Zanclean flood

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Gibraltar Strait (A) and the Strait of Sicily
(F) about 5.3 million years ago
Artistic interpretation of the flooding of the Mediterranean through the Gibraltar Strait
Computer simulation of the flooding of the Mediterranean through the Gibraltar Strait, with the vertical scale exaggerated for better visualization. The view in this image is from the southwest of Gibraltar, with the future Iberian Peninsula in the center-left, northwest Africa in the lower-right, and the British Isles in the upper-left corner.

The Zanclean flood or Zanclean deluge is theorized to have refilled the Mediterranean Sea 5.33 million years ago.[1] This flooding ended the

age which is the name given to the earliest age on the geologic time scale of the Pliocene
.

According to this model, water from the Atlantic Ocean refilled the dried up basin through the modern-day Strait of Gibraltar. Ninety percent of the Mediterranean Basin flooding occurred abruptly during a period estimated to have been between several months and two years, following low water discharges that could have lasted for several thousand years.[3] Sea level rise in the basin may have reached rates at times greater than ten metres per day (thirty feet per day). Based on the erosion features preserved until modern times under the Pliocene sediment, Garcia-Castellanos et al. estimate that water rushed down a drop of more than 1 kilometre (0.6 mi) with a maximum discharge of about 100 million cubic metres per second (3.5 billion cubic feet per second), about 1,000 times that of the present-day Amazon River. Studies of the underground structures at the Gibraltar Strait show that the flooding channel descended gradually toward the bottom of the basin rather than forming a steep waterfall.[4]

Background

The geologic history of the

Western Mediterranean and the Eastern Mediterranean is unclear;[10] it is possible that interconnected seas remained on the floor of the Mediterranean.[11]

The presence of Atlantic fish in Messinian deposits[11] and the volume of salt deposited during the Messinian Salinity Crisis implies that there was some remnant flow from the Atlantic into the Mediterranean even before the Zanclean flood.[6] Already before the Zanclean flood, increased precipitation and runoff had lowered the salinity of the remnant sea,[7] leading to the deposition of the so-called "Lago Mare" sediments,[12] with some water putatively originating in the Paratethys north of the Mediterranean.[13]

Event

The Zanclean flood occurred when the

captured the Atlantic Ocean[9] and that the Strait did not exist before this erosion event.[15]

During the flood, a channel formed across the Strait of Gibraltar,[14] which starts at the Camarinal Sill in the Strait of Gibraltar.[16] The channel is eroded into the seafloor of the Alboran Sea,[17] splits around the Vizconde de Eza high of the Alboran Sea[18] and eventually connects with the Alboran Channel before splitting into several branches that end in the Algero-Balear basin.[16][19] The channel has a U-like shape in its starting region, which is consistent with its formation during a giant flood.[20] The formation of the channel mobilized about 1,000 cubic kilometres (240 cu mi) of rock,[21] which was deposited in the Alboran Sea in the form of giant submarine bars.[22] The sector of the Zanclean channel that passes through the Camarinal Sill may have a different origin, however.[10]

Whether the Zanclean flood occurred gradually or as a catastrophic event is controversial,[23] but it was instantaneous by geological standards.[12] The magnitude of a catastrophic flood has been simulated by modelling. One single-dimensional model assumes a catastrophic flood of more than 10–100 sverdrup.[note 1] Another estimate assumes that after the first breach of the sill, the flowing water eroded the threshold and formed the channel across the Gibraltar strait, increasing the flow of water which in turn increased the erosion until water levels rose enough in the Mediterranean to slow the flood.[20]

Under such a scenario, a peak discharge of over 100,000,000 cubic metres per second (3.5×109 cu ft/s) occurred with water velocities of over 40 metres per second (130 ft/s); such flow rates are about a thousand times larger than the discharge of the

gyres in the Alboran Sea during the flooding[24] and that the flood eroded the Camarinal Sill at a rate of 0.4–0.7 metres per day (1.3–2.3 ft/d).[28] The exact size of the flood is dependent on the pre-flood water levels in the Mediterranean and higher water levels there would result in a much smaller flood.[29]

