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Lairg Gravity Low
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A BURIED PRECAMBRIAN IMPACT CRATER IN SCOTLAND

The Stac Fada Member is a melt-bearing sandstone unit within the Stoer Group (Mesoproterozoic, 1.2Ga) of north-west Scotland. Once regarded as volcaniclastic in origin, it was reinterpreted as an impact ejecta deposit following the discovery in it of shocked quartz and geochemical anomalies. The continuity of this impact deposit along the Stoer Group outcrop (>50km) and its substantial thickness (4-12m) suggests relative proximity (a few tens of km) to a large impact crater (tens of km diameter), but locating it has been hindered by the limited extent of the present outcrop, that is truncated by faulting and erosion. An offshore location to the west, beneath a thick Mesozoic succession in the Minch Basin, was proposed by Amor et al. but various directional indicators associated with the Stac Fada Member, from ejecta intrusions along bedding planes immediately beneath it, to erosional troughs eroded into its top, consistently indicate emplacement of ejecta from the east. No surface manifestation of an impact crater has been identified but there is a remarkable correspondence between the craters location, as inferred from these directional data, and the position of the Lairg Gravity Low, a conspicuous geophysical anomaly centred more than 50 km east of the Stoer Group outcrop. Proximal-distal facies changes along the outcrop of the Stac Fada Member are consistent with this inferred relationship between the ejecta deposit and the gravity low.
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Stoer Crater
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When heaven and earth collide
Long before Scotland was Scotland, when the population consisted only of green algae and the Highlands were as dry as Death Valley, a large natural object fell out of space and struck the Earth near where the village of Stoer now stands, in Sutherland. This incident occurred 1.2 billion years ago, but it has only been confirmed in the last few months.

"If the same thing happened today, all the trees in Aberdeen would be felled. The trees in Inverness would actually ignite. Most man-made structures would collapse. Everything made of paper would burn. You wouldn't be safe in Glasgow. But sitting here, we would be vapourised" - planetary geologist Scott Thackrey.

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RE: Stoer Group
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Geologists have uncovered evidence of the biggest meteorite crater ever found in Britain and Ireland.
The study findings solve a long-standing puzzle about a layer of rock that stretches for about 31 miles (50 kilometres) in northwest Scotland.

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"Chemical testing of the rocks found the characteristic signature of meteoritic material, which has high levels of the key element iridium, normally only found in low concentrations in surface rocks on Earth. We found more evidence when we examined the rocks under a microscope; tell-tale microscopic parallel fractures that also imply a meteorite strike" - Ken Amor,  Oxford University's Department of Earth Sciences, co-author on the Geology paper.

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Ullapool impact
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Evidence of the biggest meteorite ever to hit the British Isles has been found by scientists from the University of Oxford and the University of Aberdeen.
The scientists believe that a large meteorite hit northwest Scotland about 1.2 billion years ago near the Scottish town of Ullapool.


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RE: Stoer Group
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It is a mystery which has puzzled generations of geologists the origins of a layer of stratified rock trapped in the sediments which now form part of the coastline of north-west Scotland.
Scientists suspected for years that the curious seam could have been formed by volcanic activity millions of years ago.
But it was revealed yesterday that the 40-mile long rock layer was formed when the biggest meteorite ever to strike what is now the British Isles hit the Earth close to present-day Ullapool with the force of a 145,000 megaton bomb.

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5.53297W_57.98202N
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Latitude: 57.98202, Longitude: -5.53297


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Evidence of the biggest meteorite ever to hit the British Isles has been found by a team of scientists.
Researchers from the universities of Oxford and Aberdeen think a large object hit north-west Scotland about 1.2 billion years ago.
The space rock struck the ground near the present-day town of Ullapool, they report in Geology journal.

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Title: A Precambrian proximal ejecta blanket from Scotland
Authors: Kenneth Amor, Stephen P. Hesselbo, Don Porcelli, Scott Thackrey, and John Parnell

Ejecta blankets around impact craters are rarely preserved on Earth. Although impact craters are ubiquitous on solid bodies throughout the solar system, on Earth they are rapidly effaced, and few records exist of the processes that occur during emplacement of ejecta. The Stac Fada Member of the Precambrian Stoer Group in Scotland has previously been described as volcanic in origin. However, shocked quartz and biotite provide evidence for high-pressure shock metamorphism, while chromium isotope values and elevated abundances of platinum group metals and siderophile elements indicate addition of meteoritic material. Thus, the unit is reinterpreted here as having an impact origin. The ejecta blanket reaches >20 m in thickness and contains abundant dark green, vesicular, devitrified glass fragments. Field observations suggest that the deposit was emplaced as a single fluidised flow that formed as a result of an impact into water-saturated sedimentary strata. The continental geological setting and presence of groundwater make this deposit an analogue for Martian fluidised ejecta blankets.

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