Mud Mounds Research Articles

An overlooked contribution to Devonian studiesin the Holy Cross Mts: rediscovering Alexei Doronin’s 1893 article on the Kadzielnia Limestone

The unused Kadzielnia quarry in Kielce is the most publicly known geological site in the Holy Cross Mts and its geotouristic landmark (now the Kadzielnia Park and Reserve). The ‘rocky’ (coral) Kadzielnia Limestone, corresponding to a stromatoporoid-microbial mud mound, now treated as the Kadzielnia Massive Limestone Member of the Kowala Formation, has been studied for almost 200 years. This large bioherm is famous for its exceptionally diverse fossil inventory. The history of its geological exploration is insufficiently known, as exemplified by the overlooked contribution of Alexei Doronin, a master’s student at the Imperial University of Warsaw (IUW). In 1893, under the guidance of Professor Vladimir Amalitsky, he published a note on the age of the Kadzielnia Limestone. The paleontological basis for this discussion was the IUW student’s fossil collection, in which Doronin identified 28 taxa, mainly brachiopods (19 species). He was the first to recognize the occurrence of gastropods (e.g., Loxonema) and crinoids, and at least four species of brachiopods (e.g., Dielasma sacculus). In a comprehensive brachiopod-based stratigraphic discussion, Doronin emphasized the great similarity of the Kadzielnia assemblage to the Middle Devonian fauna of Western Europe, but also including the typical Upper Devonian species Rhynchonella cuboides. Ultimately, he advocated assigning a terminal Middle Devonian age to the Kadzielnia Limestone. Despite this erroneous dating, Doronin’s noteworthy but unnoticed contribution holds significant implications not only for further study of Kadzielnia but also for understanding the development of geosciences in the late 19th century in the Congress Poland (then part of partitioned Poland within the Russian Empire), including the academic role of the IUW. Unfortunately, for reasons unknown, the scientific career of Amalitsky’s talented pupil never truly began.

Depositional model of the Member Deng-2 marginal microbial mound-bank complex of the Dengying Formation in the southwestern Sichuan Basin, SW China: Implications for the Ediacaran microbial mound construction and hydrocarbon exploration

Recent advances in hydrocarbon exploration have been made in the Member Deng-2 marginal microbial mound-bank complex reservoirs of the Dengying Formation in the western Sichuan Basin, SW China, where the depositional process is regarded confusing. The microfacies, construction types, and depositional model of the Member Deng-2 marginal microbial mound-bank complex have been investigated using unmanned aerial vehicle photography, outcrop section investigation, thin section identification, and seismic reflections in the southwestern Sichuan Basin. The microbialite lithologic textures in this region include thrombolite, dendrolite, stromatolite, fenestral stromatolite, spongiostromata stone, oncolite, aggregated grainstone, and botryoidal grapestone. Based on the comprehensive analysis of “depositional fabrics–lithology–microfacies”, an association between a fore mound, mound framework, and back mound subfacies has been proposed based on water depth, current direction, energy level and lithologic assemblages. The microfacies of the mound base, mound core, mound flank, mound cap, and mound flat could be recognized among the mound framework subfacies. Two construction types of marginal microbial mound-bank complex have been determined based on deposition location, mound scale, migration direction, and sedimentary facies association. Type Jinkouhe microbial mound constructions (TJMMCs) develop along the windward margin owing to their proximity to the seaward subfacies fore mound, with a northeastwardly migrated microbial mound on top of the mud mound, exhibiting the characteristics of large-sized mounds and small-sized banks in the surrounding area. Type E’bian microbial mound constructions (TEMMCs) primarily occur on the leeward margin, resulting from the presence of onshore back mound subfacies, with the smaller southwestward migrated microbial mounds existing on a thicker microbial flat. The platform margin microbial mound depositional model can be correlated with certain lateral comparison profile and seismic reflection structures in the 2D seismic section, which can provide references for future worldwide exploration. Microbial mounds with larger buildups and thicker vertical reservoirs are typically targeted on the windward margin, while small-sized microbial mounds and flats with better lateral connections are typically focused on the leeward margin.

