Monday, May 20, 2013

Ancient Australian Dunes

Lens cap (bottom, left of center) for scale.

Lens cap (middle, left of center) for scale

I'm working on my next Death Valley post, but in the meantime, here are two quick photos of some beautiful cross-bedding in the Mereenie Sandstone at Kings Canyon, Australia.  360 Ma, there was an inland dune field here. That's right, these were sand dunes! Unlike the coastal dunes on Lake Ontario that are made up of beach sand, these ancient Australian dunes are thought to have formed in a desert. The Australian deserts today have dunes too.

Source: Thompson, R., 1995, A guide to the geology and landforms of Central Australia: Northern Territory Geological Survey, Alice Springs, Northern Territory, Australia.

Friday, May 17, 2013

Death Valley: Dante's View

I don't think I was prepared for how amazing Death Valley would be. I'm not sure what I expected, but there was a little bit of everything there. The SU Geology Club spent a couple of days there on our spring break field trip, and it was just enough to get a thirst for more. Death Valley's dramatic landscapes are the result of recent rifting and extension but the rocks in the basin record a longer history of the western margin of North America (Miller, 2005).

Death Valley is approximately 200 km long and varies from 8-25 km in width, with 1-3 km deep sediments filling the steeply walled valley (Hussein et al, 2011).

Dante's View overlooks Death Valley from an elevation of 5474 feet (1669 m). If you can get up before dawn to get there, you will be rewarded by a gorgeous sunrise behind the peaks to the east and you'll see the light creep down into the valley. Some of my sunrise photos are at the end of this post. 

Dante's View is on the Black Mountains which have been uplifted along the still active Black Mountains fault zone (Miller, 2005). Across the valley are the Panamint Mountains. From Telescope Peak (the highest point in Death Valley National Park) to Badwater Basin (the lowest point in North America), there is an elevation difference of 11,331 feet (3455 m).

Telescope Peak.
~11,000 feet (3000 m) of elevation change

Death Valley is a classic example of Basin and Range topography: uplift of mountains along parallel normal faults leaves linear valleys between the mountain ranges (Hill and Troxel, 1966).  It is also a great place to see alluvial fans. It's hard to get a sense of how big alluvial fans are unless you can see just how thick they are:

Daylight has almost reached the tops of the alluvial fans.
Yes, they really do go nearly halfway up the mountains!

In the early morning light, shadows mark the canyons that feed the alluvial fans.
The shadow of the Black Mountains still covers most of the alluvial fan and the valley floor.

Many channels can be seen flowing down the fans
Panamint Mountains and the shadow of the Black Mountains in Death Valley.

References Cited:

Hill, M., and Troxel, B., 1966, Tectonics of Death Valley region, California: Geological Society of
America, v. 77, p. 435–438.

Hussein, M., Serpa, L., Valasco, A., and Doser, D., 2011, Role of sedimentation in continental rifting
from comparing two narrow rift valleys the Salton Trough and Death Valley-California: Natural Science, v. 03, no. 11, p. 927–935.

Miller, M., 2005, Geological landscapes of the Death Valley region: Earth-Science Reviews, v. 73, no.
1-4, p. 17–30.