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New plant fossil records and paleoclimate analyses of the late Pliocene Citronelle Formation flora, U.S. Gulf Coast

Debra Z. Stults and Brian Axsmith

Plain Language Abstract

The Neogene plant fossil record is extremely poor in eastern North America, and the Citronelle Formation flora of Alabama is the only one from the late Pliocene (~ 3 million years ago). This paper includes descriptions of 23 woody flowering fossil plants from the Citronelle Formation in southern Alabama. Most of the fossils are closely related to plants still living in southern Alabama today, such as hickory, maple, and sycamore, although previous studies have documented some no longer occurring at all in North America north of Mexico. In addition to documenting the plant diversity at this time, this study attempts to reconstruct the climate. This is important, as the late Pliocene was a relatively recent time of global warmth. Two climate reconstruction techniques based on the tolerances of nearest living relatives, and two based on the leaf shapes were attempted. Surprisingly, the results overall suggest that the mean annual temperature (average) was similar to modern levels or even slightly lower, and precipitation levels were lower despite the global warmth of that time. This flora, therefore, provides a unique window on the floristic and paleoecological history of the southeastern United States.

Resumen en Español

Nuevos registros fósiles de plantas y análisis paleoclimáticos de la flora de la Formación Citronelle del Plioceno tardío, Costa del Golfo de Estados Unidos

El Plioceno tardío fue un momento importante del relativamente reciente calentamiento global, y anunció el fin del Neógeno. Sin embargo, los fósiles de plantas de esta época son poco comunes en América del Norte. Este estudio proporciona una descripción detallada de 23 taxones fósiles de plantas que representan 14 familias de angiospermas leñosas de la Formación Citronelle de finales del Plioceno tardío (Piacenziense mediano) en la costa de Alabama. Esta es la única asociación significativa de megafósiles de plantas del Plioceno tardío en el este de América del Norte, y una de las pocas de todo el Neógeno de esta región. Muchos de los megafósiles de plantas son los primeros registros de su especie, y varios están adecuadamente identificados a nivel de especie. En general, la composición florística es similar a la de la moderna Costa del Golfo. Estos resultados, junto con los registros anteriores, forman la base de las estimaciones paleoclimáticas cuantitativas obtenidas mediante el análisis del margen de la hoja (LMA), el Método de Coexistencia (CoA), la Bioclimatic Analysis/Mutual Climate Range Technique (BA/MCRT), y el programa climático de análisis multivariante de restos foliares (CLAMP). El análisis CLAMP mostró la mayor disparidad site-to-site y proporcionó valores anormalmente bajos de la media anual de temperaturas (MAT) y de la media anual de precipitaciones (MAP). Los resultados del LMA, análisis CoA, y BA/MCRT parecen mejores aproximaciones en este caso, ya que las estimaciones del clima obtenidas están más cerca de las aproximaciones independientes y los valores modernos. Los resultados de BA/MCRT MAT eran más convincentes para 18ºC. No obstante, se esperaba que los resultados MAT fuesen mayores, ya que el Piacenziense mediano fue una época de calentamiento global. Las estimaciones de precipitación por debajo de los valores modernos obtenidos en todos los análisis pertinentes son consistentes con la presencia de pino blanco en la flora Citronelle.

Palabras clave: Alabama; Piacenziense; Plioceno; Formación Citronelle; floras neógenas; paleoclima

Traducción: Enrique Peñalver

Résumé en Français

Nouveaux fossiles de plantes et analyses de paléoclimats de la flore du Pliocène récent de la formation de Citronelle, côte du Golfe des États-Unis

