DOCSLIB.ORG

Mechanisms of Sediment Compaction Responsible

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Mechanisms of Sediment Compaction Responsible MECHANISMSOF SEDIMENT COMPACTIONRESPONSIBLE FOR OIL FIELD SUBSIDENCE. A thesis submitted to the University of London (University College London) for the degree of Doctor of Philosophy in the Department of Geological Sciences. by Michael Anthony Addis October 1987 -1- to my parents for all their encouragement -11- Abstract During the production of a hydrocarbon reservoir, the compaction of weakly cemented sedimentary materials can result from increases in effective stress, and lead to surface subsidence. Such a phenomenon has recently been observed in the oil and gas bearing chalk fields in the Central North Sea. In order to evaluate the compaction potential of sedimentary materials during exploitation of a reservoir, laboratory experiments- were performed on chalks and clays. These experiments were predominantly'Ký (zero lateral strain) tests. The tests were performed in a high pressure triaxial cell, the development of which continued throughout the experimental 'programme. Tests performed on chalks from the Central North Sea, and from two in onshore sites southern -England showed similar deformational trends. The analyses of these results concentrated on the variables of testing and the possible errors resulting from the use of laboratory data in the modelling of field situations. The analyses of the tests also include a comparison between the experimental methods and the interpretation of the results of this study and those of other workers on the subject of reservoir compaction. A parametric description of the compaction of chalk is presented as a summary to these tests. w Two compaction tests on clay samples from the Central North Sea were also undertaken. The clays were uncemented and show contrasting behaviour to the chalks. These tests were performed to evaluate the amount of compaction likely to occur in the overburden of a hydrocarbon reservoir during production. The results of the deformational trends obtained from this study -111- are compared to those obtained by other workers, with particular reference to the changes in physical parameters during compaction. This follows a literature survey into hydrocarbon reservoir compaction. The K0 tests performed in this study are thought to represent the condition of sediment burial in a tectonically inactive basin. This subject is briefly reviewed, and the relevance of the results presented earlier discussed in terms of the prediction of stresses existing within differing lithologies. The analysis of the results have been performed using parameters commonly in used soil mechanics, this seemed to be appropriate for the deformations undergone by the materials used in this study. -1V- Acknowledgements During the period of research the author has been in receipt of a Natural Environment Research Grant, whibh is duly acknowledged. During the three years of research the author has been associated with three colleges in the University of London. The first two years of the research were performed while a student at the Geology Department of King's College, now sadly "mergered" in outer London. The final year was spent as a student of University College. During the three years, the experimental" work was performed in the soil laboratories in the Department 'of Civil Engineering, at Imperial College. As such I am indebted to many people from the three institutions to numerous to mention. I would however like to thank the chief technicians from King's and University College, Mr. J Congram and Mr. R Dudman respectively, for ensuring relatively few hickups along the way. I would especially like to thank the technical staff of the soil laboratories who have provided excellent support to this study, with much input into the equipment design and construction, as well as many other subject areas. I am sure that without their expertise, help and patience this study would not have been possible. Mr. S. Ackerley, Mr. L. Spall, Mr. G. Keefe, Mr. A. Bolsher and Mr. R. Hare are gratefully acknowledged. I would also like to thank Mrs. E. Gibbs for all her help, and for her forgiveness during times of oil leaks. Particular thanks are given to Mr. S. Ackerley whose enthusiasm, general willingness to do the impossible and his patience with an ignorant geologist is gratefully appreciated. Technical help was also provided by Mr. T. Osbourne and Mr. S. at -V- University College and Mr. R. Giddons in the Department of geological sciences, Imperial college who are duely thanked. During the initial set up of the apparatus the help of Mr. B. Clarke in