Late Aptian Research Articles

Early Cretaceous atmospheric CO2 estimates based on stomatal index of Pseudofrenelopsis papillosa (Cheirolepidiaceae) from southeast China

Estimates of the atmospheric carbon dioxide concentration levels were made for three time intervals of the Early Cretaceous using the stomatal indices of an extinct fossil conifer, Pseudofrenelopsis papillosa (Chow et Tsao) Cao ex Zhou. The fossil materials were collected from the upper Hauterivian, upper Aptian, and upper Albian of the Lower Cretaceous in the Fujian and Jiangxi Provinces of southeast China. The estimated paleo-CO2 (pCO2) was 600–1300 ppmv from the late Hauterivian to the late Albian based on the ratio between the stomatal indices of fossil species P. papillosa and those of four modern nearest living equivalent (NLE) species, using Carboniferous and recent standardizations. The results showed a low value of 595–957 ppmv in the late Hauterivian, and a high value of 805–1292 ppmv in the late Albian, which was only slightly higher than the value of 753–1210 ppmv in the late Aptian. Our calculated CO2 values were consistent with GECORB II, and similar to the previously published estimates of CO2 based on stomatal indices or carbon isotopes. Thus, it could be inferred that the stomatal index of P. papillosa is a potential indicator for estimating the pCO2 content during the geological history. Furthermore, the global mean land surface temperature (GMLST) was estimated based on the CO2 data. This showed that the change ratios of GMLST increased from 2.8 to 4.7 °C in the late Hauterivian to 3.6–5.5 °C in the late Albian and 3.8–5.7 °C in the late Aptian. It appears that the temperature gradually increased from the early to late Early Cretaceous.

The stable O- and C-isotope record of fossils from the upper Barremian–lower Albian of the Caucasus — palaeoenvironmental implications

Late Barremian to early Albian palaeotemperatures have been determined through oxygen isotope analyses of well-preserved brachiopod, bivalve, gastropod and ammonite shells, and belemnite rostra from the Caucasus. Results from calcitic invertebrate skeletal elements from the upper Barremian Sartousiana, Securiformis and Waagenoides zones indicate palaeotemperatures of 19.2, 12.0–17.1 and 11.3–14.3 °C, respectively. In contrast, early Aptian fossils of the Weissi and Deshayesi zones reveal significantly higher palaeotemperatures (20.5–22.3 and 17.1 °C, respectively), than those obtained from brachiopod shells of the Securiformis Zone. Isotopic palaeotemperature data are not available for the Furcata Zone in the Caucasus. The warmest conditions in our study interval developed during the late Aptian Melchioris-Abichi Chrone according to data on bivalves, gastropods and the ammonite Parahoplites (20.8–27.1 °C) and the Subnodosocostatum Chrone (?25.3 °C), on the basis of a shell of the oyster Amphidonte. However, the potential influence of minor freshwater incursions into the upper epipelagic zone in which Amphidonte lived, as well as the predominance of ammonites that preferred cool conditions in the Subnodosocostatum Zone, leads to an alternative interpretation in which cooling initiated at the beginning of the late Aptian. There remains considerable uncertainty in the interpretation of δ18O values in fossils from the Subnodosocostatum Zone but it is possible that one or two cooling events interrupted the warmest conditions during the late Aptian. The highest δ13C values derived from fossils found in the Subnodosocostatun Zone (up to 8.3 and 3.9‰ for shallow-water bivalves and deeper-dwelling belemnite taxa, respectively) have been linked to an episode of late Aptian volcanic activity. On the basis of our stable oxygen isotope record, two ethological groups can be recognised among Aptian ammonites from the Caucasus: cool and thermophilic dwellers. All Early Cretaceous belemnites from this area seem to have had a preference for cool-water conditions.

