Carbonate Systems During the Olicocene-Miocene Climatic Transition E-Book

• Herausgeber: John Wiley & Sons
• Kategorie: Wissenschaft und neue Technologien
• Serie: International Association Of Sedimentologists Series
• Sprache: Englisch

Seitenzahl: 750

Veröffentlichungsjahr: 2011

Beschreibung

The Oligocene and Miocene Epochs comprise the most important phases in the Cenozoic global cooling that led from a greenhouse to an icehouse Earth. Recent major advances in the understanding and time-resolution of climate events taking place at this time, as well as the proliferation of studies on Oligocene and Miocene shallow-water/neritic carbonate systems, invite us to re-evaluate the significance of these carbonate systems in the context of changes in climate and Earth surface processes. Carbonate systems, because of a wide dependence on the ecological requirements of organisms producing the sediment, are sensitive recorders of changes in environmental conditions on the Earth surface. The papers included in this Special Publication address the dynamic evolution of carbonate systems deposited during the Oligocene and Miocene in the context on climatic and Earth surfaces processes focusing on climatic trends and controls over deposition; temporal changes in carbonate producers and palaeoecology; carbonate terminology; facies; processes and environmental parameters (including water temperature and production depth profiles); carbonate producers and their spatial and temporal variability; and tectonic controls over architecture. This book is part of the href="http://www.sedimentologists.org/">International Association of Sedimentologists (IAS) Special Publications. The Special Publications from the IAS are a set of thematic volumes edited by specialists on subjects of central interest to sedimentologists. Papers are reviewed and printed to the same high standards as those published in the journal href="http://www.iasnet.org/publications/sed.php">Sedimentology and several of these volumes have become standard works of reference.

Leseprobe

Contents

Miocene carbonate systems: an introduction

CLIMATIC TRENDS AND CONTROLS OVER DEPOSITION

TEMPORAL CHANGES IN CARBONATE PRODUCERS

CARBONATE TERMINOLOGY

ENVIRONMENTAL CONTROLS OVER DEPOSITIONAL FACIES AND PROCESSES

CARBONATE PRODUCERS AND PALAEOECOLOGY

GEODYNAMIC CONTROLS OVER ARCHITECTURE

FUTURE INITIATIVES

REFERENCES

A synthesis of Late Oligocene through Miocene deep sea temperatures as inferred from foraminiferal Mg/Ca ratios

ABSTRACT

INTRODUCTION

METHODS

RESULTS

DISCUSSION

CONCLUSION

ACKNOWLEDGEMENTS

REFERENCES

Latitudinal trends in Cenozoic reef patterns and their relationship to climate

ABSTRACT

INTRODUCTION

DATABASE AND METHODS

RESULTS

DISCUSSION

CONCLUSIONS

REFERENCES

Carbonate grain associations: their use and environmental significance, a brief review

ABSTRACT

INTRODUCTION

EXISTING CLASSIFICATIONS OF CARBONATE-GRAIN ASSOCIATIONS

INFLUENCES ON CARBONATE-GRAIN DISTRIBUTION

DISCUSSION

CONCLUSION

ACKNOWLEDGEMENTS

REFERENCES

Temperate and tropical carbonate-sedimentation episodes in the Neogene Betic basins (southern Spain) linked to climatic oscillations and changes in Atlantic-Mediterranean connections: constraints from isotopic data

ABSTRACT

INTRODUCTION

GEOLOGICAL SETTING

UPPER MIOCENE-PLIOCENE PLATFORM CARBONATES IN THE MEDITERRANEAN-LINKED BASINS

ALTERNATING UPPER MIOCENE HETEROZOAN-PHOTOZOAN CARBONATE-SEDIMENTATION EPISODES

LOWER PLIOCENE HETEROZOAN CARBONATE-SEDIMENTATION EPISODE

CONCLUSIONS

ACKNOWLEDGMENTS

REFERENCES

Facies models and geometries of the Ragusa Platform (SE Sicily, Italy) near the Serravallian―Tortonian boundary

ABSTRACT

INTRODUCTION

GEOLOGICAL SETTING

STRATIGRAPHIC FRAMEWORK

METHODS

FACIES-ZONE MODELS AND PLATFORM GEOMETRY

DISCUSSION

CONCLUSIONS

ACKNOWLEDGMENTS

REFERENCES

The sensitivity of a tropical foramol-rhodalgal carbonate ramp to relative sea-level change: Miocene of the central Apennines, Italy

