Boring Algae Research Articles

Devonian Boring Algae or Fungi Associated with Micrite Tubules

The process of skeletal micritization by boring thallophytes (algae and fungi) is known from modern carbonate environments and probably occurred as far back as the Ordovician. Boring thallophytes, probably fungi, possibly algae, were the cause of at least some skeletal micritization in Devonian reef complexes in western Canada. In situ endolithic filaments, of 3 μm and 5 μm diameter, occur associated with a micrite rim and micrite tubules in the corallite of an Upper Devonian tetracoral from the Miette reef complex. The filaments are found in the micrite rim around the coral, in the micrite tubules, and in unmicritized parts of the corallite, often oriented normal to the corallite wall and with the same trend as the tubules. Infestation and micritization began well before the corallite was buried, probably while the coral was alive, and continued for some time after death.

THE GENESIS OF CONDENSED SEQUENCES IN THE TETHYAN JURASSIC

Pelagic limestones of the west Sicilian Middle Jurassic are used as type examples in this examination of Tethyan condensed sequences. Two main processes were involved in the genesis of this type of deposit: stratigraphic condensation (minimal sediment input) and reworking. The lack of nannoplankton during most of the Jurassic caused stratigraphic condensation, and the particular environment in which these beds were deposited – that of topographic high – was considerably influenced by currents; thus reworking led to a further reduction in sediment thickness. The presence of algal stromatolites in certain condensed sequences and the traces of boring algae in associated ferromanganese nodules suggest deposition within the photic zone. A maximum depth of 200 metres is inferred. Many features of condensed sequences are comparable with those on Recent seamounts; these include presence of ferromanganese nodules and crusts, mixed faunas, calcarenite lenses, algal biscuits, and evidence of submarine solution and lithification. Jurassic Tethyan condensed sequences can thus be interpreted as ancient seamount deposits.

Selective Bivalve Shell Destruction in Marine Environments, A Field Study

ABSTRACT Eighty four single valves, equally divided between the bivalve species M. mercenaria, Argopecten i. irradians and Mya arenaria, were submerged for three years in a shallow, low energy, sublittoral environment. Weight changes, modifications in shell characteristics, the growth of attached epifauna, and the effects of boring algae were recorded on a yearly basis. Valves with greater surface area per unit weight suffer a greater weight change, are more subject to breakage, and are more heavily encrusted with attached epifauna than those with less surface area per unit weight. These differences are explained in terms of differential burial; shells with less surface area per unit weight being buried more rapidly than thinner and lighter valves, which are maintained above the ediment-water interface. Solution appears to be the chief destructive agent below the sediment-water interface whereas boring marine organisms are the dominant agent in shell destruction above the interface. Comparison with other environments indicates that shell destruction is 150 to 1000 times more rapid in surf zones when abrasion is the principal destructive agent, than it is in low energy sublittoral environments. The paleoecologic implications of differential shell burial and destruction are examined.

Ecological Aspects of Some Coral-Boring Gastropods and Bivalves of the Northwestern Red Sea

More than 17 molluscan species were obtained from burrows in coral substrata at Al-Ghardaga (Hurghada on maps) on the Red Sea coast, six of which in particular bore into livingcolonies. The species reported in this paper belong to the families Mytilidae, Coralliophilidae, and Gastrochaenidae. The direction of boring in living corals is to the outside, the borers keeping pace with the growing coral layer to maintain their burrows open. Coral growth is generally of a higher rate than that of borers, and burrows are accordingly mostly much larger than their inhabitants. There is evidence in such cases that burrows form initially by growth of coral around the settling young. Boring of Lithophaga species is mostly due to the abrasive action of the shell which moves straight and posteroventrally without any rotation. Incoralliophilids, boring is also executed mechanically by the turning movements of the shell. Boring in dead coral is directed inwards, and burrows are nearly as large as the borers. The latter avoid the blocking of their burrows ( e.g. , by a living coral incrustation) either by great siphonal extension ( Rocellaria ) or the free ends of the shell may be strengthened to maintain the capability of boring in the opposite direction ( Lithophaga laevigata ). Both L. luevigata and Modiola chmamomeus bore mainly mechanically by the rocking movements of the shell. Chemical boring is still a possibility,particularly in the posterior narrow region of burrows of Modiola lodging the extended pallial siphons which are deprived of any effective mechanical devices for boring. Therole of boring algae in rarefying bored coral material has also to be included as an indirect chemical factor.

