Description: During ODP Leg 123, Sites 765 and 766 were drilled to examine the tectonic evolution, sedimentary history, and paleoceanography of the Argo Abyssal Plain and lower Exmouth Plateau. At each site, the quality of magnetostratigraphic and biostratigraphic records varies because of complicating factors, such as the predominance of turbidites, the presence of condensed horizons, or deposition beneath the CCD. Based primarily on the presence of nannofossils, the base of the sedimentary section at Site 765 was dated as Tithonian. A complete Cretaceous sequence was recovered at this site, although the sedimentation rate varies markedly through the section. The Cretaceous/Tertiary boundary is represented by a condensed horizon. The condensed Cenozoic sequence at Site 765 extends from the upper Paleocene to the lower Miocene. A dramatic increase in sedimentation rate was observed in the lower Miocene, and a 480-m-thick Neogene section is present. The Neogene section is continuous, except for a minor hiatus in the lower Pliocene. The base of the sedimentary section at Site 766 is Valanginian, in agreement with the site's position on marine magnetic anomaly Mil. Valanginian to Barremian sediments are terrigenous, with variable preservation of microfossils, and younger sediments are pelagic, with abundant well-preserved microfossils. Sedimentation rate is highest in the Lower Cretaceous and decreases continually upsection. Upper Cenozoic sediments are condensed, with several hiatuses.

Description: Belemnites (order Belemnitida), a very successful group of Mesozoic cephalopods, provide an important clue for understanding Mesozoic marine ecosystems and the origin of modern cephalopods. Following current hypotheses, belemnites originated in the earliest Jurassic (Hettangian, 201.6–197 Ma) with very small forms. According to this view their paleobiogeographic distribution was restricted to northern Europe until the Pliensbachian (190–183 Ma). The fossil record is, however, biased by the fact that all the previous studies on belemnites focused on Europe. Here we report two belemnite taxa from the Hettangian of Japan: a new species of the Sinobelemnitidae and a large taxon of the suborder Belemnitina. The Sinobelemnitidae, which may be included in the future in a new suborder, have also been recorded from the Triassic of China, specimens so far poorly understood. The presence of a very large rostrum attributed to the Belemnitina suggests in addition that a diverse belemnite fauna evolved earlier than previously thought. Our new findings therefore (1) extend the origin of the belemnites back by ~33 m.y. into the Triassic, (2) suggest that this group did not necessarily originate in northern Europe, and (3) imply that belemnites survived the Triassic–Jurassic extinction, one of the five big mass extinctions in the Phanerozoic. Since belemnites provided a considerable amount of food as prey, the origination of belemnites is probably an important event also for the evolution of their predators, such as marine reptiles and sharks.

Description: The paleoclimatology and paleoceanology of the Late Jurassic and Early Cretaceous are of special interest because this was a time when large amounts of marine organic matter were deposited in sediments that have subsequently become petroleum source rocks. However, because of the lack of outcrops, most studies have concentrated on low latitudes, in particular the Tethys and the “Boreal Realm,” where information has been based largely on material from northwest Germany, the North Sea, and England. These areas were all south of 40°N latitude during the Late Jurassic and Early Cretaceous. We have studied sediment samples of Kimmeridgian (∼154 Ma) to Barremian (∼121 Ma) age from cores taken at sites offshore mid-Norway and in the Barents Sea that lay in a narrow seaway connecting the Tethys with the northern polar ocean. During the Late Jurassic-Early Cretaceous these sites had paleolatitudes of 42–67°N. The Late Jurassic-Early Cretaceous sequences at these sites reflect the global sea-level rise during the Volgian-Hauterivian and a climatic shift from warm humid conditions in Volgian times to arid cold climates in the early Hauterivian. The sediments indicate orbital control of climate, reflected in fluctuations in the clastic influx and variations in carbonate and organic matter production. Trace element concentrations in the Volgian-Berriasian sediments suggest that the central part of the Greenland-Norwegian Seaway might have had suboxic bottom water beneath an oxic water column. Both marine and terrigenous organic matter are present in the seaway sediments. The Volgian-Berriasian strata have unusually high contents of organic carbon and are the source rocks for petroleum and gas fields in the region. The accumulation of organic carbon is attributed to restricted conditions in the seaway during this time of low sea level. It might be that the Greenland-Norwegian segment was the deepest part of the transcontinental seaway, bounded at both ends by relatively shallow swells. The decline in organic matter content of the sediments in the Valanginian-Hauterivian indicates greater ventilation and more active flow through the seaway as the sea level rose. The same benthic foraminifera assemblages are encountered throughout the seaway. Endemic assemblages of arenaceous foraminifera in the Volgian-Berriasian give way to more diverse and cosmopolitan Valanginian-Hauterivian benthic communities that include calcareous species. The foraminiferal assemblages also suggest low oxygen content bottom waters during the earlier Cretaceous, changing to more fully oxygenated conditions later. The calcareous nannoplankton, particularly Crucibiscutum salebrosum, which is rare at low latitudes and abundant in high latitudes, reflect the meridional thermal gradient. They indicate that the Greenland-Norwegian segment of the seaway was north of a subtropical frontal zone that acted as a barrier between the Tethyan and Boreal Realms. This implies the existence of stable climatic belts during the early Valanginian and Hauterivian, significant meridional temperature gradients, and moderate “ice house” conditions.

