Quaternary Period in the United States (eBook)

B.F. Atwater, A.R. Gillespie, S.C. Porter (Herausgeber)

eBook Download: PDF

2003 | 1. Auflage
594 Seiten
Elsevier Science (Verlag)
978-0-08-047409-0 (ISBN)

Infos

This book reviews advances in understanding of the past ca. two million years of Earth history - the Quaternary Period - in the United States. It begins with sections on ice and water - as glaciers, permafrost, oceans, rivers, lakes, and aquifers. Six chapters are devoted to the high-latitude Pleistocene ice sheets, to mountain glaciations of the western United States, and to permafrost studies. Other chapters discuss ice-age lakes, caves, sea-level fluctuations, and riverine landscapes.

With a chapter on landscape evolution models, the book turns to essays on geologic processes. Two chapters discuss soils and their responses to climate, and wind-blown sediments. Two more describe volcanoes and earthquakes, and the use of Quaternary geology to understand the hazards they pose.

The next part of the book is on plants and animals. Five chapters consider the Quaternary history of vegetation in the United States. Other chapters treat forcing functions and vegetation response at different spatial and temporal scales, the role of fire as a catalyst of vegetation change during rapid climate shifts, and the use of tree rings in inferring age and past hydroclimatic conditions. Three chapters address vertebrate paleontology and the extinctions of large mammals at the end of the last glaciation, beetle assemblages and the inferences they permit about past conditions, and the peopling of North America.
A final chapter addresses the numerical modeling of Quaternary climates, and the role paleoclimatic studies and climatic modeling has in predicting future response of the Earth's climate system to the changes we have wrought.

