Falla Formation

The chemical composition of the tuff in the FaUa Formation in Table 10.10 resembles the composition of volcaniclastic sandstone of the Buckley Formation (Table 10.9). Both rock types are silica- and aluntina-rich with low concentrations of FeO, MgO, and CaO and comparatively high concentrations of alkali oxides. Barrett et al. (1986) concluded that the tuff of the Falla Formation has a rhyolitic composition. Table 10.10 also contains the chemical analysis of a trachyte pebble from the Falla Formation on Mt. Falla. 

TheFaUaFormation of the Beardmore and Shackleton glacier areas is time-equivalent to the Lashly Formation of southern Victoria Land because both formations contain leaves of Dicroidium. However, the tuff beds at the top of the Falla Formation occur only in the Beardmore Glacier area (Barrett et al. 1986). The presence of Dicroidium odontopteroides indicates a Middle to Late Triassic age for the Falla Formation (Townrow 1967). The fossil plants in the Beacon rocks of the Beardmore area were described by Taylor and Smoot (1985a, b), Stubblefield and Taylor (1985), and Pigg and Taylor (1985). 

The layers of the tuff near the top of the FaUa Formation and a trachyte pebble collected on Mt. FaUa were dated by isotopic methods. The pebble (F218A-19) was analyzed by the whole-rock K-Ar method which yielded a date of 197.7 2.7 Ma (Barrett and Elliot 1972). A ch ical analysis of this pebble is contained in Table 10.10 and Fig. 10.15. Barrett et al. (1986) recalculated the K-Ar date of this pebble to 203 3 Ma by using the constants of Steiger and lager (1977). Barrett and Elliot (1972) also reported a whole-rock K-Ar date of 183.2 10 Ma (recalculated to the constants of Steiger and lager 1977) for a dolerite boulder in a lenticular lahar deposit 120 m below the lowest flow of 

Kirkpatrick Basalt (Ferrar Group) at the Otway Massif (85°27 S, 172°00 E). The K-Ar dates of the trachyte pebble and the basalt boulder constrain the age of the Falla Formation to be younger than 203 3 Ma but older than 183.2 10 Ma. 

---

The Section Peak Formation was deposited on the margins of Rennick basin after that basin was filled by sediment of the Takrouna Formation. The rocks of the Section Peak Formation resemble sedimentary rocks that occur at the top of the Lashly Formation in the Allan Hills (Table 10.2). Collinson et al. (1986) suggested that the Section Peak and Lashly formations are similar to the Late Triassic Falla Formation in the Beardmore and Shackleton glacier areas. 

The middle part of the Fremouw Formation is composed predominantly of mudstone that is overlain by the volcanic sandstone of the upper part of the formation. The middle and upper parts of the Fremouw Formation contain plant fossils but no fossil vertebrates have been found. The mudstone and volcanic sandstone are recessive and are overlain by the more resistant cliff-forming quartz sandstone of the Falla Formation. 

Fig. 10.14 The southern part of the Queen Alexandra Range in Fig. 10.13 exposes the Fremouw and Falla formations of the Beacon Supergroup as well as the overlying Prebble Formation and Kirkpatrick Basalt of the Ferrar Group. This part of the Queen Alexandra Range is located west of the Beardmore Glacier and east of the Walcott Nive. Excerpt of the Buckley Island (S V 61-60/3) and Cloudmaker (SV 51-60/4) topographic maps of Antarctica. US Geological Survey, 1967, Washington, DC...

Table 10.10 Chemical analysis of four samples of tuff of rhyolitic composition and of one pebble of volcanic rock from the Falla Formation in the Beardmore Glacier area (Barrett et al. 1986)= ...

Fig. 10.15 The classification of volcanic rocks, based on their concentrations of Na O + K O and SiO in weight percent, indicates that the tuff of the Falla Formation ranges in composition from dacite to rhyolite, whereas a pebble of volcanic rock is intermediate in composition between trachyte and trachyandesite. The numbered fields are identified as follows (1) Basalt, (2) Basaltic andesite, (3) Hawaiite, (4) Mugearite and Trachybasalt, (5) Benmoreite, (6) Phonolite, (7) Phonolite tephrite, (8) Basanite and Tephrite, (9) Nephelinite, and (10) Phonolitic nephelinite. Solid circles Falla Tuff solid circle inside circle Average of four samples of tuff Cross trachyte pebble (Adapted from Wilson 1989 Faure 2001 data from Barrett et al. 1986)...

