Sedimentary geology and stratigraphy

Neoproterozoic deglacial sediments and their hydrocarbon source rock potential

by Daniel Le Heron

Le Heron, D.P., Craig, J. (in press). In: Glaciogenic Reservoirs. Geological Society, London, Special Publications.

Considerable interest is awakening in Neoproterozoic petroleum systems, which represent a frontier research area in... more Considerable interest is awakening in Neoproterozoic petroleum systems, which represent a frontier research area in the Earth Sciences. Many strata deposited during the Cryogenian have a role to play in such petroleum systems, with viable source rocks and live oils, despite deposition before the evolution of most extant clades. Life forms likely to have contributed, in variable concentrations, to Neoproterozoic hydrocarbon source rocks include eukaryotic microalgae, bacteria, chlorophyte micoalgae, marine pelagophyte algae and dinoflagellates. The glaciations of a“Snowball” or “Slushball” Earth, or deposited under a “Zipper Rift” scenario, are believed to be intimately associated with the deposition of hydrocarbon source rocks. Deglaciation may have culminated in anoxic basins, with high TOC shales and “cap carbonates” deposited in depressions carved by ice sheets or alternatively deposited in restricted half graben a Rodinia began to fragment. One such example is the case of post-Sturt glaciation shales and dolostones in the Centralian Superbasin, an amalgam of basins almost continent-wide in Australia. In the southen part of this superbasin, data from the Marmot MMDD-1 drillcore (Stuart Shelf) together with published data on organic enrichment in the central part of the superbasin (Amadeus Basin), are used to infer the existance of a major organically-enriched mud blanket resulting from Sturtian deglaciation. 

Neoproterozoic-Devonian stratigraphic evolution of the eastern Murzuq Basin, Libya: a tale of tilting in the central Sahara

by Daniel Le Heron

Le Heron, D.P., Meinhold, G., Bergig, K. in press. basin Research, doi: 10.1111/j.1365-2117.2012.00555.x

The Murzuq Basin is one of the most petroliferous basins of North Africa. Its remote eastern flank, has been largely... more The Murzuq Basin is one of the most petroliferous basins of North Africa. Its remote eastern flank, has been largely ignored since early reconnaissance work in the 1950s and 1960s. This paper presents new stratigraphic and sedimentological data on the Neoproterozoic through Devonian succession from the Mourizidie and Dor el Gussa regions. The Neoproterozoic to Cambrian Mourizidie and Hasawnah formations in the eastern part of the Mourizidie dip to the east and north-east, resting directly on late Precambrian metasediments and granitoids. These strata record the initial progradation of sand-dominated braidplain systems upon peneplained Precambrian basement. Rhyolite clasts in the Hasawnah Formation may record tectonically driven uplift and unroofing in the southern Tibesti Massif or tectonomagmatic rejuvenation to the south of this massif. In the western part of the Mourizidie region, Late Ordovician through Silurian strata (Mamuniyat and Tanezzuft–Akakus formations) directly overlie late Precambrian metasediments and granitoids, and dip at a low angle toward the west into the Murzuq Basin. Elsewhere at the eastern Murzuq Basin flank, in Dor el Gussa, Late Ordovician glaciogenic sediments rest with angular unconformity upon shallow marine sandstones of Cambrian–Ordovician age. This angular unconformity may also occur in the Mourizidie region and indicates widespread tectonism, either as a result of a Middle–Late Ordovician orogenic event, far-field tectonism related to the opening of the Rheic Ocean along the northern margin of Gondwana, or alternatively crustal depression associated with the growth of Late Ordovician ice sheets. Unconformity development was also probably associated with glacial incision. Following ice sheet retreat, isostatic rebound during deglaciation resulted in uplift of tens to hundreds of metres, locally removing all Cambrian and Ordovician formations. Rising sea levels in the Silurian led to deposition of the Tanezzuft Formation on Precambrian basement in the northwestern Mourizidie region.

