The type of Aplosmilia vidali Angelis d’Ossat, 1905 (Scleractinia; Early Cretaceous)

Se revisa la especie de coral escleractinio Aplosmilia vidali Angelis d’Ossat, 1905 del Cretácico inferior y se le asigna un lectotipo. La forma solitaria pertenece al género Tiarasmilia y es probablemente un sinónimo anterior a la especie-tipo de este género, Tiarasmilia casteri Wells, 1932.Se revisa la especie de coral escleractinio Aplosmilia vidali Angelis d’Ossat, 1905 del Cretácico inferior y se le asigna un lectotipo. La forma solitaria pertenece al género Tiarasmilia y es probablemente un sinónimo anterior a la especie-tipo de este género, Tiarasmilia casteri Wells, 1932.The Early Cretaceous Scleractinian coral species Aplosmilia vidali Angelis d’Ossat, 1905 is revised and a lectotype is designated. The solitary coral belongs to the genus Tiarasmilia and is probably a senior synonym of the type species of this genus, Tiarasmilia casteri Wells, 1932

Remarks on the genus Angelismilia Reig, 1988 (Scleractinia, Early Cretaceous)

Puntualizaciones sobre el género Angelismilia Reig. 1988 (Scleractinia, Cretácico temprano). Se revisa el género AngelismiliaReig, 1988, un coral del Albiense temprano, en base a un sintipo y a material adicional procedentedel área de los tipos. Angelismilia, anteriormente considerado un coral con septos perforados y establecido sin una posición sistemática, tiene septos compactos y palios, siendo asignado a la familia Caryophylliidae.The Early Albian coral genus AngelismiliaReig, 1988 is revised using a syntype of the type species as well as topotypical material from the type area. Angelismilia, formerly considered a coral with perforated septa that was created without indicating its systematic position, has compact septa and pali. For this reason it is placed in the family Caryophylliidae.Puntualizaciones sobre el género Angelismilia Reig. 1988 (Scleractinia, Cretácico temprano). Se revisa el género AngelismiliaReig, 1988, un coral del Albiense temprano, en base a un sintipo y a material adicional procedentedel área de los tipos. Angelismilia, anteriormente considerado un coral con septos perforados y establecido sin una posición sistemática, tiene septos compactos y palios, siendo asignado a la familia Caryophylliidae

The genus BrachyserisAlloiteau 1946/47 and remarks on Latimaeandraraea felixi Angelis d’Ossat, 1905 (Scleractinia; Cretaceous)

El género BrachyserisAlloiteau 1946/47 y puntualizaciones sobre Latimaeandraraea felixiAngelis d’Ossat, 1905 (Scleractinia; Cretácico). Se estudia el coral Latimaeandraraea felixidel Albiense temprano mediante láminas delgadas obtenidas a partir de su holotipo. Ello ha permitido precisar la estructura de detalle del esqueleto y su posición sistemática, aunque su asignación genérica es cuestionable. La especie se relaciona con el género Brachyserisaunque se distingue por la ausencia del patrón típico (la formación de murallas toliformes en dos niveles distintos) del género. Se revisa el género Brachyserisen base al holotipo y a material topotípico de la especie-tipo. El género está relacionado con otros géneros de la familia Leptophylliidae como Microphyllia, Thalamocaeniopsis, Trigerastraea y Vallimeandray, muy probablemente, está limitado al Cretácico tardío.The Early Albian coral species Latimaeandraraea felixi is investigated on the basis of thin sections obtained from the holotype. Its fine skeletal structure and systematic position are elucidated, but its generic position remains questionable. It is most closely related to the genus Brachyserisfrom which it differs by lacking the typical pattern (forming tholiform walls in two different levels) of this genus. The genus Brachyserisis considered in greater detail on the basis of the holotype and topotypical material of the type species. It is related to other Leptophyllid genera such as Microphyllia, Thalamocaeniopsis, Trigerastraea and Vallimeandra, but is very probably restricted to the Late Cretaceous

Suppression of ferromagnetism in CeSi_1.81 under temperature and pressure

We have studied the pressure dependence of the magnetization of single crystalline CeSi_1.81. At ambient pressure ferromagnetism develops below T_C = 9.5 Below ~ 5 K an additional shoulder in low-field hysteresis loops and a metamagnetic crossover around 4 T suggest the appearance of an additional magnetic modulation to the ferromagnetic state. The suppression of the magnetic order in CeSi_1.81 as function of temperature at ambient pressure and as function of pressure at low temperature are in remarkable qualitative agreement. The continuous suppression of the ordered moment at p ~ 13.1 kbar suggests the existence of a ferromagnetic quantum critical point in this material.Comment: 9 pages, 9 figures, to be published in Physical Review

