Silke Voigt

Alternative global Cretaceous paleogeography

Plate tectonic reconstructions for the Cretaceous have assumed that the major continental blocks—Eurasia, Greenland, North America, South America, Africa, India, Australia, and Antarctica—had separated from one another by the end of the Early Cretaceous, and that deep ocean passages connected the Pacific, Tethyan, Atlantic, and Indian Ocean basins. North America, Eurasia, and Africa were crossed by shallow meridional seaways. This classic view of Cretaceous paleogeography may be incorrect. The revised view of the Early Cretaceous is one of three large continental blocks— North America–Eurasia, South America–Antarctica-India-Madagascar-Australia; and Africa—with large contiguous land areas surrounded by shallow epicontinental seas. There was a large open Pacific basin, a wide eastern Tethys, and a circum- African Seaway extending from the western Tethys (“Mediterranean”) region through the North and South Atlantic into the juvenile Indian Ocean between Madagascar-India and Africa. During the Early Cretaceous the deep passage from the Central Atlantic to the Pacific was blocked by blocks of northern Central America and by the Caribbean plate. There were no deep-water passages to the Arctic. Until the Late Cretaceous the Atlantic-Indian Ocean complex was a long, narrow, sinuous ocean basin extending off the Tethys and around Africa. Deep passages connecting the western Tethys with the Central Atlantic, the Central Atlantic with the Pacific, and the South Atlantic with the developing Indian Ocean appeared in the Late Cretaceous. There were many island land areas surrounded by shallow epicontinental seas at high sea-level stands.

The Cenomanian - Turonian of the Wunstorf section - (North Germany): global stratigraphic reference section and new orbital time scale for Oceanic Anoxic Event 2

The Cenomanian–Turonian Boundary Event (CTBE) is reflected by one of the most extreme carbon cycle perturbations in Earths history and is characterized by the widespread occurrence of sediments indicating oxygen deficiency in oceanic waters (Oceanic Anoxic Event 2 = OAE 2). At Wunstorf (northern Germany) the CTBE is represented by a 26.5 m thick sedimentary succession consisting of rhythmically bedded laminated black shales, dark organic-rich marls and marly limestones yielding abundant micro- and macrofossils, making the locality particularly well suited to serve as an international standard reference section for the CTBE. In 2006 a newly drilled continuous core recovered 76 m of middle Cenomanian to middle Turonian sediments. A high-resolution carbonate δ13C curve derived from core samples resolves all known features of the positive δ13C anomaly of OAE 2 with high accuracy. Throughout the middle Cenomanian – middle Turonian succession, the δ13C curve shows numerous small-scaled positive excursions, which appear to be cyclic. High-resolution borehole geophysics and XRF core scanning were performed to generate two time series of gamma-ray data and Ti concentrations for the CTBE black shale succession. Hierarchical bundling of sedimentary cycles as well as spectral analysis and Gaussian filtering of dominant frequencies reveal cycle frequency ratios characteristic for short eccentricity modulated precession (100 kyr, 21 kyr). This new orbital time scale provides a time estimate of 430–445 kyr for the duration of OAE 2 and refines the existing orbital age models developed at localities in the English Chalk, the Western Interior Basin and the Tarfaya Basin. Based on the new age model and high-resolution carbon isotope correlation, our data allow for the first time a precise basin-wide reconstruction of the palaeoceanographic modifications within the European shelf sea during OAE 2.

Late Cretaceous carbon isotope stratigraphy in Europe: Correlation and relations with sea level and sediment stability

Abstract Upper Cretaceous (Upper Cenomanian to Lower Coniacian) stable carbon isotope stratigraphy of German hemipelagic marls (borehole Dresden-Blasewitz), pelagic carbonates (quarries Salzgitter-Salder and Sohlde), and of two Turonian to Santonian pelagic sections in the northern Alpine Helvetic Zone, supplemented by published carbon isotope data (Kent, southern England; Gubbio, Italy), are used for correlations of northern temperate (boreal) and Tethyan sections. General carbon isotopic trends are different in pelagic and hemipelagic carbonates, probably in response to the input of terrestrial organic carbon to the inner shelf carbon reservoir (including sediments). The global component in the carbon isotope stratigraphy is best recorded in pelagic carbonates. Sufficient biostratigraphic control is present to correlate all sections across facies boundaries and between the two biogeographic provinces. Hiatuses produce breaks in the gradual carbon isotopic trends and their duration can be estimated relative to complete sections. A broad δ13C minimum straddles the Turonian-Coniacian boundary at the proposed boundary stratotype Salzgitter-Salder, with its center about 0.5–1 m below the biostratigraphic reference level (first occurrence of C. rotundatus Fiege sensu Troger non Fiege). Increases and maxima of pelagic δ13C values occur during phases of sediment accumulation. Decreasing pelagic °13C values and minima characterise phases of sediment erosion. The amplitudes of these stratigraphic fluctuations may indicate the intensity of sediment reworking. Changes in the sediment accumulation/erosion ratio and accompanied carbon isotopic variation may be related to short-term sea-level fluctuations and their effect on fine-grained sediment stability.

