Step-wise extinctions at the Cretaceous-Tertiary boundary and their climatic implications

A comparative study of planktonic foraminifera and radiolarian assemblages from the Cretaceous-Tertiary (K-T) boundary section of the Beloc Formation in the southern Peninsula of Haiti, and the lowermost Danian sequence of the Micara Formation in southern Cuba reveals a remarkable pattern of step-wise extinctions. This pattern is consistent in both places despite the widely different lithologies of the two formations. Because of a step-wise extinction and the delayed disappearance of taxa known to be more representative of cooler water realms, it is inferred that a cooling trend which characterized the close of the Maastrichtian and the onset of the Tertiary had the major adverse effect on the existing biota. Although repetitive lithologic and faunal fluctuations throughout the Maastrichtian sediments found at Deep Sea Drilling Project (DSDP) site 146/149 in the Caribbean Sea indicate variations reminiscent of known climatically induced cycles in the Cenozoic, rapid biotic succession appears to have taken place during a crisis period of a duration greater than 2 mission years. Widespread and abundant volcanic activities recorded in the Caribbean area during the crisis period gives further credence to earlier contention that intense volcanism may have played a major role in exhacerbating pre-existing climatic conditions during that time

Paleomagnetic Results from the Cretaceous Dumisseau Formation of Haiti

Paleomagnetic studies of basalts and sediments from the Dumisseau Formation show that: 1) The basalt magnetizations are characterized by very low coercivlty components. The sediments have generally higher but more variable stabilities against alternating field (AF) treatment compared to the basalts. The 200 oe AF mean directions for the Dumlsseau basalt and sediment sites tend to fall near the present geomagnetic dipole field direction corresponding to the Latitude of Haiti. It is suggested that these rocks carry predominantly secondary magnetization of recent origin and there is little evidence for the preservation of remanent magnetization which may correspond to the time of formation of the rock units in the Late Cretaceous. 2) The remanent magnetic properties of the basalts, particularly those from the upper part of the formation in the Dumisseau area, are very similar to those reported for basalts recovered in the Caribbean DSDP Leg 15, Sites 146, 150, 151, 152 and 153, suggesting also similarities in their petrotectonic origin

Towards new insights in the phylogeny of the Spermacoce clade: an integrative taxonomic approach using morphology, anatomy, ecology and phylogenetics reveáis the new genus Leonoria

Phylogenetic inference analyses o f two nuclear and four plastid DNA markers from 82 accessions representing 19 genera o f the Spermacoce clade (Spermacoceae-Rubiaceae) confirm that the Brazilian genus Denscantia is biphyletic. By the analyses o f reproductive morphological characters, foliar morpho-anatomy and histochemical, geographical distribution ranges, and ecological niche derived from climatic space, Denscantia caldcóla is shown as a distinct lineage from the other Denscantia species, indicating its taxonomic segregation into a new monospecific genus Leonoria. Significant morphological diíferences o f Leonoria with Denscantia were found in inflorescence organization, stigma shape, fruit dehiscence, and pollen morphology. Morphoanatomical variation among leaf traits were found in epidemial cells, occurrence o f trichomes, mesophyll histochemical, and vascular organization. Analysis o f occurrence records o f 205 specimens demonstrates a clear ecological distinction between o f Denscantia s.s. and Leonoria, which is ecologically confined to limestone outcrops associated with seasonally dry forests. The current study demonstrates the importance of an integrative taxonomic approach - in which múltiple disciplines are combined - to the unravel complex taxonomic pattems within Rubiaceae. The genus Leonoria, to be newly described, is dedicated to Professor Elsa Leonor Cabral

Productividad cianobacteriana, variaciones del carbono orgánico y facies de la Formación Indidura (Cenomaniano-Turoniano), noreste de México

