NINETEEN The origin of the modern Amazon rainforest...
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Amazonia, Landscape and Species Evolution: A Look into the Past, 1st edition. Edited by C. Hoorn and F.P. Wesselingh. © 2010 Blackwell Publishing NINETEEN The origin of the modern Amazon rainforest: implications of the palynological and palaeobotanical record Carlos Jaramillo 1 , Carina Hoorn 2 , Silane A.F. Silva 3 , Fatima Leite 4 , Fabiany Herrera 1 , Luis Quiroz 5 , Rodolfo Dino 6 and Luzia Antonioli 7 1 Smithsonian Tropical Research Institute, Balboa, Republic of Panama 2 University of Amsterdam, The Netherlands 3 Instituto Nacional de Pesquisas da Amazonia-INPA, Manaus, Brazil 4 University of Brasília, Brazil 5 Smithsonian Tropical Research Institute, Balboa, Republic of Panama, and University of Saskatchewan, Canada 6 Cidade Universitária – Ilha do Fundão, Rio de Janeiro, Brazil 7 Universidade Estadual do Rio de Janeiro (UERJ), Rio de Janeiro, Brazil Abstract Northern South America harbours a highly diversified forest vegetation. However, it is not clear when this remarkable diversity was attained and how it was produced. Is the high diversity the product of a positive speciation–extinction balance that accumulated species over long time periods, or is it the product of high origination rates over short time periods, or both? Middle Cretaceous floras, although very poorly studied, are dominated by non-angiosperm taxa. By the Paleocene, pollen and macrobotanical fossils suggest that the basic phylogenetic composition and floral physiognomy of Neotropical rainforests were already present. Hence there was a profound change in Amazonian flora during the Late Cretaceous, that still needs to be documented. Levels of Paleocene diversity are much lower than those of modern tropical rainforests. By the Early Eocene, however, pollen diversity was very high, exceeding values of modern rainforests. At the Eocene- Oligocene a major drop in diversity coincided with an episode of global cooling. The palynological and palaeobotanical records of Amazonia suggest that high levels of diversity existed during the Miocene, a period when the boundary conditions for sustaining a rainforest (e.g. low seasonality, high precipitation, edaphic het- erogeneous substrate) were met. The predecessor of the present rainforest was formed during the Paleogene and Neogene when the western Amazon lowlands were affected by Andean tectonism, which radically changed drainage systems and promoted wetland development. An overall global cooling during the Neogene also may have affected the rainforest, decreasing its area and expanding adjacent savanna belts. Recent events like the Quaternary ice ages also played a role in the forest dynamics and composition, although it seems to have been minor. In this chapter we will review the main characteristics of the Neogene palynological and palaeobotani- cal records in Amazonia, and we will make some comparisons with pre- and post-Neogene records. The data indicate that the Amazonian rainforest is more likely to be a product of a dynamic geological history stretching back over the past 25 million years rather than the last few hundred thousand years. Hoorn_ch19_Final.indd 317 Hoorn_ch19_Final.indd 317 10/24/2009 1:56:59 Shobha 10/24/2009 1:56:59 Shobha
Transcript of NINETEEN The origin of the modern Amazon rainforest...
Amazonia, Landscape and Species Evolution: A Look into the Past, 1st edition. Edited by C. Hoorn and F.P. Wesselingh. © 2010 Blackwell Publishing
NINETEEN
The origin of the modern Amazon rainforest: implications of the palynological and palaeobotanical recordCarlos Jaramillo1, Carina Hoorn2, Silane A.F. Silva3, Fatima Leite4, Fabiany Herrera1, Luis Quiroz5, Rodolfo Dino6 and Luzia Antonioli7
1Smithsonian Tropical Research Institute, Balboa, Republic of Panama2University of Amsterdam, The Netherlands3Instituto Nacional de Pesquisas da Amazonia-INPA, Manaus, Brazil4University of Brasília, Brazil5Smithsonian Tropical Research Institute, Balboa, Republic of Panama, and University of Saskatchewan, Canada6Cidade Universitária – Ilha do Fundão, Rio de Janeiro, Brazil7Universidade Estadual do Rio de Janeiro (UERJ), Rio de Janeiro, Brazil
Abstract
Northern South America harbours a highly diversifi ed forest vegetation. However, it is not clear when this remarkable diversity was attained and how it was produced. Is the high diversity the product of a positive speciation–extinction balance that accumulated species over long time periods, or is it the product of high origination rates over short time periods, or both? Middle Cretaceous fl oras, although very poorly studied, are dominated by non-angiosperm taxa. By the Paleocene, pollen and macrobotanical fossils suggest that the basic phylogenetic composition and fl oral physiognomy of Neotropical rainforests were already present. Hence there was a profound change in Amazonian fl ora during the Late Cretaceous, that still needs to be documented. Levels of Paleocene diversity are much lower than those of modern tropical rainforests. By the Early Eocene, however, pollen diversity was very high, exceeding values of modern rainforests. At the Eocene-Oligocene a major drop in diversity coincided with an episode of global cooling. The palynological and palaeobotanical records of Amazonia suggest that high levels of diversity existed during the Miocene, a period when the boundary conditions for sustaining a rainforest (e.g. low seasonality, high precipitation, edaphic het-erogeneous substrate) were met. The predecessor of the present rainforest was formed during the Paleogene and Neogene when the western Amazon lowlands were affected by Andean tectonism, which radically changed drainage systems and promoted wetland development. An overall global cooling during the Neogene also may have affected the rainforest, decreasing its area and expanding adjacent savanna belts. Recent events like the Quaternary ice ages also played a role in the forest dynamics and composition, although it seems to have been minor. In this chapter we will review the main characteristics of the Neogene palynological and palaeobotani-cal records in Amazonia, and we will make some comparisons with pre- and post-Neogene records. The data indicate that the Amazonian rainforest is more likely to be a product of a dynamic geological history stretching back over the past 25 million years rather than the last few hundred thousand years.
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318 C. Jaramillo et al.
Introduction
The Cretaceous and Cenozoic history of the Neotropical rain-forest is still not well understood. Very few studies of Cretaceous Amazonian fl oras have been done. Most of the Cretaceous stud-ies have been carried out in the eastern margin of South America (e.g. Herngreen 1973, 1975; Regali et al. 1974; De Lima 1979), and most of them have focused on palynology.
Paleogene records, mainly deriving from northern South America, show that a rainforest with family-level fl oristic com-position and leaf physiognomy similar to modern Neotropical rainforests already existed by the Middle Paleocene (Wing et al. 2004; Doria et al. 2008; Herrera et al. 2008a). However, its diversity was much less than modern lowland Neotropical rainforests (Wing et al. 2004; Jaramillo et al. 2007a). The be-ginning of the Eocene shows a very rapid increase in diversity and the radiation of several Neotropical plant families. Levels of diversity by the Middle Eocene were greater than those of modern Amazonian forests (Jaramillo et al. 2006). Eocene paly-nofl oras contain a large number of pollen taxa that range into the Neogene and are more similar to each other than to the Paleocene palynofl oras. At the Eocene-Oligocene boundary a marked decrease in diversity occurred, and the number of pol-len taxa fell below modern levels. This drop correlates with a major global cooling and the beginning of the Antarctic glacia-tion (Jaramillo et al. 2006).
The Neogene was a period characterized by a changing climate, fl uctuating sea levels and tectonic instability (Zachos et al. 2001). These three phenomena all left their mark in the Amazonian land-scape and its vegetation development (see Chapter 26). Although the Neogene sedimentary record is incomplete, outcrops along the rivers and well data obtained through mineral exploration together have provided us with an insight into the vegetational history.
The record of plant diversity in the Amazons is still incomplete. Nevertheless, palynological and palaeobotanical data reveal that during the Neogene Amazonia already was covered by a highly diversifi ed and multistratifi ed forest that varied in composition and distribution over time under the infl uence of the major events (Hoorn 1993, 1994a, 1994b, 2006). The potential effect on Amazonian forests of global cooling and possible associated changing precipitation patterns over the last 5 million years is unclear. Preliminary evidence suggests a major reduction in area from that formerly covered by rainforest. Areas in northern Venezuela (e.g. Urumaco in Falcon Dept.) that were fl oristically similar to Amazonia during the Late Miocene, became isolated by the rise of the Andes and subsequently underwent a transforma-tion to dry vegetation. There was also an extensive development of tropical savannas, that further encroached on the Amazonian rainforest. The overall effect of this reduction in forested area on Amazonian vegetation is unclear, but it might have caused a loss in diversity. However, it is now evident that the Quaternary gla-cial cycles did not signifi cantly affect diversity in Amazonia (Bush 1994; Rull 2008; see also Chaper 20). Amazonian Holocene cores do not show a signifi cant change in diversity or fl oristic compo-sition. Furthermore, most of the species dated using molecular techniques indicate origination ages older than 2 million years ago (Rull 2008).
