Re-assessment of ammonoid specimens from the Early Carboniferous Protocanites Beds of the Badenweiler-Lenzkirch Zone (Schwarzwald, Central Variscan Belt): Age constraints for a lithostratigraphic key bed

Abstract The Protocanites Beds of the Black Forest Massif (Germany) form an important lithostratigraphic key bed, as the index fossils contained in this formation enable correlation within large areas of the internal Zone of the central Variscan Belt of Europe. Furthermore, the formation provides significant information on the geodynamic evolution of the Moldanubian Zone. The stratigraphic age of the formation has been a subject of controversy in the past; a Devonian to Viséan age has been proposed. In order to determine the age of the Protocanites Beds, two ammonoid specimens from the Protocanites Beds of Schönau are re-described here. They belong to Becanites abnobensis and Pericylcus princeps and fix the stratigraphic position of the Protocanites Beds to the early Late Tournaisian

Comparative geochemistry of Early Carboniferous marine red beds (MRBs) and their significance for deep time paleoceanographic reconstructions

Marine red beds (MRBs), also known as oceanic red beds (ORBs), are reddish colored sediments deposited within the marine realm that have been stained during deposition and/or early diagenesis because of changes in the ocean water chemistry in response to paleoceanographic and paleoclimatological factors. Although common throughout the Phanerozoic, marine red beds have mostly been investigated in Upper Cretaceous successions as CORBs (Cretaceous Oceanic Red Beds) - their occurrence and paleoceanographic context within the Paleozoic has yet to be studied in detail. Here we describe and interpret the high-resolution litho- and chemofacies of Early Carboniferous (Late Viséan) marine red beds from the northern coast of Menorca (Balearic Islands, Spain) that mark a rapid transition from siliceous radiolarian chert deposition to re-worked carbonate debrites followed by typical European Culm facies. The succession was deposited within a strait-like narrow basin that formed part of the Alboran-Kabylian-Peloritan-Calabrian terrane in the Western Paleotethys Ocean prior to the onset of the Variscan Orogeny. The marine red bed geochemistry is described in terms of the three geochemical endmembers Al-MRBs (clayey), Ca-MRBs (calcareous) and Si-MRBs (siliceous) by using XRF-derived Al2O3, CaO, and SiO2 concentrations. This study finds that Viséan marine red beds from Menorca are predominantly Al-MRBs with subordinate Ca-MRBs. Furthermore, we compare the bulk rock geochemistry of the Viséan marine red beds of this study with the geochemical data of Paleozoic, Mesozoic and Cenozoic marine red beds available in the existing literature (Cambrian, Silurian, Jurassic, Cretaceous, Paleogene and recent Pacific Ocean red clays) to highlight the significance of marine red bed occurrences in relation to (paleo-)bioproductivity fluctuations, deep-water oxygenation and oceanic redox transitions. This study finds that Phanerozoic marine red beds are dominantly Al-MRBs and Ca-MRBs, while Si-MRBs are less common. The Early Carboniferous marine red beds of the present study were formed in a distal, deeper-marine environment under oxic-suboxic, oligotrophic conditions. A lack of any significant Fe2O3T enrichment points towards a more complex diagenetic process for the origin of the red color imparted in Phanerozoic MRBs

Population dynamics of galeate acritarchs at the Cambrian-Ordovician transition in the Algerian Sahara

International audienc

Southern Ocean carbon sink enhanced by sea-ice feedbacks at the Antarctic Cold Reversal

The Southern Ocean occupies 14% of the Earth’s surface and plays a fundamental role in the global carbon cycle and climate. It provides a direct connection to the deep ocean carbon reservoir through biogeochemical processes that include surface primary productivity, remineralization at depth and the upwelling of carbon-rich water masses. However, the role of these different processes in modulating past and future air–sea carbon flux remains poorly understood. A key period in this regard is the Antarctic Cold Reversal (ACR, 14.6–12.7 kyr bp), when mid- to high-latitude Southern Hemisphere cooling coincided with a sustained plateau in the global deglacial increase in atmospheric CO2. Here we reconstruct high-latitude Southern Ocean surface productivity from marine-derived aerosols captured in a highly resolved horizontal ice core. Our multiproxy reconstruction reveals a sustained signal of enhanced marine productivity across the ACR. Transient climate modelling indicates this period coincided with maximum seasonal variability in sea-ice extent, implying that sea-ice biological feedbacks enhanced CO2 sequestration and created a substantial regional marine carbon sink, which contributed to the plateau in CO2 during the ACR. Our results highlight the role Antarctic sea ice plays in controlling global CO2, and demonstrate the need to incorporate such feedbacks into climate–carbon models