Traces In the Dark--Sedimentary Processes and Facies Gradients In the Upper Devonian-Lower Mississippian Upper Shale Member of the Bakken Formation, Williston Basin, North Dakota, U.S.A.--Discussion

Schieber, Jüergen

doi:10.2110/jsr.2014.73

Cited by 10 publications

(6 citation statements)

References 15 publications

(17 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…These observations are consistent with previous interpretations of Bakken trace fossils and geochemistry which hypothesized low‐oxygen but not anoxic conditions for intervals in the Bakken black shales (Egenhoff & Fishman, ; Fishman et al ., ; cf . comment by Schieber, ). An alternative hypothesis posits that in seasonal or climate‐driven oxic/anoxic to euxinic fluctuations Late Devonian ichnofauna could persist (Boyer et al ., ), corroborated by ichnofauna recognized elsewhere in the Bakken (Angulo & Buatois, ).…”

Section: Discussionmentioning

confidence: 93%

Authigenic carbonate burial in the Late Devonian–Early Mississippian Bakken Formation (Williston Basin, USA)

2020

View full text Add to dashboard Cite

Late Devonian (Famennian) marine successions globally are typified by organic-rich black shales deposited in anoxic and euxinic waters and the cessation of shelf carbonate sedimentation. This global 'carbonate crisis', known as the Hangenberg Event, coincides with a major extinction of reefbuilding metazoans and perturbations to the global carbon cycle, evidenced by positive carbon-isotope excursions of up to 4&. It has been suggested that authigenic carbonate, formed as cements in sedimentary pore spaces during early burial diagenesis, is a significant mass fraction of the total global carbon burial flux, particularly during periods of low oxygen concentration. Because some authigenic carbonate could have originated from remineralization of organic carbon in sediments, it is possible for this reservoir to be isotopically depleted and thereby drive changes in the carbon isotopic composition of seawater. This study presents bulk isotopic and elemental analyses from fine-grained siliciclastics of the Late Devonian-Early Mississippian Bakken Formation (Williston Basin, USA) to assess the volume and isotopic composition of carbonates in these sediments. Carbonate in the Bakken black shales occurs primarily as microscopic disseminated dolomite rhombs and calcite cements that, together, comprise a significant mass-fraction (ca 9%). The elemental composition of the shales is indicative of a dynamic anoxic to sulphidic palaeoenvironment, likely supported by a fluctuating chemocline. Despite forming in an environment favourable to remineralization of organic matter and the precipitation of isotopically depleted authigenic carbonates, the majority of carbon isotope measurements of disseminated carbonate fall between À3& and +3&, with systematically more depleted carbonates in the deeper-water portions of the basin. Thus, although there is evidence for a significant total mass-fraction of carbonate with contribution from remineralized organic matter, Bakken authigenic carbonates suggest that Famennian black shales are unlikely to be sufficiently 13 C-depleted relative to water column dissolved inorganic carbon to serve as a major lever on seawater isotopic composition.

show abstract

Section: Discussionmentioning

confidence: 93%

Authigenic carbonate burial in the Late Devonian–Early Mississippian Bakken Formation (Williston Basin, USA)

2020

View full text Add to dashboard Cite

show abstract

“…Reineck, 1963;Potter et al, 1980;Droser and Bottjer, 1986), as used in Lazar et al (2014). It should be noted that this scheme does not consider cryptobioturbation by meiofauna that obscures lamina boundaries and erases subtle sedimentary features (Schieber, 2003(Schieber, , 2014 (OM) in a pore space. Volume loss by driving out volatile components is interpreted to be caused by the heat from the milling beam, because the cracks were visible from the onset of SEM imaging.…”

Section: Exploring Ion Milling Artifactsmentioning

confidence: 99%

An SEM Study of Porosity in the Eagle Ford Shale of Texas—Pore Types and Porosity Distribution in a Depositional and Sequence-stratigraphic Context

Schieber¹,

Lazar²,

Bohacs³

et al.