A new reef classification model with insights into Phanerozoic evolution of reef ecosystems

AbstractOrganic reefs are largely calcareous build‐ups of sessile organisms, commonly in shallow marine ecosystems, with a long Precambrian to Modern history. Despite a long history of study, the reef classification is still open to development due to reefs encompassing diverse organic and inorganic components with various imprecise and synonymous terms. In this study, a new classification model for organic reefs is expressed in two hierarchical levels.Level 1: Reef outline geometry has two major forms: bioherms (prominent relief and laterally constrained) and biostromes (low relief and large lateral extension interbedded with non‐reef sediments), within which constructional components highly vary.Level 2: Four reef constructor groups form end‐members in a pyramid diagram: macroskeleton (S), microbia (Mi), matrix (Ma) and cement (C). Thus five reef types are recognized depending on the composition and structure of these constructors: (i) S‐supported reef; (ii) Mi‐supported reef (calcimicrobial and agglutinated microbial); (iii) Ma‐supported reef (cluster and carbonate mud mound); (iv) C‐supported reef; and (v) hybrid component‐supported reef (comprising two or more major types of reef components). This arrangement makes a more streamlined and accessible reef classification than prior schemes. Two associated non‐reef habitats that may grade into reefs are relevant: debris biostromes/banks and level‐bottom communities containing taxa found in adjacent reefs. Based on this ‘SMiMaC’ model, the structural evolution of reef ecosystems is demonstrated for the Phanerozoic, characterized by S‐supported and hybrid‐supported, and Mi‐supported and Ma‐supported structures under cooling and intense warming climates, respectively.

Revisiting the upper Visean mud mounds from Derbyshire (UK): the role of brachiopods in their growth

Several brachiopod-rich mud mounds occur in the upper Visean (Brigantian) of the Derbyshire Carbonate Platform succession in UK. The re-evaluation of the lithofacies architecture of a Derbyshire mud mound complex, developed in an intraplatform middle-ramp environment, led to the recognition of three lithofacies associations: (a) a 10 m thick basal unit of automicrite boundstone with siliceous sponge spicules and brachiopod–bryozoan packstone to wackestone beds; (b) a 10 m thick, 250 m wide, lens-shaped, convex-up massive core of clotted peloidal micrite and fenestellid bryozoan boundstone with sponge spicules; (c) inclined brachiopod–bryozoan–crinoid packstone flank beds. In the mud mound complex core, most of the carbonate mud with clotted peloidal and structureless micrite fabric is the result of biologically induced and influenced in-situ precipitation processes (automicrite). Brachiopods are not, as previously thought, limited to storm-scoured “pockets” in the mud mound complex core but are abundant and diverse in all lithofacies and lived on the irregular mud mound complex surface concentrating in depressions sustained by automicrite boundstone and the growth of bryozoans and sponges. The upper Visean Derbyshire mud mounds are, thus, representatives of a newly defined fenestellid bryozoan–brachiopod–siliceous sponge mud mound category, occurring in various middle–upper Visean Western European sites, a sub-type of the fenestellid bryozoan–crinoid–brachiopod Type 3 buildups of Bridges et al. (1995). These mud mounds, and other types of brachiopod-rich buildups, developed in carbonate platform settings between fair-weather and storm wave base, in dysphotic environments with dispersed food resources during the Visean. Brachiopod mud mound colonisation was favoured by moderate water depth, availability of food resources, and diverse substrates.

Reef Complexes of the Late Ordovician–Early Silurian Altai Basin: Classification, Structure, Paleobiota, and Paleogeography

Abstract —The paper presents data on the classification, structure, and biota of reef complexes from the Late Ordovician–early Silurian Altai Basin. The early Paleozoic history of the Altai Basin included the early–middle Katian, late Katian, early Hirnantian, late Telychian, and middle–late Sheinwoodian events of large-scale reef formation which produced framework reefs, mud mounds, and coral meadows. The early Paleozoic reefs of the area formed at rates of 40 to ~12 cm per thousand years. The late Telychian reef system, which formed in 0.51–1.0 Myr, occupied the largest area of the basin. The lateral extent of reef systems in the Late Ordovician–early Silurian basin of Altai depended more on the rates of vertical and lateral growth, as well as on the previous sea bottom topography and clastic inputs, than on the duration of reef formation. Carbonate deposition in the Altai basins of that time can be simulated with a general model implying formation of distal barrier reefs.

