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Title: Longitudinal stratigraphic variation in turbidite sand sheet systems : can we detect regular stratigraphic cycles that imply allogenic progradation & retrogradation patterns?
Author: Wu, Jianan
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 2019
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Attempts have been made in the past to link stratigraphic cycles, i.e. thickening and coarsening upward turbidite sequences to progradation, and thinning and fining upward to retrogradation. However, if turbidity currents experience more autogenic processes (e.g. compensation stacking in a laterally unconfined environment), the relationship between stratigraphic cycles and such vertical sequences may be more complex. In this study, three confined sand sheet systems——two units in the Cretaceous Cerro Toro Formation in Southern Chile and one example from Oligocene Grès de Peïra Cava in SE France, were studied in detail along depositional dip including facies analysis, vertical thickness trends, and variation of stratigraphic cycles. The thesis demonstrates that stratigraphic cycles can be detected by semi-quantitative statistical methods. Along depositional dip, stratigraphic cycles (thickening and coarsening upward then thinning and fining upward) are probably asymmetrical in proximal areas but appear to be more symmetrical in distal areas. During an allogenically waxing then waning sediment supply, there is a corresponding progradation then retrogradation process. Conglomerate layers, an upper well sorted and coarser grained layer, parallel stratification with obvious grain size difference between adjacent laminae, basal coarse grains with a sharp grain size break to the overlying sandstone and erosion surfaces, could act as bypass indicators, which are more abundant in proximal areas and around the maximum progradation phase. Turbidity currents may become 'self-organized' down-dip, i.e. transfer from fluctuating energy to overall waning energy, and degree of bypass may significantly decrease to distal areas.
Supervisor: Kneller, Ben C. Sponsor: China Scolarship Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Turbidites ; Geology, Stratigraphic