Quaternary Urban Geology and the Foundation of Heritage Building: Notable Historical Cases in Sawahlunto, Indonesia

Sawahlunto is a city located in West Sumatra, Indonesia, known as a city rich in coal mining activities and often referred to as the “City of Batubara.” The history of Sawahlunto coal mining dates back to the Dutch colonial era in the late 19th century when coal was discovered in the area. It has been designated as a national geopark area (KGN) in 2018 and then designated as a UNESCO World Heritage Site (WDU) in 2019. One of its prominent landmarks is the Ombilin Coal Mine, which. Sawahlunto also boasts other historical landmarks and preserved buildings. The study objectives are: to identify rock types, topographic features, and other phenomena, along with measurements of heritage buildings; to analyze the rock distribution for determining the origin of rocks for heritage buildings in urban development and to describe the heritage building; and to describe the development of heritage building in Sawahlunto The mixed method was incorporated, where geological mapping method was used to determine information on the distribution of rocks and material origin for urban development, heritage building foundation analysis and content analysis on heritage buildings. The study found the building materials are rocks from the result of erosion originating around the city of Sawahlunto are: Sedimentary rock facies in the Ombilin Basin. The heritage buildings used local materials as they were abundant during that time. Sawahlunto’s heritage buildings not only have historical and cultural heritage, but also contain urban geological heritage that should be further studied as part of urban development.


Introduction
In 2018, Sawahlunto, spanning an area of 177.5 km 2 , was granted National Geopark status, signifying its geological wealth, biodiversity, and cultural uniqueness (Oktariadi, Yuliawati et al., 2016), as well as sustainable utilization of resources.This designation aims to preserve and sustainably manage geological and cultural heritage of the region (Font et al., 2021;Longoria et al., 2021;Oliveira-Duarte et al., 2021).
The National Geopark comprises 30 geological and 20 non-geological sites, featuring remarkable rock formations, geological structures, fossil sites, and other captivating phenomena (Rohaendi et al., 2022).In-depth mapping and studies are conducted to comprehensively understand the characteristics and importance of each site.Additionally, the non-geological sites encompass biological richness, cultural and historical aspects, and sustainable human activities.These may range from natural parks to historical sites, and local cultural heritage locations.Szepesi et al., 2018).This convention acknowledges the complex interaction of humanity with the natural environment, emphasizing the paramount importance of maintaining a harmonious balance between the two.Furthermore, its objectives include strengthening the credibility of the World Heritage List, ensuring effective conservation of World Heritage properties, promoting capacity-building measures, increasing public awareness, and involving communities in the convention implementation process (Cardoso et  The study area of Sawahlunto, situated in a valley surrounded by mountains, is renowned for its rich mining historical as one of the largest coal mining regions in Sumatra.Currently, this city has become a popular tourist destination due to its historical sites, mining museums, and captivating natural beauty (Syafrini et al., 2022).

Field Geological Mapping and Heritage Building Foundation Analysis
In this study, geological mapping was conducted, which involved direct field observations to identify rock types, topographic features, and other phenomena, along with measurements and evaluation of their distribution to determine the origin of rocks for urban development (Corona et  Evolution of Traditional Building Foundation Types: This encompassed the evolution of foundation types created in building built before the first industrial revolution.
Underpinning: A method applied to strengthen and stabilize foundation of building.This involves excavating the underneath soil and replacing it with concrete or other materials to increase the depth and bearing capacity of foundation.
Preservation: An approach focusing on the maintenance, stabilization, and repair of existing historical materials, thereby retaining the evolving form of the property over time.This is particularly relevant to preserving foundation of heritage building, as well as their historical and cultural significance to ensure structural integrity and safety (Arfa et  Geological Formations: The region possesses several significant geological formations (Prayitno et al., 2019).This includes the Silungkang Formation consisting of sandstone, claystone, and a thin layer of coal, which originated during the Early Triassic to Intermediate periods.Another one is the Tuhur Formation comprising sandstones, claystone, and breccia, formed in the Late Triassic period to the Early Jurassic (Qin et al., 2021).
Geological Structure: The area is influenced by complex geological structures, featuring folds and faults that direct the movement of rocks, forming distinctive structural patterns.These structures play a crucial role in the formation and distribution of mineral resources, including coal (Prayitno et al., 2019).
Coal Resources: The abundant coal deposits in the area have been a primary factor contributing to the development of the coal mining industry (Rohaendi et al., 2022;Syafrini et al., 2022).
National Geopark: Sawahlunto holds the status of being among the Indonesian National Geoparks, encompassing the city and its surroundings.The geopark serves as a focal point for studies, preservation, and education concerning geological heritage and natural wealth of the area.Moreover, it has become a popular tourist destination for visitors interested in geological and mining historical (Ahmed,

