Introduction

Understanding the geological and geoheritage characteristics of geoparks has become a topic of growing international interest, particularly within the frameworks of geoconservation, sustainable geotourism, and Earth science education. UNESCO Global Geoparks serve as vital platforms for integrating scientific research with education and community engagement. The Khon Kaen Geopark (KKGp), situated in northeastern Thailand, is a prime example, encompassing a diverse range of geological features including dinosaur fossil sites, paleo-river channels, and ancient Sīma stones—each possessing both scientific and cultural significance1,2,3,4.

This study focuses on the eastern sector of KKGp, a region structurally influenced by the Nam Phong Fault (NPF) and Phu Kradung Fault (PKF). These fault systems are believed to have played a crucial role in shaping the geomorphological landscape of the geopark. However, their detailed structural impact and tectonic history remain insufficiently explored. The primary aim of this research is to investigate the structural controls governing landform development within KKGp by integrating satellite imagery interpretation with systematic field-based structural analysis. Additionally, the study identifies and evaluates geological evidence for the occurrence and distribution of the Maha Sarakham Formation (MSF), a concealed but geologically significant unit within the Khorat Plateau.

Although several geosites within the geopark—such as dinosaur footprints, sandstone formations, and boundary stone (Sīma) heritage—have been the subject of prior studies1,2,3,4 an integrated structural and geomorphological analysis using remote sensing and field validation has yet to be conducted. This research addresses that gap through a multidisciplinary approach combining remote sensing, structural geology, and stratigraphic assessment to provide a more holistic view of the region’s geological evolution.

A notable geomorphological feature of KKGp is the so-called “Mickey Mouse Valley,” a rare triple-lobed landform that is exceptionally uncommon among global geoparks. Its distinctive shape and origin underscore both the scientific novelty and aesthetic value of the geopark, enhancing its potential for global recognition. Ultimately, this study not only contributes to the academic understanding of fault-controlled landform development and subsurface stratigraphy in the Khorat Plateau but also provides key geological documentation in support of KKGp’s second-round evaluation for designation as a UNESCO Global Geopark. By linking advanced geoscientific methods with geoconservation and geotourism, the work aligns with international efforts to promote sustainable regional development through geoscience.

Regional geology of the Khorat plateau

The Khorat Plateau in northeastern Thailand exhibits a complex geological history that spans from the Paleozoic to the Mesozoic eras, marked by major tectonic events including craton collisions, marine transgressions, and basin inversions5,6,7,8,9,10,11,12,13,14,15.

During the Late Carboniferous to Permian periods, tectonic activity involving the separation and subsequent collision of the Indochina and South China cratons led to the development of major fault systems5,6,7,8,9 notably the Song Ma Fault. This tectonic regime is believed to have played a crucial role in the development of the so-called “Isan Sea,” a shallow to deep marine environment that existed during the Carboniferous period and is now concealed beneath the Phu Phan Range10. The term Isan refers to the northeastern region of Thailand, which is extensively covered by Mesozoic sedimentary rocks belonging to the Khorat Group10,11,12,13,14,15. These deposits, which overlie older Paleozoic basement rocks, reflect a long and complex geological history influenced by regional tectonic activity, subsidence, and marine incursions16,17,18,19,20. During the Late Carboniferous to Permian periods, sedimentation occurred within two distinct marine basins: the Isan Sea and the Nam Duk Sea18,19,20. The Isan Sea, trending northwest–southeast, was characterized by shallow to deep marine deposition, while the Nam Duk Sea, oriented north–south across the western Khorat Plateau, accumulated deeper marine sediments. Permian sedimentation ceased with the onset of the first phase of the Indosinian orogeny during the Early Triassic3,19,20. This event caused basin inversion and reactivation of pre-existing faults. The Lower Nam Phong Formation marks the termination of Triassic sedimentation and represents one of the earliest post-rift stratigraphic units in the region5,6. A subsequent collisional event between the Yangtze and Sino-Korean blocks during the Late Triassic, known as the second phase of the Indosinian orogeny, resulted in further inversion of Triassic half-grabens and full grabens—referred to as the first Triassic Basin Inversion5,6.

Following the second phase of the Indosinian orogeny, renewed subsidence occurred across the region, giving rise to deposition of the Khorat Group19,20,21,22,23,24,25. Notably, enhanced subsidence is thought to have occurred in the southwestern Khorat Plateau, evidenced by the deposition of the Phu Kradung Formation unconformably overlying the Nam Phong Formation20,25,26. In the mid-Cretaceous, a collision between the Western Myanmar block and the SIBUMASU block triggered a second phase of Triassic basin inversion (Triassic Basin Inversion II)5,6,21,22,23,24,25. This event generated board basins that initially accumulated saline sediments13,27later transitioning to aeolian deposits15.

The Khorat Plateau, with an average elevation of approximately 300 m above mean sea level, is characterized by relatively simple geological structures, distinctly separated from the continental platform of northern mainland Asia7,8,9,28. Furthermore, the uplift of the plateau may have been caused by epeirogenic movements and broad warping that occurred from the late Paleogene to the Quaternary period39. Geologically, the Khorat Plateau is divided into two lowlands: the Udon–Sakon Basin in the north and the Khorat–Ubon Basin in the south, separated by the NW–SE-trending Phu Phan Range30,31. These basins are elevated above the Central Plain, particularly along their western, southern, and southeastern margins, forming escarpments or, in places, mountainous topography. The plateau exhibits a general eastward and southeastward tilt, descending from the northern and western regions28.

