Paleoceanographic environment in Gyangzê, South Tibet during the Jurassic-Cretaceous boundary interval

doi:10.13745/j.esf.sf.2019.8.24

Abstract

Abstract:

In order to investigate the evolution of marine sedimentary environments during the Jurassic-Cretaceous transition in the Gyangzê area, South Tibet, we collected samples from the Jiabulagou section, and performed major, trace and rare earth element analysis. The discrimination diagrams (Fe₂O₃+MgO vs. TiO₂ or Al₂O₃/SiO₂) showed that, from the Late Jurassic Weimei Formation to the Early Cretaceous Jiabula Formation, the tectonic setting in the study area is mainly oceanic island arc. The index elements of Mn, Fe, V, Co, Ni and REE, and U/Th, V/Cr, Sr/Ba, La_n/Yb_n and V/(V+Ni) ratios showed that the deposition conditions evolved from the Weimei Formation environment, characterized by shallow sea, oxygen-enriched, high-salt and high deposition rate, to the Early Cretaceous Jiabula Formation environment, featuring deep sea, water stratification and decreasing sedimentation rate, with obvious characteristics of deep sea sedimentary environment. The geochemical data were consistent with tectonic discrimination diagram, i.e., shallow sea facies sediment, indicated by sandstone in the Weimei Formation, and siltstone in the lower and calcareous mudstone in the upper Jiabula Formation, experienced water changes from shallow to deep.

Key words: Jurassic-Cretaceous boundary, geochemical characteristics, paleoceanographic environment, Gyangzê aera, South Tibet

CLC Number:

GAO Lianfeng, LI Puzhuang, ZHANG Zhenguo, WAN Xiaoqiao, XIA Shiqiang, DONG Guiyu, WANG Zhaosheng, LENG Chunpeng, ZHANG Ying, YAO Jiming, ZHANG Linting, YU Jiangtao, YIN Shiyan. Paleoceanographic environment in Gyangzê, South Tibet during the Jurassic-Cretaceous boundary interval[J]. Earth Science Frontiers, 2020, 27(4): 272-281.

Figures/Tables 9

References 46

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样号	w_B/%
样号	SiO₂	Al₂O₃	Fe₂O₃	MgO	CaO	Na₂O	K₂O	MnO	TiO₂	P₂O₅	FeO	LOI
1	57.77	19.39	7.40	0.793	0.405	0.520	4.07	0.005	1.03	0.158	0.71	7.62
2	62.05	15.14	9.79	1.090	0.578	0.354	2.55	0.021	1.05	0.145	1.75	6.57
3	66.65	13.97	7.53	0.951	0.492	0.404	2.31	0.016	1.08	0.123	1.90	6.15
4	64.06	16.27	7.20	0.953	0.609	0.442	2.84	0.011	1.11	0.125	1.25	6.05
5	63.02	16.04	7.71	1.021	0.452	0.411	2.81	0.008	1.21	0.144	1.91	6.85
6	60.76	16.64	9.24	1.081	0.598	0.477	2.62	0.041	1.05	0.135	2.50	6.61
7	62.08	15.28	9.98	0.882	0.473	0.424	2.52	0.011	1.13	0.131	1.75	6.61
8	57.01	18.85	9.43	1.240	0.705	0.548	3.07	0.025	1.12	0.160	2.25	7.23
9	59.19	18.33	8.51	1.231	0.707	0.685	3.10	0.053	1.21	0.140	1.90	6.53
10	57.28	22.01	5.81	0.668	0.450	0.920	3.99	0.009	1.06	0.081	1.00	7.18
11	60.85	16.84	8.81	1.091	0.630	0.654	2.78	0.068	1.18	0.125	2.00	6.68
12	57.46	19.27	8.41	1.051	0.515	0.808	2.96	0.016	1.23	0.166	1.75	7.72
13	63.41	16.73	7.87	1.210	0.501	0.716	2.50	0.016	1.12	0.136	4.45	5.53
14	58.78	18.08	8.89	0.899	0.489	0.713	2.91	0.025	1.22	0.165	1.85	7.60
15	57.48	19.05	8.16	1.061	0.526	0.746	3.16	0.016	1.23	0.188	2.30	7.91
16	57.93	18.80	8.52	1.261	0.580	0.787	3.04	0.029	1.19	0.169	2.95	7.24
17	62.39	14.15	9.51	1.601	2.010	0.639	1.81	0.025	1.18	0.134	6.35	6.35