ABSTRACT

INTRODUCTION

GEOLOGICAL SETTING

METHODS

RAMP SEDIMENTS OF THE ”CALCARI A BRIOZOI E LITOTAMNI“ FORMATION

DISCUSSION

CONCLUSION

ACKNOWLEDGMENTS

REFERENCES

Facies and sequence architecture of a tropical foramol-rhodalgal carbonate ramp: Miocene of the central Apennines (Italy)

ABSTRACT

INTRODUCTION

GEOLOGICAL SETTING

METHODS

DEPOSITIONAL ENVIRONMENT

MAIN DISCONTINUITY SURFACES

SEQUENCE STRATIGRAPHY

DISCUSSION AND CONCLUSION

SUMMARY AND CONCLUDING REMARKS

ACKNOWLEDGEMENTS

REFERENCES

Facies and stratigraphic architecture of a Miocene warm-temperate to tropical fault-block carbonate platform, Sardinia (Central Mediterranean Sea)

ABSTRACT

INTRODUCTION

GEOLOGICAL SETTING AND STRATIGRAPHY

THE SEDINI LIMESTONE UNIT

SELECTED TRANSECTS

DISCUSSION

CONCLUSIONS

ACKNOWLEDGEMENTS

REFERENCES

Coralline algae, oysters and echinoids – a liaison in rhodolith formation from the Burdigalian of the Latium-Abruzzi Platform (Italy)

ABSTRACT

INTRODUCTION

GEOLOGICAL SETTING

METHODS

RESULTS

DISCUSSION

CONCLUSION

ACKNOWLEDGMENTS

REFERENCES

Palaeoenvironmental significance of Oligocene–Miocene coralline red algae – a review

ABSTRACT

INTRODUCTION

OLIGOCENE CORALLINE ALGAE

MIOCENE CORALLINE ALGAE

CONCLUSIONS

ACKNOWLEDGMENTS

REFERENCES

Molluscs as a major part of subtropical shallow-water carbonate production – an example from a Middle Miocene oolite shoal (Upper Serravallian, Austria)

ABSTRACT

INTRODUCTION

GEOLOGICAL SETTING

RESULTS

INTERPRETATION

CONCLUSIONS

ACKNOWLEDGEMENTS

REFERENCES

Echinoderms and Oligo-Miocene carbonate systems: potential applications in sedimentology and environmental reconstruction

ABSTRACT

INTRODUCTION

ECHINODERM SKELETON

GEOCHEMISTRY OF THE ECHINODERM SKELETON

ECHINODERM TAPHONOMY

ECHINODERMS AS COMPONENTS IN OLIGO-MIOCENE CARBONATES

ECHINODERMS AS PALAEOECOLOGICAL TOOLS IN OLIGO-MIOCENE SEDIMENTS

CONCLUSIONS

ACKNOWLEDGEMENTS

REFERENCES

ADDENDUM

Coral diversity and temperature: a palaeoclimatic perspective for the Oligo-Miocene of the Mediterranean region

ABSTRACT

INTRODUCTION

CORAL TAXONOMIC RICHNESS AND TEMPERATURE

TESTING THE “ENERGY HYPOTHESIS”

DISCUSSION

CONCLUSIONS

ACKNOWLEDGMENTS

REFERENCES

Late Oligocene to Miocene reef formation on Kita-daito-jima, northern Philippine Sea

ABSTRACT

INTRODUCTION

GEOLOGICAL SETTING

MATERIALS AND METHODS

BOREHOLE CARBONATES

REEF FORMATION ON KITA-DAITO-JIMA SINCE 25 Ma

CONCLUSIONS

ACKNOWLEDGMENTS

REFERENCES

Carbonate production in rift basins: models for platform inception, growth and dismantling, and for shelf to basin sediment transport, Miocene Sardinia Rift Basin, Italy

ABSTRACT

INTRODUCTION

GEOLOGICAL FRAMEWORK

OUTCROP DESCRIPTION

DISCUSSION

CONCLUSIONS

REFERENCES

Index

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This edition first published 2010, © 2010 by International Association of Sedimentologists

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Library of Congress Cataloguing-in-Publication Data

Carbonate systems during the Oligocene-Miocene climatic transition/edited by M. Mutti, W. Piller, and C. Betzler.

p. cm. - (Special publication… of the international association of sedimentologists; no. 42)

Includes bibliographical references and index.

