Exact Stratigraphic Position Research Articles

First record of trace fossils in the Ediacaran–Cambrian transition on the northern Gondwana platform (Anti-Atlas, Morocco)

The Anti-Atlas Mountains of Morocco preserve one of the most complete latest Neoproterozoic to Cambrian stratigraphic successions worldwide, with high-resolution chemostratigraphic δ13Ccarb coverage. However, the exact stratigraphic position of the Ediacaran–Cambrian boundary remains unresolved. Until now, no trace fossils or body fossils have been recorded from the terminal Ediacaran strata in the Anti-Atlas Mountains. The only exception is a discoidal body fossil-like structure from the shallow-marine sandstones of the Ediacaran Tabia Member, Adoudou Formation, in the Taroudant Group in the Igherm inlier. For the first time, we document the occurrence of abundant trace fossils from the base of the Adoudou Formation, including Treptichnids, Monomorphichnus isp., Helminthoidichnites isp., Gordia isp., Palaeophycus isp., Planolites isp., and Conichnus isp. The integration of both trace fossils and carbon isotope δ13Ccarb records suggests that the Ediacaran–Cambrian transition in the Sous Basin can be placed at the contact between the Tifnout and Tabia Members, which chemostratigraphically coincides with the large negative δ13Ccarb excursion that had been previously suggested for the Ediacaran–Cambrian boundary (BACE) in the western Anti-Atlas Mountains.

Nearctic Pleistocene ungulates from the Pampean region (Argentina) in the historical collections of Santiago Roth in Switzerland: an overview

Nearctic ungulates such as artiodactyls, perissodactyls, and proboscideans arrived in South America during the Great American Biotic Interchange. Among them are camelids, cervids, tayassuids, equids, tapirids and gomphotherids. A historical collection of Nearctic ungulates from Pleistocene deposits of the Pampean region in Argentina is here studied and described. The collection consists of specimens collected by Santiago Roth in the nineteenth century and brought to Europe, where they are housed in the paleontological collections of the University of Zurich and the Natural History Museum of Geneva. Among the taxa reported here are Notiomastodon platensis,Lama guanicoe, Hemiauchenia paradoxa, Tayassu pecari, Morenelaphus sp., Hippidion cf. H. principale, Equus cf. E. neogeus, and other indeterminate gomphotherids, camelids, tayassuids, cervids, and equids. The exact stratigraphic position of these fossils collected more than 130 years ago is in many cases uncertain. The historical collection is still relevant for taxonomic studies and for offering new insights into palaeobiogeography and palaeobiology of mammalian fauna of the region during the Pleistocene.

A high-precision U–Pb zircon age constraints the timing of the faunistic and palynofloristic events of the Carnian Ischigualasto Formation, San Juan, Argentina

The Late Triassic represents records many of the most critical biotic crises in life-history (from Carnian to the end-Triassic extinction, ETE). Some hypotheses propose that these life changes were linked with shifts in the environmental setting during the initial stages of the Pangea breakup. These crises were likely not sudden events but a series of step-changes that reached their peak at the end of the Triassic. The Carnian-Norian Ischigualasto Formation is a world-renown terrestrial sequence that records both the Triassic Dinosaur Diversification Event (DDE) and at least one crucial terrestrial environmental and biotic turnover. A notable increase in humidity and volcanism was the setting of critical faunal replacement represented by the passage of the Hyperodapedon-Exaeretodon-Herrerasaurus to Exaeretodon tetrapod biozones. That environmental modification, together with the paleofaunistic turnover, has been accurately constrained by a new high-precision CA-TIMS U/Pb zircon age of 228.91 ± 0.14 Ma obtained from a tuff layer located in the exact stratigraphic position of the major biotic-paleoenvironmental disturbance in the middle part of the Valle de la Luna Member, at ~310 m from the base of the Ischigualasto Formation. Palynological assemblages containing the first records in westernmost Gondwana of European Tethyan and Onslow palynological species are also recognized close to the dated tuff level. Thus, this age is the first isotopic record for the Onslow Microflora diagnostic species in Gondwana. Moreover, the CA-TIMS date promotes a discussion about the accurate chronostratigraphic position for the beginning (after the Carnian Pluvial Event) of a series of environmental-biological disturbances that culminated at the end of the Triassic.

