Term
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Definition
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Term
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Definition
| The wearing away of the Earth's surface by the action of wind, water or ice dragging sediment over it, or hurling it at a surface. |
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Term
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Definition
| Finding the age of a rock quantitatively. E.g. by radiometric dating. |
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Term
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Definition
| Marks place where the adductor muscles attached to inside of a bivalve or brachiopod shell. Adductor muscles contract to close the shell. |
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Definition
| Sediments deposited by wind. |
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Definition
| Fine sediments deposited on the edges of rivers, generally making up the floodplain. |
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Definition
| Group of Cephalopods that lived in the Jurassic and Cretaceous. Had complicated suture lines. Used as zone fossils. |
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Term
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Definition
| Class of Cephalopods that includes Goniatites, Ceratites and Ammonites, all zone fossils. |
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Definition
| Igneous rock texture where the vesicles are later infilled by minerals deposited from groundwater. |
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Definition
| Mineral formed in metamorphism of rocks, usually medium grade contact metamorphism. Has four crystals joined together to form a diamond with a cross inside. |
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Definition
| A finely crystalline intermediate igneous rock comprising feldspar, mica and amphibole. |
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Definition
| Production of intermediate forms of magma. Occurs at subduction zones due to the introduction of water into the mantle which lowers its temperature. Leads to explosive volcanic eruptions. |
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Definition
| A break in time recorded by a break in the stratigraphy, over which the angle of the dip of beds above and below changes. |
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Definition
| Crystal which Is poorly formed and has no clear shape. |
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Term
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Definition
| Compacted coal which is hard with a bright, shiny lustre and does not dirty your hands. |
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Term
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Definition
| Folded rock, shaped like an "n", where the oldest rock are in the middle of the fold. |
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Definition
| A dip that is measured to be less than the maximum inclination. |
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Definition
| Sandstone that contains at least 25% feldspar, and mostly quartz. |
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Definition
| A fold with limbs of the different lengths, asymmetrical about the axial plane. |
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Definition
| Layer within the solid, upper mantle that is can flow very slowly (rheid). Corresponds to the seismic low velocity zone, beneath the 1300°C isotherm. |
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Definition
| The wearing down of sedimentary grains due to collisions with other grains during transport. |
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Definition
| Plane that joins all the hinges of all the beds in a fold. It bisects the fold. |
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Definition
| The line that marks the axial plane on the Earth's surface |
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Definition
| Line that marks the top of the axial plane along the fold. |
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Definition
| The thin layer of metamorphosed country rock around an igneous intrusion. |
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Definition
| A finely crystalline mafic rock comprising plagioclase feldspar and pyroxene and sometimes olivine. |
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Definition
| Production of mafic magma. Occurs at mantle plumes and Mid-Oceanic Ridges. Produces runny lava and shield volcanoes. |
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Definition
| A major igneous intrusion consisting of many plutons joined together. |
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Definition
| A layer of sedimentary rock that can be cm- to m-scale. |
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Definition
| The centimetre to metre-scale layers of sedimentary rock (also called strata) |
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Definition
| The top boundary of a subducted oceanic plate at a subduction zone, where earthquakes occur and indicate the position of the subducted slab. |
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Definition
| A biologically formed sedimentar rock composed of fragmented fossils. |
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Definition
| The mechanical and chemical weathering of rocks by plant roots or burrowing. |
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Definition
| Coal that has been put under some compaction. The coal we burn. |
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Definition
| A class of molluscs with a shell made of 2 valves of equal size and shape. The line of symmetry runs between the 2 valves. |
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Definition
| The hard parts of an organisms such as a skeleton or shell. |
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Definition
| A seismic wave that travels through the interior of the Earth. Includes P and S waves. |
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Term
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Definition
| The larger valve (shell) of a Brachiopod. |
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Term
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Definition
| A phlum of marine invertebrates comprising two valves (shells), one of which is larger than the other. A line of symmetry runs down the middle of each valve. |
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Definition
| A sedimentary rock dominated by angular clasts of greater than sand size, set within a finer grained matrix. |
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Definition
| Radiometric dating using the decay of radioactive Carbon-14 isotopes, which occurs at a constant rate. Requires organic material to be present in the rock and rock younger than 50,000 years as the half-life is short. |
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Definition
| A type of fossilisation where the organic material is replaced by calcite. |
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Definition
| A mineral comprising calcium carbonate. Makes up limestone, chalk and marble. |
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Definition
| Reaction between carbonic acid and minerals |
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Term
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Definition
| The process by which pressure of burial removes the volatiles from organic material, leaving a film of carbon. |
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Term
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Definition
| The infill of a mould with sediment or mineral to form a replica of the original shape of the fossil or sedimentary structure. |
