Recognition of Chute Channels in Outcrops and Cores, Paleocene-Eocene Sedimentary-Hosted Uranium Deposits, with Implications to ISR, South Kazakhstan

Abstract

Chute channels are erosional channels that form when the river straightens the course across the point bar or the floodplain. Despite their short-time lifecycle and small size with respect to the main channel, they can have a large impact on river morphology and the rock record by eroding fine-grained deposits, disturbing classical fining-upward successions, and introducing new sandy bodies. This thesis investigates the recognition of chute channels in outcrops, cores, and subsurface well data from Paleocene–Eocene sedimentary-hosted uranium deposits in South Tortkuduk, Chu-Sarysu Basin, South Kazakhstan, and evaluates their importance for in-situ recovery (ISR). The study combines outcrop logging, UAV-based photogrammetry, detailed core description, interpretation of geophysical well logs, parallel cross-sections, slice maps, and 3D surface modelling. In outcrops, chute channels are recognized by characteristic concave-up erosional surfaces. In the subsurface, they are identified by truncation of point bar successions, repeated lowering of correlated welltops across sections, and compatible geometry on maps and interpolated surfaces. The results show that chute channels are present both in coeval outcrops and in the South Tortkuduk subsurface dataset, where they form geobodies significantly smaller than the main channel belt. The main contribution of this thesis is methodological. The proposed recognition workflow is based on erosion-first, stratigraphy-based welltop placement, where chute channels are recognized through disruption of the expected stratigraphic order rather than by tracing sand bodies only. This approach improves understanding of local erosional conduits in fluvial architecture. For ISR, the significance of the study lies in the ability of chute channels to connect permeable geobodies and disturb assumed barrier continuity, which is important for predicting subsurface flow pathways.