The effects of astronomically forced climate change on hemipelagic carbonate sedimentation in a tectonically active setting: the Albian Mioño Formation in Castro Urdiales (Cantabria, N Spain)

Our understanding of the stratigraphic expression of astronomically driven climate-change cycles in the Milankovitch frequency band has improved significantly in recent decades. However, several aspects have been little studied to date, such as the nature of the climatically regulated environmental processes that ultimately control cyclic sedimentation. Similarly, relatively little is known about the expression of Milankovitch cycles in successions accumulated in tectonically active basins. In order to fill this knowledge gap, the Albian hemipelagic deposits of the Miono Formation exposed in Castro Urdiales (Basque-Cantabrian Basin) are studied herein. These deposits were accumulated during a rifting phase with strong tectonic activity. The sedimentological, petrographic and cyclostratigraphic analysis demonstrates that, despite the synsedimentary tectonic instabilities and some diagenetic overprinting, the hemipelagic carbonate alternation was astronomically forced 110.68-110.47 Ma. Seasonality fluctuations driven by precession cycles caused periodic (20 ky) variations in the rate of carbonate productivity (abundance of pelagic calcareous plankton and micrite exported from adjacent shallow-water areas) and/or siliceous dilution (terrestrially derived siliciclastic sediment supply and siliceous particle production by sponges). These variations resulted in the formation of marly limestone beds when annual seasonality was low (i.e., boreal summer at aphelion, winter at perihelion) and the accumulation of marlstones when seasonality increased (i.e., boreal summer at perihelion, winter at aphelion). The incidence of these processes increased and decreased in line with seasonality modulation by short-eccentricity cycles of 100 ky. In conclusion, this study shows that Milankovitch cycles can be reliably recorded in hemipelagic successions accumulated in tectonically active settings if sediment gravity flows or other disturbances do not affect autochthonous sedimentation.Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature. Research funded by the MCIN/AEI project PID2019-105670GB-I00/AEI/10.13039/501100011033 of the Spanish Government and by the Consolidated Research Group IT160222 of the Basque Government

CALCAREOUS PLANKTON BIO-EVENTS IN THE MIOCENECASE PELACANI SECTION (SOUTH-EASTERN SICILY, ITALY)

The upper Serravallian-Lower Tortonian Case Pelacani section in Sicily is represented by the epipelagic sediments of the Tellaro Formation. Along the section, which was sampled in four easily correlatable segments, a more or less continuous sequence of lithologic couplets, with whitish marls and blackish levels in the lower part and whitish marls and whitish more indurated levels in the upper part are present. The distribution of the most common taxa of planktonic foraminifera and calcareous nannofossils was quantitatively estimated in 316 samples, collected every 20 cm along the section which is 66.35 m thick. This allowed to identify eleven planktonic foraminifera (but only the eight marker events were quantitatively estimated) and five calcareous nannofossil bio-events.  Their astrochronology is reported by correlation with the cyclostratigraphic results obtained for this section in a different paper. The ages are well comparable with the ages published for the same events in other Mediterranean sections. Paleomagnetic analysis along 30 meters in the central part of the section gave puzzling results and therefore no reliable magnetostratigraphy could be obtained. The Case Pelacani section, straddling the stratigraphic interval between slightly below the first occurrence and slightly above the first regular occurrence of Neogloboquadrina acostaensis , is a good candidate for the definition of the GSSP (Global Stratigraphic Section and Point) of the Tortonian. Independently from the selected section, we suggest to define the Serravallian/Tortonian boundary in a level coincident or near the last occurrence of Paragloborotalia siakensis, as already proposed, or coincident with or near the last common occurrence of Globigerinoides subquadratus. This latter level virtually coincides with the first common occurrence of Globigerinoides obliquus obliquus and is slightly above the last common occurrence of Discoaster kugleri, which occurs only 2.25 meters (and 3 precessional cycles) below in the studied section.&nbsp

The Global Stratotype Sections and Points for the bases of the Selandian (Middle Paleocene) and Thanetian (Upper Paleocene) stages at Zumaia, Spain

