238
Hiatuses have fonned even in periods in whieh thermohaline eireulation is believed to have been sluggish.
Few loeations have been found in the present-day oeeans
where a really eomplete Cenozoie seetion exists. However,
beeause of the limits of stratigraphie resolution, short hiatuses remain diffieult to be identified.
MaeLeod and Keller (1991) have stressed the importanee of hiatuses as a signifieant faetor for the far-reaehing
global events at the Cretaeeous/Tertiary (KlT) boundary.
They postulate that mass extinetion, abrupt shifts in earbon
isotope abundances, and speeifie traee element eoneentrations in deep-sea sediments are related to long intervals of
nondeposition. The stratigraphie hiatuses may have resulted from a marked sea-level rise during the latest
Maastriehtian and earliest Danien. This eaused the loeus of
sediment deposition to migrate landward aeross the eontinental shelf, where stratigraphie seetions are more or less
eomplete over the same time interval (cf. Seet. 7.3). In any
ease, the effeets of ineomplete or extremely eondensed
stratigraphie deep-sea reeords should be taken into aeeount
when rare events such as bolide impacts and their eonsequenees for the evolution of marine organisms are diseussed.
5.5.4
Summary (Deep-Marine Erosion
and Redeposition)
Erosion and redeposition in the deep sea is
more eornrnon than previously thought. Bottom
eurrents are strengthened along the slopes of
topographical highs (eontour eurrents) where
they ean erode large furrows and undereut
slopes.
The redeposited silt and mud, including
biogenie skeletal material, often form very
large sediment drifts or eontourites, overridden
by smaller sediment waves. These features
may alternate with deep-sea fans and beeome
ineorporated into slope aprons.
- Deep-marine erosion and nondeposition is intensified in times of strong thermohaline eirculation and leaves behind many stratigraphie
hiatuses which cornrnonly cannot be correlated
over long distances.
5.6 Paleoceanography
5.6.1 Introduction
In the last decade, paleoceanography has become a
field of great interest. The term paleoceanography
eomprises not only ocean eirculation and related processes, such as water chemistry, recycling of nutrients, organic productivity, etc., but also the (changing) configuration ofthe continents (paleogeography)
and climate change (paleoclimatology) in the past.
Variations and trends in the evolution of the global
Chapter 5 Oceanic Sediments
climate have become an issue of outstanding importance in our modem world. Climate and ocean circulation are closely linked. To predict the future evolution of the climate, the factors controlling the past
climate have to be known. One of the best records of
the past climate are marine sediments and their biota.
Reeently, high-resolution studies on long sediment
cores gained by deep-sea drilling have provided extensive data for the reconstruction of the climate history of the Neogene and Quaternary periods. Both
marine and nonmarine sediments are in turn largely
controlled by paleoceanography.
For all these reasons, paleoceanography is a eomplex topic for which the cooperation of several dis eiplines is necessary, including oceanographers, climatologists, glaeiologists, sedimentologists, marine biologists, geochemists, and others. In addition, extraterrestrial processes playa significant role in triggering short-term climatic variations. The longer term
evolution of the Earth is affected by peaks in the volcanic activity, associated with rapid oeean spreading
or specific magmatic plumes generating large igneous provinces. Plate tectonic reconstructions, periods
of mountain building, and even the evolution of life
(e.g. plants spreading out on the continents, or the
appearance of specific planktonic organisms in the
ocean) have to be taken into account.
Presently, detailed investigations on Neogene and
Quaternary marine sediments have reached astate in
which sound syntheses are possible. For older periods, our knowledge of the paleoeeanographic situations is still limited, although many attempts have
been made to reconstruct and better understand these
paleo-environments (cf. Seet. 7.8).
In this book, the impaet of paleoceanography on
sedimentary proeesses is of primary interest. However, only abrief introduction can be given here.
One of the first summaries of our knowledge in paleogeography has already been presented by Schopf (1980). In
the meantime numerous articles have been published deseribing speeifie sediment sueeession of deep-sea eores
(e.g. in the "Initial" and "Seientifie Reports" of the DeepSea Drilling Projeet, DSDP, and the Oeean Drilling Program, ODP). The~e publieations eontain detailed information on the stratigraphy and sedimentary eharaeteristics of
the eores, including biostratigraphy, oxygen isotope stratigraphy based on planktonie and benthie foraminifera, the
type and provenanee of organie matter, ete. These "proxy"
data are used to infer paleo-temperatures of surfaee and
bottom waters, marine organie produetivity, the depth of
the CCD and the redox eonditions in deep water. With the
aid of this infonnation, the loeation and effieieney of the
fonner oeean eireulation ean be evaluated. Many articles
dealing with paleoeeanography are published in the journals "Paleoeeanography" and "Palaeogeography,
Palaeoclimatology, Palaeoeeology", and others. Quite a
number of them presents summaries for speeifie topies in
this field.
Overviews of the geologie and sedimentary history of all
oeeans basins, including the Gulf of Mexieo, the Caribbean
Hiatuses have fonned even in periods in whieh thermohaline eireulation is believed to have been sluggish.
