A tectonic model for the onshore Kutai Basin, East Kalimantan

Abstract

Past structural geological models for the Samarinda Anticlinorium have included gravity-driven slumping, shale diapirism and thrusting related to regional tectonic events. New geological cross-sections utilizing LASMO-acquired data over structures in the Runtu Block have been constructed from both surface geological measurements and 1993–1994 vintage seismic data. Relatively rigid deltaic and shelf sediments have been deformed into box-folds, above disharmonically folded shale-rich pro-delta and bathyal sediments. Detachment of these structures appears to be at the top of, or within, over-pressured shales at the base of Lower Miocene deltaic packages. Gravity data, acquired along with seismic data, suggests semi-regional uplifts of the underlying over-pressured strata which would have been initially deposited as a flat or gently inclined unit. Basement configuration is not visible on seismic but gravity and aeromagnetic data show that it is deep throughout the study area, ranging between 7 and 14km. The implication of the structural models is that relatively small amounts of shortening are interpreted to have occurred across these near-surface structures and that the amount of relative uplift is large. This model suggests that basin inversion may be the cause of the structural styles illustrated in this paper. Data presented supports a tectonic model for the central Kutai Basin involving inversion of a deep Palaeogene rift basin which gives rise to apparent broad regional folding of the shale rich over-pressured section. Closer spaced folding in the near surface, normally pressured and thus less ductile deltaic and shelf section of the Samarinda Anticlinorium, is a result of the same inversion.

Dating Borneo's Deltaic Deluge: Middle Miocene Progradation of the Mahakam Delta

“…The thick Neogene section in the Kutai Basin (up to 14 km) was entirely derived from the island of Borneo as result of inland uplift (Chambers and Daley 1997;Cloke et al 1999;Hall and Nichols 2002). During the middle Miocene the depocenter for this basin shifted to the Samarinda area.…”

“…1). Seismic studies have demonstrated that the NNE-SSWtrending ridges that dominate the region are expressions of tight linear anticlines and broader synclines (Chambers and Daley 1997;Cloke et al 1999). Beds typically strike at 24u-40u with an eastward dip of 50u-70u.…”

“…Located in the middle of the Indo-Pacific biodiversity hotspot, the seas around Borneo contain the most biodiverse coral reef communities in the world (Myers et al 2000;Hughes et al 2002;Renema et al 2008). Centered in this hotspot is the hydrocarbonrich Kutai Basin (Chambers and Daley 1997;Cloke et al 1999;Cibaj et al 2007). Strong deltaic sedimentation within the basin initiated within the early Miocene and continues presently (Moss and Chamber 1999;Wilson and Moss 1999;Hall and Nichols 2002).…”

Tectonic Evolution of the Sanga Sanga Block, Mahakam Delta, Kalimantan, Indonesia

“…The anticlines are separated by broad, open synclines (cf. Chambers and Daley, 1997). The western surface expression of the Mahakam fold belt has been termed the Samarinda anticlinorium (Ott, 1987).…”

“…Many geodynamic models have been proposed for the formation of this fold belt (cf. Ferguson and McClay, 1997;Chambers and Daley, 1997). Early models postulated that the fold belt k9218 P e la r a n g was formed by gravity gliding driven by uplift produced by Miocene orogenesis in western Kalimantan, with eastward-vergent collapse of the brittle overburden above overpressured shales (Ott, 1987).…”