Callovian-Oxfordian sedimentary microfacies in the middle of Block B on the right bank of the Amu Darya Basin, Turkmenistan

The right bank of the Amu Darya Basin enjoys abundant natural gas resources, on which the Callovian-Oxfordian strata in the middle of Block B serve as the major horizons for natural gas production. However, the characteristics and distribution patterns of the sedimentary microfacies in these strata are yet to be further explored. Based on the analysis of data on drilling, logging, cores, and thin sections from 29 typical wells, as well as the regional sedimentary background, this study inferred that the middle of Block B evolved from the Callovian ramp platform into the Oxfordian rimmed platform. Moreover, this study determined that the inner-ramp intertidal-subtidal shallow-water subfacies mainly developed during the Callovian and transitioned into the shallow shelf subfacies during the Oxfordian. This study identified eight sedimentary microfacies, namely reef knoll, reef-shoal complex, bioclastic shoal, psammitic shoal, bioherm, lime mud mound, intershoal (intermound), and static-water mud. Based on research into the high-precision sequence-sedimentary microfacies framework, this study built a geological model for the development of sedimentary microfacies in the study area. According to this geological model, the sedimentary microfacies in the study area are characterized by vertical alternation of reef-shoal complex, bioclastic (psammitic) shoal, bioherm, and intershoal microfacies. Moreover, they show the development of reef knoll, reef-shoal complex, bioclastic (psammitic) shoal, and bioherm (or lime mud mound) laterally from west to east, with the physical properties of the reservoirs deteriorating from west to east accordingly. The microfacies of reef-shoal complex and the bioclastic (psammitic) shoal predominate in the study area, and their deposition and development are controlled by sequence boundaries and are also affected by paleo-landforms. The Oxfordian reef-shoal complexes were largely inherited from the Callovian uplifts and show lateral seaward progradation.

Reef-associated depositional environments in the lowermost Cretaceous facies (Berriasian) from the Eastern Prebetic domain (South-Iberian Palaeomargin, SE Spain)

The Berriasian carbonate successions cropping out in the shallow-water platform of the easternmost Prebetic Domain (SE Spain) involve reef-associated environments including a diverse epibiota with diceratid representatives unreported so far. Interpretation of different sub-environments suggests a proximal-distal shallow platform transect. In the shallowest nearshore environment, high energy conditions are recorded, with fine-grained bioclasts interbedded with episodes with black pebbles. Subsequently, a more restricted intra-platform environment is represented by oncoidal rudstones with benthic foraminifera, photophilic microencrusters, microbial-type coatings, mud mounds and a rich record of epibenthic biota preserved in life position (diceratid patches, stromatoporoids, and a diverse coral assemblage). This association points to relatively stable and restrictive low-energy conditions in a proximal shallow-water subtidal environment below the fair-weather wave base. Distally, a deeper, opener setting is established. Here, phaceloid and thin-laminated corals are preserved in life position in a calpionellid-rich matrix typifying a mesophotic reefal complex with clear open marine influence. Biostratigraphical analysis performed mainly on benthic foraminifera, algae, diceratids, and coral representatives allows to specify a Berriasian age for these facies. New occurrence data are also reported, such as the oldest record of the coral genus Floriastrea worldwide. The highly diverse coral assemblages reveal a species-level taxonomic divergence in relation with taxa from the same biochore and palaeogeographical domain, supporting the endemic condition for this fauna. The first report of diceratids in the Eastern Prebetic around the J/C transition evokes Heterodiceras as possible precursor of the Cretaceous rudist build-ups developed in the Urgonian platforms in the Prebetic Domain.

