cullen et al 2012 paleomagnetism crocker formation gsa geosphere

1146

Paleomagnetism of the Crocker Formation, northwest Borneo: Implications for late Cenozoic tectonics

Andrew B. Cullen1,2, M.S. Zechmeister3,4, R.D. Elmore3, and S.J. Pannalal3

1Shell International Exploration and Production Company, 100 Hoekstade, Rijswijk, Netherlands2Chesapeake Energy Corporation, 6100 N. Western Avenue, Oklahoma City, Oklahoma 73118, USA3ConocoPhillips School of Geology and Geophysics, 100 E. Boyd Street, Norman, Oklahoma 73019, USA4Shell Exploration and Production Company, 150 North Dairy Ashford, Houston, Texas 77079, USA

ABSTRACT

Tectonic models for Borneo’s Cenozoic evolution differ in several aspects, par-ticularly in the extent to which they include paleomagnetic data suggestive of strong counterclockwise rotation between 30 and 10 Ma. Key areas are undersampled. We present the results of a paleomagnetic study of Eocene to Early Miocene sandstones from northwest Sabah, principally from the Crocker Formation. We obtained reliable site means from 11 locations along a 250 km northeast-southwest transect using thermal demagnetization to isolate characteristic remanent magnetization (ChRM) directions. The Crocker Formation sandstones are per-vasively remagnetized; pyrrhotite dominates the ChRM signal. Locations can be grouped into different domains on the basis of the rela-tive sense of rotation about a vertical axis. Mean ChRM directions for seven locations between Kota Kinabalu and Keningau (dec-lination, dec 12°–19°; inclination, inc –22°–23°) indicate minor clockwise rotation and modest tilting, whereas two locations near Tenom (dec 321°–345°, inc –6°–24°) record counterclockwise rotation and modest tilt-ing. Although we cannot precisely date the age of remagnetization, the results of fold tests from 4 locations, interpreted within the regional structural framework, strongly indi-cate that remagnetization occurred between 35 and 15 Ma, the waning stages of the Sara-wak orogeny to an early phase of the Sabah orogeny. Our results pose serious diffi culties for current tectonic models in which Bor-neo rotates 50° counterclockwise as a rigid block between 30 and 10 Ma. With respect to prior paleomagnetic studies, we suspect that an early episode of strong regional counter-clockwise rotation (before 35 Ma) was over-

printed not only by differential clockwise rotation of crustal blocks during opening of the South China Sea (32–23 Ma), but also locally by a younger (after 10 Ma) counter-clockwise rotation.

INTRODUCTION

The Cenozoic tectonic evolution of Southeast Asia refl ects the complex interactions of rifting, subduction, continental collision, and large-scale continental strike-slip faulting. The island of Borneo is at the leading edge of several conti-nental blocks that protrude from Southeast Asia as a wedge into the Indo-Australian and Phil-ippine Sea plates (Fig. 1A). There are two end members of tectonic models for Borneo (Figs. 1B, 1C): collision-extrusion (Briais et al., 1993; Replumaz and Tapponnier, 2003) and subduction-collision (Hamilton, 1979; Lee and Laver, 1995; Hall, 1996). These models differ in four princi-pal aspects: (1) the mechanism responsible for rifting and seafl oor spreading in the South China Sea ca. 32–16 Ma (Briais et al., 1993); (2) the timing and amount of displacement along the large intercontinental strike-slip faults such as the Red River fault (Leloupe et al., 1995; Searle, 2006); (3) the amount of proto–South China Sea crust subducted beneath Borneo (Rangin et al., 1999; Lee and Laver, 1995; Hall, 2002; Cullen, 2010); and (4) the magnitude and nature of the late Tertiary rotation of Borneo (Hall, 1996, 2002; Murphy, 1998).

In the collision-extrusion model (Fig. 1B), India’s collision with Asia progressively dis-places the Sundaland, Indochina, and South China blocks to the southeast along intercon-tinental strike-slip faults (e.g., Mae Ping and Red River faults). In this model, Borneo, south Palawan, and north Palawan rotate clockwise (CW) ~25° along with the Indochina block as the South China Sea opens as a large-scale

pull-apart basin (Briais et al., 1993; Replumaz and Tapponnier, 2003); the amount of seafl oor spreading is approximately balanced by 600 km of left-lateral displacement along the Ailao Shan–Red River fault zone. In the collision-extrusion model, there is no Tertiary subduction under northwest Borneo, and mass is conserved by subduction in the Pacifi c Ocean.

The subduction-collision model (Fig. 1C) features long-lived subduction (Eocene–Early Miocene) beneath northwest Borneo during which an extensive amount of proto–South China Sea oceanic crust is consumed. Subduc-tion terminates progressively (southwest to northeast) as blocks of continental crust (Luco-nia, Dangerous Ground, and Reed Bank) collide with northwest Borneo and Palawan (Holloway, 1982; Lee and Laver, 1995; Hall, 1996; Longley, 1997). In this model, there is less displacement along the Red River fault and because it largely decoupled from extension in the South China Sea, CW rotation of Borneo is not required. The subduction-collision model has several permu-tations. The most widely cited reconstructions are those of Hall (1996, 2002); honoring Fuller et al.’s (1999) interpretation of regional paleo-magnetic data, these reconstructions show an acceleration in subduction rate driven by strong (~50°) counterclockwise (CCW) movement of Borneo as a rigid block between 30 and 10 Ma. Murphy (1998) and Morley (2002) pointed out, however, that the lack of known regional structures of suffi cient magnitude to accom-modate such a large rotation poses a challenge to the interpretation of the paleomagnetic data. Hutchison (2010), drawing attention to the lack of paleomagnetic data in key areas of Borneo, suggested that the large oroclinal bend in Bor-neo’s interior highlands is strong evidence that Borneo did not deform as a single rigid block.

There are two fundamental issues regarding the paleomagnetic evidence for the rotation of

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Geosphere; October 2012; v. 8; no. 5; p. 1146–1169; doi:10.1130/GES00750.1; 16 fi gures; 2 tables.Received 8 September 2011 ♦ Revision received 23 March 2012 ♦ Accepted 27 March 2012 ♦ Published online 18 September 2012

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Paleomagnetism of the Crocker Formation, NW Borneo

Geosphere, October 2012 1147

Borneo, remagnetization and sampling density. Although the regional paleomagnetic data com-piled by Fuller et al. (1999) included strongly rotated, weakly rotated, and nonrotated sites, their analysis excluded weakly rotated and nonrotated sites older than 10 Ma on the prem-ise that those sites were remagnetized to the modern geomagnetic fi eld direction. The data compiled by Fuller et al. (1999) are heavily weighted toward the southern part of Borneo

(136 sites from the Schwaner Mountains, South Kalimantan, Central Kalimantan, and Sara wak) and Palawan (38 sites); only 9 sites are from Sabah. In interpreting the paleomagnetic record from Borneo, Fuller et al. (1999, p. 21) stated, “…fall back to an essentially rigid plate model with much of Kalimantan, Sarawak and south-ern Sabah participating in a rotation of about 50° CCW between 30 and 10 Ma.” The nuance of this statement is signifi cant; south Palawan’s

~60° CCW rotation by the end of the Oligocene (Almasco et al., 2000) predates the proposed CCW rotation of southern and central Borneo, which implies the presence of a signifi cant right-lateral shear zone between northern Sabah and the rest of Borneo. Although such a shear zone has not been identifi ed onshore, the 20 Ma and 15 Ma reconstructions by Hall (2002) show the development of a dextral transform fault offshore along the Balabac line (Milsom et al.,

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Figure 1. (A) Regional tectonic and geological features by ETOPO2v2 (http://www.ngdc.noaa.gov/mgg/fl iers/01mgg04.htmlbathymetry) and Shuttle Radar Topography Mission digital elevation model (yellow and brown <1000 m elevation). Inset box shows outline of map of Figure 2B. Major tectonic elements: IAP—Indo-Australian plate, ICB—Indochina block, PSP—Philippine Sea plate, SCB—South China block, SLB—Sundaland block, CS—Celebes Sea, SS—Sulu Sea, SCS—South China Sea. (Fault patterns are from Morley, 2002; Pubel-lier et al., 2005; Fyhn et al., 2009; Cullen et al., 2010). Heavy lines with fi lled triangles mark subduction zones; dashed lines with fi lled triangles mark active deep-water thrust belts adjacent to Neogene basins (BB—Baram Basin, KB—Kutei Basin, SB—Sandakan Basin, TB—Tarakan Basin). Fault zones and older tectonic boundaries: ADL—Andag line, BAL—Balabac line, BRL—Baram line, EVF—East Vietnam fault zone, LL—Lupar line, TL—Tinjar line, MPFZ—Mae Ping fault zone, RRFZ Red River fault zone, THFZ—Tua Hoa fault zone, UBF—Ulugan Bay fault, SF—Sangkulirang fault zone. Outline of oceanic crust and seafl oor-spreading anomalies in SCS in dashed lines are from Barckhausen and Roeser (2004) and Hsu et al. (2004). DG—Dangerous Grounds, MB—Macclesfi eld Bank, RB—Reed Bank, SP—south Palawan, NP—north Palawan, LUC—Luconia. (B, C) Two end-member models for the region’s late Cenozoic tectonic evolution discussed in text (adapted from Cullen et al., 2010).



Cullen et al.

1148 Geosphere, October 2012

1997) between Sabah and Palawan (Fig. 1) that accommodates the movement of Palawan dur-ing of the opening of the South China Sea. The kinematics of the fault predict CW rotation of Palawan rather than the CCW rotation of Bor-neo. In a study of peninsular Malaysia, Richter et al. (1999) similarly concluded that, if the regional Southeast Asia paleomagnetic data are taken at face value, there must have been bound-aries between CCW rotating blocks.

Sabah occupies a critical position with respect to constraining the Cenozoic rotational history of Borneo, but is an undersampled area with respect to the surrounding regions. We address that short-coming and report the results of a paleomagnetic

study of 40 sites at 14 locations in northwest Sabah that sampled Eocene to Early Miocene sandstones of the Crocker, West Crocker, Meli-gan, and Kudat Formations (Fig. 2).

REGIONAL GEOLOGICAL FRAMEWORK

Borneo’s geological framework consists of three fundamental parts (Fig. 3): southwest Kalimantan, the interior highlands, and the sur-rounding coastal lowlands with offshore basins. Southwest Kalimantan, Indonesia, is a Paleo-zoic cored fragment of Australian Gondwana that was accreted to Indochina during the Creta-

ceous (Metcalf, 2011). Late Mesozoic continen-tal arc igneous rocks in the Schwaner Mountains of Kalimantan provide suitable paleomagnetic data (Haile et al., 1977). Borneo’s interior high-lands are dominated by the Rajang-Embaluh supergroup, a thick succession of strongly deformed Late Cretaceous to Paleogene deep-water clastic sediments lifted to present-day elevations of >1 km. The depositional and struc-tural history of the Rajang-Embaluh supergroup is widely interpreted in terms of an accretion-ary prism (Hamilton, 1979; Rangin et al., 1990; Tongkul, 1997a; Bakar et al., 2007). Hutchison (1996) and Moss (1998), however, suggested that the younger units of this succession postdate

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Figure 2. (A) Stratigraphic column (modifi ed from Cullen, 2010; Lambiase et al., 2008). BMU—Base Miocene unconformity, DRU—deep regional unconformity, SOU—Sarawak orogeny unconformity, SRU—shallow regional unconformity. (B) Simplifi ed geological map of western Sabah (Tongkul, 1997b; Tate, 2001; Hutchison, 2005; Tongkul, 2006) showing locations and units sampled: Cr—Crocker Forma-tion (squares), KD—Kudat Formation (hexagon), Mlg—Meligan sandstone (circles), WCr—West Crocker (circles). Other abbreviations: KoK—city of Kota Kinabalu, KGV—Keningau Valley, MK—Mount Kinabalu pluton, Tbr—Temburong Formation, TO—Telupid ophio-lite (ultramafi c rocks shown in dark gray), SP—Sook Plains, TBV—Tambunum Valley, TNV—Tenom Valley, BL—Belud (BL) location, TS—TS car wash location, KK—Kota Kinabalu location, BS—Bukit Sepanger, NX—Nexus, JS—Jalan Salaiman, LK—Lok Kawi, KG—Keningau Pass, TN—Tenom, KM—Kampong Mua, KGV—Keningau Valley (see text).





subduction and record deposition in a marginal ocean basin that was subsequently deformed during the Sarawak orogeny (discussed in the following). The coastal lowlands and offshore areas of Borneo are occupied by Neogene fore-land basins that contain as much as 10 km of largely shallow-marine successions that record extensive denudation, 4–6 km, of the interior

highlands (Hamilton, 1979; Hall and Nichols, 2002; Morley and Back, 2008).

The igneous record of northern Borneo is rather sparse. The oldest igneous rocks are a series of Mesozoic aged variably serpentinized ultramafi c bodies and chert-spillite assemblages (Hutchison, 1975) that crop out in north-central Sabah (near the village of Telupid), on islands

northeast of Sabah, and on south Palawan (Fig. 3). A regional Bouguer gravity high that extends between these outcrops is interpreted as a region-ally extensive late Mesozoic ophiolite complex (Cullen, 2010). Paleomagnetic data indicating very strong CCW rotation of the ophiolites at Telupid and south Palawan (Fuller et al., 1999; Almasco et al., 2000) support that interpretation.

