The second core has been described, acquiring seismic data for site selection.

The official CASEIS Cruise Blog is located here: http://www.ipgp.fr/caseis This official blog is written by my shift-mate Lola Johannes.

We continued working on our two cores today! We are also acquiring seismic data.

• Here are the core sections from our second core layed out prior to being imaged by the MST true color RGB scanner. The uppermost core (section I) is on the left and the lowest core section (section VI) is on the right. This core is 8.63 m in length. The top of the cores are on the far side of the table.

• Here is Quentin #2 beginning to scan one of these core sections.

• The previous shift had successfully completed splitting and describing the core sections from core #2. Our shift then collected U-Channel samples. These are 2 cm by 2 cm samples that run the entire length of the core. These samples will be used by a graduate student (Quentin #2) to analyze the paleomagnetic properties of these cores. These samples will be analyzed at Dr. St-Onge's paleomagnetometry lab. Here is Quentin #1 collecting a U-Channel sample from one of the sections of core CAS16-02PC.

• Here is Quentin #2 cleaning the U-Channel so that we can place a lid on it.

• Finally, we place special "magnetic-property-free" tape (like a birthday gift all wrapped up) on the ends of the U-Channel sample. Then we place these into a "D-Tube" to be shipped to Quebec.

• Shortly after our shift began, the sun rose and we all took a few minutes to embrace the day with the beautiful view. Too many times we do not enjoy this and simply work through it. But today, we took this moment of beauty for ourselves.

• Time for my second sleep (we have two 4 hour shifts) so that I can be well rested for tonight's shift. We will be acquiring two more cores tonight, so will be very busy in the core lab very soon. The cores will be located near the yellow and red dots to the northwest of the green dot labeled 1 in the map below.

Cores are being described now!

The official CASEIS Cruise Blog is located here: http://www.ipgp.fr/caseis This official blog is written by my shift-mate Lola Johannes.

We started describing cores today!

• Here are all but one of the core sections form our first core CAS16-01PC. The top of each core is on the far side of the table and the uppermost section is on the left. The core on the right is more gray and is probably from the Pleistocene, while the more brown cores are from the Holocene. The missing core section (being analyzed) shows the transition between the upper brown/red sediments and the lower gray sediments. These cores are full of turbidites and hemipelagites. For example, on the lowest section, there is a dark section about 40% of the way up from the base that gets lighter in value upwards. There is another example of this about 60% up from the base of this core section. The base of these darker layers are the bases of some turbidites.

• Here Dr. Ratzov is training students how to "log" a core with a core sheet. You met my shift-mates in the last blogpost here.

• Here are two shiftmates from the previous shift finishing up a core description (Kay is on the left, with the lab coat). We can see that it is fun to describe the sediment stratigraphy (while I think it is fun, they were actually smiling because everyone has fun having their photo being taken).

• Here Dr. Beck is training two more of my shift mates on how to prepare a lithostratigraphic log. Julia from a different shift is observing and finds it funny that I keep taking photos of everyone.

• Here my cabin mate Quentin (from Quebec) is describing a core section.

• Here we can join in the pleasure of seeing the first core split and cleaned. After preliminary observations, these cores are quite promising to hold a vast treasure of geological data. I cannot wait until we see the next core!!! And, by the look on Herve's and Nathalie's faces, neither can they!

• Here is a panorama from my cell phone showing the core section (on the left) that I was describing (section IV, the fourth section from the top) and a section that we saw the previous shift describing in the photo above. This photo is distorted, but gives us an idea of what is in the core. The section that I described is the core that does not appear to have as much layering (laminations).

• Here is the lithologic log from my section.