ISBN 978-1-4443-3791-4 (hardcover: alk. paper)

1. Rocks, Carbonate. 2. Geology, Stratigraphic-Oligocene. 3. Geology, Stratigraphic-Miocene. 4. Paleoclimatology-Oligocene. 5. Paleoclimatology-Miocene. I. Mutti, M. (Maria) II. Piller, Werner E. III. Betzler, Christian.

QE471.15.C3C376 2010

552’.58-dc22

2010017502

A catalogue record for this book is available from the British Library.

Set in 10/12 pt Melior by Thomson Digital, Noida, India

Miocene carbonate systems: an introduction

MARIA MUTTI, WERNER PILLER and CHRISTIAN BETZLER

The Oligocene and Miocene comprise the most important phases in the long-term, step-wise global cooling that, during the Cenozoic, led from a greenhouse to an icehouse Earth. Recent major advances in the understanding and time-resolution of climate events taking place at this time, as well as the proliferation of studies on Oligocene and Miocene shallow-water/neritic carbonate systems, invite us to re-evaluate the significance of these carbonate systems in the context of changes in climate and Earth surface processes. These changes can be traced by the palaeoecology and palaeobiogeography of neritic and pelagic biota. Additionally, the skeletons of these biota represent archives for proxy data, such as stable isotopes. Stable isotopes can be used to trace steps of climate change and track associated changes in Earth surface processes such as continental weathering and runoff, sea-level changes, current circulation patterns, and surface water temperatures. As has been demonstrated during the past decades, carbonate systems, because of a wide dependence on the ecological requirements of organisms producing the sediment, are sensitive recorders of changes in environmental conditions on the Earth surface.

This Special Publication is based on scientific contributions presented at an international workshop entitled “Evolution of Carbonate Systems during the Oligocene-Miocene Climatic Transition” that took place in Potsdam in February 2005. The workshop, sponsored by the European Science Foundation (ESF) and the Deutsche Forschungsgemeinschaft (DFG), had the objective of addressing the dynamic evolution of carbonate systems deposited during the Oligocene and Miocene in the context on climatic and Earth surfaces processes specific for this time interval. In order to shed new light on this subject, this volume addresses a number of key issues including: climatic trends and controls over deposition; temporal changes in carbonate producers and palaeoecology; carbonate terminology; facies; processes and environmental parameters (including water temperature and production depth profiles); carbonate producers and their spatial and temporal variability; and tectonic controls over architecture.

CLIMATIC TRENDS AND CONTROLS OVER DEPOSITION

The main controls over shallow-water carbonate assemblages on shorter time scales are ambient water temperature, nutrient content, and salinity of the water masses. Palaeotemperature reconstructions, based on integrated oxygen-isotope records and Mg/Ca ratios of foraminifera tests show that important temperature variations took place during the Oligocene and Miocene, and that some are out of phase with the main glaciation events. Their magnitude is large enough to cause shifts in benthic communities.

The paper by Billups and Scheidereich discusses the application of Mg/Ca in foraminifera for separating the effect of temperature versus ice volume on oxygen isotope records. They illustrate examples from the Oligocene/Miocene boundary and the Middle Miocene. Of great relevance to carbonate studies, their results indicate that intervals of oxygen-isotope excursions are mostly out of phase with the reconstructed palaeotemperature changes. This implies that a simple correlation between carbonate facies changes and the oxygen-isotope curve is a flawed approach. Furthermore, the temperature fluctuations recorded by Ca/Mg variations at one single location are higher than previously assumed, and can reach several degrees Celsius in amplitude. This is sufficient to trigger significant faunal turnovers and the shifting of an environment from the tropical to the temperate domain.

It should be noted that the time resolution available in most shallow-water carbonate records is not adequate enough to be compared with climatic events as recorded by deep-sea records. In part, there is an intrinsic limitation regarding achievable age resolution of shallow-water strata. However, additional efforts should be made to achieve the best possible resolution, by integrating different dating schemes. This is necessary to resolve the entire climatic transition and its detailed effects on carbonate deposition.

