Sedimentary Rocks. Weathering. Mechanical & Chemical Weathering. Sediments. Lithification. Deposition. Transport. Erosion.

Transcription

1 Lithification Sedimentary Rocks Sediments Deposition Transport Erosion Weathering Weathering The sediments that make up sedimentary rocks are produced by: Mechanical & Chemical Weathering

2 Mechanical Weathering Chemical Weathering

3 p.22 Mineral Stability Products of Weathering Lithic (Rock) Fragments (granite, basalt, schist, etc.) Dissolved Ions (Calcium, Potassium, Sodium, etc.) Rust Minerals (Hematite, Goertite, etc.) Clay Minerals (Bentonite, Montmorillonite, etc.) Residual Minerals (Quartz, Orthoclase, Muscovite, etc.)

4 Erosion & Transport Water Wind Ice Gravity Deposition

5 Lithification Sediment Rock Cementation Typical Cement: Calcite Quartz

6 Sedimentary Rocks Identification Note: Use the same terms to describe sediments & sedimentary rocks. Only difference is lithification! Rock Identification is based on: Composition What minerals make up the rock? Texture What is the shape, size and orientation of the mineral grains that make up the rock? Major Difference: Crystalline vs. Clastic

7 Types of Sedimentary Rocks Detrital Rocks Chemical Rocks vs. Difference: Texture Detrital (Clastic Texture) vs. Chemical (Crystalline Texture)

8 Detrital Rock Composition Detrital Rocks Lithic Fragments Quartz Clay Minerals Fossil Fragments Rust Minerals Orthoclase Muscovite / Biotite Detrital Rock Texture Clastic Texture Grain Size Grain Sorting Grain Rounding Sediment Maturity

9 Grain Size Gravel 2mm Sand 1/16 mm Mud - Silt 1/256 mm Mud - Clay Detrital Rock Names (Based Primarily on Grain Size) Gravel Sized: Conglomerate Sand Sized: Sandstone Mud Sized: Mudstone Siltstone Shale

10 Sorting Grain Roundness

11 Gravel Sized Detrital Rocks (Subdivided Based on Grain Roundness) Conglomerate Breccia Maturity Mature Well Sorted Well Rounded All Quartz Immature Poorly Sorted Angular grains Mixed Composition including clay

12 Quartz Sandstone Lithic Sandstone Sandstones (Subdivided based on maturity) Arkose (Sandstone) Greywacke Sandstones Under a Scope

13 p. 29 Detrital Sedimentary Rock ID Clastic (Detrital) Sedimentary Rocks Grain Size Roundness Sorting Composition Name Gravel-sized (> 2 mm) Rounded Angular Moderate to poor Moderate to poor Fragments of any rock type Fragments of any rock type CONGLOMERATE BRECCIA Sand-sized (visible grains up to 2 mm) Rounded Well All Quartz - usually white to tan Subrounded to Angular Subrounded Moderate to poor (few grains >2mm) Moderate to well Feldspar (usually orthoclase), micas, quartz, and other minerals Quartz, lithic fragments, and other minerals QUARTZ SANDSTONE ARKOSE (Arkosic Sandstone) LITHIC SANDSTONE Rounded to angular Moderate Quartz and rock fragments mixed with >15% clay; often gray colored GRAYWACKE SANDSTONE Silt-sized (feels gritty) (to small to see) Well Clay and quartz (but usually too small to see) SILTSTONE Clay-sized (feels smooth) (to small to see) Well Clay (but usually too small to see); Massive Clay (but usually too small to see); Breaks into semi-flat layers MUDSTONE SHALE Chemical Rock Texture Crystalline Texture Coarse Fine

14 Chemical Sedimentary Rocks (Names based primarily on composition) Composition Calcite Quartz (silica) Halite Gypsum Carbon / Plant Remains Basic Rock Name Limestone Chert Rock Salt Rock Gypsum Peat or Coal Chemical Rocks (Names based mainly on composition) Crystalline Limestone Limestones Fossiliferous Limestone Chalk

15 Chemical Rocks (cont.) Evaporites Chert Rock Salt Rock Gypsum Coal p. 30 Chemical Sedimentary Rock ID Chemical, Biochemical & Organic Sedimentary Rocks Composition Texture Name Calcite (acid reaction) Dolomite (acid reaction) Crystalline - medium to coarse (visible) grains Crystalline - grains too small to see Abundant fossils in a fine- to coarse-grained crystalline matrix Fine-grained powder, earthy smell (often black, gray, or white) Crystalline - fine to coarse grained CRYSTALLINE LIMESTONE MICRITE FOSSILIFEROUS LIMESTONE CHALK DOLOSTONE Quartz Crystalline - grains too small to see; conchoidal fracture CHERT (scratches glass) Fine-grained powder, earthy smell (no acid reaction) (often white) DIATOMITE Gypsum Crystalline - fine to coarse grained ROCK GYPSUM Halite (tastes salty) Plant Remains (Carbon) Crystalline - fine to coarse grained Fibrous, brownish plant material; soft Dense, black masses; depending on grade may be dull to vitreous; lower grades may contain minor fossils ROCK SALT PEAT COAL

16 Sedimentary Rocks on Earth Sedimentary Rocks Interpretations

17 What do Sedimentary Rocks Record? Source of sediment Erosion and Transport Agent Distance of Transport Depositional Environment Paleogeography/Tectonic Setting Interpretation of Composition Detrital Rocks: Source of sediment Exposure to Weathering (Distance of Transport) (Type of Climate)

18 Note About Detrital Rock Color & Composition Grain Size Smaller is often darker Composition Carbon - black or brown Quartz - tan, clear, white Orthoclase - orange Depositional Environment Iron on land - red Iron in deep, oxygen poor water - green Interpretation: Grain Size Gravel High Energy River, Beach, Landslide Sand River, Beach, Desert Silt Delta, Shallow Ocean Clay Low Energy Deep Ocean, Lake, Swamp

19 Detrital Rock Names (Based Primarily on Grain Size) Gravel Sized: Conglomerate Sand Sized: Sandstone Mud Sized: Mudstone Siltstone Shale Interpretation: Sorting Interpretation: Poorly Sorted Well Sorted Transport Agent Gravity and Glaciers (and Rivers) Water and Wind

20 Clast Supported Conglomerate (River Deposits) Matrix Supported Conglomerate (Glacial/Landslide Deposits) 2.2 Gyr Conglomerate Modern Glacial Sediments

21 Interpretation: Grain Roundness Short Interpretation: Distance of Transport Far Limestone Crystalline Limestone Fossiliferous Limestone Chalk

22 Formation of Limestone Calcite Precipitates in Warm Water Water Under Low Pressure (Shallow) Or It is secreted by biological organisms Clams, Mussels, Scallops, etc. Corals Foraminifera Limestone Represents: Shallow Tropical Ocean

23 Black Sea Chalk (Coccolithophores)

24 Travertine (Limestone) Chert (Flint, Jasper, Agate )

25 Diatom Steletons Chert Represents Deep Ocean

26 Evaporites: Bonneville Salt Flats, Utah Rock Gypsum Rock Salt Isolated, Arid, Salty Sea/Lake Peat and Coal Swamp, Bog

27 Intermission: Quiz What can you say about the history of this rock? Deposited in a beach/ river or desert, very far from the source of the sediment. Quartz Sandstone Intermission: Quiz What can you say about the history of this rock? Shale Deposited in a quiet water environment (deep ocean, lake, lagoon). Dark color implies oxygen-poor environment, rich in organic material.

28 Intermission: Quiz What can you say about the history of this rock? Deposited in a shallow tropical ocean. Limestone