Wave-tide depositional setting on the Middle to Late Miocene outcrops in Miri, Sarawak and Brunei Darussalam, Northwest Borneo

A ~125 m thick shallowing-upward arenaceous succession from the Badalgarh Formation, Bayana basin, India provided the opportunity to document shelf to foreshore transition from a paleoproterozoic rift set-up. Process-based facies analysis allowed identification of 12 different shallow-marine facies types, grouped under four different facies associations namely (i) lower offshore or open shelf, (ii) upper offshore to distal lower shoreface, (iii) lower to middle shoreface and (iv) upper shoreface to foreshore. From unequivocal dominance of wave- and storm-generated features and fortuitous documentation of tide-generated structures in upper offshore, lower and middle shoreface settings, we infer a tide-influenced, wave-dominated coast at the Badalgarh Sea. From measurement of different vector attributes through the studied succession, we infer (i) near east–west orientation for the Badalgarh shoreline, (ii) storm deposits as products of shore-perpendicular return flow, and (iii) tidal peak flow at a high angle with the shoreline and confined in the upper offshore, lower and middle shoreface settings. A gradational transition from offshore to lower shoreface and, in turn, to middle and upper shoreface suggests accretionary character for the Badalgarh shoreface in a high-gradient rift setting. Overlying deep water (distal offshore) argillaceous marine strata, the arenaceous shallowing-upward Badalgarh succession is interpreted as a product of highstand systems tract (HST) constituted of stacked tens- to hundreds of meter-thick shallowing-upward depositional cycles. Since the abrupt shift in facies type (shallow to deep water) across the upper boundaries of depositional cycles is not unambiguous, we intend to assign these cycles as genetic stratigraphic cycles or T-R cycles over ‘parasequence’.

Sedimentological and ichnological studies of the Late Maastrichtian to Danian Nsukka Formation in the Okigwe area of the Anambra Basin, Southeastern Nigeria were carried out to ascertain the lithofacies and to reconstruct the depositional environment. The lithofacies include concretionary black shale (F1), heterolithic facies (F2), bioturbated mudstone (F3), bioturbated sandstone (F4), ripple-bedded sandstone (F5), cross-bedded sandstone (F6), parallel-bedded sandstone (F7), bioturbated black shale (F8), and bioturbated shelly sandstone (F9). Some of the beds are significantly bioturbated with bioturbation index (BI) ranging from 3 to 5. Five lithofacies associations were distinguished and interpreted as follows: lithofacies association I represents offshore to lower shoreface transition sediments; lithofacies association II is middle to lower shoreface; lithofacies III comprises upper shoreface to foreshore and lagoon/bay sediments; lithofacies association IV is of upper shoreface origin; and lithofacies association V is proximal offshore. The shallow marine setting was dominated by currents, waves and occasional storm. The trace fossil assemblage comprises Ophiomorpha nodosa and Skolithos linearis representing the Skolithos ichnofacies and Thalassinoides suevicus, Teichichnus rectus, Paleophycus herberti and Planolites montanus representing the Cruziana ichnofacies. The six trace fossils described in this study are equally distributed into two ethological categories, domichnia (dwelling burrows) and fodinichnia (feeding burrows). The distribution of the two ethological categories in the sediments within the shallow marine environment was controlled by the energy of the environment, amount of organic detritus, degree of oxygenation and salinity.

The lower shoreface: Morphodynamics and sediment connectivity with the upper shoreface and beach

