Introduction

The term “geoheritage” was initially defined by Brocx and Semeniuk (2007) to denote intrinsically or culturally significant geological sites providing insights into Earth’s evolution, applicable in research, teaching, or referential contexts. The Danxia geoheritage has become a focal point of interest (e.g., Chen 1984; Liu 1986; Liu and Huang 1991; Peng 2000; Jiang et al. 2009; Zhu et al. 2010; Li et al. 2013; Xu et al. 2013; Qiu et al 2015; Chen et al. 2022; Li et al. 2022; Shi et al. 2022; Shu et al. 2022; Jia et al. 2023), particularly intriguing due to its concentration in three primary areas in China: the South China region, the Sichuan Basin, and the Qilian-Liupan regions (Yan et al. 2019; Fig. 1). This study seeks to address the scientific inquiry of why these Danxia landforms are clustered together and whether there exists a genetic link among them.

Fig. 1
figure 1

Distribution of Danxia landforms in China with point densities (modified after Yan et al. 2019)

Full size image

The Sichuan Basin, situated in the western portion of the Yangtze Block, is an intracontinental sedimentary basin that has undergone multiple tectonic changes influenced by both trans-Eurasian Tethys and circum-Pacific tectonics (e.g., Yan et al. 2018; Yan and Qiu 2020). While numerous studies have explored Danxia landforms in the Sichuan Basin, the majority have focused on tourism, education, and landform preservation (e.g., Guo et al 2008; Luo and Wang 2015; Qiu et al. 2015). Conversely, literature concerning tectonic evolution has predominantly emphasized geodynamics, regional metallogeny, and oil–gas storage/destruction effects (e.g., Jia et al. 2006; Liu et al. 2018). Notably, the genesis of Danxia landforms in the Sichuan Basin and its connection to regional tectonic evolution remain inadequately addressed.

The formation of Danxia landforms is commonly associated with red bed deposition, post-depositional structural activity, and subsequent erosion following red bed uplift (Ren 2009; Jiang et al. 2009, 2013; Zhu et al. 2009; Chen et al. 2019; Peng et al. 2020, 2023; Wang 2021; Li et al. 2023; Yang et al. 2023; Zhang et al. 2023). Various methods have been proposed to comprehensively understand the Danxia formation process, such as microscopic observation (Jiang et al. 2013; Wang 2021) for investigating depositional environments, geometry (Ren 2009; Chen et al. 2019; Peng et al. 2020; Li et al. 2023) and remote sensing imagery (Yang et al. 2023; Zhang et al. 2023) analyses for discerning tectonic stress field characteristics and erosion degrees, and isotopic dating (Zhu et al. 2009; Peng et al. 2023) for studying the geochronology of structural activity.

In this study, we collected and utilized ASTER Global Digital Elevation Model (ASTER GDEM) and Landsat8 images covering the southern Sichuan Basin for terrain analysis and regional structure interpretation. Additionally, field investigations were conducted on 35 Danxia landforms to comprehend their types and spatial distribution in the region. Geometry characteristics of joints associated with the Danxia landforms were measured to analyze the tectonic stress field. The results were then employed to discuss the relationship between Danxia landform formation and regional tectonic evolution. This achievement significantly contributes to a nuanced understanding of the spatial distribution of Danxia landforms in China.

Background

Regional Geology

The Sichuan Basin, situated in the western part of the South China Block, is surrounded by distinct geological features, including the Qinling Orogen to the north (Meng and Zhang 2000; Dong et al. 2011), the Daliangshan Fold Belt to the south, the Longmenshan-Daliangshan Fold-and-Thrust Belts to the west (Roger et al. 2010), and the Qiyaoshan Fold–Thrust Belt to the southeast (Fig. 2). Over geological time, it transformed from a passive continental margin into a foreland basin during the Triassic to Cretaceous era, subsequently undergoing exhumation and structural modification in the Cenozoic (Sun et al. 2018; Mu et al. 2019). Comprising both a sedimentary basement and cover, the cover primarily consists of Palaeozoic and middle Mesozoic strata characterized by shallow marine deposits and younger terrestrial strata.

