Sedimentary Environments PDF

18/04/2024 Sedimentary Environments 1  18/04/2024 Sedimentary Environments A geographic setting where sediment is accumulating and/or erosion occurs; Physically chemically and bio...

18/04/2024 Sedimentary Environments 1  18/04/2024 Sedimentary Environments A geographic setting where sediment is accumulating and/or erosion occurs; Physically chemically and biologically distinct from adjacent terrane Differentiated using their properties: Physical : geology, geomorphology, climate, temperature and depth (marine) Chemical : salinity, O 2 content Biological : fauna and flora Sedimentary Environments 2  18/04/2024 Braided Fluvial Meandering Lacustrine Continental Aeolian or Terrestrial Glacial Lobate Terrigenous Transitional Mixed carbonate: (Shorelines) terrigenous Linear Carbonate Reef Shelf Marine Submarine channel & fan Pelagic Classification of Major Depositional Environments Sedimentary Facies A mass of sedimentary rock which can be distinguished from others having the same age in terms of geometry, lithology, sedimetary structure, paleocurrent pattern and fossil content (Selley, 1970) 3  18/04/2024 How to recognize the environment Geometry a function of pre-depositional topography, geomorphology and its post-depositional history Fan-shape of an alluvial fan, triangular shape of deltas How to recognize the environment Lithology parameters easily observed and has environmental significance grain size, sorting, shape, and texture often reflect process of the environment Sand deposits of desert environments vs. silt- to clay-sized sediments of lake environments 4  18/04/2024 How to recognize the environment Sedimentary Structures important indicators of sedimentary environment Cross-bedding for river (fluvial) environments How to recognize the environment one of the most important tools in identifying the depositional environment two assumptions are made: the fossil lived in the place where it was buried Iguanadon tracks at Dinosaur Ridge, the habitat of the fossil can be Colorado deduced either from its morphology or from studying its living descendants (if there are any) Trace fossils are useful: they occur in situ (cannot be reworked) some trace fossils characterize particular environments Coral fossils and bioturbation 5  18/04/2024 Sedimentary Environments Fluvial Drainage Basin (a.k.a Watershed) fundamental geomorphological unit within which precipitation is transferred to the sea, lake or larger river 6  18/04/2024 Fluvial Stream – a water flowing through a channel; River – stream that carry substantial amounts of water and have numerous tributaries. (tributaries vs distributaries) Tributary (small creek or river that runs into a larger one) Mouth (empties into lake or ocean often forms a delta with extensive wetlands) 7  18/04/2024 Fluvial Base level – lowest elevation to which a river can erode its channel = to the level at which the mouth of a stream enters its ultimate base level- the ocean, or temporary base levels such as a lake, or a trunk stream; Knickpoint – a point of sudden change in channel slope (e.g. water falls because of resistamt rock type) Graded stream - has the necessary slope to maintain the minimum velocity required to transport the material 8  18/04/2024 Fluvial Graded stream - has the necessary slope to maintain the minimum velocity required to transport the material Fluvial Shaping stream valleys: a. Valley deepening – when stream’s gradient is steep and channel is above base level (=rapids and waterfalls) 9  18/04/2024 Fluvial Shaping stream valleys: b. Valley widening – when stream approaches graded condition, energy is directed side to side (= erosional floodplain – a broad valley of alluvium) Shaping stream valleys: C. Incised meanders & stream terraces: valley widening phase → uplift or base lvl decreased Fluvial 10  18/04/2024 Fluvial 11  18/04/2024 Fluvial Meandering streams – streams that move in sweeping bends on deep and smooth channels while carrying most of their load (mostly mud sized to fine gravel) as suspension Meandering streams 12  18/04/2024 Oxbow lake formation Fluvial Evolution from point bars & cut banks to oxbow lakes & cutoffs 