Fossil Zones Research Articles

Magnetostratigraphy of the Pliocene Masol Formation, Siwalik Frontal Range, India: Implications for the age of intentional cut-marked fossil bones

The sedimentary Masol Formation, at least 165 m thick, is located in the Indian Siwalik Frontal Range and outcrops in the Chandigarh Anticline. It includes a fossiliferous zone called the Quranwala Zone (QZ) in its lower part. These fossils are characteristic of the Late Pliocene (Tatrot). Previous magnetostratigraphy showed that the QZ was deposited during the Gauss chron, with a short magnetic excursion at the base of the QZ, but the Gauss-Matuyama reversal was imprecisely identified in the stratigraphy of the Masol Formation. Following cut marks on fossil bones discovered in the QZ, we conducted a new magnetostratigraphy study to clarify their age. Our results indicate that detrital hematite is the main magnetic carrier and confirm that the entire Masol Formation was deposited during the Gauss Chron, whereas the Gauss-Matuyama reversal is outside the study area. Comparison between the magnetic excursion previously found at the base of the QZ and others identified elsewhere in a different sedimentary context and dated between 2.62 and 2.95 Ma, gave a range of sedimentation rates between 0.41 and 3.75 m.kyr-1 for the minimum thickness of the Gauss chron recorded in the Masol Formation. However, only rates less than 1 m.kyr-1 are consistent with the Late Pliocene deposits observed in the Siwalik. Magnetostratigraphy and obtained sedimentation rates conclude that the cut and percussion marks on the fossil bones have a minimum age of 2.68 Ma and a maximum age of 2.95 Ma. This evidence of intentional hominin activity is thus the oldest known in Asia.

Nejdia Arkell, 1952, an Early Jurassic (Toarcian) ammonite from the Marrat formation, Central Saudi Arabia

ABSTRACT The present article describes the ammonite fauna from the genus Nejdia, pertaining to the Early Jurassic (Toarcian) deposits of the upper Marrat Formation, exposed in the southwest of Riyadh, capital city of Saudi Arabia, Nejd region. The fossiliferous zone is spread within an area of circa 40 km long, consisting of: light-brown limestone, including interbedded lime-mud at the lower part, yellow and red, clayish limestone at the middle part, cream, dense limestone at the upper part. The cliff forming Marrat Formation contains ammonites Nejdia and Parahildaites belonging to the upper member as well as Bouleiceras and Protogrammoceras in the lower member. At least four species of ammonites from Nejdia genus have been identified. They can be essentially distinguished through the differences in suture line shapes and the whorl section. The associated fauna contains mainly: brachiopods Calyptoria, echinoids Acrosalenia, bivalves. http://zoobank.org/References/7b33f54f-599a-4394-8f2f-95d3c2c631d9

Active and fossil hydrothermal zones of the Apacheta volcano: Insights for the Cerro Pabellón hidden geothermal system (Northern Chile)

Sulphate, clay, silica and oxide-hydroxide minerals were identified by means of fieldwork, XRD and SEM, both in the active and fossil zones of the Cerro Apacheta volcano (Cerro Pabellón geothermal field, northern Chile). Mineral assemblages and their spatial distribution in the active zone allow defining Superficial advanced argillic alteration facies associated with Argillic alteration facies, consistent with an acid-sulphate steam-heated environment. Poor crystallized kaolinite and cristobalite (opal-C), alunite in the steaming ground, alunogen and Mg-Zn-Cu-rich smectite in the fumarolic deposits represent the main mineralogical associations of this zone. The same two facies are defined in the fossil zone, interpreted as related to a superficial epithermal environment, with well crystallized kaolinite, alunite-natroalunite, pyrophyllite, mixed opal-A-opal C/T-quartz and Mg-Zn-Cu-rich Illite/Smectite (I/S). The presence and distribution of Mg-Zn-Cu rich montmorillonites and beidellites in the active and fossil zones are used as indicative of the hot mineralized vector fluids. In the active zone they would be interpreted alternatively as the result of an in situ argillic alteration, overlapping steam-heated typical assemblages and mineral associations formed in the fumarolic zones, or having an “allochthonous” origin, being formed at depth within the superficial part of the clay cap and subsequently transported to the surface during phreatic eruptions or fluidized events. The distribution of the hydrothermal alterations is likely related to the intersection of NW-SE and NE-SW structures, linked to the Pabelloncito graben, a primary feature in the control of the circulation of hydrothermal fluids towards the surface.

