BilimTook.com BilimTook.com BilimTook.com BilimTook.com BilimTook.com BilimTook.com BilimTook.com BilimTook.com BilimTook.com CHAPTER – 1 GENERAL GEOLOGY 1.1. GEOLOGY- A FASCINATING DISCIPLINE OF NATURAL SCIENCE Our home planet “The Earth” is a member of the solar system. Also known as the ‘Blue Planet’, it is the only heavenly body of revolution that has a delicate balance of physico-chemical conditions, which support sustenance of life that is unique and special. Geology is a natural scientific discipline and is a term derived from the summation of two ‘Greek’ words such as ‘Ge or Geo’ meaning the earth and ‘Logos’ meaning science or discourse. It pertains to the study of the earth as a whole or part thereof. In a broader sense, geology could be reframed as ‘Earth Science’ which considers the whole earth as closed system, which is ever dynamic and a mosaic of four interactive parts that are ever changeable both among and within them. These four parts are called four reservoirs of materials of the earth (Fig.1.1) which also represent the four open systems such as (i) THE ATMOSPHERE which surrounds the – earth’s surface as a continuous canopy (layer) composed of a gaseous mixture of nitrogen (N), oxygen (O), hydrogen (H), carbon Fig.1.1: Reservoirs of earth materials and transfer of energy - 1 - BilimTook.com dioxide (CO2) and water vapour (H2O↑). (ii) THE HYDROSPHERE which forms the storehouse of earth’s total water regime comprising the oceanic and sea water, stream (river) water, lake water, surface run-offs, frozen water in form of snow and ice, and underground water (iii) THE GEOSPHERE, which is the solid earth composed of soils, regolith (loosely cemented rock particles), solid rocks, layers of rock-metal association and metallic alloys (Fe-Ni), as is observed and interpreted from the top towards the centre of the earth. (iv) THE BIOSPHERE which forms the earth’s organic world comprises of the living beings and the undecomposed organic matters. This sphere persists through all the aforesaid spheres. Biosphere is considered as an informal sphere as against the former three, which are the formal ones. Geology, as a word was first used by the Swiss natural scientist named Jean - Andre Deluc in 1778 and was later introduced as a formal and fixed scientific term by Horace - Benedict de Saussure. The term ‘Geology’ or the ‘Earth Science’ in a nutshell pertains to the scientific study of the earth, its composition, structure, physico-chemical attributes, developmental history and above all the natural processes, which shape it. The earth is essentially a closed system or very close to it in which the energy reaches the earth from the sun and eventually returns to the space as long wave radiations (Fig. 1.1). 1.2. SCOPE OF GEOLOGY The scope of geology covers a rather wide spectrum in conjunction with other fundamental and applied scientific disciplines such as Physics, Chemistry, Botany, Zoology, Geography and Planetary and Atmospheric sciences. With time, new frontiers of advanced subjects like Geophysics, Geochemistry, Geobotany, Bio-geology, Environmental geology, Astro-geology have also come up. Even - 2 - BilimTook.com with a subject like political science, it has a link forming an interdisciplinary subject called ‘Geo-politics’. In anthropological and archaeological disciplines, geology enters as a subject to deal with the socio-physical aspects of human race and the stone and metallic implements used during different lithic (Paleolithic, Mesolithic, Neolithic) and later ages. This subject also enters to the remote discipline of ancient history. An important sub-discipline of geology is ‘Economic Geology’ - an applied branch which is directly linked with the study of the vast kingdom of metallic and nonmetallic economic minerals including the industrial minerals and rocks. Economic geology plays a vital role in boosting the developmental growth and industrial strength of the nations and their people. 1.3. SUBDIVISIONS (BRANCHES) OF GEOLOGY The domain of geology abounding its widened scope is further divisible into a seemingly great number of subdivisions termed as the branches for the sake and convenience of systematic study. The main and allied branches of geology may be named as follows: Main (Principal) Branches Allied Branches (i) General geology (x) Engineering geology (ii) Physical geology (Geomorphology) (xi) Marine geology (iii) Geotectonics (xii) Geophysics (iv) Mineralogy (Crystallography inclusive) (xiii) Geochemistry (v) Petrology (Igneous, Sedimentary and (xiv) Geo-hydrology / Metamorphic) Hydrogeology (vi) Structural geology (xv) Environmental geology (vii) Historical geology or Stratigraphy (viii) Palaeontology (ix) Economic geology - 3 - BilimTook.com The cardinal themes of the main branches are briefed as follows: 1.3.1. General Geology: It is the formal branch of geology that deals with the broad features / aspects of the earth in particular and the other members of solar family with the Sun as the kingpin and sole controller. It also deals with certain principal aspects of the cosmos - the ordered universe. The features of the earth include its origin, age, constitution, internal structure and the depth zones of the marine (oceanic) realms. 