Las rocas de edad Cenomaniano-Turoniano normalmente asignadas a la Formación de Indidura en México nororiental (Estado de Coahuila) contienen facies distintivas que son indicativas de una variabilidad espacial importante a través de la plataforma de carbonatos. Se han seleccionado tres secciones estratigráficas para probar si estas diferencias existen. La sección de Las Delicias (estratotipo) esta caracterizada por capas naranja claro de biocalciruditas (10-30 centímetros de espesor). Las estructuras internas primarias están ausentes. Los aloquímicos consisten esencialmente en asociaciones ricas en fósiles de equinodermos, pelecípodos, así como amonitas y foraminíferos planctónicos. El contenido de carbonato total (CaCO3) varía entre 48% y 94%, y el contenido de carbono total orgánico (TOC) entre 0,7% y 1,5%.La sección del Cañón La Casita, está al sureste de Las Delicias. Esta consiste en capas café claro amarillento de biocalcilutitas y lutitas laminadas verde oliva a grises con espesores de 3 a 30 cm. No se observa ninguna estructura interna deposicional; en las secciones delgadas se observa claramente abundante bioturbación. Los aloquímicos esencialmente son fragmentos esparcidos de foraminíferos planctónicos y radiolarios concentrados en madrigueras. El carbonato total (CaCo3) varía entre el 0,8% y 59,3%, mientras que el TOC varia entre el 0,17% y 5,8%. En contraste con estas sucesiones pobremente laminadas, en la Sierra de Parras, al sur de La Delicias y al oeste de la Casita, la sucesión se presenta como intercalaciones rítmicas de lutitas laminadas grisverdosas y negroparduzcas con espesores de 8 a 200 cm y biocalcilutitas margosas de 5 a 100 cm de espesor. Ambas facies exhiben estructuras internas similares organizadas en forma de laminillas duales paralelas “varvas” de < 3 mm de espesor, que contienen escasos foraminíferos planctónicos esparcidos en las laminillas oscuras. No se hay restos de epifauna, salvo esporádicos pelecípodos (Inocerámidos). El contenido de carbonato total (CaCO3) varía entre 43% y 78,3%, mientras que el contenido de TOC es relativamente alto con valores entre 7,3% y 24,3%, consistentemente superiores a 20%. La observación, de las laminillas presentes en las facies del área de Parras, muestra que sus diferencias composicionales están asociadas a la variabilidad en la abundancia de esferas microscópicas o “micro-oolitos.” Estas estructuras son interpretadas como de un posible origen cianobacteriano y se entienden como ciclos que representan eventos de florecimientos de cianobacterias, las cuales permanecieron dominantes a lo largo de la sucesión. Aún más, las lutitas laminadas y biocalcilutitas negras y ricas en TOC de la región de Parras documentan unas condiciones paleoceanográficas únicas, las cuales estaban caracterizadas por aguas oceánicas relativamente pobres en oxígeno.La distribución de la epifauna y las variaciones de carbón/carbonato en la región de Parras, sugieren que en los fondos de acumulación hubo fuertes eventos rítmicos de disoxia/anoxia. Esto contrasta claramente con los sedimentos de las áreas de Las Delicias y de La Casita, en las que se documentan condiciones del fondo diferentes, donde la epifauna bentónica y la fauna planctónica y nectónica pudieron proliferar. Asumiendo que estas facies son coetáneas, los análisis de microfacies y de TOC de estas rocas demuestran aún más las diferencias entre estas áreas

A Large Brightness Enhancement of the QSO 0957+561 A Component

We report an increase of more than 0.2 mag in the optical brightness of the leading image (A) of the gravitational lens Q0957+561, detected during the 09/2000 -- 06/2001 monitoring campaign (2001 observing season). The brightening is similar to or even greater than the largest change ever detected during the 20 years of monitoring of this system. We discuss two different provisional explanations to this event: intrinsic source variability or microlensing (either short timescale microlensing or cessation of the historical microlensing). An exhaustive photometric monitoring of Q0957+561 is needed until summer of 2002 and during 2003 to discriminate between these possibilities.Comment: 13 pages including 3 figures and 1 table. Accepted for publication in ApJ Let

Does the current taxonomic delimitation of Galianthe find support in phylogenetic perspective?

