island on which 75 of the surface is covered by pleistocene and holocene sediments and volcanics a detailed study of the drainage pattern and its discontinuities in the agusan davao and the cotabato basins when compared with field data radar data and subsurface structures observed on seismic documents enables a correlation of distant seismic lines and features existing on the basin edges the drainage network analysis based on description and interpretation of drainage anomalies and frequency allows us to distinguish 1 subhomogenous drainage areas which correspond to areas bearing consistent geological characteristics and 2 drainage anomalies the results have been checked in the field and compared with the tectonic features in the mountainous areas the extension of these structures could then be traced confidently further towards the flat lowlands we point out the presence of two distinct anomaly directions that intersect in eastern mindanao 1 numerous nnw anomalies in the intra arc basin of agusan davao and both pacific and central cordilleras appear as young features in the morphology and are due to strike slip faults of the arc continent collision some of the faults have proven to be reactivated middle miocene faults related to the initial rifting of the agusan davao basin 2 n s anomaly directions are transpressive ridges due to the collision except one anomaly which corresponds to the trace of the philippine fault zone and connects with the collisional features in contrast the cotabato basin in western mindanao lies between two terranes of different nature in the cotabato basin area the nw and nnw anomaly directions are also present and similarly correspond to strike slip faults and thrust related folds respectively pull apart basins occur in places where sagging is evidenced an additional set of anomalies trends ene and corresponds to the active extensional field below the quaternary sediments some of the en echelon features corresponding to blind flat and ramps structures were identified these observations provide reference examples for the evolution of basins generated within the compressive and strike slip setting of accreted belts

thrust tectonics along the north western continental margin of sabah borneo widely accepted plate tectonic models suggest that an inactive subduction zone lies along the north west continental margin of sabah in contrast interpretation of reflection seismic data acquired by bgr shows an autochthonous continental terrane comprising an oligocene to early miocene carbonate platform being progressively overthrust by an allochthonous rock complex progressive compression resulted in the development of four structural zones imbricated thrust sheets zone iii two thrust sheet systems one on top of the other zone iv a complex zone with multiphase deformation zone v and piercement ridges zone vi

the banda celebes sulu basin a trapped piece of cretaceous eocene oceanic crust the banda celebes and sulu basins are poorly understood marginal seas located at the junction of the eurasian indian australian and pacific philippine sea plates the incompleteness of the data sets the complex geology of the surrounding islands and the late cenozoic evolution involving subduction rifting transform faulting and island arc collision have complicated tectonic interpretation of the region the banda basin is underlain by oceanic crust1 3 bowin et al 2 and lapouille et al 3 have suggested that it is a trapped oceanic basin which was once continuous with the late jurassic argo abyssal plain off north west australia similarly the celebes and sulu basins are also underlain by oceanic crust4 6 on the basis of newly identified magnetic reversal ages fig 1 heat flow data and on land geological studies we suggest that the celebes and sulu seas may have been continuous with the banda basin this cretaceous eocene basin has been dissected into its present configuration by tertiary tectonic processes

disobedient sediments can feedback on their transportation deposition and geomorphology abstract most sediments are obedient to the winds waves and currents which direct their transportation and deposition it has long been recognized however that the grain size and or grain kind of sediments can feedback on the processes of their own transportation deposition and geomorphology as well as that of succeeding deposits this note is to review three examples of marine sediments in which a single grain size or grain kind produces multiple feedbacks tidal bars of holocene ooid sands on great bahama bank are an example of multiple feedbacks of one grain kind on tidal currents wave action and accumulations these feedbacks are responsible for the distinctive pattern of elongated bars and channels which in turn amplify tidal currents the near constant movement of grains on the shallow bars and in the channels is where pellet nuclei are coated to form ooids thus the development and growth of bars feeds back to produce more ooids regional encrinites which consist predominantly of the disarticulated highly porous skeletons of crinoids are common from ordovician to jurassic during blooms of these filter feeders the resulting grains which are equivalent to quartz grains a tenth of their size can be entrained by currents as low as a knot ca 0 5 m s the resulting mobile substrate deters other invertebrates taphonomic feedback and results in the prevalence of layering produced by traction transport of low velocity the belt of mud extending for some 1600 km between the amazon and orinocco rivers is a special example of the feedback of mud on depositional processes sedimentary structures and geomorphology of the accumulations the clay rich mud from the amazon produces fluid mud which dampens and transforms wave action from the open sea to promote its own accumulation in giant bars in the inner shelf and shoreline with a variety of familiar laminations the result is a wedge of mud rich deposits some 24 m thick and 30 km wide capped with cheniers of sand which has prograded seaward in some 6000 years

bacterial mediation red matrices diagenesis devonian montagne noire southern france abstract two devonian red carbonate rock sections are studied in the montagne noire at coumiac frasnian famennian and at the pic de vissou eifelian givetian the sediments are grey red mudstones and wackestones rich in pelagic fossils they are characteristic of an outer ramp the coumiac sequence is condensed with numerous hardgrounds and hiatuses the pic de vissou succession is more complete and of shallower origin in both cases the origin of the red coloration of the micritic matrix is probably linked to bacterial activity which produced submicronic hematite both iron and manganese concentrations are low average 0 2 bacteria form ferruginous microstromatolites blisters microtufts hedgehogs filling sponge perforations and thin continuous mineralized films probably biofilms hardgrounds are underlined by ferruginous microstromatolites the origin of the matrix color is probably related to the destruction of these bacterial constructions the submicronic hematite ultimately coating the crystal faces of the calcite mosaic during early lithification microfissures appeared and were invaded by microbial colonies scanning electron microscopy sem shows that these colonies are composed of spheroidal beads this suggests continuity of the bacterial activity during early diagenesis later on these early fissures were cut by burrows subsequently a secondary fissure network transected all the previously mentioned sedimentary structures this late fissure network is characterized by diagenetically remobilized hematite and or calcite the latest alterations are stylolites and ultimate tectonic fractures