13  18/04/2024 Fluvial Flood plains – low lying areas along the sides of a river that during regular times of heavy water flow can be flooded by spill over from the river Fluvial Natural levees – levees that parallel their channel on both banks built by years of successive floods Bankswamps and Yazoo tributary 14  18/04/2024 Candon, Ilocos Sur Pampanga river 15  18/04/2024 Fluvial Braided streams – streams that flow on complexly networked diverging/converging channels. Stream’s load- coarse material (sand and gravel) with a highly variable discharge. elongate structures where coarse sediments are deposited during periods of low discharge. 16  18/04/2024 Fluvial Braided streams Abra River, Ilocos Sur Bucao River, Botolan, Zambales 17  18/04/2024 Fluvial Drainage Patterns – response of the drainage system to the type of material and structures (folds, faults and fractures) present in an area. DENDRITIC Uniform underlying bedrock Drainage Igneous rocksPatterns Flat-lying sedimentary rocks Most common drainage pattern on all scales. Determined by direction of slope of land RECTANGULAR Common in faulted or fractured igneous rock Often control pattern of streams Guides directions of valleys 18  18/04/2024 TRELLIS Most common in tilted and folded sedimentary or metamorphic rocks Formed by alternating less resistant and resistant layers. e.g. Appalachians RADIAL Develops in isolated volcanic cones and domal uplifts Often localized. earth.jsc.nasa.gov/sseop/images/EFS/lowres/STS068/STS068-253-7.jpg www.proprofs.com/quiz-school/upload/yuiupload/1226500853.jpg Kazakhstan Alluvial fans fan-shaped deposits that accumulate along steep mountain fronts; prevalent in mountainous & arid regions; As mountain stream emerge onto a relatively flat low-land, gradient drops & a large portion of sediment load is deposited. Bajada – coalescing alluvial fans 19  18/04/2024 Alluvial fans Alluvium: freshly eroded sediments carried by streams (coarse sediments) usually sandstone and conglomerate poor sorting, grading Map cone-shaped x-section Alluvial fans Sibuyan Island Laur, Nueva Ecija 20  18/04/2024 Lacustrine Lake - landlocked body of standing, non-marine water; ephemeral; excluding small ponds/ puddles Lacustrine 21  18/04/2024 Some “seas” that are actually lakes Tectonic Setting Lakes originate through: subsidence of land isolation of a part of the ocean, either by local constructive processes of sediment deposition or by crustal uplift glacial erosion and deposition on the continents volcanoes -pyroclastic damming, crater collapse(caldera) through eruption or tectonic processes damming by landslides meteorite impacts 22 18/04/2024 23  18/04/2024 Tectonic lakes Tectonic lakes 24  18/04/2024 Lacustrine circular or elongate in plan view; lenticular in cross section Sediment sorting? Oxic and anoxic conditions? Typical sequence - coarsening upward from laminated shales, marls, and limestones to crossbeds of sandstones Quiet waters, energy: low, sedimentation: relatively slow Mud-sized sediments: laminated (beds snow melt in summer note, that movement is fastest at the center Basal slip Plastic flow Piggy back (cracks → crevasses) Glacial Valley (Alpine) Glaciers: high elevation mountain tops, occupy valleys as stream of ice bounded by steep rock walls; valley glaciers can be long or short, wide or narrow, single or branching tributaries Continental Ice Sheets: larger scale than valley glaciers (Greenland and Antartic); occupies 10% of Earth’s land area Ice shelves: extensions of ice sheets on the adjacent ocean 32  18/04/2024 Glacial Glacial erosion Plucking - loosening and lifting sediments of all sizes; when ice melts, it leaves unsorted sediments generally called glacial drift Glacial Glacial erosion Abrasion - like a sandpaper which smoothen the interface; if glacier carries rock fragments → glacial striations 33 18/04/2024 34  18/04/2024 Glacial Glacial deposition: Moraines: ridges of till; Some are common only to mountain valleys (lateral and medial); others are associated with areas affected by ice sheets or valley glaciers (end and ground moraines). Glacial 35  18/04/2024 Glacial Glacial deposition a.Till (tillite when