Palynology
Cretaceous Amazonia
Cretaceous sequences of intracratonic Brazilian basins are mostly characterized by terrestrial siliciclastic rocks (see Chapters 3 & 7), which often give a poor yield of palynomorphs. The Cretaceous Alter do Chão Formation forms the basal unit of the Javari Group, which represents the beginning of the fi nal sedimentation episode in the Amazonas and Solimões Basins. Fossils are rare in the pre-dominantly fl uvial Alter do Chão Formation and limited to single fi ndings. Price (1960) found a terapode tooth in the upper part of the formation in the 1-NO-1-AM well in the Amazonas Basin. Daemon & Contreiras (1971) dated the formation as Cenomanian to Maastrichtian, based on the correlation with the K-400-K-600 palynozones defi ned in the Barreirinhas Basin by Lima (1971). They also mentioned the occurrence of teeth and fragments of vertebrates in the upper part of the formation.
Daemon (1975) analysed the palynology of two wells that drilled the formation (1-NO-1-AM and 1-AC-1-AM), and esta blished an early Albian to early Cenomanian age for the lower part of the for-mation, and a late Cenomanian to Turonian age for the middle part. The upper part remained undated. The age was given by correlation with the palynostratigraphic scheme of Lima (1971) and Herngreen (1973) for the Barreirinhas Basin. Dino et al. (1999) studied 43 core samples from the Alter do Chão Formation in 1-NO-1-AM and 9-FZ-28-AM wells (Fig. 19.1). They described two sequences in the formation. The predominantly sandy lower sedimentary sequence was formed during the late Aptian-Albian from terrigenous infl uxes fed by cycles of anastomosing fl uvial systems with secondary aeo-lian reworking. At the base, unconformably overlying the Andirá Formation, there are meandering deposits with abandoned channels fi lled with clay. Those clays are rich in vegetal, amber fragments, root prints, fi sh remains, freshwater ostracods and conchostracan frag-ments. The upper sequence accumulated during the Cenomanian. It is almost entirely composed of fi ne-grained sediments that are interpreted to represent fl uvial-deltaic-lacustrine settings.
Dino et al. (1999) identifi ed two distinct palynofl oras (see Fig. 19.1). Characteristic pollen and spores from the late Aptian-Albian palynofl ora (from the lower sequence) and the Cenomanian fl ora from the upper sequence are listed in Tables 19.1& 19.2.
The Cretaceous vegetation was completely dominated by non-angiosperm taxa (ferns and gymnosperms), with very few angio-sperms, unlike modern tropical forests, which are populated chiefl y by angiosperms (Gentry 1982).The presence of large numbers of spores, pollen grains and woody fragments of terrestrial origin, as well as the absence of marine elements, suggests a strong continen-tal infl uence during the deposition of the Cretaceous Alter do Chão Formation. The low frequency of palynomorphs produced by plants better adapted to dry climates (e.g. Classopollis, Equisetosporites and Gnetaceaepollenites) suggests that the Alter do Chão Formation was not deposited under arid climatic conditions.
Paleogene northern South America
Tropical Paleogene palynology of tropical South America has been widely researched since the 1950s (Van der Hammen 1954, 1956a,
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Origin of the modern Amazon rainforest 319
1956b, 1957a, 1957b, 1958; Van der Hammen & Wymstra 1964; Van Hoeken-Klinkenberg 1964, 1966; Van der Hammen & García 1966; Gonzalez-Guzman 1967; Germeraad et al. 1968; Doubinger 1973, 1976; Regali et al. 1974; Van der Kaars 1983; Guerrero & Sarmiento 1996; Jaramillo & Dilcher 2000, 2001; Jaramillo 2002; Jaramillo et al. 2005a, 2005b, 2007a; Pardo-Trujillo et al. 2003; Jaramillo & Rueda 2004; Santos et al. 2008), and an electronic morphologi-cal database (Jaramillo & Rueda 2008) has been compiled. About 450 fossil species have been named. Most of the work has been
1-NO-1-AM9-FZ-28-AM
2-MD-1-AM
North Platform
South Platform
Central Trough
os SOUTH HINGE
A B C
63º 30' 57º 30' 51º 30'
1º 00'
3º 00'
5º 00'
51º 30'57º 30'63º 30'
1º 00'
3º 00'
5º 00'
1-AC-1-PA
Fig. 19.1 Locations of the wells analysed and key palynomorphs found in the Cretaceous Alter do Chão Formation. (a) Triorites africaensis; (b) Galeacornea causea; (c) Elateroplicites africaensis.
Table 19.1 Characteristic pollen and spores of the late Aptian-Albian palynoflora from the lower sequence of the Brazilian Alter do Chão Formation.
Araucariacites australis
A. guianensis
Afropollis jardinus
Callialasporites dampieri
Cicatricosisporites avnimelechi
Classopollis alexi
Crybelosporites pannuceus
Cyathidites australis
Dictyophyllidites harrisii
Equisetosporites ambiguus
Exesipollenites tumulus
Inaperturopollenites simplex
Klukisporites variegatus
Sergipea variverrucata
S. simplex
Spheripollenites scabratus
Table 19.2 Characteristic pollen and spores of the Cenomanian palynoflora from the upper sequence of the Brazilian Alter do Chão Formation.
Classopollis alexi
Elateroplicites africaensis (with two appendages)
Galeacornea causea
Gnetaceaepollenites similis
G. crassipolli
G. clathratus
Psilastephanosporites brasiliensis
Triorites africaensis
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320 C. Jaramillo et al.
done in Colombia, Venezuela and coastal areas of Brazil. The overall palynofl ora shows a fl uctuation in forest diversity that correlates with global temperatures. Diversity increased in periods of glo-bal warming and decreased during global cooling (Jaramillo et al. 2006). Published data also suggest the absence of extensive savan-nas and a more regional extent of the Amazonian forest reach-ing northern Colombia and Venezuela (Jaramillo 2002), possibly also the result of the slightly more southerly location of the South American continent, which resulted in the region being several degrees closer to the Equator (Pardo-Casas & Molnar 1987).
Paleogene fl oras lack the Asteraceae and have low abundances of Poaceae, which are very common in many Neogene tropical South American fl oras. Eocene fl oras also seem to have been more diverse than Early Miocene fl oras (Jaramillo et al. 2006).
The Paleogene record from the present-day Amazonian region is virtually undocumented due to the absence of outcrops of this age and because this interval has not yet been studied in available cores. Future studies can address this issue by looking at exposed deposits in the sub-Andean zone and Andes of Peru, Bolivia and Ecuador.
Neogene Amazonia
Palynological sampling locations, lithologies and processing methods
The margins of the Amazonian rivers and their overbanks are mostly covered by lush rainforest with a predominance of taxa such as Cecropia, Mauritia and Malvaceae. Occasionally, the densely forested river margins provide a glimpse of the Neogene record that forms a signifi cant part of the Amazonian subsurface. These sediments provide us with an insight into past deposition-al environments and are suitable for palynological analysis and palaeovegetation reconstructions.
The most productive sediments for palynological sampling are organic-rich clays, lignites and siltstone, which are often intercalated in the fl uvial and lacustrine sequences. A detailed impression of the vegetation development in a fl uvial system over time can be obtained by sampling at small intervals of c. 10 cm. Subsequently these samples then should be processed in the laboratory, depending on their lithology, consolidation and pres-ence of calcium carbonate. As palynological particles behave as sediment particles, a concentration of larger or smaller fragments may result, depending on the technique used (Leite 2006). In some studies a clay defl occulating technique was used (Hoorn 1993, 1994a, 1994b, 2006) whereas other studies applied hydrofl uoric acid (HF) (Rebata et al. 2006; Latrubesse et al. 2007) or a combi-nation of HF and decantation. When different processing tech-niques are used, i.e. including different mesh sizes for separating larger and smaller fragments and decanting, the palynological results may be different and, consequently, diffi cult to compare.
