Geology Reference
In-Depth Information
Benson, R.H. (1984): Estimating greater paleodepths with
ostracodes, especially in past thermospherics oceans. -
Palaeogeography, Palaeoclimatology, Palaeoecology,
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61-106
Cisne, J.I., Gildner, R.F. (1988): Measurement of sea level
change in epeiric seas: The Middle Ordovician Transgres-
sion in the North American Midcontinent. - SEPM Spe-
cial Publication,
42
, 217-225
Ekdale, A.A. (1988): Pitfalls of paleobathymetric interpreta-
tions based on on trace fossils assemblages. - Palaios,
3
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464-472
Geister, J. (1984): Die paläobathymetrische Verwertbarkeit
der scleractinen Korallen. - Paläontologische Kursbücher,
2
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Hallam, A. (ed., 1967): Depth indicators in marine sedimen-
tive water depths. The western part of the Algerian
Béchar Basin contains Mississippian carbonates that
form superposed shoaling-upward sequences consist-
ing of sponge-bryozoan-crinoid reef mounds and bed-
ded shelf carbonates deposited on a ramp. Recogniz-
ing paleobathymetric zones is the basis for a facies
model that assists in the hydrocarbon exploration of
the up to 1200 m thick sequence (Bourque et al. 1995;
Madi et al. 1996).
Basics: Paleowater depths
Bathurst, R.G.C. (1967): Depth indicators in sedimentary
carbonates. - Marine Geology,
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, 447-471
Plate 108 Recognizing Paleowater Depths
The
Early Carboniferous carbonate ramp of the Béchar Basin in western Algeria
offers the possibility of check-
ing the value of algae and other microfossils as indicators of bathymetric zones and in distinguishing different
parts of a homoclinal ramp. Because of their sensitivity to the various spectra of visible light, the distribution of
small encrusting green and red algae can be used to determine depth-related zones. The absence of green algae is
interpreted as indicating deposition within the aphotic zone, whereas the presence of red algae combined with the
absence of green algae is thought to indicate the lower part of the photic zone with little light (dysphotic). The
abundance of dasyclad green algae is indicative of the upper part of the photic zone.
The example reflects the profile of many other Early Carboniferous ramps with low-energy mud-rich 'Waul-
sortian' mounds in the lower part (see Pl. 144), crinoid banks in the central part and high-energy calcareous sands
in the upper part (Wright 1986; Jeffery and Stanton 1996).
The plate displays facies-diagnostic algae and foraminifera characterizing the shallow photic and dysphotic
parts of the Viséan ramp. Not shown are facies-diagnostic biota of the mound facies (cf. Fig. 12.12). Ungdarel-
lacean and stacheinacean red alga are characteristic constituents of Carboniferous platforms and ramps (see Sect.
16.3.2.1; Box 10.2). The fossils shown on the plate occur in bedded skeletal grainstones and packstones depos-
ited at shallow well-illuminated water depths (-> 1 and 9) and in somewhat deeper, less illuminated environ-
ments below the fair-weather wave base (-> 2-8, 10).
1
Algal-foraminiferal grainstone
with the dasyclad alga
Koninckopora
. Upper ramp. Photic bathymetric zone 1.
2
Foraminiferal grainstone with Saccaminopsis.
The uniserial test consists of globular and ovate chambers. The
Saccaminopsis
microfacies is common in Early Carboniferous shelf carbonates. Massive skeletal grainstone forming a
cap on the top of the mounds. Dysphotic bathymetric zone 5.
3-4
Green alga
Exvotarisella
Elliott. The thallus corresponds to a cylindrical tube. The central part is subdivided by irregular
cavities formed by thick pseudosepta (PS). The alga is a common element of Late Viséan-Namurian shelf carbonates.
Lower ramp. Dysphotic bathymetric zone 5.
5
Green alga
Issinella
characterized by
an erect cylindrical shape and a fibro-radial wall, perforated by thin unramified
branches. The alga is known from the Middle Devonian to the Late Viséan. Lower ramp. Upper part of the dysphotic
bathymetric zone 5.
6
Red algal grainstone with
Fasciella
encrusting bryozoans (B). Characteristic criteria of the alga are irregular concentric
layers of elongated, undulating cells and a yellowish hyaline structure. Known from the Viséan to the Bashkirian.
Fasciella
is common in high-energy environments. Lower ramp. Dysphotic bathymetric zone 4.
7-8
Red alga Ungdarella
Maslov with microbial encrustations (ME) characterized by ramified growth, rectangular and
subquadratic cells and yellowish-hyaline structure. Known from the latest Viséan to the Early Permian. Massive crinoid
mound facies. Lower ramp. Dysphotic bathymetric zone 4.
9
Red alga Epistacheoides
Petryk and Mamet. The encrusting form resembles
Ungdarella,
but differs in the vesicular
central and the rectangular peripheral cells. This alga and similar taxa are common constituents of Viséan and Middle
Carboniferous carbonate ramps. Upper ramp. Photic bathymetric zone 1.
10
Red alga Stacheia
Brady, a thin encrusting form consisting of one or two rows of cells. Wall structure yellowish-hyaline.
Known from the Viséan and the Middle Carboniferous. Massive skeletal grainstone forming a cap on top of the mounds.
Lower ramp. Dysphotic bathymetric zone 4.
-> 1-10 from Madi et al. 1996
