U.S. Department of the Interior U.S. Geological Survey
Pliocene Terrestrial Environments and Data/Model Comparisons
Abstracts From A USGS Workshop, Herndon, Virginia, May 22 - 23, 1993
Edited by Robert S. Thompson
Open-File Report 94-23
This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards and stratigraphic nomenclature. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
1994 Contents
Page
Introduction (R.S. Thompson)...... 1
Terrestrial palynological and paleobotanical records of Pliocene age from Alaska and Yukon Territory (T.A. Ager) ...... 2
Palynological records of the Pliocene in Baffin Bay and Labrador Sea (A. de Vernal)......
Pliocene pollen data set dynamics: Tulelake, California, and Lost Chicken Mine, Alaska (D.P. Adam)......
Palynological records from Pliocene sediments in the California region: Centerville Beach, DSDP Site 32, and the Anza-Borrego Desert (R.F. Fleming)...... 11
Mid-Pliocene vegetation, environment, and climate in the western interior of the United States (R.S. Thompson)...... 16
Palynological record from the North Atlantic region at 3 Ma: vegetational response to a period of global warmth (D.A. Willard)...... 21
Neogene palynofloras and terrestrial paleoenvironments in northern Latin America (A. Graham)...... 23
Paleoclimatic conditions around 3 million years BP: pollen evidence from Colombia (H. Hooghiemstra)...... 31
Mediterranean Pliocene vegetation and climate: how to quantify the climate parameters? (J.-P. Sue, A. Drivaliari, E. Bessais, J. Guiot, A. Bertini, S. Leroy, R. Cheddadi, J. Ferrier, and D. Duzer)...... 38
Steps toward drier climatic conditions in north-western Africa during the Upper Pliocene (L.M. Dupont and S. Leroy)...... 44
An attempt to reconstruct temperature and rainfall from the Pliocene pollen record in Ethiopia (R. Bonnefille, D. Jolly, and F. Challe)...... 52
Some manifestations of Pliocene warming in southern Africa (L. Scott and T. C. Partridge)...... 54
Landscape and climate of the southwestern Russian Plain in the Pliocene (T.V. Svetlitskaya)...... 56 Landscape and climate of the south-central and southeastern Russian Plain in the Pliocene (O.K. Borisova)...... 61
GCM Simulations of the Pliocene climate: feedbacks, Ocean transports, and CO2 (M. Chandler)...... 65
Considerations for the PRISM paleoclimate study (L.C. Sloan)...... 69
Use of a high-resolution atmospheric model for simulations of paleo climate (S.W. Hostetler, F. Giorgi, G.T. Bates, and PJ. Bartlein)...... 71
The forward-modeling approach in paleoclimatic analysis: middle- Pliocene vegetation distributions in North America (PJ. Bartlein)...... 73
Acknowledgments...... 90
Appendix I...... 91
11 Illustrations (listed by first author and figure number)
Page
Adam Figure 1. Plots of pine pollen percentage vs. TCT from Tulelake, California...... ^ 9
Adam Figure 2. Plot of Lost Chicken, Alaska pollen samples against DerrendedCorrespondence Analysis axes 1 and 2...... 10
Fleming Figure 1. Sketch map showing position of Centerville Beach, DSDP Site 32, and Anza-Borrego...... 14
Fleming Figure 2. Relative abundance profile of Pinus and TCT pollen from DSDP Site 32...... 15
Thompson Figure 1. Map of sites mentioned in text...... 19
Thompson Figure 2. Changes in the relative abundance of conifers through the Pliocene and earliest Pleistocene in southern Idaho and adjacent Oregon...... 20
Willard Figure 1. Location of sites analyzed for pollen, North Atlantic Ocean transect...... 22
Graham Figure 1. Map showing placement of localities discussed in text and chart illustrating the approximate ages of the formations present at these localities...... 26
Graham Figure 2. Correlation of the Paraje Solo Formation with marine faunal zones ...... 27
Graham Figure 3. Cenozoic benthic marine temperature curve with the approximate ages of formations discussed in the text...... 28
Graham Figure 4. Position of the Paraje Solo Formation in relation to the nannofossil zones. From Machain-Castillo (1985)...... 29
Hooghiemstra Figure 1. Altitudinal distribution of vegetation belts in the Eastern Cordillera of Colombia...... 34
Hooghiemstra Figure 2. Map of Colombia and the high plain of Bogota in the Eastern Cordillera ...... 35
Hooghiemstra Figure 3. Pollen percentage diagram of the 540-430 m interval of the Funza II core...... 36 iii Hooghiemstra Figure 4. Summary pollen diagram Funza II (540-430 m interval) with pollen zones and tentative correlation with the deep- sea oxygen isotope stratigraphy ...... 37
Sue Figure 1. Selected Pliocene localities in the Mediterranean region...... 42
Sue Figure 2. Chronological assignment of some selected Pliocene sections in the Mediterranean region...... 43
Dupont Figure 1. Location of OOP site 658...... 49
Dupont Figure 2. Pollen data and inferred paleoclimatic changes for OOP site 658...... 50
Dupont Figure 3. Running mean of percentages for selected pollen taxa...... 51
Svetlitskaya Figure 1. Pliocene localities on the Southwestern Russian Plain... 60
Borisova Figure 1. Pliocene stages and inferred vegetation for three regions of the southern Russian Plain...... 64
Chandler Figure 1. Pliocene and modern annual ocean heat transports for the Atlantic Ocean...... 67
Chandler Figure 2. Water vapor, cloud coverage, and ground albedo in the northern hemisphere as a function of latitude in the GISS Pliocene GCM simulation ...... 67
Chandler Figure 3. Levels of ocean heat transport required to generate PRISM sea-surface temperatures at varying level of atmospheric CO2 concentrations...... 68
Bartlein Figure 1. Examples of indeterminacy of paleoclimatic evidence...... 83
Bartlein Figure 2. Response surface for Picea mariana (black spruce)...... 84
Bartlein Figure 3. Response surface for Quercus alba (white oak) ...... 85
Bartlein Figure 4. Response surface for Artemisia tridentata (sagebrush)...... 86
Bartlein Figure 5. Distribution maps for Picea mariana (black spruce)...... 87
Bartlein Figure 6. Distribution maps for Quercus alba (white oak)...... 88
Bartlein Figure 7. Distribution maps for Artemisia tridentata (sagebrush)...... 89
IV Introduction: USGS Workshop on Pliocene Terrestrial Environments and Data/Model Comparisons
Robert S. Thompson
Over the last several years, the U.S. As part of this effort, the U.S. Geological Geological Survey's PRISM (Pliocene Survey Global Change and Climate History Research, Interpretation, and Synoptic Program sponsored a workshop on Mapping Project) project has accumulated "Pliocene Terrestrial Environments and information for a "snapshot" description of Data/Model Comparisons," which was held global marine and terrestrial conditions for in Herndon, Virginia, on May 22 and 23, the mid Pliocene, the last period in Earth 1993. This report presents the abstracts from history when globally warm conditions the Herndon workshop. The primary persisted over hundreds of thousands of objectives of this meeting were to review years. PRISM researchers and collaborators the available data on mid-Pliocene are analyzing times-series of environmental terrestrial environments, and to provide a changes both marine and nonmarine forum for geological researchers and settings to determine the amplitude and climate modelers to discuss the uses of periodicity of Pliocene climatic changes, and palynological and other terrestrial are assembling gridded data sets of environmental data in initializing and vegetation cover to provide boundary validating GCM simulations of past conditions for General Circulation Model climates. (GCM) simulations. Palynological and other terrestrial data will also being employed in validation exercises of Pliocene climate simulations provided by researchers using Goddard Institute for Space Studies (GISS) and NCAR (National Center for Atmospheric Research) GCMs. Terrestrial Palynological And Paleobotanical Records Of Pliocene Age From Alaska And Yukon Territory
Thomas A. Ager, U.S. Geological Survey, Denver, CO 8O225
A joint research project initiated in 1990 temperature is -28° C, mean July temperature by the U.S. Geological Survey and the is 16.4° C, and mean annual precipitation is Geological Survey of Canada, entitled "Late only 168 mm. Cenozoic climate history of Alaska and Pollen and spores recovered from the Yukon," has conducted three field Nenana Gravel include Pinus*, Picea, Larix, investigations thus far (1990, 1991, 1992). Tsuga*, Abies*, Betula, Alnus, Diervilla-Weigela*, Many of the deposits investigated are of and a number of herbaceous taxa that are rare middle to late Miocene age, but several are of or absent from Miocene deposits from the Pliocene age. One of the Pliocene deposits same region (taxa marked with asterisks in investigated is the Nenana Gravel in the this abstract no longer grow in the Alaska Alaska Range in southern central Alaska, Range or elsewhere in interior Alaska). Some which forms a thick mantle on the north flank herb taxa, such as Polemonium, did not evolve of the Alaska Range. Gravel deposits provide until Pliocene time, and others appear to have only rare opportunities for preserving fossil played only a very minor role in the regional assemblages, but pollen and spores have been vegetation prior to the Pliocene. The presence recovered from mudstone layers within the during the Pliocene of taxa such as Tsuga and gravels. The Nenana Gravel is important Abies that are now missing from the interior because the gravels were deposited during or region suggests that a highly continental immediately following the period of rapid climate was not yet fully developed. MAT in uplift of the Alaska Range, an event that the lowlands of the interior was probably greatly influenced the climate of the interior. near 3° C, and permafrost was absent except Current evidence indicates that the major at higher elevations. As mentioned above, uplift of the Alaska Range began in early deposition of the Nenana Gravel may have Pliocene time, ca. 4-5 Ma. Fission-track ages begun by ca. 5 Ma (based on the uplift history on granitic rocks now exposed in core of the of the Alaska Range) and may have continued Alaska Range date the initial uplifting and until ca. 2.8 Ma (based on the age of the unroofing of the crystalline core. The timing Jumbo Dome igneous intrusion that deformed of tectonic events leading to the uplift of the deposits of this gravel unit in one area of the Alaska Range are highly relevant to Alaska Range at 2.8 Ma [minimum date]). understanding the regional versus global Another apparent Pliocene gravel deposit climate influences. The development of the was found in ancient terrace deposits of the arcuate, east-west trending high Alaska Yukon River near Circle, Alaska. It contains a Range in early Pliocene time significantly pollen flora that matches closely that in the altered the regional climate of interior Alaska. Nenana Gravel. The pollen flora does not The rising mountains increasingly limited match closely any known Miocene or northward penetration of moist air masses Pleistocene floras from the region. The plant from the north Pacific from reaching the macrofossils identified from the gravel interior. The climate of the interior is now deposits near Circle contain taxa that range in highly continental, characterized by long, age from late Miocene to Pliocene. severely cold winters and warm summers. Paleomagnetic samples from one exposure of Precipitation is low. At Fort Yukon, for the terrace gravel deposits have reversed example, the modern mean annual polarity, which provides some small temperature (MAT) is -6.4° C, mean January constraint on the age of the deposit. At present, I believe that the age of the gravels is mossy ground cover. The Lost Chicken flora probably between ca. 5 and 3 Ma. The gravel lacks Tsuga, in contrast to late Miocene and deposits contain wood (Picea, Abies*, Pinus*), older Pliocene floras from interior Alaska. cones (Picea and an undescribed species of The climate was warmer than the present Larix}, needles (Picea, Pinus), and seeds (Holocene) interglacial in Alaska. MAT was (Prunus*, Epipremnum*, Hypericum*, Aracites*, probably ca. 2-3° C, vs. ca. -7° C today at the Weigela*, Aralia*, and many others). This flora nearby community of Chicken. represents a transitional stage between the On the North Slope of Alaska, the Fish late Miocene floras, which are relatively rich Creek site provides some information on the in conifer taxa but poor in herbaceous taxa, early development of tundra or tundra-like and Quaternary interglacial boreal forest vegetation during the late Pliocene, probably floras which are relatively depauperate in about 2.4 Ma. Tree and shrub elements of the conifer and broadleaf taxa but rich in older Fish Creek pollen flora include Picea*, herbaceous taxa. Pinus*, Larix*, Abies*, Betula, Alnus*, Salix, and Another informative site is at Ch'ijee's Ericaceae. Herbs are well-represented, and Bluff, an exposure on the Porcupine River in include Cyperaceae (most abundant), northern Yukon. Unit 1 at the base of the Gramineae, Artemisia, Compositae bluff contains a flora that is probably mid- (Tubuliflorae), Caryophyllaceae, and Pliocene age (ca. 3.5-2.5 Ma), but this age Valeriana. Pollen data within the Fish Creek assignment is based mostly on the seed site records a progressive loss of trees and assemblage and needs to be refined through shrubs, reflecting onset of colder glacial additional research. The unit 1 deposits are climates in northern Alaska. rich in wood, including beaver-chewed The Pliocene history of climate and Abies*, Pinus* (Strobus group), Larix, and ecological changes in Alaska and northern Picea. Cones in the deposit are identified as Canada are still poorly understood, although Picea, Larix cf. L minuta, and Pinus* (5-needle progress is being made to identify and and 2-needle types). Seeds from the deposit investigate such deposits. One of the major include Betula, Alnus, Larix*, Comptonia*, problems inhibiting progress has been Sambucus*, Carex, Sparganium, and inadequate age control for some of the most Potamogeton. important fossil localities. Because the precise An additional very important Pliocene site biostratigraphic ranges of many of the is Lost Chicken Mine in east-central Alaska, Pliocene taxa from the region are poorly where the sediments contain a tephra that has known, the fossil assemblages alone can only been fission-track dated at 2.9 + 0.2 Ma (see provide broad-range age assignments. The Adam, this volume). This late Pliocene best hope of reconstructing a detailed deposit contains a proto-boreal forest fossil Pliocene terrestrial record from the region assemblage of Picea, Larix (not L. laricina, the may be from the drilling project planned for only larch species in Alaska today), Pinus*, 1994 at Fort Yukon, in interior Alaska. At that Abies?*, Corylus*, Betula, Alnus, and Ericaceae. location we may obtain a long Neogene In contrast to the older Pliocene floras from record (about 15 Ma) in about 300 meters of the Nenana Gravel and the terrace gravels sediment core. A water well log from Fort near Circle, the Lost Chicken Mine site has Yukon suggests that the subsurface sediments yielded only a sparse herbaceous flora. This are mostly lacustrine. may reflect a dense forest cover, with few openings for herbaceous taxa, and perhaps a Palynological Records Of The Pliocene In Baffin Bay And Labrador Sea
Anne de Vernal, GEOTOP, Montreal, Canada
Pliocene deposits are virtually absent in temperate and humid conditions prevailed eastern Canada, a region marked by strong according to the significant occurrence of glacial erosion during the late Quaternary. Sciadopitys and Tsuga; and (2) inputs of shrub However, drilling in the adjacent marine taxa pollen grains (Betula, Alnus and basins, the Labrador Sea and the Baffin Bay Ericaceae) originating from an open (Leg 105 of the Ocean Drilling Program), has vegetation of forest tundra and shrub tundra led to the recovery of nearly continuous related to a humid subarctic climate. The Pliocene sequences. The palynology of these pollen and spores content of sediments Pliocene sequences provides information probably relate to atmospheric influxes from about terrestrial climate on adjacent land southeastern Canada, where temperate (pollen and spores) and sea-surface conditions prevailed, in addition to fluvial conditions (dinoflagellate cysts and inputs from southern Greenland, where prasinophyte phycoma). subarctic climate can be inferred. The The palynological record of Labrador Sea Pliocene interval, including the Gauss is from the ODP Site 646 located on the chronozone, is marked by small scale southwest Greenland rise. The chronostratig- fluctuations in concentrations and taxa raphy is well constrained by the marine percentages, indicating changes in microfossil biostratigraphy and the magneto- vegetational cover, hydrological conditions stratigraphy. Sedimentation rates appear over southern Greenland and/or atmospheric relatively uniform throughout the sequence trends across the Labrador Sea. A major shift and average ~9 cm/ka. Palynological in the Pliocene palynological record of the analyses were performed in the Plio- Labrador Sea occurs at about 2.5 Ma, Pleistocene sediments (480-0 m; 5.4-0 Ma) at coinciding with the first regional input of ice- 1.5 m intervals, which provided a time rafted debris and the initiation of glaciations resolution of ca. 16 kyr. The Pliocene deposits about the North Atlantic Ocean a drastic are characterized by abundant prasinophytes drop in pollen and spore concentrations is (Cymatiosphaera) and dinoflagellate cysts accompanied by the decline of Sciadopitys and (Protoperidiniales and Gonyaulacales). In the Tsuga, which indicates impoverishment of the Gauss chronozone (3.4-2.47 Ma), the marine vegetational cover and significant cooling in palynomorph assemblages reflect relatively the source areas. low salinity (varying from 32 to 35%o), likely In the central Baffin Bay, the drilling of due to freshwater runoff, and cool conditions 1200 m of sediment at ODP Site 645 revealed (ca. 8 to 11 °C in summer) rather similar to a sequence spanning the entire Neogene. The present. Most samples are characterized by marine microfossil records are poor, notably abundant pollen (>1000/cm3), suggesting the because of sparse productivity and because of existence of a dense vegetation over the biogenic carbonate dissolution. Nevertheless, source areas, the eastern Canada and the magnetostratigraphy and a few biostrati- Greenland. The assemblages are dominated graphic datums allowed to set a reasonable by Pinus with common Picea, Tsuga, chronostratigraphy. Sedimentation rates Sciadopitys, Betula and Alnus, along with throughout the Plio-Pleistocene are relatively Pteridophyte and Sphagnum spores. Such high, (13.5 cm/kyr). Palynological analyses assemblages suggest influx from two main were performed at 1.5 to 3.0 m interval in sources: (1) tree-pollen fluxes originating Pliocene sediments. Above the Gilbert-Gauss from a coniferous forest, where cool boundary (3.4 Ma), the marine palynomorph assemblages are dominated by prasinophytes During the Pliocene, the transition between and protoperidiniales, which indicate a low the subarctic and low Arctic bioclimatic zones salinity (<30%o), estuarine type environment. was probably located in the southern Baffin Abundant pollen and spores (up to Bay region, 5° to 7° north of the present limit. 50,000/cm3) were recovered in most Pliocene The Gauss interval is marked by fluctuations samples, which indicates a dense vegetational in pollen and spore concentrations and cover in adjacent terrestrial areas, the Baffin percentages. These variations may reflect Island and Greenland. The assemblages are changes in vegetation source, fluvial inputs, characterized by both coniferous trees (Pinus atmospheric trends and/or sedimentary and Picea) and non-arboreal (Alnus, Betula, processes. They probably respond to climatic Ericaceae, Sphagnum) components. Such fluctuations, which may also be related to assemblages closely resemble those of the recurrent growth and decay of ice caps in modern Hudson Bay: they suggest the circum-Arctic areas as shown by ice-rafting existence of coniferous boreal forest to shrub deposition in Baffin Bay. However, strong tundra vegetation with extensive peatlands in increase in ice-rafting deposition related to terrestrial regions surrounding Baffin Bay. major glaciation is dated back to ca. 2.5 Ma. Pliocene Pollen Data Set Dynamics: Tulelake, California, And Lost Chicken Mine, Alaska
David P. Adam, U.S. Geological Survey, Menlo Park, CA 94025
Pollen data sets of Pliocene age from underlying dynamic structure. Assuming continental sites are relatively rare. Pollen that the sequence of pollen samples through work with a paleoecological slant has focused time is known, the dynamics can be primarily on deposits of Holocene and Upper investigated by plotting the samples in Quaternary age, which are common and Stratigraphic order in some appropriate phase readily sampled in many regions. space, chosen so as to clarify the patterns Stratigraphic palynologists, in contrast, have present in the data. This approach to past focused on pre-Pliocene deposits; most of the vegetation dynamics is illustrated below pollen grains encountered in Pliocene using data from Tulelake, California, and Lost deposits cannot be distinguished from Chicken mine, Alaska. modern forms, and the simple presence or absence of particular forms is not as Tulelake informative as it is for older deposits. Although many or most of the pollen The Tulelake record is from a 334-m core types important in Pliocene deposits that spans the past 3 Myr (Adam et al., 1989, represent plants still extant, the associations 1990). Initial inspection of the pollen diagram formed by those plants in the past may well suggested that the behavior of pine pollen vs. have been different than those of today. Even TCT (Taxodiaceae, Cupressaceae, and if Pliocene pollen assemblages have modern Taxaceae) pollen varied through time in a analogs, those analogs often represent significant way. A plot of pine vs. TCT pollen geographical ranges far removed from the for the entire section (6A) was not helpful, but Pliocene sites. For example, poorly-preserved a plot of the Pliocene part of the core (6B) pollen samples from the Pliocene Santa Clara indicated a well-developed pattern of Formation near San Francisco contain up to variability between the two types. When 50% spruce (Picea) pollen; spruce does not stratigraphically adjacent samples are occur in the area today (Adam et al., 1983). connected with lines (Figure 1C), the nature Pollen records from the Pliocene often of the underlying dynamics of the data set span rather long time intervals; the longer the emerge. Nearly all of the connecting lines interval under study, the more work is have a negative slope, indicating that when required to achieve fine time resolution. Time pine increases, TCT decreases and vice versa. series are thus often severely under sampled Only rarely do both types increase or decrease compared to Holocene studies, with sampling together. intervals measured in millennia rather than Comparison of the pattern of pine vs. TCT centuries or decades. Pollen zones then tend pollen discussed above with modern data to be characterized not only by the from central California suggested that the late frequencies of the various pollen types within Pliocene climate at Tulelake had much in them, but also by the nature of the variability common with the present climate at middle within and between types. elevations along the western slope of the Because pollen assemblages from Pliocene Sierra Nevada near Yosemite, and with the deposits often suggest climatic conditions climate that prevailed at lower elevations in significantly different from those of today, it the northern California Coast Ranges during is important to understand not only the the cooler parts of deep-sea oxygen isotope nature of the assemblages, but their Stage 5 (Adam et ai, 1990). Comparison of the various sites was greatly facilitated by the Discussion phase-plot technique illustrated here. Changes in the vegetational dynamics Lost Chicken Mine recorded in the Tulelake and Lost Chicken data sets are reflected in the phase plots The Lost Chicken Mine is a working shown in figures 1 and 2 by changes in the placer mine along the Taylor Highway in slopes of the lines connecting stratigraphically east-central Alaska (see also Ager, this adjacent points. Particular dynamic regimes volume). It includes exposures of plant- and are represented by elongate clouds of points mammal-bearing fluvial sediments and peats in the phase space. These clouds are roughly of upper Pliocene age, as indicated by the linear in the examples selected, but Lost Chicken tephra layer, with a glass curvilinear clouds may also occur. The isothermal fission-track age of 2.9±0.2 Ma character of a cloud representing a single (John Westgate, oral communication). Thirty- regime should be independent of the time seven pollen samples were analyzed from intervals between samples; this property is various stratigraphic units; age relationships useful in dealing with Pliocene data sets that between samples are sometimes clear but usually lack detailed time control. Shifts in sometimes inferred. The Pliocene samples the location or orientation of the cloud are apparently represent a warm interval at or best identified through inspection of the near the end of the Gauss Normal sequence of lines connecting the points in paleomagnetic chron; the Holocene samples stratigraphic order; the shifts show up as all predate the White River Ash, which has an abrupt changes in slopes of the lines. age of 1200 years (Pewe, 1975). The method illustrated here is intended to The pollen counts were reduced to a augment rather than supplant standard condensed data set and subjected to a methods of interpretation. It provides a way detrended correspondence analysis (DCA; to characterize groups of samples that covary, Gauch, 1982). The DCA reduced the data set and to contrast them with adjacent groups. to four primary orthogonal axes that When samples are spaced relatively far apart summarize the variability within the data. compared to the frequencies of the Because each axis reflects patterns of underlying climate signals, such character variability that apply to the entire data set izations may provide useful insights into the rather than just to individual variables, shifts behavior of the record. in the behavior of the data with respect to these axes are likely to reflect changes in the References dynamics of the underlying climate system than simple plots of one taxon versus another. Adam, D. P., Adams, D. B., Forester, R. M., The pollen samples are plotted against the McLaughlin, R. J., Repenning, C. A., and first two DCA axes in 7, with samples from Sorg, D. H., 1983, An animal- and plant- the same stratigraphic unit in known fossil assemblage from the Santa Clara stratigraphic order connected by lines. The Formation (Pliocene and Pleistocene), Holocene samples (29-33) are clearly set apart Saratoga, California, in Andersen, D. W., from the other samples, which are all Pliocene and Rymer, M. J., eds., Tectonics and in age. In addition, inspection of the sequence sedimentation along faults of the San of samples through time suggests that the Andreas System: Los Angeles, Society of Pliocene samples represent two separate Economic Paleontologists and dynamic regimes: (1) Axis 1 and Axis 2 scores Mineralogists (Pacific Section), p. 105-110. positively correlated, and (2) Axis 1 and Axis 2 scores negatively correlated. Adam, D. P., Sarna-Wojcicki, A. M., Rieck, H. Adam, D. P., Bradbury, J. P., Rieck, H. ]., and J., Bradbury, J. P., Dean, W. E., and Sarna-Wojcicki, A. M., 1990, Environ Forester, R. M., 1989, Tulelake, California: mental changes in the Tule Lake basin, the last 3 million years. Palaeogeography, Siskiyou County, California, from 3 to 2 Palaeoclimatology, Palaeoecology, v. 72, million years before present: U.S. p. 89-103. Geological Survey Bulletin 1933,13 p.
