modified after MG of USSR (1969)

Moghilev-Podolisk Group Nagoriany Formation Kalius Member Kalius Member - gray to black argillites, occasionally interbedded by nodular and lenticular phosphorites and cone-in-cone carbonate mounds and crusts. modified after Velikanov et al., 1983

Study area – northern part of the Republic of Moldova Study area – northern part of the Republic of Moldova. Naslavcea village and Naslavcea quarry

Boundary between Quaternary alluvial deposits (Q) and the Kalius Member (PR3) Naslavcea quarry

Outcrop N1 N 48⁰ 28’ 48.1” E 27⁰ 33’ 48.8” Altitude = 104 m (Naslavcea quarry) N 48⁰ 28’ 48.1” E 27⁰ 33’ 48.8” Altitude = 104 m

Outcrop N2 N 48⁰ 27’ 55.5” E 27⁰ 35’ 01.6” Altitude 103m (Naslavcea village, near the church) N 48⁰ 27’ 55.5” E 27⁰ 35’ 01.6” Altitude 103m

Measured rock-eval pyrolysis and additional derived parameters Sample Depth (m) S1 S2 S3 Tmax TOC(%) MINC(%) HI OI S1+S2 PI S2/S3 PC SD065 143.8-199.4 0.16 2.12 0.31 438 1.08 0.13 196 29 2.28 0.07 6.84 0.19 RZ021 192.5-242.5 0.01 0.09 0.24 436 0.06 0.15 150 400 0.10 0.38 RZ023 178.0-181.5 0.08 1.69 0.22 0.89 0.34 190 25 1.77 0.05 7.68 K1 0.60 439 0.67 0.12 90 19 0.66 4.62 K2 0.04 443 0.54 111 15 0.64 7.50 K3 0.03 0.11 0.18 442 1.99 61 100 0.14 0.21 0.61 K4 441 0.30 70 30 2.33 0.02 K5 0.20 5.67 75 0.17 1.07 K6 0.39 444 6.52 47 229 K7 445 0.36 1.39 94 2.00 K8 0.48 440 0.50 96 22 0.51 4.36 K9 0.68 0.55 124 18 0.71 6.80 K10 0.25 4.79 72 88 0.82 K11 0.84 138 33 0.90 4.20 K12 0.78 0.41 0.62 126 66 0.85 1.90 K13 0.52 106 40 0.59 2.62 K14 0.35 0.56 86 62 1.37 K15 0.00 10 257 K16 0.70 0.37 189 K17 0.43 153 K18 0.63 23 147 K19 21 159 K20 0.65 0.29 224 K21 5 273 K22 14 286 K23 437 367 -  Terminology: S1 = mg HC/g rock S2 = mg HC/g rock S3 = mg CO2/g rock PI (Production Index) = S1/(S1+S2) HI (Hydrogen Index) = mg HC/g Corg OI (Oxygen Index) = mg CO2/g Corg

Modified van Krevelen diagram

Cross plot of rock-eval Tmax verus Hidrogen Index (HI) data showing the range in thermal maturity as well as hydrocarbon generative (kerogen) types of samples

HI (Hydrogen Index) versus TOC plots of samples

(after Waples’ Method, 1985) Quantitative (Volumetric) Molel for calculating the volume of hydrocarbons (after Waples’ Method, 1985) HC = (k)*(TOC)*(HI)*(f), where: HC – hydrocarbon volume in million of barrels/cubic mile; when transformed into SI units: million of barrels/cubic mile * 0.0381247 = million m3/km3; k – conversion constant (0.7 of a shale of approx. 2300 – 2400 kg/m3 specific weight gives a hydrocarbon equivalent of approximately 900 kg/m3 oil; TOC – average content of the total organic carbon in wt.%; HI – average hydrogen index in mg of hydrocarbons/g TOC; f – fractional conversion (0) – immature organic matter and (1) – mature organic matter; the considered values are based on measured vitrine reflectance; Average TOC = 0.8 % Average HI = 180 mg HC/g Corg Kerogen type III can generate 20% oil and 80% gas. Oil = 20% * 0.8 % = 0.16 Gas = 80 % * 0.8% = 0.64 TOC (Total Organic Carbon) HI (Hydrogen Index) k (conversion constant) f ?

Maturation Early Peak Late Maturity Ro (%) Tmax (◦C) Immature 0.20–0.60 <435 Mature Early 0.60–0.65 435–445 Peak 0.65–0.90 445–450 Late 0.90–1.35 450–470 Postmature >1.35 >470 Conversion values from Tmax to Vitrinite Reflectance (Ro) (after Peters and Cassa, 1994) Tmax 438⁰C <-> Ro 0.62-0.63

Ro = 0.62-0.63; For oil f = 0; For gas f = 0.02; Curves showing the relationship between Ro values and fractional conversion (f) of Types III (humic to mixed), II (kerogenous to kerogenous bacterial), and I (kerogenous algal) kerogens to oil (top, left to right) and gas (bottom) (after Sluijk and Nederlof, 1984).

Obtained volumes: Volume of generated oil = 0.7 (k) * 0.16 (TOC) * 180 (HI) * 0 = 0 millions of m3 per km3; Volume of generate gas = 0.7 (k) * 0.64 (TOC) * 180 (HI) * 0.02 = 1.6128 million barrels oil equivalent in gas; or 9.6768 billion cubic feet per cubic mile of source rock; or 0.065739 million m3 per km3 of source rock; For expulsion of hydrocarbons to take place, a threshold value of the generation of approximately 50 million barrels of hydrocarbons must be reached (after Momper, 1978). No hydrocarbons were generated during the geological time.

Conclusions: the analyzed samples show that the range in thermal maturity is between 435-440 ⁰C, thus they are in the early mature window; the modified van Krevelen diagram and the HI versus Tmax cross plot indicates that the kerogen type in the Kalius Member is primarily Type III gas-prone kerogen, but there is also a type II/III oil/gas-prone kerogen input; based on the obtained data the Neoproterozoic Kalius Member is a potential source rock that could generate hydrocarbons if the proper geological conditions are met; it is possible that hydrocarbons where generated at depths higher than 1000 m, but the analyses of cores from new boreholes is required;

References: 1. K. E. Peters, M. R. Cassa, Applied source rock geochemistry, AAPG Memoir 60, 1994, pp. 93-120 2. L. Nunez-Betelu, J. I. Baceta, Basics and application of Rock-Eval/TOC pyrolisis: an example from the uppermost Paleocene/lowermost Eocene in the Basque Basin, western Pyrenees, 1994, pp. 43-62 3. J. A. Momper., Oil migration limitations suggested by geological and geochemical considerations, in Physical and Chemical Controls on Petroleum Migration: AAPG Continuing Education Course Note Series, No.8, Tulsa, American Association of Petroleum Geologists, 1978, pp. B1-B60. 4. D. Sluijk, and M. H. Nederlof, Worldwide geological experience as a systematic basis for prospect appraisal, in G. Demaison and R.J. Murris, eds., Petroleum Geochemistry and Basin Evaluation: American Association of Petroleum Geologists Memoir 35, Tulsa, American Association of Petroleum Geologists, 1984, pp. 15-26. 5. D. W. Waples, Geochemistry in Petroleum Exploration. D. Reidel Publishing Company, 1985, pp. 73-154 6. В. А. Великанов, Е. А. Асеева, М. А. Федонкин, Венд Украйны, Наукова Думка, 1983, с. 159. 7. Министерство Геологий СССР, Геология МССР, Издательство Недра, Москва, 1969, с. 452