Biostratigraphy and palaeogeography of lower Devonian Chitinozoans, from East and West Moesia, Romania

The knowledge on the biostratigraphy of Moesia has been supplemented based on chitinozoan assemblages in two boreholes, one from East Moesia and the second one from West Moesia. Previous contributions on chitinozoans, acritarchs and miospores, using only the optical microscopy corroborated by macrofaunal data have been already published. An Upper Lochkovian succession could be identified and a more accurate position of the Lower - Middle Devonian boundary is proposed in the borehole from East Moesia. The Emsian is documented in the borehole from West Moesia. The geographical position of East Moesia and possibly West Moesia during the Lower Devonian is similar to those from Northern Gondwanan localities as demonstrated by the chitinozoan assemblages recognized in the present work. Systematic notes, including biometric investigations and SEM images are provided for selected taxa of taxonomic significance and palaeogeographical distribution

Graptolites et Chitinozoaires Siluriens de la vallée de la Burdinale, Massif du Brabant, Belgique

Assemblages of graptolites and chitinozoans are descnbed respectively by B. RICKARDS and J. VERNIERS from Silurian deposits which were studied in the Burdinale valley by J. VERNIERS (Ph. D. dissertation, 1976). These assemblages allow biostratigraphic zonations covering a time interval from late Llandovery to middle Wenlock

Stratigraphy and paleoenvironments of the early to middle Holocene Chipalamawamba Beds (Malawi Basin, Africa)

We describe the Chipalamawamba Beds, early to middle Holocene deposits at the southern margin of long-lived Lake Malawi. The beds are exposed because of downcutting of the upper Shire River. The Chipalamawamba sediments are medium to coarse, yellow to brown sands deposited in lenses varying in horizontal extent from a few meters to several hundreds of meters. Four units are recognized; the first three mainly contain lacustrine sediments deposited during lake high stands about 10.6–9.7 cal ka BP (Unit 1), 7.6–6.5 cal ka BP (Unit 2) and 5.9–5.3 cal ka BP (Unit 3). Sediments of Unit 4 overlay Units 1 to 3, are coarser and display regular foresets and oblique-bedding, suggesting deposition in riverine environments after installation of the Shire River (~ 5.5–5.0 ka BP). Freshwater mollusk assemblages and bioturbation regularly occur in the lacustrine sediments, but are largely absent from Unit 4. Diverse and often contradicting hypotheses on the lake levels of Lake Malawi have been proposed for the early and middle Holocene. The Chipalamawamba Beds allow straightforward recognition of water levels and provide strong evidence for oscillating lake levels during this period, rather than continuous high or low levels. Sedimentation rates have been high and individual shell beds have typically been deposited during a few decades. Because the Chipalamawamba Beds contain a sequence of mollusk assemblages with intervals between subsequent shell beds ranging from a century to a few millennia, they enable paleontological analysis of the fauna with an unusually high temporal resolution. That some mollusk lineages inhabiting Lake Malawi are in the early stages of diversification and radiation increases the paleobiological relevance of these beds

Chitinozoan biozonation and new lithostratigraphical data in the upper Ordovician of the Fauquez and Aquempont areas (Brabant Massif, Belgium)

A chitinozoan biozonation is established for the Upper Ordovician rocks of the Sennette valley in the Fauquez area and the Asquempont area, revising the existing chitinozoan biozonation of the Brabant Massif. The chitinozoans of five formations (the Ittre, Bornival, Huet, Fauquez and Madot formations) are studied from 70 samples. The chitinozoan biozonation is correlated with Baltoscandia and the Avalonian Upper Ordovician type sections in the U.K. This correlation provides an accurate dating of the studied formations. A megaslumping event, affecting a part of the Ittre and Bornival Formation and causing the overturning of a pile of sediments estimated at minimum 200 m thick, may be placed in the mid Oandu (Cheneyan, middle Caradoc, early Stage 6"?). The volcanic rocks in the Fauquez area, formally thought to be restricted to the Ashgill, are confined to the late Caradoc - early Ashgill timespan. In addition to this, this paper presents new lithostratigraphical data on the Ittre Formation and the lower member of the Bornival Formation

New evidence for the Hirnantian (Upper Ordovician) in Belgium? An integrated isotiopical, biostratigraphic and sedimentologic approach

International audienceN/

The stratigraphy of the type locality of the ?Late Wenlock/Early Ludlow Mont Godart formation and the Early Ludlow Ronquières formation, Brabant Massif

The Silurian of the Brabant Massif crops out in the Sennette valley, near Ronquières. From these outcrops, the Mont Godart Formation is defined and the formerly poorly defined Ronquières Formation is redescribed in detail. Seven informal units, four of them divided into subunits, are distinguished in the Ronquières Formation. Based on Chitinozoa and graptolites, the age of the Mont Godart Formation is estimated possibly latest Homerian (Wenlock) or earliest Gorstian (Ludlow) and that of the Ronquières Formation as Gorstian (Ludlow). Four sedimentological facies occur: mud-grade turbidites predominate and are interbedded in anoxic laminated hemipelagites. Oxic bioturbated hemipelagites and metabentonites occur rarely. The palaeoenvironment of the sedimentary basin is interpreted as a turbiditic fan system directed to the east in a E-W trending trough with apparently northward directed currents. A major megacycle spans both formations. Relatively high energy sediments are present in the bottom of the Mont Godart Formation and in the top of the Ronquières Formation. Less energetic sediments, indicating a deeper sea environment, are found in between. A similar cycle of deepening and shallowing has also been observed in the late Wenlock and early Ludlow of the Welsh Borderland and of Gotland on the Baltic platform

A distinctive marginal marine palynological assemblage from the Přídolí of northwestern Saudi Arabia

A rare occurrence of a rich and diverse palynological assemblage from the Tawil Formation is described from well JLMD-EW-8 in northwestern Saudi Arabia. The composition of this assemblage strongly indicates a middle Přídolí age. The assemblage encountered contains very characteristic chitinozoans, acritarchs, tasmanitids, freshwater algae, scolecodonts, eurypterid cuticle and other organic remains. Land-derived miospores are also common and two new cryptospore species (Cymbohilates jalamidensis and Gneudnaspora sordida) are herein formally described. Most taxa of taxonomic interest and useful for regional and intercontinental correlation are illustrated. The palaeogeographic distribution of this assemblage is also discussed as organic-walled microphytoplankton, chitinozoans and miospores encountered in the studied samples correlate well with similar assemblages from various Algerian, Libyan, and Ibero-armorican localities (i.e. Ibarmaghian regions). This corresponds to what is considered as a transgressive middle Přídolí event in the Algerian Sahara, with non-marine intervals bracketing this brief marine sea-level rise. This event is likely to have extended into all of north Gondwana, including Arabia, and can be correlated to the S50 Maximum Flooding Surface from the sequence stratigraphic framework defined in the Neftex Geodynamic Earth Model