README
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Dataset title:
Data for: Episodic records of deep microbial methanogenesis throughout the Caledonian mountain range exhumation

Recommended Citation: van Dam, F. (2026). Data for: Episodic records of deep microbial methanogenesis throughout the Caledonian mountain range exhumation (Version 1) [Data set]. Linnaeus University. https://doi.org/10.5878/3e25-9238
See the Researchdata.se catalogue entry for this dataset - accessible via the DOI link above - for compete metadata, including the dataset description, contact information and information about how to obtain the dataset. 


Responsible organization: Femke van Dam, Linneaus University

Description: Data for the article "Episodic records of deep microbial methanogenesis throughout the Caledonian mountain range exhumation". Data from the COSC-2 borehole in central Sweden (63.3124° N, 13.5259° E) at an elevation of 320 m with a depth of 2276 m from the surface. Data encompasses mineral analysis, including isotopic, age, and clumped isotopic analysis of calcites. Fluid analysis include hydrogeochemistry, gas composition and gas isotopic composisiton of hydrocarbons. 


Essential information for dataset reuse.
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Seven 0.6 L fluid samples were collected from different depths of the COSC-2 borehole using a Leutert Positive Displacement Sampler (PDS). The sampler was lowered into the borehole on a four-conductor logging cable and opened at the target depth by a trigger signal from the surface. Once opened, fluid entered the sampler under the elevated pressure of the borehole fluid column, continuously expanding the sampling volume. This technique allowed sampling under constant pressure and minimizes e.g., uncontrolled degassing. After 0.6 L of fluid had entered the sampler, the inlet valve was closed from the surface and the sampler retrieved under in situ pressure conditions. At the surface, the sample was transferred into a steel cylinder while maintaining in situ pressure. In a field laboratory, the fluid was then transferred into a glass apparatus with a defined volume for phase separation and subsampling of gas and water. Details on the sampling process, sample transfer, and fluid separation into gas and water phases are provided in Regenspurg et al. (2010) and Feldbusch et al. (2018). At 975 m depth the sampling was later repeated using packers and a pressurized in situ sampling device (PAKO). Pump samples were also taken from 40 m depth and spontaneously separated gas collected at the wellhead. Hydrogeochemistry, stable isotopes of water, gas composition and isotopic compositions of hydrocarbons were analysed from these samples. 

Thirteen rock core intervals containing open, partly sealed, or completely sealed fractures and vugs were targeted and sampled for secondary minerals coatings, focusing on calcite and pyrite. The crystals were characterized under a stereomicroscope and identified directly on the uncoated surfaces of fractures using a FEI Quanta 650 FEG scanning electron microscope (SEM) equipped with an integrated energy dispersive spectroscopy (EDS). On these samples different analyses were completed: SIMS, LA-ICP-MS U-Pb carbonate geochronology and carbonate clumped isotopes of calcites.

Dataset descriptions
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README.txt
Minerals and hydrogeochemistry
	Supplementary Data S1 Calcite carbon isotope compositions
	Supplementary Data S2 Calcite oxygen isotope compositions
	Supplementary Data S3 Pyrite sulfur isotope compositions
	Supplementary Data S4 Carbonate clumped isotope compositions reporting summary 
	Supplementary Data S5 Carbonate clumped isotope compositions full summary 
	Supplementary Data S6 δ18O of fluids
	Supplementary Data S7 Hydrogeochemistry of modern groundwater
	Supplementary Data S8 U-Pb Analytical protocol
	Supplementary Data S9 U-Pb full data
	Supplementary Data S10 U-Pb summary report
Gas compositions
	Table 1 Total hydrocarbon gas (THCG) composition in %THCG
	Table 2 Isotope composition (in ‰) 
	Table 3 Gas composition (% of total volume)
 



Reference information
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Abbreviations:
C1: methane
C2: ethane
C3: propane
C4: butane
C5: pentane



Data Quality:
Note that sample L067-17 in file S5 is only a single measurement due to insufficient amount of material. 
