Journal
PALAEOGEOGRAPHY PALAEOCLIMATOLOGY PALAEOECOLOGY
Volume 561, Issue -, Pages -Publisher
ELSEVIER
DOI: 10.1016/j.palaeo.2020.110039
Keywords
Hyperpycnite; Trace fossils; Core analysis; Prodelta
Funding
- AEI/FEDER, UE [CGL2017-89618-R]
- PAI [RNM369]
- Secretaria de Estado de I+D+I, Spain [CGL2015-66835-P, PID2019-104625RB-100]
- FEDER Andalucia [B-RNM-072-UGR18]
- Junta de Andalucia [P18-RT-4074, RNM-178]
- Universidad de Granada [UCE2016-05]
- Aker BP
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This study analyzed sedimentary structures in a 50 m-thick package of terrestrial organic debris-rich sandstone bodies alternating with burrowed siltstones in the Betic Cordillera, Spain. Two types of sandbodies were identified, and the study highlights the importance of ichnological analysis for understanding hyperpycnal flows. The findings suggest the need for multi-scale analysis focusing on trace fossils and physical sedimentary signatures to improve our understanding of river-derived sustained-flow turbidites.
Hyperpycnal flows have been widely described in different lacustrine and marine environments but sedimentary structures and fossil content in hyperpycnites often offer limited information about the palaeoenvironmental conditions. This limitation can be improved by ichnological analysis, which has been recently used as a tool to differentiate between different type of subaqueous deposits, even though still only a few detailed ichnological studies on hyperpycnites exist. In order to bridge this gap in knowledge, a 50 m-thick package of terrestrial organic debris-rich, dominantly structureless and well-sorted sandstone bodies alternating with burrowed siltstones (Upper Miocene, Betic Cordillera, Spain) is here analyzed. This study is based on observations of a well-exposed outcrop and cores from a well drilled just behind the outcrop to bridge field-scale observational gaps. Two type of sandbodies were typified on the basis of their stratigraphic architecture, physical sedimentary structures, and ichnofacies in the fine-grained deposits embedding them: (1) Lobate to channelized-top sand-stones embebbed into silty sands with dominant highly variable degree of bioturbation by Taenidium and Schaubcylindrichnus (depauperate Cruziana ichnofacies) and interpreted as proximal marine sustained hyperpycnites in prodelta settings; and (2) channelized-lobate (cut-and-fill sequence) sandstones embebbed into siltstones with dominant Nereites and Phycosiphon (Nereites ichnofacies) interpreted as distal hyperpycnites developed in offshore settings. The studied succession is interpreted to represent the progradation of a sandy hyperpycnal system along a prodelta to starved offshore setting with high variability in grain-size, benthic food and oxygen content. Results of this study suggest that a multi-scale analysis focused on trace fossils and physical sedimentary signatures is needed to get a better understanding of these river-derived sustained-flow turbidites (hyperpycnites) that are less well known than their conventional surge-type turbidite counterparts.
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