1. RESULTS AND DISCUSSION
The Hydrocarbon Potential of the Triassic Lockatong formation in the Newark Basin.
Yoana Boleaga - Kingsborough Community College, 2001 Oriental Boulevard, Brooklyn, NY 11235
Larbi Rddad - Kingsborough Community College, Earth and Planetary Sciences, Department of Physical Sciences, 2001 Oriental Boulevard, Brooklyn, NY 11235
INTRODUCTION
The Triassic and Early Jurassic formations in the Newark basin have been investigated for their depositional setting, sedimentology, and hydrogeology. Few researchers, however, have studied these formations for their hydrocarbon potential (petroleum, gas) [1], [2] .
The present study is a contribution to the hydrocarbon potential of the Triassic Lockatong Formation. It aims at characterizing the quantity and quality of the black shale of this formation in the Nursery and Titusville cores in the Newark basin (Fig.1).Total organic carbon (TOC) is analyzed to evaluate the richness of organic matter. The degree of maturity is evaluated to find out the maturity of the organic matter (immature, mature, or over mature). The identification of the quality of organic matter (Type I, II, and or III Kerogen) is attempted.
Fig. 4. Plot HI vs OI in Nursery (brown circle) and Titusville (yellow circle) cores of the Newark basin.
The Tmax values are widespread ( °C) and are unreliable due to the very low S2 values. The available R0 data vary from 1.94 to 2.69% (mean=2.34%) [4]. Using the equation Tmax = (R )/0.018 [5] and the available R0 data, the calculated Tmax range from 506 to 547 °C (Tmax avg. = 527 °C) and is about 531 °C for the Nursery and Titusville cores respectively. These Tmax values along with R0 values clearly indicate that the organic matter of the analyzed samples are over mature and had already generated hydrocarbons (oil and gas). The over maturity of organic matter is confirmed by the very low genetic potential (GP= S1+S2) values ranging from 0.15 to 0.46 mg HC/g rock and the low S2/S3 ratio (0.5 – 1.24). The low Production Index (PI) values, which indicate either low maturity or over maturity [6] further confirms that the studied cores are over mature.
The over maturity of the organic matter of the analyzed samples had dramatically reduced its hydrogen content, and thus its HI. Using an average TOC of 1.1 wt%, an estimated PI of 60%, and the maximum HI of 110 mg HC/g TOC, the calculated initial HI (HI0) was about 275 mg HC/g TOC. This initial HI value fall into the HI range of Type II/III kerogen which produced oil and gas in the past.
Fig. 2. Plot of TOC vs Depth (A), HI vs depth (B), and S1/TOC*100 vs Depth (C) in the Nursery (brown circle) and the Titusville (yellow circle) cores of the Newark basin.
RESULTS AND DISCUSSION
I- Organic matter richness
The overall black color of the studied black shale samples may give a general idea about the rock’s organic matter richness, but it is not always a reliable indicator. The Total Organic Carbon (TOC), however, provides a good indication about the organic matter richness of source rocks. The TOC values range from 0.50 to 2.72 % (mean=1.2%) respectively for the Nursery and Titusville cores (Fig. 2A, Fig. 3). These TOC values indicate that these samples are fair to good source rock for hydrocarbons (oil and gas). The plot TOC vs S2 diagram further confirms this conclusion (Fig. 3).
GEOLOGICAL CONTEXT
The early Mesozoic Newark basin was formed during the Triassic rifting of Pangaea. The structuration of the basin into a half-graben was caused by the reactivation of the Normal NE-SW-trending faults. This basin was successively filled with fluvial/alluvial sediments (Stockton Formation), dark to gray lacustrine sediments (Lockatong Formation), red clastic sediments (Passaic Formation), and finally Early Jurassic sediments intercalated with basaltic flows [3] During the opening of the Atlantic Ocean, a post-Middle inversion occurred resulting in compressional tectonic activity. This tectonic event led to the compression and structuration of the present day Newark basin.
CONCUSION
The Rock-Eval analysis of the black shale samples of the Lockatong Formation revealed that they are fair to good source rock of hydrocarbons. Due to the over maturity, the organic matter of these black shale samples, probably of type II/III, have no more generative hydrocarbon potential. Almost all hydrocarbons have been already generated.
Fig. 3. Plot TOC vs S2 in Nursery (brown circle) and Titusville (yellow circle) cores of the Newark basin.
II- Organic matter quality and maturity
The Hydrogen Index (HI) versus Oxygen Index (OI) diagram, presented in Figure 4, gives information regarding the type of kerogen. The plot of the data in the HI vs OI diagram put the studied samples at the end of the evolutionary paths of Type I, II, and III. This position of the data is due to the over maturity of organic matter. Based on HI values, the organic matter seems to be of type III (Fig.2B). However, it is difficult to determine the type of organic matter due to its over maturity. The hydrogen index (HI) of the analyzed samples is less than 200 mg HC/g TOC (Fig. 2B). These HI values were most likely not originally low, but rather reveal loss in hydrogen content due to the organic matter maturity as indicated by S1/TOC vs Depth (Fig. 2C).
Acknowledgement
The first author would like to thank Louis Stock Alliance Program (LSAMP) for providing her with this opportunity to carry out this research and participate in this program under the supervision of Dr. Rddad. We also would like to thank Dr. Marjorie McDonough and Robert Schacter at Kingsborough for coordinating the KCC LSAMP activities. We are also grateful to Kingsborough's Associate Provost Dr. Reza Fakhari for his ongoing support throughout this entire project. 
References
[1] Spiker, E, C., Kotra, R. K., Hatcher, P. G., Gottfried, R. M., Horan, M. F., and Olsen P. E Source of kerogen in black shales from the Newark and Hartford Basins, eastern United States, in Froelich, A. J., and Robinson, G. R., eds., Studies of the Early Mesozoic basins of the eastern United States: U. S. Geological Survey Bulletin 1776, pp
[2] Malinconico, M.L., 2002, Lacustrine organic sedimentation, organic metamorphism, and thermal history of selected early Mesozoic Newark supergroup basins, eastern U.S.A.: Columbia University Ph.D. dissertation, New York, New York, 419 p.
[3] Olsen, P. E., 1986, Milankovitch cycles in Early Mesozoic rift basins of Eastern North America provide physical stratigraphy and time scale for understanding basin evolution: Lamont (Newsletter), v. 13, 5-6.
[4] Malinconico, M.L., 2010, Synrift to early postrift basin-scale groundwater history of the Newark basin based on surface and borehole vitrinite reflectance data, in Herman, G.C., and M.E. Serfes, eds., Contributions to the Geology and Hydrogeology of the Newark Basin: N.J. Geological Survey Bulletin 77, Chapter C., p. C1-C38
[5] Peters, K. E., Walters, C. C., and Moldowan, J. M The biomarker guide, second edition, volume I, biomarkers and isotopes in petroleum systems and human history. United Kingdom, Cambridge University Press, 476 p.
[6] Peters, K. E., and M.R. Cassa, Applied source rock geochemistry, chapter 5, in Magoon, L.B., and W.G. Dow, eds., The petroleum system—from source to trap: AAPG Memoir 60, pp. 93–120.
Fig. 1. Geologic cross section A-B in the Newark basin showing the Titusville and Nursery cores (A) and location of A-B cross section in the Newark basin (B) (after [3])