• After the cores equilibrated with the temperature of the MST room, they were analyzed. Then they were cut by a paired saw set up, lengthwise, and split into an archive and a working half. I will post photos of that when we do this during our shift (or if I am awake when someone else does it). But, before we started, we had a fire drill. This took us to plage 6 (deck 6), where we got to watch the streamer in action. I know it is not exciting from this view, but we are collecting seismic data that will be important to interpret the structural geology and relations between the upper plate and megathrust in this location. Below is a photo of Drs. Nathalie Fueillet and Guillaume St-Onge. Nathalie is smiling because she is pleased with our excellent progress. We have collected two great cores (more on that below) and are acquiring high quality seismic data. I will post more on the seismic data once it is analyzed and prepared for (preliminary) presentation.

• After the core is split, the archive half is scanned with a real color (RGB) scanner. Then the MST instrument is reconfigured to collect photospectometry and point magnetic susceptibility data (high resolution mag sus). As I mentioned, I will talk more about the initial full core MST analyses when it happens during my shift (so I can take photos). The photospectrometry allows spectral analyses of the cores. Below is the the configuration showing the spectrometer on the left (beige and tan) and the point mag sensor (the white device) immediately to the right. Not the radioactive sign. That is the 137Cs radiation source used to estimate the down-core density profile. The core moves from the right to the left.

• Here is the computer showing the profile of mag sus and average reflectometry.

• We started by having Georgi train the students on how to describe a core. There are a number of ways to do this and he updated my description so that my description was consistent with others. Here is a photo of Georgi training the students.

We have collected our second core: CAS16-02PC

The official CASEIS Cruise Blog is located here: http://www.ipgp.fr/caseis This official blog is written by my shift-mate Lola Johannes.

Our Second core, CAS16-02PC, arrives on board.

• Today, as I arrived to my shift at 4 AM, Dr. Georgy Ratzov filled Dr. Christian Beck and I in about what we could expect for our shift and what he learned from prior shifts. The second core had just been pulled out of the seafloor and was on its way to the surface, so we had a little time to get ready to process the core. I mentioned the steps in the last blog post here. We would basically prepare, label, and cut the core up to let it sit to later be scanned by the MSCL team.
• Here Dr. Christian Beck awaits the arrival of the core on the ship. He is observing to see if there is sediment on the outside of the core, which would indicate that the core had been embedded in the seafloor. When this core was being pulled out, there was not much tension on the wire (so it was not stuck in the mud with much coupling, unlike the first core).

• Here we can see that the core is on board now. The next step is to rotate the core up to be parallel with the deck and then be placed in the white rollers on the right. Then the core catcher (a device that keeps the sediment in the core when the core is removed from the sea floor) is removed and the white PVC core liner is pulled out of the core barrel.

• Then Dr. Christian Beck (I call him "le chirurgien" (the surgeon) as we cut the liner with a butcher's saw) cuts the top of the core at the top of the sediment. The sediment does not completely fill the liner in most, but not all, cases. Lola Johannes awaits to place a cap on the top of the core.

• Then we clean, dry, and label the core liner. We mark it at 150 cm intervals to guide our surgeon precision cutting. Dr. Beck learned to cut wood from his grandfather who was a carpenter. I get to cut some of the sections and I tell him that it was also my grandfather who was a carpenter as well.

• Here is my entire team. From left to right: Gaelle, Lola Johannes, Chloe Seibert, Marie, Quentin, Christian Beck, and me (Jason Patton) behind the lens. We are cutting the last cut of this core, but not the final cut (which Dr. Beck remarked about the last Pink Floyd album.

• Here is the last section of this core, at the base of the core. These are the typical labels on the side of the core and the end caps. We will then move these core sections into the MST lab to acclimate to the temperature of the instrument

• Here the cores are lined up to be scanned for their geophysical properties.

• This plot of the CHIRP seismic data show the basin in which this second core was collected. There is a pencil line showing the location of the core. The vertical axis is in meters (and is approximate because the depth is calculated with an assumed velocity, which is unknown). We think that the core bottomed out in the dark reflector just above the 5820 depth line (representing a layer with an increased impedance compared to the overlying layer, possibly a thick clay unit).