Geologic setting of Khon Kaen geopark

The Khon Kaen Geopark (KKGp), located within the Khorat Plateau, is predominantly composed of continental sedimentary sequences belonging to the Khorat Group1,2,3,4,20,32. These formations exhibit a broad range of stratigraphic ages and include, in ascending order: the Nam Phong Formation (NPF), Phu Kradung Formation (PKF), Phra Wihan Formation (PWF), Sao Khua Formation (SKF), Phu Phan Formation (PPF), and Khok Kruat Formation (KKF), along with Quaternary alluvial deposits (Qa) as shown in (Fig. 1). The absence of the Maha Sarakham (MSF) and Phu Thok formations is the only factor preventing the whole stratigraphic sequence of the Khorat Group from being present in the park.

Structurally, the KKGp exhibits gentle folding and flexural deformation, which may reflect tectonic reactivation during the Paleogene, associated with the Himalayan orogeny21,22,23,24,25. The NW–SE-oriented folds and low-angle faults observed across the Khorat Plateau are indicative of crustal deformation resulting from compressional tectonics21,22,23,24,25. These structural patterns, along with the evolution of crustal architecture, are recorded in the folding geometries present within the geopark and support the interpretation that this region lies on the western margin of the Indochina block20.

In 1971, Ridd conducted a geomorphological study that led to the identification of the Three Pagodas Fault and the Mae Ping Fault33 which are now recognized as major structural features in Southeast Asia. This pioneering work demonstrated the effectiveness of geomorphological analysis as a tool for fault identification and structural geological interpretation. Although satellite imagery has become increasingly prominent in modern structural analysis—owing to its extensive coverage and high resolution—topographic maps continue to play a critical role in geological investigations, particularly in the identification of lineaments, fault traces, and deformation patterns within the landscape.

Results

Field observation

The study sites are distributed across Phu Wiang District (eastern lowland area) and Wiang Kao District (western valley area) within the KKGp. These locations were selected to facilitate detailed field investigations and lithological sampling aimed at improving the understanding of the region’s structural geology (Table 1).

Fig. 1
figure 1

Geological map of Khon Kaen Geopark showing field data collection sites and geological cross-sections along lines A–A′ and B–B′, illustrating the folding structures within the area. Lithological data are adapted from DMR31 with the Kms unit derived from this study. Bedding in the Phu Wiang Mountain is sourced from Singtuen et al.3 while structural data and field observations were conducted in this study. The maps were created using QGIS version 3.14.16 and Microsoft PowerPoint for Mac version 16.90.2 (24102719). The numbered symbols correspond to the study locations listed in (Table 1). Seismic data acquired along Highway No. 12 in the southern part of the Khon Kaen Geopark (red line). Seismic Image courtesy of Nares Sattayarak.

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A total of 13 sites were examined. Sites KK1 to KK3 encompass exposures of the NPF and PKF along the eastern margin of the geopark (Fig. 2a and c). The site KK1 presents a perfect section of NPF that is maroon or reddish purple clastic sedimentary rocks, while the site KK2 is at the boundary of NPF and PKF. In addition, the KK3 is the site that shows medium to thin beds of maroon sandstone of NPF with many directions of joint sets. Sites KK4 to KK6 are located within Phu Wiang National Park, where the PWF is prominently exposed (Fig. 2d and f). Site KK7 lies along the eastern flank of the Phu Wiang Valley and is characterized by the SKF (Fig. 2g), while site KK8 is situated in the south-central sector of the study area, also within the extent of the NPF (Fig. 2h). Sites KK9 and KK10 are located along the southern margin of the valley, where the PWF is again exposed (Fig. 2i and j). Sites KK11 and KK12, positioned in the northern-central region, reveal significant structural features, including folded strata (Fig. 2k), fault zones (Fig. 2l), and a basal conglomerate (Fig. 2n) unit within the NPF. The final site, KK13, is located in the central basin of the Phu Wiang Valley and presents the first documented field evidence of halite (rock salt) deposits associated with the Maha Sarakham Formation (MSF) within the Khon Kaen Geopark (Fig. 2m). Importantly, this site provides the first field-based evidence confirming the presence of the Maha Sarakham Formation (MSF) within the Khon Kaen Geopark, as indicated by exposed halite (rock salt) deposits.

Table 1 The location, formation, and result of the petrographic analysis of representative samples.
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Interpretation of satellite imagery

Structural interpretation based on satellite imagery and topographic analysis has identified multiple lineament trends across the Khon Kaen Geopark (KKGp), as presented in (Fig. 3). These lineaments—interpreted as faults, fracture zones, or joints—exhibit five dominant orientations: east–west (E–W), northeast–southwest (NE–SW), northwest–southeast (NW–SE), north-northeast–south-southwest (NNE–SSW), and north-northwest–south-southeast (NNW–SSE).

Two prominent E–W trending lineaments are located in the southwestern portion of the study area, both cutting across the Phra Wihan Formation (PWF). Their alignment with nearby drainage systems implies tectonic control over fluvial development, possibly through fault-guided erosion or uplift-related channel migration.