The global stratotype sections and points for the bases of the Selandian (Middle Paleocene) and Thanetian (Upper Paleocene) stages have been defined in the coastal cliff along the Itzurun Beach at the town of Zumaia in the Basque Country, northern Spain. In the hemipelagic section exposed at Zumaia the base of the Selandian Stage has been placed at the base of the Itzurun Formation, ca. 49 m above the Cretaceous/ Paleogene boundary. At the base of the Selandian, marls replace the succession of Danian red limestone and limestone-marl couplets. The best marine, global correlation criterion for the basal Selandian is the second radiation of the important calcareous nannofossil group, the fasciculiths. Species such as Fasciculithus ulii, F. billii, F. janii, F. involutus, F.pileatus and F. tympaniformis have their first appearance in the interval from a few decimetres below up to 1.1 m above the base of the Selandian. The marker species for nannofossil Zone NP5, F. tympaniformis, first occurs 1.1 m above the base. Excellent cyclostratigraphy and magnetostratigraphy in the section creates further correlation potential, with the base of the Selandian occuring 30 precession cycles (630 kyr) above the top of magnetochron C27n. Profound changes in sedimentology related to a major sea-level fall characterize the Danian-Selandian transition in sections along the margins of the North Atlantic. The base of the Thanetian Stage is placed in the same section ca. 78 m above the Cretaceous/Paleogene boundary. It is defined at a level 2.8 m or eight precession cycles above the base of the core of the distinct clay-rich interval associated with the Mid-Paleocene Biotic Event, and it corresponds to the base of magnetochron C26n in the section. The base of the Thanetian is not associated with any significant change in marine micro-fauna or flora. The calcareous nannofossil Zone NP6, marked by the first occurrence of Heliolithus kleinpelli starts ca. 6.5 m below the base of the Thanetian. The definitions of the global stratotype points for the bases of the Selandian and Thanetian stages are in good agreements with the definitions in the historical stratotype sections in Denmark and England, respectively

Geochronological accuracy around the cretaceous paleogene boundary interval insights and challenges to the age of chron C29r and intervening events

The need for precise and accurate time constraints in Earth sciences is pivotal to successfully unravel geological mechanisms and rates of processes. Timescale accuracy is a prerequisite for reliable event correlation and to disentangle intricate complex climatic and biotic changes. The late Cretaceous, a time interval of major biodiversity adjustments culminating in the end-Cretaceous mass extinction, has been the subject of intense debates regarding not only its causes but also the timing. The Cretaceous-Paleogene (K-Pg) boundary occurs within Chron C29r. Its numerical age and the relative position within C29r has changed significantly over different instances of the GPTS. The radiometric absolute age of the K-Pg boundary has now been established at 66.043 ± 0.043 Ma by high-precision 40 Ar/ 39 Ar dating on tektites and bentonites associated with the boundary. The age close to 66 Ma is compatible with astronomical tuned chronologies derived from integrated magneto/chemo/biostratigraphic studies from marine sequences that have provided complete orbital chronologies for the Maastrichtian and Paleocene at eccentricity resolution (~100-400 ky). These studies also place the K-Pg halfway C29r with a calibrated Chron duration of ~710 ky. However, a recent chronostratigraphic study of the terrestrial K-Pg transition in the Hell Creek region (Montana) including 40 Ar/ 39 Ar dating of 15 tephra layers challenge the duration of C29r to as brief as ~345 ky. Here, the chronological framework of C29r is reappraised and studied at orbital precession resolution (~21 ky) using an array of deep sea records and new data from pelagic strata from the Bjala section (Bulgaria) and the Mudurnu-Goynuk basin (NW Turkey)

A Santonian Campanian boundary locality from North western Turkey

A Santonian-Campanian boundary section, close to the village of Göynük in Northwestern Turkey (Bolu province), was recorded and examined in respect to nannofossil and foraminiferal biostratigraphy, magnetic susceptibility, as well as magnetic polarity. During the Late Cretaceous, the Mudurnu-Göynük basin was located in the northern Tethyan Ocean, on the Sakarya continent (between the Intra-Pontide Ocean and northern branch of the Tethys). The section yields reddish hemipelagic to pelagic deposits. The stratigraphically older part is characterised by uniform limestone. Towards the top, the section displays marls and marly limestones with frequent tuff intercalations. The section represents a hemipelagic to pelagic environment. Planktonic foraminifera prevail in numbers and represent a typical Santonian to Campanian foraminifera community. Benthic foraminifera are sparse. Biostratigraphic data suggest an age from the late Santonian Dicarinella asymetrica to the early Campanian Globotruncanita elevata planktonic foraminifera zone (nannofossil zones CC16-CC18). By investigation of magnetic polarity, the older part of the section can be assigned to the Santonian C34 normal, while the base-Campanian reversal C33r is evident in the upper part of the section. Results from the assessment of magnetic susceptibility give evidence for Milankovitch cycles. We witness a strong signal for what would presumably be the 400 kyr eccentricity cycle. The Campanian interval measured at this section gives results of unusually high values for magnetic susceptibility. Compared to the older part of the section, we find values twice as high in the younger interval. As evidence for volcanic activity is frequent in the Campanian part of the section, the abrupt shift in the magnitude of magnetic susceptibility values may be explained by volcanic admixture. Apart from implications for biostratigraphy and palaeoenvironments, the record of frequent volcanic activities in this Santonian-Campanian boundary section might also provide insights in the history of volcanic events in the Northwestern Tethyan realm

Orbital variations in planktonic foraminifera assemblages from the Ionian Sea during the Middle Pleistocene Transition

