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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