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Retizonomonoletes hunanensis Fang et al. 1993 and the Retispora lepidophyta morphon
... The only evidence for the age of these event deposits is a miospore fossil from the Tianxinping Shale. According to Steemans et al. (1996), the 48-to 65-mm diameter size of Retispora lepidophyta (Kedo) is indicative of the upper part of the LN Zone, i.e. the equivalent of the ckI to kockeli conodont Zone. ...
... The miospore Retispora lepidophyta (Kedo) has been found in the lowermost 15 cm of the shale (Steemans et al., 1996). This miospore assemblage is considered as belonging to a marginal coastal, lowland swamp environment (Streel et al., 2000). ...
The global End-Devonian Hangenberg Event was one of the most important mass extinction events during the Phanerozoic eon. The stratigraphical, paleontological, and sedimentological evolution of strata equivalent to the Hangenberg Event have been widely investigated in three depositional environments of shallow-marine platform, of margin and upper slope, and of deep-water facies along the South China Platform. In this representative region within the eastern Paleotethys, the volcanic tuffs, storm deposits, and microbialites deposited during the time of the Hangenberg Event differ from the record of the Hangenberg Crisis in the Rhenish Slate Mountains of Germany, which is a standard for the western Paleotethys. The Upper Crisis Interval (so-called Stockum Limestone Event) in the Rhenish record is interpreted as correlative to the aftermath of the Hangenberg Event in South China rather than a crisis record per se. The unique Cap Microbialite of peloids and oncoids in South China is linked to onset of a new shallow-marine ecosystem characterized by microbe resurgence during a delayed biotic recovery. This microbialite resurgence in association with low-diversity metazoan ecosystems may be a common feature of post-extinction episodes. The new synthesis of records from South China provide insights into global changes that contributed to the Hangenberg biotic extinctions.
... The spore data give an inconsistent or contradictory result. Tan et al. (1987) found a number of spores in Unit 36 (Fig. 5), including Verrucosisporites nitidus, the index species of the LN Zone, whereas Steemans et al. (1996) suggested the upper part of the LV Zone (below the (Lower) Si. praesulcata Zone) based on size measurements of Retispora lepidophyta in Unit 36. However, they indicate in the meantime that the D-C boundary lies within the same unit or at the top of Unit 36. ...
... sulcata Zone limestone^) and the Sujiaping section (Tan et al. 1987;Bai et al. 1994: the Devonian Cystophrentis-and Quasiendothyra-bearing grey bio-intraclastic calcisiltitic limestone is directly overlain by Carboniferous grey bio-intraclastic calcisiltitic limestone bearing the foraminifer Vicinesphaera angulata-Bisphaera malevkensis Assemblage of Wang 1987). Wang and Yin (1985) and Wang et al. (1987); Huangmao - Bai et al. (1994); Malanbian - Tan et al. (1987), with the spore from Steemans et al. (1996) and lithologies of the Malanbian Fm. modified from Qie et al. (2015); Muhua II - Hou et al. (1985); Muhua III - Bai et al. (1994) and Hou et al. (1985). Numbers on the right of the lithologic column indicate bed number in the original source reference Apart from South China, Hangenberg Black Shale equivalents are also well developed in Tibet (lower part of Zhangdong Formation, Tulong Section, Liu et al. 2018), which belonged in the Devonian and Carboniferous to a different terrain/microcontinent. ...
The Hangenberg Crisis at the end of the Devonian is marked by a sudden global mass extinction (main Hangenberg Event), which was especially severe for ammonoids. Among the order Clymeniida, only the cymaclymeniids survived for a short time. We report the first discovery of Postclymenia cf. evoluta in South China in equivalents of the Hangenberg Black Shale (the regional Changshun Shale) at the Jiarantang section in Guizhou. The South China plate was far away and completely different from the Euramerica continent, where the Hangenberg Event/Crisis was first recognised. The presence of similar ammonoids as in contemporaneous beds of the Rhenish Massif, Germany, suggests close faunal relationship through the Palaeotethys Ocean. It agrees with a sudden spread of opportunistic extinction survivors with the initial Hangenberg Transgression. The regional facies and faunal succession at Jiarantang confirms previous concepts of a eustatically driven, significant transgressive-regressive couplet in the lower/middle crisis interval. The near-global distribution of cymaclymeniid survivors shows that their extinction at the end of the extended crisis interval must have been caused by a so far neglected, small-scale global extinction event in the open marine realm.
