







Study with the several resources on Docsity
Earn points by helping other students or get them with a premium plan
Prepare for your exams
Study with the several resources on Docsity
Earn points to download
Earn points by helping other students or get them with a premium plan
Community
Ask the community for help and clear up your study doubts
Discover the best universities in your country according to Docsity users
Free resources
Download our free guides on studying techniques, anxiety management strategies, and thesis advice from Docsity tutors
An in-depth exploration of the geological processes of weathering, sedimentation, and the formation of sedimentary rocks. Topics include the disintegration and decomposition of rock (weathering), the production of sediment from pre-existing rock, and the transportation and deposition of sediment by various agents. The document also covers the mineralogy of parent rocks, the role of water and carbon dioxide in chemical weathering, and the formation of clay minerals. Additionally, it discusses the stability of minerals, the influence of temperature on mineral stability, and the factors affecting weathering rates. The document concludes with an overview of sedimentary structures and environments.
Typology: Lecture notes
1 / 13
This page cannot be seen from the preview
Don't miss anything!
Overview of Sedimentary Rocks
I. Basic Definitions
A. Denudation of the Earth's surface
B. Weathering - disintegration and decomposition of rock at or near the surface of the earth, fragmenting rock into particles
C. Sediment - fragments of rocks and/or minerals that are produced from the weathering of pre-existing rock
D. Erosion - incorporation and transportation of sediment by a mobile agent
E. Mass wasting - transfer of rock material downslope under the influence of gravity
II. Weathering - surface processes operating on rock from the earth's crust
A. Driving mechanism of rock weathering
B. Physical or Mechanical Weathering
(1) e.g. weathering of granite produces sediment rich in feldspar and quartz
a. liquid water to ice: ~9% volume expansion b. "wedging" apart pieces of rock to form sediment
(1) e.g. TALUS SLOPES - found at base of cliffs or mountain fronts
b. Sheeting - rock breaking into concentric, onion-like slabs
C. Chemical Weathering
a. Chemical agents of weathering:
(1) Water - H 2 O - universal solvent (a) dipolar molecule
(2) Carbon dioxide - CO 2 - Carbon dioxide dissolved in water (H 2 0), produces carbonic acid (H 2 CO 3 ),
(a) hydrogen in the acid readily displaces any metal ions in minerals and results in producing clay minerals (hydrous aluminum silicates).
b. Clay Minerals - the stable end product of chemically weathering silicate minerals ("igneous minerals")
(1) "Clay" - two uses of the term (a) a grain size term (very fine mud particles) (b) a mineral family i) hydrous layered minerals ii) stable minerals at Earths' surface
a. the higher the temperature of mineral formation, the less stable the mineral is chemically at the Earth's surface b. vice - versa, lower-termp. minerals are more stable
(1) e.g. quartz is very stable at Earth's surface (a) commonly forms sand at the beach
D. Rates of Weathering (How fast, over time, rocks weather)
a. compaction - as sediments accumulate and become buried with time, the weight of overburden compact the sediment
(1) clay minerals are cohesive (sticky) and serve as a binding agent for sediment (2) compaction also involves dehydration and hardening of sediment into rock
b. cementation - solutions carry ions into pours between sediments, with time ions may be precipitated as cements under appropriate chemical condition.
(1) Common cements include calcite, silica, and iron oxide.
C. Sedimentary Rock Types/Classification
Detrital vs. Chemical Sedimentary Rocks.
a. Composition: sediments composed of quartz, clay, feldspars, and associated array of just about any other mineral in lesser proportions (e.g. amphibole, or any of silicate/igneous minerals, as well as recycled sedimentary rocks).
(1) E.g. Granite is weathered - produces quartz, and feldspars, plus mica: quartz is most resistant mineral and as a result is most common remnant product.
(2) the composition of the original rock (ig., sed., met.) that is weathered will have a direct influence on the composition of the sediment/sed. rock that results.
b. Texture of Sediment - size, shape and arrangement of sediment grains in the rock
(1) Sediment Size Classification (i.e. Average Diameters of Particles) Sediment Size Resulting Rock
Clay = < 1/512 mm = < 0.002 mm Shale or Mudstone Silt = 1/512 - 1/16 mm = 0.002 - 0.0625 mm Siltstone Sand = 1/16 - 2 mm = 0.0625 -2.0 mm Sandstone Gravel = >2.0 mm Conglomerate / Breccia Pebbles= 2.0 - 64 mm Cobbles = 64 - 256 mm Boulders = >256 mm
(2) Grain Shape
(a) Angular vs. Rounded Grains i) Rounded Grains = more transport / tumbling (b) Spherical vs. Non-spherical Grains
(3) Grain Sorting
(a) Degree to which grains are same size
i) poorly sorted sediment - different sizes ii) highly sorted sediment - same size
c. Detrital Rock Types (shale, sandstone, conglomerate)
(1) Shale - detrital sed. rock consisting of lithified clay and silt sized particles, very small particles < 1/16 mm (must use microscope to see particles),
(2) Sandstone - detrital sed. rock made up of sand sized grains.
