A 2 Sedimentary Processes Rocks Sedimentary Processes Weathering

A 2 Sedimentary Processes & Rocks

Sedimentary Processes Weathering • Types • Erosion • Products • Transportation • Rates • Deposition • Mineral Susceptibility • Diagenesis Sedimentary Environments • Marine – deep/shallow • Land – glacial/alluvial/desert • Transitional – delta/beach Maturity SEDIMENTARY ROCKS Sedimentary Structures • Bedding • Cross-bedding & graded bedding • Desiccation cracks • Ripple marks & sole marks • Textural maturity • Compositional maturity Sedimentary Rocks • Conglomerate & Breccia • Sandstones • Shale/siltstone/mudstone • Limestone/chalk/coal/halite/gypsum Fragmental Chemical & Biogenic

How can sedimentary rocks be classified? Coarse >2 mm Medium 0. 06 - 2 mm Fine <0. 06 mm (<63 µm) Grain Size Sediment Name Rock Name >256 mm 64 - 256 mm 4 - 64 mm 2 - 4 mm Boulders Cobbles Pebbles Granules Conglomerate (rounded fragments) Breccia (angular fragments) 1 – 2 mm 0. 5 – 1 mm 0. 25 – 0. 5 mm 0. 125 – 0. 25 mm 0. 06 – 0. 125 mm Very coarse sand Coarse sand Medium sand Fine sand Very fine sand Sandstone 4 µm – 63 µm <4 µm Silt Clay Siltstone Mudstone/Shale 1 µm = micrometer = 0. 001 mm • Arkose • Greywacke • Orthoquartzite • Desert sst

Summary - Classifying clastic sedimentary rocks Fragmental/Clastic Coarse Medium Fine Very Well Sorted Boulder >256 mm Cobble 64 - 256 mm Pebble 4 - 64 mm Granule 2 - 4 mm Very coarse 2 -1 mm Coarse 1 - 500 um Medium 500 - 250 um Fine 250 - 125 um Very fine 125 - 63 um Silt 63 - 4 um Siltstone Clay <4 um Mudstones/Shales Well Sorted Moderately Sorted Arkose Orthoquartzite Desert Sandstone Greywacke Poorly Sorted Rounded Sub-Angular Conglomerate Breccia-Conglomerate Breccia

Sediments to Rock 1. Define the following terms: • • • - unconsolidated material deposited by water, ice or wind Sediment Particle - in general language - a piece. Geological language, same as grain. Clast - a particle within a rock which has been broken off a pre-existing rock. Clastic - a group of sedimentary rocks composed of particles e. g. sandstone. Fragment - a large clast, usually of a rock (no definite size limit) Grain - a small clast, usually of a mineral (no definite size limit) 2. How long does it take to turn a sediment into a rock? - millions of years 3. The major assumption which underlies sedimentary rocks is the Principle of Uniformitarianism. What does this mean and why is an understanding of this principle crucial to making sense of sedimentary rocks 4. Draw the rock cycle.

Sedimentary Processes Weathering 4 agents of transportation: • Rivers • Sea Erosion • Wind • Ice Transportation Deposition 3 processes of weathering: • Physical • Chemical • Biological 5 processes of erosion: • Abrasion • Attrition • Hydraulic action • Cavitation • Plucking 3 processes of deposition: • Loss of energy • Accumulation of dead animals • Precipitation Lithification 2 processes of lithification: • Compaction • Cementation

Weathering Two main types of weathering were covered at AS. What are these, and what are the main products? 1. Physical weathering which produces rock and mineral fragments. 2. Chemical weathering which leads to the production of new minerals and products in solution.

Weathering • Describe what each type of weathering is? • Explain how it works? • What are the specific products of this weathering? Carbonation Hydrolysis Frost shattering Oxidation Exfoliation Salt crystallisation

Chemical Weathering Oxidation 4 Fe. Si. O 3 + O 2 2 Fe 2 O 3 + 4 Si. O 2 Carbonation CO 2 + H 2 O H 2 CO 3 + Ca. CO 3 Ca + 2 HCO 3 Hydrolysis Ca Na K ALSi. O + H 2 O Al. Si. O(OH) + K + Ca + Na + 2 HCO 3

Weathering If exposures of basalt, granite and orthoquartzite each underwent chemical weathering, explain which of the rock types would be likely to show a surface coating of iron oxide. Basalt & granite – they contain mafic minerals (augite, hornblende & biotite mica). Chemical weathering of these minerals releases Fe 2+ ions which are immediately oxidized to Fe 3+ and deposited as ferric oxide (rust). Quartzite – composed entirely of quartz & so has no mafic minerals.

