Colin W. Stearn

Effect of the Frasnian-Famennian extinction event on the stromatoporoids

Although Paleozoic stromatoporoids were drastically reduced in abundance and diversity by the Frasnian-Famennian (F/F) mass extinction event, at least 20 genera (mostly labechiids and clathrodictyids) are known from latest Devonian rocks. Some typical Frasnian genera survived the F/F crisis to die out in early Famennian time, and others took part in the Strunian resurgence of the stromatoporoids. Small stromatoporoid reefs are known from Famennian and Strunian rocks. The history of the group suggests a large, rapid, but progressive environmental change at the F/F boundary and the survival of genera better adapted to cool water.

Rate of bioerosion by parrotfish in Barbados reef environments

ABSTRACT Six species of parrotfish (Scaridae) in reef environments on the west coast of Barbados show a variety of feeding behaviours. They were observed to spend 80% of their time feeding on surfaces covered with filamentous algae and 20% on sand. Only Sparisoma viride consistently leaves well-defined scars on live coral. The biomass of all parrotfish species in the three environments studied ranges from 20 to 58 kg/ha (2 to 5.8 g·m-2). The gut turnover rate of these parrotfish is estimated at 8 times per day. The composition of the sediments in the reef environments was compared to that in the guts of the various parrotfish species to determine the amount of sediment produced from the rocky substrate and the amount of sediment recycled by parrotfish feeding. Spari oma viride is the only species that causes significant bioerosion and new sediment production; the other parrotfish recycle old sediment. The rate of bioerosion on the fringing reef is 61 g·m-2·a-1, on the bank reef it is 40 g·m-2·a-1, and the Moorings study area 168 g·m-2·a-1.

The shapes of Paleozoic and modern reef-builders; a critical review

Paleoecologists studying Paleozoic reef-builders have interpreted their growth forms as responses to conditions of depth and turbulence in reef complexes. Comparison of the shapes of Paleozoic stromatoporoids and corals with the growth forms of modern scleractinians has been used to reconstruct Paleozoic conditions. A review of shape zonation on modern reefs indicates that no general pattern is applicable to all reefs and variations in shape are the result of the interaction of many environmental factors with the genetically dictated growth pattern of the coral. In most zones of a reef a wide range of shapes co-exist. The growth forms of corals on modern reefs are not a simple vegetative response to the many environmental parameters that have been shown to influence form, but are constrained by phylogenetic and developmental influences as well as functional ones. Interpretations of the environments of western Canadian and other mid-Paleozoic reefs have been based on the growth forms of stromatoporoids. The environmental significance of the shapes has been deduced from comparison with the shapes of modern scleractinians, functional morphology, nature of the enclosing sediment, position of growth, position within the reef, and diversity gradients. The validity of these criteria is open to question and considerable doubt remains concerning the significance of the growth forms. The shapes of reef animals are not specific guides to environments of modern reefs and should not be expected to be guides for ancient ones.

The effect of Hurricane Allen on the Bellairs fringing reef, Barbados

On August 4, 1980 Hurricane Allen damaged the northern fringing reef located just offshore from the Bellairs Research Institute of McGill University on the west coast of Barbados. During the summer and one winter month of 1981 a resurvey of the reef was done and the results were compared with a similar survey made in 1974. On a reefal scale the changes in the proportion of substrates before and after Hurricane Allen were statistically significant for all substrates and species with the exception of Millepora spp. Among the corals, Porites porites has been most affected by the catastrophe: its coverage was reduced by 96%. The other corals (Siderastrea sidera, Porites astreoides, Montastrea annularis, and Agaricia agaricites) were reduced by 75 to 25%. Onshore transport is suggested by the high abundance of Acropora cervicornis (20%) and Madracis mirabilis (30%) in the rubble on the fringing reef (the former only grows seaward of the reef). Offshore transport is suggested by the relatively poor representation of Porites porites (32%) in the rubble. Shannon-Weaver diversity indices of the corals dropped from 1.61 to 1.26. The changes in diversity are best explained by the intermediate disturbance hypothesis.

