Sedimentary rocks

Sedimentary rocks

Formed at or near Earth's surface via erosion, deposition, and lithification.

Formation temperature of sedimentary rocks

Form at 0-250 degrees C, <10 km below the surface.

Carbonate weathering vs silicate weathering

Carbonate weathering transports CO2 between the atmosphere and ocean, while silicate weathering removes CO2 from the atmosphere for long term storage.

Clastic sedimentary rocks

Composed of fragments of pre-existing rocks/minerals.

Non-clastic rocks

Biochemically precipitated.

Classification of sedimentary rocks

Texture based on grain size, sorting, and shape.

Composition of sedimentary rocks

Can be mafic or felsic.

90% quartz

Quartz arenite.

10-25% feldspar

Subfeldspathic arenite.

25% feldspar

Arkosic arenite (arkose).

10-25% lithics

Sublithic arenite.

25% lithics

Lithic arenite.

Main components of sedimentary rocks

Quartz, feldspar, and lithics.

Process of forming sedimentary rocks

Sediment -> weathering and transport -> site of deposition -> lithification -> sedimentary rocks.

Siliciclastic sedimentary rocks

Contain mostly quartz and clay due to their stability during weathering and transport and their abundance.

Non-clastic sedimentary rocks

precipitated by organisms or abiotically

Chemical sediments

coal, carbonates, evaporates; good indicators of environmental conditions

Biochemical carbonates

calcite, aragonite, dolomite

Allochems

grains within carbonate rocks

Bioclasts

pieces of fossil

Ooids

spherical grains with concentric layers

Intraclasts

fragments of preexisting carbonate rock that has been eroded

Peloids

spherical or ellipsoidal grains composed of microcrystalline carbonate with no internal structure; usually fecal pellets

Graded bedding

Bedding normally gets finer as it goes upwards; this is called normal grading.

Reverse grading

Occurs due to the Bagnold dispersive force.

Bedding scale

laminated -> thinly bedded -> medium bedded -> thick

Tabular bedding

parallel and planar

Planar cross-bedding

straight crested ripples/dunes; show direction of past currents

Trough cross-bedding

Curved bounding surfaces formed by the migration of 3D bedforms

Bedform

Morphological feature formed by the interaction between a flowing fluid and a sediment; informs about flow energy and transport direction.

Imbrication

Depositional fabric in which clasts align and overlap; shows direction of flow.

Fluvial environment

Have a scroll bar, point bar, upstream bar, central bar, and downstream bar.

Golovinsky/Walther's law

Beds that occur in conformable vertical successions of strata were deposited laterally.

Scroll bar pattern

shows the course of the old river

Crevasse splay sands

flat, tabular beds

Point bars

lateral accretion surfaces

Fining upward trend

Gravel in channel, sand in point bar, mud in floodplain/overbank.

Back reef and reef flat

zone of high evaporation and evaporite minerals (gypsum, halite)

Reef crest and reef front

zone of encrusting mineral vertebrates (coral, bryozoans, echinoderms)

Fore reef

zone of reef debris