Three-Dimensional Reconstruction of Meander-Belt Evolution, Cretaceous Mcmurray Formation, Alberta Foreland Basin, Canada

Abstract

The three-dimensional reconstruction of meander-belt deposits from ancient strata provides insight into the formative processes of meander-bend evolution and paleogeographic interpretations. A significant challenge to such analyses is limited exposures in outcrop belts and widely spaced or sparse subsurface datasets. An unprecedented dataset consisting of 600 km 2 of 3-D seismic data and over 1000 well penetrations from the Cretaceous McMurray Formation in northeastern Alberta, Canada, provides a unique opportunity to characterize an ancient continentalscale river system. Paleochannels ranged from 475 to 1180 m wide and from 35 to 50 m deep, with meander-belt width-to-thickness ratios between 107:1 and 401:1. The data reveal evidence for intra-point-bar erosion and punctuated rotation, counterpoint bar development, and protracted channel cutoff and meander-loop abandonment. Observations enable interpretation of morphodynamic processes that are commonly observed in modern systems, yet rarely described from the rock record. A 3-D geocellular model and reconstructed paleochannel migration patterns reveal the evolutionary history of seventeen individual meander belt-elements, including point bars, counterpoint bars, and their associated abandoned channel fills, which have been mapped using core, FMI logs, and seismic data. Results of the study show that intrapoint-bar erosion surfaces bound accretion packages characterized by unique accretion directions, internal stratigraphic architecture, and lithologic properties. We provide evidence for channel-belt-edge confinement and development of a counterpoint bar, as well as the deposition of side bars and preservation of a mid-channel bar during meander-bend abandonment. Analysis of changes in meander-belt morphology over time reveal a decrease in channel-belt width/thickness ratio and sinuosity, which we compare with observations from the lower Mississippi River and attribute to the landward migration of the paleo-backwater limit due to transgression of the Cretaceous Boreal Sea into the Alberta foreland basin.

Evolution of an ancient (Lower Cretaceous) marginal‐marine system from tide‐dominated to wave‐dominated deposition, McMurray Formation

“…The thickest expressions of FA3 in the GPV may be western extensions of both B2 (PS B) and B1 (PS G) channel belts defined by Hein et al . (), and extend down from allogenic flooding surfaces capping PS B and PS G. In this case, FA3 deposits should be similar to or genetically related to B2 and B1 channels, the latter of which have been interpreted as fluvial (Durkin et al ., ,b; Horner et al ., ) or fluvial–estuarine deposits (Hubbard et al ., ; Hein et al ., ) within a continental‐scale drainage system (Benyon et al ., ; Blum & Pecha, ). However, the B2 and B1 channel belts to the east of GPV are diachronous, and it is probable that as the system occupying the Main Fairway prograded north (for example, tide‐dominated delta; Ranger & Gingras, ), deposits genetically related to FA3 were reworked by more proximal channel deposits (i.e.…”

Two Dimensional Model for Backwater Geomorphology: Darby Creek, PA

“…The depth of 1D model captures the change in WSE across the BW transition, which allows the 2D model to capture the sediment flux. The current approaches in geomorphological assessment in the BW zone are mainly limited to either a few years-worth or thousands years of geomorphic changes [29][30][31][32][33][34][35][36][37][38]. In contrast, the presented integrated model builds on the existing body of knowledge in geosciences which can predict geomorphological alterations in the BW zone of the rivers over a short to intermediate time scale applicable to civil engineering applications.…”

3-D stratigraphic mapping using a digital outcrop model derived from UAV images and structure-from-motion photogrammetry

“…Stratigraphic surfaces resulting from ancient fluvial processes record spatial and temporal changes in river morphology at multiple hierarchical levels and inform our understanding of morphodynamics and paleoenvironments (Jordan and Pryor, 1992;Durkin et al, 2017). Fluvial deposits are highly heterogeneous and challenging to map in outcrop due to lateral and vertical variability, as well as inconsistent exposure (Miall, 1988;Labourdette and Jones, 2007;Pranter et al, 2007;Calvo and Ramos, 2015;Durkin et al, 2015a).…”