New results on the stratigraphy and sedimentary environment of the Middle Jurassic strata of the Murihiku Terrane in the Waikawa district, Southland, New Zealand, are presented. This area has not been subjected to study for a long time, although the Murihiku Terrane is important to understand the Mesozoic geology of New Zealand. Stratigraphically, from bottom to top, the sequence consists of lithofacies associations A, B, C, and D, distinguished by their lithology. Lithofacies association A (250 m thick) is composed of boulder‐grade conglomerate, coarse‐grained massive sandstone, trough cross‐stratified sandstone, and minor fine‐grained sediments. Lithofacies association B (90 m thick) contains alternating beds of sandstone and siltstone and fossil‐bearing massive siltstone. Lithofacies association C (280 m) consists of poorly to moderately sorted pebble‐cobble conglomerates and trough or planar cross‐stratified sandstones. The characteristic lithofacies of lithofacies association D (>140 m) are planar cross‐stratified sandstone, planar horizontally stratified sandstone, grey siltstone, and carbonaceous beds. The depositional age was deduced from bivalve fossils in lithofacies association B, which indicate a Middle Jurassic (Temaikan: Bajocian‐Callovian) age. Paleocurrent flow directions were from the southwest in lithofacies association A and from the southeast in lithofacies associations C and D. Clast compositions also differed between lithofacies associations A and C; andesite volcanic clasts were dominant in A, and rhyolite volcanic clasts were dominant in C. The major sedimentary environments were terrestrial and shallow marine and were affected by sea‐level changes. The sediments of lithofacies association B were deposited during periods of transgression and high sea level, and the boundary between lithofacies associations B and C is a depositional‐sequence‐bounding unconformity. Fluvial sedimentation became dominant in lithofacies associations C and D. Due to progressive aggradation of the sedimentary basin, the gradient became gentle, and the fluvial pattern changed from a braided to a meandering river. The sediment source, as determined from paleocurrent analyses and clast compositions, was also different from that of lithofacies association A. Thus, the Waikawa district sediments apparently were derived from multiple sources. The provenance of the Murihiku Terrane sediments was probably a primitive volcanic or continental margin arc. Volcanic activity in the hinterland fed large amounts of volcanic detritus to the region by flood, debris flow, and fluvial transport.

Field surveys and numerical simulations were conducted to examine lithostratigraphic cyclicity in strike-slip basins, which is still poorly understood due to its complexity. The basin-filling processes in strike-slip basins are closely associated with regional tectonics represented by configuration of faults and spatial/temporal variations in the slip rate. We attempted to bridge the gap between qualitative sedimentary facies analyses and quantitative numerical models in order to better understand the formation of these sedimentary successions. This paper focuses on the Izumi Group (Upper Cretaceous), southwest Japan, which was deposited in an elongate basin (300 km long by 10–20 km wide) along the Median Tectonic Line, which at the time of deposition was a sinistral strike-slip fault related to oblique subduction along a forearc margin. The depositional environments of the group were deduced from five lithofacies associations (LAs): submarine channel-fill facies (LA I), proximal facies of lobes or frontal splays (LA II), distal facies of lobes or frontal splays (LA III), slope-apron facies (LA IV), and basin floor facies (LA V). LAs I–III represent point-sourced submarine channel–fan successions in the axial facies, with unidirectional paleocurrent directions from ENE to WSW, and LAs IV–V constitute the marginal facies, the paleoslope of which dipped to the SSW. Two units of submarine channel–fan successions are stacked with ~10 km of eastward (backward) shift. Each unit shows a cyclic lithostratigraphy of rapid upward coarsening and thickening in the lower part (~350 m thick) and gradual upward fining and thinning in the upper part (1–3.5 km thick). It is estimated to have taken 5–7 × 10 5 yr for 10 km offset on each stratigraphic unit based on the depositional ages. Although many processes can control the stratigraphic architecture, such as global and local sea level, climate, and tectonics, the stratigraphic cyclicity observed in the study area is closely related to the depocenter migration, suggesting that fault movement was the primary control on the stratigraphy. On the assumption that the formation and filling processes of the Izumi sedimentary basin were basically controlled by strike-slip faults, a numerical simulation suggests that episodic changes in fault-slip rate or sediment-supply rate could control the stratigraphic cyclicity. In this paper, we propose a model where cyclic stratigraphy is ascribed to temporal variations of fault activity controlling accommodation generation, sediment supply, and relative sea level, which could generate cyclic stratigraphy associated with depocenter migration in strike-slip basins.

Subaqueous sediments comprise the cores of a group of drumlins formed at about 17 ka YBP towards the margin of the Late Pleistocene ice sheet is Galway Bay, western Ireland. Four major lithofacies associations (L.F.A.s) are identified. Regional ice flow patterns and isostatic depression together with sedimentary characteristics indicate that the three lowermost L.F.A.s accumulated in shallow-water settings fed by meltwater venting under high hydrostatic pressure. These sediments are tabular, lensate or channelled and have not been deformed by glacially-influenced tectonics. L.F.A.1 is an apron of interbedded mud and muddy diamict deposited from sediment plumes and ice-rafting. L.F.A.2 infills channels cut in the underlying muddy diamict and consists of interbedded poorly-sorted pebbly gravels, sands and diamicts formed by sediment gravity flows. L.F.A.3 is tabular and comprises a massive diamict derived from powerful meltwater jets. L.F.A.4 is a massive diamict carapace which overlies stratified facies and was deposited by basal ice processes. The model presented envisages subaqueous deposition below floating ice followed by till deposition and drumlinization. Coarsening upwards facies transitions are interpreted in terms of progressive change from ice-distal to ice-contact sedimentation. The sequence preserved in the drumlin cores forms part of a regional apron of sediments probably of glaciomarine origin which normally occurs in front of the drumlin belt in Irish coastal areas. Deposition probably occurred in isostatically-depressed zones around the drumlin ice sheet when high relative sea levels occurred. Local streamlining of ice marginal sequences was probably a result of accelerated ice flow triggered by rapid calving, subglacial channel development, sea level change or soft bed conditions. It is concluded that high relative sea levels, calving and high longitudinal stretching rates provide suitable mechanisms which help to explain drumlinization and the rapid disintegration of the last ice sheet in western Ireland.

