Editing Ross Sea (section)

== Geology ==
=== The continental shelf ===
[[File:GPM 16 fred Ross CC.pdf|thumb|Bathymetric map of the Ross Sea, Antarctica]]

The Ross Sea (and [[Ross Ice Shelf]]) overlies a deep [[continental shelf]]. Although the average depth of the world's continental shelves (at the [[Continental shelf|shelf break]] joining the continental slope) is about 130 meters,<ref>{{Cite book|title=Oceanography: A view of the Earth|last=Gross|first=M. Grant|publisher=Prentice Hall|year=1977|edition=6|location=New Jersey|page=28}}</ref><ref>{{Cite book|title=Submarine Geology|last=Shepard|first=F.P.|publisher=Harper & Row|year=1963|edition=2|location=New York|pages=264}}</ref> the Ross shelf average depth is about 500 meters.<ref name=":0">{{Cite book|chapter-url=http://deepseadrilling.org/28/volume/dsdp28_34.pdf|last1=Hayes|first1=D.E.|last2=Davey|first2=F.J.|doi=10.2973/dsdp.proc.28.134.1975|url-status=live|archive-url=https://web.archive.org/web/20170715031355/http://deepseadrilling.org/28/volume/dsdp28_34.pdf|archive-date=15 July 2017|df=dmy-all|title=Initial Reports of the Deep Sea Drilling Project, 28|volume=28|year=1975|chapter=A Geophysical Study of the Ross Sea, Antarctica}}</ref> It is shallower in the western Ross Sea (east longitudes) than the east (west longitudes).<ref name=":0" /> This over-deepened condition is due to cycles of erosion and deposition of sediments from expanding and contracting ice sheets overriding the shelf during [[Oligocene]] and later time,<ref name=":1">{{Cite journal|last1=Bartek|first1=L. R.|last2=Vail|first2=P. R.|last3=Anderson|first3=J. B.|last4=Emmet|first4=P. A.|last5=Wu|first5=S.|date=1991-04-10|title=Effect of Cenozoic ice sheet fluctuations in Antarctica on the stratigraphic signature of the Neogene|journal=Journal of Geophysical Research: Solid Earth|language=en|volume=96|issue=B4|pages=6753–6778|doi=10.1029/90jb02528|bibcode=1991JGR....96.6753B |issn=2156-2202}}</ref> and is also found on other locations around Antarctica.<ref>{{Cite journal|last=Barker, P.F., Barrett, P.J., Camerlenghi, A., Cooper, A.K., Davey, F.J., Domack, E.W., Escutia, C., Kristoffersen, Y. and O'Brien, P.E.|year=1998|title=Ice sheet history from Antarctic continental margin sediments: the ANTOSTRAT approach|journal=Terra Antarctica|volume=5|issue=4|pages=737–760}}</ref> Erosion was more focused on the inner parts of the shelf while deposition of sediment dominated the outer shelf, making the inner shelf deeper than the outer.<ref name=":1" /><ref>{{Cite book|title=Geology and Seismic Stratigraphy of the Antarctic Margin|last1=Ten Brink|first1=Uri S.|last2=Schneider|first2=Christopher|last3=Johnson|first3=Aaron H.|publisher=American Geophysical Union|year=1995|isbn=9781118669013|editor-last=Cooper|editor-first=Alan K.|pages=1–24|language=en|chapter=Morphology and stratal geometry of the Antarctic continental shelf: insights from models|doi=10.1029/ar068p0001|editor-last2=Barker|editor-first2=Peter F.|editor-last3=Brancolini|editor-first3=Giuliano|hdl = 1912/1602}}</ref>

