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6 principles of flow and sedimentation
- 1. All natural systems tend toward a state of equilibrium that reflects and optimum use of energy. This state of equilibrium is expressed as a graded profile in fluvial systems, or as a base level in coastal to marine systems. Along such profiles, there is a perfect balance between sediment removal and accumulation.
- 2. Fluid and sediment gravity flows tend to move from high to low elevations, following pathways that require the least amount of energy for fluid and sediment motion.
- 3. Flow velocity is directly proportional to slope magnitude.
- 4. Flow discharge (subaerial or subaqueous) is equal to flow velocity times cross-sectional area.
- 5. Sediment load (volume) is directly proportional to the transport capacity of the flow, which reflects the combination of flow discharge and velocity.
- 6. the mode of sediment transport (bedload, saltation, suspension) reflects the balance between grain size/weight and flow competence.
The product of sedimentation in a particular depositional environment; hence, it includes the 3d assemblage of strata whose geometry and facies lead to the interpretation of a specific paleodepositional environment. They form the building blocks of systems tracts.
5 principles of sedimentation
- 1. Walther's law, within a relatively conformable succession of genetically related strata, vertical shifts of facies reflect corresponding lateral shifts of facies.
- 2. The direction of lateral facies shifts (progradation, retrogradation) reflects the balance between sedimentation rates and the rates of change in te space available for sediment to accumulate.
- 3. Processes of aggradation or erosion are linked to the shifting balance between energy flux and sediment supply, excess enercy flux leads to erosion, excess sediment load triggers aggradation.
- 4. The bulk of clastic sediments is derived from elevated source areas and is delivered to sedimentary basins by river systems.
- 5. As environmental energy decreases, coarser-grained sediments are deposited first.
- the aspect, appearance, and characteristics of a rock unit, usually reflecting the condition of its origin; esp. as differentiating the unit from adjacent or associated units. A particular combination of lithology, structural and textural attributes that defines features different from other rock bodies.
- Facies are controlled by sedimentary processes that operate in particular areas of the depositional environments. Hence, the observation of facies helps with the interpretation of syn-depositional processes.
- Groups of facies genetically related to one another and which have some environmental significance.
- The understanding of facies associations is a critical element for the reconstruction of paleo-depositional environments. In turn, such reconstructions are one of the keys for the interpretation of sequence stratigraphic surfaces.
- A general summary of a particular depositional system, involving many individual examples from recent sediments and ancient rocks.
- A facies model assumes predictability in the morphology and evolution of a depositional environment, inferring "standard" vertical profiles and lateral changes of facies. Given the natural variability of allocyclic and autocyclic processes, a dogmatic application of this idealization introduces a potential for error in the interpretation.
- Colluvial and alluvial fans
- fluvial environments
- lacustrine environments
- aeolian environments
Coastal (marginal marine) environments
- River mouth environments
- -regressive river mouths ie. deltas
- -transgressive river mouths ie. estuaries
- Open shoreline (beach) environments
- Shallow marine environments
- -inner and outer shelf
- Deep marine environments
- -continental slope
- -abyssal plain (basin floor)
A vertical change of facies implies a corresponding later shift of facies within a relatively conformable succession of genetically related strata.
(soil science) deals with the study of soil morphology, genesis, and classification.
formation of soil
the physical, biological, and chemical transformations that affect sediments and rocks exposed to subaerial conditions.
(fossil soils) are buried or exhumed soil horizons that formed in the geological past on ancient landscapes.
Data prove to provide the most compelling evidence for sequence delineation, paleogeographic reconstructions, and stratigraphic correlations, especially when dealing with lithologiclly monotonous successions that lack any high-resolution time control.
Help to determine where unconformities precisely occur.
Applications of pedological studies
- 1. Interpretations of ancient landscapes, from local to basin scales.
- 2. interpretation of ancient surface processes (sedimentation, nondeposition, erosion), including sedimentation rates and the controls thereof.
- 3. Interpretations of paleoclimates, including estimations of mean annual temperatures.
- 4. Stratigraphic correlations, and the cyclic change in soil characteristics in relation to base-level changes.
