Late Maastrichtian–Paleocene chronostratigraphy from Seymour Island,James Ross Basin,Antarctic Peninsula:Eustatic controls on sedimentation

The Paleocene(66–56 Ma)was a critical time interval for understanding the geological history in high palaeolatitudes after the end of Cretaceous event(recovery from mass extinction,palaeoclimate,global sea level changes,among others).The sedimentary succession from Seymour Island(Antarctic Peninsula)provides key reference material from this important phase of the early Cenozoic.A detailed age model is proposed for the López de Bertodano Formation(LBF),Sobral Formation(SF)and Cross Valley–Wiman Formation(CVWF)based on a new magnetostratigraphic section which integrates previous dinoflagellate cyst biostratigraphy,Iridium anomaly(K-Pg boundary),U-Pb zircon dating(airfall tuff)and strontium isotope values from macrofossils.The new composite magnetostratigraphic section,which includes the Cretaceous–Paleogene boundary,has been correlated to the GPTS from C29r up to C24r.The top of the LBF is confirmed as latest Maastrichtian to earliest Danian(~65.4 Ma)in age.The overlying SF is mostly Danian in age(~65.2–~63 Ma)and CVWF is Selandian–Thatenian(~61.3–56.9 Ma).LBF,SF and CVWF are unconformity-bounded units(alloformations)that record the geological evolution of the James Ross Basin during a period of relative decreasing tectonism but coeval with volcanic activity.Unconformity based internal units have been recognized,dividing each formation into allomembers(LBF:Molluscan and Cenozoic;SF:A,B and C;CVWF:Díaz,Ara?ado,Bahía Pingüino).The new age model allows correlation of base-level changes with eustatic sea-level fluctuations.The bases of the SF and CVWF are correlated with the 65.3 and 61.5 Ma sea level lowstands.

Antarctic Paleontological Heritage:Late Cretaceous–Paleogene vertebrates from Seymour(Marambio)Island,Antarctic Peninsula

Antarctica has significant environmental,scientific,historic,and intrinsic values,all of which are worth protecting into the future.This continent has a discrete number of places of scientific interest that exhibit great potential as natural heritage sites;its geodiversity is of fundamental importance to scientific values of the continent,and the pursuit of geological and paleontological knowledge has had a strong influence on its historical values.Seymour Island was once called the‘Rosetta Stone’of Southern Hemisphere paleobiology,because this small island provides the most complete and richly fossiliferous Late Cretaceous–Paleogene sequence in Antarctica.In particular,fossil vertebrates form part of the evidence used in reconstructing the history of life on Antarctica.Paleontological heritage is considered a subset of geo-heritage that embodies both natural and historical components which has received only indirect recognition.Seymour Island is an outstanding paleontological area with high heritage value of its Late Cretaceous/Paleogene vertebrates and should be considered for geo-conservation and protection.This paper reviews vertebrate fossil occurrences and outcrops on Seymour Island and discusses some threats to these fossil sites.

Contributions to the knowledge of Antarctodon sobrali(Mammalia:Astrapotheria)from the Eocene of Antarctica

The Astrapotheria constitutes one of the five orders of extinct South American native ungulates,with a fossil record that also extends to the Eocene of the Antarctic Peninsula.In contrast to the abundant specimens known for litoptern Sparnotheriodontidae and metatherians,astrapotheres are represented by scant remains assigned to the endemic Antarctodon sobrali and indeterminate astrapotheres,restricted to levels 35C_(u0)and 35n of the Cucullaea I Allomember of the La Meseta Formation.The discovery of alower molar assignable to this species in the Eocene levels of Seymour(Marambio)Island,enables a revision of the diagnosis and the homologies of the dental characters used to describe this taxon.A reanalysis of its phylogenetic relationships reveals the nearly simultaneous presence of basal astrapotheres in the early Eocene of Itaboraí(Brazil),Patagonia,and West Antarctica.These taxa are characterized by lacking dental specializations usually associated with more abrasive diets like terminal forms of Uruguaytheriinae and Astrapotheriinae.Antarctodon appears to have thrived on the Antarctic continent during the Early Eocene Climatic Optimum within the paleoclimatic context of a hot-house world.Unlike present conditions in Antarctica where no terrestrial mammals inhabit,the early Eocene climate was characterized by warmer temperatures and a biologically diverse environment rich in primary producers,dominated by Nothofagus forests,encompassing both deciduous and evergreen forests,which supported a diverse assemblage of continental vertebrates.

Middle Eocene chondrichthyan fauna from Antarctic Peninsula housed in the Museo de La Plata,Argentina

In recent years,the taxonomy and systematics of the cartilaginous fish taxa from the Eocene La Meseta Formation of Seymour(Marambio)Island,Antarctica have been extensively discussed in a series of papers,resulting in a complete revision of the Antarctic Eocene ichthyofauna housed in the Vertebrate Paleontology collection of the Museo de La Plata,Argentina.This collection constitutes one of the largest and taxonomically most diverse in the world,with approximately 20000 specimens,which provides a solid database used for the analysis of qualitative and quantitative chondrichthyan taxonomic composition.The information provided herein might be useful to understand the sudden decline in chondrichthyan taxonomic diversity towards the top of La Meseta Formation as well as its potential relationship with environmental changes during the Eocene.

Review of the Cretaceous avian diversity of Antarctica:a changing scenario for the evolution of early Neornithine birds

The worldwide record of Cretaceous Neornithes and Neornithine-like birds is both controversial and poorly understood.However,in recent years,the Antarctic continent has yielded a substantial number of Maastrichtian avian specimens,contributing significantly to our understanding of the early evolution of this group.Simultaneously,the keen interest and collaborative efforts of various paleornithologists have resulted in a wealth of knowledge,which we have thoroughly reviewed,updated,and discussed in the context of recent discoveries.

