Sedimentology + Stratigraphy

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Is a measure of the “peakedness” of a dataset such as the grainsize of a sediment (therefore sorting)
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The volume of open space within a sample (relative to the total volume of that sample).
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the ability of a medium to allow the movement of a fluid through its structure m^2
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Hydrolysis Reaction
reaction between minerals and hydrogen ions (H+).
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Reaction between oxygen and cation of a molecule
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essentially the blanket of unconsolidated sedimentwhich lies on top of bedrock
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they have been transported into their environment of deposition. All clastic rocks by definition fall into this category.
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sediment weathered in-situ.
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Chemical Sediment
precipitate directly from the environment due to supersaturation of the fluid as a result of changes in P, T, mineral concentration etc.
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Biological Sediment
are formed through biochemical pathways, which are dependant on both the organisms metabolism and the physical conditions of the environment.
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Precipitate from hypersaline brines (fluids containing lots of salts) due to water input being less than water output.
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from the “rusting of the oceans” whereby oxygen reacted with dissolved iron in the oceans to form insoluble iron oxides (haematite, magnetite) which accumulated on the sea-floor in banded sequences inter- bedded with shale and chert.
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Salt Pans
Salt-pans are undrained depressions in which water gathers and evaporates, wind is an important control of evaporation
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are saline coastal lakes
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are inter‐ or supra‐ (above) tidal areas where salts accumulate in the near surface
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"Hopper" haylite
forms due to rapid salt crystallisation, typically at the water surface.
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Crusts and Mega Polygons
Evaporite structure formed from the volume change of water in a mineral.
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Chicken-wire, enterolithic gypsum/anhydrite
forms when the form the insitue crystalisation of anyhydrite/gypsum where the crystals displace the original sediment around them to thin strings.
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Coal Sources
1) Vitrinites 2) Liptinites 3) Ash 4) Inertites
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organic remains of creatures that have, due to conditions of their environment of deposition and maturation, been protected from decomposition and preserved over geological timescales.
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Biogenic Chert/Flint
Biogenic sediments typically comprise more robust (inorganic but biogenic) mineralised remains of creatures – shells, bones, teeth etc.
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Biological Clasts
comprise any fragments of a creatures mineralised skeleton. A staggering array has been developed during the history of the planet but at different stages distinct bioclasts dominated certain environments
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Concentrically coated grains with a nucleus of variable composition smaller then 2mm
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a term used for a rock that consists almost entirely of the transported, abraded, and hydrodynamically sorted fragments of invertebrate shelly material
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is a pure carbonate rock comprising plates from degraded coccolithophore algae.
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Carbonate Compensation Depth
There is a depth limit where carbonate minerals will not form due to higher pressures increasing the solubility of CO32- depends on 1) PH of water 2) Temp of water 3) Water chemistry
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Reynolds Number
Dimensionless parameter to describe whether a flow is laminar or turbulent.
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Laminar Flow
(Re =
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Turbulent Flow
(Re = >2000) , although net movement is in one direction, stream lines cross and mix.
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Froude Number
A Hydraulic jump occurs where a flow transitions from thin supercritical flow to thicker subcritical flow-> standing wave
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Stokes Law
Determines the settling rates of particles through a still fluid. Coarsest grains settle first and are found at the base of beds. Particle shape is not taken into account though - platy particles settle more slowly than spherical grains of the same m
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Bernoulli equation
Explains the lift experienced by everything from planes to particles in fluids. When a flows cross-sectional area is constricted, Pressure decreases and velocity increases.
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Where a particle moves through a medium by "hopping"
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Nature of Sedimentary Boundary determined by..
the speed and magnitude of the change in conditions
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Indistinct/Diffuse Boundaries
typically represent more gradual changes in conditions
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Reason for cross bedding
They form from the migration of depositional surfaces – delta fronts, dune faces, ripples etc.
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Ripple Index
= Ripple Wavelength/Ripple Height
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Ripple symmetry index
= Long Ripple Face/Short Ripple Face Side
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Erosional Structure
Formed by the erosive action of currents and the physical interaction of objects (transported by the flowing fluid) with the sediment surface
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Distinctive “heel-shaped” scours which are deep and bulbous at their upstream end and flare and merge with the bed at their downstream end. Variable in scale.
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Water Escape/ Desiccation
Form through the loss of sediment-supporting water due to either very sudden events or more gradual change
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large-scale breccia formed in active continental margin settings. Individual “clasts” of up to 1 km.
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show little or no deformational internal structure
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Slumps will illustrate...
complex internal folding and faulting.
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Chemogenic Structures
From the moment of sedimentation, minerals within the rock (or circulating fluids) are subject to remobilisation and removal or concentration to form a variety of chemogenic structures.
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centimetre-sized calcite cavity fills with a flat/undulose lower surface and an irregular upper surface.
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are irregular cavities that can form due to gas production within the sediment (typically small), irregular folds in algal or other organic structures (elongate/planar) or burrows (tubular). They are common in algal, restricted environments.
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Geopetal structures
comprise a primary cavity (typically within a bioclast) which has been partially filled by sediment with the remaining void later often completely filled with cement, leaving a permanent record of the depositional horizontal.
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Form as a result of pressure dissolution. This is whereby minerals, when subjected to enought pressure returen to solution.
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Areas of differential compostiotion
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Sedimentary petrology
the study of sedimentary rocks and the processes and conditions of their formation.
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Defines all the physical and chemical changes which occur after the initial deposition of a sediment and subsequently, before, during and after it is lithified
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Cemented Shelter Porosity
Porosity that occurs when a grain or clast shelters an area from a matrix, creating a pores space.
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Moldic Porosity
Occurs when grain or clast forms into dissolution
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Early diagenesis at shallow burial. Where interactions with pore waters occur sediment is still nuder influence of dep system.
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Middle diagenisis. Where compaction occurs, porosity is destroyed and cement forms.
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Final diagenisis occurs after uplift. This is where factors such as weathering and erosion take place.
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The volume of open space within a sample (relative to the total volume of that sample).

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Hydrolysis Reaction


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