Pt 3 Flashcards
14C half life
This is 5730 years which makes carbon 14 unuseful for dating things older than 50 kyr
18O vs. evaporation, precipitation, glaciation, land, lakes
the heavier 18O is preferred in a liquid state so evaporation will leave more of the heavier isotope and precipitation will prefer the heavier isotope.
This means that during glacial highs the ocean has high 18O and during warm periods it has more 16O because ice partitions 16O.
This also means that at latitude extremes and at high elevation there will be less 18O.
As lakes become more arid they become enriched in the heavier isotope.
Abrupt contacts
These are the most common contacts that directly separate lithologically different beds. AKA a sharp contact.
Abyssal Plane Depositional Environment
These are dominated by hemipelagic muds and ooze oftentimes bioturbated. The water in the deep water is very cold but is oxygenated because of deep sea churning related to more briny fluid circulation (glaciers do not freeze salt)
Accumulation and preservation space
The accumulation space is the area of elevation available for accumulating material.
There is an erosional line that defines the preservation space by being the space where migration will not erode the material.
Preservation space can change due to compression/subsidence, rising water table, or changes in migration.
Acme zone
This is the zone of maximal abundance. It is important for climate studies and used in reference to pollen counts and similar measures that can be compared as a ratio.
Actualism
The present processes approximate the past but it must be interpreted with a grain of salt.
Aggradation
This is the vertical build up of the sedimentary sequence. It usually coincides with a relative rise in sea level that is even with the amount of sediment supply.
In comparison progradation is the lateral outward motion of sedimentary sequences.
ahermatypic coral deposits
These will be more likely be framestones where the allochems are bound at deposition because of the calmer enviroment.
Allochems
These include ooids, pisoids, peloids, oncoids, and intrachlasts. It includes any carbonate clasts with D>fine sand (63microns)
Allochthonous carbonates
This is all carbonates with coarse grains (10% has D>2mm) that are not organically bound at deposition indicating that grains were transported.
If it is grain supported it is a packstone.
If it is matrix supported grainstone.
If there are more than 10% grains then it is a wackestone.
If there are less than 10% grains than it is a mudstone.
Allocyclic succession
These are cause by external influences like tectonics or climate. They are widespread and not limitted to one basin.
Alpha Decay
This is the release of 4He causing the daughter atom to have 2 less protons, neutrons, and electrons.
Angular Unconformity
This is when younger sediment sits about older strata that is older and was tilted, folded, and eroded.
Assemblage Zone
This is marked by the appearance of one fossil within an assemblage. It is notable because it is the time when all the fossils are present.
Assimilation
This is the integration of gaseous 14C within CO2 in organic compounds, primarily plants.
Attentuation
This is the idea that high frequency waves do not penetrate deep into the subsurface and have lower resolution whereas long wavelengths have better resolution at high depths because they do not attenuate.
Autocyclical successions
These are like cyclical successions that are controlled by interbasin processes and therefore lack lateral continuity.
This includes the tetonic spurts related to alluvial fan deposits.
Back Barrier deposits
The sub-enviroments of this area vary with the barrier island configuration but can show signs of being marshy (anoxic, organics) to bidirectional channelized flow that produces lenticular and flaser bedding.
Barred/Borderland Basins
These are “underwater lakes” related to shallow marine depressions that are in the “anoxic zone” where water does not circulate and is not readily replenished with oxygen. It occurs on the continental slope where deposition does not occur.
These basins are most common where structure controls (West Coast CA) and are significant because they, like lakes, accumulate alot of organic sediment which create oil shales and can record cyclical depositions related to paleoclimates. Additionally, ferromanganese and phosphorites can precipitate here.
Barrier island facies from backshore to offshore
root traces within fine sands. coals and other lagoon deposits
Eolian dunes (trough cross beds, 3d ripples)
Swash-related deposits (planar beds or multidirectional trough cross beds). Well-sorted, mature sediments.
There are increasingly massive beds of coarse sediments as the breaker zone is at a lower depth.
alternating muds and sands grading into fine sands with bioturbation
Barrier Island Facies Model
General shift from eolian to shallow marine.
Barrier Island Reaction to Eustatic SL Shifts
Transgression: The Barrier islands erode and slump into deeper water
Regression: They prograde like shores or dunes. The Back-barrier becomes increasingly brackish and is capped by evaporites.
Barrier Island Subenviroments
There is the subtidal/subaerial barrier-beach complex: Sand islands about 1-20 m thick and long. This protects the coast from high energy waves.
Back-barrier region: calm, swampy/marshy areas aka a lagoon
Inlet-Channel complex: This is the calmish breaks in the barrier islands that allow for water to transfer between the back and front areas.
Base Level:
This is the plane/surface where total erosion=total deposition. It is usually just below the sea level for most systems and/or lake level also said to be where rivers end in a deposystem.
If sediments are above the base level, then deposition is a short-term placement
Baseline
This is the “elevation” that separates erosion and deposition. It is most commonly marked by the current sea level.