Workflow in sequence strat
- Step 1. Tectonic setting, type of sed basin need a basin-subsidence
- step 2 paleodepositional environments
- step 3 sequence strat framework a. Stratal terminations b. stratigraphic surfaces c. Systems tracts and sequence
Mechanisms of crustal subsidence
- 1 crustal thinning
- 2 mantle lithospheric thinning
- 3 sedimentary and volcanic loading
- 4 tectonic loading
- 5 subcrustal loading
- 6 asthenospheric flow
- 7 crustal densification
- Terrestrial rift valleys
- proto oceanic rift troughs
- Continental rises and terraces
- continental embankments
- intracratonic basins
- continental platforms
- active ocean basins
- oceanic islands, aseismic ridges and pateaus
- dormant ocean basins
- threch-slope basins
- Fore-arc basins
- intra-arc basins
- back-arc basins
- retro-arc foreland basins
- remnant ocean basins
- peripheral foreland basins
- piggyback basins
- foreland intermontane basins (broken foreland)
- Transtensional basins
- transpressional basins
- transrotational basins
- Intracontinental wrench basins
- successor basins
Retroarc foreland figure 2.63
Greater subsidence toward load-> divergent time lines
Flex urial tectonics
partitioning of the foreland system in response to orgenic loading
long-wavelength lithospheric deflection in response to subduction processes.
thermal subsidence+mechanical subsidence (extensional tectonics) + sediment (isostatic) loading
- Interplay between accommodation and sedimentation
- area of epeiric (epicontinental) seaway may change with no eustatic change
- underfilled phase
- deep marine environment in the foredeep
- flexural uplift>dynamic subsidence
- dynamic subsidence>flexural uplift
- shallow marine environment across the foreland system
- dynamic subsidence>flexural uplift
- fluvial environment across the foreland system
- flexural uplift>dynamic subsidence
Defined by: nature of the contact nature of the depositional systems, types of stratal terminations, depositional trends above and below
Identify systems tracts and define sequence
- Stratal stacking patterns
- Architectural position
continuous subsurface imaging; tectonic setting; structural sytles; regional stratigraphic architecture; imaging of depositional elements; geomorphology
Vertical stacking patterns; grading trends; depositional systems; depositional elements; inferred lateral facies trends; calibration of seismic data
Lithology; textures and sedimentary structures; nature of stratigraphic contacts; physical rock properties; paleocurrents in oriented core; calibration of well-log and seismic data
3D control on facies architecture; insights into process sedimentology; lithofacies; depositional elements; depositional systems; all other applications afforded by core data
Depositional environment; depositional processes; diagenesis; absolute ages; paleoclimatespaleoclimates
Depositional environments; depositional processes; ecology; relative ages
Degree of soil formation (soil maturity) related to?
- rates of base level change
- controls rates of fluvial aggradation and channel amalgamation
- low sed rate->good paleosol
- best developed at sequence boundary
basic principles of ichnology
- 1. Trace fossils generally reflect the activity of soft-bodied organisms, which commonly lack hard (preservable) body parts. In many environments, such organisms represent the dominant component of the biomass.
- 2. Trace fossils may be classified into structures reflecting bioturbation (disruption of original stratification or sediment fabric; e.g., gracks, trails, burrows); biostratification (stratification created by organism activity; e.g., biogenic graded bedding, biogenic mats); biodeposition (production or concentration of sediments by organism activity; e.g. fecal pellets, products of bioerosion); or bioerosion (mechanical or biochemical excavation by an organism into a substrate; e.g. borings, gnawings, scrapings, bitings).
- 3. Trace fossils reflect behavior patterns, and so they have long temporal ranges. This hampers biostratigraphic dating, but facilitates paleoecological comparisons of rocks of different ages. Basic behavior patterns include resting, locomotion, dwelling and feeding, all of which can be combined with excape or equilibrium structures.
- 4. Trace fossils are sensitive to water energy (hence, they may be used to recognize and correlate event beds), substrate coherence, and other ecological parameters such as salinity, oxygen levels, sedimentation rates, luminosity, temperature, and the abundance and type of nutrients.
- 5. Behavior patterns depend on ecological conditions, which in turn relates to particular depositional environments. Hence, trace fossils tend to have a narrow facies range, and can be used for interpretations of paleo-depositional environments.
- 6. Trace fossils tend to be enhanced by diagenesis, as opposed to physical or chemical structures which are often obliterated by dissolution, staining or other diagenetic processes.
- 7. An individual trace fossil may be the product of one organism (easier to interpret), or the product of two or more different organisms (composite structures, more difficult to interpret).
