Peter Bengtson

Stratigraphy and evolution of the Cretaceous forearc Celica- Lancones basin of southwestern Ecuador

The “Celica–Lancones” forearc Basin of southern Ecuador and northern Peru is located between the Paleozoic Amotape–Tahuin Massif to the west and NW and the continental volcanic arc to the east and SE. The study of nine sections and exhaustive sampling of the poorly fossiliferous, mainly clastic Cretaceous deposits of this Basin allowed us to define five distinct series, which display two depositional periods. The first period corresponds to the development of an Early (?) and Middle Albian carbonate shelf, interrupted during Late Albian times by the creation of a tectonically generated trough filled by turbidites of Late Albian–Coniacian age. Geological mapping indicates that this “Celica–Lancones Basin s.s.” includes distinct tectonic units, characterized by distinct early Late Cretaceous stratigraphic series and separated by major faults. These units can be grouped into two main paleogeographic domains. The southeastern one comprises mainly volcaniclastic deposits, whereas the northwestern domain exhibits quartz-rich deposits. Between Early Coniacian and Middle Campanian times, the “Celica–Lancones Basin s.s.” forerarc trough was deformed and eroded as a result of the Late Cretaceous “Peruvian” tectonic phase. The second period corresponds to the latest Cretaceous, during which a new forearc basin was created (Paita–Yunguilla Basin), which is much wider and strikes obliquely with respect to the Celica–Lancones Basin. The sediments of the Paita–Yunguilla Basin exhibit a comparable succession of Campanian–Maastrichtian age throughout the area and conceal the tectonic juxtaposition of the early Late Cretaceous tectonic units. The occurrence of thick Early(?) Maastrichtian coarse-grained conglomerates and breccias express a new significant tectonic event.

Sedimentary and tectonic evolution of the arc zone of Southwestern Ecuador during Late Cretaceous and early Tertiary times

Abstract The eastern part of the “Celica basin” of southwesternmost Ecuador exhibits Late Cretaceous to Tertiary sediments which belong to the magmatic arc paleogeographic zone. Important N-S to NE-trending faults separate a western, mainly Late Cretaceous series (Rio Playas) from an eastern succession (Catamayo-Gonzanama) of (?) Late Cretaceous to early Tertiary age. The analysis of these sediments indicates a complex geologic history, which recorded the main stages of the early tectonic evolution of the Andes. In the Rio Playas area, a submarine andesitic volcanic pile (Celica Fm) represents the products of a volcanic arc of probably Albian age. It is apparently overlain by a thick, early Late Cretaceous series of volcanic flows and coarse-grained volcaniclastic high-density turbiditic beds (Alamor Fm), the deposition of which might result from the Mochica phase (late Albian-early Cenomanian) Deformation, uplift and erosion (early Peruvian phase) are followed by the sedimentation of unconformable marls and greywackes of marine open shelf to deltaic environment. These comprise Santonian and/or Campanian fine- to mediumgrained deposits (Naranjo Fm), abruptly overlain (late Peruvian phase ?) by fan-delta coarse-grained marine deposits of latest Cretaceous age (Casanga Fm) They are locally capped by undated, partly volcaniclastic red beds, indicating an important regression/uplift of latest Cretaceous-early Tertiary age. In the Catamayo-Gonzanama area, thick subaerial andesitic volcanic rocks (Sacapalca Fm) are intruded by Paleocene to early Eocene plutons and are overlain by undated fluvial red beds. They express uplift movements of latest Cretaceous-early Tertiary age. To the South, these are capped by slumped lacustrine black shales and greywackes of possible Maastrichtian-Paleocene age (Gonzanama Fm) Farther north, the Sacapalca volcanics and red beds are overlain by variegated shales, sandstones and conglomerates, dated as latest Oligocene-early Miocene (Catamayo Fm) They are eroded by an angular unconformity and capped by early Miocene volcanics and sediments, which express an early Miocene deformation phase. The apparent sedimentary hiatus including most of Eocene-Oligocene times is interpreted as a result of the late Paleocene and late Eocene Incaic tectonic phases.

