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Quantitative interpretation of an evolving ancient river system
Author(s) -
BRIDGE JOHN S.,
DIEMER JOHN A.
Publication year - 1983
Publication title -
sedimentology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.494
H-Index - 108
eISSN - 1365-3091
pISSN - 0037-0746
DOI - 10.1111/j.1365-3091.1983.tb00698.x
Subject(s) - geology , overbank , point bar , alluvium , floodplain , sedimentology , geomorphology , meander (mathematics) , channel (broadcasting) , alluvial plain , hydrology (agriculture) , paleontology , fluvial , geometry , geotechnical engineering , structural basin , ecology , mathematics , engineering , electrical engineering , biology
Multistorey sandstone bodies described from the Upper Devonian‐Lower Carboniferous of Kerry Head (Ireland) are interpreted as deposits of aggrading, perennial, river channels migrating laterally across alluvial plains. Point bars displayed surface features such as scroll bars, chute channels and chute bars. Relatively uncommon channel fills are both coarse‐ and fine‐grained. Quantitative interpretation of the sandstone bodies was accomplished by comparison with a physical model that predicts the sedimentology of single point bar deposits developed in channels of prescribed geometry and hydraulics. This analysis reveals that the separate storeys (point bars) in each sandstone body were deposited in a single channel belt in which channel geometry and hydraulics varied little with time (order of 10 3 yr) and space (order of 10 3 m). Two southerly flowing rivers of markedly different size were responsible for all sandstone bodies: bankfull widths, depths and mean velocities of both rivers varied little with time (order of 10 5 yr), implying a stable climatic setting. Channel sinuosities were usually 1.15–1.2 throughout the succession. Both rivers decreased in mean channel slope as time progressed, in association with a rising base‐level and a shoreline encroaching from the south. Using Bridge & Leeder's (1979) alluvial stratigraphy model, the nature and distribution of channel sandstone bodies relative to overbank deposits in the succession can be explained by an average (compacted) floodplain deposition rate of about 0.005 m yr −1 , if avulsion occurred with a frequency of about once every 10 3 yr. Local variation in the relative amount of channel sandstone in the succession is probably due to local tectonic control of deposition.