• In summary, here is a map showing our first two core sites. Our Port of Call, Pointe-a-Pitre is shown on the Island of Guadeloupe (PTP). The two cores are the blue dots labeled 1 and 2. The other dots are potential core locations, with color designating the priority.

Our first core: CAS16-01PC

The official CASEIS Cruise Blog is located here: http://www.ipgp.fr/caseis This official blog is written by my shift-mate Lola Johannes.

The first series of business today was the safety meeting. Safety First! We watched a presentation, went to try on the survival suits, and then learned how to get into the survival boats.



• Then we toured the bridge and Nathalie and Guillaume got a chance to sit in the Captain's chairs.


• Here is the inside of the survival boat, which is stocked with water and food I probably cannot eat, along with a large supply of lovely smelling diesel (which will keep us alive, so I would not complain about it)

• Here is Lulu editing the multibeam data. I introduced myself and told her I have done this too. Later we met and talked more. I learned some French from her. Basically, we use sonar to estimate the depth of the seafloor assuming something about the velocity of sound in water. We use sound velocity profiles to correct for this. After the raw data are collected, corrected for the ship's position and movement, they need to be edited to remove outliers. This is tedious but very important work.

• Here I am observing them place the core in the water for the first time! There is a piston core and a trigger weight. When the trigger hits the seafloor, the latch that holds the piston corer above the seafloor lets go. There is a weight of about 4,000 kg on the top of the piston core and when it hits the seafloor is pushes in with several hundred thousand foot pounds of force.

• Here is a pano from the fantail.

• Here, the trigger weight is connected to the trigger arm (the white bar angled down away from the main core and weight stand). They are just about to lower this corer into the water. We are all very excited! Captain Phillipe is also here to see that everything goes smoothly. He is very interested in the success for this cruise and the science crew has lots of confidence that he supports our work.

• We were quite successful today! The Calypso piston corer can collect cores with up to three 12 m sections (36 m). We chose to use 1 - 12 m section to begin with. The core deployed efficiently.
• While the core assembly was being prepared, my shift (4-8 PM) prepared the lab to process the cores once they come up to the ship. We constructed core holders to place the cores in when they are (1) being described and (2) sitting around waiting to be analyzed or stored in cardboard in boxes. We did not have enough materials for the core holders, but the ship's crew, the engineers, let us use some wood collected from pallets to construct these important devices.

The general core curation process is as follows (much is similar to how we do this on the cruises that I have participated on (R/V Roger Revelle and R/V Tommy G. Thompson):
1. The liner comes out of the core barrel (the engineers do this).
2. We cut the top of the core close to where the top of the sediment is and cap it.
3. We rinse the core line and dry it off; then label it with markers.
4. We then cut the core in 1.5 m sections, capping the ends as we go.
5. The cores then get stored for 12 hrs to acclimate to the temperature.
6. The core section are then scanned using a multi core sensing logger (MSCL, made by GEOTEK) to collect density, P-wave seismic velocity, resistivity, and loop magnetic susceptibility.
7. The core is then split lengthwise according to the labeling. One side is the archive (A) half and the other side is the work (W) half.
8. The archive half is cleaned and then sent to the MSCL (aka MST, for multi sensor track) to have true color imagery (RGB) collected. The archive half may be stored to do more analysis later (point mag. sus. or X-Ray Fluorescence (XRF) which can tell about the elemental composition of the sediments), before storing in the cardboard boxes.
9. The work half is cleaned and then described using lithologic and biologic observations (aka the lithologic description). After being described, the work half will have u-channels (2X2 cm samples, the entire length of the core) taken for analysis by Guillaume St-Onge (CT scanning, geomagnetic measurements, etc.)
10. The work half is then sealed in plastic and stored in cardboard boxes for shipping back to the core repository somewhere in France.
• Here is a photo of our discovery of the top of the first core. Nathalie Fueillet is handing off a sample to Cpt. Phillipe. The top of the core is abundant with planktonic Foraminifera. Given that this core was collected at ~5200 m water depth, the previous data about the CCD (Carbonate Compensation Depth) is confirmed (at least so far). This means that this core will have material with which to analyze for radiocarbon age determinations. Note the sediment in the shore core section (this is the sediment from which I observed the Forams.

