DOCSLIB.ORG

Confined Turbidite Systems

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Confined Turbidite Systems Downloaded from http://sp.lyellcollection.org/ by guest on September 27, 2021 Confined turbidite systems SIMON A. LOMAS 1 & PHILIPPE JOSEPH 2 1Baker Atlas Geoscience, Stoneywood Park North, Aberdeen AB21 7EA, UK (e-mail." [email protected]) 2IFP School/Geology-Geochemistry Division, Institut Franfais du P~trole, 228-232, avenue Napoleon Bonaparte, 92852 Rueil Malmaison Cedex, France (e-mail." [email protected]) Abstract: Deep-water sedimentation is currently a major focus of both academic research and industrial interest. Recent studies have emphasized the fundamental influence of sea- floor topography on the growth and morphology of submarine 'fans': in many turbidite systems and turbidite hydrocarbon reservoirs, depositional system development has been moderately to strongly confined by pre-existing bounding slopes. This publication examines aspects of sediment dispersal and accumulation in deepwater systems where basin-floor topo- graphy has profoundly affected deposition, and the associated controls on hydrocarbon reservoir architecture and heterogeneity. The papers herein offer a global perspective which is wide-ranging in terms of both approach and location, including contrasting case studies of outcrop, subsurface, modern and experimental systems. Confined turbidite systems are those deepwater are applied equally to process (ponded turbidity clastic depositional systems whose development current), depositional product (ponded turbidite) has been fundamentally constrained by pro- and basin/stratigraphic behaviour (ponded depo- nounced basin-floor topography. Many early centre). We favour the more general term con- conceptual and experimental models of turbidity finement to describe situations where sediment current deposition and submarine fan develop- gravity flows and their deposits are appreciably ment envisaged essentially unconfined radial affected by the presence of significant basin- development of lobe and fan-shaped deposi- floor topography, but without the connotation tional bodies. However, a wealth of case studies of complete containment. now available from many contrasting turbidite Closely associated with the concept of confined systems worldwide makes it clear that, in many deposition are the notions of flow reflection and basins, both sediment dispersal patterns and the deflection. In their study of ponded Quaternary geometries of depositional bodies have been pro- sediments in valleys on the flanks of the foundly affected by pre-existing or developing Mid-Atlantic Ridge, Van Andel & Komar (1969) basin-floor relief. It seems that perhaps most speculated that the rebound of turbidity currents large natural turbidity currents, particularly in off the bounding slopes was responsible for intracontinental basins, are not free to spread repeated grading profiles seen in their piston radially across a uniform basin floor. cores. Picketing & Hiscott (1985) recognized con- Van Andel & Komar (1969) used the term tainment of turbidity currents in the Cloridorme ponding to refer to a situation in which turbidity Formation (Ordovician of Qu6bec) from reversals currents of sufficiently large volume are fully of palaeocurrent indicators, which they inter- contained by an area of enclosed bathymetry. preted as the result of deflection and reflection of Similarly, Picketing & Hiscott (1985) used the part of large-volume turbidity currents from con- term contained turbidites to describe beds depos- fining slopes. Similar evidence of divergent palaeo- ited from turbidity currents that were confined flow indicators has subsequently been recognized within a basin too small to permit sustained at outcrop in various other successions represent- unidirectional flow. The terms ponding and, to a ing depositional systems where turbidity currents lesser extent, containment, are now generally have interacted with basin-bounding or intra- used to indicate a situation in which sediment basinal slopes (e.g. Kneller et al 1991; Smith, this gravity flows fill the floor of an enclosed depres- volume), and the likely effects of such interaction sion and are unable to surmount the bounding have been widely investigated through physical slopes (or 'sills') which bound that depositional experiments (e.g. Simpson 1987; Muck & Under- area ('mini-basin', 'silled sub-basin' or 'ponded wood 1990; Alexander & Morris 1994; Kneller depocentre'). Thus, essentially all of the sediment 1995; AI Ja'Aidi et al., this volume). carried into the depositional area by that flow will Implicit in the concept of confinement is the be trapped and deposited there. The same terms relationship of flow magnitude to size of From: LOMAS, S. A. & JosEen, P. (eds) 2004. Confined Turbidite Systems. Geological Society, London, Special Publications, 222, 1-7. 