Biology Reference
In-Depth Information
Figure 3.2
Marine gastropod
Turritella
from surface outcrop of the Gatún Formation, in the
canal region of Panama.
period, adjustments can be made in the calculations, and the technique can
be used to estimate both temperature and ice volume. If there is disagree-
ment, as there has been until recently for the early Tertiary, then different
estimates of the paleotemperature will result.
Part of the problem was that through the 1980s, there was little reason
to believe glaciers had been present in the Arctic and Antarctic during the
early Tertiary when climates were warm or warmer than at anytime since
100 Ma. Then Birkenmajer (1988) found evidence for mountain glaciers in
Antarctica, now recognized as beginning about 43 Ma (Sluijs et al. 2006;
Stoll 2006). Ice was present in the Arctic as early as 45 Ma (DeCanto et al.
2008; Jahren et al. 2009; but see Edgar et al. 2007); Spielhagen and Tripati
(2009) believe temperatures periodically reached near freezing in the Arc-
tic in the early Tertiary; Eldrett and colleagues (2009) note possible alpine
outlet glaciers in Greenland at 33.5 Ma; and Davies, Kemp, and Pike (2009)
suggest intermittent winter sea ice was even present in the Late Cretaceous.
In considering these dates, it is important to note that some are concerned
with the earliest onset of glaciation, others with the presence of seasonal
