Origin and timing of siderite cementation in Upper Ordovician glaciogenic sandstones from the Murzuq basin, SW Libya

M. A K El-ghali, K. G. Tajori, H. Mansurbeg, N. Ogle, R. M. Kalin

Research output: Contribution to journalArticle

12 Citations (Scopus)

Abstract

The origin and timing of siderite cementation have been constrained in relation to depositional facies and sequence stratigraphy of Upper Ordovician glaciogenic sandstones from the Murzuq basin, SW Libya. Optical microscope, backscattered electron imagery, and carbon and oxygen stable isotope analysis have revealed that siderite is of eo- and mesogenetic origin. Eogenetic siderite is Mg-poor with a mean composition of (Fe91.7Mg1.5Ca0.3Mn6.5)CO3, and occurs in paraglacial, tide-dominated deltaic highstand systems tract (HST) sandstones, in paraglacial, foreshore to shoreface HST sandstones and in postglacial, Gilbert-type deltaic lowstand systems tract (LST) sandstones. This siderite is typically of meteoric water origin that influxed into the LST and HST sandstones during relative sea level fall and basinward shift of the strandline. Mesogenetic siderite, which engulfs and thus postdates quartz overgrowths and illite, is Mg-rich with a mean composition of (Fe72.2Mg21.7Ca0.8Mn5.3)CO3 and occurs in the paraglacial, tide-dominated deltaic HST sandstones, in paraglacial foreshore to shoreface HST sandstones, in glacial, tide-dominated estuarine transgressive systems tract (TST) sandstones, in postglacial, Gilbert-type deltaic LST sandstones, and in postglacial, shoreface TST sandstones. δ18OV-PDB values of this siderite, which range between -22.6 and -13.8‰, suggest that precipitation has occurred from evolved formation waters with δ18O values between -14.0 and +1.0‰ and was either meteoric, mixed marine-meteoric and/or marine in origin by assuming postdating quartz overgrowths and illite temperature between 80 and 130 °C.

Original languageEnglish
Pages (from-to)459-471
Number of pages13
JournalMarine and Petroleum Geology
Volume23
Issue number4
DOIs
Publication statusPublished - May 2006

Fingerprint

Libya
siderites
cementation
systems tract
siderite
sandstones
Ordovician
time measurement
sandstone
highstand
basin
lowstand
tides
Postglacial
illite
tide
quartz
strandline
stratigraphy
formation water

Keywords

  • Depositional facies
  • Glaciogenic sandstone diagenesis
  • Sequence stratigraphy
  • Siderite
  • SW Libya
  • the Murzuq basin
  • Upper Ordovician

ASJC Scopus subject areas

  • Economic Geology
  • Geology
  • Geophysics
  • Stratigraphy

Cite this

Origin and timing of siderite cementation in Upper Ordovician glaciogenic sandstones from the Murzuq basin, SW Libya. / El-ghali, M. A K; Tajori, K. G.; Mansurbeg, H.; Ogle, N.; Kalin, R. M.

In: Marine and Petroleum Geology, Vol. 23, No. 4, 05.2006, p. 459-471.

Research output: Contribution to journalArticle

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AB - The origin and timing of siderite cementation have been constrained in relation to depositional facies and sequence stratigraphy of Upper Ordovician glaciogenic sandstones from the Murzuq basin, SW Libya. Optical microscope, backscattered electron imagery, and carbon and oxygen stable isotope analysis have revealed that siderite is of eo- and mesogenetic origin. Eogenetic siderite is Mg-poor with a mean composition of (Fe91.7Mg1.5Ca0.3Mn6.5)CO3, and occurs in paraglacial, tide-dominated deltaic highstand systems tract (HST) sandstones, in paraglacial, foreshore to shoreface HST sandstones and in postglacial, Gilbert-type deltaic lowstand systems tract (LST) sandstones. This siderite is typically of meteoric water origin that influxed into the LST and HST sandstones during relative sea level fall and basinward shift of the strandline. Mesogenetic siderite, which engulfs and thus postdates quartz overgrowths and illite, is Mg-rich with a mean composition of (Fe72.2Mg21.7Ca0.8Mn5.3)CO3 and occurs in the paraglacial, tide-dominated deltaic HST sandstones, in paraglacial foreshore to shoreface HST sandstones, in glacial, tide-dominated estuarine transgressive systems tract (TST) sandstones, in postglacial, Gilbert-type deltaic LST sandstones, and in postglacial, shoreface TST sandstones. δ18OV-PDB values of this siderite, which range between -22.6 and -13.8‰, suggest that precipitation has occurred from evolved formation waters with δ18O values between -14.0 and +1.0‰ and was either meteoric, mixed marine-meteoric and/or marine in origin by assuming postdating quartz overgrowths and illite temperature between 80 and 130 °C.

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