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© CRC LEME 2007 Regolith What's all that about? Ian Roach MCA Lecturer, CRC LEME
© CRC LEME 2007 What is Regolith? Regolith is a word derived from: –rhegos (Gr.) = blanket or cover; and, –lithos (Gr.) = rock. Regolith literally means "rock blanket".
© CRC LEME 2007 What is Regolith? Term introduced by Merrill (1897). Redefined in Eggleton (2001): Or "Everything between fresh rock and fresh air"! "The entire unconsolidated or secondarily recemented cover that overlies coherent bedrock, that has been formed by weathering, erosion, transport and/or deposition of older material. The regolith thus includes fractured and weathered basement rocks, saprolites, soils, organic accumulations, volcanic material, glacial deposits, colluvium, alluvium, evaporitic sediments, aeolian deposits and groundwater."
© CRC LEME 2007 What is Regolith? Rowley Twidale (1990): Is there an image problem here? "The Regolith is a mass of weathered material that is charged with salts and biota....it is a suppurating mass that gradually consumes any blocks enclosed within it, and is gradually gnawing away at....the bedrock. In general, the regolith is a discontinuous, festering veneer…". In: Groundwater Geomorphology. Geological Society of America Special Publication 252.
© CRC LEME 2007 What is Regolith? What is regolith geoscience? –The science of the regolith and the landscapes in which it occurs. –The study of the inter- relationships between: The Lithosphere; The Hydrosphere; The Atmosphere; The Biosphere Modified after Taylor & Eggleton 2001
© CRC LEME 2007 What is Regolith? It is everything between fresh rock and fresh air. It includes: –weathered rock; –eruptive volcanic materials; –sediments; –gasses; –water; –biota.
© CRC LEME 2007 Regolith includes: Weathered rock: –physically weathered rock - fragments of the original; –chemically weathered rock - new minerals, solutions and resistate minerals; –at the earth's surface; –within solid, unweathered rock bodies around fractures and joints within the earth.
© CRC LEME 2007 Regolith includes: Sediments - mainly unconsolidated: –various environments - fluvial, slope deposits, lacustrine, marine, aeolian, glacial; –may be physico-chemical: Those derived by processes associated with: –Eh (electron potential) or redox reactions; –pH (hydrogen potential, or acid-base) changes; –saturation (evaporation). biochemical. –may be detrital: distribution controlled by hydraulics of water, air and ice.
© CRC LEME 2007 Regolith includes: Volcanic materials - fresh or weathered: –loose ash; –welded ash (ignimbrite); –lava; –hyaloclastite (explosively disrupted lava formed in water bodies).
© CRC LEME 2007 Regolith includes: Gasses: –most soil and regolith gasses are different in composition to surface air: < O 2 ; > N 2, CH 4, H 2 O.
© CRC LEME 2007 Regolith includes: Water: –contains many solutes: cations (Fe 2+, Ca 2+, Na +, etc.); anions (Cl -, HCO 3-, SO 4 2-, etc.). –aerosols.
© CRC LEME 2007 Regolith includes: Biota—an important and major part of the regolith. A wide variety of both "bugs" and plants occur including: plant roots; invertebrates (termites, worms, ants, etc.); micro-organisms (diatoms, bacteria, fungi, etc); occasional vertebrates (wombats, rabbits, etc.). Biota both physically and chemically affect the regolith.
© CRC LEME 2007 What is Regolith? Having said that, which is the regolith here...? Regolith Bedrock Modified after Taylor & Eggleton 2001
© CRC LEME 2007 What is Regolith?
© CRC LEME 2007 Where is Regolith? No easy answer. In Australia, regolith is everywhere. All of Australia has been exposed to weathering since the Tertiary, but some may be much older. Modified after Taylor & Eggleton 2001 after Beckmann 1983
© CRC LEME 2007 Where is Regolith? Australia 1:5 million regolith materials map Image courtesy Geoscience Australia
© CRC LEME 2007 Where is Regolith? Principal present global weathering types modified after Taylor & Eggleton 2001 after Thomas 1994
© CRC LEME 2007 Where is Regolith? Regolith is everywhere. Modern regolith processes are principally climate- controlled (except in areas with strongly active tectonics), thus similar weathering processes are occurring at similar latitudes, e.g., Australia, Southern Africa and South America, North America, Europe and Russia. Regolith may be modified by geologically recent events such as large-scale glaciation (North America, Europe, Russia) or desertification (North Africa, Middle East).
© CRC LEME 2007 Regolith and climate Strakhov (1967) described distribution & depth of weathering on a global scale. This is a reasonable 1st approximation of global regolith distribution. Modified after Taylor & Eggleton 2001
© CRC LEME 2007 Regolith and climate Most studies of global regolith distribution are climate-based; this is a major shortcoming. You will see that much of the regolith preserved in Australia is relict—it is not related to the current climate. Strakhov assumed tectonic stability and that regolith was thicker where climates are warmer and wetter. Reality tells us that regolith preservation is controlled largely by (neo)tectonics and that the present is not necessarily the key to the past!
© CRC LEME 2007 Why study Regolith? Now, having been through all of that… What possible advantage would a knowledge of regolith have for you?
