Short length-scale variability of hybrid event beds and its applied significance

Abstract

Please cite this article as: Fonnesu, M., Haughton, P., Felletti, F., McCaffrey, W., Short length-scale variability of hybrid event beds and its applied significance, Marine and Petroleum Geology (2015), doi: 10.1016/j.marpetgeo.2015.03.028. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Variable character and diverse origin of hybrid event beds in a sandy submarine fan system, Pennsylvanian Ross Sandstone Formation, western Ireland

“…The larger entrained clasts are unlikely to have been suspended in the flows and these were carried as traction load or within a shearing bed layer that evolved down‐dip into a well‐developed H3 division emplaced en masse or in a series of pulses. Clasts may have been incorporated in the flows by a delamination process whereby muddy substrate was actively ‘peeled’ into the flow following scour expansion by basal sand injection (Fonnesu et al ., ). This must have occurred over an extensive area because mud clast‐rich event beds are present in the ‐03 and ‐05 cores and further down‐dip at Ballybunion at this level, extending over at least 20 km obliquely down‐dip.…”

“…The unusual coarse‐grained texture and low gamma ray character of the R5 and R10 sandstones, as well as the occurrence of HEB8 in all three units support a link between all three bed types. Type HEB2 is thus interpreted as the down‐dip and/or lateral expression of HEB1 beds (Fonnesu et al ., ). The character of HEB8 resembles the graded sand–mud couplets capping HEB2 beds (H4/H5 divisions), and this suggests that the former may be a distal run‐out facies of sandier HEB1 and HEB2 event beds left up‐dip.…”

The stratigraphic record and processes of turbidity current transformation across deep‐marine lobes

“…Martinsen et al ., ; Sullivan et al ., ). In these fine‐grained systems, complicated facies and facies distributions, which diverge significantly from classical turbidite models, are reported from medial and distal lobe settings (Haughton et al ., , ; Sylvester & Lowe, ; Talling et al ., , ; Amy & Talling, ; Ito, ; Barker et al ., ; Davis et al ., ; Hodgson, ; Kane & Pontén, ; Pyles & Jennette, ; Talling, ; Grundvåg et al ., ; Terlaky & Arnott, ; Fonnesu et al ., ; Southern et al ., , ; Spychala et al ., in press). Such beds have been termed ‘hybrid event beds’ by Haughton et al .…”

Turbidite, debrite, and hybrid event beds in submarine lobe deposits of the Palaeocene to middle Eocene Kapit and Pelagus members, Belaga Formation, Sarawak, Malaysia

“…The overlying upper interval is interpreted as a debrite, based on the structureless ungraded and matrix‐rich character of the sandstone beds, and the abundance of chaotically organized mudstone and sandstone clasts. The systematic repeated association in BT5a and BT5b of turbidite sandstone overlain by debrite is consistent with a genetic relationship between the upper and lower intervals, with the different intervals representing separate but temporally closely related flow phases within a single gravity flow event (Fonnesu, Felletti, Haughton, Patacci, & McCaffrey, ; Fonnesu, Haughton, Felletti, & McCaffrey, ; Fonnesu, Patacci, Haughton, Felletti, & McCaffrey, ; Haughton et al, , ; Hodgson, ). The gravity flow event was originally fully turbulent (lower interval) but evolved into a cohesive, laminar debris flow (upper interval “linked debrite,” sensu Haughton et al, ), with the debris flow phase travelling on the previously deposited turbidite sand bed.…”

“…The common occurrence of dewatering structures in the lower interval sandstone, sand injections penetrating into the upper interval and deformed clasts in the upper interval provide evidence for active dewatering during overriding debrite emplacement, thus supporting emplacement of the debrite immediately after deposition of the lower interval turbidite. The presence of concentrations of mud clasts below the upper interval muddy sandstone is consistent with flow transformation through erosional bulking, where the initially turbulent flow is charged with mud clasts, which disintegrate, increasing the clay concentration of the flow and suppressing turbulence (Fonnesu et al, , , ; Haughton et al, ; Kane et al, ). These bipartite to tripartite beds are referred to in the literature as hybrid event beds (HEBs), with the upper interval muddy sandstone referred to as a “linked” debrite (Haughton et al, , ).…”