Proterozoic-like/type basal Triassic microbial build-ups of unusual height in Armenia.

The Griesbachian part of the Marmarasar Formation (Kara Baglyar) [1] in the Zangakatun (Sovetachen) section (Armenia) is characterized by microbial build-ups, spaced from 5 to 20m and surrounded by thin-bedded platy lime mudstone in a deep ramp environment. Above a basal carbonate fan crust follows a succession of thrombolitic domal forms, some of them up to 1.5m thick. The synoptic relief of the thrombolite head is estimated at 40-60cm above the muddy sea bottom. The overturned cone-shaped build-up geometry has a top head diameter up to 8m width consisting of numerous thrombolite domes, and an usual height of up to 15m. The water depth is interpreted below storm wave base and the asymmetrical build-up growth hints to a steady bottom current. Changes in the paleo-environment at the top of the kummeli conodont zone end the thrombolite growth. The overall duration of these post-extinction microbial build-ups is estimated at 700'000 years. Comparable Late Proterozoic Conophyton-Jacutophyton biostromes of the Atar area (Mauritania) [2], grown in apparently similar 80-100m water depth with quiet conditions, also show a high synoptic relief here of more than 2m above sea-bottom and decametric columnar branching build-ups. Due to a similarly large accommodation space the Zangakatun microbial reefs seem to follow the same build-up strategy

A highly diverse bivalve fauna from a Bithynian (Anisian, Middle Triassic) Tubiphytes ‐microbial buildup in North Dobrogea (Romania)

This paper describes a rich bivalve fauna from the Tubiphytes‐Limestone Member (Bithynian, early middle Anisian) of the Caerace Formation in North Dobrogea (Romania). We report 51 bivalve species, including 7 new species and 2 new genera: Atrina multicostata sp. nov., Pinna simionescui sp. nov., Chlamys (Praechlamys) prima sp. nov., Entolium reticulatum sp. nov., Scythentolium anisicum sp. nov., Romaniamya mahmudiaensis gen. et sp. nov. and Praedicerocardium vetulus gen. et sp. nov. The latter taxon represents the oldest Triassic megalodontoid. We provide detailed descriptions of the bivalve fauna, discuss the ecology and compare species richness in the Early and Middle Triassic, showing that the bivalve assemblage of North Dobrogea is much more diverse than all previously described Early Triassic bivalve faunas, but not as rich as several faunas from the late Anisian and Ladinian. The relative richness of the Dobrogea fauna with respect to geologically older and younger faunas suggests that it represents an early stage of the main rediversification of bivalves after the end‐Permian mass extinction

The Main Stage of Recovery from the End-Permian Mass Extinction: Ecology and Species Richness in Middle Triassic Marine Level-Bottom Communities

