Marco Vecoli - Academia.edu (original) (raw)
Papers by Marco Vecoli
An updated Furongian stratigraphic framework for South-Western Europe
This study focuses on the thermal maturity assessment of Silurian-Devonian sediments from the Gha... more This study focuses on the thermal maturity assessment of Silurian-Devonian sediments from the Ghadamis Basin, North Africa, comparing optical and geochemical analyses of palynomorphs. In southern Tunisia, the investigated subsurface cored section comprises the Argiles Principales Formation of Silurian age. In Libya, the succession studied covers the Awaynat Wanin III and IV formations, assigned to the Late Devonian (Frasnian-Famennian). Geochemical approaches used to reconstruct thermal alteration of sediments necessitate advanced, relatively expensive analytical techniques. In this study, the effectiveness of the less costly, relatively simple approaches of visually assessing palynomorph colour to determine thermal alteration (i.e., SCI: Spore Colour Index, TAI: Thermal Alteration Index and PDI: Palynomorph Darkness Index) was evaluated. SCI and TAI are qualitative methods, strictly related to the operator's perception, which use ten and five point scales respectively, to characterize colour in terms of illustrated specimens and/or descriptions. In contrast, PDI is obtained from the measurement of the red, green and blue (RGB) intensities of light transmitted through palynomorphs, using standard optical microscopes and digital cameras. The palynomorph-based thermal alteration estimates were compared to Rock-Eval pyrolysis data from the same samples. This calibration showed a linear relationship between these quantitative parameters and PDI. These results show that PDI is more reliable than the SCI and TAI methods.
Carnets de Géologie, 2005
HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
Chitinozoan biostratigraphy in the Ordovician of Saudi Arabia
European Palaeobotany and Palynology Congress, Aug 12, 2018
Revue de Micropaléontologie, 2017
Abstract. A database of all reported Ordovician-Silurian land plant megafossil and dispersed spor... more Abstract. A database of all reported Ordovician-Silurian land plant megafossil and dispersed spore assemblages has been assembled. For each assemblage a list of taxa has been prepared and its location plotted on new palaeocontinental reconstructions. These new data compilations are analyzed with respect to palaeophytogeographical differentiation and various patterns of taxon diversity and morphological disparity that emerged during the origin, adaptive radiation and geographical spread of land plants. Our analyses include new quantitative assessments.
The contribution of palynology to the stratigraphy of the north-western sector of the Ghadamis Basin
A review of Silurian dispersed spore assemblages from the Arabian Plate: biostratigraphy and palaeogeography
Peer reviewe
Geobios, 2001
Micropalaeontology of a Moroccan Ordovician deposit yielding softbodied organisms showing Ediacar... more Micropalaeontology of a Moroccan Ordovician deposit yielding softbodied organisms showing Ediacara-like preservation [Micropal6ontologie d'un d6p6t ordovicien marocain produisant des organismes ~ corps mou pr6serv6 d'une fa~on comparable ~ la pr6servation 6diacarienne].
Palynostratigraphy of upper Cambrian-upper Ordovician intracratonic clastic sequences, North Africa
Bollettino Della Societa Paleontologica Italiana, 1999
Detailed palynological study of subsurface sections in the Algerian Sahara (boreholes Nl-2 and Uc... more Detailed palynological study of subsurface sections in the Algerian Sahara (boreholes Nl-2 and Uc-101) and southern Tunisia (boreholes Sn-1 and St-1) enables precise dating and intrabasinal and extrabasinal stratigraphic correlation. Most of the study samples proved palyniferous, yielding abundant, well preserved acritarchs (148 species) together with infrequent prasinophytes (2 species). Seven acritarch assemblage zones are recognizable, ranging in age from late Cambrian to late Ordovician (Ashgill) as follows: Timofeevia lancarae-Cristallinium randomense (Late Cambrian), Timofeevia phosphoritica-Dasydiacrodium caudatum (latest Cambrian), Acanthodiacrodium simplex-Arbusculidium destombesii (basal Tremadoc), Acanthodiacrodium angustum-Vulcanisphaera britannica (early Tremadoc), Arbusculidium filamentosum-Coryphidium bohemicum (late Arenig), Frankea sartbernardensis-Vogtlandia ramificata (Llanvirn), and Evittia remota-Villosacapsula setosapellicula (Ashgill) zones. Lower Tremadoc ass...
