Pleistocene cold climate groundwater silicification, Jbel Ghassoul region, Missour Basin, Morocco

Abstract

Surficial silicifications have been long considered to be indicative of warm and dry climates. Here we describe various forms of supergene silicification in a Miocene lacustrine sequence in the Missour Basin near Jbel Ghassoul (Morocco) in a landscape with accentuated relief. The silicification is almost exclusively limited to a 10-40 m wide zone from the edges of scarp and mesa landforms. This distribution is interpreted to record the locations where groundwaters which produced the silicification discharged from a higher level paleolandscape. The main component of the silica was imported late and significantly postdates the deposition of the sediments. This implies that significant volumes of silica-bearing solutions flowed through these formations in response to an hydraulic gradient generated by relief. Silicification thus occurred only after uplift and incision of the sedimentary fill of the Missour Basin. The zones of silicification of the Jbel Ghassoul sequence can be linked geomorphically to remnants of high level pediments that have been dated in the literatures as early to middle Pleistocene and interpreted to have been formed during cold climates. Low temperatures in outcrops near the discharge zones during cold periods is considered to be a key factor in silica precipitation from groundwaters.

Diagenetic silica enrichment and late‐stage groundwater activity in Gale crater, Mars

“…As stated previously, however, no evidence of high‐temperature mineral phases that might indicate a hydrothermal environment have been observed in Gale crater. Accordingly, more relevant analogues to the observed silica enrichment may be found in the silica cements that are ubiquitous in clastic sedimentary rocks on Earth, where cements are generally associated with lower temperature (<80°C) formation conditions [e.g., McBride , ; Vagle et al , ; Thiry et al , ]. Typically, Earth silica cements are made of quartz, but diagenetic conditions at Gale crater were apparently inappropriate to the maturation of the observed amorphous products to a more stable quartz phase.…”

The Middle Atlas Geological karsts forms: Towards Geosites characterization

“…The HMMB area (Médard et al, 2014) is located between the tabular plateau in the North and the thrust of the High Atlas to the South. This is a large corridor with different evaporitic series installed during the evolution of the Messinian subsident basin inside the folded upper Jurassic limestone.…”

Hydration of Na-saturated synthetic stevensite, a peculiar trioctahedral smectite

“…Stevensite, whose layer charge deficit originates from the presence of octahedral vacancies, is a common smectite in lacustrine environments (Eberl et al, 1982;Khoury et al, 1982;Jones, 1986;Thiry et al, 2014;Bentz and Peterson, 2020;De Oliveira Nardi Leite et al, 2020) By contrast, hydration of stevensite, whose layer charge deficit originates from the presence of octahedral vacancies. Compared to saponite and hectorite, its hydration has received much less attention although early reports mention a very specific behavior (Brindley, 1955;Faust et al, 1959;Shimoda, 1971).…”