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

carbonate gravity flow deposition along a platform margin scarp silurian north greenland abstract an extensive carbonate platform fringed the north greenland cratonic margin in the middle ordovician early silurian and was bordered by a steep erosional bypass escarpment dipping about 45 in silurian times a huge elongate sand rich submarine fan developed in the deep water basin north of the platform sourced from the rising caledonian mountain belt to the east longitudinal siliciclastic turbidite deposition in the basin was punctuated by coarse grained carbonate debris flows and turbidity currents derived from the carbonate platform four main episodes of carbonate sedimentation are recognized represented by composite sheets tens of meters thick transport mechanisms included rock fall grain flow debris flow sandy turbidity current and dilute low density muddy turbidi y current the four conglomerate units span a period during which the height of the scarp decreased from 1300 to 0 m due to progressive infilling of the basin by turbidites the carbonate conglomerates deposited when scarp relief was at a maximum primarily record rock fall and viscous debris flow processes they form persistent sheets that extended up to 50 km out onto the basin floor and they constructed significant topographic highs that may have influenced siliciclastic turbidite dispersal patterns in the basin the youngest conglomerate unit was deposited following foundering of the outer platform and onlap of basinal sediments to the lip of the platform debris from carbonate build ups to the south flowed northwards to be deposited as thick conglomerate beds immediately north of the relict platform scarp the conglomerates show giant load structures pronounced pinch and swell indistinct low angle foreset bedding and abrupt snout like distal wedging out of beds such features may have resulted from a change in flow properties on passing over the buried scarp from the lithified outer platform onto rapidly deposited water rich sandy turbidites the decrease in scarp height from 1300 to 0 m thus influenced transport mechanisms of carbonate gravity flows but the overall geometry and organization of the individual base of slope units remained unchanged they all have the character of debris sheets organized systems such as fans are absent

pegmatite emplacement in the serido belt northeastern brazil late stage kinematics of the brasiliano orogen abstract geometric and kinematic analysis was performed in an area located in the central part of the serido belt ne brazil where supracrustal rocks affected by polyphase deformation are well exposed the first event recognized in this area and regionally known as the d 2 deformation is characterized by top to the south thrust tectonics while a second one d 3 deformation is marked by upright folds strike slip or transpressive shear zones and the development of flower structures major pegmatite swarms were emplaced during and late as regards the second event dated ca 580 ma being part of the brasiliano orogeny similar dyke swarms are known from the nigerian shield these pegmatite swarms provide reliable kinematic markers of the late evolutionary stage of the neoproterozoic trans sahara borborema collisional belt mineralogical geometric and kinematic features support two stages of pegmatite emplacement during the strike slip event i older syn d 3 homogeneous pegmatites intruded mostly along lithological and structural discontinuities such as foliation surfaces ii late d 3 heterogeneous pegmatites were emplaced along tension gashes and other dilation structures the heterogeneous pegmatites are economically more important being exploited for precious metals and stones as well as industrial minerals

geometry spatial arrangement and origin of carbonate grain dominated scour fill and event bed deposits late jurassic jubaila formation and arab d member saudi arabia

brazilian structural provinces an introduction abstract the territory of brazil coincides almost entirely with the south american platform the crystalline core of the continent its basement is composed of ancient metamorphic and igneous rocks and it has not suffered any tectonic regeneration since the beginning of the phanerozoic sedimentary rocks with almost horizontal bedding cover this crystalline basement this latter shows ages as old as early precambrian although ages between 500 and 1000 m y are conspicuously frequent the cratonic areas became consolidated more than 1700 m y ago whereas the fold belts formed essentially between 500 and 1700 m y ago the sedimentary cover accumulated from the early silurian in three large intracratonic basins until the platform became completely stabilized a late jurassic to early cretaceous reactivation caused by the break up of the ancient gondwana continent created another basin sequence chiefly along the atlantic continental margin based on the nature of the crystalline basement rocks and the sedimentary cover ten structural provinces can be distinguished 1 rio branco province in the north of the country occupied by the guyana shield and still only poorly known with an important fold belt developed during the so called transamazonian cycle 2000 200m y with high grade metamorphic rocks and only slight influence of later events 2 tapajos province in central brazil corresponding to the amazonas or guaporecraton showing chiefly precambrian crystalline rocks and behaving as an cratonic area during the phanerozoic 3 sa o francisco province located on the atlantic shield with its basement covered by rocks of different ages chiefly affected by the brasiliano cycle between 1000 and 500 m y and constituting another cratonic area 4 tocantins province between the amazonas and sa o francisco cratons with the oldest rocks in its centre ages over 2600 m y and at the eastern and western borders metamorphic sequences of various fold belts and almost no phanerozoic deposits 5 mantiqueira province located along the southern part of the atlantic coast affected chiefly by the brasiliano folding cycle 6 borborema province in the northeast brazilian fold belt affected by the brasiliano cycle in a very complex way and with important faulted zones it was reactivated in phanerozoic times when also sedimentary covers accumulated 7 amazonas province represented by the amazonas sedimentary basin syneclise and subdivided into four parts by three important arcs 8 parnaiba province coinciding with the piauf maranha o syneclise and filled with a rather thick sedimentary sequence 9 paranaprovince the sedimentary basin of southern brazil in which the well known late paleozoic glaciation features are found and which possesses an extensive cover of basaltic rocks of late jurassic to early cretaceous age 10 coastal province and continental margin the youngest structural unit developed during the separation of the continent and represented by rift valleys and coastal basins filled with mesozoic cenozoic deposits of various kinds

a review of gold mineralization styles in finland a wide range of styles of gold mineralization has been recognized in finland including orogenic metamorphosed epithermal skarn or epigenetic ironstone hosted intrusion related nonskarn massive sulfide hosted paleoplacer and placer deposits gold production in the past was principally as a byproduct from the mining of paleoproterozoic base metal massive sulfide deposits this situation has changed during the last decade with the closure of some base metal mines and the commencement of production from recently discovered gold only deposits gold mineralization occurred during distinct episodes of crustal evolution in finland several late archean greenstone belts in the karelian craton in eastern and northern finland contain orogenic gold deposits dated at about 2 75 to 2 70 ga suggesting a coherent and pervasive tectonic and metallogenic event in the paleoproterozoic low grade the main accretionary stage of the svecofennian orogeny in finland culminated with metamorphism and deformation between 1 89 and 1 86 ga during that time intrusion related au cu mineralization took place in both syntectonic porphyry stocks and their wall rocks in and close to the archean proterozoic margin orogenic gold mineralization took place at or slightly after the metamorphic peak throughout the svecofennian domain possibly also overprinting massive sulfide and intrusion related occurrences it is notable that the largest orogenic deposits are located within discrete plutons rather than hosted by supracrustal sequences this may be a consequence of the rheological contrasts between plutons and the supracrustal lithologies the paleoproterozoic lapland domain in the northern part of the country records a protracted and complicated evolution involving multiple episodes of rifting magmatism sedimentation and alteration culminating at around 1 9 ga with the collision of the karelian craton the svecofennian fold belt to the south and the kola craton to the north these deformational events led to orogenic gold mineralization throughout the proterozoic greenstone belts of northern finland at about 1 89 to 1 86 ga during and soon after the peak of metamorphism and deformation skarnlike or epigenetic ironstone hosted deposits were also formed during the orogeny in the western and southwestern parts of the lapland domain probably somewhat later at around 1 86 ga the most favorable sites for mineralization are regionally extensive zones of early albitization that predate gold mineralization the deposition of molasselike sediments during the terminal stages of the svecofennian orogeny and weathering of both orogenic and syngenetic sulfide mineralization also prior to 1 8 ga produced placer accumulations now paleoplacers in the conglomerates of the uppermost formation of the central lapland greenstone belt placer deposits of controversial origin and provenance have also been worked for many years in the glaciofluvial sediments of northernmost finland the areas with greatest potential for the discovery of new orogenic gold deposits in finland are the late archean and paleoproterozoic greenstone belts in eastern finland and lapland respectively some fe cu au skarns or epigenetic ironstone hosted deposits have been mined in the past and there may be potential for the discovery of larger iron oxide copper gold systems in the western central lapland greenstone belt for intrusion related nonskarn mineralization the most promising areas are close to the raahe ladoga suture and the potential for additional metamorphosed and deformed epithermal mineralization exists in the tampere schist belt the significant number of gold occurrences already known in these areas highlights the potential for new discoveries

tectonic evolution of south america during the late proterozoic abstract this paper discusses the evolution and the late proterozoic assembly of the south american continent i e the west gondwana under the light of global tectonics the northern portion of the continent the amazonian craton is a pre brasiliano domain it may be a fragment derived from laurentia this domain behaved as a large continental plate which was accreted to the central and southeastern portions of the continent brasiliano domain the brasiliano domain had a more complex history and composition during the brasiliano cycle middle proterozoic to early paleozoic in the brasiliano domain several late proterozoic continental plates have been identified sao luiz west africa congo kasai sao francisco rio de la plata arequipa antofalla which acted as forelands to the brasiliano orogenic belts that surround and amalgamate these plates smaller fragments of pre brasiliano continental lithosphere are common in the interior of the brasiliano orogenic belts and played diversified roles microplates microcontinents structural highs some of them have acted as true backlands hinterlands flanked by arc magmatism two principal types of brasiliano orogenic belts are recognized between the continental plates a marginal orogenies to the late proterozoic plates with pelitic carbonatic rocks and discrete volcanism which were thrust by collision onto the margin of the plates and which seem to represent final products of previous passive margin sequences b distal orogenics internal belts within the continental masses sometimes a branching system of orogenics that contain varied clastic and minor carbonate sedimentary rocks accompanied by important bimodal volcanism and calc alkaline plutonism for these orogenies a greater variety of basinal scenarios and tectonic settings may be visualized the amalgamation of the continent during the late proterozoic i e the formation of the brasiliano structures indicates the existence of practically synchronous multilateral stresses within lithospheric plates this can be produced by complementary adjustment of the continental plates as a response to major global events elsewhere analogous to modern continental collisions two large and important tectonic zones may be candidates to such a scenario the hijaz mozambique zone site of connection of east and west gondwana and the transbrasiliano lineament which cuts across south america and extends to north africa following the zone of connection between pre brasiliano and brasiliano domains other small ocean openings and closings inside the various brasiliano areas dom feliciano gariep for instance were minor events and complementary to the other two major tectonic zones mentioned above

microstructural evolution of the serido belt ne brazil the effect of two tectonic events on development of c axis preferred orientation in quartz the polyphase evolution of the serido belt ne brazil includes d crust formation at 2 3 2 1 ga d 2 thrust tectonics at 1 9 ga and crustal reworking by d 3 strike slip shear zones at 600 ma microstructural investigations within mylonites associated with d 2 and d 3 events were used to constrain the tectono thermal evolution of the belt d 2 shear zones commenced at deeper crustal levels and high amphibolite facies conditions 600 650 degreesc through grain boundary migration subgrain rotation and operation of quartz q prism slip continued shearing and exhumation of the terrain forced the re equilibration of high t fabrics and the switching of slip systems from c prism to positive and negative a rhombs during d 3 enhancement of ductility by dissipation of heat that came from syn d 3 granites developed wide belts of amphibolite facies mylonites continued shearing uplift and cooling of the region induced d 3 shear zones to act in ductile brittle regimes marked by fracturing and development of thinner belts of greenschist facies mylonites during this event switching from a prism to a basal slip indicates a thermal path from 600 to 350 degreesc therefore microstructures and quartz c axis fabrics in polydeformed rocks from the serido belt preserve the record of two major events which includes contrasting deformation mechanisms and thermal paths c 2003 elsevier ltd all rights reserved

