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Coordinates: 74°S 65°E / 74°S 65°E / -74; 65
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Ellsworth Land Volcanic Group
Stratigraphic range: Toarcian
~183.4–177.5 Ma
TypeGeological formation
Sub-units
  • Mount Poster Formation
  • Sweeney Formation
UnderliesAnderson Formation (In part)
Thickness600-2000 m
Lithology
PrimarySilicic ignimbrites
OtherMudstone, Sandstone
Location
Coordinates74°S 65°E / 74°S 65°E / -74; 65
RegionAntarctic Peninsula
Country Antarctica
ExtentEllsworth Land
Type section
Named forEllsworth Land
Named byHunter & Cantrill
Ellsworth Land Volcanic Group is located in Antarctica
Ellsworth Land Volcanic Group
Ellsworth Land Volcanic Group (Antarctica)

The Ellsworth Land Volcanic Group is a geological formation in the Latady Basin, Ellsworth Land, Antarctic Peninsula, with a calculated maximum depositional age of 183.4 ± 1.4 Ma, and a younger age around 177.5 ± 2.2 Ma, covering the Toarcian stage of the Jurassic Period in the Mesozoic Era.[1] This group is made up of volcanoclastic material, with the Mount Poster Formation, composed of silicic ignimbrites, and the Sweeney Formation, consisting of a mix of basaltic and sedimentary facies.[1]

The Mount Poster Formation was the first described in 1985, found on the locality of the same name, with exposures across northwestern areas of the southern Black Coast, Orville Coast, and eastern Ellsworth Land. It was found to be made of pyroclastic rocks along lava flows, all from intracaldera origin, interbedded with few sedimentary rocks. Originally, dating analyses indicated ages 189 ± 3 Ma-188 ± 3 Ma for the lowermost sections (Lower Pliensbachian), and 167 ± 3 Ma (Bathonian) for different locations within the formation, yet was latter constrained to the Toarcian-only, between 183-177 Ma.[1] Due to this datations it was alocated in the lowermost section of the Jurassic Latady Basin layers, overlied by what was defined back then as "Latady Formation" (now Latady Group), now proven to be the Sweeney Formation.[2] The Sweeney Fm rocks outcrop on W Potter Peak, Mount Jenkins, Mount Edward, Mount Ballard and Mount Wasilewski. Local vulcanism is know to have continued in the Middle-Late Jurassic, as evidenced in the Latady Group deposition.[3] The Ellsworth Land Volcanic Group belongs to the Patagonia-Antarctic Peninsula sequence, along the Brennecke Formation, form part of the wider first-stage event (V1) of the Chon Aike Province, proving connection with both areas in the Early Jurassic, with the closest unit being the Marifil Formation.[4][5] The sedimentary layers are correlated with the Cañadón Asfalto Formation along with the Lonco Trapial Formation, Bajo Pobre Formation, Cañadón Huemules Formation and Roca Blanca Formation in Argentina.[6][7]

Geology and Stratigraphy

The Antarctic Peninsula has been traditionally interpreted as a native continental arc, yet more recent studies suggest it is a collection of terranes merged onto the Gondwana margin.[8] In the Antarctic Peninsula and eastern Ellsworth Land, volcanic and plutonic rocks formed during the subduction of oceanic lithosphere, marking different periods of volcanic activity. These rocks, part of the Antarctic Peninsula Volcanic Group, range from Early Jurassic to Tertiary age and exhibit various facies and ages, though their relationships are not fully understood.[3] The Mesozoic volcanic-sedimentary layers in the Ellsworth land sit atop older metamorphosed sedimentary rocks, like Ordovician to Permian basement on the Trinity Peninsula Group.[9] Plutonic rocks, forming widespread outcrops, dominate the Antarctic Peninsula's igneous landscape, with their full extent and connectivity still not fully understood due to limited exposure and data availability.[9]

The Ellsworth Land Volcanic Group underlies parts of the southern Antarctic Peninsula and eastern Ellsworth Land. At Mount Poster, these volcanic rocks, up to 600 meters thick, and probaly exceeds 2 kilometers in total thickness, yet is difficult to know.[10] Ellsworth Land intertongues with the Sweeney Fm and is overlied by the Latady Group, marked by intense folding, thrust faulting, and pluton intrusion during the Late Jurassic to Early Cretaceous period.[3]

