I. P. Martini

Tectono-sedimentary characteristics of Late Miocene-Quaternary extensional basins of the Northern Apennines, Italy

Abstract Extensional and compressional regimes exist at the same time in adjacent parts of the Northern Apennines (Italy), and the former regime succeeded the latter at the same place as the thrust mountain front moved eastward since Miocene times. Numerous extensional basins have developed west of the present mountain divide. The westernmost ones formed over attenuated continental crust since Late Miocene and have been subjected to several subsidence and uplift events, with rates of subsidence generally faster than rates of sedimentation. They contain continental deposits overlain by gypsum-bearing Upper Miocene marine sequences and siliciclastic, marine Pliocene deposits. These basins were affected by shallow magmatism and are still experiencing high geothermal gradient and late to post-magmatic activities, such as in the renowned thermal region of Larderello. To the east, closer to the present mountain divide, the extensional basins formed later, from Pliocene to Quaternary, contain continental (fluvial and lacustrine) deposits and have not experienced near-surface magmatic activities. The sedimentary fill architecture of the Apennine extensional basins is similar to that of other European, American and African extensional or transtensional systems. For instance, a common characteristic is the prevalence of large alluvial fan deposits at the hanging-wall shoulder of half-grabens, coarser, smaller, alluvial fans at the footwall shoulder, and some fluvial deposits introduced longitudinally. Unlike the African rifts though, the sedimentary facies distribution of extensional basins which developed in active orogenic zones such as in the Apennines, may be strongly affected by uplifting, steep mountain slopes and can have large, thick, coarse alluvial fans also on the footwall side of the half-grabens.

Late glacial and postglacial environmental changes : Quaternary, Carboniferous-Permian, and Proterozoic

Part I The quarternary - the last glaciation and deglaciation: northern hemisphere (Laurentide) deglaciation - processes and responses of ice sheet/ocean interactions the last Scandinavian ice sheet and its down-wasting environment and climate of Sartan maximum and the late glacial in Siberia termination of the pleistocene and holocene changes in South America and other glaciated parts of the southern hemisphere. Part II The quarternary - macro-processes: sediment deformation beneath the Laurentide ice sheet megafloods and glaciation. Part III The permo-carboniferous - a paleographic reconstruction: Permian world topography and climate. Part IV The permo-carboniferous - the distribution and effect of the major glaciers of Gondwana glacial-postglacial transition in the late Paleozoic basins of southern South America a review of the permo-carboniferous glaciation in Africa transition from freezing to subtropical climates in the permo-carboniferous of Afro-Arabia and India Permian postglacial environments of the Australian Plate upper paleozoic glacial and postglacial deposits, central Transantarctic mountains, Antarctica some problems of the Permian (Asselian) glaciation and the subsequent climate in the Permian. Part V An older, precambrian glaciation - a comparative analysis: tectonic and glacio-eustatic controls on postglacial stratigraphy - proterozoic examples. Part IV quaternary and permo-carboniferous terrestrial weathering and organic deposits interpreting glacial climate from detrital minerals in sediments paleosols of the northern part of North America - their features and significance as indicators of past climates cold temperate peats and coals - their sedimentology and composition recent cold climate peats of central Canada and permo-carboniferous coals of Gondwana.

Pleistocene glacio-lacustrine deltaic deposits of the Scarborough Formation, Ontario, Canada

Abstract The late Pleistocene Scarborough Formation of the Lake Ontario Basin represents a lacustrine-deltaic sequence strongly affected by a nearby glacier. It shows gradual upward coarsening and thickening of layers from varve-like, clay-rich rhythmites at the base to channelized cross-bedded sands at the top. Thick, lensing, “massive” layers (Cm) of silty sand are found interstratified with thin layers of silt and clay in the lower and middle parts of the sequence. These “massive” layers were probably formed by subaqueous gravity flows of material in part derived directly from a glacier. Absence of pebbles and of other features such as glacial silt-pellets suggests dispersal away from the foot of the glacier rather than deposition under floating ice. Varve-like rhythmites, pollen and insect fauna indicate subarctic to arctic climatic conditions at the time of sediment deposition. The large amount of sand in the upper part of the formation is best explained as derived from active outwash fans. Similar fans were formed during the last deglaciation in southern Ontario and can be observed on the landscape.

