T3S5_O1 Beds, Bars, Bends, Banks and Basins: Construction of the Seascape and Deep-Marine Strata by Turbidity Currents Mohrig, D. The University of Texas at Austin, Department of Geological Sciences, 2275 Speedway, M.S. C9000, Austin, TX 78712, USA (mohrig@jsg.utexas.edu) I will combine results from laboratory experiments with analyses using industry-grade seismic volumes and sediment-transport calculations in order to highlight a set of properties for deep-marine systems that I think are important and possibly underappreciated when it comes to interpreting the evolutions of seascapes and their deposits. The presentation will only consider turbidity currents and focus on two topics: (1) the substantial differences in patterns and character of bed-elevation change associated with net-erosional versus strongly depositional turbidity currents; and (2) common remobilization of sandy turbidites as relatively dense, laminar flows shortly after their deposition from suspension. Each topic will be discussed in the context of improving accuracy in predicting both seascape evolution and the distribution of rock properties within deep-marine strata. Results from laboratory currents traversing both straight and sinuous channels will be used to highlight the substantially different patterns of bed evolution associated with net-erosional versus strongly depositional turbidity currents. For the net-erosional currents, locations of bed degradation and aggradation are strongly influenced by pre-existing surface topography. In particular, local bed slope and bed roughness control what is a relatively patchy distribution of sites of significant bed-elevation change. While bed evolution tied to the net-erosional currents is characterized by spatial heterogeneity, the strongly depositional currents lay down continuous beds with smoothly varying changes in bed thickness and grain size. These changes in bed thickness and grain size are insensitive to the local bed topography and associated spatial accelerations, making these deposits properties relatively easy to accurately predict. I will outline how relatively simple and accurate models for deep-water strata can be built by embracing the locality in erosional patterns and the non-locality of depositional patterns associated with turbidity currents. In addition, laboratory currents document how the outer banks of channel bends can switch from sites of focused sidewall erosion to sites of deposition depending on whether the currents are producing bypassing or channel-filling conditions. The lateral movement of channel bends and growth of channel sinuosity only occurs when the turbidity currents are at least weakly net erosional in their transport properties. Depositional currents accumulate sediment at the site of the outer bank, preserving this sidewall and reducing the overall sinuosity of a submarine channel as it aggrades. Results of minibasin filling by laboratory turbidity currents highlight a significant remobilization of original turbidites as high density, laminar flows. In the laboratory this remobilization can occur immediately following original suspension deposition, driven by the metastable character of the original deposits and the stress applied to their surfaces by overriding currents. Original turbidites always drape minibasin topography while all of the sandy ponded deposits in the experimental minibasins are the products of remobilized turbidites. Interestingly, these two styles of deposits, original versus remobilized, are indistinguishable in vertical section when using only sedimentary structures, grain size and sorting as discriminators. Remobilized sandy turbidites are also observed in experimental submarine channels, leading to the development of beds that onlap channel sidewalls with high angles. These lab results will be compared to seismic images and core in order to argue that the amount of early remobilized sand in deep-water strata is probably underappreciated.

T3S5_O2 Sedimentary facies produced by turbidity currents moving inside soft muddy substrates Baas, Jaco H.1, Manica, Rafael.2, Puhl, Eduardo.2, Verhagen, Iris.1 1 School of Ocean Sciences, Bangor University, Menai Bridge, Isle of Anglesey, LL59 5AB, Wales, United Kingdom (j.baas@bangor.ac.uk) 2 NECOD/IPH/UFRGS, Departamento de Hidromecânica e Hidrologia. Porto Alegre, Brazil Laboratory experiments on the interaction of cohesionless coal-laden turbidity currents with cohesive soft muddy substrates have revealed a new type of turbidity current characterised by horizontal flow within the substrate. These remarkable 'intrabed' turbidity currents formed when the cohesive substrate contained enough pore water to behave as a fluid mud, and when the density of the turbidity current was higher than that of the upper part of the density-stratified mud deposit. The current kept its characteristic shape and fundamental turbulent properties whilst flowing within the bed, yet the mud above the flow remained largely undisturbed until the top of the current emerged above the bed surface, which was up to 0.1 m behind the current's nose. At the location of emergence, the mud was swept over the top of the head as either mud clasts or as less coherent elongated clouds of mud. The intrabed turbidity currents formed turbidite deposits with a large variety of potentially diagnostic textures and structures. Mixing of coal and mud resulted in deposits with chaotic textures, containing both randomly distributed mud and clasts of mud. Vertical mixing dominated; hardly any horizontal movement was required to generate the chaotic textures. These deposits could therefore be mistaken for debrites. Elongated horizons of coal and mud were identified within the turbidites, given the deposits a stratified character. Interestingly, these horizons formed after the current had passed, when the turbidite started to load into the underlying fluid mud and small mud volcanoes formed at the interface between the eroded bed and the base of the turbidite. These strata are therefore interpreted as sediment injections. The load structures were ubiquitous, and their size was related to the weight of the turbidite and the local density of the mud deposit, which in turn was controlled by the depth of erosion. Deposits with sedimentary structures that resemble those in the laboratory-scale intrabed turbidites have been found in the deep-marine Aberystwyth Grits of West Wales, United Kingdom.

T3S5_O3 The nature of turbidity currents in the ocean; how do they go so far? Kneller, Ben1., Nasr-Azadani, Mohamad 2. 1 University of Aberdeen, School of Geosciences, Aberdeen, AB24 3UE, UK . b.kneller@abdn.ac.uk 2 University of California at Santa Barbara, Department of Mechanical Engineering, Santa Barbara, CA 93106 A large proportion of the sediment generated by erosion of the continents is ultimately delivered to the deep ocean to form submarine fans, being carried to the margins of these fans by turbidity currents that flow through submarine channels that may be hundreds or even thousands of kilometers long. The persistence of these flows over extremely long distances with gradients that may be 10-4 or less, while maintaining sediment as coarse as fine-grained sand in suspension, is enigmatic, given the drag that one would expect to be experienced by such flows, and the effects of progressive dilution by entrainment of ambient seawater. The commonly-held view of the flow structure of turbidity currents, based on many laboratory and numerical simulations and rare observations in the ocean, is that of a vertical profile of time-averaged horizontal velocity with a maximum value close the bed (typically 10-20% of the total height of the current, e.g. Xu et al., 2010), which is broadly similar to that of powder snow avalanches in subaerial environments. The form of this profile is largely due to much higher drag on the upper boundary than on the lower. This upper boundary drag is related to Kelvin-Helmholtz instabilities generated by shear between the current and the ambient seawater. Turbulent kinetic energy distribution is dominated by shear-generation of turbulence at the upper boundary. We question this classical view for the case of flows on the extremely low gradients of the ocean floor, and suggest some possible conditions that may lead to stably-stratified currents, with dramatically reduced drag, and a fundamentally different mean and turbulent velocity structure, in which the majority of turbulence is generated at the lower boundary. The majority of the entrainment of ambient seawater into the turbidity current also occurs via the Kelvin-Helmholtz instabilities. Recent analysis of submarine levees (Birman et al., 2009; Nakajima & Kneller, 2013) suggests that there may be little or no entrainment of ambient fluid in turbidity currents flowing over low gradients, implying that K-H instabilities may be absent under these conditions. Kelvin-Helmholtz instabilities (and associated drag) result when the destabilizing effect of fluid shear exceeds the stabilizing effect of density stratification within the turbidity current; the dimensionless ratio of these two influences is the gradient Richardson number:

where ! is density, !a is the density of the ambient seawater, u is time-averaged local horizontal component of velocity, and z is the vertical coordinate. Where Rig exceeds a value of 0.25 the stratification is likely to be stable, and no K-H instabilities will form, eliminating much of the drag and entrainment. We report the results of direct numerical simulations that help to constrain the conditions under which such currents may form. In order to model accurately the potentially stabilizing effect of significant density gradients within such currents, it is necessary to abandon the Boussinesq approximation (under which density variations appear only in the buoyancy term), and explicitly model the influence of density variations.

Rig =g!! /!z

!a

"

#$

%

&'

!u /!z( )2

Simulations reported by Sequeiros at al. (2010) show the type of velocity profiles expected in flows without K-H instabilities, which they relate to Froude-subcritical flow. We suggest that the real cause of such profiles is the presence of stable density stratification, and that they are far more representative of the structure of turbidity currents in long fan channels than are the more familiar profiles commonly reported. References Birman, V.K., Meiburg, E. & Kneller, B., 2009. J. Fluid Mech., 619, 367–376. Nakajima, T. & Kneller, B., (in press). Sedimentology. doi: 10.1111/j.1365-3091.2012.01366.x Sequeiros, O. E.; Spinewine, B., Beaubouef, R.T., Sun, T. García, M.H. & Parker, G. 2010. J. Hydr. Eng,

136, 412-433

T3S5_O4 Flow concentration, mean particle grain-size and particle grain-size standard deviation controls on laboratory turbidity current deposition K. Yam,, A. Burns, D. Ingham and W.D. McCaffrey School of Earth and Environment, University of Leeds, United Kingdom (yamks85@gmail.com) A series of lock-release generated laboratory turbidity current experiments was performed in order to investigate the effect of varying the initial concentration, particle grain size, and particle grainsize standard deviation on the propagation and deposit characteristics of the flows. Flows of low concentration or carrying coarse particles were found to exhibit linearly decreasing patterns of longitudinal deposit mass. Increasing flow concentration or decreasing particle size progressively caused the deposits to exhibit a constant mass profile for the first half of the deposit followed by a linear decrease for the second half. Changing the particle size standard deviation does not cause a significant change in the deposit mass profile but significantly influences the grain size characteristics of the deposit. There is only a small decrease in the grain size of the deposit of flows carrying particles with standard deviation 8-11µm whereas the decrease is large for flows carrying particles with standard deviation 18. The result suggests that particle fractionation within turbidity currents is inhibited when the grain size standard deviation is less than 11 µm in these experiments. A criterion for the inhibition of the particle fractionation can be derived by non-dimensionalising the standard deviation using mean particle grain-size. However, further experiments on larger flows are required to confirm the scale independence of such a criterion. Acknowledgements This research was funded by the Turbidites Research Group Consortium (Anadarko, BG, BP, ConocoPhilips, Devon Energy, Maersk, Marathon, Nexen, Petronas, Statoil and Woodside).

