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The plane or junction, marked by the thick green line, between both sets of strata is the unconformity.At Thornton Force the junction is marked by a basal conglomerate.
It could also be immediately confirmed in the base office once maps and cross sections are updated and the rock units confirmed.The laws of physics and chemistry that governed geologic processes in the past are the same as those that govern processes now and in the future.The geologic timescale is a chronology (calendar) of events on Earth based on obtaining ages of past events.Sediments are usually laid down in horizontal beds.Any observable tilting or swirling is due to disruption of the process. Material that intrudes or cuts into a horizontal bed is assumed to be younger than the material that is disrupted.When found in rocks as far away as Australia you could reasonably expect those rocks to be the same age as those in Cliviger Valley!
A third fact emerges from the study of stratigraphy - the UNCONFORMITY.
These ages have been derived from relative dating and absolute dating (radiometric dating) of rock layers and fossils.
(a) Relative Dating This technique uses principles of stratigraphy (rock strata) and the study of fossils (palaeontology) to determine the relative ages of rocks and sediments. Field geologists' rely on a number of simple techniques for dating rocks and constructing geological successions. The Law of Strata Identified by Fossils is a little bit more complex.
The table below summarises key features: Gastrioceras listeri is a particularly good example of a ZONE fossil.
As it is free swimming it could have travelled a considerable distance.
Techniques of accurately dating rocks is crucial in establishing the time-gap that exists.