Geological controls on the geometry of incised‐valley fills: Insights from a global dataset of late‐Quaternary examples

Abstract

Incised valleys that develop due to relative sea‐level change are common features of continental shelves and coastal plains. Assessment of the factors that control the geometry of incised‐valley fills has hitherto largely relied on conceptual, experimental or numerical models, else has been grounded on case studies of individual depositional systems. Here, a database‐driven statistical analysis of 151 late‐Quaternary incised‐valley fills has been performed, the aim being to investigate the geological controls on their geometry. Results of this analysis have been interpreted with consideration of the role of different processes in determining the geometry of incised‐valley fills through their effect on the degree and rate of river incision, and on river size and mobility. The studied incised‐valley fills developed along active margins are thicker and wider, on average, than those along passive margins, suggesting that tectonic setting exerts a control on the geometry of incised‐valley fills, probably through effects on relative sea‐level change and river behaviour, and in relation to distinct characteristics of basin physiography, water discharge and modes of sediment delivery. Valley‐fill geometry is positively correlated with the associated drainage‐basin size, confirming the dominant role of water discharge. Climate is also inferred to exert a potential control on valley‐fill dimensions, possibly through modulations of temperature, peak precipitation, vegetation and permafrost, which would in turn affect water discharge, rates of sediment supply and valley‐margin stability. Shelves with slope breaks that are currently deeper than 120 m contain incised‐valley fills that are thicker and wider, on average, than those hosted on shelves with breaks shallower than 120 m. No correlation exists between valley‐fill thickness and present‐day coastal‐prism convexity, which is measured as the difference in gradient between lower coastal plains and inner shelves. These findings challenge some concepts embedded in sequence stratigraphic thinking, and have significant implications for analysis and improved understanding of ‘source to sink’ sediment route‐ways, and for attempting predictions of the occurrence and characteristics of hydrocarbon reservoirs.

Driving processes and recognition criteria for complex subaerial unconformities in a non‐marine succession: Implications for basin margin shaping during forced regressions

“…The high degree of amalgamation of channel units and the poor preservation of fine‐grained deposits at the base of Interval 2 reflect low to moderate accommodation rates (Catuneanu, ). This juxtaposition of fluvial deposits — with evidence of subaerial exposure of deltaic deposits of Interval 1 — is preserved within irregular depressions with a localized distribution, showing dimensions of tens of metres thick and less than 15 km wide (Figs and ); all of this suggests that Interval 2 represents incised‐valley fills (Dalrymple et al ., ; Leeder & Stewart, ; Gibling, ; Blum et al ., ; Wang et al ., ) (Fig. B and C).…”

“…In this case, delta‐front deposits (FAs 2 and 3) of Interval 1 are overlain by aeolian facies (FAs 11 and 12) of Interval 3. The composite surface is represented by a sub‐horizontal, extensive subaerial exposure surface situated above, and lateral to, adjacent depressions, suggesting that it may represent interfluve areas (O'Byrne & Flint, ; Maynard et al ., ; Tesson et al ., ; Holbrook & Bhattacharya, ; Wang et al ., ). These areas away from active fluvial incision and fluvial deposition were characterized by non‐accumulation and bypass.…”

Palaeohydrological characteristics and palaeogeographic reconstructions of incised‐valley‐fill systems: Insights from the Namurian successions of the United Kingdom and Ireland

“…The IVF dimensions are derived from the original source work, either obtained from the primary text or measured directly on figures using image-analysis software (ImageJ;Schneider et al, 2012). The measurement of IVF dimensions follows the method by Wang et al (2019). IVF thickness (T) is defined as the vertical distance between the elevation of the lowermost point of the erosional IVF base and the height of the interfluves at the valley margins.…”

“…Here, 'fast' is defined with respect to a theoretical equilibrium time, which characterizes the natural response time of a depositional basin to imposed change and is primarily determined by basin dimensions, sediment supply and water discharge (Paola et al, 1992). Considering the similarity in magnitude and frequency of eustatic sea-level changes during Namurian and late-Quaternary times, and given the relatively quiescent tectonic context of the Namurian basins of the UK and Ireland, the scaling relations developed from the late-Quaternary valleys (Wang et al, 2019) can be tentatively applied to the Namurian examples in this work. Accordingly, drainage areas of 10 incised valleys considered in this work have been estimated based on the approximated IVF cross-sectional area, utilizing the scaling relationship derived from Fig.…”

“…The results of regression analysis between these two variables (power-law relationship and R 2 ) are reported in respective boxes. late-Quaternary examples (Wang et al, 2019). A scaling relation between drainage area and IVF cross-sectional area for late-Quaternary IVFs from passive continental margins (Fig.…”