Principles of Animal Ecology

A minimum sea-level curve for the past 10,000 years has been constructed on the basis of radiocarbon dates of Acropora palmata (Lamarck) samples from the shallow-water framework of both relict and modern reefs of the tropical western Atlantic. A. palmata framework is a reliable reference for reconstructing the history of late Quaternary sea levels owing to its restricted depth range (<1 to 5 m), the lack of postdepositional transport of A. palmata framework, the ease of obtaining uncontaminated samples, and the minimal compaction of A. palmata reef facies. The minimum sea-level curve constructed in this study is useful not only in evaluating the reliability of present and future Holocene sea-level curves for the western Atlantic, but also in estimating paleo-water depths in the study of Holocene reef history of this area.

Acropora palmata reef framework: A reliable indicator of sea level in the western atlantic for the past 10,000 years

Presumed barriers to early dolomitization in normal seawater-derived pore fluids at earth-surface temperatures appear to be overcome within some anoxic, organic-rich sediments as a result of bacterial sulfate reduction and methanogenesis. These processes may promote early dolomitization, particularly during methanogenesis and late stages of sulfate reduction, by concurrently raising and sustaining high pH and high total alkalinity and CO 3 2- concentrations in pore fluids, and by simultaneously either decreasing Mg and Ca hydration or by promoting crystal surface reactions with less hydrated Mg-Ca neutral ion pairs. Volumetrically significant quantities of dolomite are associated with sulfate reduction and/or methanogenesis within peritidal, shallow-marine, and deep-sea deposits. Average concentrations of organogenic dolomite are as much as 70% in some Holocene peritidal deposits, and 28% in Mesozoic to Quaternary deep-sea sediments. Organogenic dolomites are mainly cements, and contain relatively low concentrations of Sr and Mn. Sulfate-reduction dolomites generally are Fe-deficient because of concurrent pyrite precipitation, whereas methanogenetic dolomites may be somewhat more ferroan as Fe substitutes for depleting Mg. Sources of Mg and Ca for dolomite are diffusion from overlying seawater and/or dissolution of precursor carbonate sediments. Dolomites are characterized by a wide range in δ 13 C values wherein those of sulfate reduction versus methanogenetic origin typically are 13 C-depleted and 13 C-enriched, respectively. The extent of 13 C depletion or enrichment, however, depends on the extent of organodiagenetic reactions and amount of 13 C contributed by seawater diffusion, and commonly results in overlap of δ 13 C dolomite values. The range of δ 18 O dolomite values is somewhat more restricted, and generally reflects differences in pore-fluid temperature and salinity. Some of the unresolved issues in organogenic dolomitization are: the relative efficiencies of sulfate reduction versus methanogenesis in promoting dolomitization, depths of dolomite formation inferred on the basis of δ 18 O dolomite values and probable sources of Mg and Ca, and the mode of dolomitization with progressive burial into methanogenetic zones.

Organogenic Dolomitization in Peritidal to Deep-Sea Sediments

Trace fossils at discontinuity surfaces may be classified as three distinct ’ assemblages, according to their time relationship with the depositional hiatus. These assemblages may be called the “preomission,” “omission “and “postomission” suites. Discrimination of these suites is essential for the stratinomic interpretation of the discontinuity surface. The three suites may represent the same ichnocoenose in different modes of preservation, or the appearance of a new ichnocoenose may suggest the environmental conditions responsible for the omission of sediments and the resumption of deposition.

Trace Fossils at Omission Surfaces

Growth kinetics and composition of magnesian calcite overgrowths precipitated from seawater: Quantitative influence of orthophosphate ions

The inner shelf platform off North Eleuthera consists of a series of terraces at 6 m, 8 m, 20 m, and 35 m depth, respectively. The boundary between 6 and 8 m terraces is marked by a near continuous reef ridge, landward and seaward of which isolated reef structures are found. Reefs are aggregates of pillar structures, which in turn are composed of columnar, club-shaped or mushroom-shaped pillars of corals. The dominant primary framebuilder above 3 m depth isAcropora palmata; below corals of the generaMontastrea andDiploria, Porites astreoides andP. porites also contribute to the frame, as does the hydrozoanMillepora. The secondary framebuilders start developing and changing the shape of the frame as soon as they find suitable substrates; most important are coralline red algae, which encrust internal and external surfaces, but also may fuse the components of the frame; other organisms just add to the frame. In contrast boring and rasping organisms destroy the frame. Constructing or destructing organisms were found living on every surface, external or internal, accreting or diminishing.

Interaction of genetic processes in holocene reefs off North Eleuthera Island, Bahamas

The dualism in carbonate geochemistry — organic or inorganic production — leads to an erroneous definition of the carbonate system. A different formulation of the chemical mechanism is proposed where traces of transition metals together with organic matter in natural environments play a central role in carbonate production. This approach is verified in a series of experiments using natural and artificial sea water and as chelating agents citric, tartaric, malonic, and oxalic acids with five transition metals: Ni, Co, Fe, Mn and Zn. The final product of carbonate precipitation depends on the type of metal acting as a central atom. In the series Ni, Co, Fe, Mn, Zn the potential for calcium uptake increases from Ni to Zn, while magnesium uptake increases in the opposit direction from Zn to Ni. Dolomite can precipitate from Mg-rich natural waters by the catalytic effect of Fe(II)-chelates. If the waters containing Fe(II)-chelates are exhausted with respect to magnesium carbonate, they will attack dolomite to form calcite.

https://link.springer.com/content/pdf/10.1007/BF01824903.pdf

Some phenomenological aspects of carbonate geochemistry. The control effect of transition metals — Reply

An Investigation of the distribution of Ca2+, Mg2+, Na+, Sr2+ and K+ as well as O18 and C13 in void-filling cements out of three fossil reefs — of Devonian and Triassic ages — shows a rhythmic fluctuation of these parameters in the successive layers. This reflects a similar change in the salinity conditions during cementation. It also leads to the presumption that the void filling process starts in early stages with a semi-closed system and later passes into a relatively closed one. Results obtained from factor analysis support this hypothesis. The original mineralogic constitution of the cements must have followed the rhythmic fluctuation of salinity with the result of forming alternative layers of aragonite and calcite. These lead, through inversion and grain growth, in later diagenetic stages to the formation of fibrous calcite. Blocky calcite represents the last stage of cementation. It crystallises out of exhausted solutions and shows no signs of inversion. Multivariate analysis of all investigated parameters reveals three factors. These were interpreted as representing Salinity, Temperature and original Mineralogy.

Petrography and geochemistry of carbonate void-filling cements in fossil reefs

At the VIII. International Sedimentological Congress held in Heidelberg in 1971, a symposium with the above title was convened; a selection of the papers presented is assembled in this issue. In the introduction the approaches of the following studies are reviewed to show some trends and problems in reef research.

Heinrich Zankl

Papers

Interaction of genetic processes in holocene reefs off North Eleuthera Island, Bahamas

Some phenomenological aspects of carbonate geochemistry. The control effect of transition metals — Reply

Petrography and geochemistry of carbonate void-filling cements in fossil reefs

Ecology, sedimentology, and diagenesis of recent and fossil reefs