DOCSLIB.ORG

Transport of Sediments by Waves, Adriatic Coastal Shelf, Italy^ R

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Transport of Sediments by Waves, Adriatic Coastal Shelf, Italy^ R THE AMERICAN ASSOCIATION OF PETROLEUM GEOLOGISTS BULLETIN V. S1, NO. 7 (JULY, 1967). P. 1304-I3I9. 12 FIGS. TRANSPORT OF SEDIMENTS BY WAVES, ADRIATIC COASTAL SHELF, ITALY^ R. PASSEGA,=' A. RIZZINI,' AND G. BORGHETTP Bartlesville, Oklahoma, and Milan, Italy ABSTRACT Knowledge of marine-sediment transport in shallow water is as yet insufficient to give much help to the geologist who maps the distribution of ancient sandstone bodies. In order to improve this knowledge, the bottom sediments of the Adriatic Sea near the Italian coast were sampled and ana­ lyzed, lliese sediments were transported as uniform suspensions. A close relation was found between certain grain-size parameters, particularly the 1 percentile, and sea depth, indicating that turbulence induced by waves was a major factor in the sand distribution. Another important factor that generally has been overlooked is percentage of sand in the sedi­ ment source for the area. If these source sediments contain little sand and consist almost entirely of silt and clay, the sand remains close to shore. If, however, sand is the predominant constituent of the source sediments, as commonly occurred in ancient seas, sand probably can be spread by waves across extensive areas as deep as wave base The grain size of the sand also is an important factor in its distribution, some sand suspensions being displaced by gravity and some not. Therefore, grain size may determine the transport mechanism and, thus, the sediment distribution. An understanding of these factors by the petroleum geologist is essential in his mapping and projection of sandstone deposits in the subsurface. INTRODUCTION Such fundamental information as the sediment Vertical and areal variations in the character­ content of bottom water during storms is not istics of sands are a controlling factor of sand­ available. Even less is known about the direction stone reservoir characteristics. If the reservoir is of transport, down- or upslope, of sands of a stratigraphic trap, petroleum accumulation is a different grain size. result of these variations. Studies of Recent and ancient sediments are The economic significance of the characteristics mainly descriptions of sediments as they are of sand deposits induces petroleum geologists to in­ found and observed. In order to obtain the fun­ vestigate genesis and diagenesis of the sand. The damental information still lacking, there now is a present paper discusses a particular genesis: for­ need for field research on the dynamics of sedi­ mation of sand deposits by waves. mentation. In recent years considerable progress has been The present paper is an investigation of the made in sedimentation research. The environment mechanism of sand distribution in a limited area of deposition commonly, but not always, can be of the Adriatic coastal shelf along the east coast identified. The regional direction of currents in of Italy. Movement of sand was not observed di­ many cases is indicated by sedimentary struc­ rectly but was reconstructed to explain the pres­ tures. Unfortunately, little progress has been ent distribution. Texture was compared with the made in one fundamental field—that of sediment texture of other sediments to determine the transport, to which the characteristics of sedi­ transport mechanism. Information also was ob­ ments are closely related. tained by comparing the grain-size distribution in Among various modes of transport of sand, this area with similar distributions on shelves of distribution by waves formed the largest volume other seas. of ancient marine sand deposits. Yet little is known about the action of waves on the sedi­ SAMPLING ments of an open shelf. Systematic observations Adriatic bottom sediments were sampled along supporting the opinions commonly expressed on the Italian coast in an area between the ports of the maximum depth of wave action are lacking. Ortona and Pescara, from the 10- to the SO-meter isobaths. This area, shown on Figure 1, is 22 kilo­ ' Published by permission of AGIP Direzione Min- eraria. Manuscript received, October 25, 1965; ac­ meters long and 10 kilometers wide. cepted, October 19, 1966. Only the uppermost part of the sediments was ^ Consultant. sampled and it was assumed that this part was ' Geologist, AGIP Direzione Mineraria. deposited since the sea attained its present level. 1304 TRANSPORT OF SEDIMENTS BY WAVES, ADRIATIC COASTAL SHELF, ITALY 130.S In view of the nearness of the shore and the close relation between certain sediment character­ istics and sea depth, this assumption is justified. Samples were taken from a trawler equipped with an echo meter while the trawler successively followed the 10-, IS-, 20-, 2S-, 30-, 40-, and SO-meter isobaths. Along each of these isobath lines, sampling sta­ tions were spaced at approximately l,SOO-meter intervals. At each station two or three samples were taken. Sand was sampled with a grab sam­ pler, and samples of homogeneous texture were selected for grain-size analyses. Muds were sam­ pled with a short core barrel, but only the upper­ most part of the core was analyzed. The total number of stations is 106 and the total number of samples 267. The samples were treated by hydrogen perox­ FIG. 1.