Introduction

Sediment thickness plays an important role in UNCLOS article 76, since it is used to define the Gardiner formula points. These are points where the thickness of sedimentary rocks is at least 1 per cent of the shortest distance to the foot of the continental slope.

NOAA/NGDC provides a sediment thickness grid of the Worlds Oceans here: http://www.ngdc.noaa.gov/mgg/sedthick/index.html. This dataset is very coarse and will not be accepted by the Commission. It is however a dataset which can provide you with an overview of where you might potentially have enough sediments to use the Gardiner formula.

In this section we will use a sediment thickness grid to identify areas where there might be enough sediments to identify Gardiner points. Then in the next section we will take a closer look at seismic data in order to calculate the sediment thickness more accurately.

Exercises

Sediment Thickness Grid

Exercise

Display Sediment Thickness Grid

In the folder 3. Sediment Data / Grids right click Sediment Thickness and click Map Data
The grid displayed shows thickness in meter and has no reference to depth. Blue is the thickest part while red is the thinnest part.
In 1. Maritime lines / 60M lines display all your Hedberg points.
Try to identify an area where you might have enough sediments.

Calculate 1% distance to FOS

In the next exercises we are going to identify the areas of the grid where the thickness is more than 1% of the distance back to the closest foot of slope point. Geocap can calculate this in one operation taking all FOS points into account.

Exercise

Calculate 1% of the distance to the closest FOS point

In the folder 3. Sediment Data / Grids right click Sediment Thickness and click Generate >1% dist to fos Area
In the menu that pops up, click the Browse icon and browse for the Northern Plateau dataset in the 2. Seabed / Foot of slope / Region Groups folder.
Make sure that Store in project is unchecked.
Click Execute
Click OK to close the menu
The area displayed has a thickness which is more than 1% of the distance back to one or more of the foot of slope points in the Northern Plateau dataset.

In the next section we will take a closer look at the area in the north.

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