morphometric analysis of colanguil river basin and flash flood hazard san juan argentina this work analyzes various morphometric characteristics of the colanguil river basin in order to evaluate flash flood hazards such high water events pose a risk to the similarly named small village located at the basin s foot area for this purpose the basin is divided into seven sub basins and some basic measurements surface perimeter basin length river beds elevations and slope of the main river bed and of a number of minor river beds are calculated these measurements permit to predict approximately the behavior of the basin in the presence of a series of theoretical rainstorms that may generate unusual runoff volumes that make up such flash floods

controls on focused flow and dispersed flow deepwater carbonates miocene agua amarga basin spain abstract common models for carbonate slope or basin margin sedimentation emphasize the contrasts between linear sediment sources and point sediment sources geologic mapping and high resolution stratigraphic study of a set of miocene outcrops exceptional for their three dimensional exposure and preservation of paleotopography demonstrates that paleotopographic focus or lack thereof may be a dominant control on geometries and sediment character of sediment gravity flow deposits in line sourced systems in the agua amarga basin se spain basin topography is initially modified by subaerial exposure and erosion of volcanic basement to form paleovalley systems after late miocene marine inundation topography is partially modified by infilling of high energy shallow water heterozoan deposits units 1 and 2 that subdued topography in one area to produce a ramp like surface but did not significantly infill a large paleovalley located in another area further relative rise in sea level resulted in an extensive reefal platform that formed along a paleo high adjacent to both features la rellana platform subsequent sediment gravity flow deposits shed from this reefal platform followed two pathways down the ramp like surface dispersed flow or into the large flooded paleovalley focused flow deposits within each system display contrasting lithofacies architectures these deepwater deposits units 3 7 in this study consist of carbonate breccia facies coarse facies graded skeletal packstone facies coarse facies and planktonic foraminifera rich facies fine facies that are interpreted as sediment gravity flow deposits and pelagic sediments relative sea level fluctuations resulted in deepwater facies variations in the large paleovalley as a result of significant backstepping and progradation of the rellana reefal platform on a gently sloping surface fining of basinal deposits and shelfward migration of the locus of deposition for sediment gravity flows is associated with sea level rise coarsening of basinal deposits and basinward migration of the locus of deposition for sediment gravity flows is associated with stillstand and relative fall in sea level both relationships demonstrate a direct link between the locus of reefal platform growth and style of basin sedimentation early parts of relative rises in sea level late parts of highstands and falling stages led to transport of abundant coarse sediment into the basin focused flow deposits were line sourced and funneled into the axis of a large margin parallel paleovalley and confined to a channel volume ratio of coarse facies to fine facies is estimated at 0 7 deposits in proximal paleovalley locations display compensation geometries around positive relief on debrites channelization erosional truncation lapout against paleovalley walls and some drape as a result of lateral confinement and proximity to the sediment source deposits in distal paleovalley locations display increasingly tabular geometries as a result of decreasing lateral confinement and concentration of coarse grained sediment gravity flows down depositional dip dispersed flow deposits were line sourced into the basin along a gently inclined ramp like surface that lacked paleotopographic focus volume ratio of coarse facies to fine facies is estimated at 0 1 the less complex sheet like depositional geometries and locations of these deposits result from the absence of lateral confinement and subtle changes in substrate slope focused flow sediment gravity flow deposits that are confined by topographic elements such as channels are most likely to form sizeable accumulations of coarse facies with characteristics most appropriate for conventional oil and gas exploration there are many paleotopographic configurations that can lead to focusing of flows so this deepwater carbonate system may be more common than previously recognized

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

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

deciphering potential groundwater zone in hard rock through the application of gis remote sensing and geographic information system has become one of the leading tools in the field of hydrogeological science which helps in assessing monitoring and conserving groundwater resources it allows manipulation and analysis of individual layer of spatial data it is used for analysing and modelling the interrelationship between the layers this paper mainly deals with the integrated approach of remote sensing and geographical information system gis to delineate groundwater potential zones in hard rock terrain the remotely sensed data at the scale of 1 50 000 and topographical information from available maps have been used for the preparation of ground water prospective map by integrating geology geomorphology slope drainage density and lineaments map of the study area further the data on yield of aquifer as observed from existing bore wells in the area has been used to validate the groundwater potential map the final result depicts the favourable prospective zones in the study area and can be helpful in better planning and management of groundwater resources especially in hard rock terrains

seismic architecture of a lower cretaceous platform to slope system santa agueda and poza rica fields mexico two three dimensional seismic data sets over the albian western golden lane margin and time equivalent basinal deposits of poza rica field allowed us to investigate the linked architecture of a steep sided carbonate platform el abra formation and a thick accumulation of redeposited carbonate sediment at the toe of the slope and in the basinal area tamabra formation regional seismic cross sections show that the most aggrading albian platform has an eroded platform top a scalloped margin and a channelized slope that are equivalent to a 20 km 12 4 mi wide westward thinning thick toe of slope apron made of chaotic contorted mounded moderate to high amplitude reflections detailed reflection geometries in the albian toe of slope and basinal deposits consist of chaotic to short discontinuous low amplitude reflection at the toe of the slope of the golden lane platform laterally changing to a discontinuous mounded shingling reflection which ultimately turns into high amplitude parallel reflections we interpret this lateral change to reflect the seismic signature of the change from the block and debris flow dominated toe of slope area to debris flow and concentrated density flow deposits in the basin that ultimately grade laterally into pelagic deposits on a flattened seismic slice mounded reflections correspond to lobate to fan shaped seismic events several kilometers wide that are interpreted as a carbonate basin floor fan comparison between core and seismic data shows a dominance of debris flows in the lower two albian sequences albian 1 and albian 2 that grade vertically into more lobate concentrated density flows and turbidites in the upper two albian sequences albian 3 and albian 4 seismic data used in this study combined with core observations do not support the interpretation of the albian tamabra formation being of shallow water origin seismic features identified as basin floor fan channel and debris flow deposits have a shape and size that are similar to those of other redeposited basinal carbonate deposits elsewhere the seismic architecture shows that the poza rica field is a typical example of thick accumulation of grainy porous carbonate deposits in a basinal setting this example shows the potential of a large hydrocarbon accumulation in a tectonically modified stratigraphic trap around shallow water carbonate platforms

ductile duplexing at a bend of a continental scale strike slip shear zone example from ne brazil abstract during the pan african orogeny the borborema province in ne brazil developed a continental scale shear zone system that comprises ne and ew trending ductile strike slip shear zones remote sensing and structural mapping has revealed a pattern of arcuate anastomosing strike slip shear zones separating sigmoidal lenses of less deformed material located at the western end of the ew trending patos shear zone which is one of the largest shear zones of the province this structure of imbricate shear zones was initiated under high temperature deformation conditions it is interpreted as a ductile strike slip duplex and may represent a kinematic pattern for strain accommodation in response to a bend of a ductile mega shear zone

giant sector collapse structures scalloped margins of the yangtze platform and great bank of guizhou china implications for genesis of collapsed carbonate platform margin systems

automated recognition of valley lines and drainage networks from grid digital elevation models a review and a new method abstract the literature on valley and drainage line recognition from grid digital elevation models dems is reviewed two problems preventing the successful delineation of fully connected drainage networks of single line width are identified a the positioning of the ends of drainage networks and b the assignment of drainage directions to a dem in particular the assignment of drainage directions across flat areas and at closed depressions in the dem pits a new method for drainage network delineation is suggested which incorporates an alternative method for drainage direction assignment over a dem this method is found to produce realistic directions and performs well on two complex dems

trap and seal analysis in carbonate shelf margin stratigraphic trap exploration example from the lower miocene zhujiang formation pearl river mouth basin people s republic of china abstract carbonate shelf margin stratigraphic traps are a particularly risky play type because the same diagenetic factors responsible for secondary reservoir quality enhancement can be responsible for degrading seal quality and increasing trap risk the zhujiang fm prograded westward off the dongsha massif initially as a ramp which evolved into a prograding and aggrading shelf margin seismic interval velocity analysis modeled with data from a nearby oil bearing pinnacle reef indicates a thick porosity zone at the shelf margin wedging and pinching out eastward core data from the pinnacle reef indicated a short term exposure event was responsible for significant early secondary porosity enhancement this also may have influenced the adjacent shelf area enhancing porosity in the shelf margin but reducing seal capacity in the equivalent up dip shelf sequence the seal competency of the overlying hanjiang shales was demonstrated by hydrocarbons sealed in the adjacent pinnacle reef seal risk was evaluated by mercury injection capillary pressure analysis in a shelf carbonate well updip from the margin it was determined that the up dip shelf seal is sufficient to hold an economically favorable 300 500 ft 90 150 m hydrocarbon column seismic evidence revealed several large mega slumped portions of the shelf margin producing scalloped areas extending severalmore kilometers back into the shelf subsequent filling of these reentrants could produce lateral sealing by juxtaposing hanjiang shales against the sides of the remnant zhujiang carbonate salient the slump scar on the south side of the salient did not downcut to a significant stratigraphic depth to provide a critical closure to trap a minimum hydrocarbon column to meet economic thresholds less

drainage morphometry of himalayan glacio fluvial basin india hydrologic and neotectonic implications morphometric analysis being widely used to assess the drainage characteristics of the river basins has been found to be a useful tool to delineate the glacial till covered overburden material as well as to identify areas prone to flash floods in present studies a number of parameters including the stream frequency drainage density and drainage texture suggest that the unconsolidated unstratified and highly permeable glacially deposited overburden till material facilitates the infiltration of snowmelt and rainwater in the pindari glacio fluvial basin eastern kumaun himalaya india likewise other till overburden covered glacial and proglacial areas of higher himalayan regions have been contributing to the groundwater budget the shape parameters further suggest that the sub basins with higher form factor are more prone to flash floods besides this the anomalies in the morphometric parameters have been found to be a useful tool to delineate zones of active tectonics in such areas

sequence stratigraphy and systems tracts of a mixed carbonate and siliciclastic platform basin setting the albian of lunada and soba northern spain in the lunada soba carbonate platform basin setting albian of basque cantabrian region northern spain nine type 1 depositional sequences have been identified their boundaries represent times of complete exposure of the platform with accompanying karstification and fluvial erosion relative sea level falls of 15 50 m have been estimated from depths of erosion or from diagenetic effects on platform materials and facies analysis during lowstands deposits of the corresponding systems tract onlapped the platform foreslope or filled incised valleys on the platform top these deposits comprise a variety of facies limestone megabreccias derived from the platform margin allodapic grainstones hemipelagic marls fine grained turbiditic sandstones basinal lutites fine gra ned estuarine sandstones bank bafflestones and grainstones fluvio deltaic pebbly conglomerates and sandstones and shallow water orbitolinid grainstones relative sea level rises were characterized by deposition of monotonous marls in the basin and by the growth of coral rudist mud mounds and accumulations of skeletal grainstones and marls sometimes with back stepping stacking on the platform during highstands hemipelagic marls and prodeltaic and talus delta lutites and sandstones dominated in the basin whereas coral wackestones and orbitolinid grainstones sometimes with prograding clinoforms dominated on the platform transgressive surfaces have erosion or simply omission features such as pebble lags or numerous burrows respectively no well developed condensed sections exis and they are represented by thin beds of marls rich in orbitolinids transgressive and highstand systems tracts are normally difficult to differentiate both in the basin and on the platform but in sequences with an accused wedge shape the presence of back stepping and prograding stacking patterns makes it easier four main types of sequences are documented based on geometrical characteristics three of them are continuous from the platform to the basin tabular wedge shaped with tilted base and wedge shaped with incised base the fourth type scalloped is discontinuous from the platform to the basin it results from the collapse of the platform margin whose debris contributed to form the following sequence and the unveiling of the underlying sequence at the site of collapse most of the sequence boundaries suggest a tectonic influence and three of them show angular unconformities in the basin margin and or the inner platform these angular unconformities show major erosional vacuities at the cores of anticlines on the inner platform they are attributed to phases of accentuated transpression in a major strike slip tectonosedimentary environment related to the opening of bay of biscay a local curve of albian relative sea level changes correlates in part with the eustatic curve of the vail charts

