Geology Reference
In-Depth Information
Fig. 15.24
Generalized vertical sections showing stratigraphic
positions of tidal facies (tidal shelf, tidal flat, tidal channel and
rhythmites) in relation to underlying and overlying facies. Also
shown are inferred upward-deepening and upward-shoaling
trends that are interpreted to represent transgressive and highstand
systems tracts, respectively (Data for Moodies Group of Eureka
Syncline adapted from Eriksson
1977
; Moodies of Dycedale
Syncline from Eriksson et al.
2006
; Mount Guide Quartzite
from Simpson and Eriksson
1991
; Elatina Formation adapted
from Lemon and Gostin
1990
); Coronation Formation based on
core observations. See text for details on sedimentology of
tidal facies
as transgressive systems tract deposits and accommo-
dation leading to their preservation likely resulted from
a combination of sea-level rise and subsidence. The
Upper Mount Guide Quartzite likewise overlies braided
alluvial facies of the Lower Mount Guide Quartzite
and records upward-deepening. In common with
the Moodies Group in the Dycedale Syncline, no con-
densed-section deposit is preserved. Notwithstanding,
the vertical succession of facies in the Mount Guide
Quartzite is compatible with a transgressive systems
tract (Fig.
15.24
). The maturity of the Upper Mount
Guide Quartzite and the repetitive nature of the similar
shallow-subtidal to tidal-flat parasequences reflect a
balance between sediment supply and long-term sub-
sidence both of which are consistent with a basin that
was undergoing thermotectonic subsidence (Eriksson
et al.
1994
). Stacked parasequences in the Upper
Mount Guide Quartzite are considered to record low-
amplitude/high-frequency sea-level fluctuations rather
than jerky subsidence (Eriksson and Simpson
1990
).
Fischer plots of parasequence thickness versus time
reveal a longer-term sea level change on the order of
1.5 Ma (Eriksson and Simpson
1990
).
Rhythmites in the Elatina Formation in Australia
and the Coronation Formation in South Africa are
developed within upward-shoaling components of
unconformity-bounded sequences (Fig.
15.24
). Tidal
rhythmites in the Elatina Formation are interpreted as
progradational deltaic facies (Williams
2000
) in which
preservation resulted from aggradation in a subtidal
setting during highstand of sea level. Paleocurrent data
and paleogeographic reconstruction for the Elatina
Formation (Preiss
1987
) indicate that the Reynella and
Elatina rhythmites were deposited near the margin of a
marine gulf in distal ebb tidal delta setting (Williams
1991
). Rhythmites in the Coronation Formation
are similarly interpreted as the deposits of a progra-
ding delta at highstand of sea level. The sequence
stratigraphic setting of the rhythmites beneath the
Livingstone Reef (placer) is not known nor is that of
the Weeli Wolli iron-formation but, in both cases,
the absence of wave- and current-produced structures
implies sufficient accommodation to maintain the
depositional interface below storm wave base.
15.6
Stratigraphic Successsions
and Modern Analogs
Holocene analogues are widely developed for the
Precambrian tidal facies highlighted in the preceding
section. A modern counterpart for the Moodies Group
