Middle Albian Research Articles

Ramp sedimentation across a middle Albian, Arctic embayment: Influence of subsidence, eustasy and sediment supply on stratal architecture and facies distribution, Lower Cretaceous, Western Canada Foreland Basin

AbstractRegional mapping of Middle Albian, shallow‐marine clastic strata over ca 100 000 km2 of the Western Canada Foreland Basin was undertaken to investigate the relationship between large‐scale stratal architecture and lithology. Results suggest that, over ca 5 Myr, stratal geometry and facies were dynamically linked to tectonic activity in the adjacent Cordillera. Higher frequency modulation of accommodation is most reasonably ascribed to eustasy. The Harmon and Cadotte alloformations were deposited at the southern end of an embayment of the Arctic Ocean. The Harmon alloformation, forming the lower part of the succession, constitutes a wedge of marine mudstone that thickens westward over 400 km from <5 m near the forebulge to >150 m in the foredeep. Constituent allomembers are also wedge‐shaped but lack distinct clinothems, a rollover point or downlapping geometry. Ubiquitous wave ripples indicate that the sea floor lay above storm wave base. Deposition took place on an extremely low‐gradient ramp, where accommodation was limited by effective wave base. Lobate, river‐dominated deltas fringed the southern margin of the basin. The largest deltas are stacked in the same area, suggesting protracted stability of the feeder river. A buried palaeo‐valley on the underlying sub‐Cretaceous unconformity may have influenced compaction and controlled river location for ca 3 Myr. Adjacent to the western Cordillera, a predominantly mudstone succession is interbedded with abundant storm beds of very fine‐grained sandstone and siltstone that reflect supply from the adjacent orogen. Bioturbation indices in the Harmon alloformation range from zero to six which reflects the influence of stressors related to river‐mouth proximity. Harmon alloformation mudstone grades abruptly upward into marine sandstone and conglomerate of the overlying Cadotte alloformation. The Cadotte is composed of three allomembers ‘CA’ to ‘CC’, that represent the deposits of prograding strandplains 200 × 300 km in extent. Allomembers ‘CA’ and ‘CB’ are strongly sandstone‐dominated, whereas allomember ‘CC’ contains abundant conglomerate in the west. The dominantly aggradational wedge of Harmon alloformation mudstone records flexural subsidence driven by active thickening in the adjacent orogen: the high accommodation rate trapped coarser clastic detritus close to the basin margin. In contrast, the tabular, highly progradational sandstone and conglomerate bodies of the Cadotte alloformation record a low subsidence rate, implying tectonic quiescence in the adjacent orogen. Erosional unloading of the orogen through Cadotte time steepened rivers to the extent that they delivered gravel to the shore. These observations support an ‘anti‐tectonic’ model of gravel supply proposed previously for the United States portion of the Cretaceous foreland basin. Because Cadotte allomembers do not thicken appreciably into the foredeep, accommodation changes that controlled these transgressive–regressive successions were probably of eustatic origin.

A late Albian ammonite assemblage from the mid- Cretaceous succession at Annopol, Poland

Abstract A previously unrecorded ammonite assemblage, comprising Lepthoplites sp., Callihoplites tetragonus (Seeley, 1865), C. cf. tetragonus, Arrhaphoceras cf. substuderi Spath, 1923, Cantabrigites sp., Stoliczkaiella (Stoliczkaiella) sp., Hamites cf. duplicatus Pictet and Campiche, 1861, H. cf. subvirgulatus Spath, 1941, and H. cf. venetzianus Pictet, 1847, is described from the mid-Cretaceous condensed succession at Annopol, Poland. These specimens are preserved as pale phosphates or sandstone moulds in a bed of reworked phosphatic nodules near the top of the Albian. This assemblage has many species in common with the late late Albian faunas from condensed deposits of England, Switzerland, and France. The presence of Callihoplites tetragonus indicates the lowermost upper upper Albian Mortoniceras fallax Zone. The ammonites studied are the youngest elements in the phosphate bed, which also contains taxa as old as the middle Albian Hoplites dentatus Zone. This bed originated through condensation and reworking of nodules and fossils in a period of low net sedimentation rate, being probably a reflection of a sea-level drop at the boundary between the classic ammonite zones of Mortoniceras inflatum and Stoliczkaiella dispar.

