Report on our Excursion to the Lake District

2nd to 10th July 2004

Led by Dr. Pat Brenchley

The excursion was based at Rickerby Grange in Portinscale, near Keswick where we were very well looked after. Each morning our leader, Pat Brenchley, late of Liverpool University, would come round and lead us off to look at the geology of the Lakes. The weather was pretty good - we only got soaked on one day.

We had 6 days doing geology.

• Day 1 covered the Skiddaw Slates. We went over the Whinlatter Pass, stopping at Scawgill Bridge, then to Buttermere, up to Moss Force and then home via Braithwaite. Eileen Lewis has written about this, and some pictures can be seen here.

• Day 2 covered the Borrowdale Volcanic Series. We drove to Seathwaite and walked up the Sourmilk Gill to look at the waterlain tuffs. There are some pictures here.

• Day 3 covered the Borrowdale volcanics of the Carrock Fell area. And we have some pictures here.

• Day 4 was the day we looked at the Borrowdale Volcanics between Great and Little Langdales, especially on Side Pike. Jim Napper has written about these rocks. And we have some pictures here.

• Day 5 let us look at the Ordovician and Silurian cover of the Borrowdale Volcanic Series near Coniston Water. We have a few pictures here.

• Day 6 took us to St Bees Head where we looked at the Carboniferous and Permian rocks. Janice Theis has written about this, and there are some photographs here.

As you may see we moved from the older rocks to the younger. The Skiddaw Slates of Lower Ordovician age represent the filling in of the closing Iapetus Ocean. The Borrowdale Volcanic Series are the igneous activity associated with the oceans closing. The Upper Ordovician and Silurian the shelf sediments once the ocean had closed. The Old Red, Carboniferous and Permian were laid down after the Caledonian folding.

Eileen Lewis's account of Day 1. And some photographs.

Our first day was spent examining the Skiddaw Slates, which are of Lower Ordivician age. They are hundreds of metres thick, the result of mud deposited in a deep basin during the closure of the Iapetus Ocean. There were some associated turbidity currents, and sedimentation was also affected by the Causey Pike Fault.

The Buttermere Basin is composed of material slid from the south across the fault into a deeper part of the basin. This has produced large flat lying sedimentary folds associated with the sediment. It was these we looked at first in Scawgill Quarry where the Loweswater Flags are exposed. It is situated, north of the Causey Pike Fault, in the Buttermere Basin and all the material here is fine grained mudstone with occasional thin sandstones. Undulating ripples, vertically accreting ripples, migrating ripples and flute casts were seen. Graptolites have been found - in particular the tetragraptus of the Arenig Zone; helping to date this rock.

Our second stop was south of the Causey Pike Fault, in the quarry at Buttermere. The slates here have a much steeper angle of dip - around 80°, with the bedding and the cleavage almost parallel. These rocks have tectonic folds of Silurian age superimposed on the turbidites. We examined the rock face to try to determine the younging direction and direction of closure of the fold seen.

This is an atypical section of the Buttermere Slates because it preserves lumps of sediments of an earlier age. It is contemporaneous with, but slightly younger than the Loweswater Group. The clasts within it have been dated and include some from the Loweswater Group. Large sedimentary slides have carried material from Loweswater Group to Buttermere and this has been deposited as clasts within the Buttermere rocks. This type of deposit is termed an olistostrome and very large clasts within it are called olistoliths. Our third stop was at the top of Newlands Valley, still south of the Causey Pike Fault, by Moss Force where an olistolith in the form of a large sandstone block, carried from the Loweswater Group can be seen in the upper part of the waterfall.

Our next stop was lower down the Newlands Valley at Rigg Beck quarry which is still in the Buttermere Basin and just south of the Causey Pike Fault. Here a slumping olistostrome was seen where sideways closing folds are piled one on top of another. Movement along the Causey Pike Fault has had a significant effect on the slumping and deposition in the Buttermere Basin Group. It is a syn-sedimentary fault within the basin, originally due to extensional forces, but later compression during the Caledonian orogeny produced folding within the sediments and, at depth, lower beds were refolded, and Causey Pike Fault became Causey Pike Thrust, bringing sediments up with it.

Our final stop, to look at more of the Buttermere Basin Beds, completed the day and we returned to Portinscale via Braithwaite.

