Abstract The SE Asian gateway is the connection from the Pacific to the Indian Ocean and it has diminished from a wide ocean to a complex narrow passage with deep barriers ( Gordon et al. 2003 ) as plate movements caused Australia to collide with SE Asia. It is one of several major ocean passages that existed during the Cenozoic but has received much less attention than others that opened, such as the Drake Passage, Tasman Gateway, Arctic Gateway or Bering Straits, or that closed, such as the Panama Gateway or Tethyan Gateway (e.g. von der Heydt & Dijkstra 2006 ; Lyle et al. 2007 , 2008 ). It is not entirely clear why there has been this comparative neglect, but it may reflect the relative limited knowledge of the large and remote areas of Indonesia and the western Pacific, in particular their geological history, and the relatively small number of active researchers in this large region. Unlike the Panama Gateway and Tethyan Gateway the SE Asian gateway is still partly open and the ocean currents that flow between the Pacific and Indian Oceans have been the subject of much recent work by oceanographers (e.g. Gordon 2005 ). We now know that the Indonesian Throughflow, the name given to the waters that pass through the only remaining low latitude oceanic passage on the Earth, plays an important role in Indo-Pacific and global thermohaline flow ( Gordon 1986 ; Godfrey 1996 ), and it is therefore probable

Three time lines through the neritic stratigraphic record distributed around the northern margin of the Australo-Antarctic Gulf (AAG) mark three fundamental shifts in global environments collectively comprising the Auversian facies shift. The three lines are: (1) the beginning: the Khirthar transgression and the onset of neritic carbonate accumulation in the Bartonian Age (preceding onset of the Middle Eocene climatic optimum [MECO]); (2) the midlife change (Bartonian-Priabonian transition): the shift from carbonate-rich to carbonate-poor, higher-nutrient environments under estuarine circulation, causing widespread dysaerobia culminating in opaline silicas; and (3) the Eocene-Oligocene = Priabonian-Rupelian boundary and glaciation during oxygen isotope event Oi-1, with return of improved ventilation in neritic environments and resumption of carbonate accumulation. Meanwhile, it was warm and very wet at ~60°S. In developing a scenario for the death of the AAG, the birth of the Southern Ocean, and the transition from Paleogene greenhouse Earth to Neogene icehouse Earth, the neritic record of the northern margin is more in accord with the “Dinocyst biogeographic hypothesis” than with the “Tasman gateway hypothesis.”

Abstract Understanding of Earth’s transition from a warm, ice-free Cretaceous to today’s bipolar glaciation is hotly debated. The Oligocene–Miocene boundary is marked by a brief glacial event followed by an interval of colder temperatures. Changes are small compared to the major Antarctic ice build-up at the Eocene–Oligocene boundary and establishment of a permanent Antarctic ice-sheet in the mid-Miocene. However, fossil evidence from low latitudes, including the faunal turnover which originally defined the Oligocene–Miocene boundary, indicates a reversal in trans-Atlantic flow, i.e. from westward to eastward, at this time. Modelling results suggest that a combined narrowing of the Tethys Seaway and deep opening of Drake Passage, and hence inception of Antarctic circumpolar circulation, drove reorganization of the patterns of ocean circulation. Despite evidence for a shallow Drake Passage opening in earliest Eocene time and subsequent deepening, a comparison of Southern Ocean isotopic records suggests that circumpolar circulation did not exist prior to c. 26 Ma. In fact, sedimentary records of a grain-size current-speed indicator from the Tasman Gateway reveal a singular, marked increase immediately preceding the initial Miocene event. The likely driver of this increase is inception of the full Antarctic Circumpolar Current. Among possible causes of early Cenozoic climate deterioration, the opening of seaways appears to play the major role. Extreme orbital configurations and p CO 2 -drawdown may act as reinforcing factors.