Biochronology and paleoclimatic implications of Middle Eocene to Oligocene planktic foraminiferal faunas

Planktic foraminiferal assemblages have been analyzed quantitatively in six DSDP sites in the Atlantic (Site 363), Pacific (Sites 292, 77B, 277), and Indian Ocean (Sites 219, 253) in order to determine the nature of the faunal turnover during Middle Eocene to Oligocene time. Biostratigraphic ranges of taxa and abundance distributions of dominant species are presented and illustrate striking similarities in faunal assemblages of low latitude regions in the Atlantic, Pacific and Indian oceans. A high resolution biochronology, based on dominant faunal characteristics and 55 datum events, permits correlation between all three oceans with a high degree of precision. Population studies provide a view of the global impact of the paleoclimatic and paleoceanographic changes occurring during Middle Eocene to Oligocene time.Planktic foraminiferal assemblage changes indicate a general cooling trend between Middle Eocene to Oligocene time, consistent with previously published oxygen isotope data. Major faunal changes, indicating cooling episodes, occur, however, at discrete intervals: in the Middle Eocene 44-43 Ma (P13), the Middle/Late Eocene boundary 41-40 Ma ( ), the Late Eocene 39-38 Ma ( ), the Eocene/Oligocene boundary 37-36 Ma (P18), and the Late Oligocene 31-29 Ma ( ). With the exception of the boundary, faunal changes occur abruptly during short stratigraphic intervals, and are characterized by major species extinctions and first appearances. The Eocene/Oligocene boundary cooling is marked primarily by increasing abundances of cool water species. This suggests that the boundary cooling, which marks a major event in the oxygen isotope record affected planktic faunas less than during other cooling episodes. Planktic foraminiferal faunas indicate that the boundary event is part of a continued cooling trend which began during the Middle Eocene.Two hiatus intervals are recognized in low and high latitude sections at the Middle/Late Eocene boundary and in the Late Eocene ( ). These hiatuses suggest that vigorous bottom water circulation began developing in the Middle Eocene, consistent with the onset of the faunal cooling trend, and well before the development of the psychrosphere at the boundary.     

British mammals in the Tertiary period

British Tertiary mammals are best represented in the Eocene and earliest Oligocene epochs. Additional occurrences are from the Miocene and Late Pliocene. The Eocene is marked by the occurrence of various extinct orders as well as the appearances of some of the earliest and must primitive artiodactyls and perissodactyls. The appearances in the Early Eocene and Early Oligocene represent major dispersal events, reflecting penecontemporaneous palaeogeographic changes. In the intervening timespan Britain was part of an European island, sharing its endemic terrestrial fauna. From the late Middle Eocene to earliest Oligocene, the British record is detailed enough to trace successive changes in the patterns of diversity and faunal turnover, which may relate to changing climate as well as to the dispersal events. It has been shown that changes in patterns of ecological diversity through the Eocene and earliest Oligocene match vegetational changes judged from plant fossils. They suggest a gradual transition from closed forest in the Early Eocene to a more open environment with reedmarsh and wooded patches by the end of the epoch.     

Deep-sea benthonic foraminiferal faunal turnover near the Eocene/Oligocene boundary

Eocene-Oligocene deep-sea benthonic foraminifera in D.S.D.P. Site 277 in the southwest Pacific have been analyzed to determine the benthonic foraminiferal response to the development of the psychrosphere near the Eocene/Oligocene boundary. Biostratigraphic ranges of 41 taxa show that 23 taxa are found throughout the Late Eocene to Early Oligocene sequence, while 18 taxa exhibit first or last occurrences. Comparison of the faunal changes in Site 277 with a benthonic foraminiferal oxygen isotope record shows that the development of the psychrosphere did not have a profound effect upon the benthonic foraminifera, and the overall faunal change preceding and subsequent to the bottom-water circulation event occurred gradually. The inferred water-mass event affected the relative abundance of one species, Epistominella umbonifera. The lack of major faunal changes at the Eocene/Oligocene boundary in Site 277 probably reflects either wide environmental tolerances of the benthonic foraminifera, or a bottom-water temperature change less than 3°C.Examination of previously published benthonic foraminiferal biostratigraphic data from D.S.D.P. Sites 167, 171, 357, 360, 363, and 400A, and deep-sea ostracode data from D.S.D.P. Leg 3 show faunal changes occurred during discrete intervals in the Middle Eocene-Early Oligocene. The faunal patterns from these data and from Site 277 show that the Eocene/Oligocene cooling event did not cause rapid, catastrophic changes of the benthonic faunas of the open ocean, although significant faunal changes are associated with the water mass event in Sites 167, 171 and 400A.The benthonic faunal changes in Middle Eocene-Early Oligocene time are consistent with the gradual decrease of inferred bottom-water temperatures, based on previously published oxygen isotopic data. The δ ¹⁸O Eocene/Oligocene enrichment of 0.76‰ is a major event in the Southern Ocean oxygen isotopic record, but is considerably less in magnitude than the 1.75-2.00‰ change that occurred gradually from mid-Early Eocene to the Eocene/Oligocene boundary. The benthonic foraminiferal and isotopic data indicate that bottom-water circulation may have developed during the Middle Eocene to Early Oligocene interval, with the 3°C bottom-water cooling near the Eocene/Oligocene boundary representing part of this development.     