Le Pliocène récent était un épisode récent et important de réchauffement global, annonçant la fin de la période du Néogène. Cependant, les fossiles de plantes du Pliocène récent sont rares en Amérique du Nord. Cette étude présente des descriptions détaillées de 23 taxons de plantes fossiles représentant 14 familles d'angiospermes ligneuses provenant du Pliocène récent (Plaisancien moyen) de la formation de Citronelle sur la côte de l'Alabama. Cela représente le seul assemblage important de mégafossiles de plantes dans la partie orientale de l'Amérique du Nord, et un des seuls assemblages du Néogène de cette région. Cet assemblage comprend de nombreuses premières occurrences, et plusieurs sont identifiées de manière certaine au niveau spécifique. Globalement, la composition de cette flore est similaire à celle de la côte actuelle du Golfe. Ces découvertes, combinées aux précédents signalements, forment la base d'estimations quantitatives des paléoclimats utilisant l'analyse du bord des feuilles (LMA, « Leaf Margin Analysis »), l'Approche de Coexistence (CoA, « Coexistence Approach »), l'Analyse Bioclimatique/la Technique des Amplitudes Climatiques Mutuelles (BA/MCRT, « Bioclimatic Analysis/Mutual Climate Range Technique »), et le programme multivarié feuilles-climats (CLAMP, « climate leaf multivariate program »). L'analyse du CLAMP a obtenu la disparité inter-sites la plus importante et a fourni des valeurs de températures moyennes annuelles (TMA) et de précipitations moyennes actuelles (PMA) anormalement basses. Les analyses de LMA et de CoA, et les résultats de la BA/MCRT sont probablement de meilleurs indicateurs dans ce cas, car les estimations climatiques obtenues sont plus proches des valeurs actuelles et de celles obtenues par des indicateurs indépendants. Les résultats de TMA de la BA/MCRT sont les plus crédibles avec une estimation à 18°C. Néanmoins, des résultats de TMA plus élevées étaient attendus, car le Plaisancien moyen était une période globalement chaude. Les estimations de précipitations plus basses que les valeurs modernes, obtenues par toutes les analyses pertinentes, sont cohérentes avec la présence de pins blancs dans la flore de Citronelle.

Mots-clés : Alabama ; Plaisancien ; Pliocène ; formation de Citronelle ; flores néogènes ; paléoclimat

Translator: Antoine Souron

Deutsche Zusammenfassung

Neue Nachweise fossiler Pflanzen und eine paläoklimatische Analyse der spätpliozänen Citronelle Formation Flora, Golfküste, USA

Das späte Pliozän war eine wichtige Zeit mit einer relativ kurz zurückliegenden globalen Warmzeit und dem beginnenden Ende des Neogens. Pflanzenfossilien aus dieser Zeit sind jedoch in Nordamerika selten. Diese Studie liefert detaillierte Untersuchungen von 23 fossilen Pflanzentaxa, die 14 holzige Angiospermen-Familien aus der spätpliozänen (mittleres Piacenzium) Citronelle Formation des küstennahen Alabama repräsentieren. Dies ist die einzige signifikante spätpliozäne megafossile Pflanzenassemblage aus dem östlichen Nordamerika und eine der wenigen aus dem gesamten Neogen in dieser Region. Viele sind die ersten Nachweise ihrer Art und mehrere konnten sicher bis auf das Artniveau bestimmt werden. Allgemein ähnelt die Zusammensetzung der Pflanzen der der heutigen Golfküste. Diese Ergebnisse bilden zusammen mit vorangehenden Nachweisen die Basis für quantitative paläoklimatische Schätzungen mit Blattrandanalyse (LMA), dem Koexistenz-Ansatz (CoA), der bioklimatischen Analyse/ Mutual Climate Range Technik (BA/MCRT) und dem Climate Leaf Multivariate Programm (CLAMP). Mit der CLAMP-Analyse ergaben sich die größten Unterschiede zwischen den Fundstellen und es traten ungewöhnlich niedrige Werte für die Jahresdurchschnittstemperaturen und Jahresniederschlagswerte auf. Die Ergebnisse der Analysen mit LMA, CoA und BA/MCRT sind vermutlich bessere Proxys in diesem Fall, da die erhaltenen Klimaschätzungen näher an den unabhängigen Proxys und modernen Werten liegen. Die Ergebnisse mit BA/MCRT MAT waren bei 18° am überzeugendsten. Dennoch waren höhere MAT-Ergebnisse erwartet worden, da das mittlere Piacenzium eine globale Warmzeit war. Die erhaltenen Niederschlags-Schätzungen, die bei allen relevanten Analysen unter den heutigen Werten lagen stimmen mit dem Vorkommen von Weymouth-Kiefern innerhalb der Citronelle Flora überein.

