Kevin T. Pickering

Deep-water facies, processes and models: a review and classification scheme for modern and ancient sediments

Abstract A review of previous work on modern and ancient deep-water facies, processes and models is presented with a new classification scheme involving 40 distinct facies related to 15 conceptually distinct facies groups. These facies are fixed points in a spectrum of facies generated in a process continuum from resedimentation processes, through semi-permanent bottom-currents, to pelagic settling. In essence, the scheme is descriptive of the sedimentary attributes of sediments, although it is designed to aid interpretation of possible sediment transport/deposition processes. The classification scheme is three-tier with facies classes, groups and constituent facies, and is hierarchical to allow flexibility in its use. There are seven facies classes, with Classes A–E defined largely on the basis of grain-size differences, Class F on the basis of internal organization, and Class G on composition. The facies classes are: Class A, gravels, muddy gravels, gravelly muds, and pebbly sands, with ⩾ 5% gravel grade; Class B, sands, with ⩾ 80% sand grade and 80% mud, ⩾ 40% silt and 0–20% sand; Class E, muds and clays, with ⩾ 95% mud grade, For the purpose of large-scale mapping or reconnaissance fieldwork, either the level of facies classes or groups may be appropriate, whereas for more detailed sedimentology the more detailed facies level will be necessary.

Architectural Elements and Growth Patterns of Submarine Channels: Application to Hydrocarbon Exploration

Modern and ancient submarine channels show a wide range of architectural styles. Architectural element analysis is a useful descriptive means to characterize the type of channel fill, show the interconnectivity and lateral continuity of sand bodies, and interpret the causal sedimentary processes. This paper combines a review of the literature on submarine channels with new observations and analysis, and proposes architectural element models for submarine channels, in particular, demonstrating how these models can be applied to interpreting the sequential fill of ancient submarine channels. Data for the dimensions and degrees of lateral continuity and vertical connectivity of channel elements, such as those giving rise to reservoir heterogeneities in hydrocarbon exploratio , are presented for a variety of examples of architectural elements, providing quantitative information for reservoir analog models.

Sediment deformation and hydrogeology of the Nankai Trough accretionary prism: Synthesis of shipboard results of ODP Leg 131

The main objective of Leg 131 was to provide data on the deformational processes and associated hydrogeology of the Nankai prism toe. Drilling succeeded, for the first time in the history of ocean drilling, in penetrating the complete sedimentary sequence to basaltic basement, reaching 1327 mbsf (metres below seafloor) with good core recovery (55%). Excellent correlation of the lithology and structure, including the frontal thrust and the decollement, with seismic reflection images was also determined. Bedding dips, faults and shear bands analyzed in the cores confirm the pattern of deformation to be mainly due to NW-SE shortening, as expected from the plate tectonic convergence vector. Below the decollement, no significant deformation features were observed, indicating that the decollement is a sharp discontinuity in stress transmission. Physical properties data show major discontinuities at the decollement, notably an increase in porosity below the later. This may indicate excess pore pressure in the subducted section and decollement zone. A less marked increase in porosity below the frontal thrust may reflect the youthfulness of this feature. Attempts to make downhole measurements were severely hampered by unstable hole conditions, but useful constraints have been placed on the thermal regime, and some calibration of laboratory physical properties toin-situ conditions has been provided, andin-situ stress and pore pressure were measured in the uppermost sediments. Evidence of channelized fluid flows is inconclusive. No sharp geochemical signatures or unequivocal geochemical anomalies indicative of channelized fluid flow were found. Thermal measurements are not significantly different from those predicted by a purely conductive heat flow model. A signature of low chloride pore water near the decollement may partly be related to smectite diagenesis but may also be due to episodic fluid flow events. We conclude that dewatering probably occurred dominantly through diffuse flow throughout the accreted sediments at this site.

