Hanson Formation

Hanson Formation Stratigraphic range: Pliensbachian ~188.5–182.7 Ma PreꞒ Ꞓ O S D C P T J K Pg N [1]
The Hanson Formation is located in the Transantarctic Mountains
Type	Geological formation
Unit of
Sub-units	Three informal members
Underlies	Prebble Formation
Overlies	Falla Formation
Thickness	237.5 m (779 ft)
Lithology
Primary	Sandstone, tuffite
Other	Climbing-ripple lamination, horizontal lamination, and accumulations of clay-gall rip-up clasts
Location
Coordinates	84°18′S 166°30′E / 84.3°S 166.5°E / -84.3; 166.5Coordinates: 84°18′S 166°30′E / 84.3°S 166.5°E / -84.3; 166.5
Approximate paleocoordinates	57°30′S 35°30′E / 57.5°S 35.5°E / -57.5; 35.5
Region	Mount Kirkpatrick, Beardmore Glacier
Country	Antarctica
Type section
Named for	The Hanson Spur
Named by	David Elliot
Hanson Formation (Antarctica)

The Hanson Formation (also known as the Shafer Peak Formation) is a geologic formation on Mount Kirkpatrick and north Victoria Land, Antarctica. It is one of the two major dinosaur-bearing rock groups found on 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 some Mesozoic specimens, but most of it is as yet unexcavated. Part of the of the Transantarctic Mountains, it lies below the Prebble Formation and above the Falla Formation.^[2] The formation includes material from volcanic activity linked to the Karoo-Ferar eruptions of the Lower Jurassic.^[3][4] The climate of the zone was similar to that of modern southern Chile, humid, with a temperature interval of 17–18 degrees.^[5] The Hanson Formation is correlated with the of the Eisenhower Range and Deep Freeze Range, as well as volcanic deposits on the Convoy Range and Ricker Hills of southern Victoria Land.^[2]

History[]

The Victoria Group (also called Beacon Supergroup) from the Central Transantarctic Mountains was defined by Ferrar in 1907, when he described the "Beacon Sandstone" of the sedimentary rocks in the valleys of the Victoria Land.^[6] Following this initial work, the term "Beacon System" was introduced for a series of similar sandstones and associated deposits that were recovered locally.^[7] Later the "Beacon Sandstone Group" was assigned to those units in Victoria Land, with Harrington in 1965 proposing the name for different units that appear in the Beacon rocks of 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 glacial deposits.^[8] It was not until 1963 that there was an establishment of the Gondwana sequence: the term Falla Formation was chosen to delimit a 2300 ft (700 m) series of lower quartz sandstone, a middle mica-carbon sandstone and an upper sandstone-shale unit.^[9] The formation lying above the Falla Formation and below the Prebble Formation was then termed the Upper Falla Formation, with considerable uncertainty about its age (it was calculated from the presence of 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] Later works tried to set it between the Late Triassic (Carnian) and the Lower-Middle Jurassic (Toarcian–Aalenian).^[11] The local Jurassic sandstones were included in 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 in the central Transantarctic Mountains and the Mawson Formation (and its unit, then separated, the Carapace Sandstone) in southern Victoria Land.^[12] The Mawson Formation, identified at the beginning as indeterminate tillite, was later placed in the Ferrar Group.^[13]

Extensive fieldwork later demonstrated the need for revisions to the post-Permian stratigraphy.^[14] It was found that only 282 m of the upper 500 m of the Falla Formation as delimited in 1963 correspond to the sandstone/shale sequence, with the other 200 m comprising a volcaniclastic sequence.^[14] New units were then described from this location: the Fremouw Formation and Prebble Formation, the latter term being introduced for a laharic unit, not seen in 1963, that occurs between the Falla Formation and the .^[14][15] A complete record was recovered at Mount Falla, revealing the sequence 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, that led this to be considered a different formation, especially as it shows 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.^[2]

The Shafer Peak Formation was named from genetically identical deposits from north Victoria Land (exposed on Mt. Carson) in 2007 and correlated with the Hanson Formation, defined as tuffaceous deposits with silicic glass shards along with quartz and feldspar.^[16] Later works, however, have equated it to a continuation of the Hanson Formation.^[17]

The name "Hanson Formation" was proposed for the volcaniclastic sequence that was described in Barrett's 1969 Falla Formation essay.^[14] The name was taken from the Hanson Spur, which lies immediately to the west of Mount Falla and is developed on the resistant tuff unit described below.^[2]

Paleoenvironment[]

The Hanson Formation was developed in a Rift Valley where palaeotopographical confinament guided the deposition of fluvial strata, as well Volcanic materials from far sources, in a similar way to modern Waimangu Volcanic Rift Valley of New Zealand

