Holocene marine terraces on two salt diapirs in the Persian Gulf, Iran: age, depositional history and uplift rates

Abstract

Slightly inclined Holocene marine terraces cover parts of two circular salt diapirs (Hormoz and Namakdan) in the Persian Gulf. Their relative altitude above present sea level results from a combination of general marine transgression/regression affecting the whole area, and of local uplift related to salt diapirism. Differential uplift rate of the studied diapirs in centre-to-rim profiles was calculated from results based on: (i) radiocarbon ages of skeletal remains of benthic faunas (19 samples), which originally grew close to sea level; (ii) original altitude of samples, estimated from general sea-level oscillation curves for the last 10 kyr, and (iii) present sample altitude measured in the field.Calculated uplift rates increase from rim to centre on both diapirs in the range from: 2 mm yr À1 at the rim to 5-6 mm yr À1 at the interior of Hormoz, and 1-3 mm yr À1 at the rim to 3-5 mm yr À1 at the interior of Namakdan. Such uplift rate distributions fit into the parabolic profile of Newtonian fluid rather than to profiles typical for pseudoplastic fluids. The increase in uplift rate with distance from rim to centre of diapirs is gradual as demonstrated also by generally smooth surface of marine terraces. No tectonic dissections were found. The depositional history on both salt diapirs is similar although they are situated more than 100 km apart. Marine sedimentation started at about 9.6k cal. yr BP on Hormoz and at 8.6k cal. yr BP on Namakdan. Owing to rapid transgression, the sea partially truncated both salt diapirs and rapidly deepened, and carbonate mud was deposited on the peripheries of both salt diapirs. Between 7 and 5k cal. yr BP beach deposition replaced carbonate mud. Soon after 5k cal. yr BP, the sea retreated from most of the marine terraces on both salt diapirs.

Surficial deposits on salt diapirs (Zagros Mountains and Persian Gulf Platform, Iran): Characterization, evolution, erosion and the influence on landscape morphology

“…The thickness of the Holocene residuum attains only a few meters, indicating that the rock salt was protected from seawater only by a few meters of material. Dating of the Holocene marine terraces indicated that submarine residuum formation occurred in the period of 9-6 kyr BP (Bruthans et al, 2006). Fig.…”

“…They consist mostly of detrital limestone, gravels and carbonate mud. Bruthans et al (2006) described these sediments in detail.…”

Evolution of salt diapir and karst morphology during the last glacial cycle: Effects of sea-level oscillation, diapir and regional uplift, and erosion (Persian Gulf, Iran)

“…The U-series age is 350-250 kyr BP, however, the samples N8 have been recrystallized to calcite and the ages are not conclusive (compare with Pirazzoli et al, 2004). The SE margin of the Namakdan diapir is covered by a 10 m-thick Holocene marine terrace 5-8 cal kyr BP in age (Bruthans et al, 2006a).…”

“…The central part of the diapir is ∼120 m a.s.l. The southern marginal zone of the island is formed by sub-vertical strata of Miocene siliciclastics overlain by an angular unconformity of Pleistocene deposits (IOOC, 1969;Bruthans et al, 2006a). The surface of the diapir is mostly covered with thin weathering residua (Bruthans et al, 2000(Bruthans et al, , 2009.…”

“…For the periods of prominent sea-level fall and lowstands, on the other hand, the base level was considered to be slowly lowering, and well above the sea level (due to the long distance between the coastline and the Namak diapir and due to the lag of stream incision behind sea-level fall). The position of the base level can be inferred from the presence of marine deposits in the Holocene (Bruthans et al, 2006a) and from the position of sample N12.…”