Nd-isotope ratios of Cretaceous sediment samples

The role that meridional overturning circulation (MOC) patterns played in poleward heat transport during the extreme warmth of the Early to Late Cretaceous is a fundamental and unresolved question in climate dynamics. In order to address this question we must determine where deep waters formed, and how they may have circulated during periods of extreme warmth. Here we present late Albian through Maastrichtian (105 to 65 Ma) Nd isotope records from Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) sites in the proto-Indian Ocean and the tropical Pacific. Comparison of these data with previously published records indicates deep-water formation in the Indian sector of the Southern Ocean began at least ?105 Ma, extending the record of high-latitude convection back into the Early Cretaceous prior to the peak warmth of the mid-Cretaceous. The growing body of data supports a mode of MOC in part characterized by high-latitude downwelling during the peak of greenhouse warmth of the Mesozoic and Cenozoic. However, this mode of MOC likely was characterized by numerous locations of deep convection that were regionally important, but not significant in terms of a globally overturning circulation due to paleogeographic and bathymetric barriers.

Benthic foraminiferal number of specimens in Cretaceous samples of various DSDP and ODP Sites (Table 2)

Benthic foraminifera from 24 DSDP/ODP sites were investigated to assess their global horizontal and vertical distribution in the deep-sea environment at the end of the Cretaceous period. The samples analyzed are from the late Maastrichtian and within the planktic foraminiferal Abathomphus mayaroensis Zone from a wide range of oceans and paleolatitudes, including the low-latitude Sites 10 and 384 (Atlantic Ocean), 47, 171, 305, and 465 (Pacific Ocean), the mid-latitude Sites 20, 111, 356, 363, 516, 525, 527, 548, and 605 (Atlantic Ocean), 216, 217, and 758 (Indian Ocean), and the high-latitude Sites 208 (Pacific Ocean), 689,698,700,738 and 750 (Southern Ocean). Correspondence analysis, based on the 75 most common taxa, shows a clear biogeographic trend along the first correspondence axis by arranging the sites in paleolatitudinal order. The assemblages from the Tethyan Realm (i.e., low latitudes) are marked by abundant heavily calcified buliminids (such as Bulimina incisa, B. trinitatensis, B. velascoensis, and Reussella szajnochae) and Aragonia spp., whereas high-latitude faunas are characterized by abundant Alabamina creta, Gyroidinoides quadratus, and Pullenia coryelli. The results indicate that the faunas at low and high latitudes, respectively, were influenced by quite different environmental conditions. This is based on the much higher abundance of infaunal morphotypes at low and mid latitudes compared to high latitudes, suggesting that the biogeographic trend found in the data set coincides with the trophic regime at the various sites. The results also provide support for the hypothesis that postulates two simultaneous sources and mechanisms for deep-water formation during the Late Cretaceous, including warm, saline deep water produced by evaporation at low (equatorial) latitudes in contrast to the formation of cold deep waters at high (southern) latitudes.

Stable isotopic composition and carbonate concentrations of sediments of the Cretaceous/Paleogene boundary in the Antarctic

