Alkenones are biomarkers derived exclusively from species of haptophyte algae. The relative abundance of di- to tri-unsaturated C₃₇ alkenones expressed as U^K'₃₇ is widely applied as a sea surface paleotemperature proxy for Cenozoic marine sediments. However, the absence of alkatrienones prior to the Eocene has precluded application of the U^K'₃₇ proxy for assessment of Cretaceous paleoclimates. Herein, we report a C₄₀ alkatrienone (tetraconta-9E, 16E, 23E-trien-3-one; C_40:3 Et) in deep-sea sediments from southern high latitudes (International Ocean Discovery Program: IODP site U1516). This discovery extends the geologic record of alkatrienones to the late Cenomanian, ∼70 million years earlier than previous reports. The parallel occurrence of higher abundances of a C₄₀ alkadienone (tetraconta-16E, 23E-dien-3-one; C_40:2 Et) allowed calculation of the U^K’₄₀ unsaturation index, comparable to U^K’₃₇. Stratigraphic variations in the δ¹³C of C_40:2 Et revealed an elevated (∼1.5 ‰) positive carbon isotope excursion (CIE) relative to those observed in carbonate from other OAE2 sequences likely reflecting a decrease in global pCO₂. The U^K’₄₀ profile suggests a concurrent drop in sea surface temperature associated with the decline in pCO₂ during the early phase of OAE2. The timing of these environmental perturbations in the southern high latitude of the proto-Indian Ocean suggests they were triggered by volcanism associated with large igneous province (LIP) formation.

烯酮是专门源自触生藻类物种的生物标志物。^{以 U K'} ₃₇表示的二至三不饱和 C ₃₇烯酮的相对丰度被广泛用作新生代海洋沉积物的海面古温度代理。然而，始新世之前不存在链三烯酮，因此无法应用 UK ^' ₃₇代理来评估白垩纪古气候。在此，我们报告了南部高纬度地区深海沉积物中的 C ₄₀链三烯酮（tetraconta-9 E、 16 E、 23 E -trien-3-one；C _40:3 Et）（国际海洋发现计划：IODP 站点 U1516） ）。这一发现将链三烯酮的地质记录延伸至塞诺曼阶晚期，比之前的报道早约 7000 万年。较高丰度的 C ₄₀链二烯酮（tetraconta-16 E、23 E -dien-3-one；C _40:2 Et）的并行出现允许计算 UK ^' ₄₀不饱和指数，与 UK ^' ₃₇相当。_{C 40:2} Et的 δ ¹³ C 的地层变化揭示了相对于其他 OAE2 序列碳酸盐中观察到的正碳同位素偏移 (CIE) 升高 (∼1.5 ‰)，这可能反映了全球p CO ₂的减少。U ^K' ₄₀剖面表明，在 OAE2 早期阶段，海面温度同时下降，与p CO ₂下降有关。原印度洋南部高纬度地区这些环境扰动的发生时间表明，这些环境扰动是由与大型火成岩省（LIP）形成相关的火山活动引发的。