Geology Reference
In-Depth Information
at a species level during the Middle Triassic (Flügel
1985). Late Jurassic and Early Cretaceous platforms
were characterized by highly diversified associations,
both at a genus and species level. Starting in the Ap-
tian, dasyclads decline significantly at a generic level
during the Late Cretaceous before reaching high diversi-
ties and global distribution again in the Early Tertiary
(Fig. 10.16).
Critical lists of dasyclad species are available for
the Permian and Triassic (Granier and Grgasovic 2001),
Jurassic and Cretaceous (Bassoullet et al. 1978; Deloffre
1993), and Tertiary (Deloffre and Genot 1982; Deloffre
and Granier 1992).
Plates 60 to 64 show some typical and common
dasyclads occurring in Carboniferous to Paleocene shal-
low-marine carbonates.
marine; only a few modern and some Tertiary taxa be-
came adapted to hypersaline and brackish waters), wa-
ter energy (low, generally subtidal) and depth (below
low tide down to about 30 m, commonly < 5 meter).
Dasyclads are found in open lagoons, protected but open
bays and in the shelter of ridges.
The ecological requirements of post-Paleozoic dasy-
clads are regarded as similar to those of their living
descendants (Elliott 1978, 1981). Deviations of distri-
butional patterns of Permian and Triassic dasyclads
from the recent shallow-water model have been ex-
plained by substrate control (Flügel 1981). Some algal
remains attributed to 'marine' dasyclads have been re-
ported from Early Permian lacustrine sediments and
explained by wind drift of cysts from marine environ-
ments to terrestrial sites (Schneider and Gebhardt 1992;
Pl. 131/4).
Environmental
constraints:
Modern dasyclads oc-
cur predominantly in tropical and subtropical environ-
ments but are also found in temperate waters, e.g. the
Mediterranean. Their distribution is controlled by wa-
ter temperature (warm waters, mostly within the 20°
isoclyne), substrate (sand and mud), salinity (normal
Significance of dasyclad algae
Sedimentological significance
: Since the Carbonif-
erous, the accumulation of dasyclad bioclasts contrib-
uted significantly to the formation of shallow-marine,
Plate 63 Early Cretaceous Dasyclad Green Algae
Similar to the Late Jurassic, algal carbonates were also essential in the formation of Early Cretaceous platforms.
More than 150 species have been described from Early Cretaceous deposits. The greatest wealth of species
occurs in the Barremian. Berriasian-Valanginian and Barremian-Aptian assemblages differ in species composi-
tion and abundance. Dasylad assemblages allow regional biozonations (e.g. Bucur 1994; Bodrogi et al 1994).
The large number of species decreased dramatically from the Aptian to the Albian. Dasyclads assist in differenting
the paleoenvironments of various parts of platforms (Peybernes 1979; Fig. 10.19), and in evaluating cyclo-
stratigraphic units (Schindler and Conrad 1994). Some widely distributed genera in the Tethyan region are
shown on this plate.
1
Bakalovaella elitzae
(Bakalova). Early Cretaceous (Late Barremian-Early Aptian): Southern Romania.
2
Salpingoporella
ex. gr.
muehlbergi
(Lorenz). Oblique longitudinal section (OS) and transverse section (TS). Thallus
cylindrical. Only primary branches are arranged perpendicularly to the main axis in euspondyl whorls (arrows).
Salpingoporella
is common in back-reef and open-lagoonal sediments. Early Cretaceous (Barremian-Aptian): Resita-
Moldova Noua zone, southwestern Romania.
3
Salpingoporella
ex gr.
melitae
Radoicic. Oblique longitudinal section. Elongated cylindrical thallus. Same locality as -> 2.
4
Pseudocymopolia jurassica
(Dragastan). The oblique longitudinal section through two segments (S) exhibits primary and
densely spaced secondary branches (arrow). Note the distinct annulation of the thallus. Same locality as -> 2.
5
Neomeris
cretacea
Steinmann. Arrows point to the sporangia characteristic of the species. Early Cretaceous: Southern
Romania.
6
Pseudoactinoporella fragilis
Conrad. Transverse section. Simple branches increasing in size outwardly (phloiophore).
The distributional pattern of the branches indicates that the branches are arranged obliquely to the central stem. Early
Cretaceous (Barremian): Romania.
7
Algal wackestone with
Salpingoporella dinarica
Radoicic. This facies is common in restricted parts of Aptian carbonate
platforms. The association of the species with ostracods, charophytes and specific foraminifera in the Valanginian indi-
cates pond environments in strongly protected lagoons. Early Cretaceous (Valanginian): Apennines, southern Italy.
8
Shallow-marine algal-foraminiferal limestone with miliolid foraminifera and dasyclad algae (
Cylindroporella
, note the
spherical sporangia growing attached to the main axis, choristospore type; center). Inner shallow platform. Early Creta-
ceous: Subsurface, United Arabian Emirates.
