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Alluvial fan and wetland interactions: evidence of seasonal slope wetlands from the Silurian of south central Wales, UK
Author(s) -
HILLIER ROBERT D.,
WATERS RICHARD A.,
MARRIOTT SUSAN B.,
DAVIES JEREMY R.
Publication year - 2011
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.1365-3091.2010.01184.x
Subject(s) - geology , ephemeral key , alluvium , water table , wetland , alluvial fan , tributary , hydrology (agriculture) , alluvial plain , groundwater recharge , deposition (geology) , debris , geochemistry , geomorphology , paleontology , oceanography , sediment , sedimentary rock , groundwater , ecology , aquifer , geotechnical engineering , cartography , geography , biology
Distal environs of the Ludlow‐age Trichrug Formation from south central Wales (UK) detail deposition on the outer fringe of an ephemeral debris flow‐dominated alluvial fan. Debrites and subordinate sheetflood deposits are interbedded with sporadic thin sandstone‐dominated heterolithic units deposited in shallow, ephemeral ponds in the axial valley. The latter slope wetland system fringed the permeable alluvial fan deposits, being maintained by streamflow, precipitation and ground water recharge. A prolonged high water table is indicated by low chroma intervals interpreted as the result of gleying. A variety of redoximorphic indicators, including colour mottling and ferricrete concretions, are evidence of iron mobilization and concentration associated with a seasonally fluctuating water table. The slope wetlands were colonized periodically by Skolithos ‐generating organisms, most likely to have been arthropods. The widespread occurrence of redoximorphic indicators and ferricrete contrasts markedly with calcrete Vertisols in penecontemporaneous continental deposits (Lower Old Red Sandstone) of the region. It is likely that the alluvial fan‐toe area was the site of a wetland depression, which maintained a high, though fluctuating, water table. In contrast the alluvial channel reaches of the surrounding drainage network were significantly better drained, with floodplains prone to wetting and drying and Vertisol palaeopedogenesis.