I DEPOSITI DEL PLEISTOCENE INFERIORE DELLA BASSA VAL DI CECINA (TOSCANA, ITALIA): RICOSTRUZIONE STRATIGRAFICO–DEPOSIZIONALE E PROPOSTA DI SUDDIVISIONE IN UNITA’ ALLOSTRATIGRAFICHE

by Florence ReSeT

Giovanni Sarti, Andrea Ciampalini, Ilaria Consoloni & Andrea Cerrina Feroni

Fault array evolution in extensional basins: insights from statistical analysis of gravel deposits in the Cecina River (Tuscany, Italy)

by Florence ReSeT

Andrea Ciampalini, Ilaria Consoloni, Giovanni Sarti

Two statistical analyses of gravel clasts from the Lower Pleistocene deposits in the Lower Cecina Valley (Tuscany,... more Two statistical analyses of gravel clasts from the Lower Pleistocene deposits in the Lower Cecina Valley (Tuscany, Italy) have been combined to unravel changes in the palaeo-drainage system. Data from 16 outcrops were collected and 6400 clasts described. Facies analysis, micro-palaeontology and macro-palaeontology and petrographic characteristics of the gravel deposits have highlighted the presence of three allostratigraphic units. Clast lithology is the main discriminator among these units. Cluster and principal component analyses of the 6400 clasts have improved understanding of the stratigraphy of the Lower Pleistocene deposits and constrain the re-routing of the lower palaeo-Cecina River from a supposedly south-east to north-west direction to the present east to west direction. Short rivers feeding small fan deltas represented by the oldest allostratigraphic units were abandoned in the Lower Pleistocene, when the re-routing of the Cecina River caused the capture of these streams. This evolution suggests a change in the tectonic regime of the area. The fan deltas developed on the hanging wall of normal faults sub-parallel to the coast; a change to a transtensile tectonic regime caused the deviation of the main river channel toward the present coast and the formation of a pull-apart basin, which is now exploited by the Cecina River. This study illustrates the value of lithological analyses of gravel deposits for understanding the tectonic evolution of an area.

BURIAL DATING OF LATE-CENOZOIC DEPOSITS USING IN-SITU PRODUCED COSMOGENIC NUCLIDES

by Florence ReSeT

Andrea Ciampalini, Cristina Persano, Derek Fabel, Marco Firpo

Dating the Miocene to Pleistocene deposition of fluvial and deltaic sediments is often difficult because of the... more Dating the Miocene to Pleistocene deposition of fluvial and deltaic sediments is often difficult because of the absence of suitable biostratigraphic markers. Temporal limits on sediment deposition, however, are fundamental constraints in many geological, geomorphological, stratigraphical and archeological studies. In particular a dated stratigraphy of sedimentary basins provides information about timing of evolution of the sediment source and routing system due to tectonics, sea-level and/or climate changes. Traditional techniques, such as luminescence, radiocarbon dating of organic material, etc. only permit us to date sediments that are no older than ~250,000 years. Recently a method for dating sediment burial using the radioactive decay of cosmogenic nuclides 26Al and 10Be has been developed. 26Al and 10Be are produced by the continuous bombarding by high-energy cosmic rays of the Earth surface where they penetrate into rocks and sediments at a depth that varies, depending on rock density, between 2 and 3 m. The long half-life of the 26Al (7.05X105 yr) and 10Be (1.5X106 yr) make them optimal for dating sediments that were deposited over the past five million years, as long as the sediments were at the surface and exposed to cosmic rays before sedimentation and burial. The sediments that can be dated using the cosmogenic isotopes technique need to have the following characteristics: (1) quartz needs to be present and have been exposed at the surface for a time necessary to accumulate measurable cosmogenic radionuclides concentration (i.e., depending
on latitude and altitude, at least ~ 200 years); (2) transport time needs to have been negligible (3) burial was rapid and deep (>10 m) to avoid cosmogenic nuclides production after deposition, otherwise a correction needs to be introduced. This method is useful in many Italian areas where deltaic or fluvial Miocene to Pleistocene deposits crop out.

The use of multivariate statistics to determine the paleoenvironmental distribution of Lower Carboniferous Foraminifera from Ireland

by Stephen Gallagher

Late Dinantian (Lower Carboniferous) platform carbonate stratigraphy of the Buttevant area North Co. Cork, Ireland

