SEDIMENTARY GEOLOGY OVERVIEW Andrew S. Madof Orals Review January 12, 2007

SEDIMENTARY GEOLOGY = Sedimentology (process) + Stratigraphy (response) Sedimentology = study of PROCESSES (i.e. production, composition, transport, and deposition of sediment) Stratigraphy = study of RESPONSES (i.e. inferring the controls on the spatial and temporal changes of strata) → exact processes that created the rocks can’t be know because only the rocks are left, not the processes

Sedimentation And Sedimentary Rocks Sedimentary Rocks: Form 75% of the rocks exposed at the Earth’s Surface Are the reservoirs for fossil fuels, iron and aluminum ores, and groundwater Record of Earth’s history

Sediment Sediment = loose, solid particles and can be: –Terrigenous = fragments from silicates (igneous and/or metamorphics) –Biogenic = fossils (carbonate - reefs; silicates - forams) –Chemical = precipates (halite, gypsum, anhydrite, etc…) - note: with chemical sedimentary rocks, evaporation > precipitation and/or supersaturation in closed basins (lakes or oceans) Classified by particle size –Boulder - >256 mm –Cobble - 64 to 256 mm –Pebble - 2 to 64 mm –Sand - 1/16 to 2 mm –Silt - 1/256 to 1/16 mm –Clay - <1/256 mm

Grain size (diameter) and grain-shape depend on: Transport media: rivers (pebbles bounce on river bottom, sand moved in traction, and silt/clay suspended in water column); oceans and lakes (near-shore and deep-water systems); glaciers (sediment moved on glacier bottom); wind (sand dunes) Distance from parent rock: the longer the distance traveled, generally the smaller and the more well-rounded the grains (due to higher kinetic energy) Mineral hardness: the harder the parent rock, the longer it will take the sediments to erode (example: silicates are more resistant to weathering and erosion than feldspars, and this is why beaches are often comprised of sand, not feldspar-rich sediments) Consider: sorting (= range of grain sizes) → winds sort well (meaning grain sizes are very similar); glaciers sort poorly (meaning there is a large spread of grain sizes in glacial deposits) Grain size

Classification Of Sedimentary Rocks DETRITAL (TERRIGENOUS) SEDIMENTARY ROCKS: Mudstones Sandstones Conglomerates Breccias DETRITAL SEDIMENTARY ROCKS: Classification Based On Particle Size a) All detrital rocks are clastic b) Sand and silt are predominantly quartz c) Finer-sized particles of clay minerals

SANDSTONES: a) 25% of all sedimentary rocks b) Sandstone particles (1/16-2 mm in diameter) c) Practical uses of sandstones: buildings and reservoir for fossil fuels and groundwater CONGLOMERATES AND BRECCIAS: a) Grain diameters larger than 2 mm b) Conglomerates have rounded grains c) Breccias have angular grains

Breccia (from fault motion?) Sandstone

MUDSTONES: a) More than half of all sedimentary rocks b) Contain the smallest particles (0.004 mm in diameter) c) Environments of deposition: lakes, lagoons, deep ocean basins, river floodplains d) Color variety of shale represents mineral composition e) Practical uses of shale: bricks, ceramics, cement, and oil shale

Chemical Sedimentary Rocks Inorganic Chemical Sedimentary Rocks a)LIMESTONE (inorganic): I) FORMATION II) Oolitic Limestone III) Tufa IV) Travertine

Lithification = Turning Sediment Into Sedimentary Rock Diagenesis = Changes in the sediment due to increased heat, pressure, and circulating groundwater Lithification = Compaction + Cementation Compaction = Diagenetic process by which the weight of overlying materials reduces the volume of sedimentary body (decreases porosity)

Cementation: Precipitation of dissolved ions in the pore space a) calcium carbonate - CaCO 3 b) silica - SiO 2 c) iron compounds - Fe +2 and Fe +3 Texture of Rock: Formed by compaction and cementation of sediment particles Recrystallization: recrystallization of certain unstable minerals into new, more stable minerals (this happens primarily in carbonates, when you start with carbonate mud [a.k.a. micrite] heat it up, then cool it to form larger grains [a.k.a. sparite]) Cementation & Recrystallization

Types of Sediment

Common Geological Environments

Locations of Subsurface Evaporites

Sedimentary Structures Bedding (stratification): arrangement of sediment particles into distinct layers A) Changes in sediment change bedding B) Changes in transport energy change bedding Normally graded bedding: sediment layer (formed by a single depositional event) in which particle size varies gradually with the coarsest particles on the bottom (note: inversely graded bed = fines on bottom and coarse grains on top )

Cross-bedding: sedimentary layers deposited at an angle to the underlying set of beds Surface sedimentary features A) Ripple Marks: small surface ridges produced when water or wind flows over sediment after it is deposited B) Mudcracks: occur on the top of a sediment layer when muddy sediment dries and contracts Cross-bedding and Mudcracks

Development of Cross-Bedding

Asymmetric and Symmetric Ripples river or wind currents (uni-directional) tidal currents (bi-directional)

Formation of Coal from Swamp Deposits

Initial Deposits of Flat/Tabular Clay

Formation of Ooliths

Origin of Mud Cracks

Lithification of Sediments

Sedimentary Facies Formation

Sediment in a Stream

Marine sedimentary environment

Landward Migration of Shoreline = Regression (regression can either form due to 1) lower sea level or 2) shoreline building basinward [a.k.a. progradation])

Graded Bedding = Vertical Decrease of Sediment Size Turbidity Current = PROCESS Turbidite = RESPONSE