Corals on the slope (Aptian, Maestrat Basin, Spain)

The term "reef" has been frequently misused when applied to fossil coral communities. Our popular but biased view of coral community structure based on the idyllic picture of recent tropical reefs has failed to recognize that, in many fossil examples, alternative states of community structure with no or limited framework may occur. The Aptian colonial scleractinians analysed in the western Maestrat Basin (eastern Spain) constitute an example of non-reef-building coral populations, which thrived in marly slope settings. These corals developed within the photic zone but below the storm wave-base. All colonies are found well-preserved in life position. They are mostly decimetres in size and mainly occur isolated giving rise to a continuous and uniform (dominated by domal and massive forms) unbound growth fabric with a low to medium degree of development (coral skeletal volume = 5-20%). Occasionally, however, colonies growing on top of each other forming small metre-sized bioherms are also present. A total of 21 species were identified. Coral diversity in each sample location varies between three and nine species. These numbers of species are comparable with those exhibited by coeval coral assemblages from other basins of the Tethys, but are comparatively low when compared with diversities exhibited by many Recent and fossil coral communities. The corals studied apparently found optimal ecological conditions for their development on the marly slopes of the western Maestrat Basin. This is primarily expressed in the unusually large dimensions (up to 2.3 m in width) of some of the coral colonies when compared to other Cretaceous occurrences, and in the persistence and resilience of the coral populations. The observed coral genera and species (suborders Archeocaeniina, Faviina, Fungiina and Microsolenina) are very common in the time interval between the Barremian and the Early Albian and most of them have been reported from several other localities in the western and central Tethyan realm. In addition, the coral-bearing levels also contain the poorly known and exotic genera Agrostyliastraea and Procladocora. There are no significant differences at species level or in community structure between the Early and Late Aptian faunas investigated. Therefore, the coral communities as well as the environmental conditions controlling them would have been relatively stable during the time intervals when these corals flourished. An important palaeoecological implication is that comparatively low species diversities and the absence of reef frameworks do not necessarily imply unfavourable environmental conditions for coral growth. Furthermore, this study may serve as an example for the analysis of other level-bottom coral communities displaying a loose growth fabric

Magnetic behavior of single crystalline Ho2_2PdSi3_3

The magnetic behavior of single-crystal Ho$_2$PdSi$_3$, crystallizing in an AlB$_2$-derived hexagonal structure, is investigated by magnetic susceptibility ($\chi$) and electrical resistivity ($\rho$) measurements along two directions. There is no dramatic anisotropy in the high temperature Curie-Weiss parameter or in the $\rho$ and isothermal magnetization data, though there is a noticeable anisotropy in the magnitude of $\rho$ between two perpendicular orientations. The degree of anisotropy is overall less prominent than in the Gd (which is an S-state ion!) and Tb analogues. A point of emphasis is that this compound undergoes long range magnetic ordering below 8 K as in the case of analogous Gd and Dy compounds. Considering this fact for these compounds with well-localised f-orbital, the spin glass freezing noted for isomorphous U compounds in the recent literature could be attributed to the role of the f-ligand hybridization, rather than just Pd-Si disorder.Comment: Physical Review B, in pres

Electronic structure and nesting-driven enhancement of the RKKY interaction at the magnetic ordering propagation vector in Gd2PdSi3 and Tb2PdSi3

We present first-time measurements of the Fermi surface and low-energy electronic structure of intermetallic compounds Gd2PdSi3 and Tb2PdSi3 by means of angle-resolved photoelectron spectroscopy (ARPES). Both materials possess a flower-like Fermi surface consisting of an electron barrel at the G point surrounded by spindle-shaped electron pockets originating from the same band. The band bottom of both features lies at 0.5 eV below the Fermi level. From the experimentally measured band structure, we estimate the momentum-dependent RKKY coupling strength and demonstrate that it is peaked at the 1/2 GK wave vector. Comparison with neutron diffraction data from the same crystals shows perfect agreement of this vector with the propagation vector of the low-temperature in-plane magnetic order, thereby demonstrating the decisive role of the Fermi surface geometry in explaining the complex magnetically ordered ground state of ternary rare earth silicides.Comment: 4 pages, 4 figure