—Map of Adriatic Sea, showing area of study. ide in order to destroy the organic matter with­ out acid treatment. The fraction coarser than 31 deepest parts of the oceans, but the mechanism microns was analyzed with sieves. The finer frac­ that triggers these currents generally is still a mat­ tion was dispersed with pyrophosphate and ana­ ter for speculation. In certain areas, however, as lyzed with pipette.* at the mouth of the Congo River, it is probable The grain-size analyses of the samples taken that dense sand suspensions transported by rivers along each isobath were represented by a CM during floods can overcome the density difference pattern. An attempt was made to reconstruct the between salt and fresh water and flow as turbidi­ sedimentation by using these patterns. ty currents into submarine canyons. Waves are the transport agent that moved the BRIEF REVIEW OF MARINE SEDIMENT TRANSPORT largest volume of ancient sands. Waves act on relatively shallow bottoms on which the orbital The purpose of this work is to give a better motion, flattened by action of the bottom, creates understanding of sediment distribution by marine an alternate to-and-fro current. agents. Reliable information supplied by the Numerous laboratory experiments and theoreti­ study of present oceans is available only for cer­ cal studies have been made to explain the action tain environments. of waves on bottom sediments. The movement of Longshore currents, fairly well known, can natural or artificial sediments also has been transport sand and pebbles for distances of more traced on nearshore ocean bottoms. As yet this than 100 kilometers along the shore in a narrow work has not led to the formulation of well-estab­ belt only a few dozen meters wide. lished laws controlling sediment motion. Tidal currents may be swift in areas where It generally is accepted that shallowing waves tides are restricted by the topography. Transport induce a shoreward bottom current that tends to by these currents was studied in tidal channels keep sand near the shore. This current probably and over shallow banks. Sand waves moving at is compensated for a certain distance above bot­ present on the continental shelf off the south and tom by a seaward counter-current, or laterally by east coasts of England have been attributed to rip currents. tidal action. The transport mechanism, however, At times, a seaward bottom counter-current is not well understood. may be induced by the wind blowing the surface Something is known about turbidity currents water onshore. which transport sand and a few pebbles to the Some oceanographers still believe that sand can 'Analyses were made in the Geochemical Labora­ not be transported by waves for considerable dis­ tories of AGIP, Direzione Mineraria. tances from shore, or much deeper than 30 me- 1306 R. PASSEGA, A. RIZZINI, AND G. BORGHETTI ters. These same oceanographers also believe that size and depth of bottom sediments sampled the position of the mud line, i.e., the lower limit along profiles of several coastal shelves are plot­ of sand deposition, indicates the limit of wave ted on Figure 2. With the exception of the Adri­ action on sand. atic profile (I), these profiles were constructed The study of ancient sediments casts some from published data. For stations where several doubt on these concepts. Passega (1962, p. 118) samples had been taken, the median shown on Fig­ showed that the widespread distribution of some ure 2 is the largest median. marine sands could be explained only by the con­ Profiles II, III, and IV are on the southern temporaneous distribution of sand by waves California shelf near La Jolla (Inman, 1953, across extensive areas of the sea floor. He sug­ 1957). Another California shelf, discussed by gested that a reason for the difference between Trask (1955), is represented by profile V. present-day marine transport and the distribution Profiles VI and VII are situated on the shelf of of these ancient sands is a difference in the grain the Rhone delta, discussed by Kruit (1955). size and volume of the sediments supplied to the Figure 2 shows clearly that, in the same area basin (Passega, 1962, p. 117-118; 1964, p. and at the same depth, the bottom sediment tex­ 837-838). This concept is discussed further in ture differs greatly. Medians of profile II are view of the results of the present study. twice as great as those of profiles III and IV. Ideas about the limit of wave action gradually Between profiles VI and VII, the difference is are changing. Recently silt suspensions by waves even larger.
