GEO 309: Sedimentation Stratigraphy - Test 1
What is buoyant force (Fb)?
(Archimedes' law) the product of the mass of the fluid displaced by the particle and the acceleration of the external force (gravity). Mass = Volume * Density Fb - 4/3 * [pi] * r^3 * pf * g
What is characteristic of a low-density turbidity current?
- <30% grains - smaller grain sizes - often tail of flow - thin-bedded deposits - fine-grained at base - good grading - laminations, cross-bedding common - scour-marks common
What is characteristic of a high-density turbidity current?
- >30% sediment grains - coarser grain sizes - often head of flow - thick-bedded deposits - poor grading - few internal sedimentary structures - scour marks rare
What is physical weathering?
- abrasion - frost-wedging - insolation effects - root-wedging - salt-wedging - transport
What can trigger a turbidity current?
- earthquakes - storms - sediment failure along slopes
What are the differences between evaporites in marine and non-marine environments?
- lateral extent (M = ?, NM = ?) - mineralogy (M = ?, NM = ?)
What is characteristic of a turbidity current body?
- uniform, steady velocity - velocity > head velocity, feeds head - near uniform thickness - can be area of erosion or deposition
More than _____% of the exposed rocks on the Earth's surface are sedimentary.
70
CARBONATE ROCKS
CARBONATE ROCKS
What is Reynold's Number?
Inertial Forces (causes turbulence) divided by Viscous Forces (suppresses turbulence). R sub e = UL / v U = mean velocity of the flow L = water depth v = viscosity large = turbulent small = laminar
Turbulent versus laminar is a function of _____.
Re
Why are sedimentology and stratigraphy important?
- They host most of the natural resources on the planet (oil, gas, water, ore deposits. - Sedimentary rocks preserve a unique archive of Earth's geologic history (e.g. climate & tectonics). - Sedimentology is significant for energy, resources, environment, economy.
What is a bed?
- a layer with similar composition, texture, and/or structure - separated by bedding (or "bounding surface") - > 1 cm in thickness - can contain subdivisions
Describe anhydrite...
- anhydrous calcium sulfate mineral - orthorhombic, one perfect cleavage and two other good cleavages - white to colorless, aggregates (nodular) to laminated - stable at higher pressures and temperatures than gypsum
What is characteristics of current ripples?
- asymmetrical in profile - very sinuous crests, broken into curved crests - cross laminations dipping in one direction
What are the main carbonate minerals in limestone?
- calcite (inorganic or organic/skeletal) - aragonite (mostly biogenic) - dolomite (mostly diagenetic, also microbial precipitate)
Describe gypsum...
- calcium sulfate mineral - monoclinic with one perfect cleavage, and usually white or colorless, but sometimes gray or reddish - can scratch with finger nail
What are the types of non-clastic sedimentary rocks?
- carbonates - others (coal, ironstones, phosphates, siliceous deposits) - evaporites
What are the three main erosional structures?
- channels (meters in scale) and scour-and-fill structures (centimeters in scale) - scour and tool marks (groove/gutter casts and flute casts)
What are the two types of conglomerate textures?
- clast-supported (orthoconglomerate): clasts are in contact with each other and matrix is < 20% - matrix-supported (paraconglomerate): matrix is > 20%
What are the main characteristics of sparry calcite or sparite?
- coarse-grained calcite crystals that appear clear to translucent in plane light
What are some examples of biogenic carbonate sources from plants?
- coccoliths - oncoids
What is characteristic of a turbidity current head?
- concentration of coarser particles - most intense turbulence - often region of erosion - overhanging - velocity slower than body
List deformational sedimentary structures...
- convolute bedding (disruption of laminae) - flame structures - ball and pillow structures - synsedimentary folds - dish and pillar structures - load casts - mudcracks (desiccation driven) - syneresis (cracks; shrinkage of sediment without desiccation; formed by the contradiction of clay in response to changes in the salinity of a liquid surrounding a deposit) - pits - rill and swash marks - sedimentary dikes (forceful injection of liquified sands)
Describe halite...
- cubic - perfect cleavage - mostly (cubic) - colorless, reddish - forms mostly as crust - can form salt dikes or salt domes, "salt tectonics"
What is characteristic of a liquefied or fluidized sediment flow deposits?
