Finally after having to do a complete re-record Seminar 3 has been nailed and is now ready for publication. Due to the number of slides and the resulting file size without unacceptable loss of quality I have had to split the presentation into two parts. Part 2 naturally should be watched after Part 1.
As a reminder Seminar 3 covers the first of the three major rock groups, the Sedimentary Rocks. An important group of rocks for those in the UK and in the UK construction business rocks from this group will generally be those which structures are either founded on or lie within. This rule certainly applies to most of England and large parts of Scotland, Wales and Northern Ireland as well, plus our friends in the Republic of Ireland.
Part 1:
Part 1 covers what sedimentary rocks are, how geologists classify them,
the processes of erosion, transport and deposition of sediment,
sedimentary structures and the lithification and diagenesis.
Within Part 1 I am not convinced that my verbal description of how cross bedding forms is that clear so I have reproduced the decription from Wikipedia, which gives as good a description as I have come accross.
Cross-bedding is formed by the downstream migration of bedforms such as ripples or dunes in a flowing fluid (or under the action of wind in the air)
. The fluid flow causes sand grains to saltate (migrate or carried within the fluid close to the sediment surface)
up the upstream ("stoss") side of the bedform and collect at the peak until the angle of repose is reached. At this point, the crest of granular material has grown too large and will be overcome by the force of the depositing fluid, falling down the downstream ("lee") side of the dune. Repeated avalanches will eventually form the sedimentary structure known as cross-bedding, with the structure dipping in the direction of the paleocurrent (reproduced under Wikimedia Creative Commons Share-Alike License).
I hope that this description together with the images in the set of slides for part 1 (Slide 27) will make how cross beddings form understandable.
and Part 2:
Part 2 looks at a number of common sedimentary rocks.
The posting of Seminar 3 means I am now up to date with Seminars being delivered since I started this blog, although it is slightly out of sequence in terms of posting date. The next Seminar will be No. 18, which will be the second of two on Glacial Geology (the first one was No. 16). This will be a new one not delivered previously. In terms of the re-runs, No. 7 is the next in sequence which will be the first of several on aspects of Palaeontology or the study of fossils. As usual when the recording files are available they will be posted for the reader to view.