114 E 116 E 118 E112 E110 E

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Figure 3. (A) Regional geological framework of Borneo (simplifi ed after Tate, 2001; Hutchison, 2005). Abbreviations as in Figures 1 and 2. SPSO, south Palawan Sabah ophiolite, is outlined in black dashes with ultramafi c outcrops shown in dark gray. Sintang igneous suite is in white triangles; Paleogene fl ysch deposits are in light green with fold belt trend in green dashes showing oroclinal bend in highland; Plio-cene–Pleistocene volcanic plateaus are in white with small v symbols; gray X marks—Mount Kinabalu pluton. Plots of previously published paleomagnetic results (Fuller et al., 1991, 1999; Lumadyo et al., 1993; Schmidtke et al., 1990) are grouped into domains (discussed in text). The pie diagram plots show the range of data shaded, with the average declinations shown with arrows. On the plot for Sabah, KQ denotes Kappa Quarry intrusion. Figures with photos refer to locations in Figure 3. CCW—counterclockwise; CW—clockwise; C.E.—central east-ern. (B) The regional Bouguer gravity fi eld (Cullen et al., 2010); red corresponds to high Bouguer values, blue to low values.



Cullen et al.


The Sintang igneous suite in southern Sara-wak and central Kalimantan comprises Oligo-cene–Miocene calc-alkaline stocks and dikes that are an important element of the paleo-magnetic record, in part because several of these intrusions have absolute age determina-tions (Schmidtke et al., 1990; Lumadyo et al., 1993; Fuller et al., 1999; Prouteau et al., 2001). In northwest Sabah, Mount Kinabalu is a Late Miocene (7.85–7.22 Ma) granitic pluton that intrudes the Crocker Formation and older ultra-mafi c rocks (Vogt and Flower, 1989; Cottam et al., 2010). A satellite stock related to Mount Kinabalu is one of the paleomagnetic sites of Fuller et al. (1999). The central highlands are capped locally by a dissected tableland of fl at-lying basalt fl ows that have whole-rock K-Ar dates between 1.8 and 1.3 Ma (van de Weerd, 1987). The paleomagnetic record from all 17 sites at 3 different locations more than 30 km apart is excellent, and records nonrotated reversed directions and an average inclination similar to those of the present fi eld (Lumadyo et al., 1993).

In the northwest Borneo region, Cenozoic deformation has resulted in the development of several regional angular unconformities (Bol and van Hoorn, 1980; Levell, 1987; Hutchison, 1992) that have been interpreted as the products of two episodes of orogeny: the Eocene Sara-wak orogeny and the Middle to Late Miocene Sabah orogeny (Hutchison, 1996). Regional unconformities mark the end of a series of events that occurred prior to the unconformity, not the events themselves; even a short orogeny lasts ~20 m.y. (Dewey, 2005). Thus, although Late Miocene deformation and basin inver-sion in southeast Sabah has been attributed to the Meliau orogeny (Balaguru et al., 2003; Balaguru and Hall, 2008), the short-term aspect of those events suggests that the Meliau orogeny is a continuation of the Sabah orogeny rather than a third orogeny.

Tectonic models for Borneo’s two principal episodes of orogenesis envision a series of conti-nental blocks progressively colliding with Sara-wak, then Sabah, and lastly Palawan (Longley, 1997; Hall, 1996; Murphy, 1998). Two episodes of strong deformation are recognized within our study area (D1 folds are refolded by D2); these episodes can be interpreted as the records of either separate pulses within the continuum of one orogeny or as the products of two distinct orogenies. The expression of orogenesis on Bor-neo has been strongly infl uenced by its tropical climate; high erosionally driven denudation rates have prevented building of topographic relief suffi cient to trigger tectonic denudation by extensional orogenic collapse and exposure of a metamorphic core (Hall and Nichols, 2002).

In the case of the Sabah orogeny, isostatically driven uplift related to delamination of the lower crust or slab detachment exerted a postcolli-sional buoyant infl uence on the orogen (Hutchi-son et al., 2000; Morley and Back, 2008).

Sarawak Orogeny

The Sarawak orogeny is defi ned by a pro-found angular unconformity that truncates iso-clinally folded members of the Rajang-Embaluh supergroup (Hutchison, 1996), which makes a large oroclinal bend in the central highlands and then extends into Sabah; the upper member, the Crocker Formation, is the principal unit sam-pled in this study. Hutchison (2010) interpreted this oroclinal bend as the result of indentation owing to collision of the Luconia block during the Sarawak orogeny. The Sarawak orogeny unconformity is diachronous, becoming pro-gressively younger to the northeast. In Kaliman-tan, the unconformity is capped by the Nyaan Volcanics, dated as 48.6 Ma (Moss, 1998), whereas in Sarawak, biostratigraphic data indi-cate that the limestone cover sequences are Late Eocene, ca. 38 Ma (Hutchison, 2005). Although outcrops exposing this unconformity were not identifi ed, Hutchison (1996) interpreted the Sarawak orogeny unconformity to extend into Sabah, where Late Eocene to Oligocene sand-stones that contain ultramafi c rock fragments crop out in central Sabah near the Telupid ophiolite and in northwest Sabah, on the Kudat Peninsula, have been interpreted as being above a Late to Middle Eocene unconformity (Cullen, 2010; Rangin et al., 1990). In addition, Schluter et al. (1996) identifi ed a Late Eocene uncon-formity throughout the southern South China Sea where Oligocene limestones overlie Late Eocene marine clastic rocks. Thus, the body of evidence suggests that the Sarawak orogeny was of greater regional extent and magnitude than its provincial name implies.

Sabah Orogeny

The Sabah orogeny was fi rst proposed by Hutchison (1996) to account for uplift of the Crocker Formation onshore and the formation offshore of the deep regional unconformity (ca. 15 Ma) and shallow regional unconformity (ca. 9 Ma; Bol and van Hoorn, 1980; Levell, 1987). These unconformities are progressively younger to the northwest and their development is attributed to basinward tilting of a set of inde-pendently deforming basement blocks (Levell , 1987). An older (20–22 Ma) unconformity identifi ed in southeast Sabah (Balaguru and Nichols, 2004) is in the equivalent stratigraphic position as the top of the Crocker (base of the

Miocene) unconformity identifi ed in onshore western Sabah (van Hattum et al., 2006). These older unconformities are a strong indication that the Sabah orogeny commenced in the earliest Miocene. Whether the Sabah orogeny was ini-tiated by collision of the Dangerous Grounds with Borneo owing to CCW rotation of Borneo (Hall, 2002) or by underthrusting of the Dan-gerous Grounds driven by rifting in the South China Sea is an issue addressed in this study. The Dangerous Grounds are composed of small islands and shallow reefs in the eastern South China Sea that have formed on blocks of rifted continental crust.

Meliau Episode

The Meliau orogeny refers to latest Miocene deformation in southeast Sabah that is charac-terized by sinistral transpression that resulted in minor localized inversion and reactivation of older structures rather than regional uplift and orogenesis (Balaguru et al., 2003; Balaguru and Hall, 2008). Interpreted within the context of a phase of the Sabah orogeny, the Meliau epi-sode corresponds to formation of the shallow regional unconformity, which is characterized by compressive wrench faulting (Levell, 1987). In their study of the deep-water fold-and-thrust belt of the Baram Basin, Hesse et al. (2009) concluded that an along-strike decrease between total shortening and gravity-driven shortening refl ects a southwest to northeast increase in the amount of Pliocene to Holocene basement-involved shortening, a conclusion that implies young regional CCW rotation consistent with sinistral transpression.

PREVIOUS PALEOMAGNETIC STUDIES

Since Fuller et al.’s (1999) review of the paleomagnetism of the greater South China Sea region, no signifi cant regional studies have been published. Although Almasco et al. (2000) presented a thorough analysis of the paleomag-netic record of Palawan, major aspects of that work were fi rst discussed by Fuller et al. (1999). Within that discussion of previous work, we highlight uncertainties and problems, some of which were noted by Fuller et al. (1999). To maintain continuity, we retain the same geo-graphic domains and the criterion for site reli-ability used by Fuller et al. (1999); reliable sites have α

95 < 20 (α

95 is the 95% confi dence

ellipse). Rather than displaying separate pie diagrams for strongly rotated, weakly rotated, and nonrotated sites, the data from each domain are plotted on a single diagram to highlight the range of rotational variation (Fig. 3).





West Kalimantan

Late Mesozoic igneous rocks in the Schwaner Mountains yielded what Haile et al. (1977) considered “satisfactory paleo-magnetic data” from 46 of 48 oriented block samples. Haile et al. (1977), interpreting the data as recording a primary magnetization acquired when the rocks originally cooled, determined a Late Cretaceous paleomagnetic pole for West Kalimantan. Although the dec-linations and inclinations have signifi cant scatter, the results indicate CCW rotation with a maximum and average of 78° and 49°, respectively (Fig. 3). Negligible latitudinal differences between the present-day and Late Cretaceous magnetic poles for West Kali-mantan and the Malay Peninsula led Haile et al. (1977) to conclude that these areas have remained close to their present latitudes and have behaved as a unit that rotated CCW ~50° since the middle Cretaceous. These conclu-sions indicate that the Sundaland block has behaved as a unifi ed tectonic element during the Cenozoic, and imply that paleomagnetic sites from this block should have inclinations close to the present-day geomagnetic fi eld, unless they have undergone rotation about a horizontal axis.

Northwest Borneo

The northwest Borneo domain (Figs. 3 and 4A) refers to the area between the Schwaner Mountains and the coastal area around the city of Kuching (Sarawak, Malaysia), where shal-low intrusions of the Sintang igneous suite yield excellent paleomagnetic data that record a range of CCW rotated sites, as well as two weakly CW rotated sites (Schmidtke et al., 1990; Fuller et al., 1999). The average and maximum rotations for the entire data set are 18.9° CCW and 51° CCW, respectively. Using the absolute age determi-nations from the intrusions at four sites, Fuller et al. (1999) interpreted these data as recording progressively larger CCW rotations of a primary magnetization in increasingly older intrusions, 16.4 Ma to 25.8 Ma. Weakly CCW and CW rotated sites were considered to be remagnetized to the present fi eld, but no analytical data were published in support of that interpretation.

The intrusions near Kuching can be grouped into two categories with respect to composition and age (Prouteau et al., 2001): calc-alkaline diorites (22.3–25.8 Ma) and adakitic micro-tonalites (14.6–6.4 Ma). The dates reported by Prouteau et al. (2001) are important because absolute ages can be assigned to the Kuch-ing Quarry and Bukit Stabor sites, which were

listed as Oligocene–Miocene by Schmidtke et al. (1990). An estimate for the absolute age of other sites can also be assigned on the basis of the composition of the intrusions sampled: calc-alkaline diorites (23.34 Ma) and adakitic micro-tonalites (11.2 Ma). In addition, red mudrocks of the Eocene Silantek Formation also show a range in CCW rotations (Schmidtke et al., 1990). The Silantek Formation is considered to have been deposited ca. 40 Ma (Hutchison, 2010), but may extend into the Early Oligo-cene (Hutchison, 2005) and we assign an age of 35 Ma, latest Eocene. A plot of age versus rotation (inset, Fig. 4B) shows that the amount of CCW rotation increases with age in the north-west Borneo domain. For the igneous rocks with CCW rotation the rate is 3.62°/m.y. At the equatorial latitudes of Borneo, this angular rate implies plate motion of ~4 cm/yr.

Several aspects of the data in the Kuching area merit discussion within the context of tec-tonic models incorporating 50° CCW of a rigid Borneo between 30 and 10 Ma.

1. The Kuching Airport and Kuching Quarry sites (12.2 ± 0.2 Ma, Prouteau et al., 2001) record 2.7° CW and 1.1° CCW rotations, respectively. Fuller et al. (1999) interpreted these weakly rotated sites as being remagnetized to the pres-ent magnetic fi eld. However, these sites record

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Penkurari 14.6 ± 0.4. Ma

Gunung Plandok 6.4 ± 0.2. Ma

Gunung Serambu 11.3 ± 0.3. Ma

Gunung Murong9.3 ± 0.2. Ma

Bau Rd dec 358 / inc +23

Kuching Quarry 12.2 ± 0.3 Madec. 359 / inc -2.1

Pulau Silak 23.7 MaGunung Bush 22.3 MaTiram 21.9 Ma

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A

B

Figure 4. Sintang igneous rocks (fi lled polygons) and paleomagnetic sites (open circles) of the Kuching area, northwest Borneo domain (Schmidtke et al., 1990; Prouteau et al., 2001). Inset to upper right plots age versus rotation: black diamonds have absolute age determina-tions, gray diamonds have ages estimated based of composition of igneous rocks (see text for discussion), squares are sites in Kalimantan (Fuller et al., 1999), gray circles are red beds from the Silantek Formation, and dashed line is regression through the four sites near Kuching having absolute age determinations. CCW—counterclockwise.



Cullen et al.


much shallower inclinations (–2.1° and 2.8°) than that of the present fi eld inclination near Kuching (–20°), which implies rotation about horizontal axes. Because the Kuching Airport and Quarry sites appear to be structurally dis-turbed, their declination data can also be inter-preted as recording rotation to near the present fi eld as an alternative to remagnetization.

2. The Airport and Kuching Quarry sites are ~10 km from the Bukit Stabor site. If the former sites are remagnetized, then remagnetization at the Airport and Kuching Quarry sites is a local event that occurred within the past 10 m.y.

3. Bukit Stabor (12. 9 ± 0.3 Ma; Prouteau et al., 2001) records 8° CCW rotation. If CCW rotation ceased ca. 10 Ma, then the Bukit Stabor site sug-gests that rotation of Borneo ceased abruptly.

4. Gunung Serapi, the oldest site, shows the most rotation (28.8 Ma, 51° CCW), but has a low inclination (–1.2°) relative to that of its paleo-latitude, which should be similar to its present-day latitude if the interpretation of the West Kalimantan data is correct. The inclination at Gunung Serapi suggests rotation about an inclined axis, although Schmidtke et al. (1990) made no structural correction. We suggest that at least part of the observed rotation can be attributed to local deformation, as suggested for the Kuching Quarry and Kuching Airport sites.

