Dolomitization in the Lower Cambrian Longwangmiao Formation in northeastern Yunnan: Insights from a simulation study

doi:10.13745/j.esf.sf.2023.2.87

Abstract

Abstract:

The Guixi outcrop is located at the southernmost margin of the Sichuan Basin, northeastern Yunnan. The Longwangmiao Formation in the outcrop experienced strong dolomitization activity and developed widespread micritic limestone, arenaceous limestone, micritic dolomite, dolomitic limestone and calcareous dolomite. The three limestone-transition-dolomite cycles in the outcrop were characterized by presence of large quartz grains, and appeared mostly dark red under cathodoluminescence, with observable gypsum. Geochemical tests showed that the isotopic compositions of limestone-dolomite in cycle 1 were: carbon, -0.78‰--0.49‰, oxygen, -9.28‰--8.96‰, strontium, 0.70979554-0.71218318, calcium, 0.54‰-1.12‰; in cycle 2: carbon, 0.37‰-0.41‰, oxygen, -9.76‰-9.64‰, strontium, 0.71008711-0.71374167, calcium, 0.63‰-0.81‰; and in cycle 3: carbon, -0.03‰-0.23‰, oxygen, -9.90‰--9.24‰, strontium, 0.70990934-0.71237617, calcium, 0.56‰-0.94‰. The strontium and calcium isotope values were obvious low in limestone and high in dolomite. Calcium isotope simulation revealed the Mg²⁺ concentration in dolomitized fluid in cycle 1 was twice the seawater equivalent (105.64 mmol/kg, Mg²⁺/Ca²⁺ = 1.99), in cycle 2 seven times (369.74 mmol/kg, Mg²⁺/Ca²⁺ = 6.79), and in cycle 3 2.3 times (121.48 mmol/kg, Mg²⁺/Ca²⁺ = 2.29). Temperature simulation revealed the temperature of dolomitization fluid was around 30 ℃. The above results indicate dolomitization in the Longwangmiao Formation in northeastern Yunnan was mainly by seepage reflux.

Key words: Northeast Yunnan, Longwangmiao Formation, dolomitization, calcium isotope, fluid temperature simulation, fluid element simulation

CLC Number:

LI Keran, YANG Di, SONG Jinmin, LI Zhiwu, JIN Xin, LIU Fang, YANG Xiong, LIU Shugen, YE Yuehao, FAN Jianping, REN Jiaxin, ZHAO Lingli, XIA Shun, CHEN Wei. Dolomitization in the Lower Cambrian Longwangmiao Formation in northeastern Yunnan: Insights from a simulation study[J]. Earth Science Frontiers, 2024, 31(2): 313-326.

Figures/Tables 11

References 83

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样品号	岩性	旋回	w_B/%
样品号	岩性	旋回	CaO	MgO
hx-3-1B	粉屑泥晶灰岩	1	50.40	3.32
hx-3-2B	粉屑泥晶灰岩		52.83	2.92
hx-4-1B	含灰白云岩		38.27	17.26
hx-4-2B	泥晶-粉晶白云岩		32.43	21.34
hx-5-1B	微晶灰岩	2	51.12	2.54
hx-5-2B	灰质云岩		41.87	9.23
hx-6-1B	泥晶白云岩		31.54	20.03
hx-6-2B	含砂屑泥晶灰岩	3	49.24	3.93
hx-6-3B	白云质灰岩		45.23	10.55
hx-6-4B	泥-粉晶白云岩		30.62	22.63
hx-6-5B	泥-粉晶灰岩		51.27	1.21

样品号	岩性	旋回	w_B/%
样品号	岩性	旋回	CaO	MgO
hx-3-1B	粉屑泥晶灰岩	1	50.40	3.32
hx-3-2B	粉屑泥晶灰岩		52.83	2.92
hx-4-1B	含灰白云岩		38.27	17.26
hx-4-2B	泥晶-粉晶白云岩		32.43	21.34
hx-5-1B	微晶灰岩	2	51.12	2.54
hx-5-2B	灰质云岩		41.87	9.23
hx-6-1B	泥晶白云岩		31.54	20.03
hx-6-2B	含砂屑泥晶灰岩	3	49.24	3.93
hx-6-3B	白云质灰岩		45.23	10.55
hx-6-4B	泥-粉晶白云岩		30.62	22.63
hx-6-5B	泥-粉晶灰岩		51.27	1.21

