#1

nd Stone often with some

in Here is your first Forum Fri Jul 11, 2014 2:04 pm
by lluggg590 • 6 Posts

Geology of the Wessex Coast


Lepe Beach is situated southeast of the New Forest and is the closest mainland coast to the Isle of Wight. There are exposures here of Devensian Gravel (Pleistocene) overlying, at one location, an Ipswhichian Interglacial deposit with elephant remains, and a lower and older gravel. Beneath the Pleistocene gravels are the clays of the Headon Hill Formation (Solent Group), although exposures are small. On the beach at Lepe are various rocks which have been brought in for sea defences, as balast, from shipwrecks, or transported for building purposes. These include much Bembridge Limestone, Purbeck Stone including a dinosaur footprint, and Carboniferous Limestone.


The car park at Lepe Beach is on a small promontory of subangular flint gravel. This was formerly the location where the Dark Water stream flowed out to sea. This remained the situation until early in the 19th century when a new opening was made in about the middle of the valley. The former eastern opening near Stone Point (using the term point in the modern sense, that is near the car park), had been the result of deflection of the channel by flint shingle moving eastward by longshore drift. From the information of old maps this would have taken place in the 18th century or earlier. The deflection might have been associated with the great hurricane of 1703 (Daniel 's Storm), although it could have developed gradually. The former site of the stream channel is the low ground where the cafe, shop and toilets are now situated (not an ideal place but probably there because first development was close to the road and beach).


After the channel was abandoned here the beach seems to have built up with the local shingle, and is now a small and low type of barrier beach. In the past shingle could have come from the cliffs of the Lepe House and Inchmery area. Sea defences with rock armour just to the west of the Watch House now ensure that the supply is cut off, at least from a westerly direction. The groynes here do not show a marked direction of longshore drift, and the location http://www.broncosofficialonlinestore.com/Lamin_Barrow_Jersey_Broncos seems almost nodal and like down (east across the Solent) on a more limited scale. However, lack of resupply of shingle from the west suggests that depletion may occur at the car park in due course. There has not been major erosion at the main part of the car park, though, in recent years, but it is now commencing to the east of the car park. The gravel footpath at the foot of the old cliffs has now largely gone as a result of coast erosion.


At the back of the car park are old cliffs dating from the 18th century. They are rather degraded but still quite recognisable as cliffs. They are not yet undergoing erosion again, except to the east, as mentioned above. That eastern part is going to provide good geological exposures sooner or later, and it may be helpful in interpreting the Pleistocene Interglacial deposits, discussed elsewhere in this webpage.


The overview is fairly obvious. The car park at Lepe will be eroded away and/or flooded over sooner or later and the old cliffs at the back will be undergoing active erosion again. More rapid erosion seems likely on the west side. Further away to the west shingle will probably continue to accrete in the area northeast of Stansore Point (where the relics of World War II works are present). As shown below, there are already a good shingle bank with some overwash broncosofficialonlinestore.com/Bradley_Roby_Jersey_Broncos fans there.


There are various blocks of rock that are visible on the shore at Lepe Beach when the tide is very low. Others have been removed because they may useful in an area where stone blocks are not commonly available. Bembridge Limestone and some other rock types present here are discussed below. No evidence was found to indicate that these are erratics and they are associated with blocks of cement and some concrete. They have probably been brought here by human agency at various times, perhaps in connection with former sea walls or buildings or as ship ballast. Some rock debris might possibly be connected with the presence of the Roman road, or perhaps with ancient stone transport to Beaulieu Abbey or other historic sites. Amongst these rocks on the low tide shore a dinosaur footprint was found by Keith Talbot and Richard Carpenter in 1993. The photographs above show the position and the general environment. The slab has been kept in a garden fishpond since the date of discovery. It shows some minor effects of dissolution but does not include boring by marine organisms so it is unlikely that it has been in the sea for a very long period of time, although, of course, it could have been buried in mud.


