Open AccessGraptolite dynamics in Silurian and Devonian time
Author(s) -
T. N. Koren
Publication year - 1987
Publication title -
bulletin of the geological society of denmark
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.674
H-Index - 28
eISSN - 2245-7070
pISSN - 0011-6297
DOI - 10.37570/bgsd-1986-35-16
Subject(s) - paleontology , pelagic zone , ordovician , extinction (optical mineralogy) , geology , devonian , extinction event , carbonate platform , late devonian extinction , carbonate , oceanography , sedimentary depositional environment , carboniferous , population , biological dispersal , materials science , demography , structural basin , sociology , metallurgy
On the basis of biostratigraphic data known at present some preliminary attempts are made to evaluate graptolite dynamics, that is changes in graptolite diversity in time and space within pelagic fades of Silurian and Early Devonian age. For the comparative studies of diversity fluctuations versus some major environmental changes a standard graptolite zonation is used. Several critical and more or less well studied stratigraphical intervals are chosen; among them the Ordovician/Silurian, Sheinwoodian/Gorstian and Gorstian/Ludfordian boundary beds. For each level the most complete reference sections are analyzed. Special attention is given to the graptolite extinction, specification and radiation events within these time intervals. They might have been partly connected with or influenced by the environmental factors as a result of eustatic sea-level and climate changes, alteration of anoxic conditions, migration of carbonate sedimentation in pelagic direction, and other globally detectable events. The graptolite evolution during the time of monograptid existence can be subdivided into three phases using the comparison of the amplitude of the extinction-origination events and repeatability of the synphasic cycles.