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:

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

Baseline Sediments Nautical mile( M ) Oceanic crust Crystalline continental crust Foot of slope 1 % of distance to foot of slope Determination of the outer edge of the continental margin by sediment thickness Continental margin

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

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.

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.

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

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

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

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

Definition of sediments (continued) CLCS/11, Fig. 8.1

Definition of sediments (continued) The sediments may include interbedded volcanic material like volcaniclastics deposits and lavas. See CLCS/11, paragraphs 8.1.6, & Fig. 10

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

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

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 ”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

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

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)