Products of Weathering What sedimentary rocks would be formed?

Products of Weathering What sedimentary rocks would be formed?

Products of Weathering Original Mineral Feldspar KNa. Al. Si. O Ferromagnesian Fe. Mg. Si. O Muscovite mica KAl. Si. O Quartz Si. O Calcite Ca. CO 3 Chemical Weathering Process Hydrolysis Oxidation Hydrolysis Solid Product Clay Iron oxide Clay Soluble Product K, Na, Ca Si 0 K - Quartz grains - Carbonation - Ca

Susceptibility to Weathering ~1200°C Olivine Augite Plagioclase feldspar (Mg Fe) Si. O 2 Ca Mg Fe Si. O 2 Hornblende Plagioclase feldspar Ca Mg Si. O 2 Biotite mica Fe Mg K Al Si. O 2 Orthoclase feldspar Muscovite mica ~600°C Ca Al Si. O 2 Quartz Si. O 2 K Al Si. O 2 Na Al Si. O 2

Rates of Weathering 4 Fe. Si. O 3 + O 2 CO 2 + H 2 O Ca Na K ALSi. O + H 2 O 2 Fe 2 O 3 + 4 Si. O 2 H 2 CO 3 + Ca. CO 3 Ca + 2 HCO 3 Al. Si. O(OH) + K + Ca + Na + 2 HCO 3 Frost shattering/ freeze-thaw

Rates of Weathering Joints Faults Fractures Bedding planes Pore spaces Rock

Rates of Weathering Feldspar Ca. CO 3 Biotite mica Augite Quartz Feldspar

Rates of Weathering

Summary of Weathering 1. Why do rock outcrops disintegrate, leaving shattered fragments to accumulate on hill slopes? By physical weathering (frost shattering) – expansion of water on freezing in cracks & joints exerts pressure breaking rocks apart. 2. How can quartz minerals be extricated from the rocks from which they are derived ? Physical weathering (frost shattering) may have shattered rock into smaller fragments which were then attacked by chemical weathering. Then chemically less resistant minerals would have been decomposed, leaving a residue of chemically resistant quartz grains. . 3. Where does mud come from (i. e. the clay minerals that make up the muds we see in places like river estuaries)? Mud consists predominantly of clay minerals. These are the products of the chemical weathering of various Al-bearing minerals such as feldspar & mica.

The photograph below is a side view of an igneous body. Explain the features shown in the photograph [4] • Dolerite igneous body, with cooling joints and pressure release joints • Clay from the hydrolysis of plagioclase feldspar. • Red-brown staining due to oxidation of augite. • Spheroidal shapes due to preferential weathering along joints.

Triangular Graphs Q – 50% RF – 20% F – 30% 20% 30%

Triangular Graphs 3% Q – 68% RF – 3% F – 29% 68% 29%

Triangular Graphs Arkose Q – 40% F – 55% RF – 5%

Triangular Graphs ARKOSE

Maturity of Sedimentary Rocks Minerals in sedimentary rocks 1. Extent of chemical weathering 2. Type & amount of transportation Sandstone – 70% quartz & 30% orthoclase feldspar What can you tell about the chemical weathering experienced by the original rock? Not much chemical weathering because feldspar unweathered.

Maturity of Sedimentary Rocks Compositionally Immature • undecomposed rock fragments • feldspar • ferromagnesian minerals Compositionally Mature • quartz • clay minerals End products of chemical weathering Compositional maturity describes ……… … the amount of weathering a sediment has suffered.

Maturity of Sedimentary Rocks Examine Rock Specimen B by hand & hand lens: • There is more than 1 mineral present What minerals are they? What are their relative proportions in the rock? Explain how you made your identification Examine picture of RS B through the microscope. Draw & label a sketch of the rock to show the minerals. How compositionally mature would you say this rock is? • Repeat these stages for Rock Specimen G

Rock Specimen B

Rock Specimen G

Maturity of Sedimentary Rocks What is Rock B? Rock Specimen B: Mineral 1 – quartz (~75%) Arkose • grey • glassy • not scratched by steel blade Mineral 2 – feldspar (~25%) • rectangular • white or pink • white powder Rock B is compositionally immature because there is a high proportion of feldspar.

Maturity of Sedimentary Rocks Rock Specimen G: • Minerals too small to be seen by eye or a hand lens. • Grey colour • Scratched easily Mineral 1 - clay What is Rock G? Mudstone Rock G is compositionally mature because there is a high proportion of clay.