Structure, age, and mechanism of emplacement of the Amur and Kiselevka–Manoma accretionary complexes of the lower Amur region, Russian Far East

The Amur and Kiselevka–Manoma accretionary complexes belong to the Cretaceous Khingan–Okhotsk active continental margin, which was formed in the east of Eurasia as a result of the subduction of the Pacific oceanic plates. The Kiselevka–Manoma complex is composed of oceanic pelagic and hemipelagic sedimentary rocks and intraplate oceanic basalts. It is located to the southeast, along the ocean-faced front of the Amur complex, which is predominantly composed of turbidites of the convergent boundary of lithospheric plates. The biostratigraphic study of radiolarians from rocks of the frontal part of the Amur complex allowed us to correlate them with rocks of the Kiselevka–Manoma complex and to define the period of accretion to be from the Late Aptian to the Middle Albian. The tectonostratigraphic interrelations of these two contrasting lithotectonic complexes are established and two possible models of their common emplacement are suggested. Both models suppose a continuous spatiotemporal relation of complexes with the primary paleolocation of the Kiselevka–Manoma complex in front of (on the ocean side) the Amur complex. The frontal part of the Amur complex and the Kiselevka–Manoma complex were emplaced synchronously with the western part of the East Sakhalin accretionary complex. This scenario defines the Early Cretaceous tectonic zonation of the region and the choice of the appropriate paleotectonic model. At the end of the Early Cretaceous, a single convergent boundary of the lithospheric plates is suggested with the position of the Sakhalin island arc system south of the Khingan–Okhotsk active continental margin.

Un silicoflagelado en el Albiano medio de la Cuenca Austral, Argentina.

Calcareous nannofossil biostratigraphic investigations of Cretaceous sediments within the southern high latitude Austral Basin, Argentina, have revealed the presence of a fragment of a silicoflagellate possibly belonging to the species Variramus aculeifera (Deflandre) McCartney, Wise, Harwood and Gersonde. Although only a fragment was identified in the samples examined from this locality, its presence is important, as it is only the second documented occurrence of an Early Cretaceous silicoflagellate. The specimen was found in a subsurface sample from the informal Palermo Aike Formation at Austral Basin. This stratigraphic level is interpreted as middle Albian on the basis of calcareous nannofossil biostratigraphy. The specimen consists of a fragmented strut with broken spines at the base, which allows the observation of the hollow skeletal structure. The strut is curved and slightly expanded at the widest part, which are characteristics diagnostic of the genus Variramus.

Microstratigraphy and interpretation of the karst sedimentary fillings associated to the Aptian–Albian unconformity in Jebel Semmama (central Tunisia)

In this paper, the aim was proposing a new microstratigraphy and interpretation of the karst sedimentary fillings associated to the Aptian–Albian unconformity in Jebel Semmama, central Tunisia. In all the previous studies, this unconformity was interpreted as the result of a major sea-level fall followed by a continuous emersion of the Aptian platform that lasted broadly the Lower and Middle Albian. In the present work, the field examination of the exposure surface in Jebel Semmama area in central Tunisia shows several centimetric epikarsts filled with different marine and non-marine deposits. According to the sedimentologic and microstratigraphic analyses, the karstic fillings may be linked with several sea-level oscillation cycles. Accordingly, the presence of such fillings suggests that the Aptian platform was not continually emerged during the lower and middle Albian as already assumed in previous works. Rather, it was episodically inundated by marine incursions. At least eighteen different sedimentary fillings have been recognized and sampled from the epikarsts. As these fillings are never totally regrouped in the same epikarst, the reconstruction of their microstratigraphy was based on (i) identification of their facies (ii) comparison and correlation of the different fillings between epikarsts (iii) analysis of the stratigraphic relation between the different fillings. A composite microstratigraphic column was established, it shows a regular alternation of shallow marine and non-marine deposits which are arranged into nine karstic sedimentary cycles. The latter may understandably be the result of nine relative sea-level oscillation cycles that broadly happened during the Lower and Middle Albian. For lack of biostratigraphic markers, the previous karstic cycles remain neither dated nor correlated with any eustatic chart. Moreover, the previous cycles have been controlled by significant local salt tectonics.

