Chapter 8 Sedimentary Rocks Part2 u Types of sedimentary rock u Sedimentary structures

Types of sedimentary rocks Sediment originates from mechanical and/or chemical weathering Rock types are based on the source of the material Clastic rocks – transported sediment as solid particles Chemical/Biochemical rocks – sediment that was once in solution Sedimentary rocks

Chapter 8Sedimentary rocks u Clastic sedimentary rocks Size of clasts (particles) v gravel bigger than 2 mm conglomerate (1/10 inch) or breccia v sand sand-sized (1/16-2) sandstone v silt, clay very fine-grained (<1/16) shale, mudstone,siltstone common namesizeDetrital rock See Table 8.3

conglomeratesandstonesiltstoneshale claysiltsandgravel sediments sedimentary rocks

Chapter 8Sedimentary rocks u Clastic sedimentary rocks Siltstone, Mudstone & Shale v silt & clay-sized particles (clay, silt), particles too small to identify w/ eye v over 1/2 of all sedimentary rocks v deposited in quiet (slow moving) water - deep ocean & continental slope - lakes - floodplains (siltstone) Shale w/plant remains v shale beds often underlay groundwater conduits v raw material for brick, tile, pottery, china v shale+limestone= Portland cement v shale may contains fossils, oily organics, breaks along bedding planes

Chapter 8Sedimentary rocks u Clastic sedimentary rocks Sandstone v composed of sand grains v 2nd most abundant sedimentary rock v deposited by moderate currents: - rivers & deltas - beaches - wind (sand dunes) v mostly quartz (strong & chemically stable, but may also contain volcanic rock) See Fig for major groups of sandstone

Chapter 8Sedimentary rocks u Clastic sedimentary rocks Sandstone v sorting degree of similarity in particle size

Chapter 8Sedimentary rocks uClastic sedimentary rocks Sandstone v shape degree of roundedness

Chapter 8Sedimentary rocks u Clastic sedimentary rocks Conglomerate v composed mostly of gravel pebbles to boulders v poorly sorted v deposited by strong, turbulent currents: - big flooding rivers - steep streams (near mountains) - glaciers

Chapter 8Sedimentary rocks u Clastic sedimentary rocks Breccia v conglomerate with angular grains v didn’t travel far

Chapter 8Sedimentary rocks u Chemical sedimentary rocks v derived from material carried in solution to lakes/seas v 2 types of precipitation - chemical - biochemical v precipitation from solution to form “chemical sediments” See Table 8.4

Chapter 6Sedimentary rocks u Chemical sedimentary rocks Limestone v composed primarily of calcite (calcium carbonate CaCO 3 ) v 10% of all sedimentary rocks (by volume) v most abundant chemical sedimentary rock v Marine biochemical limestones form as coral reefs, coquina (broken shells), and chalk (microscopic organisms) v Inorganic limestones include travertine (caves) and oolitic limestone (tropical beach environment)  Dolostone: dolomite=CaMg(CO 3 ) 2 Typically formed secondarily from limestone

Chapter 6Sedimentary rocks u Chemical sedimentary rocks v coquina (rock of shell fragments): bioclastic Organic rock of biochemical origin

Chapter 6Sedimentary rocks u Chemical sedimentary rocks Fossiliferous limestone

Coral reefLimestone cliff (Guadalupe Mountains Natl Park, TX)

How to build a carbonate platform See Figure story 8.16

How to build an atoll See Box 8.1 Darwin’s theory on atolls (1831)

Chapter 8Sedimentary rocks u Chemical sedimentary rocks Common chemical sedimentary rocks Chert  Made of microcrystalline silica (SiO 2 )  Varieties include flint and jasper (banded form is called agate) Agate

Chapter 8Sedimentary rocks u Chemical sedimentary rocks Evaporites v water evaporates and triggers the deposition of salts v sequence of precipitation: calcite (calcium carbonate), gypsum (calcium sulfate), rock salt (halite, NaCl); bitter salts (potassium and magnesium salts) (a) calcite

Chapter 8Sedimentary rocks u Chemical sedimentary rocks Evaporites v water evaporates and triggers the deposition of salts v ancient seawater basins evaporated and deposited salt Salt flats, UtahDeath valley, Calif. v sequence of precipitation: carbonate, gypsum (calcium sulfate), rock salt (halite, NaCl); bitter salts (potassium and magnesium salts)

Chapter 8Sedimentary rocks u Chemical sedimentary rocks Evaporites- the story of the Mediterranean Fig During the Miocene, lower sea level almost shut down the inflow of Atlantic surface water into the Mediterranean over the Strait of Gibraltar. Evaporation removed vast quantities of water and left behind evaporative sediments that underlay the sediments in the Mediterranean today.

Chapter 8Sedimentary rocks u Chemical sedimentary rocks Coal v buried and compacted plant material v different kinds of coal, depending on formation process

Sedimentary structures (Physical features) 1. Layers (bedding, or “strata”) 2. Cross-bedding 3. Graded beds 4. Ripple marks 5. Mud cracks

Sedimentary structures (Physical features) 1. Layers (bedding, or “strata”)  each layer is unique  deposited horizontally  separated by bedding planes

Sedimentary structures (Physical features) 2. Cross-bedding  tilted bedding  commonly ancient sand dunes  river deltas, flow channels

Sedimentary structures (Physical features) 3. Graded beds  particles within a layer gradually change: v coarse at bottom v fine at top  rapid deposition from water w/ varying sed. sizes Colorado River

Sedimentary structures (Physical features) 4. Ripple marks  wavy surfaces in sand: current ripple marks  tell direction of current because they are perpendicular to flow See Fig. 8.8

Sedimentary structures (Physical features) 5. Mud cracks sediment alternatively wet/dry shallow lakes, desert basins flood plains

Some MC questions… Which of the following sets of processes is written in order of increasing temperature? A. sedimentation, metamorphism, diagenesis B. diagenesis, sedimentation, metamorphism C. sedimentation, diagenesis, metamorphism D. metamorphism, diagenesis, sedimentation

Some MC questions… What type of sediments are accumulations of solid fragments produced by weathering? A. biochemical sediments B. chemical sediments C. clastic sediments D. all of the above

Some MC questions… Which of the following statements about transportation of sediment is false? A. Smaller particles settle faster than larger particles. B. As a current slows, the largest particles start to settle. C. Faster currents carry larger particles than slower currents. D. Rivers and ocean currents move much more material than do air currents.

Some MC questions… In what type of environment did the ripples depicted above most likely form? A. beach (waves) B. desert (wind) C. alluvial (stream) D. delta (river + tides)

Some MC questions… Which of the following minerals is least likely to occur in a marine evaporite environment? A. calcite B. gypsum C. halite D. quartz