Data Assimilation for a Geological Process Model Using the Ensemble Kalman Filter

We consider the problem of conditioning a geological process-based computer simulation, which produces basin models by simulating transport and deposition of sediments, to data. Emphasising uncertainty quantification, we frame this as a Bayesian inverse problem, and propose to characterize the posterior probability distribution of the geological quantities of interest by using a variant of the ensemble Kalman filter, an estimation method which linearly and sequentially conditions realisations of the system state to data. A test case involving synthetic data is used to assess the performance of the proposed estimation method, and to compare it with similar approaches. We further apply the method to a more realistic test case, involving real well data from the Colville foreland basin, North Slope, Alaska.Comment: 34 pages, 10 figures, 4 table

Source-to-sink analysis in an active extensional setting: Holocene erosion and deposition in the Sperchios rift, central Greece

We present a source-to-sink analysis to explain sediment supply variations and depositional patterns over the Holocene within an active rift setting. We integrate a range of modelling approaches and data types with field observations from the Sperchios rift basin, Central Greece that allow us to analyse and quantify (1) the size and characteristics of sediment source areas, (2) the dynamics of the sediment routing system from upstream fluvial processes to downstream deposition at the coastline, and (3) the depositional architecture and volumes of the Holocene basin fill. We demonstrate that the Sperchios rift comprises a 'closed' system over the Holocene and that erosional and depositional volumes are thus balanced. Furthermore, we evaluate key controls in the development of this source-to-sink system, including the role of pre-existing topography, bedrock erodibility and lateral variations in the rate of tectonic uplift/subsidence. We show that tectonic subsidence alone can explain the observed grain size fining along the rift axis resulting in the downstream transition from a braided channel to an extensive meander belt ( > 15 km long) that feeds the fine-grained Sperchios delta. Additionally, we quantify the ratios of sediment storage to bypass for the two main footwall-sourced alluvial fan systems and relate the fan characteristics to the pattern and rates of fault slip. Finally, we show that ≥40% of the sediment that builds the Sperchios delta is supplied by ≤22% of the entire source area and that this can be primarily attributed to a longer-term (~10 6 years) transient landscape response to fault segment linkage. Our multidisciplinary approach allows us to quantify the relative importance of multiple factors that control a complex source-to-sink system and thus improve our understanding of landscape evolution and stratigraphic development in active extensional tectonic settings

Characterizing Water on Early Mars through the Geomorphic Analysis, Crater-Age Dating, and Sediment Transport Modeling of Valley Networks and Deltas

The presence of valley networks across much of the ancient surface of Mars, together with the locations and morphologies of the ancient Martian deltas and paleolakes, provides strong evidence that the Martian surface environment was once capable of sustaining liquid water at the surface. Many of the largest valley networks have characteristics consistent with their formation primarily by precipitation and surface runoff. However, the timing and duration of clement conditions on Mars has remained unclear. Ten of the largest valley networks on Mars were mapped, crater-age dated, and analyzed to understand changes in fluvial erosion during early Martian history. Crater-age dating of individual valley networks revealed ages that cluster in the Late Noachian and Early Hesperian, consistent with their formation during a period of enhanced fluvial erosion and incision on Mars. Formation timescales of the valley networks were investigated through the use of three different sediment transport models, the Darcy-Weisbach flow velocity equation, and a variety of parameters to encompass a range of possible formation conditions. With runoff rates similar to intense storms in arid regions on Earth, the minimum formation timescales of these Martian valley networks range from 10^5 to 10^7 years. Shorter formation timescales require hurricane-scale flows that, if minimized with assumptions of continuous formation unlike even terrestrial rates, could complete large valley network formation in as little as 200 to 5000 years, though this is not the preferred interpretation. Investigating the effects of changing hydrologic and sedimentary conditions on Martian delta formation with 3-D modeling indicates that significant off shore sedimentation is common, particularly with high river discharge scenarios. These results have important implications for the formation timescales of the deltas and the lack of identifiable deltas on Mars today. While the results of this thesis do not support impact-induced climate change as the mechanism for creating precipitation sufficient to incise the large valley networks, neither do they extend the amount of time required to form the features beyond their range in age, consistent with hypotheses that precipitation was constrained to a relatively short period of Martian history near the Noachian-Hesperian boundary, approximately 3.6 to 3.8 Ga