An oil-producing stromatoporoid patch reef in the Famennian (Devonian) Wabamun Formation, Normandville Field, Alberta

The Normandville oilfield in the Peace River district of northcentral Alberta produces oil and gas from a stromatoporoid patch reef about 70 m below the top of the Wabamun Formation. Fracturing of the limestone associated with a set of northwestsoutheast striking faults has increased the porosity of the reservoir. The patch reef and its associated facies constitute the Normandville zone. The reef is 1.5 km2 in area and 10 m thick. The following lithofacies are distinguished in the zone: 1) the platform facies of nodular limestone that overlies and underlies the reef 2) the reef facies of stromatoporoid framestone and boundstone with minor rudstone, floatstone, and grainstone, 3) the reef-margin facies of stromatoporoid floatstone and rudstone with minor brachiopod and crinoid wackestone and packstone, 4) the cap facies of peloidal and skeletal grainstone, and 5) the off-reeffacies of peloidal and skeletal wackestones and packstones. The stromatoporoid fauna of five species is dominated by two species, one of Labechia and the other of Stylostroma. Stromatoporoids were reduced in numbers and diversity at the Frasniani Famennian extinction event but retained the ability to make reefs. Famennian faunas contain remnants of Frasnian genera and are marked by the resurgence of the order Labechiida. We review the world distribution of Famennian and Strunian stromatoporoids and revise generic assignments of many species. On a global scale, we find the faunas divided into three assemblages: 1) labechiids characterized by Stylostroma, 2) mixed labechiids and clathrodictyids with species of Atelodictyon, and 3) clathrodictyids without labechiids. The third assemblage is confined to western Europe and Kazakhstan in areas of the late Devonian Paleotethys ocean.

Carbonate-siliciclastic Facies Transition and Reef Growth on the Northeast Coast of Barbados, West Indies

ABSTRACT On most of the insular shelf around Barbados, carbonate sediments are now accumulating from the growth of reefs, the contributions of the skeletons of carbonate-secreting organisms, and the erosion of the Pleistocene coral cap that covers six-sevenths of the island. However, after heavy rains, water laden with siliciclastic sediment eroded from the Scotland district (where the coral cap is breached) is discharged from four main rivers onto the northeast coast insular shelf. The coarse-grained material is transported as bedload onto an offshore sand ramp, over the shelf break into deeper water, or is incorporated into adjacent beaches. The fine-grained sediment is directed northward along the shore within a sediment plume by the equatorial current. Fine sediment settling out of the plu e is deposited on a spur and groove system and reefs growing on a deeper-water platform north of the sand ramp. Nearshore, the transition from the siliciclastic sediments to carbonate sediments is located on a submerged barrier reef at the seaward margin of a shallow-water platform. The facies transition on the deeper-water platform is gradual near the southern edge of the deeper-water reefs. Distribution of benthic biota and the growth of reefs are controlled by a combination of siliciclastic influx and shelf floor topography. The deeper-water reefs grow despite the periodic blanketing by fine siliciclastic sediment settling from the sediment plume that accumulates around them.

A REVISION OF ANOSTYLOSTROMA, ATELODICTYON, AND RELATED GENERA (PALEOZOIC STROMATOPOROIDEA)

ABSTRAcr- Laminae of genera considered in this revision are sheets of planar, compact tissue (order Clathrodictyida) or a network formed by arms (colliculi) emerging from pillars (order Actinostromatida). Pillars, confined to a single interlaminar space, are simple rods, branch upwards, or have complex cross sections. The scope of Anostylostroma is limited to species with complexly upwardly branching pillars and simple planar laminae. Species with predominantly y- or v-shaped pillars are removed to Schistodictyon. Simplexodictyon is limited to species with double laminae formerly referred to Diplostroma. A new genus, Petrostroma (type species: Simplexodictyon simplex Nestor), is proposed for species with simple, planar laminae and rodlike pillars. The scope of Atelodictyon is restricted to species with planar, simple laminae resembling the type species and many species with laminae formed of colliculi previously placed in this genus are assigned to Aculatostroma. Other genera discussed include: Crumplestroma and Coenellostroma (both synonyms of Aculatostroma), Pseudoactinodictyon, Stelodictyon, Clathrodictyon, and Nexililamina and Coenostelodictyon (both synonyms of Schistodictyon).

Ichnofossils within Tetradium and related genera

An ichnofossil formed by an organism that preferentially burrowed the micritic sediment filling corallites of tetradiids has an axial passage that may be filled with sediment or calcite spar and a surrounding affected zone of concentric structure formed by the alignment of grains. More than one such burrow may occur in a single corallite. A larger ichnofossil that destroyed both septa and walls of the corallites is associated with the smaller ichnofossils.

BIOSTRATIGRAPHY OF DEVONIAN STROMATOPOROID FAUNAS OF ARCTIC AND WESTERN CANADA

Abstract Through a review of older type collections and identifications of undescribed collections, using a broad species definition, the Devonian succession is divided into 10 assemblages. The names of many species are revised. With the exception of the Pragian, all stages of the system are represented by one or more assemblages. The ranges of important taxa are plotted and shown to be relatively short and diagnostic of the 10 intervals. In the absence of conodonts in the reef facies, stromatoporoids offer a supplementary method of correlation. Many species occurring in Canada can be recognized in the stromatoporoid faunas of the former Soviet Union, China, Europe, and Australia.