Wednesday, 5 August 2020

Tropical Storm Isias kills at least twelve in Puerto Rico, the Dominican Republic, the Bahamas, and the United States.

Tropical Storm Isias has killed at least twelve people as it swept across the Caribbean and the Eastern Seaboard of the United States. The storm reached hurricane strength in the Caribbean, sweeping to the south of Puerto Rico, where it caused high winds and flooding, and led to three known deaths. Chiche Peguero, 53, of Río San Juan in María Trinidad Sánchez Province, who was electrocuted by a falling power line, a woman drowned after being swept into a river in Rincón Province, and a five-year-old boy who was killed by a falling tree at Altamira in Puerto Plata Province. Across the island about 448 000 people were left without electricity, and many roads were flooded. severley hampering travel and communication. The storm swept across the Dominican Republic, causing widespread flooding, and causing the death of a horse and its rider who were again hit by a falling power line. The storm reached the Bahamas on 31 July 2020, causing widespread flooding and wind-damage, before moving towards the coast of the United States.

Workers clearing debris left by Hurricane Isias in the Dominican Republic. Erika Santelices/AFP.

The passed to the east of Florida on 1 August 2020, causing some flooding and power outages, but few serious problems, however as it made landfall in North Carolina it caused more severe flooding, and triggered a series of tornadoes, one of which struck a trailer park in Bertie County, killing at least two people, with around twenty injured and three more still missing. From here it passed northward through Virginia, Maryland and Delaware, causing widespread flooding, wind damage and power-outages, with one person killed in Milford, Delaware, when her vehicle was struck by a falling tree. The storm caused further flooding in Pennsylvania, where it claimed another life as a 44-year-old woman and her car were swept away by floodwaters in Lehigh County.

Damage to boats at Southport Marina in Brunswick County, North Carolina, following the passage of Hurricane Isias. Ken Blevins/Star News.

Further north the storm caused flooding and tornadoes in New Jersey, causing damage to a number of homes and businesses, and the collapse of a church steeple in Ocean City. A 21-year-old man drowned off the coast of Cape May in New Jersey, another person was killed when a falling tree hit their car in Queens, New York, and a third death was also caused by a falling tree in New Haven County, Connecticut.

Damage to hourses in Cape May County, New Jersey, caused by Tropical Storm Isias. NCB10.

Tropical storms are caused by solar energy heating the air above the oceans, which causes the air to rise leading to an inrush of air. If this happens over a large enough area the inrushing air will start to circulate, as the rotation of the Earth causes the winds closer to the equator to move eastwards compared to those further away (the Coriolis Effect). This leads to tropical storms rotating clockwise in the southern hemisphere and anticlockwise in the northern hemisphere. These storms tend to grow in strength as they move across the ocean and lose it as they pass over land (this is not completely true: many tropical storms peter out without reaching land due to wider atmospheric patterns), since the land tends to absorb solar energy while the sea reflects it.

The path and strength of Tropical Storm Isias. Thick line indicates the past path of the storm (till 9.00 am GMT on Wednesday 5 August 2020), while the thin line indicates the predicted future path of the storm, and the dotted circles the margin of error at nine and twenty one, hours ahead. Colour indicated the severity of the storm. Tropical Storm Risk.

Despite the obvious danger of winds of this speed, which can physically blow people, and other large objects, away as well as damaging buildings and uprooting trees, the real danger from these storms comes from the flooding they bring. Each drop millibar drop in air-pressure leads to an approximate 1 cm rise in sea level, with big tropical storms capable of causing a storm surge of several meters. This is always accompanied by heavy rainfall, since warm air over the ocean leads to evaporation of sea water, which is then carried with the storm. These combined often lead to catastrophic flooding in areas hit by tropical storms.

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Magnitude 4.8 Earthquake in Kasai-Central Province, Democratic Republic of the Congo.

The United States Geological Survey Recorded a Magnitude 4.8 Earthquake at a depth of 10.0 km about 37 km to the east of the town of Demba in Kasai-Central Province, Democratic Republic of Congo, slightly before 1.45 pm local time (slightly before 11.45 am GMT) on Tuesday 4 August 2020. There are no reports of any damage or casualties associated with this event at this time, but it may have been felt locally.

The approximate location of the 4 August 2020 Kasai-Central Province Earthquake. USGS.

South Kivu lies to the west of the Great Rift Valley, which is slowly splitting the African Plate in two along a line from the Red Sea through Ethiopia, and which includes the great lakes and volcanoes of east-central Africa. This has the potential to open into a new ocean over the next few tens of millions of years, splitting Africa into two new, smaller, continents; Nubia to the west and Somalia to the east.

 Movement on the African Rift Valley, with associated volcanoes. Rob Gamesby/Cool Geography.

Witness accounts of Earthquakes can help geologists to understand these events, and the structures that cause them. The international non-profit organisation Earthquake Report is interested in hearing from people who may have felt this event; if you felt this quake then you can report it to Earthquake Report here.

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Tuesday, 4 August 2020

Understanding the nature of Trojan-Like Orbit of P/2019 LD2 (ATLAS).

The Jupiter Trojans are small solar system bodies that share Jupiter’s orbit around the Sun and reside in one of two 'clouds' associated with the stable L4 and L5 Lagrange regions located 60 ahead of and behind the planet in its orbit. Their origins are currently uncertain, with potential scenarios under debate including formation near their current locations and capture by Jupiter from source regions farther out in the Solar System. Observational studies have shown the population to consist primarily of C-, P-, and D-type asteroids, where measurements of low densities for some objects indicate that they could be highly porous, volatile-rich, or both. Thermal models have shown that water ice could remain preserved on Jupiter Trojans over the age of the solar system under just 10 cm of dust at their poles to 10 m of regolith elsewhere. Thus, cometary activity could be possible on Trojans, perhaps triggered by impacts and driven by hypervolatile species like carbon monoxide or carbon dioxide. No active Trojans have been reported to date, however.

