University of Malaya AAPG SC organized the first ever field trip, entitled ‘Uncover the Beauty of Miri’ on 17 - 19 November 2017. Ten Undergrads took part, two of whom were on the AAPG Student Chapter committee - Shakirah Hazlan as the Project Director & Nor Fatihah Salim as the Vice Director. The participants were selected based on their outstanding academic performance by our instructor, Dr. Meor Hakif Amir Hassan.
On 17 November 2017, after checking into accommodations, we visited our first outcrop, Bukit Song South and Bukit Song North, to study the Lambir Formation which was deposited in Middle Miocene. At Bukit Song South, the lithology present was interbedding of fine sandstone and mudstone which dipped 120 degrees in SW direction. Many sedimentological structures were identified such as cross beds, mud clasts, planar laminations, and ripples. Hence, it was not surprising for Lambir FM to be known as one of the best outcrops in the world to study sedimentological structures. Coal clasts were also abundantly found in coarse sandstone, located at the south area of Lambir FM. Trace fossils like ophiomorpha were observed, indicating marine and fluvial depositional environments. Next, we went to Bukit Song North which generally had the same lithological units, but dipped in the opposite direction. Hence, a mega anticline inbetween these two outcrops might be present. Anticline was a great example of structural traps for deposition of oil and gas, and it was aided by the presence of impermeable mudstone/shale seal that prevented oil seepage. At night, we enjoyed the great view of Miri Town from Grand Old Lady and Pantai Labong.
The next day, we departed for Gua Niah at 8 am. After two hours, we finally reached Niah National Park. The entrance fee was only Ringgit Malaysia 10/person, but the view of the cave was magnificent and priceless. Visitors were required to cross Niah River by boat before hiking for another 2km into the jungle to reach the well-known Niah Cave. Limestone decorated the hiking tracks. However, no presence of bedding was observed as limestone was chemically unstable and could be easily destroyed. Niah Limestone was a part of Subis Limestone with the age of Early Miocene and deposited in a low land forest. In comparison with Gua Tempurung which was more confined, Gua Niah consisted of huge pores, allowing sunlight into the cave hence escalating the growth of algae. Besides, we could tell that Gua Niah was relatively younger as the fallen boulders had not undergone cementation yet. After taking pictures as memories around the cave, we left the national park and headed for the aerial overview of Niah activity at a nearby hill.
At this outcrop, the participants were amazed by the breathtaking view of Subis Limestone which stood 350m on a flat surface of Setap Shale.
Based on the karst features, we could predict that the sea level rose rapidly during 16-23 Ma ago and the growth of carbonate platform could not catch up with the rising sea level, hence forming a wedding cake structure. Furthermore, Subis Limestones consisted of steep-sided walls and an elongated flat surface on top of the platform. Niah also was a good analog of Luconia Province which was deposited in Miocene in deltaic environment.
On 19 November 2017, the last outcrop we visited was Airport Road Anticline, close to our accommodations. Lithologically, there were fine sandstone and mudstone. Planar laminations, Hummocky stratification, ripples, mud clasts and other sedimentological structures were found. As it was deposited in a shallow marine environment, trace fossils were abundantly observed everywhere around the outcrop. Some of the fossils appeared in 3D as they were filled by siderite, iron-cemented. In addition, at the South area, we identified a normal fault dipped in 24 degrees towards NNE.
All in all, this field trip definitely has widened our perspective on the oil-bearing sedimentary strata in Miri. On top of that, our knowledge about sedimentology was well freshened during this 3 day - 2-night field trip. This field trip would not be possible wihout the financial assistance given by various parties. This project had received RM3000 of sponsorship from University of Malaya AAPG SC and RM300 as a personal funding from Deputy Dean of Postgraduate, Professor Dr. Ismail Yusoff. Thank you to all our sponsors and our instructor, Dr. Meor Hakif Amir Hassan for the very well coordinated field trip.