late devonian carbonate margins and foreslopes of the lennard shelf canning basin western australia part a development during backstepping and the aggradation to progradation transition abstract carbonate reefal margin and foreslope settings are characteristically heterogeneous and difficult to predict due to a spectrum of sediment source factories resedimentation processes resultant deposit types and controlling parameters in particular the effects of changes in long term accommodation on the composition architecture and sediment distribution patterns of carbonate margin foreslope basin systems are poorly understood upper devonian frasnian outcrop exposures along the lennard shelf northeast canning basin western australia were investigated to assess the development of reefal margin and foreslope settings during long term 1 platform backstepping with aggradational pulses and 2 across the transition from platform aggradation to progradation measured sections tied to interpreted photomosaics and detailed mapping using aerial photographs were collected from the south lawford range and windjana gorge areas the exposures reveal distinctive differences in foreslope grain composition deposit characteristics and proportions margin morphology and stratigraphic expression 1 during platform evolution between backstepping events and 2 depending on position within the long term accommodation setting between backstepping events aggradational margins can be classified as growth escarpments with associated grain dominated onlapping foreslope deposits margins across the long term transition from aggradation to progradation evolved from erosional escarpments with onlapping debris deposits to accretionary interfingering configurations development of growth escarpments between backstepping events was a function of vertical reefal growth from sustained high accommodation conditions during the long term transgressive systems tract coupled with a frasnian reefal assemblage that responded to light and tracked relative sea level this net vertical reefal growth also resulted in relative margin stability and the deposition of grain dominated foreslopes conversely margins were highly unstable and underwent repeated failure across the long term aggradation to progradation transition reflecting a lack of underlying substrate to support basinward advance and resulting in debris dominated foreslopes these observations provide relationships that predict margin and foreslope associations of facies scale heterogeneity and seismic scale geometry within a low frequency sequence stratigraphic framework

palaeogeographical reconstructions of the pan african brasiliano orogen closure of an oceanic domain or intracontinental convergence between major blocks abstract a reconstruction of the pan african brasiliano orogen has become possible thanks to new data from the southern pan african belt and by using published data geological mapping which included structural thermobarometric and geochemical studies in togo and neighbouring countries have enabled to define the existence of a preorogenic continental rift whose closure followed soon after its opening continental crust convergence induced an oblique collision that caused nappe stacking this involved external nappes thrust over the west african craton intermediate nappes including metabasic rocks with eclogitic assemblages and internal nappes composed of highgrade anatectic gneiss and intrusive granite and charnockite comparison with data from other regions hoggar adrar des iforas northeastern brazil nigeria central africa has led to the recognition of a pre orogenic continental rift that bordered the west africa sao francisco congo cratons in the southern part of the chain farther north in the hoggar and adrar des iforas this continental rift opened on a wider oceanic domain which involved a passive margin along the west african craton and an active margin to the east after these rifting and subduction stages continental collision followed that was dominated by strike slip movement oblique to the plate boundaries the general organization of the pan african brasiliano belt can be considered as the result of a confrontation between three major continental domains these were the west african and sao francisco congo cratons and a reworked shield composed in its inner part of polycyclic basement rocks and bounded by a fringe of monocyclic metasedimentary thrust belts that faced the cratons

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

quantitative analysis of morphometric parameters of kali river basin southern india using bearing azimuth and drainage bad calculator and gis this study deals with the application of visual basic program bearing azimuth and drainage bad calculator which employs a new and easy methodology for extraction of watershed morphometric parameters using bad calculator morphometric analysis was carried out for the kali river basin of southwest coast of india the basin forms a part of the western ghats which is an important mountain range of the indian sub continent and runs nearly parallel to the coast spatial maps of six morphometric parameters have been prepared from the results obtained various linear areal shape and relief morphometric parameters of fifth and sixth order basins have been calculated and interpreted majority of the sub basins show less uniform values 3 to 4 of rbm which indicate the uniform and systematic branching pattern of streams high dd zones are found in the western ghats region whereas low dd zones are observed in the eastern part of the basin and near the estuary the eastern part of the basin shows low fs values whereas nw and sw parts of the basin show high fs values compared to manual measurement bad calculator requires minimal time to quantify the morphometric parameters experimental results show that the software is effective in calculating drainage parameters such as drainage density frequency bifurcation ratio etc using the text file of esri shapefile

a mesozoic time scale we present an integrated geomagnetic polarity and stratigraphic time scale for the triassic jurassic and cretaceous periods of the mesozoic era with age estimates and uncertainty limits for stage boundaries the time scale uses a suite of 324 radiomenc dates including high resolution 40 ar 39 ar age estimates this framework involves the observed ties between 1 radiometric dates biozones and stage boundaries and 2 between biozones and magnetic reversals on the seafloor and in sediments interpolation techniques include maximum likelihood estimation smoothing cubic spline fitting and magnetochronology

three dimensional geological and synthetic seismic model of early permian redeposited basinal carbonate deposits victorio canyon west texas the lower permian outcrops of victorio canyon in the sierra diablo mountains in west texas show undisturbed stratigraphy of carbonate toe of slope and basinal deposits these rocks consist of a vertical stack of carbonate debris flow deposits and hyperconcentrated density flow deposits thick skeletal ooid grainstone deposited as basin floor fans various reworked muddy carbonate deposits and fine siliciclastic siltstones this succession was deposited within five sequences that include the upper hueco formation late wolfcampian through the bone spring formation middle leonardian using a ground based light detecting and ranging generated high resolution digital outcrop model dom aged as a template we mapped and digitized the stratigraphy of the toe of slope and basinal deposits on the 5 cm 2 in precision dom on the basis of the digitized stratigraphic contacts several regional surfaces were constructed and a 3 d geocellular model was built facies information within this model is extrapolated from measured section data using both a kriging algorithm and stochastic simulations using impedance values extracted from a subsurface analog a 3 d impedance model was created for both the kriged and the stochastic models both models incorporate fine scale stratigraphic architecture in addition the stochastic impedance model incorporates spatially correlated noise resulting in more realistic synthetic seismograms three dimensional synthetic seismograms were calculated at 20 40 and 80 hz the reservoir prone facies is skeletal ooid grainstone deposited as a 1 5 km 750 m 0 93 mi 2460 ft basin floor fan up to 15 m 49 ft thick this basin floor fan is subtly imaged in vertical seismic section at a frequency below 80 hz it is however better recognized on time slices with peak frequency as low as 20 hz and even better delineated on horizon slices that parallel the stratigraphy

the 3 5 ga sao tome layered mafic ultramafic intrusion ne brazil insights into a paleoarchean fe ti v oxide mineralization and its reworking during west gondwana assembly abstract the sao tome mafic ultramafic intrusion located in the borborema province ne brazil consists of a group of metamorphosed dismembered intrusive rocks composed of ol websterite and clinopyroxenite which host stratiform meter sized massive ilmenite magnetite lenses with up to 1 98 wt v2o3 in magnetite the ol websterite rocks display dark discontinuous olivine bands intercalated with cumulate augite whereas the clinopyroxenite rocks are composed mainly of anhedral augite the mineral chemistry analysis of the mafic phases resulted in contents up to fo87 28 and 4605 ppm of ni in the olivine crystals and high mgo augite 22 59 wt mgo suggesting that these rocks formed from the differentiation of a primitive fertile peridotite melt the retention of high nickel contents in the olivine crystals despite the crustal contaminated signature revealed by sm nd isotopes suggests that there was no early sulfur saturation in the magma additionally the magnetite crystallization did not trigger sulfur saturation inhibiting ni cu sulfide precipitation or even the formation of individual platinum group metals pgm grains metamorphism at amphibolite facies conditions resulted in the development of penetrative foliation and mineral assemblages wherein tschermakite is dominant ultimately the metasomatic imprint included the following stages 1 a k p h2o stage represented by newly formed phlogopite apatite chlorite and hornblende 2 a calcic stage with epidote group minerals calcite and minor pyrite and 3 the least potassic alteration forming diablastic phlogopite and microcline la icp ms u pb zircon data reveal a concordant age of 3506 29 ma for the sao tome intrusion interpreted as the igneous crystallization age and thus it represents the oldest record of continental crust generation in south america 40ar 39ar phlogopite dating on the other hand revealed plateau ages of 597 5 ma and 517 6 ma these ediacaran to cambrian ages represent the emplacement of local granites which bear heavily on the source of magmatic fluids

the 3 4 3 5 ga sao jose do campestre massif ne brazil remnants of the oldest crust in south america abstract the oldest fragment of continental crust recognized in south america occurs as an isolated archean enclave in northeastern brazil s borborema province ca 600 ma brasiliano pan african orogenic belt this archean fragment the sao jose do campestre massif is surrounded by large tracts of 2 2 2 0 ga paleoproterozoic gneisses and is located more than 600 1500 km from the much larger assemblages of archean rocks found in the sao fransciso and amazonian cratons located to the south and west respectively geochronological studies of the sao jose do campestre massif show that its oldest rocks contain zircons with u pb ages up to 3 5 ga and sm nd tdm model ages of more than 3 7 ga indicating that they represent reworked crust this older nucleus is flanked by both reworked and juvenile 3 25 and 3 18 ga rocks which are intruded by both 3 00 and 2 69 ga plutonic bodies the protracted evolution the sao jose do campestre massif is consistent with that of a larger continental mass as opposed to a small crustal fragment that grew in isolation as such the sao jose do campestre massif is interpreted as representing a detached piece of an evolved craton that became entrained with younger rocks during a subsequent paleoproterozoic accretionary orogenic event this hypothesis is bolstered by the presence of paleoproterozoic gneisses that envelop the sao jose do campestre massif as well as the existence of ca 2 0 ga metamorphic zircon and monazite within its rocks the occurrence of several different archean cratonic basement inliers within the greater paleoproterozoic crustal framework of the borborema province suggests that cratonic slices spalled off one or more larger archean masses prior to the ca 2 2 2 0 ga paleoproterozoic orogenic collage a important challenge is to link these older fragments to their parent cratons although results are not unique the pattern of ages and isotopic signatures observed in the sao jose do campestre massif is similar to that seen in parts of the sao francisco craton and it is possible that the sao jose do campestre massif is a fragment of an archean continental fragment formed during an episode of continental breakup prior to 2200 ma

seismic attribute technology for reservoir forecasting and monitoring during the 1970s and 1980s the seismic attributes most used in petroleum exploration were amplitude based instantaneous attributes however in the 1990s seismic attribute technology has dramatically advanced in several directions techniques now range from single trace instantaneous event attribute computations to more complex multitrace windowed seismic event attribute extractions to the generation of seismic attribute volumes applications run from simple amplitude anomaly detection to monitoring fluid front movement over time

toe of slope of a cretaceous carbonate platform in outcrop seismic model and offshore seismic data apulia italy synthetic seismic models of outcrops in the early cretaceous slope of a carbonate platform on the gargano promontory southern italy were compared to an offshore seismic section south of the promontory outcrops of the same age on the promontory have the same sequence stratigraphic characteristics as their offshore equivalent and are the only areas where the transition from platform to basin of early cretaceous is exposed on land two adjacent outcrop areas were combined into one seismic scale lithologic model with the aid of photo mosaics measured sections and biostratigraphic data velocity density and porosity measurements on spot samples were used to construct the impedance model seismic models were generated by vertical incidence and finite difference programs the results indicate that the reflections in the seismic model are controlled by the impedance contrast between low porous intervals rich in debris from the platform and highly porous intervals of pelagic lime mudstone nearly devoid of debris finite difference seismic display showed best resemblance with the real seismic data especially by mapping a drowning unconformity

