6: Sedimentology and Stratigraphy
- Page ID
- 37108
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“Time, which measures everything in our idea, and is often deficient to our schemes, is to nature endless and as nothing; it cannot limit that by which alone it had existence; and as the natural course of time, which to us seems infinite, cannot be bounded by any operation that may have an end, the progress of things upon this globe, that is, the course of nature, cannot be limited by time, which must proceed in a continual succession.”
James Hutton, “Theory of the Earth”, 1788
Rocks to a geologist are like books and ancient manuscripts to a historian as they contain a record of past events, environments, climates, and life. But the rock record is incomplete, like a book with missing chapters or pages. In order to reconstruct the history of the Earth from the rock record, geologists have to try and figure out what is missing. Is it time? How much time? Have some of the rocks been eroded and moved to another location? These are the scientific puzzles that motivate geologists.
The formation of sediment and sedimentary rock involves many physical, chemical and biological processes. The journey from loose sediment to hammer-ringing rock is one of the marvels of the geological world. Deciphering this journey requires us to delve into the rock record.
Imagine that a local geologist tells you that the rocks in your backyard were originally deposited as sand and mud in shallow seas, where beaches and broad coastal tidal flats passed seawards to deeper waters, and landwards to marshes and scrubby coastal plains across which rivers and streams coursed. How did our geologist figure this out? What is it that geologists see in the rocks that helps them paint this picture of a world that existed so many millions of years ago?