palaeoenvironmental changes at col des tribes montagne noire france a reference section for the famennian of north gondwana related areas we present detailed biostratigraphy based on conodonts and palaeoenvironmental trends deduced from microfacies and conodont abundance through the famennian late devonian at col des tribes montagne noire france the succession is characterized by micritic limestones deposited in settings oscillating between mid to outer ramp facies contain poor fauna widely dominated by nektonic organisms this section is complete and one of the most conodont rich for the famennian of the north gondwana related area the upper kellwasser event frasnian famennian boundary and the hangenberg devonian carboniferous boundary have been lithologically identified they are characterized by decimetre thick black dysoxic to anoxic argillaceous sediments the condroz and annulata events although not materialized by lithological changes have been positioned due to the precise stratigraphy the first event occurred during the deposition of condensed ferruginous facies griotte limestones and the second event during the deposition of micrites barren of benthic fauna the combination of information from both facies and conodont biofacies changes allows a general sea level curve through the entire famennian for north gondwana to be proposed for the first time at col des tribes the general trend is a slight deepening upwards from triangularis to trachytera zones then a pronounced shallowing upwards trend from upper trachytera to praesulcata zones this curve correlates with the well known reference curve from euramerica concerning the late famennian trachytera to praesulcata zones there are some discrepancies in minor cycles which can be explained by tectonical phenomena at the onset of the edification of the variscan belt in europe

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

collision rotation and the initiation of subduction in the evolution of sulawesi indonesia the island of sulawesi indonesia has been shaped and deformed as a result of collision with the sula platform a sliver of continental material from the northern margin of australia new guinea the collision has resulted in rotation of the north volcanic arm of sulawesi and the development of the accretionary wedge of the north sulawesi trench the north sulawesi trench changes laterally from a zone of no active deformation in the eastern part to a wide accretionary wedge in the west early stages of thrusting produce a steep frontal slope 8 16 indicative of relatively high basal shear stress whereas the more advanced western zone of thrusting produces a gentle 2 slope consistent with low basal shear stress reported paleomagnetic data suggest post late eocene counter clockwise rotation of the north arm and the offshore geophysics are explained by a pivot of the north arm with respect to the celebes basin about the eastern end of the arc convergence between the north banda basin and southeast sulawesi is documented by the presence of the tolo thrust its outcrop is strongly arcuate and its accretionary wedge varies in width from a minimum of a few kilometers at each end to a maximum of 30 40 km in the central part the northern end transforms to the leftlateral matano fault with a reported offset of 20 km the southern end of the thrust projects toward the deformed rocks of buton but the structural relations there are not clear the matano fault zone appears to connect westward with the palu fault which forms the western transform of the north sulawesi trench the palu matano fault system acts as a trench trench transform between the north sulawesi trench and the tolo thrust and this system is described by the same rotation pole as that for the sulawesi north arm

lithofacies character and architecture across a pennsylvanian inner platform transect sierra de cuera asturias spain abstract seismic scale outcrops of lower pennsylvanian steep margined carbonate platforms in northern spain sierra de cuera cantabrian mountains provide the opportunity to link depositional facies to platform interior architecture lithofacies character vertical stacking patterns and spatial distribution of depositional facies and shallowing upward cycles were investigated to provide a semiquantitative depositional model for inner platform strata a 70 m thick succession of eight shallowing upward cycles 2 5 15 m thick was studied across a 2 km wide transect cycles consist of algal bioherms and skeletal packstone lithofacies association b deposited in an open marine and sub wave base environment which are locally lateral to crinoid dominated packstone lithofacies association d lithofacies association b developed on a transgressive one meter thick high energy coated grain grainstone lithofacies association a and is overlain by open marine to restricted lagoonal deposits lithofacies association c indicative of decreased paleo water depth cycle boundaries are marine flooding surfaces occurring at the base of lithofacies a and the top of lithofacies c petrographic and outcrop evidence of subaerial exposure is conspicuously lacking cycle and lithofacies thickness varies laterally and all the lithofacies can be either continuous for the 2 km width of investigation or discontinuous terminating within tens to hundreds of meters in most of the cycles the lithofacies succession changes laterally because of lateral facies transitions between lithofacies b and d and pinching out of lithofacies a and c meter scale variations in depositional topography are related to the stacked lens shaped bioherms assigned to lithofacies b and appear to control the thickness and lateral continuity of the overlying facies sierra de cuera strata do not resemble other pennsylvanian cycles driven by high frequency high amplitude glacio eustasy which are commonly characterized by subaerial exposure surfaces developed on subtidal deposits except for the absence of peritidal facies and the presence of low relief algal bioherms on the platform top the necessary accommodation to enhance the growth of bioherms on the platform top was probably due to high frequency 100 240 ky moderate amplitude nearly 40 m sea level fluctuations combined with subsidence rates of 70 140 m my tectonic subsidence might have been responsible for the lack of evidence of subaerial exposure surfaces in the examined moscovian strata the studied inner platform lithofacies character and architecture were controlled by the interplay of high frequency changes in accommodation and the presence of meter scale depositional topography attributed to lateral variations of carbonate accumulation

