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Bear Gulch Limestone facts for kids

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Bear gulch montana sea urchin
Bear Gulch fossil sea urchin, species unknown.
Falcatus falcatus 01
Falcatus falcatus

The Bear Gulch Limestone in Montana is a fossiliferous lagerstätte, a limestone layer laid down in the Bashkirian Stage of the early Pennsylvanian epoch of the Carboniferous period, about 318 mya.

This lens of limestone was laid down in a surrounding matrix that indicates a landscape of mudflats and braided channels (linear sandstone seams) in fresh and brackish water, in an arid climate (gypsum formation). Magnetic orientation of particles relative to the bedding planes of the strata suggest a latitude of about 12°N, a tropical siting.

Fossils

In the Bear Gulch Limestone, many genera of fossil fishes and some invertebrates were occasionally preserved in detail when they died and sank to the bottom of a shallow marine or estuarine lagoon. In such cases, conditions on the silty bottom preventing the usual bacterial decomposition are usually invoked, characterized as close to anoxic, thus suppressing ordinary bacterial decomposition; however, fossils of fishes of distinctly bottom-dwelling type are present, and traces of worm burrows or similar bottom disturbance show that sufficient oxygen was available in the upper levels of bottom silt. Pulses of hypoxic or anoxic conditions and perhaps periodic episodes of heavy siltation—the lagoon laid down up to 90 ft/30 m of limestone during its existence— may have been involved.

The numerous genera and many body types represented by fossils are witnesses to a highly diversified paleoecology with many available niches to be filled by specialist fauna.

Images for kids

  • Belantsea montana

    Belantsea montana

  • Debeerius

    Debeerius ellefseni

  • Echinochimaera meltoni (fossil fish) (Bear Gulch Limestone, Upper Mississippian; Montana, USA) (33784748875)

    Echinochimaera meltoni

  • Harpacanthus2DB

    Harpacanthus fimbriatus

  • Heteropetalus elegantulus Bear Gulch Montana USA

    Heteropetalus elegantulus

  • StethacanthusesDB 2

    Stethacanthus altonensis and Stethacanthus productus

  • Thrinacoselache gracia

    "Thrinacoselache" (Thrinacodus) gracia

  • †Discoserra pectinodon Unt Karbon Bear Gulch Montana USA Ch2431

    Discoserra pectinodon

  • †Paratarrasius hibbardi Carboniferous Bear Gulch, Montana

    Paratarrasius hibbardi

  • †Allenypterus montanus Unt Karbon Bear Gulch Montana USA Ch927

    Allenypterus montanus

  • †Caridosuctor populosum Unt Karbon Bear Gulch USA Ch1056

    Caridosuctor populosum

  • †Aenigmacaris cornigerum SCHRAM & HORNER 1979

    Aenigmacaris cornigerum

  • 20200924 Anderella parva

    Anderella parva

  • †Dithyrocaris rolfei Unt Karbon Bear Gulch Montana USA Ar2547

    Dithyrocaris rolfei

  • Ar1050 Perimecturus rapax Unt Karbon Bear Gulch Montana USA

    "Perimecturus" rapax

  • †Tyrannophontes acanthocercus Unt Karbon Bear Gulch Montana USA Ar886a

    Tyrannophontes (Daidal) acanthocercus

  • Reticycloceras sp Carboniferous Bear Gulch Montana USA Mo1832b

    Reticycloceras sp.

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