Four major NE–SW trending lineaments are distributed throughout the western and central regions of the basin. These trends correspond spatially with large-scale antiforms, indicating a likely origin as compressional or transpressional structures. In the central basin, fault-aligned drainage dissects multiple lithostratigraphic units including the Phra Wihan, Sao Khua, Phu Phan, and Khok Kruat Formations. One significant fault zone intersects the Nam Phong Formation (NPF) and is topographically expressed as a major flexural fold, suggesting an active or reactivated fault with considerable displacement history.

Five NW–SE trending lineaments are concentrated in the northern section of Phu Wiang National Park. These are interpreted as joint sets or minor fault zones, inferred from linear drainage channels that cut across resistant strata of the Phra Wihan, Sao Khua, and Phu Phan Formations. Similar trends are evident in the park’s southern sector, where fracture systems dissect the PWF and influence the development of linear valleys and fault-controlled escarpments.

Fig. 2
figure 2

Outcrop characters and field observations in Khon Kaen Geopark, illustrating lithological and structural characteristics. Lithologic features include: (a) reddish sedimentary sequence at KK1 (236675E 1842550 N), (b) brownish sandstone at KK2 (226253E 1849158 N), (c) thin- to medium-bedded reddish sandstone at KK3 (222432E 1839402 N), (d) white sandstone cliff at KK4 (209779E 1858235 N), (e) white sandstone waterfall at KK5 (207778E 1858099 N), (f) dinosaur footprint in the Phra Wihan Formation at KK6 (209622E, 1856274 N)1 (g) reddish sandstone of the Sao Khua Formation at KK7 (217378E 1849227 N), (h) reddish sandstone of the Nam Phong Formation at KK8 (222488E 1836052 N), (i) white sandstone of the Phra Wihan Formation at KK9 (196145E 1831633 N), and (j) white sandstone cliff of the Phra Wihan Formation at KK10 (196207E 1831578 N). Macrostructural features recorded at KK11 (229013E 1856227 N) include: (k) a folding structure showing bedding orientation consistent with compressional tectonics, and (l) a slickenside surface on a thrust fault, indicating fault movement direction. Additional lithologic units include: (m) rocksalt of the Maha Sarakham Formation at KK13 (216587E 1847412 N), and (n) basal conglomerate of the Lower Nam Phong Formation at KK12 (234242E 1855298 N).

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Fig. 3
figure 3

Lineament structures in the Khon Kaen Geopark, Northeastern Thailand, shown over a topographic base map derived from NASA’s shuttle radar topography mission (SRTM) and 20 m-resolution digital elevation model (DEM) imagery, with modifications adapted from Singtuen et al.4. Lineament features were manually interpreted and subsequently redrafted and overlaid onto the topographic base using Microsoft PowerPoint for Mac version 16.90.2 (24102719). Red lines indicate observed lineaments, dashed red lines represent inferred lineaments, and black lines denote major fold structures, including anticlines and multi-phase synclines. Arrows show fold axis orientations. Numbered symbols correspond to study sites listed in (Table 1).

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Two NNE–SSW trending lineaments in the central area are interpreted as reverse or oblique-slip fault zones that deform the Nam Phong Formation. These structures form narrow ridges aligned with the fault traces, implying uplift or lateral displacement. In the western sector, similarly trending faults cut across the Phu Kradung and Phra Wihan Formations, generating ridge-like topographic features suggestive of compressive tectonics.

Additionally, two NNW–SSE trending lineaments are identified in the northern part of Phu Wiang National Park. These structures appear to control drainage directionality and are interpreted as tension fractures formed in response to regional extensional or transtensional stress fields.

The primary drainage systems in the study area include Huai Hua Khaen, Huai Lam Phaning, Huai Nam Phuai, and Huai Hua Sai Khao, all of which ultimately discharge into the Nam Phong Reservoir. In elevated terrain, surface runoff patterns closely follow structural features—particularly faults and joint networks—producing a rectilinear drainage pattern characteristic of structurally influenced fluvial systems. In contrast, lowland zones exhibit sinuous, meandering channels, indicative of fluvial maturity and reduced structural control. This variation in drainage morphology provides essential insight into the dynamic interplay between tectonics, rock resistance, and geomorphology within the KKGp.

Seismic interpretation

Seismic reflection data acquired along Highway 12 in the southern part of the Khon Kaen Geopark (KKGp) delineate the subsurface architecture of the Nong Ruea sedimentary basin. This basin manifests as a north–south-oriented half-graben, bordered by steeply inclined fault planes and exhibiting asymmetric subsidence patterns. Stratigraphic interpretations of the seismic profiles reveal infill sequences composed of syn-rift to post-rift deposits, which are lithologically and chronostratigraphically analogous to the Huai Hin Lat Formation. These strata display internal seismic reflectors typical of fluvial to lacustrine depositional systems, with onlapping geometries toward the basin margins. A major reverse fault along the eastern boundary offsets the Nam Phong Formation by several hundred meters, suggesting post-depositional compressional reactivation, plausibly during the Himalayan Orogeny. This structural discontinuity, along with observed deformation geometries (Fig. 1), provides compelling evidence for basin inversion processes and underscores the influence of both Indosinian and Himalayan-related tectonic phases on the regional structural framework21,22,23,24,25,26.