© CRC LEME 2007 Ecology and biodiversity River Red Gum Mulga Casuarina sp. weathered bedrock Colluvial mantle buried palaeochannel extant channel chenopod shrubland
© CRC LEME 2007 National Parks Most national, etc., parks depend on scenery and/or ecological niches for their existence: Wilsons Promontory - dissected Cretaceous ? weathering profiles with younger weathering and materials; Kosciuszko - dissected planated and uplifted Mesozoic? land surface; Uluru - desert landscapes, monoliths; Kakadu - Quaternary and Proterozoic landscapes and ecology; Yosemite - glacial landscapes with active uplift due to hotspot volcanism; Stonehenge - regolith materials (sarsen stones or silcrete).
© CRC LEME 2007 Natural Resource Management Recent regolith work in Central western NSW: salts shown to be largely aeolian, minor rock weathering; salts stored in weathered rock (regolith); salt released by rising groundwaters; groundwater flow controlled by buried landscapes. Understanding salinity depends on weathering history; landscape evolution; climate past and present; realization that Australia has always been salty.
© CRC LEME 2007 Greenhouse –As rocks weather they consume CO 2 : they tend to become carbonated at Earth's surface, especially under arid conditions. –Additional CO 2 creates additional carbonic acid, creating more weathering. –Weathering buffers greenhouse in the long term.
© CRC LEME 2007 Engineering 2:1 lattice clays and self-mulching clay soils expand when wetted (smectite 9.6 Å dry - 15.5 Å wet), strong pressures are developed during wetting/drying. Optical fibre cable laying is a problem; cables can be progressively strained and snapped in swelling soils. Building foundations in swelling ground must be specially treated. Road pavement stabilization a problem in areas with swelling ground. Aggregate from regolith materials for road/rail base (silcrete, calcrete, ferricrete). Each with own problems.
© CRC LEME 2007 Agriculture All agriculture occurs within the regolith What about hydroponics? –Where do they get their fertilisers from? Agriculture strongly relies on the upper part of the regolith, soil. Regolith studies are crucial for soil management: Stability/erodability; Salinity issues; Plant health (soil nutrient deficiencies/overabundances).
© CRC LEME 2007 Mineral exploration Positive effects of regolith processes: –larger target halo; –Useful sampling media: Regolith carbonates and Au; Ferruginous regolith and base metals/Au/PGE; Biota and base metals/Au/PGE Negative effects of regolith processes: –deposits hidden by transported regolith. Need to first understand regolith structure and landscape relationships, then choose appropriate sampling media and exploration strategies.
© CRC LEME 2007 CommodityReservesProduction (t)Export Value ($M) Bauxite5.7x10 9a 56.6x10 6a $126 a Aluminana16.7x10 6c $4,110 c Gold + 5,589t a 258 c $5,551 c Iron ore14.6x10 9 t a 234x10 6c $8,101 c Magnesite930x10 6a 3.83x10 6a na Manganese133x10 6a 3.4x10 6c$ 399 c Diamond59x10 6 c a 20.6x10 6 c c $456.1 c Claysna59.7x10 3c $12.4 c Gypsumna3.94x10 6b $15.1 c Opalnana$47.28 c Alluvial sapphiresnana$1.08 c Ilmenite217x10 6 t a 1.93x10 6c $77.0 c Rutile20.2x10 6 t a 163x10 3c $98.2 c Zircon30x10 6 t a 441x10 3c $285 c Saltna11.2x10 6c $194.6 c $19,473.76 Resources Regolith-derived natural resources: a GA 2005 mineral resources figures, b ABARE 2003, c ABARE 2006, otherwise 1996 BRS extractable resources figures + includes supergene ores.
© CRC LEME 2007 So there you have it... Life on earth evolves around the evolving regolith. We rely on the regolith to maintain our daily needs. In weathered terrains we need to explore within and underneath the regolith for mineral deposits. We need to understand the regolith to sustainably manage our natural resources.
© CRC LEME 2007 References ABARE 2003, 2006. Australian Commodity Statistics 2003, 2006. Http://www.abare.gov.au/ (Australian Bureau of Agricultural and Resource Economics). Beckmann G.G. 1983. Development of old landscapes and soils. In: Soils, an Australian viewpoint. CSIRO, Melbourne, 51-72. Eggleton R.A. (ed.) 2001. The Regolith Glossary. CRC LEME 144 pp. Merrill G.P. 1897. A treatise on rocks, rock weathering and soils. Macmillan, New York, 411 pp. Thomas M.F. 1994. Geomorphology in the tropics: a study of weathering and denudation in low latitudes. John Wiley, New York, 460 pp. Taylor G. & Eggleton R.A. 2001. Regolith Geology and Geomorphology. John Wiley & Sons Ltd, Chichester, 375 pp. Twidale C.R. 1990. In: Groundwater Geomorphology. Geological Society of America Special Publication 252. Walther J. 1916. Das geologische Alter und die Bildung des Laterits. Petermanns Geographischer Mitteilungen 62, 1-7, 46-53. Strakhov N.M. 1967. Principles of lithogenesis. Oliver and Boyd, Edinburgh. Acknowledgment: parts of this lecture are derived from an earlier version by Graham Taylor
© CRC LEME 2007 Regolith Profiles Types, Materials, Genesis and Terrestrial Processes Mehrooz F Aspandiar CRC LEME WASM, Curtin University of Technology.
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