The size distribution of framboidal pyrite in modern sediments : an indicator of redox conditions

A rapid sequencing method for ribosomal RNA was applied to the resolution of evolutionary relationships among Metazoa. Representatives of 22 classes in 10 animal phyla were used to infer phylogenetic relationships, based on evolutionary distances determined from pairwise comparisons of the 18S ribosomal RNA sequences. The classical Eumetazoa are divided into two groups. Cnidarians arose from a protist ancestry different from the second group, the Bilateria. Within the Bilateria, an early split gave rise to Platyhelminthes (flatworms) and the coelomate lineage. Coelomates are thus monophyletic, and they radiated rapidly into four groups: chordates, echinoderms, arthropods, and eucoelomate protostomes.

https://science.sciencemag.org/content/sci/239/4841/748.full.pdf

Molecular phylogeny of the animal kingdom

The Palaeocene/Eocene thermal maximum, ~55 million years ago, was a brief period of widespread, extreme climatic warming1, 2, 3, that was associated with massive atmospheric greenhouse gas input4. Although aspects of the resulting environmental changes are well documented at low latitudes, no data were available to quantify simultaneous changes in the Arctic region. Here we identify the Palaeocene/Eocene thermal maximum in a marine sedimentary sequence obtained during the Arctic Coring Expedition5. We show that sea surface temperatures near the North Pole increased from ~18 °C to over 23 °C during this event. Such warm values imply the absence of ice and thus exclude the influence of ice-albedo feedbacks on this Arctic warming. At the same time, sea level rose while anoxic and euxinic conditions developed in the ocean's bottom waters and photic zone, respectively. Increasing temperature and sea level match expectations based on palaeoclimate model simulations6, but the absolute polar temperatures that we derive before, during and after the event are more than 10 °C warmer than those model-predicted. This suggests that higher-than-modern greenhouse gas concentrations must have operated in conjunction with other feedback mechanisms—perhaps polar stratospheric clouds7 or hurricane-induced ocean mixing8—to amplify early Palaeogene polar temperatures.

/pdf/subtropical-arctic-ocean-temperatures-during-the-palaeocene-1iu2p4jtlb.pdf

Subtropical Arctic Ocean temperatures during the Palaeocene/Eocene thermal maximum

Formation processes of framboidal pyrite

Stable isotopic data from marine limestones and their constituent fossils and marine cements can provide quantitative evidence for changes in global climate and ocean circulation. Oxygen isotopic data can indicate changes in temperature and ocean composition whereas stratigraphic variation in carbon isotope ratios may reflect changes in the carbon cycle that can be linked to changes in oceanic productivity and atmospheric greenhouse gases. Terrestrial carbonates–meteoric cements, calcretes and speleothems–similarly offer significant potential for understanding the evolution of terrestrial climates by providing evidence for the composition of rainwater and the nature of vegetative cover.Primary environmental isotopic signals may be obscured by the effects of post-depositional diagenetic alteration. Cementation and replacement reactions can take place in a wide range of diagenetic environments; the diagenetic history of an individual limestone is determined by a combination of its mineralogical diagenetic potential and depositional setting, together with subsequent changes in relative sea-level and burial history. Carbon isotopic values are less prone to alteration during diagenesis than oxygen values but shifts can be significant where organogenic carbon is incorporated. Linear covariation of carbon and oxygen values is not a reliable indicator of diagenetic alteration: water-rock interaction and fluid mixing may produce non-linear distributions.Attempts to determine long-term changes in climatic and oceanographie conditions through isotope stratigraphy of shallow-water limestones must include an assessment of the diagenetic history of the materials analysed. Petrographic examination using conventional microscopy backed up, where appropriate, by cathodoluminescence and scanning electron microscopy together with elemental and strontium isotopic analysis can help to identify the effects of diagenetic alteration. Where material with a range of different degrees of alteration is preserved in the same sediment it may be possible to compare patterns of isotopic and elemental variation and to attempt to unravel the effects of diagenesis in order to determine primary, environmental, isotopic signals. Recent research has shown that these techniques can be successfully employed in both Phanerozoic and Precambrian sediments.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0016756800008244

Climatic and oceanographic isotopic signals from the carbonate rock record and their preservation

In the southern and central Black Sea, reduced sulfur comprises nearly 1% of the total particulate flux in the anoxic water column, as measured by time-series sediment traps. Sulfur isotopic composition of particulate sulfide fluxes indicates an origin near the oxic-anoxic interface, where dissolved sulfide is isotopically heavier than dissolved sulfide below 175 m due to chemical oxidation A strong seasonal correlation exists between sulfur and organic carbon fluxes; this, together with particulate sulfide precipitation at the oxic-anoxic interface, suggests that sulfides are scavenged from the interface during maximum production of settling organic aggregates, particularly during the late summer coccolithophorid blooms. Sulfide precipitation deeper in the water column and in sediments may be limited by availability of iron and/or polysulfides, since there are no particulate sulfide fluxes which have the same isotopic composition as ambient dissolved sulfide at trap depths. Since sulfides in surface sediments are often isotopically similar to dissolved sulfide at the top of the sulfide zone and to sediment trap fluxes, sedimentary sulfides could originate from metal sulfide fluxes forming at the oxic-anoxic interface and would reflect sulfur-cycling processes at the oxic-anoxic interface Sedimentary sulfate reduction rates estimated from assuming 65–80% utilization of particulate organic carbon fluxes agree reasonably well with other estimates of sulfate reduction and sulfide production rates. A sulfur isotope-based box model for sulfur cycling between dissolved and particulate phases in the water column and sediments is presented.

