 |
| Titel |
The Cenomanian-Turonian boundary event, biotic turnover, and global environmental change: evidence from boreal chalks and tethyan black shales |
| VerfasserIn |
I. Jarvis, J. S. Lignum, M. A. Pearce, B. A. Tocher |
| Konferenz |
EGU General Assembly 2009
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250024071
|
|
|
|
|
|
| Zusammenfassung |
| Cenomanian-Turonian boundary (CTB) times, around 93.6 Ma, were a period of dramatic
palaeoenvironmental change associated with an episode of significant biotic turnover. The
boundary interval is characterized globally by a large positive excursion of δ13C in
marine carbonates, and both marine and terrestrial organic matter, indicating a major
change in the dynamics of the global carbon cycle. The latest Cenomanian – early
Turonian saw perhaps the highest post-Early Palaeozoic eustatic highstand of sea level,
and the deposition of black shales in basinal and oceanic areas, generating one of
the World’s most important petroleum source rock intervals. Increased primary
productivity and sluggish oceanic circulation caused widespread oxygen depletion in
oceanic water columns that led to one of very few truly global oceanic anoxic events
(OAE2).
Organic-walled dinoflagellate cyst (dinocyst) and geochemical records across the
Cenomanian-Turonian boundary (CTB) are compared between a NW European boreal Chalk
reference section in southern England, and a north tethyan hemipelagic black shale-bearing
succession in the Vocontian Basin, SE France. High-resolution correlation between the
sections has been achieved using planktonic foraminifera, calcareous nannofossil, and
dinocyst biostratigraphy, integrated with carbon isotope chemostratigraphy. The
sections show remarkably similar stratigraphic trends despite representing different
palaeolatitudes and different biotic provinces (boreal versus tethyan), and contrasting
lithofacies associations (pelagic chalks and marls versus organic-rich shales and
limestones).
Dinocyst fertility indexes indicate that an upwelling-driven productivity pulse
accompanied a eustatic sea-level fall that preceded the rise in δ13C values marking the onset
of OAE2. A marine productivity collapse in the Chalk Sea and tethyan marginal basins
during the latest Cenomanian is evidenced by the falling absolute and relative abundance of
peridinioid dinocysts, believed to be the product of heterotrophic dinoflagellates. This biotic
change accompanied transgression and sharply rising sea-surface temperatures, following an
Atlantic-wide episode of short-lived cooling. CTB biotic turnover in epicontinental and
marginal seas was driven largely by water mass changes rather than oxygen depletion. |
|
|
|
|
|
|