Ch5_ Fluvial Depositional System

8/9/2019 Ch5_ Fluvial Depositional System

http://slidepdf.com/reader/full/ch5-fluvial-depositional-system 1/41

FLUVIAL DEPOSITIONAL SYSTEM

Fluvial sedimentation is primarily ontrolled !y t"e #luvial proesses$

mostly related to rivers% T"ree ma&or types o# #luvial sedimentation are

identi#ied'

Alluvial Fan Sedimentation

Alluvial Plain Sedimentation

Me(a#an Sedimentation



An alluvial fan is a fan shaped body of coarse grained sediments, formed bymountain stream at the base of a mountain front where a steeper slope

changes abruptly into a gentle slope.

Alluvial #an s"o)s t)o types o# deposits

1. Debris flow deposits

2. Water laid deposits (Stream channel, Sheet flood, Sieve

Alluvial Fan Sedimentation















Alluvial Plain Sedimentation Alluvial plains are vast areas formed by river channel activity, flood processes.

*iver +"annel Deposits

'ivers occur in straight, braided, meandering and anastomosing patterns.

n a river channel deposition ta)es place essentially as fluvial bars, which

are braid bars, point bars and lateral bars.

*ase of a river channel deposit shows a channel lag deposit followed by

fluvial bar deposits.

+luvial bar deposits are made up of mostly fining upward seuences,

showing from bottom towards top, large-scale cross-bedding, hori"ontal

bedding, small ripple bedding, silty hori"ontal bedding and mud.

Architectural element analysis is helpful in identification of nature of sand

bars. &icroforms (ripples, mesoforms (megaripples and macroforms (unit

bar are identified.























T"e ei("t !asi ar"itetural elements in #luvial

deposits% ,Miall -.//a$ !0 modi#ied #rom Maill -./1





























Me(a#an Sedimentation

Me(a#ans are lar(e4si5ed #ans #ormed in "umid limate !y lar(e rivers )it" "u(e

)ater and sediment supply% T"e #ans s"o) anastomosin( and diver(in( river

"annels )"i" &oin to(et"er at t"e distal end o# t"e me(a#an%

T"e me(a#an deposits s"o) a distint 5onation into #our 5ones #rom pro6imal todistal part%

Zone I

Area o# (ravelly$ s"allo) !raided "annels%

Zone II

Sandy !raid plain )it" many s"allo) "annels%Zone III

Area o# anastomosin( "annels%

Zone IV

Area o# meanderin( "annels )it" !road inter#luves%











Terminal #ans

In semi4arid limate )it" lo) (radient and lar(e sediment supply #ine4

(rained #ans are developed% In terminal #ans$ a6ial stream !ran"es

into small distri!utaries )"i" lose t"eir identity in lo)er #an% T"erivers an !e desri!ed as distributive river system% In t"e lo)er #an

area small )ater !odies and #e) ep"emeral streams are present%

Pro6imal part s"o)s mainly sandy deposit$ middle part s"o)s muddy

sediments )it" sandy lenses$ t"e lo)er part is made up o# muddy

sediments )it" rare t"in sandy "ori5ons%





Documents

Ch5_ Fluvial Depositional System