Tension gashes in Malmesbury metasediments near Sea Point Contact
A small structural geology treat – several en echelon arrays of tension gashes (quartz-filled veins) in Malmesbury Group metasediments, Sea Point, South Africa.
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Viewing the Sea Point migmatite through the lens of GigaPan
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
Friday fold: isoclinal fold in ferruginous pelite and chert of the Fig Tree Group
A quick Friday fold – Ulundi Formation, basal Fig Tree Group of the Barberton Greenstone Belt, exposed in a creekbed etched into the trace of the Sheba Fault. This is one of the outcrops I visited one week ago today as part of the pre-IGC field trip to the Barberton. The rocks are iron-rich cherts … Read more
Archean microbial mats in the news and in GigaPan
The news yesterday of 3.7 Ga stromatolites in Greenland prompts a closer look at 3.22 Ga microbially-induced sedimentary structures in the Barberton Greenstone Belt’s Moodies group sandstones.
Ball & pillow and other sedimentary structures in Graafwater Formation, Table Mountain
In Cape Town for the International Geological Congress, Callan hikes up Table Mountain and finds some superb primary sedimentary structures in sands and shales of the Graafwater Formation.
Friday fold: roadside in Ladismith/Kleinkaroo
Martin Schmidt again contributes a fold – this time from his summer trip to South Africa: Pretty great! This is part of the Cape Fold Belt. Perhaps some of you will drive by it when you go to the International Geological Congress in South Africa later this month! You can view the site in the … Read more
Three new 3D rock sample models
Pahoehoe “ropes” on a basalt, sample site unknown: Archean gneiss from the Gallatin Range of Montana: Tafoni in Malmesbury Group turbidites, South Africa:
Mirage, by Nina Burleigh
My latest audiobook consumed during my commute was the story of Napoleon Bonaparte’s (why do we always call him by his first name?) ill-fated expedition to Egypt in 1798. Napoleon brought with him a corps of “savants,” natural historians, engineers, artists, and musicians, charged with documenting the history and natural history of Egypt, and helping … Read more
Friday fold: Sliced BIF from Joburg
The Friday fold is a trio of hand samples of folded banded iron formation from South Africa. Collected in 2012 as float from the “contorted bed” outcrop in downtown Johannesburg, these samples are only now being cut and polished in the lab at NOVA.
Dwyka Tillite in South Africa
My wonderfully named e-buddy Martin Bentley recently took a field trip to a quarry in South Africa (between Grahamstown and Fort Beaufort) where the Dwyka Formation is exposed: This poorly sorted sedimentary rock (a ‘diamictite’) is usually interpreted as glacial deposits (lithified till, or ’tillite’). Alfred Wegener cited these rocks and accompanying glacial striations (and … Read more
Dark Star Safari by Paul Theroux
The week before last, on the flight home from Texas, I finished reading Dark Star Safari, Paul Theroux’s 2004 account of traveling overland through Africa from Cairo to Cape Town. I’ve enjoyed Theroux’s traveling writing very much over the years, and although he’s written some great novels (I’m thinking of Mosquito Coast), most of them … Read more
Friday fold: Martin’s metamorphics
A guest “Friday fold” from South Africa: folded gneisses, flavored with other treats of a geological nature.
Friday fold: Gansbaai
A small mountain inland of Gansbaai, South Africa (where one goes to cage-dive with great white sharks) shows some of the folding characteristic of the Cape Fold Belt. Let’s zoom in… A few bedding traces annotated, to ease your armchair fold-viewing experience. I think this is my final photo from South Africa… Wow. Only took … Read more
Friday fold: Hoerikwaggo Trail 5
We wrap up our week-long odyssey along South Africa’s Hoerikwaggo Trail with a look at something we look at every Friday: folds! In this case, we’ll be examining folds in the bedding layers of the Table Mountain Sandstone.
Hoerikwaggo Trail 4: fynbos vegetation
Callan continues his week-long recounting of his five-day backpacking trip from the Cape of Good Hope to Cape Town, South Africa, along the Hoerikwaggo Trail. Today, we examine the ‘fynbos’ plants seen along the trail.
Hoerikwaggo Trail 3: Joints, veins, and Liesegang banding
Callan continues his week-long recounting of his five-day backpacking trip from the Cape of Good Hope to Cape Town, South Africa, along the Hoerikwaggo Trail. Today, we examine the jointing, oxidizing and reducing fluid flow, and the emplacement of ore veins.
Hoerikwaggo Trail 2: the Table Mountain Sandstone
Callan continues his week-long recounting of his five-day backpacking trip from the Cape of Good Hope to Cape Town, South Africa, along the Hoerikwaggo Trail. Today, we examine the Table Mountain Sandstone.
Hoerikwaggo Trail 1: the hike
Callan begins a week-long recounting of his five-day backpacking trip from the Cape of Good Hope to Cape Town, South Africa, along the Hoerikwaggo Trail. Today, we examine scenery and logistics of the trail.
A few folds from Betty’s Bay
Here are a few folds in the quartzites of the Cape Fold Belt, exposed on the mountainsides of the Harold Porter Botanical Gardens in Betty’s Bay, South Africa. Hillside #1: Zooming in closer: Annotated (bedding traced out): Hillside #2: Zooming in on summit region: Annotated (bedding traced out): Zooming in on the central portion of … Read more
Salt crystals in a tidal pool, Hermanus
Last winter, around 10 months ago, Lily and I were walking along the shore of Hermanus, South Africa, when I saw a little closed-drainage pool in the sandstone, harboring a briny distillation of the South Atlantic Ocean. Neat salt “rim” on the edge of the pool… Also note the ~cubic crystals at the bottom of … Read more