- deposits often thick, poorly sorted - identified by fluid escape structures
What is chemical weathering?
- dissolution... of calcite, halite, gypsum, carbonates by acidic meteoric water - hydrolysis... between silicate minerals and acids to form clays - oxidation & reduction... of iron and manganese-bearing silicate minerals; iron sulfides
How do you describe grain shape?
- form (equant to platy) - roundness/angularity - surface texture (pitted to smooth)
Inorganic precipitation...
- has a preferecnce for calcite vs aragonite seas, Mg2+ rich seas favor aragonite - ooids: composition reflect ocean chemistry
Where can you find quartz?
- igneous - metamorphic - hydrothermal - biogenic - very stable, abundant, easily recycled
How does the CO2 decrease?
- increase temperate - decrease pressure - both result in an increase in pH and lower solubility of CO2
Organic precipitation...
- is a direction extraction (forams and corals) photosynthesis (cyanobacteria and coccoliths) and more
Why is grain size important?
- it gives us information on physical processes and depositional environments - it controls porosity and permeability (e.g. oil and gas reservoir quality, groundwater reservoir volume and movement)
What else can be found in sandstone compositions other than quartz and feldspar?
- mafic minerals (amphibole, biotite, pyroxene) - heavy minerals (garnet, zircon) - rock fragments or lithics (volcanic, chert)
What physical properties must be considered when calculating sediment transport?
- mass - forces - pressure - density (mass/volume) - viscosity
What are some examples of biogenic carbonate sources from skeletal material?
- mollusks - stromatolite - nanoplankton - cephalopod - corals - crinoids
Where can you find feldspar?
- most abundant crustal mineral - mostly igneous - weathered to clays
What are the three categories of biogenic structures?
- mottled bedding (a surface that has been disrupted by bioturbation) - stromatolites (shallow = more bulbous, deep = more columnar) - trace fossils from tracks, trails, burrows, and borings: ichno fossils
What is characteristic of a grain flow?
- occur on steep surfaces, near angle of repose (30 degrees) - cohesion often causes cohesionless sediment to be piled up beyond angle of repose - grain-to-grain contact supports flow - most commonly observed in aeolian environments (sand dunes) - deposits are difficult to preserve
What are some examples of non-biogenic carbonate sources?
- ooids - peloids - interclasts
What controls the precipitation of CaCO3?
- pH (loss of CO2 causes H+ to decrease and pH to increase = precipitate CaCO3)
What are the two types of conglomerate compositions?
- polymictic: made of clasts of varying composition (metamorphic, igneous, sedimentary, interclasts) - olimictic: made of clasts of the same composition
What is characteristic of a debris flow deposit?
- poorly sorted, large range of grain sizes (mud matrix) - often thick, lack internal layering (massive) - base may show evidence of shearing or scouring - either no grading, normal, or reverse grading
What are amalgamated beds?
- similar characteristics, but different depositional units - separated by erosional surface called amalgamation surface
List deformational sedimentary processes...
- slump - load - injections - fluid-escape - desiccation - impact
What is characteristics of wave ripples?
- symmetrical in profile - long, straight to gently sinuous crests - wave cross laminations dipping in both direction
What are the largest scale pieces of information preserved in sedimentary rock?
- tectonics (internal forces): large-scale processes affecting the structure of Earth's crust. - climate (external forces): through the product of processes such as erosion and deposition.
What are the main characteristics of carbonate mud or micrite?
- they are made of fine-grained calcium carbonate particles less than 4 μm across - they form by chemical precipitation of CaCO3 out of saturated water
What is characteristic of a turbidity current tail?
- thins rapidly away from body - becomes more dilute - area of deposition
What are the main categories of trace fossils?
- trypanites (rocky coats) - glossifungites (coast line, semi-consolidated substrate) - skolithos (sandy shore) - cruziana (sublittoral zone) - zoophycos (bathyal zone; maybe any anoxia) - nereties (abyssal zone)
What is characteristic of a turbidity current?
- turbulence causes sediment to become suspended - creates a density contrast with surrounding water - flow stops when density contrast is reduced by settling
What is characteristic of a liquefied or fluidized sediment flow?