[[File:Ross Sea Antarctica sea floor geology.svg|thumb|Ross Sea Antarctica sea floor geology showing major basins and drill sites|alt=|left|314x314px]]Seismic studies in the latter half of the twentieth century defined the major features of the geology of the Ross Sea.<ref name=":2">{{Cite book|title=The Antarctic continental margin : geology and geophysics of the western Ross Sea|date=1987|publisher=Circum-Pacific Council for Energy and Mineral Resources|others=Cooper, Alan K., Davey, Frederick J., Circum-Pacific Council for Energy and Mineral Resources.|isbn=978-0933687059|location=Houston, Texas|oclc=15366732}}</ref> The deepest or basement rocks, are faulted into four major north trending [[graben]] systems, which are basins for sedimentary fill. These basins include the Northern and Victoria Land Basin in the west, the Central Trough, and the Eastern Basin, which has approximately the same width as the other three. The Coulman High separates the Victoria Land Basin and Central Trough and the Central High separates the Central Trough and Eastern Basin. The majority of the faulting and accompanying graben formation along with crustal extension occurred during the rifting away of the [[Zealandia]] microcontinent from Antarctica in Gondwana during [[Cretaceous]] time.<ref>Lawver, L. A., and L. M. Gahagan. 1994. "Constraints on timing of extension in the Ross Sea region."  ''Terra Antartica''1:545–552.</ref> [[Paleogene]] and [[Neogene]] -age and faulting and extension is restricted to the Victoria Land Basin and Northern Basin.<ref>{{Cite journal|last1=Davey|first1=F. J.|last2=Cande|first2=S. C.|last3=Stock|first3=J. M.|date=2006-10-27|title=Extension in the western Ross Sea region-links between Adare Basin and Victoria Land Basin|journal=Geophysical Research Letters|language=en|volume=33|issue=20|doi=10.1029/2006gl027383|bibcode=2006GeoRL..3320315D |issn=0094-8276|url=https://authors.library.caltech.edu/45879/1/grl22102.pdf|doi-access=free}}</ref><ref>{{Cite journal|last1=Granot|first1=Roi|last2=Dyment|first2=Jérôme|date=2018-08-09|title=Late Cenozoic unification of East and West Antarctica|journal=Nature Communications|language=en|volume=9|issue=1|pages=3189|doi=10.1038/s41467-018-05270-w|issn=2041-1723|pmc=6085322|pmid=30093679|bibcode=2018NatCo...9.3189G }}</ref>

=== Stratigraphy ===
[[Basement (geology)|Basement]] grabens are filled with rift sediments of uncertain character and age.<ref name=":2" /> A widespread [[unconformity]] has cut into the basement and sedimentary fill of the large basins.<ref name=":2" /><ref>{{Cite book|title=Geology and seismic stratigraphy of the Antarctic margin, 2|date=1997|publisher=American Geophysical Union|others=Barker, Peter F., Cooper, Alan K.|isbn=9781118668139|location=Washington, D.C.|oclc=772504633}}</ref> Above this major unconformity (named RSU-6<ref>Hinz, K., and M. Block. 1984. "Results of geophysical investigations in the Weddell Sea and in the Ross Sea, Antarctica." In ''Proceedings of the Eleventh World Petroleum Congress (London 1983)'', edited by World_Petroleum_Council, 279–291. Chichester, West Sussex: John Wiley and Sons Ltd.</ref>) are a series of glacial marine sedimentary units deposited during multiple advances and retreats of the [[Antarctic ice sheet|Antarctic Ice Sheet]] across the sea floor of the Ross Sea during the [[Oligocene]] and later.<ref name=":1" />

