Abstracts: Fluvial Systems in Mountain Belts and Foreland Basins: An Alpine-Himalayan Perspective

ELLIOTT, TREVOR,

Fluvial systems are a prime means of sediment dispersal from uplifting mountain belts to subsiding foreland basins. Deposition in the basins may be a direct result of fluvial processes (e.g., the present-day Indo-Gangetic foreland basin and the Oligocene-Miocene Ebro basin) or the rivers may supply deeper basin turbidite systems (e.g., Alpine "flysch" basins). Fluvial processes not only contribute to the filling of basins but also to the total mass balance of the orogen via their role in denudation and the uplift/exhumation history of the orogen. To comprehensively explore the implications of fluvial systems for the geodynamics of mountain belts, one must investigate the entire system, not just the sedimentation history of the depositional element that is preserved in the depositional basin.

Fluvial systems comprise three main zones: (1) a drainage basin from which water discharge and sediment load are largely derived; (2) a sediment transfer zone in which major valley-bound trunk rivers and their tributaries transmit the sediment load down the regional gradient; and (3) a receiving basin in which the sediment is deposited and stored. In mountain belts these zones of the fluvial system generally occur in specific, structurally defined regions. The hinterland drainage basin is mainly located in the internal zones, where high rates of uplift create conditions of net erosion and high sediment yield. Fluvial transfer zones are sited in the inner part of the external zones of the mountain belt, where thin-skinned thrusting and folding produce highly differential, localized areas of uplift and subsidence. The depositional basins include thrustsheet-top basins located in the outer parts of the external zones and foreland basins beyond the thrust front. Key aspects of fluvial systems in mountain belts will be highlighted in the lecture using information from the Alpine-Himalayan mountain belt: evidence for river capture events in the hinterland, the recognition of transfer zone paleovalleys, and structural controls on sediment transport pathways.

AAPG Search and Discovery Article #90938©1997-1998 AAPG Distinguished Lecturers