Load more

Recommended publications
  • Sediment Transport and the Genesis Flood — Case Studies Including the Hawkesbury Sandstone, Sydney
    Sediment Transport and the Genesis Flood — Case Studies including the Hawkesbury Sandstone, Sydney DAVID ALLEN ABSTRACT The rates at which parts of the geological record have formed can be roughly determined using physical sedimentology independently from other dating methods if current understanding of the processes involved in sedimentology are accurate. Bedform and particle size observations are used here, along with sediment transport equations, to determine rates of transport and deposition in various geological sections. Calculations based on properties of some very extensive rock units suggest that those units have been deposited at rates faster than any observed today and orders of magnitude faster than suggested by radioisotopic dating. Settling velocity equations wrongly suggest that rapid fine particle deposition is impossible, since many experiments and observations (for example, Mt St Helens, mud- flows) demonstrate that the conditions which cause faster rates of deposition than those calculated here are not fully understood. For coarser particles the only parameters that, when varied through reasonable ranges, very significantly affect transport rates are flow velocity and grain diameter. Popular geological models that attempt to harmonize the Genesis Flood with stratigraphy require that, during the Flood, most deposition believed to have occurred during the Palaeozoic and Mesozoic eras would have actually been the result of about one year of geological activity. Flow regimes required for the Flood to have deposited various geological cross- sections have been proposed, but the most reliable estimate of water velocity required by the Flood was attained for a section through the Tasman Fold Belt of Eastern Australia and equalled very approximately 30 ms-1 (100 km h-1).
    [Show full text]
  • Sediment Transport in the San Francisco Bay Coastal System: an Overview
    Marine Geology 345 (2013) 3–17 Contents lists available at ScienceDirect Marine Geology journal homepage: www.elsevier.com/locate/margeo Sediment transport in the San Francisco Bay Coastal System: An overview Patrick L. Barnard a,⁎, David H. Schoellhamer b,c, Bruce E. Jaffe a, Lester J. McKee d a U.S. Geological Survey, Pacific Coastal and Marine Science Center, Santa Cruz, CA, USA b U.S. Geological Survey, California Water Science Center, Sacramento, CA, USA c University of California, Davis, USA d San Francisco Estuary Institute, Richmond, CA, USA article info abstract Article history: The papers in this special issue feature state-of-the-art approaches to understanding the physical processes Received 29 March 2012 related to sediment transport and geomorphology of complex coastal–estuarine systems. Here we focus on Received in revised form 9 April 2013 the San Francisco Bay Coastal System, extending from the lower San Joaquin–Sacramento Delta, through the Accepted 13 April 2013 Bay, and along the adjacent outer Pacific Coast. San Francisco Bay is an urbanized estuary that is impacted by Available online 20 April 2013 numerous anthropogenic activities common to many large estuaries, including a mining legacy, channel dredging, aggregate mining, reservoirs, freshwater diversion, watershed modifications, urban run-off, ship traffic, exotic Keywords: sediment transport species introductions, land reclamation, and wetland restoration. The Golden Gate strait is the sole inlet 9 3 estuaries connecting the Bay to the Pacific Ocean, and serves as the conduit for a tidal flow of ~8 × 10 m /day, in addition circulation to the transport of mud, sand, biogenic material, nutrients, and pollutants.