Late Middle Pleistocene interglacial sediments from Buivydžiai site, eastern Lithuania: A problem of chronostratigraphic correlation

A number of interglacial sections discovered in the eastern part of Lithuania and suggested as Snaigupėlė Interglacial were attributed to the Saalian Complex Stage of Middle Pleistocene. However, the exact stratigraphical position and correlation of these interglacial sections are still arguable. Recent investigations were performed to get a clearer insight into the stratigraphy and sedimentation palaeoenvironment of the Snaigupėlė Interglacial sediments outcropping in Buivydžiai section and included complex proxies: pollen, plant macrofossils, diatoms, loss on ignition, magnetic susceptibility and optically stimulated luminescence dating. Interglacial sediments occur at the lowermost part of the exposure and reach more than 7 m thick. Palaeobotanical investigations confirm deposition of studied sediments during the different climatic stages of the interglacial. An attempt at correlation between the Buivydžiai section vegetational changes with vegetational succession obtained from north-central Europe allowed finding out some similarities with the Schöningen/Lublinian Interglacial. The OSL dating results do not contradict such a proposition as the two sand samples lying below the interglacial gyttja show sedimentation of this layer during the 300.5 ± 20.9 ka and 317.3 ± 21.8 ka time or MIS 9. However, recently obtained data are insufficient for grounding the correlation of studied section. Certainly, additional chronostratigraphic investigations would be valuable and may contribute to the solution of the sediment age and correlation problem.

Tracing multiple resedimentation on an isolated karstified plateau: The bauxite-bearing Miocene red clay of the Southern Bakony Mountains, Hungary

The Vöröstó (=Red Lake) Formation, located in the Southern Bakony Mountains and the Balaton Highlands (Hungary), is a red, clayey continental assemblage containing hard, up to fist-sized bauxite pebbles, occurring in a large apparent stratigraphic gap between underlying karstified Triassic carbonates and mid’ Miocene to Quaternary cover. The origin and the exact stratigraphic position of the assemblage have been controversial for a long time. In this study, petrographic observations on the bauxite pebbles revealed common features with Cretaceous bauxite deposits known in the region, whereas heavy mineral composition of the red clay matrix is similar to those known from the Eocene bauxite horizon of the region. Single grain zircon U–Pb ages obtained from the bauxite pebbles and their red clayey matrix show similar late Archean to Jurassic age components. Additionally, Cenozoic U–Pb ages are well represented in the mostly euhedral zircon crystals separated from the red clays, whereas this volcanogenic contribution completely missing from the bauxite pebbles. SEM morphology and related EDX chemical analysis of clay minerals indicate polygenetic, detrital origin for the red clays. The main source material of the bauxite bearing Vöröstó Formation is most probably local Cretaceous and Eocene bauxite deposits exposed during the middle-late Miocene. These tropical weathering products were partly decomposed and degraded, but dilution by siliciclastic contribution is negligible. We suggest a transport mechanism dominated by local redeposition of mostly pelitic and allitic material through seasonal muddy debris flows within a karstic landscape.

Magnetic stratigraphy constraints on the Matuyama–Brunhes boundary recorded in a loess section at the southern margin of Chinese Loess Plateau

Although the Matuyama-Brunhes boundary (MBB) in the Chinese Loess Plateau (CLP) is very important in reliably correlating Quaternary loess with other sediments in the world, particularly with marine and polar ice cores, its exact stratigraphic position remains controversial. Previous investigations usually placed the MBB between paleosol unit S8 and loess unit L8 in various locations. To better understand the spatial differences in the MBB position, a high-resolution paleomagnetic study was conducted in a loess section of the Lantian Basin at the southern margin of the CLP. The results show that the MBB is situated in the middle of the relatively weak paleosol unit S7, consistent with a recent report on the MBB based on a Be-10 study from the Xifeng and Luochuan loess sections of the central CLP. However, the regional anomalously low magnetic susceptibility in paleosols S7 and S8 indicates that it is more reliable to determine the paleoclimate boundaries between loess and paleosol horizons of this segment with median grain size. Then, the MBB in the Yushan section can be correlated with the bottom of paleosol S7, corresponding to the older part of interglacial marine isotope stage 19. This result temporally reconciles the striking discrepancy of the position of the MBB recorded in between loess and other typical sedimentary sequences, and further confirms that the stratigraphic position of the MBB could spatially vary to a certain extent due to regional sedimentary or paleoclimatic conditions in the marginal areas of the CLP. In the Yushan section, the high-frequency variations of paleomagnetic directions during a long period of similar to 31 ka before the MBB, however, could not be attributed to a genuine response to the true geomagnetic behaviour. Moreover, the climate offset defined by the magnetic susceptibility and median grain size of the section can be preliminarily attributed to the regional geology and paleoenvironment background. A multiproxy-based stratigraphic division is considered very necessary when paleomagnetic and climatic boundaries are defined exactly in a specific area of the southern CLP.