The remarkable tridactlyl footprint was found in a slab of Purbeck stone between (the present) Stone Point and Stansore Point. The Bradley Roby Broncos Jersey location was on the stony and muddy low tidal flats, west of Stansore Point and just on the western side of the supposed end of the Roman Road. Dinosaur footprints are present in the Middle Purbeck Building Stones of the Isle of Purbeck from Swanage westward. They also occur at the Purbeck type section in Durlston Bay and at Worbarrow Bay. In Durlston Bay one would be unlikely to find such footprint without a search of thousands of slabs of Purbeck Stone. It is therefore very unusual to find such a slab near Stone Point where there is only a limited number of pieces of Purbeck stone. Searching and selection by humans from the rocks of the Isle of Purbeck has to have taken place at some stage and then the slab has to have been moved to Stone Point. It is not known how or when this happened. The occurrences of significant amounts of Purbeck stone in the Lepe Beach area are at three sites, sea defence works near the Watch House, slabs at the outfall beneath the beacon of Stansore Point and in addition the isolated four blocks of Purbeck Marble discussed below. The dinosaur footprint was presumably brought to the Stone Point area during the transport of one of these shiploads of stone, but probably not that for the sea defences.


The slab is of ostracodal biomicrite with thin shelled bivalves and gastropods, and with some chert. The small gastropod Valvata and the 'pond snail' Viviparus appear to be present. There are some scattered, brown, phosphatic fish scales or teeth. The small (about 2 mm), oval, ostracods are often paired. The particular bed has not yet been firmly identified, but the limestone is of Cherty Freshwater Member type and is probably similar to that of bed DB103 of Clements Durlston Bay log. The comparison with bed will be investigated further. The footprint has relatively long and narrow toe impressions, and is like those sometimes referred to in textbooks as of theropod type. It is relatively large compared to the examples from the Lower Purbeck of the Isle of Portland, but quite normal in size for a Middle Purbeck footprint. Somewhat similar footprints have been found in the Middle Purbecks (Pink Bed of the Intermarine Member) at Locks Quarry, Acton near Swanage in 1967, as shown in a photograph above, although in these the central toe is rather longer and straighter.


On the 4 June 2004, more than 10 years after the initial Lamin Barrow Broncos Jersey discovery, another piece of the same type of limestone with ostracods, bivalves, Viviparus and chert was found on the west of Stone Point. It was noticed by Keith Talbot in the company of Maldwin Drummond, Gary Momber and Ian West. This triangular piece was highly etched by water, the chert suggesting that about 0.5 cm had been dissolved away on the outside.


Captain Aubrey Story, managing director of the New Hippodrome, Southampton, who is spending the summer in the caravan site at Lepe and Peter Andrews who is also in the colony, were setting nets at low tide on Lepe foreshore when Capt. Story found that he was walking on remains of one deck of a ship submersed in the sand. They managed to dig out one of the ribs. This gave a clue as to the size of the ship which was roughly hewn and had wooden pegs attached to it. Captain Story told an "Echo" reporter. So far as I can trace no one in the district knew anything about the wreck which was still covered by several inches of water when we found it.


"During the last few days [tides ??] have been unusually low and it was at the extreme edge of the water that we found the wreck. Under the planking which seems to be part of a deck there was a quantity of stone which had been worked and some pieces of marble in the rough. "From what we could see before the tide hid the wreck it is a sort of [ship?] with a beam of about twenty feet. When the tide is low enough again we are going to do a bit more exploring.


More recently, in early 2004, four large blocks of Purbeck Marble were found just west of Stansore Point (the original Stone Point), near Lepe Beach by Keith Talbot and Ian West when searching the area at low spring tide. We were not looking for the ship remains but came across the relics by chance. The stones certainly seem to be the remains of the old shipwreck, initially discovered in 1938. Keith found some old timber nearby, although that may or may not have been related. It mostly seems now to be just large stone blocks and little else. They are scoured by the very strong tidal currents just here. Some details of the marble slabs are shown in photographs taken at the time. The Purbeck marble blocks are just offshore of land which owned by Mr Maldwin Drummond, owner of the Cadland Estate. This is private land but with a footpath on the shore from Lepe Country Park. The area is patrolled by rangers from the Country Park.


