University of Isfahan Journal of Stratigraphy and Sedimentology Researches 2008-7888 42 1 2026 03 21 Palaeobiogeographical study of the Late Ordovician brachiopods of Iran based on quantitative analysis Palaeobiogeographical study of the Late Ordovician brachiopods of Iran based on quantitative analysis 55 79 29579 10.22108/jssr.2025.143712.1304 FA Akbar Sohrabi Assistant Professor, Department of Geology, University of Tabriz, Tabriz, Iran 0000-0002-5320-7238 Journal Article 2024 12 23 Abstract Brachiopods, as one of the most important benthic fauna in the Late Ordovician, show a great abundance and diversity in many continents. In this study, a quantitative approach of multivariate analyses was conducted in order to study the palaeobiogeography of the brachiopods of Iran and their relationship with the brachiopods from other parts of the world, such as Baltica, Avalonia, Laurentia, South China, Kazakhstan, France, and Portugal, during the Late Ordovician (early Katian). Based on the results of the cluster analysis (CA), six main clusters and two sub-clusters were distinguished. The results obtained from the principal component analysis (PCA) method indicate the differentiation of seven main groups and show a high similarity with the main clusters obtained from the CA method. Based on the results of CA, the brachiopods of Bojnourd, Iran, are placed in a separate cluster together with the Avalonian brachiopods such as Shropshire, Powys (Wales), Anglesey (Wales), and Meath (Ireland). Based on the PCA scatter plot, the brachiopods of Bojnourd are placed in the same group with the Avalonian brachiopods. They are distinguished from the brachiopods of the Zagros and Anarak regions in central Iran, which form a separate group with the brachiopods of France, Portugal, and Morocco. The results of the PCA method indicate that the brachiopods from intracratonic Laurentian Basin such as New York, Manitoulin Island, Kentucky, and Indiana form a distinct group and are differentiated from brachiopods from continental margin such as the Appalachian Basin, Tyrone (Northern Ireland), and Girvan (Scotland). Keywords: Brachiopods, Late Ordovician, Palaeobiogeography, Multivariate analyses, Katian Introduction During the Late Ordovician, much of Laurentia was covered by a shallow epicontinental sea that created carbonate platforms in the intracontinental basins and pericratonic shelves (Finnegan et al. 2012). This marine transgression event and the creation of carbonate structures likely indicate a greenhouse warming episode in the Late Ordovician. In addition, some sedimentological and geochemical data support the hypothesis of a cooling episode in the Late Ordovician, leading to the cold and glacial climate of the Hirnantian (Page et al. 2007; Trotter et al. 2008; Buggisch et al. 2010). Interpretations of the climate change during the Late Ordovician are controversial and, like the Boda event in the late Katian, have been interpreted as both a warming and a cooling episode (Fortey & Cocks 2005; Cherns & Wheeley 2007). As one of the most important groups of marine invertebrates of the Paleozoic, brachiopods have a high diversity and abundance in the Ordovician and are therefore of great importance in palaeobiogeographic studies. According to Webby (2000), major fossil groups such as brachiopods show three global diversity maximum during the “Great Ordovician Diversification Event,”. Each palaeocontinent had different brachiopod diversification trajectories during the Ordovician. Based on Harper & Rong (2001), rhynchonelliform brachiopods diversified during the Dapingian and Darriwilian. The Ordovician brachiopods of Baltica show four diversity maxima in the mid-Darriwilian, late Darriwilian, late Sandbian, and late Katian and are different from the brachiopod diversity curves of Avalonia and Gondwana. The brachiopods of Gondwana had one diversity maxima during the late Sandbian (Hints & Harper 2001; Harper & Mac Nicaill 2002; Harper 2006). In South China, brachiopods had three diversity maxima in the early Floian, late Darriwilian, and late Katian (Zhan & Harper 2006). During the late Darriwilian, the earliest rhynchonellid brachiopods appeared in shallow marine environments of palaeotropical regions, including Laurentia, Siberia, and Kazakhstan (Jin 1996). During the Sandbian and early Katian, the total number of rhynchonellide genera increased from five to fifteen. By the late Katian, rhynchonellide brachiopods became widespread in the epicontinental seas of Laurentia and some of the genera such as