Palaeoenvironment, palaeogeography, and palaeoclimatology of the Mississippian carbonate ramp in the Alborz tectonostratigraphic zone: Implications for deciphering the controlling factors on ramp evolution

The Mississippian successions of the Alborz tectonostratigraphic zone have been studied in several sections (Dozdehban, Naserabad, Shahmirzad, and Mighan) extending from north to southeast. The sedimentological data indicate three main facies associations (FA): (FA1) a basin to distal outer ramp of low‐energy, low‐oxygen environment with low bioturbation and less developed in situ fossils; (FA2) a middle ramp facies accompanied by storm‐induced sediments (tempestites), echinoderm‐dominated mud mounds, and high fragmentation of skeletal components; and (FA3) an inner ramp facies, represented by sand shoal, and lagoonal/back‐barrier, mainly characterized by the dominance of oolitic, bioclast, and intraclast grainstones. The sedimentary features imply the formation of the succession on a broad flat‐topped, high‐to‐moderate‐energy shelfal carbonate ramp which had been open to the N/NE, the downslope direction, as revealed by local palaeoenvironmental reconstructions. Analysis of several proxies indicates a subtropical palaeoclimate evidenced by (a) widespread tempestite facies and occurrence of storm‐depositional processes, (b) diverse and abundant pellet‐forming thalassinoideans and burrowing echinoids trace fossil assemblages, (c) geochemical proxy indicating a palaeotemperature of 23°–25°, and (d) a rich subtropical heterozoan fossil association. The data provided here imply the palaeolatitudinal position of the Alborz Mississippian ramp is 30–40°S along the southern margin of the Palaeotethys.

Brachiopod fauna from upper Visean, Mississippian, mud mounds in Derbyshire, UK

Brachiopod fauna from upper Visean, Mississippian, mud mounds in Derbyshire, UK

Cephalopod accumulations from the Late Ordovician of Cumbria: Mud mounds and stromatolites

Accumulations of cephalopods in the Late Ordovician (Katian [Ka4]) Troutbeck Siltstone Member of the Ash Gill Mudstone Formation at Skelghyll Beck in the Lake District and in the Keisley Limestone Formation of the Cross Fell Inlier contribute toward an understanding of their respective depositional environments as well as the palaeogeography of the southeastern margins of the Lakesman Terrane. The accumulation present in the Troutbeck Siltstone Member is interpreted as having been deposited in a shallow, near-shore lagoon that supported stromatolite growth. The shore lay to the north of this site. Geopetals infilling cephalopods forming concentrations in the Keisley Limestone Formation indicate that the conchs came to rest on angles of 30–40° to horizontal. The lithologies of the matrix suggest that they were deposited in cavities or fissures from which fine-grained carbonate was either excluded or winnowed away. Both observations accord with hypotheses that the Keisley Limestone Formation represents the remnants of a carbonate mud mound, and facilitate comparison with the contemporaneous Boda mounds of Siljan, Sweden. Comparison with local late Katian – Hirnantian successions indicate that the Keisley mound would have formed a prominent feature on the sea floor, becoming largely buried by argillaceous sediments during the Hirnantian.

Addressing a Phanerozoic carbonate facies conundrum—sponges or clotted micrite? Evidence from Early Silurian reefs, South China Block

We describe Early Silurian carbonate reef facies containing amalgamated micritic masses, commonly layered, interpreted to have formed by bacterial processes creating clotted fabrics. However, some curved structures in these masses resemble published images of interpreted sponges, raising the question of their nature, relevant to many carbonate studies including reefs and mud mounds throughout the Phanerozoic. Many lithistid sponges are well-established but others are open to interpretation. For keratose sponges, Cambrian examples are known, but several interpreted cases in later rocks are not confirmed; one example in Devonian and Triassic rocks using 3D imaging did not lead to firm verification. Thus criteria to distinguish sponges and clotted micrites remain problematic. A careful approach to interpretation of such sponges is needed, they might instead be microbially-mediated clotted micritic masses. The difficult process of 3D reconstruction is likely needed to resolve this interesting issue of interpretation.

