Continent-Ocean Transition or Boundary? Crowd-Sourced Seismic Interpretations of the East-India Passive Margin

On the edge of our continents, oceanic crust meets continental crust. At passive margins, those where there is no active tectonics, subduction or transform faulting, these crustal types are connected as sharp continent-ocean boundaries (COB) or as diffuse continent-ocean transition (COT) zones. Passive margins are hard to explore and consequently relatively little is known about their morphology or the geological processes of their formation. Here we elicit and analyze seismic image interpretations of the passive margin offshore East India conducted by 17 groups of geoscientists to better understand the differences, or lack therein, of COB or COT interpretations of the margin. The group interpretations provide a wide range of margin models, five of which are abrupt COB based and 11 which are diffuse COT based. However, interpretations within the COB set vary in the placement of the boundary line between continental and oceanic crust, the boundary placement lying within the range of interpreted COT zones, with the average COB location falling in the center of the interpreted COT zones. These crowd-sourced results are then compared with 10 published interpretations across the margin, which show COB and COT zones falling in the same area. These findings raise questions as to the real differences in COB and COT models and the geological processes involved in their formation. Considering this, we discuss the implications for passive margin models and the use of Wisdom of Crowds-type approaches in reflecting on both the range of interpretation-based models and in the value of determining average model approaches.

Automated summary

This article analyzes seismic image interpretations of the passive margin offshore East India by 17 groups of geoscientists. The findings show differences in interpreting continent-ocean boundaries and transition zones, but the placement of the boundary line falls within the range of interpreted transition zones. Comparisons with published interpretations also support these findings. These results have implications for passive margin models and the use of Wisdom of Crowds-type approaches.