Bulletin of the Geological Society of Malaysia, No. 66, December 2018, pp. 129 – 140
Mohamad Ezanie Abu Samah*, Che Aziz Ali, Kamal Roslan Mohamed & Nurul Afifah Mohd Radzir
Program Geologi, Fakulti Sains dan Teknologi, Universiti Kebangsaan Malaysia, Bangi, 43600, Malaysia
*Correseponding author email address: mohamadezanie@yahoo.com
Abstrak: Endapan mikrobial jujukan Batu Kapur Setul diwakili oleh pembentukan lapisan stromatolit, thrombolit dan onkolit. Setiap struktur mikro-organisma ini menunjukkan sifat fizikal yang berubah daripada geometri berbentuk lurus, beralun, turus, selari serta jaringan kompleks. Hasil cerapan log sedimen pada jujukan batu kapur (Ahli Setul Bawah dan Ahli Setul Atas) di kawasan Pulau Langgun dan Perlis telah mengenalpasti beberapa pengelasan fasies mikrobial antaranya seperti fasies thrombolit berstruktur jaringan kompleks (Ftk), fasies stromatolit berstruktur selari (Fss), fasies stromatolit berstruktur kompaun (Fst-Fsa), fasies onkolit (Fso), fasies stromatolit berstruktur turus (Fst), fasies stromatolit berstruktur alunan (Fsa) dan fasies stromatolit berstruktur lurus (Fsl). Penguasaan thrombolit dan stromatolit selari di kawasan Pulau Langgun membuktikan pertumbuhan ini dikawal sepenuhnya oleh arus gelora kuat yang menyebabkan proses kerukan betindak secara aktif pada topografi struktur mikrobial tersebut. Pembentukan onkolit dan stromatolit bersifat turus, beralun dan lurus pula menguasai pertumbuhan di kawasan Perlis. Fasies yang berubah secara beransur-ansur ini menunjukkan pertumbuhannya dikawal oleh faktor kedalaman persekitaran, di mana kemasukan bahan sedimen mikrobial untuk berinteraksi dengan mikro-organisma adalah bergantung kepada keluasan ruang pertumbuhan yang tersedia. Di dalam konteks tafsiran paleo-sekitaran, setiap pembentukan fasies memberi gambaran bahawa ianya terendap pada persekitaran karbonat berlaut cetek iaitu melibatkan zon sub-pasang surut hingga supra-pasang surut. Taburan fasies yang berubah secara beransur menandakan jujukan perlapisan batu kapur adalah bercirikan semakin mencetek ke atas dengan faktor kawalan yang dipengaruhi oleh kedalaman persekitaran, proses hidrodinamik, biologi dan kimia.
Kata kunci: Stromatolit, thrombolit, onkolit, fasies mikrobial, paleo-sekitaran karbonat laut cetek
Abstract: Microbial deposits in Setul Limestone succession are represented by stromatolites, thrombolites and oncolites layers. Each microorganism exhibits physical geometries that change either from straight, wavy, parallel or network-like complex structure. The results of sedimentary logging on the limestone sequences (Lower Setul Member and Upper Setul Member) in Langgun Island and Perlis area have identified a several microbial facies such as network-like complex thrombolitic facies, parallel stromatolitic facies, compound stromatolitic facies, oncolites facies, columnar stromatolitic facies, wavy stromatolitic facies and straight stromatolitic facies. Thrombolites and parallel stromatolites, dominating in Langgun Island area prove that the growth of microbial is controlled by the strong current flow which causes active scour process in the topography of the microbial structure. On the other hand, the formation of oncolites and columnar, wavy and straight stromatolites are dominant in Perlis area. The gradual changes of microbial facies indicate that the growth of structures is controlled by the environmental depth, in which the influx of organosedimentary materials that interact with micro-organisms relies on the availability of accomodation space. In the context of the paleo-environment interpretation, it is shown that the microbial facies are deposited in shallow marine carbonate environments from subtidal to supratidal zone. The gradual changes of microbial facies distribution indicate that the limestone succession is characterised by the shallow upward sequences that is influenced by the depth of the environment, the hydrodynamic, biological and chemical processes.
Keywords: Stromatolites, thrombolites, onkolites, microbial facies, shallow marine carbonate
https://doi.org/10.7186/bgsm66201816
