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

揭示苏格兰东北部上侏罗统物质流沉积物的构造和气候控制

• 批准号: 1809490
• 金额: --
• 依托单位: The Open University
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2016
• 资助国家: 英国
• 起止时间: 2016 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-1809490
• 关键词: Unravelling; tectonic; climatic; controls; Upper

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.

倾斜表面上沉积物堆积的灾难性破坏产生了所有沉积物中最具视觉效果的一些。这些矿床也带来了一些科学挑战，包括了解可变的沉积速率、横向变化、沉积过程和对沉积的控制。了解海洋物质流沉积物是很重要的，因为除了提出工程挑战外，它们还形成烃类的储集层和烃源岩。本项目将研究苏格兰东北部沿着海岸出露的壮观的基默里纪至提顿纪（上侏罗纪）物质流沉积物[1，2，3]。这些岩石沉积在邻近赫尔姆斯代尔断层系统的海洋中，该断层系统在侏罗纪期间活动。不寻常的是，这个质量流系统是活跃的超过8马的地球历史，并包含一个频谱的质量流沉积岩崩角砾岩，泥石流和均质砂岩浊积岩。因此，这些暴露提供了一个自然的实验室，以考虑长期对质量流沉积物的外部控制。初步的层序地层学结果表明，虽然构造影响沉积物供应、沉积物的局部分布和长期旋回性;但沉积物可分为与多塞特[2，4]和其他地方的半远洋沉积层序年龄相同的沉积层序旋回，这意味着气候控制。此外，在多塞特[4]继承证明米兰科维奇周期表明，有一个强大的气候控制在这个时候。一个工作的假设是，海平面升降引起沉积物不稳定，导致更高的能量和粗粒度的质量流沉积，而海平面升降导致较低的能量质量流沉积，如浊积岩。 上图：Helmsdale附近壮观的物质流沉积物的一部分将成为本研究的重点。下图：研究区域的典型前滨和悬崖暴露。本项目的主要目标是：1.制作图解日志和地图，以记录时间和空间上的矿床性质。完成泥岩的孢粉学分析，将数据与已发表的菊石生物地层学相结合，并为额外的区域对比制定生物地层时间表。3.分别利用孢粉丰度和保存率定性估计风化速率和搬运的变化.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，以此来批判性地评估构造和气候对沉积物包装的相对作用。