the Engineering Geology section in Imperial College was sought and willingfully obtained on many occasions; Iwould like to express my thanks for his help and advice. My period of work at the soils laboratory, Imperial College was a true education and I must thank my colleagues in this group for answering my many questions patiently., regardless of the elementary nature of these, and for their encouragement during this study. My many thanks *go to Mr A. J. Bond, Dr. G. T. Dounias, Mr. D. French, Mr. J. Hellings, Mrs. G. N. Georgiannou Lesas, Dr. M. Maccarini, Mr. M. Mahmoud, Dr. J. Maswoswe, Mr. D. L. Nyaoro, Dr. E. Ovando-Shelley, Mr. D. Schreiner, Dr. S. Shibuya and Mr. D. Toll, Mrs. T. Tika Vaffilikos. I would also like to thank Dr. M. Maccarini for our many discussions on the behaviour of cemented materials and his ready exchange of ideas. The help of Mr. D. Toll and use of his computer software. expertise and for the calculation of results is gratefully appreciated. Use of software developed by Mr. A. J. Bond for the 3-dimensional plots is also gratefully appreciated by the author. I am very grateful to have been able to work at the soil mechanics laboratories, and as such I must thank the head of the soil mechanics section, Prof. J. B. Burland for this opportunity. I would also like to express my gratitude to the academic staff of the section, Dr. R. J. Chandler, Prof. J. N. Hutchinson, Dr. R. Jardine, Dr. S. Leroueil (visiting academic), Dr. D. M. Potts, Prof. A. W. Skempton, Dr. P. R. Vaughan and particularly Dr. A. E. Skinner, for many stimulating and enlightening discussions. Many thanks go to the Norwegian Petroleum Directorate for allowing -vi- me the opportunity of working on samples obtained from the North Sea. I would especially like to thank Mr. K. Tonstad, Mr. 0. P. Berget and Mr. P. E. Overli, for many fruitful discussions. Colleagues at King's College and University College are also thanked for all their support and help in very many ways, my thanks go to Dr. H. Chen, Mr. M. J. Leddra, Mr A. Goldsmith, and Miss N. A. Yassir. I am especially grateful to Miss N. A. Yassir for correcting my grammar -a most unenviable task, many thanks. At this point I would like to express my gratitude to my numerous co-tenants/ colleagues for their patience with the author during the period of research, as well as for their welcome distractions and excellent company, these include Mr. H. Davies, Miss K. Jeffr*ey, Miss K. Lewin, Mr. J. Morris, Mr. A. Pritchard, Mr. M. Shaw, Dr. J. Williams, and Miss M. White. It only remains for me to thank my supervisor, Dr. M. E. Jones for his help and encouragement, and for directing me towards a very interesting area of study. His support is acknowledged and appreciated especially in times of critisism from the author. I would finally like to express my appreciation to my family and especially-to my parents, who have always encouraged and supported me, not only through this period of research, but through my whole education, the good and not so good times. My thanks are insufficient to express my gratitude. -vii- Contents i Title ............... 111 Abstract ............... Acknowledgements Contents .............. viii List-of figures ............... Xl List tables of ............... xvi Glossary terms of ............. xviii Chapter 1 Introduction 1 ............... Chapter 2 Aspects 8 of compaction ............... 2.1 Introduction 8 ............... 2.2 The 10 principle of effective stress ............... 2.3 Undrained pore pressure response ............... 18 2.3.1 Sample 20 saturation ............... 2.4 One dimensional 21 consolidation ............... 2.5 Representations in 24 of stress states sediments ........... 2.5.1 Stress paths ............... 24 2.5.2 Critical state model ............... 28 2.6 Mechanical behaviour of chalks ............... 34 2.6.1 Behaviour bonded of particulate materials ........ 34 2.6.2 Stress-strain characteristics of weakly cemented sedimentary materials ............... 39 2.6.3 Compaction 42 of chalk .............. 2.6.3. i Normal 42 consolidation ............... 2.6.3. ii Secondary 49 consolidation/creep ............. 2.6.3. iii Summary 50 of salient points ............... 2.7 Strain 50 rate effects ............... 2.8 Effects temperature 59 of on consolidation ............... Chapter 3 Experimental 66 methodology and materials .............. 3.1 Introduction 66 ............... 3.2 The 68 coefficient of earth pressure at rest ............... 3.2.1 Introduction 68 ............... 3.2.2 Relationships 71 of Ko ............... 3.2.2. i Ko 0' 71 relationship ............... 3.2.2.11 K° 73 --V relationship ............... 3.2.3 Laboratory determination 74 of K ............... 