by Stephen Gallagher

A thick sequence of late Dinantian (Asbian±Brigantian) carbonates crop out in the Buttevant area, North Co. Cork,more A thick sequence of late Dinantian (Asbian±Brigantian) carbonates crop out in the Buttevant area, North Co. Cork,
Ireland. A mud-mound unit of early Asbian age (the Hazelwood Formation) is the oldest unit described in this work.
This formation is partly laterally equivalent to, and is overlain by, over 500 m of bedded platform carbonates which
belong to the Ballyclogh and Liscarroll Limestone Formations. Four new lithostratigraphic units are described within
the platform carbonates: (i) the early Asbian Cecilstown Member and (ii) the late Asbian Dromdowney Member in
the Ballyclogh Limestone Formation; (iii) the Brigantian Templemary Member and (iv) the Coolbane Member in the
Liscarroll Limestone Formation.
The Cecilstown Member consists of cherty packstones and wackestones that are inferred to have been deposited below
fair-weather wavebase. This unit overlies and is laterally equivalent to the mud-mound build-up facies of the Hazelwood
Formation. The Dromdowney Member is typi®ed by cyclic-bedded kamaenid-rich limestones possessing shell bands,
capped by palaeokarst surfaces, with alveolar textures below and shales above these surfaces. The carbonates of this unit
were deposited at or just below fair-weather wavebase, the top of each cycle culminated in subaerial emergence. The
Templemary Member consists of cyclic alternations of subtidal crinoidal limestones capped by subtidal lagoonal crinoid-
poor, peloidal limestones possessing coral thickets. Intraclastic cherty packstones and wackestones characterize the
Coolbane Member, which is inferred to have been deposited below fair-weather wavebase but above storm wavebase.
The early Asbian Cecilstown Member has a relatively sparse micro- and macrofauna, typi®ed by scattered Siphono-
dendron thickets, archaediscids at angulatus stage and common Vissariotaxis. Conversely, macro- and microfauna is
abundant in the late Asbian Dromdowney Member. Typical late Asbian macrofossils include the coral Dibunophyllum
bipartitum and the brachiopod Davidsonina septosa. The base of the late Asbian (Cf6g Subzone) is recognized by the ®rst
appearance of the foraminifers Cribrostomum lecompteii, Koskinobigenerina and the alga Ungdarella. The Cf6g Subzone
can be subdivided into two biostratigraphic divisions, Cf6g1 and Cf6g2, that can be correlated throughout Ireland.
Relatively common gigantoproductid brachiopods and the coral Lonsdaleia duplicata occur in the Brigantian units. The
base of the Brigantian stage (Cf6d Subzone) is marked by an increase in the abundance of stellate archaediscids,
the presence of Saccamminopsis-rich horizons, Loeblichia paraammonoides, Howchinia bradyana and the rarity of
Koninckopora species.
Changes in facies at the Cecilstown/Dromdowney Member and the Ballyclogh/Liscarroll Formation boundaries
coincide closely with the changes in fossil assemblages that correspond to the early/late Asbian and the Asbian/Brigantian
boundaries. These facies changes are believed to re¯ect major changes in relative sea-level on the Irish platforms. The sea-
level variations that are inferred to have caused the facies changes at lithostratigraphic boundaries also brought in the new
taxa that de®ne biostratigraphic boundaries. Moreover, many of the Dinantian stage boundaries that are de®ned bio-
stratigraphically in Great Britain, Belgium and the Russian Platform also coincide with major facies boundaries caused
by regressive and transgressive episodes. The integration of detailed biostratigraphic analyses with facies studies will lead
to better stratigraphic correlations of Dinantian rocks in northwest Europe.

he stratigraphy and cyclicity of the late Dinantian platform carbonates in parts of southern and western Ireland

by Stephen Gallagher

Foraminiferal biofacies of the Miocene warm to cool climatic transition in the Port Phillip Basin, Southeastern Australia

by Stephen Gallagher

Tertiary "deep lead" palaeoriver systems and their relationship to basin evolution, Victoria

by Stephen Gallagher

Revised Mid to Late Eocene Stratigraphy and architecture of the margins of the Eucla and Bremer Basins

by Stephen Gallagher

Lower Carboniferous (Late Visean) platform development and cyclicity in southern Ireland: foraminiferal biofacies and lithofacies evidence

by Stephen Gallagher

Sonic velocity, submarine canyons and burial diagenesis in Oligocene-Recent cool water carbonates, Gippsland Basin, SE Australia

by Stephen Gallagher

he Miocene palaeoenvironmental and palaeoceanographic evolution of the Gippsland Basin, Southeast Australia; a record of Southern Ocean change

by Stephen Gallagher

Controls on Seaspray Group sonic velocities in the Gippsland Basin a multidisciplinary approach to the canyon "seismic velocity problem

by Stephen Gallagher

Fault array evolution in extensional basins: insights from statistical analysis of gravel deposits in the Cecina River (Tuscany, Italy)

