Late Holocene to Recent aragonite-cemented transgressive lag deposits in the Abu Dhabi lagoon and intertidal sabkha

Yuzhu Ge*, Chelsea L. Pederson, Stephen W. Lokier, Jan P. Traas, Gernot Nehrke, Rolf D. Neuser, Katja Götschl, Adrian Immenhauser*

*Corresponding author for this work

Research output: Contribution to journalArticle

Abstract

Modern cemented intervals (beachrock, firmgrounds to hardgrounds and concretionary layers) form in the lagoon and intertidal sabkha of Abu Dhabi. Seafloor lithification actively occurs in open, current‐swept channels in low‐lying areas between ooid shoals, in the intertidal zone of the middle lagoon, some centimetres beneath the inner lagoonal seafloor (i.e. within the sediment column) and at the sediment surface the intertidal sabkha. The concept of ‘concretionary sub‐hardgrounds’, i.e. laminar cementation of sediments formed within the sediment column beneath the shallow redox boundary, is introduced and discussed. Based on calibrated radiocarbon ages, seafloor lithification commenced during the Middle to Late Holocene (ca 9000 cal yr bp), and proceeds to the present‐day. Lithification occurs in the context of the actualistic relative sea‐level rise shifting the coastline landward across the extremely low‐angle carbonate ramp. The cemented intervals are interpreted as parasequence boundaries in the sense of ‘marine flooding surfaces’, but in most cases the sedimentary cover overlying the transgressive surface has not yet been deposited. Aragonite, (micritic) calcite and, less commonly, gypsum cements lithify the firmground/hardground intervals. Cements are described and placed into context with their depositional and marine diagenetic environments and characterized by means of scanning electron microscope petrography, cathodoluminescence microscopy and Raman spectroscopy. The morphology of aragonitic cements changes from needle‐shaped forms in lithified decapod burrows of the outer lagoon ooidal shoals to complex columnar, lath and platy crystals in the inner lagoon. Precipitation experiments provide first tentative evidence for the parameters that induce changes in aragonite cement morphology. Data shown here shed light on ancient, formerly aragonite‐cemented seafloors, now altered to diagenetic calcites, but also document the complexity of highly dynamic near coastal depositional environments.
Original languageEnglish
Pages (from-to)2426-2454
Number of pages29
JournalSedimentology
Volume67
Issue number5
DOIs
Publication statusPublished - 1 Aug 2020

Keywords

  • Carbonate cement
  • early-marine cementation
  • Gulf
  • hardgrounds
  • seawater chemistry

ASJC Scopus subject areas

  • Geology
  • Stratigraphy

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