Fig. 2
figure 2

Geological map delineating the distribution of Jurassic to Cretaceous strata and major terranes (modified after Li et al. 2018)

Full size image

The Triassic strata, distributed along the Huayinshan fault, include the Feixianguan (T1f), Jialingjiang (T1j), Leikoupo (T2l), and Xujiahe (T3x) Formations. The Feixianguan (T1f) Formation comprises crystalline debris tuff and shale intercalated with sandstone and limestone. The Jialingjiang (T1j) Formation is predominantly composed of limestone and dolomite intercalated with mudstone, siltstone, and tuff. The Leikoupo (T2l) Formation consists of dolomite intercalated with dolomitic mudstone and gypsum-salt rock. The Xujiahe (T3x) Formation contains feldspar quartz sandstone intercalated with mud shale.

The Jurassic strata, widespread in the southern Sichuan region, include the Zhenzhuchong (J1z), Ziliujing (J1zl), Xintiangou (J2x), Shaximiao (J2s), Suining (J3s), and Penglaizhen (J3p) Formations. The Zhenzhuchong (J1z) and Ziliujing (J1zl) Formations are primarily composed of mudstone with minor quartz sandstone. The Xintiangou (J2x) Formation consists of quartz sandstone with minor mudstone. The Shaximiao (J2s) Formation contains mudstone and feldspar quartz sandstone. The Suining (J3s) Formation is composed of calcareous mudstone intercalated with feldspar quartz sandstone. The Penglaizhen (J3p) Formation comprises feldspar quartz sandstone and calcareous mudstone.

The Cretaceous strata consist of the Wotoushan (K1w), Daerdang (K1d), Sanhe (K2s), and Gaokanba (K2g) Formations. The Wotoushan Formation (K1w) comprises feldspar quartz sandstone intercalated with mudstone. The Daerdang (K1d) Formation is characterized by massive feldspar quartz sandstone. The Sanhe (K2s) Formation consists of argillaceous detritus feldspar sandstone and mudstone. The Gaokanba (K2g) Formation is dominated by fine to silty feldspar sandstone intercalated with mudstone (Li et al. 2018; Liu et al. 2021a, b).

Danxia Landforms in Southern Sichuan Basin

The Danxia landforms discovered, undergoing development, and currently operational are comprehensively detailed in Table 1, with corresponding photos and locations presented in Figs. 3 and 4, respectively. The southern Sichuan Basin encompasses five cities—Yibin, Leshan, Luzhou, Zigong, and Neijiang. Among these, Yibin, Leshan, and Luzhou stand out with a wealth of Danxia resources, featuring renowned sites like Sunanzhuhai, Leshan Giant Buddha, Huangjinglaolin, Tianxiandong, Fobao, Danshan, Huagaoxi, Qidonggou, Baxianshan, Muchuanzhuhai, and Huatianjiudi. Additionally, ongoing development efforts focus on sites such as Danshanbishui, Shiguhongyanwo, Mabiandanxia, and Biyunshan. The Zigong, while boasting numerous Danxia resources like Feilongxia and Jinhuasuoluogu, does not enjoy the same level of fame as Yibin, Leshan, and Luzhou. Conversely, Neijiang exhibits a scarcity of prominent Danxia resources, with the Daxia resource presence being notably limited in comparison to other cities in the region.

Table 1 The Danxia landforms in the southern Sichuan Basin
Full size table
Fig. 3
figure 3

Typical photographs showing different types of Danxia landforms in the southern Sichuan Basin

Full size image
Fig. 4
figure 4

Landsat8 truth color image showing distributions of different types of Danxia landforms, Late Jurassic, and Cretaceous red beds, regional faults, and folds

Full size image

Methodology

Remote Sensing Dataset

The original operational land imager (OLI) and thermal infrared sensor (TIRS) images, encompassing the study area were acquired during the dry season on Mar 29th, 2019 (LC81280402019088LGN00), Apr 18th, 2018 (LC81290392018108LGN00 & LC81290402018108LGN00), and May 2nd, 2020 (LC08_L2SP_128039_20200502_20200820_02_T1) by the Landsat 8 satellite and were retrieved from the GSCloud platform (http://www.gscloud.cn/home). Each image includes one panchromatic band (band 8), eight multi-spectral bands (bands 1–7 and 9), and two thermal infrared bands (bands 10 and 11). The spatial resolution of band 8 is 15 m, and the multi-spectral bands have resolutions of 30 m. While the spatial resolutions of the infrared bands are originally 100 m, they were re-sampled to 30 m. The cloud content of the product is less than 1%. Additionally, alongside the OLI and TIRS images, twelve ASTER Global Digital Elevation Model (ASTER GDEM) images (N28-30E103-106) with a spatial resolution of 30 m covering the study area were downloaded from the GSCloud platform. Table 2 provides the essential details of these remote sensing data.