Quantitative analysis of the geometry of submarine channels: Implications for the classification of submarine fans

Certain attributes of submarine channels measured from GLORIA sidescan sonar data from 16 different submarine fans indicate similarities with fluviatile systems. Channel width, depth, meander radius and wavelength, sinuosity, and gradient were measured. This approach makes it possible to identify high- sinuosity, low-gradient (e.g., Indus Fan channels) and low-sinuosity, high- gradient (e.g., Porcupine Seabight channels) channel systems as end members. Current classifications of submarine fans relate fan shape to grain size or sediment caliber and therefore are inadequate, principally because the shape of the fan is strongly controlled by the shape of the receiving basin, which in turn is dependent upon parameters such as tectonics and diapirism. Overall fan shape is almost invariably independent of the physics of sediment transport. Rather than fan shape, the geometry and other characteristics of submarine channels and canyons provide a more promising means of differentiating deep- marine turbidite systems.

Late Ordovician–early Silurian destruction of the Iapetus Ocean: Newfoundland, British Isles and Scandinavia—a discussion

The available data from Newfoundland, the British Isles and Scandinavia suggest that by late Ordovician–early Silurian times the ocean separating Laurentia from Eastern Avalonia and Baltica had partly closed with the consumption of intervening oceanic crust. Marine seaways, however, persisted until the middle or late Silurian. Phases of crustal transtension and transpression, predominantly under a major sinistral shear couple, occurred throughout the Silurian and early Devonian until the remnant Iapetus Ocean was completely destroyed. The most appropriate Recent plate tectonic models for Silurian sedimentation between Eastern Avalonia and Laurentia are probably the deep-marine foreland basins between Timor and the northern Australian margin, or between Taiwan and mainland China.

Restoration and evolution of the intermontane Indus molasse basin, Ladakh Himalaya, India

Abstract Collision of the Indian Plate with the Karakorum Plate-Lhasa Block during the Eocene (ca. 55-50 Ma) created predominantly a S- or SW-verging thrust culmination across the Himalaya. During the late Tertiary, two molasse basins existed — the Siwalik Bain, formed in the late Miocene to Present on the Indian foreland south of the Himalaya, and the mid-Eocene to late Miocene Indus Basin along the Indus Suture Zone north of the High Himalaya. The Indus Basin is approximately 2000 km long, extending eastwards from Ladakh across South Tibet. A balanced cross-section along the Zanskar River shows a minimum 36 km shortening in the Eocene-?late Miocene molasse, and suggests that the minimum basin width was approximately 60 km in Ladakh. More than 2000 m of post-Eocene alluvial fan, fluvial and fluvio-lacustrine sediments accumulated in the Ladakh sector with petrographies suggesting derivation mainly from the deeply dissected and uplifted northern granodioritic Ladakh batholith (Aptian-Eocene), with only minor amounts of debris derived from the deformed southern Tethyan passive margin. Palaeocurrents show predominant E-W, axis-parallel, sediment transport, with subordinate lateral input paths being preserved. The Indus molasse basin is deformed by numerous, post-Eocene, N-directed backthrusts, many of which cut the entire stratigraphy and, therefore, were active at least into late Tertiary times.

Accretion of Japanese island arcs and implications for the origin of Archean greenstone belts

The present-day region of arc-arc collision between the Izu-Bonin Arc and mainland Japan (Honshu Arc) in the western Pacific (called the Izu Collision Zone or ICZ) provides a useful kinematic model for the development of many Archean greenstone belts. The compositional assemblage, thermal structure and structural style of the crust in the ICZ are very similar to those inferred for many Archean greenstone belts. In both cases, thick, young and flaky arc crust with a high heat flux is in collision with another crustal block. The ICZ has resulted in the imbrication of very thick slices of crust and associated sediments juxtaposed against older accretionary prisms. Many Archean greenstone belts show similar geological features, and we suggest that the incremental imbrication of the crust was a common tectonic style in some Archean convergent margins.

