Baked fanglomerate

A quick post to share a few images of an outcrop I visited last September out in California’s Owens Valley. This is a spot where alluvial fans coming off the eastern Sierra Nevada were overrun by a basaltic lava flow (Jeff, Kim, Fred, and Kurt for scale): The unofficial term for these conglomerates deposited by … Read more

Transect debrief 3: Rodinian rifting

The Grenville Orogeny, responsible for Virginia’s basement complex, was one mountain-building event among many that helped put together a Mesoproterozoic supercontinent called Rodinia. But Rodinia didn’t last: it broke apart during the Neoproterozoic to form the Iapetus Ocean basin. This rifting event is recorded in Virginia’s Blue Ridge province in the Swift Run Formation and … Read more

Is this dike a feeder?

A new paper in the journal Geology examines an interesting question: how can you tell feeder dikes from non-feeder dikes? The answer is, normally you can’t. Normally, there’s no way to tell for sure whether a given dike actually funneled magma to the paleo-surface, or whether it never reached the paleo-surface. The reason for this … Read more

Crucifix Site 1: Sediments

On the September 2009 GSA field forum in the Owens Valley, the final stop of our first day was to check out the so-called “Crucifix Site,” along Chalk Bluff Road (north of Bishop, California, at the southern margin of the Volcanic Tableland). It’s called the “Crucifix Site” because there is a metal cross erected there: … Read more