integration of hydrological factors and demarcation of groundwater prospect zones insights from remote sensing and gis techniques the study demonstrates the potential of geographical information system and statistical based approaches to identify the hydrological processes and demarcate the groundwater prospect zones of the gangolli basin karnataka state india the basin is situated in humid tropical climate and influenced by three major rivers viz kollur 6th order stream chakra 6th order stream and haladi 7th order stream which cover an area of 1 512 km2 and cumulative length of 84 km various thematic maps drainage geomorphology geology slope soil lineament and lineament density were prepared using survey of india topographic maps indian remote sensing irs p6 images and other published maps hydrogeomorphologic characteristics were correlated with different morphometric parameters to identify the hydrological processes and demarcate the groundwater potential zones of the basin all the hydrological units and morphometric parameters were assigned suitable weightages according to their relative importance to groundwater potentiality to identify the most deficit surplus zones of groundwater based on hydrological characteristics integrated thematic maps reveal that 14 217 km2 of basin area falls under very good 32 486 km2 under good 23 353 km2 under moderate and 30 443 km2 under poor zones for groundwater potential from the sub basin wise prioritisation it has been inferred that sb iii scored highest groundwater potential followed by sb x result of morphometric analyses with the hydrologic parameters indicates that 99 area of sb iii and sb x are under very good to moderate groundwater potential zone this study clearly demonstrates that hydrological parameters in relation with morphometric analyses are useful to demarcate the prospect zones of groundwater

seismic stratigraphy of the chalk group in the norwegian central graben north sea abstract the late cretaceous to early palaeogene chalk group in the norwegian central graben contains prolific hydrocarbon reservoirs that have been producing at high rate for more than forty years based on integration of regionally extensive 3d seismic data and numerous wells this paper describes the seismic development of the chalk group with particular focus to the syndepositional geomorphological features produced by the activity of bottom currents and large scale gravity flows using standard seismic stratigraphic interpretation techniques eight seismic sequence boundaries are identified which in turn define seven seismic stratigraphic sequences characterized by different seismic facies and well log signatures the seismic sequences can be grouped into three sequence groups that reflect the general tectono stratigraphic evolution of the chalk depositional system in the norwegian central graben during the late cretaceous uplift of the lindesnes ridge and the albuskjell anticline due to inversion tectonic and halokinesis modified the physiography of the norwegian central graben basin and affected the style of chalk sedimentation by influencing the location and importance of gravity flows in addition bottom currents sea level fluctuations and environment changes significantly influenced the chalk depositional system creating regional unconformities and influencing the input of terrigenous material in the chalk epeiric sea

automated river course ridge and basin delineation from digital elevation data starting from a digital elevation model dem formed by a triangular irregular network tin of facets an algorithm that allows for the tracking of the path of steepest slope downstream or upstream from any point on the topographic surface has been developed the analysis shows that when starting such a path in a downstream upstream direction from point p down up to a point m and then from point m in an upstream downstream direction and if the path returns to point p then the segment pm corresponds to a pure streamline otherwise it corresponds to a river course ridge this property allows an easy way to delineate the network of river courses and ridges likewise the repetitive use of this algorithm allows for the definition of basin and sub basins also called contributing areas to any point on a river course finally it is shown how a regular grid dem can be treated as a particular case of the tin dem which gives generality to the presented procedures

drainage morphometry and its influence on hydrology in an semi arid region using srtm data and gis an attempt has been made to study drainage morphometry and its influence on hydrology of peddavanka watershed south india drainage networks for the sub basins were derived from topographical map 1 50 000 and shuttle radar topographic mission srtm digital elevation model dem data used for preparing elevation slope and aspects maps geographical information system gis was used in evaluation of linear areal and relief aspects of morphometric parameters the study reveals that srtm dem and gis based approach in evaluation of drainage morphometric parameters and their influence on hydrological characteristics at watershed level is more appropriate than the conventional methods the mean bifurcation ratio r b of the entire basin is 3 88 which indicate that the drainage pattern is not much influenced by geological structures viii sub basin have high elongation ratio r e basin relief b h ruggedness number rn and time of concentration t c it indicates that the erosion and peak discharges are high in these basins therefore the construction of the check dams and earth dams will help in reducing peak discharge on the main channel these studies are very useful for implementing rainwater harvesting and watershed management

permian wolfcamp limestone reservoirs powell ranch field eastern midland basin deep water carbonate channel reservoirs form important oil reservoirs along the toe of the eastern shelf of the permian basin in west texas in northwestern glasscock county these wolfcamp reservoirs are leonardian early permian in age and define high energy channels incised into surrounding carbonate detritus and basinal shale porous grain flow material filling these channels along with encasing detritus was derived from the shallow shelf located six miles to the east reservoirs are in packstone and grainstone facies and have significant interparticle and moldic porosity relevant exploration began in the 1960s but expanded slowly thereafter due to lack of success caused by complex patterns of channel occurrence results of a three dimensional 3 d seismic survey conducted in 1990 have greatly enhanced the identification and mapping of productive channels in the powell ranch field complex wells in this complex are capable of flowing 400 1200 bbl of oil per day and have reserves ranging from 0 2 to 1 3 mbo the new 3 d data have improved the relevant geologic model and dramatically increased rates of drilling success application of such data to this setting offers a potential model for other parts of the permian basin

permian wolfcamp limestone reservoirs powell ranch field eastern midland basin discussion the open quotes ep however its economic importance and geological complexity and the question of whether his model can be extended to other areas in the permian basin warrant this discussion

morphometric analysis of morar river basin madhya pradesh india using remote sensing and gis techniques hydrogeological mapping and drainage analysis can form an important tool for groundwater development assessment of drainage and their relative parameters have been quantitatively carried out for the morar river basin which has made positive scientific contribution for the local people of area for the sustainable water resource development and management geographical information system has been used for the calculation and delineation of the morphometric characteristics of the basin the dendritic type drainage network of the basin exhibits the homogeneity in texture and lack of structural control the stream order ranges from first to sixth order the drainage density in the area has been found to be low which indicates that the area possesses highly permeable soils and low relief the bifurcation ratio varies from 2 00 to 5 50 and the elongation ratio 0 327 reveals that the basin belongs to the elongated shaped basin category the results of this analysis would be useful in determining the effect of catchment characteristics such as size shape slope of the catchment and distribution of stream net work within the catchment

the significance of morphometric analysis for obtaining groundwater potential zones in a structurally controlled terrain watershed development and management plans are more important for harnessing surface water and groundwater resources in arid and semi arid regions to prepare a comprehensive watershed development plan it becomes necessary to understand the topography erosion status and drainage patterns of the region this study was undertaken to determine the drainage characteristics of pageru river basin using topographical maps on a scale of 1 50 000 the total area of the pageru river basin is 480 km2 it was divided into x sub basins for analysis the drainage patterns of the basin are dendritic and include a sixth order stream the quantitative analysis of various aspects of a river basin drainage network characteristics reveals complex morphometric attributes the streams of lower orders mostly dominate the basin the development of stream segments in the basin area is more or less affected by rainfall the elongated shape of the basin is mainly due to the guiding effect of thrusting and faulting the erosional processes of fluvial origin have been predominately influenced by the subsurface lithology of the basin

halokinetic sequences in carbonate systems an example from the middle albian bakio breccias formation basque country spain in diapir flanks unconformity bounded sedimentary packages associated with gravity driven deposits controlled by the ratio between the rates of sediment accumulation and diapir growth can be interpreted in the context of halokinetic sequences the bakio breccias formation basque country spain corresponds to redeposited carbonate deposit that developed in response to the bakio diapir growth during the middle albian these deposits provide on of the rare documented example of carbonate dominated halokinetic sequences the bakio breccias formation consists of an alternation of clast and matrix supported breccias calcirudite calcarenite and marl deposited along the flanks of the diapir the description and the analysis of the bakio breccias formation lead to a new model for carbonate dominated halokinetic sequences these sequences differ from their siliciclastic counterpart because sediment accumulation rate is controlled by carbonate platform growth on the topographic relief top of the diapirs while sediments are preferentially deposited in the mini basins adjacent of the diapirs in siliciclastic settings during transgressive system tract carbonate platform are able to keep up with the sea level rise and to aggrade on top of the diapirs forming thick and resistant roof which is assumed to limit the diapir growth and thus to favour the development of halokinetic sequences with low angle unconformities wedge halokinetic sequences during late highstand system tract deposition and lowstand system tract if present platform progradation results in high sediment accumulation in the adjacent depocenters loading the autochthonous salt layer and promote diapir growth and creation of topographic relief in addition if the diapir roof reaches emersion karstification of the carbonate platform top may also favour roof destruction and diapir growth depending on the thickness of the roof developed previously and the amplitude of the sea level fall the halokinetic sequences with the emersion and the karstification of the carbonate platform may display high angle unconformities hook halokinetic sequences furthermore gravity driven deposits are assumed to be more common in carbonate dominated halokinetic sequences compared to their siliciclastic counterparts since carbonate platform aggradation creates steep slopes on the diapir margins leading to the partial collapse of the margin even when limited diapir growth occurs the carbonate dominated halokinetic sequence model proposed here is an important tool for the prediction of potential reservoir distribution seal and hydrocarbon migration in flanks of salt diapirs where carbonate platform developed

the distribution of skarns in british columbia and the chemistry and ages of their related plutonic rocks british columbia contains at least 694 recorded skarns as defined by burr 1977 that range from small occurrences to deposits exceeding 20 million metric tons of ore skarns have accounted for nearly 90 percent of the iron magnetite 80 percent of the tungsten 16 percent of the gold and 12 percent of the copper produced by hard rock mining in the province copper skarns make up almost half of the occurrences the other skarn classes in decreasing abundance are fe 21 pb zn 11 w 7 au 4 mo 3 and sn 0 4 a small group 2 lack significant metallic minerals but represent potential industrial mineral deposits three separate plutonic episodes were responsible for most of the skarns the earliest and most significant occurred during the early to middle jurassic when over half of the skarns developed later important episodes during the cretaceous and eocene oligocene accounted for 17 and 9 percent respectively skarns in british columbia are distributed across 19 tectono stratigraphic terranes however there is a marked spatial and temporal relationship between certain metallic classes of skarn their metal production and the character and origin of the host terranes despite having abundant plutonic rocks terranes of the coast belt host only 4 percent of the province s skarns and these have had negligible metal production the terranes in the north american basement and craton host 5 percent of the skarns but these have been responsible for all of the w produced however terranes dominated by oceanic island arc rocks contain over 80 percent of the skarns and have accounted for virtually all the fe cu au ag and zn produced the majority of british columbia s fe cu and au skarns developed during early to middle jurassic oceanic island arc activity in wrangellia quesnellia and stikinia by contrast nearly all the w skarns are related to a belt of cretaceous plutons that intrude sedimentary rocks deposited either close to or on the ancestral north american continent in many terranes there is no consistent relationship between the number of skarn occurrences and metal production wrangellia hosts nearly all the fe skarns and has accounted for virtually all the 35 million metric tons of magnetite produced in british columbia yet it also has the largest number of cu skarns of any terrane but has had only one fifth the skarn copper production of quesnellia both major and trace element analyses indicate that the plutonic rocks associated with fe cu au and to a lesser extent mo skarns are chemically distinct from those associated with w and sn skarns plutons related to the former group are relatively undifferentiated and fe rich their nb y and rb contents are characteristic of volcanic arc granites those associated with w and sn skarns are highly differentiated fe poor large ion lithophile elements rich and represent within plate intrusions copper and au bearing skarns are currently the most economically attractive targets for skarn exploration in british columbia and this study indicates that island arc assemblages in the quesnellia terrane or in correlative rocks elsewhere have the best exploration potential for these metals