3.2.3.1 Requirements 74 for the K° test .............. 3.2.3. ii Methods of measuring K° during 75 zero lateral strain tests ............... 3.2.3. iii Recommendations for lateral strains 77 during K tests ............... 3.2.4 K high 78 at stresses .. "............ 3.2°. 4. i Previous K 78 high pressure experiments ..... 3.2.4. ii K derived from angles o? internal friction ............... 79 -viii- 80 3.3 Constant rate of strain tests ............... 80 3.3.1 Introduction ............... 81 3.3.2 Interpretation of the CRS test ............... 90 3.4 Compaction tests in the high pressure oedometer ......... 91 3.5 Materials used in this study ............... 91 3.5.1 Introduction ............... 91 3.5.2 The geology of chalk ..............
Load more

Recommended publications
  • Sediment Diagenesis
    Sediment Diagenesis http://eps.mcgill.ca/~courses/c542/ SSdiedimen t Diagenes is Diagenesis refers to the sum of all the processes that bring about changes (e.g ., composition and texture) in a sediment or sedimentary rock subsequent to deposition in water. The processes may be physical, chemical, and/or biological in nature and may occur at any time subsequent to the arrival of a particle at the sediment‐water interface. The range of physical and chemical conditions included in diagenesis is 0 to 200oC, 1 to 2000 bars and water salinities from fresh water to concentrated brines. In fact, the range of diagenetic environments is potentially large and diagenesis can occur in any depositional or post‐depositional setting in which a sediment or rock may be placed by sedimentary or tectonic processes. This includes deep burial processes but excldludes more extensive hig h temperature or pressure metamorphic processes. Early diagenesis refers to changes occurring during burial up to a few hundred meters where elevated temperatures are not encountered (< 140oC) and where uplift above sea level does not occur, so that pore spaces of the sediment are continually filled with water. EElarly Diagenesi s 1. Physical effects: compaction. 2. Biological/physical/chemical influence of burrowing organisms: bioturbation and bioirrigation. 3. Formation of new minerals and modification of pre‐existing minerals. 4. Complete or partial dissolution of minerals. 5. Post‐depositional mobilization and migration of elements. 6. BtilBacterial ddtidegradation of organic matter. Physical effects and compaction (resulting from burial and overburden in the sediment column, most significant in fine-grained sediments – shale) Porosity = φ = volume of pore water/volume of total sediment EElarly Diagenesi s 1.
    [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]
  • Sedimentary Test 2 Review Guide Making Sedimentary Rocks 1
    Name: KEY Unit III: Section 3: Sedimentary Processes Earth & Environmental Systems Science Test 2 Review Guide Sedimentary Test 2 Review Guide Making Sedimentary Rocks 1. What vocabulary word describes turning sediment into solid rock? Lithification = compaction + cementation 2. List and describe the processes to form sediment and then a sedimentary rock in order? - Weathering – breaking down - Erosion – moving/transporting sediment - Deposition – putting sediment into place Sediment MADE! Lithification: Turning sediment into a solid rock -Compaction – generally through burial and reduces pore space -Cementation – gluing sediment together using a mineral water solution Sedimentary Rock MADE! 3. What acts as glue to form Clastic and Bioclastic textured sedimentary rocks? Water moves through soil and rocks and dissolves minerals along the way. The mineral water solution settles in the sediment, the water evaporates, and the minerals are left behind to bind sediment. Uniformitarianism and Stratigraphy 4. What geological principle states that the same processes that operate today also operated in the past? Uniformitarianism – James Hutton 5. List and describe the 3 laws of Stratigraphy: -Law of Horizontal Deposition – Sediment is deposited and lithified in flat layers -Law of Superposition – oldest layers are on the bottom and youngest is on the top -Law of Cross-cutting – anything that cuts across sedimentary layers (faults or igneous intrusions) are younger than the layers that they cut across 6. What is an unconformity? Any process that disturbs sedimentary layers 7. List and describe the 3 types of unconformities: -Angular – beds are tilted (by plate tectonics), weathered and eroded, and new beds are placed on top at a different angle -Nonconformity – Igneous beds eat through sedimentary beds from the bottom -Disconformity – Sedimentary beds are missing due to weathering and erosion generally drawn as a straight squiggly line.
