Eocene Miocene Research Articles

Born of fire, borne by water – Review of paleo-environmental conditions, floristic assemblages and modes of preservation as evidence of distinct silicification pathways for silcrete floras in Australia

Fossil plants in sub-basaltic andfluvial silcretes differ in their geological setting, silica source, taphonomy, preservation and the plants and communities represented: these factors collectively indicate distinct silicification pathways. This review shows that the floras in sub-basaltic silcretes are mostly autochthonous, being derived from the local vegetation, whereas the floras in inland fluvial silcretes are transported andallochthonous. The floras in both are three-dimensionally preserved. The plantsin sub-basaltic silcretes areusually permineralised, preserving internal anatomy and cellular morphology, whereas the plants in inland fluvial silcretes occur as moulds/impressions that may preserve epidermal andsurface features. Both types of silcrete floras offer insights into past environments and ecological drivers. Terrestrial (ground-dwelling) ferns are frequently preservedin situin sub-basaltic silcretes whilst in the inland fluvial silcretes they are represented only by pinnule fragments or abscised pinnules. The extraordinary anatomical preservation of soft tissues in sub-basaltic silcretes, e.g., exocarps of fruits, bark on wood, actively growing vegetative shoots (fern croziers) and root nodules, is evidence of rapid burial by volcanogenic sediments and subsequent silicification by silica-richgroundwaters. The source of silica was hydrothermal fluids released at the time of eruption and/or the weathering of overlying volcanics, and the acidic (humic) conditions resulting from buried plant material provided ideal geochemical conditions for silica precipitation and plantpermineralisation. The sub-basaltic silcrete floras formed contemporaneously with Eocene–Miocene volcanism in eastern Australia, whereas the formation of inland pedogenic and fluvial silcretes was probably initiated during the Paleocene–Eocene Thermal Maximum (PETM). The fine surface preservation of plants in inland fluvial silcrete floras indicates rapid burial but no organic material is preserved, probably because oxidising groundwaters stripped out the organics before silicification occurred. The comparatively less silica-rich groundwaters associated withfluvial silcretes and the sandy substrates would have further contributed to the loss of plant material.

East Greenland Prograded Margin and Oceanic Composite Tectono-Sedimentary Element, offshore East Greenland

Abstract The East Greenland Prograded Margin and Oceanic Composite Tectono-Sedimentary Element (EGPMO CTSE) consists of the East Greenland Prograded Margin Tectonic-Sedimentary Element (TSE) and the East Greenland Oceanic (EGO) TSE located over continental and oceanic crust, respectively. The East Greenland Prograded Margin TSE (EGPM TSE) is made up of six segments, with their basal part deferring from Maastrichtian to Miocene in age. The variation reflects the different timing in transition from syn- to post-rift, controlled by the lateral migration of rifting and diachronic continental break-up in the northern North Atlantic. The post-rift history can be subdivided into a pre-break-up Maastrichtian–Paleocene post-rift phase developed entirely offshore NE Greenland and an earliest Eocene–Miocene syn- to post-break-up phase developed in the wake of progressive continental rupture. Finally, the CTSE started to develop as a unified body from Miocene time after the complete separation of Greenland from Eurasia and the Jan Mayen microcontinent. The EGO TSE has formed since the earliest Eocene commencement of seafloor spreading. The structural and depositional outline of the EGPMO CTSE depicts its tectonic history but also reflects phases of volcanism, denudation and intensified icehouse conditions since the middle Miocene that were triggered by the opening of the Fram Strait and the uplift of East Greenland. The first major northern hemisphere glaciations started in NE Greenland. Glaciations expanded southwards during the late Miocene as the Denmark Strait was transgressed and cold surface water from the high arctic started flowing along SE Greenland, cooling the region. The petroleum potential of the EGPM TSE is conceivably modest but a potential exists locally offshore northern NE Greenland where hydrocarbons sourced mainly from the Jurassic–Cretaceous section may have charged structures cored by Maastrichtian–Eocene sandstone reservoirs sealed by overlying marine mudstones.