    [Show full text]
  • The Role of Geology in Sediment Supply and Bedload Transport Patterns in Coarse Grained Streams
    The Role of Geology in Sediment Supply and Bedload Transport Patterns in Coarse Grained Streams Sandra E. Ryan USDA Forest Service, Rocky Mountain Research Station, Fort Collins, Colorado This paper compares gross differences in rates of bedload sediment moved at bankfull discharges in 19 channels on national forests in the Middle and Southern Rocky Mountains. Each stream has its own “bedload signal,” in that the rate and size of materials transported at bankfull discharge largely reflect the nature of flow and sediment particular to that system. However, when rates of bedload transport were normalized by dividing by the watershed area, the results were similar for many sites. Typically, streams exhibited normalized rates of bedload transport between 0.001 and 0.003 kg s-1 km-2 at bankfull discharges. Given the inherent difficulty of obtaining a reliable estimate of mean rates of bedload transport, the relatively narrow range of values observed for these systems is notable. While many of these sites are underlain by different geologic terrane, they appear to have comparable patterns of mass wasting contributing to sediment supply under current climatic conditions. There were, however, some sites where there was considerable departure from the normalized range of values. These sites typically had different patterns and qualitative rates of mass wasting, either higher or lower, than observed for other watersheds. The gross differences in sediment supply to the stream network have been used to account for departures in the normalized rates of bedload transport observed for these sites. The next phase of this work is to better quantify the contributions from hillslopes to help explain variability in the normalized rate of bedload transport.
    [Show full text]
  • Modeling and Practice of Erosion and Sediment Transport Under Change
    water Editorial Modeling and Practice of Erosion and Sediment Transport under Change Hafzullah Aksoy 1,* , Gil Mahe 2 and Mohamed Meddi 3 1 Department of Civil Engineering, Istanbul Technical University, 34469 Istanbul, Turkey 2 IRD, UMR HSM IRD/ CNRS/ University Montpellier, Place E. Bataillon, 34095 Montpellier, France 3 Ecole Nationale Supérieure d’Hydraulique, LGEE, Blida 9000, Algeria * Correspondence: [email protected] Received: 27 May 2019; Accepted: 9 August 2019; Published: 12 August 2019 Abstract: Climate and anthropogenic changes impact on the erosion and sediment transport processes in rivers. Rainfall variability and, in many places, the increase of rainfall intensity have a direct impact on rainfall erosivity. Increasing changes in demography have led to the acceleration of land cover changes from natural areas to cultivated areas, and then from degraded areas to desertification. Such areas, under the effect of anthropogenic activities, are more sensitive to erosion, and are therefore prone to erosion. On the other hand, with an increase in the number of dams in watersheds, a great portion of sediment fluxes is trapped in the reservoirs, which do not reach the sea in the same amount nor at the same quality, and thus have consequences for coastal geomorphodynamics. The Special Issue “Modeling and Practice of Erosion and Sediment Transport under Change” is focused on a number of keywords: erosion and sediment transport, model and practice, and change. The keywords are briefly discussed with respect to the relevant literature. The papers in this Special Issue address observations and models based on laboratory and field data, allowing researchers to make use of such resources in practice under changing conditions.
    [Show full text]
  • Bedload Equation for Ripples and Dunes
    Bedload Equation for Ripples and Dunes GEOLOGICAL SURVEY PROFESSIONAL PAPER 462-H Bedload Equation for Ripples and Dunes By D. B. SIMONS, E. V. RICHARDSON, and C. F. NORDIN, JR. SEDIMENT TRANSPORT IN ALLUVIAL CHANNELS GEOLOGICAL SURVEY PROFESSIONAL PAPER 462-H An examination of conditions under which bed- load transport rates may be determined from the dimensions and speed of shifting bed forms UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1965 UNITED STATES DEPARTMENT OF THE INTERIOR STEWART L. UDALL, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 - Price 20 cents (paper cover) CONTENTS Page Page Symbols. _______________________ ___________________ IV Bedload Transport __ ______________ . _____ ___ __ HI Abstract __ __________ ___ ___ .__._--_____._..___ HI Conclusions_______________ ________ _________ _ ____ 7 Introduction ____________________ _______ _ 1 References cited. ___________________ _ __ ___________ 9 ILLUSTRATIONS Page FIGURES 4-7. Relation of Page FIGURE 1. Definition sketch of dunes. H2 4. V.to(V-V H5 . Vs 2. Comparison of computed bedload with 5. 6 observed bed-material load__________ 3 V-VQ g 6. h to 3. Comparison of computed and observed (V V\ bedload.___________________________ 7. qriOToV[~y~ )______ _______ 8 TABLE Page TABLE 1. Variables considered. H2 m LIST OF SYMBOLS C Chezy coefficient Ci A constant D Mean depth g Accleration due to gravity h Average ripple or dune amplitude KI, K2) Ka, KI, K5 Constants q_b Bedload, by volume or weight qr Bed material load S Slope of the energy gradient t Time V Mean velocity VQ Noneroding mean velocity Vs Average velocity of ripples or dunes in the direction of flow x Distance parallel to the direction of flow y Elevation of the bed above an arbitrary horizontal datum 7 Unit weight of the fluid 5 A transformation, 5=x Vst TO The shear stress at the bed X Porosity of the sand bed d Partial derivative SEDIMENT TRANSPORT IN ALLUVIAL CHANNELS BEDLOAD EQUATION FOR RIPPLES AND DUNES By D.
