Invertebrate Trace Fossil in Ironstone
Incertae sedis; difficult to assign species without diagnostic surface textures like Ophiomorpha pellets. • Trace fossil (ichnofossil) of an invertebrate, preserved in an iron-rich sedimentary matrix.
Geological Period
Likely Paleozoic to Mesozoic era, possibly Pennsylvanian or Cretaceous depending on regional formation.
Estimated Age
Approx. 66 to 320 million years, based on common ironstone nodule formations.
Preservation Type
Authigenic mineralization (iron-replacement) and cast/mold preservation within a concretionary nodule.
Condition Assessment
Fair; the specimen is fragmentary and weathered, lacking the sharp definition required for high-grade diagnostic identification.
Taxonomic Classification
Ichnogenus: Likely cf. Thalassinoides or Ophiomorpha (based on burrow-like structure).
Morphological Description
Exhibits a cylindrical to sub-cylindrical structure partially embedded in the matrix. Surface shows irregular, rugose textures and longitudinal striations suggestive of burrowing activity or internal casting of a hollow tube.
Rock Matrix
Ironstone or ferruginous siltstone/sandstone. High limonite or hematite content giving the characteristic brownish-orange and dark grey coloration.
Formation & Location
Possible associations include the Mazon Creek formation (USA) or similar ironstone-bearing formations in the UK or North America.
Size & Dimensions
Approximately 5-8 cm in width, which is consistent with medium-sized invertebrate burrows or decapods.
Value & Rarity
Estimated Market Value
$10.00 - $30.00 USD
Auction Estimate
$20.00 - $50.00 USD
Rarity Assessment
Common; ironstone nodules containing trace fossils or fragmentary remains are geographically widespread.
Scientific Significance
Provides data on bioturbation and the behavior of ancient bottom-dwelling organisms (infauna) within anoxic or iron-rich paleoenvironments.
Preparation Recommendations
No chemical cleaning required. Dry brush to remove loose dust. Keep in a low-humidity environment to prevent further oxidation or 'shale rot'.
Notable Features
Distinct color contrast between the dark interior core and the oxidized orange-brown exterior crust of the siderite/ironstone nodule.