Essentials of Geology, Chapter 7 Sedimentary Rocks

7.2 How is siltstone different from shale?

- Siltstone lacks fissility like shale. - Silt-sized particles and contains less clay sized mat'l than shale and mudstone

7.1 What are the three categories of sedimentary rock?

1. Detrital sedimentary rock - accumulation of material that originates and is transported as solid particles derived from both mechanical and chemical weathering. 2. Chemical sedimentary rock - material that was precipitated from water by either inorganic or organic means 3. Organic sedimentary rock - organic carbon from the remains of plants that died and accumulated on the floor of a swamp. Coals is the primary example.

What is glacial float?

A glacier carries rocks hundreds of miles and drops it as it melts

7.2 What is the chief component of sedimentary rocks?

Clay and qtz are the main constituents of sed r. Clay minerals are the most abundant product of chemical weathering of silicate minerals - feldspar. Qtz is freed from granite. Others include mica

7.7 Describe the past environs for the following: Conglomerate Arkose Carbonaceous shale

Conglomerate may indicate high energy environment like surf One or rushing stream where only coarse materials remain and finer particles are ket suspended. Arkose it may signify a dry climate where little chemical alteration of feldspar is possible. Carbonaceous shale is a sign of low energy, organic-rich environ like a swamp.

7.2 What are the Detrital Sed Rocks and their particle sizes?

Conglomerate/Breccia - Coarse - >256 mm Sandstone - Medium - 1/16 -256 mm Siltstone - Fine - 1/256 - 1/16 mm Shale/Mudstone - V. Fine - <1/256

7.7 What are the three common categories for sedimentary environs?

Continental Marine Transitional (shoreline)

7.3 What is coquina and chalk?

Coquina is a limestone formed from biological processes; it is coarse rock composed of poorly cemented shells and shell fragments. Chalk is also a limestone formed from same process; its porous rock made up almost entirely of hard parts of microscope marine organisms.

7.3 Which marine organism creates large quantities of marine limestone?

Corals - secrete calcareous ooze (calcium carbonate); although small they create massive coral reefs. Algae live with the corals and help to cement the entire structure into a solid mass.

7.7 What is facies and how does is it used to describe a set of sediments?

Facies is a portion of rock unit that posses a distinctive set of characteristics that distinguishes it from other parts of the same unit. When examined in cross section from one end to the other, each facies grades lateral into another that formed at the same time but that exhibits different characteristics. Eg... Sand on beach is deposited -- finer muds deposit further offshore -- further out u have increased bio activity & land derived sediments are scarce

7.7 What is the relationship between graded beds and turbidity currents?

Graded beds are most characteristic of rapid deposition from water containing sediment of varying sizes. With rapid energy loss in a current, varying sizes will settle out. The largest will settle first followed by progressively smaller grains. Turbidity currents are a result of dense sediment-laden water moving downstream as a result of continental shelf and/or slope dislodgment; throwing sediment into suspension. The mud choked water is denser than seawater so it will flow downslope, eroding and accumulating more sediment where graded bedding will occur once again.

7.2 How is shale different from mudstone?

If rock breaks into chunks or blocks it is mudstone.

7.3 What are the two ways chemical ppt may occur?

Inorganic = evaporation and chemical activity -> sediments. Eg. dripstone that decorates caves (calcite crystals) and salt left behind when body of sea water evaporates Organic = water dwelling organisms form chemical sediments that are biochemical in origin. Organisms take in dissolved minerals to form shells and other hard parts. When they die, their skeletons are left behind where they collect on floor of lake or ocean as biochemical sediment.

7.2 Of the detrital sed rocks, list their characteristics from v. fine to coarse: CONGLOMERATE/BRECCIA

Rock: Conglomerate/Breccia (aka gravel) Text: coarse, > 2 mm Formed: gravels accumulate in variety of environs and usually indicate steep slopes or very turbulent currents; coarse particles reflect energetic mtn streams or result from strong wave activity along a rapidly eroding coast; some glacial and landslide deposits also contain lots of gravel. Chcts: poorly sorted; space between particles contains sand or mud. Chem chcts: Devp'mnt: Economics:

7.2 Of the detrital sed rocks, list their characteristics from v. fine to coarse: SANDSTONE

Rock: Sandstone (aka Quartz Sandstone when qtz predominate); others: arkose or dirty sandstone (qtz + feld + mica) Tapeats Sandstone and graywacke (qtz + feld + rock frags) Hawick Grp Scotland and associated with submarine deposits called turbidity currents. Text: med, < 1/16 - 2 mm Formed: form in variety of environs; composition, shape, sorting of grains provides info on environ in which sediments were deposited. Most sandstones form through the accumulation of river sediments on the seabed. They are then compressed and uplifted to form new lands. Chcts: most abundant rock (20% of entire grp); sorting is done on scale of v poorly sorted - poorly sorted - well sorted - v well sorted (particles with nearly all the same size); - wind blown sand is better sorted than wave activity - deposits sorted by wave better sorted than minerals deposited in streams - Poorly sorted materials occur when turbulent stream transitions to gentle slope of mtn.; quick change in velocity - Particle shape (angularity and sphericity) -> the more rounded the more time the grain has spent in transport via air or water where abrasion has smoothed over the grain. V angular -> traveled short distance. So sandstone containing signifiant amounts of feldspar and angular grains of ferromagnesian minerals underwent little chemical weathering and transport and was probably deposited close to the source are of the rock particles. Chem chcts: chemical and mech'l weathering will remove weaker and less stable minerals like Feld and ferromagnesian; leaving behind the more stable qtz. Devp'mnt: Sandstone, sedimentary rock formed by the cementing together of grains of sand. The usual cementing material in sandstone is calcium carbonate, iron oxides, or silica, and the hardness of sandstone varies according to the character of the cementing material; quartz sandstones cemented with quartz are the hardest Economics:

7.2 What is fissility?

The property of splitting easily into thin layers along loosely spaced, parallel surface, such as bedding planes in shale.

7.2 Discuss the origin and hx of Detrital Sed rocks

- Gravity moves solid particles downstream (eg., landslides) - Glaciers, wind, rivers transport sediments - Sediments reach ocean floor via deposition of particles produced from glacial ridges, dunes, flood plains, and deltas - Chem & Mech weathering decompose & disintegrate rock (act as feeder stock for the weathering down to sediments process) - Soluble products of chem weathering dissolve in ground water - Dissolved material ppt out -> source for refs bldg & deposits rich in shells - END -> sediments curried in oc floor -> compacted & cemented into solid (s) rock; form from solid products of weathering.

7.5 What is diagenesis and give an example?

A collective term for tall the chemical and physical and biological changes that take place after sediments are deposited and during and after lithification to form sedimentary rock. Recrystallization = the development of more stable minerals from less stable ones; like, aragonite is less stable form of calcium carbonate (CaCO3). Aragonite is secreted by marine organisms to form shells and other hard parts such as the skeletal structured produced by corals. As they are buried as sediment, aragonite will recrystalize to more stable CaCO3 => limestone. Another example is plant material => coal

7.4 Coal is an Organic Sed Rock. Describe its formation.

Accumulation of plant remains in swamp conditions -> little to no O2 to aid in decomposition (oxidation) -> acids liberated by the plant decomposition impede bacteria's ability to complete the decomposition process -> Formation of peat (soft brown coal) -> partial decomposition of plant remain in O2 poor swam creating layer of peat -> slowly changes to Lignate (soft brown coal) -> burial increases temp of sediments as well as pressure -> Formation of lignite and bituminous coal (soft black coal) -> hi temps -> chem rxns. w/in plant material => water & organic gases (volatiles) -> increase load (temp+press) squeezes out water and volatiles -> leaving behind fixed carbon => greater C content greater coals energy ranking as fuel -> Formation of anthracite coal (hard coal) -> when subjected to folding and deformation associated with mtn. bldg., heat + press cause further loss of volatiles and water, increasing [c] of fixed C.

7.3 Limestone is chiefly made up of what mineral?

Calcite (CaCO3) and forms either by inorganic or as a result of biochemical processes. The marine biochemical form is the most common. - coral reefs - tiny floating oc plants and animals (coccoliths & foraminiferae) - other critters (clams)

7.3 Which of the chemical sed rocks is very compact and hard?

Chert is compact and hard. It is made of microcrystalline qtz (SiO2). Color variations related to trace elements present in the rock. - Jasper, Flint, Chert arrowhead, Petrified wood

7.7 What is cross-bedding?

Cross-bedding is when sed r. is inclined to the horizontal. They are most characteristic of sand dunes, river deltas, and certain stream channel deposits.

7.6 What are the classifications of sedimentary rock?

Detrital Sed R Coarse (>2 mm) - Gravel - Conglomerate Coarse (>2 mm) - Gravel - Breccia Med (1/16-2mm) - Sand - Sandstone (arkose) Fine (1/256-1/16 mm) - Mud - Siltstone V. Fine (<1/256 mm)- Mud - Shale or Mudstone Chemical/Org Sed R Calcite - nonclastic, fine->coarse - Crystalline Limestne/Travertine Calcite - Clastic, visible shells - Coquina (Biochem Limestne) Calcite - Clastic, v. sizes - Fossilferous Limestne (Biochem Limestne) Calcite - Clastic, Micro - Chalk (Biochem Limstne) Qtz - Nonclastic, v fine crystalline - Chert, Flint, Jasper Gypsum - Nonclastic, fine-coarse crystalline - Rock Gypsum Halite - Nonclastic, fine-coarse crystalline - Rock Salt Altered Plant frags - nonclastic, fine gr - bituminous coal

7.3 How are chemical sed rock different from detrital?

Detrital sed rocks formed from solid products of weathering. Chemical sed rocks derived from ions that are carried in solution to lakes and seas. These ions ppt-out to form chemical sediments like limestone, chert, and rock salt

7.3 Which Chemical Sed rock is similar to Limestone?

Dolostone is closely related to limestone. Limestone will react with HCL but dolostone (unless its in powder form) will not react. Abundant in many ancient sed rock successions.