Identification of the Mode of Evolution in Incomplete Carbonate Successions

Background: The fossil record provides the unique opportunity to observe evolution over millions of years, but is known to be incomplete. While incompleteness varies spatially and is hard to estimate for empirical sections, computer simulations of geological processes allow to examine the biasing effects of the incompleteness in silico. We combine simulations of different modes of evolution (stasis, (un)biased random walks) with deposition of carbonate platforms strata to examine how well the mode of evolution can be recovered from fossil time series, and how test results vary between different positions in the carbonate platform and multiple stratigraphic architectures generated by different sea level curves. Results: Stratigraphic architecture and position along an onshore-offshore gradient has only a small influence on the mode of evolution recovered by statistical tests. Tests fail to identify the correct mode of evolution even in the absence of stratigraphic biases, for adequate models, and under excellent sampling conditions. Visual examination of trait evolution in lineages shows that rather than stratigraphic incompleteness, maximum hiatus duration determines how much fossil time series differ from the original evolutionary process. Directional evolution is more prone to the biasing effects of stratigraphy, turning it into apparent punctuated anagenesis. In contrast, stasis remains unaffected. Conclusions: - Tests for the mode of evolution should be reviewed critically, as they do not identify the correct (simulated) mode of evolution, even for adequate models, in the absence of stratigraphic effects, and for exceptionally long time series. - Fossil time series favor the recognition of both stasis and complex, punctuated modes of evolution. - Not stratigraphic incompleteness, but the presence of rare, prolonged gaps has the largest biasing effect on trait evolution. This suggests that incomplete sections with regular hiatus frequency and durations can potentially preserve evolutionary history without major biases

Short communication: Landlab v2.0: a software package for Earth surface dynamics

umerical simulation of the form and characteristics of Earth's surface provides insight into its evolution. Landlab is an open-source Python package that contains modularized elements of numerical models for Earth's surface, thus reducing time required for researchers to create new or reimplement existing models. Landlab contains a gridding engine which represents the model domain as a dual graph of structured quadrilaterals (e.g., raster) or irregular Voronoi polygon–Delaunay triangle mesh (e.g., regular hexagons, radially symmetric meshes, and fully irregular meshes). Landlab also contains components – modular implementations of single physical processes – and a suite of utilities that support numerical methods, input/output, and visualization. This contribution describes package development since version 1.0 and backward-compatibility-breaking changes that necessitate the new major release, version 2.0. Substantial changes include refactoring the grid, improving the component standard interface, dropping Python 2 support, and creating 31 new components – for a total of 58 components in the Landlab package. We describe reasons why many changes were made in order to provide insight for designers of future packages. We conclude by discussing lessons about the dynamics of scientific software development gained from the experience of using, developing, maintaining, and teaching with Landlab

Combining Discrete Element and Process-based sedimentary models: a new tool to model syntectonic sedimentation

[eng] In order to understand the current state of the natural rocky environment and its heterogeneity, we require to study the interaction and time evolution of the numerous geological processes that have contributed to the geological reality we observe today. Given this, the thesis presented here concerns itself with numerical modelling of geological processes. The forward numerical model developed during this thesis is able to simulate deformation and sedimentation in one single setting. To do this, the model uses a novel approach that combines a Discrete Element Model (DEM) and a process- based sedimentary model, Simsafadim (SFM) to link both processes, deformation and sedimentation. The discrete element model (DEM) deals with the simulation of deformation in different materials in 2D and 3D. It is primarily used to investigate the propagation and evolution of deformation in the upper crust caused by tectonic movements. Simsafadim (SFM) is a process-based numerical forward model, which simulates subaqueous clastic transport and sedimentation in three dimensions, including processes of carbonate interaction, production, transport and sedimentation. It can model efficiently the distribution of facies and the depositional architectures in a sedimentary basin and it is a powerful tool for the 3D prediction of stratigraphic structures. Merging both codes provides a new tool for geological modelling in which deformation is influenced by the presence of syntectonic sediment dispersal and deposition. In addition, the tectonic processes change the topographic surface, which influences fluid flow, transport and, consequently, sedimentation in the process-based sedimentary model. The interaction of tectonic and sedimentary processes allows us to study the propagation of deformation in the syntectonic materials as well as how these new sediments influence the propagation of deformation in the pretectonic unit. The model is applied in two different cases studies, in order to test the viability of the new model, as well as to achieve new insight in the respective themes treated: 1) First case study: the effect of normal faulting and a relay ramp on sediment dispersal. The model is used to study the sedimentary infill in an extensional basin, specifically related to a relay ramp system. To perform the test study two configurations are designed: with one normal fault, and with two overlapping normal faults linked by a relay ramp. The different results show that the source area location in relation to the available accommodation space plays the major role in the distribution of different sediment types into the basin. Nonetheless, when the source area for water and sediment is defined as regional and parallel to the fault, the grain size distribution obtained by the two overlapping faults linked by a relay ramp have clear asymmetries when compared with the ones obtained by one-fault configurations. Therefore, the different extensional experiments allow us to conclude that the configuration with a relay ramp can play an important role in the distribution of the sediments into the basin. 2) Second case study: The effect of syntectonic sedimentation on fold geometry The numerical is used to investigate the effect of syntectonic sedimentation on fold geometry and specifically related to a delta progradation surrounded by two growing anticlines. To the initial tectonic configuration that reproduces the growth of two faults, two different cases of the sedimentary model are considered: without sediments, and considering syntectonic sedimentation. Summing up, the main results obtained for these experiments conclude that the syntectonic sedimentation is controlling the mechanism of fold growth and the final fold geometry: the left-side fold shows a left-vergent asymmetric anticline. Moreover, the strain suggests that this anticline is passing from a detachment fold (without sediments) to a fault propagation fold basinwards (with sediments). As a consequence, the inner syncline and the related sedimentary basin are also changing in transversal and longitudinal direction, being wider with syntectonic sedimentation.[cat] El objectiu principal d'aquesta tesi és donar un pas endavant en el coneixement dels processos geològics que intervenen en la formació de les conques sedimentàries mitjançant la creació d'un model numèric per modelitzar la sedimentació sintectònica en un ambient subaquàtic. El model numèric desenvolupat en aquesta tesi és capaç de modelitzar la sedimentació clàstica subaquàtica i la deformació de la unitat pretectònica en una sola configuració. Per fer això, el model combina dos models ja existents: un model d'elements discrets per simular la deformació de la unitat pretectònica (DEM) i un model sedimentari basat en processos, per modelitzar la sedimentació clàstica subaquàtica Simsafadim (SFM). La unió d'aquest dos models, DEM i SFM, proporciona una nova eina per a la modelització geològica. En el nou model, l’evolució de deformació en la unitat pretectònica canviarà la topografia de la conca, que afectarà directament la batimetria, influenciant així els processos de transport i sedimentació que hi tenen lloc. Alhora, aquesta evolució de la deformació de la unitat pretectònica estarà influenciada per la presència dels nous materials sintectònics. Amb aquesta doble interacció tectònica-sedimentària del nou model, també es pot estudiar la deformació en els materials sintectònics. Aquesta nova eina de modelització permet simular i analitzar diferents arquitectures deposicionals sintectòniques i escenaris geològics més complexos. Tant per ampliar el coneixement de com els processos de sedimentació-deformació interactuen en alguns ambients tectònics, com per comprovar l'eficàcia del model, la nova eina s'aplica a dos casos diferents: 1) En primer lloc s'utilitza el model numèric en un ambient extensional per estudiar l'impacte que té la presència de falles normals i les corresponents zones de relleu en la distribució del sediment a la conca. Quan es compara la distribució de sediment obtinguda amb una configuració de dos falles amb una rapa de relleu, amb la distribució de sediment obtinguda amb una configuració d'una sola falla, els resultats mostren asimetries, tant longitudinals com perpendiculars a les estructures. 2) En el segon cas s'estudia l'efecte de la sedimentació sintectònica sobre la geometria final d'un plec. Els resultats, obtinguts a partir de la comparació de l'evolució de les estructures considerant o no considerant sedimentació sintectònica, estableixen que la sedimentació sintectònica pot afectar tant al mecanisme de formació del plec com a la seva geometria final

