CHAPTER 8: SEDIMENTARY ROCK

Sedimentary rock is formed from the weathered and eroded remains of other rocks Many of the rock layers in this photograph are composed of sediments that accumulated on the seafloor. What evidence would reveal to a geologist that a rock formed in a marine environment?

Sedimentary Rock Most of Earth’s surface is covered with layers of loose sediment >75% of the land surface is Sedimentary Rock

Why study sedimentary rocks? Fossiliferous Cambrian Burgess Shale at Mt. Stephen, BC They reflect physical and chemical characteristics of their source environments and depositional processes They contain direct and indirect evidence of life and its evolution They can be interpreted to understand geological history The are the source of important resources, including metals, building materials and energy Planetary nebula remaining mineral particles and gas after a star explodes Steven Earle Triassic limestone being quarried for cement at Texada Island, BC Steven Earle

There are three common types of sediment: Clastic, Chemical, and Biogenic CLASTIC SEDIMENTS are broken and eroded pieces of rocks and minerals deposited by water, wind, ice, or some other physical process What is the main mineral in this sandy sediment? What else might be present?

Chemical and Biogenic Sediments CHEMICAL SEDIMENTS are produced by inorganic (nonbiological) precipitation of dissolved compounds (e.g., through evaporation) BIOGENIC SEDIMENTS are produced by organic (biological) precipitation of the remains of living organisms Comet exhibiting coma (tail)

Change in Sediments Sediments change as they are transported across Earth’s surface… en route to their depositional environment What are the likely depositional environments of these three types of sediment?

Particle Size Reflects Depositional Energy

Sorting Particles separated based on grain size

Decreasing grain size with increased transport distance and decreased energy level Suggested tips to give students: During World War II, geologists employed by the military carried out studies of the sea floor, mapping deep-sea trenches. The purpose of the study was to discern possible hiding places for enemy and Allied Forces submarines.

? Coral Pink Sand Dunes, southern Utah Steven Earle What does multi-generational mean in this context? Why are these grains so well rounded and so dominated by quartz? 0.1 mm Close-up view of the multi-generational fine-grained sand at the Coral Pink Sand Dunes Steven Earle

Clastic Grains Clastic grains combine with chemical and biogenic sediments through either organic or inorganic precipitation. The black material in these thin sections photographs is organic matter.

Sedimentary Basins Dissolved compounds are transported from weathering sites into Sedimentary Basins

Sediments evolve during transportation and deposition . Unstable grains (olivine, pyroxene, feldspar, amphibole, and others) become less abundant Stable grains (quartz, clays, muscovite) become more abundant Biogenic sediments accumulate Chemical sediments may become more abundant

The Sedimentary Cycle Sediment becomes sedimentary rock during the sedimentary cycle Sediments typically accumulate at rates of less than 1 mm per year. How long would it take to accumulate 1000 m of sediment at a rate of 0.2 mm/year? Suggested tips to give students: http://www.wiley.com/college/strahler/0471480533/animations/ch14_animations/walk_ring_fire.html is an animation showing localities around the Ring of Fire. People who live around the Ring of Fire are in continuous danger from earthquakes and volcanic activity.

Lithification Lithification is caused by compaction and cementation

The important types of clastic sedimentary rock Distinguished by: grain size and shape grain type (mineralogy) texture of the grains, matrix and cements Why are they called clastic sedimentary rocks? What is a clast?

Types of Sediment Specific combinations of texture and composition for each type. Determined by sediment’s history: transport energy and distance, weathering intensity, and composition of source rock.

Important clastic sedimentary rocks conglomerate breccia quartz sandstone arkose What is the textural difference between conglomerate and breccia? What are the compositional differences between quartz sandstone, arkose and lithic sandstone? lithic sandstone siltstone claystone shale

Chemical sedimentary rocks Rock salt Gyspum Chert Travertine

Biogenic Sedimentary Rock Skeletal limestone Chalk Coal What do skeletal limestone, chalk and coquina have in common? Coquina

Sedimentary rocks preserve evidence of past environments and ecology

Continental depositional environments Wetland, alluvial fan, stream, desert, lake, glacier – which is which? Do all of these environments exist in Canada?

Coastal depositional environments Barrier island, carbonate lagoon, beach, tidal wetland, delta – which is which? Do all of these environments exist in Canada?

Marine Environments of deposition

Primary sedimentary structures record modern and ancient sedimentary processes Ripples Mud Cracks

Cross-bedding in eolian sandstones, Zion Canyon, Utah Steven Earle Graded bedding in submarine fan rocks, Gabriola Island ,BC Steven Earle Bedding in fluvial and lacustrine deposits, Horseshoe Canyon, Alberta

Choose four depositional environments in this figure Choose four depositional environments in this figure. For each, describe the texture of the sediments likely to form there. Consider the beach and glacier. If the sediment source for each was granitic mountains, predict the composition of sediments in each case. Haiti, 2010

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