Holocene Foraminifera as Indicators of Relative Estuarine-Lagoonal and Oceanic Influences in Estuarine Sediments of the River Murray, South Australia

Abstract

In southeastern South Australia, the River Murray debouches through a coastal barrier separating euryhaline estuarine-lagoonal waters from the Southern Ocean. Depending upon the relative freshwater outflow of the river and ingress of the ocean, water salinity varies greatly within the lower estuary. Ammonia beccarii and Elphidium articulatum are euryhaline species of foraminifera that characterize the estuary and back-barrier Coorong Lagoon. The inner-shelf marine environment hosts an assemblage in which Discorbis dimidiatus, E. crispum, E. macelliforme, and various cibicidid species predominate. In cored sediments recovered from the shallow lower estuary, the relative abundance of A. beccarii + E. articulatum was compared with that of D. dimidiatus + E. crispum + E. macelliforme + other species. These data, and AMS radiocarbon ages determined for foraminifera and ostracods, provide evidence of a change from maximum oceanic influence (5255 ± 60 yr B.P.) to maximum estuarine influence (3605 ± 70 yr B.P.). Over this same time interval, sea level fell relatively by about 2 m. However, the event was also contemporaneous with falling water levels in several Victorian lakes, and it is thus attributed to onset of climatic aridity. Reduced precipitation in the River Murray catchment and reduced freshwater outflow enhanced development of the flood-tide delta and constriction of the mouth.

Late Quaternary terrigenous sediments from the Murray Canyons area, offshore South Australia and their implications for sea level change, palaeoclimate and palaeodrainage of the Murray–Darling Basin

“…The present level of late Holocene grain-size distribution with a predominance of silt, and clay mineral composition with kaolinite and illite as the main minerals, was reached by 4 ka and fluctuated only slightly since then, indicating aeolian dust as the main source of terrigenous influx today. Considering the limitations of our age model these findings are remarkably consistent with palaeoclimatic evidence from the Coorong Lagoon (Cann et al, 2000b) and southeastern Australian lake levels (Bowler and Hamada, 1971;Bowler, 1981;De Deckker, 1982;Chivas et al, 1993;Stanley and De Deckker, 2002), showing that the onset of more arid conditions began around 5.5 ka and reached a maximum at 3.6 ka.…”

Middle–late Holocene Caribbean aridity inferred from foraminifera and elemental data in sediment cores from two Cuban lagoons

“…Within a given lagoon or estuary, salinity is a function of sea-level, barrier configuration and freshwater input, the latter a consequence of changing precipitation and evaporation rates. The multiple variables influencing salinity can make identification of the primary cause of salinity shifts difficult (Brewster-Wingaard and Ishman, 1999, Cann et al, 2000, Cann and Cronin, 2004, Cheng et al, 2012, Gabriel et al, 2008, Peros et al, 2007a, van Hengstum et al, 2010.…”

Palaeolimnological evidence for the independent evolution of neighbouring terminal lakes, the Murray Darling Basin, Australia

“…The mouth has rapidly migrated to the north-west since the 1960s (Bourman & Murray-Wallace, 1991) and the sediments in the channel inside the mouth are accreting rapidly (Bourman & Barnett, 1995). Historically, the Goolwa channel carried *70% of the Murray River flow as it is considerably deeper and less sinuous than the other channels between Lake Alexandrina and the Coorong (Cann et al, 2000).…”