9.4 - Fluvial, Lacustrine, Karst, and Caves PDF

Fluvial Environment Del Rosario, CCE u dominated by running water u Mostly concerned with rivers and its surroundings Mountain headwater streams f low swiftly down steep slopes and cut a deep v -sh ap ed vall ey. Rapids and waterfalls are commo . Low-e levation streams merge and flow down gen...

Fluvial Environment Del Rosario, CCE u dominated by running water u Mostly concerned with rivers and its surroundings Mountain headwater streams f low swiftly down steep slopes and cut a deep v -sh ap ed vall ey. Rapids and waterfalls are commo . Low-e levation streams merge and flow down gentler slopes. The val ley broadens and the river eg ins to eander. At an even lower eleva1ion a river wanders and meanders slowly across a broad, nearly flat valley. At its mouth it may divide into many separate channels a~ it flows across a delta built up of river- borne sediments and into thE! sE!a . Adapted from: Vinarao, C. T (2018) Types of river channels: u Straight u Anastomosing u Meandering u Braided Channel type varies with slope and river discharge, and there could be transitional phases in between types anastomosi ng meandering ----- c::::> straight braided (after Miall 1977 Straight Rivers u Constrained u Rare and unstable. http://www.seddepseq.co.uk/depositional_env/ Fluvial/Fluvial.htm Anastomosing Rivers u Anastomosing channel systems are characterized by two or more channels with high channel stability, but not channels filled with shifting mid-channel bars; u Stable compared to braided channels, but subject to frequent avulsions – river jumps between a few used and unused, but well-defined channels. u Often developed in well vegetated settings with gravel beds. http://www.seddepseq.co.uk/depositional_env/ Fluvial/Fluvial.htm Meandering Rivers u single thread channel, sinuous plan form, point bars in each bend. u Moderate width-to-depth ratios, cohesive banks, associated with levees, and fine-grained floodplain sediments. u Transport material both as suspended and bed load u Normally form in coastal plains u Has regular pattern of flow http://www.seddepseq.co.uk/depositional_env/ Fluvial/Fluvial.htm Meandering Rivers F lo o d p la in Crevas se splay Cut b a nk -~ -..-~ :: . . . ... ,.._ M, .i. . . . .. Lateral accreti on ~ ... I \ \ '\ .; Cha Overba nk deposit s nnel d e http://www.seddepseq.co.uk/depositional_env/ p o s it Fluvial/Fluvial.htm Braided Rivers u Multiple-thread channels, dominated by mid channel bars u Large width-to-depth ratios, very unstable with frequent lateral shifts. u Often totally re-arranged by large floods, no levees, non-cohesive banks. http://www.seddepseq.co.uk/depositional_env/ Fluvial/Fluvial.htm Braided Rivers tated \/ege bars iorrner f\00 dplain o.llid-Ch ann iv• bars bani< over ·ts depos1 Channe \ de Posit http://www.seddepseq.co.uk/depositional_env/ Fluvial/Fluvial.htm sar ~aces su1, Sediment transport in rivers Sediment transported by rivers may vary with its: u Channel type u Rate of flow u Discharge u Most sediments are carried by flow in the channel, then deposited as leeves when the rivers flood (overbank deposits), being deposited either on sides of the channel or in bars in between. Meandering River deposits u FINING UPWARD u Fine grained overbank deposits cap the sandy channel succession u Better sorting u Composed mostly of sand and mud u Shows general upward decrease in energy floodplain Point bar top Point bar Channel floor Adapted from: Vinarao, C. T (2018) Braided River deposits u COARSENING UPWARD u Bed-load dominated u Mostly stacked braid bar sands and gravels u Braid bar conglomerates have imbricated clasts which indicates flow direction floodplain Stacked braid bars Channel floor (after Cant