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Trond H Torsvik - One of the best experts on this subject based on the ideXlab platform.
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continental break up and collision in the neoproterozoic and palaeozoic a tale of Baltica and laurentia
Earth-Science Reviews, 1996Co-Authors: Trond H Torsvik, Mark A. Smethurst, Joseph G. Meert, Martin D Brasier, Bryan A Sturt, W S Mckerrow, H J WalderhaugAbstract:During the Neoproterozoic and Palaeozoic the two continents of Baltica and Laurentia witnessed the break-up of one supercontinent, Rodinia, and the formation of another, but less long-lived, Pangea. Baltica and Laurentia played central roles in a tectonic menage a trois that included major orogenic events, a redistribution of palaeogeography and a brief involvement of both with Gondwana. Many of these plate re-organisations took place over a short time interval and invite a re-evaluation of earlier geodynamic models which limited the speeds at which large continental plates could move to an arbitrarily low value. Baltica and Laurentia probably shared a common drift history for the time interval 750 – 600 Ma as they rotated clockwise and drifted southward from an equatorial position during the opening of the Proto-Pacific between Laurentia and East Gondwana (initial break-up of Rodinia). On their combined approach toward the south pole, Baltica and Laurentia were glaciated during the Varanger glaciations. Although the two continents drifted toward the south pole during the Late Proterozoic, they began to separate at around 600 Ma (rift to drift) to form the Iapetus Ocean through asymmetric rifting and relative rotations of up to 180°. Initiation of rifting on the Baltic margin is marked by the 650 Ma Egersund tholeiitic dykes (SW Norway) which contain abundant lower crustal zenoliths, and the tholeiitic magma was probably derived from a mantle plume. In latest Precambrian time, the final redistribution of Rodinia is characterised by high plate velocities. In particular, Laurentia began a rapid, up to 20 cm/yr, ascent to equatorial latitudes and essentially stayed in low latitudes throughout most of the Palaeozoic. The high velocities suggest either that Laurentia was pushed off a lower mantle heat anomaly originating from supercontinental mantle insulation or that Laurentia was pulled toward a subduction-generated cold spot in the proto-Pacific. Baltica, except for a short and rapid excursion to lower latitudes in the Late Vendian, remained mostly in intermediate to high southerly latitudes and closer to the Gondwana margin until Early Ordovician times. In Early Ordovician times, Arenig-Llanvirn platform trilobites show a broad distinction between the continents of Laurentia/Siberia/North China Block (Bathyurid), Baltica (Ptychopygine/ Megalaspid) and the areas of NW Gondwana/Avalonia/Armorica (Calymenacean-Dalmanitacean). During the Ordovician, Baltica rotated and moved northward, approaching close enough to Laurentia by the late Caradoc for trilobite and brachiopod spat to cross the intervening Iapetus Ocean. Docking appears to have been irregular both in time and manner: the collision between Scotland/Greenland and western Norway resulted in the early Scandian Orogeny in the Silurian (c. 425 Ma), but further south, there is evidence of late Silurian impingement with subduction of Avalonian continental crust (in England and Ireland) below the eastern edge of Laurentia until the Emsian. In the northern Appalachians the main time of collision appears to have been during the Emsian/Eifellian Acadian Orogeny. Recent analyses invalidates the traditional concept of a sustained orthogonal relationship between Baltica and Laurentia across a single Iapetus Ocean throughout the Caledonide evolution. The active margin of Baltica (Scandinavian Caledonides) faced Siberia during the Late Cambrian and Early Ordovician with oceanic separation between these landmasses in the order of 1200–1500 km. This may explain the local occureences of Siberia-Laurentian type Bathyarid tribobite faunas in Central Norwegian Caledonian nappes, earlier interpreted as Laurentia-Baltica trilobite mixing. Subsequent counterclockwise rotation of Baltica transferred the Caledonian margin in the direction of Laurentia by Silurian times, when the two continents once again started to collide to form Euramerica. This rotation, along with the strongly asymmetric opening of the Iapetus at around 600 Ma, demonstrates a complexity in Precambrian-Palaeozoic plate tectonics, i.e. a collage of metastable plate boundaries which have perhaps too often been simplified to an orthagonal Wilson cycle tectonic scenario.
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Continental break-up and collision in the Neoproterozoic and Palaeozoic — A tale of Baltica and Laurentia
Earth-Science Reviews, 1996Co-Authors: Trond H Torsvik, Mark A. Smethurst, Joseph G. Meert, Martin D Brasier, Bryan A Sturt, W S Mckerrow, H J WalderhaugAbstract:During the Neoproterozoic and Palaeozoic the two continents of Baltica and Laurentia witnessed the break-up of one supercontinent, Rodinia, and the formation of another, but less long-lived, Pangea. Baltica and Laurentia played central roles in a tectonic menage a trois that included major orogenic events, a redistribution of palaeogeography and a brief involvement of both with Gondwana. Many of these plate re-organisations took place over a short time interval and invite a re-evaluation of earlier geodynamic models which limited the speeds at which large continental plates could move to an arbitrarily low value. Baltica and Laurentia probably shared a common drift history for the time interval 750 – 600 Ma as they rotated clockwise and drifted southward from an equatorial position during the opening of the Proto-Pacific between Laurentia and East Gondwana (initial break-up of Rodinia). On their combined approach toward the south pole, Baltica and Laurentia were glaciated during the Varanger glaciations. Although the two continents drifted toward the south pole during the Late Proterozoic, they began to separate at around 600 Ma (rift to drift) to form the Iapetus Ocean through asymmetric rifting and relative rotations of up to 180°. Initiation of rifting on the Baltic margin is marked by the 650 Ma Egersund tholeiitic dykes (SW Norway) which contain abundant lower crustal zenoliths, and the tholeiitic magma was probably derived from a mantle plume. In latest Precambrian time, the final redistribution of Rodinia is characterised by high plate velocities. In particular, Laurentia began a rapid, up to 20 cm/yr, ascent to equatorial latitudes and essentially stayed in low latitudes throughout most of the Palaeozoic. The high velocities suggest either that Laurentia was pushed off a lower mantle heat anomaly originating from supercontinental mantle insulation or that Laurentia was pulled toward a subduction-generated cold spot in the proto-Pacific. Baltica, except for a short and rapid excursion to lower latitudes in the Late Vendian, remained mostly in intermediate to high southerly latitudes and closer to the Gondwana margin until Early Ordovician times. In Early Ordovician times, Arenig-Llanvirn platform trilobites show a broad distinction between the continents of Laurentia/Siberia/North China Block (Bathyurid), Baltica (Ptychopygine/ Megalaspid) and the areas of NW Gondwana/Avalonia/Armorica (Calymenacean-Dalmanitacean). During the Ordovician, Baltica rotated and moved northward, approaching close enough to Laurentia by the late Caradoc for trilobite and brachiopod spat to cross the intervening Iapetus Ocean. Docking appears to have been irregular both in time and manner: the collision between Scotland/Greenland and western Norway resulted in the early Scandian Orogeny in the Silurian (c. 425 Ma), but further south, there is evidence of late Silurian impingement with subduction of Avalonian continental crust (in England and Ireland) below the eastern edge of Laurentia until the Emsian. In the northern Appalachians the main time of collision appears to have been during the Emsian/Eifellian Acadian Orogeny. Recent analyses invalidates the traditional concept of a sustained orthogonal relationship between Baltica and Laurentia across a single Iapetus Ocean throughout the Caledonide evolution. The active margin of Baltica (Scandinavian Caledonides) faced Siberia during the Late Cambrian and Early Ordovician with oceanic separation between these landmasses in the order of 1200–1500 km. This may explain the local occureences of Siberia-Laurentian type Bathyarid tribobite faunas in Central Norwegian Caledonian nappes, earlier interpreted as Laurentia-Baltica trilobite mixing. Subsequent counterclockwise rotation of Baltica transferred the Caledonian margin in the direction of Laurentia by Silurian times, when the two continents once again started to collide to form Euramerica. This rotation, along with the strongly asymmetric opening of the Iapetus at around 600 Ma, demonstrates a complexity in Precambrian-Palaeozoic plate tectonics, i.e. a collage of metastable plate boundaries which have perhaps too often been simplified to an orthagonal Wilson cycle tectonic scenario.
