Environmental changes during marl-limestone formation: evidence from the Gargasian (Middle Aptian) of La Marcouline Quarry (Cassis, SE France)
Limestone-marl alternations are usually interpreted to reflect cyclic paleoenvironmental fluctuations linked to Milankovitch-scale climate variations. However, the impact of diagenesis on lithological differentiation can be overprinted on the primary signal.In order to evaluate environmental variati...
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| Format: | Article |
| Language: | English |
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Association Carnets de Geologie
2007-02-01
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| Series: | Carnets de Géologie |
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| Online Access: | http://paleopolis.rediris.es/cg/CG2007_A01/index.html |
| _version_ | 1827838984606187520 |
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| author | Beltran Catherine Rafélis Marc de Renard Maurice Moullade Michel Tronchetti Guy |
| author_facet | Beltran Catherine Rafélis Marc de Renard Maurice Moullade Michel Tronchetti Guy |
| author_sort | Beltran Catherine |
| collection | DOAJ |
| description | Limestone-marl alternations are usually interpreted to reflect cyclic paleoenvironmental fluctuations linked to Milankovitch-scale climate variations. However, the impact of diagenesis on lithological differentiation can be overprinted on the primary signal.In order to evaluate environmental variations during the deposition of the Gargasian hemipelagic limestone-marl alternations from the "La Marcouline" quarry (SE France), we have applied a multi-discipline approach (carbonate geochemistry, micropaleontology and mineralogy). The work uses of a method of granulometric separation of the main carbonate particles which (1) allows the characterization and quantification of the compositions of the carbonate phases of both lithologies and (2) gives access to the geochemical signatures of similar carbonate (bio-) particles in each lithology.The quantifications show that micarb constitutes a significant portion (around 40 per cent) of the sediments. Their geochemical signatures indicate that most of them were formed by fine fragmentation of nannoconid tests. Based on these interpretations, our results indicate that nannoconids are the major constituents of both the marly limestone and the marl layers and that both lithologies are similar in composition.The coccolith assemblages (mainly Watznaueria spp.) of the limestone and marl layers are similar and equally well-preserved. Changes in oxygen and carbon isotopic ratios express cyclic fertility and salinity/temperature variations in surface waters. The marls indicate higher fertility and lower salinity (or higher temperature) conditions than those denoted by the marly limestones.Although diagenesis has not altered these rhythmites no strong evidence has been found for linking classical processes such as dilution or productivity cycles to the composition of the sediments (carbonate constituents and clay mineralogy).This study demonstrates that La Marcouline succession has retained, as recorded by geochemical proxy, its primary environmental variations. Nevertheless, the homogeneity in both lithotypes of sedimentological parameters (clay mineralogy, sediment composition, ...) seems to indicate that these fluctuations did not affect the ecosystem strongly enough to cause marked differences in the composition of marls and marly-limestones. |
| first_indexed | 2024-03-12T07:14:54Z |
| format | Article |
| id | doaj.art-12658508ae6c4966a22ccce94cde6282 |
| institution | Directory Open Access Journal |
| issn | 1765-2553 1634-0744 |
| language | English |
| last_indexed | 2024-03-12T07:14:54Z |
| publishDate | 2007-02-01 |
| publisher | Association Carnets de Geologie |
| record_format | Article |
| series | Carnets de Géologie |
| spelling | doaj.art-12658508ae6c4966a22ccce94cde62822023-09-02T22:52:00ZengAssociation Carnets de GeologieCarnets de Géologie1765-25531634-07442007-02-01CG2007A01Environmental changes during marl-limestone formation: evidence from the Gargasian (Middle Aptian) of La Marcouline Quarry (Cassis, SE France)Beltran CatherineRafélis Marc deRenard MauriceMoullade MichelTronchetti GuyLimestone-marl alternations are usually interpreted to reflect cyclic paleoenvironmental fluctuations linked to Milankovitch-scale climate variations. However, the impact of diagenesis on lithological differentiation can be overprinted on the primary signal.In order to evaluate environmental variations during the deposition of the Gargasian hemipelagic limestone-marl alternations from the "La Marcouline" quarry (SE France), we have applied a multi-discipline approach (carbonate geochemistry, micropaleontology and mineralogy). The work uses of a method of granulometric separation of the main carbonate particles which (1) allows the characterization and quantification of the compositions of the carbonate phases of both lithologies and (2) gives access to the geochemical signatures of similar carbonate (bio-) particles in each lithology.The quantifications show that micarb constitutes a significant portion (around 40 per cent) of the sediments. Their geochemical signatures indicate that most of them were formed by fine fragmentation of nannoconid tests. Based on these interpretations, our results indicate that nannoconids are the major constituents of both the marly limestone and the marl layers and that both lithologies are similar in composition.The coccolith assemblages (mainly Watznaueria spp.) of the limestone and marl layers are similar and equally well-preserved. Changes in oxygen and carbon isotopic ratios express cyclic fertility and salinity/temperature variations in surface waters. The marls indicate higher fertility and lower salinity (or higher temperature) conditions than those denoted by the marly limestones.Although diagenesis has not altered these rhythmites no strong evidence has been found for linking classical processes such as dilution or productivity cycles to the composition of the sediments (carbonate constituents and clay mineralogy).This study demonstrates that La Marcouline succession has retained, as recorded by geochemical proxy, its primary environmental variations. Nevertheless, the homogeneity in both lithotypes of sedimentological parameters (clay mineralogy, sediment composition, ...) seems to indicate that these fluctuations did not affect the ecosystem strongly enough to cause marked differences in the composition of marls and marly-limestones.http://paleopolis.rediris.es/cg/CG2007_A01/index.htmllimestone-marl alternationstable isotopesAptianGargasiancalcareous nannofossilsgranulometric separation |
| spellingShingle | Beltran Catherine Rafélis Marc de Renard Maurice Moullade Michel Tronchetti Guy Environmental changes during marl-limestone formation: evidence from the Gargasian (Middle Aptian) of La Marcouline Quarry (Cassis, SE France) Carnets de Géologie limestone-marl alternation stable isotopes Aptian Gargasian calcareous nannofossils granulometric separation |
| title | Environmental changes during marl-limestone formation: evidence from the Gargasian (Middle Aptian) of La Marcouline Quarry (Cassis, SE France) |
| title_full | Environmental changes during marl-limestone formation: evidence from the Gargasian (Middle Aptian) of La Marcouline Quarry (Cassis, SE France) |
| title_fullStr | Environmental changes during marl-limestone formation: evidence from the Gargasian (Middle Aptian) of La Marcouline Quarry (Cassis, SE France) |
| title_full_unstemmed | Environmental changes during marl-limestone formation: evidence from the Gargasian (Middle Aptian) of La Marcouline Quarry (Cassis, SE France) |
| title_short | Environmental changes during marl-limestone formation: evidence from the Gargasian (Middle Aptian) of La Marcouline Quarry (Cassis, SE France) |
| title_sort | environmental changes during marl limestone formation evidence from the gargasian middle aptian of la marcouline quarry cassis se france |
| topic | limestone-marl alternation stable isotopes Aptian Gargasian calcareous nannofossils granulometric separation |
| url | http://paleopolis.rediris.es/cg/CG2007_A01/index.html |
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