The Middle Pleistocene Transition (1.2-0.7 Ma) is the most recent re-organization of the global climate system which includes variations in the frequency and amplitude of glacial/interglacial cycles, increased ice sheet volume, sea surface temperature cooling and a significant drop in the CO2 atmospheric levels. Here we present high-resolution planktonic foraminifera data (mean sampling resolution of about 780 years) from core LC10 recovered in the Ionian Sea (eastern Mediterranean), between 1.2 and 0.9 Ma. Selected taxa, among them G. ruber, T. quinqueloba and G. bulloides, show significant periodicities that can be associated to orbital cycles, mainly precession and obliquity. The planktonic foraminifera based paleoclimatic curve exhibits a cooling linear trend that can be associated to similar phenomena observed in the North Atlantic. On the other hand, we refer to the influence of the North African Monsoon the occurrence of two peaks of the low-salinity tolerant species G. quadrilobatus that fall in coincidence of sapropel layers. Finally, we discuss the distribution pattern of N. pachyderma sinistral coiling, with peaks up to about 20% between MIS 30 and 28, and compare it to middle-late Quaternary records of the Sicily Channel and western Mediterranean

Calcareous nannofossil response to Late Cretaceous climate change in the eastern Tethys (Zagros Basin, Iran)

14 pagesInternational audienceConiacian to Maastrichtian changes in calcareous nannofossil assemblages have been investigated in the eastern Tethyan Shahneshin section (central Zagros Basin, Iran). The nannofossil assemblages are mainly composed of Watznaueria spp. (avg. 54%), Retecapsa spp (avg. 7.9%), Cribrosphaerella ehrenbergii (avg. 7.7%) and Micula spp. (avg. 5.7%). Throughout the late Campanian, there is a trend to lower abundances in Watznaueria spp. together with increasing abundances of C. ehrenbergii and Arkhangelskiella cymbiformis, which are considered in this basin as the main cool-water taxa. Our results reveal that, despite a diagenetic impact on calcareous nannoflora, a number of primary paleoecological trends are preserved which depict well features of the progressive Late Cretaceous cooling. The first pronounced cooling episode occurs across the late Campanian to early Maastrichtian. The onset of pronounced cooling in the eastern Tethys appears to occur prior to the Campanian/Maastrichtian Boundary event (CMBE) δ13C negative excursion, in contrast with the Boreal realm where pronounced cooling only occurs in the early Maastrichtian, postdating the onset of the CMBE. The coincidence of this earlier cooling in the Zagros Basin with an interval characterized by a significant increase in benthic foraminifera suggests an amplified response of the assemblage due to a change to shallower environments. Hence, the late Campanian calcareous nannofossil assemblage turnover in central Zagros is either a response to an early cooling trend in the eastern Tethys or to sea-level fall or both. The mid-Maastrichtian warming and late Maastrichtian cooling episodes are also delineated in the nannofossil assemblage of Shahneshin and likely correlate with similar episodes in the Boreal Realm

Calcareous plankon bio-events in the Miocene Case Pelacani section (Sicily, Italy)

7noreservedThe upper Serravallian-lower Tortonian Case Pelacani section in Sicily is composed of the epipelagic sediments of the Tellaro Formation. The section, made of four easily correlated segments, records a more or less continuous sequence of lithologic couplets, with whitish marls and blackish levels in the lower part and whitish marls and whitish, more indurate levels in the upper part. The distribution of the most common taxa of planktonic foraminifera and calcareous nannofossils was estimated quantitatively in 316 samples, collected every 20 cm along the section which is 66.35 in thick. Eleven planktonic foraminifera (only the eight marker events were estimated quantitatively) and five calcareous nannofossil bio-events were identified. Their astrochronology was extrapolated by correlating them with the cyclostratigraphic results obtained for this section, and published separately. The ages compare well with the ages published for the same events in other Mediterranean sections. Paleomagnetic analysis along 30 meters in the central part of the section gave puzzling results and therefore no reliable magnetostratigraphy could be obtained. The Case Pelacani section, straddling the stratigraphic interval which starts slightly below the first occurrence and ends slightly above the first regular occurrence of Neogloboquadrina acostaensis, is a good candidate for the definition of the GSSP (Global Stratigraphic Section and Point) of the Tortonian. Independently from the section selected, we suggest to define the Serravallian/Tortonian boundary in a level coincident with or near the last occurrence of Paragloborotalia siakensis, as previously proposed, or coincident with or near the last common occurrence (LCO) of Globigerinoides subquadratus. This latter level virtually coincides with the first common occurrence (FCO) of Globigerinoides obliquus obliquus and is slightly above the last regular occurrence (FRO) of Discoaster kugleri, which occurs only 2.25 meters (and 3 precessional cycles) below in the section under study.mixedDI STEFANO, E.; BONOMO, S.; CARUSO, A.; DINARÉS-TURELL, J.; FORESI, L. M.; SALVATORINI, G.; SPROVIERI, R.DI STEFANO, E.; Bonomo, S.; Caruso, A.; DINARÉS-TURELL, J.; Foresi, L. M.; Salvatorini, G.; Sprovieri, R