1,721,214 research outputs found
The contribution of fossils to chronostratigraphy, 150 years after Albert Oppel
No full textThe 150th anniversary of the death of Albert Oppel (1831–65) provided the opportunity to celebrate this outstanding stratigrapher with a Thematic Issue dedicated to the importance of fossils for dating and correlating of sedimentary rocks. In this issue, we analyse Oppel’s significant contribution to modern chronostratigraphy, before exploring the Phanerozoic through all its major fossil groups, to verify if fossils are still able to make a significant contribution to chronostratigraphy. The extraordinary merit of Oppel’s work has been the demonstration that fossils can be used to sub-divide sedimentary sequences into zones, which in turn might be organized in higher chronostratigraphical units. The zone for Oppel is characterized by the distinctive fossil content, and his view strongly influenced the development of the standard chronostratigraphical scale for about one century, until the introduction, in the 1950s, of the log-based range chart as the common practice to study the fossil record of sedimentary successions. This approach forced the stratigraphers to shift the focus from the fossil content of the zones to their boundaries. This new view allowed for the introduction of new kind of zones with precisely defined boundaries based on bioevents and to the decline of the Oppel Zone. This turning point in the history of chronostratigraphy was fuelled by the International Commission on Stratigraphy programme of definition of the units of the International Chronostratigraphic Chart based on the boundary stratotype and point (GSSP) concept, which started in 1973
Calcareous nannofossil from the hemipelagic lower Ypresian Arnakatxa section (Basque-Cantabrian basin, western Pyrenees)
No full textHere we present calcareus nannofossil and colour datasets from the hemipelagic lower Ypresian Arnakatxa section (Basque-Cantabrian basin, western Pyrenees). The Arnakatxa coastal cliffs, which constitute the present study area, are located approximately 15 km northwest of Bilbao (43°23'34.4N, 2°59'24.2W, altitude 0 m). The expanded hemiplegic succession offered a potentially valuable orbitally paced geological record. Sampling was carried out in 2015. For the study of calcareous nannofossils 65 hand samples were collected (average spacing of about 50 cm). For colour analysis, 635 rock-powder samples were collected (average resolution of ~5 cm) using a standard cordless drill with an 8 mm bit. Slides for nannofloral analysis were prepared according to Flores and Sierro (1997), avoiding any mechanical or physical disturbance of the samples that could modify the original fossil assemblages. A Zeiss Axioplan2 petrographic microscope at 1250× magnification was used to analyze the samples. Quantitative analysis was performed by counting at least 300 specimens per sample. Additionally, three random traverses (~9 mm2) were analyzed on each slide in order to detect rare but biostratigraphically significant species. The rock powder samples were stored in transparent antiglare prismatic plastic vials (3 ml) and scanned at high-resolution (600 dpi) using a desktop office scanner in a dark room. The average colour value of a homogeneous rectangular area covering 10-20% of the scanned image of each vial was measured using ImageJ software version 1.50i. Average colour value represents to the mean pixel RGB value of the selected area, which is equivalent to the brightness value. In order to perform a cyclostratigraphic analysis, the colour data series was linearly interpolated and the LOESS regression trend subtracted. The Astrochron code commands used to perform that spectral analysis are herein available
(Fig. 5) Stratigraphic distribution of middle Paleogene calcareous nannofossils in the Bottaccione section, Italy
No full textPoint distance is the sample level (m). Species abundance: A = abundant (>10 %), C = common (1-10 %), F = few (0.1-1 %), R = rare (<0.1 %), - = not presen
(Table 5) Abundance of selected helicoliths at DSDP Site 82-563 in the North Atlantic
No full textRelative to a count of about 1500 coccoliths and plotted as number of specimens/1000 nannofossil
(Table 6) Abundance of selected discoasters at DSDP Site 82-563 in the North Atlantic
No full textRelative to a count on about 3000 coccoliths and plotted as number of specimens/1000 nannofossils. Abundance of D. deflandrei and D. signus are relative to 100 discoaster
(Fig. 7) Stratigraphic distribution of Paleogene calcareous nannofossils in the Contessa Highway section, Italy
No full textPoint distance is the sample level (m). Species abundance: A = abundant (>10 %), C = common (1-10 %), F = few (0.1-1 %), R = rare (<0.1 %), - = not presen
(Table 2) Calcareous nannofossil distribution and relative abundance in ODP Hole 114-703A
No full textSpecies abundances: A = Abundant (1 specimen per field of view), C = common (1 specimen per 1 to 2 fields), F = few (1 specimen per 2 to 10 fields), R = rare (1 specimen per 10 to 100 fields), RR = very rare (1 specimen per >100 fields), - = not present
(Table 3) Distribution of calcareous nannofossils at DSDP Site 82-563 in the North Atlantic
No full textDerived from a count of 500 specimens; Discoaster druggii and Discoaster kugleri are indicated as number of specimens relative to about 3000 coccoliths. The presence of species out of a count of 500 coccoliths is indicated with <0.
(Table 4) Distribution of sphenoliths at DSDP Site 82-563 in the North Atlantic
No full textDerived from a count of 100 specimens. The presence of species out of a count of 100 sphenoliths is indicated with <0.
The Scaglia Toscana Formation of the Monti del Chianti: new lithostratigraphic and biostratigraphic data
Full text linkThe Scaglia Toscana Formation (Scisti Policromi Auctt.) is one of the most investigated formations of the Tuscan Nappe. The formation is widely exposed in the Chianti Mounts and despite the number of studies in this area, some aspects remain poorly known and debated.In this paper new litho- and bio-stratigraphic data from eight key-sections distributed over the entire area are provided and discussed in order to clarify the stratigraphic relationships among different lithostratigraphic members, as well as the depositional ages of each member. The formation was deposited in the Cretaceous-Oligo-cene time interval and it can be subdivided into five lithostratigraphic members: i) the “Argilliti di Brolio” (wine-red shales with sporadic siliceous calcilutites and rare interbedded cherts); ii) the “Marne del Sugame” (red and pink marls, calcareous marls and marly limestones
with interbedded calcarenitic beds and ruditic lens-shaped bodies including calcareous-siliceous clasts); iii) the “Argilliti di Cintoia” (grey-green to black shales, locally with manganese-rich siliceous calcilutites and cherts); iv) the “Calcareniti di Montegrossi” (thin beds of calcilutites and calcarenites with varicoloured shaly-marly interbeds); and v) the “Argilliti e Calcareniti di Dudda” (alternating thin beds of calcilutites and calcarenites with varicoloured shaly-marly interbeds). These members were deposited in a marine environment and have been interpreted as deposited in a turbiditic system, in which shaly and calcareous turbiditic members have been attributed to a basin plain below the CCD, whereas the marls and marly limestones of the Marne del Sugame Member were deposited in a slope/ramp environment above or close to the CCD. Furthermore, the combination of these new
data with structural informations coming from the literature allowed a better paleogeographic reconstruction of the paleobasin. In order to better explain these data, the paper is accompanied by two geological maps realized in the past but never distributed. The two geological maps, at the scale of 1:25,000, cover the whole area from the Cintoia (south of Florence) to the San Gusmè (north of Siena) villages
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