--> ABSTRACT: Lacustrine Microbial, Skeletal, and Associated Carbonate Lithofacies in the Miocene Idaho Hot Springs Limestone, USA — Vertical and Lateral Distribution at the Parasequence to Sequence Scale, by Bohacs, Kevin; Demko, Timothy ; Lamb-Wozniak, Kathryn A.; Kaczmarek, Stephen E.; Lash, Catherine; Cleveland, David; Eleson, Jason ; Fabijanic, Matt; McLaughlin, Orla; Gibbins, Stacie ; #90142 (2012)

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Lacustrine Microbial, Skeletal, and Associated Carbonate Lithofacies in the Miocene Idaho Hot Springs Limestone, USA — Vertical and Lateral Distribution at the Parasequence to Sequence Scale

Bohacs, Kevin *1; Demko, Timothy 1; Lamb-Wozniak, Kathryn A.2; Kaczmarek, Stephen E.3; Lash, Catherine 5; Cleveland, David 1; Eleson, Jason 2; Fabijanic, Matt 2; McLaughlin, Orla 2; Gibbins, Stacie4
(1) ExxonMobil Upstream Research Company, Houston, TX.
(2) ExxonMobil Exploration Company, Houston, TX.
(3) Bridgewater State University, Bridgewater, MA.
(4) Esso Indonesia Inc., Jakarta, Indonesia.
(5) Montana State University, Bozeman, MT.

The Idaho Hot Springs Limestone accumulated during the late Miocene in a series of lakes in extensional basins during active volcanism. Lithofacies include microbial boundstone (open-framework bioherms, tightly cemented biostromes, and grain coatings), grainstone, wackestone, micrite, and diatomite. Grainstone occurs between and within bioherm complexes. A typical succession has isolated concave-upward conical arborescent bioherms separated by skeletal-dominated grainstone at the base, overlain by upward expanding, increasingly arborescent bioherms with minor surrounding biostromal boundstone, and topped by widely expanded to interlinked arborescent bioherms surrounded by thick involute biostromal boundstone. Parasequence-scale successions are separated by thin bedsets of dominantly horizontal biostromal boundstone with subjacent zones of early diagenetic alteration that we interpret to record lacustrine flooding surfaces. Lithofacies also vary laterally at the km scale, mapped over an area of >50 km2. Lake plain and supralittoral zones are dominated by poorly sorted clastic lithofacies with abundant roots and trace fossils. Littoral to proximal sublittoral zones contain poorly sorted clastics, micrite, and wackestone with widely spaced, short (< 33 cm) bioherms. Bioherms are larger, taller (< 242 cm), and more closely spaced towards the medial sublittoral zone, where skeletal-oncoidal grainstone are more common between bioherm complexes. Distal sublittoral bioherms are shorter (< 20 cm), less complex, and more widely spaced. Profundal lithofacies include wackestone and micrite, with various admixtures of diatomite. The distribution and character of diagenetic cements and pore types are strongly influenced by lithofacies and position with parasequence and parasequence set. Microbialites and grainstones have the best preserved primary porosity. Much diagenetic alteration appears to record early subaerial exposure. Microbialites are recrystallized to varying degrees, but primary pores are largely preserved. Intra-microbial pores display some post-depositional dissolution and only minor cementation. Grainstones have primary interparticle pores and moldic pores associated with meteoric inversion, which occurs more abundantly near parasequence tops. Blocky meteoric phreatic calcite cements are present in minor amounts with a patchy distribution. Patchy dolomite (replacement and cement), chalcedonic quartz cement, and pedogenic textures also occur.  

 

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California