Palynological indications for Silurian – earliest Devonian age strata in the Netherlands

Abstract Knowledge of the stratigraphic development of pre-Carboniferous strata in the subsurface of the Netherlands is very limited, leaving the lithostratigraphic nomenclature for this time interval informal. In two wells from the southwestern Netherlands, Silurian strata have repeatedly been reported, suggesting that these are the oldest ever recovered in the Netherlands. The hypothesised presence of Silurian-aged strata has not been tested by biostratigraphic analysis. A similar lack of biostratigraphic control applies to the overlying Devonian succession. We present the results of a palynological study of core material from wells KTG-01 and S05-01. Relatively low-diversity and poorly preserved miospore associations were recorded. These, nonetheless, provide new insights into the regional stratigraphic development of the pre-Carboniferous of the SW Netherlands. The lower two cores from well KTG-01 are of a late Silurian (Ludlow–Pridoli Epoch) to earliest Devonian (Lochkovian) age, confirming that these are the oldest sedimentary strata ever recovered in the Netherlands. The results from the upper cored section from the pre-Carboniferous succession in well KTG-01 and the cored sections from the pre-Carboniferous succession in well S05-01 are more ambiguous. This inferred Devonian succession is, in the current informal lithostratigraphy of the Netherlands, assigned to the Banjaard group and its subordinate Bollen Claystone formation, of presumed Frasnian (i.e. early Late Devonian) age. Age-indicative Middle to Late Devonian palynomorphs were, however, not recorded, and the overall character of the poorly preserved palynological associations in wells KTG-01 and S05-01 may also suggest an Early Devonian age. In terms of lithofacies, however, the cores in well S05-01 can be correlated to the upper Frasnian – lower Famennian Falisolle Formation in the Campine Basin in Belgium. Hence, it remains plausible that an unconformity separates Silurian to Lower Devonian strata from Upper Devonian (Frasnian–Famennian) strata in the SW Netherlands. In general, the abundance of miospore associations points to the presence of a vegetated hinterland and a relatively proximal yet relatively deep marine setting during late Silurian and Early Devonian times. This differs markedly from the open marine depositional settings reported from the Brabant Massif area to the south in present-day Belgium, suggesting a sediment source to the north. The episodic presence of reworked (marine) acritarchs of Ordovician age suggests the influx of sedimentary material from uplifted elements on the present-day Brabant Massif to the south, possibly in relation to the activation of a Brabant Arch system.</jats:p

Biogeochemical evolution and organic carbon deposition on the Northwestern European Shelf during the Toarcian Ocean Anoxic Event

The Toarcian Oceanic Anoxic Event (T-OAE, ~183 Ma) represents a well-known episode of organic-rich deposition, which is accompanied by a substantial negative carbon-isotope excursion (CIE). Underpinning the relationships between the carbon-cycle perturbation, ocean anoxia, primary productivity feedbacks and the enrichment of sedimentary organic carbon remains a major challenge. Here, we present high-resolution geochemical, palynological and organofacies data from three lower Toarcian successions from the NW European shelf, spanning the T-OAE. Chronostratigraphic calibration of the successions is achieved through organic carbon isotope (δ 13C) records. Iron-speciation and major and trace-element data indicate that bottom-waters were euxinic and intermittently anoxic-ferruginous prior to, throughout and beyond the CIE. In terms of organofacies and palynological composition, the CIE-interval is dominated by dense clusters of amorphous organic matter containing abundant small spherical prasinophyte cysts (Halosphaeropsis liassica). The peak CIE is bracketed by a major increase in abundance of prasinophycean vegetative cysts (Tasmanites and Pleurozonaria spp.). On the basis of their modern physiology, this suggests shoaling of the chemocline into the photic zone. The combined proxy data suggest a scenario in which anoxygenic photosynthetic productivity proliferated in nutrient-rich, anoxic to seasonally euxinic surface-waters of the stratified NW-European shelf during the CIE. A return to oxic-marine conditions is recorded by the recurrence of organic-walled dinoflagellate cysts in accordance with enhanced water column mixing post CIE. This is concurrent with a gradual termination of strongly stratified conditions across the NW-European shelf

Biogeochemical evolution and organic carbon deposition on the Northwestern European Shelf during the Toarcian Ocean Anoxic Event