First Eocene–Miocene anuran fossils from Peruvian Amazonia: insights into neotropical frog evolution and diversity

AbstractAnurans are one of the most diverse vertebrate groups, particularly in Amazonia, where species richness exceeds that of anywhere else. Amazonian frogs belong to three main lineages (Hyloidea, Microhylidae and Pipidae), each of which diversified during the Cenozoic. However, due to the virtual absence of an anuran fossil record in that area, the evolutionary history of modern lineages has so far remained accessible only via molecular data. In recent decades, a series of field campaigns in Peruvian Amazonia led to the discovery of an unparalleled set of anuran bone fragments, scattered across different sites spanning the Eocene–Miocene time interval. Here, we describe these first Palaeogene and early Neogene anurans from Peru with a focus on humeral and ilial morphology, identifying five humeral and five ilial morphotypes. Humeral morphotypes suggest the presence of different lineages of Brachycephaloidea in Peruvian fossil assemblages, whereas ilial morphotypes suggest the presence of Leptodactylidae, although leptodactylid‐like ilia also occur in some extant brachycephaloids. Pipids were also identified based on both humeral and ilial fragments. This study fills a major temporal and geographical gap in the evolutionary history of South American anurans, while further uncovering a lack of knowledge in the skeletal morphology of extant anuran families, as well as their inter‐ and intra‐species variability.

Eocene–Miocene tectonic reworking of the southeastern Tibetan Plateau: Geochronological and geochemical records from granitoids along the Ailao Shan–Red River Shear Zone

The convergence of the Indian Plate and Eurasia shaped the Earth’s broadest and highest-elevation collisional system and topographic growth, which is not simply illustrated by ongoing contractional deformation. The Cenozoic magmatism along the Ailao Shan-Red River Shear Zone (ARSZ), linking surface geology with deep lithospheric processes, provides additional information regarding the age and progressive deformation of the India-Asia collision. In this study, we present new zircon U–Pb geochronological, elemental geochemical and zircon Hf isotopic data for the Eocene–Miocene granitoid to resolve the southeastern Tibetan Plateau deformation history. The Jinping granitoids in the southern ARSZ were dated at 37.5–33.6 Ma. They show similar geochemical characteristics (whole-rock major oxides, trace element, Sr–Nd–Pb isotopic and zircon in-situ Hf isotopic data) with respect to coeval potassic granitoids in NW Yunnan, suggesting their origination from partial melting of thickened lower crust with additional contribution from enriched mantle-derived magmas. Leucogranite samples within the ARSZ yielded distinctive zircon U–Pb ages of 28.3 Ma and 18.5 Ma. Geochemical features suggest that they were derived from a heterogeneous crustal source consisting of metasediments and metabasites. Our results, along with those previous studies, suggest that the widespread potassic magmatism in the central and southeastern Tibetan Plateau is related to lithospheric mantle upwelling, which resulted in the partial melting of the thickened lower crust and a short-lived crustal extension during a period of decreased convergence rate. Subsequently, the orogenic-scale sinistral strike-slip movement provided shearing heat for generating leucogranites within the shear zones during the late Oligocene–Miocene. The plateau-wide shift in stress reorganization and tectonic reworking led to the lateral extrusion of the SE Tibetan Plateau and its attainment of modern high elevation.

Evolving Eocene–Miocene seasonality decoded from aragonitic laminae deposited within the Qaidam Basin, North Tibetan Plateau

A thorough understanding of sub-decadal paleoclimate variability typically depends on ultra-precise geochronological constraints that are rarely obtained. While the seasonally resolved nature of varved successions enlarges the opportunity, their identification beyond Quaternary ages is difficult; thus is frequently met with skepticism. The Cenozoic strata in the Qaidam Basin, for instance, feature expanded rhythmite successions, whereas the periodicity of these laminae remains to be explored. Targeting Eocene- (VE; ∼42.0 Ma), Oligocene- (VO; ∼26.9 Ma) and Miocene-aged (VM; ∼19.5 Ma) intervals, herein we report layer-based petrographic observations coupled with mineralogical and phase-specific geochemical analyses of millimeter-scale rhythmic alterations between yellowish- and grayish-colored aragonitic layers. Noting a constant δ13Ccarb offset (∼ 2.8‰) between yellowish- and grayish-colored laminae, these isotope data imply seasonally paced alternations between microbial induction and inorganic carbonate precipitation. In addition, covariations between inorganic oxygen isotope (δ18Ocarb) and elemental ratios (e.g., Mn/Fecarb, Sr/Basilic and Chemical Index of Alteration, CIAsilic) reveal evolving seasonality, capturing Eocene–Oligocene aridification followed by an early Miocene reversal. Therefore, the varved fill of the Qaidam Basin serves as an annually resolved, and as yet under-explored, archive of evolving Cenozoic paleoseasonality in the aftermath of the Indo–Asia collision.