Large igneous provinces and organic carbon burial: Controls on global temperature and continental weathering during the Early Cretaceous

There is an abundance of evidence for short intervals of cold climatic conditions during the Early Cretaceous. However, the lack of a high-resolution, long-term Early Cretaceous paleotemperature record hampers a full-scale synthesis of these putative “cold snap” episodes, as well as a more holistic approach to Early Cretaceous climate changes. We present an extended compilation of belemnite-based oxygen, carbon and strontium isotope records covering the Berriasian–middle Albian from the Vocontian Basin (SE France). This dataset clearly demonstrates three intervals of cold climatic conditions during the Early Cretaceous (late Valanginian–earliest Hauterivian, late early Aptian, latest Aptian–earliest Albian). Each of these intervals is associated with rapid and high amplitude sea-level fluctuations, supporting the hypothesis of transient growth of polar ice caps during the Early Cretaceous. As evidenced by positive carbon isotope excursions, each cold episode is associated with enhanced burial of organic matter on a global scale. Moreover, there is a relatively good match between the timing and size of large igneous province eruptions and the amplitude of Early Cretaceous warming episodes. Altogether, these observations confirm the instrumental role of atmospheric CO2 variations in driving Early Cretaceous climate change. From a long-term perspective, the coupling of global paleotemperature and seawater strontium isotopic ratio during the Early Cretaceous is best explained by temperature-controlled changes of continental crust weathering rates.

Isotopic seawater temperatures in the Albian Gault Clay of the Boulonnais (Paris Basin): palaeoenvironmental implications

Oxygen isotopes were measured on several types of fossil hardparts from the Gault Clay Formation including benthic and planktonic foraminifera, belemnite guards, and fish small-teeth. Belemnites δ18O values indicate low temperatures (13.5–19.3°C) with an increase from the Middle to Late Albian. Foraminifera provide variable δ18O values, some too low to be relevant in terms of temperature (until 42°C). These low values probably result from a diagenetic alteration of the foraminiferal tests even though SEM observations revealed well-preserved microstructures. However, higher foraminiferal δ18O values recorded in some levels indicate temperatures in the range of previously published estimates for the Albian at comparable palaeolatitudes. In these levels, temperatures inferred from benthic and planktonic foraminiferal δ18O range between 15–17°C and 27–30°C respectively, during the Middle–Late Albian interval. This slight increase in temperature is coherent with the long-term warming that characterises the Aptian–Cenomanian interval. The temperature difference between sea-surface and bottom waters fits well with a deposition at a palaeodepth of about 180m in lower offshore environments, assuming a temperature gradient with depth comparable to the modern one in similar epicontinental tropical environments. Fish small-teeth indicate a temperature range from 22 to 28°C consistent with previously published data from planktonic foraminifera, with a greater variability recorded during the late than during middle Albian. This correspondence suggests that small-teeth assemblages may be dominated by pelagic fishes, thus recording upper ocean temperatures. Finally, the markedly lower temperatures recorded by the belemnite guards compared to other analysed materials suggest a necto-benthic mode of life of belemnites.

Cretaceous angiosperm pollen from the Kachaike Formation, south-western Santa Cruz Province, Argentina

Thirty-three angiosperm pollen species are here reported from mid-Cretaceous deposits of the Kachaike Formation, Austral Basin, southern Argentina. Clavatipollenites is the most abundant angiosperm genus, with six well-defined morphological groups recognised on the basis of their reticulum morphology and sculpture. Pollen of eudicots are scarce, represented by tricolpate (Psilatricolpites spp. and Tricolpites spp.), tricolporoidate and tricolporate morphotypes (Dryadopollis spp.). Increasing complexity in the aperture structure is seen throughout the sequence; tricolpate and tricolporoidate forms are recorded in almost all samples, while tricolporate pollen grains are restricted to the middle and upper levels of the unit. The high species richness and abundance of monocolpate-ulcerate angiosperm related to monocots or magnoliids sensu lato recorded in the unit is comparable to that previously recognised in other assemblages from the early and middle Albian of the southern (e.g. Australia) and northern hemispheres (e.g. Western Portuguese basin, Europe). The recorded increase in the number of angiosperm species towards the middle and upper parts of the Kachaike Formation, with the presence of monocolpate, tricolpate, tricolporoidate and tricolporate pollen, suggests an early-early middle Albian age for these parts of the unit, in agreement with the early Albian age proposed for its basal levels on the basis of dinoflagellates.

