Deep to shallow-marine sedimentology and impact of volcanism within the Middle Triassic Palaeo-Tethyan Semantan Basin, Singapore

The Middle Triassic Pulau Ayer Chawan Formation is a predominantly deep-marine, occasionally shallow-marine sedimentary succession, deposited in the Singapore sector of the Palaeo-Tethyan Semantan Basin. The formation provides an important record of the dynamic interplay between a siliciclastic sedimentary system and the products of an adjacent active volcanic arc. It is characterised by six sub-environments, including: deep-marine turbidite fan, deep-marine background sedimentation, subaqueous debris cone, shallow-marine, volcanically-sourced turbidite fan, and hyaloclastite mound or ridge. Turbidite fan deposits preserve the input of both siliciclastic and volcaniclastic sediments from the shelf, transported into the deep-marine environment by a suite of subaqueous sediment gravity flow processes, including: turbidity currents; mixed flow types (hybrid event beds); concentrated and hyper concentrated sediment gravity flows, and debris flows. Thick heterolithic successions of debrites were likely sourced through regular collapse of an unstable shelf. The presence of hybrid event beds, encountered within the deep-marine turbidite fans, supports a slope that was out-of-grade, and may have been actively retreating towards the hinterland. Together, these factors suggest regional-scale uplift of the eastern margins of the Semantan Basin during Triassic times, most likely facilitated through volcanic activity in the adjacent Palaeo-Tethys Sukhothai Arc. Evidence for contemporaneous, arc-related magmatism includes ubiquitous volcaniclastic sedimentary rocks within formation, including pyroclastic density current deposits and perhaps more-strikingly through the hyaloclastites of the Nanyang Member. The hyaloclastites formed through quenching of magmas delivered into the deep-marine setting from a series of sub-sea vents or mounds

Developing a framework of Quaternary dune accumulation in the northern Rub' al-Khali, Arabia

Located at the crossroads between Africa and Eurasia, Arabia occupies a pivotal position for human migration and dispersal during the Late Pleistocene. Deducing the timing of humid and arid phases is critical to understanding when the Rub' al-Khali desert acted as a barrier to human movement and settlement. Recent geological mapping in the northern part of the Rub' al-Khali has enabled the Quaternary history of the region to be put into a regional stratigraphical framework. In addition to the active dunes, two significant palaeodune sequences have been identified. Dating of key sections has enabled a chronology of dune accretion and stabilisation to be determined. In addition, previously published optically stimulated luminescence (OSL) dates have been put in their proper stratigraphical context, from which a record of Late Pleistocene dune activity can be constructed. The results indicate the record of dune activity in the northern Rub' al-Khali is preservation limited and is synchronous with humid events driven by the incursion of the Indian Ocean monsoon

Gone with the wind: dune provenance and sediment recycling in the northern Rub’ al-Khali, United Arab Emirates

The Rub’al-Khali dune field in southern Arabia is the largest sand sea in the world. Deciphering thepalaeoenvironmental history of the Rub’al-Khali is critical to understanding its role as a barrier to human migration, dispersaland settlement. To determine sediment provenance and transport pathways, we combined data from a geological mappingproject with traditional heavy mineral optical point-counting methods, heavy mineral geochemical fingerprinting and detritalzircon U–Pb geochronology of Miocene and Quaternary sediments in the United Arab Emirates (UAE). Detrital zircon U–Pbage spectra demonstrate that most Neogene and Quaternary sediments in the UAE are ultimately sourced from the PrecambrianArabian Shield. Heavy mineral and geochemical signatures indicate that the dune sands are locally recycled from the deflationof Miocene sandstones and Quaternary siliciclastic palaeodunes exposed along the Arabian Gulf coast, whereas carbonatepalaeodunes along the Gulf coast are derived from the deflation of sediments deposited by the Tigris–Euphrates River system inthe Gulf during Pleistocene lowstands. In the eastern Emirates, Miocene and Quaternary alluvial fan deposits emanating fromthe Hajar Mountains have an ophiolitic heavy mineral signature. The data reveal new insights into the origin and developmentof the Rub’al-Khali dune field

Paleozoic to Cenozoic sedimentary bedrock geology and lithostratigraphy of Singapore