Installing a prototype wind turbine to produce energy in Antarctica to allow a permanent Colombian scientific base to be established

This study was performed to support an expeditionary team of Colombian scientists seeking to promote and undertake research in various scientific fields in Antarctica.The work was part of the Colombian Antarctic Program,which comprises various projects intended to lead to a permanent Colombian scientific base being established in the Antarctic.The first step involved installing a Colombian-made wind turbine to produce electricity at a permanent base.The aeolian turbine was designed to provide sufficient electricity to illuminate and heat a small base.The turbine was constructed using readily accessible materials but taking the Madrid Protocol environmental regulations into consideration.The project was performed at the Argentinian Antarctic Marambio Station on Seymour Island,off the Antarctic Peninsula.An initial field study performed in 2015 was the first of three phases of the project.In the initial phase,local meteorological data were gathered to support development of a prototype turbine and to allow a design to be selected that was robust enough for the extreme environmental conditions.The wind turbine was then constructed in Colombia.The second phase involved transporting the turbine to Antarctica and installing it at the Marambio Station in 2018.Finally,the physical conditions of structural and electronic components of the turbine were carefully inspected at the beginning of 2020(after the turbine had operated continually for^2 years)to allow repairs to be made and any necessary re-engineering to be performed.

The fossil record of birds from the James Ross Basin,West Antarctica

The fossil record of birds from Antarctica is concentrated in the James Ross Basin,located in north-east of the Antarctic Peninsula.Birds are here represented by an extensive Paleogene record of penguins(Sphenisciformes)and Cretaceous–Paleogene record of Anseriformes,followed by other groups with a minor representation(Procellariiformes,Falconiformes,and Pelagornithidae),and others previously assigned controversially to“Ratites”,Threskiornithidae,Charadriiformes,Gruiformes,Phoenicopteriformes,and Gaviiformes.We provide a complete update of these records,commenting on the importance of some of these remains for the evolution of the major clades.

The fossil record of durophagous predation in the James Ross Basin over the last 125 million years

We review the evidence for predation of shelly benthic prey over 125 million years of earth history in the James Ross Basin,Antarctica(~65°S).Although poor in the Early Cretaceous lower parts of the sequence,which represent essentially deeper water facies,evidence for both potential crushers and drillers becomes more apparent in the Santonian–Campanian Santa Marta Formation,and by the Maastrichtian López de Bertodano Formation there is an extensive fossil record of drill holes attributable to naticid gastropods,and some evidence of crushing by decapods crustaceans and possibly other taxa too.This continues at a similar level of intensity across the K/Pg boundary into the Danian Sobral Formation,but is less well constrained in the latest Paleocene–Early Eocene.The most extensive record of predation occurs in the Middle Eocene section of the La Meseta Formation on Seymour Island which also records the highest levels of benthic diversity within the entire basin.This key section is providing some important new evidence to suggest that the rate of acceleration of benthic predation intensity through the Late Mesozoic–Early Cenozoic in the polar regions may be similar to that seen in lower latitude regions.Predator–prey interaction was a key factor in the evolution of polar marine faunas too.

南极半岛西摩岛始新世拉揭塞塔组Teredolites遗迹化石研究

Teredolites遗迹化石是一类赋存于海相地层中的以木质基底为特征的钻孔遗迹组合,是由海相钻木类双壳动物(如船蛆、海笋等)寄生于漂浮或沉入海洋的树干中形成。Teredolites遗迹化石可指示浅海沉积环境,提供寄生木材的分类信息、古地理信息以及埋藏过程中的环境信息。本文研究了南极半岛西摩岛拉揭塞塔组顶部首次发现的一例Teredolites longissimus(Apectoichnus longissimus)遗迹化石,层位时代为晚始新世,根据木基底内保存的船蛆化石的发育特征和分布特征,确定本例为船蛆幼年群体对木基底的初期感染形成的钻孔遗迹。利用场发射扫描电镜(FESEM)和X射线能谱仪(EDS)对基底木化石和船蛆化石进行深入研究分析,将本例Teredolites遗迹化石的基底木化石定为裸子植物罗汉松科(Podocarpaceae)叶枝杉型木属未定种(Phyllocladoxylon sp.),证实了叶枝杉型木属在西摩岛上的分布延续至始新世晚期;船蛆化石内部赋存大量草莓状黄铁矿,其中粒径超过10μm的草莓状黄铁矿占比达39.2%,最大粒径达到44μm,粒径的统计和分析显示其形成于氧化水体沉积环境,证明始新世晚期南极半岛地区古海洋处于氧化海状态。

Eocene Antarctica:a window into the earliest history of modern whales

The Eocene–Oligocene Southern Ocean is thought to have played a major role in cetacean evolution.Yet,fossils from its heart—Antarctica—are rare,and come almost exclusively from the Eocene La Meseta and Submeseta formations of Marambio(Seymour)Island.Here,we provide a summary and update of this crucial fossil assemblage,and discuss its relevance in the broader context of cetacean evolution.To date,Eocene specimens from Antarctica include basilosaurids,a group of archaic stem cetaceans that had already fully adapted to life in water;and the archaic toothed mysticete Llanocetus,the second oldest crown cetacean on record(ca.34 Ma).This Eocene co-occurrence of stem and crown cetaceans is highly unusual,and otherwise only observed in Peru.Though related,at least some of the Antarctic species appear to be different from,and notably larger than their Peruvian counterparts,suggesting an early differentiation of the high latitude cetacean fauna.