The late Dinantian platform carbonate successions of the Burren, Buttevant and Callan areas in Ireland have been correlated using detailed litho- and biostratigraphy. Several subdivisions or lithofacies associations (LA) of the Asbian to Brigantian part of the succession have been recognized in each area (lithofacies associations 1–5). Holkerian(?) to early Asbian ramp carbonates of LA 1 underlie the late Asbian successions in both the Burren and Buttevant areas. The influx of the bilaminar palaeotextulariid Cribrostomum lecomptei coincides with the onset of late Asbian shallow-marine cyclic platform sedimentation (LA 2) in all areas. The sediments of LA 2 have abundant Kamaenella and foraminifera, and are characterized by palaeokarstic surfaces and shales that cap a minimum of nine shallowing-upward minor cycles in the Burren and Buttevant areas. Two new biostratigraphic subdivisions (Cf6γ1 and Cf6γ2) of the late Asbian/Cf6γ subzone are described for the first time in this part of the succession. Brigantian sedimentation (LA 3) is typified by amalgamated beds of crinoidal limestone and abundant Asteroarchaediscidae. Thin peloidal limestones with coral thickets cap shallowing-upward cycles within this succession. These cycles, which are thinner and less numerous than those of the underlying late Asbian, rarely terminated in emergence, but most reached shallow subtidal depths prior to the next transgression. The change in cyclicity style across the Asbian/Brigantian boundary may be related to the sedimentation rates of the crinoidal limestones, due to increases in cyclic oscillation in the Brigantian. Brigantian LA 4 is characterized by deep subtidal cherty limestones, with abundant algal-coated wackestone intraclasts. Fasciella and Howchinia bradyana are typical microfossils. No cyclicity is observed, probably owing to the deep subtidal nature of this unit. LA 4 is overlain by another unit of cyclic crinoidal limestones (LA 5) in the Burren, which has no correlatives in the other areas studied. The succession in all areas is unconformably overlain by Namurian siliciclastic rocks. The nature and number of minor cycles in the late Dinantian of Ireland is similar to those of platform successions of the same age elsewhere in the British Isles, suggesting that eustatic changes were one of the major controls on cyclicity during the late Dinantian.

Trace fossil assemblages from a variety of outcropping tidal and shoreface facies in the Belait Formation of Brunei Darussalam were characterized to determine their value in distinguishing shallow marine sedimentary environments on a low energy margin. Most trace fossil assemblages in tide-dominated environments have a proximal Cruziana ichnofacies, although higher energy tidal channels have a distal Skolithos ichnofacies. Tidal sand flats tend to have more diverse and abundant traces than tidal channels. Trace fossils are more abundant in tidal mud flat facies than in tidal channels and sand flats, and whilst mud flat assemblages are more diverse than tidal channel assemblages, they are less diverse than sand flat assemblages. Generally, these assemblages are similar to those in equivalent depositional environments in higher tidal range settings. W ave-dominated environments also have Cruziana assemblages, except for the upper shoreface that has a distal Skolithos assemblage. Lower shoreface assemblages are more abundant and diverse than upper shoreface assemblages and belong to the proximal Cruziana ichnofacies. Trace fossils are more abundant and diverse in offshore transition facies than in either the upper or lower shoreface and belong to the distal Cruziana ichnofacies; assemblages in interbedded storm sands often include a minor component of the Skolithos ichnofacies. These assemblages are comparable to those from wave-dominated deposits from higher energy settings, except for the upper shoreface environment which contains a lower energy assemblage than in equivalent facies elsewhere. T race fossils tend to be less diverse, less abundant and individual traces generally are smaller in tide-dominated depositional environments when compared to wave-dominated depositional environments. Also, Ophiomorpha form complex burrow systems in wave-dominated environments in contrast to simple burrows in tide-dominated environments.

