Foundation Geology

• Aeolian deposits: 

Sediments deposited by wind.

• Ammonites: 

Extinct marine cephalopods with coiled shells, common fossils in Mesozoic marine rocks.

• Anhydrite:

An evaporite mineral composed of anhydrous calcium sulphate (CaSO₄), often associated with gypsum.

• Angular fragments: 

Rock or mineral pieces with sharp, unworn edges, characteristic of breccia.

• Archosaurs:

A group of reptiles that includes crocodiles, pterosaurs, and dinosaurs.

• Belemnites: 

Extinct marine cephalopods with internal, bullet-shaped shells, common fossils in Jurassic and Cretaceous marine rocks.

• Braided rivers: 

Rivers that consist of a network of small channels separated by small and temporary islands called braid bars. They form in areas with high sediment load and variable discharge.

• Breccia: 

A clastic sedimentary rock composed of large, angular fragments of minerals or rocks cemented together by a fine-grained matrix.

• Calcareous: 

Containing calcium carbonate; refers to rocks rich in calcite or similar minerals.

• Cenozoic Era: 

The current geological era, following the Mesozoic Era, characterised by the rise of mammals.

• Chalk: 

A soft, white, porous limestone composed predominantly of the skeletal remains of microscopic marine algae called coccolithophores.

• Chicxulub asteroid impact: 

The asteroid impact event approximately 66 million years ago that is widely accepted as the cause of the Cretaceous-Paleogene extinction event.

• Coccolithophores: 

Microscopic, single-celled marine algae that produce intricate calcium carbonate plates (coccoliths) which accumulate to form chalk.

• Conglomerate: 

A clastic sedimentary rock composed of rounded fragments of minerals or rocks cemented together by a fine-grained matrix, differing from breccia by its rounded fragments.

• Continental drift: 

The gradual movement of the continents across the Earth's surface through geological time.

• Cross-bedding: 

Layers within a sedimentary rock that are inclined at an angle to the main bedding planes, formed by the migration of ripples or dunes under moving fluid (wind or water).

• Dimetrodon: 

A genus of extinct synapsids (often mistakenly called a dinosaur) from the Permian period, known for its large sail-like back structure.

• Edaphosaurus: 

A genus of extinct synapsids from the Permian period, a herbivore with a distinctive spiky sail on its back.

• Evaporite minerals: 

Sedimentary minerals (like gypsum and halite) that form from the evaporation of water, leaving behind dissolved salts.

• Exeter Group: 

The oldest Permian rock formation in the Sidmouth district, consisting of breccia, sandstone, and mudstone.

• Fluvial sediments: 

Sediments deposited by rivers or streams.

• Glauconite: 

A green iron-potassium phyllosilicate mineral of the mica group, typically found in marine sedimentary rocks, indicating specific marine environmental conditions.

• Gondwana: 

The southern supercontinent that formed part of Pangea during the Paleozoic and Mesozoic eras, later breaking into modern continents like South America, Africa, Australia, Antarctica, and India.

• Gypsum: 

A soft, white or colourless mineral composed of calcium sulphate dihydrate (CaSO₄·2H₂O), used in plaster, drywall, and as a fertiliser.

• Halite: 

The mineral form of sodium chloride (NaCl), commonly known as rock salt, formed by the evaporation of saline water.

• Intraformational conglomerate: 

A conglomerate rock where the clasts (rock fragments) are derived from within the same sedimentary formation as the matrix, typically due to penecontemporaneous erosion.

• Laurasia: 

The northern supercontinent that formed part of Pangea during the Mesozoic Era, later breaking into modern continents like North America, Europe, and Asia.

• Lystrosaurus: 

A genus of herbivorous, mammal-like reptiles (therapsids) that thrived in the early Triassic Period following the Permian-Triassic extinction event.

• Mesozoic Era: 

The geological era spanning from about 252 to 66 million years ago, known as the "Age of Reptiles" and divided into the Triassic, Jurassic, and Cretaceous periods.

• Micaceous: 

Containing mica, a group of sheet silicate minerals, which can give rocks a shiny or flaky appearance.

• Mosasaurus: 

A genus of large, predatory marine reptiles that dominated the oceans during the Late Cretaceous Period.

• Mudstone: 

A fine-grained sedimentary rock formed from mud or clay particles, typically more acidic in composition than calcareous rocks.

• Otter Sandstone Formation: 

A Middle Triassic geological formation exposed in the Sidmouth area, characterised by reddish-brown aeolian and fluvial sandstones.

• Oxidizing conditions: 

Environmental conditions where oxygen is readily available, often leading to the formation of iron oxides (red colours).

• Paleozoic Era: 

The geological era spanning from about 541 to 252 million years ago, preceding the Mesozoic Era, ending with the Permian Period.

• Pangea: 

A supercontinent that existed during the late Paleozoic and early Mesozoic eras, formed from the collision of all Earth's continental landmasses.

• Panthalassa: 

The vast global ocean that surrounded the supercontinent Pangea.

• Permian Exeter Group: 

The oldest rock unit in the Sidmouth district, dating from the Permian Period.

• Permian-Triassic Extinction Event: 

Also known as the "Great Dying," the largest mass extinction in Earth's history, occurring at the boundary between the Permian and Triassic periods.

• Plesiosaurs: 

A group of large, long-necked marine reptiles that lived from the Jurassic to the Late Cretaceous periods.

• Pterosaurs: 

Extinct flying reptiles that lived during the Mesozoic Era, unrelated to dinosaurs but coexisted with them.

• Reduction patches: 

Areas within a rock that have undergone chemical reduction, often resulting in colour changes (e.g., grey-green spots from iron sulphides).

• Reducing conditions: 

Environmental conditions where oxygen is scarce or absent, often leading to the formation of sulphide minerals.

• Rhynchosaurs: 

A group of herbivorous Triassic reptiles with beak-like snouts.

• Sedimentary breccias: 

Breccias formed by the accumulation of angular rock fragments transported by processes like landslides or mudflows.

• Selenite: 

A translucent, crystalline variety of gypsum, often found as clear, tabular crystals.

• Shingle: 

A type of sediment composed of rounded, smooth stones, commonly found on beaches and coastlines.

• Sidmouth Mudstone Formation: 

A Mid Triassic geological formation, basal to the Mercia Mudstone Group, composed of red-brown mudstones and siltstones.

• Siltstone: 

A sedimentary rock composed primarily of silt-sized particles.

• Supercontinent: 

A large landmass consisting of most or all of Earth's continental crust.

• Tectonic plates: 

Large, rigid slabs of Earth's lithosphere that move slowly over the mantle, causing earthquakes, volcanic activity, and mountain building.

• Temnospondyl amphibians: 

A diverse group of primitive amphibians that flourished during the Carboniferous, Permian, and Triassic periods.

• Therapsids: 

A group of synapsids ("mammal-like reptiles") that flourished during the Permian and early Triassic periods, including the ancestors of mammals.

• Triassic-Jurassic extinction event: 

A mass extinction event at the boundary between the Triassic and Jurassic periods, affecting both marine and terrestrial life.

• Tyrannosaurus Rex: 

A large, carnivorous theropod dinosaur that lived during the Late Cretaceous Period.

• Upper Greensand Formation: 

A Cretaceous geological formation (glauconitic sandstone) that forms prominent escarpments in the Sidmouth district.