87Sr/86Sr chemostratigraphy of Neoproterozoic Dalradian carbonates below the Port Askaig Glaciogenic Formation, Scotland

Sawaki, Yusuke; Kawai, T.; Shibuya, Takazo; Tahata, Miyuki; Omori, Soichi; Komiya, Tsuyoshi; Yoshida, Naohiro; Hirata, Takafumi; Ohno, Takeshi; Windley, Brian F.; Maruyama, Shigenori

doi:10.1016/j.precamres.2010.02.021

Cited by 42 publications

(43 citation statements)

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“…Moreover, using a common temperature for structurally controlled dolomite formation, 150°C (°F), (Davies and Smith, 2006) and the δ 18 O measured in the dolomite, a reconstructed δ 18 O of the dolomitizing fluid would give reasonable results for a subsurface brine in Ediacaran host rock, −1 to +1‰ VSMOW (Figure 11). In contrast, the δ 18 O values measured in limestone are interpreted to be reset (compared to the signature at the time of limestone deposition) because of recrystallization at high temperature during deep burial; they are about 5‰ more depleted than time-equivalent marine carbonates (Burns et al, 1994;Sawaki et al, 2010).…”

Section: Origin Of Dolomitizing Fluidsmentioning

confidence: 90%

Dimensions, texture-distribution, and geochemical heterogeneities of fracture–related dolomite geobodies hosted in Ediacaran limestones, northern Oman

et al. 2014

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A B S T R A C TPredicting spatial distribution, dimension, and geometry of diagenetic geobodies, as well as heterogeneities within these bodies, is challenging in subsurface applications, and can impact the results of reservoir modeling. In this outcrop-based study, we generated a data set of the dimensions of fracture-related dolomite geobodies hosted in Ediacaran (Khufai Formation) limestones of the Oman Mountains that are up to several hundreds of meters long and a few tens of meters wide. The dolomite formed under burial conditions by fluids that interacted with siliciclastic layers, as demonstrated by the enriched Fe (up to 4.4%) and Mn (up to 0.8%) contents and 87 Sr∕ 86 Sr (∼0.710) signatures. Dolomitization probably occurred during the Hercynian Orogeny (or pre-Permian) because dolomitization predates some folding and pre-Permian rocks have seen intense deformation related to the Carboniferous Hercynian Orogeny. Moreover, dolomitization occurred between the onset and termination of bedding-parallel stylolitization and thus most likely before deep burial related to the Alpine Orogeny. Hence, dolomitization most likely occurred before deep burial related to the Alpine Orogeny and during or following the intense deformation related to the Carboniferous Hercynian Orogeny had affected pre-Permian rocks. The clumped-isotope signature yields a temperature of approximately 260°C (500°F), interpreted as the apparent equilibrium temperature obtained during uplift after deepest burial during the Late Cretaceous. Lateral transects across the dolomite bodies show that zebra dolomite textures are common throughout the body and that vugs are more common at the rim than the center of the bodies. Moreover, a weak geochemical trend exists with more depleted 18 O, Fe, and Mn concentrations in the core than at the rim of the dolomite bodies. These results show that minor heterogeneities exist within the dolomite bodies investigated. These data contrast with previous studies, in which more significant variation is reported in width of the dolomitization halo and texture for larger dolomite bodies that formed in host rocks more permeable than the examples from the Oman Mountains.

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Section: Origin Of Dolomitizing Fluidsmentioning

confidence: 90%

Dimensions, texture-distribution, and geochemical heterogeneities of fracture–related dolomite geobodies hosted in Ediacaran limestones, northern Oman

et al. 2014

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“…Application of these correlation tools on a regional to continental scale has been extensive (e.g. Misi et al ., ; Prave et al ., ; Jones et al ., ; Sawaki et al ., ). By the time of the Halverson et al .…”

Section: Chemical Sedimentology: Atmospheric and Hydrospheric Signalsmentioning

confidence: 96%

Sedimentological perspectives on climatic, atmospheric and environmental change in the Neoproterozoic Era