by Ilaria Consoloni

ANDREA CIAMPALINI, ILARIA CONSOLONI, GIOVANNI SARTI. Sedimentolgy, 58, 1895-1913

Two statistical analyses of gravel clasts from the Lower Pleistocene deposits in the Lower Cecina Valley (Tuscany,... more Two statistical analyses of gravel clasts from the Lower Pleistocene deposits in the Lower Cecina Valley (Tuscany, Italy) have been combined to unravel changes in the palaeo-drainage system. Data from 16 outcrops were collected and 6400 clasts described. Facies analysis, micro-palaeontology and macro-palaeontology and petrographic characteristics of the gravel deposits have highlighted the presence of three allostratigraphic units. Clast lithology is the main discriminator among these units. Cluster and principal component analyses of the 6400 clasts have improved understanding of the stratigraphy of the Lower Pleistocene deposits and constrain the re-routing of the lower palaeo-Cecina River from a supposedly south-east to north-west direction to the present east to west direction. Short rivers feeding small fan deltas represented by the oldest allostratigraphic units were abandoned in the Lower Pleistocene, when the re-routing of the Cecina River caused the capture of these streams. This evolution suggests a change in the tectonic regime of the area. The fan deltas developed on the hanging wall of normal faults sub-parallel to the coast; a change to a transtensile tectonic regime caused the deviation of the main river channel toward the present coast and the formation of a pull-apart basin, which is now exploited by the Cecina River. This study illustrates the value of lithological analyses of gravel deposits for understanding the tectonic evolution of an area.

Fault array evolution in extensional basins: insights from statistical analysis of gravel deposits in the Cecina River (Tuscany, Italy)

by Andrea Ciampalini

A. CIAMPALINI, I. CONSOLONI, G. SARTI, Sedimentology 58, Issue 7, pages 1895–1913, 2011

Two statistical analyses of gravel clasts from the Lower Pleistocene deposits in the Lower Cecina Valley (Tuscany,... more Two statistical analyses of gravel clasts from the Lower Pleistocene deposits in the Lower Cecina Valley (Tuscany, Italy) have been combined to unravel changes in the palaeo-drainage system. Data from 16 outcrops were collected and 6400 clasts described. Facies analysis, micro-palaeontology and macro-palaeontology and petrographic characteristics of the gravel deposits have highlighted the presence of three allostratigraphic units. Clast lithology is the main discriminator among these units. Cluster and principal component analyses of the 6400 clasts have improved understanding of the stratigraphy of the Lower Pleistocene deposits and constrain the re-routing of the lower palaeo-Cecina River from a supposedly south-east to north-west direction to the present east to west direction. Short rivers feeding small fan deltas represented by the oldest allostratigraphic units were abandoned in the Lower Pleistocene, when the re-routing of the Cecina River caused the capture of these streams. This evolution suggests a change in the tectonic regime of the area. The fan deltas developed on the hanging wall of normal faults sub-parallel to the coast; a change to a transtensile tectonic regime caused the deviation of the main river channel toward the present coast and the formation of a pull-apart basin, which is now exploited by the Cecina River. This study illustrates the value of lithological analyses of gravel deposits for understanding the tectonic evolution of an area.

Post-LGM deglaciation in Pine Island Bay, West Antarctica

by Alexandra Kirshner

published in Quaternary Sciences Reviews
Co-authored with John B. Anderson, Martin Jakobsson, Matthew O’Regan, Wojciech Majewski, Frank O. Nitsche

To date, understanding of ice sheet retreat within Pine Island Bay (PIB) following the Last Glacial Maximum (LGM) was... more To date, understanding of ice sheet retreat within Pine Island Bay (PIB) following the Last Glacial Maximum (LGM) was based on seven radiocarbon dates and only fragmentary seafloor geomorphic evidence. During the austral summer 2009–2010, restricted sea ice cover allowed for the collection of 27 sediment cores from the outer PIB trough region. Combining these cores with data from prior cruises, over 133 cores have been used to conduct a detailed sedimentological facies analysis. These results, augmented by 23 new radiocarbon dates, are used to reconstruct the post-LGM deglacial history of PIB.

Our results record a clear retreat stratigraphy in PIB composed of, from top to base; terrigenous sandy silt (distal glacimarine), pebbly sandy mud (ice-proximal glacimarine), and till. Initial retreat from the outer-continental shelf began shortly after the LGM and before 16.4 k cal yr BP, as a likely response to rising sea level. Bedforms in outer PIB document episodic retreat in the form of back-stepping grounding zone wedges and are associated with proximal glacimarine sediments. A sub-ice shelf facies is observed in central PIB and spans ∼12.3–10.6 k cal yr BP. It is possible that widespread impingement of warm water onto the continental shelf caused an abrupt and widespread change from sub-ice shelf sedimentation to distal glacimarine sedimentation dominated by widespread dispersal of terrigenous silt between 7.8 and 7.0 k cal yr BP. The final phase of retreat ended before ∼1.3 k cal yr BP, when the grounding line migrated to a location near the current ice margin.