Chronological studies of Shuidonggou (SDG) Locality 1 and their significance for archaeology

Shuidonggou Locality 1 (SDG 1), discovered in 1923, is one of the most important Upper Paleolithic sites in China, and excavations since its discovery have produced abundant cultural remains and other materials. However, only limited ranges of dating methods have been applied to the site. This study discusses the results of dating samples by optically stimulated luminescence (OSL) from two sections at SDG 1. Medium grained (45–63 μm) quartz was extracted and used for age determination by the single aliquot regeneration (SAR) protocol. The OSL ages of five samples from the cultural layer in the section excavated in 1963 were between 32 ± 3 ka and 39 ± 4 ka, and four samples from the cultural layer excavated in 1980 were dated from 42 ± 3 ka to 46 ± 3 ka. The OSL data were consistent with newly acquired AMS 14C dates. The dating results show that ages varied from ca. 22 ka to 46 ka for the cultural layer at SDG 1. The onset of Levalloisian blade technology in China is dated to ca. 43 ka at SDG 1, perhaps reflecting a fast dispersal of modern humans, and earlier than previously thought. Systematic excavation at SDG 1 is needed to establish the exact stratigraphic position of Paleolithic assemblages in order to discuss their relationships with initial Upper Paleolithic industries in Eurasia.

Discussion on ‘A high-precision U–Pb age constraint on the Rhynie Chert Konservat-Lagerstätte: time scale and other implications’

We welcome the contribution of Parry et al . (2011) concerning the age of the globally important Rhynie hot-spring system, Aberdeenshire, Scotland. However, although we accept that they have provided a valuable and robust U–Pb age constraint for the Milton of Noth Andesite and the Rhynie outlier stratigraphic succession, we do not accept that they have constrained the timing of hot-spring activity, as suggested. The geophysical trace of the unexposed Milton of Noth Andesite indicates that it lies immediately adjacent to the Rhynie Fault Zone and runs parallel to it for some 2 km. It may even lie within the Rhynie Fault Zone (see discussion by Rice & Ashcroft 2004). Its stratigraphic position is therefore uncertain. Parry et al . (2011) stated that the exact stratigraphic position is not important because their preferred stratigraphic locations lie within the Tillybrachty Sandstone and Dryden Flags Formations, both of which have consistently yielded spores belonging to the polygonalis–emsiensis Spore Assemblage Biozone. This assertion is not valid. The polygonalis–emsiensis Spore Assemblage Biozone may have lasted several million years and thus, potentially, there could be a significant hiatus between eruption of the andesite and the onset of hot-spring activity. They further assume that the andesite was linked to an andesitic magma chamber at depth, which powered the hydrothermal system. This remains speculation. Accepting the uncertainty in the stratigraphic position and by asserting a maximum thickness of sediment between the andesite and the Rhynie Cherts and a conservative deposition rate, Parry et al . (2011) attempted to temporally link the andesite to the cherts by calculating the time interval represented by the intervening sediment. The estimation of time depends on the absence of unconformities, disconformities and faulting, with such assumptions and uncertainties casting doubt on the thickness of the intervening sediments …

Chitinozoan biostratigraphy of the Upper Ordovician D. clingani and P. linearis graptolite biozones on the Island of Bornholm, Denmark

