scholarly journals Ichnological analysis at the Fonte Coberta section (Lusitanian Basin, Portugal): Approaching depositional environment during the Toarcian oceanic anoxic event (T-OAE)

2018 ◽  
Vol 33 (2) ◽  
pp. 261 ◽  
Author(s):  
Olmos Miguez-Salas ◽  
Francisco J. Rodríguez-Tovar ◽  
Luis V. Duarte
Keyword(s):  
Depositional Environment ◽  
Environmental Parameters ◽  
Single Species ◽  
Trace Fossil ◽  
Anoxic Conditions ◽  
Oceanic Anoxic Event ◽  
Fossil Assemblage ◽  
Anoxic Event ◽  
High Degree ◽  
Lusitanian Basin

The Toarcian Oceanic Anoxic Event (T-OAE) is commonly related with an extended marine mass extinction and global oceanic anoxic conditions. However, recently it has been demonstrated that local palaeotopography/palaeogeography can determinate the absence of anoxic conditions, being other limiting environmental parameters of higher signifi cance. The detailed study of the Fonte Coberta section (Lusitanian Basin, Portugal) shows significant changes in the macrobenthic community at the lower Toarcian (Levisoni Zone) sediments during the event. In the study section, this interval presents a high degree of bioturbation with a relatively abundant and moderately diverse trace fossil assemblage dominated by Thalassinoides, with punctual Spongeliomorpha. The ichnotaxonomical study conducted on this trace fossil assemblage has allowed the recognition of a single species of Thalassinoides, T. suevicus Rieth, with two different morphotypes (I and II), as well the differentiation of Spongeliomorpha aff . iberica Saporta. The distribution of these ichnospecies, including the differentiated morphogroups, along the studied interval, corresponding to the T-OAE, allows refining depositional conditions as changes in the substrate consistency related to variations in relative sea level. Ichnological analysis reveals as a proxy to improve sequence stratigraphy characterization for the Lusitanian Basin during the T-OAE.

The chemostratigraphy and environmental significance of the Marlstone and Junction Bed (Beacon Limestone, Toarcian, Lower Jurassic, Dorset, UK)

2021 ◽  
pp. 1-15
Author(s):  
Hugh C. Jenkyns ◽  
Sophie Macfarlane
Keyword(s):  
Carbon Isotope ◽  
Oxygen Isotopes ◽  
Lower Jurassic ◽  
Carbon And Oxygen Isotopes ◽  
Oceanic Anoxic Event ◽  
Nodular Limestone ◽  
Anoxic Event ◽  
Reference Curves ◽  
High Degree ◽  
Organic Rich Sediment

Abstract Two fallen blocks of the Marlstone and stratigraphically overlying Junction Bed sampled on the beach below Doghouse Cliff in Dorset, UK (Wessex Basin) have been examined for carbon and oxygen isotopes of bulk carbonate as well as for strontium, carbon and oxygen isotopes and Mg:Ca ratios in the contained belemnites. The sequence, which contains most of the Toarcian zones and subzones within a metre or less of grey to yellow to pink, red and brown fossil-rich nodular limestone, is extremely condensed and lithologically similar to pelagic red limestones of the Tethyan Jurassic that are locally mineralized with Fe-Mn oxyhydroxides (e.g., Rosso Ammonitico). Strontium-isotope ratios of the contained belemnites are compatible with existing reference curves and both blocks show a rise to more radiogenic values post-dating the Pliensbachian–Toarcian boundary. The high degree of correlation between the relatively negative carbon and oxygen isotopes of the bulk carbonate is compatible with significant diagenetic overprint, and contrasts with higher carbon-isotope values in coeval condensed coccolith-rich limestones elsewhere. Evidence for the characteristic signature of the Toarcian Oceanic Anoxic Event, as represented by organic-rich sediment, is absent, possibly owing to a stratigraphic gap. Both blocks exhibit abrupt carbon-isotope shifts to lower values, one of which could represent the limbs of an incompletely recorded negative excursion associated with the Toarcian Oceanic Anoxic Event. That the Toarcian Oceanic Anoxic Event was also a significant hyperthermal is illustrated in both blocks by a drop in oxygen-isotope values and rise in Mg:Ca ratios of belemnites close to the base of the Junction Bed in the lowest part of the serpentinum zone.

Opportunistic behaviour after the Toarcian Oceanic Anoxic Event: The trace fossil Halimedides

2019 ◽  
Vol 520 ◽  
pp. 240-250 ◽  
Author(s):  
Francisco J. Rodríguez-Tovar ◽  
Olmo Miguez-Salas ◽  
Javier Dorador ◽  
Luis V. Duarte
Keyword(s):  
Trace Fossil ◽  
Oceanic Anoxic Event ◽  
Opportunistic Behaviour ◽  
Anoxic Event

Devonian depositional environments in the Darwin Mountains: Marine or non-marine?