The Hanson Formation accumulated in a rift environment, being dominated by two types of facies: coarse- to medium-grained sandstone and tuffaceous rocks & minerals on the fluvial strata, which suggest the deposits where influenced by a large period of silicic volcanism, maybe more than 10 million years based on the thickness.^[18] When looking at the composition of this tuffs, fine grain sizes, along others aspects such as bubble-wall and tricuspate shard form or crystal-poor nature trends to suggest this volcanic events developed as distal Plinian Eruptions (extremely explosive eruptions), with some concrete layers with mineral grains of bigger size showing that some sectors where more more proximal to volcanic sources.^[18] The distribution of some tuffs with accretionary lapilli, found scattered geographically and stratigraphically suggest transport by ephemeral river streams, as seen in the of New Zealand.^[18] The sandstones where likely derived of low-sinuosity sandybraided stream deposits, having interbeds with multistory cross-bedded sandstone bodies, indicators of either side channels or crude splay deposits and concrete well-stratified sections representing overbank deposits and/or ash recycled by ephemeral streams or aeolian processes.^[18] Towards the upper layers of the formation the influence of the Tuff in the sandstones get more notorious, evidenced by bigger proportions of volcanistic minerals and ash-related materials embedded in between this layers. Overall, the unit deposition bear similarities to the several-hundredmetres-thick High Plains Cenozoic sequence of eastern Wyoming, Nebraska and South Dakota, with the fine-grained ash derived from distal volcanoes.^[18]

Tectonically, based on the changues seen in the sandstone composition and the apperance of volcanic strata indicates the end of the so called foreland depositional section in the Transantarctic Mountains, while appearance of arkoses with angular detritus and common Garnet points to local Paleozoic basement uplift.^[11] The Rift Valley deposition is recovered in several coeval and underliying points, with it´s thickness as indicator of palaeotopographical confinament of palaeoflows coming generally to the NW quadrant, creating a setting that received both sediment derived from the surrounding rift shoulders and ash from distal eruptions.^[19] The Main fault inditacor of this rift has been alocated around the Marsh Glacier, with the so called Marsh Fault that breaks apart Precambrian rocks and the Miller Range, with other faults including a W-facing monocline that lies parallel and east of the Marsh Fault, a NW–SE-striking small graben in thec southern Marshall Mountains, the fault at the Moore Mountains, the undescribed monocline facing east in the Dominion Range and an uplifted isolated fault in the west of Coalsack Bluff.^[11] Marsh Fault was likely active during the early Jurassic, leading to a development of an extensive rift valley system several thousand kilometres long along which basaltic magmatism was focused later towards the Pliensbachian, when the Hanson Formation deposited, somehow similar to East African Rift Valleys and specially Waimangu Volcanic Rift Valley, with segmentation in the rift and possible latter reverse faulting.^[18]

.

Paleofauna[]

The first dinosaur to be discovered from the Hanson Formation was the predator Cryolophosaurus, in 1991; it was 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. Surprising was the discovery of prosauropod remains, which were found commonly on other continents only until the Early Jurassic. However, the bone fragments found in the Hanson Formation were dated to the Middle Jurassic, millions of years later. In 2004, paleontologists discovered partial remains of a large sauropod dinosaur that has not yet been formally described.

Synapsida[]

Taxon	Species	Location	Material	Notes	Images
Tritylodontidae[20][21][22]	Indeterminate	Mt. Kirkpatrick	An isolated upper postcanine tooth, FMNH PR1824	A cynodont, incertade sedis within Tritylodontidae. It is believed to be related to the Asian genus Bienotheroides.[21] Probably the largest member of the family, and among the largest post-Triassic synapsids, over 1.6 m long, it was probably as robust as a modern wolverine.[21]	Tritylodon, example of Tritylodontidae cynodont

Pterosauria[]

Taxon	Species	Location	Material	Notes	Images
Dimorphodontidae?[20][22][23]	Indeterminate	Mt. Kirkpatrick	Humerus	A pterosaur. Nearly the same size as YPM Dimorphodon. Its morphotype is common for basal pterosaurs, such as those in Preondactylus or Arcticodactylus.	Dimorphodon, an example of a dimorphodontid pterosaur

Ornithischia[]

Taxon	Species	Location	Material	Notes	Images
Ornithischia?[20][24][25][26]	Indeterminate	Mt. Kirkpatrick	Vertebrae Femur Possible caudal vertebrae	A dinosaur, described as 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."[25]	Eocursor, example of basal Ornithischian

Sauropodomorpha[]