Animation showing the motion of the Jupiter Trojan Asteroids. Petr Scheirich/Astronomical Institute of the Czech Academy of Sciences/NASA.

P/2019 LD2 was discovered on 10 June 2019 at a heliocentric distance of 4.666 AU (4.666 times the average distance at which the Earth orbits the Sun) by the 0.5-m Asteroid Terrestrial-Impact Last Alert System telescope on Mauna Loa in Hawaii. Suspected cometary activity in discovery images analysed by the ATLAS team was confirmed by follow-up observations on 11, 13, and 29 June 2019. The object currently has Jupiter Trojan-like orbital elements, with a semimajor axis (average distance from the Sun) of 5.3279 AU, an eccentricity of  0.1407, and inclination relative to the plain of the Solar System of 11.517. If P/2019 LD2 is in fact a Jupiter Trojan, it would represent a unique opportunity to study the volatile content and behavior of a member of this population of objects for the first time and to use the results of those investigations to constrain models of solar system formation.

The calculated orbit and current position of  P/2019 LD2 (ATLAS). JPL Small Body Database.

However, a heliocentric ecliptic latitude and longitude plot of P/2019 LD2 and other Jupiter Trojans at the time of the object’s discovery gives an indication that P/2019 LD2 might not be a true Jupiter Trojan, as it much closer to Jupiter in ecliptic longitude (roughly 10°) than any other Jupiter Trojans (roughly 40-100°) and does not clearly belong to either the L4 or L5 clouds. Dynamical analyses suggest that P/2019 LD2’s orbital elements are unstable, inconsistent with the behavior expected of a true Jupiter Trojan, while similar analyses disputing P/2019 LD2’s classification as a Jupiter Trojan were reported by amateur astronomers Sam Deen and Tony Dunn in posts to the Minor Planet Mailing List.

In a paper published on the arXiv database at Cornell University on 28 July 2020, and submitted to the journal Icarus, Henry Hsieh of the Planetary Science Institute and the Institute of Astronomy and Astrophysics at Academia Sinica, Alan Fitzsimmons of the Astrophysics Research Centre at Queens University Belfast, Bojan Novaković of the Department of Astronomy at the University of Belgrade, and Larry Denneau and Aren Heinze of the Institute for Astronomy at the University of Hawaii, present numerical integration results confirming and characterizing the non-Trojan-like dynamical behavior of P/2019 LD2 and briefly discuss the implications of this object for current and future surveys.

To assess P/2019 LD2’s dynamical nature, Hsieh et al. generated 100 dynamical clones drawn from the multivariate normal distribution for the object (as of i June 2020), defined by an orbital covariance matrix, provided by the JPL Small Bodies Database. Dynamical clones werer used to assess the amount of potential divergence due to chaos in P/2019 LD2’s predicted orbital evolution that could occur due to the object’s orbital element uncertainties. Hsieh et al. also performed the same procedure for six reference Jupiter Trojans: (588) Achilles, (624) Hektor, and (659) Nestor from Jupiter’s L4 Trojan cloud and (617) Patroclus, (884) Priamus, and (1172) Aneas from the L5 cloud. They then conducted backward and forward numerical integrations for all objects and their clones for 1000 years in each direction, using the Bulirsch-Stöer integrator in the Mercury N-body integration package. To study the long-term stability of P/2019 LD2, Hsieh et al. conducted forward integrations for 1 million years for all test particles. All integrations accounted for gravitational perturbations from the seven major planets except for Mercury and used an initial time step of 0.1 days. In all integrations, particles are removed when they reach over 100 AU from the Sun. Non-gravitational forces were not included.

An image of P/2019 LD2 (ATLAS) taken from the Las Cumbres Observatory at Cerro Tololo in Chile on 11 June 2019. James Armstrong/Institute for Astronomy/Las Cumbres Observatory/Space.com.

Hsieh et al. confirm that P/2019 LD2 is only temporarily in a Jupiter Trojan-like orbit, while they find its overall dynamical behavior to be that of an active Centaur transitioning into a Jupiter-family comet. Hsieh et al. found that P/2019 LD2’s semimajor axis became Jupiter Trojan-like (with a semi-major axis of between 5.0 and 5.4 AU) in July 2018 and will remain in that range until February 2028. The transitions into and out of P/2019 LD2’s current orbit correspond to close encounters with Jupiter for all P/2019 LD2-associated test particles (i.e., the object itself as well as all of its dynamical clones) Hsieh et al.'s integrations when the object passed within 0.09 AU (or 0.25 of the Jupiter Hill radius, where 0.355 AU is Jupiter’s Hill radius; the radius within which an object can potentially become a satellite of Jupiter) from Jupiter on 20 February 2017, and will pass within 0.12 AU (0.34 Jupiter Hill radius) from Jupiter on 12 May 2028.

Immediately prior to reaching its current Jupiter Trojan-like orbit in July 2018, P/2019 LD2’s orbital elements. An object is considered a Centaur if both its perihelion (the closest point on its orbit to the Sun) and its semi-major axis (average distance from the Sun) fall between the orbit's of Jupiter and Neptune, and it is not in a 1:1 mean-motion resonance with any planet. P/2019 LD2 is expected to return to a Centaur-like orbit in February 2028 and remain there until February 2063, when a very close encounter with Jupiter at 0.03 AU (0.08 of the Jupiter Hill radius) in January 2063 will lower both its semimajor axis and perihelion distance to well inside the orbit of Jupiter, at which point, the object will be considered a Jupiter Family Comet. For comparison, integrations of our reference Trojans indicate that they remain on stable orbits for the duration of both our backward and forward 1000-year integrations. While the eccentricities of some of these objects drift smoothly over time and their semi-major axis and perihelion exhibit small oscillations, Hsieh et al. see none of the sharp orbital element changes exhibited by P/2019 LD2.