The Eagle Ford Shale

View full text Add to dashboard Cite

Although typically considered with a focus on high-resolution petrography, shale porosity should not be thought of as a stand-alone petrographic feature. Shale and mudstone porosity is the outcome of a long succession of processes and events that span the continuum from deposition through burial, compaction, and late diagenesis. For the Eagle Ford Shale this journey began with accumulation in intra-shelf basins at relatively low latitudes on a southeast-facing margin during early parts of the late Cretaceous. To understand the factors that generated and preserved porosity in this economically important interval, a scanning electron microscope study on ion-milled drill-core samples from southern Texas was conducted to understand the development of petrographic features and porosity and place them in stratigraphic context. The studied samples show multiple pore types, including pores defined by mineral frameworks (clay and calcite), shelter pores in foraminifer tests and other hollow fossil debris, and pores in organic material (OM). In many instances, framework and shelter pores are filled with OM that has developed pores due to maturation. Large bubble pores in OM suggest that hydrocarbon liquids were left behind in or migrated into these rocks following petroleum generation and that the bubbles developed as these rocks experienced additional thermal stress. These larger OM pores indicate deeper seated interconnection on ion-milled surfaces and in three-dimensional image stacks.

show abstract

“…Egenhoff & Fishman, 2013;Ma et al, 2016;Borcovsky et al, 2017;DeReuil & Birgenheier, 2019;Biddle et al, 2021). Yet, whereas probing and expanding the limits of benthic life into the realm of presumably 'forbidding' organic-rich muds is a much-needed endeavour, doubts have been raised previously about the validity of these claims via comparisons to potential modern equivalents and the impact of compaction on burrows made in water-rich sediments (Schieber, 2014).…”

Section: Application To Perceived Micro-burrows In Shalesmentioning

confidence: 99%

“…Burrow traces can be exceedingly subtle (Schieber, 2003; and references therein) and their recognition subjective to the point where identical images can lead to starkly divergent assessments (cf. Egenhoff & Fishman, 2013;Schieber, 2014). The fact that meiofaunal fabric disruption is well-known from modern muds (Pike et al, 2001;Bernhard et al, 2003) certainly justifies giving this process due consideration in the study of ancient mudstones and shales.…”

Section: Introductionmentioning

confidence: 99%

Cryptic burrow traces in black shales – a petrographic Rorschach test or the real thing?

et al. 2021

View full text Add to dashboard Cite

In black shale studies, apparent lack of bioturbation is commonly taken as an indication of anoxic bottom waters. Yet, modern oxygen-stressed environments show that even at suboxic levels (0.0 to 0.2 ml l À1 oxygen), microscopic eukaryotic benthic organisms live in the uppermost millimetres to centimetres of the substrate. Known as meiofauna, these organisms disturb the primary fabric as they move through the sediment. These modern examples inspired students of the rock record to report sub-millimetre irregularwiggly features in black shale thin sections as meiofaunal burrows. Preparation flaws in thin section manufacture can cause reduced light transmission that results in darkened regions when viewed in transmitted light, and one wonders whether micro-burrows reported in the literature are indeed burrows, or alternatively artifact-induced optical illusions. Examining shale thin sections of Archean to Tertiary age showed: (i) that burrow-like features are common regardless of age; and (ii) that burrow identification varies significantly between observers. When transposing locations of presumed traces onto scanning electron microscope images of the same field of view (diamond polished surface), no evidence of fabric modification at locations of presumed burrows was observed. Microfabric within and outside 'burrows' was the same, and larger fabric elements traversed 'burrows' uninterrupted. Once both sides of the rock slice were polished, presumed burrows could no longer be observed, indicating that damage to the underside of the thin section caused the mistaken identification of micro-burrows. Because burrows emplaced in water-rich muds must undergo substantial compaction-induced 'flattening' and deformation prior to lithification, geometries of presumed burrows that disagree with a plausible compaction regime provide an additional filter to separate potential burrows from artifact-induced features. Recognizing meiofaunal disruption is an important aspect for accurate palaeoenvironmental interpretation of black shales. Yet, initial assessment via optical microscopy needs to be verified through scanning electron microscope-based examination of shale fabrics.

show abstract

Traces In the Dark--Sedimentary Processes and Facies Gradients In the Upper Devonian-Lower Mississippian Upper Shale Member of the Bakken Formation, Williston Basin, North Dakota, U.S.A.--Discussion

Cited by 10 publications

References 15 publications

Authigenic carbonate burial in the Late Devonian–Early Mississippian Bakken Formation (Williston Basin, USA)

Authigenic carbonate burial in the Late Devonian–Early Mississippian Bakken Formation (Williston Basin, USA)

An SEM Study of Porosity in the Eagle Ford Shale of Texas—Pore Types and Porosity Distribution in a Depositional and Sequence-stratigraphic Context

Cryptic burrow traces in black shales – a petrographic Rorschach test or the real thing?

Contact Info

Product

Resources

About