Advances in sequence stratigraphy and the development of depositional models have helped explain the origin of genetically related sedimentary packages during sea level cycles. These concepts have provided the basis for the recognition of sea level events in subsurface data and in outcrops of marine sediments around the world. Knowledge of these events has led to a new generation of Mesozoic and Cenozoic global cycle charts that chronicle the history of sea level fluctuations during the past 250 million years in greater detail than was possible from seismic-stratigraphic data alone. An effort has been made to develop a realistic and accurate time scale and widely applicable chronostratigraphy and to integrate depositional sequences documented in public domain outcrop sections from various basins with this chronostratigraphic framework. A description of this approach and an account of the results, illustrated by sea level cycle charts of the Cenozoic, Cretaceous, Jurassic, and Triassic intervals, are presented.

https://science.sciencemag.org/content/sci/235/4793/1156.full.pdf

Chronology of fluctuating sea levels since the triassic.

The Intergovernmental Panel on Climate Change (IPCC) Technical Paper Climate Change and Water draws together and evaluates the information in IPCC Assessment and Special Reports concerning the impacts of climate change on hydrological processes and regimes, and on freshwater resources – their availability, quality, use and management. It takes into account current and projected regional key vulnerabilities, prospects for adaptation, and the relationships between climate change mitigation and water. Its objectives are:

/pdf/climate-change-and-water-2dpc0zbpsj.pdf

Climate change and water.

The chemical composition of subducting sediment and its consequences for the crust and mantle

Global cooling in the Cenozoic, which led to the growth of large continental ice sheets in both hemispheres, may have been caused by the uplift of the Tibetan plateau and the positive feedbacks initiated by this event. In particular, tectonically driven increases in chemical weathering may have resulted in a decrease of atmospheric C02 concentration over the past 40 Myr.

Tectonic forcing of late Cenozoic climate

Revision of the GEOCARB model (Berner, 1991, 1994) for paleolevels of atmospheric CO2, has been made with emphasis on factors affecting CO2 uptake by continental weathering. This includes: (1) new GCM (general circulation model) results for the dependence of global mean surface temperature and runoff on CO2, for both glaciated and non-glaciated periods, coupled with new results for the temperature response to changes in solar radiation; (2) demonstration that values for the weathering-uplift factor fR(t) based on Sr isotopes as was done in GEOCARB II are in general agreement with independent values calculated from the abundance of terrigenous sediments as a measure of global physical erosion rate over Phanerozoic time; (3) more accurate estimates of the timing and the quantitative effects on Ca-Mg silicate weathering of the rise of large vascular plants on the continents during the Devonian; (4) inclusion of the effects of changes in paleogeography alone (constant CO2 and solar radiation) on global mean land surface temperature as it affects the rate of weathering; (5) consideration of the effects of volcanic weathering, both in subduction zones and on the seafloor; (6) use of new data on the d 13 C values for Phanerozoic limestones and organic matter; (7) consideration of the relative weather- ing enhancement by gymnosperms versus angiosperms; (8) revision of paleo land area based on more recent data and use of this data, along with GCM-based paleo-runoff results, to calculate global water discharge from the continents over time. Results show a similar overall pattern to those for GEOCARB II: very high CO2 values during the early Paleozoic, a large drop during the Devonian and Carbonifer- ous, high values during the early Mesozoic, and a gradual decrease from about 170 Ma to low values during the Cenozoic. However, the new results exhibit considerably higher CO2 values during the Mesozoic, and their downward trend with time agrees with the independent estimates of Ekart and others (1999). Sensitivity analysis shows that results for paleo-CO2 are especially sensitive to: the effects of CO2 fertilization and temperature on the acceleration of plant-mediated chemical weathering; the quantitative effects of plants on mineral dissolution rate for constant temperature and CO2; the relative roles of angiosperms and gymnosperms in accelerating rock weather- ing; and the response of paleo-temperature to the global climate model used. This emphasizes the need for further study of the role of plants in chemical weathering and the application of GCMs to study of paleo-CO2 and the long term carbon cycle.