5. Sites from Late Eocene to Early Oligocene (ca. 35 Ma) red beds in the upper member of the Silantek Formation are less rotated (maximum

of 42° CCW) than the older Gunung Serapi site (51° CCW). This suggests that the Silantek Formation has rotated differentially CCW with respect to Gunung Serapi.

6. In relation to the Siburan site near Kuching, the dated igneous sites from Kalimantan (Fuller et al., 1999) appear to introduce a short-term reversal in the sense rotation between 16 and 19 Ma (Fig. 4B).

The northwest Borneo domain data clearly convey a sense of CCW rotation. In detail, how-ever, the data suggest that the domain did not behave as a single rigid block. The northwest Borneo domain is along a northwest-southeast–striking early Tertiary suture, known as the Lupar line (Fig. 1), which represents a poten-tial complicating factor when interpreting this domain’s paleomagnetic data. We suspect that some measured rotations in this domain refl ect localized deformation related to reactivation of faults along this suture. Because the sampled intrusions are represented by only single sites, the hypothesis that some of the observed CCW rotations are related to minor shear zones could be tested by sampling multiple sites from indi-vidual intrusions.

Central and East Kalimantan

The central and eastern Kalimantan domain is in the Indonesian highlands of Borneo. Paleo-magnetic data collected by multiple workers

cover a larger area than the northwest Borneo domain (Figs. 3 and 5A). Flat-lying Pliocene–Pleistocene basalts yield reliable paleomagnetic data from 17 sites at 3 different locations more than 30 km apart that record nonrotated, but reversed, declinations with an average inclina-tion close to that of the present fi eld (Lumadyo et al., 1993). These locations provide an impor-tant control point when considering the timing and sense of rotation in other areas. The Sintang suite and older Eocene sites yield rotated and nonrotated sites. The average and maximum rotations are 15° CCW and 60° CCW, respec-tively (Lumadyo et al., 1993; Fuller et al., 1999; Moss et al., 1998). The overall sense and amount of rotation are similar to those observed in the northwest Borneo domain. The large range of rotations within and between locations having similar ages suggests that central and eastern Kalimantan did not rotate as a coherent rigid block (Fig. 5B).

In the Telen-Malnyu area, four closely spaced sites from the Sintang intrusions have age determinations that cluster tightly around 23 Ma, yet show rotations that range from 16° to 60° CCW (Fuller et al., 1999; Moss et al., 1997). The observed range in rotations between these sites could be attributed to dif-fering degrees of remagnetization, as proposed by Fuller et al. (1999). The Telen-Malnyu sites are along the Bengalon fault zone, which is described as a complex set of interconnecting

Nakan

Telen-Malnyu

L. BagunNaga Ruan

0

2N

114E 116E 118E

100 km

0

10

20

30

40

–60 –50 –40 –30 –20 –10 0 10

AgeMa

Degrees rotation (negative is CCW)A

B

Figure 5. (A) Map showing paleomagnetic sites of the central Kalimantan domain (Lumadyo et al., 1993; Moss et al., 1997; Fuller et al., 1999). Location names refer to nearby villages: Nakan (white triangles), Telen-Malnyu (gray triangles), Long (L.) Bagun (black square), Nagu Ruan (white square); gray circles are sedimentary rocks. SFFZ—Sangkulirang fault; BFZ—Bengalon fault zone. (B) Plot of age versus rotation plot with symbols as in Figure 5A. CCW—counterclockwise.





en echelon normal faults that form the bound-ary between the northern Kutei Basin and the Mangkalihat Peninsula (Cloke et al., 1999; Moss, 1998). Relatively steep inclinations at the Telen-Malnyu sites (18°–45°) are consistent with rotation from normal faulting. We consider that differential rotation owing to oblique slip within the Bengalon fault zone is an equally valid explanation for the observed range in the declinations at the Telen-Malnyu sites.

In the Nakan area, lava fl ows in the Sintang suite and Eocene units were sampled at eight locations (Lumadyo et al., 1993); the lava fl ows in the Nakan area have been dated as 14 and 22 Ma (van de Weerd et al., 1987), and we use the average of these two dates, 18 Ma, for the Nakan sites. Sites from the Nakan area data pass a regional fold test and display weak CW and CCW rotations; magnetite is the primary mag-netic carrier (Lumadyo et al., 1993). Lumadyo et al. (1993) interpreted the data to record a non-rotated primary magnetization, whereas Fuller et al. (1999) suggested that the sites record per-vasive remagnetization. Eocene sandstones from the Nakan area yield Cretaceous zircons (Moss et al., 1998). Because the onset temperature for annealing zircon (~200 °C) is lower than the Curie temperature of magnetite (580 °C), remag-netization of the Nakan area must be the result of a diagenetic (chemical) event rather than a thermal event. Chemical remagnetization of igneous rocks can be associated with low-grade metamorphism (Ahmad et al., 2001; Yo-ichero et al., 2000). Thin sections of the Nakan samples, however, show little to no alteration to support the hypothesis of a diagenetic and/or epithermal event (Lumadyo et al., 1993). The fact the Nakan sites pass a tilt test requires that remagnetization predated folding, which is related to Early to Middle Miocene inversion in the Kutai Basin (Cloke et al., 1999). Therefore, even if the Nakan sites have been remagnetized, they should still record a component of postfolding CCW rota-tion. Pending analytical evidence to the contrary, we believe that the Nakan sites represent folded nonrotated primary magnetization.

Palawan and Celebes Sea

Palawan, located north of Sabah and west of the main Philippine archipelago, consists of two blocks of contrasting geology juxtaposed across the Ulugan Bay fault (Figs. 1 and 3). Late Paleo-zoic and Mesozoic sedimentary rocks compose much of the north Palawan block, whereas the south Palawan block is dominated by the south Palawan ophiolite of Late Cretaceous–Eocene age (Raschka et al., 1985; Almasco et al., 2000). Although only 38 of 147 paleomagnetic sites are rated reliable (e.g., α

95 < 20°), those sites provide

a reasonable paleomagnetic record for both Pala-wan blocks. Mesozoic sediments from the north Palawan block have declinations spread over 40° CW rotation, but only minimal differences in their inclinations, and are interpreted to have been remagnetized prior to opening of the South China Sea (ca. 32 Ma) and to record differential CW rotations about vertical axes during rifting (Almasco et al., 2000). The Espina basalts on the south Palawan block record rotated 65° CCW and have inclinations suggesting a paleolatitude near the present Celebes Sea (Almasco et al., 2000). The Celebes Sea also rotated CCW rotation in Late Eocene and Early Oligocene time (Shibuya et al., 1991); this led Almasco et al. (2000) to conclude that the Celebes Sea and south Palawan block shared a common rotational history. Fuller et al.’s (1999) suggestion that, although they record different paleomagnetic results, the north and south Palawan blocks have a common origin, is in agreement with Hinz and Schluter’s (1985) interpretation that Palawan region is underlain by stretched continental crust and that both the north and south Palawan blocks are parts of a microcon-tinent carried south by South China Sea seafl oor spreading. These blocks are linked by a cover sequence of Late Cretaceous to Eocene quartz-rich turbidites having granitic and acidic volcanic rock fragments that record a South China Sea provenance (Suzuki et al., 2000). Therefore, both Palawan blocks appear to share an early tectonic history involving very strong CCW rotation fol-lowed by CW rotation during rifting of the South China Sea.

Sabah

The paleomagnetic record for Sabah is based on a preliminary study by Schmidtke et al. (1985) that was included in syntheses by Fuller et al. (1991, 1999). Although only fi ve loca-tions have reliable data and augmenting analyti-cal work was not published, several important observations can be made (Fig. 3). A single site from a Late Miocene satellite stock (Kappa Quarry) of the Kinabalu pluton near the city of Kota Kinabalu shows weak (11°) CCW rotation (Fuller et al., 1999). Near the village of Telu-pid in central Sabah, Cretaceous cherts from an ophiolitic assemblage record very strong (79°) CCW rotation; although not classifi ed as reliable, associated spillites also record strong (47°) CCW rotation. Along the coast near Kota Kinabalu, three sites from marine red mudstones in the Crocker Formation record strong (average 77°) CCW rotation. Although no specifi c data were presented, Fuller et al. (1999) commented that the associated Crocker sandstones are mostly remagnetized close to the present fi eld, and that some sites have minor CW rotation.

GEOLOGICAL SUMMARY OF UNITS SAMPLED

Crocker Formation

The Crocker Formation is an assemblage of deep-water clastic rocks that includes the medium- to coarse-grained sandstones cored for this study. We obtained a suffi cient number of cores from the Crocker Formation at 11 dif-ferent locations to cover a wide geographic area (Fig. 2). At several additional locations along older road cuts (such as the Bukit Melinsung sec-tion of Lambiase et al., 2008), the unit was too weathered and argillaceous to collect intact cores.

There are two contrasting models for the paleogeographic setting of the Crocker Forma-tion: (1) a basin-fl oor megafan of fi rst-cycle sandstones derived from the Kalimantan domain (Crevello, 2001; van Hattum et al., 2006; Jack-son et al., 2009), and (2) multiple, smaller, toe-of-slope fans derived largely from older mem-bers of the Rajang-Embaluh Group (Lambiase et al., 2008; Cullen, 2010). The Crocker Forma-tion has a steep southeast regional dip, but is deformed locally into large-scale folds. Oppos-ing limbs of individual folds were cored at four locations (Bukit Sepanger, Kota Kinabalu [KK], Kinabalu Industrial [KI], and Tenom). The Crocker Formation records two major epi-sodes of deformation (Fig. 6) that we attribute to the Sarawak and Sabah orogenies, ca. 40 and 20 Ma, respectively.

The age of the Crocker Formation is poorly constrained. At the regional scale, Wilson (1964) assigned an Eocene–Early Miocene age for the formation. Recent studies suggest that the out-crops around Kota Kinabalu are Late Eocene in age (Lambiase et al., 2008; Cullen, 2010). We note that the strong rotation recorded in the Crocker mudstones has sense and magni-tude similar to those recorded in older units at Telupid, south Palawan, and the Celebes Sea. Assigning an Oligocene to Early Miocene age for the red mudrocks of the Crocker Formation (ca. 25 Ma) implies rotation rate of 5.1°/m.y., considerably faster that the rate calculated for the northwest Borneo domain, 3.62°/m.y. Thus, the paleomagnetic data are consistent with the Late Eocene age for the Crocker Formation in the area of Kota Kinabalu.

Kudat Formation

The Early Miocene Kudat Formation crops out on the Kudat Peninsula within a series of northwest-southeast–striking thrust sheets (Tongkul, 1994, 2006). Near Kota Belud at the southwest end of the peninsula, where the Crocker Formation has been thrust over



Cullen et al.


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the Kudat Formation , the structural grain changes nearly 90°. Despite poor outcrop expo-sures on the Kudat Peninsula, we cored four sites, including opposing limbs of an anticline. The site statistics are poor (Table 1). Although these data are included primarily for the pos-sible interest of others, we stress that these data indicate 45° CCW rotation of a postfolding characteristic remanent magnetization (ChRM) carried by pyrrhotite.

West Crocker Formation

The West Crocker Formation sandstones are fi ne- to medium-grained arenites that represent the coarser grained lateral equivalents of the Temburong Formation shales (Wilson, 1964). Although regional structural dip is steep to the southeast, the Temburong–West Crocker strata are complexly folded. The Sipitang-Tenom

road, traversing the Crocker Ranges, is domi-nated by outcrops of Temburong mudrocks. Exposures of the West Crocker Formation along the coastal highway are too deeply weathered to extract intact cores. The Kampong Mua loca-tion is our only data point for the West Crocker Formation.

Meligan Sandstone

The Early Miocene Meligan sandstone crops out mainly in Brunei and Sarawak and consists of cross-stratifi ed, well-sorted, coarse to medium quartz arenites that record deposi-tion in shoreface to shallow-marine environ-ments (Sandel, 1996; Hutchison, 2005). The Meligan sandstone is preferentially preserved in deeply eroded synclines and its contact with the Temburong is locally unconformable. The Meligan sandstone is considered to document

a regression at the top of the Temburong For-mation related to the proto–Champion delta (Sandal, 1996).