Beach Morphology
Moving seaward:
- Eolian dunes (backshore) grade into the beach that starts with the foreshore this area is below the high tide line
- This grades into a steeper subaqueous zone that is the surf zone
- The base of the surf zone is at the low tide line where another steep dip occurs and this is the breaker zone
- There is then another sloe and that becomes the transition zone and grades into offshore
- Nearshore describes the areas in the surf, breaker, and transition zone.
Beta minus decay
This is when an electron switches to a proton increasing mass number by 1
beta plus decay
This is when a proton switches to a nuetron and loses an electron.
biofacies in submarine fans
Fossils (often broken and rearranged) are very important to these sedimentologists because they are indicators of depth.
Calcium carbonate compensation depth
This is the depth in the ocean where supply=dissolution. It decreases towards the cold poles that can have more carbon dioxide in solution. The lysocline refers to the gradient of carbonate compesation.
Dissolution is preferred in environments with low T, low pH (basic), and low CaCO3. At the equator the warm water lowers the CCD because of the increased supply of carbonates.
Carbon 14 formation
14N+ 1nuetron -> +EMR -> 14C + 1proton
Carbon 14 vs. time
The production of carbon 14 changes with time so to calibrate its use we use the ratio of 14C/ 12C within tree rings.
Carbon Cycle/places of assimilation
Carbon 14 is sequestered from the atmosphere either as CO2 is plants which can then be eaten or as rain (H2CO3-)
Either way it ends of in the ground or as runoff which can then end up in the ocean and sequestered as carbonates. It can also become gaseous again when it decays to 14N
Carbonate ramps
These are similar to continental ramps but with carbonates. The inner shelf have grain/packstones, the outer shelf has pack,wackestones, the slope has wackestone with LS intraclasts that transition to deep water carbonates (micrites). This occurs on the inside of Florida. They differ from reefs sedimentologically by not having framestones or boundstones.
Cenozoic fossils
Pollen, foramifera, diatoms, radiolarians, plankton, mammals
chalk
An earthy LS derived from ooze. It forms in the deep ocean floor particularly near the equator and is more than 50% of the ocean floor and more than two thirds of carbonates.
Chronostratigraphic Units
These are “reference” layers that are used to be related to other rocks. This is like the Jura section of W. Germany for the Jurrassic.
This where rock=time
Chronostratigraphy and Geochronology
Chronostratigraphy is the practice of using observed time to define rocks and successions of rocks. Geochronology is the practice of geologic time.
Clinoforms
This is a fancy term for inclined strata.
Coastal Sand Belt
These are barrier islands. They form in wave dominated coastal systems.
Common Decay series for geochronometry.
Uranium lead dating: This is on the scale of millions to billions of years.
Rb->Ar: This is on the scale of millions to billions of years but makes the bold assumption diffusion=0
14C : ~50 kyr
Fission tracking: 500kyr -> 1 byr
Common Source of Radiogenic Isotopes
The most common source of radiogenic isotopes is from within Earth (lead, uranium, plutonium…)
Common uses of absolute dating
Zircons: deriterial zircons can be used to find the absolute oldest time of deposition.
Authigenic minerals: Direct dating of K-spar using 40K -> 40Ar. This is good because argon is inert. Other gases react with the mineral and thus cannot be used.
Shells/bones/organics: 14C
Igneous associations: Date igneous intrusions and use logic to constrain system.
Competence ADD FBD
The maximum particle size that a flow can move.
Determines by if the flow can exert a force that is greater than tauc
Concordance
This refers to how overlying parasequence beds are conformable. This is what is meant by concordance. It is a place of continuous building out.
Concurrent Range Zone
This is the overlap of LAD and FAD. It is important because it constrains the system.
Conformable strata
This is when there is unbroken/continuous deposition. Beds are separated by conformities and hiatuses are lacking.
Contacts
These represent lithological unit interfaces
Control Points
These are places in the rock record where we have absolute data to constrain the system of interest.
Correlation
Relating units based on age, lithology, or fossil content in geographic space (x,y,z).
Correlation chart
This relates formations or facies to time at various locations.
Cosmogenic Isotopes
This is the formation of radiogenic isotopes from the interactions of atoms with electromagnetic radiation. This is most commonly seen with 14C.
Cross section
This is the observed sequence of rocks as a function of depth.
Curie Point
This is the temperature (~500oC) that magnetically susceptible reorient with the local declination.
Cyclical Sedimentation
This is strata that show characteristic patterns from repeated shifts in the depositional process.
Examples include turbidites, laminated evaporites, LS-shale sequences, coal cyclotherms, black shales, and cherts.
Dating glacial deposits
These are generally difficult to date because they have very low biogenic materials but if they are interbedded with basalts like some in the Andes are it makes things easier.
Decay Constants
This is marked by lambda and represents atoms/time period
Declination
This is the directional vector of the magnetic field at a given point
delta 18O
This is the ratio of 18O/ 16O *1000
Diastems
These are short hiatuses like within microlaminae that are often ignored in the bigger picture.
Discontinuity
This is when both rocks on a contact are sedimentary and of similar character but a clear erosional surface exists between the two surfaces.