0305-8719/04/$15.00 9The Geological Society of London 2004. Downloaded from http://sp.lyellcollection.org/ by guest on September 27, 2021 2 S. A. LOMAS & P. JOSEPH depocentre. The general concept of flow efficiency in varied modern and ancient examples. The (e.g. Mutti 1979) is helpful here, describing a author emphasizes the contrasting behaviour flow's ability to deliver sediment, especially and architectural characteristics of coarse- sand, in a basinward direction. Thus, small grained/sand-rich and fine-grained/mud-rich volume, low-efficiency sediment gravity flows end-member systems but reminds us of the may behave in an effectively unconfined manner inadequacy of general models in capturing the even in small basins. Conversely, very large mag- variability of these real cases. The practical lim- nitude flows may interact with marginal confining itations of idealised models arise either from slopes even in large basins. Of course, if a con- emphasis on only one or two aspects or from fined depocentre is filled more quickly than the over-simplification (being too general to display topographic relief grows, the surface area of the architectural details). Bouma advocates the con- basin floor will increase with time. Hence, if struction of case-specific models based on a sediment supply characteristics remain similar, reconstruction of the specific natural controls successive depositional systems would be and their interactions in the generation and deliv- expected to :reflect progressively decreasing con- ery of sedimentary particles, the evolving basin finement. The reverse scenario could develop in configuration and processes of deposition and certain compressional settings. possible redeposition in that basin. In most of the studies detailed in this volume, Smith takes an alternative look at patterns of the origin of the confining topography is tectonic: sediment dispersal on topographically complex large-scale structural features, local fault scarps, slopes, distinguishing two conceptual end- folds or more subtle perturbations of basin-floor member systems, which he refers to as 'cascades gradients with associated tilting and faulting. In of silled sub-basins' and 'connected tortuous other instances, basin-floor relief is the result of corridors'. The first scenario is essentially a refine- slope collapse masses, halokinesis, mud diapirism ment of the 'fill-and-spill' model that emerged and, to a limited extent, differential compaction. from studies of the northern Gulf of Mexico The collection of papers hosted in this volume slope (e.g. Winker 1996; Prather et al 1998). In is not intended to provide an exhaustive treat- the 'connected tortuous corridors' scenario, ment of the subject of confined deepwater flows partly circumvent bathymetric obstacles, sedimentation, but rather to bring together a but follow a (laterally confined) continuous tortu- diverse assortment of approaches and observa- ous path down the slope. From two-dimensional tions which have a bearing on this topic. We sections, these two scenarios may be difficult to have ordered the contributions to reflect the distinguish (i.e. apparently separate sub-basins varying approaches of the researchers. Here may be directly connected out of the plane of we present an overview of those contributions section), although recognition of stratal onlap and the new perspectives they afford, and draw against a confining frontal slope should be diag- attention to promising channels (and lobes?) for nostic of the fill of a true silled sub-basin. future research. We are pleased that several of the systems described in the following papers are not widely known. It is hoped that the juxta- Experimental studies position of conceptual reviews, experimental work and case-studies of outcrop, subsurface Laboratory experiments have offered crucial and modern systems will stimulate new insights insights into the potential effects of basin-floor and connections and highlight key general ques- topography on sedimentation (e.g. Simpson tions which surmount the usual bounding slopes 1987; Kneller et al., 1991; Alexander & Morris of these scientific sub-communities. 1994). A! Ja'Aidi et al. outline a series of scaled experiments (using ballotini and silica flour to model sand and mud) to investigate how flow Overviews of confined turbidite systems volume, density and grain-size distribution affect the transport efficiency of turbidity cur- Two review papers introduce the broad-scale rents (i.e. their ability to carry 'sand' basinward) context of controls on, and patterns of, confined and the geometric characteristics of the resulting turbidite system development from contrasting deposits. In general, these experiments reaffirm viewpoints. intuitive expectations
Load more

Recommended publications
  • Geologic Storage Formation Classification: Understanding Its Importance and Impacts on CCS Opportunities in the United States