Description: The stable isotope ratios (δ18O, δ13C) of the aragonite of cuttlebones of Sepia officinalis were measured on a high resolution scale where every septum was measured. Our studies aim at understanding whether variations of the isotope signature are controlled by ontogenetic and/or ecological factors. Five specimens were reared from eggs under known water temperatures, a sixth specimen was caught in the German part of the North Sea. The data suggest that the oxygen isotope composition is in isotopic equilibrium with the surrounding seawater and reflects ambient temperature. Migration and seasonal temperature changes are visible in the acquired data set. The carbon isotope signature shows signs of biofractionation and no direct correlation to the oxygen signature as far as ontogeny and ecology are concerned.

Description: Nutrients and sea-surface temperature were likely the most important paleoecological parameters that controlled the composition of Late Cretaceous calcareous nannofossil assemblages. The extinct nannofossil taxa Biscut u m spp., Tranolithus orionatus and Zeugrhabdotus spp. are commonly thought to have preferred nutrient-rich surface waters. In order to test this hypothesis, calcareous nannofossils from two lower Turonian nearshore sections (Bochum, Herne; northwest Germany) were studied. These sections, which reflect a mesotrophic and perhaps cool paleoenvironment, contain well-preserved and highly diverse calcareous nannofossil assemblages yielding 92 species. Based on the first occurrences of Eprolithus eptapetalus , Quadrum gartneri , and Eiffellithus eximius , both sections have been assigned an early Turonian age. The most common taxa are Watznaueria barnesiae , Zeugrhabdotus spp., Biscutum constans , Prediscosphaera cretacea , and Tranolithus orionatus . In combination with previously published data from pelagic settings of the same area, these new findings allow the reconstruction of a nearshore-offshore transect. In proximal sections the abundances of B . constans and T. orionatus are higher than in coeval assemblages from distal localities. Zeugrhabdotus spp. shows no specific preference, whereas W . barnesiae is more common in open ocean settings. These findings suggest that B. constans and T. orionatus preferred more fertile and perhaps cooler nearshore habitats whereas W. barnesiae was adapted to oligotrophic and probably warmer paleoenvironments.

Description: The early Aptian was characterized by the widespread occurrence of anoxia in the oceans, known as Oceanic Anoxic Event (OAE) 1a. Intense degassing from submarine volcanic plateaus presumably resulted in high atmospheric CO 2 concentrations, culminating in greenhouse conditions. OAE 1a can, therefore, be considered as a past "natural experiment" important to understand the future evolution of our climate. Paleotemperature estimates for OAE 1a are, however, predominantly based on bulk oxygen isotopes, which are susceptible to diagenetic overprinting, while TEX 86 paleotemperature estimates are limited in number or derived from stratigraphically poorly constrained sections. Here we reconstructed for the first time sea-surface water temperatures (SSTs) based on the TEX 86 paleothermometer from an OAE 1a section from the middle northern latitudes (39°N paleolatitude). We find a SST rise starting prior to OAE 1a and reaching a maximum during the event, with SSTs of ~31–34 °C, 4–9 °C higher than those of older Hauterivian–lower Aptian sediments from the same sedimentary basin. The end of OAE 1a is marked by relatively lower SSTs of ~30 °C. These observations are supported by belemnite-based oxygen-isotope ( 18 O Bel ) data and calcareous nannofossils. Our integrated data set clearly indicates that "super greenhouse" conditions prevailed during OAE 1a at northern latitudes. SSTs are similar to those estimated for coeval low-latitudinal sites, suggesting that an equable warm climate, with reduced latitudinal gradients, characterized the early Aptian.

