sedimentary structure - chiang mai...

SEDIMENTARY STRUCTURE• Erosional sedimentary structures•Flute marks, Groove marks, Channels and scours

•Depositional sedimentary structures•Bedding and lamination, Current ripples, Dunes,

•Cross stratification (Cross bedding, Cross lamination)

•Graded bedding, mudcracks

•Post-depositional sedimentary structures•Slides and slumps, overturned cross bedding,

•Convolute bedding, Load casts, dish-and-pillar structure

•Biogenic sedimentary structures1

Flute marks

Flute marks on sole of turbidite. Flow from bottom to top

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Groove marks

Groove marks on sole of turbidite sandstone.

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Channel and scours

• Downcutting of channel sands into horizontally bedded floodplain mudrocks

•Sandstone at arrow is a crevasse splay deposit.4

Lamination

Silt-grade quartz laminae alternate with clay and organic-rich laminae.

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Parting lineation

Parting lineation or primary current lineation on the bedding plane surface of fluvial sandstone.

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Ripple terminology

Current ripples are small-scale bedforms. They are asymmetric with a steeper, downstream-facing lee sideand a gentle upstream-facing stoss side.

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The shape of the crests of ripples

Terminology for the shape of the crests of ripples and dunes formed by unidirectional currents.

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Current ripples

Current ripples (flow to the right) with crests showing straight to catenary shape. 9

Planar cross stratificationThis structure formed through the migration of straight-crested ripples,producing planar cross lamination.

This planar cross bedding is produced from the downcurrent migration of straight-crested subaqueous dunes.

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Trough cross stratificationTrough cross stratification formed through migration of 3D bedforms, lunate and sinuous dunes,producing trough cross bedding. Liguoid ripples give a trough cross lamination.

Trough cross bedding in a fluvial channel sandstone.

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Herring-bone cross bedding

Herring-bone cross bedding formed through

tidal current reversals, in shallow-marine sediment.12

Climbing ripples

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Where there is rapid deposition, ripples build up as well as forward, so that a ripple ‘climbs’ up the stoss-side of the one downstream. This produces climbing-ripple cross lamination

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Flaser bedding and lenticular bedding

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Flaser bedding

Lenticular

bedding

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Wave-formed ripples

. Ripple profiles are symmetrical and crests bifurcate. Lacustrine sandstone. 15

Interference ripples

.Ripples on tidal flats show complicated patterns resulting from changes in water depth, and wind and runoff direction.

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Hummocky cross stratification

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An undulating bedding which is thought to be formed by wave-generated oscillatory flows or combined flows (waves plus currents)produced by the passage of storms.

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Hummocky cross stratification

. Hummocky cross bedding in shallow-marine sandstone.

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Aeolian cross bedding

.The large scale, set heights are 5-10 m.

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Convoluted lamination

. Convoluted and deformed lamination in a thin siliciclastic turbidite.

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Overturned planar cross bedding

.Planar cross bedding showing overturning in downstream direction. Braided-stream sandstone.

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Load casts

Large load casts on the underside of fluvial sandstone.

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Sandstone pillows

Sandstone pillows formed by loading into mud (now fissile shale). 23

Trace fossils

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A. Crawling trails on base of turbidite sandstone.

B. Vertical dwelling burrows, filled with oolite.

C. Feeding-burrow system.

D. Borings of the bivalve.

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The End

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