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

morphometrical analysis of two tropical mountain river basins of contrasting environmental settings the southern western ghats india the morphometric analysis of river basins represents a simple procedure to describe hydrologic and geomorphic processes operating on a basin scale a morphometric analysis was carried out to evaluate the drainage characteristics of two adjoining mountain river basins of the southern western ghats india muthirapuzha river basin mrb in the western slopes and pambar river basin prb in the eastern slopes the basins forming a part of the proterozoic high grade southern granulite terrain of the peninsular india are carved out of a terrain dominantly made of granite and hornblende biotite gneisses the western ghats forming the basin divide significantly influences the regional climate i e humid climate in mrb while semi arid in prb the survey of india topographic maps 1 50 000 and shuttle radar topographic mission digital elevation data were used as the base for delineation and analysis both river basins are of 6th order and comparable in basin geometry the drainage patterns and linear alignment of the drainage networks suggest the influence of structural elements the rb of either basins failed to highlight the structural controls on drainage organization which might be a result of the elongated basin shape the irregular trends in rb between various stream orders suggest the influence of geology and relief on drainage branching the dd values designate the basins as moderate to well drained with lower infiltration rates the overall increasing trend of rl between successive stream orders suggests a geomorphic maturity of either basins and confirmed by the characteristic i hyp values the re values imply an elongate shape for both mrb and prb and subsequently lower vulnerability to flash floods and hence easier flood management the relatively higher rr of prb is an indicative of comparatively steeply sloping terrain and consequently higher intensity of erosion processes further the derivatives of digital elevation data slope aspect topographic wetness index and stream power index showing significant differences between mrb and prb are useful in soil conservation plans the study highlighted the variation in morphometric parameters with respect to the dissimilarities in topography and climate

a jurassic tongue of the ocean infilled with oolitic sands the belluno trough venetian alps italy abstract the belluno trough is a narrow and elongate basin on the northwestern corner of the apulian plate continental margin it acquired topographic identity in early liassic time during the breakup of a widespread upper triassic carbonate shelf at the beginning liassic the belluno trough was a starved depression accumulating euxinic mudstone and bounded by two shallow water carbonate banks trento and friuli platforms this typical bahamian physiography lasted until late liassic time when the shallow water trento platform collapsed tectonically and suddenly drowned tilting northward and breaking along an old tectonic line it became therefore a submerged pelagic plateau in the meantime the western edge of the friuli platform now the windward margin of an oceanic platform turned into a prolific super producing oolite factory quite soon the oolite sands of the friuli margin started to flow down the slope reaching the basin through numerous entry points and gradually building a complex of coalescent deep sea fans which prograding westward infilled the belluno trough the fans terminated westward against the faulted edge of the trento plateau on which above a karst like surface locally encrusted with manganese red nodular ammonitic limestone was slowly accumulating northward where the topographic relief decreased the oolite fans could spill over the escarpment onto the edge of the plateau by the end of middle jurassic time the belluno trough was no longer a submarine depression but a gentle slope connecting the friuli platform to the deep pelagic trento plateau in callovian time probably because of a short drop in sea level large parts of the friuli platform were exposed to subaerial diagenesis during the subsequent oxfordian transgression the resulting rocky bottom became the substratum for an extensive growth of reefal organisms hydrozoans corals rudists which fringed the friuli platform for the whole malm and cretaceous times

magnetic fabric and pluton emplacement in a transpressive shear zone system the itaporanga porphyritic granitic pluton northeast brazil the itaporanga granitic pluton intruded into the lithological contact separating neoproterozoic pelitic metasediments from meso to paleoproterozoic rocks that constitute the cachoeirinha belt of northeastern brazil an aureole of pelitic gneisses containing sillimanite and andalusite indicates that emplacement occurred at 12 15 km depth the objective of this work is a detailed study of its magmatic structures mainly by means of anisotropy of magnetic susceptibility ams regularly spaced sampling 61 stations yielded a magnetic fabric map which shows two domains 1 a western lobe which has lineations close to vertical and e trending foliations that merge southwestward as the transcurrent igarassi shear zone is approached isz and 2 an eastern lobe showing se trending lineations associated with inward dipping magmatic foliation situated in the center of the lobe the magnetic fabric is mostly paramagnetic in origin i e related to crystallographic preferred orientation of biotite and hornblende a low susceptibility magnitude 0 4 10 3 si typically of the ilmenite series granites is found in porphyritic granites diorites or their hybrid products hysteresis data indicate that the ferrimagnetic contribution to the bulk susceptibility does not reach 30 the magma was emplaced into a chamber developed by local wnw ese extension induced by an overall n s shortening melt ascent may have been facilitated by the pre existence of a steep fault zone bounding crustal discontinuities the magma must have ponded along a mechanical barrier formed by the contact between phyllitic metapelites and its gneissic basement which controlled the final emplacement structures of the pluton

the serido group of ne brazil a late neoproterozoic pre to syn collisional basin in west gondwana insights from shrimp u pb detrital zircon ages and sm nd crustal residence tdm ages abstract the serido group is a deformed and metamorphosed metasedimentary sequence that overlies early paleoproterozoic to archean basement of the rio grande do norte domain in the borborema province of ne brazil the age of the serido group has been disputed over the past two decades with preferred sedimentation ages being either paleoproterozoic or neoproterozoic most samples of the serido formation the upper part of the serido group have sm nd tdm ages between 1200 and 1600 ma most samples of the jucurutu formation the lower part of the serido group have tdm ages ranging from 1500 to 1600 ma some basal units have tdm ages as old as 2600 ma reflecting proximal basement thus based on sm nd data most if not all of the serido group was deposited after 1600 ma and upper parts must be younger than 1200 ma cathodoluminescence photos of detrital zircons show very small to no overgrowths produced during ca 600 ma brasiliano deformation and metamorphism so that shrimp and isotope dilution u pb ages must represent crystallization ages of the detrital zircons zircons from meta arkose near the base of the jucurutu formation yield two groups of ages ca 2200 ma and ca 1800 ma in contrast zircons from a metasedimentary gneiss higher in the jucurutu formation yield much younger ages with clusters at ca 1000 ma and ca 650 ma zircons from metasedimentary and metatuffaceous units in the serido formation also yield ages primarily between 1000 and 650 ma with clusters at 950 1000 800 750 and 650 ma thus most if not all of the serido group must be younger than 650 ma because these units were deformed and metamorphosed in the ca 600 ma brasiliano fold belt during assembly of west gondwana deposition probably occurred ca 610 650 ma soon after crystallization of the youngest population of zircons and before or during the onset of brasiliano deformation the serido group was deposited upon paleoproterozoic basement in a basin receiving detritus from a variety of sources the jucurutu formation includes some basal volcanic rocks and initially received detritus from proximal 2 2 2 0 ga transamazonian to late paleoproterozoic 1 8 1 7 ga basement provenance for the upper jucurutu formation and all of the serido formation was dominated by more distal and younger sources ranging in age from 1000 to 650 ma we suggest that the serido basin may have developed as the result of late neoproterozoic extension of a pre existing continental basement with formation of small marine basins that were largely floored by cratonic basement subjacent oceanic crust has not yet been found immature sediment was initially derived from surrounding land as the basin evolved much of the detritus probably came from highlands to the south present coordinates alternatively if the patos shear zone is a major terrane boundary the basin may have formed as an early collisional foredeep associated with south dipping subduction in any case within 30 million years the region was compressed deformed and metamorphosed during final assembly of west gondwana and formation of the brasiliano pan african fold belts

strain transfer at continental scale from a transcurrent shear zone to a transpressional fold belt the patos serido system northeastern brazil during the brasiliano pan african orogeny a complex continental scale pattern of east west transcurrent shear zones and northeast trending fold belts formed in the northern and central borborema province of northeastern brazil the east west shear zones have been usually regarded as slightly younger features but the study of the most spectacular case of intersection between these two structures the patos shear zone and the serido transpressional belt leads to a different tectonic model satellite imagery and structural petro logical and geophysical data support the interpretation that these structures 1 are in structural continuity and 2 formed simultaneously under amphibolite facies metamorphic conditions that led to partial melting this suggests a model of strain transfer at the scale of the orogen at the eastern end of the patos east west dextral shear zone the strain that accommodated the relative motion of the northern block was transferred to the northeast trending serido belt where it resulted in folding strike slip faulting and stretching parallel to the strike of the belt

complex seismic trace analysis of thin beds displays of complex trace attributes can help to define thin beds in seismic sections if the wavelet in a section is zero phase low impedance strata whose thicknesses are of the order of half the peak to peak period of the dominant seismic energy show up as anomalously high amplitude zones on instantaneous amplitude sections these anomalies result from the well known amplitude tuning effect which occurs when reflection coefficients of opposite polarity a half period apart are convolved with a seismic wavelet as the layers thin to a quarter period of the dominant seismic energy thinning is revealed by an anomalous increase in instantaneous frequency this behavior results from the less well known but equally important phenomenon of frequency tuning by beds which thin laterally instantaneous frequency reaches an anomalously high value when bed thickness is about a quarter period and remains high as the bed continues to thin in this paper complex trace analysis is applied to a synthetic model of a we

seismic architecture of a miocene isolated carbonate platform and associated off platform strata central luconia province offshore malaysia abstract rather than being homogeneous and isotropic many isolated carbonate platforms in the geologic record include internal heterogeneity and complex geometric relations with off platform strata on their flanks to better understand stratal architecture of a miocene isolated platform central luconia offshore malaysia this study integrates core log and seismic data revealing stratal terminations and geometries that define several seismic stratigraphic units a thick in the basal seismic unit the initial deposits of the carbonate buildup is 4 5 km across this thick includes abrupt thinning to the west and east with onlap onto its flanks but continues outside of the survey area to the north and south above a mappable surface a less extensive 2 5 km seismic unit represents a backstepped isolated platform platform stage 1 across a pronounced normal fault on the east southeast margin of the platform occur marked isochron and seismic character changes with thicker carbonates on the downthrown western block the northern and western margins are not faulted a third seismic unit representing a smaller elongate the most marked stratigraphic theme within the isolated platform is the successive backsteps but the pattern is complicated by interactions with the basinal strata superposition and cross cutting relations document that isolated platform sourced flanking beds wings interfinger with basinal clinoforms wedges as defined by geometries on the margins and flanks of platform stages the platform evolution also was influenced markedly by syndepositional structural activity although structural trends changed from the initial buildup to later platform stages the results and comparison with other isolated platforms demonstrate the complex controls on carbonate platform growth and interactions with basinal siliciclastics

gold potential of the pan african trans sahara belt and prospect for further exploration abstract the trans sahara belt is one of the mobile belts formed during the pan african orogeny that spans between 870 and 550 ma the trans sahara belt was formed as result of the collision between the converging west african craton congo craton and the sahara metacraton continental blocks the belt with major exposure in the tuareg and dahomeyan consists of pre neoproterozoic basement which were thoroughly reworked during the pan african orogeny neoproterozoic metasedimentary and metavolcanics and syn tectonic pan african granitoids which intrude archean and paleoproterozoic rocks the trans sahara belt though less endowed when compared to older archean orogenic greenstone belts in terms of gold mineralization displays reasonable gold mineralization in both the tuareg shield and dahomeyan shield with about 160 tons of gold reported so far across the belt mineralization is associated with varying lithologies across the belt and appears to have been regionally controlled by n s trending pan african shear zones in the tuareg shield mineralized quartz veins are associated with syntectonic granitoids mylonitic and meta volcanosedimentary rocks conversely gold mineralization is only associated with metasediments and migmatite gneisses in the dahomeyan shield with occurrences largely confined to metasedimentary sequence in benin and nigeria the prevailing tropical climate in the dahomeyan shield has also facilitated secondary concentration of gold in alluvial bed of river draining supracrustal rocks hosting primary gold mineralizations the occurrence of primary mineralization in variety of rocks across the tuareg and dahomeyan shield and widespread occurrence of placer gold deposits in the dahomeyan shield justifies the need for further exploration and evaluation of mineralization potential the emplacement of gold which occur between 535 and 500 ma is controlled by n s trending pan african mega shear zones however at the district scale it is evident that the pan african mega shear zones are not the only important structures lower order faults and shear zones are important structures to consider in exploration targeting exploration particularly at district scale might benefit from gis based prospectivity mapping considering the mineralizations are generally structural controlled gis based prospectivity mapping which integrates multifaceted digital data sets can provide a foundation for vectoring towards explorations targets in many mineralized districts within the trans sahara belt