development of a late visean mississippian mixed carbonate siliciclastic platform in the guadalmellato valley southwestern spain abstract the penas rubias syncline southwestern spain exposes a well preserved shallow water platform succession containing a spectrum of facies corresponding to inner platform intertidal to supratidal environments across to deeper water middle to outer platform environments nineteen microfacies are recognized which are grouped into seven facies association corresponding to siliciclastic deltaic bars mixed carbonate siliciclastic shoals carbonate mud mound boundstones background platform carbonates background platform siliciclastics mixed tempestites and deep water siliciclastic shales and sandstones the age of the succession was determined mainly by foraminiferans and calcareous algae which permit the succession to be assigned to the late brigantian latest visean this upper brigantian platform is the only record of sedimentation of this age in the region and thus is key for interpreting the sedimentary and tectonic evolution of the carboniferous rocks in sierra morena biotic and sedimentological features were analyzed in order to assess the controls on the sedimentation several factors have influenced sedimentological changes turbidity subsidence siliciclastic discharges storms and bioturbation the siliciclastic discharges exerted a considerable control on the basal deposits mostly in their percentage of quartz sand grains and as microconglomerates however they did not develop as large deltaic deposits and their influence can be considered as virtually negligible in regards to the remaining part of the succession turbidity as a result of higher percentage of silt and mud in suspension seems to be the main factor controlling the change between the older intertidal deposits in the inner platform to the younger subtidal deposits of the middle and outer platform as a result of the increase of the mud and silt in suspension facies changed first to marlstones and nodular argillaceous limestones and second to predominantly calcimicrobial boundstones and shales in the uppermost part of the carbonate succession as well as showing a marked change from photic controlled benthic faunal and microfloral assemblages to assemblages more tolerant or better adapted to muddier dysphotic substrates bioturbation is also interpreted as one of the main controls influencing the different type of boundstones in the middle platform permitting the vertical growth of dome shaped mud mounds or as sheet like deposits storm influences seem to have exerted some control on the positive relief of the dome shaped boundstones which are usually capped by tempestites the differential subsidence observed in the northwestern sector of the platform allowed the accumulation of many stacked dome shaped mounds a feature not recognized in southeastern parts the general stratigraphical sequence seems to be controlled by eustasy and synsedimentary tectonics the overall succession exhibits a pronounced deepening upwards transgressive sequence from siliciclastic delta bars mixed shoals carbonates and shales of the middle platform with the growth of calcimicrobial boundstones and dark green shales passing up into black shales at the top of the sequence in the outer platform and possibly submarine slope settings although this transgressive sequence is in harmony with the 3rd order glacioeustatic cycle defined for the late brigantian in the western palaeotethys all these brigantian rocks accumulated in a synsedimentary extensional regime which is related to the initiation of a sinistral strike slip regime previously recognized as affecting only serpukhovian and younger rocks in sierra morena these synsedimentary faults allow us to recognize significant lateral variations in thickness over short distances

sedimentary patterns and geometries of the bahamian outer carbonate ramp miocene lower pliocene great bahama bank core logging and high resolution seismic data from odp leg 166 were used to analyse deposits of the neogene miocene lower pliocene bahamian outer carbonate ramp ramp sediments are cyclic alternations of light and dark grey wackestones packstones with interbedded calciturbidite packages and minor slumps cyclicity was driven by high frequency sea level changes light grey layers containing shallow water bioclasts were formed when the ramp exported material whereas the dark grey layers are dominantly pelagic calciturbidites are arranged into mounded lobes with feeder channels internal bedding of the lobes shows a north directed shingling as a result of the asymmetrical growth of these bodies calciturbidite packages occur below and above sequence boundaries indicating that turbidite shedding occurred during third order sea level highstands and lowstands highstand turbidites contain shallow water components such as green algal debris and epiphytic foraminifera whereas lowstand turbidites are dominated by abraded bioclastic detritus gravity flow depocentres shifted from an outer ramp position during the early miocene to a basin floor setting during the late miocene to early pliocene this change was triggered by an intensification of the strength of bottom currents during the tortonian which was also responsible for shaping the convex morphology of the outer ramp the miocene and lower pliocene of the leeward flank of great bahama bank provides an example of the poorly known depositional setting of the outer part of distally steepened carbonate ramps the contrast between its sedimentary patterns and the well known upper pliocene quaternary slope facies associations of the flat topped great bahama bank shows the strong control that the morphology of a carbonate platform exerts on the depositional architecture of the adjacent slope and base of slope successions

spatio temporal evolution of a tertiary carbonate platform margin and adjacent basinal deposits abstract the variability in low to moderate energy carbonate platform margins is poorly known from the geological record here the spatial and temporal evolution of platform margin and adjacent basinal deposits is evaluated from the little known tertiary kedango limestone that developed in a semi enclosed marine embayment in se asia the hypothesis here is that platform margin development will reflect regional and perhaps global influences such as tectonics eustasy or biotic change rather than windward leeward effects and storms that typically impact strongly upon open oceanic platforms the development of the carbonate platform was determined through logging petrography facies evaluation provenance and high resolution dating studies eleven carbonate facies were identified from the 30 km long western margin of the 600 m thick platform and its adjacent slope and basinal deposits larger benthic foraminifera and coralline algal packstones and wackestones dominated in shallow waters during the oligo miocene coral patch reef related floatstones rudstones and less commonly boundstones were also present on the platform top perhaps surprisingly for a low energy platform there was considerable variation along the platform margin and much reworking of material into slope and basinal deposits during the oligo miocene reworked material includes shallow water bioclasts clasts from older siliciclastics fresh feldspars lithified slope and platform top carbonate clasts some of the latter showing evidence for karstification the western platform margin varied laterally over a few kilometres from a gently sloping unrimmed platform to a probable bank top with in places coral fringed bypass and erosional faulted escarpment margins eustasy may have influenced shallowing and deepening trends on the platform top but apparently had little impact on mass wasting instead platform margin development was strongly impacted by tectonics including active faulting terrestrial runoff together with changes in carbonate producers and local variability on the platform top