Inhalt

THE Q ATERNARY PERIOD 
1 
Chapter 1 11
The southern Laurentide Ice Sheet 11
Changing Attitudes and Approaches 11
Mapping and Compilations of Glacial Geology and Geomorphology Since 1965 12
New Data Sources 13
Advances in Glacial Sedimentology and Geomorphology 14
Paleoglaciology Comes of Age 14
Deforming Bed or Sliding of Basal Debris-Rich Ice? 14
Temperature Conditions at the Glacier Bed 16
Extent and Thickness of a Subglacial Water Layer 17
Other Aspects of Ice Dynamics 17
Chronology and Climate History 18
Conclusions 20
Acknowledgements 20
References 20
Chapter 2 27
The Cordilleran Ice Sheet 27
Introduction 27
Chronology and the Stratigraphic Record 27
Quaternary Framework 27
Tectonic Setting 30
Evidence of Pre-Fraser History and Depositional Environments 30
Puget Lowland 30
Eastern Washington 38
Chronology of the Fraser Glaciation 38
Northern Puget Lowland/Southern Fraser Lowlands 38
Central Puget Lowland 39
Eastern Washington 40
Sea-Level Record 40
Eustasy 40
Global Record 40
Regional Expression 40
Isostasy 41
Global Record 41
Regional Expression 41
Tectonics 42
Physical Behavior of the Cordilleran Ice Sheet 43
Ice-Sheet Reconstruction 43
Meltwater 43
Missoula Floods 45
Summary 48
Acknowledgements 48
References 48
Chapter 3 55
Controls, history, outbursts, and impact of large Late-Quaternary proglacial lakes in North America 55
Introduction 55
Controls on the Depth and Extent of Ice-Marginal Lakes 55
A Brief History of Large Proglacial Lakes in North America 58
Speculation About the History of Lakes During Advance of the LIS 59
History and Interrelationship of Lakes Formed During Ice Retreat, Before 13,000 14C yr B.P. 60
History and Interrelationship of Lakes Formed After 13,000 14C yr B.P. 61
The Impact of Large Glacial Lakes on Climate and Oceans 67
Acknowledgements 68
References 68
Chapter 4 73
Pleistocene glaciations of the Rocky Mountains 73
Introduction 73
Status in 1965 73
Advances since 1965 73
Quaternary Geochronologic Studies 75
Selected Relative-Age Methods 75
Pre-Bull Lake Glacial Deposits 75
Bull Lake Glaciation 76
Combined K-Ar and Obsidian Hydration Dating 76
Cosmogenic Exposure Dating of Bull Lake Deposits 76
Discussion of Age and Correlation of the Bull Lake Glaciation 77
MIS 4 or Early Wisconsinan Glaciation 78
Numerical Ages of Pinedale Deposits 78
Cosmogenic Surface Exposure Ages of Pinedale Deposits 79
Discussion of Pinedale Ages 80
Obsidian-Hydration Age of Pinedale Glaciation 80
Moraines Attributed to Younger Dryas 80
Other Rocky-Mountain Glaciation Studies 81
Modeling Glacial Flow 81
Sedimentology of Glacial Deposits 81
Pleistocene Climates 81
Possible Uplift and Subsidence 82
Conclusions and Recommendations for Future Study 82
Acknowledgements 82
References 83
Chapter 5 87
Quaternary alpine glaciation in Alaska, the Pacific Northwest, Sierra Nevada, and Hawaii 87
Introduction 87
Alaska 87
Status in 1965 87
Glacial-Geologic Research Between 1965 and 1990 88
Progress During the Last Decade 89
Brooks Range 89
Ahklun Mountains 89
The North Pacific Coast 90
On-Going Efforts 90
Cascade Range and Olympic Mountains, Washington and Oregon 91
Status of Alpine Glacial Studies in 1965 91
Pleistocene Glaciation in the Cascade Range 91
Pleistocene Glaciation on the Olympic Peninsula 93
Holocene Glaciation in the Cascades 93
Post-1965 Studies of Pleistocene Glaciation 93
Washington Cascades 93
Mapping and Relative-Age Control 93
Earliest-Dated Cascade Glaciation 94
Glaciation of Mt. Rainier Volcano 94
Glaciation of Upper Yakima River Drainage 94
Glaciation of Icicle Creek Drainage 95
Time of Maximum Late Pleistocene Advance 95
Late-Glacial Ice Advances 95
Olympic Mountains 97
Oregon Cascades 97
Mount Jefferson 97
Mountain Lakes Wilderness 97
Holocene Glacier Advances 97
Early Holocene (?) Advance 97
Neoglacial Ice Advances 98
Washington Cascades 98
Olympic Mountains 98
Oregon Cascades 98
Reconstructed Equilibrium-Line Altitudes 98
Sierra Nevada, California 98
Refinements to the Glacial Sequence 99
Pliocene and Early Pleistocene Glaciations 99
Mono Basin and Tahoe Glaciations 101
Late Pleistocene Glaciations 102
Post-Tioga Advances 102
Numerical Dating of Glaciations 103
Lake-Sediment Cores 104
Equilibrium-Line Altitude 105
Glaciation of Hawaii 105
Challenges for the Future 107
References 107