Maturity of Sedimentary Rocks

Maturity of Sedimentary Rocks 1 mm

Maturity of Sedimentary Rocks Texturally Immature • sub-rounded • poorly sorted • large grains Texturally Mature • well rounded • well sorted • small grain size Textural maturity describes ……… …. the time and distance a sediment has been transported.

Maturity of Sedimentary Rocks Minerals in sedimentary rocks 1. Extent of chemical weathering 2. Type & amount of transportation Medium-grained, moderately sorted & sub-rounded Texturally immature 70% quartz & 30% orthoclase feldspar Compositionally immature What can you tell about the chemical weathering experienced by the original rock and the following sediment transport?

What can you tell about the chemical weathering experienced by the original rock and the following sediment transport? Medium-grained, moderately sorted & sub-rounded Texturally immature Arkose 70% quartz & 30% orthoclase feldspar Compositionally immature The sediments forming this arkose have not undergone much chemical weathering, probably due to a lack of water. The sediments have also not been transported very far or for very long (suggests desert conditions? ).

Sediment Transportation What factors affect how much sediment can be transported? • turbulence • speed of flow • viscosity • density • grain size Predict how each of these characteristics will affect how much sediment is transported. Describe the characteristics of ice, wind & water in terms of the first 3 bullet points.

Sediment Transportation Sediment Entrainment & Deposition by Water

Sediment Transportation

Sediment Transportation

Sediment Transportation

Sediment Transportation

Summary of Sediment Transportation 1. Explain why water can transport larger particles than wind. 2. How do water and wind transport different sized particles? 3. Explain how sorting of sediments occurs when transported by water or wind. 4. Describe the shape & surface structure of material transported by water and wind. 5. Brainstorm a list of factors which can determine the transport history of a sedimentary rock.

1 mm = 1000 microns

Transport History & Environments of Deposition of Sedimentary Rocks 1. Lithology Texture Grain size • Energy levels • Distance transported Gravel or coarser = High & short Medium to coarse sands = Medium Fine sands, silts & clays = Low & long Coarse & fine = Fluctuating energy levels Grain shape • Type of transport • Distance transported Grain sorting • Type of transport • Time in transport Grain surface • Type of transport Fabric (relationship between the grains & the matrix) Grain-supported Matrix-supported Intensive reworking Common in tills, By waves/currents debris flows deposits

Transport History & Environments of Deposition of Sedimentary Rocks 1. Lithology Mineralogy Immature minerals Mature minerals Iron oxide

Sediments from solution Why is the sea salty? Why does the composition of seawater in the open oceans stay constant, instead of becoming ever more salty?

Classifying limestones by their grain types Examine Specimens H - K 1. Describe colour of grains & matrix 2. Relationship between grains & matrix (fabric) 3. Shapes of grains & estimate the size 4. Origin of grains 5. Sketch grains from microscope view on board 6. Biogenic limestone or chemical limestone

Specimen H

Specimen I

Specimen J

Specimen K

H Colour – grains Dark grey I J K Creamy-white Grey White Grain-supported Matrix-supported Shape Rounded/coiled Rounded Too varied Rounded Size 2 – 5 mm 0. 5 -1 mm 1 – 2 mm <0. 05 mm Fossils Ooids Fossils Coccoliths - matrix Pale grey Fabric Origin Sketch Quartz centre Concentrically layered Coccoliths Biogenic or chemical Biogenic Rock Name Shelly Limestone Oolitic Limestone Shelly Limestone Chalk Chemical Biogenic

Diagenesis Research the changes that occur when sediment is changed to rock p. 56 - 57. 1. Draw a flow diagram to show the processes involved in diagenesis. 2. Make notes on these processes.

Pressure dissolution is a process of compaction when quartz grains are progressively buried, the pressure at the grain contacts increases until the quartz begins to melt slightly and dissolve. Compaction is an important first step in lithification where the pressure of the overlying sediments packs the grains closer together and more efficiently, reducing the volume of pore space and squeezing out the pore water. Lithification is a diagenetic process in which loose, unconsolidated sediments in is converted into sedimentary rocks by compaction & cementation. Cementation is the second stage of lithification, and involves the gluing together of compacted grains to form a rock. Often compaction alone will not produce a lithified rock. Diagenesis the group of processes which change sediment into a sedimentary rock after deposition has occurred, because of this they are referred to as post-depositional processes. Mineral changes Mineral alignment Diagenesis often results in the formation of new minerals which grow in the sediment or sedimentary rock. is a process during compaction, where any elongated or flaky grains such as clay or mica will become aligned parallel to the bedding plain. This alignment of clay minerals may lead to mudstone and shales splitting easily into layers and being known as fissile.

