Windmill Islands 1:10000 Geology GIS Dataset

Full description

This dataset is a geological map of the Windmill Islands, mapped at a nominal scale of 1: 25 000. The map is of lithological units. Structures, etc are ignored.
There is a separate, associated, dataset on geological samples and analyses which has its own metadata record with ID wind_geosamp.

A map was produced using this data in February 1997 (see link below).

Lineage

Progress Code: completed

Statement: Lineage The first source of geological data for this project was: Blight, D.F. 1975. The Metamorphic Geology of the Windmill Islands and adjacent coastal areas. PhD thesis. University of Adelaide. This includes a geological (lithological) map, a structural geology map and a map showing the location of samples taken. In 1994, the project to compile the most up-to-date geological map was initiated by Rupert Summerson, Mapping Officer, Antarctic Division as part of the Windmill Islands GIS Pilot Project. Copies of a 1: 50 000 base map, derived from aerial photography acquired in 1993-94 were sent to the following people in 1994 for drawing up their versions of the geology: Mr Nick Post, Department of Applied Geology, University of New South Wales. Dr Kurt Stuwe, Department of Geology, University of Adelaide. Dr Richard Price, La Trobe University. Mr Post is currently (May 1996) writing a doctoral thesis on the geology of the area having spent two field seasons in the area in 1993-94 and 1994-95. Dr Stuwe and Dr Price each spent a field season in the Windmill Islands during the summer of 1993-94. Mr Post's map, a paper to which Dr Stuwe contributed (Paul, E. et al. 1995 - see references below.) and Dr Blight's map from his PhD thesis were then supplied to Mr Bob Tingey at Australian Geological Survey Organisation for adjudication and synthesis into a definitive map. This was then digitised in September 1994 by Rupert Summerson at ERIN (Environmental Resource Information Network, DEST). In January 1996, the project was recommenced at the National Resource Information Centre, Bureau of Resource Sciences and the data were built into lithology polygons by Robert Smart and Rupert Summerson. Large scale hard copy maps were then distributed to Mr Post, Dr Stuwe and Dr Paul (University of Adelaide) for comment. It was agreed by all parties that the lithology polygons should match exactly the rock outcrop polygons in the "TOPOPOLY" coverage (topography - polygons) supplied by AUSLIG. These were derived photogrammetrically from aerial photography acquired by AUSLIG as surveying contractors to the Antarctic Division during the summer of 1993-94. Consequently, the TOPOPOLY coverage was copied to a new coverage and the lithological boundaries within the TOPOPOLY coverage were either copied from the existing lithology coverage, were digitised from revised maps supplied by Mr Post as annotations on the hard copy maps sent out or were digitised from Paul, E. 1995. The result is a new coverage called Lithology - this coverage. Positional Accuracy The positional accuracy of the rock outcrops is that of the TOPOPOLY coverage. Users should refer to the metadata for that coverage. The positional accuracy of the lithological boundaries within these is estimated to be 12.5 metres. Attribute accuracy In most cases there is universal acceptance of the rock type at a particular location - eg charnockite on Browning Peninsula. It other places where the geology is more complex, there is some difference in the nomenclature of particular rock types. The classification used in this dataset follows Mr Post's schema which has been largely accepted by others working in this area. Some residual differences may persist however. Dr Stuwe has expressed a firm opinion that the depiction of the occurrence of metapelites is of particular importance because they help to establish the metamorphic grade (ie temperature and pressure). The metapelites on Bosner and Herring Islands are particularly interesting mineralogically and have been shown as separate units rather than being lumped together with metapsammites. At some time in the future as the science of geology evolves, there may be major revisions of the classification scheme. Logical consistency The following tests have been carried out on this dataset: 1. Polygon labelling. All polygons have unique labels and attributes attached. 2. Polygon closure. All polygons close. 3. Overshoots and undershoots. There are a number of deliberate undershoots and overshoots (dangles) which represent sheer zones and dykes. 3. Line labelling. All lines are labelled in accordance with Australian Standard AS 2482-1989. The first four digits are a feature code in accordance with Appendix C. The fifth digit is a modifier as per the list below. (Up to eight digits are allowed). FEATURE: COAST (40030) CONNECTOR (0) EARLY_APLITE_DYKE (51075) GEOLOGICAL_BOUNDARY_POS_ACC (51131) GEOLOGICAL_BOUNDARY_POS_APX (51132) LATE_DOLERITE_DYKE (51074) MAP_BOUNDARY (36110) MN_CU_RICH_METASEDIMENT_LAYER (51133) MORAINE (51120) ROCK (51130) SCREE (51060) SHEAR_ZONE_INFERRED (51072) SHEAR_ZONE_POS_APPROX (51071) ULTRAMYLONITE_ZONE_POS_APPROX (51073) Completeness Lithological data within the area are complete with the exception of 30 polygons of unknown lithology. Attribute data are complete for the whole dataset including the polygons of unknown lithology. The classification method has been to follow that of the field geologists and is considered to be exhaustive. Any generalisation has been done by the field geologists, not at the GIS stage. Dolerite dykes and most Early Aplite dykes are up to 4 metres in width and are represented as line features. The dykes on Herring Island, some of which are Early Aplite dykes, are thicker and are represented by polygons, true to scale. The copper/manganese-rich metasediment layer on Clark Peninsula is about 10 metres thick and is represented by a line feature. The underlying topographic data is at a minimum resolution of 5 metres and, where known, the lithology of a feature of a dimension big enough to have been captured has been applied. No clustering has been applied - where a polygon exists in "TOPOPOLY", the lithology has been included, even if "unknown". The only lines to have been smoothed are small dykes, shear zones and ultramylonite zones. The geological data are taken exclusively from field data. Verification is therefore the responsibility of the field geologists. The sheer zones in the Browning Peninsula area are classified as inferred on the basis of geological evidence.