The transgressive-regressive cycle of the Romualdo Formation (Araripe Basin): Sedimentary archive of the Early Cretaceous marine ingression in the interior of Northeast Brazil

Geologic events related to the opening of the South Atlantic Ocean deeply influenced the sedimentary record of the Araripe Basin. As consequence, upper stratigraphic units of the basin record a marine ingression in northeastern Brazil during the late Aptian. The timing and stratigraphic architecture of these units are crucial to understand the paleogeography of Gondwana and how the proto-Atlantic Ocean reached interior NE Brazil during the early Cretaceous. This marine ingression is recorded in the Araripe Basin as the Romualdo Formation, characterized by a transgressive-regressive cycle bounded by two regional unconformities. In the eastern part of the basin, the Romualdo depositional sequence comprises coastal alluvial and tide-dominated deposits followed by marine transgressive facies characterized by two fossil-rich intervals: a lower interval of black shales with fossil-rich carbonate concretions (Konservat-Lagerstätten) and an upper level with mollusk-dominated shell beds and shelly limestones. Following the marine ingression, an incomplete regressive succession of marginal-marine facies records the return of continental environments to the basin. The stratigraphic framework based on the correlation of several sections defines a transgressive-regressive cycle with depositional dip towards southeast, decreasing in thickness towards northwest, and with source areas located at the northern side of the basin. The facies-cycle wedge-geometry, together with paleocurrent data, indicates a coastal onlap towards NNW. Therefore, contrary to several paleogeographic scenarios previously proposed, the marine ingression would have reached the western parts of the Araripe Basin from the SSE.

Late Aptian (Cretaceous) climate changes in northeastern Brazil: A reconstruction based on indicator species analysis (IndVal)

The flora preserved in upper Aptian rocks of South America and Africa is typical of warm climate conditions and commonly associated with semi-arid to arid climate. Warmth-loving conifers of the family Cheirolepidiaceae and their pollen Classopollis are recorded in upper Aptian rocks in most of the South Atlantic margin basins. However, an increase in indicators of humid conditions (e.g., ferns) is recorded in most sedimentary basins of Brazil. The method of indicator species analysis (IndVal) was applied as a tool for reconstructing the vegetation during the late Aptian. The IndVal index expresses which taxa are strongly associated with particular groups of samples. The vegetation reflects climate changes, and the IndVal indices illustrate how the taxa interacted through time and reveal patterns in the changing composition of the vegetation. The material studied derives from two well sections drilled through the Riachuelo Formation in the Sergipe Basin, GTP-17-SE (Angico Member, 70 samples) and GTP-24-SE (Taquari Member, 108 samples). The indicator species are strongly associated with particular stratigraphic intervals. IndVal indices for the Angico section indicate seven taxa associated with four intervals, viz. Classopollis classoides (Interval AS-1); Callialasporites segmentatus and Cicatricosisporites avnimelechi (Interval AS-2); Verrucosisporites spp. and Cicatricosisporites microstriatus (Interval AS-3); Araucariacites australis and Cyathidites spp. (Interval AS-4). Values for the Taquari section indicate nine taxa associated with four intervals, viz. Classopollis classoides (Interval TS-1); Uesuguipollenites callosus, Callialasporites segmentatus Bennettitaepollenites regaliae, Cyathidites spp., Cicatricosisporites spp. and Araucariacites australis (Interval TS-2); Retitriletes spp. (Interval TS-3); Araucariacites australis and Verrucosisporites spp. (Interval TS-4). Two phases, dry and wet, are recognized in both sections. The dry phase is characterized by high to very high abundance of Classopollis classoides. A conspicuous change in vegetation is recorded, with an increase in ferns and upland flora, in particular Araucariacites australis. A. australis is the second most abundant terrestrial palynomorph. In the late Aptian of South America and Africa Araucariacites is generally associated with an upland flora and warm and humid climates, which may explain its association with fern spores. The replacement of Classopollis by Araucariacites and ferns reflects a change from a dry to wet phase. The change in flora may be the result of dislocation of the Intertropical Convergence Zone (ITCZ) and a relative sea-level rise.