Hiscobeccus was endemic to Laurentia (Sohrabi & Jin 2013a). The controlling mechanism for the major changes in biogeographic patterns is not well understood. Because of the importance of the Katian brachiopods in palaeogeographic interpretations, a quantitative approach was conducted to investigate the Katian brachiopods of Iran and other regions of the world. Measuring the faunal similarity of the Iranian brachiopods with those from other regions of the world can provide a comprehensive interpretation of the palaeoclimatic and palaeogeographic control on the brachiopods’ evolution and their changing biogeographic patterns. Material & Methods In this study, the palaeobiogeography of the Late Ordovician brachiopods was investigated. The brachiopod data were compiled from various regions, including Baltica, Avalonia, Laurentia, Australia, Kazakhstan, France, South China, Portugal, Morocco, and Iran. Most of the brachiopod data in the present study are from the formations of the early Katian. The Laurentian brachiopods data were obtained from various regions of North America, including the Ottawa Valley, Lake Simcoe, northern Rocky Mountains, western Newfoundland, Manitoulin Island, New York, Kentucky, Indiana, Oklahoma, South Dakota, Nevada, California, Mississippi Valley, Champlain Valley, Hudson Valley, Appalachian Valley, Girvan (Scotland), and Tyrone (Northern Ireland). The brachiopods of Baltica are from the eastern Baltic (Estonia and Lithuania) of Keila and Oandu age (Rõõmusoks 2004; Hints 1998, 2010). The brachiopods of southern Norway are from the Oslo-Asker area, which are related to deep-water facies (Hansen 2008). The Late Ordovician brachiopods of Avalonia are from Waterford and Wexford (southeast Ireland), Meath (east Ireland), and Powys and Anglesey (Wales) (Cocks 2008). In Britain and Ireland, the late Sandbian–early Katian strata include Scotland, Shropshire, Wales, and Ireland. The brachiopods of Scotland are from the Caradoc aged formations in the Girvan area including the Craighead Limestone, Myoch Formation, Whitehouse Bay, and Albany Mudstone Formation. The brachiopods of the Shropshire region include the Caradoc aged formations such as the Acton Scott, Onny Shale, Cheney Longville, Spy Wood Grit, Horderley Sandstone, Whittery Shale, Hagley Shale, Whittery Volcanic, Hoar Edge Grit, Woolston, Smeathen Wood Beds, and Cheney Longville formations. The brachiopods of northwest Wales, Anglesey, include Sandbian–early Katian formations such as the Garn Formation, Llanbabo Formation, and Crewyn Formation. In northern Ireland, the brachiopods are from the Tyrone region including the Bardahessiagh Formation of the Burrellian age. The brachiopods of southern and southeastern Ireland are from Meath, Wexford, and Waterford and include the Burrellian age formations of the Duncannon Group, such as the Annestown Formation, Lower Tramore Volcanic Formation, Grange Hill Formation, Upper Tuffs and Shales of Grangegeeth Volcanic Series, Collon Formation, and Clashford House Formation. The early Katian brachiopods of Kazakhstan are related to the Chu–Ili, Ishim–Selety, and Boshchekul terrains and include the Anderken and Dolankara formations (Popov et al. 2002; Nikitin et al. 2006). In South China, the early Katian brachiopods include the Pagoda Formation (Zhan & Jin 2007; Bergstrӧm et al. 2009). The early Katian brachiopods of Portugal are related to the Cabeço do Peão and Ferradosa formations (Henry & Romano 1978; Cooper 1980; Romano 1980, 1982, 1991; Young 1985, 1988). In Morocco, the Late Ordovician brachiopods are from the Khabt-el-Hajar Formation (Fortey & Cocks 2005). Most of the Katian rhynchonelliform brachiopods of Gondwana are from the western Mediterranean regions such as France, Spain, and Portugal (Torsvik & Cocks 2011). In Iran, the Late Ordovician brachiopods include the Bojnourd region (Ghelli Formation), the Anarak region in Central Iran (Chah Gonbad Formation), and the Zagros region (Siahu Formation). Multivariate analyses: The data used in this study include a large number of genera in general, as well as a large number of endemic genera from different regions. In this study, multivariate analyses were conducted based on the early Katian brachiopods dataset to investigate the palaeobiogeography of the brachiopods of Iran and their relationships with the other brachiopods from Baltica, Avalonia, Laurentia, Australia, Kazakhstan, France, South China, Portugal, and Morocco. The dataset was generated based on binary data that includes 261 brachiopod genera of the early Katian