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

tertiary and quaternary magmatism in mindanao andleyte philippines geochronology geochemistry and tectonic setting abstract a set of 230 igneous rock samples from leyte and mindanao philippines has beenstudied for their major and trace element chemistry mineralogy and geochronology 40k 40ar dating several volcanic sectors have been distinguished according to their geographic position tectonic framework and geologic history a in leyte the ophiolitic basement at 50 ma is morb type but characterized by negative nb 0 anomalies typical of back arc basalts miocene 20 and 11 ma and late pliocene to quaternary magmas 2 5 0 4 show typical island are talc alkaline characteristics in eastern mindanao eocene 47 46 ma magmatic rocks are arc tholeiitic while those of miocene 18 6 ma and early pliocene 4 5 ma age are generally talc alkaline dacites of 12 ma age have adakitic compositions the young 3 ma volcanics in surigao and north davao are mostly adakitic although talc alkaline basalts and basaltic andesites dated at 0 9 ma overlie adakites in surigao b in daguma oligocene 30 ma arc tholeiitic diorites intrude older arc sequences miocene0 17 0 7 7 ma dikes and flows in both daguma and sarangani peninsula are mostly talc alkaline andesites although minor adakites dated back to 18 ma have been found overlying undated breccias in daguma in southeast daguma the tale alkaline volcanic substratum of pliocene recent volcanoes is 8 6 ma old quaternary 1 83 ma to present andesitec and dacitic volcanics in mt parker and mt matutum southwest daguma are either talc alkaline or adakitic while mt blit northwest daguma is built up by 2 5 ma old hfse enriched basalts 1 ma old normal talc alkaline andesites and 0 8 ma old adakites c in central mindanao miocene andesites yield ages of 20 and 16 ma pliocene 2 5 ma 0 volcanism is dominated by talc alkaline and hfse enriched basalts and basaltic andesites quaternary lavas i ma to present range in character from tale alkaline to shoshonitic and exhibit wide variations in their trace element behavior d miocene lavas of 19 11 ma age in zamboanga are mostly talc alkaline though a lone 0 18 ma old adakite was also encountered pliocene quaternary basalts and basaltic andesites dated back to 2 2 1 ma are hfse enriched such that some display positive nb anomalies in spidergrams adakites of 3 8 0 7 ma age are located nearer the sulu trench the compositional variety of tertiary recent island arc magmatism in leyte and mindanao couldbe linked to the tectonic settings prevailing during each magmatic phase and is here utilized to refine paleokinematic reconstruction of the tectonic history of the philippine archipelago the identification of adakites at certain time periods is used to date timings of subduction initiations and arc polarity reversals major and abrupt changes in geochemical compositions are well exhibited by the pliocene pleistocene volcanism involving the collision related shift from talc alkaline to shoshonitic volcanism in central mindanao and adakite production in all the volcanic sectors defined the origin of the hfse enrichments among lavas younger than 3 ma could be attributed to the presence in their mantle source of an oib component or alternatively to the enrichment of this mantle source through percolation of slab derived melts

lithofacies and depositional processes on a high steep margined carboniferous bashkirian moscovian carbonate platform slope sierra del cuera nw spain the depositional slope of the sierra del cuera a carboniferous bashkirian moscovian high steep margined carbonate platform provides excellent cross sections of lithofacies zonations and associated stratal geometries the steep 30 40 and nearly planar upper slope is dominated by massive sheet like layers of microbial cement rich boundstone which alternate with intercalations of red stained bryozoan cementstone with crinoids and brachiopods the slightly gentler 20 26 and concave upward lower slope is characterized by clast supported resedimented deposits the upper slope extended from platform break to ca 300 m water depth whereas lower slope sediments were deposited in water depths up to 600 700 m at which level the slope beds flatten to a few degrees toe of slope and interfinger with spiculitic and argillaceous basinal sediments between 250 and 450 m water depth boundstones and breccias alternated in a transitional zone the lower slope sediments include clast supported breccias with radiaxial fibrous cement in interparticle space mud to clast supported breccias with red stained carbonate mud matrix and packstone to grainstone and rudstone beds most of the clasts comprise boundstone reworked from an upper slope setting and smaller grains are platform and slope derived a pervasive submarine cementation occurs along the upper two thirds of the flank and this stabilized the slope slope deposition is interpreted as follows during active boundstone accretion microbial boundstone layers slid off and formed breccia tongues extending from the lower upper slope down to the toe of slope rock falls and avalanches were generated whenever the shear strength of the substrate of loose or partly lithified sediment was exceeded upper slope boundstone accretion and shedding independent of the depth of light penetration controlled most of the depositional processes on the slope cement dominated intervals are considered to be related to early highstand and or flooding phases relative sea level fluctuations and or associated changes in the water conditions are believed to be responsible for intervals of low boundstone production or cement precipitation whether the in situ boundstone and breccia are preferentially related to lowstand or highstand periods is as yet unclear

upper plate deformation induced by subduction of a volcanic arc the snellius plateau molucca sea indonesia and mindanao philippines abstract the northern molucca sea shows the incipient subduction of a composite oceanic and arc volcanic block the snellius halmahera block shb multi beam reflectivity seismic and gravity data obtained during the modec marine survey showed that the shb disappears beneath the accretionary wedge and the outer ridge of the sangihe arc to the north in mindanao island ongoing convergence generated shortening of the forearc basin and the backthrusting of the shb meanwhile a classical system of paired subduction philippine trench and strike slip fault philippine fault was installed the transition from lithospheric subduction to crustal overthrusting is located where the philippine trench sensu stricto begins and also coincides with the off shore extension of the philippine fault we observe a reversal of the thrusts from an eastward vergence in the molucca sea to a westward vergence in mindanao island this reversal takes place at the latitude where the forearc area emerges by uplift and the downgoing crust shb deepens resulting in a strong gravity low centered above the accretionary wedge the philippine fault initiated in a place where the crust was sliced off by a transfer zone which marked the northern termination of the molucca sea and drags northward a sliver of the previously accreted shb the northward drifting of this sliver created an extension which however cannot account for the gravity low we propose that the shortening and the uplift of the upper plate were induced by the buoyancy of the subducted unit shb and triggered the thrust reversal

calciturbidite composition related to exposure and flooding of a carbonate platform triassic eastern alps the compositional variation of calciturbidites pedata potschen formation deposited adjacent to the dachstein formation carbonate platform in the triassic hallstatt basin was analysed using detailed field measurements and point counting of thin sections the 35 m long section is located in the northern calcareous alps of austria six point count groups were distinguished separating basinal from platform derived input summary statistics cluster and correspondence analysis of the point count data reveals a close relationship between the biota present on the dachstein carbonate platform and the calciturbidite composition the variations in turbidite composition are attributed to fluctuations in sea level and resulting flooding and exposure of the platform which alternately created and destroyed shallow water habitats on the platform top

