Fabian Duque-Botero, Resevoir and Seal Prediction, Chevron ETC, 1500 Louisiana Street, Houston, TX 77021, phone: 8328546850, fabian.duque@chevron.com, Florentin J.M-R. Maurrasse, Department of Earth Sciences, Florida International University, 11200 SW 8th Street PC-344, Miami, FL 33199, and Mihaela Carmen Melinte, National Institute of Marine Geology and Geoecology - Geomar, Dimitrie Onciul Street, No. 23-25, Bucharest, 024053, Romania.

Sediments of the Indidura Formation in the Parras Mountains, NE Mexico, consist of a series of conspicuous interbeds of highly laminated biocalcilutites and marlstones. Close observation reveals that light laminae are related to higher concentration of calcareous microspheroids, whereas dark laminae contain less carbonate and enriched in organic carbon. Wavelet transforms and time series were used to investigate the different degrees of cyclic changes.

Identification of calcareous nannofossils zones CC-10 to CC-13 allowed the determination of sedimentation rates of 6.2 and 10.1 cm/ka that were used to transform thickness to calendar years. Findings indicate that variability at the field scale correlates with Milankovicth precession cycle of about 23.000 years. At the microscopic scale analysis reveals that laminae register much shorter-term climatic variability that occurred at periodicities of 10-15 year pulses similar to present day solar Schwabe cycles.

We interpret changes as indicated by organic geochemistry to be the result of fluctuating cyanobacterial productivity, which increased during peak precession periods with low sediment supply and high recycling of nutrients. A similar situation is inferred at millimetric scale, were nutrient variability that was controlled by periodic increased in pluviosity at the decadal scale, which in turn generated enhanced/decreased productivity conditions where calcifying cyanobacterial bloomed.

Present work shows that climatic variability at solar scale during peak precession cycles was the dominant factor in the accumulation of this organic rich sequence and points to the importance of cyanobacterial derived organic matter as potential contributors to the generation hydrocarbons rocks in the sedimentary record.