Geochemical Characteristics of Middle Ordovician in Western Margin of Ordos Basin and Its Implication on Paleoenvironment

doi:10.19657/j.geoscience.1000-8527.2020.012

Abstract

Abstract:

Western margin of the Ordos basin is located at the tectonic junction between Eastern and Western China, and its end Ordovician tectonic architectural change has attracted wide research attention. Middle Ordovician carbonate rocks in the Laoshidan profile are selected as the research target here. Through geochemical analysis, we aim to reconstruct the paleoenvironment and explore the various sedimentary and geochemical features that can serve as tectonic indicators. Our results indicate that: (1) Sandaokan and Zhuozishan formations have δ ¹⁸O=-5.2‰ to -8.9‰ (average -7.0‰) and δ¹³C=1.3‰ to -1.8‰ (average -0.1‰). δ¹⁸O values rise from the bottom upward with a slight drop at the top of Zhuozishan Formation,the same trend is present for the δ ¹³C values; (2) Paleotemperature of seawater likely fluctuated during the early period and then decreased from 32.7 ℃ to 15.7 ℃ gradually, whereas the Z values maintain an increasing trend, indicating deepening seawater and increasing salinity; (3) Geochemical proxies of major and trace elements are well consistent and indicate a transgressive sedimentary setting in the Middle Ordovician. The petrographic features reveal that the content of terrigenous clastic minerals in the carbonates decreases gradually from the Sandaokan Formation to the Zhuozishan Formation, reflecting a transition from the restricted platform to open platform environment. Considering also the regional Mid-Ordovician tectonic background, the western margin of Ordos basin may have already been dominated by a foreland basin tectonic system,with gradually increasing influence from the collisional orogeny between the Alxa Block and North China Block. This results in the paleogeomorphologic highs in the northwest and lows in the southeast of the Ordos basin, leading to the K-rich brine accumulation in the latter. We suggest that the secondary sag in southeast part of salt basin is the key exploration target area for marine potash deposits.

Key words: western margin of Ordos basin, Middle Ordovician, stable isotope, normal and trace element, paleoenvironment

CLC Number:

JIANG Suyang, HUANG Wenhui, ZHANG Yongsheng. Geochemical Characteristics of Middle Ordovician in Western Margin of Ordos Basin and Its Implication on Paleoenvironment[J]. Geoscience, 2020, 34(03): 545-553.