- unconsolidated grains normally in contact with each other - pore water pressure increases, grains loose contact, supported by fluid - will begin to flow if on a slope or with a shear stress applied - as fluid is removed from flow, grains re-establish contact, deposit freezes - "freezing" starts at base of deposit - results in upward movement of pore fluid and fluid escape structures
What are the types of clastic sedimentary rocks?
- volcaniclastics - terrigenous clastics (mudrocks, sandstones, conglomerates)
_____% of Phanerozoic rocks are evaporites
1%
What controls sedimentation?
1. Amount of material available in the source (erosion). 2. Space available in the basin (accommodation space). This is a function of tectonics and sea level. 3. Preservation potential.
How do turbidity currents move?
1. Head passes first, is erosive, scoured base 2. Density starts to change, velocity decreases 3. Stoke's law, largest grains settle first 4. Type of grading: normal (sand to silt) 5. Froud Number starts high, gets smaller
What are the 3 components of limestone?
1. biogenic (skeletal fragments) 2. non-biogenic carbonates (ooids, etc.) 3. carbonate mud or micrite
What are the 3 main types of carbonaceous sedimentary rocks?
1. bituminous sandstone 2. lignite 3. anthracite
The 4 main areas of carbonate production include:
1. carbonate platforms (non-reef) 2. organic reef environments 3. slope basin carbonates-or carbonate ramps 4. mixed carbonated-silicotic systems (non-reef)
What are the 4 types of sedimentary structures?
1. depositional 2. erosional 3. deformational 4. biogenic
How do we describe sedimentary rocks?
1. grain texture (grain size, grain shape, porosity and permeability, grain orientation) 2. composition 3. sedimentary structure
The three most common evaporite minerals are...
1. gypsum (CaSO4 * 2H20) 2. halite (NaCl) 3. anhydrite (CaSO4)
What are the three main parts of a turbidity current?
1. head 2. body 3. tail
What are the 3 types of bedding?
1. planar bedding 2. laminated bedding 3. graded bedding (normal, inverse, massive)
What are the 5 main types of bedforms?
1. ripples 2. dunes 3. plane beds 4. antidunes 5. chutes & pools Flow velocity increases down the list.
How do current ripples and dunes form?
1. saltation (Bernoulli effect) 2. rolling 3. suspension
What are the three principles that came from Steno?
1. superposition 2. original horizontality 3. lateral continuity
What are the 5 types of cross-bedding or cross stratification?
1. tabular (planar) cross-bedding 2. tough cross-bedding 3. ripple cross-lamination 4. flaser and lenticular bedding 5. hummock cross-stratification (HCS)
What are the 4 types of sediment gravity flow?
1. turbidity current 2. liquefied/fluidized sediment flow 3. grain flow 4. debris flow
The definite sequence of evaporation and evaporite deposition: 50% ... 20% ... 10% ... <10% ...
50% ... original volume: iron oxides, aragonite, and other carbonates 20% ... original volume: gypsum 10% ... original volume: halite <10% ... magnesium sulfates, chlorides, K salts
A conglomerate is a sedimentary rock composed of _____.
>30% of clasts > 2mm
What is a foreset?
???
What is a bedform?
A feature that develops at the interface of fluid and a moveable bed, and is the result of bed material being moved. They form at the time of deposition of the sediment and are governed by flow conditions. (density, *velocity*, *size*, viscosity, wave period).
How do we settle a particle back down?
A function of viscosity, size, shape, and density of the particle.
What is the Wentworth scale?
A geometric scale of grain size from largest to smallest. BOULDER, cobble, pebble, granule, sand, silt, CLAY.
What is a debris flow?
A highly concentrated sediment-water mixture driver by its own weight. (Cohesive mud matrix supports large grains) Initiate on slopes > 10 degrees, but can flow on slows < 5 degrees.
What is grain sorting? How do you describe it?
A measure of the range of grain sizes present and the magnitude of the spread or scatter of these sizes around the mean size. - well sorted to poorly sorted
What is a pisoid?
A protolithic ooid, usually larger and less round.
What is bituminous sandstone?
A sandstone with a large amount of organic material, or a "sandy" coal.
What is Stoke's Law?