Chapter 6 115
Coupling ice-sheet and climate models for simulation of former ice sheets 115
Introduction 115
Overview of Ice Sheets and Late Pleistocene Climate Change 115
Development of Coupled Ice-Sheet/Climate Models 117
Ice-Sheet Models 117
Coupled Ice-Sheet Climate Modeling 119
Current State of Coupled Modeling 120
Snapshot Method 120
Matrix Method 121
Alternative Methods: Reduced Climate Models 122
Regional Climate Modeling 122
The Ice-Sheet Climate Interface: Mass-Balance Modeling 125
Marine Ablation 125
Surface Ablation 126
Accumulation 128
Model Resolution Considerations for Mass Balance Modeling 129
Summary and Priorities for Model Development 129
Acknowledgements 130
References 130
Chapter 7 137
Permafrost process research in the United States since 1960 137
Introduction 137
Permafrost and Climate Change 137
Impact of Climate Change on Permafrost 137
Archives of (100-100,000 year) Climate Change in Permafrost 138
Cryosphere/Climate Change Feedbacks 139
Fundamental Permafrost Processes 140
Heat Transport 140
Freezing in Porous Media and Frost Heaving 140
Frost Heaving 140
Unfrozen Water and Solutes 140
Freezing in Rock and Frost Weathering 141
Soils and Patterned Ground 141
Soil Processes 142
Sorted Patterned Ground 143
Field and Laboratory Studies 143
Theoretical Studies 143
Non-Sorted Patterns: Polygons 145
Landscape Features and Processes 145
Solifluction and Soil Creep 145
Rock Glaciers 146
Concluding Remarks 147
Acknowledgements 147
References 148
Chapter 8 157
Quaternary sea-level history of the United States 157
Introduction 157
Florida 160
Florida Keys: Mid-Pleistocene Interglacial High Sea Stands 161
Florida Keys: The Last Interglacial Period 162
Florida Keys: A Sea-Level High Stand Late in the Last Interglacial Period 162
Sea Level During the Last Glacial Period and the Holocene: Caribbean Islands and Florida 163
Hawaiian Islands 164
Pre-last Interglacial High Stands of Sea 164
The Waimanalo Limestone and the Last Interglacial Period 164
Origin of High-Elevation Marine Deposits on Lanai 166
Sea-Level Low Stands Recorded on Hawaii 166
Holocene Sea-Level History on the Hawaiian Islands 167
Pacific Coast 167
Introduction: The Nature of the Pacific Coast Record 167
Sea-Level History Before the Last Interglacial Period 167
Aminostratigraphy and U-Series Ages of the Last Interglacial Period on the Pacific Coast 168
Sea-Level Positions protect protect unhbox voidb@x penalty @M {}100,000 and protect protect unhbox voidb@x penalty @M {}80,000 yr Ago on the Pacific Coast 170
Alaska 171
Mid-Pleistocene Sea-Level History 171
Last Interglacial Sea-Level History 173
Sea-Level History of the Last Glaciation 173
Atlantic Coast 173
Introduction: The Nature of the Atlantic Coast Record 173
Uranium-Series Dating of the Atlantic Coastal Plain Quaternary Coastal Record 176
Aminostratigraphy and Quaternary Chronology, Chesapeake Bay to Northern Florida 176
Chesapeake Bay, Delmarva Peninsula, and Norfolk Arch 179
Albemarle Embayment, Northeastern North Carolina 180
Cape Fear Arch 180
Sea Islands Section 181
Gulf Coast 181
Summary: Atlantic and Gulf Coasts 182
Early Pleistocene to Last Interglacial Period 182
Last Interglacial and Last Glacial Periods 182
Records of Holocene Sea-Level Rise, Atlantic and Gulf Coasts 182
Unresolved Issues on the Atlantic Coastal Plain 183
Summary 183
Acknowledgements 184
References 184
Chapter 9 195
Western lakes 195
Status of Western Lake Studies in 1965 195
New Approaches and Technologies 195
Sediment Coring 195
Methods of Age Control 195
Climate Change Proxies 197
Development and Application of Numerical Models of looseness -1 the Effect of Climate Change on the Thermal Structure, Hydrologic Balance, and Isotopic Composition of Lakes 202
The Response of Western Lake Research to Shifts in looseness -1 the Prevailing Hypothesis of Climate Forcing 203
The Croll-Milankovitch Hypothesis 203
Abrupt Millennial-Scale Climate Change 203
Concluding Remarks 207
Summary 207
Thoughts on the Future of Lake-Based Studies of Climate Change 207
References 208
Chapter 10 215
Isotopic records from ground-water and cave speleothem calcite in North America 215
Introduction 215
Types of Records and Mechanisms of Formation 215
The delta18O Record 216
Speleothems 216
Paleoclimate Reconstructions 217
