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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 67 (1983)

Issue: 3. (March)

First Page: 429

Last Page: 429

Title: Oil-Bearing Glacial Deposits from Permo-Carboniferous Haushi Group, Oman: ABSTRACT

Author(s): J. H. Braakman, B. K. Levell, K. W. Rutten

Article Type: Meeting abstract


A sequence of glacial and related deposits up to 700 m (2,296 ft) thick in the lower part of the Haushi Group contains significant quantities of oil in several fields in south and central Oman and is the main exploration target along the eastern flank of the South Oman salt basin. More than 300 well penetrations demonstrate that the glacial deposits extend over more than 60,000 km2 (23,166 mi2) in outcrop and subsurface. The Late Carboniferous to Early Permian Haushi Group (dated through palynology) unconformably overlies Precambrian to Devonian rocks of the Huqf and Haima Groups with, locally, a considerable paleorelief. The glacial deposits are overlain by fluvial and shallow marine deposits of the upper Haushi Group which include a fossiliferous l mestone dated as Early Permain (probably Sakmarian).

The glacial origin of units within the lower part of the Haushi Group is established from the outcrop area on the west flank of Huqf massif where striated pavements of Precambrian dolomite have been found. One pavement is directly overlain by a 4 m (13 ft) thick diamictite interpreted as a basal till. In nearby exposures striated boulders have been found.

Both in the outcrops and in the subsurface diamictites with abundant far-traveled material (granite and volcanic boulders) occur. They are considered to be mostly debris-flow deposits of glacially transported material. Their common interbedding with "varved" shales with dropstones is diagnostic of a glaciolacustrine setting. The association of varved shales and diamictites is commonly of sealing quality.

Reservoirs in the glacial sequence are formed by sandstones and clast to matrix-supported sandy conglomerates which are interpreted as deltaic and fluvial deposits. Depositional models and paleogeographic reconstructions have been made with the help of core studies and correlation of facies units using wireline logs. These correlations demonstrate the limited lateral predictability of reservoirs which is not unexpected in view of the geometrical complexity of many modern glacial deposits.

The geometry of facies units is, however, also complicated by syndepositional subsidence, due to both progressive dissolution of Precambrian salt, and to differential erosion at the contact between the glacial sediments and the underlying, unconsolidated sands of the Haima Group.

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