Cambrian small skeletal fossil and carbon isotope records of the southern Huangling Anticline, Hubei (China) and implications for chemostratigraphy of the Yangtze Platform

Rich small skeletal fossil assemblages are described from the Yanjiahe Formation and Tianzhushan Member of southern Huangling Anticline. The Anabarites trisulcatus– Protohertzina anabarica Assemblage Zone (Small Skeletal Fossil Zone 1) is recognized in the middle to upper Yanjiahe Formation, while the thin topmost conglomeratic limestone unit yielded a mixed assemblage resulting from reworking and redeposition of source material of Small Skeletal Fossil Zones 1 to 3 (including Anabarites trisulcatus, Protohertzina anabarica, P. unguliformis, Watsonella crosbyi, Aldanella attleborensis, Anabarella plana). Our revised biostratigraphic correlation indicates the existence of longer hiatuses in the Yanjiahe Formation and between the Yanjiahe and Shuijingtuo formations. The obtained δ13Ccarb values in our profile deviate in some details from those of some previous reports. Based on the new biostratigraphic correlation, the δ13Ccarb trend records values oscillating between −3 to +4.4‰ in the upper Anabarites trisulcatus - Protohertzina anabarica Assemblage Zone, which is unusual for the Yangtze Platform. This interval of positive δ13Ccarb values in the upper Yanjiahe Formation and the Dahai Member of eastern Yunnan are here interpreted to reflect the impact of a local aquafacies. Moreover, it is here argued that the selection of a carbon isotope peak as a primary index tool in the Laolin section for defining the Cambrian Stage 2 must be treated with caution, as this isotope excursion is influenced by a regional water mass and does not reflect an open marine seawater signature, underlining other technical and theoretic concerns on the general application of chemostratigraphy in Cambrian shallow-water carbonate platforms. Overall we suggest that chemostratigraphic correlations need to be supported by biostratigraphic tools.

Messor barbarus ants as soil bioturbators: Implications for granulometry, mineralogical composition and fossil remains extraction in Somosaguas site (Madrid basin, Spain)

Few studies have inquired about the relationship between myrmecological activity and the granulometry and mineralogy of sediments of a palaeontological site. The objectives of this article are to determine the sedimentological or mineralogical distinctions produced by ants of the species Messor barbarus when excavating their nests and extracting grains and vertebrate fossil remains from the Miocene palaeontological site of Somosaguas (Madrid, Spain), to evaluate the degree of taphonomic influence this myrmecological activity has on the fossil remains, and to decide whether or not it can be used as a tool for palaeontological prospection. Results show that Messor barbarus does not alter fossil remains when examined under a 10× binocular magnifying glass. Ants preferentially extract from the ant nest grains of medium sizes (0.25–2 mm) compared to the non-ant-modified soils, and also extract a higher quantity of feldspars. These significant granulometric and mineralogical modifications should be considered when carrying out compositional, sedimentological or stratigraphical studies, since these can become biased and alter geological interpretations as provenance or palaeoclimatic signal. Grain size selection could be due to Messor barbarus' physical capacities or the use of clay particles as cementing elements in nests. Mineralogical distinction may be related to feldspars' embayments and pits filled with finer material (mainly smectites), making transportation and pheromone impregnation easier.Results show that the ant mounds had increasing concentrations of fossil remains the nearer they were from the main excavation area, therefore the study of ant mounds in potentially fossiliferous zones can indeed be used as a new method of palaeontological prospection.

