Review: Short-term sea-level changes in a greenhouse world - A view from the Cretaceous

© 2015. This review provides a synopsis of ongoing research and our understanding of the fundamentals of sea-level change today and in the geologic record, especially as illustrated by conditions and processes during the Cretaceous greenhouse climate episode. We give an overview of the state of the art of our understanding on eustatic (global) versus relative (regional) sea level, as well as long-term versus short-term fluctuations and their drivers. In the context of the focus of UNESCO-IUGS/IGCP project 609 on Cretaceous eustatic, short-term sea-level and climate changes, we evaluate the possible evidence for glacio-eustasy versus alternative or additional mechanisms for continental water storage and release for the Cretaceous greenhouse and hothouse phases during which the presence of larger continental ice shields is considered unlikely. Increasing evidence in the literature suggests a correlation between long-period orbital cycles and depositional cycles that reflect sea-level fluctuations, implying a globally synchronized forcing of (eustatic) sea level. Fourth-order depositional sequences seem to be related to a ~. 405. ka periodicity, which most likely represents long-period orbital eccentricity control on sea level and depositional cycles. Third-order cyclicity, expressed as time-synchronous sea level falls of ~. 20 to 110. m on ~. 0.5 to 3.0. Ma timescales in the Cretaceous, are increasingly recognized as connected to climate cycles triggered by long-term astronomical cycles that have periodicity ranging from ~. 1.0 to 2.4. Ma. Future perspectives of research on greenhouse sea-level changes comprise a high-precision time-scale for sequence stratigraphy and eustatic sea-level changes and high-resolution marine to non-marine stratigraphic correlation

New insights on the Sorbas Basin (SE Spain): the onshore reference of the Messinian Salinity Crisis

International audienceThe Sorbas Basin is the land reference of the Messinian Salinity Crisis (MSC) that affected the Mediterranean Sea in the latest Miocene. Its stratigraphy has been re-visited using calcareous nannofossils and planktonic foraminifers, which provide a reliable biostratigraphic frame and lead to particularly specify the relationships between the Sorbas and Zorreras members with Yesares evaporites.The evaporites overlie a shallowing upward sequence ending with the deposition of the Reef Unit and Terminal Carbonate Complex (TCC) on the periphery of the basin. The reefal carbonates of the TCC are overlain by clastic deposits that are foreset beds of post-MSC Gilbert-type fan deltas developed on the northern edge of the basin. These sedimentary structures are separated from reefal carbonates and the Reef Unit by the Messinian Erosional Surface (MES). The various facies of the Sorbas Member have been correlated with the bottomset beds of the Gilbert-type fan deltas despite some differences in palaeobathymetry. In the southeastern periphery of the basin, the MES separates the Sorbas Member from the Yesares gypsums. In the central part of the basin, a hiatus characterizes the contact between these members. The Zorreras Member postdates the MSC and entirely belongs to Zanclean. Its white “Lago Mare” layers are lagoonal deposits, the fauna of which is confirmed to result from Mediterranean–Paratethys high sea-level exchange after the post-MSC marine reflooding of the Mediterranean Basin.This study allows to re-assert the two-step scenario of the MSC (Clauzon et al., 1996) with the following events:- at 5.971–5.600 Ma, minor sea-level fall resulting in the desiccation of this peripheral basin with secondary fluctuations;- at 5.600–5.460 Ma, significant subaerial erosion (or lack of sedimentation) caused by the almost complete desiccation of the Mediterranean Sea;- instantaneous marine reflooding, accepted at 5.460 Ma, followed by continuing sea-level rise

Crustal Strain in the Marmara Pull-Apart Region Associated With the Propagation Process of the North Anatolian Fault

International audiencePropagation processes of plate-scale faults through continental lithosphere are poorly documented. The North Anatolian Fault (NAF) is a continental right-lateral transform with striking evidence for propagation processes in the Marmara Sea pull-apart region. Earlier work (Armijo et al., 1999, https://doi.org/10.1130/0091-7613(1999)0272.3.CO;2) suggests that in the Dardanelles, where the principal, northern branch of that fault (NNAF) enters into the Aegean: (1) a fold-thrust system has progressively developed above the NNAF fault tip, at the WSW corner of the Marmara Sea pull-apart. The main anticline formed there was sheared and its SW half laterally offset by ~70 km to the SW; (2) the timing of structure development appears correlated with sea level changes associated with the Messinian Salinity Crisis. Our new description of the Dardanelles (or Ganos-Gelibolu) fold-thrust system is based on structural mapping, field observations, and calcareous nannoplankton analyses to date key sedimentary units. Our results provide tight constraints on the main pulse of folding associated with propagation of the tip of the NNAF: it took place in the late Miocene to earliest Pliocene (5.60 to 5.04 Ma), before deposition of undeformed Pliocene marine sediments. The folding is mostly coeval with the Messinian Salinity Crisis and accommodated several kilometers of shortening at the fault tip. After full propagation of the NNAF up to the surface, the folded structure was sheared and right laterally offset, with an average 14 mm/year of slip rate during the past ~5 Myrs. A reconstruction of tectonic evolution suggests a flower structure nucleating and taking root at the tip of the fault