Oftentimes the base of the younger layer has lag gravels eroded from the layer below. These are likely due to environmental shifts, or widespread shifts in uplift.
Dolomite Problem
This is the issue that dolomite does not readily precipitate in normal conditions and requires a “pump” to be precipitated yet there seems to be a abnormally massive amount of natural dolomite in the geo-history of earth.
Dolomitization
This is the diagenetic alteration of LS to produce dolomite. It occurs at a depth of 500-3000 m and requires Mg rich water circulating through relatively porous LS and higher temperatures.
Downlap
This is the termination of inclined strata against a lower angle surface. It marks the seaward depositional limit and thus oftentimes represents progradation.
Dunham Carbonate Classification
A classification system that enables classification via hand specimen that emphasizes the grain packing, micrite abundance, and grain binding.
Mud-supported rocks include mudstone (<10% grains) and wackestone (>10% grains)
Grain supported rocks include packstone (>1% mud) and grainstone (<1%mud)
Allochthonous is for coarse sediment not bound at deposition wheras autochtonoous is for coarse grains that are bounded at deposition.
Epicontintental Seaways
These are like pericontinental seas but they are within the continent and are surrounded by land on both sides (Hudson Bay). They differ from normal seas because of limited fetch. This results in a large amount of organic shales similar to lakes with low wave circulation. They also can have storm dominated coastlines that create hummocky cross stratification.
Episodic Sedimentation
This relates to Saddler’s studies and says that rapid events that deposit large amounts of sediment are more likely preserved and therefore the stratigraphic record is likely to be a series of episodic depositional events separated by non-deposition.
Erosional Surface
These are surfaces that are subaerial uncomformaties that form during a sea regression
Eustatic Sea Level/Eustasy
This is where the average sea level is relative to the Center of Earth.
Eustatic sea level changes
This defines global shifts in seal level largely thought to be due to changes in contintental ice reserves, ocean basin volume, aquifer storage, and ocean temperature.
When there is an increase in seafloor spreading there is an increase in sea level.
Evidence for uncommon events having higher preservation
If comparing extreme events (floods, meteorites, rock falls) they appear more often in the stratigraphic record than their recurrence interval would indicate
Fabric
This is how sediments within a rock are related to one another. It can be said to be the internal organization of particles.
It is composed of grains, matrix, cement, porosity, permeability, grain contacts, and sorting.
Facies
This is a recognizable lithology or group of lithologies. It is the “sum of a sedimentary rocks lithologic character and acts as a class of deposit type.”
They are not dependent on locale only on the nature of the rocks. They can be lumped together to create sequences of facies (Bouma Sequence).
These are objective observations of rocks that do not vary with time. interpretations vary with time.
Facies features (10)
This includes grain size/maturity/composition, beforms, structures, geochemical character, diagenetic alternations, fossils, or geophysical character (polarity or magnetic susceptibility)
FAD/LAD
This is the first appearance datum and the last appearance datum.
There is a regional and global distinction as well. Appearance is local and emergence is absolute.
Falling Stage Systems Tract
There is a base level fall at the shoreline and forced regression of the shoreline. This is accompanied by subaerial erosion landward, high rates of progradation and offlap on the shelf-edge delta. There is significant progradation of deep-water lobes/splays.
Ferestrae
These are fossil algea with holes.
Flooding Surface
These are the sharp contacts that form during transgressive lags.
Forced Regression
This is progradation driven by base-level fall which forces a regressive shoreline regardless of the sediment input. It will have progradation with downstepping (seaward movement of shoreline)
Foreshore sediments
The primary process that dominates sediments is wave breaking and this is because as the wave depth approaches 0 the Froude Number approaches infinity (Fr=V/(gD)^.5) Which results in fine upper flow planar bed laminae with good sorting.
If there are larger particles there may be imbrication that is leaning in the foreshore direction.
Foreshore, Backshore, nearshore, shoreface and offshore
Foreshore is the area that is flooded by tides daily
Backshore is the coast
nearshore is always underwater but waves occur
shoreface is the subtidal to wave base area
offshore is the region prior to breaking
Formal Stratigraphic Units (2 types)
Formations: This is 1+ group of facies strictly defined by lithology and bounded by lithologic changes. These must be mappable at a regional scale at Earth’s surface and acts as the base unit for other lithostratigraphic units.
Allostratigraphic Units: These are mappable stratoform bodies defined by bounding.
Formation Nomenclature:
This is “geographic name” + “formation” OR “rock type”
Formations
This is a lithologically distinctive stratigraphic unit that is large enough to be mapped at a regional scale on Earth’s surface. These are often composed of 1+ lithosomes with member beds and groups/supergroups. They act as the base stratigraphic unit.
Formations
This is a deposit that can be mapped on the surface. They are observed from the surface or mapped with seismology. They are gross lithology (sequence of facies) of a rock mass and represent a unit of stratigraphy.
They differ from facies by being a facies because they can be deposited in different sedimentary deposystems. Within a formation a facies may grade or extend beyond the formation and because it is an objective description the same facies can be found in multiple formations across the flobe.
