Anaerobic bacteria break down organic matter using sulfate ( SO42−SO sub 4 raised to the 2 minus power ), generating bicarbonate ( HCO3−HCO sub 3 raised to the negative power ) and hydrogen sulfide (
, meaning they are born from life. In warm, shallow, clear tropical seas, organisms like corals, algae, and mollusks extract calcium carbonate ( cap C a cap C cap O sub 3 ) from seawater to build their shells and skeletons.
. Classic examples include (concentrically laminated spherical grains formed in agitated, supersaturated waters) and whitings (sudden, massive suspensions of microcrystalline aragonite needles in shallow bank interiors). 3. Classical Depositional Environments
Trigonal structure containing 4 to over 30 mol% MgCO3MgCO sub 3
(often induced by wave agitation or temperature spikes), inorganic calcite or aragonite precipitates directly from the water column. This mechanism produces ooids (spherical, concentrically laminated grains) and whitings (sudden, cloud-like suspensions of fine-grained carbonate mud). Depositional Components: Grains and Matrix origin of carbonate sedimentary rocks pdf extra quality
Occurs when falling sea levels expose platforms to fresh rainwater. Dissolution dominates, leaving moldic porosity where unstable aragonite shells dissolve entirely. Calcite precipitates as freshwater phreatic cement.
Equant calcite cementation, neomorphism of aragonite to calcite. Destroys primary porosity; stabilizes mineralogy. Mechanical and chemical compaction, stylolitization. Reduces volume; creates pressure-solution seams. Dolomitization
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The global tectonic cycle modulates the magnesium-to-calcium ( Anaerobic bacteria break down organic matter using sulfate
: Karst terrains developed in limestone supply fresh drinking water to approximately a quarter of the global population.
Origin of Carbonate Sedimentary Rocks: Processes, Environments, and Diagenetic Pathways
) coincide with rapid seafloor spreading, promoting the precipitation of low-Mg calcite. Evolutionary Milestones
High photosynthetic activity removes CO2CO sub 2 , shifting the balance to promote CaCO3CaCO sub 3 precipitation. 3. Mechanisms of Formation: Sedimentary Components Carbonate Ramps: Gently sloping surfaces (
Carbonate sedimentary rocks —primarily limestones and dolomites—are unique because they are often "born, not made." Unlike sandstone or shale, which form from the erosion of older rocks, carbonates are typically the product of biological activity and chemical precipitation within a marine environment. The Biological Engine The vast majority of limestone begins with marine organisms
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Shallow platforms bounded at the margin by a high-energy barrier, such as continuous coral-algal reefs or ooid shoals. The barrier absorbs wave energy, creating a low-energy, protected lagoon on the landward side. Carbonate Ramps: Gently sloping surfaces (