New ⁴⁰Ar/³⁹Ar, magnetostratigraphic and biostratigraphic constraints on the termination of the Badenian Salinity Crisis:Indications for tectonic improvement of basin interconnectivity in Southern Europe

Widespread evaporites were deposited in large parts of the Central Paratethys during the so-called Badenian Salinity Crisis (BSC). The adverse environmental conditions that accompanied the BSC triggered a demise in the basin's marine fauna, inducing the so-called middle-Badenian-extinction-event. While tectonic activity preconditioned the Central Paratethys for isolation, it has recently been shown that the BSC was eventually triggered by the base-level drop accompanying the Mi3b global cooling event, which terminated the Middle Miocene Climatic Optimum. Here, we provide new constraints on the termination of the BSC by 40Ar/39Ar dating of a volcanic ash layer, located in a marl succession several meters above the Badenian evaporites of the Slănic Syncline in the Romanian East Carpathians. The results reveal that the BSC ended before 13.32 ± 0.07 Ma. Comparison with previously obtained geochronological results in Poland constrains the duration of the BSC to 500 kyr, assuming evaporite deposition in the Central Paratethys occurred as one event. The obtained 40Ar/39Ar results are complemented with paleomagnetic and micropaleontological analyses. These reveal that the investigated post-BSC marl interval in the Slănic Syncline was deposited in a period of reversed polarity corresponding to C5AAr. This is in agreement with calcareous nannoplankton from the same interval that belong to the NN6 zone. Ostracod and foraminifera marker species are indicative of the middle part of the regional Badenian stage, traditionally known as the Wielician. The foraminiferal assemblage is nevertheless very similar to Serravallian assemblages from the Mediterranean, which suggests that, in addition to a connection between the Central Paratethys and the Eastern Paratethys, there was a marine connection with the Mediterranean following the BSC. A comparison with post-BSC successions in Ukraine and Poland illustrates that the BSC was terminated by a transgression that re-installed normal marine conditions in the Carpathian foredeep. This basin-wide transgression resulted from reconnection of the Carpathian Foreland Basin with the Mediterranean and Eastern Paratethys, which improved the exchange of water and fauna. Global eustacy cannot explain re-connection of these basins, because global sea level on average remained just as low after the BSC as it had been during the crisis. The improved interconnectivity between the basins must therefore have been primarily caused by tectonic modification of the interconnecting gateways. Geodynamics thus played a crucial role in the re-establishment of a flourishing marine environment

New 40Ar/39Ar, magnetostratigraphic and biostratigraphic constraints on the termination of the Badenian Salinity Crisis : Indications for tectonic improvement of basin interconnectivity in Southern Europe

Widespread evaporites were deposited in large parts of the Central Paratethys during the so-called Badenian Salinity Crisis (BSC). The adverse environmental conditions that accompanied the BSC triggered a demise in the basin's marine fauna, inducing the so-called middle-Badenian-extinction-event. While tectonic activity preconditioned the Central Paratethys for isolation, it has recently been shown that the BSC was eventually triggered by the base-level drop accompanying the Mi3b global cooling event, which terminated the Middle Miocene Climatic Optimum. Here, we provide new constraints on the termination of the BSC by 40Ar/39Ar dating of a volcanic ash layer, located in a marl succession several meters above the Badenian evaporites of the Slănic Syncline in the Romanian East Carpathians. The results reveal that the BSC ended before 13.32 ± 0.07 Ma. Comparison with previously obtained geochronological results in Poland constrains the duration of the BSC to 500 kyr, assuming evaporite deposition in the Central Paratethys occurred as one event. The obtained 40Ar/39Ar results are complemented with paleomagnetic and micropaleontological analyses. These reveal that the investigated post-BSC marl interval in the Slănic Syncline was deposited in a period of reversed polarity corresponding to C5AAr. This is in agreement with calcareous nannoplankton from the same interval that belong to the NN6 zone. Ostracod and foraminifera marker species are indicative of the middle part of the regional Badenian stage, traditionally known as the Wielician. The foraminiferal assemblage is nevertheless very similar to Serravallian assemblages from the Mediterranean, which suggests that, in addition to a connection between the Central Paratethys and the Eastern Paratethys, there was a marine connection with the Mediterranean following the BSC. A comparison with post-BSC successions in Ukraine and Poland illustrates that the BSC was terminated by a transgression that re-installed normal marine conditions in the Carpathian foredeep. This basin-wide transgression resulted from reconnection of the Carpathian Foreland Basin with the Mediterranean and Eastern Paratethys, which improved the exchange of water and fauna. Global eustacy cannot explain re-connection of these basins, because global sea level on average remained just as low after the BSC as it had been during the crisis. The improved interconnectivity between the basins must therefore have been primarily caused by tectonic modification of the interconnecting gateways. Geodynamics thus played a crucial role in the re-establishment of a flourishing marine environment