- 8. An individual organism may generate different structures corresponding to different behavior in similar substrates, or to identical behavior in different substrates. At the same time, identical structures may be generated by different organisms with similar behavior.
extensional stretching, erosion during uplift, and magmatic withdrawal
Cooling of lithosphere following either cessation of stretching or heating due to adiabatic melting or rise of asthenospheric melts
Sedimentary and volcanic loading
Local isostatic compensation of crust and regional lithospheric flexure, dependent on flexural rigidity of lithosphere, during sedimentation and volcanism
local isostatic compensation of crust and regional lithospheric flexure, dependent on flexural rigidity of underlying lithosphere, during overthrusting and/or underpulling
Lithospheric flexure during underthrusting of dense lithosphere
dynamic effects of asthenospheric flow, commonly due to descent or delamination of subducted lithosphere
Increased density of crust due to changing pressure/temperature conditions and/or emplacement of higher-density melts into lower-density crust
Terrestrial rift valleys
- rifts within continental crust commonly associated with bimodal volcanism.
- Modern example-Rio Grand Rift
Proto-oceanic rift troughs
- incipient oceanic basins floored by new oceanic crust and flanked by young rifted continental margins.
- modern-Red Sea
Continental rises and terraces
- Mature rifted continental margins in intraplate settings at continental-oceanic interfaces.
- Modern example-East coast of USA
- progradational sediment wedges constructed off edges of rifted continental margins.
- Mondern example-mississippi gulf coast
- Broad cratonic basins floored by fossil rifts in axial zones.
- Modern example-chad basin(Africa)
- Stable cratons covered with thin and laterally extensive sedimentary strata.
- Modern example-Barents sea (Asia)
Active ocean basins
- Basins floored by oceanic crust formed at divergent plate boundaries unrelated to arc-trench systems (spreading still active).
- Modern example-Pacific Ocean
Oceanic islands, aseismic ridges and plateaus
- Sedimentary aprons and platforms formed in intraoceanic settings other than magmatic arcs.
- Modern example-Emperor-Hawaii seamounts
Dormant ocean basins
- Basins floored by oceanic crust, which is neither spreading nor subducting (no active plate boundaries within or adjoining basin).
- Modern example-Gulf of Mexico
- Deep troughs formed by subduction of oceanic lithosphere.
- Modern example- Chile Trench
- Local structural depressions developed on subduction complexes.
- Modern example- Central America Trench
- Basins within arc-trench gaps.
- Modern example- Sumatra
- Basins along arc platform, which includes superposed and overlapping volcanoes.
- Modern example- Lago de Dicaragua
Oceanic basins behind intraoceanic magmatic arcs (including interarc basins between active and remnant arcs), and continental basins behind continental-margin magmatic arcs without foreland fold-thrust belts.Modern example-Marinas
retro-arc foreland basins
- Foreland basins on continental sides of continental-margin arc-trench systems (formed by subduction-generated compression and/or collision).
- Modern example-andes foothills
remnant ocean basins
- Shrinking ocean basins caught between colliding continental margins and/or arc-trench systems, and ultimately subducted or deformed within suture belts.
- modern example-bay of Bengal
peripheral foreland basins
- Foreland basins above rifted continental margins that have been pulled into subduction zones during crustal collisions (primary type of collision-related forelands).
- Modern example-Persian Gulf
- Basins formed and carried atop moving thrust sheets.
- Modern example-Peshawar Basin (Pakistan)
Foreland intermontane basins (broken forelands)
- Basins formed among basement-cored uplifts in foreland settings.
- Modern example-Sierras Pampeanas basins (Argentina)
- Basins formed by extension along strike-slip fault systems.
- Modern example-salton sea (California)
- Basins formed by compression along strike-slip fault systems.
- Modern example-Santa Barbara Basin (California)
- Basins formed by roatation of crustal blocks about vertical axes within strike-slip fault systems.
- Modern example-Western Aleutian fore-arc
intracontinental wrench basins
- Diverse basins formed within and on continental crust owing to distant collisional processes.
- Modern example-Quaidam Basin (China)
- Former failed rifts at high angles to continental margins, which have been reactivated during convergent tectonics, so that they are at high angles to orogenic belts.
- Modern example-Mississippi Embayment
- Rifts formed at high angles to orogenic belts, without preorogenic history (in contrast with aulacogens).
- Modern example-Baikal Rift (Siberia)
- Basins formed in intermontane settings following cessation of local orogenic or taphrogenic activity.
- Modern example-Southern Basin and Range (Arazona)
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