Annalisa Ferretti

FIRST RECORD OF ORDOVICIAN CONODONTS FROM SOUTHWESTERN SARDINIA

A first illustration of Ordovician conodonts from Sardinia is briefly given. The assemblage, belonging to the HDS biofacies, indicates an early-middle Ashgillian age.

Exceptionally preserved conodont apparatuses with giant elements from the Middle Ordovician Winneshiek Konservat-Lagerstätte, Iowa, USA

Abstract. Considerable numbers of exceptionally preserved conodont apparatuses with hyaline elements are present in the middle-upper Darriwilian (Middle Ordovician, Whiterockian) Winneshiek Konservat-Lagerstätte in northeastern Iowa. These fossils, which are associated with a restricted biota including other conodonts, occur in fine-grained clastic sediments deposited in a meteorite impact crater. Among these conodont apparatuses, the common ones are identified as Archeognathus primus Cullison, 1938 and Iowagnathus grandis new genus new species. The 6-element apparatus of A. primus comprises two pairs of archeognathiform (P) and one pair of coleodiform (S) elements. The 15-element apparatus of I. grandis n. gen. n. sp. is somewhat reminiscent of the prioniodinid type and contains ramiform elements of alate (one element) and digyrate, bipennate, or tertiopedate types (7 pairs). Both conodont taxa are characterized by giant elements and the preservation of both crowns and basal bodies, the latter not previously reported in Ordovician conodont apparatuses. Comparison of the apparatus size in the Winneshiek specimens with that of the Scottish Carboniferous soft-part-preserved conodont animals suggests that the Iowa animals were significantly larger than the latter. The apparatus of A. primus differs conspicuously from the apparatuses of the prioniodontid Promissum from the Upper Ordovician Soom Shale of South Africa although the apparatus architecture of I. grandis n. gen. n. sp. shows some similarity to it. Based on the Winneshiek collections, a new family Iowagnathidae in Conodonta is proposed.

PROBLEMATIC PHOSPHATIC PLATES FROM THE SILURIAN–EARLY DEVONIAN OF BOHEMIA, CZECH REPUBLIC

Abstract Problematic phosphatic elements are reported for the first time from Bohemia, Czech Republic, and are attributed to Eurytholia bohemica n. sp. Similar mineralized elements, interpreted as sclerites, were known only in a very narrow interval from Middle-Late Ordovician beds bordering the Iapetus Ocean. This new report comes from the Silurian and Early Devonian and provides a significant range extension for these Problematica as well as an enlargement of their geographic extent. Comments open new perspectives in the interpretation of these elements.

The Hercynian Arburese Tectonic Unit of SW Sardinia: New stratigraphic and structural data

New structural and biostratigraphic data, mainly based on conodonts, permit the recognition of three different sub-units within the Hercynian Arburese Tectonic Unit of SW Sardinia, which are here described. Some stages and conodont biozones of Silurian-Early Devonian age are reported for the first time in Sardinia.

Diagenesis does not invent anything new: Precise replication of conodont structures by secondary apatite

Conodont elements are important archives of sea/pore water chemistry yet they often exhibit evidence of diagenetic mineral overgrowth which may be biasing measurents. We decided to investigate this phenomenon by characterising chemically and crystallographically, the original biomineral tissue and the diagenetic mineral nature of conodont elements from the Ordovician of Normandy. Diagenetic apatite crystals observed on the surface of conodont elements show distinctive large columnar, blocky or web-like microtextures. We demonstrate that these apatite neo-crystals exhibit the same chemical composition as the original fossil structure. X-ray microdiffraction has been applied herein for the first time to conodont structural investigation. Analyses of the entire conodont element surface of a variety of species have revealed the existence of a clear pattern of crystal preferred orientation. No significant difference in unit cell parameters was documented between the newly formed apatite crystals and those of the smooth conodont surfaces, thus it emerges from our research that diagenesis has strictly replicated the unit cell signature of the older crystals.

Silurian agglutinated foraminifera from the Dingle Peninsula, Ireland

An assemblage of primitive agglutinated foraminifera is reported for the first time from Silurian limestones from the Dingle Peninsula, Ireland. The assemblage is dominated by tubothalamids (Rectoammodiscus and rare Sansabaina), with less abundant monothalamids (Psammosiphonella and Psammosphaera). At the species level, the agglutinated foraminiferal assemblage is identical to those described previously from the Silurian of North America but is of lower diversity. The foraminiferal assemblage has limited potential for stratigraphic correlation as long-ranging taxa are present. The co-occurring conodont fauna enables an assignment to the early Ludlow. RIASSUNTO [Foraminiferi agglutinanti nel Siluriano della Penisola di Dingle, Irlanda] Viene qui descritta per la prima volta una associazione di foraminiferi agglutinanti all’interno di calcari siluriani della Penisola di Dingle, Contea di Kerry, Irlanda sud-occidentale. La collezione è stata rinvenuta nel residuo di campioni trattati per la preparazione di conodonti. I foraminiferi sono dominati da tubotalamidi (Rectoammodiscus e rari Sansabaina), mentre più rari sono i monotalamidi (Psammosiphonella e Psammosphaera). A livello specifico l’associazione presente in Irlanda è identica a quella descritta in precedenza nel Siluriano del Nord America, anche se presenta minore diversità. Tutte le specie rinvenute hanno una lunga distribuzione stratigrafica, e quindi ricoprono un significato limitato per correlazioni stratigrafiche. La fauna a conodonti ritrovata nei campioni ha permesso una attribuzione dei foraminiferi agglutinanti alla parte iniziale del Ludlow.

Europa im Paläozoikum

Kaum jemand wurde Europa in Abbildung 2A erkennen, einer Karte unseres Kontinents vor 480 Millionen Jahren. Das heutige Europa ist wahrhaftig ein Flickenteppich aus alten Kontinental-Blocken, jeder von ihnen mit einer langen geologischen Geschichte, die im Laufe des Phanerozoikums zusammengeschweisst wurden. Laurentia, Baltica, Avalonia und Gondwana sind die bekanntesten alten Kontinental- Schollen; daneben gibt es einige weniger bekannte Terranes, die meisten im gegenwartigen Mittel- und Sudeuropa. Einige dieser Kontinental-Blocke wie Avalonia und Baltica sind fast ganzlich Teile Europas geworden, wahrend andere wie Laurentia und Gondwana nur kleine Stucke beigetragen haben. Ferner wurden kleinere Stucke kontinentaler Kruste erst an Europa angelagert, dann wieder endgultig von Europa getrennt. Die geologische Geschichte Europas wird daher beherrscht durch bedeutende Ereignisse wie die Kollision von Kontinenten, Offhung und Schliessen alter Ozeane und durch die Auffaltung von Gebirgszugen.