Adam, D.P., and Vagenas, G.L., 1990, Pollen Gauch, H.G., Jr., 1982, Multivariate Analysis data for a 3-m.y. core record from in Community Ecology: Cambridge, Tulelake, Siskiyou County, California: England, Cambridge University Press, 298 U.S. Geological Survey Open-File Report P- 90-65,307 p. Pewe, T.L., 1975, Quaternary stratigraphic nomenclature in unglaciated central Alaska: U.S. Geological Survey, Professional Paper 862,32 p. A Tulelake Tulelake entire section 3.1-2.0 Ma
9»
o O O O ooo
o o °°o6
10 20 30 40 50 60 70 SO M 100 10 20 30 40 50 60 70 M 90 PINE POLLEN. IN PERCENT c Tulelake 3.1-2.0 Ma
10 20 30 40 50 60 70 M »0 PINE POLLEN. IN PERCENT
Figure 1. Plots of pine pollen percentage vs. TCT (Taxodiaceae, Cupressaceae, and Taxaceae) pollen from Tulelake, Siskiyou County, California. A) data for entire section; B) data for samples with ages from 2.0-3.1 Ma; C) same data as in B7 but with stratigraphically adjacent samples connected by lines. Data are from Adam and Vagenas (1990). 100-
,10
0-
100 AXIS 1
Figure 2. Plot of Lost Chicken, Alaska, pollen samples against Detrended Correspondence Analysis axis 1 and 2. Plot symbols represent various stratigraphic units, numbers are sample numbers (some numbers are "missing"), and arrows indicate direction of stratigraphic succession (older to younger). Palynological Records From Pliocene Sediments In The California Region: Centerville Beach, DSDP Site 32, And The Anza-Borrego Desert
R. Parley Fleming, U.S. Geological Survey, Denver, CO 80225
Localities along the west coast of North in Pliocene sediments of Site 32 is less America have been selected for palynological abundant than amounts reported by Heusser analysis to provide a basis for evaluating and Balsam (1977) for modern sites from the terrestrial vegetation patterns along the northeast Pacific Ocean. Adam et al. (1990) Pacific Coast of North America during the developed a model for the Tule Lake, Pliocene. Preliminary results from three of California, core record in which increased these localities (Figure 1) demonstrate the Pinus and decreased TCT indicate cooler nature of the material that is available, the conditions in Pliocene time, though perhaps types of information that can be obtained, and still warmer than today. Other elements of the problems associated with extracting the modern California flora present in Site 32 paleoclimate estimates in this area. samples include Quercus, Artemisia, Chenopodiaceae, and Asteraceae. Exotic taxa DSDP Site 32 that may be relictual from the California Miocene include Carpinus,Carya, Ilex, Leg 5 of the Deep Sea Drilling Project Taxodium, Tilia, Pterocarya, and Ulmus. (DSDP) drilled Site 32 (37° 7.63' North, 127° Sequoia pollen is significantly reduced in 33.38' W) near the seaward margin of the all Site 32 samples, relative to today. One of submarine Delgada Fan off the coast of the most important factors controlling the California. This fan contains a mixture of distribution of Sequoia is fog. Low amounts of terrigenous and clastic sediments derived Sequoia pollen at Site 32 may reflect climatic mostly from areas now drained by the San conditions less favorable for the formation of Joaquin and Sacramento Rivers. During the fog. The presence of Taxodium suggests that Pliocene, the Delgada Fan presumably the summers may have been wetter than received sediment from the same general today. area, although a marine embayment filled Results of DECORANA (Detrended much of the Great Valley of California. Correspondence Analysis) reveal patterns in Previous biostratigraphic studies based on the overall data matrix from Site 32 that may diatoms, planktonic foraminifera, and relate to overall paleoclimatic variability with calcareous nannofossils provide a temporal fluctuations apparently occurring on a 200- framework for Site 32 (Barren, 1992). Samples 400 k cycle. Inspection of the data matrix for palynology were collected from a nearly reveals that these fluctuations are in part complete sequence from about 4.5 Ma to related to changes in the relative abundances about 3 Ma (younger Pliocene sediments were of mixed conifers (Picea, Tsuga heterophylla, not recovered). Age estimates for these and Abies). Because these taxa along the samples were determined by extrapolating Pacific Northwest coast are controlled to a from the existing biostratigraphic framework large degree by moisture, the fluctuations based on other microfossils. may reflect variations in precipitation during Pollen of Taxodiaceae-Cupressaceae- the Pliocene. Taxaceae (TCT) accounts for more than 50% Preliminary analysis of the palynological of the pollen sum in most palynological data from Site 32 reveals patterns that suggest assemblages from Site 32, although some departures from modern climatic conditions assemblages are dominated by Pinus (e.g., at during the Pliocene. Some taxa have -3.75 Ma and -3.00 Ma; see Figure 2). Pinus increased or decreased relative abundances
11 when compared to their relative abundance in Anza-Borrego Desert modern marine core top samples. Quantification of these differences in terms of The Anza-Borrego Desert State Park is temperature and precipitation awaits located in the Salton Trough of southern acquisition of reliable modern pollen data sets California. Badland exposures in the park from marine core tops in the northeast Pacific. include a thick sequence (-4600 m) of Pliocene and Pleistocene sediments. Much of Centerville Beach this sediment was derived from the ancestral Colorado River as it deposited its sediment The Centerville Beach section is located in load into the Gulf of California. Detailed the Eel River basin of northern California (40° paleomagnetic studies have been integrated 32.5' N, 124° 22.5' W). This section contains with radiometric dates on volcanic ashes and approximately 1800 m of marine mudstones, provide an excellent temporal framework for siltstones, and sandstone that were deposited Pliocene rocks at Anza-Borrego (Johnson d in the Humboldt basin along the western al, 1983; Opdyke et ai, 1977). edge of the North American Plate. Palynology samples were collected Previous workers have developed a throughout the 2-4.5 Ma interval, with closely temporal framework for the Centerville Beach spaced samples above and below the 3 Ma section based on microfossil biostratigraphy, horizon. Unfortunately, samples processed paleomagnetism, and radiometric dating of from about 3 Ma are barren or only volcanic ashes (Barren, 1992; McCrory, 1990). marginally productive. However, some Additional paleomagnetic studies are samples from about 3.5 Ma and older are underway to refine the magnetostratigraphy productive. Although palynological recovery in the Gauss paleomagnetic chron. from the Anza-Borrego section is apparently Palynological samples from the Centerville inadequate for evaluating paleoclimate at 3 Beach section have proven to be productive; Ma, reworked fossils in the section may additional sampling may be necessary to provide important insight into climatic obtain a complete time series and to verify conditions of the Colorado Plateau during the preliminary results. Pliocene. Palynological results from the Centerville Pollen assemblages recovered from the Beach section are only preliminary but lower part of the Anza-Borrego section suggest that the variability observed in DSDP contain several species of Cretaceous pollen Site 32 may also be present at Centerville and spores. Some of these species are Beach. Plots of the mixed conifer group distinctive and have restricted (Picea, Tsuga heterophylla, Abies} display biostratigraphic and paleobiogeographic fluctuations on about the same frequency as ranges in the Western Interior of North at Site 32 and appear to be approximately in America. Proteaddites spp. first appear in the phase with these. Coincidence of these Coniacian and range through the patterns between Centerville Beach and Site Maastrichtian; they are present in 32 suggests that the variability may reflect a sedimentary rocks throughout the Western climatic, as opposed to a taphonomic, signal. Interior. Aquilapollenites spp. and Mancicorpus Around 2.5 Ma, the mixed conifer group spp. first appear in the Campanian and also shows an increase in relative abundance, range through the Maastrichtian; they are possibly reflecting a southern shift of the present in the northern part but are absent mixed conifer forests of the Pacific Northwest. from rocks in the southernmost part of the This is perhaps related to the pre-Pleistocene Western Interior. The southernmost extent of glaciation at approximately this time. the latter taxa forms a line that approximately
12 parallels the Utah-Arizona and Colorado- Barron, J. A., 1992, Paleoceanographic and New Mexico boundaries. tectonic controls on the Pliocene diatom The stratigraphic distribution of these record of California, in Tsuchi, Tyuichi, Cretaceous taxa in Pliocene sediments of and Ingle, J.C., Jr., editors, Pacific Anza-Borrego suggests that erosion of Neogene Environment, Evolution, and Cretaceous rocks containing Proteacidites, but Events: Proceedings of the 5th lacking Aquilapollenites and Mancicorpus, had International Congress on Pacific Neogene begun by the early Pliocene. Erosion into Stratigraphy, International Geological Cretaceous rocks containing Aquilapollenites Correlation Program 246, p. 25-41. and Mancicorpus did not begin until about 3.7 Ma and supports the hypothesis that the Heusser, L. E., and Balsam, W. L., 1977, Pollen cutting of the Grand Canyon occurred during distribution in the northeast Pacific the Pliocene, accompanied by extensive and Ocean: Quaternary Research v. 7, no. 1, p. rapid erosion of Cretaceous and older rocks. 45-62. Cretaceous pollen and spores were transported as detritus down the Colorado Johnson, N.M., Officer, C.B., Opdyke, N.D., River to the ancestral Gulf of California. Woodard, G.D., Zeitler, P.K., and Lindsay, Rapid erosion and transport of this amount of E.V., 1983, Rates of late Cenozoic material requires significantly increased tectonism in the Vallecito-Fish Creek precipitation on the Colorado Plateau during basin, western Imperial Valley, California: the Pliocene. This is consistent with climate Geology, v. 11, p. 664-667. models involving wetter summers and wetter winters induced by relatively recent uplift of McCrory, P.A., 1990, Neogene paleocean- the Colorado Plateau. ographic events recorded in an active- margin setting Humboldt basin, References California: Palaeogeography, Palaeo- climatology, Palaeoecology, v. 80, p. 267- Adam, D. P., Bradbury, J. P., Rieck, H. }., and 282. Sarna-Wojcicki, A. M., 1990, Environ mental changes in the Tule Lake Basin, Opdyke, N.D., Lindsay, E.H., Johnson, N.M., Siskiyou and Modoc Counties, California, and Downs, T., 1977, The paleo- from 3 to 2 million years before present: magnetism and magnetic polarity U. S. Geological Survey Bulletin 1933, 13 stratigraphy of the mammal-bearing P- section of Anza-Borrego State Park, California: Quaternary Research, volume 7, p. 316-329.
13 Centerville Beach
Site 32
PACIFIC OCEAN
0 200km
Figure 1. Sketch map showing position of Centerville Beach, DSDP Site 32, and Anza-Borrego.
14 Percent 20 40 60 80
3.0
3.5--
co
0 O)
4.0 --
Pinus TCT undlfferentiated 4.5-- DSDP Site 32
Figure 2. Relative abundance profile of Pinus and TCT pollen from DSDP Site 32.
15 Mid-Pliocene Vegetation, Environment, And Climate In The Western Interior Of The United States
Robert S. Thompson, U.S. Geological Survey, Denver, CO 80225
Tectonic basins in the western interior of isotopes from calcite veins at Furnace Creek, the United States contain thick sedimentary California (near Death Valley Winograd et sequences that preserve records of long-term al., 1985) indicate that high Pliocene moisture climatic changes. However, the same forces levels continued until the last million years, that built these basins led to mountain when (presumably) the uplift of the Sierra building and the development of rain- Nevada and Transverse ranges blocked the shadows that impose local signals on the incursions of moisture from the Pacific into records of climatic variations. The modern the interior. Geological studies from the high climate in the northern portion of this region central Sierra Nevada suggest that as recently is dominated by winter precipitation as 3 Ma this mountain mass was significantly associated with the westerlies, while the lower than today (Huber, 1981), and much of southeastern sector receives significant the modern aridity of the West must be tied to summer rainfall from subtropical monsoonal the development of regional rain shadows sources. Except for higher mountains, the since the mid Pliocene. entire region is semi-arid to arid, due to the In southwestern Idaho, the Glenns Ferry rain-shadows of major mountain masses and Formation appears to represent a deep (>300 to the distance from the oceans. Seasonal m?) long-lived Pliocene lake in the modern temperature variations are extreme, especially Snake River drainage. Pollen data from a ~3.7 under the highly continental climate of the to -3.4 Ma section at the eastern margin of northern interior. this system (Leopold and Wright, 1985) Vertebrate paleontological and paleo- record a near-modern flora with a sequence of botanical data suggest that temperature from steppe to forest and back to steppe. extremes were less than today during much Sedimentological variations between lake- of the Pliocene, and paleohydrological and margin sands and lignites suggest shorter palynological records from this region (figure term, lower-amplitude climatic fluctuations 1) indicate that conditions were also much also occurred that are not reflected in the wetter. Lacustrine conditions occurred in pollen record. now-arid settings at Searles Lake (Smith, Farther west, a record from the deeper 1984) and other sites in southern California water sediments from near the town of and adjacent Nevada (e.g. Amargosa Desert Bruneau, in the east-central part of the Glenns Hay et al, 1986; Hoover, 1989); central Ferry Formation, apparently covers portions Arizona (Verde Valley Nations et al., 1981), of the period from -3.0 to -2.48 Ma and southern Arizona (St. David Formation (Thompson, 1992). Very few exotic Tertiary Wang et al., 1991; Safford and San Simon elements are present in this diagram, and the Valleys Gray, 1961; Tomida, 1987); central vegetation fluctuates between three forest Utah; and southern Idaho and adjacent periods and three steppe periods before the Oregon and Wyoming. The most detailed lake becomes shallow (still within Gauss chronology is from Searles Lake, where Chron). Unlike at Fossil Gulch, no sedimentary and geochemical data indicate sedimentological variations from this deeper- sustained moisture from 3.2 to 2.6 Ma, water environment correspond with the followed by aridity until 2.0 Ma. Deuterium pollen fluctuations. Younger pollen
16 assemblages from the Bruneau Formation at the Pliocene and early Pleistocene in this this site indicate a cold steppe environment region. sometime in post-Olduvai Matuyama time. The information presented here provide The undated Glenns Ferry pollen only a sketch of Pliocene conditions in the assemblages from a well site in the town of western interior. Much more work is Vale, Oregon, contain palynological required to segregate the influences of global assemblages similar to the forest periods at climate change from the regional aridification the Bruneau site, and the longer (but also caused by mountain-building through the late undated) Mountain Home Idaho core records Neogene and Quaternary. a forest to steppe oscillation similar to those in the Bruneau core. The West Weiser References outcrop, near the western extent of the Glenns Ferry Formation domain, is presumably >4 Gray, J.,1961, Early Pleistocene paleoclimatic Ma and is strongly dominated by conifers and record from Sonoran Desert, Arizona: contains more Tertiary elements than Science v. 133, p. 38-39. sediments post-dating this time. To the east of the Glenns Ferry deposits, Hay, R.L., Pexton, R.E., Teague, T.T., and the INEL (Idaho National Engineering Kyser, T.K., 1986, Spring-related Laboratory) 2-2a core from southeastern carbonate rocks, Mg clays, and associated Idaho contains episodic lacustrine deposits minerals in Pliocene deposits of the separated by thick sequences of basalts. As Amargosa, Nevada and California: with the Glenns Ferry palynological data, this Geological Society of America v. 97, p. site records fluctuations between steppe and 1488-1503. forest dominance through the Pliocene. Assemblages thought to date ~4 Ma are Hoover, D.L., 1989, Preliminary description of dominated by conifers and are more diverse Quaternary and late Pliocene surficial than younger pollen spectra (Thompson, deposits at Yucca Mountain and vicinity, 1991). Pollen assemblages dated from -3.0 Nye County, Nevada: U.S. Geological Ma are dominated by steppe taxa, which give Survey Open-File Report 89-359. 45 p. way to conifers by -2.9 Ma. Spectra dated to -2.4 Ma contain low abundances of Huber, N.K., 1981, Amount and timing of late coniferous and other arboreal taxa and Cenozoic uplift and tilt of the central resemble late Pleistocene glacial-age pollen Sierra Nevada, California evidence assemblages from southern Idaho. from the upper San Joaquin River Basin: Coniferous taxa are somewhat more U.S. Geological Survey Professional Paper abundant by 2.0 to 1.8 Ma, but did not recover 1197. 28 p. their pre-2.4 Ma levels. Figure 2 illustrates the long-term Leopold, E.B. and Wright, V.C, 1985, Pollen Pliocene/early Pleistocene vegetation history profiles of the Plio-Pleistocene transition of southern Idaho and adjacent Oregon: in the Snake River Plain, Idaho: in diverse early Pliocene coniferous forests with Smiley, C.J. (ed.), Late Cenozoic History of Tertiary elements gave way to modern steppe the Pacific Northwest: American dominance over this period (presumably due Association for the Advancement of in part to developing rain shadows). Science, Pacific Division. Pp. 323-348. However, this trend was not monotonic, and apparent Milankovitch band high-amplitude Nations, J.D., Hevly, R.H., Blinn, D.W., and fluctuations were recorded in forest/steppe Landye, J.J., 1981, Paleontology, paleo- cycles. With the exception of the apparent ecology, and depositional history of the glacial-age steppe period (-2.4 to -2.0 Ma), Miocene-Pliocene Verde Formation, the palynological record suggests that Yavapai County, Arizona: Arizona Geol. conditions were wetter than today through Society Digest v. 13, p. 133-149.
17 Smith, G.I., 1984, Paleohydrologic regimes in Tomida, Y., 1987, Small mammal fossils and the southwestern Great Basin, 0 3.2 my correlation of continental deposits, Safford ago, compared with other long records of and Duncan Basins, Arizona, USA. "global" climate: Quaternary Research v. National Science Museum, Tokyo. 135 p. 22, p. 1-17. Wang, Y., Cerling, T.E., Smith, G.A., Thompson, R.S., 1991, Pliocene environments Geissman, J.W., Quade, J., Lindsay, E.H., and climates in the western United States. and Bowman, J.R., 1991, Climatic and Quaternary Science Reviews v. 10, p. 115- ecologic changes during the Pliocene and 132. early Pleistocene in southeastern Arizona: stable isotopic records from the St. David Thompson, R.S., 1992, Palynological data Formation. Geological Society of America from a 989-ft (301-m) core of Pliocene and Abstracts with Programs, 1991 Annual early Pleistocene sediments from Bruneau, Meeting, San Diego. P. A301. Idaho. U.S. Geological Survey Open-File Report 92-713. 28 p. Winograd, I.J., Szabo, B.J., Coplen, T.B., Riggs, A.C., and Kolesar, P.T., 1985, Two-million- year record of deuterium depletion in Great Basin ground waters: Science v. 227, p. 519-522.
18 Pacific Ocean
Figure 1. Sites mentioned in text Key to sites: a) Scarles Lake, b) Amargosa Desert and Furnace Creek, c) San Pedro Valley (St. David Formation), d) Safford and San Simon Valleys, e) Verde Valley, f) Central Utah, g) West Weiser and Vale, h) Bruneau, Mountain Home, and Fossil Gulch, i) Idaho National Engineering Laboratory (INEL) core site.
