Stratigraphic development of an Upper Jurassic deep marine syn‐rift succession, Inner Moray Firth Basin, Scotland

Abstract

The stratigraphic development of an Upper Jurassic syn‐rift succession exposed at outcrop in the Inner Moray Firth Basin has been investigated using high‐resolution biostratigraphy and sedimentology. A continuous 970 m thick section, exposed in the hangingwall of the Helmsdale Fault was logged in detail. The succession spans 8 Ma and contains eight lithofacies types, which indicate deposition in a deep marine setting. Boulder beds contain large, angular clasts, with bed thicknesses typically >2 m and poor sorting suggesting deposition by debris flows. An inverse clast stratigraphy is observed; the oldest boulder beds contain sandstone clasts of Upper Old Red Sandstone (ORS) with younger debris flows containing clasts of Middle ORS calcareous siltstone. A marked change from siliciclastic to carbonate dominated sedimentation occurred during the Early Tithonian, interpreted primarily as a result of change in lithologies in the footwall catchment from sandstone to calcareous siltstone, which reduced supply of siliciclastic sediment. Secondary factors are identified as increased aridity in the Early Tithonian, which reduced sand supply from the hinterland and a third‐order Early Tithonian eustatic sea‐level rise, which trapped coarser clastic sediment within the hinterland. Biostratigraphy allows calculation of variations in sedimentation rates with recognition of: (1) an early rift phase characterised by sandy turbidite deposition, when sedimentation rates averaged 0.08 m/ky, (2) a rift climax phase from the Early Kimmeridgian where sedimentation rates increased steadily to a maximum of 0.64 m/ky in the Early Tithonian, with strata dominated by boulder scale clast‐supported debris flows and (3) a late stage of rifting from the mid Tithonian, where sedimentation rates decreased to 0.07 m/ky. Overall sedimentation rates are comparable to those of other deep marine rift basins. Unroofing a resistant lithology on the footwall of a rift has important implications for siliciclastic sediment supply in rift basins.

Unravelling key controls on the rift climax to post‐rift fill of marine rift basins: insights from 3D seismic analysis of the Lower Cretaceous of the Hammerfest Basin, SW Barents Sea

“…In summary, during the rift climax stage, the geometry, distribution of depositional systems and the input of sediments in a basin are controlled by the interaction of several variables such as: 1) variability along the strike of the main bounding faults (Gawthorpe et al, 1990;Gupta et al, 1998;McLeod et al, 2002;Elliott et al, 2012Elliott et al, , 2017Elliott et al, , 2017; 2) diachronous movement of the faults; and 3) nature of the feeder system (Reading & Richards, 1994;Stow et al, 1996;Galloway, 1998;Gawthorpe & Leeder, 2000;Leppard & Gawthorpe, 2006). Although variations in footwall lithology are not considered here, this may be an important factor affecting the amount of coarsegrained sediment transported into the basin (McArthur et al, 2013). Fig.…”

“…The infill of marine rift basins is controlled by several variables: climate, eustatic sea-level, subsidence, drainage evolution, footwall lithology, nature of the feeder system (e.g. point source, multiple source or linear source), variability along the strike of the faults and basin physiography (Stow et al, 1996;Ravn as & Steel, 1998;Allen & Densmore, 2000;Gawthorpe & Leeder, 2000;McArthur et al, 2013;Sømme et al, 2013;Elliott et al, 2017). Some of these variables are determined by the evolution of fault propagation, which typically depends on the stage of the rift evolution (Cowie et al, 2000;Gawthorpe & Leeder, 2000).…”

“…Much effort has been made to understand the variables controlling the sedimentation in rift systems (e.g. Prosser, 1993;Nøttvedt et al, 1995;Gupta et al, 1998;Ravn as & Steel, 1998;Cowie et al, 2000;Gawthorpe & Leeder, 2000;Gabrielsen et al, 2001;Leppard & Gawthorpe, 2006;Zachariah et al, 2009;McArthur et al, 2013;Elliott et al, 2017). In addition, tectonostratigraphic models have been developed for single rift systems (Gawthorpe & Leeder, 2000), and more recently updated to include multiphase rifts (Henstra et al, 2017).…”

Depositional model for lacustrine nearshore subaqueous fans in a rift basin: The Eocene Shahejie Formation, Dongying Sag, Bohai Bay Basin, China

“…During the tectonically active stage, instantaneous and intense movements of boundary faults lead to rapid decrease of the absolute lake level. The latter forces the movement of water body to steep slope zones, with the consequent rapid increase of water depth, accommodation space above lake level and subaqueous accommodation space in steep slope zones (McArthur et al, 2013;Zhou et al, 2014;Henstra et al, 2016). These changes occur because water volume in the lacustrine basin remains almost constant and very small volumes of sediment are deposited during the short period of boundary fault activity (Fig.…”

“…To date, deep-water sedimentation processes and depositional characteristics of coarsegrained sediment gravity-flow deposits in rift systems have been studied in both modern rift lakes (Nelson et al, 1986(Nelson et al, , 1999Colman et al, 2003;Lykousis et al, 2007;Lyons et al, 2011;Karp et al, 2012) and ancient analogues (Anad on et al, 1991;Lin et al, 1991;Shanmugam & Moiola, 1995;Ravn as & Steel, 1998;Gawthorpe & Leeder, 2000;Bruhn & Vagle, 2005;Larsen et al, 2010;Liu et al, 2010;McArthur et al, 2013;Jia et al, 2014;Zhou et al, 2014;Henstra et al, 2016;Elliott et al, 2017). However, no appropriate depositional models have been proposed for nearshore subaqueous fans developed close to steep slopes of lacustrine rift basins.…”