Taxonomic study of the Cretaceous lacewing family Babinskaiidae (Neuroptera: Myrmeleontoidea: Nymphidoidae), with description of new taxa

The Cretaceous lacewing family Babinskaiidae comprises nine species in seven genera, of which two new genera and one new species are described herein: Parababinskaia elegans gen. et sp. nov. from the late Aptian Crato Formation of Brazil, and Pseudobabinskaia gen. nov. (with the only species Pseudobabinskaia martinsnetoi Lu et al., 2017, comb. nov.) from mid-Cretaceous Burmese amber. The reduction of the veins AA2 and AA3 in the hind wing is an autapomorphy of the family. Babinskaiidae are most closely related to Nymphidae, and have probably evolved as a side branch of these. The superfamily Myrmeleontoidea is divided into two epifamilies: Nymphidoidae whose MP (or M) is long, not fused with CuA, and trichosors are present (Nymphidae, Babinskaiidae), and Myrmeleontoidae whose MP is crossvein-like, then fused with CuA, and trichosors are lost (Araripeneuridae, Ascalaphidae, Myrmeleontidae, Nemopteridae, Palaeoleontidae). The aligned crossveins 1r-m and 1m-cu in the forewing is probably the only venational autapomorphy of the Myrmeleontoidea.

Mecochirus Germar (Decapoda: Glypheoidea) in the Lower Cretaceous of Queensland

JELL, P.A., WOODS, J.T. & COOK, A.G., May 2017. Mecochirus Germar (Decapoda: Glypheoidea) in the Lower Cretaceous of Queensland. Alcheringa 41, 514–523 ISSN 0311-5518.Three new species of glypheoid decapod crustaceans, Mecochirus mcclymontorum, M. bartholomaii and M. lanceolatus, are described from the late Aptian of the Eromanga, Carpentaria and Maryborough basins, respectively. The first two occur in the Doncaster Member of the Wallumbilla Formation and the last in the Maryborough Formation. This is the first record of Mecochirus Germar, 1827 or the Mecochiridae Van Straelen, 1925 in Australia and one of only a few Cretaceous occurrences of this largely Jurassic genus.Peter A. Jell [amjell@bigpond.com], Jack T. Woods and Alex G. Cook [alex.cook@y7mail.com], School of Earth Sciences, The University of Queensland, St Lucia Queensland 4072, Australia.

Activation of stylolites as conduits for overpressured fluid flow in dolomitized platform carbonates

Abstract This study investigates the Late Aptian–earliest Albian platform carbonates of the Benicàssim area (Maestrat Basin, Spain) in order to assess the relationship between bed-parallel stylolites and the flow of diagenetic fluids during dolomitization and subsequent hydrothermal alteration. Dolostones and burial dolomite and calcite cements were studied by a combination of field geology and standard petrographic and isotope analysis. Field data indicate that dolostones are closely associated with seismic-scale synsedimentary faults, preferentially replace grain-dominated facies and typically show wavy dolomitizing fronts that mostly correspond to bed-parallel stylolites. The dolostones are corroded and contain bed-parallel pores that are filled with hydrothermal saddle dolomite and blocky calcite cements. This late calcite cement frequently engulfs clasts of the host dolostones, suggesting that hydraulic brecciation likely associated with overpressured fluid occurred. Results indicate that stylolites play a key role in the distribution of dolostones and subsequent hydrothermal mineralization. During the replacement stage, stylolites acted as baffles for the dolomitzing fluids controlling lateral fluid flow and resulting in the stratabound dolostone distribution. During the post-dolomitization stage, stylolites became preferred pathways for overpressured hydrothermal corrosive and mineralizing fluids that likely came from the underlying basement, and increased bed-parallel stylolitic porosity and probably also permeability.

