Implications for Danxia Surveying and Monitoring
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Geoheritage (2015) 7:307–318 DOI 10.1007/s12371-015-0160-1 ORIGINAL ARTICLE Petrology and Spectroscopy Studies on Danxia Geoheritage in Southeast Sichuan Area, China: Implications for Danxia Surveying and Monitoring Jun-Ting Qiu1,2 & Peng-Ju Li 3 & Zhang-Fa Yu2 & Ping Li2 Received: 25 May 2015 /Accepted: 20 September 2015 /Published online: 12 October 2015 # The European Association for Conservation of the Geological Heritage 2015 Abstract This paper presents the achievements of petrology Keywords Danxia . Remote sensing . Petrology . and spectroscopy studies on rock samples collected from Spectroscopy . Surveying . Monitoring Danxia outcrops in southeast Sichuan area. The petrological study based on thin section observations was carried out using a polarizing microscope indicating that the Danxia rocks are Introduction mainly composed of quartz, plagioclase, and lithic grains, with hematite, limonite, and calcite cements. Some plagio- The Danxia landform (or Danxia geoheritage) named after the clase and lithic grains are altered to clay minerals, while quartz Danxia Mountain (Chen 1984) in Guangdong Province, grains are resistant to such alterations. The reflectance spectra China, is a type of petrographic geomorphology associated of Danxia rocks were determined with an ASD spectrometer. with erosional sandstone and conglomerates with a red color All the measured spectra share similar characteristics that are (Liu 1986;LiuandHuang1991; Peng 2000; Zhu et al. 2010). different from those of granitic rocks and other land covers, In 2010, the Mount Danxia, accompanied with other five typ- such as vegetation, water, and soil. The spectra also have ical Danxia landforms, was inscribed as a World Heritage Site absorption features at ~840, ~2210, and ~2339 nm that are with a general name of BChina Danxia^ (The World Heritage respectively related to hematite and limonite cements, altered Committee 2010). The grand and beautiful landscape of this clay minerals, and calcite cement. Application experiments landform makes it an important sightseeing resource and at- suggest that remote sensing can be a useful tool for Danxia tracts numerous tourists every year. In addition, the geological surveying and monitoring, but its capability relies on spectral phenomena, such as stratification, foliation, joint, and fault, in and spatial resolutions. Danxia, are valuable for geologists’ investigation on tectonic and sedimentary histories during the Cretaceous Period. Because of its high aesthetics, economic, educational, and scientific interests, a lot of efforts have been made since the Electronic supplementary material The online version of this article 1920s to explore this feature, and many national geological (doi:10.1007/s12371-015-0160-1) contains supplementary material, which is available to authorized users. parks have been established to develop and protect this kind of non-renewable tourism resource and study material (e.g., * Peng-Ju Li Jiang et al. 2009;Lietal.2013;Xuetal.2013;Zhang2013). [email protected] Traditional exploration and monitoring of Danxia is based mainly on manual work that is often inefficient and impracti- cal, as some regions, like mountainous areas, are usually in- 1 School of Earth Sciences and Resources, China University of Geosciences, 29 Xueyuan Road, Beijing 100083, China accessible. In contrast, remote sensing technology, which per- mits data on inaccessible regions to be obtained economically 2 National Key Laboratory of Science and Technology on Remote Sensing Information and Image Analysis, Beijing Research Institute and rapidly, may provide an alternative way to survey, moni- of Uranium Geology, Beijing 100029, China tor, and study Danxia. For example, digital elevation models 3 School of Economics and Management, Sichuan University of (DEMs) have been used to analyze the geomorphology of Science and Engineering, Zigong 643000, China Danxia landforms (Liu et al. 2007; Huang et al. 2010; 308 Geoheritage (2015) 7:307–318 Zhang et al. 2011;Fang2014), and several parameters, such as other structural-controlled landforms. Therefore, additional stream gradient index (SLK), hypsometric integral (HI), hyp- constrains on Danxia exploration are needed. sometric curve (HC), and slope index (SI), have been pro- Materials on the Earth’s surface that interact with the elec- posed to quantitatively describe the geomorphical characteris- tromagnetic waves emitted by the sun can be recorded by tics of Danxia (Liu et al. 2007; Zhang et al. 2011; Fang 2014). remote sensing sensors in the form of spectra. These spectra, Previous studies suggested that negative lineaments extracted like human fingerprints, can be used to search for materials from DEMs reflect