Stable isotopic records across the Cretaceous/Paleogene (K/P) boundary in Maud Rise Holes 689B and 690C indicate that significant climatic changes occurred during the latest Cretaceous, beginning approximately 500 k.y. prior to the mass extinction event and the enrichment of iridium at the K/P boundary (66.4 Ma). An oxygen isotopic decrease of ~0.7 per mil - ~1.0 per mil is recorded in the Late Cretaceous planktonic and benthic foraminifers between 66.9 and 66.6 Ma. The negative isotope excursion was followed by a positive excursion of similar magnitude between 66.6 Ma (latest Cretaceous) and ~66.3 Ma (earliest Paleocene). No other isotopic excursions of this magnitude are recorded in the planktonic and benthic microfossil records 1.0 m.y prior to, and for 2.0 m.y following the mass extinction event at the K/P boundary. The magnitude and duration of these isotopic excursions were similar to those at the Paleocene/Eocene and Eocene/Oligocene boundaries. A major d13C excursion occurred 200 k.y. prior to the boundary, involving a positive shift in planktonic and benthic d13C of ~0.5 per mil - 0.75 per mil. Similar changes observed in other deep-sea sequences indicate that this reflected a global change in d13C of the oceanic total dissolved carbon (TDC) reservoir. The magnitude of this inferred carbon reservoir change and its association with high latitude surface-water temperature changes recorded in the d18O records implies that it was linked to global climate change through feedback loops in the carbon cycle. At the K/P boundary, the surface-to-deep water d13C gradient is reduced by approximately 0.6 per mil - ~0.2 per mil. However, unlike sequences elsewhere, the planktonic-benthic d13C gradient (Delta d13C) was not eliminated in the Antarctic. The surface-to-deep water gradient was re-established gradually during the 400 k.y. following the mass extinction. Full recovery of the Delta d13C occurred by ~60.0 Ma. In addition to the reduced vertical d13C gradient across the K/P boundary, there was a negative excursion in both planktonic and benthic d13C beginning approximately 100 k.y. after the boundary (66.3 Ma). This excursion resulted in benthic d13C values in the early Paleogene that were similar to those in the pre-K/P boundary intervals. This negative shift appears to reflect a change in the d13C of the oceanic TDC reservoir shift that may have resulted from reduced carbon burial and/or increased carbon flux to the oceans. Any model that attempts to explain the demise of the oceanic plankton at the end of the Cretaceous should consider the oceanic environmental changes that were occurring prior to the massive extinction event.

The origin of modern crocodyliforms: new evidence from the Cretaceous of Australia

While the crocodyliform. lineage extends back over 200 million years (Myr) to the Late Triassic, modern forms - members of Eusuchia - do not appear until the Cretaceous. Eusuchia includes the crown group Crocodylia, which comprises Crocodyloidea, Alligatoroidea and Gavialoidea. Fossils of non-crocodylian eusuchians are currently rare and, in most instances, fragmentary. Consequently, the transition from Neosuchia to Crocodylia has been one of the most poorly understood areas of crocodyliform evolution. Here we describe a new crocodyliform from the mid-Cretaceous (98-95 Myr ago; Albian-Cenomanian) Winton Formation of Queensland, Australia, as the most primitive member of Eusuchia. The anatomical changes associated with the emergence of this taxon indicate a pivotal shift in the feeding and locomotor behaviour of crocodyliforms - a shift that may be linked to the subsequent rapid diversification of Eusuchia 20 Myr later during the Late Cretaceous and Early Tertiary. While Laurasia (in particular North America) is the most likely ancestral area for Crocodylia, the biogeographic events associated with the origin of Eusuchia are more complex. Although the fossil evidence is limited, it now seems likely that at least part of the early history of Eusuchia transpired in Gondwana.

Distribution of Upper Cretaceous deep water agglutinated foraminifera in sediments of the North Atlantic and its marginal seas (Tab. 1)

The stratigraphic and biogeographic distribution of more than 170 species of deep-water agglutinated benthic foraminifers (DWAF) from the North Atlantic and adjacent marginal seas has been compared with paleoenvironmental data (e.g. paleobathymetry, oxygenation of the bottom waters, amount of terrigenous input and substrate disturbance). Six general types of assemblages, in which deep water agglutinated taxa occur, are defined from the Turonian to Maastrichtian times: 1. High latitude slope assemblages 2. Low to mid latitude slope assemblages 3. Flysch-type assemblages 4. Deep water limestone assemblages (,,Scaglia,,-type) 5. Abyssal mixed calcareous-agglutinated assemblages 6. Abyssal purely agglutinated assemblages Latitudinal differences in faunal composition are observed, the most important of which is the lack or extreme paucity of calcareous forms in high latitude assemblages. East-to-west differences appear to be of comparatively minor importance. Most DWAF species occur in all studied regions and are thus considered as cosmopolitan. Biostratigraphic turnovers in the taxonomic content of assemblages are observed in the lowermost Turonian, mid-Campanian and in the upper Maastrichtian to lowermost Paleocene. These datum levels correspond to inter-regional and time-constant paleooceanographic events, which probably also affected the deep-water benthic biota. This allows us to use deep-water agglutinated foraminifers for biostratigraphy in the North Atlantic sequences deposited below CCD and to geographically extend the currently used zonal schemes which have been established in the Carpathian and Alpine areas.

