Clastic Sedimentary and Its Environments

Clastic sediment rocks are rocks which are formed from broken pieces of other pre-existing rocks by physical weathering. Then, rock particles are transported to lower lying areas. Mechanically eroded small pieces of rocks are usually formed in an angular shape because of a natural fracture point when erosion takes place initially.

When rock particles are transported, their shapes become rounded because of abrasion. Figure 1 demonstrates the shape of clastic particles. Furthermore, rock particles will be sorted due to conditions; for example, the flow rate of water transporting particles, size and weight of rocks, and the hardness of each rock. Eroded rock particles will be more rounded and well sorted as time progresses.  Figure 2 shows the definition of clastic particle sorting.

shape of clastic particle

Figure 1 – Shape of Clastic Particles

Figure 2 – Sorting of clastic sedimentary rocks

(Ref Image: http://www.tankonyvtar.hu/hu/tartalom/tamop425/0038_foldrajz_mineralogy_Da/images/Fig_2_7.jpg)

Environments For Clastic Sedimentary

Alluvial

Alluvial environment includes meander belts on flood plains, river channels (fluvial), alluvial fans and alluvial plains. When water flows, it erodes substances from fast flowing regions and deposits the material in slow moving areas. So, channels will move over time due to this action. When channels move, a distinctive sedimentary sequence is built. Coarse sands / gravels are on the floor of a channel and fine particles, such as silts and clays are on top of the flood plan. This case is known as a fining upward alluvial cycle.

Desert

This environment is dry, so sand in a desert will be blown by the wind. This will result in sand dune formations (Figure 3) which are characterized, as well sorted sand, with cross bedding features.

Figure 3 – Sand Dune

(Ref Image: https://c2.staticflickr.com/6/5176/5419017309_3dc12d3d9c.jpg)

Deltaic

Deltas are formed where rivers meets the sea. Deltaic environment (Figure 4) has a mixed geological characteristic characterized by deposit patterns of alluvial freshwater and fossiliferous marine life.

Figure 4 – Deltaic Environment

(Ref Image: http://w3.salemstate.edu/~lhanson/gls214/images2/delta_struct.gif)

Beach and Bar

Beach and bar sands occur from wave motion and particles in this environment are typically well rounded and sorted. Bedding inclines toward the sea and oscillation ripples in a surf zone.

Shallow Marine

 Shallow marine environment is sedimentation on continental shelves, which is determined by tidal currents and wave bottoms.

Turbidite

Turbidite is formed by submarine slumps when sediment at the top slope is dislodged and moves as a turbid flow down the slope.

Figure 5 – Diagram of Sedimentary

(Ref Image: https://classconnection.s3.amazonaws.com/900/flashcards/2771900/png/depositional_envmts1360714480033.png)

References 

Richard C. Selley, 2014. Elements of Petroleum Geology, Third Edition. 3 Edition. Academic Press.

Norman J. Hyne, 2012. Nontechnical Guide to Petroleum Geology, Exploration, Drilling & Production, 3rd Ed.. 3 Edition. PennWell Corp.

Richard C. Selley, 1997. Elements of Petroleum Geology, Second Edition. 2 Edition. Academic Press.

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