Quantitative Stratigraphy, Splining and Geologic Time Scales - Geomathematics: Theoretical Foundations, Applications and Future Developments - page 350

Cretaceous Biostratigraphic Correlations, offshore Norway
Error bars show 95% confidence limits

6610/3-1 6607/5-1 6507/2-2 6507/2-3 6507/6-2 6406/2-1 35 /3 -4 35/12-1

-1000 -1000

370

29

255

29 255

-500 -500

330

255
370
330

82
16
212
93

82

82

82

0

0

16

212

212

212

500 500

93

61

61

Fig. 9.33 CASC well correlation output for 9 of the 97 events in Fig. 9.32 . Output was flattened
on event 16 ( Hedbergella delroensis LO) (Source: Agterberg et al. 2013 , Fig. 11)

events and Santonian Inoceramus needles LCO event are considered flooding
surfaces (FS). These three events represent reliable regional correlation levels,
with below-average standard deviations. They reflect considerable marine trans-
gression accompanied by slow sedimentation. In Gradstein and Agterberg ( 1998 )
RASC variance analysis was used to demonstrate that the lower Cenomanian Lange
sands (between the two Hedbergella levels in Fig. 9.34 ) and the middle
Cenomanian to Turonian Lysing sands (above the Hedbergella LCO level) are
not seismic markers or well log 'sheet sands' in a correlative sense as had been
assumed before, but show more complex correlation patterns in line with the
sedimentological interpretation that they are debris flow and turbidite sands.

9.5 Construction of Geologic Time Scales

This section contains a review of how geologic timescales were created in the past.
During the last 50 years, successive international timescales have been constructed.
There has been continuous improvement in geochronological dating methods as
well as in chronostratigraphic positioning of the rock samples subjected to age
determination (also see Sect. 3.1.6 ). These improvements have led to changes in
statistical methods used to estimate the ages of stage boundaries. The last interna-
tional geologic time scale (GTS2012) is shown in Fig. 9.35 .