Area Ground Floor Stewart Building Site of Special Scientific Interest Alexandra Wharf SITE MANAGEMENT STATEMENT ZE1 0LL Tel: 01595 693345 Site code: 755 Fax: 01595 692565

Purpose This is a public statement prepared by SNH for owners and occupiers of the SSSI. It outlines the reasons it is designated as an SSSI and provides guidance on how its special natural features should be conserved or enhanced. This Statement does not affect or form part of the statutory notification. We welcome your views on this statement.

Natural features of Gutcher SSSI Condition of feature (date monitored) Structural and metamorphic geology: Moine. Favourable, maintained (January 2003)

Description of the site The site is important because it contains a lot of information about the formation and closure of the Iapetus Ocean. The metamorphosed rocks show the extent of the deformation that accompanied ocean closure. The Valayre gneiss, is important because it holds key information on how the different parts that make up came together. It marks an important boundary between rocks of different origin. This site is not only important in the study of Shetland but also in a Scottish context because the rocks present can be matched with those found on the Mainland to provide a picture of the events that shaped .

The island of Yell is composed mainly of metamorphic rocks (rocks which have been altered by extreme heat and pressure) belonging to a rock unit called the Yell Sound Division. These are very similar to the rocks of the Moine Supergroup, which underlies much of the northern Highlands of Scotland. They were originally laid down around 900 million years ago as thick layers of sand and mud in shallow water on the margins of an ancient ocean. Burial converted these sediments into sedimentary rocks – sandstone and mudstone.

Since then the rocks have been involved in two mountain building periods (orogenies) as a result of continental collisions driven by plate tectonics. The first orogeny around 800 million years ago is poorly understood and left little evidence in the rocks as its effects were overwritten by the later and more significant Caledonian orogeny. This was caused by collision between North America and western Europe around 450 million years ago which created a range of fold mountains running from northern Norway to Scotland. The high temperatures and pressures generated in these collisions altered the original rocks into their present form.

Metamorphism converts sandstone into psammite or, if the original sand was almost pure quartz, quartzite. Mudstone is altered to schist – a rock that splits easily because of the parallel

1 alignment of certain minerals, particularly mica. The Yell Sound Division consists essentially of large areas of psammites separated by layers of quartzite and schist. In the east of Yell, the rocks of the Yell Sound Division are separated from those formed from slightly younger sediments - known as the Dalradian Supergroup - by a band of rocks known as the Boundary Zone. This includes a rock known as the Valayre Gneiss which contains spectacular large crystals of microcline feldspar. This feature allows it to be traced from Gutcher, down the east coast of Yell and through the of Shetland. The Boundary Zone also includes a band up to a kilometre in width, known as the Slide, where the rocks have been deformed, shattered and recrystallised. This is the result of movement along a major fault at some time during the Caledonian orogeny which slid the different aged Moine and Dalradian rocks alongside each other.

Most of the rocks that are found within the Gutcher SSSI belong to the youngest part of the Yell Sound Division. These rocks are mainly metamorphosed sediments, but they also contain metamorphosed basalt, possibly resulting from magma injected between the layers of sediment as the sea floor stretched prior to ocean closure. The origin of some of the rocks within Gutcher SSSI is the subject of current debate. These are rocks made up mainly of quartz and pink microcline feldspar. These have been interpreted as sedimentary rocks that have been subjected to such high temperatures that they have partially melted, however they could have originated as granite that was injected into the rocks in a similar way to the basalts. The site also contains a variety of other igneous rocks that were intruded during the later stages of metamorphism and hence escaped much of the deformation seen in the other rocks.

Past and present management The site consists of sea cliffs and foreshore rock exposures and has not been subject to any practical management with the exception of the area below the Gutcher quarry. This was originally opened to provide rock to construct the inter-island ferry terminal in the 1970s, before the site was notified. It was granted planning permission to extend the workings shortly after notification – although it was realised that this would destroy or obscure some of the rock outcrops within the SSSI, it would also create fresh exposures of the same rock units which could enhance its value for research.

Objectives for Management (and key factors influencing the condition of natural features) We wish to work with the owners and occupiers to protect the site and to maintain and where necessary enhance its features of special interest. SNH aims to carry out site survey, monitoring and research as appropriate, to increase our knowledge and understanding of the site and its natural features. 1. To maintain the physical and visual integrity of the rock exposures The interests of the site are the rock exposures along the coast and foreshore and any activities which would obscure these in the medium or long term would be damaging and should be avoided. Wave action and erosion generally keep the exposures clean but material, particularly heavy objects (eg boulders) dumped on the foreshore could obscure exposures for some time.

Date last reviewed: 25 February 2011

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