Hsieh et al. found that the orbital evolution trajectories of P/2019 LD2 and all of its dynamical clones in our integrations between 1851 and 2063 are nearly identical, suggesting that their results likely reliably capture P/2019 LD2’s true orbital evolution during this period. However, before and after this time period, which is bracketed by close encounters with Jupiter at distances of 0.5 AU (1.4 of the Jupiter Hill radius) in November 1850 and 0.03 au (0.08 of the Jupiter Hill radius) in January 2063, trajectories from Hsieh et al.'s integrations for P/2019 LD2 and its dynamical clones diverge widely. This divergence is a result of the chaotic nature of P/2019 LD2’s orbit, especially during close encounters with Jupiter, and indicates that predictions about the object’s dynamical behavior before 1851 or after 2063 should be regarded as highly uncertain. Consideration of non-gravitational perturbations due to cometary outgassing could introduce even more uncertainty to our analysis of P/2019 LD2’s orbital evolution, but given the expected weakness of any cometary activity at these large heliocentric distances, Hsieh et al. expect outgassing perturbations to be essentially negligible compared to e ffects from the close encounters with Jupiter.

In Hsieh et al.'s 1 million year forward integrations of its nominal orbit, the semi-major axis of P/2019 LD2 passes 100 AU (and is removed from the integrations) in 990 000 years (with many significant orbital element changes during that time), while the semi-major axis all but three of its dynamical clones also pass 100 AU within 1 million years with a median lifetime of 110 000 years. This dynamical evolutionary behavior is consistent with current short-period comets, and contrasts sharply with our six reference Trojans, all of which remain in e ffectively the same orbits for the full 1 million year integrations, further highlighting the dynamical distinction between P/2019 LD2 and true Jupiter Trojans.

Despite the findings described above, it is possible that P/2019 LD2 could have been a true Jupiter Trojan in the past and was driven onto its current orbit by non-gravitational perturbations arising from its cometary activity or other e ects. Jupiter Trojans are expected to occasionally escape from their stable orbits due to chaotic di usion or collisions, and potentially contribute to other populations such as Centaurs and Jupiter Family Comets, and cometary non-gravitational perturbations could certainly accomplish similar e ffects. Given the object’s clearly un-Trojan-like recent orbital history, however, we consider this to be an implausible scenario. There is no reason that P/2019 LD2’s current transient resemblance to Jupiter Trojans should suggest that it is necessarily more likely than any other Centaur to have been a Jupiter Trojan in the past. Nonetheless, a future analysis of escape trajectories from the Trojan clouds involving non-gravitational perturbations due to cometary outgassing could be useful for assessing the potential contribution of active Jupiter Trojans to the Centaur and Jupiter Family Comets populations. In the meantime, observational characterisation of P/2019 LD2’s surface to determine if it has the ultrared colours of other Centaurs or has C-, P-, or D-type colours similar to other Jupiter Trojans would be very useful for confirming the object’s true origin.

While P/2019 LD2 is not a true Jupiter Trojan, its discovery is nonetheless instructive. Current surveys like ATLAS will continue to discover active objects, some of which may belong to populations not previously known to exhibit activity, and upcoming surveys like the Vera C. Rubin Observatory’s Legacy Survey of Space and Time promise to discover even more. The temporary capture of objects onto Trojan-like orbits is not expected to be frequent, but also not exceedingly rare, where Hsieh et al. note that temporary satellite captures could also be found to have nominally Trojan-like orbital elements. As such, more cases like P/2019 LD2 should be expected in the future.

Computationally scalable approaches for accurately dynamically classifying objects of interest discovered by wide-field surveys in a timely manner will be needed for both largescale population studies and investigations of individual targets, especially as discovery rates increase. To identify true Jupiter Trojans, possible approaches include using Lyapunov Characteristic Exponent values or proper orbital elements to ensure that a given object is in a stable 1:1 mean-motion resonance with Jupiter. Both proper orbital elements and Lyapunov Characteristic Exponent values are currently provided by the AstDyS-2 website for all numbered and multi-opposition Jupiter Trojans, and preparations are being made to continue doing so in the Legacy Survey of Space and Time era, although their computation typically requires relatively high-quality orbits. For newly discovered objects of high interest that have lower-quality orbits, it may be useful to develop mechanisms for performing more rapid preliminary dynamical analyses using N-body integrations as was done in this work (perhaps also allowing for cometary non-gravitational perturbations).

While recent sharp decreases in P/2019 LD2’s semimajor axis and perihelion distance are perhaps the most plausible trigger of its current activity, tidal disruption or resurfacing from the object’s close encounter with Jupiter in 2017 could also have contributed to making cometary activity more likely by disrupting surface material and excavating buried surface ice. In this regard, systematic N-body integration analyses could also be useful for identifying small bodies that have experienced recent close planetary encounters so that they can be monitored for possible cometary activity.

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Monday, 3 August 2020

The Ba Moussa West Coral fauna, a new Early Carbiniferous Coral assemblage from central Morocco.

Mississippian rocks are common in the Moroccan Meseta. They have been studied and described by French geologists since the beginning of the twentieth century. The Mississippian stratigraphic successions are clearly different in the western and in the eastern parts of the Meseta. The succession was considered quite continuous from the Devonian to the Serpukhovian. However, sedimentation in the eastern part of the central Meseta (Azrou-Khenifra Basin) is more complicated. It took place in both a shallow-water carbonate platform and a deeper water flysch basin, within a tectonically active setting, involving movements of blocks, and transgressions and regressions that produced some gaps and unconformities. Sedimentation during the Tournaisian, early and mid Visean in the basin is regarded as being absent by some authors, whereas continuous or sporadic sedimentation during that time interval is suggested by others.