SAMPLING AND ANALYTICAL METHODS

Our sampling program comprises 42 sites from 15 locations that form a northeast-south-west transect along the western coast of Sabah (Fig. 2) that is favorably oriented to cross pos-sible northwest-southeast shear zones. Although the Crocker Formation was the principal unit sampled (12 locations), the end points of this transect included locations from the Kudat For-mation (4 sites), the West Crocker Formation (3 sites), and Meligan sandstone (2 sites). Most locations have multiple sites and each site con-sists of ~8 oriented 2.5-cm-diameter drill cores. At fi ve locations the exposures were suitable

TABLE 1. SITE MEANS

Site FormationLat(°N)

Long(°E) Strike Dip

Dec(°)

Inc(°)

α95

In situ KTilt dec

(°)Tilt inc

(°)Tmax(°C) N/N0

BL1 Crocker 6.2918 116.3588 50 90 NC NC NC NC NC NC NC 0TS1 Crocker 6.1680 116.2920 59 70 37.5 16.6 11.1 126 55.4 43.4 325 3/6JS1 Crocker 6.0381 116.1417 199 94 15.6 –0.4 19.3 17 19.6 –3.4 420 5/6LK1 Crocker 5.8339 116.0433 5 71 19 13.9 14.8 40 22.9 –8.3 340 4/5NX1 Crocker 6.1048 116.1341 55 85 10.9 13 7.9 59 68.3 44 340 7/8NX2 Crocker 6.1150 116.1170 47 66 11.4 2.5 9.2 54.0 33.4 33.3 380 6/6KI1 Crocker 6.0829 116.1600 35 100 16.7 5 16.4 23 11.6 3 420 4/6KI2 Crocker 6.0805 116.1576 237 88 0.4 –5.7 8.9 106 64.3 –56.4 460 4/6KI3 Crocker 6.0805 116.1576 237 88 31.2 –0.6 13.9 44 56.7 –25.8 375 4/6BS1 Crocker 6.0670 116.1549 35 58 3.5 13.9 15.5 25 30.5 33.9 320 5/8BS2 Crocker 6.0670 116.1549 35 58 9.7 5.5 14.3 42 25.9 24.3 325 4/7BS3 Crocker 6.0670 116.1549 27 66 19.4 9.2 10.7 75 32.4 10.6 350 4/7BS4 Crocker 6.0670 116.1549 30 58 7.4 17.6 8.7 825 34.1 28.1 310 2/5BS5 Crocker 6.0670 116.1549 30 58 8.8 –2.8 15.4 37 16 16.3 350 4/4BS6 Crocker 6.0670 116.1549 30 58 3.1 2.6 15.3 37 17.3 24 320 4/4BS7 Crocker 6.0667 116.1563 31 86 11.8 18.4 18.4 26 49.1 19.5 330 4/5BS8 Crocker 6.0667 116.1563 31 86 3.2 16.3 11.5 65 47.3 27.8 325 4/5BS9 Crocker 6.0667 116.1563 46 129 24 –9.5 18.9 17 52.5 23 325 4/6BS10 Crocker 6.0667 116.1563 44 133 12.8 –9.1 12.5 55 59.4 28.8 280 5/7BS11 Crocker 6.0667 116.1563 45 124 30 –11.4 15.4 26 43.7 18.7 325 4/6ME1 Crocker 6.0454 116.0937 75 130 257 –32.8 12.1 104 280.2 21.8 325 4/6ME2 Crocker 6.0454 116.0937 75 135 246 –23.7 0.5 990 278.1 10.5 345 4/6KK1 Crocker 6.0498 116.1613 270 58 15.5 –17.2 13.5 345 47.1 –69.6 450 2/4KK2 Crocker 6.0498 116.1613 265 71 359.9 –22.2 39.5 42 119.9 –84.5 340 2/4KK3 Crocker 6.0496 116.1616 19 71 9.7 –6.2 34.4 –3 10.1 6.7 400 2/4KK4 Crocker 6.0496 116.1616 19 71 0.4 13 26.8 22 25.9 21.5 400 4/4KG1 Crocker 5.4381 116.1061 25 45 19.2 13.1 16.3 18 30.3 13.3 420 6/8KG2 Crocker 5.4381 116.1061 25 45 6.2 22.3 16 24 28.8 28.6 420 5/8KGV Crocker 5.3210 116.1386 323 27 333.7 18.2 16.2 239 340.8 11.4 400 5/6TN1 Crocker 4.9940 115.8699 305 22 327.6 24 11.9 444 334.5 14.2 340 2/6TN2 Crocker 4.9940 115.8699 305 22 345.7 0 15.9 61 343.6 –14.1 330 3/6TN3 Crocker 5.0039 115.8439 65 43 352.6 8.5 45.1 9 1.9 48.7 325 3/5TN4 Crocker 5.0039 115.8439 65 43 321 –6.2 13.3 87 321.1 2.5 420 3/7KM1 West Crocker 4.9809 115.6985 255 6 NC NC NC NC NC NC NC 0/3KM2 West Crocker 4.9992 115.6782 165 84 NC NC NC NC NC NC NC 0.3KM3 West Crocker 4.9992 115.6782 0 55 NC NC NC NC NC NC NC 0*/3SP1 Meligan 5.0027 115.5441 70 35 NC NC NC NC NC NC NC 0/2SP2 Meligan 5.0389 115.5206 200 85 NC NC NC NC NC NC NC 0/3KD1 Kudat 7.0386 116.7491 323 29 297.1 39 21.5 19 323.7 45.6 440 4/8KD2 Kudat 6.9062 116.7251 100 70 359.2 4.2 8.3 87 334.9 71 300 5/9KD3 Kudat 6.9157 116.7624 285 65 341.5 –4.7 20.7 36 322.7 –45.9 300 3/7KD4 Kudat 6.8629 116.6999 220 64 292.9 34.1 36.6 12 294 –27.7 450 3/6

53.4–552.18040.6116375.5KKFMGPNote: All sites are sandstones. Dips >90° are overturned beds. NC—No characteristic remanent magnetization signal. PGMF—Present-day geomagnetic magnetic

field (100 yr average). Calculated using National Oceanic and Atmospheric Administration National Geophysical Data Center web site (www.ngdc.noaa.gov/). Dec—declination; Inc—inclination; K—a measure of grouping; α95 is the 95% cone of confidence. Tilt dec and Tilt inc are values after structural correction. Tmax—the maximum temperature that a linear component could be identified on the orthogonal plots. N/N0—the number of specimens with direction versus the number of demagnetized specimens. TN—Tenom, KK—Kota Kinabalu.



Cullen et al.


to confi dently sample opposed anticlinal limbs to conduct tilt tests. To minimize the effects of tropical weathering and oxidation, our sampling program targeted fresh exposures from new housing and road construction.

Subsets of cores from each site were cut into standard paleomagnetic specimens (2.5 × 2.3 cm) and their natural remanent magnetiza-tions (NRM) was measured using a 3-axis 2G Enterprises DC-SQUID cryogenic magnetom-eter housed in a magnetically shielded space at the University of Oklahoma. To isolate possible primary and secondary NRM components, our specimens were subjected to stepwise demagne-tization: 174 specimens were thermally demag-

netized in 35 steps to 700 °C; 36 additional specimens were demagnetized using alternating fi eld (AF) techniques in 12 steps to 100 mT. The AF demagnetized samples tended to have non-linear decay of NRM, making it diffi cult to iso-late any stable remanent magnetization; there-fore only thermally demagnetized specimens were subsequently analyzed. When subjected to thermal demagnetization, more than 98% of the specimens from the Crocker and Kudat Forma-tions showed linear decay of NRM (Fig. 7), and their ChRM was isolated using the least squares method of Kirschvink (1980).

Site mean ChRMs were obtained by averaging individual core specimen mean ChRMs with a

maximum angular deviation of <15° using Fisher (1953) statistics. For sites from the limbs of sin-gle folds, the site means from both limbs were subjected to a fold test following the method of Enkin (2003). This fold test method determines the timing of ChRM acquisition relative fold-ing and potentially provides critical constraints for the relative timing of deformation. Sites are deemed to pass a fold test if the site means are more tightly clustered after correcting for the structural tilt; they fail a fold test if the site means are better grouped in situ and become more scat-tered as the result of structural correction. Based on the outcome of the fold test, a location ChRM direction was obtained by averaging.

NX1 TN4

KM2

SP1

280°C

280°C

200°C

200°C300°C

300°C

W, Up

W, Up

W, Up

W, Up

A

C

D

B

E, Down

E, Down E, Down

E, Down

S, S

S, S S, S

S, SN, N

N, N N, N

N, N

NRM

NRM

NRM

NRM

NRM

NRM

NRMNRM

340°C

340°C

340°C

400°C

420°C

420°C200°C0.1 mA/m

0.1 mA/m

0.1 mA/m

0.1 mA/m

Figure 7. Orthogonal vector plots of thermally demagnetized specimens from the Crocker Formation. (A) Nexus (NX1). (B) Tenom (TN4). (C) West Crocker Formation (Kampong Mua, KM2). (D) Meligan sandstone (Sipitang location specimen-1, SP1). A and B show maximum laboratory unblocking temperatures of 340 °C and 420 °C for isolation of the characteristic remanent magnetization (ChRM), suggesting that pyrrhotite and magnetite are the magnetic remanence carriers, respectively. C and D show absence of a ChRM signal. White sym-bols—vertical component; black symbols—horizontal component; NRM—natural remanent magnetization.





Following the convention used by Fuller et al. (1999), only those site means with α

95 < 20° are

deemed reliable. Dispersion caused by paleo-secular variation of the geomagnetic fi eld is an issue that should be addressed when assessing if a declination could due to tectonic rotation. Secular variation is at a minimum at low lati-tudes and multiple sites were collected over a large area to average the secular variation. In addition, if the rocks contain secondary magne-tization, remagnetization processes commonly take a long enough time to average secular variations. If the ChRM is primary and the age of the rock unit is known, then the calculated directions give an estimate of the paleolatitude at acquisition. If the ChRM is secondary, then the age of remagnetization is critical for inter-preting the structural history of that unit.

Selected core specimens (8) representative of the different rock formations were subjected to saturation isothermal remanent magnetization (SIRM) tests, determining the dominant mag-netic minerals in each formation. An isother-mal remanent magnetization (IRM) acquisition curve for each specimen was obtained by pulse magnetization in 26 steps to 2500 mT. Because magnetic minerals (e.g., magnetite, pyrrhotite, and hematite) acquire IRM at different rates and saturate over a range of specifi c fi eld intensities, IRM acquisition curves provide information on the presence and relative amounts of the mag-netic minerals in a specimen (Kruiver et al., 2001; Heslop et al., 2002, 2004). Analysis of the IRM acquisition curves was conducted using the IRMUNMIX 2.2 software program (Heslop et al., 2002) and cumulative log-Gaussian (CLG) analysis was performed using the IRM-CLG 1.0 (Kruiver et al., 2001) to model the different coer-civity contributions (Heslop et al., 2004).

LOCATION RESULTS

The site statistics are tabulated in Table 1. The majority of our locations are within 10 km of Kota Kinabalu, where the averaged magnetic fi eld for the past 110 years is declination (dec) 1.25°E, inclination (inc) –4.35° (Table 1). As previously noted, fl at-lying Pliocene–Pleisto-cene basalts in central Kalimantan have similar small (reversed) declinations and low negative inclinations. Therefore, in discussion of our data, the present-day magnetic fi eld is used the reference fi eld.

Crocker Formation

The Belud (BL) location, a weathered road cut 50 km north of Kota Kinabalu, carried no stable remanence. This was the only such nega-tive result from the Crocker Formation.

The TS car wash location (TS), a fresh quarry 30 km north of Kota Kinabalu, yielded a single site. Stable ChRM directions with maximum unblocking temperatures of 325 °C suggest that pyrrhotite is the magnetic remanence car-rier (Table 1). The in situ location mean has dec 37.5° and inc 16.6°; respective tilt-corrected val-ues are 55.5° and 43.4° (Fig. 8A).

Jalan Salaiman (JS) and Lok Kawi (LK) are single site locations; Jalan Salaiman is within Kota Kinabalu and Lok Kawi is 15 km south of Kota Kinabalu and occupies an intermedi-ate geographic position relative to the southern

Keningau and Tenom locations (Fig. 2). The maximum unblocking temperatures for speci-mens from sites JS1 (420 °C) and LK1 (340 °C) indicate that magnetite and pyrrhotite are the respective chief magnetic remanence carriers (Table 1). The Jalan Salaiman in situ location mean has dec 15.6° and inc –0.4°; respective tilt-corrected values are 19.6° and –3.4° (Fig. 8B). The Lok Kawi in situ location mean has dec 19.9° and inc 13.9°; respective tilt-corrected values are 22.9° and –8.3° (Fig. 8C).

The Nexus (NX) location is the westernmost of four locations (NX, KI, Bukit Sepanger [BS],

N

TSin situ

Specimen Mean ChRMs

TStilt corrected

Specimen Mean ChRMs

S

W E

α95 = 11.1 α95 = 11.1

S

N

N

LKin situ

Specimen Mean ChRMs

LKtilt corrected

Specimen Mean ChRMs

S

W W

α95 = 14.8 α95 = 14.8

S

N

N

JSin situ

Specimen Mean ChRMs

JStilt corrected

Specimen Mean ChRMs

W W

α95 = 19.3 α95 = 19.3

N

A

B

C

Figure 8. Stereoplots showing in situ and tilt-corrected specimen means and location mean characteristic remanent magnetizations (ChRMs) and α95 values. (A) TS car wash. (B) Jalan Salaiman (JS). (C) Lok Kawi (LK). Filled circles—positive inclinations; open circles—negative inclinations; square—location mean.



Cullen et al.


and KK) that traverse two folds 15 km north of Kota Kinabalu (Fig. 9A). The NX specimens show a linear decay indicating a single compo-nent of magnetization having a northern ChRM (Fig. 7A); maximum temperature (Tmax) and IRM data indicate that pyrrhotite is the domi-nant ChRM carrier (Tables 1 and 2). The NX sites have α

95 < 10° (Table 1). The in situ site

means have dec 10.9° and 11.2°, and inc 13° and 2.5°. The tilt-corrected site means have dec 68.3° and 33.4° and inc 44° and 33.3° (Table 1). The α

95 of the in situ location mean is signifi -

cantly lower than that for the tilt-corrected loca-tion mean, showing that the ChRM was acquired after tilting (Fig. 9B).

The KI location is an anticlinal fold with a steeply dipping overturned eastern limb (Fig.