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Ordovician palaeogeography of Siberia and adjacent continents
Journal of the Geological Society, 1995Co-Authors: Trond H Torsvik, Bryan A Sturt, W S Mckerrow, J. Tait, V. M. Moralev, D. RobertsAbstract:Ordovician palaeomagnetic data from the upper reaches of the Lena River, Southern Siberia, confirm and refine the earlier reported data sets. Ordovician palaeomagnetic poles from Siberia define a systematic southwesterly apparent polar wander (APW) trend during Ordovician times (mean south poles: 500 Ma: 42°N, 310°E; 467 Ma: 27°N, 314°E; 460 Ma: 23°N, 313°E; 448 Ma: 22°N, 301°E and 437 Ma: 0N, 290°E). A primary or early magnetization age is verified by the reversal stratigraphy. Siberia was geographically inverted at low southerly latitudes during the Latest Cambrian and Early Ordovician and drifted slowly northward and across the equator at an average palaeo-latitudinal velocity of c. 5cm/year. In Early Ordovician times, Avalonia and the European Massifs (e.g. Armorica and Bohemia) were located together with Gondwana in high southerly latitudes, Laurentia was positioned in equatorial latitudes whereas Baltica was located at intermediate southerly latitudes. Siberia was probably located north of Baltica in latest Cambrian–Early Ordovician times. Subduction-related, eclogite-facies metamorphism in latest Cambrian–Early Ordovician time in the Scandinavian Caledonides occurred in an ocean-continent transition zone marginal to Baltica but facing northern Siberia, and thus throws doubt on traditional Baltic-Laurentian correlations during this particular time period. With Baltica rotating counterclockwise during the Ordovician, the plate scenario allows for a Siberian source for Late Ordovician sedimentation in some areas of maritime Laurentia and perhaps even northern Norway. It also helps to explain the imposition of a deep-seated, sinistral strike-slip, fault regime between the obliquely converging Baltica and Laurentia, a transcurrent system which may have led to the permissive ascent of calc-alkaline granitoid magmas in favourable sites prior to the main stages of Scandinavian orogenic deformation. Recent proposals that Laurentia formed a conjugate margin to the South American part of Gondwana during Ordovician times are permissible from palaeomagnetic data, but a tight continental fit during the entire Ordovician is contradicted by biogeographic data. The tight palaeomagnetic fit could perhaps be an artefact of inaccuracies in the palaeomagnetic record for Gondwana.
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Baltica a synopsis of vendian permian palaeomagnetic data and their palaeotectonic implications
Earth-Science Reviews, 1992Co-Authors: Trond H Torsvik, Mark A. Smethurst, Allan Trench, Niels Abrahamsen, Erik HalvorsenAbstract:Torsvlk, T H, Smethurst, M A., Van der Voo, R, Trench, A, Abrahamsen, N and Halvorsen, E, 1992 Baltlca. A synopsis of Vendlan-Permmn palaeomagnetic data and their palaeotectonlc implications Earth-Sci. Rev, 33 133-152. In light of recent additions to the Palaeozoic palaeo-magnetlc data-base, particularly for the Ordovlclan era, a revised apparent polar wander (APW) path for Baltica has been constructed following a rigorous synthesis of all Late Precambrlan-Perm lan data The APW path is characterized by two prominent loops Firstly, a Late Precambrlan-Camb rlan loop probably relating to a rifting event and secondly, a younger loop relating to a Mid-Silurian (Scandlan) colhsion event These features Imply major change In plate-tectonic reconfiguratlon Baltlca probably represented an individual continental unit m Early Palaeozoic times and was positioned m high southerly latitudes in an "'inverted" geographic orientation In such a reconstruction Baltlca was separated from the northern margin of Gondwana by the Tornqulst Sea and from Laurentla by the Iapetus Ocean The Tornqulst Zone is thus interpreted as a passive or dextral transform margin during the early Palaeozoic While undergoing counter-clockwise rotations (up to 1 6°/Ma), Baltica drifted northward through most ol the Palaeozoic, except for a short period of southerly movement in Late Silurian-Early Devonian times after colhslon with Laurentla. Rapid movements in latitude (up to 9 cm/yr) are noted m Late Precambrlan/earl y Palaeozoic times and slgmficant decrease in velocities throughout Palaeozoic time probably reflect the progressive amalgamation of a larger continent by Early-Devonian (Euramerlca) and Permian (Pangea) times The Tornqulst Sea had a principal component of palaeo-east-west orientation. Hence it is difficult to be precise in the timing of when micro-continents such as Eastern Avalonla and the European Masslfs ultimately collided along the southwestern margin of Baltica These micro-continents are considered to have been peripheral to Gondwana (m high southerly latitudes) during the Early Ordovlclan. Eastern Avalonla clearly had rifted off Gondwana by Llanvlrn-Llanded o times and may have collided with Baltlca during Late Ordovlclan times, although the present available Sdunan palaeomagnetlc data from Eastern Avalonia may suggest colhslon in Late Silurian times Across the lapetus facing margin of Baltica, Laurentla was s~tuated in equatorml to southerly latitudes during most of the Lower Palaeozoic These continents collided in Mid-Silurian times, l e a first collision between southwestern Norway and Greenland/Scotla nd which gave rise to the early Scandlan Orogeny (425 Ma) in southwestern Norway possible followed by a later, but less dramatic, Scandlan event in northern Norway at around 410 Ma Since Baltlca was geographically reverted m early Palaeozoic times, the colhsional margin could not have been a margin that once rifted off Laurentm as assumed in a number of plate-tectonic models
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Baltica a synopsis of vendian permian palaeomagnetic data and their palaeotectonic implications
