Antonio C. Rocha-Campos

Patterns of late Palaeozoic deglaciation in the Paraná Basin, Brazil

Abstract The Itarare Subgroup (Middle Carboniferous-Early Permian) of the Parana Basin of southeastern Brazil contains the thickest, most extensive and one of the longest records of late Palaeozoic glaciation in all of the Gondwana supercontinent. Glacially controlled deposition started as early as the Middle Carboniferous when lobate termini of ice streams from the Windhoek Ice Sheet (WIS), and Rio Grande do Sul and Asuncion ice caps moved into the Parana Basin. Lobes reached sea-level and advanced grounded at least as far as 200 km into the basin, stabilizing as tidal/intertidal margins. Glaciation and glacial sedimentation occurred penecontemporaneously with the transgressive phase of the late Palaeozoic tectonic cycle of the Parana Basin, while Gondwana was gradually moving away from the South Pole. Evolution involved complex interaction of tectonic, palaeogeographic and palaeoclimatic factors. Initial flooding of the basin by an epicontinental sea in the Middle Carboniferous may have provided moisture necessary for the growth of glaciers. Conversely, episodes of sea-level rise probably affected the stability of marine glaciers. The palaeoclimatic setting for the WIS and other ice masses at the margins of the Parana Basin was mostly temperate. Multiple ice advances are evidenced by subglacial tillites resting on striated and/or glaciotectonized basement and deformed glacigenic sediments identified at different stratigraphic levels in the Itarare Subgroup. Glaciation reached its maximum expansion sometime between the Late Carboniferous and Early Permian, gradually diminishing and vanishing in the late Early Permian. The reconstructed palaeogeographic evolution favors a model of irregular melt back of ice masses, particularly along the eastern margin of the Parana Basin, in analogy with the deglacial pattern of the Pleistocene Laurentide ice sheet, in North America. Retreat of marine glaciers was mostly associated with relatively simple accumulations, or complex build-ups of ice contact/proglacial facies associations in glacial estuarine embayments. Fast retreat was mainly controlled by decoupling associated with sea-level rise and intense calving. In the terrestrial environment, more fragmentary evidence shows that retreat may have involved several mechanisms including downwasting of stagnant/inactive ice margins and destabilization by surging of glaciers moving over deformable sediments. Highstand sea-level following ice wastage is often marked by widespread deposition of relatively thin marine beds. At least four stratigraphically different basinwide marine “horizons” are recognized. Isostatic rebound of deglaciated margins of the Parana Basin is recorded by transition from deep marine beds to shallowing/coarsening upward, prograding sequences of littoral/fluvio-deltaic facies basinwards, sourced from raised basin margins. Eventually, upon emersion, these constituted platforms for interglacial and postglacial peat development. Although glaciation lasted for a long time, glacial sedimentation alternated with relatively long periods of intense and widespread subaerial and subaquatic (submarine) reworking of previously deposited glacigenic sediments and deposition of “normal”, non-glacial sediments, that comprise the bulk of the Itarare Subgroup sequence. Thin coal beds, which locally rest on fossil soils, denote climatic amelioration during these interglacial phases.

