AAPG Europe Regional Conference, Global Analogues of the Atlantic Margin

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The influence of halokinesis in the trajectory and geometry of prograding clinoforms: insights from the Tyddlybanken Basin, Norwegian Barents Sea

Abstract

Clinoforms of different scales have been observed in the modern and ancient sedimentary record, along coastlines, deltas, and continental margins (Helland-Hansen and Hampson, 2009). They generally consist of a topset, foreset and bottomset, with the intersection between topset and foreset defining the rollover point. The position of the rollover point and foreset angle through time are used to predict the distribution of fluviodeltaic and shallow marine sandstones, and the timing of sand bypass to the slope and basin floor (Johannessen and Steel, 2005; Helland-Hansen and Hampson, 2009). High foreset angles are commonly associated with coarse-grained sediments (e.g. Patruno et al., 2015). However, other factors can control the foreset angle such as sediment supply, relative sea level, and basin physiography (Ross et al., 1994; Pirmez et al., 1998). Although the trajectory and geometry of clinoforms in foreland basins (e.g. Johannessen and Steel, 2005), passive margins (e.g. Steckler et al., 1999) , and continental rift basins (e.g. Patruno et al., 2015) have been described in several publications, few works describe the influence of halokinesis on the trajectory and geometry of clinoforms in salt-related basins (e.g. Ge et al., 1997). The present study focusses on the Tyddlybanken Basin, a small salt-influenced basin in the eastern side of the Norwegian Barents Sea (Rowan and Lindsø, 2017) (Fig. 1). The basin consists of an NW–SE elongated salt wall surrounded by minibasins at the basin axis, while salt pillows are present at basin boundaries. NNW–prograding clinoforms have been identified in Triassic strata, whereas SSW-prograding clinoforms characterize the Lower Cretaceous strata. This study utilizes 2D seismic reflection data and combines 2D sequential restorations with trajectory and geometry analysis of clinoforms to: (1) identify the main periods of halokinesis of the Tyddlybanken Basin; and (2) understand the impact of salt movement on the geometry and trajectory of Lower Cretaceous clinoforms. Based on structural restorations, the onset of salt mobilization occurred during the Early-Middle Triassic causing the formation of minibasins and salt structures that remained active until the end of the Cretaceous. This episode was followed by Late Cretaceous-Cenozoic regional contraction and erosion, which caused the rejuvenation of salt structures. The trajectory and geometry of the Lower Cretaceous clinoforms indicate three episodes of minibasin infill: (1) decrease in accommodation space and subsequent falling trajectory with low foreset angles (1.55 to 2.92°) induced by the growth of the underlying salt pillow at the minibasin boundary; (2) sharp ascending trajectory followed by an increase in foreset angle from 2.92 to 3.14° due to larger accommodation space and steeper minibasin physiography caused by salt withdrawal; (3) moderate ascending trajectory accompanied by a decrease in foreset angle from 3.14 to 1.55°, which reflect the period of minibasin overfill and clinoform bypass of the salt diapir. These preliminary results indicate that: (1) Salt movements control the accommodation space of prograding clinoforms producing ascending or falling trajectories in response to salt withdrawal or uplift; (2) Changes in foreset angle observed in salt minibasins are not a direct consequence of lithological changes. Instead, they are related to basin physiography modifications caused by the salt movement underneath. This study provides a seismic example of how salt tectonics locally influence the trajectory and geometry of prograding clinoforms, having implications for the understanding of the minibasin infill and reservoir prediction in salt-related basins triggered by sediment progradation.