The Blackleaf Formation is a

geologic formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics ( lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exp ...

Montana Montana () is a U.S. state, state in the Mountain states, Mountain West List of regions of the United States#Census Bureau-designated regions and divisions, division of the Western United States. It is bordered by Idaho to the west, North ...

. It preserves

fossils A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

dating back to the

Albian The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous Epoch/ Series. Its approximate time range is 113.0 ± 1.0 Ma to 100.5 ± ...

to Cenomanian stages of the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

period Period may refer to: Common uses * Era, a length or span of time * Full stop (or period), a punctuation mark Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (or rhetorical period), a concept ...

.Blackleaf Formation
at

Fossilworks Fossilworks is a portal which provides query, download, and analysis tools to facilitate access to the Paleobiology Database, a large relational database assembled by hundreds of paleontologists from around the world. History Fossilworks was cre ...

.org

Description

The formation comprises an isolated, sinuous

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates ...

body sitting within and crosscutting a succession of three mudrock units. The lowermost mudstone is greater than 35 cm in thickness, light greenish grey and weakly calcareous. This unit exhibits extensive dark reddish grey mottling over its uppermost portion. Additionally, carbonate nodules as much as 4.5 cm in diameter form a discontinuous layer of 20–25 cm below the sharp upper contact of the unit. A dark greenish-grey

claystone Mudrocks are a class of fine-grained siliciclastic sedimentary rocks. The varying types of mudrocks include siltstone, claystone, mudstone, slate, and shale. Most of the particles of which the stone is composed are less than and are too sm ...

succeeds vertically. This 25 cm thick unit is calcareous with a platy structure and grades upwards into a greenish grey blocky mudstone with some organics. This third unit encloses the upper portion of the sedimentary structure and bears a sharp, irregular contact with an overlying burrowed dark red claystone. The lithology of the structure contrasts sharply with the surrounding host mudrock and facilitates recognition of the structure in the field.Lima Peaks
at

.org The lower, bone-bearing portion consists of 25–30 cm of medium to fine, calcareous greenish-grey sandstone, moderately sorted with abundant

plagioclase Plagioclase is a series of tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continuous solid solution series, more pro ...

and other

volcano A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plates ...

genic grains. Small (3–6 mm), rounded mud clasts are common in the coarser basal portion. This structureless unit fines upwards with an increasing clay content. A thin, 1–2 cm thick, grey claystone separates this lower sand- stone from an upper fine sandstone. The bedding parallels that of the host mudrocks. Reduced clay content, grey colour and larger (approx. 10 mm), platy mud clasts distinguish this unit from the otherwise similar, lower sandstone. A thin (less than 1 cm) rim of tan claystone with abundant calcite veins separates the lower portion of the structure from the host mudrocks.

Fossil content

The following fossils were reported from the formation: ;Reptiles * '' Oryctodromeus cubicularis''Varricchio et al., 2007 * '' Bernissartia sp.'' * '' Glyptops sp.''Ullmann et al., 2012 * Ankylosauridae indet. * Chelydridae indet. * Dromaeosauridae indet. * Goniopholididae indet. * Hadrosauridae indet. * Testudines indet. * Tyrannosauridae indet. ;Fish * Neopterygii indet. ;Flora * '' Araliaephyllum westonii''Crabtree, 1987 * '' cf. Aralia wellingtonia'' * '' Araliopsoides cf. cretacea'' * '' cf. Aspidophyllum trilobatum'' * '' cf. Ficus ovatifolia'' * '' cf. Celastrophyllum sp.'' * '' Cinnamomoides sp.'' * '' Nymphaeites sp.'' * '' Platanophyllum sp.'' * '' cf. Protophyllum sp.''

References

Bibliography

* * * {{cite LSA , last=Crabtree , first=D. R , year=1987 , title=Angiosperms of the Northern Rocky Mountains: Albian to Campanian (Cretaceous) megafossil floras , journal=

Annals of the Missouri Botanical Garden The ''Annals of the Missouri Botanical Garden'' is a long-established major peer-reviewed journal of botany, established in 1914 by the Missouri Botanical Garden, under the directorship of botanist and phycologist, George Thomas Moore, and still ...

, volume=74 , pages=707–747 Geologic formations of Montana Cretaceous System of North America Cretaceous Montana Albian Stage Cenomanian Stage Mudstone formations Sandstone formations Shale formations Siltstone formations Deltaic deposits Fluvial deposits Lacustrine deposits Ooliferous formations Paleontology in Montana

Description

Fossil content

See also

References

Bibliography