Earth-Science Reviews, 1992Co-Authors: Trond H Torsvik, Mark A. Smethurst, Allan Trench, Niels Abrahamsen, Rob Van Der Voo, Erik HalvorsenAbstract:Torsvlk, T H, Smethurst, M A., Van der Voo, R, Trench, A, Abrahamsen, N and Halvorsen, E, 1992 Baltlca. A synopsis of Vendlan-Permmn palaeomagnetic data and their palaeotectonlc implications Earth-Sci. Rev, 33 133-152. In light of recent additions to the Palaeozoic palaeo-magnetlc data-base, particularly for the Ordovlclan era, a revised apparent polar wander (APW) path for Baltica has been constructed following a rigorous synthesis of all Late Precambrlan-Perm lan data The APW path is characterized by two prominent loops Firstly, a Late Precambrlan-Camb rlan loop probably relating to a rifting event and secondly, a younger loop relating to a Mid-Silurian (Scandlan) colhsion event These features Imply major change In plate-tectonic reconfiguratlon Baltlca probably represented an individual continental unit m Early Palaeozoic times and was positioned m high southerly latitudes in an "'inverted" geographic orientation In such a reconstruction Baltlca was separated from the northern margin of Gondwana by the Tornqulst Sea and from Laurentla by the Iapetus Ocean The Tornqulst Zone is thus interpreted as a passive or dextral transform margin during the early Palaeozoic While undergoing counter-clockwise rotations (up to 1 6°/Ma), Baltica drifted northward through most ol the Palaeozoic, except for a short period of southerly movement in Late Silurian-Early Devonian times after colhslon with Laurentla. Rapid movements in latitude (up to 9 cm/yr) are noted m Late Precambrlan/earl y Palaeozoic times and slgmficant decrease in velocities throughout Palaeozoic time probably reflect the progressive amalgamation of a larger continent by Early-Devonian (Euramerlca) and Permian (Pangea) times The Tornqulst Sea had a principal component of palaeo-east-west orientation. Hence it is difficult to be precise in the timing of when micro-continents such as Eastern Avalonla and the European Masslfs ultimately collided along the southwestern margin of Baltica These micro-continents are considered to have been peripheral to Gondwana (m high southerly latitudes) during the Early Ordovlclan. Eastern Avalonla clearly had rifted off Gondwana by Llanvlrn-Llanded o times and may have collided with Baltlca during Late Ordovlclan times, although the present available Sdunan palaeomagnetlc data from Eastern Avalonia may suggest colhslon in Late Silurian times Across the lapetus facing margin of Baltica, Laurentla was s~tuated in equatorml to southerly latitudes during most of the Lower Palaeozoic These continents collided in Mid-Silurian times, l e a first collision between southwestern Norway and Greenland/Scotla nd which gave rise to the early Scandlan Orogeny (425 Ma) in southwestern Norway possible followed by a later, but less dramatic, Scandlan event in northern Norway at around 410 Ma Since Baltlca was geographically reverted m early Palaeozoic times, the colhsional margin could not have been a margin that once rifted off Laurentm as assumed in a number of plate-tectonic models
Erik Halvorsen - One of the best experts on this subject based on the ideXlab platform.
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Baltica a synopsis of vendian permian palaeomagnetic data and their palaeotectonic implications
Earth-Science Reviews, 1992Co-Authors: Trond H Torsvik, Mark A. Smethurst, Allan Trench, Niels Abrahamsen, Erik HalvorsenAbstract:Torsvlk, T H, Smethurst, M A., Van der Voo, R, Trench, A, Abrahamsen, N and Halvorsen, E, 1992 Baltlca. A synopsis of Vendlan-Permmn palaeomagnetic data and their palaeotectonlc implications Earth-Sci. Rev, 33 133-152. In light of recent additions to the Palaeozoic palaeo-magnetlc data-base, particularly for the Ordovlclan era, a revised apparent polar wander (APW) path for Baltica has been constructed following a rigorous synthesis of all Late Precambrlan-Perm lan data The APW path is characterized by two prominent loops Firstly, a Late Precambrlan-Camb rlan loop probably relating to a rifting event and secondly, a younger loop relating to a Mid-Silurian (Scandlan) colhsion event These features Imply major change In plate-tectonic reconfiguratlon Baltlca probably represented an individual continental unit m Early Palaeozoic times and was positioned m high southerly latitudes in an "'inverted" geographic orientation In such a reconstruction Baltlca was separated from the northern margin of Gondwana by the Tornqulst Sea and from Laurentla by the Iapetus Ocean The Tornqulst Zone is thus interpreted as a passive or dextral transform margin during the early Palaeozoic While undergoing counter-clockwise rotations (up to 1 6°/Ma), Baltica drifted northward through most ol the Palaeozoic, except for a short period of southerly movement in Late Silurian-Early Devonian times after colhslon with Laurentla. Rapid movements in latitude (up to 9 cm/yr) are noted m Late Precambrlan/earl y Palaeozoic times and slgmficant decrease in velocities throughout Palaeozoic time probably reflect the progressive amalgamation of a larger continent by Early-Devonian (Euramerlca) and Permian (Pangea) times The Tornqulst Sea had a principal component of palaeo-east-west orientation. Hence it is difficult to be precise in the timing of when micro-continents such as Eastern Avalonla and the European Masslfs ultimately collided along the southwestern margin of Baltica These micro-continents are considered to have been peripheral to Gondwana (m high southerly latitudes) during the Early Ordovlclan. Eastern Avalonla clearly had rifted off Gondwana by Llanvlrn-Llanded o times and may have collided with Baltlca during Late Ordovlclan times, although the present available Sdunan palaeomagnetlc data from Eastern Avalonia may suggest colhslon in Late Silurian times Across the lapetus facing margin of Baltica, Laurentla was s~tuated in equatorml to southerly latitudes during most of the Lower Palaeozoic These continents collided in Mid-Silurian times, l e a first collision between southwestern Norway and Greenland/Scotla nd which gave rise to the early Scandlan Orogeny (425 Ma) in southwestern Norway possible followed by a later, but less dramatic, Scandlan event in northern Norway at around 410 Ma Since Baltlca was geographically reverted m early Palaeozoic times, the colhsional margin could not have been a margin that once rifted off Laurentm as assumed in a number of plate-tectonic models
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Baltica a synopsis of vendian permian palaeomagnetic data and their palaeotectonic implications