accuracy of interpolation techniques for the derivation of digital elevation models in relation to landform types and data density one of the most important scientific challenges of digital elevation modeling is the development of numerical representations of large areas with a high resolution although there have been many studies on the accuracy of interpolation techniques for the generation of digital elevation models dems in relation to landform types and data quantity or density there is still a need to evaluate the performance of these techniques on natural landscapes of differing morphologies and over a large range of scales to perform such an evaluation we investigated a total of six sites three in the mountainous region of northern laos and three in the more gentle landscape of western france with various surface areas from micro plots hillslopes and catchments the techniques used for the interpolation of point height data with density values from 4 to 109 points km2 include inverse distance weighting idw ordinary kriging ok universal kriging uk multiquadratic radial basis function mrbf and regularized spline with tension rst the study sites exhibited coefficients of variation cv of altitude between 12 and 78 and isotropic to anisotropic spatial structures with strengths from weak with a nugget sill ratio of 0 8 to strong 0 01 irrespective of the spatial scales or the variability and spatial structure of altitude few differences existed between the interpolation methods if the sampling density was high although mrbf performed slightly better however at lower sampling densities kriging yielded the best estimations for landscapes with strong spatial structure low cv and low anisotropy while rst yielded the best estimations for landscapes with low cv and weak spatial structure under conditions of high cv strong spatial structure and strong anisotropy idw performed slightly better than the other method the prediction errors in height estimation are discussed in relation to the possible interactions with spatial scale landform types and data density these results indicate that the accuracy of interpolation techniques for dem generation should be tested not only in relation to landform types and data density but also to their applicability to multi scales

influence of mining activity on the downstream sediments of scheelite mines in currais novos ne brazil the study area is one of the most important mineral provinces of the rio grande do norte state ne brazil which has been extensively exploited since 1940 this article presents a geochemical investigation of stream sediments taken in the drainage system between the brejui and barra verde scheelite mines and the gargalheiras municipal reservoir in acari city in addition to the major elements the trace elements v cr co ni cu zn as rb sr zr mo sn ba w were analyzed and compared to metal levels reported in the literature for the same area the elements w mo cu sn and in part zn are enriched in sediments of rivulets forming the drainage system close to the mining district this is due to emission from uncovered mine waste dumps dispersion of elements is controlled by both aeolian as well as fluvial transport the concentration of cu in stream sediments close to the mines reaches toxic levels at the mouth of the drainage system to the reservoir the elements w and mo are still enriched in the stream sediments relative to the geogenic background by factors of 15 and 11 respectively this indicates the probable influence of mining activity to the reservoir sediments and mobilization of w and mo in the reservoir water cannot be ruled out

carbonate shelf evolution during the oligocene to early miocene insights from shelf architecture lithofacies and depositional models of the kujung formation offshore east java indonesia

characterization of the devonian kharyaga carbonate platform russia integrated and multiscale approach abstract the devonian carbonate platform obj 2 of the kharyaga field russia has been operated by total since 1999 and produces 42 api oil rich in h2s a multidisciplinary sedimentological structural stratigraphic and geomechanical modeling and multiscale study was made of the field integrating seismic micro resistivity log and core data to characterize the reservoir the kharyaga carbonate platform is characterized by complex relationships among sea level variations subsidence and sedimentation rates the field is divided into a platform edge barrier zone in the southern area and back barrier and lagoon environments to the north each characterized by different facies distribution and dynamic behavior the platform shelf and the reef flat show dome shaped thrombolites the back barrier is characterized by grainstone shoals associated with columnar stromatolites whereas the lagoon comprises peloidal wackestones and packstones associated with laminated fenestral stromatolites significant and prolonged subsidence in both the lagoon and the platform edge is associated with partial emergence of the platform reef as shown by karst development seismic interpretation highlighted both underlying north south structures and syndepositional east west collapse faults along the southern barrier edge two dimensional and three dimensional sedimentological modeling of the obj 2 calibrated by well data and core analyses allowed the simulation of alternative scenarios to explain the evolution of the carbonate platform during the devonian and suggested the observed facies distribution is compatible with the presence of a fixed outer platform edge represented by east west faults the carbonate platform of the kharyaga field exhibits complex behavior hydrocarbon hc accumulation and flow is controlled by the interplay of primary porosity karst distribution and structural discontinuities faults and fractures besides the role of the karstification this paper mainly focuses on the role played by tectonic structures on the evolution of the carbonate platform and on the hc flow from drill stem test data east west faults and karsts are considered as major permeability heterogeneities but interference tests showed more complex fluid pathways at the smaller scale microresistivity images show dominant northeast southwest and northwest southeast fracture sets in the central barrier forming an interconnected flow network with the seismic faults geomechanical modeling suggests that these fractures are subseismic structures linked to inherited deep seated faults active at the time of fracturing in addition to the listric reservoir faults

platform margin collapse during famennian reef evolution canning basin western australia sedimentological investigations of well exposed slope strata in the upper devonian reef complexes of the northern canning basin lead to a sequence stratigraphic interpretation that differs from others based on predictive models in which coarse carbonate debris deposits are regarded as lowstand deposits in the upper frasnian famennian napier range slope succession we recognize an important phase of platform margin collapse during a sea level highstand in the middle famennian at this time the reef rimmed margin was rapidly prograding and the platform was producing carbonate grains notably ooids and peloids that were being transported by turbidity currents to the slope and basin floor periodic collapse of the platform margin led to deposition on the slope of allochthonous blocks of reefal limestone and channelized debris flow units intercalated with the ooid peloidal turbidites and quartzo feldspathic sandstones collapse of the early cemented margin was probably triggered by gravitational instability caused by oversteepening during rapid progradation and or tectonic activity with falling blocks initiating some of the debris flows

the upper cretaceous carbonates of the gargano murge region southern italy a model of platform to basin transition the outcrops in gargano murge region are good examples of the upper cretaceous carbonate systems of the peri adriatic area they enable the architecture and the processes of the platform to basin transition to be studied in detail the platform carbonates are juxtaposed to the deeper marine carbonates by the intermediary of a faulted scarp the base of slope is characterized by bioclastic and conglomeratic aprons interbedded with pelagic mudstones the outer shelf domain which was the prolific source of rudistid bioclastic aprons is not preserved the platform is mainly built of mud dominated transgressive systems tracts whereas highstand systems tracts are developed as bioclastic base of slope aprons the volume of the resedimented bioclasts largely exceeds the volume of missing outer shelf indicating that carbonate production and sediment bypass are more critical for this stratigraphic response than carbonate erosion the lowstands which were controlled by tectonic deformations are characterized by base of slope breccia and blocks eroded from the shelf edge this erosion resulted in the progressive retreat of the shelf edge the best potentials for hydrocarbon reservoir are found in the bioclastic base of slope aprons formed during the cenomanian and maastrichtian highstands this model is considered as an analog for the hydrocarbon reservoirs formed by the deep marine deposits of cretaceous tamabra limestone in the gulf of mexico

prioritization of malesari mini watersheds through morphometric analysis a remote sensing and gis perspective geographical information system and remote sensing are proven to be an efficient tool for locating water harvesting structures by prioritization of mini watersheds through morphometric analysis in this study the morphometric analysis and prioritization of ten mini watersheds of malesari watershed situated in bhavnagar district of saurashtra region of gujarat state india are studied for prioritization of mini watersheds morphometric analysis is utilized by using the linear parameters such as bifurcation ratio drainage density stream frequency texture ratio and length of overland flow and shape parameters such as form factor shape factor elongation ratio compactness constant and circularity ratio the different prioritization ranks are assigned after evaluation of the compound factor digital elevation model from shuttle radar topography mission digitized contour and other thematic layers like drainage order drainage density and geology are created and analyzed over arcgis 9 1 platform combining all thematic layers with soil and slope map the best feasibility of positioning check dams in mini watershed has been proposed after validating the sites through the field surveys

3 d seismic discontinuity for faults and stratigraphic features the coherence cube seismic data are usually acquired and processed for imaging reflections this paper describes a method of processing seismic data for imaging discontinuities e g faults and stratigraphic features one application of this nontraditional process is a 3 d volume or cube of coherence coefficients within which faults are revealed as numerically separated surfaces figure 1 compares a traditional 3 d reflection amplitude time slice with the results of the new method to our knowledge this is the first published method of revealing fault surfaces within a 3 d volume for which no fault reflections have been recorded

platform margin collapses and sequence stratigraphic organization of carbonate slopes cretaceous eocene gargano promontory southern italy we describe the sequence stratigraphic organization and the associated sedimentological characteristics of cretaceous to eocene slope and base of slope carbonate successions the study area is located in the gargano promontory which belongs to the stable foreland of southern italy the succession consists of three superimposed depositional sequences separated by major unconformities the upper two sequences are clear examples of sequence stratigraphic organization in fact they both start with huge megabreccia wedges lst followed upward by thin pelagic units tst and a thick package of calciturbidites and debrites that alternate with pelagic mudstone hst the cretaceous highstand systems tract is clearly arranged in a number of coarsening upward cycles while the eocene one which also comprises a toplap shallow water unit is not the gargano stratigraphic palimpsest and the entire margin of the apulia platform show remarkable similarities with present day carbonate platform margins and slopes where irregular convex bankward embayments suggest large scale failures it is clear that classic sequence stratigraphic organization can result from simple platform dismantling having no or little time relation with global sea level fluctuations in fact as the margin failure lst interrupts the carbonate production a period of starvation tst along the entire slope and base of slope follows necessarily finally when the margin once again becomes active and productive sediment exportation starts again and the system begins to prograde hst

early and late pan african orogenies in the air assembly of terranes tuareg shield niger our study of the 60 000 km 2 air massif which comprises the southeastern extension of the tuareg shield in the niger republic has identified three major displaced terranes aouzegueur barghot and assod6 these terranes were all affected differentially by the pan african orogeny during an early major phase 750 660 ma and a late follow up phase 650 580 ma the greenschist facies aouzegueur terrane comprises an ophiolite and is intruded by a late kinematic mediumk calc alkaline tonalite trondhjemite granodiorite ttg suite 730 ma the amphibolite facies barghot terrane made up of a basement and a supracrustal sequence is intruded by late to post kinematic high k calcalkaline granitoids 715 665 ma both terranes form a nne to e verging belt thrust 680 670 ma upon an unknown eastern rigid continent and are covered unconformably by an early pan african molasse in contrast the amphibolite facies assod6 terrane composed of a basement and several supracrustal sequences collided with the eastern rigid block without being thrust upon it tibetan type crustal thickening occurred and ht lp metamorphism proceeded to regional anatexis enhanced by widespread emplacement of anatectic granites of lower crustal origin 670 ma this thermal event is attributed to the delamination of the continental lithospheric mantle and consequent rise of the asthenosphere the late pan african phase affecting mainly the assod6 terrane is marked by the intrusion of high k calc alkaline n s elongated batholiths 645 580 ma and by right lateral displacement along the n s raghane mega shear zone located on the edge of the eastern rigid continent this movement along the northern extent of the rigid continent in eastern hoggar 8 30 e created the tiririne intracontinental linear fold belt made up of early panafrican molasse in the model proposed we estimate that the assod6 terrane driven by an oblique spreading ridge moved to the north over a distance of 1000 km during 60 ma along the lithospheric raghane shear zone the latter was the subsequent locus of the silurian devonian alkaline ring complexes the calc alkaline granitoids are regarded as subduction related mantle products contaminated by lower and medium level crust the model and mechanisms proposed can be applied to the entire tuareg shield

