CLINOFORM GEOMETRY AND SEISMIC FACIES OF LOWER AND MIDDLE EOCENE CARBONATE SEQUENCES, SIRTE BASIN, NORTH CENTRAL LIBYA

ABSTRACT New collections of plant macrofossils and radiometric dates from the Herren beds of north-central Oregon provide the opportunity to document floral communities and calculate foliar-derived climate estimates from the warm early Eocene and the cooler middle Eocene. Plant macrofossils were collected from one fluvial site at East Birch Creek approximately 2 m below a 51.9 ± 0.9 Ma tuff. Collections were also made at two co-occurring fluvial sites at Arbuckle Mountain, whose ages are constrained to ca. 44.5–43.8 Ma based on a dated tuff from Willow Creek (44.5 ± 0.8 Ma) and reported ages for the overlying Clarno Formation. Floral findings show an almost complete vegetation overturn, with only two genera (Glyptostrobus and Allantodiopsis) appearing in both floras. Both floras are species poor, but the older East Birch Creek flora has higher richness and evenness than the younger Arbuckle Mountain flora. The four named genera at East Birch Creek are taxa found throughout Eocene North America; named genera at Arbuckle Mountain also include taxa restricted to the Pacific Northwest. Leaf margin analysis and leaf area analysis of the East Birch Creek community suggest a warmer and possibly wetter (mean annual temperature 23.4 ± 4.3 °C; mean annual precipitation 206 +89, -63 cm) climate than the Arbuckle Mountain flora (16.4 ± 4.2 °C; 165 +50, -71.4 cm). This research provides a framework for future research on Eocene floristic, environmental, and climatic trends of the Pacific Northwest.

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Seismic attributes for description of reef growth and channel system evolution — Case study of Intisar E, Libya

Interpretation ◽

10.1190/int-2015-0017.1 ◽

2016 ◽

Vol 4 (1) ◽

pp. SB1-SB11 ◽

Cited By ~ 4

Author(s):

Yichuan Wang ◽

Christoph Georg Eichkitz ◽

Marcellus Gregor Schreilechner ◽

Gabor Heinemann ◽

John C. Davis ◽

...

Keyword(s):

Seismic Attributes ◽

Seismic Facies ◽

Seismic Survey ◽

Turbidity Currents ◽

Reef Growth ◽

Geologic History ◽

Channel System ◽

Sirte Basin ◽

Occurrence Matrix

A 3D seismic survey over the Intisar E field in the Ajdabiya Trough of the Sirte Basin, Libya, revealed a channel-like feature in Eocene carbonates that wraps around the pinnacle reef that contains the reservoir. We have used coherence, curvature, and spectral decomposition seismic attributes to determine the morphology and gray-level co-occurrence matrix attributes to define seismic facies within the feature. These indicated that the channel originated by submarine scouring caused by downslope movement of turbidity currents. Erosion was followed by the deposition of successive layers of carbonate debris in the channel. Stratigraphic correlations with the adjacent pinnacle reef revealed that the channel was cut during the late stage of reef growth, and a second channel formed after the Intisar E reef ceased to grow. Differences in seafloor elevation over the reef probably diverted turbidity currents so channels were not cut into the reef, breaching the reservoir. This interpreted geologic history may explain why some pinnacle reefs in the Intisar complex contained giant reservoirs, whereas others were barren.

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Eocene Ginkgo leaf fossils from the Pacific Northwest

Canadian Journal of Botany ◽

10.1139/b02-097 ◽

2002 ◽

Vol 80 (10) ◽

pp. 1078-1087 ◽

Cited By ~ 18

Author(s):

George E Mustoe

Keyword(s):

British Columbia ◽

Pacific Northwest ◽

Ginkgo Biloba ◽

Middle Eocene ◽

Washington State ◽

North Central ◽

Lacustrine Deposits ◽

South Central ◽

The Pacific ◽

Ginkgo Leaf

Middle Eocene lacustrine deposits in south-central British Columbia and north-central Washington state preserve two types of Ginkgo leaves. A morphotype characterized by deeply divided multiple lobes is herein described as Ginkgo dissecta sp.nov. Leaves that are either undivided or shallowly divided into bilobate symmetry are indistinguishable from foliage of extant Ginkgo biloba Linnaeus. These fossils contradict the widely held belief that only a single Ginkgo species, Ginkgo adiantoides (Unger) Heer, inhabited Cenozoic forests.Key words: British Columbia, Eocene, fossil, Ginkgo adiantoides, Ginkgo biloba, Ginkgo dissecta, McAbee, Republic, Tertiary, Washington.

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