Earth-Science Reviews, 1992Co-Authors: Trond H Torsvik, Mark A. Smethurst, Allan Trench, Niels Abrahamsen, Rob Van Der Voo, Erik HalvorsenAbstract:Torsvlk, T H, Smethurst, M A., Van der Voo, R, Trench, A, Abrahamsen, N and Halvorsen, E, 1992 Baltlca. A synopsis of Vendlan-Permmn palaeomagnetic data and their palaeotectonlc implications Earth-Sci. Rev, 33 133-152. In light of recent additions to the Palaeozoic palaeo-magnetlc data-base, particularly for the Ordovlclan era, a revised apparent polar wander (APW) path for Baltica has been constructed following a rigorous synthesis of all Late Precambrlan-Perm lan data The APW path is characterized by two prominent loops Firstly, a Late Precambrlan-Camb rlan loop probably relating to a rifting event and secondly, a younger loop relating to a Mid-Silurian (Scandlan) colhsion event These features Imply major change In plate-tectonic reconfiguratlon Baltlca probably represented an individual continental unit m Early Palaeozoic times and was positioned m high southerly latitudes in an "'inverted" geographic orientation In such a reconstruction Baltlca was separated from the northern margin of Gondwana by the Tornqulst Sea and from Laurentla by the Iapetus Ocean The Tornqulst Zone is thus interpreted as a passive or dextral transform margin during the early Palaeozoic While undergoing counter-clockwise rotations (up to 1 6°/Ma), Baltica drifted northward through most ol the Palaeozoic, except for a short period of southerly movement in Late Silurian-Early Devonian times after colhslon with Laurentla. Rapid movements in latitude (up to 9 cm/yr) are noted m Late Precambrlan/earl y Palaeozoic times and slgmficant decrease in velocities throughout Palaeozoic time probably reflect the progressive amalgamation of a larger continent by Early-Devonian (Euramerlca) and Permian (Pangea) times The Tornqulst Sea had a principal component of palaeo-east-west orientation. Hence it is difficult to be precise in the timing of when micro-continents such as Eastern Avalonla and the European Masslfs ultimately collided along the southwestern margin of Baltica These micro-continents are considered to have been peripheral to Gondwana (m high southerly latitudes) during the Early Ordovlclan. Eastern Avalonla clearly had rifted off Gondwana by Llanvlrn-Llanded o times and may have collided with Baltlca during Late Ordovlclan times, although the present available Sdunan palaeomagnetlc data from Eastern Avalonia may suggest colhslon in Late Silurian times Across the lapetus facing margin of Baltica, Laurentla was s~tuated in equatorml to southerly latitudes during most of the Lower Palaeozoic These continents collided in Mid-Silurian times, l e a first collision between southwestern Norway and Greenland/Scotla nd which gave rise to the early Scandlan Orogeny (425 Ma) in southwestern Norway possible followed by a later, but less dramatic, Scandlan event in northern Norway at around 410 Ma Since Baltlca was geographically reverted m early Palaeozoic times, the colhsional margin could not have been a margin that once rifted off Laurentm as assumed in a number of plate-tectonic models
Mark A. Smethurst - One of the best experts on this subject based on the ideXlab platform.
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continental break up and collision in the neoproterozoic and palaeozoic a tale of Baltica and laurentia
Earth-Science Reviews, 1996Co-Authors: Trond H Torsvik, Mark A. Smethurst, Joseph G. Meert, Martin D Brasier, Bryan A Sturt, W S Mckerrow, H J WalderhaugAbstract:During the Neoproterozoic and Palaeozoic the two continents of Baltica and Laurentia witnessed the break-up of one supercontinent, Rodinia, and the formation of another, but less long-lived, Pangea. Baltica and Laurentia played central roles in a tectonic menage a trois that included major orogenic events, a redistribution of palaeogeography and a brief involvement of both with Gondwana. Many of these plate re-organisations took place over a short time interval and invite a re-evaluation of earlier geodynamic models which limited the speeds at which large continental plates could move to an arbitrarily low value. Baltica and Laurentia probably shared a common drift history for the time interval 750 – 600 Ma as they rotated clockwise and drifted southward from an equatorial position during the opening of the Proto-Pacific between Laurentia and East Gondwana (initial break-up of Rodinia). On their combined approach toward the south pole, Baltica and Laurentia were glaciated during the Varanger glaciations. Although the two continents drifted toward the south pole during the Late Proterozoic, they began to separate at around 600 Ma (rift to drift) to form the Iapetus Ocean through asymmetric rifting and relative rotations of up to 180°. Initiation of rifting on the Baltic margin is marked by the 650 Ma Egersund tholeiitic dykes (SW Norway) which contain abundant lower crustal zenoliths, and the tholeiitic magma was probably derived from a mantle plume. In latest Precambrian time, the final redistribution of Rodinia is characterised by high plate velocities. In particular, Laurentia began a rapid, up to 20 cm/yr, ascent to equatorial latitudes and essentially stayed in low latitudes throughout most of the Palaeozoic. The high velocities suggest either that Laurentia was pushed off a lower mantle heat anomaly originating from supercontinental mantle insulation or that Laurentia was pulled toward a subduction-generated cold spot in the proto-Pacific. Baltica, except for a short and rapid excursion to lower latitudes in the Late Vendian, remained mostly in intermediate to high southerly latitudes and closer to the Gondwana margin until Early Ordovician times. In Early Ordovician times, Arenig-Llanvirn platform trilobites show a broad distinction between the continents of Laurentia/Siberia/North China Block (Bathyurid), Baltica (Ptychopygine/ Megalaspid) and the areas of NW Gondwana/Avalonia/Armorica (Calymenacean-Dalmanitacean). During the Ordovician, Baltica rotated and moved northward, approaching close enough to Laurentia by the late Caradoc for trilobite and brachiopod spat to cross the intervening Iapetus Ocean. Docking appears to have been irregular both in time and manner: the collision between Scotland/Greenland and western Norway resulted in the early Scandian Orogeny in the Silurian (c. 425 Ma), but further south, there is evidence of late Silurian impingement with subduction of Avalonian continental crust (in England and Ireland) below the eastern edge of Laurentia until the Emsian. In the northern Appalachians the main time of collision appears to have been during the Emsian/Eifellian Acadian Orogeny. Recent analyses invalidates the traditional concept of a sustained orthogonal relationship between Baltica and Laurentia across a single Iapetus Ocean throughout the Caledonide evolution. The active margin of Baltica (Scandinavian Caledonides) faced Siberia during the Late Cambrian and Early Ordovician with oceanic separation between these landmasses in the order of 1200–1500 km. This may explain the local occureences of Siberia-Laurentian type Bathyarid tribobite faunas in Central Norwegian Caledonian nappes, earlier interpreted as Laurentia-Baltica trilobite mixing. Subsequent counterclockwise rotation of Baltica transferred the Caledonian margin in the direction of Laurentia by Silurian times, when the two continents once again started to collide to form Euramerica. This rotation, along with the strongly asymmetric opening of the Iapetus at around 600 Ma, demonstrates a complexity in Precambrian-Palaeozoic plate tectonics, i.e. a collage of metastable plate boundaries which have perhaps too often been simplified to an orthagonal Wilson cycle tectonic scenario.
