Carbonate Clasts
Carbonate clasts are rock fragments derived either by erosion of ancient limestones exposed on land or by erosion of partially or completely lithified carbonate sediments within a depositional basin. [1]
Types of Carbonate Clasts
Extraclasts
Extraclasts are carbonate clasts derived from older limestones present in land sources located outside the depositional basin. [1] These clasts may have iron-stained rims resulting from weathering, may contain recrystallized veins inherited from the parent rock, or may display other properties that distinguish them from intraclasts. [1]
Intraclasts
Intraclasts are carbonate clasts derived from within the basin by erosion of semiconsolidated carbonate sediments from the seafloor, adjacent tidal flats, or a carbonate beach (beach rock). [1]
Lithoclasts (Limeclasts)
The distinction between fragments of ancient, weathered limestones and penecontemporaneously produced intraclasts is often difficult to make. [1] Lithoclast (or limeclast) is a nonspecific term that can be used for carbonate clasts when this distinction cannot be made. [1]
Physical Characteristics
Size Range
Lithoclasts range in size from very fine sand to gravel, although sand-size fragments are most common. [1]
Rounding and Shape
Carbonate clasts generally show some degree of rounding, indicative of transport, but subangular or even angular clasts are not unusual. [1]
Internal Features
Some clasts display internal textures or structures such as lamination, older clasts, siliciclastic grains, fossils, ooids, or pellets, but others are internally homogeneous. [1]
Sedimentological Significance
The distinction between extraclasts and intraclasts has important implications for interpreting the transport and depositional history of limestones. [1] A limestone composed mainly of gravel-size limeclasts is a kind of intraformational conglomerate. [1]
Clasts are not the most abundant type of carbonate grain in ancient limestones, but they occur with sufficient frequency in the geologic record to show that the clast-forming mechanism was a common process. [1]
Related Topics
Weathering
Weathering is the physical disintegration and chemical decomposition of older rock that produces solid particulate residues - resistant minerals and rock fragments - and dissolved chemical...
Conglomerate
Conglomerates occupy a paradoxical position in sedimentary geology: they are volumetrically minor - probably less than 1 percent by weight of the entire sedimentary rock mass - yet they are...
Ooids
The term ooid is applied as a general name to coated carbonate grains that contain a nucleus of some kind - a shell fragment, pellet, or quartz grain - surrounded by one or more thin layers or...
References & Citations
- 1.Principles of Sedimentology and Stratigraphy Boggs
Master UPSC Geology Optional
Ex-ONGC Geologist & Rank Holder
Learn the exact analytical answer-writing patterns needed for UPSC Optional from an AIR 2 & AIR 25 holder.
Offline in Delhi