from 30 geographical regions. In this dataset, the geographic regions were selected as locations and the brachiopod genera as variables (presence or absence). The dataset was subjected to multivariate analyses using PAST software (Hammer et al. 2001; Hammer & Harper 2006), which was developed for analyzing paleontological data. In order to distinguish the distribution patterns of the brachiopods in time and space, cluster analysis (CA) and principal component analysis (PCA) methods were employed. To perform cluster analysis (CA), a dendrogram algorithm was generated based on the paired group method by using the Raup-Crick similarity coefficient. The Raup-Crick similarity coefficient shows fully segregated clusters. The dataset was also subjected to PCA by using the variance-covariance algorithm in PAST software. The result was plotted in the PCA scatterplot, based on principal components 1 (X-axis) and 2 (Y-axis), which correspond to eigenvalues 1 and 2, respectively. Discussion of Results & Conclusions In this study, the results of multivariate analyses of the Late Ordovician (early Katian) brachiopods from 30 geographical regions including Laurentia, Baltica, Avalonia, South China, Kazakhstan, France, Portugal, Morocco, and Iran indicate several palaeogeographic patterns. Based on the results of CA and PCA, several clusters and groups were recognized. The results of CA indicate several distinct clusters. Based on the CA dendrogram, five main clusters (A–F) and four subclusters (A1 and A2) were identified. Cluster A consists of two subgroups, clusters A1 and A2. Cluster A1 contains the brachiopods of Lithuania-North Estonia in the East Baltic, which indicate relatively shallow and warm-water carbonate environments during the early Katian. Cluster A2 comprises the brachiopods from Shropshire, Meath (Ireland), Anglesey and Powys in Wales, and Bojnourd in Iran. The cluster of Bojnourd brachiopods with the brachiopods of Shropshire, Meath (Ireland), and other Welsh regions indicates the close affinity of the Bojnourd brachiopod fauna with those of Avalonia during the early Katian. Cluster B includes western Newfoundland, New York, Kentucky, Indiana, Manitoulin Island, Lake Simcoe, British Columbia, Appalachian Basin, Great Basin, Tyrone (Northern Ireland), and Girvan (Scotland). Western Newfoundland, New York, Kentucky, Indiana, Manitoulin Island, and Lake Simcoe were located on tropical carbonate platforms at mid- to high-latitudes. The Appalachian Basin (from Pennsylvania and Tennessee to Alabama), British Columbia (Advanced Formation), Girvan (Scotland), and Tyrone (Northern Ireland) represent the continental margin of Laurentia during the Late Ordovician. Cluster C includes brachiopods from southeastern Ireland (Wexford and Waterford), South China, and southern Norway (Oslo-Osker), and corresponds to cluster D in the PCA plot. Cluster D in the CA analysis represents the brachiopods from France and Portugal. Cluster E in this dendrogram includes the brachiopods from the Zagros and Anarak regions of Iran. Cluster F in the dendrogram includes the brachiopod faunas of Kazakhstan terranes such as Chu-Il, Boshchekul, and Ishim-Selety and shows low similarity with the brachiopod faunas from other regions. The brachiopod faunas of Morocco are separated from other brachiopod faunas in this dendrogram, which indicates their low similarities with the brachiopod fauna from other areas. In the PCA method, the brachiopod data were scattered in the PCA plot based on principal components 1 (X-axis) and 2 (Y-axis). According to the PCA scatterplot, seven groups A1, A2, B, C, D, E, and F were distinguished, which are similar to the clusters identified in the CA dendrogram. Group A1 consists of the brachiopod faunas from the eastern Baltic, Lithuania, and northern Estonia, and shows consistency with cluster A1 in the CA plot. Group A2 includes the brachiopod faunas from Shropshire, Powys (Wales), Anglesey (Wales), Meath (Ireland), and Bojnourd (Iran). It is interesting to note that the brachiopod faunas of the Bojnourd region are located among the Avalonian brachiopods within cluster A2 in the CA diagram. Group B includes the brachiopod faunas of epicontinental Laurentian such as Lake Simcoe, Manitoulin Island, New York, Kentucky, and Indiana and are located in proximity to the Avalonian regions. The position of the brachiopod faunas of Bojnourd close to the Avalonian and epicontinental Laurentian brachiopod faunas indicates the similarity of the brachiopods from this region of Kopeh-Dagh in northwestern