T3S5_O5 Sedimentary facies of cyclic steps in sandy and gravelly turbidite sequences George Postma1, Kick Kleverlaan2, Matthieu Cartigny3 1 Faculty of Geosciences, Utrecht University, PO BOX 80.021, 3508TA Utrecht, The Netherlands, 2 Sedimentology Consultant, a/b "Hoop op Welvaart", Zeeburgerdijk 585, 1095 AE Amsterdam, The Netherlands 3 National Oceanographic Centre, University of Southampton Waterfront Campus, European Way, Southampton SO14 3ZH, United Kingdom In modern canyon and slope settings large, tens of meters size bedforms have been identified on multi beam and side scan sonar images that have recently been interpreted and identified as cyclic steps. Such bedforms were not recognized in outcrop and core, as yet. Experiments show that cyclic steps preserve quite differently compared to the common subcritical bedforms, because they migrate upslope instead of downslope: the lee-side of the bedform erodes, while their stoss side aggrades. Experimental work demonstrates that cyclic steps produce a variety of bedform facies that we have now recognized in outcrop and are described here. Characteristic features include facies directly related to the hydraulic jump and facies characteristic for acceleration of the flow after the jump. The jump forms the trough of the bedform, where the substrate is eroded and ripped up and where intraformational clasts are produced. Experiments show that at the jump locality the forward movement of the suspension is momentarily stalled and dominated by rapid hindred settling of the coarsest grains to produce structureless and possibly coarse-tail graded deposits. Deposits of the hydraulic jump grade into backset beds of the stoss side of the bedform with characteristic crude and spaced stratifications and also plane bed laminations of the upper flow regime. Gravelly backsets are generally steeply dipping upslope, while sandy backset beds are generally deposited at low upslope dipping angles. Multi turbidite events produce bioturbated intercalated muds and low angle truncations in these stratifications. The facies that characterizes these bed forms have been described previously in idealized vertical sequences as units of high density turbidity currents, but have not yet been interpreted to represent supercritical bedforms. It is likely that their large size, which is in the order of 30 m for gravelly and up to hundreds of meters for sandy steps may have hindered their recognition in outcrop so far.

T3S5_O6 Complexities of channel overbank architectures and their distinctive thin-bedded turbidite facies – review using outcrop and modern seafloor data Hansen, L., Kneller, B., Callow, R. University of Aberdeen, Department of Geology and Petroleum Geology, Aberdeen, AB24 3UE, UK (larissa.hansen@abdn.ac.uk) Submarine channel related thin-bedded turbidites deposited by channel-overbank flow make up a large proportion of the area within and around submarine channels. Despite their thin-bedded nature they often contain very laterally continuous sandstone beds that can form significant reservoirs. Modern sea-floor data demonstrate a number of distinct depositional environments for thin-bedded facies around submarine channels, but these can be difficult to differentiate in outcrop and the subsurface. The lateral variations of sand content, palaeocurrents and sedimentary structures may be used to establish a framework for distinguishing different thin-bedded turbidite facies, in particular levees and terraces. Detailed investigation of previously studied outcrops in southern Chile (Upper Cretaceous Cerro Toro Formation) has revealed hitherto un-described complexities within thin-bedded turbidite facies. This complexity is emphasized by comparison with modern seafloor data from the Gioia Basin of the Tyrrhenian Sea, north of Sicily, which clearly shows the interaction between overbank areas of different channels, forming complex topography and creating geometries and facies relationships that would be difficult to identify in outcrop. The field work in Chile involved construction of multiple detailed sedimentary logs within two exposed sections composed of thin-bedded turbidites perpendicular to palaeoflow of the adjacent channels, providing data on bed thickness, sedimentary structures, palaeocurrent directions and ichnofacies. The results of this study highlight the ambiguities previously noted in the literature over the context of these thin-bedded turbidites, in terms of existing models for channel-related thin-bedded turbidites. Our data show that both bed thickness and proportion of sandstone (‘net-to-gross’ in reservoir terms) decrease away from the channel that is closest to the studied thin-bed sections and at the same stratigraphic level, but palaeocurrents are, enigmatically, indicative of flow towards the channel. These thin-bedded turbidites have previously been interpreted as levee deposits, but this study shows that some of the indicators used to identify levees are absent. The outcrop may represent a terrace deposit associated with an as-yet unidentified channel, or some hybrid setting. The study of the modern system in the Gioia Basin involved detailed investigation of high-resolution bathymetric data and CHIRP sub-bottom profiles. Various overbank architectural elements have been identified, which show interactions between overbank flow from three separate channels. This interaction creates complex topography, including sediment waves that modify the levee overbank geometries and divert sediment to depositional areas further from the channel. A number of terraces have also been identified within the channels, whose surfaces can have multiple erosional scours and some small channels, and which sometimes merge with the external levees. Comparing outcrop and modern sea-floor data it becomes clear that channel overbank areas are complex and variable environments in which overbank sedimentation from different channels can combine to produce complex morphologies and architectures. The Cerro Toro Formation represents the fills of many channels, some of which may have been active synchronously; it is likely that their overbank areas were as complex and interactive as those seen in the Gioia Basin of the Tyrrhenian Sea. Very detailed studies of thin-bedded turbidite outcrops will be required in order to diagnose their depositional environments, and especially to characterize and differentiate them in the subsurface.

T3S5_O7 The influence of flow efficiency on submarine lobe architecture and facies distributions in a base-of-slope setting Menno Hofstra1, David M. Hodgson1, Jeffrey Peakall1, Stephen S. Flint2, A. Prélat3 1Stratigraphy Group, School of Earth & Environment, University of Leeds, UK (eemh@leeds.ac.uk) 2Stratigraphy Group, School of Earth, Atmospheric and Environmental Sciences, University of Manchester, UK 3Stratigraphy Group, Department of Earth Science & Engineering, Imperial College London, UK The base-of-slope tract in submarine fan systems is commonly marked by a transition from a channel dominated to a lobe dominated framework. This, therefore, records the processes of sediment gravity flows passing from confined to unconfined environments, which change in location and character through time. This results in a complex fragmented stratigraphic record. One approach to help to understand ancient base-of-slope systems is to set-up good constraints in attempting to identify individual architectural elements and their process sedimentology. Unit 5 is a ~100 m thick succession in the youngest submarine fan within the Skoorsteenberg Formation of the Tanqua depocentre (South Africa). This unit shows a large-scale transition from submarine slope, dominated by levee confined channel systems, to the base-of-slope, which is dominated by depositional lobes. At the Blauwkop farm locality a 35 m thick portion of Unit 5 is well exposed on multiple outcrop faces over a 9 km2 area, which allows 3D architectural constraint. This includes correlating key surfaces between measured sections, tied to palaeocurrent measurements. The collected data show a complicated depositional history with multiple erosive, by-pass and aggradational stages. A laterally extensive succession of medium thick-bedded (0.3-1.5 m) climbing ripple dominated fine-grained sandstones is interbedded with thin-bedded siltstones which show a relatively high proportion of spatial variability, together with thick-bedded (1-4 m) banded fine-grained sandstones. Previous interpretations have classified these as a combination of distal channel bodies, channel margins, levee and overbank deposits. However, here these are reinterpreted as frontal lobes. Banded sandstones are interpreted here as deposits from transitional flows, due to the result of partial turbulence suppression. The ripple structures within the medium-thick bedded sandstones are often complicated and indicate highly depletive and aggrading turbulent flow conditions. Facies distribution characteristics are believed to be substantially different between the frontal lobes and terminal lobes identified farther downstream. Higher up within the section, the system shows an increase in scouring and evidence of sediment bypass. Two erosional confined northward orientated channel complexes incised into the previously deposited frontal lobe complex. The whole system is overlain by a late stage lobe indicating a final retrogradational stage. An important controlling factor for early or late basin floor deposition is believed to be the quantity of mud within incoming flows. This is largely controlled by erosion of the muddy substrate upstream and/or loss of mud by flow-stripping which can vary over time. Overall, the frontal lobe deposits within the Blauwkop area are indicating the inability of flows to sustain themselves, which might be related to relatively low internal mud content. Instead, terminal lobes are possibly fed by more efficient and relatively mud-rich flows of sufficient duration, to fully develop hybrid flows which dominate deposition in the fringes of terminal lobes. The relative position of lobe deposition to the break-of-slope also has influence on the abruptness of changes in confinement, which stimulates rapid suspension fall-out at the base-of-slope. Together these may provide an explanation for the large differences in facies distribution patterns between frontal and terminal submarine lobes.

 

 

T3S5_O8 Evolution, architecture and stratigraphy of Froude supercritical submarine fans David Hoyal1, Timothy Demko1, George Postma2, Robert Wellner1, Vitor Abreu1, Juan Fedele1, Darren Box1, Anthony Sprague1, Kaveh Ghayour1, Paul Hamilton1,3 and Kyle Strom3 1ExxonMobil Upstream Research Company, david.c.hoyal@exxonmobil.com, Houston, TX 2University of Utrecht, Utrecht, Netherlands 3University of Houston Department of Civil and Environmental Engineering, Houston, TX Sandy submarine fans from steep tectonically active margins were once considered a universal fan type, but improved geophysical imaging has revealed that the motif is not universal and differs from passive margin fans dominated by muddy levees developing on lower slopes. Nevertheless, the distinctive properties of these ‘steep’ Froude supercritical fans suggest a unique fan mode with repeatable morphodynamic processes and stratigraphic patterns. This idea, that distributive system architecture is strongly controlled by the densimetric Froude number (Fr’=U/(g’h)1/2, g’=g(ρ/ Δρ) through its influence on free surface (1-D) flow structure, channel-lobe interaction, information transfer, and channel progradation is supported by hydraulic theory, tank experiments, and numerical models. 'Steep' fans are usually small (< 10km), a fact attributed to coarse sediment sourced from steep short catchments, but could alternatively be explained by hydraulic jumps which limit channel extension or short avulsion lengths associated with steeper slopes. Typical geometries include large-scale backsets as a lobe is propagated upstream by a migrating hydraulic jump. In cross section this process produces a simple mounded lobe superimposed on a channel geometry typically referred to as a "steershead". The model is tested on examples of "steep" fans from outcrop and high resolution seismic including Brushy Canyon (Texas), Ainsa (Spain), Tabernas/Sorbas (Spain), Karoo (RSA), Golo (Corsica) and East Breaks (GOM). Supercritical bedforms and bedform sequences observed are consistent with the interpretation of supercritical fans. Interesting questions with important implications for reservoir architecture include: to what degree does submarine fan architecture depend on source grain size (provenance) versus differences in local slope and related hydraulic regime (e.g., Froude regime)?; to what degree can fans be described by steady and more continuous mesoscale morphodynamic processes rather than discontinuous (unsteady) flows?; is it possible that the structure of 'steep' fans is more a function of supercritical flow and is relatively robust to different grain sizes so long as there is sufficient bedload to amplify hydraulic instabilities like hydraulic jumps?; conversely, is levee growth typically related to subcritical flow in the channel and backwater that pushes suspended sediment overbank?; is the ratio of suspended load to bedload, strongly modulated by the deep water density flow hydrodynamics, an important control on system morphology? Typical processes of supercritical fans include: • Perched supercritical fans develop at the "toe of slope" instead of the basin floor, an observation

explained by retardation of channel extension under supercritical conditions. • Sand is selectively deposited on a clinoform (sand trap) while muds are washed down the steeper slope. • Sand may be sourced by erosion of upstream channel fills (bed aggradation) due to increased flow

thickness in choked subcritical reaches which are drawn-down by a supercritical avulsion. • Systematic changes in slope following avulsion lead to morphodynamic/stratigraphic cycles and

systematic vertical successions. As slope decreases flows transition from jets, to hydraulic jumps (supercritical choke) to backwater (subcritical choke) each with a particular sub-cycle and stratal style.