The end-Permian mass extinction was the most devastating mass extinction in Earth’s history regarding marine life. It occurred around 252 million years ago and its aftermath provides an ideal test case to identify the main drivers of biodiversification. Hitherto, research on the recovery of marine level-bottom communities almost exclusively concentrated on the Early Triassic, the approximately five million years after the extinction event. However, the main recovery phase of marine level-bottom communities started during the Middle Triassic, which is characterized by a sudden increase in species richness and important ecological changes, such as the resurgence of large carbonate platforms. Nevertheless, despite representing a crucial time interval in the rediversification process, research on the Middle Triassic has largely been neglected in this regard.This thesis addresses the recovery of marine level-bottom faunas after the end-Permian mass extinction in its full length and ecological context, with a focus on the so far poorly studied Middle Triassic. The main objectives were (1) to improve our understanding of the ecology and taxonomic composition of marine level-bottom faunas in the aftermath of the end-Permian mass extinction, (2) to identify the effects of the newly arising large carbonate platforms on the evolution of marine level-bottom faunas (3) to use the diversification patterns of different taxa and ecological guilds to identify the main drivers of biodiversification by testing different diversification models. To accomplish this, I examined Middle Triassic level-bottom communities under three different aspects that are each represented by one chapter of this thesis. Chapter I is a synecological study that was carried out in the Schlern and Seiser Alm area (South Tyrol, Italy). I investigated the highly diverse faunas from the lagoonal Schlernplateau beds (Schlern Mountain) and the adjacent basinal Pachycardientuffe (Seiser Alm), which both date from the late Ladinian (late Middle Triassic). I present the first detailed palaeoecological analysis of both faunas and discuss their palaeoecology as well as species distribution in the context of their depositional environment. Furthermore, I compare their species richness with other Early and Middle Triassic level-bottom communities to identify changes in species richness throughout this time interval. This study shows that (1) the fauna of the Pachycardientuffe derived from different environmental settings, thus demonstrating the complete regional species richness, (2) the fauna of the Schlernplateau beds is clearly more diverse than all Early Triassic benthic communities, indicating a remarkable increase in species richness during the Middle Triassic and (3) the taxonomic composition of level-bottom communities changed during the Middle Triassic from bivalve-dominated to gastropod-dominated, the latter being almost exclusively associated with large carbonate platforms. Chapter II addresses the effects of the newly arising large carbonate platforms on the rediversification of bivalves. This study was performed on a Bithynian (early middle Anisian, early Middle Triassic) bivalve fauna associated with a Tubiphytes-microbial buildup from North Dobrogea (Romania), which represents one of the oldest Triassic large carbonate platforms. I provide detailed taxonomic descriptions of the 51 reported bivalve species that belong to 39 genera. This includes seven species and two genera, which are newly described. Among them is the oldest Triassic megalodontoid, a taxon of great ecological importance later in the Triassic. Furthermore, I discuss the ecology of the bivalves, reconstruct their palaeoenvironment and compare their species richness with other Early and Middle Triassic bivalve faunas. Although results of rarefaction analysis suggests that the actual species richness of the investigated bivalve fauna might have been much higher, it is clearly more diverse than older or contemporary faunas but considerably less diverse than younger faunas. This suggests the beginning of their recovery in the Bithynian. Their high degree of endemism and the pervasive byssally attached mode of life are signs of their adaptation to the new habitat type provided by the Tubipyhtes-microbial buildup. Chapter III is a palaeoecological synthesis that provides an overview of the large-scale recovery of marine level-bottom communities from the end-Permian mass extinction over a period of 15 million years. This synthesis is based on a combination of own and literature data. Altogether I analysed 1562 species belonging to 13 higher taxa and 12 ecological guilds from 37 Early and Middle Triassic lithological units, representing different environmental settings, in terms of species richness as well as guild-species diversity (number of species per guild). Furthermore, I use the recovered diversification trajectories to test different diversification models. The rediversification of different taxa and ecological guilds started simultaneously in the Bithynian. The number of species increased hyperbolically and levelled out during the Middle Triassic. This supports a competition-driven diversification model, in which interspecific competition reversed escalating effects on diversification rates to damping. Other ecological feedbacks such as niche construction, habitat alteration and endemism are discussed in the context of the newly arising large carbonate platforms. In addition, I present the hypothesis that the dominance of gastropods in Middle Triassic level-bottom communities associated with large carbonate platforms is connected to the proliferation of dasycladacean algae, which were important carbonate producers in these large carbonate platforms that served gastropods as feeding grounds. My thesis provides a comprehensive picture about the recovery of marine level-bottom communities after the end-Permian mass extinction over a period of 15 million years. It shows a marked increase in species richness during the Middle Triassic, provides an overview about taxonomic and ecological changes throughout this time interval, discusses the effects of the newly arising carbonate platforms on the evolution of level-bottom communities and identifies biotic interactions as the main driver of diversification after the mass extinction event. Therefore, my dissertation does not only provide an important contribution to the understanding of the recovery of level-bottom communities after the end-Permian mass extinction but also on the diversification of benthic macroinvertebrates in general

The main stage of recovery after the end-Permian mass extinction: taxonomic rediversification and ecologic reorganization of marine level-bottom communities during the Middle Triassic

The recovery of marine life from the end-Permian mass extinction event provides a test-case for biodiversification models in general, but few studies have addressed this episode in its full length and ecological context. This study analyses the recovery of marine level-bottom communities from the end-Permian mass extinction event over a period of 15 Ma, with a main focus on the previously neglected main phase during the Middle Triassic. Our analyses are based on faunas from 37 lithological units representing different environmental settings, ranging from lagoons to inner, mid- and outer ramps. Our dataset comprises 1562 species, which belong to 13 higher taxa and 12 ecological guilds. The diversification pattern of most taxa and guilds shows an initial Early Triassic lag phase that is followed by a hyperbolic diversity increase during the Bithynian (early middle Anisian) and became damped later in the Middle Triassic. The hyperbolic diversity increase is not predicted by models that suggest environmental causes for the initial lag phase. We therefore advocate a model in which diversification is primarily driven by the intensity of biotic interactions. Accordingly, the Early Triassic lag phase represents the time when the reduced species richness in the wake of the end-Permian mass extinction was insufficient for stimulating major diversifications, whereas the Anisian main diversification event started when self-accelerating processes became effective and stopped when niche-crowding prevented further diversification. Biotic interactions that might drive this pattern include interspecific competition but also habitat construction, ecosystem engineering and new options for trophic relationships. The latter factors are discussed in the context of the resurgence of large carbonate platforms, which occurred simultaneously with the diversification of benthic communities. These did not only provide new hardground habitats for a variety of epifaunal taxa, but also new options for grazing gastropods that supposedly fed from microalgae growing on dasycladaceans and other macroalgae. Whereas we do not claim that changing environmental conditions were generally unimportant for the recovery of marine level-bottom communities, we note that their actual role can only be assessed when tested against predictions of the biotic model

Palaeoecology of Late Ladinian (Middle Triassic) benthic faunas from the Schlern/Sciliar and Seiser Alm/Alpe di Siusi area (South Tyrol, Italy)