Diversity, Distribution, Systematics and Conservation Status of Podocarpaceae

Among conifer families, Podocarpaceae is the second largest, with amazing diversity and functional traits, and it is the dominant Southern Hemisphere conifer family. However, comprehensive studies on diversity, distribution, systematic and ecophysiological aspects of the Podocarpaceae are sparse. We aim to outline and evaluate the current and past diversity, distribution, systematics, ecophysiological adaptations, endemism, and conservation status of podocarps. We analyzed data on the diversity and distribution of living and extinct macrofossil taxa and combined it with genetic data to reconstruct an updated phylogeny and understand historical biogeography. Podocarpaceae today contains 20 genera and approximately 219 taxa (201 species, 2 subspecies, 14 varieties and 2 hybrids) placed in three clades, plus a paraphyletic group/grade of four distinct genera. Macrofossil records show the presence of more than 100 podocarp taxa globally, dominantly from the Eocene-Miocene. Australasia (New Caledonia, Tasmania, New Zealand, and Malesia) is the hotspot of living podocarps diversity. Podocarps also show remarkable adaptations from broad to scale leaves, fleshy seed cones, animal dispersal, shrubs to large trees, from lowland to alpine regions and rheophyte to a parasite (including the only parasitic gymnosperm-Parasitaxus) and a complex pattern of seed and leaf functional trait evolution.

Orogens of Big Sky Country: Reconstructing the Deep‐Time Tectonothermal History of the Beartooth Mountains, Montana and Wyoming, USA

AbstractArchean rocks exposed in the Beartooth Mountains, Montana and Wyoming, have experienced a complex >2.5 Gyr thermal history related to the long‐term geodynamic evolution of Laurentia. We constrain this history using “deep‐time” thermochronology, reporting zircon U‐Pb, biotite40Ar/39Ar, and zircon and apatite [U‐Th(‐Sm)]/He results from three transects across the basement‐core of the range. Our central transect yielded a zircon U‐Pb concordia age of 2,805.6 ± 6.4 Ma. Biotite40Ar/39Ar plateau ages from western samples are ≤1,775 ± 27 Ma, while those from samples further east are ≥2,263 ± 76 Ma. Zircon (U‐Th)/He dates span 686.4 ± 11.9 to 13.5 ± 0.3 Ma and show a negative relationship with effective uranium—a proxy for radiation damage. Apatite (U‐Th)/He dates are 109.2 ± 23.9 to 43.6 ± 1.9 Ma and correlate with sample elevation. Multi‐chronometer Bayesian time‐temperature inversions suggest: (a) Cooling between ∼1.90 and ∼1.80 Ga, likely related to Big Sky orogeny thermal effects; (b) Reheating between ∼1.80 Ga and ∼1.35 Ga consistent with Mesoproterozoic burial; (c) Cooling to ≤100°C between Mesoproterozoic and early Paleozoic time, likely reflecting continental erosion; (d) Variable Paleozoic–Jurassic cooling, possibly related to Paleozoic tectonism and/or low eustatic sea level; (e) Rapid Cretaceous–Paleocene cooling, preceding accepted proxies for flat‐slab subduction; (f) Eocene–Miocene reheating consistent with reburial by Cenozoic volcanics and/or sediments; (g) Post‐20 Ma cooling consistent with Neogene development of topographic relief. Our results emphasize the utility of multi‐chronometer thermochronology in recovering complex, non‐monotonic multi‐billion‐year thermal histories.