Earth-Science Reviews, 2004
Acritarchs, the fossilizable, resting cysts of phytoplanktonic algal protists, are the dominant c... more Acritarchs, the fossilizable, resting cysts of phytoplanktonic algal protists, are the dominant component of marine organicwalled microfossils in the Palaeozoic. The majority of acritarchs show strong similarities with dinoflagellate cysts in morphological and biogeochemical features, as well as distributional patterns in the sediments. The production of these organicwalled microfossils and their distribution and survivorship in the sediments were controlled by differences in ecological tolerances and life cycle (autecology) of the planktonic parent organisms. Calculation of evolutionary rates and development of a detailed diversity curve at specific level, form the basis for discussing the influence of global palaeoenvironmental perturbations on the evolution of organic-walled microphytoplankton in northern Gondwana during latest Cambrian through Ordovician times. The potential of acritarchs for biostratigraphic correlation at the regional scale (northern Gondwana domain) is much improved by our detailed revision of distributional patterns of 245 acritarch taxa. The most important Cambro-Ordovician acritarch bio-events are short periods of diversification, which also correspond to introduction of morphological innovations, observed in latest Cambrian and earliest Tremadoc, late Tremadoc, early Arenig, basal Llanvirn, and latest Ashgill, and an important extinction phase in the early Caradoc. Overall, acritarch diversity increased from the basal Ordovician up to the middle Llanvirn, then declined in the early and middle Caradoc. During Ashgill times, the assemblages are poorly diversified at the generic level as a result of a combined effect of sea level drawdown and onset of glacial conditions, but no major extinction event is observed in connection with the end-Ordovician biotic crisis. The peak in acritarch diversity during Middle Ordovician times appears to be correlated to maximum spread of palaeogeographical assembly. Acritarch dynamics appear largely uncorrelated to second order sea-level oscillations; the primary abiotic controls on acritarch evolution were palaeogeographical and the associated palaeoceanographic changes (especially during Middle Ordovician), and the end-Ordovician palaeoclimatic shift.
New palynomorphs from the Ordovician–Silurian boundary interval: Eastern North America and Saudi Arabia
Palynology, 2017
ABSTRACT A distinctive coenobial palynomorph, Speculaforma gen. nov., and its two new species, S.... more ABSTRACT A distinctive coenobial palynomorph, Speculaforma gen. nov., and its two new species, S. delicata and S. elongata, are described from the Llandovery Grimsby Formation, Medina Group, from New York and are part of a more diverse palynomorph assemblage. Speculaforma delicata was also recovered from the Tuscarora Formation, West Virginia, and subsurface Hirnantian sediments in southern Saudi Arabia. Speculaforma is questionably assigned to the Hydrodictyaceae within the order Chlorococcales based on its geometrically regular coenobia. It is considered to be a freshwater or brackish-water alga. Occurring with this coenobium are two new acritarchs, Lunataforma parallela gen. et sp. nov. and Pertusidisca quadripora gen. et sp. nov. These acritarchs have been recovered from near-shore marine settings, in both North America and Saudi Arabia; but in North America Lunataforma was also recovered from sediments considered to represent an open marine environment.
Palynology, 2017
Cryptospores from the Dapingian-Darriwilian Kanosh Shale at Fossil Mountain, Utah, USA, occur as ... more Cryptospores from the Dapingian-Darriwilian Kanosh Shale at Fossil Mountain, Utah, USA, occur as tetrads, dyads, irregular clusters, or planar sheets of spore dyads. These spore 'thalli' are placed into the new taxon Grododowon orthogonalis gen. et sp. nov. based on the nature of division patterning and gross overall shape. The antithetic hypothesis of embryophyte origins dictates that spores evolved first and that the vegetative sporophyte evolved later via mitotic cell divisions that preceded meiosis and spore formation. We interpret the planar spore sheets of Grododowon gen. nov. to have formed via the cooption of a prior vegetative gametophytic developmental pattern which was expressed in the zygote, resulting in a two-dimensional, thalloid bauplan. However, the ploidy of the resultant 'spores' as haploid is necessarily conjectural, and this pattern of growth is clearly not the ancestral condition in the streptophyte lineage that gave rise to the first axial plant sporophyte.
