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The periodic acid-Schiff (PAS) reaction, a polysaccharide indicator, stains the mucus linings of recent burrows and the linings and infillings of some trace fossils. The technique is easy to use, and may be useful in estimating population densities and interpreting mode of origin of trace fossils.

Intertidal sediments of the Minas Basin, a macrotidal estuary at the head of the Bay of Fundy, can be subdivided into six major facies: tidal marsh, beach, mudflat, sandflat, channel lag, and sandbar. Each is characterized by its grain size distributions, sedimentary structures, and biological communities. These sedimentary facies occur in three types of high-to-low tide zonation, depending on the local sediment source and wave and current energy. The Holocene stratigraphy presently preserved in the upper intertidal zone of Minas Basin consists of a relatively thin (on the average less than 1-2 m) wedge of sediment overlying bedrock. Only in a few sheltered locations, where deposits accumulate to several meters, is the marine transgressive stratigraphy well represented. The hypothetical progradational or marine regressive stratigraphy of upper intertidal sediments would probably resemble, from top to bottom, the high to low tide sequence of facies occurring today on sheltered tidal flats. Lebensspuren would provide the most reliable representation of the ecology of intertidal sediments in Minas Basin. They are useful in delineating communities as well as being sensitive indicators of sediment deposition. Microfauna are too easily transported or reworked. Field data from relict intertidal deposits (dated 2300-3400 yr. B.P.) indicate calcareous organism hard parts would probably provide a biased fossilized record. Indirect evidence is discussed, which suggest in situ dissolution of shells in certain intertidal sediments.

Iceland spar (calcite) crystals, placed in the shallow subtidal marine environment at Discovery Bay, Jamaica, are infested by the filamentous endolithic (boring) alga Ostreobium sp. Within 25 days after the crystals are placed in the sea, filaments project from the substrate into the sea; between 65 and 95 days the exposed filaments become completely calcified by low Mg calcium carbonate, both internally and externally. The submarine precipitation of calcium carbonate occurs only upon dead filaments and takes place at a geologically very rapid rate. The breakage of exposed calcified filaments is estimated to produce about 1 cm3/m2/yr of micrite-size carbonate. This is a source of mud-size materials, not only in the back reef and reef lagoon, but also within the reef itself. The coalescence of dense populations of exposed calcified filaments could produce a micrite envelope about a grain, without the destruction or alteration of the grain periphery associated with the classical mechanisms of micrite envelope formation Such micrite envelopes would be wholly constructive in origin, the product of precipitation of calcium carbonate on algal filaments outside the substrate, rather than within it.

The boring sponge Cliona caribbaea is ubiquitous on the shallow terraces around Grand Cayman Island, British West Indies, occurring as brown sheets covering and growing over both live corals and hard substrate. Throughout the zone of the radial grooves, on the southwest corner of Grand Cayman, C. caribbaea covered 5% of the total bottom area between -1 and -10 m. Values up to 10% occurred commonly. Lateral extension rates were 4 cm/yr. The sponge removes an average of 20% (up to 45%) of the substrate, which has an average specific gravity of 1.7. Conservative estimation of typical rates of substrate removal yields 8 kg/m2/yr, a value of about double the typical rates of reef calcification. The silt produced by the sponge is rapidly transported downslope.

Skeletal carbonate sediments on the lagoon floor of Davies Reef (Great Barrier Reef, Australia) are subject to intense attack by microboring organisms, principally algae. The rate at which this microboring process dissolves carbonate was measured experimentally. Fresh, unbored, molluscan sand samples placed in the shallow lagoon (5 m water depth) experienced a weight loss of about 0.9 g/30 g sample (or 3%) in one year due to dissolution of carbonate by microborers (revealed by direct measurement of weight change and point-count analysis). This figure may be converted to about 350 g CaCO3 dissolved/m2 lagoon floor/year, which is equivalent to between 18 and 30% of the sediment influx rate to this lagoon, averaged over the past 9,000 years. Consideration of the exp rimental design suggests that the experiment underestimated the true rate of microboring in lagoon floor sediments. We conclude that the extent of microboring in carbonate sands may provide information on the rate of sediment deposition, and that dissolution of carbonate sediments by microborers is a significant factor in whole-reef CaCO3 budgets.