Schlüsselwörter: Alabama; Piacenzium; Pliozän ; Citronelle Formation; neogene Floren; Paläoklima

Translator: Eva Gebauer

Arabic

550 arab

Translator: Ashraf M.T. Elewa

 

 

TABLE 1. Taxa used in Coexistence Approach analysis (CoA). C.Form= Citronelle Formation combined sites, H=HMR site, LS=Lamberts Station site, PP=Perdido Park site, RB=Red Bluff site, Sc=Scarborough site, Organs recognized per taxon: P=pollen, L=leaf, F=fruit, C=catkin.

Fossil taxa C.Form H LS PP RB Sc Organ
Acer rubrum X     X   X L
Acer saccharinum X         X L
Acer sp. X   X   X   PL
Alnus sp. X X X X X   P
Betula nigra X     X   X LF
Betula sp. X   X   X   PLF
Carpinus caroliniana X     X   X LFC
Carpinus sp. X   X   X   LFC
Carya aquatica X   X     X L
Carya sp. X X X X X X PLC
Castanea sp. X     X   X L
Chenopodiaceae X X         P
Clethra sp. X     X     L
Cornus sp. X       X   F
Crataegus sp. X     X   X L
Cyrilla racemiflora X X         F
Fagus sp. X   X X   X P
Fraxinus sp. X   X   X X PL
Gaylussacia sp. X         X L
Gordonia sp. X     X     L
Ilex sp. X X   X     PL
Juglans sp. X   X X X X P
Lindera sp. X     X     L
Liquidambar styraciflua X X   X X X PL
Liriodendron X X         PL
Liriodendron tulipifera X         X L
Magnolia sp. X X   X     PL
Myrica sp. X X X   X X PL
Nyssa aquatica X     X   X LF
Nyssa sp. X X X   X X PLF
Persea sp. X     X     L
Pinus sp. X X X X X X PL
Planera aquatica X X X     X LF
Platanus occidentalis X         X LF
Platanus sp. X     X X   PLF
Populus deltoides X         X L
Populus sp. X   X   X   PL
Ptelea trifoliata X     X     L
Pterocarya sp. X         X LF
Quercus falcata X     X   X L
Quercus nigra X         X L
Quercus virginiana X     X X X LF
Quercus sp. X X X X X X PLFC
Rhus sp. X X     X   P
Rubus sp. X   X       L
Salix sp. X X X X X X PL
Sassafras sp. X     X     L
Smilax sp. X   X       L
Taxodium distichum X X X X X X PLF
Trapa sp. X     X X X F
Ulmus sp. X X X X X X PL
Vaccinium sp. X         X L
Vitis rotundifolia X     X   X LF
Vitis sp. X X     X   PLF

TABLE 2. Taxa used in Bioclimatic Analysis/Mutual Climate Range Technique (BA/MCRT).

Acer rubrum Castanea sp. Liquidambar styraciflua Platanus occidentalis Quercus sp.
Acer saccharinum Clethra sp. Liriodendron Platanus sp. Rhus sp.
Acer sp . Cornus sp. Liriodendron tulipifera Populus deltoides Salix sp.
Alnus sp. Crataegus sp. Magnolia sp. Populus sp. Sassafras sp.
Betula nigra Cyrilla racemiflora Myrica sp. Ptelea trifoliate Taxodium distichum
Betula sp. Fagus sp. Nyssa aquatica Pterocarya sp. Ulmus sp.
Carpinus caroliniana Fraxinus sp. Nyssa sp. Quercus falcata Vaccinium sp.
Carya aquatica Gordonia sp. Persea sp. Quercus nigra  
Carya sp. Ilex sp. Planera aquatica Quercus virginiana  

TABLE 3. CLAMP scoring of Citronelle Formation sites.