... Given that the ages of the two volcanic units are analytically indistinguishable, we quote Tucker et al.'s (1998) reported mean of all 207 Pb/ 206 Pb ages (363.6 ± 1.6 Ma). Owing to a doubtful index fossil specimen (Retizonomonoletes lepidophyta?), the horizon was originally assumed to belong to the pusillites-lepidophyta miospore zone (equivalent to being located within the Upper expansa conodont zone; Ziegler and Sandberg, 1990) of the upper Famennian (McGregor and McCutch eon, 1988), but has more recently been attributed to R. cassicula (now R. macroreticulata) by Steemans et al. (1996). As R. macroreticulata appears in the Uppermost marginifera conodont zone in Belgium (Streel and Loboziak, 1996), the biostratigraphic range of the two dated volcanic rocks is now inter-preted to range from the Uppermost marginifera to the Upper expansa conodont zone (Streel, 2000). ...
... Given that the ages of the two volcanic units are analytically indistinguishable, we quote Tucker et al.'s (1998) reported mean of all 207 Pb/ 206 Pb ages (363.6 ± 1.6 Ma). Owing to a doubtful index fossil specimen (Retizonomonoletes lepidophyta?), the horizon was originally assumed to belong to the pusillites-lepidophyta miospore zone (equivalent to being located within the Upper expansa conodont zone; Ziegler and Sandberg, 1990) of the upper Famennian (McGregor and McCutch eon, 1988), but has more recently been attributed to R. cassicula (now R. macroreticulata) by Steemans et al. (1996). As R. macroreticulata appears in the Uppermost marginifera conodont zone in Belgium (Streel and Loboziak, 1996), the biostratigraphic range of the two dated volcanic rocks is now inter-preted to range from the Uppermost marginifera to the Upper expansa conodont zone (Streel, 2000). ...
Four TOC-rich shale intervals spanning the Frasnian–Famennian (F–F) boundary were recovered in a drillcore (West Valley NX-1) from western New York (USA) and radiometrically dated using Re–Os. Two of the black shale intervals (WVC785 from ∼ 2.9 m below, and WVC754 from ∼ 6.4 m above the F–F boundary, respectively) yielded statistically overlapping ages with uncertainties of < 1.1%. An interpolated age and associated graphically determined uncertainty of 372.4 ± 3.8 Ma provides new absolute age constraints on the F–F boundary. This date is ∼ 4.1 Ma younger than the latest proposed F–F boundary age of 376.1 Ma obtained by interpolation of U–Pb dates from volcanic zircon [Kaufmann, B., 2006. Calibrating the Devonian Time Scale: A synthesis of U–Pb ID-TIMS ages and conodont stratigraphy. Earth-Science Reviews 76, 175–190], and within uncertainty of the International Commission on Stratigraphy accepted date of 374.5 ± 2.6 Ma. A third date (from sample WVC802, ∼ 8.2 m beneath the F–F boundary) yielded an imprecise age of 357 ± 23 Ma, owing in part to a limited Re/Os range. The initial 187Os/188Os (0.45 to 0.47), reflecting contemporaneous seawater Os values, are low but similar to the value of 0.42 reported for the Exshaw Fm (Canada) at the Devonian–Mississippian boundary (ca. 361 Ma) [Selby D., Creaser R.A., 2005. Direct radiometric dating of the Devonian–Mississippian time-scale boundary using the Re–Os black shale geochronometer. Geology 33, 545–548]. This may suggest fairly constant and low global continental weathering rates during the Late Devonian, although in view of the short residence time of Os in seawater (∼ 1–4 × 104 yr), further measurements are needed to assess potential short-term variation in seawater Os ratios. Owing to low Os and Re abundances at the F–F boundary, our data are inconsistent with long-term volcanism and bolide impact as potential Late Devonian mass extinction mechanisms. In addition, the Frasnian–Famennian ocean appears to have been depleted with respect to Re, possibly indicating an exhaustion of the Re seawater reservoir owing to high burial rates of redox-sensitive elements under dysoxic/anoxic conditions leading up to the F–F boundary.
