Phk

Figure 8.19 (a) General track for the period 40 to 0 Ma. (b) and (c) Details of track.

addition could have triggered the recent phase in Alpine deformation). It was immediately obvious, therefore, that all events listed in Table 8.3 should be tested for correlation with stratigraphical boundaries.

Of the 30 events listed in Table 8.3, eight are related to continental plateau basalts (indicated by * in Table 8.3). To these we add Popagai and Manicouagan, making a total of 10 continental impacts which probably had little, or only modest, effects upon the oceans. There are six events (numbered 1-6 in Table 8.3) which we infer to be multiple impacts, which landed in a continental and also in a marine environment. Hence, we can infer that, in the Upper Phanerozoic, there were probably at least 28 major marine impacts. That is, of the total number of impacts in this period, about one third struck continental areas and two thirds were oceanic impacts. It will be noted that this ratio is a reasonable representation of the relative areas of the two types of lithospheres.

Of the 26 inferred oceanic events, all are closely related in time to an Era, Sub-era, Epoch or Age, stratigraphical boundary.

This is a most remarkable correlation. The obvious conclusion, we suggest, is that stratigraphy, in the Upper Phanerozoic, at least, is largely determined by major impacts.

Figure 8.20 (a) General track of S America from 260 to 0 Ma of a point in southern S America is shown. A map of the track from 252 to 248 Ma, (aj) records a very minor track change of about 2° at 250 Ma, with no detectable alteration in velocity. This is the only location for a small reaction to what elsewhere (with the possible exception of Borneo) is recorded as a major event. (b) Track from 256 to 200 Ma shows abrupt changes at 238.2, 220 and 208 Ma.

Figure 8.20 (a) General track of S America from 260 to 0 Ma of a point in southern S America is shown. A map of the track from 252 to 248 Ma, (aj) records a very minor track change of about 2° at 250 Ma, with no detectable alteration in velocity. This is the only location for a small reaction to what elsewhere (with the possible exception of Borneo) is recorded as a major event. (b) Track from 256 to 200 Ma shows abrupt changes at 238.2, 220 and 208 Ma.

Figure 8.21 (a and b) The track from 196 to 96 Ma. Moderate or large track anomalies are shown at 195, 188, 171.5, 152, 142, 135, 133.5, 127.5, 119, 116 and 110.3 Ma.

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