Leaf character Scarborough site % Perdido Park site % Combined Sites %
Lobed 14 21 17
No teeth 36 47 48
Regular teeth 49 30 35
Close teeth 14 7 10
Round teeth 14 16 13
Acute teeth 52 37 40
Compound teeth 13 5 8
Nanophyll 0 0 0
Leptophyll I 3 0 2
Leptophyll II 7 8 8
Microphyll I 19 19 22
Microphyll II 36 59 45
Microphyll III 28 14 21
Mesophyll I 3 0 2
Mesophyll II 3 0 2
Mesophyll III 0 0 0
Emarginate Apex 0 0 0
Round Apex 20 16 14
Acute Apex 62 74 69
Attenuate Apex 18 10 17
Cordate Base 39 18 25
Round Base 9 8 11
Acute Base 52 74 64
L:W <1:1 14 1 7
L:W 1-2:1 48 47 47
L:W 2-3:1 28 45 38
L:W 3-4:1 10 4 7
L:W >4:1 0 3 2
Obovate 24 26 25
Elliptic 45 49 42
Ovate 32 25 32
Completeness 88 85 88

TABLE 4. Coexistence Approach analysis (CoA) results and modern value comparisons. MAP, PWTM, PRDM, PWMM results are in mm/year. C.Form= Citronelle Formation combined sites, H=HMR site, LS=Lamberts Station site, PP=Perdido Park site, RB=Red Bluff site, Sc=Scarborough site , Baton Rouge, Mobile, and Pensacola are modern sites. See text for details.

Site MAT °C CMMT °C WMMT °C MAP PWTM PDRM PWMM
C.Form 14.4-20.8 4.3-12.6 25.6-27.9 1122-1250 142-146 50-55 99-142
HMR 13.6-21.1 4.3-13.3 25.6-27.9 961-1355 109-195 50-55 99-176
LS 13.3-21.1 -0.1-12.6 25.6-27.9 897-1258 109-146 50-55 84-142
PP 14.4-21.1 3.7-13.3 25.6-28.1 1122-1355 142-192 43-61 142-177
RB 13.3-21.1 -0.1-12.6 25.6-27.9 897-1520 109-185 50-55 84-172
Sc 13.3-20.8 0.7-12.6 25.6-27.9 1003-1250 116-146 50-61 94-142
Baton Rouge 19.8 9.9 27.9 1547 170 89 170
Mobile 19.3 10.5 27.5 1684 183 83 166
Pensacola 19.8 10.3 27.8 1580 188 89 188

TABLE 5. Citronelle Formation taxa establishing Coexistence Approach analysis (CoA) interval boundaries.

  MAP1122
250 mm
PWTM 142
46 mm
PDRM 50
55 mm
PWMM 99
142 mm
Established Min-value Persea sp. Gordonia sp. Planera aquatica Gordonia sp.
Established Max-value Carya aquatica
Populus deltoides
Carya aquatica Carpinus sp. Carya aquatica
  MAT
14.4 - 20.8°C
CMMT
4.3 - 12.6°C
WMMT
25.6 - 27.9°C
Established Min-value Gordonia sp.
Persea sp.
Quercus. virginiana
Cyrilla racemiflora
Gordonia
sp.
Persea sp.
Persea sp.
Taxodium distichum
Quercus virginiana
Established Max-value Acer sacharinium
Vaccinium sp.
Carya aquatica Cyrilla racemiflora
Nyssa
sp.

TABLE 6. Coexistence Approach analysis (CoA), Bioclimatic Analysis/Mutual Climate Range Technique (BA/MCRT), Leaf Margin Analysis (LMA) results comparisons.

Method MATºC WMMTºC
July MT
CMMTºC
Jan MT
MAP mm PWMM mm
July MP
PDRM mm
Jan MP
CoA 14.4 - 20.8 25.6 - 27.9 4.3 - 12.6 1122 - 1250 99 - 142 50 - 55
BA/MCRT 18 27 5-7.4 1190 - 1325 125 85 - 105
LMA 19.3 +/- 2.6          
Current Mobile, AL 19.3 27.5 10.5 1684 166 83

TABLE 7. CLAMP results and modern value comparisons. GRIDMet3brAZ climate values from CLAMP website (clamp.ibcas.ac.cn/ Clampset2.html). GSP (growing season precipitation) is in mm. LGS (length of growing season) is in months. Sc = Scarborough site, PP = Perdido Park, C. Form = Combined Citronelle Formation sites. a = Modern values from NOAA Climatography of the United States No. 81 (01 Alabama). b = Removed three coldest months (period between first freeze of season to last freeze of season) according to NOAA for adjusted LGS and GSP.