Large predatory marine reptiles from the Albian–Cenomanian of Annopol, Poland

AbstractDuring the Early–Late Cretaceous transition, marine ecosystems in Eurasia hosted a diverse set of large predatory reptiles that occupied various niches. However, most of our current knowledge of these animals is restricted to a small number of bonebed-like deposits. Little is known of the geographical and temporal extent of such associations. The middle Albian – middle Cenomanian phosphorite-bearing succession exposed at Annopol, Poland produces numerous ichthyosaurian and plesiosaurian fossils. These are mostly isolated skeletal elements (e.g. teeth, vertebrae), but disarticulated partial skeletons and an articulated, subvertically embedded ichthyosaur skull are also available. The following taxa are identified: ‘Platypterygius’ sp., cf. Ophthalmosaurinae, Ichthyosauria indet.,Polyptychodon interruptus, Pliosauridae indet., Elasmosauridae indet. and Plesiosauria indet. The large-sized ichthyosaur ‘Platypterygius’ and the pliosauridPolyptychodon interruptuspredominate within the upper Albian – middle Cenomanian deposits. The Annopol record, combined with data from England, France and western Russia, suggests that ‘Platypterygius’ andPolyptychodon interruptusformed a long-term, stable ecological sympatry in marine ecosystems of the European archipelago, at least during the Albian – middle Cenomanian. In addition, the marine reptile assemblage from Annopol is distinct from other Eurasian ecosystems in containing also elasmosaurids in its Albian portion.

Synextensional mid-Cretaceous stratigraphic architecture of the eastern Basque–Cantabrian basin margin (western Pyrenees)

The tectonosedimentary study of the southern and north-western margins of the Bortziri–Cinco Villas Palaeozoic Massif, which constitute the eastern margin of the Basque–Cantabrian basin, has yielded a detailed synrift stratigraphic architecture and led to the proposal of formal lithostratigraphic units, as well as to an interpretation of the evolution of different marine depositional systems during Aptian to Cenomanian times. During this time interval, carbonate platform to deeper siliciclastic depositional systems were deposited transgressively onto the margin of the Bortziri–Cinco Villas Palaeozoic Massif.The onset and evolution of sedimentary depositional systems were controlled by strong synsedimentary tectonic activity. The analysis and interpretation of the sedimentary systems has permitted the characterization of 5 tectonosedimentary phases separated by 5 main discontinuities (D1 to D5): Phase I, early Aptian–early Albian; Phase II, middle Albian; Phase III, late Albian–latest Albian; Phase IV, latest Albian–early Cenomanian; Phase V, early Cenomanian–Campanian.The observed tectonic and sedimentary features indicate the presence of regional transtensional strain during all the tectonosedimentary phases, except for Phase IV when compressive features are recognized related to the main basement faults. All of the above-mentioned tectonosedimentary phases correlate well with major Pyrenean tectonosedimentary events related to the opening of the Bay of Biscay and the Central Atlantic during the Cretaceous.