Cenozoic deep-sea ostracods from Maud Rise, Weddell Sea, Antarctica (ODP Site 689): a palaeoceanographical perspective

Cenozoic palaeoceanography of the Maude Rise, Weddell Sea, Antarctica, has been investigated using Palaeocene to Quaternary deep-sea ostracod faunas from 23 samples of ODP Site 689. The abundance of ostracods is high enough only during the Palaeogene (Palaeocene-Oligocene) to allow palaeoceanographical inferences based on changes in diversity, dominance, endemism and faunal turnover (first and last occurrences). The abundance is particularly high throughout the Palaeocene and Eocene, but declines irreversibly near the Eocene/Oligocene boundary. The diversity increases more or less continuously from the Early Palaeocene to the Middle Eocene, and then it generally decreases throughout the remaining part of the Palaeogene (Middle Eocene-Oligocene); an exception is a positive peak in the Shannon-Weaver index in a single sample in the Late Oligocene. No positive peaks in diversity and taxa originations (first occurrences) at c. 40-38 Ma, occurs at Site 689; so the site provides no evidence for the establishment of the psychrosphere at this time. This corroborates similar regional results from an earlier study of benthonic foraminifera. Explanations for this may be related to Late Eocene-Early Oligocene changes in sedimentology and clay-mineralogy (associated with the progressive cooling of the Antarctica) which could have negatively affected abundance and diversity locally at Site 689. Alternatively, by this time, the ostracod fauna could also have been subjected to selective removal (with possible local extinction) of taxa (due to increased ventilation) or to thanatocoenosis dissolution (due to a decrease in temperature and availability of CaCO₃). A further possibility may be related to the fact that Site 689 was at intermediate water depths and may have remained within older water masses near the Eocene/Oligocene boundary. Failing these explanations, the results could indicate that the Late Eocene-Early Oligocene palaeoenvironmental changes in the world oceans were more gradual and occurred over a longer time interval than the global ostracod data show, at least at southern high latitudes.     

Upper Eocene larger foraminiferal–coralline algal facies from the Klokova Mountain (southern continental Greece)

Within the Gavrovo–Tripolitza area (southern continental Greece), marine carbonate platforms existed from the Late Triassic to the Late Eocene. The Middle–Upper Eocene marine shallow-water carbonates of the Klokova Mountain represent remnants of the large volumes of sediment that were produced on a middle ramp sedimentary system which culminated in the Lower Oligocene terrigenous deposits. Facies analysis of Bartonian–Priabonian shallow-water carbonate successions and the integration with palaeoecological analysis are used to produce a detailed palaeoenvironmental model. In the proximal middle ramp, porcelaneous foraminiferal packstone facies is characterised by larger foraminifera such as Praturlonella and Spirolina. These forms thrived in a shallow-water setting with low turbidity, high-light intensity and low-substrate stability. The foraminiferal packstone facies, the thin coralline wacke–packstone facies and the rhodolith packstone facies deposited approximately in the same depth range adjacent to one another in the middle-ramp. Nummulitids (Nummulites, Assilina, Pellatispira, Heterostegina and Spiroclypeus) increase in abundance in the middle to distal mid-ramp together with the orthophragminids. Coralline algae, represented by six genera, are present in all facies. Rhodoliths occur in all facies but they show different shapes and growth forms. They develop laminar sub-ellipsoidal shapes in higher turbulence conditions on mobile sand substrates (foraminiferal packstones and rhodolith rudstones), whilst sub-discoidal shapes often bound by thin encrusting coralline plants in lower hydrodynamic settings. The distinctive characteristics of the palaeoecological middle-ramp gradient are an increase in dominance of melobesioids, a thinning of the encrusting coralline plants and a flattening of the larger benthic foraminiferal shells.     

