Upper Homerian (Silurian) high-resolution correlation using cyclostratigraphy: an example from western Lithuania

Abstract

ABSTRACT:Radzevičius, S., Tumakovaitė, B. and Spiridonov, A. 2017. Upper Homerian (Silurian) high-resolution correlation using cyclostratigraphy: an example from western Lithuania. Acta Geologica Polonica, 67 (2), 307-322. Warszawa.The Gėluva regional stage stratigraphically corresponds to the late Wenlock. This time interval witnessed significant graptolite extinctions and turnovers of conodont faunas, as well as a large positive Mulde carbon isotopic excursion. Thus, the development of a detailed stratigraphy is a necessary step in understanding the complex patterns of regional and global variations in the sediments accumulating during the time interval studied. Therefore, in this contribution we present a cyclostratigraphic analysis of gamma ray (GR) logs from four wells, which are located in the deep water facies belt of the Lithuanian part of the Silurian Baltic Basin of the Gėluva regional stage. The analysis was performed using REDFIT spectral estimation, continuous wavelet transform and signal filtering techniques. As a result two 4 th order and five 5 th order cycles were distinguished and named in all sections. The correlation of cycles between sections was calibrated with the graptolite biozones. The comparative analysis revealed that intra-basinal cyclostratigraphic correlation could achieve resolution of the order of several tens of thousands of years.

Graptolite turnover and δ13Corg excursion in the upper Wenlock shales (Silurian) of the Holy Cross Mountains (Poland)

“…5) (Radzevičius et al 2014b). Similar cyclicities were found in other mid-upper Homerian geological sections of West Lithuania (Radzevičius et al 2017). The Gėluva age corresponds to the mid-later Homerian, namely from 428.45 ± 0.35 Ma to 427.86 ± 0.32 Ma (total ~ 0.59 Ma) (Cramer et al 2015).…”

Cyst size trends in the genus Leiosphaeridia across the Mulde (lower Silurian) biogeochemical event

“…Similarly, previous synoptic studies have shown a close association of acritarch and prasinophyte diversity with global and regional fluctuations in sea level on time scales of millions to tens of millions of years , Delabroye et al 2011, Venckutë-Aleksienë et al 2016. This suggests the importance of sea level dynamics in modulating evolutionary and ecological change in Paleozoic marine phytoplankton as- th order sea level cycles (from (Radzevičius et al 2017). The smoothed non-linear trends in A-C were determined using 5 th order orthogonal polynomial regression.…”

“…The studied core yielded one of the richest arrays of data in the world on the paleoenvironmental changes during the Mulde Event, ranging from graptolite, conodont, brachiopod, polychaete and microphytoplankton biostratigraphy and paleoecology, to stable carbon isotope chemostratigraphy and natural gamma ray cyclostratigraphy (Brazauskas & Paškevičius 1981;Paškevičius 1997;Martma et al 2005;Ekleris & Radzevičius 2014;Radzevičius et al 2014bRadzevičius et al , 2017Venckutë-Aleksienë et al 2016). Additionally, this core contains a stratotype of the lower boundary of the Gëluva regional stage (Kojelë et al 2014), and therefore it is a reference section for the detailed regional stratigraphical correlation and the detection of paleoclimatological and paleobiological patterns.…”

“…In order to gain insights into the mechanisms controlling body size distribution changes of the analyzed green algae we also plotted the time series of proxies: the filtered curve of 4 th order sea level fluctuations (Radzevičius et al 2017) which were proposed to represent the 400 ka eccentricity Milankovitch cycles (Radzevičius et al 2014a). The 4 th order sedimentary cycles were distinguished based on the REDFIT statistical testing (Schulz & Mudelsee 2002) of the natural gamma ray signal with the subsequent band-pass Gaussian filtering of the ≈ 20 m long (measured on the thickness scale) cycles from the original signal using package 'astrochron' in the R computational environment (Meyers 2015, R Development Core Team 2015) (more details can be found in Radzevičius et al 2017).…”

“…The 4 th order sedimentary cycles were distinguished based on the REDFIT statistical testing (Schulz & Mudelsee 2002) of the natural gamma ray signal with the subsequent band-pass Gaussian filtering of the ≈ 20 m long (measured on the thickness scale) cycles from the original signal using package 'astrochron' in the R computational environment (Meyers 2015, R Development Core Team 2015) (more details can be found in Radzevičius et al 2017). The symmetry of the distinguished sea level cycles (the rising and falling limbs are almost symmetrical) is expected since we are dealing with a deep-water sedimentary system.…”