(5) 2-3 cm darker brownish and slightly carbonaceous rock
, with abundant brachiopod shells and fragments in the upper part.
It was emplaced over metamorphosed pelitic, calcareous and carbonaceous rocks
ranging from Precambrian (Manglaur formation) to Triassic (Saidu formation) (Ahmad et al., 1998).
Roughly two-thirds of Cuba's territory is karstic, with an abundance of limestone, marlstone, marble and other carbonaceous rocks
. All these rocks are actively dissolved by surface runoff and groundwater instead of normal erosion.
Metasedimentary rocks are represented by phyllites, siltstones, carbonaceous rocks
, sandstones, grits and conglomerates.
If the oceans turn acid--as they are already doing--the only known way to reverse this is the slow weathering and dissolution of limestone mountain ranges and carbonaceous rocks
into the sea, a process that takes millions of years.
Finer material is also derived from the downfall of finely laminated clayey carbonaceous rocks
. The freeze-thaw processes taking place in the joints are the main agents responsible for the formation of rock falls.
If chlorine is present it needs to be converted to a chloride salt and not hydrogen chloride unless wet carbonaceous rocks
Previous studies demonstrate that the complex geochemical interaction of auriferous fluids with the carbonaceous rocks
probably led to gold precipitation [2,3].
Usually the content of crystalline rocks in the gravel-pebble fraction of glaciofluvial deposits is 10-15% higher than in tills, whereas the content of carbonaceous rocks
in them is correspondingly lower (Raukas 1978).