    [Show full text]
  • BUIL])ING STON.E O·F WASHINGTON
    BUIL])ING STON.E o·f WASHINGTON By WAYNE S. MOEN Washington Department of Conservation Division of Mines and Geology Bulletin No. 55 1967 State of Washington DANIEL J. EV ANS, Governor Department of Conservation H. MAURICE AHLQUIST, Director DIVISION OF MINES AND GEOLOGY MARSHALL T. HUNTTING, Supervisor Bulletin No. 55 BUILDING STONE OF WASHINGTON By WAYNE S. MOEN STATE PRINTING PLANT. OLYMPI A , WASHINGTON 1967 For sale by Department Pof? ceConsl]SliARYervation, Olympia, Washington. PACIFIC NORTHWEST FOREST AND RANGE EXPERIMENT STATION etnDTLAND. OR£00N CONTENTS Poge Introduction 7 General history .. ...... ...........................•............ 8 Production and vo lue . 10 Forms of building stone . 12 Field stone . 12 Rough building stone . 13 Rubble . • . 14 Flogging (flagstone) . 14 Ashlar . .. ......... ........ , ................. , . , . 15 Crushed stone . 16 Terrozzo . 17 Roofing granules.............. .... ..... ......... 18 Exposed aggregate . 18 Reconstituted stone . • . 19 Landscape rock . 20 Area coverage of bui Iding stone . 21 Acquisition of bui )ding stone . 22 Examination of stone deposits . 23 General quarrying methods . 24 Physical properties of building stone . 26 Strength . 26 Hardness and workabi Iity . • . 27 Color . 28 Alteration ....•...................... , ........... , . 29 Porosity and absorption ...........•. : . 31 Testing of building stone... .. .................... ................ 33 Common building stones of Washington . 34 Granite . 35 Geology and distribution . 35 Physical properties . 38 Varieties
    [Show full text]
  • Part 629 – Glossary of Landform and Geologic Terms
    Title 430 – National Soil Survey Handbook Part 629 – Glossary of Landform and Geologic Terms Subpart A – General Information 629.0 Definition and Purpose This glossary provides the NCSS soil survey program, soil scientists, and natural resource specialists with landform, geologic, and related terms and their definitions to— (1) Improve soil landscape description with a standard, single source landform and geologic glossary. (2) Enhance geomorphic content and clarity of soil map unit descriptions by use of accurate, defined terms. (3) Establish consistent geomorphic term usage in soil science and the National Cooperative Soil Survey (NCSS). (4) Provide standard geomorphic definitions for databases and soil survey technical publications. (5) Train soil scientists and related professionals in soils as landscape and geomorphic entities. 629.1 Responsibilities This glossary serves as the official NCSS reference for landform, geologic, and related terms. The staff of the National Soil Survey Center, located in Lincoln, NE, is responsible for maintaining and updating this glossary. Soil Science Division staff and NCSS participants are encouraged to propose additions and changes to the glossary for use in pedon descriptions, soil map unit descriptions, and soil survey publications. The Glossary of Geology (GG, 2005) serves as a major source for many glossary terms. The American Geologic Institute (AGI) granted the USDA Natural Resources Conservation Service (formerly the Soil Conservation Service) permission (in letters dated September 11, 1985, and September 22, 1993) to use existing definitions. Sources of, and modifications to, original definitions are explained immediately below. 629.2 Definitions A. Reference Codes Sources from which definitions were taken, whole or in part, are identified by a code (e.g., GG) following each definition.
