A database solution for the quantitative characterisation and comparison of deep-marine siliciclastic depositional systems

In sedimentological investigations, the ability to conduct comparative analyses between deep-marine depositional systems is hindered by the wide variety in methods of data collection, scales of observation, resolution, classification approaches and terminology. A relational database, the Deep-Marine Architecture Knowledge Store (DMAKS), has been developed to facilitate such analyses, through the integration of deep-marine sedimentological data collated to a common standard. DMAKS hosts data on siliciclastic deep-marine system boundary conditions, and on architectural and facies properties, including spatial, temporal and hierarchical relationships between units at multiple scales. DMAKS has been devised to include original and literature-derived data from studies of the modern sea-floor, and from ancient successions studied in the sub-surface and in outcrop. The database can be used as a research tool in both pure and applied science, allowing the quantitative characterisation of deep-marine systems. The ability to synthesise data from several case studies and to filter outputs on multiple parameters that describe the depositional systems and their controlling factors enables evaluation of the degree to which certain controls affect sedimentary architectures, thereby testing the validity of existing models. In applied contexts, DMAKS aids the selection and application of geological analogues to hydrocarbon reservoirs, and permits the development of predictive models of reservoir characteristics that account for geological uncertainty. To demonstrate the breadth of research applications, example outputs are presented on: (i) the characterisation of channel geometries, (ii) the hierarchical organisation of channelised and terminal deposits, (iii) temporal trends in the deposition of terminal lobes, (iv) scaling relationships between adjacent channel and levee architectural elements, (v) quantification of the likely occurrence of elements of different types as a function of the lateral distance away from an element of known type, (vi) proportions and transition statistics of facies in elements and beds, (vii) variability in net-to-gross ratios among element types

The thick-bedded tail of turbidite thickness distribution as a proxy for flow confinement: examples from Tertiary basins of central and northern Apennines (Italy)

This study reviews the thickness statistics of non-channelized turbidites from four tertiary basins of Central-Northern Apennines (Italy), where bed geometry and sedimentary character have been previously assessed. Though very different in terms of size and, arguably, character of feeder system, these basins share a common stratigraphic evolution consisting in transition from an early ponded to a late unconfined setting of deposition. Based on comparison of thickness subsets from diverse locations and stratigraphic heights within the studied turbidite fills, this paper seeks to answer the following questions: i) how data collection procedures and field operational constraints (e.g. measure location, outcrop quality, use of thicknesses data from single vs. multiple correlative sections, stratigraphic thickness of the study interval) can affect statistics of sample data? ii) how depositional controls of confined vs. unconfined turbidite basins can result in different thickness-frequency distributions?; and iii) is there in thickness statistics a ‘flow confinement’ signature which can be used to distinguish between confined and unconfined turbidites? Results suggest that: i) best practices of data collection are crucial to a meaningful interpretation of sample data statistics, especially in presence of stratigraphic and spatial trends of turbidite bed thickness; ii) a systematic bias against cm-thick Tcd Bouma sequence turbidites exists in sample data, which can result in the low-end tail of empirical thickness-frequency distributions to depart significantly from the actual distribution of turbidite thickness; and iii) thickness statistics of beds starting with a basal Ta/Tb Bouma division bear a coherent relationship to the transition from ponded to unconfined depositional settings, consisting in reduction of variance and mean and, consequently, parameters, or even type, of best fit model distribution. This research highlights the role of flow stripping, sediment by-pass and bed geometry in altering the initial thickness distribution of ponded turbidites and suggests how fully ponded mini-basins represent the ideal setting for further research linking turbidite thickness statistics and frequency distribution of parent flow volumes