Basin evolution in the arc-arc Izu Collision Zone, Mio-Pliocene Miura Group, central Japan

A comparative study of the present collision zone between the Izu–Bonin Ridge (island arc) with mainland Japan (Honshu Arc), and the Mio-Pliocene of onshore SE Japan, suggests that arc—arc collision processes and the resulting stratigraphic successions may be repetitious and predictable. Arc—arc collision has led to the incremental accretion of segments of delaminated Izu—Bonin Arc crust onto the Honshu Arc, associated with the sequential southward migration in jumps of the plate boundary and trench. Prior to accretion of a segment of Izu-Bonin Arc crust, the leading edge underwent uplift to generate an approximately trench-parallel topographic high, the Zenisu Ridge being the present example with the Hayama-Mineoka uplift zone as a Mio-Pliocene example. The ridge separated a northern trench or trough from a southern intra-oceanic arc basin. During collision-accretion, the trench received both Honshu Arc-derived, terrigenous, and Izu-Bonin Arc-derived volcaniclastic, sediments, whereas the arc basin tended to receive only arc deposits. During the final stages of accretion, the arc basin began to receive ever-increasing volumes of terrigenous, Honshu Arc-derived, detritus fed through basement-controlled canyons. The accretionary process was accompanied by intense deformation and the residual deep-marine basin was then infilled above an angular unconformity.

Glacio-eustatic control on deep-marine clastic forearc sedimentation, Pliocene-mid-Pleistocene (c. 1180–600 ka) Kazusa Group, SE Japan

Glacio-eustasy has been shown to be a primary control on sedimentation in the open ocean and along passive continental margins, but its importance in clastic-dominated deep-marine sequences at active plate margins remains poorly understood. In order to test the relative importance of glacio-eustasy at tectonically active plate margins during times of substantial polar ice, a high-resolution δ1SO and δ13C record from planktonic foraminifera (Globorotalia inflata) was undertaken from the Plio-Pleistocene (c. 1180–600 ka) Kazusa Group, a forearc basin fill, onland SE Japan. This was combined with a high-resolution study of the magnetic susceptibility, total organic carbon, and %CaCO3 in order to evaluate the response to any glacio-eustatic changes in continental-margin sedimentary processes. The sections reveal globally recognized glacial-interglacial cycles, with sandy intervals correlating with inferred glacials, suggesting that relative sea-level changes during glacial-interglacial cycles exerted the primary control on sediment accumulation in the deep-marine forearc basin. Cross-spectral analysis of δ18O and δ 13C data from the inter-turbidite hemipelagic and pelagic mudstones reveals Milankovitch control both at precession and eccentricity modes, with a shift in their relative importance at about 900 ka. The results of this study have important implications for stratigraphers and sedimentologists because they show that at times when there is substantial polar ice: (1) the main control on sediment accumulation at active plate margins is glacio-eustatic, and (2) support the sequence stratigraphic paradigm developed from passive continental margins that global sea-level changes exert a primary control on siliciclastic deposition.

Deltas—sites and traps for fossil fuels

Report of a joint British Sedimentological Research Group/Petroleum Group meeting held on 21 and 22 April 1987 at the Geological Society of London, Burlington House, Piccadilly. The meeting was organized by M. K. G. Whateley and K. T. Pickering. This successful international meeting was convened to fill a considerable hiatus which has occurred since the flurry of conferences on deltaic sedimentation took place in the early and mid-1970s. It was felt that significant advances have been made in our understanding of deltas as sites and tra for fossil fuels and a timely forum was required to enable workers to disseminate their knowledge. The two-day meeting included 27 papers and 8 posters covering modern and ancient deltas in marine to fresh-water environments. Topics included: processes, facies models, petroleum, gas and coal related deltaic environments, together with general case studies. A Special Publication of the Geological Society of London will be published within about a year from the date of the meeting. The meeting attracted about 180 speakers and delegates from Germany, France, Norway, Canada, Italy, Denmark, USA and Britain. Following the two days of plenary sessions, there was a two-day field trip led by Professor Trevor Elliot to the Westphalian of North Devon, and a two-day field trip led by Professor John Collinson to the Namurian of the Pennines. At the weekend following the field trips, there was a one-day core workshop in Edinburgh, organized by the British Geological Survey, looking at the Jurassic Brent cores from the northern North Sea.