Galianthe Griseb. is a neotropical genus comprising 50 species divided into two subgenera: G. subgen. Galianthe (41 spp.), characterized by homogeneous morphological traits, with species further divided into two sections (G. secc. Galianthe and G. secc. Laxae); and G. subgen. Ebelia (14 spp.) with more heterogeneous morphological characteristics. Due to its morphological similarity with other genera, Galianthe has historically been associated with Borreria, Spermacoce, Diodia (based on fruit type), as well as Denscantia and Emmeorhiza (based on inflorescence type). In recent years, molecular studies have established Galianthe as a basal genus within the Spermacoce clade, closely related to other genera such as Carajasia and Schwendenera. Despite the progress made in recent molecular studies, the studies have focused on a limited number of species within the genus, failing to encompass all infrageneric categories. Questioning of the current taxonomic delimitation of the genus, this study aims to test the monophyly of Galianthe and explore its infrageneric and interspecific phylogenetic relationships. Three markers (two nuclear: ITS, ETS, and one plastid: rps16) were utilized, encompassing 107 entities, including 42 Galianthe species, thereby representing 76% of the current genus diversity, as well as 17 closely related genera within the Spermacoce clade. The phylogenetic results confirm the monophyly of Galianthe, revealing the presence of three major subclades. Subclades I and II comprise several G. subgen. Ebelia species, whereas subclade III consists of all G. subgen. Galianthe species plus G. angulata. Regarding the sections, monophyly was not supported. Based on these findings, it can be concluded that G. subgen. Ebelia is paraphyletic, G. subgen. Galianthe is potentially paraphyletic due to G. angulata, and there is no clear distinction between the sections

Operator independent reliability of direct augmented reality navigated pedicle screw placement and rod bending

Background AR based navigation of spine surgeries may not only provide accurate surgical execution but also operator independency by compensating for potential skill deficits. “Direct” AR-navigation, namely superposing trajectories on anatomy directly, have not been investigated regarding their accuracy and operator's dependence. Purpose of this study was to prove operator independent reliability and accuracy of both AR assisted pedicle screw navigation and AR assisted rod bending in a cadaver setting. Methods Two experienced spine surgeons and two biomedical engineers (laymen) performed independently from each other pedicle screw instrumentations from L1-L5 in a total of eight lumbar cadaver specimens (20 screws/operator) using a fluoroscopy-free AR based navigation method. Screw fitting rods from L1 to S2-Ala-Ileum were bent bilaterally using an AR based rod bending navigation method (4 rods/operator). Outcome measures were pedicle perforations, accuracy compared to preoperative plan, registration time, navigation time, total rod bending time and operator's satisfaction for these procedures. Results 97.5% of all screws were safely placed (<2 mm perforation), overall mean deviation from planned trajectory was 6.8±3.9°, deviation from planned entry point was 4±2.7 mm, registration time per vertebra was 2:25 min (00:56 to 10:00 min), navigation time per screw was 1:07 min (00:15 to 12:43 min) rod bending time per rod was 4:22 min (02:07 to 10:39 min), operator's satisfaction with AR based screw and rod navigation was 5.38±0.67 (1 to 6, 6 being the best rate). Comparison of surgeons and laymen revealed significant difference in navigation time (1:01 min; 00:15 to 3:00 min vs. 01:37 min; 00:23 to 12:43 min; p = 0.004, respectively) but not in pedicle perforation rate. Conclusions Direct AR based screw and rod navigation using a surface digitization registration technique is reliable and independent of surgical experience. The accuracy of pedicle screw insertion in the lumbar spine is comparable with the current standard techniques

Variaciones espaciales y temporales del registro del límite K/T en Haiti: implicaciones acerca del evento o eventos