10A). The location comprises 3 sites with acceptable α

95 values. Unblocking temperatures

ranged from 460 to 375 °C, suggesting that pyrrho tite and magnetite are the magnetic rema-nence carriers (Table 1). The KI in situ location mean has dec 16.1° and inc –0.4°; respective tilt-corrected values are 53.2° and –23.3° (Fig. 9C). The in situ location mean has a signifi -cantly lower α

95, indicating that ChRM acquisi-

tion postdates folding at this location. The red mudrocks exposed in the overturned limb of the KI anticline (Fig. 9A) represent the same Crocker Formation lithology that records 77° CCW rotation (Fuller et al., 1999). Although we were unable to recover intact core speci-mens of the red mudrocks at the KI location and could not determine chief magnetic remanence

carrier(s), Crevello (2001) reported that the red mudrock facies is hematitic. We suspect that hematite is the dominant magnetic mineral and the ChRM in the red mudrocks represents a pre-folding, possibly primary, signal.

The Bukit Sepanger (BS) location consists of 11 sites where more than 500 m of continu-ous stratigraphic succession is exposed (Fig. 10A). All sites have stable ChRM directions. The tight cluster of unblocking temperatures about a mean of 323 °C (Table 1) indicates that pyrrhotite is the magnetic remanence carrier. The respective in situ and tilt-corrected Bukit Sepanger location mean ChRM directions are dec 12.8°, inc 4.6° and dec 35.5°, inc 17.2°. The α

95 of the in situ location mean, 8.0, is sig-

nifi cantly lower than that for the tilt-corrected

Ocean

Unit with red mudrocksNX 3,4 KI 3,4KI 1,2

BS 1-12 KK 1-4

Nexus Member

NX 1,2,

Maju Member

KI 1 KI 2, 3

5 kmNW SE

A

B C

2 km

N

W

α95 = 23.9 α95 = 68.0 α95 = 25.3 α95 = 64.7

WE E

NXin situ

Site Mean ChRMs

KIin situ

Site Mean ChRMs

NXtilt corrected

Site Mean ChRMs

KItilt corrected

Site Mean ChRMs

S S S S

NN N

Figure 9. (A) Cross section through the NX-KI-BS-KK (see Fig. 2 for abbreviations) locations showing KI and KK anticlines used for fold tests; no vertical exaggeration. Inset photo shows overturned red mudrocks that record strong counterclockwise rotation. (B) NX in situ and tilt-corrected specimen mean and location mean characteristic remanent magnetizations (ChRMs) and α95 values. (C) KI values.





location mean, 14.6 (Fig. 10B), which indicates that the ChRM was acquired after tilting. Dur-ing progressive untilting, optimal grouping for the location mean occurred at 50% untilting, which suggests that ChRM acquisition was late synfolding to postfolding. At the southeast end of this location, the Crocker Formation is locally overturned, forming a small kink fold (Fig. 10C). Sites BS7–BS11 are from a single bed in both the upright and overturned limbs of that kink fold. The ChRMs from the overturned limb (BS9–BS11) have negative inclinations, whereas sites from the upright limb (BS7–BS9) have positive inclination. Because the sites are within a single bed, the simplest explanation for these opposed inclinations is that the kink fold postdates ChRM acquisition. Restoring the overturned limb to the 86° southeast dip it had prior to development of kink fold results in posi-tive inclinations for all 5 sites (Fig. 10C), which indicates that the kink fold postdates ChRM acquisition.

To test our kink-fold hypothesis, we recal-culated the in situ location mean for the Bukit Sepanger location after making a structural correction for the kink fold, restoring it to it a prekink dip of 86° southeast. This test reduced the α

95 value from 8.6 to 5.9 (Fig. 10D) and sup-

ports the hypothesis that kink folding postdates ChRM acquisition. Establishing the age of the kink fold offers a way place a lower (younger) age limit for timing ChRM acquisition. The Bukit Sepanger sites are within the footwall of a thrust fault that postdates tilting (Lambiase et al., 2008). We interpret the kink fold and

small thrusts observed at the location (Fig. 10C) to result from footwall deformation beneath the younger thrust fault.

The Kota Kinabalu (KK) location consists of four sites from opposed limbs at the crest of a small upright anticline. The α

95 values for the

site means from this location are poor relative to the other locations along the NX-KK transect, a circumstance we attribute to a combination of localized crestal faulting and late-stage fl uid fl ow, as indicated by mild hematite staining (Fig. 11A). For the only site deemed reliable, KK1, the in situ and tilt-corrected site mean ChRM directions are dec 15.5°, inc –17.2 and dec 47.1°, inc 69.6° (Table 1). We note that α

95 for in situ location mean is lower than that

for the tilt-corrected location mean (Fig. 11B), which is consistent with the postfolding ChRM acquisition from other limbs of the NX-KI-BS-KK folds.

The Keningau Pass (KG) location consists of two closely spaced sites from southeast-dipping outcrops exposed during construction of the Papar-Keningau road over the Crocker Range (Fig. 2). The Keningau Pass site means are reli-able, and unblocking temperatures of ~420 °C suggest that magnetite is the dominant magnetic remanence carrier (Table 1). The in situ site means have dec 19.2° and 6.2° and inc 13.1° and 22.3°. The tilt-corrected site means have dec 30.3° and 28.8° and inc 13.3° and 28.6° (Table 1; Fig. 12A).

The Keningau Valley (KGV) location con-sists of a single site from a ridge separating the Keningau and Tenom Valleys on the eastern side

of the Crocker Range (Fig. 2). This ridge, as well as a similar feature between Keningau and Tambunum, is interesting from a regional struc-tural perspective because the northwest strike of the Crocker Formation is nearly orthogonal the main Crocker Range and the Keningau Pass location. The results from the Keningau Valley location are reliable, and maximum unblocking temperatures (400 °C) indicate that magnetite and/or pyrrhotite are magnetic remanence car-riers (Table 1).

The in situ location mean has dec 337.5° and inc 18.2°; respective tilt-corrected values are 340.8° and 11.4° (Table 1; Fig. 12B). In the absence of multiple sites for a structural correc-tion, we prefer interpreting the CCW rotation at Keningau Valley as recording post-ChRM acquisition deformation similar to our other locations.

The Tenom (TN) location consists of four sites near the crest of the Tenom Pass in a road recently cut through the Crocker Range between Sipitang and Tenom. Sites TN1 and TN2 are from east-dipping limb and sites TN3 and TN4 are from the steeply west dipping forelimb of an asymmetric anticline, which is locally over-turned (Fig. 13A). Of the four Tenom sites, three are deemed reliable. IRM data and maximum unblocking temperatures ranging from 310 to 420 °C indicate that pyrrhotite and/or magnetite are the magnetic remanence carriers (Tables 1 and 2). The respective in situ and tilt-corrected Tenom location mean ChRM directions are dec 331.4°, inc 5.9 and dec 333.1°, inc 0.9. The α

95 of the in situ location mean is signifi cantly

lower than that for the tilt-corrected location mean (Fig. 13B). A fold test using the 3 reliable Tenom sites gave the best grouping of data at 32.1% ± 14.0% untilting, indicating that mag-netization was acquired late synfolding to post-folding.

West Crocker Formation

The Kampong Mua (KM) location consists of three sites from a compact anticline along the Sipitang-Tenom road (Figs. 2 and 13A). Although the outcrop exposure was fresh and competent to core, none of the specimens ana-lyzed gave stable magnetic remanence when thermally demagnetized (Fig. 7C). The IRM data indicate that hematite is present (Table 2). These results contrast with the Crocker Forma-tion, which is dominated by pyrrhotite and mag-netite in its magnetic mineralogy. Considering the fresh nature of this road cut location, the lack of a preferred magnetic orientation suggests that the hematite refl ects primary deposition as a heavy mineral rather than in situ oxidation and/or weathering.

TABLE 2. MINERAL MAGNETIC DATA

Formation Site SIRM B1/2 DPContribution

(%)Magnetic mineral

Crocker BS4 1.30 45.7 0.34 57.0 Magnetite0.74 56.2 0.12 33.0 Pyrrhotite0.22 562.3 0.34 10.0 Hematite

NX2 1.00 38.2 0.23 39.5 Magnetite1.30 67.6 0.16 43.7 Pyrrhotite0.29 939.7 0.37 11.3 Hematite

KK1 0.31 27.4 0.42 24.3 Magnetite0.94 63.5 0.23 72.7 Pyrrhotite0.04 929.0 0.18 3.0 Hematite

KG1 4.73 46.7 0.31 67.6 Magnetite2.30 127.4 0.42 32.4 Pyrrhotite

TN1 1.20 41.5 0.28 45.8 Magnetite1.20 68.9 0.20 46.2 Pyrrhotite0.20 549.5 0.59 8.0 Hematite

West CrockerTemburong KM1 1.10 55.0 0.42 6.3 Pyrrhotite

16.00 1905.5 0.23 93.7 Hematite

Meligan SP1 1.10 55.0 0.31 100.0 Pyrrhotite

Kudat KD4 1.40 57.7 0.23 1.9 Pyrrhotite70.0 891.3 0.38 98.1 Hematite

Note: SIRM—saturation isothermal remanent magnetization in 10–3 A/m; B1/2 is the mean remanence coercivity (in mT); DP is the half-width of the distribution (in mT). These mineral magnetic parameters were obtained from measured IRM acquisition curves, following Kruiver et al. (2001). Site abbreviations are those used in text.



Cullen et al.


NW

SE

A

50 m

Ove

rturn

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8

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NW

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1 m

Incl

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tilt-c

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Site

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n C

hRM

s

E

NNN

α 95 =

8.0

α 95 =

14.

6

α 95 =

8.0

α 95 =

5.9

Fig

ure

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of B

ukit

Sep

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r (B

S) s

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Meligan Sandstone

The Sipitang (SP1, SP2) locations do not carry stable magnetic remanence when ther-mally demagnetized (Fig. 7D). The IRM sig-nal from the Meligan sandstones shows that pyrrhotite is present (Table 2); we interpret as a primary accessory heavy mineral. At the SP2 location, the Meligan was so tightly cemented that it was necessary to collect an oriented block sample for coring with a drill press in the labora-tory; this suggests that it has not been affected by surfi cial oxidation.

DISCUSSION

This study represents the most comprehen-sive paleomagnetic sampling program under-taken in Sabah to date; 11 of 15 locations along a 250 km northeast-southwest transect have reliable site means. Our results present us with four straightforward observations. We believe, however, that the paleomagnetic database is not yet suffi cient to draw tightly constrained conclusions integrated within a regional tec-tonic framework. Therefore, we direct our dis-cussion toward framing testable hypotheses

drawn from our observations, which if answered should allow more rigorous tectonic models to be advanced.

Pervasive Remagnetization of the Crocker Sandstones

Locations having reliable ChRM site means recorded declinations and inclinations that are distinctly different from the present-day geo-magnetic fi eld (Table 1). For example, the mean ChRM direction derived from the 19 reliable sites around Kota Kinabalu (dec 13.39°, inc

B

+ +

α95 = 58.2 α95 = 180.0

KK In situ

Site Mean ChRMs

KK

EW

N N

SS

tilt corrected Site Mean ChRMs

A

NW SE

Figure 11. (A) Outcrop photo of crest of Kota Kinabalu (KK) location anticline; circles are site locations. (B) In situ and tilt-corrected speci-men and location means, characteristic remanent magnetizations (ChRMs), and α95 values for the KK anticline location.



Cullen et al.


3.22°) records a relative CW rotation with a positive rather than negative inclination. Our data demonstrate that the Crocker Formation sandstones record an older remagnetization event, rather than carrying the signal of the present-day fi eld as was suggested by Fuller et al. (1999; commenting on their unpublished data). The widespread geographic coverage of our locations suggests that remagnetization was a regional event. Apatite fi ssion track and vitrinite refl ectance data indicate that maximum burial temperatures for the Crocker Formation were ~150–200 °C (Hutchison et al., 2000; Anuar et al., 2003). In thin section, the Crocker Formation sandstones lack quartz overgrowths and sutured grain contacts that would indicate relatively deep and hot maximum burial condi-tions. These paleotemperature indicators sug-gest that the burial temperatures never exceeded the Curie temperature for either pyrrhotite or

A

KG 1,2 In situ

site mean ChRMs

+

KGV In situ

Specimen means

B

N N

SS

E

α95 = 16.0α95 = 16.3

E

Figure 12. Stereoplots showing in situ and tilt-corrected specimen mean characteristic remanent magnetizations (ChRMs) and α95 values. (A) Keningau Pass (KG) location. (B) Keningau Valley (KGV) location.

B

10 km VE 2XA

WNW ESWSP1

SP2 KM 1-3

TN3-4 TN-1Tmbr

MLG

Cr

Tenom Fault WCR

Cr

N N

S

W E

TNtilt corrected

Site Mean ChRMs (α95 < 20)

TNin situ

Site Mean ChRMs (α95 < 20)

S

α95 = 22.9 α95 = 38.0

Figure 13. (A) Cross section from Sipitang (SP) to Tenom (TN) (modifi ed from Wilson, 1964; Cullen, 2010) through the SP, Kampong Mua (KM), and TN locations. (B) Stereoplots show in situ and tilt-corrected site mean characteristic remanent magnetizations (ChRMs) and α95 values for the TN location. Disharmonic folding in the Temburong Formation is schematically depicted, but is in accordance with fi eld observations.





magnetite. Crocker sandstones showed a single linear decay trend during thermal demagnetiza-tion, indicating a single event (Fig. 7).

