Deep fluids migration and submarine emersion of the Kalang Anyar mud volcano (Java, Indonesia): A multidisciplinary study

This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.


53
The north-eastern part of the island of Java is part of a back-arc basin containing a petroleum 54 province that is characterized by numerous modern and palaeo-piercement structures (e.g. mud 55 volcanoes, buried vents, and diapirs). The region contains evidence of extensive interactions 56 between gravitatively-unstable buoyant shales, faulting, hydrothermal activity, and hydrocarbons  The objective of this study is to present a multidisciplinary study of Kalang Anyar MV, based on 90 geological and geophysical field surveys and geochemical analyses of samples. The results provide 91 evidence of deep gas sources in relation to tectonic structures, on the mud volcano plumbing 92 system, and on the recent history of extrusion and its geohazard potential. To our knowledge, this 93 is the first survey of an Indonesian mud volcano that aims to quantify its gas emissions and 94 compare them with similar structures elsewhere on the planet. It is also the first study of a mud 95 volcano that records a progression from submarine to terrestrial activity. reproducibility for measurements of  13 C (1s=0.1‰) and D-CH4 (1σ=1‰) is better than 0.2‰ and 145 2.5‰ respectively. 146 At one site with sustained gas seepage, a sample for He analyses was collected in annealed copper 147 tubes sealed directly in the field using a cold welding clamp. The sample was analysed at the INGV 148 laboratory in Palermo. After standard purification procedures, 3 He, 4 He and 20 Ne, and the 4 He/ 20 Ne 149 ratios were determined by separately injecting He and Ne into a split flight tube mass spectrometer 150 (GVI-Helix SFT, for He analysis) and then into a multicollector mass spectrometer (Thermo-151 Helix MC plus, for Ne analysis). The analytical error was generally less than 1%. The R/RA values 152 were corrected for atmospheric contamination based on the 4 He/ 20 Ne ratio (Sano and Wakita,153 1988). The results are given in R/Ra notation, where R is the sample 3 He/ 4 He ratio and Ra is the 154 atmospheric 3 He/ 4 He ratio, 1.39×10 -6 . The Ar-isotope composition was measured in a 155 multicollector mass spectrometer (GVI Argus), for which the analytical uncertainty was 0.5%. The  were selected for dating, as having the greatest likelihood of meeting these criteria.

179
Shells were selected for analysis on the basis of stable isotopic results (see Table 1 200 We completed 27 CH4 and CO2 flux measurements crossing the MV along the A-A' profile using 201 the West Systems™ portable fluxmeter equipped with CO2 and CH4 detectors. The CH4 flux meter 202 is a TLD Tunable Laser Diode spectrometer (West Systems™) that allows the measurement of gas 203 fluxes in the range from 1.5 up to 1000 moles m −2 d −1 . The CO2 detector is a LICOR-LI820, which 204 is very accurate in the range from 1.5 up to 300 moles m −2 d −1 . The acquired data were statistically 205 and graphically processed with the Statistica 10 and Grapher 18 software. The total CO2 and CH4 206 soil release was estimated from the measured flux values following the approach described by  To identify seismic signals potentially associated to bubbling observed at the main seepage sites, 211 we deployed 4 broadband seismometers (three 120s Trillium compact and one Leinartz 3Dlite 212 equipped with Nanometrics Centaurus digitizers) for 24 hours. The differences in seismic signals 213 were found to be drastically different between day and night. This is due to day-time human   (Fig. 1D). Type 1 is present in the NE part of the structure and is densely packed with 237 bivalves (chemoherms) (Fig. 3A-B). Type 2 crops out at several localities in the southern part,     Fig. 1D.

249
Radiocarbon ( 14 C) measurement (Table 1) were performed on shells to constrain the time period 250 during which these organisms were living. The bivalve clams collected from carbonate blocks 251 J o u r n a l P r e -p r o o f Type 1 (JV08-02S) returned a measured 14 C age of 44917 ± 1306 BP. As this age is inconsistent 252 with submarine conditions in the study area (see discussion), we did not proceed with calibration 253 of the measured age (see section 5.2). For oyster shells cemented outside the carbonate blocks 254 Type 2 (sample JV08-03S) the measured 14 C age was 2167 ± 37 BP. The calibrated calendar age 255 range for this sample at 2 sigma (95.4% confidence) is 1890-1488 BP.   (Table 3).          The total output of macroseeps measured in the active crater zone (Fig. 1D) Table 4). The scatter plot of CH4 vs CO2 (Fig. 5C) shows that a good correlation is present only 319 on the measured macroseeps (r = 0.9).  (Table 5).

370
The cements of authigenic carbonate blocks and ridges sampled at Kalang Anyar MV ( which is in agreement with isotopic analyses of currently seeping gas at the crater site (Table 2-3).

375
Similar to many other seepage sites, the Kalang Anyar carbonates are associated with bivalves 376 (clams and oyster) that also reveal negative δ 13 C values (Fig. 4). Clams (Type 1, δ 13 C =-12.2‰) 377 are cemented within the methanogenic carbonate and during their growth, also incorporated some  Radiocarbon ( 14 C) results from bivalve shells that were living during the precipitation of 387 methanogenic carbonates are best candidates to constrain the age of submarine methane seepage.

388
When dating the bivalves, it is important that the 14 C/ 12 C of the shells (from which the %Modern 389 C and 14 C age are calculated) represents the dissolved inorganic carbon (DIC) of the seawater at 390 the time the shell was precipitated. In the setting of Kalang Anyar MV, two potential carbon 391 sources can be identified. First, the DIC of the ocean water for the region, which best represents 392 the 'true' 14 C age (and calendar age, following calibration) at the time the shell was living. Second,

393
DIC from geological sources (e.g. from the seepage of methane), which is older and likely to 394 be 14 C-dead' at source. The measured 14 C/ 12 C ratio (and hence radiocarbon age) of the shells is a 395 weighted average of these two possible end members. The greater the contribution of geological 396 carbon (through localized methane seepage), the greater will be the 'apparent' 14 C age of the 397 sample. In principle it is possible to correct for the geological contribution through an isotope 398 mass-balance approach using a system such as δ 13 C and/or δ 18 O. However, this requires an 399 accurate assessment of the end member values and the uncertainty associated with these. We chose 400 not to attempt correction for the incorporation of geological carbon and instead use the ages of the 401 samples to constrain the chronology of events in a general sense, providing only maximum ages.

402
The 14 C results for sample JV08-02S show a value of 0.37 ± 0.06 %MC which translates to a 14 C 403 age of ~45 Ka BP (see Table 1). This age is inconsistent with regional evidence that at this time  Table 1). We hypothesise that through diagenetic processes the 13 C-408 J o u r n a l P r e -p r o o f depleted methanogenic cement is incorporated in the bivalve shells (although this is not strongly 409 revealed by the isotope analyses). We cannot currently solve this issue without a wider programme 410 of investigation, and, in light of this uncertainty, we decided not to consider the 14 C analytical 411 results for sample JV08-02S in our interpretation of the timing of activity at the study site.