Cenozoic tectonics of New Guinea
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Abstract:
Major hydrocarbon discoveries have been made in eastern and westernmost New Guinea, and there is great potential for additional discoveries. Although the island is a type locality for arc-continent collision during the Cenozoic, the age, number, and plate kinematics of the events that formed the island are vigorously argued. The northern part of the island is underlain by rocks with oceanic island arc affinities, and the southern part is underlain by the Australian continental crust. Based on regional sedimentation patterns, it is argued herein that the Cenozoic tectonic history of the island involves two distinct collisional orogenic events.The first Cenozoic event, the Peninsular orogeny of Oligocene age (35–30 Ma), was restricted to easternmost New Guinea. Emergent uplifts that shed abundant detritus resulted from the subduction of the northeastern corner of the Australian continent beneath part of the Inner Melanesian arc. This collision uplifted the Papuan ophiolite and formed the associated mountainous uplift that was the primary source of siliciclastic sediments that largely filled the Aure trough. Between the Oligocene and Miocene, the paleogeography of the region was similar to present-day New Caledonia. The continental crust under central and western New Guinea remained a passive margin.The second event, the Central Range orogeny, began in the latest middle Miocene, when the bulldozing of Australian passive-margin strata first created emergent uplifts above a north-dipping subduction zone beneath the western part of the Outer Melanesian arc. The cessation of carbonate shelf sedimentation and widespread initiation of siliciclastic sedimentation on top of the Australian continental basement is dated at about 12 Ma. This collision emplaced the Irian ophiolite and created the present mountainous topography forming the spine of the island.Keywords:
New guinea
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Salt tectonics
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Integration of biostratigraphy and magnetostratigraphy is essential to the development of a worldwide biomagnetochronology. Drilling on the Exmouth Plateau during Ocean Drilling Program Leg 122 recovered an almost complete Cenozoic stratigraphic sequence at Site 762. Sediments at this site contain abundant, diverse, and generally well-preserved calcareous nannofossils. The continuity of the stratigraphic sequence, good preservation of the taxa, and availability of magnetostratigraphic measurements on the same cores offered an opportunity to construct a detailed first-order biomagnetochronology for Cenozoic calcareous nannofossils at Site 762. In the authors study, 104 nannofossil evolutionary first occurrences/last occurrences are correlated with magnetostratigraphy for the first time. The new biomagnetochronologic determinations include 28 dates in the Paleocene, 47 in the Eocene, 14 in the Oligocene, 11 in the Miocene, one in the Pliocene, and three in the Pleistocene. In addition, 71 first/last occurrences are determined for species whose first/last occurrences have previously been reported from other areas. The accurate assessment of the reliability (the synchroneity and/or diachroneity) of magnetically dated first occurrences/last occurrences over a wide latitudinal range depends on a data base consisting of many such age assignments. The large number of new dates reported here, and the complementary information on previously published dates, willmore » add significantly to the refinement of Cenozoic biomagnetochronology.« less
Magnetostratigraphy
Sequence (biology)
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Vertebrate paleontology
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