The Chalk Group (Upper Cretaceous) of the Northern Province, eastern England – a review

A review of the Chalk of the Northern Province recognizes six formations, five of which (Hunstanton, Ferriby, Welton, Burnham and Flamborough formations) crop out in northern Norfolk, Lincolnshire and Yorkshire, and a sixth (Rowe Formation) is buried beneath the drift of Holderness. The Hunstanton, Ferriby and Flamborough formations are largely devoid of flints, whereas the Welton (other than its two basal members) and Burnham formations have nodular and tabular flints, respectively. Previous work on the lithostratigraphy and marker beds is presented, and an overview of the distribution of the more important macrofossils is provided. Especial attention is given to the succession at Speeton through the Hunstanton, Ferriby and lower Welton formations with details of the oxygen and carbon isotope signatures. The Speeton section is internationally important because of its expanded Albian-Mid Cenomanian succession. Small sections of the Burnham Formation in Speeton–Buckton cliffs are also presented for the first time. The appendix reviews the relevant Cretaceous stage boundaries with reference to the Chalk of the Northern Province together with details of the fossil zones that are used in this paper.

A multiple sulfur isotope study through the volcanic section of the Troodos ophiolite

Multiple S isotope systematics (δ34S and Δ33S) and high resolution in-situ S isotope measurements offer new perspectives on the study of biological and abiotic cycling of sulfur in hydrothermal systems. We applied these techniques to the Tethyian Troodos ophiolite (91Ma) from Cyprus, one of the best-preserved remnants of oceanic crust in the world, using materials from deep drill cores and surface sampling. We focused on the volcanic section of the ophiolite, including the hydrothermal massive sulfide deposit at Agrokipia, which represents a fossil zone of high-temperature fluid upwelling, and the Akaki river section which displays a range of lower temperature alteration types.The δ34S and Δ33S values of bulk and SIMS (secondary ion mass spectrometry) analyses from the Agrokipia sulfide deposits show that the sulfide minerals are largely derived from thermochemical reduction of entrained seawater sulfate and leached H2S from the “root zone” of hydrothermal upwelling. The contributions of these two sources can vary substantially within individual sulfide grains, indicating a very dynamic mixing between these sulfur sources. Microbial reworking of the sulfide mound is recorded in a sample with very elevated Δ33S values (0.22‰).The Akaki and Agrokipia volcanics experienced low temperature sulfur loss and removal of heavier sulfur isotopes due to partial oxidation by microbes. While some intervals gained sulfur, and have δ34S and Δ33S values indicative of microbial sulfate reduction. REE-data of vein quartz containing pyrite with δ34S=~−21‰ implies local ephemeral hydrothermal upwelling in the lower Akaki volcanics, possibly associated with the late stage boninitic magmatic activity in the Troodos ophiolite, suggesting that microbial sulfate reduction in oceanic crust may continue for 10–15Ma in crustal sections with prolonged igneous activity such as Troodos.

Discriminating ecological and evolutionary controls during the Ediacaran–Cambrian transition: Trace fossils from the Soltanieh Formation of northern Iran