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Continental break-up and collision in the Neoproterozoic and Palaeozoic — A tale of Baltica and Laurentia
Earth-Science Reviews, 1996Co-Authors: Trond H Torsvik, Mark A. Smethurst, Joseph G. Meert, Martin D Brasier, Bryan A Sturt, W S Mckerrow, H J WalderhaugAbstract:During the Neoproterozoic and Palaeozoic the two continents of Baltica and Laurentia witnessed the break-up of one supercontinent, Rodinia, and the formation of another, but less long-lived, Pangea. Baltica and Laurentia played central roles in a tectonic menage a trois that included major orogenic events, a redistribution of palaeogeography and a brief involvement of both with Gondwana. Many of these plate re-organisations took place over a short time interval and invite a re-evaluation of earlier geodynamic models which limited the speeds at which large continental plates could move to an arbitrarily low value. Baltica and Laurentia probably shared a common drift history for the time interval 750 – 600 Ma as they rotated clockwise and drifted southward from an equatorial position during the opening of the Proto-Pacific between Laurentia and East Gondwana (initial break-up of Rodinia). On their combined approach toward the south pole, Baltica and Laurentia were glaciated during the Varanger glaciations. Although the two continents drifted toward the south pole during the Late Proterozoic, they began to separate at around 600 Ma (rift to drift) to form the Iapetus Ocean through asymmetric rifting and relative rotations of up to 180°. Initiation of rifting on the Baltic margin is marked by the 650 Ma Egersund tholeiitic dykes (SW Norway) which contain abundant lower crustal zenoliths, and the tholeiitic magma was probably derived from a mantle plume. In latest Precambrian time, the final redistribution of Rodinia is characterised by high plate velocities. In particular, Laurentia began a rapid, up to 20 cm/yr, ascent to equatorial latitudes and essentially stayed in low latitudes throughout most of the Palaeozoic. The high velocities suggest either that Laurentia was pushed off a lower mantle heat anomaly originating from supercontinental mantle insulation or that Laurentia was pulled toward a subduction-generated cold spot in the proto-Pacific. Baltica, except for a short and rapid excursion to lower latitudes in the Late Vendian, remained mostly in intermediate to high southerly latitudes and closer to the Gondwana margin until Early Ordovician times. In Early Ordovician times, Arenig-Llanvirn platform trilobites show a broad distinction between the continents of Laurentia/Siberia/North China Block (Bathyurid), Baltica (Ptychopygine/ Megalaspid) and the areas of NW Gondwana/Avalonia/Armorica (Calymenacean-Dalmanitacean). During the Ordovician, Baltica rotated and moved northward, approaching close enough to Laurentia by the late Caradoc for trilobite and brachiopod spat to cross the intervening Iapetus Ocean. Docking appears to have been irregular both in time and manner: the collision between Scotland/Greenland and western Norway resulted in the early Scandian Orogeny in the Silurian (c. 425 Ma), but further south, there is evidence of late Silurian impingement with subduction of Avalonian continental crust (in England and Ireland) below the eastern edge of Laurentia until the Emsian. In the northern Appalachians the main time of collision appears to have been during the Emsian/Eifellian Acadian Orogeny. Recent analyses invalidates the traditional concept of a sustained orthogonal relationship between Baltica and Laurentia across a single Iapetus Ocean throughout the Caledonide evolution. The active margin of Baltica (Scandinavian Caledonides) faced Siberia during the Late Cambrian and Early Ordovician with oceanic separation between these landmasses in the order of 1200–1500 km. This may explain the local occureences of Siberia-Laurentian type Bathyarid tribobite faunas in Central Norwegian Caledonian nappes, earlier interpreted as Laurentia-Baltica trilobite mixing. Subsequent counterclockwise rotation of Baltica transferred the Caledonian margin in the direction of Laurentia by Silurian times, when the two continents once again started to collide to form Euramerica. This rotation, along with the strongly asymmetric opening of the Iapetus at around 600 Ma, demonstrates a complexity in Precambrian-Palaeozoic plate tectonics, i.e. a collage of metastable plate boundaries which have perhaps too often been simplified to an orthagonal Wilson cycle tectonic scenario.