the surface expression of Danxia valleys with a similar spectrum and to investigate the composition of and cliffs that may be associated with joints, faults, and shear the material (e.g., Nair and Mathew 2014). Unfortunately, due zones (Fang 2014). Additionally, many Danxia outcrops are to limited knowledge of the spectral characteristics of Danxia exposed in areas with a relatively high slope index (Liu et al. outcrop, the capability of remote sensing in surveying and 2007). Although DEMs have the advantage of revealing re- monitoring Danxia based using spectral feature was not been gional terrains, thus have been treated as candidates for well understood. Danxia exploration, they are usually problematic as the geo- The Sichuan Basin in southwest China is characterized morphic characteristics represented by SLK, HI, HC, and SI by widely distributed Cretaceous to Paleogene red sedi- are not unique to Danxia but may be also the characteristics of ments. Associated Danxia outcrops are well developed Fig. 1 a Location of the study area in China. b Digital elevation map (ASTER DEM) of the study area with locations of the Tianxiandong, Huagaoxi, and Danshan parks Geoheritage (2015) 7:307–318 309 Fig. 2 Sedimentary sequence of the red strata in the study area (modified after Luo 2010) and valuable for tourism and geological studies. Because bed^ in China) exposed in the study area include the many areas around the basin have low accessibility, sys- Cretaceous Woshantou (K1-2w)andSanhe(K2S)forma- tematic analysis of the spectral characteristics of Danxia tions and the Paleogene Liujia (E1l) Formation (Fig. 2) outcrops will be helpful for Danxia surveying for these (Luo 2010). The Woshantou Formation is a set of red- areas using remote sensing technology. Based on the fi- dish to deep-red conglomerate and sandstone with silt- nancial supports from Sichuan University of Science and stone and limestone interlayers, which rests Engineering and Tourism Bureau of Sichuan Province, disconformably upon the Jurassic Penglaizhen we carried out spectroscopy and petrology studies on Formation (Fig. 2), and contains the Early Cretaceous rocks from the Danxia in southeast Sichuan, in an at- charophyte fossils, Mesochara symmetrica.TheSanhe tempt to understand their spectral features and to evalu- Formation consists of deep-red fine-grained sandstone ate the capability of remote sensing in Danxia surveying with minor mudstone, which is characterized by rhyth- and monitoring. Additionally, the spectral and petrologi- mic layering, and contains ostracods (Cypridea sp. and cal features of Danxia in southeast Sichuan investigated Eucypris sp.) and conchostracans (Calestherites sp.). in this study provide good information for further com- The Liujia Formation is composed of reddish to deep- parative studies of Danxia elsewhere in China. red sandstone with minor mudstone and also contains ostracods (Eucypris sp. and Paracypris sp.). The disconformity between the Jurassic Penglaizhen Study Area Formation and the Cretaceous Woshantou Formation suggests that the terrigenous sediments, the main com- The study area is situated in the southeast of the position of the red strata, started to deposit in the south- Sichuan Basin, within the west of the Yangtze Block east of the Sichuan Basin during the Early Cretaceous. (Fig. 1a, b). The red sedimentary strata (called Bred The continuous erosion after Eocene uplift of the red 310 Geoheritage (2015) 7:307–318 Fig. 3 a Tabular cross-bed with essentially planar bounding surfaces; b trough cross-bed with curved bounding surfaces; c air- raid shelter; d watch tower; e 3D topography of the Huagaoxi Park (source from Google Earth), from which the half-graben and normal faults can be identified; f paralleled normal faults; g Cyathea spinulosa; h exposed Danxia outcrop in the Danshan Park strata that eventually created the Danxia landforms, an important geophenomenon that can tell geologists many which offer both scenic beauty and geological signifi- things about ancient environments, such as the paleocurrent cance, is crucial to the understanding of the sedimentary and the environmental conditions at the time of deposition. history of the Sichuan Basin. Cross-beds in the Tianxiandong Park can be divided into the Over the last decade, many Danxia parks in the southeast tabular cross-beds (Fig. 3a) that have essentially planar SichuanareahavebeenestablishedfortourismandDanxia bounding surfaces and the trough cross-beds (Fig. 3b) that conservation. The Tianxiandong Park is located to the south of are featured by curved or scoop-shaped bounding surfaces. the Luzhou city (Fig. 1b). It is characterized by cross-bedding, The individual beds of tabular and trough cross-beds range Geoheritage (2015) 7:307–318 311 Fig. 4 Photographs of the Danxia outcrops in Danshan,