The SIRM data from the Crocker sandstones show that both pyrrhotite and magnetite are present (Table 2) and the range in Tmax (280–450 °C) suggests that both phases may carry the ChRM (Table 1). In considering these observa-tions in relation to time-temperature remag-netization curves for magnetite and pyrrhotite (Dunlop et al., 2000), we favor interpreting the ChRM in the Crocker Formation sandstones, particularly for pyrrhotite, as a chemical (dia-genetic) rather than thermal event. A number of chemical mechanisms have been proposed for the origin of the ChRMs that reside in pyrrho tite and magnetite in sedimentary rocks; pyrrho-tite mechanisms include authigenesis caused by preexisting magnetite reacting with pyrite during burial metamorphism under reducing conditions (Gillett, 2003), oxidation of pyrite (Salmon et al., 1988), and thermochemical sulfate reduction (Peirce et al., 1998). These mechanisms can be related to such processes as migration of hydrocarbons (Machel and Bur-ton, 1991), diagenesis of gas hydrates (Housen and Musgrave, 1996), and release of pore fl uids (Urbat et al., 2000). Late-stage remagnetization by the diagenetic formation of sulfi de-bearing minerals, such as pyrrhotite, is documented on the island of Sakhalin and may be related to migration of hydrocarbons (Weaver et al., 2002). Magnetite ChRMs can be explained by burial diagenetic mechanisms such as maturation of organic matter (Banerjee et al., 1997; Blumstein et al., 2004) and clay diagen-esis (Katz et al., 2000), or by fl uid migration events (Elmore et al., 1999, 2001). In light of the orogenic setting of northwest Borneo, we attribute acquisition of the ChRM signal in the Crocker Formation sandstones as the product of large-scale fl uid fl ow in a foreland basin, as has been documented in similar settings elsewhere (e.g., Elmore et al., 2001; Enkin, 2003). Our site mean declinations are all northward with shallow inclinations from the Crocker Forma-tion, indicating that they record normal polarity magnetization. Because the late Cenozoic is a time of rapidly alternating normal and reversed polarity states, we consider crystallization of the phases carrying the ChRM to have occurred in a relatively short interval, 1–2 m.y.

It is remarkable that the red mudrocks of the Crocker Formation in the Kota Kinabalu area show strong CCW rotation (Fuller et al., 1991), whereas the mean paleomagnetic direc-tion derived for the sandstones around Kota Kinabalu (JS, LK, NX, KI, BS, and KK in Fig. 2) shows weak CW rotation. As a work-ing hypothesis we propose that the ChRM in

red mudrocks preserves an older, probably primary, magnetization that was not reset by expelled foreland basin fl uids owing to the impermeable nature of the Crocker Formation mudrocks. If so, the amount of CCW rotation in the mudrocks is even greater than reported when corrected for the younger CW rotation recorded in the Crocker sandstones. The strong CCW rotations observed in Eocene and older units in south Palawan, the Celebes Sea, and central Sabah (Fig. 3) lead us to interpret the paleomagnetic data from the Crocker Formation as indirectly supportive of an Eocene age for the Crocker Formation.

No ChRM Signal in the West Crocker and Meligan Sandstones

In contrast to the Crocker Formation, nei-ther the West Crocker nor Meligan sandstones yielded a ChRM signal, even though the IRM data indicate that hematite and pyrrhotite, respectively, are present. The Kampong Mua and Sipitang samples are from fresh outcrops that lacked the argillaceous weathering profi le that characterized the Belud location, the only other location that lacked a ChRM signal. We tentatively interpret the West Crocker and Meli-gan sites as never having acquired a ChRM sig-nal, rather than as having acquired such a signal and subsequently having it obliterated by later events such as weathering. We acknowledge that, owing to the limited number of sites in these units, this interpretation should be tested with additional sampling and analyses.

The supposition that the Meligan and West Crocker Formations were not affected by the same fl uids that pervasively remagnetized the Crocker Formation is consistent in treating these units as a tectonostratigraphic element that is distinctly different from the Crocker Forma-tion (Fig. 2). From this viewpoint, the Crocker Formation was thrust over the foreland basin sediments of the Sarawak orogeny (i.e., West Crocker and Temburong Formations) along such faults as the Tenom fault during the Sabah orogeny (Figs. 2 and 13A; Cullen, 2010). Because the Sabah orogeny does not appear to have produced the pervasive remagnetization recorded in the Crocker Formation, we suggest that remagnetization of the Crocker Formation records basin-wide fl uid expulsion related to the Sarawak orogeny.

Age of ChRM Acquisition

We treat the Crocker Formation as Late Eocene in age (albeit with a range of uncer-tainty, 35 ± 5 Ma), similar to the age of the red beds in the Silantek Formation (northwest Bor-

neo domain). Remagnetization of the Crocker Formation sandstones generally postdates folding, although tilt tests from the Tenom and Bukit Sepanger locations suggest remagnetiza-tion could be a late synfolding. Working with a relatively small, but extremely well exposed outcrop at Bukit Sepanger, Lambiase et al. (2008) documented two episodes of folding. The earliest episode, D1, records syndeposi-tional folding in an active deep-water fold-thrust belt during generation of the large-scale folds of the NX-KK cross section (Fig. 9A). During the second episode of deformation (D2), the D1 folds were recumbently. The east-dipping limb of our Bukit Sepanger sites has been inter-preted as being in the footwall of a younger (D2) thrust fault (Lambiase et al., 2008). Strong D2 deformation cutting across earlier D1 structures is also observed at Bandar Sierra, 3.5 km east of Bukit Sepanger (Fig. 6B). In Cullen (2010), this earlier phase of deformation was attributed to the Late Eocene to Early Oligocene Sara-wak orogeny. The structural relations at Bukit Sepanger offer the possibility for establishing the relative timing of remagnetization, if the ChRM signal was acquired prior to the second episode of deformation and if the age of the sec-ond deformation can be established.

As shown earlier, restoration of the over-turned limb of the kink fold at Bukit Sepanger improved the pre-tilt location mean (Fig. 10D) and restored the negative inclinations (BS9–BS11) back to the positive inclinations that char-acterize the site (Fig. 10C). This suggests that development of the kink fold postdates ChRM acquisition. During our reconnaissance program, block samples collected from overturned beds at 2 sites from Maju East, 500 m east of Bukit Sepanger, yielded reliable site means (Table 1; Fig. 14B) that we initially considered to record extremely strong CCW rotation, similar to the Crocker Formation red mudrocks. Subsequent to our full fi eld program, the Maju East site was further cleared for additional housing, exposing an antiformal syncline that records large-scale recumbent refolding of the Crocker Formation (Fig. 6A). This new exposure led us to reconsider our original interpretation at the Maju East loca-tion in terms of refolding during D2. Although we do not know the precise orientation of the D2 fold axis, and therefore cannot correctly restore the lower limb of the recumbent fold at the Maju East site, several lines of evidence suggest that the D2 fold axis was subhorizontal. First, out-crop patterns of long linear ridges and the gentle plunge of fold axes (our observations, and map from Crevello, 2001) suggest that tilting is minor. Second, because southwest to north-east paleofl ow directions (reviewed by Hutchi-son, 2005) are nearly orthogonal to regional



Cullen et al.


+

ME 1-2

In Situ

D2 correction assuming horizontal axis

500 cm

A B

ME 1-2

C

20 cm

50 cm

20 cm

1 m

Figure 14. (A) Outcrop photo of Maju East location showing large load casts on overturned limb of antiformal syncline. (B) Stereoplot shows in situ mean characteristic remanent magnetizations (ChRMs) with a notional structural correction for D2 deformation assuming a horizontal fold axis. (C) Horizontal to gently plunging fl ute marks and load casts in Crocker Formation sandstones.





shortening (southeast-northwest), the amount of plunge on folds can be estimated from the inclination of fl ute marks and load casts. Over the entire study area, including Maju East, these features plunge gently (Fig. 14C). Our inclina-tion data are also consistent with minimal post-ChRM tilting. Using a horizontal fold axis as a fi rst-order approximation for unfolding D2, the Maju East data restore to a pre-D2 CW rotation similar to that observed at Bukit Sepanger (Fig. 14B), although with larger declinations and inclinations.

We cannot put an absolute age on the tim-ing of D2. It is observed at several locations in the Kota Kinabalu area, suggesting that it not a local event confi ned to Bukit Sepanger. In the shallow offshore, immediately west of our study area, seismic data (Cullen, 2010, fi gs.

6, 11, and 23 therein) show that the shallow regional unconformity (ca. 8.2 Ma) is virtu-ally undeformed, which puts a lower limit on D2. In contrast, the section beneath the deep regional unconformity is strongly folded. Although the pre–deep regional unconformity phase of the Sabah orogeny represents a good candidate for the relative timing D2 (between 22 and 15 Ma), we indicated here that the Sabah orogeny did not appear to produce per-vasive remagnetization. Therefore, we must also consider D2 as a continuation of the Sara-wak orogeny, a strong possibility in light of late-synfolding ChRM acquisition indicated at Tenom and Bukit Sepanger. The preponder-ance of evidence suggests that remagnetization of the Crocker Formation sandstones occurred between 15 and 35 Ma, that is, between devel-

opment of the deep regional unconformity and the waning stages of the Sarawak orogeny (Figs. 2 and 15).

CW and CCW Rotations Observed

In contrast to the CCW rotations that domi-nate West Kalimantan, northwest Borneo, cen-tral Kalimantan, south Palawan, and the older units in Sabah, both CW and CCW rotations are observed in the Crocker Formation (Fig. 15). The different polarities in rotations are not ran-domly distributed, but rather can be grouped into three discrete geographic domains (Fig. 16). In the Kota Kinabalu area, the Crocker Formation sandstones record an average of 12° CW rota-tion. It is interesting that a single site from a Late Miocene (8.2 Ma) granite near Kota Kinabalu

0

10

20

30

40

50

60

70

80

90

–100 –80 –60 –40 –20 0 20 40 60

Age Ma

degrees rota�on (CCW is nega�ve)

Crocker Sandstones

Crocker mudstones

Telupid chert

Kappa granite

NWB Igneous

NWB redbeds

CE Kalimantan

SW Kal

SP

N P

Figure 15. Plot of rotation versus age for all data (this study; Fuller et al., 1991, 1999; Lumadyo et al., 1993; Schmidtke et al., 1990). Dashed vertical lines show uncertainty in the age of the Crocker Formation; open dashed green circles indicate age of sandstones with fi lled green circles indicating our best estimate for the age of characteristic remanent magnetization acquisition. CCW—counterclockwise; CE—central eastern; SP—south Palawan; NP—north Palawan; NWB—northwest Borneo; SW Kal—southwest Kalimantan.



Cullen et al.


shows 11° CCW rotation (Fuller et al., 1999); this could be related to the Meliau episode of the Sabah orogeny. If additional sampling confi rms that Late Miocene CCW rotation occurred over a larger area of the pluton, then it would imply that the Crocker sandstones in the Kota Kinabalu domain may have actually undergone 23° CW rotation, consistent with the extrusion-collision model for opening the South China Sea. Near the Keningau Pass area (KG1 and KG2), the Crocker Formation sandstones also show mild CW rotation similar to that of the Kota Kinabalu area, indicating a large domain of CW rotation. South of the KG1 and KG2 locations, however, Crocker sandstones from the Tenom and Kenin-gau Valley locations record a change in the polar-ity of rotation, showing moderately strong CCW rotation. How far this CCW rotated domain extends to the southwest is not known, due to lack of sampling; further work is needed.

The data from the Kudat Peninsula, although of marginal quality, indicate fairly strong (46°) CCW rotation that appears to postdate folding of Oligocene to Early Miocene sandstones. An Early Miocene or younger age CCW rota-tion of the Kudat Peninsula is problematic not only to the data around Kota Kinabalu, but also with respect to the data indicating that south Palawan’s CCW rotation was concluded by the Oligocene (Almasco et al., 2000). If accepted at face value, the data imply that these areas moved independently at different times.

CONCLUSIONS

Reliable ChRM measurements from Ceno-zoic sandstones of the Crocker and Kudat For-mations at 12 locations along a 250 km north-east-southwest transect on the northwest side of Sabah, Malaysia, show that these sandstones are

pervasively remagnetized. Rock magnetic analy-ses indicate the ChRM signal in the Crocker Formation sandstones resides in pyrrho tite and magnetite. Fold tests at fi ve locations show that ChRM acquisition postdates folding. Sandstones from the Temburong–West Crocker and Meli-gan units lack stable remanence, suggesting that these units had a different diagenetic history than the Crocker Formation sandstones.

Placing constraints on the timing for ChRM acquisition is problematic. A mean paleomag-netic direction using 6 locations in the Kota Kinabalu area indicates that the Crocker sand-stones record 12° CW rotation that postdates folding related to the Sarawak orogeny (D1). A second episode of deformation (D2), recorded at Bukit Sepanger, Maju East, and Bandar Sierra, appears to postdate ChRM acquisi-tion. D2 deformation was suffi ciently intense to recumbently fold the D1 (pre-ChRM) folds.

43 degSite

rotation

No ChRM

13

2628

KD

TS

NX-KI-BS-KK

LK

KGV

KG

TN

BL

KM

SP

MK

JS

TO

1619

3812

11

N

50 km

Figure 16. Vertical-axis rotation estimates derived from the locality means plotted on a digital elevation model. Arrows show sense of rotation. Smaller gray symbol shows clockwise rotation for single site at the Kappa Quarry discussed in text. ChRM—characteristic remanent magnetization. For abbreviations, see Figure 2.





Placed within a regional geological context and previous paleomagnetic studies, we suggest the following sequence of events. An early epi-sode (before 35 Ma) of strong regional CCW rotation, recorded in the red mudrocks of the Crocker Formation, ended with the Sarawak orogeny, during which the Crocker Formation was strongly deformed (D1) and its sandstones pervasively remagnetized during regional fl uid expulsion. Owing to their impermeable nature, mudrocks of the Crocker Formation were not remagnetized during the Sarawak orogeny. A younger episode of deformation (D2) that postdates ChRM acquisition in the Crocker sandstones may represent an early (ca. 15–22 Ma) phase of the Sabah orogeny or the waning late stages of the Sarawak orogeny (ca. 35 Ma). Therefore, we interpret that acquisi-tion of the ChRM signal in the Crocker sand-stones around the Kota Kinabalu area occurred between 15 and 35 Ma. Limited data from the West Crocker and Meligan units indicate that the Sabah orogeny had little effect with respect to remagnetization.

