Joep E.A. Storms

A Revised Chronology for Mississippi River Subdeltas

Radiocarbon measurements by accelerator mass spectrometry relating to three of the four late Holocene Mississippi River subdeltas yielded consistent results and were found to differ by up to 2000 carbon-14 years from previously inferred ages. These geological dataare in agreement with archaeological carbon-14 data and stratigraphic ages based on ceramic seriation and were used to develop a revised chronologic framework, which has implications for prehistoric human settlement patterns, coastal evolution and wetland loss, and sequence-stratigraphic interpretations.

Process-Response Modeling of Wave-Dominated Coastal Systems: Simulating Evolution and Stratigraphy on Geological Timescales

ABSTRACT Numerical modeling on a geological timescale is a rapidly expanding tool to investigate controls on formation of the stratigraphic record. Modeling enables us to test existing ideas, but verification of model results is commonly difficult. Many models are based on geometric or diffusion rules, yet neither type of model has much relevance with actual processes that control sedimentary systems. Here we describe a process-response approach to model the evolution and stratigraphy of wave-dominated coastal systems in two dimensions, based on simple approximations of cross-shore erosion and sedimentation. Separating erosion and deposition functions enables us to simulate coastal evolution, stratigraphy, erosion surfaces, and transport of multiple-grain-size classes. The simulated stratigraphic record contains detailed information on grain size and stratal geometry. We calibrated the model with data sets on coastal transgression in the Caspian Sea, Dagestan, and on grain-size distributions at the island of Terschelling, The Netherlands. Furthermore, hypothetical examples are presented to show the effect of changes in sea level and sediment supply, substrate slope, and sediment size distribution. These tests show that the model is capable of reproducing widely accepted conceptual models of coastal evolution on geological timescales (progradation, aggradation, and various modes of retrogradation).

Event-based stratigraphic simulation of wave-dominated shallow-marine environments

Abstract The presence of event beds in the shallow-marine stratigraphic record indicates formation is governed by high magnitude–low frequency processes rather than low magnitude–high frequency processes. In this paper, a 2-D multiple grain-size process-response model (BARSIM) is presented, which uses event deposition to simulate stratigraphic response to changes in sea level and sediment supply. BARSIM uses variable time steps to simulate individual storm (event) and fair-weather periods. Deposition during storm conditions solely consists of reworked shoreface sediment, while fair-weather deposits consist of reworked shoreface sediment combined with sediment supplied by littoral drift and suspension. Simulations using variations in sea level, sediment supply (both amount and grain-size) and wave-height regime result in distinct depositional patterns, stratal geometry and bed characteristics. Model results indicate that both wave-height regime and grain-size of supplied sediment have considerable effect on shoreface morphology and stratal characteristics. Unraveling coastal evolution from the shallow-marine stratigraphic record may therefore be more difficult than previously assumed, as both variables are expected to vary over geologic time scales.

Modeling of a mixed‐load fluvio‐deltaic system

Present?day observations and classical classification schemes of alluvial deltas address feeder channel dynamics and multiple sediment fractions. However, high?resolution physics?based mathematical models have not been applied to address formation of both fluvio?deltaic links (channels) and nodes (diffluences and confluences), and their stratigraphy. Here, we present a simulated delta system under riverine forcing that shows striking similarity to its counterparts recognized in field and laboratory studies. These findings include distinct shifts in river planimetrical mode and altimetry, deltaic mouth bar and distributary formation, lateral fining in migrating?meander bend axes and fining?upward patterns in passive delta?plain distributaries.

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 Tc-division separately from the massive and plane parallel-laminated Tab-divisions in Bouma-type turbidites. TDURE consists of three modules. In the first module, the accumulation time for theTa- and Tb-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 Tab- and Tbc-boundaries. In the second module, angle of climb of ripples, thickness of the Tc-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 Tc-division. In the third module, the expected development of ripple size across the Tc-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 Tc-division, and 19 and 16 min for the Tabc-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 Tbcboundary in both beds, ripple size at the Tcd-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 turbiditycurrent dynamics. q 2000 Elsevier Science B.V. All rights reserved.

The Impact of Rapid Sea Level Changes on Recent Azerbaijan Beach Ridges

Abstract A ground-penetrating radar survey of a newly formed series of beach ridges along the southern Azerbaijan coast, Caspian Sea, illustrates rapid coastal response to the most recent sea level fall of 0.8 m in the Caspian Sea between 1995 and 1999. Effects of seasonal sea level fluctuations as well as individual storm occurrences can be linked to depositional beds on the ground-penetrating radar profiles. The beach ridge system is swash built and formed primarily under fair weather conditions. Ridge and swale topography can be related to seasonal sea level change. The rapid sea level change in the Caspian Sea combined with surface and subsurface data on coastal beach ridges provides a unique opportunity to observe and reconstruct coastal evolution at a resolution not possible along other oceanic coasts.

