Numair A. Siddiqui

Landscape response to progressive tectonic and climatic forcing in NW Borneo: Implications for geological and geomorphic controls on flood hazard

Empirical models have simulated the consequences of uplift and orographic-precipitation on the evolution of orogens whereas the effects of these forcings on ridgelines and consequent topography of natural landscapes remain equivocal. Here we demonstrate the feedback of a terrestrial landscape in NW Borneo subject to uplift and precipitation gradient owing to orographic effect, and leading to less-predictable flooding and irreversible damages to life and property. Disequilibrium in a large catchment recording the lowest rainfall rates in Borneo, and adjacent drainage basins as determined through χ, a proxy for steady–state channel elevation, is shown to result in dynamic migration of water divide from the windward-side of the orogen towards the leeward-side to attain equilibrium. Loss of drainage area in the leeward-side reduces erosion rates with progressive shortening resulting in an unstable landscape with tectonic uplift, gravity faults and debris flows. 14C dating of exhumed cut-and-fill terraces reveal a Mid–Pleistocene age, suggesting tectonic events in the trend of exhumation rates (>7 mm a−1) estimated by thermochronology, and confirmed by morphotectonic and sedimentological analyses. Our study suggests that divide migration leads to lowered erosion rates, channel narrowing, and sediment accretion in intermontane basins on the leeward-side ultimately resulting in enhanced flooding.

Bilinear Extrapolation for Geocellular Reservoir Connectivity and Flow Simulation

Reservoir connectivity is one of the main subsurface uncertainties in the assessment and improvement of many oil and gas fields. The main objective of this paper is to analyze the static and dynamic connectivity of the selected shallow-marine sandstone facies through construction of gridded-based units for flow behavior/patterns. Prior to the generation of the sandstone facies connectivity and flow simulation, outcrop log data are input into the modeling software. The exposer used for the facies connectivity and flow simulation was ranging from 1 to 500 cm. The measurements of permeability values were taken on each of the grid, which were bilinear extrapolated, to populate the surface with permeability variation. Detailed analysis of the sedimentology and interpretation of three major sandstone facies is used as a framework to build the geocellular facies connectivity and flow simulation. The sandstone facies of HCSS shows more uniform and have linear connectivity, fallow by sub-layer gridding. In case of HBCBS, horizontal sweep is more effective as compared to vertical, because of thin mudstone deposited at the base of each layer boundaries which resist to sweep vertically. Whereas TCBS, WFBS, and BS show the distribution of different qualities of sandstones and bioturbation in the grid block model, burrows filled with mud which acts as impermeable pathways within moderate to low-quality sandstone.

Sandstone Facies Reservoir Properties and 2D-Connectivity of Siliciclastic Miri Formation, Borneo

Reservoir connectivity and modeling in siliciclastic deposits are quit challenging in terms of its distribution and quality prediction. The objective of this paper is to demonstrate the different aspects of reservoir properties to construct static connectivity model and its heterogeneity distribution in siliciclastic Miri Formation, Borneo. Field description in terms of facies, distribution, and dimensions of sand bodies and rock samples, for grain-size and petrographic analysis, were used to quantify and examine seven different types of sandstones: (i) hummocky cross-stratified sandstones, with medium- to fine-grained sand with 86.4% sand and 13.6% mud, O = 20.4–32.07%, k = 6.78 md; (ii) herringbone cross-bedded, with coarse to fine-grain having 92.7% sand and 7.3% mud, O = 12.2–31.3%, k = 17.7 md; (iii) trough cross-bedded sandstones, with very-fine- to medium-sized grains having 86.6% sand and 13.4% mud, O = 16.8–35.5%, k = 5.97 md; (iv) wavy- to flaser-bedded, silty sand to very-fine-grained sand with 48.1% sand and 51.9% mud, O = 7.6–19.4%, k = 2.31 md; thickness varies from 2–9 m; (v) cross-bedded sandstone, with fine to medium grain having 89.2% sand and 10.8% mud, O = 10–12.8%, k = 12.2 md; thickness from 2–3 m; (vi) bioturbated sandstone, having silty sand to fine-grained sand with 72–86% sand and 28–14% mud, O = 2.4–6.8%, k = 5.2 md; the sandstone thickness from 1–3 m; and (vii) massive sandstone, with very fine to medium grain representing 94.8% sand and 5.2% mud, O = 14–25.8%, k = 4.3 md; thickness from 1–5 m. The results show that sandstones of HCSS and HBSC are better sorted, with minimal mud content, with the depositional pattern with increasing vertical and lateral connectivity, even in bioturbated rich sand, as compared to other sandstone facies. On the other hand, sandstones of BS and CB are of poor quality in terms of grain sorting and poro-perm. This may reflect the heterogeneity in different facies and affect the connectivity with in sand bodies.

Cenozoic development of southwestern Malay Basin: new insights from subsidence analysis and thermal history

Subsidence and thermal history analysis are carried out in order to investigate the Cenozoic basin development of the southwestern (Tenggol Arch and basinal side) part of the Malay basin. Structurally, the southwestern part consists of normal faults and horst and graben geometry. Tectonic subsidence curves show that the basinal side is more active than the Tenggol Arch due to movement along normal faults. Cenozoic development initiated with the deposition of sedimentary Units M & L (Oligocene) and the activation of the Tenggol fault on the basinal side. Several periods of accelerated and slow subsidence are observed during the Oligocene to Middle Miocene that could be associated with changes in regional stresses caused by pulsating plate movement. The Malay Basin experienced inversion throughout the Middle to Late Miocene related to mantle induced slab avalanche effect, causing relatively higher tectonic subsidence rates on the Tenggol Arch compared to the basinal side, suggesting that the Tenggol Arch is less affected by inversion than the basinal side. After a period (Late Miocene) of non-deposition, the basin was reactivated (Pliocene to recent) due to thermal relaxation with thick sedimentation. Paleo heat flows estimated utilizing a novel technique introduced in this study and present day heat flow calibrated using BHT data further supports our results, in that increase in heat flow is related to rapid tectonic subsidence. An anomalously high heat pulse affected the basin during inversion and could be the cause of meta-sediment formation whereas present heat flows, although high compared to average basins, shows decreasing trend from the inversion period.