=== Geologic drilling ===
Drill holes have recovered cores of rock from the western edges of the sea. The most ambitious recent efforts are the [[Cape Roberts Project]] (CRP) and the [[ANDRILL]] project.<ref>{{Citation|last1=Barrett|first1=P. J.|title=Sedimentology and petrology of core from DVDP 15, western McMurdo Sound|date=1981|work=Dry Valley Drilling Project|pages=281–314|publisher=American Geophysical Union|language=en-US|doi=10.1029/ar033p0281|isbn=978-0875901770|last2=Treves|first2=S. B.}}</ref><ref>{{Cite journal|last1=Davey|first1=F. J.|last2=Barrett|first2=P. J.|last3=Cita|first3=M. B.|last4=van der Meer|first4=J. J. M.|last5=Tessensohn|first5=F.|last6=Thomson|first6=M. R. A.|last7=Webb|first7=P.-N.|last8=Woolfe|first8=K. J.|date=2001|title=Drilling for Antarctic Cenozoic climate and tectonic history at Cape Roberts, Southwestern Ross Sea|journal=Eos, Transactions American Geophysical Union|language=en|volume=82|issue=48|pages=585|doi=10.1029/01eo00339|bibcode=2001EOSTr..82Q.585D |issn=0096-3941|doi-access=}}</ref><ref>{{Cite journal|last1=Paulsen|first1=Timothy S.|last2=Pompilio|first2=Massimo|last3=Niessen|first3=Frank|last4=Panter|first4=Kurt|last5=Jarrard|first5=Richard D.|date=2012|title=Introduction: The ANDRILL McMurdo Ice Shelf (MIS) and Southern McMurdo Sound (SMS) Drilling Projects|journal=Geosphere|language=en|volume=8|issue=3|pages=546–547|doi=10.1130/ges00813.1|bibcode=2012Geosp...8..546P |issn=1553-040X|doi-access=free|url=https://www.openaccessrepository.it/record/105153/files/fulltext.pdf}}</ref> [[Deep Sea Drilling Project]] (DSDP) Leg 28 completed several holes (270–273) farther from land in the central and western portions of the sea.<ref name=":3">{{Citation|last1=Hayes|first1=D.E.|date=1975|chapter-url=http://deepseadrilling.org/28/volume/dsdp28_36.pdf|publisher=U.S. Government Printing Office|doi=10.2973/dsdp.proc.28.136.1975|access-date=2018-08-28|last2=Frakes|first2=L.A.|title=Initial Reports of the Deep Sea Drilling Project, 28|volume=28|chapter=General Synthesis, Deep Sea Drilling Project Leg 28|doi-access=free}}</ref> These resulted in defining a stratigraphy for most of the older glacial sequences, which comprise Oligocene and younger sediments. The Ross Sea-wide major unconformity RSU-6 has been proposed to mark a global climate event and the first appearance of the Antarctic Ice Sheet in the Oligocene.<ref>{{Citation|last1=Anderson|first1=John B.|title=Cenozoic glacial history of the Ross Sea revealed by intermediate resolution seismic reflection data combined with drill site information|date=1992|work=The Antarctic Paleoenvironment: A Perspective on Global Change: Part One|pages=231–263|publisher=American Geophysical Union|language=en-US|doi=10.1029/ar056p0231|isbn=978-0875908236|last2=Bartek|first2=Louis R.}}</ref><ref>{{Citation|last1=Brancolini|first1=Giuliano|title=Seismic Facies and Glacial History in the Western Ross Sea (Antarctica)|date=2013-03-16|work=Geology and Seismic Stratigraphy of the Antarctic Margin|pages=209–233|publisher=American Geophysical Union|language=en|doi=10.1029/ar068p0209|isbn=9781118669013|last2=Cooper|first2=Alan K.|last3=Coren|first3=Franco}}</ref><ref>{{Cite journal|last=Decesari, Robert C., Christopher C. Sorlien, Bruce P. Luyendyk, Douglas S. Wilson, Louis Bartek, John Diebold, and Sarah E. Hopkins|date=2007-07-24|title=USGS Open-File Report 2007-1047, Short Research Paper 052|journal=Regional Seismic Stratigraphic Correlations of the Ross Sea: Implications for the Tectonic History of the West Antarctic Rift System|volume=2007|issue=1047sir052|doi=10.3133/of2007-1047.srp052|issn=0196-1497}}</ref>

During 2018, Expedition 374 of the [[International Ocean Discovery Program]] (IODP), the latest successor to the DSDP, drilled additional holes (U1521–1525) in the central Ross Sea for determining [[Neogene]] and [[Quaternary]] ice sheet history.<ref>{{Cite book|title=International Ocean Discovery Program Expedition 374 Preliminary Report|last=Robert M. McKay; Laura De Santis; Denise K. Kulhanek; and the Expedition Scientists 374|date=2018-05-24|publisher=International Ocean Discovery Program|series=International Ocean Discovery Program Preliminary Report|language=en|doi=10.14379/iodp.pr.374.2018}}</ref>