The Toarcian Oceanic Anoxic Event (T-OAE, ~183 Ma) represents a well-known episode of organic-rich deposition, which is accompanied by a substantial negative carbon-isotope excursion (CIE). Underpinning the relationships between the carbon-cycle perturbation, ocean anoxia, primary productivity feedbacks and the enrichment of sedimentary organic carbon remains a major challenge. Here, we present high-resolution geochemical, palynological and organofacies data from three lower Toarcian successions from the NW European shelf, spanning the T-OAE. Chronostratigraphic calibration of the successions is achieved through organic carbon isotope (δ 13C) records. Iron-speciation and major and trace-element data indicate that bottom-waters were euxinic and intermittently anoxic-ferruginous prior to, throughout and beyond the CIE. In terms of organofacies and palynological composition, the CIE-interval is dominated by dense clusters of amorphous organic matter containing abundant small spherical prasinophyte cysts (Halosphaeropsis liassica). The peak CIE is bracketed by a major increase in abundance of prasinophycean vegetative cysts (Tasmanites and Pleurozonaria spp.). On the basis of their modern physiology, this suggests shoaling of the chemocline into the photic zone. The combined proxy data suggest a scenario in which anoxygenic photosynthetic productivity proliferated in nutrient-rich, anoxic to seasonally euxinic surface-waters of the stratified NW-European shelf during the CIE. A return to oxic-marine conditions is recorded by the recurrence of organic-walled dinoflagellate cysts in accordance with enhanced water column mixing post CIE. This is concurrent with a gradual termination of strongly stratified conditions across the NW-European shelf

Quantitative organic-walled dinoflagellate cyst stratigraphy across the eocene-oligocene transition in the Gulf of Mexico : A record of climateand sea level change during the onset of antarctic glaciation

The Eocene – Oligocene Transition (EOT, ~34–33.5 Ma) marks a major transition in Cenozoic climate evolution through the relatively rapid establishment of a continental-scale ice sheet on Antarctica. The EOT is characterized by two ~200 kyr spaced shifts (termed EOT-1 and Oi-1) in the oxygen isotopic composition (δ18O) of benthic foraminifera, representing both changes in continental ice-volume and temperature. Estimates of the timing and magnitude of these changes during this critical phase in Earth’s climatic evolution are controversial. Here we present marine palynological assemblage data, in particular of organic-walled dinoflagellate cysts (dinocysts), across a classic upper Eocene to lower Oligocene neritic succession cored in Alabama, USA; the Saint Stephens Quarry (SSQ) borehole. These palynological data combined with lithological information allow the identification of three sequence boundaries across the EOT. Critically, we identify a sequence boundary at the level corresponding to the EOT-1. Integrated sea level and paleotemperature records show that EOT-1 primarily represents cooling with some minor and transient continental ice sheet expansion. Furthermore, we identify a significant hiatus, likely caused by major sea level fall at the base of Magnetochron C13n that corresponds to the Oi-1 shift. This clarifies the δ18O records from SSQ that essentially lack the expected pronounced shift to positive δ18O values so characteristic for Oi-1. Furthermore, we document originations and extinctions of potentially temperature-sensitive dinocysts associated with the EOT-1. In contrast, the Oi-1 does not stand out as period of substantial dinoflagellate turnover. The combined results illustrate that major cooling, limited and transient ice growth and major biotic change were occurring before the full-size expansion of the Antarctic cryosphere

Stratigraphic calibration of Oligocene-Miocene organic-walled dinoflagellate cysts from offshore Wilkes Land, East Antarctica, and a zonation proposal

There is growing interest in the scientific community in reconstructing the paleoceanography of the Southern Ocean during the Oligocene-Miocene because these time intervals experienced atmospheric CO2 concentrations with relevance to our future. However, it has remained notoriously difficult to put the sedimentary archives used in these efforts into a temporal framework. This is at least partially due to the fact that the bioevents recorded in organic-walled dinoflagellate cysts (dinocysts), which often represent the only microfossil group preserved, have not yet been calibrated to the international timescale. Here we present dinocyst ranges from Oligocene-Miocene sediments drilled offshore the Wilkes Land continental margin, East Antarctica (Integrated Ocean Drilling Program (IODP) Hole U1356A). In addition, we apply statistical means to test a priori assumptions about whether the recorded taxa were deposited in situ or were reworked from older strata. Moreover, we describe two new dinocyst species, Selenopemphix brinkhuisii sp. nov. and Lejeunecysta adeliensis sp. nov., which are identified as important markers for regional stratigraphic analysis. Finally, we calibrate all identified dinocyst events to the international timescale using independent age control from calcareous nanoplankton and magnetostratigraphy from IODP Hole U1356A, and we propose a provisional dinoflagellate cyst zonation scheme for the Oligocene-Miocene of the Southern Ocean

Late Eocene Southern Ocean Cooling and Invigoration of Circulation Preconditioned Antarctica for Full-Scale Glaciation