Paleomagnetic data from the Crocker and Kudat sandstones can be grouped in three large-scale domains on the basis of differences in the direction, amount, and timing of rotation. The Kudat domain shows moderate CCW rotation that appears to postdate folding of Early Mio-cene sediments. In the central domain (Kota Kinabalu to Keningau Pass) minor CW rotation occurred between 15 and 35 Ma, and could be attributed to opening of the South China Sea. The southwest domain (Tenom and Keningau Valley) records late synfolding to postfolding ChRM acquisition and moderate CCW rotation. The opposed sense of rotation between the cen-tral and southwest domains is problematic for interpreting CW rotation of the central domain in terms of opening of the South China Sea. The minor CCW rotation at the single site from the Late Miocene Kappa Quarry stock (Fuller et al., 1999) adds further complexity to defi ning the region’s rotational history because it suggests local overprinting of younger rotation related to the Meliau orogeny.

We consider the present data set insuffi cient to support little more than speculation with respect to interpreting the precise boundaries and origin of the different rotated domains in Sabah in context of a detailed tectonic frame-work. We believe, however, that the full regional data set (Figs. 3 and 15) is suffi ciently robust to support two broad conclusions regarding the region’s tectonic evolution. First, in accord with all earlier studies, Sabah, along with the entire region, rotated CCW prior to 30 Ma. Second, the younger CW and CCW rotations are too complex to reconcile with models that show

the entire island of Borneo and south Palawan rotating CCW as a rigid block between 30 and 10 Ma. Instead the data imply that strain has been partitioned in a complex manner with several overprinting episodes of deformation. The present data, including regional geological mapping and age determinations, are not suf-fi cient to resolve the manner in which strain has been partitioned. However, the recovery of reliable paleomagnetic data over a wide area of Sabah should encourage workers to collect additional paleomagnetic data to help resolve remaining structural, tectonic, and diagenetic questions.

ACKNOWLEDGMENTS

We thank Ibrahim bin Amnan (Minerals and Geo-science Department of Malaysia, Sabah) for approving export permits for our samples. We also thank Calum Macdonald of Shell E&P for his role in approving the funding for this study and for granting Cullen time to lead in the fi eld work, and Chris Morley and three anonymous reviewers for their constructive criticisms and comments that enabled us to sharpen the focus of our work within the limitations of the data.

REFERENCES CITED

Ahmad, M.N., Fujiwara, Y., and Paudel, L.P., 2001, Remag-netization of igneous rocks in Gupis area of Kohistan arc, northern Pakistan: Earth, Planets and Space, v. 53, p. 373–384.

Almasco, J.N., Fuller, M., Rodolf, K., and Frost, G.M., 2000, Paleomagnetism of Palawan, Philippines: Journal of Asian Earth Sciences, v. 18, p. 369–389, doi:10.1016/S1367-9120(99)00050-4.

Anuar, A., Abolins, P., Crevello, P., and Abdullah, W.H., 2003, A geochemical evaluation of the West Crocker Formation—Clues to deepwater source rock facies. Paper 6: Proceedings, Geological Society of Malaysia Petroleum Geology Conference and Exhibition, Kuala Lumpur, Malaysia, p. 39–40.

Bakar, Z.A., Madon, M., and Muhamud, A.J., 2007, Deep-marine sedimentary facies in the Balaga Formation (Cretaceous–Eocene), Sarawak: Observations from new outcrops in the Sibu and Tatau area: Geological Society of Malaysia Bulletin, v. 53, p. 35–45.

Balaguru, A., and Hall, R., 2008, Tectonic evolution and sedimentation of Sabah, north Borneo, Malaysia: American Association of Petroleum Geologists, 2008 International Conference, Cape Town, South Africa, Search and Discovery Article 30084.

Balaguru, A., and Nichols, G., 2004, Tertiary stratigraphy and basin evolution, southern Sabah (Malaysian Bor-neo): Journal of Asian Earth Sciences, v. 23, p. 537–554, doi:10.1016/j.jseaes.2003.08.001.

Balaguru, A., Nichols, G., and Hall, R., 2003, The origin of the circular basins of Sabah: Geological Society of Malaysia Bulletin, v. 46, p. 333–351.

Banerjee, S., Elmore, R.D., and Engel, M.H., 1997, Chemi-cal remagnetization and burial diagenesis: Testing the hypothesis in the Pennsylvanian Belden Formation, Colorado: Journal of Geophysical Research, v. 102, p. 24,825–24,842, doi:10.1029/97JB01893.

Barckhausen, U., and Roeser, H.A., 2004, Seafl oor spread-ing anomalies in the South China Sea revisited, in Clift, P., et al., eds., Continent-ocean interactions within East Asian marginal seas: American Geophysi-cal Union Geophysical Monograph 149, p. 121–125, doi:10.1029/149GM07.

Blumstein, A.M., Elmore, R.D., Engel, M.H., Elliot, C., and Basu, A., 2004, Paleomagnetic dating of burial diagenesis in Mississippian carbonates, Utah: Journal of Geophysical Research, v. 109, B04101, doi:10.1029/2003JB002698.

Bol, A.J., and van Hoorn, B., 1980, Structural styles western Sabah offshore: Geological Society of Malaysia Bul-letin, v. 12, p. 1–16.

Briais, A., Patriat, P., and Tapponnier, P., 1993, Updated interpretation of magnetic anomalies and sea fl oor spreading stages in the South China Sea: Implications for the Tertiary tectonics of Southeast Asia: Jour-nal of Geophysical Research, v. 98, p. 6299–6328, doi:10.1029/92JB02280.

Cloke, I.R., Moss, S.J., and Craig, J., 1999, Structural con-trols on the evolution of the Kutai Basin, East Kaliman-tan: Journal of Asian Earth Sciences, v. 17, p. 137–156, doi:10.1016/S0743-9547(98)00036-1.

Cottam, M., Hall, R., Sperber, C., and Armstrong, R., 2010, Pulsed emplacement of layered granite: New high-precision age data from Mount Kinabalu, North Bor-neo: Geological Society of London Journal, v. 167, p. 49–60, doi:10.1144/0016-76492009-028.

Crevello, P.D., 2001, The great Crocker submarine fan: A world-class foredeep turbidite system: Proceedings, Indonesian Petroleum Association, 28th Annual Con-vention, Jakarta, p. 378–407.

Cullen, A.B., 2010, Transverse segmentation of the Baram-Balabac Basin, NW Borneo: Refi ning the model of Borneo’s tectonic evolution: Petroleum Geoscience, v. 16, p. 3–29, doi:10.1144/1354-079309-828.

Cullen, A.B., Reemst, P., Henstra, G., Gozzard, S., and Ray, A., 2010, Rifting of the South China Sea: New per-spectives: Petroleum Geoscience, v. 16, p. 273–282, doi:10.1144/1354-079309-908.

Dewey, J.F., 2005, Orogeny can be very short: National Academy of Sciences Proceedings, v. 102, p. 15,286–15,293, doi:10.1073/pnas.0505516102.

Dunlop, D. J., Ozdemira, O., Clark, D. A., and Schmidt, P. W., 2000, Time–temperature relations for the remag-neti za tion of pyrrhotite (Fe7S8) and their use in estimating paleotemperatures: Earth and Planetary Science Letters, v. 176, p. 107–116.

Elmore, R.D., Banerjee, S., Campbell, T., and Bixler, G., 1999, Paleomagnetic dating of ancient fluid-flow events and paleoplumbing in the Arbuckle Moun-tains, southern Oklahoma, in Parnell, J., ed., Dat-ing and duration of fluid flow events and rock-fluid interaction: Geological Society of London Special Publication 144, p. 9–25, doi:10.1144/GSL.SP.1998.144.01.02.

Elmore, R.D., Kelley, J., Evans, M., and Lewchuk, M., 2001, Remagnetization and orogenic fl uids: Testing the hypothesis in the central Appalachians: Geophysical Journal International, v. 144, p. 568–576, doi:10.1046/j.0956-540X.2000.01349.x.

Enkin, R.J., 2003, The direction correction tilt test: An all-purpose tilt/fold test for paleomagnetic studies: Earth and Planetary Science Letters, v. 212, p. 151–166, doi:10.1016/S0012-821X(03)00238-3.

Fyhn, M.B., Boldreel, L.O., and Nielsen, L.H., 2009, Geo-logical development of the Central and South Viet-namese margin: Implications for the establishment of the South China Sea, Indochinese escape tectonics and Cenozoic volcanism: Tectonophysics, v. 478, p. 184–214, doi:10.1016/j.tecto.2009.08.002.

Fisher, R.A., 1953, Dispersion on a sphere: Royal Society of London Proceedings, v. 217, p. 295–305, doi:10.1098/rspa.1953.0064.

Fuller, M., Haston, R., Lin, J.L., Richter, B., Schmidtke, E., and Almasco, J., 1991, Tertiary paleomagnetism of regions around the South China Sea: Journal of Southeast Asian Earth Sciences, v. 6, p. 161–184, doi:10.1016/0743-9547(91)90065-6.

Fuller, M., Ali, J.R., Moss, S.J., Frost, G.M., Richter, B., and Mahfi , A., 1999, Paleomagnetism of Borneo: Journal of Asian Earth Sciences, v. 17, p. 3–24, doi:10.1016/S0743-9547(98)00057-9.

Gillett, S.L., 2003, Paleomagnetism of the Notch Peak contact-metamorphic aureole, revisited: Pyrrhotite from magnetite + pyrite under submetamorphic condi-tions: Journal of Geophysical Research, v. 108, 2446, doi:10.1029/2002JB002386.

Haile, N.S., McElhinny, M.W., and McDougall, I., 1977, Palaeomagnetic data and radiometric ages from the Cretaceous of West Kalimantan (Borneo) and their signifi cance in interpreting regional structure: Geo-



Cullen et al.


logical Society of London Journal, v. 133, p. 133–144, doi:10.1144/gsjgs.133.2.0133.

Hall, R., 1996, Reconstructing Cenozoic SE Asia, in Hall, R., and Blundell, D.J., eds., Tectonic evolution of Southeast Asia: Geological Society of London Spe-cial Publication 106, p. 153–184, doi:10.1144/GSL.SP.1996.106.01.11.

Hall, R., 2002, Cenozoic geological and plate tectonic evolu-tion of SE Asia and the SW Pacifi c: Computer-based reconstructions, model and animations: Journal of Asian Earth Sciences, v. 20, p. 353–431, doi:10.1016/S1367-9120(01)00069-4.

Hall, R., and Nichols, G.J., 2002, Cenozoic sedimentation and tectonics in Borneo: Climatic infl uences on oro-genesis, in Jones, S.J., and Frostlick, L., eds., Sediment fl ux in basins: Causes, controls, and consequences: Geological Society of London Special Publication 191, p. 5–22, doi:10.1144/GSL.SP.2002.191.01.02.

Hamilton, W., 1979, Tectonics of the Indonesian region: U.S. Geological Survey Professional Paper 1078, 345 p.

Heslop, D., Dekkers, M.J., Kruiver, P.P., and Van Oorschot, I.H.M., 2002, Analysis of isothermal remanent magneti sation acquisition curves using the expectation-maximisation algorithm: Geophysics Journal Inter-national, v. 148, p. 58–64.

Heslop, D., McIntosh, G., and Dekkers, M.J., 2004, Using time- and temperature-dependent Preisach models to investigate the limitations of modelling isothermal remanent magnetization acquisition curves with cumu-lative log Gaussian functions: Geophysics Journal International, v. 157, p. 55–63.

Hesse, S., Back, S., and Franke, D., 2009, The deep-water fold-and-thrust belt offshore NW Borneo: Gravity-driven versus basement-driven shortening: Geologi-cal Society of America Bulletin, v. 121, p. 939–953, doi:10.1130/B26411.1.

Hinz, K., and Schluter, H.U., 1985, Geology of the Dan-gerous Grounds, South China Sea, and the continen-tal margin of southwest Palawan: Results of SONNE cruises SO-23 and SO-27: Energy, v. 10, p. 297–315, doi:10.1016/0360-5442(85)90048-9.

Holloway, N.H., 1982, North Palawan Block, Philippines—Its relation to Asian mainland and role in the evolution of South China Sea: American Association of Petro-leum Geologists Bulletin, v. 66, p. 1355–1383.

Housen, B.A., and Musgrave, R.J., 1996, Rock-magnetic signature of gas hydrates in accretionary prism sedi-ments: Earth and Planetary Science Letters, v. 139, p. 509–519, doi:10.1016/0012-821X(95)00245-8.

Hsu, S., Yeh, Y., Doo, W., and Tsai, C., 2004, New bathym-etry and magnetic lineations identifi cations in the northernmost South China Sea and their tectonic implications: Marine Geophysical Researches, v. 25, p. 29–44, doi:10.1007/s11001-005-0731-7.

Hutchison, C.S., 1975, Ophiolite in Southeast Asia: Geological Society of America Bulletin, v. 86, p. 797–806, doi:10.1130/0016-7606(1975)86<797:OISA>2.0.CO;2.

Hutchison, C.S., 1992, The Eocene unconformity in south-east and east Sundaland: Geological Society of Malay-sia Bulletin, v. 32, p. 69–88.

Hutchison, C.S., 1996, The ‘Rajang accretionary prism’ and ‘Lupar Line’ problem of Borneo, in Hall, R., and Blundell, D.J., eds., Tectonic evolution of Southeast Asia: Geological Society of London Special Publi-cation 106, p. 247–261, doi:10.1144/GSL.SP.1996.106.01.16.

