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USGS Open-File Report 94-023

Mediterranean Pliocene Vegetation And Climate: How To Quantify The Climate Parameters?

Jean-Pierre Suc
Androniki Drivaliari
Ezzedine Bessais
Université Montpellier II, Montpellier, France
Joèl Guiot
Faculté Saint-Jérôme, Marseilles, France,
Adele Bertini
Université Montpellier II, Montpellier, France, and Dipartimento di Scienze della Terra, Firenze, Italy
Zhuo Zheng
Université Montpellier II, Montpellier, France, and Zhonghshan University, Guangzhou, China
Sidi-Mohamed Abdelmalek
Université Montpellier II, France, and Université d'Oran Es-Sénia, Oran, Algeria
Filomena Diniz
Departamento de Geologia, Lisbon, Portugal
Nathalie Combourieu-Nebout
Université de Paris, Paris, France
Suzanne Leroy
IGBP PAGES, Bern, Switzerland
Rachid Cheddadi
Centré Universitaire, Arles, France
Jacqueline Ferrier
Danièle Duzer
Université Montpellier II, Montpellier, France
The present vegetation of the Mediterranean region is controlled by physiographic and climatic peculiarities: The factors above result in a very complex mosaic structure of the vegetation which contrasts with the latitudinal (thermic) zonation of Central and North Europe.

The Mediterranean early-middle Pliocene climate reconstruction expresses the evolution from tropical/subtropical to warm-temperate conditions before the onset of the glacial-interglacial cycles (Suc et al., 1992).

Pollen Data

Pollen records and their chronological controls. More than 60 sections (boreholes and outcrops) have been investigated (the 45 most significant ones are located on figure 1). They represent more than 1,300 pollen spectra (at least 600,000 counted pollen grains) and more than 250 identified taxa. Synthetic pollen diagrams are constructed after the ecological arrangement of the taxa presented in detailed pollen diagrams (Suc, 1984).

Figure 1. Selected Pliocene localities in the Mediterranean region
This figure is available as a GIF, PICT, or TIFF (line-art) image. It has a large legend which is included below.
Figure 2. Chronological assignment of some selected Pliocene sections in the Mediterranean region
This figure is available as a GIF, PICT, or TIFF (line-art) image.
Most of the localities are coastal marine deposits in which the chronostratigraphic control is precisely provided by foraminifer and nannoplankton records, sometimes associated with magnetostratigraphy and radiometric measurements (fig. 1). The age of some sections is known from mammals in association with magnetostratigraphy, and only a few sections are not well-dated (fig. 1). The large number of well-dated pollen records provides a suitable basis for vegetation reconstruction through the entire Pliocene (fig. 2).

5.2 to 3.2 Ma. Pollen localities in this age range are very numerous because of the "sudden" inundation of the Messinian canyons by the lowermost Pliocene transgression. Very diverse landscapes are recorded, reflecting both different latitudes and local/regional features. These include:

  1. The Atlantic face where subtropical (Taxodiaceae) and warm-temperate trees dominated and Ericaceae were abundant. The north-south thermic gradient promoted differences in the frequency of thermophilous elements. Humid conditions prevailed.

  2. The southern Mediterranean open xeric vegetation which began south of Barcelona. Herbs, including sub-desertic taxa (Lygeum, Calligonum, Nitraria, Neurad, Agavaceae, etc.) were predominant. Tropical (megathermic) plants were still scarcely represented in lower latitudes (Southern Spain, Tunisia, Sicily, Crete, Egypt, Israel). The modern Mediterranean xerophytes were important in some places (Catalonia, Sicily). A xeric-thermic gradient controlled the plant distribution in this area. The large latitudinal distribution of such assemblages supports the theory that seasonally dry climates occurred in this region as far back as the Miocene (Suc et al., 1992).

  3. The northwest Mediterranean region (from the Pyrenees to mid-Italy) was characterized by high relief, which induced the formation of altitudinal forest belts. The lower belt was mainly occupied by Sequoia- type, the middle belt with Cathaya and Cedrus, and the upper belt with Abies and Picea. Mediterranean xerophytes were relatively scarce, and on the whole, the pollen records indicate cooler and more humid conditions than the lower Mediterranean latitudes.

  4. The northeast Mediterranean region which appears to have been cooler than the previous region. Warm-temperate forests alternated with grasslands (Gramineae). The influence of mountains is obvious, chiefly in Bulgaria, and Mediterranean xerophytes increased southward.

  5. The Nile area was almost exclusively inhabited by a savanna-like vegetation, including desertic elements. Tropical plants were present.

  6. Local swamp environments are represented by assemblages that contain high percentages of Taxodium-type, Nyssa, Symplocos, Myrica, Cyrillaceae- Clethraceae, etc. They occurred only in Portugal (Rio Maior), Catalonia (Garraf 1), and Rumania (Ticleni).
3.2 to 2.6 Ma. The same environmental and geographic subdivisions existed as during the previous period. Only some localities record changes at 3.2 Ma (Rio Maior, Garraf 1, Nice area, Ticleni), with the disappearance or the decrease of the most thermophilous elements only the most humid places (local marshes and steep slopes). It has been interpreted as the emergence of cool winters, i.e. a well-marked seasonal thermic rhythm to be superimposed to the pre-existing pluvio-metric one. Therefore, the rather constant climatic conditions of this period are considered as nearly similar (except a slightly higher level in temperature) to the present conditions. So, it can be used as a suitable reference in modeling the forthcoming warming due to the greenhouse effect.