Additional Aptian–Albian ammonoids from Patagonia

Late Aptian–early Albian ammonoids of southern Patagonia are described. They are represented by Carinophylloceras collignoni Klinger, Wiedmann and Kennedy, Phyllopachyceras reymenti sp. nov., Tetragonites heterosulcatus Anthula, Anagaudryceras sacya (Forbes), Puzosia cf. rectecostata Collignon and Douvilleiceras mammillatum Schlotheim. T. heterosulcatus Anthula occurs in the Peltocrioceras deeckei Assemblage Zone (≈Jacobi Standard Zone, upper Aptian), and all the other species have been recorded from the lower Albian Aioloceras argentinum and/or Aioloceras rollerii Assemblage Zones (≈Mammillatum Standard Zone, lower Albian). The late Aptian–early Albian ammonoid fauna here described indicates a direct migration route with central Tethys, through southeastern Africa and supports for this time correlation of the Austral faunal region with the European Standard.

Taxonomy and stratigraphy of late Barremian–Albian species of Horiopleura Douvillé (Hippuritida, Polyconitidae) of the Mediterranean and southwestern Asian regions

The genus Horiopleura Douvillé is restricted to the Mediterranean and southwestern Asian regions, and is represented by eight species developed during the late Barremian–Albian. This revision of species contributed to delineate generic and specific characters. The definition of species is based on a set of external and internal qualitative and quantitative characters, the key characters being size, radial bands, ornamentation and the presence of a left posterior canal. Morphometry documents the dimorphism of some species, corroborated by regression analysis. Horiopleura dumortieri is an upper Barremian–lowermost Bedoulian species from SE France, Horiopleura brevis n. sp. is a Bedoulian, Mediterranean species, extending to the lower Gargasian, Horiopleura gigantea (pro Monopleura) is a Bedoulian species, restricted the Ukrainian Carpathes. Horiopleura lamberti and H. almerae are Upper Aptian to lower Albian species, and are known from Southern Europe and North Africa. Horiopleura haydeni is essentially late Aptian and typifies the southwestern Asia “Yasin fauna”. Horiopleura distefanoi and H. gemmellaroi (both formerly placed in Polyconites) are restricted to the Albian of the peri-Adriatic regions and North Africa, the former being present in the Middle East. Multiple correspondence analysis using six categorical variables and their categorical states, applied to the comparison of species, tends to corroborate our overall taxonomic frame-work, and reveals three groups of species with distinctive ages.

Evolution and palaeogeographical dispersion of the radiolitid rudist genus Auroradiolites (Bivalvia, Hippuritida) with descriptions of new material from Tibet and archived specimens from Afghanistan

AbstractDiagnostic characters of the recently established new genus of radiolitid rudist Auroradiolites include an entirely compact outer shell layer, a distinctly convex upper (left) valve and a robust myocardinal apparatus surrounding a strongly internally projected ligamentary infolding. Until now, A. biconvexus (previously considered to be exclusively late Albian in age) has been reported only from the Langshan Formation, which crops out along the northern portion of the Lhasa block, Tibet. Here, it is recorded for the first time from the Sangzugang Formation of the Xigaze Forearc Basin, situated on the southern margin of the Lhasa block. A. biconvexus differs from the south‐west Asian type species A. gilgitensis (late Aptian to Albian) by its relatively larger size, more strongly domed left valve and distinct radial undulations of the outer shell layer. The characters of A. gilgitensis are further clarified from archived material from central Afghanistan, also newly identified and described herein. All Auroradiolites records to date are revised. The recognition of examples of A. biconvexus from upper Aptian strata increases both the stratigraphical and geographical ranges of the species, indicating that it had already branched off from A. gilgitensis in the late Aptian. Some new radiolitid specimens that combine both compact and cellular calcitic outer shell layer structures are also described from the Langshan Formation, but a number of internal differences from Auroradiolites cast doubt on their constituting a sister group to the latter and we assign them to Eoradiolites cf. hedini. Rather, the evolution of Auroradiolites directly from the ancestral radiolitid genus Agriopleura is favoured on the grounds of parsimony. So far, the genus Auroradiolites has been recorded from Iran, central and eastern Afghanistan, the type locality of Yasin in north‐western Pakistan, southern and northern Ladakh, the Lhasa block, as well as Hokkaido in northern Japan. During the late Aptian to Albian interval, all of these localities were associated with terranes and blocks that were limited to the north‐eastern margin of Tethys and the western Pacific margin, making Auroradiolites an indicator of a SW Asian to Pacific faunal province.