Description: We describe a device for random settling preparation of calcareous nannoplankton (coccolith) samples. The device allows easy draining and cleaning, as well as sedimentation at different heights of the water column through the use of different slide carriers. Reproducibility and accuracy of the device has been tested with standardised microbeads as spiking material. In applying counting techniques with different equations for determining absolute abundances, we discovered major anomalies in the calculated results that we interpreted as being due to the effect of convection currents within the device and the usage of elevated cover slides. A modified formula that corrects for the influence of elevated cover slides in random settling experiments is therefore proposed. Although the settling method is more time-consuming than standard smear-slide techniques, additional information is gained about the spatial and temporal distribution of coccoliths. These are important for palaeoecological and palaeobiogeographical interpretations.

Description: 1] The paleoclimatology and paleoceanology of the Late Jurassic and Early Cretaceousare of special interest because this was a time when large amounts of marine organic matterwere deposited in sediments that have subsequently become petroleum source rocks.However, because of the lack of outcrops, most studies have concentrated on lowlatitudes, in particular the Tethys and the âBoreal Realm,â where information has beenbased largely on material from northwest Germany, the North Sea, and England. Theseareas were all south of 40°N latitude during the Late Jurassic and Early Cretaceous. Wehave studied sediment samples of Kimmeridgian (~154 Ma) to Barremian (~121 Ma) agefrom cores taken at sites offshore mid-Norway and in the Barents Sea that lay in a narrowseaway connecting the Tethys with the northern polar ocean. During the Late Jurassic-EarlyCretaceous these sites had paleolatitudes of 42â67°N. The Late Jurassic-Early Cretaceoussequences at these sites reflect the global sea-level rise during the Volgian-Hauterivian anda climatic shift from warm humid conditions in Volgian times to arid cold climates in theearly Hauterivian. The sediments indicate orbital control of climate, reflected in fluctuationsin the clastic influx and variations in carbonate and organic matter production. Traceelement concentrations in the Volgian-Berriasian sediments suggest that the central part ofthe Greenland-Norwegian Seaway might have had suboxic bottom water beneath an oxicwater column. Both marine and terrigenous organic matter are present in the seawaysediments. The Volgian-Berriasian strata have unusually high contents of organic carbonand are the source rocks for petroleum and gas fields in the region. The accumulation oforganic carbon is attributed to restricted conditions in the seaway during this time of lowsea level. It might be that the Greenland-Norwegian segment was the deepest part of thetranscontinental seaway, bounded at both ends by relatively shallow swells. The decline inorganic matter content of the sediments in the Valanginian-Hauterivian indicates greaterventilation and more active flow through the seaway as the sea level rose. The same benthicforaminifera assemblages are encountered throughout the seaway. Endemic assemblages ofarenaceous foraminifera in the Volgian-Berriasian give way to more diverse andcosmopolitan Valanginian-Hauterivian benthic communities that include calcareous species.The foraminiferal assemblages also suggest low oxygen content bottom waters during theearlier Cretaceous, changing to more fully oxygenated conditions later. The calcareousnannoplankton, particularly Crucibiscutum salebrosum, which is rare at low latitudes andabundant in high latitudes, reflect the meridional thermal gradient. They indicate that theGreenland-Norwegian segment of the seaway was north of a subtropical frontal zone thatacted as a barrier between the Tethyan and Boreal Realms. This implies the existence ofstable climatic belts during the early Valanginian and Hauterivian, significant meridionaltemperature gradients, and moderate ice-house conditions.