Revue de Micropaléontologie, 2017
Revue de micropaléontologie xxx (2016) xxx-xxx Original article Wall ultrastructure of the oldest... more Revue de micropaléontologie xxx (2016) xxx-xxx Original article Wall ultrastructure of the oldest embryophytic spores: Implications for early land plant evolution Ultrastructure de la paroi des plus anciennes spores embryophytiques : implications pour l'évolution des plantes primitives terrestres
Plant evolution and terrestrialization during Palaeozoic times—The phylogenetic context
Review of Palaeobotany and Palynology, 2016
Abstract Terrestrialization probably began more than one billion years ago and irreversibly alter... more Abstract Terrestrialization probably began more than one billion years ago and irreversibly altered biogeochemical processes at planetary scale. In this paper, we focus on the terrestrialization process of the Streptophyta, the division that includes charophytes and land plants (embryophytes) and whose members are today ecologically dominant in all terrestrial environments. The timing and the phylogenetic context of the early evolution of land plants are reviewed. The available information on the relationships within embryophytes and related organisms is compiled in two informal consensus trees based either on morphological/anatomical or on molecular data. We also consider the algal/embryophyte transition through the analysis of the evidence provided by microfossils (cryptospores and spores). The ongoing debate about the definition of the term cryptospores, but more importantly about the biological affinities of these microfossils that are possibly derived from early land plants, is discussed. All important clades of embryophytes, with a focus on their Palaeozoic representatives, are described; the significance of several embryophyte key characters is evaluated. The terrestrialization of land plants evolved in different steps. The new term “proembryophytic phase” is introduced to define the very long period of time during which the green algae ancestor of land plants acquired all the evolutionary characters that ultimately allowed their terrestrialization since the late Precambrian. An “eoembryophytic phase”, spanning the Middle-Upper Ordovician, is defined based on the occurrence of the earliest evidence of liverwort-like plants. The inception of the trilete spores in Late Ordovician times is then taken to define the start of the eo/eutracheophytic phase, which lasts until the first occurrence of vascular plant macrofossils in the Silurian.
High-Resolution Integrated Palynological and Graptolite Biozonation in the Early Silurian of the Arabian Plate
Upper Cambrian acritarchs from the subsurface Arabian Gulf, Saudi Arabia
Mass-wasting triggered by the end-Triassic mass-extinction
An updated Furongian stratigraphic framework for South-Western Europe
This study focuses on the thermal maturity assessment of Silurian-Devonian sediments from the Gha... more This study focuses on the thermal maturity assessment of Silurian-Devonian sediments from the Ghadamis Basin, North Africa, comparing optical and geochemical analyses of palynomorphs. In southern Tunisia, the investigated subsurface cored section comprises the Argiles Principales Formation of Silurian age. In Libya, the succession studied covers the Awaynat Wanin III and IV formations, assigned to the Late Devonian (Frasnian-Famennian). Geochemical approaches used to reconstruct thermal alteration of sediments necessitate advanced, relatively expensive analytical techniques. In this study, the effectiveness of the less costly, relatively simple approaches of visually assessing palynomorph colour to determine thermal alteration (i.e., SCI: Spore Colour Index, TAI: Thermal Alteration Index and PDI: Palynomorph Darkness Index) was evaluated. SCI and TAI are qualitative methods, strictly related to the operator's perception, which use ten and five point scales respectively, to characterize colour in terms of illustrated specimens and/or descriptions. In contrast, PDI is obtained from the measurement of the red, green and blue (RGB) intensities of light transmitted through palynomorphs, using standard optical microscopes and digital cameras. The palynomorph-based thermal alteration estimates were compared to Rock-Eval pyrolysis data from the same samples. This calibration showed a linear relationship between these quantitative parameters and PDI. These results show that PDI is more reliable than the SCI and TAI methods.
Carnets de Géologie, 2005
HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
Chitinozoan biostratigraphy in the Ordovician of Saudi Arabia
European Palaeobotany and Palynology Congress, Aug 12, 2018
Revue de Micropaléontologie, 2017
Abstract. A database of all reported Ordovician-Silurian land plant megafossil and dispersed spor... more Abstract. A database of all reported Ordovician-Silurian land plant megafossil and dispersed spore assemblages has been assembled. For each assemblage a list of taxa has been prepared and its location plotted on new palaeocontinental reconstructions. These new data compilations are analyzed with respect to palaeophytogeographical differentiation and various patterns of taxon diversity and morphological disparity that emerged during the origin, adaptive radiation and geographical spread of land plants. Our analyses include new quantitative assessments.