Structural analysis

The bedding orientations recorded at multiple sites throughout the study area consistently reflect a regional northeast–southwest (NE–SW) structural trend, with dips predominantly directed toward the northwest (Fig. 4). At Study Site 1 (UTM 236668E 1842847 N), southwest of Non Sombun Prachasarn School, bedding strikes 352° and dips 26°NW, revealing a northwest–southeast (NW–SE) trend with northeastward dip (Fig. 4a). A similar NW–SE strike is observed at Study Site 2 (UTM 226253E 1849158 N), where the beds dip southwestward, indicating regional structural deformation (Fig. 4b).

Shifts in bedding orientation are evident at Study Site 3 (UTM 222432E 1839402 N), east of Wat Ang Sila, which records an ENE–WSW strike of 261°/07°NE (Fig. 4c). At Study Site 4 (UTM 222418E 1839421 N) within Phu Wiang National Park, bedding trends 196°/12°NW, marking a subtle variation within the dominant structural pattern (Fig. 4d). These directional changes, while locally variable, still align with broader tectonic influences in the region.

Study Sites 5 and 6 (UTM 207844E 1858410 N and UTM 209622E 1856274 N, respectively) present bedding attitudes of 233°/15°NW and 081°/05°SE (Fig. 5d and e), indicating both regional tilting and local structural divergence. At Study Site 7 (UTM 217378E 1849227 N), located at Wat Chan Khema Ram, the measured bedding of 183°/13°NW fits well within the established NE–SW regional orientation (Fig. 4f). Likewise, Study Site 8 (UTM 222488E 1836052 N) displays a bedding orientation of 194°/08°NW (Fig. 4g), reinforcing the structural coherence across the area.

At the southwesternmost exposures—Study Sites 10 and 11 (UTM 196145E 1831633 N and 196207E 1831578 N)—the bedding orientations of 253°/17°NW and 254°/17°NW (Fig. 5h and i) further confirm a sustained northwestward dip direction. These structural alignments, coupled with consistent lithological characteristics, suggest a pervasive tectonic influence across the Nam Phong Formation exposures.

Fig. 4
figure 4

Stereonet and rose diagram illustrating the orientation data of bedding planes: (a) Nam Phong Formation at KK1 (236675E, 1842550 N), (b) Phu Kradung Formation at KK2 (226253E, 1849158 N), (c) thin- to medium-bedded Nam Phong Formation at KK3 (222432E, 1839402 N), (d) Phra Wihan Formation at KK4 (209779E, 1858235 N), (e) Phra Wihan Formation at KK5 (207778E, 1858099 N), (f) Phra Wihan Formation at KK6 (209622E, 1856274 N), (g) Sao Khua Formation at KK7 (217378E, 1849227 N), (h) Nam Phong Formation at KK8 (222488E, 1836052 N), and (i) Phra Wihan Formation at KK9 (196145E, 1831633 N) and KK10 (196207E, 1831578 N). The stereonet presents the spatial distribution of dip and strike measurements, while the rose diagram summarizes the frequency of bedding orientations, highlighting dominant structural trends in the area.

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The interpretation of fault orientations and deformation styles has been revisited to highlight their implications within the broader context of regional tectonic stress regimes and basin evolution. The fracture systems observed across the study sites demonstrate a range of orientations, suggesting the influence of both compressional and extensional tectonic forces throughout the evolution of the basin.

At Study Site 1, two dominant joint sets—014°/49°SE and 190°/58°NW—form a conjugate pattern indicative of regional compressive stress, which likely contributed to structural compartmentalization during basin formation. Study Site 2, although lacking explicit joint measurements, shows consistent bedding orientations and stratigraphic continuity with Site 1, implying a shared deformation history and similar stress conditions.

Study Site 3 presents a more complex fracture network with four joint sets (084°/78°SE, 179°/75°SW, 002°/81°SE, and 114°/74°SW), suggesting the superposition of extensional and compressional regimes. This complexity may be attributed to polyphase tectonic activity or fault block rotations within the basin margin. Likewise, Site 4 shows evidence of multidirectional fracturing with joint sets at 240°/80°NW, 325°/80°NE, 061°/83°SE, and 168°/80°SW. These are likely the result of later tectonic reactivations, perhaps associated with post-rift basin inversion or strike-slip movements along nearby fault systems.

At Study Sites 5 and 6, the steeply inclined joints further reflect localized stress concentrations. Particularly, Site 6 displays two distinct joint orientations—069°/76°NW and 244°/62°NE—possibly developed near a subsidiary fault zone or fracture corridor. Study Site 7, though lacking detailed joint data, exhibits consistent bedding and lithological features that imply tectonic overprint similar to neighboring sites. Study Site 8 demonstrates minor weathering and jointing congruent with the broader regional structural trends.

Finally, Sites 10 and 11 reinforce the structural framework observed elsewhere. Site 11, in particular, provides compelling evidence of active tectonics through the identification of a right-lateral strike-slip fault along bedding planes, demonstrating horizontal displacement and adding further support to the influence of strike-slip dynamics in shaping the basin’s structural architecture.

