SSP
Stratigraphy, Sedimentology and Palaeontology

Stratigraphy, Sedimentology and Palaeontology

Ocean drilling: 50 years of explorations

After 50 years of ocean explorations, scientists continue to rely on cored material from beneath the ocean floor. The material recovered during oceanographic expeditions constitutes, in fact, a great archive where to look for answers to unravel the Earth’s system history. Over the last decades, subsequent scientific ocean drilling programs (Deep Sea Drilling Project, Ocean Drilling Program, and Integrated Ocean Drilling Program) allowed to gain precious records which have provided information about Earth’s dynamic nature including ocean circulation, climate change, ocean basin formation as well as evolution and adaptation of oceanic life forms. The integration of the dataset deriving from offshore sites with available information obtained from onshore sedimentary successions, constitutes the base for improving the Geological Time Scale and for a better understanding of the physical, chemical and biological processes controlling the formation and distribution of sediments and sedimentary rocks. For this reason, the ocean drilling is never stopping:  the ongoing program “Exploring the Earth under the sea of the International Ocean Discovery Program (IODP), continues to provide scientists with deep-time archive to be studied (http://www.iodp.org).

                                                    Joides resolution (from www.iodp.org)

The topics related to the IODP include climate and ocean change, biodiversity and origin of life, the Earth in motion, and the Earth structure and dynamics in relation with its surface environment. Following the variety of topics addressed, the oceanographic expeditions require, first, specialists of different disciplines on board. Eight IODP expeditions were conducted in 2017 for more than 60 scientists from different countries involved on board. It is, therefore, a fascinating opportunity for experts and young career scientists to participate to an expedition.

 

Scheduled expeditions for 2018 (from www.iodp.org)

In Europe, the European Consortium for Ocean Research Drilling (ECORD) unites 15 countries (14 European countries and Canada) and provides mission-specific platforms for IODP expeditions. Three Platform Providers conduct IODP expeditions: U.S.A. and Japan operate deep-sea drillships with the JOIDES Resolution and Chikyu respectively. ECORD is responsible for funding and implementing mission-specific platform (MSP) expeditions. Cored material is available for all scientist and there are three IODP core repositories located in Germany (IODP Bremen Core Repository), College Station, Texas (IODP Gulf Coast Repository), and Kochi, Japan. Scientists may visit any one of the facilities for onsite research or request samples for analysis purposes. Archived cores include not only IODP samples, but also those retrieved in the two older IODP legacy programs (DSDP and ODP).

IODP Bremen core repository (from www.marum.de)

If you are a scientist from ECORD member countries willing to participate to one expedition, you should check the ECORD website (http://www.ecord.org ) where open calls and related information about how to participate to an IODP expedition are provided.

Otherwise, do not miss to visit the ECORD booth at EGU 2018 this year! There will also be dedicated IODP-ICDP sessions to celebrate 50 years of successful explorations as for example EOS18 “ECORD IODP Outreach: Past, Present and Future”, US4 “Fifty years of International Ocean Drilling”, and SSP1.2. “Achievements and perspectives in scientific ocean and continental drilling” which will constitute good opportunities to acquire information on previous and new expeditions as well as to get in touch with other scientists!

So…never stop exploring!

SSP blog goes live!

SSP blog goes live!

We are delighted to officially launch the blog of the Stratigraphy, Sedimentology and Palaeontology (SSP) division of the EGU! Our community is broad and interdisciplinary, and we hope to establish a platform for sharing up-to-date information on SSP related topics such as (but not limited to):

  • Latest news, publications and reviews in SSP academic and applied research;
  • Recent development in analytical and technological approaches and modelling;
  • Field trips, workshops, conferences, and meetings.

This is a blog from and for the SSP community and we welcome contributions from students, early and senior professionals of the field. For further information on how to get involved please contact our SSP ECS Representative Alena Ebinghaus (aebinghaus@abdn.ac.uk).

Best wishes, and enjoy following us!