microbially induced fe and mn oxides in condensed pelagic sediments middle upper jurassic western sicily abstract this article presents a petrographic comparison of the rosso ammonitico facies of western sicily and the original rosso ammonitico veronese of northern italy based on a total of 27 sections the rosso ammonitico has been the subject of numerous controversies that range from bathyal to shallow water platform sedimentation therefore it seemed interesting to verify if the term rosso ammonitico has the same geologic connotation from region to region the middle upper jurassic rosso ammonitico of western sicily is a condensed succession formed during a period of extensional synsedimentary tectonics related to the spreading of the ionian ocean slope to basin or pelagic carbonate deposits characterize the sedimentation which consists of reddish mudstones and wackestones the abundant fauna is composed of radiolarians protoglobigerinids saccocoma bositra associated with ammonites a few ferruginous hardgrounds fe mn oxide crusts and mn coated condensation horizons are also present the red matrices contain abundant fe mn encrusted microbored and bioeroded bioclasts sporadic fe mn oncolites composed of amorphous mn minerals and goethite are also conspicuous the matrix as well as the shells and the fillings of the complex associated veinlets are frequently altered into calcite microsparite submicronic iron bacterial and fungal filaments associated with mineralized extracellular polymeric substances eps are observed in the matrix they record dysaerobic microenvironments at or near the sediment water interfaces early mineralized discontinuities enhanced by subsequent pressure dissolution are reported in the succession mn ni bacterial filaments are exceptionally observed in the cortex of the fe mn oncolites as a consequence of an early lithification the mn filaments are poorly preserved the pigmentation of the rock is due to the dispersion of submicronic oxyhydroxides now goethite and amorphous iron formed by bacterial mediation during early diagenesis in microaerophilitic environments as in the case of the original rosso ammonitico veronese fe and mn bacteria fungi were able to produce bioconstructions which have no bathymetric significance the limiting factor must have been the oxygen content which was low in these very quiet and relatively deep environments thus the rosso ammonitico of northern and southern italy have a number of points in common but some obvious dissimilarities are observed that explain some of the various sedimentological interpretations among them the chemical composition is of particular importance more fe is present in veneto northern italy while mn is associated with the sicilian rosso ammonitico the sicilian localities were more proximal to oceanic magmatic sources which were related to the activity of the oceanic crust

waulsortian type bioherm development and response to sea level fluctuations upper visean of bechar basin western algeria abstract an exceptionally well developed and well preserved upper visean succession rich in sponge bryozoan crinoid mounds in the foreland carboniferous bechar basin northwestern algerian sahara is described and discussed the succession is composed of recurrent facies mosaics forming individual superposed members an ideal member is made up of two distinct fades assemblages the lower assemblage forms the actual mounds and is composed of sponge bafflestone wackestone at the base overlain by massive sponge fenestellid bafflestone wackestone and capped by massive crinoid wackestone with bedded flanks of lithoclastic wackestone in contrast to massiveness of the mounds the upper facies assemblage is composed of well bedded crinoid packstone grainstone and ooid grainstone with local rugose coral and algal foraminiferal banks on the basis of benthic assemblages and nature of substrate seven bathymetric zones are defined and indicate that each member of the bioherm rich formations is a shallowing upward parasequence controlled by an asymmetrical transgressive regressive cycle the local curve of relative sea level for the late visean shows 13 cycles interpreted as fourth order eustatic sea level changes each cycle averaging half a million years in duration third order cycles could not be identified the platform model proposed is a distally steepened ramp 15 20 km wide that developed in a rapidly subsiding foreland basin lateral distribution of facies on the ramp depended strongly on local tectonic setting whereas vertical development was controlled by sea level fluctuation the deep water mud rich sponge bryozoan crinoid mounds developed in 100 150 m water depths during phases of sea level highstand whereas deposition of shallow water facies occurred on top of the mounds in less than 70 80 m water depths during regressive phases the bechar mounds share similarities with the classical lower carboniferous waulsortian mounds but they differ in two aspects the abundance of large sponges which is unique and their vertical zonation wherein basal facies consist of sponge dominated assemblages the proposed model can serve as a tool in developing exploration strategies in the search for hydrocarbon reservoirs in the bechar basin because the peculiar architecture of the platform may provide suitable plumbing systems for fluid migration and the depositional signature of the mounds and associated facies is possibly recognizable on seismic profiles

facies patterns and depositional environments of palaeozoic cephalopod limestones abstract in the eastern anti atlas morocco a platform and basin topography was established during the late devonian probably as a result of early variscan tensional tectonics cephalopod limestones were deposited on shallow pelagic platforms platform slopes and shallow slowly subsiding basins on the platform a transition from land areas into nearshore quartzose brachiopod coquinas crinoidal limestones condensed cephalopod limestones and finally into nodular limestones is observed the latter often become disintegrated into incipient debris flows which pass into nodular limestone marl alternations of a shallow basin deeper basins with shale sedimentation lack cephalopod limestones similar facies types also occur in the late devonian of the montagne noire france rheinisches schiefergebirge west germany moravian karst czechoslovakia holy cross mountains poland and in the early carboniferous of the cantabrian mountains spain due to strong late variscan compressional tectonics and limited outcrops detailed facies patterns could not be mapped in these regions but the same facies types as in the eastern anti atlas suggest similar coast platform slope and shallow basin topographies during cephalopod limestone deposition water depth on the platforms was in the order of several tens to about one hundred metres as is inferred from repeated subaerial exposures and distinctive depositional and faunal floral features water depth in the adjacent shallow basins might have reached several hundreds of metres cephalopod limestones represent a typical stage in the evolution of geosynclines characterized by extremely low sedimentation rates 1 5 m m y 1 this stage is preceded by deposition of thick neritic clastics and or carbonates and is succeeded by deposition of deep water clastics or flysch

are beds in shelf carbonates millennial scale cycles an example from the mid carboniferous of northern england abstract the mid carboniferous strata of northern england are characterised by mixed clastic carbonate cycles yoredale cyclothems attributed here to the short eccentricity milankovitch rhythm in a typical cycle transgressive normal marine shelf carbonates are succeeded by marine shales then highstand prodelta mudstones and delta front delta top sandstones with local coals a detailed study of one cycle the great limestone cyclothem of the northern pennines alston block reveals that within the transgressive carbonates the beds averaging 75 cm in thickness and defined by mm shale partings or cm mudrock layers form two thinning upward to thickening upward bed sets individual beds and the bed sets can be correlated across the region oxygen isotope and strontium trace element data also reveal patterns of increasing and decreasing values through the limestone which broadly correspond to the bed thickness cycles the beds are interpreted as millennial scale cycles the result of high frequency arid humid climatic fluctuations the bed sets are interpreted as the response to a longer term arid humid climate and sea level cycle driven by the precession rhythm it is postulated that millennial scale climatic changes which are a well known feature of the quaternary and are here inferred for the carboniferous were responsible for the deposition of the beds that are a characteristic feature of many marine sedimentary successions in the geological record the most likely over riding control is fluctuations in solar output

