SEDIMENTS AND SEDIMENTARY ROCKS

Sediments are the weathered debris of pre-existing rocks that are carried away and eventually deposited elsewhere.

Transportation = movement of sediments from source area towards depositional area as solid particles or in solution.

Sedimentary rocks preserve a record of the ancient environment.

 

 

Lithification = compaction and cementation of sediments as they are buried, forming Sedimentary Rocks.

Diagenesis = Compaction, Recrystallization, Solution, Precipitation of grains and cement, altering Sedimentary Rocks.

 

Things You Can Describe

Composition, Particle Size, Shape, Roundness, Sphericity, Sorting, Cement and Matrix, Orientation, Packing, Structures

 

SEDIMENT TYPES

Clastic (=Detrital) - sediments derived from the solid products of mechanical and chemical weathering. Upon Lithification, these sediments form Clastic (=Detrital) Rocks.

Chemical - sediments formed as a result of inorganic or biochemical precipitation of materials dissolved during chemical weathering. Upon Lithification, these sediments form either Chemical or Biochemical Rocks.

     - biochemical

 

Cements and Matrix = What fills in the spaces between grains/clasts ANDwhat keeps the grains together as a rock

 

Shale

The most prominent shale in Kentucky is the Chattanooga (also called New Albany and Ohio) Shale, which crops out in southern Kentucky and around the Knobs area. It is brownish black, silty, pyritic, bituminous, and carbonaceous. This Chattanooga black shale contains sufficient organic matter to burn, and several attempts have been made to mine this "oil shale" as a fuel source.

The New Providence and Nancy Shales of Mississippian age, which also crop out in south-central Kentucky and around the Knobs area, are used in the brick industries of Kentucky. They are a bright-green to greenish-gray, relatively soft, plastic clay-shale.

http://www.uky.edu/KGS/coal/webrokmn/pages/sedrocks.html#clays

 

Sandstones

Sandstones are very resistant to erosion and form bluffs, cliffs, ridges, rapids, arches, and waterfalls. Sandstones and conglomerates are responsible for most of the rugged topography in eastern Kentucky. Loose or unconsolidated sands cover much of the Jackson Purchase area of western Kentucky. These sands are varicolored, but commonly white to light brown.

Silica (quartz-rich) sands and sandstones of high purity (white color) are used extensively in the glass industry for manufacturing window glass, light bulbs, and containers. At present, glass sands are obtained from unconsolidated deposits near New Concord, Calloway County. Tightly cemented sandstone is used as a building stone.

http://www.uky.edu/KGS/coal/webrokmn/pages/sedrocks.html#clays

 

Types of Sandstones:

Arkose – feldspar-rich

Wacke – clay-rich

Arenite – quartz-rich

 

Breccia

A type of Conglomerate with Angular Fragments- close to source

·         Explosive

·         Fault-relate

·         Hydrothermal

 

CHEMICAL SEDIMENTS AND ROCKS

  • Classification Based primarily on mineral composition.
  • Carbonates:
  • Limestone - forms from calcite and aragonite (CaCO3).
  • Dolostone - forms from dolomite [MgCa(CO3 )2]
  • Silicates
  • Chert (including flint, jasper, and agate) - forms from precipitation of silica (SiO2) either inorganically, or biochemically as organism hard parts (e.g., silica shells, spines, plates, etc.).
  • Evaporites:
  • Rock Salt (=Halite) - NaCl salt.
  • Rock Gypsum - Gypsum (CaSO4 H2O); used for wallboard, etc.

 

Chemical Sediments

Limestone       –   CaCO3   –  calcite

Gyprock          –   CaSO4   –  gypsum

Rock Salt        –   NaCl       –  Halite

Coal                 -    C       -        Lignite, Subituminous, Bituminous

 

Precipitation from Seawater; Evaporation of 1000 m of seawater would produce:

K and Mg salts

Halite  (13.7 m)

Anhydrite + Halite

Anhydrite

Gypsum (.75m)

 

ORGANIC SEDIMENTARY ROCK 

COAL = Compacted Plant Material rich in Organic Carbon

Formed in wet-land areas where many trees grew and were eventually buried in organic-rich muds.

One of very few rock types that consists mostly of a non-mineral (Plant Material).

Some coals have minor amounts of mineral matter which cause major environmental problems:

--Pyrite (FeS2) --> "Acid Rain" when burned with coal and resulting SO2 gas mixes with water vapor in atmosphere.

 

CEMENTATION
CLASTIC SEDIMENTS AND SEDIMENTARY ROCKS

Classification based primarily on grain size which reflect velocity/turbulence (energy) conditions.

 LOW ENERGY------------------------------------------------ HIGH ENERGY

 FINE GRAINED --------------------------------------------- COARSE GRAINED

 CLAY - SILT - SAND - GRANULES - PEBBLES - COBBLES - BOULDERS

 CLAYSTONE SILTSTONE SANDSTONE CONGLOMERATE & BRECCIA

 

Breccia = A type of Conglomerate - with Angular Fragments; explosive, fault-related, hydrothermal - close to source

 

 

SEDIMENTARY ENVIRONMENTS

Clastic and Chemical rocks represent distinct sedimentary environments.

In general, Clastic Sediments are deposited in environments where rivers and other transportation agents (such as wind, gravity, animals, etc.) can move sediments from their sources to sites of deposition.

 

Chemical sedimentation predominates wherever a fluid is oversaturated with some chemical component.

A few examples:

  • Calcium (as limestone) is deposited in warm shallow seas, such as the Florida coast.
  • Sodium and Chlorine are deposited (as halite) in dry arid plains, such as the Bonneville Salt Flats.
  • Animals help deposit chemicals
  • Marine animals with shells, such as clams, lobsters, etc., make their shells from the elements Calcium, Oxygen, and Carbon (and some other stuff, too.)
  • Where do these elements come from?
  • The shell materials come from sea water. So, as shells accumulate on the sea floor, the elements once in the water become a sediment, soon to be a sedimentary rock.
  • Mixed Clastic and Chemical Rocks
  • Either alternation of conditions, high concentration of fossil shells, or transportation of one type of sediment into the domain of the other by floods, storms, or other high velocity/high turbulence events (= high-energy events) could result in the deposition of mixed clastic and chemical rocks.

 

Sedimentary Structures

·         Cross-Beds

·         Ripple Marks

·         Graded Bedding

·         Mudcracks (desiccation cracks)

·         Raindrop impressions, feeding trails, etc.

·         Load features

 

Changing environments means   changing rock types  -  Fig. 7.37

As the environment shifts ……                 (onshore in this case)

the sediments deposited reflect the shift – but in vertical succession

 

Be able to interpret the clues and explain the environments of deposition for these examples of sediments/sedimentary rocks.

Granite cobble + quartz sand conglomerate

Olivine and biogenic carbonate sandstone

Clay+organic+pyrite-rich shale

Quartz+gypsum+lithics sandstone

Oolitic limestone cemented by gypsum

Mudcracks + coral fragments + leaves