Taxon	Species	Location	Material	Notes	Images
Glacialisaurus[27][20][25][26][28][22]	Glacialisaurus hammeri	Mt. Kirkpatrick	Partial right astragalus Medial and lateral distal tarsals Partial right metatarsus	A Sauropodomorph, member of the family Massospondylidae. Related to Lufengosaurus of China.	Glacialisaurus reconstruction
Massopoda[26][29]	Indeterminate	Mt. Kirkpatrick	Nearly complete juvenile skeleton	On exhibit at the Natural History Museum of Los Angeles County. More derived than the anchisaurian below; probably near but not in the Sauropoda.[29][30]
Anchisauria[26][29]	Indeterminate	Mt. Kirkpatrick	Several vertebrae Pelvic material	Possible member of Anchisauria within Massopoda. On exhibit at the Natural History Museum of Los Angeles County.[29][30]	Inaccurate (quadrupedal) reconstruction of this species (left), along with Glacialisaurus (center)
Sauropoda[27][31][22][32]	Indeterminate	Mt. Kirkpatrick	Three metre-wide pelvis Ilium Vertebrae Limb elements	A possible Pulanesaura-grade sauropod, less derived than Kotasaurus. The presence of Glacialisaurus in the Hanson Formation with advanced true sauropods shows that both basal and derived members of this lineage existed side by side in the early Jurassic.[27][31][28]

Theropoda[]

Taxon	Species	Location	Material	Notes	Images
Coelophysoidea?[33]	Indeterminate	Mt. Kirkpatrick	Distal left femur, FMNH PR1822	A theropod; previously considered Glacialisaurus remains but may instead be in a genus near Coelophysis.[33]	FMNH PR1822, assigned to Glacialiasaurus
Coelophysidae?[34][35]	Indeterminate	Mt. Kirkpatrick	Teeth	Described as "halticosaurid teeth"	Coelophysis, an example of a coelophysid
Neotheropoda[34][35]	Indeterminate	Mt. Kirkpatrick	Teeth	Described as "dromeosaurid? teeth", it is probably either a Tachiraptor-grade averostra, a Coelophysis-like form, or possibly even a basal tetanuran
Cryolophosaurus[23][36][20][22][30]	Cryolophosaurus ellioti	Mt. Kirkpatrick	Partial skull and partial postcranium[37] Remains of a second specimen collected in 2010[38] Juvenile teeth[39]	Incertade sedis within Neotheropoda, probably related to the Averostra. Initially described as a possible basal tetanuran; subsequent studies have pointed out relationships with Dilophosaurus from North America. It is the best characterized dinosaur found in the formation, and was probably the largest predator on the ecosystem.[20]	Mounted skeleton of Cryolophosaurus

Arthropoda[]

At southwest Gair Mesa the basal layers represent a lake shore and are characterised by the noteworthy preservation of some arthropod remains.^[40]

Taxon	Species	Location	Stratigraphic position	Material	Notes	Images
Scoyenia[40]	Scoyenia isp.	Mount Carson Shafer Peak Suture Bench	Lower Hanson Formation	Burrows	Burrow fossils in lacustrine environment, probably made by arthropods
Diplichnites[40]	Diplichnites isp.	Mount Carson Shafer Peak	Lower Hanson Formation	Trace fossils	Trace fossils in lacustrine environment, probably made by arthropods (arachnids or myriapods)
Lioestheria[41]	Lioestheria longacardinis Lioestheria maugerensis	Mauger Nunatak	Lower and Middle Hanson Formation	Isolated valves	A clam shrimp (“conchostracan”), member of the family .
[41]	Euestheria juravariabalis	Mauger Nunatak	Lower and Middle Hanson Formation	Isolated valves	A clam shrimp (“conchostracan”), member of the family .
[41]	Palaeolimnadia glenlee	Storm Peak Mauger Nunatak	Lower and Middle Hanson Formation	Isolated valves	A clam shrimp (“conchostracan”), member of the family Limnadiidae.
Conchostraca[40]	Indeterminate (various)	Mount Carson Shafer Peak Suture Bench Southwest Gair Mesa	Lower and Middle Hanson Formation	Isolated valves	Numerous conchostracan remains, found associated with lagoonar deposits and major indicators of water bodies locally along Scoyenia burrows
Ostracoda[40]	Indeterminate (various)	Southwest Gair Mesa	Middle Hanson Formation	Isolated valves	Numerous ostracodan remains, found associated with lagoonar deposits and indicators of water bodies locally along Scoyenia burrows and conchostracans
Coleoptera[40]	Indeterminate (various)	Mount Carson Shafer Peak	Lower Hanson Formation	Isolated elytron	Indeterminate beetle remains
Blattidae[40]	Indeterminate	Southwest Gair Mesa	Middle Hanson Formation	Complete specimen	Akin to the genus Periplaneta

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.^[42] In the north Victoria Land region, plant remains occur at the base of the lacustrine beds directly underlying the initial pillow lavas at the top of the sedimentary profile. Some of the layers of Shafer Peak include remains of an in situ stand gymnosperm trees:

• At Mount Carson, at least four large tree trunks were found on a exposed bedding plane. The wood is coalified and only partially silicified, with the largest stem reaching a diameter of nearly 50 cm.^[40]
• In Suture Bench, silicified tree trunks are found buried in situ along lava flows. Some specimens have several holes or tunnels less than 1 cm wide that may represent arthropod borings.^[40]

Palynology[]

Likely that (at least parts of) the palynomorph contents of these samples may derive from accessory clasts of underlying host strata that were incorporated and reworked during hydrovolcanic activity^[43]

Macroflora[]

Genus	Species	Location	Stratigraphic position	Material	Notes	Images
[46][47]	Marchantites mawsonii	Carapace Nunantak (reworked)	Middle Hanson Formation	Thalli	A liverwort of the family Marchantiales. Reworked from the Hanson Formation to the Mawson Formation, this liverwort is related to modern humid-environment genera.
[48]	Isoetites abundans	Mount Carson	Lower and Middle Hanson Formation	Stems	A lycophyte of the family Isoetaceae. Specimens resemble Australian ones of similar age.
Equisetites[48]	Indeterminate	Mount Carson	Lower and Middle Hanson Formation	Fragments of rhizomes, unbranched aerial shoots, isolated leaf sheaths and nodal diaphragms	A sphenophyte of the family Equisetaceae. Sphenophytes are common elements of Jurassic floras of southern Gondwana.	Example of Equisetites specimen
Cladophlebis[46][47]	Cladophlebis oblonga	Carapace Nunantak (reworked) Shafer Peak	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 in humid environments.	Example of Cladophlebis specimen
[48][49]	Clathropteris meniscoides	Shafer Peak Mount Carson	Lower and Middle Hanson Formation	Leaf segments	A Polypodiopsidan of the family Dipteridaceae. It was the first record of the genus and species from the Antarctica. Specimens from Shafer Peak occur in a tuffitic mass-flow deposit and are associated with abundant charred wood indicating wildfires.[49]	Example of specimen
[49]	Polyphacelus stormensis	Mount Carson	Lower and Middle Hanson Formation	Leaf segments	A Polypodiopsidan of the family Dipteridaceae. Closely related to Clathropteris meniscoides.
[48]	cf. Matonidium goeppertii	Mount Carson	Lower and Middle Hanson Formation	Pinna portions	A Polypodiopsidan of the family Matoniaceae.	Example of specimen
Coniopteris[48]	Coniopteris murrayana Coniopteris hymenophylloides	Mount Carson	Lower and Middle Hanson Formation	Pinna fragments	A Polypodiopsidan of the family Dicksoniaceae.	Example of Coniopteris specimen
Dicroidium[1]	Dicroidium sp.	Shafer Peak	Lower and Middle Hanson Formation	One cuticle fragment on slide	A Pteridosperm/Seed Fern of the family Corystospermaceae. Dicroidium plants only gradually began to disappear and lingered on in Jurassic floras as minor relictual elements in more modern vegetation communities dominated by conifers, Bennettitales, and various ferns.[1]	Example of Dicroidium specimen
Otozamites[48]	Otozamites linearis Otozamites sanctae-crucis	SW Gair Mesa Mount Carson Shafer Peak	Lower and Middle Hanson Formation	Pinnately compound leaves	A cycadophyte of the family Bennettitales.	Example of Otozamites specimen
Zamites[48]	Indeterminate	Mount Carson	Lower and Middle Hanson Formation	Fragment of a large, pinnately compound leaf	A cycadophyte in the Bennettitales.	Example of Zamites specimen
[48]	Indeterminate	Mount Carson	Lower and Middle Hanson Formation	Trapeziform fragment of a scale leaf	A cycadophyte in the Bennettitales.
[48]	Indeterminate	Mount Carson	Lower and Middle Hanson Formation	Cone scales	A member of the Pinales in the Voltziales.
[48]	Indeterminate	Mount Carson	Lower and Middle Hanson Formation	Cuticles	A member of the Pinales of the family Cupressaceae.
Elatocladus[48]	Indeterminate	Mount Carson	Lower and Middle Hanson Formation	Cuticles	A member of the Pinales of the family Cupressaceae.	Example of Elatocladus specimen
Pagiophyllum[46][47][48]	Indeterminate	Carapace Nunantak (reworked) Mount Carson	Middle Hanson Formation	Leaves Cuticles	A member of the Pinales of the family Araucariaceae. Reworked from the Hanson Formation to the Mawson Formation, representative of the presence of arboreal to arbustive flora.	Example of Pagiophyllum specimen
[46][47]	Nothodacrium warrenii	Carapace Nunantak (reworked)	Middle Hanson Formation	Leaves	A member of the 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[]