Data-Driven, Multi-Model Workflow Suggests Strong Influence from Hurricanes on the Generation of Turbidity Currents in the Gulf of Mexico

Turbidity currents deliver sediment rapidly from the continental shelf to the slope and beyond; and can be triggered by processes such as shelf resuspension during oceanic storms; mass failure of slope deposits due to sediment- and wave-pressure loadings; and localized events that grow into sustained currents via self-amplifying ignition. Because these operate over multiple spatial and temporal scales, ranging from the eddy-scale to continental-scale; coupled numerical models that represent the full transport pathway have proved elusive though individual models have been developed to describe each of these processes. Toward a more holistic tool, a numerical workflow was developed to address pathways for sediment routing from terrestrial and coastal sources, across the continental shelf and ultimately down continental slope canyons of the northern Gulf of Mexico, where offshore infrastructure is susceptible to damage by turbidity currents. Workflow components included: (1) a calibrated simulator for fluvial discharge (Water Balance Model - Sediment; WBMsed); (2) domain grids for seabed sediment textures (dbSEABED); bathymetry, and channelization; (3) a simulator for ocean dynamics and resuspension (the Regional Ocean Modeling System; ROMS); (4) A simulator (HurriSlip) of seafloor failure and flow ignition; and (5) A Reynolds-averaged Navier–Stokes (RANS) turbidity current model (TURBINS). Model simulations explored physical oceanic conditions that might generate turbidity currents, and allowed the workflow to be tested for a year that included two hurricanes. Results showed that extreme storms were especially effective at delivering sediment from coastal source areas to the deep sea, at timescales that ranged from individual wave events (~hours), to the settling lag of fine sediment (~days)

Short communication: Landlab v2.0: a software package for Earth surface dynamics

Numerical simulation of the form and characteristics of Earth's surface provides insight into its evolution. Landlab is an open-source Python package that contains modularized elements of numerical models for Earth's surface, thus reducing time required for researchers to create new or reimplement existing models. Landlab contains a gridding engine which represents the model domain as a dual graph of structured quadrilaterals (e.g., raster) or irregular Voronoi polygon-Delaunay triangle mesh (e.g., regular hexagons, radially symmetric meshes, and fully irregular meshes). Landlab also contains components - modular implementations of single physical processes - and a suite of utilities that support numerical methods, input/output, and visualization. This contribution describes package development since version 1.0 and backward-compatibility-breaking changes that necessitate the new major release, version 2.0. Substantial changes include refactoring the grid, improving the component standard interface, dropping Python 2 support, and creating 31 new components - for a total of 58 components in the Landlab package. We describe reasons why many changes were made in order to provide insight for designers of future packages. We conclude by discussing lessons about the dynamics of scientific software development gained from the experience of using, developing, maintaining, and teaching with Landlab.</p