Does correlation necessarily imply causation? In scientific research, it is common to fit correlation coefficients or goodness-of-fit (R²) values to explore causal relationships. However, these factors might merely represent "geological survivors."

         For instance, in archaeological studies (the following example is exaggerated to illustrate the core argument):

        (1) An extraterrestrial scholar visiting Earth observes that ancient human structures are typically located in remote mountainous areas, while modern buildings dominate plains. Through big data analysis, they hypothesize that ancient humans inhabited mountains and modern humans live in plains.

        (2) During an expedition to Mount Everest, they discover human waste and remains along the trail but none in inland plains, concluding that ancient humans inhabited high-altitude regions. This hypothesis is further "validated" by inferring that these areas were unsuitable for modern humans due to climate change, implying ancient climates were warmer and Earth is cooling.

        (3) Geochemical analyses reveal abundant organic matter and positive carbon isotope excursions, "confirming" global cooling.

        This reasoning chain, while seemingly logical, is absurd.

         In geology, similar mathematical correlations are often erroneously elevated to causal relationships. Examples include:

        (1) In black shales, total organic carbon (TOC) content often correlates positively with volcanic ash interlayer density. Scholars propose volcanic activity enhanced productivity (Frogner et al., 2001; Lin et al., 2011; Zhao et al., 2019; Liu et al., 2022; Xie et al., 2023). Volcanic ash promoted siliceous/calcareous organisms like graptolites and algae (Wang et al., 2022). Volcanism could induce water column anoxia (Walker-Trivett et al., 2024), boosting productivity and organic preservation.

        (2) Many supergiant sedimentary deposits (e.g., Mn, P, barite ores) co-occur with organic-rich shales (Fan et al., 1998; Qin et al., 2009; Li et al., 2022). This association is attributed to organic matter adsorbing metals (e.g., uranium) and clay minerals sequestering carbon (Murray & Jagoutz, 2023).

        (3) Gravity flows and volcaniclastic deposits are common in shales. The Pingliang Formation and Beiguoshan Formation in southern Ordos exhibit gravity flows and tuffaceous layers (Wang et al., 2015); the Wufeng-Longmaxi Formation in Upper Yangtze contains gravity flows (Wang et al., 2023) and bentonite (Xie et al., 2023). Similar features occur in Triassic Feixianguan and Xujiahe formations in Sichuan Basin. Consequently, gravity flows are deemed "major geological events" driving shale formation.

        What underlies these phenomena? Shales record paleoenvironmental/paleogeographic information, with potential causal links to mineralization and geological processes. However, black shales not only preserve these records but also concentrate organic matter. Analyzing shale depositional environments and organic enrichment patterns, particularly in black shales, aids in mineral exploration and reinterpreting "major events."

        By studying modern carbon sequestration and paleogeography, this paper examines Wufeng-Longmaxi black shale environments and elemental correlations, proposing the "geological survivorship effect." Confined water bodies act as preservation sites for organic matter, minerals, and deposits (e.g., gravity flows), with surviving elements/phenomena persisting in geological records (Fig. 1). Open environments fail to concentrate elements due to dilution/degradation. Confinement refers to both morphological enclosure and limited area—large lakes like Xingkai fail to accumulate organic matter (surface TOC: 0.5%), while small Xiao Xingkai Lake (TOC: 10%) succeeds. Similarly, Fuxian Lake (TOC: 2%) contrasts with neighboring Xingyun Lake (TOC: 20%). Basin margins in Songliao Basin's Yingcheng Formation accumulate organics in restricted settings, unlike central areas. Thus, Sichuan Basin's Wufeng-Longmaxi shales formed in cold-humid, transgressive lagoonal settings, with climate and water confinement being primary controls. Organic-rich shales and associated elements lack direct causation, exemplifying survivorship bias.

Fig. 1 Divergence in organic enrichment between confined and open environments.

         This perspective offers new insights into shale organic enrichment. A case study:

         The Late Ordovician Wufeng-Longmaxi black shales in Sichuan Basin contain abundant bentonite bands correlated with TOC. The underlying Katian Baota Formation (limestone) lacks such features. Some attribute this to volcanism boosting productivity during warmer Hirnantian transgressions. However, the Katian Baota Formation formed in open marine settings, preventing preservation despite potential volcanism. Meanwhile, Ordos Basin's Beiguoshan Formation records gravity flows and volcaniclastics in warm-climate mudstones, yet lacks organic enrichment. Thus, the absence of volcaniclastic records in Sichuan's Katian does not imply global volcanic quiescence, nor does bentonite presence in Hirnantian indicate heightened activity—a manifestation of the geological survivorship effect (no record ≠ non-occurrence).

