e-SOTER field correlation tour (part I): Hainan

The climate is tropical monsoon climate and tropical oceanic climate. A dry and rainy season can be distinguished. There are tropical storms and typhoons during summer. The average annual temperature ranges from 22-26°C. From January to February, the average temperature is 16-24°C, while from July to August the average temperature is 25-29°C.
More than 7 million people live in Hainan, which is one of the famous oversea districts of China. More than 1.2 million people are ethnic minorities, namely Li, Miao, Hui and others. Various ethnic minorities still retain their unvarnished customs and living habits.
The island is China's tropical crop base. The output of rubber accounts for more than 60% of China. In addition, sisal, coffee, coconut tree, pineapple and other tropical crops are cultivated. The forest is rich in precious lumber, medicinal plants, precious birds and beasts. The sea area is rich in grouper, sea turtle, lobster, etc. (Zhang et al. 2010).

Petrography of Hainan
The petrographic inventory of Hainan comprise among the igneous rocks mainly basalt and granite, followed by granodiorite and rhyolite. The metamorphic rocks consist mostly of gneiss and migmatite. The sediments and sedimentary rock consist of sand, gravel, siltstone, claystone, mudstone and shale.

Soils of Hainan
The major reference soil groups according to WRB classification are Acrisols, Ferralsols, Nitisols, and Cambisols. This reference soil groups are assisted by Phaezems, Leptosols, and Fluvisols. In the frame of the e-SOTER field correlation tour some of the major reference soil groups of Hainan were examined. In the following a brief description of the visited soil profiles is given.

Profile 1
Soil type: Ferralsol
Uncertainty: due to a lack of analytical data, a classification as Nitisol can not be excluded
Parent rock: gravel (in the upper part), the parent material of the lower part  was not visible
Position: N19° 59.776' E110° 10.183'

Figure1: Ferralsol 

Interpretation: Soil formation of a first Ferralsol through tropical weathering of an unknown parent (rock) material. Afterwards, erosion of the upper part of the soil profile (Ferralsol 1) by a stream, and deposition of fluvial gravel occurred. The profile was then located in an alluvial plain. Over the years, the site came increasingly out of the range of the stream and its floods, as indicated by the decrease of coarse fragments. During the existence of the alluvial plain, the gravel layer of the new soil profile contained groundwater and a pisoplinthic horizon developed within the loamy soil above at the top of the saturated zone. Due to uplift of the area, valleys incised into the alluvial plain and the groundwater aquifer felt dry. Since that time the profile is located on a peneplain representing the remnant of the former alluvial plain.  Continuous weathering under tropical climate erased all rock fragments except of the resistant quartz components. Finally a second Ferralsol developed on top of the former fluvial deposits. According to Pedoja et al. (2008), the uplift rates of Hainan range between 6 and 7 cm per thousand years. Nowadays, the former groundwater horizon is approximately 20 m above the present groundwater level. Taking the mentioned uplift rates into account, the formation of the pisoplintic horizon occured at least  285,000 years ago.

Profile 2
Soil type: Luvic Phaeozem (Endoskeletic)
Parent rock: basalt
Position: N19° 51.239' E110° 20.860'

Figure 2: Phaeozem on basalt

Profile 3
Soil type: Cutanic Acrisol (Hyperdystric, Profondic, Chromic)
Parent rock: gravel (in the upper part), the parent material of the lower part  was not visible
Position: N18° 38.014' E109° 42.518'

Figure 3: Acrisol on granite

Qixian hotspring
The Qixian hotspring is located in the Qixianling National Forest Park in Baoting district, Hainan province. This area is rich in hotspring resources, whereas the hottest water has a temperature of 93°C.

Figure 4: Qixian hotspring located in the Qixianling National Forest Park, Baoting district, Hainan province.

Profile 4
Soil type: Acrisol
Parent rock: granite
Position: N18° 54.337' E109° 30.809'

Profile 5
Soil type: Acric Ferralsol (Dystric, Chromic)
Parent rock: granite
Position: N19° 29.450' E109° 28.854'

Figure 6: Ferralsol on granite

Profile 6
Soil type: Acric Nitisol (Dystric, Rhodic)
Parent rock: basalt
Position: N19° 46.300' E110° 00.328'

Figure 7: Nitisol on basalt

References
Pedoja, K., Shen, J.-W., Kershaw, S., Tang, C., 2008. Costal Quarternary morphologieson the northern coast of the South China Sea, China, and their implications for current tectonic models: A review and preliminary study. Marine Geology 255: 103-117.

Zhang, G., Zhao, Y., Qi, Z., 2010. Field correlation tour guide of e-SOTER China pilot area.  Field guide, unpublished.

Continue with: e-SOTER field correlation tour part II : Guandong