Early Diagenetic Silica Deposition in Algal Cysts and Spores: A Source of Sand in Black Shales?
ABSTRACT Devonian black shales deposited on the North American craton contain abundant Tasmanites cysts. Although these are typically flattened because of compaction, a small proportion are filled with diagenetic silica. The latter are spherical to ellipsoidal (0.1-0.5 mm), and filled with chalcedony, microquartz and megaquartz, and single quartz crystals. Chalcedonic cyst fillings are preserved best in cheat and phosphate nodules, whereas megaquartz and single quartz crystals are most common in shale matrix. Together with colloform textures, this suggests that the various silica types originated from recrystallization of early diagenetic silica deposits. Thin sandstone beds in the Chattanooga Shale (e.g., Bransford Sandstone) contain abundant quartz sand that is much coarser than the detrital quartz component of the underlying black shales. Because of this, their quartz component is thought to have been transported over considerable distances from the basin margin. However, because certain shale horizons contain as much as 10% silicified cysts that upon reworking could have yielded quartz grains of fine to coarse sand size, the quartz component of these sandstone beds may actually have formed in situ. Indeed, petrographic examination of the sandstone beds shows them to contain quartz grains with morphological and textural features of "cyst" quartz (e.g., rounding, sphericity, chalcedony, pyrite inclusions, lobate grain margins). Thus, silica deposition in algal cysts may provide a significant component of intrabasinal quartz sand in shale sequences. Distinction of this type of quartz from extrabasinal detrital quartz is important to the reconstruction of the depositional history of shale sequences.
Sedimentary features indicating erosion, condensation, and hiatuses in the Chattanooga Shale of Central Tennessee : Relevance for sedimentary and stratigraphic evolution
Recent investigations show that the finely laminated and highly carbonaceous Upper Devonian Chattanooga Shale of central Tennessee accumulated in relatively shallow water, prone to influence by storm waves and episodic erosive events. Recurring erosive events of variable strength and/or duration are indicated by truncation surfaces beneath which from a few centimeters to more than a meter of section is missing. That the seabed was close to or within reach of storm waves through large portions of Chattanooga history is suggested by hummocky cross-stratified sand and silt beds, and mud tempestites. In many places truncation surfaces cut underlying beds at a very shallow angle, or even become conformable to under- and overlying beds. In hand specimen or thin section, these essentially invisible erosion surfaces may be associated with one or more of the following features: (I) sharp-based shale beds, (2) basal sand lags (some mm to cm thick), (3) bone beds, (4) abundant reworked pyrite, (5) conodont or Lingula lags, (6) soft sediment deformation of shale laminae below erosion surface, and (7) localized low-angle truncation of shale laminae. On erosion surfaces, the concentration of reworked pyrite (framboids, fecal pellets, fills of Tasmanites cysts, pyritic ooids) can in places lead to pyrite enrichment by a factor of 20-30 relative to normal black shale, and may give rise to sharp-based beds of pyritic shale. Diffuse-based pyritic shale beds, lacking an association with erosional features, but otherwise texturally identical, have also been observed. In these beds, the very strong enrichment of diagenetic (pyrite) and biogenic (conodonts) components suggests minimal terrigenous sedimentation, probably an indication of condensation and/or hiatuses. Pyritic shale beds as thick as 10 cm have been found, possibly representing as much as 2-3 m of eroded and reworked (sharp-based) or condensed section (diffuse-based). This makes them potentially significant stratigraphic elements (marker horizons). Erosion or condensation on the cm scale might be due to local conditions, and seems to define macroscopic bedding in outcrops of the Chattanooga Shale. Meter-scale erosion and thick pyritic beds on the other hand define substantial discontinuities that may well be the result of more regional phenomena, such as a basin-wide lowering of sea-level. In order to see whether these latter features are expressions of sequence boundaries in slowly accumulating black shale sequences, work is underway to test whether they correlate with transgressive-regressive cycles found in the Upper Devonian of the Catskill Delta.
