Sedimentary Structure

SEDIMENTARY STRUCTURES 

      Introduction

Sedimentary structures are important attribute of sedimentary rocks. They are best observed in field rather than in hand specimens or thin sections, because these are the large scale features of sedimentary rocks. They are very diverse and many can occur in any lithology and can occur on the upper and lower surfaces of beds as well as within beds (Tucker, 1918)

The Sedimentary structures are generated by a variety of sedimentary processes, including fluid flow, sediment gravity flow, soft-sediment deformation and biogenic activity. They are of special interest to geologist as a tool for interpreting ancient depositional environments. Now, we know enough about the origin of sedimentary structures from experimental investigations and field studies to use them for evaluating such aspects of ancient sedimentary environments as sediment-transport mechanism, paleocurrent flow directions, relative water depths and relative current velocities (Boggs, 1994).

In the areas of folded and disturbed rocks, sedimentary structures can be used to identify the way up of the strata i.e. the tops and bottoms of beds and thus to determine if the sedimentary sequences are in depositional stratigraphic order or have been over-turned by tectonic forces.

Sedimentary structures develop before, during and after deposition and through biogenic process. It is convenient to recognize four categories of sedimentary structures (Tucker, 1918).

·         Erosional sedimentary structures

·         Syn-depositional sedimentary structures

·         Post-depositional sedimentary structures

·         Biogenic sedimentary structures

All the four types of sedimentary structures are well preserved in the formations and have been observed during the fieldwork and are listed below (Table ).

 Observed Sedimentary structures

Sedimentary Structures			Formation
Erosional	Channels		Baghanwala Formation
Syn-Depositional	Cross bedding	Wedge-planar cross-bedding	Kamlial Formation
		herring-bone cross-bedding	Jutana Formation
	Lenticular Bedding		Baghanwala Formation
	Flaser Bedding		Baghanwala Formation
	Ripple marks	Symmetric	Baghanwala Formation
		Asymmetric
		Linguoid Ripples
Post-depositional	Stylolites		Juttana Formation
	Salt Pseudo morphs		Baghanwala Formation
Biogenic	Burrows	Horizontal	Kussak Formation/Jutana Formation