INITIAL MORPHOLOGIC AND STRATIGRAPHIC DELTA EVOLUTION RELATED TO BUOYANT RIVER PLUMES

Abstract : This paper presents the results of a numerical model study on initial delta formation in basins of different water depths. A process-based model (Delft3D-Online) is used to calculate fluid flow and sediment transport patterns at a newly formed river effluent. In abse nce of wave and tidal forcing, the river effluent is fully river dominated. The model results are interpreted in terms of morphology and stratigraphy. For the shallow basin case, the delta develops as a complex pattern of channels and shoals analogous to Wax delta. The simulated delta development in the deep basin is markedly different and resembles a classic prograding bird foot delta morphology. Typical clay-rich prodelta deposits underlie sandy bar and channel deposits. The top of the sedimentary sequence consists of a clay -rich delta plain deposit. The potential of the process-based model to simulate typical delta morphologies and a realistic stratigraphy provides many new opportunities to bridge typical engineering and geological research approaches.

Process-response modelling of fluvio-deltaic stratigraphy

Abstract Numerical modelling is a tool to investigate the controls on the formation of the stratigraphic record on geological timescales. The model presented in this paper (DELTASIM) uses a process-response approach that simulates the stratigraphy of fluvial-dominated deltaic systems in two dimensions, based on simplified diffusion rules of cross-shore sedimentation. Net sedimentation is calculated for individual grain-size classes as the sum of independent erosion and deposition functions, enabling simulations of fluvio-deltaic stratigraphy besides clinoform evolution. Critical sediment transport parameters are validated using synthetic data from a process-based morphodynamic model, DELFT3D. Generic experiments show the effect of changes in sea level, sediment supply, offshore gradient and sediment size distribution. These experiments show that the model is fully capable of reproducing classic concepts of delta development on geological timescale. Such experiments allow students a possibility to evaluate the controls on the formation of the stratigraphic record. DELTASIM has been successfully applied to improve the understanding of the sedimentary evolution of a real-world fluvial-dominated delta in the Caspian Sea. Additional functionality encompasses a stochastic discharge model that can be used as input to simulate series of scenarios of delta development using the models rapid run time to our advantage. This functionality enables us to present probabilistic output of longitudinal stratigraphic sections as an alternative to the deterministic predictions often made by stratigraphic models. The characteristics of the model; simplicity, speed and compatibility of the output to conceptual sequence stratigraphic models make DELTASIM suitable as a teaching tool.

Multiscale curvatures for identifying channel locations from DEMs

Abstract Curvature based methods are suitable for channel identification in digital elevation models. One obstacle in using these methods is the fact that channels generally occur at multiple scales in the landscape, from small creeks to large rivers. In this paper, we show how likely channel pixels can be identified simultaneously at a range of scales using multiscale curvature operators applied to digital elevation models. Our proposed Hyperscale Channel Extraction (HCE) method localizes channels at the smallest scale while simultaneously tracking the shape of the channel at a full interval of scales (the hyperscale). We test the method using two different types of curvature, and apply and validate it to a catchment representing terrain with a high slope sampled by airborne laser altimetry. The test results demonstrate that by explicitly employing the extra dimension of scale to localize channels, (a) we are able to robustly identify channel pixels, as possible channel locations are tracked through a full interval of scales, (b) no more a priori determination of the relevant scale is necessary, and (c) only one parameter remains to be set: a threshold on the curvature value that has a clear physical interpretation.

Analysis Tools to Quantify the Variability in Deltaic Geological Models Using Delft3D Simulation Results

The process of constructing geological models is used on various scales in mining, oil and gas exploration, hydrology as well as in large construction projects. Development of geological models is a complex process consisting of various phases. A large degree of uncertainty is introduced from the interpretation of the data to the construction of the geological model. To arrive at the best approximation of the subsurface, relevant analogues are identified and consulted. Therefore, uncertainties originate from unknown depositional processes, but also from uncertain correlation between the study area and the analogues. We developed a set of tools to quantify the variability in deltaic geological models resulting from these uncertainties. These tools were applied to an ensemble of simulations generated in Delft3D by processed-based forward modelling. We show how a set of analyses can be used to quantify the differences in the resultant delta deposits. Analyses investigated channel networks, topographic profiles and sediment distribution in the delta. The tools make use of the unique advantages of numerical forward models, allowing single variables to be studied at high spacial and temporal resolution.