Four‐dimensional Variability of Composite Halokinetic Sequences

Abstract

The architecture of salt diapir-flank strata (i.e. halokinetic sequences) is controlled by the interplay between volumetric diapiric flux and sediment accumulation. Halokinetic sequences consist of unconformity-bounded packages of thinned and folded strata formed by drapefolding around passive diapirs. They are described by two end-members: (i) hooks, which are characterized by narrow zones of folding (<200 m) and high taper angles (>70°); and (ii) wedges, typified by broad zones of folding (300-1000 m) and low taper angles (<30°). Hooks and wedges stack to form tabular and tapered composite halokinetic sequences (CHS), respectively. CHSs were most thoroughly described from outcrop-based studies that, although able to capture their high-resolution facies variations, are limited in describing their 4D variability. This study integrates 3D seismic data from the Precaspian Basin and restorations to examine variations in CHS architecture through time and space along diapirs with variable plan-form and cross-sectional geometries. The diapirs consist of curvilinear walls that vary from upright to inclined and locally display well-developed salt shoulders and/or laterally transition into rollers. CHS are highly variable in both time and space, even along a single diapir or minibasin. A single CHS can transition along a salt wall from tabular to tapered geometries. They can be downturned and exhibit rollover-synclinal geometries with thickening towards the diapir above salt shoulders. Inclined walls present a greater proportion of tapered CHSs implying an overall greater ratio between sediment accumulation and salt-rise relatively to vertical walls. In terms of vertical stacking, CHS can present a typical zonation with lower tapered, intermediate tabular and upper tapered CHSs, but also unique patterns where the lower sequences are tabular and transition upward to tapered CHS. The study demonstrates that CHSs are more variable than previously documented, indicating a complex interplay between volumetric salt rise, diapir-flank geometry, sediment accumulation and roof dimensions. 1.

Salt-magma interactions influence intrusion distribution and salt tectonics in the Santos Basin, offshore Brazil

“…The Santos Basin located offshore south-eastern Brazil and formed in the Early Cretaceous (~130-125 Ma; Barremian-to-Early Aptian) due to the opening of the South Atlantic Ocean (Figs 1a and b) [e.g., Davison et al, 2012;Mohriak et al, 1995;Quirk et al, 2012]. During the post-rift, in the latest Aptian to possibly earliest Albian (~116-111 Ma), a ~2-3.5 km thick evaporite-dominated layer was deposited across the basin, covering a sag basin sedimentary succession (Figs 1a and b) [e.g., Davison et al, 2012;Karner and Gambôa, 2007;Pichel and Jackson, 2020;Rowan, 2014].…”

“…extensional) diapirs, which resulted in the formation of a large (>50 km wide), oceanward-dipping rollover within the Late Cretaceous and early Cenozoic strata (Fig. 1c) [e.g., Jackson et al, 2015b;Mohriak et al, 1995;Pichel and Jackson, 2020]. Intermediate translation during this period was characterised by the development of ramp-syncline basins, passive diapirs, and localized contraction and extension occurring in response to salt movement over a prominent base-salt relief (Fig.…”

“…Away from the Merluza Graben and its overlying rollers, salt diapirs are flanked by 3-4 s TWT thick, Upper Cretaceous-to-Lower Cenozoic minibasins (Figs 2, 4c, and 5). Composite halokinetic sequences, defined by thinning and upturn of strata at the diapirs flanks [sensu Giles and Rowan, 2012;Pichel and Jackson, 2020], are present at the edges of these minibasins between H2 (near Coniacian-Santonian boundary) and H7 (intra-Paleogene) (e.g., Figs 2 and 4c).…”

Halokinetic modulation of sedimentary thickness and architecture: a numerical modelling approach

“…Rodriguez et al 2018;Pichel et al 2019), and the Precaspian Basin (e.g. Duffy et al 2017;Pichel and Jackson 2020). There is therefore a need to better understand the interactions of sedimentary processes and routing with topographic relief associated with salt tectonics to provide insight into sediment routing patterns around topography (e.g.…”

“…There is therefore a need to better understand the interactions of sedimentary processes and routing with topographic relief associated with salt tectonics to provide insight into sediment routing patterns around topography (e.g. Ribes et al 2015;Cumberpatch et al 2021a;Giles and Lawton 2002;Rowan et al 2003;Pichel and Jackson, 2020). As a consequence, this can improve predictions of reservoir distribution and trap geometry and style for carbon storage (e.g.…”