Deep-water channel-lobe transition zone dynamics: Processes and depositional architecture, an example from the Karoo Basin, South Africa

Brooks, Hannah L.; Hodgson, David M.; Brunt, Rufus L.; Peakall, Jeff; Hofstra, Menno; Flint, Stephen S.

doi:10.1130/b31714.1

Cited by 75 publications

(178 citation statements)

References 105 publications

(214 reference statements)

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Section: The Laingsburg and Fort Brown Formationsmentioning

confidence: 78%

“…The recognition of intraslope lobes in Units D/E, E, and F ( Figueiredo et al, 2010;Spychala et al, 2015), and coarse-grained bypassdomi nated zones, consisting of thin channel-levee deposits and channel-lobe transition zones (sensu Mutti, 1995;Van der Merwe et al, 2014;Brooks et al, 2018b) supports the presence of a stepped slope profile at the time of E and F deposition (e.g., Figs. 1B and 1C; Van der Merwe et al, 2014;Brooks et al, 2018b). This paper focuses on the sedimentology and stratigraphic architecture of the thinner units (A/B, B/C, and D/E) in order to decipher the origin and presence of fixed and dynamic slope topography throughout the deposition of the Laingsburg and Fort Brown formations, that resulted in the formation of a stepped slope profile (Van der Merwe et al, 2014;Brooks et al, 2018b).…”

Section: The Laingsburg and Fort Brown Formationsmentioning

confidence: 78%

“…Regional paleoflow is toward the northeast and east throughout the succession with the main deep-water sediment entry point located to the southwest ( Van der Merwe et al, 2014). Regional-scale mapping of successive slope to basin-floor systems (Units D-F) in the Laingsburg depocenter indicates the presence of a confining, lateral basin margin to the south of the depocenter, oriented east-to-west ( Van der Merwe et al, 2014;Brooks et al, 2018b).…”

Section: Geology Of the Karoo Basinmentioning

confidence: 99%

“…2B), and intersected in a number of cored research boreholes. Detailed mapping and physical correlation of all units utilizes a regional stratigraphic framework established from previous studies (Grecula et al, 2003;Figueiredo et al, 2010Figueiredo et al, , 2013Di Celma et al, 2011;Flint et al, 2011;Hodgson et al, 2011;Kane and Hodgson, 2011;Brunt et al, 2013aBrunt et al, , 2013bMorris et al, 2014aMorris et al, , 2014bMorris et al, , 2016Van der Merwe et al, 2014;Spychala et al, 2015Spychala et al, , 2017aBrooks et al, 2018b). The Laingsburg and Fort Brown formations have been divided into four composite sequence sets, the first comprising Unit A, the second Units A/B and B, the third Units B/C, C, and D; and the fourth Units D/E, E, and F .…”

Section: The Laingsburg and Fort Brown Formationsmentioning

confidence: 99%

“…Regional mapping and correlation of units C to F have demonstrated an archi tectural change from sand-attached (Units C and D) to sand-detached channel-lobe transition zones (Units E and F; Van der Merwe et al, 2014;Brooks et al, 2018b). The recognition of intraslope lobes in Units D/E, E, and F ( Figueiredo et al, 2010;Spychala et al, 2015), and coarse-grained bypassdomi nated zones, consisting of thin channel-levee deposits and channel-lobe transition zones (sensu Mutti, 1995;Van der Merwe et al, 2014;Brooks et al, 2018b) supports the presence of a stepped slope profile at the time of E and F deposition (e.g., Figs.…”

Section: The Laingsburg and Fort Brown Formationsmentioning

confidence: 99%

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Disconnected submarine lobes as a record of stepped slope evolution over multiple sea-level cycles

et al. 2018

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The effects of abrupt changes in slope angle and orientation on turbidity current behavior have been investigated in numerous physical and numerical experiments and examined in outcrop, subsurface, and modern systems. However, the long-term impact of subtle and evolving seabed topography on the stratigraphic architecture of deep-water systems requires fine-scale observations and extensive 3-D constraints. This study focuses on the Permian Laingsburg and Fort Brown formations, where multiple large sand-rich systems (Units A-F) have been mapped from entrenched slope valleys, through channel-levee systems, to basin-floor lobe complexes over a 2500 km 2 area. Here, we investigate three thinner (typically <5 m in thickness) and less extensive sand-rich packages, Units A/B, B/C, and D/E, between the large-scale systems. Typically, these sand-rich units are sharp-based and topped, and contain scours and mudstone clast conglomerates that indicate deposition from high-energy turbidity currents. The mapped thickness and facies distribution suggest a lobate form. These distinctive units were deposited in similar spatial positions within the basin-fill and suggest similar accommodation patterns on the slope and basin floor prior to the larger systems (B, C, and E). Stratigraphically, these thin units represent the first sand deposition following major periods of shut-down in sediment supply, and are interpreted as marking a partial re-establishment of sand delivery pathways creating "disconnected lobes" that are fed mainly by flows sourced from failures on the shelf and upper slope rather than major feeder channel-levee systems.Thickness and facies patterns throughout the deep-water stratigraphy suggest seabed topography was present early in the basin formation and maintained persistently in a similar area to ultimately form a stepped slope profile. The stepped slope profile evolved through three key stages of development: Phase 1, where sediment supply exceeds deformation rate (likely caused by differential subsidence); Phase 2, where sediment supply is on average equal to deformation rate; and Phase 3, where deformation rate outpaces sediment supply. This study demonstrates that smaller systems are a sensitive record of evolving seabed topography and they can consequently be used to recreate more accurate paleotopographic profiles.

