The Ordovician acritarch genus Coryphidium

Abstract

The acritarch genus Coryphidium Vavrdová 1972 is one of the most frequently recorded acritarch taxa in the Ordovician. The original diagnoses, stratigraphical ranges and geographical distribution of all Coryphidium species are critically evaluated in a review of published literature supplemented by studies of material from the British Isles, Belgium, the Czech Republic, Germany, Spain, Morocco, Algeria, Tunisia, Lybia and China, including sections from type areas. The taxonomic concept of the genus is here rationalized: the genus Coryphidium is emended and the informal category of coryphid acritarchs is introduced to include all morphotypes with the characteristic vesicle shape of the two genera Coryphidium and Vavrdovella Loeblich and Tappan 1976. Nine of the previously described species can be attributed to the genus, and two other species possibly belong to it. The attribution to Corphydium of the species C. sichuanense Wang and Chen 1987 is rejected here. Intraspecific variability is very important and the attribution of Coryphidium specimens at the specific level is sometimes difficult. The genus is found in all palaeoenvironments from nearshore to offshore settings and apparently does not occupy specific palaeoecological niches. Coryphidium is very useful biostratigraphically and palaeobiogeographically. The review indicates that the genus first appears in the uppermost Tremadocian Araneograptus murrayi graptolite Biozone and is common through the upper Lower Ordovician and the Middle Ordovician, while Upper Ordovician occurrences might be the result of reworking. Palaeogeographically, Coryphidium is an indicator of the peri-Gondwanan acritarch "palaeoprovince" during the Early/Middle Ordovician.

Palynology of the Ordovician Kanosh Shale at Fossil Mountain, Utah

“…The Peri-Gondwana Province is characterized by the genera Arbusculidium , Arkonia , Coryphidium , Dicrodiacrodium , Frankea , and Striatotheca (Li, 1987; Colbath, 1990; Albani et al, 1991; Brocke et al, 1995; Vecoli, 1999; Servais et al, 2003; Vanguestaine and Wauthoz, 2011). The differentiation of this acritarch bioprovince began in the late Tremadocian, with the first representatives of the genus Striatotheca and Coryphidium appearing in the stratigraphic record (Tongiorgi and Di Milia, 1999; Brocke et al, 1995; Servais et al, 2008). None of these Peri-Gondwanan taxa are present in the Kanosh Shale assemblage.…”

Middle Ordovician acritarchs and problematic organic-walled microfossils from the Saq-Hanadir transitional beds in the QSIM-801 well, Saudi Arabia

“…12), that clearly shows a thicker-walled vesicle. Neither the successive emendations of the genus by Colbath (1986) and Servais (1993), nor the discussions and remarks on the genus by Fatka et al (1997) and Vecoli et al (1999a, b) Burmann, 1970, which differs in having a darker and thicker-walled vesicle, and an important variability in the termini of processes, in the form and number of pinnae.…”

First Appearance Datums (FADs) of selected acritarch taxa and correlation between Lower and Middle Ordovician

“…-The genus Coryphidium (Fig. 5G), reviewed by Servais et al (2008), is a common component of acritarch assemblages from the Floian to Darriwilian stages of Perigondwana, but its first occurrence is in the uppermost Tremadocian. The genus has not been recorded from Baltica or Laurentia (Servais & Fatka 1997) and is one of the taxa used to define the Perigondwanan acritarch province (Li 1989;Servais et al 2003;Molyneux et al 2013).…”