样品号	岩性	旋回	δ¹³C/‰	δ¹⁸O/‰	⁸⁷Sr/⁸⁶Sr	δ^44/40Ca/‰	Z
hx-3-1B	粉屑泥晶灰岩	1	-0.49	-8.96	0.709 486 69	0.56±0.038	121.83
hx-3-2B	粉屑泥晶灰岩		-0.78	-9.51	0.709 795 54	0.54±0.098	120.96
hx-4-1B	含灰白云岩		-0.54	-8.82	0.713 720 45	0.92±0.072	121.80
hx-4-2B	泥晶-粉晶白云岩		-0.64	-9.28	0.712 183 18	1.12±0.105	121.36
hx-5-1B	微晶灰岩	2	0.412	-9.765	0.710 087 11	0.63±0.053	123.27
hx-5-2B	灰质云岩		0.33	-8.79	0.709 236 59	0.77±0.067	123.59
hx-6-1B	泥晶白云岩		0.37	-9.46	0.713 741 67	0.81±0.075	123.34
hx-6-2B	含砂屑泥晶灰岩	3	-0.03	-9.9	0.709 909 34	0.56±0.093	122.30
hx-6-3B	白云质灰岩		-0.04	-8.69	0.712 437 24	0.47±0.041	122.89
hx-6-4B	泥-粉晶白云岩		0.23	-9.245	0.712 376 17	0.94±0.042	123.16
hx-6-5B	泥-粉晶灰岩		-0.68	-9.55	0.710 639 33	0.59±0.088	121.15

样品号	岩性	旋回	δ¹³C/‰	δ¹⁸O/‰	⁸⁷Sr/⁸⁶Sr	δ^44/40Ca/‰	Z
hx-3-1B	粉屑泥晶灰岩	1	-0.49	-8.96	0.709 486 69	0.56±0.038	121.83
hx-3-2B	粉屑泥晶灰岩		-0.78	-9.51	0.709 795 54	0.54±0.098	120.96
hx-4-1B	含灰白云岩		-0.54	-8.82	0.713 720 45	0.92±0.072	121.80
hx-4-2B	泥晶-粉晶白云岩		-0.64	-9.28	0.712 183 18	1.12±0.105	121.36
hx-5-1B	微晶灰岩	2	0.412	-9.765	0.710 087 11	0.63±0.053	123.27
hx-5-2B	灰质云岩		0.33	-8.79	0.709 236 59	0.77±0.067	123.59
hx-6-1B	泥晶白云岩		0.37	-9.46	0.713 741 67	0.81±0.075	123.34
hx-6-2B	含砂屑泥晶灰岩	3	-0.03	-9.9	0.709 909 34	0.56±0.093	122.30
hx-6-3B	白云质灰岩		-0.04	-8.69	0.712 437 24	0.47±0.041	122.89
hx-6-4B	泥-粉晶白云岩		0.23	-9.245	0.712 376 17	0.94±0.042	123.16
hx-6-5B	泥-粉晶灰岩		-0.68	-9.55	0.710 639 33	0.59±0.088	121.15

样品号		1 000lnδ^44/40Ca_{calcite-dolomite}/‰	Mg/(Mg+Ca)	温度/℃
hx-3-1B	粉屑泥晶灰岩	-0.34	0.06	56.09
hx-3-2B	粉屑泥晶灰岩	-0.36	0.05	61.59
hx-4-1B	含灰白云岩	0.02	0.29	36.71
hx-4-2B	泥晶-粉晶白云岩	0.22	0.37	29.76
hx-5-1B	微晶灰岩	-0.27	0.04	57.35
hx-5-2B	灰质云岩	-0.13	0.07	49.98
hx-6-1B	泥晶白云岩	-0.09	0.07	35.52
hx-6-2B	含砂屑泥晶灰岩	-0.34	0.03	59.40
hx-6-3B	白云质灰岩	-0.2	0.17	34.52
hx-6-4B	泥-粉晶白云岩	0.04	0.34	37.78
hx-6-5B	泥-粉晶灰岩	-0.31	0.02	49.78