    [Show full text]
  • Descriptions of Common Sedimentary Environments
    Descriptions of Common Sedimentary Environments River systems: . Alluvial Fan: a pile of sediment at the base of mountains shaped like a fan. When a stream comes out of the mountains onto the flat plain, it drops its sediment load. The sediment ranges from fine to very coarse angular sediment, including boulders. Alluvial fans are often built by flash floods. River Channel: where the river flows. The channel moves sideways over time. Typical sediments include sand, gravel and cobbles. Particles are typically rounded and sorted. The sediment shows signs of current, such as ripple marks. Flood Plain: where the river overflows periodically. When the river overflows, its velocity decreases rapidly. This means that the coarsest sediment (usually sand) is deposited next to the river, and the finer sediment (silt and clay) is deposited in thin layers farther from the river. Delta: where a stream enters a standing body of water (ocean, bay or lake). As the velocity of the river drops, it dumps its sediment. Over time, the deposits build further and further into the standing body of water. Deltas are complex environments with channels of coarser sediment, floodplain areas of finer sediment, and swamps with very fine sediment and organic deposits (coal) Lake: fresh or alkaline water. Lakes tend to be quiet water environments (except very large lakes like the Great Lakes, which have shorelines much like ocean beaches). Alkaline lakes that seasonally dry up leave evaporite deposits. Most lakes leave clay and silt deposits. Beach, barrier bar: near-shore or shoreline deposits. Beaches are active water environments, and so tend to have coarser sediment (sand, gravel and cobbles).
    [Show full text]
  • Erosion and Sediment Transport
    Erosion and sediment transport Lecture content Skript: Ch. VIII – rationale for understanding and modelling erosion and sediment transport processes – surface erosion – mechanisms – interaction with climate, land cover and topography – annual scale surface erosion model – sediment transport in streams – mechanisms – measurements – sediment characterisation – condition for incipient motion – sediment transport equation Hydrology – Erosion and Sediment Transport – Autumn Semester 2017 1 Erosion and sediment transport is driven • by hydrological processes in the watershed • by stream hydraulics in rivers plays an important role with regard to • evolution of landscape • loss of agricultural soils • stability of river beds • water resources infrastructures (dams, …) • natural hazards • coastal processes ⤵ Brienzersee,)Hochwasser)2005) Hochwasser/Murgang) Copyright © Philip Owens 2002 Hydrology – Erosion and Sediment Transport – Autumn Semester 2017 2 Examples of effects of erosion and sediment transport on water infrastructures • filling in of reservoirs – reduces the active volume of the reservoir intake – can put at risk the correct operation of the reservoir organs (e.g. intakes) multipurpose • river bed aggradation reservoir deposited sediments = dead volume – due to sediment deposition after a flood event – due to imbalance between sediment supply from upstream and flow energy • scour in river beds and embankment erosion – undermines the stability of river cross sections • pumps and turbines ⤵ • water supply derivations • ecosystems •
    [Show full text]
  • Sandstone Problems
    CONSERVATION TALK Michael Trinkley Why Sandstone Monuments Have So Many Problems Whether in the Carolinas, Utah or Massachusetts biggest cause is the effect of moisture, brought on by many sandstone are in very poor condition. Why? And capillary action, humidity and even a monument's perhaps even more importantly, what can be done? environment and micro-climate. Sources not related to Sandstone is a sedimentary rock, meaning that moisture include solar and UV radiation, as well as minerals or organic particles have settled in layers and the structural issues-although I don't believe any of these layers have gradually formed into rock. They often (but not are as important as moisture. Contributing to the always) have distinct bedding planes-or layers. Geologists problems caused by moisture are salts and air pollution. generally divided sedimentary rocks into three categories So let's look at a few of the more common problems. and most of what we see in cemeteries may be classified as Keep in mind that relatively little conservation research "clastic." These are formed by the accumulation of has been conducted concerning these problems, so there mechanically distintegrated rocks that are cemented remains much debate-and few simple answers. together. Air pollution can cause what are known as Sandstones are composed of quartz, feldspar, silicates, pollution crusts-often hard and brittle, leaving the stone mica, hornblende, and clay minerals that are cemented with beneath soft, friable, and disaggregating. They may also either siliceous or carbonate/calcite cement (see Table 1). It be known as carbon deposits. Found in urban settings is largely these cementing materials that affect the they are formed from pollution products, including longevity of one sandstone over another.