As noted above, the remains of the ship when first found in 1938 still included some timber decking. Most or all of this now seems to have been destroyed. Captain Story reported the presence of "marble" and it is not clear whether he recognised this, at the time, as Purbeck Marble, a gastropod limestone not real marble, but he might have done so. He mentioned some worked stone in addition to the "marble" blocks (although this might refer to worked Purbeck marble). There is a remote possibility that the dinosaur footprint found by Keith Talbot in a nearby area was once part of this stone cargo.


After we had rediscovered the wreck in 2004, the marine archaeologist Gary Momber made a limited excavation at low tide but he was unable to find any timber or anything of particular significance. As far as I know the remains of the wreck remain without further investigation. It is a difficult site that is under water except in very low, spring tides. Even then, little time is available to examine before it is once again covered with water. The wreck remains undated. Some photographs and further notes on the Purbeck marble follow.


Various views are provided above of four rectangular blocks of limestone which were found by Ian West and Keith Talbot on the lower shore during an unusually low tide near Lepe Beach. These are of Cretaceous gastropod limestone, the 'Purbeck marble'. This is not true marble just an old name for a type of limestone that could be sculpted. It seems unlikely that the blocks are simply joint bounded (see photographs of Purbeck Marble at Peveril Point below) and have regular forms. Measurements from an initial survey and plan suggests that these have been crudely worked into rectangular blocks of up to 227cm (7ft 4.5 inches) in length . They are partly covered in seaweed but do not seem to have any surface carvings. Unlike the many blocks on the beach at Durlston Bay, Swanage, they are not very rounded and have clearly been quarried from one of the thicker 'marble' beds.


For much of the time these blocks are under water, and they are partially buried in sand, gravel and mud. If the visitor just wishes to see Purbeck Marble then it is preferable not to go here, but to visit Peveril Point, Swanage where much more of it is easily accessible on the shore at all tides and most is in good clean condition without seaweed. The blocks at Lepe are of special interest, though, because there is no outcrop of Purbeck Marble in that area, or indeed on the Isle of Wight across the Solent.


Shown above is Purbeck Marble in situ in the Isle of Purbeck, the region of Dorset from whence the blocks have come. A thin vertical bed of Purbeck Marble at Peveril Point is shown in the left image, at the northern end of Durlston Bay, Swanage. This is the " Marble" and is relatively thin. The "Blue Marble" and the "Red Marble" are also present in the cliffs here and are about 1.2m (4 feet) thick. In the right image the Blue Marble is shown within a small syncline on the beach. These thicker beds would have been more suitable for quarrying. The colours incidently are very variable, even within an individual bed, and are mainly the result of the extent of oxidation of the glauconite.


The Purbeck Marble at Lepe is typical of that present in the Isle of Purbeck from Durlston Bay, Swanage westward to Blashenwell and in thinner beds to Lulworth Cove and beyond. The old map below shows the location of the main Purbeck Marble quarries at a late stage in its workings. It was extensively quarried and transported to Cathedrals for interior ornamental work in the 14 century. Much was used for pillars and much was also used for tombs.