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Term
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Definition
| A material that binds sedimentary grains together. |
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Definition
| Head' part of a trilobite. Contains the compound eyes, glabella and can have a fringe around it. |
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Definition
| Class of Molluscs including Ammonoids, Nautiloids, Squid, Octopus. |
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Term
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Definition
| A type of ammonoid that existed in the Triassic. Has a moderately elaborate suture line. |
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Term
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Definition
| A sedimentary rock made from coccoliths and foraminifera (both microfossils that make a carbonate skeleton) |
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Term
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Definition
| Weathering that produces ions that are removed in solution leaving an insoluble residue. Included carbonation and hydrolysis. |
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Definition
| The edge of an igneous intrusion that has cooled rapidly so it has very fine crystals. |
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Term
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Definition
| A stony meteorite with the same overall composition of the Earth. |
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Term
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Definition
| A small piece of rock that has ben derived by weatherng and erosion. The building block for clastic sedimentary rocks. |
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Term
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Definition
| Sediments made up of fragments of pre-existing rock |
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Term
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Definition
| Sedimentary rock made up of layer of clay minerals. |
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Definition
| The line of weakness with a crystal structure. |
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Definition
| A sedimentary rock comprising layers of plant material laid down in anoxic conditions. |
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Definition
| Crystals or grains that are bigger than 2mm. |
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Definition
| Plankton that make a carbonate skeleton, that when they accumulate on the bottom of the sea, make up chalk. |
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Term
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Definition
| Many corals stuck together, forming a a large skeleton of polygonal individal coralets each with septa. |
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Definition
| Joints formed as a result of contraction on cooling of igneous rocks, E.g. Giant's Causeway. |
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Definition
| Rock that is strong, does not deform under pressure, such as limestone or granite but will form fractures and joints if the stress is too great. |
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Definition
| Eye of a trilobite, comprising many calcite plates that were used as lenses to focus the light. |
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Definition
| Force trying to push rocks together. The Earth's crust will be shortened. |
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Term
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Definition
| Transfer of heat in solids. |
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Term
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Definition
| A sedimentary rock comprising large, rounded clasts within a finer matrix. |
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Term
| Conservative Plate Boundary |
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Definition
| Plate boundary where no crust is made nor destroyed. Also known as a transform boundary. For instance, San Andreas Fault, California. Made of strike-slip faults, also known as wrench or tear faults. |
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Term
| Constructive Plate Boundary |
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Definition
| New material is created. Also called a divergent plate boundary. For instance, Mid Oceanic Ridge or Rift Valley. |
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Term
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Definition
| Solid state recrystallisation by heat without pressure which produces an unfoliated metamorphic rock. |
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Term
| Continental Collision Zone |
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Definition
| Plate margin where 2 continental plates meet and form fold mountains. E.g. Himalayas formed by India moving into Asia. |
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Term
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Definition
| Less dense, thick crust that underlies continents. Can be 0-3950Ma old. Average composition similar to granite. |
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Term
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Definition
| The large-scale horizontal movement of continents during geological time. |
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Term
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Definition
| Large-scale tranfer of heat through liquids or gases. |
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Term
| Convergent Plate Boundary |
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Definition
| Crust is 'destroyed'. Also called a destructive plate boundary. For instance, subduction zone or continental collision zone. |
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Definition
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Term
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Definition
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Term
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Definition
| Any rock into which an igneous rock is intruded. |
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Term
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Definition
| Highest point of a folded bed. |
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Term
| Cross-Bedding (Cross-stratification) |
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Definition
| Sedimentary structures formed by the migration of dunes by wind or water. Can be used as a way-up and palaeocurrent indicator. |
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Term
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Definition
| The uppermost rigid, brittle layer of the Earth above the Moho that less dense. |
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Term
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Definition
| A rock comprising crystals rather than grains. |
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Term
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Definition
| The temperature at which the orientation of a magnetic minerals becomes fixed when they cool past it. |
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Term
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Definition
| Accumulation of fossils that have been moved between death and fossilisation. They are often aligned to the current, sorted in size and broken up. |
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Term
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Definition
| Laying down of sediment that occurs when a transporting agent loses energy. |
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Term