A new species of the spore genus Costatoperforosporites from Early Cretaceous deposits in Portugal and its taxonomic and palaeoenvironmental significance

A new species of spore, Costatoperforosporites friisiae sp. nov., is described from the Early Cretaceous (late Aptian–early Albian) deposits of Catefica in the Lusitanian Basin, western Portugal. Although the morphology of the muri is clearly of the Cicatricosisporites type, the presence of micropores on these sculptural elements and within the intervening grooves is a particularly distinctive feature and more typical of spores that have been attributed previously to Costatoperforosporites. As a result, this genus is emended not only to accommodate Costatoperforosporites friisiae but also to differentiate it more clearly from other, similar, murornate genera. It is considered to represent the family Anemiaceae. So far, Costatoperforosporites friisiae has only been encountered in the Catefica palynoflora. The presence of many other pteridophyte spores, especially of schizaealean derivation, together with abundant cheirolepidiacean remains at this locality, strongly suggests a warm, moist climate and diverse source vegetation.

Carbonate microfacies and chemostratigraphy of a late Aptian–early Albian marine distal section from the primitive South Atlantic (SE Brazilian continental margin): Record of global ocean-climate changes?

Late Aptian–early Albian limestones from the eastern Brazilian continental margin record the early evolution of the South Atlantic Ocean. In Tethyan and North Atlantic domains, a planktic foraminiferal turnover and organic-rich deposits related to Oceanic Anoxic Event 1b (OAE 1b) point to major ocean-climate changes through this interval. Coeval organic-rich deposits of the South Atlantic Ocean have been interpreted as the product of restricted circulation rather than attributed to a global event. However, previous investigations of the early marine phase of South Atlantic lack data from more distal facies, making correlations to global events difficult. Here, we present C, O, and Sr isotopes, elemental geochemistry, TOC and pyrolysis data, as well as a microfacies analysis of an upper Aptian–lower Albian distal section from the Campos Basin (southeastern Brazil). Our focus is on the paleoenvironmental characterization of and the possible association between organic-rich deposits and major perturbations related to Aptian–Albian transition. Five microfacies associations (MA) were identified in the informal units I and III, which were deposited in the neritic region on a carbonate ramp. Organic-rich deposits were described in unit III, composed of planktic-dominated wackestones interbedded with black shales, in a distal dysoxic to anoxic environment. The carbonates 87Sr/86Sr ratios showed a drastic increase (0.7072–0.7074), interpreted as enhanced chemical weathering, supported by the increase of continental input to the top of section. This trend was accompanied by a long-term δ13Ccarb negative excursion, which were assigned to the latest late Aptian–early Albian interval of the isotope reference curves, in accordance with the described occurrence of Colomiella recta. This scenario matches those proposed for the late Aptian–early Albian transition and OAE 1b set, as an enhanced greenhouse stage, pointing to the influence of the referred ocean-climate changes on the deposition of organic-rich deposits of the early South Atlantic Ocean. This investigation gives more evidences that these perturbations were a widespread event, as a product of broad-scale disturbances in the global carbon cycle which also controlled organic deposition and preservation on restricted settings.

