Periglacial involutions, large folded recumbent folds and tectonic overprints at Putrajaya


Author : H.D. TjiaPublication : Bulletin of the Geological Society of MalaysiaVolume : 48Page : 97-102Year : 2004


Description

Bulletin of the Geological Society of Malaysia, Volume 48, June 2004, pp. 97-102

 

Periglacial involutions, large folded recumbent folds and tectonic overprints at Putrajaya

H.D. TJIA

Institute for Environment and Development (LESTARI), Universiti Kebangsaan Malaysia, 43600 Bangi. Selangor Darul Ehsan

 

Abstract: The development of Putrajaya and Cyberjaya brought to light many new outcrops of black pelite, buff to reddish brown psammite and subordinate bands of light-coloured tuffaceous or loessic material. Most of the outcrops are in advanced weathered states. The nature of the fresh rock was identified in drill cores acquired for foundation designs. These rocks are geochemically similar to the Upper Palaeozoic Kenny Hill Formation, although the dominant dark colour is rarely found among the Kenny Hill strata in the type area of Kuala Lumpur. At Salak Tinggi, Kenny Hill-like strata is marked by an Agathiceras sp. fossil (Early Permian) and also contains a pebbly horizon of interpreted glacigenic origin. The Putrajaya-Cyberjaya rock assemblage is therefore interpreted as being of Gondwanan origin. At "Cyberjaya Hill", bands of light-coloured tuff(?) or loess(?) were irregularly deformed into crinkles of varied wave lengths and shapes that contrast with the more systematically folded larger structures. The disharmonic character of the crinkles suggests these to represent periglacial involute structures. The larger folds are tectonic and developed as recumbent structures that became refolded into open warps. These two tectonic fold sets are coaxial about a north-southerly trend. Indications of tectonic transport of the recumbent folds include to the west, southeast and east.

 

Abstrak: Pembukaan tanah meluas bagi penubuhan Putrajaya dan Cyberjaya telah mengungkap banyak singkapan baru yang terdiri daripada batuan pelit hitam, psamit berwarna perang-karat serta sejumlah kecil lapisan berbahan tuf atau loes yang berwarna cerah. Pada singkapan kebanyakan batuan didapati dalam keadaan terluluhawa; batuan segar dikenali dalam inti gerudi. Sifat geokimia batuan sarna dengan formasi Kenny Hill (Bukit Tungku) walaupun warna gelapnya tidak am bagi formasi Kenny Hill. Fosil Agathiceras sp. dalam batuan serupa Kenny Hill di Salak Tinggi menunjukkan usia Perm Awal. Suatu lapisan berpebel serta canggaan-dalam- keadaan-lembut di singkapan yang sama ditafsirkan sebagai hasil aktiviti berkaitan pergerakan glasier atau "iceberg". Berdasarkan hujah di atas, persekutuan batuan Putrajaya-Cyberjaya telahpun dianggap berasalmula di benua Gondwana. Pada "Bukit Cyberjaya", didapati lapisan nipis berwarna cerah yang mungkin mewakili tuf atau loes. Lapisan tersebut telah tercangga kepada lipatan berpanjang gelombang dan berbentuk kurang menentu dan oleh kerananya menampakkan lipatan tak-harmoni. Bentuk lipatan tak-harmoni jelas bertentangan dengan bentuk bersistem daripada lipatan tektonik bersaiz lebih besar. Perlipatan dalam keadaan-lembut dianggap telah mewujudkan lipatan tak harmoni itu yang boleh dikelaskan sebagai involusi periglasial. Lipatan tektonik berbentuk rebah yang telah dicangga sekali lagi kepada lipatan terbuka. Kedua-dua struktur tektonik tercangga mengikut paksi lebih kurang utara-selatan. Angkutan tektonik yang boleh dikesan ialah ke barat, ke tenggara dan ke arah timur.

https://doi.org/10.7186/bgsm48200419