and Walker 1976) Adapted from: Vinarao, C. T (2018) Lacustrine Environment Factors controlling sedimentation u Lake size u Closed basin vs. open basin u Water chemistry u Amount of sediment entering the basin u Latitude (seasonality) u Shape of basin (shallow vs. deep) u Regional tectonics u Water temperature u Wind Types of lakes u Freshwater lakes- low salinity, low rate of dissolved ions, and can either be hydrologically open or closed. u Saline lakes- high salinity; dissolved ions became concentrated due to evaporation, and is hydrologically closed. u Ephemeral lakes- mainly occurs in arid regions; temporary bodies of water created due to rainstorms on catchment areas and exist for only a few months or years. Layers of a lake Sediment input from river ....... Warm , buoyant wate r Overflow (low density) Fine sediment deposited from suspension Lake surface Oxic Thermocline - - - -~ - - - - - - -- - - - - - - - T - -, - : : : I I I I Underflow {high density) Sediment deposited as turbidite - -,- --,- - y y : - Epilimnion • Warm r - -r - - T- - : : : : : : Hypolimnion • Col d I I I I I I ' : -,- - -,- - -,-- - .-- - - - - - -- - - - - - -- - - 1 ' ' y ' y • Anoxic Cold, dense water Fig. 10.3 The thermal stratification of fresh lake\ ater resuJts in a more oxic, upper layer, the epilimnion, and a oolder, anoxic lower layer, the hypolinm.ion. Sedimentation in the lake is controlled by this density stratification above and below the thermodine. Adapted from: Vinarao, C. T (2018) Sed mentat on mech an1sms 1n a therm,ally strat1f1ed lak e 1 1 1 Ba:sin 1 Lacustrine Deposits Characteristics of lake deposits: u Moderately well sorted sandstones, mudstone, fine grained limestones, and evaporites u Often thin-bedded u Presents wave ripples and fine parallel lamination u Some deposits may contain fossils of algal organisms or uncommon shells u May be deep dark in color, especially for deep lake sediments Lacustrine facies u Epilimnic Facies: Oxygenated lake facies Coarse -groined pebbly sandstone, erosively based m (.) Display evidences of wave or current process Occasionally pervasive bioturbation & plant fossils -15 z ~ ...J u Hypolimnic Facies t---::-c--'--:::,--,----...,...,..;.i t=::::z::::::::::::.:e::::::!::f Silt y shale and Cl. fine-gro ined sandstone 0,5 to 7% roe UJ Finely-laminated terrigenous biogenic and authigenic materials - J:~ 7 ':::._'l::._-:::_r-.;:;c-.~-::i-c:....,-::..-1:::t Laminated block mudstone with organic bonds, mica and windblown quartz 21010 % (.) Ephemeral facies roe Dessication cracks, evaporites Reflects climatically controlled changes in depth and extent Carbonate bonds Silty shale Occasionally turbidite sands u Sandy si It stone with plant debr is 5 Massive mudstone with algal bonds, ostracod layers fi:I::::z::::::z:::::=l and micrit ic -=---=-===---= limestone ...J 0 Cl. >J: u Lake-shore facies Represents shallow or ramped margins Laminated block mudstone 0 Adapted from: Vinarao, C. T (2018) References u Vinarao, C. T. (2018). Stratigraphy, Fluvial and Alluvial Environment, Lacustrine Environment, (Power Point Presentation), Adamson University, Ermita, Manila, PH u Fluvial Environments, http://www.seddepseq.co.uk/depositional_env/Fluvial/Fluvial. htm u Sedimentary Environments, Fluvial Environments, http://www.thisoldearth.net/Geology_Online1_Subchapters.cfm?Chapter=5&Row=4 u Lacustrine Environment, https://landscape.soilweb.ca/lacustrine-environment/ CLIMATIC CONDITIONS polar regions cool-humid sub-humid, sub-arid deserts tropical rainforest lack karst well-delveloped karst karst is inhibited not karst-prone well-delveloped karst REFERENCES: Lutgensi Fi Tarbuck E. (2012). Essentials of Geology. Atienza, J (2017). Karst Topography [Powerpoint Presentation].