1993 ◽  
Vol 5 (2) ◽  
pp. 211-220 ◽  
Author(s):  
Ken J. Woolfe
Keyword(s):  
Fresh Water ◽  
Depositional Environment ◽  
Trace Fossils ◽  
Depositional Environments ◽  
Trace Fossil ◽  
Glacier Area ◽  
Red Beds ◽  
Fossil Assemblage ◽  
Considerable Debate

The depositional environment of the Devonian Taylor Group has been subject to considerable debate for over 30 years. The debate stems largely from a belief that the abundant and diverse trace fossils represent a marine ichnofauna, whereas sedimentary features, including palaeosols, desiccation polygons and red beds, are more typical of a non-marine setting. The debate is reconciled by a reinterpretation of the trace fossil assemblage which shows that the trace fossils comprise a typical fresh water (Scoyenia ichnofacies) assemblage, and their occurrence in the Taylor Group in the Darwin Glacier area is entirely consistent with deposition in a mixed fluvial-lacustrine-subaerial environment.

The impact of the Pliensbachian-Toarcian crisis on belemnite diversity and size distribution

2020 ◽  
Author(s):  
Kenneth De Baets ◽  
Patrícia Rita ◽  
Luís Vítor Duarte ◽  
Pascal Neige ◽  
Laura Piñuela ◽  
...  
Keyword(s):  
High Resolution ◽  
Species Turnover ◽  
Adult Size ◽  
Oceanic Anoxic Event ◽  
Species Cluster ◽  
Anoxic Event ◽  
Major Bottleneck ◽  
Scaling Analyses ◽  
The Impact ◽  
Lusitanian Basin

<p>The Pliensbachian–Toarcian transition has been considered a major bottleneck in the early evolution of belemnites, probably related to major palaeoenvironmental and climatic changes during the Early Toarcian. Previous research has focused on the study of belemnites from higher, temperate latitudes, while high-resolution studies on diversity and size of subtropical belemnite assemblages in the northwest Tethys are comparatively rare. The lack of high-resolution (ammonoid subzone) abundance data on diversity and size distributions of belemnite assemblages does not allow separating changes during the Pliensbachian–Toarcian boundary event from those during the Toarcian anoxic event. Sample standardized diversity analyses on new data from Iberian sections suggest the Pliensbachian–Toarcian corresponds to a slight decrease in diversity and an adult size decrease within dominant species. Cluster and non-metric multidimensional scaling analyses, however, indicate that the largest changes in diversity and palaeogeographic distribution of belemnite assemblages occurred during the Toarcian oceanic anoxic event (TOAE) rather than the Pliensbachian–Toarcian boundary. In southern basins like the Lusitanian Basin and Riff Mountains, belemnites even disappear entirely during the TOAE. More generally, the TOAE corresponds with an increase in body size of belemnite assemblages driven by species turnover. The lack of widespread anoxia in southern basins of the northwest Tethys indicates that direct impact of warming or increased pCO2 triggered by volcanism as well as indirect effects on nutrient availability and productivity might have played an important role during both crises.</p>

scholarly journals The palynological response to the Toarcian Oceanic Anoxic Event (Early Jurassic) at Peniche, Lusitanian Basin, western Portugal

2017 ◽  
Vol 137 ◽  
pp. 46-63 ◽  
Author(s):  
Vânia F. Correia ◽  
James B. Riding ◽  
Luís V. Duarte ◽  
Paulo Fernandes ◽  
Zélia Pereira
Keyword(s):  
Early Jurassic ◽  
Oceanic Anoxic Event ◽  
Anoxic Event ◽  
Lusitanian Basin

Selective incidence of the toarcian oceanic anoxic event on macroinvertebrate marine communities: a case from the Lusitanian basin, Portugal

Lethaia ◽  
2017 ◽  
Vol 50 (4) ◽  
pp. 548-560 ◽  
Author(s):  
Olmo Miguez-Salas ◽  
Francisco J. Rodríguez-Tovar ◽  
Luís V. Duarte
Keyword(s):  
Oceanic Anoxic Event ◽  
Marine Communities ◽  
Anoxic Event ◽  
Lusitanian Basin

scholarly journals The effects of the Jenkyns Event on the radiation of Early Jurassic dinoflagellate cysts

2021 ◽  
pp. SP514-2020-255
Author(s):  
Vânia F. Correia ◽  
James B. Riding ◽  
Luís V. Duarte ◽  
Paulo Fernandes ◽  
Zélia Pereira
Keyword(s):  
Species Richness ◽  
New Species ◽  
Lower Jurassic ◽  
Early Jurassic ◽  
Dinoflagellate Cysts ◽  
Oceanic Anoxic Event ◽  
Anoxic Event ◽  
Northern Regions ◽  
Prolonged Recovery ◽  
Lusitanian Basin

AbstractThis contribution is an overview of the Early Jurassic dinoflagellate cysts of the Lusitanian Basin in Portugal, with particular emphasis on the effects of the Jenkyns Event (Toarcian Oceanic Anoxic Event - T-OAE) on the evolution of this planktonic group. We review and discuss data from 214 samples from six Lower Jurassic successions (upper Sinemurian-upper Toarcian) in the Lusitanian Basin. The late Pliensbachian radiation of dinoflagellate cysts was well recognised in this basin. The pre-Jenkyns Event interval is highly productive, with maximum abundance and species richness values. However, this palaeoenvironmental perturbation severely affected the evolution of this group for the remainder of the Early Jurassic. The prolonged recovery of the dinoflagellates in the Toarcian following the Jenkyns Event is not typical of the northern regions (Arctic and Boreal realms), where new species began to evolve earlier compared with southern European basins.

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