On way to first coring site CAS16-01PC

The official CASEIS Cruise Blog is located here: http://www.ipgp.fr/caseis This official blog is written by my shift-mate Lola Johannes.

We embarked at about 08:00 on Sunday, 2016/05/29. The team is excited to get to sea, including me.

• Here we can see that the science crew is anticipating a successful cruise. There is a ferry ship passing us on the port side, probably travelling to one of the islands to the south of Guadeloupe.

• Everyone is taking photos of the soon to be far off land and of each other.

• Here is the view from the stern as we left the port of Pointe-a-Pitre. We headed almost due south until we passed the shallow shelf. I could see regions of bright seafloor pass beneath the ship, so the water was quite clear and shallow.

• Here is a map that shows some targeted core sites. The green dots are the better choices and red are lower priority for various reasons (source isolation from land or other core site sediment sources, geomorphology, etc.). The color represents elevation in meters. Underneath the elevation data is a slopeshade map, with dark shades representing steeper slopes and lighter values representing shallower slopes. I prefer slopeshades over hillshades because hillshade maps are biased relative to the orientation of the artificial sunlight. The port of Pointe-a-Pitre is shown as a white dot and labeled "PTP."
• In a few hours we will arrive at the green dot labeled "1" and take our first core. This core will be a short core because we want to test our ability to sample the sediment without damaging the coring equipment. The coring engineers here are some of the best in the world and we have the longest piston coring device in the world. Each core section is 12 meters and the longest configuration is with 3 sections. If the sediment is too stiff, the core barrels can be bent and twisted. This happened when this "calypso" corer was used in Sumatra. So, we will first collect a 1 section core (12 m).
• Then we will wait 12 hours before we can analyze the core for the sediment to equalize in temperature. While we wait, we will conduct some geophysical exploration (multibeam sonar bathymetry, CHIRP seismic, and streamer seismic). After that, we will head for the green core labeled "2" and collect our second core. It is possible we will collect a longer core. Then more geophysical exploration. At some point, we will collect geophysical data in the deep part of the map, the subduction zone trench and collect cores, one of which is labeled "3."

• As with all coring cruises, the plans will change with our experience. I will update the core locations as we collect them and create new maps showing our intended regions of exploration.

The night before

The official CASEIS Cruise Blog is located here: http://www.ipgp.fr/caseis This official blog is written by my shift-mate Lola Johannes.

Today we had our first cruise meeting. Nathalie Fueillet (the Principal Investigator for this cruise) told us in French what our shifts were and the general plan for the next few days to a week. Frederica translated for me (thanks Fred). This ship runs on two four hour shifts for most scientists (except Hervé, the post doc, who has a 12 hour shift). 12 hour shifts are long, but not as long as a 24 hour shift (which was my shift on my Sumatra cruise in 2007). I told Hervé to look at the positive that 12 i much less than 24... So, I am lucky to have two 4 hour shifts, 4-8 AM and 4-8 PM. I am on the coring team. The cruise also has a blog and I will post links to their posts as we go along.

We went out for our last night on the town before the cruise. We saw some great karaoke at this place near the marina in Pointe-a-Pitre. This was where all the locals come to to party. I ordered some wine and later some french fries. The waiter (owner) said "french fries" and I said for the dumb American. He laughed and gave me a 'local' style fist bump (I have been watching him do it with his friends). Here is a photo of him wishing us a farewell. The guy to the right of Guillaume St-Onge is the owner. Other cruise participants, including Nathalie Fueillet (turquoise shirt), are in the photo too.

Here is a photo of the ship the night before we head for our first coring site tomorrow. I will post a map tomorrow of where we are going. We will collect a core, conduct some geophysical investigations (shallow and deep seismic, multibeam bathymetry), then collect more cores, rinse and repeat.