The pull apart-type Tardets-Mauléon Basin, a key to understand the formation of the Pyrenees

Contrary to recent conceptual models, we evidence that the Mauléon Basin does not only result from the Pyrenean tectonic inversion of an aborted Albian rift involving a N-S extreme crust thinning, with related detachment and mantle exhumation. It actually corresponds to an element of this rift system where E-W dominant regional sinistral strike slip faulting between its European and Iberian margins generated as early as the Latest Aptian (Clansayesian) an oblique pull apart-type basin: the Tardets-Sorholus Trough. Then, towards the Late to Latest Albian period, the active transverse, SW-NE oriented, Barlanès and Saison listric faults provided the main crustal thinning leading locally (Urdach) to mantle exhumation. Finally, at the beginning of the Late Cretaceous, the trough widened through transtension motion (N-S distension associated with E-W sinistral strike slip) leading to the creation of the Mauléon Basin. This geodynamic evolution gives to the Mauléon Basin its logical place between the western Bilbao Basin where oceanic crust developed through dominant N-S extension process and the central and eastern north Pyrenean basins where dominant E-W left lateral strike slip then transpressive motion preclude mantle denudation. From the Late to Latest Cretaceous, the inverted motion turning to generalized regional transpression led to the closure of the trough, then, by gradual uplift from east to west, to the formation of the Pyrenean range.

Lithostratigraphy and Microbiostratigraphy of Gadvan and Darian Formations in South Semirom, East of Zagros Basin, South-Central Iran

This research focuses on the lithostratigraphy and microbiostratigraphy implications of the Gadvan and Darian Formations in a part of Zagros sedimentary basin. The Gadvan and Darian Formations in the study area with a thick-ness of 520 meters consist of gray to green marls and shales, dark-grey limestones and Orbitolina limestone with Late Barremian-Aptian age. According to the lithostratigraphic investigations, the Gadvan and Darian Formations in the study area are subdivided into eleven units. The upper boundary of the Darian Formation with the Kazhdomi Formation and the lower boundary of Gadvan Formation with the Fahliyan Formation are in the form of disconformity. Micropaleontological study of the Gadvan and Dariyan Formations has led to the recognition 20 families, 45 genera, 35 species of benthic foraminifera, 2 genera of pelagic foraminifera and 8 genera and species of the calcareous algae. In this research, three biozones have been recognized by distribution of the larger benthic foraminifera in the Gadvan and Dariyan Formations of the South Semirom, including: 1) Palorbitolina lenticularis-Choffatella decipiens Concurrent Range Zone (middle Late Barremian to early Early Aptian); 2) Praeorbitolina cormyi-Orbitolina (Mesorbitolina) lotzei Assemblage Zone (late Early Aptian); 3): Orbitolina (Mesorbitolina) texanae-Orbitolina (Mesorbitolina) parva Assemblage Zone (Middle to Late Aptian). Based on the identified foraminifera, the age of the Gadvan and Darian Formations in the study area is assigned to Late Barremian to Aptian.

Diversity dynamics of Early Cretaceous brachiopods in the tectonic units of Serbia: regional versus global patterns

The Danubian, Getic, and Vardar tectonic units of Serbia (northern Neo-Tethys) provide a rich palaeontological record permitting quantitative assessment of the Early Cretaceous brachiopod diversity dynamics. The compilation and the subsequent revision of the available information permit to document the stratigraphical ranges of 44 species, 26 genera, 15 families, and 11 superfamilies. Three diversity peaks (Late Valanginian, Early Barremian, and Early Albian) are established, as well as the Late Barremian–Late Aptian long-term diversity decline. Brachiopods were absent in the Berriasian–Early Valanginian, Late Hauterivian, and the Middle–Late Albian. It is established that the post-Early Barremian diversity decline occurred chiefly because of rare taxa appearances. The vulnerability of representatives of the superfamilies Terebratuloidea and Hemithiridoidea to external influences shaped the regional diversity dynamics of brachiopods. The amplitude of changes of the assemblage composition through the epoch was high. There were both similarities and dissimilarities between the regional and global diversity dynamics of brachiopods, and weak correspondence between the patterns is an evidence of heterogeneity of the Early Cretaceous brachiopod diversity changes in the global space. For instance, the Barremian radiation did not occur on the planetary scale. The interplay of the global factors (global diversity dynamics, eustatic changes, and oceanic anoxic events) and the regional factors (e.g., changing depositional environment) is proposed to explain the observed diversity patterns.

