MIDDLE MIOCENE WAVE INFLUENCED TIDAL DOMINATED LAMBIR FORMATION, MIRI, SARAWAK: CASE STUDY IN TUSAN BEACH AND LAMBIR HILL

Abstract

The Middle Miocene sedimentary faciess classified as the Lambir Formation at Tusan Beach and Lambir Hill is revealed as tide dominated with exposed minor wave regimes association. Evidence of wave dominated facies is displayed mostly on shoreline deposits, such as planar cross stratified (PcS), swaley cross stratified (ScS), swaley-Hummocky cross stratified (SHcS) and hummocky cross stratified (HcS). The facies analysis reveals four facies associations, namely; foreshore facies association, upper shoreface, middle shoreface and lower shoreface. Whereas, tide dominated regime resulted three major facies association: tidal sand bar (TSB) facies association, tidal sand flat facies association (TSF) and subtidal mud flat (SMF). TSB facies association was developed from tide influenced shoreline that represented by herringbone cross stratified sandstone bed. The occurrence of herringbone cross stratified and other tidally structures within same facies explain that the current activities are in reversal process (flood and ebb). TSF and SMF facies associations, are widely distributed in the central Miri region including part of Lambir Hill and the Nakat River area. Wide exposure of frequent heterolitic beds, suggest that the Lambir Formation was deposited within the tidal flat environment.

Keywords

• Wave dominated facies
• tide dominated facies
• shoreface
• heterolitic