Late Paleozoic glaciotectonic structures in northern Paraná Basin, Brazil

Abstract Fluviatile–deltaic sediments containing thin coal layers, and glaciofluvial sediments of the Itarare Subgroup (late Paleozoic) cropping out near Cerquilho, northern Parana Basin, exhibit post-depositional deformation such as recumbent and drag folds, shear fractures, faults and shear lamination. The deformation occurs in an interval of 3–4 m thick and is confined between horizontal strata. The deformed strata are directly overlain along a horizontal erosional/tectonic contact surface by a silty–sandy, massive, 1 m thick, clast-poor tillite. Deformation shows a consistent geometry indicating a predominant vergence toward the SSW having been developed under a horizontal stress oriented from NNE to SSW. The deformation is interpreted to be of glaciotectonic origin associated with an ice readvance in the area. The glacier moved toward the SSW on relatively soft, deformable sediments, depositing the subglacial till on top of them. The tillite shows parallel, upglacier-dipping shear fractures at its base and wedge-like intrusions into the underlying sandstone, probably formed during its subglacial deposition. The tillite is overlain by cyclic (braided stream) fluviatile, sandstone beds. The top of these shows deformations (small recumbent folds and reverse faults) below another clast-poor, silty–sandy tillite. This could represent another glacial readvance with subglacial deposition of till. Occurrence of glaciotectonic deformation overlain by subglacially deposited tillites in the Cerquilho area indicates glacier readvances and permanence of the glacial influence in the upper part of the Itarare Subgroup. Absence of incorporated material from the underlying deformed sediments in the tillite and the style of the deformations suggest an unfrozen, water-saturated, mostly unconsolidated substratum. These conditions may have generated instability and fast ice flow of the glacier. They also suggest that the sediment may have most likely failed in this manner under rapidly applied stresses associated with a surging behavior of the retreating glacier.

Early Miocene bivalves from the Cape Melville Formation, King George Island, West Antarctica

Seven species of marine bivalves, including six new taxa, are described from the Cape early Miocene Melville Formation which crops out on the Melville Peninsula, King George Island, West Antarctica. The bivalve assemblage includes representatives of the families Nuculidae, Ennucula frigida sp. nov., E. musculosa sp. nov.; Malletidae, Neilo (Neilo) rongelii sp. nov.; Sareptidae, Yoldia peninsularis sp. nov.; Limopsidae, Limopsis psimolis sp. nov.; Hiatellidae, Panopea (Panopea) sp. cf. P. regularis; and Pholadomyoida (Periploma acuta sp. nov.). Species studied come from four sedimentary sections measured in the upper part of the unit. Detailed morphologic features of nucloid and arcoid species are exceptionally well preserved and allow for the first time reconstruction of muscle insertions as well as dentition patterns of Cenozoic taxa. Known geological distribution of the species is in agreement with the early Miocene age assigned to the Cape Melville Formation. The bivalve fauna from Cape Melville Formation is the best known from Antarctic Miocene rocks, a time of complex geologic, paleogeographic and paleoclimatic changes in the continent. The new fauna introduces new taxonomic and palaeogeographic data that bear on the question of opening of sea gateways and distribution of Cenozoic biota around Antarctica.

Glacially striated, soft sediment surfaces on late Paleozoic tillite at São Luiz do Purunã, PR

Striae and furrows found on the upper surfaces of three stratigraphically superposed decimetric beds of late Paleozoic lodgement tillite of the Itarare Subgroup in the northern Parana Basin were engraved by ploughing of clasts and possibly also ice protuberances at the base of the glacier, on unconsolidated to partially consolidated sediment. Associated features indicate that the rheology of the bed varied from stiff during lodgement to soft and deformable during ploughing. Poor drainage of meltwater at the glacier-bed interface may have contributed to lower the strength of sediment to deformation. The deformed interval was probably generated during a single glacial phase or advance of a glacier grounding in a marine or lacustrine water body. Changes in the dynamics of the glacier involving slow and fast flow were correlated respectively with alternation of deposition and erosion. The proposed model is analogous to that of lodgement till complexes from the Pleistocene of the northern hemisphere. Retreat of the glacier was probably fast, followed by settling of muds on top of the upper striated and furrowed surface, and progradation of deltaic sands during post-glacial time.

