II II II II II - Geoscience Australia

Extensive bodies of marine water occupied the sub-Murray and Arckaringa basins of
the southern interior. Very impoverished faunas of foraminifera (O'Brien, 1986a) and
gastropods and foraminifera (Townsend & Ludbrook, 1975) respectively, point to
conditions too stressful for most marine organisms, probably because of regular large
influxes of meltwater into these semi-enclosed embayments from the adjacent ice
caps. The question arises as to how these isolated marine basins were connected to
the world ocean. No connection was possible across the Kanimblan highlands to the
east, nor is there any evidence of contemporary marine sediments to the north or in
the Officer Basin. The most reasonable route seems to lie to the southeast, to the
north and/or west of Tasmania, via a Red Sea-type passage filling a rift valley along
the site of the later break between Antarctica and southern Australia. Much of this
narrow connecting sea would have been covered by an ice shelf, as the Antarctic ice
cap advanced across into Tasmania, Victoria and South Australia. The location of a
southern entrance to the Arckaringa Basin is unclear; the only known evidence for
one is the 90 m-thick sequence of fine-grained sediments of uncertain age and affinity
in the Mallabie Depression.
The Canning Basin, apart from the partial ice cover already alluded to, contained cold
marine water, which became deeper, or at least quieter, in the latter part of the interval
(Forman & Wales, 1981; Towner & Gibson, 1983a). Ice-rafted dropstones are a
feature of the sequence. In the Bonaparte Basin, the sea regressed during the
interval, with nearshore and high-energy barrier and beach facies grading up to fluvial
and lacustrine deposits (Laws & Brown, 1976; Mory & Beere, 1988). Again there is
evidence of ice-rafting, by seasonal or glacial ice. The presence of some deltas is
inferred on the map, as is the extent of the fluvial area beyond the coastal zone.
Alluvial fans formed in response to basin and hinterland uplift, and some fed directly
into the sea (Mory & Beere, 1988). Regression is also indicated in the Rob Roy 1 well
(Browse Basin), where the sequence begins as marine, but grades up to non-marine
(Crostella, 1976). The Scott Plateau area off northwestern Australia may have been
above sea level and eroding at this time (Stagg, 1978; Allen & others, 1978).
Sediments of tentative Stage 2 age have been intersected in the Tasman 1 and Kulka
1 wells in the Arafura Basin (Petroconsultants Australasia, 1989). The sequence at
Tasman 1 is fine-grained, with minor coal implying non-marine facies. That at Kulka
1 comprises fine-grained clastics of uncertain, probably marine, origin.
Fluvial deposition probably took place over much of the land area of the continent,
especially in outwash aprons along the margins of ice sheets, but most of these
deposits have not survived later erosion. However, in the Officer, southern Canning,
Pedirka and Cooper Basins, as mentioned previously, glaciofluvial units have been
preserved by basin subsidence. The eastern Galilee Basin received fluvial and
fluviolacustrine sediments from surrounding erosional highlands (Hawkins, 1978). The
Denison Trough of the Bowen Basin holds a great thickness of terrestrial Reids Dome
beds, but the base of the pile in the main graben complex has not yet been reached
by drilling and its age is unknown. On the map it is assumed that filling of the trough
began during this time slice. Certainly in the Strathmuir Synclinoriunn to the northeast,
the fluvial basal portions of the Carmila beds (with interbedded volcanics) were being
laid down at this time. Another fluvial facies of note is the lower Temi Group, within
the Werrie and Temi Basins in eastern New South Wales.
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