Halite fluid inclusions and the late Aptian sea surface temperatures of the Congo Basin, northern South Atlantic Ocean

The Aptian stage represents a pivotal transition of the Cretaceous climate of the Earth but a comprehensive picture of the climate conditions is still unavailable due to the fragmentary paleotemperature records of the mid-late Aptian interval, especially in the Central Segment of South Atlantic region In this region extensive and thick salt sequence severely limiting the applicability of traditionally used paleotemperature proxies. In this paper, we present new quantitative sea surface temperatures from Congo Basin, during the late Aptian based on homogenization temperatures (Th) of fluid inclusions of halite. Homogenization temperatures concentrated at 25–35 °C are consistent with previous climate model results and represent the prevailing sea surface temperatures in the Congo Basin. The derived maximum sea surface temperature is 46.5 °C and much higher than existing paleotemperature records for the late Aptian, apparently representing local hot climate conditions. However, it is comparable with temperature records from many ancient and modern evaporitic basins where potash deposits also largely developed as seen in the Congo Basin. Significant cooling by about 5 °C was identified by both maximum (ThMax) and average (ThAverage) homogenization temperatures of halite during the late Aptian. A comparison of our results with records from other places leads to the conclusion that the observed declining sea surface temperatures of the Congo Basin represent the regional response to global climate cooling in the late Aptian. However, the amplitude, short-term oscillation pattern and worldwide correlation of this cooling is still difficult to assess due to often imprecise and poorly resolved age data, emphasizing the need of better constraint chronologies. Homogenization temperatures of halite fluid inclusions demonstrate the potential of the method to reliably track environmental and climatic changes of the past, especially in evaporitic settings of the Phanerozoic where other climate proxies are often not available.

Palaeogeographic regulation of glacial events during the Cretaceous supergreenhouse.

The historical view of a uniformly warm Cretaceous is being increasingly challenged by the accumulation of new data hinting at the possibility of glacial events, even during the Cenomanian–Turonian (∼95 Myr ago), the warmest interval of the Cretaceous. Here we show that the palaeogeography typifying the Cenomanian–Turonian renders the Earth System resilient to glaciation with no perennial ice accumulation occurring under prescribed CO2 levels as low as 420 p.p.m. Conversely, late Aptian (∼115 Myr ago) and Maastrichtian (∼70 Myr ago) continental configurations set the stage for cooler climatic conditions, favouring possible inception of Antarctic ice sheets under CO2 concentrations, respectively, about 400 and 300 p.p.m. higher than for the Cenomanian–Turonian. Our simulations notably emphasize that palaeogeography can crucially impact global climate by modulating the CO2 threshold for ice sheet inception and make the possibility of glacial events during the Cenomanian–Turonian unlikely.

Recognition of wave-influenced deltaic and bay-margin sedimentation, Bluesky Formation, Alberta