Morphology and recent sediments of the lower anastomosing reaches of the Attawapiskat River

The Attawapiskat River is one of the major low-gradient rivers which cross the flat wetlands of the Hudson Bay Lowland. It has a nival regime leading to strong, short-duration spring floods during which considerable amount of sediment is carried. For the remainder of the year only organic matter is transported in solution and suspension. The land is isostatically rebounding after the Pleistocene glaciations. The river downcuts through the softer Holocene estuarine basal clays and the Pleistocene tills, to the Paleozoic carbonate bedrock. The river develops an anastomosing pattern in the lower reaches and it acquires an irregular meandering character inland. It does not construct a significantly thick delta as the river-borne sediments are dispersed along the coasts by tides, longshore currents and ice rafting. The river is subjected to frequent ice jams in its lower reaches as warmer southern waters flow toward the still frozen mouth and sea. During the jams, secondary channels become active, floodings develop and sedimentation occurs on the levees. Ice scours and ice-rafted materials affect the river banks greatly. The principal sedimentary environments within the river consist of: (1) erosional shoals covered by boulder and pebble lags over till: (2) sorted coarse to medium-sized sands in junction bars downstream from islands; these sands frequently develop gas bubbles, and they contain characteristic fining-upward sequences from boulder pavements at the base, grading up into rippled sand with abundant organic matter, grading up into laminated silt and sand and organic matter; (3) secondary channels, which develop thin silty and clay drapes on eroded hard substratum and are filled eventually by thick peats; and (4) river banks which show well-developed regressive sequences from Pleistocene tills at the base, overlain by estuarine sparsely fossiliferous clays, capped by thin conglomeratic units with abundant reworked Macoma balthica shells, grading upward into upper tidal flat sand, irregularly laminated sand and silt of marshes, and regular interbedding of sand, silt and organic layers of the levees at the top.

Syntectonic sedimentation in a Middle Triassic rift, northern Apennines, Italy

Abstract The anatomy of the sedimentary and volcanic fill of a Middle Triassic continental rift at the western margin of the Tethys is illustrated by the study of a 250 m thick sequence on the Tyrrhenian coasts of the Northern Apennines. This sequence contains two cycles of sedimentation: 1. (a) The lower cycle comprises a basal transgressive sequence from continental alluvial fans to shallow marine carbonates, and an upper sequence which correspond to an increasing tectonic activity (submarine syntectonic facies assemblage). The lower part of the last assemblage is characterized by a thick (22 m), rapidly deposited sequence of coarse carbonate breccias with minor calcareous sandy turbidites. This is overlain by channelized red beds of submarine fans composed of close interstratification and juxtaposition of carbonate breccias with red clastic matrix, and red sandy quartz pebble conglomerates and silty sands. Interbedded alkaline pillow lava record penecontemporaneous submarine eruptions. The lavas are capped by thin red cherty (diaspri) crusts. The lower cycle of sedimentation ends with a karstic surface on relatively deep marine carbonate layers. This suggests a rapid emersion due to the arrest and reversal of the downsinking of the initial (“aborted” or failed) rift. 2. (b) The upper cycle of sedimentation starts with more mature fluvial red beds and changes upward into shallow marine sands and carbonates. This upper cycle represents an early stage of evolution of a new major rift. This second major rift led, in Jurassic times, to the opening of an oceanic area between Europe and western Italy.

Cold climate peat formation in Canada, and its relevance to Lower Permian coal measures of Australia

Abstract Canada is a vast, cold country. Large expanses of wetlands occur whose characters change predictably over continental distances along north-south temperature gradients and coastal-inland precipitation trends. The changing climatic conditions during the Holocene have influenced the initiation and rates of peat formation. For instance, most of the peats of south-central Canada are not older than 5000 years B.P. Those in the Arctic regions are fossil deposits of the hypsithermal times of 7–8000 years B.P., maintained at the surface because of the low rates of peat oxidation. An analysis of the environments of formation and of the stratigraphy of recent peats, which formed under cold to cold-temperate climate in Canada, forms the basis for a comparative study and a better understanding of the Permo-Carboniferous coals of Gondwanaland (Brazil, South Africa and Australia). Much of the stratigraphic complexities that occur in the peat sequences are blurred out during organic decomposition and metamorphism leading to coal formation. However, some of the major features of the sequences that develop in string fens (from basal sedge peats up to sedge-woody peats), and in boreal and cold-temperate bogs and swamps (from basal lacustrine deposits with some reworked and algal rich sediments, grading upward into sedge peats, to Sphagnum -sedge peat, to Sphagnum -woody or just woody peats) may be recognizable in banded coal seams. It is suggested that future detailed comparative microfacies analyses of the cold peat sequences of Canada and the Lower Permian coal seams of Australia will allow better reconstructions and understanding of ancient wetlands, without exclusively using the less appropriate, albeit better known, recent models of subtropical swamps.

Ordovician alluvial fan to marine shelf transition in SW Sardinia, Western Mediterranean Sea: tectonically (“Sardic phase”) influenced clastic sedimentation