Petrography and provenance

The majority of the analyzed reddish sandstone samples from Nam Phong and Phu Kradung Formations in Khon Kaen Geopark are classified as arkosic sandstones, specifically arkose, subarkose, and lithic arkose (Table 1) —sedimentary rocks that display a distinct clastic texture composed predominantly of sand-sized detrital grains (Figs. 5 and 6a). These rocks exhibit varying proportions of quartz (Q), feldspar (Fs), and lithic fragments (Lt) as shown in Fig. 5a, with minor matrix and cement components. Cement is dominantly siliceous, with subordinate calcareous and ferruginous (Fe³⁺) phases.

Samples KK1-1, KK1-3, KK2-2, and KK3-1 exhibit typical arkosic sandstones (Fig. 6a), with quartz contents ranging from 14 to 30% and feldspar between 10% and 20% (Fig. 5a and d). These sandstones are generally well sorted, fine to medium grained, and exhibit grain-supported frameworks with angular sand-sized clasts.

Lithic arkoses (e.g., KK1-2, KK2-1, KK3-2) contain elevated lithic fragment contents (40–54%) with subordinate feldspar (Fig. 5b and f). These rocks suggest a mixed sediment provenance, potentially incorporating volcanic, metamorphic, and sedimentary source materials. The presence of tourmaline and chlorite—especially in samples KK2-1 (Fig. 5c) and KK2-3—supports contributions from metamorphic or hydrothermally altered source regions.

Sample KK8-1 is classified as subarkose (Fig. 6a), distinguished by relatively high quartz content (42%) and reduced lithic content (20%) as shown in Fig. 6g. It is well sorted, fine grained, and exhibits a grain-supported fabric with angular grains. The cement is predominantly siliceous with minor calcareous material, indicating greater compositional maturity or reworking of arkosic sediments.

Fig. 5
figure 5

Photomicrographs of limestone under cross-polarized light from representative samples in (Table 1): (a) arkose sample KK1-1, (b) lithic arkose sample KK1-2, (c) lithic arkose sample KK2-1, (d) arkose sample KK2-2, (e) arkose sample KK3-1, (f) lithic arkose sample KK3-2, (g) subarkose sample KK8-1, (h) subarkose sample KK9-1, and (i) latite conglomerate from the KK12 site. Qz: quartz, Fs: feldspars, Pl: plagioclase, Opq: opaque minerals, Lt: lithic fragments, Zrn: zircon, CC: calcite, Hbl: hornblende, Ms: muscovite, Chl: chlorite, glass: volcanic glass.

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Samples KK9 and KK10 differ markedly from the aforementioned arkosic sandstones (Fig. 6a) in both color and texture. These rocks are white, very well sorted, and composed of medium-sized sand grains ranging from 0.3 to 0.5 mm in diameter (Fig. 5h). The clasts are grain-supported with parallel grain boundaries and exhibit angular to subangular shapes, indicating deposition in a high-energy environment with limited post-depositional compaction. Accessory minerals identified in thin section include muscovite, with minor occurrences of hornblende, garnet, zircon, and tourmaline. This mineral assemblage suggests input from a mixed provenance, including metamorphic and possibly igneous sources.

Siliceous cement predominates across the suite, while calcareous and ferruginous cements are locally developed. Matrix content ranges from 0 to 25%, with the highest values recorded in lithic-rich samples. The occurrence of iron oxides in samples such as KK3-2 and KK3-3 points to post-depositional diagenetic alteration under oxidizing conditions, likely associated with meteoric fluid infiltration. Calcareous cement is notably present in samples KK1-2 (Figs. 5b), KK1-3, KK2-2, and KK3-1 (Figs. 5e), suggesting early-stage cementation under conditions favorable to carbonate precipitation. Opaque secondary minerals are commonly observed in minor amounts (1–3%), often associated with fine muscovite or biotite flakes.

Only one sample, KK12, is of volcanic origin and has been petrographically classified as latite (Fig. 5i). This rock is characterized by the presence of K-feldspar phenocrysts, hornblende, and devitrified volcanic glass. The groundmass displays a combination of seriated, felted, and intersertal textures, with well-developed amygdaloidal structures. Secondary alteration phases include opaque minerals, hematite or iron hydroxide, and probable zeolitic minerals. These petrographic features are indicative of an intermediate volcanic rock that has experienced substantial post-emplacement alteration under subaerial or low-grade hydrothermal conditions.

The reddish sandstones from the Nam Phong and Phu Kradung Formations, along with the white sandstone samples (KK9–KK10) from the Phra Wihan Formation within the Khon Kaen Geopark, were plotted on ternary diagrams of quartz–feldspar–lithic fragments (Qt–F–Lt) and monocrystalline quartz–feldspar–lithic fragments (Qm–F–Lt). The majority of the samples fall within fields corresponding to dissected arc, transitional arc, basement uplift, transitional continental, recycled orogen, craton interior, and mixed provenance sources (Fig. 6b and c). Furthermore, the classification of lithic fragments using the Lm–Lv–Ls (metamorphic–volcanic–sedimentary lithics) ternary diagram (Fig. 6d) indicates a provenance associated with a magmatic arc setting. Additionally, plots of polycrystalline quartz (Qp) against lithic fragments (Fig. 6e) suggest derivation from tectonic environments such as collision suture fold-thrust belts, subduction complexes, and arc orogens.

