Search

Petrography of recrystallised ikaite from Ocean Drilling Program material has been presented previously from Nankai Trough and Congo (ex-Zaire) deep-sea fan. This paper expands on the Nankai Trough ikaite observations, drawing on evidence from Laptev Sea, South Georgia, Okhotsk Sea, and coastal lagoon Point Barrow. However, even though many ikaite and glendonite sites occur at high latitudes, it cannot be that ikaite forms exclusively in polar environments, as demonstrated by the occurrences in the low latitude low temperature deep sea sediments offshore Gulf of Guinea (Angola Congo) and mid-latitude deep-sea trenches offshore Japan. Recrystallised ikaite occurs as mm large, zoned calcite crystals in all samples, along with secondary phases of calcite. Our data set is unique in that the origin, storage, and recrystallisation process of natural formed ikaite is recorded in detail and confirms that glendonite petrographic characteristics are a consequence of the structure and chemistry of recrystallising ikaite and not the physical or geochemical environment. The transformation of man-made ikaite to calcite as recorded in laboratory studies, is a process very similar to the one we have observed for natural ikaite. Most significant is that there is variation in the order of the calcite types within a single sample, leading to the conclusion that the variation is a consequence of impurities and geochemical variability in the ikaite, not the external environment. Morphological observations reveal similarities in ikaite and glendonite, this and the similarity in internal textures in glendonite and recrystallised ikaite confirms that glendonite may be used as an indicator of past presence of ikaite. [ABSTRACT FROM AUTHOR]

Throughout the animal kingdom, adaptive colouration serves critical functions ranging from inconspicuous camouflage to ostentatious sexual display, and can provide important information about the environment and biology of a particular organism (1,2). The most ubiquitous and abundant pigment, melanin, also has a diverse range of non-visual roles, including thermoregulation in ectotherms (3,4). However, little is known about the functional evolution of this important biochrome through deep time, owing to our limited ability to unambiguously identify traces of it in the fossil record (2). Here we present direct chemical evidence of pigmentation in fossilized skin, from three distantly related marine reptiles: a leatherback turtle (5), a mosasaur (6) and an ichthyosaur (7). We demonstrate that dark traces of soft tissue in these fossils are dominated by molecularly preserved eumelanin, in intimate association with fossilized melanosomes. In addition, we suggest that contrary to the counter shading of many pelagic animals (8,9), at least some ichthyosaurs were uniformly dark-coloured in life. Our analyses expand current knowledge of pigmentation in fossil integument beyond that of feathers (2,10), allowing for the reconstruction of colour over much greater ranges of extinct taxa and anatomy. In turn, our results provide evidence of convergent melanism in three disparate lineages of secondarily aquatic tetrapods. Based on extant marine analogues, we propose that the benefits of thermoregulation and/or crypsis are likely to have contributed to this melanisation, with the former having implications for the ability of each group to exploit cold environments., On rare occasions, the fossil record reveals examples of exceptional preservation, in which decay-prone tissues, such as skin, are preserved as 'an organic film' (11) with a high degree of [...]

The Paleocene-Eocene Thermal Maximum (PETM; ~ 55.9 Ma) was a period of rapid and sustained global warming associated with significant carbon emissions. It coincided with the North Atlantic opening and emplacement of the North Atlantic Igneous Province (NAIP), suggesting a possible causal relationship. Only a very limited number of PETM studies exist from the North Sea, despite its ideal position for tracking the impact of both changing climate and the NAIP explosive and effusive activity. Here we present sedimentological, mineralogical, and geochemical proxy data from Denmark in the eastern North Sea, exploring the environmental response to the PETM. An increase in the chemical index of alteration and a kaolinite content up to 50 % of the clay fraction indicate an influx of terrestrial input shortly after the PETM onset and during the recovery, likely due to an intensified hydrological cycle. The volcanically derived minerals zeolite and smectite comprise up to 36 % and 90 % of the bulk and clay mineralogy respectively, highlighting the NAIPs importance as a sediment source for the North Sea and in increasing the rate of silicate weathering during the PETM. XRF element core scans also reveal possible hitherto unknown NAIP ash deposition both prior to and during the PETM. Geochemical proxies show that an anoxic environment persisted during the PETM body, possibly reaching euxinic conditions in the upper half with high concentrations of Mo (> 30 ppm), S (~ 4 wt %), and pyrite (~ 7 % of bulk), and low Th/U (< 2 ppm). At the same time, export productivity and organic matter burial reached its maximum intensity. These new records reveal that negative feedback mechanisms including silicate weathering and organic carbon drawdown rapidly began to counteract the carbon cycle perturbations and temperature increase, and remained active throughout the PETM. This study highlights the importance of shelf sections in tracking the environmental response to the PETM climatic changes, and as carbon sinks driving the PETM recovery. [ABSTRACT FROM AUTHOR]