Hanson Formation

The Hanson Formation is a geologic formation on Mount Kirkpatrick, Antarctica. It is one of only two major dinosaur-bearing rock groups found on the continent of Antarctica to date; the other is the Snow Hill Island Formation and related formations from the Late Cretaceous of the Antarctic Peninsula. The formation has yielded only a handful of Mesozoic specimens so far and most of it is as yet unexcavated. Part of the Victoria Group of the Transantarctic Mountains, it is below the Prebble Formation and above the Falla Formation.[1] The Formation is related to the Volcanic Activity Linked to the Karoo-Ferar eruptions on the Lower Jurassic.[2][3][4] The climate of the zone was similar to the modern Southern Chile, Humid, with a temperature interval of 17–18 degrees.[5]

Hanson Formation Stratigraphic range: Late Sinemurian-Lower Pliensbachian ~194–188.5 Ma PreꞒ Ꞓ O S D C P T J K Pg N
The Hanson Formation is located on the Transantarctic Mountains
Type	Geological formation
Unit of	Victoria Group
Sub-units	Three informal members
Underlies	Prebble Formation
Overlies	Falla Formation
Thickness	237.5 m (779 ft)
Lithology
Primary	Sandstone, tuffite
Location
Coordinates	84.3°S 166.5°E
Approximate paleocoordinates	57.5°S 35.5°E
Region	Mount Kirkpatrick, Beardmore Glacier
Country	Antarctica
Type section
Named for	The Hanson Spur
Named by	David Elliot
Hanson Formation (Antarctica)

History

The Victoria Group (also called Beacon Supergroup) from the Central Transantarctic Mountains where defined by Ferrar in 1907, when he described the "Beacon Sandstone" on the sedimentary rocks on the Valleys of the Victoria Land.[6] Following this initial work, the term "Beacon System" was introduced to recover a series of similar Sandstones and associated deposits that where recovered locally.[7] Latter the "Beacon Sandstone Group" was put for those units on the Victoria Land, with Harrington in 1965 proposing the name for different units that appar on the Beacon Rocks on South Victoria Land, the beds below the Maya Erosion Surface, the Taylor Group and the Gondwana Sequence, including the Victoria Group.[8] This work left out several older units, such as the Permian Coal Measures and the Glacial deposits.[8] It was not until 1963 that there was an establishment of the Gondwana sequence, where the Falla Formation was named delimited for a 2300 ft (700 m) series of lower Quartz Sandstone, a medium Mica-Carbon Sandstone and an upper Sandstone-Shale Unit.[9] The "Upper Falla Formation" was then named, being exposed with considerable uncertainty about it´s age and the Prebble Formation (Tought it was stimated from the Glossopteris-bearing beds (Early Permian) and the assumed possibility that the rocks were older than Dicroidium-bearing beds, thought to be Late Triassic, in the Dominion Range).[10] Other latter works tried to set it between the Late Triassic (Carnian) and the Lower-Middle Jurassic (Toarcian-Aalenian).[11] The Local Jurassic Sandstones were included on the Victoria Group, with the Beacon unit defined as a Supergroup in 1972, comprising beds overlying the pre-Devonian Kukri Erosion Surface to the Prebble Formation on the Central Transantarctic Mountains, and the Mawson Formation (And it´s unit then separated, the Carapace Sandstone) in Southern Victoria Land.[12] The Mawson Formation, identified at the beginning as indeterminate Tillite was placed on the Ferrar Group Latter.[13] Extensive fieldwork on the area of the Transantarctic Mountains were done later, which demonstrated the need for revisions to the post-Permian stratigraphy.[14] It was recovered that only 282 m of the 1963´s upper 500 m of the Falla Formation correspond with the Sandstone/Shale sequence and that 200 m was composed by a volcaniclastic sequence.[14] It was then, that after this discovery several works ended describing new units on the location: the Fremouw Formation and Prebble Formation, being this last one introduced for a laharic unit, not seen in 1963, that occurs between the Falla Formation and the Kirkpatrick Basalt.[15][14] It was also recovered a complete record at Mount Falla, revelating the sequence from of events in the [[Transantarctic Mountains]] spanning the interval between the Upper Triassic Dicroidium-bearing beds and the Middle Jurassic tholeiitic lavas.[14] The upper part of the Falla Formation contains recognizable primary pyroclastic deposits, exemplified by resistant, laterally continuous silicic tuff beds, what led to consider this unit as a different formation, more after seeing that the change is related with erosion associated with tectonic activity that preceded or accompanied the silicic volcanism and marked the onset of the development of a volcano-tectonic rift system.[1]

Description

The name Hanson Formation was proposed for the volcaniclastic sequence that was described on Barrett’s 1969 Falla Formation essay.[14] The name was taken from the Hanson Spur, that lies immediately at the west of Mount Falla and is developed on the resistant tuff unit described below.[1]

