Lecture 6 Sedimentary Rock (catch up to clastic rocks)

Shale

• fine grained clastic sedimentary rock

• Splits into thin layers (fissile)

• Silt and clay sized grains

• Sediment deposited in lake bottoms, river deltas, flood plains, and on deep ocean floors

Siltstone

• slightly coarser grained then shales

• Lacks fissility

Claystone

• Mainly clay sized grains

• Non-fissile

Mudstone

• silt and clay sized grains

• Massive/blocky

Mud Rock Shale

form in similar environments to sandstones, only deposited under lower energy conditions (i.e. "quieter" locations) with finer particles (clay, silt)

Carbonates

Contain CO3 as part of their chemical composition

•Limestone is composed mainly of calcite

•Most are biochemical, but can be inorganic

•Often contain easily recognizable fossils

•Chemical alteration of limestone in Mg-rich water solutions can produce dolomite

Chert

Hard, compact, fine-grained, formed almost entirely of silica

•Can occur as layers or as lumpy nodules within other sedimentary rocks, especially limestones

Evaporites

Form from evaporating saline waters (lake, ocean)

•Common examples are rock gypsum, rock salt, and manganese nodules.

Non clastic rocks (limestone)

A biogenic sedimentary rock composed of the mineral calcite (CaCO3), which bubbles in acid. 

Coal

Sedimentary rock forming from compaction

•    of partially decayed plant material

•Organic material deposited in water with low oxygen content (i.e., stagnant)

Oil and natural gas

Originate from organic matter in marine sediment

•Subsurface “cooking” can change organic solids to oil and natural gas

•Can accumulate in porous overlying rocks

Stages of coal formation

Peat, lignite, bituminous and anthracite. The heat and pressure of the overburden after burial increases with each stage of development

Formation of oil and gas

formed from the remains of prehistoric organisms that are broken down over millions of years. This process happens deep underground in sedimentary rock. 

Geological formations

a body of rock formed over time with a distinct set of characteristics that distinguishes it from other rock formations. 

Geological contact

A separation between two distinct rock units that form a sedimentary contact and exists among other contacts

Delta

Area that bridges the land and the shelf

Particle size is clastic sedimentary rocks

reflects the physical energy of  the depositional environment (e.g. deep ocean vs. river, lake, desert, or mountain)

Source area

Locality that eroded and provided sediment

•Sediment composition, shape, size and sorting are indicators of source rock type and relative location

Depositional environment

Location where sediment came to rest

•Sediment characteristics and sedimentary structures (including fossils) are indicators

•Examples: glacial valleys, alluvial fans, river channels and floodplains, lakes, deltas, beaches, dunes, shallow marine, reefs, deep marine

Environment of deposition

Glacial Environments

•Tillites

•Alluvial Fan

•Arkose

•River Channel and Flood Plain

•Interbedded shales and sandstones; cross-bedded

•Lake

•Shales; interbedded siltstones and mudstones

•Delta

•Alluvium (a mixture of sand, silt, and clay particles) are  carried by a river and deposited at its mouth where the water slows down.

Environmental Conditions

Influence many aspects of sedimentary deposits such as texture, fossils, and primary sedimentary structures

Clean sandstone

Quarts sandstone that is predominantly quartz. Around 90%

Dirty sandstone

Graywacke is a mixture