TEMPORAL CHANGES IN CARBONATE PRODUCERS

Based on a literature compilation, Kiessling (2005) introduced the apparent paradox of expanding reef habitats during the Cenozoic at a time of longer term cooling. The greatest increase in recorded reef sites was from the Late Oligocene to the Early Miocene, whereas preserved reef volumes increased most strongly from the Early to Middle Miocene. Average reef diversity peaked in the Late Oligocene and then declined towards the Late Miocene, whereas the global diversity of scleractinian corals steadily increased through the Oligocene and Miocene, and there were almost no extinctions at the genus level across the Oligocene–Miocene boundary. Kiessling (2005) argued that neither climatic data nor any other quantified physico-chemical parameter are able to explain the large expansion of reefs across the Oligocene–Miocene boundary, thus implying a predominantly biological control.

In this volume, Perrin and Kiessling show that most Cenozoic buildups occur within a latitudinal belt broadly centred on the tropical regions and slightly shifted to the north. During the Cenozoic, the reef belt shows both gradual latitudinal shifts and latitudinal contraction/expansion. In particular, the latitudinal width of the reef belt seems to have been reduced near the Eocene-Oligocene boundary and increased again after the Rupelian. It was wider than today during most of the Miocene, its widest extension occurring during the Middle Miocene.

Bosellini and Perrin analyze patterns of generic richness and inferred palaeotemperatures for each stage of the Oligocene-Miocene time interval and compare it with global palaeoclimatic curves based on stable oxygen isotopes. Except for the Mid-Miocene Climatic Optimum, which is not recorded in the generic richness of the Mediterranean z-coral communities, their coral richness-derived palaeo-temperatures correlate with the palaeoclimatic trends based on the isotopic curves. Their results show a gradual increase of temperature from the Early to the Late Rupelian and a gradual widening of the temperature range after the Burdigalian by progressively adapting to a larger temperature range from the mid-Miocene onwards to the Messinian.

CARBONATE TERMINOLOGY

Researchers with different focuses and expertise tend to use different terminology to describe carbonate sediments. The general consensus is that this is a problem affecting communication and identification of the real scientific problems. Furthermore, using different terminology considerably reduces the possibility to compare different study areas. Currently, there are two major terminologies in use for the description of neritic carbonates. One is based on the observation of the most important sediment-forming components (chlorozoan, foramol: Lees & Buller, 1972; Lees, 1975), the other takes into account the feeding priorities of the carbonate-producing biota (hetero-zoan, photozoan: James, 1997). None of the systems ultimately allows the reconstruction of controlling factors, such as water temperature or nutrient content. It can be argued that only descriptive terms should be used and an interpretative terminology should be avoided. In this volume, Kindler and Wilson provide a review of carbonate grain associations, and stress the need for a purely descriptive nomenclature to define regionally important groupings of carbonate deposits.

ENVIRONMENTAL CONTROLS OVER DEPOSITIONAL FACIES AND PROCESSES

A major compilation at the Mediterranean scale published in 1996 (SEPM Concepts in Sedimentol-ogyand Paleontology, Volume 5), mainly focused on reefal (scleractinian) carbonate systems, but also brought attention to the existence of distinct systems referred to as “non-tropical” or “cool-water” carbonates. Over the last decade, a number of studies have focused on these carbonates and have generated debate over the environmental and climatic parameters controlling the occurrence of these carbonate systems.

The main controls over carbonate assemblages and the resulting depositional facies on shorter time scales are temperature, nutrients and salinity of the water masses in which the biota live, and on longer time scales are biological evolution, geodynamics and changes in palaeogeography. It is essential to understand the degree to which carbonate facies assemblages record the effects of temperature changes versus nutrients or other environmental changes. This issue is of relevance with regard to how changes in carbonate facies can be related to the climatic changes specific to the time interval. It has been observed that local parameters may play an overriding role that can mask the global signal. Therefore it is necessary to understand regional settings before making global implications. Topography and geomorphology of an area are important concerns that may strongly affect depositional systems.

Martin, Braga, Sanchez-Almazo and Aguirre give an overview of Miocene carbonate platforms in the western Mediterranean. Lithofacies changes of carbonate rocks in the stratigraphic record at the margins of the Neogene basins in southern Spain were mainly the result of temperature variations during the Late Neogene. These variations promoted the alternation of non-tropical and tropical carbonate deposition during the last 10Myr in the region. The authors state that heterozoan carbonates accumulated on ramps during sea-level lowstands, whereas photozoan carbonates accumulated during rising sea-level and highstands. Changes in sea-surface temperatures, reconstructed on the basis of fossil assemblages and stable isotope analyses, are considered to have been the major control.