After 2.6 Ma. The earliest glacial-interglacial cycles are characterized in the north Mediterranean area by steppe-like vegetation (with Artemisia and Ephedra) alternating with forest environments (mainly constituted by warm-temperate elements). These steppe assemblages appear obviously warmer than those of the late Pleistocene glacials. There is no evidence of change in the southern Mediterranean region, except in the Nile area, where the Compositae increased within the herb group. In middle and northern oceanic Europe, these cycles corresponded to temperate forest and tundra-like (Gramineae, Cyperaceae, Ericaceae) alternations. In the Alps, the climate fluctuations are marked by temperate-altitudinal forest replacements.

Quantitative Paleoclimatic Estimates

It is difficult to estimate the peri-Mediterranean Pliocene climate because of the little latitudinal variation of plants on the one hand, of the non-existence of analogues in the present vegetation on the other hand. Thus a climate reconstruction is only possible if one takes into account some of the climatically-significant taxa and their respective relative occurrence in modern pollen spectra. A first attempt of estimation of the climate parameters is in progress, initially considering only the open vegetation environments. This approach will be progressively applied to forest assemblages.

References

Key to numbered items in the legend for Figure 1

  1. Relief
  2. Continuous sections interesting the entire Pliocene ( chronostratigraphic control provided by foraminifers and/or nannoflora).
  3. Sectons comprised between 5.2 and 3.2 Ma (chronostratigraphic control provided by foraminifers and/or nannoflora).
  4. Sectons comprised between 5.2 and 3.2 Ma (chronostratigraphic control provided by foraminifers and/or nannoflora, and by magnetostratigraphy).
  5. Sections comprised between 3.2 and 2.6 Ma (chronostratigraphic control provided by foraminifers and/or nannoflora).
  6. Sections younger than 2.6 Ma (chronostratiphic control provided by foraminifers and/or nannoflora).
  7. Sections younger than 2.6 Ma (chronostratiphic control provided by foraminifers and/or nannoflora, and by magnetostratigraphic and radiometric datations).
  8. Lower to Middle Pliocene sections with unsatisfactory chronologic control.
  9. Section younger than 2.6 Ma dated by paleomagnetic and radiometric measurements.
  10. Section younger than 2.6 Ma dated by mammals and magnetostratigraphy.

Localities shown on Figure 1:

  1. Rio Maior (Diniz, 1984)
  2. Carmona (Suc & Ferrier, unpublished)
  3. Andalucia G1 (Bessais, unpublished).
  4. Habibas 1 (Suc, 1989)
  5. Arzeu 1 (Abdelmalek, unpublished)
  6. Sidi Brahim (Abdelmalek, unpublished)
  7. San Onofre (Bessaid & Cravatte, 1982)
  8. Tarragona E2 (Bessais & Cravatte, 1982)
  9. Garraf 1 (Suc & Cravatte, 1982)
  10. Papiol (Suc & Cravatte, 1982)
  11. Ciurana (Suc & Cravatte, 1982)
  12. Ba–olas-Bobila Ordis (Julia & Suc, 1980)
  13. Canet 1 (Cravatte et al., 1984)
  14. Le Boulou (Suc et al., 1992)
  15. Autan 1 (Cravatte & Suc, 1981)
  16. Cap d'Agde 1 (Suc, 1989)
  17. Cessenon (Suc, 1981; Suc & Drivaliari, 1991)
  18. Bernasso (Suc, 1978; Leroy, 1990)
  19. Celleneuve (Suc, 1973)
  20. Pierrefeu 1 (Suc, unpublished)
  21. Iscles 1 (Suc, unpublished)
  22. Cagnes-sur-mer - La Combe (Zheng, 1990)
  23. Saint-Martin du Var (Zheng, 1990)
  24. Saint-Isidore (Zheng, 1990)
  25. Castello d'Appio (Zheng, 1990)
  26. Cava di Villanova (Zheng, 1990)
  27. Stirone (Bertini, 1992)
  28. Monticino 87 (Bertini, 1992)
  29. Maccarone (Bertini, 1992)
  30. Camerota (Brenac, 1984)
  31. Crotone (Combourieu-Nebout, 1990; Combourier-Nebout & Vergnaud Grazzini, 1991)
  32. Capo Rossello (Suc & Bessais, 1990)
  33. Punta Piccola (Suc, unpublished)
  34. Qued Tellil (Suc, unpublished)
  35. Qued Galaa (Suc, unpublished)
  36. Jeriba (Suc & Ferrier, unpublished)
  37. Ticleni (Drivaliari, 1993)
  38. Lozenec (Drivaliari, 1993)
  39. Ravno-PolŽ (Drivaliari, 1993)
  40. Nireas 1 (Drivaliari, 1993)
  41. Nestos 2 (Drivaliari, 1993)
  42. Kremmidia (Combourieu-Nebout, unpublished)
  43. Aghios Vlassios (Drivaliari, 1993)
  44. Naf 2 (Drivaliari, 1993)
  45. Gan Yavne 5 (Drivaliari, 1993)
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