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Stratigraphy and Sedimentation
Published in Supriya Sengupta, Introduction to Sedimentology, 2017
A parasequence is ‘a relatively conformable, genetically related succession of beds or bedsets bounded by marine flooding surfaces or their correlative surfaces.’ A parasequence set is ‘a succession of genetically related parasequences that form a distinctive stacking pattern, bounded, in many cases, by major marine flooding surfaces and their correlative surfaces. Parasequence and parasequence set boundaries form in response to an increase in water depth. Under certain depositional conditions parasequence and parasequence set boundaries may coincide with sequence boundaries’ (Van Wagoner et al. 1990).
Fluvial sequences and basin development in the northern Galilee Basin
Published in Australian Journal of Earth Sciences, 2018
In wireline logs, two sequences are represented in the Jochmus Formation (Figure 14). The lowermost of these, sequence 4, commences with a basal cylinder-shaped parasequence set that is coarse-grained with minor serration in the northern wells possibly reflecting a glaciogenic influence. This becomes finer-grained to the south with highly developed serration indicating pelitic intercalations in Carmichael-1 and Lake Galilee-1. This represents a degradational systems tract with development of low-sinuosity, sandy braided-channel facies grading southwards to low-sinuosity, anastomosing-channel facies that display no lateral amalgamation. A disconformable lower boundary shows localised paleovalley or paleo-valley infill. This could reflect local tectonic readjustment associated with general basin subsidence. This interval is succeeded by a transitional systems tract composed of thick, bell-shaped parasequences with fining upwards tendencies. These represent a high sinuosity anastomosing fluvial-channel facies with minor floodplain facies developed during a slow increase in accommodation. The majority of the lower Jochmus Formation comprises this systems tract. Sequence 4 is completed with an aggradational systems tract consisting of thick, bell-shaped parasequence sets that represent a fluvial facies. This is characterised by floodplain sediments with restricted, high sinuosity fluvial-channel fill that fines upwards to fine-grained carbonaceous mudstone, carbonaceous siltstone and sandstone. This interval comprises the Edie Tuff Member.