SEDIMENTOLOGI DAN STRATIGRAFI HOLOSEN DATARAN PANTAI MEDAN - BELAWAN SEKITARNYA, SUMATERA UTARA

Studi sedimentologi dan stratigrafi endapan Kuarter di dataran pantai Medan – Belawan dibedakan menjadi enam lingkungan pengendapan. Yaitu endapan-endapan rawa, laut, pantai, rawa bakau, dataran banjir, dan alur sungai. Berdasarkan korelasi perubahan lingkungan pengendapan secara lateral dan vertikal, rangkaian sedimen Kuarter tersebut dapat dibedakan menjadi empat Interval Pengendapan (I – IV). Setiap interval dicirikan oleh berubahnya lingkungan yang dikontrol oleh perubahan iklim dan muka laut Holosenl. Perkembangan dari endapan Kuarter dan pengisisan cekungan cekungan di daerah dataran pantai Medan – Belawan dipengaruhi oleh peristiwa global. Perubahan dari sirkulasi iklim dan turun naiknya muka laut selama proses pengendapan berlangsung adalah berkaitan dengan perisitiwa global tanpa dipengaruhi oleh efek tektonik. Studi yang dilakukan mencakup analisis sedimentologi dan stratigrafi terhadap empat belas pemboran yang dilakukan di sepanjang lintasan yang berarah utara – selatan dari Medan hingga Belawan. Kedalaman pemboran berkisar antara 5,0 hingga 15,0 m.Kata Kunci: Sedimentologi dan stratigrafi, Holosen, dataran pantai Studies of sedimentology and Stratigrafi on Quaternary deposits in the coastal plain of Medan– Belawan surroundings, North Sumatera revealed six depositional environments. These are swamp, marine, beach, marsh, floodplain, and channel deposit environments. Based on the correlation of the lateral and vertical variation of the depositional environment, whereas the successsion of the Quaternary sediments can be divided into four sedimentary intervals (I – IV). Each interval is typically for environment changes which is controlled by sea level and climatic especially during Holosen. The development of the Quaternary sediments and basin fill in the coastal plain of Medan to Belawan area was influenced by global events. Changes in climatological and relative sea level during during depostional processes were included clobal changes without influenced by tectonic. The study was based on analyses of sedimentology and stratigraphy of fourteen borehole information obtained along the North to South traverse from Medan to Belawan. The penentration of the bore head varied from 5.0 to 15.0 m. Keywords: Sedimentology and stratigraphy, Holosen, coastal plain

Mycorrhizal Conifer Roots From the Lower Cretaceous of the Otway Basin, Victoria

Fossil roots with nodular and abbreviated lateral roots are described from the Devils Kitchen locality within the Lower Cretaceous Otway Group. The general morphology of these roots indicates a mycorrhizal association, the oldest such record from Australia. Based on the root morphology and associated megaflora it is considered that the roots are coniferous (Taxodiaceae or Podocarpaceae); an association of the roots with foliage of Geinitzia tetragona sp. nov., which is possibly taxodiaceous, is indicated. The major role of nodular mycorrhizal roots in extant plants is phosphate uptake which enhances minor nitrogen uptake. It is suggested that the fossil roots may have had a similar role. The Devils Kitchen locality is interpreted as a levee or near channel deposit with better drainage andlor a nutrient-poor soil relative to other soils in the sequence. The atypical plant associations of Cladophlebis australis, C. sp. b, and Geinitzia tetragona sp. nov. are a reflection of the above.

An analysis of the molluscs from an Ipswichian interglacial river channel deposit at Maxey, Cambridgeshire, England

SummaryA freshwater and land molluscan assemblage from an Ipswichian stream channel at Maxey, Cambridgeshire, is discussed. The presence of Belgrandia marginata and Vallonia enniensis suggests that summer temperatures may have been somewhat warmer in the Ipswichian period. The assemblage represents the silting processes under relatively quiet water conditions, possibly in a side channel or backwater of a meandering river system.

The fauna of the channel deposit of early Saalian age at Brandon, Warwickshire

A fauna consisting of both vertebrates and invertebrates is described from an early Saalian deposit at Brandon, Warwickshire. Some 77 taxa, mostly Coleoptera, including 6 not now occurring in Britain, are recorded and though this is a very limited fauna, possibly due to rapidity of deposition, it is interesting as being probably the first to be described from this time horizon. The animal assemblage suggests deposition in a lake or slowly flowing river bordered by reeds and rushes with a Salix thicket on the surrounding ground. A climate cooler than that of today though not of arctic severity is indicated.