Unravelling the tectonic and climatic controls on Upper Jurassic mass flow deposits in NE Scotland

倾斜表面上沉积物堆积的灾难性破坏产生了所有沉积矿床中最具视觉效果的一些。这些矿床也提出了许多科学挑战，包括了解变化的沉积速率、横向变化、沉积过程和沉积控制。了解海相质量流沉积非常重要，因为它们既构成了油气的储层，也构成了烃源岩。该项目将研究在苏格兰东北部沿海暴露的壮观的kimmeridian - Tithonian（上侏罗统）体流沉积[1,2,3]。这些岩石沉积在侏罗纪时期活动的Helmsdale断裂系统附近的海洋中。不同寻常的是，这个质量流系统活跃了超过8 Ma的地球历史，包含了一系列的质量流沉积，从岩石落角砾岩、碎屑流、均质砂岩到浊积岩。因此，这些暴露提供了一个天然的实验室来考虑长期对质量流沉积的外部控制。层序地层学初步结果表明，构造作用影响了沉积物的供给、局部分布和长期旋回；这些沉积可以被归为沉积层序旋回，其年龄与多塞特[2,4]和其他地方的半深海沉积层序相同，这意味着气候控制。在多塞特[4]演替中进一步证实的米兰科维奇旋回表明，这一时期有很强的气候控制作用。一个可行的假设是，海平面上升引起沉积物不稳定，导致能量更高、颗粒更粗的质量流沉积，而海平面上升导致能量更低的质量流沉积，如浊积岩。上图：赫姆斯代尔附近壮观的质量流沉积物的一部分，这将是本研究的重点。下图：研究区域典型的前海岸和悬崖暴露。本项目的主要目标是：1。构建图形日志和地图，记录矿床在时间和空间上的性质。完成泥岩孢粉学分析，结合已发表的菊石生物地层学资料，建立生物地层时间尺度，进一步进行区域对比。3. 3 .分别利用孢态丰度和保存度对风化速率和迁移的变化进行定性估计。构建沉积物的层序地层学解释，并通过与其他地方的剖面进行比较，批判性地评估构造和气候对沉积物包装的相对作用。

The catastrophic failure of sediment accumulations on inclined surfaces produces some of the most visually dramatic of all sedimentary deposits. These deposits also present a number of scientific challenges including understanding the variable sedimentation rates, lateral changes, depositional processes and controls on sedimentation. An understanding of marine mass flow deposits is important because as well as presenting engineering challenges they form both reservoir and source rocks for hydrocarbons.This project will examine the spectacular Kimmeridgian to Tithonian (Upper Jurassic) mass flow deposits that are well exposed along the coast in NE Scotland [1, 2, 3]. These rocks were deposited in the sea adjacent to the Helmsdale Fault system which was active during the Jurassic. Unusually, this mass flow system was active for over 8 Ma of Earth history and contains a spectrum of mass flow deposits from rock fall breccias, debris flows and homogenized sandstones to turbidites. These exposures thus provide a natural laboratory to consider the external controls on mass flow deposits over a long time period. Preliminary sequence stratigraphic results suggest that whilst tectonics influenced the sediment supply, local distribution of the deposits and the long term cyclicity; the deposits can be grouped into depositional sequence cycles that are the same age as hemipelagic depositional sequences in Dorset [2, 4] and elsewhere implying a climatic control. Furthermore proven Milankovitch cycles in the Dorset [4] succession demonstrate that there is a strong climatic control at this time. A working hypothesis is that eustatic sea-level fall caused sediment instability resulting in higher energy and coarser-grained mass flow deposits, whereas eustatic sea-level rise resulted in lower energy mass flow deposits such as turbidites. Upper image: Part of the spectacular mass flow deposits near Helmsdale that will be the focus of this study.Lower image: Typical foreshore and cliff exposures in the study area.The main objectives of this project are to:1. Construct graphic logs and maps to record the nature of the deposits in time and space.2. Complete palynological analysis of the mudrocks, integrate data with published ammonite biostratigraphy and develop biostratigraphic timescales for extra regional correlation. 3. Obtain a qualitative estimate of changes in weathering rate and transportation using palynomorph abundances and preservation respectively.4. Construct a sequence stratigraphic interpretation of the deposits and use this to critically assess the relative role of tectonics and climate on the sediment packaging by comparison with sections elsewhere.