... 15 and 16) found only one doubtful specimen (Retizonomonoletes lepidophyta?) of the index fossil of the pusillites-lepidophyta Zone. Moreover, that specimen is attributed rather to R. cassicula (now R. macroreticulata) by Steemans et al. (1996) and it appears earlier in the Uppermost P. marginifera conodont zone in Belgium (Streel and Loboziak, 1996). Therefore, the biostratigraphic range of the two dated volcanic rocks of Mount Pleasant Caldera Complex must be extended downward and comprises now the interval from the Uppermost P. marginifera to the Upper P. expansa conodont zone (Streel, 2000). ...
The recalibrated Devonian time scale represents an important improvement of Devonian chronology regarding two aspects. Firstly, a data set of 13 biostratigraphically well-bracketed U–Pb ID–TIMS zircon and monazite ages constitutes the framework of the scale. Secondly, approximately time-linear biostratigraphic scales have been used for the interpolation between the isotopic ages. The new construction thus represents a ‘biochronometric’ time scale, which allows the assignment of numeric ages not only to stage boundaries but also to each biozone boundary. The method of interpolation applied also enables the projection of the geochronological error onto the time scale. According to the newly calibrated scale, the Devonian lasted 57.4 ± 5.7 Ma from 418.1 ± 3.0 to 360.7 ± 2.7 Ma. This is, compared to previously published time scales, the longest time span ever calculated for this period. The age interpolations for the eight stage boundaries are:View Within ArticleThe duration of the Middle Devonian is calibrated here as quite short with 8.2 Ma and the Emsian and the Famennian are the longest stages with interpolated durations of 17.2 and 15.4 Ma, respectively. Together, all Devonian stages contain 57 conodont zones (including subzones, according to the standard conodont zonation) giving a mean duration of about 1 Ma. In the highly resolved part of the time scale (mid-Eifelian to the Devonian–Carboniferous boundary), zonal resolution averages 0.6 Ma. In contrast, the lowest resolution is shown in the early Emsian to mid-Eifelian interval with zonal durations of up to 5.5 Ma (serotinus Zone).
Latest Devonian to early Late Carboniferous palynozones of northern Brazilian basins are revised and correlated with equivalent miospore biozones of western Europe. It is concluded that certain biozones in PETROBRAS' earlier regional scheme for the Lower Carboniferous are actually indistinguishable, because age implications and stratigraphic ranges of their zonal species are now known to differ markedly from those given in older Brazilian literature. A regional unconformity separates Late Visean strata from early Late Tournaisian or older sediments in the Amazon and western Solimoes Basins, as possibly also in the Parnaiba Basin. Marine faunal controls for Late Carboniferous carbonates, within sections of Amazonian basins which contain taeniate pollen, are partly discussed with reference to U.S. Midcontinent data, and demonstrated to exclude pre-Westphalian age assignments. On the other hand, a possible Late Namurian age is acceptable from the palynological viewpoint for the oldest, dominantly terrigenous part of the Late Carboniferous sequence in the Solimoes Basin. This lacks taeniate bisaccates and seems to have no sedimentary equivalent in the neighbouring Amazon Basin. Results of the present study indicate that additional palynological investigations are needed in Early and Late Carboniferous sections of the Parnaiba and Solimoes Basins.
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Palynomorph distribution in Euramerica and western Gondwana, from the Latest Givetian to the Latest Famennian, may be explained, to some extent, by climatic changes. Detailed miospore stratigraphy dates accurately the successive steps of these changes. Interpretation is built on three postulates which are discussed: Euramerica at slightly lower latitudes than generally accepted by most paleomagnetic reconstructions; a conodont time-scale accepted as the most used available subdivision of time; and Late Devonian sea-level fluctuations mainly governed by glacio-eustasy. The Frasnian–Famennian timescale is also evaluated.
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