Fig. 6
figure 6

Diagrams of plotted petrographic data of sedimentary rocks in Khon Kaen Geopark. (a) Qt–F–Lt name classification diagram34 (b) Qt–F–Lt, and (c) Qm–F–Lt diagrams with tectonic fields35 (d) Lm–Lv–Ls diagrams with tectonic fields36 and (e) Qp–Lv–(Ls + Lm) diagrams with tectonic fields37. Qt: total quartz, Qm: monocrystalline quartz, Qp: polycrystalline quartz, F: feldspar (plagioclase and K-feldspar), L: lithic fragment, Lt: lithic fragment and polycrystalline quartz, Ls: sedimentary lithic grains, Lv: volcanic lithic grains, Lm: metamorphic lithic grains.

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Accessory minerals, including muscovite (Ms), biotite (Bt), chlorite (Chl), tourmaline (Tur), and zircon (Zrn), are present in trace amounts and occur as either detrital grains or diagenetic overgrowths. The presence of these minerals supports a source area associated with a volcanic arc or orogenic belt. Moreover, the angular to sub-angular nature of the detrital grains, along with the occurrence of heavy minerals such as hornblende, garnet, tourmaline, and zircon, suggests a relatively short transport distance from the source rocks, indicating limited sedimentary reworking and proximity to a tectonically active provenance.

Discussion

Geological framework and interpretation of the Khon Kaen geopark

To enable a comprehensive structural interpretation and establish a solid framework for understanding regional tectonics, detailed field investigations and lithological characterizations have been systematically conducted within the KKGp. These analyses are essential for elucidating the tectonic processes that have shaped the current landscape, offering a refined understanding of the geological evolution and its implications for the present-day structural configuration.

Detailed field investigations and lithological characterizations confirm the presence of six key sedimentary formations within the Khon Kaen Geopark (KKGp): the Nam Phong, Phu Kradung, Phra Wihan, Sao Khua, Phu Phan, and Khok Kruat Formations. Importantly, the discovery of salt-bearing layers in the central Phu Wiang Basin constitutes the first direct evidence of the Maha Sarakham Formation within the geopark. As the only unit in the Khorat Group containing halite27,38,39its identification links the KKGp more closely with the broader evaporitic systems of the Khorat Plateau and enhances the regional stratigraphic framework.

The Nam Phong and Phu Kradung Formations, composed predominantly of reddish, fine- to medium-grained sandstones interbedded with mudstones, are highly susceptible to weathering. Their immature textural and compositional characteristics, along with poor cementation (dominated by iron oxides and minor carbonates), result in low mechanical strength. These properties account for the extensively eroded and low-relief landforms typical of the eastern sector of the geopark.

In contrast, the Phra Wihan Formation, characterized by well-cemented, quartz-rich sandstones3forms prominent mesa-type landforms with steep escarpments. These elevated landforms exhibit central erosional depressions where younger formations are preserved, demonstrating the direct influence of lithological resistance on geomorphological expression.

Petrographic analysis confirms that the sandstones of the Nam Phong and Phu Kradung Formations are primarily feldspathic litharenites and sublitharenites. These were deposited in fluvio-lacustrine environments with significant volcanic influence. The Nam Phong Formation in particular contains angular volcanic fragments, ranging from andesitic to basaltic clasts, suggesting deposition near a proximal magmatic arc. Thin-section analysis at Site KK12 reveals volcanic conglomerates with latite clasts in a sandstone matrix, confirming a syn-depositional volcanic input likely associated with the Indosinian orogeny during the Late Triassic–Early Jurassic. This supports a sediment supply derived from nearby magmatic arc systems, enriching the tectonostratigraphic interpretation of the region.

Structural framework and basin evolution

The erosional weakness of the Nam Phong and Phu Kradung Formations arises from their immature grain composition and rapid sedimentation from unstable source terrains, which restricted the formation of durable grain contacts. This supports a tectonic setting where high sediment flux, linked to volcanic arc activity, resulted in poorly consolidated units. Such interpretations align with the regional tectonostratigraphic evolution of the Khorat Plateau, highlighting dynamic interactions between sedimentation and volcanism.

Structurally, KKGp reflects a complex deformation history shaped by multiple tectonic phases:

  • The western sector exhibits multi-phase antiformal folds and domino-style rollovers, indicating progressive shortening and fault block rotation.

  • The southwestern zone is defined by an E–W trending dextral strike-slip fault, which accommodated significant lateral displacement during regional shearing.

  • A NNE–SSW low-angle reverse fault dominates the central area, accommodating crustal shortening under compressive stress.

  • The eastern sector features NE–SW-trending antiformal structures and reverse faulting, reflecting tectonic reactivation and post-rift inversion processes.

Together, these elements outline a region undergoing progressive deformation and basin reconfiguration, transitioning from extensional rifting to compressional inversion.

The multisynclinal geometry of the basin—characterized by broad synclines bounded by low-relief anticlines—is consistent with an intracontinental sag basin. Mesozoic non-marine sediment accumulation within these synclines supports long-term subsidence and basin development during tectonic quiescence, punctuated by deformation episodes.