19 100%i
West 80%- Weiser
60%
ro o 40% INEL
INEL 20% Bruneau INEL y Bruneau INEL Fossil Gulch
1.5 2.0 2.5 3.0 3.5 4.0 4.5 ESTIMATED AGE (MA)
Figure 2. Changes in the relative abundance of conifers through the Pliocene and earliest Pleistocene in southern Idaho and adjacent Oregon. Palynological Record From The North Atlantic Region At 3 Ma: Vegetational Response To A Period Of Global Warmth
Debra A. Willard, U.S. Geological Survey, Res ton, VA 22092
Middle Pliocene pollen assemblages from Pollen assemblages from the shallow- sites from 27° - 67° N (Fig. 1) were analyzed marine sediments of the Yorktown Formation to study the latitudinal distribution of in southeastern Virginia are dominated by vegetation during the middle Pliocene "warm Pinus with Quercus, Carya, and Sciadopitys interval" around 3 Ma and to determine what pollen commonly present. The closest mechanism for warming corresponds best to modern analogs are from North Carolina and climatic estimates based on vegetation data. South Carolina, indicating Pliocene The samples at the five sites were selected to temperatures about 2° C warmer than today bracket the time interval around 3 Ma as and higher precipitation levels. The Pinecrest closely as possible, based on the best available Beds of southwestern Florida also are age data. dominated by Pinus pollen, with Quercus and Pollen assemblages from OOP Site 642 in taxodiaceous pollen abundant. These the Norwegian Sea and Pliocene strata from assemblages are analogous to modern the Tjornes Peninsula of Iceland are assemblages from sites along the coast of dominated by Pinus and Picea pollen. Florida that represent the longleaf/slash pine Quercus, Alnus, Betula, and Ilex pollen also are forests that cover much of the Atlantic Coastal present at both sites, as well as Castanea Plain and indicate no significant differences (Tjornes), Sciadopitys, and Pterocarya (Site 642). between Pliocene and modern temperatures The presence of pollen from plants presently or precipitation in this subtropical region. found in more temperate regions today The presence of vegetation characteristic suggests that Pliocene temperatures were of temperatures much warmer than present at warmer than today at both sites; Tjornes high latitudes grading southward to present- probably had winter temperatures at least 4° day temperatures at low latitudes is similar to C warmer than those of today. patterns shown by marine invertebrates in Samples from deep-ocean sediments from both degree and timing of change. ODP Site 646 in the Labrador Sea) are Comparison of the marine and terrestrial dominated by Pinus pollen, with Picea records indicate that they responded to subdominant and Abies, Betula, Alnus, climate forcing mechanisms in phase with Quercus, Sciadopitys, and Tsuga present in each other. The relatively greater most samples (see also de Vernal, this amplification of temperatures at subarctic volume). These assemblages were compared sites is consistent with predictions by general to modern samples using the Modern Analog circulation models using increased meridional Technique (MAT) of dissimilarity coefficients, heat transport as the mechanism for middle and the closest modern analogs are from Pliocene warming in the northern Newfoundland and Nova Scotia. If the hemisphere. Further research on lower source area for pollen at Site 646 was latitude and southern hemisphere sites Labrador or Quebec, as suggested by present should help determine whether Pliocene wind patterns, then these data indicate a circulation patterns in southern oceans northward expansion of the northern differed appreciably from those of today and hardwood forest into Labrador and Quebec whether they exerted similar controls on and indicate that Pliocene temperatures in terrestrial vegetation. those regions were at least 3.5° C warmer than today with higher precipitation levels.
21 80" W 80- N
jornes beds o Site 642
Yorktown Formation
Figure 1. Location of sites analysed for pollen, North Atlantic transect,
22 Neogene Palynofloras And Terrestrial Paleoenvironments In Northern Latin America
Alan Graham, Kent State University, Kent, OH 44242
The database for estimating Tertiary fauna, indicating an inner neritic environment terrestrial paleoenvironments in northern of deposition and representing a local marine Latin America (Mexico, Central America, The transgression of short duration in the Antilles), based on palynological evidence, is northern part of the basin. By upper shown in Fig. 1 (see Note 1). The localities are Agueguexquite time brackish and continental scattered, and collectively provide only a low- conditions returned." The Paraje Solo resolution picture of environmental change. palynoflora contains an abundant brackish Therefore, several floras must be used to Rhizophora (mangrove) and diverse inland to establish trends leading into the Pliocene. upland continental component, suggesting The two most relevant to the PRISM deposition at the time and under the workshop are from the Gatun Formation, conditions described for the upper Canal region of Panama, and the Paraje Solo Agueguexquite sediments. Akers (1979) Formation near Coatzacoalcos, southern presented a similar stratigraphy and age Veracruz state, Mexico. The chronological assignment of the Lower Concepcion through control on the pollen/spore-bearing part of Agueguexquite formations (Figs. 2 and 3) the Gatun Formation is adequate for age based on calcareous nannofossils and planktic assignment, but not precise. In a recent foraminifera. He concluded (p. 4) that "the review of the marine record Coates et al. Agueguexquite Formation must be (1992) note (p. 827) that nannofossils from the considered to be of middle Pliocene age, and middle part of the formation indicate an age it probably belongs just above the precise range of 8.2-5.6 Ma. The 'terrestrial' phase middle of zone N20." Thus, the Paraje Solo (coastal mangrove zone) is subsurface and plant microfossils are Pliocene, and probably lacks marine palynomorphs (e.g., middle Pliocene from that part of the dinoflagellates) sufficient for tying it to the formation equivalent to the Agueguexquite, marine chronology. However, the ~mid-N20, -3-4 Ma. pollen/spore-bearing lignitic material is from The microfossils include wind-blown and the upper part of the formation (top of solid water-transported forms, and preserve an rock; cores SL-49, SL-103). Coates et al (1992, environmental record for areas delimited p. 827) state that "Gatunian" facies persist in mostly by physiography. For Panama (Gatun Costa Rica during the Pliocene, but are absent Formation) the reconstructions are probably from Panama after the earliest Pliocene. applicable to most of southern Central Thus, the maximum age of the plant America where land surfaces were primarily microfossils is considered latest Gatun time east-west trending and where physiographic (5.6 Ma) or slightly younger. relief was moderate. For Mexico (Paraje Solo The age of the Paraje Solo Formation is Formation) the reconstructions are probably better constrained through marine faunal valid for the eastern escarpment of the Sierra assemblages in the overlying Agueguexquite Madre Oriental within southern and central and underlying Upper Concepcion Veracruz state where latitudinal extent and Formations within zone N20 (Fig. 2) (see Note physiographic diversity was greater. 2). Machain-Castillo (1985, p. 123) notes that The palynological data can provide a "the Paraje Solo may be in part general quantitative estimate of climate at contemporaneous to the Agueguexquite. The individual sites, but only a broad picture of Agueguexquite strata contain the youngest regional and long-term changes. This is due (middle N20), most abundant, and diverse more to the scattered occurrence of the
23 material than to the imprecise nature of the similar to those of present during the late technique. Miocene/earliest Pliocene, and probably since The available data suggests that from the the middle to late Eocene (Gatuncillo flora). Eocene (Chapelton, Gatuncillo floras) through The situation at comparable low to mid- the lower Miocene (Uscari, Culebra, altitudes in Veracruz (latitude 18° N) by Cucaracha, and La Boca floras) current Paraje Solo time (mid-Pliocene) was different. tropical conditions and relatively low relief The present-day tropical rain forest was characterized much of northern Latin poorly developed to absent, mid-altitude America south of Mexico. In southern (presently 1000-2000 m) temperate commun Central America conditions had changed by ities were prominent in the lowland basin of Gatun time. Pollen of the Gramineae deposition, and Picea (spruce) was present. (grasses), which was virtually absent in the Spruce occurs today in Mexico only in the lower Miocene, increased to 7.5%. Maximum mountains 1000 km or more to the north. The estimated elevations increased from -1200- common factor in these changes is lower 1400 m to -1700 m. Greater environmental temperature. As an estimate, a MAT lower by and habitat diversity resulted in greater biotic -2-3° C than at present would likely produce diversity, with the number of taxa increasing the observed differences between modern and from 44, 55, 21, and 54 types in the lower the Paraje Solo vegetation. The present MAT Miocene floras noted above, to 110 types in at Coatzacoalcos is 25.3° C (range 22-27° C), the Gatun Formation. In addition to and annual rainfall is 2726 mm (range 50-525 individual elements, there was also a greater mm, driest season January through March diversity of communities. All elements in the with some rain falling in every month). The lower Miocene floras can be accommodated in four forest types- tropical wet, tropical mid-Pliocene MAT is thus estimated at ~23°. moist (including mangrove forest), The lack of other fossil floras in the region premontane wet, and possibly premontane make it impossible to detect when the time moist. By Gatun time there were seven forest changes from lower Miocene to Paraje Solo types with 11 or more taxa that can occur in conditions began. However, some estimate each community- tropical moist (38 taxa), can be gained by extrapolating from two tropical wet (31), premontane wet (27), other lines of evidence. Preliminary study of premontane moist (21), lower montane moist the Oligo-Miocene Simojovel flora (Chiapas, (12), premontane rainforest (11), and tropical Mexico) shows a mangrove forest, with oak- dry forest (11). The first six of these are pine woodland grading upwards into more similar to the modern vegetation of lowland temperate communities on the adjacent to moderate-altitude habitats on the northern slopes. Since this is similar to much of the (Atlantic) side of Panama where the following modern local vegetation, it seems reasonable climates prevail (Barro Colorado Island, to conclude that the Neogene cooling trend Gatun Lake): average annual rainfall 2750 had not set in there by late Oligocene-early mm/yr (range 1900-3600 mm, strongly Miocene time. Also, the benthic marine seasonal, dry season January through April); temperature curve (Fig. 4) suggests the middle Miocene as a likely time, which is MAT 27° C (annual range 21-32° C). The consistent with the limited paleobotanical presence of the tropical dry forest suggests evidence. altitudes had reached a point where moist Atlantic winds were deflected to create the If it is assumed that temperatures at 18° N drier Pacific side as at present (1700 mm/yr at latitude were -3° cooler than at present Balboa). The close relationship between the (Paraje Solo flora), and that at 9° N latitude Mio-Pliocene Gatun vegetation and the contemporaneous to somewhat older lowland modern lowland to mid-altitude communities climates were comparable to the present suggests that the primary forcing mechanism (Gatun flora), it is tempting to reconstruct for vegetational change at latitude 9° N was intervening terrestrial MATs by lapse rate physiographic relief. Coastal climates were methodologies (yielding -0.3° C/l° latitude).
24 The figure may ultimately prove to be Akers, W. H. and Koeppel, P.E., 1973, Age of approximately correct, but there is little some Neogene formations, Atlantic corroborative evidence. Also, the Paraje Solo coastal plains, United States and Mexico. communities were growing under or adjacent Proc. Symposium Calcareous to continental conditions in an area of Nannofossils, Gulf Coast Sect. Soc. Econ. significant physiographic relief. Thus, any Paleontologists Mineralogists, p. 80-93. exogenic change in climate read from the vegetational history would be magnified by Coates, A. G., Jackson, J., Collins, L.S., the response of communities growing along Cronin, T.M., Dowsett, H. J., Bybell, L. M., steep altitudinal gradients. In contrast, the Jung, P. and Obando, J. A., 1992, Closure Gatun communities were growing on islands of the Isthmus of Panama: the near-shore and peninsulas of low physiographic relief marine record of Costa Rica and western and any exogenic change in climate would be Panama. Geological Society of American dampened. Some general estimate of Bulletin v. 104,814-828. temperatures in the uplands can be gained from the current worldwide mean altitudinal Donnelly, T. W., Home, G. S., Finch, R. C, lapse rate of 5.0-6.0° C/km. and Lopez-Ramos, E, 1990, Northern At present it is not possible to determine Central America: the Maya and Chortis more precisely the range of terrestrial blocks. In: G. Dengo and J. E. Case (eds.), paleoclimatic variability in northern Latin The Geology of North America, Vol. H, America during the Pliocene from the floras The Caribbean Region. Geological Society available. Eventually, data from the of America, Boulder, pp. 37-76. Guastatoya and Herreria Formations of Guatemala may prove useful. Machain-Castillo, M. L., 1985, Ostracode biostratigraphy and paleoecology of the References Pliocene of the Isthmian salt basin, Veracruz, Mexico. Tulane Studies Geol. Akers, W. H., 1979, Planktic foraminifera and Paleontol. v. 19,123-139. calcareous nannoplankton biostratig- raphy of the Neogene of Mexico. Tulane Studies Geol. Paleontol. v. 15: 1-32.
25 8GUASTATOYAS iSAN
Figure 1. Geographic distribution of principal palynofloras of the southern Gulf-Caribbean region. Stippling indicates study completed; open areas indicate floras under study or revision. PANAMA MEXICO PUERTO RICO COSTA RICA GUATEMALA JAMAICA HAITI igiiggPAIR AJ E W8& iGUASTATiDYA": ^GATUN^^ ^;i|| > SOLO..|:i:|:;:::! :!SAN JACINTOi u iBpRRiqslllf :?Htil§Hiiii
MIOCENE M ?iTBOCA"^P L ^CUCARACHAJ JCULEBRA ftgg ^USCARI^i
U SIMOJOVEL SAN OLIGOCENE M SEBASTIAN
L
U : GATUNCILLO: X->»KV.V.V.V.V.X-:-»».-:
EOCENE M iCHAPELTON !
L
PALEOCENE
Figure 2. Stratigraphic distribution of principal palynofloras of the southern Gulf-Caribbean region. Stippling indicates study completed; open areas indicate floras under study or revision. -1
+ 15- -+15
-+10
O O 00 m -+5 Z m -+3 TJ O) O -0 r~ --1 m
0 20 30 40 50 60 70 MILLIONS OF YEARS
Figure 3. Palynofloras of the southern Gulf-Caribbean region plotted on the benthic paleotemperature curve. ZONE FORMATION
N 21
CEDRAL
AGUEGUEXOUITE PARAJE SOLO N 20 " FIUSOLA
UPPER CONCEPCION
LOWER CONCEPCION
N 19 ENCANTO
N 18
Figure 4. Position of the Paraje Solo Formation in relation to the nannofossil zones (from Machain-Castillo 1985).
29 Notes
Note 1 Note 2
Notes on the charts: 1) There are no Notes on Fig. 2. 1) Ostracodes listed for extensive, well-preserved, recently Lower and Upper Concepcion bed studied Tertiary macrofossil floras (N19-20) are Actinocythereis known from the region. The only vineyardensis, Touroconcha lapidiscola, sizable flora (the Oligocene San and abundant Hulingsina sp. 1, Sebastian flora of Puerto Rico) was last Henryhowella ex. gr. asperrima, and studied in 1928. All terrestrial Puriana spp. In addition, Upper paleoenvironmental estimates Concepcion species include abundant presented here are based on plant Cyprideis spp., Perissocytheridea spp., microfossil evidence. Basslerites? sp., Malzella conradi, and 2) The markings indicate different Echinocythereis margaritifera absent stages in the completion of the studies from the Lower Concepcion (Machain- (stipple study complete and results Castillo, 1985). published; others in progress). The 2) From the Agueguexquite Formation Chapelton study is in press as part of Akers (1979) lists the following GSA Memoir 182. planktic foraminifera-G/obzgerimz 3) Samples from Guatemala that have bulloides apertura, G. bulloides bulloides, yielded palynomorphs (fair to poor) G. juvenilis, Globigerinoides obliquus are from the Padre Miguel Group extremus, G. obliquus obliquus, (now excluding the younger San Globigerinoides quadrilobatus Jacinto Formation; radiometric data quadrilobatus, G. ruber, Globorotalia indicates the Padre Miguel ignimbrites (Globorotalia) cultrata limbata, G. erupted between 19 and 14 Ma - (Turborotalia) acostaensis acostaensis, G. middle to late Miocene), Barrios (T.) acostaensis humerosa, Hastigerina sequence (possibly Barrios Formation, (Hastigerina) siphonifera siphonifera, Miocene), the Guastatoya Formation Orbulina universa, and Sphaeroideinella (age unknown, possibly Pliocene), and dehiscens dihiscens forma immatura; and the Herreria (Pliocene, and possibly the following calcareous nannofossils equivalent to the upper part of the (in addition to those listed in Akers Guastatoya). Information on the and Koeppel, 1973, p. 83) - Ceratolithus Barrios Formation fide Burkart (pers. cristatus, Coccolithus doronicoides, comm.), all other from Donnelly et al. Cyclococcolithina leptopora, C. (1990). The Guatemalan lignites are macintyrei, Discoaster brouweri, D. not coastal brackish-water deposits pentaradiatus, D. surculus, D. variabilis, containing Rhizophom (mangroves) as Gephyrocapsa caribbeanica, G. reticulata, are the others, but were deposited in Helicopontosphaera kamptneri, H. sp., swamps that periodically became Lithostromation perdurum, and saline through evaporation, as Pseudoemiliania lacunosa. indicated by gypsum crystals (Burkart, pers. comm.).
30 Paleoclirnatic Conditions Around 3 Million Years BP: Pollen Evidence From Colombia
Henry Hooghiemstra, Amsterdam University, The Netherlands
Introduction with the oxygen isotope record of OOP Site 677 (E. Pacific). It is expected that the pollen In the Eastern Cordillera of Colombia, the record can be correlated with the deep-sea high plain of Bogota (ca. 25x40 km in size) record up to about oxygen isotope stage 110 represents the bottom of a former lake that when samples are available at 20 cm distance occupied a subsiding intermontane basin. (Hooghiemstra, in prep.) Pollen records from deep bore holes represent Several phases in the evolutionary history the period from the Late Pliocene to latest of the montane forests and paramo vegetation Pleistocene. Climatic changes are well in the Eastern Cordillera of Colombia can be documented by the pollen rain that is recognized. Late Pliocene and Pleistocene conserved in the slowly accumulating lake climatic change and the closure of the sediments of the Bogota basin. The tropical Panamanian Isthmus had a substantial Andes especially seem to be in a favorable influence on the development of these position to register climatic change. A change montane ecosystems. in climatic conditions results mainly in a vertical shift of vegetation belts over the Paleoclimatic Conditions At Ca. 3 mountain slopes (Fig. 1). The different Ma vegetation belts stay in the vicinity and are registered continuously by their intercepted The interval 540-465 m core depth (3.2-2.7 pollen. The sediments of the Bogota basin Ma) shows warm climatic conditions and (2550 m alt.) accumulated in an elevation that pollen spectra have no late Quaternary lies halfway between the highest position of analogs. The basin had just started to the upper forest line during interglacial accumulate lacustrine and river sediments, conditions (c. 1800 m alt.), rendering the after a period in which sediment only Bogota sediments a sensitive recorder of accumulated in the perifere valleys. The paleoclimatic change in northern Latin upper limit of the subandean forest belt was America. situated at some 500 m lower elevation than today. In the Andean forest belt Podocarpus Pollen Data And Time Control rich forest, Hedyosmwn-Weinmannia forest (a precursor of the modern Weinmannietum), and A new 586 m long core Funza II (Fig. 2) Vallea-Miconia forest, respectively, were the was recovered from the sediments of the high main constituents with increasing elevation. plain of Bogota. Results of the palynological Hypericum and Myrica played an important analysis of 430-540 m core depth, representing part in the timberline dwarf forests, which the estimated time interval 3.2-2.36 Ma, with possibly constituted a substantial transitional sample distances of 100 cm are presented (Fig. zone from the early Andean forest belt (upper 3), The interval 586-540 m of the sediment montane forest belt) to the open grassparamo core was poor in pollen recovery or barren. belt. The contribution of herbs to the paramo Time control of the Funza II core is based on vegetation, dominated by Gramineae and zircon fission-track datings of intercalated Compositae, seems less diverse than during volcanic ash horizons. In addition, the upper the late Quaternary. The late Pliocene (upper) part of pollen record Funza II could be Andean forests were more open than during correlated in detail with pollen record Funza the middle and late Quaternary, as I; the latter has been graphically correlated heliophytic elements, such as Borreria, were
31 abundant (Fig. 3). The composition of forests References on the high plain was dynamic: arboreal taxa with pioneer qualities (Dodonaea, Eugenia) and Andriessen, P.A.M., Helmens, K.F., other taxa (Symplocos, Ilex) constituted Hooghiemstra, H., Riezebos, P.A. and Van seemingly at irregular intervals azonal forests der Hammen, T., submitted. Absolute in the basin. The upper forest line oscillated chronology of the Pliocene-Quaternary most of the time from 2800 to 3600 m sediment sequence of the Bogota area, elevation. The average annual temperature Colombia: Quaternary Science Reviews. on the high plain was c. 22.5-16.5°C. Using composite pollen records Van der Hooghiemstra, H. (in prep.), Climatic cooling Hammen also documented warmer and paleoecological conditions at the conditions in sediments from the area of the Pliocene-Pleistocene boundary in the high plain of Bogota during Pliocene time Funza II pollen record (Eastern Cordillera, (Van der Hammen et al, 1973). Recently Colombia): interval 3.2-2.8 Ma. additional evidence for warmer late Pliocene climatic conditions was collected on the basis Hooghiemstra, H. and Sarmiento, G., 1991, of plant macrofossils from this area (Wijninga New long continental pollen record from and Kuhry, submitted). Although these a tropical intermontane basin: Late fragments of pollen records most probably Pliocene and Pleistocene history from a evidence phases of the final upheaval of the 540 m core: Episodes v. 14, p. 107-115. Eastern Cordillera, which has a 'cooling' effect on the pollen records, the continuous Funza II Hooghiemstra, H. and Cleef, A.M., pollen record does evidence climatic change. (submitted), Lower Pleistocene and Upper It is expected that part of the variability Pliocene glaciations and forest documented in the Funza II summary development in the Eastern Cordillera of diagram (Fig. 3) is associated with the initial Colombia: pollen record Funza II (205-540 stage of development of the large tectonic m core interval): Palaeo-geography sedimentary basin of Bogota. Palaeoclimatology Palaeo-ecology.
Potential Use Of Pollen Data As Imbrie, J., Hays, J.D., Martinson, D.G., Modern/Future Analogs Mclntyre, A., Mix, A.C., Morley, J.J., Pisias, N.G., Prell, W.L., and Shackelton, The late Pliocene (3.2-2.8 Ma interval) N.J., 1984, The orbital theory of pollen spectra differ significantly from the Pleistocene climate: support from a late Quaternary ones. It is inferred that the revised chronology of the marine 9^O late Pliocene Andean forests were of a more record, in Berger, A., Imbrie, J., Hays, J., open character (e.g. presence of Borreria, Kukla, G., and Saltzman, B., eds., originally a savanna element) whereas Milankovitch and climate, Part 1: important elements of the present-day forest Dordrecht, Reidel., p. 269-305, belt (Alnus and Quercus) were absent. Estimation of the altitudinal position of the Van der Hammen, T., 1974, The Pleistocene upper forest line, therefore, is less accurate changes of vegetation and climate in than during more recent intervals of the tropical South America: Journal of pollen record. However, accumulating Biogeography v. 4, p. 3-26. evidence and better understanding of these late Pliocene ecosystems will enable to provide quantitative paleoclimatic estimates concerning temperature ranges and climatic variability (Hooghiemstra, in prep.).
32 Van der Hammen, T., Werner, J.H. and Van Wijninga, V.M. and Kuhry, P. (submitted), Dommelen, H., 1973, Palynological record Late Pliocene paleoecology of the Guasca of the upheaval of the northern Andes: a Valley (Cordillera Oriental, Colombia): study of the Pliocene and Lower Review of Palaeobotany and Palynology. Quaternary of the Colombian Eastern Cordillera and the early evolution of it high-Andean biota: Review of Palaeo botany and Palynology v. 16, p. 1-122.
33 PRESENT 20,000-14,000 yr BP
5000 -j
superparamo 4000 grassparamo subparamo
3000
2000 -I
03 1000 TJ .savannas " /^ savannas West ' warm tropical forest East -' warm tropical forest
* high plain of Bogota * Magdatena River //// xerophytic vegetation -^ upper forest line
Figure 1. Altitudinal distribution of vegetation belts in the Eastern Cordillera of Colombia at present and during the last glacial maximum. Vertical shifts of the vegetation belts are mainly related to changes in temperature and form the basic mechanism of registration of climatic change (after Van der Hammen, 1974).