Invertebrates from the Low Head Member (Polonez Cove Formation, Oligocene) at Vaureal Peak, King George Island, West Antarctica

Abstract Eight taxa of marine invertebrates, including two new bivalve species, are described from the Low Head Member of the Polonez Cove Formation (latest early Oligocene) cropping out in the Vauréal Peak area, King George Island, West Antarctica. The fossil assemblage includes representatives of Brachiopoda (genera Neothyris sp. and Liothyrella sp.), Bivalvia (Adamussium auristriatum sp. nov., ?Adamussium cf. A. alanbeui Jonkers, and Limatula (Antarctolima) ferraziana sp. nov.), Bryozoa, Polychaeta (serpulid tubes) and Echinodermata. Specimens occur in debris flows deposits of the Low Head Member, as part of a fan delta setting in a high energy, shallow marine environment. Liothyrella sp., Adamussium auristriatum sp. nov. and Limatula ferraziana sp. nov. are among the oldest records for these genera in King George Island. In spite of their restrict number and diversification, bivalves and brachiopods from this study display an overall dispersal pattern that roughly fits in the clockwise circulation of marine currents around Antarctica accomplished in two steps. The first followed the opening of the Tasmanian Gateway at the Eocene/Oligocene boundary, along the eastern margin of Antarctica, and the second took place in post-Palaeogene time, following the Drake Passage opening between Antarctic Peninsula and South America, along the western margin of Antarctica.

PENNSYLVANIAN PTERIOMORPHIAN BIVALVES FROM THE PIAUÍ FORMATION, PARNAÍBA BASIN, BRAZIL

Abstract Dolostones of the upper Piauí Formation, Parnaíba Basin, northern Brazil, preserve a rich and diversified invertebrate fauna of Morrowan to Desmoinesian age. Among bivalves, Heteroconchia (15 species) is the most diversified, followed by Pteriomorphia (11 species), and rare endobenthic species of the Palaeotaxodonta (three species). Eleven species of Pteriomorphia are described, including representatives of the genera Parallelodon?, Myalina?, Septimyalina, Caneyella?, Leptodesma (Leptodesma), L. (Leiopteria), Meekopinna?, Aviculopinna?, and Aviculopecten. A new combination, Etheripecten trichotomus, and the oldest member of the Anomiidae recorded, Pindorama nordestina n. gen. and sp., also are described. Details of muscle scars and hinge characters have been recovered for several taxa, thereby refining the knowledge for species diagnoses. Fossil beds in the Esperança and Mucambo dolostones reveal episodic burial of bivalves in life position. These are internally complex, multistory fossil concentrations recording background and episodic processes. Hence, those fossil concentrations show high degrees of time-averaging and poor paleoecological resolution (except for the bivalves preserved in situ).

Shell beds from the Low Head Member (Polonez Cove Formation, early Oligocene) at King George Island, west Antarctica: new insights on facies analysis, taphonomy and environmental significance

Abstract Shell bed levels in the Low Head Member of the early Oligocene Polonez Cove Formation at King George Island, West Antarctica, are re-interpreted based on sedimentological and taphonomic data. The highly fossiliferous Polonez Cove Formation is characterized by basal coastal marine sandstones, overlain by conglomerates and breccias deposited in fan-delta systems. The shell beds are mainly composed of pectinid bivalve shells of Leoclunipecten gazdzickii and occur in the basal portion of the Low Head Member. Three main episodes of bioclastic deposition are recorded. Although these shell beds were previously interpreted as shelly tempestites, we present an alternative explanation: the low fragmentation rates and low size sorting of the bioclasts resulted from winnowing due to tidal currents (background or diurnal condition) in the original bivalve habitat. The final deposition (episodic condition) was associated with subaqueous gravity driven flows. This new interpretation fits with the scenario of a prograding fan-delta front, which transported shell accumulations for short distances near the depositional site, possibly between fair-weather and storm wave bases. This work raises the notion that not every shell bed with similar sedimentological and taphonomic features (such as geometry, basal contact, degree of packing and shell orientation in the matrix) is made in the same way.

