A new record of the Toarcian oceanic anoxic event from Scotland (UK) and environmental responses

2021 ◽  
Author(s):  
Wenhan Chen ◽  
David Bryan Kemp ◽  
Tianchen He ◽  
Chunju Huang
Keyword(s):  
Chemical Weathering ◽  
Coarse Grained ◽  
Global Ocean ◽  
Geochemical Data ◽  
Oceanic Anoxic Event ◽  
Organic Carbon Isotope ◽  
Anoxic Event ◽  
Geographic Differences ◽  
Environmental Responses ◽  
Global Carbon

<p>The early Toarcian oceanic anoxic event (T-OAE, ~183 Ma) was characterized by a prominent environmental perturbation, likely associated with a large amount of <sup>12</sup>C-enriched carbon released into the global ocean-atmosphere system. This effusion caused a marked disruption to the global carbon cycle and propagated a series of remarkable changes in ocean chemistry and climate. Although the T-OAE has been recognized worldwide, clear geographic differences in the character of the event and its environmental effects have been recognized. Here, we present new geochemical data from a lower Toarcian succession on the Isle of Raasay, NE Scotland (Hebrides Basin, Northwest European Shelf). Organic carbon isotope data through the Raasay section reveal a pronounced negative excursion, similar to that recognised globally. The excursion interval is enriched in organic matter, and redox sensitive element data suggest that suboxic bottom water conditions contemporaneously occurred, likely interspersed with anoxic episodes. Our findings contrast with evidence of more pervasive anoxia/euxinia in nearby basins, and emphasize how deoxygenation was spatially variable within the T-OAE. Inorganic geochemical data and sedimentological observations suggest a significant enhancement in chemical weathering and coarse-grained detrital flux during the T-OAE on Raasay. These findings support evidence from other localities for a strengthening of hydrological cycling in response to global warming during the T-OAE.</p>

Carbon cycle perturbation and mercury anomalies in terrestrial Oceanic Anoxic Event 1b from Jiuquan Basin, NW China

2022 ◽  
pp. SP521-2021-149
Author(s):  
Xiangdong Zhao ◽  
Daran Zheng ◽  
He Wang ◽  
Yanan Fang ◽  
Naihua Xue ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Carbon Cycle ◽  
Central Italy ◽  
Lacustrine Sediments ◽  
Terrestrial Ecosystem ◽  
Western Tethys ◽  
Oceanic Anoxic Event ◽  
Anoxic Event ◽  
Carbon Reservoir ◽  
Global Carbon

AbstractThe Oceanic Anoxic Event (OAE) 1b is well documented in western Tethys, however, records in Eurasia are still lacking. Here, we carried out high-resolution organic carbon isotope (δ13Corg), total organic carbon (TOC) contents and mercury (Hg) concentrations analysis of the lacustrine sediments from the Xiagou and Zhonggou formations in the Hanxiagou section, Jiuquan Basin, northwestern China. The lacustrine δ13Corg curve presents three stages of negative excursions above the basalt layer dated at 112.4 ± 0.3 Ma in the lowermost Zhonggou Formation. The three negative δ13Corg excursions, well corresponded with the three subevents (Kilian, Paquier, and Leenhardt) of the OAE1b in Poggio le Guaine (central Italy), Vocontian Basin (SE France) and St Rosa Canyon (NE Mexico) sections, supporting the record of the terrestrial OAE 1b in the Jiuquan Basin. Five mercury enrichment (ME) intervals in Hg/TOC ratios were recognized, indicating that the pulsed volcanism from the southern Kerguelen Plateau likely triggered the OAE 1b. However, the decoupling between NIE shifts and mercury enrichments signifying other carbon reservoir (with no link to mercury) probably contributed to the global carbon cycle perturbation during the OAE 1b period. Our results provide direct evidence to link the OAE 1b and terrestrial ecosystem in the Eurasia.

scholarly journals Latitudinal differences in the amplitude of the OAE-2 carbon isotopic excursion: <i>p</i>CO<sub>2</sub> and paleoproductivity