Iran with those of Laurentia and Avalonia during Katian time. With the onset of the marine transgression over Laurentia during the early Katian, the brachiopod faunas of North America began to show a distinction between pericratonic and intracratonic settings. Scoto-Appalachian brachiopod fauna on the southeastern margin of Laurentia were more closely related to the brachiopod fauna of Avalonian and deep-water Baltica facies than to the intracratonic Laurentian fauna. In contrast, the intracratonic (epicontinental) Laurentian brachiopod fauna was more similar to the Lithuanian-northern Estonian brachiopod fauna than to the Scoto-Appalachian brachiopod fauna on the cratonic Laurentian margin. Group C, in the right portion of the PCA plot, shows brachiopods from the Appalachian, Girvan (Scotland), and Tyrone (Northern Ireland) regions. This group, which is clearly separated from the fauna of other regions especially Laurentia, is consistent with the concept of the Scoto-Appalachian fauna that introduced by Jaanusson (1979) and Whittington and Williams (1955). Group D in the PCA diagram corresponds to brachiopod faunas from the Oslo-Oskar area (Norway), South China, and southeastern Ireland (Wexford-Waterford), which corresponds to cluster C in the CA diagram. Group E includes brachiopods from the Zagros and Anarak regions of Iran, Morocco, France, and Portugal. In the CA diagram, the brachiopod faunas from the Zagros and Anarak regions are grouped in cluster E, and the brachiopod faunas from France and Portugal are grouped in cluster D, which indicates the high similarity of the brachiopods of these regions. The group F in the PCA plot corresponds to cluster F in the CA diagram and is related to the brachiopods of the Chu-Il, Boshchekul, and Ishim-Selety regions of Kazakhstan. According to the results of the CA and PCA, the brachiopods of the Kazakh regions show low similarity to the brachiopods of Laurentia, Baltica, and Avalonia, which could be due to the presence of endemic species in the Kazakh regions and very limited faunal connection with the brachiopods of the other areas during the Katian. The brachiopod faunas of epicontinental Laurentia from the Ottawa Valley, Lake Simcoe, Ontario, Manitoulin Island, western Newfoundland, New York, Hudson Valley, Champlain Valley, Kentucky, Indiana, Mississippi Valley, and Oklahoma show a higher similarity to the brachiopod faunas of mainly Avalonian origin than to the Scoto-Appalachian brachiopods of pericratonic regions. The early Katian Scoto-Appalachian brachiopods show a higher affinity to the brachiopods from the western margin of Laurentia such as the northern Rocky Mountains in British Columbia and Great Basin. The differentiation of Laurentian pericratonic and intracratonic brachiopod fauna during the early Katian has been interpreted as a palaeobiogeographical pattern (Sohrabi & Jin 2013). Based on the results of this study, the brachiopods of the Bojnourd region of Iran show more similarity with the Avalonian brachiopods rather than with the brachiopod faunas of the Zagros and Central Iran regions, as shown in cluster A2 in CA and Group 2 in the PCA diagram. The high degree of faunal similarity between the brachiopods of the Bojnourd region and the Avalonian brachiopods could be related to similar environmental conditions of these brachiopods during the early Katian. The close faunal affinity of the brachiopod faunas of the Bojnourd and Kopeh-Dagh regions with those of Avalonia was more likely attributable to the position of Bojnourd region of Iran at relatively lower latitudes which had different environmental conditions than those of the Zagros and Central Iran regions during the early Katian. Also, the low degree of faunal similarity between the Bojnourd brachiopods and the brachiopods of the same age in the Zagros and Central Iran regions could be interpreted as the beginning of brachiopod endemism in the Bojnourd region during the Late Ordovician (early Katian). During the early Katian, the Kopeh-Dagh region of Iran was more likely part of the microplates (terranes) adjacent to the supercontinent of Gondwana at similar latitudes to Avalonia and separated from the Zagros and Central Iran regions. The close similarity of the brachiopod faunas of Zagros and Central Iran with the brachiopods of France and Portugal, which were parts of high-latitude Gondwana, indicates their Gondwana palaeogeographical affinity during the Katian. By collecting more Late Ordovician brachiopods from different regions of Iran and compiling a comprehensive