Table 2 Basic information about the remote sensing data used in this study
Full size table

Terrain Analysis

The ENVI 5.3 software (https://www.nv5geospatialsoftware.com/Products/ENVI) was employed for terrain analysis. Initially, twelve ASTER GDEM images with a spatial resolution of 30 m were mosaicked to create a comprehensive image covering the entire study area. Subsequently, this composite image was utilized to compute slopes using the “Topographic Model” function. The resulting slopes were categorized into two groups: high-angle and low-angle, with a designated cutoff value of 40° (Qiu et al. 2015). The subset representing the high-angle group was then exported as a raster GeoTIFF file.

Regional Structural Interpretation

Faults and fractures were discerned by analyzing a remote sensing image, emphasizing alterations in rock units induced by displacement and deformation. In this investigation, structural separations were identified through the interpretation of Landsat 8 images using a specific band combination (Red, band 4; Green, band 3; Blue, band 2). The identification process relied on observable evidence, including variations in vegetation, deviations in stream paths, and abrupt lithological changes manifested as alterations in hues and textures within the images. The outcomes of this analysis were exported as a raster GeoTIFF file.

Field Investigation and Measurement of Joint Geometry

A field route survey was conducted on the Danxia landform sites enumerated in Table 1, wherein photographs and GPS locations of the sites were systematically captured and documented. The mechanical and kinematic properties of joints were assessed by interpreting field geological phenomena, including the distinctive features of joint planes. Geometry parameters such as dip and strike of the joints were measured using a geological compass and subsequently represented in stereographic projections through the CGDK (Qiu et al. 2013) add-in of CorelDRAW software (https://www.coreldraw.com/en/).

Results

Types and Distribution of Danxia Landforms

Based on a comprehensive field investigation covering approximately 150 sites (refer to Appendix Table 4) encompassing 35 Danxia landforms in the southern Sichuan Basin, a categorization of Danxia tourism resources into four distinct types based on their geometry characteristics has been identified. These types include (1) cliff type, (2) peak type, (3) cave type, and (4) valley type. The cliff type further comprises (1–1) natural cliff type and (1–2) manually modified cliff type. The natural cliff type is formed solely through geological processes, whereas the manually modified cliff type undergoes artificial alterations, such as cliff carvings and cliff architectures. The peak type is subdivided into (2–1) cluster type and (2–2) butte type. The cluster type may manifest as multiple peaks arranged in a line or a single peak with barrier-like characteristics, while the butte type is characterized by isolated single peak. Cave type is delineated by semi-closed caves developed along bedding planes. The valley type assumes a “V” shape, featuring red sandstone at the valley bottom often accompanied by a river. Illustrative photographs depicting various Danxia types are presented in Fig. 3. The occurrence and distribution of each Danxia type are itemized in Table 3 and graphically depicted in Fig. 4.

Table 3 Statistic table showing different types of Danxia landforms in southern Sichuan Basin
Full size table

Distribution of Sedimentary Strata, Fold, and Fault

The results of structure interpretation based on remote sensing imagery were rigorously scrutinized through a comparative analysis with the structural map and geological map of Sichuan Province, along with on-site field verification. The validated outcomes are illustrated in Fig. 4. The fold structures identified exhibit trending directions categorized into E-W, N-S, NE-SW, NNE-SSW, and NNW-SSE groups, determined by the axial surfaces of these structures. Concurrently, the fault structures predominantly trend in NE-SW and NNE-SSW directions, with secondary orientations observed in NW–SE and N-S directions. Given that Danxia landforms are typically associated with Upper Jurassic and Cretaceous Formations, the stratigraphic distribution is also presented in Fig. 4. Notably, the Cretaceous strata are predominantly situated along the periphery of the basin, whereas Upper Jurassic formations are concentrated in the central region of the basin.