Paleocene reefs on the Maiella Platform Margin, Italy: An example of the effects of the cretaceous/tertiary boundary events on reefs and carbonate platforms

Summary Reef facies, reef types and their biotic associations in the Maiella platform margin (central Italy) provide qualitative evidence for a significant reef decline across the Cretaceous/Tertiary (K/T) boundary, and indicate two phases of reef recovery during the Paleocene. Rudists dominated the reef community until the latest Cretaceous. A significant sea-level fall around the time of the K/T boundary is documented by a truncation surface associated with emersion. During sea-level highstands in the Danian to Early Thanetian and, more extensively, during the Late Thanetian, coral-algal patch-reefs grew along the platform margin and top. Already in the Danian to Early Thanetian, the reef communities were more diverse and the constructional types more evolved than previously known from this time. Differences between the Danian to Early Thanetian coral association, the Late Thanetian association, and Late Cretaceous coral faunas may have ecological or evolutionary causes. Repeated emergence produced a complex diagenetic history in the Danian to Lower Thanetian limestones. All Paleocene reefs were displaced by gravitative redeposition. Coral-algal reefs are less important in the Early to mid Eocene, when alveolinid foraminifera dominated on the Maiella shelf. Reefs on the Maiella platform diversified and attained large sizes in the Late Eocene to Early Oligocene, as known from other Mediterranean platforms. The external controls on the Late Cretaceous to Oligocene evolution and demise of reef communities that are most easily demonstrated with our data are sealevel fluctuations and climate change. We propose that the change in reef biota and reef types across the K/T boundary and during the Early Tertiary were important causes of the parallel changes in platform growth style.     

A paleoenvironmental standard section for Early Ilerdian tropical carbonate factories (Corbieres, France; Pyrenees, Spain)

Early Ilerdian (Early Eocene, Shallow Benthic Zones 5 and 6) carbonate systems of the Pyrenees shelf were deposited after a time of severe climatic (‘Paleocene–Eocene Thermal Maximum, PETM’) and phylogenetic (‘Larger Foraminifer Turnover’) changes. They reflect the radiation of nummulitid, alveolinid, and orbitolitid larger foraminifera after remarkable biotic changes at the end of the Paleocene, and announce their subsequent flourishing in the Middle Eocene.A paleoenvironmental model for tropical carbonate environments of this particular time interval is provided herein. During the Early Ilerdian, the inner and middle ramp deposits from Minerve, Campo and Serraduy revealed the end-member of a tropical carbonate factory with carbonate production dominated by the end-members of biotically (photo-autotrophic skeletal) controlled and biotically induced carbonate precipitation. Inner platform environments are dominated by alveolinids and in part by orbitolitids, middle platform environments are dominated by nummulitids. Corals are present, but they do not form reefs, which is a typical feature for the Eocene. Nummulite shoal complexes, which are well-known from the Middle Eocene are also absent during the studied Early Ilerdian interval, which may reflect the early evolutionary stage of this group.     

Microfacies and sequence stratigraphy of the Amapá Formation, Late Paleocene to Early Eocene, Foz do Amazonas Basin, Brazil

On the basis of thin-section studies of cuttings and a core from two wells in the Amapá Formation of the Foz do Amazonas Basin, five main microfacies have been recognized within three stratigraphic sequences deposited during the Late Paleocene to Early Eocene. The facies are: 1) Ranikothalia grainstone to packstone facies; 2) ooidal grainstone to packstone facies; 3) larger foraminiferal and red algal grainstone to packstone facies; 4) Amphistegina and Helicostegina packstone facies; and 5) green algal and small benthic foraminiferal grainstone to packstone facies, divisible locally into a green algal and the miliolid foraminiferal subfacies and a green algal and small rotaliine foraminiferal subfacies. The lowermost sequence (S1) was deposited in the Late Paleocene–Early Eocene (biozone LF1, equivalent to P3–P6?) and includes rudaceous grainstones and packstones with large specimens of Ranikothalia bermudezi representative of the mid- and inner ramp. The intermediate and uppermost sequences (S2 and S3) display well-developed lowstand deposits formed at the end of the Late Paleocene (upper biozone LF1) and beginning of the Early Eocene (biozone LF2) on the inner ramp (larger foraminiferal and red algal grainstone to packstone facies), in lagoons (green algal and small benthic foraminiferal facies) and as shoals (ooidal facies) or banks (Amphistegina and Helicostegina facies). Depth and oceanic influence were the main controls on the distribution of these microfacies. Stratal stacking patterns evident within these sequences may well have been related to sea level changes postulated for the Late Paleocene and Early Eocene. During this time, the Amapá Formation was dominated by cyclic sedimentation on a gently sloping ramp. Environmental and ecological stress brought about by sea level change at the end of the biozone LF1 led to the extinction of the larger foraminifera (Ranikothalia bermudezi).     

