Sedimentary Environment, Sedimentary Facies and Sedimentary Models. PDF

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Sedimentary Environment, Sedimentary Facies and Sedimentary Models DEEPCHAND V DEPARTMENT OF GEOLOGY UNIVERSITY OF KERALA [email protected] INTRODUCTION • Sedimentary Environment, Sedimentary Facies and Sedimentary Models are linked together DEPOSITIONAL SYSTEM approach to origin of sedimen...

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Sedimentary Environment, Sedimentary Facies and Sedimentary Models DEEPCHAND V DEPARTMENT OF GEOLOGY UNIVERSITY OF KERALA [email protected]

INTRODUCTION • Sedimentary Environment, Sedimentary Facies and Sedimentary Models are linked together DEPOSITIONAL SYSTEM approach to origin of sedimentary rock • Depositional environment Process • Facies Product (Sedimentary Rock) • Ancient Depositional environment of a SR compared with Modern Depositional environment

SEDIMENTARY ENVIRONMENTS • Modern Earth’s surface Laboratory of Geologists • Study of process of formation of sediments and resultant Deposits. • PRINCIPLE OF UNIFORMITARIANISM Present is the key to the past Number of Origin of ancient sedimentary rock PHYSIOGRAPHIC UNITS

GEOMORPHOLO GY OF EARTH

• • • •

LAND

OCEAN

Mountains Deserts Deltas Valleys

• Continental shelves • Submarine fans • Abyssal planes

physiographic types are finite dfv

SEDIMENTARY ENVIRONMENTS • From this observation it follows that the surface of the earth may be classified into different sedimentary realms or environments. • SEDIMENTARY ENVIRONMENT “Part of earth surface which is physically, Chemically and biologically distinct from adjacent areas” (Selley, 1970)

• Examples Sand desert, deltas, Sub marine fans etc.

SEDIMENTARY ENVIRONMENTS • PHYSICAL PARAMETERS OF SEDIMENTARY ENVIRONMENTS

VELOCITY DIRECTION VARIATION OF WIND WAVES FLOWING WATER WEATHER AND CLIMATE Temperature Rain and Snow Fall Humidity

SEDIMENTARY ENVIRONMENTS CHEMICAL PARAMETERS OF SEDIMENTARY ENVIRONMENTS • Composition of water that cover sedimentary environment • Geochemistry of the rock of the catchment area of terrestrial environment

SEDIMENTARY ENVIRONMENTS BIOLOGICAL PARAMETERS OF SEDIMENTARY ENVIRONMENTS • FLORA Land over grazing Increase the rate of erosion defoliation of one area and Increase the deforestation the rate of deposition in Over cultivation elsewhere • FAUNA Marine environment Presence of lowliest form of life and their skeletons contribute sediment formation presence of water changes equilibrium conditions and precipitate minerals e.g. carbonate rocks and organic reefs

Environments of erosion, equilibrium and deposition • Modern sedimentological research 1. Environments of Erosion 2. Environments of Equilibrium/Non deposition 3. Environments of Deposition Environments of Erosion Typically terrestrial Large mountain areas Weathering is intense Erosion is rapid Presence of local sedimentation by glacial, mud and flash floods local sedimentations are ephemeral

Soil profiles are develop on bed rock or sediment Also occur on cliffed coastlines and under sea Canyons and current scouring shelves are active regions Environment of deposition On both land and marine area The submarine areas dominated by deposition process than erosion 90% of world sedimentation on subaques environment 60% among this total volume composed of Submarine and Shoreline deposites Predominates subaqueous

Environment of Equilibrium

 Third category Occur in both land and marine “For a long period of time are neither sites of erosion nor of deposition” These site has high stability Environments experience intense Chemical alteration E.g. land Great peneplain of continental interior open to sky for million years  development of weathering profile and soil formation Laterite and Bauxite horizons Sea weak area of erosion and deposition react with sea water and formation of Manganese crusts, Phosphatisation and other diagenetic changes

Laterite horizon

A great piedmont

• Sedimentary geology primarily concerned with depositional environments • Make distinction and interpret depositional environment of ancient rocks • also preserve structures • Sediments + Fossils originated in erosional and equilibrium environment • They are continues with Depositional environment • E.g. An ancient river channel Cross bedding  Direction force depositing nature current composition + texture of sand source rock in erosional env fossilised tree trunk indicate env of equilibrium

ENVIRONMENTS CLASSIFIED

• Classification of sedimentary rocks in to various groups and sub groups • Based on detailed analysis of sedimentary environments

ENVIRONMENTS CLASSIFIED

• This classification has limited use in sedimentological studies • Reasons 1.limited number of significant environments rocks originated from spelean, glacial, abyssal environment are rare on earth 2.difficult to found depth of water in which marine deposits originated possible to equate position of sequence with respect to shore line but hard to equate with depth so classification of marine environment with depth hard to apply ancient sediments

Crosby’s classification • Crosby (1972) proposed a new useful classification • He studied modern environments and include many Minor sub environments in his classification • Also prepared classification of marine environments based on water depth water circulation energy level

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Classification of major depositional environments • Major depositional environments  1.quantitatively significant 2.can be apply to the study of ancient sediments

Major depositional environments

• Three major environments 1.continental 2.transitional (shoreline) 3.marine • No room for rare glacial and cave deposits in continental environments • Swamp deposits omitted and included to be sub environment of fluvial deposits • Shorelines are classified into lobate and linear. They are recognizable by estuaries of present day • Cliffed coastlines are omitted. They are environments of non deposition • Tidal flats, tidal channels,lagoons,salt marshes and barrier bars are considered to be sub group of deltaic environment.

