Period Of Marine Sedimentation Research Articles

Facies partitioning and stratal pattern in salt-controlled marine to continental mini-basins: Examples from the Late Oligocene to Early Miocene of the Sivas Basin, Turkey

The Sivas Basin (Turkey) records a complex interaction between sedimentation, salt tectonics and regional shortening leading to the formation of numerous mini-basins. The segmentation into mini-basins was initiated during the Oligocene by the deposition of the fluvio-lacustrine Karayun Fm. This continental succession is overlain abruptly by an Oligo-Miocene shallow marine succession Karacaoren Fm, which comprises two main sub-environments: (i) mixed deltaic and carbonate ramp, (ii) coastal plain and lagoon. The Karacaoren Fm, forms a marine succession more than 1500 m thick that passes vertically upwards into a continental succession, the fluvial-dominated Benlikaya Fm. These two formations are the focus of the present study. During the period of marine sedimentation, the competing accumulation of carbonates and clastics is related not only to the topography inherited from salt tectonics, but also to relative sea-level variations expressed by two large-scale transgressive regressive cycles. We analyse these complex facies and stratal relationships to illustrate the modifications induced by salt tectonics. This study is based on extensive fieldwork and mapping making use of numerous measured stratigraphic sections and aerial photos over a large area comprising more than fifteen adjacent outcropping mini-basins. The aim of this study is to provide a detailed description of the stratigraphic relationships, correlations and sedimentary systems distribution in mini-basins during deposition of the Oligo-Miocene shallow marine and continental successions. We first clarify the vertical stratigraphic succession of the Oligo-Miocene marine and continental deposits and establish correlations between the studied mini-basins. These correlations then allow us to characterize and assess the local effects of salt withdrawal in relation to the regional forcings associated with flexural subsidence, tectonic shortening and relative sea-level changes. An improved understanding of the complex interactions of these variables provides a framework to distinguish the mechanisms that control facies distribution and stratal geometry in salt basins.

A late Holocene palaeoenvironmental record from Altona Bay, St. Croix, US Virgin Islands

Geografisk Tidsskrift, Danish Journal of Geography 108(2):59–70, 2008 A reconstruction of the palaeoenvironmental development of Altona Bay, St. Croix, northeastern Caribbean, has been made based on the sedimentological, geochemical and pollen analyses of a 1.83 m long vibracore. For chronological control, AMS 14C measurements were made at 5 levels downcore. The sedimentary sequence covers the last c. 4,700 years, containing both (mangrove) peat and fine-grained clastic sediment units. Comparison with regional Holocene sea level data demonstrates a gradual marine flooding of a mangrove environment around 3,500 cal BP was presumably related to a regional late Holocene sea-level rise, from a position, c. 2 m lower than present. After a c. 1,000 year period of marine sedimentation lasting until c. 2,500 cal BP, renewed formation of tropical wetland occurred at the site. This development may be attributed to the increased isolation of the shallow Altona Bay, most likely due to sea- ward formation of a well-developed spit system and possibly under the influence of enhanced storm-wave action in the period between c. 4,000 and 2,200 cal BP. Since the 1960's the repeated passage of severe hurricanes (e.g. Hugo, 1989) has had a significant impact on the sedimentation pattern of the bay and has caused a major hiatus and the recent deposition of sediments immediately overlying the c. 2,500 year old peat.

Quaternary evolution of the southern sector of the Campanian Plain and early Somma-Vesuvius activity: insights from the Trecase 1 well

The present review of data on the Trecase 1 well, including stratigraphy, updated 40 Ar/39Ar ages and the results of newly performed calcareous nannofossil studies, serves to resolve the chronological contradictions pointed out by Bernasconi et al. (1981) and Balducci et al. (1983) concerning the onset of volcanic activity in the area now occupied by the Somma-Vesuvius Volcanic Complex. New 40 Ar/39Ar data indicate that volcanic activity in this area started about 0.4 myr B.P. After such time, tephritic magmatic activity, distributed in small scattered centers, developed and alternated with periods of volcanic quiescence and marine sedimentation. This first phase of magmatic activity ended in the Vesuvian area about 0.3 myr B.P. and was followed by a period of marine sedimentation in a marginal environment. Complete emergence of the shoreline occurred about 37,000 yr B.P. as a result of sea level changes during the last glacial period and deposition of the 60 m thick Campanian ignimbrite (CI). Volcanic activity reappeared in the Vesuvian area only after the CI eruption. Magma rising along and at the intersection of linear and curved tectonic and volcano-tectonic elements (linked to the pre-existing Pleistocene tectonic trend and formation of the vast Phlegraean Fields caldera) formed a number of small lava and scoria edifices. One of these tephritic centers lies above the CI deposits under the Trecase 1 well area. The CI bottom in the Trecase 1 well is currently at an altitude of − 120 m a.s.l.; this allows estimating the maximum tectonic subsidence over the last 37,000 yr. by the southern sector of the Vesuvian area to be about 30 m.

