Hurricane Helene - an Interesting Video

A correspondent brought THIS VIDEO to my attention. I concerns the devastation brought about by Hurricane Helene. He comments:- 

This is a fascinating piece, because in the second section of the destroyed road, it looks to me that the road has been built on an ancient river course that has been reactivated for the first time in centuries. 

 Two Indoor Courses from Nick Chidlaw

Nick Chidlaw has asked me to pulicise the following two courses to be held in November. Happy to oblige.

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I am offering two 1-day indoor courses to be run in November, if there is sufficient interest and enrolments to make them viable. 

These courses are independent of one-another  - you can enrol on either or both, according to your interest and availability. 

The courses are being offered on the same weekend: some people who live a substantial distance away may be interested in both courses and this would make attending them more workable. Venue: The Chantry, Thornbury, South Gloucestershire www.thechantry.org.uk. Do let me know if you need advice on accommodation options.

I hope you find these proposals of interest, and to hear from you soon.

Nick Chidlaw 

Title:  The Chalk Group exposed at Westbury Chalk Quarry, west Wiltshire 

Saturday 23rd November 10.00 am - 5.00 pm

Image: Westbury Chalk Quarry in the 1990's. Extraction and processing ended before 2010; the site has since been gradually weathering and becoming overgrown.

In Late Cretaceous times (100 - 66 million years ago), the area of the earth's crust that became the British Isles lay about 45 degrees north of the equator and had a warm, subtropical arid climate. The global climate was much warmer than today, and sea surface temperatures around Britain are thought to have been around 28 degrees C.  An absence of polar ice caps ensured higher sea levels; these were compounded by very active tectonic plate growth and associated buoyancy of ocean ridges, displacing ocean water onto the continents. Across the British crust, few land areas remained, and the sea is thought to have been at times as much as 500m deep. Its sea bed was mainly a quiet environment, where sediment accumulated, often without disturbance. Material from the land consisted of occasional inputs of clays, and the waters were consequently very clear.  The warm, clear waters contained abundant dissolved lime, and near the surface innumerable microscopic calcareous algae were present, taking from this lime to build their  shells. Their consumption by planktonic crustaceans, and incorporation into faecal pellets, is thought to have enabled them to sink to the sea floor and accumulate, to form the  Chalk Group. In the Westbury area, crustal subsidence was lower than in some other parts of Britain, and in consequence the stratigraphic succession is thinner: this has resulted in a wide variety of Chalk Group stratigraphic units being exposed at Westbury Chalk Quarry. On this one-day course, powerpoint-based lectures will provide an introduction, geological history, and description of geologists' methods for studying the Chalk Group; this will be followed by a practical session in which specimens of mineral and rock types collected from Westbury Chalk Quarry will be examined under the tutor's guidance.

No prior geological knowledge or of the study location would be assumed. 

Tuition fee: £33.00

Contact tutor Dr Nick Chidlaw nickchidlaw@gmail.com to enrol and for any queries. 

Deadline for course viability: Friday 1st November. If the course has become viable (minimum 10 enrolments) by this date, enrolments will be able to continue until 1 week (Saturday 16th November) before the course runs. 

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Title: Indoor practical course using hand specimens: metalliferous mineralisation within a sedimentary rock host

Sunday 24th November 10.00 am - 5.00 pm.

Image: an example of a metalliferous mineralisation setting in sedimentary rocks (not from the case to be studied on this course).

On this course hand specimens of minerals and sedimentary rocks are examined by attendees, using guidance notes to systematically determine, as far as possible, the identity of each specimen. This is good practise in learning how to analyse minerals and rocks, giving those on the course experience which they can use in the future to independently determine what specimens might me that they collect themselves, or are asked by others to identify. The course develops knowledge in attendees of the limits of hand specimen identification, and where laboratory methods would be needed to take the identification further; a number of possibilities may be concluded for some of the hand specimens.This process occupies most of the time on the course. The identifications of the minerals and rock specimens will then be given by the tutor, so that attendees will know which they have correctly determined, or where improvements can be made. 

Attendees are then each given an A3-sized annotated diagram on which they allocate the identified minerals and rocks. This diagram is of an actual example of metalliferous ore deposits within a series of sedimentary rocks, which have been, and continue to be, mined today. Attendees are to fill in blanks in the annotations, through knowledge they have gained from the specimen identification process, and from advised reading material brought to the course (including via online sources using attendees' smartphones / laptops).

