13 research outputs found
Down-Dip Termination of the Carboniferous Ross Fan System in the Inner Shannon Area, Western Ireland - New Insight from Core and Outcrop
IAS Annual Meeting, 20 - 24 June 2015Scattered outcrops and limited borehole data in the inner Shannon estuary and mid-Clare are critical to constrain the down-dip extension of the Ross system. Previous outcrop studies have described a much thinner Ross section at Inishcorker and Foynes (over 50 km east of the Ross type section on the Loop Head) involving only the youngest Ross cycles in the west. A re-interpretation of the inner Shannon outcrops is now possible given a new GSI 09/04 borehole in the Inishcorker area, a re-analysis of Foynes Island sections and new biostratigraphic dat
Flow transformations and mud partitioning across submarine fan fringes
Highly efficient sediment gravity flows can bypass mid-fan channels and lobes and deposit significant volumes of sand, mud, and particulate organic matter in outer-fan and basin-plain settings. The Serpukhovian to Bashkirian fill in the Shannon Basin, western Ireland, includes deep-water fan deposits (Ross Sandstone Fm) that gradationally overlie basin-floor shales (Clare Shale Fm). As part of a broader progradational succession, the upward transition from muddy basin floor to sandy fan preserves the stacked deposits of settings present prior to, and outboard of, mid-fan channels and lobes. Three fully cored boreholes and associated wireline data constrain the facies tracts in an 18-km-long panel oriented oblique to original depositional dip. Two distal successions dominated by hybrid event beds (HEBs) are recognized, separated by a prominent condensed section. The lower Cos-heen system includes m-thick, tabular HEBs with prominent linked debrites that pass down dip into much thinner sandstones overlain by sand-speckled mudstone caps that thicken distally before thinning. The latter are interpreted as secondary mudflows released following reconstitution of more thoroughly mixed sections of the up-dip linked debrites. Significant bypass and accumulation of mud by this mechanism helped heal local topography and maintain a relatively flat sea floor, promoting an overall tabular geometry for the deposits of larger volume hybrid flows reaching the distal sector of the basin. The overlying distal Ross system fringe is characterized by very fine- to fine-grained sandstones and is lateral to compensationally stacked lobes farther to the west. It has a progradational (at least initially) stacking pattern, facies transitions developed over shorter length scales, and includes outsized event beds, but these are thinner than those in the Cosheen system. Common banding and evidence for turbulence suppression by dispersed clay rather than entrained mud clasts indicate that these were transitional flows. In this case, event beds are inferred to taper distally, with significant mud emplaced by plug flow retained as caps to sandy event beds rather than bypassing down-dip. Different flow transformation mechanisms thus impacted how mud was partitioned across the fringe of the two systems, and this influenced bed geometries, larger scale bed stacking patterns, and stratigraphy. Whereas the flow-efficiency concept stresses the ability of flows to carry sand in a basinward direction, it is also imperative to consider the variable efficiency of mud transport given the operation of clay-induced flow transformations. These can either promote bypass or trigger premature fallout of mud, with implications for how systems fill accommodation, bed-scale facies transitions, and the burial and preservation of particulate organic carbon fractionated along with the clay in deep-water system fringes.Science Foundation IrelandGeological Survey Ireland (GSI) Griffith Geoscience AwardEquinor AS
The Fosado Turbidite Channel Complex (Eocene, South-Central Pyrenees, Spain)
BSRG Annual Meeting, Hull, United Kingdom, 18-21 December, 2013In the Ainsa basin, the Castissent sequence has been subdivided
in two different composite depositional sequences: Castissent-1 (Cs-1) and
Castissent-2 (Cs-2). This study focuses on the lower part of Cs-1, where the
Fosado Channel Complex lies. Cs-1 was deposited synchronously with a high-deformation
phase in the Pyrenean orogeny (Upper Ypresian to Lower Lutetian), with strong tectonic
reactivation of the South-Central Pyrenean Unit; sediments were affected by the
Atiart thrust (east) and later on by Los Molinos thrust (west). So far, the
knowledge about Cs-1 was mainly its stratigraphic position within the Torla
turbidite system, its physical correlation with the fluvio-deltaic feeding
system of Castissent Fm. s.s., as
well as its facies detail of the uppermost individual channel (the Fosado
channel, s.s.), which has been used as
a facies model for channel margin settings. Nevertheless, its high resolution
stratigraphic study, its facies associations and architecture, still remains
unknown in detail. Therefore, it has been possible to map and redefine the
extension of the Atiart unconformity in the hanging wall of Los Molinos thrust.
