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The role of shelf morphology on storm‐bed variability and stratigraphic architecture, Lower Cretaceous, Svalbard
Sedimentology ( IF 2.6 ) Pub Date : 2020-08-13 , DOI: 10.1111/sed.12791
Sten‐Andreas Grundvåg 1 , Mads E. Jelby 2 , Snorre Olaussen 3 , Kasia K. Śliwińska 4
Affiliation  

The dominance of isotropic hummocky cross‐stratification, recording deposition solely by oscillatory flows, in many ancient storm‐dominated shoreface–shelf successions is enigmatic. Based on conventional sedimentological investigations, this study shows that storm deposits in three different and stratigraphically separated siliciclastic sediment wedges within the Lower Cretaceous succession in Svalbard record various depositional processes and principally contrasting sequence stratigraphic architectures. The lower wedge is characterized by low, but comparatively steeper, depositional dips than the middle and upper wedges, and records a change from storm‐dominated offshore transition – lower shoreface to storm‐dominated prodelta – distal delta front deposits. The occurrence of anisotropic hummocky cross‐stratification sandstone beds, scour‐and‐fill features of possible hyperpycnal‐flow origin, and wave‐modified turbidites within this part of the wedge suggests that the proximity to a fluvio‐deltaic system influenced the observed storm‐bed variability. The mudstone‐dominated part of the lower wedge records offshore shelf deposition below storm‐wave base. In the middle wedge, scours, gutter casts and anisotropic hummocky cross‐stratified storm beds occur in inferred distal settings in association with bathymetric steps situated across the platform break of retrogradationally stacked parasequences. These steps gave rise to localized, steeper‐gradient depositional dips which promoted the generation of basinward‐directed flows that occasionally scoured into the underlying seafloor. Storm‐wave and tidal current interaction promoted the development and migration of large‐scale, compound bedforms and smaller‐scale hummocky bedforms preserved as anisotropic hummocky cross‐stratification. The upper wedge consists of thick, seaward‐stepping successions of isotropic hummocky cross‐stratification‐bearing sandstone beds attributed to progradation across a shallow, gently dipping ramp‐type shelf. The associated distal facies are characterized by abundant lenticular, wave ripple cross‐laminated sandstone, suggesting that the basin floor was predominantly positioned above, but near, storm‐wave base. Consequently, shelf morphology and physiography, and the nature of the feeder system (for example, proximity to deltaic systems) are inferred to exert some control on storm‐bed variability and the resulting stratigraphic architecture.

中文翻译:

架子形态对风暴床变异性和地层构造的作用,下白垩统,斯瓦尔巴特群岛

在许多古老的以风暴为主的海岸-陆架演替中,各向同性的山岗交错分层占主导地位,仅通过振荡流来记录沉积。根据常规沉积学调查,这项研究表明,斯瓦尔巴特群岛下白垩统中三个不同且地层分离的硅质碎屑楔形物的暴雨沉积物记录了各种沉积过程,并且主要对比了层序地层构造。下部楔形物的特征是与中部和上部楔形物相比沉积低,但较陡的沉积倾角,并记录了由风暴为主的近海过渡(下部岸面到风暴为主的三角洲)-远三角洲前缘沉积的变化。各向异性的山岗交叉分层砂岩层的发生,可能在此过程中出现的高坪流源的冲刷和充填特征,以及楔形区此部分内的波变浊度表明,与河流三角洲系统的接近度影响了观测到的风暴床变异性。下楔的以泥岩为主的部分记录了风暴波基下的近海陆架沉积。在中间的楔形中,冲刷,天沟形铸件和各向异性的山形交叉分层风暴床发生在推断的远侧环境中,与在回生堆积副序列的平台断裂处的测深台阶有关。这些步骤引起了局部的,陡峭的沉积倾角,促进了向盆地方向流动的产生,这些流动偶尔冲刷到底层海底。风暴波和潮流的相互作用促进了大规模的发展和迁移,复合床形和较小规模的山形床形被保存为各向异性的山形交叉分层。上楔块由厚厚的,向海的,连续的,各向同性的,带有交叉分层的,含沙质层的砂岩层组成,这些砂岩层是由于在一个浅的,缓缓倾斜的斜坡式架子上的发育而造成的。相关的远端相的特征是大量的透镜状波状波纹交叠层状砂岩,表明盆地底部主要位于风暴波基的上方,但附近。因此,推断出架子的形态和地貌以及馈线系统的性质(例如,靠近三角洲的系统)可以对风暴床的变化性和由此产生的地层学结构施加某种控制。
更新日期:2020-08-13
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