Few loeations have been found in the present-day oeeans
where a really eomplete Cenozoie seetion exists. However,
beeause of the limits of stratigraphie resolution, short hiatuses remain diffieult to be identified.
MaeLeod and Keller (1991) have stressed the importanee of hiatuses as a signifieant faetor for the far-reaehing
global events at the Cretaeeous/Tertiary (KlT) boundary.
They postulate that mass extinetion, abrupt shifts in earbon
isotope abundances, and speeifie traee element eoneentrations in deep-sea sediments are related to long intervals of
nondeposition. The stratigraphie hiatuses may have resulted from a marked sea-level rise during the latest
Maastriehtian and earliest Danien. This eaused the loeus of
sediment deposition to migrate landward aeross the eontinental shelf, where stratigraphie seetions are more or less
eomplete over the same time interval (cf. Seet. 7.3). In any
ease, the effeets of ineomplete or extremely eondensed
stratigraphie deep-sea reeords should be taken into aeeount
when rare events such as bolide impacts and their eonsequenees for the evolution of marine organisms are diseussed.
5.5.4
Summary (Deep-Marine Erosion
and Redeposition)
Erosion and redeposition in the deep sea is
more eornrnon than previously thought. Bottom
eurrents are strengthened along the slopes of
topographical highs (eontour eurrents) where
they ean erode large furrows and undereut
slopes.
The redeposited silt and mud, including
biogenie skeletal material, often form very
large sediment drifts or eontourites, overridden
by smaller sediment waves. These features
may alternate with deep-sea fans and beeome
ineorporated into slope aprons.
- Deep-marine erosion and nondeposition is intensified in times of strong thermohaline eirculation and leaves behind many stratigraphie
hiatuses which cornrnonly cannot be correlated
over long distances.
5.6 Paleoceanography
5.6.1 Introduction
In the last decade, paleoceanography has become a
field of great interest. The term paleoceanography
eomprises not only ocean eirculation and related processes, such as water chemistry, recycling of nutrients, organic productivity, etc., but also the (changing) configuration ofthe continents (paleogeography)
and climate change (paleoclimatology) in the past.
Variations and trends in the evolution of the global
Chapter 5 Oceanic Sediments
climate have become an issue of outstanding importance in our modem world. Climate and ocean circulation are closely linked. To predict the future evolution of the climate, the factors controlling the past
climate have to be known. One of the best records of
the past climate are marine sediments and their biota.
Reeently, high-resolution studies on long sediment
cores gained by deep-sea drilling have provided extensive data for the reconstruction of the climate history of the Neogene and Quaternary periods. Both
marine and nonmarine sediments are in turn largely
controlled by paleoceanography.
For all these reasons, paleoceanography is a eomplex topic for which the cooperation of several dis eiplines is necessary, including oceanographers, climatologists, glaeiologists, sedimentologists, marine biologists, geochemists, and others. In addition, extraterrestrial processes playa significant role in triggering short-term climatic variations. The longer term
evolution of the Earth is affected by peaks in the volcanic activity, associated with rapid oeean spreading
or specific magmatic plumes generating large igneous provinces. Plate tectonic reconstructions, periods
of mountain building, and even the evolution of life
(e.g. plants spreading out on the continents, or the
appearance of specific planktonic organisms in the
ocean) have to be taken into account.
Presently, detailed investigations on Neogene and
Quaternary marine sediments have reached astate in
which sound syntheses are possible. For older periods, our knowledge of the paleoeeanographic situations is still limited, although many attempts have
been made to reconstruct and better understand these
paleo-environments (cf. Seet. 7.8).
In this book, the impaet of paleoceanography on
sedimentary proeesses is of primary interest. However, only abrief introduction can be given here.
One of the first summaries of our knowledge in paleogeography has already been presented by Schopf (1980). In
the meantime numerous articles have been published deseribing speeifie sediment sueeession of deep-sea eores
(e.g. in the "Initial" and "Seientifie Reports" of the DeepSea Drilling Projeet, DSDP, and the Oeean Drilling Program, ODP). The~e publieations eontain detailed information on the stratigraphy and sedimentary eharaeteristics of
the eores, including biostratigraphy, oxygen isotope stratigraphy based on planktonie and benthie foraminifera, the
type and provenanee of organie matter, ete. These "proxy"
data are used to infer paleo-temperatures of surfaee and
bottom waters, marine organie produetivity, the depth of
the CCD and the redox eonditions in deep water. With the
aid of this infonnation, the loeation and effieieney of the
fonner oeean eireulation ean be evaluated. Many articles
dealing with paleoeeanography are published in the journals "Paleoeeanography" and "Palaeogeography,
Palaeoclimatology, Palaeoeeology", and others. Quite a
number of them presents summaries for speeifie topies in
this field.
Overviews of the geologie and sedimentary history of all
oeeans basins, including the Gulf of Mexieo, the Caribbean