Role of the Blue-Green Alga Girvanella in Skeletal Grain Destruction and Lime-Mud Formation in the Lower Ordovician of West Texas

ABSTRACT Marginal grain corrosion on calcareous grains present in the Lower Ordovician (El Paso Group) mound carbonates of west Texas, appears to be caused by the boring and perforating action of the primitive filamentous blue-green alga Girvanella. This boring and perforating action of algal filaments results in profound marginal corrosion of the skeletal and nonskeletal grains, and ultimately leads to grain breakdown and micrite formation within the corrosion rim. The mechanism of the algal boring and perforating process is unknown. Neither do we know much about the cause for the precipitation of micrite within the algal corrosion rim. Our observations tend to indicate that the micrite precipitation may be related to the algal life processes and decay. Partial recrystallization of the micritic corrosion rim or envelope around the grains occurs frequently. This may indicate prior leaching and the remobilization of the carbonate component during the penetrative stage of the algal filaments, or sometime during their decay. The boring and perforating action of the primitive filamentous algae appears to be a major influence in carbonate grain alteration, destruction, and eventual micrite formation. These primitive algae occur in sediments ranging in age from the Precambrian to the Recent where they are found abundantly in shallow water environments, generally shallower than 50 meters, and in all climatic zones. It is thought that the boring algae are important agents in early diagenetic particle and grain breakdown in carbonate sediments.

Bahamian Oölitic Sand

Deposits of oölitic aragonite sand are being formed in a discontinuous belt in very shallow waters along the margins of the Great Bahama Bank. In a studied area south of Bimini, there is strong negative correlation between water depth and oölitic structure of the grains suggesting that waters less than six feet deep are optimal for oölite formation. The largest percentage of oölitically coated grains, and the grains with the greatest number of lamellae are concentrated in, and just below, the intertidal zone, where they are in contact with sea water judged to be supersaturated (metastable) with respect to aragonite. The metastable condition is believed to result from the fact that tidal flow over the barrier rim of the shelf lagoon brings relatively cool, -rich water into a shallow, heated, turbulent zone so rapidly that organic extraction of calcium carbonate does not keep pace with the increase in carbonate saturation due to loss. Each oöid consists of a nucleus, usually an abraded shell fragment or a recrystallized fecal pellet, surrounded by a concentrically laminated envelope, which may range in size from a thin, superficial coating to a layer comprising seven-eighths of the volume of the grain. Grains with a thick, laminated envelope tend to be subspherical or ellipsoidal. Grains with few layers may be any shape, depending on the form of the nucleus. The distinctive and environmentally significant feature of these grains is judged to be the laminated layer. Consequently, the term "oöid" is here used for grains displaying this structure, regardless of the shape. 'Oölite" refers to aggregates of oöids. The concentric lamination of the envelope is due to the presence of distinct, relatively unpigmented, lamellae which are regular in thickness (about one to three μ) and composed of submicroscopic crystals of aragonite with c-axes oriented tangential to the lamination. In addition to these oriented aragonite lamellae the envelope contains unoriented cryptocrystalline aragonite, generally more heavily pigmented and occurring both as discontinuous layers and lenses intercalated between oriented aragonite lamellae and as irregular blebs transecting the concentric structure. A fabric seemingly identical to that of the unoriented cryptocrystalline aragonite of the envelope occurs also in pellet nuclei and in recrystallized skeletal grains. Thus the unoriented fabric is at least in part demonstrably a product of recrystallization, but it may in part result from interstitial precipitation. The grains contain much organic matter, which occurs both as perforating filamentous algae and as a gelatinous substance resembling organic detritus and tending to concentrate in the unoriented aragonite. It is concluded that the oriented lamellae represent grain growth by the addition of aragonite at the grain surface as a physicochemical precipitate. The unoriented aragonite is believed to result from interstitial re-crystallization (and possibly precipitation) associated with organic matter incorporated in the grain (1) as the organic fraction of a fecal pellet, (2) as an adherent film of organic detritus, and (3) as remains of boring algae.