Publication Date:
2021-03-29
Description:
Fossil catshark egg capsules, Scyliorhinotheca goederti gen. et sp. nov., are reported from a Late Eocene deep−water
methane−seep calcareous deposit in western Washington State, USA. The capsules are preserved three−dimensionally and
some show mineralized remnants of the ribbed capsule wall consisting of small globular crystals that are embedded in a
microsparitic matrix. The globules are calcitic, but a strontium content of 2400–3000 ppm suggests that they were origi−
nally aragonitic. The carbonate enclosing the egg capsules, and the capsule wall itself, show 13C values as low as
−36.5‰, suggesting that formation was induced by the anaerobic oxidation of methane and hence in an anoxic environ−
ment. We put forward the following scenario for the mineralization of the capsule wall: (i) the collagenous capsules expe−
rienced a sudden change from oxic to anoxic conditions favouring an increase of alkalinity; (ii) this led to the precipitation
of aragonitic globules within the collagenous capsule wall; (iii) subsequently the remaining capsule wall was mineralized
by calcite or aragonite; (iv) finally the aragonitic parts of the wall recrystallized to calcite. The unusual globular habit of
the early carbonate precipitates apparently represents a taphonomic feature, resulting from mineralization mediated by an
organic matrix. Taphonomic processes, however, are at best contributed to an increase of alkalinity, which was mostly
driven by methane oxidation at the ancient seep site
Keywords:
Elasmobranchia; Scyliorhinidae; taphonomy; exceptional preservation; collagen; Late Eocene; Washing− ton State; USA.
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551
Language:
English
Type:
article
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publishedVersion
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