1.3.2. Physical Geology: It serves as a tool to understand the physical process, which moulds the earth surface. The terms, synonymous with this branch, are ‘geomorphology’ and ‘dynamic geology’. This branch deals with (i) the geometry (ii) origin and developmental history of landform features of mountains, plateaus, valleys, rivers, lakes, glaciers, deserts, oceans and ground water (iii) geological work of the exogenetic (external) geological agents mentioned above, in constantly transforming the features of the earth’s surface and (iv) aspects of natural geologic phenomena such as denudation, weathering, erosion, mass wasting, landsides, soil creep, avalanches and soil erosion. 1.3.3. Geotectonics: This branch deals with the major and very large sized structures of the earth’s lithosphere (the crust and its lower part) and their changes produced by crustal deformation brought about by the interplay of the earth’s endogenetic (internal) forces. It describes and explains the geometry and mode of formation of the mega (very large scale) crustal features and their causative processes. These features are lofty fold mountains, block mountains, rift valleys, mid-oceanic ridges, geosynclines, and island arcs etc. It also deals with the global concepts of isostasy, eustasy (sea level changes), continental drift, convection cells, seismicity, ocean-floor-spreading and the plate-tectonics. In a simple sense, this sub-discipline deals with the movements of various crustal parts and the - 4 - BilimTook.com formation of resultant large scale crustal and infra-crustal features. 1.3.4. Mineralogy: It. is a formal branch that deals with the atomic structure, physico-chemical and optical properties of the minerals present in the earth’s lithosphere and the crust in particular. Crystallography is an important sub-branch which describes the internal atomic structure in a three dimensional perspective and the external geometric forms of the crystalline minerals. The mode of occurrence, genesis and uses of minerals are also studied in this branch. 1.3.5. Petrology: It is the branch that studies the mode of occurrence, textures, structures, mineralogical and chemical compositions, classification and genesis of the rocks of igneous, sedimentary and metamorphic classes, present in the crust and below it. Each major rock class is further divisible into sub-branches such as plutonic, hypabyssal and volcanic types in case of igneous rocks; residual, mechanical, chemical and organic types in case of sedimentary rocks and into contact (thermal), dynamo-thermal, plutonic and cataclastic types of metamorphic rocks. All the three major classes of igneous, sedimentary and metamorphic rocks are, thus, further divisible into relatively smaller sub-types. 1.3.6. Structural Geology (or Structure): Under the influence of tectonic forces, crustal deformations take place in plastic, elastic and brittle stages of the rocks to produce a great variety of geological structures such as folds, faults, joints, rock cleavages, foliations and lineations. The total aspects of these structural elements in respect of their geometry, attitude, classification, mode of formation and causes constitute the bulk of structural geology. 1.3.7. Stratigraphy or Historical Geology: Broadly stratigraphy deals with the succession of geologic events and / or rock layers from the beginning of the crustal formation up to the present time. It aims at establishing and describing the correct - 5 - BilimTook.com order of superposition of rock-units on the earth’s surface. Thus, it actually establishes the correct succession of rock formations / layers. It thereby unfolds the history of geological events on the earth from the geologic past to the present time and hence it is also referred to as historical geology as a synonym. 1.3.8. Palaeontology: It deals with the morphologic characteristics, modes of preservation, taxonomic classification, geological history of the ancient lives - both invertebrates, vertebrates and of plants. Thus, it consists of many sub- branches namely, Invertebrate Palaeontology, Vertebrate Palaeontology, Palaeobotany, Palynology, Micropalaeontology, Ichnology etc. Fossils are remains of geologically very old and ancient lives in form of entire body or hard parts, which are calcified, and / or silicified