This 3rd order sequence boundary at the base of Cs-1 separates: (1)
a lower mud-dominated unit, with a high content in debris flow deposits and
fine-grained turbidites; and (2) the upper unit, mainly composed by a
channel-overbank complex (channel-levee), forming sandy packages belonging to
highly-heterogeneous channels. In the stacking pattern of the Fosado complex two
main growing stages have been identified: Cs-1a and Cs-1b. Cs-1a displays a
relatively high percentage of sand content in individual channels; on the
contrary, Cs-1b is a mud-dominated unit, mainly composed by fine-grained channels
and their related overbank deposits. This last unit would be the lowermost part
of the slope fan related with the Castissent deltas. Consequently, the
study has focused on the channel complex of Cs-1a unit, where a stacking
pattern with unconformities is described and has led to organize it hierarchically
in five 4th-order sequences (high resolution seismic scale). Each channel group
shows a nested stacking pattern, with hyperconcentrated flow deposits at the
base, and lateral and vertical accretion (up to 200x20 m), which is probably
indicative of large-scale high-sinuosity channels.UAB - Stratigraphy Grou
Sedimentology of the upper Ross Formation (Pennsylvanian) in borehole GSI 09/05 at Ballybunion, Co. Kerry
Irish Geological Research Meeting, March 1 - 3, 2013, University of Ulster, Magee College, Derry, Northern IrelandThe Pennsylvanian Ross Sandstone Formation is well
exposed around the Shannon Estuary, in western Ireland. It forms the deep-water
part of a major shallowing-upward succession filling the Clare Basin and it has
been extensively used as a turbidite reservoir analogue and for subsurface
training.
Since 2009, a major program of behind-outcrop drilling
targeting the Ross Sandstone Formation has been undertaken in west Co. Clare (Loop
Head) and across the Shannon estuary in Co. Kerry. To date, most of the focus has been on boreholes acquired on Loop Head. These
have provided a composite vertical section through the Ross Sandstone Formation
and a framework for interpreting bed type variations and overall system
evolution. Now, the emphasis is changing to examine lateral variability away
from Loop Head using a new core at Ballybunion in the lowermost Ross Sandstone
Formation, together with legacy data and two recent GSI slim-holes (at
Inishcorker and Ballybunion).
This poster focuses on first results from the GSI 09/05 borehole,
located c.4.3 km north of Ballybunion town. This 150
m long slim-hole core intersects the upper Ross Formation as confirmed by
correlation with a measured outcrop section on the adjacent cliff c.1.2 km away.