Eustatic sea-level record for the Cenomanian (Late Cretaceous)—Extension to the Western Interior Basin, USA

A combination of biostratigraphic markers (ammonites, inoceramid bivalves) and carbon isotope excursions is employed to establish a high-resolution correlation between the middle to late Cenomanian successions of the Western Interior Basin (USA) and the Anglo-Paris Basin (southern UK). Sequences identified from sedimentologic criteria in the Pueblo succession and elsewhere in the Western Interior Basin are shown to coincide precisely with globally recognized sea-level events and were therefore under eustatic control. This evidence refutes arguments that Cenomanian sequences in the Western Interior Basin were formed by local tectonic events. The interaction of longer-term tectonic movements and more rapid eustatic change may have simply enhanced the amount of erosion associated with sequence boundaries. A crossplot of radiometric ages derived from North American bentonites against an orbitally tuned time scale developed in the Anglo-Paris Basin provides support for the argument that the sequences were controlled by the 405-k.y.-long eccentricity cycle.

Global correlation of Upper Campanian - Maastrichtian successions using carbon-isotope stratigraphy: development of a new Maastrichtian timescale

Carbon-isotope stratigraphy has proven to be a powerful tool in the global correlation of Cretaceous successions. Here we present new, high-resolution carbon-isotope records for the Global Boundary Stratotype Section and Point (GSSP) of the Maastrichtian stage at Tercis les Bains (France), the Bottaccione and Contessa sections at Gubbio (Italy), and the coastal sections at Norfolk (UK) to provide a global δ13C correlation between shelf-sea and oceanic sites. The new δ13C records are correlated with δ13C-stratigraphies of the boreal chalk sea (Trunch borehole, Norfolk, UK, Lagerdorf-Kronsmoor-Hemmoor section, northern Germany, Stevns-1 core, Denmark), the tropical Pacific (ODP Hole 1210B, Shatsky Rise) and the South Atlantic and Southern Ocean (DSDP Hole 525A, ODP Hole 690C) by using an assembled Gubbio δ13C record as a reference curve. The global correlation allows the identification of significant high-frequency δ13C variations that occur superimposed on prominent Campanian-Maastrichtian events, namely the Late Campanian Event (LCE), the Campanian-Maastrichtian Boundary Event (CMBE), the mid-Maastrichtian Event (MME), and the Cretaceous-Paleogene transition (KPgE). The carbon-isotope events are correlated with the geomagnetic polarity scale recalculated using the astronomical 40Ar/39Ar calibration of the Fish Canyon sanidine. This technique allows the evaluation of the relative timing of base occurrences of stratigraphic index fossils such as ammonites, planktonic foraminifera and calcareous nannofossils. Furthermore, the Campanian-Maastrichtian boundary, as defined in the stratotype at Tercis, can be precisely positioned relative to carbon-isotope stratigraphy and the geomagnetic polarity timescale. The average value for the age of the Campanian-Maastrichtian boundary is 72.1 ± 0.1 Ma, estimated by three independent approaches that utilize the Fish Canyon sanidine calibration and Option 2 of the Maastrichtian astronomical timescale. The CMBE covers a time span of 2.5 Myr and reflects changes in the global carbon cycle probably related to tectonic process rather than to glacio-eustasy. The duration of the high-frequency δ13C variations instead coincides with the frequency band of long eccentricity, indicative of orbital forcing of changes in climate and the global carbon cycle.

Cenomanian–Turonian composite δ13C curve for Western and Central Europe: the role of organic and inorganic carbon fluxes

Abstract Detailed δ 13 C stratigraphies have been published recently for several Cenomanian–Turonian pelagic sections of southern England, and the Lower Saxony basin of Germany. The observed changes in the δ 13 C record provide a useful tool for high-resolution stratigraphic correlation, and are used here to create a composite Cenomanian–Turonian δ 13 C curve in a time-related framework. A best fit curve to 673 carbon isotope data is provided using the LOWESS regression scatterplot smoother. The long-term trend of the smoothed composite δ 13 C profile varies on time scales of 10 6 years, and shows stable δ 13 C values through the Lower Cenomanian, an increase in the Middle and Upper Cenomanian, with a major positive excursion around the Cenomanian–Turonian boundary, and a decrease through the Lower and Middle Turonian. Short-term fluctuations vary on time scales of 10 5 years, and dominated the δ 13 C signal in the higher Middle and Upper Turonian. Changes of the Cenomanian–Turonian δ 13 C record have commonly been explained by variations in the organic carbon flux to the sedimentary reservoir, in response to eustatic sea-level change. However, mass balance consideration suggests also an influence of carbonate production and burial rate on the δ 13 C signal. Enhanced inorganic carbon burial increased the ratio of the inorganic to organic carbon fluxes and shifted the 13 C/ 12 C ratio to more negative values. This pattern may be observed in the Early and Middle Turonian δ 13 C long-term record, and correlates with the spatial expansion of pelagic carbonate deposits in epicontinental seas. Short-term δ 13 C variations could be either a directly response to short-term sea-level changes, reflecting local conditions in the European epicontinental sea, or could represent changes in oceanic 12 C storage in response to the varying intensity of thermohaline circulation.