Abstract The late Aptian to early Albian Bluesky Formation of Alberta is characterized by complex vertical and lateral associations of siliciclastic sediments deposited during overall transgression of the Boreal sea. As the Bluesky Formation is host to substantial subsurface bitumen deposits of the Peace River oil sands, a refined understanding of vertical and lateral facies distributions is essential for exploration and exploitation activity. To aid in achieving this goal, high-resolution core logging was completed on a 40 core dataset within Ranges 16–17W5M, and Townships 82–84 (approximately 215 km2). We identify 16 distinct facies comprising 5 facies associations (FA1–FA5). These facies associations include: 1) FA1 – Wave-dominated, fluvially influenced embayment delta; 2) FA2 – Fluvially-dominated, tidally-influenced distributary channel; 3) FA3 – Fluvially and tidally influenced delta; 4) FA4 – Marine-embayment shoreface to offshore; and, 5) FA5 – Mixed energy estuary. The evolution of these facies associations suggest periodic progradation within an overall back-stepping, transgressive, marine-embayment system. Through combination of sedimentary and ichnological characteristics, this research has led to the identification of wave-influenced deltaic and marine-embayment sedimentary environments previously un-documented within the Peace River oil sands. Additionally, proximal-distal depositional trends obscured by the complex facies distributions were identifiable using ichnological criteria. It is intended that the sedimentological and ichnological characteristics identified herein will aid in the recognition of similar embayment-type settings in other ancient datasets.

Black shale deposition and early diagenetic dolomite cementation during Oceanic Anoxic Event 1: The mid-Cretaceous Maracaibo Platform, northwestern South America

Thin laterally continuous organic-rich dolomitic marlstones were deposited in the extended Late Aptian - Early Albian epicontinental sea of northwestern South America. These intervals are the proximal equivalents of thick hemipelagic black shale-ammonitic floatstone couplets, deposited in the distally stepped, differentially subsiding part of the Maracaibo Platform. The marlstones reflect the dynamic conditions resulting from orbital forcing mechanisms and can be genetically related to (1) minor sea-level changes, (2) proximal turnovers in marine productivity, and (3) sudden climate shifts affecting mid-Cretaceous shoaling upward, shallow marine, carbonate cyclicity. Therefore, the marlstones may well be linked to the multiple environmental perturbations collectively referred to as Oceanic Anoxic Event 1. The interstitial euhedral dolomite has a medium crystallinity, and exhibits unusual textural relations with framboidal pyrite and gypsum. The authigenic mineral assemblage also includes quartz, Ca-F apatite, and barite, which together with the chemical signals of dolomite, point to an unsteady climate regime. Bulk-rock biomarker parameters, rare earth element geochemistry, and iron speciation data point to widespread photic zone anoxia and transient shallow marine euxinia by the time of deposition, with climatic instability driving the delivery of oxidized detritus from the hinterlands. These conditions led to a schizohaline redox stratified environment favorable to dolomite precipitation. In such a depositional setting, the bio-utilization of Fe, Mn, and sulfur for organic matter respiration sustained elevated pore-water alkalinity and pH, and allowed for the pre-compactional growth of interstitial dolomite.

Stratigraphic and geochemical expression of Barremian–Aptian global climate change in Arctic Svalbard

Significant changes in global climate and carbon cycling occurred during the Early Cretaceous. This study examines the expression of such climatic events in high-latitude Svalbard together with the stratigraphic utility of carbon-isotope stratigraphies. Isotopic analysis of fossil wood fragments (from the Rurikfjellet, Helvetiafjellet, and Carolinefjellet formations, Festningen, Spitsbergen) record a distinctive pattern including a negative isotope excursion preceding a positive event, correlatable with the global early Aptian isotope event. Our carbon-isotope profile improves the stratigraphic correlation and relative dating of the succession. We show that the upper part of the Helvetiafjellet Formation was deposited during the early Aptian, and not the late Barremian, as previously thought. Furthermore, we estimate an age for the abrupt contact of the Rurikfjellet Formation with the overlying Helvetiafjellet Formation (associated with a pulse of igneous activity) to be ca. 129 Ma or ca. 124 Ma, depending on which age model for the Early Cretaceous is used. The well-known dinosaur footprints of the Helvetiafjellet Formation at Festningen are constrained to the middle Barremian and, coupled with floral data, support a warm late Barremian prior to the Aptian carbon-isotope event. The appearance of glendonites at 655 m in the Carolinefjellet Formation is consistent with global cooling in the late Aptian–early Albian.