UNIVERSITY OF SOUTH ALABAMA Last time we covered 1 Types of Sediment 2 Sedimentary Rock Classification 3 Sediment Transport GY 111 Physical Geology Lecture 15 Sedimentary Environments 1 Alluvial Fans Rivers Deltas Types of Sedimentary Rocks Classification of Sediment and Sedimentary Rocks Siliciclastic Rock Name 1 siliciclastic 2 biochemical 3 chemical 4 organic Classification of Sediment and Sedimentary Rocks Sedimentary Rocks Four distinct classes 1 Siliciclastic 2 Biochemical 3 Chemical 4 Organic 1 Sediment Transport Bed load sediment sand and gravel transported along the bed of a river Suspended load sediment clay and silt transported within the water column of a river Solute load dissolved minerals transported in a river Today s Agenda 1 Depositional Environments in general 2 Alluvial fans and their rocks 3 Meandering Rivers 4 Deltas Web notes 15a Alluvial Fans Web notes 15b Rivers and Deltas Lab Manual Chapter 3 Depositional Environments Depositional Environments Depositional or sedimentary environments Places where sediment is deposited i e sediment sinks Depositional or sedimentary environments Places where sediment is deposited i e sediment sinks They are numerous Sedimentologists study sedimentary rocks to reconstruct past environments of deposition Depositional Environments Depositional or sedimentary environments Places where sediment is deposited i e sediment sinks They are numerous Alluvial Fans Fan shaped deposits of siliciclastic sediment deposited at the base of mountains Sedimentologists study sedimentary rocks to reconstruct past environments of deposition 2 Alluvial Fans Alluvial Fans Fan shaped deposits of siliciclastic sediment deposited at the base of mountains Gravel to clay sized Angular to sub rounded immature 1 km Alluvial Fans Alluvial Fans 1 km 1 km Alluvial Fans Alluvial Fans Fan head 1 km 1 km 3 Alluvial Fans Fan head Alluvial Fans mid fan Fan head mid fan Fan toe 1 km Alluvial Fans 1 km Alluvial Fans Alluvial plain Fan head mid fan Fan toe 1 km Alluvial Fans 1 km Alluvial Fans ie grad 1 km nt 1 km 4 Alluvial Fans Alluvial Fans wind ient grad 1 km Alluvial Fans 2 km Alluvial Fans 2 km Alluvial Fans 2 km Alluvial Fans 2 km 2 km 5 Alluvial Fans view from the top Alluvial Fans Best developed in arid regions Alluvial Fans Alluvial Fans Best developed in arid regions Best developed in arid regions Best developed in tectonically active areas Best developed in tectonically active areas From Walker R G 1980 Facies Models Geological Association of Canada Alluvial Fans Alluvial Fans Best developed in arid regions Best developed in arid regions Best developed in tectonically active areas Best developed in tectonically active areas Formed primarily through the action of water flow From Walker R G 1980 Facies Models Geological Association of Canada Lateral fining 6 Alluvial Fans Walker R G and James N P 1992 Facies Models Response to Sea Level Change Geological Association of Canada 409p Alluvial Fans Best developed in arid regions Best developed in tectonically active areas Formed primarily through the action of water flow but there are also landslide deposits mass flow Alluvial Fans sedimentary sections Walker R G and James N P 1992 Facies Models Response to Sea Level Change Geological Association of Canada 409p Alluvial Fans breccia arkose Red shale Nemec W and Steel R J 1984 Alluvial and coastal conglomerates their significant features and some comments on gravelly mass flow deposits In Koster E H and Steel R eds Sedimentology of Gravels and Conglomerates Canadian Society of Petroleum Geologists Mem 10 1 31 GY 344 Lect 14 p 46 Types of Rivers Alluvial Fans sedimentary sections Interbedded brecccia arkose beds Braided Nemec W and Steel R J 1984 Alluvial and coastal conglomerates their significant features and some comments on gravelly mass flow deposits In Koster E H and Steel R eds Sedimentology of Gravels and Conglomerates Canadian Society of Petroleum Geologists Mem 10 1 31 Anastamosing Meandering Walker R G and James N P 1992 Facies Models Response to Sea Level Change Geological Association of Canada 409p GY 344 Lect 14 p 47 7 Meandering Rivers Sinuous single channel drainage systems Meandering Rivers Meandering Rivers Are characterized by a distinct suite of facies and processes Meandering Rivers The channel meanders across the flood plain Oxbow lakes Levees Floodplains Cut banks Point bars Yazoo streams Cutoffs Meandering Rivers Sinuous single channel drainage systems Typically form on low gradient alluvial plains Deposition occurs on the inside of meander loops point bar Meandering Rivers Large point bars may consist of numerous accretionary ridges 8 Meandering Rivers Erosion occurs on the outside of meander loops cut bank Meandering Rivers Meandering Rivers Water velocity is greatest where the channel is deepest resulting in a corkscrew corkscrew flow pattern Meandering river channels are asymmetrical deepest near cut bank Meandering Rivers Vortices can be either singular or complex Either way it results in a sieving sieving action during point bar deposition http www geocities com sogodbay Images SDK Inecar03 jpg Meandering Rivers Sediment eroded from the cutbank is transported onto the point bar where the current is slower Deposition Meandering Rivers The bottom of the channel is frequently characterized by a channel lag of gravel and boulders conglomerate Erosion 9 Meandering Rivers Apart from deposition in channels rivers periodically flood resulting in sedimentation on flood plains Meandering Rivers Apart from deposition in channels rivers periodically flood resulting in sedimentation on flood plains Red shale http www fes uwaterloo ca geomatics images mississippi flood NASA jpg Deltas Deltas The first depositional environment described in the historical record Delta siliciclastic depositional environments formed at the point where rivers meet bodies of water http www tulane edu sanelson images delta gif Greeks Anthony when visiting the Egyptians Cleopatra noticed that the Nile flowed over a broad triangular shaped area before it flowed into the Mediterranean Sea http www sas upenn edu earth assets images photos GRLFig1 jpg Deltas Deltas This area resembled the Greek letter delta Deltas come in several different morphologies that are controlled by the interaction between 3 major processes 1 Wave Energy 2 Tidal Energy 3 River Input http www sas upenn edu earth assets images photos GRLFig1 jpg http clasticdetritus com category delta 10 Delta