Land and sea study of the northeastern golfe du Lion rifted margin: the Oligocene – Miocene of southern Provence (Nerthe area, SE France)

In the western Mediterranean Sea, the Liguro-Provençal Basin (LPB) is a key area for studying passive margins because of its recent formation and abundance of onshore and offshore data. The Nerthe area located in the northern margin of LPB provides the unique continuous Oligo-Miocene deposits contemporaneous of the transition rifting to drifting. However, the age of the deposits remains debated and the link between outcrops and offshore seismic data is poorly constrained. The purpose of this paper is double. First, we intend to propose a new chronostratigraphic frame based on bio- (planktonic foraminifera, calcareous nannofossils) and magneto-stratigraphy. Second, we aim to make, through the integration of new highly time-resolved seismic data and field works, a coherent onshore-offshore link concretized by a 3D geological model. The new temporal and spatial data presented in this paper allow correlating the Oligo-Miocene sequences, defining their geometry and specifying precisely the timing of syn- and post-rift stages. The first marine transgression is now precisely dated latest Chattian within the syn-rift deposits and appears to be synchronous with the first marine deposits in the offshore wells and other marginal basins. The transition from syn-rift to post-rift appears to last 3.3 Ma at maximum, between 21.8 and 18.5 Ma (late Aquitanian to early Burdigalian). It is underlined by two major erosional unconformities bearing a hiatus of around 1 Ma. The post-rift started with a major marine transgression that is now dated from middle Burdigalian, at around 18.5 Ma, as elsewhere in the LPB. Contrarily to recent proposals, the post-rift deposits are widely represented on the northeastern margin of the "Golfe du Lion". There, the subsidence of the margin was low during the syn-rift and the transitional periods and high during the post-rift. The onset of this high post-rift subsidence appears to be synchronous with the slowdown of the Corsica-Sardinia block (CSb) motion

Ages and stratigraphical architecture of late Miocene deposits in the Lorca Basin (Betics, SE Spain): New insights for the salinity crisis in marginal basins

Unlike most Neogene basins of the Betic Cordillera where the Salinity Crisis is dated to the Messinian, a contradictory Tortonian dating was proposed for evaporites of the Lorca Basin. As a consequence, complex structural models have been proposed in the literature to explain this discrepancy in the timing of evaporites. In order to integrate the Lorca Basin into the geological context of the western Mediterranean domain during the Late Miocene, new sedimentological and stratigraphical studies coupled with new dating were performed, which allow us to propose a Messinian age for both diatomite-bearing deposits and evaporites of the Lorca Basin. These new ages challenge the idea of a Tortonian salinity crisis in the Lorca Basin. Three main events of base-level drop were evidenced during the Messinian. Each event is correlated with successive steps of basin restriction. Shallow salina evaporites were deposited after a base-level fall during the Messinian before a final base-level drop, which led to the entire exposure of the basin. This last exposure is interpreted as coeval with the deposition of first evaporites and halite in the deep Mediterranean basins. The reflooding which allowed the deposition of brackish deposits and a short-lived marine incursion occurred at the end of the Messinian. Base-level drops occurred during eustatic falls amplified by the gradual uplift of the Betic Cordillera. The exhumation of the Tercia ridge along the strike-slip Alhama de Murcia fault system during the Messinian probably favoured the gradual restriction of the basin. A discussion on correlations of main unconformities between several Neogene basins of the Betics is proposed, suggesting a similar structural evolution at the regional scale

