Environmental Engineering Reference
In-Depth Information
beyond the scope of this topic these results, plus similar findings from Sicily (e.g.
Hilgen, 1991), reflect the importance of orbital characteristics as influences on
regional/global climates, which in turn affect vegetation communities and earth-
surface processes. Undoubtedly the Atlas, Apennines, Albanian Alps, etc. were
similarly influenced by the climatic changes of the early Pliocene.
3.37 to 2.62
×
10
6
years ago
Conditions described above continued during the latter part of the Pliocene. De-
clines in some thermophilous species indicate declining temperatures, increased
annual temperature gradients and more pronounced seasonality. Toward the close
of this period there is evidence for glaciation. This is reflected in Figure 2.1, which
shows the oxygen-isotope stratigraphy for the last 3.2 million years. Between 3.37
and 2.62 million years ago warm-cool oscillations occurred, with an overall trend
for cooling, but c. 2.62 million years ago the amplitude of the cycles deepened. This
date correlates with the onset of glacial conditions globally (see below).
2.3 The Quaternary period
The redefined base of the Quaternary period encompasses what was the final stage
of the Pliocene; it is the third of the stages identified by Suc (1984) and Suc
et al.
(1995) and coincides with the onset of glaciation on a global scale. The type site is
situated in the Mediterranean in the sedimentary sequence at Monte San Nicola,
Sicily, and is the base of the former Pliocene unit known as the Gelasian. The
stratigraphy of this sequence is given in Figure 2.2, which shows that considerable
depositional changes occurred. The former Quaternary type site at Vrica, Calabria,
the base of which is dated at 2.47 million years old, is now considered to encompass
the second stage of the revised Pleistocene, which is itself a combination of the Qua-
ternary and the Holocene (Gibbard
et al.,
2009). The Quaternary is characterized by
recurring climatic cycles comprising cold and warm stages of almost equal duration
at the beginning, and then long cold stages and short warm stages, the temperature
difference between which intensified c. 900 000 years ago as shown in the oxygen-
isotope stratigraphy of Figure 2.1. In relation to Mediterranean mountain environ-
ments these climatic cycles have caused considerable ecological and environmental
change as tree lines have marched up and down mountains, and ecosystems at all
altitudes and latitudes have reconfigured in terms of species composition.
2.62 to 1.8
×
10
6
years ago
Fossil pollen assemblages in marine cores from the northern Mediterranean pre-
sented by Suc (1984), Suc
et al.
(1995) and Popescu
et al.
(2010) show that the