=== Basement ===
The nature of the basement rocks and the fill within the grabens are known in few locations. Basement rocks have been sampled at DSDP Leg 28 drill site 270 where [[metamorphic rock]]s of unknown age were recovered,<ref name=":3" /> and in the eastern Ross Sea where a bottom dredge was collected.<ref name=":4">{{Cite journal|last1=Siddoway|first1=Christine Smith|last2=Baldwin|first2=Suzanne L.|last3=Fitzgerald|first3=Paul G.|last4=Fanning|first4=C. Mark|last5=Luyendyk|first5=Bruce P.|date=2004|title=Ross Sea mylonites and the timing of intracontinental extension within the West Antarctic rift system|journal=Geology|language=en|volume=32|issue=1|pages=57|doi=10.1130/g20005.1|bibcode=2004Geo....32...57S |issn=0091-7613}}</ref> In both these locations the metamorphic rocks are [[mylonite]]s deformed in the [[Cretaceous]] suggesting extreme stretching of the Ross Embayment during that time.<ref>Fitzgerald, P. G., and S. L. Baldwin. 1997. "Detachment Fault Model for the Evolution of the Ross Embayment." In ''The Antarctic Region: Geological Evolution and Processes'', edited by C. A. Ricci, 555–564. Siena: Terra Antarctica Pub.</ref><ref name=":4" />

'''Marie Byrd Land''': Rocks exposed in western [[Marie Byrd Land]] on the [[King Edward VII Land|Edward VII Peninsula]] and within the [[Ford Ranges]] are candidates for basement in the eastern Ross Sea.<ref>{{Cite journal|last1=Luyendyk|first1=Bruce P.|last2=Wilson|first2=Douglas S.|last3=Siddoway|first3=Christine S.|date=2003|title=Eastern margin of the Ross Sea Rift in western Marie Byrd Land, Antarctica: Crustal structure and tectonic development|journal=Geochemistry, Geophysics, Geosystems|language=en|volume=4|issue=10|page=1090 |doi=10.1029/2002gc000462|bibcode=2003GGG.....4.1090L |s2cid=2310914|issn=1525-2027|doi-access=free}}</ref> The oldest rocks are [[Permian]] sediments of the Swanson Formation, which is slightly metamorphosed. The Ford granodiorite of [[Devonian]] age intrudes these sediments. Cretaceous Byrd Coast granite in turn intrudes the older rocks. The Byrd Coast and older formations have been cut by [[basalt]] [[Dike swarm|dikes]]. Scattered through the Ford Ranges and Fosdick Mountains are late [[Cenozoic]] [[volcanic rock]]s that are not found to the west on Edward VII Peninsula. Metamorphic rocks, [[migmatite]]s, are found in the [[Fosdick Mountains]] and [[Alexandra Mountains]].<ref>Luyendyk, B. P., S. M. Richard, C. H. Smith, and D. L. Kimbrough. 1992. "Geological and geophysical investigations in the northern Ford Ranges, Marie Byrd Land, West Antarctica." In ''Recent Progress in Antarctic Earth Science: Proceedings of the 6th Symposium on Antarctic Earth Science, Saitama, Japan, 1991'', edited by Y. Yoshida, K. Kaminuma and K. Shiraishi, 279–288. Tokyo: Terra Pub.</ref><ref>{{Cite journal|last1=Richard|first1=S. M.|last2=Smith|first2=C. H.|last3=Kimbrough|first3=D. L.|last4=Fitzgerald|first4=P. G.|last5=Luyendyk|first5=B. P.|last6=McWilliams|first6=M. O.|date=1994|title=Cooling history of the northern Ford Ranges, Marie Byrd Land, West Antarctica|journal=Tectonics|language=en|volume=13|issue=4|pages=837–857|doi=10.1029/93tc03322|bibcode=1994Tecto..13..837R|issn=0278-7407}}</ref> These were metamorphosed and deformed in the Cretaceous.<ref>Siddoway, C., S. Richard, C. M. Fanning, and B. P. Luyendyk. 2004. "Origin and emplacement mechanisms for a middle Cretaceous gneiss dome, Fosdick Mountains, West Antarctica (Chapter 16)." In ''Gneiss domes in orogeny'', edited by D. L. Whitney, C. T. Teyssier and C. Siddoway, 267–294. Geological Society of America Special Paper 380.</ref><ref>{{Cite journal|last1=Korhonen|first1=F. J.|last2=Brown|first2=M.|last3=Grove|first3=M.|last4=Siddoway|first4=C. S.|last5=Baxter|first5=E. F.|last6=Inglis|first6=J. D.|date=2011-10-17|title=Separating metamorphic events in the Fosdick migmatite-granite complex, West Antarctica|journal=Journal of Metamorphic Geology|language=en|volume=30|issue=2|pages=165–192|doi=10.1111/j.1525-1314.2011.00961.x|s2cid=1977832 |issn=0263-4929}}</ref>