The contribution of palynology to the stratigraphy of the north-western sector of the Ghadamis Basin
A review of Silurian dispersed spore assemblages from the Arabian Plate: biostratigraphy and palaeogeography
Peer reviewe
Geobios, 2001
Micropalaeontology of a Moroccan Ordovician deposit yielding softbodied organisms showing Ediacar... more Micropalaeontology of a Moroccan Ordovician deposit yielding softbodied organisms showing Ediacara-like preservation [Micropal6ontologie d'un d6p6t ordovicien marocain produisant des organismes ~ corps mou pr6serv6 d'une fa~on comparable ~ la pr6servation 6diacarienne].
Palynostratigraphy of upper Cambrian-upper Ordovician intracratonic clastic sequences, North Africa
Bollettino Della Societa Paleontologica Italiana, 1999
Detailed palynological study of subsurface sections in the Algerian Sahara (boreholes Nl-2 and Uc... more Detailed palynological study of subsurface sections in the Algerian Sahara (boreholes Nl-2 and Uc-101) and southern Tunisia (boreholes Sn-1 and St-1) enables precise dating and intrabasinal and extrabasinal stratigraphic correlation. Most of the study samples proved palyniferous, yielding abundant, well preserved acritarchs (148 species) together with infrequent prasinophytes (2 species). Seven acritarch assemblage zones are recognizable, ranging in age from late Cambrian to late Ordovician (Ashgill) as follows: Timofeevia lancarae-Cristallinium randomense (Late Cambrian), Timofeevia phosphoritica-Dasydiacrodium caudatum (latest Cambrian), Acanthodiacrodium simplex-Arbusculidium destombesii (basal Tremadoc), Acanthodiacrodium angustum-Vulcanisphaera britannica (early Tremadoc), Arbusculidium filamentosum-Coryphidium bohemicum (late Arenig), Frankea sartbernardensis-Vogtlandia ramificata (Llanvirn), and Evittia remota-Villosacapsula setosapellicula (Ashgill) zones. Lower Tremadoc ass...
Earth-Science Reviews, 2004
Acritarchs, the fossilizable, resting cysts of phytoplanktonic algal protists, are the dominant c... more Acritarchs, the fossilizable, resting cysts of phytoplanktonic algal protists, are the dominant component of marine organicwalled microfossils in the Palaeozoic. The majority of acritarchs show strong similarities with dinoflagellate cysts in morphological and biogeochemical features, as well as distributional patterns in the sediments. The production of these organicwalled microfossils and their distribution and survivorship in the sediments were controlled by differences in ecological tolerances and life cycle (autecology) of the planktonic parent organisms. Calculation of evolutionary rates and development of a detailed diversity curve at specific level, form the basis for discussing the influence of global palaeoenvironmental perturbations on the evolution of organic-walled microphytoplankton in northern Gondwana during latest Cambrian through Ordovician times. The potential of acritarchs for biostratigraphic correlation at the regional scale (northern Gondwana domain) is much improved by our detailed revision of distributional patterns of 245 acritarch taxa. The most important Cambro-Ordovician acritarch bio-events are short periods of diversification, which also correspond to introduction of morphological innovations, observed in latest Cambrian and earliest Tremadoc, late Tremadoc, early Arenig, basal Llanvirn, and latest Ashgill, and an important extinction phase in the early Caradoc. Overall, acritarch diversity increased from the basal Ordovician up to the middle Llanvirn, then declined in the early and middle Caradoc. During Ashgill times, the assemblages are poorly diversified at the generic level as a result of a combined effect of sea level drawdown and onset of glacial conditions, but no major extinction event is observed in connection with the end-Ordovician biotic crisis. The peak in acritarch diversity during Middle Ordovician times appears to be correlated to maximum spread of palaeogeographical assembly. Acritarch dynamics appear largely uncorrelated to second order sea-level oscillations; the primary abiotic controls on acritarch evolution were palaeogeographical and the associated palaeoceanographic changes (especially during Middle Ordovician), and the end-Ordovician palaeoclimatic shift.