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Definition
| Fossils that have been weathered out of an older sediment and then form clasts in a younger one. |
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Term
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Definition
| Cracks formed in clay-rich sediments as water evaporates from them. Can be used as way-up structures. |
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Term
| Destructive Plate Boundary |
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Definition
| Crust is 'destroyed'. Also called a convergent plate boundary. For instance, subduction zone or continental collision zone. |
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Term
| Dextral Strike-Slip Fault |
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Definition
| Fault with only horizontal movement, where the opposite side of the fault is seen to move to the right. |
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Term
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Definition
| All physical, chemical and biological processes that occur in a sediment after deposition and before metamorphism that lithify the sediment to form a rock |
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Term
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Definition
| Marks place where the diductor muscles attached to inside of a brachiopod shell. Adductor muscles contract to open the shell. |
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Term
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Definition
| A coarsely crystalline intermediate igneous rock comprising feldspar, mica and amphibole. |
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Term
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Definition
| Maximum angle between the horizontal and geological surface such as a bedding surface or fault. |
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Term
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Definition
| A fault where the movement is in the same direction as the angle of dip, including normal and reverse faults. |
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Term
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Definition
| The process whereby minerals that make-up the fossils are dissolved away and removed in solution by groundwater. |
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Term
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Definition
| New material is created. Also called a constructive plate boundary. For instance, Mid Oceanic Ridge or Rift Valley. |
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Term
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Definition
| A medium crystalline mafic rock comprising plagioclase feldspar and pyroxene and sometimes olivine. |
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Term
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Definition
| Side of the fault that has moved down. |
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Term
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Definition
| A discordant igneous intrusion, usually made of mafic rock |
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Term
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Definition
| All crystals in an igneous rock are the same size. |
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Term
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Definition
| Major unit of geological time, e.g. Palaeozoic, Mesozoic and Cenozoic. |
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Term
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Definition
| Removal of weathered material, usually by the physical action of transported fragments. |
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Term
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Definition
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Term
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Definition
| Minerals formed by the evaporation of saline water, for example, halite and gypsum. |
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Term
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Definition
| Also known as onion-skin weathering, where sheets of rock split off due to expansion and contraction of minerals during daily heating and cooling. |
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Term
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Definition
| Force trying to pull rocks apart. The Earth's crust will be lengthened. |
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Term
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Definition
| Igneous rocks cooled from molten magma on the surface very quickly. Crystal size is very small. E.g Basalt, Rhyolite. |
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Term
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Definition
| The environment of deposition. E.g. Fluvial facies, would be sediments deposited in a river. |
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Term
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Definition
| The amount a fault has moved in the direction of the fault plane. |
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Term
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Definition
| A fracture in the rock along which there has been an observable amount of displacement. |
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Term
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Definition
| A rock composed of fraggments produced by rocks fractured during faulting. |
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Term
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Definition
| Surface along which movement of a fault takes place. |
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Term
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Definition
| Sediment or crystals less than 0.5mm big, or cannot be made out. |
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Term
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Definition
| Combines with load structures. Formed by the deposition of heavy sand on top of water-logged mudstone which subsequently deforms and forms flame structure. |
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Term
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Definition
| Igneous rock texture produced when silicic magma flows and the light and dark minerals line up with the flow as they cool. |
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Term
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Definition
| Sediments laid down by rivers |
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Term
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Definition
| Sedimentary structure found on the base of a bed, formed as a result of erosion caused by turbulent flow. Can be used as a way-up structure as well as a palaeocurrent indicator. |
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Term
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Definition
| Section of a fold between one hinge and the next, forming the side of a fold |
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Term
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Definition
| A repeated planar feature in a rock which may be defined by composition or alignment of minerals |
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Term
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Definition
| Side of a fault that lies below the fault plane. |
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Term
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Definition
| The remains of living organisms, either body fossils or trace fossils. |
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Term
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Definition
