Ingleton: Sedimentary structures

© Craven & Pendle Geological Society

Isoclinal folding

Possible ripple marks

Tool Marks

Possible Fute Cast

Sedimentary structures are an important feature in the Ingletonian rocks. They can be used to work out the conditions of deposition and the direction of currents. This is especially useful in areas like this where the rocks have been intensively folded. In view of the age of the these rocks, interpreting these structures needs to be carefully applied in the field!

Isoclinal Folding

The top photograph shows small-scale isoclinal folding ( a special case of overturned fold) in the Ingletonian turbidite. An isoclinal fold is where both the limbs of a fold dip towards the same direction. In a fold like this, one limb looks normal while the other limb appears to be overturned towards the other.

Ripple Marks

The Ingletonian show evidence of ripple marks. Both wind and water can displace sediment to make ripples. In the case of the Ingletonian greywackes, these ripples are formed in marine waters and are therefore wave-formed or current ripples. They are of value in determining the way-up of the beds.

Tool Marks

These form when objects being carried along in the current come into contact with the sediment surface. There are a number of different ways that geologists' describe them i.e. prod, roll, brush, bounce marks. They can be used to determine the direction of current flow. Usually the sharp end marks the direction in which the current was travelling.

Flute Casts

These can be elongate or triangular (heel-shaped) with either a rounded or pointed upstream end, flaring in downstream direction. Often they form through local scouring by eddies in currents and are typically found throughout turbidite sequences. Geologists' generally find that flute casts are reliable means of determining palaeocurrent direction.