Ute Mann

Surface water productivity and paleoceanographic implications in the Cenozoic Arctic Ocean

] Study of bulk nitrogen contents and isotopic composition in Arctic Ocean sequences (Integrated OceanDrilling Program Expedition 302) over the past 60 Ma revealed changes in the export flux and sources ofsedimentary nitrogen. The paleoproductivity calculated from the fraction of organic nitrogen to total nitrogen isdistinctly lower (<20 g C m

Organic Facies Variations, Source Rock Potential, and Sea Level Changes in Cretaceous Black Shales of the Quebrada Ocal, Upper Magdalena Valley, Colombia

A 290-m-thick middle Cretaceous black shale sequence in the upper Magdalena Valley, a present-day intramontane basin located between the Central and Eastern cordilleras of Colombia, was investigated with organic-geochemical and microscopic analyses. As a result of the investigation, we were able to (1) differentiate four organic facies types, (2) estimate their source rock potential, and (3) integrate these facies into a sequence stratigraphic framework. The four organic facies types were type C, BC, B, and D. Type C contains a distinct terrigenous organic matter component in lowstand or highstand deposits. Organic facies type BC is characterized by an increase and a better preservation of marine organic matter. BC belongs to the lower part of the transgressive systems tract. Sediments of organic facies type B have the highest amount of marine organic matter due to excellent preservation under anoxic conditions. The absence of bioturbation and the enrichment of trace metals are further implications for deposition under anoxic conditions. Facies type B is found in the upper part of the transgressive systems tract and contains the best petroleum source rock potential. Facies B occurrence coincides with sea level highstand and correlates especially with a maximum flooding in northern South America during the Turonian. Organic facies type D is also related to highstand deposits, but shows a high rate of reworking and degradation of organic matter.

Improved hydrocarbon charge prediction by source-rock modelling

Predictions of initial source-rock distribution, thickness and quality are key input parameters to quantitative basin models. This article describes a workflow where process-based modelling of deposition and preservation of organic matter at basin scale is performed to provide the input to modelling of hydrocarbon generation and expulsion from source rocks. As the vertical resolution of the depositional- and source-rock models is significantly higher than for conventional basin models, a means of upscaling the source-rock properties is needed when providing these as input to hydrocarbon generation modelling. To illustrate the modelling workflow, an example from the Triassic Kobbe Formation of the Norwegian Barents Sea was used. Two alternative source-rock models for the Kobbe Formation were constructed and discussed. During the modelling process preservation conditions were fine-tuned to better match local well data within the Nordkapp Basin. The second model provided a better calibration both for the source-rock model to the well data and for the secondary migration model to known hydrocarbon accumulations of the Nordkapp Basin.