| A crack in the rock along which no displacement can be observed. |
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Term
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Definition
| Weathering cause by the expansion of freezing water in fracture which forces the rocks apart. |
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Term
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Definition
| A coarsely crystalline, mafic igneous rock, comprising plagioclase feldspar, pyroxene and amphibole with minor olivine. |
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Term
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Definition
| A permanent gap between valves of infaunal bivalves which have a siphon so long they cannot withdraw it all into their shells. |
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Term
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Definition
| Spines that come from the pointed part of a trilobite's head. |
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Term
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Definition
| The list of geological time periods in order. |
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Term
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Definition
| The rate of increase in temperature with depth._x000D_ |
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Term
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Definition
| The central part of the head of a trilobite that contains the stomach. |
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Term
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Definition
| Sediments formed by a glacier. |
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Term
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Definition
| Igneous rock texture that looks like glass. |
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Term
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Definition
| High temperature and pressure metamorphic rock. Coarsely crystalline with gneissose banding. Typically made of quartz and feldspar in the light bands, and biotite mica and other mafic minerals in the dark bands. |
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Term
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Definition
| Metamorphic texture found in gneisses, showing band of light minerals and dark minerals. |
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Term
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Definition
| An ammonoid that evolved in the Carboniferous and Permian. Has a simple suture line. |
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Term
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Definition
| A sedimentary structure were the largest clasts are found at the base, and the smallest at the top. Commonly found in turbidites and used as a way-up structure. |
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Term
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Definition
| A coarsely crystalline, silicic igneous rock comprising quartz, feldspar and mica. |
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Term
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Definition
| Texture of metamorphic rocks that contain interlocking crystals all the same size. |
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Term
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Definition
| A planktonic, organism from the Palaeozoic era. Used as a zone fossil, particularly in the Ordovician and Silurian. |
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Term
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Definition
| Minerals that crystallise out from a magma are often more dense and sink to the bottom. For instance, there is often a layer of olivine at the base of large mafic intrusions. |
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Term
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Definition
| A sandstone with more than 50% feldspar and rock fragments. |
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Term
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Definition
| Lines on a bivalve and brachiopod that mark its progressive growth. |
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Term
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Definition
| The boundary between the solid, peridotite, lower mantle and the liquid, outer core made of iron-nickel alloy. |
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Term
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Definition
| The time taken for half the unstable parent atoms of decay and form stable daughter products. |
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Term
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Definition
| Defined using the Mohs scale. |
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Term
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Definition
| Side of a fault that lies above the fault plane. |
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Term
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Definition
| A type of superficial deposit, basically a bucket term. |
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Term
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Definition
| The line marking the most sharply curved part of the fold. |
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Term
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Definition
| The line along which the two bivalve valves are joined by a ligament. |
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Term
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Definition
| Contact metamorphic mudstone, high-grade. Dark grey, brittle and hard rock. Compare with hornfels. |
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Term
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Definition
| A volcano within a plate, which is the surface expression of a mantle plume |
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Term
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Definition
| Reaction between minerals and water, causing the minerals to decompose. |
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Term
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Definition
| Rocks formed from molten rock, either intrusively or extrusively. |
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Term
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Definition
| A fold with an axial plane that is at an angle from vertical. |
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Term
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Definition
| Rock that is weak and deforms greatly under pressure, such as clay and mudstone. Folds easily. |
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Term
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Definition
| Also known as a zone fossil. Fossils that can be used to tell the age of the rocks they are in. Need to be widespread, easily recognisable, had rapid evolution, abundant and are well preserved. |
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Term
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Definition
| The solid central part of the Earth, made of iron-nickel alloy that sit beneath the Lehmann discontinuity. |
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Term
| Intermediate igneous rock |
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Definition
| An igneous rock with medium grey colour, containing minimal quartz, plagioclase feldspar and some mafic minerals, e.g. andesite, microdiorite and diorite. |
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Term
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Definition
| Igneous rocks cooled slowly from molten magma under ground. Crystal size is large. E.g Gabbro, granite. |
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Term