New data on middle and late Albian foraminifera and biostratigraphy of the northern palaeobiogeographical district of western Siberia

Abstract The present paper discusses foraminiferal assemblages and biozones established on the basis of studies of samples from ten borehole sequences of the Khanty-Mansiysk Horizon in the Samotlor area of the northern palaeobiogeographical district of western Siberia (Russia). In this region, middle and late Albian foraminiferal assemblages were first distinguished in western Siberia. Levels from which these assemblages have been recovered, are here referred to the following foraminiferal zones, the Ammobaculites fragmentarius-Gaudryinopsis filiformis Zone (middle Albian) and the Ammotium braunsteini-Verneuilinoides borealis assanoviensis Zone (upper Albian). Zonal assemblages are dominated by representatives of the orders Ammodiscida, Textulariida and Ataxophragmiida. Species of the ataxophragmiid genera Verneuilinoides, Pseudoverneuilina and Gaudryinopsis are the most characteristic, inclusive of several key index forms. Foraminiferal tests consist of agglutinated quartz-silica, the wall microstructure being almost exclusively medium and coarse grained. In specific composition, the Albian assemblages from the Samotlor area are similar to those from Transuralia (Russia) and to the Canadian Province, which, together with West-Siberian Province, forms the Arctic palaeobiogeographical realm

Record of Albian to early Cenomanian environmental perturbation in the eastern sub-equatorial Pacific

The present paper documents and discusses a new Albian–early Cenomanian carbon isotope (δ13Ccarb and δ13Corg) curve from the subequatorial Eastern Pacific in Peru. Chemostratigraphic evidences for the expression of the OAE1b set and for OAE1c and OAE1d are presented. This dataset is relevant inasmuch as previous work is strongly biased towards study sites in North America (Western Interior Basin), in Europe (Tethys) and the Pacific realm. A comparison of the carbon isotope stratigraphy obtained in Peru with published sections from the Central and Western Pacific, the Western Atlantic and Northern and Western Tethys reveals an overall good agreement supporting the global nature of the isotope patterns described here. The δ13C from Peru record is constrained by biostratigraphic evidence and 87Sr/86Sr isotope stratigraphy using well-preserved oyster shells. Furthermore, we document the development of a heterozoan epeiric–neritic mixed carbonate–siliciclastic ramp in the Western Platform of Peru and its corresponding sedimentary facies associations. This dataset was used to elucidate the complex interplay of climatic changes, nutrient supply, and platform drowning, leading to the following conclusions: (i) an upper Aptian–lower Albian major change from siliciclastic-dominated to carbonate sedimentation coincided with the impact of the Kilian Level, (ii) a lower Albian incipient platform drowning linked to the impact of the Paquier Level, (iii) A lower middle Albian major demise of neritic carbonate production that coincides with the Leenhardt Level, followed by middle Albian condensed sedimentation that reports prominent negative values in δ13Ccarb prior to the onset of OAE1c and (iv) finally, renewed carbonate ramp production during the upper Albian–lower Cenomanian. The data shown here represent the foundation for future work documenting the mid-Cretaceous of Peru and its implications for the palaeoceanography of the SE subequatorial Pacific.

Cretaceous faunas from Zululand and Natal, South Africa. The ammonite subfamily Mantelliceratinae Hyatt, 1903

The Lower and basal Middle Albian ammonite Subfamily Lyelliceratinae Spath, 1921 is reviewed, and restricted to the genera Tegoceras Hyatt, 1903, Lyelliceras Spath, 1921, and Pseudobrancoceras Kennedy, 2004. An evolutionary origin in Brancoceratinae Spath, 1934 is proposed. The South American taxa from Colombia and Peru referred to Tegoceras, Lyelliceras, Prolyelliceras Spath, 1930b, and its synonym Ralphimlayites Etayo-Serna, 1979, are lyelliceratine homoeomorphs, derived independently from Brancoceratinae. The North African 'Prionotropis' radenaci Pervinquiere, 1907 is tentatively referred to Prolyelliceras, while 'Lyelliceras' flandrini Dubourdieu, 1953 is a further lyelliceratine homoeomorph subgenerically or generically distinct from Prolyelliceras. The following are described from KwaZulu : Tegoceras mosense (d'Orbigny, 1841), T. collignoni (Breistroffer, 1953), T. camatteanum (d'Orbigny, 1841), Lyelliceras lyelli (d'Orbigny, 1841), L. pseudolyelli (Parona & Bonarelli, 1897), L. latili sp. nov., and Pseudobrancoceras versicostatum (Michelin, 1838). On the basis of this revision, a sequence of four faunas are recognized, characterized, successively, by the presence of 1: Tegoceras gladiator and Aioloceras, 2: Tegoceras camatteanum; 3: Lyelliceras pseudolyelli, and 4: Lyelliceras lyelli, the appearance of the last-named marking the base of the Middle Albian Substage.

