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Po2017 005 Sh001.Pdf STRATIGRAPHY AND SEDIMENTOLOGY OF THE CHINITNA FORMATION, INISKIN–TUXEDNI BAYS AREA, SOUTH-CENTRAL ALASKA—LATE MIDDLE JURASSIC DEPOSITIONAL SYSTEMS AND PETROLEUM PROSPECTIVITY IN COOK INLET FOREARC BASIN 3 STRATIGRAPHIC ARCHITECTURE 4 PETROLOGY AND RESERVOIR QUALITY: Qt Qm Trystan M. Herriott1, Marwan A. Wartes1, Richard G. Stanley2, Paul L. Decker3, Kenneth P. Helmold3, and Nina T. Harun1 Alaska Department of PAVELOFF SILTSTONE MEMBER PAVELOFF Increasing maturity/stability 1 NATURAL Saddle Mountain from continental block Alaska Division of Geological & Geophysical Surveys, Fairbanks, AK (trystan.herriott@alaska.gov) 3.2 provenances 2 3 RESOURCES DIVISION OF OIL AND GAS Craton Interior U.S. Geological Survey, Menlo Park, CA; Alaska Division of Oil and Gas, Anchorage, AK Jcp1 ~95 m Recycled s 2 ransitional Continental Orogen T e CONTEXT, HIGHLIGHTS, AND RESULTS ABSTRACT SEDIMENTOLOGY d o Circum-Pacific The Chinitna Formation of lower Cook Inlet is a depositional systems with probable delta associations M Oil production in Cook Inlet forearc basin is from Tertiary reservoirs Jct Volcanoplutonic ~700-m-thick marine unit that crops out near the supplied coarse sediment during onset of each cycle. AVELOFF ILTSTONE EMBER Suites P S M l a t arc-proximal forearc basin margin. Two members of The conglomerate at Chisik Island highlights marked Dissected Arc i r Oil source rocks in the basin occur in the Middle Jurassic Tuxedni Group and/or Triassic stratigraphy t comparable thickness are mapped as Tonnie Siltstone base-level fall (10s of m of incision), probably e Increasing ratio of D (Bathonian–Callovian) and Paveloff Siltstone represents shelf-valley fill, and is tentatively associated 3.1 Oblique aerial view eastward of Paveloff Siltstone Member north- plutonic to volcanic Does the Middle Jurassic Chinitna Formation have oil reservoir potential? east of Johnson River in the Slope Mountain area. A thick, channelized sources in magmatic f (Callovian). Geologic mapping, stratigraphic with Paveloff rather than Tonnie. Overlying arc provenances o succession at the base of Paveloff is well developed and clearly ex- reconnaissance, and sedimentologic work provide new finer-grained successions in both members may reflect Transitional Arc i t pressed at this locality and dominantly comprises sandstone (see Jcp ). Basement Uplift m insights into the Chinitna. waning deltaic influences as near-shore environments 1 Li Note high-relief erosional surface that cuts Jcp2 and is filled by Undissected Arc 1 Chinitna Formation comprises ~700 m of dominantly ne-grained marine forearc basin strata Provenance fields from Dickinson (1985; A ~70-m-thick channelized conglomerate were transgressed during rising base level, diminishing 3.1 3.3 13TMH058B 13TMH058B slumped, channelized, and tabular-bedded packages of Jcp3. Photo- Saddle Mountain oil stained oil stained in Provenance of Arenites [p. 333–361]) package at Chisik Island is reportedly associated with sediment supply to prodelta settings in shelfal water graph by M.A. Wartes. F L P K Sedimentologic work suggests primarily shallow-marine deposition, but there are indications that some Tonnie, but field relations indicate these beds may be depths ranging down to—and perhaps below—storm 3.2 Oblique aerial view southward of tabular-bedded (lower part) to channelized (upper part) Jcp within cliff-face exposure ~1.5 km west younger than Tonnie. Nevertheless, lower Tonnie wave base. Continued transgressions likely terminated 1 2 of Triangle Peak. Channel fills are sandstone and conglomerate and Chinitna strata may record deep-water (for example, slope) sedimentation exposures near Tonnie Peak do host channelized, direct deltaic inputs into outer shelf settings. The Jn commonly >10 m thick. Convolute-stratified sandstones are sugges- Jn cross-stratified sandstone. At Iniskin Bay, part of lower lithologically monotonous, gullied upper parts of each tive of rapid dewatering in a high-sedimentation-rate setting. Herriott Mountain-scale exposures reveal stratigraphic cycles in the Chinitna Formation Tonnie exhibits thin, sharp-based sandstone intercalated member may record highstand normal regressions— et al. (2016: doi: 10.14509/ 29539) interpreted Jcp here as likely record- Sedimentary textures, structures, bedding character and 2.1 Jcp 1 Coarse-grained basal successions in each member are lowstand systems tracts with bioturbated siltstone; hummocky cross-stratified rather than continued transgressions—when muddy geometries, and fossil assemblages observed throughout 2 Jcp ing deltaic processes. Photograph by T.M. Herriott. sandstone is also present. Reconnaissance of upper clinoforms(?) of delta- to slope-scale relief prograded Paveloff Siltstone Member are principally consistent with 4 3.3 Oblique aerial view southeastward of Paveloff in the Red Glacier Jcp Jcp ~140 m of erosional 3 ? 