Ruchonnet and Kindler present a study based on the Ragusa Platform in south-eastern Sicily and show how two different facies models must be used to describe the internal architecture of this carbonate edifice of latest Serravallian to Tortonian age. During the Late Serravallian, a heterozoan system dominated the inner ramp and was characterized by biota of the foramol association, with rhodoliths dominating the mid-ramp. During the Early Tortonian, a photozoan association dominated, with chlorozoan biota in the inner ramp and branching corallinaceans and rhodoliths in the middle ramp. This change in biotic assemblages had profound consequences for the overall geometry of the platform, which evolved from a Late Serravallian distally steepened ramp to a flat-topped platform in the Early Tortonian.

Brandano, Westphal and Mateu-Vicens discuss a case of Miocene carbonates from the central Apennines and analyze this record with regard to the problem of the sensitivity of a foramol-rhodalgal carbonate ramp to sea-level changes. They argue that the middle and outer ramp deposits are remarkably monotonous, implying that they do not record high-frequency sea-level fluctuations.

Brandano, Corda and Castorina integrate data from sedimentological and microfacies analyses to reconstruct the depositional model of a carbonate platform outcropping in the central Apennines. They recognize a narrow inner zone dominated by red algae and rhodoliths, a middle zone dominated by rhodoliths and larger foraminifera, and an outer ramp with three different subzones. These consist of a proximal zone dominated by bryozoan colonies, bivalves and echinoids, an intermediate zone with benthic and planktic foraminifera, echinoids and bivalves, and a distal zone with marls with silica-sponge spicules and calcarenites with mollusc, bryozoan and echinoid debris. The strati-graphic architecture reflects two second-order sequences.

Benisek, Marcano, Betzler and Mutti present a case study from the Sedini Limestone in northern Sardinia, where both heterozoan and photozoan assemblages occur, offering an ideal opportunity to demonstrate: (1) the importance of different biotic assemblages in determining the depositional architecture; and (2) the role of differential early diagenesis in stabilizing depositional facies, thus affecting depositional geometries. They recognize two depositional sequences. The lower one is a homoclinal ramp characterized by heterozoan assemblages. The upper sequence documents a progressive steepening of the carbonate platform slope and is dominated by photozoan assemblages. The differential distribution and amount of early cements in both sequences support the observed changes in overall depositional geometry. Early diagenetic features are rare in the lower sequence but rich and diverse in the upper sequence, allowing facies stabilization and the development of steep progradational slopes.

CARBONATE PRODUCERS AND PALAEOECOLOGY

The participation of a wide range of specialists with different expertise and professional backgrounds at the workshop provided a unique perspective into approaching the significance of carbonate facies in a broader palaeoecological and palaeoclimatic context. First, it is clear that the palaeoecological information that can be extracted from biotic assemblages is too often ignored by physical sedimentologists. For example, in addition to corals, molluscs, red algae, larger benthic foraminifera and echinoids all have a very clear palaeoecological signal, providing information on water depth, temperature and salinity, which are critical for sedimentological interpretations. However, this information is available in most cases only if the proper taxonomic identifications are made. Acquiring this information calls for very close co-operation across expertise boundaries. It was also noticed that bryozoa are the group of biocalcifiers least understood in terms of palaeoecological requirements. However, the discussion showed that palaeoecological reconstruction of carbonate sedimentary systems based on taxonomy also has its limits. Whereas Miocene and younger assemblages are very similar to Holocene associations, Oligocene and older assemblages have different compositions on the generic and species level.

In this volume, Brandano and Piller present a detailed palaeoecological study of a 7 m thick rho-dolith interval from the middle ramp of the Lower Miocene Latium-Abruzzi carbonate platform in central Italy. They describe in detail the morphology and the taxonomy of the corallines and provide criteria for a palaeodepth reconstruction. Sedi-mentological and biogenic criteria indicate a low energy environment. Therefore the movement of rhodoliths cannot be generated by palaeocurrents, but by biogenic activities, particularly those of regular echinoids.

Braga, Bassi and Piller provide a review of the palaeoenvironmental significance of coralline red algae occurring both in reef-related carbonates and as the main components in shallow-water hetero-zoan settings from temperate regions. They show how the known distribution of corallines in the Oligocene does not suggest any palaeogeographi-cal differentiation. In contrast, for the Miocene, the occurrence of taxa still living today allows the rough differentiation of the following palaeobiogeographic regions: (a) a tropical region (characterized by thick Hydrolithon plants and Aethesolithon); (b) a subtropical Mediterranean (with common Spongites and Neogonolithion species); and (c) a temperate region with shallow-water assemblages dominated by Lithophyllum. Furthermore, it is possible to identify changes in assemblages and growth forms occurring with depth, proving a very useful palaeobathymetric tool.