Missionary Bay, north Queensland, is an example of a tropical modern depositional environment dominated by mangrove swamps. Several major sedimentary facies are represented: coastal sands, brackish-water peats, intertidal organic muds (on which the mangroves are developed), low-tide muds, channel deposits, inshore muds, sandy bay-bottom muds, inshore sands, inshore carbonate sands, and deltaic sands. Large amounts of mangrove litter are carried in nearly anoxic creeks to the bay. Bay-bottom sediments have only a shallow upper oxidized layer, and are strongly reducing at depth. Organic carbon values for most of the inshore sediments range from 1 to 2%. Total lipid content of the bay-bottom sediments is very high. Sediments average 0.15% by weight total lipids, or about 6% of the total organic carbon. These high values are attributed to the lipid-rich mangrove litter. Sedimentation rates for the bay-bottom sediments are high, about 1 cm/year. Progradation rates are also high, about 1 m/year. Including offshore fringing reefs and inshore sands, the total area of the system is several hundred square kilometers. Anoxic conditions of transport and deposition, plus the high sedimentation rates, suggest that the low-tide muds and bay-bottom muds are excellent source rock analogs. Progradation and accumulation could result in a section about 50 m thick, with lipid-rich sediments interfingering with barrier sands, fringing reefs, channel sands, and deltaic sands. The section will be capped and sealed by brackish-water peats with a mud matrix. This system is of potential value as a conceptual model for hydrocarbon accumulations on ancient tropical coastline .

Endolithic (boring) algae are the direct or indirect agents of important erosive and early diagenetic processes in carbonate sediments. Algae boring into carbonate grains produce micrite envelopes by repeated boring and infilling of borings by precipitated micrite, as described by Bathurst. However, the algae also produce micrite envelopes outside grains by the calcification (cementation) of exposed dead endolithic filaments, a process which reduces intergranular porosity. Algal filaments grow through the micrite envelopes into intergranular pores, and live within the pores as chasmolithic algae (living in holes not of their own creation); after death these may become calcified to produce an intertwined mesh of calcified filaments on which later micrite and microspar cements precipitate. The calcified intergranular filaments and associated cements further reduce intergranular porosity (and possibly permeability) and s rve to bind the grains. Micrite envelopes also may be produced beneath algal-mucous coats through a process of etching and dissolution, resulting in a highly microporous residue micrite. Girvanella and similar Paleozoic and Mesozoic algae may represent calcified algae similar to those described previously, in which cement precipitates on dead algal thalli. Girvanella may be a diagenetic taxon, produced from many algal genera, rather than a discrete biologic form.

On some intertidal fine sands of the Minas Basin, Bay of Fundy, the tubicolous spionid polychate Spiophanes wigleyi coexists with the paraonid polychate, Paraonis fulgens. Paraonis feeds on diatoms buried on bedding planes within the sediment, and produces spiral traces 2-3 cm in diameter. Sediment preferences of both worms seem related to feeding behaviour: population densities of Spiophanes were positively correlated with mean grain size, and not with sorting, while population densities of Paraonis were not correlated with mean grain size, but were positively correlated with sorting. If found preserved in the fossil record, Spiophanes tubes would probably be identified as Skolithos, a trace fossil associated with the nearshore zone. Paraonis spirals bear a superficial resemblance to other spiral traces, such as Spiroraphe, found at abyssal depths.

Grains at the margins of Ordovician and Silurian Skolithos were oriented significantly parallel to the trace in vertical section, and tangential to the margin in horizontal section. Control analyses showed no similar orientations developed away from the traces. Microprobe analyses of the same traces showed anomalous concentrations of cations at trace margins. Similar analyses of impregnated Holocene burrows suggest that these cation concentration gradients are not diagenetic. Control analyses of various inorganic sedimentary structures showed that the chemical anomalies are biologically produced. Similar petrographic and geochemical studies on structures of questionable origin in the Huronian Bar River Formation produced identical results to the Recent, Silurian, and Ordovician examples. These techniques allow objective criteria to be employed to differentiate between organic and inorganic sedimentary structures.