Subject index
Adoptive immunotherapy A1, A63, A63, A64, A64, A65, A66, A68, A69, A69, A70, A70, A71, A71, A72, A72, A73, A73, A74, A75, A76, A78, A79, A79, A7, A80, A80, A81, A81, A82, A84, A85, A86, A86, A88, A88, A89, A90, A90, A91, A92, A93, A93, A94, A95, A95, A96, A96, A97, A97, A98, A98, A99, A99, A102, A103, A104, A104, A166, A167, A169, A170, A174, A177, A179, A181, A182, A199, A204, A205, A21, A215, A220, A231, A231, A243, A251, A254, A25, A276, A287, A304, A307, A310, A315, A316, A316, A329, A331, A333, A357, A358, A369, A405, A441, A442, A458, A458, A459, A459, A461, A461, A463, A468, A468, A479, A492, A497, A497, A56, A58, A58, A59, A60, A60, A61, 1, 100, 101, 102, 103, 104, 106, 109, 111, 112, 113, 114, 115, 116, 117, 119, 120, 122, 123, 124, 125, 127, 128, 129, 13, 130, 131, 133, 134, 136, 139, 140, 141, 142, 146, 147, 148, 149, 150, 152, 153, 154, 155, 156, 157, 158, 159, 160, 161, 163, 164, 165, 166, 167, 169, 173, 174, 175, 272, 273, 278, 280, 285, 290, 293, 297, 298, 324, 333, 335, 35, 353, 360, 379, 380, 400, 414, 418, 42, 454, 470, 493, 500, 504, 513, 515, 516, 542, 545, 549, 598, 599, 614, 675, 737, 739, 764, 765, 766, 767, 770, 771, 772, 780, 781, 801, 822, 830, 831, 89, 91, 92, 94, 95, 96, 98 Angiogenesis A108, A155, A171, A200, A201, A214, A228, A265, A305, A349, A350, A359, A410, A47, A48, A480, A483, A519, A5, 181, 257, 281, 327, 328, 351, 374, 435, 495, 583, 584, 602, 683, 76, 78, 802, 808, 873, 9 Antibody A7, A73, A81, A86, A91, A8, A99, A9, A104, A108, A108, A109, A109, A111, A115, A119, A126, A128, A130, A135, A138, A141, A144, A151, A153, A159, A160, A163, A164, A164, A171, A172, A175, A176, A2, A187, A193, A193, A195, A195, A198, A199, A20, A209, A212, A225, A229, A230, A23, A233, A233, A235, A239, A239, A240, A242, A244, A244, A245, A245, A246, A247, A247, A24, A250, A256, A260, A261, A266, A267, A268, A269, A273, A275, A286, A288, A292, A293, A296, A299, A300, A307, A3, A308, A31, A318, A324, A35, A334, A334, A336, A338, A339, A342, A343, A344, A344, A346, A346, A351, A351, A353, A356, A360, A361, A363, A368, A369, A370, A371, A372, A372, A373, A374, A376, A377, A378, A378, A379, A379, A380, A380, A388, A391, A399, A399, A41, A402, A410, A410, A411, A412, A414, A417, A418, A419, A419, A420, A422, A422, A423, A426, A427, A428, A428, A430, A431, A432, A434, A434, A435, A446, A454, A455, A459, A463, A465, A468, A468, A469, A474, A481, A483, A50, A486, A487, A491, A502, A502, A504, A507, A507, A508, A510, A511, A512, A512, A516, 12, 122, 133, 141, 151, 16, 167, 17, 174, 181, 182, 184, 185, 188, 195, 203, 210, 215, 218, 227, 231, 237, 243, 250, 253, 261, 262, 265, 267, 268, 281, 282, 287, 288, 3, 305, 313, 315, 317, 318, 323, 325, 34, 342, 348, 369, 377, 378, 38, 384, 385, 387, 393, 394, 395, 399, 401, 402, 403, 404, 405, 406, 407, 41, 412, 421, 428, 429, 438, 439, 442, 443, 450, 453, 469, 472, 476, 478, 480, 483, 486, 499, 5, 501, 51, 519, 531, 55, 550, 552, 557, 561, 562, 569, 571, 572, 573, 576, 578, 586, 587, 590, 594, 603, 605, 607, 612, 615, 616, 617, 618, 619, 621, 622, 626, 629, 630, 631, 632, 633, 634, 635, 647, 653, 665, 666, 67, 670, 683, 684, 686, 687, 690, 693, 696, 697, 698, 699, 702, 703, 704, 711, 713, 714, 715, 718, 721, 722, 725, 726, 727, 745, 757, 760, 766, 772, 776, 780, 781, 785, 793, 804, 808, 81, 812, 814, 820, 842, 843, 846, 851, 852, 853, 856, 858, 860, 861, 869 Antigen presenting cells A67, A79, A80, A92, A95, A96, A99, A99, A101, A102, A102, A108, A108, A111, A129, A139, A160, A166, A177, A178, A183, A191, A191, A213, A220, A221, A245, A254, A256, A262, A266, A275, A314, A322, A327, A328, A35, A335, A345, A359, A359, A360, A361, A364, A366, A368, A369, A371, A372, A403, A409, A411, A411, A418, A422, A433, A449, A48, A468, A471, A472, A4, A50, A495, A502, A506, A513, A514, A515, 108, 128, 130, 153, 157, 160, 166, 167, 168, 169, 170, 181, 182, 188, 217, 235, 263, 271, 290, 291, 299, 310, 311, 349, 360, 362, 404, 418, 421, 431, 438, 453, 510, 526, 538, 540, 55, 553, 575, 601, 602, 603, 605, 610, 611, 612, 615, 617, 618, 672, 682, 685, 686, 695, 703, 724, 748, 78, 780, 787, 790, 8, 81, 828, 842, 849, 862, 864, 868 Autoimmunity A8, A116, A15, A180, A181, A22, A380, A387, A394, A395, A402, A408, A502, A510, 16, 197, 27, 295, 296, 37, 637, 645, 657, 658, 671, 680, 843, 856