Classroom presentations to accompany Understanding Earth, 3rd edition prepared by Peter Copeland and William Dupré University of Houston Chapter 7 Sediments and Sedimentary Rocks

Tom Bean/DRK

Processes of the rock cycle Weathering Erosion Transportation Deposition (sedimentation) Burial Diagenesis

Sedimentary Stages in the Rock Cycle Fig. 7.1

Sedimentary rock (a) Rock resulting from the consolidation of loose sediment that has been derived from previously existing rocks and accumulated in layers (detrital or clastic) (b) Rock formed by the precipitation of minerals from solution by either organic or inorganic processes (chemical)

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

Transport and deposition of clastic sediments Movement of sediment by wind, ice or water. Mode of transport produces distinctive deposits.

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

Transport affects the sediment in several ways 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 amount of transport.

Rex Elliott Fig. 7.2 Well-sorted Sand

Poorly-sorted Sand Rex Elliott Fig. 7.2

Roundness and sphericity Fig. 7.3

Types of detrital rocks Largely based on the size of the particles, which may be anything. Conglomerate Breccia Sandstone (quartzite, arkose, greywacke) Shale Mudstone Siltstone

Sedimentary structures stratification = bedding = layering Produced due to differences in 1. size of particles 2. kinds of particles

Clues to interpreting sedimentary environment Sedimentary structures Sorting, roundness, sphericity Sequence of beds

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

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 (dissolution CaCO 3 dependant on P)

Chemical environments: Evaporites Restricted environments (Mediterranean Sea, Texas coast) Minerals precipitate according to solubility. Gypsum Halite 50%90% CaSO 4 2H 2 O NaCl

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

Graded bedding Scale may be mm to m

Turbidity currents Suspension of water, sand, and mud that moves downslope (often very rapidly) due to its greater density than that of the surrounding water (often triggered by earthquakes) Speed of turbidity currents first appreciated in 1920 — breaking of phone lines in the Atlantic; also gave indication of distance traveled by a single deposit

Other up indicators Cross-bedding Ripple marks Mudcracks Raindrop impressions Fossils (some may have been preserved in growth position)

From sediment to sedimentary rock (lithification) Compaction: reduces pore space Clays and muds are up to 60% water; 10% water after compaction. Cementation: chemical precipitation of mineral material between grains (SiO 2, CaCO 3, Fe 2 O 3 ) binds sediment into hard rock Recrystallization: P and T increase with burial 30°C/km or 1°C/33 m 2

Unconformity Buried surface of erosion

Fig. 7.4 Characteristics of a Sedimentary Environment

Fig. 7.5 Common Sedimentary Environments

Peter Kresan Fig. 7.6 Cross-bedded Sandstone

Formation of Cross-beds Fig. 7.7

Raymond Seiver Fig. 7.8 Modern Rippled Sand

Reg Morrison/Auscape Fig. 7.8 Ancient Ripple-marked Sandstone

MODERNANCIENT Mudcracks

Fig. 7.9

Chip Clark Bioturbation Tracks and Tunnels

Typical Alluvial Cycle Deposited by a Migrating River Fig. 7.11

Fletcher & Baylis/Photo Reseaerchers Fig Partial Alluvial Cycles in China

Products of lithification

Fig Compaction (Primarily of Muds) Precipitation of new minerals or additions to existing ones

Fig Dissolution of More Soluble Minerals Recrystallization of Unstable Minerals

Fig Quartz grain Calcite cement Peter Kresan

Fig Relative Abundance of Sedimentary Rock Types Relative Abundance of Sedimentary Rock Types

Fig. 7.15a Conglomerate Breck Kent

Fig. 7.15bFig. 7.15a Sandstone Breck Kent

Fig. 7.15c Shale D. Cavagnaro/Visuals Unlimited

Four Major Groups of Sandstones Fig. 7.16

Fig. 7.16a Quartz Arenite: Pure Quartz

Fig. 7.16b Arkose: Feldspar-rich

Fig. 7.16c Lithic Sandstone: Rock Fragment-rich

Fig. 7.16d Graywacke: Matrix-rich

Foraminifer in the Eye of a Needle Fig Chevron Corporation

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

Breck Kent Fig. 7.19a Limestone

Breck Kent Fig. 7.19b Gypsum

Breck Kent Fig. 7.19c Halite

Breck Kent Fig. 7.19d Chert

Fossiliferous Limestone Peter Kresan

One Model for the Formation of Evaporites

Rifting can create a sedimentary basin