The Ellsworth Land VG shows considerable alteration and metamorphism, leading to challenges with volcanic sections correlation due to variations in rock types and minor faulting, with an estimated thickness of roughly 1000 meters in the Sweeney Mountains, where is present in most peaks, where is characterized by silicic ignimbrite, featuring diverse weathering patterns and lithology dominated by feldspar-rich ignimbrite. Additionally, it contains lithic-rich sections with quartzite fragments and traces of red mudstone, along with late-stage epidote and quartz veining. Well-consolidated units exhibit distinguishable fiamme, while less consolidated ignimbrites contain flattened pumices, occasionally found alongside deformed ignimbrites.[1] The sedimentary facies are more typically tens of metres thick, with a maximum of ∼300 m black finely laminated mudstone and sandstone.[1]

Age

Analyses using an ion-microprobe reveal that the intracaldera ignimbrites in the Mount Poster Formation formed around 183.4 ± 1.4 Ma around the same time as volcanic activity in other regions like Karoo-Ferrar and the Transantarctic Mountains. Zircon analysis were conducted on eight samples of silicic ignimbrite spanning from the Sweeney Mountains to Lyon Nunataks, with ages ranging from 185.2 ± 1.5 Ma to 177.5 ± 2.2 Ma, while detrital zircons from sedimentary rocks at Potter Peak West indicate again 183 ± 4 Ma. These findings indicate that volcanic activity began either slightly before or at the same time as the initial non-volcanic sedimentation in the Sweeney Formation.[1]

Paleoenvironment

The ELVG was developed in a heavily volcanic landscape, with rhyolitic Caldera deposits of the Moun Poster (ex. Volcán Chaitén) associated with freshwater layers & disrupted vegetation of the Sweeney Fm (Yellowstone as example)

Local vulcanism was likely dominated by large-volume (Ultra-Plinian) eruptions, providing a potential rhyolitic volcanic source to nearby Transantarctic Area (ex. Mawson Formation).[11] The Mount Poser layers suggests they were likely deposited within a Volcanic crater, indicated by similar composition, strong bonding, extensive layering, and the presence of faults and dykes around the edges that mark the boundaries of such crater, resembling units recovered in western United States and Alaska, where volcanic activity created similar landscapes. The differences seen on the layers might indicate different volcanic events from various centers, possibly forming a series of connected or nested craters.[1] The sedimentary layers near the volcanic ones often show signs of heat damage or disturbance by the volcanics: red mudstone next to basaltic flows turns black, and disrupted bedding underlies lava bodies. Sedimentary layers mainly consist of well-sorted sandstone and siltstone with ripple patterns, suggesting deposition in freshwater, likely in a lacustrine body with associated subaerial fluvial units. Fossil plant remains indicate a terrestrial environment, with conifers dominating and suggesting a preference for volcanic-rich soil.[1] Lacustrine layers with volcanic influence are recovered in the connected Cañadón Asfalto Formation.[12]


Fossil content

The fossil palaeoassemblage is dominated by plants, suggesting a fully terrestrial or lacustrine setting, withtout any marine evidence. The material is dominated by wood trunks and root horizons. The leaf-based macroflora is conifer-dominated and corresponds to genera recovered in the Argentinian Cañadón Asfalto Formation, where cuticular analisis of the same taxa suggests common environmental stress.[13] This fits also with the local foliar remains, that areconsistent with growth between eruptive phases.

Coniferophyta

Genus Species Location Member Material Ecogroup Palaeoclimate requirements Notes Images

Brachyphyllum[1]

  • Brachyphyllum spp.
  • Potter Peak West
  • Sweeney Formation

Branched shoots

Upland, Lowland and Riverside

?Warm to temperate, relatively wet

Plants of the family Araucariaceae or Cheirolepidiaceae

Elatoclaudus[1]