Some Results From Outside North America 220
Devils Hole 221
The delta13C Record 223
Speleothems 225
Devils Hole 225
Where Isotope Studies from Speleothem and Ground-Water Calcite Stand 226
Acknowledgements 227
References 227
Chapter 11 231
Rivers and riverine landscapes 231
Introduction 231
Advances in Understanding 231
Types of Channels 231
Post-Glacial Changes 235
Anthropogenically Induced Changes 239
Flow Regulation 241
Emerging Research Directions 244
Summary 246
Acknowledgements 247
References 247
Chapter 12 257
Landscape evolution models 257
Introduction 257
A Taxonomy of Landscape Evolution Models 257
Qualitative Models: Classic Paradigms of Long-Term Landscape Evolution 258
Base Level, Erosion, and Landscape Genesis - Powell (1875) 259
Form and Process - Gilbert (1877, 1909) 259
The Geographic Cycle - Davis (1889, 1899a, 1932) 260
Slope Replacement - Penck (1924, 1953) 261
Pediplanation - L.C. King (1953, 1967) 263
Dynamic Equilibrium - Hack (1960) 263
Process Linkage - Bull (1991) 264
Geodynamic and Surficial Process Feedbacks - Molnar & England (1990)
Physical Models 266
Drainage Networks 267
Hillslopes 267
Alluvial and Bedrock Channels 268
Process Sedimentology 268
Numeric Models 268
Surrogate Models 269
Multi-Process Landscape Models 271
Coupled Geodynamic-Surface Process Models 273
Different Approaches 274
Concluding Synthesis: Landscape Evolution Models and Geomorphic Frontiers 277
Acknowledgements 279
References 279
Chapter 13 285
Eolian sediments 285
Introduction 285
Late Quaternary Loess and Eolian Sand in the Central U.S. 286
Loess in the Central United States 286
Stratigraphy and Chronology 286
Sedimentology and Mineralogy 288
Paleoenvironments and Paleoclimate 289
Eolian Sand in the Central United States 289
Stratigraphy and Chronology 289
Sedimentology and Mineralogy 290
Paleoenvironments and Paleoclimate 290
Eolian Sediments in the Lower Mississippi Valley and the Southeastern U.S. 290
Loess in the Lower Mississippi Valley 290
Loess Distribution 290
Stratigraphy and Chronology 291
Sedimentology and Mineralogy 291
Paleoenvironments and Paleoclimate 291
Eolian Sand in the Atlantic Coastal Plain 293
Distribution of Sand Dunes and Sand Sheets 293
Stratigraphy, Chronology, and Sedimentology 295
Paleoenvironments and Paleoclimate 296
Eolian Sediments in Alaska 296
Loess in Alaska 296
Stratigraphy and Chronology 296
Sedimentology and Mineralogy 298
Paleoenvironments and Paleoclimate 298
The Alaskan Loess Record of the Last Glacial Cycle 299
Sand Dunes and Sand Sheets in Alaska 300
Eolian Sediments in the Desert Southwest U.S. 300
Eolian Systems in Southwestern Deserts 300
Mojave Desert 300
Colorado and Lower Sonoran Deserts 302
Colorado Plateau Desert 302
Chihuahuan Desert 303
Relations to Paleoclimate and Paleohydrology 303
Eolian Sediments in the Pacific Northwest U.S. 303
Loess on the Columbia Plateau 304
Distribution 304
Stratigraphy and Chronology 304
Sedimentology and Mineralogy 307
Paleopedology and Paleoenvironments 307
Sand Dunes on the Columbia Plateau 308
Loess on the Snake River Plain 309
Distribution and Thickness 309
Stratigraphy, Paleopedology, and Chronology 309
Sand Dunes on the Snake River Plain 310
Summary 310
Acknowledgements 310
References 310
Chapter 14 321
Soils and the Quaternary climate system 321
Introduction: Quaternary Soil Interpretation 321
Soil Formation Pathways Related to Climate 321
Pathway Models 322
Rates of Soil Formation Under Warm/Wet and Warm/Dry Climates 322
Importance of Thresholds 323
Soil Geomorphic Processes and Soil Preservation 324
Interpretations of Climate State Changes from Soils 325
Climate State Changes 325
Preserved Soils as Indicators of Climate State Changes 326
Importance of the Holocene Process Studies 326
How Long was the Last Interglaciation? 327
The Last Interglaciation of the U.S. Mid-Continent 328
Did Landscape Respond to Stadial/Interstadial Variability? 330
Importance of Dust and Loess in Global Processes 331
Future Challenges for Pedology in Landscape, Ecosystem and Climate Models 331
Soil Chronology and Rates 332
Variations in Soil-Water Balance 332
Soil Duration and Dynamic Equilibrium 332
Assessing Human Impacts 333
Soil-System Models 334
References 334
Chapter 15 341
Earthquake recurrence inferred from paleoseismology 341
Introduction 341
Eastern California Shear Zone 341
