Applications of Forward Stratigraphic Modelling in Modern Siliciclastic Settings: A Case Study from the Fraser River Delta, Canada

Forward stratigraphic modelling (FSM) is a relatively new approach that is used to test the importance of parameters that control stratigraphic stacking patterns and to reveal uncertainties such as sedimentation rate and accommodation space. Although FSM is commonly employed in the study of ancient systems, it is rarely applied to modern settings. The Fraser River Delta in Canada provides an opportunity to test applications of FSM in recently deposited sediments in an active sedimentary basin. Because it is un-dammed, the river enables comparison of the modern and ancient systems. It is also a well-studied river system, with sufficient data to generate a realistic model for predicting future scenarios. In this study, Dionisos software is used, and the evolution of the delta over the past 10,000 years is successfully simulated in two steps (5000 years each) using both realistic and real-time data. The main controlling parameters are observed to be the sediment supply and water discharge values, and to a lesser extent, sea level variation. Several possible future scenarios are tested, changing the main parameters to understand and to predict future morphological changes and stacking patterns. Increasing the main parameter values resulted in progradation, while reducing resulted in erosion, particularly in the subaqueous section of the delta. The results of this study can be used to calibrate numerical modelling applications in both modern and ancient deltaic settings

Facies Modelling of a Tide-Influenced, River-Dominated Delta, Fraser River Delta, British Columbia, Canada

The Fraser River delta is a tide-influenced, river-dominated delta that exhibits distinct asymmetry in sedimentological and neoichnological character between the updrift (south) and downdrift (north) sides of the delta front and upper prodelta (< 200 m water depth). The updrift portion consists mainly of sands and heterolithic sand and mud bedsets with low bioturbation intensities (BI 0-3). Trace suites are sporadically distributed and include elements of the Skolithos Ichnofacies. The downdrift portion is composed of homogeneous mud beds and bedsets with significantly higher intensity of bioturbation (BI 3-6). Trace suites are attributable to the Cruziana Ichnofacies. The asymmetrical distribution of sediment and burrows on the delta is primarily controlled by strong northward-directed tidal currents. Physical sedimentary processes differ significantly between updrift and downdrift sides of the delta. The updrift delta is mainly an area of erosion in which strong tidal currents scour previously deposited sediments. This scouring reveals underlying sandy paleo-distributary channel deposits. The downdrift delta, on the other hand, is an area of net sediment (predominantly mud) accumulation. Sandy material eroded from the updrift delta is trapped within a deep submarine channel and does not get redistributed to the downdrift delta. This results in contrasting substrate types between the updrift and downdrift delta. The asymmetrical character of the Fraser River delta is similar in its sedimentological signature, but ichnologically distinct, from the wave-dominated asymmetric delta model. Neoichnological trends are opposite to that observed in wave-dominated asymmetrical deltas, in that the trace diversity and density are higher on the downdrift side of the delta front than the updrift side. Based on the results presented herein, a new tidally asymmetric delta model is proposed which, overall, leads to a more robust asymmetric delta model. The most important aspect of this new model is that tidally-influenced asymmetric deltas are not depth-dependent, and therefore, they have greater potential to develop in deep water settings than wave-dominated asymmetric deltas

Possibly the oldest fish-made resting traces

The Silurian Sharawra Member (middle to late Llandoverian) in Saudi Arabia exhibits unique surface traces with exceptional preservation: Seven small, wing-shaped structures occur on a sandstone slab showing well-defined hummocky cross-stratification having a few decimeters wavelength covered with a thin mud layer. These traces are preserved as concave epirelief along with elongated internal striae and surrounded with slightly elevated levees. Preservation of these delicate, 10-20 mm long and ~10 mm wide traces suggests that they were formed after a storm event when mud has already settled to the sediment surface. The lack of wave-generated sedimentary structures implies deposition between fair-weather and storm-wave base probably preventing further rapid reworking by waves. Based on their geometry, internal pattern and spatial distribution, these wing-shaped traces are interpreted to have been produced by relatively stationary bottom-feeding fish, morphologically similar to ancestors of Gobiidae, probably in the Actinopterygii class. The majority of fish-made trace fossils records feeding and locomotion behaviour, whereas the wing-shaped traces are interpreted to represent resting structures made by fish that pressed their fins downward on the muddy sediment surface and hence, represent undertracks. These structures are also possibly the oldest fish-made structures documented thus far. These wing-shaped traces are described as Pisquiesichnus dashtgardi igen. et isp. nov. in this study

Deep Learning Applications in Geosciences: Insights into Ichnological Analysis

Ichnological analysis, particularly assessing bioturbation index, provides critical parameters for characterizing many oil and gas reservoirs. It provides information on reservoir quality, paleodepositional conditions, redox conditions, and more. However, accurately characterizing ichnological characteristics requires long hours of training and practice, and many marine or marginal marine reservoirs require these specialized expertise. This adds more load to geoscientists and may cause distraction, errors, and bias, particularly when continuously logging long sedimentary successions. In order to alleviate this issue, we propose an automated technique to determine the bioturbation index in cores and outcrops by harnessing the capabilities of deep convolutional neural networks (DCNNs) as image classifiers. In order to find a fast and robust solution, we utilize ideas from deep learning. We compiled and labeled a large data set (1303 images) composed of images spanning the full range (BI 0–6) of bioturbation indices. We divided these images into groups based on their bioturbation indices in order to prepare training data for the DCNN. Finally, we analyzed the trained DCNN model on images and obtained high classification accuracies. This is a pioneering work in the field of ichnological analysis, as the current practice is to perform classification tasks manually by experts in the field

Salinity indicators in sediment through the fluvial-to-marine transition (Fraser River, Canada).

Many sediment attributes have been proposed as proxies for determining salinity conditions under which sediment is deposited, and six attributes (Sr/Ba-HAc, Sr/Ba-NH4Ac, δ13Corg, C/N, and the relative abundances and concentrations of dinoflagellate cysts) are compared here. In this paper, sediment attributes from the Fraser River Delta, Canada and surrounding coastal areas are compared by depositional position along the fluvial-to-marine transition, by salinity, and by sedimentological characteristics. Along the fluvial-to-marine transition, most attributes exhibit distinct trends between parts of the river that experience sustained marine water (saltwater) influence over seasonal and tidal timeframes, and parts that experience only freshwater or periodic saltwater influence. No attributes are reliable indicators of depositional position where saltwater incursion is short lived or where water is fresh. Where marine influence is sustained, Sr/Ba-HAc and Sr/Ba-NH4Ac are the most reliable positional indicators along the fluvial-to-marine transition. When compared strictly to salinity, Sr/Ba-HAc, Sr/Ba-NH4Ac, and δ13Corg all correlate predictably except in delta front and prodelta settings. Our data show that all six sediment attributes are heavily impacted by river-derived sedimentation, and it is not appropriate to compare values from strongly river-influenced settings (e.g., deltas) with those from weakly river-influenced settings (e.g., bays and estuaries)