Mountain Growth under the Combined Effects of Paleostress and Paleoclimate: Implications from Apatite (U-Th)/He Thermochronology of Taibai Mountain, Central China

Abstract Tectonics and climate are the two competitive factors sculpturing landforms. Observations on the Earth surface are affected by signals from both tectonic and climatic agents. How to clarify these signals is a key issue. We categorize factors affecting mountain growth as horizontal (extension, compression, and transpression) and vertical (mantle upwelling and climate change) forces to evaluate the driving forces of accelerated exhumation in Taibai Mountain. Based on apatite (U-Th)/He thermochronology, we document two stages of accelerated exhumation at ca. 52-46 Ma and ca. 24-19 Ma from the age-elevation relationship, confirmed by 1D half-space modeling and QTQt inverse modeling. In the framework of paleostress, the two accelerated exhumation events occurred during transpressional periods in the early Eocene and late Oligocene-early Miocene in East China. These two events were triggered by the localized contractional deformation at the intersection of the North Qinling and Fengxian-Taibai faults: The opposite-direction shearing of these two faults was responsible for the former event with an unroofing magnitude of ~1 km; the same-direction shearing of the two faults resulted in the latter event with an unroofing magnitude of ~0.6 km. The far-field effects of both India-Eurasia collision and Pacific subduction drove the accelerated exhumation at ca. 52-46 Ma. The lateral extrusion of the Tibetan Plateau acted as the main driving force for the accelerated exhumation at ca. 24-19 Ma, which may have been slightly influenced by the intensified Asian summer monsoon in the early Miocene.

Integrative taxonomy on the rare sky-island Ligidium species from southwest China (Isopoda, Oniscidea, Ligiidae)

BackgroundThe sky-island Ligidium species fauna in southwest China is poorly known. Before this study, six of the seven sky-island species of the genus were known to be endemic to southwest China. In morphology, Ligidium species are often difficult to identify, and an appraisal of integrative taxonomy is needed.ResultsWe integrated morphology and molecular analyses to delimit Ligidium species. Molecular species delimitation based on distance- and evolutionary models recovered seven-candidate lineages from five gene markers (COI, 12S rRNA, 18S rRNA, 28S rRNA and NAK). We also estimated that the species divergences of sky-island Ligidium in southwest China started in late Eocene (40.97 Mya) to middle Miocene (15.19 Mya).Four new species (L. duospinatum Li, sp. nov., L. acuminatum Li, sp. nov., L. rotundum Li, sp. nov. and L. tridentatum Li, sp. nov.) are described. Morphological confusion among L. denticulatum Shen, 1949, L. inerme Nunomura & Xie, 2000 and L. sichuanense Nunomura, 2002 is clarified by integrative taxonomy.ConclusionThis work confirms that an integrative approach to Ligidium taxonomy is fundamental for objective classification, and deduced the uplift of Qinghai-Tibetan Plateau in the late Eocene and middle Miocene as one of the principal reasons for the species divergences of sky-island Ligidium in southwest China. We also inferred that sky-island mountains have a huge reserve of higher Ligidium species diversity.

Sealing capability of the Eocene–Miocene Horda and Lark formations of the Nini West depleted oil field – implications for safe CO2 storage in the North Sea

The Nini West depleted oil field in the Siri Canyon, Danish North Sea, is considered a potential storage site for safe sequestration of CO2 to fulfill Denmark's ambition to reduce CO2 emissions using carbon capture storage (CCS) technologies. The Paleocene Nini West sandstone reservoir is overlain by several caprocks forming a 900 m thick seal complex composed of the regionally distributed Eocene–Miocene Horda and Lark formations. The integrity and capacity of the seal complex has been evaluated using a multidisciplinary analytical approach integrating organic and inorganic compositional data, physical properties, wireline logs, and mud gas data. The seal complex consists of clay-dominated mudstones with a relatively homogenous lithology constituting a tight seal. Mud gas logs are introduced as a novel proxy for seal integrity in a CCS context, and they show only very limited vertical gas migration has occurred from the reservoir into the basal part of the seal. Average porosities range from ∼15–20% and both measured and modelled average permeabilities range from only 0.11–0.39 μD. The seal mudstones have narrow unimodal pore throat size distributions, and 40% of the samples have extremely small median pore throat radius r50. The seal has high supercritical (sc)CO2 displacement pressures, and it can hold back a vertical column of scCO2 of minimum ∼600 m providing a comfortable seal safety column-overhead. The current findings have relevant application to other depleted oil fields and saline aquifers with similar seals in the larger Central Graben area in the North Sea.