Late Paleozoic exhumed glacial erosive landscape in Salto, SP

SUMMARY OF COMMUNICATIONS stone with dropstone on the roche moutonnee from Salto,to cross-bedded and “convoluted” sandstone beds in theriver channel, toward NW. They are interpreted as proxi-mal and distal glacial facies respectively, associated withan advance and retreat of the glacier.Those rocks are overlain by an extensive andthick shale (pellitic) section that may representthe deposit of a marine transgressive post-glacialepisode. Dropstones in the shale denote presenceof icebergs and permanence of glacial influence dur-ing sedimentation. — ( December 14, 2001 ). ∗ Supported by FAPESP 00/6039-6.**E-mail: jbviviani@aol.com MULTIDISCIPLINARY THEMES Alcides N. Sial and Valderez P. Ferreira(Organizers) EFFICIENT ALGORITHMS FOR PACKING BOXESINTO CONTAINER Sostenes L. S. Lins Departamento de Matematica, CCEN, Universidade Federalde Pernambuco, Recife, PE, Brazil. The problem of packing boxes into bigger boxes(containers) is a practical problem which, by its economi-cal significance, deserves a serious and inspired scientificapproach. From a strictly mathematical point of view, itis an incredibly challenging problem which badly needsgood heuristics to solve it. We have been involved in try-ing to find such heuristics since 1997. These heuristicsuse new concepts in graph theory (the tets), in data struc-ture (the phormas), and used some classical algorithms astopological sorting and the coding of combinatorial ob-jects to approach real world packing problems. A distin-guished feature of our approach is the visual treatment ofthe spatial packing: we produce a sequence of homoge-neous increments (a loading plan) in the packings whichmakes it easy to visualize and to actually produce the so-lutions found.We have produced a set of effective heuristics fordealing with real world box packing problems: we permitvarious types of boxes, various types of containers, de-mand requirements on the boxes and the information onwhichboxtypescanchangeitsverticaldirection. Theim-plementation of our heuristics produces very good pack-ings as compared with non-scientific ones: typically weput 7% to 12% more boxes. The full paper related to thesematters is scheduled to be published this year (2002) inthe European Journal of Operations Research.A computer package named ExpedPlex is under de-velopment, where the pertinent algorithms are being effi-ciently implemented. — (

A (tidal-marine) boulder pavement in the late Cenozoic of Seymour Island, West Antarctica: contribution to the palaeogeographical and palaeoclimatic evolution of West Antarctica

Abstract We report here the discovery of a boulder pavement cropping out at the base of the Hobbs Glacier Formation (Miocene), on the northern sector of Seymour Island (Isla Marambio), West Antarctica, along the contact with the underlying La Meseta Formation (Eocene). The feature described has many points in common with boulder pavements developed in tidal-marine environments. The clasts of the pavement are mostly boulders and bear up to three sets of glacial striae on their bevelled truncated surfaces, but are not elongate parallel to them or bullet shaped. No diamictite body was identified associated with the boulder pavement. These features differ from those of boulder pavements described from terrestrially glaciated Cenozoic deposits and may indicate a shallow glaciomarine environment for the late Cenozoic of Seymour Island.

Chapter 50 Moema laminites: a newly recognized Neoproterozoic (?) glaciogenic unit, São Francisco Basin, Brazil

Abstract A recently identified diamictite and silt-clay laminite, which discordantly overlie the Archaean basement and underlie the Neoproterozoic Bambui Group, have been informally named as the Moema Laminites. They are preserved at the southwestern margin of the São Francisco Basin in southeastern Brazil, and are widely distributed in the central-western Minas Gerais state. They crop out discontinuously over at least 140 km along a north–south direction. The nomenclature of and stratigraphic relationships between the Moema Laminites and other isolated Neoproterozic occurrences of similar rocks are in a state of flux. Two exceptionally good exposures of the Moema Laminites show good evidence for deposition under glacial conditions. At the Formiga locality, a single glacial advance is registered by a deformation tillite, while overlying laminite records deposition in a post-glacial, probably marine basin following deglaciation. At the SAFFRAN quarry, striations on a bedding plane may have been caused by floating sea-ice that just touched the bottom of the basin. Much additional work is needed to establish relationships between the Moema Laminites and other similar occurrences. If these and Moema Laminites are shown to be Cryogenian glacial deposits, the area covered by the Cryogenian glaciations in the São Francisco basin is much larger than formerly believed.