Biostratigraphy
Miocene sediments in western Amazonia are known as Pebas Formation (in Peru) and Solimões Formation in Brazil but also the deposits extend into Colombia and Ecuador. The Pebas/Solimões
Formation contains abundant fossiliferous levels with vertebrate, invertebrate and plant remains (e.g. Maia et al. 1977; Latrubesse et al. 2007; see also Chapters 15–18). Outcrop samples generally give a very good snapshot of palaeovegetation and its diversity. Outcrops in the Amazon often occur far apart from each other, do not extend beyond 60 m of vertical exposure, and their strata have low dipping angles. Therefore it is diffi cult to correlate between outcrops and establish their relative age. Core material offers a complementary view of the Amazonian Neogene by obtaining more complete stratigraphic successions that may not be available in outcrops.
A series of exploration wells were drilled in Amazonia during the 1970s (Maia et al. 1977) and remained stored in the Geological Service of Brazil Manaus offi ces (Brazil). These wells have pro-vided an initial biostratigraphic framework (Hoorn 1993) and are currently the subject of further study. The Neogene succession in Amazonia is very condensed, in about 300–600 m of vertical section, making the study of these sediments a complex problem because of both condensation and hiatuses.
Well data permit a subdivision into palynological zones, which have been correlated to Caribbean zonations (Germeraad et al. 1968; Lorente 1986) that have been calibrated with nanoplankton and foraminifera (Muller et al. 1987). The existing biozonation for Amazonia (Hoorn 1993) is complemented with more recent well data from Late Miocene and Pliocene intervals, as shown in Fig. 19.2.
Hoorn (1993) defi ned fi ve palynological zones in northwestern Amazonia:
Verrutricolporites 1 Acme Zone (Early Miocene);Retitricolporites2 Acme Zone (Early Miocene);Psiladiporites3 -Crototricolpites Concurrent Range Zone (late Early to early Middle Miocene);Crassoretitriletes4 Interval Zone (Middle Miocene);Grimsdalea5 Interval Zone (late Middle-early Late Miocene).
These zones were established using the palynological information of 54 samples from two wells: 1AS-4a-AM (04°23´S, 70°55´W) and 1AS-51-AM (01°51´S, 69°02´W) and were correlated with assemblages described by Lorente (1986) for northern Venezuelan sedimentary basins.
Recent palynological studies have found two additional, younger zones in northwestern Amazonian sediments (Silva et al. in press), the Asteraceae- Fenestrites zone and Psilatricolporites caribbiensis zone of Lorente (1986). The most important species for each zone are illustrated in Fig. 19.2, and an overview of taxa is provided in Table 19.3.
The Neogene Amazonian fl uvial landscape and the effect of episodic marine incursions
Early to early Middle Miocene
Mangrove fl oras dominated eastern Amazonia near Belen (Leite 2004), while fl uvial systems of local origin prevailed in western Amazonia (Hoorn 1994a), and scattered lacustrine settings existed near the incipient Andean Eastern Cordillera (Gomez et al. 2009).
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Tab
le 1
9.3
Sum
mar
y of
the
pal
ynom
orph
spe
cies
des
crib
ed f
or t
he N
eoge
ne o
f A
maz
onia
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tura
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n/s
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nia
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eog
ene)
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xon
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ffi n
ity
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gy
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uth
or*
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trile
tes
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gine
llace
aeM
onta
ne a
nd lo
wla
nd f
ores
tVa
n de
r H
amm
en 1
956
ex P
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ie 1
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baca
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tes
arar
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rens
isBo
mba
cace
ae, C
eiba
Rain
fore
st a
nd m
arsh
for
est,
low
land
Hoo
rn 1
994a
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baca
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bacu
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mba
cace
ae, P
achi
ra a
quat
ica
Rain
fore
st a
nd m
ixed
sw
amp
Mul
ler
et a
l. 19
87
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baca
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tes
baum
falk
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nd f
ores
t, a
long
cre
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and
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rent
e 19
86
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mie
ntoe
nsis
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bax
Low
land
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alo
ng c
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erso
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; Els
ik, 1
968
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mui
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baco
psis
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land
for
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ng c
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tes
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baca
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land
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ng c
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per
1960
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vain
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es c
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ton?
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der
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men
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ra 1
964
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vain
aper
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oran
thac
eae,
Hed
yosm
umM
onta
ne a
nd lo
wla
nd f
ores
tH
oorn
199
4b
Cla
vam
onoc
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tes
sp.
Palm
ae, I
riart
eaLo
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nd a
nd p
re-m
onta
ne f
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onza
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man
196
7
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vatr
ilete
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p.Se
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nella
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l. 19
74
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polle
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igia
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ps(T
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gart
194
0); N
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an 1
965
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ssie
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pert
ites
colu
mbi
anus
Legu
min
osae
, Pap
ilion
oide
aeLo
wla
nd f
ores
tD
ueña
s 19
80
Cra
ssor
etitr
ilete
s va
nraa
dsho
oven
ii
Schi
zace
ae, L
ygod
ium
mic
roph
yllu
mM
arsh
es a
nd s
wam
psG
erm
eraa
d et
al.
1968
Cric
otrip
orite
s gu
iane
nesi
sLe
idel
mey
er 1
966
Cro
totr
icol
pite
s an
nem
aria
eEu
phor
biac
eae,
Cro
ton
Low
land
and
mon
tane
for
est
Leid
elm
eyer
196
6
Cyp
erac
eaep
ollis
Cyp
erac
eae
Sava
nnas
and
sw
amps
Kru
tzsc
h 19
70
Cya
thea
cidi
ites
spp.
Cya
thea
cea
Mon
tane
reg
ion
Coo
kson
194
7 ex
Pot
onie
195
6
Del
toid
ospo
ra a
drie
nnis
Pter
idac
eae,
Acr
ostic
hum
aur
eum
Clo
se t
o m
angr
ove
vege
tatio
n(P
oton
ie &
Gel
letic
h 19
33) F
rede
rikse
n 19
73
Echi
dipo
rites
bar
beito
ensi
sPa
lmae
, Kor
thal
sia
fero
xLo
wla
nd f
ores
tM
ulle
r et
al.
1987
Echi
nosp
oris
spp
.Th
elyp
tera
ceae
-Ath
yria
ceae
-Mar
athi
acea
eK
rutz
sch
1967
Echi
perip
orite
s sp
p.M
alva
ceae
Van
der
Ham
men
& W
ymst
ra 1
964
Echi
perip
orite
s ak
anth
osVa
n de
r H
amm
en &
Wijm
stra
196
4
Echi
perip
orite
s es
tela
eM
alva
ceae
-Con
volv
ulac
eae
Coa
stal
veg
etat
ion
Ger
mer
aad
et a
l. 19
68
Echi
tric
olpo
rites
mcn
eilly
iA
ster
acea
eO
pen
vege
tatio
nG
erm
eraa
d et
al.
1968
Echi
tric
olop
orite
s sp
inos
usA
ster
acea
eO
pen
vege
tatio
nG
erm
eraa
d et
al.
1968
Echi
tric
olpo
rites
mar
iste
llae
Bom
baca
ceae
-Mal
vace
aeLo
wla
nd f
ores
tM
ulle
r et
al.
1987
Echi
trile
tes
cf. m
uelle
riSe
lagi
nella
ceae
?Re
gali
et a
l. 19
74
Ephe
drip
ites
renz
onii
Ara
ceae
, Spa
tiphy
llum
Her
bs a
nd e
piph
ytes
Due
ñas
1986
Ephe
drip
ites
sp.
Ephe
drac
eae
Dry
for
est
Bolk
hovi
tina
1953
Fene
strit
es s
pino
sus
Ast
erac
eae
Van
der
Ham
men
195
6 ex
Lor
ente
, 198
6
Fove
otril
etes
orn
atus
Rega
li et
al.
1974
Hoorn_ch19_Final.indd 322Hoorn_ch19_Final.indd 322 10/24/2009 1:57:02 Shobha10/24/2009 1:57:02 Shobha
Grim
sdal
ea m
agna
clav
ata
Palm
aeG
erm
eraa
d et
al.
