MAL20

Feathers are a diagnostic character of birds, and yet new fossils show they likely originated more than 100 million years before the first birds. In fact, feathers probably occurred in all dinosaur groups, and in their cousins, the pterosaurs, as we showed in 2019. This finding confirms current knowledge of the genomic regulation of feather development. Our work stems from ten years of collaboration with Chinese colleagues, during which we set ourselves the task of understanding fossil feathers. Our first discovery was to answer the question, ‘Will we ever know the colour of dinosaurs?’. In 2010, we were able to announce the first objective evidence for colour in a dinosaur. Using ultrastructural studies of fossil feathers, we identified melanosomes for the first time in dinosaur feathers, and these demonstrated that Sinosauropteryx had ginger and white rings down its tail. Studies of other dinosaurs identified patterns of black, white, grey, brown, and ginger. This is part of a new wave in Palaeobiology where we apply objective approaches to provide testable hypotheses, once thought impossible in the historical sciences.

Benton, M.J., Dhouailly, D., Jiang, B.Y., and McNamara, M. 2019. The early origin of feathers. Trends in Ecology & Evolution 34, 856-869 (doi: 10.1016/j.tree.2019.04.018).

https://dinocolour.blogs.bristol.ac.uk/

https://dinosaurs.blogs.bristol.ac.uk/

How to cite: Benton, M.: The evolution of feathers, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-574, https://doi.org/10.5194/egusphere-egu21-574, 2021.

During the late Miocene, meridional sea surface temperature gradients, deep ocean circulation patterns, and continental configurations evolved to a state similar to modern day. Deep-sea benthic foraminiferal stable oxygen (δ¹⁸O) and carbon (δ¹³C) isotope stratigraphy remains a fundamental tool for providing accurate chronologies and global correlations, both of which can be used to assess late Miocene climate dynamics. Until recently, late Miocene benthic δ¹⁸O and δ¹³C stratigraphies remained poorly constrained, due to relatively poor global high-resolution data coverage.

Here, I present ongoing work that uses high-resolution deep-sea foraminiferal stable isotope records to improve late Miocene (chrono)stratigraphy. Although challenges remain, the coverage of late Miocene benthic δ¹⁸O and δ¹³C stratigraphies has drastically improved in recent years, with high-resolution records now available across the Atlantic and Pacific Oceans. The recovery of these deep-sea records, including the first astronomically tuned, deep-sea integrated magneto-chemostratigraphy, has also helped to improve the late Miocene geological timescale. Finally, I will briefly touch upon how our understanding of late Miocene climate evolution has improved, based on the high-resolution deep-sea archives that are now available.

How to cite: Drury, A. J., Westerhold, T., Hodell, D. A., Lyle, M., John, C. M., Shevenell, A. E., Röhl, U., and Wilkens, R.: Deep-sea panoramas: Progress and remaining challenges in late Miocene stratigraphy and climate, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11904, https://doi.org/10.5194/egusphere-egu21-11904, 2021.

It is challenging to compare Recent or Holocene accumulation rates of shallow-marine carbonates with accumulation rates interpreted from the fossil sedimentary record. Today, a single coral branch can grow up to 10 cm/year, and vertical accumulation rates may reach 1.4 cm/year if the ecological conditions are favorable for the carbonate-producing organisms and if there is space to accommodate the sediment. However, due to common reworking and transport by waves and currents, and because of potential subaerial exposure, the time-distribution within the sedimentary record is highly irregular.

In ancient carbonate sequences, this time-distribution is difficult to evaluate, and a time-resolution as high as possible has to be sought for. Identification of the record of orbital cycles (Milankovitch cycles) is the best way to obtain a relatively narrow time-window, which in the best case corresponds to the 20-kyr precession cycle. During green-house conditions, orbitally-induced climate cycles translated into more or less symmetrical sea-level cycles, which at least partly controlled sediment production and accumulation. This allows for a sequence-stratigraphic subdivision of each individual depositional sequence. Thus, a time-frame is given for the interpretation of facies evolution and sedimentary structures within such a sequence.