Topographic and Geomorphic Features

The outcomes of the digital elevation model and slope analysis are presented in Fig. 5. Evidently, there is a gradual decrease in altitude from the edge of the basin towards the interior. Altitude changes facilitate the classification of three distinct regions: the mountain region, transition region, and plain region. The mountain region is characterized by elevated altitudes, while the plain region exhibits lower altitudes. Notably, all 35 identified Danxia landforms are situated in the mountain and transition regions, with none in the plain region. Regardless of whether it is the mountain or transition region, the known Danxia landforms are consistently associated with areas characterized by steep slopes. Specifically, in the transition region, viable Danxia landforms can still develop in areas with steep slopes, even if the altitudes of such areas are not exceptionally high.

Fig. 5
figure 5

Topographic map showing different types of Danxia landforms and areas with steep slopes

Full size image

Geometry of Joint

In the “Topographic and Geomorphic Features” section, remote sensing and GIS technologies were employed to identify regional folds and faults, crucial for comprehending the stress field within the southern Sichuan Basin. Alongside these structures, joints offer valuable insights into the stress field based on rock shear criteria. Given that joints cannot be directly identified on remote sensing imagery, we conducted field investigations to measure the geometry of joints in red sandstones, as illustrated in Fig. 6a and c. This exploration revealed the presence of two distinct groups of conjugate shearing joints. The first group encompasses joints with azimuths ranging from 310 to 335° and dip angles within the range of 63 to 72°, as well as joints with azimuths between 172 and 181° and dip angles spanning from 70 to 81° (Fig. 6b). The second group includes joints characterized by azimuths ranging from 210 to 225° and dip angles from 76 to 82°, alongside joints with azimuths spanning from 242 to 252° and dip angles ranging from 76 to 85° (Fig. 6d). Notably, the first group is intersected by the second group, as depicted in Fig. 6e, suggesting that the second group formed subsequent to the formation of the first group.

Fig. 6
figure 6

a and c Diamond conjugate shear joints; b and d stereographic projections of conjugate shear joints; e chessboard-like joints, of which the 335°/64°group was cut by the 242°/76°group

Full size image

Discussion

The Interplay of Danxia Landforms with Strata, Topography, and Structure

Danxia, a distinctive landform, emerges through the erosion of red beds primarily composed of terrigenous clastic rocks such as mudstone, sandstone, and conglomerate. In the southern Sichuan Basin, Danxia landforms are intricately linked to Late Jurassic to Cretaceous red beds, with 21 landforms associated with the former and 29 with the latter (Fig. 7a). This study categorizes Danxia landforms into four types: cliff, peak, cave, and valley. The distribution includes 32 landforms for the cliff type, 7 for the peak type, 6 for the valley type, and 5 for the cave type. Altitudinally, 26 Danxia landforms are situated between 400 and 600 m above sea level, 16 above 800 m, 4 between 200 and 400 m, and the remaining 4 between 600 and 800 m (Fig. 7c). Remarkably, all valley-type Danxia landforms are developed in Cretaceous strata, predominantly positioned above 800 m sea level, with two exceptions located between 400 and 800 m. In contrast, the other three types manifest in both Late Jurassic and Cretaceous strata across all altitudes without specificity. Furthermore, the majority of Danxia landforms are situated in areas with steep slopes (Fig. 5), where fractures, folds, and joints are well developed (Figs. 4, 6). Notably, the formation of Danxia landforms is intricately tied to geological structures. For instance, many cliffs and peaks align with or are intersected by joints and faults, while certain cliffs emerge at the uplifting terminations of folds. Additionally, lateral erosion of water flow can give rise to caves within cliffs.