Modern Deformation and Earthquakes 341
Prehistoric Earthquakes 342
Implications and Challenges 343
New Madrid Seismic Zone 343
Paleoseismic Evidence 344
Prehistoric Earthquakes 346
Implications and Challenges 347
Cascadia Subduction Zone 347
Coseismic Subsidence 348
Prehistoric Earthquakes 349
Implications and Challenges 353
Summary 353
Acknowledgements 353
References 353
Appendix A 359
Chapter 16 361
Quaternary volcanism in the United States 361
Introduction 361
Cascade Volcanic Arc 361
Caldera-Forming Events 362
Evolution of Major Composite Cones 365
Mafic Fields 367
Western Cordillera Volcanic Loci Beyond the Cascades 367
Northern Basin and Range Province 368
Margin of Colorado Plateau-Rio Grande Region 369
Western Basin and Range Province 370
Western California 371
Alaska 371
Aleutian Volcanic Arc 372
Aniakchak Volcano 373
Katmai Volcanic Cluster 373
Recent Eruptions 374
Redoubt Volcano 374
Crater Peak 374
Wrangell Mountains 375
Southeast Alaska 375
West-Central Alaska 375
Alaskan Tephrochronology 375
Hawaiian Islands 376
Growth Stages of a Hawaiian Volcano 377
Giant Submarine Landslides 379
Summary 380
Acknowledgements 381
References 381
Chapter 17 391
Late-Quaternary vegetation history of the eastern United States 391
Introduction 391
Chronology 392
Databases 393
Quantitative Techniques 393
Vegetation Reconstruction 393
Climate Reconstruction 394
Rates of Change 394
Plant Migration and Range Expansion 394
Migrational Lag Versus Equilibrium 396
Physiological Controls on Paleovegetation 397
Picea 397
Ambrosia 398
Late-Glacial Biomes in the Midwest 399
Late-Glacial Climatic Oscillations 400
The Early Holocene Pine Zone in the Northeast 401
Early and Mid-Holocene Vegetation and Climate in the Midwest 402
Time-Transgressive Versus Synchronous Change 403
Conclusions 404
Acknowledgements 404
References 405
Chapter 18 413
Quaternary vegetation and climate change in the western United States: Developments, perspectives, and prospects 413
Introduction 413
The Western United States 413
State of Knowledge in 1965 415
Advances in Reconstructing Paleoclimate 417
Present-Day Plant Distributions and Climate Data 417
Dating Techniques 417
Pollen Records 418
Packrat Middens 419
Sampling 420
Analysis 421
Radiocarbon Dating 421
Calibration 421
Paleoclimatic Reconstructions 422
Databases 422
Isotopes from Plant Tissues 422
Phytoliths 424
Other Evidence of Vegetation Change 424
Paleoclimatic Reconstructions 424
Non-Climatic Factors That Influence Vegetation 424
Atmospheric CO2 Concentrations 425
Influence of Disturbance Regimes 425
Prehistoric Humans 425
Historic Humans 425
Non-Native Invasive Species 426
Human Alteration of Fire Regimes 426
Development and Application of Models 426
Potential Future Vegetation Change 428
Summary 428
References 429
Chapter 19 437
Results and paleoclimate implications of 35 years of paleoecological research in Alaska 437
Introduction 437
The Last Glacial Maximum 438
Spatial and Temporal Patterns of Change Since the LGM 441
Late Glaciation (14,000-11,000 14C yr B.P./16,800-13,000 cal yr B.P.) 441
The Late Glacial-Early Holocene Transition (11,000-9000 14C yr B.P./protect protect unhbox voidb@x penalty @M {}13,000-10,000 cal yr B.P.) 442
The Early to Mid-Holocene (9000-6000 14C yr B.P./protect protect unhbox voidb@x penalty @M {}10,000-6800 cal yr B.P.) 443
The Mid- to Late Holocene (6000 14C yr B.P. to Present/protect protect unhbox voidb@x penalty @M {}6800cal yr B.P. to Present) 444
Key Issues for Further Study 445
Acknowledgements 446
References 446
Chapter 20 451
Quaternary history from the U.S. tropics 451
Introduction 451
Climate History 451
Tropical Temperatures During the Last Glacial Maximum 451
Late Quaternary Regional Circulation in the North Pacific 452
South Pacific and Caribbean Climate History 455
Sea Level 456
Interglacial Sea-level Maxima 456
Late-Glacial and Holocene Sea Level History 457
Biogeography 458
Sea Level and Biogeography 458
Quaternary Extirpations, Extinctions, and Introductions 459
Initial Settlement 459
Increasing Disturbance and Development of Agriculture 459
Secondary Effects of Animal Extinctions and Introductions 460
Summary 461
Acknowledgements 461
References 461
Chapter 21 469
Climatically forced vegetation dynamics in eastern North America during the late Quaternary Period 469
