Sporomorph Record Research Articles

On the Taxonomic Resolution of Pollen and Spore Records of Earth’s Vegetation

Premise of research. Pollen and spores (sporomorphs) are a valuable record of plant life and have provided information on subjects ranging from the nature and timing of evolutionary events to the relationship between vegetation and climate. However, sporomorphs can be morphologically similar at the species, genus, or family level. Studies of extinct plant groups in pre-Quaternary time often include dispersed sporomorph taxa whose parent plant is known only to the class level. Consequently, sporomorph records of vegetation suffer from limited taxonomic resolution and typically record information about plant life at a taxonomic rank above species.Methodology. In this article, we review the causes of low taxonomic resolution, highlight examples where this has hampered the study of vegetation, and discuss the strategies researchers have developed to overcome the low taxonomic resolution of the sporomorph record. Based on this review, we offer our views on how greater taxonomic precision might be attained in f...

Southern high-latitude terrestrial climate change during the Palaeocene–Eocene derived from a marine pollen record (ODP Site 1172, East Tasman Plateau)

Abstract. Reconstructing the early Palaeogene climate dynamics of terrestrial settings in the high southern latitudes is important to assess the role of high-latitude physical and biogeochemical processes in the global climate system. However, whereas a number of high-quality Palaeogene climate records has become available for the marine realm of the high southern latitudes over the recent past, the long-term evolution of coeval terrestrial climates and ecosystems is yet poorly known. We here explore the climate and vegetation dynamics on Tasmania from the middle Palaeocene to the early Eocene (60.7–54.2 Ma) based on a sporomorph record from Ocean Drilling Program (ODP) Site 1172 on the East Tasman Plateau. Our results show that three distinctly different vegetation types thrived on Tasmania under a high-precipitation regime during the middle Palaeocene to early Eocene, with each type representing different temperature conditions: (i) warm-temperate forests dominated by gymnosperms that were dominant during the middle and late Palaeocene (excluding the middle/late Palaeocene transition); (ii) cool-temperate forests dominated by southern beech (Nothofagus) and araucarians that transiently prevailed across the middle/late Palaeocene transition interval (~ 59.5 to ~ 59.0 Ma); and (iii) paratropical forests rich in ferns that were established during and in the wake of the Palaeocene–Eocene Thermal Maximum (PETM). The transient establishment of cool-temperate forests lacking any frost-sensitive elements (i.e. palms and cycads) across the middle/late Palaeocene transition interval indicates markedly cooler conditions, with the occurrence of frosts in winter, on Tasmania during that time. The integration of our sporomorph data with previously published TEX86-based sea-surface temperatures from ODP Site 1172 documents that the vegetation dynamics on Tasmania were closely linked with the temperature evolution in the Tasman sector of the Southwest Pacific region. Moreover, the comparison of our season-specific climate estimates for the sporomorph assemblages from ODP Site 1172 with the TEX86L- and TEX86H-based temperature data suggests a warm bias of both calibrations for the early Palaeogene of the high southern latitudes.

Paleotropical pollen grains from the Neuquén Group, Patagonia, Argentina

This paper discusses the presence of elater-bearing pollen grains and other characteristic paleotropical palynomorphs in the mid to Late Cretaceous Neuquen Group at the El Zampal locality, south of Mendoza Province, Argentina. The elaterates characterize the equatorial paleofloristic province in the Albian-Cenomanian. The species Elateroplicites africaensis is present in the pollen assemblage recovered from the lower section of the Huincul Formation, a basal unit of the studied Neuquen Group. It represents the first record of elater-bearing pollen grains in Argentina and marks their southernmost extension. Other conspicuous paleotropical elements recorded in different lithostratigraphic units of the Neuquen Group include gymnospermous polyplicate pollen grains and angiosperm pollen, including two species of the periporate pollen genus Cretacaeiporites and the triporate pollen species Confossia vulgaris. The paleobiogeographic and biostratigraphic significance of the paleotropical sporomorph record in the Cretaceous palynofloras of the Neuquen Group at El Zampal is herein discussed.