Fossil Use with abundance, body size, duration of existence, range, geography, and habitat
Abundance: increased abundance increases the probability of any fossil being preserved.
Body size: An increased body size decreases the preservation probability
Duration: Fossils that have been around for a very long time are abundant but they are not precise.
Range: Endemic (restricted) vs. Cosmopolitan (wide)
Biogeography: Some regional species are particularly useful for precision.
Habitat: some habitats (low E) are more likely to preserve fossils.
Fractionation
This is the slight shifts in deposition based on atomic mass. These have the greatest impact on phase changes.
light isotopes tend to have slightly weaker bonds and are slightly more volatile.
Froude Number
A dimensionless unit that describes how a surface wave passes through a liquid. The denominator describes the velocity of a surface wave through water and the numerator is the velocity of flow. Therefore a Fr<1 means that the wave’s velocity is greater than the flow’s.
Fr=V/(gD).5 D=water depth
Full sedimentary cycle
Starting at a maximum flooding there is the onset of a forced regession
There is then progradation and subaerial erosion that ends with the lowstand system tract and the minimum flooding surface and there is a brief normal regression as the base level slowly begins to rise.
Rapid base level rise leads to backstepping and a trnsgression which ends with another short normal regression as base level rise slows.
Genetically related sediments
This simply means the sediments were deposited in a laterally continuous segment aka Walthers law holds true.
geochronologic units
This is the relative times based on type sections and chronostratigraphy. It was described before formalized time units so each passage of time is unequal.
It is based on superposition
Geochronometry
This is the absolute measure of time by unstable isotope analyses. It was established very early (11 years) after Bequerel discovered radioactivity and was used in the early 1900’s to prove was much older than previously though because they forgot to consider that potassium decay in the crust creates a large amount of heat.
Geomagnetic time scale before jurrasic
This is done through using core from some of the rift valleys that record polarity.
Global Boundary Stratotype Section and Point (GSSP)
This is the “golden spike” used at the base of highest quality column that represents a geochronological sequence.
Modern days we use biostratigraphy or changes in isotopes to mark the shifts between time units.
Gradational Contacts
These show a gradual shift in the depositional enviroment.
Gravity Flows
Characterized by a mass of sediment forming a flow with or without significant fluid composition and is propelled by the particle mass.
This includes density flows (turbidity flows)
Half life
This is the time it takes for have of the parent atoms to decay into daughter atoms and is given by ln(2)/lambda or .693/lambda.
Hemipelagic muds
These are muds that are partly from continental sources. They are usually ~5% organics, ~40% silt and deposit through suspension settling. They are largely red and brown clays, loess from wind, glacial sediments, and colvanic ash.
Hiatus length as a f(unconformity)
From the smallest to largest gap:
Paraconformity, discontinuity, angular unconformity, and non-conformity
Hierarchy of Lithostratigraphic Units (8)
Supergroup
Group
Formation
Member: these can intraformational
Lens
Tongue: This is like a member that specifically begins in one formation and pinches out within another
Bed
Flow: This is like a bed reserved for volcanics
Large scale high angle cross stratification
This is a term that describes the large troughs that form due to grain fall during dune migration. In comparison the low angle trough cross stratification is because of translatent ripple migration.
Highstand systems tract
This is when there is little or deceleterating transgression so there is low rates of progradatation and aggradation. Base level rises at the shoreline and normal regression occurs
How did we develop magnetic polarity
This was developed when using big magnets to track the sea floor and try to find German submarines in WW2.
How does CaCO3 extraction, photosynthesis, organic decay, feeding/deposition, and bacteria influence precipitation?
Extraction increases the amount of shells and exoskeletons which create more allochems/micrite.
Photosynthesis lowers carbon dioxide and increases pH. This increases the amount of ooids/micrite.
Decay of soft tissues increases pH and increases precipitation
Feeding and digestion creates pellets.
Bacteria conduct ion exchange and precipitas carbonates.
How does sea level influence submarine fans?
This determines the type of sediment in the fan.
During low stands they are very sandy from beaches being eroded by rivers and subaerial exposure. During this time the fan also has less vertical accumulation and is much more planar.
During highs they are more vertical and have more muddy sediments. They tend to be restricted to the continental slope.
Ideal Transgression/Regression Sequence
The ideal transgressive sequence will start on a beachfront environment with planar sands that transition to siltstones, shales, and then limestones at the highest sea levels. The reverse will occur during the following regression. The transgression usually does not exist.
Inclination
This is a correction angle related to a deviation of magnetic north from vertical. At the equator inclination is 0.
Induced/Anomolous Magnetic Field
This is a magnetically induced field carried by local materials like Fe3O4 (magnetite), FeTiO3 (ilmitite), Fe2O3(hematite)
Intercolated
This is interbeds that progressively fine or thicken.
Interpretting shavian correlation slope change
A change in the slope either means that either section either increases or decreases sedimentation but the slope is a non-unique solution to be confident of which mechanism is dictating the curve. Look at the core to interpret the change in sedimentation.
