Plate Tectonics, Sedimentary Rocks, and Geologic History

Comprehensive practice cards covering Earth science fundamentals, sedimentary processes, stratigraphic principles, and significant events in the geologic time scale with specific focus on the Arabian Plate and UAE regional examples.

Lithosphere

The outer solid layer of the Earth consisting of the crust and the uppermost mantle, characterized as being brittle and elastic.

Asthenosphere

The layer below the lithosphere extending to an average depth of about $300\,km$ in the mantle; it allows rocks to flow plastically under stress due to high temperatures and moderate confining pressures.

Orogenesis

A term referring to the processes and study of mountain building.

Geosynclinal theory

A mid-19th-century mountain-building theory developed by James Hall and James Dwight Dana suggesting that mountain chains correspond to original lines of greatest sediment accumulation.

Synclinorium

The resulting mountain chain following the "quick mountain-making crisis" as described in James Dwight Dana's formulation of the geosynclinal theory.

Seafloor spreading

The process where rocks on either side of ridges occur in paired polarity reversals, or "magnetic stripes," with members of each pair exhibiting the same polarity but alternating between normal and reversed.

Polar-Wander Curves

Plots mapping the directions in which continents moved through time relative to stationary magnetic poles, determined from the directions of magnetization and latitudes of rocks.

Slab pull

A plate tectonic driving mechanism where the weight of a down-going slab of lithosphere in a subduction zone pulls the rest of the trailing plate along with it.

Ridge push

A movement mechanism where slabs of lithosphere slide off topographic highs at spreading ridges and rift zones formed by rising warm asthenospheric mantle.

Passive margins

Continental margins that are not currently associated with any large-scale tectonic activity or plate boundaries.

Obduction

The tectonic process involving the overthrusting of oceanic lithosphere onto continental lithosphere at convergent plate boundaries.

Lithification

The collective set of processes, such as compaction and cementation, by which loose sediments are transformed into solid sedimentary rock.

Terrigenous Sedimentary Rocks

Rocks derived from preexisting rocks through the processes of weathering, erosion, transport, and deposition, classified by grain sizes such as gravel, sand, and mud.

Evaporites

A group of chemical sedimentary rocks, including gypsum, anhydrite, and halite, generated by precipitation from water as it evaporates.

Oöids

Round or ellipsoidal sand-size sedimentary grains formed when $CaCO_3$ precipitates inorganically out of seawater.

Progradation

The process by which a coast builds out toward the sea because a river delivers more sediment than waves and currents can remove, common in delta formation.

Benthic

A term referring to bottom-dwelling organisms of the marine realm, collectively known as the benthos.

Carbonate Compensation Depth (CCD)

The ocean depth, typically greater than $4000\,m$, where calcium carbonate sediments dissolve due to the level of dissolved carbon dioxide in the water.

Taphonomy

The study of the processes involved in the formation and preservation of fossils.

Ichnofossils

Trace fossils, such as tracks, trails, and burrows, which reflect the behavior of preexisting organisms.

Permineralization

A fossilization process where secondary minerals fill the pore spaces of originally porous hard parts, such as vertebrate bones or invertebrate shells.

Carbonization

The most common form of soft-part preservation where volatile components are "burned off" during burial and heating, leaving behind nonreactive carbon-rich substances.

Coprolites

Solid excretory waste products of animals that are preserved in the geologic record and used to determine diet and habitat.

Principle of Superposition

The stratigraphic principle stating that in any undeformed sequence of sedimentary rocks, each bed is older than the layers above and younger than the layers below.

Principle of Original Horizontality

The principle stating that layers of sediment are generally deposited in flat-lying, horizontal positions.

Unconformity

A gap in the geologic record representing a period of erosion or non-deposition.

Half-life

The specific amount of time required for fifty percent of a radioactive parent isotope to decay into its stable daughter product.

Walther’s Law

A principal stating that the vertical succession of facies reflects the lateral changes in environment, assuming no unconformities are present.

Index fossils

Fossils used for biostratigraphy that are easily identified, widespread, abundant, and have a limited vertical range in geologic time.

Transgression

The landward advance of a shoreline resulting in the spreading of the sea over land, often producing a fining-upward sequence of sediments.

Regression

The seaward advance of a shoreline, often caused by a fall in sea level or high sediment delivery.

Ammonoids

Coiled cephalopod mollusks that evolved in the Devonian and serve as essential Mesozoic index fossils; they died out at the end of the Mesozoic Era.

Ostracoderms

Extinct Paleozoic fishes characterized by "bony skin" that disappeared at the end of the Devonian.

Fusulinids

A group of large, rapidly evolving foraminifera that are useful index fossils for Late Carboniferous and Permian strata.

Amniotic egg

The key evolutionary feature in the origin of reptiles that allowed vertebrates to reproduce away from bodies of water for the first time.

Hexacorals

A newly evolved group of corals that became the dominant reef builders during the Triassic and remains successful today.

Rudists

Large, surface-dwelling bivalve mollusks of the Cretaceous that grew cone-shaped shells and formed bank-like reefs.

Angiosperms

The group of flowering plants that appeared in the Cretaceous, utilizing animals for pollination and seed dispersal.

Nummulitid Foraminifera

Large benthic foraminifera with algal symbionts that serve as major index fossils for the Eocene epoch.

Messinian salinity crisis

An event between $5$ and $6\,Ma$ ago when the Mediterranean Sea became isolated and dried up, resulting in salt deposits up to $2000\,m$ thick.