In a paper published in the Journal of Palaeogeography on 11 February 2020, Sergio Rodríguez of the Universidad Complutense de Madrid and the Instituto de Geociencias at the Consejo Superior de Investigaciones Científicas, Ian Somerville of the School of Earth Sciences at University College Dublin, Pedro Cózar, also of the Instituto de Geociencias at the Consejo Superior de Investigaciones Científicas, Javier Sanz-López of the Departmento de Geología at the Universidad de Oviedo, Ismael Coronado of the Institute of Paleobiology, Felipe González of the Departmento de Ciencias de la Tierra at the Universidad de Huelva, Ismail Said, also of the Universidad Complutense de Madrid, and Mohamed El Houicha of the Laboratoire de Géodynamique et Géomatique at the Université Chouaïb Doukkali, report the recent discovery of a relatively rich Mississippian (early Visean) Coral fauna in the southern part of the Azrou-Khenifra Basin, describe the Corals in detail and their host limestone rocks, and comment on their comparison and affinity with other coeval Coral assemblages in North Africa, Europe and southwest Asia. The microfossil content was also studied to enhance the biostratigraphic discussion and significance of the Coral fauna.

The beginning of Carboniferous sedimentation in the Khenifra region, which lies in the southern part of the Azrou-Khenifra Basin and contains the largest Mississippian outcrops in the eastern central Meseta, is usually considered to occur within the widely known late Visean transgression. However, two early Visean transgressions have been cited. The first one is imprecisely located as “to the north of Ba Moussa (point 1)”. The second one was equated with the base of V2b of mid Visean age.

In the southwestern margin of the Azrou-Khenifra Basin at Sidi Lamine and Tabainout, a thick shallow-water carbonate succession with basal Mississippian conglomerate and sandy limestone can be seen to rest unconformably on older (Ordovician) tilted siltstones and sandstones. A similar relationship is seen at the southeastern margin of the basin at Tiouinine where shallow water sandy limestones rest unconformably on red Ordovician sandstones.

(a) Location of Khenifra in central Morocco; (b) Geological map of Azrou-Khenifra Basin with Ba Moussa West coral fauna locality and other Coral localities mentioned in the text; (c) Simplified geological sketch map of Ba Moussa West area and the location of the studied limestone horizons BMW1 and BMW2. hV-Fm1, Lower Visean; hV-Fm2, Upper Visean. Rodríguez et al. (2020).

The eastern part of the Azrou-Khenifra Basin, northwest of Khenifra, is a region of mostly deep-water rythmic mudstones. However, recent field investigations at Ba Moussa West, northwest of a nappe folded as a north-south trending syncline, and approximately 3 km northwest of Khenifra city margins, have discovered two pale gray weathering limestone units within a thick dark gray siltstone and shale rhythmic succession. These limestones contain abundant corals that form the focus of this paper. The limestone units form two distinct parallel ridges, some 50m apart, and traceable laterally for over 200 m. They form prominent features on the landscape, compared to the subdued topography of the more easily eroded mudstones which encase the limestones. The beds dip steeply to the east (70°) and in places can be vertical. The two ridges expose respectively, 4.90m and 4.10m thicknesses of well-bedded limestones (with beds ranging typically from 10 to 40 cm thick) with thin dark gray shale interbeds.

(a) View looking south of limestone ridge (BMW1) about 5 m thick showing steeply dipping beds overlain and underlain by softer shales; (b) Limestone bed with large angular quartzite and sandstone lithoclasts (beside coin) succeeded by thin laminated sandy limestone and black shales, in turn overlain by bioclastic limestone rich in Corals; solitary Rugose Coral Siphonophyllia (black arrows) and Cerioid Tabulate Coral Turnacipora (white arrow), coin diameter is 2.5 cm; (c) Close-up view of richly bioclastic limestone bed with sharp base, showing abundant transverse sections of Siphonophyllia and Sychnoelasma (black arrows), hammer length is 40 cm; (d) Coarse-grained crinoidal limestone with longitudinal and transverse sections of Siphonophyllia khenifrense; (e) Thin section of rudstone at BMW1 showing bioclasts and lithoclasts. Abbreviations: br, brachiopod; bz, bryozoan; co, coral; cr, crinoid; gr, gastropod; st, sandstone; (f) Thin section of rudstone at BMW2 showing bioclasts and lithoclasts. Abbreviations: br, brachiopod; co, coral; cr, crinoid; sl, siltstone; st, sandstone. Rodríguez et al. (2020).

The limestones are variable in composition and texture, comprising coarse-grained, bioclastic and lithoclastic calcirudites, rich in crinoids, thick-shelled Brachiopods and relatively abundant Corals. The limestone beds consist of numerous sedimentary events. Some have sharp, erosive bases and show grading with laminated tops. Large angular lithoclasts of sandstone and siltstone (up to 20 cm in diameter) occur in some beds. Other limestones are buff weathered, fine-grained, laminated calcarenites. Under the petrological microscope two microfacies are differentiated. The first microfacies, which is less common, is a laminated Crinoidal wackestone-packstone containing small fragments of Crinoidal plates, Corals and Bryozoans. The second one, which is dominant, is a polymictic rudstone with fragmented Corals, Crinoids, Bryozoans, Brachiopods, Trilobites, Gastropods, Bivalves, Foraminifers and angular to subangular grains of quartzite sandstone and siltstone. The disposition of siliciclastic clasts and bioclasts is random in some beds, suggesting rapid sedimentation, but in some beds, most clasts are disposed mainly parallel to the stratification. The fragmentation of bioclasts is also variable.

The limestones can be regarded as proximal debris flow and multistorey high-density turbidite bodies, with numerous event beds, deposited in a prevailing succession of distal turbidite beds. Thus, the coral assemblage is allochthonous and may have been transported far from its original depositional shelf setting.