2011 ◽  
Vol 8 (3) ◽  
pp. 6191-6226 ◽  
Author(s):  
E. C. van Bentum ◽  
G.-J. Reichart ◽  
A. Forster ◽  
J. S. Sinninghe Damsté
Keyword(s):  
North Atlantic ◽  
Co2 Sequestration ◽  
North Atlantic Ocean ◽  
Carbon Isotopic Composition ◽  
Black Shales ◽  
High Productivity ◽  
Oceanic Anoxic Event ◽  
Carbon Isotopic ◽  
Anoxic Event ◽  
Global Carbon

Abstract. A complete, well-preserved record of the Cenomanian/Turonian (C/T) Oceanic Anoxic Event 2 (OAE-2) was recovered from Demerara Rise in the southern North Atlantic Ocean (ODP site 1260). Across this interval, we determined changes in the stable carbon isotopic composition of sulfur-bound phytane (δ13Cphytane, a biomarker for photosynthetic algae. The δ13Cphytane record shows a positive excursion at the onset of the OAE-2 interval, with an unusually large amplitude (~7 ‰) compared to existing C/T proto-North Atlantic δ13Cphytane records (3–6 ‰). Overall, the amplitude of the excursion of δ13Cphytane decreases with latitude. Using reconstructed sea surface temperature (SST) gradients for the proto-North Atlantic, we investigated environmental factors influencing the latitudinal δ13Cphytane gradient. The observed gradient is best explained by high productivity at DSDP Site 367 and Tarfaya basin before OAE-2, which changed in overall high productivity throughout the proto-North Atlantic during OAE-2. During OAE-2, productivity at site 1260 and 603B was thus more comparable to the mid-latitude sites. Using these constraints as well as the SST and δ13Cphytane-records from Site 1260, we subsequently reconstructed pCO2 levels across the OAE-2 interval. Accordingly, pCO2 decreased from ca. 1750 to 900 ppm during OAE-2, consistent with enhanced organic matter burial resulting in lowering pCO2. Whereas the onset of OAE-2 coincided with increased pCO2, in line with a volcanic trigger for this event, the observed cooling within OAE-2 probably resulted from CO2 sequestration in black shales outcompeting CO2 input into the atmosphere. Together these results show that the ice-free Cretaceous world was sensitive to changes in pCO2 related to perturbations of the global carbon cycle.

Provenance and depositional characteristics of Lathi Formation in southern part of Jaisalmer Basin: Implications for exploration of sandstone type uranium mineralization

2021 ◽  
Vol 38 (1) ◽  
pp. 41-50
Author(s):  
Shijo Mathew ◽  
Pritam Karmakar ◽  
Rajeev Bidwai ◽  
S K Sharma ◽  
Navin Goyal ◽  
...  
Keyword(s):  
Chemical Weathering ◽  
Gravity Data ◽  
Source Area ◽  
Sedimentary Facies ◽  
Climatic Conditions ◽  
Uranium Mineralization ◽  
Coarse Grained ◽  
Geochemical Data ◽  
Carbonaceous Matter ◽  
Jaisalmer Basin

