Hanson Formation

 ( Geologic Formations Of Antarctica ) 

The Shafer Peak section flora is the typical reported in warm climates. Compared with the underlying Triassic layers, warm and overall humid, possibly more strongly seasonal, specially notorious by the abundance of Cheirolepidiaceae pollen, a key thermophilic element. Yet the dominance of this pollen doesn't indicate proper dry conditions, as for example mudcrack and other indicators of strong dry seasons are mostly absent, while common presence of the invertebrate ichnogenus Planolites indicates the local fluvial, alluvial or lacustrine waters where likely continuous all year, as well the presence of abundant Otozamites trends to suggest high humidity. Overall points to frost-free setting with strong seasonality in day-length given the high latitude, perhaps similar to warm-temperate, frost-free forest and open woodland as in North Island of New Zealand. Despite the proper conditions, peat accumulation was rare, mostly due to the influence of local volcanism, with common wildfire activity as show charred coalified plant remains. At Mount Carson associations of sphenophyte rhizomes and aerial stems, as well isoetalean leaves suggest the presence of overbank deposits that were developed in ephemeral pools that lasted enough to be colonized by semiaquatic plants.

Tectonically, based on the changes seen in the sandstone composition and the appearance 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 Palaeozoic basement uplift. The Rift Valley deposition is recovered in several coeval and underlying points, with its thickness as indicator of palaeotopographical confinement 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. The Main fault indicator of this rift has been allocated 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 the 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. 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.