Cretaceous faunas from Zululand and Natal, South Africa. The Albian ammonite genus Douvilleiceras de Grossouvre, 1894

The cosmopolitan ammonite genus Douvilleiceras de Grossouvre, 1894, is the commonest ammonite in the Lower and lower Middle Albian in northern KwaZulu-Natal. Two variable, dimorphic species, D. mammillatum (Schlotheim, 1813) and D. inaequinodum (Quenstedt, 1849) are recognized, of which the majority of previously named taxa referred to the genus are regarded as synonyms.

Paraptychodus washitaensis n. gen. et n. sp., of Ptychodontid shark from the Albian of Texas, USA

A new genus and species of Ptychodontiform elasmobranch, Paraptychodus washitaensis n. gen. et n. sp. is described on the basis of 13 teeth from the Middle Albian Duck Creek Formation of the Washita Group in north central Texas, USA. This material is significant as it demonstrates an intermediate tooth form between the Lonchidiidae and Ptychodus with regard to occlusal ornamentation of the crown and tooth root morphology; the new taxon represents the earliest member of the family Ptychodontidae in North America. Analysis of dental characters and stratigraphic occurrences within the family suggests that P. washitaensis is a basal taxon and is the most recent ancestor of Ptychodus. Morphological trends of derived species of Ptychodus demonstrate continuous specialization in tooth crown morphologies. The diagnosis of P. washitaensis from the upper Albian of Texas adjusts the stratigraphic distribution of the genus Ptychodus to lower Cenomanian through lower Campanian.

The Lindi Formation (upper Albian–Coniacian) and Tanzania Drilling Project Sites 36–40 (Lower Cretaceous to Paleogene): Lithostratigraphy, biostratigraphy and chemostratigraphy

The 2009 Tanzania Drilling Project (TDP) expedition to southeastern Tanzania cored a total of 572.3m of sediments at six new mid-Cretaceous to mid-Paleocene boreholes (TDP Sites 36, 37, 38, 39, 40A, 40B). Added to the sites drilled in 2007 and 2008, the new boreholes confirm the common excellent preservation of planktonic and benthic foraminifera and calcareous nannofossils from core samples that will be used for biostratigraphy, evolutionary studies, paleoceanography and climatic reconstructions from the Tanzanian margin, with implications elsewhere. The new sites verify the presence of a relatively expanded Upper Cretaceous succession in the region that has allowed a new stratigraphic unit, named here as the Lindi Formation (Fm), to be formally defined. The Lindi Fm (upper Albian to Coniacian), extending ∼120km between Kilwa and Lindi, comprises a 335-m-thick, outer-shelf to upper-slope unit, consisting of dark gray claystone and siltstone interbeds, common finely-laminated intervals, minor cm-thick sandstones and up to 2.6% organic carbon in the Turonian. A subsurface, composite stratotype section is proposed for the Lindi Fm, with a gradational top boundary with the overlying Nangurukuru Fm (Santonian to Maastrichtian) and a sharp bottom contact with underlying upper Albian sandstones.The section cored at TDP Sites 36 and 38 belongs to the Lindi Fm and are of lower to middle Turonian age (planktonic foraminifera Whiteinella archaeocretacea to Helvetoglobotruncana helvetica Zones and nannofossils subzones UC6b±UC7). The lower portion of TDP Site 39 (uppermost part of the Lindi Fm) is assigned to the lower to upper Coniacian (planktonic foraminifera Dicarinella concavata Zone and nannofossils zone UC 10), while the remaining part of this site is attributed to the Coniacian–Santonian transition and younger Santonian (planktonic foraminifera D. asymetrica Zone and upper part of nannofossils zone UC10). TDP Site 37 recovered relatively expanded (150m thick), monotonous calcareous claystones from the lower to upper Maastrichtian (planktonic foraminifera Pseudoguembelina palpebra to Abathomphalus mayaroensis Zones and nannofossils zones UC19 to UC20aTP) that were separated by a hiatus and/or a faulted contact from overlying brecciated carbonates of the Selandian (middle Paleocene: PF Zone P3 and nannofossil zone NP5). The lower portion of TDP Sites 40A and 40B recovered sandstones and conglomerates barren of microfossils. Their overlying parts were assigned to incomplete sections of the nannofossil zones NC6A to NC8 (uppermost Barremian to lower Albian). Benthic foraminiferal assemblages allowed the Barremian to lower Aptian to be identified in TDP Sites 40A and 40B, while the upper Aptian to middle Albian (Hedbergella trocoidea to Ticinella primula Zones) were assigned using planktonic foraminifera. Cores recovered at TDP 39 (Coniacian–Santonian) and at TDP Sites 40A and 40B (Barremian–middle Albian) represent the first time that these two intervals have been continuously cored and publicly documented in Tanzania.Bulk sediment isotope records generated for the new sites show lower δ18Ocarb values in the Turonian and Santonian (∼−3.5‰ to −5‰) than in the Maastrichtian (∼−3‰), a situation consistent with extreme global warmth in the older intervals and cooling toward the end of the Cretaceous. Also, similar to Turonian sites from previous TDP expeditions, a negative δ13Corg excursion was detected across the W. archaeocretacea–H. helvetica boundary of TDP Site 36 (close to, but above, the Cenomanian-Turonian boundary). This excursion probably responded to local processes in the region, but it is unknown whether they were related to the recovery phase from Ocean Anoxic Event 2.

