7.9 Cyclo- and Event Stratigraphy
- The generation of peritidal and subtidal carbonate
cycles seems to be favored during second and third
order TST and early HST, whereas LST hampers or
prevents carbonate cycles on the tops of carbonate
buildups.
- Periodic limestone-marl suecessions and black shalelimestone altemations, deposited on the outer shelf or
in the deeper sea, form preferentiaBy during the transition from TST to HST, i.e. under relatively "stable"
conditions within the condensed section (cf. Fig.
7.42b; e.g. Niebuhrand Prokoph 1997).
In deep-sea regions near the shelves and continents, periods
of rising and high sea level appear to favor the accumulation
of sediments rich in carbonate (productivity cycles), while
during falling sea level carbonate deposition tends to become
more diluted (dilution cycles) or replaced hy siliciclastic materials, including turbidites. Redox cycles are commonly associated with TST and HST of 3rd and higher order sea-Ievel
changes (Ricken 1994).
If cyclic bedding ean be reliably dated, e.g. with the
aid of oxygen isotopes and magnetostratigraphy from
the present back into the past, the stratigraphie resolution of longer sequences can be significandy refined.
Further back in geological time, cyclic bedding including bundles of beds, mosdy renders "floating time
scales" (Fig. 7.47).
- EpisodicaBy generated event beds, such as mass
flows, tempestites, and turbidites, seem to be largely
associated with the prograding phases ofLST and late
HST, particularly so for high-frequency and high-amplitude sea-level oscillations (cf. Seet. 7.9.6; Einseie
1996).
- Widely extended "Ineursion epiboles" (appearanee
of new speeies) indicate relative sea-level highstands;
"eeological epiboles" (population bursts) often record
enhanced water circulation during lowering sea level.
- Stratal diseontinuities on land, such as clastic lags
and soils may be subsequendy removed by subaerial
meehanical and ehemieal erosion. Karstified surfaces
and thiek duricrusts are usually better preserved and
can be weB identified.
- In shallow seas, erosionallags and various skeletal
concentrations are assoeiated with surfaces of regression and transgression and therefore diachronous.
They preferentially occur at the transition from LST to
TST (regressive and transgressive lags are often
mixed), around the transition from TST to HST (e.g.
mid-cycle condensed shell beds; Abbott 1997) along
the shallow portion of the maximum flooding surfaee
Fig. 7.46. a Marine basin margin and various proces ses generating skeletal concentrations along
onshore-offshore gradient. Note life position of organisms in soft mud, winnowing, abrasion and
redeposition. (Modified from Fürsich and Oschmann
1993). b In situ winnowing andreworking: autogenie
mode. c Most of the skeletal remains come from
379
(MFS), and at the top of HST. Lag eoncentrations in
the LST either display an erosional base due to emergence or subaqueous erosion, or they represent hiatal
concentrations as a result of sediment bypassing (e.g.
shelly shoals). Apart from these weIl defined positions
within 3rd order sequences, shell coneentrations ofthe
event and eomposite types can also appear within individual systems tracts, or they cap parasequences
(KidweIl 1993).
- Toward basin margins (decreasing subsidence rates)
the stratal discontinuities of successive transgressiveregressive cycles tend to merge (cf. Fig. 7.15). Then
they form pronounced composite lags and skeletal concentrations representing hiatuses of increasing time
span.
These rules may serve as a complementary tool, besides lithostratigraphy, biostratigraphy, magneto-stratigraphy, stable isotopes and radiometry, to describe
and interpret stratigraphie sections and fades tracts of
third-order sequence cycles.
other locations: allogenic mode. Both band c may be
colonized by sessile epifauna (gravel dweIlers).
d The skeletal concentrations evolve from (± single)
event concentrations via composite concentrations to
hiatal and lag concentrations with decreasin~ rates of
sediment buildup. (After Kidwe1l1993, modlfied)
- The generation of peritidal and subtidal carbonate
cycles seems to be favored during second and third
order TST and early HST, whereas LST hampers or
prevents carbonate cycles on the tops of carbonate
buildups.
- Periodic limestone-marl suecessions and black shalelimestone altemations, deposited on the outer shelf or
in the deeper sea, form preferentiaBy during the transition from TST to HST, i.e. under relatively "stable"
conditions within the condensed section (cf. Fig.
7.42b; e.g. Niebuhrand Prokoph 1997).
In deep-sea regions near the shelves and continents, periods
of rising and high sea level appear to favor the accumulation
of sediments rich in carbonate (productivity cycles), while
during falling sea level carbonate deposition tends to become
more diluted (dilution cycles) or replaced hy siliciclastic materials, including turbidites. Redox cycles are commonly associated with TST and HST of 3rd and higher order sea-Ievel
changes (Ricken 1994).
If cyclic bedding ean be reliably dated, e.g. with the
aid of oxygen isotopes and magnetostratigraphy from
the present back into the past, the stratigraphie resolution of longer sequences can be significandy refined.
Further back in geological time, cyclic bedding including bundles of beds, mosdy renders "floating time
scales" (Fig. 7.47).
- EpisodicaBy generated event beds, such as mass
flows, tempestites, and turbidites, seem to be largely
associated with the prograding phases ofLST and late
HST, particularly so for high-frequency and high-amplitude sea-level oscillations (cf. Seet. 7.9.6; Einseie
1996).
- Widely extended "Ineursion epiboles" (appearanee
of new speeies) indicate relative sea-level highstands;
"eeological epiboles" (population bursts) often record
enhanced water circulation during lowering sea level.
- Stratal diseontinuities on land, such as clastic lags
and soils may be subsequendy removed by subaerial
meehanical and ehemieal erosion. Karstified surfaces
and thiek duricrusts are usually better preserved and
can be weB identified.
- In shallow seas, erosionallags and various skeletal
concentrations are assoeiated with surfaces of regression and transgression and therefore diachronous.
They preferentially occur at the transition from LST to
TST (regressive and transgressive lags are often
mixed), around the transition from TST to HST (e.g.
mid-cycle condensed shell beds; Abbott 1997) along
the shallow portion of the maximum flooding surfaee
Fig. 7.46. a Marine basin margin and various proces ses generating skeletal concentrations along
onshore-offshore gradient. Note life position of organisms in soft mud, winnowing, abrasion and
redeposition. (Modified from Fürsich and Oschmann
1993). b In situ winnowing andreworking: autogenie
mode. c Most of the skeletal remains come from
379
(MFS), and at the top of HST. Lag eoncentrations in
the LST either display an erosional base due to emergence or subaqueous erosion, or they represent hiatal
concentrations as a result of sediment bypassing (e.g.
shelly shoals). Apart from these weIl defined positions
within 3rd order sequences, shell coneentrations ofthe
event and eomposite types can also appear within individual systems tracts, or they cap parasequences
(KidweIl 1993).
- Toward basin margins (decreasing subsidence rates)
the stratal discontinuities of successive transgressiveregressive cycles tend to merge (cf. Fig. 7.15). Then
they form pronounced composite lags and skeletal concentrations representing hiatuses of increasing time
span.
These rules may serve as a complementary tool, besides lithostratigraphy, biostratigraphy, magneto-stratigraphy, stable isotopes and radiometry, to describe
and interpret stratigraphie sections and fades tracts of
third-order sequence cycles.
other locations: allogenic mode. Both band c may be
colonized by sessile epifauna (gravel dweIlers).
d The skeletal concentrations evolve from (± single)
event concentrations via composite concentrations to
hiatal and lag concentrations with decreasin~ rates of
sediment buildup. (After Kidwe1l1993, modlfied)