34 Ecuador v >
High plain of Bogotd
Madrido o Q Mosquera/ BOGOTA
3500-4000 m 3000-3500 m I f 3000m Tequendama Falls Hiah plain ( I of Bogota (2550-2600 m)
Hg. 2. Map of Colombia and the high plain of Bogota* in the Eastern Cordillera, indicating the geographical setting of the sites of the long continental pollen records near the village of Funza.
35 ON
grtssparamo EH Andean forest (included In the pollen sum) E3J cubparamo f^l ubandean tore*! (from: Hooghiemstra & Cleef, submitted)
Figure 3. Pollen percentage diagram of the 540-430 m interval of the Funza II core (Eastern Cordillera, Colombia, 2550 m alt.) analyzed with 100 cm sample distance. Records of selected pollen taxa are presented. The pollen zones are provisional and will be defined more precisely after the present time resolution of c. 6000 years has been increased (Hooghiemstra, in prep.). Time control of the lower part of the Funza II core is provided by a zircon fission-track dating of an intercalated volcanic ash horizon at 506 m core depth (2.74 ± 0.63 Ma; Andriessen et al, submitted). (The upper part of the Funza pollen record is correlated with the OOP Site 677 oxygen isotope record (Shackleton and Hooghiemstra in Andriessen et al., 1993). Note the absence of Alnus and Quercus in this part of the record (northern hemisphere taxa which arrived in the Eastern Cordillera during middle Pleistocene time after having passed the Panamanian landbridge). rt H« 'r) tr 3 H' n> rt OQ ro o o d 18O stages o o "O (tentative correlation) ro ro ro ro H- C/i bo CD Age (Ma) rt C CO CO o o X 9 ^ T3 &J OQ O M U1 UI n> M ^ oU. alit Depth (m) 3 M fl> tj H« 3 O CO h-1 O N M rt o n> O 3 3 T3 (D (^ CO f^ Pollen record Funza II CO rt OQ
rt rt OQ 3 hrj rt C -n n n n n n n rt N ro ro ro ro ro ro ro H* &3 i X X X X X X X Pollen zones Funza II o> 01 ** CO ' ro -» o
Ol Ol en O1 O1 -»:«. 4^ 4^ -F*. -P* -> CO ro O O (O 00 CD ^. o 10 »4 >4 CO O £> CD Ol CO 8' Depth (m) I -> b en o 0 0 0 O b b b w i i « 4 I 1 o CO CO CO CJ ro ro ro ro ro roi 00 (Ma) ro _*. 0 O (O CD CO ^ 01 to; Estimated age ro CD -* 01 ro CO CD
OQ n> en Mediterranean Pliocene Vegetation And Climate: How To Quantify The Climate Parameters?
Jean-Pierre Sue, Androniki Drivaliari, and Ezzedine Bessais, Universite Montpellier II, Montpellier, France Joel Guiot, Faculte Saint-Jerome, Marseilles, France, Adele Bertini, Universitie Montpellier II, Montpellier, France, and Dipartimento di Scienze della Terra, Firenze, Italy Zhuo Zheng, Universite Montpellier II, Montpellier, France, and Zhonghshan University, Guangzhou, China Sidi-Mohamed Abdelmalek, Universite Montpellier II, France, and Universite d'Oran Es-Senia, Oran, Algeria Filomena Diniz, Departamento de Geologia, Lisbon, Portugal Nathalie Combourieu-Nebout, Universite" of Paris, Paris, France Suzanne Leroy, IGBP PAGES, Bern, Switzerland Rachid Cheddadi, Centre Universitaire, Aries, France Jacqueline Ferrier and Daniele Duzer, Universite Montpellier II, Montpellier, France
The present vegetation of the Pollen Data Mediterranean region is controlled by physiographic and climatic peculiarities: Pollen records and their chrono the longitudinal length of the sea and logical controls. More than 60 sections the presence of West-East oriented (boreholes and outcrops) have been mountains (Pyrenees, Alps, partly investigated (the 45 most significant ones are Carpathians, Caucasus), which con located on figure 1). They represent more stitute barriers for plant migrations; than 1,300 pollen spectra (at least 600,000 the southward extension of areas of counted pollen grains) and more than 250 high relief associated with peninsulas identified taxa. Synthetic pollen diagrams are (Spain, Italy, Greece) which provides constructed after the ecological arrangement a penetration of boreal environments of the taxa presented in detailed pollen into the warm Mediterranean region; diagrams (Sue, 1984). a double seasonal rhythm (cool Most of the localities are coastal marine winter, warm summer; dry summer, deposits in which the chronostratigraphic humid spring and autumn) of the control is precisely provided by foraminifer climate which shows a high and nannoplankton records, sometimes variability according to the Atlantic associated with magnetostratigraphy and air mass effects, desert influence and radiometric measurements (fig. 1). The age of local orientation. some sections is known from mammals in The factors above result in a very complex association with magnetostratigraphy, and mosaic structure of the vegetation which only a few sections are not well-dated (fig. 1). contrasts with the latitudinal (thermic) The large number of well-dated pollen zonation of Central and North Europe. records provides a suitable basis for vege The Mediterranean early-middle Pliocene tation reconstruction through the entire climate reconstruction expresses the evolution Pliocene (fig. 2). from tropical/subtropical to warm-temperate 5.2 to 3.2 Ma. Pollen localities in this conditions before the onset of the glacial- age range are very numerous because of the interglacial cycles (Sue et al, 1992). "sudden" inundation of the Messinian
38 canyons by the lowermost Pliocene trans in Bulgaria, and Mediterranean gression. Very diverse landscapes are xerophytes increased southward. recorded, reflecting both different latitudes E. The Nile area was almost exclusively and local/regional features. These include: inhabited by a savanna-like vege A. The Atlantic face where subtropical tation, including desertic elements. (Taxodiaceae) and warm-temperate Tropical plants were present. trees dominated and Ericaceae were F. Local swamp environments are repre abundant. The north-south thermic sented by assemblages that contain gradient promoted differences in the high percentages of Taxodium-type, frequency of thermophilous elements. Nyssa, Symplocos, Myrica, Cyrillaceae- Humid conditions prevailed. Clethraceae, etc. They occurred only B. The southern Mediterranean open xeric in Portugal (Rio Maior), Catalonia vegetation which began south of (Garraf 1), and Rumania (Ticleni). Barcelona. Herbs, including sub- 3.2 to 2.6 Ma. The same environ desertic taxa (Lygeum, Calligonum, mental and geographic subdivisions existed Nitraria, Neurad, Agavaceae, etc.) were as during the previous period. Only some predominant. Tropical (megathermic) localities record changes at 3.2 Ma (Rio Maior, plants were still scarcely represented Garraf 1, Nice area, Ticleni), with the in lower latitudes (Southern Spain, disappearance or the decrease of the most Tunisia, Sicily, Crete, Egypt, Israel). thermophilous elements only the most humid The modern Mediterranean places (local marshes and steep slopes). It has xerophytes were important in some been interpreted as the emergence of cool places (Catalonia, Sicily). A xeric- winters, i.e. a well-marked seasonal thermic thermic gradient controlled the plant rhythm to be superimposed to the pre distribution in this area. The large existing pluvio-metric one. Therefore, the latitudinal distribution of such rather constant climatic conditions of this assemblages supports the theory that period are considered as nearly similar seasonally dry climates occurred in (except a slightly higher level in temperature) this region as far back as the Miocene to the present conditions. So, it can be used as (Sue eial, 1992). a suitable reference in modeling the C. The northwest Mediterranean region forthcoming warming due to the greenhouse (from the Pyrenees to mid-Italy) was effect. characterized by high relief, which After 2.6 Ma. The earliest glacial- induced the formation of altitudinal interglacial cycles are characterized in the forest belts. The lower belt was north Mediterranean area by steppe-like mainly occupied by Sequoia-type, the vegetation (with Artemisia and Ephedra) middle belt with Cathaya and Cedrus, alternating with forest environments (mainly and the upper belt with Abies and constituted by warm-temperate elements). Picea. Mediterranean xerophytes These steppe assemblages appear obviously were relatively scarce, and on the warmer than those of the late Pleistocene whole, the pollen records indicate glacials. There is no evidence of change in the cooler and more humid conditions southern Mediterranean region, except in the than the lower Mediterranean Nile area, where the Compositae increased latitudes. within the herb group. In middle and D. The northeast Mediterranean region northern oceanic Europe, these cycles which appears to have been cooler corresponded to temperate forest and tundra- than the previous region. Warm- like (Gramineae, Cyperaceae, Ericaceae) temperate forests alternated with alternations. In the Alps, the climate grasslands (Gramineae). The influ fluctuations are marked by temperate- ence of mountains is obvious, chiefly altitudinal forest replacements.
39 Quantitative Paleoclimatic Combourieu-Nebout, N. and Vergnaud- Estimates Grazzini, C, 1991, Late Pliocene Northern Hemisphere glaciation: the continental It is difficult to estimate the peri- and marine responses in the central Mediterranean Pliocene climate because of Mediterranean: Quaternary Science the little latitudinal variation of plants on the Reviews v. 10, p. 319-334. one hand, of the non-existence of analogues in the present vegetation on the other hand. Cravatte J., Matias I. and Sue J.-P., 1984, Thus a climate reconstruction is only possible Nouvelles recherches biostratig-raphiques if one takes into account some of the sur le Pliocene du Roussillon: Geologic de climatically-significant taxa and their la France, 1-2, p. 149-163. respective relative occurrence in modern pollen spectra. A first attempt of estimation Cravatte, J. and Sue, J.-P., 1981, Climatic of the climate parameters is in progress, evolution of northwestern Mediter-ranean initially considering only the open vegetation area during Pliocene and early Pleistocene environments. This approach will be by pollen-analysis and forams of drill progressively applied to forest assemblages. Autan 1: Chronstratigraphic correlations, Pollen et Spores, v. 23 (2), p. 247-258. References Diniz, R, 1984, Apports de la palynologie a la Bertini, A., 1988, Palinologia ed aspetti connaissance du Pliocene portugais. Rio amnientali del versante adriatico dell Maior: un bassin de reference pour Appennino centro-settentrionale durante 1'histoire de la flore, de la vegetation et du il Messiniano e lo Zancleano: Ph.D. thesis, climat de la faqade atlantique de 1'Europe Univ. Firenze. 88 p. meriodionale: Thesis, Univ. Montpellier II. 230 p. Bessais, E. and Cravatte, }., 1988, Modi fications latitudinales des ecosystemes Drivaliari, A., 1993, Images pollinques et vegetaux pliocenes en Mediterranee nord- paleoenvironements au Neogene occidentale d'apres des analyses superieur en Mediterranee orientale. polliniques en Catlogne meridionale: Aspects climatiques et paleo- Geobiosv. 21 (1), p. 49-63. geographiques d'un transect latitud-inal (de la Roumanie au delta du Nil): Ph.D. Brenac, P., 1984, Vegetation et climat de la thesis, Univ. Montpellier II, 333 p. Campanie du sud (Italie) au Pliocene final d'apres 1'analyse pollinique des depots de Julia, R. and Sue, J.-P., 1980, Analyse Camerota: Ecologia Mediterranea v. 10 (3- pollinique des depots lacustres du 4), p. 207-216. Pleistocene inferieur de Banyoles (Banolas, site de la Bobila Ordis - Combourieu-Nebout, N., 1990, Les cycles Espagne): un element nouveau dans la glaciaire-interglaciaire en region reconstitution de 1'histoire mediterraneenne de -2,4 a -1,1 Ma: paleoclimatique des regions mediter- analyse pollinique de la serie de Crotone raneennes d'Europe occidentale: Geobios (Italie meridionale): Paleobiologie v. 13(1), p. 5-19. Continentale, v. 17, p. 35-59.
40 Leroy, S., 1990, Paleoclimats plio-pleistocenes Sue, J.-P. and Bessais, E., 1990, Perennite d'un en Catlogne et Languedoc d'apres la climat thermo-xerique en Sicile avant, palynologie de formations lacustres. pendant, apres la crise de salinite Thesis, Univ. Louvain-la-Neuve, Belgium. messinienne. C.R. Academie des Sciences 522 p. de Paris v. (2), 310,1701-1707.
Sue, J.-P., 1973. Etude palynologique des Sue, J.-P., Clauzon, G., Bessedik, M., Leroy, S., marnes de Celleneuve (Pleistocene Zheng, Z., Drivaliari, A., Roiron, P., inferieur): Herault. Bull. Ass. fr. etude Ambert, P., Martinell, J., Domenech, R., Quaternaire v. 34 (1), p. 13-24. Matias, I., Julia, R., and Anglada, R., 1992, Neogene and lower Pleistocene in Sue, J.-P., 1978, Analyse pollinique de depots southern France and northeastern Spain. plio-pleistocenes du sud du Massif Mediterranean environments and climate. basaltique de 1'Escandorque (serie de Cahiers Micro paleontologie v. 7, no. 1-2, Bernasso - Lunas, Herault - France): p. 165-186. Pollen et Spores v. 20 (4), p. 497-512. Sue, J.-P. and Cravatte, J., 1982, Etude palynoloqique du Pliocene de Catalogne Sue, J.-P., 1981, La vegetation et le climat du (nord-est de 1'Espagne). Paleobiologie Languedoc (sud de la France) au Pliocene continentale v. 13, no. 1, p. 1-31. moyen d'apres la palynologie: Paleobiologie continentale v. 12, p. 7-26. Sue, J.-P. and Drivaliari, A., 1991, Transport of bisaccate coniferous fossil pollen grains to Sue, J.-P., 1984, Origin and evolution of the coastal sediments. An example from the Mediterranean vegetation and climate in earliest Pliocene Orb ria (Languedoc, Europe: Nature v. 307, p. 429-432. southern France): Review of Palaeobotany and Palynology v. 70, p. 247-253. Sue, J.-P., 1989, Distribution latitudinale et etagement des associations vegetales au Zheng, Z., 1990, Vegetation et climats Cenozoique superieur dan 1'aire ouest- neogenes des Alpes Maritimes franco- mediterranenne. Bulletin de la Societe italiennes d'apres les donnees de 1'analyse Geologique de France v. 8, no. 5,3, p. 541- palynologique: Paleobiologie Continentale 550. v. 17, p. 217-244.
41 Fig. 1. Selected Pliocene pollen localities in the Mediterranean region. Legend. 1. Relief. 2. Continuous sections interesting the entire Pliocene (chronostratigraphic control provided by foraminifers and/or nannoflora). 3. Sections comprised between 5.2 and 3.2 Ma (chronostratigraphic control provided by foraminifers and/or nannoflora). 4. Sections comprised between 5.2 and 3.2 Ma (chronostratigraphic control provided by foraminifers and/or nannoflora, and by magnetostratigraphy). 5. Sections comprised between 3.2 and 2.6 Ma (chronostratigraphic control provided by foraminifers and/or nannoflora). 6. Sections younger than 2.6 Ma (chronostratigraphic control provided by foraminifers and/or nannoflora). 7. Sections younger than 2.6 Ma (chronostratigraphic control provided by foraminifers and/or nannoflora, and by magnetostratigraphic and radiomethc datations). 8. Lower to Middle Pliocene sections with unsatisfactory chronologic control. 9. Section younger than 2.6 Ma dated by paleomagnetic and radiometric measurements. 10. Section younger than 2.6 Ma dated by mammals and magnetostratigraphy. Localities. 1, Rio Maior (Diniz, 1984). 2, Carmona (Sue & Ferrier, unpublished). 3, Andalucia Gl (Bessais, unpublished). 4, Habibas 1 (Sue, 1989). 5, Arzeu 1 (Abdelmalek, unpublished). 6, Sidi Brahim (Abdelmalek, unpublished). 7, San Onofre -(Bessais & Cravatte, 1982). 8, Tarragona E2 (Bessais & Cravatte, 1982). 9, Garraf 1 (Sue & Cravatte, 1982). 10, Papioi (Sue & Cravatte, 1982). 11, Ciurana (Sue & Cravatte, 1982). 12, Bafiolas - Bobila Ordis (Julia & Sue, 1980; Leroy, 1990). 13, Canet 1 (Cravatte et al., 1984). 14, Le Boulou (Sue et al., 1992). 15, Autan 1 (Cravatte & Sue, 1981). 16, Cap d'Agde 1 (Sue, 1989). 17, Cessenon (Sue, 1981; Sue & Drivaliari, 1991). 18, Bernasso (Sue, 1978; Leroy, 1990). 19, Celleneuve (Sue, 1973). 20, Pierrefeu 1 (Sue, unpublished). 21, Iscles 1 (Sue, unpublished). 22, Cagnes-sur-mer - La Combe (Zheng, 1990). 23, Saint-Martin du Var (Zheng, 1990). 24, Saint-Isidore (Zheng, 1990). 25, Castello d'Appio (Zheng, 1990). 26, Cava di Villanova (Zheng, 1990). 27, Stirone (Bertini, 1992). 28, Monticino 87 (Bertini, 1992). 29, Maccarone (Bertini, 1992). 30, Camerota (Brenac, 1984). 31, Crotone (Combourieu-Nebout, 1990; Combourieu-Nebout & Vergnaud Grazzini, 1991). 32, Capo Rossello (Sue & Bessais, 1990). 33, Punta Piccola (Sue, unpublished). 34, Oued Tellil (Sue, unpublished). 35, Oued Galaa (Sue, unpublished). 36, Jeriba (Sue & Ferrier, unpublished). 37, Ticleni (Drivaliari, 1993). 38, Lozenec (Drivaliari, 1993). 39, Ravno-Pole* (Drivaliari, 1993). 40, Nireas 1 (Drivaliari, 1993). 41, Nestos 2 (Drivaliari, 1993). 42, Kremmidia (Combourieu-Nebout, unpublished). 43, Aghios Vlassios (Drivaliari, 1993). 44, Naf 2 (Drivaliari, 1993). 45, Gan Yavne 5 (Drivaliari, 1993).
42 Ma STRATI L 0 C A L i T I E s STRAT; Ma GRAPHY ;RAPUY P 0 -1 - P 0 1 i 31 L C L C E E I 15 E E I N I N S E 12 S E _ T T 7 1 P 8 36 P 2 I _-2 I 34 3(3 44 I A A P C c _ E 0 8v E L o. 37 24 N I Z Z -3 _ 3 I 5 I 0 33 A A C N N " E Z 40 Z N A A -4 - 1620 --4 E N 43 N C C % 3' L ( L - 2 i - E 27 5 E f 1- A I 4 17 A N -5 _ N 5
MIOCENE 10 2329 38 34
Fig. 2. Chronological assignment of some selected Pliocene sections in the Mediterranean region. Locality numbers, see fig. 1.