临夏盆地早中新世上庄组的巨獠犀门齿化石(英文)

记述了在临夏盆地早中新世地层中发现的兰州巨獠犀(Aprotodon lanzhouensis)的下门齿化石,其特点为非常粗壮并强烈弯曲。新材料的发现使巨獠犀在临夏盆地的延续时代跨越渐新世/中新世界线的推测得到完全证实。巨獠犀分布的地质时代和地理范围与巨犀重合,但巨獠犀的化石地点和个体数量都相当稀少。巨獠犀的下颌形态功能特点指示其生活于晚始新世至早中新世中国西北、南亚和中亚干旱环境地带中镶嵌分布的少量近水环境。巨獠犀在中中新世之前彻底绝灭,其原因可能是气候变化的结果,也说明临夏盆地早中新世的环境特征与晚渐新世的疏林系统相似,而不同于中中新世的茂密森林。     

Middle Eocene–Early Pliocene Subantarctic planktic foraminiferal biostratigraphy of Site 1090, Agulhas Ridge

The analysis of planktic foraminiferal assemblages from Site 1090 (ODP Leg 177), located in the central part of the Subantarctic Zone south of South Africa, provided a geochronology of a 330-m-thick sequence spanning the Middle Eocene to Early Pliocene. A sequence of discrete bioevents enables the calibration of the Antarctic Paleogene (AP) Zonation with lower latitude biozonal schemes for the Middle–Late Eocene interval. In spite of the poor recovery of planktic foraminiferal assemblages, a correlation with the lower latitude standard planktic foraminiferal zonations has been attempted for the whole surveyed interval. Identified bioevents have been tentatively calibrated to the geomagnetic polarity time scale following the biochronology of Berggren et al. (1995). Besides planktic foraminiferal bioevents, the disappearance of the benthic foraminifera Nuttallides truempyi has been used to approximate the Middle/Late Eocene boundary. A hiatus of at least 11.7 Myr occurs between 78 and 71 m composite depth extending from the Early Miocene to the latest Miocene–Early Pliocene. Middle Eocene assemblages exhibit a temperate affinity, while the loss of several planktic foraminiferal species by late Middle to early Late Eocene time reflects cooling. During the Late Eocene–Oligocene intense dissolution caused impoverishment of planktic foraminiferal assemblages possibly following the emplacement of cold, corrosive bottom waters. Two warming peaks are, however, observed: the late Middle Eocene is marked by the invasion of the warmer water Acarinina spinuloinflata and Hantkenina alabamensis at 40.5 Ma, while the middle Late Eocene experienced the immigration of some globigerinathekids including Globigerinatheka luterbacheri and Globigerinatheka cf. semiinvoluta at 34.3 Ma. A more continuous record is observed for the Early Miocene and the Late Miocene–Early Pliocene where planktic foraminiferal assemblages show a distinct affinity with southern mid- to high-latitude faunas.     

海南岛第三纪沉积环境与古植物群落的多样性及其变迁

海南岛第三纪沉积类型及古植物群落复杂多样,早第三纪主要为河湖泊,湖泊相和湖沼相等沉积,晚期发生海侵,开始出现海陆交相沉积;古植物群落主要有：温带山地针叶林和落叶阔叶林,亚热带常绿和落叶阔叶林,晚晚开始出现红树林,总体属温暖湿珠亚热带气候,晚第三纪海侵加大,沉积为型为滨海相,滨海－浅海相,浅海相及深水广海相等海相沉积,在滨海地区红树林面积大大增加,盆地中心平原地上展为低地热带雨林,总体属炎热潮湿的热带气候,但在海南岛西部和西北部仍发育有山地雪松和云杉林,上新世时植被类型逐渐接近现今当地的面貌,深入研究本区第三纪古环境与古植物群落的变迁对海南岛现代生物多样性形成机制的研究具有重要意义。     

