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Earth Science Conservation Review
| Millin Bay | Down |
| Site number: | 656 | ||
| Locality Type: | Foreshore | Status: | ASSI |
| Grid Reference: | J630495 Centroid | ||
| Google maps: | 54.36851,-5.49193 | ||
| County: | Down | Council area: | Ards & North Down Borough Council |
| Period: | Silurian | ||
| Lithostrat: | Hawick Group, Kearney Siltstone Formation, Tara Sandstone Formation, Millin Bay Formation | ||
| Site Description | |
|---|---|
| Introduction: | |
Millin Bay is situated on the Irish Sea coast of the Ards Peninsula about 1km south of Knockinelder Bay and Quintin Bay. Access to the site is via the road branching left at the western end of Knockinelder Bay (Fig. 25). In Millin Bay, folded turbidite facies rocks (Hawick Group) contain structures typical of Caledonian deformation seen elsewhere across the Down-Longford Belt. The axis of a major Caledonian fold known as the Millin Bay Anticline runs through the Bay. | |
| Description: | |
The strata in Millin Bay consist of turbidite facies rocks (greywacke and shale) which are part of the Hawick Group (Silurian). Anderson (1978) identified three distinct formations in and around Millin Bay (the Tara Sandstone Formation, Millin Bay Formation and Kearney Siltstone Formation). Strata at this locality form the Millin Bay Anticline, a major regional structure which has been mapped to the SW across the Ards Peninsula and for a distance of 12km across the nearby Lecale Peninsula. In Millin Bay, the change in younging directions across the fold hinge can be clearly demonstrated using upwards fining sedimentary features in the turbidite units, particularly in the Tara Sandstone Formation. On the northern limb of the Millin Bay Anticline as far north as Quintin Bay, a series of well-developed F1 folds plunge at angles up to 50° east and have well-developed axial-planar cleavage (S1). In most cases S1 intersects bedding parallel to the fold hinges. However, at some localities the S1 cleavage is rotated clockwise relative to the F1 hinges and is no longer axial-planar. Examples of this divergent cleavage can be seen north of the Coastguard Station on the southern limb of the Millin Bay Anticline and on the northern limb of the anticline between Millin Bay and Quintin Bay. The principle structures in Millin Bay are related to D1 deformation during NW-directed subduction of the Iapetus Oceanic crust. This process resulted in the formation of an imbricate stack of fault-bounded tectonic blocks. Subsequent deformations were related to the final closure of Iapetus and subsequent uplift of the accretionary prism. The rocks in Millin Bay have undergone a regional metamorphism during which they experienced very-low grade prehnite-pumpellyite facies conditions. | |
| Notes: | |
For general information on the Structural Geology of Northern Ireland, directions to other Structural Geology sites and an extensive reference list see Key Site 641 - Introduction to the Structural Geology of N. Ireland. The full range of ESCR site relating to the Lower Palaeozoic are as follows: Outer Ards Stratigraphic, Palaeontological and Structural sites Coalpit Bay – Lower Palaeozoic (record no. 1350) Helen’s Bay – Grey Point – Lower Palaeozoic (record no. 1351) Kearney Point – Knockinelder Bay – Lower Palaeozoic (record no. 1352) Orlock Bridge – Lower Palaeozoic (record no. 1353) Tieveshilly – Carrstown – Lower Palaeozoic (record no. 1354) Orlock Bridge - Structural (record no. 652) Whiskin Rocks - Structural (record no. 653) White House Port, Cloghy - Structural (record no. 654) Knockinelder Bay and Kearney Point - Structural (record no. 655) Millin Bay - Structural (record no. 656) Pomeroy area Craigbardahessiagh and Bardahessiagh River – Palaeontology (record no. 29) Lime Hill Farm – Palaeontology (record no. 33) Little River and Slate Quarry Bridge – Palaeontology (record no. 31) | |
| Keywords | |
|---|---|
| Rocks: | Greywacke, Shale, Turbidite |
| Structures: | anticline, graded bedding, cleavage, fold |
| Access | |
|---|---|
| Approach: | Access to the site is via the road branching left at the western end of Knockinelder Bay (Fig. 25). |
| Record type: | ESCR report | Recorded by: | T.P. Johnston |
| Entered by: | E M Porter | ||
| Last updated: | 23/09/03 | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Millin Bay, County Down, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=656. Accessed on 2026-11-06. |
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