Early to Middle Eocene vegetation dynamics at the Wilkes Land Margin (Antarctica)

The early Eocene epoch was characterized by extreme global warmth, which in terrestrial settings was characterized by an expansion of near-tropical vegetation belts into the high latitudes. During the middle to late Eocene, global cooling caused the retreat of tropical vegetation to lower latitudes. In high-latitude settings, near-tropical vegetation was replaced by temperate floras. This floral change has recently been traced as far south as Antarctica, where along the Wilkes Land margin paratropical forests thrived during the early Eocene and temperate Nothofagus forests developed during the middle Eocene. Here we provide both qualitative and quantitative palynological data for this floral turnover based on a sporomorph record recovered at Integrated Ocean Drilling Program (IODP) Site U1356 off the Wilkes Land margin. Following the nearest living relative concept and based on a comparison with modern vegetation types, we examine the structure and diversity patterns of the Eocene vegetation along the Wilkes Land margin. Our results indicate that the early Eocene forests along the Wilkes Land margin were characterized by a diverse canopy composed of plants that today occur in tropical settings; their richness pattern was similar to that of present-day forests from New Caledonia. The middle Eocene forests were characterized by a canopy dominated by Nothofagus and exhibited richness patterns similar to modern Nothofagus forests from New Zealand.

Palynostratigraphy and vegetation history of the Triassic–Jurassic transition in East Greenland

We present a palynological study of a terrestrial Triassic–Jurassic (Tr–J; c . 200 Ma) boundary section at Astartekløft, East Greenland. We have generated a new palynostratigraphic scheme and vegetation history for this locality, and have integrated these with existing carbon isotope records. Samples for palynological analysis were collected from precisely the same stratigraphic horizons as plant macrofossils and samples used for geochemical analyses. Our results highlight four local sporomorph assemblage zones that are compositionally distinct from each other at Astartekløft. The extremely low abundance of Classopollis pollen in all samples, and the pronounced decline of Ricciisporites tuberculatus during the Late Rhaetian are notable features of the sporomorph record of Tr–J vegetation at Astartekløft. Correlation of Astartekløft and a marine Tr–J boundary section at St Audrie’s Bay, UK, provides no support for the idea that extinction and diversity loss in terrestrial ecosystems preceded biotic change in marine ecosystems at the Tr–J. Instead, the available data support suggestions that the onset of the Tr–J biotic crisis was synchronous in terrestrial and marine environments. Peak extinction among plants at Astartekløft occurred relatively late in the sequence of events across the Tr–J, and may represent a response to long-term cumulative effects of volcanism at this time. Supplementary material Plates of selected sporomorphs recovered from Astartekløft and a full pollen diagram are available at www.geolsoc.org.uk/SUP18553 .

Regional-scale spatial heterogeneity in the late Paleocene paratropical forests of the U.S. Gulf Coast

The study of spatial patterns in biotic compositional variability in deep time is key to understanding the macroecological response of species assemblages to global change. Globally warm climatic phases are marked by the expansion of megathermal climates into currently extra-tropical areas. However, there is currently little information on whether vegetation in these “paratropical” regions resembled spatially modern tropical or extra-tropical biomes. In this paper we explore spatial heterogeneity in extra-tropical megathermal vegetation, using sporomorph (pollen and spore) data from the late Paleocene Calvert Bluff and Tuscahoma Formations of the formerly paratropical U.S. Gulf Coast (Texas, Mississippi, and Alabama). The data set comprises 139 sporomorph taxa recorded from 56 samples. Additive diversity partitioning, nonmetric multidimensional scaling, and cluster analysis show compositional heterogeneity both spatially and lithologically within the U.S. Gulf Coastal Plain (GCP) microflora. We then use sporomorph data from Holocene lake cores to compare spatial patterns in the late Paleocene GCP with modern tropical and extra-tropical biomes. Distance decay analysis of the Holocene data reveals a higher rate of spatial turnover in tropical versus extra-tropical vegetation types, consistent with a latitudinal gradient in floral compositional heterogeneity. The specific combination of rate and scale dependency of distance decay in the Holocene assemblages prevented us from associating the late Paleocene GCP with any particular modern biome. Our results demonstrate the importance of spatial scale, taphonomy, and lithology in determining patterns of spatial heterogeneity, and show the potential of the fossil sporomorph record for studying spatial patterns and processes in deep time.