The two limestone horizons (BMW1 and BMW2) were sampled and corals were collected. Samples from BMW1 contain almost entire Brachiopods and Corals, whereas in BMW2 most bioclasts are completely broken and very few Coral specimens are identifiable at generic or specific level. The coral assemblage is relatively rich, but their diversity is quite low (5 genera and 7 species). The assemblage comprises solitary Rugose Corals and Tabulate colonies. Many corals are well preserved and nearly complete, missing only the apexes and showing sometimes compressed calices when they show few skeletal elements and are filled with muddy sediment. However, others are completely fragmented or crushed or have lost much of their dissepimentaria. Fifty specimens were collected, of which 38 have been definitively identified.

Thin sections of samples were studied to describe the microfossil content. Owing to the brecciated character of many beds, including boulders of large size, only the fine-grained limestones yield Foraminifers. Assemblages are relatively abundant in those fine-grained limestones, although specimens are commonly crushed, and diversity is limited to a few genera. Assemblages from BMW1 are slightly richer than BMW2, although this may be the result of more intense sampling and sectioning.

A large sample from limestone BMW1 (3.8 kg weight) was etched with 8%–10% buffered formic acid solution, following the standard technique to avoid damaging. The low abundance of Conodont elements includes one complete P1 element and six broken elements with upper surface damaged and a few with surface dissolution, which could be in relation to significant transport and resedimentation of elements. The colour of Conodonts shows values of 4.5 to 5 for the alteration index. Reworking of Conodonts may be causing a higher colour alteration index value, but small recrystallised apatite surface is observed in Conodonts. Some specimens preserve a smooth surface, but etched surfaces with pits are often discerned. It suggests short heating on proximity to an igneous intrusion.

Conodonts from samples of BMW1. (a)–(b) Fragment of element of Kladognathus sp., DGO 15624, and detail of the face where breakage shows a lamellar inner structure and small apatite crystal 2–3 μm in size interpreted as recystallized and, later, slight dissolution; (c)–(e) Aboral and oral views of Mestognathus cf. beckmanni, DGO 15625, and detail of the margin of the platform with a strong dissolution located on the ornamentation of ridges and carina causing the inversion of surface relief; (f) Oral view of Polygnathus lobatus with pits due to dissolution of the Conodont surface, DGO 15622; (g) Gnathodus pseudosemiglaber, DGO 15623; (h)–(i) Oral and aboral views of Polygnathus inornatus, DGO 15621. Conodonts are stored in the Museum of Geology of the University of Oviedo. Rodríguez et al. (2020).

The allochthonous shales embedding the limestone horizons were sampled for palynomorphs. A total of 12 shale samples were crushed and dissolved following the classical extraction techniques. After complete removal of carbonate and silicate minerals, the organic remains were oxidized with Fuming Schulze solution and mounted in slides for microscope analysis. Palynomorphs recovered from shales are dominated by phytoclasts and, in minor proportions, by spores, whereas organic-walled marine microphytoplankton and amorphous organic matter are virtually absent. The reduced number of spores and their irregular state of preservation precluded further taxonomic identification. The large proportion of equidimensional to lath-shaped phytoclasts and the absence of marine components may be explained by the intense reworking and effective dilution associated to low-density turbidity currents. The brownish-black to black colour of spores and phytoclasts points to a thermal alteration index which essentially agrees with the colour alteration index values observed for conodonts from the limestone sample.

The Coral assemblage from Ba Moussa West contains a new species of Siphonophyllia, with other solitary Rugose Corals, such as Sychnoelasma urbanowitschi, Cravenia lamellata, Cravenia tela, and Cravenia rhytoides. Colonial Tabulate Corals recorded include Turnacipora megastoma, and Pleurosiphonella crustosa. Themost abundant specimens collected belong to the genus Siphonophyllia (20) and Turnacipora (7). Most other species are represented only by three specimens or less.

The assemblage is similar to that described from lower Visean (Arundian) Moel Hiraddug Formation in North Wales, UK. In both regions the large Siphonophylliid Corals represent the dominant component in dark gray bioclastic limestone and shale lithofacies, in which colonial Rugose Corals are absent. However, the Ba Moussa succession has a lower diversity Coral assemblage and the specimens are not as well preserved. This may be explained by the sedimentological setting at Ba Moussa, with the Corals occurring in graded limestone beds containing large exotic clasts, interpreted as debris flow and proximal turbidite deposits.

The stratigraphic range of Sychnoelasma urbanowitschi, and the three species of Cravenia (Cravenia lamellata, Cravenia tela, and Cravenia rhytoides) is very restricted, typically diagnostic of the early Visean throughout Western Europe. Turnacipora megastoma occurs also, typically in the early Visean.

The Ba Moussa West assemblage has similarities with Tafilalt in Eastern Morocco, where a richer early Visean solitary Rugose assemblage is recorded including Cravenia, Siphonophyllia and Sychnoelasma, but where colonial Rugose genera are also absent. Similar assemblages containing dominant Cyathopsids plus Sychnoelasma, Pleurosiphonella and Micheliniids have been reported in Canada and United States, and in Mid-Asia.

The Ba Moussa limestone beds are clearly older than other Mississippian sections in the Khenifra area, as confirmed by the associated Foraminifers and Conodonts. Coral assemblages from Tabainout and Sidi Lamine, 20 km and 30 km respectively, further west of Ba Moussa West, at the western margin of the Azrou-Khenifra Basin, contain fasciculate and massive colonial Rugose Coral genera (Siphonodendron and Lithostrotion) of late Visean (Asbian) age. Both sections have basal transgressive deposits with in situ shallow-water limestones containing ooids and Calcareous Algae. At Tiouinine, 8 km southeast of Khenifra on the eastern margin of the basin, very rich and diverse late Visean (Brigantian) Coral assemblages form a reefal tract. The early Visean age of the Ba Moussa West limestone correlates with the early Visean age of the transgressive point 1, located to the north of Ba Moussa.

