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Changing sea-level and coal

Glossary
Diagram: Changing Sea Level and coal
Diagram showing the formation of a typical cyclothemsequence (from bottom to top).
© Elizabeth Pickett, 2022

Sea-levels in the Carboniferous were constantly changing. When sea-level was low, the deltas built out into the sea and swampy conditions prevailed, covered with vegetation. When sea level rose, the deltas and associated forests were drowned, and sea life returned with the occurrence of limestones. This cycle happened many times, building up repeating layers of limestone, mudstone, sandstone, fossil soils and sometimes thin coals.  These cycles, known as ‘cyclothems’,

Source: https://dalesrocks.org.uk/swaledale/carboniferous-layers-of-the-landscape/changes-and-cycles/

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A

Anthropomorphic: Refers to the attribution of human characteristics or behaviors to non-human entities, often used in the context of describing objects, animals, or natural features.

B

Basalt: A dark, fine-grained volcanic rock that is rich in iron, magnesium, and calcium. It is commonly found in the Earth’s oceanic crust.

Beach: A landform along the shoreline of a body of water, typically consisting of sand, pebbles, or other sediments, and subject to the action of waves and tides.

Boulder Clay: A type of clayey glacial till deposited by melting glaciers, containing a mixture of clay, silt, sand, and larger boulders.

C

Calcium Carbonate: A chemical compound with the formula CaCO3, found in various forms, including limestone, chalk, and marble. It is a common substance in rocks and the main component of shells.

Cementation: The process of binding and solidifying loose particles or sediments into a cohesive rock through the deposition of minerals, often by the infiltration of mineral-laden water.

Chalk: A soft, white, porous sedimentary rock composed of calcium carbonate, often formed from the remains of microscopic marine organisms.

Clay: A fine-grained natural rock or soil material that is predominantly composed of clay minerals. It is plastic when wet and hardens when fired or dried.

Conglomerate: A sedimentary rock composed of rounded gravel-sized clasts (rock fragments) held together by a matrix of finer-grained material.

Crystalline: Having a structure characterized by the regular arrangement of atoms or molecules in a repeating pattern, forming crystals.

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D

Deformation: The alteration of the shape or size of a rock mass due to stress, often occurring along faults or as a result of tectonic forces.

Delta: A landform formed at the mouth of a river where sediment is deposited as the river flows into a larger body of water, such as a lake or an ocean.

Deposition: The process by which eroded sediments are dropped or settled in a new location, often due to a decrease in the energy of the transporting medium (wind, water, ice).

Desert: A dry, arid region with little rainfall, characterized by sparse vegetation and often featuring sand dunes.

Dolomites: Historically, the Upper Permian rocks in County Durham have been referred to as the Magnesian Limestone, that is magnesium-rich calcite. However, these days we would call these rocks dolomites, since they are composed of that mineral rather than calcite. The sediments would originally have been precipitated as CaCO3 but they were dolomitised by refluxing seawater and hypersaline water soon after deposition. Original limestone is only present in the lower parts of the Raisby and Ford Formations, and locally in the slope sediments of the Roker Formation.  In some places, the dolomites have been altered back to limestone, a process called dedolomitisation. This occurs in some parts of the Roker Formation in particular, well seen in the area of Marsden.  

E

Estuary: A semi-enclosed coastal body of water where freshwater from rivers and streams meets and mixes with saltwater from the ocean.

Erosion: The process of wearing away or breaking down rocks and soil through natural forces such as wind, water, and ice.

Evaporation: The conversion of water from a liquid to a vapor, usually driven by heat from the sun.

Evaporites: A type of sedimentary rock, formed as water evaporates leaving behind dissolved minerals and salts.  

Extrusive: Refers to igneous rocks formed from lava that has erupted onto the Earth’s surface and cooled rapidly.

F

Fault: A fracture in the Earth’s crust along which movement has occurred.

Fine-grained: Refers to rocks or sediments with small particle sizes, such as clay or silt.

Floodplain: Flat or gently sloping land adjacent to a river that is periodically flooded and covered with sediments.

Folds: Bends or curves in rock layers caused by tectonic forces.

Foreset: The inclined layer of sediments deposited by migrating dunes or other sedimentary processes.

Fossil: The remains or traces of ancient organisms preserved in rocks, often used for dating and interpreting past environments.

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G

Glacial Till: A type of sedimentary material directly deposited by a glacier as it moves and melts

Glacier: A large mass of ice that moves slowly over land, formed from the accumulation and compaction of snow.

