Submarine lobes have various geometries and stacking patterns, whose differences are likely to be the result of variations in flow efficiency and degree of confinement. This study examines four contrasting units with differing flow efficiency and confinement, to evaluate their roles on bed geometries and stacking patterns. Three of these occur in the Late Palaeozoic Paganzo basin, NW Argentina: the Las Lajas system is developed in a 0.8 km wide palaeofjord; the Cerro Bola system (of which two different units were studied) was deposited in a larger sub-basin, of least 20 km width. The Paine C system of the late Cretaceous Magallanes Basin in Chile is confined by an incision surface 3 km wide. 78 individual beds in the four units have been chosen to calculate flow efficiency and degree of confinement. Individual flow efficiency has been estimated semi-quantitatively by a bed’s outcrop cross sectional area (as a proxy for flow volume) and percentage of mud in the beds (as a relative estimate for that in the flows). The degree of confinement experienced by the flows was assessed semi-quantitatively by dividing the flow efficiency by the maximum preserved basin dimension. It is found that: 1) Degree of confinement (efficiency divided by maximum preserved basin dimension) influences individual bed geometry, highly confined flows having a higher tabularity (smaller thinning rate); 2) In highly confined settings, individual beds stack vertically, whereas in unconfined systems, they stack compensationally; 3) Highly confined or high efficiency flows have higher tabularity (smaller thinning rate), which implies that truly sheet-like systems are only developed in highly confined and high efficiency systems. The generic model of architecture of submarine lobes and turbidite sheet systems, as a function of flow efficiency and degree of confinement, could be applied widely to sheet-like systems both at outcrop and in the subsurface.
Bibliographical noteThe authors would like to acknowledge the support of the PRAX 2 Joint Industry Project at the University of Aberdeen, funded by Petrochina, Statoil, BP and Det Norske (now AkerBP), which has allowed us to undertaken this study. We are grateful to Professor Bryan Cronin who provided much assistance and advice in the field. We also wish to thank Jianan Wu and Guilherme Bozetti for their assistance in the field. Three reviewers (Mike Mayall, Georgios Pantopoulos and an anonymous
reviewer) provided very constructive and crucial ideas, which have greatly improved the manuscript.
- submarine lobes
- flow efficiency
- degree of confinement
- turbidite sheet system
- stacking patterns