Early Tertiary fossil plants and paleoclimate of Lanzhou Basin

Fossil plants from the lower part of Xianshuihe Formation in the Lanzhou Basin, Gansu Province were studied. The flora contains 29 species, representing 20 genera and 12 families, which include Lauraceae ( Daphnogene ), Lardizabalaceae ( Akebia ), Berberidaceae ( Berberis ), Ulmaceae ( Planera, Ulmus, Zelkova ), Betulaceae ( Alnus, Carpinus ), Myricaceae( Myrica ), Salicaceae ( Populus, Salix), Myrsinaceae(Ardisia), Rosaceae ( Prunus, Sorbus, Sorbaria, Spiraea ), Leguminosae ( Gleditsia, Sophora), Anacardiaceae (Rhus), Caprifoliaceae(Viburnum). An analysis of the floristic elements and their foliar physiognomy shows that most members of the flora are deciduous broad-leaved trees or shrubs with a few evergreen shrubs. The most noteworthy species is Rhus turcomanica which was present in the Middle Eocene to Late Eocene of Central Asia (Kazakhstan, Turkmenistan). Generally, Rhus turcomanica occurred at the same beds as Palibinia, an extinct fossil plant whose presence indicates a subtropical dry climate. Another species, Sorbaria callicomifolia Kornilova was present from the Early Oligocene to Early Miocene of Central Asia (Kazakhstan and Turkmenistan). According to an analysis of spores and pollen, this flora contains over 20 species. It is predominated by the angiosperm pollen. There appeared Ephedripites and Nitrariadites which were important elements in the dry area. Ephedripites was found from the Upper Cretaceous to Early Tertiary. Nitrariadites occurred in the Late Miocene, whereas Rhus turcomanica and Sorbaria callicomifolia were both reported in the subtropical dry area from the Middle Eocene to Early Oligocene. The latest record of Rhus turcomanica is from the Middle Eocene to Early Oligocene of Central Asia. The presence of this element in the lower part of Xianshuihe Formation may indicate that itsage is the latest stage of the Early Oligocene.     

兰州盆地早第三纪植物及古气候意义

化石采自甘肃省兰州盆地咸水河组底部,经研究认为有29种,归属20属12科。它们是：樟科 Lauraceae (Daphnogene),木通科Lardizabalaceae(Akebia),小檗科Berberidaceae(Berberis),榆科Ulmaceae (Planera,Ulmus,Zelkova),桦木科Betulaceae(Alnus,Carpinus),杨梅科Myricaceae(Myrica),杨柳科Sali- caceae(Populus,Salix),紫金牛科Myrsinacese(Ardisia),蔷薇科Rosaceae (Prunus,Sorbus,Sorbaria,Spir- aea),豆科Leguminosae(Gleditsia,Sophora),漆树科 Anacardiaceae(Rhus),忍冬科Caprifoliaceae(Viburnum) 等。经植物区系组成与叶相分析显示,该植物区系的大多数成员是落叶阔叶乔、灌木,少数为常绿灌木。其中特殊的分子是 Rhus turcomanica Korov．ex Vassilvesk,该成分是早第三纪中、晚期的标志化石植物。另一化石植物 Sorbaria callicomifolia Kornilova曾出现在中亚的早渐新世,最晚至早中新世。同一层位采集的孢粉样分析结果显示：该组合仅约20种,种类相对贫乏,并以被子植物的花粉占优势。其中出现裸子植物的麻黄粉,被子植物的白刺粉及蒿粉等,这几个类型均指示沉积时期经历干旱气候。综合植物大化石及孢粉分析研究,均出现一些指示气候为亚热带干旱或周期性干旱气候的特点,并据Rhus turcomanica出现的最晚记录,推测咸水河组底部的地质时代大约是早渐新世晚期。     

History of the development of the temperate forest flora in Kazakhstan,U.S.S.R. from the Oligocene to the Early Miocene

Exact dating of the floras existing in western Kazakhstan during the Oligocene and Early Miocene permits a detailed examination of the formation of a temperate flora during the Rupelian (Early Oligocene), Chattian (Late Oligocene), Aquitanian (the beginning of Early Miocene) and the Burdigalian (end of Early Miocene) Ages and at the same time an establishment of the sequence in the origin and the disappearance of a flora of Turgayan type (the “Turgayan flora” of Kryshtofovich) in Kazakhstan. The most important aspects (composition and terminology) of a previous subtropical flora of a Drevlyanian (possibly Volynian) ecological type (the “Poltavian” flora of Kryshtofovich), which had developed in Kazakhstan and the Ukraine during the Eocene, are also discussed. The text is intended for botanists of various special interests, e.g., paleobotanists, phytogeographers and floristicians, as well as for geologists, especially stratigraphers and paleogeographers. The bibliography comprises more than 200 references and there are seven tables.     