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Definition
| Meteorite derived from the core of larger bodies in space, made of the same material as our core, i.e. iron-nickel alloy. |
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Term
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Definition
| The production of volcanoes above an oceanic-oceanic subduction zone. Comprising intermediate lavas. |
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Term
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Definition
| Fold with near parallel limbs. |
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Term
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Definition
| A fracture in competent rocks along which no observable movement has occurred. Can be formed by folding (tension joints) formed parallel to the axial plane. |
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Term
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Definition
| A type of radiometric dating based on the decay of radioactive K-40, to its stable daughter isotope Ar-40. |
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Term
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Definition
| A projecting rib around the edge of an ammonite. |
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Term
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Definition
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Term
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Definition
| Molten rock erupted onto the Earth's surface |
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Term
| Law of Cross Cutting Relationships |
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Definition
| A geological surface that cuts across another must be younger than the one it cuts across. |
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Term
| Law of Included Fragments |
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Definition
| Fragments found within another rock, for instance large clasts within a sedimentary rock, must be older than the rock in which they are contained. |
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Term
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Definition
| Rocks beneath others are older than those above them, unless the area has been overturned. |
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Term
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Definition
| Boundary between the liquid,outer core and the solid, inner core. |
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Term
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Definition
| Accumulation of fossils that have not been moved between death and fossilisation. They are preserved in the orientation they were in life. |
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Term
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Definition
| Coal which has not been buried deeply and in which woody material can still be recognised. Also known as brown coal. |
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Term
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Definition
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Term
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Definition
| A sedimentary rock made of calcite, commonly with fossils in it. |
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Term
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Definition
| The process of changing unconsolidated sediment into rock. |
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Term
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Definition
| Topmost layer of the Earth, including the crust and the topmost upper mantle. Base of the lithosphere is taken as the 1300°C isotherm which can vary between 5km at the Mid Oceanic Ridge to 300km below fold mountains at continental collision zones. |
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Term
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Definition
| Combines with flame structures. Formed by the deposition of heavy sand on top of water-logged mudstone which subsequently deforms and forms flame structure. |
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Term
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Definition
| The way light reflects off a mineral, for instance, vitreous (glassy), pearly. |
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Term
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Definition
| Igneous rocks with dark coloured minerals, such as amphiboles and pyroxenes and little quartz. Includes basalt, dolerite and gabbro. |
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Term
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Definition
| Molten rock within the Earth |
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Term
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Definition
| A value for the Earth's magnetic filed that is different from the expected value. |
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Term
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Definition
| The angle of dip of the magnetic field lines. It is the angle made with the horizontal of a compass needle free to rotate in 3D. |
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Term
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Definition
| Made of solid peridotite that can flow (especially the asthenosphere). Divided into upper and lower mantle. |
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Term
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Definition
| A stationary area of high heat flow in the mantle, which rises from great depths and produces magma that feeds hot spot volcanoes. |
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Term
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Definition
| A metamorphic rock that can be either generated by contact or regionally metamorphism of limestone. |
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Term
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Definition
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Term
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Definition
| The background material in a rock, consisting of small particles in which larger fragments occur. |
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Term
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Definition
| 0.5-1.5mm grains of sand or crystals in an igneous rock |
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Term
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Definition
| Generated by heat and/or pressure. |
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Term
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Definition
| The area around an igneous intrusion that has been metamorphosed by heat. Width can be affected by things such as volume of intrusion, heat of intrusion and angle of the dip of the intrusion. |
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Term
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Definition
| Solid state recrystallisation under pressure with or without heat causing the new minerals to align in a direction perpendicular to the dominant stress. |
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Term
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Definition
| Rock formed by recrystallisation in the solid state of any rock subjected to heat and pressure. |
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Term
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Definition
| Metamorphosed sandstone, either contact or regional metamorphism. |
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Term
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Definition
| Fragments of debris that falls to Earth. There are 2 sorts: stony and iron. |
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Term