(Table 1) Stable isotope record of Middle Cretaceous benthic foraminifera

Preservation of planktic foraminiferal calcite has received widespread attention in recent years, but the taphonomy of benthic foraminiferal calcite and its influence on the deep-sea palaeotemperature record have gone comparatively unreported. Numerical modeling indicates that the carbonate recrystallization histories of deep-sea sections are dominated by events in their early burial history, meaning that the degree of exchange between sediments and pore fluids during the early postburial phase holds the key to determining the palaeotemperature significance of diagenetic alteration of benthic foraminifera. Postburial sedimentation rate and lithology are likely to be important determinants of the paleoceanographic significance of this sediment-pore fluid interaction. Here we report an investigation of the impact of extreme change in sedimentation rate (a prolonged and widespread Upper Cretaceous hiatus in the North Atlantic Ocean) on the preservation and d18O of benthic foraminifera of Middle Cretaceous age (nannofossil zone NC10, uppermost Albian/lowermost Cenomanian, ~99 Ma ago) from multiple drill sites. At sites where this hiatus immediately overlies NC10, benthic foraminifera appear to display at least moderate preservation of the whole test. However, on closer inspection, these tests are shown to be extremely poorly preserved internally and yield d18O values substantially higher than those from contemporaneous better preserved benthic foraminifera at sites without an immediately overlying hiatus. These high d18O values are interpreted to indicate alteration close to the seafloor in cooler waters during the Late Cretaceous hiatus. Intersite differences in lithology modulate the diagenetic impact of this extreme change in sedimentation rate. Our results highlight the importance of thorough examination of benthic foraminiferal wall structures and lend support to the view that sedimentation rate and lithology are key factors controlling the paleoceanographic significance of diagenetic alteration of biogenic carbonates.

Öate Cretaceous to early Paleogene nutrient and paleoproductivity records of ODP Leg 171 sites

We evaluate phosphorus (P) and biogenic barium (bio-Ba) as nutrient burial and export productivity indicators for the Late Cretaceous and early Paleogene, combining these with calcium carbonate (CaCO3), organic carbon (C), and bulk CaCO3 C isotopes (d13C). Sample ages span 36-71 Ma (~1 sample/0.5 m.y.) for a depth transect of sites in the western North Atlantic (Blake Nose, Ocean Drilling Program Leg 171B, Sites 1052, 1051, and 1050). We use a multitracer approach including redox conditions to investigate export productivity surrounding the global Paleocene d13C maximum (~57 Ma). Reducing conditions render most of the bio-Ba record not useful for export productivity interpretations. P and organic C records indicate that regional nutrient and organic C burial were high at ~61 and ~69 Ma, and low during the Paleocene d13C maximum, a time of proposed global high relative organic C burial. Observed organic C burial changes at Blake Nose cannot explain this C isotope excursion.

Systematic review of Late Jurassic sauropods from the Museu Geológico collections (Lisboa, Portugal)

The Museu Geológico collections house some of the first sauropod references of the Lusitanian Basin Upper Jurassic record, including the Lourinhasaurus alenquerensis and Lusotitan atalaiensis lectotypes, previously considered as new species of the Apatosaurus and Brachiosaurus genera, respectively. Several fragmentary specimens have been classical referred to those taxa, but the most part of these systematic attributions are not supported herein, excluding a caudal vertebra from Maceira (MG 8804) considered as cf. Lusotitan atalaiensis. From the material housed in the Museu Geológico were identified basal eusauropods (indeterminate eusauropods and turiasaurs) and neosauropods (indeterminate neosauropods, diplodods and camarasaurids and basal titanosauriforms). Middle caudal vertebrae with lateral fossae, ventral hollow border by pronounced ventrolateral crests and quadrangular cross-section suggest for the presence of diplodocine diplodocids in north area of the Lusitanian Basin Central Sector during the Late Jurassic. A humerus collected from Praia dos Frades (MG 4976) is attributed to cf. Duriatitan humerocristatus suggesting the presence of shared sauropod forms between the Portugal and United Kingdom during the Late Jurassic. Duriatitan is an indeterminate member of Eusauropoda and the discovery of new material in both territories is necessary to confirm this systematic approach. The studied material is in according with the previous recorded paleobiodiversity for the sauropod clade during the Portuguese Late Jurassic, which includes basal eusauropods (including turiasaurs), diplodocids and macronarians (including camarasaurids and basal titanosauriforms).