Correlation is based on goniatite-rich "marine bands", distinctive thick
sandstone units and slump bodies. Three marine bands are identified, the
uppermost being unusually thick (c.4.5 m) and provisionally equated with the R. paucicrenulatum
band marking the top of the Ross Sandstone Formation on Loop Head. The core
records an upward transition from well-bedded sandstones (turbidites and
subordinate hybrid event beds) interpreted as stacked lobe deposits to more
amalgamated sandstones towards the top of the formation indicating increased
channelisation. A major composite slump body (25 m thick) occurs below the
central marine band. This remobilised both sand-prone and silty deposits and is
significantly thicker than any of the slump units identified in the Loop Head
cores and outcrop.Four-year Griffith Geoscience funded PhD StudentshipFour-year Griffith Geoscience funded PhD StudentshipConference website: http://www.igrm2013.info/AD 08/01/201
Facies and internal stratigraphic variability in the Ross Sandstone Formation (Pennsylvanian), western Ireland - new borehole data from south of the Shannon Estuary
30th IAS Meeting of Sedimentologists, Manchester, United Kingdom, 2-5 September, 2013The 500 m thick Ross Sandstone Formation is well
exposed in sea cliffs facing the Atlantic and along the Shannon Estuary in
western Ireland. It forms the sandy deep-water part of a major
shallowing-upward Pennsylvanian succession. Over the last four years, a major
behind-outcrop drilling program targeting the Ross Sandstone Formation has been
undertaken, focussing primarily on the Loop Head peninsula in west Clare. This
has provided a full composite Ross cored section that underpins a new understanding
of bed-scale variability and the wider evolution of the system. The focus has
recently shifted to the key Ballybunion section on the south side of the River Shannon,
obliquely down-dip from the Loop Head area (c. 18 km from the tip of the Loop)
and is important in that previous outcrop studies have inferred that (1) the
distinctive character of the lower Ross here with its abundant hybrid event
beds may reflect a marginal position; and (2) extra sandy section may be present
in the uppermost Ross due to offset stacking of the youngest sandy lobes. Two
new cores are now available ¿behind¿ the Ballybunion section - a 200 m PQ
borehole straddling the lower Ross and the upper part of the underlying Clare Shale
Formation (12-CE-UCD-09), and a 151.5 m long, cored slimhole with associated
wireline log data acquired by the Geological Survey of Ireland (GSI 09/05). The
latter is 1.1 km along strike from coastal exposures of the upper Ross and the
study reported here focusses on the relationship of the section acquired in
this borehole to the local cliffs and to upper Ross outcrops on the north side
of the River Shannon at Kilcredaun, some 4.6 km away. Correlation is based on
goniatite-rich ¿marine bands¿, legacy biostratigraphic data (new determinations
are underway), and a number of laterally extensive slump bodies which form
distinctive marker beds.
The GSI 09/05 core contains three thin goniatite-rich
levels, and a fourth candidate level, each interpreted as marine bands. These
separate sand-prone packages, interpreted as stacked isolated to amalgamated
lobe units, and at least two mass-transport units (MTDs), the lower and
thickest of which is 25.5 m thick (true thickness). In the local cliffs to the
west, all four marine bands can be identified, as well as the two MTDs. In
addition, a third MTD is more obvious in the cliff. The lobe sandstones are
dominated by deposits of high-density turbidity currents; amalgamated
sandbodies become more abundant upwards. Hybrid event beds are rare (<10%)
compared to lower in the formation. At least 50% of the sandbodies extend from
the core to the adjacent outcrop without change; the remainder show a change
from deposition from high- to low-concentration flows or vice versa. Overall,
the Ballybunion Ross section is 480 m thick, broadly similar to the thickness established
by drilling on the Loop. At longer length scales, all but the upper marine band
are found at Kilcredaun. Correlatives of the two MTD units also occur in the
core here, although the thickest slump has become thinner and muddier.