The Schlern and Seiser Alm area (South Tyrol, Italy) is a classical locality for studies of Middle Triassic platform to basin transitions, yet details of the palaeoecology of the rich benthic faunas of this area have been insufficiently known. We present herein a detailed palaeoecological study of the fauna from the Schlernplateau beds (Late Ladinian to Early Carnian) and the more or less time-equivalent Pachycardientuffe (Late Ladinian), which is based on quantitative faunal data. Both the palaeoecology and sedimentary features suggest that the fauna of the Schlernplateau beds represents a lagoonal soft-bottom fauna. The high species richness of the fauna and the locally restricted occurrences of fossils indicate an open-lagoon setting palaeogeographically close to an ocean inlet. The high evenness of the fauna is probably a result of time-averaging. In contrast, the fauna of the Pachycardientuffe shows clear indications of transportation. Ecological features of this fauna andpalaeogeographic reconstructions suggest three potential source areas: (1) the lagoon represented by the Schlernplateau beds, (2) the reef fringing this lagoon and (3) a shallow clastic coast of a nearby volcanic island and/or submarine high.A comparison between diversities of selected Early and Middle Triassic lithological units revealed the increasing species richness of all major benthic taxa during the Middle Triassic and a shift from bivalve-dominated Early Triassic faunas to gastropod-dominated faunas. Keywords Middle Triassic · Biotic recovery · Quantitative faunal analyses · Palaeoecology · Palaeoenvironmen

New Triassic Aviculopectinoidea (Bivalvia), with notes on the taxonomic concept of the superfamily

We describe two new genera of Triassic Aviculopectinoidea: Cristaflabellum n. gen., which is biconvex and has a strongly plicate shell, and Globodiscus n. gen., which is equiconvex and externally smooth or nearly so. Globodiscus contains the new species G. kiliani n. gen. n. sp. and G. vinzenti n. gen. n. sp. In order to make the taxonomic concept of the superfamily Aviculopectinoidea more consistent with that of its sister group Pectinoidea (scallops), we use tribes rather than families or subfamilies for accommodating the new taxa. Cristaflabellum is placed in the tribe Antijanirini (previously family Antijaniridae), whereas Globodiscus is made the type genus of the new tribe Globodiscini. Both tribes are placed within the family Aviculopectinidae, which is revised to include both equiconvex and inequiconvex taxa. We suggest that tribes are a more appropriate taxonomic rank for many of the previously erected species-poor families and subfamilies of Aviculopectinoidea. UUID: http://zoobank.org/d143663a-9016-459f-8e24-660102adcf6a</jats:uri

BASAL INDUAN (EARLY TRIASSIC) GIANT SPONGE-MICROBIAL BUILD-UPS IN ARMENIA: MICROFACIES ANALYSES AND CARBON ISOTOPE STUDIES

oai:serval.unil.ch:BIB_D03A5752AA5AThe Transcaucasia area (central Armenia) offers the opportunity to study a distinctive sponge-microbial community development in the aftermath of the end-Permian mass extinction (Permian-Triassic Boundary sponge-microbialites PTBSM): isolated communities started to built vertical edifices up to 12 m high during Griesbachian times (Induan, Lower Triassic), and show two growth phases within a pelagic carbonate ramp. The first sponge-microbial build-ups, which are rich in sponge spicules, co-occur with impressive calcium carbonate crystal fans (CCFs) that vary in thickness between 5 cm to 2 m. A comparison between the δ13C values from the PTBSM that formed during the first growth phase and the surrounding sediment revealed a remarkable differences: the δ13Cmicrobialite values are up to 2.3‰ more positive than the corresponding δ13Csediment values

Sponge-microbial build-ups from the lowermost Triassic Chanakhchi section in southern Armenia: Microfacies and stable carbon isotopes

The end-Permian mass extinction was the most severe biotic crisis in Earth's history. In its direct aftermathmicrobial communities colonized some of the space left vacant after the severe decline of skeletal metazoans.The Permian-Triassic boundary microbialites were peculiarly abundant on low-latitude shallow-marine carbonateshelves of central Tethyan continents. Armenia features particularly well preserved and diverse basalTriassic sponge-microbial build-ups (BTSMBs), which were not studied in detail to date. Here, the Chanakhchisection in southern Armenia is described petrographically and by means of stable isotope analyses. TheArmenian BTSMBs formed in a distally open marine setting on a pelagic carbonate ramp in the course of twophases of microbial growth during the Induan (Lower Triassic). The BTSMBs are represented by predominantlythrombolitic but also dendrolitic and digitate stromatolite biostromes and mounds that vary in height between5 cm to 12 m. The digitate stromatolites are associated with calcium carbonate crystal fans (CCFs). Microfaciesanalyses revealed that the BTSMBs exhibit a number of different growth forms and internal fabrics. The formationof CCFs was apparently not devoid of biological influence and took place above the sediment surface. Theabundance of sponges in the BTSMBs reveals that ecologically complex metazoan-microbial reefs have beenpresent already early after the end-Permian mass extinction. However, the formation of biostromes and moundsdid not depend on sponges or other metazoans. BTSMBs that formed during the second microbial growth phaserevealed similar δ13C-values like the surrounding sediment. In contrast, the δ13Cmicrobialite and δ13Csediment valuesfrom the BTSMBs and CCFs of the first growth phase show a difference of up to +2.3‰, suggesting a significantinfluence of photoautotrophy during microbially induced carbonate precipitation