GEO 142 LECTURE 3 TODAYS MATERIAL: Sedimentary Environments Sedimentary Environments Entrainment Entrainment Transport Transport Deposition Deposition

GEOL 332 Course Schedule (updated)

Sedimentary Rock Description: Color Color Composition Composition Texture Texture Structure Structure Fossils Fossils Geometry Geometryhttp://core.ecu.edu/geology/rigsbyc/rigsby/Sedimentology/OrangeBible.html

Particle Size Distribution (Sorting) In statistics, the standard deviation is a measure that is used to quantify the amount of variation or dispersion of a set of data values. (SD or σ) The example at the right is called a “normal” or “Gaussian” distribution.

Particle Size Distribution (Sorting) Histogram, frequency distribution and cumulative frequency curves of grain size distribution data. Note that the grain size decreases from left to right.

Particle Size Distribution (Skew) negative skew: The left tail is longer; the mass of the distribution is concentrated on the right of the figure. The distribution is said to be left- skewed, left-tailed, or skewed to the left. positive skew: The right tail is longer; the mass of the distribution is concentrated on the left of the figure. The distribution is said to be right- skewed, right-tailed, or skewed to the right.

Indicators of Maturity Roundness Roundness Sphericity Sphericity Mineralogy Mineralogy

Sedimentary Environments control: The energy required to move the particle(s) The energy required to move the particle(s) The distance travelled by the particle(s) The distance travelled by the particle(s) The source of sediment, the location of sedimentation The source of sediment, the location of sedimentation

Sedimentary Processes Flowchart: Source Material Source Material Weathering Weathering Transport Transport Deposition Deposition Diagenesis Diagenesis

LEARN: Cenozoic: Periods Periods Epochs Epochs Mesozoic: Periods Periods Epochs Epochs Paleozoic: Periods Periods Precambrian: EONs EONs 1.Name 2.Beginning and Ending time (Ma)

A summary of the principal sedimentary environments Nichols, 2009

The pathway of processes involved in the formation of a succession of clastic sedimentary rocks, part of the rock cycle.

Components: 1.Grains 2.Matrix 3.Porosity 4.Cement

Snowfall adds to the mass of a glacier in the accumulation zone and as the glacier advances downslope it enters the ablation zone where mass is lost due to ice melting. Glacial advance or retreat is governed by the balance between these two processes.

Glacial landforms and glacial deposits in continental glaciated areas

At continental margins in polar areas, continental ice feeds floating ice sheets that eventually melt releasing detritus to form a till sheet and calve to form icebergs, which may carry and deposit dropstones.

The geomorphological zones in alluvial and fluvial systems: in general braided rivers tend to occur in more proximal areas and meandering rivers occur further downstream.

Several types of river can be distinguished, based on whether the river channel is straight or sinuous (meandering), has one or multiple channels (anastomosing), and has in- channel bars (braided). Combinations of these forms can often occur.

Types of alluvial fan: debris-flow dominated, sheet flood and stream-channel types – mixtures of these processes can occur on a single fan.

Facies distribution in a freshwater lake with dominantly clastic deposition.

A cross-section from the continental shelf through the continental slope and rise down to the abyssal plain.

Delta deposition can be divided into two sub environments, the delta top and the delta front.

Differences in the grain size of the sediment supplied affect the form of a delta: (a) a high proportion of suspended load results in a relatively small mouth bar deposited from bedload and extensive delta-front and prodelta deposits (a) a high proportion of suspended load results in a relatively small mouth bar deposited from bedload and extensive delta-front and prodelta deposits (b) a higher proportion of bedload results in a delta with a higher proportion of mouth bar gravels and sands.

(a)A delta prograding into shallow water will spread out as the sediment is redistributed by shallow- water processes to form extensive mouth-bar and delta-front facies. (b)In deeper water the mouth bar is restricted to an area close to the river mouth and much of the sediment is deposited by mass-flow processes in deeper water.

Depositional environments on a submarine fan.

Principles of superposition: (a) a ‘layer-cake’ stratigraphy; (b) stratigraphic relations around a reef or similar feature with a depositional topography.

Gaps in the record are represented by unconformities: (a) angular unconformities occur when older rocks have been deformed and eroded prior to later deposition above the unconformity surface; (b) disconformities represent breaks in sedimentation that may be associated with erosion but without deformation.

Zonation schemes used in biostratigraphic correlation. (Adapted from North American Commission on Stratigraphic Nomenclature 1983.)

The main decay series used in radiometric dating of rocks: the K– Ar, Rb–Sr and U–Pb systems are the ones most commonly used.

In marine seismic reflection surveys the ship tows the energy source, the airgun, and the receivers either as a single line or in multiple lines to generate a 3-D survey.

Nichols, Sedimentology and Stratigraphy, Wiley & Blackwell, pp Laminar and turbulent flow of fluids through a tube Laminar and turbulent flow of fluids

The lift force resulting from the Bernoulli effect causes grains to be moved up from the base of the flow. Nichols, Sedimentology and Stratigraphy, Wiley & Blackwell, pp. 432.

Particles move in a flow by rolling and saltating (bedload) and in suspension (suspended load). Nichols, Sedimentology and Stratigraphy, Wiley & Blackwell, pp. 432.

The Hjülstrom diagram shows the relations between the velocity of a water flow and the transport of loose grains. Once a grain has settled it requires more energy to start it moving than a grain that is already in motion. The cohesive properties of clay particles mean that fine- grained sediments require relatively high velocities to re- erode them once they are deposited, especially once they are compacted. (From Press & Siever 1986.)

Nichols, Sedimentology and Stratigraphy, Wiley & Blackwell, pp Upward Fining in a bedUpward Coarsening in a bed Upward Fining and Upward Coarsening within individual beds and fining-up and coarsening-up patterns in a series of beds.

Silt Turbidite: Structural divisions follow Bouma (1962) as modified by van der Lingen (1969). Mud turbidite facies model. Structural divisions after Piper (1978) and Stow (1977).