Sedimentary Structures Mud Cracks

1 Summary of common chemical sedimentary rocks nLimestone (organic and inorganic), coquina, and chalk nChert nEvaporites nCoal - today 2 8) Coal (organic) LIGNITE Soft, brown coal; moderate energy 3 Table 6.2 of textbook. Rocks to know 4 SEDIMENTARY ENVIRONMENTS MARINE AND CONTINENTAL 5 Transitional (shoreline) environments Tidal flats, Deltas, Estuaries 6 Grand Canyon 7 Sedimentary facies 8 Sedimentary structures nProvide information useful in the interpretation of Earth history 9 Beds of ripple marks 10 “fossil” ripple marks 11 Symmetrical and assymetrical ripples 12 Formation of cross beds 2) Cross-bedding Strata (beds) are inclined at an angle to the horizontal bedding plane 13 Environments in which ripple marks and cross bedding occurs nSand dunes in deserts and beaches nSandy ocean beaches nPoint bars in river channels 14 Cross bedding in ancient sand dunes 15 Graded Bedding 16 Graded beds Particle size varies from coarse to fine 17 Mud cracks 1 18 What sedimentary environment is represented by these fossil mud cracks? 19 Fossils: Evidence of past life nBy definition, fossils are the traces or remains of prehistoric life now preserved in rock 20 Some types of fossils nOriginal mineral matter nAltered e.g. original mineral replaced by another mineral nCasts and molds nFoot prints nTrails nBurrows 21 Spider preserved in amber 22 Natural casts of shelled invertebrates 23 Dinosaur footprint in limestone 24 Animal trail 25 Geologically fossils are important for several reasons nAid in interpretation of the geologic past nServe as important time indicators nAllow for correlation of rocks from different places 26 Example: Using interpretations of sedimentary environments and fossil assemblages to understand the ancient climate of Antarctica 27 Map of Antarctica 28 When did the major Ice sheets come into existence? 29 The effect of melting about 75% of the West Antarctic 2 Ice Sheet 30 Lat. 85°S on the Beardmore Glacier the Polar Plateau is on the horizon 31 Meyer Desert Formation glacial deposits of the Oliver Bluffs 32 Bedded sandstone and tillite outcrop 33 Soft-sediment fold in outwash sandstone 34 Thin parallel-bedded sediments indicate deposition in a lake. So how did the boulder get there? 35 Ice bergs from glaciers calving in a glacial lake in Patagonia, South America 36 Peat interbedded between thin marlstone beds 37 Fossil wood 38 Fossil Nothofagus (Southern Beech) leaf from a deciduous shrub 39 The branching tissue of a cushion plant. The plant was buried in its growth position by outwash. 40 Bolax gummifera – cushion plant from the alpine zone in southernmost South America 41 Fossil seeds of vascular plants. Most of the seeds are identified as Ranunculus species (buttercups) 42 Buttercup (Ranunculus pachyrrhizus) from the alpine zone in New Zealand 43 Freshwater molluscs represented by a species of the pill clam, Pisidium, and a species of lymnaeid gastropod (scale bar = 1 mm) 44 Fossil Weevil (Beetle) parts 45 Fossil fish tooth from the Meyer Desert Formation 46 Fjord in southwestern Greenland today = Antarctica before the expansion of the ice sheets! 47 Map of southern Chile and Argentina 48 Cushion heath and prostrate Nothofagus in the mountains of Isla Navarino, southern Chile. Growth season is 2-3 months with average temperatures of 4-5ºC. 49 Acknowledgement: Dr. Allan C. Ashworth 3.

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Sediment and Sedimentary Rocks
Sediment and sedimentary rocks • Sediment • From sediments to sedimentary rocks (transportation, deposition, preservation and lithification) • Types of sedimentary rocks (clastic, chemical and organic) • Sedimentary structures (bedding, cross-bedding, graded bedding, mud cracks, ripple marks) • Interpretation of sedimentary rocks Sediment • Sediment - loose, solid particles originating from: – Weathering and erosion of pre- existing rocks – Chemical precipitation from solution, including secretion by organisms in water Relationship to Earth’s Systems • Atmosphere – Most sediments produced by weathering in air – Sand and dust transported by wind • Hydrosphere – Water is a primary agent in sediment production, transportation, deposition, cementation, and formation of sedimentary rocks • Biosphere – Oil , the product of partial decay of organic materials , is found in sedimentary rocks Sediment • 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 From Sediment to Sedimentary Rock • Transportation – Movement of sediment away from its source, typically by water, wind, or ice – Rounding of particles occurs due to abrasion during transport – Sorting occurs as sediment is separated according to grain size by transport agents, especially running water – Sediment size decreases with increased transport distance From Sediment to Sedimentary Rock • Deposition – Settling and coming to rest of transported material – Accumulation of chemical
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Sedimentary Structures
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Sedimentary Structures & Palaeocurrent Analysis
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