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Section: The Laingsburg and Fort Brown Formationsmentioning

confidence: 78%

Section: The Laingsburg and Fort Brown Formationsmentioning

confidence: 78%

Section: Geology Of the Karoo Basinmentioning

confidence: 99%

Section: The Laingsburg and Fort Brown Formationsmentioning

confidence: 99%

Section: The Laingsburg and Fort Brown Formationsmentioning

confidence: 99%

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Disconnected submarine lobes as a record of stepped slope evolution over multiple sea-level cycles

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Channel incision into a submarine landslide on a Carboniferous basin margin, San Juan, Argentina: Evidence for the role of knickpoints

Allen

Gomis‐Cartesio

Hodgson

et al. 2022

The Depositional Record

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Emplacement of submarine landslides, or mass-transport deposits, can radically reshape the physiography of continental margins, and strongly influence subsequent sedimentary processes and dispersal patterns. Typically, progressive healing of the complicated relief generated by the submarine landslide occurs prior to progradation of sedimentary systems. However, subsurface and seabed examples show that submarine channels can incise directly into submarine landslides.Here, the evolution of a unique exhumed example of two adjacent, and partially contemporaneous, submarine channel-fills is documented. The channels show deep incision (>75 m), and steep lateral margins (up to 70°), cut into a >200 m thick submarine landslide. The stepped basal erosion surface, and multiple terrace surfaces, are mantled by clasts (gravels to cobbles) reflecting periods of bedloadderived sedimentation, punctuated by phases of downcutting and sediment bypass. The formation of multiple terrace surfaces in a low aspect ratio confinement is consistent with the episodic migration of knickpoints during entrenchment on the dip slope of the underlying submarine landslide. Overlying sandstone-rich channel-fills mark a change to aggradation. Laterally stacked channel bodies coincide with steps in the original large-scale erosion surface, recording widening of the conduit; this is followed by tabular, highly aggradational fill. The upper fill, above a younger erosional surface, shows an abrupt change to partially confined tabular sandstones with normally graded caps, interpreted as lobe fringe deposits, which formed due to down-dip confinement, followed by prograding lobe deposits. Overlying this, an up-dip avulsion induced lobe switching and back-stepping, and subsequent failure of a sandstone body up-dip led to emplacement of a sandstone-rich submarine landslide within the conduit. Collectively, this outcrop represents episodic knickpoint-generated incision, and later infill, of a slope adjusting to equilibrium. The depositional signature of knickpoints is very

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Channel‐lobe transition zone development in tectonically active settings: Implications for hybrid bed development

Brooks

Itô

Zuchuat

et al. 2022

The Depositional Record

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Channel‐lobe transition zones are dynamic areas located between deepwater channels and lobes. Presented here is a rare example of an exhumed channel‐lobe transition zone from an active‐margin setting, in the Kazusa forearc Basin, Boso Peninsula, Japan. This Plio‐Pleistocene outcrop exposes a thick (tens of metres) channel‐lobe transition zone succession with excellent dating control, in contrast to existing poorly dated studies of thinner (metres) deposits in tectonically quiescent settings. This high‐resolution outcrop permits the roles of climate and associated relative sea‐level changes on stratigraphic architecture to be assessed. Three development stages are recognised with an overall coarsening‐upward then fining‐upwards trend. Each stage is interpreted to record one obliquity‐driven glacioeustatic sea‐level fall‐then‐rise cycle, based on comparison with published data. Deposition of the thickest and coarsest strata, Stage 2, is interpreted to record the end of a period of relative sea‐level fall. The thinner and finer strata of Stages 1 and 3 formed during interglacial periods where the stronger Kuroshio Oceanic Current, coupled to increased monsoonally driven tropical cyclone frequency and intensity, likely resulted in inhibited downslope sediment transfer. A key aspect of channel‐lobe transition zone deposits in this case is the presence of a diverse range of hybrid beds, in contrast to previous work where they have primarily been associated with lobe fringes. Here hybrid bed characteristics, and grain‐size variations, are used to assess the relative importance of longitudinal and vertical segregation processes, and compared to existing models. Compared to channel‐lobe transition zones in tectonically quiescent basin‐fills, this channel‐lobe transition zone shows less evidence of bypassing flows (i.e. thicker stratigraphy, more isolated scour‐fills, fewer bypass lags) and has significantly more hybrid beds. These features may be common in active basin channel‐lobe transition zones due to: high subsidence rates; high sedimentation rates; and disequilibrium of tectonically active slopes. This disequilibrium could rejuvenate erodible mud‐rich substrate, leading to mud‐rich flows arriving at the channel‐lobe transition zone, and decelerating rapidly, forming hybrid beds.

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Deep-water channel-lobe transition zone dynamics: Processes and depositional architecture, an example from the Karoo Basin, South Africa

Abstract: This is a repository copy of Deep-water channel-lobe transition zone dynamics: Processes and depositional architecture, an example from the Karoo Basin, South Africa.

Cited by 75 publications

References 105 publications

Disconnected submarine lobes as a record of stepped slope evolution over multiple sea-level cycles

Disconnected submarine lobes as a record of stepped slope evolution over multiple sea-level cycles

Channel incision into a submarine landslide on a Carboniferous basin margin, San Juan, Argentina: Evidence for the role of knickpoints

Channel‐lobe transition zone development in tectonically active settings: Implications for hybrid bed development

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