Sedimentary Flashcards

Question

Continental Shelves?

Answer 1

* Staging post between erosion of continents and final deposition in deep ocean * Sediment dispersed by a complex mix of tides, waves and ocean currents * Wide spread sands, muds and carbonates * Sediments on shelf regularly reworked and replaced

Answer 2

• Factors leading to carbonate precipitation: Warm temperature; Low pressure; Agitation (Well oxygenated) = promote the formation of carbonates in shallow tropical marine environments. • Carbonate sediment tends to be autochthonous - forms where it is deposited • Warm shallow seas often thought as Carbonate factories due to carbonate production • From carbonate settings allochthonous carbonate material can be exported to adjacent environments • All of these promote the formation of carbonates in shallow tropical marine environments. Thus, carbonates form in water that is not deep to begin with, and carbonate environments tend to shoal upward toward the surface, forming carbonate platforms. • Most carbonate production is biogenic. Because carbonate secreting critters tend to be intolerant of muddy waters, carbonate dominated environments tend to be distinct from clastic environments. • Carbonate factories frequently shallow to the surface where they may be exposed due to sea level fluctuations on various time scales, resulting in erosion and karstification.

Answer 3

* Oolite is a sedimentary rock made up of ooids (ooliths) that are cemented together. * Ooids are spheroidal grains with a nucleus and mineral cortex accreted around it. Nucleus is usually either mineral grain or biogenic fragment. * Directly ppt from warm seawater * The term “ooid” is grains < 2 mm in diameter. * Larger grains pisoids (pisoliths)

Answer 4

• Piles of intergrown organismal skeletons and sediment that form a rigid wave-resistant interlocking framework. • Framework tends to represent a minority of actual reef volume, most of which is carbonate sediment infilling pore space. • Type of reef depends upon the topography of the continental shelf, degree of exposure to wind, waves, and currents. Fringing reef - between continent and sea (one side on land Atoll - reef surround lagoon with sea on exterior side Barrier reef - reef forms a lagoon between continent and sea

Answer 5

 Forereef: Sediment shed off of the reef front (includes reef slope and proximal talus)  Reef framework and crest: The densest zone of in situ framework growth. The crest receives the most wave energy.  Backreef: Including reef flat, backreef sands, and lagoonal muds. Sheltered from wave energy by reef front. (sheltered, fine sediments) How reefs have changed: • Mostly due to extinction • Framework builders (corals) are generally only 10% of the total volume of the reef other components: o Carbonate mud (micrite) o Skeletal elements o Cement • Reefs have been around since the Cambrian

Answer 6

Sedimentary structures such as ripples and cross-bedded strata indicate the organism lived in moving water where sediment was moved by currents. §Broken shells may indicate pounding by waves as on a beach or created during storm conditions. §Diagenesis including the rate of burial, the starting pore fluid chemistry and later mineral replacements within sediment can significantly influence the preservation potential of a fossil or enhance it §Murky waters, with low light levels and lots of suspended sediment particles can be determined by the type of sedimentary rock and associated sedimentary structures. Filter feeding organisms such as corals are not usually found in muddy waters because the suspended sediments clog their filters. §Oxygen levels are critical to all organisms. If there is insufficient oxygen in the water, relatively few organisms may have lived in such an environment. However, in oxygen deficient waters organic material in sediments can be well preserved.

Answer 7

• Location: o Neritic: On the continental Margin o Oceanic (Pelagic): overlaying the oceanic crust • Water depth: o Pelagic: below 3000m o Hemi pelagic: 200-3000m • Grain size: o Sand, silt, clay • Origin: o Authigentic or autochthonous: precipitation from solution • Hydrogenous: abiogenic (inorganic) • Biogenous: produced by biological activity o Allochthonous: carried into the oceans as solid phases • Luthogenous/terrigenous: from Earth’s crust • Cosmogenous: extraterrestrial materials • Sedimentation rate: o Non-pelagic: form at rates higher than 1cm/1000y o Pelagic: from at rates lower than 1cm/1000y o Relic: sedimentation rates of – or less (net dissolution)

Answer 8

Turbidity Currents: • Main agent for transporting shallow-water sediment into deep water dwon submarine canyons on to submarine canyons on to submarine fans and the ocean floow • Speed depends on slope and amout of sediment (current density) ``` Turbidities: • Fining upwards sequence in deep sea setting • Bouma Sequence o Muds – often bioturbated o Parallel laminated silts o Cross laminated fine sands o Plannar laminated fine-to-medium sands o Sand and any larger grains the turbidity current was carrying at the time of deposition ```

Answer 9

* Cosmic dust found in red clay * Composed of iron-nickel and magneitie formed by oxidation during passage through Earth’s atmosphere –are 50-200 microns in diameter * Aound 300x103 tonnes of cosmic/meteoritic dust falls on the Eath’s surface each year