• Shelf deposits can be recognized by lithology,paleantology,sedimentary features and structural settings • Reefs are part of carbonate environments but their significance in geologic column give them independent status • Submarine fan and channel environments produced by current activities • Pelagic deposits open sea deposits large fine grained chemical deposits argillaceous, calcareous or siliceous may great depth or distance from land

SEDIMENTARY FACIES • After examines sedimentary environments it is possible study about their ancient products. • 1815, William Smith “Geological map of England and Wales, with part of Scotland” • Based on sequence of strata in different rocks and different fossil assemblages • Stratigraphic palaeontology  some fossils appeared to restrict in certain geological time spans, but others long ranging but appeared to occur certain rocks • From this observation 1838,Prevost proposed “Formations” for lithostartigraphic units

SEDIMENTARY FACIES • Simultaneously 1838, Gressly coined “Facies” for rock units by lithological and palaeontological criteria. To began

• From ninetieth centaury onwards maps are prepared based on lithological and palaeontological criteria's • Rock units are called “Formation” or “Facies” by different geologists. • 1865, Lyell

SEDIMENTARY FACIES • Stratigraphic nomenclature of American commission on stratigraphic nomenclature. Definition of formation

• Paleogeography and tectonic situation of rock became parameters geosynclinals, orogenic and shelf facies come in to use • Krumbein lithofacies=variation in lithological aspects bio facies= variation in biological aspects tectofacies = laterally varying tectonic aspects

SEDIMENTARY FACIES • Facies applied to describe seismic data mounded, even and controlled to interpret sedimentary environments • Definition of sedimentary facies by Moore Sedimentary facies is defined an any restricted part of a designated stratigraphic unit which exhibits characters significally different from those of other parts of the unit

• Parameters of facies 1.geometry 2.lithology 3.paleontology 4.sedimentary structures 5.paleo currents

Difference between facies and environment

SEDIMENTARY MODELS • Sedimentary model is a tool for industrial and academic geologists • Sedimentary models help us to interpret and predict geologic data • Sedimentary models use both concepts of facies and environment • Sedimentary models are based on 2 observations and 1 interpretation to attain a conclusion

SEDIMENTARY MODELS • Observation 1 Finite number of sedimentary environments are present on earth surface . No similar environments are identical, they show transitions

• Observation 2

There are finite number of Facies in geological record with respect to time and space . No similar facies to be identical, they shows transitions

• Interpretation

Ancient sedimentary environments of unknown origin can be matched with modern deposits of known origin. So depositional environments of ancient deposits may be discovered

• Conclusion there are finite number of sedimentary environments and which deposits sedimentary facies. These can be classified into ideal systems and models • Pettijohn and Potter sedimentary model describes recurring pattern of sedimentation there is a close relation between arrangements of major sedimentation in basin and direction structures.

PIEDMONT FANGOMERATES • Piedmont zones  landform created at the foot of a mountain

PIEDMONT FANGOMERATES

PIEDMONT FANGOMERATES • Alluvial cones and heads of alluvial valley boulder beds and conglomerate gravity slides • Diamictites  pebbly sand stone and siltstone mud flows • Poorly sorted sandstone(massive) flash flood • So piedmont zones are characterized by coarse gran sized massive sub horizontal beds absence of fossil

• FANGOMERATES deposits of piedmont zone • Modern piedmont zones are present around mountain chains from artic to equator • Examples Rocky mountain , Torridon group of northwest Scotland

FLUVIAL PROCESS AND MODELS • Processes and deposits of modern rivers studied intensively • Development of human civilisations on major alluvial valleys • Ganges, Indus, The Nile, The Mississippi • Farming, irrigation, water supply, communications and pollution

Fluvial process and modern alluvium

Fluvial process and modern alluvium • Gradational down slope piedmont fans alluvial environment • Alluvial environment divided into two braided and meander environment • Piedmont alluvial fan flood plain • Changes in gradient, grain size, sorting • Braided channels steep slope, coarse, gravelly, sediment, ephemeral • Meandering fine grained, sediment, gentle gradient, study discharge

Alluvium of braided rivers The alluvium of braided river systems consists, largely of 1.channel lag gravels 2.cross- bedded channel bar 3.braid bar sands

Depositional architecture of a braided river: lateral migration of the channel and the abandonment of bars leads to the build-up of channel-fill successions.

Alluvium of meandering rivers

Depositional architecture of a meandering river: sandstone bodies formed by the lateral migration of the river channel remain isolated when the channel avulses or is cut-off to form an oxbow lake.

• Alluvium deposited by meandering fluvial system consist of; 1.scoured intra formational erosion surface across older alluvium or bedrock 2.channel lag conglomerate 3. cross-bedded sand bar 4. rippled sandstone 5. overbank mud.

ECONOMIC ASPECT OF FLUVIAL DEPOSIT. • Fluvial deposits are of great economic importance for many reasons. They serve; • as aquifers or petroleum reservoirs, because of their porosity and permeability. • as the hosts for deposits of coal, uranium, and placer minerals. • hosts for placer ores of detrital heavy minerals notably gold (Bache, 1987).

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