28. GP3501 German Bight Exercise
How I constructed the Maps
Three maps were produced from Seismic lines gathered from the German Bight region of
the North Sea. There were two different kinds of maps produced, the first was a TWT
structure contour map of the Mid-Miocene Unconformity (mMU). This map had contour
thicknesses of 50m and was produced by marking depths e.g. 900, 950, 1000, etc on the
provided grid with all the seismic lines in their relative orientations. This was carried out for
each of the nine seismic lines and contours were created by joining areas of equal height
(Depth ms TWT) on the maps. The location of faults was recorded on the map
The second type of map produced was a TWT thickness map of seismic stratigraphic units 2a
and 2b. A map was produced for each unit and the thicknesses of the units were contoured
across the seismic map grid. The thickness of each stratigraphic unit was recorded at key
thicknesses e.g. 50, 100, 150 ms TWT, etc and this was marked on the grid and then
contours were joined, producing two TWT thickness maps. On these maps, the direction of
progradation was determined and marked as well as faults, including their type and throw.
What I found out from the Maps
The structure contour map of the mMU provided an insight into the nature of the
unconformable surface. The surface appears to be much deeper in the top left of the map
seen on lines GR86-015 and GR86-104 with a maximum depth of 1260 ms TWT. This is
compared to where it is shallower in the bottom right corner of the map seen on lines
GR86-019 and GR86-107 with a minimum depth of 700ms TWT. The map can be split into
two main structures: at the top of the map a synclinal structure plunging towards the top
left of the map, and at the bottom of the map, an anticlinal structural plunging towards the
bottom left of the map. The shallowest and deepest parts of the map are both shaded in
making them easy to identify.
The Unit 2A TWT thickness map illustrates how the thickness of the unit varies across this
area of the German Bight. On GR86-016 at 2700 is where the thickest part of the unit can be
found. It is the thickness between the green-orange reflectors marked on each of the nine
seismic lines. The greatest volume of sediment is located here. Sediment is deposited on the
slope basin wards. It is deposited in forests (clinoforms) which are prograding out in the
basin. The earliest deposits have an inclination of around 12 degrees with reflectors further
up in the succession having a steeper angle of around 25 degrees. The inclination is less than
Unit 2b and this is due to it lying lower in the rock record and having a reduced maximum
thickness of 215 ms TWT, over 100 ms TWT less than Unit 2b. A depocenter is marked on
this map, it is shaded in light blue and represents where the thickness of the unit exceeds
200m ms TWT.
The Unit 2B TWT thickness map shows the thickness of the unit across the German Bight. On
GR86-104 at 3850 is where the thickest part of the Unit 2b can be found. This is observed on
the nine seismic lines by the thickness between the yellow and green horizons. The greatest
volume of sediment is present at this location being 330ms TWT thick. Sediment is
deposited on the slope in forests (clinoforms) which are prograding out into the basin. The
earliest slope deposits are gently sloping at around 15 degrees. Further up in the succession,
as progradation continues the deposits are more steeply inclined up to 45 degrees. So, as
29. progradation continues out into the basin the clinoforms (reflectors) become steeper. They
are much steeper than the Unit 2a clinoforms below. Steeper clinoforms allow for more
sediment to accumulate, so the direction of the steepest reflector will be the direction of
greatest progradation. There are multiple progradation directions as indicated by brown
arrows on the map. I believe the unit 2b structure to represent a prograding delta with delta
lobes representing areas with differing progradation directions.
Basin Architecture
I believe the sedimentary units 2a & 2b represent facies of a prograding delta out into a
sedimentary basin. Their thicknesses vary throughout and the thickest areas represent the
delta front. Other prograding lobes can be identified and represent delta lobes. These can
be observed on the accompanying maps and interpreted seismic lines.
Key for Seismic lines:
Red = Fault with arrows indicating displacement
Blue = Interpretation of internal structure within the units. This colour was used to highlight
the seismic facies for easy identification of offlap, downlap, onlap and clinoforms.
Green = 750 ms TWT on intersection of GR86-017 and GR86-105
Yellow = 535 ms TWT on intersection of GR86-017 and GR86-105
Orange = 800 ms TWT on intersection of GR86-017 and GR86-105
Pink = Mid-Miocene Unconformity 1025 ms TWT on intersection of GR86-017 and GR86-105
Any additional info was annotated on the Seismic lines. There are some vertical
marks/measurements on the seismic lines from calculating thicknesses and depths. These
can be ignored.