The nature of the Cambrian Explosion, one of the most critical events in Earth history, has been a major topic of discussion. The trend of increasing morphological complexity and taxonomic diversity of trace fossils within this interval has been used as evidence of the true evolutionary nature of the Cambrian Explosion. However, the distribution of trace fossils is controlled by a complex interplay between evolutionary and ecological constraints. The pre-trilobite Soltanieh Formation of northern Iran displays a significant vertical facies recurrence, allowing comparison of identical environments through time; therefore, its study provides a test case for evaluating the role of evolutionary and ecological controls on lower Cambrian trace-fossil distribution. An integrated study of sedimentary facies, small shelly fossil zones, sequence stratigraphy, and distribution of associated trace fossils indicates a complex interplay of these two sets of factors. The distribution and preservation of diagnostic early Cambrian trace fossils in the Lower Shale Member of the Soltanieh Formation is very likely to have been controlled by facies, especially within storm-generated siltstone-shale intercalations providing better preservation potential for interfacial trace fossils, therefore delaying the stratigraphic occurrence of Treptichnus pedum. In contrast, evolutionary innovations exerted the primary control on trace-fossil distribution in the Upper Shale Member, where the vertical distribution of trace fossils strongly matches that observed worldwide. This result suggests that, although trace fossils provide a valid means of global correlation, placing trace fossil assemblages within a paleoenvironmental and sequence-stratigraphic framework is a prerequisite of any sound evaluation of the evolutionary and biostratigraphic implications of trace fossils.

A deep root for the Cambrian explosion: Implications of new bio- and chemostratigraphy from the Siberian Platform

Much uncertainty remains as to the temporal relationship between the Ediacaran and Cambrian biotas, yet this is critical to our understanding of the rise of metazoans. Here we present new high-resolution carbon isotope chemostratigraphy and biostratigraphy for a terminal Ediacaran to Cambrian succession on the eastern Siberian Platform, Russia, which shows the presence of a succession of diverse fossil assemblages before the start of the basal Cambrian negative carbon isotope excursion (BACE). Soft-bodied Ediacaran biota ( Beltanelliformis ) occur before the start of the late Ediacaran positive carbon isotope plateau (EPIP), a mixed Ediacaran and Cambrian skeletal biota ( Cloudina , Anabarites , Cambrotubulus ) appears within the EPIP, and diverse Cambrian-type small shelly fossils including Protohertzina and other protocondonts, halkieriids, chancelloriids, hyoliths, hyolithelminthes, and the burrowing trace fossil Diplocraterion appear at the beginning of the BACE. These integrated data show that taxa attributed to so-called Ediacaran and earliest Cambrian skeletal biotas in fact overlap without notable biotic turnover, and thus refute the presence of a large isotope excursion coincident with mass extinction of all Ediacaran biota. We propose a new biozone, the Cloudina - Namacalathus - Sinotubulites Assemblage Zone, to precede the known small shelly fossil (SSF) zones. These observations raise doubts as to whether there is any true separation between the Ediacaran and Cambrian skeletal biotas, and suggest that there is a deep root for the Cambrian explosion of metazoans.

Seawater storage and element transfer associated with mantle serpentinization in magma-poor rifted margins: A quantitative approach

Continental breakup in magma-poor rifted margins can develop, in some instances, after the formation of a wide exhumed domain that can be several hundreds of km wide. As exhumation of the continental mantle occurs serpentinization, due to seawater circulation, can extend as far down as 5–6 km, as observed in refraction seismic data. The impact caused by the process of serpentinization within the evolving ocean may have the potential to change: (i) seawater chemistry; (ii) sustain the evolution of primitive life; (iii) control depositional environments; and (iv) form weak zones preferentially used during the formation, reactivation and subduction of distal rifted margins. Based on geological observations, and geophysical and geochemical data from present-day and fossil zones of exhumed continental mantle, we present a first-order quantification showing that approximately 0.380 km3 of water per km2 can be stored in the mantle. Using simple methods, it can be shown that serpentinization may account for a significant loss of Si, Mg, Fe, Mn, Ca, Ni and Cr during serpentinization of mantle rocks. In particular during latest stages of rifting, when basins are often restricted and seaways are not yet connected, exhumation and the serpentinization of large areas of continental mantle may result in a major transfer of elements between the main Earth reservoirs, such as the mantle and seawater.

