Cantwell Formation
Geologic formation in Alaska, United States
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The Cantwell Formation is a geologic formation in Alaska. It preserves fossils dating back to the Cretaceous period, it has also yielded numerous dinosaur tracks at Denali National Park. Contemporary therizinosaurid and hadrosaurid trackways in the formation indicate that the area was once a major point of immigration between Asia and North America during the Late Cretaceous for many families of dinosaur. Fossil plants of water lilies found in the same area suggest the presence of wetlands, ponds or other large standing bodies of water.[1]
| Cantwell Formation | |
|---|---|
| Stratigraphic range: Cretaceous | |
Denali National Park tectonic history | |
| Type | Formation |
| Location | |
| Region | Alaska |
| Country | United States |
Footprints discovered in the formation include those of theropods, hadrosaurs, ceratopsians, pterosaurs and birds, notably the Magnoavipes denaliensis.[2][1]
Description
The Cantwell Formation represents a Late Cretaceous fluvial succession in Denali National Park containing dinosaur trackways, invertebrate traces, and plant fossils. Sedimentary facies represent a lateral succession from alluvial fan and braided river deposits, to coastal fluvial and lacustrine environments with marshy overbanks, proximal estuary consisting of laterally avulsed distributary channels, intertidal estuarine deposits, and finally tidally influenced marginal marine environments.[3]
A leaf analysis of the Sable Mountain flora was used to estimate a mean annual temperature of 7.42 °C (45.36 °F), a warm month mean temperature of 17.1 °C (62.8 °F), and a cold month mean temperature of −2.3 °C (27.9 °F). Growing season precipitation was estimated at 229.4 millimetres (9.03 in) over a period of 4.8 months. These results demonstrate a cool temperate, seasonal paleoclimate with short dry summers and cold wet winters.[4] Dating of ash layers in the formation indicate this floral assemblage straddled the Campanian-Maastrichtian boundary, a period of rapid global cooling.[5]
Flora
Color key
|
Notes Uncertain or tentative taxa are in small text; |
| Taxa | Species | Locality | Material | Notes | Images |
|---|---|---|---|---|---|
| Alnites | A. sp. | Similar to extant Alnus.[4] | |||
| Asplenium | A. sp. | ||||
| Cf. Castaliites | cf. C. sp. | Leaf morphotaxon.[4] | |||
| Cephalotaxopsis | C. sp. | Belongs to Taxaceae.[5] | |||
| Corylites | C. beringianus | Similar to extant Corylus.[4] | |||
| Cladophlebis | C. sp. | ||||
| Cf. Craspedodromophyllum | cf. C. sp. | Belongs to Betulaceae.[4] | |||
| Equisetum | E. arcticum | ||||
| Glyptostrobus | G. sp. | ||||
| Fagales indet. | Leaf morphotypes.[4] | Belongs to the “Higher Hamamelids”.[4] | |||
| Cf. Kenella | cf. K. sp. | Seeds[4] | |||
| Larix | L. sp. | Needle bundles.[5] | Originally described as Cf. Pseudolarix.[1] | ||
| Metasequoia | M. occidentalis | ||||
| Menispermites | M. septentrionalis | Belongs to Menispermaceae.[4] | |||
| M. sp. | Another Menispermoid.[4] | ||||
| Cf. Nuphar | cf. N. sp. | Similar to extant Nuphar.[1] | |||
| Parataxodium? | Indeterminate | In need of revision.[4][6] | |||
| Cf. Phragmites | cf. P. sp. | ||||
| Picea | P. sp. | Needles, ovuliferous cone.[5] | |||
| Pinus | P. sp. | Needle bundles.[5] | |||
| Pityophyllum? | indeterminate | Indeterminate Pinaceous needles.[5] | |||
| Platanites | P. sp. | Belongs to Platanaceae.[4] | |||
| Pseudoprotophyllum | P. sp. | Another Platanoid.[4] | |||
| Cf. Sparganium | cf. S. sp. | ||||
| Trochodendroides | T. richardsonii | Belongs to Cercidiphyllaceae.[4] | |||
| T. sp. | A Trochodendroid.[4] | ||||
| Tumion | T. gracilis | ||||
| Cf. Viburniphyll | cf. V. sp. | Similar to extant Viburnum.[4] | |||
| Cf. Zizyphoides | cf. Z. sp. | Another Trochodendroid.[4] |