1968
Het
eroc
olpi
tes
inco
mpt
usM
elas
tom
atac
eae,
Mic
onia
?C
omm
on in
Mau
ritia
und
erst
orey
(Am
azon
ia)
Van
der
Ham
men
195
6 ex
Hoo
rn 1
993
Het
eroc
olpi
tes
rotu
ndus
Com
bret
acea
e-M
elas
tom
atac
eae
Hoo
rn 1
993
Het
eroc
olpi
tes
verr
ucos
usM
elas
tom
atac
eae
Mon
tane
clo
ud f
ores
t an
d lo
wla
nd f
ores
tH
oorn
199
3
Ilexp
olle
nite
s sp
.A
quifo
liace
ae, I
lex
Mon
tane
clo
ud f
ores
t an
d lo
wla
nd f
ores
tTh
ierg
art
1937
ex
Poto
nie
1960
Jand
ufou
ria s
aem
rogi
form
is
Bom
baca
ceae
, Cat
oste
mm
aLo
wla
nd f
ores
t, a
long
cre
eks
and
river
sG
erm
eraa
d et
al.
1968
Kuy
lispo
rites
wat
erbo
lkii
Cya
thea
ceae
, Cya
thea
hor
rida
Mon
tane
reg
ion
Poto
nie
1956
Laev
igat
ospo
rites
cat
anaj
ensi
sBl
echn
acea
e, B
lech
num
Low
land
to
high
mou
ntai
ns, s
wam
ps a
nd m
arsh
esG
erm
eraa
d et
al.
1968
Mag
nape
ripor
ites
spin
osus
Gon
zale
z-G
uzm
an 1
967
Mag
nast
riatit
es g
rand
iosu
sPt
erid
acea
e, C
erat
opte
risA
quat
ic f
erns
, sha
llow
lake
s an
d riv
ers
(Ked
ves
& S
ole
de P
orta
196
3) D
ueña
s 19
80
Mar
goco
lpor
ites
vanw
ijhei
Legu
min
osae
, Cae
salp
inio
deae
, Cae
salp
inea
bo
nduc
or
coria
riaC
oast
al v
eget
atio
nG
erm
eraa
d et
al.
1968
Mat
onis
porit
es m
ulle
riM
aton
iace
ae-D
icks
onia
ceae
-Cya
thea
cea,
H
emite
liaPl
ayfo
rd 1
982
Mau
ritid
iites
fra
ncis
coi
Palm
ae, M
aurit
iaLo
wla
nd s
wam
ps(V
an d
er H
amm
en 1
956)
Van
Hoe
ken-
Klin
kenb
erg
1964
Mon
opor
opol
leni
tes
annu
latu
sPo
acea
eO
pen
vege
tatio
n an
d fl o
atin
g m
eado
ws
(Van
der
Ham
men
, 195
4) J
aram
illo
&
Dilc
her
2001
Mul
timar
gini
tes
vand
erha
mm
enii
Aca
ntha
ceae
, Tric
hant
era-
Brav
aisi
aLo
wla
nd f
ores
tG
erm
eraa
d et
al.
1968
Psila
step
hano
colp
orite
s m
arin
amen
sis
Sapo
tace
aeLo
wla
nd f
ores
tH
oorn
199
4a
Psila
step
hano
colp
orite
s m
atap
ioru
m
Hoo
rn 1
994a
Psila
step
hano
colp
orite
s sc
hnei
deri
Rhiz
opho
race
ae?
Coa
stal
man
grov
e ve
geta
tion
Hoo
rn 1
993
Perf
otric
olpi
tes
digi
tatu
sC
onvo
lvul
acea
e, M
erre
mia
Low
land
for
est
Gon
zale
z-G
uzm
an 1
967
Perin
omon
olet
es s
pp.
Asp
leni
acea
e, A
sple
nium
-The
lypt
erac
eae
(The
lypt
eris
)K
rutz
sch
1967
Peris
ynco
lpor
ites
poko
rnyi
Mal
pigh
iace
aeLo
wla
nd f
ores
tG
erm
eraa
d et
al.
1968
Podo
carp
idite
s sp
.Po
doca
rpac
eae,
Pod
ocar
pus
Mon
tane
and
low
land
for
est
Coo
kson
194
7 ex
Cou
per
1953
Poly
adop
olle
nite
s sp
p.Le
gum
inos
ae, M
imos
oide
aeLo
wla
nd f
ores
tPfl
ug
& T
hom
son
1953
Poly
adop
olle
nite
s m
aria
eLe
gum
inos
ae, M
imos
oide
ae, A
caci
aLo
wla
nd f
ores
tD
ueña
s 19
80
Poly
podi
aceo
ispo
rites
pot
onie
iPt
erid
acea
e, P
teris
Low
land
to
high
mou
ntai
nsK
edve
s 19
61
Prot
eaci
dite
s cf
. tria
ngul
atus
Sapi
ndac
eae-
Prot
eaec
eae
Lore
nte
1986
Prox
aper
tites
ter
tiaria
Ann
onac
eae,
Cre
mat
ospe
rma
Low
land
for
est
Van
der
Ham
men
& G
arci
a M
utis
196
5
(Con
tinue
d)
Hoorn_ch19_Final.indd 323Hoorn_ch19_Final.indd 323 10/24/2009 1:57:02 Shobha10/24/2009 1:57:02 Shobha
Polle
n/s
po
res
Am
azo
nia
(N
eog
ene)
Taxo
no
mic
affi
nit
yEc
olo
gy
Au
tho
r*
Psila
dipo
rites
min
imus
Mor
acea
e, F
icus
-Art
ocar
pus-
Soro
cea
Low
land
for
est
Van
der
Ham
men
& W
ijmst
ra 1
964
Psila
dipo
rites
red
unda
ntis
Mor
acea
eLo
wla
nd f
ores
tG
onza
lez-
Guz
man
196
7
Psila
mon
ocol
pite
s am
azon
icus
Palm
ae, E
uter
pePo
orly
dra
ined
soi
ls, l
owla
nd f
ores
tH
oorn
199
3
Psila
mon
ocol
pite
s na
nus
Palm
aeLo
wla
nd f
ores
tH
oorn
199
3
Psila
mon
ocol
pite
s rin
coni
iPa
lmae
Low
land
for
est
Due
ñas
1986
Psila
perip
orite
s m
inim
usA
mar
anth
acea
e-C
heno
podi
acea
eRe
gali
et a
l. 19
74
Psila
perip
orite
s m
ultip
orus
Hoo
rn 1
994b
Psila
step
hano
colp
orite
s fi s
silis
Poly
gala
ceae
Leid
elm
eyer
196
6
Psila
step
hano
porit
es h
erng
reen
iiA
pocy
nace
aeLo
wla
nd f
ores
tH
oorn
199
3
Psila
tric
olpi
tes
acer
bus
Gon
zale
z-G
uzm
an 1
967
Psila
tric
olpi
tes
anco
nis
Hoo
rn 1
994a
Psila
tric
olpi
tes
min
utus
Gon
zale
z-G
uzm
an 1
967
Psila
tric
olpi
tes
papi
lioni
form
isRe
gali
et a
l. 19
74
Psila
tric
olpi
tes
pulc
her
Wijm
stra
197
1
Lada
khip
olle
nite
s si
mpl
ex(G
onza
lez-
Guz
man
, 196
7) J
aram
illo
&
Dilc
her
2001
Psila
tric
olpo
rites
aff
. Sap
otac
eae
Sapo
tace
aeLo
wla
nd f
ores
tVa
n de
r H
amm
en 1
956
ex V
an d
er
Ham
men
& W
ijmst
ra 1
964
Psila
tric
olpo
rites
ata
laye
nsis
Hoo
rn 1
993
Psila
tric
olpo
rites
cos
tatu
sD
ueña
s 19
80
Psila
tric
olpo
rites
cra
ssoe
xina
tus
Hoo
rn 1
993
Lana
giop
ollis
cra
ssa
Thea
ecea
e, P
ellic
iera
rhi
zoph
ora
Coa
stal
man
grov
e ve
geta
tion,
beh
ind
Rhiz
opho
ra(V
an d
er H
amm
en &
Wym
stra
196
4)
Fred
erik
sen,
198
8
Psila
tric
olpo
rites
cya
mus
Van
der
Ham
men
& W
ijmst
ra 1
964
Psila
tric
olpo
rites
dev
riesi
iH
umiri
acea
e, H
umiri
aLo
wla
nd f
ores
tLo
rent
e 19
86
Psila
tric
olpo
rites
div
isus
Sapo
tace
aeLo
wla
nd f
ores
tRe
gali
et a
l. 19
74
Psila
tric
olpo
rites
exi
guus
Hoo
rn 1
993
Psila
tric
olpo
rites
gar
zoni
iH
oorn
199
3
Psila
tric
olpo
rites
labi
atus
Sapo
tace
ae, P
oute
riaRa
info
rest
, alo
ng c
reek
s an
d riv
ers
Hoo
rn 1
993
Psila
tric
olpo
rites
mag
nipo
ratu
sLe
gum
inos
ae?