Fig. 7
figure 7

Statistic results showing the relationships between different types of Danxia landforms and a the Late Jurassic and Cretaceous red bed b fault, fold and joint structure c different altitudes

Full size image

Peng et al. (2013) proposed a model delineating the evolutionary stages of Danxia landforms, encompassing six phases: Early Youth, Late Youth, Early Adulthood, Late Adulthood, Early Decline, and Late Decline. However, a contrasting viewpoint was presented by Zhang et al. (2018), contending that the Danxia Mountain, representative of the Late Adulthood stage, is older than the Jianglang Mountain, typifying the Late Decline stage. Notably, prior studies (Liu et al. 2021a, b) highlight a surface denudation of 1.5–4.0 km in the south Sichuan Basin during the Cenozoic, with varying degrees of denudation observed in specific regions such as Leshan, Zigong, Neijiang, Yibin, and Luzhou (ranging from 1.5 to 3.5 km). This suggests a gradually diminishing denudation trend. Nevertheless, a paradox emerges as the Danxia landforms in Leshan and Yibin exhibit notable similarities, contrary to the distinctions proposed by Peng et al. (2013). Furthermore, despite comparable denudation levels in Yibin and Luzhou, the prevalence of valley-type Danxia landforms is more pronounced in Luzhou, situated at a higher altitude than Yibin. Consequently, the applicability of the model proposed by Peng et al. (2013) appears constrained to specific Danxia instances and may not universally hold across different locations. The diverse initial conditions and evolutionary environments present in distinct places underscore the need for a nuanced understanding of Danxia landform evolution.

Interconnection of Danxia Development and Tethys Evolution

The Danxia landforms in the South Sichuan Basin are intricately tied to Late Jurassic to Cretaceous strata. In the Late Jurassic period, the northeastern margin of the Yangtze Craton and the western Jiangnan Orogen experienced uplift and denudation due to the combined effects of southward thrusting of the Qinling Orogen (e.g., Yan et al. 2018), and the northwestward expansion of the Jiangnan Orogen and Chuanexiang fold-thrust belt (e.g., Yan et al. 2003; Li et al. 2014; Qiu et al. 2016). This led to extensive fluvial–deltaic–lacustrine depositions across the northern, eastern, southern, and central Sichuan Basin (Guo et al. 1996; Wang and Xu 2001; Liu et al. 2005, 2010). During the Early Cretaceous, the intra-cratonic depression of the Sichuan Basin subsided westward, resulting in fluviolacustrine depositions along the west and southwest sides of the basin (Li et al. 2018). Subsequently, in the Late Cretaceous, continuous compression from the Qinling Orogen uplifted and denuded the northern Sichuan Basin rapidly. Sediments from the Songpan-Ganzi terrane, the Longmenshan thrust belt, and the uplifted areas of the northern and northeastern Sichuan Basin were transported and deposited in the south and southwest sides of the basin (e.g., Yan et al. 2011; Cook et al. 2013; Li et al. 2018). The red beds formed by the aforementioned Jurassic and Cretaceous deposits provided the material foundation for the subsequent formation of Danxia landforms.

It is noteworthy that the Danxia landforms in the South Sichuan Basin are influenced by faults, folds, and joints. The fold structures are categorized into E-W, N-S, NE-SW, NNE-SSW, and NNW-SSE groups (Fig. 4), among which the E-W and NE-SW groups indicate maximum compressive stresses in the directions of N-S and NW–SE, while the N-S, NNE-SSW, and NNW-SSE groups indicate a sub-E-W maximum compressive stress. Fault structures, including N-S and NE-SW reversed faults (Fig. 4), suggest maximum compressive stresses in the directions of E-W and NW–SE. The age of the youngest deformed or broken rock associated with these structures suggests their formation in the Cenozoic era, indicating changes in the tectonic stress field during this period.

Guo and Dong (2019) reported the shear failure angle of ~ 22° for sandstone, namely only diamond conjugate shear joints can be observed in sandstone for the same tectonic stress field. Field investigations reveal two groups of conjugate shear joints (Fig. 6), one indicating a sub-E-W maximum compressive stress (Fig. 6b) and the other representing a NW–SE maximum compressive stress (Fig. 6d). The cross-cut relationship between these two groups (Fig. 6e) implies a change in the direction of maximum compressive stress during the Cenozoic, aligning with the proposed tectonic events by Wang et al. (2014). This shift, from sub-E-W compression related to the eastward expansion of the Tibetan Plateau (25–30 Ma) to NW–SE compression associated with the southeastward extrusion of the Chuandian fragment (12.8–15.4 Ma), underscores the dynamic tectonic evolution of the region.