'''The Ross Supergroup system and Beacon Supergroup''': Ross System rocks exposed in [[Victoria Land]] and in the [[Transantarctic Mountains]] on the western side of the Ross Sea<ref name=":5">{{Cite book|last1=Faure|first1=Gunter|last2=Mensing|first2=Teresa M.|date=2011|title=The Transantarctic Mountains|language=en-gb|doi=10.1007/978-90-481-9390-5|isbn=978-1-4020-8406-5}}</ref><ref name=":6">{{Cite book|title=The Ross orogen of the Transantarctic Mountains|last=Stump|first=Edmund|date=1995|publisher=Cambridge University Press|isbn=978-0521433143|location=Cambridge [England]|oclc=30671271}}</ref> are possible basement rock below the sedimentary cover of the sea floor. The rocks are of upper [[Precambrian]] to lower [[Paleozoic]] in age, deformed in many places during the Ross Orogeny in the [[Cambrian]].<ref name=":6" /> These [[miogeosyncline]] [[metasedimentary]] rocks are partly composed of [[calcium carbonate]], often including [[limestone]]. Groups within the Ross System include the Robertson Bay Group, Priestley Group, Skelton Group, Beardmore Group, Byrd Group, Queen Maud Group, and Koettlitz Group.  The Robertson Bay Group compares closely with other Ross System members. The Priestley Group rocks are similar to those of the Robertson Bay Group and include dark slates, [[argillites]], [[siltstones]], fine [[sandstones]] and limestones. They can be found near the Priestley and Campbell glaciers. For thirty miles along the lower [[Skelton Glacier]] are the calcareous [[greywackes]] and argillites of the Skelton Group. The region between the lower [[Beardmore Glacier]] and the lower [[Shackleton Glacier|Shackelton Glacier]] sits the Beardmore Group. North of the [[Nimrod Glacier]] are four block faulted ranges that make up the Byrd Group. The contents of the Queen Maud Group area are mainly post-tectonic [[granite]].

[[Beacon Supergroup|Beacon Sandstone]] of [[Devonian]]-[[Triassic]] age<ref>{{Cite journal|last=Barrett|first=P. J.|date=1981|title=History of the Ross Sea region during the deposition of the Beacon Supergroup 400–180 million years ago|journal=Journal of the Royal Society of New Zealand|language=en|volume=11|issue=4|pages=447–458|doi=10.1080/03036758.1981.10423334|issn=0303-6758|doi-access=|bibcode=1981JRSNZ..11..447B }}</ref> and the [[Karoo-Ferrar|Ferarr]] volcanic rocks of [[Jurassic]] age are separated from the Ross Supergroup by the [[Kukri Peneplain]]. Beacon rocks are reported to have been recovered in the drill cores of the Cape Roberts Project at the western edge of the Ross Sea.<ref>Barrett, P. J., C. R. A. Fielding, and S. Wise, eds. 1998. ''Initial Report on CRP-1, Cape Roberts Project, Antarctica''. Vol. 5, ''Terra Antartica''. Siena: Terra Antartica.</ref><ref>Barrett, P.J., F.J. Davey, W.U. Ehrmann, M.J. Hambrey, R. Jarrard, J.J.M. van der Meer, J. Raine, A.P. Roberts, F. Talarico, and D.K. Watkins, eds. 2001. ''Studies from the Cape Roberts Project, Ross Sea, Antarctica, Scientific Results of CRP-2/2A, Parts I and II''. Vol. 7, ''Terra Antartica''.</ref><ref>Barrett, P. J., M.  Massimo Sarti, and S. Wise, eds. 2000. ''Studies from the Cape Roberts Project, Ross Sea, Antarctica: Initial report on CRP-3''. Vol. 7, ''Terra Antartica''. Siena: Terra Antarctica Pub.</ref><ref>Barrett, P.J. 2007. "Cenozoic climate and sea level history from glacimarine strata off the Victoria Land coast, Cape Roberts Project, Antarctica." In ''Glacial Sedimentary Processes and Products'', edited by M.J. Hambrey, P. Christoffersen, N.F. Glasser and B. Hubbart, 259–287. Blackwell: International Association of Sedimentologists.</ref>