Sedimentary Rocks

Sedimentary Petrology- What is it? Study origin, occurrence, mineral comp. & texture of sed rks. Study origin, occurrence, mineral comp. & texture of sed rks. Depositional environment usually not emphasized Depositional environment usually not emphasized Emphasize sed rocks– their description & classification Emphasize sed rocks– their description & classification

Why study sedimentary rocks/sediments?   Sedimentary rocks make up only 7.9% of the Earth’s crust.

  66% of surface Earth covered by sediment or sedimentary rocks.   Humans interact with the Earth largely at or near its surface.

On surface we….. Grow food on it. Build structures on it. Take resources from it.

At the same time we….. Modify its physical and chemical properties so that it is no longer useable. Important to understand properties of the sedimentary cover and have systematic methods for describing these properties. Hide garbage and other waste material in it.

More Reasons to Study Sed Rocks Sedimentary rocks-- best evidence of earth history because: Sedimentary rocks-- best evidence of earth history because: Often contain fossils, properties to establish environments, and Often contain fossils, properties to establish environments, and Often provide geologic age of materials. Often provide geologic age of materials. Record sedimentological, chemical, fossil; evidence of changing tectonics & paleoceanography Record sedimentological, chemical, fossil; evidence of changing tectonics & paleoceanography Economic significance Economic significance Grand Canyon

Origin of Sediments  A. Weathering  Chemical  Mechanical  Weathering provides raw materials

Erosion Erosion is the displacement of solids (soil, mud, rock, and so forth) by the agents of wind, water, ice, or movement in response to gravity soilmudrockgravitysoilmudrockgravity 1. Wind 2. Water 3. Ice

Deposition  Where sediments accumulate  Environments  Beaches  Lakes  Slopes  Rivers

Cementation/Compaction  Sediment may be compacted  Cement precipitates in voids

Extent Of Sedimentary Rocks Cover 66% cont. surface, much ocean floor Cover 66% cont. surface, much ocean floor Ig & met rocks unstable at surface Ig & met rocks unstable at surface Form under dif. TP regimes Form under dif. TP regimes Surface= LTLP regime Surface= LTLP regime Form in less O2, CO2, H2O Form in less O2, CO2, H2O Minerals break down Minerals break down Form grains & clays Form grains & clays Break down due to weathering Break down due to weathering

Sedimentary RK Types & Lithologies Clastic/Detrital Clastic/Detrital Formed of particles derived from pre- existing rks Formed of particles derived from pre- existing rks Chemical precipitates Chemical precipitates Precipitate from solution Precipitate from solution 95%=S.S, L.S, Mudrock 95%=S.S, L.S, Mudrock Sandstone % Sandstone % Form in high energy environment Form in high energy environment Some in low energy Some in low energy Mud <.06mm; sand mm Mud <.06mm; sand mm

Quartz Rich Sandstone

Quartz Rich Sandstone Microphotograph

Arkose

Conglomerate

Breccia

Carbonate (CO 3 ) Rocks CO 3 rocks =10-15% of sed rocks CO 3 rocks =10-15% of sed rocks CaCO 3 (Arag/Calcite); CaMg (CO 3 ) 2 (Dolomite) CaCO 3 (Arag/Calcite); CaMg (CO 3 ) 2 (Dolomite) Also Siderite (FeCO 3 ), Magnesite (MgCO 3 )-rare Also Siderite (FeCO 3 ), Magnesite (MgCO 3 )-rare Most-hard parts of org. Most-hard parts of org. Deep H 2 O corrosive Deep H 2 O corrosive Most CO 3 =shallow H 2 O Most CO 3 =shallow H 2 O Transitional rocks Transitional rocks Coquina-SS or CO 3 Coquina-SS or CO 3 Marl-CO 3 & clay Marl-CO 3 & clay

Coquina

Mudrocks Mudrocks 65% Mudrocks 65% Most abundant-65% of sedimentary rocks Most abundant-65% of sedimentary rocks Not well studied Not well studied Common due to Ig/met rocks Common due to Ig/met rocks Composed of 20% qtz & 80% other silicates Composed of 20% qtz & 80% other silicates Qtz stable others not Qtz stable others not Detrital content Detrital content Qtz common Qtz common Minor felds Minor felds Found low energy environment Found low energy environment Mudstone mostly silt/clay Mudstone mostly silt/clay