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Definition
| A medium crystalline intermediate igneous rock comprising feldspar, mica and amphibole. |
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Term
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Definition
| A medium crystalline, silicic igneous rock comprising quartz, feldspar and mica. |
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Term
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Definition
| Divergent plate margin generating new oceanic crust. |
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Term
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Definition
| A naturally-occurring, inorganic, crystalline, chemical compound or element that have unique properties and defining characteristics. |
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Term
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Definition
| A fracture in the rock that has been filled by precipitation of minerals from groundwater. Often the target of mining. |
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Term
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Definition
| Boundary between the crust and the upper mantle |
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Term
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Definition
| The impression of the outside or inside of a fossil. |
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Term
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Definition
| Sedimentary rock made of mud-sized particles, includes shale (well layered), siltstone and claystone (no layering visible) |
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Term
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Definition
| A fault with vertical movement, where the hanging wall moves down relative to the footwall. The area extends. |
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Term
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Definition
| More dense, thin crust that underlies oceans. Can be 0-200Ma old. Average composition similar to basalt. |
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Term
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Definition
| Deep ocean trench marking the position of a subduction zone. |
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Term
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Definition
| Spherical, concentric calcium carbonate balls formed by chemical precipitation around a nucleus such as a sand grain in warm tropical shallow water, as they are moved by waves. |
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Term
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Definition
| Limestone made from ooliths |
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Term
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Definition
| Fold with a large interlimb angle, i.e. wide spread limbs. |
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Definition
| Mountains formed by continental collision. |
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Definition
| The liquid part of the Earth, made of iron-nickel alloy. Sits between the Gutenburg Discontinuity and the Lehman Discontinuity. |
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Definition
| Ancient magnetism preserved in rocks |
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Definition
| The line on a bivalve shell that marks the limit of the attachment of soft tissue. |
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Definition
| An indent in the pallial line that represents the area into which the siphon is withdrawn when the shell is closed. |
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Definition
| Where a proportion of the minerals have a lower melting point, allowing them to melt while the rest remains solid. |
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Definition
| Plant debris that has been laid down but not compacted. Preliminary to coal. |
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Definition
| A fleshy stalk made mainly of muscle,which attached a brachiopod to the substrate. |
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Definition
| A hole in a brachiopod's valve out of which the pedicle emerges. |
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Definition
| The largest valve of a brachiopod. Usually contains a hole for the pedicle to protrude through. |
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Definition
| The ability of a fluid to pass through a rock. |
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Definition
| Ultamafic igneous rock composed of olivine and pyroxene with a coarse crystal size. |
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Definition
| Unit of geological time, e.g. Cambrian, Silurian, Jurassic. |
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Definition
| A large crystal that has grown very slowly at great depths, within a finer-crystalline matrix. Granite often has a large phenocrysts of orthoclase feldspar. |
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Definition
| Weathering by physical means, such as freeze-thaw, exfoliation etc. |
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Definition
| Produced when mafic lava is erupted underwater. Has a rounded top, and either a rounded base or shaped like a bulb, with a glassy rim. |
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Definition
| Organisms that float in sea water. |
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Definition
| Large intrusive body of magma, that has risen through the crust because it is hot and less dense than the rocks around it, and then cooled slowly. Usually of granitic composition. |
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Definition
| The volume of pore space in a rock. |
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Definition
| Igneous rock texture where a rock has cooled in two stages, to form large phenocrysts that have cooled very slowly in a finer-crystalline matrix that has cooled quicker. |
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Definition
| A large crystal that has grown during recrystallisation in a metamorphic rock and is surrounded by a finer grained groundmass of other crystals. Compare with a phenocryst in igneous rocks. |
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Term
| Pressure release weathering |
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Definition
| Expansion and fracturing of rock due to removal of overlying rocks. |
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Term
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Definition
| Primary seismic waves, arrive first at a seismometer after an earthquake, compressional wave. |
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Definition
| The 'tail' part of a trilobite, made of fused segments. |
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Definition
| The replacement of organic material with pyrite. |
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Definition
| All fragmental materials formed by explosive eruptions, including bombs, blocks, lapilli and ash. |
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Definition
| The constant rate at which unstable radioactive isotopes decay to form their stable daughter isotopes. |
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Definition
| Uses the ratio of radioative parent isotopes to their stable daughter isotopes, which decay at a constant rate, to calculate the age of a rock. |
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Definition
| Solid state process that changes minerals into new crystalline metamorphic minerals. |
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Definition
| A fold with a horizontal axial plane |
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Definition