The assemblage in samples from BMW1 contains the Foraminifers Earlandia vulgaris, Earlandia elegans, Endothyra spp., Endothyra similis, Endolaxina sp., Endothyranopsis (Eosinopsis) sp., Eosparastaffella sp., Eosparastaffella concinna, Eosparastaffella evoluta, Eosparastaffella interiecta, Eosparastaffella macdermoti, Eosparastaffella aff. macdermoti, Eosparastaffella ovalis, Eosparastaffella simplex, Eosparastaffella tumida subsp. 1, Eosparastaffella vdovenkoae, Eotextularia diversa, Granuliferella sp., Globoendothyra sp., Lapparentidiscus sp.,? Lituotubella sp., Mediocris mediocris, Mediocris ovalis, Mediocris aff. ovalis, Omphalotis sp., Pseudoplanoendothyra sp., Septabrunsiina sp., Septaglomospiranella sp., Spinobrunsiina sp., Spinolaxina sp., Tetrataxis sp. and Urbanella (Brenckleites) fragilis. The Algospongia recorded are very common Kamaena delicata and Palaeoberesella lahoseni, as well as Stacheoides spissa and Exvotarisella sp.

(a) Eotextularia diversa, BMW1, Pc4367; (b) Latiendothyranopsis sp., BMW2; (c) Omphalotis sp., BMW1, Pc4364; (d) Eoparastaffella tumida, BMW1, Pc4364. (e) Granuliferella sp., BMW1, Pc4364; (f) Mediocris aff. ovalis, BMW1, Pc4366; (g) Eoparastaffella simplex, BMW1, Pc4366; (h) Eoparastaffella ex gr. simplex (Eoparastaffella tumida subsp. 1), BMW1, Pc4367; (i) Eoparastaffella aff. concinna, BMW1, Pc4365; (j) Eoparastaffella evoluta, BMW2; (k) Eoparastaffella vdovenkoae, BMW1, Pc4366; (l) Eoparastaffella macdermoti, BMW1, Pc4364; (m) Eoparastaffella ovalis, BMW1, Pc4367; (n) Endolaxina sp., BMW1, Pc4367; (o) Pseudoplanoendothyra sp., BMW1, Pc4364; (p) Endothyranopsis (Eosynopsis) sp., BMW1, Pc4364. Scale bar same for all figures. Rodríguez et al. (2020).

The assemblage is characterized by a high diversity in Eoparastaffella species, and in particular, the first species with pointed periphery in the last whorl, Eoparastaffella tumida subsp. 1 and Eoparastaffella ex gr. simplex. Although the marker for the base of the MFZ9, as well as the marker for the base of the Visean, Eoparastaffella tumida subsp. 1 is derived from Eoparastaffella simplex from the basal levels of the MFZ9, and thus, the assemblages can be attributed to the base of the Visean. It is noteworthy for the occurrence of Eoparastaffella concinna and Eoparastaffella evoluta, also derived from Eoparastaffella simplex in more advances stages of the MFZ9.

The foraminiferal assemblage recorded in BMW2 is composed of Earlandia minor, Earlandia vulgaris, Endothyra spp., Endothyra ex gr. bowmani, Endothyra prisca, Endothyra similis, Eotextularia diversa, 'Glomospira' sp., Eoparastaffella sp., Eoparastaffella concinna, Eoparastaffella interiecta, Eoparastaffella macdermoti, Eoparastaffella simplex, Eoparastaffella tumida subsp. 1, Eoparastaffella vdovenkoae, Mediocris mediocris, Latiendothyranopsis sp., Omphalotis sp., Plectogyranopsis sp., and Pseudoplanoendothyra sp. This assemblage also contains the pointed and slender Eoparastaffella, including Eoparastaffella. concinna, which is a more evolved form than the ancestral stock of pointed Eoparastaffella. In consequence, the assemblage is also assigned to an advanced stage in the MFZ9. The Algospongia recorded in those levels contain Palaeoberesella lahoseni, Kamaena delicata, Issinella sp., and Exvotarisella sp.

The Conodont fauna studied in samples from BMW1 includes Polygnathus inornatus, Polygnathus lobatus (that is usually related with the first species), and a fragment of Polygnathus sp. These taxa were usually described in the early to mid Tournaisian SiphonodellaPolygnathus inornatus Assemblage Zone in the British Isles. However, it has been indicated that Polygnathus inornatus ranged up to the upper Tournaisian Gnathodus typicus Conodont Zone in Cornwall (UK). Polygnathus inornatus have been reported in the upper Tournaisian Scaliognathus anchoralis Zone of the Moravia-Silesia and the Dinant-Namur basins, and in the earliest Visean, just at the first occurrence of Pseudognathodus homopunctatus in the Belgian area. A late Tournaisian to early Visean age is supported by the occurrences of one P1 element of Gnathodus pseudosemiglaber, one P1 fragment of Mestognathus sp. and one P2 element probably corresponding to Kladognathus sp. The fragment of Mestognathus sp. shows dissolution of the carina and ornamentation of the platform, and the blade and the dorsal part of the platform are broken. The parapet area is close to that described in Mestognathus praebeckmanni. The secondary keel seems to be formed with a basal groove, as in Mestognathus beckmanni, but the specimen is broken. The first occurrence of Mestognathus beckmanni was indicated just below the lower boundary of the Visean Stage at the Global Boundary Stratotype Section in the Pengchong section, South China and in a few localities of Western Europe, although it is often recorded in Visean beds. The early Visean Pseudognathodus homopunctatus species is lacking in Rodríguez et al.'s sample.