Autochthonous facies and allochthonous debris flows compared: Early oligocene carbonate facies patterns of the Lower Inn Valley (Tyrol, Austria)

Summary This study presents a microfacies analysis and palaco-environmental interpretations of Early Oligocene carbon ates from the Lower Inn Valley Tertiary (“Unterinntal-Terti?r”) of Austria. The well preserved biogenic components allow detailed investigations of component relationships and controlling ecological parameters. The carbonates are dominated by coralline algae, corals, small and large benthic foraminifers, bryozoans and lithoclasts. Bivalves, gastropods, echinoderms, brachiopods and serpulids are subordinate. The limestones are present as A) autochthonous carbonates transgressing directly above the Triassic basement and B) allochthonous debris flows within deeper-water marls. These carbonates are found within the Paisslberg Formation. The Werlberg Member within this formation, pertains to the autochthonous carbonates and larger debris flows. Five facies types are separated following fabric analysis and statistical treatment (correlation, cluster analysis, principal components analysis) of semi-quantitative data consisting of component frequencies of thin sections. Facies distribution patterns are principally controlled by variations in substrate characteristics, turbulence and light along a depth gradient. Reconstruction of facies pattern distribution reveal both lateral and proximal-distal facies trends: coral-coralline algal facies, coralline algal facies as well as foraminiferal facies were situated in shallower environments, laterally adjacent to each other. These grade distally into coralline algal-bryozoan facies, bryozoan facies and finally into mollusc rich marls. Debris flows consisting of reworked material from all of the known facies (bioclastic packstone facies) is restricted to the debris flow and possible represents transport induced differentiation of components and grain size within distal debris flows.     

Facies,paleoenvironment, carbonate platform and facies changes across Paleocene Eocene of the Taleh Zang Formation in the Zagros Basin,SW-Iran

The Paleocene–Eocene Taleh Zang Formation of the Zagros Basin is a sequence of shallow-water carbonates. We have studied carbonate platform, sedimentary environments and its changes based on the facies analysis with particular emphasis on the biogenic assemblages of the Late Paleocene Sarkan and Early Eocene Maleh kuh sections. In the Late Paleocene, nine microfacies types were distinguished, dominated by algal taxa and corals at the lower part and larger foraminifera at the upper part. The Lower Eocene section is characterised by 10 microfacies types, which are dominated by diverse larger foraminifera such as alveolinids, orbitolitids and nummulitids. The Taleh Zang Formation at the Sarkan and Maleh kuh sections represents sedimentation on a carbonate ramp.

The deepening trends show a gradual increase in perforate foraminifera, the deepest environment is marked by the maximum occurrence of perforate foraminifers (Nummulites), while the shallowing trends are composed mainly of imperforate foraminifera and also characterised by lack of fossils in tidal flat facies.

Based on the facies changes and platform evolution, three stages are assumed in platform development: I; algal and coralgal colonies (coralgal platform), II; coralgal reefs giving way to larger foraminifera, III; dominance of diverse and newly developing larger foraminifera lineages in oligotrophic conditions.     

Tracing the Origin and Diversification of Dipodoidea (Order: Rodentia): Evidence from Fossil Record and Molecular Phylogeny

Dipodoidea are a diverse rodent group whose earliest known record is from the Middle Eocene. The evolution and diversification of this superfamily have been documented by fossils and comparative morphology, but have not yet been studied from the perspective of molecular phylogeny. This study is the first attempt to reconstruct an extensive phylogeny of Dipodidae and estimate divergence times based on a nuclear gene coding for interphotoreceptor retinoid-binding protein. We found that there is a wide measure of agreement with the fossil record. Each of the three ecological groups of the extant Dipodoidea (sicistines, zapodines, and jerboas) has its distinctive distribution; the distribution patterns have been shaped by the dispersal events. The key events of paleogeographic distribution coincided with major paleoenvironmental events in the Cenozoic. The first important diversification phase occurred during the period from the Oligocene to Early Miocene, when global climate underwent major changes beginning with the Eocene/Oligocene boundary. The second adaptive radiation occurred within jerboas and was associated with the expansion of open habitat starting with the late Middle Miocene. The diversification of jerboas can be correlated with habitat changes in response to global and regional climatic events.     