43 Steps Toward Drier Climatic Conditions In North-Western Africa During The Upper Pliocene
Lydie M. Dupont, Institut fur Palynologie und Quartfirwissenschaften der Universitfit, Gttttingen, Germany Suzanne Leroy, IGBP PAGES, Bern, Switzerland
A 200 m long marine pollen record from OOP (1991) on Mediterranean sapropels. However, 658 (21 °N, 19°W) reveals cyclic fluctuations the ages of ODP 659, and thus of ODP 658, are and long-term variation in vegetation and consistently 0.13 Ma older than those continental climate of north-western Africa obtained by Raymo et al. (1989) from the N from 3.7 to 1.7 Ma. Atlantic (DSDP 607). Correlation of ODP 658 OOP Site 658 (Ocean Drilling Program, leg with ODP 659 and DSDP 607 revealed a 108) is situated north-west of Africa (Fig. 1) at hiatus at 154 mbsf and several coring gaps a water depth of 2263 m on the continental (Tiedemann, 1991). The time resolution of the slope 160 km west off Cape Blanc. It is located pollen record of ODP 658 (401 samples) below an important near-shore up welling exceeds 1 sample per 5 ka except for the cell induced by the trade winds. The position mentioned gaps and spans the period from at a terrace of the continental slope between 3.7 to 1.7 Ma. two major canyon systems restricts Nowadays, at latitudes between 19°N and disturbance of the sediment record by lateral 21 °N, the climatic sensitive Sahelian down-slope transport of particles to a vegetation gives way to the desert. In the minimum (Ruddiman et al., 1988). The upper adjacent East Atlantic, at 21°N, ODP 658 is 100 meters of sediment covering the Brunhes located where north-easterly trade winds are Normal Polarity Chron and the lower 200 overlain by the mid-tropospheric African meters representing the Upper Pliocene are Easterly Jet (Fig.l; AEJ, summer maximum of separated by a hiatus spanning the Lower the Saharan Air Layer). Trade winds Pleistocene (Sarnthein and Tiedemann, 1989). transport pollen from their source areas in the The high sedimentation rate, due to high Mediterranean and the Sahara to the marine organic production in the up welling zone site (Hooghiemstra et al., 1986). Dust and combined with high Saharan dust influx, pollen from the Sahel and the southern Sahara provides a Plio-Pleistocene record of high are carried into altitudes of the AEJ (1 GOO- quality in which bioturbation hardly obscures 5000 m) by strong, heat induced squall lines. the fine-scale resolution up till 1000 years Then, the AEJ carries pollen from latitudes (Tiedemann et al., 1989). between 16°N and 20°N westwards and The time-scale of the sequence (Fig. 2) is northwards over the Atlantic. Modern provided by biostratigraphy, palaeo- transport of pollen grains by river discharge magnetism, and oxygen isotope stratigraphy and ocean currents is insignificant (Ruddiman et al., 1988; Sarnthein and (Hooghiemstra, 1989; Dupont and Agwu, Tiedemann, 1989; Tiedemann, 1991). The ages 1991). of the isotope stages of ODP 658 are derived For the Pliocene and the Pleistocene, the by comparison with ODP 659 (18.05'N, sedimentology of ODP 658 shows dust 21.02'W; Tiedemann, pers. comm. 1992). That transport into the Atlantic by winds (trades time-scale reaches back 5 Ma (Tiedemann and and African Easterly Jet) as well as clay Sarnthein, in press). The ages of the ODP 659 transport by rivers (Tiedemann et al., 1989; time-scale are similar to the independent Tiedemann, 1991). On the one hand, quartz calibrations of Shackleton et al (1990) on content and siliciclastics (eolian dust > 6 Pacific sediments (ODP 677) and of Hilgen micron) indicate wind vigor, while on the
44 other hand, the clay content illustrates the vegetation or even deserts and, therefore, as a importance of river discharge to the reflection of drier climate. Few of the shifts formation of the sediment. The pollen record have been recorded before 3 Ma, but they of ODP 658 confirms the conclusion drawn regularly occur from 2.61 Ma onwards. from sedimentary analysis (Tiedemann, 1991) The pollen record of ODP 658 shows a of persistent river discharge prior to 3.4 Ma. large number of short-time ( < 50 ka) Afterwards, river discharge subsequently fluctuations (Fig. 2) in vegetation and climate ceased. River-borne pollen seems abundant from 3.74 to 1.71 Ma corresponding to the until 2.97 Ma. oxygen isotope record: dry periods correlate An estimation of trade wind vigor is given with large global ice-volume and humid by the sum of those pollen taxa that have their periods with small global ice-volume. On top main source areas in the northern Sahara and of these cycles, several periods, at ca. 3.5, 3.2, North Africa: Ephedra, Artemisia, and Pinus, and 2.5 Ma, mark irreversible changes in the plus Asteraceae Liguliflorae for periods after development of vegetation and climate. 2.9 Ma. Generally, the strength of the trades A humid, probably warm, climate with was much lower during the Pliocene than weak trade winds prevailed from 3.74 to 3.48 during the late Pleistocene (Fig. 3). Trade Ma (Zone I). According to percentages of winds were very weak until 3.17 Ma resulting Rhizophora pollen exceeding 10%, mangrove in low transport of pollen from north of the swamps were growing near Cape Blanc Sahara. However, at 3.26 Ma, trade-wind around 3.70 Ma, probably in connection with vigor probably increased for a short period. a paleoriver. Percentages of the sum of pollen Stepwise increase of the level of trade-wind from Sudanian and Guineian vegetation, i.e. strength is found at 3.17, 2.76, and 2.61 Ma. from wooded savanna, woodland and During the final Pliocene, trade winds are tropical forest, repeatedly exceed 5%. It rather strong with exception of the period indicates that forest and savanna had a between 1.87 and 1.85 Ma. The record of distribution at least as north as. 21°N. The trade-wind indicators corroborates the period may be correlated in northwestern estimates of wind strength by grain size Europe to Brunssumian C of the Dutch analysis of ODP 658, ODP 659 and DSDP 397 palynostratigraphy (Zagwijn, 1960) and Zone showing an increase of the trade winds Pic of the north-western Mediterranean area between 3.2 to 2.6 Ma (Tiedemann et al, 1989; (Sue, 1984). Tiedemann, 1991). The period from 3.48 to 3.25 Ma (Zone H) Studies on time-slices of the Holocene shows five dry phases. Three of them, at 3.48, optimum and the Last Glacial Maximum 3.35, and 3.26-3.27 Ma, show high percentages revealed the latitudinal stable position of the of Amaranthaceae-Chenopodiaceae pollen AEJ during the last glacial-interglacial cycle (50%) indicating arid conditions. Two other and the increasing strength of the trade winds dry phases, at 3.44-3.40 and 3.31 Ma, are less during glacial times (Hooghiemstra, 1988). prominent: they show high percentages of During the Brunhes Chron, latitudinal shifts Caryophyllaceae but the percentages of up to 10° of latitude for the vegetation zones Amaranthaceae-Chenopodiaceae hardly of Sahara, Sahel, and savanna were registered exceed 40%. High percentage values ( > 20%) through the AEJ carrying pollen grains from are found for Asteraceae Liguliflorae between those vegetation zones, which occurred at 3.44 and 3.40 Ma, and at ca. 3.27 Ma latitudes between 16°N and 20°N. These shifts presenting a no-analogue situation. The are reflected in the progression of percentage youngest and most arid phase shows a maximums of Cyperaceae, Poaceae, CCA percentage maximum of Ephedra of 4% at 3.26 (sum of Caryophyllaceae, Chenopodiaceae, Ma. This phase could correspond to a drop in and Amaranthaceae), Artemisia, and Ephedra winter sea surface temperatures in the (Fig. 2H, arrows; Dupont and Hooghiemstra, Mediterranean Sea (Zachariasse et al.', 1990) 1989; Dupont et al, 1989). Each of them is and a decline of thermophilous elements in interpreted as a southward extension of dry pollen records of coastal swamps and
45 mountain slopes of the Mediterranean area between 3.25 and 2.6 Ma, mean percentages of (Sue ei ai, 1992). From the sedimentary record tropical forest elements ( > 2%) indicate a of OOP 658, Tiedemann (1991) concluded an northern extent of forests that probably increase of eolian activity, especially trades, shifted southwards after 2.6 Ma. After 2.8 Ma, around 3.26 Ma. The period from 3.48 to 3.25 a declining trend in mean percentages of Ma records through the course of several Poaceae indicates a reduction of savanna oscillations a trend toward more aridity and vegetation (including wooded savanna and an extension of open vegetation types in dry open forest), probably as a result of the north-western Africa probably in relation to development of a desert vegetation in north the onset of the trade winds and the first western Africa. Percentages of Asteraceae Northern Hemisphere's glaciations. Liguliflorae reach high values prior to 3.2 Ma, Humid conditions re-established between but decline to low values afterwards. From 3.25 and 3.19 Ma (beginning of Zone Ilia) 2.7 Ma on, mean percentages of CCA reach indicated by high percentages of tropical high values (around 40%), comparable to forest ( > 2%) and Cyperaceae ( > 15%). those for the Brunhes indicating aridity in Afterwards, the climate progressively north-western Africa. Mean percentages of becomes drier again and percentages of Ephedra and Artemisia of the Pliocene are five Cyperaceae decline (end of Zone Ilia). times lower than those of the late Pleistocene During the next period from 2.97 to 2.61 Ma indicating that arid periods were still less (Zone Illb), prevailing percentages of grass prolonged and/or less severe during the pollen (Poaceae up to 70%) are followed by Pliocene. percentage maximums of CCA ( > 50%), at 2.73 and 2.69 Ma, Ephedra ( > 5%) at 2.69 Ma, and the first maximum of Artemisia (2%) at 2.66 Ma. A slight increase in trade-wind strength occurred at 2.76 Ma. The period may References be correlated to the Reuverian in the Netherlands and to the Mediterranean pollen Dupont, L.M. and Agwu, C.O.C., 1991, zone PII (Zagwijn and Sue, 1984). Environmental control of pollen grain The isotope Stages 104 (2.60 Ma), 100 distribution patterns in the Gulf of Guinea (2.53), and 98 (2.49 Ma) record high and offshore NW-Africa. Geol. Rundschau percentages of Ephedra (ca. 3%), Artemisia ( > v. 80, p. 567-589. 2%), and CCA ( > 50%) indicating severe dry periods. They start a climatic regime in north Dupont, L.M. and Hooghiemstra, H., 1989, western Africa resembling glacial to The Saharan-Sahelian boundary during interglacial cycles that result in arid cold and the Brunhes chron. Acta Bot. Neerl. v. 38, humid warm phases. The period is correlated p. 405-415. with the Praetiglian and the lower part of the Lieth-series (Ekholt Glacial; Mencke, 1975). Dupont, L.M., Beug H.-J., Stalling H., and Within the period between 2.6 and 1.7 Ma Tiedemann, R., 1989. First palynological (Zone IV), only two extended humid periods results from site 658 at 21 °N off northwest occur corresponding to the weakly developed Africa: pollen as climate indicators. In isotope Stages 76 and 68. Ruddiman, W., Sarnthein, M., et a/.,1989. Long-term variation (Fig. 3) indicates a Proceedings of the Ocean Drilling Project, first step toward drier climate between 3.5 Scientific Results v. 108, p. 93-111. and 3.2 Ma and a second, stronger one starting at about 2.6 Ma. The percentage Hilgen, F.J., 1991, Astronomical calibration of maximums of Rhizophora ( > 5%) indicate that Gauss to Matuyama sapropels in the until 1.9 Ma, mangrove swamps irregularly Mediterranean and implication for the occurred near Cape Blanc (i.e. 5° north of their geomagnetic polarity time scale. Earth present northern limit). Prior to 3.5 Ma, and Planet. Sci. Lett. v. 104, p. 226-244.
46 Hooghiemstra, H., 1988, Palynological Shackleton, N.J., Berger, A. and Peltier, W.R., records from northwest African marine 1990, An alternative astronomical sediments: a general outline of the calibration of the lower Pleistocene interpretation of the pollen signal: Phil. timescale based on ODP Site 677: Trans. Trans. R. Soc. Lond. B, v. 318, p. 431-449. R. Soc. Edinburgh. Earth Sciences v. 81, p. 251-261. Hooghiemstra, H., 1989, Variations of the NW African trade wind regime during the last Sue, J.-P., 1984, Origin and evolution of the 140 000 years: changes in pollen flux Mediterranean vegetation and climate in evidenced by marine sediment records. In Europe: Nature, v. 307, p. 429-432. Leinen, M. and Sarnthein, M. (eds). Paleoclimatology and Palaeometeor- Sue, J.-P., Clauzon, G., Bessedik, M., Leroy, S., ology: Modern and Past Patterns of Global Zheng, Z., Drivaliari, A., Roiron, P., Atmospheric Transport. NATO ASI, C Ambert, P., Martinell, ]., Domenech, R., 282, Kluwer, Dordrecht, p. 733-770. Matias, I., Julia, R. and Anglada, R., 1992, Neogene and Lower Pleistocene in Hooghiemstra, H., Agwu, C.O.C. and Beug, Southern France and Northeastern Spain: H.J., 1986, Pollen and spore distribution in Mediterranean environments and climate. recent marine sediments: A record of NW- Cahiers de Micropaleontologie v. 7, no. 1- African seasonal wind patterns and 7, p. 165-186. vegetation belts: "Meteor"-Forschungs- Ergebnisse C, v. 4O, p. 87-135. Tiedemann, R., 1991, Acht Millionen Jahre Klimageschichte von Nordwest Afrika Menke, B., 1975, Vegetationsgeschichte und und Palao-Ozeanographie des angren- Florenstratigraphie Nordwestdeutschl- zenden Atlantiks Hochauflosende ands im Pliozan und Friihquartar. Mit Zeitreihen von ODP-Sites 658-661: Thesis, einem Beitrag zur Biostratigraphie des Universitat Kiel, 127p. Weichselfriihglazials: Geol. Jb. A, 26, p. 3- 151. Tiedemann, R., Sarnthein, M. and Stein, R., 1989, Climatic changes in the western Raymo, M., Ruddiman, W.F., Backman, J., Sahara: Aeolo-marine sediment record of Clement, B. and Martinson, D., 1989, Late the last 8 million years (sites 657-661): Pliocene variation in Northern Proceedings of the Ocean Drilling Project, Hemisphere ice sheets and North Atlantic Scientific Results, v. 108, p. 241-277. deep water circulation: Paleo- ceanography, v. 4, no. 4, p. 413-446. Tiedemann, R. and Sarnthein, M., in press, Astronomical time scale for the Pliocene Ruddiman, W.F., Sarnthein, M., Baldauf, J., et Atlantic 918O and dust flux records of al, 1988, Proc, Init. Repts., 108(A): Ocean ODP Site 659: Paleoceanography. Drilling Programp. 931-946. Zachariasse, W., Gudjonsson, L., Hilgen, F., Sarnthein, M. and Tiedemann, R., 1989, Langereis, C., Lourens, L., Verhallen, P. Towards a high-resolution stable isotope and Zijderveld, J., 1990, Late Gauss to stratigraphy of the last 3.4 million years: early Matuyama invasions of sites 658 and 659 off northwest Africa, in Neogloboquadrina atlantica in the Ruddiman, W.F., Sarnthein, M., et al., 1989: Mediterranean and associated record of Proceedings of the Ocean Drilling Project, climatic change: Paleoceanography v. 5, Scientific Results, v. 108, p. 167-185. no. 2, p. 239-252.
47 Zagwijn, W.H., 1960, Aspects of the Pliocene Zagwijn, W.H. and Sue, J.-P. 1984, and Early Pleistocene vegetation in the Palynostratigraphie du Plio-Pleistocene Netherlands: Mededelingen Geol. Sticht., d'Europe et de Mediterranee nord- C 3(5), Maastricht, 78p. occidentales: correlations chronostrati- graphiques, histoire de la vegetation et du climat: Paleobiologie continental, v. 14, no. 2, p. 475-483.
48 savanna and dry optn forest
sw-fttonsoon Atlantic Ocean w
Figure 1. Location of ODP Site 658 (21°^ 19°W; black dot), surface winds (trades and monsoon; black arrows) and mid- tropospheric winds (African easterly Jet; open arrows), modern vegetation zones (Mediterranean, Saharan, Sahelian, savanna and dry open forest, tropical rain forest).
49 A BCD EF G HI J KLM
- -2.6 A aCDEFGHlJ K LM
2.7 i.a
2.8
2.9
-3
3.1
-3.2
-3.3
o a 40 a at ion*
0 20 40 68 flt 100%
Figure 2. From left to right: (A) Pollen zones in roman numbers, Arabic numbers refer to oxygen isotope stages. (B) Arrows indicate the steps toward drier climatic conditions. (C) Declining trend in river discharge. (D) Increasing trend in trade-wind vigor. (E) Declining trend in grass- rich vegetation types like savanna and open forest. (F) Occurrence of mangroves near Cape Blanc. (G) Extent of the tropical forest to 21 °N. (H) Arrows denote levels that show a progression of percentage maximums of pollen taxa indicating a southward shift of dry vegetation. (I) Percentages of Rhizophora plus tropical forest elements (hatched left). (J) Percentages of Cyperaceae plus Poaceae (open left). (K) Percentages of CCA (sum of Caryophyllaceae and Amaranthaceae-Chenopodiaceae) plus Asteraceae (open right). (L) Percentages of Artemisia plus 'Mediterranean' elements (hatched right). (M) Percentages of Ephedra (black). Time-scale in Ma on the vertical axis after Tiedemann et al. (in press). Oxygen isotope taxonomy after Tiedemann (1991). 50 OOP658 running mean (45ka)
1 1 10 1 i 1 10 %
Figure 3. Running mean (9 equidistant samples 5 ka apart) of percentages of the following pollen taxa: tropical forest, Rhizophora, Poaceae (grasses), CCA (sum of Caryophyllaceae and Amaranthaceae- Chenopodiaceae), Asteraceae Liguliflorae, Artemisia, Ephedra, and trade-wind indicators. Time-scale in Ma on the vertical axis.
51 An Attempt To Reconstruct Temperature And Rainfall From The Pliocene Pollen Record In Ethiopia
R. Bonnefllle, D. Jolly and F. Challe, CNRS Luminy, Marseille, France
The deposits of the Hadar Formation have changes as those indicating a noticeable recently been redated using single-crystal cooling. Although the Pliocene pollen data laser-fusion ^Ar/^Ar technique (Walter can be interpreted as indicating conditions and Aronson, in press) to between 3.4 ± 0.04 much more humid than the arid climate that Ma and 2.92 ± Ma (Walter, 1993). The best prevails in the Hadar region today, the palynological data from this formation is factorial analysis indicates close affinities with from an organic clay below the Kadamoumou modern pollen data from the dry forests of Basalt (Bonnefille et al, 1987). Based on an northeastern Ethiopia but not with the wettest estimated mean sediment accumulation rate forests of southwestern Ethiopia. This is a of 80 cm/kyr (Walter, in press), these clear indication of the eastern limit of humid sediments were apparently deposited over a lowland and highland forests, and that they few tens-of-thousands of years (20 to 30,000 did not reach the 40° longitude at that time. years?) that began a few thousand years after Palynologists have developed a statistical the deposition of the volcanic ash SHT, which methodology which enables the quantitative is precisely dated at 3.4 ± 0.04 Ma (Walter and reconstruction of climatic parameters. We Aronson, in press). have been successful in reconstructing such The new presentation of the results in this parameters for the Holocene and Late Glacial report focuses on a comparison of the fossil pollen data in Central Africa. Because the data with an extensive modern data set (118 Pliocene pollen can be identified by spectra) covering all the vegetation types comparison with the modern taxa, an attempt encountered on an altitudinal gradient from was made to apply such a quantitative 500 to 4000 meters elevation. Statistical reconstruction of climatic parameters to the Factorial Analysis was carried out both on the Pliocene record, using the modern pollen data modern (118) and the fossil pollen spectra set from Eastern Africa. The results of this (18), with the fossil data being considered as essay show that a possible short cooling event supplementary elements. In this procedure, associated to more humid conditions could local aquatics and grasses are excluded, and have occurred around 3.4 Ma ago. But the statistical treatment is applied to the quantitative estimate of this cooling would pollen counts for the 189 identified taxa. The need a better evaluation for the amplitude of statistical results show a distribution of the the Ethiopian plateau uplift in the Hadar area. modern samples into four distinct altitudinal The modern pollen data set from Ethiopia vegetation zones, with the fossil samples from expresses a clear pattern for the decreasing Hadar linked to modern samples taken from temperature gradient with increasing altitude, vegetation existing now at altitude above 500 nevertheless a more reliable result can only be meters. Therefore, the statistical analysis achieved when pollen data from the Last confirms previous interpretation of the past Glacial Period in Ethiopia are obtained, in vegetation interpreted as similar to that order to constrain the coefficients for presently known in the Ethiopian mountains. evaluating the climatic parameters. However, the interpretation of the pollen record should take into account possible rifting that might have occurred since the deposition of the Hadar Formation, and could produce, in the pollen assemblages, the same
52 References Walter, R.O. and Aronson, J.L., 1993, Age and sources of the Sidi Hakoma Tuff Hadar Bonnefille, R., Vincens, A., and Buchet, G., Formations: Journal of Human Evolution, 1987, Palynology, stratigraphy, and v. 25, p. 229-240. paleoenvironment of a Pliocene hominid site (2.9-3.3 M.Y.) at Hadar, Ethiopia: Walter, R.O., in press, The age of Lucy and Palaeogeography, Palaeoclimatology, First Family: laser-fusion 40Ar/39Ar Palaeoecology, v. 60, p. 249-291. dating of the Denen Dora and lower Kada Hadar Members of the Hadar Formation: Nature.
53 Some Manifestations Of Pliocene Warming In Southern Africa
L. Scott, University of the Orange Free State, Bloemfontein, South Africa T. C. Partridge, Transvaal Museum, Pretoria, South Africa
Pliocene vegetation types in southern insights into the amplitude and timing of Africa, especially those of the Middle Pliocene changes in the subcontinent. High Pliocene, are not well documented. They can marine terraces at elevations up to 90 m are be reconstructed in part on the basis of associated with an extensive terrestrial fauna palynological data from the interior and the at Langebaanweg on the western Cape coast, western coastal and offshore regions. Pollen and provide important proxy evidence of spectra from marine deposits off the northern early - mid Pliocene deglaciation. The upper Namibian coast (van Zinderen Bakker, 1984) terraces of the Vaal River contain sparse which can broadly be assigned to the middle Pliocene fossils; their massive gravel Pliocene, contain relatively prominent armoring is indicative of semi-arid Chenopodiaceae pollen, and are interpreted alluviation, probably towards the end of the here as reflecting a tropical climate, possibly Gauss chron. At about the same time a shift is associated with more intense evaporation. evident within the hominid-bearing cave Early Pliocene pollen accompanying fauna deposits of the interior from sub aqueous from the Varswater Formation at accumulation to of predominantly fine clastic Langebaanweg, in the "Mediterranean" sediments to an influx of courser colluvial southwestern Cape Province, indicates that elements under the influence of episodic swampy conditions existed in a fynbos sheetfloods. Major carapaces of the Ghaap (macchia) environment, with a suggestion of escarpment, which accumulated between 2.4 slightly more tropical characteristics than at Myr and the middle Pleistocene can also be present (Scott, in press). Middle- to late- linked to cycles of spring activity under semi- Pliocene (ca. 3 Myr) cave breccias at arid climatic conditions. In sumr a growing Makapansgat in the interior of the body of evidence is coming to hand which subcontinent (Cadman and Rayner, 1989), documents an important shift from relatively and a coprolite from these layers (this report), warm, mesic conditions during the Pliocene contain "Bushveld" pollen types, but exotic to the recurrent cool, relatively dry cycles Pinus contaminants suggest that the spectra which typified much of the Quaternary. were probably derived from the modern environment. Pollen from terminal Pliocene References to early Pleistocene travertines in the Sterkfontein and Kromdraai sites of the Cadman, A. and Rayner, R.J., 1989, Climate highveld grassland region, tentatively change and the appearance of indicates open Protea savanna at that time. In Australopithecus africanus in the comparison with older strata from Makapansgat sediments: Journal of Sterkfontein, these deposits contain a fauna Human Evolution, v. 18, p. 107-113. indicative of relatively open vegetation (Vrba 1985). It can be assumed therefore, that the Scott, L., in press, Pollen Evidence for preceding mid-Pliocene vegetation contained vegetation and climate change in southern denser woodland, although there are no Africa during the Neogene and independent palynological data to support Quaternary: Proceedings of Conference on this. Paleoclimate and Evolution, Airlie, Geomorphological and sedimentological Virginia, submitted to Yale University data provide independent support for some Press. of these conclusions and provide further
54 van Zinderen Bakker, E.M., 1984, Vrba, E.S., 1985, Early hominids in southern Palynological evidence for Late Cenozoic Africa updated observations on arid conditions along the Namibia coast chronological and ecological background, from Holes 532 and 530A, Leg 75, Deep in, Tobias, P. H., ed., Hominid Evolution: Sea Drilling Project: Initial Reports of the Alan R. Liss, New York, p. 195-200 . Deep Sea Drilling Project v. 75, p. 763-768.