Sedimentology and seismic geomorphology of Paleocene coastal peatlands from the offshore Gippsland Basin, SE Australia

The Eocene–Miocene succession of the onshore Gippsland Basin is host to some of the world's thickest coal seams. Here, we document well-preserved Paleocene coals from the offshore Gippsland Basin. The Paleocene sediments in the basin consist of three stacked coastal units, known informally here as T8, T7 and T6, in order of decreasing age. Each unit consists of, from seaward to landward, a sediment starved marine facies, a sand-rich, wave-dominated shoreface facies, lower coastal plain tidal and peatland facies, and upper coastal plain sandy, fluvial facies. Seismic amplitude extractions reveal unprecedented details of the peatland palaeogeography. The early Paleocene T8 palaeogeography reveals a wave-dominated, sandy strandplain seaward of a >1000 km2 lower coastal plain peatland. The peats extend inland to ~35 km from the paleocoastline and are dissected by a series of meandering and anastomosing channel systems. This geometry is remarkably similar to the modern tropical peatlands of the Rajang Delta in Sarawak, where forested domed peats have formed over tidal and shoreline sediments. The Paleocene coals of the Gippsland Basin have likely formed in a very similar stratigraphic setting and provide a large-scale ancient example of lower coastal plain coal deposition.

Activation of Ad Damm shear zone, western Saudi Arabian margin, and its relation to the Red Sea rift system

Abstract The Ad Damm shear zone (ADSZ) is a major mylonitic right-lateral structure that bounds the Jeddah terrane to the north from the Asir terrane to the south. High-resolution field mapping coupled with petrological and geochemical analyses indicate that Jeddah terrane is characterized by heterogeneous magmatism with extensive meta-basalt intruded by silicic plutons of varying size. South of the ADSZ, Asir terrane is characterized by larger scale granitic batholiths. A younger generation of Eocene–Miocene basaltic dikes cut the mylonitic shear zone at a high angle. Petrographic analyses of the ADSZ mylonitic rocks indicate dynamic recrystallization and grain-size reduction, suggesting high-temperature recrystallization. Field observations also found a lack of low-temperature fault zone rocks (e.g. gouge) except for isolated brittle slickensides. Spider diagrams of Jeddah, Asir terranes, and ADSZ rocks are characterized by an arc-related signature, which related to the amalgamation of Jeddah and Asir terranes and defined ADSZ as Neoproterozoic structure. In contrast, Eocene–Miocene basaltic dikes and southern basaltic flow are represented by a rift-related signature, which associated with the development of the Red Sea rift system. Offshore, south of the ADSZ, the Red Sea rift exhibits well-developed linear magnetic anomalies and large topographic escarpment perpendicular to the rift margin, but they are not present north of it. In addition, recent seismicity recorded along the ADSZ and differences in the crustal thickness and characteristics of Asir and Jeddah terranes, collectively, make ADSZ acted as an active crustal boundary and still influence the ongoing tectonic evolution of the Red Sea rift.

The Cenozoic evolution of the Intrarif (Rif, Morocco)

AbstractThis paper provides an understanding of the sedimentary-tectonic evolution of the Cenozoic strata of the El Habt and Ouezzane Tectonic Units (Intrarif, External Rif) in Morocco. New data provide information about the depositional architecture and enable a correlation of the evolution of the External Rif in Morocco with that of the Betic Cordillera in Spain and the Tunisian Tell, which provides new insights for hydrocarbon exploration in the region regarding possible source, reservoir, and seal rocks. The reconstructed Cenozoic succession was bio-chronologically defined, and the major unconformities and stratigraphic gaps were identified. The presence of these unconformities allowed three main stratigraphic sequences to be defined by age: Danian p.p., early Ypresian–early Bartonian p.p., and the early Rupelian–early Serravallian p.p. Three secondary stratigraphic sequences in the former upper main sequence were also defined by age: early Rupelian–late Chattian p.p., Burdigalianp.p., and the Langhian–Serravallian p.p. The depositional setting evolved from deep basin during the Late Cretaceous–Paleocene to external platform-slope during the Eocene–Miocene. The Cenozoic sandstones contain metamorphic and sedimentary rock fragments derived from a recycled orogen source area. The clay mineralogy in the Cenozoic strata consists of associations of Ill+(I–S) ± Sme, Ill+(I–S) ± Sme+Kln and Ill+(I–S) ± Sme+Kln+Chl. These associations indicate an initial unroofing in the Paleogene period, then in the Cretaceous period, and finally in the Late Jurassic period during the Eocene–Oligocene. This detritus was followed by variable amounts of a sedimentary mix of Paleogene to Late Jurassic terrains due to several phases of erosion and deposition partly related to syn-sedimentary tectonics during the Miocene. Equivalent features (similar types of sediments, tectofacies, gaps, and unroofing) were also recognized along the Betic Cordillera in Spain and Maghrebian Chain (Morocco and Tunisia) and interpreted as related to a pre-nappe tectonic activity of soft basement folding, which occurred during the Paleogene after the generalized tectonic inversion (from extension to compression) occurred in the Late Cretaceous. The Upper Cretaceous is considered to be the hydrocarbon source rock, while the fractured Eocene and the porous Oligo-Miocene suites are proposed as possible hydrocarbon reservoirs. The Cenozoic stratigraphic architecture and the nappe structure of the region could provide the necessary trap structures.