Halite

Cementation A. Rks get lithified B. Sed accumulation leads to compaction; porosity reduced C. Most common cements--SiO 2, CaCO 3, iron-oxide

Thickness of Sedimentary rocks 1.8km-continent., 0.3km-oceanic 1.8km-continent., 0.3km-oceanic Difficult to measure-where does meta begin Difficult to measure-where does meta begin 20,000m in some basins 20,000m in some basins

Major Settings for Sediment Accumulation—Sedimentary Basins Oceanic basins Oceanic basins Garben along cont. margins Garben along cont. margins Arc-trench systems Arc-trench systems Suture belt basins Suture belt basins Intracratonic basin Intracratonic basin

Oceanic Basins Coarser seds on continental margin Coarser seds on continental margin Fine grained seds in deep ocean Fine grained seds in deep ocean >4000m- generally no CO3 seds. >4000m- generally no CO3 seds. Red clays & siliceous shells make up most of deep ocean sediments Red clays & siliceous shells make up most of deep ocean sediments

Rifted Continental Margin Form when continent rifted- get extension Form when continent rifted- get extension e.g S. America rifted from Africa e.g S. America rifted from Africa First get volcanics & non-marine seds. First get volcanics & non-marine seds. Periodic flooding- get evaporites Periodic flooding- get evaporites Then shallow to deep marine rocks with more rifting Then shallow to deep marine rocks with more rifting

Arc Trench Systems- Trench seds=Turbidites Trench seds=Turbidites Forearc-overlie oceanic or transitional crust Forearc-overlie oceanic or transitional crust Volcanic seds & sed from pluton or uplifted trench/slope break Volcanic seds & sed from pluton or uplifted trench/slope break Great Valley=Forearc basin Great Valley=Forearc basin Forearc=shelf, deltaic, terrestrial Forearc=shelf, deltaic, terrestrial Intra arc Intra arc Turbidites & volcani material from Arc Turbidites & volcani material from Arc Retroarc basin=backarc basin Retroarc basin=backarc basin

Suture belt basin Form where have cont- cont. collision Form where have cont- cont. collision Basins form in suture zone Basins form in suture zone Seds=clastic from erosion of continent. Seds=clastic from erosion of continent.

Intracratonic Basins Origin not well understood Origin not well understood Downbowing next to cont. margin Downbowing next to cont. margin Aborted cont. rifting Aborted cont. rifting Local cooling of asthenosphere Local cooling of asthenosphere Get cratonic seds. Get cratonic seds. Mostly non-marine & shallow marine seds.- well rounded Mostly non-marine & shallow marine seds.- well rounded

Stop Here Stop Here

III) Clastic/Detrital Components A Clays--sheet-like silicates B Quartz C Feldspars--unstable--fast erosion and deposition D Micas--unstable--fast erosion and deposition

IV) Size Distribution A. Know scale B. Provide info about depo. env. C. Greater energy to transport larger particles D. Clays accumulate in quiet water

V) Clastic Rk types A. Shale--clay and silt particles 1. Particles are microscopic 2. quiet water, non-turbulent deposition 3. Settle following flocculation 4. Form laminae/massive beds 5. Fissil=shale; non-fissil=mudstone 6. Generally recessive

B. Sandstone 1. Made of sand-sized grains 2. Deposited in a variety of environments 3. Sorted to poorly sorted 4. Wind deposits better sorted than water- tranported deposits?

B. Sandstone Continued 5. Shape of grains--rounded to angular, related to distance or time of transport 6. Sandstone types i. quartz arenite ii. arkose iii. graywacke iv. lithic sandstone 7. conglomerate/breccias i. good for provenance ii. not transported far

VI) Chemical Sed Rks A. Inorganic precipitates B. Biochemical Rks C. LS most abundant chemical sed rk 1. composed of calcite 2. mostly marine 3. Corals= warm water, shallow tropical environment; <30 lat

Other Chemical Sed Rks Continued D. Rk types 1. chalk 2. travertine 3. oolitic l.s E. Dolomite 1. calcium magnesium carbonate 2. Rks=dolostone

Chemical Sed Rks Continued F. Chert 1. composted of microcxline qtz 2. nodules and layers, biochemical rks G. Evaporites Halite, Gypsum