ABSTRACT During the Paleocene–Eocene, the Earth experienced the warmest conditions of the Cenozoic and reduced equator-to-pole temperature gradients. Compared to low- and mid-latitude sites, Paleogene environmental changes are less documented in Arctic regions, although such high latitude areas constitute a critical domain to constrain global climate changes. Floral and faunal assemblages indicative of exceptionally warm and humid conditions during the late Paleocene–early Eocene have been reported in several localities around the Arctic Ocean. Additional studies are required to ascertain the effects of Paleocene–Eocene global environmental changes on western Arctic regions. Here we present multiproxy data from early Eocene deltaic plain sediments of the Mackenzie Delta (Canada). This environment is characterized by littoral forest, including swamp, showing that the mangrove Avicennia grew in Arctic Canada near 75°N under air temperatures averaging 21–22 °C annually and 10–14 °C in winter and with precipitation of 1200–1400 mm/yr. Kaolinite contents are high (up to 75% of clay assemblages), as under a modern subtropical climate. The Avicennia pollens recently found in the New Siberian Islands and in Arctic Canada imply that warm and wet conditions were widespread along the Arctic coast during the early Eocene. It also suggests a marine connection between the Arctic Basin and the mid-latitude oceans. We propose that an oceanic current must have connected the Arctic Basin to the Atlantic and/or Pacific and that an internal current developed in the Arctic Basin since the early Eocene.

Abstract Bulk organic geochemical and microscopic studies (Rock-Eval pyrolysis, light transmitted–uv microscope) were carried out on the shales of the Upper Triassic–Middle Jurassic Shemshak Group in the northern, central and southern Alborz Range of northern Iran. Total organic carbon (TOC) values range from 0 to 29.4 wt% (1.2 wt% on average) indicating a generally poor–moderate organic carbon content. Upper Triassic shales in the lower part of the Shemshak Group have been mainly deposited in marine/lake settings under dysoxic–anoxic conditions, with TOC=0.7 wt% on average. Toarcian–Aalenian shales in the upper part of the Shemshak Group were deposited under comparatively deeper marine oxic–dysoxic conditions with the lowest TOC contents recorded (0.3 wt% on average). Carbonaceous shales at different stratigraphic levels of the Shemshak Group show the highest TOC contents (14.2 wt% on average). T max values range from 439 to 599 °C (average 500 °C), indicating that the organic matter has experienced high temperatures during deep burial and active post-sedimentary tectonics. The hydrogen index (HI)– T max diagram shows the presence of Type IV kerogen of altered organic matter with a very low mean HI value. The palynofacies is characterized by the dominance of amorphous organic matter probably predominately derived from degradation of marine–non-marine phytoplankton. The Upper Shemshak Group has low potential to produce petroleum, whereas the Lower Shemshak Group is an important effective petroleum source rock in the Alborz Range. The latter may have generated a considerable amount of petroleum at some localities (e.g. Tazareh and Paland) in the geological past.

Abstract About 70% of the total world petroleum resources are concentrated in the Tethyan realm, the Mesozoic deposits being the most prolific source rocks of these oil and gas reserves. To understand the depositional controls of these organic-rich facies at the scale of the Tethys is a challenging problem. A recent set of paleoenvironmental maps for the Tethyan realm allows integration of source-rock mapping with other mappable geologic information. This integrated approach is attempted here for three short time intervals of the Mesozoic: Toarcian, Kimmeridgian, and Cenomanian, all of which were periods of good source-rock deposition. The source-rock distribution during the Toarcian shows a contrast between the western European and Tethyan realms. While there are high concentrations of organic matter corresponding to thick deposits in the western European realm, there are only lower concentrations within thin sedimentary sequences in the Tethyan realm. Although the organic facies are similar in both settings, widespread anoxia must have existed in western European epicontinental seas, while the preservation of organic matter in the Tethyan realm must be related to morphological factors. During the Kimmeridgian, preservation of marine organic matter was important in epicontinental platforms as well as in newly created margins. The Cenomanian is also clearly associated with good preservation of oil-prone source rocks, especially in low latitudes. During this interval, numerous organic-rich shale deposits are preserved, whatever the environment: on platforms as well as in basins. Whereas the northern shelves seem more favorable for organic concentration than the Tethyan margins during the Toarcian—and probably also during the Kimmeridgian—the reverse is true for the black shales preserved during the Cenomanian. During these three intervals of enhanced marine organic-carbon preservation, the distribution of source rocks was controlled both by plate movements that influenced opening or closing of seaways, basin morphologies and their evolution; and by paleocurrents and paleoclimates. Critical to future global source-rock mapping is the refinement of stratigraphic dating, in order to identify the synchronism of source-rock deposits and to better understand their distribution in time and space.

Abstract Geochemical studies to characterize the amount, origin, and petroleum potential of organic matter in Toarcian rocks have been performed on samples from outcrops and cores within the Mediterranean area and the Middle East. Maps were prepared to show the concentration and nature of organic matter during Toarcian time. These maps show great heterogeneity in the quantity and type of organic matter: (1) marine planktonic material deposited in reducing environments in shallow–water basins in northwestern Europe, or in deep basins in the Tethys; (2) terrestrial organic matter from higher plants, that is moderately degraded along the northern Tethyan margin and in the northern North Sea; and (3) residual or oxidized organic matter that occurs in most of the Tethys basins. These data show the existence of several environments where organic matter was preserved during the Toarcian anoxic event.