Harzhauser and Piller point out how molluscs are generally strongly underrated when interpreting carbonate systems in the circum-Mediterranean area, because of taphonomic loss and because taxo-nomic interpretation in thin-sections is difficult. They argue that this affects mostly small-sized gastropod species that, however, display a high diversity within modern carbonate systems. Mollusc shells may contribute up to 80% of the sediment within nearshore settings and especially around Miocene oolite shoals. Nevertheless, in most micro-facies studies this highly indicative and extremely species-rich group is just referred to as “gastropod”, “bivalve” or, at the most accurate, as “oyster” or “pectinid”. Obviously, such identifications are meaningless in terms of ecology or biogeography. They emphasize the importance of a classical, taxonomy-oriented palaeontology in any facies-analysis.

Kroh and Nebelsick show that echinoderms and their debris can contribute considerable sediment to Oligo-Miocene carbonate systems. They review the morphology of the echinoderm skeleton of all five extant echinoderm classes and discuss reproduction and growth of echinoderms, the chemistry of the skeleton, and the crystallography and diagenesis of echinoderm ossicles. The composition of the echinoderm fauna in carbonate environments and their abundance is also controlled by climate. Many groups are currently restricted to certain climate zones, and in particular the shallow water forms are sensitive to temperature changes. Additionally, echinoderms are useful tools for palaeoenvironmental reconstruction as they are sensitive to water agitation, currents, depth and type of substrate.

GEODYNAMIC CONTROLS OVER ARCHITECTURE

Geodyamic, by affecting topography and the subsidence regime of an area is a fundamental control that may strongly affect depositional systems. Iryu, Inagaki, Suzuki and Yamamoto present the results of investigations on a drill core on Kita-daito-jima, a carbonate island, lying ~350 km east of Okina-wa-jima (southwestern Japan). The reconstructed Oligocene to Pliocene age-depth section of Kita-daito-jima shows that: (1) reef formation on Kita-daito-jima was controlled by combined effects of sea-level changes and tectonic movements (subsidence and uplift); and (2) two types of reef formation may be recognized, the growth of which kept up with the subsidence of the island and the rapid reef formation which commenced at sea-level falls.

Vigorito and, Murru and Simone present sedimentary and architectural patterns of Miocene carbonate successions deposited in the Sardinia Rift Basin in three different physiographic settings: (1) narrow rift-related submerged valleys; (2) isolated fault-blocks in the axial portion of the rift; and (3) small basins located at the edge of the rift itself. Palaeophysiography and in turn pre-and syn-sedimentary tectonics appear to exert a major control over facies distribution and depositional architectures as well as over the location and morphology of the carbonate factories.

FUTURE INITIATIVES

Many possible future research topics were discussed at the workshop:

It is crucial to note the importance of sea-level changes and the necessity to enhance time-resolution to achieve a better fit and understanding of forcing mechanisms.One very interesting idea was to compare the role of nutrients and light adaptation to evolutionary patterns. This could be applied to the average depth of coral growth and to how the size of larger foraminifera (Lepidocyclina) changes with respect to depth of the photic zone (small-shallow, large-deeper).It is necessary to “bring some order” into the spatial and temporal distribution of these carbonate systems, to develop maps for different time slices, and to recognize spatial changes with latitude, as well as temporal changes associated with climatic evolution.Before such maps can be compiled, it is necessary to rationalize the terminology used, largely because the different terminologies and study approaches in use hinder the possibility of a direct comparison of existing data.Finally, studies on neritic carbonates should be better compared to basinal, pelagic records, where complementary information on climate and oceanographic parameters is recorded.

We would like to thank all the reviewers who have helped to shape this volume, including Torsten Bickert, Dirk Nurnberg, Nancy Budd, Katharina Billups, Jochen Halfar, Jeff Lukasik, Cedric John, Toni Simo, John Reijmer, Andre Freiwald, Lucia Simone, Andrea Knoerich, Phil Bassant, Georg Warrlich, Giovanna della Porta, Wolf-Christian Dullo, James Nebelsick, Martyn Pedley, Thilo Bechstadt, Gregor Eberli, Finn Surlyk and Arndt Peterhansel.