Introduction 469
Data and Methods 470
Records of Pollen, Lake Levels, and Vegetation Change 470
Independent Climate Estimates 471
Results 475
North American Climates Over the Past 21,000 Years 475
Individualistic Responses by Taxa to Orbital-Scale Climate Change 478
Zoomed-in View of Climate and Vegetation History in New England 480
Individualistic Responses by Taxa to Millennial-Scale Climate Change 481
Linking Orbital and Millennial Scales of Vegetation Change 481
Summary of Results 482
Discussion 482
Conclusions 484
Acknowledgements 484
References 485
Chapter 22 489
Holocene fire activity as a record of past environmental change 489
Introduction 489
Refinements in Charcoal Analysis 489
Macroscopic Charcoal Analysis 490
Other Proxy Indicators of Fire 490
Modern and Past Fire-Climate Linkages 493
Fire Weather and Fire Climate 493
Fire-Climate Linkages on Holocene Time Scales 493
Discussion 496
Summary 496
Acknowledgements 497
References 497
Chapter 23 501
Interannual to decadal climate and streamflow variability estimated from tree rings 501
Introduction 501
Hydroclimatic Applications of the Continental Network of Tree-Ring Chronologies 501
Tree-Ring Estimates of Climate Forcing Factors 504
Multiproxy Paleoenvironmental Research and Tree Rings 505
Human Impacts of Tree-Ring Reconstructed Climate Extremes 506
Multi-Century Long Tree-Ring Chronologies 508
Conclusions 511
Acknowledgements 512
References 512
Chapter 24 515
Quaternary Coleoptera of the United States and Canada 515
Introduction 515
Early Pleistocene and Late Tertiary Assemblages 515
Beringian Assemblages 516
Pacific Northwest Assemblages 517
Rocky Mountain Assemblages 518
California Assemblages 518
Southwestern Desert Assemblages 519
Mid-Continental Assemblages 519
Acadian Assemblages 521
Holocene Assemblages 521
Conclusions 522
Future Studies 522
References 523
Chapter 25 529
Vertebrate Paleontology 529
Introduction 529
Biostratigraphy and Chronostratigraphy 529
Biogeography 532
Non-Analog Faunas and Taphonomy 534
Extinctions and Conservation 535
Isotopes, Ecology, and Diet 536
Phylogenetic Studies and DNA 537
Some Regional Highlights 537
Alaska 537
Great Basin 538
Idaho 538
Colorado 539
Wyoming 539
South Dakota 540
Kansas 540
Missouri Valley 540
Texas 540
Florida 541
Appalachian Mountains and Allegheny Plateau 542
Outlook Prospectus 543
Dedication 543
References 543
Chapter 26 549
Peopling of North America 549
Introduction 549
Peopling of North America - ca. 1965 549
Research Directions Since 1965 550
Peopling of North America - A Current Perspective 553
The Geography of Colonization 553
A Matter of Timing 554
Questions of Origin 555
The Clovis Archaeological Record 557
Human Hunting and Pleistocene Mammalian Extinctions 560
Living and Learning on a New Landscape 562
The End of the Era 563
Where Do We Go Next? - Unresolved Issues in the Peopling of North America 565
Acknowledgements 566
References 566
Chapter 27 575
Modeling paleoclimates 575
Introduction 575
Climate-System Modeling 575
Climate-System Variables 576
Boundary Conditions 576
Slow-Response Variables 577
Fast-Response Variables 577
Subsystem Variables 577
The Climate-Modeling Problem 577
Climate Models 577
Model Applications 578
Time-Evolution Applications 578
Spatial-Pattern Applications 578
Subsystem (Process-Model) Applications 578
Model Comprehensiveness 579
Conceptual Models 579
Elemental (or Low-Dimensional) Models 580
EMICs (Earth-System Models of Intermediate Complexity) 580
Comprehensive Models - GCMs 580
Comprehensive Models - ESMs 581
VII INQUA Congress (1965) 581
Climate Modeling in the VII INQUA Congress Materials 581
Conceptual Models 581
Elemental Models 582
Comprehensive Models 582
Subsequent Developments 582
Synopsis of Results from Modeling Quaternary Paleoclimates of North America 582
Temporal Variations of Climate 582
Cenozoic Cooling and the Quaternary Ice Age 583
Millennial-Scale Variations 583
Spatial Patterns of Fast-Response Variables - LGM to Present 584
The LGM-to-Present "Natural Experiment" 584
LGM-to-Present Simulations for North America 584
Existing and Emerging Issues in Paleoclimatic Modeling 588
Model and Data Resolution 588
Variables 589
Experimental Design 589
Paleoclimatic Diagnostics 589
Summary 590
Acknowledgements 590
References 590

