Pensacola Mountains

The Pensacola Mountains in Fig. 8.6 are located along the southern coast of the Ronne Ice Shelf and about 175 km northeast of the Thiel Mountains. This large 

---

L. Schmidt, A. B. Ford, and Robert D. Brown of the U.S. Geological Survey collected a float specimen of natural coke at Aztec Nunatak in the Pensacola Mountains to complete the list of coal localities now known along the Trans-antarctic Mountains. 

PawPaw Formation Calcareous marl East Texas, USA Pepper Shale East Texas, USA Pierre Shale South Dakota, USA 29 samples Phosphatic pebbles and cements Dover Sandstone, Pensacola Mountains, Antarctica Phosphorite (typical values)... 

Fig. 2.1 Antarctica is conventionally oriented as shown and is subdivided into East Antarctica, West Antarctica, and the Antarctic Peninsula. The Transantarctic Mountains extend from northern Victoria Land along the Ross Sea and the Ross Ice Shelf toward the Pensacola Mountains adjacent to the...

The Thiel and Pensacola mountains were mapped by geologists of the US Geological Survey (Schmidt and Ford 1969). The geologic map of the Shackleton Range was published by Clarkson (1982) and by Clarkson et al. (1995) based on field work of geologists from many countries. The Theron Mountains were discovered and described by members of the Commonwealth Trans-Antarctic Expedition (1955-1958 Section 1.5.4 Stephenson 1966). 

Fig. 8.1 The eastern end of the Transantarctic Mountains consists of the Horlick Mountains, the Thiel Mountains, the Pensacola Mountains, the Shacldeton Range, and the Theron Mountains. These mountain ranges are separated from each other by large gaps covered by the East Antarctic ice sheet and in this way occupy about 1,300 km of the total length of the Transantarctic Mountains. AU of these distant mountains have been mapped by geologists (e.g., Mirsky 1969 Davis and Blankenship 2005 Schmidt and Ford 1969 Clarkson et al. 1995) (Adapted from Craddock 1982)...

Schmidt and Ford (1969) mentioned that a thin layer of marble in the Mt. Walcott Formation contains stromatolites. However, Storey and Macdonald (1987) and Pankhurst et al. (1988) later stated that these stro-matohtes are actually composed of interlaminated calcareous siltstone and limestone that underwent soft-sediment deformation. The same authors did find abundant echinoderm plates and sponge spicules similar to Protospongia fenestrata which occurs in the Middle Cambrian Nelson Limestone of the Pensacola Mountains (Weber and Fedorov 1980, 1981). The Mt. Walcott Formation also contains trace fossils (Planolites and Chondrites). Although Planolites has been found in rocks that are 1,000 milhon years old, the earhest appearance of Chondrites is in rocks of Cambrian age. Therefore, Pankhurst et al. (1988) concluded that the paleontological evidence supports a Phanerozoic age for the Mt. Walcott Formation, whereas Schmidt and Ford (1969) had previonsly assigned it a probable Neoproterozoic age. 

Fig. 8.6 The Patuxent Range of the Pensacola Mountains is separated from the Thiel Mountains by a distance of about 200 km that is covered by the Eiast Antarctic Ice Sheet. The only other mountains close to the Patuxent Range are the Pecora Esetupment and the Rambo Nunataks. The northern part of the Pensacola Mountains includes the Neptune Range, the Forrestal Range, and the Dufek Massif (Adapted from the Geologic Map of Antarctica in Craddock 1982)...

The Pensacola Mountains were discovered on January 13, 1956, during a transpolar reconnaissance flight by the US Navy. They were observed again on October 23, 1957, by Captain Finn Ronne of the US Navy and Dr. Edward C. Thiel during a flight from Ellsworth Station to the Dufek Massif. 

The publications arising from these studies were listed by Stump (1995) in a review of the geology of the Pensacola Mountains... 

The northern Pensacola Mountains are dominated by the Dufek Massif which consists of a very large body of layered gabbro and ultramafic rocks of Jurassic age (Ford 1970 Ford and Kistler 1980). This body extends to the southeast across the Sallee Snowfield in Fig. 8.6 to the Forrestal Range where it covers the folded sedimentary rocks of Paleozoic age that also occur in the Neptune Range. The structure and origin of the Dufek Massif is presented in Chapter 13. 