• Froude number should decrease upwards in lobes but the trend may be disrupted by progradation or lobe backstepping.

T3S5_O9 An integrated outcrop and subsurface study of the Solitary Channel Complex (Tabernas Basin, Spain) Arbués, P.1, 2, Granado, P.1, 3, De Matteis, M.1, 2, Cabello, P.1, 2, López-Blanco, M.1, 2, Marzo, M.1, 2, Muñoz, J.A.1, 3, Abreu, V.4. 1 Geomodels Research Institute, C/ Martí i Franquès s/n 08028, Universitat de Barcelona, Barcelona, Spain (pau.arbues@ub.edu) 2 Departament d'Estratigrafia, Palentologia i Geociències Marines, Universitat de Barcelona, C/ Martí i Franquès s/n 08028 Barcelona, Spain 3 Departament de Geodinàmica i Geofisica, Universitat de Barcelona, C/ Martí i Franquès s/n 08028 Barcelona, Spain 4 Exxon-Mobil Upstream Research Company, P.O. Box 2189, Houston, USA The Miocene E-W striking Tabernas basin (Almería, Spain) developed during the collision between Africa and Iberia and was one of the back-arck extensional basins connecting the Mediterranean Sea with the Atlantic Ocean. The Tabernas basin fill includes the Late Tortonian-Messinian Solitary Channel. With exceptional outcrops, the Solitary Channel has been used as analogue to the prolific turbidite systems in offshore Angola, and remains as a potential good analogue for deepwater plays in the Mediterranean region. The aim herein is to provide scope on the geometry and architecture of the Solitary Channel from a new dataset. This dataset integrates conventional outcrop data, digital outcrop models (LiDAR and Multiview 3D) and subsurface data. The subsurface data are more than 100 m of continuous core recovered at 97% from two wells, related downhole geophysical data, and a geoelectrical tomography profile oriented perpendicular to palaeoflow and passing by the drilled wells. Results show that the studied Solitary Channel is almost exclusively dominated by sandstones and gravelly sandstones. The prevalence of graded bedding indicates a dominance of turbidites in front of debrites. The individual graded units are dominated by the Ta and Tb Bouma divisions, and thus deposited from both high and low-density turbidity currents. Drill core studies confirmed that a gravelly sandstone facies, generally present below Ta divisions, is characterized by AB-plane imbricated clasts. This evidences bedload transport. The mean orientation of the imbrication planes was found to indicate palaeoflow parallel to that derived from the scour and tool marks present in the outcrop. Furthermore, the gravelly sandstone facies exhibits crude bedding dipping perpendicular to palaeoflow, which is interpreted as the product of bar migration normal to the channel-axis. Data on bedding attitudes were collected from many other structures; from direct compass measurements, from digital outcrop models, and complemented with attitudes from the combined interpretation of acoustic televiewer images and drill core. The results contribute to the discussion of the fundamental architectural components of the channel-complex in terms of backwards inclined sandy macroforms and/or Lateral Accretion Packages. On the broader scale, the study of the subsurface data revealed that the base of the channel complex is located significantly deeper than it had been interpreted from outcrop. Also that the channel-complex can be subdivided into four main sequences of elementary channel-fills. Each sequence records incision, followed by broadening, with vertically-stacked channel-axes. The channel-axes of consecutive sequences of elementary channel-fills are southeastwards stepped; the channel-axes of the oldest sequences of elementary channels are rich in deposits from high-density turbidity currents by contrast to the youngest sequences, which are dominated by low-density turbidity current deposits. These changes reflect lateral migration and backstepping of the system, and can be discussed in terms of the swing of a meandering channel and tectonically driven gradient changes. Acknowledgments

We acknowledge financial support from ExxonMobil and Project MODELGEO (CGL2010-15294). ROXAR is acknowledged for donation of RMS licenses.

T3S5_O10 Outcrop examples of supercritical morphodynamic successions in the deposits of steep, sandy submarine fans: Ainsa and Tabernas basins, Spain Demko, T1.,Hoyal, D1., Ghayour, K1., Abreu, V1., Selvam, B1., Rosin, M1., Postma, G2. 1 ExxonMobil Upstream Research, Houston, TX 77252 (timothy.m.demko@exxonmobil.com) 2 Utrecht University Outcrops of submarine fan deposits from steep, sandy depositional settings have been examined in order to define and identify morphodynamic successions that capture the mode and variation of lithofacies characteristics and stratal architecture. A morphodynamic succession is a set of genetically-related strata that record the evolution of flow conditions deduced from these units, meaning that the strata were deposited as a result of the interaction of a sediment-laden flow or flows with the bed that imparted a characteristic texture, fabric, stratal architecture, and depositional geometry. Outcrops in the Eocene Ainsa basin and Miocene Tabernas basin of Spain preserve deepwater strata that were deposited in tectonically-active settings, with accommodation strongly influenced by active structures and sediment supply fed by nearby high-relief source areas. Both basins preserve examples of connected, time-equivalent depositional systems that can be traced, in a source-to-sink manner, from fluvial/alluvial to marginal-marine/deltaic to slope channel and finally deepwater lobe settings. Strata at the channel-lobe transition zones (CLTZ) in these deposits are characterized by lithofacies assemblages that have a distinct grain size trends, sedimentary structures, stacking pattern, and stratal geometry. These assemblages, typically 1-5 m thick, have a sharp, erosional basal surface, often exhibiting soft-sediment deformation features (flame structures). The basal surface truncates underlying strata, with cm’s to m’s of relief, and the sediment immediately above often contains locally-derived rip-up clasts. This basal portion is the coarsest-grained (medium sand to cobble conglomerate) part of the succession, and typically is massive/structureless, or exhibits contorted crude bedding. Where thickest, and also where the basal surface exhibits the most erosional relief, the basal portion of the assemblage commonly is characterized by large-scale backset cross bedding, which resemble planar/tabular cross beds but dip counter to the dominant flow direction. The beds and bedsets that make up the backset crossbedding are comprised of cm to dm scale crude stratification, with grain sizes that alternate between coarser (imbricate cobbles to coarse to medium sand) and finer (coarse to medium sand) components. If locally-derived rip-up clasts are present, they may be aligned, and/or imbricated, along the backset bedding set or coset boundaries, and diminish in size and abundance in a down-palaeocurrent direction. The crudely stratified or backset bedded units are overlain by units characterized by finer-grained (medium-fine) inclined planar/spaced stratification and wavy to hummocky-like cross stratification. The lithofacies packages thin down-palaeocurrent at the expense of the lower, coarser units, and may consist solely of these finer-grained spaced and/or wavy stratified subunits at their most distal end within the CLTZ, or grade into other lithofacies in the deepwater lobe deposits. These lithofacies assemblages are interpreted to be morphodynamic successions deposited by aggrading cyclic steps formed at the CLTZ by supercritical sediment gravity flows. Erosion and soft-sediment deformation at the base of the succession forms by scour and fluidization of underlying sediments, while overlying crude and crude backset bedding encroaches up-current into the scour as a series of traction carpets. Sediment down-current of the scour is deposited as traction carpets and aggrading anitidunes. Stacks of these successions formed as trains of aggrading cyclic sets moved up through the CLTZ, forming an overall fining-upward package.

 

T3S5_O11 Flysch turbidite shelf model Higgs, Roger Geoclastica Ltd, Bude, Cornwall EX23 8LQ, UK (rogerhiggs@geoclastica.com) By general accord, the HAM (Hecho, Annot, Marnoso-arenacea) flysch accumulated on a deep-sea fan and basin plain in 3 foreland-basin axial gulfs, supplied longitudinally. Shared published traits include: flysch hallmark cyclicity of alternating thinner-bedded (e.g. cm or dm) and thicker-bedded (dm or m) turbidite “packets” 1-30 m thick; intra-HAM incised “channels” (m-km wide; 5 m to over 100 m deep); Nereites, Zoophycos and Cruziana ichnofacies; bathyal-type forams; common HCS beds (cm-dm) and mud-draped scours (MDSs). Consensus on 400-800 m water depths poses a problem: if not storm erosion, what prevented further shallowing while over 4 km (H, M) accumulated? This and the HCS suggest a possible shelf origin for flysch, with implications for its use as reservoir outcrop analogues. HAM flysch bathymetric reassessment must ignore ichnofossils, to avoid circularity, as Seilacher’s original Nereites-type formations are flysch; moreover, Nereites- and Zoophycos-type associations are known in shelf deposits. The HCS beds, inferred by most HAM workers to be internal-wave-modified turbidites, are interpreted here as shelf tempestites, while HAM turbidites (Lowe-, Bouma-type) are megaflood hyperpycnites supplied to the shelf via a gulf-head delta. The shelf was long (epeiric gulf), confined laterally by orogen and forebulge, and ended at a continental slope (into a remnant ocean) or intermediate slope (cf. modern Adriatic foreland basin’s 200 km NW shelf, passing SE into two “pits” and ocean beyond). The “fan” was just a sandier inner shelf (gulf). The “channels” are shelf-indenting submarine canyons. Tsunamis moving up-gulf deposited “megaturbidites” (H, M) of forebulge carbonate debris. HAM “bathyal” forams reflect upwelling-slope conditions (seabed organic-rich, dysoxic) replicated on the shelf by prolific hypopycnal inflow (nutrients) causing high phytoplankton productivity, hence bottom dysoxia, enhanced by thermohaline stratification (hypopycnal fresh water; subtropical lack of winter overturn). Hypo- and mesopycnites are expected. Many HAM “linked debrites” and “slumps” are probably in situ seismites, predictable in any foreland-basin, low-gradient environment. HAM flysch cyclicity records glacioeustatic water-depth oscillations; the thinner-bedded packets represent highstands (interglacials). Much of the shelf remained submerged at lowstands as Eocene-Miocene long-term (1-5 Ma) glacioeustatic amplitude was low (30-80 m) and axial-delta progradation limited (see below). The sharp change in bed thickness from packet to packet suggests falls and rises large enough (2-20 m?) to significantly alter the proximality, yet too brief (0.1-1ka?) for more than 1 or 2 events to occur during each fall or rise, implying rapid fall/rise rates (c. 2 cm/yr) like those of Quaternary sub-10 ka cycles (2 ka solar cycle?). Milankovitch- and solar-cycle convolution explains packet-thickness variability. Accentuating the bed-thickness jump, hyperpycnicity was ‘easier’ at lowstands, as the basin-axial trunk river was more incised, curbing its expansion (deceleration) onto the interfluves during floods, ensuring higher river velocity (turbidity, density); thus, lowstand hyperpycnal flows were so frequent and sustained that most river-supplied sediment bypassed the shore, slowing delta advance in favour of shelf aggradation. Each fall forced a simultaneous increase in seabed storm-wave power (shallowing) and proximality (subtly coarser fairweather mud), conserving the shelf equilibrium profile. During low- and highstands alike, each megastorm shaved the aggrading shelf back down to equilibrium, removing a thin (cm-dm) fairweather layer of mud and/or hyperpycnite sand, leaving behind a subsidence-accommodated increment capped by a MDS or a tempestite with or without HCS. The flysch-shelf model is non-actualistic (Quaternary eustatic amplitude too high).