Lesser Antilles Historic Seismicity

Here is an earthquake history poster for the Lesser Antilles volcanic arc. I queried the USGS website for earthquakes of magnitude M ≥ 6.0 from Jan. 1900 through May 2016.

I include some inset figures.
• In the upper left corner I include a plate tectonic map from Pindell and Kennan (2009).
• In the upper right corner I include a figure from Fueillet et al. (2011) that shows felt regions of the two largest historic earthquakes associated with the subduction zone. These earthquakes are pre-instrumental, so the estimates of size are based upon observations of intensity.
• In the lower left corner is a figure from Hough (2013) that shows the felt reports from the Feb. 8, 1843 earthquake.

The Lesser Antilles subduction zone has a short record of earthquakes and there is little known about the prehistoric record of earthquakes. Given a record of a few hundred years, and that subduction zone earthquakes typically have recurrence intervals spanning this long to thousands of years, it is important to develop a prehistoric record of earthquakes spanning multiple earthquake cycles. Given that there appear to be cycles of cycles (a.k.a. supercycles, Sieh et al., 2008), this paleoearthquake record needs to span many many earthquake cycles. How long is long enough? Nobody knows because (1) not many fault systems have been studied like this and (2) nobody has observed subduction zones for this long (tens of thousands of years).

Hough (2013) presented an analysis of felt reports for the 1843 earthquake. This earthquake was probably on the subduction zone fault, but we do not really know since it happened before we had seismometers that would allow us to locate the earthquake. Hough (2013) suggests that the pre-1900 record of historical earthquakes is under-reported and magnitudes are under-estimated. Hough uses felt records to suggest that prior estimates of the magnitude for the 1843 earthquake were too small. Macroseismic effects from the earthquake were used to estimate a magnitude of M 7.5-8 (Bernard and Lambert, 1988). Feuillet et al., (2011) reconsiders the intensities of this event. Feuillet et al. (2011) focus on accounts from the Lesser Antilles and their estimated magnitude is M = 8.5, with an estimated rupture length of 300 km. Hough uses felt reports and compares these records with other subduction zone earthquakes. Below is a plot showing her comparisons. I include the figure caption below the figure as a blockquote.

Intensities versus distance. Intensity values for (red circles) the 8 February 1843 Lesser Antilles earthquake, (gray circles) the 2011 Tohoku-Oki earthquake, and (black circles) the 2010 Maule, Chile earthquake . Values are plotted versus epicentral distance, for the 1843 earthquake assumed to be 17.5 N, 60.5 W; the precise assumed epicenter is in question but does not significantly change the data points at regional distances.

Feuillet et al (2002) suggest that there is oblique convergence that leads to strain/slip partitioning. They place a forearc sliver fault along the volcanic arc (where the islands are). This figure below shows this shear couple across the subduction zone. I include their figure caption below the figure as a blockquote.

Tectonic model of the Lesser Antilles Arc. 500 m bathymetric contours are from Smith and Sandwell [1997]. Structural interpretation of accretionary prism is based on analysis of bathymetric and topographic contour patterns. Black arrows along the trench: NAM/CAR boundary-parallel slip with rates indicated [DeMets et al., 2000]. Large white arrows: NAM/CAR and SAM/CAR motion vectors from DeMets et al. [2000] and Weber et al. [2001], respectively. NAM/CAR GPS relative motion vectors measured at Aves and Sainte Croix are indicated [DeMets et al., 2000]. Black double arrows, local direction of extension deduced from fault geometry and distribution. Half black arrows, slip on oblique or strike slip faults. 1, in light gray, zone of sinistral extensional shear; 2-transition zone; 3-in dark grey, zone of dextral oblique thrusting. White large half arrows indicate sinistral and dextral motion along the trench, respectively.

