Abstract
Aruwakkalu fossil bed is a part of Sri Lanka’s Jaffna limestone, which underlies the whole of Jaffna Peninsula and extends southwards mostly along the west coast. Previous authors have suggested that Aruwakkalu contains a rich assemblage of vertebrate and invertebrate fossils. We sought to confirm the Burdigalian age of this northwestern Miocene deposit at Aruwakkalu on the basis of the foraminifer Pseudotaberina malabarica, an index fossil of the Burdigalian stage. General and timeline collections were made at seven selected sites and the fossils collected were identified. The study sites contained six sedimentary layers of which, third and sixth from top were fossiliferous. The sixth (deepest) layer was dominated by gastropod fossils while the third was dominated by fossils of giant oysters. Fossils of P. malabarica were recovered both from timeline and general collections. In the timeline collection, samples of this index fossil were recovered only from the gastropod layer, suggesting that P. malabarica existed during the time the gastropod layer was being laid down, thus confirming a Burdigalian age for the latter, and helping to date a substantial portion of the Sri Lankan fossil fauna with confidence. Key words: Pseudotaberina malabarica; foraminifera; index fossil; Miocene; gastropod layer; oyster layer DOI: http://dx.doi.org/10.4038/cjsbs.v40i2.3933 CJSBS 2011; 40(2): 163-174
Highlights
Cenozoic era, known as Age of Mammals (Deraniyagala, 1969a) comprises two periods, the Tertiary (65.5-2.6 mya) and the Quaternary (2.6 mya to the present)
Microspheric forms were recovered from the timeline collection at Alahakoon site, while megalospheric forms were recovered from general collection at Peella site
The Tertiary and Quaternary exposures along the northwestern of part of Sri Lanka is composed of both Miocene and late Pleistocene deposits
Summary
Known as Age of Mammals (Deraniyagala, 1969a) comprises two periods, the Tertiary (65.5-2.6 mya) and the Quaternary (2.6 mya to the present). Aruwakkalu has been subjected to strong elevational changes, probably due to block faulting, which is evident in the positioning of the islands along the Kalpitiya shoreline and the ridges along the eastern shore of Dutch Bay. the Jaffna bed is considered to be a marine deposit, fossils of terrestrial reptiles and mammals, often associated with estuarine habitats, have been discovered from the “Malu member”, located along the eastern shoreline of Dutch Bay. the Jaffna bed is considered to be a marine deposit, fossils of terrestrial reptiles and mammals, often associated with estuarine habitats, have been discovered from the “Malu member”, located along the eastern shoreline of Dutch Bay This suggests that, at least in some areas, fossil accumulation took place under fluvial and estuarine conditions (Deraniyagala, 1969a)
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