Bulletin of the Geological Society of Malaysia, Volume 72, November 2021, pp. 151 – 163

Explanation of marine lake formation at Misool Raja Ampat West Papua, Indonesia

Gandi Y.S. Purba^1,*, Lukas Rumenta², Purwanto², Leontine E. Becking^3,4, Eko Haryono⁵

1 Department of Marine Science, Faculty of Fisheries & Marine Science, Universitas Papua, Gunung Salju St. Manowari-West Papua, Indonesia 98314
2 The Nature Conservancy, Indonesia Marine Program, Pengembak St. No. 2, Sanur-Bali, Indonesia 80228
3 Department of Marine Animal Ecology, Wageningen University and Research, De Elst 1-Wageningen, The Netherlands
4 Wageningen Marine Research, Wageningen University and Research, Ankerpark 4-Wageningen, The Netherlands
5 Faculty of Geography, Universitas Gadjah Mada, Bulak Sumur-Yogyakarta, Indonesia 55281
* Corresponding author email address: g.purba@unipa.ac.id

Abstract: Marine lake in a karst landscape is one of the macro karst forms known as doline and is only found in some locations in the world. Moreover, the theory of marine doline formation is always associated with global sea-level rise which differs from one place to another due to several factors. This research was conducted to understand the formation process of marine lakes in Misool and how the water fills the basins formed especially at Holocene time. This was achieved by obtaining information on the longest underwater terrace which is also the longest standing water position recorded on the sea wall. The marine terraces were measured by sounding profiles to the sea bordering the seven marine lakes including Lenmakana, Balbullol, Lenkafal, Keramat, Karawapop, Keramat-2, and Keramat-3 as well as Harapan Jaya Sea. A total of 24 profiles were measured and stable isotopes δ18O and δD of water samples were used to determine the origin of water in the lakes. The results showed the longest terrace was at the depth of ˗33 and ˗3 m while the references from the area closest to Misool showed the same water level positions at 10,500 BP and 6,985 BP. Furthermore, the composition of δ18O and δD from lake water indicated the water samples were a mixture of groundwater and seawater with the seawater having the more dominant concentration and this allows it to fill the lake first through a previously formed cavity system.

Keywords: Marine lake, Raja Ampat, karst, sea-level rise, stable isotope

DOI: https://doi.org/10.7186/bgsm72202112