Table 3: Selected trace-element data from samples of the Shawan Formation in the Chunfeng oilfield.

Well Name	lithology	Sr/10-6	Ba/10-6	V/10-6	Ni/10-6	Th/10-6	U/10-6	Sr/Ba	Th/U	V/(V+Ni)
Z609-M	limestone	256	278	54.4	14.6	3.21	27.8	0.92	0.12	0.79
Z612-N	Limestone	361	240	32.5	18.9	3.41	29.0	1.50	0.12	0.63
Z601-F	Sandstone	145	186	47.7	1.3	3.12	7.1	0.78	0.44	0.97
Z612	Limestone	252	226	49.6	13.8	3.36	28.6	1.12	0.12	0.78
Z608	Limestone	207	230	24.6	12.5	3.23	27.6	0.90	0.12	0.66
Z6-C	Sandstone	196	236	80.3	3.1	3.26	6.7	0.83	0.49	0.96
Z602	Limestone	195	750	56.8	33.2	3.55	23.2	0.26	0.15	0.63
Z601-D	Sandstone	169	195	46.9	10.1	3.21	6.3	0.87	0.51	0.82
Z601-A	Limestone	565	220	38.6	15.0	3.33	25.8	2.57	0.13	0.72