Sediments and Sedimentary Rocks © Houghton Mifflin 1998; N. Lindsley-Griffin, LAYERED ROCKS, PARIS CANYON, ARIZONA Geology Today Barbara W. Murck & Brian J. Skinner

Rock Cycle Weathering, Erosion, Deposition Sediments Sediments unconsolidated particles created by weathering of rock by chemical and mechanical means J. R. Griffin, 1999

Rock Cycle Deposition, Compaction, Lithification Sedimentary rock Rock formed from weathered products of pre-existing rocks, plus or minus fossils that have been transported, deposited and lithified J. R. Griffin, 1999

Sediments N. Lindsley-Griffin, Bedding is the best clue that a rock is sedimentary. Also termed strata, layering. (Fig. 8.2, p. 219) Capital Reef National Park, Utah

Lithification - loose sediment changes to sedimentary rock: grains in matrix, cement. COMPACTION - pore space decreases, water forced out CEMENTATION - dissolved ions precipitate between grains RECRYSTALLIZATION - less stable minerals change to more stable forms (Figs. 8.4B, p. 221; 8.9, p. 225) Lithification N. Lindsley-Griffin, 1999.

The SIZE of the particle transported depends on the density and speed of the transporting medium and the slope angle.... Clastic Sediments Buffalo, WY

N. Lindsley-Griffin, Sorting - the range in clast sizes. Poorly sorted = great size variation. Well-sorted = grains all about the same size. Clastic Sediments Fig. 8.4, p. 221

N. Lindsley-Griffin, Sphericity - how equidimensional are the grains ? Round vs. angular - how sharp are the corners? Clastic Sediments Fig. 8.4, p. 221

Clastic Sediments N. Lindsley-Griffin, Size of clast or fragment: gravel (pea size and larger) -- CONGLOMERATE sand (pin head) -- SANDSTONE silt (grain of table salt) -- SILTSTONE clay (particle of flour) -- SHALE, CLAYSTONE Mud is a mixture of clay and silt -- MUDSTONE Fig. 8.3, p. 220

Houghton Mifflin 1998; N. Lindsley-Griffin, 1999 BRECCIA Angular fragments of rock in finer-grained matrix CONGLOMERATE Rounded pebbles of rock in finer-grained matrix Clastic Sediments These are lithic clasts

N. Lindsley-Griffin, Clast size, sorting, roundness, and sphericity suggest: how far it traveled nature of transporting medium how sediment was deposited Clastic Sediments Glacial Till, Matanuska Glacier, AK (Fig. 8.4A, p. 221) Quartz sand, St. Peter Sandstone, WI (Fig. 8.4B, p. 221)

N. Lindsley-Griffin, COMPOSITION of the clastic particle depends on source: white coral sand, Bora Bora green olivine sand, Hawaii Clastic Sediments

N. Lindsley-Griffin, COMPOSITION of the clastic particle depends on strength of particle vs. distance traveled basalt weathers quickly, is found only close to its source quartz travels long distances Clastic Sediments Basalt sand, Hawaii Quartz sand, Oregon

SAND can be any composition... but most is quartz because it is: –durable –chemically stable N. Lindsley-Griffin, 1999.

Chemical Sediments N. Lindsley-Griffin, Precipitated from dissolved matter in sea or lake water: - through activities of plants and animals (but not their remains) - through evaporation of water containing dissolved ions Banded Iron Formation, western Australia (Fig. 8.10, p. 225)

Evaporites form where dissolved ions are concentrated by evaporation Chemical Sediments

N. Lindsley-Griffin, Evaporites: Least soluble carbonates (limestones) precipitate first Sulfates (anhydrite, gypsum) precipitate next Most soluble halides (rock salt) precipitate last Chemical Sediments Great Salt Lake, Utah

Manganese nodules (manganese oxides) precipitate directly from sea water in the deep ocean Chemical Sediments

N. Lindsley-Griffin, Composed of the remains of plants and animals. Bioclastic sediments consist of broken clasts of remains. Coquina - shells and shell fragments (Fig. 8.8, p. 225) Biogenic Sediments

N. Lindsley-Griffin, Biogenic Sediments Coral reefs, where most limestones form, require certain conditions: Shallow water where light penetrates Warm water - tropical or temperate Little land-derived detritus

N. Lindsley-Griffin, Biogenic Sediments Coral reefs support a complex ecosystem that develops around the coral framework. Algae form a symbiotic relationship with corals

N. Lindsley-Griffin, Biogenic Sediments Sediment in the lagoon (quiet water behind reef) is biogenic calcareous mud which will form limestone

N. Lindsley-Griffin, Deep ocean biogenic sediments are mostly microscopic fossil shells: Calcareous (foraminifers, nannofossils) - CHALK Siliceous (radiolarians, diatoms, sponges) - CHERT Biogenic Sediments

Clastic sediments clastic rocks = siliciclastic rocks conglomerate, breccia, sandstone, siltstone, mudstone, shale, claystone Chemical sediments chemical sedimentary rocks gypsum, rock salt, phosphorite banded iron formation (a few limestones) Biogenic sediments biogenic rocks limestone, dolostone = carbonate rocks chert peat, coal N. Lindsley-Griffin, Sedimentary Rock Names

N. Lindsley-Griffin, Graded bedding: coarse grains at sharp base. Grains gradually become smaller upwards. Sedimentary Structures (Fig. 8.6, p. 223)

Sedimentary Structures N. Lindsley-Griffin, Turbidites form in deep ocean. - rhythmic layering - graded bedding (Fig. 8.17, p. 237)

N. Lindsley-Griffin, Ripple marks on bedding surfaces: sediments were deposited in water, usually shallow, with waves or currents. Sharp crests point upwards, rounded troughs point downwards. (Fig. 8.11, p. 230) Sedimentary Structures

N. Lindsley-Griffin, Mudcracks: sediments on drying mud flats or lake bottoms. Cracks polygonal, narrow to “V” downwards. (Fig. 8.11, p. 230)

Interpreted from composition, texture, structures Alluvium (left): sorted layers, rounding, mixed clasts Lahar (above): no layers, angular, volcanic clasts Sedimentary Environments N. Lindsley-Griffin, 1999.

Turbidites (right): beds graded from sand up to clay size Beach (below): steep cross bedding, very well sorted quartz sand, fossil seashells Sedimentary Environments N. Lindsley-Griffin, 1999.

Sedimentary Environments N. Lindsley-Griffin, Loess, an eolian sediment: uniform silt size massive - no structures deposited by wind common all over Nebraska - both field trips (Fig. 8.15, p. 235)

Sedimentary Environments N. Lindsley-Griffin, Eolian cross bedding, formed in sand dunes, preserves the steep front face (downwind) gentle back face (upwind) Fig. 8.7, p. 224

Sedimentary Environments N. Lindsley-Griffin, Varves record annual cycles (usually glacial lakes): light silt deposited in warm months, dark clay-rich layers in winter months. Fig. 8.5, p. 222

Sedimentary Environments N. Lindsley-Griffin, Fig. 8.14, p. 233