The stratigraphic record of submarine channel-lobe transition zones

Channel-lobe transition zones (CLTZs) represent critical areas between the submarine slope and basin floor systems, where sediment gravity flows transition from confined to unconfined. In modern systems, this area is characterised by a distinctive assemblage of erosional and depositional features. However, the transfer of the CLTZ into the stratigraphic record is not well constrained. By the detailed study of various well-constrained exhumed base-of-slope systems within the Tanqua and Laingsburg depocentres of the Karoo Basin, South Africa, the sedimentary and stratigraphic record of CLTZs is investigated. The first detailed study of key depositional and erosional bedforms that characterise ancient CLTZs, including sediment waves and giant scour-fills, are presented. Their process record suggests complicated flow-bedform interactions, where both the preservation and sedimentary characteristics are dependent on the evolution of the feeder channel and the lateral position to the channel-mouth. Within the base-of-slope environments, juxtaposition of lobes and channel-fills is common. The lobes in these proximal fan environments are sandstone-prone and differ in facies and architectural characteristics to lobes downdip on the basin floor. The sand-rich nature and juxtaposition of elements in ancient CLTZs means that they are considered attractive hydrocarbon reservoir targets in the subsurface. However, fine-scale reservoir modelling and streamline simulations suggests that the relatively limited sand-volume of channel-fills in comparison to lobe deposits in these environments can have a negative impact on reservoir performance due to its effect on reservoir connectivity. Overall, the stratigraphic record of CLTZs shows high diversity in architecture, facies characteristics and volume, which can be related to three primary controls: a) spatial variability, b) flow efficiency and c) channel evolution. These three controls infer that CTLZs are highly dynamic, migrating and changing in dimensions over time; this needs to be considered when assessing how CLTZs are recorded in the rock record

Inverse and Forward Modelling of Shallow-Marine Stratigraphy

This thesis presents the development and application of a numerical inverse and forward model of stratigraphy applied to shallow-marine wave-dominated sedimentary systems. The approach links a “process-based” forward model of stratigraphy (i.e. BARSIM, developed by J.E.A. Storms, University of Delft) to a fully non-linear stochastic inverse scheme. The inverse problem has been formulated using a Bayesian framework in order to sample the full range of uncertainty and explicitly build in prior knowledge. The methodology combines Reversible Jump Markov chain Monte Carlo and Simulated Tempering algorithms which are able to deal with variable dimensional inverse problems and multi-modal posterior probability distributions, respectively. The numerical scheme requires the construction of a likelihood function to quantify the agreement between simulated and observed data (e.g. sediment ages and thicknesses, grain-size distributions). Prior to real case study applications, the method has been successfully validated on different scenarios built from synthetic data, in which the impact of data distribution, quantity and quality on the uncertainty of the inferred environmental parameters were investigated. The numerical scheme has then been applied to two case studies: the outcrop-constrained Lower Cretaceous “Standardville” parasequence of the Aberdeen Member of the Blackhawk Formation (Boock Cliffs, Utah, U.S.A.) and the Emsian sub-surface data of South Algeria. The inverse modelling scheme successfully reproduced stratigraphic architecture in both cases, within the constraints of the input data quality. The inferences of the relative sea level, sediment supply and wave regime histories contribute to the understanding of mechanisms that produced the observed stratigraphy. Of equal importance, the inverse results allowed complete characterisation of uncertainties in these forcing parameters and in the stratigraphic architecture developed in between data constraints. These results suggest that the inverse model may ultimately provide a process-based geological complement to standard geostatistical tools for the static characterization of hydrocarbon reservoirs

Shoreface response to sea level change and the evolution of barrier coasts

This thesis investigates shoreface response to sea level change, and the evolution of wave-dominated coastal barrier systems, in response to late-Quaternary and future environmental change. A numerical stratigraphic model (BARSIM) was calibrated using chronostratigraphic evidence from barrier coasts of southeastern Australia, and was used to explore shoreface response and coastal evolution during the last-glacial cycle and Holocene highstand. The modelling supported previous suggestions that Holocene strandplain progradation was primarily sourced from disequilibrium-stress-induced onshore sand supply, due to the erosion of lower-shoreface sand bodies (e.g. coastal barriers that were overstepped during late transgression). Simulated mid- to late-Holocene sea-level fall, within the bounds of existing evidence, was insufficient to supply observed strandplain progradation. Furthermore, external sand supply resulted in progradation well beyond the depth of present-day barrier complexes. Highstand barrier stacking was found to vary with prior transgressive-barrier behaviour: sea level change and substrate physiography controlled barrier rollover and overstepping behaviours, which resulted in alternative stacking relationships. Hypothetical forward simulations were also carried out to assess the sensitivity of shoreface response (i.e. active shoreface extent, depth-dependent shoreface response rates) and coastal evolution to sea level change. For increasing rates of sea level change typical of the late Quaternary and projected sea-level rise (0.05-10 mm/yr), time-invariant active-shoreface behaviour contracted from the lower shoreface toe to the surf zone. Depth-dependent lower-shoreface erosion was most significant for mesoscale coastal evolution (i.e. 102-105 yrs), which is characterised by partial shoreface activity. The findings suggest that depth- and timescale-dependent shoreface response limit the reliability of equilibrium-profile models for mesoscale problems

