Geology Reference
In-Depth Information
Phylogenetic analysis of higher taxa of brachiopods. -
Lethaia,
26
, 1-5
Kaesler, R.L. (ed., 1997): Brachiopoda (revised), part 1. -
Treatise on Invertebrate Paleontology, 60 pp., Lawrence
(Geological Society of America)
Kaesler, R.L. (ed., 2000): Brachiopoda (revised), part 2 and
3. - Treatise on Invertebrate Paleontology, 960 pp.,
Lawrence (Geological Society of America)
Rowell, A.J., Grant, R.E. (1987): Brachiopoda. - In: Board-
man, R.S., Cheetham, A.H., Rowell, A.J. (eds.): Fossil in-
vertebrates. - 445-496, Palo Alto (Blackwell)
Vörös, A. (1986): Brachiopod palaeoecology on a Tethyan
Jurassic seamount (Pliensbachian, Bakony Mountains,
Hungary). - Palaeogeography, Palaeoclimatology, Palaeo-
ecology,
57
,241-271
Williams, A. (1990): Biomineralization in the lophophorates.
- In: Carter, J.G. (ed.): Skeletal biomineralization: pat-
terns, processes and evolutionary trends. - Volume I, 67-
83,volume II (atlas), pls. 141-156, New York (Van
Nostrand)
Williams, A., Rowell, A.J. (1965a): Brachiopod anatomy. -
Treatise on Invertebrate Paleontology, part H, volume I,
6-57, Lawrence (Geological Society of America)
Williams, A., Rowell, A.J. (1965b): Brachiopod morphology.
- Treatise on Invertebrate Paleontology, part H, volume I,
57-138, Lawrence (Geological Society of America)
Further reading:
K123
nas in the Mesozoic. From about the mid-Jurassic on-
wards, the articulate brachiopods retreated to cryptic
tropical reef niches, or were confined to colder and
deeper waters. Only three groups (rhynchonellids and
terebratulids and the inarticulate Lingulata) crossed the
Cretaceous-Tertiary boundary and are still present to-
day.
Brachiopod limestones:
Accumulations of brachio-
pod shells are abundant in Paleozoic limestones (Pl.
102/1, Pl. 132/10) and common in Mesozoic limestones.
Brachiopod limestones originated in different deposi-
tional environments (shelves, ramps, slopes) and be-
came more frequent in the Silurian and Devonian. Shell
beds composed of brachiopods can not be compared
with bivalve shell beds because of differences in skel-
etal mineralogy (Low-Mg calcite vs. aragonite), a stron-
ger tooth-socket hinge (holding the valves together af-
ter death), lack of ligament forcing the valves apart like
bivalves, and low vulnerability to predators and boring
organisms (Copper 1997). Some brachiopod shell beds
are composed of in-situ assemblages of life and dead
shells, others by transported assemblages deposited by
currents within depressions of the sedimentary surface
or accumulated on the surface as 'dunes' (Hagdorn and
Mundlos 1982).
The accumulation of shells related to a transport of
brachiopods from shallow to deep-water environments
is demonstrated by the Jurassic
Hierlatz facies
of the
Calcareous Alps and the Carpathians. This facies is one
of the most characteristic Early Jurassic facies in the
western Tethys. It comprises typically variegated pre-
dominantly brachiopod limestones and crinoid-brachio-
pod limestones that overlie drowned Late Triassic car-
bonate platforms or occur as fillings of neptunian dikes.
Associated biota are bivalves, gastropods and small am-
monites. Brachiopods and crinoids lived originally in
moderate water depths on the top of seamounts, from
where they were transported as a bypass margin de-
posit to the slopes and foot of the seamounts (Vörös
1986; Uchman and Tchoumatchenco 1994).
10.2.4.2 Bivalves
Bivalves are the most important mollusks contributing
to the bioclast content of limestones, both in marine
environments (since the Cambrian, and abundant in the
Mesozoic and Cenozoic) and in freshwater and brack-
ish environments (since the Carboniferous).
Morphology and classification:
Bivalves (also called
pelecypods or lamellibranchs) have a layered shell con-
sisting of tw
o valves. The valves may be either equal
or unequal in shape and size. Most bivalves articulate
along a hinge line by means of teeth and sockets. The
plan of symmetry passes between the two valves par-
allel to the hinge line. Each valve contains a thin or-
ganic covering (periostracum) and multiple layers of
carbonate. The carbonate shell layers consist entirely
of calcite, entirely of aragonite or of a mixture of ara-
gonite and calcite in alternating layers.
Basics: Brachiopods
Cambell, J.D., Lee, D.E., MacKinnon, D.I. (eds., 1990): Bra-
chiopods through time. - Proceedings of the second Inter-
national Brachiopods Congress, University of Otago,
Dunedin, New Zealand, 580 pp., Rotterdam (Balkema)
Copper, P. (1997): Articulate brachiopod shell beds: Silurian
examples from Anticosti, eastern Canada. - Geobios,
29
,
133-148
Copper, P., Jin, J.S. (eds., 1996): Brachiopods. - 373 pp.,
Rotterdam (Balkema)
Broadhead, T.W. (ed., 1981): Lophophorates. Notes for a short
course. - 251 pp., Cincinnati (Paleontological Society)
Popov, E.L,.Bassett, M.G., Holmer, L.E., Laurie, J. (1993):
Shell structure:
Common calcitic microstructures are
foliated, prismatic, crossed-laminar and homogeneous.
Microstructures can sometimes be used to attribute shell
fragments seen in thin sections to major taxonomic
units. Excellent summaries of microstructural types can
be found in Majewske (1974) and Carter (1980, 1990).
Majewske provides a key which should enable fami-
lies with related microstructures to be identified.
