Title:
|
Devonian plant assemblages from Venezuela
|
A rich macroflora has been collected from eleven localities in the Lower Member of
the Campo Chico Formation in the Cafto Colorado area of the Sierra de Perija, Western Venezuela.
A new geological map of the area has been produced. The sediments were deposited in a deltaic
environment. Faunal evidence suggests an age between early Givetian and Late Devonian.
Palynological preparations suggest an age of Givetian or latest Eifelian for the lower plant-bearing
horizons. The plants themselves indicate a latest Eifelian-early Frasniana age.
Some nineteen plant taxa are recorded, including five new genera and ten new
species. They occur principally as compression fossils, although fragmentary permineralised
material was discovered The lycophyte flora is composed of at least eight species belonging to the genera Ledercqia, Colpodexylon, Haskinsia, Archaeosigillaria and Lycopodites. Zosterophylls
include Sawdonia and Serrulacaulis. Axes of Taeniocrada'-like appearance have probable S-type
water conducting cells. Two species belonging to two new genera are attributed to the
Trimerophytina, the definition of this subdivision being broadened. A new cladoxylopsidh as fertile
ultimate appendages branched in a three-dimensional dichotomous manner, and recurved pairs of
terminal sporangia. A compression fossil is possibly related to Iridopteridales. One species remains
incertae sedis. The progymnosperms(including ?Rellimia) and a number of types of sterile axes
remain unworked. Contributions have been made to the knowledge of existing taxa, particularly
Archaeosigillaria, Haskinsia, Colpodexylon and Serrulacaulis.
Eifelian/Frasnian floras world-wide are discussed. The Venezuelan flora,
particularly the lycophyte element, is most similar to Givetian and early Frasnian assemblages
from New York State, and less so to the German and Belgian assemblages which lack diverse
lycophytes. A brief investigation of the biogeography of the Devonian has suggested a
palaeogeographic model which is relatively consistent with the biogeographical data, and that the
Venezuelan assemblages may not be representative of other Gondwanan floras
|