Intertonguing
This is a form of lateral discontinuity where blocky or bladey intermittent spurts of a different lithology exist.
Is sedimentation quantized
Yes. Saddler’s studies show that the system is either depositing or not.
Isochronous
This is the basis of sequence stratigraphy/correlative beds that looks as strata bounds as being from one point in time. When looking at isochronous surfaces, like bedding planes, we assume that they extend laterally to represent some time.
Isolith Maps
These show how one unit shifts in thickness laterally.
Isopach maps
These show lines of equal sediment thickness not of equal lithology
Isotope
This is an atom with equal electrical properties (electrons and protons) but a different mass.
lapout
This is a change in the depositional environment or a movement of the preservation space. It is hard to distinguish in outcrops because they are oftentimes small shifts in the strata angles.
Law of “Faunal Succession”
This was William Smith’s (a UK canal engineer) idea that fossils changed in the stratigraphic record through a process.
Lithology
The study and description of objective physical characteristics of a rock. Often segmented by color, rock type, mineralogy, grain size.
This is seperated into lithostratigraphic units that are rock units seperated by lithologic changes.
Lithostratigraphic unit inputs (2)
Stratotype: This is the unique stratigraphy or type of rock unit that is exclusively correlated to lithology not time.
Lithosome: This is a rock mass with complex boundaries with other nearby rock masses
Lithostratigrapy
The is the recognition, subdivision, equivalency of sedimentary rocks on the basis of lithology.
Lowstand systems tract
This at a minimum flooding surface where there is a small base level rise at the shoreline and normal regression. It is marked by fluvial onlap, small rates of progradation.
Magnetic Excursions
This is fluctuations of inclination within a given period of polarity. The magnetic field pole can vary by as much as 45o. This changes the magnitude and direction of remnant sediments and can be used to have greater precision regarding the deposition age. Generally they occur on a timescale of 500-3000 years.
Magnetic Reversals
This is the switch of the magnetic field (N and S switch). This happens between 100-1000’s of years. It occurs over a very short time period.
Magnetic sediments
In low energy environments, as particles that are magnetically susceptible settle, they will reorient themselves with the local magnetic field. Thus their orientation is proportional to the orientation and strength of the magnetic field at the point in time they settled.
Magnetic Susceptibility
This is the ease to which something is magnetically oriented. It is used in magnetostratigraphy to ID specific sediments, provenance, and correlation.
Magnetostratigraphic correlation
This is the process of using control points and remnant polarities to identify when sediments were deposited. It generally assumes that bed thickness is proportional to how long it took to deposit the sediments which assumes that there are no hiatuses within the section.
Main Magnetic Field
This is the magnetic field produced by the outer core and would be homogenous without local deviation.
Marl
A mudstone with interlayers of siliclastic mud or silt that is torigenous.
Mass Spectrometer
This is a fancy particle accelerator that put particles around a curve and uses the difference in mass to orient their path. They intersect a sensor at different positions and the position is proportional to their mass. The mass of the atoms is used to identify the elements present.
Max low sea level in Pleistocenes
100-120 m below current sea level
Maximum Flooding Surface
This is where sea level stabilized at its deepest point. It is seen in the seismic section by where the seaward downlaps switch from backstepping to prograding during regression.
Measured Sections
These descriptions of a section of rock act as samples for the development of regional correlation charts.
Different measured sections are compared based on their marker horizon which is the known boundary, geophysical property, lithology, or datum.
Mesozoic fossil assemblages
These are most notably marked by the Permian extinction
ammonites, forminferons, pollen, ostracodes, marine fossils
Modern reef controls
Reef formers aka Corals: Hermatypic corals are tropical shallow corals that rapidly build
Ahermatypic corals are deep water corals that are very slow to build
Reef Binders: These are algaes that laterall bind things
Net transport of sediment due to waves
There is an assymmetry of velocity where it peaks when moving beachward. This means that there is only transport in the forward motion of sediments.
Nonconformity
This is when sediments overlay meta or igneous rocks. This represents a significant time gap, uplift, and erosion.
Normal and Reverse Polarity
Normal polarity is black. Reverse polarity is white. We are currently in a normal version of polarity.
Normal Regression
Progradation driven by sediment supply. Sedimentation rates outpace the rates of base-level rise at the coastline.
Ocean Anatomy
Starting at a passive margin there is the Continental shelf (low dip), which then has the shelf break at ~100 km from the shore and depths of ~200 m. This is followed by the erosive continental slope (~4o slope) and meets the continental rise which is subaqueous fans. This grades into the Abyssal Plane (slope=0) until the MOR is reached.
The only difference in an active margin is everything is called a trench.
Oceanic/Deep-Water sedimentology
These are rarely studied because they only exist as ompholites, have very low sedimentation rates, and economic value.
Generally along the continental slope submarine canyons have turbidity flows and in the deep oceans there is very slow sediment accumulation from loess, glaciers/icebergs, and MOR’s.
Offlap
This is the progressive offshore shift of updip terminations. It is marked by updip terminations ending on older beds. It is diagnostic for forced regressions and base level lowering. There are lower angle strata intersecting higher angle underlying beds.
