┌────────────────────────────────────────┐ │ Dunham Depositional Framework │ └───────────────────┬────────────────────┘ │ ┌─────────────────────────────────────────┴─────────────────────────────────────────┐ ▼ ▼ [ Mud-Supported Fabric ] [ Grain-Supported Fabric ] ├── Mudstone ( 10% grains; baffles) └── Grainstone (Mud-free; high wave action)
Carbonate rocks (limestones and dolostones) constitute approximately 20-25% of the sedimentary rock record. Unlike siliciclastic rocks, which are derived from the weathering of pre-existing rocks, carbonates are predominantly at or near the site of deposition.
Landward <--------------------------------------------------------------------> Seaward [ Tidal Flat / Evaporites ] ---> [ Inner Lagoon ] ---> [ Reef/Ooid Shoal Margin ] ---> [ Slope / Deep Basin ] Carbonate Platform Configurations
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The Dunham Classification (1962, Modified by Embry and Klovan 1971) origin of carbonate sedimentary rocks pdf extra quality
Low marine
Dominated by abiotic precipitation induced by microbial metabolic processes (e.g., sulfate reduction, photosynthesis), this factory thrives in environments hostile to complex eukaryotes. It produces vast quantities of micrite, peloidal muds, and microbialites (stromatolites and thrombolites), particularly common in Precambrian and early Paleozoic sequences. 5. Diagenetic Pathways: From Sediment to Rock
The "origin" of carbonate rocks has changed drastically over geologic time due to biological evolution and shifts in seawater chemistry (Sandberg's Cycle).
Diagenetic processes and their effects
Unlike siliciclastic sediments derived from land weathering, carbonate rocks are born directly within the depositional basin. They are predominantly organic or biochemical in origin. Biologically Induced and Controlled Precipitation
Carbonate rocks are classified by their texture and the ratio of grains to mud: Carbonate Rocks - Geology is the Way
The origin of carbonate sedimentary rocks is an intricate chronicle of Earth's oceanographic, biological, and tectonic history. Because these rocks are chemical and biochemical archives, their stable isotope compositions (
Additional resources for this book can be found at , including downloadable figures, teaching materials, and supplementary readings. The Dunham Classification (1962, Modified by Embry and
A key distinction sets carbonate rocks apart from siliciclastic (sandstone, shale) deposits: , meaning they originate within the basin where they are deposited, rather than being transported from distant source areas. This characteristic profoundly influences their texture, composition, and interpretive value for paleoenvironmental reconstruction.
┌────────────────────────────────────────┐ │ Primary Carbonate Mineral Pathways │ └───────────────────┬────────────────────┘ │ ┌────────────────────────────┼────────────────────────────┐ ▼ ▼ ▼ [ Aragonite ] [ Calcite (LMC/HMC) ] [ Dolomite ] Orthorhombic polymorph. Trigonal polymorph. Ordered Mg-Ca lattice. High Sr substitution. Low/High Mg incorporation. Predominantly diagenetic. Aragonite is the orthorhombic polymorph of CaCO3CaCO sub 3
Significant in the Paleozoic and Mesozoic.