A Death Valley Mystery

Before There Was Life, There Was Limestone

Now There is Life, and Some of that Pre-Life Limestone is Exposed in Titus Canyon

Several years ago I joined a few colleagues for a drive through Titus Canyon.  It led to several pages of pictures that you can see by clicking on the link below (use your browser's "back" button to come back):

Go to Titus Canyon Pages                             Skip the chatter and go on to the pictures of this mystery feature

One of those Titus Canyon pages had this photo, which I simply suggested to be a picture of an erosional feature:

 

At the time I took the picture, I recall thinking that it is hard to see how water, occasionally rushing down the canyon and moving anything up to giant boulder size downstream, could create such a pattern of limestone rock chunks embedded in a calcium-carbonate-silica cement, in turn embedded in what was obviously a very high pile of layers of limestone rock laid down in series by ancient seas.  

I wondered, but that was as far as I got.

So imagine my surprise and delight to get a picture in my email of this very spot saying it was a collapsed, infilled cave!  OK, sounds good, but how can that be?

The suggestion caused me to look at several websites discussing infilled, collapsed caves: one of them mentioned this very formation in Titus Canyon, the other discussed such features in the Ozarks.  And when I began to look at collapsed caves in limestones I saw hundreds of websites describing such features around the globe!

One site discussing the Titus Canyon feature (link removed, it no longer works) had 
a photo of this same Titus Canyon feature on that page, and a discussion which said 
there are two possible explanations.  It said:

The last two sentences seem to argue against the tectonics/deposition point of view. The clasts, or rock fragments, are long and have sharp angles and so have not rolled around much, if at all, in turbulent waters.

The other site I located had several pages on sinkholes in the karst (limestone) terraines of the Ozarks. These are apparently collapsed caves filled with clays and sediments, and with highly mineralized deposits in some areas.  So the infilling was by erosion of materials from the surface.  Later, the infilled cave was buried by new sea incursions depositing a new limestone layer, or perhaps several layers, over them. In the Ozarks these features are allegedly plentiful.  (Used to have a link here but it too stopped working).

In the case of the Ozarks, caves formed, collapsed, were filled in, and then a sea came and added another layer of limestone over the top of it all.  This preserved depositis of fine clays and minerals that were later mined, so these features were popular with prospectors, at least for a while (limited size and volume).

In Titus Canyon the cave probably collapsed while there were just a few overlying layers of limestone, and the entire area was exposed to weather at the surface.  Fresh rainwater seeped through the rock, dissolving caves into it, and some of the caves collapsed just like in any karst terrain.  The cave roof provided the infilling debris, clasts, and maybe some came from the overlying layers through a 'chinmeying' process of collapses from above.  

Fresh water infiltrationcontinued, picking up calcium carbonate and silica from overlying layers, and as it moved down it warmed up and very slowly dropped its load of calcite and silica.  Over eons, this cemented the broken mass of rock fragments together in a whitish matrix.  The broken pieces of limestone that fell in are now darker chunks of limestone encased in a calcite-silica glue, white.  The pieces or clasts still have the sharp angles they fell in with.  They can be very large.  No water transport was involved because that would have rounded edges and smoothed the rubble pieces.

I did not realize, really, until I looked at a number of web sites, that the collapse of limestone caves is so common that its surface expressions are what defines "karst" terrain, named for a type of terrain found in Slovenia.   

Another interesting place to visit on the world wide web is the USGS page describing the geology of Death Valley National ParK.  Here one learms why there are no fossils in these old limestones: they were laid down in shallow seas without life, long before the first living things moved in the seas or on the earth.  Pre-Life Canyon?  Nope, Titus Canyon.

So, these rocks are really, really old.  But we are not, so let's take a walk and a look some more on the next page:

More pictures of Titus Canyon and this mystery feature

 Go enjoy the sand dunes instead

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