Site MAT C°; 2SD WMMT C°; 2SD CMMT C° 2SD LGS; 2SD GSP; 1SD
Sc 11.8; 9.5 - 14.1 23.1 1.5; -2.3 - 5.3 7.0; 5.6 - 8.4 728; 527 - 929
PP 13.9; 11.6 - 16.2 22.8 5.6; 1.8 - 9.4 7.9; 6.5 - 9.3 1055; 854 - 1256
C.Form. 13.4; 11.1 - 15.7 23.3 4.3; 0.5 - 8.1 7.7; 6.3 - 9.1 946; 745 - 1147
Mobile, AL a 19.3 27.5 10.1 12 1683
Mobile, AL b       9 1289
 

stultsDebra Z. Stults. Biology Department, University of South Alabama, Mobile, AL 36688, USA. This email address is being protected from spambots. You need JavaScript enabled to view it.

Debra Stults earned an M.S. in Biology and Ph.D. in Marine Sciences, with studies focusing on paleobotany, palynology, paleoclimatology, and paleo-CO2 atmospheric concentrations during the Late Neogene. She is currently involved in research on Upper Cretaceous through Pleistocene floras from various sites along the Mid-Atlantic to Gulf of Mexico Coastal Plains. Her primary goals center on continued paleobotanical research at the University of South Alabama. A portion of her time on campus is spent teaching biology students. The route to paleobotany was not a direct one, as a B.S. degree in Medical Technology attests. Thus, she will also continue with clinical duties at the University of South Alabama Children's and Women's Hospital.

 

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axsmithBrian Axsmith. Biology Department, University of South Alabama, Mobile, AL 36688, USA. This email address is being protected from spambots. You need JavaScript enabled to view it.

Brian Axsmith is a Professor in the Biology Department at the University of South Alabama, where he teaches Ecology and Evolution, Evolutionary Biology, and the Evolution of Vascular Plants. He is also Graduate Coordinator for the department's MS program. His main research interests are the Mesozoic paleobotany of eastern North America and China, and the Neogene of the Gulf Coastal Plain. Much of his work has dealt with the evolution of conifers, but he has worked on nearly every major group of vascular plants. When not working on fossil plants, he plays bass in several local groups. 

 

FIGURE 1. Index map of plant fossil localities of the Citronelle Formation.

figure1

FIGURE 2. Representative Aquifoliaceae through Juglandaceae from the Citronelle Formation. 1. Ilex sp. leaf (UF 19210-062063), scale bar equals 5 mm. 2. Clethra cf. alnifolia (UF 19210-062064) partial leaf, arrow indicates mucronate tooth apex, scale bar equals 5 mm. 3. Close-up of Figure 2.2 Clethra leaf, note mixed-percurrent tertiaries, scale bar equals 2.5 mm. 4. Extant Clethra alnifolia leaf from USAM herbarium for comparison with Figure 2.2, scale bar equals 5 mm. 5. Gaylussacia sp. leaf (UF 19315-062065), scale bar equals 5 mm. 6. Extant Gaylussacia sp. from USAM herbarium for comparison with Figure 2.5, scale bar equals 5 mm. 7. Vaccinium sp. leaf (UF 19315-062066), scale bar equals 5 mm. 8. Close-up of Vaccinium leaf margin from Figure 2.7 showing teeth, scale bar equals 2.5 mm. 9. Carya fruit (UF 19315 - 062068), scale bar equals 5 mm. 10. Carya sp. catkin with in situ pollen (UF 19315 - 062067), scale bar equals 5 mm. 11. Carya sp. pollen tetrad from specimen in Figure 2.10, scale bar equals 10 µm.

figure2

FIGURE 3. Representative Juglandaceae from the Citronelle Formation (continued). 1. Carya cf. aquatica leaflet (UF 19315-062069), scale bar equals 5 mm. 2. Epifluorescence micrograph of leaf from Figure 3.1, note peltate hairs, scale bar equals 125 µm. 3. Carya cf. tomentosa leaflet (UF 19315-062070), scale bar equals 2 cm. 4. Carya species #3 partial leaflet (UF 19210-062071), scale bar equals 5 mm. 5. Carya cf. aquatica leaf margin of Figure 3.1, scale bar equals 2.5 mm, 6. Carya cf. tomentosa leaf margin of Figure 3.2, scale bar equals 5 mm. 7. Carya species #3 of Figure 3.4 leaf margin, scale bar equals 2.5 mm.

