Indonesian Journal on Geoscience

9

Authors: Asep Kurnia Permana, Aris Kusworo, and Andi Heri Prastian

The Triassic rocks of the (West) Timor Basin mainly deposited in the marine environment have been identified. The fine-grained clastic and carbonate rocks of this Triassic marine facies are considered to be the most promising source rocks potential in this basin. Geochemical and petrographic data from outcrop samples of the Triassic carbonate of Aitutu Formation are presented in this paper, in terms of the organic maturation, kerogen type, and the origin of the organic matter. Some representative selected samples were subjected to Rock-Eval Pyrolysis, vitrinite reflectance measurement, and thermal alteration index determination as well as bitumen extraction. The extracts were then analyzed by the GC-MS (Gas Chromatography-Mass Spectrometry). The samples were collected from a marine deposit of the Triassic sequence. The TOC (Total Organic Carbon) values of the analyzed samples range between fair and rich level (0.51% - 9.16%, wt.%, TOC), whilst the kerogen is dominated by Type II with minor Type III. The organic matter was considered to be predominantly oil/gas prone with lesser gas prone potential. The thermal maturity assessed from Tmax, TAI, and vitrinite reflectance shows an immature to early peak mature stage. The biomarkers indicate mainly that the organic matter was derived from mixed source rocks facies containing alga debris and higher plant terrestrial origin.

13

Authors: Benyamin Sapiie and Meli Hadiana

Unstable water table would lead to moist condition in the uppermost layer of the ombrotrophic peat, favoring fungi to grow. This is confirmed by the higher abundance of sclerotinite maceral in samples from the upper part of the coal core. Sandbox experiment is one of the types of analogue modeling in geological sciences in which the main purpose is simulating deformation style and structural evolution of the sedimentary basin. Sandbox modeling is one of the effective ways in conducting physically modeling and evaluates complex deformation of sedimentary rocks. The main purpose of this paper is to evaluate structural geometry and deformation history of oblique convergent deformation using of integrated technique of analogue sandbox modeling applying to deformation of Seram Fold-Thrust-Belt (SFTB) in the Seram Island, Eastern Indonesia. Oblique convergent strike-slip deformation has notoriously generated area with structural complex geometry and pattern resulted from role of various local parameters that control stress distributions. Therefore, a special technique is needed for understanding and solving such problem in particular to relate 3D fault geometry and its evolution. The result of four case (Case 1 to 4) modeling setting indicated that two of modeling variables clearly affected in our sandbox modeling results; these are lithological variation (mainly stratigraphy of Seram Island) and pre-existing basement fault geometry (basement configuration). Lithological variation was mainly affected in the total number of faults development. On the other hand, pre-existing basement fault geometry was highly influenced in the end results particularly fault style and pattern as demonstrated in Case 4 modeling. In addition, this study concluded that deformation in the Seram Island is clearly best described using oblique convergent strike-slip (transpression) stress system.