    [Show full text]
  • Scientist Guide the Crayon Rock Cycle
    Scientist Guide The Crayon Rock Cycle Introduction Soil is one of Earth’s most important natural resources. It is the bridge between the living and non- living worlds and ultimately where most of our food originates. Soil is composed of organic materi- al (humus), water, air and minerals. Rocks are mixtures of minerals such as quartz, feldspar, mica and calcite. They are the source of all soil mineral material and the origin of all plant nutrients with the exception of nitrogen, hydrogen and carbon. As rock is chemically and physically weathered, eroded and precipitated, it is trans- formed into soil. The rock cycle shows how rocks change over time by a variety of physical and chemical processes (see Figure 1). Natural processes that are part of the rock cycle include weathering, erosion, lithifi- cation, metamorphism, melting and cooling. • Weathering involves both the chemical and physical IGNEOUS ROCK Weathering breakdown of rock at or near the Earth’s surface. and Erosion Cooling This results in accumulation of sediments – loose materials, such as rock and mineral fragments, or Sediment Magma pieces of animal and plant remains that have been transported. Lithification (Compaction and Cementation) Melting • Erosion is the process by which soil and rock are removed from the Earth’s surface by exogenic SEDIMENTARY METAMORPHIC processes, such as wind or water flow, and then ROCK ROCK transported and deposited in other locations. Metamorphism (Heat and/or Pressure) • Lithification is the transformation of sediment into rock. The main processes involved in lithification are: Figure 1. o Cementation – large sediments are held together by natural cements.
    [Show full text]
  • SUBMERGENCE and EMERGENCE of Rock Layers with Respect to Sea Level
    SUBMERGENCE AND EMERGENCE of Rock Layers With Respect to Sea Level The building up and wearing away of Earth's Crust. Follow the progression of illustrations to see the roles that submergence and emergence of rock layers play in both the addition of rock material to earth's surface as well as its removal. The Key: Be sure to look at the key before observing the Illustration 1: Sedimentary Rocks are typically layered series of illustrations. horizontally and the Law of Superposition dictates that, Notice that not only do symbols exist for sandstone, shale unless overturning of rock layers has occurred, the oldest and conglomerate, but also for the loose sediments that rock layers are towards the bottom of a rock column while will eventually lithify to become these rock types. the youngest layers are at the top. This illustration depicts layers of sedimentary shale, sandstone and limestone, exposed at earth's surface. Illustration 2: The rock layers have been submerged, Illustration 3: Over time the processes of compaction possibly due to crustal movement or to a rise in sea level. and cementation will lithify these loose sediments turning All rock layers are now underwater and there exists the them into sedimentary rocks. The newly lithified rock possibility for additional, loose sediments to be deposited layer will be on top of the original layers shown in on top of the preexisting layers. Illustration 1 and it will be the youngest layer by L. Immoor 2006 Geoteach.com 1 comparison. Notice the unconformity in this illustration. The unconformity is evidenced by the wavy, eroded top surface of a rock layer.
