Qualla: Orcadian Basin https://qualla.com/orcadian-basin en-us © 2026 Bendyline Mon, 20 Jul 2026 10:21:25 GMT Qualla serial false Qualla support@bendyline.com yes https://qualla.com/_m/g/f/q/z/orcadian-basin-wp/hero-small.webp Qualla: Orcadian Basin https://qualla.com/orcadian-basin Orcadian Basin: Introduction https://qualla.com/orcadian-basin/ Photo credit Mikenorton, CC BY-SA 3.0. Four hundred million years ago, before there were Orkneys, before there was a North Sea, a great freshwater lake spread across what is now northeastern Scotland. Geologists call it Lake Orcadie. At its deepest interval, the lake covered at least 50,000 square kilometers and plunged to depths of 100 metres or more. Fish swam at its surface, sank through anoxic gloom at the bottom, and were sealed into mud that would harden into flagstone. Drift north today from the Moray Firth toward Shetland and you are flying above the buried floor of that vanished sea.

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Image: Mikenorton | CC BY-SA 3.0

]]> Sun, 31 May 2026 00:00:00 GMT https://qualla.com/_m/g/f/q/z/orcadian-basin-wp/gfqz-orcadian-basin-intro.mp3 0:06 1 full Orcadian Basin: A Lake the Size of a Country https://qualla.com/orcadian-basin/ Photo credit Mikenorton, CC BY-SA 3.0. The Orcadian Basin formed in the Devonian period, after the great Caledonian mountain-building event that crumpled Scotland against Greenland and Scandinavia. As the crust cooled and stretched, fault blocks dropped and filled with sediment. Rivers fed the depression. Eventually a...

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Image: Mikenorton | CC BY-SA 3.0

]]> Sun, 31 May 2026 00:00:00 GMT https://qualla.com/_m/g/f/q/z/orcadian-basin-wp/gfqz-orcadian-basin-a-lake-the-size-of-a-country.mp3 0:06 2 full Orcadian Basin: The Achanarras Window https://qualla.com/orcadian-basin/ Photo credit Mikenorton, CC BY-SA 3.0. Of all the layers in the basin, one stands out: the Achanarras Fish Bed Member. Deep, anoxic, and stable for an unusually long stretch of geological time, the Achanarras lake preserved fish in extraordinary detail. The quarry near Thurso, in Caithness, has yielded specimens of ev...

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Image: Mikenorton | CC BY-SA 3.0

]]> Sun, 31 May 2026 00:00:00 GMT https://qualla.com/_m/g/f/q/z/orcadian-basin-wp/gfqz-orcadian-basin-the-achanarras-window.mp3 0:06 3 full Orcadian Basin: Flagstones for Neolithic Hands https://qualla.com/orcadian-basin/ Photo credit Mikenorton, CC BY-SA 3.0. When the lake dried and the millennia rolled on, its mudstones and siltstones hardened into thinly bedded flagstone that splits clean along the bedding. Neolithic builders on Orkney noticed. The walls of Skara Brae, the great chambered tomb of Maes Howe, the Ring of Brodgar, and ...

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Image: Mikenorton | CC BY-SA 3.0

]]> Sun, 31 May 2026 00:00:00 GMT https://qualla.com/_m/g/f/q/z/orcadian-basin-wp/gfqz-orcadian-basin-flagstones-for-neolithic-hands.mp3 0:06 4 full Orcadian Basin: Oil Below, Hills Above https://qualla.com/orcadian-basin/ Photo credit Mikenorton, CC BY-SA 3.0. The same organic-rich shales that preserved Achanarras fish also acted as petroleum source rock. The Beatrice oilfield in the Inner Moray Firth produces hydrocarbons that began as Devonian algae and bacteria, cooked over hundreds of millions of years. The visible Orkney and Shetl...

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Image: Mikenorton | CC BY-SA 3.0

]]> Sun, 31 May 2026 00:00:00 GMT https://qualla.com/_m/g/f/q/z/orcadian-basin-wp/gfqz-orcadian-basin-oil-below-hills-above.mp3 0:06 5 full Orcadian Basin: The View from Above https://qualla.com/orcadian-basin/ Photo credit Mikenorton, CC BY-SA 3.0. From cruising altitude over the northern North Sea, the basin is invisible - just water, oil platforms, and the green smudges of Orkney and Shetland. But geology shapes everything you see. The Great Glen Fault, running from Inverness to the Moray Firth, passes through what was on...

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Image: Mikenorton | CC BY-SA 3.0

]]> Sun, 31 May 2026 00:00:00 GMT https://qualla.com/_m/g/f/q/z/orcadian-basin-wp/gfqz-orcadian-basin-the-view-from-above.mp3 0:06 6 full