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The intensifying oil slicks exert deleterious effects on coral reefs, hence attracting many investigations on coral's tolerance and resilience to anthropogenic oil pollution. We hypothesize that intense seafloor hydrocarbon seepages in the past could also produce oil slicks and subsequently contaminate coral reefs nearby, which may provide clues on their responses to natural oil contamination. Here, a long coral reef core (NK1) drilled in the isolated Meiji Atoll in the southern South China Sea is analyzed for aliphatic hydrocarbons to test this hypothesis. Two depth intervals, centered at 45–65 m and 95–110 m, corresponding to ages of ca. 0.3–0.6 Ma and 1.3–1.5 Ma, respectively, are characterized by geological-configured hydrocarbons indicative of ancient natural oil pollution. Because the Meiji Atoll stands on a volcanic seamount and in isolation in the sea, we deem that natural oils were incorporated into contemporary coral reefs by surface oil slicks, which were derived from hydrocarbon seepages at the seafloor of the adjacent petroliferous basins. The natural hydrocarbon seepages should result from regional tectonic movements that occurred extensively in the middle and late Pleistocene, likely in association with the arc-continent collision in the Taiwan region since 2 Ma. Albeit the two significant contamination events, it appears that they exerted insignificant disturbances on the growth and development of coral reefs, perhaps protected by certain holobiotic oil-degrading bacteria as indicated by excess production of bacterial branched fatty acids during the events. Our study thus suggests a high resilience of coral reefs to oil pollution under natural conditions, which, of course, does not mean that they would survive readily from the abrupt and intense anthropogenic pollution. [Display omitted] • Oil hydrocarbons were incorporated into ancient coral reefs in the southern SCS. • Oil hydrocarbons resulted from natural seafloor seepage due to tectonic activity. • Tectonic seepage events occurred extensively in the middle and late Pleistocene. • Regional tectonic activity was likely related to arc-continent collision in Taiwan. • Coral reefs show a high resilience to oil pollution under natural conditions. [ABSTRACT FROM AUTHOR]

The Shin-Yan-Ny-Hu (SYNH) MVs are typical subaerial mud volcanoes in southwestern Taiwan. The lipid biomarkers and their stable carbon isotopes were firstly examined to delineate the mud breccia sources, depositional environments, thermal maturity, probable source strata and the migration framework of volcanic fluid. The sediment organic matter within active SYNH MVs principally stemmed from the petroleum derivatives, bacteria and terrigenous C 3 plants suggested by the following indicators: the CPI of n -alkanes (∼1); the distribution and δ13C values of saturate, fatty acids and the plot of Pr/ n -C 17 vs. Ph/ n -C 18 ratios. The Pr/Ph ratios, the plot of Pr/ n -C 17 vs. Ph/ n -C 18 and the plot of Pr/Ph vs. O/C 30 Hopane ratios implied that the sediment organic matter was deposited in a marine deltaic sedimentary environment under an oxic depositional environment. The C 30 βα/C 30 αβ, T max , 22 S/(22 S + 22 R) ratios of homohopane (C 31) and bishomohopane (C 32), MPI 1 , MPI 2 , F 1 , F 2 , T max vs. HI and the Pr/ n -C 17 vs. Ph/ n -C 18 ratios revealed that the Type III organic material was early thermal maturity and the burial depth of mud breccia matrix was estimated around 4–5 km bsf. • The organic matter of SYNH MVs was derived from petroleum derivatives, bacteria and terrestrial higher plants. • The mud breccia matrix was deposited in a marine deltaic environment under an oxidized sedimentary environment. • The source organic matter was early thermal maturity, and the burial depth of mud breccia matrix was about 4–5 km bsf [ABSTRACT FROM AUTHOR]