The final part of the course will be an informal powerpoint-based lecture identifiying and describing the actual example of mineralisation being studied.  

No prior knowledge of geology would be assumed. 

Tuition fee: £33.00

Contact tutor Dr Nick Chidlaw nickchidlaw@gmail.com to enrol and for any queries. 

Deadline for course viability: Friday 1st November. If the course has become viable (minimum 10 enrolments) by this date, enrolments will be able to continue until 1 week (Saturday 16th November) before the course runs. 

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 Earth may once have had a ring like Saturn

I came across THIS ARTICLE in New Scientist and was impressed by the way so many concepts are combined. 

There is a cluster of meteor impacts (21 of them) dated in the Ordovician after 466 million years ago. If you undo the subsequent movements of the continents you find most of the impacts were near the equator of the period. 

There is a period starting in 466Ma and lasting for 40 million years where there is a higher level of chondrite material in the rocks than one would expect.

THE PAPER on which the New Scientist article is based, gives an explanation for all this. The Earth had a near miss from a large chondrite meteorite. It did not strike the Earth but broke up due to the gravitational forces occassioned by its closeness to the Earth.

The meteorite debris formed a ring around the equator and bits of it fell to Earth in the subsequent few million years to give the impacts close to the equator. Smaller bits falling gave the increase in chondrite flux.

It may be connected that the Earths temperature dropped at this time to the lowest temperature of the last 540 m.y. Perhaps the postulated ring caused this.

 Down to Earth Extra October 2024

The October 2024 edition of Down to Earth Extra has been published. You can download it HERE or you can read it below.

 Mantle Waves Form Mountains

This ARTICLE, based on THIS PAPER in Nature, suggests that the splitting apart of a continental plate affects not only the area near the rift zone, but also the interior of the continent. 30 or 40 km of the roots of the continent are stripped away and this wave of root erosion moves towards the interior of the craton. And this results in an increase in altitude of the land surface.

I always thought that high land required deep roots - think of the deep crust below the Tibetan plateau. Here the suggestion is that the removal of roots allows the land to rise, like a baloon rising when the sandbags are thrown overboard.

The example cited is the Drakensberg of South Africa. This, and similar, if less impressive formations, form escarpments around the cratons formed at the breakup of Gondwana. The paper suggests that the coastal escarpments of Brazil and the Western Ghats of India have a similar origin.

a, Rifting causes edge-driven convection in the mantle, rift-flank uplift and escarpment formation. b, Rayleigh–Taylor instability migrates along the lithospheric root, resulting in convective removal of the TBL of the lithospheric keel, driving kimberlite volcanism11, isostatic uplift and denudation. c, Escarpment becomes a pinned drainage divide that is locally breached by the main rivers draining the plateau. Meanwhile, the convective instability continues to migrate towards the continental interior, leading to isostatic uplift, a shift in the locus of erosion and plateau formation (Fig. 4).

The authors believe that they explain why the interior of the cratons is so high and also the occurrence of kimberlites.

This is a very complex subject and I do not pretend to understand much of the arguments but read the papers and come to your own conclusions.

 Down to Earth Extra September 2024

The September 2024 edition of Down to Earth Extra has been published. You can download it HERE or you can red it below.

 Orcadian Basin Rock at Stonehenge!

I expect you all have heard that the Altar Stone at Stonehenge has been proved to be from the Old Red Sandstone (ORS) of North East Scotland. The original paper is in Nature and can be read HERE. 

The Altar Stone, seen here underneath two bigger Sarsen stones, which new research suggests is actually Scottish not Welsh © Professor Nick Pearce/PA Wire

Nature has also provided a video which is well worth viewing.

The origen has been established using extremely sophisticated analysis techniques on individual crystals in a couple of thin sections. These proved that the zircon, rutile and apatite crystals present (and there were not many of them!) could only come from the Orcadian Basin. The Nature paper goes into excruciating detail on this, but it is summed up in the following figure.

How the stone got to Stonehenge will, no doubt, lead to furious debate. Tha Nature article posits that it was "anthropogenically transported"! What I find more interesting is why the builders of Stonehenge thought that a stone from so far away was necessary for the site.