the influence of different simplified sliding block models and input parameters on regional predictions of seismic landslides triggered by the northridge earthquake abstract regional seismic landslide hazard maps are based on predictions of rigid sliding block displacement derived from estimates of earthquake ground shaking topography geology and shear strength the confidence in these predictions requires comparisons with field observations of landslide occurrence during previous well documented earthquakes this paper presents a comparison between observed landslides from the 1994 northridge california earthquake and predicted landslides based on sliding block displacement estimates seven empirical displacement models each of which uses a different combination of ground motion parameters are investigated to evaluate which models and associated ground motion parameters best predict seismic landslides using best estimates of ground shaking and shear strength properties from the northridge earthquake sliding displacements are calculated and compared with the locations of observed landslides only 20 40 of the observed landslides are captured and the total area of predicted landslides is much larger than observed the ability to predict landslide occurrence accurately depends less on the displacement model and associated ground motion parameters and more on the uncertainty in the model parameters particularly the assigned shear strengths because current approaches do not take into account the spatial variability of shear strength within individual geologic units the accuracy of the predictive models is controlled predominantly by the distribution of slope angles within a geologic unit assigning overly conservative low shear strength values results in a higher percentage of landslides accurately identified but also results in a large over estimation of the total landslide area making more accurate maps of seismic landslide hazards will require methods to define intra formational variations in shear strength

mississippian coral assemblages from the khenifra area central morocco biostratigraphy biofacies palaeoecology and palaeobiogeography abstract analysis of mississippian coral assemblages from the khenifra region of central morocco together with data from foraminiferal algal microfossils has established new age dating of 5 localities within the azrou khenifra basin souk el had and sidi lamine where corals occur mainly in biostromes protected by oolitic shoals tabainout where corals have been recorded in different environments related to microbial mounds alhajra almatkouba where corals occur in biostromal reworked beds and tiouinine where corals occur in a well structured fringing reef this study demonstrates the presence of richer more diverse coral assemblages than previously recorded in a variety of environmental settings these coral assemblages strengthen correlations with the adarouch area in the ne part of the azrou khenifra basin it is emphasised that in the upper visean there are close similarities with rugose coral assemblages in other parts of the western palaeotethys including north africa sw spain and nw europe and that all belong to the same biogeographic province

the palaeoecological distribution of the endothyroids foraminifera in the guadiato area sw spain mississippian abstract this paper focusses on the distribution and methodological problems that are observed in the palaeoecological analyses of the endothyroids from the guadiato area in the southwestern part of the iberian peninsula in spite of a long history of taxonomical and biostratigraphical studies on endothyroids there have been few investigations of their palaeoecology and taphonomy the guadiato area contains a sequence of upper visean to pendleian marine carbonates the upper visean units were deposited in a storm dominated ramp the pendleian strata were deposited in a tectonically controlled shelf with narrow platform facies supra inter and subtidal and a wide area of slope deposits some of the foraminiferal assemblages of this succession typify intertidal facies and incipient shoals and are regarded as para autochthonous other assemblages such as the endothyroids in the higher part of the pendleian slope are of doubtful allochthony it is likely that endothyroids did not live in slope facies it was too deep but the extent of their transportation cannot be determined since their tests do not show signs of abrasion several factors controlled the endothyroid distribution such as salinity and depth deposits formed in high energy environments such as shoals and tidal flats were not favourable for the endothyroids particular palaeoecological factors also determine the distribution of certain families subfamilies or genera one of these factors is relative environmental stability for example some endothyroids that lack secondary deposits the archaediscinae and endothyra priscella were more abundant in stable environments in contrast other genera with secondary deposits the asteroarchaediscinae omphalotis and the evolved endothyra were more abundant in unstable or fluctuating microfacies this factor however did not control the distribution of every genus because this difference is not observed in some species of genera with or without secondary deposits e g globoendothyra

internal structure and depositional environment of late carboniferous mounds from the san emiliano formation carmenes syncline cantabrian mountains northern spain well exposed mounds are common in limestone of the late carboniferous san emiliano formation cantabrian mountains northern spain they occur as obvious primary topographic features careful study of the mound intervals and surrounding strata revealed the internal structures of mounds and the factors controlling their growth the substrate 2 3 m of the mounds consists of greyish to reddish bedded oolitic and oncolithic packstone and grainstone crinoids fragments of the alga epimastopora and rarely bryozoans are present ooids and oncoids indicate a wave dominated high energy environment presence of quartz indicates the influence of terrigenous siliciclastic input mound intervals 6 12 m thick are characterized by skeletal microbial boundstone donezellid algae agglutinated worm tubes and calcisponges are the dominant fossils smaller foraminifers gastropods and brachiopods are also present a peloidal clotted matrix is characteristic and accounts for more than 30 of the mound volume intraframe pores are mainly filled by peloidal sediment and early marine cement intermound strata are approximately one third as thick as time equivalent mounds mound fossils algae agglutinated worm tubes and sponges are uncommon however intermound strata are generally more diverse than the mounds containing fusulinids smaller foraminifers bryozoans gastropods crinoids and bioclasts some of these fossils have micritic envelopes bedded packstone and grainstone 3 6 m thick with siliciclastic debris rugose corals and chaetetid sponges characterize the capping facies coated grains and small ooids are uncommon this facies indicates shallowing to a higher energy environment and or a higher input of siliciclastics inhibiting mound growth mounds are interpreted to have accreted in a quiet environment below wave base this position is comparable to the depositional environment inferred for many late paleozoic mounds described elsewhere e g from texas and new mexico canadian archipelago and carnic alps in austria mound relief is explained by 1 accumulation of peloidal clotted sediments limited to boundstone and probably related to microbial activities 2 widespread marine cementation within this area and 3 low export of mound fossils to intermound areas the position of the mounds within the sequence and their initiation size and termination seem to be mainly controlled by sea level fluctuations and siliciclastic input d 2001 elsevier science b v all rights reserved

