Mesozoic stratigraphy and paleontology of Misool Archipelago, Indonesia

Abstract

The Mesozoic rocks which are exposed mostly on the southern half of Misool and adjacent islets, eastern Indonesia, include Triassic (Anisian to Norian), Jurassic (Toarcian to Tithonian) and Cretacecus strata. They are underlain by low metamorphosed Ligu Formation of Siluro·Devonian age unconfonnably and overlain, by Tertiary rocks probaly confonnably. The Tiassic consists of the Keskain Fonnation (Anisian to Ladinian), and the Bogal Formation with its Lios Member (Camian to Norian). The Jurassic is represented by the Yefbie Formation (Late Toarcian to Late Callovian), Demu Formation (Late Callovian to Late Oxfordian), and Lelinta Fonnation (Late Oxfordian to Early ð€€¸erriasian). The Formation (Early Berriasian to Aptian), Waaf Formation (Late Aptian to Early Suntonian), Fafanlap Formation and Yabatano Member (Late Santonian to Maastrichtiasn) and Daram Fonnotion (Latest Maastrichtian to Paleocene) constitute the Cretaceous sequence. A major unconformity occured in early Jurassic time. Most of the age determinations are based on ammonoids although they are not found in all sections. Belemnites which were studied by A.B. Challinor helped with many of the age conclusions especially in the upper Middle Jurassic to Lower Cretaceous. Incorpopration of knowledge from other groups such as bivalves and dinoflagellates provides more confident correlations although in some cases ages are still rather arbitrary. In the Tiassic, the Lios Member of the Bogal Formation has the most abundant and diverse fauna. In the Jurassic, the Yefbie and Lelinta Formations are the most fossiliferous. The Gamta Formation contains only belemnites in its lower part and the Fafanlap Formation includes mostly inoceramids in its lower part. Most Cretaceous rocks do not contain macrofossils but are rich in microfossils (Globotruncanidae, Globigerinidae etc.). Most of the Jurassic formations were deposited as the resu1t of rift­drift processes on the northern margin of the Australian segment of the Gondwanan continent. Biostratigraphic correlation within Indonesia is attempted as well as with other regions. In the Triassic the Misool Archipelago was related to Buru, Scram and Sumatra Islands, although common species are very few. The Triassic of Misool Archipelago, especially the Lios Member, also has very similar faunas to the European Alps and Mediterranean, with the presence of Rhabdoceras suessi, Palaeocardita trapezoidalis etc. The Jurassic of M.isool is very similar to Sula Island on the basis of the bivalve content, but differs from Sula in that good ammonite assemblages are replaced by assemblages of belemnites (see Challinor, 1989). M.isool Archipelago, can also be correlated with Central Irian Jaya on the basis of ammonites fauna such as Fonrannesia killiani. From the ammonite fauna, the Misool Jurassic is also correlable with that of the European Alps, North America, Chile, Argentina, New Zealand, Northwestern Australia, nonh and south Tibet, Himalaya etc. However, with some areas correlation is based only on a few species and sometimes only on cosmopolitan genera. For the Cretaceous correlation within Indonesia is more difficult, because Misool Archipelago has few macrofossils of that age. However, microfossils such as Globotruncanidae and Globigerinidae are widely distributed in eastern Indonesia, although not studied in this work. Correlation with the European Cretaceous and other parts of the world is probably potentially very promising using microfossils. However, based on common inoceramids in the Middle Campanian, Misool Archipelago is corre1ab1e with Madagascar. Paleogeographically Misool Archipelago in the Triassic occupied the southeastern margin of the Tethys Sea as indicated by common species Palaeocardita trapezoidaiis, Rhabdoceras suessi, "Thecosmiiia" sp. etc. In Jurassic time Misool Archipelago more or less occupied the same position as in the Tiassic, but the fauna was more diverse and shows similar paleoenvironments to those in Argentine/Chile, Northwest Australia and south and north Tibet, especially in the Middle Jurassic. Faunal associations in Triassic, Jurassic and Cretaceous rocks of Misool were analysed and used to attempt paleoecological analysis. Five faunal association of this area are distinguished as follows: ,1. Daonella Facies 2. Mixed Fades 3. Ammonoid Facies 4. Brachiopod Facies 5. Benthic Bivalve Facies. The Mesozoic rocks of Misool are believed to have been deposited in marine conditions ranging from neritic to continental slope environments, probably slightly deeper (bathyal) in the Cretaceous judging from the microfaunas although in the uppermost Cretaceous it was probably slightly shallower. In the early Triassic block faulting affected the Misool area but since that time it has been relatively stable and situated on the northern margin of the Australian-Gondwana continent. The eustatic curve for the area is correlable with the global curve for the Mesozoic. Slight differences are shown by lithologic differences, strata in Misool being rather uniform and thin. Faunal diversity is generally correlable with trangressions and regressions, and in the Jurassic there is positive correlation of the peaks of trangression with global peaks.