A new lithostratigraphical framework for Singapore is proposed, based on the analysis of c. 20,000 m of core recovered from 121 c. 205 m deep boreholes and augmented with 218 field localities from across Singapore. The new framework describes a succession dating from the Carboniferous to the Quaternary. New U-Pb detrital zircon dates and fossil analysis were used to constrain the ages of key sedimentary units. The oldest known sedimentary rocks in Singapore are found to be the deformed Carboniferous (Mississippian) Sajahat Formation. These are succeeded by the newly erected, Middle and Upper Triassic, marine to continental Jurong Group and Sentosa Group successions that accumulated in the southern part of the Semantan Basin. The Jurong Group comprises four formations: the Tuas Formation, the Pulau Ayer Chawan Formation, the Pandan Formation and the Boon Lay Formation. The Sentosa Group contains two formations: the Tanjong Rimau Formation and the Fort Siloso Formation. In Singapore, the depositional record during this time is related to late Permian to Triassic arc magmatism in the southern part of the forearc basin to the Sukhothai Arc. The Jurong and Sentosa groups were deformed and weakly metamorphosed during the final stages of the Late Triassic to Early Jurassic orogenic event, deformation that led to the formation of the syn-orogenic conglomerates of the Buona Vista Formation. Following this, two distinct Lower Cretaceous sedimentary successions overstepped the Jurong and Sentosa group strata, including the Kusu Formation and the Bukit Batok Formation, both deposited in the southern part of the Tembeling Basin. A series of Neogene to Quaternary formations overly the Mesozoic and Palaeozoic stratigraphy, including the Fort Canning Formation, Bedok Formation and the Kallang Group

Ductile and brittle deformation in Singapore: a record of Mesozoic orogeny and amalgamation in Sundaland, and of post-orogenic faulting

Singapore bedrock geology is dominated by late Permian to Triassic arc magmatism and a genetically related, essentially Middle to Upper Triassic, marine to fluvial volcano-sedimentary inner forearc succession. These Mesozoic strata are deformed into a pattern of NE-translated ductile–brittle deformation structures during the latest Triassic to earliest Jurassic collision and amalgamation of the Sibumasu continental block with the southern part of the Sukhothai Arc. The subduction-related magmatic complex represented in Singapore by the granitic to gabbroic plutons of the Bukit Timah Centre likely acted as a backstop to thrusting at this time. Collisional tectonics drove progressive shortening and steepened earlier-formed inclined asymmetrical folds, culminating in the regional-scale development of a non-coaxial, NE-vergent and NE-facing, fold and thrust system. In Singapore, the Murai Thrust and Pasir Laba Thrust are identified as major elements of this system; both are associated with SW-dipping thrust-imbricate duplex slices. Two distinct early Cretaceous (Berriasian and Barremian) sedimentary successions overstep these collisional tectonic structures. An array of mostly NE–SW and ENE–WSW trending faults and fractures acts as an important control on bedrock unit distribution across Singapore and are most likely generated by Cenomanian dextral shear stress. That stress locally reactivated faults initiated during orogeny, or even earlier. Knowledge of the geotechnical impact of these structural features is critical to both future development and ongoing management of the subsurface in Singapore

The igneous rocks of Singapore: new insights to Palaeozoic and Mesozoic assembly of the Sukhothai Arc

Six plutons of granitic to gabbroic rocks have been recognised in the poorly exposed ground of north and east Singapore using new data from borehole cores and field observations. Five of the plutons were emplaced sequentially during the period 285–230 Ma, and these have been grouped within a single parent unit (Bukit Timah Centre) in a new lithodemic framework for Singapore. These plutons record the development of early Permian to Triassic arc-related magmatism towards the southern end of the Sukhothai Arc system of Thailand, Peninsular Malaysia and Indonesia. Compositional trends in the plutons record decreasing crustal contribution as the arc matured. The volcanosedimentary succession underlying southwest Singapore records contemporaneous deposition in the forearc basin, and includes pyroclastic units of sufficient thickness and extent to be assigned ‘member’ status in a new lithostratigraphical framework for Singapore. The largest pyroclastic unit, which is >150 m thick, developed as volcanic activity peaked at c. 242 Ma and is correlated with a large (probably caldera-forming) eruption of one of the Permo-Triassic plutons. The composition, typology and age of the Bukit Timah Centre plutons confirm their affinity with Eastern Belt intrusions of the Eastern Province (one of three granitoid provinces in Southeast Asia), and support a widely accepted model that Eastern Province granitoids formed in an Andean-type setting as Palaeo-Tethys crust descended beneath the Indochina–East Malaya block. Widespread development of hydrothermal-tuffisite in the Permo-Triassic intrusions is correlated tentatively with rapid uplift following slab breakoff, when arc activity ceased in the Singapore region in the interval c. 230–205 Ma. A sixth pluton, much younger than (and unrelated to) the Bukit Timah Centre, was emplaced in northeast Singapore in the Upper Cretaceous