4 3 Coarse detritus was exported beyond the outcrop belt during these lowstands Tonnie reveals a finer-grained interval with local into the basin during later periods of base-level rise; the shallow-marine sedimentation in delta, prodelta, and relief on this surface ? area northwest of Lenore Hill. Stratigraphic architecture here is similar ? ~270 m gully-scale channel-forms and mainly fine-grained fills. strongest evidence for this scenario occurs in Paveloff, outer-shelf settings. Some exposures clearly indicate rela- ? to the exposure at 3.1, which lies ~12 km to the northeast. Note, how- ? Finer-grained middle and upper parts of each member are transgressive and highstand systems tracts, tively steep depositional gradients, potentially reflecting ? Jcp3 ever, greater relief along the Jct–Jcp contact here than is observed at A generally comparable stratigraphic stacking motif is where the largest channel-form approaches submarine- 3.1, 3.2, or 3.7, and the seemingly sand-rich nature (see lighter-brown- delta-scale clinoform foresets; however, deep-water pro- Jcp1 ? although stratigraphic relations within mid-Pavelo may reect an additional base-level cycle documented in Paveloff. A ~100-m-thick succession of canyon-scale. weathering strata) of lowermost Jcp . Two scenarios regarding the cesses associated with slope-scale clinoforms may also ? ~105 m 3 Jcp2 tabular and channelized sandstone and conglomerate Rock-Eval pyrolysis results from 44 samples (12 occur in the Paveloff (see 3.7). 2.1 Detailed study of upper genesis of the basal Jcp3 surface are considered below. Photograph by ȝP ȝP ȝP M.A. Wartes. Jcp Pavelo sandstones are feldspathic and generally have <6% porosity and <0.2 millidarcies permeability commonly occurs at this member’s base, and from Tonnie, 32 from Paveloff) indicate poor petroleum Paveloff at Chinitna Bay reveals a thick (~160 m), locally 1 4 hummocky cross stratification is also noted. Regionally, source potential, with total organic carbon values of slumped (above left) succession of chiefly Jct See Herriott et al. (2016: doi: 10.14509/29539) for further discussion of Jct Paveloff Siltstone Mbr.—East shore Oil Bay Paveloff Siltstone Mbr.—East shore Oil Bay Paveloff Siltstone Mbr.—South shore Chinitna Bay overlying finer-grained deposits are observed. Upper 0.14–0.69 weight percent and S2 values of 0.00–0.57 lithologically monotonous, thoroughly bio- 3.1 and 3.2. Subscripted architectural units are further described in 3.7. ĭ N PG ĭ N PG ĭ N PG turbated, very-fine-grained sandstone and 2.3SEE 2.3SEE SEE 5 Paveloff at Chinitna Bay comprises more than 160 m of milligrams hydrocarbon per gram of rock. Thermal 13A027-323.8A $$ 70+% 5 Oil-stained basal Pavelo (Jcp1) crops out at Chinitna Bay siltstone with locally discrete Phycosiphon 2.3 bioturbated, very fine-grained sandstone with maturity of the samples ranges from ~0.7% Ro at Oil trace fossils (above right); subordinate thin Sandstones in Pavelo Siltstone Member consist large- 1 subordinate coarser, sharp-based sandstone; slump scars Bay to 0.85–1.20% Ro at Iniskin Bay based on beds of fine-grained sandstone are com- EXPLANATION TONNIE SILTSTONE MEMBER ly of calcic plagioclase (average 47%) that have been The depositional-systems and sequence-stratigraphic framework of this study—and an oil-stained and channels with m-scale relief are principally filled Rock-Eval Tmax, spore color, and vitrinite reflectance monly ripple laminated (right). Photographs partially to totally albitized and lesser amounts of inter- with fine-grained detritus. Mountain-scale exposures analyses. Sampled Chinitna sandstones are mainly by M.A. Wartes. 2.2 Excellent exposures of formation/member contact disrupted perspective of mediate volcanic rock fragments (average 19%). Some exhibit even larger channel-forms in upper Paveloff, feldspathic and generally have less than 6% porosity lower Paveloff occur in the Tonnie Peak area, stratigraphy 3.4 grains are euhedral plagioclase crystals, suggesting oil stained outcrop—demonstrate that viable scenarios exist for oil reservoirs in the Chinitna Formation where probable hummocky cross-stratified intra-member contact derivation from relatively unconsolidated crystal tus. 0.1 including a slump-associated feature with ~140 m of and less than 0.2 millidarcies permeability. ~1m approximate stratigraphic sandstones are observed. Photographs by 2.2 thickness Grain sizes range from coarse silt to ne-grained sand stratigraphic relief. Nevertheless, migrated oil is documented in a lower P.L. Decker. 2.3 Detailed study of Paveloff in large-scale erosional surface with onlap at arrow through most of the Pavelo, but coarse- and very Chinitna
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