anatomy of a modern open ocean carbonate slope northern little bahama bank the open ocean carbonate slope north of little bahama bank consists of a relatively steep 4 upper slope between water depths of 200 and 900 m and a more gentle 1 2 lower slope between depths of 900 and 1300 m the upper slope is dissected by numerous small submarine canyons 50 150 m in relief that act as a line source for the downslope transport of coarse grained carbonate debris the lower slope is devoid of any well defined canyons but does contain numerous small 1 5 m hummocks of uncertain origin and numerous larger 5 40 m patchily distributed ahermatypic coral mounds sediments along the upper slope have prograded seaward during the cenozoic as a slope front fill seismic facies of fine grained peri platform ooze surface sediments show lateral gradation of both grain size and carbonate mineralogy with the fine fraction derived largely from the adjacent shallow water platform near surface sedimentary facies along the upper slope display a gradual downslope decrease in the degree of submarine cementation from well lithified hardgrounds to patchily cemented nodular ooze to unlithified peri platform ooze controlled by lateral variations in diagenetic potential and or winnowing by bottom currents submarine cementation stabilizes the upper part of the slope allowing upbuilding of the platform margin and controls the distribution of submarine slides as well as the headward extent of submarine canyons where unlithified sediments are heavily bioturbated and are locally undergoing dolomitization upper slope sediments are also conditioned eustatically resulting in vertical cyclic sequences of diagenetically unstable aragonite and magnesian calcite rich and stable calcite rich carbonates that may explain the well bedded nature of ancient peri platform ooze sequences lower slope sediments have prograded seaward during the cenozoic as a chaotic fill seismic facies of coarse grained carbonate turbidites and debris flow deposits with subordinate amounts of peri platform ooze coarse clasts are internally derived from fine grained upper slope sediments via incipient cementation submarine sliding and the generation of sediment gravity flows gravity flows bypass the upper slope via a multitude of canyons and are deposited along the lower slope as a wedge shaped apron of debris parallel to the adjacent shelf edge consisting of a complex spatial arrangement of localized turbidites and debris flow deposits a proximal apron facies of thick mud supported debris flow deposits plus thick coarse grained ta turbidites grades seaward into a distal apron facies of thinner grain supported debris flow deposits and thinner finer grained ta b turbidites with increasing proportions of peri platform ooze both the geomorphology and sedimentary facies relationships of the carbonate apron north of little bahama bank differ significantly from the classic submarine fan model as such a carbonate apron model offers an alternative to the fan model for palaeoenvironmental analysis of ancient open ocean carbonate slope sequences

morphometric evaluation of papanasam and manimuthar watersheds parts of western ghats tirunelveli district tamil nadu india a gis approach a morphometric analysis was carried out to describe the topography and drainage characteristics of papanasam and manimuthar watersheds these watersheds are part of western ghats which is an ecologically sensitive region the drainage areas of papanasam and manimuthar watersheds are 163 and 211 km2 respectively and they show patterns of dendritic to sub dendritic drainage the slope of both watersheds varied from 0 to 59 and 0 to 55 respectively moreover the slope variation is chiefly controlled by the local geology and erosion cycles each watershed was classified as a fifth order drainage basin the stream order of the basin was predominantly controlled by physiographic and structural conditions the increase in stream length ratio from lower to higher order suggests that the study area has reached a mature geomorphic stage the development of stream segments is affected by rainfall and local lithology of the watersheds

seismic interpretation of carbonate depositional environments most seismic stratigraphic or seismic lithologic interpretations have been applied to clastic depositional systems because of their unique sedimentologic and mineralogic characteristics carbonate rocks are more difficult to study using seismic data increased knowledge of carbonate deposits and their petrophysical parameters and higher quality geophysical tools now permit a better understanding of carbonate rocks using seismic images in this paper seismic facies of carbonate rocks are characterized step by step from the basin to the supratidal environment 1 pelagic deposits shales and micritic limestone layers exhibit continuous parallel reflections with an apparently high frequency chalk deposits display continuous high amplitude reflections at the top and base with an internal reflection free zone 2 talus deposits are characterized by discontinuous oblique reflections of high amplitude carbonate debris flow generates chaotic reflections with hummocky surfaces channels exhibit erosional truncations 3 reef barriers are mound shaped biogenic deposits that display marginal onlapping reflections overlying reflections drape the reefs and underlying reflections exhibit pull up or pull down effects hyperbolic diffractions also may occur 4 platform border sands are mound shaped oblique reflections of moderately high amplitude 5 inner shelf strata are characterized by parallel continuous reflections typically displaying low frequency patch reefs may be distinguished within the inner shelf system mound shape drape of overlying reflections velocity anomalies and spurious events 6 where dolomitized the intertidal to supratidal facies exhibit a marbled zone a practically reflection free zone with a few discontinuous reflections diagenetic events such as paleokarst zones may be delineated using special analyses involving amplitude offset variations the study of carbonate depositional environments and petrophysical characteristics provides a more complete geologic insight including relative changes in sea level within a sedimentary basin such studies are fundamental in analyzing carbonate reservoirs and their paleogeographic settings

sedimentary dynamics along carbonate slopes bahamas archipelago hydroacoustic and sedimentological data in the santaren channel covering both the leeward slope of great bahama bank and the windward slope of cay sal bank allow new insights into carbonate platform slope sedimentation the data document the interplay between depositional and erosive processes on both slopes through time and provide information on the current regime and its influence on the slope sedimentary processes this study emphasizes the diversity and complexity of the slope morphology and the sediment distribution of the youngest high frequency sequence which has developed since the last glacial maximum the processes triggering slope failures and the formation of channels and gullies differ on both slopes at the leeward slope of the great bahama bank extensive slope failures occurred primarily during sea level lowering following an interglacial these slope failures created a slope morphology that channelizes the exported platform sediments during the subsequent highstand at the windward slope of cay sal bank contour currents and the local tectonic regime are responsible for slope failures during sea level lowstands downwelling induces turbidity currents the interaction of turbidity and contour currents leads to the formation of a system of furrows and slope parallel sediment ridges the discovered heterogeneities in slope sedimentation improve the understanding of carbonate slope sedimentation and provide implications for sequence stratigraphic interpretation of carbonate platform slopes

mid cretaceous basin margin carbonates east central mexico isolated high relief carbonate platforms developed in the intracratonic basin of east central mexico during albian cenomanian time relief on the platforms was of the order of 1000 m and slopes were as steep as 20 43 basin margin debris aprons adjacent to the platforms comprise the tamabra formation in the sierra madre oriental at the eastern margin of the valles san luis potosi platform an exceptionally thick 1380m progradational basin to platform sequence of the tamabra formation can be divided into six lithological units basinal carbonate deposition that preceded deposition of the tamabra formation was emphatically punctuated by an allochthonous reef block 1 km long by 0 5 km wide with a stratigraphic thickness of 95 m it is encased in tamabra formation unit a approximately 360 m of peloidal skeletal wackestone and lithoclastic skeletal packstone that includes some graded beds unit b is 73 m of massive dolomite with sparse skeletal fragments and intraclasts unit c 114m thick consists of structureless skeletal wackestone passing upward into graded skeletal packstone interlaminated lime mudstone and fine grained bioclastic packstone with prominent horizontal burrows are interspersed near the top unit d is 126 m of breccia with finely interbedded skeletal grainstone and burrowed or laminated mudstone the breccias contain a spectrum of platform derived lithoclasts and basinal intraclasts up to 10 m in size the breccias are typically grain supported rudstone with a matrix of lightly to completely dolomitized mudstone or skeletal debris beds are up to several metres thick unit e is 206 m of massive sucrosic dolomite that replaced breccias unit f is approximately 500 m of thick bedded to massive skeletal packstone with abundant rudists and a few mudstone intraclasts metre scale laminated lime mudstone beds are interspersed the section is capped by el abra formation platform margin limestone consisting of massive beds of caprinid packstone and grainstone with many whole valves depositional processes within this sequence shift from basinal pelagic or peri platform sedimentation to distal platform derived muddy turbidity currents with a large slump block unit a through more proximal coarser and cleaner turbidity currents unit b c to debris flows incorporating platform margin and slope debris units d e finally a talus of coarse reef derived bioclasts unit f accumulated as the platform margin prograded over the slope sequence interspersed basinal deposits evolved gradually from largely pelagic to include influxes of dilute turbidity currents units containing turbidites with platform derived bioclasts reflect flooding of the adjacent platform breccia blocks and lithoclasts were probably generated by erosion and collapse of the platform during lowstands laminated black pelagic carbonates locally cherty are interbedded with both breccias and turbidites at least those interbedded with turbidites may have been deposited within an expanded mid water oxygen minimum zone during relative highstands of sea level they are in part coeval with mid cretaceous black shales of the atlantic ocean

long term event stratigraphy of the apulia platform margin upper jurassic to eocene gargano southern italy abstract the upper jurassic to eocene apulia platform margin and the eastward transition to the adjacent basinal deposits are well exposed in the gargano promontory southern italy a carbonate block that is part of the slightly deformed foreland of the southern apennine thrust belt the long term stratigraphy of this margin and slope transect is punctuated by five major dynamic phenomena that subdivide the succession into six second order sequences these events include 1 a valanginian drowning unconformity 2 an early aptian albian drowning and demise of the platform 3 late albian cenomanian platform margin failures 4 a santonian campanian retreat of the platform margin and 5 eocene uplift and platform margin collapse the first event is documented worldwide and is probably eustatic in origin the second is concomitant with some oceanic anoxic events oae the last three processes are probably related to foreland reaction to subduction and collision in the dinarides and hellenides thrust belts the ultimate cause of the albian cenomanian failures is more problematic a worldwide eustatic regression is documented at this time but regional geology seems to favor tectonic uplift

the use of reflectance spectroscopy and the prehnite spectral index to target gold mineralization at the bonfim polymetallic skarn deposit serido mobile belt borborema province brazil abstract the serido mobile belt hosts numerous mineralized skarns in the borborema province northeastern brazil the bonfim w mo au bi te skarn occurs within a neoproterozoic metasedimentary sequence serido group within marble and schist lenses or at the contacts between both an asd fieldspec 3 high resolution spectrometer was used to characterize the mineralogy of a representative drill core interval 181 m from the bonfim deposit in order to generate the spectral characterization to define the gold mineralization skarns are characterized by the presence of diopside actinolite tremolite clinozoisite zoisite muscovite and prehnite prehnite and epidote constitute the main components of the calc silicate assemblage associated with late stage gold mineralization the diagnostic absorption feature of prehnite at 1478 nm oh can be used to identify its presence and the prehnite index proposed in this case study a reflectance ratio of 1465 nm 1478 nm allows highlighting the prehnite enriched sections along the core geochemical data show a positive correlation between gold and the presence of a prehnite absorption at 1478 nm the results suggest that the prehnite spectral signature can be used as a reliable and efficient rapid indicator for gold skarns perhaps under geologically similar circumstances to those at bonfim

w au skarns in the neo proterozoic serido mobile belt borborema province in northeastern brazil an overview with emphasis on the bonfim deposit the serido mobile belt smb is located in the borborema province in northeastern brazil and consists of a gneiss basement archean to paleo proterozoic a metasedimentary sequence marble quartzites and schists and the brasiliano igneous suite both of neo proterozoic age in this region skarns occur within marble and at the marble schist contact in the metasedimentary sequence most of the skarn deposits have been discovered in the early 1940s and since then they have been exploited for tungsten and locally gold recently the discovery of gold in the bonfim tungsten skarn has resulted in a better understanding of the skarn mineralization in this region the main characteristics of the smb skarns are that they are dominantly oxidized tungsten skarns with the exception of the itajubatiba and bonfim gold bearing skarns which are reduced based on pyrrhotite as the dominant sulfide garnet with high almandine and spessartine component and elevated gold contents in the bonfim deposit pressure estimates indicate that the skarns formed at 10 to 15 km depth the mineralized skarns present the prograde stage with almandine diopside anorthite and actinolite magnesio hornblende and titanite apatite allanite zircon and monazite as accessory minerals the retrograde stage is characterized by alkali feldspar clinozoisite zoisite sericite calcite and quartz scheelite occurs in four ore shoots distributed within the marble and at the marble schist contact the main ore body is 5 120 cm wide and contains an average of 4 8 wt wo3 which occurs in the basal marble schist contact fold hinges appear to control the location of high grade scheelite the late stage gold mineralization contains bismite bi2o3 fluorine bearing bismite native bismuth bismuthinite bi2s3 and joseite bi4 te s 3 and also chlorite epidote prehnite chalcopyrite and sphalerite this gold bismuth tellurium mineralization exhibits a typical late character and occurs as a black fine grained mineral assemblage controlled by conjugate brittle ductile faults and extensional fractures that crosscut not only the banding in prograde skarn but also the retrograde alkali feldspar and clinozoisite zoisite sericite assemblage the au bi te bearing minerals are intergrown with retrograde epidote prehnite chlorite chalcopyrite and sphalerite indicating that gold mineralization at bonfim is linked to a late stage skarn event the polymetallic nature of the bonfim deposit can be used as an important guide for the exploration of this type of skarn deposit in the borborema province which potentially contains significant new undiscovered gold and polymetallic deposits