neogene arc continent collision in sabah northern borneo malaysia abstract the neogene evolution of sabah can be interpreted in terms of an arc continent collision initiated during early middle miocene time and followed by intraplate shortening the latter being active in this area at the present day the volcanic arc of late oligocene middle miocene age is imbricated with melanges and thrust northwestward on a polyphase deformed turbiditic sequence of late cretaceous middle miocene age crocker range intraplate shortening is seen in the thrusting and folding offshore sabah along the palawan north borneo trench and also by broad open folds and strike slip faulting in the previously sutured terranes this collision can either be interpreted as the final stage of southward subduction of the hypothetical proto south china sea or the result of back thrusting of the sulu volcanic arc resulting from the subduction of the celebes sea toward the north

tectonic setting of western pacific marginal basins abstract global kinematics as well as magnetic anomalies of marginal basins with continental geology and paleomagnetic data as additional constraints are used to present a set of reconstructions of the western pacific marginal basins between 56 ma and the present at key periods 56 43 32 20 12 and 3 ma our model accounts for the rapid motion of exotic terranes along the whole of the western pacific convergent zone marginal basins appear to open in a great variety of tectonic settings the two extreme examples being the mariana trough where trench suction may be the predominant driving force and the south china sea where intracontinental deformation appears to be the major mechanism the study of marginal basins is a 3 d problem which must take into account the whole tectonic context subduction related tectonics in cross section and upper plate deformation in map view and not only a 2 d problem the classical trench arc back arc problem

tectono stratigraphic terranes and detachment faulting of the south china sea and sulu sea abstract geoscientific data acquired from the south china sea and sulu sea areas by bgr since 1977 are compiled and interpreted as comprehensive data sets together with available information of commercial wells and drillsites of the ocean drilling program odp generalized stratigraphy and lithology are discussed and correlated with the interpreted seismic profiles on the basis of the stratigraphic and structural analysis 5 main tectono stratigraphic terranes are defined for the south china sea and 4 main terranes for the sulu sea respectively the dangerous grounds reed bank palawan nw borneo trough and palawan island represent terranes of continental origin which developed on the proto china margin by uniform sense low angle simple shearing within the crust in late cretaceous to early paleocene this rift was abandoned and a new westward propagating rift system developed north of the dangerous grounds reed bank area from the middle eocene to the oligocene early miocene together with seafloor spreading in the south china sea basin the leading edge of the southward drifting continental terranes collided with the late cretaceous to early eocene subduction complex of the northernmost terrane of the proto sulu sea continuous convergence of these terranes back arc spreading creating the se sulu sea terrane and the assumed anti clockwise rotation of borneo are responsible for the complex collision compression structures of the sulu sea terranes including the formation of splinters of oceanic crust major right lateral wrench systems are nnw sse running up to 500 km long and cut across most of the identified terranes wrenching presumably ceased 12 to 16 myr ago

hemipelagic and turbiditic mudstone facies associations in the upper cretaceous gosau group of the northern calcareous alps austria abstract turbiditic and hemipelagic mudstones from the upper cretaceous to lower paleocene nierental formation of the northern calcareous alps austria can be differentiated by employing relatively simole laboratory and higher hemipelagic mudstones turn out to be characterized by finer grain sizes of the non carbonate fraction and higher carbonate contents sediment colour bioturbation distribution of microfossils weathering characteristics and bed sequence analysis were used as additional criteria to recognize the genetically different mudstone types for acquiring the non carbonate grain size data the samples were leached in hydrochloric acid and the remaining siliciclastic material was used for analysis with a sedigraph the median values of the grain size distributions of the turbidite mudstones reach up to 9 7 whereas the hemipelagic median values lie between 9 5 and 10 8 carbonate contents of the turbidite mudstones range between 22 and 68 those of the hemipelagic mudstones between 58 and 82 single bed profiles show distinct vertical trends of both grain size and carbonate content values for the turbidite mudstone division no such trends exist in the hemipelagic mudstone beds five basic types of turbiditic and or hemipelagic mudstones can be recognized 1 turbidite hemipelagite couplets 2 pure hemipelagic mudstone sequences 3 hemipelagic mudstone sequences with very thin turbiditic interacalations 4 a thorouthly mixed turbiditic hemipelagic mudstone type which is characterized by intense bioturbations and 5 mud turbidites without any hemipelagic intervals most of these types occur simultaneously at different localities of the nierental formation

upper devonian and mississippian foraminiferal and rugose coral zonations of belgium and northern france a tool for eurasian correlations the radiation of early carboniferous foraminifers and rugose corals following the devonian carboniferous crisis offers the best tool for high resolution correlations in the mississippian together with the conodonts in the tournaisian notably in the namur dinant basin however some of the guides are facies controlled and an integrated approach combining biostratigraphy sedimentology and sequence stratigraphy is critical to identify delayed entries potential stratigraphic gaps and to avoid diachronous correlations the main difficulty is in correlating shallow and deeper water facies at any given time in existing zonations the visean part of the scheme is always more detailed reflecting the widespread development of shallow water platforms in the early visean which created conditions more suitable for foraminifers and rugose corals over large areas in contrast the tournaisian zones less well documented reflect unfavourable environmental conditions in the lower ramp dinant sedimentation area and pervasive dolomitization of the inner ramp condroz and namur sedimentation areas recent progress in understanding the belgian early carboniferous sequence stratigraphy and lithostratigraphy and revision of the biostratigraphy of the key sections strongly modify former biostratigraphic interpretations improvements mainly concern the latest devonian the late tournaisian and the early visean the late devonian and the tournaisian are equated with foraminifer zones dfz1 to dfz8 and mfz1 to mfz8 respectively the visean correlates with zones mfz9 to mfz14 zone mfz15 straddles the visean namurian boundary and zone mfz16 is the youngest mississippian zone the rugose corals allow the recognition of ten zones rc0 to rc9 covering the strunian late famennian to serpukhovian interval discrepancies with former zonations are discussed the moliniacian stage is emended to restore the coincidence between its base and that of the visean