Figures/Tables 8

References 33

[1]	杨俊杰. 鄂尔多斯盆地构造演化与油气分布规律[M]. 北京: 石油工业出版社, 2002: 1-38.
[2]	何自新. 鄂尔多斯盆地演化与油气[M]. 北京: 石油工业出版社, 2003: 3-18.
[3]	王振涛, 周洪瑞, 王训练, 等. 鄂尔多斯盆地西缘北部奥陶纪盆地原型:来自贺兰山和桌子山地区奥陶系的沉积响应[J]. 地质论评, 2016,62(4):1041-1061.
[4]	BAI Y L, WANG X M, LIU H Q, et al. Determination of the borderline of the western Ordos basin and its geodynamics background[J]. Acta Geologica Sinica, 2006,80(6):792-813.
[5]	黄思静, 石和, 毛晓冬, 等. 早古生代海相碳酸盐的成岩蚀变性及其对海水信息的保存性[J]. 成都理工大学学报(自然科学版), 2003,30(1):9-18.
[6]	DERRY L A, KETO L S, JACOBSEN S B, et al. Sr isotopic variations in Upper Proterozoic carbonates from Svalbard and East Greenland[J]. Geochimica et Cosmochimica Acta, 1989,53(9):2331-2339.
[7]	YANG J, SUN W, WANG Z, et al. Variations in Sr and C isotopes and Ce anomalies in successions from China: evidence for the oxygenation of Neoproterozoic seawater?[J]. Precambrian Research, 1999,93(2/3):215-233.
[8]	黄思静. 海相碳酸盐矿物的阴极发光性与其成岩蚀变的关系[J]. 沉积与特提斯地质, 1990,10(4):9-15.
[9]	KAUFMAN A J, KNOLL A H, AWRAMIK S M. Biostratigraphic and chemostratigraphic correlation of Neoproterozoic sedimentary successions: upper Tindir Group, northwestern Canada, as a test case[J]. Geology, 1992,20(2):181-185.
[10]	黄思静, 裴昌蓉, 卿海若, 等. 四川盆地东部海相下—中三叠统界线的锶同位素年龄标定[J]. 地质学报, 2006,80(11):1691-1698.
[11]	黄思静. 上扬子二叠系—三叠系初海相碳酸盐岩的碳同位素组成与生物绝灭事件[J]. 地球化学, 1994,23(1):60-68.
[12]	李任伟, 陈锦石, 张淑坤. 中元古代雾迷山组碳酸盐岩碳和氧同位素组成及海平面变化[J]. 科学通报, 1999,44(16):1697-1702.
[13]	姚泾利, 王保全, 王一, 等. 鄂尔多斯盆地下奥陶统马家沟组马五段白云岩的地球化学特征[J]. 沉积学报, 2009,27(3):381-389.
[14]	EPSTEIN S, MAYEDA T K. Variation of ¹⁸O content of waters from natural sources [J]. Geochimica et Cosmochimica Acta, 1953,4(5):213-224.
[15]	CRAIG H. The measurement of oxygen isotope paleotemperatures in Tongiorgi[J]. Stable Isotopes in Oceanographic Studies and Paleotemperature, 1965,12(1):1-30.
[16]	邵龙义. 碳酸盐岩氧、碳同位素与古温度等的关系[J]. 中国矿业大学学报, 1994,23(1):39-45.
[17]	黄宝春, 朱日祥, OTOFUJI Y, 等. 华北等中国主要地块早古生代早期古地理位置探讨[J]. 科学通报, 2000,45(4):337-345.
[18]	SHIELDS G A, CARDEN G A F, VEIZER J, et al. Sr, C, and O isotope geochemistry of Ordovician brachiopods: A major isotopic event around the Middle-Late Ordovician transition[J]. Geochimica et Cosmochimica Acta, 2003,67(11):2005-2025.
[19]	BASSETT D, MACLEOD K G, MILLER J F, et al. Oxygen isotopic composition of biogenic phosphate and the temperature of Early Ordovician seawater[J]. Palaios, 2007,22(1):98-103.
[20]	TROTTER J A, WILLIAMS I S, BARNES C R, et al. Did cooling oceans trigger Ordovician biodiversification? Evidence from conodont thermometry[J]. Science, 2008,321:550-554. DOI URL PMID
[21]	KEITH M L, WEBER J N. Carbon and oxygen isotopic composition of selected limestones and fossils[J]. Geochimica et Cosmochimica Acta, 1964,28(10/11):1787-1816.
[22]	张秀莲. 碳酸盐岩中氧、碳稳定同位素与古盐度、古水温的关系[J]. 沉积学报, 1985,3(4):17-30.
[23]	刘英俊, 曹励明. 元素地球化学[M]. 北京: 科学出版社, 1984: 1-110.
[24]	HAQ B U, SCHUTTER S R. A chronology of Paleozoic sea-level changes[J]. Science, 2008,322:64-68. URL PMID
[25]	DARBY B J, GEHRELS G E. Detrital zircon reference for the North China block[J]. Journal of Asian Earth Sciences, 2006,26(6):637-648.
[26]	张进, 李锦轶, 刘建峰, 等. 早古生代阿拉善地块与华北地块之间的关系:来自阿拉善东缘中奥陶统碎屑锆石的信息[J]. 岩石学报, 2012,28(9):2912-2934.
[27]	吴素娟, 张永生, 邢恩袁. 桌子山地区奥陶系乌拉力克组碎屑岩地球化学特征及其对物源的制约[J]. 地质学报, 2016,90(8):1860-1873.
[28]	高振中, 罗顺社, 何幼斌, 等. 鄂尔多斯地区西缘中奥陶世等深流沉积[J]. 沉积学报, 1995,13(4):16-26.
[29]	高振中, 罗顺社, 何幼斌, 等. 鄂尔多斯西缘奥陶纪海底扇沉积体系[J]. 石油与天然气地质, 1995,16(2):119-125.
[30]	费安玮, 刘成林, 甘军, 等. 鄂尔多斯盆地三道坎组混合沉积的生物扰动构造与古地理[J]. 中国地质, 2004,31(4):347-355.
[31]	王振涛, 郑绵平. 华北克拉通西北缘中—晚奥陶世构造体制转换事件的新发现及对找钾的启示[J]. 地球学报, 2017,38(增刊):3-6.
[32]	张永生, 郑绵平, 包洪平, 等. 陕北盐盆马家沟组五段六亚段沉积期构造分异对成钾凹陷的控制[J]. 地质学报, 2013,87(1):101-109.
[33]	樊馥, 张永生, 郑绵平, 等. 陕北奥陶纪盐盆马五6时期东、西部盐坳沉积环境对比研究[J]. 地质学报, 2015,89(11):2141-2151.