    BEST PRACTICES for: Geologic Storage Formation Classification: Understanding Its Importance and Impacts on CCS Opportunities in the United States First Edition Disclaimer This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference therein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed therein do not necessarily state or reflect those of the United States Government or any agency thereof. Cover Photos—Credits for images shown on the cover are noted with the corresponding figures within this document. Geologic Storage Formation Classification: Understanding Its Importance and Impacts on CCS Opportunities in the United States September 2010 National Energy Technology Laboratory www.netl.doe.gov DOE/NETL-2010/1420 Table of Contents Table of Contents 5 Table of Contents Executive Summary ____________________________________________________________________________ 10 1.0 Introduction and Background
    [Show full text]
  • Contourites and Associated Sediments Controlled by Deep-Water Circulation Processes: State-Of-The-Art and Future Considerations
    2nd Deep-Water Circulation Congress, 10-12 Sept. 2014, Ghent, Belgium Contourites and associated sediments controlled by deep-water circulation processes: state-of-the-art and future considerations Michele Rebesco1, Francisco Javier Hernández-Molina2, David Van Rooij3 and Anna Wåhlin4 1 OGS, Istituto Nazionale di Oceanografia e di Geofisica Sperimentale, Borgo Grotta Gigante 42 /C, 34010, TS, Italy; ([email protected]) 2 Department of Earth Sciences, Royal Holloway University of London, Egham, Surrey TW20 0EX, UK; ([email protected]) 3 Department of Geology and Soil Science, Ghent University, B-9000 Gent, Belgium; ([email protected]) 4 Department of Earth Sciences, University of Gothenburg, PO Box 460, SE-405 30 Göteborg, Sweden; ([email protected]) Abstract: The contourite paradigm was conceived a few decades ago and about 120 major contourite areas are presently known associated to myriad oceanographic processes, which involve dense bottom currents, tides, eddies, deep-sea storms, internal waves and tsunamis. The increasing recognition of these deposits is influencing palaeoclimatology & palaeoceanography, slope-stability/geological hazard assessment, and hydrocarbon exploration. Nevertheless, there is a pressing need for a better understanding of the sedimentological and oceanographic processes governing contourites. Persistent oceanographic processes significantly affect the seafloor, resulting in a continuous spectrum of depositional and erosional features. Although much progress has been made in the large-scale, geophysically based recognition of these deposits, there remains a lack of unambiguous and commonly accepted diagnostic criteria for deciphering the small-scaled contourite facies and for distinguishing them from turbidite ones. Similarly, the study of sandy deposits generated or affected by bottom currents offers great research potential: these deposits might prove invaluable as future reservoir targets.
    [Show full text]
  • An Ontological Model for Turbidite Channel Migration
    An Ontological Model for Turbidite Channel Migration Fabrício Henrique Rodrigues, Luan Fonseca Garcia, Renata dos Santos Alvarenga, Mara Abel Instituto de Informática - Universidade Federal do Rio Grande do Sul (UFRGS) {fabricio.rodrigues, luan.garcia, rsakuchle, marabel}@inf.ufrgs.br Abstract. Geology interpretation applies abductive reasoning to determine, from the actual existent rock units, the processes that create these occurrences. In particular, modelling the sedimentary processes of erosion and deposition, are of crucial importance for understanding the spatial distribution of the rock bodies that configure actual petroleum reservoir. This paper proposes an ontological model for turbidite channel migration, which is an important event in the formation of turbidite systems, a common type of reservoir. The proposed model is based on the Unified Foundational Ontology and presents both a high level description of the event as well as details its main composing events, namely erosion, transportation and deposition of sediments. 1. Introduction Ontologies can be regarded as explicit specifications of conceptualizations (Gruber, 1993). In a practical sense, an ontology formally describes the concepts of a given domain and the relationships among them. Such concepts may represent both things that exist (usually called objects) as well as things that happen (usually called events). In spite of that, there is a somewhat widespread view that objects are ontologically prior to events1, according to which objects are all that exists and events exist just as the distribution of matter and objects in space and time (Galton, Mizoguchi, 2009). Nevertheless, from chemical reactions to business transactions, it seems that great part of our reality is fundamentally dependent on events (Casati, Varzi, 2015).
