and the angle of these troughs is in the order of around 25 degrees dipping in a north – south direction. Due to the increasing jointing in the Blantyre, we can surmise that the sandstone is influenced very little by the hydrothermal fluids, and preferentially weathers mud clasts. The environment here is one that has not as much water moving through, and the jointed layering could be as a result of drought at the time. This unit proceeds for some time until migrating alluvial fans cover the Blantyre Sandstone creating thick paraconglomerate layers above. Gilbert River Formation The Gilbert River Formation consists of paraconglomerate litharenite layers. In the lower part of the formation flaser cross bedding in fine grained sandstone is found in abundance, however a little further up the system becomes awash with volcanic and chert clasts typical of alluvial debris. These then are buried underneath fine grained material once more until a significant occurrence of fining upwards in thin layers shows a sharp change in depositional environment. The formation proceeds to become much more coarse grained and large, pebble to cobble sized clasts are enclosed. These are also noted to be largely sedimentary and volcanic in origin. The paleocurrent values for the formation are also highly variable, denoting a high energy flow regime with sufficient force to move large amounts of sediment. This is shown well in Plate 10 below and the imbrication of these pebble clasts is a good indicator for flow direction. From the state of the system it can be confirmed that the flow regime of the beds has changed over time, with the most definite change marked by the thin, fining upwards bedding. The most logical control on these being the fact that the formation has had an influx of fluids most likely from the coastline splaying out into an alluvial fan. The final section of the Gilbert River Formation is baked by the overlying Sturgeon Basalt, and this has created the baked psammite layer at the top of the Gilbert River Formation. See also List of canyons References External links Porcupine Gorge Challenge Canyons and gorges of Queensland Shire of Flinders (Queensland) North West Queensland