dataset, a better interpretation of the palaeobiogeographic pattern of the brachiopods can be obtained, which could result in a more accurate palaeogeographic positioning of Iran during the Late Ordovician. Abstract Brachiopods, as one of the most important benthic fauna in the Late Ordovician, show a great abundance and diversity in many continents. In this study, a quantitative approach of multivariate analyses was conducted in order to study the palaeobiogeography of the brachiopods of Iran and their relationship with the brachiopods from other parts of the world, such as Baltica, Avalonia, Laurentia, South China, Kazakhstan, France, and Portugal, during the Late Ordovician (early Katian). Based on the results of the cluster analysis (CA), six main clusters and two sub-clusters were distinguished. The results obtained from the principal component analysis (PCA) method indicate the differentiation of seven main groups and show a high similarity with the main clusters obtained from the CA method. Based on the results of CA, the brachiopods of Bojnourd, Iran, are placed in a separate cluster together with the Avalonian brachiopods such as Shropshire, Powys (Wales), Anglesey (Wales), and Meath (Ireland). Based on the PCA scatter plot, the brachiopods of Bojnourd are placed in the same group with the Avalonian brachiopods. They are distinguished from the brachiopods of the Zagros and Anarak regions in central Iran, which form a separate group with the brachiopods of France, Portugal, and Morocco. The results of the PCA method indicate that the brachiopods from intracratonic Laurentian Basin such as New York, Manitoulin Island, Kentucky, and Indiana form a distinct group and are differentiated from brachiopods from continental margin such as the Appalachian Basin, Tyrone (Northern Ireland), and Girvan (Scotland). Keywords: Brachiopods, Late Ordovician, Palaeobiogeography, Multivariate analyses, Katian Introduction During the Late Ordovician, much of Laurentia was covered by a shallow epicontinental sea that created carbonate platforms in the intracontinental basins and pericratonic shelves (Finnegan et al. 2012). This marine transgression event and the creation of carbonate structures likely indicate a greenhouse warming episode in the Late Ordovician. In addition, some sedimentological and geochemical data support the hypothesis of a cooling episode in the Late Ordovician, leading to the cold and glacial climate of the Hirnantian (Page et al. 2007; Trotter et al. 2008; Buggisch et al. 2010). Interpretations of the climate change during the Late Ordovician are controversial and, like the Boda event in the late Katian, have been interpreted as both a warming and a cooling episode (Fortey & Cocks 2005; Cherns & Wheeley 2007). As one of the most important groups of marine invertebrates of the Paleozoic, brachiopods have a high diversity and abundance in the Ordovician and are therefore of great importance in palaeobiogeographic studies. According to Webby (2000), major fossil groups such as brachiopods show three global diversity maximum during the “Great Ordovician Diversification Event,”. Each palaeocontinent had different brachiopod diversification trajectories during the Ordovician. Based on Harper & Rong (2001), rhynchonelliform brachiopods diversified during the Dapingian and Darriwilian. The Ordovician brachiopods of Baltica show four diversity maxima in the mid-Darriwilian, late Darriwilian, late Sandbian, and late Katian and are different from the brachiopod diversity curves of Avalonia and Gondwana. The brachiopods of Gondwana had one diversity maxima during the late Sandbian (Hints & Harper 2001; Harper & Mac Nicaill 2002; Harper 2006). In South China, brachiopods had three diversity maxima in the early Floian, late Darriwilian, and late Katian (Zhan & Harper 2006). During the late Darriwilian, the earliest rhynchonellid brachiopods appeared in shallow marine environments of palaeotropical regions, including Laurentia, Siberia, and Kazakhstan (Jin 1996). During the Sandbian and early Katian, the total number of rhynchonellide genera increased from five to fifteen. By the late Katian, rhynchonellide brachiopods became widespread in the epicontinental seas of Laurentia and some of the genera such as Hiscobeccus was endemic to Laurentia (Sohrabi & Jin 2013a). The controlling mechanism for the major changes in biogeographic patterns is not well understood. Because of the importance of the Katian brachiopods in palaeogeographic interpretations, a quantitative approach was conducted to