New reconstruction of Weichselia reticulata (Stokes et Webb) Fontaine in Ward emend. Alvin, 1971 based on fertile remains from the middle Albian of Spain

Exceptionally well-preserved specimens from the middle Albian of Spain corresponding to a nearly complete fertile frond and fragments of pinnae containing soral clusters of the tree fern Weichselia reticulata have provided new data about the structure and arrangement of pinnae and their associated fertile reproductive structure. This new material has been compared with the previous studies, and recostructions of this fern and the new data indicate the segregation of vegetative and fertile fronds within the main stipe of this fern.

Allostratigraphy and paleogeography of the Harmon and Cadotte members of the Peace River Formation (Middle Albian), west-central Alberta and adjacent British Columbia

Abstract The mudstone-dominated Harmon and sandstone-dominated Cadotte members of the Peace River Formation were deposited during the middle Albian in the southern end of a Boreal marine embayment that occupied the foredeep of the Western Canada Foreland Basin. Sandstone of the Cadotte Member represents a shoreface environment and has traditionally been interpreted as the updip equivalent of offshore Harmon mudstone. Allostratigraphic correlation, based on marine flooding surfaces and unconformities shows that the Harmon alloformation can be divided into five regionally-mappable allomembers. Similar erosion surfaces allow the Cadotte alloformation to be divided into three allomembers. The new allostratigraphy shows that the informal Harmon and Cadotte alloformations do not have an interfingering relationship and hence are not genetically related. Harmon and Cadotte allomembers have been mapped over about 100 000 km2, but show no evidence of stratal lap-out or depositional topography; it is concluded that deposition took place on a shallow marine ramp of very low relief. The vertical stacking of Harmon and Cadotte allomembers across the foredeep indicates that rates of accommodation and sediment supply remained in approximate equilibrium throughout deposition of these units. In the far southern and eastern parts of the study area, changing gamma ray log response suggests that marine deposits of both the Harmon and Cadotte alloformations grade laterally into coeval coastal plain deposits that are mapped in outcrop as Gates Formation whereas in subsurface wireline log picks, these rocks are usually included in the Upper Mannville Group. The lateral boundary between offshore mudstone and coeval nearshore muddy sandstone can be mapped within individual Harmon allomembers; the mudstone to sandstone boundary has a lobate to cuspate pattern in plan view, suggesting that, at the southern extremity of the ‘Harmon Sea’ rivers built elongate deltas in a very shallow-water, low wave-energy setting. Lenticular, sharp-based sandstone bodies 17–42 m thick hang from allomember bounding surfaces in both the Harmon and Cadotte alloformations; these sandbodies probably represent paleovalley fills. Valley incision may have been linked to relative sea-level changes that also gave rise to the marine transgressive surfaces that are traceable over the entire study area. In the east, both the Cadotte and Harmon alloformations are completely truncated by a bevelling unconformity at the base of the Paddy and the laterally-contiguous Joli Fou alloformation.