The Purbeck Marble is a fine grained and easily carved limestone, a type of freestone without internal bedding planes on which it might split. The Lepe material has not been examined petrographically but hand lens observations show that it is almost identical to the familiar Dorset rock type. It consists of shells of the lake snail Viviparus. (1947) identified the particular gastropod as Viviparus cariniferus (J. de C. Sowerby). The gastropod diameters range from 2mm to about 3.5 mm. In addition to the complete gastropods there is a small proportion of broken shell material and some "nesting". Glauconite is of the dispersed type, rather than as obvious grains, and is frequently within gastropod shells. The presence of authigenic glauconite in a low salinity, almost freshwater, bed has for a long time been a topic of interest to sedimentologists. Some reworked Portland glauconite does occur in the Upper Purbeck strata but there is little doubt that in addition, as in this case, glauconite originated in the nearly freshwater lake, perhaps partly because of the the significant iron input near the Purbeck Wealden junction. An interesting aspect of the Lepe block examined is that the glauconite is unoxidised even within one centimetre of the block surface. Clearly the block has never been subaerially weathered and this good preservation is due to almost continuous submergence. There is a little limonitic browning on the outer part but the stone seems almost as fresh as though it has come directly from the quarry. The presence of allochems larger than 1mm in a pale buff micritic matrix places this rock as a biomicrudite according to Folk's Classification. Students may refer to it as a "biomicrite" using Folk in basic form for simplicity, but in fact it is really in the rudite category. In terms of textural maturity it is a packed biomicrudite. Using Dunham's Classification it is a gastropod packstone. Although it is a feature that is normally more easily seen in thin section, even with the hand lens some geopetal fabrics are visible. These consist of partial fillings of the lower part of gastropods with micritic sediment, the remainder, formerly empty part, of the shell interior being occupied by sparry calcite. If it was necessary to do so, it is possible to recognise the original "way up" of the specimen.


It is clear that the Purbeck Marble has been imported into the Beaulieu River by ship. A Purbeck Marble font of about 1300 was present in the old church or chapel at Lower Exbury (See Exbury Gardens and Steam Railway website for an illustration of the old chapel). In 1907 it was moved to the present Exbury Church ( and , 1978).


The 14th century seems to have been a particular time of transport of Purbeck Marble by sea. An example of the records of shipping associated with the Purbeck marble industry is provided by the following extract from (1948) : " A warrant was addressed in 1374 to the Keepers of the Port of Poole in Dorset ordering them to release from arrest the ship Margarete of Wareham, of 48 tons burthen, with two high tombs of marble for the Earl of Arundel and Eleanor his late wife, one great stone for the Bishop of Winchester, and other things of theirs which were on board. ." It is also of interest that Purbeck Marble has been used in the 12th century for grave slabs at Carisbrooke on the Isle of Wight.


The ship was presumably wrecked on the Horseshoe Spit in about the 14th century and buried under sand. It is just a matter for speculation as to whether the ship was trying to enter the Beaulieu River and head for Exbury Church or Beaulieu Abbey. It is recent erosion of the surrounds of the spit from the 1930s onwards has revealed the remains of the wreck. (A human skeleton found in the mud some years ago to the west of Horseshoe Spit, near the present car park, and photographed by Keith Talbot, may or may not have any connection with the shipwreck)


For more on the history of the use of Purbeck Marble see (2008), p. 72 et seq.


(In case it has relationship to the shipwreck with Purbeck Marble blocks, it may worth mentioning that A. J. and Edmund de Rothschild (1982) refer to the occurrence of a large stone slab about 8 feet long and 18 inches wide in a field next to Bill Birch's house in Lower Exbury Road.


This is about the same size as the shipwrecked slabs.


It was on a mound, but when excavated it was found to have iron hinges on its hidden side, and was assumed to be just an old gatepost. It probably has no connection, at all with the shipwrecked blocks but is mentioned just in case it should prove to be of Purbeck Marble.)


Blocks of Bembridge Limestone with conspicuous fossil shells of Galba longiscata (a late Eocene pond snail) are common on the low tide shore at Lepe Beach. This rock (known in the past as Binstead Stone) has been much used in old buildings and in the walls of Southampton. It is not as strong and resistant as Portland Stone or Carboniferous Limestone from the Mendips so it is not in general use now.


Portland Stone often with some Purbeck Stone has been much used in modern sea defences as at Lepe and elsewhere, but Carboniferous Limestone from near Frome is now much favoured for rock armour and is a recent addition to the shore. The Bembridge Limestone is probably from very old sea defences, piers or buildings. It is probably not of special significance that blocks occur at the end of the Roman road because they are also present westward to at least the outfall of the Dark Water.


In addition there are many blocks of cement, some with a rounded or sack like exterior. There is some concrete with obvious flints. Some Purbeck and Portland stone occurs particularly near the Dark Water outfall and the Watch House. Many of these are probably derived from old sea walls or small jettys.

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