A single solid sphere settling in a fluid has a terminal settling velocity which is uniquely related to its diameter. D sub st = sqrt( 18[mu]V / g(p sub s - p sub l) ) D = particle size diameter mu = viscosity of fluid V = velocity g = gravity p sub s = density of solid p sub l = density of liquid
What is a turbidity current?
A turbidity current is most typically an underwater current of usually rapidly moving, sediment-laden water moving down a slope; although current research indicates that water-saturated sediment may be the primary actor in the process. Turbidity currents can also occur in other fluids besides water.
What type of fluid is in a debris flow?
Bingham plastic.
CLASTIC SEDIMENTARY ROCKS
CLASTIC SEDIMENTARY ROCKS
What are allochems?
Carbonate grains that are distinct from matrix. (skeletal fragments)
What are salt casts?
Casts in sedimentary rock of salt deposits deposits where salt had been present prior to removal.
What is the Goldich Stability Series?
Composition and mineral stability analysis of minerals.
What is a liquefied or fluidized sediment flow?
Concentrated dispersions of grains in which the sediment is support by upward escape of flow of pore water or by injection of water from below.
What is the Carbone Factory?
Defined by Schlager (2005) as the shallow illuminated seafloor (photic/euphotic zone), where sediment particles are generated within sea water from the crystallization of skeletal remains or precipitation out of sea water.
What is a turbidite Bouma Sequence?
E. Massive, ungraded mudstone, possible bioturbation, pelagic seds. D. Lower flow regime, planar laminated siltstone. C. Ripple laminated fine-grained sandstone, flame/convolute lamination. B. Upper flow regime, planar laminated medium-grained sandstone. A. Normally graded sandstone, coarse grains or rip-up clasts at the base scoured base.
What are groove clasts?
Elongate, straight positive relief structures.
FLUID DYNAMICS
FLUID DYNAMICS
What is Walther's Law? Who prosed it?
Facies that are found today in a vertical sequence are the product of a series of depositional environments which lay laterally adjacent to each other. Johannes Walter (1860-1937)
What are peloids?
Fecal pellets. Round particles made up of fine-grained CaCO3 found in sediments without any concentric structure.
What is the gravitational force (Fg) on a sphere?
Fg = 4/3 * [pi] * r^3 * ps * g
What are the 2 main naming schemes for carbonate rocks?
Folk and Dunham
Subcritical to supercritical is a function of _____.
Fr
How does sediment move to form bedforms?
Fr < 1: Lower Flow Regime ... sediments migrate downstream Fr = 1: Plane-bed stage ... ripples and dunes are destroyed Fr > 1: Upper Flow Regime ... sediments migrate upstream, forming antidunes
What are interclasts?
Fragments of calcium carbonate material that has been partly lithified and then broken up and reworked to form a clast which is incorporated into the sediment.
What is anthracite?
High grade coal, looks shiny.
INTRODUCTION
INTRODUCTION
What is the Froude Number?
Inertial Forces divided by Gravity Forces Fr = U / sqrt(gL) Fr < 1, subcritical Fr > 1, supercritical
What are laminae?
Layers < 1 cm in thickness
What is lignite?
Lower grade, progressively "duller" and softer".
What type of fluid is in a liquefied flow?
Newtonian fluid (high viscosity)
OTHER CHEMICAL ROCKS
OTHER CHEMICAL ROCKS
Deep water carbonates are formed by...
Planktonic organisms in the photic zone that later die and fall to the bottom of the ocean.
Why was the Permian Period the time of the greatest evaporite depostion?
Presumably because much of the great supercontinent of Pangea lay in low-latitude belt of continental aridity in what we call, in the present time, the "horse latitudes".
What is the difference between QFL and QFR?
QFL includes only fine grained lithics, while QFR includes all polycrystalline lithic fragments.
What does the Folk naming scheme rely on?
Relative abundance of (1) carbonate grains or allochems, (2) microcrystalline carbonate mud (micrite), and sparry calcite cement (sparite). First, determine if it is micrite or sparite. Then determine how abundant the carbonate grains and abundant are. Last (ex: sparce biosparite)
What does the Dunham naming scheme rely on?
Relative abundance of allochems and micrite or sparite, but doesn't consider identity of grain.
