A prograding margin during global sea‐level maxima: an example from Mahajanga Basin, northwest Madagascar

Abstract

The Mesozoic shelf margin in the Mahajanga Basin, northwest Madagascar, provides an example where inherited palaeobathymetry, coupled with sea‐level changes, high sediment supply and fluctuations in accommodation influenced the stacking patterns and geometry of clinoforms that accreted onto a passive rifted margin. Two‐dimensional (2D) seismic profiles are integrated with existing field data and geological maps to study the evolution of the margin. The basin contains complete records of transgression, highstand, regression and lowstand phases that took place from Jurassic to Cretaceous. Of particular interest is the Cretaceous, Albian to Turonian (ca. 113‐93 Ma), siliciclastic shelf margin that prograded above a drowned Middle Jurassic carbonate platform. The siliciclastic phase of the shelf margin advanced ca. 70 km within ca. 20 My, and contains 10 distinct clinoforms mapped along a 2D seismic reflection data set. The clinoforms show a progressive decrease in height and slope length, and a fairly constant slope gradient through time. The successive shelf edges begin with a persistent flat to slightly downward‐directed shelf‐edge trajectory that changes to an ascending trajectory at the end of clinoform progradation. The progressive decrease in clinoform height and slope length is attributed to a decrease in accommodation. The prograding margin is interpreted to have formed when siliciclastic input increased as eastern Madagascar was uplifted. This work highlights the importance of sediment supply and inherited palaeobathymetry as controls on the evolution of shelf margins and it provides a new understanding of the evolution of the Mahajanga Basin during the Mesozoic.

Amended lithostratigraphy of the Cretaceous Bagh Group, Western Lower Narmada Valley, India: A comparison with pervasive Tethyan basins

“…Kachchh Basin (after Arora, Banerjee, & Dutta, 2015;Bansal, Banerjee, Pande, Arora, & Meena, 2017;Bhatt & Patel, 2017;Biswas, 2016;Desai, Patel, Shukla, & Surve, 2008;Fürsich, Pandey, Alberti, Mukherjee, & Chauhan, 2020;Krishna, 1987;Sarkar, Banerjee, Chakraborty, & Bose, 2002), WLNV (based on present study), ELNV (Bhattacharya and Jha, 2014;Bhattacharya, Jha, & Mondal, 2020;Jaitly and Ajane, 2013;Ruidas et al, 2018), and Carnarvon Basin (after Geoscience Australia, 2013;Hocking et al, 1987;Kelman et al, 2013;Williamson et al, 2012 Krishna, 2017). Geological timescale after Gradstein, Ogg, and Hilgen (2012) tongues (Obrist-Farner, Ball, McGilvery, & Rogers, 2017). During the Early Cretaceous, commencement of fluviatile sedimentation took place with the reactivation of the Son-Narmada Lineament in the LNV (Tripathi & Lahiri, 2000).…”