Pichot et al. (2012) study the fracture zones as expressed by the Barracuda and Tiburon Ridges. These are somewhat related to some fracture zones that extend from the Mid Atlantic Ridge. These structures may be responsible for segmentation of the subduction zone (earthquakes or volcanism). This is one of the hypotheses that will be tested by conducting this marine paleoseismology research. The Tiburon rise does cause a major inflection of the subduction zone fault, so it is reasonable to think that this may cause segmented rupture along the megathrust. Below are three figures. First is a map that shows bathymetry and gravity data for the region between the Lesser Antilles and the Mid Atlantic Ridge (Pichot et al., 2012). The lower figure pair shows (a) these ridges as they relate to bathymetry and faults in the accretionary prism and (b) these structures as expressed as gravity anomalies (Pichot 2012). Below each figure I include their figure caption as a blockquote.

The Atlantic Ocean between 2°N and 22°N. A) 1×1 min-Satellite free air gravity map (V18.1 fromSandwell and Smith, 2009),with,NAm, NorthAmerica Plate; Car, Caribbean Plate; SAm, South America Plate; Afr, Africa Plate; MAR, Mid-Atlantic-Ridge; AR, Aves Ridge; LA, Lesser Antilles; TB, Tiburon Rise; BR, Barracuda Ridge; RT, Royal Trough; RR, Researcher Ridge; Caribbean structural geology after Pindell and Kennan (2009).B) Bathymetric map (Smith and Sandwell, 1997) with, BAP, Barbados Ridge accretionary prism; ORS, Orinoco river system; ADSF,Amazon Deep Sea Fan, DAP, Demerara abyssal plain.C) Regionalmap showing Atlantic Ocean and the study area in red box. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fold axes (folds) and overlap (thrusts) (black line) parallel to the front of accretion. In continuation of wrinkles Barracuda and Tiburon, their axes are a sub-parallel towards the axis of wrinkles

Wrinkles Barracuda, Tiburon and Saint Lucia's characterized by gravimetric anomalies to the positive open. Wrinkles Barracuda and Tiburon are limited respectively to the north and south by the graves of Barracuda and Tiburon. The front of the accretion prism is represented by the black line with triangles. The free air gravity anomaly map is from Sandwell and Smith (2009).

References:
• Bernard, P. and Lambert, J., 1988. Subduction and seismic hazard in the northern Lesser Antilles: Revision of historical seismicity, Bull. Seismol. Soc. Am. v. 78, p. 1965–1983
• Feuillet, N., Manighetti, I., and Tapponier, P., 2002. Arc parallel extension and localization of volcanic complexes in Guadeloupe, Lesser Antilles in Journal of Geophysical Research, v., 107, DOI:10.1029/2001JB000308
• Feuillet, N., Beauducel, F., Tapponnier, P., 2011. Tectonic context of moderate to large historical earthquakes in the Lesser Antilles and mechanical coupling with volcanoes in Journal of Geophysical Research, v. 116, DOI:10.1029/2011JB008443.
• Hough, S., 2013. Missing great earthquakes in Journal of Geophysical Research: Solid Earth, v. 118, p. 1098-1108.
• Pichot, J., 2012. The Barracuda Ridge and Tiburon Rise, East of the Lesser Antilles: origin, evolution and geodynamic implications. [Ph.D. Thesis] l’Université de Bretagne Occidentale 286 pp.
• Pichot, T., Patriar, M., Westbrook, G.K., Nalpas, T., Gutscher M.A., Roest, W.R., Deville, E., Moulin, M., Aslanian, D., and Rabineau, M., 2012. The Cenozoic tectonostratigraphic evolution of the Barracuda Ridge and Tiburon Rise, at the western end of the North America-South America plate boundary zone in Marine Geology, v. 303-306, p. 154-171
• Pindell, J.L. and Kennan, L., 2009. Tectonic Evolution of the Gulf of Mexico, Caribbean and northern South America in the mantle reference fram: an update, in James, K., Antonieta-Lorente, M., and Pindell, J.L., (eds), The geology and evolution of the region between North and South America, Geological Society of London Special Publication.

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