Broad, boulder-strewn intertidal flats border the shores of Pangnirtung Fiord, Baffin Island. These intertidal flats support a benthic biota dominated by bivalves, sedentary polychaetes and phaeophycean algae. The assemblage of organisms inhabits a variety of substrates ranging from muddy sand through gravelly sand and boulders. Six depositional environments defined on the basis of sediment texture, primary sedimentary structures and their associated macrofauna and ichnofauna are recognized on Pangnirtung Fiord intertidal flats. Proceeding seaward, these are beaches, sand bars, muddy sand flats, Macoma balthica sand flats, Arenicola marina sand flats, and boulder barricades. Such sediments, in outcrop, may differ only subtly from their equivalents in other latitudes. Modern biogenic structures provide essential information for environmental reconstruction in Arctic marginal marine environments. Their use in sedimentology is enhanced by the low preservation potential of primary sedimentary structures and shell material as a result of disturbance by drift ice, bioturbation, and dissolution. The ichnofauna exhibiting the greatest preservation potential is characterized by vertical domichnia of bivalves and polychaetes and resembles the ichnofauna recorded on the Bay of Fundy intertidal flats.

Intertidal sediments of the Minas Basin support an estimated 24 109Macoma balthica. Excreta occurs as either loose coils or strings of pseudofeces, or as small cylindrical fecal pellets, both of which are easily transported. Fecal pellets are picked up with fine sand and settle out of suspension with coarse silt. Some pellets last at least one tidal cycle before breaking down into sand grains and mucus-bound aggregates of mud and silt. Each clam produces about 0.5 g (dry weight)/day of excreta, most of which is resuspended by tidal currents. In the areas of highest recorded population densities (3.500/m2), feeding would remove about one foot of sediment (28 cm) per year. Total daily contribution of excreta to the Minas Basin by the 24 billion Macoma amounts to about 6 109 g (dry weight) of sediment or about 10,000 m3 of wet excreta. This material is likely a valuable food source and is distributed throughout the Minas Basin by tidal currents.

Ecologic and taphonomic impacts of volcanic ashfall on a Pleistocene nearshore hard-bottom community and a Cretaceous offshore soft-bottom community are compared and contrasted. The hard-bottom (reef) community, dominated by sessile, epifaunal organisms, was devastated by rapid deposition of volcanic sediment. In contrast, the offshore community, dominated by motile, burrowing organisms, was considerably less affected, since many of these organisms could escape burial. These examples emphasise the potential bias that volcanism may introduce into the fossil record, particularly the over-representation of sessile fauna. The new substrate provided by volcanic sediment inhibited the re-establishment of the reef community, but was not sufficiently different from terrigenous mud to alter the structure of the offshore community. Unlike other agents of rapid burial (e.g. storms, mass wastage), volcanic sedimentation in these settings was not accompanied by a significant increase in hydraulic energy. Consequently, faunal remains were buried in situ and rapidly isolated from the destructive effects of subsequent hydraulic disturbance, scavenging, bioerosion and bioturbation. In both of the examined settings, this contributed to exceptional preservation of skeletal remains. Preservation was also promoted by early diagenetic cementation. In the reef setting, cementation of ash was laterally continuous, whereas in the offshore setting, early diagenetic minerals were precipitated as small concretionary bodies. Both styles of early diagenetic cementation enhanced preservation by effectively armouring buried fauna from destructive taphonomic processes. OTaphonomy, coral reef, fossil preservation, fossil lagerstiftten, volcanic ash, benthic communities, fossil diagenesis, concretions, Bearpaw Formation, Cretaceous, Pleistocene, Alberta, Indonesia.