Regional-scale spatial heterogeneity in the late Paleocene paratropical forests of the U.S. Gulf Coast

The study of spatial patterns in biotic compositional variability in deep time is key to understanding the macroecological response of species assemblages to global change. Globally warm climatic phases are marked by the expansion of megathermal climates into currently extra-tropical areas. However, there is currently little information on whether vegetation in these “paratropical” regions resembled spatially modern tropical or extra-tropical biomes. In this paper we explore spatial heterogeneity in extra-tropical megathermal vegetation, using sporomorph (pollen and spore) data from the late Paleocene Calvert Bluff and Tuscahoma Formations of the formerly paratropical U.S. Gulf Coast (Texas, Mississippi, and Alabama). The data set comprises 139 sporomorph taxa recorded from 56 samples. Additive diversity partitioning, nonmetric multidimensional scaling, and cluster analysis show compositional heterogeneity both spatially and lithologically within the U.S. Gulf Coastal Plain (GCP) microflora. We then use sporomorph data from Holocene lake cores to compare spatial patterns in the late Paleocene GCP with modern tropical and extra-tropical biomes. Distance decay analysis of the Holocene data reveals a higher rate of spatial turnover in tropical versus extra-tropical vegetation types, consistent with a latitudinal gradient in floral compositional heterogeneity. The specific combination of rate and scale dependency of distance decay in the Holocene assemblages prevented us from associating the late Paleocene GCP with any particular modern biome. Our results demonstrate the importance of spatial scale, taphonomy, and lithology in determining patterns of spatial heterogeneity, and show the potential of the fossil sporomorph record for studying spatial patterns and processes in deep time.

Taxonomic resolution of the Triassic–Jurassic sporomorph record in East Greenland

Abstract. Sporomorphs (pollen and spores) provide valuable information about vegetation history over a range of temporal and spatial scales. However, sporomorphs can be morphologically invariant among species within genera, and among genera within certain families. In some cases, the parent plant of a sporomorph is unknown. These factors blur the relationship between sporomorph assemblages and the source vegetation, and reduce the taxonomic precision of vegetation reconstructions based on sporomorphs. This study investigates the taxonomic precision with which sporomorphs record vegetation across the Triassic–Jurassic transition (Tr–J) at Astartekløft, East Greenland. Results indicate that reconstructions of Tr–J vegetation at Astartekløft based on sporomorphs are hampered by considerable taxonomic imprecision. Something is known of the botanical affinity of almost all sporomorphs at Astartekløft at the class level, but just 50% of sporomorph taxa have a known botanical affinity at the family level. Additionally, ~23% of all sporomorph taxa at Astartekløft have affinities to more than one parent plant class, and ~36% of sporomorph taxa have affinities to more than one parent plant family. This taxonomic imprecision should be accounted for when interpreting percentage diagrams of sporomorph taxa across the Tr–J.

An explanation for conflicting records of Triassic–Jurassic plant diversity

Macrofossils (mostly leaves) and sporomorphs (pollen and spores) preserve conflicting records of plant biodiversity during the end-Permian (P-Tr), Triassic-Jurassic (Tr-J), and end-Cretaceous (K-T) mass extinctions. Estimates of diversity loss based on macrofossils are typically much higher than estimates of diversity loss based on sporomorphs. Macrofossils from the Tr-J of East Greenland indicate that standing species richness declined by as much as 85% in the Late Triassic, whereas sporomorph records from the same region, and from elsewhere in Europe, reveal little evidence of such catastrophic diversity loss. To understand this major discrepancy, we have used a new high-resolution dataset of sporomorph assemblages from Astartekløft, East Greenland, to directly compare the macrofossil and sporomorph records of Tr-J plant biodiversity. Our results show that sporomorph assemblages from the Tr-J boundary interval are 10-12% less taxonomically diverse than sporomorph assemblages from the Late Triassic, and that vegetation composition changed rapidly in the boundary interval as a result of emigration and/or extirpation of taxa rather than immigration and/or origination of taxa. An analysis of the representation of different plant groups in the macrofossil and sporomorph records at Astartekløft reveals that reproductively specialized plants, including cycads, bennettites and the seed-fern Lepidopteris are almost absent from the sporomorph record. These results provide a means of reconciling the macrofossil and sporomorph records of Tr-J vegetation change, and may help to understand vegetation change during the P-Tr and K-T mass extinctions and around the Paleocene-Eocene Thermal Maximum.

The Red Hills Mine palynoflora: A diverse swamp assemblage from the late Paleocene of Mississippi, U.S.A.