Results
The discovery of abundant coal deposits in Sawahlunto was found to play a crucial developmental role in the mining economy.Coal serves as a vital natural resource, widely used as fuel in industries, transportation, and heating.Notably, the Dutch government discovered the great economic potential of the coal mine in this region and sought to optimize resource exploitation.
The city has been recognized as the oldest coal mining site in Southeast Asia.In 1882, an integrated coal industry was established in this region by the Dutch East India Company (Vereenigde Oost-Indische Company/VOC) to supply energy resources for the late 19th-century Industrial Revolution in Europe.Following the closure of the mine in 2000, there was a transition from a mining-centric economy to an ultimate focus on tourism.The coal mining heritage, embodied in the beauty of old building, former infrastructure, and post-mining landscapes, has attracted visitors and highlighted the tangible and intangible value of heritage.These features connect visitors with the past, providing insights into the mining tradition and cultural identity of the community, thereby serving as a primary motivation.
The erosion of rocks surrounding the city led to the formation of various materials, including Sedimentary rock facies in the Ombilin Basin study area, grouped into four classes as described below.Limestone, originating from the Silungkang and Tuhur Formation (Moss &;Howells, 1996), dating back to 248-243 million years ago, served as an adhesive material between other materials (Mulyana et al., 2015).Furthermore, the pointed stone formations situated around Sungai Cacang Hamlet, Silungkang Oso Village, Silungkang District, Sawahlunto City, offered extraordinary beauty, attracting visitors as a popular photography spot and even functioning as a location for extreme sports such as rock climbing.
The Lunto River, stretches approximately 18 km within the Ombilin and Selo River Sub-Watershed, as well as Kuantan River Watershed (Hasbi et al., 2017).Additionally, it carries various materials including stone, sand, and brick, originating from the surrounding areas.

Ombilin Coal Mining Heritage of Sawahlunto
The Ombilin Coal Mining Heritage of Sawahlunto, constructed by the Netherlands colonial government in the late 19th century, represented an extensive technological ensemble.This was designed to exploit the rich Ombilin coal deposits and also consisted of twelve components located in three functionallyrelated areas, namely: Area A: This encompassed open pit mines, labyrinthine underground mining tunnels, on-site coal processing facilities, and a purpose-built mining town in Sawahlunto.
Area B: This comprised the transportation system, including railways, cable cars, and port facilities.Area C: This consisted of supporting infrastructure, such as the water supply system, power plant, and administrative building.
The Ombilin Coal Mining Heritage stood as a remarkable example of a complex technological ensemble, planned and built as a fully-integrated system.This was designed to enable efficient deepbore extraction, processing, transport, and shipment of industrial-quality coal.Moreover, the site demonstrated a significant exchange of mining technology between Europe and the associated colonies during the late 19th and early 20th centuries.In 2019, it was inscribed on the World Heritage List of UNESCO.The mining area continued to attract visitors, remaining a popular tourist destination in Sawahlunto.

Conclusions
In conclusion, the presence of coal mining has contributed to the preservation of various building, including colonial-era structures such as Dutch-style town halls, old mining offices, and residential houses that reflect the architectural styles of the time.Materials were derived from local resources and the development of transportation facilities and infrastructure in Sawahlunto City Area showcase the enduring legacy of the coal mining industry in this region.
al., 2023; Aquilué et al., 2021; Lu et al., 2022; Melelli, 2019; Pando et al., 2022; Urban Geosites as an Alternative Geotourism Destination, 2017).Additionally, the analysis and management of heritage building foundation employed various methods, including: Foundation Behavior Analysis: Different approaches and methods were utilized to analyze the behavior of historical building foundation.

Table 1 .
Classification of Sedimentary Rock Facies at Ombilin Basin