Primary Structure - Structure Geology(Chap 2)

PRIMARY STRUCTURES

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Ce01082741 CE01082754 CE01082122 CE01082758 CE0105171

1. Abdelrahman Hosameldin
2. AHMED MOHAMED HOSSEINI
3. Muhammad Irfan
4. Mahboob gamal mahboob
5. Sulaiman Arif Abidin

PRIMARY - - STRUCTURE

• Original features of both Igneous & Sedimentary Rocks which resulted from deposition & emplacement.

• Primary Structures originate during the early formation of rocks

- Forms before sediments Lithified(Deposition phase)

- Forms before lava becomes volcanic/extrusive rocks

- Forms before magma becomes plutonic/intrusive rocks

• Because of this, the structure reflects all 3 conditions during Sedimentation, Volcanism, & Intrusion.

TYPES OF PRIMARYSTRUCTURE

Flow Layering

Bedding

• This type of structure is equivalent in Igneous Rocks

• Change in color, texture, composition, & resistance to erosion

- Graded Bedding -

• The bottom layers usually have coarsed-grain rocks
• As the layer progress upwards, the rocks there are usually more fined.

- Cross Bedding -

• Layers of sedimentary rocks that horizontally inclines.
• Forms in depositional environments where flowing mediums, typically water is held.

- Ripple Marks -

Primarily cause by agitation of water, wind, or both

Symmetrical Ripple Marks

Asymmetrical Ripple Marks

• Form due to back & forth motion of waves or tides.

• Form due to motions of waves or tides in one direction.

• Commonly found from Previously Shallow Waters.

• Commonly found at Previously Formed Rivers.

- Pillow Structures -

• Generally flattened with rounded tops.
• The texture on the surface is more fine-grained (rapid cooling) than the inner part of the rock.
• The inner part of the rock is slightly coarse (slow cooling).

- Mud Cracks -

• Cause when mud loses its water content which in result contracts forming cracks.
• The cracks are usually polygonial shape.

Soft Sediment Deformation Structure

This form of structure occurs before sediments are fully consolidated

The structures can also be formed by tectonic activities which occurs in between primary & secondary structure "gray zone"

Penecontemporaneous - In geological term is; the result of something that occurs immediately after deposition(process) in a particular layer of rock(stratum).

Penecontemporaneous Fold

• These folds commonly associate with changes in layer thickness.
• They could be considered as Irregularly Contorted Beds or Beds that seemingly looks twisted or bent.
• They are also Intraformational which means that they are restricted to narrow stratigraphic intervals.

Penecontemporaneous Faulting

• Same as Penecontemporaneos Fold but just partially or specifically Partly Consolidated Sediments.

The purpose of Primary Structures

1. Used as facing indicators to define whether the structure is in a Primary State or a Secondary State.
2. Determine the flow direction of streams, ocean currents, winds, & lava.
3. May be used for quantative strain analysis.

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