Sm–Nd evidence for high‐grade Ordovician metamorphism in the Arunta Block, central Australia

Sm–Nd ages from the Harts Range in the south‐eastern Arunta Inlier in central Australia indicate that regional metamorphism up to granulite facies occurred in the Early Ordovician (c. 475 Ma). This represents a radical departure from previous tectonic models for the region and identifies a previously unrecognized intraplate event in central Australia. Peak metamorphic assemblages (800 °C and 10.5 kbar) formed at around 476±14 Ma and underwent approximately 4 kbar of near‐isothermal decompression at 475±4 Ma. A coarse‐grained unfoliated garnet–clinopyroxene‐bearing marble inferred to have recrystallized late in the decompressional evolution, gives an age of 469±7 Ma. Two lines of evidence suggest the Early Ordovician tectonism occurred in an extensional setting. First, the timing of the high‐grade lower crustal deformation coincides with a period of marine sedimentation in the Amadeus and Georgina basins that was associated with a seaway that developed across central Australia. Second, isothermal decompression of lower crustal rocks was associated with the formation of a regional, sub‐horizontal mid‐crustal foliation. In the Entia Gneiss Complex, which forms the structurally lowest part of the Harts Range, upper‐amphibolite facies metamorphism (c. 700 °C, 8–9 kbar) occurred at 479±15 Ma. There is no evidence that P–T conditions in the Entia Gneiss Complex were as high as in the overlying units. This implies that the extensional system was reworked during a later compressional event. Sm–Nd data from the mid‐amphibolite facies (c. 650 °C and 6 kbar) detachment zone that separates the Irindina Supracrustal Assemblage and Entia Gneiss Complex give an age of 449±10 Ma. This age corresponds to the timing of a change in the pattern and style of sedimentation in the Amadeus and Georgina basins, and indicates that the change in basin dynamics was associated with mid‐crustal deformation. It also suggests that compressional deformation culminating in the Devonian to Carboniferous (400–300 Ma) Alice Springs Orogeny may have begun as early as c. 450 Ma. At present, the extent of Early Ordovician tectonism in central Australia is unknown. However, granulite facies metamorphism and associated intense deformation imply an event of regional extent. An implication of this work is that high‐grade lower crustal metamorphism and intense deformation occurred during the development of a broad, shallow, slowly subsiding intraplate basin.

Messinian stromatolite‐thrombolite associations, Santa Pola, SE Spain: an analogue for the Palaeozoic?

ABSTRACTStromatolite‐thrombolite associations are the dominant facies forming large portions of the Santa Pola carbonate platform (SE Spain) during deposition of the Terminal Carbonate Complex (TCC). The TCC, the last period of marine sedimentation in the Western Mediterranean associated with the Messinian Salinity Crisis, comprises a NE‐SW trending thrombolite reef with occasionally interlayered stromatolite horizons and a predominantply stromatolite and oolite facies in the back‐reef area. The stromatolites are mainly dome shaped, but fine‐columnar or wavy‐undulose forms can occur. The stromatolites form huge bioherms, extending tens to hundreds of metres. They are finely laminated with alternating layers of dolomicrite and dolomicrospar. The dolomicrite layers appear to be a primary dolomite precipitate, whereas the dolomite crystals in the dolomicrospar layers apparently formed around a meta‐stable nuclei which was subsequently dissolved or degraded. The low content of sand‐sized particles in the stromatolitic layers indicates formation under low‐energy conditions, possibly on a tidal flat. As reported from other areas in the Western Mediterranean, deposition of the TCC at Santa Pola was apparently cyclic, whereby stromatolites generally terminate each depositional cycle. Subtidal Conophyton stromatolites, possibly the only known occurrence younger than Palaeozoic, are, however, found on the reef slope at the base of the first TCC depositional cycle. The dolomitic nature of the unadulterated stromatolitic laminations and the association of stromatolites and thrombolites as platform builders were a common feature in the Early Palaeozoic but are unusual in post‐Ordovician carbonate facies. We propose that the conditions during TCC deposition were very restricted, possibly reflecting an environment similar to that of the Early Palaeozoic.