Diagenesis the group of processes which change sediment into a sedimentary rock after deposition has occurred, because of this they are referred to as post-depositional processes. Lithification is a diagenetic process in which loose, unconsolidated sediments in is converted into sedimentary rocks by compaction & cementation. Compaction is an important first step in lithification where the pressure of the overlying sediments packs the grains closer together and more efficiently, reducing the volume of pore space and squeezing out the pore water. Cementation is the second stage of lithification, and involves the gluing together of compacted grains to form a rock. Often compaction alone will not produce a lithified rock. Pressure dissolution is a process of compaction when quartz grains are progressively buried, the pressure at the grain contacts increases until the quartz begins to melt slightly and dissolve. Mineral alignment is a process during compaction, where any elongated or flaky grains such as clay or mica will become aligned parallel to the bedding plain. This alignment of clay minerals may lead to mudstone and shales splitting easily into layers and being known as fissile. Mineral changes Diagenesis often results in the formation of new minerals which grow in the sediment or sedimentary rock.

Pressure dissolution

Indicators of particular climatic zones: Desert Environment Glacial Environment Tropical Shallow Marine Lithology, fossils & sedimentary structures describe a sedimentary facies.

Indicators of particular environments: Fluvial Environment Deltaic Environment Shallow Marine Deep Environment Marine Environment Lithology, fossils & sedimentary structures describe a sedimentary facies.

Sedimentary environments: • Alluvial • Deltaic • Desert • Glacial • Deep marine • Shallow marine Lithology Fossils Sedimentary Structures Lithology, fossils & sedimentary structures describe a sedimentary facies.

Backshore Zone Foreshore Zone Shoreface Zone Offshore Transition Zone Offshore Zone ROCESSES STRUCTURES FOSSILS MINERALOGY TEXTURE Mean high tide • very well sorted • very well rounded • fine-medium sand • frosted grains • well sorted • well rounded • medium-coarse sand • well sorted or • well rounded • coarse pebbles • fine-medium • glassy grains sand • glassy grains • quartz • rock fragments • rootlets • trace fossils (worm burrows) • fragments of shells • asymmetrical dunes • cross-stratification • aeolian (wind) • medium energy Mean low tide Fairweather wave-base • well sorted • well rounded • fine silt Storm wave-base • very well sorted • fine silt & clay • silt • clay • quartz • silt • trace fossils (worm burrows) • some fragments of shells (b, b, g) • trace fossils (worm burrows) • no fragments • bivalves, brachiopods, gastropods • some wave-formed ripples • wave ripples • hummock & basins • planar stratification • chevron cross- • hummocky cross • chevron cross-stratification • breaking waves (water) • fairweather waves • storm waves only • high energy • medium energy • low energy • lamination • flocculation • very low energy

Backshore Foreshore Shoreface Offshore transition zone Offshore Dune Beach

Discuss the extent to which the occurrence of greywackes and their sedimentary structures, interbedded with black graptolitic shales, indicates that parts of Britain once experienced deep-water marine conditions. (25 marks)

Greywackes description: texture/mineralogy turbidites/bottom of continental slope "any" environment/ rapid deposition Black anaerobic/lack of oxygen -deep water/ocean floor could be shallow(er) – just lack of oxygen Graptolitic pelagic/fragile/pyritisation -float into deeper waters/lack scavengers/weathering/erosion found in deposits of all depths extinct – problematic preservation/shale key feature Shales fine-grained / travel distance/sorting -no current any depth Sedimentary structures grading description: fining upwards/rapid deposition from turbidity currents (Any valid sedimentary structure with context e. g. current bedding; bottom structures etc. ) Early Palaeozoic age for deep water as indicated by graptolites = zone fossils Allow "negatives" e. g. lack of brachiopods, corals, trilobites, limestones etc, etc. Total 25

Sedimentary Structures

Sedimentary Structures

Sedimentary Structures

Sedimentary Structures

Sedimentary Structures

Sedimentary Structures

Sedimentary Structures

Sedimentary Structures • Laminations • Bedding • Graded Bedding • Cross Bedding • Desiccation Cracks • Sole Marks • Ripple Marks

Sedimentary Environments 1. Continental Environments 2. Transitional Environments 3. Marine Environments

Continental Environments Channel Aeolian/Desert Point bar

Transitional Environments

Marine Environments