    [Show full text]
  • Turbidites in a Jar
    Activity— Turbidites in a Jar Sand Dikes & Marine Turbidites Paleoseismology is the study of the timing, location, and magnitude of prehistoric earthquakes preserved in the geologic record. Knowledge of the pattern of earthquakes in a region and over long periods of time helps to understand the long- term behavior of faults and seismic zones and is used to forecast the future likelihood of damaging earthquakes. Introduction Note: Glossary is in the activity description Sand dikes are sedimentary dikes consisting of sand that has been squeezed or injected upward into a fissure during Science Standards an earthquake. (NGSS; pg. 287) To figure out the earthquake hazard of an area, scientists need to know how often the largest earthquakes occur. • From Molecules to Organisms—Structures Unfortunately (from a scientific perspective), the time and Processes: MS-LS1-8 between major earthquakes is much longer than the • Motion and Stability—Forces­­ and time period for which we have modern instrumental Interactions: MS-PS2-2 measurements or even historical accounts of earthquakes. • Earth’s Place in the Universe: MS-ESS1-4, Fortunately, scientists have found a sufficiently long record HS-ESS1-5 of past earthquakes that is preserved in the rock and soil • Earth’s Systems: HS-ESS2-1, MS-ESS2-2, beneath our feet. The unraveling of this record is the realm MS-ESS2-3 of a field called “paleoseismology.” • Earth and Human Activity: HS-ESS3-1, In the Central United States, abundant sand blows are MS-ESS3-2 studied by paleoseismologists. These patches of sand erupt onto the ground when waves from a large earthquake pass through wet, loose sand.
    [Show full text]
  • Turbidite System Architecture and Sedimentary Processes Along Topographically Complex Slopes: the Makran Convergent Margin
    Sedimentology (2010) doi: 10.1111/j.1365-3091.2010.01168.x Turbidite system architecture and sedimentary processes along topographically complex slopes: the Makran convergent margin JULIEN BOURGET*,1, SEBASTIEN ZARAGOSI*, NADINE ELLOUZ-ZIMMERMANN , NICOLAS MOUCHOTà, THIERRY GARLAN§, JEAN-LUC SCHNEIDER*, VALENTINE LANFUMEY– and SIGFRIED LALLEMANTà *Universite´ de Bordeaux, UMR CNRS 5805 EPOC, Avenue des Faculte´s, F-33405 Talence, France (E-mail: [email protected]) IFP, Geology-Geochemistry-Geophysics, 1 & 4 avenue de Bois Pre´au, F-92852 Rueil-Malmaison, France àUniversite´ de Cergy-Pontoise, GEC, 5, mail Gay-Lussac, F-95031 Cergy-Pontoise, France §SHOM, Centre Hydrographie, BP 426, F-29275 Brest, France –IFREMER, GM/LES, BP70, F-29280 Plouzane´ Cedex, France Associate Editor – Subhasish Dey ABSTRACT This study investigates the morphology and Late Quaternary sediment distribution of the Makran turbidite system (Makran subduction zone, north- west Indian Ocean) from a nearly complete subsurface mapping of the Oman basin, two-dimensional seismic and a large set of coring data in order to characterize turbidite system architecture across an active (fold and thrust belt) margin. The Makran turbidite system is composed of a dense network of canyons, which cut into high relief accreted ridges and intra-slope piggyback basins, forming at some locations connected and variably tortuous paths down complex slopes. Turbidite activity and trench filling rates are high even during the Holocene sea-level highstand conditions. In particular, basin-wide, sheet- like thick mud turbidites, probably related to major mass wasting events of low recurrence time, drape the flat and unchannellized Oman abyssal plain. Longitudinal depth profiles show that the Makran canyons are highly disrupted by numerous thrust-related large-scale knickpoints (with gradients up to 20° and walls up to 500 m high).