| The solid state recrystallisation of a rock under heat and pressure, to create a foliated metamorphic rock. |
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Definition
| Dating the age of rocks relative to one another, but without knowing the numerical ages of each rock unit. Uses fossils, law of superposition etc. |
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Definition
| Magnetism shown in the rocsk due to the alignment of their magnetic minerals according to the Earth's magnetic field at the time of their formation. |
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Definition
| Atom by atom substitution of one mineral for another. |
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Definition
| Fault with vertical movement, where the hanging wall moves up and over the footwall. The area is compressed. |
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Definition
| A solid material that flows |
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Definition
| A finely crystalline, silicic igneous rock comprising quartz, feldspar and mica. |
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Term
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Definition
| A divergent plate boundary that occurs within a continent. E.g. East African Rift Valley. |
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Definition
| Smaller sedimentary structures (cm-scale) formed by the migration of ripples by medium-energy water or wind. Ripples can be symmetrical or asymmetrical depending on whether the current is two-way (wave) or one-way (current). |
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Definition
| An aggregation of minerals that show a textural relationship between them. |
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Definition
| Secondary seismic waves, shear waves. |
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Definition
| Transport of material by bouncing. |
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Definition
| A sedimentary rock comprising sand grains, variably compacted and cemented. |
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Definition
| Medium grade metamorphic rock with aligned mica crystals and commonly garnet porphyroblasts. Shiny. |
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Definition
| The texture in medium and coarsely crystalline metamorphic rocks formed by the preferred alignment of flat/tabular minerals. The alignement is perpendicular to the direction of maximum pressure applied during metamorphism. No traces of original bedding remain. |
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Definition
| Rock composed of clasts, grains or fossils that hav been lithified by the processes of compaction and diagenesis. |
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Definition
| Speed at which a wave travels through the Earth. |
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Term
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Definition
| A wave that travels through the Earth. Includes P, S and L waves. |
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Term
| Seismological Low Velocity Zone |
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Definition
| The area within the upper mantle, that roughly corresponds to the asthenosphere, where the velocity of seismic waves is reduced as it is partially molted. |
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Definition
| Radiating calcite plates that support a coral skeleton. |
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Term
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Definition
| The area on the Earth's surface that cannot be reached by S-waves due to their inability to pass through the molten outer core, or P-waves due to their refraction by the liquid outer core. |
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Definition
| A layered sedimentary rock made of mud. |
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Term
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Definition
| Bivalves have a line of symmetry between its two shells. A brachiopod has a line of symmetry down the middle of its shell. |
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Definition
| The replacement of organic material with silica. |
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Definition
| Igneous rocks with a lot of quartz in them, light in colour and also contains feldspar and mica. E.g. granite, microgranite and rhyloite. |
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Term
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Definition
| A concordant igneous intrusion, usually made of mafic rock. |
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Term
| Sinistral Strike-Slip Fault |
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Definition
| Fault with only horizontal movement, where the opposite side of the fault is seen to move to the left. |
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Term
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Definition
| A soft tissue part of a bivalve that takes in fresh water and filters it, and removes used water. Aids respiration and feeding. |
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Term
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Definition
| A low-grade, regionally metamorphic rock with slaty cleavage derived from mudstone. |
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Term
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Definition
| The texture in fine grained rocks formed by low grade regaional metamorphism. Platy minerals recrystallise perpendicular to the direction of stress applied during metamorphism so that the rock splits into thin sheets. |
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Term
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Definition
| Polishing and striations found on a fualt place indicating the direction of relative movement. |
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Term
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Definition
| Sedimentary structures that form due to high-energy currents on a bed. Can be way-up structure. |
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Term
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Definition
| A singular coral, shaped like a variably bent ice-cream cone. |
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Term
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Definition
| The degree to which particles are the same size. |
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Term
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Definition
| Contact metamorphic mudstone, medium-grade. Consists of medium grey rock with darker spots. Compare with hornfels. |
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Term
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Definition
| The stack of thecae of a graptolite built up to form a colony. |
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Term
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Definition
| Meteorites of a similar composition to the world as a whole, see Chondrites. |
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Term
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Definition
| The colour of the powder left by rubbing a mineral on a streak plate. |
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Term
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Definition
| Direction at right angles to the dip. There isa zero dip in this direction,. It is a bearing measured from north using a compass. |
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Term
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Definition
| Fault where movement is only horizontal. Can be sinistral (left-handed) or dextral (right-handed). |
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Term
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Definition