Depositional environments and facies development of the Cenomanian–Turonian Galala and Maghra el Hadida formations of the Southern Galala Plateau (Upper Cretaceous,Eastern Desert,Egypt)

The Cenomanian–Turonian (Upper Cretaceous) Galala and Maghra el Hadida formations of the Southern Galala Plateau in Wadi Araba (northern Eastern Desert, Egypt) represent marine depositional systems developing in response to the early Late Cretaceous transgression at the southern margin of the Neotethyan Ocean in tropical paleolatitudes. A facies analysis (litho-, bio- and microfacies) of these successions shows the presence of 22 facies types (FTs, six are related to the Galala Formation, while the Maghra el Hadida Formation is represented by 16 FTs). The Galala Formation was deposited in a fully marine lagoonal environment developing in response to a latest Middle to early Late Cenomanian transgression. The rich suspension- and deposit-feeding macrobenthos of the Galala Formation indicate meso- to eutrophic (i.e., green water) conditions. The facies types of the uppermost Cenomanian–Turonian Maghra el Hadida Formation suggest deposition on a homoclinal carbonate ramp with sub-environments ranging from deep-subtidal basin to intertidal back-ramp. Major and rapid shifts in depositional environments, related to (relative) sea-level changes, occurred in the mid-Late Cenomanian, the Early–Middle Turonian boundary interval, the middle part of the Middle Turonian and the Middle–Late Turonian boundary interval.     

Transgressive–regressive sequences on the slope of an isolated carbonate platform (Middle–Late Permian, Laibin, South China)

From the Middle to Late Permian, the Laibin area in Guangxi, South China, was situated on the slope of an isolated carbonate platform, on which continuous marine successions were deposited. Two global stratotype sections for the boundary between the Guadalupian (Middle Permian) and Lopingian (Late Permian) are located at Penglaitan and Tieqiao in the Laibin area, respectively, and thus are chosen for study. At the two locations, 14 facies are recognized in the Maokou and Heshan Formations, and they are further grouped into four facies associations (basin, lower slope, upper slope, and platform margin). Six main transgressive–regressive (TR) sequences are identified in strata from the Roadian (Middle Permian) to the Wuchiapingian (Late Permian). They are conformable marine sequences that were little influenced by regional uplift (Dongwu Movement) and so provide a good record of the sea-level changes in South China at this time. Based on the significant taxonomic selection and controversial marine faunal loss in the end-Guadalupian mass extinction, and the Middle-Late Permian sea-level changes recorded by the TR sequences in the Laibin area, it is suggested that this extinction event might have been triggered by the reduction and loss of shallow-marine habitat area caused by the end-Guadalupian regression. The global cooling and Emeishan volcanism also occurring at this time could have further enhanced this extinction event.     

The Middle Caradoc Facies and Faunal Turnover in the Late Ordovician Baltoscandian palaeobasin

A Late Ordovician episode of remarkable biotic, climatic, sea level and facies changes, named here as the Middle Caradoc Facies and Faunal Turnover, took place in the Baltoscandian area. This paper presents an integrated overview of these changes in the critical middle Caradoc interval. Data are given on carbonate rock composition, distribution and grain-size composition of the siliciclastic material and the carbon isotopic composition of whole-rock carbonates in cores of Estonia and Sweden.

The Middle Caradoc Facies and Faunal Turnover can be described as a succession of related environmental changes. The turnover began with a positive excursion in carbonate δ¹³C and continued with sea level changes that led to a sedimentary hiatus on the shelf and a change from carbonate-dominated to siliciclastic-dominated sedimentation in the basin. The turnover ended with an extinction event and associated microfaunal crisis.

The middle Caradoc turnover in Baltoscandia is comparable to a similar succession of changes in North America. The turnover affected two palaeocontinents, and reflects a widespread, possibly global environmental change. Onset of glaciation on Gondwana and/or increased orogenic activity might have initiated the changes in ocean circulation and led to the initial carbon isotope excursion. The following sea level rise and faunal changes affected several different continents.