Quaternary stratigraphy of the fladen area, central North Sea: A multidisciplinary study

AbstractBased on detailed stratigraphic investigations on a 200.6m long core (BGS borehole No. 81/26) from the Fladen Ground area (British sector), core material from the Sleipner field (Norwegian sector) and shallow seismic profiles between the core‐sites, the following conclusions are drawn: (1) The North Sea was glaciated sometime during th elaterpart of Matuyama reversed period. A complete glacial‐interglacial‐glacial cycle is recorded in these sediments. (2) In a period of marine sedimentation in the Middle Pleistocene, a transgression‐regression cycle under boreal‐arctic regime is recorded. (3) The Fladen area has subsided between 0.9 and 0.6 m/ka through the later parts of the Quaternary (4) A major glacial event dated at between 130 and 200 ka is recorded as a thick till unit in 81/26. This till, which was deposited by ice moving from the southwest (Scotland), probably represents a period when the Scandinavian and British ice sheets coalesced in the North Sea. (5) Based on the seismic data and the stratigraphy of the Sleipner core, an ice‐free, open embayment/dry land is favoured for the central North Sea during the Late Weichselian. (6) From the amino‐acid data, it is shown that there has been an episodic style of sedimentation through the Quaternary. (7) of the investigated sediments (which span the last 1 mill. year) ca 98% have been deposited under arctic to boreal‐arctic conditions.

Large‐volume rhyolite ash flow eruptions and submarine caldera collapse in the Lower Mesozoic Sierra Nevada, California

The Mineral King roof pendant in the southern Sierra Nevada, California, provides a view of a Triassic and early Jurassic submarine caldera complex which was tilted to vertical and intruded by middle Cretaceous granitoids. An estimated 90 km3 of rhyolitic and 10 km3 of andesitic volcanic rocks are interstratified with marine sandstones, siltstones, limestones, and conglomerates. Periods of volcanotectonic activity alternated with periods of marine sedimentation, Volcanic eruptions at Mineral King resulted in (1) deposition of widespread, very thick sheets of rhyolite ash flow tuff and (2) construction of small (1–8 km3) andesitic stratocones. Growth faults, fault talus aprons, slide blocks, slumps, and debris flows found in association with these volcanic deposits indicate that the eruptive phases represent periods of great seismic activity. Interuptive phases were periods of volcanic and tectonic quiescence during which sequences of shallow to deep marine sediments were deposited. Four different times at Mineral King, eruption of large volumes of rhyolite ash flow tuff resulted in catastrophic caldera collapse and ponding of single ash flow tuffs to thicknesses greater than 0.5 km. Only minimum volumes can be estimated for three of these intracaldera tuffs because they are truncated by younger granites. Volumes are estimated to be at least 25 km3 each, placing these tuffs in the lower size range of epicontinental ring structures. The fourth caldera, the Vandever Mountain caldera, is entirely preserved in the roof pendant. The vertically dipping strata of the Vandever Mountain caldera provide an unusual opportunity to examine a submarine caldera in cross section. Evidence for caldera subsidence during the eruption of the Vandever Mountain rhyolite ash flow tuff includes the following: (1) the great thickness of the ash flow tuff and the rapid accumulation of the tuff during progressive draw‐down of a compositionally zoned magma chamber, (2) high‐angle faults which pond the ash flow tuff and offset underlying but not overlying stratigraphy, and (3) megabreccia and slide blocks up to 0.5 km long that were derived from the caldera wall and floor and incorporated into the ash flow tuff as it filled the caldera. Disruption of the caldera floor was intense near the caldera margin but negligible along most of its length, owing to pistonlike subsidence of an intact cylinder of crust. Small‐volume ash flow eruptions occurred along an incipient, “leaky” ring fracture zone prior to the caldera‐forming eruption of the Vandever Mountain ash flow tuff. The Vandever Mountain caldera was not affected by resurgent doming or late stage rhyolite magmatism in the cross‐sectional view provided by the Mineral King roof pendant.

General Outlines of Epeirogenesis and Sedimentation in Region Between Safaga, Quseir, and Southern Wadi Qena Area, Eastern Desert, Egypt

The Egyptian region of the Red Sea depression attained its present configuration primarily as a result of a series of epeirogenic movements. The area between Quseir, Safaga, and the southern part of Wadi Qena was subjected to a series of alternations between major faulting and regional uplift. Structurally, the basement complex of the Red Sea mountain range (west side of Red Sea) constitutes a major horst with a general Erythrean structural direction (northwest-southeast). East of the horst, toward the Red Sea coast, is a group of step faults, ranging in age from post-early Eocene to Pleistocene-Recent. These main faults were shoreline zones during periods of marine sedimentation. The whole area was subjected to successive uplifts, forming an anteclise whose axis parallel d the present Red Sea mountain range.