8 research outputs found
Silurian graptolite biostratigraphy of the RöstÄnga-1 drill core, Scania:a standard for southern Scandinavia
The Rostanga-1 core from west-central Scania provides the most complete succession of the Sandbian (Upper Ordovician) through lower Telychian (Silurian, Llandovery) strata of southern Scandinavia. The Hirnantian is identified in the Kallholn Formation by the presence of a Metabolograptus persculptus Biozone fauna. The Akidograptus ascensus, Parakidograptus acuminatus, Cystograptus vesiculosus and Monograptus revolutus biozones can be differentiated in the Rhuddanian. Following a considerable gap (Demirastrites triangulatus Biozone to a level within the Pribylograptus leptotheca Biozone), the succession resumes. The Aeronian also includes the Lituigraptus convolutus and Stimulograptus sedgwickii biozones. The Stimulograptus halli Biozone appears to be missing, but the Telychian Spirograptus guerichi to Streptograptus crispus biozones have been recognized
Advances in the Ordovician graptolite biostratigraphy of the St Petersburg area, Russia
The Ordovician shallow-water shelf deposits rich in benthic fauna are exposed along the Russian part of the BalticâLadoga Klint. Graptolites occur only at some stratigraphic levels, being comparatively numerous in marls and clays and very rare in carbonate layers. Since the 19th century graptolites have been collected from exposures of the Pakerort, Hunneberg, Billingen, and Volkhov regional stages (TremadocianâDapingian), while in the UhakuâIdavere stratigraphic interval (Darriwilianâlower Sandbian) rare graptolites have been found in boreholes. Up to now, only some collections have been systematically studied. On the basis of new graptolite finds, recently the Pterograptus elegans Biozone was established in the upper Aseri Stage and the Nemagraptus gracilis Biozone in the lower Kukruse Stage. Detailed sampling of the Shundorovo Formation (upper Idavere Stage) resulted in the discovery of numerous diplograptids at five stratigraphic levels, in association with various dendroids. These diplograptids were provisionally assigned to ?Archiclimacograptus antiquus lineatus Elles & Wood. A systematic description of the late Darriwilian and early Sandbian diplograptids is under preparation
The Rapid Outbursting Star GM Cep: An EX-or in Tr 37?
We present optical, IR and millimeter observations of the solar-type star
13-277, also known as GM Cep, in the 4 Myr-old cluster Tr 37. GM Cep
experiences rapid magnitude variations of more than 2 mag at optical
wavelengths. We explore the causes of the variability, which seem to be
dominated by strong increases in the accretion, being similar to EX-or
episodes. The star shows high, variable accretion rates (up to ~10
Msun/yr), signs of powerful winds, and it is a very fast rotator (Vsini~43
km/s). Its strong mid-IR excesses reveal a very flared disk and/or a remnant
envelope, most likely out of hydrostatic equilibrium. The 1.3 millimeter fluxes
suggest a relatively massive disk (Mdisk~0.1 Msun). Nevertheless, the
millimeter mass is not enough to sustain increased accretion episodes over
large timescales, unless the mass is underestimated due to significant grain
growth. We finally explore the possibility of GM Cep having a binary companion,
which could trigger disk instabilities producing the enhanced accretion
episodes.Comment: 43 pages, including 10 figures, ApJ in pres
Optical photometry of GM Cep: evidence for UXor type of variability
Results from optical photometric observations of the pre-main sequence star
GM Cep are reported in the paper. The star is located in the field of the young
open cluster Trumpler 37 - a region of active star formation. GM Cep shows a
large amplitude rapid variability interpreted as a possible outburst from EXor
type in previous studies. Our data from BVRI CCD photometric observations of
the star are collected from June 2008 to February 2011 in Rozhen observatory
(Bulgaria) and Skinakas observatory (Crete, Greece). A sequence of sixteen
comparison stars in the field of GM Cep was calibrated in the BVRI bands. Our
photometric data for a 2.5 years period show a high amplitude variations (Delta
V ~ 2.3m) and two deep minimums in brightness are observed. The analysis of
collected multicolor photometric data shows the typical of UX Ori variables a
color reversal during the minimums in brightness. On the other hand, high
amplitude rapid variations in brightness typical for the Classical T Tauri
stars also present on the light curve of GM Cep. Comparing our results with
results published in the literature, we conclude that changes in brightness are
caused by superposition of both: (1) magnetically channeled accretion from the
circumstellar disk, and (2) occultation from circumstellar clouds of dust or
from features of a circumstellar disk.Comment: 7 pages, 3 figures, accepted for publication in Ap&S
New records of brachiopods and crinoids from the Silurian (Wenlock) of the southern Urals, Russia
Crinoids and brachiopods are described from the Silurian Uzyan Formation of the Zilair Zone in the southern Urals. The occurrence of the graptolites Coronograptus praedeubeli suggests a late Homerian (Wenlock) age for the strata. A new disparid crinoid, Cicerocrinus gracilis Donovan sp. nov., is the oldest known member of this genus. It has a long, flexible and homeomorphic column, and a tall bryozoan palaeontology terminology (IBr2) (second primibrachial) axillary. All species of Cicerocrinus described previously have been limited to the Ludlow of the British Isles, Sweden and Estonia, and the Pridoli of Estonia. The poorly preserved brachiopod fauna is represented by small atrypid (Atrypa? sp.) and dalmanellid brachiopods (Levenea? sp.). The reported assemblage generally inhabited deep-water environments