Lignites from the Red Hills Mine in Mississippi, U.S.A. contain pollen and spores derived from paratropical swamp vegetation on the U.S. Gulf Coast during the Late Paleocene. Most previous studies of the Gulf Coast sporomorph record have been limited to a restricted taxonomic group, or merely those taxa that are relevant to biostratigraphy, meaning that the true sporomorph diversity may be higher than previously appreciated. Eight samples were collected for palynological analysis from the Red Hills Lignite Mine in Ackerman, Mississippi. All the taxa observed during counting (a minimum of 300 grains per sample) were included in the sample count. Rarefaction, relative abundance distributions, and non‐metric multidimensional scaling were used to analyze floral composition, richness, and evenness. The lignite samples are heterogeneous in terms of composition and relative abundances, indicating patchiness in the swamp communities. Clay horizons representing temporary marine incursions contain significantly higher proportions of bisaccate pollen, which may have originated a considerable distance inland from the swamps. These samples therefore represent a much larger source area (regional to sub‐continental), compared to the local signal contained in the lignite samples. Richness in the Red Hills Mine assemblage is higher than has previously been recorded for the Late Paleocene of the eastern Gulf Coast. This, combined with the recognition of 23 previously undescribed taxa, suggests that a detailed reappraisal of the Gulf Coast Paleocene sporomorph record is needed to improve understanding of the evolution of the North American vegetation type.

COMPARISONS BETWEEN PALAEOCENE–EOCENE PARATROPICAL SWAMP AND MARGINAL MARINE POLLEN FLORAS FROM ALABAMA AND MISSISSIPPI, USA

Abstract: Climate warming at the Palaeocene/Eocene boundary (c. 55.8 Ma) had significant permanent affects on paratropical and warm‐adapted vegetation types. Pollen and spore records which document vegetation turnover from the eastern US Gulf Coast have all been taken from sediments of marginal marine depositional environments. Pollen and spores (sporomorphs) are preserved excellently in these marginal marine depositional environments but these assemblages contain grains transported from many different vegetation types and over huge geographic distances. Currently it is unclear whether the turnover from important paratropical areas like the US Gulf Coast is a reflection on actual vegetation change in the local region or from source areas far away in the continental interior. Sporomorph data from 20 former swamps (lignites) from the Nanafalia, Tuscahoma and Hatchetigbee formations in Mississippi and Alabama, USA, are used to test the fidelity of the marine sporomorph record across the Palaeocene–Eocene transition. Data show that extinction is noted in the swamp record (≥7 per cent of Palaeocene taxa) and that swamps were susceptible to immigration in the Early Eocene with the first occurrences of Brosipollis spp. (Burseraceae), Dicolpopollis spp. (Palmae), Nuxpollenites psilatus (Loranthaceae) and Platycarya spp. (Juglandaceae). Swamps have higher within‐sample diversity in the Eocene but higher among‐sample diversity in latest Palaeocene–earliest Eocene samples, which parallels exactly diversity trends estimated from marine sporomorph assemblages. Palms also increase in abundance in the Eocene. The swamp data demonstrate that the flora growing in these ancient paratropical forests was diverse (c. 120 taxonomic groups) but incorporated an unusual admixture of plants with modern tropical affinities together with those that now live in modern temperate to subtropical North America.

THE RED HILLS MINE PALYNOFLORA: A DIVERSE SWAMP ASSEMBLAGE FROM THE LATE PALEOCENE OF MISSISSIPPI, U.S.A.

Lignites from the Red Hills Mine in Mississippi, U.S.A. contain pollen and spores derived from paratropical swamp vegetation on the U.S. Gulf Coast during the Late Paleocene. Most previous studies of the Gulf Coast sporomorph record have been limited to a restricted taxonomic group, or merely those taxa that are relevant to biostratigraphy, meaning that the true sporomorph diversity may be higher than previously appreciated. Eight samples were collected for palynological analysis from the Red Hills Lignite Mine in Ackerman, Mississippi. All the taxa observed during counting (a minimum of 300 grains per sample) were included in the sample count. Rarefaction, relative abundance distributions, and non-metric multidimensional scaling were used to analyze floral composition, richness, and evenness. The lignite samples are heterogeneous in terms of composition and relative abundances, indicating patchiness in the swamp communities. Clay horizons representing temporary marine incursions contain significantly higher proportions of bisaccate pollen, which may have originated a considerable distance inland from the swamps. These samples therefore represent a much larger source area (regional to sub-continental), compared to the local signal contained in the lignite samples. Richness in the Red Hills Mine assemblage is higher than has previously been recorded for the Late Paleocene of the eastern Gulf Coast. This, combined with the recognition of 23 previously undescribed taxa, suggests that a detailed reappraisal of the Gulf Coast Paleocene sporomorph record is needed to improve understanding of the evolution of the North American vegetation type.