Sinemurian ammonites from Male Karpaty Mts, Western Carpathians, Slovakia. Part 3: Asteroceratinae, Eoderoceratidae, Oxynoticeratidae and rare taxa

Third study of the extremely rich ammonite fauna from the Chtelnica condensed section mainly includes numerous representatives of families Asteroceratinae and Eoderoceratidae. These are accompanied by far less numerous Oxynoticeratidae, Echioceratidae and Hypasteroceratinae. Ammonites of the subfamily Asteroceratinae are relatively scarce in Bed 4 but are the essential part of the association of Bed 5. Asteroceratinae of the Bed 4 include Caenisites and Carpathiceras gen. nov. Bed 5 contains Asteroceras, Eparietites and Epophioceras. Eoderoceratidae are represented by Microderoceras, Xipheroceras and Promicroceras. Echioceratidae include Tmaegophioceras, Hypastero ceratinae are represented by Hypasteroceras and Oxynoticeratidae by Oxynoticeras. For a peculiar form with an intermediate morphology between Arietitidae and Oxynoticeratidae, Chtelnicaceras nov. gen. is introduced here. The age range of the condensed Bed 4 is from the middle– late Bucklandi Chronozone to Turneri Chronozone. The age range of Bed 5 is emended here, representing the Obtusum to early Raricostatum Chronozone.

Sedimentary archives of climate and sea-level changes during the Holocene in the Rhône prodelta (NW Mediterranean Sea)

A 7.38 m long sediment core was collected from the eastern section of the Rhône prodelta (NW Mediterranean) at 67 m water depth. A multi-proxy study (including sedimentary facies, benthic foraminifera, ostracods, and clay mineralogy) provides a multi-decadal to century-scale record of climate and sea-level changes during the Holocene. The early Holocene is marked by alternative silt and clay layers interpreted as distal tempestites deposited in a context of rising sea level. This interval contains shallow infra-littoral benthic meiofauna (e.g., Pontocythere elongata, Elphidium spp., Quinqueloculina lata) and formed between ca. 20 and 50 m water depth. The middle Holocene (ca. 8.3 to 4.5 ka cal. BP) is characterized, at the core site, by a period of sediment starvation (accumulation rate of ca. 0.01 cm yr−1) resulting from the maximum landward shift of the shoreline and the Rhône outlet(s). From a sequence stratigraphic point of view, this condensed section, about 35 cm thick, can be identified on seismic profiles as a maximum flooding surface that marks the transition between delta retrogradation and delta progradation. The transition between the early Holocene deposits and the middle Holocene condensed section is marked by a gradual change in all proxy records. Following the stabilization of sea level at a global scale, the late Holocene is marked by the establishment of prodeltaic conditions at the core site, as shown by the lithofacies and by the presence of benthic meiofauna typical of the modern Rhône prodelta (e.g., Valvulineria bradyana, Cassidulina carinata, Bulimina marginata). Several periods of increased fluvial discharge are also emphasized by the presence of species commonly found in brackish and shallow-water environments (e.g., Leptocythere spp.). Some of these periods correspond to the multi-decadal to centennial late Holocene humid periods recognized in Europe (i.e., the 2.8 ka event and the Little Ice Age). Two other periods of increased runoffs at ca. 1.3 and 1.1 ka cal. BP are recognized, which are likely to reflect periods of regional climate deterioration that are observed in the Rhône watershed. Conversely, the Migration Period Cooling (ca. 1.4 ka cal. BP) and the Medieval Climate Anomaly (ca. AD 950–1250) correspond locally to periods of increased dryness.

Taphocoenoses and diversification patterns of calcimicrobes and calcareous algae, Ordovician, Tarim Basin, China

