Arthur Saller 1. Search and Discovery Article #51393 (2017)** Posted June 26, Abstract

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1 PS Mixed Carbonates and Siliciclastics North of the Mahakam Delta, Offshore East Kalimantan, Indonesia* Arthur Saller 1 Search and Discovery Article #51393 (2017)** Posted June 26, 2017 *Adapted from poster presentation given at AAPG 2017 Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017 See similar articles Search and Discovery Article #50847 (2013) and Search and Discovery Article #30014 (2003) **Datapages 2017 Serial rights given by author. For all other rights contact author directly. 1 Cobalt International Energy, Houston, Texas, United States (sallerarthur@gmail.com) Abstract For the last 7 million years, carbonates have been mixed with siliciclastics north of the Mahakam delta, offshore East Kalimantan, Indonesia. The distribution of carbonates is controlled by the location of deltas, currents transporting siliciclastics, rates of sea level rise, and depositional bathymetry. At the present time, modern carbonates are deposited locally north of the delta while large amounts of sand and shale are coming out of the delta. In the late Pleistocene, carbonate mounds and shelf margin carbonates grew during transgressions when siliciclastic shorelines moved landward. Mounded carbonates preferentially occur on the upthrown side of faults, while shelf margin carbonates grew on underlying siliciclastic or carbonate shelf margins. Thin shales accumulated in lows between carbonate mounds. During highstands of sea level, siliciclastics prograded basinward across the shelf. Many carbonate mounds drowned and were covered with siliciclastics. At the shelf margin, carbonates prograded landward during highstands of sea-level. During the last 7 m.y., shelf margins have been generally backstepping landward north of the Mahakam delta because of rapid subsidence and currents transporting most deltaic clays to the south. Carbonates repeatedly grew during transgressions. During the latest Miocene and Pliocene, thick very elongate carbonates grew on the underlying siliciclastic shelf margins while thinner roughly circular mounds grew on depositional and structural highs of the shelf interior. Most of the carbonates are covered by highstand siliciclastics. The shelf margin and mounded carbonates are mainly lime grainstone and boundstones with good porosity. Unfortunately, shales covering carbonates are downlapping packages that were generally not effective seals. References Cited Crumeyrolle, P., and I. Renaud, 2003, Quaternary Incised Valleys and Low Stand Deltas Imaged with 3D Seismic and 2D HR Profiles, Mahakam Delta, Indonesia: AAPG International Conference & Exhibition, Barcelona, Spain, September 21-24, 2003, Search and Discovery Article #90017 (2003). Website accessed June 2017.

2 Saller, A.H., S.W. Reksalegora, and P. Bassant, 2011, Sequence Stratigraphy and Growth of Shelfal Carbonates in a Deltaic Province, Kutai Basin, Offshore East Kalimantan, Indonesia, in W.A. Morgan, A.D. George, P.M. Harris, J.A. Kupecz, and J.F. Sarg (eds.), Cenozoic Carbonate Systems of Australasia: Society for Sedimentary Geology Special Publication 96, p

3 Mixed Carbonates and Siliciclastics, North of the Mahakam Delta, Offshore East Kalimantan, Indonesia For the last 7 million years, carbonates have mixed with siliciclastics north of the Mahakam delta, offshore East Kalimantan, Indonesia The distribution of carbonates is controlled by the location of deltas, currents transporting siliciclastics, sea level rises & falls, and depositional bathymetry. LATE PLEISTOCENE CYCLES (300 KY PRESENT) Highstands & lowstands are dominated by siliciclastics. Seismic & well data with U-Th dating allow During Transgressions & Rapid Sea Carbonates accumulate during transgressions carbonate & siliciclastic deposition to be Level Rises, Siliciclastic Shorelines when rising sea level pushes shorelines landward. put onto the eustatic sea level curve Moved Landward & Carbonates PHILIPPINES MALAYSIA Study Area Grew, especially on Shelf Margins INDONESIA 1 Northern Area EAST KALIMANTAN Kutai Basin Kutai Basin started with Paleocene & Eocene rifting & fluvial deposition. Oligocene transgression caused widespread carbonate deposition. Miocene uplift in Central Borneo initiated deltaic deposition with eastward progradation into the subsiding Kutai basin from Miocene to present MAKASSAR STRAIT Mahakam Delta Central Area At the present, modern carbonates are deposited locally north of the delta while large amounts of sand and clay are coming out of the delta. Siliciclastic Shorelines & Deltas Prograded Basinward 18 Ka Lowstand Present Highstand Shelf N Shelf Margin Carbonates 20 km During the last 7 m.y., shelf margins have been generally backstepping landward north of the Mahakam delta because of rapid subsidence and currents transporting most deltaic clays to the south 130 Ka Lowstand Ka Highstand Material in these posters is from Saller, A.H., S.W. Reksalegora, and Philip Bassant, 2011, Sequence Stratigraphy and Growth of Shelfal Carbonates in a Deltaic Province, Kutai Basin, Offshore East Kalimantan, Indonesia, in W.A. Morgan, A.D. George, P.M. Harris, J.A. Kupecz, and J.F. Sarg, eds., Cenozoic Carbonate Systems of Australasia: Society for Sedimentary Geology Special Publication 96, p