The geologic map of the Pensacola Mountains prepared by Schmidt and Ford (1969) lists an extensive sequence of sedimentary and interbedded volcanic rocks identified in Table 8.3. Schmidt and Ford (1969) observed that the oldest rocks in all parts of the Pensacola Mountains are interbedded layers of graywacke and shale which they named the Patuxent Formation. The rocks of the Patuxent Formation are... 

Schmidt and Ford (1969) estimated that the total thickness of the sedimentary rocks and lava flows in the Pensacola Mountains is between 14.3 and 16.3 km... 

Fig. 8.7 The Patuxent Range forms the most southerly part of the Pensacola Mountains. It consists of nunataks composed of the Patuxent Formation (as revised by RoweU et al. 2001) which forms the local basement complex. The metasedimentary rocks of the Patuxent Formation are isoclinally folded and consist of a repetitious sequence of graywacke and slate. These rocks are younger than the fossiliferous Nelson Limestone which is late Middle Cambrian. The map area also contains outcrops of Devonian sandstone south of the Patuxent Range and of Permian siltstone and shale of the Pecora Formation in the Pecora Excarpment (Adapted from Schmidt and Ford 1969 with information from Rowell et al. 2001)...

Fig. 8.8 The basement rocks of the Neptune Range in the Pensacola Mountains consist of the isoclinally folded metasedimentary rocks of the Hannah Ridge Formation (defined by Rowell et al. 2001) which is unconformably overlain by the Nelson Limestone (late Middle Cambrian) followed by the Gambacorta Rhyolite and the Wiens Formation (Cambro-Ordovician). These basement rocks were locally intruded by the Serpan Granite and by the hypabyssal Mount Hawkes Porphyry. The Paleozoic sedimentary rocks include the Gale Mudstone which is a trUite of Permian age which resembles the Buckeye Tillite of the Beacon Supergroup in the Ohio Range of the Horlick Mountains (Adapted from Schmidt and Ford 1969 with information from Stump 1995)...

Fig. 8.16 The hypothetical cross-section of the Pensacola Mountains at about 500 Ma extends from the eastern Neptune Range to the Schmidt Hills and the Patuxent Range. The diagram offers a plausible explanation why turbidites that are older than the Nelson Limestone in the Neptune Range appear to be younger that the Nelson Limestone in the Schmidt Hills and in the Patuxent Range. The solution to this riddle is that the turbidites in the Schmidt Hills and in the Neptune Range look alike in the field but were actually deposited at different times. Therefore,...

In the Schmidt Hills the turbidites of the Patuxant Formation contain diabase sills, pillow basalt, and fel-sic porphyry. In the Williams Hills the Patuxant Formation contains basalt flows and felsic porphyry, but diabase sills are absent. In spite of its close proximity to the Schmidt and Wilhams hills, the turbidite basement complex of the main body of the Neptune Range does not contain basaltic or felsic volcanic rocks. The difference has been attributed to the presence of a fault in the Roderick Valley that lies between the Neptune Range and the Schmidt and William hills and that may have moved these parts of the Pensacola Mountains closer together. 

A unique feature of the Pensacola Mountains is that Paleozoic formations of the Neptune and the Forrestal ranges were folded during the Weddell Orogeny of late Paleozoic age. This event distinguishes the Paleozoic formations of the Pensacola Mountains from the sedimentary rocks of the Beacon Supergroup elsewhere in the Transantarctic Mountains which have low dips of less than 10° and were folded only locally along faults. 

The Argentina Range is an extension of the Pensacola Mountains along the coast of the Ronne Ice Shelf. This small mountain range consists of three clusters of nunataks located at about 82°20 S and 042°00 W which form the Schneider Hills, Mt. Ferrara, and the Panzarini Hills in Fig. 8.17. The Schneider Hills are separated from the Dufek Massif and the Forrestal Range of the Pensacola Mountains by the Support Force Glacier which channels the East Antarctic Ice Sheet into the Ronne Ice Sheet. 

Jurassic Ferrar Dolerite. Sills of the Ferrar Dolerite are not common elsewhere in the Pensacola Mountains except, of course, in the Dufek Massif where the gab-bros have been correlated with the sills of the Ferrar Dolerite. 

---