The Cadna-owie Formation is a
Geological formation
A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics (lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock expo ...
of
Early Cretaceous
The Early Cretaceous (geochronology, geochronological name) or the Lower Cretaceous (chronostratigraphy, chronostratigraphic name) is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 143.1 ...
age located in the
Eromanga Basin
The Eromanga Basin is a large Mesozoic sedimentary basin in central and northern Australia. It covers parts of Queensland, the Northern Territory, South Australia, and New South Wales, and is a major component of the Great Artesian Basin. The Er ...
.
Description
The exposed Cadna-owie Formation consists of
bioturbated, carbonaceous, cross-bedded and level bedded fine to medium
sandstone
Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...
, with minor coarse sandstone intervals, that directly overlies fresh or weathered bedrock. The lower part of the formation incorporates extensive
boulder
In geology, a boulder (or rarely bowlder) is a rock fragment with size greater than in diameter. Smaller pieces are called cobbles and pebbles. While a boulder may be small enough to move or roll manually, others are extremely massive. In ...
facies,
conglomerate, lonestones,
dropstones,
tillite
image:Geschiebemergel.JPG, Closeup of glacial till. Note that the larger grains (pebbles and gravel) in the till are completely surrounded by the matrix of finer material (silt and sand), and this characteristic, known as ''matrix support'', is d ...
and tillite lenses described as the Livingston Tillite Member. The upper part of the formation is marked by an
unconformity
An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval ...
of regional extent with the overlying Trinity Well Sandstone representing a hiatus encompassing the
Barremian
The Barremian is an age in the geologic timescale (or a chronostratigraphic stage) between 125.77 Ma (million years ago) and 121.4 ± 1.0 Ma (Historically, this stage was placed at 129.4 million to approximately 125 million years ago) It is a ...
.
Environment
The Cadna-owie Formation was deposited in very shallow marine to non-marine conditions, with
cross-stratification
In geology, cross-bedding, also known as cross-stratification, is layering within a stratum and at an angle to the main bedding plane. The sedimentary structures which result are roughly horizontal units composed of inclined layers. The origina ...
at some levels indicating deposition above
storm wave base.
Livingston Tillite Member
Facies recording extensive boulder beds, conglomerate, and tillite lenses represent flowtill in a proximal
fluvioglacial ice-contact setting. Other associated facies record
palynoflora used to date the Member as
Valanginian
In the geologic timescale, the Valanginian is an age or stage of the Early or Lower Cretaceous. It spans between 137.05 ± 0.2 Ma and 132.6 ± 0.2 Ma (million years ago). The Valanginian Stage succeeds the Berriasian Stage of the Lower Cretac ...
.
Trinity Well Sandstone
The bouldery sandstones, conglomerate, and tillite described as the Sheehan Tillite Member represent
subglacial deposition or in a proximal ice-contact setting as well as
proglacial, with deposition occurring as lenses of
morainal debris shed from
icebergs
An iceberg is a piece of fresh water ice more than long that has broken off a glacier or an ice shelf and is floating freely in open water. Smaller chunks of floating glacially derived ice are called "growlers" or "bergy bits". Much of an ic ...
floating in a shallow sea as the glacier melted.
See Also
*
Fossiliferous stratigraphic units in Australia
**
Wonthaggi Formation
The Wonthaggi Formation is an informal geological Formation (geology), formation in Victoria, Australia whose strata date back to the Early Cretaceous. It is part of the Strzelecki Group within the Gippsland Basin. Dinosaur remains are among the ...
, Contemporaneous fossiliferous formation of the Gippsland Basin
**
Bulldog Shale, Aptian to Albian fossiliferous formation
References
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