Oldest sea floor
This is the Jurassic oceanic plates that are on the East coast. This is the oldest constraint that we have for general paleomagnetism.
Onlap and types
This is when low angle cross-strata intersect with a higher angled stratigraphic surface. It marks the lateral termination of a sedimentary unit at its depositional limit.
Types: Marine, coastal, and fluvial
Onlap, coastal
Refers to the termination of low-angle strata against more inclined ravinement surfaces in the shallow water strata.
Onlap, Fluvial
Refers to the termination of low angle strata against a more inclined terrestial surface. This occurs during base level rises. If it is a normal regression it will be on top of toplap surfaces and if its in a trasgression it will be on an subaerially eroded surface.
Onlap, Marine
This is the termination of low-angle strata against a steeper stratigraphic surface against an underlying continental slope that is diagnostic of transgression.
Ooze
This is biogenic mud that is common on the abyssal plane. There are two types:
Calcareous fine sand and siliceous ooze from radiolarians and diatoms.
Paleozoic Fossils
Trilobite, canadats, graptolites, fosilinids
Paraconformity
This is where there are parallel beds without distinct erosional surfaces that are oftentimes only confirmed because of dating methods
Parasequences
These are genetically related sediment packages that form a sequence. They are bounded by a marine flooding surface or conformable surface with above/below beds. They are usually on the scale of ~1-20 m.
To analyze parasequence sets in terms of base level/sedimentation rates look at where units start and end to define if there is progradation, aggradation, or retrogradation.
Pelagic sediments
These are derived from the ocean. They include pelagic clays that are derived from loess and calcareous/siliceous ooze.
Peritidal Shoaling Cycles
This refers the cyclical carbonate beds related to Milankovitch cycles.
Thick beds relate to shallow water and shales are deep water. They may also include transgressive lags and drowned carbonate platforms.
pH controlling factor
Biology controls pH by extracting CO2, bioturbing the base, producing organic acids, and producing shells.
Pinchout
This is a form of lateral discontinuity where the shift between lithologies comes to a point or an alternative wedge shape.
Principle of lateral continuity
This says that sediments are generally laid down on horizontal planes that extend in xyz directions
Principle of Lateral Continuity
This basically says that rocks extend laterally showing similar depositional environments and are shown in cross sections where measured sections act as samples related on marker horizons (chronostratigraphic layers), geophysics (magnetic susceptibility), lithology, or datum (base value=0)
Prograding sabkah
While subtidal there are lime muds that has a sharp contact with peloidal grainstones marking the inter-tidal perdiod that transition to a stromatilitic boundstone. This becomes supratidal with the appearence of massive anhydrite, muddy evaporites, and topped with a salt crust.
Progressive graded contacts
These show a gradual change in quality within differing beds. For example SS to sandy shale to shale representing prograding finer grains.
Proximal vs. Distal Turbidites
Proximal turbidites refers to turbidites that have prominent A-C horizons and form on or near the continental shelf. They are up to a meter thick.
Distal turbidites have more intense C-E layers and refers to deeper ocean turbidites.
Radiogenic Isotope Decay
This is when unstable isotopes radioactively decay creating new daughter atoms at a predictable rate that makes them very useful for timing things.
Regression
This is movement of the shoreline towards the ocean or sea. It can occer due to a lowering of sea level or an increase of sediment
Regressive Phase
This is when the sea level lowers.
Relative Sea Level
This is the elevation of the water column with respect to a datum slightly below the ocean floor.
Relative sea level changes
This represents local uplift, subsidence, or ocean upwelling because relative sea level is the sea level with respect to basement rocks.
Relatively Conformable
This refers to a sequence that only has diastoms
sabkah
These are supratidal flats flooded episodically during storms. They tend to be very flat with subsidence. They are similar to playas.
Commonly include algal mats, evaporites, dessication structures, thin muds, fine grained sands. They will tend to form marls.
Saddler: Implications
Sections of sediment representing longer timespans are more likely to have non-deposition.
Saddlers sediment accumulation rate studies
Hypothesis: If sedimentation is continuous then measured sedimentation rates should be independent of the timespan of deposition.
Data: 25,000 + data based on cores, 14C, other radiometric dating, and measured sections
Findings: The shorter the timespan of deposition, the higher the rate of deposition.
Seismic Stratigraphy
This is the use of sound wave two way travel time and amplitude to “see” subsurface surfaces, differentiate materials, and then conduct sequence stratigraphy.
Sequence
This is a genetically related package of sediment bounded at the top and bottom by sequence boundaries (significant stratigraphic surfaces marking a change in the depositional system). These boundaries are either unconformities or the down-dip conformable surfaces that can be regionally traced (downlap onto ocean floor).
They are usually on the scale of 1+ km and correspond to a full stratigraphic cycle of depositional environment shifts.