Hoo
rn 1
993
Psila
tric
olpo
rites
nor
mal
isG
onza
lez-
Guz
man
196
7
Psila
tric
olpo
rites
obe
sus
Sapo
tace
aeLo
wla
nd f
ores
tH
oorn
199
3
Ranu
ncul
acid
ites
oper
cula
tus
Euph
orbi
acea
e, A
lcho
rnea
Low
land
and
mon
tane
for
est,
in A
maz
onia
al
ong
river
s(V
an d
er H
amm
en &
Wym
stra
, 196
4)
Jara
mill
o &
Dilc
her
2001
Psila
tric
olpo
rites
silv
atic
usBu
rser
acea
e-Sa
pota
ceae
Low
land
for
est
Hoo
rn 1
993
Tab
le 1
9.3
Con
tinue
d.
Hoorn_ch19_Final.indd 324Hoorn_ch19_Final.indd 324 10/24/2009 1:57:03 Shobha10/24/2009 1:57:03 Shobha
Tetr
acol
poro
polle
nite
s tr
ansv
ersa
lisSa
pota
ceae
Low
land
for
est
(Due
ñas
1980
) Jar
amill
o &
Dilc
her
2001
Psila
brev
itric
olpo
rites
tria
ngul
aris
(Van
der
Ham
men
& W
ymst
ra 1
964)
Ja
ram
illo
& D
ilche
r 20
01
Psila
tric
olpo
rites
var
ius
Due
ñas
1983
Psila
tric
olpo
rites
ven
ezue
lanu
sLo
rent
e 19
86
Psila
trile
tes
aff.
Lop
hoso
ria
Psila
trile
tes
aff.
Pyt
irogr
amm
a
Psila
trile
tes
loba
tus
Hoo
rn 1
994b
Psila
trile
tes
peru
anus
Pter
idac
eae,
Pte
ris r
angi
ferin
aLo
wla
nd t
o hi
gh m
ount
ains
Hoo
rn 1
994b
Psila
trip
orite
s co
rsta
njei
Rubi
acea
e, F
aram
ea?
Mon
tane
and
low
land
for
est
Hoo
rn 1
993
Psila
trip
orite
s de
silv
aeLe
gum
inos
ae, C
aesa
lpin
ioid
eae
Low
land
for
est
Hoo
rn 1
993
Psila
trip
orite
s sa
rmie
ntoi
Hoo
rn 1
993
Retib
revi
tric
olpi
tes
retib
olus
Leid
elm
eyer
196
6
Retib
revi
tric
olpi
tes
yava
rens
isH
oorn
199
3
Retim
onoc
olpi
tes
absy
aeM
yris
ticac
eae,
Viro
laM
arsh
and
low
land
rai
n fo
rest
Hoo
rn 1
993
Retim
onoc
olpi
tes
long
icol
patu
sPa
lmae
Low
land
for
est
Lore
nte
1986
Retim
onoc
olpi
tes
max
imus
Palm
aeLo
wla
nd f
ores
tH
oorn
199
3
Retim
onoc
olpi
tes
retif
ossu
latu
sPa
lmae
Low
land
for
est
Lore
nte
1986
Retis
teph
anop
orite
s cr
assi
annu
latu
sBo
mba
cace
ae, Q
uara
ribae
aM
arsh
and
low
land
rai
nfor
est
Lore
nte
1986
Retit
ricol
pite
s le
wis
iiW
ijmst
ra 1
971
Retit
ricol
pite
s an
toni
iG
onza
lez-
Guz
man
196
7
Retit
ricol
pite
s ca
quet
anus
Bom
baca
ceae
-Tili
acea
e?Lo
wla
nd f
ores
tH
oorn
199
4a
Retit
ricol
pite
s co
lpic
onst
rictu
sH
oorn
199
4a
Retit
ricol
pite
s de
pres
sus
Wijm
stra
197
1
Retit
ricol
pite
s la
long
atus
Wijm
stra
197
1
Retit
ricol
pite
s lo
rent
eae
Bom
baca
ceae
, Bom
bax
Low
land
for
est,
alo
ng c
reek
s an
d riv
ers
Hoo
rn 1
993a
Retit
ricol
pite
s m
aled
ictu
sG
onza
lez-
Guz
man
196
7
Retit
ricol
pite
s m
atur
usG
onza
lez-
Guz
man
196
7
Retit
ricol
pite
s si
mpl
exA
naca
rdia
ceae
?Lo
wla
nd f
ores
tG
onza
lez-
Guz
man
196
7
Retit
ricol
pite
s tu
bero
sus
Bom
bace
ae-T
iliac
eae?
Low
land
for
est
Hoo
rn 1
994a
Retit
ricol
pite
s w
ijnin
gae
Ster
culia
ceae
-Tili
acea
e?H
oorn
199
4a
Retit
ricol
porit
es c
aput
oiH
oorn
199
3
Retit
ricol
porit
es c
rass
icos
tatu
sRu
biac
eae
Mon
tane
and
low
land
for
est
Van
der
Ham
men
& W
ijmst
ra 1
964
Retit
ricol
porit
es c
rass
opol
aris
Hoo
rn 1
994a
Retit
ricol
porit
es e
llipt
icus
Van
Hoe
ken-
Klin
kenb
erg
1964
(Con
tinue
d)
Hoorn_ch19_Final.indd 325Hoorn_ch19_Final.indd 325 10/24/2009 1:57:04 Shobha10/24/2009 1:57:04 Shobha
Polle
n/s
po
res
Am
azo
nia
(N
eog
ene)
Taxo
no
mic
affi
nit
yEc
olo
gy
Au
tho
r*
Rhoi
pite
s gu
iane
nsis
Tilia
ceae
-Ste
rcul
iace
ae(V
an d
er H
amm
en &
Wym
stra
196
4)
Jara
mill
o &
Dilc
her
2001
Rhoi
pite
s hi
spid
us(V
an d
er H
amm
en &
Wym
stra
196
4)
Jara
mill
o &
Dilc
her
2001
Retit
resc
olpi
tes?
irre
gula
risEu
phor
biac
eae,
Am
anoa
Low
land
for
est,
alo
ng c
reek
s an
d riv
ers
(Van
der
Ham
men
& W
ymst
ra 1
964)
Ja
ram
illo
& D
ilche
r 20
01
Retit
ricol
porit
es k
aars
iiEu
phor
biac
eae,
Dal
echa
mpi
aLo
wla
nd f
ores
tH
oorn
199
3
Retit
ricol
porit
es la
tus
Wijm
stra
197
1
Retit
ricol
porit
es le
ticia
nus
Hoo
rn 1
993
Retit
ricol
porit
es m
ilnei
Hoo
rn 1
993
Retit
ricol
porit
es o
blat
usH
oorn
199
4a
Retit
ricol
porit
es p
oric
onsp
ectu
sLe
gum
inos
aeH
oorn
199
4a
Retit
ricol
porit
es p
ygm
aeus
Hoo
rn 1
994a
Retit
ricol
porit
es s
anta
isab
elen
sis
Hoo
rn 1
994a
Retit
ricol
porit
es s
olim
oens
isH
oorn
199
3
Retit
ricol
porit
es t
icun
eoru
mH
oorn
199
3
Retit
ricol
porit
es w
ijmst
rae
Hoo
rn 1
994a
Retit
ripor
ites
aff.
Dur
oia
Rubi
acea
eM
onta
ne a
nd lo
wla
nd f
ores
t(V
an d
er H
amm
en 1
956)
Ram
anuj
am 1
966
Retit
ripor
ites
dubi
osus
Gon
zale
z-G
uzm
an 1
967
Retis
teph
anop
orite
s an
gelic
usG
onza
lez-
Guz
man
196
7
Rugo
trile
tes
sp.
Van
der
Ham
men
195
6 ex
Pot
onie
195
6
Rugu
tric
olpo
rites
spp
.G
onza
lez-
Guz
man
196
7
Rugu
tric
olpo
rites
arc
usC
hrys
obal
anac
eae,
Lic
ania
Low
land
for
est
and
sava
nnas
Hoo
rn 1
993
Sync
olpo
rites
ani
balii
Sapi
ndac
eae
Low
land
for
est
Hoo
rn 1
994a
Step
hano
colp
ites
sp.