Jim Napper's account of Day 4

A visit to Side Pike, Langdale, to observe Subaerial Pyroclastics

1. The exposures were recorded on ascending crags and started with weathered bedded tuffs showing cross stratification deposited by pyroclastic surge and fall. Some beds contained fiamme i.e. elongated streaks of squeezed pumice fragments. There were also examples of low angle truncation. The tuffs were eutaxitic.

2. An example of an ignimbrite base overlain by diffuse silica poor beds showing cleavage. The bedding was truncated by a breccia of eutaxitic tuffs varying from jigsaw fits to fiamme orientations showing considerable movement. The Brecciation was possibly the result of a phraetic explosion.

3. Large fiamme were observed in massive lapilli, some outstanding on a weathered surface, also joint surfaces revealing frayed fiamme ends. Poor sorting and lack of bedding indicates this to be ignimbrite produced by pyroclastic flow.

Measurements of fiamme were taken i.e. length/thickness ratio and showed 8:1 flattening. Generally flattening ratios increased towards the centre point and decreased upwards representing a single cooled unit.

4. Examination of fiamme showed a progressive flattening ratio of 35:1 decreasing upwards again due to cooling and a decreasing load.

5. Overlying the ignimbrite was a fine grained porcellaneous tuff with accretionary lapilli, a crystal poor ash probably co-ignimbrite ash fall from a pyroclastic eruption. Above the ash flow was a 2m. cross bedded fine to coarse grain tuff with sorting and undulating sandwall suggesting a pyroclastic surge deposit. This was overlain by a coarse breccia containing pink clasts of eutaxitic lapilli. Nearby was an exposure showing some andesitic sediments with laminations and cross laminations with occasional ripples and scour surfaces overlain with silt interclasts also evidence of soft sediment deformation.

6. Further soft sedimentation disruption with penecontemporaneous faulting, slide surfaces with vertical and overturned bedding. The possible cause of the disruption was thought to be volcanic seismic activity.

The Side Pike locations are a small part of a large complex with mega breccias of up to 0.5km. across. Originally the blocks were a coherent unit, the seismic activity reactivated the beds causing fracturing , disruption and liquefaction enabling the blocks to sink and rotate to different orientations. This could have occurred during a caldera collapse.

Janice Theis's account of day 6. And some photographs.

SALTOM BAY AND WHITEHAVEN

Our trip to the Lakes in July met with unsettled weather, but the hotel (near Keswick) more than made up for this in the way of comfort and welcome.

On a day of intermittent rain, we first visited Saltom Bay, and fought our way down a lushly overgrown path down to the beach, where we found a wave cut platform. This vegetation appeared to be of recent growth and lushness, perhaps as a result of climate change. The rocks in this area have been subject to many geological events throughout time, sometimes on the edges of plates, and at other times affected by marine ingress, or deposition from uplift in other areas. Here at Saltom Bay, the rock sequence was Silurian turbidites, then Old Red Sandstone was formed around the edges of lakes. The Carboniferous limestone found here was deposited in shallow seas (before the Palaeozoic sequence was uplifted). Following the end of the Lower Carboniferous, the Coal Measures were laid down.

 After this came the Variscan orogeny to the south of this region, causing block uplift in Northern parts such as the Pennines and Lake District. Late Permian uplifts led to breccias flowing off at edges of Lake District, and one of these breccias are found here.

During the Zechstein sea episode, evaporites were formed here, then arid sandstone. St Bee's sandstone is the Permian reservoir rock for North Sea gas. It is nearly all fluvatile in nature, formed by broad, free flowing rivers forming parallel laminated sandstones, which had sheet floods from time to time. There is some stratification, and traces of migrating sandwaves. Big channels are visible at some levels in the sequence. In the past, there was anhydrite mining here. On top of the wave cut platform, we could see the base of Permian, a Brockram breccia lying unconformably on top of the Carboniferous unconformity. On top again, we saw yellow dolomite, which may have been becoming saline as part of the Zechstein transgression. On top of this again can be found shallow marine fauna.

We then moved along the coast (in the rain) to Whitehaven, where the Carboniferous Westphalian is exposed. This formation is delta related, laid down in fresh standing water. Bivalves are sometimes found there above the coal seams.

I found this area very bleak and dreary. I was glad to escape to Carlisle on our free day and was lucky to have a sunny day to enjoy the rolling countryside on the journey there.