Wyniki wyszukiwania - BazTech

1

Diatom biofacies in the SW Gulf of Gdańsk and the Vistula Lagoon (the southern Baltic Sea) as indicators of the basin evolution in the Middle and Late Holocene

Witak M.

Oceanological and Hydrobiological Studies

|

2013

|

Vol. 42, No. 1

70-88

EN

This article presents results of diatom analysis of seven sediment cores taken from various depths of the Gulf of Gdańsk between the Hel Peninsula and the coast of Gdańsk and Gdynia. Further eight cores were drilled in the northern, southern and central part of the Vistula Lagoon. The present investigations enabled the determination of: (i) differentiation of diatom assemblage zones, (ii) correlation of palaeoecological units with reference to the following stages: Mastogloia Sea, Littorina Sea, Post-Littorina Sea, including the latest environmental changes associated with an anthropogenic factor, (iii) description of the defined diatom biofacies based on statistical analysis, (iiii) reconstruction of spatial and temporal development of both basins with the emphasis on the role of inflows of sea and river waters.

2

Biofacies and palaeoenvironments of the Jurassic Shaqra Group of Saudi Arabia

Hughes G.

Volumina Jurassica

|

2008

|

Vol. 6, no. 1

33-45

EN

The Jurassic succession in Saudi Arabia consists of seven formations, forming the Shaqra Group, of which most are carbonate and some are partly evaporitic, and is of economic importance because it hosts twelve hydrocarbon reservoirs, including the Arab-D Reservoir within the world’s largest oilfield at Ghawar. The Minjur-Marrat formational boundary marks the Triassic-Jurassic boundary, of which the Marrat is dated as Toarcian. A significant unconformity separates this unit from the overlying Dhruma Formation, of Bajocian to Bathonian ages. The Tuwaiq Mountain Formation, of Callovian age, overlies the Dhruma Formation, with reduced hiatus. The Hanifa Formation, of Oxfordian age, is separated from the Tuwaiq Mountain Formation by a minor hiatus, as are the successive Jubaila, Arab and Hith formations, of Kimmeridgian to Tithonian ages. The Jurassic-Cretaceous boundary is currently placed within the lower part of the overlying Sulaiy Formation. A combination of semi-quantitative micropalaeontological and macropalaeontological analysis of closely-spaced thin sections from these carbonates displays a tiered relay of clearly defined microbiofacies cycles. These cycles reveal palaeoenvironmental trends that subdivide the succession into parasequences, transgressive and highstand systems tracts that are not always evident from the sedimentology alone. The biofacies approach to elucidating palaeoenvironmental variations of the Shaqra Group provides significant insights to the Jurassic history of the Arabian Plate, as well as serving to explain the origin and stratigraphic location of hydrocarbon reservoirs, seals and potential source rocks. The Shaqra Group spans at least 36 Ma, and qualifies as a second order depositional sequence, within which the formations can be considered as third order sequences. Better chronostratigraphic constraint of the depositional sequences reveals elevated subsidence rates for the Dhruma, Tuwaiq Mountain and Hanifa formations that can be related to established episodes of global plate readjustment. Tectonoeustatic and possibly glacioeustatic controls on depositional cyclicity probably exerted an influence on the major unconformities within the Shaqra Group.

3

Late Jurassic biofacies characteristics of Jubaila-Arab formational contact, Saudi Arabia

Al-Dhubaib A.

Volumina Jurassica

|

2006

|

Vol. 4, no. 1

83-84

EN

The lithostratigraphic relationship between the Jubaila and Arab Formations is not fully understood and is often misinterpreted in the subsurface. Since the type section of the Jubaila is in the outcrop and that of the Arab is subsurface, there is no common feature to easily define the contact in subsurface. The highly productive Arab-D reservoir spans the Jubaila and Arab Formations. One reservoir layer in Ghawar field (at the top of reservoir zone 2B) is considered in previous studies to possibly equate with the Jubaila-Arab formational boundary, and it is confirmed in this study (Fig. 1). Using semi-quantitative micropalaeontological analysis of thin sections from three localities in Riyadh area where the Jubaila and lower Arab Formations are exposed enables recognition of this boundary in eight wells from eight fields in the east of Saudi Arabia. In this study, the Arab-D reservoir has been divided into nine biofacies that characterize the Jubaila and Arab Formations and the nature of the Jubaila-Arab formational contact. Calibration of the wireline logs with these biofacies will assist in the recognition of this event in uncored wells, and assist in regional Arab-D reservoir layering. Such information will also contribute to improve the understanding of intra-Arab-D reservoir sequence stratigraphy, palaeoenvironmental and sedimentological variations and unexpected production behavior of the reservoir.

4

Late Famennian pelagic shark assemblages

Ginter M.

Acta Geologica Polonica

|

2000

|

Vol. 50, no. 3

369-386

EN

Chondrichthyan microremains from a section at Soureille d'Izarne (Montage Noire, southern France), with a new species,Thrinacodus tranquillus sp.n., are described and compared to several other late Famennian pelagic chondrichthyan assemblages.Three general chondrichthyan biofacies are distinguished: shallow water Protacrodus biofacie; intermediate Phoebodus-Thrinacodus biofacies, characteristic of moderately deep,open shelves; and deep water Jalodus biofacies The intermediate biofacies is the most widely distributed and usually yields the richest and most diverse assemblages