Abstract A localized Lower Ordovician, early Caledonian structural event (“Sardic phase”) is recorded in SW Sardinia by an angular and erosional unconformity, faulting, and mild folding. This event was accompanied by sedimentation of a transgressive, clastic unit (“Puddinga Beds”) which is particularly well developed along a major fault system (Gonnesa fault zone). There, the “Puddinga Beds” range from basal interfingering fans (some formed by coarse carbonate and schist-clasts others by schist-clasts only), to fluvio-lacustrine mud and gravelly sandstone, to coastal muddy and sandy deposits, and to fossiliferous restricted marine shelf sediments. The existence of the slightly compressive “Sardic phase” in SW Sardinia and quasi-coeval calc-alkaline volcanism and an extensional structural phase (“Sarrabese phase”) in central-east Sardinia, suggest transcurrent faulting. The calc-alkaline acid volcanism is also interpreted by some authors to indicate that the rifted basins developed in backarc position. The non-volcanic sequence of SW Sardinia analyzed in this paper was probably formed in basins developed on the northern margin of the Gondwanaland craton. This Sardinian system may be the eastward extension of transcurrent rifts which have also been recently reported from NW Spain. Structural activity has been the predominant control on sedimentation; however, worldwide, recurring, low sea-level stands may have influenced the sedimentation of the lower part of the “Puddinga Beds”, and the deglaciation of the Saharan Ice Sheet has contributed to the uppermost Ordovician-early Silurian deepening of the euxinic shelf.

Morphology and Sediments of the Emergent Ontario Coast of James Bay, Canada

Ontario is a maritime province, although this is not commonly realized. It has more than 2500 km of coasts along the Great Lakes and 1130 km along the brackish waters of James and Hudson Bay. The coasts are underlain by a variety of bedrock types, from hard crystalline Precambrian igneous and metamorphic rocks, to Paleozoic soft shales and fractured carbonates. The shores of James Bay in particular are rapidly emerging (70-100 cm/century) as response to residual post-glacial isostatic rebound. The shores are flat (order of 0.5-1.0 m/km), and because of their northern trend they contain the transition from a southern forested permafrost-free area to a northern tundra area with continuous permafrost. These coasts enclose one of the largest wetlands of the world, the Hudson Bay Lowland, where sequences of forested beach ridges and old promonotories record the different stages of Holocene emergence of the land. Shallow wide embayments mostly underlain by marine clay of an early post-glacial Tyrrell sea have been occupied by large river throughout the Holo-

Regional Analysis of Sedimentology of Medina Formation (Silurian), Ontario and New York

The sedimentologic characteristics of the Medina Formation (Silurian) were examined in the sections exposed along the Niagara escarpment in Ontario and New York. The vertical and lateral variations of the textures, fabrics, sedimentary structures, and faunal assemblages indicate a mixed environment of deposition best explained by a deltaic-shallow marine model of sedimentation. The growth of the Medina clastic sequence was related to shifting deltas which, locally, reached the area cut by the natural cross section of the Niagara escarpment. The primary constructive phases of these Medina deltas are well developed in the vicinity of Fulton and between Medina City and Rochester, New York. A third area of direct deltaic clastic input in the Medina sea is present in parts of he DeCew and Niagara Gorge sections. In the Niagara-Ontario area, however, the marine forces were competent enough to rework and redistribute most of the delta-born sediments. The combination of a relatively slow rate of clastic input, a shallow Silurian sea, and a very slow subsidence of the depositional basin yielded a complex interfingering of deltaic topset environments and of prodelta and/or interdeltaic environments. The topset to shoreline environments are characterized by channel sedimentation, beaches, tidal flats--as demonstrated by the presence of Lingula shells still in living position--and high tidal flats to floodplain settings where burrowing organisms flourished. The prodelta parts of the deltas, or the more open-marine environments, are represented by the dolomites and t e gray and red shaly and silty sequences with minor carbonates, which compose the Medina sections in the Hamilton area and which thin eastward and pinch out in the vicinity of Medina City, New York. The Medina Formation is gas productive directly south of the outcrop section, and the constructed sedimentation model can be of value to predict the best reservoir trends in the subsurface.

Siliciclastic-carbonate sequences of Miocene grabens of northern Sardinia, western Mediterranean Sea

Abstract The small crustal block of Sardinia Island (western Mediterranean) underwent major rifting events during Oligocene-Early Miocene (Aquitanian), Early Burdigalian, and Plio-Pleistocene times. Sedimentation in the resulting extensional and transtensional basins was affected by both local tectonic and worldwide sea-level changes. The mixed siliciclastic-carbonate sequences which developed, are readily comparable with those predicted by sequence stratigraphy. This paper focuses on the post-volcanic, Uppermost Burdigalian to Lower Messinian (?) sedimentation at the confluence between a main N-S trending basin and a secondary SW-NE trending graben, in northern Sardinia. Silty marlstones of Late Burdigalian-Early Langhian age characterize the central part of the main basin, whereas variable siliciclastic and carbonate sequences affected by up to three major transgression and regression cycles developed at its margins and at the confluence with the smaller graben. Differential movements along the main boundary fault led to rotation of blocks which localized narrow, elongated offshore algal carbonate platforms. Low sea-level stand led to deep erosion (type 2 sequence boundary) of these carbonates and to the formation of siliciclastic sandy lowstand wedges. High sea-level stand led to re-establishment of algal platforms at the shelf margin which were bounded farther inland by siliciclastic-carbonate mixed parasequences. Although it is not possible to date directly every stratigraphic unit, local sequences are well structured and can be tentatively correlated with reported worldwide transgressive-regressive events.