    [Show full text]
  • Meulemans 2020
    Urban Pedogeneses. The Making of City Soils from Hard Surfacing to the Urban Soil Sciences Germain Meulemans To cite this version: Germain Meulemans. Urban Pedogeneses. The Making of City Soils from Hard Surfacing to the Urban Soil Sciences. Environmental Humanities, [Kensington] N.S.W.: Environmental Humanities Programme University of New South Wales, 2020, 12 (1), pp.250-266. 10.1215/22011919-8142330. hal-02882863 HAL Id: hal-02882863 https://hal.archives-ouvertes.fr/hal-02882863 Submitted on 27 Jun 2020 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Urban Pedogeneses The Making of City Soils from Hard Surfacing to the Urban Soil Sciences GERMAIN MEULEMANS Centre Alexandre-Koyré, IFRIS, France Abstract This article examines the rise of urban soils as a topic of scientificinquiryandeco- logical engineering in France, and questions how new framings of soil as a material that can be designed reconfigure relationships between urban life and soils in a context of fast- growing cities. As a counterpoint to the current situation, the article first examines how the hard-surfacing of Paris, in the nineteenth century, sought to background the vital qualities of soils in urban areas, making their absence seem perfectly stable and natural.
    [Show full text]
  • Why and How Do We Study Sediment Transport? Focus on Coastal Zones and Ongoing Methods
    water Editorial Why and How Do We Study Sediment Transport? Focus on Coastal Zones and Ongoing Methods Sylvain Ouillon ID LEGOS, Université de Toulouse, IRD, CNES, CNRS, UPS, 14 Avenue Edouard Belin, 31400 Toulouse, France; [email protected]; Tel.: +33-56133-2935 Received: 22 February 2018; Accepted: 22 March 2018; Published: 27 March 2018 Abstract: Scientific research on sediment dynamics in the coastal zone and along the littoral zone has evolved considerably over the last four decades. It benefits from a technological revolution that provides the community with cheaper or free tools for in situ study (e.g., sensors, gliders), remote sensing (satellite data, video cameras, drones) or modelling (open source models). These changes favour the transfer of developed methods to monitoring and management services. On the other hand, scientific research is increasingly targeted by public authorities towards finalized studies in relation to societal issues. Shoreline vulnerability is an object of concern that grows after each marine submersion or intense erosion event. Thus, during the last four decades, the production of knowledge on coastal sediment dynamics has evolved considerably, and is in tune with the needs of society. This editorial aims at synthesizing the current revolution in the scientific research related to coastal and littoral hydrosedimentary dynamics, putting into perspective connections between coasts and other geomorphological entities concerned by sediment transport, showing the links between many fragmented approaches of the topic, and introducing the papers published in the special issue of Water on “Sediment transport in coastal waters”. Keywords: sediment transport; cohesive sediments; non cohesive sediments; sand; mud; coastal erosion; sedimentation; morphodynamics; suspended particulate matter; bedload 1.
    [Show full text]
  • Compaction Trend and Its Implication in the Overpressures Estimate for the Formations of the Colombian Foothills of the Eastern Plains
    COMPACTION TREND AND ITS IMPLICATION IN THE OVERPRESSURES ESTIMATE FOR THE FORMATIONS OF THE COLOMBIAN FOOTHILLS OF THE EASTERN PLAINS Javier-Oswaldo Mendoza1*, Jael-Andrea Bueno2, Darwin Mateus3* and Luis-Eduardo Moreno4 1 Universidad Industrial de Santander, Bucaramanga, Santander, Colombia 2 Universidad Industrial de Santander, Bucaramanga, Santander, Colombia 3 Ecopetrol S.A. – Instituto Colombiano del Petróleo, A.A. 4185 Bucaramanga, Santander, Colombia 4 Universidad Industrial de Santander, Bucaramanga, Santander, Colombia e-mail: [email protected] [email protected] (Received, April 15, 2009; Accepted June 16, 2010) he main objective of this article is to raise a hypothesis to explain the main causes of overpressure in the formations of the Tertiary sequence for the stratigraphic column of the Colombian Foothill. For Tthis purpose it was conducted an analysis of compaction trends from the Guayabo Formation until the unit C8 of the Carbonera Formation; in the area of foreland, where the tectonic affectation has been minimal. This analysis integrates the most representative basins modeling and tectono-stratigraphic events for such sedimentary sequence. It mapped overpressure areas, comparing them with geological parameters such as the subsidence, uplift, heat flow and speeds of sedimentation, to identify relations of these parameters with the overpressure of the area. As the main result, it stresses the identification of different sedimentation and compacting rates for each tectono-stratigraphic sequence and its relationship with the overpressure of the formations. These differences are represented in specific equations presented in this work. One of the main conclusions relates the rapid uplift of the basin, occurred in mid Miocene and the lack of liberation of stresses; as one of the causes of the pressures that are currently observed.