El registro en la capa del límite K/T (KTB), en diferentes localidades de la Península Meridional de Haití, muestra claras evidencias de disrupciones físicas causadas por el impacto postulado de un bólico al final del Maastrichtiense. Tanto el registro bioestratigráfico como el litológico de la capa KTB, en diferentes localidades, muestra también diversos grados de mezcla, con componentes faunísticos de edades congruentes con los bioeventos característicos de la transición del límite, equivalentes a la parte terminal de la Zona de Abathomphalus mayaroensis y partes de las Zonas de Guembelitria cretacea y de Parvularugoglobigerina eugubina. La nanoflora calcárea también muestra taxones de la transición, concurrentes con los datos de foraminíferos, e indicativos de las Subzonas de Micula murus y Micula prinsii, así como de la Subzona de Cruciplacolithus primus (CP1a), del Paleoceno basal. La capa del límite tiene variaciones en su potencia, con un máximo de 75cm en el estratotipo de la Formación Beloc, y a techo de la capa principal tectítica hay un máximo de iridio. Los análisis geoquímicos y la datación radiométrica han demostrado también que las esférulas son tectitas (Premo e Izett, 1991) que pueden estar relacionadas cronológicamente con el evento de impacto registrado en Chicxulub, Yucatán, México, hace 65 Ma. Aún más, las delicadas estructuras sedimentarias primarias en la capa del límite son constantes en todos los afloramientos, aunque hay diferencias espaciales incluso a corta distancia. Además, en las áreas adyacentes al estratotipo (Platon Piton y Madame Toussaint) se encuentra una capa volcanogénica, bajo el nivel tectítico principal relacionado con el evento de Chicxulub, que muestra una laminación cruzada, tanto conspicua como críptica, indicativa de procesos de flujo complejos, multifásicos y subacuáticos que afectaron a la sedimentación de forma parecida a la del lecho KTB. Se conocen tales estructuras como características de la acción de ondas oscilantes sobre la cohesión de los sedimentos. El movimiento de las aguas asociado con un seiche es el único análogo actual conocido de un flujo subacuático que proporcione un mecanismo plausible para explicar el que varios niveles de la columna de agua, en una gran cuenca, pueden oscilar para desarrollar las estructuras observadas. Dada la magnitud del impacto del bólido, debieron desarrollarse ‘megaseiches’ en los océanos a escala mundial y, subsecuéntemente, se producirían otros ‘megaseiches’ más localizados durante los reajustes principales de la corteza. Esos fenómenos pueden así explicar la heterogeneidad de pautas y discrepancias faunísticas observadas en varias localidades del KTB, de distinta profundidad de depósito, en el mundo. Las estructuras representan un registro de los movimientos del agua y de la resuspensión de los sedimentos en momentos diferentes. Tal como se ha observado en seiches modernos a pequeña escala, la duración y atenuación de los movimientos del agua y la magnitud de la tracción y resuspensión estuvieron controlados por diversos modos oscilatorios que dieron lugar a complejas estructuras sedimentarias y al retrabajamiento de los microfósiles

A Robust Determination of the Time Delay in 0957+561A,B and a Measurement of the Global Value of Hubble's Constant

Photometric monitoring of the gravitational lens system 0957+561A,B in the g and r bands with the Apache Point Observatory (APO) 3.5 m telescope during 1996 shows a sharp g band event in the trailing (B) image light curve at the precise time predicted from the observation of an event during 1995 in the leading (A) image with a delay of 415 days. This success confirms the "short delay," and the lack of any feature at a delay near 540 days rejects the "long delay" for this system, resolving a long-standing controversy. A series of statistical analyses of our light curve data yield a best fit delay of 417 +/- 3 days (95% confidence interval). Recent improvements in the modeling of the lens system (consisting of a galaxy and cluster) allow us to derive a value of the global (at z = 0.36) value of Hubble's constant H_0 using Refsdal's method, a simple and direct distance determination based on securely understood physics and geometry. The result is H_0 = 63 +/- 12 km/s/Mpc (for Omega = 1) where this 95% confidence interval is dominated by remaining lens model uncertainties.Comment: accepted by ApJ, AASTeX 4.0 preprint, 4 PostScript figure

Driving two atoms in an optical cavity into an entangled steady state using engineered decay

We propose various schemes for the dissipative preparation of a maximally entangled steady state of two atoms in an optical cavity. Harnessing the natural decay processes of cavity photon loss and spontaneous emission, we use an effective operator formalism to identify and engineer effective decay processes, which reach an entangled steady state of two atoms as the unique fixed point of the dissipative time evolution. We investigate various aspects that are crucial for the experimental implementation of our schemes in present-day and future cavity quantum electrodynamics systems and analytically derive the optimal parameters, the error scaling and the speed of convergence of our protocols. Our study shows promising performance of our schemes for existing cavity experiments and favorable scaling of fidelity and speed with respect to the cavity parameters.Comment: 37 pages, 14 figure