T3S5_O12 What is the effect of sea level on frequency of sediment transport to distal basin plains, and what are the global implications? Clare, M.1, Talling, P.1, Hunt, J.1, and Challenor, P.2 1 National Oceanography Centre, Southampton, United Kingdom (m.clare@fugro.co.uk) 2 College of Engineering, Mathematics and Physical Sciences, Exeter University, United Kingdom

It has been proposed that sea level fluctuations are a major control on the frequency of large submarine landslides and resulting sediment density flows. These processes can transport hundreds to several thousand cubic kilometres of sediment across remarkable distances, and play a significant role in global sediment transport. Large volume turbidites in distal deep-sea basins can therefore provide a record of landslide and flow frequency. Here we analyse the frequency of landslide-triggered turbidites from two recent systems and one outcrop study. The recurrence times of turbidity currents is inferred from intervals of hemipelagic mud that form by fallout of background sediment between turbidity currents, and the average accumulation rate of hemipelagic mud between dated horizons. There is very little erosion below turbidite beds in the study locations; hence they represent an almost continuous sedimentary record. This method has the advantage of providing information on the timing of many different slides from a small number of cores, with such large numbers (> 100) of beds needed for robust statistical analysis. This study determines whether a common frequency distribution is seen for recurrence intervals in different locations, and the nature of any such distribution. It assesses whether recurrence intervals are influenced by sea level through robust statistical tests. A Poisson process is identified for recurrence intervals of turbidites in the Balearic Abyssal Plain (N=151 over last 150 ka) and Madeira Abyssal Plain (N=186 over last 7 Ma) based on analysis of core samples. Fitting an exponential regression to recurrence intervals for each catalogue shows good agreement. This suggests that events occur independent of time, and that the system does not retain any memory. The probability of an event occurring does not depend on the time since the last event. The regression analysis demonstrates that the influence of sea level on event timing is not statistically significant, even at the 90% level. Hurst exponent values of between 0.5 and 0.6 indicate a lack of temporal clustering (i.e. near-randomness). An exponential distribution is also indicated through fitting the catalogues to a Generalised Linear Model using a Gamma curve (dispersion parameter, α ≈ 1.2). This combination of outcomes provides good support for the conclusion of near-random input of sediment by submarine slides. This is hypothesised to be a more general relationship that may hold for other distal basin plain settings. A proportional hazards model is applied to test the effect of sea level and its derivative against recurrence rate, independent of any assumptions about its frequency distribution. Surprisingly, this does not show statistical significance either. This suggests that sea level variations are not a major or preconditioning factor for large submarine landslides and subsequent delivery of sediment to distal deep sea basins. Finally, some initial findings of an outcrop study from the Zumaia Flysch in Northern Spain are presented. This provides some insight into long term (>10 Ma) influence of sea level and climatic oscillations on frequency of turbidite recurrence. The results presented here have significant implications for geohazard assessment, and on whether the application of sequence stratigraphic models is appropriate for distal, deep water settings. The apparent lack of sea level control on event frequency that is identified here indicates that the latter should be approached cautiously.

T3S5_O13 Conglomerates from Upper Jurassic gravity flow deposits of Western Chukotka, NE Russia Vatrushkina E.V., Tuchkova M.I. Geological Institute of the Russian Academy of Sciences, Pyzhevsky lane 7, 119017 Moscow, Russian Federation (evat_095@mail.ru, tuchkova@ginras.ru) Studied region is situated in Western Chukotka of Northeastern Russia. We examined the SW part of Arctic Alaska; Chukotka microplate, Chukotka terrane. The Chukotka terrane is represented mostly by Paleozoic and Mesozoic deposits of a passive continental margin. Clastic sediments of the Triassic turbidite complex were sourced from a southerly (present day coordinates) metamorphic terrain (Tuchkova, 2009). The Lower Jurassic sedimentary rocks are located only on a narrow area, on the left bank of the Rauchua River. Middle Jurassic deposits are absent (Gorodinskiy, 1963). The Upper Jurassic - Lower Cretaceous clastic sediments were deposited in several depressions. Sedimentary rocks sequences are intruded by post-collision plutons dated by U-Pb (SHRIMP-RG) - 115-117 Ma (Katkov, 2010). The Jurassic - Cretaceous deposits were formed in a different geodynamic and palaeogeographic environment in comparison to the Triassic rocks. During this time syn-orogenic sedimentation occurred with the Early Cretaceous collision of the Arctic Alaska - Chukotka microplate with the North Asian craton. According to our previous research, these sedimentary sequences are mostly clastic basinal gravity flow deposits derived from mixed sources that include basinal clastic rocks, coarse crystalline rocks and volcanic rocks. The main object of this work is to refine provenance data by examining the geochemical composition of the conglomerates. Detailed description of Upper Jurassic sequences with conglomerates in Myrgovaam, Rauchua and Upper Pegtymel depressions has been conducted. The Upper Jurassic sediments of the Myrgovaam basin are represented by Oxfordian-Kimmeridgian Rauchua suite. The Rayuchua deposits are composed of massive sandstones with interbedded mudstones and unconformably overlie Triassic turbidities. The Rauchua sandstones contain two types of mudstones fragments. First are small angular intraclasts, second are larger isometric fragments. To identify the origin of mudstones fragments, they were analyzed by ICP-MS and were compared with the Triassic and Upper Jurassic clastic rocks. Geochemical characteristics of the small angular intraclasts are very similar to the Triassic mudstone, and the large isometric fragments are identical to the host sandstones. These similarities elucidate on the hydrodynamic process during sedimentation and the presence of the Triassic mudstone in source area. In the Rauchua depression the Tithonian deposits are represented by interbedded sandstones, siltstones and mudstones with conglomeratic lenses, inferred to be submarine channel deposits. The conglomerate pebbles are dominated by mudstone and siltstone, along with subordinate fragments of quartz vein and volcanic rocks. To identify the composition of the volcanic rocks in the source area, volcanic pebbles were analyzed by ICP-MS. On the discriminant diagrams by Wood andesite occupy the field of island arc volcanics (calc-alkaline varieties). These data suggest presence of island arc formations in the source area. The Tithonian sediments of the Upper Pegtymel basin are represented by tilloid formation. The tilloid clasts comprise angular to rounded clastic and volcanic rocks fragments. The geochemical composition of clastic and volcanic pebbles indicate the presence of Triassic mudstone and island arc volcanics in source area. Acknowledgments This work was funded by the RFBR project № 11-05-00787a, № 12-05-31432 and scientific school № SS-5177.2012.5

T3S5_O14 Provenance studies of Late Jurassic-Early Cretaceous gravity flows in the Danish Central Graben, North Sea Nielsen, M.T.1, Weibel, R.2 and Friis, H.1

1 Department of Geoscience, Aarhus University, Høegh-Guldbergs Gade 2, 8000 Aarhus, Denmark (*margrethe.thorup@geo.au.dk) 2 Geological Survey of Denmark and Greenland (GEUS), Øster Voldgade 10, 1350 Copenhagen K, Denmark Upper Jurassic-Early Cretaceous gravity flow sands occur intercalated with the mud dominated basin infill of the Tail End Graben, Danish North Sea, which formed as part of the of the Mesozoic North Sea rift zone. The gravity flow sandstones were deposited within the Farsund Formation (equivalent to the Kimmeridge Clay Formation), which is the main source rock in the area. Today the sandstones attract attention as they form possible oil/gas reservoirs. It has previously been suggested that the gravity flow sandstones were deposited by a shared basin-axial transport system coming from the North. Other options are that they were derived from local sources on the sitting wall to the West or they could have formed from slides on the hanging wall of the Coffee Soil Fault towards the East. Petrography of thin sections and statistical analysis of total bulk-rock geochemistry of samples from cored intervals of 8 wells within and near the Tail End Graben form the basis of the study. The provenance of the sandstones is inferred from framework grain composition, grouping of geochemical data by multivariate analysis of geochemical data and plots of immobile elements such as Zr, Ti and Nb. Correlation of the geochemical data with previously collected data of cored Upper Jurassic sandstones from the broader Upper Jurassic Danish Central Graben was carried out in order to understand if the gravity flow sands share provenance with older sandstones in the area. The samples generally show good intra well correlation, both petrographically and geochemically, and the sandstones of each well tend to correlate with sandstones of other wells in the same geographical area. Based on the petrography the sandstones, they were divided into four groups dominated by 1) monocrystalline quartz grains, 2) metamorphic rock fragments, 3) biogenic carbonate and chert particles, 4) mixed composition. The multivariate analysis of the bulk-rock geochemical data supports this division. This division of the framework grains into distinct groups and the fact that the samples correlate geographically indicate that the gravity flow sandstones were derived from local sources and not one basin-axial flow. Compared to the earlier deposited Upper Jurassic sandstones, i.e. the Heno Formation from the Danish Central Graben, the gravity flow sandstones differ in that they are generally less mature than the earlier deposited sandstones and are characterized by being richer in carbonate, apatite and albite. The low maturity of the sandstones, the higher carbonate and apatite contents may be ascribed to the fact that the deposition took place instantaneously and in a deep marine environment. The higher albite content and corresponding higher plagioclase/K-feldspar content may indicate activation of a different sediment source than the sediment source(s) responsible for most of the previously deposited Jurassic sandstones. Via provenance indicators the gravity flow sandstones of the Late Jurassic-Early Cretaceous Central Graben were allocated to four markedly different groups that are geographically consistent. The gravity flow systems are thus interpreted to have been derived from various local sources andnot merely the basin axial transport system. Acknowledgements Some of the data and interpretations presented are part of an ongoing industry-sponsored project at GEUS focusing on the Jurassic petroleum system in the Danish Central Graben. The abstract is published with the acceptance of the Geological Survey of Denmark and Greenland.

