USGS Home
Contact USGS
Search USGS

Figure 83. (A) Large, angular, blackened pebbles embedded in naturally brown, layered, fine-grained calcrete or soilstone crust form a breccia. Breccias are consolidated coarse-grained clastic rocks whose fragments are angular and consist of any type of pre-existing rock. This sample is from Ramrod Key (lower Keys, Fig. 77C). (B) A well-cemented, multicolored, artificially blackened breccia was collected at a depth of ~6 m below sea level from quarry tailings in a solution pit on Big Pine Key. Note layered crust on left side of specimen. Blackened fragments include pre-existing calcrete and fossiliferous Key Largo Limestone. Left part of cut specimen was heated in the laboratory to reproduce darkening similar to colors of blackened pebbles widely found in the Pleistocene record (Shinn and Lidz, 1988). Original rock colors are visible in unheated section at right.

Printable Version (1.3 MB PDF)

Can't see the printable PDF version? Get the free Adobe Acrobat® Reader.

Coastal & Marine Geology Program > Center for Coastal & Watershed Studies > Professional Paper 1751