Sequence of Marine Evaporite Precipitation
This depends on exact chemistry but,
~40 ppm CaCO3 = calcite
~40-60 ppm (Ca,Mg)CO3=dolomite
~60-270 ppm CaSO4H2o*2H2O=gypsum + anhydrite (dehydrated gypsum)
>270 ppm NaCl = halite +- sylvite
Sequence Stratigraphy
This is based on the idea of separating surfaces based on chronostratigraphic significance. It combines the two approaches of correlating rocks using lithology and facies to recognize packages of deposition. It is most often used to recognize a cycle of relative sea-level change and/or sediment supply.
Andy def: The study of rock relationships within the chronostratigraphic framework of unconformities and correlative conformities
Sequence sub-division
Sequence -> Parasequence Set -> Parasequence -> Bed sets -> Beds -> Laminae Sets -> Laminae
Shavian Correlation
This was created by an oil guy that thought that regional biases made biostratigraphy poor. The idea is to plot appearance vs. depth so that you can create a relationship between the depths of the two boreholes.
small delta sign
This stand for the ratio of the heavy isotope to the light isotope. Mathmetically it is shown as 1000((sample-standard)/standard)
Thus positive values show a greater proportion of heavy isotope than is within the standard.
Spontaneous Nuclear Fission
This is when atoms split, like within an atomic bomb. It is very rare but does occur in nature.
Stable isotopes
These are isotopes that do not decay over time. They have similar electric properties but behave physically and sometimes chemically different.
stratigraphic record completeness
This idea is that no section is ever fully complete because there is always some erosion or non-deposition. Completeness is a function of the rate of deposition at one point in time.
Generally beds represent “instant” deposition that are altered during non-deposition.
Stratigraphic sequence features
There are two components, the depositional sequence which is the genetically related conformable sediments bounded by the uncomformitites/correlative uncomformaties.
Submarine Canyons
These are about 100 meter deep subaqueous canyons that formed during the Pleistocene. These oftentimes lead into canyons that were never at the surface (1000’s of meters deep) that are from continued turbidity flows.
Submarine fans
These are oftentimes at the base of the continental slope and are large wet alluvial fan like deposits. They are often sand dominated turbidites that have erosional features, troughs, tool marks, and soft sediment deformation.
Compared to alluvial fans these will have trace fossils, grey anoxic shales, pelagic sediments, and turbidites.
Syndepositional deformation
This is related to soft sediment deformation common on deltas.
Synthem
This is an allostratigraphic unit that is bounded by uncomformities.
System Tract
These are a linkage of contemporaneous deposition systems forming a subdivision of a sequence. They are interpreted based on stratal stacking patterns, position within the sequence, and types of bounding surfaces. Their timing is inferred relative to a curve that describes shoreline base level changes.
This is the concept that certain sedimentation patterns can occur during linked shoaling cycles. They often include many facies that are not linked by the same environment but the same change in processes.
Taxon Range Zone
This is the time range of a single species (LAD-FAD)
Tempesites
These are sandy cross bedded beds that form from storms where the suspended sands rapidly settle out of suspension. Oftentimes this is couples with mudstones.
Temporal Stratigraphic Categories
These are all conceptual categories
geochronological units are divisions of time based on the rock record and superposition
Polarity-chronologic units are divisions of time found via polarity
Dichronic Units: there are unequal spans of time that are identified because of diachronous rock bodies (rocks with 1 or more bounding surfaces that are not developed at the time of deposition aka time synchronous)
Geochronometric units: Isochronous units (of equal timespan) and are direct divisions of geo-time in years
Time Divisions of rock and modifiers
This is the era (Mesozoic), Period (Jurassic), Epoch (Early/lower), Age (Hettongian) distinction.
It is academic
Modifiers include the early, middle, and late times which are abstract.
Time-Rock Divisions and Modifiers
This is the erothem, system, series, stage, zone system that is used in the field.
The modifiers include lower, middle, and upper based on how someone would observe the rocks.
Toplap
Termination of inclined strata against an overlying lower angle surface, mainly resulting from nondeposition or very minor erosion. Strata lapout in the landward direction at the top of the bed. This signifies the base level at the time of deposition. They are most common in normal regressions. Look for the upper beds becoming tangential shoreward.
Topsets, Foresets. and Bottomsets
Topsets are fluvial deposits from the river. They are dominated by sands, gravels, muds, organics (from interweaved lagoons and marshes)
Foresets are silty sands with lightly dipping beds. Also called subaqueous delta plain.
Bottomsets are from suspension settling that are fine laminae that dip more steeply seaward. This is also called the prodelta.
Transgression
Transgression
This is the rise of ocean levels. It is unlikely to be preserved than regressive phases.
Transgression
This is the term that describes the landward shift of the shoreline.
Transgressional Lag
This is the term that underpins the idea that transgression is often not preserved within the sedimentological record. This is because the sediment will be deposited laterally and not vertically.
Transgressive/regressive barrier island deposits
During periods of transgression the islands are eroded away and will often “slump” into the ocean creating soft sediment deformation structures
During periods of regression the barrier islands prograde to form lee side dune cross beds, sand avalanches, and slump structures. Of significance is that the back-barrier environment
can become isolated and thus grades into evaporites.