Detrital zircons record the evolution of the Cathaysian Coastal Mountains along the South China margin

AbstractThe Cathaysian Coastal Mountains are thought to be an ancient high‐topographic feature that existed along the margin of South China. They are characterised by extensive Jurassic–Cretaceous magmatism; however, their formation mechanism and timing remains uncertain. In this paper, we present sedimentological and detrital zircon analyses from Cretaceous–Eocene strata and drainage sediments from Hainan Island. Our analyses show a change in provenance from a proximal Cathaysian Coastal arc source in Cretaceous strata to a widely distributed intra‐island granite source in the Eocene strata and modern river sediments. Reconstruction of the crustal thickness evolution for the South China margin from Eu/Eu*‐in‐zircon proxy shows significant crustal thickening during the Late Jurassic–Cretaceous, thereby suggesting the existence of the Cathaysian Coastal Mountains. Together with a compilation of detrital zircon U‐Pb ages in the northern basins of the South China Sea margin, we conclude that the Cathaysian Coastal Mountains extended from the Red River region to Taiwan along the South China margin during the Late Jurassic–Cretaceous and then collapsed/eroded from northeast to southwest during the Eocene–Miocene. This large mountain range supplied detrital sediments to the marginal basins in the northern South China Sea and formed a topographic barrier that prohibited moist Pacific air to reach the relatively arid inland area of South China during the Late Jurassic–Cretaceous.

Ichnofabric analysis as a tool for characterization and differentiation between calcareous contourites and calciturbidites

ABSTRACTThe Eocene–Miocene Cyprus paleoslope system records complex deep-marine sedimentation comprising background vertical settling of autochthonous pelagic–hemipelagic particles (chalks) which were punctuated by calcareous bottom currents (contourites) and gravity flows (calciturbidites). The Eocene Lefkara Formation at the Petra Tou Romiou beach section (Cyprus) shows the incidence of deep-marine bottom currents and distal turbiditic episodes in a context of pelagic–hemipelagic sedimentation. Trace-fossil analysis of this section, using an ichnofabric approach (i.e., ichnodiversity, Bioturbation Index, Bedding Plane Horizontal Index and crosscutting relationships), was conducted to precisely describe the paleoenvironmental conditions of this complex setting. Ichnofabric analysis allow the characterization and differentiation of sporadic turbiditic events that disrupted both pelagic–hemipelagic and contourite deposition. Calciturbidite intervals show ichnofabrics consisting of postdepositional U-shaped traces (i.e., Arenicolites isp., ?Diplocraterion isp.,) and vertical borings typical of consolidated substrates. High-energy sandy contourite deposits are dominated by horizontal deposit-feeder traces and the development of ichnofabrics with Planolites isp., and Thalassinoides isp. The record of ichnofabrics with slightly deformed Planolites in the interbeds of sandy contourites or in the transition between the facies reveals variations in sedimentation in the bi-gradational contourite succession, and can potentially act as an indicator of depositional hiatus.

