For an ever-so-slightly delayed (cough) blog update we’re off to the beautiful Yorkshire Dales, or to be precise, the wonderfully named Norber.
Norber is a classic type locality for a glacial erratic, a piece of rock that is different from those surrounding it due to having been transported by ice. Here, boulders of cross-bedded Silurian greywacke perch on pedestals of Carboniferous limestone after being plucked from the valley floor and and being transported both downstream and up the sides of the valley by glacial action.
Many of us are familiar with making small-scale macro and micro geological observations on field trips and in labs, peering curiously (we hope) at bedding planes, grain boundaries, fossils and outcrop structure. However, it is equally as important to take a step back and consider how these minute details impact on the landscape and topography around us. Here in Britain, we are lucky to have incredibly diverse geology in a relatively small area, and these large scale mega observations* can prove pretty valuable in plotting out large scale features, such as major fault lines and distinct changes in rock type or structure.
Along with old-school paper maps, this is where Google Earth really comes into its element. Being able to see aerial imagery along with elevation and alternative viewing angles means you really can explore the world from your desk (or even sofa). So, carrying on the theme of the exotic, we’re off to Hull. Continue reading →
Last weekend I decided to spread my wings, or boot-laces, and escape from the Vale of York to pastures new. Just for the day though, let’s not be too rash. We headed on the slow train out of York to Hebden Bridge, which took about an hour and a half and was definitely one of the more pleasant journeys I’ve had with Northern Rail.
Geologically speaking, the train line marks out a good transect of Late Palaeozoic and Early Mesozoic palaeoenvironments. In the Vale of York, Permian sandstones, siltstones and muds from lakes and lagoons are often overlain by thick Quaternary clays, sands and gravels, again laid down by lakes and rivers at the turn of the last glaciation. Where the bedrock is closer to the surface, the ploughed fields are stained red from the vibrant iron oxides in the rock.
For a brief overview, here’s a screencap from the marvellous BGS Geology of Britain Viewer:
Carrying on with Friday’s theme of rooting through old photos, I thought I’d share a few from a family trip to the Scilly Isles way back in 2008.
Aerial view from the incoming helicopter
I mentioned in a previous post the great Cornubian Batholith, an enormous granite body that makes many appearances across the south-west of England. The granite was emplaced during the Late Permian, as part of the later stages of the Variscan Orogeny. As well as the many tors of Devon and Cornwall, one of these outcrops is the characteristic archipelago of the Scilly Isles, a scattering of islands clustered beyond Land’s End. Up until around 500 AD (a mere blink of an eye from a geologist’s perspective), the islands were one large outcrop, before rising sea levels split it into around fifty-five separate islands and islets.
Out of these fifty-five, only five of the islands are currently inhabited: St Mary’s, St Agnes, St Martin’s, Bryher and Tresco. At extreme low tides it is also possible to walk (or at least paddle!) between some of the islands, and the relatively recent sea level rise means that ancient field boundaries are also exposed by the receding water. From above, the Scilly Isles look like a tropical paradise, with their isolated white sand beaches. At times you could be forgiven for the mistake, as the westerly position of the archipelago means that they are exposed to the warming effects of the Gulf Stream. However, it is far more likely that it is due to the high quartz content of the eroding granite!
Now, these photos are from a looong time ago, so apologies for the rather dodgy nature, but I thought I’d provide a quick overview of my time in paradise!
Incoming swell at the appropriately named Hell Bay
Here we have a photo from a fieldtrip way back in 2012 to Cornwall, the most southwesterly county in England. This is taken from the viewing platform at the Wheal Martyn china clay mine with some atmospheric fog and mist as a free gift (the fog didn’t actually lift for the whole week we were in Cornwall, so we never got a half decent view of one of the most beautiful areas of Britain).
For a special treat I’m delivering a winning combo of a Throwback Thursday and a Photo Friday, and today’s exotic location is the Isle of Arran, on the west coast of bonnie Scotland (not to be confused with the Aran Isles off the coast of Ireland).
Arran is a bit of a Mecca for geologists, as it has an enormous variety of lithologies and geological processes packed into a relatively small area (it’s about an hour’s drive top to bottom).
Mafic dyke stretching out to sea, illustrating the difference in resistance between Palaeogene basalt and Triassic sandstone
I first encountered Arran’s geology way back in 2010, being the destination for my AS and A-Level geology field course (for non-UK readers this is age 16-18).
It goes without saying that Arran is one of the best field locations to study the law of cross-cutting relationships, as there are numerous outcrops illustrating the relationship between the metamorphic, sedimentary and igneous chapters in Arran’s history.
An unconformity is a surface that represents a gap in geological time, a period of non-deposition or even erosion of the Earth’s surface. The gap can represent a missing thousand, million or billion years or so, giving a huge insight into the geological processes that have acted on the area.
Angular Unconformity near Friar’s Point on Barry Island. Rucksack and half a PhD student for scale.
As far as lumps of bare rock go, unconformities are pretty cool to look at. This fine example comes from Barry Island in Wales, the home of Gavin and Stacey and not actually an island anymore. The rocks are the base of the photo are 335 million year old bedded Carbonifererous limestones, whereas those at the top of the sequence are 200 million year old Triassic breccias and sandstones.
So what happened in the 135 million years between these two sequences of sediment being laid down? Continue reading →
Now, we all know about Dorset’s Jurassic coast, the World Heritage site and quintessentially British landscape. I’m northern, and therefore a bit biased, but I think that our other Jurassic coast here in Yorkshire is wrongfully overlooked.
The Yorkshire Jurassic coast wraps itself around the North York Moors, with Robin Hood’s Bay pretty much bang in the centre of the succession of rocks.
Geological Map of the Yorkshire Coast. Image courtesy of the British Geological Society
Considering Robin Hood was a Nottinghamshire lad, which is a fair way from Yorkshire, it seems a rather obscure choice of name for the small fishing village at the northern end of the bay. However, according to local legend (ahem… Wikipedia) French pirates busy raiding and pillaging the village were accosted by the aforementioned Mr Hood, who then returned the loot to the poor people in the village. At the time of writing, it is unclear as to whether the merry men were involved.
From a viewpoint on the southern headland of the bay, Ravenscar, the geological structure controlling the coastal morphology is obvious, especially at low tide.
Looking north towards the village from Ravenscar
As the sea retreats, a wonderful cross section of the imaginatively named Robin Hood’s Bay dome is exposed. Protected at each end by sandstone headlands of the Staithes Sandstone Formation (~190 Ma), the exposed softer mudstones of the Redcar Mudstone Formation (~200 Ma) have been preferentially eroded to produce the wide arc of the bay we see today. Along with individual strata, known locally as ‘scaurs’ from the Old Norse word for ‘rock’, the cross section also shows a number of radial faults aligned to the centre of the dome. One of these can be seen at the bottom of the photo above.
Written In Rock 