Differentiating tide-influenced and tide-dominated deltas: Devonian - - PowerPoint PPT Presentation

Differentiating tide-influenced and tide-dominated deltas: Devonian Baltic Basin Piret Plink-Bjorklund

MAIN POINTS:

• facies, architecture & stratigraphy of tide-influenced and –dominated deltas
• the nature of tidal signatures in both delta types
• recognition criteria for both delta types
• controls on the occurrence of tide-dominated vs tide–influenced deltas
• implications for potential sediment delivery beyond the shelf edge
• implications for reservoir characteristics

DEFINITIONS:

Tide-dominated delta = Most river-derived sediment is reworked by tides Tide-influenced delta = River influence is stronger: tides rework part of the river-derived sediment

Devonian Baltic Basin

redrawn from Lazauskiene et.al. (2002)

Devonian Baltic Basin

Delta front & prodelta: TIDE-DOMINATED DELTAS

• accretion packages, 5-10 m thick, thin

& fine seaward

• accretion surfaces 7-10 degrees in

proximal part, erosion common

• accretion surfaces become gentler

seaward

Delta front & prodelta: TIDE-DOMINATED DELTAS

Vertical trends: CU packages from prodelta muds to distal and proximal delta front Prodelta muds: mudstones + SiS & SS, & carbonate interlayers Distal delta front: flaser-, wavy- & lenticular-bedding, planar lamination,

• ccasional wave ripples, vfSS, SiS,

MS, double and single mud & mica drapes, neap-spring cyclicity bidirectional paleocurrents Proximal delta front: x-strat, large- scale x-strat, planar laminated SS, double and single mud & mica drapes, neap-spring cyclicity; bidirectional paleocurrents

Delta front & prodelta: Tide-dominated deltas

erosion on delta front delta front consists of tidal bars double mud drapes, neap- spring cyclicity

Delta front & prodelta: TIDE-DOMINATED DELTAS Delta front deposits dominate volumetrically the tide-dominated deltas

landward seaward

Delta front & prodelta: TIDE-INFLUENCED DELTAS

1) Facies and geometries of tide-influenced delta front & prodelta deposits = as in tide-dominated deltas

Delta front & prodelta: TIDE-INFLUENCED DELTAS

2) Delta front deposits form volumetrically a minor part of tide-influenced deltas Oblique seaward/strike view 1) Facies and geometries of tide-influenced delta front & prodelta deposits = as in tide-dominated deltas

Delta plain: TIDE-DOMINATED DELTAS

Delta plain = tidal flats, some distributary channels, tidal channels Sandy, mixed to muddy tidal flats: Flaser-, wavy & lenticular bedding, marlstones, bioturbation, roots Supratidal: brecciated, massive, laminated mudstones and siltstones, carbonate interlayers, roots Channels: x-strat, compound cross- strat, rippled, sandstones to mudstones, mud-clast conglomerates, bidirectional paleocurrent directions, mica & mud drapes

Delta plain: TIDE-DOMINATED DELTAS

Delta plain = tide dominated No fluvial dominated delta plain

Delta plain: TIDE-DOMINATED DELTAS

Subaerial delta plain = paleosols

Delta plain: TIDE-DOMINATED DELTAS

Delta plain deposits are tide dominated in the tide-dominated deltas Delta plain deposits volumetrically minor in the tide-dominated deltas

landward seaward

Delta plain: TIDE-INFLUENCED DELTAS

Delta plain = distributary channels with different dergees of tidal influence; overbank fines, overbank lakes, crevasse splays and channels, tidal channels

Delta plain: TIDE-INFLUENCED DELTAS

Distributary channels: Multiple erosion surfaces, X-strat, downstream and lateral accretion sets (mid-channel and lateral bars); overturned x-strat, mica or mud drapes, normally-graded x-strat, compound x-strat

Delta front tidal bars Distributary channels

Delta plain: TIDE-INFLUENCED DELTAS

Delta plain: Tide-influenced deltas

Distributary channels: tidal influence increases seaward

Delta plain: TIDE-INFLUENCED DELTAS

Tide-influenced downstream accreting bars: Large-scale x-strat, x-strat at the top

Delta plain: TIDE-INFLUENCED DELTAS

Tide-influenced downstream accreting bars: Large-scale x-strat, x-strat at the top

Delta plain: TIDE-INFLUENCED DELTAS

Overbank/interdistributary: lakes, interdistributary bays, some tidal flats, floodplain (desiccation cracks, roots, fish scales, mudstones)

Delta plain: TIDE-INFLUENCED DELTAS

Overbank/interdistributary: lakes, interdistributary bays, some tidal flats, floodplain (desiccation cracks, roots, fish scales, mudstones)

Delta plain: TIDE-INFLUENCED DELTAS

2) Delta plain deposits volumetrically dominate the tide-influenced deltas Oblique seaward/strike view 1) Fluvial to tide-influenced fluvial delta plain in the tide-influenced deltas

Why no fluvial delta plain in TIDE-DOMINATED DELTAS?

• dominated by delta

front facies

• small proportion of

distributary channel fill facies

• no “fluvial” delta

plain, just tidal flats and paleosols

• high tidal energy

relative to fluvial input: tides able to rework most river- derived sediments

• effectively

redistribute sediments from river mouth (elongate MB), no bifurcation, no aggradation of a fluvial delta plain

TIDE-INFLUENCED DELTAS?

• dominated by delta

plain facies with distributary channels, overbank deposits, lakes

• delta front similar

to tide-dominated deltas

• higher fluvial

input, compared to the tidal current sediment removal efficiency and sediment redistribution

• MB accumulation in

river mouths, channel bifurcation and development of multiple distributary channels

• delta front

dynamics similar to tide-dominated deltas

MAKES SENCE?

D2am D2gj D2br D2ar D2nr D2pr 30 80 95 97 109 47 Eifelian Givetian

Fluvial to estuarine system Transgressive mixed carbonate- siliciclastic shallow marine system Tide-dominated deltas Aggradational to backstepping tide-influenced deltas and lateral coeval estuaries

Tide-dominated deltas formed during initial progradation, tide-influenced deltas formed during max progradation

Tide-influenced deltas

SO WHAT?

• In tide-dominated deltas the best sands are in delta-front tidal bars
• In tide-influenced deltas the best sands are on delta plain and in delta-front tidal bars
• Different lateral extent and shape: in tide-dominated deltas laterally restricted sand

depocenters, in tide-influenced deltas more latearally amalgamated sands, restricted mud depocenters

• Different stratigraphic architecture: in tide-dominated deltas delta-front sands

between prodelta/lower delta front heterolithics and tidal flat heterolithics

• Tide-influenced deltas effectively deliver sediment into the basin due to the high

fluvial supply

• Tide-dominated deltas effectively deliver sediment into the basin due to the effective

basinward sand redistribution

• Different stratigraphic architecture: in tide-influenced deltas delta-front sands

amalgamated with delta-plain sands – very thick sand-rich successions