The Lawn Hill annulus: An Ordovician meteorite impact into water-saturated dolomite

The Lawn Hill Impact Structure (LHIS) is located 250 km N of Mt Isa in NW Queensland, Australia, and is marked by a highly deformed dolomite annulus with an outer diameter of ~18 km, overlying low metamorphic grade siltstone, sandstone, and shale, along the NE margin of the Georgina Basin. This study provides detailed field observations from sections of the Lawn Hill annulus and adjacent areas that demonstrate a clear link between the deformation of the dolomite and the Lawn Hill impact. 40Ar-39Ar dating of impact-related melt particles provides a time of impact in the Ordovician (472 ± 8 Ma) when the Georgina Basin was an active depocenter. The timing and stratigraphic thickness of the dolomite sequence in the annulus suggest that there was possibly up to 300 m of additional sedimentary rocks on top of the currently exposed Thorntonia Limestone at the time of impact. The exposed annulus is remarkably well preserved, with preservation attributed to postimpact sedimentation. The LHIS has an atypical crater morphology with no central uplift. The heterogeneous target materials at Lawn Hill were probably low-strength, porous, and water-saturated, with all three properties affecting the crater morphology. The water-saturated nature of the carbonate unit at the time of impact is thought to have influenced the highly brecciated nature of the annulus, and restricted melt production. The impact timing raises the possibility that the Lawn Hill structure may be a member of a group of impacts resulting from an asteroid breakup that occurred in the mid-Ordovician (470 ± 6 Ma)

A tale of two telescopes: North Queensland and the 1882 transit of Venus

The 1882 transit of Venus offered the final opportunity for astronomers to use these rare events to pin down the distance from the Earth to the Sun. A British party based itself in southern Queensland, but total cloud cover prevented any observations being made on the critical day. In this paper we trace the preparations of the British party, and then show how they laid the foundations for the development of astronomy in Queensland by selling their two 6-in Cooke refractors before returning to Britain. Both instruments were purchased by a Townsville amateur astronomer, Edwin Norris, and although he installed one in an observatory, he made little use of it. However, he subsequently sold the other telescope to J. Ewen Davidson of Mackay, who also erected an observatory for it. Davidson then used his instrument for cometary astronomy, in the process discovering two new comets, one of which now bears his name. Unfortunately, recent attempts to track down the present whereabouts of the two telescopes have failed