A combined geophysical and lithological study on eruptive history and Quaternary lacustrine stratigraphy of a maar in Leizhou Peninsula, China

Journal of Palaeogeography

Table 2 Major element concentrations (in wt.%) of selected samples from the JDY15B core

Sample	B03–44	B06–26	B09–33	B20–13	B39–48	B48–10
Depth (m)	2.55 (Unit 7)	5.31 (Unit 7)	8.00 (Unit 6)	18.88 (Unit 4)	39.90 (Unit 3)	48.60 (Unit 1)
Rock type	Fine sand	Clay	Clay	Diatomite	Scoria	Basalt
SiO₂	71.62	73.96	66.31	66.11	51.22	50.91
Al₂O₃	11.23	11.60	14.53	11.14	16.20	16.10
TFe₂O₃	8.59	5.88	8.11	6.58	11.12	10.86
MgO	0.16	0.37	1.43	0.75	7.89	8.55
CaO	0.06	0.17	0.57	0.55	8.56	8.55
Na₂O	0.01	0.03	0.13	0.09	3.32	3.15
K₂O	0.05	0.07	0.44	0.53	0.75	0.81
TiO₂	2.47	2.34	1.22	1.13	1.39	1.29
MnO	0.02	0.02	0.03	0.10	0.15	0.14
P₂O₅	0.03	0.05	0.06	0.14	0.21	0.20
LOI	5.19	5.33	6.72	11.59	−0.65	−0.41
Total	99%	100%	100%	99%	100%	100%
CIA^a	99	98	93	90	56	56

1) ^a Chemical index of alteration (CIA) = Al₂O₃/(Al₂O₃ + CaO + Na₂O + K₂O) × 100
2) Six samples were selected from different lithological units. Samples B03–44, B06–26, and B09–33 from Unit 7 (alluvial facies) and Unit 6 (shallow-lake facies) show depletion of Mg, Ca, K and Na elements and high CIA values, indicating extreme weather intensity. Sample B20–13 from Unit 4 (deep-lake facies) shows a relatively high SiO₂ (66.11 wt.%), which is a result of abundant diatoms. Samples B39–48 and B48–10 from Unit 3 and Unit 1, respectively, are identical to the Late Cenozoic basalts (quartz tholeiites) in Leizhou Peninsula