/pdf/geocarb-iii-a-revised-model-of-atmospheric-co2-over-4jxmgwzkl6.pdf

Geocarb III: A Revised Model of Atmospheric CO2 over Phanerozoic Time

Plate tectonic reconstructions for the Cretaceous have assumed that the major
continental blocks—Eurasia, Greenland, North America, South America, Africa, India,
Australia, and Antarctica—had separated from one another by the end of the Early
Cretaceous, and that deep ocean passages connected the Pacific, Tethyan, Atlantic, and
Indian Ocean basins. North America, Eurasia, and Africa were crossed by shallow
meridional seaways. This classic view of Cretaceous paleogeography may be incorrect.
The revised view of the Early Cretaceous is one of three large continental blocks—
North America–Eurasia, South America–Antarctica-India-Madagascar-Australia;
and Africa—with large contiguous land areas surrounded by shallow epicontinental
seas. There was a large open Pacific basin, a wide eastern Tethys, and a circum-
African Seaway extending from the western Tethys (“Mediterranean”) region
through the North and South Atlantic into the juvenile Indian Ocean between
Madagascar-India and Africa. During the Early Cretaceous the deep passage from
the Central Atlantic to the Pacific was blocked by blocks of northern Central America
and by the Caribbean plate. There were no deep-water passages to the Arctic. Until
the Late Cretaceous the Atlantic-Indian Ocean complex was a long, narrow, sinuous
ocean basin extending off the Tethys and around Africa.
Deep passages connecting the western Tethys with the Central Atlantic, the
Central Atlantic with the Pacific, and the South Atlantic with the developing Indian
Ocean appeared in the Late Cretaceous. There were many island land areas surrounded
by shallow epicontinental seas at high sea-level stands.

Alternative global Cretaceous paleogeography

Evolving ideas about the Cretaceous climate and ocean circulation

New thoughts about the Cretaceous climate and oceans

Calcareous nannoplankton organisms evolved rapidly during the Cenozoic, and are of great value as stratigraphic indicators. A large number of species exhibit world wide distribution, so that this group of fossils is very useful in transoceanic correlation. Calcareous nannofossils may often be recovered from relatively shallow water sediments, permitting the zonation established in pelagic sediments to be used in shelf deposits. The event which ended the Cretaceous almost annihilated Mesozoic calcareous nannoplankton floras. Highly diversified assemblages of Maastrichtian coccoliths were replaced by early Danian assemblages having only a few genera and species. Species diversity increased rapidly during the Paleocene, and by the middle Paleocene had reached a level comparable to that in the late Mesozoic. Discoasters, which due to their large size are very easy to observe and use stratigraphically, first appeared in the middle Paleocene. Late Paleocene, early and middle Eocene pelagic sediments contain a remarkable succession of rapidly evolving calcareous nannoplankton assemblages, culminating in a diversity maximum in the early Lutetian. Later in the Lutetian, a sudden decline in the number of species occurred, and the late Eocene is characterized by relatively monotonous, slowly evolving calcareous nannoplankton floras. Many species characteristic of the late Eocene became extinct in the latest Eocene or early Oligocene. Large calcareous nannofossils, particularly discoasters, are rare in the Oligocene, but forms bearing smaller coccoliths evolved rapidly. Early Miocene calcareous nannofloral assemblages were dominated by an abundance of stout asteroliths belonging to the Discoaster deflandrei plexus. In the middle Miocene, these were replaced by rich asterolith assemblages with many delicate forms having long, thin arms. The number of species of asteroliths and coccoliths again reached a maximum in the early Pliocene. During the Pliocene a number of species, particularly discoasters, declined and became extinct. The last asterolith, Discoaster brouweri, became extinct at the Nebraskan-Aftonian boundary in the Gulf Coast region. During the Pleistocene, species bearing small coccoliths evolved rapidly, and modern assemblages are dominated by a species which first appeared in the Wisconsinan. The zonation based on calcareous nannoplankton fossils, proposed here, approximates the stratigraphic resolution which can presently be achieved using planktonic foraminifera. However, monographic studies have been completed only for the Paleocene-lower Eocene, and uppermost Pliocene-Pleistocene-Recent intervals. Stratigraphic resolution should be considerably improved when detailed studies of the middle Eocene-upper Pliocene interval, now in progress, are completed.

William W. Hay

Papers

Alternative global Cretaceous paleogeography

Evolving ideas about the Cretaceous climate and ocean circulation

New thoughts about the Cretaceous climate and oceans

Calcareous Nannoplankton Zonation of the Cenozoic of the Gulf Coast and Caribbean-Antillean Area, and Transoceanic Correlation (1)

Detrital sediment fluxes from continents to oceans