Fig. 10.16 Whole-rock samples of tuff from the upper part of the Falla Formation define a straight line on the Rb-Sr isochron diagram. The slope and intercept of the line yield a date of 196.4 12.2 Ma (A = 1.42 x lO- year"9 and initial "Sr/ Sr ratio of 0.71220 0.00129, respectively. Sample F240 was excluded from the isochron because it appears to have lost radiogenic Sr or gained rubidium. The data points are identified by the sample numbers of P.J. Barrett (Data from Faure and Hill 1973)...

Fig. 10.17 The whole-rock K-Ar dates of a trachyte boulder from Mt. Falla and of a Ferrar Dolerite boulder from the Otway Massif, reported by Barrett and Elliot (1972), constrain the age of the tuff in the upper part of the Falla Formation. Both K-Ar dates were recalculated to the constants recommended by Steiger and Jager (1977). The whole-rock Rb-Sr date (Fig. 10.16) of the Falla tuff (196.4 12.1 Ma, X = 1.42 x 10 year"0 calculated from data by Faure and Hill (1973), indicates an Early Jurassic to Late Triassic age for the upper part of the Falla Formation. The boundary between the Late Triassic and Early Jurassic at 205.1 Ma is based on the time scale of the lUGS (2002)...

The Triassic rocks of the Fremouw and Falla formations consist of interbedded sandstone and mudstone some of which are carbonaceous. The volcaniclastic rocks of the Prehble Formation top the sequence and are overlain by lava flows of the Kirkpatrick Basalt of Jurassic age. The Beacon rocks in the Shackleton Glacier area were intruded by voluminous sills of the Ferrar Dolerite. 

The Falla Formation is composed of sandstone, shale, and tufifaceous beds as defined by Barrett et al. (1986) in the Queen Alexandra Range. In the Shackleton Glacier area only the lower part of the formation is present composed primarily of quartz sandstones which... 

Vavra CL (1982) Provenance and alteration of the Triassic Fremouw and Falla formations central Transantarctic Moimtains, Antarctica. Ph.D. dissertation, Department of Geology and Mineralogy, The Ohio State University, Columbus, OH... 

Bones of vertebrate animals were also recovered from the upper Eremouw Formation in Gordon Valley in the Queen Alexandra Range (Fig. 10.14) and from the upper Falla Formation on Mt. Kirkpatrick (Hammer et al. 1987). The Fremouw Formation in Gordon Valley actually contains foot prints of vertebrates which were described and photographed by Macdonald et al. (1991). The bones recovered by W.R. Hammer and his... 

The flora that has been preserved in the Beacon Supergroup of the Transantarctic Mountains and in Australia, South Africa, India, and South America contain leaves of Glossopteris, Gangamopteris, and Dicroidium, as well as gymnospermous trees (Meyer-Berthaud and Taylor 1989), cycads, ferns, and palyno-morphs (pollen, spores, and acritarchs). The fossilized remains of these plants occur primarily in the Buckley, Fremouw, and Falla formations. 

Ftuabee MJ, Taylor TN, Taylor EL (1989) Pollen and spore assemblages from the Falla Formation (Upper Triassic), central Transantarctic Mounteiins, Antarctica. Rev Palaeobot Palynology 61 101—138... 

Hammer WR, Hickerson WJ, Krippner S, Tamplin J (1991) Therapsid, temnospondyls, and dinosaurs from the Fremouw and Falla formations, Beardmore Glacier region, Antarctica, Antarctic J US 26(5) 19-20... 

In the Queen Alexandra Range of the Central Transantarctic Mountains diamictites and pyroclastic rocks of the Prebble Formation occur below the Kirkpatrick Basalt. The Prebble Formation overUes the felsic tuffs of the upper Falla Formation which Elliot (1996) renamed the Hanson Formation. Whole-rock samples of the tuff yielded a Rb-Sr date of 186 9 Ma corresponding to an Early Jurassic age (Faure and Hill 1978) which was later confirmed by Hammer and Hickerson (1994) based on the bones of tetrapod vertebrates. 

Faure G, HiU RL (1963) Age of the Falla Formation (Triassic), Queen Alexandra Range. Antarctic J US 8(5) 264-266... 

Triassic Fremouw and Falla formations in the Queen Alexandra Range was documented by Vavra et al. (1981) and Vavra (1982). 

---