The last decade saw a revival of the debate on the exact stratigraphical position of the Upper Ordovician P. linearis graptolite biozone. Chitinozoan biostratigraphy can be useful to help address this question. Here, we provide a high-resolution chitinozoan biostratigraphy through the Dicellograptus Shale Formation at Vasagård on the Island of Bornholm (Denmark), which recently also was subject to a thorough revision of its graptolite fauna, representing the Dicellograptus folicaceus, Dicranograptus clingani and Pleurograptus linearis biozones. We have identified close to 9000 individual chitinozoan vesicles from 26 samples through the upper c. 9m of the Dicellograptus Shale Formation. The Spinachitina cervicornis, Fungochitina spinifera and Tanuchitina bergstroemi chitinozoan biozones are identified, and their boundaries carefully calibrated against the revised graptolite biostratigraphy. A correlation with the chitinozoan biozonation in the British Cautley district, which has a predominantly Baltoscandian, mid-latitude signature and is well-correlated with the graptolite and shelly fauna biozones described from the historical type region, is established.

Revisiting the stratigraphic position of the Matuyama–Brunhes geomagnetic polarity boundary in Chinese loess

It is commonly accepted that the climate records in Chinese loess can be correlated well with that in marine sediments. However, discrepancies for the stratigraphic position of paleomagnetic polarity reversal boundary seriously restrict an accurate teleconnection between these two archives. For example, the exact stratigraphic position of the whole Matuyama–Brunhes (MB) transitional polarity zone remains uncertain in Chinese loess. In this study, an accurate transitional zone of the MB reversal from the Mangshan profile, southeast margin of the Chinese Loess Plateau (CLP), was statistically determined using multiple subsets of parallel samples. By integrating results from the central CLP, the whole MB transitional zone is consistently located across the pedostratigraphic and climatostratigraphic transitional zones between S8 and L8 over a wide region of the CLP. This conclusion further supports that the paleosol unit S8 should be teleconnected to the marine oxygen isotope stage 19 rather than 21, and thus unambiguously supplies an accurate age control in constructing a new loess time scale.

Latest on the absolute age of the Paleocene–Eocene Thermal Maximum (PETM): New insights from exact stratigraphic position of key ash layers + 19 and − 17

We constructed a precise early Eocene orbital cyclostratigraphy for DSDP Site 550 (Leg 80, Goban Spur, North Atlantic) utilizing precession related cycles as represented in a high-resolution X-ray fluorescence based barium core log. Based on counting of those cycles, we constrain the exact timing of two volcanic ash layers in Site 550 which correlate to ashes + 19 and − 17 of the Fur Formation in Denmark. The ashes, relative to the onset of the Paleocene–Eocene Thermal Maximum (PETM), are offset by 862 kyr and 672 kyr, respectively. When combined with published absolute ages for ash − 17, the absolute age for the onset of the PETM is consistent with astronomically calibrated ages. Using the current absolute age of 28.02 Ma for the Fish Canyon Tuff (FCT) standard for calibrating the absolute age of ash − 17 is consistent with tuning option 2 in the astronomically calibrated Paleocene time scale of Westerhold et al. (2008) [Westerhold, T., Röhl, U., Raffi, I., Fornaciari, E., Monechi, S., Reale, V., Bowles, J., and Evans, H.F., 2008, Astronomical calibration of the Paleocene time: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 257, p. 377–403]. Using the recently recalibrated absolute age of 28.201 Ma for the FCT standard is consistent with tuning option 3 in the astronomically calibrated Paleocene time scale. The new results do not support the existence of any additional 405-kyr cycle in the early Paleocene astronomically tuned time scale.

U–Pb geochronology and Hf isotope ratios of magmatic zircons from the Iberian Pyrite Belt

