Deep Water Systems and Sequence Stratigraphy. By: Matt Kyrias, Chris Majerczyk, Nick Whitcomb, Wesley Vermillion

Transcription

1 Deep Water Systems and Sequence Stratigraphy By: Matt Kyrias, Chris Majerczyk, Nick Whitcomb, Wesley Vermillion

2 Contents Gravity Flow Depositional Elements Defined References NOTE: Source uses seismic data but that will not be at our disposal in Ireland. We ll try to explain to you what the different depositional environments look like in the field.

3 Gravity-Flow Depositional Elements Turbidity-flow leveed channels Channel overbank sediment Distributary-channel complexes Crevasse-splay complexes Debris-flow channels, lobes, and sheets ALL elements characterized by direct deposition onto or into (through erosion) the immediately underlying substrate

4 Turbidity-Flow Leveed Channels: Basics Commonly form in slope and basin floor environments Widths range from m Wide range of sinuosity Channels meander downstream Extent of contact between sand-prone part of channel and levee is important

5 Turbidity-Flow Leveed Channels: Cont. Posamentier and Kolla, 2003

6 Channel Meander Loops Uniformitarianism? Deep water vs. alluvial systems Morphological similarities is a result of processes that involve dynamic interaction of flows, sediments, and terrain gradient

7 Meandering Channels & Avulsion Avulsion- a sudden cutting off of land by flood, currents, or change in course of a body of water. - Change in flow parameters associated with changes upslope or on the staging area. - Avulsion channels form systematically, beginning down-system and gradually forming further up-system. - Large-scale avulsion events are relatively rare, but where present may yield good reservoir lithologies.

8 Overbank/Levee Deposits - Associated with deep-water channels, and overbank flow out of adjacent channels. - Often an order of magnitude wider than their associated channel. - Flow directed away from the channel in close proximity to the levee crest. - Results in thickened section on the stoss side of the sediment waves - Levees characterized by sediment wave development, not present in other systems. - Contain reservoir-quality thin bedded sandstones.

9 SEDIMENT WAVES

10 Frontal Splay Complexes A process of flaring out from a confined to unconfined system This causes lobate structures to form The transition from confined to unconfined can be related to a progressive lowering of levee height down system to where the high density part of the turbidity flow is no longer confined Such a shift of transition down system would be associated with a progressive overall grain size decrease

11 Frontal Splay Complex: Diagram

12 Frontal Splay Complex: Cont There is minimal loss of sand within these flows due to the high density part of the flow remains effectively confined by levee walls Down system there is a gradual increase of net sand deposited on levees, and as the system loses sand the levees loose height The high density part of the flow eventually breaks through the levee splaying out in a braided pattern. This also leads to channel avulsion

13 Crevasse and Overbank Splays Where the levee is breached crevasse splay complex form. This is similar to formation of avulsion channels. A network of channels form and produce sheet like sand rich deposits Debris flow: sheets, Lobes, and Channels Debris flows deposits have a common characteristic of long linear grooves that reflect the basal surface

14 Controls on Deep-Water Sedimentation Controls on the occurrence of sand-rich deepwater sedimentation The presence of sand in the shelf-margin staging area Steep slopes immediately after the staging area Sea-level falls sufficient to expose most of the shelf

15 Controls on Deep-Water Sedimentation: Cont Controls on the style of deep-water deposition Sand to mud ratio within the material delivered to the deep water Basin physiography Magnitude, duration, and frequency of depositional events Sediment delivery mechanisms Single source versus multiple smaller sources Rheology and concentration of sediment gravity flows Bottom-current activity

16 Sequence Stratigraphic Significance Typical deep-water sequence Debris-flow deposits at base Splay-complex-dominated turbidite deposits Period of sea-level fall Leveed-channel-dominated deposits Period of sea-level stillstand and slow rise Debris-flow deposits Capped by condensed-section deposits Posamentier and Kolla, 2003

17 Conclusions While the paper dealt mainly with seismic data, we discussed what could be relevant to Ireland. Turbidity-flow leveed channels, meander loops, overbank or levee deposits, frontal splay deposits, crevasse splays or overbank splays, and debris-flows were discussed. The controls on deep-water sedimentation were also discussed along with a general sequence stratigraphy.

18 References Posamentier, H. W. and Kolla, V. (2003). Seismic geomorphology and stratigraphy of depositional elements in deep water. Journal of Sedimentary Research. vol. 73 no