The flood affected only the

Straits of Sicily) formed a barrier separating its basin from the Eastern Mediterranean basin[30] that probably overflowed through the Noto Canyon across the Malta Escarpment;[31] in addition a sill may have existed in the eastern Alboran Sea at this time.[32] During the flooding across the Noto Canyon, vortices and reverse flows occurred,[33] and large amounts of sediments were emplaced in the Ionian Sea.[34] While it was at first assumed that the filling of the eastern Mediterranean would have taken thousands of years, later estimates of the size of the Strait of Gibraltar channel implied that it would have taken much less, potentially less than a year until reconnection.[35]

A large flood is not the only explanation for the reconnection of the Mediterranean with the Atlantic and concomitant environmental changes; more gradual reflooding of the Mediterranean including reflooding through other water sources is also possible.[36][37][38] The absence of a catastrophic flooding event is supported by geological evidence found along the southern margin of the Alboran Sea.[39] On the other hand, deposits found around the Malta Escarpment imply that one intense flood led to the reconnection across the Straits of Sicily.[40]

Timing

The timing of the Zanclean flood is uncertain, with one possibility being a flood around 5.33 million years ago;[41] the end of the Messinian/Miocene and beginning of the Zanclean/Pliocene is usually associated with the flood.[42] The main Zanclean flood may have been preceded by an earlier smaller flood event,[10][43] and the presence of deep sea terraces has been used to infer that the refilling of the Mediterranean occurred in several pulses.[44] Complete refilling of the Mediterranean may have taken about a decade.[7]

Consequences

The Zanclean flood created the Strait of Gibraltar; it is doubtful that tectonic or volcanic events could have created the strait since the main plate boundaries do not run through the strait and there is little seismic activity in its area.[45] The current morphology of the strait is characterized by two aquatic sills: Camarinal Sill, which is 284 m (932 ft) at its deepest point; and the deeper Espartel Sill[46] farther west. The narrowest part of the strait is located east of either sill,[47] and it is considerably deeper than the sills.[46] It is possible that these sills were formed after the flood through gravity-induced movement of neighbouring terrain.[48]

The Zanclean flood caused a major change in the environment of the Mediterranean basin; the continental "Lago Mare" facies was replaced by Zanclean deep sea deposits.[7] The flood may have affected global climate, considering that the much smaller flood triggered when Lake Agassiz drained did result in a cold period.[49] The hypothesized remote effects reached as far as the Loyalty Ridge next to New Caledonia in the Southern Hemisphere.[50]

Rising sea levels made the deeply

cetaceans and their ancestors and pinnipeds to colonize the Mediterranean from the Atlantic.[55]

Evidence of the flooding has been obtained on Zanclean-age sediments, both in boreholes and in sediments that were subsequently uplifted and raised above sea level.[56] A sharp erosional surface separates the pre-Zanclean flood surface from the younger deposits, which are always marine in origin.[57]

The waters flooding into the

Western Mediterranean probably overspilled into the Ionian Sea through Sicily and the Noto submarine canyon[58] offshore Avola;[59] the spillover flood had a magnitude comparable to the flood in the Strait of Gibraltar.[60] The rates at which the Mediterranean filled during the flood were more than enough to trigger substantial induced seismicity.[61] Resulting large landslides would have sufficed to create large tsunamis with wave heights reaching 100 m (330 ft), evidence of which has been found in the Algeciras Basin.[62] The infilling of the basin created tectonic stresses, which would have influenced the development of the Apennine Mountains.[63]

Similar megafloods

Similar floods have occurred elsewhere on Earth throughout history; examples include the

Snake River Basin, and the Black Sea deluge hypothesis that postulates a flood from the Mediterranean into the Black Sea through the Bosporus.[64]

Research history

In his book Historia Naturalis, Pliny the Elder mentions a legend that Hercules dug the Straits of Gibraltar between the Mediterranean and the Atlantic Ocean, connecting the two.[65] The actual Zanclean flood theory however only arose during the 1970s, when it became clear that salt deposits and a widespread erosion surface in the Mediterranean had been emplaced during a prolonged sea level lowstand, and that the subsequent reflooding took place in only a few millennia or less.[66]

See also

  • Black Sea deluge hypothesis – hypothetical flood scenario
  • Outburst flood – high-magnitude, low-frequency catastrophic flood involving the sudden release of water
  • Atlantropa, a proposed dam in the Strait of Gibraltar that would have partially reversed the effects of the Zanclean flood.