Lauraceous Fossil Flowers from the Kamikitaba Assemblage (Coniacian, Late Cretaceous) of Northeastern Japan (Lauraceae)

A new genus and species of Lauraceae, Microlaurus perigynus gen. et sp. nov. is described based on fossil charcoalified flower buds recovered from the Kamikitaba assemblage (early Coniacian, Late Cretaceous; ca. 89 million years before present (myr BP)) in the Ashizawa Formation (Asamigawa Member) of the Futaba Group in northeastern Japan. Analysis of the internal structure of the fossil buds using synchrotron-radiation X-ray microtomography (SRXTM) at the 2-BM-B beamline of the Advanced Photon Source (APS), Argonne National Laboratory, shows that the flowers are small, pedicellate, bisexual, trimerous, and actinomorphic, with small outer tepals, larger inner tepals, three whorls of stamens, an innermost androecial whorl composed of staminodia, and a unicarpellate gynoecium containing a single ovule. Microlaurus perigynus is assigned to the Lauraceae based on the regular trimerous floral organization and other details of floral structure, but it is distinguished from most previously described lauraceous fossil flowers by the poorly differentiated filament and anther in the stamens of the third whorl and the marked size difference between the small outer tepals and the large inner tepals. Also unusual are the paired glandular appendages that appear to be associated with the first (outermost) whorl of stamens, rather than the stamens of the third whorl, although the precise position is not fully clear. The same feature occurs in Hernandiaceae, the sister group of Lauraceae, as well as in Powhatania connata, an earlier but fragmentary lauralean fossil flower from the Early to Middle Albian of Virginia. Microlaurus perigynus adds to the floral diversity of Lauraceae known from the Late Cretaceous, and its presence in the Kamikitaba assemblage from Japan underlines the broad geographic distribution and floristic significance of lauraceous plants during the Late Cretaceous.

Sedimentary and structural record of the Albian growth of the Bakio salt diapir (the Basque Country, northern Spain)

AbstractHowever salt has a viscous rheology, overburden rocks adjacent to salt diapirs have a brittle rheology. Evidence of deformation within the overburden has been described from diapirs worldwide. Gravity‐driven deposits are also present along the flanks of several diapirs. The well‐known example from the La Popa Basin in northern Mexico shows that such deposits may be organized into halokinetic sequences. This leads to several questions: (i) How does diapir growth contribute to overburden deformation? (ii) Are halokinetic sequence models valid for other areas beyond the La Popa Basin. The Bakio diapir and its well‐exposed overburden in Basque Country, Spain provides key elements to address these questions. The Bakio diapir consists of Triassic red clays and gypsum and is flanked by synkinematic middle to upper Albian units that thin towards the diapir. The elongate diapir parallels the Gaztelugatxe normal fault to the NE: both strike NE–SW and probably formed together during the middle Albian, as synkinematic units onlap the fault scarp. The diapir is interpreted as a reactive diapir in response to middle Albian motion on the Gaztelugatxe fault. The rate of salt rise is estimated to be about 500 m Myr−1 during this passive stage. During Late Albian, the diapir evolved passively as the Gaztelugatxe fault became inactive. Synkinematic units thinning towards the diapir, major unconformities, slumps and other gravity‐driven deposits demonstrate that most deformation related to diapir growth occurred at the sea floor. Halokinetic sequences composed of alternating breccias and fine‐grained turbidites recorded cyclic episodes of diapir flank destabilization. This work provides insights into drape fold and halokinetic sequence models and offers a new simple method for estimating rates of diapir growth. This method may be useful for outcrop studies where biostratigraphical data are available and for other passive diapirs worldwide.