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Calcretes related to phreatophytic vegetation from the Middle Triassic Otter Sandstone of South West England
Author(s) -
PURVIS K.,
WRIGHT V. P.
Publication year - 1991
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.1365-3091.1991.tb00366.x
Subject(s) - geology , cementation (geology) , paleosol , carbonate , sedimentary depositional environment , geochemistry , paleontology , geomorphology , archaeology , loess , geography , materials science , structural basin , cement , metallurgy
Carbonate cementation in the Triassic Otter Sandstone of Budleigh Salterton, SW England, occurs in two distinct forms: large, vertical, concentrically zoned cyclinders, and thin subhorizontal sheets. The former represent rhizocretions of the tap roots of phreatophytic plants which colonized bars and abandoned channels on a large braidplain. The sheets represent cementation around ancient water‐tables. The precipitation of the rhizocretions took place, at least in part, during the life of the plants and δ 13 C and δ 18 O values support the view that evapo‐transpiration induced carbonate precipitation. Palaeosol profiles are rare in the Otter Sandstone, reflecting the geomorphological instability of the braidplain surfaces. In contrast, rhizocretionary and sheet calcretes, which formed several metres below the active depositional surface, are abundant because they had a high preservation potential.