Paleofauna

The first dinosaur to be discovered from the Hanson Formation was the predator Cryolophosaurus in 1991, which was then formally described in 1994. Alongside these dinosaur remains were fossilized trees, suggesting that plant matter had once grown on Antarctica's surface before it drifted southward. Other finds from the formation include tritylodonts, herbivorous mammal-like reptiles and crow-sized pterosaurs. Surprisingly were the discovery of prosauropod remains, which were found commonly on other continents only until the Early Jurassic. However, the bone fragments found at the Hanson Formation were dated until the Middle Jurassic, millions of years later. In 2004, paleontologists discovered partial remains of a large sauropod dinosaur that has not formally been described yet.

Synapsida

Genus	Species	Location	Material	Notes	Images
Tritylodontidae[16][17][18]	Tritylodontidae Indeterminate	Mt. Kirkpatrick	FMNH PR1824, an isolated upper postcanine tooth.	A Cynodont, incertade sedis inside Tritylodontidae. It was found related with the Asian genus Bienotheroides.[17] Probably the largest member of the family, and among the largest post-triassic Synapsids, with a length over 1.6 m long, was probably robust as a modern Wolverine.[17]	Tritylodon, example of Tritylodontidae cynodont

Pterosauria

Genus	Species	Location	Material	Notes	Images
Dimorphodontidae?[16][18][19]	Dimorphodontidae? Indeterminate	Mt. Kirkpatrick	Humerus	A Pterosaur, possible member of the family Dimorphodontidae. Nearly the same size as YPM Dimorphodon. Its affinities haven't been compared, but its numeral morphotype is common for basal pterosaurs, like in Preondactylus or Arcticodactylus, so can be related to this genera.	Dimorphodon, example of Dimorphodontid Pterosaur

Ornithischia

Genus	Species	Location	Material	Notes	Images
Ornithischia?[16][20][21][22]	Ornithischia? Indeterminate	Mt. Kirkpatrick	Vertebrae Femur Possible caudal vertebrae	A Dinosaur, possible member of the Ornithischia Group. Described as a Newly discovered species, a four or five-foot ornithischian or bird-hipped dinosaur, is on its way back to the United States in about 5,000 pounds of rock.[21] Recent publications list it as a chimaera with Anchisaurid material.[23]	Eocursor, example of basal Ornithischian

Sauropodomorpha

Genus	Species	Location	Material	Notes	Images
Glacialisaurus[24][16][21][22][25][18]	Glacialisaurus hammeri	Mt. Kirkpatrick	Partial right astragalus medial and lateral distal tarsals partial right metatarsus	A Sauropodomorph, member of the family Massospondylidae. It was found to be related with the genus Lufengosaurus of China.	Glacialisaurus Reconstruction
Massopoda[22][26]	Massopoda Indeterminate	Mt. Kirkpatrick	Nearly complete juvenile skeleton	A Sauropodomorph, incertade sedis inside Massopoda. Exposed on the Antarctic Dinosaur Exhibit of NHM of Los Angeles, like Sauropodomorph B. Is cited more derived than Sauropodomorph B., probably near sauropoda, but it wasn´t considered a proper Sauropod.[26][27]
Anchisauria[22][26]	Anchisauria Indeterminate	Mt. Kirkpatrick	Several vertebrae Pelvic material	A Sauropodomorph, possible member of Anchisauria inside Massopoda. Exposed on the Antarctic Dinosaur Exhibit of NHM of Los Angeles.[26][27]	Innacurate (Cuadrupedal) restoration of Sauropodomorph B (Small) along with Glacialisaurus
Sauropoda[24][28][18][29]	Sauropoda Indeterminate	Mt. Kirkpatrick	Three metre-wide pelvis Ilium Vertebrae Limb elements.	A Sauropodomorph, incertade sedis inside Sauropoda. A possible Pulanesaura-grade Sauropod, less derived than Kotasaurus. The presence of Glacialisaurus in the Hanson Formation with advanced true sauropods shows that both primitive and advanced members of this lineage existed side by side in the early Jurassic Period.[24][28][25]