Textauszug

The southern Laurentide Ice Sheet

David M. Mickelson1 [e-mail]; Patrick M. Colgan2 [e-mail]    1 Department of Geology and Geophysics, University of Wisconsin Madison, Weeks Hall, 1215 West Dayton Street, Madison, WI 53706-1692, USA
2 Department of Geology, Grand Valley State University, 1 Campus Drive, Allendale, MI 49401, USA

Publisher Summary

This chapter discusses the advances in the understanding of the southern Laurentide Ice Sheet (LIS) and its deposits since the publication of the Quaternary of the United States in 1965. The late Wisconsin southern LIS consists of thin, gently sloping lobes with low-driving stresses. The southernmost lobes have a wet bed to the margin and surges are probably common. Ice lobes in lowlands may be fed by ice streams. Not until after the late glacial maximum does ice warm to the margin. There are profound differences in the distribution and character of landforms, such as moraines, drumlins, and tunnel channels, and differences are likely to be in subglacial processes, with a soft-deforming bed occurring in places and sliding dominating in others. The extent of early Wisconsin and mid-Wisconsin ice is now thought to have been less extensive than previously interpreted. A wide array of global climate records shows that the LIS responds to climate changes and may also cause changes in climate because of the discharges of melt water and icebergs into the North Atlantic.

Changing Attitudes and Approaches

The publication of the Quaternary of the United States (Wright & Frey, 1965) for the 1965 INQUA Congress in Denver was a milestone that summarized our knowledge of the Quaternary of the U.S. in a single volume. Glacial geology was a major component of the volume, and it contained 125 pages on the Laurentide Ice Sheet (LIS) in the U.S. In the present volume, almost 40 years later, many fewer pages are devoted to the same topic, indicating the vast increase in other aspects of Quaternary studies. In the U.S., glacial geology has expanded greatly in knowledge and interest, and now glacial geologists have a much richer field and variety of techniques with which to study Quaternary history. The other chapters in this book are a clear indication of the diversity of fields that now make up what traditionally was classified as glacial geology or did not exist before 1965.

Radiocarbon dating remains the most important tool for determining the chronology of the last glaciation. Accelerator mass spectrometry (AMS) has allowed dating of smaller and somewhat older samples. Tree-ring calibration of the radiocarbon time scale has resulted in dating accuracy not possible 40 years ago. Newer dating methods such as thermoluminescence, amino-acid racemization, paleomagnetism, and cosmogenic-isotope methods have yielded mixed results, but have the potential to improve our interpretations of glacial chronology, especially those of the pre-late Wisconsin.

There have been revolutionary changes in the way we study glacial sediments and reconstruct their depositional environments. Genetic classifications have been replaced by descriptive lithofacies approaches, which focus on modern-process analogs for interpretations of depositional environments. Correlations of till units from one area to another are now approached with more caution, and the use of facies models facilitates the understanding of complex glacial sequences. Geophysical techniques have been used to explore lake basins and subsurface stratigraphy. Models of glacial landform genesis are also driven by modern analogs and interpretations made in modern glacier settings.

There have been major changes in our understanding of pre-late Wisconsin events since 1965. The terms “Nebraskan” and “Kansan” are no longer used, and now there is evidence of at least six pre-Illinoian glaciations in the continental record. Flint (1971), in a widely used textbook, hinted that there might be problems with correlations of what was called “Nebraskan Drift,” but nevertheless used the terminology accepted at that time. Based on the oxygen-isotope record from the oceans, we now know that there were clearly more than four glacial and interglacial episodes during the Pleistocene. Much work remains to be done to unravel this continental record of early glaciations and correlate it to the ocean record. There has been debate about the extent of the early Wisconsin Glaciation as well. In many areas, particularly in northern Illinois and southern Wisconsin, deposits thought to be of this age now appear to be older.