55 Landscape And Climate Of The Southwestern Russian Plain In The Pliocene
Tanya V. Svetlitskaya, Russian Academy of Sciences, Moscow, Russia
Along the northern coast of the Black sea Pontian Stage (5.4-4.7 Ma) on the southwestern Russian Plain, inter- bedded continental and marine sediments During the Novorossijskoe substage, at cover the entire Pliocene. The fossil floras the beginning of the Pontian age, the Zanklian and faunas of these deposits have been transgression united the Black and Caspian studied in detail, providing the basis for Seas with the Mediterranean. By the end of paleoclimatic interpretations and biostrati- early Pontian time (-5.0 to 4.9 Ma?) the sea graphic correlations. This report discusses retreated southwestward and the greater part the most complete sections from this region, of the southwestern Russian Plain was concentrating on sites where there are distinct exposed. boundaries between stages and horizons and Marine faunas indicate that the early where there are abundant paleontological Pontian sea was closed and brackish. The data from marine mollusks, gastropods, mollusks assemblages from these deposits ostracodes and terrestrial mammals and include Unio and Anodonta, while the palynological data. The Pliocene of this ostracode fauna includes Caspiella, Bakunella region is divided into three stages (based on and Leptocythere. From these data Ivchenko paleontological assemblages) which are (from (1986) estimated that the mean annual water older to younger) the Pontian, Kimmerian, temperature was near +12° to +15°C (today Kuajlnician. Nine sections were studied from near the city of Odessa the mean annual fluvial terraces above the flood-plains of the water temperature is +9.6°C). In the early rivers Byk and, Kuajlnik; from the coastal Pontian forest-steppe prevailed in the western terrace scarps above Khadzibejsky bay and part of the region under investigation pine from the Kertch peninsula of Crimea (Fig. 1). forests grew in the river valleys, and the Paleomagnetic studies for each of these northern part was occupied by mixed conifer- sections were carried out in Laboratory of the broadleaved forests. Moscow University following the method of By the middle of Novorossijskoe time A. Khramov and L. Cholpo (1967). some aridification had taken place in the east Paleoclimatic reconstructions are based on and the role of open vegetation communities paleofloristic data from the above mentioned increased. Chenopodiaceae were important sections studied by S.V. Siabraj and on in these communities and possibly these published materials from adjacent regions (A. included halophytes, which may have Negru (1986), S. Medianik (1985), and N. occupied the recently exposed Black Sea shelf. Shchekina (1979) The methodology used to In the west such changes of the climate estimate paleoclimatic conditions on the basis were not registered and forest-steppe of fossil floras was developed by V. Grichuk vegetation continued to grow. By the end of (1987), following the concepts of J. Iversen this period forests dominated in both the east (1941) and modified to be applied to Tertiary and in the west. These were primarily broad- floras. In the following text I present leaved formations with Ulmus, Zelkova, and paleogeographical reconstructions developed Fagus. The climate was similar to the from our paleomagnetic and paleofloristic contemporary climate of the southern Crimea research, combined with previously coast, but the presence of exotic taxa suggest published information. that it was something warmer than today
56 (January mean temperature ~ +5°C and July ~ temperature increase occurred during +25°C) deposition of the sediments of the The Pontian stage of the history of the Kamyshburun horizon (4.2 - 4.0 Ma). Mean Hipparion fauna is poorly represented in the January temperature rose by almost 2°C (to former USSR. Only scattered small 6°C) and mean July temperature rose from occurrences of mammals bones have been 22°C to 23°C. found in southern Ukraine. This "Tauric The Kuchurganian and Moldavian faunal complex" (Korotkevich, 1988) includes the complexes that developed during the first occurrence of Paracamelus, while typical Kimmerian time indicate the progressive members of the Hipparion fauna were not aridification. The earlier (Kuchurganian) present at this time. The increased abundance included in its composition the main elements of ostriches suggests greater availability of of the Hipparion fauna: Deinotherium, open dry areas. However, the presence of Zygolophodon, Hipparion, and Tapirus, and is certain water-swamp birds and tortoises largely dominated by forest and forest-steppe points to the development of marshlands and species. The Moldavian faunal assemblage warm-water environments, whereas the reflects the progressive drying of the climate: abundance of Cervus and Proboscidea indicate taxa characteristic of humid environments the presence of wooded vegetation. On the disappear and inhabitants of open areas such whole, this faunal assemblage reflects as Paracamelus and Equus (which makes the moderately warm and relatively dry climate. first appearance here) and more moderate climate appear (Korotkevich, 1986). The Kimmerian Stage (4.7-3.4 Ma) climate was apparently humid and moderately warm (January - above +4°C; July In the middle Pliocene more land was ~ +22°C). exposed and sea waters were confined to within the limits of the modern Black Sea and Kuajlnician Stage (3.4-2.3.Ma) Caspian Sea depressions. The Kimmerian Black Sea basin was closed with brackish In the late Pliocene this region was an water. The marine fauna of this period elevated plain on which the modern river included Dreissenidae, Cardiidae, endemic network was formed, the sea basin remained gastropods, Viviparus, Melanopsis, Planorbis only at the south of the area. It was a closed and the freshwater ostracodes Caspiela and basin with brackish water , but its salinity Caspiocypris. The majority of the marine fauna was less than in Kimmerian time. The marine had a boreal character with few fauna was inherited the main features of Mediterranean taxa. At this time the broad- Kimmerian fauna, but was less diverse. The leaved forests were composed mostly of heat- mollusks Limnocardium, and Dreissena loving and moderately heat-loving species: appeared during the Kuajlnician, and Acer, Quercus, Juglans, and less common gastropods were represented primarily by the Castanea, Morus, Carya, Fraxinus, and Tilia. By fresh-water forms Planorbis, Valvata, and the end of this period the proportion of Melanopsis. Ostracodes include the typically steppe elements increased and steppe and fresh-water and brackish-water taxa Cypria forest-steppe landscapes appeared. kurlaevi and Cyprideis. Paleobotanic data from middle Kimmerian Mixed conifer/broad-leaved forests grew sediments indicate a warmer and more humid along the northern Black Sea coast at the climate than previously. During the first half beginning of this time, suggesting more of the Kimmerian, the percentage of humid conditions than earlier. Acer, Tilia, subtropical genera in the flora (Pittosporum, Fagus, and Quercus grew with more Parrotia, Nyssa, Aralia, Magnolia, Staphylea, thermophilous trees such as Pterocarya, Taxodium) increased over the levels seen Zelkova, Fraxinus, Morus, and Juglans. To the during late Pontian, suggesting that east relatively moist steppe vegetation was temperatures had increased. The maximum present. Compared with that of the
57 Kimmerian, the terrestrial vegetation of References Kuajlnik time had lower representations of broad-leaved trees and higher levels of steppe Grichuk, V.P., Zelikson, E.M., and Borisova, taxa. The climate was rather warm and O.K., 1987, Reconstrukcia klimaticheskich humid, with mean January temperature near pokozatelej rannego Kajnozoja po +4°C and July mean temperature near +22°C paleofloristicheskim dannym (The A substantial reduction of the forest area reconstruction of the climatic parameters occurred at the end of the Kuajlnik time, and of early Cenozoic by paleofloristic data), among the remaining trees pine and dark- in Klimaty Zemli v geologiceskom coniferous types (Picea, Abies, Tsuga, etc.) proschlom (Climates of the Earth on the prevailed. The diversity and number of geological past): Nauka, Moscow, p. 69- broad-leaved trees and other warmth-loving 78. species decreased. Pollen spectra of Kuajlnik deposits are close in composition to those of Iversen, J., 1944, Viscum, Hedera, and Ilex as the early Pleistocene and only rare pollen climate indicators: Geol. foren. Stockh., grains of Myricaceae, Moraceae, Rutaceae and forh., v. 66, p. 463-483. Taxodium allow us to assign these deposits to the Pliocene. Collectively, these data point to Khramov, A.N., and Cholpo, L.E., 1967, an intensification of aridification and a Paleomagnetism, Nedra, Leningrad, 252 decrease in temperature. P- This is the time of the appearance of the Chaperon fauna 1 assemblage which includes Korotkevich, E.L., 1988, Istoria formirovania many modern elements. Warmth-loving hipparionovoj fauny Vostochnoj Evropy animals (giraffes, Tapirus, Deinotherium) (The history of Hipparion fauna formation disappeared by this time and the warm- in the East Europe): Naukova Dumka, moderate types (apart from Archidiscodon, Kiev, 160 p. Equus, Cervus, Dicerorinus etruscus, etc.) occured more widely (Korotkevich,1988). Medianik, S.I., 1985, Palynologicheskaya Fauna data indicate arid climatic conditions harakteristika ponticheskich otlozenij u s. and small mammal assemblages indicate Vinogradovka, Moldavoskoj SSR (The steppe vegetation. The climate was palynology characteristics of Pontian apparently dry with moderately warm sediments near village Vinogradovka, temperatures (January about +4°C; July Moldavskaya SSR): Proceedings of the +22°C). Academy of Science of Modvava, v. 10, p. 55-58. Conclusions Negru, A.G., 1986, Poznemiocenovaya flora In the beginning of the Pliocene forest- jugo-zapada evropejskoj tchasti SSSR (po steppe vegetation covered most of the paleocarpologicheskim dannym) (The southern Russian Plain. By middle Pliocene floras of the late Miocene of the South time temperate broad-leaved forests begin to western European part of the USSR (on prevail, and by the late Pliocene increasingly the paleocarpological data)) [abs.]: arid and cold conditions led to more open Doctor's Thesis of Biology, Kischinev, 49 landscapes with steppe and forest-steppe P- vegetation. The warmest climates of the Pliocene occurred in middle Kimmerian time (-4.2 to 4.0 Ma), but warmer than modern conditions continued until approximately 2.5 Ma.
58 Shekina, N.A., 1979, Istoria flory i rastitelnosti European of the USSR in late Miocene- juga evropeiskoj chasti SSSR v pozdnem early Pliocene): Naukova Dumka, Kiev, miocene-rannem pliocene (The history of 197 p. flora and vegetation of the South
59 _50°N
_ 45° N
Figure 1. Site Locations, Southwestern Russian Plain
l.BigFontan 2. Eltigen 3. Grebenniki 4. Cherevychny 5. Vinogragovka 6. Novoelizavetovka 7. Ripa Skorcelskaya 8. Dolinskoe 9. Borisovka
60 Landscape And Climate Of The South-Central And Southeastern Russian Plain In The Pliocene
Olga K. Borisova, Russian Academy of Sciences, Moscow, Russia
Pliocene conditions on the Russian Plain are found in the southwest of Astrakhan can be reconstructed from data provided by district and in Kalmykiya, where they are many researchers over the past 50 years. represented by limestones and clays with Palynological studies were carried out on the interbedded sands and shells (the Russian Plain by Drs. E. Ananova, V. Novorossiysk substage). These sediments Grichuk, N. Shchekina, S. Syabray, N. contain rare shells of Congeria sp. and a Kovalenko, Yu. losifova and many others; variety of ostracodes: Cyprideis torosa, plant macro fossils were studied by A. Negru; Bakunella guriana and others. These deposits and faunal research was done by E. were probably formed in a brackish water Korotkevich (large mammals), V. shallow inlet of the Pontian marine basin. Topachevsky and R. Krasnenkov (small Continental deposits of the Pliocene on mammals), G. Karmishina (ostracodes), L. the southeastern Russian Plain (the Il'ina (gastropods), L. Nevesskaya and A. Kushumskaya suite) are more widespread Chepalyga (mollusks). Paleoclimatic estimates and accumulated from late Miocene through were obtained from the modern climatic the early and middle Pliocene time. These ranges of Pliocene plant taxa following the layers overlie eroded deposits of varying ages climagram methodology of V. Grichuk (1985). and origins and underlie Akchagylian marine Pliocene deposits of the south-central and layers. southeastern Russian Plain are correlated Upper Pliocene deposits in this region are with the stratigraphical sequence of the mainly of marine origin and are related to a circum-Black Sea region, which in turn is transgressions of the Caspian Sea. The correlated (on the basis of faunal and Akchagylian stage (poorly dated, but paleomagnetic data) with the Mediterranean estimated to range from 3.5 - 2.0 Ma) is stratigraphical framework. Pliocene subdivided into three substages on the basis stratigraphy of the Don Plain is not worked of mollusk and ostracode faunas and on out in detail, as the sediments of the age are palynological data. The Apsheronian stage usually of fluvial origin, and thus their (about 2.0 - 0.7 Ma) is thought to be a part of distribution is discontinuous, and detailed Pliocene in this region, although some inter-correlations are impossible. Generally researchers regard it as a part of the Pliocene deposits of this region are Eopleistocene. Apsheronian deposits are very subdivided into the Usmanskaya and widespread and are represented both by Krivoborskaya suites, which in turn include a marine and continental facies. number of subdivisions. The sediments are At the beginning of Pontian time, the mainly sands, loams and clays. The deposits Zanklian transgression united all the marine of three fluvial cycles can be found within the basins of southern Europe, including the Krivoborskaya suite, the middle one Caspian Sea. At the end of the early Pontian corresponding to the Caspian Akchagylian (-5.0 Ma) there was a major regression, and stage and the upper one to the Caspian the Caspian Sea lost its connection to the Apsheronian stage (Nalivkin, Sokolov, et ai, Black Sea. During the early Pontian in the 1986). southwestern region, forest and forest-steppe Pliocene deposits in the south-astern vegetation dominated under warm and rather Russian Plain are more widespread than on dry climatic conditions (estimated mean the Don Plain. Sediments of Pontian age January temperature was 3° C, and that of (early Pliocene, approximately 5.4 - 4.7 Ma) July 24° C). In the Don River basin steppe
61 vegetation was predominant at this time, and southeastern Russian Plain. During late only riparian forests existed in this region Kushum time, steppe vegetation was partly (Populus tremula, Alnus incana, A. glutinosa, replaced by forest-steppe and forest. Along etc.). Unfortunately the modern climatic with coniferous forests, broad-leaved ranges of these species are too broad to vegetation was widespread, with different estimate paleotemperatures from this area. species of Ulmus, Celtis, Juglans, Pterocarya, The southeastern part of the Russian Plain Liquidambar and others. The climate remained was occupied by forest-steppe and steppe warm (mean January temperature = ~ 1° C, vegetation. The climate was rather warm, as July temperature = ~ 20° C) and became more indicated by the presence of thermophilous humid. Farther to the south on coast of the mollusks and ostracodes. Caspian Sea surface Caspian Sea, shells of the heat-loving temperatures were estimated from strontium mollusks Unio and Valvata were found in the isotopes on Unio and Valvata shells to range layers of the same age, confirming the between 11° and 22° C, which is characteristic interpretation of a warm middle Pliocene. of the subtropical zone (N. Yasamanov, pers. The Caspian Sea regressed to near its comm.). modern level in the beginning of the late During the middle Pliocene (the Pliocene (a continuation of the lowering of sea Kimmerian stage of the Black Sea regional level that began in Kimmerian time), and a stratigraphy), marine basins occupied only river pattern similar to that of today was the depressions of the Black and Caspian established. A reduction of forest cover took Seas. In the circum-Black Sea region broad- place during the Kujalnik stage in the leaved forests with thermophilous elements northern Black Sea region, and forest-steppe were widespread. The reconstructed vegetation was replaced by steppe. The flora temperatures for the interval from 4.0 to 4.2 was very similar to that of today, and only the Ma are the warmest of the Pliocene, and at the presence of rare pollen grains of exotic taxa end of Kimmerian the area of forest cover was allow us to consider these layers to be of reduced due to drier climatic conditions. Pliocene age. Clearly the climate became Faunal assemblages also changed, as animals drier and cooler during the late Pliocene. typical of open landscapes, such as Equus and During the early Akchagylian substage Paracamelus, appeared. (corresponding to the Kujalnik) in the Don Middle Pliocene deposits are scattered on river basin, steppe vegetation existed with the south-central Russian Plain, and patches of riparian forests. The middle palynological data are sparse. The lower Akchagylian is marked with cooling which is Kimmerian fauna in this region includes reflected in a spread ofBetula (arboreal pollen steppe species (Cricetulus, Spalax, etc.). Later spectra are dominated by Betula in these in the Kimmerian faunal assemblage became deposits), and micromammal faunal more heat-loving and included some tropical assemblages confirm the existence of dry elements. Its composition also included open landscapes. A new stage of forest characteristic forest inhabitants (for example, expansion indicates that warming took place Pliopetaurista), which may imply more moist later in the middle Akchagylian. More humid conditions. Terrestrial mollusk faunas also conditions allowed broad-leaved trees such as point to warm climatic conditions: Quercus and Tilia to grow in this region, and thermophilous species of the forest-steppe thermophilous mollusks, including Striatura, zone were present, along with several Hawaia, Parmacella and others, were identified subtropical taxa (Striatura, Hawaia, and five in deposits of this age. species of Gastropoda). Based on these data, Profound cooling occurred in late the lower Kimmerian can be regarded as the Akchagylian time, when exotic thermo warmest part of the Pliocene. philous taxa died out. The northern part of At the beginning of the middle Pliocene Don River basin was occupied by forest- steppe landscapes dominated by steppe vegetation, while the southern part Chenopodiaceae were prevalent in the had steppe vegetation. These interpretations
62 from pollen data are confirmed by fauna greater continentality and aridity in the east assemblage that contain the steppe taxa Equus than in the west. Overall, since the time of stenonis, Paracamelus and Struthio. The final maximum warmth during the middle part of late Pliocene on the Don Plain is Pliocene Kimmerian stage a similar pattern characterized by temperate climate and toward greater continentality and aridity forest-steppe vegetation. through time can be seen in any given On the southeastern Russian Plain, late subregion of the southern Russian Plain. The Pliocene vegetation was dominated by steppe climatic oscillations on the background of this and forest-steppe. Coniferous trees were more general trend can be seen more clearly by common than broad-leaved ones in the time sequence of landscape change in the forests, and the flora included a small number southeastern Russian Plain. The middle of subtropical elements than in Kushum time. Pliocene (early Kimmerian) time can be The paleobotanical data suggest that mean regarded as the climatic optimum of the January temperature was about 0°C, and that Pliocene in the southern Russian Plain. of July was about 20°C. The ostracode For the warm global climates of the assemblages include paleoarctic taxa such as Pliocene, the highest amplitude climatic Candona and Iliocypris, indicating cooler water fluctuations were expressed in the eastern, conditions than occurred earlier in the more continental, part of the southern Pliocene. Russian Plain. In contrast, under the cold The middle part of the Akchagylian was global climates of the late Quaternary, the warmest within the late Pliocene; climatic fluctuations were greater in western vegetation was dominated by mixed Europe than in the east. coniferous-broadleaved forests, and heat- loving taxa of mollusks were abundant in the References Caspian Sea. Mean January temperature was about 2°C, that of July 21 °C. Grichuk, V.P., 1985, Reconstruction of the In the late Akchagylian a new cooling main climatic indexes on the basis of flora took place, marked by the spread of and an estimation of its accuracy, in coniferous forests of Pinus, Picea and Tsuga. Metody reconstruktaii paleoklimatov The flora became more depauperate than (Methods of paleoclimatic earlier, and increasing aridity is interpreted reconstructions): Nauka Publishing, from a spread of the steppe vegetation at the Moscow, p. 20-28 (in Russian). end of Akchagylian time. During the final part of the Pliocene (the Apsheronian stage) Nalivkin, D.V., Sokolov, B.S., Editors-in- further cooling and drying occurred on the Chief, 1986, Stratigrafiya SSSR, southeastern Russian Plain, and steppe Neogenovaya Sistema, Polutom 2 vegetation became dominated by Artemisia (Stratigraphy of the USSR, Neogene and Chenopodiaceae associations. System, v. 2), Nauka Publishing, Moscow, In general, for any stage within the 443 p. (in Russian). Pliocene the same pattern can be observed:
63 Pliocene of the Southern Russian Plain
Southwest South-Central Southeast
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Figure 1. Pliocene stages and inferred vegetation for three regions of the southern Russian Plain.
64 GCM Simulations Of The Pliocene Climate: Feedbacks, Ocean Transports, And CO2
Mark Chandler, NASA/GISS, New York, New york 10O25
Estimates of sea surface temperatures at high latitudes and diminished warming (SSTs), based on marine microfauna, reveal nearer to the equator. The GCM yields the existence of a middle Pliocene warm temperature increases up to 10°C along the period between about 3.15 and 2.85 million Arctic coasts and shows greatest warming in years ago (Dowsett et al., 1992). Terrestrial the winter. Although the original pollen records, although not as well dated, temperature increase is driven by warmer also show evidence for a warmer climate at SSTs, much of the continental interior about this same time in the Pliocene and, warming is generated by an ice-albedo further, indicate that continental moisture feedback, as reduced snow cover in the levels varied significantly from the present warmer climate increases the absorption of day. The cause of the altered climate is not solar radiation at the surface during winter known with certainty, but sensitivity months [figure 2], Further warming at high experiments, conducted using the Goddard latitudes comes from the increased levels of Institute for Space Studies General atmospheric water vapor (a greenhouse gas) Circulation Model (GISS GCM), have that are a result of the warm, ice-free ocean indicated that warmer climates, such as those conditions. Despite the generally warmer of the Pliocene, can be simulated by using climatic conditions, some areas show overall increased ocean heat transports (Rind and cooling. Notably, East Africa cools by 2 to 3° Chandler, 1991) [figure 1]. Dowsett et al C due to increased low-level cloud cover (1992) suggested that this might be the case which reflects large amounts of incoming for the Pliocene, based on the distribution of solar radiation back to space. This result is North Atlantic SSTs. consistent with the single palynological One test of this hypothesis is to supply record that exists for that region. Pliocene SSTs, together with an estimate of Model-data moisture estimates show far the terrestrial vegetation coverage, as less consistency than do the temperature boundary conditions in a GCM simulation, estimates, not a surprising result given the and to examine the temperature feedbacks complexities involved in modeling hydrologic and moisture changes that result. processes using coarse-grid numerical models Consistency between the palynological like the GISS GCM. The most common estimates of climate and the simulation discordance seems to be an underestimation results provide one level of validation for the of the increased wetness suggested by pollen GCM; the GCM then provides a method for records at several localities throughout the investigating the atmospheric processes Northern Hemisphere. The model's simple involved in maintaining the warmer climate. ground hydrology responds to the warmer Using the GISS GCM together with summer ground temperatures by drying out PRISM Northern Hemisphere ocean surface while the diminished intensity of the and vegetation boundary conditions atmospheric circulation (a result of reduced (Chandler et al., submitted; Dowsett et al., latitudinal temperature gradients) decreases submitted) we found both consistencies and the amount of moisture advected from over inconsistencies between model and data- the oceans to the continents. In the Arctic, generated paleoclimate estimates. Generally, where modern tundra environments were temperature estimates show the greatest replaced by Pliocene boreal forests, the consistency, with both model and data altered boundary conditions required that indicating significantly warmer temperatures wetter soil moisture conditions be specified.
65 The Pliocene Arctic soils remained wetter Dowsett, H. J., Cronin, T. M., Poore, R. Z., than the present day, indicating that the Thompson, R. S., Whatley, R. C, and specified wet conditions were in equilibrium Wood, A. M., 1992, Micropaleon-tological with the simulated climate. evidence for increased merid-ional heat In addition to the above experiment, transport in the North Atlantic Ocean several simulations were conducted using during the Pliocene: Science, v. 258, p. increased levels of atmospheric carbon 1133-1135. dioxide; higher CO2 amounts have also been proposed as a potential cause of the warmer Dowsett, H. J., Thompson, R. S., Barren, J. A., Pliocene climates (Crowley, 1991). Rind and Cronin, T. M., Ishman, S. E., Poore, R. Z., Chandler, (1991) pointed out that SST Willard, D. A., and Holtz, T. R., Jr., patterns such as the one seen in the Pliocene submitted, Paleoclimatic reconstructions are inconsistent with CO2 generated of a warmer Earth: PRISM Middle warming, however, it is possible that some Pliocene Northern Hemisphere Synthesis: combination of CO2 increase and ocean heat Global and Planetary Change Section of transport change could have resulted in the Palaeogeography, Palaeo-climatology, warmer Pliocene surface temperatures. Palaeoecology. Figure 3 shows the various levels of ocean heat transport required to generate the PRISM Raymo, M. E. and Rau, G., 1992. Plio- SSTs given various atmospheric CC>2 Pleistocene atmospheric CO2 levels increases. The graph indicates that with inferred from POM 313C at DSDP Site 607 modern ocean heat transports (0% increase) (Abstract). Eos, Transactions of the CC>2 levels must have been at least 1400 ppm American Geophysical Union, 1992 Fall (4.5 times the modern value) in order to Meeting Supplement, no. 73, p. 95. generate the global warming of the Pliocene. So far, estimates based on carbon isotope Rind, D., and Chandler, M.. A., 1991, measurements by Raymo and Rau (1992) Increased ocean heat transports and suggest that Pliocene CO2 levels were, at warmer climate: Journal of Geophysical most, 100 ppm greater than today. Research, v. 96, p. 7437-7461. References
Chandler, M. A., Rind, D., and Thompson, R. S., submitted, A simulation of the middle Pliocene climate using the GISS GCM and PRISM Northern Hemisphere Boundary Conditions: Global and Planetary Change Section of Palaeogeography, Palaeo- climatology, Palaeoecology.
