It was five years ago when I first visited Sea Point, the outcrop on the coast of the Cape Peninsula where the Cape Granite (~540 Ma) intrudes the (meta-)sedimentary rocks of the Malmesbury Group. The outcrop is (a) beautiful and evocative, and (b) of historical importance, as Charles Darwin visited it while on the voyage … Read more
It’s time to cover the third and final unconformity I observed this summer in the North-West Highlands of Scotland: the unconformity between the Neoproterozoic Torridonian Group below and the Cambrian Ardvreck Group above. Where I saw it, south of Loch Assynt on the mountain called Beinn Garbh (north of Canisp), it actually is displayed alongside … Read more
Let’s now profile the next unconformity in the sequence of pulses of erosion and deposition recorded in the North-West Highlands of Scotland. For a reminder, here’s a cartoon cross-section through the four relevant units: Today, we’ll look at the contact between the Lewisian Gneiss and the Torridonian Group (Diabeg Formation), marked with a “2” on … Read more
First in a series profiling the three unconformities to be found in the North-West Highlands of Scotland. Today: the sub-Stoer unconformity as exposed at Clachtoll. Explore a Proterozoic buried topography topped with coarse, angular breccia.
This is the Split Rock at Clachtoll, on the shore of the North-West Highlands of Scotland. You’re looking out to sea, over the Minch. It’s the site that graces the cover of the excellent book A Geological Excursion Guide to the North-West Highlands of Scotland, by Kathryn Goodenough and Marten Krabbendam. “Clach toll” apparently means … Read more
When in Shetland, one of my first stops was the museum in Scalloway, and one of the ancillary benefits of visiting there is the castle next door: Scalloway Castle includes building stones derived from the local limestone – a Neoproterozoic unit that has recently been chemostratigraphically correlated with Snowball Earth cap carbonates elsewhere in the … Read more
Here’s a visualization combination that leverages the advantages of the GIGAmacro system with the 3D ‘virtual sample’ perspective of the Sketchfab-hosted model: the same sample presented in both formats. In this case, it’s a lovely example of cleavage refraction going from meta-clay-shale (now ‘slate’) through a graded bed of fine sand and silt. [gigapan id=”187755″] … Read more
An inaugural visit to an outcrop in Shenandoah National Park reveals the signature of lava flows ~600 million years old.
Here are three more of my Photoscan-generated, Sketchfab-hosted 3D models of rock samples: Mud cracks in Tonoloway Formation tidal flat carbonates, Corridor H, West Virginia: Diorite from the eastern Sierra Nevada of California: Vein cross-cutting foliated & lineated gneiss, Blue Ridge basement complex, Virginia:
As longtime readers know, late summer is when my Rockies students submit their final projects – web-based explanations of key geologic sites they examined during the trip. Today, I offer you a guest blog post by student John Leaming. You’ll notice that I’m not *completely* absent from the post, however – I make a couple … Read more