The Late Cretaceous bivalve Didymotis GERHARDT, 1897 from Sergipe, Brazil

KurzfassungDie geographisch weit verbreitete, oberkretazi-sche MuschelgattungDidymotisGErhardt, 1897 hat nur eine kurze stratigraphische Reichweite, vom oberen Turon bis in das unterste Coniac. Aus vielen Teilen der Erde wurden drei Häufigkeitsmaxima, bekannt alsDidymotis Events 0,1 und II, beschrieben. Ferner istDidymotis anhand ihrer Morphologie und der charakteristischen Schalenskulptur leicht zu identifizieren, was zu ihrer Verwendbarkeit als wichtige Leitform für die Stratigraphie der Oberkreide beiträgt. Das Vorkommen vonDidymotis im Sergipe-Becken in Nordostbrasilien wird innerhalb eines überregionalen biostratigraphischen Rahmens diskutiert und eine Korrelation mit demDidymotis Event II vorgeschlagen.AbstractThe geographically widespread Upper Cretaceous bivalve genusDidymotisGerhardt, 1897 has a short stratigraphie ränge, from the upper Turonian to the lowermost Coniacian. Three acme occurrences, known asDidymotis events 0, I, and II, are recognised in many parts of the world. The morphology and the characteristic ornamentation ofDidymotis make it an easily identifiable genus, which contributes to its usefulness as a biostratigraphic tool for the Upper Cretaceous. The occurrence ofDidymotis in the Sergipe Basin in north-eastern Brazil is discussed within the global biostratigraphic framework and correlation withDidymotis event II proposed.

Mid-Cretaceous inoceramids from Sergipe, Brazil: a progress report

The Cenomanian-Coniacian Cotinguiba Formation of the Sergipe Basin in northeastern Brazil (Figure 1) contains the largest and most diverse assemblage of mid-Cretaceous Inoceramidae (Bivalvia) yet known from the Southern Hemisphere. Preliminary studies of material collected suggest that at least 5 late Cenomanian, 25 Turonian and 29 early Coniacian species and subspecies of this biostratigraphically important family are present in the formation. We present here a status report of a long-term project on the Brazilian inoceramids initiated in 1970 at Uppsala University. The project is currently focused on taxonomic (E.G.K.) and biostratigraphical (E.G.K. & P.B.) studies of the Sergipe inoceramids; in addition, more detailed biostratigraphical work based on bed-by-bed collecting from the Retiro area in Sergipe, and revision of mid-Cretaceous inoceramid material in Brazilian institutions, are being carried out by M. H. R. Hessel as part of a Ph.D. project at Uppsala University. For details of the geology of the Sergipe Basin, with notes on the faunas of the Cotinguiba Formation, the reader is referred to Bengtson (1983). The great majority of the inoceramids of the Sergipe Basin are cosmopolitan taxa that are best known from localities throughout the Euramerican

Late Aptian (Cretaceous) paleoceanography of the South Atlantic Ocean inferred from dinocyst communities of the Sergipe Basin, Brazil

The late Aptian (Early Cretaceous) is a crucial time interval for understanding the paleoceanographic changes in the Southern Hemisphere. Oceanographic changes in the emerging South Atlantic Ocean during this interval are reflected in the stratigraphic distribution of dinoflagellate communities recorded in the Muribeca and Riachuelo formations of the Sergipe Basin in northeastern Brazil. The Subtilisphaera community, in the lower and middle parts of the section, appears to be related to the Subtilisphaera Ecozone and suggests the onset of Tethyan influence in the central South Atlantic, in a restricted to inner-neritic environment. The succeeding Spiniferites community, in the middle part of the section, represents the first significant transgression, probably of eustatic origin. The Cyclonephelium-Exochosphaeridium community, in the upper part of the section, appears to be related to an oceanic event characterized by intermittent dysoxic-anoxic conditions. The uppermost part of the section is dominated by the Spiniferites community, related to a progressive regional transgression and culminating in an open-marine, fully Tethyan environment in the central part of the widening South Atlantic.

The ammonite fauna and genesis of a mid-Cretaceous siliceous oolite from the Alagoas Basin, Brazil

Abstract Acanthoceratid ammonites from near Maceio, in the State of Alagoas, provide evidence of a mid-Cretaceous marine incursion into the present onshore part of the Alagoas Basin. The ammonites Pseudocalycoceras sp. cf. P. harpax (Stoliczka, 1864) and Kamerunoceras sp. are assigned a late Cenomanian age. The rock is a siliceous oolite that occurs as derived nodules and fragments in late Cenozoic continental sediments. It is interpreted as an originally calcareous oolite formed in a near-shore, high-energy environment. Absence of primary cement suggests that silicification took place early in diagenesis. The silicified, and therefore more resistant material from the original Cenomanian sequence was reworked and redeposited with the Cenozoic sediments. The age, indicated by the ammonites, suggests that the original deposition was related to the global late Cenomanian—early Turonian sea-level rise.

