Day 2 Sedimentary Petrology Flashcards
Physical destruction of the original rock
Mechanical weathering
Loose deposits are converted into rocks through the processes of:
Diagenesis and Lithification
Solid fragments and mineral particles from mechanical weathering
Detritus or clastic material
Sediments with clastic textures
Terrigenous sediments
Decomposes minerals in the rocks
Chemical weathering
Greek, meaning correct or true. Truly chemical sediments which are products of chemical decomposition
Orthochemical sediments
Greek, meaning different. Organisms have caused the precipitation of the major sedimentary mineral components, or the precipitated minerals have undergone substantial movement (and redeposition) after crystallization
Allochemical sediments
Consists of detrital grains, which forms the framework of the rock, joined together by cement.
Terrigenous sedimentary rocks.
Consists of large clasts (boulders, cobbles, pebbles, granules) with or without a sandy matrix
Conglomerates and breccias
Show more pronounced rounding of clasts
Conglomerates
Contain more angular clasts
Breccia
Coarse-grained pyroclastics (volcanic debris) with a grain size over 32mm
Agglomerate or volcanic breccia
Finer-grained (2 and 0.062 mm grain size) and most easily classified by determining the amounts of clastic (framework) grains composed of quartz (and chert), feldspar, and lithic fragments
Sandstones
When the sandstone matrix contitutes more than 10 volume percent of the rock
Wacke
Mostly dark gray sandstones with abundant matrix
Greywacke
Sandstones made up of chiefly volcanic fragments, volcanic glass, and crystals. Tend to be green because of chlorite.
Volcaniclastics
General term for sediments composed mainly of silt-sized (0.062 - 0.004 mm) and clay-sized (<0.004mm) particles
Mudstone
Silt-particle size
Siltstones
Clay particle size; nonfissile, commonly with a massive or blocky texture
Claystones
Characterized by its fissility (ability to split into thin sheets), generally parallel to bedding
Shale
With a well-developed cleavage, which may or may not be parallel to the bedding, and is commonly the result of metamorphism
Slate
Emphasizes the depositional texture
Dunham’s Classification of Limestones
Consists more than 10% grains in a microcrystalline ooze (micrite)
Wackestones
Grain-supported limestone with micrite matrix and sparry calcite cement
Packstone
Grain-supported limestone with very little micrite
Grainstone
Equivalent to biolithite, a limestone made up or organic structures that grew in situ, forming rock mass during growth
Boundstone
Formed by direct precipitation
Orthochemical sedimentary rocks
Fine-grained poorly cemented; Soft and low density pure carbonate.
Chalk
Calcite recrystallizes easily, and secondary dolomite, replaces the original calcium carbonate; often destroys the texture of original carbonate
Dolomitization
A very fine-grained carbonate precipitate that has settled to the bottom of the basin
Microcrystalline ooze
Coarser in grain size than the ooze and tends to be clear or translucent; a pre-filling cement that was precipitated in place
Sparry calcite cement
Fragments of weakly consolidate carbonate sediment that have been torn up, transported, and redeposited by currents within the basin of deposition
Intraclasts
In a size range of 0.1 to 1.0 mm in diameter, are spherical, show radial and concentric structures, and resemble fish roe. They are commonly formed by chemical accretions around nuclei such as shell fragments, pellets, or quartz sand grains.
Oolites
Remains of organisms
Fossils
Well-rounded, homogenous aggregates of microcrystalline calcite in a size range of 0.03 to 0.2 mm in diameter, feces of mollusks, worms, and crustaceans.
Pellets
Consists of a matrix of allochemical constituents and sparry calcite cement
Type I (Folk’s Classification of Limestones)
Variable percentage of allochemical grains in a microcrystalline matrix
Type 2 (Folk’s Classification of Limestones)
Microcrystalline calcite matrix only (micrite)
Type 3
