Sedimentology of late glacial clays in lacustrine basins, Central Ireland

• Published in: Quaternary science reviews Vol. 16; no. 7; pp. 779 - 791
• Main Authors: Van Der Meer, Jaap J.M., Warren, William P.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 1997
• ISSN: 0277-3791; 1873-457X
• DOI: 10.1016/S0277-3791(97)00022-X

Distal bottom sediments of a large ice marginal (interdomal) lake that covered most of the central part (midlands) of Ireland during the last deglaciation were poorly known. Recent work centred on two raised-bog covered basins confirmed relatively thick distal glaciolacustrine sediments. Undisturbed samples taken in 100 mm cores enabled thin sectioning and micromorphological analysis to be carried out. The upper part of the fine sediment (mostly clay), which is apparently homogenous at the macroscopic level, is shown to have been bedded or laminated and subsequently homogenised by load-casting. With depth, bedding or lamination becomes more common until the whole deposit is very finely and rhythmically laminated. Turbidites, a consequence of density underflows, together with coarse sediment rain-out and dropstones confirm a likely ice marginal environment. The finer sediment towards the top of the sequence reflects increasing distality. Synsedimentary folding and faulting, load-casting and water-escape structures point to rapidly accumulating sediment in an unstable sedimentary environment. The lack of bioturbation is not surprising and apparent minor traces towards the base of the rhythmites seems most likely to relate to synsedimentary faulting.