样品编号	层位	岩石类型	稳定同位素		Z	t/℃
样品编号	层位	岩石类型	δ¹³C/‰	δ¹⁸O/‰	Z	t/℃
1	O₂s	中薄层石灰岩	-1.2	-8.9	120.4	32.7
2	O₂s	中薄层石灰岩	0.4	-7.3	124.5	24.9
3	O₂s	中薄层石灰岩	-2.3	-9.1	118.1	33.7
4	O₂s	中薄层石灰岩	-1.8	-8.0	119.6	28.2
5	O₂s	中薄层石灰岩	-1.8	-8.7	119.3	31.7
6	O₂z	泥粉晶石灰岩	-1.0	-8.2	121.2	29.2
7	O₂z	泥粉晶石灰岩	-1.1	-7.6	121.3	26.3
8	O₂z	泥粉晶石灰岩	-1.3	-7.9	120.7	27.7
9	O₂z	泥粉晶石灰岩	-0.2	-7.0	123.4	23.5
10	O₂z	泥粉晶石灰岩	-0.8	-7.4	122.0	25.3
11	O₂z	泥粉晶石灰岩	-0.5	-6.8	122.9	22.6
12	O₂z	泥粉晶石灰岩	-0.2	-6.9	123.5	23.0
13	O₂z	泥粉晶石灰岩	-0.2	-7.1	123.4	24.0
14	O₂z	泥粉晶石灰岩	0.5	-6.3	125.2	20.3
15	O₂z	泥粉晶石灰岩	1.2	-6.0	126.8	19.0
16	O₂z	泥粉晶石灰岩	1.3	-5.3	127.3	16.1
17	O₂z	泥粉晶石灰岩	1.2	-5.2	127.2	15.7
18	O₂z	泥粉晶石灰岩	0.6	-6.0	125.5	19.0
19	O₂z	泥粉晶石灰岩	0.6	-6.8	125.1	22.6

样品编号	层位	岩石类型	稳定同位素		Z	t/℃
样品编号	层位	岩石类型	δ¹³C/‰	δ¹⁸O/‰	Z	t/℃
1	O₂s	中薄层石灰岩	-1.2	-8.9	120.4	32.7
2	O₂s	中薄层石灰岩	0.4	-7.3	124.5	24.9
3	O₂s	中薄层石灰岩	-2.3	-9.1	118.1	33.7
4	O₂s	中薄层石灰岩	-1.8	-8.0	119.6	28.2
5	O₂s	中薄层石灰岩	-1.8	-8.7	119.3	31.7
6	O₂z	泥粉晶石灰岩	-1.0	-8.2	121.2	29.2
7	O₂z	泥粉晶石灰岩	-1.1	-7.6	121.3	26.3
8	O₂z	泥粉晶石灰岩	-1.3	-7.9	120.7	27.7
9	O₂z	泥粉晶石灰岩	-0.2	-7.0	123.4	23.5
10	O₂z	泥粉晶石灰岩	-0.8	-7.4	122.0	25.3
11	O₂z	泥粉晶石灰岩	-0.5	-6.8	122.9	22.6
12	O₂z	泥粉晶石灰岩	-0.2	-6.9	123.5	23.0
13	O₂z	泥粉晶石灰岩	-0.2	-7.1	123.4	24.0
14	O₂z	泥粉晶石灰岩	0.5	-6.3	125.2	20.3
15	O₂z	泥粉晶石灰岩	1.2	-6.0	126.8	19.0
16	O₂z	泥粉晶石灰岩	1.3	-5.3	127.3	16.1
17	O₂z	泥粉晶石灰岩	1.2	-5.2	127.2	15.7
18	O₂z	泥粉晶石灰岩	0.6	-6.0	125.5	19.0
19	O₂z	泥粉晶石灰岩	0.6	-6.8	125.1	22.6

