The most recent, detailed study carried out in the Kolbano area is that of
Sawyer et a l, 1993. On the basis of detailed fieldwork and micropalaeontological
dating of samples collected, the stratigraphy of Charlton (1987) was revised and new age constraints were placed on the formations described. The stratigraphy proposed
by Sawyer et a l, 1993 is outlined in the following paragraphs.
Oe Baat Formation
Several modifications to Charlton’s (1987) study of the Oe Baat Formation
were proposed by Sawyer et al.
• An age revision from Oxfordian to Tithonian (Charlton 1987) to Tithonian to
Berriasian. However, Charlton, 1987, actually dated the Oe baat Formation as early Callovian to late Tithonian not Oxfordian to Tithonian as stated by Sawyer
et a l 1993.
• Reclassification of an Oe Baat conglomerate facies as part of the overlying Ofu
Formation (although Charlton, 1987 did not describe a conglomerate facies from the Oe Baat Formation).
• Division into two primary facies, a massive sandstone member with accessory glauconite and a well bedded opal-cemented glauconitic member (as in Charlton & Wall, 1994).
The massive sandstone member consists of alternating siltstones and sandstones. At the base of the section are brown-black silts and shales. The shale is dated as Late Jurassic (Tithonian ) in age. A gradational lower contact of the glauconitic member with the massive facies is inferred on the basis of age relationships. Three samples from the glauconitic member were dated as Berriasian, a fourth as late Tithonian to Berriasian. The glauconitic facies is thought by the authors to be a lateral equivalent of the lower section of the Nakfunu Formation.
Nakfunu Formation
Several changes were made to the Nakfunu Formation as described by Charlton (1987).
• Formation subdivision into two members, the Oinlasi and Tuke members,
distingiushed by colour. The Oinlasi member is described as iron red, alternating with buff orange and subordinate grey, yellow and green. The Tuke member is described as being compositionally similar but is coloured a homogenous light to slate grey, subordinate beds being dark grey, sometimes black and including highly fractured shales.
• An age refinement (see below).
• The identification of a distal calcarenite facies equivalent to the Oe Baat Formation.
The Nakfunu lithologies are described as consisting of radiolarites, claystones, calcilutites, interbedded shales and less commonly calcarenites, wackestones and packestones. The two members are synchronous. The formation is dated on results from 38 samples giving Early Cretaceous ages in two age range populations; Berriasian to Aptian and Hauteriviau to Aptian with a major non-depositional hiatus between the Albian and Turonian. Furthermore, the authors identify what they believe to be a distal calcarenite facies equivalent to the bedded glauconitic facies of the Oe Baat Formation. On the basis of age relationships and allogenic composition they claim that the base of the Nakfunu Formation is equivalent to the glauconitic facies of the Oe Baat Formation. They interpret the distal calcarenite facies as having been deposited downslope by a turbidity current pulse.
Palaeontological data also indicates that the Nakfunu Formation is synchronous with the lower portion of the Menu Formation (see below). This study therefore highlights the diachronous nature of the formations described. The Nakfunu Formation is interpreted as having been deposited during a gradual Early Cretaceous eustatic sea level rise that culminated in the Albian. Foraminifera are described as rare/absent whilst radiolaria and nannofossils are common.
Menu Formation
This unit is described by the authors as being lithologically similar to the Tertiary Ofu Formation and includes some of the units assigned by Charlton (1987) to the Borolalo Formation. It consists of Early through to Late Cretaceous age light red, pink and white calcilutites. Bedding is on a scale of greater than 6cm but less than 60cm. The limestones may contain l-2cm horizons and nodules of red chert with intense internal cleavage.
The authors suggest a stratigraphie contact with the Ofu Formation on the basis of lithological similarities. They believe the original contact between Menu and Nakfunu Formations to also be stratigraphie. The Menu Formation is dated as Berriasian to Maastrichtian with sediments representing the Albian to Turonian missing. The Menu lithologies are interpreted as having been deposited as distal calciturbidites in a deep marine setting similar to that of the Ofu Formation.
Ofu Formation
The authors divided the Ofu Formation into three mappable units, the Boti member, the Borolalo member and the Oeleu member.
• Boti Member - This is described as being the most common member. It consists of cream-white calcilutites mixed with subordinate amounts of pink or orange to white. Red, brown and blue-grey chert nodules and lenses are common. On results from 18 samples, the member is dated as mid Eocene (Lutetian to early Pliocene (Zanclian) age with a depositional hiatus in the late Oligocene.
Borolalo Member - The authors state that the primary difference between the Borolalo and Boti member is colour. They describe the Borolalo member as pink and light orange. Seven samples date the member as being of late Paleocene (Thanetian) to early Pliocene (Zanclian) age. The Danian and Eocene to Oligocene are not observed. The authors claim that there is some evidence that the Borolalo beds grade into the overlying Boti member. Both units are diachronous.
Oeleu Member - This member is described as maroon to brick red calcareous mudstones with interbedded grey to reddish calcarenites. The Oeleu member is
not common and is always found between the Boti and Borolalo members. It’s age, based on only two samples, has been determined by the authors as early Oligocene and mid Miocene to early Pliocene. It is believed to be a condensed section reflecting one of the major tectonic episodes.
Sonalete Formation
The Sonalete Formation, included by Charlton (1987) as part of the Kolbano sequence, is assigned by the authors to the Viqueque Sequence which predominantly consists of Plio-Pleistocene sediments of synorogenic origin. They believe that variation between the Sonalete Formation of Charlton (1987) and the Viqueque Formation of their study to be too small to justify separate classification.
3.2.5 Harsolumakso et al^ 1995
The stratigraphie outline presented by Harsolumakso et al. (1995) places
parautochthonous (Triassic-Pleistocene) sediments of West Timor into a series of
facies. The facies defined by Harsolumakso et al., would appear to represent portions
of the formational units described by previous authors and therefore part of their total lithological variation. This meant that it was quite difficult to accurately correlate the formations defined as part of the present study and those previously described by
Charlton (1987) and Sawyer et a l, (1993) with the facies groups of Harsolumakso et
a l 1995. Due to the extensive lithological variation present on Timor confusion
between lithologies of different formations or even different lithotectonic units can occur and so very detailed descriptions of lithologies are necessary if this is to be prevented.
However, from the details given by Harsolumakso et a l (1995) in the
lithological log (Figure 3, p. 885) it would appear that the lower part of facies F can
be correlated with the Oe Baat Formation. The upper part of facies F (and possibly the lower part of facies G) seems to correlate with part of the Nakfunu Formation. The upper part of facies G (and possibly part of facies H) may correlate with the Menu
Formation as defined by Sawyer et a l, 1993 (see Figure 3.2). The correlation of facies
H and I with the Tertiary, predominantly limestone, formations as defined in this
1993) is not really possible from the lithological descriptions given by Harsolumakso
et a l, (1995).