Tuff‐bearing upper Cambrian to lowermost Ordovician strata on Ko Tarutao island, Satun province, southernmost peninsular Thailand, contain a rich trilobite fauna relevant to global biostratigraphy, peri‐Gondwanan palaeogeography and shifting evolutionary mode. This area of Sibumasu, a lower Palaeozoic marginal Gondwanan terrane, is shown to have been closely associated with Australia, North China (Sino‐Korea) and other continental fragments from the supercontinent's northern equatorial sector, including South China at that time. Shared faunas also suggest a Kazakhstani and Laurentian association. Collections from eight sections yielded 10 newly discovered species and one new genus from ancient shoreface and inner shelf siliciclastic deposits. With the new taxa and revision of taxa known previously, we refine the age of the upper two formations of the Tarutao Group to the middle of Cambrian Stage 10, and lower–middle Tremadocian. Two biozones are erected for Sibumasu: the
Cambrian and earliest Ordovician fauna and geology of the Sông Đà and adjacent terranes in Việt Nam (Vietnam)
Abstract Later Cambrian and earliest Ordovician trilobites and brachiopods spanning eight horizons from five localities within the Sông Mã, Hàm Rồng and Đông Sơn formations of the Thanh Hóa province of Việt Nam, constrain the age and faunal affinities of rocks within the Sông Đà terrane, one of several suture/fault-bounded units situated between South China to the north and Indochina to the south. ‘Ghost-like’ preservation in dolomite coupled with tectonic deformation leaves many of the fossils poorly preserved, and poor exposure precludes collecting within continuously exposed stratigraphic successions. Cambrian carbonate facies pass conformably into Lower Ordovician carbonate-rich strata that also include minor siliciclastic facies, and the recovered fauna spans several uppermost Cambrian and Lower Ordovician biozones. The fauna is of equatorial Gondwanan affinity, and comparable to that from South China, North China, Sibumasu and Australia. A new species of Miaolingian ‘ptychopariid’ trilobite, Kaotaia xuanensis , is described. Detrital zircon samples from Cambrian–Ordovician rocks of the North Việt Nam and Sông Đà terranes, and from Palaeozoic samples from the Trường Sơn sector of Indochina immediately to the south, contain a predominance of ages spanning the Neoproterozoic period and have a typical equatorial Gondwanan signature. We associate the Cambrian and Tremadocian of the Sông Đà terrane with areas immediately to the north of it, including the North Việt Nam terrane and the southern parts of Yunnan and Guangxi provinces of China.
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- NSF-PAR ID:
- 10333998
- Date Published:
- Journal Name:
- Geological Magazine
- Volume:
- 159
- Issue:
- 1
- ISSN:
- 0016-7568
- Page Range / eLocation ID:
- 55 to 80
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Eosaukia buravasi Zone, encompassing all Cambrian sections from Ko Tarutao, and theAsaphellus charoenmiti Zone, encompassing the Tremadocian fauna discussed herein. The new genus isTarutaoia and new species areTsinania sirindhornae ,Pseudokoldinioidia maneekuti ,Pagodia ?uhleini ,Asaphellus charoenmiti ,Tarutaoia techawani ,Jiia talowaois ,Caznaia imsamuti ,Anderssonella undulata ,Lophosaukia nuchanongi andCorbinia perforata . Other taxa reported for the first time from Tarutao areMansuyia ? sp.,Parakoldinioidia callosa Qian,Pseudagnostus sp.,Homagnostus sp.,Haniwa mucronata Shergold,Haniwa sosanensis ? Kobayashi,Lichengia simplex Shergold,Pacootasaukia sp.,Wuhuia ? sp.,Plethopeltella sp.,Apatokephalus sp.,Akoldinioidia sp. 1 andKoldinioidia sp. -
null (Ed.)Abstract The Ao Mo Lae Formation of the Tarutao Group crops out on Thailand's Tarutao Island and contains a diverse assemblage of late Furongian trilobite taxa, including several endemic forms. This study presents a new genus and species, Satunarcus molaensis , discovered at two locations on the island. A cladistic analysis of the kaolishaniid subfamily Mansuyiinae in light of Satunarcus and similar genera known from across upper Cambrian equatorial Gondwanan rocks suggests that the subfamily is polyphyletic in its current definition, and thus is not a natural group. Separating Mansuyia Sun, 1924 from the other taxa conventionally placed in Mansuyiinae permits recognition of a previously unrecognized monophyletic subfamily Ceronocarinae new subfamily. As established herein, this kaolishaniid subfamily contains Satunarcus n. gen. and all genera previously recognized as Mansuyiinae. with the exception of Mansuyia itself. Ceronocarinae n. subfam. occur in middle Jiangshanian to middle Cambrian Stage 10 sedimentary rocks from Australia, South China, North China, and Sibumasu, with most genera endemic to Australia. UUID: http://zoobank.org/618c5136-73f0-4912-a7d3-e56559d2a76cmore » « less
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Many large fault zones record multiple reactivations that can be difficult to resolve and interpret in the field. Here, we use examples from Vermont and New Zealand to illustrate how structural data combined with 40Ar/39Ar geochronology can be used to reconstruct fault reactivation histories and interpret their possible origins. In SW New Zealand, the Spey-Mica Burn fault zone parallels a transpressive boundary between the Pacific and Australian plates. Integrated structural and 40Ar/39Ar data obtained from pseudotachylyte, mylonite, and other fault rocks allow us to distinguish successive phases of faulting (i.e., reactivations) from cases where different styles of brittle and ductile deformation occurred simultaneously (or nearly so) in the fault zone. Apparent age spectra from multiple minerals show age gradients that reveal four reactivations spanning ~20 Ma. The style and timing of these events correlate well to times of increased convergence rate and collisions between oceanic ridge segments and a nearby trench. Fault zones in NW Vermont also record different styles of reactivation. The Hinesburg Thrust (HT), which juxtaposes Late Proterozoic-Early Cambrian rift clastic rocks against Ordovician carbonate rocks of the Champlain Valley belt, includes a ~30 m thick zone of mylonite that is cut by a cataclastic fault and deformed by folds. 40Ar/39Ar data suggest the mylonite formed during the Ordovician Taconic orogeny and later was folded into a series of domes and basins during the Late Silurian-Devonian Acadian orogeny. Farther west, the Champlain thrust fault (CT) juxtaposes Cambrian dolostones against Ordovician calcareous shales. Superposed faults within the foot wall of the CT show a progressive change in movement direction from W-directed thrusting, to NW-directed thrusting, to N-S slip, and NE-SW slip. These changing slip directions appear to reflect wholly Taconic motion along a north-dipping lateral ramp between Burlington and Shelburne where the CT cuts up section to the south. Acadian reactivation of the CT appears restricted to late folding similar to the HT. These examples highlight the utility of combining structural data with 40Ar/39Ar geochronology to unravel slip histories in continental fault zones and to distinguish among the different styles and origins of fault reactivation.more » « less
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- Journal Article:
- https://doi.org/10.1017/S0016756821000844