Sedimentary geology of glacial and periglacial gravel bodies (SW-Germany) : Dynamic stratigraphy and aquifer-sedimentology

Würmian, coarse-grained meltwater deposits were studied in more than 70 gravel pits of SW-Germany. The heterogeneity + complexity of sedimentary architecture of gravel bodies + its distribution within the Rhine glacier area + its discharge zones required the use of sedimentological, stratigraphic, geophysical + hydrological methods. In order to understand the processes of formation the principles of ‘Dynamic Stratigraphy' were applied. Stratigraphic units were classified into a hierarchy of temporal + spatial scales (1. particles; 2. strata; 3. depositional elements; 4. facies bodies; 5. sequences; 6. basin fills). Their genesis + geophysical record but also their relevance for hydrogeology is discussed. A particular focus is placed on the qual. + quant. characterization of fluvial gravel-bed deposits which represent important groundwater storages in many valley fills in Europe. The translation of sedimentary units into hydrogeological properties (lithofacies - hydrofacies; depositional elements - correlation structures; gravel body architectures - heterogeneity patterns) provided important fluid-flow parameters. Detailed outcrop-wall maps were digitalized + transformed into 2-dimensional permeability fields. The simulations show how sedimentary architectures determine the flow-paths + -velocity of groundwater. 3-D georadar surveys were carried out. The method resolves a detailed structural image of the spatial subsurface architecture and allows the recognition of the different gravel bodies. Quantified geometrical data from both braided river deposits + meandering river deposits are documented. Various meltwater-controlled facies bodies were formed during an overall ice-retreat of the Würmian Rhine glacier. A summary of lithofacies types, stratal organizations and deformation structures is documented.Würmzeitliche, grobklastische Schmelzwasserablagerungen wurden in mehr als 70 Kiesgruben in SW-Deutschland untersucht. Um die Bildungsprozesse zu verstehen, wurde die Methodik der ‚Dynamischen Stratigraphie' angewandt. Sedimentäre Einheiten werden dabei in eine Hierarchie zeitl. + räuml. Größenmaßstäbe eingeordnet (1. Partikel, 2. Schichtung, 3. Ablagerungs-Elemente, 4. Fazies-Körper, 5. Sequenzen, 6. Beckenfüllungen). Neben ihrer Genese + geophys. Erfassung wird auch die Bedeutung für die Hydrogeologie diskutiert. Ein Schwerpunkt der Arbeit liegt auf der Charakterisierung von fluviatilen Kiesablagerungen. Proglaziale ‚braided river'-Ablagerungen unterscheiden sich anhand der Ausbildung + Häufigkeit von Lithofaziestypen + Ablagerungs-Elementen sowie des sedimentären Stapelungsmusters. Die Übersetzung der Grundtypen von Kieskörpern in hydrogeologische Heterogenitäten (Lithofazies - Hydrofazies, Ablagerungs-Elemente – Korrelationsstrukturen, Kieskörperarchitektur – Heterogenitätsmuster) lieferte wichtige Parameter zur Ermittlung des Fließverhaltens von Grundwasser. Resultate numerischer Aufschlussmodellierungen zeigen, wie die sedimentäre Genese sowohl die Fließpfade als auch die Fließgeschwindigkeit bestimmen. Zus. wurden 3-D Georadar Messungen durchgeführt. Die Methode liefert ein genaues strukt. Bild der Architektur des Untergrundes. Die Reflektionen können besonders hinsichtlich der Ablagerungs-Elemente interpretiert + dadurch die Kieskörpertypen unterschieden werden. Es werden quantifizierte geometrische Daten sowohl von ‚braided river'- Ablagerungen als auch von ‚meandering river'- Ablagerungen dokumentiert. Vielfältige schmelzwasser-kontrollierte Fazieskörper sind während des Zerfalls + Rückzugs des würmzeitlichen Rheingletschers entstanden. Mittels Aufschlussanalysen, Georadarmessungen + der Landschaftsmorphologie konnten verschiedene Ablagerungsmilieus rekonstruiert werden. Dokumentiert werden Lithofaziestypen, Schichtungsmuster + Deformationsstrukturen