    [Show full text]
  • Hybrid Turbidite-Drift Channel Complexes: an Integrated Multiscale Model A
    https://doi.org/10.1130/G47179.1 Manuscript received 7 November 2019 Revised manuscript received 27 January 2020 Manuscript accepted 28 January 2020 © 2020 The Authors. Gold Open Access: This paper is published under the terms of the CC-BY license. Published online 18 March 2020 Hybrid turbidite-drift channel complexes: An integrated multiscale model A. Fuhrmann1, I.A. Kane1, M.A. Clare2, R.A. Ferguson1, E. Schomacker3, E. Bonamini4 and F.A. Contreras5 1 Department of Earth and Environmental Sciences, University of Manchester, Williamson Building, Oxford Road, Manchester M13 9PL, UK 2 National Oceanography Centre, European Way, Southampton SO14 3HZ, UK 3 Equinor, Martin Linges vei 33, 1364 Fornebu, Norway 4 Eni Upstream and Technical Services, Via Emilia 1, 20097 San Donato Milanese, Milan, Italy 5 Eni Rovuma Basin, no. 918, Rua dos Desportistas, Maputo, Mozambique ABSTRACT sedimentological model for bottom current– The interaction of deep-marine bottom currents with episodic, unsteady sediment gravity influenced submarine channel complexes. flows affects global sediment transport, forms climate archives, and controls the evolution of continental slopes. Despite their importance, contradictory hypotheses for reconstructing past GEOLOGICAL SETTING flow regimes have arisen from a paucity of studies and the lack of direct monitoring of such The Jurassic to Paleogene basins offshore of hybrid systems. Here, we address this controversy by analyzing deposits, high-resolution sea- East Africa formed during the breakup of Gond- floor data, and near-bed current measurements from two sites where eastward-flowing gravity wana (Salman and Abdula, 1995). Following flows interact(ed) with northward-flowing bottom currents. Extensive seismic and core data Pliensbachian to Aalenian northwest-southeast from offshore Tanzania reveal a 1650-m-thick asymmetric hybrid channel levee-drift system, rifting, ∼2000 km of continental drift took place deposited over a period of ∼20 m.y.
    [Show full text]
  • A Few of Turbidite Characteristic Feature in the Vicinity of Bantarujeg (Abdurrokhim)
    A Few of Turbidite Characteristic Feature In the Vicinity of Bantarujeg (Abdurrokhim) A FEW OF TURBIDITE CHARACTERISTIC FEATURE IN THE VICINITY OF BANTARUJEG Abdurrokhim Laboratorium Sedimentologi dan Geologi Kuarter, Jurusan Geologi FMIPA – UNPAD ABSTRACT The traversing of Cilutung River exposes the sedimentary rock which is corresponding to turbidity system sedimentation. In around Bantarujeg area, the composite lithology is characterized by monotonous of poorly sorted tuffaceous sandstone interbedded with mudstone of classical turbidite; coarse grain of pebbly sandstone; interbedded tuffaceous sandstone and mudstone of slump deposits; disorganized pebble-coble-sized components of mud supported; massive sandstone and polymix breccia. A genetic unit based on sedimentary processes is more reliable in order to grouping the lithostratigraphic units. Keyword: system sedimentation, turbidity ABSTRAK Lintasi S. Cilutung menyingkapkan batuan sedimen yang sesuai dengan sistem sedimentasi turbidit. Di sekitar area Bantarujeg, batuan ditandai oleh batupasir tufaaan porositas buruk selang-seling dengan batulempung turbidite klasik; batupasir kerikilan berbutir kasar; selang-seling batupasir tufaan dan endapan slum batulempung; batupasir masive dan breksi polimiks. Satuan genetika berdasarkan proses sedimentasi lebih dapat dipercaya dalam rangka menggolongkan satuan litostratigrafi. Kata kunci : sistem sedimentasi, turbidit INTRODUCTION of the observation product from the field will be documented and reported Bantarujeg is the town, lies about periodically. Since the lithology 15 km south of Majalengka. characteristic, disperse and variation Department of Geology Universitas of composition vertically or laterally Padjadjaran have been utilizing this are rapid changing, the sedimentary area for student mapping exercise rock characteristic is the focused since three years ago in order to observation in this time. accelerate the time of student To simplify the grain size-based of graduation without reducing the lithology name, sand/sandstone is tutoring stuff.