Based on this hypothesis, two examples are presented, both from the Swiss and French Jura Mountains. A 2-m thick (decompacted) Oxfordian sequence displays carbonate-dominated transgressive deposits followed by marl-dominated highstand deposits. The sequence took 20 kyr to build, but sediment accumulation was episodically interrupted by storm events, and a hardground formed during maximum flooding. The maximum rate of sea-level rise is estimated at 30 cm/kyr (which is ten times slower that today’s sea-level rise). The second example is of Berriasian age and shows a 45-cm thick bed of beachrock composed of slabs of oolite. The bed overlies tidal-flat deposits and is capped by a 4-cm thick calcrete crust, over which follows a polymictic conglomerate. According to the cyclostratigraphic analysis, this sequence represents 100 kyr. Ooid production and beachrock formation can happen within a few 100 to a few 1000 years, and the formation of the calcrete took a few 1000 years more. The rest of the time available thus is represented by the transgressive surface at the base of the sequence, by subaerial exposure, and especially by the conglomerate composed of different facies that formed, were cemented, and then were reworked during several 20-kyr cycles.

The conclusion is that, by careful analysis of ancient shallow-marine carbonate sequences and within a cyclostratigraphic framework, depositional processes may be reconstructed and compared with processes that can be observed and quantified in the Holocene and today, and this at comparable time-scales. Thus, a dynamic and realistic picture of the ancient depositional systems is offered.  

How to cite: Strasser, A.: Coral meets Milankovitch – or: time-distribution in shallow-marine carbonate sequences , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1766, https://doi.org/10.5194/egusphere-egu21-1766, 2021.

Geochemical records from incremental carbonate archives, such as fossil mollusk shells, contain information on climate and environmental change at the resolution of days to decades (e.g. Schöne and Gillikin, 2013; Ivany, 2012). These high-resolution paleoclimate data, providing snapshots of past climate change on a human scale, complement more conventional reconstructions on a geological timescale of thousands to millions of years. Recent innovations in geochemical techniques such as high-resolution trace element and clumped isotope analyses provide the unique potential to improve the accuracy and resolution of these high-resolution climate reconstructions in the near future (see e.g. de Winter et al., 2020a; b; Caldarescu et al., 2021). However, to be able to make the most out of these new techniques requires a more detailed understanding of the timing and mechanisms of mollusk shell growth as well as the relationship between environment and shell chemistry on daily to weekly timescales.

The UNBIAS (UNravelling BIvAlve Shell chemistry) project combines investigations on lab-grown modern bivalve shells with reconstructions based on fossil shell material from past greenhouse periods in an attempt to improve our understanding of short-term temperature variability in warm climates. Samples from cultured shells labeled with a novel trace element spiking method are used to calibrate accurate temperature reconstructions from bivalve shells using the state-of-the-art clumped isotope method. As a result, we present a temperature calibration of clumped isotope measurements on aragonitic shell carbonates. New statistical routines are developed to accurately date microsamples within shells relative to the seasonal cycle (ShellChron; de Winter, 2020) and to strategically combine these microsamples for seasonal reconstructions of temperature and salinity from fossil shells (seasonalclumped, de Winter et al., 2020c; de Winter, 2021). We present the first results of this integrated seasonal reconstruction approach on fossil bivalve shells from the Pliocene Warm Period and Late Cretaceous greenhouse of northwestern Europe as well as an outlook on future plans within the UNBIAS project.

References

Caldarescu, D. E. et al. Geochimica et Cosmochimica Acta 294, 174–191 (2021).

de Winter, N. J. ShellChron v0.2.8: Builds Chronologies from Oxygen Isotope Profiles in Shells. (2020).

de Winter, N. J. seasonalclumped v0.3.2: Toolbox for Seasonal Temperature Reconstructions using Clumped Isotope Analyses. (2021).

de Winter, N. J. et al. Paleoceanography and Paleoclimatology 35, e2019PA003723 (2020a).

de Winter, N. J. et al. Nature Communications in Earth and Environment (in review; 2020b) doi:10.21203/rs.3.rs-39203/v2.

de Winter, N., Agterhuis, T. & Ziegler, M. Climate of the Past Discussions 1–52 (2020c) doi:https://doi.org/10.5194/cp-2020-118.

Ivany, L. C. The Paleontological Society Papers 18, 133–166 (2012).

Schöne, B. R. & Gillikin, D. P. Palaeogeography, Palaeoclimatology, Palaeoecology 373, 1–5 (2013).

How to cite: de Winter, N., Witbaard, R., Müller, I., Kocken, I., Agterhuis, T., Boer, W., de Nooijer, L., Reichart, G.-J., Wacker, U., Fiebig, J., Goolaerts, S., and Ziegler, M.: Advances in high-resolution paleoclimate reconstructions using growth experiments, age modelling and clumped isotope analyses, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6120, https://doi.org/10.5194/egusphere-egu21-6120, 2021.