T3S5_O15

Types and origin of the sediment waves on the northeastern slope, South China Sea

Zhong, Guangfa.1, Wang, Liaoliang.2, Cartigny, Matthieu J. B.3, Kuang, Zenggui.2, Guo, Yiqun.2 1 State Key Laboratory of Marine Geology, Tongji University, 200092-Shanghai, China (gfz@tongji.edu.cn) 2 Guangzhou Marine Geological Survey, 510760-Guangzhou, China 3 Southampton Oceanography Centre, SO14 3ZH-Southampton, UK

High-resolution multibeam bathymetric data, coupled with multichannel seismic profiles, were utilized to

investigate the types and origin of the sediment waves in the northeastern slope of the South China Sea,

between the Dongsha Islands to the west and the Taiwan Island to the east. In the region, numerous

downslope-trending canyons and inter-canyon ridges are developed. The canyons disappear on the slope or

coalesce downslope, and finally merge into the famous N-S-extending Penghu Canyon. The latter is the

northward extending of the Manila Trench. These canyons act as important transportation conduits for clastic

sediments.

In the study area, numerous large-scale sediment waves and related bedforms are developed. These sediment

waves or bedforms may occur on the canyon floors and canyon walls, appear on the canyon levees or outside

of the canyon mouths. They may also cover the inter-canyon ridges. The sediment waves are generally

kilometers in wavelength, and tens of meters in wave height. Most of the sediment waves are aligned along

the slope. They are usually asymmetric in cross-sections with a gentler slopes and thicker beds on the

upslope side and a steeper sloping downslope side covered with thinner beds, and therefore migrate upslope.

Some waves, however, on the inter-canyon ridges or the canyon walls may display no systemic variations in

symmetry. In addition, it is noted that the undulations on the canyon floors are usually distributed in trains,

consisting of alternate scours and steps, which are very similar to the step-pools on mountain streams.

By analyzing the geometry and internal structures of the sediment waves, we successfully differentiated

different origin types of the sediment waves associated with confined and unconfined turbidity currents, as

well as gravitational deformation processes, respectively. Most of the sediment waves on the inter-canyon

ridges and steep canyon walls are suggested resulting from gravitational deformation processes like slumping

and creeping. The sediment waves on the canyon levees or outside of the canyon months are presumably

generated by overspilled or unconfined turbidity currents. The undulated scours and steps on the canyon

floors are interpreted as cyclic steps, which are bedforms associated with supercritical turbidity currents.

Acknowledgments

This research was funded by China National Natural Science Foundation (Grant Nos. 91028003 and

41076020).

T3S5_O17 Lateral variability in hybrid event beds at short length scales: outcrop case studies and applied significance Fonnesu, M.1, Haughton, P.D.W.1, McCaffrey, W.D.2, Davis, C. 3 and Felletti, F.4 1 UCD School of Geological Sciences, University College of Dublin, Belfield, Dublin 4, Ireland (marcofonnesu86@gmail.com) 2 School of Earth Sciences, University of Leeds, Leeds LS2 9JT, UK 3 Shell UI-Europe, 1 Altens Farm Road, Nigg, Aberdeen, AB12 3FY, UK 4 Dipartimento di Scienze della Terra, Università degli Studi di Milano, Via Mangiagalli 34, 20034 Milano, Italy Hybrid event beds (HEBs) are a type of deep-water sediment gravity flow deposit characterised by a basal clean sandstone (a turbidite) overlain by a variety of muddier and less permeable sandy facies (including debrites) emplaced as part of the same transport event. They are thought to form from flows that were at least partly turbulent, but that also had zones of damped turbulence beneath which clay and sand were emplaced together as linked debris flows. To date, a number of studies have highlighted the common presence of HEBs in the outer and marginal parts of deep-water systems where they replace beds composed dominantly of clean sand up-dip and/or axially over scales of kms to 10s km. In addition to these broad patterns, important yet poorly understood short-length facies changes (over metres to 100s m) can occur that modify the overall texture and reservoir characteristics at or beneath typical spacing of production wells. Short-length scale transitions from turbidites to HEBs and between different types of HEB may be particularly common where flows are forced to decelerate against confining basin floor topography but the outcrop studies reported here suggest that this local variability can also be present even in relatively flat basin floor settings. The nature and origin of the short-length scale transitions has been addressed in four well-exposed HEB-prone outcrops: the Miocene Cilento Flysch and Cretaceous-Paleocene Gottero Sandstone, both in Italy, the Carboniferous Mam Tor Sandstone in northern England, and the basal Ross Sandstone Formation, western Ireland, also Carboniferous in age. These outcrops are used to inform a revised model for the sandstone geometry for the critical transition from up-dip turbidite to fringing hybrid event bed incorporating small-scale lateral variability. A series of detailed correlation panels (up to 1.7 km long) show marked lateral variations in internal bed make-up for most of the hybrid event beds studied. This variability typically involves lateral changes in the proportions of the cleaner basal sandstone and the overlying muddy sandstone division, or in the amount and texture of muddy component of the debritic division and the scale of substrate blocks it contains. Generally, these changes occur without substantial change in the overall event bed thickness. The variability is inferred to reflect the complex fingering between the up-dip sandstone-dominated part of the event bed and the down-dip linked debrite. Ultimately this may relate to the pattern and mechanism of up-dip erosion and entrainment of mud clasts into the flow. Local patterns of stream-wise erosion (expressed as elongate scour fields) may result in linear trains of mud clasts and near-bed clay that induce variable turbulence damping across the width of the flow. Once formed, the linked debris flows can also locally remove some or all of the just-deposited basal sand, especially where large entrained rafts of substrate plough into it. The variable thickness and continuity of the basal clean sandstone and the rugosity on the contact with the overlying debrite have important implications for reservoir characterisation. Significant variability in bed character at interwell scale can be anticipated and the intra-bed rugosity may impact on drainage and sweep efficiency during hydrocarbon production, particularly in cases where the lower sandstone is locally completely removed.

T3S5_O18 Facies Analysis and Interpretation of Avulsion Splay Successions in the Paleogene Wilcox Formation, Deep Water Gulf of Mexico Bruce Power1, Julian Clark1, Jacob Covault2, Andrea Fildani1, Morgan Sullivan2, Brooke Carson3, Larry Zarra3 and Brian Romans4 1Chevron Energy Technology Company, 6001 Bollinger Canyon Rd., San Ramon, CA 94583 2Chevron Energy Technology Company, 1500 Louisiana St., Houston, TX 77002 3Chevron North America Exploration and Production, 1500 Louisiana St., Houston, TX 77002 4Virginia Polytechnic Institute and State University, Department of Geosciences, 4044 Derring Hall, Blacksburg, VA 24061 The Wilcox Formation (Paleocene-Eocene) in the deepwater Gulf of Mexico comprises a thick (2000-6000 feet; 600-1800 m), sandstone-rich succession of deep water sedimentary rocks interpreted to have been deposited in channelized and unconfined lobe/sheet systems in slope and basin floor environments. Over the last decade, the Wilcox Formation has emerged as a major hydrocarbon reservoir, and is the focus of significant exploration and development activity within the petroleum industry. Argillaceous sandstone beds are a common occurrence in sediments of the deep water Wilcox Formation. They are interpreted to be deposited by gravity driven flows that are transitional between laminar and turbulent flow, and are classified as hybrid event beds. In the Wilcox Formation, these hybrid event beds are interpreted to occur in two distinct facies associations. They are most commonly interpreted to have been deposited in medial to distal unconfined lobe/sheet environment, an interpretation that is consistent with their observed presence in many other deep water systems. The argillaceous character of hybrid event beds is interpreted to reflect longitudinal flow evolution of the turbidity current event, in which the silt/clay to sand ratio is interpreted to increase with increasing runout length. This change in grain size ratio of suspended sediment dampens turbulence, causing rapid deposition of both sand and argillaceous grains together. The resulting deposits contain significantly greater amounts of argillaceous silt and clay than would be found in a sand bed deposited as a turbidite. The Wilcox Formation also contains intervals with abundant hybrid event beds that are interstratified with strata interpreted as to have been deposited in channel and overbank environments. Interpretation of these hybrid event–dominated intervals as distal lobe/sheet sediments is challenging, as it requires repeated large magnitude shifts of depositional environment from proximal to distal. Equally challenging would be interpreting these intervals as channel margin deposits. Channelized environments are interpreted to be dominated by deposits that reflect higher energy turbidity current processes and through-going flow to more distal environments. These argillaceous intervals with abundant hybrid event beds are interpreted to represent the initial deposits of channel avulsion. The mixture of hybrid event beds, debrites, and turbidite sands and shales is interpreted to be deposited by the initial flows of a channel that has broken through its confining levee, and is forming an avulsion splay in what was previously an unconfined environment. A distinctive aspect of the interpreted avulsion splay intervals is that they commonly underlie confined channel or levee/overbank intervals, and are interpreted to have a genetic relationship to these overlying channelized strata. Similar deposits of argillaceous sandstones in the Neoproteropzoic Isaac Formation of the Windermere Supergroup (east-central British Columbia, Canada) have also been interpreted as hybrid event beds in avulsion-related crevasse splay deposits.