REFERENCES

Kiessling, W. (2005) Long-term relationships between ecological stability and biodiversity in Phanerozoic reefs Nature,433, 410–413.

James, N.P. (1997) The cool-water carbonate depositional realm. In: Cool-water Carbonates (Eds N.P. James and J.A.D. Clarke). SEPM Spec. Publ.,56, 1–20.

Lees, A. (1975) Possible influence of salinity and temperature on modern shelf carbonate sedimentation. Mar. Geol,19, 59–198.

Lees, A. and Buller, A.T. (1972) Modern temperate-water and warmwater shelf carbonate sediments contrasted. Mar. Geol.,13, 67–73.

A synthesis of Late Oligocene through Miocene deep sea temperatures as inferred from foraminiferal Mg/Ca ratios

KATHARINA BILLUPS and KATHLEEN SCHEIDERICH[1]

School of Marine Science and Policy, University of Delaware, 700 Pilottown Road, Lewes, DE 19958, USA (E-mail: [email protected])

[1]Present address: Department of Geology, University of Maryland, College Park, MD20742, USA.

ABSTRACT

Published benthic foraminiferal Mg/Ca records have been compiled that span the latest Oligocene through Miocene, including new data for the South Atlantic. This synthesis, the first such of Mg/Ca data, necessitates consideration of uncertainties and limitations and provides a general perspective on the evolution of deep-sea temperatures over this period. Published Mg/Ca records show temperature patterns through the Miocene that are consistent with those first synthesized by Kennett (1985) utilizing isotope and other data. Accordingly, the early Miocene was an interval of relative warmth culminating in a climatic optimum at ~16 Ma that was characterized by the warmest (Mg-derived) temperatures of the past 20 million years. After the climatic optimum, palaeotemperatures dropped by 3–4 °C during the second major advance of Antarctic ice between ~15 Ma and 13 Ma. For the late Miocene, between 11 and 8.5 Ma, a distinct increase in benthic foraminiferal Mg/Ca ratios at two Atlantic sites provides evidence for deep to intermediate water circulation changes. Thereafter, temperatures close to modern are recorded at all sites. Assuming constant seawater Mg/Ca ratios through time, it can be concluded that the early Miocene climate was generally warmer than today and that by the late Miocene temperatures approached modern values.

Keywords Oligocene, Miocene, palaeotemperatures, palaeoclimate, palaeoceanography, foraminifera.

INTRODUCTION

The Miocene, a time of climatic extremes ranging from an early Miocene climatic optimum at about 16 Ma to the mid-Miocene period of ice growth on Antarctica between about 15 and 13 Ma, has long been of particular interest to palaeoceanographers. A volume synthesizing Miocene climate was published in 1985 in the context of the Cenozoic Paleoceanography Project (Kennett, 1985). Quantitative micropalaeontological data and stable- isotope records provided a view of the evolution of Miocene climate primarily based on results from the Deep Sea Drilling Project. Accordingly, multispecies planktonic oxygen-isotope records from throughout the world ocean suggested that during the early Miocene, surface-water temperatures were warm and meridional surface-water temperature gradients were small, with modern ocean conditions developing after the mid-Miocene expansion of the Antarctic ice sheet (Savin et al., 1985). Benthic foraminiferal faunal assemblages from the Pacific Ocean also indicated warm deep- waters and a less well-stratified water column, in comparison to the modern ocean (Woodruff et al., 1985). Many of the modern forms of benthic foraminifera first appeared during the mid-Miocene, indicative of deep water cooling (Woodruff et al., 1985). In short, these earlier studies documented a relatively warm early Miocene, followed by cooling of high-latitude surface and Pacific deep waters concurrent with mid-Miocene ice sheet expansion.

Much of what is known about past climate change (including the Miocene) comes from the oxygen-isotopic composition of benthic foraminifera. Although this proxy outlines large-scale climate change, the absolute magnitude and the relationship between ice growth and decay and ocean temperature changes cannot be determined uniquely. Foraminiferal δ18O values reflect the δ18O value of seawater due to global storage of ice at the poles and regional changes such as evaporation and precipitation at the sea surface, as well as the water temperature in which the organism calcifies. Thus, certain assumptions are required in order to interpret the records with respect to any of the palaeoenvironmental indicators (e.g. ice volume versus palaeotemperature). This inherently limits the degree to which past changes in temperature and ice-volume can be quantified.