Giant Meteorite Strike - the Pluses and Minuses

A correspondent sent me THIS LINK, concerning a giant meteor strike which happened ~3.26 Ga in what is now the Barberton Greenstone Belt of South Africa. I now know that 8 meteorite impacts (identified by small spherules and iridium anomalies) occurred in the greenstone belt. They have been given S numbers and here we are dealing with S2.

The size of the meteor was huge - 40 to 60km across. The Earth it struck was very different from that of today - mostly sea with a few continents. Life was single celled organisms. The meteorite created a 500km crater, a cloud of hot rock dust that circled the globe, ripped up the sea bed and created a huge tsunami. 

But it is not all bad news. Phosphorus and iron were churned up and dispersed. This could be considered as the spreading of fertiliser! It is always good to look on the bright side of life!

The basis of the BBC article is THIS ACADEMIC PAPER. This goes into the minutiae of the investigation and gives much greater detail. 

Rock and thin section images of the Bruce’s Hill and Umbaumba sections. (A–C) Outcrop photos of the Umbaumba section. (A) Overview of the Umbaumba section showing, from base to top, BWBC, S2, fallback layer, and BWBC. (B) S2 spherule bed. (C) Lower part of the fallback layer showing fine laminations. This black chert is composed of silicified carbonaceous matter, siliciclastic debris, and impact-generated dust settling out of the atmosphere. (D and E) Outcrop photos of the Bruce’s Hill section. (D) BWBC below S2. (E) Alternating siliciclastic and siderite-rich chert beds. (F–G) Representative thin section images of carbonaceous matter. (F) Laminated carbonaceous chert below S2 in the Umbaumba section (SI Appendix, Fig. S4). Red arrows indicate fractures filled by chert. (G) Clots of carbonaceous matter and other siliciclastic debris from the fallback later in the Umbaumba section.

 Etheldred Benett Memorialised

Etheldred Benett unveiling 

All Saints Church, Norton Bavant 24th September 2024

A chance reference to Etheldred Benett crossed my desk some years ago and I was immediately hooked. To discover that this remarkable woman was born and lived in Wiltshire, just a few miles from my own home village, was a revelation. It turned out that she also explored the surroundings of my own village, Dinton, looking for fossils. She found at least one, an unidentified ammonite. I subsequently found that she was but one, albeit the most fascinating, of geology’s early pioneers, and the only woman, among those who were very active in Wiltshire, Wiltshire can rightly claim to have made a unique contribution to the development of our science in the 18th and 19th centuries. (See Sarum Chronicle issue 2022 ISBN 978-1-9161359-5-6)

A few years before its unveiling in 2022 in Lyme Regis, a young local girl had asked her mother why there was no statue to such a famous fossil collector as Mary Anning, a contemporary of Etheldred Benett. By May of that year, over £100k had ben raised and the statue was unveiled by such luminaries as Prof Alice Roberts and Prof Hugh Torrens. I spoke to Prof Torrens on the day and outlined plans for a more modest memorial for our local hero, EB. As the person who rediscovered her collection at the Philadelphia Academy of Natural Science in the US he was delighted. Alas, now, due to health reasons,  he cannot receive emails so probably does not know that EB’s memorial has been installed.

I visited All Saints Church in the village of Norton Bavant near Warminster to see the Benett family mausoleum and the family chapel. The Benetts were huge landowners which included the manor house in Norton Bavant where EB lived for 43 years. To my surprise there was not a single reference to EB in the church for her geological work. That just had to change!

My approaches and suggestions to the Parochial Church Council (PCC) were positively received so then the task of raising funds to pay for a memorial board kept me busy. The PCC had the daunting task of applying for a faculty, the permission to make changes to the church given by the local diocesan authorities, nearly always a tortuous event.

All my enquiries for a grant received a positive response. I am truly grateful for the financial support that made the memorial possible. The sponsors were:

• Wiltshire Council which gave the largest sum as allocated by the Area Board for the Warminster area.
  
  
• HOGG gave a contribution and gave advice on the wording used on the memorial board.
  
  
• The Curry Fund of the GA gave funds. Dennis Curry, who was a gifted geologist, was the oldest son of the founder of Curry’s the electrical retailer. He took over the firm on the death of his father. His generous gift of shares to the GA provided the capital for the establishment of the Curry Fund which makes grants to support geological projects throughout the country. This is not the first time that the Wiltshire Geology Group has used grants from the Curry Fund. Some years ago when Curry’s, the business, was involved in restructuring an individual involved bought Pyt House, the birthplace of EB. That property is now on the market again at £18 million – small world!
  
  
• Lovell Stone now own Chicksgrove Quarry near Tisbury, the location for EB’s first ever measured and labelled geological section in 1815, described as ‘an indefatigable feat’. Simon Hart, the CEO also made a donation.
  
  
• Professor Renee Clarey of Mississippi State University also secured a donation from the Geological Association of America. 

Following an item in a geological email I received indicating that Prof Clarey was preparing a data base of locations important in the historical development of geology, I wrote enquiring if Chicksgrove Quarry was on her list. It was not but Prof Clarey and I exchanged a number of emails and on a conference visit to the UK we met and I took her to Chicksgrove Quarry. We were also generously invited to lunch with Sir Henry Rumbold and his wife who live at Hatch House, once part of John Benett’s vast estate. Sir Henry is a descendant of one of EB’s brothers (EB never married) and has displayed at his home a portrait of EB as a young woman as shown on the memorial board.

The unveiling took place on 24th September in All Saints churchyard. Twenty people were in attendance, including Sir Henry Rumbold, a representative from Wiltshire Council, members of the PCC, WGG members, the current owner of EB’s old home next to the church and a journalist from the Warminster Journal. Kindly provided by the PCC, we enjoyed tea and refreshments in the church, following the formalities.

After nearly 200 years, EB now has a modest memorial in her home churchyard which captures a little of her huge contribution to the early development of the science of geology.

Etheldred Benett – RIP.

Steve Hannath

Chair of Wiltshire Geology Group

 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.