From lagoons to mud mounds: palaeoecology of the Givetian to Frasnian stromatoporoids from the Holy Cross Mountains, Poland

Stromatoporoids are an extinct group of Palaeozoic sponges that dominated the Devonian carbonate buildups. Although their general environmental requirements are known, their palaeoecological preferences at genus level are less studied. Seven stromatoporoid associations are distinguished within the Givetian (Middle Devonian; associations 1–3) and Frasnian (Upper Devonian; associations 4–7) of the Holy Cross Mountains in Poland, namely: (1) Arctostroma–Pseudoactinodictyon; (2) Actinostroma–Clathrocoilona; (3) Atelodictyon–Stachyodes; (4) Amphipora–Pseudoactinodictyon; (5) stromatoporoid–microbialite bafflestone and bindstone; (6) Stictostroma–tabulate corals; and (7) Hermatoporella–Stictostroma. Stromatoporoid associations 1–3 are late Givetian to earliest Frasnian in age, while associations 4–7 are from the early to middle Frasnian. Associations 1 and 4 occupied calm and shallow parts of the carbonate platform, associations 2 and 7 thrived in more agitated waters, whereas other associations inhabited the deeper, low-energy environments and mud mounds of the platform slope. General stromatoporoid diversity at genus level is high, but individual associations consist of 4–10 genera. Stromatoporoids of associations 1–2 and 7 are overturned and/or broken/redeposited, and hydrodynamically unstable, sediment-laden facies dominate the stromatoporoid-bearing Devonian carbonate platform facies of the Holy Cross Mountains. Lagoonal and biohermal environments were inhabited by dendroid, laminar and domical stromatoporoids, whereas digitate shapes are common within the associations that formed in more agitated water. Most representatives of the order Clathrodictyida were prone to physical destruction and inhabited low-energy settings. Genera having skeleton supported by thick pillars or network of oblique elements, less affected by physical skeletal breakage, thrived in agitated waters.

A new large mound dwelling chiton (Mollusca), from the Late Ordovician Boda Limestone of central Sweden

ABSTRACT A new rare Upper Ordovician mound dwelling palaeoloricate chiton is described as Crassaplax collicola gen. et sp. nov. from three large isolated intermediate valves from the Katian carbonate mud mounds of the Boda Limestone in the Siljan district of central Sweden. Together with the previously known Spicuchelodes? sp., also from the Boda Limestone, these are the only known Late Ordovician mound dwellers so far among the palaeoloricates, adding to Ordovician environments with reported chiton remains. Crassaplax collicola is distinguished from other Ordovician palaeoloricate chitons by their thick and large valves that can be 2 cm in length, and especially the clear differentiation between the lateral and central valve areas.

Upper Devonian (Frasnian) stromatactis-bearing mud mounds, western Alberta, Canada: reef framework dominated by peloidal microcrystalline calcite

ABSTRACT Two well-preserved mud mounds, approximately 50 m thick, in the Mount Hawk Formation (Upper Devonian, Frasnian) in western Alberta provide an unparalleled opportunity to study the microstructure of this reef type in detail for this time interval. This reveals that they are composed dominantly of peloidal sediments—more than a quarter of mud mound volume—along with dense micrite, particulate micrite, bioclasts, and stromatactis cavities. Five types of peloids are differentiated: bacterial, cyanobacterial, bioclastic, intraclastic, and pseudo-peloids. Bacterial peloids were generated by bacterial metabolic activities with possibly some contribution from organomineralization in areas within spicular networks. Three subtypes of cyanobacterial peloids are distinguished based on whether they are physically reworked calcified filaments, aggregates of calcified coccoids, or precipitated within stromatolite-forming cyanobacterial mats or biofilms. Bioclastic peloids are fully micritized fragments of skeletons and shells. Intraclastic peloids are eroded fragments of early-lithified matrix. Pseudo-peloids represent artifacts of poorly preserved sponge spicular networks reflecting the interplay between dissolution of spicules and organomineralization. The distribution of the various peloid types shows specificity in different microfacies. They prove to be valuable paleoecological indicators, and taken together suggest that the mud mounds accreted within the photic zone above storm wave base but below the fair-weather wave base, during deposition of a transgressive and perhaps highstand systems tracts. They are the products reflecting a dynamic balance between constructional versus destructive processes. Bacterial peloids combined with dense micrite constitute the framework, which in turn makes up close to 40% of the mud mounds. This indicates that microbial activities are responsible for the early-indurated framework. The onset of bacterial peloid formation in the bedded sediment immediately underlying the mud mounds further demonstrates that it may have been a necessary precursor to mud-mound initiation. Bacterial peloids appear to characterize most Paleozoic and Mesozoic reefal mud mounds as an essential framework element.