investigate the Katian brachiopods of Iran and other regions of the world. Measuring the faunal similarity of the Iranian brachiopods with those from other regions of the world can provide a comprehensive interpretation of the palaeoclimatic and palaeogeographic control on the brachiopods’ evolution and their changing biogeographic patterns. Material & Methods In this study, the palaeobiogeography of the Late Ordovician brachiopods was investigated. The brachiopod data were compiled from various regions, including Baltica, Avalonia, Laurentia, Australia, Kazakhstan, France, South China, Portugal, Morocco, and Iran. Most of the brachiopod data in the present study are from the formations of the early Katian. The Laurentian brachiopods data were obtained from various regions of North America, including the Ottawa Valley, Lake Simcoe, northern Rocky Mountains, western Newfoundland, Manitoulin Island, New York, Kentucky, Indiana, Oklahoma, South Dakota, Nevada, California, Mississippi Valley, Champlain Valley, Hudson Valley, Appalachian Valley, Girvan (Scotland), and Tyrone (Northern Ireland). The brachiopods of Baltica are from the eastern Baltic (Estonia and Lithuania) of Keila and Oandu age (Rõõmusoks 2004; Hints 1998, 2010). The brachiopods of southern Norway are from the Oslo-Asker area, which are related to deep-water facies (Hansen 2008). The Late Ordovician brachiopods of Avalonia are from Waterford and Wexford (southeast Ireland), Meath (east Ireland), and Powys and Anglesey (Wales) (Cocks 2008). In Britain and Ireland, the late Sandbian–early Katian strata include Scotland, Shropshire, Wales, and Ireland. The brachiopods of Scotland are from the Caradoc aged formations in the Girvan area including the Craighead Limestone, Myoch Formation, Whitehouse Bay, and Albany Mudstone Formation. The brachiopods of the Shropshire region include the Caradoc aged formations such as the Acton Scott, Onny Shale, Cheney Longville, Spy Wood Grit, Horderley Sandstone, Whittery Shale, Hagley Shale, Whittery Volcanic, Hoar Edge Grit, Woolston, Smeathen Wood Beds, and Cheney Longville formations. The brachiopods of northwest Wales, Anglesey, include Sandbian–early Katian formations such as the Garn Formation, Llanbabo Formation, and Crewyn Formation. In northern Ireland, the brachiopods are from the Tyrone region including the Bardahessiagh Formation of the Burrellian age. The brachiopods of southern and southeastern Ireland are from Meath, Wexford, and Waterford and include the Burrellian age formations of the Duncannon Group, such as the Annestown Formation, Lower Tramore Volcanic Formation, Grange Hill Formation, Upper Tuffs and Shales of Grangegeeth Volcanic Series, Collon Formation, and Clashford House Formation. The early Katian brachiopods of Kazakhstan are related to the Chu–Ili, Ishim–Selety, and Boshchekul terrains and include the Anderken and Dolankara formations (Popov et al. 2002; Nikitin et al. 2006). In South China, the early Katian brachiopods include the Pagoda Formation (Zhan & Jin 2007; Bergstrӧm et al. 2009). The early Katian brachiopods of Portugal are related to the Cabeço do Peão and Ferradosa formations (Henry & Romano 1978; Cooper 1980; Romano 1980, 1982, 1991; Young 1985, 1988). In Morocco, the Late Ordovician brachiopods are from the Khabt-el-Hajar Formation (Fortey & Cocks 2005). Most of the Katian rhynchonelliform brachiopods of Gondwana are from the western Mediterranean regions such as France, Spain, and Portugal (Torsvik & Cocks 2011). In Iran, the Late Ordovician brachiopods include the Bojnourd region (Ghelli Formation), the Anarak region in Central Iran (Chah Gonbad Formation), and the Zagros region (Siahu Formation). Multivariate analyses: The data used in this study include a large number of genera in general, as well as a large number of endemic genera from different regions. In this study, multivariate analyses were conducted based on the early Katian brachiopods dataset to investigate the palaeobiogeography of the brachiopods of Iran and their relationships with the other brachiopods from Baltica, Avalonia, Laurentia, Australia, Kazakhstan, France, South China, Portugal, and Morocco. The dataset was generated based on binary data that includes 261 brachiopod genera of the early Katian from 30 geographical regions. In this dataset, the geographic regions were selected as locations and the brachiopod genera as variables (presence or absence). The dataset was subjected to multivariate analyses using PAST software (Hammer et al. 2001; Hammer & Harper 2006), which was