Stéphane, Guilhem, Cinzia, Chris and Alena

Xenoconformity! Welcome to the new-born in the stratigraphy family

Xenoconformity! Welcome to the new-born in the stratigraphy family

Every geologist has heard at least once in his career the term unconformity and all its different flavours (e.g. disconformity, paraconformity, angular unconformity, etc…). These terms are part of the basic learning in geology, often taught during first year classes in Stratigraphy. Well, it seems we’ll have to add one term in these lectures: Xenoconformity!

In a recently published paper, Carroll1 discusses some peculiar stratigraphic surfaces that do not fit into the available stratigraphic lexicon, namely those associated with conformable non-Waltherian facies changes…

…“Sorry… What the heck are you just talking about?!!…”.

Ok, let’s summarize that. The term conformable refers to a stratigraphic surface, i.e. a surface separating two distinct beds, that do not show any sign of hiatus, meaning that the two successive beds were deposited on top of each other without any significant time span or tectonic activity in between them. The barbaric “Non-Waltherian facies change” calls upon your sedimentological background and the well-known Walther Law. This latter stipulates that those facies that were once laterally adjacent (i.e. referring to change of space at a given time) are ideally recorded continuously in vertical sedimentary successions (i.e. referring to change of time at a given point of space). Any vertical change that deviate from this hints at a “non-Waltherian” facies change, implying that something odd, such as a time gap for instance, is occurring within the sedimentary record. These are mostly unconformity surfaces.

Yet, what happens when sedimentary systems abruptly change due to geologically instantaneous environmental change? If there’s no erosion or time gap associated with this event in the stratigraphic record (i.e. it is not recorded by an unconformity surface), how do we call it? A xenoconformity! Before Carroll’s paper, all the available stratigraphic terms required either a temporal discontinuity, adherence to Walther’s law, or both. As such, none was strictly applicable to these peculiar surfaces, hence the significant leap forward.

An example? Have a look at this lowermost Toarcian surface from the deep-water setting in the Central High Atlas of Morocco. It marks the transition from limestone-marl alternations to a purely siliciclastic (clay-dominated, with several occurrences of siltstone beds) sequence. It is the deep-water record of the regional demise of the Pliensbachian neritic carbonate factory, following a major environmental upheaval that took place at the stage boundary2. During the Jurassic, there was no significant pelagic carbonate factory. So almost all deep-water carbonate muds were ultimately sourced from the export of shallow-water benthic carbonates. If there’s no neritic carbonate factory anymore, there’s no more carbonate mud to be exported. Throughout Morocco, the Pliensbachian-Toarcian boundary event resulted also in a complete reorganisation of the sedimentary dynamic: On the one hand, during the Pliensbachian, there were thriving carbonate platforms all around the High Atlas basins. On the other hand, during the Toarcian, a siliciclastic sedimentary system developed as a result from the accompanying climatic switch, from arid to humid conditions. A typical non-Waltherian facies change. Moreover, there is no sedimentological or biostratigraphic evidence for a hiatus associated with this surface. There you go; you’re seeing your first xenoconformity!

Picture caption: Pliensbachian-Toarcian (Lower Jurassic) transition close to Amellago (Central High Atlas, Morocco). Limestone-marl alternations are abruptly followed by a clay-dominated sequence, without any evidence for a hiatus in between the two. The resulting surface (red arrow) is a xenoconformity. See Bodin et al.2 for more details on the environmental events occurring at this stage boundary.

 

There’s still a lot of time ahead before this new term becomes of common usage by the stratigraphers in peculiar, and the geological community in general, but let’s face it: it elegantly fills a gap in our stratigraphic lexicon applicable to a domain, rapid geological/environmental changes, that is the focus of much studies. Hence, xenoconformities formalise in stratigraphic term the sedimentary record of so-called environmental “tipping points”.

 

1 Carroll A.R. (2017). Xenoconformities and the stratigraphic record of paleoenvironmental change. Geology 45 (7), 639–642.

2 Bodin S., Krencker F.-N., Kothe T., Hoffmann R., Mattioli E., Heimhofer U., Kabiri, L. (2016). Perturbation of the carbon cycle during the late Pliensbachian – Early Toarcian: New insight from high-resolution carbon isotope records in Morocco. Journal of African Earth Sciences 116, 89–104.