The characteristics and controlling factors of facies-controlled coastal eogenetic karst: insights from the Fourth Member of Neoproterozoic Dengying Formation, Central Sichuan Basin, China

Karst porosity system is widely developed in the Fourth Member of Neoproterozoic Dengying Formation in Central Sichuan Basin of China. The result of the previous exploration in this area based on the theory of telogenetic karst, which mainly focused on the fracture/fault belt especially in the karst slope, leaves much to be desired. Though a systematically geological research in this study, it is found that the dissolution holes are mainly concentrated on the mud mound deposits and granular rocks. Both of them have a greater primitive porosity and permeability than the micrite that originally formed in low-energy environments, which is facies controlled. On the basis of the above and the fact that a tectonic movement has caused a massive subaerial exposure of the formation that only experienced a shallow burial, it is proposed that the paleokarst porosity system is the product of eogenetic karst. Two-stage eogenetic karsts have been interpreted: the syngenetic exposure caused by the short-term relative sea-level fluctuation and the exposure caused by the uplift of the second phase of Tongwan tectonic movement. The meteoric alteration in syngenetic period is commonly marked by the development of intergranular pores but on a small scale. It is believed to be important for providing a good pore-permeability foundation for the later eogenetic karst. The later exposure occurs immediately at the end of the deposition of the Fourth Member of Dengying Formation that only experienced a shallow burial. Since the effect of compaction and cementation in this shallow burial before uplift is relatively weak, only the micrite has been densified and retaining the majority of original pores in the carbonate mounds and grain shoals as paths for karst flow. Moreover, combined with the geological background and seismic profile, it can be ascertained that the karst occurs in a coastal environment. Twelve meteoric lenses have been interpreted after recovering the karst palaeogeomorphology. The scale of the meteoric lens and the reservoir performance have shown a decreasing tendency from the coastal to the inland area, which also confirms this view. The results of this research have put emphasis on the lithologic differentiation in eogenetic karst and the geographical location of karst development thus might provide a reference for further reservoir prediction in this area and other similar places.

Ordovician carbonate mud mounds of the Baltoscandian Basin in time and space – A geophysical approach

Carbonate mud mounds developed within the Baltoscandian Basin, an epicratonic basin on the Baltica palaeocontinent, during the Ordovician. In the Upper Ordovician succession of the Baltoscandian Basin, a large number of mud mounds are present at three stratigraphic levels namely, the Kullsbergs mounds (late Sandbian-early Katian), Nabala and Rakvere mounds (middle Katian), and the Boda mounds (late Katian). These formed in a subtropical-tropical carbonate platform environment, covered by a shallow epicontinental sea. The mud mounds at these stratigraphic levels beneath and around Gotland have been characterized using a comprehensive seismic and well dataset acquired during a period of hydrocarbon exploration and exploitation which began more than 30 years ago. Interpretation of the largely unpublished seismic data in this study provides details on the distribution of mound complexes in the basin and constraints on the geometry of the mounds. Detailed structure contour maps of the top and the base of the Ordovician succession beneath Gotland based on the seismic interpretation are presented. The results give a comprehensive characterization of carbonate mud mound generation on Gotland which may help in understanding the distribution patterns of similar mound complexes in other parts of the Ordovician world formed in similar environments.

Recurring cryptic ecosystems in Lower to Middle Devonian carbonate mounds of Hamar Laghdad (Anti-Atlas, Morocco)

Exceptionally well-preserved fossil cryptic communities have been discovered in submarine cavities of the Lower and Middle Devonian (Emsian to Givetian) mud mounds in the Hamar Laghdad area (Anti-Atlas, Morocco). The cryptic biota encrusted the roofs of the cavities and grew predominantly oriented upside down. These unique coelobiotic communities were dominated by various solitary rugose corals, which very often displayed a “calice-in-calice” growth pattern. Apart from the rugosans, the cavities were inhabited by other sessile invertebrates: tabulate corals, cladochonids, crinoids and lithistid sponges. Many of the skeletons were encrusted by microbial structures. The high density of organisms overgrowing each other points to intensive competition for space in all studied Devonian submarine crypts. The late Emsian to latest Givetian cavities were colonised by various sets of coelobiotic inhabitants mostly originating from the surrounding deep-water marine environments. It is suggested that the local species pool was a decisive factor in determining the ecological succession and taxonomic structure of cryptic communities. The changes in taxonomic composition and diversity, over time and space, were primarily related to variations in local physical environment. Consequently, the communities in crypts affected by venting of high-temperature fluids or hydrocarbon seepage were of low diversity and included endemic elements and characteristically small specimens.

