The formation of flocculated clay laminae in the sediments of a meromicticlake

Sediments of Lake Fidler, a meromictic lake in south-west Tasmania, contain distinctive laminae. In order to determine their composition and formation , these laminae were studied using a combination of X-ray analysis, scannin g electron microscopy, X-ray diffraction and vibrational spectrometry. Resu lts indicated that the laminae were composed of clay originating from the a djacent Gordon River estuary. The clay was also found as part of the genera l sediment matrix of the core. The evidence indicates that the laminae are formed during incursions of brackish water from the adjacent Gordon River e stuary into Lake Fidler which cause the flocculation of clay minerals in th e water column. These clay minerals then sink rapidly to the sediments to f orm laminae. Although the formation of these laminae pre-dates meromixis, t heir mode of formation corroborates the theory that meromixis is maintained ectogenically by periodic inflows of brackish water replenishing monimolim netic salts.