Lecture 6:

Sedimentology: a refresher on basinal shales,

turbidites and deep-sea sediments

.

Models of Basin Fill

A digression – why deep-water interests?

Exploration areas in 2000, with deep-water in black

Stow and Mayall, 2000

Stow et al., in Reading’s text 1996

Controls on Deep-Water Sedimentation

TODAY: examine three aspects…….

• Turbidity currents and deep-water sediment dispersal• Submarine fans and sedimentary sequences• Black Shales and fine-grained sedimentation

loftingplume

ramb1<rflow<ramb2

descendingplume

rflow>ramb1

overflow

rflow<ramb

1

underflow

rflow>ramb2

interflow

ramb1<rflow<ramb2

ramb1

ramb2

Hyperpycnal

Hypopycnal

Mesopycnal or

Initiation of turbidity currents

•Slope failure (surge)•Waves/shelf reworking (surging)•Breaching (surging/sustained)•Sustained underflows (fluvial source; sustained)

Kneller & Buckee, 2000

Experimental Density Current

The idealised turbidity current: inception to deposition

...................the Bouma Sequence

Normally graded, very coarse to medium sand (and gravel)without tractional structures, erosive base with sole marks

… representing rapid deposition & turbulence suppression

Medium to fine sand with plane-parallel lamination… representing deposition on upper flow regime plane bed

Very fine sand to coarse silt with ripple cross-lamination, climbing ripples, wavy lamination and/or convolutions

… representing deposition in lower flow regime

Alternation of even silt and mud laminae… representing shear sorting during deposition of fines

Homogenous to finely laminated mud … representing deposition from low-density tail of turbidity current followed by settling from (hemi)pelagic suspension

Proximity to source area

TabcdeTa Tab Tabc

top-missing

downflow sortingthrough deposition

and bypassing

Proximal Distal

velocityaccumulative

depletive

NON-UNIFORM

time

waxingwaning

UNSTEADY STEADY

Temporal changes in velocity Spatial changes in velocity

from Christopher Kendall’s USC website

from Christopher Kendall’s USC website

Stow et al., in Reading’s text 1996

Dispersal of sediment to deepwater

from Christopher Kendall’s USC website

Mud-rich Fan

from Christopher Kendall’s USC website

Sand-rich Fan

from Christopher Kendall’s USC website

Mixed Sand-Mud rich Fan

from Christopher Kendall’s USC website

from Christopher Kendall’s USC website

from Christopher Kendall’s USC website

Chapin et al., 1994

The principal architectural elements in deep-water sedimentary systems

Stow and Mayall, 2000

The principal architectural elements in deep-water sedimentary systems

Stow and Mayall,

2000

The principal architectural elements in deep-water sedimentary systems

Stow and Mayall, 2000

from Christopher Kendall’s USC website

Scales of Hierarchy

from Christopher Kendall’s USC website

Droz et al., 2000

An example: the Zaire Fan

Droz et al., 2000

An example: the Zaire Fan

Stow and Mayall, 2000Erosion on fans

Pyles, 2008

Western Eire- types of facies

Western Eire – Ross Fm model??

Chapin et al., 1994

Western Eire –Ross Fm model??

Pyles, 2008

Western Eire – deep water architecture

Preservation of Organic Matter in Deep Marine Environments

Stow and Mayall, 2000

Wignall, 1994

Depositional processes and products of fine-grained sediments

Wignall, 1994

Oxygen levels in sedimentary environments

Western Eire – black shale

PaleoenvironmentPaleoecologyGeochemistry

References

See GEOL440 Sedimentology lectures (see website)Chapters by Walker and Postamentier in Facies Models Revisited

Chapin, M.A., Davies, P., Gibson, J.L. & Pettingill, H.S. 1994, Reservoir architecture of turbidite

sheet sandstones in laterally extensive outcrops, Ross Formation, western Ireland. In Weimer, P.,

Bouma, A.H. & Perkins, R.F (eds), Submarine fans and turbidite systems, GCSSEPM Foundation

15th Annual Research Conference, 53-68.

Collinson, J.D., Martinsen, O. Bakken, B. and Kloster, A. 1991, Early fill of the western Irish

Namurian Basin: a complex relationship between turbidites and deltas. Basin Research, 3, 223-

242.

Lien, T., Walker, R. & Martinsen, O., 2003. Turbidites in the Upper Carboniferous Ross Formation,

western Ireland: reconstruction of a channel and spillover system. Sedimentology 50: 113-148.

Stow, D.A.V., and Mayall, M. 2000 Deep-water sedimentary systems: New models for the 21st

century, Marine and Petroleum Geology, 17, 125-135.

Stow, D.A.V., Hue. A.-Y. and Betrand, P. 2001 Depositional processes of black shales in deep

water, Marine and Petroleum Geology, 18, 491-498.

Strachan, L.J. 2002 Slump-initiated and controlled syndepositional sandstone remobilization: an

example from the Namurian of County Clare, Ireland. Sedimentology, 49, 25–42.

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Next week

Carboniferous seafloor communities,

paleoecology and trace fossils