    [Show full text]
  • Chapter 6: Sedimentary and Metamorphic Rocks
    66 SediSedimentarymentary What You’ll Learn andand • How sedimentary rocks are formed. • How metamorphic rocks are formed. MMetamorphicetamorphic • How rocks continuously change from one type to another in the rock cycle. RRockockss Why It’s Important Sedimentary rocks pro- vide information about surface conditions and organisms that existed in Earth’s past. In addition, mineral resources are found in sedimentary and metamorphic rocks. The rock cycle further pro- vides evidence that Earth is a dynamic planet, con- stantly evolving and changing. To find out more about sedimentary and metamor- phic rocks, visit the Earth Science Web Site at earthgeu.com Mount Kidd, Alberta, Canada 120 DDiscoveryiscovery LLabab Model Sediment Layering Sedimentary rocks are usually 4. Quickly turn the jar upright and found in layers. How do these layers set it on a flat surface. form? In this activity, you will investi- Observe In your science journal, gate how layers form from particles draw a diagram of what you observe. that settle in water. What type of parti- 1. Obtain 100 mL of soil from a loca- cles settled out first? tion specified by your teacher. What type of parti- Place the soil in a tall, narrow, jar. cles form the topmost layers? How is this 2. Add water to the jar until it is activity related to the three-fourths full. Put the lid on layering that occurs the jar so that it is tightly sealed. in sedimentary rocks? 3. Pick up the jar with both hands and turn it upside down several times to mix the water and soil.
    [Show full text]
  • The Influence of Soil Compaction on Runoff Formation. a Case Study
    geosciences Article The Influence of Soil Compaction on Runoff Formation. A Case Study Focusing on Skid Trails at Forested Andosol Sites Julian J. Zemke * , Michel Enderling, Alexander Klein and Marc Skubski Department of Geography, Institute for Integrated Natural Sciences, University Koblenz-Landau, Campus Koblenz, 1, 56070 Koblenz, Germany; [email protected] (M.E.); [email protected] (A.K.); [email protected] (M.S.) * Correspondence: [email protected]; Tel.: +49-261-287-2282 Received: 11 March 2019; Accepted: 6 May 2019; Published: 8 May 2019 Abstract: This study discusses the influence of soil compaction on runoff generation with a special focus on forested Andosol sites. Because of their typical soil physical characteristics (low bulk density, high pore volumes) and the existent land use, these areas are expected to show low to no measurable overland flow during heavy rainfall events. However, due to heavy machinery traffic in the course of forestry actions and pumice excavations, skid trails have been established. Here, a distinct shift of soil dry bulk density (DBD) was observable, using a detailed soil mapping and data interpolation in order to generate in-depth DBD-cross profiles. Additionally, infiltration measurements and rainfall simulations (I = 45 mm h 1, t = 30 min) were conducted to evaluate effects · − of observed soil compaction on infiltration rates and overland flow formation. Results show that soil compaction was increased by 21% on average in skid trail wheel ruts. As a consequence, observed runoff was 8.5-times higher on skid trails, while saturated hydraulic conductivity was diminished by 36%. These findings show, that soil compaction leads to a higher possibility of runoff formation during heavy rainfall events, especially at sites which showed initial conditions with presumably low tendencies of runoff formation.