Evolutionary History and Taxonomic Reappraisal of Coral Reef Rabbitfishes (Siganidae): Patterns of Lineage Diversification and Speciation

Simple SummaryHerbivorous fish are recognized as being ecologically important to the health and survival of coral reef ecosystems because they remove algal turfs growing on corals. Apart from being one of the major components of herbivorous fish communities, rabbitfish are also characterized by possessing rabbit-like mouths. A total of 29 species of rabbitfish are confined to a single genus, Siganus, fish that are highly sought after for the aquarium trade and for food by humans. Natural hybridization between some species that have parapatric distributions across the Indo-West Pacific region may have homogenized their genotypic and morphological features. Relatively little is known, however, about how environmental factors may affect phylogenetic relationships among these siganid species. Based on sequencing of eight siganid species collected from the South China Sea and meta-analysis of sequences from ten siganid species retrieved from the NCBI database, we applied an integrated morphological–molecular approach to elucidate phylogenetic relationships and demographic histories of these species. Our results highlight that diversification and speciation of siganid species were influenced by a series of paleo-climatic events, changes to natural geographical distributions, and associated environmental changes. The target species were differentiated by body shape, and two morphometric parameters, notably body depth and snout length. Our results provide considerable baseline knowledge for strategizing improvement of both breeding and conservation programs for rabbitfish.Rabbitfish (Siganidae) are coral reef fish that are distributed across diverse habitats that include estuaries, mangroves, reefs, and even seaweed mats. Given their ecological diversity and natural widespread distributions across the Indo-Pacific region, we were interested to investigate the evolutionary history of this group and patterns of divergence that have contributed to their present-day distributions. In the present study, samples were collected from the South China Sea to study taxonomic and phylogenetic relationships, and divergence times. We investigated the taxonomic relationships among modern rabbitfish species, reconstructed their molecular phylogeny, and estimated divergence times among selected lineages based on a fragment of the mtDNA cytochrome oxidase I (COI) and sequences of the nuclear rhodopsin retrogene (RHO). Our results indicate that modern rabbitfish likely originated in the Indo-West Pacific during the late Eocene [37.4 million years ago (mya)], following which they diverged into three major clades during the Pliocene/Pleistocene. Subsequent diversification and origins of the majority of siganids may likely be associated with episodes of paleo-oceanographic events, including greenhouse and glaciation events (Eocene–Miocene) as well as major plate tectonic events (Pliocene–Pleistocene). Some modern siganid species may naturally hybridize with congeneric species where their geographical ranges overlap. A comprehensive taxonomic analysis revealed that the phylogeny of Siganidae (cladogenesis of Clades I, II, and III) is characterized by divergence in several external morphological characters and morphometric parameters. Our study demonstrates that morphological characteristics, geographical heterogeneity, and environmental change have contributed to siganids’ historical diversification.

Shoreline evolution from the Late Cretaceous to the Miocene: A record of eustasy, tectonics and palaeoceanography in the Gippsland Basin

AbstractWell‐developed clastic shoreline systems have been deposited in the Gippsland Basin over a 70 Ma period, from the latest Cretaceous to the present day. Twenty‐three stacked coastal units have been mapped and described in the Traralgon and Balook formations of the Latrobe and Seaspray groups. These units are made up of prograding and backstepping shoreface deposits, which, in plan view, display well‐developed strandline geometries at the terrestrial–marine interface. Shoreface deposits are interpreted to include prograding beach, barrier island and transgressive beach deposits. The lower coastal plain is characterised by persistent deposition of coals despite changes in shoreface type and significant palaeoclimate fluctuations. These coastal deposits display approximately 123 km of transgression from the Late Cretaceous shoreline at the base of the study interval to the mid Miocene Yallourn Formation near the top. The Late Cretaceous and Palaeocene shoreline deposits individually prograde and are separated by flooding surfaces reflecting eustatic changes. Overall they display long‐term backstepping behaviour (retrogradation) as a result of basin subsidence. Though shorelines of the Eocene–Miocene are distinctly transgressional, probably reflecting basin subsidence, in the mid‐Miocene they become individually and collectively progradational. A series of unconformities in the Oligocene, coupled with Miocene progradation, likely reflects a combination of a compressional tectonic regime and glacioeustatic fluctuations. Despite major changes in the tectonics and palaeoclimate, basin subsidence appears to be the dominant driver for changes in shoreline location.