New palynomorphs from the Ordovician–Silurian boundary interval: Eastern North America and Saudi Arabia
Palynology, 2017
ABSTRACT A distinctive coenobial palynomorph, Speculaforma gen. nov., and its two new species, S.... more ABSTRACT A distinctive coenobial palynomorph, Speculaforma gen. nov., and its two new species, S. delicata and S. elongata, are described from the Llandovery Grimsby Formation, Medina Group, from New York and are part of a more diverse palynomorph assemblage. Speculaforma delicata was also recovered from the Tuscarora Formation, West Virginia, and subsurface Hirnantian sediments in southern Saudi Arabia. Speculaforma is questionably assigned to the Hydrodictyaceae within the order Chlorococcales based on its geometrically regular coenobia. It is considered to be a freshwater or brackish-water alga. Occurring with this coenobium are two new acritarchs, Lunataforma parallela gen. et sp. nov. and Pertusidisca quadripora gen. et sp. nov. These acritarchs have been recovered from near-shore marine settings, in both North America and Saudi Arabia; but in North America Lunataforma was also recovered from sediments considered to represent an open marine environment.
Palynology, 2017
Cryptospores from the Dapingian-Darriwilian Kanosh Shale at Fossil Mountain, Utah, USA, occur as ... more Cryptospores from the Dapingian-Darriwilian Kanosh Shale at Fossil Mountain, Utah, USA, occur as tetrads, dyads, irregular clusters, or planar sheets of spore dyads. These spore 'thalli' are placed into the new taxon Grododowon orthogonalis gen. et sp. nov. based on the nature of division patterning and gross overall shape. The antithetic hypothesis of embryophyte origins dictates that spores evolved first and that the vegetative sporophyte evolved later via mitotic cell divisions that preceded meiosis and spore formation. We interpret the planar spore sheets of Grododowon gen. nov. to have formed via the cooption of a prior vegetative gametophytic developmental pattern which was expressed in the zygote, resulting in a two-dimensional, thalloid bauplan. However, the ploidy of the resultant 'spores' as haploid is necessarily conjectural, and this pattern of growth is clearly not the ancestral condition in the streptophyte lineage that gave rise to the first axial plant sporophyte.
Revue de Micropaléontologie, 2017
Revue de micropaléontologie xxx (2016) xxx-xxx Original article Wall ultrastructure of the oldest... more Revue de micropaléontologie xxx (2016) xxx-xxx Original article Wall ultrastructure of the oldest embryophytic spores: Implications for early land plant evolution Ultrastructure de la paroi des plus anciennes spores embryophytiques : implications pour l'évolution des plantes primitives terrestres
Plant evolution and terrestrialization during Palaeozoic times—The phylogenetic context
Review of Palaeobotany and Palynology, 2016
Abstract Terrestrialization probably began more than one billion years ago and irreversibly alter... more Abstract Terrestrialization probably began more than one billion years ago and irreversibly altered biogeochemical processes at planetary scale. In this paper, we focus on the terrestrialization process of the Streptophyta, the division that includes charophytes and land plants (embryophytes) and whose members are today ecologically dominant in all terrestrial environments. The timing and the phylogenetic context of the early evolution of land plants are reviewed. The available information on the relationships within embryophytes and related organisms is compiled in two informal consensus trees based either on morphological/anatomical or on molecular data. We also consider the algal/embryophyte transition through the analysis of the evidence provided by microfossils (cryptospores and spores). The ongoing debate about the definition of the term cryptospores, but more importantly about the biological affinities of these microfossils that are possibly derived from early land plants, is discussed. All important clades of embryophytes, with a focus on their Palaeozoic representatives, are described; the significance of several embryophyte key characters is evaluated. The terrestrialization of land plants evolved in different steps. The new term “proembryophytic phase” is introduced to define the very long period of time during which the green algae ancestor of land plants acquired all the evolutionary characters that ultimately allowed their terrestrialization since the late Precambrian. An “eoembryophytic phase”, spanning the Middle-Upper Ordovician, is defined based on the occurrence of the earliest evidence of liverwort-like plants. The inception of the trilete spores in Late Ordovician times is then taken to define the start of the eo/eutracheophytic phase, which lasts until the first occurrence of vascular plant macrofossils in the Silurian.
High-Resolution Integrated Palynological and Graptolite Biozonation in the Early Silurian of the Arabian Plate
Upper Cambrian acritarchs from the subsurface Arabian Gulf, Saudi Arabia
Mass-wasting triggered by the end-Triassic mass-extinction