Controls on shallow-marine stratigraphy; a process-response approach

This thesis is concerned with the interface between land and sea. The interaction of coastal evolution and the sedimentary record, in this case of a wave-dominated coastal system, over geological timescales (< 105 y) is investigated in relation to their forcing parameters such as relative sea-level change, sediment supply, and wave climate. The preserved sediments record the dynamics of the coastal system in stacked but uncomplete sediment packages, which formed as the coastline migrated in landward or seaward direction resulting from erosion and deposition of sand and clay along the shallow parts of the coastal system (< 100 m waterdepth). If we want to understand coastal evolution over geological timescales, we must be able to read or interpret the stratigraphic record. Reconstructing coastal evolution from preserved shallow-marine stratigraphy is very difficult. The sediment record is not complete due to phases of erosion and we know little about past local changes in relative sea level, sediment supply, and wave climate. Also, the individual effects of these variables on coastal evolution and the stratigraphic record are poorly known. As the processes that drive coastal evolution, and therefore the resulting sedimentary record, act over thousands of years it is not possible to simply take measurements and make observations. Nevertheless, the stratigraphic record is the key to understand coastal evolution over geological timecales because it is the only physical evidence. Therefore a two dimensional numerical model has been developed which simulates the processes which are presumably important for coastal evolution and the formation of the stratigraphic record over long timescales. This model, its development and some applications are described in this thesis with the goal of increasing our understanding of coastal dynamics over geological timescales.Civil Engineering and Geoscience

Data from the Lake Strynevatnet Research

Dataset from paper: Source to Sink Reconstruction of a Holocene Fjord-infill: depositional patterns, suspended sediment yields, wind-induced circulation patterns and trapping efficiency for Strynevatnet, inner Nordfjord, Norway, published in Sedimentary Record. Contains geophysical data and GPS locations and Delft3D input files

Duration of deposition from decelerating high-density turbidity currents

Using recent advances in the stability analysis of current ripples, a new model for the calculation of duration of sediment deposition from decelerating high-density turbidity currents is proposed. The model, named TDURE, refines a duration model proposed by Allen (1991) (J. Sediment. Petrol. 61, 291-295) by calculating the accumulation time of the rippled T(c)-division separately from the massive and plane parallel-laminated T(ab)-divisions in Bouma-type turbidites. TDURE consists of three modules. In the first module, the accumulation time for the T(a)- and T(b)-divisions is approximated by assuming a linear decrease in sedimentation rate with height in the turbidite. As in the original model, a straight line is fitted through inferred sedimentation rates at the T(ab)- and T(bc)-boundaries. In the second module, angle of climb of ripples, thickness of the T(c)-division and grain size distribution are used in empirical relationships between ripple migration rate and a grain-related mobility parameter to estimate the accumulation time of the T(c)-division. In the third module, the expected development of ripple size across the T(c)-division is calculated using empirical relationships between rate of development of ripple height and grain-related mobility parameter, and subsequently compared with the observed development of ripple size in the turbidite. In this way, the accuracy of the accumulation time calculated in module 2 can be verified independently. TDURE was tested using Bouma-type turbidites from the Doheny Channel (Capistrano Fm., CA, USA) and the Flysch di Motta (Calabria, Italy). Accumulation times of 12 and 10.75 min for the T(c)-division, and 19 and 16 min for the T(abc)-sequence were calculated for the Doheny Channel and the Flysch di Motta turbidites, respectively. Although module 3 underestimates the rate of development of current ripples near the T(bc)-boundary in both beds, ripple size at the T(cd)-boundary is calculated accurately. The underestimation of development rate may be caused by differences between flow conditions in experimental flumes on which the model calculations are based and turbidity-current dynamics. (C) 2000 Elsevier Science B.V. All rights reserved

Modelling astronomical climate signals in fluvial stratigraphy

Orbital climate forcing is demonstrated to result in cyclic changes as reflected in the catchment, including precipitation, temperature, vegetation, sediment supply and water discharge. All of these are known to largely impact alluvial architecture. Climate change related to the 21-kyr precession cycle was proposed as driver of regularly-alternating river avulsion and overbank phases in the Eocene Willwood Formation of the Bighorn Basin, Wyoming, USA (Abels et al. 2013; 2016). This study aims to explore the conditions that are favourable for these climate cyclic signals to be preserved in the fluvial stratigraphy

Automatic detection of buried channel deposits from dense laser altimetry data

The formation of the current Rhine-Meuse delta mainly took place during the last 12 000 years. Consecutive avulsions, i.e. sudden changes in the course of river channels, resulted in a complicated pattern of sandy channel deposits, surrounded by peat and clay. Knowledge of this pattern is not only interesting from a geohistorical viewpoint, but is also essential when planning and maintaining constructions like roads and dikes. Traditionally, channel deposits are traced using labor intensive soil drilling. Channel deposits are however also recognizable in the polder landscape by small local elevation changes due to differential compaction. The purpose of this research is to automatically map channel deposits based on a structural analysis of high resolution laser altimetry data. After removing infrastructural elements from the laser data, local feature vectors are built, consisting of the attributes slope, curvature and relative elevation. Using a maximum likelihood classifier, 75 million gridded laser points are divided into two classes: buried channel deposits and other. Results are validated against two data sets, an existing paleographic map and a set of shallow drilling measurements. Validation shows that our method of channel deposit detection is hampered by signal distortion due to human intervention in the traditional polder landscape. Still it is shown that relative young deposits (4 620 to 1 700 years Before Present) can be extracted from the laser altimetry data.Remote SensingAerospace Engineerin