The cephalopods of the Kullsberg Limestone Formation, Upper Ordovician, central Sweden and the effects of reef diversification on cephalopod diversity

The cephalopods collected from the mud mounds of the Kullsberg Limestone Formation, late Sandbian–earliest Katian(?), south central Sweden, are highly diverse and comprise 26 identifiable species of 12 families and six orders in a sample of c. 180 specimens. The assemblage is strongly dominated by orthocerids in abundance and diversity. In contrast, the time-equivalent assemblage of the reef limestone of the Vasalemma Formation of Estonia is dominated by actinocerids and less diverse. Only one-third of the species co-occur in these two palaeogeographically relatively close assemblages. The taxonomic composition of the Kullsberg assemblage is, on the order level, more similar to that of the late Katian–early Hirnantian Boda Limestone Formation of south central Sweden, which represents a similar relatively deep depositional environment. The high local differentiation of cephalopod reef faunas exemplifies the importance of the emergent Baltic reef habitats in diversification processes during the early Late Ordovician. Of the described taxa, the following are new: Beloitoceras thorslundi sp. nov., Cameroceras motsognir sp. nov., Clothoceras thornquisti gen. et sp. nov., Danoceras skalbergensis sp. nov., Discoceras amtjaernense sp. nov., D. nilssoni sp. nov., Endoceras naekki sp. nov., Furudaloceras tomtei gen. et sp. nov., Isbergoceras consobrinum gen. et sp. nov., I. niger gen. et sp. nov., Isorthoceras nikwis sp. nov., I. sylphide sp. nov., I. urdr sp. nov., I. verdandi sp. nov., Kullsbergoceras nissei gen. et sp. nov., Ordogeisonoceras uppsalaensis sp. nov. and Valkyrioceras dalecarlia gen et sp. nov.http://zoobank.org/urn:lsid:zoobank.org:pub:F5243F9B-547C-424F-895F-6CCECA8BBF11

Placodermi from the Early Devonian Kess-Kess mounds of Hamar Laghdad, Southern Morocco

Late Devonian placoderms from Morocco are know since the1930s and were described in detail. Earlier collections and descriptions, however, demonstrated the range of placoderm fossils in Morocco from the Emsian up to the Famennian. Subsequently, more material was discovered and research focused on the description of new anatomical details visible after applying acid preparation, mainly of Early Devonian material. The distribution of placoderm remains and occurence in association with Kess-Kess mud mounds at Hamar Laghdad is not yet mentiones in detail in the literature and some diagnostic remains of Antineosteus lehmani are described herein for the first time from this locality in the Tafilalt.

Jurassic reef events in the Moroccan Atlas: A review

In the Moroccan Atlas, sedimentary deposits provide important data on reef events that characterize the Jurassic period. Recent work allows us to enhance knowledge of the Jurassic reefs in the Atlas, in particular their age, character and palaeogeographic distribution. Numerous localities with sponge-microbial mud mounds, coral reefs, and lithiotid bioherms are recorded from the Middle and High Atlas regions. These different biogenic constructions occupy different palaeogeographic settings: on the top of tilted blocks within the basin center; in slightly deeper positions, at the basin platform junction; and on adjacent platforms in the middle of the coastal area. The main episodes of reef building span nearly 30 million years, as follows: (1) Sinemurian, (2) early Pliensbachian, (3) late Toarcian, (4) Aalenian–early Bajocian (pars), and (5) late Bajocian. These five distinct reef events can be linked with general fluctuations of sea level and tectonism, and have palaeoclimatic implications.