Gogo Formation
Encyclopedia
The Gogo Formation in the Kimberley region of Western Australia
is a Lagerstätte
that exhibits exceptional preservation of a Devonian
reef
community.
, shale
and calcarenite
with numerous limestone
concretions. These concretions are resistant to weathering, producing extensive nodule fields on the ground in areas where the surrounding rock has eroded away.
The Gogo sediments represent deep, Hypoxia (environmental)
seafloor deposits in the vicinity of a large tropical reef composed primarily of algae
and stromatoporoids during the Frasnian
faunal stage
of the Late Devonian. Associated stratigraphic units which comprise this ancient reef system are the Windjana Formation (the actual reef structures), Pillara Limestone (reef platform) and the Sadler Formation (fore-reef deposits).
s and tentaculids are also known from the formation, but their soft tissue is not preserved.
The calcareous concretions formed around objects from the shallow reef areas which sank into the deep anoxic basins. The concretions sometimes contain the remains of fish, whose bodies are often preserved complete in three-dimensions due to rapid encasement and the slow rate of decay in the oxygen-poor surroundings. By repeated baths in a dilute acid solution, the matrix is dissolved away via a process of acid etching to reveal delicate fish fossils, some retaining impressions of soft tissues.
The discovery of Materpiscis
, a placoderm preserved with an embryonic juvenile still attached by its umbilical cord, has revealed that at least some placoderms gave birth to live young
.
, of Museum Victoria
in Melbourne, in Swimming in Stone: the Amazing Gogo Fossils of the Kimberley (Fremantle: Fremantle Arts Centre) 2007.
Western Australia
Western Australia is a state of Australia, occupying the entire western third of the Australian continent. It is bounded by the Indian Ocean to the north and west, the Great Australian Bight and Indian Ocean to the south, the Northern Territory to the north-east and South Australia to the south-east...
is a Lagerstätte
Lagerstätte
A Lagerstätte is a sedimentary deposit that exhibits extraordinary fossil richness or completeness.Palaeontologists distinguish two kinds....
that exhibits exceptional preservation of a Devonian
Devonian
The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...
reef
Reef
In nautical terminology, a reef is a rock, sandbar, or other feature lying beneath the surface of the water ....
community.
Sedimentology
Unweathered sections of the Gogo Formation are made of siltstoneSiltstone
Siltstone is a sedimentary rock which has a grain size in the silt range, finer than sandstone and coarser than claystones.- Description :As its name implies, it is primarily composed of silt sized particles, defined as grains 1/16 - 1/256 mm or 4 to 8 on the Krumbein phi scale...
, shale
Shale
Shale is a fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite. The ratio of clay to other minerals is variable. Shale is characterized by breaks along thin laminae or parallel layering...
and calcarenite
Calcarenite
thumb|250px|The [[Pietra di Bismantova]] in central [[Italy]] is an example of calcarenite formation.Calcarenite is a type of limestone that is composed predominately, more than 50 percent, of detrital sand-size , carbonate grains...
with numerous limestone
Limestone
Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....
concretions. These concretions are resistant to weathering, producing extensive nodule fields on the ground in areas where the surrounding rock has eroded away.
The Gogo sediments represent deep, Hypoxia (environmental)
Hypoxia (environmental)
Hypoxia, or oxygen depletion, is a phenomenon that occurs in aquatic environments as dissolved oxygen becomes reduced in concentration to a point where it becomes detrimental to aquatic organisms living in the system...
seafloor deposits in the vicinity of a large tropical reef composed primarily of algae
Algae
Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...
and stromatoporoids during the Frasnian
Frasnian
The Frasnian is one of two faunal stages in the Late Devonian epoch. It lasted from 385.3 ± 2.6 million years ago to 374.5 ± 2.6 million years ago. It was preceded by the Givetian stage and followed by the Famennian stage...
faunal stage
Faunal stage
In chronostratigraphy, a stage is a succession of rock strata laid down in a single age on the geologic timescale, which usually represents millions of years of deposition. A given stage of rock and the corresponding age of time will by convention have the same name, and the same boundaries.Rock...
of the Late Devonian. Associated stratigraphic units which comprise this ancient reef system are the Windjana Formation (the actual reef structures), Pillara Limestone (reef platform) and the Sadler Formation (fore-reef deposits).
Fossil preservation
The fossils of the Gogo formation display three-dimensional soft-tissue preservation of tissues as fragile as nerves and embryos with umbilical cords. Over fifty species of fish have been described from the formation, and arthropods (including phylocarids and eurypterids) are similarly well-preserved. Nautiloids, goniatiteGoniatite
Goniatites are extinct ammonoids, shelled cephalopods related to squid, octopus, and belemnites, that form the order Goniatitida. The Gonatitida originated from within the more primitive anarcestine ammonoids in the Middle Devonian some 390 million years ago...
s and tentaculids are also known from the formation, but their soft tissue is not preserved.
The calcareous concretions formed around objects from the shallow reef areas which sank into the deep anoxic basins. The concretions sometimes contain the remains of fish, whose bodies are often preserved complete in three-dimensions due to rapid encasement and the slow rate of decay in the oxygen-poor surroundings. By repeated baths in a dilute acid solution, the matrix is dissolved away via a process of acid etching to reveal delicate fish fossils, some retaining impressions of soft tissues.
The discovery of Materpiscis
Materpiscis
Materpiscis is a genus of ptyctodontid placoderm from the Late Devonian located at the Gogo Formation of Western Australia...
, a placoderm preserved with an embryonic juvenile still attached by its umbilical cord, has revealed that at least some placoderms gave birth to live young
Vivipary
Vivipary has two different meanings. In animals, it means development of the embryo inside the body of the mother, eventually leading to live birth, as opposed to laying eggs...
.
History
The reef, which now stands up abruptly in the western Australian desert (as the Windjana Limestone), was first identified in 1940 by paleontologist Curt Teichert, who discovered the first fossil fish from the region. It has been described for the layman by the driving force behind collecting expeditions at the Gogo Reef for the last two decades, John LongJohn A. Long (paleontologist)
John Albert Long is an Australian paleontologist who is currently the Vice President of Research and Collections at the Natural History Museum of Los Angeles County. He is also an author of popular science books. His main area of research is on the fossil fish of the Late Devonian Gogo Formation...
, of Museum Victoria
Museum Victoria
Museum Victoria is an organisation which operates three major state-owned museums in Melbourne, Victoria, Australia; these are: the Melbourne Museum, the Immigration Museum and Scienceworks. It also manages the Royal Exhibition Building and a storage facility in Melbourne's City of Moreland.Museum...
in Melbourne, in Swimming in Stone: the Amazing Gogo Fossils of the Kimberley (Fremantle: Fremantle Arts Centre) 2007.