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

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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.