Sulfur, iron and organic carbon fluxes in the Black Sea: sulfur isotopic evidence for origin of sulfur fluxes

The longest records of earthquake activity1 may be preserved near the edges of carbonate platforms where reefs have bordered active faults. Because the carbonate sediments build up almost to low tide level, because their character and lithification are very sensitive to deviations from that datum, and because they commonly lithify soon after deposition2, strata can precisely record changes in lithospheric flexure3, which in turn record the buildup and release of elastic strain energy during stick–slip faulting. The approximate stratigraphy is predictable for a given history of faulting. Comparison of predictions with observations leads to an explanation for some of the hemicyclic sedimentary sequences common4–6 on carbonate platforms. These records are important for characterizing the seismicity of Atlantic-type continental margins in general. After rifting, faults evidently remain active7, but major earthquakes are so rare that their recurrence times cannot be established from direct observations.

Earthquakes recorded stratigraphically on carbonate platforms

Coenocorrelation is the correlation of positions in a stratigraphic sequence with corresponding positions along a paleoenvironmental gradient through gradient analysis of fossil communities. By ordination of community samples, the distribution and abundance of taxa along a depth gradient can be translated into a continuous scale that accurately measures the gradient and thus makes possible analysis of facies change on a continuum. The procedure is tested using data on marine benthic invertebrates along ten time-parallel transects down an Ordovician basin slope (Trenton Group, New York). Reversals between transgression and regression revealed in coenocorrelation curves served nearly as well as bentonite beds in time-correlation of sections. Ordinations gave estimates of depositional strike in close agreement with estimates from physical indicators. Walther's Law of Facies is evidently a more rigorous, quantifiable generalization than it has been revealed to be through classificatory approaches to communities and environments.

Coenocorrelation: gradient analysis of fossil communities and its applications in stratigraphy

Is there a grand pattern to the evolution of global biota and ecological systems? This question, which has lately attracted much thought, can rather more easily be approached through considering the relative microcosm of a major taxonomic group evolving within a major adaptive zone. This paper examines the evolution of aquatic free-living arthropods, the occupants of one such adaptive zone, from the Cambrian to the present. Combining established ideas on arthropod evolution with new ideas on measurement, it first develops a quantitative measure of the morphological complexity of arthropod limb mechanisms which in turn provides a rough measure of ecological specialization for the respective animals. This measure is then applied to study of the evolution of the world fauna of aquatic free-living arthropods as reflected in the fossil record. The paper analyzes evolutionary patterns thus revealed, and tests the idea that, within an adaptive zone, the specialization of its occupants increases with their taxonomic diversity. Upshots from the study are surprising estimates for rates of taxonomic diversification and rough quantitative estimates for the percentage completeness of the fossil record through geologic time for taxa of different ranks. Simpson (1969) and May (1973) both wondered whether certain regularities in taxonomic diversity data from the fossil record might not reflect some grand strategy in the evolution of global ecological systems. Paleontologists have begun to further examine such patterns in the evolution of world biota and to interpret them in terms of the evolution of the ecological systems those biota may represent (e.g., Simpson, 1969; Valentine, 1969a,b, 1971, 1973a,b; Valentine and Moores, 1970, 1972; Flessa and Imbrie, 1971, 1973; Raup, 1972). The essence of the approach taken by Valentine and others are the beliefs that a biota is constituted as a hierarchy of taxonomically and ecologically structured systems, that taxonomic structure in some way reflects ecological structure, and that the history of a biota as a system can reliably be interpreted through analysis of data from the fossil record (Valentine, 1968). The kinds and number of kinds of organisms comprising a biota constitute its taxonomic structure. The functional relationships among organisms which, if strong enough, may unite populations, communities, and perhaps an entire biota

Evolution of the world fauna of aquatic free-living arthropods.

Temperature-salinity (T-S) profiles in ancient seawater can be estimated from oxygen isotopic compositions of well-preserved calcitic fossils sampled from known paleodepth gradients. The proposed model uses isotopic compositions of fossils to determine possible combinations of temperature and salinity during deposition (given estimates of average salinity, isotopic composition, and net global hydrologic fractionation for ancient oceans). Increasing density with depth constrains those combinations to narrow ranges. This graphic method superposes curves for density and isotopic composition in T-S space, to reveal possible ancient T-S profiles. Application of this method to oxygen isotope data from Ordovician brachiopods deposited on the eastern continental slope of North America demonstrates its usefulness and yields a stable seawater column in which brackish intermediate waters overlie warmer, more saline deep waters.

John L. Cisne

Papers

Sulfur, iron and organic carbon fluxes in the Black Sea: sulfur isotopic evidence for origin of sulfur fluxes

Earthquakes recorded stratigraphically on carbonate platforms

Coenocorrelation: gradient analysis of fossil communities and its applications in stratigraphy

Evolution of the world fauna of aquatic free-living arthropods.

Paleoceanographic modeling of temperature-salinity profiles from stable isotopic data