SEDIMENT GRAVITY FLOWS
SEDIMENT GRAVITY FLOWS
SEDIMENTARY STRUCTURES: PART 1
SEDIMENTARY STRUCTURES: PART 1
SEDIMENTARY STRUCTURES: PART 2
SEDIMENTARY STRUCTURES: PART 2
What are sediment gravity flows?
Sediment transported by the effect of gravity acting directly on the sediment or rock.
What mechanisms have operated in the past to extract silica from water, principally seawater, to form chert?
Siliceous test or shells left over from dead microorganisms.
What are ooids?
Spherical bodies of calcium carbonate less than 2 mm in diameter. They form by chemical precipitation out of agitated water saturated in calcium carbonate in warm waters.
What are cross-cutting relationships? Who proposed them?
States that a rock unit, sediment body, or fault that cuts another geologic unit is younger than the unit that was cut. Hutton (1726-1797) Lyell (1845-1920)
What is the support mechanism of a debris flow?
Strength of matrix.
What scales are used to determine grain size? When is each scaled used?
The Wentworth Scale is used in the field while the Phi Scale is used in the lab.
What is drag force (Fd)?
The force generated at the surface of a particle every time there is a relative velocity between the particle and the fluid. Fd = A * p sub f * V^2/2 * Cd Cd = drag coefficient For laminar flow: Cd = 24 * [mu]/V * D * p sub f
What is chert?
The general term for very fine-grained and non-porous sedimentary rocks that consist mostly or entirely of silica, in the form of either amorphous silica or microcrystalline quartz. Flint is the non-scientific form.
What is faunal (fossil or biotic) succession? Who proposed it?
The principle that body fossils occur in strata in a definite determinable order. Williams Smith (1769-1839)
What is uniformitarianism? Who proposed it?
The principle that processes acting upon the Earth today have also operated in the geologic past. "The past is the key to the present." James Hutton (1726-1797)
The Dunham classification is based on...
The proportion of carbonate mud (matrix) present versus framework grains (allochems).
What is stratigraphy?
The science of layered rocks developed from three principles first states by Nicolaus Steno (1638-1687)
What is sedimentology?
The study of the processes of formation, transport, and deposition of material that accumulates as sediment in sedimentary basins in continental and marine environments and eventually forms sedimentary rocks.
What is the Carbonate Compensation Depth?
The water depth at which the rate of supply of calcium carbonate from the surface is equal to the rate of dissolution.
What are flute casts? What can they tell us?
They are scours dug into soft, fine sediment which typically get filled by an overlying bed (hence the name cast). Elongate, positive relief structure with bulbous noses. They can possibly indicate paleo flow direction.
What is the support mechanism of turbidity current?
Turbulent fluid.
What type of fluid is in a debris flow?
Turbulent fluid.
How do you write Stoke's Law equation to solve for velocity?
V = ( 1 * (psolid - pfluid) * g * d^2 ) / 18*[mu]
What were the sources of the silica for chert?
Volcanic activity and silicic clastic rivers.
The Folk classifications requires _____.
a microscopic analysis
A rock composed of about 75% broken shelly fragments in a matrix of carbonate mud is _____.
abioclastic packstone
Gypsum, halite, and trona are important industrial and _____ that are used to make plaster and "drywall".
agricultural minerals
"Carbonates are _____, not _____." -Noel P. James
born; made
The _____ can tell you whether a rock's cross-bedding is planar or trough.
bounding surface
What is framestone or "reef rock"?
carbonate mass built from in-place, cemented organisms (corals, worm tubes)
Carbonate growth and production are intimately tied with the _____ of the ocean; _____, _____, _____, and _____ exert the most dominant controls.
chemistry light; pH; temperature; nutrients
What is rudite or rudstone?
clast-supported limestone conglomerate of intraformational origin
What are the two main categories of sedimentary rocks?
clastics & non-clastics
Gravity can act both in _____ and _____ environments.
continental (subaerial); marine (subaqueous)
What are the 2 types of ripples
current ripples & wave ripples
As velocity increases, pressure _____. This is called _____.
decreases; Bernoulli's Principle
What does a T increase do to the CCD? Does it get shallower or deeper?
deeper
Would you expect a shallower or deeper CCD in areas of upwelling?
deeper
Evaporite minerals precipitate in a _____ that was first demonstrated by Usiglio in 1848.
definite sequence
What term is driving the velocity of a turbidity current?
density contrast
Carbonates undergo extensive _____ because the original minerals are metastable.
diagenetic alteration
This term is used for all deposits that are composed of minerals that originally precipitated from saline solutions concentrated by solar evaporation.
evaporites
True or False: Stoke's Law implies that high-density minerals settle slower than low-density minerals.
false
True or False: Fluids can play a role by reducing friction and are the main drivers.
false "...but are not the main drivers."
