The Hanson Formation (also known as the Shafer Peak Formation) is a geologic formation on Mount Kirkpatrick and north Victoria Land, Ross Dependency, 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 Victoria Group of the Transantarctic Mountains, it lies below the Prebble Formation and above the Falla Formation. The formation includes material from volcanic activity linked to the Karoo-Ferar eruptions of the Lower Jurassic. The climate of the zone was similar to that of modern southern Chile, humid, with a temperature interval of 17–18 degrees. The Hanson Formation is correlated with the Section Peak Formation of the Eisenhower Range and Deep Freeze Range, as well as volcanic deposits on the Convoy Range and Ricker Hills of southern Victoria Land. Recent work has successfully correlated the Upper Section Peak Formation, as well unnamed deposits in Convoy Range and Ricker Hills with the Lower Hanson, all likely of Sinemurian age and connected by layers of silicic ash, while the upper section has been found to be Pliensbachian, and correlated with a greater volcanic pulse, marked by massive ash inputs.
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. Following this initial work, the term "Beacon System" was introduced for a series of similar sandstones and associated deposits that were recovered locally. 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. This work left out several older units, such as the Permian coal measures and glacial deposits. 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. 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). Later works tried to set it between the Late Triassic (Carnian) and the Lower-Middle Jurassic (Toarcian–Aalenian). 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. The Mawson Formation, identified at the beginning as indeterminate tillite, was later placed in the Ferrar Group. Extensive fieldwork later demonstrated the need for revisions to the post-Permian stratigraphy. 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. 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 Kirkpatrick Basalt. 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. 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. 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. Later works, however, have equated it to a continuation of the Hanson Formation, as part of the upper member. The name "Hanson Formation" was proposed for the volcaniclastic sequence that was described in Barrett's 1969 Falla Formation essay. 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.
Paleoenvironment
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