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Baltica a synopsis of vendian permian palaeomagnetic data and their palaeotectonic implications
Earth-Science Reviews, 1992Co-Authors: Trond H Torsvik, Mark A. Smethurst, Allan Trench, Niels Abrahamsen, Erik HalvorsenAbstract:Torsvlk, T H, Smethurst, M A., Van der Voo, R, Trench, A, Abrahamsen, N and Halvorsen, E, 1992 Baltlca. A synopsis of Vendlan-Permmn palaeomagnetic data and their palaeotectonlc implications Earth-Sci. Rev, 33 133-152. In light of recent additions to the Palaeozoic palaeo-magnetlc data-base, particularly for the Ordovlclan era, a revised apparent polar wander (APW) path for Baltica has been constructed following a rigorous synthesis of all Late Precambrlan-Perm lan data The APW path is characterized by two prominent loops Firstly, a Late Precambrlan-Camb rlan loop probably relating to a rifting event and secondly, a younger loop relating to a Mid-Silurian (Scandlan) colhsion event These features Imply major change In plate-tectonic reconfiguratlon Baltlca probably represented an individual continental unit m Early Palaeozoic times and was positioned m high southerly latitudes in an "'inverted" geographic orientation In such a reconstruction Baltlca was separated from the northern margin of Gondwana by the Tornqulst Sea and from Laurentla by the Iapetus Ocean The Tornqulst Zone is thus interpreted as a passive or dextral transform margin during the early Palaeozoic While undergoing counter-clockwise rotations (up to 1 6°/Ma), Baltica drifted northward through most ol the Palaeozoic, except for a short period of southerly movement in Late Silurian-Early Devonian times after colhslon with Laurentla. Rapid movements in latitude (up to 9 cm/yr) are noted m Late Precambrlan/earl y Palaeozoic times and slgmficant decrease in velocities throughout Palaeozoic time probably reflect the progressive amalgamation of a larger continent by Early-Devonian (Euramerlca) and Permian (Pangea) times The Tornqulst Sea had a principal component of palaeo-east-west orientation. Hence it is difficult to be precise in the timing of when micro-continents such as Eastern Avalonla and the European Masslfs ultimately collided along the southwestern margin of Baltica These micro-continents are considered to have been peripheral to Gondwana (m high southerly latitudes) during the Early Ordovlclan. Eastern Avalonla clearly had rifted off Gondwana by Llanvlrn-Llanded o times and may have collided with Baltlca during Late Ordovlclan times, although the present available Sdunan palaeomagnetlc data from Eastern Avalonia may suggest colhslon in Late Silurian times Across the lapetus facing margin of Baltica, Laurentla was s~tuated in equatorml to southerly latitudes during most of the Lower Palaeozoic These continents collided in Mid-Silurian times, l e a first collision between southwestern Norway and Greenland/Scotla nd which gave rise to the early Scandlan Orogeny (425 Ma) in southwestern Norway possible followed by a later, but less dramatic, Scandlan event in northern Norway at around 410 Ma Since Baltlca was geographically reverted m early Palaeozoic times, the colhsional margin could not have been a margin that once rifted off Laurentm as assumed in a number of plate-tectonic models
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Baltica a synopsis of vendian permian palaeomagnetic data and their palaeotectonic implications
Earth-Science Reviews, 1992Co-Authors: Trond H Torsvik, Mark A. Smethurst, Allan Trench, Niels Abrahamsen, Rob Van Der Voo, Erik HalvorsenAbstract:Torsvlk, T H, Smethurst, M A., Van der Voo, R, Trench, A, Abrahamsen, N and Halvorsen, E, 1992 Baltlca. A synopsis of Vendlan-Permmn palaeomagnetic data and their palaeotectonlc implications Earth-Sci. Rev, 33 133-152. In light of recent additions to the Palaeozoic palaeo-magnetlc data-base, particularly for the Ordovlclan era, a revised apparent polar wander (APW) path for Baltica has been constructed following a rigorous synthesis of all Late Precambrlan-Perm lan data The APW path is characterized by two prominent loops Firstly, a Late Precambrlan-Camb rlan loop probably relating to a rifting event and secondly, a younger loop relating to a Mid-Silurian (Scandlan) colhsion event These features Imply major change In plate-tectonic reconfiguratlon Baltlca probably represented an individual continental unit m Early Palaeozoic times and was positioned m high southerly latitudes in an "'inverted" geographic orientation In such a reconstruction Baltlca was separated from the northern margin of Gondwana by the Tornqulst Sea and from Laurentla by the Iapetus Ocean The Tornqulst Zone is thus interpreted as a passive or dextral transform margin during the early Palaeozoic While undergoing counter-clockwise rotations (up to 1 6°/Ma), Baltica drifted northward through most ol the Palaeozoic, except for a short period of southerly movement in Late Silurian-Early Devonian times after colhslon with Laurentla. Rapid movements in latitude (up to 9 cm/yr) are noted m Late Precambrlan/earl y Palaeozoic times and slgmficant decrease in velocities throughout Palaeozoic time probably reflect the progressive amalgamation of a larger continent by Early-Devonian (Euramerlca) and Permian (Pangea) times The Tornqulst Sea had a principal component of palaeo-east-west orientation. Hence it is difficult to be precise in the timing of when micro-continents such as Eastern Avalonla and the European Masslfs ultimately collided along the southwestern margin of Baltica These micro-continents are considered to have been peripheral to Gondwana (m high southerly latitudes) during the Early Ordovlclan. Eastern Avalonla clearly had rifted off Gondwana by Llanvlrn-Llanded o times and may have collided with Baltlca during Late Ordovlclan times, although the present available Sdunan palaeomagnetlc data from Eastern Avalonia may suggest colhslon in Late Silurian times Across the lapetus facing margin of Baltica, Laurentla was s~tuated in equatorml to southerly latitudes during most of the Lower Palaeozoic These continents collided in Mid-Silurian times, l e a first collision between southwestern Norway and Greenland/Scotla nd which gave rise to the early Scandlan Orogeny (425 Ma) in southwestern Norway possible followed by a later, but less dramatic, Scandlan event in northern Norway at around 410 Ma Since Baltlca was geographically reverted m early Palaeozoic times, the colhsional margin could not have been a margin that once rifted off Laurentm as assumed in a number of plate-tectonic models
Allan Trench - One of the best experts on this subject based on the ideXlab platform.