Pass
ifl or
acea
e?Va
n de
r H
amm
en 1
954
ex P
oton
ie 1
960
Step
hano
colp
ites
evan
sii
Mul
ler
et a
l. 19
87
Sync
olpo
rites
spp
.Va
n de
r H
amm
en 1
954
ex P
oton
ie 1
960
Sync
olpo
rites
inco
mpt
usLo
rant
hace
ae?
Van
Hoe
ken-
Klin
kenb
erg
1964
Spiro
sync
olpi
tes
spira
lisG
onza
lez-
Guz
man
196
7
Scab
ratr
ipor
ites
redu
ndan
sG
onza
lez-
Guz
man
196
7
Stria
topo
llis
cata
tum
bus
Legu
min
osae
, Cae
salp
inoi
deae
Low
land
for
est
(Gon
zale
z-G
uzm
an 1
967)
Tak
ahas
hi a
nd
Jux
1989
Sync
olpo
rites
por
icos
tatu
sM
yrth
acea
eM
onta
ne a
nd lo
wla
nd f
ores
tVa
n H
oeke
n-K
linke
nber
g 19
66
Tab
le 1
9.3
Con
tinue
d.
Hoorn_ch19_Final.indd 326Hoorn_ch19_Final.indd 326 10/24/2009 1:57:05 Shobha10/24/2009 1:57:05 Shobha
Tric
hoto
mos
ulci
tes
Palm
ae, B
actr
isLo
wla
nd f
ores
tC
oupe
r 19
53
Verr
ucat
ospo
rites
spp
.Pfl
ug
1952
ex
Poto
nie
1956
Verr
ucat
ospo
rites
usm
ensi
sPo
lypo
diac
eae,
Ste
noch
laen
a pa
lust
risTe
rres
tria
l, m
onta
ne a
nd lo
wla
nd f
ores
t(V
an d
er H
amm
en 1
956)
Ger
mer
aad
et a
l. 19
68
Verr
ucat
otril
etes
cf.
bul
latu
sC
yath
eace
ae, A
lsop
hyla
Mon
tane
reg
ion
Van
Hoe
ken-
Klin
kenb
erg
1964
Verr
utric
olpo
rites
rot
undi
poris
Van
der
Ham
men
& W
ijmst
ra 1
964
Verr
utril
etes
spp
.Va
n de
r H
amm
en 1
956
ex P
oton
ie 1
956
Zono
cost
ites
duqu
eiRh
izop
hora
ceae
, Rhi
zoph
ora
Coa
stal
man
grov
e ve
geta
tion
Ger
mer
aad
et a
l. 19
68
Zono
cost
ites
ram
onae
Rhiz
opho
race
ae, R
hizo
phor
aC
oast
al m
angr
ove
vege
tatio
nD
ueña
s 19
80
Alg
ae
Botr
yoco
ccus
Chl
orop
hyta
, Bot
ryoc
occu
sPl
ankt
onic
alg
ae, f
resh
wat
er
Pedi
astr
umC
hlor
ophy
ta, B
otry
ococ
cus
Plan
kton
ic a
lgae
, fre
sh w
ater
Mar
ine
org
anis
ms
Din
ofl a
gella
te c
ysts
Din
ofl a
gella
te c
ysts
Fres
h an
d m
arin
e w
ater
s
Fora
min
ifer
linin
gs
Rew
ork
ed
Gem
mam
onoc
olpi
tes
(Eoc
ene)
Gem
mas
teph
anop
orite
s (P
aleo
gene
)
Elat
erat
e po
llen
(Cre
tace
ous)
Acr
itarc
h (P
aleo
zoic
)
Spor
es (P
aleo
zoic
)
Retit
ricol
pite
s ty
pe 9
20
(Ven
ezue
la)
*Aut
hor
refe
renc
es a
re g
iven
in J
aram
illo
& R
ueda
(200
8).
Hoorn_ch19_Final.indd 327Hoorn_ch19_Final.indd 327 10/24/2009 1:57:05 Shobha10/24/2009 1:57:05 Shobha
328 C. Jaramillo et al.
Late Pliocene-Pleistocene
There is a large hiatus in sedimentation in Amazonia during the Pliocene to Early Pleistocene (Latrubesse et al. 2007). Subsidence in the western Amazonian basins ceased and deposition became confi ned to the increasingly incised valleys of the major rivers in the region and the Amazon Fan (see Chapter 11). Potential outcrops and borehole intervals containing Late Pliocene and Pleistocene strata may be found in the sub-Andean zone.
The Neogene of northern South America: the Urumaco region
The Urumaco Formation is formed by Upper Miocene deltaic deposits that were accumulated in the Falcon Basin, western Venezuela. Lithologically, the formation is characterized by a complex alternation of medium- to fi ne-grained sandstone, organic-rich mudstone, coal, shale and thick-bedded limestone coquinas. These sediments were deposited in a prograding strand-plain-deltaic complex. The thickness of the Formation ranges between 1100 and 1800 m (Díaz de Gamero & Linares 1989). Based on lithofacies, the formation is divided into three units. Shales of the Lower and Upper members represent deposition of low-energy suspension on the shelf and prodelta. Hummocky cross-bedded sandstones represent progradation of wave- and storm-dominated deposition in the delta front, locally overlain by massive mudstones and organic-rich fi ne-grained sediments of the interdistributary bay in the Lower member. Channelized sandstones in the Middle member represent deposition in termi-nal distributary channels. Subaquatic dunes formed the sandy fi ll of these highly incised channels. The Upper member was depos-ited mainly on the delta plain.
Palynofl oras from the Urumaco Formation are similar to Miocene fl oras from Amazonia (Table 19.4). The high degree of similarity suggests a continuation of the Amazonian forest into the Urumaco region of northwestern Venezuela during the Miocene.
The latest Miocene-Early Pliocene Codore Formation over-lies the Urumaco Formation. It is composed of grey-mottled to reddish massive-bedded mudstones interbedded with thick- to thin-bedded, massive, fi ne-grained sandstones, and fi ning-upward sequences of thick- to medium-bedded trough cross-stratifi ed, medium- to coarse-grained sandstone. The Codore Formation accumulated in a fl oodplain environment, exposed during long periods to subaerial conditions, refl ecting a fl uctuating water table. The contact between the Urumaco and Codore Formations represents a major change in the dynamics of the sedimentary environments. This change is probably related to the collapse of the gigantic Urumaco Delta during the Late Miocene and its replace-ment with red-bed deposits that show a decrease in subsidence, sediment supply, subaerial exposure and palaeosoil formation, |and possibly correlates with a major uplift of the northern Andes and the eastward shift in the course of a proto-Orinoco River (Diaz de Gamero 1996; Quiroz & Jaramillo in press). A large change has also been documented in the fi sh faunas (see Chapter 17). Floras of the Codore Formation do not resemble Miocene Amazonian palynofl oras, indicating that the Amazon-type of forest in the Urumaco region was replaced by the dry vegetation that domi-nates the region today. This change could also be correlated with
The most characteristic palynological associations in the fl uvial settings contained a wide variety of rainforest taxa belonging to families such as the Arecaceae, Melastomataceae, Sapotaceae, Euphorbiaceae, Leguminosae, Annonaceae and Malpighiaceae amongst many others (see Plate 13 & Table 19.3). The most abun-dant taxa were those nearest to the aquatic depositional environ-ment such as Mauritia (Mauritiidites), a palm that formed palm swamps, accompanied by taxa from the fl uvial overbanks such as Amanoa (Retitrescolpites? irregularis), Alchornea (Ranunculacidites operculatus) and Malvaceae (several types). The aquatic (mostly freshwater) nature of these settings is confi rmed by taxa such as the fern Ceratopteris (Magnastriatites grandiosus), a small aquatic fern bordering lakes and riverbanks (Germeraad et al. 1968) and the algae Botryococcus and Azolla. This predominantly fl uvial setting was occasionally disrupted by marine infl uence, as con-fi rmed by the presence of a brackish-water association formed by the mangrove pollen of Rhizophora (Zonocostites ramonae) and marine palynomorphs such as dinofl agellate cysts and chitinous foraminiferal test linings.