TAXONOMY AND AFFINITIES OF AFRICAN CENOZOIC METATHERIANS

The record of extinct African metatherians (Mammalia, Theria) is scanty, restricted in time (Eocene–Miocene), and its taxonomy is still subject of debate. A review of all African metatherians, or alleged metatherians, known up to now, led us to the recognition of only three taxa referable to this group: (1) Kasserinotherium tunisiense (Peradectoidea?), from the early Eocene of Tunisia; (2) Peratherium africanum (Herpetotheriidae), from the early Oligocene of Egypt and Oman, and (3) an indeterminate Herpetotheriidae? from the early Miocene of Uganda. Herpetotheriids probably reached Afro-Arabia from Europe in one or more dispersal waves since the early Oligocene. Kasserinotherium, on the contrary, suggests an earlier (Paleocene) arrival from South America, judging from its alleged affinities with South American and Australian taxa. Such a migration event (probably, through a filter corridor such as the Rio Grande Rise-Walvis Ridge system in the South Atlantic) may also explain the enigmatic presence of polydolopimorphian metatherians in the Cenozoic of central Anatolia (Turkey). A more radical hypothesis is that all European (Eurasian?) Marsupialiformes have an ultimate origin in South America, from where they dispersed via Africa by the Paleocene–earliest Eocene.

Apprehending novel biodiversity redux – thirteen new genera and three new families of Zealandian Bryozoa, with the first living species of the Eocene‒Miocene genus Vincularia (Vinculariidae)

AbstractThirteen new genera and three new families of cheilostome Bryozoa are described from the New Zealand biogeographic region, centred on Zealandia, between 26.42° (northern Norfolk Ridge) and 54.02°S latitude (south-east Campbell Plateau) from coastal waters to bathyal depths (46‒1676 m). The new genera, comprising 15 new and one previously described Zealandian species, are: Elementella (Elementellidae n. fam.), Niwapora, Quasicallopora, Quitocallopora, Judyella (Calloporidae), Ellisantropora (Antroporidae), Rhizellisina (Ellisinidae), Radixenia (Calloporoidea incertae sedis), Granomurus (Granomuridae n. fam.), Carolanna (Bugulidae), Borioplebs (Borioplebidae n. fam.), Seabournea (Cribrilinidae) and Waeschenbachia (Romancheinidae). A new Recent species of the otherwise Eocene‒Miocene genus Vincularia is also described from deep water on the Three Kings Ridge. Two new combinations are created – Judyella precocialis (Gordon, 1984) and Ellisantropora aggregata (Gordon, 1984). Ellisantropora tilbrooki sp. nov. is also introduced for a species from Torres Strait. Four of the deep-sea genera (three from one station on the northern Norfolk Ridge, one from a station on the Three Kings Ridge) have species with plesiomorphies or distinctive skeletal characters that suggest they are relict. Almost half of the new species form spot-like colonies on hard substrata.

The Gondwanan heritage of the Eocene–Miocene Patagonian floras

The breakup of Gondwana and the associated climatic changes led to the fragmentation of floras that were once connected across the Southern lands. The diversity of the Gondwanan remnants has long been assumed to have fluctuated in Patagonia across the Cenozoic, although it has never been quantified so far. Here we address when the major floristic members of the Gondwanan legacy (e.g., southern beeches, proteas, podocarps, gumtrees) expanded, contracted, or became extinct during the Patagonian biogeographic isolation (Eocene–Miocene) on the basis of the re-assessment of the fossil record (i.e., woods, leaves, and spore-pollen grains). We found that the Patagonian floras experienced moderate to severe shifts in the diversity of the Gondwanan component —relative to the total flora— with the highest estimates in the late Eocene–early Oligocene (~50%) and the lowest estimates in the late Miocene (~20%) according to the fossil pollen record. The most important floristic changes include two major replacements: 1) tropical Gondwanan taxa (e.g., Akania, Eucalyptus, Gymnostoma) by typically cool-temperate taxa (e.g., Nothofagaceae) in the Eocene, and 2) humid taxa (e.g., Podocarpaceae) by arid-adapted floras, mostly of non-Gondwanan affinity, across the Miocene. The variation in diversity of the Gondwanan component from Patagonia shows a striking resemblance to that from Australia for the same period, probably indicating a global-scale driver of floristic turnover (e.g., global cooling conditions). Today, the Patagonian subantarctic forests harbor only about ~15% of the Gondwanan diversity, representing a three-fold decrease from its climax in the late Eocene–early Oligocene.