Lithostratigraphy of Masol paleonto-archeological localities in the Quranwala zone, 2.6 Ma, Northwestern India

Since 2008, the ‘Siwaliks’ Indo-French Program of Research has surveyed the north of the Chandigarh anticline (Siwalik Frontal Range [SFR], northwestern India) in the Masol inlier known for its Plio-Pleistocene transitional fauna (2.6Ma). Twelve paleonto-archeological localities have been identified in the Quranwala fossiliferous zone, where many fossils and stone tools are lying on the outcrops or included in the erosional debris of the same layers. Cut-marks on a few fossil bones attest to the presence of hominins. This paper presents the detailed lithostratigraphy of these paleontological and archeological localities and their position in the stratigraphic log of the Quranwala zone reconstructed for the Masol anticline.

Magnetic polarity of Masol 1 Locality deposits, Siwalik Frontal Range, northwestern India

The Mio-Pleistocene Siwalik formations have been known worldwide since the 19th century for their fossil hominoids. Numerous paleomagnetic studies have contributed to build the chronological framework of the Siwalik Group subdivided into Lower, Middle and Upper Siwalik Subgroups. Our study concerns the Tatrot Formation (Late Pliocene) of the Upper Siwalik Subgroup located at Masol in the Chandigarh Siwalik Frontal Range (India), and is accessible by the Patiali Rao River. At Masol (district Mohali, Punjab), the erosion of the anticline structure has formed an inlier and exposed paleontological assemblages characterizing the Late Pliocene “Quranwala fossiliferous zone”. Since 2008, the Indo-French research program, “Siwaliks”, has conducted surveys in the Masol inlier and has collected stone tools on the surface of the outcrops among fossilized bones, a few with cut marks. The first cut-marked bone was discovered in 2009 at Masol 1 (M1). The study of the magnetic polarities of some stratigraphic units of M1 revealed that the deposits recorded a normal polarity. According to the paleontology and the previous magnetostratigraphy of the Patiali Rao, it appeared that the deposits of Masol 1 are older than the Gauss-Matuyama reversal, dated to 2.58 Ma.

Barremian-Aptian-Albian carbon isotope segments as chronostratigraphic signals: Numerical age calibration and durations

Chemostratigraphic signals are becoming common tools in chronostratigraphic correlations. Specifically total organic and carbonate carbon percentages (TOCorg/carb) and carbon isotope curves are diagnostic in Cretaceous Aptian-Albian-Cenomanian strata. Cretaceous carbon isotope signals define oceanic anoxic events (OAEs) and have been subdivided into successive segments. These segments are used as correlation markers because they represent oceanographic and depositional conditions, and hence, incur time significance. Although the segments have been integrated with biovents in key sections, numerical ages of the segments have yet to be calibrated. Because direct correlation of these segments of carbon isotope curves with interbedded radiometrically dated beds is not possible currently, other methods must be applied to interpolate numerical ages. Graphic plots of five sections successfully integrate carbon isotope segments with established numerically dated chronostratigraphicmarkers. Carbon isotope segments were first defined in European Tethys Cismon and Rotter Sattel Barremian-Albian sections. The Aptian segments were subsequently identified in the Mexican Santa Rosa Canyon sectionwhere the lower Albian segments were defined. Each section haswell documented microfossils andmagnetochrons that relate the segments to biozones. These bioevents and chronozones enable the carbon segments to be integrated with a comprehensive Cretaceous time scale, the CRECSDB42. Ages assigned to the segments enable them to be used in sections where local fossil zones are recorded such as in the Chihuahua basin in northernMexico. The age calibration of carbon isotope segments measures the durations of the oceanic isotopic excursions. The durations fluctuate up to and after OAE 1a at irregular frequencies different from climatic cycles. Changing durations of carbon isotope segments may be clues to changes in processes or the effects of the process that altered the ocean carbon reservoir in addition to climatic changes.