  • Elatocladus confertus
  • Elatoclaudus jabalpurensis

Upland and Lowland

Warm to temperate, can withstand long periods of drought; seasonal climate

Plants of the family Cupressaceae

See also

References

  1. ^ a b c d e f g h i j HUNTER, M. A.; RILEY, T. R.; CANTRILL, D. J.; FLOWERDEW, M. J.; MILLAR, I. L. (2006-09-28). "A new stratigraphy for the Latady Basin, Antarctic Peninsula: Part 1, Ellsworth Land Volcanic Group". Geological Magazine. 143 (6): 777–796. doi:10.1017/s0016756806002597. ISSN 0016-7568.
  2. ^ LAUDON, T. S.; THOMSON, M. R. A.; WILLIAMS, P. L.; MILLIKEN, K. L.; ROWLEY, P. D.; BOYLES, J. M. (1983). "The Jurassic Latady Formation, southern Antarctic Peninsula". Antarctic Earth Science: 308–314.
  3. ^ a b c ROWLEY, P. D.; SCHMIDT, D. L.; WILLIAMS, P. L. (1982). "Mount Poster Formation, southern Antarctic Peninsula and eastern Ellsworth Land" (PDF). Antarctic Journal of the United States. 17 (2): 38–39.
  4. ^ PANKHURST, R. J.; RILEY, T. R.; FANNING, C. M.; KELLEY, S. P. (2000-05-01). "Episodic Silicic Volcanism in Patagonia and the Antarctic Peninsula: Chronology of Magmatism Associated with the Break-up of Gondwana". Journal of Petrology. 41 (5): 605–625. doi:10.1093/petrology/41.5.605. ISSN 1460-2415.
  5. ^ Riley, Teal R.; Burton-Johnson, Alex; Flowerdew, Michael J.; Poblete, Fernando; Castillo, Paula; Hervé, Francisco; Leat, Philip T.; Millar, Ian L.; Bastias, Joaquin; Whitehouse, Martin J. (2023). "Palaeozoic – Early Mesozoic geological history of the Antarctic Peninsula and correlations with Patagonia: Kinematic reconstructions of the proto-Pacific margin of Gondwana". Earth-Science Reviews. 236: 104265. doi:10.1016/j.earscirev.2022.104265. ISSN 0012-8252.
  6. ^ Bouhier, V. E.; Franchini, M. B.; Caffe, P. J.; Maydagán, L.; Rapela, C. W.; Paolini, M. (2017). "Petrogenesis of volcanic rocks that host the world-class AgPb Navidad District, north Patagonian massif: comparison with the Jurassic Chon Aike volcanic province of Patagonia, Argentina". Journal of Volcanology and Geothermal Research. 338 (5): 101–120. doi:10.1016/j.jvolgeores.2017.03.016. Retrieved 9 August 2022.
  7. ^ Cabaleri, N.; Volkheimer, W.; Armella, C.; Gallego, O.; Silva Nieto, D.; Páez, M.; Koukharsky, M. (2010). "Estratigrafía, análisis de facies y paleoambientes de la Formación Cañadón Asfalto en el depocentro jurásico Cerro Cóndor, provincia del Chubut". Revista de la Asociación Geológica Argentina. 66 (3): 349–367. Retrieved 2022-09-05.
  8. ^ VAUGHAN, ALAN P. M.; STOREY, BRYAN C. (2000). "The eastern Palmer Land shear zone: a new terrane accretion model for the Mesozoic development of the Antarctic Peninsula". Journal of the Geological Society. 157 (6): 1243–1256. doi:10.1144/jgs.157.6.1243. ISSN 0016-7649.
  9. ^ a b Riley, Teal R.; Flowerdew, Michael J.; Pankhurst, Robert J.; Curtis, Mike L.; Millar, Ian L.; Fanning, C. Mark; Whitehouse, Martin J. (2016-11-03). "Early Jurassic magmatism on the Antarctic Peninsula and potential correlation with the Subcordilleran plutonic belt of Patagonia". Journal of the Geological Society. 174 (2): 365–376. doi:10.1144/jgs2016-053. ISSN 0016-7649.
  10. ^ Wilch, T. I.; McIntosh, W. C.; Panter, K. S. (2021). "Chapter 5.4a Marie Byrd Land and Ellsworth Land: volcanology". Geological Society, London, Memoirs. 55 (1): 515–576. doi:10.1144/m55-2019-39. ISSN 0435-4052.
  11. ^ Schöner, R.; Viereck-Goette, L.; Schneider, J.; Bomfleur, B. (2007). "Triassic-Jurassic sediments and multiple volcanic events in North Victoria Land, Antarctica: A revised stratigraphic model". Open-File Report. doi:10.3133/ofr20071047srp102. ISSN 2331-1258.
  12. ^ Cabaleri, N.; Volkheimer, W.; Armella, C.; Gallego, O.; Silva Nieto, D.; Páez, M.; Koukharsky, M. (2010). "Estratigrafía, análisis de facies y paleoambientes de la Formación Cañadón Asfalto en el depocentro jurásico Cerro Cóndor, provincia del Chubut". Revista de la Asociación Geológica Argentina. 66 (3): 349–367. Retrieved 2022-09-05.
  13. ^ Sender, Luis Miguel; Escapa, Ignacio H; Cunéo, Rubèn (2015). "Diversidad de coníferas de la Formación Cañadón Asfalto (Jurásico Inferior- Medio) en la Patagonia central Argentina: aplicación de nuevas técnicas en el estudio de cutículas fósiles". Ameghiniana. 52 (4): 39. Retrieved 8 September 2022.

Category:Geologic formations of Antarctica Category:Jurassic System of Antarctica Category:Toarcian Stage Category:Mudstone formations Category:Tuff formations Category:Lacustrine deposits Category:Paleontology in Antarctica

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