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Fig. 6.1. The structure of the Global Paleomagnetic Database (GPMDB). Tables are linked as either one to one (single-headed arrows) or one to many (single- to double-headed arrows) relationships. From McElhinny and Lock (1996), with permission from Kluwer Academic Publishers.

paleomagnetic pole positions determined worldwide since the work of Chevallier (1925). The database was first established in 1991 using the Oracle™ relational database management system for personal computers (McElhinny and Lock, 1990a, b; Lock and McElhinny, 1991; McElhinny and Lock, 1993) and is updated at least every two years and sometimes more frequently. In 1994 it was moved to the new Microsoft Access™ relational database system, which was much better suited to running on a personal computer (McElhinny and Lock, 1996). The database files are available on the internet from World Data Center A in Boulder, Colorado, U.S.A. (http://www.ngdc.noaa.gov), or can be queried directly from the internet site at the Norwegian Geological Survey in Trondheim, Norway (http.V/dragon. ngu. no/Palmag/paleomag. htm).

The GPMDB is a fully relational database and it enables researchers to search for data according to various selection criteria. Its structure is shown in Fig. 6.1. However, no judgment or opinion is given regarding any individual entry in the database, except where data are superseded by later studies of the same formation and at the same localities as previous studies. Therefore, it is important that, to assist with data selection, careful use be made of the parameters included in the database.

Most of the important parameters required by the reliability criteria of Van der Voo (1990a), discussed in §6.2.1, are included in the tables ROCKUNIT and PMAGRESULT (McElhinny and Lock, 1990b). The rock age and its estimated error (required for criterion 1) are given in ROCKUNIT. The parameters k (KD in the database), N, and a95 (ED95 in the database), whose minimum values are required by criterion 2, are given in PMAGRESULT. In the same table is a parameter called the Demagcode (DC), which summarizes the demagnetization procedures carried out and has integer values 0-5 as explained in Table 6.2. Criterion 3 can only be satisfied when DC > 3. A summary of the various tests carried out is given in the column TESTS using symbols F (fold test), F* (synfold test), Fs (fold test with strain removal), G (conglomerate test), G* (intra-formational conglomerate test), C (baked contact test), C* (inverse contact test), R (reversals test) and M (rock magnetic tests such as those described in §3.5). When the symbol for the field test is followed by a + sign this indicates that the test is positive as required for criterion 4, with a - sign indicating a negative test.

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