The lower Jurassic Lathi Formation covers about 900 sq. km area and forms the lowermost unit of Jaisalmer Basin of western Rajasthan. Lithologically the Lathi Formation comprises of conglomerate, sandstone, siltstone, shale and mudstone. The sandstones are generally medium- to coarse-grained, moderately sorted and show variation in colour, grain-size and texture. Petrographic studies indicate a mixed provenance for the Lathi sandstone. On the basis of geochemical data, theses sandstones are classified into sub-arkose, litharenite and sub-litharenite. Palaeo-weathering indices such as CIA (80.45), CIW (85.23) and PIA (84.23) suggest moderate to high degree of chemical weathering of the source area, intermediate and felsic igneous provenance, under humid to semi-humid climatic conditions. Further, the geochemical data indicate the sedimentation in a passive continental margin setting. The Bouguer gravity image clearly depicts the north westward slope of the basement. Modelling studies of the gravity data revealed average depth to the basement as 800m, 400m and 250m respectively in northwest, central and southeastern parts of the surveyed area. Exploration activities by Atomic Minerals Directorate for Exploration and Research have resulted in location of several uranium anomalies in the Lathi Formation. Lathi Formation is characterised by many favourable parameters such as fertile provenance, arkosic sandstones intercalated with shale/mudstone, reduced sedimentary facies with carbonaceous matter, lignite and pyrite deposited in continental to marginal marine environment. Malani Igneous Suit and metamorphic rocks constitute the basement for Jaisalmer Basin. Malani rhyolites and granites are fertile source of uranium, containing 6.7 ppm and 9.2 ppm average and intrinsic uranium respectively. Presence of carbonaceous matter and pyrite bearing sandstones, indicative of reducing environment at depth below water table (R.L. 150 m), was reported during subsurface exploration in Lathi sandstone which is a favourable condition for Lathi sediments to host uranium mineralization.

Links between temperature changes and oceanic-plateau emplacement during the Cenomanian–Turonian Oceanic Anoxic Event (OAE 2)

2020 ◽  
Author(s):  
Lawrence Percival ◽  
Niels van Helmond ◽  
David Selby ◽  
Steven Goderis ◽  
Phillipe Claeys
Keyword(s):  
High Temperatures ◽  
Sea Surface ◽  
Global Ocean ◽  
Sea Surface Temperatures ◽  
Cold Event ◽  
Oceanic Anoxic Event ◽  
Oceanic Plateau ◽  
Surface Temperatures ◽  
Anoxic Event ◽  
Osmium Isotope

&lt;p&gt;The Cenomanian&amp;#8211;Turonian boundary interval (~94 Ma) was marked by a period of climatic turbulence, and featured the widespread expansion of strongly oxygen-depleted conditions across a large part of the global ocean; collectively these environmental degradations are referred to as an oceanic anoxic event or OAE (specifically OAE 2 for this time interval).&amp;#160;Extremely high sea-surface temperatures are documented for several regions during OAE 2, likely beginning at the onset of the event, but a shift towards colder conditions during the early stages of the OAE (the Plenus Cold Event or PCE) is also recorded in several locales, before a return to a very warm climate during the latter part of the crisis. The overarching high temperatures are thought to have resulted from major volcanic activity during the emplacement of one or more oceanic plateaus, as evidenced by a globally documented shift in osmium-isotope ratios to very unradiogenic values just below the base of OAE strata that indicates a very large flux of mantle-like osmium to the open ocean at that time. Intriguingly, the PCE cooling has been shown as likely non-synchronous globally, suggesting a local control in addition to/instead of global forcing; whilst the high temperatures associated with OAE 2 appear to have continued long after the OAE itself ceased.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;This study presents new osmium-isotope data from the New Jersey shelf of the proto-North Atlantic (ODP Leg 174AX: Bass River), correlating the results with a previously generated sea-surface temperature dataset from the same site. These results are then compared with other temperature archives and osmium records of oceanic-plateau activity for OAE 2. The new data indicate intense oceanic-plateau activity prior to and in the earliest stages of the OAE, with a decline in mantle-osmium output before the end of the event, consistent with previous findings. However, when the osmium data are directly correlated with temperature records, both at Bass River and other sites, they clearly show that not only were high sea-surface temperatures maintained after the OAE, but also after oceanic-plateau activity (and presumably associated volcanism and CO&lt;sub&gt;2&amp;#160;&lt;/sub&gt;emissions) fell. Thus, a reduction in mantle carbon output did not manifestly result in an immediate reduction of atmospheric CO&lt;sub&gt;2&lt;/sub&gt;. Moreover, the beginning of the osmium recovery broadly correlates with the end of the PCE cooling at all locations where both osmium and temperature trends have been studied. Consequently, although the PCE cooling was not globally synchronous and its precise timing at individual locations was likely controlled by local processes, some feature of the oceanic-plateau development allowed the cooling spells to occur when plateau activity was most intense, before a reduction in that intensity stymied the spread of cold conditions and resulted in the restoration of high temperatures in the latter stages of the OAE and beyond. These data highlight the need for further work to understand the complexity of and nuances in the relationships between large-scale volcanism and major climate/environment perturbations, both for OAE 2 and for other events.&lt;/p&gt;