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Baltica a synopsis of vendian permian palaeomagnetic data and their palaeotectonic implications
Earth-Science Reviews, 1992Co-Authors: Trond H Torsvik, Mark A. Smethurst, Allan Trench, Niels Abrahamsen, Rob Van Der Voo, Erik HalvorsenAbstract:Torsvlk, T H, Smethurst, M A., Van der Voo, R, Trench, A, Abrahamsen, N and Halvorsen, E, 1992 Baltlca. A synopsis of Vendlan-Permmn palaeomagnetic data and their palaeotectonlc implications Earth-Sci. Rev, 33 133-152. In light of recent additions to the Palaeozoic palaeo-magnetlc data-base, particularly for the Ordovlclan era, a revised apparent polar wander (APW) path for Baltica has been constructed following a rigorous synthesis of all Late Precambrlan-Perm lan data The APW path is characterized by two prominent loops Firstly, a Late Precambrlan-Camb rlan loop probably relating to a rifting event and secondly, a younger loop relating to a Mid-Silurian (Scandlan) colhsion event These features Imply major change In plate-tectonic reconfiguratlon Baltlca probably represented an individual continental unit m Early Palaeozoic times and was positioned m high southerly latitudes in an "'inverted" geographic orientation In such a reconstruction Baltlca was separated from the northern margin of Gondwana by the Tornqulst Sea and from Laurentla by the Iapetus Ocean The Tornqulst Zone is thus interpreted as a passive or dextral transform margin during the early Palaeozoic While undergoing counter-clockwise rotations (up to 1 6°/Ma), Baltica drifted northward through most ol the Palaeozoic, except for a short period of southerly movement in Late Silurian-Early Devonian times after colhslon with Laurentla. Rapid movements in latitude (up to 9 cm/yr) are noted m Late Precambrlan/earl y Palaeozoic times and slgmficant decrease in velocities throughout Palaeozoic time probably reflect the progressive amalgamation of a larger continent by Early-Devonian (Euramerlca) and Permian (Pangea) times The Tornqulst Sea had a principal component of palaeo-east-west orientation. Hence it is difficult to be precise in the timing of when micro-continents such as Eastern Avalonla and the European Masslfs ultimately collided along the southwestern margin of Baltica These micro-continents are considered to have been peripheral to Gondwana (m high southerly latitudes) during the Early Ordovlclan. Eastern Avalonla clearly had rifted off Gondwana by Llanvlrn-Llanded o times and may have collided with Baltlca during Late Ordovlclan times, although the present available Sdunan palaeomagnetlc data from Eastern Avalonia may suggest colhslon in Late Silurian times Across the lapetus facing margin of Baltica, Laurentla was s~tuated in equatorml to southerly latitudes during most of the Lower Palaeozoic These continents collided in Mid-Silurian times, l e a first collision between southwestern Norway and Greenland/Scotla nd which gave rise to the early Scandlan Orogeny (425 Ma) in southwestern Norway possible followed by a later, but less dramatic, Scandlan event in northern Norway at around 410 Ma Since Baltlca was geographically reverted m early Palaeozoic times, the colhsional margin could not have been a margin that once rifted off Laurentm as assumed in a number of plate-tectonic models
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Baltica a synopsis of vendian permian palaeomagnetic data and their palaeotectonic implications
Earth-Science Reviews, 1992Co-Authors: Trond H Torsvik, Mark A. Smethurst, Allan Trench, Niels Abrahamsen, Erik HalvorsenAbstract:Torsvlk, T H, Smethurst, M A., Van der Voo, R, Trench, A, Abrahamsen, N and Halvorsen, E, 1992 Baltlca. A synopsis of Vendlan-Permmn palaeomagnetic data and their palaeotectonlc implications Earth-Sci. Rev, 33 133-152. In light of recent additions to the Palaeozoic palaeo-magnetlc data-base, particularly for the Ordovlclan era, a revised apparent polar wander (APW) path for Baltica has been constructed following a rigorous synthesis of all Late Precambrlan-Perm lan data The APW path is characterized by two prominent loops Firstly, a Late Precambrlan-Camb rlan loop probably relating to a rifting event and secondly, a younger loop relating to a Mid-Silurian (Scandlan) colhsion event These features Imply major change In plate-tectonic reconfiguratlon Baltlca probably represented an individual continental unit m Early Palaeozoic times and was positioned m high southerly latitudes in an "'inverted" geographic orientation In such a reconstruction Baltlca was separated from the northern margin of Gondwana by the Tornqulst Sea and from Laurentla by the Iapetus Ocean The Tornqulst Zone is thus interpreted as a passive or dextral transform margin during the early Palaeozoic While undergoing counter-clockwise rotations (up to 1 6°/Ma), Baltica drifted northward through most ol the Palaeozoic, except for a short period of southerly movement in Late Silurian-Early Devonian times after colhslon with Laurentla. Rapid movements in latitude (up to 9 cm/yr) are noted m Late Precambrlan/earl y Palaeozoic times and slgmficant decrease in velocities throughout Palaeozoic time probably reflect the progressive amalgamation of a larger continent by Early-Devonian (Euramerlca) and Permian (Pangea) times The Tornqulst Sea had a principal component of palaeo-east-west orientation. Hence it is difficult to be precise in the timing of when micro-continents such as Eastern Avalonla and the European Masslfs ultimately collided along the southwestern margin of Baltica These micro-continents are considered to have been peripheral to Gondwana (m high southerly latitudes) during the Early Ordovlclan. Eastern Avalonla clearly had rifted off Gondwana by Llanvlrn-Llanded o times and may have collided with Baltlca during Late Ordovlclan times, although the present available Sdunan palaeomagnetlc data from Eastern Avalonia may suggest colhslon in Late Silurian times Across the lapetus facing margin of Baltica, Laurentla was s~tuated in equatorml to southerly latitudes during most of the Lower Palaeozoic These continents collided in Mid-Silurian times, l e a first collision between southwestern Norway and Greenland/Scotla nd which gave rise to the early Scandlan Orogeny (425 Ma) in southwestern Norway possible followed by a later, but less dramatic, Scandlan event in northern Norway at around 410 Ma Since Baltlca was geographically reverted m early Palaeozoic times, the colhsional margin could not have been a margin that once rifted off Laurentm as assumed in a number of plate-tectonic models
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Cambrian-Ordovician paleogeography of Baltica
Geology, 1991Co-Authors: T. H. Torsvik, P. D. Ryan, Allan Trench, David A. T. HarperAbstract:Recent paleomagnetic data and existing paleontological evidence show that Baltica occupied temperate southern latitudes during Cambrian and Early Ordovician time, but was inverted with reference to its present orientation. Hence the currently opposed margins of the Baltic and Laurentian shield were not conterminous in the early Paleozoic. Laurentian and Baltic late Precambrian rifting episodes may therefore have occurred along unrelated continental margins. Closure of the Tornquist sea was accompanied by the counterclockwise rotation of Baltica relative to Avalonia in Early to Middle Ordovician time. This rotation, initiated in Late Cambrian-Early Ordovician time, was coeval with the Finnmarkian orogeny in the northern Scandinavian Caledonides.