Despite the crucial role of epibenthic primary producers (cyanobacteria, green and red algae), no diversity curves for calcimicrobes and calcareous algae are available to assess the pyramiding paleoecology characterizing the Ordovician biodiversification episode. A total of 24 taxa of calcimicrobes and calcareous algae are identified from a Dapingian to lower Katian succession of carbonate sedimentary rocks exposed at the Leyayilitag ridge, Bachu Uplift, Tarim Basin, northwest China. Calcimicrobes (14 taxa), Dasycladales (seven taxa), Bryopsidales (one taxon), and Cyclocrinales (two taxa) contribute to five distinct taphocoenoses characterizing a suite of carbonate mounds. In stratigraphic order, these are calathid sponge mounds, algal calcimicrobial mounds, algal mounds, algal reefs, and calcimicrobial mounds. Within the lower Katian Belodina confluens Zone, the diversity increases substantially from around 5 to more than 20 taxa per 2 Ma. This increase in diversity is based on new calcimicrobes (Bija, Ortonella, Garwoodia, Hedstroemia, Rothpletzella, Phacelophyton, Rauserina) and the diversification of Dasycladales and Cyclocrinales. By comparison, the global diversity of calcimicrobes and calcareous algae (derived from literature data) started to increase earlier, namely within the late Darriwilian Pygodus serra Zone (offset of about 4 Ma). This offset might be due to the peculiar lithology of the Sandbian Tumuxiuke Formation (condensed section of red nodular limestones bounded by disconformities). However, a similar temporal offset is recorded for calathid sponge mounds; therefore, the Tarim tectonic microplate (Tarim Block) might display an endemic–anachronistic character. The diversity curves of Ordovician benthic primary producers (calcimicrobes, calcareous algae) are similar to those recorded by some fossil groups, in particular eleutherozoan echinoderms.

Palynological Zonations and Sequence Stratigraphic Analysis of Sediments in Benin West-1, Anambra Basin, Nigeria

Palynoflora analyses from Benin west -1, Anambra Basin has unfold three palynozones based on abundance, composition of palynoflora and cluster analysis. Palynozone-1 has been dated as Late Maastrichtian age and belong to the lowermost Imo Shale, palynozone-2; Middle Eocene and palynozone -3 is dated Lutetian to Bartonian age. Sediments between depth intervals of 2649-2560 m is marked a sequence boundary, 1650-2560 m, and 970-1190 m is delineated as high stand system tract. Shaly intervals from the depth of 1644 m, and 1234 m recorded acme of palynoflora (Zonocostites ramonae, Monoporites annulatus, Verrucatosporites spinosus, Botryococcus braunii) and probably fingerprints a condensed section. The condensed section intervals (1644 m and 1234 m) may depict good source rock and exploration targets.

Taphonomic analysis and sequence stratigraphy of the Albarracinites beds (lower Bajocian, Iberian range, Spain). An example of shallow condensed section

Several ammonite fossil assemblages from Sierra de Albarracín (Teruel, Castilian Branch) contain abundant specimens of the Ovale and Laeviuscula zones (lower Bajocian, Middle Jurassic), including microconchs and macroconchs of the characteristic genus Albarracinites. Over 1500 ammonites from the type horizon of the species A. albarraciniensis, in the outcrop of Masada Toyuela, have been studied. Ammonites are commonly preserved as phosphatized, calcareous, concretionary internal moulds (mean size = 50.5 mm) of unflattened shells, partially or completely filled with relatively heterogeneous mudstone to wackestone sediment. Incomplete, fragmented phragmocones with calcitic septa are the dominant remains, generally bearing traces of rounding, incrustation and bioerosion. Taphonomic data, such as the predominant taphonomic populations of type 3, composed of reelaborated, relatively heterogeneous concretionary internal moulds, isolated concretionary body chambers and hollow ammonites, bearing traces of abrasion, bioerosion and encrusting organisms, are indicative of low rate of sedimentation and occasional high rate of sediment accumulation, due to sedimentary winnowing and bypassing interrupted by storm depositional events, in shallow-water marine environments. The exceptional occurrence of taphonic populations of type 2 belonging to Albarracinites and Hebetoxyites, with dominant shells of pre-adults and absence of juveniles, suggests autochthonous biogenic production of shells by indigenous populations of Sub-Mediterranean taxa at the Iberian platform system. In the outcrop of Masada Toyuela, the Albarracinites beds correspond to a condensed section, developed in shallow-water, open-marine, carbonate environments of the External Castilian platform. The sharp, irregular base of beds and the normal grading of reworked elements suggest these carbonate deposits were affected by tractive currents, scouring and redeposition. Limestone beds represent storm-related sedimentary events, whereas the local marly intervals represent background-sedimentation time-intervals of winnowing and bypassing on the seafloor. This condensed section is composed of at least four, decimetric or centimetric, expanded-deposit intervals, stacked and showing an overall thinning upward, which constitute a deepening sequence developed during two biochrons. Taphonomic results also corroborate the development of an incipient-deepening phase, which represents the first episode of a deepening half-cycle of third order, in the Albarracín area within the Castilian platform, during the Ovale and Laeviuscula biochrons (early Bajocian).