Tectonic evolution and regional context

The structural and tectonic evolution of KKGp is intrinsically linked to the interactions among the Indochina, South China, SIBUMASU, and West Burma blocks. Early Triassic (Rifting Phase): Initial deformation resulted from N–S extension during the amalgamation of the Indochina and South China blocks26. This led to the development of half-graben basins, such as the Nong Ruea Basin (Fig. 1), likely associated with the Huai Hin Lat Formation. Although lithological evidence is limited due to poor exposure, stratigraphic correlation supports this interpretation.

During the Late Cretaceous, the collision between the SIBUMASU and Indochina blocks generated an east–west (E–W) compressional regime, inverting earlier extensional faults and producing N–S-trending structures. This tectonic inversion displaced the Nam Phong Formation by several hundred meters and propagated faulting into the overlying Phra Wihan Formation, forming prominent cliffs along the western margin of the Khorat Plateau. Low-angle ENE–WSW reverse faults further uplifted the Nam Phong Formation along the basin center. Evidence of uplift and lateral displacement within the formation supports a basin-wide inversion event. These features align with seismic data indicating post-depositional deformation of the Khorat Group linked to subduction-related compression between the Burma and SIBUMASU blocks around 70 ± 20 Ma, possibly extending into the Early Paleogene (Fig. 7a)5,21,26,40,41,42.

Fig. 7
figure 7

Structural model illustrating tectonic influences on the geomorphology of Khon Kaen Geopark, Thailand. (a) Initial stage: Reactivation of pre-existing Triassic faults as reverse faults in the central region of the study area, resulting from east–west compressional stresses during the Late Cretaceous, possibly extending into the Paleogene. (b) First episode of fold development associated with northeast–southwest maximum principal stress (σ1) during the Eocene. (c) Subsequent phase of folding and fracturing aligned in a northwest–southeast orientation, attributed to the clockwise rotation of maximum compressive stress to a west–east direction during the Miocene. These deformation events are supported by AFT thermochronological data from Mesozoic siliciclastic rocks in the Phu Phan Mountain Range30 as well as geochronological investigations from previous studies41,42.

Full size image

These findings align with seismic data indicating postdepositional compression of the Khorat Group, triggered by subduction-related stresses between the Burma and SIBUMASU microplates around 70 ± 20 Ma41,42. This compression phase caused reactivation of pre-existing extensional faults, leading to uplift, fault inversion, and the development of steep structural scarps along the western margin of the plateau (Fig. 7a). Evidence for continued deformation into the Early Paleogene emerges from stratigraphic unconformities and fault displacement preserved in upper Khorat Group formations, underscoring a prolonged compressional regime.

Eocene (~ 37 Ma; Himalayan Phase I): NE–SW compressional stress associated with the first Himalayan orogenic event41,42 produced significant flexural folding and NW–SE oriented fracturing (Fig. 7b). These structures are corroborated by apatite fission track (AFT) thermochronology from the Phu Phan Range30which reveals cooling ages consistent with burial-associated heating followed by uplift during the Eocene. This tectonic episode contributed to continued crustal shortening and the reconfiguration of structural fabrics across the region.

Miocene (Himalaya II Phase): A clockwise rotation of the compressive stress field (WSW–ENE) initiated the third phase of basin inversion5,6 characterized by widespread strike-slip faulting, orthogonal fold interference patterns, and stepwise regional uplift (Fig. 7c). These processes overprinted earlier fold geometries and reflected the reactivation of fault systems. The resulting structural overprints and uplift have significantly influenced the present-day landscape of northeastern Thailand.

Impacts on geomorphology and geoconservation

The present-day landscape of Khon Kaen Geopark (KKGp) is a direct outcome of prolonged tectonic activity, diverse lithological compositions, and intense climatic weathering. These dynamic processes have produced distinct geomorphic features that are both scientifically significant and geotouristically valuable:

  • Phu Wiang Range: Characterized by pop-up structural geometries resulting from strike-slip faulting and uplift. These movements have created rugged relief and elevated blocks, offering natural cross-sections through multiple stratigraphic units.

  • Mesa Topography of the Phra Wihan Formation: The plateau-like landforms are shaped by differential erosion, with the quartz-rich, resistant sandstone forming flat-topped mesas that stand prominently above the surrounding terrain. This landscape reflects both tectonic uplift and the durability of the rock against weathering.

  • Eastern Lowlands (Nam Phong Formation): In contrast, this area exhibits low-lying, undulating terrain shaped by the rapid weathering of weakly cemented sandstones and mudstones. Structural uplift followed by prolonged erosion has subdued the relief, emphasizing lithological control on erosion patterns.

These geomorphological contrasts are not merely scenic or topographic anomalies—they are vital indicators of the region’s tectonic history, sedimentary architecture, and litho-structural interactions. Understanding these landforms is essential for interpreting the broader geological evolution of the Khorat Plateau. Furthermore, the diversity and accessibility of these features within KKGp offer significant opportunities for geoconservation, geoeducation, and sustainable geotourism development. Protecting these landforms ensures the preservation of valuable geological heritage and supports the Geopark’s role as a natural laboratory for scientific research and public engagement.

Scientific, educational, and heritage significance

Khon Kaen Geopark (KKGp) serves as a vital natural laboratory where geological heritage, scientific research, and community participation are deeply interconnected1,2,3,4. As part of the aspiring UNESCO Global Geopark network, KKGp preserves a well-exposed geological archive of the Khorat Plateau, marked by Mesozoic sedimentary successions, tectonic deformation, and fossil-rich stratigraphy. These features provide key evidence for reconstructing paleoenvironments and understanding regional geodynamics.

