From the Wallace Line to the Lupar Line, basin and province limits and the quasi-linear features that define them are a function of our always-incomplete knowledge. We tend to forget that in our daily work but the authors have repeatedly run into the issue preparing a series of articles in SEAPEX Press. As we reviewed and updated a 2006 regional exploration study of the South China Sea basins and adjacent regions, incorporating nearly two decades of new material in the source study, we gained a new appreciation for geologists who named these features.

When comparing published maps of various vintages to our latest compilations of potential field data, we noted variations in well-known features. This variation is common as interpretations develop - see Eagles et al., 2015 compilations of global COB lines, particularly their Fig 9, South China Sea; and for the West Baram -Tinjar line, Cullen, 2014. Our own work developed accuracy as our archive of images broadened, allowing for separation of geo-cartoons or rough illustrations from the careful depictions of geology. We improved selected material with higher-resolution re-scans and more accurate georeferencing tools. We found drafting errors including scale changes at country boundaries; misalignment of lat-long tics versus cultural data; mislabeling of coordinates, well & field names; and typos everywhere. We noticed where “lines” were located at data or map edges and often failed the good-match eyeball test against maps of adjacent areas. At this point, we were doing the 80% of work that produced 20% of our nuggets (the Reverse 80:20 Rule) but as Jess Kozman would say, you need clean data to make progress.

We then compared the cleaned-up maps and profiles to correlative features on our early 2023 gravity and mag imagery, applying structural geologic principles to the revealed sedimentary/crustal architectures. Our Figure 1 illustrates a mismatch between Savva, 2014 and our gravity expressions of the West Baram Line (WBL). Note also distinct orientations of Layang Layang (ENE) and Tepat (NW) features within the SW-trending Borneo Trough.

In summary, problems often stemmed from the application of ‘lineament thinking’ to the real world. “Line” terminology in Borneo, for example, has been applied to multiple features, reflecting attempts to integrate something that is inherently static (an alignment) into a highly dynamic tectonic history. The “lines” often are given to a geographic distribution of parameters that may be extensional or inverted with related pressure transitions, plus variability in time and kinematic function. We provide examples with reasons for our adjustments (or acceptances of) a range of geologic lines and invite discussion on how closely we have approached “truth.”