    [Show full text]
  • Tectonically Quiescent Drainage, Song Gianh, Central Vietnam 3
    1 Controls on Erosion Patterns and Sediment Transport in a Monsoonal, 2 Tectonically Quiescent Drainage, Song Gianh, Central Vietnam 3 4 Tara N. Jonell1∗, Peter D. Clift1, Long Van Hoang2, Tina Hoang3, Andrew Carter4, Hella 5 Wittmann5, Philipp Böning6, Katharina Pahnke6 and Tammy Rittenour7 6 7 1 – Department of Geology and Geophysics, Louisiana State University, Baton Rouge, 8 LA 70803, USA 9 2 - Hanoi University of Mining and Geology, Duc Thang, North Tu Liem, Ha Noi, 10 Vietnam 11 3 - School of Geosciences, University of Louisiana at Lafayette, Lafayette LA 70504, 12 USA 13 4 - Department of Earth and Planetary Sciences, Birkbeck College, London, WC1E 7HX, 14 United Kingdom 15 5- Helmholtz Centre Potsdam, GFZ German Research Center for Geosciences, 16 Telegrafenberg, 14473 Potsdam, Germany 17 6- Max Planck Research Group for Marine Isotope Geochemistry, Institute for Chemistry 18 and Biology of the Marine Environment (ICBM), University of Oldenburg, 26129 19 Oldenburg, Germany 20 7 - Department of Geology, Utah State University, Logan UT 84322, USA 21 22 Abstract 23 Keywords: provenance, erosion, monsoon, Vietnam 24 The Song Gianh is a small, monsoon-dominated river in northern central Vietnam 25 that can be used to understand how topography and climate control continental erosion. 26 We present major element concentrations, together with Sr and Nd isotopic compositions, 27 of siliciclastic bulk sediments to define sediment provenance and chemical weathering 28 intensity. These data indicate preferential sediment generation in the steep, wetter upper 29 reaches of the Song Gianh. In contrast, detrital zircon U-Pb ages argue for significant flux 30 from the drier, northern Rao Tro tributary.
    [Show full text]
  • Maggie Williams Particle Size, Shape and Sorting: What Grains Can Tell Us
    Particle size, shape and sorting: what grains can tell us Maggie Williams Most sediments contain particles that have a range of sizes, so the mean or average grain size is used in description. Mean grain size of loose sediments is measured by size analysis using sieves Grain size >2mm Coarse grain size (Granules<pebble<cobbles<boulders) 0.06 to 2mm Medium grain size Sand: very coarse-coarse-medium-fine-very fine) <0.06mm Fine grain size (Clay<silt) Difficult to see Remember that for sediment sizes > fine sand, the coarser the material the greater the flow velocity needed to erode, transport & deposit the grains Are the grains the same size of different? What does this tell you? If grains are the same size this tells you that the sediment was sorted out during longer transportation (perhaps moved a long distance by a river or for a long time by the sea. If grains are of different sizes the sediment was probably deposited close to its source or deposited quickly (e.g. by a flood or from meltwater). Depositional environments Environment 1 Environment 2 Environment 3 Environment 4 Environment 5 Environment 6 Sediment size frequency plots from different depositional environments • When loose sediment collected from a sedimentary environment is washed and then sieved it is possible to measure the grain sizes in the sediment accurately. • The grain size distribution may then be plotted as a histogram or as a cumulative frequency curve. • Sediments from different depositional environments give different sediment size frequency plots. This shows the grain size distribution for a river sand.
    [Show full text]