Geology Chapter 6: Sedimentation Processes

Study Notes

Physical weathering: Disintegration of rocks into smaller fragments without chemical alteration.
Chemical weathering: Decomposition of rocks through chemical reactions.

Figure 6.1 illustrates the processes (weathering, erosion, transportation, deposition, burial, and diagenesis) in cyclical form, visualized with a cross-section of Earth's layers.
- Shows the weathering and erosion of rocks at the surface
- Shows the transportation of materials, such as via streams, wind, or glaciers
- Shows the accumulation of sediments in valleys
- Shows sediments undergoing compaction and lithification.

Current strength and distance of transportation can affect:
- Size of clastic particles
- Sorting of clastic particles
- Rounding of clastic particles
Figure 6.6 displays images of well-sorted and poorly-sorted sand, illustrating the variation in particle size
Figure 6.7 shows the rounding of sand grains, dependent on the distance traveled.

Table 6.1 details the minerals present in sediments derived from granite, differentiating by weathering intensity (low, medium, high).

Figure 6.8 provides a diagram illustrating how sedimentary basins develop on rifted continental margins. This shows the process from splitting of the continental crust, to the formation of rift valleys, to the filling of the depression with sediment from shallow oceans.

Continental: Lakes, alluvial, desert, glacier
Shoreline: Deltas, beaches, tidal flats
Marine: Deep sea, continental shelf, organic reef, continental margin and slope
Figure 6.9 visually outlines these varied sedimentary settings, illustrating their characteristics.

Environments of siliciclastic sediments: Continental (alluvial, desert, lake, glacial), Shoreline (deltas, beaches, tidal flats), Marine (shelf, margin, slope, deep sea)
Environments of chemical and biological sediments: Carbonate deposits (organic reefs, beaches, shelves, tidal flats), Siliceous environments (deep sea), Evaporite environments (lakes).
Table 6.2 lists major chemical and biological sedimentary environments with their agents of precipitation and resulting sediments.

All features related to sediments during deposition.
- Bedding or stratification
- Cross-bedding
- Graded bedding
- Ripples
- Bioturbation structures
Figure 6.11 displays cross-bedding patterns in both deserts and beaches, illustrating their directionality.
Figure 6.13 exemplifies ripple marks, with symmetrical and asymmetrical patterns.
Figure 6.12 illustrates modern and ancient ripple marks.
Figure 6.14 displays bioturbation structures.
Figure 6.15 is a Visual aid to bedding sequence from different depositional environments

Compaction reduces sediment volume and expels water.
Cementation (Precipitation of minerals binding sediments together).
Figure 6.16 depicts diagenetic processes, including compaction and cementation, and the outcomes of different sedimentary rocks which result from these processes.

Classification of sediments by particle size
- Gravel: Boulder, cobble, pebble
- Sand
- Silt
- Mud
- Clay
Table 6.3 provides a table about the particle size of sediments and resulting sedimentary rocks, such as conglomerate, sandstone, siltstone, mudstone, shale, and claystone.
Four important sandstone groups: Arkose, Lithic, Quartz arenite, Graywacke (Figure 6.20).

Chemical Sedimentary rocks: Limestone, Chert, Organics, Phosphorite
Biological Sedimentary rocks: Dolostone, Iron formation, Evaporite
Table 6.4 details the classification of biological and chemical sediments and sedimentary rocks by chemical composition.
Figure 6.22 displays pictures of Limestone, Chert, Gypsum, and Halite.

A geologist might derive conclusions on sandstone origin by looking at the composition and sedimentary structures showing the source material of the granite.
The greater intensity and wider extent of weathering over recent 10 million years is evident in sediments as more eroded minerals in recent sediments compared to older ones.
Sands on a basalt mountain coastal range would be expected to be made up of fragments of basalt in various sizes and degrees of rounding.