    [Show full text]
  • A Case Study from the Al Batha Turbidite System, Oman Margin
    Sedimentary Geology 229 (2010) 144–159 Contents lists available at ScienceDirect Sedimentary Geology journal homepage: www.elsevier.com/locate/sedgeo Hyperpycnal-fed turbidite lobe architecture and recent sedimentary processes: A case study from the Al Batha turbidite system, Oman margin J. Bourget a,⁎, S. Zaragosi a, T. Mulder a, J.-L. Schneider a, T. Garlan b, A. Van Toer c, V. Mas d, N. Ellouz-Zimmermann e a Université Bordeaux I, UMR CNRS 5805 EPOC, Avenue des Facultés, F-33405 Talence, France b SHOM, Centre Hydrographie, BP 426, F-29275 Brest, France c LSCE/IPSL, CEA–CNRS–UVSQ, F-91198 Gif sur Yvette Cedex, France d IFREMER, GM/LES, BP70, F-29280 Plouzané Cedex, France e Institut Français du Pétrole (IFP), rue Bois Préau, F-92852 Rueil-Malmaison, France article info abstract Available online 5 April 2009 The main sediment depocenter along the Oman margin is the Al Batha turbidite system that develops in the Gulf of Oman basin. It is directly connected to the wadi Al Batha, and forms a typical sand and mud rich point Keywords: source system that acts as regional sediment conduit and feeds a ~1000 km2 sandy lobe. Turbidite system The Al Batha lobe depositional architecture has been investigated in detail using very high-resolution Oman margin seismic, multibeam echosounder data and sediment cores. Several scales of depositional architecture can be Lobe observed. The Al Batha lobe is composed of several depositional units, made of stacked elementary sediment Hyperpycnite fl Gravity flow bodies (thinner than 5 m) that are each related to a single ow event.
    [Show full text]
  • A New Depositional Model for the Classical Turbidite Locality at San
    A new depositional model AUTHORS Hilario Camacho ϳ Department of for the classical turbidite Geological Sciences, University of California, Santa Barbara, Building 526, Santa Barbara, locality at San Clemente California, 93106; [email protected] Hilario Camacho received a B.Sc. degree in State Beach, California geology from the Universidad de Granada, Spain, in 1992 and an M.S. degree from Hilario Camacho, Cathy J. Busby, and Ben Kneller California State University, Long Beach. He is currently a Ph.D. candidate at the University of California, Santa Barbara, and is chief geologist at Signal Hill Petroleum, Inc., in Long ABSTRACT Beach, California. His research interests are focused on fluid flow in sedimentary basins, The Miocene turbidite system exposed in the beach cliffs at San oil generation and migration, and siliciclastic Clemente State Beach, California, has been used by industry and diagenesis. academia alike as a field laboratory. It has been used as an analog ϳ for petroleum reservoirs in the Los Angeles Basin and other areas. Cathy J. Busby Department of Geological Sciences, University of California, Santa We interpret the turbidite system at San Clemente State Beach to Barbara, Building 526, Santa Barbara, represent the fill of a single turbidite channel that aggraded sub- California, 93106; [email protected] vertically. This interpretation is based on construction of a detailed photomosaic, mapping of three-dimensional facies distributions, Cathy Busby received her B.S. degree from the University of California at Berkeley in measurement of representative sections, and collection of new pa- 1977 and her Ph.D. from Princeton University leocurrent data; we also extended this analysis to outcrops not pre- in 1983.
    [Show full text]
  • Hybrid Turbidite-Drift Channel Complexes: an Integrated Multiscale Model A
    https://doi.org/10.1130/G47179.1 Manuscript received 7 November 2019 Revised manuscript received 27 January 2020 Manuscript accepted 28 January 2020 © 2020 The Authors. Gold Open Access: This paper is published under the terms of the CC-BY license. Hybrid turbidite-drift channel complexes: An integrated multiscale model A. Fuhrmann1, I.A. Kane1, M.A. Clare2, R.A. Ferguson1, E. Schomacker3, E. Bonamini4 and F.A. Contreras5 1 Department of Earth and Environmental Sciences, University of Manchester, Williamson Building, Oxford Road, Manchester M13 9PL, UK 2 National Oceanography Centre, European Way, Southampton SO14 3HZ, UK 3 Equinor, Martin Linges vei 33, 1364 Fornebu, Norway 4 Eni Upstream and Technical Services, Via Emilia 1, 20097 San Donato Milanese, Milan, Italy 5 Eni Rovuma Basin, no. 918, Rua dos Desportistas, Maputo, Mozambique ABSTRACT sedimentological model for bottom current– The interaction of deep-marine bottom currents with episodic, unsteady sediment gravity influenced submarine channel complexes. flows affects global sediment transport, forms climate archives, and controls the evolution of continental slopes. Despite their importance, contradictory hypotheses for reconstructing past GEOLOGICAL SETTING flow regimes have arisen from a paucity of studies and the lack of direct monitoring of such The Jurassic to Paleogene basins offshore of hybrid systems. Here, we address this controversy by analyzing deposits, high-resolution sea- East Africa formed during the breakup of Gond- floor data, and near-bed current measurements from two sites where eastward-flowing gravity wana (Salman and Abdula, 1995). Following flows interact(ed) with northward-flowing bottom currents. Extensive seismic and core data Pliensbachian to Aalenian northwest-southeast from offshore Tanzania reveal a 1650-m-thick asymmetric hybrid channel levee-drift system, rifting, ∼2000 km of continental drift took place deposited over a period of ∼20 m.y.
