Abstract The Great Amazon Reef System is a living biogenic mesophotic reef ecosystem that has been recently described along the shelf break of Brazil. An exploration mission was carried out in 2019 along the outer edge of the French Guiana Shelf. A side-scan sonar survey was conducted to locate reef outcrops and allowed twelve in situ 80 to 120 m depth dives and sampling of the reef rocks and peripheral sands. The majority of the hard-rocks are composed of biological concretions. However several fragments revealed the inside presence of sandstone clasts. These clasts, more or less enveloped by biogenic coatings, probably represent destroyed clasts of underlying or neighboring beachrock banks. Their dominant cement is micritic (high-magnesian calcite); the intergranular or extragranular porous field was later filled with low-magnesian sparry calcite. The sand or gravel that accumulated near the barrier mainly consist of the blunt debris of coastal fauna and flora associated with different carbonate or ferruginous neoformed ooids. At 104 m depth, ooids extracted from Dive 11 samples dated from the start of MIS2 (27,370 cal yr BP) and attest to the presence of a significant coastal accumulation. At this same site, cementing did not take place until about 3,500 years later (23,990 cal yr BP). The cement of a nearby beachrock indicates a much more recent age (16,170 cal yr BP). Lastly, the age of 4,100 year BP measured on the barnacles attached to the top of the reef attests to the late Holocene reef's biological activity.
Submap (www.submap.fr) is a web-tool for generating maps and cross-sections, and for displaying datasets of subduction zone areas. Maps and (cross-)sections rely on the (Py)GMT library and global geophysical databases. Submap is also a mean for sharing our own Submap database, which compiles data on subduction kinematics, on the characteristics of the convergent plates and on their geometry, as well as on the seismogenic characteristics of the subduction interface along 260 transects evenly distributed across all active oceanic subduction zones. What makes this tool so special is that one can access over 200 tectonic parameters for every transect with a single click. , as new studies are produced by the Submap team or by the wider community. The idea of developing such a tool arose from the subduction zone comparative study carried out by Arnauld Heuret during his PhD thesis in 2005. In a first version (2009), we proposed an aid to the rapid creation of MAPS and SECTIONS using global databases (topo-bathymetry, gravimetry, age of the seafloor, seismicity) using the GMT library in a way that was transparent to the user via a query page. We then added the possibility to extract a number of characteristic parameters for the 260 transects composing the Submap database (module Sub-DATA in 2013). This database has grown over years, incorporating, for instance, new parameters describing the seismogenic zone after we published a global study on this . In 2023, we decided to fully redesign the web-tool. A major effort has been made to facilitate the use on all types of screens (computers, tablets). We enhanced the range and the rendering of documents made available for download, and the tool was made accessible to all audiences. In terms of content, a new module called MAP-Subquake now allows to plot the rupture envelopes for selected subduction earthquakes together with the roughness of the subducting seafloor facing the ruptures. The latter dataset comes from Submap team publications in 2018. Moreover, several parameters were revised or added to the Submap dataset, such as the sediment thickness in the trench or in the subduction channel, and the kinematics. We are currently working on the geometric characteristics of the volcanic arcs and on a better representation of the strain in the upper plate, planning to update the database by the end of the year. Submap is primarily a useful working tool for research on subduction zones, as it lists and displays a vast amount of complementary data in an optimized format that facilitates comparative analysis. It is also a meaningful tool for teaching at secondary and higher-education levels, as a support for courses or as part of tutorials or individual work for high school and university students. It can be used to quickly obtain accurate documents to support workshops, for example to determine the best segmentation criteria in order to define the seismic hazard of a zone, or simply to study the lateral variations of certain parameters of a subduction zone.
Logging data are measurements of physical properties of the formation surrounding a borehole, acquired in situ after completion of coring (wireline logging) or during drilling (Logging-While-Drilling, LWD). The range of data (resistivity, gamma radiation, velocity, density, borehole images,…) in any hole depends on the scientific objectives and operational constraints.
Warmer temperatures and higher sea level than today characterized the Last Interglacial interval [Pleistocene, 128 to 116 thousand years ago (ka)]. This period is a remarkable deep-time analog for temperature and sea-level conditions as projected for 2100 AD, yet there has been no evidence of fossil assemblages in the equatorial Atlantic. Here, we report foraminifer, metazoan (mollusks, bony fish, bryozoans, decapods, and sharks among others), and plant communities of coastal tropical marine and mangrove affinities, dating precisely from a ca. 130 to 115 ka time interval near the Equator, at Kourou, in French Guiana. These communities include ca. 230 recent species, some being endangered today and/or first recorded as fossils. The hyperdiverse Kourou mollusk assemblage suggests stronger affinities between Guianese and Caribbean coastal waters by the Last Interglacial than today, questioning the structuring role of the Amazon Plume on tropical Western Atlantic communities at the time. Grassland-dominated pollen, phytoliths, and charcoals from younger deposits in the same sections attest to a marine retreat and dryer conditions during the onset of the last glacial (ca. 110 to 50 ka), with a savanna-dominated landscape and episodes of fire. Charcoals from the last millennia suggest human presence in a mosaic of modern-like continental habitats. Our results provide key information about the ecology and biogeography of pristine Pleistocene tropical coastal ecosystems, especially relevant regarding the—widely anthropogenic—ongoing global warming.
