Basin-f ill Comple xes
England is shown in Fig. 9.19. The debate regarding
the reliability of the meso them concept (Holdsworth
and Collinson 1988; Leeder 1988) illustrates the
difficulty in reconstructing complex litho- and biostratigraphic patterns in tectonically active areas
and in unraveling the various causes of cyclicity
(Chaps. 11, 13). Leeder (1988) noted that new
biostratigraphic data and revised sedimentological interpretations that emphasize autogenic deltaic progradation cast doubt on the reality of
Ramsbottom's mesothems.
Large-scale, regionally extensive, sand-dominated, fining- and coarsening-upward cycles, typically 100 m or more in thickness, are common in
nonmarine deposits. References to several examples
are given in Table 9.1. Commonly, such cycles are
areally very extensive. For example, Fig. 9.20 illus6
\
0
>00
'm
5
\ ease of Molteno outcrop
\
)
4
·G>
�
'
3
2
\
I
/ ::
267
trates the extent of six such cycles in the Triassic
Molteno Formation of the Karoo Basin in South
Africa. One of these cycles extends for more than 400
km down depositional dip into the basin interior. A
comparable subsurface example, from a different
basin, is illustrated in Fig. 9.21. This diagram shows
that the «high-order" cycles (those corresponding to
group 10 of this book) form the largest of three scales
of cyclicity, including allogenic "medium-order"
cycles and fully autogenic «low order" cycles. Steel
and Ryseth (1990) extended this type of analysis
throughout much of the northern North Sea basin,
on the basis of seismic evidence (Fig. 9.22) and additional subsurface well correlation (Fig. 9.23). They
were able to relate the origins of the sequences to
the tectonic history of the area, as discussed further
in Chap. 13. Biostratigraphic evidence available to
LESOTHO
�Trough
�cross-beds
�Oe!ormed
�cross-beds
� Flat bedding l!ll'l lil shale with I;
ll!ll ra.re eoal
�Pl anar
f;SSSj crosswbeds
�Ripple
roo:1Pebhles.
�
� lamiMtlon l£...2.21 g�� J �� s
and �Plant maw>al
Fig. 9.20. Six cycles in the Molteno Formation (Triassic) of the Karoo Basin in South Africa. (Turner 1983)
England is shown in Fig. 9.19. The debate regarding
the reliability of the meso them concept (Holdsworth
and Collinson 1988; Leeder 1988) illustrates the
difficulty in reconstructing complex litho- and biostratigraphic patterns in tectonically active areas
and in unraveling the various causes of cyclicity
(Chaps. 11, 13). Leeder (1988) noted that new
biostratigraphic data and revised sedimentological interpretations that emphasize autogenic deltaic progradation cast doubt on the reality of
Ramsbottom's mesothems.
Large-scale, regionally extensive, sand-dominated, fining- and coarsening-upward cycles, typically 100 m or more in thickness, are common in
nonmarine deposits. References to several examples
are given in Table 9.1. Commonly, such cycles are
areally very extensive. For example, Fig. 9.20 illus6
\
0
>00
'm
5
\ ease of Molteno outcrop
\
)
4
·G>
�
'
3
2
\
I
/ ::
267
trates the extent of six such cycles in the Triassic
Molteno Formation of the Karoo Basin in South
Africa. One of these cycles extends for more than 400
km down depositional dip into the basin interior. A
comparable subsurface example, from a different
basin, is illustrated in Fig. 9.21. This diagram shows
that the «high-order" cycles (those corresponding to
group 10 of this book) form the largest of three scales
of cyclicity, including allogenic "medium-order"
cycles and fully autogenic «low order" cycles. Steel
and Ryseth (1990) extended this type of analysis
throughout much of the northern North Sea basin,
on the basis of seismic evidence (Fig. 9.22) and additional subsurface well correlation (Fig. 9.23). They
were able to relate the origins of the sequences to
the tectonic history of the area, as discussed further
in Chap. 13. Biostratigraphic evidence available to
LESOTHO
�Trough
�cross-beds
�Oe!ormed
�cross-beds
� Flat bedding l!ll'l lil shale with I;
ll!ll ra.re eoal
�Pl anar
f;SSSj crosswbeds
�Ripple
roo:1Pebhles.
�
� lamiMtlon l£...2.21 g�� J �� s
and �Plant maw>al
Fig. 9.20. Six cycles in the Molteno Formation (Triassic) of the Karoo Basin in South Africa. (Turner 1983)