The new species of Siphonophyllia is named Siphonophyllia khenifrense, which refers to the town of Khenifra within the Azrou-Khenifra Basin in Morocco. Seventeen whole specimens were recovered, all from Ba Moussa West, as well as 29 transverse sections and 15 longitudinal sections.

The whole specimens are cylindrical Corallites between 20 mm and 40 mm in alar diameter and recorded fragments are up to 20 cm long, often without calice. The dissepimentarium is often abraded. The outer wall is thin.

Siphonophyllia khenifrense. (a)–(c) Holotype DPM BMW1-1: (a) DPM BMW1-1A, transverse section., (b) DPM BMW1-1B, transverse section., (c) longitudinal sections; (d)–(e) DPM BMW1-6: (d) transverse section, (e) longitudinal sections; (f)–(g) DPM BMW1-20: (f) longitudinal sections, (g) transverse section.; (h) DPM BMW2-16, transverse section; (i) DPM BMW2-4, transverse section; (j) Wall microstructure in Siphonophyllia khenifrense, DPM BMW1-1, L, Lamellae; (k) Septal microstructure in Siphonophyllia khenifrense, DPM BMW2-16, Gr, Granular axial septum; F, Fibronormal middle zone; L, Lamellar external zone. Black arrows indicate the position of the cardinal septum. Corals are housed in the Geodinamica, Estratigrafía y Paleontología Department of the Universidad Complutense de Madrid. Rodríguez et al. (2020).

The tabularium diameter varies from 17 mm in immature stage to 31 mm in adult stage. The tabularium is wide, 3/5 to more than 4/5 Corallite diameter; the variation in tabularium width is a function of the age of the specimen (immature vs mature Corallite) and variation in the width of the dissepimentarium, which although generally narrow, can also be variably preserved. The number of major septa ranges commonly between 42 and 61, but up to 68 may be present. The septa are long, almost reaching the axis in immature stage but withdrawn from the centre in mature adult stage. They are straight to slightly flexuous in the tabularium, thinning axially and straight to sinuous in the dissepimentarium. Major septa are strongly thickened in the tabularium but are thin in the dissepimentarium; septa can be slightly thicker in cardinal quadrants and thinner in counter quadrants. The minor septa are also thickened where they penetrate slightly into the tabularium, but not as thick as majors; in the dissepimentarium they are thin. They are variable in length, from 1/4 to 1/3 length of majors. The cardinal septum is slightly shorter in most mature Corallites and located in a closed small cardinal fossula. It is often flanked by two major septa which are shorter than the others. Counter septum is inconspicuous, but shorter in late adult stages.

The dissepimentarium is narrow (typically 1/10 to 1/5 Corallite diameter) and mainly composed of interseptal regular dissepiments. The dissepiments are more irregular in the external part of the dissepimentarium, with occasional lonsdaleoid dissepiments. Typically 3 to 6 rows of slightly angular concentric dissepiments are present in the dissepimentarium. In longitudinal section, the dissepiments are small and elongate. They are declined to the tabularium from 60° to 70°.

The tabulae are mostly complete flat domes with some splitting; horizontal, medially sagging and convex tabulae can be present, sloping down peripherally to prominent gutters. They are relatively widely spaced numbering between 6 and 12 each centimetre.

The wall microstructure is microlamellar, as well as the septal stereoplasm and thickenings of tabulae and dissepiments. The septal mesoplasm is granulofibrous with incipient development of microtrabeculae. The tabulae and dissepiments are microgranular.

At least four transgressive phases have been differentiated in the Azrou-Kenifra Basin which were related with fault activity and resedimentation on the margins of tectonic blocks. The early Visean Corals at Ba Moussa West are the oldest occurrence in this basin, and are an important fauna differentiated from the commonly described faunas in late Visean beds of the western margin of the basin at Sidi Lamine and Tabainout, as well as in the northern part of the basin at Adarouch.

The early Visean age in the MFZ9 is older than the previously considered age for North Ba Moussa point 1 (Zone 11 or equivalent MFZ10), in spite of Foraminifer species that was based on their zonal correlation, Earlandia vulgaris and Eotextularia diversa, are also occurring in samples from BMW1 and BMW2 (assigned here to the MFZ9).

The Ba Moussa West succession is a resedimented body of shale, siltstone and limestone with early Visean microfossils and Corals, indicating that the probable age of sedimentation was very close to that of skeletal growth of the components. The corals and microfossils correspond to shallow-water taxa dwelling on a neighbouring sedimentary relief. The coralline assemblage shows a distinctive dominance of solitary rugosans, the absence of colonial Rugosans and occurrence of colonial Tabulate Corals. Moreover, the solitary forms are dominated by Siphonophyllia khenifrense and Sychnoelasma urbanowitschi, and the Tabulate Coral Turnacipora megastoma. A similar association of Siphonophyllia aff. garwoodi and Sychnoelasma urbanowitschi is known from the early Visean of the Laval syncline in Normandy (north France), although with colonial Rugosans there (Solenodendron spp.). This colonial genus is not recorded in the Azrou-Khenifra Basin first until the late Visean.

This colonial genus is not recorded in the Azrou-Khenifra Basin first until the late Visean. However, none of the seven listed key taxa of this subzone are recorded in Morocco, although the genera Siphonophyllia, Cravenia and Sychnoelasma are present. Perhaps of greater significance though, is that whereas Siphonophyllia hawbankense is only recorded in the underlying upper Tournaisian RC4ß1 subzone, a new taxon Siphonophyllia hawbankense subsp. A which starts in this subzone, extends into RC4ß2 subzone. The strong possibility exists though, that this corresponds to the small Siphonophyllia urbanowitschi of Ba Moussa, which represents the transition to larger typical forms in RC5 Zone.

