Sarsquoy, Mill Sound, Dingieshowe and Taracliff Bay to Newark Bay – an excursion
From: Fannin, Nigel G.T. Edinburgh Geological Society field excursion Orkney May 1991 (unpublished)
- 1 Locality 1 Sarsquoy (HY 500 097)
- 2 Locality 2 Mill Sand (HY 517 080)
- 3 Locality 3 Dingieshowe (HY 550 035)
- 4 Locality 4 Taracliff Bay (HY 554 034) to Newark Bay (HY 568 038)
- 5 Locality 5 Point Of Ayre (HY 591 038) to Greenigeo Taing (HY 592 042)
- 6 Locality 6 Tommy Tiffy (HY 591 050)
- 7 Locality 7 Gearsan (HY 595 078)
- 8 Locality 8 Highland Park Distillery (HY 452 095)
Locality 1 Sarsquoy (HY 500 097)
A double ayre (gravel beach) encloses two brackish lagoons on the eastern side of the Bay of Inganess. Cloven Ayre, the inner beach, is now completely vegetated with a narrow gap at its eastern end. The outer spit, Long Ayre, is un-vegetated, more mobile and almost entirely encloses the lagoon.
Three Tills are exposed in the nearby cliffs. The colours are believed to reflect differing ice flow directions over different local lithologies and not distinct ice advances. The age of the till is unknown. The basal till is grey and is overlain by a brown till which in turn is overlain by a red till. The lagoon has been used as a harbour since Viking times and old moorings are found along the southern side of the outer lagoon.
Locality 2 Mill Sand (HY 517 080)
Another well developed ayre can be seen at Mill Sands. This will be briefly examined depending on the state of the tide.
Locality 3 Dingieshowe (HY 550 035)
Here a sandy ayre (tombolo) has extended to link what was the island of Deerness to the Mainland. The ayre is markedly asymetrical with a steep southerly face and a narrow beach profile. On the north side there is an extensive area of sheltered intertidal sand flats. The ayre is composed of irregular dune mounds and ridges up to 9 m high. At the eastern, down wind, end a vegetated machair area has developed.
Locality 4 Taracliff Bay (HY 554 034) to Newark Bay (HY 568 038)
The coast between Taracliff Bay and Newark Bay exposes a fairly continuous, eastwardly dipping succession of strata from the Rousay Beds to the base of the Middle Eday Sandstone.
At the western end of the section, greenish-buff, silty sandstones belonging to the Upper Rousay Flags are exposed in vertical cliffs and on a 200 m wide shore platform. The flags are much paler in colour than the underlying Stromness Flags and yield a slightly different fossil fauna. They are succeeded upwards by the Passage Beds which form a transition to the Lower Eday Sandstones; the Passage Beds are thickest in the south (260 m in South Ronaldsay) and thin northwards until in Eday and Sanday the junction of the Upper Rousay Flags with the Lower Eday Sandstone is abrupt. The Passage Beds show an increasing coarsening upwards, the predominantly silty Rousay Beds eventually giving way to the arenaceous Lower Eday Sandstones.
The cliffs to the west of Muckle Castle, provide one of the best exposures of the Lower Eday Sandstones in Orkney and show over 175 m of quartzitic, well-bedded sandstones displaying cross laminations and channelling. Near the Castle the junction of the Sandstones with the Eday Flags is faulted and obscured by igneous rock, originally thought to be a lava flow, but now recognised as an intrusive olivine dolerite. The Muckle Castle stack is composed almost entirely of this intrusion but bears a thin capping of sediment and the igneous rock can be seen in the cliffs opposite and traced for a short distance inland; to the west it is fault bounded and to the east it lies against sandstones contorted in its emplacement and overlain by a tuffaceous horizon with igneous blocks.
It has been interpreted as a volcanic plug of Middle Old Red Sandstone age.
The Eday Flags show their thickest development within the Taracliff section- from being 150 m thick here they decrease northwards to 100 m in Shapinsay, 50m in Stronsay, and only 10m in Sanday. To the east of Muckle Castle the Flags are exposed for almost 200 m until at HY 563 033 they abut against a series of interbedded tuffaceous sandstones; at the same horizon lavas are exposed on the eastern coast of Deerness at the Point of Ayre, but only tuffs are exposed on the southern shore. Further to the east lies a sequence of Eday Flags in which a rhythmical pattern of sedimentation becomes more pronounced; the Flags continue to HY566036 where they give way to the coarser sediments of the Middle Eday Sandstone. As in the Stromness Flags, fish remains occur in the deepwater facies of the Eday Flags.
The red-yellow Middle Eday Sandstones form the cliffs on the western side of Newark Bay; they comprise a series of fining-upward cycles each made up of a sandstone unit 50 cm - 2 m thick overlain by deep purple, poorly laminated, sandy siltstones and sandstone with thin ribs of commonly convoluted sandstone. These beds grade upwards into massive bedded sandstones. They are well exposed in the cliffs but access to parts of the section is difficult.
Locality 5 Point Of Ayre (HY 591 038) to Greenigeo Taing (HY 592 042)
At the Point of Ayre there are two lava flows of alkaline olivinedolerite with interstitial analcime and natrolite. One is very thin; the other is at least 7 m thick and has a scoriaceous top, sand-filled fissures and pipe amygdales. North of the Point, towards Greenigeo Taing there are some well exposed cyclic units of the lacustrine/fluvial Eday Flags facies.
Locality 6 Tommy Tiffy (HY 591 050)
The Transition Beds between the Rousay Flags and Lower Eday Sandstone, here about 21m thick, will be studied at Tommy Tiffy. They consist of alternating beds of purplish and yellowish siltstone and thin sandstone ribs. The sandstone ribs become progressively thicker and more closely spaced as the sequence is ascended. The highest fish bed in the Rousay Flags will be examined in this locality.
Locality 7 Gearsan (HY 595 078)
'The Gloup' is a large isolated blowhole separated from the shore cliff by a 25m wide rock bridge. This is the best example of a blowhole in Orkney.
Locality 8 Highland Park Distillery (HY 452 095)
An evening (7.30p.m.) visit for hardy folk for a tour and samples.
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