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Article 76, paragraph 4 a)
For the purposes of this Convention, the coastal
State shall establish the outer edge of the
continental margin wherever the margin extends
beyond 200 nautical miles from the baselines from
which the breadth of the territorial sea is
measured, by either
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Article 76, paragraph 4 a)
(i) a line delineated in accordance with
paragraph 7 by reference to the outermost fixed
points at each of which the thickness of
sedimentary rocks is at least 1 per cent of the
shortest distance from such point to the foot of
the continental slope or
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Determination of the outer edge of the
continental margin by sediment thickness
Baseline
Continental margin
Foot of slope
Sediments
1 of distance
to foot of slope
Crystalline continental crust
Oceanic crust
Nautical mile( M )
100
200
300
400
0
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STATEMENT OF UNDERSTANDING CONCERNING A SPECIFIC
METHOD TO BE USED IN ESTABLISHING THE OUTER EDGE
OF THE CONTINENTAL MARGIN
Final Act of third UN Conference- Annex II
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Final Act - Annex II
A request from the Third Conference to the CLCS
to let itself be governed by a set of special
rules for the coastal States in the southern part
of the Bay of Bengal. These rules aim to
compensate for the exceptional shape and sediment
distribution of the continental margin in this
region.
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Final Act - Annex II (continued)
The essence of these special rules is that
paragraph 4 (a) (i) and (ii) of article 76 is
replaced by a provision that the outer edge of
the continental margin may be established by
straight lines not exceeding 60 nautical miles
connecting fixed points at which the sediment
thickness is not less than 1 kilometre.
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Application of Gardiner Rule
A coastal State that intends to apply this
provision will have to document the position of
the foot of the continental slope and the
thickness of sediments in a seaward direction
from it. CLCS/11, paragraph 8.1.4
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Application of Gardiner Rule (cont)
Implementation of provision involves -
identification of the sediment/basement
interface - the calculation of sediment
thickness - identifying the variability of
sediment distribution CLCS/11, paragraph
8.1.4
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Definition of sediment thickness
The sediment thickness at any location on the
continental margin is the vertical distance from
the sea floor to the top of the basement at the
base of the sediments, regardless of the slope of
the sea floor or the slope of the top basement
surface. CLCS/11, paragraph 8.1.8
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Definition of sediments
.... The sediments may comprise a pre-rift and a
syn-rift sequence overlaid by a post-rift
sediment wedge (fig. 8.1). If syn-rift or
pre-rift sediments are preserved below the
post-rift unconformity, these may be included in
the sediment thickness estimation. CLCS/11,
paragraph 8.2.16
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Definition of sediments (continued)
CLCS/11, Fig. 8.1
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Definition of sediments (continued)
The sediments may include interbedded volcanic
material like volcaniclastics deposits and
lavas. See CLCS/11, paragraphs 8.1.6, 8.2.18
8.4.3
Fig. 10
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Relevant geophysical data
Primary data - Seismic reflection data
(multi-channel superior) - Seismic
refraction/wide angle reflection data - Well
data Complementary data - Gravity field data -
Magnetic field data
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Well data sources

• Petroleum industry exploration wells, especially
  deep water wells
• Wells from the Deep Sea Drilling Program
• Wells from the Ocean Drilling Program

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Depth conversion
The estimation of sediment thickness requires
the depth conversion of the interpreted profiles
and maps. This depth conversion of the
geophysical data should be documented by the
relevant database and the description of the
method applied. CLCS/11, paragraph 8.3.1 Depth
conversion of seismic data requires velocity data
to build a velocity model for the sediment wedge.
Such velocity models describe the vertical and/or
lateral variation in seismic propagation
velocities within the sedimentary
sequences. CLCS/11, paragraph 8.3.9
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Minimum requirements

• Document required sediment thickness at fixed
  points at a maximum spacing of 60 M
• For each fixed point, document the geological
  interpretation and present both the original and
  the interpreted data
• For each fixed point, document the method for
  depth conversion and the parameters involved
• Document the expected ranges of error

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Selection of fixed points

• The coastal State may choose the outermost
  location where the required sediment thickness
  occur within and below the same continuous
  sedimentary apron, irrespective of lateral
  variations in sediment thickness
• Document the continuity between the sediments at
  those points and the sediments at the foot of the
  continental slope
• (see CLCS/11, paragraph 8.5.3)