Sediments and Sedimentary Rocks Geology Today Barbara W

Sediments and Sedimentary Rocks Geology Today Barbara W. Murck & Brian J. Skinner LAYERED ROCKS, PARIS CANYON, ARIZONA © Houghton Mifflin 1998; N. Lindsley-Griffin, 1999.

Rock Cycle Weathering, Erosion, Deposition 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 Bedding is the best clue that a rock is sedimentary. Also termed strata, layering. (Fig. 8. 2, p. 219) Capital Reef National Park, Utah N. Lindsley-Griffin, 1999.

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. 4 B, p. 221; 8. 9, p. 225) N. Lindsley-Griffin, 1999.

Clastic Sediments The SIZE of the particle transported depends on the density and speed of the transporting medium and the slope angle. . N. Lindsley-Griffin, 1999. Buffalo, WY

Sorting - the range Clastic Sediments in clast sizes. Poorly sorted = great size variation. Well-sorted = grains all about the same size. Fig. 8. 4, p. 221 N. Lindsley-Griffin, 1999.

Clastic Sediments Sphericity - how equidimensional are the grains? Round vs. angular - how sharp are the corners? Fig. 8. 4, p. 221 N. Lindsley-Griffin, 1999.

Clastic Sediments 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 N. Lindsley-Griffin, 1999.

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

Clastic Sediments Clast size, sorting, roundness, and sphericity suggest: how far it traveled nature of transporting medium how sediment was deposited Glacial Till, Matanuska Glacier, AK (Fig. 8. 4 A, p. 221) N. Lindsley-Griffin, 1999. Quartz sand, St. Peter Sandstone, WI (Fig. 8. 4 B, p. 221)

Clastic Sediments COMPOSITION of the clastic particle depends on source: white coral sand, Bora green olivine sand, Hawaii N. Lindsley-Griffin, 1999.

Clastic Sediments 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 Basalt sand, Hawaii N. Lindsley-Griffin, 1999. Quartz sand, Oregon

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

Chemical Sediments 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 N. Lindsley-Griffin, 1999. Banded Iron Formation, western Australia (Fig. 8. 10, p. 225)

Chemical Sediments Evaporites form where dissolved ions are concentrated by evaporation

Chemical Sediments Evaporites: Least soluble carbonates (limestones) precipitate first Sulfates (anhydrite, gypsum) precipitate next Most soluble halides (rock salt) precipitate last Great Salt Lake, Utah N. Lindsley-Griffin, 1999.

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

Biogenic Sediments 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) N. Lindsley-Griffin, 1999.

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, 1999.

Biogenic Sediments Coral reefs support a complex ecosystem that develops around the coral framework. • Algae form a symbiotic relationship with corals N. Lindsley-Griffin, 1999.

Biogenic Sediments Sediment in the lagoon (quiet water behind reef) is biogenic calcareous mud which will form limestone N. Lindsley-Griffin, 1999.

Biogenic Sediments Deep ocean biogenic sediments are mostly microscopic fossil shells: • Calcareous (foraminifers, nannofossils) - CHALK • Siliceous (radiolarians, diatoms, sponges) - CHERT N. Lindsley-Griffin, 1999.

Sedimentary Rock Names 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, 2000.

Sedimentary Structures Graded bedding: coarse grains at sharp base. Grains gradually become smaller upwards. (Fig. 8. 6, p. 223) N. Lindsley-Griffin, 1999.

Sedimentary Structures Turbidites form in deep ocean. - rhythmic layering - graded bedding (Fig. 8. 17, p. 237) N. Lindsley-Griffin, 1999.

Sedimentary Structures 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) N. Lindsley-Griffin, 1999.

Sedimentary Structures Mudcracks: sediments on drying mud flats or lake bottoms. Cracks polygonal, narrow to “V” downwards. (Fig. 8. 11, p. 230) N. Lindsley-Griffin, 1999.

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

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

Sedimentary Environments 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) N. Lindsley-Griffin, 1999.

Sedimentary Environments Eolian cross bedding, formed in sand dunes, preserves the steep front face (downwind) gentle back face (upwind) Fig. 8. 7, p. 224 N. Lindsley-Griffin, 1999.

Sedimentary Environments Varves record annual cycles (usually glacial lakes): light silt deposited in warm months, dark clay-rich layers in winter months. N. Lindsley-Griffin, 1999. Fig. 8. 5, p. 222

Sedimentary Environments Fig. 8. 14, p. 233 N. Lindsley-Griffin, 1999.