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PLoS One
2012 Jan 01;711:e49798. doi: 10.1371/journal.pone.0049798.
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Ophiuroids discovered in the middle triassic hypersaline environment.
Salamon MA
,
Niedźwiedzki R
,
Lach R
,
Brachaniec T
,
Gorzelak P
.
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Echinoderms have long been considered to be one of the animal phyla that is strictly marine. However, there is growing evidence that some recent species may live in either brackish or hypersaline environments. Surprisingly, discoveries of fossil echinoderms in non-(open)marine paleoenvironments are lacking. In Wojkowice Quarry (Southern Poland), sediments of lowermost part of the Middle Triassic are exposed. In limestone layer with cellular structures and pseudomorphs after gypsum, two dense accumulations of articulated ophiuroids (Aspiduriella similis (Eck)) were documented. The sediments with ophiuroids were formed in environment of increased salinity waters as suggested by paleontological, sedimentological, petrographical and geochemical data. Discovery of Triassic hypersaline ophiuroids invalidates the paleontological assumption that fossil echinoderms are indicators of fully marine conditions. Thus caution needs to be taken when using fossil echinoderms in paleoenvironmental reconstructions.
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23185442
???displayArticle.pmcLink???PMC3501475 ???displayArticle.link???PLoS One
Figure 1. Fossil locality and geological setting.Map of Poland with investigated area indicated and enlargement of Upper Silesia with the sampled Wojkowice Quarry (circle). Figure slightly modified from [25].
Figure 2. Stratigraphical section of Triassic sediments with ophiuroids.(A) Section of the northern and southern part of the Wojkowice Quarry (from [25]). 1, dolomitic limestones and marls; 2, cellular dolomitic limestones; 3, organodetrital limestones with bivalve detritus and columnals; 4, marly limestones; 5, pelitic limestones with abundance shells of bivalves; 6, pelitic limestones; 7, wavy limestones; 8, nodular limestones; 9, vertebrate remains; 10, Dadocrinus columnals; 11, encrinid columnals; 12, intraclasts; 13, regurgitalites; 14, Rhizocorallium commune; 15, numerous gastropods; 16, numerous Plagiostoma; 17, numerous Pseudocorbula sp.; 18, numerous Gervillia sp.; 19, Thalassinoides; 20, Holocrinus columnals; 21, layer(s) with presently recorded ophiuroids. I, Roetian; II, “limestones with Entolium and Dadocrinus unit”; III, “first wavy limestones unit”; IV, “cellular limestones unit”; V, “thick-bedded limestones” and “wavy limestones unit”. (B) Investigated section of “first wavy limestones unit” and “cellular limestones unit”; S1–S7 = rock samples for boron content analyses. Scale bar equals 1 m. (C) Enlargement of the ophiuroid layer. Arrows show the place of accumulations. Scale bar = 10 cm. (D) Slab (described in the paper as no. 1) with ophiuroid accumulation. (E) SEM micrographs of the oral view of the ophiuroid disc. (F) SEM micrographs of the aboral view of the near complete ophiuroid specimen. (G) SEM micrographs of the contact of arm plates showing relicts of the stereom microstructure. Scale bar = 10 mm.
Figure 3. Petrographical and cathodoluminescent features of the layer with ophiuroids.(A) Fine-grained dedolomites under transmitted light and (B) in crossed-nicoles. (C) Laminated dedolomites with irregulary distributed voids under transmitted light. (D) Laminated and microfolded dedolomites under cathodoluminescence. (E) Pseudospar crystals and rhombohedral crystals of calcitized dolomites and pseudomorphs after gypsum (arrows) in crossed-nicoles. (F) Rhombohedral crystals of calcitized dolomites under cathodoluminescence showing zoned crystal growth. Dolomite rhomboids have non-luminescent and bright orange luminescent zones. Non-luminescent areas are due to Fe rich diagenetic fluids and the incorporation of Fe in the dolomite lattice (“quench ion”) during crystal gwowth, bright orange luminescent areas indicates changes in the diagenetic fluid chemistry into Mn enrichment and the incorporation of Mn in the dolomite lattice (“activator ion”) during crystal growth.
Figure 4. CL-activated UV-VIS spectrum of the luminescent dolomite (see
Figure 3F
). Spectrum shows Mn2+ emission maximum at ca. 660 nm (Mn2+ activation in the MgCO3 position).