Evidence for Late Cretaceous (Late Turonian) climate cooling from oxygen-isotope variations and palaeobiogeographic changes in Western and Central Europe

Trends of stable oxygen-isotope data through four European sections of Middle–Upper Turonian sediments show three phases of synchronous variations, each phase having a duration of about 250 ka. The isotopic variations are independent of local facies, sedimentary thickness and diagenetic history. Two positive δ18O shifts are associated with a southward spread of northern macrofaunas. This coincidence of geochemical and palaeontological data implies that the δ18O trends reflect a southward shift of cooler water masses. This southward extension of cooler waters was caused by changes in ocean circulation and was associated with a major regression in the early Late Turonian.

Campanian – Maastrichtian carbon isotope stratigraphy: shelf-ocean correlation between the European shelf sea and the tropical Pacific Ocean

The long-term climate cooling during Campanian - Maastrichtian times is not well understood to date, especially because of the uncertainty introduced by low temporal resolution of biostratigraphy and the pronounced provincialism between tropical and temperate taxa. Two new high-resolution carbon isotope records derived from the boreal shelf-sea section at Lagerdorf-Kronsmoor-Hemmoor, northern Germany and the tropical Pacific at Deep Sea Drilling Project Site 305, Shatsky Rise, reduce these uncertainties. The records can be correlated with an accuracy not achieved by biostratigraphic methods so far. Distinct carbon isotope events in the late Campanian and the early Maastrichtian can be identified at both localities suggesting to represent global carbon cycle perturbations. Especially, the negative carbon isotope excursion in the early Maastrichtian, a pronounced feature of open-ocean records from the Pacific and Southern oceans, is recognized for the first time at a shelf-sea locality related to the North Atlantic Ocean. Furthermore, two short-term positive excursions are identified as superimposed signals to this event. The improved stratigraphy provides the unique opportunity to recognize leads and lags between the carbon cycle and ocean circulation of different marine settings and ecosystems, leading to a better understanding of their causes and effects.

Late Turonian (Cretaceous) climate cooling in Europe: faunal response and possible causes

Abstract Isochronous variations of δ18O curves within several European basins indicate a period of Late Turonian climate cooling, which is characterized by two distinct cooling phases, separated by a period of climate stability. Literature data for macrofauna (ammonites, echinoids, and belemnites) indicate that the cooling phases are associated with a southward shift of taxa. Concomitant Late Turonian events (volcanism and relative sea-level changes) suggest the migration to be triggered mainly by relative sea-level falls. The inferred cooling phases are seen in context with a general cooling trend due to the decrease in Mid-Cretaceous volcanogenic CO2 emission. Short-term stagnation of cooling in the Late Turonian has been probably triggered by renewed volcanism. Due to the general high temperatures during Mid-Cretaceous times, a glacio-eustatic explanation for the coincidence of cooling and sea-level fall is considered unlikely.

A Selachian Freshwater Fauna from the Triassic of Kyrgyzstan and Its Implication for Mesozoic Shark Nurseries

ABSTRACT Habitat partitioning and site fidelity of spawning grounds are well-documented phenomena in extant selachians, but little is known about the reproductive strategies of their fossil relatives. Here we describe the selachian fauna of the Middle to Late Triassic Madygen Formation in southwestern Kyrgyzstan, Central Asia, based on several dozen tooth crowns and egg capsules. The material is assigned to three new taxa: Lonchidion ferganensis, sp. nov., and Palaeoxyris alterna, sp. nov., being teeth and egg capsules of hybodontid sharks, and Fayolia sharovi, sp. nov., being egg capsules of probable xenacanthids. Teeth of L. ferganensis, sp. nov., were almost exclusively found in pelecypod-rich shallow lacustrine mudstones and belong to juvenile individuals. Oxygen and strontium isotope data of tooth enameloid indicate freshwater conditions of the ambient water at the time of tooth mineralization. The egg capsules are common findings in near-shore lake deposits as well. Considering the mass co-occurrence of juvenile teeth and egg capsules in the study area, we propose that hybodontid/xenacanthid sharks recurrently occupied littoral zones of the Madygen lake for spawning. The small number of full-grown individuals points to habitat partitioning of juveniles and adults wherefore the study site is interpreted as a shark nursery. The oviposition strategies inferred from this fossil example are remarkably similar to those of modern sharks, suggesting that the reproductive patterns seen in extant sharks originated well before the Cenozoic.