Evaluating the use of clay mineralogy, Sr-Nd isotopes and zircon U-Pb ages in tracking dust provenance: An example from loess of the Carpathian Basin

by Gábor Újvári

Gábor Újvári, Andrea Varga, Frank C. Ramos, János Kovács, Tibor Németh, Thomas Stevens (2012)
Chemical Geology 304-305, 83-96, doi: 10.1016/j.chemgeo.2012.02.007

Multiple competing hypotheses have been proposed to explain the source of loess dust in the Carpathian Basin yet none... more Multiple competing hypotheses have been proposed to explain the source of loess dust in the Carpathian Basin yet none has been demonstrated. Here bulk and grain-size differentiated Nd and Sr isotopic and bulk and clay mineralogical compositions, together with detrital zircon ages and morphologies from loess along the Danube in the Carpathian Basin are used to demonstrate that no single method is capable of unequivocally isolating sources, yet combined, they allow for discriminating likely provenance. Zircon ages indicate multiple sources for Carpathian Basin loess, restricting the use of bulk or grain-size differentiation methods. Ambiguities are further highlighted by the fact that the Sr-Nd isotopic composition of Greenland dust is very similar to Carpathian loess. This match demonstrates that such methods are not always capable of unequivocally excluding unlikely potential source areas and implies that current hypotheses regarding the origin of Greenland dust require further evaluation. Sr isotopes are also limited by high dolomite contents of loess, while palygorskite is of questionable utility as a Saharan dust indicator due to its rapid weathering under typical Carpathian climates. In terms of specific Carpathian loess sources, alluvial fans of the Danube River likely contribute, but detrital zircon ages and morphologies suggest that a proportion directly originates from eroded uplands and local rocks throughout the basin, while detrital dolomite implies local, primary sources such as the Transdanubian Range. An upper limit of 5-10% is placed on the North African contribution to fine dust in loess of the mid-Carpathian Basin based on mineralogy and grain size. Overall, results suggest that the single grain (zircon) approach is likely the most diagnostic method to identify sources in loess studies, although to solve complex provenance issues, simultaneous consideration of the isotopic characteristics of more than one heavy (or light) mineral is required.

Pleistocene palaeoecology and environmental change on the Darling Downs, southeastern Queensland, Australia

by Gilbert Price

Price, G.J., Sobbe, I.H., 2005. Pleistocene palaeoecology and environmental change on the Darling Downs, southeastern Queensland, Australia. Memoirs of the Queensland Museum 51, 171-201.

A diverse Pleistocene fossil assemblage was recovered from a site (QML1396) exposed in the southern banks of Kings... more A diverse Pleistocene fossil assemblage was recovered from a site (QML1396) exposed in the southern banks of Kings Creek, Darling Downs, southeastern Queensland. The site includes both high-energy lateral channel deposits and low-energy vertical accretion deposits. The basal fossil-bearing unit is laterally extensive, fines upward and its geometry and sedimentary structures suggest deposition within a main channel. The coarse channel fill passes upward into overbank levee deposits made up of lenticular sandy-shelly strata alternating with muds. Several taphonomic biases relating to preservation of different faunal groups and skeletal elements was discerned. Biases may be related to fluvial sorting of the assemblage, but causes for differences between the preservation and accumulation of mammal versus non-mammal terrestrial vertebrates remain unclear. In general, the vertebrate material was accumulated and transported into the deposit from the surrounding proximal floodplain. The assemblage is composed of 44 species including molluscs, teleosts, anurans, chelids, squamates, and small and large-sized mammals. Palaeoenvironmental analysis suggests that a mosaic of habitats, including vine thickets, scrublands, open sclerophyllous woodlands interspersed with sparse grassy understories, and open grasslands, were present on the floodplain during the late Pleistocene. From sedimentological and ecological data, it is evident that increasing aridity during the late Pleistocene led to woodland and vine thicket habitat contraction, and grassland expansion on the floodplain. At present, there is no evidence to support the suggestion that the retraction of late Pleistocene Darling Downs habitats was due to anthropogenic factors.