Posted by: paulgarner | June 21, 2010

Catching up

My sabbatical comes to a close at the end of this month and I can hardly believe it. I haven’t accomplished half the things I wanted to, although it’s been great to spend a bit more time helping around the house and garden, as well as catching up on some reading and taking the opportunity to have a short holiday in North Wales with my wife following a recent family wedding. While on holiday we visited the Great Orme at Llandudno, where I spotted a roughly metre-long, oblong boulder on display. It had this text attached to it: “This boulder was one of many that fell onto the Marine Drive on 10th June 1993 as a result of the floods in which 5 inches of rain fell in a 3 hour period. It was not the biggest!” I thought it was a modest reminder of the power of moving water to rapidly erode and deposit sedimentary material. We also visited Charles Darwin’s home town of Shrewsbury, just across the English border in Shropshire, where I took this photo of Horace Montford’s bronze sculpture of the man himself outside the town library. Until 1882 the building was the home of Shrewsbury School which Darwin attended as a boy.

I’ve also been able to make a few brief field excursions, including to Mam Tor in Derbyshire which provides a magnificent section through a series of interbedded Namurian sandstones and shales (see photo to right). The sandstones are generally understood to be deep water distal turbidites, and display classic sole markings such as flutes, grooves and load casts (Allen 1960). Each sandstone layer was undoubtedly deposited rapidly, although large amounts of time are usually thought to be represented by the slow accumulation of shales between each turbidite incursion. However, the general laminated appearance of the shales and the absence of extensive bioturbation suggests that even the shale layers may not represent a great deal of time. If that’s the case, the entire succession at Mam Tor may have been deposited in a fairly short amount of time.

I also visited a significant, though visually pretty unimpressive, outcrop of Upper Jurassic limestone in Commissioners’ Pit near Upware in Cambridgeshire. This disused pit exposes about six metres of Oxfordian sediments, the upper three metres being a resistant, coral-rich limestone and the lower three metres a softer ooidal and pisoidal limestone yielding bivalves and echinoids. There are supposed to be horizons of in situ coral growth, although I wasn’t able to see much evidence of that. However, my inspection was fairly cursory because I was being eaten alive by insects, so it’s quite possible I missed something. I’ll have to take a closer look some other time.

Reference

Allen J. R. L. 1960. The Mam Tor sandstones, a “turbidite” facies of the Namurian deltas of Derbyshire, England. Journal of Sedimentary Petrology 30(2):193-208.

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