| The process by which oceanic crust is forced underneath other oceanic or continental crust |
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Term
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Definition
| A destructive plate margin, where an oceanic crust is forced down beneath either another oceanic or continental crust. |
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Term
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Definition
| A moderately formed crystal, somewhere between anhedral (poor) and euhedral (well) formed crystals. |
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Term
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Definition
| The soil and subsoil layer that you get on top of the true bed rock if you dig down. |
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Term
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Definition
| Earthquake waves that do not travel through the body of the Earth but only in the uppermost crust. Comprise both shear and oscillatory waves. |
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Term
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Definition
| Transport of material in water or air without it touching the Earth's surface. |
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Term
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Definition
| The line along which the internal walls of an ammonoid meet the outside wall. |
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Term
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Definition
| A fold with limbs of the same length, symmetrical about the axial plane. |
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Term
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Definition
| A "u"- shaped fold, where the youngest beds are in the middle of the fold. |
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Term
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Definition
| Part of the hinge line in a bivalve or brachiopod that join the valves together. |
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Term
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Definition
| The inter-relationship and nature of grains or crystals within a rck. |
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Term
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Definition
| Individual cup in which one graptolite organism (zooid) lives. |
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Term
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Definition
| Segment of a trilobite comprises a pair of legs, a pair of gills and a covering to protect them. |
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Term
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Definition
| The 'body' part of a trilobite, divided into thoracic segments. |
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Term
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Definition
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Term
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Definition
| Fold with a small interlimb angle, i.e. narrowly-spread limbs. |
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Term
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Definition
| The fossilised indication that an organism has lived there. For instance, burrows, footprints, resting traces. |
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Term
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Definition
| Strike-slip fault with only horizontal movement. |
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Term
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Definition
| An organism from the Palaeozoic era. An marine arthropod. |
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Term
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Definition
| Lowest point of a folded bed. |
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Term
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Definition
| The amount of VERTICAL movement on a fault measured between the top of the same bed seen on both sides of the fault. |
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Term
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Definition
| A sedimentary rock consisting of pyroclastic material. |
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Term
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Definition
| A deposit that reduces in grain size upwards of greywackes deposited by a turbidity current. |
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Term
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Definition
| A high velocity current that flows down gentle gradients because the sediment dispersed within it makes it denser than sea water, like an underwater avalanche. |
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Term
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Definition
| Occurs when two separate crystals share some of the same parts of another crystal. Like Siamese twins. |
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Term
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Definition
| An igneous rock with no quartz in it, dominated by olivine and pyroxene. E.g. peridotite. |
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Term
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Definition
| Area of a valve marking the point of first growth. |
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Term
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Definition
| A gap in time that is recorded by an absence of rock deposition, with younger rocks above and older rocks below. Usually there is a different dip and/or strike of the rocks above and below this surface and there may also be a conglomerate along the surface. |
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Term
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Definition
| The present is the key to the past. The idea that geological processes that are acting today have acted in the same way through geological past. |
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Term
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Definition
| Return of buried rocks to the Earth's surface by tectonic forces. |
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Term
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Definition
| A fold with a vertical axial plane. |
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Term
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Definition
| Side of the fault that has moved up. |
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Term
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Definition
| Igneous rock texture where gas bubbles are trapped in the lava as it cools rapidly. |
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Term
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Definition
| A fragment of 'foreign' rock included in an igneous rock, which has come from a different source. |
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Term
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Definition
| Characteristic used to determine which way up a bed is, and therefore which beds are older and which younger. E.g. Roots, flute casts, Flame and Soul structures, Shape of vesicles in lava |
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Term
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Definition
| The in-situ breakdown of rocks. |
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Term
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Definition
| Also known as an index fossil. Fossils that can be used to tell the age of the rocks they are in. Need to be widespread, easily recognisable, had rapid evolution, abundant and are well preserved. |
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