ABSTRACTA late Pleistocene morainal bank is sited in a depocentre to the lee of a major rock ridge, near Greystones, in the western Irish Sea Basin. During deglaciation the ridge provided a pinning point during tidewater wastage northwards. Sedimentation patterns and palaeocurrent data show morainal bank growth by discharge from a single basal efflux located to the east or south‐east of the ridge during ice marginal re‐equilibration.The four lithofacies associations which are recognized from the western part of the formerly more extensive apron are related largely to variable jet and plume sedimentation. At the base of the 1.6 km long exposure, Lithofacies association 1 (massive mud, muddy diamict and laminated mud) was deposited from turbid plumes, variable ice rafting and traction current activity. Lenticular units of gravels within this mud bank record high energy pulses and sediment fluxes from the efflux jet. Lithofacies association 2 (sands, laminated muds and muddy diamict) is discontinuous and occurs within basins along a marked erosion surface cut in Lithofacies association 1. It is associated with a decrease in jet strength, traction currents and suspension sedimentation. Lithofacies association 3 is a tabular body of interbedded diamicts and gravels which is present along the entire section. It documents the decay phase of re‐equilibration as the ice margin disintegrated catastrophically and released large volumes of heterogeneous sediment which was resedimented by quasicontinuous mass flow. Lithofacies association 4 consists of stratified and massive gravels within distributary channels cut into underlying facies and represents the last phase of meltwater activity.Sediment geometries, particularly sedimentary contrasts representing erosion surfaces at a variety of scales and abrupt textural contrasts are attributed to jet switching. Lithofacies association 1 (60%) and Lithofacies association 3 (30%) are the dominant facies. In favourable topographic settings this stratigraphic couplet is a signature for re‐equilibrated ice margins in isostatically depressed basins dominated by tidewater fronts, rapid ice flux and high relative sea level.Morainal banks document rapid environmental change and in the Irish Sea Basin they form part of a deglacial event stratigraphy related to unstable tidewater margins and high relative sea level. Deglaciation was therefore controlled primarily by high relative sea level rather than climatic forcing. Facies variations should therefore not be used for stratigraphic correlations in place of direct stratigraphy. This type of situation may be more common than hitherto realized in Late Pleistocene, mid‐latitude shelves where most of the preserved stratigraphy is characterized by complex, interbedded sequences formed when isostatic depression exceeded sea‐level fall.

The sedimentology and depositional environment of D2 sand in part of the Greater Ughelli depobelt have been studied using well logs and core data. Three wells were correlated to establish the lateral continuity of the D2 sand across the field and standard gamma ray log trends was used to infer depositional environments. Cored section of well B was described to identify lithology and delineate depositional environments based on facies types and sedimentary structures. Petrophysical characteristics of the reservoir of interest was generated using Archie Equation for water saturation, Timur formula for permeability computation and porosity values was determined quantitatively from density log. The results of the analysis showed that the D2 sand cut across the field. The reservoir displayed a funnel shaped coarsening upward gamma ray motif typical of a deltaic and progradational depositional profile. Four facies associations indicating four subenvironments within the deltaic front have been identified from the cored interval (3444.5 to 3458.5 m) of the D2 reservoir. Each facies unit was identified based on lithology and sedimentary structures of the core sample, textural characteristics and gamma ray log trend. The four lithofacies associations: A, B, C and D include muddy heterolithic sandstone, trough cross stratified sandstone, sandy/silty mudstone and crossbedded sandstones. These facies correspond to Lower Shoreface, Upper Shoreface, Tidal Flat and Channel sand respectively. Petrophysical analysis revealed the trend of reservoir quality within the facies. Porosity range from 0.79 to 10.32%, whereas permeability from 0.25 to 8.8 mD. Water saturation is high (0.8) within the poor quality facies and 0.3 in the highest porosity and permeability interval. Good porosity and permeability occurred within the channel and upper shoreface facies, whereas the tidal flat and lower shoreface have poor porosity and permeability values. The Shoreface facies has the best reservoir properties (10.32% porosity and 8.8 mD permeability) due to lack of shale intercalations and good sorting resulting from the sediments being properly reworked by wave action. The Channel facies (D) deposited by high energy current also has good reservoir properties, especially towards its base. The Tidal Flat facies has the lowest reservoir quality due to high proportion of shale/Clay that creates permeability barriers and occurred between the Upper shoreface facies and Channel sand facies. Sedimentology and depositional environments of facies have significant control on the quality of sand bodies.