样号	w_B/%
样号	SiO₂	Al₂O₃	Fe₂O₃	MgO	CaO	Na₂O	K₂O	MnO	TiO₂	P₂O₅	FeO	LOI
1	57.77	19.39	7.40	0.793	0.405	0.520	4.07	0.005	1.03	0.158	0.71	7.62
2	62.05	15.14	9.79	1.090	0.578	0.354	2.55	0.021	1.05	0.145	1.75	6.57
3	66.65	13.97	7.53	0.951	0.492	0.404	2.31	0.016	1.08	0.123	1.90	6.15
4	64.06	16.27	7.20	0.953	0.609	0.442	2.84	0.011	1.11	0.125	1.25	6.05
5	63.02	16.04	7.71	1.021	0.452	0.411	2.81	0.008	1.21	0.144	1.91	6.85
6	60.76	16.64	9.24	1.081	0.598	0.477	2.62	0.041	1.05	0.135	2.50	6.61
7	62.08	15.28	9.98	0.882	0.473	0.424	2.52	0.011	1.13	0.131	1.75	6.61
8	57.01	18.85	9.43	1.240	0.705	0.548	3.07	0.025	1.12	0.160	2.25	7.23
9	59.19	18.33	8.51	1.231	0.707	0.685	3.10	0.053	1.21	0.140	1.90	6.53
10	57.28	22.01	5.81	0.668	0.450	0.920	3.99	0.009	1.06	0.081	1.00	7.18
11	60.85	16.84	8.81	1.091	0.630	0.654	2.78	0.068	1.18	0.125	2.00	6.68
12	57.46	19.27	8.41	1.051	0.515	0.808	2.96	0.016	1.23	0.166	1.75	7.72
13	63.41	16.73	7.87	1.210	0.501	0.716	2.50	0.016	1.12	0.136	4.45	5.53
14	58.78	18.08	8.89	0.899	0.489	0.713	2.91	0.025	1.22	0.165	1.85	7.60
15	57.48	19.05	8.16	1.061	0.526	0.746	3.16	0.016	1.23	0.188	2.30	7.91
16	57.93	18.80	8.52	1.261	0.580	0.787	3.04	0.029	1.19	0.169	2.95	7.24
17	62.39	14.15	9.51	1.601	2.010	0.639	1.81	0.025	1.18	0.134	6.35	6.35

地层	参数类型	w_B/%
地层	参数类型	SiO₂	Al₂O₃	TiO₂	Fe₂O₃	FeO	MnO	CaO	Na₂O	K₂O	P₂O₅	MgO
维美组 J₃w	最高值	66.65	19.39	1.21	9.98	2.50	0.053	0.707	0.685	4.07	0.160	1.240
	最低值	57.01	13.97	1.03	7.20	0.71	0.005	0.405	0.354	2.31	0.123	0.793
	平均值	61.40	16.66	1.11	8.53	1.77	0.021	0.577	0.474	2.877	0.140	1.027
甲不拉组 K₁j	最高值	63.41	22.01	1.23	9.51	6.35	0.068	2.010	0.920	3.99	0.188	1.601
	最低值	57.28	14.15	1.06	5.81	1.00	0.009	0.450	0.639	1.81	0.081	0.668
	平均值	59.45	18.12	1.176	8.25	2.83	0.026	0.713	0.748	2.894	0.146	1.105

地层	参数类型	w_B/%
地层	参数类型	SiO₂	Al₂O₃	TiO₂	Fe₂O₃	FeO	MnO	CaO	Na₂O	K₂O	P₂O₅	MgO
维美组 J₃w	最高值	66.65	19.39	1.21	9.98	2.50	0.053	0.707	0.685	4.07	0.160	1.240
	最低值	57.01	13.97	1.03	7.20	0.71	0.005	0.405	0.354	2.31	0.123	0.793
	平均值	61.40	16.66	1.11	8.53	1.77	0.021	0.577	0.474	2.877	0.140	1.027
甲不拉组 K₁j	最高值	63.41	22.01	1.23	9.51	6.35	0.068	2.010	0.920	3.99	0.188	1.601
	最低值	57.28	14.15	1.06	5.81	1.00	0.009	0.450	0.639	1.81	0.081	0.668
	平均值	59.45	18.12	1.176	8.25	2.83	0.026	0.713	0.748	2.894	0.146	1.105

样号	w_B/10^-6
样号	Sc	V	Cr	Mo	Ni	Co	Cu	Zn	Rb	Sr	Ba	Hf	Th	U
1	18.5	253	127	0.559	14.6	2.76	24.1	61.5	164	123	1 205	7.02	25.4	2.77
2	15.9	183	89.5	0.996	40.8	16.5	28.5	117	92.5	84.0	845	5.53	22.8	2.33
3	13.2	153	77.1	0.818	32.7	11.9	19.0	180	87.6	84.9	753	5.70	20.8	2.17
4	14.5	168	86.5	0.598	40.6	14.2	21.5	120	106	97.3	849	6.01	24.2	2.39
5	15.9	190	92.9	0.419	26.6	6.93	18.1	92.2	106	98.0	853	5.12	20.1	2.15
6	18.0	201	98.2	0.716	39.3	16.1	27.8	133	98.5	98.4	891	5.88	24.1	2.65
7	16.0	111	83.6	0.811	38.4	19.9	22.6	92.7	90.6	83.8	708	5.04	19.8	2.04
8	19.3	216	105	0.567	46.0	18.1	35.6	140	119	108	931	6.28	23.2	2.74
9	18.2	198	98.0	0.881	48.3	21.4	47.3	135	116	106	1 010	5.63	24.1	2.96
10	20.4	151	115	0.696	18.2	8.42	48.5	64.7	166	118	1 364	6.03	27.4	3.59
11	18.6	190	94.4	0.554	30.8	10.0	46.5	144	108	97.7	963	5.73	21.7	2.75
12	18.7	215	107	0.821	32.5	8.90	36.6	111	115	104	940	5.78	25.0	2.85
13	16.2	210	102	0.746	42.1	10.4	40.7	133	95.1	82.6	862	6.09	23.5	2.90
14	19.4	221	110	0.942	38.1	24.0	34.9	120	122	97.4	1 028	6.21	25.3	3.00
15	19.4	208	111	0.583	38.3	11.9	28.5	118	126	106	1 035	6.26	24.1	3.12
16	18.5	142	107	0.768	37.4	11.7	32.3	118	118	92.4	978	5.59	24.3	2.72
17	13.9	101	81.4	0.501	33.2	11.5	20.6	117	71.1	74.5	542	5.56	20.7	2.19