Nonetheless this MTD unit can be traced widely across the Loop as a distinctive
couplet. As correlated, the Ballybunion outcrop and core suggest there may not
be an additional younger sandbody in this area, however the location appears
axial and down-dip rather than marginal in character overall.Four-year Griffith Geoscience funded PhD StudentshipDM, 3/12/201
Facies Trends and Large-Scale Architecture of the Pennsylvanian Ross Formation, Western Ireland - New Insight from Cores South of the Shannon
BSRG Annual Meeting, Hull, United Kingdom, 18-21 December, 2013The Ross Formation is well exposed in sea cliffs facing the Atlantic and Shannon estuary
in western Ireland. It forms the sandy deep-water part of a major
shallowing-upward Pennsylvanian succession. Over the last four years, a major
behind-outcrop drilling program targeting the Ross Formation has focussed
primarily on the Loop Head peninsula in west Clare. This has provided a composite
Ross cored section (490 m thick) that underpins a new understanding of bed-scale
variability and the wider vertical evolution of the system. The focus has now shifted
to the key Ballybunion section on the south side of the Shannon, which sits obliquely
down-dip (to the east) of the Loop Head area (c. 18 km away). This area is
important in that previous outcrop studies have suggested that (1) the
character of the lower Ross with its abundant hybrid event beds may reflect a
marginal fringe position; (2) an extra sandy section may be present in the uppermost
Ross due to offset stacking of the youngest lobes and (3) some of the upper
Ross mass transport units may extend across the estuary from Clare. Two new
cores are now available ¿behind¿ the Ballybunion cliff section: a 200 m long PQ
borehole straddling the lower Ross and the upper part of the underlying Clare Shale
(12-KY-UCD-09), and a 151.5 m long slimhole core acquired by the Geological
Survey of Ireland (GSI 09/05). In addition, a re-analysis of the
biostratigraphy is underway. Together the matched pair of Kerry boreholes with
the outcrop section provide a reference section (480 m thick) that can be
compared with the Loop composite section. Both sections have a distinctive
precursor cycle involving first stacked thin mudflows and then outsized and coarse
grained hybrid event beds. The muddier make-up of the latter at Ballybunion is
consistent with a down-dip position based on trends in other basins. The onset of
the main Ross system that follows is sandier at Ballybunion than at Loop
suggesting the former was more axial at this time. Thereafter hybrid event beds
appear not to be as important at Ballybunion. Several of the mass transport
units and condensed sections extend across the Shannon and tie the sections.Four-year Griffith Geoscience funded PhD StudentshipCheck if there are siginficant differences from identically entitled paper presented at a different conference 2013-12-02 JGDM, 3/12/201
Down-dip Termination of Sandy Fan Systems - New Insight from the Pennsylvanian Ross Sandstone Formation, Western Ireland
AAPG General Meeting, Calgary, Alberta, Canada, 19 - 22 June 2016The Pennsylvanian Ross Sandstone Fm. in western Ireland forms part of a thick (>2200m) progradational and shallowing-upward basin-fill succession. New and legacy borehole constraints and outcrop work on the eastward extension of the Ross help constrain the down-dip character at different levels in the fan stack
Hybrid Event Bed Character Across the Clare Shale - Basal Ross Formation Contact, Western Ireland - New Insight from Behind-Outcrop Cores
British Sedimentological Research Group (BSRG) AGM, Nottingham, UK, 21 - 22 December 2014A recent behind - outcrop drilling program targeting the Ross Formation has focussed on the Loop Head peninsula in west Clare. This has provided a fully-cored composite Ross section (490 m thick) that underpins a new understanding of bed-scale variability and the vertical evolution of the system . The work programme h as now been broadened to include the key Ballybunion section on the south side of the Shannon which sits obliquely down-dip (to the east) of Loop Head (c. 18 km away)
The Clare Shale - Basal Ross Formation Contact, Western Ireland - New Insight from Behind-Outcrop Cores
Irish Geological Research Annual Meeting, NUI Galway, Galway, Ireland, 19 - 21 February 2015A recent behind - outcrop drilling program targeting the Ross Formation has focussed on the Loop Head peninsula in west Clare. This has provided a fully-cored composite Ross section (490 m thick) that underpins a new understanding of bed-scale variability and the vertical evolution of the system . The work programme h as now been broadened to include the key Ballybunion section on the south side of the Shannon which sits obliquely down-dip (to the east) of Loop Head (c. 18 km away)
Down-dip Termination of Sandy Fan Systems - New Insight from the Pennsylvanian Ross Sandstone Formation, Western Ireland
British Sedimentological Research Group (BSRG) AGM, Keele University, UK, 19 - 22 December 2015New and legacy borehole constraints and outcrop work on the eastward extension of the Ross Formation help constrain the down-dip character of the fan stack