The Turonian-Coniacian Upper Ferron Sandstone Last Chance Delta was deposited along the western margin of the Western Interior Seaway as a wave-modified, river-dominated deltaic system. The Last Chance Delta was deposited during a slow relative sea-level rise whose rate of rise decreased with time. The sedimentation rate progressively decreased throughout the deposition of the Last Chance Delta. Architectural and sedimentological data for deltaic near-marine sandstones indicate that primary deltaic depositional style is directly correlated with degree of wave-modification, which is controlled by the ratio of sedimentation rate to the rate of relative change in sea level. The progradational parase-quence sets have a mean sandstone dip length/thickness aspect ratio of 788. The aggradational parasequence sets are shorter with a mean length/thickness of 520. The retrogradational parase-quence sets are shorter and thinner with a mean length/thickness of 397. River-dominated progradational parasequences have a mean length/thickness of 611, a mean width/thickness of 212, and a mean length/width of 1.9. River-dominated, wave-modified progradational parasequences have longer dip lengths and a higher length/thickness of 845. The aggradational parasequences have similar lengths as the wave-modified parasequences, with a mean length/thickness of 606. The retrogra-dational parasequences are short and thin, with a mean length/thickness of 793. Stream-mouth bar, reworked stream-mouth bar, and upper shoreface deposits show trends of length/thickness changing systematically with degree of wave-reworking, from a mean length/thickness of 479 (width/thickness = 256; length/width = 1.9) in river-dominated parasequences to 546 and 595 in reworked stream-mouth bar and upper shoreface deposits, respectively. Retrogradational parasequences have higher upper shoreface mean length/thickness aspect ratios of 649. Proximal delta-front, reworked proximal delta-front, and middle shoreface deposits show similar trends. River-dominated parasequences have mean proximal delta-front length/thickness of 425 (width/thickness = 472; length/width = 1.8) and reworked proximal delta-front and middle shoreface deposits have a mean length/thickness of 827 and 912, respectively. Retrogradational parasequences have a mean middle shoreface length/thickness of 807. Distal delta-front, reworked distal delta-front, and lower shoreface deposits also show similar trends. River-dominated parasequences have mean distal deltafront length/thickness ratios of 518 and reworked distal delta-front and lower shoreface deposits have mean length/thickness ratios of 819 and 2469, respectively. Retrogradational parasequences have a mean lower shoreface length/thickness of 981. Architectural and sedimentological data for fluvial channel-belt sandstones indicate that over-all geometry, internal architecture, and preserved sedimentary structures are directly correlated with sedimentation rate and rate of relative change in sea level. Internal channel belt architecture is controlled by the response of the river equilibrium profile to changes in relative sea level and shoreline position. Channel belts, from progradational parasequence sets, deposited during times of high sedimentation rate and moderate relative sea-level rise, are laterally restricted and multi-storied with channel-fill elements stacked vertically within the channel-belt boundaries. Fluvial channel belts in the upper delta plain have average width/thickness aspect ratios of 28.8; distributary channel belts located near the paleoshoreline have average aspect ratios of 19.0. Fluvial channel belts from aggradational parasequence sets deposited during times when sedimentation rate was approximately equal to the rate of relative sea-level rise are laterally extensive and multi-storied with channel-fill elements stacked laterally en-echelon. Fluvial channel belts in the upper delta plain have average width/thickness aspect ratios of 59.2; distributary channel belts, located near the paleoshoreline have a mean aspect ratio of 12.1. Channel belts from retrogradational parasequence sets deposited during times when sedimentation rate was less than the rate of relative sea-level rise are laterally extensive and sheet-like with average aspect ratios of 100.0. Their channel-fill elements generally stacked vertically within the channelbelt boundaries. Amalgamated, braided fluvial deposits occur within small high-gradient incised valleys developed during periods of 4th- and 5th-order relative falls in sea level. The preserved incisedvalley fluvial deposits, within the Last Chance Delta, range in width from 1.3–8.8 km (0.8–5.5 mi) and in thickness from 9–32 m (27–96 ft); the average width/thickness aspect ratio is 169.4 near the valley mouths and 644.1 at 10–17 km (6–11 mi) inland from the mouth.

Heterolithic Lower Rewa Sandstone of the Neoproterozoic Rewa Group, Vindhyan Basin, U. P., India: An example of tidal point bar

Ichnological characteristics and variability of Miocene deposits in the Cenozoic Niger Delta: Examples from cores in the Coastal Swamp and Offshore depobelts

Depositional environment and organic matter enrichment of the lower Cambrian Niutitang shale in western Hubei Province, South China

Sedimentology of mixed siliciclastic-carbonate system in a structurally constrained Paleogene basin: Eocene Musawa Formation in Eastern Oman Mountains