T3S5_O19 Pyroclastic turbidites of the Ukrainian Carpathians (Jurassic/Cretaceous; Kaminnyi Potik Unit) Krobicki, M.1,2, Feldman-Olszewska, A.3, Iwanczuk, J.3, Hnylko, O.4 1 Polish Geological Institute – National Research Institute, Krolowej Jadwigi 1, 41-200 Sosnowiec, Poland, michal.krobicki@pgi.gov.pl 2 AGH University of Science and Technology, Mickiewicza 30, 30-059 Krakow, Poland, krobicki@geol.agh.edu.pl 3 Polish Geological Institute – National Research Institute, Rakowiecka 4, 00-975 Warszawa, Poland, anna.feldman-olszewska@pgi.gov.pl, jolanta.iwanczuk@pgi.gov.pl 4 Institute of Geology and Geochemistry of Combustible Minerals of NAS of Ukraine, Naukova 3a, 79060 Lviv, Ukraine, ohnilko@yahoo.com The Outer Flysch Carpathians is one of the biggest belts of stacked flysch nappes in Europe which occupies a large part of central-European countries and is almost exclusively constructed by siliciclastic flysch-type rocks. The other types are represented by rare occurrence of calcareous flysch (e.g. Jurassic/Cretaceous so-called Cieszyn Formation in Czech Republic and Poland or its facial and stratigraphic equivalent – Sinaia Beds in Romania) full of allodapic carbonate intercalations with shallow-water resedimented elements as ooids, fragments of thick-shelled benthic fossils, green-algae etc. Pyroclastic turbidites are extremely sporadic and are concentrated within the Transcarpathian Ukrainian part of the Flysch Carpathians and occur in the Ukrainian-Romanian trans-border zone (Kaminnyi Potik Unit – in Ukrainian nomenclature, Black Flysch in Romanian – which is composed by dark, thin-bedded limestones, black shales, sandstones, and conglomerates of the Tithonian-Valanginian age, and containing the Jurassic/Cretaceous basic extrusive volcanics, including basaltic pillow lavas). They occur in the vicinity of Rachiv city and in SE prolongation of this unit to the Chyvchynian Mountains. Such unique flysch-type rocks are usually developed as thin intercalations both of coarse- and fine-grained calcareous pyroclastic beds within thin-bedded light and dark-gray micritic limestones sometimes with lenses of dark cherts. Sedimentologicaly we can interpret the deposits as distal deep-marine lobes of turbiditic fans. On the other hand, more coarse-grained pyroclastic sandstones and fine-grained pyroclastic conglomerates could represent deposits of more proximal turbidity currents. All these types of rocks have typical flysch-character features including sharp bed bases, clasts of allochthonous materials, fractionation of grains, cross-bedding ripple lamination and increase of pelagic character of the topmost part of beds (up to micritic limestones). The most proximal beds are characterized by chaotic calcareous-pyroclastic breccia with blocks of micritic and organodetritic limestones and basalts (even as pillow lava fragments) which occur within a volcanic/tuffitic matrix and represent, most probably, submarine debris flows. Additionally, the massive basaltic pillow lavas often co-occur with these debris flows and/or underlying pyroclastic flysch sequences. In our reconstruction, the Flysch Carpathians basin shows a continuous transition from proximal flysch-type facies on the one side, to flows of massive basaltic pillow lavas on the other side. Pyroclastic flysch is not common among global turbiditic systems of any age. Intercalations of thin tuffitic layers are common in several flysch deposits, however huge amounts of pyroclastic material are necessary to source pyroclastic turbidities seen in the Flysch Carpathians suggesting a location proximal to a strongly active volcanic source area. In addition, geochemical characteristics of the basin fill may coincide with a geotectonic regime characterized by high volume production of pyroclastic material. In our case the Jurassic-Cretaceous volcanic activity in this part of the Carpathian basins could be key to understanding the geodynamic history of the northernmost part of Neotethys.

T3S5_O20 Research on Depositional Architecture and Reservoir Quality Difference of Turbidity Channel in Submarine Fan: A Case of One Deepwater Research Area, West Africa

Yu Lin1,2, Shenghe Wu1,Yun Ling2 , Jiajia Zhang1, 1 State Key Laboratory of Petroleum Resource and Prospecting, China University of Petroleum, Beijing,

China 2 Research Centre of Reservoir Geophysics, BGP Inc. of CNPC, Hebei, China Turbidite channels within submarine fans are one of the hot fields of petroleum exploration and development

around the world. Research on depositional architecture and differences in reservoir quality is important to

improve development efficiency of turbidite channel reservoirs. This study aims to build semi-quantitative to

quantitative architecture models of example turbidite channels within the Neogene deepwater deposits of

West Africa. The mechanisms contributing to differences in reservoir quality will also be analyzed. The

research utilises sedimentary petrology, seismic sedimentology and reservoir geology and is based on data

drawn from core, well logs and seismic data. This study brings deep understanding to turbidite channel

theory and will also contribute to reducing exploration and development risk on this type of reservoir.

The research findings are: There are six orders of architecture units in the channel system, including channel

complex set, channel complex, single channel, rhythm complex, single rhythm and single litho-facies. The

sinuosity of turbidite channel system is controlled by the slope gradient; there is a negative correlation,

where, as slope gradient increases, the sinuosity of the channel system is seen to decrease. Channel systems

are nearly straight when the slope gradient is up to 4 degrees.

There are various composite patterns of single channels. According to direction and rate of migration of

single channels, the composite patterns can be divided into 4 types (lateral composite, en-echelon composite,

swinging composite and vertical composite) and 13 subtypes. There are obvious differences in the composite

patterns of each evolutionary stage of a channel system and position of channel complexes.

Based on differences in lithofacies, single channels can be divided into 4 types (type A to type D). Type A is

mainly filled with muddy deposits, type B is mainly filled with sandy low-density turbidite deposits, type C

is mainly filled with sandy high-density turbidite deposits, and type D is mainly filled with both sandy

high-density turbidite deposits and debris flow deposits. A trend from type D to type C to type B to type A is

typically found from base upward within a channel system. The width-depth ratio of single channels ranges

from 12 to 20, and the width of single channels has a positive function with depth. Single channel sand

bodies are not formed through lateral accretion, but as axial deposits.

Differences in reservoir quality of channel sand bodies in a channel system have been identified. Type III

and type II channels have the best physical properties, while type IV and type I have the worst physical

property. The permeability rhythm of single channel sand body has three styles, namely positive rhythm,

compound reverse-positive rhythm and homogeneous rhythm. The influence of channel type at each

evolutionary stage of a channel system, and the differences in physical properties of various channels,

suggest a general vertical trend in physical reservoir properties of a channel system to be high in the middle

and low at the base and top.

T3S5_P40 The impact of fault topography on turbidity currents descending from the slope to the floor of an early-stage deep-water rift basin: insights from CFD numerical simulations Ge, Z.1, Nemec, W.1, Gawthorpe, R.L.1, Rotevatn, A.1, Basani, R.2 & Hansen, E.W.M.2 1 Department of Earth Science, University of Bergen, 5007 Bergen, Norway (zhiyuan.ge@geo.uib.no) 2 Complex Flow Design A.S., 7462 Trondheim, Norway This investigation focuses on the early-stage turbiditic sedimentation in an evolving deep-water rift basin, where the paths of turbidity currents from the slope to the basin floor commonly run across growth-fault escarpments. The impact of fault topography on the turbidity current behaviour and sediment dispersal has been studied by using computational fluid dynamics (CFD) numerical code Mass-Flow 3D™. The simulation software was pre-verified by faithfully mimicking both laboratory and natural flows, and thus proved to give realistic results. The CFD software has two great advantages. First, it permits flow experiments at a natural basin scale. Second, it allows a full-time 3D monitoring of the flow in terms of its spatial distribution and all main local hydraulic characteristics, such as the principal x-y-z velocity components, velocity magnitude (geometric mean velocity), sediment concentration, bottom shear stress, turbulent shear-strain rate (turbulence intensity), dynamic viscosity and amount (thickness) of sediment deposition. No laboratory analogue experiments can possibly offer comparable details of the hydraulic and depositional behaviour of turbidity currents. For comparative purposes, one and the same sand-laden unconfined turbidity current has been used in all simulations. The first series of experiments had the turbidity current descend from an non-faulted slope of 3°, 6° and 9° onto a flat horizontal basin floor. The aim of these models was to form a reference dataset showing the behaviour of flow along its path from a variously inclined fault-free slope to the basin floor, including the effect of hydraulic jump at the slope base. In the second series of experiments, a normal synthetic fault with stepwise increased displacement was inserted at the basin floor, to represent the topographic impact of rift’s earliest faults on the flow and turbiditic sediment dispersal. In the third series of experiments, a similar normal fault with increasing relief was inserted across the flow descend path at ~2/3 of the down-slope distance, to see the influence of a slope fault escarpment on the flow behaviour. A second fault was then inserted at ~1/3 of the down-slope distance for the fourth series of simulations to study the influence of younger extensional faults in a back-stepping system. The poster displays some of the most instructive snapshots of the turbidity current behaviour in response to the four different topographic scenarios. Because of the visualization limits, the snapshots include a 2D horizontal (x-y) display, a 2D vertical (x-z) display and a 1D station-point time-series display of the flow parameters. The results show how the geomorphic slope conditions act as a ‘filter’ modulating the hydraulic properties of a descending flow, thereby determining also its further behaviour upon arrival on the basin floor. The different topographic settings considered in this study represent a typical range of fault-related geomorphic changes in an early-stage deep-water rift. Therefore, the simulation results can be regarded as tentative generic models for understanding the impact of rift-margin topography on turbidity current behaviour and sediment dispersal pattern in an evolving rift basin.

T3S5_P41

Multiple scales of waxing-waning energy cycles controls on channel architectures: San Fernando slope

channel system, Rosario Formation, Baja California, Mexico

Li P. and Kneller B.C

Department of Geology and Petroleum geology, School of Geosciences, University of Aberdeen, Aberdeen

AB24 3UE, United Kingdom (panli@abdn.ac.uk)

The upper Cretaceous San Fernando system, located on the pacific margin of Baja California Mexico, is a

well-exposed slope channel system. It permits the detailed documentation of various scales of channel

architectures and channel fills. Regional mapping, high-resolution photomosaic, detailed sedimentary

logging, photo logging, and facies transition probability analysis show that there are at least three scales of

waxing-waning energy cycles recorded by three scales of stratal packages: channel system, channel complex

set and channel element.

At the scale of channel system (3rd order sequence), the waxing phase is responsible for the regionally

distributed surface at the bottom which eroded over 250 m into the underlying slope mudstone. The waning

phase is responsible for the overall fining-upward (from conglomerates to sandstones/mudstones) and

thinning-upward channel and overbank deposits, which are capped by a thick (about 10 m) condensed

section at the top.

At the scale of channel complex set (4th order sequence), each waxing-waning energy cycle commonly

generates three stages’ deposits of a channel complex set. Stage 1 is dominated by erosional/amalgamational

channel complexes filled mainly by conglomerates; Stage 2 consists of aggradational and lateral channels

complexes dominated by sandstones and mudstone assemblage with localized conglomerates; Stage 3

comprises the abandonment of the channel complex set. This stage is composed primarily of mudstones and

can be absent due to subsequent erosion.

At the scale of channel element (high-frequency sequence), waxing-waning energy cycles give rise to

different channel architectures depending on the types of channel elements in question. Take lateral accretion

channel element as an example: the waxing part of the energy cycle generated the minor erosion surface at

the outer bank and at the base while the waning part produced the lateral accretion package and very thin

vertical aggradational package at the top.

It is assumed that the aforementioned multiple waxing-waning energy cycles are driven by some kinds of

external factors, such as sea-level, tectonic and climatic changes. But more dating and mapping work need to

be done to ascertain the specific driving forces in the future.

Acknowledgements: The authors are grateful to the sponsors for the PRACSS project. The first author also

appreciates China Scholarship Council for supporting his PhD study in the UK.

