Michał Gruszczyński

Oceanic stable isotope composition and a scenario for the Permo‐Triassic crisis

Stable carbon isotope data from brachiopod shells from the Upper Permian Kapp Starostin Formation (West Spitsbergen) indicate that the oceanic carbon isotopic ratio, which had already been very high in the late Permian, rapidly increased by almost 4 per mil and then dramatically declined by more than 10 per mil in the very latest Permian. This pattern is essentially repeated by the oxygen isotope curve. These data show that a geologically rapid switch between two fundamentally different states of the Earths exosystem occurred near the Permo‐Triassic transition. The late Permian state of the global system was profoundly different from the modern one in that vast amounts of organic carbon were stored, presumably in the form of easy‐to‐mobilize sapropel‐like deposits, below the oceanic redoxcline. Under such conditions—which we propose to call overfed ocean—nutrients were intensely recycled to seawater, thus allowing the ocean to sustain a huge standing crop of the biosphere. Deposition of large amounts of ...

Seawater strontium isotopic perturbation at the Permian-Triassic boundary, West Spitsbergen, and its implications for the interpretation of strontium isotopic data

Brachiopod shell samples from the Kapp Starostin Formation, West Spitsbergen, provide evidence for a large and rapid drop in seawater strontium isotopic ratios close to the Permian-Triassic boundary. The strontium isotopic shift is associated with similarly dramatic declines in carbon and oxygen isotope curves recorded in the same samples. This pattern can be explained by a paleoceanographic model that we have proposed previously, a model in which there is replacement of a largely stagnant, stratified ocean by a vigorously mixed one at the Permian-Triassic boundary.

Stable carbon and oxygen isotope record in the Paleogene La Meseta Formation, Seymour Island, Antarctica

Stable carbon and oxygen isotopic relations have been analysed in brachiopod, gastropod, and bivalve fossils from the La Meseta Formation (Eocene-?early Oligocene), Seymour (Marambio) Island, West Antarctica. The results indicate a shift in δ 13 C by 6 permil beginning in the middle part of the Unit II of the formation. This shift may imply a change from a largely stratified to a vigorously mixed ocean. Such an interpretation is corroborated by changes in the elemental proportions in the shell material. Alternatively, the carbon isotopic shift may be regarded as reflecting a change in the local depositional enviornment. Such an interpretation agrees with isotopic data from the Weddell Sea, which do not confirm the pattern observed in the La Meseta Formation. In any event, the oxygen isotopic curve does not decline parallel to the carbon curve and may thus imply a considerable climatic cooling event. This effect is so profound that it might be interpreted as evidence for glaciation, especially when taking into account the fact that this phenomenon coincides with the well-known cooling trend throughout the Eocene. If this interpretation is correct, the hypothesized Glaciation may possibly be correlated with the Polonez Glaciation, the largest Cenozoic glaciation known in the Antarctic Peninsula sector. Alternatively, it may be regarded as a local phenomenon, predating development of the icesheet.

A Bow-form Burrow and its Sedimentological and Paleoecological Significance

Abstract A deep-tier, bow-form burrow with a long apertural neck, and several different types of infill is described from Upper Jurassic shelfal carbonates of Saudi Arabia, Miocene pelagic packstones and wackestones of Malta, and Lower Cretaceous shoreface sands and mudrocks of southern England. The two most commonly observed types of infill are a coarse-grained infill, referred to as Glyphichnus-mode (formed by sediment entering the burrow following breakage of the apertural neck), and a laminated, muddy infill, referred to as Cylindrichnus-mode, which is considered to represent passive, draught filling through a complete burrow. The type of infill and aspects of preservation show that these burrows can be used to assess the style of sedimentation, particularly steady aggradation versus periodic erosion. At present the bow-form burrow is not assigned to a specific ichnotaxon.

On the interrelationship between temporal trends in. delta. sup 13 C,. delta. sup 18 O, and. delta. sup 34 S in the world ocean

The phenomena of (i) inverse correlation between the oceanic carbon and sulfur isotopic curves, and (ii) covariation between the oceanic carbon and oxygen isotopic curves at all their major excursions appear as paradoxes in the current paradigm of global biogeochemical cycles. These phenomena, however, are fully explicable by our model proposing that the ocean alternates between two general modes: stagnant, stratified, and net autotrophic (overfed) ocean, on the one hand, and vigorously mixed and net heterotrophic (hungry) ocean, on the other. This model is in fact strongly supported by the carbon isotopic evidence. The directions of change in the isotopic ratios of carbon, oxygen, and sulfur should be different in the lower, anoxic box of a stratified ocean than in the upper, oxic box; whereas ocean destratification and mixing of the two boxes should lead to coeval shifts in the oceanic isotopic curves of these elements. The model has far-reaching implications for (i) the causal explanation of both secular trends and major shifts in the oceanic isotopic curves, and (ii) for the application of oxygen isotopic data for paleotemperature and paleoenvironment determinations.