| Sangkarewang Formation | |
|---|---|
| Stratigraphic range: | |
| Type | Geological formation |
| Unit of | Ombilin Basin |
| Underlies | Sawahlunto Formation |
| Overlies | Brani Formation |
| Lithology | |
| Primary | Shale, sandstone |
| Other | Oil shales |
| Location | |
| Coordinates | 0°36′S 100°48′E / 0.6°S 100.8°E |
| Approximate paleocoordinates | 0°30′S 110°18′E / 0.5°S 110.3°E |
| Region | West Sumatra |
| Country |  Indonesia |
  Sangkarewang Formation (Indonesia) | |
The Sankarewang Formation is an ?Eocene-aged geological formation in Sumatra, Indonesia near Padang. It is among the very few Paleogene fossil deposits from Southeast Asia that preserves a freshwater ecosystem, and contains many of the earliest records of freshwater fish taxa that now predominate the region. Many of the fishes from this formation are well-preserved as articulated skeletons. The fossils of the formation have been known since the 1870s, although they only received significant attention during the 1930s and again starting from the mid-2010s.[1]
The age for this formation has long been disputed, with suggested ages ranging from the Cretaceous to the Miocene. Although the exact age still remains uncertain, most recent studies have settled on a tentative Paleogene age, with estimates ranging from the Paleocene[2] to the Oligocene. More recently, unpublished palynological data suggests that the overlying Sawahlunto Formation is of middle-late Eocene in age, which would most likely place the Sangkarewang Formation in the early-mid Eocene.[1]
It was deposited within the Ombilin Basin, a small Paleogene-aged rift basin that formed from deformation along the Great Sumatran fault. The Sangkarewang Formation was deposited within a freshwater rift lake that formed in this basin early on, with anoxic bottom waters allowing for the fossilization of the fish skeletons.[3][1] The Sawahlunto Formation, long exploited for its coal seams, was later deposited in the lake on top of the Sangkarewang Formation. During the Oligocene, this gave way to a river delta (the Sawahtambang Formation), and was later flooded by the sea by the Miocene (the Ombilin Formation), before a tectonic uplift raised it above the sea.[3] The formation has been explored for its oil shales.[4]
- ^ a b c Cite error: The named reference
:1was invoked but never defined (see the help page). - ^ "PBDB Collection". paleobiodb.org. Retrieved 2024-09-25.
- ^ a b Whateley, M. K. G.; Jordan, G. R. (1989). "Fan-delta-lacustrine sedimentation and coal development in the Tertiary Ombilin Basin, W Sumatra, Indonesia". Geological Society, London, Special Publications. 41 (1): 317–332. Bibcode:1989GSLSP..41..317W. doi:10.1144/GSL.SP.1989.041.01.22. ISSN 0305-8719.
- ^ Fatimah; Ward, Colin R. (2009-01-31). "Mineralogy and organic petrology of oil shales in the Sangkarewang Formation, Ombilin Basin, West Sumatra, Indonesia". International Journal of Coal Geology. CSCOP-TSOP-ICCP 2007 Selected papers from the 2007 joint meeting of CSCOP-TSOP-ICCP: Unconventional petroleum systems & advances in organic petrology and geochemistry. 77 (3): 424–435. Bibcode:2009IJCG...77..424F. doi:10.1016/j.coal.2008.04.005. ISSN 0166-5162.