Late Cretaceous palynology and paleoclimate change: Evidence from the SK1 (South) core, Songliao Basin, NE China

Cretaceous climate was warmer than today. The Songliao Basin contains one of the most important Late Cretaceous non-marine deposits in China for the research of the paleoenvironment and paleoclimate. This research is based on core samples from the SK1(S) borehole. The strata sampled are the upper part of the Quantou Formation to member 2 of the Nenjiang Formation, where spores, pollen, dinoflagellates, and other microfossils are abundantly preserved. Based on analysis of the spores and pollen fossils from the core samples, the following six fossil assemblage zones have been recognized in ascending order: The Cicatricosisporites-Cyathidites-Pinuspollenites, Schizaeoisporites-Cyathidites-Classopollis, Cyathidites-Schizaeoisporites, Schizaeoisporites-Cyathidites-Proteacidites, Proteacidites-Cyathidites-Dictyotriletes, and the Lythraites-Callistipollenites-Schizaeoisporites zones. The six fossil zones range from the late Cenomanian to early Campanian. The Late Cretaceous dinoflagellate cysts in the Songliao Basin are of high abundance and low diversity. Specific phytoplankton types reflect salinity changes of the Songliao Lake. Paleoecology of the dinoflagellates suggests that sediments of members 2 and 3 of the Yaojia Formation (K2 y 2+3) were deposited in a freshwater environment, whereas members 2 and 3 of the Qingshankou Formation (K2 q 2+3) and members 1 and 2 of the Nenjiang Formation (K2 n 1+2) were deposited in freshwater to brackish water environments. Combined with the paleoecology of dinoflagellates and the palynomorph biozones, valuable information of the paleoclimate was provided. The quantitative analyses of spores and pollen fossils, such as vegetation type, climate type, and humidity type, diversity and dominance, indicate a relatively sub-humid, mid-subtropical paleoclimate, with slight climatic fluctuation and/or temporal change.

AGN proximity zone fossils and the delayed recombination of metal lines

We model the time-dependent evolution of metal-enriched intergalactic and circumgalactic gas exposed to the fluctuating radiation field from an active galactic nucleus (AGN). We consider diffuse gas densities (n_H=10^-5-10^-3 cm^-3) exposed to the extra-galactic background (EGB) and initially in thermal equilibrium (T \sim 10^4-10^4.5 K). Once the proximate AGN field turns on, additional photo-ionisation rapidly ionises the HI and metals. The enhanced AGN radiation field turns off after a typical AGN lifetime (tau_AGN=1-20 Myr) and the field returns to the EGB intensity, but the metals remain out of ionisation equilibrium for timescales that can significantly exceed tau_AGN. We define this phase as the AGN proximity zone "fossil" phase and show that high ionisation stages (e.g. OVI, NeVIII, MgX) are in general enhanced, while the abundances of low ions are reduced. In contrast, HI re-equilibrates rapidly (<<tau_AGN) owing to its low neutral fraction at diffuse densities. We demonstrate that metal column densities of intervening gas observed in absorption in quasar sight lines are significantly affected by delayed recombination for a wide range of densities, metallicities, and AGN strengths, lifetimes, and duty cycles. We model the exceptionally strong z=0.9 NeVIII absorbers observed by Tripp et al. (2011) as arising in a possible fossil zone or near a recently turned-on AGN and we demonstrate that at low redshift even moderate strength AGN could significantly enhance the high-ion metal columns in the circumgalactic media of galaxies observed without active AGN. Fossil proximity zones may be very important during the quasar era, z \sim 2-5. AGN proximity zone fossils allow a whole new class of non-equilibrium solutions that may be applicable to a large fraction of observed metal absorbers and which could potentially change the inferred physical conditions and masses of diffuse gases.

