Geology Lecture 14: Miri Zone

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Questions and Answers

What is the age of the fauna identified in the Melinau Formation?

Lower Eocene

Lower Miocene

Upper Oligocene

Upper Eocene (correct)

What is the dip of the sequence overlying the Kelalan Formation?

10-12° towards the south

15-18° towards the east

12-15° towards the north (correct)

18-20° towards the west

What is the dominant composition of the Kelalan Formation?

Limestone, shale, and sandstone

Turbidite sequence of sandstone and conglomerate

Shale and sandstone with subordinate limestone (correct)

Tuffite, tuffaceous limestone, and shale

What is the type of unconformity between the Kelalan Formation and the overlying sequence?

Angular unconformity Signup and view all the answers

What is the characteristics of the Upper Eocene limestones in the Melinau Formation?

Massive, mainly unbedded, of high purity, and dark grey Signup and view all the answers

What is the genus of algae that occurs in great profusion in the Melinau Formation?

Archaeolithothamnium Signup and view all the answers

What is the inferred depositional environment of the Melinau Limestone Formation?

Shallow marine environment with low clastic input Signup and view all the answers

What is the age of the limestone in the Kelalan Formation?

Upper Cretaceous to Upper Eocene Signup and view all the answers

Which of the following foraminifera fossils has been recovered from the Mulu Formation?

Discocyclina sp. Signup and view all the answers

What is the characteristic of the shales that overlie the Eocene limestone?

Contain irregular clasts of Eocene limestone Signup and view all the answers

What is the orientation of the strike in the Tutoh Gorge?

NE-SW Signup and view all the answers

What is the time equivalent of the Melinau Formation in part?

Temburong and Meligan Formations Signup and view all the answers

What is the formation that overlies the Melinau Formation?

Setap Formation Signup and view all the answers

What is the maximum thickness of the Melinau Formation?

2.1 km Signup and view all the answers

What is the age of the Melinau Formation?

Late Eocene to Early Miocene Signup and view all the answers

What is the tectonic context in which the Melinau Formation was deposited?

Developing accretionary / collisional belt Signup and view all the answers

What type of rocks are characteristic of the Miri Zone?

Palaeocene to Eocene ophiolitic rocks Signup and view all the answers

What is the age of the unconformity between the Belaga, Mulu, and Kelalan Formations and the overlying Upper Eocene-Recent sediments of the Miri Zone in Sarawak?

Late Eocene Signup and view all the answers

What is the dominant type of sediment in the Oligocene-Miocene sediments of the Miri Zone?

Siliciclastics Signup and view all the answers

What is the depositional environment of the Lambir Formation?

Shallow water, deltaic-marine Signup and view all the answers

What is the age of the Mulu Formation?

Palaeocene to Eocene Signup and view all the answers

What is the tectonic significance of the Tatau-Mersing Line?

It marks the boundary between the Sibu Zone and the Miri Zone Signup and view all the answers

What is the highest mountain in the Mulu Anticlinorium?

Gunung Mulu (2376 m) Signup and view all the answers

What is the name of the zone that is structurally complex, consisting of Palaeocene to Eocene ophiolitic rocks?

Miri Zone Signup and view all the answers

Study Notes

Miri Zone

The Miri Zone is a structurally complex zone consisting of Palaeocene to Eocene ophiolitic rocks, including spilite, basalt, tuff, and radiolarian chert.
The Tatau-Mersing Line represents a major unconformity between the Belaga, Mulu, and Kelalan Formations (some of Rajang Group) and the overlying Upper Eocene-Recent sediments of the Miri Zone.
The unconformity is Late Eocene in Sarawak and Middle-Late Miocene in Sabah, suggesting that the deformation associated with the collision of the Luconia Block with the northern margin of Borneo was diachronous northward.

Mulu Formation

The Mulu Formation is a sub-metamorphosed shales and slates, inter-bedded with hard sandstones, occupying the large inlier of the Mulu Anticlinorium and the highest mountain, Gunung Mulu (2376 m).
The formation is a monotonous succession of intensely folded turbidite composed of slaty and phyllitic shales and quartz sandstones.
The best outcrops are in the Tutoh Gorge, where the sandstone beds may be as much as 150-m thick, inter-bedded with thin slates.
The formation is poorly fossiliferous, but Discocyclina sp. and Globorotalia wilcoxensis Cushman & Ponton have been recovered.

Kelalan Formation

The Kelalan Formation is a turbidite sequence mainly of shale and sandstone, with subordinate limestone, tuffite, and tuffaceous limestone.
The formation is intensely folded and the age of the limestone ranges from Upper Cretaceous to Upper Eocene.
Globotruncana sp. has been recorded only at one locality beneath the Melinau Limestone at Bukit Besungai (Northeast), indicating an Upper Cretaceous age.

Melinau Formation

The Melinau Formation (Late Eocene-Early Miocene) is exposed on the northwest flank of the Mulu range.
The formation reaches a maximum thickness of 2.1 kilometres and consists of well-cemented, partly recrystallized, and brecciated, grey to white, shallow marine carbonates.
The unit reflects depositional conditions outside the areas of substantial clastic input and was deposited over bathymetric highs, at the depositional surface overlying the developing accretionary / collisional Crocker-Rajang belt.
The formation ranges in age from Late Eocene to Early Miocene, although most of the Oligocene is missing.
The Melinau Formation is in part time equivalent to the Temburong and Meligan Formations and is overlain by the Setap Formation.

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Description

This lecture covers the Miri Zone, including its geological timings and characteristics, and its boundary with the Sibu Zone. It also discusses the Palaeocene to Eocene ophiolitic rocks and the Tatau-Mersing Line.