Middle to early Late Miocene
This time period is characterized by smectite-rich Andean-derived sediments and wetland expansion into western Central Amazonia. The pre-existing rainforest was fragmented and extensive wetlands developed. Palynologically, this period is characterized by an increment in the diversity of fern spores, increase of grasses (Monoporopollenites annulatus) and a pre-dominance of palms such as Mauritia, Grimsdalea magnaclavata an extinct taxon, Euterpe and Korthalsia. The palynological assem-blage also includes taxa indicative of an Andean source such as Podocarpus, Hedyosmum, Cyatheaceae, Hemitelia and Alsophyla. Episodic marine intervals are characterized by Rhizophora (Zonocostites ramonae) and marine palynomorphs (see Plate 13 & Table 19.3). There are several intervals with fl uvial environments with tidal infl uence prevailing, although the aquatic environment was predominantly freshwater. The latter environments were dominated by grasses (Monoporopollenites annulatus), Asteraceae (Echitricolporites spinosus) and ferns (Hoorn 1993, 1994b).
Late Miocene-Early Pliocene
The fi nal part of the Neogene Amazonian sedimentary record is represented in the Late Miocene to Early Pliocene sediments in the Acre and Amazonas states (Brazil). Palynological data suggest a diverse and well-structured forest with pollen types belonging to species from all forest strata, including grasses, herbs (Gomphrena), understorey (Rauvolfi a) and canopy species (Geissospermum, Sapium) as well as diverse types of climbing ferns (Lygodium) and epiphytes (Polypodium) (see Plate 13 & Table 19.3). The Amazon river landscape was well established by this time – the environmental stability allowed extensive development of the Amazon terra fi rme forest. Approximately 30 plant families have been identifi ed in this time period, with a predominance of Arecaceae, Poaceae, Malvaceae, Euphorbia-ceae (Alchornea), Malpighiaceae, Humiriaceae (Humiria) and Melastomataceae (Miconia).
Hoorn_ch19_Final.indd 328Hoorn_ch19_Final.indd 328 10/24/2009 1:57:06 Shobha10/24/2009 1:57:06 Shobha
Table 19.4 Pollen and sporomorph taxa shared between the Upper Miocene Urumaco Formation of Venezuela and Miocene deposits of western Amazonia.
Bombacacidites araracuarensis
B. baculatus
B. brevis
B. muinaneorum
B. nacimientoensis
B. psilatus
Burseraceae undifferentiated
Catostemma type
Chenopodipollis spp.
Clavainaperturites microclavatus
Crassiectoapertites columbianus
Crassoretitriletes vanraadshooveni
Cyatheacidites annulatus
Cyclusphaera scabrata
Deltoidospora adriennis
Echidiporites barbeitoensis
Echiperiporites akanthos
E. estelae
Echitricolporites maristellae
E. spinosus
Echitriletes muelleri
Fenestrites longispinosus
F. spinosus
Foveotriletes ornatus
Grimsdalea magnaclavata
Heterocolpites incomptus
Jandufouria seamrogiformis
Kuylisporites waterbolkii
Laevigatosporites catanejensis
Lanagiopollis crassa
Magnastriatites grandiosus
Malvacipollis spp.
Margocolporites vanwijhei
Mauritiidites franciscoi franciscoi
M. franciscoi minutus
Melastomataceae type
Monoporopollenites annulatus
Multimarginites vanderhammenii
Pachydermites diederixi
Perfotricolpites digitatus
Perisyncolporites pokornyi
Polyadopollenites mariae
Proteacidites triangulatus
Psilabrevitricolporites triangularis
Psilamonocolpites medius
P. nanus
P. operculatus
P. rinconii
Psilaperiporites minimus
P. multiporatus
P. robustus
Psilastephanocolporites matapiorum
Psilatricolporites caribbiensis
P. costatus
P. devriesii
P. divisus
P. labiatus
P. magniporatus
P. pachydermatus
P. silvaticus
P. vanus
P. venezuelanus
Retitricolpites colpiconstrictus
R. simplex
R. amazonensis
R. caputoi
R. fi nitus
R. kaarsii
R. marianis
R. oblatus
R. poriconspectus
R. santaisabelensis
R. ticuneorum
Retitriletes sommeri
Retitriporites dubiosus
Rhoipites guianensis
R. hispidus
R. squarrosus
Rugutricolporites arcus
Tetracolporopollenites maculosus
T. transversalis
Zonocostites ramonae
Hoorn_ch19_Final.indd 329Hoorn_ch19_Final.indd 329 10/24/2009 1:57:06 Shobha10/24/2009 1:57:06 Shobha
330 C. Jaramillo et al.
vegetation and climate, and it has been studied from Quaternary deposits of the Amazon Fan (Piperno 1997). It may be pos-sible to recover phytoliths from older Amazonian rocks if new techniques are applied, as has been done in Eocene rocks from North America (Strömberg 2004).
Evidence of pre-Miocene rainforests in South America
The fossil record of South American fl oras has been compiled previously (Romero 1993; Burnham & Graham 1999; Burnham & Johnson 2004). All evidence collected from macro and micro fossils suggests that during the Eocene, Neotropical rainfor-ests became established in terms of physiognomy, diversity and fl oristic composition. Pre-Eocene evidence for rainforests in South America is scant; however, recent work in Colombia has revealed that these biomes have been present at least since the Late Cretaceous. A Maastrichtian assemblage known as Guaduas fl ora from the central Andes of Colombia, located today at about 2700 m above sea level, has shown that a rainforest was already established (Gutierrez & Jaramillo 2007). This fl ora is still being studied, but preliminary analyses show that leaf physiognomy was dominated by mesophyll-macrophyll leaf sizes with brochido-dromous-eucamptodromous venation and entire margins, there-fore suggesting a warm and wet palaeoclimate, as is seen in today’s tropical rainforest. However, the Guaduas fl ora lacks key fl ori-stic elements that are present in modern Neotropical fl oras (e.g. legumes).
A second assemblage from Colombia is the Cerrejón fl ora (Wing et al. 2004), found in outcrops from Guajira Peninsula and excavated in the open-pit Cerrejón coal mine. This fl ora is Middle-Late Paleocene in age, and it was deposited in ancient lagoonal and fl ooded coastal plains environments (Jaramillo et al. 2007a). The palaeoclimate has been reconstructed from leaf margin and area analysis, giving a mean annual palaeotemperature in excess of 29°C and an annual precipitation greater than 4 m (Herrera et al. 2008b). Floristically, the fl ora is indistinguishable from liv-ing Neotropical fl oras and is dominated by Fabaceae, Arecaceae, Malvaceae, Lauraceae, Araceae, Zingiberales, Menispermaceae, Euphorbiaceae, Annonaceae, Anacardiaceae, Meliaceae and Flacourtiaceae (Doria et al. 2008; Herrera et al. 2008a, 2008b).
These two macrofl oras from Colombia are remarkable evi-dence of ancient tropical biomes, both showing that rainforest leaf physiognomy was established during the early stages of the rainforests in northern South America. Both fl oras also have low plant diversity (Gutierrez & Jaramillo 2007; Jaramillo et al. 2007a; Herrera et al. 2008b).
Macrofossil plant records from the Miocene of the Amazonia
The records of plant macrofossils from Miocene Amazonian deposits are relatively sparse. This is due to vegetation cover of possible outcrops. Furthermore, little attention has been paid in the past to wood and leaf remains, which are commonly men-tioned in stratigraphic studies of Miocene and younger rocks (Hoorn 1994b, 2006; Rossetti & Goes 2004; Campbell et al. 2006;
the extensive development of the tropical savannas in the latest Miocene, which shrunk the rainforest to its modern extent.
Palaeobotany
Plant fossils as a potential tool to reconstruct the Amazon rainforest
Macrofossil plant remains, mostly leaves, woods and seeds, have been widely reported throughout the Amazon drainage basin from Miocene to Quaternary deposits (Hoorn 1994b, 2006; Rossetti & Goes 2004; Campbell et al. 2006; Antoine et al. 2006, Goillot et al. 2007; Latrubesse et al. 2007; Pons & De Franceschi 2007; Olivier et al. 2008). However, only a few plant localities have been extensively collected and studied (Rossetti & Goes 2004; Pons & De Franceschi 2007). Here we briefl y highlight several palaeobotanical methods that should be kept in mind for future studies from Amazonia.
Leaves are among the most abundant fossil remains in fl uvial and lacustrine environments (Burnham et al. 1992), and dicot fossil leaves could be used to reconstruct the palaeoclimate. Leaf margin and area analyses (Wolfe 1979; Wilf 1997; Wilf et al. 1998) can, respectively, be used to reconstruct past mean annual tem-peratures and precipitation. These methods are based on modern correlations that relate margin and area of dicot leaves to climatic parameters. A new method, which relates the area of the fossil leaves to the extant scaling relationship between petiole width squared and leaf mass (Royer et al. 2007), could also be used to reconstruct quantitatively the mean annual precipitation for the Amazon forest in the past.
