The Rock Cycle

Sedimentary Processes1

2) & 3) Sediments are transported and deposited

4

Products of weathering

Primary Residual DissolvedMinerals Minerals Ions

Feldspar Clay minerals K+, Ca+2, Na+

Aluminum hydroxide

Fe-Mg minerals Hematite & Mg+2

Limonite

Quartz Quartz Silica

Primary Solids that Ions that are carriedMinerals remain in soil away in water

----------Detrital sediments------------------ Chemical & biochemicalsediments

Types of sediment

Detrital – mineral & rock fragments Chemical – halite (NaCl) crystals that precipitate from water

Biochemical – shells made of calcite (CaCO3) by organisms that extract the ions from water

Detrital sedimentary rocks- classified by grain size differences

Conglomerate

Breccia

Sandstone

Shale

All these rocks have clastic textures – the rocks are composed of particles (fragments) that are cemented together

Detrital sediments are sorted by the processes of transportation and deposition

Well sorted Poorly sorted

Sands and sandstones can be used to interpret the erosional history of an area and the kinds of rocks that were eroded

Well-sorted

Poorly sorted

“Mature” sediments have little feldspar. This means that the sediment was derived from weathered rocks or that the feldspar decomposed during transportation in water.

The same diagram is used to interpret the provenance (source rocks) of sediments

Placer deposit– accumulation of sand or gravel containing minerals that are highly resistant to chemical attack and economically valuable - gold, platinum, ilmenite, rutile, zircon, diamond, garnet, magnetite, corundum, monazite.

These and other chemically resistant minerals are widely used to indicate the provenance of sediments, e.g. kyanite, sillimanite, staurolite

indicate that metamorphic rocks were eroded. Diamonds indicate kimberlite; gold indicates hydrothermal veins, etc.

Chemical and biochemical sedimentary rocks

Limestones – composed of calcite

Travertine Coquina

Chalk

Deep ocean sediments are mainly fine-grained biochemical sediment called oozes, with some hydrogenous (chemical) and terrigenous (wind or water borne) detrital sediment

Calcareous & siliceous ooze

Manganese nodules are hydrogenous - they precipitate from deep ocean water when the Mn oxidizes:Mn+2 (dissolved) + O2 + 2e- = MnO2 (pyrolusite)

Banded Iron Formations – ancient (>2.5 billion year old) sedimentary deposits of iron-bearing minerals. These indicate that Earth’s early atmosphere was too poor in oxygen to oxidize iron at the site of weathering. Dissolved iron was transported in water: 4Fe+2 (dissolved) + 3O2 = 2Fe2O3 (hematite)

Phosphates form in shallow marine environments where dissolved PO4-3

is carried by upwelling of deep ocean water. These areas are biologically productive - many fossils are found, especially bone material.

Phosphate Mining of the Bone Valley Formation in Florida

Shallow basin with high rate of evaporation – Gulf of Mexico, Persian Gulf, ancient Mediterranean Sea, Red SeaSequence is: calcite, gypsum, halite with increasing evaporation

Evaporite minerals

Evaporites

Gypsum

Halite

Seawater evaporation:

1) Calcite 2) Gypsum3) Anhydrite4) Halite (95% evaporation)5) Sylvite 6) Other rare minerals

Dolomite may form afterward by reaction of Mg+2 with calcite

Continental waters:Borax & boratesNitrates

Saltdome

Sulfur is produced by sulfate reducing bacteria which consume the oxygen in gypsum or anhydrite