Crowley, T. J., 1991, Modeling Pliocene Warmth: Quaternary Science Reviews, v. 10, p. 275-282.
66 Annual Ocean Heat Transports 4
3
V) 2 o a. c 1 "E (5 0 Modem Global tE o 1 Modern Atlantic Pliocene Global 2 Pliocene Atlantic 3 -90 -60 -30 0 30 60 90
Latitude
Figure 1. Pliocene and modem annual ocean heat transports for the Atlantic Ocean.
Climate Feedback Mechanisms
-36 15 30 45 60 75 90 Latitude Figure 2. Water vapor, cloud coverage, and ground albedo in the northern hemisphere as a function of latitude in the GISS pliocene GCM simulation.
67 Change in OHT vs. Change in CO,
25 .I...I...I...I...L...I....I...L...L...L.
20
15 8-o 10
^ O 3 .s 5
0
5
10 1 2345678 Carbon Dioxide (X 315 ppm)
Figure 3. Levels of ocean heat transport required to generate PRISM sea- surface temperatures at varying levels of atmospyheric CO2 concentrations.
68 Model-Model Comparisons And Data-Model Comparisons: Considerations For The PRISM Paleoclimate Study
Lisa C. Sloan, University of California-Santa Cruz, Santa Cruz, CA 94064
Because plans in the PRISM collaboration distributions of minimum, mean annual, and call for Pliocene climate simulations to be annual amplitude of surface temperature, produced by two different climate models mean annual and seasonal precipitation, soil (GISS and NCAR), a comparison of the two moisture, runoff, and total moisture models is necessary at the start. Both models (precipitation-evaporation). Statistical differ are three-dimensional general circulation ences for these fields may prove useful. Other models (GCMs) of similar design, but there climate parameters that may be of specific are important differences in specific climatic relevance to Pliocene climate in general and processes parameterized by the models, and the PRISM data base in particular should also in spatial resolution, among other factors. be examined for these present day cases. Therefore, before Pliocene results from the Comparisons between model results and two GCMs are compared in this project, the data are an integral part of the long-term models must be compared at a present day goals of PRISM. Comparisons at various baseline climate. The strengths and stages of the project will serve as the means of weaknesses of each GCM should be evaluating both model results and the documented, and differences in model synoptic mapping efforts. These comparisons performance under present day conditions will also be used to plan for future between the models and observations must interactions of climate experiments. There are be considered before the global Pliocene several factors to consider when comparing results are examined. Some of the model model results to proxy data interpretations. characteristics have been documented by First, model spatial and temporal resolutions other model users, but we need to compare will almost certainly not correspond to the the model versions that will actually be used resolutions reflected in the paleoclimate data. at each phase of the PRISM project. We This must somehow be taken into account in should also keep in mind how the individual comparisons. Second, the GCMs param model parameterizations relate to factors eterize many processes instead of explicitly thought to be important to Pliocene climate. modeling them, and this may affect the A hierarchy of comparisons of the model results in relation to data interpretations of results should be carried out. First-order climatic factors. Third, careful consideration comparison will be of global mean annual must be given to the question of what the values, at least for temperature, precipitation, proxy data have actually recorded; do pollen top of the atmosphere energy elements, and or macrofaunal assemblages most closely general model sensitivity to forcing (e.g., CO2 reflect mean annual temperature, growing doubling). Second-order comparisons of season temperature, or some other zonal averages will include comparison of quantity(ies)? This is critical when different model output fields of temperature (annual types of proxy climate information are related and seasonal), precipitation (annual and to each other and are compared to climate seasonal), sea ice, snow, zonal wind speed at model results. Last, multiple independent near and mid troposphere levels, vertical proxy indicators for a given climate velocity at midtroposphere level, and energy parameter are useful to obtain because they components. Third-order comparisons yield multiple signals for a given system. should include global (map view) This again is useful information for
69 understanding the Pliocene climate system model results. Quantitative information and its possible forcing factors. includes minimum temperature, mean annual Proxy climate data can be compared to temperature, mean annual temperature range, model results on the basis of quantitative or mean annual precipitation, and seasonal qualitative information. Qualitative precipitation, can be used as a second-order information includes wet/dry and hot/cold test of model results, indicators which provide a first-order test of
70 Use Of A High-Resolution Atmospheric Model For Simulations Of Paleoclimate
S.W. Hostetler, U.S. Geological Survey. Boulder. CO 8O3O3 F. Giorgi and G.T. Bates. National Center for Atmospheric Research. Boulder, CO 8O3O3 P.J. Bartlein, University of Oregon, Eugene. OR 97403-1218
To demonstrate the potential for using colder than the 0 ka BP control, whereas 18 ka high resolution atmospheric models to BP July temperatures were >5°K colder than reconstruct past climates, we here discuss the July control. January precipitation over briefly simulations of 18 ka BP perpetual the region was substantially greater at 18 ka January and July climate over the western BP; however, 18 ka BP July precipitation was U.S. that have been conducted with a high- not much different than 0 ka BP, except resolution (mesoscale) atmospheric model around Lakes Bonneville and Lahontan. (RegCM). RegCM, the climate version of the Analyses indicate that the hydrologic National Center for Atmospheric Research- "signal" associated with the position and Pennsylvania State University mesoscale strength of the 18 ka BP jet stream dominate model MM4, was run with a grid spacing of the hydrologic budgets of the Bonneville and 60 km, a resolution that resolves regional Lahontan basins. Lake-atmosphere feedbacks atmospheric circulations and terrestrial isolated over the Bonneville basin indicate features (e.g., coast lines, mountains, lakes) that lake-effect precipitation is a substantial that exert strong forcings on the climate of the component of the hydrologic budget in both West. The model includes a surface physics January and July; however, such feedbacks package (Biosphere Atmosphere Transfer are minor components of the "hydrologic Scheme) that couples the biosphere with the budget of Lake Lahontan. These results may atmosphere, and a fully interactive lake help to explain the relative difference in the model to simulate lake-atmosphere feedbacks sizes of the lakes at 18 ka BP. associated with Lakes Bonneville and The modeling system used in this Lahontan. simulation of 18 ka BP climate can readily be A series of 90-day 18 ka BP and O ka BP applied to studies of pre-Pleistocene climates simulations were conducted to allow to assess, for example, the effects of uplift of estimates to be made of the general climate the Rocky mountains and Colorado Plateau or and of the effect of feedbacks between the the growth and influence of large paleolakes lakes and the atmosphere. Initial and lateral such as "Lake Idaho". Application of the boundary conditions (SSTs and vertical model to the Pliocene depends on our ability profiles of temperature, humidity, wind to provide meaningful boundary conditions velocity) for the simulations were obtained (e.g., sea level and SSTs, topography, inland from 90 days of output from the water, atmospheric composition). Global paleosimulations conducted by Kutzbach and modeling now being conducted at the Guetter (1986) with the NCAR Community Goddard Institute for Space Science and Climate Model (CCMO). The surface of NCAR ultimately will result in a "consensus" RegCM included estimated distributions of 18 Pliocene climate simulation that could be ka BP vegetation, montane glaciers, the used to provide initial and lateral boundary continental ice sheet, and the area and depth atmospheric conditions for the regional of Lakes Bonneville and Lahontan. SSTs were model. Because estimates of Pliocene features fixed at the values used by Kutzbach and such as topography and the extent of inland Guetter. water are likely to remain uncertain, the Results indicate that over the west 18 ka appropriate use of the regional model would BP January air temperatures were about 2°K be to conduct a series of sensitivity tests by
71 varying, for example, model topography to Reference provide a range of output with which to compare with geologic evidence. Compari- Kutzbach, J.E. and P.J. Guetter, 1986. The sons with the data would allow further influence of changing orbital parameters refinements of the boundary conditions in the and surface boundary conditions on model, and thus allow some degree of climate simulations for the past 18,000 convergence between the geologic data and years: Journal of Atmospheric Science, v. simulated climate. In this way, it may be 43, p. 1726-1759. possible to establish plausible Pliocene climatic conditions at a regional scale.
72 The Forward-Modeling Approach In Paleoclimatic Analysis: Middle-Pliocene Vegetation Distributions In North America
Patrick J. Bartlein, University of Oregon, Eugene, OR 97403-1218
Introduction paleoclimatic analysis (of Pliocene climates in particular) will be discussed in the next Paleoclimatic analysis can be defined as the section. Following this, an example of the joint examination of the history and causes of application of the forward-modeling past climatic variations. As such, it is an approach applied to the middle-Pliocene activity distinct from the simple distribution of several plant taxa in North reconstruction or documentation of past America will be schematically illustrated. climatic variations in the absence of a specific conceptual or mathematical model of the Inverse- and forward-modeling behavior of the climate system. Paleoclimatic approaches analysis can therefore provide the information necessary for understanding how The inverse-modeling approach. The perturbations of the large-scale controls of the "bottom-up" or inverse-modeling approach climate system including those produced by has been the usual one applied in humans govern the regional and local paleoclimatic analysis. The approach is called responses. "inverse-modeling" because conceptually, the There are two general approaches in flow of cause and effect (i.e., climatic paleoclimatic analysis: an inverse-modeling, variations cause responses in paleoclimatic or reconstruction approach, and a forward- indicators) is inverted in order to infer from modeling, or hypothesis-testing approach. the responses the nature of the causes. In The first approach, which might also be called practice, individual or groups of paleoclimatic a "bottom-up" approach, is the classical one in records are interpreted in climatic terms, paleoclimatic analysis. In this approach, producing a set of climate reconstructions. paleoclimatic evidence, in the form of These reconstructions can then be used by geological or paleoecological records, is themselves (or in combination with other interpreted in climatic terms by one means or information) to, for example, make inferences another. These reconstructions are then used about the proximate or ultimate controls of to infer (usually subjectively) the nature of the the climatic variations recorded by the data. changes in the controls of climate responsible The reconstructions may also be used to for the observed patterns. The second, or compare paleoclimates simulated by a model "top-down" approach has been less frequently with the "observations" of paleoclimate at a applied in paleoclimatic analysis. In this particular time. For example, Bartlein et al. approach, ideas about the changes in the (1984) reconstructed the temporal and spatial large-scale controls of climate are applied to patterns of July temperature and annual one or more models (conceptual as well as precipitation for the midwestern United numerical) of the climate system, and the States from fossil-pollen data, and from those resulting simulations are then compared with reconstructions described a set of changes in paleoclimatic observations. This approach is atmospheric circulation that were consistent synonymous with "paleoclimatic data-model with the data. Other examples of the comparison," or "hypothesis-testing." quantitative interpretation of fossil-pollen The properties of the forward-modeling data in climatic terms are provided by approach that favor its application in Huntley and Prentice (1988), Prentice et al
73 (1991), and Bartlein and Whitlock (1993). The variable. Such information can be used to comparison of paleoclimatic simulations with indicate when an observed response of a inferred past climates ("data-model" particular indicator may not be unam comparison) is illustrated for eastern North biguously interpretable in terms of a single America over the past 18 kyr by Webb et ai climatic variable. (in press), and for North America during the The climate system itself also contributes Eocene by Sloan and Barren (1992). to indeterminacy. Two examples illustrate There are a number of conditions and the problem (Fig. 1). In the western United assumptions both statistical and ecological States at 18 ka and at 9 ka (as well as 6 ka) that must be satisfied when making similar patterns of reconstructed effective inferences from paleoclimatic data; these have moisture anomalies (relative to present) exist been discussed in detail by Sloan and Barren (Thompson et al.f in press): drier than present (1992), and Bartlein and Webb (1985). One in the Pacific Northwest and wetter than major problem that arises in the recon present in the Southwest (see also COHMAP struction approach, even if the technical Members, 1988). The likely controls of these assumptions are satisfied, is the indeterm similar patterns can be inferred from inacy of the paleoclimatic data itself: the paleoclimatic simulations (e.g. Kutzbach and specific controls of a particular paleoclimatic Wright, 1985), and differ considerably from record cannot always be uniquely or one another (see Thompson et al, in press). unambiguously determined from the data At 18 ka, the large Laurentide ice sheet split alone. In other words, even if the the jet stream in the simulations (particularly paleoclimatic reconstructions are correct, they in winter), with the southern branch of the jet alone may not reveal the controls of the past crossing the west coast south of where it does climates. at present. At the surface in the simulations, a Indeterminacy of paleoclimatic records. glacial anticyclone developed. In the Pacific Indeterminacy of paleoclimatic records arises Northwest, these circulation changes from two sources: one intrinsic to the combined to weaken the westerly (from the paleoclimatic indicators themselves, and one west) winds at the surface, and consequently related to the nature of the climate system. to reduce precipitation. In the Southwest, the The intrinsic source of indeterminacy arises southward-displaced jet stream created more because rarely will a particular biological or onshore flow, and consequently greater geological indicator of past climate reflect a precipitation. single climatic variable. Vegetation, for In the simulations for 9 ka, greater example, is determined by a number of summer insolation than present heated the climatic variables, and interactions among center of the continent and increased the these variables is typical. Vegetation is often land/ocean temperature contrast in summer. limited by its moisture requirements as well This thermal anomaly in turn affected as by temperature, and "effective moisture" circulation, strengthening the east Pacific reflects both precipitation and evapotrans- subtropical high pressure system in summer, piration. Evapotranspiration, in turn, is and producing a "heat low" over the continent determined by a number of distinct climatic (Kutzbach, 1987). The stronger subtropical variables, as well as by the properties of the high, and the greater regional-scale soil and vegetation. Consequently, it may be subsidence associated with it, consequently difficult to identify the particular individual suppressed precipitation in the Pacific or group of climatic variables that may have Northwest, while the greater onshore flow contributed to a particular feature of a (than present) into the heat low increased paleoecological record. Derivations of the summer precipitation. response functions (either empirical or The same regional paleoclimatic anomaly theoretical) of the different paleoclimatic pattern drier than present in the Pacific indicators can illustrate how a particular Northwest and wetter than present in the indicator depends on one or more controlling Southwest apparently can result from two
74 different sets of ultimate controls, and the precipitation on the west side of the ranges reconstructed pattern of effective moisture and increasing subsidence on the east side. alone cannot discriminate between the two. This mechanism would also reduce This situation exists despite the likelihood precipitation. Within the region, decreased that the precipitation anomaly was best precipitation would likely have reduced the expressed in winter in one case and in size of the very large (relative to present) summer in the other. Further paleoclimatic Pliocene lakes, further reinforcing the drying information, such as the status of the levels of trend by reducing lake-effect precipitation. former lakes (Guiot et al., 1993), or the In this second example, although the ultimate variation in abundance of plant taxa with control of the change recorded by various specific seasonal climatic requirements paleoclimatic indicators is clear, the manner (Thompson, 1988) might be used to in which the regional response is actually differentiate between the controls, but the determined is ambiguous. Both examples effective moisture pattern alone cannot show how the bottom-up, inverse-modeling provide an unambiguous identification of the approach may be inadequate when the ultimate controls in each case. objective is to discover how changes in the A second example illustrates a case in large-scale controls of climate govern regional which the ultimate control of a response climatic responses. observable in a particular paleoclimatic The forward-modeling approach. The record is clear, but there are more than one "top-down" or forward-modeling approach in proximate controls, and it is not apparent paleoclimatic analysis begins with some which or all are important. In this example, information or assumptions regarding the the specific paleoclimatic observation is the state of the large-scale controls of climate (i.e. replacement of steppe vegetation by conifers boundary conditions") and then applies these in the basins in the interior western United to a climate model. The model in turn makes States during the Pliocene, a vegetation projections of the potential response to this change unambiguously interpretable as particular configuration of the controls. The indicating a change toward drier conditions projections made by the climate model can (Thompson, 1991). The ultimate control of then be passed to an environmental "sub this trend toward dryness clearly is the uplift model" (e.g. a hydrological (Hosteller and of western North America. But there are at Giorgi, 1993), or a vegetational (Prentice et al., least two different pathways by which this 1992a) model). The output of these large-scale control can produce drier succeeding models is then compared with the conditions within the region, however, and available paleoclimatic indicators. there are intra-regional (positive) feedbacks The climate model, as well as the that can reinforce the trend as well, adding a environmental sub-models, do not need to be third pathway. At the continental scale, the numerical models; conceptual models may uplift of western North America over the past also be used (e.g. Bartlein el al., 1991), several million years gradually strengthened although these are generally viewed as the ridge in the upper-level westerly winds inferior to numerical models. One objective that now prevails over western North of the forward-modeling approach is to America (Ruddiman and Kutzbach, 1989; expose inadequacies in any model. This Raymo and Ruddiman, 1992). This information could be then used, for example, circulation change in turn would have to advocate replacement of a conceptual increased subsidence over western North model with a numerical one, or to revise America, and consequently suppressed elements of the model or the assumed state of precipitation. At the subcontinental scale, the the controls. uplift or formation of individual ranges such In an example of this approach, Webb et as the Sierra Nevada and Cascade Range al. (1987) used output from the paleoclimatic would have increased the regional-scale simulations produced by Kutzbach and rainshadows, by increasing orographic Guetter (1986) to simulate the changing
75 distribution of vegetation in eastern North changes (based in part on numerical GCM America over the past 18,000 years, as simulations, Harrison et ai, 1992). By represented by fossil-pollen data. The perturbing the present climate of the region in paleoclimatic simulations were based on the a set of sensitivity tests with a water-balance CLIMAP Project Members (1981) model, they were able to find a plausible reconstruction of sea surface temperatures configuration of precipitation, evapotran- (SSTs) and ice-sheet size for the last glacial spiration and runoff that was consistent with maximum (LGM). Although there was both the paleoclimatic data and simulations. broad-scale agreement between the The indeterminacy problem is greatly simulations and observations, for some reduced in the forward-modeling approach. locations and time intervals (i.e. the By requiring the use of models (that usually southeastern United States during the interval must be sufficient to explain the present between 18 ka and 12 ka) there was a serious climate and in turn its influence on geological mismatch between the two. There are three and biological indicators), the approach potential sources of the mismatch: 1) implicitly recognizes the multivariate nature misinterpretation of the fossil data, 2) model of the controls of the different indicators upon inadequacy, or 3) the specification of which paleoclimatic reconstructions are inappropriate boundary conditions. In this based. For example, trade-offs between such case, the discrepancy seems assignable to the large-scale controls of regional climates as third source, in specific through: a) the atmospheric circulation and insolation might adoption of the CLIMAP SSTs for the ocean be evaluated using regional- or mesoscale- adjacent to North America these show little climate models. Similarly, the application of a difference from present, particularly in the hydrological model might reveal the relative Gulf of Mexico; and b) the inclusion of a very importance of increased precipitation as large ice sheet in the model, which resulted in opposed to decreased evapotranspiration in the simulation of relatively high temperatures producing an inferred increase in effective in the southeastern U.S. produced by moisture. adiabatic heating of air that descended from Another advantage of the forward- the broad dome of the ice sheet. modeling approach is its potential for Consequently the paleoclimatic simulations in allowing comparisons between model the southeastern U.S. also differed little from simulations and paleoclimatic evidence in present, leading to the particular mismatch regions of sparse data coverage. Kutzbach that was observed. In this example, the and Guetter (1980) examined the role that the comparison of simulated paleoecological distribution of sites that register the response responses with the observed provides to large-scale controls has in reconstructing information that can be used to enhance our those controls. In their analysis, they understanding of the how the patterns examined the degree to which (controlling) recorded in the paleoclimatic data were sea-level pressure patterns could be estimated generated. using a network of sites with observations of Forward-modeling can also be iteratively temperature and precipitation responses. applied in order to resolve apparent They found that the level of explained inconsistencies among different sources of variance of the pressure patterns was paleoclimatic data. For example, Prentice et dependent on the uniformity, density and al. (1992b) were able to resolve the apparent extent of spatial coverage of the temperature inconsistency between the observations in the and precipitation sites. At "low" site densities Mediterranean region at the LGM of steppe (below those of late-Quaternary fossil-pollen vegetation (signaling dry conditions), and sites in eastern North America or western high lake levels (signaling wet conditions). Europe, and roughly equal to the density of They combined a simple numerical model of late-Quaternary sites from western North the regional-scale water balance with a America), less than half of the variance of conceptual model of atmospheric circulation January sea-level pressure patterns could be
