Revised Stratigraphy

The best available evidence for the age of the Patuxent Formation (as redefined by Rowell et al. 2001) arises from age determinations of the Gorecki Rhyolite in the Schmidt Hills. If the Gorecki Rhyolite consists of lava flows or other kinds of volcanogenic surface deposits that are interbedded with the Patuxent Formation at Mount Gorecki and elsewhere, then age determinations of these rhyolites also date the time of deposition of the local Patuxent Formation. On the other hand, if the felsic magma of the Gorecki Rhyolite intruded the Patuxent Formation in the form of sills or small plu-tons, then the Patuxent Formation is older than isotopic dates of the felsites in the Schmidt Hills. 

Schmidt et al. (1978) considered the Gorecki Felsite in the Schmidt Hills to be interbedded with the rocks of the Patuxent Formation and Rowell et al. (1994) asserted emphatically that the age of the Patuxent Formation in the Schmidt Hills is early Paleozoic and not Neoproterozoic because the felsite at Mount Gorecki contains fragments of fossiliferous limestone derived from the Nelson Limestone  

The U-Pb date of zircon from the Gorecki Felsite (5(X) 8 Ma) confirmed that the age of the Patuxent Formation in the Schmidt Hills is in fact. Middle to Late Cambrian according to the geologic timescale of the lUGS (2002). 

The U-Pb date of the Gorecki Felsite measured by Millar and Storey (1995) implies that the age of the pillow-basalt flows in the Schmidt and William hills is also Late Cambrian to Early Ordovician. Storey et al. (1992) previously proposed that these pillow basalts were erupted during an episode of the rifting of the continental crust during which the Thiel Mountains Porphyry and the basaltic rocks in the Ellsworth Mountains were also erupted (Section 8.1.6). According to Millar and Story (1995), the episode of extensional tectonics in the far-eastern sector of the Transantarctic Mountains may have been caused by the development of a back-arc basin in response to the active subduction 

Another point to consider is that the rhyolite lavas of the Gambacorta Formation have the same age (Late Cambrian to Early Ordovician) as the Gorecki Felsite (Eastin 1970 Millar and Storey 1995 Van Schmus et al. 1997). Therefore, the rhyolites of the Gorecki Member of the Patuxent Formation and of the Gambacorta Formation in the eastern Neptune Range were erupted during the same interval of time between 488 4 and 501 3 Ma (Table 8.3). 

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Table 5.3 Revised stratigraphy of the basement rocks of the central Transantarctic Mountains (Myrow et al. 2002)...

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Fig. 3. General stratigraphy of the Tampen Spur area, revised from Campbell Ormaasen (1987) with lithostratigraphical nomenclature from Vollset Dore (1984) and Isaksen Tonstad (1989) and time scale from Gradstein et al. (1995).

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