4 Mixed Carbonates & Siliciclastics, North of the Mahakam Delta, Offshore East Kalimantan, Indonesia LATE PLEISTOCENE DEP. HISTORY G. PRESENT: HIGH SEA LEVEL TRANSGRESSIVE SHELF MARGIN & MIDDLE SHELF CARBONATES GREW ON PROGRADING HIGHSTAND TO LOWSTAND SILICICLASTICS DURING RAPID TECTONIC SUBSIDENCE (80 M/100KY) PLEISTOCENE SADEWA AREA CURRENT SEA FLOOR F. 18 KA: LOW SEA LEVEL E. 70 KA: HIGH & FALLING SEA LEVEL NORTHERN SHELF CURRENT SEA FLOOR D. 120 KA: RAPID RISING SEA LEVEL MAHAKAM DELTA FRONT SADEWA AREA SILICICLASTICS Holocene 9 m below sea floor (bsf) Upper Pleist: 21 mbsf. Lime packtone; calcitized coral (CC); dissolved small gastropod (G). Minor equant calcite cement (arrows) Slope Channels can be traced up to the Shelf Margin HST Shelf Interior Buildup on Upthrown Side of Fault Note incised valley on shelf leading to the only active slope valley Bioclast grainst.; intergranular porosity (I), moldic pores (M), benthic foram (R), planktonic foram (P), calcitized coral (CC), primary pores within coral (W), equant calcite cement (arrows). Aragonite has been pervasively dissolved; mbsf Fossiliferous wackestone with calcitic forams (arrow), calcitic coralline algae (L; stained red) and dolomitized mud (D; unstained). 62 mbsf UPPER SLOPE MIDDLE SLOPE Khristina Kirschner made the gray shaded upper to lower slope image 2 Material in these posters is from Saller, A.H., S.W. Reksalegora, and Philip Bassant, 2011, Sequence Stratigraphy and Growth of Shelfal Carbonates in a Deltaic Province, Kutai Basin, Offshore East Kalimantan, Indonesia, in W.A. Morgan, A.D. George, P.M. Harris, J.A. Kupecz, and J.F. Sarg, eds., Cenozoic Carbonate Systems of Australasia: Society for Sedimentary Geology Special Publication 96, p B. 200 KA: HIGH SEA LEVEL W Shelf image from Crumeyrolle and Renaud (2003), used with permission Prograding siliciclastics bury carbonate & no carbonate HST develops Upper Pleistocene: 39 mbsf. Lime packgrainstone. Equant calcite cement (yellow arrows). Fibrous circumgranular cement (red arrows). Rotaline forams (F), planktonic forams (P), Halimeda (H) Upper Pleistocene: 21 mbsf. Calcitized coral (CC); Minor equant calcite cement (arrows). Primary porosity (P) Shelf Shelf margin carbonate is beyond prograding siliciclastics allowing HST carbonate C. 130 KA: LOW SEA LEVEL LOWER SLOPE Bioclastic packstone with moldic porosity (M), coralline algae (A), & a large coral fragment that has been partially replaced with equant calcite cement (C). Some of the original coral has been dissolved, and moldic porosity is still open (arrows); mbsf A. 250 KA: LOW SEA LEVEL Aragonitic coral; mbsf

5 Mixed Carbonates and Siliciclastics, North of the Mahakam Delta, Offshore East Kalimantan, Indonesia TRANSGRESSIVE SHELF MARGIN & MIDDLE SHELF CARBONATES GREW ON PROGRADING SILICICLASTICS & WERE BURIED BY LATER PROGRADING SILICICLASTICS () LATE MIOCENE- PLIOCENE DEPOSITIONAL HISTORY LATE MIOCENE-PLIOCENE SHELF MARGIN CARBONATES Siliciclastic Shorelines & Deltas Prograded Basinward 3D of Top Upper Carbonate with Overlay of Carbonate Thickness MIDDLE SHELF CARBONATE IN SHALE Microporous wackestone Lime packstone. Moldic porosity (M) During Transgression & Rapid Sea Level Rises, Siliciclastic Shorelines Moved Landward & Carbonates Grew. Biggest Carbonate Buildups are on the Shelf Margin. Small Buildups on the Middle Shelf LATE MIOCENE-PLIOCENE SHELF MARGIN CARBONATE Recrystallized coral 3D of Lower Carbonate with Overlay of Thickness Bioclast grainstone with moldic porosity (M) Porous foram grainstone Material in these posters is from Saller, A.H., S.W. Reksalegora, and Philip Bassant, 2011, Sequence Stratigraphy and Growth of Shelfal Carbonates in a Deltaic Province, Kutai Basin, Offshore East Kalimantan, Indonesia, in W.A. Morgan, A.D. George, P.M. Harris, J.A. Kupecz, and J.F. Sarg, eds., Cenozoic Carbonate Systems of Australasia: Society for Sedimentary Geology Special Publication 96, p Siliciclastic Shorelines & Deltas Prograded Basinward & Buried Many Carbonates Relatively Rapid Subsidence Allow Very Rapid Carbonate Growth Recrystallized coral Porous dolomite Argillaceous wackestone with planktonic foram (deep water)