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

Devonian Baltic Basin redrawn from Lazauskiene et.al. (2002)

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

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

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 Distributary channels Delta front tidal bars

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

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

Tide-dominated deltas formed during initial progradation, MAKES SENCE? tide-influenced deltas formed during max progradation Aggradational to D 2 am 30 backstepping tide-influenced D 2 gj deltas and 80 lateral coeval estuaries Givetian Tide-influenced deltas 95 D 2 br D 2 ar 97 Tide-dominated deltas Eifelian D 2 nr 109 Transgressive mixed carbonate- siliciclastic shallow marine system 47 D 2 pr Fluvial to estuarine system

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 - Different stratigraphic architecture: in tide-influenced deltas delta-front sands amalgamated with delta-plain sands – very thick sand-rich successions - 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