developed for analyzing paleontological data. In order to distinguish the distribution patterns of the brachiopods in time and space, cluster analysis (CA) and principal component analysis (PCA) methods were employed. To perform cluster analysis (CA), a dendrogram algorithm was generated based on the paired group method by using the Raup-Crick similarity coefficient. The Raup-Crick similarity coefficient shows fully segregated clusters. The dataset was also subjected to PCA by using the variance-covariance algorithm in PAST software. The result was plotted in the PCA scatterplot, based on principal components 1 (X-axis) and 2 (Y-axis), which correspond to eigenvalues 1 and 2, respectively. Discussion of Results & Conclusions In this study, the results of multivariate analyses of the Late Ordovician (early Katian) brachiopods from 30 geographical regions including Laurentia, Baltica, Avalonia, South China, Kazakhstan, France, Portugal, Morocco, and Iran indicate several palaeogeographic patterns. Based on the results of CA and PCA, several clusters and groups were recognized. The results of CA indicate several distinct clusters. Based on the CA dendrogram, five main clusters (A–F) and four subclusters (A1 and A2) were identified. Cluster A consists of two subgroups, clusters A1 and A2. Cluster A1 contains the brachiopods of Lithuania-North Estonia in the East Baltic, which indicate relatively shallow and warm-water carbonate environments during the early Katian. Cluster A2 comprises the brachiopods from Shropshire, Meath (Ireland), Anglesey and Powys in Wales, and Bojnourd in Iran. The cluster of Bojnourd brachiopods with the brachiopods of Shropshire, Meath (Ireland), and other Welsh regions indicates the close affinity of the Bojnourd brachiopod fauna with those of Avalonia during the early Katian. Cluster B includes western Newfoundland, New York, Kentucky, Indiana, Manitoulin Island, Lake Simcoe, British Columbia, Appalachian Basin, Great Basin, Tyrone (Northern Ireland), and Girvan (Scotland). Western Newfoundland, New York, Kentucky, Indiana, Manitoulin Island, and Lake Simcoe were located on tropical carbonate platforms at mid- to high-latitudes. The Appalachian Basin (from Pennsylvania and Tennessee to Alabama), British Columbia (Advanced Formation), Girvan (Scotland), and Tyrone (Northern Ireland) represent the continental margin of Laurentia during the Late Ordovician. Cluster C includes brachiopods from southeastern Ireland (Wexford and Waterford), South China, and southern Norway (Oslo-Osker), and corresponds to cluster D in the PCA plot. Cluster D in the CA analysis represents the brachiopods from France and Portugal. Cluster E in this dendrogram includes the brachiopods from the Zagros and Anarak regions of Iran. Cluster F in the dendrogram includes the brachiopod faunas of Kazakhstan terranes such as Chu-Il, Boshchekul, and Ishim-Selety and shows low similarity with the brachiopod faunas from other regions. The brachiopod faunas of Morocco are separated from other brachiopod faunas in this dendrogram, which indicates their low similarities with the brachiopod fauna from other areas. In the PCA method, the brachiopod data were scattered in the PCA plot based on principal components 1 (X-axis) and 2 (Y-axis). According to the PCA scatterplot, seven groups A1, A2, B, C, D, E, and F were distinguished, which are similar to the clusters identified in the CA dendrogram. Group A1 consists of the brachiopod faunas from the eastern Baltic, Lithuania, and northern Estonia, and shows consistency with cluster A1 in the CA plot. Group A2 includes the brachiopod faunas from Shropshire, Powys (Wales), Anglesey (Wales), Meath (Ireland), and Bojnourd (Iran). It is interesting to note that the brachiopod faunas of the Bojnourd region are located among the Avalonian brachiopods within cluster A2 in the CA diagram. Group B includes the brachiopod faunas of epicontinental Laurentian such as Lake Simcoe, Manitoulin Island, New York, Kentucky, and Indiana and are located in proximity to the Avalonian regions. The position of the brachiopod faunas of Bojnourd close to the Avalonian and epicontinental Laurentian brachiopod faunas indicates the similarity of the brachiopods from this region of Kopeh-Dagh in northwestern Iran with those of Laurentia and Avalonia during Katian time. With the onset of the marine transgression over Laurentia during the early Katian, the brachiopod faunas of North America began to show a distinction between pericratonic and intracratonic settings. Scoto-Appalachian