Litho-, bio-, and sequence stratigraphy of the Boyle-Portwood Succession (Middle Devonian, Central Kentucky, USA)

Brett, Carlton E.; Zambito, James; Baird, Gordon C.; Aboussalam, Zhor Sarah; Becker, Ralph Thomas; Bartholomew, Alex J.

doi:10.1007/s12549-018-0323-6

Cited by 7 publications

(1 citation statement)

References 31 publications

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“…9) from a black shale in the Middle Devonian Portwood Member of Kentucky. These shales were deposited in comparatively shallow water (Schieber & Lazar, 2004;Brett et al, 2018) and thus to find bioturbation should not be considered implausible. It is indeed possible to convince oneself to see discontinuous 'wormy' features (Fig.…”

Section: The Compositional Contrast Perspectivementioning

confidence: 99%

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

et al. 2021

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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.

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Section: The Compositional Contrast Perspectivementioning

confidence: 99%