Knowledge about long-term variation of the geomagnetic dipole field remains in its nascent stage because of the paucity of reliable experimental data over geological periods. Here, we present the first robust experimental data from the largest Cretaceous flood basalt province on Earth, the ~65–66 Ma Deccan basalt within a thick (1250 m) unbiased stratigraphic section down to the basement, recovered from a drill hole of the Koyna Deep Scientific Drilling Project in the Western Ghats, India. Critical analysis of the result along with similar results of the Cretaceous age find that (i) the dipole moment during the end Cretaceous Deccan eruption is the lowest in whole of Cretaceous (ii) dipole moment at the onset/termination of the Cretaceous Normal Superchron is apparently lower relative to that in mid-superchron, however, such differences cannot be deciphered in shorter polarities probably because of insufficient time to develop recognizable variations (iii) inverse relation between dipole moment and reversal rate is lacking and (iv) a cause and effect relation between core-mantle boundary heat flux and low dipole moment that appears to be the principle governing factor in forming the Large Igneous Provinces on the surface of earth.

由于缺乏地质时期可靠的实验数据，有关地磁偶极子场长期变化的知识仍处于起步阶段。在这里，我们提供了来自地球上最大的白垩纪洪水玄武岩省的第一个可靠的实验数据，它是从科伊纳（Koyna）的一个钻孔中恢复下来的厚（1250 m）无偏地层中至基底的约65–66 Ma Deccan玄武岩印度西高止山脉的深度科学钻探项目。对结果以及与白垩纪年龄类似结果的批判性分析发现：（i）白垩纪末期癸烷喷发期间的偶极矩在整个白垩纪中是最低的（ii）白垩纪正常超旋的开始/终止时的偶极矩为相对于中超同步时期明显更低