76 explained. These results imply that where the Middle-Pliocene Vegetation density of sites with paleoclimatic evidence is Distributions in North America low, it may not be feasible to recover by inverse modeling the nature of the proximate One issue that may be addressed using controls of the climatic variations recorded at the forward-modeling approach is the those sites. comparison of different climate model Forward-modeling, in contrast, permits simulations, in order to identify which model the simulation of paleoenvironmental or particular simulation among a group is responses at a resolution determined only by "best." Such an analysis could be used to the practical limits of application of the discriminate among a number of different associated environmental sub-models. In models, in order to evaluate their ability to other words, the forward-modeling approach correctly simulate particular patterns in the could be used to generate, for example, a very data, or to determine the appropriate set of high-resolution spatial pattern of vegetation boundary conditions for a particular model types across a region, regardless of how dense that will produce a simulation consistent with the network of fossil-pollen sites in that observations. This second application is region is. Point-by-point comparisons illustrated here through simulations of the between the simulations and observations distributions of three plant taxa from North could be made where fossil data is available. America. A more telling comparison would likely result Dowsett et al. (n.d.) have compiled a data from a subjective evaluation (in light of the set of boundary conditions for the middle observed fossil-pollen data) of the predicted Pliocene that includes paleogeography, sea- vegetation pattern. surface temperatures, sea-ice and land-ice The forward-modeling approach has the extents, and surface cover. These boundary advantages of reducing the indeterminacy conditions were then used by Chandler et al. problem, and allowing paleoclimatic (n.d.) as input to the GISS (Goddard Institute hypotheses to be tested even in regions of of Space Science) general circulation model sparse coverage of paleoclimatic evidence. (GCM), to produce a simulation of middle- The inverse-modeling approach, although Pliocene climates. In the simulation of based on "observed" or "real," as opposed to Chandler et al., the concentration of carbon simulated data, suffers from indeterminacy, dioxide in the atmosphere was kept at and problems of applicability in regions of modern values, because they were not certain sparse coverage of fossil data. In summary, that CO2 concentrations during the Pliocene the forward-modeling approach can be were greater than present. This "Pliocene" applied over the entire domain of interest simulation can therefore be considered to (e.g. North America), generating predictions represent a "non-elevated-CO2" portrayal of of, for example, the past distributions of middle-Pliocene climates. Another different taxa that can be tested wherever simulation with the GISS model, performed data does exit. The inverse-modeling by Hansen et al. (1984), can be used to approach can be usefully applied in those illustrate the response of the simulated regions where data is sufficiently dense, climate to a doubling of carbon dioxide alone multiple paleoclimatic are available, and the (i.e. without any other changes in boundary assumptions that underlie the techniques conditions). This "2xCO2" simulation can used are not violated. In such regions, the approach can provide quantitative therefore be used to represent a Pliocene climate that differs from the present one only reconstructions of past climates with relatively low uncertainties. because of variations in the composition of the atmosphere. The extent to which either
77 simulation can correctly reproduce the are appropriate for simulating the broad-scale observed difference in vegetation between the distributions of plants under slowly changing middle Pliocene and present can then be used climates. to differentiate between the two controls- The response surfaces are fitted here using altered boundary conditions as opposed to a locally weighted-averaging approach elevated CC>2 in explaining the nature of the (Prentice and Solomon, 1991). The middle Pliocene climate. This example, environmental preferences of the different although rather forced, does illustrate the taxa can be illustrated by plotting the general approach of using the forward- predicted probabilities of occurrence of the modeling approach to analyze the causes of taxa on several "slices" through the climate past climates. space (Figs. 2-4). Artemisia, for example/ reaches its highest probabilities of occurrence Vegetation-Climate Relationships (indicated by shading on the figures) at And The Simulation Of Vegetation locations with relatively low July Distributions precipitation, medium July temperatures, and low January temperatures the general In the example presented here, the conditions that prevail in the lowland areas of distributions of three plant taxa were the intermountain region. simulated under three different climatic The response surfaces may be used to "scenarios." These scenarios were 1) the simulate the distributions of the different taxa observed modern climate, 2) the simulated under a particular climate by "plugging in" "Pliocene" climate, and 3) the simulated the values of the climate variables for each of "2xCO2" climate. Three taxa were selected: the 25-km grid cells and then mapping the Picea mariana (black spruce), representing the estimated probabilities of occurrence. In the boreal forest, Quercus alba (white oak), an examples here, the "Pliocene" and "2xCC>2" important constituent of the midlatitude climates that were input to the response deciduous forest, and Artemisia tridentata surfaces consisted of the simulated anomalies (sagebrush), a steppe taxon that at present is (paleoclimatic experiment minus control) abundant in the interior of western North applied to the observed modern values on the America. The ranges of these three taxa were 25-km grid. digitized from the range maps of Little (1971) and overlaid on a 25-km equal-area grid Results covering North America. Climate data (January and July temperature and The digitized range maps of each of the precipitation) were interpolated onto the three taxa are shown in the upper-left panels same grid using a procedure that of Figs. 5-7, and the simulated distributions incorporated the effects of elevation on under the present climate are shown in the climate. upper-right panels. These sets of maps Relationships between the incidence of indicate that the response surfaces are able to different plant taxa and climate are reproduce the present distributions of the summarized here using response surfaces taxa adequately. The simulated distributions (Bartlein et al., 1986; Prentice and Solomon, of the three taxa under the "Pliocene" and 1991). Response surfaces for presence- "2xCC>2" climates are shown in the lower left absence data (as obtained from range maps) and lower right panels for Figs. 5-7, illustrate the probability of occurrence of a respectively. particular taxon at different locations in the The reconstructed vegetation patterns for climate space defined by the four climatic the Pliocene (i.e. those inferred from the variables. Response surfaces represent a type paleoecological evidence) have the following of equilibrium (as opposed to dynamic) features (Dowsett et al., n.d.): Evergreen vegetation model (Prentice et al., 1993; forests (represented here by Picea) advanced Prentice and Solomon, 1991). Such models northward to the Arctic coast, while
78 maintaining their modern dominance in steppe and grassland during the Pliocene. subarctic regions. In parts of the western Under the "2xCO2" simulation, the range of interior, Picea was common, but not Artemisia is approximately the same as at dominant. Deciduous forests (represented present, while under the "Pliocene" here by Quercus) were largely at their present simulation, the range and incidence range limits during the Pliocene, but may maximum shift to the east. have extended farther north than today. Of the two simulations, the "2xCC>2" Steppe (represented here by Artemisia) was simulation produces distributions of these present across the interior of western North tree taxa that seem more consistent with the America during the Pliocene, but was vegetation reconstructions than does the possibly less abundant than at present. "Pliocene" simulation. It should be pointed Which of two climate simulations best out that neither simulation (one with Pliocene reproduces these patterns? The simulated surface boundary conditions, but no increase distributions of Picea for the "Pliocene" and in CO2, and the other with increased CO2/ "2xCO2" simulations are quite similar to one but without Pliocene surface boundary another. The distributions of Picea under both conditions) should be considered to be a "full" simulations advance at their northern edges, simulation of Pliocene climates. It is also true and there is a slight increase (although that only three taxa have been examined, and probably not significant) in Picea in the simulations of other taxa could change the Northern Rocky Mountain, region in the picture. In any case, this example shows the "Pliocene" simulation. Both simulations seem utility of the forward-modeling approach in consistent with the reconstructions (Dowsett comparing two climate-model simulations. et al., n.d.), and there is little to distinguish between them. Summary The simulated patterns of Quercus in eastern North America are quite similar In the forward-modeling approach to under the two simulations as well. Both show a northward shift in the range of the Quercus, paleoclimatic analysis, specific hypotheses about the large-scale controls of climate or the with the northward retreat of the southern climatic states that they produce are range margin slightly greater under the 2xCC>2 simulation. West of the Mississippi proposed, and used to simulate estimate the responses of different paleoenvironmental valley, however, the simulations are indicators, such as vegetation to those markedly different, with the "2xCO2" climates. These simulated responses are then simulation showing a greater northward compared to the paleoenvironmental record advance relative to present on the northern to test those hypotheses. Because this Great Plains, and the "Pliocene" simulation approach requires the specification of an showing a greater incidence on the southern explicit model that links the climatic controls Great Plains and in the interior basins of the to the environmental responses, the intermountain west, where steppe vegetation indeterminacy of the paleoclimatic indicators prevails at present. In eastern North America, is reduced. as was the case with Picea, both simulations In addition to testing specific seem consistent with the reconstructions. In paleoclimatic hypotheses, the forward- western North America, however, the high modeling approach can be used to probabilities of Quercus under the "Pliocene" discriminate among different climate models, simulation seem inconsistent with the or among different sets of boundary reconstructions. conditions for those models. In such an The simulated patterns of Artemisia differ application, the sets of paleoenvironmental more overall between the two simulations responses produced by the approach would than do the other taxa. Both patterns do show be compared to syntheses of paleoclimatic a decrease in the incidence of Artemisia, data in order to identify which simulation consistent with the reconstructions of less was most consistent with the data. This type
79 of application was illustrated here through an Chandler, M., Rind, D., and Thompson, R.S., example of the simulation of three plant taxa n.d., A simulation of the middle Pliocene by two different simulations of Pliocene climate using the GISS GCM and PRISM climates for North America. northern hemisphere boundary conditions. Acknowledgments CLIMAP Project Members, 1981, Seasonal The research was supported by the U.S. reconstructions of the earth's surface at Geological Survey's Global Change and the last glacial maximum: Geological Climate History Program and by the Climate Soc.iety of America Map and Chart Series, Dynamics Program of the National Science MC-36,p. 1-18. Foundation. Sarah L. Shafer and Bev Lipsitz helped prepare the figures. COHMAP Members, 1988, Climatic changes of the last 18,000 Years observations and References model simulations: Science v. 241, p. 1043-1052. Bartlein, P.J. and Whitlock, C, 1993, Paleoclimatic interpretation of the Elk Dowsett, H.J., Thompson, R.S., Barron, J.A., Lake pollen record, in Bradbury, J.P. and Cronin, T.M., Ishman, S.E., Poore, R.Z., Dean, W.E., eds., The Paleoenvironmental Willard, D.A., and Holtz, T.R., Jr., n.d., History of Elk Lake, A 10,000 Year Record Paleoclimatic reconstruction of a warmer of Varved Sediments in Minnesota: earth: PRISM middle Pliocene northern Geological Society of America Special hemisphere synthesis. Paper, p. 275-293. Guiot, J., de Beaulieu, J.L., Cheddadi, R., Bartlein, P.J., Anderson, P.M., Edwards, M.E., David, F., Ponel, P., and Reille, 1993, The and McDowell, P.P., 1991, A framework climate in Western Europe during the last for interpreting paleoclimatic variations in Glacial/Inter glacial cycle derived from eastern Beringia: Quaternary Inter pollen and insect remains: Palaeo- national, v. 10-12, p. 73-83 geography, Palaeoclimatology, Palaeo- ecology v. 103, p. 73-93. Bartlein, P.J., Prentice, I.C., and Webb, T. Ill, 1986, Climatic response surfaces from Hansen, J., Lacis, A., Rind, D., Russell, G., pollen data for some eastern North Fung, I., Rudey, R., and Lerner, J., 1984, American taxa: Journal of Biogeography Climate sensitivity analysis of feedback v. 13, p. 35-57. mechanisms, in Hansen, J.E., and Takahashi, T., eds., Climate Processes and Bartlein, P.J. and Webb, T. Ill, 1985, Mean July Climate Sensitivity: Geophysical temperature at 6000 yr B.P. in eastern Monograph v. 29, p. 130 -163. North America regression equations for estimates from fossil-pollen data: Harrison, S.P., Prentice, I.C., and Bartlein, P.J., Syllogeus v. 55, p. 301-342 (Climate 1992, Influence of insolation and Change in Canada 5). glaciation on atmospheric circulation in the North Atlantic sector implications of Bartlein, P.J., Webb, T. Ill, and Fieri, E.C., general circulation model experiments for 1984, Holocene climatic change in the the Late Quaternary climatology of northern Midwest: pollen-derived Europe: Quaternary Science Reviews v. estimates: Quaternary Research v. 22, p. 11, p. 283-299. 361-374.
80 Hosteller, S.W., and Giorgi, R, 1993, Use of Prentice, I.C., Cramer, W. garrison, S.P., output from high-resolution atmospheric Leemans, R., Monserud, R.A. and models in landscape-scale hydrologic Solomon, A.M., 1992, A global biome models an assess-ment: Water Resources model based on plant physiology and Research v. 29, p. 1685-1695. dominance, soil properties, and climate: Journal of Biogeography, v. 19, p. 117-134. Huntley, B. and Prentice, I.C., 1988, July temperatures in Europe 6000 years ago: Prentice, I.C., Guiot, J. and Harrison, S.P., Science v. 241, p. 687-690. 1992, Mediterranean vegetation, lake levels, and palaeoclimate at the Last Kutzbach, J.E., 1987, Model simulations of the Glacial Maximum: Nature v. 360, p. 658- climatic patterns during the deglacia-tion 660. of North America, in Ruddiman, W.F. and Wright, H.E, Jr., eds., North America and Prentice, I.C. and Solomon, A.M., 1991, Adjacent Oceans during the Last Vegetation models and global change, in Deglaciation, The Geology of North Bradley, R.S. ed., Global Changes of the America: Geological Society of America, Past: UCAR/OIES, Boulder CO, p. 365- v. K-3, p. 425-446. 383.
Kutzbach, J.E. and Guetter, P.J., 1980, On the Prentice, I.C., R.A. Monserud, T.M. Smith and design of paleoenvironmental data W.R. Emanuel, 1993, Modeling large- networks for estimating large-scale scale vegetation dynamics, in Solomon, patterns of climate: Quaternary Research A.M., and Shugart, H.H. eds., Vegetation v.l 4, p. 169-187. Dynamics and Global Change: Chapman and Hall, New York, p. 235-250. Kutzbach, J.E. and Guetter, P.J., 1986, The influence of changing orbital patterns and Raymo, M.E. and Ruddiman, W.F., 1992, surface boundary conditions on climate Tectonic forcing of late Cenozoic climate: simulations for the past 18,000 years: Nature, v. 359, p. 117-122. Journal of the Atmospheric Sciences ,v. 43, p. 1726-1759. Ruddiman, W.F. and Kutzbach, J.E., 1989, Forcing of Late Cenozoic Northern Kutzbach, J.E., and Wright, H.E., Jr., 1985, Hemisphere climate by plateau uplift in Simulation of the climate of 18,000 years southern Asia and the American West. BP-results for the North American/North Journal of Geophysical Research v. 94, no. Atlantic/European sector and comparison 18, p. 409-18,407. with the geologic record of North America: Quaternary Science Reviews, v. Sloan, L.C. and Barren, E.J., 1992, A 4, p. 147-187. comparison of Eocene climate model results to quantified paleoclimatic Little, E.L. Jr., 1971, Atlas of United States interpretations: Palaeogeography, Palaeo- Trees, vol. 1 conifers and important climatology, Palaeoecology v. 93, p. 183- hardwoods: U.S. Dept. Agriculture 202. Miscellaneous Publication no. 1146.
Prentice, I.C., Bartlein, P.J. and Webb, T. Ill, 1991, Vegetation and climate change in eastern North America since the last glacial maximum: Ecology v. 72, p. 2038- 2056.
81 Thompson, R.S., Whitlock, C, Bartlein, P.J., Webb, T. Ill, Bartlein, P.J., Harrison, S.P. and Harrison, S.P., and Spaulding, W.G., in Anderson, K.H., in press, Vegetation, press, Vegetation, lake-levels, and climate lake-levels and climate in Eastern North in the Western United States, Ch. 18, in America, Ch. 17, in Wright, H.E., Jr. et al, Wright, H.E. Jr. et al., eds., Global eds., Global Climates Since the Last Climates Since the Last Glacial Maximum: Glacial Maximum: University of University of Minnesota Press, Minnesota Press, Minneapolis, Minneapolis. Webb, T. in, Bartlein, P.J., and Kutzbach, J.E., Thompson, R.S., 1988, Western North 1987, Climatic change in eastern North America, vegetation dynamics in the America during the past 18,000 years; western United States-modes of response Comparisons of pollen data with model to climatic fluctuations, in Huntley, B., results in North America and Adjacent and Webb, T., Ill, eds., Vegetation Oceans during the Last Deglaciation, in History, Handbook of Vegetation Science, Ruddiman, W.F., and Wright, H.E., Jr., v. 7: Kluwer Academic Publishers, eds., The Geology of North America: Amsterdam, p. 415-458. Geological Society of America , v. K-3, p. 447-462. Thompson, R.S., 1991, Pliocene environments and climates in the western United States. Quaternary Science Reviews v. 10, p. 115- 132.
82 Indeterminacy of Paleoclimatic Evidence
1. Same Response Pattern / Different Ultimate Controls
18 ka 9ka large Laurentide Ice Sheet greater summer insolation V I split jet/glacial PNW ^creased land/ocean PNW / anticyclone \ SW // temperature contrast v ° vv weaker surface southward shift stronger subtropical stonger continental westerlies in jet stream high pressure system heat low I I I less onshore flow more onshore flow increased regional more onshore flow subsidence v y y v dry Pacific Northwest wet Southwest dry Pacific Northwest wet Southwest (same regional effective-moisture anomaly pattern)
2. Single Ultimate Control / Multiple Response Pathways
uplift of western North America \ continental-scale uplift subcontinental-scale uplift (Cordillera) (Sierra Nevada, Cascade Range) I stronger upper-level ridge increased orographic precipitation (west side of mountains) I increased subsidence increased regional subsidence (east side of mountains) regional-scale feedback: drier smaller lakes
reduced lake-effect precipitation steppe replaces conifer forests
Figure 1. Examples of indeterminacy of paleoclimatic evidence. Example 1 shows how the similar regional patterns of effective moisture (dry in the Pacific Northwest, wet in the southwest) can result from two different large-scale controls. See Thompson et al. (in press) for further discussion. Example 2 shows how the multiple pathways by which a single large-scale control (uplift of western North America) can produce a signal in a regional paleoclimatic indicator (i.e. steppe replacing forest in the interior western United States; see Thompson (1991) for further discussion).
83 Picea mariana
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Figure 2. Response surface for Picea mariana (black spruce). The diagram shows sixteen two-dimensional slices through a four-dimensional climate space. Each slice shows the probability of observing P. mariana as a function of January and July temperatures for the specific values of January and July precipitation given in the margin. The probabilities are shown by shading, with the lightest shade indicating zero probability. Unshaded areas represent combinations of the four variables that do not occur over North America.
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Figure 4. As in figure 2, except for Artemisia tridentata (sagebrush).
86 Picea mariana
Present Observed Present Simulated
Pliocene Simulated 2xCO2 Simulated
Figure 5. Distribution maps for Picea mariana (black spruce). The upper left-hand map shows the present distribution of P. mariana as digitized onto a 25-km grid from the range maps in Little (1971). The upper right-hand map shows the present distribution of P. mariana as simulated by plugging in the observed values of the four climate variables that define the response surface for this taxon. The probability of occurrence of this taxon at each grid point is shown by shading. The lower left-hand map shows the probability of occurrence of P. mariana as simulated by plugging in the climate values generated by the "Pliocene" simulation, and the lower right-hand map shows the probability of occurrence of P. mariana as simulated by plugging in the climate values generated by the "2xCO2" simulation. See text for details. 87 Quercus alba
Present Observed Present Simulated
Pliocene Simulated 2xCO2 Simulated
Figure 6. As in figure 5, except for Quercus alba (white oak).
88 Artemisia tridentata
Present Observed Present Simulated
Pliocene Simulated 2xCO2 Simulated
Figure 7. As in figure 5, except for Artemisia tridentata (sagebrush).
89 Acknowledgments
I thank Mary Stricker for the great help that document. Kevin Foley and Peter Schweitzer she provided in organizing the Pliocene assisted in document preparation and editing. Workshop and in the preparation of this Dick Poore, of the USGS Global Change and document. I also wish to thank Beverly Climate History Program, provided support Amato, Jill Sethaler, and Jenny Buchner for and organizational assistance for the their assistance in the preparation of this workshop.
90 Appendix I - Workshop Participants
Adam, David P. Dowsett, Harry J. U.S. Geological Survey U.S. Geological Survey Mail Stop 915,345 Middlefield Road Mail Stop 970, Menlo Park, CA 94025, USA 12201 Sunrise Valley Drive Reston, VA 22092, USA Ager, Thomas A. U.S. Geological Survey Dupont, Lydie P.O. Box 25046, MS 919 Institut fur Palynologie und Denver Federal Center Quartarwissenschaften der Universitat Denver, CO 80225, USA Wilhelm-Weber-Strafie 2, D-3400 Gottingen, Germany Barron, John A. U.S. Geological Survey Fleming, R. Parley Mail Stop 915,345 Middlefield Road U.S. Geological Survey Menlo Park, CA 94025, USA P.O. Box 25046, MS 919, Denver Federal Center Bartlein, Patrick J. Denver, CO 80225, USA Department of Geography University of Oregon Gladenkov, Andrei Eugene, OR 97403-1218 USA Institute of Lithosphere Staromonetny per. 22 Bonnefille, Raymonde Moscow 109180, Russia Laboratoire de Geologic du Quaternaire CNRS Luminy, Case 907 Graham, Alan K. 13288 Marseille cedex 09, France Biological Sciences Department Kent State University Borisova, Olga K. Kent, OH 44242, USA Institute of Geography Russian Academy of Sciences Hooghiemstra, Henry Staromonetny 29,109017 Hugo de Vries Laboratory Moscow, Russia Department of Palynology and Paleo/Actuo-Ecology Chandler, Mark Amsterdam University NASA/GISS Kruislaan318,1098SM 2880 Broadway Amsterdam, The Netherlands New York, NY 10025, USA Hostetler, Steven Cronin, Thomas M. U.S. Geological Survey U.S. Geological Survey 3215 Marine Street Mail Stop 970, Boulder, CO 80303, USA 12201 Sunrise Valley Drive Reston, VA 22092, USA Ishman, Scott E. U.S. Geological Survey de Vernal, Anne Mail Stop 970, GEOTOP 12201 Sunrise Valley Drive Universite du Quebec a Montreal Reston, VA 22092, USA Montreal H3C 3P8, Canada
91 Muhs, Daniel R. Thompson, Robert S. U.S. Geological Survey U.S. Geological Survey P.O. Box 25046, MS 424 P.O. Box 25046, MS 919, Denver Federal Center Denver Federal Center Denver, CO 80225, USA Denver, CO 80225, USA
Partridge, Timothy Willard, Debra A. Department of Palaeontology U.S. Geological Survey and Palaeoenvironmental Studies Mail Stop 970, Transvaal Museum 12201 Sunrise Valley Drive P. O. Box 413 Reston, VA 22092, USA Pretoria 0001, South Africa. Wrenn, John H. Poore, Richard Z. Center for Excellence in Palynology U.S. Geological Survey Department of Geology & Geophysics Mail Stop 955, Louisiana State University 12201 Sunrise Valley Drive Baton Rouge, LA 70803, USA Reston, VA 22092, USA Non-Workshop Participating Scott, Louis Authors Department of Botany and Genetics University of the Orange Free State Abdelmalek, Sidi-Mohamed P.O. Box 339 Institut des Sciences de la Terre Bloemfontein 9300, South Africa Universite d'Oran Es-Senia 31100 Oran, Algeria Sloan, Lisa Institute of Marine Science Bertini, Adele Applied Science Building Dipartimento di Scienze della Terra University of California at Santa Cruz 4 via G. La Pira Santa Cruz, CA 94064, USA 50121 Firenze, Italy
Sue, Jean-Pierre Bessais, Ezzedine Laboratoire de Palynologie Palynologie, ISEM Case 061, Universite de Montpellier II Universite Montpellier II F-34095 Montpellier, Cedex 5, France 34095 Montpellier Cedex 5, France
Stricker, Mary F. Challe, F. U.S. Geological Survey Laboratoire de Geologie du Quaternaire Mail Stop 955, CNRS Luminy, Case 907 12201 Sunrise Valley Drive 13288 Marseille cedex 09, France Reston, VA 22092, USA Cheddadi, Rachid Svetlitskaya, Tanya V. European Pollen Database Institute of Geography Centre Universitaire Russian Academy of Sciences 13637 Aries, France Staromonetny 29,109017 Moscow, Russia Combourieu-Nebout, Nathalie Paleontologie des Vertebres et Paleontologie Humaine Universite Paris 6 75252 Paris Cedex 05, France
92 Diniz, Filomena Guiot, Joel Departmento de Geologia Botanique Historique et Palynologie rua Escola Politecnica 58 Faculte Saint-Jerome 1294 Lisbon Codex, Portugal 13397 Marseilles Cedex 13, France
Drivaliari, Androniki Jolly, D. Palynologie, ISEM Laboratoire de Geologie du Quaternaire Universite Montpellier II CNRS Luminy, Case 907 34095 Montpellier Cedex 5, France 13288 Marseille Cedex 09, France
Duzer, Daniele Leroy, Suzanne Palynologie, ISEM IGBP, PAGES Universite Montpellier II Barenplatz2,CH-3011 34095 Montpellier Cedex 5, France Bern, Switzerland
Ferrier, Jacqueline Zheng, Zhuo Palynologie, ISEM Faculty of Geology Universite Montpellier II Zhonghshan University 34095 Montpellier Cedex 5, France 510275 Guangzhou, China
93