Trezona Formation
| Trezona Formation | |
|---|---|
| Stratigraphic range: late Cryogenian – early Ediacaran ~ | |
| Type | Formation |
| Unit of | Upalinna Subgroup |
| Sub-units | See: Members |
| Underlies | (Unconformably)
|
| Overlies | Enorama Formation |
| Lithology | |
| Primary | Packstone |
| Other | Grainstone, Limestone, Siltstone, Mudstone, Clay, Sandstone |
| Location | |
| Region | South Australia |
| Country | Australia |
The Trezona Formation is a Cryogenian to Ediacaran aged geological formation in the central Flinders Ranges of South Australia. It contains a number of fossiliferous beds, as well as a large carbon anomaly.
Geology
The formation is predominately composed of red bioclastic packstones, stromatolite bioherms within limestone, calcareous siltstone,[3] and oolitic grainstones. The bioclasts themselves are dune-cross-stratified between the larger stromatolite bioherms, and are notably diverse, containing probable microbial clasts ranging from flakes of stromatolite laminae, to ripped-up and rolled-up sediments with enhanced cohesion due to microbial mats.[1]
Members
The Trezona Formation is composed of two, informal, members. They are as follows, in ascending age:
- Siliciclastic member: This member is further divided into "upper" and "lower" sections. The lower section of the member is predominately composed of fine-grained siliciclastic and carbonate sediments. At the based of this lower section, is a thick laminae bed of cuspate stromatolites, which also contains rare columnar stromatolites. This layer is then overlain by a multitude of gray-green to red-brown mudstone and clay layers all the way to the top of the lower section, which slowly transitions from finely laminated layers to layers inter-bedded with silt and occasional fine-grained sand towards the top, before finally becoming calcareous mudstone. The upper section of the member is composed of again of fine-grained siliciclastic and carbonate sediments, also more mixed than the lower section. Within this mix there can be found the fine-grained grainstones of the formation, which are cross-bedded with intra-clastic packstone-grainstones, as well as containing fine-grained sandstone, with a higher presence columnar and domal stromatolites, whilst cuspate stromatolites become notably rarer.[4]
- Carbonate member: This member is composed primarily of mixture of siliciclastic and carbonate sediments, with a notable increase of the carbonate rocks. Cuspate stromatolites become rarer still within this member. The base of the member is composed of red-gray calcareous mudstone, which is inter-bedded with low relief, longitudinal, and domal-columnar stromatolites, as well as intra-clastic grainstone. Towards the top of the member, the richness of carbonate rocks increase greatly, with blue-brown limestone beds, composed of columnar and domal stromatolites bioherms. Oolitic grainstone can also be found in the upper sections, and is commonly found in association with the stromatolite bioherms.[4]
It conformably overlies the green shale dominated Enorama Formation, whilst it unconformably underlies the glacial Elatina Formation. In a small area of the Trezona Formation, it is overlain instead by the red clastic Yaltipena Formation.[3]
Carbon Anomaly
The formation contains evidence of what is known as the "Trezona Anomaly", which takes its name from this formation. The Trezona Anomaly takes place after what is referred to as the "Keele Peak", and precedes the Marinoan glaciation near the end of the Cryogenian, and contains a notable rise of —δ13C, with values reaching up to >9%,[5] making it the largest known δ13C excursion in Earth's history.[6] This anomaly is also found in Namibia, Norway, Scotland, Alaska and Canada.[5]
Fossils
Whilst the general flora of the Cryogenian aged beds is composed of various stromatolites and other cyanobacteria, a abundance of small three-dimensional fossils have been found. Whilst a majority of these fossils are not identical to one another, although all still share common traits, such as attaining centimetre-scale sizes, being generally ellipsoidal in shape and containing a number of interconnected canals within the fossils, some up to 1 mm (0.0 in) in diameter. The fossils remain unnamed, although they are inferred to possibly be sponge-grade organisms, being compared to the Ediacaran aged Palaeophragmodictya, also from Australia, and based on biomarkers found within similarly aged rocks within the area.[1]
Other researchers have noted that the sponge affinity may be unlikely, as the Trezona fossils do not contain characteristics seen in modern day sponges, although they do make mention of the fact that such characteristics may not have evolved at such an early point, being 90 million years older than the aforementioned Palaeophragmodictya.[7] A later study noted that a microbial or even mud chip origin for the Trezona fossils is also possible, and would go on to discount the sponge affinities, noting a more likely affinity with Calcimicrobes for the true fossils, which are commonly found in rocks of a similar age.[2] This was further backed up when researchers noted in a study that the sampled biomarkers do not provide enough evidence that the Trezona fossils are animals, let alone sponges.[8]
See also
- Neoproterozoic-related topics
References
- ^ a b c Maloof, Adam C.; Rose, Catherine V.; Beach, Robert; Samuels, Bradley M.; Calmet, Claire C.; Erwin, Douglas H.; Poirier, Gerald R.; Yao, Nan; Simons, Frederik J. (17 August 2010). "Possible animal-body fossils in pre-Marinoan limestones from South Australia". Nature Geoscience. 3 (9): 653. Bibcode:2010NatGe...3..653M. doi:10.1038/ngeo934.
- ^ a b Antcliffe, Jonathan B.; Callow, Richard H. T.; Brasier, Martin D. (November 2014). "Giving the early fossil record of sponges a squeeze". Biological Reviews. 89 (4): 972–1004. doi:10.1111/brv.12090. eISSN 1469-185X. ISSN 1464-7931.
- ^ a b Williams, G. E.; Schmidt, P. W. (17 February 2015). "Low paleolatitude for the late Cryogenian interglacial succession, South Australia: paleomagnetism of the Angepena Formation, Adelaide Geosyncline". Australian Journal of Earth Sciences. 62 (2): 243–253. doi:10.1080/08120099.2015.1003967. eISSN 1440-0952. ISSN 0812-0099.
- ^ a b O'Connell, Brennan; Wallace, Malcolm W.; Hood, Ashleigh v.S.; Rebbechi, Luke; Brooks, Hannah L. (March 2022). "Deep water cuspate stromatolites of the Cryogenian Trezona Formation". Geobiology. 20 (2): 194–215. doi:10.1111/gbi.12479. eISSN 1472-4669. ISSN 1472-4677.
- ^ a b Halverson, Galen P.; Shields-Zhou, Graham (January 2011). "Chapter 4 Chemostratigraphy and the Neoproterozoic glaciations". Geological Society, London, Memoirs. 36 (1): 51–66. doi:10.1144/M36.4. eISSN 2041-4722. ISBN 9781862393349. ISSN 0435-4052.
- ^ Rose, Catherine V.; Swanson-Hysell, Nicholas L.; Husson, Jon M.; Poppick, Laura N.; Cottle, John M.; Schoene, Blair; Maloof, Adam C. (February 2012). "Constraints on the origin and relative timing of the Trezona δ13C anomaly below the end-Cryogenian glaciation". Earth and Planetary Science Letters. 319–320: 241–250. doi:10.1016/j.epsl.2011.12.027.
- ^ Laflamme, Marc (September 2010). "Wringing out the oldest sponges". Nature Geoscience. 3 (9): 597–598. doi:10.1038/ngeo945. eISSN 1752-0908. ISSN 1752-0894.
- ^ Cunningham, John A.; Liu, Alexander G.; Bengtson, Stefan; Donoghue, Philip C. J. (January 2017). "The origin of animals: Can molecular clocks and the fossil record be reconciled?". BioEssays. 39 (1): 1–12. doi:10.1002/bies.201600120. eISSN 1521-1878. ISSN 0265-9247.