样品编号	层位	岩石类型	主量元素/%			微量元素/10^-6
样品编号	层位	岩石类型	Al	K	Mn	Sr	Zr	Rb
1	O₂s	中薄层石灰岩	0.918	0.445	0.015	568.0	12.4	8.7
2	O₂s	中薄层石灰岩	0.902	0.402	0.029	446.0	10.5	8.4
3	O₂s	中薄层石灰岩	2.290	1.140	0.036	65.8	24.5	29.5
4	O₂s	中薄层石灰岩	1.680	0.719	0.046	62.7	19.8	21.1
5	O₂s	中薄层石灰岩	0.831	0.495	0.013	333.0	10.7	8.7
6	O₂z	泥粉晶石灰岩	0.848	0.561	0.010	442.0	4.5	8.6
7	O₂z	泥粉晶石灰岩	0.395	0.220	0.011	327.0	4.5	3.8
8	O₂z	泥粉晶石灰岩	0.897	0.627	0.008	296.0	7.7	8.3
9	O₂z	泥粉晶石灰岩	0.290	0.226	0.004	275.0	3.6	2.7
10	O₂z	泥粉晶石灰岩	0.427	0.251	0.004	282.0	3.2	4.1
11	O₂z	泥粉晶石灰岩	0.336	0.203	0.003	343.0	2.5	3.4
12	O₂z	泥粉晶石灰岩	0.403	0.223	0.005	411.0	2.6	4.3
13	O₂z	泥粉晶石灰岩	0.567	0.313	0.012	311.0	6.3	6.3
14	O₂z	泥粉晶石灰岩	0.743	0.463	0.011	438.0	3.3	7.9
15	O₂z	泥粉晶石灰岩	0.749	0.452	0.015	412.0	3.4	7.2
16	O₂z	泥粉晶石灰岩	0.662	0.321	0.026	464.0	4.3	7.4
17	O₂z	泥粉晶石灰岩	1.100	0.363	0.018	291.0	7.3	11.9
18	O₂z	泥粉晶石灰岩	0.710	0.268	0.017	572.0	2.9	8.4
19	O₂z	泥粉晶石灰岩	0.576	0.188	0.016	417.0	4.7	6.9

样品编号	层位	岩石类型	主量元素/%			微量元素/10^-6
样品编号	层位	岩石类型	Al	K	Mn	Sr	Zr	Rb
1	O₂s	中薄层石灰岩	0.918	0.445	0.015	568.0	12.4	8.7
2	O₂s	中薄层石灰岩	0.902	0.402	0.029	446.0	10.5	8.4
3	O₂s	中薄层石灰岩	2.290	1.140	0.036	65.8	24.5	29.5
4	O₂s	中薄层石灰岩	1.680	0.719	0.046	62.7	19.8	21.1
5	O₂s	中薄层石灰岩	0.831	0.495	0.013	333.0	10.7	8.7
6	O₂z	泥粉晶石灰岩	0.848	0.561	0.010	442.0	4.5	8.6
7	O₂z	泥粉晶石灰岩	0.395	0.220	0.011	327.0	4.5	3.8
8	O₂z	泥粉晶石灰岩	0.897	0.627	0.008	296.0	7.7	8.3
9	O₂z	泥粉晶石灰岩	0.290	0.226	0.004	275.0	3.6	2.7
10	O₂z	泥粉晶石灰岩	0.427	0.251	0.004	282.0	3.2	4.1
11	O₂z	泥粉晶石灰岩	0.336	0.203	0.003	343.0	2.5	3.4
12	O₂z	泥粉晶石灰岩	0.403	0.223	0.005	411.0	2.6	4.3
13	O₂z	泥粉晶石灰岩	0.567	0.313	0.012	311.0	6.3	6.3
14	O₂z	泥粉晶石灰岩	0.743	0.463	0.011	438.0	3.3	7.9
15	O₂z	泥粉晶石灰岩	0.749	0.452	0.015	412.0	3.4	7.2
16	O₂z	泥粉晶石灰岩	0.662	0.321	0.026	464.0	4.3	7.4
17	O₂z	泥粉晶石灰岩	1.100	0.363	0.018	291.0	7.3	11.9
18	O₂z	泥粉晶石灰岩	0.710	0.268	0.017	572.0	2.9	8.4
19	O₂z	泥粉晶石灰岩	0.576	0.188	0.016	417.0	4.7	6.9