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

geometry and petrophysical parameters of a calcarenitic turbidite lobe barremian aptian pas de la cluse france abstract several bioclastic resedimentation systems late barremian to early aptian in age outcrop in southeastern france the upslope portion of a calcarenitic turbidite lobe outcrops as a cliff 2 3 km wide and up to 45 m high oriented roughly perpendicular to the direction of palaeoflow it has been studied through 31 sections the studied body is point sourced and corresponds to a channel lobe transition located at the toe of slope of a urgonian carbonate platform on the western edge of the vocontian trough french subalpine chains the internal geometry of the lobe is the result of repeated erosion and filling of channels creating well defined stacked units filling phases result in lobe shaped morphology units evolve from base to top in an ordered way first the sediments exported from the platform and deposited in the basin are represented by decimetre thick sheet like and fine grained bouma a e and ab e sequences in this first unit erosion is limited and represented by shallow and symmetrical channels this initial phase of deposition corresponds to the formation of a lobe with a positive morphology the next phase of system development is more erosional and this is dominated by migrating sinuous channels several metres deep filled with coarse grained poorly graded turbidites these channels are first filled through lateral accretion and then sediment spills over to create a sub lobe the mixture of channel and lobe features could be considered as a carbonate equivalent of the channel levee system of siliciclastic deposits finally the system ends with the deposition of a flat based unit this unit extends for more than 2 km and is composed of the southwards lateral accretion of hundreds of metres wide sequences each composed of a debris flow deposit capped by a coarse grained calcarenite bed these sigmoidal bodies could be the ultimate forms of a spreading out phenomenon of the lobe overall the pas de la cluse system is a coarsening upward body as the grain size is related to the nature of the material this coarsening upward implies either an evolution in the nature of the carbonate material produced on the platform from grainy to bioconstructed a displacement of the source sediment from inner platform to margin or a displacement of the channel head through time from distal to proximal the upward evolution from classic turbidites to debris flow deposits can be explained either by the way the platform facies evolved with time in a depositional sequence or through retrogressive erosion by successive slope failures that cut deeper and deeper into the platform slope although its present day porosity is low the size of the system and the fact that it is encased in marls make it an interesting outcrop analogue for hydrocarbon exploration

the pombal granite pluton magnetic fabric emplacement and relationships with the brasiliano strike slip setting of ne brazil paraiba state abstract the pombal pluton 500 km 2 a suite of diorite syenite and porphyritic granite bodies is here used to constrain kinematics of brasiliano age tectonic episodes in northeast brazil the pluton intrudes high grade to migmatitic gneiss forming the western basement of the serido belt and is located at the intersection between two sets of continental scale dextral strike slip shear zones the northern set of shear zone strikes ne sw and branches southwards into the e w patos mega shear zone a detailed microstructural and low field magnetic susceptibility study was performed to unravel the relationships between solid state deformation in the country rocks and magma emplacement porphyritic granite and syenite have quite high magnetic susceptibilities 10 3 10 2 si units indicative of magnetite as the principal carrier of susceptibility the magnetic fabric is remarkably homogeneous in orientation throughout the pluton it is characterized by a shape preferred alignment of magnetite itself parallel to the shape fabric of mainly biotite amphibole i e to the magmatic fabric even close to the contact with the high temperature mylonites of the patos shear zone south of pombal no imprint of the e w trending structures is observed in the fabrics of either the granite or the host rocks granite emplacement and its internal fabric development is concluded to be independent of the movement of the patos shear zone in the southwestern border of the pluton a low dip foliation bearing a ne sw striking lineation is shared in both the magmatic fabric of the pluton and the solid state fabric farther to the north approaching the ne sw strike slip shear zone the magmatic fabric is characterized by a steeply dipping ne striking foliation carrying a subhorizontal lineation transition from low to steep dips of the planar fabrics is progressive two models are proposed for emplacement of the pombal pluton one considers magma injection during an early episode of tangential tectonics responsible for the gently dipping foliations evolving later to strike slip deformation the other model considers that the pluton was emplaced in a pull apart domain developed in the overlapping sector of a right hand en echelon system of a dextral shear zone compatibility of these models with the tectonic evolution of the serido belt is discussed

controls on cyclostratigraphy of lower cretaceous carbonates and evaporites cupido and coahuila platforms northeastern mexico the lower cretaceous cupido barremian aptian and coahuila albian carbonate platforms of northeastern mexico exhibit thick successions of meter scale cycles deposited in three unique paleoenvironmental settings 1 the cupido shelf lagoon is composed of peritidal carbonate cycles deposited in the protected lee of a reef rimmed to barrier shoal margin 2 the restricted coahuila ramp interior consists of cyclic alternations of subtidal evaporites and peritidal carbonates 3 the deep water parts of both the cupido and coahuila platforms are composed of foraminiferal wackestones and lime mudstones interspersed with firmgrounds and hardgrounds in a cyclic arrangement vertical successions of meter scale evaporitic cycles and peritidal cycles exhibit systematic stacking patterns that build into intermediate scale high frequency sequences tens to hundreds of meters thick and large scale composite sequences hundreds of meters thick that can be correlated across the cupido and coahuila platforms these large scale stacking patterns are interpreted to reflect longterm accommodation events and when combined with the scale independent architecture of all genetic units permit the inference that all three meter scale cycle types on the cupido and coahuila platforms are also governed by relative sea level change the composition thickness and number of meter scale cycles within individual high frequency sequences can be highly variable across the cupido and coahuila platforms however even though the overall upward shallowing patterns are evident the lateral complexity of cycle architecture and distribution is interpreted to be a natural response to fluctuations in regional climate interacting with autogenic processes such as variations in carbonate production and dispersal intensity and frequency of tropical storms and monsoons thermohaline circulation patterns and ambient ocean chemistry and temperature these interacting processes created laterally variable physiographic and oceanographic conditions across the cupido and coahuila platforms complicating the sedimentary record generated by the composite sea level signal well documented evidence from barremian cenomanian pelagic cycles throughout the tethyan seaway strongly indicates that milankovitch driven climatic changes operated during the early cretaceous contemporaneous shallow marine cyclicity in several locations suggests that these climatic changes may have had globally widespread effects in an effort to link the shallow water and deep water realms we propose a model whereby milankovitch driven global climatic changes generated low amplitude high frequency eustatic fluctuations through some combination of thermal expansion and contraction of ocean water waxing and waning of small ice caps and alpine glaciers and changes in the storage capacity of aquifers and lakes to produce meter scale cycles across lower cretaceous shallow marine platforms

upper devonian buildup margin and slope development in the southern canadian rocky mountains the geometries of upper devonian mid frasnian carbonate buildup margins of the peechee member southesk formation in the southern canadian rocky mountains reflect the influence of rising sea level punctuated by stillstands most peechee buildup margins in the cordillera retrograded whereas some aggraded or prograded in response to these sea level changes and variations in the relative rates of adjacent basin filling sedimentation peechee margin accumulation and adjacent basin deposition is best explained by a reciprocal model of sedimentation thick tongues tens of meters of stromatoporoid rudstones and bioclastic grainstones aggraded vertically or retreated during periods of sea level rise as sea level decelerated carbonate production was restricted and outbuilding occurred basinal onlapping sedimentation of the perdrix formation muds increased during the ensuing stillstand of sea level subsequently a renewed episode of relative sea level rise caused build up margin retrogradation this pattern of sedimentation driven by episodic fluctuations of relative sea level occurred repeatedly during peechee time a broad scale shallowing upward trend culminated in a progressive increase up section in the abundance of submarine erosion surfaces in the eastern main ranges and paleocaliche horizons in the front ranges southwesterly paleocurrents are inferred to have influenced peechee buildup margin geometries and adjacent basin sedimentation retrograded windward margins formed in response to active currents and breaking waves along the northeastern edge of the fairholme and southesk cairn reef complexes leeward buildup margins protected from the southwest directed currents exhibit prograding geometries these characteristics are exemplified by the ancient wall complex where the windward buildup margins to the northwest and southeast are vertically aggrading whereas the coeval peechee buildup margin to the southwest prograded 2 km onlapping dysaerobic waters during upper cairn and peechee time inhibited the accumulation of forereef skeletal organisms and served as an additional control on buildup margin geometry

from the great bahama bank into the straits of florida a margin architecture controlled by sea level fluctuations and ocean currents high resolution multichannel seismic data collected across the great bahama bank margin and the adjacent straits of florida indicate that the deposition of neogene quaternary strata in this transect are controlled by two sedimentation mechanisms 1 west dipping layers of the platform margin which are a product of sea level controlled platform derived downslope sedimentation and 2 east or north dipping drift deposits in the basinal areas which are deposited by ocean currents these two sediment systems are active simultaneously and interfinger at the toe of slope the prograding system consists of sigmoidal clinoforms that advanced the margin some 25 km into the straits of florida the foresets of the clinoforms are approximately 600 m high with variable slope angles that steepen significantly in the pleistocene section the seismic facies of the prograding clinoforms on the slope is characterized by dominant partly chaotic cut and fill geometries caused by submarine canyons that are oriented downslope in the basin axis seismic geometries and facies document deposition from and by currents most impressive is an 800 m thick drift deposit at the confluence of the santaren channel and the straits of florida this santaren drift is slightly asymmetric thinning to the north the drift displays a highly coherent seismic facies characterized by a continuous succession of reflections indicating very regular sedimentation leg 166 of the ocean drilling program odp drilled a transect of five deep holes between 2 and 30 km from the modern platform margin and retrieved the sediments from both the slope and basin systems the neogene slope sediments consist of peri platform oozes intercalated with turbidites whereas the basinal drift deposits consist of more homogeneous fine grained carbonates that were deposited without major hiatuses by the florida current starting at approximately 12 4 ma sea level fluctuations which controlled the carbonate production on great bahama bank by repeated exposure of the platform top controlled lithologic alternations and hiatuses in sedimentation across the transect both sedimentary systems are contained in 17 seismic sequences that were identified in the neogene quaternary section seismic sequence boundaries were identified based on geometric unconformities beneath the great bahama bank all the sequence boundaries could be traced across the entire transect into the straits of florida biostratigraphic age determinations of seismic reflections indicate that the seismic reflections of sequence boundaries have chronostratigraphic significance across both depositional environments

catastrophic collapse of the west florida carbonate platform margin a large truncation surface has been discovered on seismic reflection profiles along the distally steepened ramp of the west florida carbonate platform margin this structure interpreted as a submarine slide scar is at least 120 km across and up to 30 km wide the slide has removed as much as 300 350 m of late paleogene and early neogene strata collapse occurred in the middle miocene within an episode of seaward progradation during a relative sea level highstand postcollapse depositional sequences thicken abruptly across the structure this suggests catastrophic slope failure gravitational instability created by high rates of sediment accumulation is believed to have been the triggering mechanism such large scale platform margin collapse is likely to generate megabreccia debris flows as well as aid in the landward retreat of precipitous high relief carbonate escarpments