Probably one reason for our rather poor understanding of pre-late Wisconsin glacial events is the decline of purely stratigraphic studies from the 1980s through the 1990s. State geologic surveys have in many cases reduced their staff and mapping has been displaced by topical studies and an emphasis on applied research related to groundwater and mineral extraction. In academia, traditional mapping and glacial stratigraphy have not been as common in the last 40 years as previously. Instead they have been replaced by, or combined with, studies of sediment genesis, glacial process, development of conceptual and quantitative models, and details of local chronology, and integrative studies of glacial deposits and other aspects of Quaternary history such as ice-marginal lakes, paleoclimatology, loess, soils, and the paleontologic record. In the 1990s the U.S. Geological Survey began to fund mapping projects in academia (EDMAP) and state geologic surveys (STATEMAP), and this has revitalized mapping of glacial deposits in the northern U.S. Since the late 1990s the Great Lakes Mapping Coalition, a joint effort of the U.S. Geological Survey and several state geologic surveys, has focused on detailed three-dimensional mapping that includes subsurface investigation. If this program continues to grow, it may re-stimulate interest in mapping glacial deposits.

Much of our improved understanding of the southern LIS has come from studies of the new field of paleoglaciology. Reconstruction of ice-sheet surfaces, interpretation of former bed conditions and discussions of sliding vs. subglacial deforming beds, estimates of sediment fluxes, interpretations of the nature and distribution of subglacial meltwater, new interpretations of landform genesis, and modeling have all been major areas of research in the last 40 years.

There have been several extensive compilations of the glacial record of the southern LIS since 1965 and we make no attempt to repeat these here. Instead, we highlight what we view as advances in our understanding of the southern LIS and its deposits since publication of the Quaternary of the United States in 1965. Events and processes along the southern margin of the LIS are closely tied to the behavior of the ice sheet in Canada, but much of this literature is not discussed here because of the scope of the book. Likewise, we refrain from discussing ancillary topics, like loess and the history of ice-marginal lakes, because these are covered elsewhere in the volume.

Mapping and Compilations of Glacial Geology and Geomorphology Since 1965

Since 1965 there have been several comprehensive reviews of the geology and geomorphology of the southern LIS. The “state-of-knowledge” was summarized by Flint in 1971 in part of his classic text. At this time, the deep marine record was only beginning to be discovered. Our understanding of modern ice-sheet dynamics in Greenland and Antarctica was in its infancy, and an understanding of surging glaciers and modern glacial environments was just emerging. Records of global climate change such as ice cores, pollen databases, loess records, and lake cores were fragmentary, few, and far between. Much of what was known was based on the incomplete terrestrial record of continental and mountain glaciation.

Throughout the 1970s and 1980s numerous records of the last glaciation were collected, analyzed, and combined into a global database (e.g. CLIMAP, 1976, 1984; COHMAP, 1988). For the INQUA meeting in Moscow, the U.S. INQUA Committee produced two volumes of edited papers on the Quaternary of the U.S. (Wright, 1983). These include a comprehensive review of the glacial record and a chronology of glacial and periglacial events during the late Wisconsin glaciation (Mickelson et al., 1983). Included were maps showing the nature of the glacier bed, moraines and other ice-margin positions, and a generalized map of landform regions. Andrews (1987) summarized major issues in understanding the whole LIS: the thickness of the ice sheet, the extent of ice during the mid-Wisconsin (marine oxygen isotope stage (OIS) 3), the timing of the late-glacial maximum, and the chronology of deglaciation. The publication Quaternary Glaciations in the Northern Hemisphere (Sibrava et al., 1986), which contains several review papers on deposits of the LIS in the United States (Brown et al., 2001; Eschman & Mickelson, 1986; Fullerton, 1986; Fullerton & Colton, 1986; Hallberg, 1986; Hallberg & Kemmis, 1986; Johnson, 1986; Lasemi & Berg, 2001; Matsch & Schneider, 1986; Stone & Borns, 1986), is the most recently published compilation covering all of the area of the LIS in the United States. Dyke & Prest (1987) and Dyke et al. (2002) summarize what is currently known about the extent and timing of the entire LIS during the last glacial maximum (LGM).

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Produkt-Details

• Erscheint lt. Verlag: 17.12.2003
• Sprache: englisch
• Themenwelt: Naturwissenschaften ► Geowissenschaften ► Geologie
• Themenwelt: Naturwissenschaften ► Geowissenschaften ► Mineralogie / Paläontologie
• Themenwelt: Naturwissenschaften ► Physik / Astronomie
• Themenwelt: Technik
• ISBN-10: 0-08-047409-8 / 0080474098
• ISBN-13: 978-0-08-047409-0 / 9780080474090