Skeletal Particles in Carbonates
Skeletal fragments occur in limestones as whole microfossils, whole larger fossils, or broken fragments of larger fossils. [1] They are by far the most common kind of grain in carbonate rocks, and they are so abundant in some limestones that they make up most of the rock. [1]
Diversity of Skeletal Particles
Fossils representing all of the major phyla of calcareous marine invertebrates are present in limestones. [1] The specific kinds of skeletal particles that occur depend upon both the age of the rocks and the paleoenvironmental conditions under which they were deposited. [1]
Age-Dependent Assemblages
Because of evolutionary changes in fossil assemblages through time, different kinds of fossil remains dominate rocks of different ages. [1] For example, trilobite skeletal remains characterize early Paleozoic rocks, but they do not occur in Cenozoic rocks, which instead commonly contain abundant foraminifers. [1]
Environmental Controls
Certain kinds of skeletal particles characterize limestones formed in different environments. [1]
High-Energy Environments
The remains of colonial corals, which build rigid, wave-resistant skeletal structures, are commonly restricted to limestones deposited in shallow-water, high-energy environments where the water was well agitated and oxygen levels were high. [1]
Quiet-Water Environments
By contrast, branching types of bryozoa are fragile organisms that cannot withstand the rigors of high wave-energy environments. [1] Thus, their remains are found mainly in limestones deposited under quiet-water conditions. [1]
Assemblage Characteristics
Depending upon paleoenvironmental conditions, skeletal remains in a given specimen of limestone may consist entirely or almost entirely of one species of organism; however, they commonly include several species. [1]
Identification Significance
The serious student of carbonate rocks must learn to identify the many kinds of fossils and fossil fragments that occur in limestones because fossils have special significance for paleoenvironmental and paleoecological interpretation. [1]
References & Citations
- 1.Principles of Sedimentology and Stratigraphy Boggs
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