scholarly journals PALEOCLIMATIC INSIGHTS ON THE CENOMANIAN-TURONIAN OCEANIC ANOXIC EVENT (OAE2) FROM NORTHERN IRAQ BASED ON CALCAREOUS NANNOFOSSILS AND GEOCHEMICAL DATA

2020 ◽  
Vol 53 (2C) ◽  
pp. 68-86
Author(s):  
Safwan Al-Lhaebi
Keyword(s):  
Trace Elements ◽  
Climatic Condition ◽  
Geochemical Data ◽  
Calcareous Nannofossils ◽  
Calcareous Nannofossil ◽  
X Ray Diffraction ◽  
X Ray ◽  
Northern Iraq ◽  
Oceanic Anoxic Event ◽  
Anoxic Event

Calcareous nannofossils, mineralogical and geochemical investigations are carried out on the Cenomanian-Turonian boundary of the Gulneri Formation in the Azmir, Dokan and Degala sections, northern Iraq. Regarding the calcareous nannofossil data CC11 and CC12 biozones were identified. A detailed investigation was carried out to identify calcareous nannofossils species. On the basis of their stratigraphic distribution, two biozones were proposed in this study; Quadrum gartneri Interval Biozone (CC11) part and Lucianrhabdus maleformis Interval Biozone (CC12) part. Correlation with other calcareous nannofossils biozones from regional schemes led to conclude that the age of the Gulneri Formation in the studied sections is the early Turonian. Mineralogical (X-ray diffraction XRD) and trace elements geochemistry (X-ray fluorescence XRF) data along with the dominance of calcareous nannofossil Watznauria that indicates warm and arid climatic condition prevailing in the Cenomanian-Turonian transition.

scholarly journals Pulsed volcanism and rapid oceanic deoxygenation during Oceanic Anoxic Event 1a

Geology ◽  
2021 ◽  
Author(s):  
Kohen W. Bauer ◽  
Cinzia Bottini ◽  
Robert Frei ◽  
Dan Asael ◽  
Noah J. Planavsky ◽  
...  
Keyword(s):  
Earth Element ◽  
Geochemical Data ◽  
Earth System ◽  
Ontong Java Plateau ◽  
Oceanic Anoxic Event ◽  
Element Abundances ◽  
The Pacific ◽  
Anoxic Event ◽  
Oceanic Anoxia ◽  
Run Up

Widespread oceanic anoxia, biological crises, and volcanic activity are associated with the onset of Early Aptian (ca. 120 Ma) Oceanic Anoxic Event 1a (OAE1a). Reconstructions of oceanic deoxygenation and its links to broadly contemporaneous volcanism, however, remain poorly resolved. We use geochemical data, including δ53Cr ratios and rare Earth element abundances, to define the timing and tempo of submarine volcanism and global oceanic deoxygenation across this event. Pacific Ocean sediments deposited in the run up to OAE1a record multiple phases of marine volcanism associated with the emplacement of Ontong Java Plateau lavas. Rapid oceanic deoxygenation followed the initial phases of volcanism and a biocalcification crisis. Large swaths of the oceans likely became anoxic from the Tethys to the Pacific Oceans in &lt;30 k.y. Oceanic anoxia persisted for almost one million years after this and was likely sustained through intensified continental and submarine weathering. These results paint a new picture of OAE1a in which volcanism, biological crisis, and oceanic deoxygenation are separated in time and linked through Earth system responses that operate on time scales of tens of thousands of years.

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