Sediments and Sedimentary Rocks Tom Bean/DRK L - 6: cd/EM - E

Sedimentary rocks 5 % by volume of the upper crust 75% by area of continental areas Often the only record of geologic events: e.g. The Himalayas will someday be sandstone

Sedimentary Stages in the Rock Cycle

2 KINDS OF SEDIMENTARY ROCKS A. DETRITAL & CLASTIC - Rock resulting from the consolidation of loose sediment that has been derived from previously existing rocks and accumulated in layers B. CHEMICAL - Rock formed by the precipitation of minerals from solution by either organic or inorganic processes

Transport and deposition of clastic sediments Movement of sediment by wind, ice or water (GEOLOGIC AGENTS). Mode of transport produces distinctive deposits. Deposit as layers - beds/strata

Transport affects the sediment in several ways - Sorting Sorting : measure of the variation in the range of grain sizes in a clastic rock or sediment Well-sorted sediments indicate that they have been subjected to prolonged water or wind action. Poorly-sorted sediments are either not far- removed from their source or deposited by glaciers.

Sorting Well-sortedPoorly-sorted

Rex Elliott Well-sorted Sand

Poorly-sorted Sand Rex Elliott

Transport affects the sediment in several ways - SHAPE Roundness Roundness : measure of how rounded the corners are Sphericity Sphericity : measure of how much it is like a sphere * Sorting, roundness, and sphericity all increase with LENGTH of transport.

Sorting Roundness

Types of detrital rocks Largely based on the size of the particles, which may be anything. Conglomerate (poorly sorted/round) Breccia (poorly sort/angular) Sandstone(quartzite, arkose, greywacke) Mudstone Siltstone Shale - most common rock on continents

Conglomerate Breck Kent

Sandstone Breck Kent

Shale D. Cavagnaro/Visuals Unlimited

SEDIMENTARY ROCKS CHEMICAL ROCK- Rock formed by the precipitation of minerals from solution by either organic or inorganic processes

Types of chemical sedimentary rocks LimestoneCaCO 3 ChertSiO 2 SaltNaCl, KCl GypsumCaSO 4 2H 2 O Coalaltered organic debris

Breck Kent Limestone

Breck Kent Halite

Breck Kent Chert

Fossiliferous Limestone Peter Kresan

Chemical environments: Evaporites Restricted environments such as Mediterranean Sea & Texas coast Minerals precipitate according to solubility. Gypsum Halite CaSO 4 2H 2 O NaCl

One Model for the Formation of Evaporites

Chemical environments: Carbonates Clear water — away from big rivers (or volcanoes) Warm water — subtropical to tropical Shallow water -- two reasons: Organic:sunlight only penetrates to about 100 m Inorganic: CCD so carbonates dissolve

Foraminifer in the Eye of a Needle Chevron Corporation

Coral Reef Surrounding Volcanic Island Jean-Marc Truchet/Tony Stone Worldwide

Common Sedimentary Environments

Clues to interpreting sedimentary depositional environments Sedimentary structures Sorting, roundness, sphericity Sequence & kinds of beds

Sedimentary structures Particular structural features can give information about the environment of deposition. Structures also help determine if a bed is right-side-up — important in deformed rocks

Peter Kresan Cross-bedded Sandstone

Turbidity currents Varves record annual cycles in glacial lakes S. C. Porter

Raymond Seiver Modern Rippled Sand

Reg Morrison/Auscape Ancient Ripple-marked Sandstone

Fig. 7.9

MODERNANCIENT Mudcracks

Chip Clark Bioturbation Tracks and Tunnels

From Peat to Coal

The end