T3S5_P42 Facies and internal stratigraphic variability in the Ross Sandstone Formation (Pennsylvanian), western Ireland - new borehole data from south of the Shannon Estuary Obradors-Latre, A., Pierce, C.S., Haughton, P.D.W., & Shannon, P.M. UCD School of Geological Sciences, University College Dublin, Dublin 4, Ireland. (arnau.obradors-latre@ucdconnect.ie) The 500 m thick Ross Sandstone Formation is well exposed in sea cliffs facing the Atlantic and along the Shannon Estuary in western Ireland. It forms the sandy deep-water part of a major shallowing-upward Pennsylvanian succession. Over the last four years, a major behind-outcrop drilling program targeting the Ross Sandstone Formation has been undertaken, focussing primarily on the Loop Head peninsula in west Clare. This has provided a full composite Ross cored section that underpins a new understanding of bed-scale variability and the wider evolution of the system. The focus has recently shifted to the key Ballybunion section on the south side of the River Shannon, obliquely down-dip from the Loop Head area (c. 18 km from the tip of the Loop) and is important in that previous outcrop studies have inferred that (1) the distinctive character of the lower Ross here with its abundant hybrid event beds may reflect a marginal position; and (2) extra sandy section may be present in the uppermost Ross due to offset stacking of the youngest sandy lobes. Two new cores are now available ‘behind’ the Ballybunion section - a 200 m PQ borehole straddling the lower Ross and the upper part of the underlying Clare Shale Formation (12-CE-UCD-09), and a 151.5 m long, cored slimhole with associated wireline log data acquired by the Geological Survey of Ireland (GSI 09/05). The latter is 1.1 km along strike from coastal exposures of the upper Ross and the study reported here focusses on the relationship of the section acquired in this borehole to the local cliffs and to upper Ross outcrops on the north side of the River Shannon at Kilcredaun, some 4.6 km away. Correlation is based on goniatite-rich ‘marine bands’, legacy biostratigraphic data (new determinations are underway), and a number of laterally extensive slump bodies which form distinctive marker beds. The GSI 09/05 core contains three thin goniatite-rich levels, and a fourth candidate level, each interpreted as marine bands. These separate sand-prone packages, interpreted as stacked isolated to amalgamated lobe units, and at least two mass-transport units (MTDs), the lower and thickest of which is 25.5 m thick (true thickness). In the local cliffs to the west, all four marine bands can be identified, as well as the two MTDs. In addition, a third MTD is more obvious in the cliff. The lobe sandstones are dominated by deposits of high-density turbidity currents; amalgamated sandbodies become more abundant upwards. Hybrid event beds are rare (<10%) compared to lower in the formation. At least 50% of the sandbodies extend from the core to the adjacent outcrop without change; the remainder show a change from deposition from high- to low-concentration flows or vice versa. Overall, the Ballybunion Ross section is 480 m thick, broadly similar to the thickness established by drilling on the Loop. At longer length scales, all but the upper marine band are found at Kilcredaun. Correlatives of the two MTD units also occur in the core here, although the thickest slump has become thinner and muddier. Nonetheless this MTD unit can be traced widely across the Loop as a distinctive couplet. As correlated, the Ballybunion outcrop and core suggest there may not be an additional younger sand body in this area, however the location appears axial and down-dip rather than marginal in character overall.

T3S5_P43 Density-driven gravity flow deposits characterised by supercritical sedimentary structures – the Favignana Calcarenite (Sicily, Italy) Slootman, A.1, De Boer, P.L.2, Moscariello, A.1 1 Earth and Environmental Sciences, University of Geneva, Rue des Maraichers 13, CH-1205, Geneva, Switzerland (Arnoud.Slootman@unige.ch) 2 Department of Earth Sciences, Faculty of Geosciences, Utrecht University, The Netherlands The eastern side of Favignana Island (19 km2), western Sicily, consists of Pleistocene calcarenites with a maximum observed thickness of 50 metres. These are characterised by a wide range of prograding sediment bodies comprising mainly (very) coarse, (in places) very porous grainstones. Some preliminary results of lithofacies analyses are presented here. Microfacies – Biological assemblages are composed of fragmented red algae, bryozoans, echinoids and (mainly benthic) foraminifera with, in places, rhodoliths and/or well-preserved mollusc shells. Microfacies are of heterozoan origin indicating relatively cool-water conditions. Lithofacies – The deposits (maximum observed thickness ca. 50 m) consist of prograding clinoforms, showing ‘massive’ beds alternating with intensely bioturbated cross-stratified beds. Massive beds may reach up to >10 m in thickness. In the proximal parts, they dip 5-10 degrees towards the south and can be traced in the field for hundreds of metres, until they finally pinch out. Massive beds are in fact not structureless, but display internal stratification varying from crude to spaced to more pronounced. Geometries within massive beds consist of backsets, foresets, wavy geometries or planar stratification, and locally display scours (1-10 metres) with gravelly infills at the base. At the distal end, were facies consist of upper plane bedding, non-bioturbated dunes (height 20-30 cm) were observed at the base. Massive beds were interpreted to be deposited from short-lived supercritical flows with Froude numbers generally decreasing from proximal to distal. Hence, sedimentary structures were formed by bedforms such as cyclic steps, chutes-and-pools, and antidunes. The top of massive beds is generally not flat, but contains depressions. During the recovery phase, i.e. the longer periods following the supercritical flows, such depressions were filled with (compound) cross-stratified beds, which are generally intensely bioturbated. In the proximal parts, cross-strata indicate a southward palaeoflow in the direction of the dips of massive beds, whereas on the more horizontal toesets, cross-strata dip is more variable. The combined observations reflect bi-modal deposition characterised by either low-energy currents or supercritical currents, probably on a cool-water carbonate ramp. The inferred critical currents, that deposited the massive beds, were interpreted to be density-driven gravity flows which emptied the carbonate factory during rare high-energy events. Between such events, there was sufficient time for the factory to recover and (compound) dunes dominated the facies during the ‘recovery’ phases. Although the Favignana Calcarenite may not be a deep-marine deposit and does not consist of classic turbidites, it may certainly serve as a case to study supercritical gravity flow processes and their deposits.

T3S5_P44 Deepwater Reservoir Architecture influenced by Large-Scale Remobilisation: an example from the Britannia Field, North Sea. Teloni, R.1, McCaffrey, W.D.1, Haughton, P.2, Patacci, M.1, Eggenhuisen, J.T.3, Butler, R.W.H.4. 1 Turbidites Research Group, School of Earth and Environment, University of Leeds, Leeds, LS9 2JT, UK (riccardo.teloni@gmail.com) 2 UCD School of Geological Science, University College Dublin, Belfield, Dublin 4, Ireland 3 Faculty of Geosciences, Utrecht University, 3508 TA, Utrecht, The Netherlands 4 Geology and Petroleum Geology, School of Geosciences, University of Aberdeen, Aberdeen AB24 3UE, UK The influence of mass-transport emplacement upon subsequent turbidite sedimentation is an important cause of deep-water reservoir heterogeneity at multiple scales. Because both the geometry and connectivity of producing sandstones may be affected, the characterization, quantification, or prediction of such heterogeneities is important for the optimization of oil and gas production. Thus the immediate aim of this work is to study in detail the interaction between MTDs and sand infill. A secondary aim is to characterise the architectural heterogeneity at the system scale induced by episodic lateral slope failure. The Aptian deep-water Britannia Sandstone Formation, Outer Witch Ground Graben, UK North Sea hosts the extensively cored Britannia gas-condensate field. In contrast to the upper reservoir zone, characterised by a series of predominantly in situ thick tabular sandstones beds, the lower and middle zones were prone to remobilisation and thus comprise a series of intercalated turbidite sands and debrites. Gross turbidite isopach variations reflecting compensation of younger deposits into the relict topography left by the mass failure. Isopach maps together with core, gamma-ray data and cuttings based data from uncored wells show that the topography of the sea floor was excavated by large-scale failures that transected and modified pre-failure sand-bodies via incision and substrate deformation. Well mixed debrites, probably initially sourced from the flanking topographic high of the Fladen Ground Spur, partially heal the accommodation space left by large-scale remobilisations. Younger turbidite sandstones, which filled the balance of the accommodation space, are characterised by the deposits of turbulent flows (producing massive facies) and transitionally turbulent flow (banded, pseudobanded, wispy laminated and mixed slurried sandstones), whose variations highlight the change in the nature of the flows influenced by sediment routing patterns through complex bathymetry. This study, in conjunction with earlier work on the same system, shows that the Britannia stratigraphy is influenced by a series of failure-infill cycles, particularly evident in the lower and the middle reservoir section. The infill deposits can form good reservoir, but have spatially restricted distributions, whereas tabular, post-healing deposits form a framework of through-going sandstone beds. Key facies can now be recognized to indicate processes of slope failure, associated debrite emplacement, turbidite sand infill and restoration of locally smooth sediment distribution pathways; this interpretative framework permits characterization of the larger scale architectural variability. Acknowledgements This research has been funded by the Turbidite Research Group at the University of Leeds. We would like to thank Britannia Operators Limited (BOL) for access to the data and permission to publish this work.

T3S5_P45

A high-resolution seismic study of the frontally confined landslide in Shenhu slope，Northern South

China Sea

Wu, J. P.1,2, Wang, Y. M.1,2 1 State Key Laboratory of Petroleum Resources and Prospecting (China University of Petroleum, Beijing),

Beijing 102249, China. (wjp_better@sina.com) 2 College of Geosciences, China University of Petroleum(Beijing), Beijing 102249, China.

Submarine slides constitute important aspects of deep-water sedimentary systems. Study of submarine slides

does much help with unveiling the deposition process occurring in deep-water settings. Using high resolution

multichannel seismic profiles, a frontally confined submarine slide is firstly discovered on the Shenhu slope

of the Northern South China Sea, which is distributed over an area of 1000 km2.

The submarine slide undergoes a restricted downslope translation and does not overrun the undeformed

downslope strata, so the seismic facies features are significantly different from the two sides of the ramp.

Internally the slide has chaotic reflectors, externally it is wedge shaped with impressive fold and thrust

structures developed in the toe domain. In comparison to unconfined submarine slides, the continuity of the

Shenhu slope frontally confined slide suggests a shorter downslope transport distance.

Combined with the seismic reflection features of the slide and comparison of the Shenhu submarine slide

with other globally distributed submarine slides, this type of submarine slide is identified through thickness

of the slide and slope angle, but the positive relief of the Yitong shoal has no effect on the Shenhu submarine

slide’s evolution.

Acknowledgements

This work was supported by the National Basic Research Program of China (NO. 2009CB219407) and the

National Natural Science Foundation of China (NO. 40972077).