Notes

  1. ^ 1 sverdrup is 1,000,000 cubic metres per second.[24] Total outflow of all rivers is about 1.2 sverdrup.[25]

References

Inline citations

  1. doi:10.1016/S0985-3111(02)01095-1
    .
  2. ISBN 978-1-4438-5773-4
    .
  3. ^ Garcia-Castellanos et al. 2009.
  4. ^ a b c Garcia-Castellanos et al. 2009, p. 778.
  5. ^ Cipollari et al. 2013, p. 473.
  6. ^ a b Periáñez & Abril 2015, p. 49.
  7. ^ a b c d e Cipollari et al. 2013, p. 474.
  8. ^ Just et al. 2011, p. 51.
  9. ^ a b Abril & Periáñez 2016, p. 242.
  10. ^ a b c Abril & Periáñez 2016, p. 243.
  11. ^ a b Stoica et al. 2016, p. 854.
  12. ^ a b Spatola et al. 2020, p. 2.
  13. ^ Stoica et al. 2016, p. 867.
  14. ^ a b Estrada et al. 2011, p. 362.
  15. ISSN 0037-0738
    .
  16. ^ a b Estrada et al. 2011, p. 369.
  17. ^ Garcia-Castellanos et al. 2020, p. 4.
  18. ^ Estrada et al. 2011, p. 368.
  19. ^ Estrada et al. 2011, p. 371.
  20. ^ a b Garcia-Castellanos et al. 2009, p. 779.
  21. ^ Garcia-Castellanos et al. 2020, p. 7.
  22. ^ Garcia-Castellanos et al. 2020, p. 8.
  23. ^ Cornée et al. 2016, p. 115,116.
  24. ^ a b Periáñez & Abril 2015, p. 55.
  25. doi:10.5670/oceanog.2010.07
    .
  26. ^ Garcia-Castellanos et al. 2009, p. 780.
  27. ^ Garcia-Castellanos et al. 2009, p. 781.
  28. ^ Periáñez & Abril 2015, p. 60.
  29. ^ Stoica et al. 2016, p. 868.
  30. ^ Just et al. 2011, p. 52.
  31. ISSN 0012-8252
    .
  32. ^ Cornée et al. 2016, p. 127.
  33. ^ Spatola et al. 2020, p. 16.
  34. ^ Garcia-Castellanos et al. 2020, p. 10.
  35. ^ Just et al. 2011, p. 53.
  36. ISSN 0091-7613
    .
  37. ISSN 0264-8172
    .
  38. ^ Garcia-Castellanos et al. 2020, p. 11.
  39. ISSN 1631-0713
    .
  40. ^ Spatola et al. 2020, p. 15.
  41. ^ Cornée et al. 2016, p. 116.
  42. ISSN 0921-8181
    .
  43. ^ Estrada et al. 2011, p. 372.
  44. ^ Estrada et al. 2011, p. 374.
  45. ^ Blanc 2012, p. 303.
  46. ^ a b Blanc 2012, p. 308.
  47. ^ Blanc 2012, p. 304.
  48. ^ Blanc 2012, p. 316.
  49. ^ Garcia-Castellanos et al. 2009, p. 779,780.
  50. S2CID 236242579
    .
  51. doi:10.1016/j.geomorph.2004.11.008
    .
  52. S2CID 163768263
    .
  53. S2CID 46858975
    .
  54. ISSN 0091-7613
    .
  55. PMID 27770981
    .
  56. ^ Cipollari et al. 2013, p. 487.
  57. ^ Nesteroff, Wladimir D.; William B.F. Ryan; Kenneth J. Hsu; Guy Pautot; Forese C. Wezel; Jennifer M. Lort; Maria B. Cita; Wolf Maync; Herbert Stradner; Paulian Dumitrica (1972). "Evolution de la sédimentation pendant le Néogène en Méditerranée d'après les Forages JOIDES-DSDP". University of Milan Institute of Geology and Paleontology Publication (in French) (125): 47–62.
  58. ^ Urlaub et al. 2018, p. 4.
  59. ^ Urlaub et al. 2018, p. 5.
  60. ^ Urlaub et al. 2018, p. 3.
  61. ^ Silva et al. 2017, p. 137.
  62. ^ Silva et al. 2017, p. 140.
  63. ISBN 978-0-8137-2557-4
    , retrieved 4 November 2022
  64. ISBN 978-0-607-97378-5
    .
  65. ^ Garcia-Castellanos et al. 2020, p. 1.
  66. ^ Garcia-Castellanos et al. 2020, pp. 2–3.

Sources

External links
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