Usually, red beds need uplift and suffer erosion to generate different types of Danxia landforms. It is generally accepted that the south Sichuan Basin weakly deformed during the Late Mesozoic but uplifted mainly in the Cenozoic. Deng et al. (2014) reported the apatite fission-track thermal history simulation results that reveal a relatively slow exhumation rate of ~ 0.15 mm/year during ~ 30 to ~ 10 Ma and a relatively rapid exhumation rate of ~ 0.4 to 0.8 mm/year since ~ 10 Ma for Daliangshan fold belt. An et al. (2008) yielded the fission track dating results for the Mabian area, southwest Sichuan basin, indicating an extensive tectonic uplift occurred since ~ 3 Ma. These apatite fission-track results further suggest a multi-stage tectonic event driven by the eastward growth of the Tibetan Plateau, during which Jurassic and Cretaceous red beds in the south Sichuan basin uplifted and exposed to the surface and suffered erosion, a situation that benefits Danxia landform formation.

Implications for Spatial Distribution of Danxia Landforms

As depicted in Fig. 8, two prominent tectonic domains shaped China from the Mesozoic to the Cenozoic: the Tethys-Himalayan tectonic domain and the Paleo-Pacific tectonic domain. Notably, the spatial distribution of Danxia landforms in the Sichuan Basin and Qilian-Liupan regions is closely linked to the Tethys-Himalayan tectonic domain, while those in the South China Region are associated with the Paleo-Pacific tectonic domain. Expanding on the discussions in the “The Interplay of Danxia Landforms with Strata, Topography, and Structure” section and the “Interconnection of Danxia Development and Tethys Evolution” section, the formation of Danxia landforms in the Sichuan Basin is genetically controlled by the periphery of the Tethys-Himalayan tectonic domain, characterized by active sedimentary and tectonic processes. This region provided the essential material, structural, and erosional foundations for the development of Danxia landforms. Similarly, the Danxia landforms in the Qilian-Liupan region also emerged along the edge of the Tethys-Himalayan tectonic domain, mirroring the conditions observed in the Sichuan Basin Region. Previous studies have established a connection between Danxia landforms in the Qilian-Liupan region and Jurassic to Cretaceous red beds formed during the uplift of the Tibetan Plateau (e.g., Zhang 2020; Ding et al. 2014a, 2014b). It is noteworthy that the Danxia landforms in the South China Region deviate from the edge of the Tethys-Himalayan tectonic domain; instead, they situate within the NE-SW trending structural belt forged by the northwestward subduction of the Paleo-Pacific Plate. Unlike their counterparts in other regions, the Danxia landforms in the South China Region are controlled by joints and faults oriented in NNW and NE directions (Lu 2014; Guo et al. 2023), aligning with the NW–SE compression (Jiang et al. 2013; Chen et al. 2019). Therefore, the distinct distribution characteristics of Danxia landforms across these regions are direct outcomes of the evolutionary trajectories of the respective tectonic domains.

Fig. 8
figure 8

Distribution of Danxia landforms with tectonic domains in China (modified after Yan et al. 2019; Qiu et al. 2022)

Full size image

Conclusions

  1. (1)

    Four distinct types of Danxia landforms—cliff, peak, cave, and valley—were meticulously observed and classified in the southern Sichuan Basin. Notably, all these types exhibit a clear preference for locations characterized by steep slopes. The valley type, specifically, tends to manifest in areas with elevated altitudes, while the other types do not display a discernible preference for specific altitude ranges.

  2. (2)

    The genesis of Danxia landforms is intricately linked to red beds deposited during the Late Jurassic to Cretaceous periods. These landforms are influenced by faults, folds, and joints that materialized during the Cenozoic era. Additionally, the Cenozoic uplift played a pivotal role in initiating a rapid denudation process of red beds, significantly contributing to the formation of Danxia landforms.

  3. (3)

    The evolution of the Tethys-Himalayan tectonic domain since the late Jurassic laid the groundwork for the material and structural aspects of Danxia landforms in the southern Sichuan Basin. This tectonic evolution exerted a considerable influence on the overall formation and progression of these unique landforms.

  4. (4)

    The distinctive distribution patterns of Danxia landforms are direct outcomes of the tectonic evolution. Notably, Danxia landforms within the same tectonic domain may be genetically related, sharing a common dynamic background that shapes their unique characteristics and features.