Download - Sed Structure
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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
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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
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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
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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
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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
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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
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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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