T3S5_P46 Segmentation and evolution of depositional architectures in the Central Canyon of the northwestern continental margins of South China Sea Xinong Xie 1, Yongchao Lu 1, Ming Su 2, Zhenfeng Wang 3, Xushen Li 3 1 Key Laboratory of Tectonics and Petroleum Resources of Ministry of Education, China University of Geosciences, Wuhan 430074, China (xnxie@cug.edu.cn) 2 Key Laboratory of Renewable Energy and Gas Hydrate, Chinese Academy of Sciences, Guangzhou 510640, China 3 China National Offshore Oil Zhanjiang Ltd., Corporation, Zhanjiang 524057, China The Central Canyon System, a large axial deepwater canyon, in the Qiongdongnan Basin was developed on the Neogene passive continental margin of the northern South China Sea. The canyon shows a WE-trending ‘S’ shaped geometry with a length of more than 570 km and a width of about 6-48 km. Two turning zones of the canyon system are in agreement with structural transfer. The western turning zone is located in a transitional area between the NW-striking Yinggehai and the NE-extending Qiongdongnan basins. The eastern turning zone is located in the Baodao depression which separates the NE and NEE striking parts of the canyon. The canyon system can be divided into three segments, from west to east these are: canyon head, western and eastern segments, respectively. Each segment has not only different morphology in section, but also has distinct depositional architectures, genetic facies and sediment-supply. In the eastern segment, the canyon has a width of 10 km and passes through the central Changchang depression, which has a ‘V’ shape showing strong downcutting. The formation of the canyon is controlled by underlying faults, which result in the occurrence of a steep southern wall to the canyon. The western segment is located in the Baodao, Songnan and Lingshui depressions, the canyon shows multiple episodic scour and infill. Its width ranges from 16 km to 48 km, in which a narrow canyon occurs in the east part of the segment constrained by the underlying faults. But in the west part of the segment in the Lingshui depression, the canyon shows much a wider canyon profile, ranging from 20 km to 48 km, which is located in the thalweg area of the deepwater environments where underlying faults are not present. The western canyon fill is composed of interbeds of turbidite channel and mass transport deposits (MTD). In the canyon head segment located in the Ledong depression of the Qiongdongnan basin and the southeastern Yinggehai basin, the canyon shows the classical ‘U’ shaped morphology in seismic profiles with the narrowest width of less then 5 km, and is filled by a suit of turbidite channel complex. The results of this study indicate that the distribution and evolution of the Central canyon in the northwestern continental margin of South China Sea are considered to be controlled by the tectonic setting, palaeo-geomorphic characteristics and sediment supply, and each of these factors has a different influence on morphology and depositional fill within the three segments of the canyon. Acknowledgements This study is supported by the National Key Natural Science Foundation of China (No.91028009) and the key project (No. 2011ZX05025-002-02).

T3S5_P47 Upper Cretaceous Slope carbonate system in South Albania: facies, sedimentary processes and geometry of the deposits in the Ionian Basin, eastern edge of Apulia Le Goff, J.1, 2, Cerepi, A.1, Swennen, R.2, Loisy, C.1, Caron, M.3, Muska, K.4, El Desouky, H.2,5 1 EA 4592 G& E, University of Bordeaux, ENSEGID, 1 allée Fernand Daguin, 33607 Pessac cedex, FRANCE, (johan.le_goff@ensegid.fr); 2 KU Leuven, Celestijnenlaan 200 E, B 3001 Heverlee, BELGIUM (Rudy.Swennen@ees.kuleuven.be); 3 Impasse de la Butte, 7, CH-1700 Fribourg, SWITZERLAND, (michele.caron@bluewin.ch); 4 Polytechnic University of Tirana, ALBANIA, (kristaqmuska@yahoo.fr); 5 Geology Department, Menoufia University, 32512 Shebin El-Kom, Menoufia, EGYPT (Geohamdy@yahoo.com) Integrated in the NNW-SSE structural deformation trend of the Ionian fold-and-thrust belt, the Upper Cretaceous carbonate deposits of the Ionian Basin expose an excellent example of a resedimentation system. Derived from the Apulian carbonate platform, sediment inflow document a wide range of depositional processes giving its architecture to the Upper Cretaceous succession, exposing a study analogue for hydrocarbon reservoirs. Previously described in terms of facies and geometry, new data provide a better understanding of depositional settings and extensional development of the carbonate gravity deposits. Seven large-scale outcrops have been studied in detail in several front thrust of the ancient basinal system. The geological surveying of the successions is mainly field-based. Investigations include a precise decimeter-scale facies description. Palaeontologic data, based on benthic foraminifera determination, and Strontium Isotope Stratigraphy, based on 87Sr/86Sr ratio analysis converted to numerical ages using the LOWESS look-up table version 4:08/04, are employed to determine the timing of carbonate deposition during the Upper Cretaceous. By means of these analytical methods, correlations are achieved to establish relationships from proximal slope to distal slope deposits. From hyperconcentrated mud-supported flows to low density calciturbiditic flows, a range of processes are specified according to the sedimentological study, leading to the establishment of a carbonate slope depositional model. The sedimentary deposition during the Upper Cretaceous reflects a contrasted evolution. Hemipelagites and low-density calciturbiditic deposits, typically accumulating until the Santonian, are gradually replaced by coarser and thicker calciturbiditic and debris-flow deposits during the Campanian. The carbonate transport-system brutally turns into a large scale slump system, showing soft-sediment deformation structures during the Maastrichtian. Three main slump layers are identified during the late Upper Cretaceous, with a first deformation level reaching up to 50 meters in thickness in the distal part of the basin. These major levels are fully consistent with tectonic triggers affecting the Apulian Platform during this period. The studied successions allowed to analyze the foredeep evolution of the Ionian Basin during the Upper Cretaceous and thus unraveled the tectono-sedimentary processes controlling the eastern edge of Apulia.

T3S5_P48 Lithology of sediments of the Permian System of Ayan-Yurahskaya zone (North-East Asia) and their probable origin Kabirova I. V. Geological Institute of the Russian Academy of Sciences, 119017, Moscow, Russia, kabirovaira@yandex.ru In North-East Asia is the Mesozoic aged Verkhoyansk-Chukotka fold region. This study was conducted in the Ayan-Yuryahskaya structural-facies zone, belonging to the Permian Okhotsk-Kulinsk province. The succession belongs to the Late Paleozoic sediments of the passive continental margin Angarida, which was part of Eastern Siberia during the late Paleozoic. A many kilometer thickness of deposits of late Paleozoic and early Mesozoic were described in 1938 by N. P. Heraskov as the Verkhoyansk clastic complex. So, under this name, the succession appears in recent publications. The basic characteristics of the Ayan- Verkhoyansk clastic complex include a high sedimentation rate and widespread flyschoid sequences characterized by various gravity driven deposits. The Verkhoyansk complex corresponds to the type of gravity driven sedimentation inherent in passive continental margin. Within the Verkhoyansk-Okhotsk province lateral variation in facies zones is observed from continental areas of the Okhotsk block to sediments of the continental slope and the base of slope, presented in the Ayan-Yuryahskaya zone. The sediments of the Permian aged Ayan-Yuryahskaya zone have an apparent thickness of over 6000 m. The Atkanskaya, Omchakskaya and Staratelskaya suites are exposed in the basins of the Tenka, Omchak and Nel-Koba Rivers, which are tributaries of the Kolyma River. The studied sedimentary units are the black shale complex, composed mainly of dark gray shales, siltstones, and minor sandstones. Typically this unit is, 63% siliceous with a high organic carbon content of 2%. Here you can see the reverse rhythmic alternation of mudstone, siltstone and sandstone, often forming graded bedding. Sandstones are fine-grained, medium-sorted and feature hydromicaceous cement; often chlorite. Clasts show medium roundness to angular shapes and are represented by quartz, feldspar, muscovite and 3-5% ore minerals. An essential element of this section is the Diamiktity ("pebble mudstone"). This features a clay-silt matrix in which there are scattered sand, gravel and pebble and boulder material making up to 45% of the unit. The well- to median-rounded clasts are typically of intermediate and basic composition. The Diamiktity forms packages that vary from thin layers to thick packages of up to 250 m along strike. Different theories on the genesis of Diamiktity exist. Initially, there was a view of the similarity of these rocks to volcanic tuffs. Later, opinion shifted to a sea-ice origin of these sedimentary structures. Detrital material may have been supplied by a volcanic arc located in the Sea of Okhotsk. Recently, it has been suggested that there is a connection between these deposits and explosive emissions from mud volcanoes. Our studies show that the question of the genesis of the Diamiktity requires further study. The assumption that the depositional fluxes were mud-stone flows and samples of comminuted fragments of quartz within these flows may indicate an explosive genesis to these sedimentary units. Acknowledgments Paper was prepared with financial support of RFBR, grant 11-05-00-950.

T3S5_P49

The sedimentary architecture, evolution history and controlling factors of the early Miocene Zhujiang

deep-water fan system in the Pearl River Mouth Basin, northern South China Sea

Zhou, W.1, Wang, Y.M.1, Xu, Q.2, Gao, X.Z.1, Li, D.2

1 College of Geosciences, China University of Petroleum, 102249-Beijing, China

(wei.zhou.lemon@gmail.com) 2 The Research institute of CNOOC, 100027-Beijing, China (xuqiang@cnooc.com.cn)

After the 23.8 Ma Baiyun Movement, the Baiyun Sag of the Pearl River Mouth Basin (PRMB) was located

in the deep-water continental slope depositional environment. In comparison with other huge deep-water fan

systems fed by large river drainage areas, the size of the early Miocene Zhujiang deep-water fan system is

relatively small. Using 3D seismic, well logging and core data, the current study documents the depositional

architecture, evolution history, and controlling factors of the early Miocene’s Zhujiang deep-water fan

system in Pearl River Mouth Basin, northern South China Sea.

Integrated analysis shows that the early Miocene Zhujiang Formation deep-water fan system primarily

developed in the lower two 3rd order sequences SQ23.8 and SQ21, whereas in the upper two 3rd order

sequences SQ17.5 and SQ16.5, the fan system could not be identified. The deep-water deposits in SQ23.8

registered as small-scale densely packed and distributed side-by-side sandy debris filled channels, whereas

SQ21 registered as large-scale channels, lobes and sheet sands. The lithofacies of the deep-water deposits in

SQ23.8 and SQ21 both show partial traction current reworked sedimentary characteristics in the background

of the gravity flow deposits. The deep-water fan system in the early Miocene evolved through three stages:

small-scale densely packed and distributed side-by-side channels in the early stage, large-scale channels,

lobes and sheet sands in the medium stage and deep-water drape deposits in the advanced stage.

Distribution of deep-water high quality sands was affected by a weakening of tectonic movement and led to a

reduction of sediment supply to the deep-water, resulting in the development of a gentle character to the

continental slope topography. The distribution of sand in the deep-water environment was likely controlled

by an inherited inflexed seabed topography caused by the burial of faults. The inherited seabed topography

may have controlled the dominant flow pathways, sediment dispersal system, sediment-input points and

depositional process of gravity flows. The change of size of deep-water fan systems is likely to have been

controlled by changes in the amount of sediment supply to the slope environment derived from the ancient

Pearl River Delta. This supply was controlled by the combined effects of the sediment supply strength of the

Pearl River and shelf palaeotopography. Sea-level variation might not have bene the main controlling factor

in the development of deep-water fan systems in this area.

Acknowledgements

The study is sponsored by the National Key Projects of Basic Research (grant no. 2009CB219407) and the

Natural Science Foundation (grant no. 40572067).