Glacial Erosion: The process by which glaciers erode and shape the landscape through the movement of ice and the entrainment of rock debris.

Grains: Individual particles, crystals, or fragments in a sediment or rock.

Granite: A coarse-grained igneous rock composed of quartz, feldspar, and mica.

Groundwater: Water that is stored beneath the Earth’s surface in porous rock or soil.

H

Hydrolysis: A chemical weathering process in which minerals are broken down by reaction with water.

I

Ice Sheet: A large mass of glacial ice covering more than 50,000 square kilometers of land.

Igneous Rock: Rock formed from the cooling and solidification of molten magma or lava.

Intrusion: A body of igneous rock that has crystallized below the Earth’s surface.

Invertebrates: Animals without a backbone, including insects, mollusks, and worms.

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J

Joints: Fractures or cracks in rocks along which there has been no significant movement.

K

L

Lagoon: A shallow body of water separated from a larger body of water by a barrier such as a reef or barrier island.

Limestone: A sedimentary rock primarily composed of calcium carbonate, often formed from the accumulation of marine fossils.

Longshore Drift: The movement of sediments along a coastline due to the action of waves and currents.

M

Meanders: Bends or loops in a river channel formed by the natural flow of water.

Metamorphic Rock: Rock that has undergone changes in mineralogy, texture, or composition due to heat, pressure, or chemically reactive fluids.

Mineral: A naturally occurring inorganic solid with a specific chemical composition and crystal structure.

Moraine: A deposit of unconsolidated glacial debris, including rocks, gravel, sand, and clay.

Mudflow: A rapid flow of mud and water down a slope, often triggered by heavy rainfall or volcanic activity.

Mudstone: A fine-grained sedimentary rock composed of compacted mud.

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N

O

Oolith: A small, rounded particle, typically composed of concentric layers of calcium carbonate.

Oolitic Limestone: A type of limestone composed of ooliths, often formed in shallow marine environments.

Oxidation: A chemical reaction in which a substance combines with oxygen, often resulting in the formation of rust.

P

Pebbles: Small, rounded stones larger than grains of sand but smaller than cobbles.

Plankton: Microscopic organisms that drift or float in aquatic environments, including both plants (phytoplankton) and animals (zooplankton).

Plate Tectonics: The theory that the Earth’s lithosphere is divided into rigid plates that move and interact at plate boundaries.

Porous: Having small openings or spaces that allow the passage of fluids or gases.

Pumice: A lightweight, porous volcanic rock formed from frothy lava with trapped gas bubbles.

Q

Quartz: A common mineral composed of silicon dioxide (SiO2) that is often found in igneous, metamorphic, and sedimentary rocks.

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R

Reef: A ridge of rock, coral, or sand at or near the surface of the water.

Rock: A naturally occurring solid aggregate of minerals, mineraloids, or organic materials.

Rock Salt: A crystalline form of salt (sodium chloride) found in sedimentary deposits.

Rounded: Having a smooth and rounded shape, often due to the abrasion of wind, water, or ice.

S

Salt: A chemical compound formed from the reaction between an acid and a base; also refers to sodium chloride, a common mineral.

Sand: Loose, granular material consisting of small rock and mineral particles, typically between 0.0625 and 2 millimeters in diameter.

Sandstone: A sedimentary rock composed of sand-sized grains cemented together.

Schist: A metamorphic rock characterized by a foliated structure and often containing minerals such as mica and quartz.

Sea-stack: A column of rock standing in the sea, typically formed by erosion and weathering.

Sediment: Particles of rock and organic material that settle on the Earth’s surface.

Sedimentary Rock: Rock formed from the accumulation and cementation of sediments.

Shale: A fine-grained sedimentary rock composed of clay minerals.

Sill: A tabular intrusion of igneous rock that has solidified between layers of pre-existing rock.

Slate: A fine-grained metamorphic rock that easily splits into thin, flat layers.

Strata: Layers or beds of rock in the Earth’s crust.

Syncline: A downward-folding, trough-like structure in layered rocks.

T

U

V

Vesicles: Small cavities or holes in rocks, often formed by the entrapment of gas bubbles during solidification.

Wave-cut-platform: A flat, elevated surface at the base of a sea cliff, formed by the erosive action of waves.

W

Wave-cut-platform: A flat, elevated surface at the base of a sea cliff, formed by the erosive action of waves.

X

Y

Z