GEOLOGICAL DATA DESCRIPTION
Geological mapping units
Mines, quarries, and mineral occurences
Details of procedures and specifications for the capture and storage of QMAP GIS data are available in Rattenbury and others (1994) and Rattenbury and Heron (1997). Information presented here is drawn from those documents and is provided to give users and potential users to a better understanding of:
DATA COLLECTION PROCEDURES
Data collection comprises three stages, data compilation, data capture, and data verification. Data verification occurs during and at the completion of both the compilation and capture stages.
Existing and new data is recorded onto a fieldsheet in as much detail as possible. This map is then simplified for use at 1:250 000 and captured into the GIS. The results of data collection process are four maps:
Data is captured into the GIS through digitising of the compilation sheet. Standard tolerances and procedures are used to ensure consistency of data capture:
The data captured in the GIS are intended for use at 1:250 000. Whilst the data were collected at 1:50 000, some simplification of linework has occurred to maintain map clarity and use of the linework at scales beyond 1:250 000 is not recommended. Point data has not been altered and can be used at scales beyond 1:250 000.
It is estimated that data attributed as accurately located will have a spatial accuracy of +/- 250 m.
After map compilation, plots from the compilation sheet are hand coloured by the geologist to ensure all polygons close, and that polygon labels are correct. Once the data has been captured into the GIS, plots at 1:50 000 are checked by the person undertaking the digitising and any corrections made. New plots are then checked by the map compiler. Edge matching of adjacent sheets in a single QMAP is followed by checks of the 1:250 000 map by the map compiler, two or more independent reviewers, and a map editor.
Attribute data is automatically validated against data dictionaries.
GEOLOGICAL DATA DESCRIPTION
Geological mapping units
Delineating geological map units is a fundamental part of the geological mapping process. Geological maps can be based on lithostratigraphy, biostratigraphy, age, and rock types, or combinations of these. For QMAP, a lithostratigraphic approach has been adopted. Mapping units are based on age and/or rock type, the major criterion being that the mapping unit adds information but does not clutter the map. A geological unit must have a significant thickness (typically greater than 5-10 m). Any units thinner than this are normally omitted, unless particular emphasis on the unit is wanted by the compiler. Additional information such as rock type, terrane, and age are stored in the GIS and retrieved according to the required mapping philosophy.
Geological polygons are stored in a coverage named GEOL_UNITS. The polygons are identified by mapping unit codes. These codes are consistent across the entire QMAP database. An abbreviated version of the unit code appears as a label on the published map to assist identification of the mapping unit.
Many mapping units transgress sheet boundaries. As a result, the dominant rock type and subsidiary rock types may contain attributes which may differ between polygons sharing the same unit code.
Geological boundary information is also stored in the GEOL_UNITS coverage. The boundaries are attributed for accuracy and type. Accuracy measures the absolute accuracy of the boundary position and/or the degree of geological uncertainty. Type defines the nature of the geological boundary.
Excel templates for the geol_units features are available to assist in attributing features.
Metamorphic grade is an important criterion for distinguishing and subdividing metamorphic rocks such as schists and gneisses, as well as much of the older, lower grade sedimentary rocks. Metamorphic grade in New Zealand has historically been determined in two ways; mineral facies through recognition of key mineral assemblage and by textural zones through recognition of degrees of foliation. Since the boundaries between mineral facies and textural zones are not coincident, these two types of metamorphic classification are separated into two polygon coverages. Metamorphic mineral facies polygons can also be supplemented by lines representing key mineral isograds.
Excel templates for the mineralmet features are available to assits in attributing features.
Excel templates for the texturalmet features are available to assist in attributing features.
Many of the textural and mineral metamorphic boundaries will be faults or geological contacts (particularly with overlying cover rocks).
Faults are of particular significance in New Zealand geology and can be described by a large number of potentially useful variables or attributes. The QMAP FAULTS coverage deals with geometrical, descriptive, and time attributes including old ("inactive") movements.
Key attributes are ACCURACY (absolute positioning and/or geological uncertainty), TYPE (unknown, normal, reverse/dextral etc), and ACTIVITY (active or inactive).
Users are warned that the ultimate dataset for active faults is GNS's Active Faults Database. The active faults stored within QMAP are a generalised version of those data.
An Excel template for fault line attributes is available to assist in attributing features.
Macroscopic and mappable folds are delineated by the fold axial surface traces in the FOLDS coverage. Key attributes are ACCURACY (absolute positioning or geological uncertainty) line symbol, TYPE (which corresponds to the symbology defined in Bishop & Phillips 1986), and ACTIVITY (active or inactive).