7.7 How do fossils help geologists figure out what past environs looked like?

Fossils are remains or traces of prehistoric life and important inclusions in sediment and sedimentary rocks. Fossils serve as useful tools that allow geologists to date and interpret past environ'l conditions; time indicators helping to correlate rocks of similar ages that are from different places.

7.3 Where does chert most commonly occur?

It is found in layered deposits called bedded cherts or as somewhat spherical masses called nodules. The bedded cherts originate from tiny marine organisms (diatoms and radiolarians) that produce hard parts from silica rather than calcium carbonate.

7.7 What is an environ of deposition or sedimentary environ?

It is the geological setting where sediment is accumulating. Ea. site is characterized by a particular combination of geological processes and environmental conditions.

7.3 What are the chemical sed rocks?

Limestone Chert Rock Salt Coal

7.3 What are examples of inorganic limestones and how they formed?

Limestones that have an inorganic origin form when chemical changes or high water temps cause calcium carbonate to ppt out of the water. Travertine - seen in caves; ground water is source of calcium carbonate -> water exposed to air -> CO2 dissolved in the water escapes => calcium carbonate to ppt.

7.7 What are ripple marks and Mud cracks?

Ripple marks are small waves created by wind or water on the surface of a sediment layer, also provide useful clues to the past environ. Mud cracks form when mud contracts upon drying out, and they indicate that the sediment was exposed to air; associated with tidal flats, shallow lakes, and desert basins.

7.2 Of the detrital sed rocks, list their characteristics from v. fine to coarse: SHALE

Rock: Shale Text: v fine, < 1/256 mm Formed: tiny grains indicate settling out in quiet, non-turb enviorns -> lagoons, lakes, river flood plains, portions of deep oc Chcts: even in quiet environ clay can remain in suspension indefinitely. Therefore, much of clay deposits only after clay coalesces with other particles to become larger aggregates. Weak, poorly cemented therefore not well lithified; crumbles easily. Does not form prominent outcrops...think grand canyon -> gentle slopes of shale and bold cliffs of more durable rock (Ign + Meta rock). Chem chcts: blk. shale = abundant org mat'l (carbon); indicating oxygen poor environs like swamps where org mat'l doesn't readily oxidize & decay. Devp'mnt: Silt + clay accumulate -> form -> think layers (laminae) of disordered arrangement leaves open space (pore space) filled w/ water -> over time -> wt of add'l layers compact and press out water => take on a more parallel alignment becoming tightly packed not allowing for cementing to occur; thus, WEAK. Economics: used for pottery, brick, tile, china, Portland cement (shale + limestone), oil and NG.

7.2 Where will you most commonly find shale as a barrier to movement of subsurface water and petroleum?

Shale beds will block further movement of water into rock layers that contain ground water. However, the opposite is true for underground reservoirs of petroleum where the shale caps the beds of oil & gas preventing them from escaping to the surface.

7.2 Current of water and air will sort particles by size. Explain how this happens.

Strong currents will move larger sized particles. Gravels can be moved by swift rivers as well as by landslide and glaciers. Less energy is required to transport sand, thus sand is found in such features as windblown dunes and some river deposits and beaches. Very little energy needed to transport clay so it will settle slowly. Clays are found in lakes, lagoons, swamps, or certain marine environs.

7.7 At any given time, the geographical setting and environ'l conditions of a sedimentary environ deter the nature of the sediments that accumulate. T or F

True. Geologists study sediments in present-day depositional environs because the features they find can also be observed in ancient sed. rocks. "The present is the key to the past"!

7.1 How does the sedimentary process begin?

Weathering begins the process. Physical disintegration and chemical decomposition of pre-existing igneous, metamorphic, and sedimentary rocks generate products subject to erosion like particles and ions in solution that will then provide the raw materials for sedimentary rock formation. Then transport occurs via groundwater runoff, streams, rivers, wind, glacier movement where soluble constituents are dissolved and carried away. They will then settle out (deposit) and continue to be moved based on continued weathering activity. They may settle in mud on floor of lake, delta, gravel bar in stream or the ocean. Ions in solution are removed when chemical or temperature changes cause material to crystallize and precipitate or when organisms remove dissolved material to build hard part such as shells. Deposition continues, older sediments are buried, layers gradually convert to sedimentary rock (lithification) by compaction and cementation. This and other changes are referred to as diagenesis = a collective term for all the changes that take place in texture, composition, and other physical properties after sediments are deposited.

7.5 What is lithification?

diagenesis includes lithification which is the process by which unconsolidated sediments are transformed into solid sedimentary rocks. Basic lithification includes compaction and cementation. Compaction - reduced pore space Cementation - calcite, silica, and iron oxide most common cements; calcite reacts to HCL.