TY - JOUR

T1 - Autogenic controls on hybrid bed distribution in submarine lobe complexes

AU - Spychala, Y.T.

AU - Hodgson, D.M.

AU - Lee, D.R.

N1 - Funding information: The authors would like to thank the local farmers of the Tanqua region of South Africa for permission to carry out field studies on their land. Further, we would like to thank Aurélia Privat for assistance in the field and the core store. Graham Botha is acknowledged for logistic help in the core store. The clarity of the manuscript was improved by constructive reviews from Marco Fonnesu and Julian Clark. The LOBE 2 consortium project, of which this research forms a part, is supported by sponsorship from Anadarko , Bayerngas Norge , BG Group , BHPBilliton , BP , Chevron , DONG Energy , ENGIE , Maersk , Marathon , Petrobras , Premier Oil , Shell , Statoil , Total , VNG Norge , and Woodside , for which the authors are grateful. The authors would like to thank the local farmers of the Tanqua region of South Africa for permission to carry out field studies on their land. Further, we would like to thank Aurélia Privat for assistance in the field and the core store. Graham Botha is acknowledged for logistic help in the core store. The clarity of the manuscript was improved by constructive reviews from Marco Fonnesu and Julian Clark. The LOBE 2 consortium project, of which this research forms a part, is supported by sponsorship from Anadarko, Bayerngas Norge, BG Group, BHPBilliton, BP, Chevron, DONG Energy, ENGIE, Maersk, Marathon, Petrobras, Premier Oil, Shell, Statoil, Total, VNG Norge, and Woodside, for which the authors are grateful.

PY - 2017/12

Y1 - 2017/12

N2 - Hybrid beds, the deposits of sediment gravity flows that show evidence for more than one flow regime (turbulent, transitional and/or laminar), have been recognized as important components of submarine lobe deposits. A wide range of hybrid bed types have been documented, however, quantitative analysis of the stratigraphic and geographic distribution of these enigmatic bed types is rare. Here, extensive exposures integrated with research borehole data from Unit A of the Laingsburg Formation and Fan 4 of the Skoorsteenberg Formation, Ecca Group, South Africa, provide the opportunity to examine geographical and stratigraphic patterns over a range of hierarchical scales. For this purpose, >23,000 individual beds have been evaluated for deposit type and bed thickness. On average, hybrid beds make up < 5% of all events and <10% of the cumulative thickness. Lobe complex 1 (LC1) of Fan 4,Skoorsteenberg Formation, preserves a prominent geographical trend of hybrid beds becoming more prevalent towards the frontal fringes of a lobe complex (up to 33.2% of beds), whereas their proportion in proximal and medial lobe complex settings is <10%. Data from Unit A, Laingsburg Formation, show hybrid beds are less common in the basal (A.1) and top (A.6) subunits compared to A.2-A.5 in both core data sets. The bases and tops of some lobe complexes (A.2, A.3 and A.5.7) are observed to be slightly enriched in hybrid beds, whereas others (A.5.1, A.5.5 and A.6.1) show no hybrid beds in their bases, which does not conform to expected allogenically-driven distributions that predict more hybrid beds during the initiation of lobe complexes. Instead, the occurrence and distribution of hybrid beds in lobe complexes are interpreted to be controlled by autogenic processes, including flow transformation processes on the basin-floor meaning enrichment in frontal lobe fringe settings. Therefore, the 1D distribution of hybrid beds in lobe complexes reflects the dominant stacking pattern of lobes within a lobe complex, with enrichment at the base and top of lobe complexes due to overall progradational to retrogradational stacking patterns. Individual lobes show a wide range of hybrid bed distributions, due to stacking patterns of the component lobe elements. These findings highlight the importance of autogenic processes rather than allogenic controls in the distribution of hybrid beds, which has implications for reservoir evaluation and the assessment of lobe stacking patterns in 1D core data sets.

AB - Hybrid beds, the deposits of sediment gravity flows that show evidence for more than one flow regime (turbulent, transitional and/or laminar), have been recognized as important components of submarine lobe deposits. A wide range of hybrid bed types have been documented, however, quantitative analysis of the stratigraphic and geographic distribution of these enigmatic bed types is rare. Here, extensive exposures integrated with research borehole data from Unit A of the Laingsburg Formation and Fan 4 of the Skoorsteenberg Formation, Ecca Group, South Africa, provide the opportunity to examine geographical and stratigraphic patterns over a range of hierarchical scales. For this purpose, >23,000 individual beds have been evaluated for deposit type and bed thickness. On average, hybrid beds make up < 5% of all events and <10% of the cumulative thickness. Lobe complex 1 (LC1) of Fan 4,Skoorsteenberg Formation, preserves a prominent geographical trend of hybrid beds becoming more prevalent towards the frontal fringes of a lobe complex (up to 33.2% of beds), whereas their proportion in proximal and medial lobe complex settings is <10%. Data from Unit A, Laingsburg Formation, show hybrid beds are less common in the basal (A.1) and top (A.6) subunits compared to A.2-A.5 in both core data sets. The bases and tops of some lobe complexes (A.2, A.3 and A.5.7) are observed to be slightly enriched in hybrid beds, whereas others (A.5.1, A.5.5 and A.6.1) show no hybrid beds in their bases, which does not conform to expected allogenically-driven distributions that predict more hybrid beds during the initiation of lobe complexes. Instead, the occurrence and distribution of hybrid beds in lobe complexes are interpreted to be controlled by autogenic processes, including flow transformation processes on the basin-floor meaning enrichment in frontal lobe fringe settings. Therefore, the 1D distribution of hybrid beds in lobe complexes reflects the dominant stacking pattern of lobes within a lobe complex, with enrichment at the base and top of lobe complexes due to overall progradational to retrogradational stacking patterns. Individual lobes show a wide range of hybrid bed distributions, due to stacking patterns of the component lobe elements. These findings highlight the importance of autogenic processes rather than allogenic controls in the distribution of hybrid beds, which has implications for reservoir evaluation and the assessment of lobe stacking patterns in 1D core data sets.

KW - Allogenic controls

KW - Autogenic controls

KW - Deepwater fans

KW - Distribution trends

KW - Hybrid beds

KW - Lobes

UR - http://www.scopus.com/inward/record.url?scp=85029550587&partnerID=8YFLogxK

U2 - 10.1016/j.marpetgeo.2017.09.005

DO - 10.1016/j.marpetgeo.2017.09.005

M3 - Article

VL - 88

SP - 1078

EP - 1093

JO - Marine and petroleum geology

JF - Marine and petroleum geology

SN - 0264-8172

ER -