A geochronology and Hf isotope study, using laser ablation-ICP-MS analysis of zircon grains, has been conducted to date felsic volcanic rocks from the Portuguese sector of the Iberian Pyrite Belt and to establish possible sources for these rocks. The ages obtained range from the Famennian to the Tournaisian, with the oldest ages reported in the Belt so far being identified in its southwestern part (Cercal area). Results also indicate that within each area, volcanism may have extended for significant periods of time. This suggests that caution is needed in interpreting possible migration trends for the volcanism, as the exact stratigraphic position of the sampled rocks is not always clear. Despite of this, the new data, coupled with previously reported information, suggests that volcanism migrated within the basin from the southwest to the northeast (present day coordinates). Projection from initial zircon ɛHf values towards the depleted mantle evolution curve, via an intermediate reservoir, allows the calculation of Hf protolith model ages that are predominantly Meso-Proterozoic. This is compatible with acid magmas resulting from the fusion of Phyllite–Quartzite (PQ) Formation metasedimentary rocks, which are beneath the volcanic rocks. This is because zircon grains from one PQ Formation sample provided Late Neo-Proterozoic ages and Paleo-Proterozoic to Late Archean U–Pb ages, and the Hf isotope signatures of these zircons can be expected to mix during fusion and result in protolith model ages that would be intermediate between the two U–Pb age populations, as recorded. Further supporting this source for the magmas, the distribution of U–Pb ages of (pre-Variscan) inherited zircon grains in the volcanic rocks is very similar to that shown by the detrital zircon grains from a PQ sample.

Vertebrate track bed stratigraphy of the Röt and basal Lower Muschelkalk (Anisian) of Winterswijk (East Netherlands)

AbstractThe 35.5 m thick Anisian section of theWinterswijkse Steen- en Kalkgroeve (Eastern Netherlands) comprises the Upper Röt (Upper Röt Claystone Member) to the basal Lower Muschelkalk (Oolith Member). In the section 15 terrestrial or marine influenced parasequences are recognized. A fourth order sequence shows the increasing marine influence. New marker beds, ten vertebrate track beds, three bone beds and cephalopod remains have been documented. This enabled correlation to other sections in NW Germany. The tracks found in the Winterswijkse Steen- en Kalkgroeve at the boundary Röt/Lower Muschelkalk are linked to the oldest known vertebrate skeleton remains of the Germanic Basin. It is the first time that the exact stratigraphic position of these vertebrate remains has been established. In the terrestrial influenced section of the Winterswijkse Steen- en Kalkgroeve, the well preserved vertebrate track ways and vertebrate fauna will be of international importance and will provide new data of theTriassic carbonate tidal flat megatracksite concept and reptiles living in this environment.

US Gulf Coast vegetation dynamics during the latest Palaeocene

Pollen and spore floras from the Bear Creek section in western Alabama (US Gulf Coast) record vegetation events from the lower to middle Tuscahoma Formation (late Palaeocene mid NP9). Sporomorphs are abundant and well preserved in these sediments and are used as a proxy to record vegetation change over time. We present results from both palynofloral and clay mineral analyses in the interval approximately 0.4–0.1 my before the Paleocene/Eocene thermal maximum (PETM); a period of transient and intense global warming that had a profound effect on animal and plant groups in high latitudes. An important factor that has a significant bearing on our understanding of turnover across the PETM is that of climate/environmental stability prior to the PETM in terrestrial ecosystems. Palynological analysis with a between sample resolution of <10 ky suggests that the vegetation type characterising the US Gulf Coastal plains was highly stable with no significant changes in composition and diversity that can be successfully correlated with orbital oscillations. Our results indicate considerable stability of the vegetation type on time-scales of 10 4–10 5 yr. Clay mineral suites show the dominance of smectite and illite throughout the studied section with minor fluctuations in the abundance of kaolinite (ranging from 2 to 10%) that indicates a high seasonality of precipitation throughout our studied section. The exact stratigraphic position of the PETM is unknown on the US Gulf Coast but data from existing publications suggests there is little change in the vegetation type across the Palaeocene/Eocene boundary with no major immigration or turnover events. Dinocysts are restricted in both diversity and occurrence but Apectodinium homomorphum is present with ∼30% abundance throughout the studied section and provides some evidence that the Apectodinium acme is not correlative with the PETM at middle latitudes.

