The OAE1b Record In The Terrestrial Sediments: Evidence From The Geochemistry Of Blackshales In The Liupanshan Group And Its Paleoclimatic Implications

The oceanic anoxic event (OAE) was coined by Schlanger and Jenkyns more than 30 years ago, explaining the Cretaceous black shale in the Pacific Ocean. Then the OAEs have been broadly researched and found that it might be the common phenomena in the ancient sea. However, those researchments mostly come from marine sediments but lack of continent record, which restrict the recognization of the global carbon cycle and climate change. The Cretaceous continental sediments are widely well exposed in the northwest of China. The Early Cretaceous Liupanshan Group is one of which is precisely constrained by magnetostratigraphy. This dissertation aims to deciphering the OAEs records in the terrestrial sediments by measuring the lithogeochemistry and isotope geochemistry of blackshales in the Liupanshan Group. This is important to understand the globle carbon cycle, climate change and continent-sea- atmosphere interaction when the OAEs happened.Analysis on the variation of element content of the black shale segment and comparison to the average shales shows that, the shales in the Liupanshan Group enrich in the content of MgO, CaO and Na2O, with SiO2/Al2O3 ratio averaged of 3.58. It also enrich in the S, As, Bi, Cr, Cs, Mo, Ni, Sr, U and W, with averaged Sr/Ba of 0.93, Sr/Cu of 26.06, w (V)/w (V+Ni) of 0.83,5U of 1.11 and w(Ce)/w(La) of 2.58. All these suggest that the black shale formed in freshwater and anoxic environment, and the climate is dry and hot.The measurement of the TOC, CaCO3,δ13Ccarb,δ18Ocarb andδ13Corg show that the black shales are rich in organic and poor in CaCO3. The variation ofδ13Ccarb is almostly in concert withδ13Corg. The carbon isotope curve can be divided into 12 stages (C1-C12), with four evident negative carbon isotope excursions of C3, C5, C10 and C12. The feature of carbon isotope exhibits that the organic carbon in the shales of the Liupanshan Group derived from the input of terrestrial plants or/and aquatic planktonic plants, while the carbon in the CaCO3 is from of the atmosphere CO2 and the decomposement of the organic materials.The variation of the black shale geochemistry of the Liupanshan group is consistent with the typical black shale of ocean anoxic setting. The assembledge of the black shales in the Liupanshan Group is similar to the black shale in the Vocontian Basin of SE France, both of them have significant negative excursions. The four excursions together with preservation of the shales in the middle segment of the Liupanshan Group probably indicate that they are respond to the OAElb, which the negative carbon excursions of C3, C5, C10 and C12 is well correlated to OAE1b Jacob, Kilian, Paquier and Leenhardt event in the Vocontian Basin of SE France. This suggests that the OAE1b is of globle significance.