Hutchison, C.S., 2005, Geology of north-west Borneo: Amsterdam, Elsevier, 421 p.

Hutchison, C.S., 2010, Oroclines and paleomagnetism in Borneo and South-East Asia: Tectonophysics, v. 496, p. 53–67, doi:10.1016/j.tecto.2010.10.008.

Hutchison, C.S., Bergman, S.C., Swauger, D., and Graves, J.E., 2000, A Miocene collisional belt in north Borneo, uplift mechanism and isostatic adjustment quantifi ed by thermochronology: Geological Society of London Journal, v. 157, p. 783–793, doi:10.1144/jgs.157.4.783.

Jackson, A., Zakaria, A.A, Johnson, H.D., Tongkul, F., and Crevello, P.D., 2010, Sedimentology, stratigraphic occurrence and origin of linked debrites in the West Crocker Formation (Oligo-Miocene), Sabah, NW Bor-

neo: Marine and Petroleum Geology, v. 26, p. 1957–1973.

Katz, B., Elmore, R.D., Cogoini, M., Engel, M.H., and Ferry, S., 2000, Associations between burial diagenesis of smectite, chemical remagnetization, and magne-tite authigenesis in the Vocontian Trough, SE France: Journal of Geophysical Research, v. 105, p. 851–868, doi:10.1029/1999JB900309.

Kirschvink, J.L., 1980, The least-squares line and plane and the analysis of paleomagnetic data: Geophysical Jour-nal of Research, v. 62, p. 699–718, doi:10.1111/j.1365-246X.1980.tb02601.x.

Kruiver, P.P., Dekkers, M.J., and Heslop, D., 2001, Quan-tifi cation of magnetic coercivity components by the analysis of acquisition curves of isothermal remanent magnetisation: Earth and Planetary Science Let-ters, v. 189, p. 269–276, doi:10.1016/S0012-821X(01)00367-3.

Lambiase, J.J., Tzong, T.Y., William, A.G., and Cullen, A.B., 2008, The West Crocker Formation of northwest Borneo: A Paleogene accretionary prism, in Draut, A.E., et al., eds., Formation and applications of the sedimentary record in arc collision zones: Geological Society of America Special Paper 436, p. 171–184, doi:10.1130/2008.2436(08).

Lee, T.Y., and Laver, L.A., 1995, Cenozoic plate recon-structions of Southeast Asia: Tectonophysics, v. 251, p. 85–138, doi:10.1016/0040-1951(95)00023-2.

Leloupe, P.H., Lacassin, R., Tapponnier, P., Scharer, U., Zhang Dalai, and Lui Xiahan, 1995, The Ailao Shan–Red River shear zone (Yunnan, China), Tertiary trans-form boundary of Indochina: Tectonophysics, v. 251, p. 3–84, doi:10.1016/0040-1951(95)00070-4.

Levell, B.K., 1987, The nature and signifi cance of regional unconformities in the hydrocarbon-bearing Neogene sequences offshore West Sabah: Geological Society of Malaysia Bulletin, v. 21, p. 55–90.

Longley, I.M., 1997, The tectonostratigraphic evolution of SE Asia, in Fraser, A.J., et al., eds., Petroleum geol-ogy of Southeast Asia: Geological Society of London Special Publication 126, p. 311–339, doi:10.1144/GSL.SP.1997.126.01.19.

Lumadyo, E., McCabe, R., Harder, S., and Lee, T., 1993, Borneo: A stable portion of the Eurasian margin since the Eocene: Journal of Southeast Asian Earth Sciences, v. 8, p. 225–231, doi:10.1016/0743-9547(93)90024-J.

Machel, H.G., and Burton, E.A., 1991, Causes and spatial distribution of anomalous magnetization in hydrocar-bon seepage environments: American Association of Petroleum Geologists Bulletin, v. 75, p. 1864–1876.

Metcalfe, I., 2011, Tectonic framework and Phanerozoic evolution of Sundaland: Gondwana Research, v. 19, p. 3–21, doi:10.1016/j.gr.2010.02.016.

Milsom, J., Holt, R., Ayub, D., and Smail, R., 1997, Gravity anomalies and deep structural controls at the Sabah-Palawan margin, South China Sea, in Fraser, A.J., et al., eds., Petroleum geology of Southeast Asia: Geo-logical Society of London Special Publication 126, p. 417–427, doi:10.1144/GSL.SP.1997.126.01.25.

Morley, C.K., 2002, A tectonic model for the Tertiary evolu-tion of strike-slip faults and rift basins in SE Asia: Tec-tonophysics, v. 347, p. 189–215, doi:10.1016/S0040-1951(02)00061-6.

Morley, C.K., and Back, S., 2008, Estimating hinterland exhumation from late orogenic basin volume, NW Borneo: Geological Society of London Journal, v. 165, p. 353–366, doi:10.1144/0016-76492007-067.

Moss, S.J., 1998, Embaluh Group turbidites in Kalimantan: Evolution of a remnant ocean basin in Borneo during the Late Cretaceous to Paleogene: Geological Society of London Journal, v. 155, p. 509–524, doi:10.1144/gsjgs.155.3.0509.

Moss, S.J., Chambers, J., Cloke, I., Carter, A., Satria, D., Ali, J.R., and Baker, S., 1997, New observations on the sedimentary and tectonic evolution of the Tertiary Kutai Basin, East Kalimantan, in Fraser, A.J., et al., eds., Petroleum geology of Southeast Asia: Geological Society of London Special Publication 126, p. 395–416, doi:10.1144/GSL.SP.1997.126.01.24.

Moss, S.J., Carter, A., Baker, S., and Hurford, A.J., 1998, A Late Oligocene tectono-volcanic event in East Kali-mantan and the implications for tectonics and sedimen-

tation in Borneo: Geological Society of London Journal, v. 155, p. 177–192, doi:10.1144/gsjgs.155.1.0177.

Murphy, R.W., 1998, SE Asia reconstruction with a non-rotating Borneo: Geological Society of Malaysia Bul-letin, v. 42, p. 85–94.

Peirce, J.W., Goussev, S.A., Charters, R.A., Ambercrombie , H.J., and DePaoli, G.R., 1998, Intrasedimentary mag-netization by vertical fl uid fl ow and exotic geochem-istry: Leading Edge, v. 17, p. 89–92, doi:10.1190/1.1437840.

Prouteau, G., Maury, R.C., Sajona, F.G., Pubellier, M., Cotten , J., and Bellon, H., 2001, Le magmatisme post-collisionnel du Nord-Ouest de Bornéo, produit de la fusion d’un fragment de croûte océanique ancré dans le manteau supérieur: Bulletin de la Société Géologique de France, v. 172, p. 319–332, doi:10.2113/172.3.319.

Pubellier, M., Rangin, C., Le Pichon, X., and Dotsea Work-ing Group, 2005, DOTSEA—Deep Offshore Tectonics of Southeast Asia; a synthesis of deep marine data in Southeast Asia: Mémoire de la Société Géologique de France and American Association of Petroleum Geolo-gists Special Publication 176, 32 p.

Rangin, C., Bellon, H., Bernard, F., Letouzey, J., Muller, C., and Tahir, S., 1990, Neogene arc-continent collision in Sabah, northern Borneo (Malaysia): Tectonophysics, v. 183, p. 305–319, doi:10.1016/0040-1951(90)90423-6.

Rangin, C., Spakman, W., Pubellier, M., and Bijward, H., 1999, Tomographic and geologic constraints on sub-duction along the eastern Sundaland continental mar-gin, South-East Asia: Bulletin de la Société Géologique de France, v. 170, p. 755–788.

Raschka, H., Nacario, E., Rammlmair, D., Samonte, C., and Steiner, L., 1985, Geology of the ophiolite of central Palawan Island, Philippines: Ofi oliti, v. 10, p. 375–390.

Replumaz, A., and Tapponnier, P., 2003, Reconstruction of the deformed collision zone between India and Asia by backward motion of lithospheric blocks: Journal of Geophysical Research, v. 108, 2285, doi:10.1029/2001JB000661.

Richter, B., Schmidtke, E., Fuller, M., Harbury, N., and Samsudin, A.R., 1999, Paleomagnetism of Peninsu-lar Malaysia: Journal of Asian Earth Sciences, v. 17, p. 477–519, doi:10.1016/S1367-9120(99)00006-1.

Salmon, E., Edel, J.B., Pique, A., and Westphal, M., 1988, Possible origins of Permian remagnetizations in Devo-nian and Carboniferous limestones from the Moroc-can Anti-Atlas (Tafi lalet) and Meseta: Physics of the Earth and Planetary Interiors, v. 52, p. 339–351, doi:10.1016/0031-9201(88)90126-4.

Sandal, S.T., 1996, The geology and hydrocarbon resources of Negara Brunei Darussalam: Seria, Brunei, Brunei Shell Petroleum and Brunei Museum, 243 p.

Schluter, H.U., Hinz, K., and Block, M., 1996, Tectono-stratigraphic terranes and detachment faulting of the South China Sea and Sulu Sea: Marine Geology, v. 130, p. 39–78, doi:10.1016/0025-3227(95)00137-9.

Schmidtke, E., Dunn, J.R., Fuller, M., and Haston, R., 1985, Preliminary paleomagnetic results from Sabah: East Malaysia: Eos (Transactions, American Geophysical Union), v. 66, p. 864.

Schmidtke, E., Fuller, M., and Haston, R., 1990, Paleo-magnetic data from Sarawak, Malaysian Borneo and the late Mesozoic and Cenozoic tectonics of Sunda land: Tectonics, v. 9, p. 123–140, doi:10.1029/TC009i001p00123.

Searle, M.P., 2006, Role of the Red River shear zone, Yunnan and Vietnam, in the continental extrusion of SE Asia: Geological Society of London Journal, v. 163, p. 1025–1036, doi:10.1144/0016-76492005-144.

Shibuya, H., Merrill, D.L., Hsu, V., and Leg 124 Shipboard Scientifi c Party, 1991, Paleogene counterclockwise rotation of the Celebes Sea—Orientation of ODP cores utilizing the secondary magnetization, in Silver, E.A., et al., Proceedings of the Ocean Drilling Program, Scientifi c results, Volume 124: College Station, Texas, Ocean Drilling Program, p. 519–523.

Suzuki, S., Takemura, S., Yumul, G.P., Jr., David, S.D., Jr., and Asiedu, D.K., 2000, Composition and provenance of the Upper Cretaceous to Eocene sandstones in Cen-tral Palawan, Philippines: Constraints on the tectonic development of Palawan: The Island Arc, v. 9, p. 611–626, doi:10.1046/j.1440-1738.2000.00306.x.





Tate, R.B., compiler, 2001, Geological map of Borneo Island: Kuala Lumpur, Geological Society of Malaysia, 2 sheets, CD-Rom.

Tongkul, F., 1994, The geology of northern Sabah, Malay-sia and its relationship to the opening of the South China Sea Basin: Tectonophysics, v. 235, p. 131–147, doi:10.1016/0040-1951(94)90021-3.

Tongkul, F., 1997a, Sedimentation and tectonics of Paleo-gene sediments in central Sarawak: Geological Society of Malaysia Bulletin, v. 40, p. 135–155.

Tongkul, F., 1997b, Polyphase deformation in the Telupid area, Sabah, Malaysia: Journal of Asian Earth Sci-ences, v. 15, p. 175–183.

Tongkul, F., 2006, The structural style of Lower Miocene sedimentary rocks, Kudat Peninsula, Sabah: Geologi-cal Society of Malaysia Bulletin, v. 49, p. 119–124.

Urbat, M., Dekkers, M.J., and Krumsiek, K., 2000, Discharge of hydrothermal fluids through sedi-

ment at the Escanaba Trough, Gorda Ridge (ODP Leg 169): Assessing the effects on the rock mag-netic signal: Earth and Planetary Science Let-ters, v. 176, p. 481–494, doi:10.1016/S0012-821X(00)00024-8.

van de Weerd, A., Armin, R.A., Mahadi, S., and Ware, P.L.B., 1987, Geologic setting of the Kerendan gas and condensate discovery: Tertiary sedimentary geol-ogy and palaeogeography of the northwestern part of the Kutai Basin, Kalimantan, Indonesia: Indonesian Petroleum Association 16th Annual Convention, Pro-ceedings, p. 317–338.

van Hattum, M., Hall, R., Pickard, A., and Nichols, G., 2006, Southeast Asian sediments not from Asia: Provenance and geochronology of north Borneo sandstones: Geol-ogy, v. 34, p. 589–592, doi:10.1130/G21939.1.

Vogt, E.T., and Flower, M.F.J., 1989, Genesis of Kinabalu (Sabah) granitoids at a subduction-collision junction:

Contributions to Mineralogy and Petrology, v. 103, p. 493–509, doi:10.1007/BF01041755.

Weaver, R., Roberts, A.P., and Barker, A.J., 2002, A late diagenetic (syn-folding) magnetization carried by pyrrhotite: Implications for paleomagnetic studies from magnetic iron sulphide-bearing sediments: Earth and Planetary Science Letters, v. 200, p. 371–386, doi:10.1016/S0012-821X(02)00652-0.

Wilson, R.A.M., and Wong, N.P.Y., 1964, The geology and mineral resources of the Labuan and Padas Valley areas, Sabah: Geological Survey of the Borneo Region of Malaysia Memoir 17, 150 p.

Yo-ichero, O., Uno, K., Higashi, T., Ichikawa, T., Ueno, T., Mishima, T., and Matsuda, T., 2000, Secondary rema-nent magnetization carried by magnetite: A comparative study of unremagnetized and remagnetized granites: Earth and Planetary Science Letters, v. 180, p. 271–285, doi:10.1016/S0012-821X(00)00169-2.



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