The Matuyama/Brunhes geomagnetic polarity transition at Lingtai and Baoji, Chinese Loess Plateau

Two sections on the Chinese Loess Plateau (CLP) at Lingtai and Baoji have been investigated to obtain detailed information about the exact stratigraphic position and the recording quality of the Matuyama/Brunhes geomagnetic polarity boundary (MBB). The continuously sampled MBB occurs in the glacial period loess layer L8 in both sections at a similar profile depth indicating comparable average sedimentation rates of about 8 cm/kyr. This stratigraphic position has been recognized in many previous Chinese loess studies and contrasts with observations in marine sediments where this polarity transition is found at the beginning of interglacial oxygen isotope stage 19. The directional patterns of the characteristic remanent magnetization (ChRM) of the two transitional loess records are inconsistent and even depend on the demagnetization technique used to isolate the ChRM. The MBB records also differ significantly from those obtained from the loess section at Weinan and at ODP site 792A near Japan. The VGP paths recorded in loess are not well defined, switch polarity several times and do not prefer specific longitudinal bands. It is suggested that the loess MBB transitional records do not reflect geomagnetic field variations directly, but are the result of a complicated magnetization lock-in mechanism. By comparison with the astronomically-tuned prediction, this process has been delayed in the loess sediment column by 1.5 to 2 m corresponding to about 25'000 yr after deposition.

A new arthropod Pygmaclypeatus daziensis from the Early Cambrian Chengjiang Lagerstätte, South China

The early Cambrian Chengjiang Lagerstatte, generally regarded as late Atdabanian (Qian and Bengtson, 1989; Bengtson et al., 1990), has become celebrated for perhaps the earliest biota of soft-bodied organisms known from the fossil record and has proven to be critical to our understanding of early metazoan evolution. The Sirius Passet fauna from Peary Land, North Greenland, another important repository of soft-bodied and poorly sclerotized fossils, was also claimed as Early Cambrian (Conway Morris et al., 1987; Budd, 1995). The exact stratigraphic position of the Sirius Passet fauna (Buen Formation) is still uncertain, although the possibility of late Atdabanian age was proposed (Vidal and Peel, 1993). Recent work dates it in the “Nevadella” Biozone (Budd and Peel, 1998). It therefore appears to be simultaneous with or perhaps slightly younger than Chengjiang Lagerstatte, Eoredlichia Biozone (Zhuravlev, 1995). The Emu Bay Shale of Kangaroo Island, South Australia, has long been famous as a source of magnificent specimens of the trilobites Redlichia takooensis and Hsunaspis bilobata. It is additionally important as the only site in Australia so far to yield a Burgess-Shale-type biota (Glaessner, 1979; Nedin, 1992). The Emu Bay Shale was considered late Early Cambrian in age (Daily, 1956; Öpik, 1975). But Zhang et al.(1980) reassessed its age based on data from the Chinese Early Cambrian. The occurrence of Redlichia takooensis and closely related species of Hsunaspis indicates an equivalence to the Tsanglangpuian in the Chinese sequence, and the contemporary South Australia fauna correlate with the Botomian of Siberia (Bengtson et al., 1990). Thus the Emu Bay Shale is younger than the upper Atdabanian Chengjiang Lagerstatte, Chiungchussuian.

A NEW ARTHROPODPYGMACLYPEATUS DAZIENSISFROM THE EARLY CAMBRIAN CHENGJIANG LAGERSTÄTTE, SOUTH CHINA

The early Cambrian Chengjiang Lagerstatte, generally regarded as late Atdabanian (Qian and Bengtson, 1989; Bengtson et al., 1990), has become celebrated for perhaps the earliest biota of soft-bodied organisms known from the fossil record and has proven to be critical to our understanding of early metazoan evolution. The Sirius Passet fauna from Peary Land, North Greenland, another important repository of soft-bodied and poorly sclerotized fossils, was also claimed as Early Cambrian (Conway Morris et al., 1987; Budd, 1995). The exact stratigraphic position of the Sirius Passet fauna (Buen Formation) is still uncertain, although the possibility of late Atdabanian age was proposed (Vidal and Peel, 1993). Recent work dates it in the “Nevadella” Biozone (Budd and Peel, 1998). It therefore appears to be simultaneous with or perhaps slightly younger than Chengjiang Lagerstatte, Eoredlichia Biozone (Zhuravlev, 1995). The Emu Bay Shale of Kangaroo Island, South Australia, has long been famous as a source of magnificent specimens of the trilobites Redlichia takooensis and Hsunaspis bilobata. It is additionally important as the only site in Australia so far to yield a Burgess-Shale-type biota (Glaessner, 1979; Nedin, 1992). The Emu Bay Shale was considered late Early Cambrian in age (Daily, 1956; Öpik, 1975). But Zhang et al.(1980) reassessed its age based on data from the Chinese Early Cambrian. The occurrence of Redlichia takooensis and closely related species of Hsunaspis indicates an equivalence to the Tsanglangpuian in the Chinese sequence, and the contemporary South Australia fauna correlate with the Botomian of Siberia (Bengtson et al., 1990). Thus the Emu Bay Shale is younger than the upper Atdabanian Chengjiang Lagerstatte, Chiungchussuian.

