Aftermath of the Sampling Party

With the aim to decide the next steps of core analysis, today we compared the cores, discuss possible transgressive sequences, and where the base of the mud depocenter is located in the Guadalquivir area of the Gulf of Cadiz. 

At first glance higher magnetic susceptibility intensities might correlate to strong reflectors within the seismic data.  When overlaying the magnetic susceptibility values versus depth over the corresponding depths on the seismio-acoustic profiles, some of the stronger reflectors did match with either a drastic increase or decrease in magnetic susceptibility intensity.  Sometimes no distinguishable reflectors matched a varying intensity.  While sampling and knowing these correlations, we would check to see if there was a visual change in the sediment lithology at those certain intervals.  Sometimes there was a definite erosional boundary between two horizons of different lithological facies, or a distinct shell and sand accumulation layer just at the level of such reflector.  Other times there was no visual indicator of any facies changes. 

This figure depicts the magnetic susceptibility intensities and induction-derived porosity associated with a core that seems to be very typical of a mud depocenter in the northern Gulf of Cadiz.  As one can see, sometimes spikes in magnetic susceptibility correlate with major reflectors in the seismic profile and other times they don’t.

 

These photos are associated to the core location where the seismic profile above was run. The first photo on the left shows the uppermost 71cm below seabed. The next three photos depict the next underlying 100cm each. The fifth photo on the right depicts the deepest 70cm of the core. The top 5cm brown mud is the very soft modern sediment surface. From about 5 to 30cm, the greyish brown depicts high bioturbation and a single burrow. From 30 to 452cm, the rest of the core, has very little visual changes with some bioturbation and shell fragments within. This is how a typical core from the mud depocenter looks like.

The next big step is to XRF scan the cores for elemental distributions that will in a first approach be used to support the high resolution core correlation depicted from the magnetic susceptibility curves. I shall have to wait till Monday to even get started on the scanning process.

In the meantime, I am using the visualization software IHS Kingdom Software to match major internal reflectors from one to the other core location.  By doing this, I expect to view the same element intensity spikes in different cores that contain the same internal reflector.  These elemental distribution patterns will also help clarify the original source of sediment in the different areas.  The sediment on the continental shelf in the northern Gulf of Cadiz is produced from mainly fluvial input with shelf currents dispersing sediment and determining deposition location.  For the most part, each river has its own type of sedimentary and geochemical signature because each river drains through different geologic provinces.  

Radiocarbon dating is also another major reason to correlate these horizons with each other.  If we know for certain that one horizon is the same in two different cores, then we would only have to send in one sample for dating purposes. Radiocarbon dating is a method that uses organisms made of carbon.  The best samples for this dating process are hundreds of foraminifera (picked with a needle under a microscope), in situ preserved bivalves or gastropods, or delicate preserved shell fragments.  If a shell is more robust or already weathered physically or biologically, it may have been reworked from an older horizon.  If we radiocarbon dated these shells, the age would be older than the true age of the deposited formation.  I am expecting the mud within the depocenter to have deposited during the Holocene.  

Beside these scientific analysis, it really does amaze me how small this world is.  I met a fellow grad student today that is Brazilian even though his heritage is Italian. MARUM has a diverse pool of international students and faculty. It also just so happens that at one point he visited Akron, Ohio (of all places); where I lived for four years. 

Living in a foreign country without knowing their language and customs can be a bit challenging, though most people in Germany speak English pretty well (this comment was added by my advisor who tries to give me a feeling that the people in many other regions of our “small” world do not speak English at all, not even few words… smiley).  I learn something new every day.  Today’s lesson was that even if the tram is completely full, you can still hear a pin drop.  I once ate crackers on the way to the University and I could not tell why everyone was staring at me.  Apparently, for the most part, all major meals are sit-down proper meals.  I rarely see someone eating while walking or during their daily commute.  

Side Note: I’m getting better at ordering food on my own. smiley

German word of the day: Acknowledgement of Receipt = Empfangsbestätigung.  I keep getting asked if I want a receipt, but I never know what the cashier is talking about. sad

Prost from across the pond,

Mary Lee