brachiopod fauna on the southeastern margin of Laurentia were more closely related to the brachiopod fauna of Avalonian and deep-water Baltica facies than to the intracratonic Laurentian fauna. In contrast, the intracratonic (epicontinental) Laurentian brachiopod fauna was more similar to the Lithuanian-northern Estonian brachiopod fauna than to the Scoto-Appalachian brachiopod fauna on the cratonic Laurentian margin. Group C, in the right portion of the PCA plot, shows brachiopods from the Appalachian, Girvan (Scotland), and Tyrone (Northern Ireland) regions. This group, which is clearly separated from the fauna of other regions especially Laurentia, is consistent with the concept of the Scoto-Appalachian fauna that introduced by Jaanusson (1979) and Whittington and Williams (1955). Group D in the PCA diagram corresponds to brachiopod faunas from the Oslo-Oskar area (Norway), South China, and southeastern Ireland (Wexford-Waterford), which corresponds to cluster C in the CA diagram. Group E includes brachiopods from the Zagros and Anarak regions of Iran, Morocco, France, and Portugal. In the CA diagram, the brachiopod faunas from the Zagros and Anarak regions are grouped in cluster E, and the brachiopod faunas from France and Portugal are grouped in cluster D, which indicates the high similarity of the brachiopods of these regions. The group F in the PCA plot corresponds to cluster F in the CA diagram and is related to the brachiopods of the Chu-Il, Boshchekul, and Ishim-Selety regions of Kazakhstan. According to the results of the CA and PCA, the brachiopods of the Kazakh regions show low similarity to the brachiopods of Laurentia, Baltica, and Avalonia, which could be due to the presence of endemic species in the Kazakh regions and very limited faunal connection with the brachiopods of the other areas during the Katian. The brachiopod faunas of epicontinental Laurentia from the Ottawa Valley, Lake Simcoe, Ontario, Manitoulin Island, western Newfoundland, New York, Hudson Valley, Champlain Valley, Kentucky, Indiana, Mississippi Valley, and Oklahoma show a higher similarity to the brachiopod faunas of mainly Avalonian origin than to the Scoto-Appalachian brachiopods of pericratonic regions. The early Katian Scoto-Appalachian brachiopods show a higher affinity to the brachiopods from the western margin of Laurentia such as the northern Rocky Mountains in British Columbia and Great Basin. The differentiation of Laurentian pericratonic and intracratonic brachiopod fauna during the early Katian has been interpreted as a palaeobiogeographical pattern (Sohrabi & Jin 2013). Based on the results of this study, the brachiopods of the Bojnourd region of Iran show more similarity with the Avalonian brachiopods rather than with the brachiopod faunas of the Zagros and Central Iran regions, as shown in cluster A2 in CA and Group 2 in the PCA diagram. The high degree of faunal similarity between the brachiopods of the Bojnourd region and the Avalonian brachiopods could be related to similar environmental conditions of these brachiopods during the early Katian. The close faunal affinity of the brachiopod faunas of the Bojnourd and Kopeh-Dagh regions with those of Avalonia was more likely attributable to the position of Bojnourd region of Iran at relatively lower latitudes which had different environmental conditions than those of the Zagros and Central Iran regions during the early Katian. Also, the low degree of faunal similarity between the Bojnourd brachiopods and the brachiopods of the same age in the Zagros and Central Iran regions could be interpreted as the beginning of brachiopod endemism in the Bojnourd region during the Late Ordovician (early Katian). During the early Katian, the Kopeh-Dagh region of Iran was more likely part of the microplates (terranes) adjacent to the supercontinent of Gondwana at similar latitudes to Avalonia and separated from the Zagros and Central Iran regions. The close similarity of the brachiopod faunas of Zagros and Central Iran with the brachiopods of France and Portugal, which were parts of high-latitude Gondwana, indicates their Gondwana palaeogeographical affinity during the Katian. By collecting more Late Ordovician brachiopods from different regions of Iran and compiling a comprehensive dataset, a better interpretation of the palaeobiogeographic pattern of the brachiopods can be obtained, which could result in a more accurate palaeogeographic positioning of Iran during the Late Ordovician.

https://jssr.ui.ac.ir/article_29579_65faa09d5d8622b26c35f67db4dd3055.pdf