A Preliminary Note on Depositional Characteristics and Optical Luminescence Age of a Marine Terrace, Strait of Çanakkale, Turkey

ABSTRACT Avcioglu, M.; Erginal, A.E.; Kiyak, N.G.; Kapan-Yesilyurt, S., and Yigitbas. 2013. A preliminary note on depositional characteristics and optical luminescence age of a marine terrace, Strait of Canakkale, Turkey This preliminary study investigated the depositional features and optical luminescence age of marine terrace sediments located on the east coast of the Strait of Canakkale, Turkey. With regard to depositional setting, the studied sequence is formed mostly of shallow marine deposits rich in quartz and oysters as well as other accessory minerals and various fossil sea shells. In vertical section, the sequence is characterized by two different stratigraphic units, i.e. a 1.50-m-thick sandy to gravely bottom unit (unit A) and an overlying 2.5-m-thick fossiliferous zone (unit B). On the basis of optically stimulated luminescence (OSL) age estimations obtained from six sampling levels from bottom to top, we determined superimposed cycles of deposition during interglacials from 246.47 ± 25.32 ka...

Progress, Problems and Prospects on the Stratigraphy and Correlation of the Kungurian Stage, Early Permian (Cisuralian) Series

Abstract:The Kungurian Stage is one of the three remaining stages of the Permian that is not yet defined at the base by a Global Stratotype Section and Point (GSSP). The candidate section at the Yuryuzan' River in the Urals yields few conodonts, and contains non‐marine sediments near the boundary. The search for a suitable, continuous marine succession is a principal task for the Subcommission on Permian Stratigraphy. The Leonardian, with its type area in the southwest United States, and in objective stratigraphic succession directly beneath the basal Guadalupian Roadian Stage, has priority to serve as a subseries of the Lower Permian. However, distinct provincialism limits the correlation of Leonardian fossil zones with the fusuline‐based Tethyan timescale. Conodonts can be correlated in many important regions on opposite sides of Pangea, yet contradictions arise when relating conodont zones with fusuline and ammonoid zones. The different taxonomic philosophies are highly suspected for the cause of the conflicts, but also there are different conodonts from the type Roadian in West Texas. Given that the Pamir and Darvaz in central Asia are difficult to access, further investigations should focus on South China, where abundant fusulines and ammonoids facilitate correlation throughout the Tethyan region, and where conodonts permit correlation with North America.

Discovery of Fossil Charophytes from the Late Triassic Xujiahe Formation and Early Jurassic Lower Yimen Formation, Sichuan Province, and Its Significance

This paper describes the fossil charophytes collected from the Late Triassic Xujiahe Formation in Dazu and Early Jurassic Lower Yimen Formation in Xichang, Sichuan Province, and their significance. Up to now, papers dealing with fossil charophytes of the Late Triassic, especially of the Early Jurassic, have been rarely published. The description of the two new species of Porochara, P. dazuensis and P. xichangensis, and their fossil assemblage not only provides an important basis for classification and correlation of red beds in southwestern China but reveals for the first time the features of the charophyte flora of the Late Triassic-Early Jurassic in the area, thus offering valuable data for the establishment of Triassic and Jurassic charophyte fossil zones in China.

A note on the biostratigraphic application of Permian plant fossils of the Normandien Formation (Beaufort Group, Northeastern Main Karoo Basin), South Africa

Two new assemblages (farms Christina and Moorfield) of plant fossils belonging to the Glossopterid flora are described from the northeastern part of the Main Karoo basin, within the Late Permian Normandien Formation, Beaufort Group, Karoo Supergroup. The Normandien Formation comprises three sandstone members (lower Frankfort, Rooinek, upper Schoondraai) each overlain by an argillaceous interval. Two informal plant fossil assemblage zones are distinguished in the field: a “Christina assemblage zone” defined by Morphotype Pnc1, Morphotype Pnc2, Morphotype Pnc3 and Morphotype Pnc7, between the Frankfort and Rooinek sandstones; a younger “Moorfield assemblage zone” between the Rooinek and Schoondraai sandstones, defined by Morphotype Pnm1 , Morphotype Pnm2, Morphotype Pnm3, Rigbya arberioides and Sphenophyllum speciosum. These two proposed plant fossil assemblage zones enable subdivision of the Dicynodon therapod assemblage zone coincident with the Normandien Formation, and the two plant fossil zones have been successfully mapped out over a large area.