figure3

FIGURE 4. Representative Lauraceae from the Citronelle Formation. 1. Lindera sp. leaf (UF 19210-062072), scale bar equals 1 cm. 2. Extant Lindera leaf from USAM herbarium for comparison with Figure 4.1, scale bar equals 1 cm. 3. Persea sp. leaf (UF 19210-062073), scale bar equals 1 cm. 4. Sassafras albidum leaf (UF 19210-062074), scale bar equals 1 cm. 5. Close-up of Figure 4.1 Lindera leaf showing high order venation, scale bar equals 2.5 mm. 6. Close-up of Figure 4.3 Persea leaf showing high order venation, scale bar equals 2.5 mm.

figure4

FIGURE 5. Representative Magnoliaceae and Oleaceae from the Citronelle Formation. 1. Liriodendron cf. tulipifera partial leaf (UF 19315-062075), scale bar equals 1 cm. 2. Close-up of Figure 5.1 Liriodendron leaf basal portion showing simple agrophic veins at arrows, scale bar equals 5 mm. 3. Magnolia cf. virginiana leaf (UF 19210-062076), scale bar equals 1 cm. 4. Close-up of Figure 5.3 Magnolia leaf showing details of fourth and fifth order veins, scale bar equals 5 mm. 5. Fraxinus sp. fruit (UF 19413-062077), scale bar equals 5 mm.

figure5

FIGURE 6. Representative Oleaceae (continued), Platanaceae, and Roseaceae from the Citronelle Formation. 1. Fraxinus leaflet (UF 19210-062078), scale bar equals 1 cm. 2. Close-up of Figure 6.1 Fraxinus leaflet showing higher order venation, scale bar equals 5 mm. 3. Platanus occidentalis leaf (UF 19210-062079), scale bar equals 1 cm. 4. Platanus occidentalis fruit (UF 19211-062080), showing persistent style at arrow, scale bar equals 1 cm. 5. Crataegus leaf species 1 (UF19315-062081) similar to C. spatulatha, scale bar equals 5 mm. 6. Close-up of Figure 6.5 Crataegus leaf showing higher order venation, scale bar equals 2.5 mm. 7. Crataegus species #2 leaf (UF 19210-062082), wedge-shaped lamina similar to C. floridana, compare with Figure 7.1 , scale bar equals 5 mm. 8. Close-up of Figure 6.7 Crataegus leaf showing higher order venation, scale bar equals 2.5 mm.

figure6

FIGURE 7. Representatives Rosaceae (continued), Salicaceae, Rutaceae, and Sapindaceae from the Citronelle Formation. 1. Extant Crataegus floridana from USAM herbarium for comparison with Figure 6. 7, scale bar equals 5 mm. 2. Rubus sp. leaf (UF 19413-062083), scale bar equals 5 mm. 3. Ptelea cf. trifoliata leaf (UF 19210- 062084), scale bar equals 5 mm. 4. Salix sp. leaf (UF 19210-062085), scale bar equals 1 cm. 5. Close-up of Figure 7.4 Salix leaf margin showing salicoid teeth, scale bar equals 2.5 mm. 6. Acer cf. rubrum basal portion of leaf (UF 19210-062087), scale bar equals 1 cm. 7. Acer cf. rubrum leaf (UF 19210-062086), scale bar equals 1 cm. 8. Extant Acer rubrum USAM herbarium for comparison with Figure 7.6-7, scale bar equals 1 cm.

figure7

FIGURE 8. Representative Sapindaceae (continued), Smilicaceae, and Ulmaceae from the Citronelle Formation. 1. Acer cf. saccharinum partial leaf (UF 19315-062088), scale bar equals 1 cm. 2. Smilax sp. partial leaf (UF 19413-062089), scale bar equals 5 mm. 3. Close-up of Figure 8.2 Smilax leaf showing higher order venation details, scale bar equals 2.5 mm. 4. Ulmus sp. leaf (UF 19413-062090), scale bar equals 5 mm. 5. Close-up of Figure 8.4 Ulmus leaf showing margin details and multiple orders of teeth, scale bar equals 2.5 mm.

figure8