lithified)– materials deposited directly by glacier; polished and scratched; if boulders in the till or lying free: glacial erratics (poorly sorted) b.Stratified drift – glacial meltwater; well sorted acc. to size (fluvial-like but clasts are polished) Sedimentary Environments 36  18/04/2024 Transitional Progradation – sediments advance towards the sea Retrogradation – sediments retreats away from the sea Transgression – landward migration of sea level Regression – seaward migration of sea level Delta - prograding depositional bodies that form at the point where a river deposits in a lake or sea. - similar morphology to an alluvial fan but deposition results from sharp reduction in velocity as a stream enters standing water / ocean 37  18/04/2024 Delta Types of Deltas A. River dominated (a.k.a birdfoot delta) large sediment volume lobate shape when moderate sediment supply elongated when sediment supply is large B. Tide dominated linear features parallel to tidal flow and perpendicular to shore (sand bars) C. Wave dominated smoothly arcuate; wave action reworks sediment. much sandier than the other types of delta; beach ridges Wave-dominated delta (Nile River) River-dominated delta (Mississippi River) Tide-dominated delta (Colorado River) 38 18/04/2024 39  18/04/2024 Beach Environment Beach – accumulation of sediment found along the landward margin of the ocean Shoreline –contact between land and sea Shore – area that extends between the lowest tide level and the highest elevation on land affected by storm waves 40  18/04/2024 Beach Environment Sandy or pebbly material Well sorted sand and pebbles either from terrestrial (e.g. volcanic fragments) or from the sea floor (e.g. corals), smoothened and rounded by wave action http://www.sandatlas.org/heavy-minerals/ http://www.neatorama.com/2011/01/11/sand-collection-up-close/ 41  18/04/2024 Beach Environment Wave erosion Wave Refraction – bending of waves; distribution of energy along shore since most waves travel toward the shore at an angle. Wave impact is concentrated against the sides and ends of headlands (landmasses extending to the sea) and weakened at bays (body of water partly enclosed by land and has a wide opening) 42 18/04/2024 43  18/04/2024 Beach Environment Longshore transport Longshore current: turbulent currents moving at an angle picks up sediments (back swash) and then deposit them (swash). Longshore drift: the movement of sediment along a beach by swash and backwash of waves that approach the shore obliquely 44  18/04/2024 Marine 45  18/04/2024 Beach Environment Spit long ridge of sand deposited by longshore current and drift; attached to land at upstream end. Tombolo a sand or gravel bar that connects an island with the mainland or another island. 46  18/04/2024 Beach Environment Sea-level Rise 47  18/04/2024 Seasonal variations Lagoon Shallow salt water body separated from the deeper sea by sandbar (exposed and submerged) or coral reef Quiet waters: fine silt and clays to mudstones and shales Overgrown with vegetation forming salt marshes, coal, peat swamps, algal mats or even evaporites 48  18/04/2024 Tidal flats / mud flats Coastal wetlands found in sheltered areas such as bays, lagoons and estuaries; affected by high and low tide water levels Low energy with little fauna and flora (because of changing salinity) Marine Continental Margins – Shallow-water areas close to shore – Shelf, slope and rise – ~15% of ocean floor Deep-ocean basins – Deep water-areas farther from land Mid-ocean ridge – Submarine mountain range 49  18/04/2024 Shallow marine Continental shelf Continuous with the coastal plain; part of the continental margin that is between the shoreline and the continental slope Shallow marine Continental shelf: Reef Environment Coral Reefs - composed of carbonate structures formed by carbonate secreting organisms; builds up on continental shelves. Types of Reefs a. Fringing Reef coral reef that is directly attached or borders the shore of an island or continent. b. Barrier Reefs long narrow coral reef parallel to shore and separated by lagoon c. Atoll continuous or broken circle of coral reef and low coral islands surrounding a central lagoon. 