What is imbrication?
flow direction
What is grainstone?
grain supported, not much mud
As a field geologist, which evaporite are you most likely to see and why?
gypsum - halite dissolves so readily in surface waters except in the most arid regions - anhydrite, being the high-pressure anhydrous form of calcium sulfate, is mostly restricted to depths greater than tens to hundreds of meters
In areas of _____ (i.e. nutrient availability, warmer water), the greater rate of supply makes the CCD deeper.
high productivity
Grain orientation is affected by _____.
imbrication
Water in the Atlantic had _____ time to accumulate CO2.
less
The total volume of evaporites is _____ than carbonates in the rock record but some individual units reach thicknesses greater than _____ km. (e.g. Miocene Messinian of the Mediterranean)
less; 1 km
What causes a turbidity current to stop flowing?
loss of density contrast by deposition
Decreased Pressure = _____ Solubility of CO2
lower
Higher Temperature = _____ Solubility of CO2
lower
Radiolarian chert is...
marine planktonic protozoans
Evaporites form in both _____ and _____ environments.
marine; non-marine
Water in the Pacific had _____ time to accumulate CO2.
more
What are the two varieties of chert?
nodular chert and bedded chert
A rock consisting entirely of ooids with no matrix would be an ____.
oolitic grainstone
Evaporites are excellent indicators of _____, as it takes a hot and arid climate for major evaporite deposits to form.
paleoclimate
Sandstone compositions are based on the relative proportions of _____, _____, and/or _____. Material in between grains in either _____ or _____.
quartz; feldspar; rock fragments matrix (fine-grained - < 30 micrometers - material that is associated with the sand grains); cement (chemical precipitant)
What is packstone?
sand-grain supported with some mud matrix
Material from carbonate sediments is extracted from the dissolved load of the _____ or other _____.
sea; other bodies of water
Evaporites can form _____ for the accumulation of petroleum hydrocarbons in reservoir rocks.
seals
In the Dunham classification, the nature of the grains or framework material form the _____.
secondary part of the classification
How do sedimentology and stratigraphy compare?
sedimentology - process oriented stratigraphy - spatial and temporal variation of sedimentary rock units
The most important forces in grain flows are _____ and _____.
shear stress (fancy T); dispersive pressure (fancy T / P = tan alpha)
Conglomerates are classified according to the ____ of the clasts and _____ of the material.
size; composition
Sandstones are classified according to the _____ of the grains and the _____ of the material.
sizes; composition
Light is the most important control on _____ because of the dominance of photo-autotrophic organisms in carbonate production—at least in the Cenozoic.
skeletal carbonate precipitation
What controls the Carbonate Compensation Depth? (CCD)
solubility of calcium carbonate
What is the naming formula for conglomerate rocks?
support (texture) + clast type + average clast size + "conglomerate" e.g. clast-supported quartzite cobble conglomerate
What is the sediment routing system?
tectonics + climate = erosion + deposition
Solubility of calcium carbonate is determined by _____, _____, and _____.
temperature; pressure; dissolved CO2 in the water
What is the Phi or "log" scale?
theta = -log base 2 * diameter
Salt domes form petroleum _____.
traps
True or False: Stoke's Law implies that slow-moving, highly viscous fluids such as mudflows and density currents can transport coasrser-grained materials more easily than less viscous fluids such as rivers and the wind, despite the normally higher velocity of these less viscous fluids.
true
What is the support mechanism in a liquefied flow?
upward escape of intergranular fluid
What is boundstone?
variable sized particles, bound by algae and cement
Debris flows have a _____ that must be overcome for flow to initiate. (Characteristic of Bingham plastic).
yield strength