Reconstruction of environmental and climatic changes in the Paleo-Kathmandu Lake during the last 700 ka: An approach from fossil-diatom study

Terrestrial paleoclimatic and paleoenvironmental records on the Indian monsoon are extremely limited, though many investigations have been done on the deep-sea sediments in the Indian Ocean during the last few decades. In order to clarify the terrestrial monsoonal climatic records during the Quaternary, we undertook core-drilling of the basin-fill sediments of the Kathmandu Valley, which is located under Indian monsoon zone. In this paper, we attempt to reconstruct the environmental changes of the Pakeo-Kathmandu Lake, on the basis of studies on the fossil-diatom collected from a 218-m-long core drilled at Rabibhawan, western central part of Kathmandu. Except the uppermost thin cover of fluvial sediments (Patan Formation), the core is continuous and mainly composed of muddy lacustrine sediments (Kalimati Formation) containing abundant fossil-diatoms, which document ecological responses to climatic and environmental changes (Sakai 2001, Hayashi et al. 2002). Mud samples were collected at 50 cm interval from 7 to 45.5 m in depth and at 2 m interval from 47.5 to 218 m in depth. We identified each species and counted the number of valves by means of a scanning electron microscope (JSM-5600) at x5,000 magnification, because dominant species in the RBcore are very small, ranging from 5 to 30 μm. For each sample, at least 300 diatom valves were counted. On the basis of relative abundance and the number of principal diatoms, eight fossil zones and three subzones in zone 2 were defined in the Kalimati Formation (Figure 1). Zone 8 at the basal part is characterized by variety of diatom assemblages and relatively low number of diatom valves, which reflect marsh or very shallow-water environments. Based on water-level indicators (ratio of planktonic diatoms to benthic diatoms and frequency of genus Aulacoseira), the water-level seems to have deepened gradually from zone 8 to zone 7, and retained deep condition from zone 6 to zone 4. Zones 6 to 4 are characterized by monodominance of Cyclotella: Cyclotella sp.1 is a characteristic in zone 5, and Cyclotella sp.2 is in zone 6 and zone 4. Number of their valves is very abundant. On the other hand, in zone 3 and zone 2, there are several dominant species and number of total diatom valves decreases. Furthermore, ratio of planktonic diatoms to benthic diatoms periodically rises and falls, which probably indicates water-level fluctuations. Especially in zone 2A, fluvial and marsh environments were expanded in marginal area of the lake, because relative abundance and number of Staurosira construens and Pseudostaurosira brevistriata, indicative species for marsh environment, become high. In zone 1, ratio of planktonic diatoms increases, which indicates the water-level rose again. But after zone 1, number of total diatom valves drastically reduces. It demonstrates that the lake was drained during a short period at about 12 ka. Comparison of environmental changes of the PaleoKathmandu Lake with δO record from a core MD900963 collected in the Indian Ocean (Bassinot et al. 1994) for the past 630 ka, shows that the water-level of the Paleo-Kathmandu Lake seems to have fallen at glacial age (MIS 14, 10, 8, 6, 2). We recognized following five major events expressed by high ratio of benthic diatoms, which indicate lowering of water-level. According to the time-scale derived from paleomagnetic study and AMS 14C dating of the core, the following stages correspond to marine isotope stages (MIS) from MIS 14 to MIS 2. Zone 5 ~ zone 4 = MIS 14 Early stage of zone 3 = MIS 10 Later stage of zone 3 = MIS 8 Later stage of zone 2C = MIS 6 Later stage of zone 2A = MIS 2 It is likely that these environmental changes of the PaleoKathmandu Lake mainly caused by fluctuations of Indian monsoon related to global climatic changes (glacial-interglacial cycle).