H Hummel - One of the best experts on this subject based on the ideXlab platform.
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delta c 13 and delta n 15 variations in organic matter pools mytilus spp and macoma balthica along the european atlantic coast
Marine Biology, 2013Co-Authors: Paolo Magni, J M Jansen, S Rajagopal, S Como, G Van Der Velde, H HummelAbstract:Stable carbon (δ 13C) and nitrogen (δ 15N) isotope (SI) values of sedimentary organic matter (SOM), seston and two dominant bivalves, Mytilus spp. and Macoma balthica, were studied at 18 stations along the European coast in spring and autumn 2004. Three main regions, the Baltic Sea (BS), the North Sea and English Channel (NS), and the Bay of Biscay (BB), were tested for possible geographic (latitudinal) differences in the SI values. In spring, only BS showed lower δ 13C values of seston and Mytilus spp., and higher δ 15N values of SOM, than NS and BB. No significant differences between the 3 regions were found in autumn. Irrespective of season and regions, Mytilus spp. was more 13C-depleted than M. balthica. δ 13C values of M. balthica, but not those of Mytilus spp., were significantly correlated with SOM. These results are consistent with differences in feeding behavior of Mytilus spp. and M. balthica, as the two species are known as obligatory-suspension and facultative-deposit feeders, respectively. In contrast, no differences in the δ 15N values of Mytilus spp. and M. balthica were found at individual stations, indicating the same trophic level of the two bivalves within the food webs. At some stations, irrespective of geographic location, both bivalves showed δ 15N values up to 18–20 ‰. These were two trophic levels higher than those found at the other stations, indicating local and/or episodic eutrophic conditions, probably due to waste water discharge, and the effectiveness of both Mytilus spp. and M. balthica as bio-indicators of anthropogenic eutrophication. Overall, our results suggest that pathways of energy flow from OM pools to dominant bivalves is more related to local environmental conditions than to geographic regions across the European coastline. This has implications for food web studies along the Atlantic coast because most of the values are consistent over a large area and show no significant differences. Therefore, the present study can be used twofold for the determination of trophic baselines and for the correction of the trophic position of consumers higher up in the food web in the case of differences in waste water discharge.
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metal sources to the baltic clam macoma balthica mollusca bivalvia in the southern baltic sea the gulf of gdansk
Marine Environmental Research, 2007Co-Authors: Adam Sokolowski, Maciej Wolowicz, H HummelAbstract:Abstract Metal concentrations of Cu, Fe, Mn, Ni, Pb and Zn in an infaunal facultative deposit-feeding bivalve, the Baltic clam Macoma balthica, in the Gulf of Gdansk (southern Baltic Sea) were assessed and compared to selected concentrations of metals in the environment. Between October 1996 and September 1997, dissolved and easy extractable (by 1 M HCl) metal fractions of total suspended particulate matter (TPM) in the overlying water and of surficial sediments (
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abnormal features of macoma balthica bivalvia in the baltic sea alerting symptoms of environmental adversity
Marine Pollution Bulletin, 2004Co-Authors: Adam Sokolowski, Maciej Wolowicz, Katarzyna Smolarzgorska, Denis Fichet, Gilles Radenac, Catherine Thiriotquievreux, H Hummel, Jacek NamieśnikAbstract:Recent studies of the Baltic clam Macoma balthica (L.) from the southern Baltic (the Gulf of Gdansk) have revealed striking morphological, histological and cytogenetic features. Strong deformation ...
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free amino acids in the clam macoma balthica l bivalvia mollusca from brackish waters of the southern baltic sea
Comparative Biochemistry and Physiology A-molecular & Integrative Physiology, 2003Co-Authors: Adam Sokolowski, Maciej Wolowicz, H HummelAbstract:Fourteen acidic and neutral free amino acids (FAA) were investigated in soft tissue of Macoma balthica from different depth zones of the Gulf of Gdansk (Baltic Sea) over a full seasonal cycle. The dry weight of the bivalves and physico-chemical parameters of overlying bottom water and surface sediments were measured simultaneously at each site. In the brackish waters of the Baltic, the main pool of FAA is composed of Ala, Gln, Arg, Gly and Orn which represent approximately 80% of the total. Compared to the full saline environments, the composition of FAA in the clams from the Baltic differs substantially. The differences can be attributed to the lower salinity of the Baltic. In the Baltic, Gly appears to play a most important role in regulating intracellular osmolarity in the clams, a function performed primarily by Tau in Atlantic and North Sea populations. Spatio-temporal variations of the FAA are affected by biotic and environmental parameters; their respective influence differs with the amino acids. The concentration of Arg depends on its uptake from the external medium. However, its level might be temporarily modified by stress-induced metabolic transformation (e.g. hydrolysis to Orn) caused by changes in the ambient environment. The concentration of Ala increases with depth, probably because of physiological adaptations of the animal to diminishing oxygen concentration through anaerobic glucose catabolism. Biosynthesis of Ala, similarly to Gln, in the shallower zone is generally related to the physiological state of an organism. The concentration of Gly is most likely regulated by internal mechanisms driven by gonadal development and reproduction. [KEYWORDS: Free amino acids; Macoma balthica; Baltic Sea; Spatial and seasonal variations]
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physiological responses of macoma balthica to copper pollution in the baltic
Oceanologica Acta, 1999Co-Authors: Adam Sokolowski, Maciej Wolowicz, H Hummel, R H BogaardsAbstract:Physiological and behavioral responses to Cu exposure were measured in the Baltic clam Macoma balthica from the Gulf of Gdansk, southern Baltic Sea. The burrowing activity, mortality rate, glycogen content, condition index and free amino acid (FAA) composition were analysed as indicators of stress in a series of field and laboratory studies. M. balthica exposed to Cu showed clear Cu-concentration related differences in burrowing activity and mortality rate, but no consistent differences in the condition index, glycogen content, and free amino acids. The clams from a less polluted area reacted more strongly and were more sensitive to additional stress as compared to organisms from a more polluted region. The effect of Cu on the ecophysiology of Baltic clams in the field was probably obscured by reproduction-related changes in the organism. The role of sediment as a potential source of Cu in the Baltic clam was discussed.
