Geology and wheeling upside down

This post isn’t about somebody overturning (I don’t think anyone did), but the reversal of expected geology in mixed sand/mud environments. I start by referring to the wheeling experience at Hawk Pride, where we fought mud that was produced from weathering (erosion) of shale and sandstones. There, we found boulders of Hartselle Fm. sandstone in a hillside with lots of shale/mud, where the ledges (an offroad term for a hard climb over a solid layer of rock) were the more resistant sandstone. BUT, those were 300 my old sediments where the quartz grains produced a silica cement, which made the “sandy” layers really hard.

As I mentioned in a previous post, these rocks are only 50 my old, and the sandstone is not cemented, which is why the layers (in total) are called the “Queen City Sand”. Here is a (poor) image that shows what I mean…

example ledge

The vehicle in the image was dragged (by winch) over a 2 foot ledge of hard rock, which can be inferred from their exit (sorry about the poor trail photos, but I forget to take them when I am worried about my own escape…a work in progress). The ledge was composed of shales like I showed in the previous post. Here is another photo of a hand sample from this area. The rock doesn’t have as many organic components but it is as resistant.

2015-05-08 18.09.38

This post is difficult to write because I didn’t take enough photos of the trail geology, but it is important to learn one lesson…time heals all sedimentary wounds…the young Eocene rocks (~50 mya) haven’t had time to heal all wounds. I mean that the organic material was still observable in a hand sample, and the sands didn’t supply silica (aka SiO2) to cement them as with older rocks. The result is that we were attempting to drive over hard shale (aka mud) layers while the sand formed nice traction surfaces to approach these ledges.

I will try and tie the environmental, geological, and wheeling aspects of this trip together in the next post, the epilogue…

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