The Gamma-ray (GR) and paleomagnetic data from the MZK2813 core in the Qaidam Basin, Northern Tibetan Plateau

Lithologies of the 200-m long core were first described and logged following standard procedures in core logging . The continuous GR data were measured using JHQ-2D logging tool based on JSS-3 gamma logging specification through pipes, with sampling resolution of 1 cm. Cubic non-magnetic boxes (2 cm × 2 cm × 2 cm) were inserted into split core sections parallel to the borehole's vertical axis, with depth and top orientation recorded, yielding 400 samples from a 200 m core (one sample per 0.5 m interval) for magnetostratigraphic dating. All samples underwent stepwise alternating field (AF) demagnetization (17 steps total: 2.5 mT increments below 30 mT, 5–10 mT increments above 80 mT). Remanent magnetization was measured using a 2G 755R cryogenic superconducting magnetometer in a magnetically shielded room (<150 nT background field) at the Institute of Earth Environment, Chinese Academy of Sciences (Xi’an), with a measurement range of 2.0×10⁻¹² to 2.0×10⁻⁴ A·m² and sensitivity of 2.0×10⁻¹² A·m².In most cases, the characteristic remanent magnetization (ChRM) was identified after removing magnetization components below 7.5 mT. Principal component analysis (PCA) using PaleoMag software was employed to determine the ChRM vector from at least four points of the stable high-temperature component. Samples with maximum angular deviation (MAD) greater than 15° or those exhibiting uncertain or irregularly jumping ChRM directions were excluded. A total of 316 samples successfully passed through this screening procedure and used to construct the paleomagnetic pole sequence.

本次研究首先依据岩心录井（core logging）标准流程，对总长200米的岩心开展岩性描述与录井工作。基于JSS-3伽马测井规范，采用JHQ-2D测井仪通过套管采集连续自然伽马（Gamma Ray, GR）数据，采样分辨率达1厘米。将2 cm×2 cm×2 cm的立方非磁性盒平行于钻孔垂直轴插入劈开的岩心段中，记录采样深度与顶面方位，最终从200米岩心中获取400份样品（每0.5米间隔采集1份），用于磁性地层定年。所有样品均开展逐步交变场（Alternating Field, AF）退磁处理，共设17个步骤：30 mT以下以2.5 mT为梯度递增，80 mT以上以5~10 mT为梯度递增。在中国科学院地球环境研究所（西安）的磁屏蔽室（背景场<150 nT）中，采用2G 755R型低温超导磁力仪测定剩余磁化强度，该仪器测量范围为2.0×10⁻¹² 至2.0×10⁻⁴ A·m²，灵敏度达2.0×10⁻¹² A·m²。多数情况下，在剔除7.5 mT以下的磁化分量后，即可识别出特征剩磁（Characteristic Remanent Magnetization, ChRM）。采用PaleoMag软件开展主成分分析（Principal Component Analysis, PCA），从稳定高温分量的至少4个数据点中拟合得到ChRM矢量。剔除最大偏角（Maximum Angular Deviation, MAD）大于15°，或特征剩磁方向不确定、呈不规则跳变的样品。最终共有316份样品通过上述筛选流程，用于构建古地磁极序列。