2016

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Sedimentological insights underpin many of the important recent advances in understanding of Earth system behaviour in the Neoproterozoic Era. This article reviews three main areas: (i) chemical proxies and their preservation, with emphasis on carbonate facies; (ii) glacial and post-glacial facies, including their age constraints; (iii) sedimentary evidence for biotic innovations and responses. Chemostratigraphy plays an important role in ordering Neoproterozoic events and defining disturbances to the carbon cycle. There is increasing attention being paid to assessing the role of diagenetic origination or modification of chemostratigraphic signals. Alongside this, new criteria for identifying primary dolomite and precursor metastable phases such as ikaite have been developed. In respect of oxygenation, geochemical proxies substantiate the concept of a Neoproterozoic Oxygenation Event as a very gradual transition, the ocean being at any one time a heterogeneous assemblage of ferruginous, sulphidic and oxic conditions, with some evidence of increasing deep-sea oxidation through the Ediacaran Period. Techniques such as Fe-speciation need to be supplemented with proxies sensitive to suboxic conditions. More generally, it is predicted that petrographically constrained microanalytical studies will also become more important in reconstructing palaeoenvironmental conditions. The global distribution of Neoproterozoic glacial deposits combined with palaeomagnetic evidence supports the concept of panglaciations in which ice sheets reached sea-level in the tropics. Advances in radiometric dating have demonstrated the synchronous onset of global (Sturtian) glaciation at 717 Ma and the demise of a second (Marinoan) glaciation at 635 Ma, and plausibly indicate long durations for each (55 Myr for Sturtian and 5 to 15 Myr for Marinoan). However, a compilation of radiometric dates indicates ambiguities indicating the need for further improvements to the radiometric and Sr-isotope database to understand events within the Sturtian time frame, the timing of onset of Marinoan glaciations, and the age and synchroneity of individual negative d 13 C anomalies. Sturtian deposits are typically thick, rift-related successions containing a range of environments influenced or dominated by dynamic glaciers, as well as ice-free marine intervals. Marinoan glacial deposits, by contrast, tend to be thin and continental. During the latter interval, oxygen isotope systematics of sulphate demonstrate that atmospheric CO 2 was high, as predicted by Snowball Earth theory, and that sedimentation was influenced by orbital forcing. The Sturtian record, by comparison, needs to be searched for evidence of cold-climate hiatuses on the one hand and orbital forcing on the other. Cap carbonate formation appears to have coincided with rising sea-levels following panglaciations. Snowball theory considers that they formed rapidly in the postglacial greenhouse, but an alternative (2016) 63, 253-306 doi: 10.1111/sed.12261 STATE OF THE SCIENCE model o...

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“…In Svalbard, the 87 Sr/ 86 Sr values then decrease to 0.7067. Ratios of 0.7064 in the Coates Lake Group and 0.7063 in the Sturt glaciation in Tasmania suggest a further decline in seawater 87 Sr/ 86 Sr. A similar rise then decline in seawater 87 Sr/ 86 Sr is known in Greenland (Fairchild et al 2000) and, more recently, Scotland (Sawaki et al 2010), so a stratigraphic horizon at c. 760 Ma could be a strong candidate for chronostratigraphic definition of the Cryogenian Period because of the coincidence of maximum pre-Sturt glaciation peaks in both d 13 C and 87 Sr/ 86 Sr within the stratigraphic range of C. buickii and B. burra.…”

Section: Australia -Canada-svalbard: 800 Mamentioning

confidence: 56%

Chapter 8 Biostratigraphy and stratigraphic subdivision of Cryogenian successions of Australia in a global context

Grey

Hill

Calver

2011

Memoirs

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Cryogenian correlation in Australia is based on an extensive data set from the Centralian Superbasin and Adelaide Rift Complex and integrates biostratigraphy and isotope chemostratigraphy to provide a three-dimensional interpretation based on outcrop and drill holes. Studies are ongoing, but newer data are consistent with the distributions discussed here. From the chemostratigraphic and biostratigraphic viewpoint, the first appearance of the acritarch Cerebrosphaera buickii, coupled with a large negative isotope excursion at c. 800 Ma, supported by the first appearance of the stromatolite Baicalia burra, seems to have potential for boundary placement. It is widely recognized across Australia and seems to have potential globally.

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87Sr/86Sr chemostratigraphy of Neoproterozoic Dalradian carbonates below the Port Askaig Glaciogenic Formation, Scotland

Cited by 42 publications

References 67 publications

Dimensions, texture-distribution, and geochemical heterogeneities of fracture–related dolomite geobodies hosted in Ediacaran limestones, northern Oman

Dimensions, texture-distribution, and geochemical heterogeneities of fracture–related dolomite geobodies hosted in Ediacaran limestones, northern Oman

Sedimentological perspectives on climatic, atmospheric and environmental change in the Neoproterozoic Era

Chapter 8 Biostratigraphy and stratigraphic subdivision of Cryogenian successions of Australia in a global context

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