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Our "limestone barrens" might more properly be called "calcareous barrens", since the underlying bedrock is primarily a MIXTURE, in varying proportions, of the calcareous rocks limestone (CaCO3) AND dolomite (CaMg(CO3)2).  Lower Ordovician Limestone Bedrock (ca. 480 million years old), of the Catoche Formation. Old Port au Choix. The tiny wild mustard, Hornungia procumbens, can be found in the cracks and fissures of this area. Photo: John Maunder. [CLICK image to enlarge.] Limestone forms in two ways: [1] By direct precipitation [less common]: Ca2+ + (CO3)2- = CaCO3 (limestone) [2] By "lithification" (ie. the turning to stone) of accumulated sedimentary remains of marine shell-bearing organisms, through "compaction" and "cementation". Such limestones are "biological sedimentary rocks". Their biological origin is revealed by the presence of fossils. Dolomite forms in two ways: [1] By direct precipitation [less common]: Ca2+ + Mg2+ + 2(CO3)2- = CaMg(CO3)2 (dolomite) [2] By the "dolomitization" of calcite (the most stable form of limestone) when magnesium ions replace calcium ions, and recrystalization occurs. 2 CaCO3 (limestone) + Mg2+ <--> CaMg(CO3)2 (dolomite) + Ca2+ Limestone that is partially replaced by dolomite is referred to as "dolomitic limestone". Physical Properties: Limestone erodes much faster than dolomite. Identification tip: Limestone "fizzes" when dilute hydrochloric acid is dripped on it; dolomite does not (unless it is scratched or powdered). The "limestone" bedrock of Newfoundland and Labrador is not all the same. Geologists have distinguished, named, and carefully mapped the geographical distribution of numerous, distinctive, geological "groups" and "formations", within our "limestone regions" - primarily on the basis of their geological age, depositional environment, form and history of deposition ["stratigraphy"], alteration, chemical composition, physical characteristics, and fossils. Bedrock "formations" are often sub-divided into "members". Bedrock Formations For an accounting of the "limestone" bedrock formations found in western Newfoundland and southern Labrador, go to the Bedrock Formations page. Bedrock Maps See: Geological Maps page. Sedimentary Processes See: Sedimentary Processes page. [Page last updated: November 12, 2021] ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... |
