Geoscience Reference
In-Depth Information
VCo palynozone between American and European
deposits, the VCo palynozone starting first
in the USA. This situation might be attributed to
contrasted climates for the two regions (Streel &
Marshall 2007). It happens however that the north-
east American miospore/conodont calibration is
far from being conclusive (Streel & Loboziak
1994). An alternative climatic v. correlation
challenge is still considered by Blieck et al.
(2010). Consequently, the VH and VCo biozones
will be treated here as a single biozone and the
localities as being more or less synchronous.
'Uppermost' Famennian localities are found
in the US, Ireland, England and Germany (Fig. 2).
In the northeast American Catskills, the Oswayo
Formation has historically yielded the first recog-
nized Devonian seed (Pettitt & Beck 1969). In
Ireland, several localities are recorded; Kiltorkan
Hill and Hook Head will not be discussed as
the seeds that were collected there have not yet
been described and are poorly understood and/or
controversial (Chaloner et al. 1977).
Ballyheigue, however, probably provides the
best preserved in terms of quality of the preservation
Upper Devonian flora (Matten et al. 1980; Matten
et al. 1984). This anatomically preserved silicified
flora is dominated by spermatophytes. This
specific facies containing in situ plants is interpreted
as levee or crevasse deposits in a marginal
Britain. The Baggy Beds and Taffs Well are of
similar age (LL-LE) (Higgs et al. 1988; O'Liath
`
in
1992) but represent two distinct palaeoenviron-
ments. The Baggy Beds are interpreted as the
shallow marine part of an inner shelf or barrier
complex (Goldring & Langenstrassen 1979). Taffs
Well deposition occurred in a more continental
context and has been interpreted as non-marine,
with a low flow regime, or as a freshwater lake
(Gayer et al. 1973). The slightly younger (LN)
Avon Gorge locality is sedimentologically poorly
understood, but a distal fluvial environment
is
proposed (Hilton 1998a).
Finally, the youngest known Famennian seed
locality is in the German Hangenberg Sandstein
at Oese. Seeds have been found in shales containing
highly fragmentary plant meso-debris (Rowe 1997).
This assemblage is interpreted as a high energy off-
shore deposit and attributed to the LN palynozone
(Higgs & Streel 1984).
Early seed plant diversity and habit
Seed plants were already diversified during the
Late Devonian (Hilton 1998b; Prestianni 2005).
Fifteen species are now described. Based on their
morphology and anatomy, seeds have been classi-
fied into five different types (Prestianni 2005): the
Moresnetia-type, Aglosperma-type, Dorinnotheca-
type, Condrusia-type and Warsteinia-type (Fig. 3).
They share an apically modified nucellus, a lobed
integument (except Condrusia) and a cupule (not
to
channel environment.
English Devonian seeds have been collected
from three main localities from southwest Great
Fig. 3. Schematic reconstruction at the same scale of the different Upper and Uppermost Devonian seed morphological
types. (a-d) Nucellus in dark grey and shown by transparency and (e) ovule is shown in dark grey and by transparency.
(a) Moresnetia-type, (b) Dorinnotheca-type, (c) Warsteinia-type, (d) Aglosperma-type and (e) Condrusia-type.