Relative motions of Africa, Iberia and Europe during Alpine orogeny

A revised kinematic model for the motions of Africa and Iberia relative to Europe since the Middle Jurassic is presented in order to provide boundary conditions for Alpine-Mediterranean reconstructions. These motions were calculated using up-to-date kinematic data predominantly based on magnetic isochrons in the Atlantic Ocean and published by various authors during the last 15 years. It is shown that convergence of Africa with respect to Europe commenced during the Cretaceous Normal Superchron (CNS), between chrons MO and 34 (120-83 Ma). This motion was subjected to fluctuations in convergence rates characterised by two periods of relatively rapid convergence (during Late Cretaceous and Eocene-Oligocene times) that alternated with periods of slower convergence (during the Paleocene and since the Early Miocene). Distinct changes in plate kinematics are recognised in the motion of Iberia with respect to Europe, indicated by: (1) a Late Jurassic-Early Cretaceous left-lateral strike-slip motion; (2) Late Cretaceous convergence; (3) Paleocene quiescence; (4) a short period of right-lateral strike-slip motion; and (5) final Eocene-Oligocene convergence. Based on these results, it is speculated that a collisional episode in the Alpine orogeny at ca. 65 Ma resulted in a dramatic decrease in the relative plate motions and that a slower motion since the Early Miocene promoted extension in the Mediterranean back-arc basins. (C) 2002 Elsevier Science B.V. All rights reserved.

Notas sobre depósitos de Taveiro estratigrafia, paleontologia, idade, paleoecologia

This paper reports some research work that has been done to support Geological Survey's field work for the 1:50.000 Carta Geológica de Portugal, (sheets 19-C Figueira da Foz and 19-D Coimbra-Lousã). Its main purpose was to establish the age of some continental formations. At Cerâmica do Mondego, Ld.ª near Taveiro, two series were observed. The lower one is mainly pelitic, montmorillonite being predominant. It also includes some sandy beds and channel deposits with high energy sediments (conglomerate with limestone pebbles). The upper series lies unconformably upon the former, and there is a neat discontinuity surface between the two. It mainly consists of sands, kaolinite being the most abundant of the clay minerals. This seems to indicate an intensive weathering, an acid, well drained environment and transportation by quite high energy running waters. No fossils were recorded. Preliminary paleontological results are presented, along with some data concerning other localities (Aveiro, etc.). Fossils found in the lower series are: gastropoda (Bulimus gaudryi, TV. 15 bed), several vertebrates (TV. 18), fishes (TV. 19?) and plants (TV. 19-TV. 24). Vertebrata belong to the same fauna as that from Vizo, Aveiro, etc. The presence of mammals is most important as only a single tooth was previously Know in Europe (Southern France) in Late Cretaceous formations. Elsewhere there are some mammalian remains in Peru besides the rich assemblages found in the USA and Mongolia. Plants are representative of the «Debeya flora» well known at several localities in Beira Litoral province, in «Buçaco sandstones», and in Lisbon's «Basaltic Complex». The most important stratigraphical conclusion is that the lower series is Upper Campanian and/or Maastrichtian in age, and not Tertiary as sometimes it has been considered. As at Aveiro, «Bebeya flora» occurs in-beds somewhat higher than those with the Aveiro-Vizo-Taveiro vertebrate fauna. Correlation with other «Debeya flora» localities are now more clear. Data concerning Taveiro lower series, in the whole, point out to a rather warm (and moist?) environment in an occasionally (seasonally?) flooded region.

Ensaio de síntese crítica acerca do Cretácico terminal e do Paleogénico de Portugal

A synthetic essay about portuguese Late Cretaceous (Upper Campanian-Maastrichtian) and Paleogene is presented. This does include most of the so far known data, a critical approach to the problems of such formations, and to previous works on them. Our viewpoints (party original) are exposed in a shorter text in French where most of the discussion was suppressed (see reference in Resumo).