(3) Conglomerate - lithified gravels (boulders, to pea sized sediment), often poorly sorted with finer sediment between gravel.
a. Processes (1) Chemical sediments may be directly precipitated under high concentrations of ions in water (e.g. halite/rock salt), or (2) ions may be "fixed" by organisms living in the water in shells, accumulation of shells may then provide material for chemical sedimentary rock.
b. Texture of Chemical Sedimentary Rocks (1) Crystalline Texture (a) sugary appearance, crystals visible to eye (b) interlocking mineral crystals (2) Microcrystalline Texture (a) crystalls too small to see, need microscrope
c. Limestone - composed of a mosaic of the mineral calcite (CaCO3) and forms by either chemical precipitation or biochemical processes. Biochemical processes account for 90% of the limestones.
d. Dolomite - similar to limestone, but has Mg incorporated into CaCO3, CaMgCO3.
e. Chert - SiO2, microscrystalline silica deposited from solution in open ocean.
f. Evaporites - chemical sed. rock that result from precipitation of minerals via evaporation of water.
(1) E.g. halite/rock salt (NaCl) and Gypsum (CaSO4). Commonly associated with shallow seas and brine lakes (e.g. Salt Lake).
g. Ironstone - composed of iron-bearing minerals (hematite, limonite)
h. Coal - carbon-based rock derived from plant material (1) Bituminous coal - "soft coal", black (2) Anthracite coal - "hard coal", brownish (3) Lignite - "brown" immature coal (4) Peat - brown / compressed plant debris
a. Clastic vs. nonclastic -
(2) Offshore (a) e.g. deep ocean b. Nonmarine - terrestrial (1) e.g. Rivers, Lakes, Glaciers
C. Sedimentary Structures
D. Stratigraphy
a. 3-D spatial geometry (1) Vertical vs. Horizontal Stratigraphic Relationships
b. Geologic time perspective: when? how long ago?
(1) Ordering of geologic events through time
V. Basics of Sediment Transportation
A. Energy vs. Mass of Sediment
a. e.g. question: could wind transport a boulder the size of this room?
a. Flowing Water / Rivers ---- gravity + climate b. Flowing Glacial Ice ------ gravity + climate c. Landslide / Rock Fall ------ gravity d. Wind Blown Sediment ---------climate / air flow
a. Energy relates directly to velocity of motion (1) stream velocity, wind velocity, etc.
B. Methods of Transporting Sediment
b. Saltation: bouncing of particles via upcurrents, and trajectory fall under force of gravity.
VI. STRATIFICATION A. Stratification = Horizontal layering of sediment under gravity
B. Internal Stratification
VII. Sedimentary Structures
A. Sedimentary Structures primarily result of physical transportation processes, or biologic processes, or post-depositional processes or chemical processes.
B. Basic Examples of Sedimentary Structures
a. Flute Casts: current-formed erosion structure, bulbous cast formed by scouring of
sediment interface, bulbous end generally points up-current.
b. Load Casts: irregular knobs found on sandstones overlying shale beds. c. Tool Marks: groove casts; infilling of mold formed by dragging object across sediment interface
a. Tracks, trails, burrows b. Bioturbation: general mixing of sediment by dirt eaters.
a. Clay shrinks as it dries, results in polygon fractures
VIII. Sedimentary Environments and Facies Analysis
A. Sedimentary Environments
a. Characteristics of a given sedimentary environment yield a specific product of sediment and/or sedimentary rock.
B. Sedimentary Products
a. Facies by definition: readily detectable and discernable characteristics (chemical, physical or biologic).
**A sedimentary facies is the product of the sedimentary environment and its processes
on landward side of island
c. Estuarine/Lagoonal: similar to lacustrine, only in marginal marine setting, water chemistry is saline, quiet water sedimentation with bio-critter processes abundant.
d. Tidal Flat: low-lying coastal areas heavily influenced by tidal rise/fall of water, tides rework sediment, bio-critter processes abundant.
(1) Shelf: encompasses sand-dominated shelf or carbonate-dominated shelf accumulations
(2) Organic Reef: biochemical build-up of carbonate structure comprised of living marine organisms, dominated by corals and algae + other critters
b. Oceanic: i.e. deeper ocean setting
(1) Slope: steep-gradient slope transitional to shallow-water shelf and deep ocean floor (a) Submarine canyons/submarine fan systems
(2) Deep-ocean Floor (a) Abyssal plain, quiet water mud accumulation