Users are warned that the ultimate dataset for active folds is GNS's Active Folds Database. The active folds stored within QMAP are a generalised version of those data.
An Excel template for fold line attributes is available to assist in attributing features.
Horizons are distinct and stratigraphically significant rock units which are essentially unmappable as polygons at 1:250 000. Because of their geological significance, however, these features are portrayed as lines in the coverage HORIZONS, with their true thickness exaggerated. These line may laterally widen into a mappable polygon.
Key attributes are ACCURACY (absolute positioning or geological uncertainty) and UNIT_CODE (unique code which matches geol_units codes where appropriate).
An Excel template for horizon line attributes is available to assist in attributing features.
The VEINS line coverage contains veins which have a mappable length ie, greater than 300 m, but an unmappable width, similar to horizons. Key attribites are ACCURACY (absolute positioning or geological uncertainty), UNIT_CODE, and MINERALOGY/ROCK_TYPE.
An Excel template for vein line attributes is available to assist in attributing features.
The DIKES line coverage contains dikes which have a mappable length ie, greater than 300 m but an unmappable width. Key attribites are ACCURACY (absolute positioning or geological uncertainty), UNIT_CODE, and MINERALOGY/ROCK_TYPE.
An Excel template for dike line attributes is available to assist in attributing features.
Lineaments are stored in the LINEARS coverage and comprise remotely-sensed trends and lineaments derived from, for instance, aerial photos, satellite imagery, and aeromagnetic and gravity surveys. Linear features that are confidently identified as geological boundaries, horizons, or faults are placed in their respective coverages with ACCURACY set to "inferred".
An Excel template for lineament line attributes is available to assist in attributing features.
Structural measurements are for GIS purposes points with attributes describing rock defect and rock fabric/strata orientation. These are portrayed through an appropriately rotated symbol. The coverage STRUCTURE contains the orientation information in AZIMUTH and INCLINATION, as well as collection information in SITE_NO and ORIGINATOR, the structure TYPE which links to a specific symbol, and relative age information in GENERATION.
An Excel template for structure point attributes is available to assist in attributing features.
QMAP involves a large component of synthesising existing geological mapping ranging from published maps to student thesis maps, and these data are not exhaustively verified. The SOURCES coverage is designed to provide information to the user on where the data have been derived. SOURCES contains both polygons and line features.
An Excel template for source feature attributes is available to assist in attributing features.
Mines, quarries, and mineral occurrences
Mines, quarries, and mineral occurrences are stored in the external GERM Mineral database. Any GIS coverages created for QMAP contain only a subset of the features and attributes of the GERM database and are a snapshot of it at the time of transfer. Details of the Germ Database can be obtained from the GNS web site.
Fossil occurrences are stored in the external Fossil Record File database. Any GIS coverage created for QMAP contains only a subset of the features and attributes of the Fossil Record File database and is only a snapshot of it at the time of transfer. Details of the Fossil Record File can be obtained from the GNS web site.
The sample locations of published radiometric ages within New Zealand are available from an Excel database as part of a joint GNS/GSNZ project. Any GIS coverage created for QMAP contains only a subset of the features and attributes of the Geochron Database.
Petrological sample data are stored in the external PET database. Any GIS coverage created for QMAP contains only a subset of the features and attributes of the PET Database and is a snapshot of it at the time of transfer. Details of the PET Database can be obtained from the GNS web site.
Landslide data are stored in the Landslide Database. The QMAP coverage contains a selection of the spatial features and few attributes.
Additional layers may be used to store important data in some map sheets.
These may include polygon coverages such as :
and point coverages such as:
The data structures of any additional layers will be included in updates of this document and will follow the structure of similar features.
Bishop, D.G.; Phillips, R. 1986. Map symbols. New Zealand Geological Survey Record 1.
Nathan, S. 1993. Revising the 1:250,000 Geological Map of New Zealand. Institute of Geological & Nuclear Sciences Science Report 93/26.
Rattenbury, M.S.; Heron, D.W.; Nathan, S. 1994. Procedures and specifications for the QMAP GIS. Institute of Geological & Nuclear Sciences Science Report 94/42.
Rattenbury, M.S.; Heron. D.W. 1997: Revised procedures and specifications for the QMAP GIS. Institute of Geological & Nuclear Sciences Science Report 97/3.
Contact QMAP Leader:
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PO Box 30-368 Lower Hutt 6315
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