        Full paper available on CNKI (DOI: 10.3975/cagsb.2024.111511):

        On Geological Survivorship Effect: A Case Study of Wufeng-Longmaxi Shale Depositional Environments in the Upper Yangtze Region

        [Link: https://link.cnki.net/urlid/11.3474.p.20241115.1126.004]

Fig. 2 Conceptual model of geological survivorship effect, showing TOC enrichment near continents in confined settings versus low TOC in open oceans. Similar patterns occur in mineralization. Recent pelagic studies (e.g., Wang et al., 2024) report 0.5% TOC in 7,223 m-deep Mariana Trench sediments.

References

[1] Zhao W., Wang X., Hu S., et al., 2019. Hydrocarbon generation characteristics of Proterozoic source rocks in China. Science China Earth Sciences, 6: 26 (in Chinese). [赵文智,王晓梅,胡素云,等.中国元古宇烃源岩成烃特征及勘探前景[J].中国科学：地球科学, 2019(6):26.]

[2] Liu Q., Li P., Jin Z., et al., 2022. Organic matter enrichment and hydrocarbon accumulation in lacustrine shales. Science China Earth Sciences, 002: 052 (in Chinese). [刘全有,李鹏,金之钧,等.湖相泥页岩层系富有机质形成与烃类富集--以长7为例[J].中国科学：地球科学, 2022(002):052.]

[3] Xie H., Liang C., Wu J., et al., 2023. Impacts of volcanism on paleoenvironment and organic enrichment. Journal of Palaeogeography, 25(4): 449-462 (in Chinese).[谢浩然, 梁超， 吴靖, 籍士超. 火山活动对沉积古环境及有机质富集的影响[J]. 古地理学报，2023,25(4)]

[4] Li Z., Qin M., Liu X., et al., 2022. Characteristics and significance of element-enriched black shales. World Nuclear Geoscience, 39(1): 14-26 (in Chinese).[李治兴, 秦明宽, 刘鑫扬, 等, 2022. 黑色岩系多元素富集层特征､成因和研究意义[J]. 世界核地质科学, 39(1): 14-26.]

[5] Wang H., Liu D., Wei Y., et al., 2022. Advances in marine shale gas enrichment theory. Coal Geology & Exploration, 50(3): 69−81 (in Chinese).[王红岩, 刘德勋, 蔚远江, 等, 2022. 大面积高丰度海相页岩气富集理论及地质评价技术进展与应用[J]. 煤田地质与勘探,50(3): 69−81.]

[6] Wang H., Yi L., Deng X., et al., 2024. Provenance and carbon sequestration in Mariana Trench sediments. Acta Geologica Sinica, 98(11): 1-15 (in Chinese). [王海峰,易亮,邓希光,等,  2024. 马里亚纳海沟挑战者深渊南坡JL7KBC03短柱样硅质软泥沉积的物源、沉积环境和碳储库效应. 地质学报，2024, 98(11).]

[7] Murray J., Jagoutz O., 2023. Ophiolite weathering and organic carbon preservation. Nature Geoscience. https://doi.org/10.1038/s41561-023-01342-9.

[8] Wang Z., Zhou H., Wang X., et al., 2015. Ordovician events in Ordos Basin. Acta Geologica Sinica, 89(11): 1987-2001 (in Chinese). [王振涛, 周洪瑞, 王训练, 等, 2015.鄂尔多斯盆地西､南缘奥陶纪地质事件群耦合作用[J].地质学报, 89(11): 1987-2001]

[9] Frogner P., Gíslason S.R., Óskarsson N., 2001. Fertilizing potential of volcanic ash. Geology, 29(6): 487-490.

[10] Walker-Trivett C.A., Kender S., Bogus K.A., et al., 2024. Kerguelen volcanism triggering Oceanic Anoxic Event 2. Nature Communications, 15: 5124.

[11] Mao Xiaoping, Chen Xiurong. 2024. The Survivor Effect of Geoscience: A Case Study of the Shale Sedimentary Environment of the Wufeng–Longmaxi Formation in the Middle–Upper Yangtze Region. Acta Geoscientica Sinica, 1-17. https://link.cnki.net/urlid/11.3474.p.20241115.1126.004

College of Energy Resources, China University of Geosciences (Beijing)

Mao Xiaoping | +86 13911360200 | WeChat: 13911360200

Beijing, December 3, 2024