    [Show full text]
  • Seismic Expression and Geological Significance of a Lacustrine Delta in Neogene Deposits of the Western Snake River Plain, Idaho1
    Seismic Expression and Geological Significance of a Lacustrine Delta in Neogene Deposits of the Western Snake River Plain, Idaho1 Spencer H. Wood2 ABSTRACT provides insight into the history of Pliocene “Lake Idaho.” The present depth of the delta/prodelta facies High-resolution seismic reflection profiles and contact of 305 m (1000 ft) is 445 to 575 m (1460–1900 well data from the western Snake River plain basin ft) below the lake deposits on the margins. Estimated are used to identify a buried lacustrine delta system subsidence from compaction is 220 m (656 ft), and within Neogene Idaho Group sediments near Cald- the remaining 225 to 325 m (740–1066 ft) is attributed well, Idaho. The delta system is detected, 305 m to tectonic downwarping and faulting. (1000 ft) deep, near the center of the basin by The original lake area had been reduced to one progradational clinoform reflections having dips of third of the original 13,000 km2 (5000 mi2) by the 2–5°, a slope typical of prodelta surfaces of modern time the delta front prograded to the Caldwell area. lacustrine delta systems. The prodelta slope relief, The original lake area may have been sufficient to corrected for compaction, indicates the delta system evaporate most of the inflow, and the lake may have prograded northwestward into a lake basin 255 m only occasionally spilled into other basins. Dimin- (837 ft) deep. Resistivity logs in the prodelta mud ished area for evaporation later in the history of the and clay facies are characterized by gradual upward lake, combined with reduced evaporation accompa- increase in resistivity and grain size over a thickness nying onset of the ice ages, may have caused the of about 100 m (300 ft).
    [Show full text]
  • Sedimentary Rocks and the Rock Cycle
    Sedimentary Rocks and the Rock Cycle Designed to meet South Carolina Department of Education 2005 Science Academic Standards 1 Table of Contents What are Rocks? (slide 3) Major Rock Types (slide 4) (standard 3-3.1) The Rock Cycle (slide 5) Sedimentary Rocks (slide 6) Diagenesis (slide 7) Naming and Classifying Sedimentary Rocks (slide 8) Texture: Grain Size (slide 9), Sorting (slide 10) , and Rounding (slide 11) Texture and Weathering (slide 12) Field Identification (slide 13) Classifying Sedimentary Rocks (slide 14) Sedimentary Rocks: (slide 15) Clastic Sedimentary Rocks: Sandstone (16) , Siltstone (17), Shale (18), Mudstone (19) , Conglomerate (20), Breccia (21) , and Kaolin (22) Chemical Inorganic Sedimentary Rocks : Dolostone (23) and Evaporites (24) Chemical / Biochemical Sedimentary Rocks: Limestone (25) , Coral Reefs (26), Coquina and Chalk (27), Travertine (28) and Oolite (29) Chemical Organic Sedimentary Rocks : Coal (30), Chert (31): Flint, Jasper and Agate (32) Stratigraphy (slide 33) and Sedimentary Structures (slide 34 ) Sedimentary Rocks in South Carolina (slide 35) Sedimentary Rocks in the Landscape (slide 36) South Carolina Science Standards (slide 37) Resources and References (slide 38) 2 What are Rocks? Most rocks are an aggregate of one or more minerals and a few rocks are composed of non-mineral matter. There are three major rock types: 1. Igneous 2. Metamorphic 3. Sedimentary 3 Table of Contents Major Rock Types Igneous rocks are formed by the cooling of molten magma or lava near, at, or below the Earth’s surface. Sedimentary rocks are formed by the lithification of inorganic and organic sediments deposited at or near the Earth’s surface. Metamorphic rocks are formed when preexisting rocks are transformed into new rocks by elevated heat and pressure below the Earth’s surface.
    [Show full text]