An investigation of a Devonian/Carboniferous Boundary section on the Bolivian Altiplano

The Devonian/Carboniferous Boundary (DCB) interval is associated with mass extinction, isotope excursions and a short glacial episode. This study investigates how boundary extinction and environmental change is expressed in the glacial high-palaeolatitudinal record of the Bolivian Altiplano (western Gondwana). A latest Devonian and early Carboniferous section has been investigated using sedimentology, palynology, total organic carbon and bulk δ13Corganic. The Colpacucho Formation is a Late Devonian shelfal–marine siliciclastic sequence. It is overlain in the study area by a unit of coarse sandstones and sandy diamictites, interpreted as glaciomarine. This distinctive glaciomarine unit is at least 7 km wide and 60–120 m thick with a variably incisive basal contact (<100 m). It is of very latest Famennian age and is a stratigraphic equivalent of proven glacigenic deposits across central South America. The offshore marine Kasa Formation overlies the glacigenic unit above a basal flooding surface. The DCB is 12 m above this flooding surface on the last occurrence of Retispora lepidophyta and significant palynological assemblage changes. This includes the loss of the Umbellasphaeridium saharicum phytoplankton bioprovince, endemic to Gondwana. Marine and terrestrial palynological extinctions are synchronous with a 2 ‰ positive carbon isotope excursion interpreted to be reflective of changes in organic matter delivery and preservation during an interval of environmental stress. These results inform wider debates on global environmental change and mass extinction at the DCB.

A new Late Triassic palynological assemblage from western Gondwana (Carrizal Formation, Marayes Basin, Argentina)

The Carrizal Formation, exposed in the Marayes-El Carrizal Basin (western Argentina), has been the focus of palaeobotanical studies since the late 1800s. The recent finding of well-preserved palyno­logical assemblages provides the first detailed studies about its palynofloras. In this paper, the 63 taxa identified in the unit are illustrated and discussed, as well as their stratigraphic distribution in equivalent palynological assemblages of Argentina. Some spore species are revised: Uvaesporites hammenii (Herbst) Césari, comb. nov., Retusotriletes wielandii (Jain) Césari, comb. nov. and Lundbladispora stellae (Herbst) Césari, comb. nov. The recognition of Cadargasporites baculatus de Jersey & Paten emend. Reiser & Williams, Craterisporites rotundus de Jersey, Enzonalasporites vigens Leschik, ­Leptolepidites argenteaeformis (Bolkhovitina) Morbey, Protodiploxypinus americus Dunay & Fisher and Rugulatisporites permixtus Playford, among others, appears to be useful for local and intercontinental correlations. A Carnian age is proposed for the palynofloras.

Palynological asemblage of the Synya Formation (Middle Triassic) from outcrops at the Kydz'rasyu River, Bol’shaya Synya Depression, the Timan-Northern Urals region

The results of palynological study of the Synya Formation (Middle Triassic) in outcrops along the Kydz'rasyu River banks are presented. The published and archival results of previous palynological investigations of the Synya deposits were used as an additional record. It was shown that the species composition of the palynological assemblage (PA) of the Synya Formation on the Kydz'rasyu River fully corresponded to the PA Converrucosisporites conferteornatus — Florinites pseudostriatus and determined the Triassic, Ladinian, age of the enclosing deposits. The results of reconstruction of the growing vegetation testified to the existence of rich and diverse vegetation in the Ladinian Age on the studied territory, where the flora of highly moistened biotopes prevailed.

Amber- and plant-bearing deposits from the Cenomanian of Neau (Mayenne, France)

A new Cenomanian amber- and plant-bearing deposit has been discovered at Neau, in the Mayenne department (France). The Cenomanian fossiliferous lignites are located in karst filling in a substratum of Cambrian limestones. The amber corresponds mainly to tiny millimetric grains, devoid of arthropod inclusions, but rich in microorganisms, especially the sheated bacteria Leptotrichites resinatus, and containing pollen grains (Classopollis) and wood fibers (Araucariacae or Cheirolepidiaceae). The lignites provide abundant conifer and ginkgoale cuticle fragments (Frenelopsis, Eretmophyllum) and a lot of palynomorphs (e.g. Gleicheniidites senonicus, Cyathidites, Deltoidospora, Appendicisporites and Cicatricosisporites). The chemical signature of the amber suggests it was produced by conifers of the extinct family Cheirolepidiaceae. According to the palynological assemblage, the age of the lignites is upper lower Cenomanian or lower mid Cenomanian. The deposit environment corresponded to the upstream portion of a mangrove or the most inner part of a lagoon.