Impact of external forcing and catchment response on sediment flux

Geoscience & EngineeringCivil Engineering and Geoscience

Late-Holocene evolution of the Mahakam delta, East Kalimantan, Indonesia

The late-Holocene Mahakam delta, located along the tropical eastern shore of Kalimantan, Indonesia, is considered to be a textbook example of a mixed tide-fluvial dominated delta system. The delta prograded about 60 km during the past 5000 years, which led to the development of a distinct network of distributary and tidal channels. Wave action is low due the limited fetch in the narrow strait of Makassar. Mahakam River discharge is about a quarter of the Mississippi River discharge and is characterized by absence of flood surges. Therefore, natural levees, crevasse splays and avulsions are absent in the delta plain. For the past four decennia, both modern and ancient Mahakam delta deposits have been studied in detail in order to better understand subsurface Miocene and Tertiary Mahakam deposits, which host large volumes of hydrocarbons. This study focuses on the dynamics and stratal patterns of delta plain, delta-front platform deposits and suspended sediments. Due to the predominance of semi-diurnal tides and the associated flow reversals, depositional patterns are highly variable which has resulted in the formation of characteristic sand-mud couplets. The distribution of the sand-mud couplets found in this study differs from previously proposed conceptual models. They are limited to the fluvial domain and form in the distributary channels (lateral channel bar) or at the fluvial dominated delta-front platform, which flanks the mouth bar deposits in offshore direction. The sand-mud couplets which formed as delta-front platform and lateral channel bar deposits are similar and can only be identified based on their 14C age. The sand content decreases significantly towards the tidal dominated areas due to limitation in transport capacity. Turbidity measurements taken in front of the river mouth also show rapid settlement of river plume sediments. Some 22 new AMS 14C dates show that late Holocene sea level history resembles the eustatic sea level curve giving a first approximation of the Late Holocene sea level history for East Kalimantan. The dates suggest that the progradational delta system evolved under conditions of slowly rising sea level, which compares well to the eustatic sea level curve. In addition, calculated averaged deposition rates of the sand-mud couplets indicate that deposition is driven by the spring-neap tide cycles instead of the daily tidal cycl

Non-linear response of the Golo River system, Corsica, France, to Late Quaternary climatic and sea level variations

Disentangling the impact of climatic and sea level variations on fluvio-deltaic stratigraphy is still an outstanding question in sedimentary geology and geomorphology. We used the Golo River system, Corsica, France, as a natural laboratory to investigate the impact of Late Quaternary climate and sea level oscillations on sediment flux from a catchment and on fluvio-deltaic stratigraphy. We applied a numerical model, PaCMod, which calculates catchment sediment production and transport and compared modeling output to the sedimentary record of the Golo alluvial-coastal plain, whose chronology was reinterpreted using new optical stimulated luminescence (OSL) ages on feldspars. Our modeling, OSL ages, and geomorphological results indicate that the two main phases of braidplain development in the Golo alluvial-coastal plain occurred during the cold–dry phases of MIS5 and during the late MIS4-early MIS3, as a consequence of high catchment erosion rates and low water discharge. Incision and sediment reworking occurred during sea level low stand periods (MIS4 and late MIS3-MIS2). High sediment flux pulses from the catchment outlet were generated during the Lateglacial and early Holocene, as a result of the release of sediments previously stored within the catchment and enhanced snowmelt. Our results suggest a non-linear response of the Golo River system to climatic and eustatic changes, caused by sediment storage within the catchment and geomorphological thresholds. This indicates that a direct comparison between palaeo-climate and stratigraphy is not possible without considering catchment sediment storage and sediment transport delays out of the catchment

Establishing 3d numerical reservoir analogues: Modelling the formation of sand bodies in deltaic environments

The assessment and production of hydrocarbon resources incorporates geological models created from core and wireline well data, as well as seismic data. This data is spatially discrete but is used create a spatially continuous model. However, the heterogeneity within depositional environments is on a smaller spatial scale than the available data resolution. The field data is therefore supplemented with relevant analogue data, often from deposits which differ in various aspects from the actual reservoir being assessed. To improve the correlation between analogues and the reservoir being studied, it is proposed that 3D numerical analogues are used in addition to the current outcrop analogues. These 3D numerical analogues can be created through process based numerical modelling and can more closely match the conditions of the reservoir being studied. In this presentation we propose a workflow to create and implement 3D numerical outcrops. We go on to show an initial stage of a proof of concept for the workflow. It is shown that using the software Delf3D, it is possible to simulate the sand bodies found in deltaic deposits, which can later act as hydrocarbon reservoirs.Geoscience & EngineeringCivil Engineering and Geoscience