La présence de fossiles marins dans le Crétacé terminal des Andes centrales et ses conséquences paléogéographiques

The Maastrichtian deposits (late Campanian? to early Danian?) of the central Andes comprise three transgressive-regressive sequences. In Bolivia (El Molino Formation) they have yielded diverse terrestrial, brackish-water or marine fossils, which make it possible to define the depositional environments at their exact stratigraphic position. Marine-influenced transgressive facies are by far the best developed in the first sequence. Among the vertebrates, five groups of fishes are restricted, with some rare exceptions, to marine environmentsl. Some other fish families, genera or species, are known to occur both in freshwater, brackish and marine environments and therefore provide no precise environmental indications. Among the invertebrates, echinoids, serpulids, foraminifera and some pelecypods and gastropods attest to a marine-influenced environment, which may however have experienced periodic salinity variations. The other pelecypods and gastropods generally indicate freshwater environments. The ostracods, often ubiquitous, only provide paleoecologic indications when they constitute oligospecific shell beds, suggesting abnormally low salinity values. Calcispheres and dinoflagellates indicate a stronger marine influence. Charophytes, especially when abundant, suggest a lacustrine environment. Because of their stratigraphic and paleogeographic positions, stromatolites may indicate intertidal to supratidal environments. The fossils most likely of marine generally occur in the transgressive lower parts of the three sequences, where marine oolites and glauconite are also observed. The often endemic nature of the marine assemblages, the common occurrence of dwarfism and the lack of true nektonic forms suggest that most part of the basin was permanently rather shallow and subjected to important, frequent and/or local, salinity variations. The freshwater fishes appear to be reworked and dissociated in the marine levels, but are better preserved in the mainly continental upper parts of the sequences. Marine fossils are rare in the upper sequence. These data contradict with interpretations which suggest that the central Andean Senonian deposits are exclusively terrestrial. Given other paleogeographic constraints, we propose that Maastrichtian sedimentation took place in a wide, elongated, subsident basin, forming the eastern foreland of the paleo-Andes and showing a “cul-de-sac” shape in the south. This restricted basin was periodically connected with the open sea through present-day Venezuela. The salinity of its southern part, situated far from the basin mouth, was shallow and affected by fresh water from inflowing rivers.

A human mandibular fragment from the Atapuerca Trench (Burgos, Spain)

A study is presented here of a human fossil found in the Atapuerca Trench (Sierra de Atapuerca, Burgos, Spain). It is a small mandibular fragment with the M 2 and M 3 in situ. It was found in 1976 close to the TG-TN complex and, unfortunately, its exact stratigraphical position is unknown. The morphology and dimensions of this human fossil are compared with the range of variation observed in the hominids from the SH site, also located in the Sierra de Atapuerca. A groove on the mesial root wall of M 2 is attributed to wear during life.

A late neolithic foundation offering from Thessaly

The excavation at Platia Magoula Zarkou, a prehistoric settlement in Thessaly, 30 km west of Larisa, was undertaken to clarify the problem of the exact chronological and stratigraphic position of the black burnished pottery, characteristic of the Larisa culture, which has hitherto been accepted as dating to the end of the Late Neolithic. The author became involved with this problem when he found black pottery together with grey pottery of the Tsangli phase, of the beginning of the Late Neolithic, at the neolithic cremation cemetery of Platia Magoula Zarkou (Gallis, 1982, 109-11 ; English summary, 234). The problem of the exact stratigraphic position of this black ware has now been solved. The dating of the Larisa culture to the beginning of the Late Neolithic (to the Tsangli phase) has now been confirmed by this excavation, as well as another similar excavation at the prehistoric settlement of Makrychori 2, 13km north of Larisa. A report of the results of these two excavations is forthcoming in Praehistorische Zeitschrift.