Taxonomic diversity dynamics of early cretaceous brachiopods and gastropods in the Azerbaijanian domains of the Lesser Caucasus (Neo-Tethys Ocean)

Dmitry Ruban

doi:10.2298/gabp1475017r

Abstract

Palaeontological data available from the Azerbaijanian domains (Somkhit-Agdam, Sevan-Karabakh, and Miskhan-Kafan tectonic zones) of the Lesser Caucasus permit reconstruction of the regional taxonomic diversity dynamics of two groups of Early Cretaceous marine benthic invertebrates. Stratigraphical ranges of 31 species and 14 genera of brachiopods and 40 species and 31 genera of gastropods are considered. The total number of species and genera of brachiopods was low in the Berriasian-Valanginian and then rose to peak in the Barremian. Then, the diversity declined in the Aptian, and brachiopods are not known regionally from the Albian. Gastropods appeared in the Hauterivian and experienced a strong radiation in the Barremian. The diversity of species and genera declined in the Aptian (with a minor radiation in the Middle Aptian), and no gastropods are reported from the Albian. Globally, the number of brachiopod genera remained stable through the Early Cretaceous, and the number of gastropod genera increased stepwise with the maximum in the Albian. The regional and global patterns of the diversity dynamics differed for the both groups of marine benthic invertebrates. The Barremian maximum of the taxonomic diversity coincided with the regional flourishing of reefal ecosystems. The taxonomic diversity dynamics of brachiopods in the Azerbaijanian domains of the Lesser Caucasus is very similar to those of the Northern Caucasus, which is an evidence of proximity of these regions during the Early Cretaceous.

Highlights

Reconstructions of regional changes in taxonomic diversity of marine organisms are highly important for understanding spatial differences of biodiversity changes registered with the available global palaeontological data (SEPKOSKI 1993, 2002; ALROY et al 2008; PURDY 2008; ALROY 2010)
The present paper focuses on the Azerbaijanian domains of the Lesser Caucasus (Fig. 1)
The total generic diversity of brachiopods mation summarized by KHALILOV & ALIYEV (1972, remained stable in the Early Cretaceous, which is dif- 2007), AKOPJAN & KHALILOV (1986), ALI-ZADEH

Summary

Introduction

Reconstructions of regional changes in taxonomic diversity of marine organisms are highly important for understanding spatial differences of biodiversity changes registered with the available global palaeontological data (SEPKOSKI 1993, 2002; ALROY et al 2008; PURDY 2008; ALROY 2010). Two groups of marine benthic macroinvertebrates, namely brachiopods and gastropods, are common in the Lower Cretaceous deposits of the study area (AKOPJAN & KHALILOV 1986; ALI-ZADEH 1988). These groups seem to be suitable for the analysis of the regional taxonomic diversity dynamics and its further comparison with the global patterns. This study is a part of the palaeobiological re-evaluation of the information about Cretaceous marine invertebrates from the Caucasus (see RUBAN 2006, 2011a; RUBAN et al 2011)

Methods

Results

Discussion

Conclusion