Geochemical and sedimentological data are presented for samples taken from a ten-metre long core section of finely-laminated, “varved” muds recovered from a present-day floodplain location sited 100 km upstream from mouth of the Murray River at Monteith in South Australia. The core presents delicately interlayered laminae consisting of finer-grained light-greenish-grey clay to very fine silt; and coarser-grained dark-grey, fine to medium silt which were deposited as a continuous sequence between ~8,500 ka and ~6,500 ka. This material is representative of a laterally continuous, 20-metre thick layer of mud spans the entire width of the bedrock valley in which the layer was deposited. The sedimentologic data indicate that the entire width of the lower Murray Valley at Monteith was occupied by large body of relatively still water when the laminated mud sequence was deposited. The geochemical data indicates that the light-coloured muds are probably dominantly derived from the Darling River Catchment while the dark-coloured silts are probably dominantly derived from the Murray River catchment; and that both laminae types were deposited in slightly to moderately saline conditions consistent with those expected in the landward portion of an elongated, estuarine, central basin environment.