Constraints on the thermal history of the Dead-Sea Graben as revealed by coal ranks in deep boreholes

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Coal ranks have been studied by vitrinite reflectance measurements in three boreholes; Zuk Tamrur 1 and Zohar 8 on the Judea Desert plateau (adjacent to the graben margin) and Amiaz 1 on a down-faulted block at the southwest Dead-Sea Graben. In the plateau boreholes, time-temperature index (TTI) calculations reveal that the coalification profile probably evolved under a Late Cretaceous thermal event with a thermal gradient of 35°-38°C/km followed by gradual decay to the present level c. 20°C/km by Miocene time. In Amiaz 1, the highest coal rank encountered, 0.5% Ro, is marginal for independent TTI calculations, however, some constraints on thermal history can be inferred. Stratigraphic and structural relationships between the 0.5% Ro isoreflectance in Amiaz 1 and the plateau boreholes reveals that most of the coalification measured in Amiaz 1 pre dates the formation of the graben and that an additional 3.4 km of Miocene-Holocene graben fill barely affected the coalification. Cessation of coalification despite increasing burial indicates that the post-Miocene thermal gradient in the Amiaz block could not have exceeded 20°-23°C/km. This finding is consistent with present day heat flow and other geophysical information. Tectonic models for the evolution of the Dead Sea Graben requiring a high thermal regime are inconsistent with the presented data. This raises questions as to the mechanism involved in the formation of rhomb-shaped grabens in general, on the one hand and for the hypothesis of the "leaky" nature of the Dead Sea transform north of the Gulf of Elat, on the other.

Original languageEnglish
Pages (from-to)135-150
Number of pages16
Issue number1-3
StatePublished - 15 Sep 1987

ASJC Scopus subject areas

  • Geophysics
  • Earth-Surface Processes


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