In addition to its academic relevance, KKGp plays a central role in promoting sustainable development through geotourism and geoeducation1,2. Ongoing studies—including the present research— address important knowledge gaps in structural geology, basin evolution, sediment provenance, and notably, the geopark’s unique morphological features that are extremely uncommon among global geoparks, adding distinctive geomorphic value to its scientific and educational appeal. These scientific efforts align closely with UNESCO expert recommendations and contribute to enhancing KKGp’s international profile.

By advancing knowledge of tectonic evolution, lithological variability, and depositional systems, this study strengthens the case for KKGp’s UNESCO nomination while supporting long-term conservation strategies and community aspirations for geoheritage-based development.

Conclusion

Complex tectonic interactions across the Khorat Plateau have given rise to structurally controlled synclinal basins, faulted escarpments, and lithologically diverse outcrops that define the landscape of Khon Kaen Geopark. Detailed lithological and petrographic analyses reveal that the Nam Phong and Phu Kradung Formations, dominated by feldspathic litharenites and sublitharenites, originated from proximal volcanic arcs, indicating a syn-orogenic depositional environment influenced by the Indosinian orogeny. The structural framework of the geopark is characterized by multi-phase deformation events, including fault inversion and folding associated with both the Indosinian and Himalayan orogenies. These events produced a complex landscape with basin-forming multisynclinal geometries and strike-slip fault systems, which are evident in the present geomorphological configuration of the region. Additionally, the interplay between structural deformation and lithological properties—particularly the contrasting erosion resistance of various formations—has shaped the distinct topography of the geopark. The findings not only enhance regional geological understanding but also contribute directly to the scientific foundation required for UNESCO Global Geopark designation. They highlight the need for continued geoscientific research to support conservation, education, and sustainable development within the geopark framework.

Methods

This investigation commenced with an extensive review of existing geological literature and technical reports pertaining to the KKGp, with particular emphasis on regional structural geology, drainage systems, topographic configurations, and tectonic evolution. Previous research provided essential contextual data for interpreting the geological setting of the study area.

Subsequent fieldwork involved systematic geological mapping and lithological sampling at selected outcrops within the study area. Structural measurements, including bedding attitudes and joint orientations, were collected using a Brunton compass. These data were analyzed through stereographic projection and rose diagram plotting to interpret the spatial geometry, orientation patterns, and kinematic significance of the observed structural features. Detailed in situ lithological descriptions were also recorded.

Thirteen representative samples from the study area were selected for petrographic and paleontological analyses. Standard thin sections, approximately 30 μm thick, were prepared from these rock samples and examined under a polarized light microscope to identify mineral assemblages and textures. Analyses were performed using ZEN core imaging software integrated with ZEISS microscopy systems, enabling high-resolution observation and image capture. The resulting petrographic and photomicrographic data provided essential information for lithological classification and contributed to confirming the provenance of the sandstones in the lower section of the Khorat Group across the study area.

Sandstone classification followed the ternary diagram of quartz (Q), feldspar (F), and lithic fragments (L) as proposed by Pettijohn34. Provenance and tectonic setting interpretations were based on a suite of compositional diagrams: (a) the Qt–F–L classification diagram34; (b) the Qt–F–L and Qm–F–L tectonic setting diagrams35; (c) the Lm–Lv–Ls diagram36; and (d) the Qp–Lv–(Ls + Lm) diagram37all of which delineate specific depositional fields associated with different tectonic settings.

Geoinformatic data were employed to support spatial and structural analysis within the Khon Kaen Geopark area. Core datasets included drainage networks, slope aspects, contour lines, and digital elevation models (DEMs). A 20-meter resolution DEM was used to enhance terrain visualization and feature delineation in combination with high-resolution topographic data from NASA’s Shuttle Radar Topography Mission (SRTM) at 30-meter resolution, accessed via the USGS EarthExplorer platform (www.earthexplorer.usgs.gov). Preliminary structural interpretation was conducted using Google Earth Pro, where lineament features were visually assessed based on ridge alignments, drainage deflections, and topographic discontinuities—features typically associated with subsurface structural elements such as faults, joints, and fold axes. These geospatial datasets were integrated with existing geological and topographic maps to refine the structural interpretation. To ensure compliance with open-access publication requirements and copyright restrictions, SRTM-derived imagery was used as the base map for figure generation. The interpreted lineaments, initially mapped in Google Earth Pro, were redrafted and layered onto the topographic base using Microsoft PowerPoint for Mac version 16.90.2 (24102719).

In addition, shallow seismic reflection data along Highway No. 12 were interpreted to delineate subsurface structural features. The integration of seismic profiles with surface geological and topographical data provided a more comprehensive understanding of the subsurface architecture and its relationship to surface morphology.

Based on the synthesis of field, remote sensing, and geophysical data, structural geological maps and stratigraphic cross-sections were constructed to depict the spatial distribution and structural framework of the lithological units. These visualizations facilitated the interpretation of tectonic deformation patterns and their influence on landscape evolution. The final phase involved a critical synthesis of all datasets to evaluate the coherence between structural trends and geomorphic features, culminating in a comprehensive report that elucidates the tectonogeomorphic evolution of the KKGp.