Correctly identifying key variables associated with the temporal and spatial distribution of prolific marine petroleum source rock (MPSR) units is of critical importance towards the future development of models accurately predicting their existence and effective exploitation. The geographic positioning and prevailing paleoclimatic conditions on paleocontinental reconstructions, in combination with the processes controlling the drowning of continental margins and parameters associated with the establishment of high biologic productivity and long term anoxic conditions within the water column, have been pursued as first-order constraints controlling the development of some prolific marine petroleum source rock (MPSR) deposits. From this, a model has been developed that accounts for the enhanced preservation of regional type-II MPSR deposits on low paleolatitudinally-positioned continental margins and shelves that have undergone depression with respect to sea level. Two 'shelf-drowning' mechanisms, continental passive margin subsidence combined with eustacy, and tectonically-induced subsidence by the loading of continental margins, are presented as effective processes that contribute towards the more efficient accumulation and preservation of some extensive marine petroleum source rock (MPSR) units.
The potential utility of this model is examined by a comprehensive analysis of an extensive active continental margin MPSR unit deposited within the late medial Ordovician Taconic Foreland Basin of eastern New York and a prolific late medial Cretaceous continental passive margin MPSR unit deposited within the Maracaibo Basin of northwestern Venezuela. The integrated use of organic geochemistry, programmed pyrolysis, and geochemical analyses of the Taconic Foreland Basin demonstrates that the Utica Formation was an organic-rich and a prolific, although now spent, MPSR unit. The existence of the Utica Formation is believed to have been the result of 'channeled-flow upwelling', within a bathymetrically-constricted collisional foreland basin, which was spatially positioned at a subsiding continental margin entering a subduction zone. The penecontemporaneous impingement of the oxygen minimum zone of the water column at the drowned continental shelf caused the establishment of long-term anoxic conditions on the outer slope of the developing foreland basin. This consequently increased the potential for the preservation, subsequent burial and compaction, and eventual conversion of organic-rich muds into a regionally important source rock unit.
Geochemical analysis of the late medial Cretaceous derived petroleum oils of the Maracaibo Basin also requires the existence of one regional MPSR unit, the La Luna Formation. This is consistent with the combination of eustatic sea level rise, and thermal subsidence, of the northern South American passive continental margin and shelf during medial Cretaceous times being coincident with the development of high biologic productivity conditions within the overlying photic zone of the water column. This was a direct result of the low paleolatitudinal positioning of the northern coastline of South America during medial Cretaceous times. The subsequent movement of the Caribbean Plate through the Proto-Caribbean Seaway in turn controlled the timing and maturation of the MPSR unit, becoming younger as collision and foredeep sedimentation progressed eastwards.
Achong, C.M., 1993. Identifying key variables associated with the
and spatial distribution of prolific marine petroleum source rock
units and its application to the Taconic Foreland Basin, eastern
Unpublished MSc. thesis, State University of New York at Albany.
University at Albany Science Library call number: SCIENCE Oversize (*) QE 40 Z899 1993 A24
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