    [Show full text]
  • Glossary of Geological Terms
    GLOSSARY OF GEOLOGICAL TERMS These terms relate to prospecting and exploration, to the regional geology of Newfoundland and Labrador, and to some of the geological environments and mineral occurrences preserved in the province. Some common rocks, textures and structural terms are also defined. You may come across some of these terms when reading company assessment files, government reports or papers from journals. Underlined words in definitions are explained elsewhere in the glossary. New material will be added as needed - check back often. - A - A-HORIZON SOIL: the uppermost layer of soil also referred to as topsoil. This is the layer of mineral soil with the most organic matter accumulation and soil life. This layer is not usually selected in soil surveys. ADIT: an opening that is driven horizontally (into the side of a mountain or hill) to access a mineral deposit. AIRBORNE SURVEY: a geophysical survey done from the air by systematically crossing an area or mineral property using aircraft outfitted with a variety of sensitive instruments designed to measure variations in the earth=s magnetic, gravitational, electro-magnetic fields, and/or the radiation (Radiometric Surveys) emitted by rocks at or near the surface. These surveys detect anomalies. AIRBORNE MAGNETIC (or AEROMAG) SURVEYS: regional or local magnetic surveys that measures deviations in the earth=s magnetic field and carried out by flying a magnetometer along flight lines on a pre-determined grid pattern. The lower the aircraft and the closer the flight lines, the more sensitive is the survey and the more detail in the resultant maps. Aeromag maps produced from these surveys are important exploration tools and have played a major role in many major discoveries (e.g., the Olympic Dam deposit in Australia).
    [Show full text]
  • Geology and Geochemistry of Abyssal Plains 7
    Geology and Geochemistry of Abyssal Plains 7 J I I F I I iG1 I 2( I I I I ~7 3( I i i 4q I r 5q I I ~H BI I r 6( I I El W I i tY" 7( I I I-- I 7 LU I a( I I I I I I I W I G I 8 10(., I I B' i 110 --4 I IJ I I 3 I I 120 I I I I p I 130 I K D I I .. 4 140 D" 9 51 i,, 150 4 I 155 E Photograph of piston core D10688 from the Madeira Abyssal Plain. Lettered units are interpreted as turbidites and numbered units are intervening pelagic layers (the numbers refer to oxygen isotope stage determination). Note bioturbation of pelagic units and tops of turbidites; coarser laminated bases of turbidites B, B 1 and G and to a lesser extent in turbidites E and F; structureless make-up of the thick turbidites; distinct colour changes in organic-rich turbidites A 1, E, F and H representing relict oxidation fronts; chemical laminae above colour changes. For more detailed discussion of these sediments see papers by Jarvis & Higgs, De Lange et al. and Weaver & Rothwell. GEOLOGICAL SOCIETY SPECIAL PUBLICATION NO 31 Geology and Geochemistry of Abyssal Plains EDITED BY P. P. E. WEAVER & J. THOMSON Institute of Oceanographic Sciences, Wormley, Godalming 1987 Published for The Geological Society by Blackwell Scientific Publications OXFORD LONDON EDINBURGH BOSTON PALOALTO MELBOURNE Geological Society Special Publications Series Editor K. COE Published for DISTRIBUTORS The Geological Society by USA and Canada Blackwell Scientific Publications Blackwell Scientific Publications Inc Osney Mead, Oxford OX2 0EL PO Box 50009, Palo Alto (Orders:Tel.
    [Show full text]