Global biogeography of Albian ammonoids; a network-based approach

Large-scale biogeographic provinces of Cretaceous ammonoids, as currently defined in the literature, were delimited using qualitative assessments of taxonomic inventories. Using aggregated species occurrences in the Paleobiology Database, we generated a geographic network to quantify connectivity of Albian epicontinental basins and used the flow-based Infomap algorithm to delineate bioprovinces. Despite taxonomic, stratigraphic, and geographic limitations of the data, the Infomap bioprovinces are largely concordant with the traditional, qualitatively derived biogeographic model, including the Boreal-Pacific Subrealm, Arctic Subrealm, Tethyan Realm, and Austral Realm. An agglomerative hierarchical cluster analysis applied to the same occurrence data failed to replicate the Infomap bioprovinces or reproduce the traditional qualitative model. The observed asymmetrical distribution of the Infomap bioprovinces is consistent with the known hemispheric differences in paleogeographic and oceanographic features of the Albian Earth. The geographic network derived from ammonoid data is twice as dense as the one derived for Albian benthic marine invertebrates and thus more effective in delineating global biogeographic units. The network-based approach establishes a reproducible quantitative framework for delineating geographic boundaries of marine bioprovinces, tracking biogeographic changes over evolutionary time scales, and identifying biotic and abiotic factors that influence global partitioning of marine biodiversity.

One hundred volumes of Geologiska Föreningens i Stockholm Förhandlingar

Abstract The now completed 100 volumes of Geologiska Foreningens i Stockholm Forhandlingar (GFF) and its history are briefly reviewed. The initiative to start this national society journal stemmed from A.E. Nordenskiold in 1871. The publication programme has developed from having been essentially author- and member-oriented to more subject-oriented. Swedish was the all-dominant language in the beginning, German and English were frequently used during the first half of this century, and English is now the official language of the journal. GFF has had 15 editors, two of whom “persisted” for some 20 years. Observations are made on the development of the contents, rate of publication, publication volume, typographical layout, abstract block, cover, instructions to authors, advertisements, financing, and subscription rates

Cellular and nuclear morphology…and calcium signaling: revealing the interplay between structure and function

Poster presentation: Calcium plays a pivotal role in relaying electrical signals of the cell to subcellular compartments, such as the nucleus. Since this one ion type is used by the cell for many processes a neuron needs to establish finely tuned calcium pathways in order to be able to differentiate multiple tasks, [1-3]. While it is known that neurons can actively change their shape upon neuronal activity, [4-7], we here present novel findings of activity-regulated nuclear morphology, [8,9]. With the help of an experimental and computational modeling approach, we show that hippocampal neurons can change the previously spherical shape of their nuclei to complex and infolded morphologies. This morphology regulation is demonstrated to be regulated by NMDA-receptor gated calcium, while synaptic and extra-synaptic NMDA-receptors elicit opposing effects on nuclear morphology, [8]. The structural alterations of the cell nucleus have significant effects on nuclear calcium dynamics. Compartmentalization of the nucleus, due to membrane infoldings, changes calcium frequencies, amplitudes and spatial distributions, [8,10]. Since these parameters have been shown to control downstream events towards gene transcription, [11,12], the results elucidate the cellular control of nuclear function with the help of morphology modulation. With respect to processes downstream of calcium, we show that histone H3 phosphorylation is closely linked to nuclear morphology. Investigating the nuclear morphologies of hippocampal neurons, two major classes were identified [9,10]. One class contains non-infolded nuclei that have the function of calcium signal integrators, while the other class contains highly infolded nuclei, which function as frequency detectors of nuclear calcium, [10]. Extending this interdisciplinary approach of investigating structure/function relationships in neurons, the effects of cellular morphology – as well as the morphology of the endoplasmic reticulum and other organelles – on neuronal calcium signals is currently being investigated. This endeavor makes use of highly detailed, three-dimensional models of neuronal calcium dynamics, including the three-dimensional morphology of the cell and its organelles.

NOOR MOHAMMAD FARSAN (1940–2003)

Noor Farsan will always be remembered for his friendliness and cheerful demeanor as well as for his contributions to paleontology. His premature death from a long-standing cancer illness on 23 April 2003, at the age of 62 is not only a great personal loss to family and friends but to the world of science as well. His passing marks the end of a unique type of research into the paleobiology of tentaculitids, in which the shell structure rather than external shell morphology of these animals was emphasized as a basis for taxonomy and phylogeny. Noor was born in Kabul, Afghanistan, on 15 September 1940. His parents divorced shortly before he was born and he was raised by his maternal grandfather. His grandfather was employed by the king of Afghanistan, who in turn was acquainted with the German emperor Wilhelm II, and …