a mid tournaisian late visean carbonate ramp reconstructed from nappes and olistolites in the southern montagne noire france abstract the mainly calcareous succession from the mid tournaisian to the lower part of the upper visean in the southern montagne noire mont peyroux nappes and cabrieres slices is sedimentologically revised from the late visean the variscan orogeny affected the area and the studied mississippian part of the succession was considered as part together with the devonian of a period of tectonic quiescence later included as nappes and olistolites in a wildflysch this study presents the facies from pelagic limestones calciturbidites bioclastic limestones and microbial limestones and the relationship between platform and calciturbidites in the pre orogenic context of the montagne noire basin during the mississippian the differences in the lithostratigraphy is analyzed by means of four tectonostratigraphical units mont peyroux nappe roquessels band cabrieres area and la serre band previously defined by other authors that together with the deep water vieussan caragnas unit not studied here due to the poverty in chronostratigraphical data allow reconstructing the original carbonate platform the latter seems to correspond to a ramp for the latest tournaisian to early visean and a distally steppened ramp from the middle visean to the early late visean including basin plain to slope as the deepest water environments and middle ramp as the shallowest except for the uppermost part of the succession where the inner ramp is recognized during this period the shallowing tendency in the tectonostratigraphic units is well marked mont peyroux nappe roquessels band cabrieres area la serre band from deeper to shallower which differs from the shallowing trend defined by previous authors during the devonian strong similarities are observed with the preserved mississippian carbonates in the mouthoumet massif to the south which might represent the shallowest water deposits of the ramp not preversed in the cabrieres la serre areas

paleomagnetic evidence for clockwise rotation of the northern arm of sulawesi indonesia abstract paleomagnetic results from the northern arm of sulawesi show that the arm has been subjected to a clockwise rotation of more than 90 and that its rotational motion began no later than the middle miocene the mean direction showing a normal polarity at the eocene to the early miocene is d 98 0 and i 6 9 a declination value of d 50 1 obtained from miocene rocks indicates a transition stage of the rotational motion the datum from plio pleistocene volcanics is d 4 6 and i 9 3 this suggests that the rotational motion terminated before the initiation of volcanic activity during the plio pleistocene

structural controls on the evolution of the kutai basin east kalimantan abstract the kutai basin formed in the middle eocene as a result of extension linked to the opening of the makassar straits and philippine sea seismic profiles across the northern margin of the kutai basin show inverted middle eocene half graben oriented nne ssw and n s field observations geophysical data and computer modelling elucidate the evolution of one such inversion fold nw se and ne sw trending fractures and vein sets in the cretaceous basement have been reactivated during the tertiary offset of middle eocene carbonate horizons and rapid syn tectonic thickening of upper oligocene sediments on seismic sections indicate late oligocene extension on nw se trending en echelon extensional faults early middle miocene n7 n8 inversion was concentrated on east facing half graben and asymmetric inversion anticlines are found on both northern and southern margins of the basin slicken fibre measurements indicate a shortening direction oriented 290 310 ne sw faults were reactivated with a dominantly dextral transpressional sense of displacement faults oriented nw se were reactivated with both sinistral and dextral senses of movement leading to the offset of fold axes above basement faults the presence of dominantly wnw vergent thrusts indicates likely compression from the ese initial extension during the middle eocene was accommodated on nne ssw n s and ne sw trending faults renewed extension on nw se trending faults during the late oligocene occurred under a different kinematic regime indicating a rotation of the extension direction by between 45 and 90 miocene collisions with the margins of northern and eastern sundaland triggered the punctuated inversion of the basin inversion was concentrated in the weak continental crust underlying both the kutai basin and various tertiary basins in sulawesi whereas the stronger oceanic crust or attenuated continental crust underlying the makassar straits acted as a passive conduit for compressional stresses

insight into the development of a carbonate platform through a multi disciplinary approach a case study from the upper devonian slope deposits of mount freikofel carnic alps austria italy the development and behavior of million year scaled depositional sequences recorded within palaeozoic carbonate platform has remained poorly examined therefore the understanding of palaeoenvironmental changes that occur in geological past is still limited we herein undertake a multi disciplinary approach sedimentology conodont biostratigraphy magnetic susceptibility ms and geochemistry of a long term succession in the carnic alps which offers new insights into the peculiar evolution of one of the best example of palaeozoic carbonate platform in europe the freikofel section located in the central part of the carnic alps represents an outstanding succession in a fore reef setting extending from the latest givetian indet falsiovalis conodont zones to the early famennian lower crepida conodont zone sedimentological analysis allowed to propose a sedimentary model dominated by distal slope and fore reef slope deposits the most distal setting is characterized by an autochthonous pelagic sedimentation showing local occurrence of thin bedded turbiditic deposits in the fore reef slope in a more proximal setting there is an accumulation of various autochthonous and allochthonous fine to coarse grained sediments originated from the interplay of gravity flow currents derived from the shallow water and deepwater area the temporal evolution of microfacies in the freikofel section evolves in two main steps corresponding to the freikofel unit 1 and the pal unit 2 limestones distal slope to fore reef lithologies and associate changes are from base to top of the section u1 thick bedded litho and bioclastic breccia beds with local fining upward sequence and fine grained mudstone intercalations corresponding in the fore reef setting to the dismantlement of the eifelian frasnian carbonate platform during the early to late frasnian time falsiovalis to rhenana superzones with one of the causes being the late givetian major rift pulse u2 occurrence of thin bedded red nodular and cephalopod bearing limestones with local lithoclastic grainstone intercalations corresponding to a significant deepening of the area and the progressive withdrawal of sedimentary influxes toward the basin in relation with late frasnian sea level rise ms and geochemical analyses were also performed along the freikofel section and demonstrate the inherent parallel link existing between variation in ms values and proxy for terrestrial input interpretation of ms in terms of palaeoenvironmental processes reflects that even though distality remains the major parameter influencing ms values carbonate production and water agitation also play an important role