Australia: The Land Where Time Began
Kalbarri Coast - Northern Perth Basin
The geology of the Kalbarri Coast is transitional between that of Perth Basin and the Southern Carnarvon Basin. To the south of Kalbarri, rocks of Triassic age extend almost to Kalbarri, and from south of Kalbarri to the north are rocks from the Ordovician and Cretaceous that characterise the Carnarvon Basin that thin and eventually terminate towards the south of Kalbarri. Near Kalbarri there are some formations that are contiguous with the Perth Basin.
At Shell House, to the south of Kalbarri, strata from the lower Triassic are exposed only in the coastal cliff section. These strata extend from the central Perth Basin out onto the continental shelf about 200 km west-northwest of Kalbarri. The disconformable Wittecarra Sandstone overlies the Tumblagooda Sandstone, in the form of a basal conglomerate, above which are silty sandstone and siltstone, sandstone and conglomerate that contain what are believed to probably be plant rootlets. This sandstone is a braided fluvial deposit, associated with soil horizons that are thought to have derived from the uppermost parts of the Tumblagooda Sandstone.
The stratigraphic position of the Wittecarra Sandstone beneath the Kockatea Shale suggests it formed in the Early Triassic, but no body fossils have been found in it. It is believed the unit may possibly correlate with the Bookara Sandstone Member, or to the north of Dongara, near the base of the Kockatea Shale at a slightly higher level. A uniform clayey siltstone, with some ferruginous layers, comprises the Kockatea Shale. It has been suggested that these layers may have originally been soil profiles or possibly calcareous. In the shale of the coastal cliffs to the south of Kalbarri a small number of conchostracans have been found (Cockbain, 1974). No other fossils have been found in the unit near kalbarri. It has been suggested that this implies deposition in a brackish lagoon. Open-marine facies form the most dominate deposits near Dongara, that is further south (Source 2).
On Murchison House Station, at Meanarra Hill, to the north of the Murchison River, and in the coastal cliffs, are the best exposures of the sedimentary deposits from the Cretaceous. Extending less than 50 km to the south of Kalbarri, they are considered to be part of the succession of the Carnarvon Basin. Along the edge of the Pillawarra Plateau on Murchison House Stsation are the best exposures of the Winning Group (in ascending order, Birdrong Sandstone, Winning Sandstone Member of the Muderong Shale, Windalia Radiolarite, and Alinga Formation) and the Haycock Marl and Toolonga Calcilutite (Clarke & Teichert, 1948; Hocking et al., 1987; Lynch, 1991). In the coastal cliffs only the Birdrong Sandstone, the lowest of the Winning Group, is present. In the Southern Carnarvon basin it is the main artesian aquifer and in the Northern Carnarvon Basin there are many petroleum accumulations.
Float (loose disconnected pieces of rock) of siliceous marine facies deposited in the shallow inner neritic zone, from the Middle to Upper Eocene, about 27 km east of kalbarri, have been found to contain many sponges, mulluscsa, bryozoans, foraminifers and serpulid worms (Haig & Mory, 2003). A maximum age for the cutting of the Murchison Gorge, in the Late Eocene, that has been claimed to be a response to tectonism in the region during the Quaternary (Playford, 2003) is implied by the elevation of about 220 m above sea level.
A calcareous aeolian deposit, the Tamala Limestone of Pleistocene age, caps the coastal gorges, reaching a thickness of more than 300 m to the north of Kalbarri. North of the Murchison River mouth the sea cliffs are comprised of Tamala Limestone, with the exception of rare exhumed hills of strata deposited in the Cretaceous and Ordovician. The original bedding has been mostly obliterated by calcrete development, the thickness being less than 15 m at both Shell House and Red Bluff.
Locality 1 - Z Bend locality is about 30 km east of Kalbarri. There are very good exposures of the redbed facies of tidal and fluvial origin, part of the Tumblagooda Sandstone Formation, from the Ordovician, part of the type section.
Locality 2 - Red Bluff Locality. 4 km south of Kalbarri. Coastal exposures of transition from fluvial to tidal in redbed facies of Tumblagooda Sandstone Formation, of Ordovician age.
Locality 3 - Stone Wall, Murchison House Station. About 18 km north-northeast of Kalbarri. Fluvial redbed facies of Tumblagooda Sandstone Formation, of Ordovician age, beneath Cretaceous deposits of the Winning Group and Toolonga Calcilutite.
Locality 4 - Yalthoo Field, Murchison House Station. About 14 km north-northeast of Kalbarri. Good exposures of shallow marine facies from the Cretaceous, that are friable, Winning Group, Haycock Marl, and Toolonga Calcilutite, that are present in landslides and gullies. Very poor exposures are found elsewhere. Type and reference sections of the Toolonga Calcilutite.
Locality 5 - Shell House. About 11 km south of Kalbarri. Very good exposures, redbed facies that are fluvial to tidal of the Tumblagooda Sandstone Formation, of Ordovician age, which is unconformably overlain by the Wittecarra Sandstone (type section), that is of Lower Triassic age, and the Kockatea Shale, shallow-marine deposits present in a small graben covered by Birdrong Sandstone of the Lower Cretaceous and the Tamala Limestone of the Pleistocene.
Locality 6 - Pencell Pool, Murchison River. About 60 km east of Kalbarri. Good exposures of redbed facies of fluvial and tidal origin,
|Author: M.H.Monroe Email: email@example.com Sources & Further reading|