In Geology an unconformity is a surface separating two rock types of different ages from one another. An unconformity represents a period of erosion or non-deposition in the sedimentary record, i.e. a gap or hiatus where we have no record of what happened.
One such unconformity is Hutton’s Unconformity. The confusing part is that the name Hutton’s Unconformity is the name given to several unconformities identified by the famous 18th century Scottish geologist James Hutton. On a recent fieldtrip to Scotland we visited Hutton’s Unconformity at Siccar Point, but other unconformities identified by James Hutton can be found on Arran and near Jedburgh.
When sediments (fragments of previous rocks) are deposited (settle before becoming a rock) they form layers of progressively younger material burying the older material. If a sedimentary rock is the correct way up the further up the rock you go the younger (closest to present day) it is.
At Siccar point we can see two distinct units rock, with the layers of rock (bedding or strata) in the upper and lower units being at different orientations from one another. This means that before the second (upper) unit was deposited the lower (older) unit was tilted and eroded, producing a gap in the geological record.
Unconformities are crucial to our current understanding of geology. They paved the way for us to consider deep time, that is essentially an appreciation of the fact it has taken a very long, yet quantifiable length of time for the rocks we observe around us to have reached their current situation. For the rocks here at Siccar point that means; deposition of the older sediments, tilting of the older sediments, erosion, then the deposition of the younger sediments on top. This order of processes cannot possibly happen quickly!
Unconformities have also been used as evidence that the mechanisms governing the production of these rocks (and the universe) have, and always will operate in an assumption known as uniformitarianism. Uniformitarianism is a counter (and more accepted view) than the opposing catastrophism, which implies that the Earth was created in a series of sudden short lived events.
Headed up to Shaftoe in Northumberland on Tuesday evening trying to make the most out of the decent weather and light evenings as the nights start to draw in.
The rock at Shafoe climbs quite differently to other venues in Northumberland in that its much more rough than the sandstone found at places like Bowden Doors and Kyloe (in and out). Its still a sandstone but with a definite feel of grit about it, similar to the rock at places like The Slipstones down in Yorkshire.The rock on the problems generally has brilliant friction and is of good quality, quite different from the much finer, softer sandstone found at nearby Corby’s…
In terms of the geology of this rougher sandstone is believed to be a fluvial deposit. This means that it is a sedimentary rock produced by a river, and is slightly younger than the Fell Sandstone which makes up Bowden and Kyloe.
Whilst on holiday in Finland last year we visited an Island not far from the centre of Helsinki and found some interesting things to look at…
The linear features here are called striations and have been gouged into this rock. They are caused by the movement of a glacier over the bedrock, through the process of abrasion. Abrasion is a term used to describe when fragments of rock captured by a moving glacier are pressed onto the surface of the underlying rock. As the glacier drags these rock fragments along lines are scraped into the rock. Striations are a common feature of glaciated landscapes and are just one of many features glaciers can produce.
Striations such as these along with other glacial landforms can help us to reconstruct the dynamics of past glaciers, and help us understand more about modern glaciers. The presence of glacial landforms where we no longer have glaciers (such as here in Helsinki) demonstrates how the environment can change over time.
If you find glacial landscapes interesting you may find Rock Paper Glacier! blog to be of interest.
This example near Helskinki really does show us that even in built up areas we can still observe the influence of the forces that shaped the landscape around us!
Before heading off to North Wales last week I went to Trowbarrow quarry in Lancashire for a quick climb and poke about but haven’t had time to post about it.
This disused quarry is a geological SSSI with lots of high quality (and some crap!) climbing on offer. One of the most prominent geological features at Trowbarrow is the near vertical nature of the bedding planes. We can see this on the photo of the main wall where the routes follow cracks along the bedding. Other interesting geological features at Trowbarrow worth seeking out include; faults, folds, fossils and apparent paleo-karst.
The photo of the main wall above is actually one from a few years ago but it hasn’t changed much, except some people say that the entire right hand side of the main wall is rotating causing the cracks to widen? The climbs on the righthand side of the main wall are looking a little ‘unstable’ but I’m sure people can make their own judgements about whether to climb them…
Like many of the climbs at Trowbarrow Coral Sea (photo above) follows the bedding plane, and as the name would suggest numerous fossils are observable all the way up.
Another feature at Trowbarrow is Fluting. This is a common feature on limestone and is caused by differential weathering and erosion. It can be observed at Trowbarrow at the top of Assagai wall, where it forms the spectacular finish to Assagai (good sling runner in the flutes!).
In terms of the climbing the obvious mid grade classics Jean Jeanie(VS 4c), Coral Sea (VS 4c) and Assagai (HVS 5a) are certainly worth a look. Polish can be a bit of a problem at Trowbarrow (especially on Jean Jeanie!) but generally the climbing is really good quality!
Apologies for the multiple posts today but there’s lots to post about since returning from Wales!
I hadn’t climbed on Lower Pen Trwyn (LPT) before but would certainly go back. In terms of the Climbing LPT has some really good routes across the grades and has the feel of sport climbing elsewhere in Europe, especially if the sun is out! Could The Orme be the Welsh answer to Kalymnos?
The approach is pretty simple (steep start) with some good geology to maintain interest on the way in. The following photos and thoughts are by no means an exhaustive study, and were captured in a passing by type manner with the intention of inspiring climbers to look around them on the way in to LPT.
Presumably the sediments above the limestone are relatively recent, and are sourced from the limestone above on the Orme? This short transportation distance however does surely not provide a satisfactory explanation as to why there is such rapid variation observable in roundness and sorting between beds?
Climbing wise Under the Boardwalk stands out as a real classic of the crag, proving to be a tricky little number requiring a sustained effort right till the end, but the crag contains abundant quality climbs. At the far right end there are several ‘easier’ sport routes in the F6a(ish) range with Beauty is Only and Skin Game being good fun.
Oh and remember that LPT is tidal, and accessible apart from about three hours either side of high tide. Its also worth noting that the 1st bolt on most climbs is pretty high (due to the tides).