Wednesday, October 28, 2009

Generalized Parent Material Map Progress

We recently generalized the existing bedrock geologic data for Clark County into 19 general lithologic categories. Our goal is to provide clear context for evaluating parent rock materials for the array of surficial deposits that we are compiling and mapping in more detail.

The units have been preliminarily divided into the following 19 categories (2 not yet used on the map):

Sedimentary Rocks (S)

Carbonates (Sc)
Limestone (Scl)
Dolomite (Scd)
Interbedded limestone and dolomite (Scld)

Siliciclastic sedimentary rocks (Ss)
Mudrock and shale (Sssh) (not yet used)
Chert and argillite (Ssc) (not yet used)
Sandstone and coarser (Ssss)
Interbedded shale and sandstone (Ssshss)

Interbedded carbonates and siliciclastic sedimentary rocks (Scs)

Igneous Rocks (I) Plutonic (p) Volcanic (v)

Felsic igneous

Intrusive (granite) (Ipf)
Extrusive (rhyolite and tuff) (Ivf)

Intermediate igneous
Intrusive (diorite) (Ipi)
Extrusive (andesite) (Ivi)

Mafic igneous
Intrusive (gabbro) (Imi)
Extrusive (basalt) (Ivi)

Mixed volcanic rocks (Ivx)

Metamorphic (M)

High grade (crystalline rocks) (Mh)
Low grade (phyllite, argillite, quartzite) (Ml)

It may be that this is more detail than is warranted...or maybe it is not quite enough...opinions will vary. The data are structured in such a way that ratcheting the detail up or down is not complicated. The goal is to work with the existing data in a consistent way across the study area.

Also, note that this project does not involve remapping any bedrock units other than where the boundaries with the Q deposits can be improved.