During the Eocene-Oligocene Transition (EOT; 34–33.5 Ma), Antarctic ice sheets relatively rapidly expanded, leading to the first continent-scale glaciation of the Cenozoic. Declining atmospheric CO2 concentrations and associated feedbacks have been invoked as underlying mechanisms, but the role of the quasi-coeval opening of Southern Ocean gateways (Tasman Gateway and Drake Passage) and resulting changes in ocean circulation is as yet poorly understood. Definitive field evidence from EOT sedimentary successions from the Antarctic margin and the Southern Ocean is lacking, also because the few available sequences are often incomplete and poorly dated, hampering detailed paleoceanographic and paleoclimatic analysis. Here we use organic dinoflagellate cysts (dinocysts) to date and correlate critical Southern Ocean EOT successions. We demonstrate that widespread winnowed glauconite-rich lithological units were deposited ubiquitously and simultaneously in relatively shallow-marine environments at various Southern Ocean localities, starting in the late Eocene (~35.7 Ma). Based on organic biomarker paleothermometry and quantitative dinocyst distribution patterns, we analyze Southern Ocean paleoceanographic change across the EOT. We obtain strong indications for invigorated surface and bottom water circulation at sites affected by polar westward-flowing wind-driven currents, including a westward-flowing Antarctic Countercurrent, starting at about 35.7 Ma. The mechanism for this oceanographic invigoration remains poorly understood. The circum-Antarctic expression of the phenomenon suggests that, rather than triggered by tectonic deepening of the Tasman Gateway, progressive pre-EOT atmospheric cooling played an important role. At localities affected by the Antarctic Countercurrent, sea surface productivity increased and simultaneously circum-Antarctic surface waters cooled. We surmise that combined, these processes contributed to preconditioning the Antarctic continent for glaciation

Stratigraphic calibration of Oligocene-Miocene organic-walled dinoflagellate cysts from offshore Wilkes Land, East Antarctica, and a zonation proposal

There is growing interest in the scientific community in reconstructing the paleoceanography of the Southern Ocean during the Oligocene-Miocene because these time intervals experienced atmospheric CO2 concentrations with relevance to our future. However, it has remained notoriously difficult to put the sedimentary archives used in these efforts into a temporal framework. This is at least partially due to the fact that the bioevents recorded in organic-walled dinoflagellate cysts (dinocysts), which often represent the only microfossil group preserved, have not yet been calibrated to the international timescale. Here we present dinocyst ranges from Oligocene-Miocene sediments drilled offshore the Wilkes Land continental margin, East Antarctica (Integrated Ocean Drilling Program (IODP) Hole U1356A). In addition, we apply statistical means to test a priori assumptions about whether the recorded taxa were deposited in situ or were reworked from older strata. Moreover, we describe two new dinocyst species, Selenopemphix brinkhuisii sp. nov. and Lejeunecysta adeliensis sp. nov., which are identified as important markers for regional stratigraphic analysis. Finally, we calibrate all identified dinocyst events to the international timescale using independent age control from calcareous nanoplankton and magnetostratigraphy from IODP Hole U1356A, and we propose a provisional dinoflagellate cyst zonation scheme for the Oligocene-Miocene of the Southern Ocean

Late Eocene Southern Ocean Cooling and Invigoration of Circulation Preconditioned Antarctica for Full-Scale Glaciation

During the Eocene-Oligocene Transition (EOT; 34–33.5 Ma), Antarctic ice sheets relatively rapidly expanded, leading to the first continent-scale glaciation of the Cenozoic. Declining atmospheric CO2 concentrations and associated feedbacks have been invoked as underlying mechanisms, but the role of the quasi-coeval opening of Southern Ocean gateways (Tasman Gateway and Drake Passage) and resulting changes in ocean circulation is as yet poorly understood. Definitive field evidence from EOT sedimentary successions from the Antarctic margin and the Southern Ocean is lacking, also because the few available sequences are often incomplete and poorly dated, hampering detailed paleoceanographic and paleoclimatic analysis. Here we use organic dinoflagellate cysts (dinocysts) to date and correlate critical Southern Ocean EOT successions. We demonstrate that widespread winnowed glauconite-rich lithological units were deposited ubiquitously and simultaneously in relatively shallow-marine environments at various Southern Ocean localities, starting in the late Eocene (~35.7 Ma). Based on organic biomarker paleothermometry and quantitative dinocyst distribution patterns, we analyze Southern Ocean paleoceanographic change across the EOT. We obtain strong indications for invigorated surface and bottom water circulation at sites affected by polar westward-flowing wind-driven currents, including a westward-flowing Antarctic Countercurrent, starting at about 35.7 Ma. The mechanism for this oceanographic invigoration remains poorly understood. The circum-Antarctic expression of the phenomenon suggests that, rather than triggered by tectonic deepening of the Tasman Gateway, progressive pre-EOT atmospheric cooling played an important role. At localities affected by the Antarctic Countercurrent, sea surface productivity increased and simultaneously circum-Antarctic surface waters cooled. We surmise that combined, these processes contributed to preconditioning the Antarctic continent for glaciation