Transgressive lag
This refers to how a rising sea level equates to a rising base level and thus the coast becomes the point of deposition. This means that the transgressive sequence will jump from coastal (sandstones, shallow marine carbonates) to deep-water deposition (Limestone and shale) and not have the gradual transition that an ideal sequence would show.
This is why trawlers off of the East coast can find mammoth tusks with only loess and biogenic sediments covering them.
Transgressive Surface
This is the surface the sea transgresses over. It seperates low stand system tracts and transgressive system tracts.
Transgressive systems tract
There is a large base level rise and transgression of the shoreline. It is marked by retrogradation (backstepping) and aggradation with more fluvial onlap.
Transition zone sediments
Finer very finely laminated sands that dip seawards
Truncation
This refers to where strata terminate against an overlying erosional surface. This surface is sometimes uneven/hackly and the clinoforms do not end tangentially but abruptly.
Toplap may develop into truncation but truncation is more extreme and implies an angular unconformity.
turbidite anatomy
Head: The erosive part of the flow that scours the base of the bed.
Body: A steady and uniform portion of flow that begins depositing a and b layers of the bouma sequence. It flows faster than the head.
Tail: Dilute part of the flow that can auto suspend fine particles.
Turbidite/Bouma Sequence
.2-.4 m deposits derived form turbidity currents with an a-layer that has a scoured base, massive granular sands, and normal grading of coarse particles.
b layer is planar bedding from the upper flow regime.
c layer has ripple structures and represents the shift from upper to lower flow regimes.
d is laminated silts with tail ripples (lower flow)
e is pelogic (oceanic) and hemipelogic muds.
turbidity flows
A type of gravity flow derived from sediment accumulation following seasonal floods, storms, quakes, or tsunamis and characterized by a shift from plastic to fluid flow. It has low viscosity, high turbulence, and lacks an internal structure.
Type Section
This is the use of biofacies and absolute dating to relate chronostratigraphic units across vast distances like oceans and continents.
Types of Density Flows
Homopycnal flow: This is when the density of the river ~ density of the water. This leads to rapid deposition (v~0)
Hyperpycnal flow: This is when the river is more dense than the water. It leads to currents that deposit fluvial materials at the basin base. This can create an anoxic environment in the base of the lake
This occurs in fluvial deltas.
Types of Stratigraphic Units based on physics (5)
Lithostratigraphic Units: These are based on the law of superposition and superposition
Lithodemic Units: These are intrusions, deformed, meta rocks that do not conform to the law of superposition
Magnetostratigraphic Units: Units defined by remnant magnetic polarity.
Pedostratigraphic unit: 1+ paleologic (soil) horizons
Allostratigraphic units: These are mappable stratiforms (formations/layers) that have bounding discontinuities
Types of stratigraphic units based on geologic age (2)
Chronostratigraphic units are bodies of rocks with known date of deposition that act as control points for other layers
Polarity-Chronostratigraphic Units: These are divisions of geologic time determined by the magnetic poarity.
Unconformity
This is a time of non-deposition that is used for separating younger and older strata based on nondepositions, erosion, or weathering.
Uniformitarianism
This says that the processes that occur now are those that occcured previously. It biases the gradual and continuous depositional events but stratigraphy is biased towards odd events that are more likely to be preserved.
Using decays
Generally we use two decay series to better constrain the system. For example using 238U and 235U.
Value of Shavian Correlation
It enables us to have a better understanding of how sediments were deposited on a regional lateral scale and enables us to have a prediction for missing boreholes. It is like psuedo-kriging.
Walther’s Law
The deposits that form together laterally are superimposed on others vertically if deposition is continuous and post-depositional structure does not shift. The failure of walther’s law is when facies “pinch-out” which indicated that the sedimentological process has terminated laterally when deposition occured.
The implication is that vertical sections reveal lateral relationships.
Water Depth
This is simply how high the average water column is with respect to the ocean floor.
Wave Base
This is the depth where wave oscillation ceases. It is roughly .5*wavelength.
Near the shore the interaction of the oscillation of the wave causes shearing.
What does the slope of a Shavian correlation mean?
The slope is related to the relative rates of sedimentation. Therefore shifts in the slope indicate a shift in sedimentation at one of the locations.
Why do reefs not form near river mouths?
There is too much siliclastic sediment that fluctuates the water composition and blocks sunlight.
Why is dolomite difficult to precipitate?
Mg(OH)2 is stronger than ca(OH)2 making it much less likely to react with carbonic acid and the kinetics for Ca is much more favored.
Dolomite is favored in high Mg/Ca ratio, low Ca/CO3 ratio, low salinity or high T (T>100C)
marine flooding surface
These are surfaces with evidence of abrupt shifts (ravinement surfaces) in water depth
Ravinement surface
This is a minor erosional surface that forms at the trangressive lag.
eustasy vs time
This describes the use of sequence stratigraphy and isotopic analysis to attempt to constrain eustatic shifts in sea level over geo-time.
This has shown large swings in the Pleistocene (+-150 m) and similar large swings throughout the Creteceous over short time periods
