Browsing by Author "Bjelica, Nikola"
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Item Compilation of widespread, Cretaceous OAE2 black shale horizons documented in wells from the Gulf of Mexico, Caribbean, and Atlantic passive margins(2018-10-18) Bjelica, NikolaOceanic anoxic events are periods in Earth’s history when oceans were depleted in dissolved oxygen and characterized by deposition of organic-rich, and black, marine sediments. Variations in δ13C are known to correlate with the presence of trace metals related to emplacement of large igneous provinces (LIPs). OAEs are now recognized to provide widespread source rocks for hydrocarbon generation. OAE2 event coincided with high sea level and was response to LIP event in the Caribbean region. This Caribbean LIP event provided the driving force for organic carbon deposition. I have compiled thickness of OAE2 black shales on the Gulf of Mexico, Caribbean and Atlantic passive margins using published well data. Gulf of Mexico black shale can vary in thickness from 45 to 150m with average TOC values in the range from 1% to 4.6%. OAE2 black shale horizons for the Caribbean region can vary in thickness from 37 to 550m with low TOC value of 0.07%. South American Atlantic basins contain black shale that varies in thickness from 11 to 610m with TOC values ranging from 1% to 36%. African Atlantic margins black shale varies in thickness from 100 to 700m with TOC values ranging from 10% to 30%.Item Estimating Vertical Motions in Texas via Hiatus Mapping and Flexural Backstripping(2022-04) Bjelica, Nikola; Colli, Lorenzo; Wu, Jonny; Madof, Andrew S.It has been proposed that Texas experienced uplift and tilt during the latter part of the Cenozoic based on onlapping strata and truncated sequences. The precise timing, spatial extent, and amplitude of these vertical motions, as well as their dynamic causes, remain poorly constrained. We analyzed regional-scale unconformities from geologic maps and regional cross-sections of Texas to compile hiatus maps at spatial scales of many hundreds of kilometers and at temporal scales of geologic epochs. This was complemented by the analysis of subsurface geometries and by a quantitative assessment of the role of post-rift thermal subsidence and lithospheric flexure induced by sediment loading. Our analysis put additional constraints on the timing of the uplift from Upper Cretaceous through Miocene and amplitude of tilting of 650 +/- 150 meters, refining our knowledge of the tectonic history of Texas. Additionally, we were able to assess that changes in dynamic support from the convecting mantle are required to explain these past vertical motions of the Texas lithosphere.