The stable isotopic signatures of Jamaica and Zanzibar coral skeletons, collected over depth and light gradients, are strongly affected by kinetic isotope effects associated with the calcification process. These kinetic effects mask δ13C metabolic signals of light availability/photosynthesis. A simple data transformation, based on oxygen isotopic variation in the skeleton, has been developed to correct for the presence of these disequilibrium kinetic influences. The resulting transformed skeletal δ13C data show significant correlation with associated tissue δ13C and with depth/light attenuation. These relationships demonstrate the value of the transformation and suggest that transformed skeletal δ13C data faithfully record the carbon isotope effect associated with photosynthesis, in which increased photosynthesis leads to skeleton enriched in the heavy isotope of carbon. Possible applications of these transformations include improved modeling of carbon fluxes in corals and more accurate reconstruction of insolation, depth, water clarity and cloudiness. The 13C transformation presented will also allow for better identification of periods of metabolic stress in corals, when growth rate effects on δ13C might normally obscure the 13C metabolic signal.

Large volumes of a gas consisting of 69 percent molecular oxygen and 31 percent molecular nitrogen with trace amounts of carbon monoxide, carbon dioxide, and methane have been found trapped inside skeletons of the common hydrozoan Millepora. Volumes were low in the morning and reached a maximum by late afternoon. The oxygen was probably produced by the endolithic (boring) algae, with which the Millepora skeletons are very heavily infested. Oxygen production by endolithic algae in Millepora and in other substrates could influence estimates of reef productivity based on measurements of dissolved gases.

Axius serratus, a crustacean thought to be extremely rare, was discovered in large numbers in polluted regions of the Strait of Canso. The shrimp may live deeper than 3 meters in the sediment; burrows are kept open to at least 2.5 meters. Sediment contained in old filled burrows is anomalous in its distribution of particle size and its content of water, organic carbon, and trace elements. These anomalous qualitites affect the geotechnical properties of sediments on the sea floor.

The 1982-1983 El Nino was the strongest such event recorded this century, resulting in widespread coral mortality in the eastern Pacific. To search for sclerochronological evidence of this event, heads of Porites lobata were sampled at different depths from several locations on the reef at Isla del Cano, Costa Rica. The 8 180 stratigraphy was obtainedfrom several hundred analyses from vertical sections through the coral heads. The timing and magnitude of the 19821983 El Nino are accurately recorded in the isotopic records, which indicate that this event was several times stronger than other "strong" El Ninios. Isla del Canio does not experience annual upwellings, and the 1982-1983 El Ninio was not accompanied by greatly increased rainfall; these factors probably explain the excellent agreement between oceanographic data and the isotopic stratigraphy. It is now possible to infer magnitude and chronology of similar climatic disturbances in core or outcrop samples, and to link this with vertical changes in reef communities.

Modern corals from Lizard Island, in Australia's Great Barrer Reef, show pronounced dark gray zones parallel to growth sufaces. These color bands are caused by increased activity of boring algae during the dry sunny season, and hence are annual. Cyclicity in algal boring activity may therefore be used to determine growth rates and life spans of some fossil organisms, and possibly the seasons of spat settling and death. Samples of Devonian stromatoporoids from Bathurst Island in the Canadian Arctic show cycles in boring intensity which suggest growth rates of about 1 cmlyr. These results are questionable, however, because the borings cross through both the lamellae and calcite cement in the interlamellar spaces. This implies early infilling of the stomatoporoid skeleton, a process which is still in debate. Ordovician solitary rugose corals from Kentucky and southern Manitoba show marked cyclicity in intensity of algal borings preserved in the epitheca. Growth rates are estimated to have been about 2 cmlyr. Both the apices and distal portions of these corals are relatively unbored. Perhaps the larvae settled during the cloudy monsoon season, and the adults died (2-3 years later) as a result of overturning and transport by monsoonal storms. Both the stomatoporoid and rugosan growth rates are as high as those shown by modern hermatypic corals, reinforcing previous suggestions that some Early Paleozoic marine invertebrates possessed zooxanthellae.