The Ba Moussa West Coral fauna, although quite restricted in its diversity, nevertheless, contains typical elements of the Western European Coral province (which includes North Africa and Nova Scotia). In particular, the dominance of solitary Rugosa and Tabulate Corals is a feature of the early Visean assemblages which are recognised in northwest Europe: Normandy (north France), southern Belgium, southwest Province, North Wales, Craven Lowlands and South Cumbria (Great Britain), and Dublin Basin (Ireland). Similar early Visean faunas with solitary rugosans are known in the eastern part of the Anti-Atlas region at Tafilalt in eastern Morocco and in the Béchar Basin in Algeria. The late Tournaisian to early Visean Rugose Coral fauna from Tafilalt is richer than that from Ba Moussa. It is dominated by solitary genera, both undissepimented (Sychnoelasma, Cravenia) and dissepimented (Bifossularia, Cyathoclisia, Clisiophyllum, Siphonophyllia, Palaeosmilia, Amygdalophyllum), and is lacking colonial Rugosans.

Palaeogeographic distribution of the Coral taxa recorded in Ba Moussa West in the Palaeotethys region and around Laurentia and Baltica. (s) Siphonophyllia, (u) Sychnoelasma urbanowitschi, (c) Cravenia, (t) Turnacipora, (p) Pleurosiphonella. (1) Ba Moussa West, (2) Tafilalt, (3) Midcontinent, (4) Western Interior, (5) Canadian Rockies, (6) Carnic Alps, (7) Western Europe, (8) Eastern Europe, (9) Moscow Basin, (10) Ural Mountains, (11) Tian-Shan (Northwest China), (12) Turkey, (13) Transcaucasia, (14) Iran, (15) Himalaya, (16) South China. Rodríguez et al. (2020).

It was previously considered that since the Azrou-Khenifra Basin only had late Visean and younger Coral assemblages, so too the Jerada Basin in northeast Morocco, they were isolated from other marine basins in the early Visean. Connections among the Azrou-Khenifra Basin, northwest Europe, Tafilalt, and other Saharian basins in Algeria (Béchar Basin) were open from the Asbian and Brigantian (late Visean). The Ba Moussa West Corals, Foraminifers and Conodonts suggest that marine seaways were available for migrations between the Azrou-Khenifra Basin and other regions from the early Visean. Similar early Visean faunas with solitary Rugosans are known in the eastern part of the Anti-Atlas region at Tafilalt, in eastern Morocco and in the Béchar Basin in Algeria. The marine connections between northwest Europe and the southern part of the Azrou-Khenifra Basin is supported by similar early Visean assemblages recognized in northwest Europe with abundant solitary Rugose and Tabulate Corals, but with colonial Rugosans: Normandy (north France), southern Belgium, southwest Province, North Wales, Craven Lowlands and South Cumbria (Great Britain), and Dublin Basin in Ireland.

In relation to the tabulate corals, the Tabulate Turnacipora megastoma in the Ba Moussa West assemblage was also known from Central Saharian basins, but also from the Chadian-Arundian (early Visean) locations in northwest Europe (UK, Ireland, France, Germany?). The occurrence of Pleurosiphonella crustosa is the first report in North Africa and suggests marine connection with the Urals. It was first described from the upper Tournaisian of Transcaucasia and its age range extends here slightly into the early Visean. The dispersion between southwest Asia (Armenia, Taurides and Alborz) and the Azrou-Khenifra Basin, via Tafilalt, Béchar and Sinai, is poorly established. Some solitary Rugosans (Siphonophyllia) are common to all areas, but others, such as Kueichouphyllum and the colonial form Eokoninkocarinia, indicative of Asiatic affinity are clearly absent in Morocco.

A new early Visean Coral assemblage has been discovered transported in the rhythmic facies deposits of the southern part of the Azrou-Khenifra Basin, northwest of Khenifra, Morroco. The Ba Moussa West coral fauna includes the new species Siphonophyllia khenifrense, as well as Sychnoelasma urbanowitschi, Cravenia lamellata, Cravenia tela, Cravenia rhytoides, Turnacipora megastoma and Pleurosiphonella crustosa. The early Visean age of the Coral assemblage is supported by microfossil data, which confirms a previous hypothesis that indicated a first transgression during the early Visean in the Carboniferous of the Meseta. The allochthonous coral assemblage was recovered from coarse-grained proximal limestone debris flow and turbidite beds within a fault-bounded rhythmic unit in the eastern part of the basin. No evidence remains of the former early Visean shallow-water platform from which the Corals were derived. All other in situ platform carbonate rocks around the southern margin of the Azrou-Khenifra Basin are of late Visean (Asbian–Brigantian) age. The early Visean Ba Moussa West Coral fauna can be compared with that from the Saharian basins of southeast Morocco and Algeria. Most of the genera and species in the Ba Moussa West assemblage are identical to those in Western Europe, indicating possible marine connections. The new Rugose species described, Siphonophyllia khenifrense, is probably endemic to North Africa. Its ecological niche in northwest Europe was occupied by Siphonophyllia cylindrica or Siphonophyllia aff. garwoodi.

The microfossil determinations provide greater precision in the age dating of the Ba Moussa West limestones. The foraminiferal assemblages from BMW1 can be attributed to the lowermost Visean (MFZ9). Similarly, the Conodont fauna recovered from the same beds, although sparse, suggests a late Tournaisian to early Visean age.

See also...

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https://sciencythoughts.blogspot.com/2020/06/spirobranchus-spp-christmas-tree-worms.htmlhttps://sciencythoughts.blogspot.com/2020/05/understanding-distribution-of-corals-on.html
https://sciencythoughts.blogspot.com/2020/05/acropora-cervicornis-assessing-success.htmlhttps://sciencythoughts.blogspot.com/2020/05/deciphering-changes-in-symbiotic.html
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