6
Reef Lime Constructions
Darwin's theory was later completely revised, while his basic idea about the
evolution of reefs is still present in modern theories on their morphogenesis
developed by Maxwell (1968) and Hopley (1983). The revision of Darwin's
theory in relation to modern reefs became necessary when proof appeared
of drastic changes in sea level, unknown to Darwin, with amplitudes over
100 m during the Pleistocene-Holocene 150-10 x 10 3 years B. P., which were
caused by periodic glaciations (Daly 1915).
The most ancient biogenic reefal constructions are known to have started
in the Precambrian. They are known as "bioherms" and "biostromes"
(Cuminga 1932) and have the shape of hillocks 2-20 m high. They consist of
amorphous (bioherms) or skeleton remains structured by lime material of
larger invertebrates (biostromes). During the Precambrian they were
constructed by calcareous blue-green algae, which accumulated lime in their
mucoid capsules. During diagenetic transformations these constructions
gave origin to stromatolites - solid lime lumps which compose the main
elements of the most ancient reef constructions (Copper 1974), which are
known from Archean (2600 x 10 6 years B.P.). But the most widespread
stroma to lithic reefal constructions were formed during the Late Precambrian
(Riphean) time 1700-670 x 10 6 years B.P. They were up to several tens of
meters thick and several hundred meters long. Reef bioherms of this type
were common in Proterozoic sediment rocks of North America, Eurasia,
Africa (Cloud and Semikhatov 1969; Kuznetzov 1986). In the Early
Cambrian more complex reef-like constructions appeared, which contained
inside a kind of framework, composed either by skeletons of bryozoans,
tubes of sedentary polychaetes - sabellarides or by colonies of archaeochaetes (Koroljuk and Mikhailova 1986). The latter were animals somewhat
similar to calcareous sponges (Zhuravleva and Myagkova 1979), while some
of them probably could have been also formed by ancient coralline algae.
They have massive, firm funnel, columnar or cup-like lime colonies, which
resemble the colonies of modern calcareous sponges or ancient rugose
corals. The archaeocyathide biostromes looked like modern patch reefs and
had a round shape with a diameter of 20-30 m (Stubblefield 1960). The
ridges of such archaeocyathid reefs were wide-pread in Early - Middle
Cambrian (520-540 x 10 6 years B.P.). At the shelf of warm seas they
formed systems of constructions 5-10 m thick, which resembled atolls or
barrier reefs (Zhuravleva 1960; Copper 1974). At that time large reef-like
biostromes were constructed by large sedentary polychaetes having massive
lime tubes. In the Late Cambrian-Early Ordovician bioherm-like reefs were
also common, constructed by massive ancient bryozoans, Trepostomata
and Cystoporata (Cuffey 1977). During the Ordovician biostrome reefal
constructions were the most widespread created by calcareous sponges
(Archaeoscyphia and Stromataporidea), by bryozoans and by the coralline
algae Celathum (LeCompte 1956; Copper 1974). At the same time the first
ancient hard corals appeared - tabulates and later rugoses (Sokolov 1955;
Ivanovski 1975).
Reef Lime Constructions
Darwin's theory was later completely revised, while his basic idea about the
evolution of reefs is still present in modern theories on their morphogenesis
developed by Maxwell (1968) and Hopley (1983). The revision of Darwin's
theory in relation to modern reefs became necessary when proof appeared
of drastic changes in sea level, unknown to Darwin, with amplitudes over
100 m during the Pleistocene-Holocene 150-10 x 10 3 years B. P., which were
caused by periodic glaciations (Daly 1915).
The most ancient biogenic reefal constructions are known to have started
in the Precambrian. They are known as "bioherms" and "biostromes"
(Cuminga 1932) and have the shape of hillocks 2-20 m high. They consist of
amorphous (bioherms) or skeleton remains structured by lime material of
larger invertebrates (biostromes). During the Precambrian they were
constructed by calcareous blue-green algae, which accumulated lime in their
mucoid capsules. During diagenetic transformations these constructions
gave origin to stromatolites - solid lime lumps which compose the main
elements of the most ancient reef constructions (Copper 1974), which are
known from Archean (2600 x 10 6 years B.P.). But the most widespread
stroma to lithic reefal constructions were formed during the Late Precambrian
(Riphean) time 1700-670 x 10 6 years B.P. They were up to several tens of
meters thick and several hundred meters long. Reef bioherms of this type
were common in Proterozoic sediment rocks of North America, Eurasia,
Africa (Cloud and Semikhatov 1969; Kuznetzov 1986). In the Early
Cambrian more complex reef-like constructions appeared, which contained
inside a kind of framework, composed either by skeletons of bryozoans,
tubes of sedentary polychaetes - sabellarides or by colonies of archaeochaetes (Koroljuk and Mikhailova 1986). The latter were animals somewhat
similar to calcareous sponges (Zhuravleva and Myagkova 1979), while some
of them probably could have been also formed by ancient coralline algae.
They have massive, firm funnel, columnar or cup-like lime colonies, which
resemble the colonies of modern calcareous sponges or ancient rugose
corals. The archaeocyathide biostromes looked like modern patch reefs and
had a round shape with a diameter of 20-30 m (Stubblefield 1960). The
ridges of such archaeocyathid reefs were wide-pread in Early - Middle
Cambrian (520-540 x 10 6 years B.P.). At the shelf of warm seas they
formed systems of constructions 5-10 m thick, which resembled atolls or
barrier reefs (Zhuravleva 1960; Copper 1974). At that time large reef-like
biostromes were constructed by large sedentary polychaetes having massive
lime tubes. In the Late Cambrian-Early Ordovician bioherm-like reefs were
also common, constructed by massive ancient bryozoans, Trepostomata
and Cystoporata (Cuffey 1977). During the Ordovician biostrome reefal
constructions were the most widespread created by calcareous sponges
(Archaeoscyphia and Stromataporidea), by bryozoans and by the coralline
algae Celathum (LeCompte 1956; Copper 1974). At the same time the first
ancient hard corals appeared - tabulates and later rugoses (Sokolov 1955;
Ivanovski 1975).