or coarsening and thickeningupward successions are common in submarine fan environments Cyclicity may result from Autocyclic processes inherent to the depositional system not driven by external forces ID: 1021013
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1. Submarine Fan Systems
2. Fining and thinning-upward or coarsening and thickening-upward successions are common in submarine fan environmentsCyclicity may result from:Autocyclic processes (inherent to the depositional system, not driven by external forces)Allocyclic processes (driven by external forces, primarily sea level, tectonics, or climate)
3. Possible causes of fining-upwards successions:channel fill and abandonmentlateral migration of lobe (from channel to margin)successive deposition of thinner beds on leveeAutocyclic processesPossible causes of coarsening-upwards successions:Progradation of fan (e.g., lobe over basin plain)lateral migration of lobe (from margin towards channel)
4. Nearby source supplies sediment directly to slopeNegative accommodation results in erosion of sedimentAllocyclic processesSubmarine fans always have accommodation space, but sea level affects proximity of sediment source and accommodation in more proximal areas
5. Sediment entry points at shoreline far from shelf edgeHigh sea level results in stable conditions near shelf edgeAllocyclic processes
6. Deep-water systems vary with:Grain size of available sedimentNature of supplying system (point source, multiple source…)Not a universal model!
7. Small, high-gradient depositional systemsDominated by debris flow conglomerates and/or brecciasPoorly organized lobes, unchannelizedGravel-rich systems
8. Mud-rich systemsChannel position more stableSlumps more frequentChannels very long and highly sinuousDeposits thin but extremely laterally extensive
9. Point source submarine fanMultiple source slope rampLinear slope apronDecreasing source stabilityIncreasing overlap of multiple source lobesDecreasing facies organization
10. Sediment gravity flows are not the only depositional processBottom currents (1-20 cm/s) are found in many places in the deep ocean, and are able to rework and transport fine sandMud-draped current ripples, 3091 m depth
11. Turbidite mudstoneIndistinctly laminated contourite siltstoneContour-parallel currents deposit or rework sediment into “contourite” units, typically fine-grained (<v. fine sand) with faint laminations or ripples