Classification Conglomerate (geology)

1 classification

1.1 texture
1.2 clast composition
1.3 clast size

classification

conglomerates may named , classified the:

amount , type of matrix present
composition of gravel-size clasts contain
size range of gravel-size clasts present

the classification method depends on type , detail of research being conducted.

a sedimentary rock composed largely of gravel first named according roundness of gravel. if gravel clasts comprise largely well-rounded subrounded, conglomerate. if gravel clasts comprise largely angular, breccia. such breccias can called sedimentary breccias differentiate them other types of breccia, e.g. volcanic , fault breccias. sedimentary rocks contain mixture of rounded , angular gravel clasts called breccio-conglomerate.

texture

conglomerates composed entirely of gravel-size clasts. typically, space between gravel-size clasts filled mixture composed of varying amounts of silt, sand, , clay, known matrix. if individual gravel clasts in conglomerate separated each other abundance of matrix such not in contact each other , float within matrix, called paraconglomerate. paraconglomerates unstratified , can contain more matrix gravel clasts. if gravel clasts of conglomerate in contact each other, called orthoconglomerate. unlike paraconglomerates, orthoconglomerates typically cross-bedded , well-cemented , lithified either calcite, hematite, quartz, or clay.

the differences between paraconglomerates , orthoconglomerates reflect differences in how deposited. paraconglomerates commonly either glacial tills or debris flow deposits. orthoconglomerates typically associated aqueous currents.

a conglomerate @ base of cambrian in black hills, south dakota.



section of polymict conglomerate offshore rock core, alaska, approximate depth 10,000 ft.



conglomerate , sandstone alternating layers - nerriga, new south wales, australia. approx 5m vertical wall of road cut (vertical marks construction machine.)


clast composition

conglomerates classified according composition of clasts. conglomerate or clastic sedimentary rock consists of single rock or mineral known either monomict, monomictic, oligomict, or oligomictic conglomerate. if conglomerate consists of 2 or more different types of rocks, minerals, or combination of both, known either polymict or polymictic conglomerate. if polymictic conglomerate contains assortment of clasts of metastable , unstable rocks , minerals, called either petromict or petromictic conglomerate.

in addition, conglomerates classified source indicated lithology of gravel-size clasts if these clasts consist of rocks , minerals different in lithology enclosing matrix and, thus, older , derived outside basin of deposition, conglomerate known extraformational conglomerate. if these clasts consist of rocks , minerals identical or consistent lithology of enclosing matrix and, thus, penecontemporaneous , derived within basin of deposition, conglomerate known intraformational conglomerate.

two recognized types of type of intraformational conglomerates shale-pebble , flat-pebble conglomerates. shale-pebble conglomerate conglomerate composed largely of clasts of rounded mud chips , pebbles held clay minerals , created erosion within environments such within river channel or along lake margin. flat-pebble conglomerates (edgewise conglomerates) conglomerates consist of relatively flat clasts of lime mud created either storms or tsunami eroding shallow sea bottom or tidal currents eroding tidal flats along shoreline.

clast size

finally, conglomerates differentiated , named according dominant clast size comprising them. in classification, conglomerate composed largely of granule-size clasts called granule conglomerate; conglomerate composed largely of pebble-size clasts called pebble conglomerate; , conglomerate composed largely of cobble-size clasts called cobble conglomerate.