50  18/04/2024 Shallow marine 51  18/04/2024 Deep marine Continental Slope between the continental shelf continental rise (oceanic trench); sedimentation is low 52  18/04/2024 Deep marine Carbonate compensation depth depth at which CaCO3 dissolution >= CaCO3 precipitation below CCD: little to no carbonates Deep marine Continental Rise gentle incline and generally smooth topography; between continental slope and abyssal plain may be cut by submarine canyons turbiditic deposits – chaotic deposits of debris from shallow environments Abyssal plains Pelagic: the ocean floor Fine-grained limestones, cherts, volcanic materials e.g. pillow lavas from submarine volcanoes Covered with pelagic mud with fine sand from distal turbidites 53  18/04/2024 Deep marine Seamounts – undersea volcanoes Guyots – tablemounts, rose above sea level in the past then eroded to a flat top by waves If above sea level: volcanic islands http://plate-tectonic.narod.ru/taneya_p ers.jpg TERRESTRIAL SEDIMENTARY ENVIRONMENTS ALLUVIAL FAN FLUVIAL LACUSTRINE DESERT (DUNES) PALUDAL Rock Type Breccia, Conglomerate Siltstone, Quartz arenite (sandstone) Peat, coal, conglomerate, sandstone shale, limestone, or gypsum black shale, arkose, siltstone, shale or evaporites (gypsum) siltstone Composition Terrigenous Terrigenous Terrigenous, carbonate, Terrigenous or Terrigenous or evaporite evaporite Color Brown or red Brown or red Black, brown, Yellow, red, Black, gray, Grain Size Clay to gravel Clay to gravel Clay to silt or sand Sand Clay to silt (Fining upward) (Coarsening upward) Grain Shape Angular Rounded to --- Rounded --- angular Sorting Poor Variable Variable Good Variable Inorganic Cross-bedding Asymmetrical Symmetrical ripples, Cross-bedding Laminated to Sedimentary ripples, Structures graded bedding cross-bedding, lamination, cross-bedding, massive graded bedding, graded bedding, tool marks mudcracks, raindrop prints Organic or --- Tracks, trails, Tracks, trails, burrows, Tracks, trails Root marks, Biogenic burrows rare stromatolites burrows Sedimentary Structures Fossils --- Rare freshwater Freshwater shells, --- Plant fossils, shells, shells, bones, fish, bones, rare freshwater bones, plant fragments plant fragments 54  18/04/2024 TRANSITIONAL SEDIMENTARY ENVIRONMENTS DELTA BARRIER BEACH LAGOON TIDAL FLAT Rock Type Sandstone, siltstone, Quartz arenite, coquina Siltstone, shale, limestone, Siltstone, shale, shale, coal oolitic limestone or gypsum calcilutite, dolostone or gypsum Composition Terrigenous Terrigenous or carbonate Terrigenous, carbonate, Terrigenous, carbonate, or evaporite or evaporite Color Brown, black, White to tan Dark gray to bl ack Gray, brown, tan gray, green, red Grain Size Clay to sand Sand Clay to silt Clay to silt (Coarsening upward) Grain Shape --- Rounded to angular --- --- Sorting Poor Good Poor Variable Inorganic Cross-bedding, Cross-bedding, Lamination, ripples, Lamination, mudcracks, Sedimentary graded bedding symmetrical ripples cross-bedding ripples, cross-bedding Structures Organic or Trails, burrows Tracks, trails, burrows Trails, burrows Stromatolites, Biogenic trails, tracks, Sedimentary burrows Structures Fossils Plant fragments, shells Marine shells Marine shells Marine shells MARINE SEDIMENTARY ENVIRONMENTS REEF CONTINENTAL SHELF CONTINENTAL SLOPE & RISE ABYSSAL PLAIN Rock Type Fossiliferous Sandstone, shale, siltstone, Litharenite, siltstone, and sh ale Shale, chert, limestone fossiliferous limestone, (or limestone) micrite, chalk, oolitic limestone diatomite Composition Carbonate Terrigenous or carbonate Terrigenous or carbonate Terrigeno us or carbonate Color Gray to white Gray to brown Gray, green, brown Black, white red Grain Size Variable, frameworks, Clay to sand Clay few to no grains Grain Shape --- --- --- --- Sorting --- Poor to good Poor Good Inorganic --- Lamination, Graded bedding, cross-bedding, Lami nation Sedimentary cross-bedding lamination, flute marks, tool marks Structures (turbidites) Organic or --- Trails, burrows Trails, burrows Trails, Biogenic burrows Sedimentary Structures Fossils Corals, marine shells Marine shells Marine shells, rare plant fragments Marine shells (mostly microscopic) 55