Mid-Pliocene

Tar sand deposits in Venezuela occur in the Officina/Tremblador tar belt that are believed to contain bitumen-impregnated sands of a similar extent to those of Alberta, Canada. The Guanaco Asphalt Lake occurs in deposits that rest on a formation of mid-Pliocene age and is closely associated with the Guanaco crude oil field that produces heavy crude oil from shale and fractured argillite of the Upper Cretaceous group. The tar sands of the Orinoco deposit are located along the southern flanks of the eastern Venezuelan basin. 

Williams, M., Haywood, A. M., Hillenbrand, C.-D. Wilkinson, I. P. 2005Z>. Efficacy of data from Pliocene planktonic foraminifer calcite for spatial sea surface temperature reconstruction comparison with a fuUy coupled ocean-atmosphere GCM and fossil assemblage data for the mid-Pliocene. Geological Magazine, 142, 399-417. 

Figure 1.159. Eu/Eu values of (A) modern sediment, hydrothermal solution and seawater and (B) mid-Miocene to early Pliocene Japan Sea see in text). Modern data are from the Pacific ocean,...

AGE EO. OLIGOCENE EARLY MIOCENE MIDDLE MIOCENE LATE MID. T "" "" PLIOCENE jaUAT. I... 

Harris L. C. and Whiting B. M. (2000) Sequence-stratigraphic signification of miocene to pliocene glauconite-rich layers on and offshore of the US mid-Atlantic margin. Sedim. Geol. 134, 129-147. 

Fig. 14. Relationships between pore-pressures, the hydrostatic gradient, the fracture pressure gradient (approximation to the minimal horizontal stress, Sf,) and the lithostatic pressure gradient (approximation to the vertical stress, S ). Pore-pressures from sea floor to base Pliocene equals hydrostatic. The yellow, dark blue and red pore-pressure trend-lines represent the pore-pressure versus depth gradients for the Paleocene-Eocene, Mid-late Cretaceous and Upper Jurassic-lowermost Cretaceous, respectively. The portion of the red trend-line below approximately 2550 m MSL equals the maximum reservoir pore-pressure trend-line of Fig. 13 and reflects the counter-pressure of the topseal controlling the pore-pressure distribution of hydraulic compartments II, III and (probably) IV.

Figure 2. Mass spectral histograms of tetrapyrrole pigments characteristic of mid-/late-diagenesis. (a) free-base 7,8-dihy-dro-DPEP-series (b) free-base DPEP-series and (c) nickel DPEP (ETIO- omitted)-series. Sample Pliocene/Miocene shale of marine origin (cf. 24).

Donovan and Harper present a study of Cenozoic brachiopod/crinoid associations with substrate types in the Caribbean. Pleistocene and Miocene occurrences are commoner than in the Pliocene, although crinoids are rare also in the Pleistocene. On the basis of the brachiopod/crinoid evidence the mid-Miocene localities studied are of deeper water origin than had been thought previously. 

---