Notas sobre depósitos de Taveiro estratigrafia, paleontologia, idade, paleoecologia

This paper reports some research work that has been done to support Geological Survey's field work for the 1:50.000 Carta Geológica de Portugal, (sheets 19-C Figueira da Foz and 19-D Coimbra-Lousã). Its main purpose was to establish the age of some continental formations. At Cerâmica do Mondego, Lda. near Taveiro, two series were observed. The lower one is mainly pelitic, montmorillonite being predominant. It also includes some sandy beds and channel deposits with high energy sediments (conglomerate with limestone pebbles). The upper series lies unconformably upon the former, and there is a neat discontinuity surface between the two. It mainly consists of sands, kaolinite being the most abundant of the clay minerals. This seems to indicate an intensive weathering, an acid, well drained environment and transportation by quite high energy running waters. No fossils were recorded. Preliminary paleontological results are presented, along with some data concerning other localities (Aveiro, etc). Fossils found in the lower series are: gastropoda (Bulimus gaudryi, TV. 15 bed), several vertebrates (TV. 18), fishes (TV. 19?) and plants (TV. 19-TV. 24). Vertebrata belong to the same fauna as that from Vizo, Aveiro, etc. The presence of mammals is most important as only a single tooth was previously know in Europe (Southern France) in Late Cretaceous formations. Elsewhere there are some mammalian remains in Peru besides the rich assemblages found in the USA and Mongolia. Plants are representative of the «Debeya flora» well known at several localities in Beira Litoral province, in «Buçaco sandstones», and in Lisbon's «Basaltic Complex». The most important stratigraphical conclusion is that the lower series is Upper Campanian and/or Maastrichtian in age, and not Tertiary as sometimes it has been considered. As at Aveiro, «Bebeya flora» occurs in-beds somewhat higher than those with the Aveiro-Vizo-Taveiro vertebrate fauna. Correlation with other «Debeya flora» localities are now more clear. Data concerning Taveiro lower series, in the whole, point out to a rather warm (and moist?) environment in an occasionally (seasonally?) flooded region.

Chromian spinels in the basalts from the Lisbon volcanic complex (portugal) and their petrogenetic implications

Chromian spinels are common in the late Cretaceous alkali basalts of the Lisbon volcanic Complex in Portugal. They occur as unzoned inclusions in magnesian olivines of all basalt types and as large spectacularly zoned grains in the groundmass of porphyritic basalts. Microprobe analysis indicate complex cationic exchange in the groundmass zoned spinels due to simple peritectic reactions and in response to changing composition of the basalt liquid. The variation of cationic distribution in zoned chromian-Spinels, reflects very accurately the changing chemistry of the cooling silicate melt and the paragenetical relations of mineral oxides and silicates. Crystallization of initial chromian spinels occurred at T~1200°C and fO2~10-8.5 atm. earlier or contemporaneously with magnesian olivine. The titanomagnetite mantles of zoned chromian spinels crystallized at T~1200°C and much lower fO2.

Le Crétacé terminal de Beira Litoral, Portugal: remarques stratigraphiques et écologiques,étude complémentaire de Rosasia soutoi (Chelonii, Bothremydidae)

The synthetic study of the uppermost Cretaceous of the Beira Litoral (fauna, flora) confirms its upper Campanian-Maastrichtian age. It shows the presence of a tropical to subtropical climate in an area constituted by a low coastal plain only occasionally linked to the sea, saturated with fresh water and possessing accordingly, a predominantely freshwater fauna (Viso, Aveiro); this plain changed towards the interior into a drier more forested zone with a more abundant terrestrial fauna which includes mammals (Taveiro). A thorough study of the chelonian Rosasia, abundant on the coastal plain, was made possible thanks to the discovery of a skull: it demonstrates that the genus belongs to the family Bothremydidae, revalided here. The composition of this family is presented, its phylogenetic and paleobiogeographic relation with the other pleurodires are analyzed, and its diagnosis established. The family is constituted of three groups; Rosasia belongs to one of these, the Bothremys group.