The macrofossil plant record also could give us clues about the origin and age of the high plant diversity of Amazonia, which is perhaps one of the most discussed topics in angiosperm evolu-tion. For instance, fossil fl owers, seeds, fruits, leaves and wood can be used to assess plant diversity in the geological past (Wing et al. 1995; Wilf & Johnson 2004). Insect damage traces in leaves can also give information about consumers (Wilf et al. 2000), correla-tions between feeding diversity and climate changes, extinctions and plant diversity (Labandeira et al. 2002).
Fossil woods may be frequently identifi ed at family level based on anatomical characters, offering a good opportunity to record plant families in the Amazon Basin. As indicators of climate, tropical fossil woods do not show a strong correlation between temperature and the growth of tree rings (e.g. Chowdhury 1964). However, recent techniques using anatomical characters such as percentages of spiral thickenings present in vessels with a diam-eter less than 100 µm, and ring-porous vessels on dicot woods are well correlated with mean annual temperature (Wiemann et al. 1998). Otherwise, chemical characteristics of fossil woods may be correlated with palaeoclimate proxies (Poole & van Bergen 2006). When fossil woods are found in situ and the base of the trunk is preserved, it is possible to calculate the structure of the forest based on the relationship between basal trunk diameter and tree height (Rich et al. 1986; Lehman & Wheeler 2001).
Phytoliths are microscopic silica fl akes present in the vascular system of only certain plant families, mostly monocots (Piperno 1988). The phytolith record offers a window to past changes of
Hoorn_ch19_Final.indd 330Hoorn_ch19_Final.indd 330 10/24/2009 1:57:06 Shobha10/24/2009 1:57:06 Shobha
Origin of the modern Amazon rainforest 331
a specifi c sample size. This is termed rarefaction analysis, a tech-nique that calculates the number of species expected for a given sample size smaller than the actual sample (Sanders 1968). This technique is used to account for differences in diversity result-ing from different sample sizes. All analyses were done in R for Statistical Computing (R-Development-Core-Team 2005) and the R package Vegan (Oksanen et al. 2005).
We compared the rarefi ed palynological diversity at a counting level of 208 grains (the pollen number of the smallest sample in the set) for samples from several Amazonian sites. Palynological data for the Miocene were taken from the literature (Hoorn 1993, 1994a, 1994b, 2006), and several cores from the Quaternary were also used, including Piusbi (Behling et al. 1998), dos Patas (Colinvaux et al. 1996), Curucab (Behling 1996) and Monica (Berrio 2002). All sites were attributed to one of four time inter-vals and the average diversity at a counting level of 208 grains was calculated for each site.
Lower Miocene: Mariñame, Tres Islas, Santa Isabel, core 1 AS04a-AM (181.8 to 275 m); Middle Miocene: Pebas, Iquitos, core AS04a-AM (89 to 2 181.7 m);Upper Miocene: Mocagua, Los Chorros East and West, Santa 3 Sofi a, and Apaporis, core AS04a-AM (23.5 to 88.9 m). Quaternary: Piusbi, Curucab, Monica and Dos Patas.4
There exists a slight trend toward decreasing diversity from the Neogene to the Quaternary (Fig. 19.3). However, the pattern is neither clear nor signifi cant. The outcomes may have been infl u-enced by the fact that the Neogene pollen data were collected with other goals in mind (mainly biostratigraphy and palaeoecology), other than analysing diversity over time. Furthermore, different depositional environments may have been analysed. Given the cooling trend of the Neogene together with the areal reduction of the fl ooded forest, which is a major provider of pollen and spores for the fossil record, a reduction in diversity is to be expected. However, further studies are needed to test this hypothesis.
Antoine et al. 2006; Pons & De Franceschi 2007; Goillot et al. 2007; Latrubesse et al. 2007; Olivier et al. 2008).
A total of 24 angiosperm families have been reported from Miocene rocks of Amazonia. Duarte (2004) described 17 fami-lies corresponding to 19 genera from fossil leaves of the Miocene Pirabas Formation from Brazil. This formation seems to have been deposited in a littoral environment. Among the families reported are Nyctaginaceae, Lauraceae, Dilleniaceae, Theaceae, Caryocaraceae, Chrysobalanaceae, Euphorbiaceae, Rutaceae, Meliaceae, Sapindaceae, Malvaceae, Myrtaceae, Melastomataceae, Rhizophoraceae, Ebenaceae, Rubiaceae and Rapataceae. The aver-age size of these fossil leaves is mesophyll, abundant acuminate apexes are preserved, and most leaves have entire margins suggest-ing a warm and humid climate. However, a more specifi c analysis of the leaf characters has not yet been carried out. Floristically, the Pirabas fl ora contains some of the most important families that make up modern Neotropical lowland rainforests (e.g. Lauraceae, Euphorbiaceae, Meliacaeae and Malvaceae). Fossil leaves related to Malvaceae (Bombacacidites) have also been reported from mangrove deposits of the Miocene Barreiras Formation of Brazil (Dutra et al. 2001).
Fossil woods from the Middle Miocene Pebas Formation of Peruvian Amazonia have been assigned to the Anacardiaceae (Anacardium), Clusiaceae (Calophyllum), Combretaceae (Buche-navia and Terminalia), Fabaceae (Andira/Hymenolobium), Humi- riaceae (Humiriastrum), Lecythidaceae (Cariniana and Eschweilera) and Meliaceae (Guarea) (Pons & De Franceschi 2007). The lack of growth rings and the family composition suggest that these fossil woods were part of terra fi rme lowland tropical rainforests (Pons & De Franceschi 2007). However, additional anato mical characters should be taken into account besides the family com-position to distinguish between riparian and terra fi rme habitat.
Fossil leaves and woods suggest that fl oristically the Miocene rainforests were similar to modern Neotropical lowland rain-forests, even at the generic level. The study of macrofossils from Neogene Amazonia is a promising fi eld, and might yield a better understanding of the palaeoclimate, the evolution of angiosperm families and animal–plant interactions, and the structure of the Miocene rainforests.
Diversity analysis
In this chapter, the word ‘diversity’ is used in its original sense to denote the number of species (Rosenzweig 1995), which is also called ‘richness’. Pollen can be a useful tool for estimating plant diversity through time (e.g. Morley 2000). It mostly refl ects genera and families (Germeraad et al. 1968; Jackson & Williams 2004), indicating that it can be used to track plant diversity at that taxonomic level through geological time.
We assessed Amazonian Neogene within-sample diversity (the number of species in a given sample) using a technique called rarefaction (Sanders 1968; Hurlbert 1971). Estimating the number of species in a sample involves counting the species in a given sample. However, the number of species depends on the number of pollen grains counted; thus, as more grains are counted, more species are found. In order to compare the diver-sity among different samples, data must fi rst be standardized to
10 20 30 40 50 60#species
Quaternary
Late Miocene
Middle Miocene
Early Miocene
Rarefied diversity, cutoff 208
Fig. 19.3 Rarefi ed diversity at a counting level of 208 grains for the Miocene and Quaternary of the Amazonian Basin. Each point represents the average diversity of a site. The bar represents the 95% confi dence interval.
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Conclusions
The Amazonian rainforest has had a long and dynamic history. Middle Cretaceous Amazonian fl oras were dominated by non-angiosperm taxa, whereas by the Paleocene, rainforests were dominated by angiosperms and were already populated by the plant families that are dominant in modern tropical Amazonian rainforests. The Neogene uplift of the Andes changed the drain-age system from south-north to west-east, and from rivers being predominantly born in the nutrient-depleted Precambrian cra-tons of South America, to rivers coming from the Andes with high levels of nutrients. The cooling trend of the Neogene probably reduced the area available for rainforests. Although quantitative studies are needed to substantiate this, a qualitative assessment suggests that the receding forest of the Late Miocene might have recovered during the Pliocene and Quaternary, but may not have regained the high diversity of the pre-Late Miocene period.
Acknowledgements
This project was supported by INPA, the Colombian Petroleum Institute, the Smithsonian Paleobiology Endowment Fund, and the Unrestricted Endowments Smithsonian Institution Grants. Juan Carlos Berrio and Herman Behling are thanked for raw pollen data. Special thanks go to M.I. Barreto for her continu-ous support and ideas. Bob Morley and Henry Hooghiemstra are acknowledged for their constructive reviews.
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