Marine karstic infillings: evidence of extreme base level changes and geodynamic consequences (Paleocene of Languedoc, south of France)

Late Jurassic platform carbonates of Languedoc (southern France) are deeply incised by Late Miocene canyons, allowing the observation of karst systems filled with sediments containing evidences of marine origin. Field and structural relationships as well as new biostratigraphic data (planktonic foraminifera and calcareous nannofossils) provide a Latest Cretaceous-Earliest Paleocene age for the major karstification and a Paleocene (Danian-Selandian) age for the sedimentary filling. The ≥ 350 m vertical extent of this karst system and its subsequent marine filling gives a minimum amplitude for the base-level variation responsible for the karstification and then the marine flooding events. The observations suggest that at least, two marine successive events occurred in the Late Danian then in Selandian time. The large amplitude of base level is not in agreement with eustatic sea-level change, and the rate of base-level change is too fast for tectonic uplift and subsidence within the tabular, poorly deformed studied area. We propose a model of a silled endoreic basin, which was dessiccated and karstified over hundreds of meters, when it was disconnected from the World Ocean, and later suddently transgressed by the Paleocene sea and the karst flooded, when the bounding sill was submerged. Such a model is similar, although with significant differences, with the later Messinian-Zanclean event that affected the Mediterranean realm

Review: Short-term sea-level changes in a greenhouse world - A view from the Cretaceous

© 2015. This review provides a synopsis of ongoing research and our understanding of the fundamentals of sea-level change today and in the geologic record, especially as illustrated by conditions and processes during the Cretaceous greenhouse climate episode. We give an overview of the state of the art of our understanding on eustatic (global) versus relative (regional) sea level, as well as long-term versus short-term fluctuations and their drivers. In the context of the focus of UNESCO-IUGS/IGCP project 609 on Cretaceous eustatic, short-term sea-level and climate changes, we evaluate the possible evidence for glacio-eustasy versus alternative or additional mechanisms for continental water storage and release for the Cretaceous greenhouse and hothouse phases during which the presence of larger continental ice shields is considered unlikely. Increasing evidence in the literature suggests a correlation between long-period orbital cycles and depositional cycles that reflect sea-level fluctuations, implying a globally synchronized forcing of (eustatic) sea level. Fourth-order depositional sequences seem to be related to a ~. 405. ka periodicity, which most likely represents long-period orbital eccentricity control on sea level and depositional cycles. Third-order cyclicity, expressed as time-synchronous sea level falls of ~. 20 to 110. m on ~. 0.5 to 3.0. Ma timescales in the Cretaceous, are increasingly recognized as connected to climate cycles triggered by long-term astronomical cycles that have periodicity ranging from ~. 1.0 to 2.4. Ma. Future perspectives of research on greenhouse sea-level changes comprise a high-precision time-scale for sequence stratigraphy and eustatic sea-level changes and high-resolution marine to non-marine stratigraphic correlation

Review: Short-term sea-level changes in a greenhouse world — A view from the Cretaceous

© 2015This review provides a synopsis of ongoing research and our understanding of the fundamentals of sea-level change today and in the geologic record, especially as illustrated by conditions and processes during the Cretaceous greenhouse climate episode. We give an overview of the state of the art of our understanding on eustatic (global) versus relative (regional) sea level, as well as long-term versus short-term fluctuations and their drivers. In the context of the focus of UNESCO-IUGS/IGCP project 609 on Cretaceous eustatic, short-term sea-level and climate changes, we evaluate the possible evidence for glacio-eustasy versus alternative or additional mechanisms for continental water storage and release for the Cretaceous greenhouse and hothouse phases during which the presence of larger continental ice shields is considered unlikely. Increasing evidence in the literature suggests a correlation between long-period orbital cycles and depositional cycles that reflect sea-level fluctuations, implying a globally synchronized forcing of (eustatic) sea level. Fourth-order depositional sequences seem to be related to a ~ 405 ka periodicity, which most likely represents long-period orbital eccentricity control on sea level and depositional cycles. Third-order cyclicity, expressed as time-synchronous sea level falls of ~ 20 to 110 m on ~ 0.5 to 3.0 Ma timescales in the Cretaceous, are increasingly recognized as connected to climate cycles triggered by long-term astronomical cycles that have periodicity ranging from ~ 1.0 to 2.4 Ma. Future perspectives of research on greenhouse sea-level changes comprise a high-precision time-scale for sequence stratigraphy and eustatic sea-level changes and high-resolution marine to non-marine stratigraphic correlation