Theropoda

Genus	Species	Location	Material	Notes	Images
Coelophysoidea?[30]	Coelophysoidea Indeterminate	Mt. Kirkpatrick	FMNH PR1822, distal left femur	A Theropod, member of the family Coelophysoidea. It is on study. Was considered Glacialisaurus remains, although can be a genus similar to Coelophysis.[30]	FMNH PR1822, assigned to Glacialiasaurus
Coelophysidae?[31][32]	Coelophysidae Indeterminate	Mt. Kirkpatrick	Teeth	A Theropod, member of the family Coelophysidae. Were described as a "Halticosaurid teeth".	Coelophysis, example of Coelophysoid
Neotheropoda[31][32]	Neotheropoda Indeterminate	Mt. Kirkpatrick	Teeth	A Theropod, incertade sedis inside Neotheropoda. Described as "Dromeosaurid? teeth", it is probably either a Tachiraptor-grade averostra, a Coelophysis-like form, or can even be a basal Tetanuran.
Cryolophosaurus[19][33][16][18][27]	Cryolophosaurus ellioti	Mt. Kirkpatrick	Partial skull and partial postcranium.[34] Remains of a second specimen were collected in 2010[35] Juvenile teeth[36]	A Theropod, incertade sedis inside Neotheropoda, probably related with Averostra. Described as a possible Basal Tetanuran, subsequent studies have point relationships with Dilophosaurus from North America. It is the most know dinosaur found on the formation, and was probably the largest predator on the ecosystem.[16]	Mounted skeleton of Cryolophosaurus

Flora

Fossilized wood is also present in the Hanson Formation, near the stratigraphic level of the tritylodont locality. It has affinities with the Araucariaceae and similar kinds of conifers.[37]

Palynology

Genus	Species	Location	Stratigraphic position	Material	Notes
Nevesisporites[38]	Nevesisporites vallatus	McLea Nunatak, Prince Albert Mountains	Lower Hanson Formation	Spores	Affinities with Bryophyta. Younger index taxa (e.g. Nevesisporites vallatus) are mostly absent and as the proportion of Classopollis is still very high.[38]
Retitriletes[38]	Retitriletes semimuris	McLea Nunatak, Prince Albert Mountains	Lower Hanson Formation	Pollen	Affinities with the family Lycopodiaceae. Rather absent on some samples.[38]
Podosporites[38]	Podosporites variabilis	McLea Nunatak, Prince Albert Mountains	Lower Hanson Formation	Pollen	Affinities with the family Gymnospermopsida. Subordinate occurrences of bryophyte and lycophyte spores are found along consistent occurrences of Podosporites variabilis.[38]
Classopollis[38]	Classopollis cf.chateaunovi Classopollis meyerianus	McLea Nunatak, Prince Albert Mountains	Lower Hanson Formation	Pollen	Affinities with the family Cheirolepidiaceae. Mostly of the samples yielded well-preserved pollen-and-spore assemblages strongly dominated (82% and 85%, respectively) by Classopollis grains.[38]

Macroflora

Genus	Species	Location	Stratigraphic position	Material	Notes
Marchantites[39][40]	Marchantites mawsonii	Transantarctic Mountains	Middle Hanson Formation	Thalli	A Liverwort of the family Marchantiales. Reworked From the Hanson Formation to the Mawson Formation, this liveworth is related to modern Humid-environment genera.
Cladophlebis[39][40]	Cladophlebis oblonga	Transantarctic Mountains	Middle Hanson Formation	Leaves and Stems	A Polypodiopsidan of the family Osmundaceae. Reworked From the Hanson Formation to the Mawson Formation, represents fern leaves common on humid envrionments.
Pagiophyllum[39][40]	Pagiophyllum sp.	Transantarctic Mountains	Middle Hanson Formation	Leaves	A Pinales of the family Araucariaceae. Reworked From the Hanson Formation to the Mawson Formation, representative of the presence of arboreal to arbustive flora.
Nothodacrium[39][40]	Nothodacrium warrenii	Transantarctic Mountains	Middle Hanson Formation	Leaves	A Pinales of the family Podocarpaceae. Reworked From the Hanson Formation to the Mawson Formation, representative of the presence of arboreal to arbustive flora.

See also

• List of dinosaur-bearing rock formations
• List of fossiliferous stratigraphic units in Antarctica
• Mawson Formation
• Shafer Peak Formation

References

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2. Ross, P.-S. et White, J.D.L. (2006) Debris jets in continental phreatomagmatic volcanoes: a field study of their subterranean deposits in the Coombs Hills vent complex, Antarctica. Journal of Volcanology and Geothermal Research 149: 62-84
3. Elliot, D. H., and D. Larsen. 1993. Mesozoic volcanism in the Transantarctic Mountains: depositional environment and tectonic setting; pp. 379–410 in R. H. Findlay, M. R. Banks, J. J. Veevers, and R. Unrug (eds.), Gondwana 8—Assembly, Evolution, and Dispersal. A. A. Balkema, Rotterdam
4. Heimann, A., T. H. Fleming, D. H. Elliot, and K. A. Foland. 1994. A short interval of Jurassic continental flood basalt volcanism in Antarctica as demonstrated by 40Ar/39Ar geochronology. Earth and Planetary Science Letters 121:19–41.
5. Chandler, M. A., D. Rind, and R. Ruedy. 1992. Pangaean climate during the Early Jurassic: GCM simulations and the sedimentary record of paleoclimate. Geological Society of America Bulletin 104:543–559
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